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

spatial patterns of glacier motion during a high velocity event haut glacier d arolla switzerland the surface motion of haut glacier d arolla switzerland was monitored at a high spatial and temporal resolution data are analyzed to calculate surface velocities surface strain rates and the components of the glacier force budget before during and after an early melt season speed up or spring event we investigate the extent to which variations in glacier motion can be attributed to hydrologically induced local forcing or to non local forcing transmitted via horizontal stress gradients enhanced glacier motion is dependent on a change in the spatial distribution of areas of high drag across the glacier

influence of subglacial drainage system evolution on glacier surface motion haut glacier d arolla switzerland 1 the relationship between the evolution of subglacial drainage system morphology and spatial patterns of glacier surface velocity was investigated using dye tracing experiments and ground surveying throughout the 1995 melt season at haut glacier d arolla switzerland with the onset of high and variable melt season discharges subglacial drainage changed from a predominantly distributed system to a predominantly channelized system the change occurred later farther up glacier during the period of drainage evolution the glacier was subjected to three periods of rapidly rising meltwater discharge the magnitude and spatial pattern of the glacier s velocity response differed between these periods and can be explained in terms of the impact of the evolving drainage system morphology on the amplitude and spatial distribution of basal hydrological forcing increasing discharge through a distributed drainage system caused widespread basal forcing and high glacier velocity increasing discharge through incipient channels below moulins not yet connected to the main channel caused more localized basal forcing and slightly increased glacier velocity increasing discharge through a fully channelized drainage system caused no significant basal forcing and glacier velocity was not significantly different from the annual deformation flow pattern empirical orthogonal function analysis of flow patterns defined two distinct spatial modes of surface velocity which corresponded closely with the drainage system morphologies inferred to be present during each event the relative importance of these modes changed through the melt season suggesting a temporal change in the spatial pattern of hydrologically induced basal forcing

basement terrane correlations and crustal recycling in the western superior province nd isotopic character of granitoid and felsic volcanic rocks in the wabigoon subprovince n ontario canada abstract the western superior province represents a collage of mesoarchean continental 3 2 2 8 ga and neoarchean continental arc and oceanic 2 8 2 66 ga crustal fragments nd isotope data presented here for 89 felsic volcanic and plutonic rocks have been combined with compiled data to generate a data set of over 240 analyses from the wabigoon and winnipeg river subprovinces these samples from both oceanic and continental environments have been used as crustal probes their nd isotopic character used to investigate the extent of basement terranes the ancestry of crustal fragments their interaction with each other and the degree of sialic crustal reworking the wabigoon and winnipeg river subprovinces include three isotopically distinct terranes 1 the winnipeg river terrane comprises the winnipeg river subprovince the north central wabigoon and the north eastern wabigoon subprovince this region is dominated by neoarchean granitoid rocks with mesoarchean vestiges of previous workers have suggested that the boundary between the western wabigoon and winnipeg river terranes represents a cryptic suture resulting from a collision at circa 2 71 ga the boundary between the western wabigoon and marmion terranes although obscured by late intrusions may be a continuation of this suture zone the boundary between the winnipeg river and marmion terranes in the central wabigoon is also cryptic isotopic data suggest that the marmion terrane is allochthonous with respect to the winnipeg river terrane common magmatism in these two terranes at 2 93 2 87 ga suggests that they may have collided during this time in the eastern wabigoon subprovince this collision zone is speculated to occur at the humboldt bay high strain zone a complex history of crustal recycling throughout the mesoarchean and neoarchean is revealed which demonstrates the importance of autochthonous development of granite greenstone terranes in a continental environment the data also support models of tectonic accretion during the archean indicated by the presence of granite greenstone terranes of allochthonous origin

geochemistry of a silicified felsic volcaniclastic suite from the early archaean panorama formation pilbara block western australia an evaluation of depositional and post depositional processes with special emphasis on the rare earth elements abstract many elements in a suite of pervasively silicified dacitic volcaniclastic and volcanic rocks from the early archaean panorama formation warrawoona group western australia were strongly depleted or enriched relative to those in equivalent unaltered units during widespread post depositional metasomatism the present compositions of the altered rocks are dominated by al 2 o 3 k 2 o and sio 2 and lie on or close to a quartz sericite mixing line the al contents were probably inherited from the original dacitic rocks while si some k and possibly rb may have been introduced during metasomatism the elements mg ca na and to a lesser extent fe mn and sr have been depleted relative to al during alteration whereas silica has been greatly enriched the high and variable ba concentrations suggest that ba like si was introduced during silicification the ree and th were relatively immobile during alteration and were diluted during silicification in the same proportion as al most of the rocks represent detrital sand and silt sized felsic tephra debris eroded from felsic volcanic rocks or ash fall deposits that underwent a short interval of transport and deposition dominated by physical rather than chemical processes a few siltstones contain clay minerals that probably formed by the chemical weathering of warrawoona group basalts the siltstones have lower th and la concentrations lower la lu ratios and higher sc and cr concentrations than felsic rocks in the suite regional alteration pervasively silicified the original sediments shortly after deposition the replacement mineral assemblage indicates a maximum temperature for hydrothermal alteration of about 350 c because of the lack of chemical weathering and the low temperature of post depositional alteration ree abundances in volcaniclastic rocks of the panorama formation reflect their felsic volcanic provenance and are interpreted to have preserved a relict magmatic signature the lack of a negative eu anomaly and high la lu ratio chondrite normalized ratio is 7 to 39 suggest that magmas of the panorama formation formed by direct melting of an eclogite residue without subsequent crystallization of feldspar during the commencement of cratonization of the pilbara block this origin differs from the origin of some other silicic volcanic rocks of the duffer formation representing earlier felsic volcanic activity of the warrawoona group that were produced by fractional crystallization from basaltic parents this suggests a polygenetic origin for felsic magmas of the warrawoona group

influence of debris cover and altitude on glacier surface melting a case study on dokriani glacier central himalaya india most of the central himalayan glaciers have surface debris layers of variable thickness which greatly affect the ablation rate an attempt has been made to relate debris cover thickness to glacier surface melting thirty stakes were used to calculate ablation for debris covered and clean ice of dokriani glacier 7km 2 from 2009 10 to 2012 13 our study revealed significant altitude wise difference in the rate of clean and debris covered ice melting we found a high correlation r 2 0 92 between mean annual clean ice ablation and altitude and a very low correlation r 2 0 14 between debris covered ice melting and altitude debris covered ice ablation varies with variation in debris thickness from 1 to 40cm ablation was maximum under debris thicknesses of 1 6cm and minimum under 40cm even a small debris cover thickness 1 2cm reduces ice melting as compared to that of clean ice on an annual basis overall debris covered ice ablation during the study period was observed to be 37 less than clean ice ablation strong downwasting was also observed in the dokriani glacier ablation area with average annual ablation of 1 82mw e a 1 in a similar period our study suggests that a thinning glacier rapidly becomes debris covered over the ablation area reducing the rate of ice loss

through water terrestrial laser scanning of gravel beds at the patch scale acquiring high resolution topographic data of natural gravel surfaces is technically demanding in locations where the bed is not exposed at low water stages often the most geomorphologically active surfaces are permanently submerged gravel beds are spatially variable and measurement of their detailed structure and particle sizes is essential for understanding the interaction of bed roughness with near bed flow hydraulics sediment entrainment transport and deposition processes as well as providing insights into the ecological responses to these processes this paper presents patch scale laboratory and field experiments to demonstrate that through water terrestrial laser scanning tls has the potential to provide high resolution digital elevation models of submerged gravel beds with enough detail to depict individual grains and small scale forms the resulting point cloud data requires correction for refraction before registration preliminary validation shows that patch scale tls through 200 mm of water introduces a mean error of less than 5 mm under ideal conditions point precision is not adversely affected by the water column the resulting dems can be embedded seamlessly within larger sub aerial reach scale surveys and can be acquired alongside flow measurements to examine the effects of three dimensional surface geometry on turbulent flow fields and their interaction with instream ecology dynamics copyright 2011 john wiley sons ltd

sediment core profiles of long chain n alkanes in the sea of okhotsk enhanced transport of terrestrial organic matter from the last deglaciation to the early holocene 1 terrestrial plant derived n alkanes c25 c35 w ere measured in three piston cores pc1 pc2 and pc4 in the sea of okhotsk covering the last 30 kyrs down core profiles of the n alkane concentrations and mass accumulation rates mar were characterized by deglacial maxima in particular cores pc2 and pc4 which were collected from the central and western sea of okhotsk respectively show a two step increase around the meltwater pulse events mwp 1a 14 5 13 5 kyr bp and 1b about 10 kyr bp this finding was interpreted by the outflow of terrestrial organic matter from the submerged land shelf to the sea of okhotsk through the east sakhalin current this study demonstrated that the sea level rise forced by global warming in the deglaciation period may have caused the enhanced transport of terrestrial organic matter in marginal seas index terms 3022 marine geology and geophysics marine sediments processes and transport 4267 oceanography general paleoceanography 1055 geochemistry organic geochemistry citation seki o k kawamura t nakatsuka k ohnishi m ikehara and m wakatsuchi sediment core profiles of long chain n alkanes in the sea of okhotsk enhanced transport of terrestrial organic matter from the last deglaciation to the early holocene geophys res lett 30 1 1001 doi 10 1029 2001gl014464 2003

influence of subglacial drainage conditions on the velocity distribution within a glacier cross section substrate properties and hydrological conditions at the base of haut glacier d arolla switzerland are nonuniform the thickness and grain size of subglacial sediment vary on length scales less than one ice thickness whereas hydrological conditions vary seasonally and on length scales of about one ice thickness transverse to ice motion there is a close relationship between the annually averaged velocity field and this nonuniformity of bed conditions basal motion dominates in an area with large water level variations in boreholes whereas ice deformation contributes significantly to total movement elsewhere localized enhanced basal motion occurs primarily in summer especially during a july spring event but this motion is barely discernible in annually averaged surface velocity measurements because transverse coupling suppresses surface expression of the basal motion discontinuity these results highlight the need to include representations of bed nonuniformity in models of glacier flow and to consider ice deformation and basal motion as interdependent processes

two contrasting granite greenstone terranes in the pilbara craton australia evidence for vertical and horizontal tectonic regimes prior to 2900ma abstract major tectono metamorphic differences between two pre 2900 ma granite greenstone terranes of the pilbara craton indicate evolution under fundamentally different tectonic regimes the east pilbara granite greenstone terrane ep contains a typical dome and basin regional structural pattern lacking any preferred orientation of domical granitoid complexes intervening synclinal greenstone belts or faults the ep greenstone succession contains no low angle thrusting is demonstrably autochthonous throughout the ep and most of its stratigraphic components are common to all the greenstone belts the oldest greenstone successions of the ep were deposited between 3515 and 3320 ma by repeated cycles of plume related mafic felsic volcanism onto 3725 3600 ma continental crust intrusion of syn volcanic tonalite trondhjemite granodiorite ttg sheets and subvolcanic laccoliths at ca 3490 3430 ma caused locally significant syn volcanic doming but had only limited penetration into the uppermost greenstone succession a major deformation event at 3315 ma is consistent with gravity driven diapiric doming of the ttg complex and sinking of denser overlying greenstones into adjacent synclines this diapiric deformation established the main features of the present dome and basin pattern subsequent monzogranite intrusion was almost entirely restricted to the cores of the granitoid domes and together with renewed diapirism at 3240 and 2950 ma amplified some of these domes into almost vertical cylindrical structures the crustal evolution of the ep cannot be satisfactorily explained using plate tectonic models the west pilbara granite greenstone terrane wp exhibits a strong northeast oriented structural grain defined by the elongation of granitoid complexes the trend of its two main greenstone belts and by numerous closely spaced east and northeast striking faults unlike the ep the wp is a collage of three separate fault bounded tectono stratigraphic domains each of which contains a unique stratigraphic succession and a separate set of tectonic structures the oldest greenstones of the wp belong to the ca 3280 3250 ma roebourne group that is restricted to the karratha domain the roebourne group is an ultramafic felsic volcanic succession with overlying subordinate clastic metasedimentary rocks isotopic data indicate that the group was deposited on ca 3480 ma crust or was derived from a source region of this age but the basal contact of the group is obscured by intrusive 3270 ma tonalite and granodiorite the roebourne group is interpreted to have formed on ep basement during rifting of the ep after which the ep and wp evolved in different tectonic environments at ca 3160 ma the karratha domain was tectonically over ridden by oceanic type crust of the regal formation indicating collision with an unknown plate to the north the regal formation forms the lower part of the cleaverville domain the upper component being the unconformable post collision ca 3020 ma cleaverville formation the sholl domain containing the 3130 3115 ma whundo group is separated from the karratha and cleaverville domains by a major long lived fault zone the sholl shear zone ssz the whundo group is a juvenile predominantly basaltic pile showing no evidence of contamination by crust older than 3280 ma and is interpreted to have been deposited on oceanic type crust in the post 3240 ma rift four granitoid complexes in the wp were mainly formed between 3015 and 2970 ma and have no age equivalents in the ep no diapiric domes are present in the wp where all deformation is interpreted to be the result of successive episodes of horizontal compression consistent with evolution in phanerozoic style plate tectonic environments

modelling ice bed coupling during a glacier speed up event haut glacier d arolla switzerland fischer u h mair d kavanaugh j l willis i nienow p hubbard b 2011 modelling ice bed coupling during a glacier speed up event haut glacier d arolla switzerland hydrological processes 2599 1361 1372

alpine subglacial hydrology abstract the size and shape of subglacial flow pathways exert a strong influence over the pressure and speed at which meltwaters are routed through glaciers these characteristics in turn influence glacier sliding velocity and the quantity and quality of bulk meltwaters discharging from glaciers in this paper we summarise four empirical research approaches that have been developed to improve our understanding of the subglacial hydrology of predominantly temperate based alpine glaciers investigations of bulk meltwater discharge and chemistry tracer studies proglacial bedrock investigations and borehole investigations as a result of linking these studies to conceptual or numerical models three arborescent and four non arborescent or distributed subglacial drainage configurations are described these drainage networks may be neither spatially nor temporally persistent but may compete with and replace each other on a seasonal basis a qualitative model of the temporal and spatial evolution of a typical alpine subglacial drainage system is advanced on the basis of research conducted at haut glacier d arolla switzerland

hyperscale terrain modelling of braided rivers fusing mobile terrestrial laser scanning and optical bathymetric mapping quantifying the morphology of braided rivers is a key task for understanding braided river behaviour in the last decade developments in geomatics technologies and associated data processing methods have transformed the production of precise reach scale topographic datasets nevertheless generating accurate digital elevation models dems remains a demanding task particularly in fluvial systems this paper identifies a threefold set of challenges associated with surveying these dynamic landforms complex relief inundated shallow channels and high rates of sediment transport and terms these challenges the morphological wetted channel and mobility problems respectively in an attempt to confront these issues directly this paper presents a novel survey methodology that combines mobile terrestrial laser scanning and non metric aerial photography with data reduction and surface modelling techniques to render dems from the resulting very high resolution datasets the approach is used to generate and model a precise dense topographic dataset for a 2 5 km reach of the braided rees river new zealand data were acquired rapidly between high flow events and incorporate over 5 x 109 raw survey observations with point densities of 1600 pts m 2 on exposed bar and channel surfaces a detailed error analysis of the resulting sub metre resolution is described to quantify dem quality across the entire surface model this reveals unparalleled low vertical errors for such a large and complex surface model between 0 03 and 0 12 m in exposed and inundated areas of the model respectively copyright 2013 john wiley sons ltd

archaean plate tectonics revisited 1 heat flow spreading rate and the age of subducting oceanic lithosphere and their effects on the origin and evolution of continents a simple model which relates the rate of seafloor creation and the age of the oceanic lithosphere at subduction to the rate of continental accretion can successfully explain the apparent differences between archaean and phanerozoic terrains in terms of plate tectonics the model has been derived using the following parameters 1 the spreading rate at mid ocean ridges 2 the age of the oceanic lithosphere at the time of subduction 3 the area age distribution of the seafloor 4 the continental surface area as a fraction of the total surface area of the earth and 5 the erosion rate of continents as a function of continental surface area and the total number of continental masses observations in phanerozoic terranes suggest that there are profound differences in the nature and volume of subduction zone igneous activity depending upon the age of the oceanic lithosphere being subducted and the nature of the overriding plate that is either continental or oceanic the subduction of young oceanic lithosphere less than 50 m y old which is thermally buoyant appears to result in a reduced volume of igneous activity most of the igneous activity caused by subduction of young oceanic lithosphere is either siliceous plutonism or bimodal tholeiitic rhyolitic volcanism when very young lithosphere is being subducted 50 m y old appears to result in greater volumes of igneous activity including the eruption of andesitic magmas thus andesites could only begin to be abundant in the rock record when older oceanic lithosphere began to be subducted our model predicts that as the earth aged and as heat flow from the interior of the earth diminished the proportion of old oceanic lithosphere being subducted increased fundamentally changing the nature of subduction zone igneous activity and the rate of continental accretion if the subduction of old oceanic lithosphere results in an 8 10 times greater volume of subduction zone magmatism our model predicts or explains all of the following observed features of earth history 1 archaean terranes appear to record two periods of rapid continental accretion between 3 8 and 3 5 b y ago and between 3 1 and 2 6 b y ago 2 there are very few differences and many marked similarities between rocks from archaean terranes and equivalent rocks from phanerozoic terranes 3 the total continental area appears to have remained essentially constant for the past 2 b y 4 archaean andesites are comparatively rare and the relative abundances of mafic and siliceous rocks appear to change during the archaean and the proterozoic with siliceous volcanics becoming proportionately more abundant in the geologic record with time 5 plutonic tonalites and trondhjemites appear to have been relatively much more abundant during the archaean plate tectonics is thus shown to have evolved over time due to a gradually decreasing rate of creation of oceanic lithosphere meaning that archaean tectonics and phanerozoic tectonics are but two points on an evolutionary continuum

optimizing photogrammetric dems for glacier volume change assessment using laser scanning derived ground control points photogrammetric processing of archival stereo imagery offers the opportunity to reconstruct glacier volume changes for regions where no such data exist and to better constrain the contribution to sea level rise from small glaciers and ice caps the ability to derive digital elevation model dem measurements of glacier volume from photogrammetry relies on good quality well distributed ground reference data which may be difficult to acquire this study shows that ground control points gcps can be identified and extracted from point cloud airborne lidar data and used to control photogrammetric glacier models the technique is applied to midtre lovenbreen a small valley glacier in northwest svalbard we show that the amount of ground control measured and the elevation accuracy of gcp coordinates based on known and theoretical error considerations has a significant effect on photogrammetric model statistics dem accuracy and the subsequent geodetic measurement of glacier volume change models controlled with fewer than 20 lidar control points or gcps from sub optimal areas within the swath footprint overestimated volume change by 14 53 over a 2 year period dems derived from models utilizing 20 25 or more gcps however gave volume change estimates within 4 of those from repeat lidar data 0 51 m a 1 between 2003 and 2005 our results have important implications for the measurement of glacier volume change from archival stereo imagery sources

the case for archaean boninites rare archaean light rare earth element lree enriched mafic rocks derived from a strongly refractory mantle source show a range of features in common with modern boninites these archaean second stage melts are divided into at least two distinct groups whundo type and whitney type whundo type rocks are most like modern boninites in terms of their composition and association with tholeiitic to calc alkaline mafic to intermediate volcanics small compositional differences compared to modern boninites including higher al2o3 and heavy ree hree probably reflect secular changes in mantle temperatures and a more garnet rich residual source whundo type rocks are known from 3 12 and 2 8 ga assemblages and are true archaean analogues of modern boninites whitney type rocks occur throughout the archaean as far back as ca 3 8 ga and are closely associated with ultramafic magmatism including komatiites in an affiliation unlike that of modern subduction zones they are characterised by very high al2o3 and hree concentrations and their extremely depleted compositions require a source which at some stage was more garnet rich than the source for either modern boninites or whundo type second stage melts low la yb and la gd ratios compared to whundo type rocks and modern boninites either reflect very weak subduction related metasomatism of the mantle source or very limited crustal assimilation by a refractory mantle derived melt regardless the petrogenesis of the whitney type rocks appears either directly or indirectly related to plume magmatism if whitney type rocks have a boninitic petrogenesis then a plume related model similar to that proposed for the modern tongan high ca boninites might apply but with uniquely archaean source compositions and source enrichment processes second stage melts from barberton s africa 3 5 ga and ca 3 0 ga rocks from the central pilbara australia have features in common with both whundo and whitney types but appear more closely related to the whitney type subduction zone processes essentially the same as those that produce modern boninites have operated since at least 3 12 ga while a uniquely archaean boninite forming process involving more buoyant oceanic plates and very inefficient mantle source enrichment may have occurred before then

the mesoarchean emergence of modern style subduction abstract well preserved volcanic sequences span the paleoarchean to neoarchean evolution of the pilbara craton in northwestern australia this region provides the best physical evidence bearing on the stage of earth s history when modern style tectonic processes began paleoarchean assemblages in the eastern nucleus of the craton the 3 51 3 24 ga pilbara supergroup show few features that can reasonably be interpreted as evidence for modern style subduction processes incompatible trace element enriched felsic volcanic horizons show geochemical evidence for the interaction between mafic magmas and crust but this evidence on its own can equally well be interpreted in terms of either a subduction enriched mantle source or local and limited assimilation of felsic crust into the voluminous tholeiitic magmas that dominate the pilbara supergroup viewed in context within the thick autochthonous and consistently upward younging pilbara supergroup these felsic units are most likely related to the same plume dominated processes that formed the basalts that dominate the supergroup it is very unlikely that modern style plate tectonic processes played any role in the paleoarchean evolution of the pilbara craton although some form of non uniformitarian e g flat subduction process may have operated in stark contrast the mesoarchean units of the west pilbara terrane and the late tectonic basins that cover that boundary between the west and east pilbara terranes show clear evidence for modern style convergent margin processes igneous rocks in this belt which flanks the old eastern cratonic nuclei have enriched geochemical signatures that cannot be accounted for by crustal contamination this region is also characterised by a linear magmatic and structural fabric by the presence of lithologically and geochronologically exotic belts and by the presence of a broad belt of isotopically more juvenile crust the collective strength of these arguments provides compelling evidence that a modern style oceanic arc fringed the east pilbara terrane at 3 12 ga and accreted to that terrane by 2 97 ga these assemblages mark the minimum age for the birth of modern style plate subduction process

formation of band ogives and associated structures at bas glacier d arolla valais switzerland hambrey m j glasser n f goodsell becky 2002 formation of band ogives and associated structures at bas glacier d arolla valais switzerland journal of glaciology 48 161 pp 287 300 keywords europe switzerland geometrical structure three dimensional structure radar observation glacier crevasse models debris interface basal ice glacial tongue stratification glacier

measurement and parameterization of aerodynamic roughness length variations at haut glacier d arolla switzerland spatial and temporal variations in aerodynamic roughness length z0 on haut glacier d arolla switzerland during the 1993 and 1994 ablation seasons are described based on measure ments of surface microtopography the validity of the microtopographic z0 measurements is established through comparison with independent vertical wind profile z0 measurements over melting snow slush and ice the z0 variations are explained through correlation and regression analyses using independent measurements of meteorological and surface variables and parameterizations are developed to calculate z0 variations for use in surface energy balance melt models several independent variables successfully explain snow z0 variation through their correlation with increasing surface roughness caused by ablation hollow formation during snow melt non linear parameterizations based on either accumulated melt or accumulated daily maximum temperatures since the most recent snowfall explain over 80 of snow z0 variation the z0 following a fresh snowfall on an ice surface is parameterized based on relationships with the underlying ice z0 snow depth and accumulated daily maximum temperatures none of the independent variables were able to successfully explain ice z0 variation although further comparative studies are needed the results lend strong support to the microtopo graphic technique of measuring z0 over melting glacier surfaces

evidence for basal cavity opening from analysis of surface uplift during a high velocity event haut glacier d arolla switzerland high rates of surface uplift and horizontal velocities were measured during a hydrologically induced spring speed up event spatial patterns of surface uplift are analyzed to estimate components of vertical motion due to flow along an inclined bed and vertical strain areas are identified where surface uplift was most likely due in part to the opening or enlargement of subglacial cavities by bed separation results suggest a widespread enlargement of subglacial cavities during the event and survival of residual cavities after the event the spatial pattern of cavity enlargement closely matches previously identified axes of preferential subglacial drainage it is suggested that localized cavity opening along axes of preferential drainage may constitute the initial stage in the seasonal development of channelized subglacial drainage it is concluded that spatial and temporal variations in glacier motion may play an active role in determining the structure and rate of development of subglacial drainage during the summer melt season

diurnal fluctuations in glacier ice deformation haut glacier d arolla switzerland mair d hubbard b nienow p willis i fischer u h 2008 diurnal fluctuations in glacier ice deformation haut glacier d arolla switzerland earth surface processes and landforms 33 8 1272 1284 sponsorship carnegie trust for the universities of scotland

lidar measurement of snow depth a review laser altimetry lidar is a remote sensing technology that holds tremendous promise for mapping snow depth in snow hydrology and avalanche applications recently lidar has seen a dramatic widening of applications in the natural sciences resulting in technological improvements and an increase in the availability of both airborne and ground based sensors modern sensors allow mapping of vegetation heights and snow or ground surface elevations below forest canopies typical vertical accuracies for airborne datasets are decimeter scale with order 1 m point spacings ground based systems typically provide millimeter scale range accuracy and sub meter point spacing over 1 m to several kilometers many system parameters such as scan angle pulse rate and shot geometry relative to terrain gradients require specification to achieve specific point coverage densities in forested and or complex terrain additionally snow has a significant volumetric scattering component requiring different considerations for error estimation than for other earth surface materials we use published estimates of light penetration depth by wavelength to estimate radiative transfer error contributions this paper presents a review of lidar mapping procedures and error sources potential errors unique to snow surface remote sensing in the near infrared and visible wavelengths and recommendations for projects using lidar for snow depth mapping

using an ultra long range terrestrial laser scanner to monitor the net mass balance of urumqi glacier no 1 eastern tien shan china at the monthly scale we describe the use of a terrestrial laser scanner tls to monitor the net mass balance of urumqi glacier no 1 eastern tien shan we used an ultra long range riegl vz 6000 tls which is specially designed for surveying snow and ice covered terrain to create repeated high spatiotemporal resolution dems focusing on the monthly scale 25 april 28 may 2015 net mass balance according to the tls derived dems the area of urumqi glacier no 1 was 1 558 km 2 on 25 april 2015 and the average surface elevation change was 0 225 m by comparing the results from the use of tls with the conventional glaciological mass balance method the correlation coefficient r 2 between glaciological elevation changes of individual stakes and the tls derived geodetic elevation change of corresponding points was 0 85 considering the uncertainty of both methods this is a promising result using the in situ measured snow densities snow pits of the glacier surface the geodetic net mass balance was 0 074 m w e which is slightly positive the mean uncertainty in the tls derived monthly net mass balance was 0 018 m w e showing that the tls surveying system presented accurate and relevant results and is therefore suitable to monitor mass balance evolution of mountain glaciers

seasonal changes in the morphology of the subglacial drainage system haut glacier d arolla switzerland dye tracing techniques were used to investigate the glacier wide pattern of change in the englacial subglacial drainage system of haut glacier d arolla during the ablation seasons of 1990 and 1991 analysis of breakthrough curve characteristics indicate that over the course of a melt season a system of major channels developed by headward growth at the expense of a hydraulically inefficient distributed system by the end of the melt season this channel system extended at least 3 3 km from the snout of the 4 km long glacier and drained the bulk of supraglacially derived meltwater passing through the glacier the upper limit of the channel system closely followed the retreating snowline up glacier rates of headward channel growth reached c 65 m d 1 although these rates decreased in the upper 1 km of the glacier where snowline retreat exposed a patchy firn aquifer it appears that the removal of snow with its high albedo and significant water storage capacity from the glacier surface resulted in a dramatic increase in the volume of runoff into moulins and in the peakedness of daily runoff cycles this induced transient high water pressures within the distributed drainage system which caused it to evolve rapidly into a channelised system it is therefore likely that at a local scale channel growth occurred down glacier from moulins and that the overall up glacier directed pattern of channel formation was caused by the retreating snowline exposing new moulins and crevasses to inputs of ice derived meltwater damping of diurnal melt inputs by storage in the firm aquifer accounts for the slowing of channel growth in the upper glacier 1998 john wiley sons ltd

morphological response of an alpine braided reach to sediment laden flow events braided gravel bed rivers show characteristic temporal and spatial variability in morphological change and bedload transport under steady flow and sediment supply rates their morphodynamic behavior and long term evolution in response to nonstationary external forcing is less well known we studied daily morphological changes in a well constrained reach of an alpine braided river that is subject to regulated sediment laden flows associated with hydroelectric power exploitation as well as occasional floods we found that net reach erosion and deposition were forced by upstream sediment supply albeit in a nonlinear fashion the spatial distribution of morphological change and inferred spatially distributed sediment transport rates varied strongly along the braided reach and between successive sequences of flushing local morphological change was driven by two factors 1 local relief leading to the preferential filling of topographic lows and erosion of highs particularly during longer duration floods which allow braided dynamics to be maintained and 2 system memory leading to a negative autocorrelation in bed level changes where erosion was followed by deposition of similar magnitude and vice versa this effect was associated with the temporary storage of high sediment loads from flushing due to the abrupt on off nature of these flows and reveals the relatively efficient transport of sediment in a river that is heavily impacted upon by flow abstraction in general the internal morphodynamics of the braided river condition their own response to external forcing events and thus sediment transfer

review of earth science research using terrestrial laser scanning abstract the application of advanced remote sensing technologies including terrestrial laser scanning tls to the earth sciences has increased rapidly in the last two decades improving the spatial and temporal resolution of data terrestrial laser scanning units have evolved into a common tool in studies of spectral and structural geology seismology natural hazards geomorphology and glaciology special consideration of the advantages and limitations of tls in each of these fields is discussed in depth in the context of important work published in each field the workflow used in a tls survey is crucial to the success of the survey and field specific earth science workflows are therefore also discussed products based on tls data such as triangulated irregular networks tin and digital surface models dsm are commonplace tools throughout the earth sciences and the use of these tools to measure slip distributions fault geometries aeolian transport river bed morphologies and flows and other research problems is expanded on where appropriate the review concludes with a discussion of recent trends in tls instrument development and their potential impact on the use of tls in the earth sciences in the future

medial moraines of the haut glacier d arolla valais switzerland debris supply and implications for moraine formation the haut glacier d arolla displays three medial moraines an ablation dominant moraine east of the glacier centre line an ice stream interaction moraine west of the glacier centre line and a medial lateral supraglacial moraine complex along the western margin of the glacier the eastern moraine is formed by the emergence of coarse angular clasts from a series of short longitudinal debris bands 1 km from the glacier terminus this debris is derived from rock falls at the glacier head wall and follows a low level transport path through the glacier the western moraine is formed partly by the direct fall of weathered debris on to the ice surface at a point 2 6 km from the snout but it receives further increments of sediment from extensive longitudinal englacial debris bands developed from the convergence of two ice streams with lateral englacial debris septa the medial lateral moraine complex is formed largely by rock falls from the western valley wall but is also nourished by a debris layer developed at the base of the small tributary glacier de la mitre this layer crops out at the eastern margin of the re sultant inset ice stream and releases more rounded abraded and comminuted rock fragments to supplement the surface debris cover of supraglacial origin

earth tide forcing of glacier drainage 1 fourier analysis reveals that winter electrical self potential sp water pressure pw and electrical conductivity ec time series collected beneath haut glacier d arolla switzerland are forced by earth and atmospheric tides forcing is dominant during periods of expanding bedrock consistent with glacier substrate deformation periodically driving water from the ice body into the bed this may modify the strength of subglacial sediments and could therefore influence glacier drainage and motion on a global scale

sediment export transient landscape response and catchment scale connectivity following rapid climate warming and alpine glacier recession abstract in the face of rapid climate warming rapid glacier recession should lead to a marked increase in the spatial extent of the paraglacial zone in glaciated drainage basins the extent of the paraglacial zone has been well established to be transient but there are very few studies of this transient response and what it means for sediment export there is good reason to expect that glacier recession could increase basin scale sediment connectivity as sediment becomes less dependent on glacier surface transport proglacial streams are more able to migrate laterally than subglacial streams and so access sediment for transport and glacier debuttressing may aid the development of gullies that can dissect moraines and so aid hillslope to proglacial zone connectivity by using records of the flushing of hydroelectric power installations we were able to develop a record of coarse sediment sand and gravel export from a basin with a rapidly retreating valley glacier the haut glacier d arolla from 1977 to 2014 modelling suggested that these data could only be partially controlled by transport capacity implying an important role for sediment supply and potentially for the influence of changing sediment connectivity indeed there was evidence of the effects of glacial debuttressing upon gullying processes and hence a possible increase in the ease of connection of upstream basins to the proglacial area more recently we were able to show possible temperature control on sediment export which may only have become apparent because of the progressive development of better sediment connectivity however whilst rapid glacier recession should result in theory in a progressive increase in connectivity of sediment sources to the basin outlet the supply to capacity ratio does not increase continually with glacier recession until maximum capacity is reached we identified two possible examples of why first gullying was also accompanied by the sediment accumulation at the base of moraines that was too coarse to be transported by the proglacial stream maintaining disconnection of the upper basins second the sediment capacity ratio appeared to be elevated during periods of more rapid retreat and we attribute this to the importance of a continued supply of unworked glacial till before fluvial reworking and sorting of freshly exposed sediment increased the resistance of sediment to entrainment and hence export rates thus the transient geomorphic response of glaciated basins to glacier recession may involve negative feedbacks that can reduce the extent to which increases in connectivity elsewhere in the basin lead to increased sediment export

shrimp u pb zircon dating of archean core complex formation and pancratonic strike slip deformation in the east pilbara granite greenstone terrain sensitive high resolution ion microprobe shrimp u pb dating of zircons from granitic rocks in the east pilbara granite greenstone terrain has provided time constraints for main tectonic events in the shaw granitoid complex and has shown that deformation was intricately related to granitoid intrusion the earliest recognized deformation activity occurred within the split rock shear zone srsz probably between 3470 and 3420 ma the timing geometry and kinematics of this shear zone suggest that it was a midcrustal detachment in a core complex type extensional setting it was active during the intrusion of synkinematic sheeted granodiorite of the north shaw suite and brittle extensional faulting within the upper crust samples of gray migmatic gneiss and a diorite that occur structurally below the srsz were dated at 3451 1 ma and 3463 2 ma respectively indicating that melting and metamorphism took place in the lower units during extension in the middle to upper crust the 3470 3420 ma extensional event is most consistent with extensional collapse possibly as a result of delamination or convectional thinning of part of the lithosphere activity on the pancratonic strike slip mulgandinnah shear zone msz was constrained by the crystallization age of a synkinematic granitic dyke to have occurred at 2934 2 ma the msz and activity on the sholl shear zone of the western pilbara at 2960 ma smith et al 1998 are consistent with a regional nw se directed compressional stress field at this time steepening of greenstone belt stratigraphy has been attributed to diapirism but probably occurred after a 3300 3200 ma compressional event and following deposition of the youngest clastic sediments in the eastern pilbara stratigraphic sequence diapiric processes did not play a major role during the early evolution of the eastern pilbara craton from 3470 to 3300 ma

an integrated structure from motion and time lapse technique for quantifying ice margin dynamics fine resolution topographic data derived from methods such as structure from motion sfm and multi view stereo mvs have the potential to provide detailed observations of geomorphological change but have thus far been limited by the logistical constraints of conducting repeat surveys in the field here we present the results from an automated time lapse camera array deployed around an ice marginal lake on the western margin of the greenland ice sheet fifteen cameras acquired imagery three times per day over a 426 day period yielding a dataset of 19 000 images from these data we derived 18 point clouds of the ice margin across a range of seasons and successfully identified calving events ranging from 234 to 1475 m2 in area and 815 8725 m3 in volume induced by ice cliff undercutting at the waterline and the collapse of spalling flakes low ambient light levels locally reflective surfaces and the large survey range hindered analysis of smaller scale ice margin dynamics nevertheless this study demonstrates that an integrated sfm mvs and time lapse approach can be employed to generate long term 3 d topographic datasets and thus quantify ice margin dynamics at a fine spatio temporal scale this approach provides a template for future studies of geomorphological change

statistical modelling of the surface mass balance variability of the morteratsch glacier switzerland strong control of early melting season meteorological conditions in this study we analyse a 15 year long time series of surface mass balance smb measurements performed between 2001 and 2016 in the ablation zone of the morteratsch glacier complex engadine switzerland for a better understanding of the smb variability and its causes multiple linear regressions analyses are performed with temperature and precipitation series from nearby meteorological stations up to 85 of the observed smb variance can be explained by the mean may june july temperature and the total precipitation from october to march a new method is presented where the contribution of each month s individual temperature and precipitation to the smb can be examined in a total sample of 2 24 16 8 million combinations more than 90 of the observed smb can be explained with particular combinations in which the may june july temperature is the most recurrent followed by october temperature the role of precipitation is less pronounced but autumn winter and spring precipitation are always more important than summer precipitation our results indicate that the length of the ice ablation season is of larger importance than its intensity to explain year to year variations the widely used june july august temperature index may not always be the best option to describe smb variability through statistical correlation

seasonal variations in ice deformation and basal motion across the tongue of haut glacier d arolla switzerland records of surface motion englacial tilt and repeat inclinometry are used to determine patterns of surface internal and basal motion across the tongue of haut glacier d arolla switzerland over temporal scales ranging from days to months findings are interpreted with reference to contemporaneous measurements of subglacial water pressures and prior knowledge of the glacier s subglacial drainage system structure long term inclinometry results show pronounced extrusion flow over a subglacial drainage axis with basal velocities up to twice those measured at the glacier surface deformation profiles are more conventional away from the drainage axis with basal velocities 60 70 of surface velocities comparison of long term tilt rates from repeat inclinometry and englacial tilt meters shows close correspondence englacial tiltmeter data are used to reconstruct internal velocity profiles and to split surface velocities into internal deformation and basal motion contributions over spring summer and autumn winter periods although spatial patterns of surface movement are similar between periods patterns of internal and basal motion are not results are interpreted in terms of the location of sticky and slippery spots with temporally changing patterns of basal drag reflecting changing distributions of water pressure

evolution of the internal drainage system in the lower part of the ablation area of storglaci aren sweden during the 1989 melt season ten tracer experiments were conducted to investigate seasonal diurnal and spatial variations in the internal drainage system in the ablation area of storglaciaren sweden dye was injected into moulins and dye concentration and discharge were monitored in two streams at the glacier terminus sydjakk and nordjakk dye emerged only in sydjakk transit velocities ranged from 0 07 to 0 29 m s implying that drainage was through a well defined conduit system velocity and discharge relations suggest that these conduits are part of a multi branched arborescent network of individually braided wide low passages a progressive decline in dispersivity during the early part of the melt season reflects structural changes in these conduits presumably including a decrease in the degree of braiding and an increase in size the system reached its late season configuration in early august by which time the energy dissipated by the flowing water would have sufficed to melt between 0 7 and 21 m 3 of ice per meter of conduit length depending on conduit size potential closure rates exceed melt rates on conduit walls throughout most of the drainage system and so conduits are probably full of water during periods of higher daily discharge with water pressures exceeding atmospheric pressure variations in tracer return curves and dispersivity on a diurnal time scale also appear to reflect changes in the degree of braiding in this case resulting from drowning of low divides between channels as discharge increases

mountain glacier velocity variation during a retreat advance cycle quantified using sub pixel analysis of aster images coverage of ice velocities in the central part of the southern alps new zealand is obtained from feature tracking using repeat optical imagery in 2002 and 2006 precise orthorectifica tion co registration and correlation is carried out using the freely available software cosi corr this analysis combined with short times between image acquisitions has enabled velocities to be captured even in the accumulation areas where velocities are lowest and surface features ephemeral the results indicate large velocities for mountain glaciers i e up to 5md 1 as well as dynamic changes in some glaciers that have occurred between 2002 and 2006 for the steep and more responsive fox and franz josef glaciers the speed increased at the glacier snout during the advance period while the low angled and debris covered tasman glacier showed no measurable velocity change velocity increases on the steeper glaciers are the result of an observed thickening and steepening of the glacier tongues as they moved from a retreat phase in 2002 to an advance phase in 2006 this contrasting behaviour is consistent with historic terminus position changes the steeper glaciers have undergone several advance retreat cycles during the observation period 1894 to present while the low angled glacier showed little terminus response until retreat resulting from the accelerating growth of a proglacial lake commenced in 1983

glacier mass balance determination by remote sensing and high resolution modelling an indirect methodology for determining the distribution of mass balance at high spatial resolution using remote sensing and ice flow modelling is presented the method based on the mass continuity equation requires two datasets collected over the desired monitoring interval i the spatial pattern of glacier surface elevation change and ii the mass flux divergence field at haut glacier d arolla valais switzerland the mass balance distribution between september 1992 and september 1993 is calculated at 20 m resolution from the difference between the pattern of surface elevation change derived from analytical photogrammetry and the mass flux divergence field determined from three dimensional numerical flow modelling constrained by surface velocity measurements the resultant pattern of mass balance is almost totally negative showing a strong dependence on elevation but with large localized departures the computed distribution of mass balance compares well r 2 0 91 with mass balance measurements made at stakes installed along the glacier centre line over the same period despite the highly optimized nature of the flow modelling effort employed in this study the good agreement indicates the potential this method has as a strategy for deriving high spatial and temporal resolution estimates of mass balance

hydrological controls on patterns of surface internal and basal motion during three spring events haut glacier d arolla switzerland three early melt season high velocity events or spring events occurred on haut glacier d arolla switzerland during the melt seasons of 1998 and 1999 the events involve enhanced glacier velocity during periods of rapidly increasing bulk discharge in the proglacial stream and high subglacial water pressures however differences in spatial patterns of surface velocity internal ice deformation rates the spatial extent of high subglacial water pressures and in rates of subglacial sediment deformation suggest different hydrological and mechanical controls the data from two of the events suggest widespread ice bed decoupling particularly along a subglacial drainage axis creating the highest rates of basal motion and plug flow in the overlying ice the other event showed evidence of less extensive ice bed decoupling and sliding along the drainage axis with more mechanical support for ice overburden transferred to areas adjacent to decoupled areas we suggest that 1 plug flow may be a common feature on glaciers experiencing locally induced reductions in basal drag 2 under certain circumstances enhanced surface motion may be due in part to non locally forced enhanced bed deformation and 3 subglacial sediment deformation is confined to a depth of the order of centimetres to decimetres

automated monitoring of subglacial hydrological processes with ground penetrating radar gpr at high temporal resolution scope and potential pitfalls kulessa b a d booth a hobbs and a l hubbard 2008 automated monitoring of subglacial hydrological processes with ground penetrating radar gpr at high temporal resolution scope and potential pitfalls geophysical research letters 35 24 l24502

decadal shoreline assessment using remote sensing along the central odisha coast india one of the major requirements of planning coastal protection works is to understand the processes of erosion deposition sediment transport flooding and sea level changes which continuously alter the shoreline significant erosion can affect the stability and productivity of aquatic environment which may have severe implications for coastal inhabitants the middle coastal plains of odisha state on the east coast of india were investigated for morphological assessment of shoreline accurate demarcations of shorelines were carried out at parts of odisha coast specifically along gahirmatha paradip and coast above devi river to quantify erosion and accretion at annual to decadal scale for the years 1990 2000 and 2012 satellite derived remote sensing data landsat and irs p6 were used in the study digital shoreline analysis system discovered the eroded and accreted parts of the study area gahirmatha and coast above devi river experienced heavy erosion during 2000 2012 compared with 1990 2000 whereas paradip coast has comparatively undergone accretion during 2000 2012 some accreted spots are identified nearby river mouths which are attributed to heavy accretion of eroded materials by the action of sediment transport the detailed analysis reveals a maximum erosion of 124 33 and 154 m in a decade at gahirmatha paradip and coast above devi river respectively southern parts of gahirmatha coast showed highly dynamic behavior near hukitola bay and barrier island and are acting as a natural breakwater to conserve the shoreline this region had undergone severe geomorphologic changes due to natural as well as human interventions and poses a threat this coast exhibits unique reasons for erosion with various degrees of combinations of sediment depletion human activities high frequency of cyclones and floods sea level rise etc this study concludes that the shoreline of odisha coast is under heavy erosion and needs scientific and management attention

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

surface velocity determination on large polar glaciers by aerial photogrammetry aerial photogrammetric block triangulation a standard and well developed technique for extending accurate control for mapping into the interior of a region from a few points of known position on its perimeter can be readily adapted to determine surface velocities on bodies of ice which are too large and often too crevassed to be studied effectively by conventional ground surveying velocities are calculated from the changes in positions of the same natural surface features determined from photography of two or more epochs and the elapsed time this method is capable of providing many uniformly spaced measurements over the whole moving ice surface thus allowing the production of maps of velocity and strain rate which are valuable in analyzing the ice flow regime results from measurements completed some years ago on byrd glacier one of the largest outlet glaciers from the east antarctic plateau are presented as an example of what the method can yield by means of doppler satellite surveying relative positions of control points for each photography epoch can be determined with sub meter accuracy making the technique suitable also in regions where no fixed land features exist a brief description of a project under way in such an area on ice stream b in west antarctica is given

an enhanced temperature index glacier melt model including the shortwave radiation balance development and testing for haut glacier d arolla switzerland an enhanced temperature index glacier melt model incorporating incoming shortwave radiation and albedo is presented the model is an attempt to combine the high temporal resolution and accuracy of physically based melt models with the lower data requirements and computational simplicity of empirical melt models represented by the degree day method and its variants the model is run with both measured and modelled radiation data to test its applicability to glaciers with differing data availability five automatic weather stations were established on haut glacier d arolla switzerland between may and september 2001 reference surface melt rates were calculated using a physically based energy balance melt model the performance of the enhanced temperature index model was tested at each of the four validation stations by comparing predicted hourly melt rates with reference melt rates predictions made with three other temperature index models were evaluated in the same way for comparison the enhanced temperature index model offers significant improvements over the other temperature index models and accounts for 90 95 of the variation in the reference melt rate the improvement is lower but still significant when the model is forced by modelled shortwave radiation data thus offering a better alternative to existing models that require only temperature data input

sequence stratigraphy of the archaean supracrustal belts of the pilbara block western australia abstract the stratigraphic succession of the 3580 2770 m y old granite greenstone terrain of the pilbara block is re assessed by the first and second order sequence stratigraphic techniques that are the standard for phanerozic terrains with the view to testing the conformity of stratigraphic cause and response a holistic tectonostratigraphic framework is presented that pairs the supracrustal and crustal rock records the resulting sequence scheme is tested against the cause of first order sequence cycles viz global sea level responses to supercontinent breakup and assembly three first order inter regional unconformities divide the stratigraphic succession of the supracrustal belts into four units of first order megasequence status in order of decreasing age these are named the warrawoona gorge creek roebourne and mount negri megasequences a total of 17 second order supersequences are also named although some may represent supersequence sets the megasequences and or their genetic crustal equivalents represent the preserved rock record of four megacycles of forearc arc and or back arc geotectonic evolution associated with the convergent margins of a pilbara continent individual supersequences are the rock record of separate second order basins or basin phases and reflect the different geotectonic components of each megasequence the four megacycles had respective longevities from oldest to youngest of 150 m y 230 m y 160 m y and 180 m y they are identical in their stratigraphic successions and predicted first order sea level cycles to phanerozoic first order tectono eustatic cycles and are interpreted as the same response to global tectonic change the warrawoona and gorge creek megacycles and the roebourne and mount negri megacycles are tectonogenetic pairs of the east pilbara and the west pilbara megacycle sets respectively the east pilbara megacycle set evolved over a period of 380 m y from 3490 ma to 3110 ma whereas the west pilbara megacycle set evolved over a period of 340 m y from 3110 ma to 2770 ma the two megacycle sets are identical in their longevity geotectonic components and predicted sea level cycles to convergent margin wilson and supercontinent cycles and are thereby interpreted individually as the oldest established records of the supercontinent cycle the implication of this interpretation is that a steady state global tectonic regime has been in operation from early in earth s history which has important consequences for theoretical modelling of the earth s early tectonic style and secular changes in its geochemical regime

qualitative and quantitative applications of lidar imagery in fluvial geomorphology the potential for geomorphological mapping and quantitative calculations of light detection and ranging lidar data within fluvial geomorphology was studied for two river catchments within belgium dijle and ambleve which differ in physical settings and floodplain morphology two commercial of the shelf lidar datasets with different specifications horizontal resolution and vertical accuracy were available for parts of the floodplains of both catchments real time kinematic rtk global positioning system gps data were used as ground truth for error calculations qualitative analysis of lidar data allowed the identification of former channel patterns levees colluvial hillslope and fan deposits these results were confirmed by field data topographic surveys and historical maps the pixel resolution proved to be an important factor in the identification of small landforms only features with a width equal to or larger than lidar resolution can be detected this poses limits on the usability of regionally available lidar data which often have a horizontal resolution of several metres the lidar data were also used in a quantitative analysis of channel dynamics in the study area the width of the dijle river channel increased 3 m on average between 1969 and 2003 a sediment budget of channel processes for the period 1969 2003 indicated a total river bank erosion of 16 1 103 m3 and a total within channel deposition of 7 1 103 m3 resulting in a net river erosion of 9 0 103 m3 or c 0 4 mg year 1 per metre river length sequential lidar data can in theory be used to calculate vertical sedimentation rates as long as there is control on the error of the reference levels used copyright 2008 john wiley and sons ltd

evolution of the southern abitibi greenstone belt based on u pb geochronology autochthonous volcanic construction followed by plutonism regional deformation and sedimentation abstract new mapping and u pb zircon geochronological results in the southern abitibi greenstone belt sagb support an autochthonous regional stratigraphy comprised of nine supracrustal assemblages rather than the collage of allochthonous terranes proposed in recent publications based on lithological and geochronological criteria these supracrustal assemblages also encompass the swayze shining tree and montcalm greenstone belts indicating that despite separation by large granitic intrusions they are in fact part of one extensive greenstone belt in conjunction with the mapping the geochronological results support coherent upward facing stratigraphic sections with about 20 of the samples containing inherited zircons with ages similar to those found in underlying assemblages the seven oldest assemblages represent semi continuous volcanism from 2750 to 2697 ma the volcanism is compositionally diverse ranging from komatiite and tholeiitic basalt to calc alkaline mafic to felsic lavas intimate intermingling of the different magma clans occurs throughout much of the stratigraphic section regional fault control on the distribution of the volcanic assemblages provides evidence for early dip slip movement associated with volcanic extension dating back to at least 2725 ma the two youngest assemblages are dominantly sedimentary and were unconformably deposited on the volcanic assemblages in close proximity to regional faults the earlier sedimentary assemblage consists of turbidites and minor iron formation deposited from 2696 to 2692 ma and the youngest one of subaerial conglomerates fluvial sandstones and alkalic to shoshonitic volcanic rocks ranging in age from 2687 to 2675 ma the sedimentary assemblages are broadly contemporaneous with the emplacement of syntectonic granitic plutons regional folding and reactivated movement on the regional faults probably related to accretion of the abitibi to the superior province craton autochthonous repetition of different geodynamic environments over the 50 million years of volcanic activity with five dominantly tholeiitic komatiitic assemblages and two dominantly calc alkaline assemblages as well as the extensive intermingling of these different magma clans in a number of the assemblages appears to be unique to the archean it suggests complex large scale and long lived interaction between mantle plumes and subduction zone magmas the nd isotope data indicate a derivation of the diverse volcanic magmas from homogeneously depleted sources with end 2 5 0 5 demonstrating a lack of contamination by ancient enriched components

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

changes in geometry and subglacial drainage of midre lovenbreen svalbard determined from digital elevation models digital elevation models dems of the bed and surface of the polythermal midre lovenbreen svalbard are used to identify changes in glacier geometry between 1977 and 1995 the calculated mean annual mass balance 0 61 m water equivalent w e a 1 is more negative than that derived from field measurements 0 35 m w e a 1 although the error associated with this value 0 7 m a 1 suggests that the difference may be accounted for by errors however similar discrepancies between dem based and field based measurements of mass balance have been reported elsewhere in svalbard although errors may be responsible patterns of surface elevation change may also be explained in terms of patterns of ablation accumulation and dynamics the theoretical structure of the subglacial drainage system is modelled using different assumptions about subglacial water pressure in 1977 and 1995 these reconstructions are compared with the observed positions of proglacial outlet streams decreasing subglacial water pressure results in a decrease in the influence of surface morphology and an increase in the role of the bed topography on drainage routing which generally leads to more dispersed drainage long term changes in the position of proglacial outlet streams occur as a result of changes in glacier geometry but short term changes may also occur in response to early season water pressures controlled by meteorological and hydrological conditions copyright 2003 john wiley sons ltd