flow directions in dikes from anisotropy of magnetic susceptibility data the bootstrap way one of the first applications of anisotropy of magnetic susceptibility ams was an attempt to determine flow directions from mafic dikes khan 1962 since the seminal work of knight and walker 1988 defining the expected behavior of ams in response to magma flow there has been increasing interest in using ams for this purpose here we present a quantitative method for interpretation of ams data from dikes using a parametric bootstrap first dikes must be sampled with at least five and preferrably more samples from within 10 cm of the dike margin the distributions of the eigenvalues and eigenvectors of the ams tensor are delineated by calculating eigenparameters of many bootstrapped paradata sets we generate paradata sets by first selecting a sample at random then calculating a replacement set of data by drawing tensor elements from normal distributions with the mean and standard deviation of the entire site the bounds containing 95 of the eigenparameters of the bootstrapped data serve as confidence limits for the parameter of interest classification of dikes proceeds as follows sites whose maximum and intermediate eigenvalues could not be distinguished are deemed uninterpretable in addition sites with principal eigenvectors with angles 45 away from the dike margin inverse or with markedly different directions on either side of the dike scissored are excluded the remaining dikes are classified as having unique flow direction information if the principal eigenvectors from at least one side are distinct from the dike plane based on the distribution of the bootstrapped principal eigenvectors if neither side has principal eigenvectors distinct from the dike plane the dikes are classified as having lineation information only a study comprising 251 dikes from the troodos ophiolite has 151 sites with directional data 38 sites with lineations only 7 inverse sites 5 scissored sites and 55 sites not fitting into any other category the flow directions interpreted from the data were generally southerly toward a fossil transform zone

flow and fabric development during the diapiric rise of magma scaled isothermal experiments of the internal circulation induced by viscous drag at a diapir country rock interface are compared with published theoretical studies of flow induced finite deformation inside a rising sphere and new numerical results are presented for the incremental strain pattern developed in spherical diapirs the results predict a time dependent deformation history within rising diapirs that produces finite strains characterized by strong oblate flattening strains at the margin and strong vertical prolate strains in the center with an intervening zone of low plane strain finite strains are discussed in terms of the different sub fabrics expected to form in granitoids after considering the history of rheology and temperature distribution in rising magma strong rheological and temperature gradients are predicted for the margins of internally circulating diapirs that can lead to the formation of strong penetrative foliations at the margin and magmatic or even isotropic fabrics in the i

inferring domain state from magnetic hysteresis in high coercivity dolerites bearing magnetite with ilmenite lamellae abstract hysteresis loops were measured for 16 dolerite samples from separate precambrian dykes whose remanence is probably primary remanence is carried by grains of magnetite subdivided into fine particles usually by ilmenite lamellae as seems common in mafic igneous rocks of high coercivity coercive force h c ranges from 9 to 40 10 3 a m 110 500 oe the ratio j rs j s of saturation remanence to saturation magnetization ranges from 0 10 to 0 45 j rs j s varies in approximate proportion to h c with a constant of proportionality appropriate for pseudo single domain magnetite with one or two domain walls per particle a cooling cycle to 77k causes large 40 on average demagnetization of j rs in most samples supporting the dominance of pseudo single domain magnetite most samples also show a large 29 on average decrease in h c on cooling to 140k suggesting magnetostrictive control of h c perhaps through internal stresses opposing domain wall motion only the three dolerites with h c greater than 30 10 3 a m 380 oe show little change in h c on cooling suggesting dominance by single domain particles with shape anisotropy in magnetite grains subdivided into single domain particles by ilmenite lamellae magnetic interaction may lower j rs j s from the expected 0 5 some theories 1 2 suggests that this is due to a self demagnetizing field from magnetic poles on the surface of each grain of magnetite subdivided by ilmenite and should be corrected for another theory 3 suggests that this correction is not necessary because the self demagnetizing field is already approximately cancelled due to magnetic poles inside each subdivided grain at the ends of magnetite particles the latter suggestion is favoured by our three highest h c dolerites whose j rs j s averages 0 42 0 04 before and 0 66 0 06 after correction for the self demagnetizing field from poles on the surface of magnetite ilmenite grains applying this correction to our other dolerites usually raises j rs j s significantly above 0 5 which is unreasonable for pseudo single domain magnetite hence correcting for self demagnetizing fields from poles on the surface of magnetite ilmenite grains in rocks is not recommended whatever the domain state

assessment of erosion and deposition in steep mountain basins by differencing sequential digital terrain models abstract digital elevation models dems built from repeated topographic surveys permit producing dem of difference dod that enables assessment of elevation variations and estimation of volumetric changes through time in the framework of sediment transport studies dem differencing enables quantitative and spatially distributed representation of erosion and deposition within the analyzed time window at both the channel reach and the catchment scale in this study two high resolution digital terrain models dtms derived from airborne lidar data 2 m resolution acquired in 2005 and 2011 were used to characterize the topographic variations caused by sediment erosion transport and deposition in two adjacent mountain basins gadria and strimm vinschgau venosta valley eastern alps italy these catchments were chosen for their contrasting morphology and because they feature different types and intensity of sediment transfer processes a method based on fuzzy logic which takes into account spatially variable dtms uncertainty was used to derive the dod of the study area volumes of erosion and deposition calculated from the dod were then compared with post event field surveys to test the consistency of two independent estimates results show an overall agreement between the estimates with differences due to the intrinsic approximations of the two approaches the consistency of dod with post event estimates encourages the integration of these two methods whose combined application may permit to overcome the intrinsic limitations of the two estimations the comparison between 2005 and 2011 dtms allowed to investigate the relationships between topographic changes and geomorphometric parameters expressing the role of topography on sediment erosion and deposition i e slope and contributing area and describing the morphology influenced by debris flows and fluvial processes i e curvature erosion and deposition relations in the slope area space display substantial differences between the gadria and the strimm basins while in the former erosion and deposition clusters are reasonably well discriminated in the latter characterized by a complex stepped structure we observe substantial overlapping erosion mostly occurred in areas that show persistency of concavity or transformation from convex and flat to concave surfaces whereas deposition prevailingly took place on convex morphologies less expected correspondences between curvature and topographic changes can be explained by the variable sediment transport processes which are often characterized by alternation of erosion and deposition between different events and even during the same event

crustal stress determination from boreholes and rock cores fundamental principles abstract obtaining quantitative information on the state of stress in the crust can only be accomplished by accessing the zone of interest by drilling the borehole cavity however disrupts the virgin stress state by concentrating stresses in predictable patterns with a number of consequences at sufficiently low stress magnitudes the concentrated stresses amplify the elastic anisotropy azimuthally around the borehole because the elastic properties of most rocks depend nonlinearly on stress at higher levels the stresses damage then fracture the rock near the wellbore wall or within a growing core stub indeed almost all of the borehole techniques indirectly measure stress through these manifestations of the concentrated stresses this contribution reviews at a fundamental level the concentration of stresses by the borehole the effects on the materials in the borehole s vicinity and how these are used to infer stress states stress concentrations applied to rocks which are generally nonlinear elastic materials induce both radial and azimuthal variations in elastic wave speeds near the borehole that can be used to infer stress directions from advanced acoustic logging methods hydraulic fractures initiate propagate and remain propped open by measured pressures that can be interpreted with knowledge of the stress concentrations to obtain quantitative stress magnitudes at higher stress levels the rock fails producing borehole breakouts or drilling induced tensile fractures both of which are indicative of stress directions and can be used to constrain stress magnitudes similarly the various styles of drilling induced core fractures indicate both stress directions and the faulting environment encountered unfortunately no method currently allows for complete determination of the stress tensor using a number of different but complementary techniques is necessary to best constrain in situ stress states

magma flow directions in dikes of the koolau complex oahu determined from magnetic fabric studies we compared the magnetic fabric with the macroscopic surface lineation direction previously assumed to be parallel with magma flow direction for 35 dikes of the koolau complex oahu anisotropy of magnetic susceptibility ams was determined for 530 samples from 59 dikes including a sill and a pluglike intrusive body and two filled lava tubes and statistically significant ams clusters were found in all but five dikes for the 35 lineated dikes the mean maximum ams direction 1 coincides with the macroscopic lineations to within 25 in 18 and to within 15 in eight the ams ellipsoid shape in about half of the samples is prolate cigar shaped and in about half is oblate pancake shaped we interpret the ams to be determined by shape anisotropy of ferromagnetic grains the mean total anisotropy is 2 2 and total anisotropy h ranges from 0 24 to as high as 14 12 the principal ams axes for samples from a dike are tightly grouped on equal area plots and for most of the dikes the minimum ams axes plot near to the pole of the dike our ams measurements enable us to infer absolute magma flow directions for half the dikes studied the maximum ams axes of samples from one side of the dike form a tight cluster on an equal area plot and those from the other side of the dike form another tight cluster the two clusters are close together separated by 10 30 for narrow dikes 100 cm wide and are farther apart 30 60 for wide dikes and are symmetrically disposed on either side of the plane of the dike we infer that these paired clusters are caused by imbrication of nonequant ferromagnetic crystals against each margin of the dike during deposition in a velocity gradient and hence indicate the flow azimuth i e the absolute magma flow direction nearly half of the dikes measured 25 gave paired ams plots in 12 the magma flowed up at low oblique angles 5 30 from the horizontal in five it flowed down at 5 20 in four it flowed horizontally 5 in three it flowed up at a steep angle 50 75 and in one it flowed down at a steep angle the magma flow in general was rarely vertical or horizontal

sediment output and effective discharge in two small high mountain catchments in the bavarian alps germany abstract sediment output solid and dissolved load from two small alpine rivers partnach and lahnenwiesgraben in the bavarian alps was measured during three summer field seasons from 2001 2003 there is high spatial variability of sediment output between the catchments and a high temporal variability between observation periods sediment transport in the partnach river reintal is dominated by solute load whereas the lahnenwiesgraben river transports a much greater proportion of solid load this difference can mainly be explained by the different lithologies of the systems the reintal catchment is dominated by massive triassic limestone in the lahnenwiesgraben catchment in addition to limestones unconsolidated rocks marls and mudstone layers are significant furthermore large rockslide dams in the partnach valley isolate large parts of the reintal catchment from solid load output the components of fluvial sediment transport were where possible calculated by using flow duration curves and rating curve techniques in the lahnenwiesgraben event specific rating curves were used to determine suspended load on the broad database of 55 measured flood events in the lahnenwiesgraben a good correlation r pearson 0 9 between event peak discharge and suspended load of the event was established effective discharge was calculated for the different types of sediment load solid and dissolved and total load in the reintal effective discharge for total load is found in low flow classes close to mean discharge because sediment output is dominated by dissolved load which has its maximum efficiency at low and moderate discharges in the lahnenwiesgraben most work is done by discharges much higher than mean discharge during extreme individual flood events

constraints on water reservoir lifetimes from catchment wide 10be erosion rates a case study from western turkey the functionality and retention capacity of water reservoirs is generally impaired by upstream erosion and reservoir sedimentation making a reliable assessment of erosion indispensable to estimate reservoir lifetimes widely used river gauging methods may underestimate sediment yield because they do not record rare high magnitude events and may underestimate bedload transport hence reservoir lifetimes calculated from short term erosion rates should be regarded as maximum values we propose that erosion rates from cosmogenic 10be which commonly integrate over hundreds to thousands of years are useful to complement short term sediment yield estimates and should be employed to estimate minimum reservoir lifetimes here we present 10be erosion rates for the drainage basins of six water reservoirs in western turkey which are located in a tectonically active region with easily erodible bedrock our 10be erosion rates for these catchments are high ranging from 170 to 1040 t km2 yr when linked to reservoir volumes they yield minimum reservoir lifetimes between 25 5 and 1650 360 years until complete filling with four reservoirs having minimum lifespans of 110 years in a neighboring region with more resistant bedrock and less tectonic activity we obtain much lower catchment wide 10be erosion rates of 33 to 95 t km2 yr illustrating that differences in lithology and tectonic boundary conditions can cause substantial variations in erosion even at a spatial scale of only 50 km in conclusion we suggest that both short term sediment yield estimates and 10be erosion rates should be employed to predict the lifetimes of reservoirs

magma flow inferred from preferred orientations of plagioclase of the rio ceara mirim dyke swarm ne brazil and its ams significance

magmatic fabric acquisition mechanisms in a syenite results of a combined anisotropy of magnetic susceptibility and image analysis study the structural significance of the anisotropy of magnetic susceptibility ams and acquisition mechanisms of silicate and ferrimagnetic mineral fabrics are investigated in the archean lebel syenite intrusion ontario canada bulk mineral subfabrics are determined by intercept counting of mineral phases in classified digital images of thin sections cut parallel to the principal planes of the magnetic fabric ellipsoids of the samples intensities shapes and principal direction orientations of the resulting intercept ellipsoids are generally similar to the corresponding ams ellipsoids differences are due mainly to bimodal distribution of mineral fabrics observed on foliation planes of some samples showing pre full crystallization textures and structural overprinting in samples deformed after crystallization subfabrics of clinopyroxene and magnetite in samples showing pre full crystallization microstructure are investigated by measuring inertia tensors of individual grain shapes the resulting inertia tensor ellipsoids indicate that magnetic fabrics in these rocks are strongly correlated to the shape preferred orientation of magnetite which is similar to the overall petrofabric of the samples crystal size distributions of clinopyroxene and magnetite indicate that they formed during in situ crystallization and that magnetite probably appeared late in the crystallization and flow history of the magma analysis of preferred orientations of these grains suggests that the petrofabrics of the samples were acquired during flow with strongly interacting grains analogous to a logjam in a river the final characteristics of the ams and silicate petrofabric are the end points of a continuous crystallization and flow history in the magma rather than transient late features

the partitioning of the total sediment load of a river into suspended load and bedload a review of empirical data the partitioning of the total sediment load of a river into suspended load and bedload is an important problem in fluvial geomorphology sedimentation engineering and sedimentology bedload transport rates are notoriously hard to measure and at many sites only suspended load data are available often the bedload fraction is estimated with rule of thumb methods such as maddock s table which are inadequately field tested here the partitioning of sediment load for the pitzbach is discussed an austrian mountain stream for which high temporal resolution data on both bedload and suspended load are available the available data show large scatter on all scales the fraction of the total load transported in suspension may vary between zero and one at the pitzbach while its average decreases with rising discharge i e bedload transport is more important during floods existing data on short and long term partitioning is reviewed and an empirical equation to estimate bedload transport rates from measured suspended load transport rates is suggested the partitioning averaged over a flood can vary strongly from event to event similar variations may occur in the year to year averages using published simultaneous short term field measurements of bedload and suspended load transport rates maddock s table is reviewed and updated long term average partitioning could be a function of the catchment geology the fraction of the catchment covered by glaciers and the extent of forest but the available data are insufficient to draw final conclusions at a given drainage area scatter is large but the data show a minimal fraction of sediment transported in suspended load which increases with increasing drainage area and with decreasing rock strength for gravel bed rivers whereby in large catchments the bedload fraction is insignificant at 1 for sand bed rivers the bedload fraction may be substantial 30 50 even for large catchments however available data are scarce and of varying quality long term partitioning varies widely among catchments and the available data are currently not sufficient to effectively discriminate control parameters

magma flow directions of shallow dykes from the east greenland volcanic margin inferred from magnetic fabric studies abstract the role played by plume generated crustal magmatic complexes in the segmentation of volcanic margins is highlighted by a preliminary study of magma flow directions in shallow intrusives from the east greenland volcanic margin we investigate the magmatic texture using anisotropy of magnetic susceptibility for eight dykes of tholeitic affinity belonging to a dyke swarm associated with the tertiary opening of the north atlantic ocean the thickness of the sampled dykes ranges from 3 to 37 m the dykes are of doleritic texture and contain up to 12 of opaque minerals and 35 of plagioclase laths dykes showing a magnetic foliation plane within the dyke plane i e a magnetic fabric usually attributed to magmatic processes represent 40 of the samples from the studied swarm these dykes have a low degree of anisotropy and their ellipsoid of magnetic susceptibility is strongly oblate inverse magnetic fabrics where the maximum principal susceptibility axis lies near the pole to the dyke account for 60 of the data we interpret these inverse fabrics either as alteration minerals with highly prolate ellipsoids of magnetic susceptibility or primary titanomagnetites with oblate ellipsoid of low anisotropy the flow direction is inferred for normal fabric dykes using the mirror imbrication of magnetic lineation analysis of thin sections shows a good agreement between magnetic fabric directions and phenocryst preferred orientations the inferred flow directions are predominantly horizontal throwing a new light on volcanic margin development

a general power equation for predicting bed load transport rates in gravel bed rivers 1 a variety of formulae has been developed to predict bed load transport in gravel bed rivers ranging from simple regressions to complex multiparameter formulations the ability to test these formulae across numerous field sites has until recently been hampered by a paucity of bed load transport data for gravel bed rivers we use 2104 bed load transport observations in 24 gravel bed rivers in idaho to assess the performance of eight different formulations of four bed load transport equations results show substantial differences in performance but no consistent relationship between formula performance and degree of calibration or complexity however formulae containing a transport threshold typically exhibit poor performance furthermore we find that the transport data are best described by a simple power function of discharge from this we propose a new bed load transport equation and identify channel and watershed characteristics that control the exponent and coefficient of the proposed power function we find that the exponent is principally a factor of supply related channel armoring transport capacity in excess of sediment supply whereas the coefficient is related to drainage area a surrogate for absolute sediment supply we evaluate the accuracy of the proposed power function at 17 independent test sites

borehole instability in high porosity berea sandstone and factors affecting dimensions and shape of fracture like breakouts abstract stress induced breakouts in vertical boreholes are failure zones caused by excessive compressive stress concentration at the borehole wall along the springline of the least horizontal far field stress wellbores are sometimes drilled into aquifers or oil reservoirs that are weak poorly consolidated and highly porous sandstone formations which are often conducive to breakout formation breakouts are an expression of borehole instability and a potential source of sand production on the other hand the breakout phenomenon can be used advantageously in obtaining an estimate of the in situ stress condition the average orientation of breakouts as identified by borehole geophysical logging is a reliable indicator of in situ stress directions it has also been suggested that breakout dimensions could potentially be used as indicators of in situ stress magnitudes the research reported here has concentrated on the unique type of breakouts observed for the first time in high porosity berea sandstone drilling experiments in rock blocks subjected to critical far field true triaxial stress regimes simulating in situ conditions induced breakouts that were unlike the dog ear ones previously observed in granites limestones and low porosity sandstones the newly observed breakouts were thin tabular and very long resembling fractures that counterintuitively extended perpendicular to the maximum principal stress we found that a narrow zone ahead of a fracture like breakout tip underwent apparent localized grain debonding and compaction in the field such zones have been termed compaction bands and are a source of concern because in oil fields and aquifers they constitute curtains of low permeability that can impede the normal flow of oil or water in order to determine whether a correlation exists between fracture like breakouts and in situ stress we conducted several series of tests in which the minimum horizontal and vertical stresses were held constant and the maximum horizontal stress h was increased from test to test these tests showed strong dependence of the breakout length on far field stress signaling that potentially the ability to assess fracture like breakout length in the field could be used to estimate in situ stress magnitudes in conjunction with other indicators another series of tests revealed that breakout length increased substantially when borehole diameter was enlarged this result suggested that in the field where wellbore size is considerably larger fracture like breakout could extend to sizable distances creating a sand production hazard two series of tests one to evaluate the effect of drill bit penetration rate and the other to verify the drilling fluid flow rate effect on breakout formation and dimensions yielded inconsistent results and showed no unique trends remarkably fracture like breakouts maintained a consistent narrow width of about 5 10 grain diameters irrespective of the test conditions this characteristic supports the suggestion that fracture like breakouts are emptied compaction bands

event based suspended sediment dynamics in a central new york watershed abstract using discharge and sediment data collected from 23 events between 2008 and 2010 in a 311 km2 watershed of central new york we investigated event sediment dynamics of the studied watershed after showing the statistical difference of the data in different seasons we examined the detailed hysteresis patterns of all events spring events had figure eight with anticlockwise figure 8 ac clockwise c anticlockwise ac and complicated patterns summer events had c ac figure 8 ac figure 8 c and complicated patterns fall and winter events had the same patterns as those in summer as well as a weak loop pattern the diversity of patterns within and between seasons suggests that detailed processes of sediment transport were not only complicated during one event but also varied from season to season although hysteresis analysis failed to identify these detailed processes and the associated sediment sources in such a relatively large watershed it successfully revealed a common feature dominating the transport processes event sediment transport was generally supply limited further analysis on the correlation between event sediment yield ssye and event peak discharge qpeak indicated that i events with clockwise patterns tended to have more ssye than those with other patterns for the same qpeak and ii data from all events may be statistically well described by a single ssye qpeak equation regardless of hysteresis patterns this equation i reveals that complicated event transport processes may be lumped into a simple process over events and ii reflects the general supply limited nature identified by hysteresis analysis using this equation and the magnitude frequency analysis we further discovered that in the past 21 years sediment was mainly transported by more frequent but relatively small discharges with the recurrence interval no more than 0 5 year

field based analysis of sediment entrainment in two high gradient streams located in alpine and andine environments abstract this paper presents an analysis of critical thresholds for bedload transport based on field measurements conducted in two small high gradient streams the rio cordon italian alps and the tres arroyos chilean andes the threshold of incipient motion was identified by using marked particles displacement and both flood and flow competence approaches the findings are expressed in terms of shields parameter dimensionless discharge and specific stream power and are used to identify the effects of relative grain size relative depth and bedform resistance overall particle entrainment tends to be size selective rather than exhibiting equal mobility and the high values of dimensionless critical shear stress observed at both study sites confirm the additional roughness effects of step pool morphologies that are very effective in reducing the bed shear stress and causing an apparent increase in critical shear stress

taking the river inside fundamental advances from laboratory experiments in measuring and understanding bedload transport processes bedload transport in gravel bed rivers impacts channel stability the lifespan of hydraulic structures physical components of aquatic habitat and long term channel evolution field measurements of bedload transport are notoriously difficult which precludes understanding many of the processes and mechanics associated with grain motion such uncertainties are exacerbated when using bedload transport equations most of which were derived using data from a single river or set of laboratory flume experiments recently laboratory experiments have focused on better quantifying the processes that impact bedload fluxes which can then be used to improve sediment transport predictions we highlight recent advances in laboratory instrumentation that can be used in bedload transport studies in particular more accurate ways to measure bedload fluxes near bed turbulence bed grain sizes and topography hold great promise laboratory experiments have also fundamentally improved our understanding of the influence of sediment supply and armoring processes on bedload fluxes and channel conditions the importance of flow hydrographs in controlling total bedload transport rates and bedload hysteresis has also been demonstrated using flume experiments finally many details about the mechanics of grain motion including flow turbulence bed arrangement and particle transport statistics are only possible through laboratory investigations and we feature key knowledge gaps that can be improved with further study

anisotropy of magnetic susceptibility in the ponta grossa dyke swarm brazil and its relationship with magma flow direction abstract measurements of anisotropy of magnetic susceptibility ams in 95 mafic dykes mainly tholeiites 10 200 m in width from the mesozoic ponta grossa swarm southern brazil revealed two main types of magnetic fabric type i fabric plane k 1 k 2 parallel to the dyke plane represents magma flow within the dykes whereas type ii plane k 1 k 3 parallel to the dyke plane is compatible with a fabric pattern reflecting vertical compaction of the magma column fabric type i dominates 51 of the dykes within the swarm whereas type ii 38 of the dykes concentrates mainly in the western region where the dykes intrude sediments considering the dykes with type i fabrics it is concluded that 58 of the dykes were fed by horizontal or sub horizontal k 1 inclinations less than 30 magmatic flow and 42 were fed by inclined to vertical k 1 inclinations more than 30 magma flow the latter are more frequent in the southeastern part of the swarm suggesting a magma source close to this area although there may have been other sources in other regions where dykes with inclined flow and distinct chemical characteristics are also found

sediment supply grain protrusion and bedload transport in mountain streams 1 steep streams occupy a large fraction of mountainous drainage basins and partially control the sediment supplied to downstream rivers in these channels sediment transport equations typically over predict bedload flux by several orders of magnitude because they do not account for sediment supply limited conditions thus accurate predictions of bedload flux require an estimate of the sediment available for transport in a given event we demonstrate through field measurements that boulder step protrusion is a proxy for sediment availability protrusion is also a function of the time elapsed since an extreme event and this simple relationship can be used to estimate the relative sediment availability at any given time in addition bedload transport predictions in a steep channel were only accurate if they included this variable protrusion predictions of sedimentation hazards water quality river restoration success long term channel network evolution and channel stability may therefore require estimates of sediment availability for transport

magnetic and plagioclase linear fabric discrepancy in dykes a new way to define the flow vector using magnetic foliation in basaltic dykes the magnetic lineation k1 maximum magnetic susceptibility axis is generally taken to indicate the flow direction during solidification of the magma this assumption was tested in tertiary basaltic dykes from greenland displaying independent evidence of subhorizontal flow the digital processing of microphotographs from thin sections cut in k1 k2 planes yields the preferred linear orientation of plagioclase which apparently marks the magma flow lineation in up to 60 of cases the angular separation between k1 and the assumed flow direction is greater than 45 this suggests that the uncorroborated use of magnetic lineations in dykes is risky a simple geometrical method is proposed to infer the flow vector from ams in dykes based solely on magnetic foliations

relationships between suspended sediment concentrations and discharge in two small research basins in a mountainous mediterranean area vallcebre eastern pyrenees abstract the relationships between suspended sediment concentrations and discharge were studied at the can vila 0 56 km2 and ca l isard 1 32 km2 sub basins of the vallcebre research area eastern pyrenees during a period of 5 years that included 67 events of diverse magnitude abandoned agricultural fields and forests are the main land use in the can vila basin whereas the ca l isard basin is mainly forested though there are also some heavily eroded landscapes badlands the most frequent events were of a single discharge peak although double and multiple peaked events were also recorded clockwise positive hysteretic loops occurred in both catchments mainly during the wet seasons when precipitation was of moderate intensity average of 18 mm h 1 and baseflow before the event was rather high average for ca l isard 8 1 l s 1 km 2 and for can vila 11 76 l s 1 km 2 the bulk of stream discharge came from saturated areas whereas sediments came mainly from the stream channels counter clockwise negative hysteretic loops were much more frequent in the ca l isard basin mainly in summer when rainfall intensity was high average of 32 5 mm h 1 and baseflow was low average for ca l isard 0 94 l s 1 km 2 and for can vila 0 73 l s 1 km 2 most of the water and sediment came from the badlands eight shaped loops occurred in transition periods mainly in the ca l isard basin

suspended sediment load during floods in a small stream of the dolomites northeastern italy abstract suspended sediment load was analyzed in a small high gradient stream of the eastern italian alps which was instrumented to measure discharge and sediment transport the ratio of suspended to total sediment yield and the relations between sediment concentration and water discharge were analyzed for seven floods which occurred from 1991 to 1996 in summer and autumn from june to october different patterns of hysteresis in the relation between suspended sediment and discharge were related to types and locations of active sediment sources the within storm variation of particle size of suspended sediment during a major flood indicates a coarsening of transported material for increasing discharge an analysis of grain size has shown that erosion areas on hillslopes were the main sources of suspended load

characteristics of sediment dynamics following large scale sediment supply events in mountain watersheds in japan abstract large scale sediment supply events lses cause not only a sudden increase in sediment discharge immediately after their occurrence but also a long term condition of elevated sediment yield in japan many lses triggered by heavy rainfall or earthquakes have created high risks for sediment related disaster however the difference between sediment dynamics following a lse triggered by rainfall and one triggered by an earthquake is unclear as the sediment dynamics due to rainfall and those due to earthquakes have not been compared using consistent methodology in this study we estimated the volume of sediment supply vl m3 time series of the volume of sediment yield vy m3year 1 and the non dimensional parameter nvy as estimated by dividing vl by the catchment area and annual maximum 3 day rainfall amount using the same methodology for 16 events in eight study basins in japan we used annual maximum 3 day rainfall amounts as a surrogate for discharge using these parameters we estimated the period over which the effect of a lse continues pls sediment retention time residence time tr1 and time for active sediment yield to recover to the background level recovery time tr2a in addition we estimated the recovery time tr2b based on when the maximum of nvy immediately after the lse decreased to a certain extent this calculation allowed us to estimate the recovery time even when background level was unknown both residence and recovery times ranged from

estimation of maximum horizontal principal stress magnitude from stress induced well bore breakouts in the cajon pass scientific research borehole in this paper we utilize the mechanical properties of core samples detailed observations of stress induced well bore breakouts and estimates of the magnitude of shmin from hydraulic fracturing experiments to construct a vertical profile of the maximum horizontal principal stress shmax to 3 5 km depth in the cajon pass borehole as in essentially all other boreholes the hydraulic fracturing stress measurements in the cajon pass borehole yielded appreciably more and more reliable data on the magnitude of the least principal horizontal stress shmin than the maximum principal horizontal stress shmax to utilize the breakout observations to constrain the magnitude of shmax a brittle failure criterion was used that is based on the effective strain energy concept this failure criterion also allows us to account for the polyaxial stress around the borehole and to incorporate the role of pore fluid pressure on rock strength in various ways a comparison of the shmax profile estimated from the breakouts with estimates of shmax obtained from the hydraulic fracturing tests indicates that they compare fairly well for the case when the effect of pore pressure on hydraulic fracture initiation is negligible the overall stress state to a depth of 3 5 km in the well corresponds to a normal strike slip faulting regime the shmax profile indicates several marked decreases in stress magnitude associated with major fault zones an observation consistent with the shmin profile obtained from hydraulic fracturing tests

hyperconcentrated flow and sediment transport at steep slopes in order to simulate a fine material slurry of a debris flow a clay suspension of various concentrations was recirculated in a steep flume the effect of an increasing fluid density and viscosity on the flow behavior and the bed load transport capacity of the flow was examined viscous effects were found to become important below a limiting particle reynolds number of about 10 above this limiting value density effects cause an increase in the bed load transport rates as compared to similar conditions with clear water as transporting fluid the experimental data in this range can be described with conventional newtonian formulas and is analyzed together with other bed load transport data two different calculation schemes are proposed for the steep slope range is n n 10 where the bed load concentration is significant with respect to the total flow depth below the critical particle reynolds number of 10 the bed load transport rates decreased strongly

drivers of erosion and suspended sediment transport in three headwater catchments of the mexican central highlands quantifying suspended sediment exports from catchments and understanding suspended sediment dynamics within river networks is important especially in areas draining erodible material that contributes to the siltation of downstream reservoirs and to the degradation of water quality a one year continuous monitoring study of water and sediment fluxes was conducted in three upland subcatchments 3 0 9 3 and 12 0 km2 located within the cointzio basin in the central volcanic highlands of mexico michoacan state two subcatchments generated high sediment exports i e huertitas 900 1500 t km 2 y 1 and potrerillos 600 800 t km 2 y 1 whereas the third subcatchment was characterized by a much lower sediment yield i e la cortina 30 t km 2 y 1 such disparities in subcatchment behaviours were associated with the presence of severely gullied areas in huertitas and potrerillos rather than with rainfall erosivity indices an adapted classification of hysteretic patterns between suspended sediment concentration ssc and discharge was proposed because 42 of flood events contributing to 70 of sediment export were not discriminated by the classical clockwise anticlockwise typology this new classification allowed the identification of relationships in the hydrosedimentary responses of successive floods a stream transport capacity limit was also detected during hydrograph recession phases overall hydrosedimentary processes proved to be seasonally dependent sediment export was repeatedly limited by the stream transport capacity during the first part of the rainy season whereas a channel minimum erosivity threshold was frequently reached at the end of the season

fabric of the rio ceara mirim mafic dike swarm northeastern brazil determined by anisotropy of magnetic susceptibility and image analysis 1 anisotropy of magnetic susceptibility ams and petrofabric studies of the early cretaceous rio ceara mirim dike swarm reveal that shape preferred orientation of opaque grains controls the magnetic fabric the 350 km long swarm is characterized by relatively thick dikes of the order of 20 m up to 150 m in width the strong magnetic susceptibility of these rocks around 5 10 2 si is attributed to magnetite with low ti content the magnetite usually forms euhedral to subhedral equant to skeletal grains the resulting ams has a large proportion of abnormal fabric types as observed in 58 of the 50 dikes studied the remaining 42 of the dikes show a normal fabric regionally characterized by steep magnetic foliations and subhorizontal lineations in the central eastern part of the swarm however the lineation plunges downdip suggesting a magmatic feeder zone the shape alignment of the plagioclase supports the inferred regional flow pattern indicating a primary origin for the normal ams inverse to highly imbricate magnetic fabrics have lineations perpendicular to or at a high angle to the dike wall a shape lineation of opaque grains lies generally close to the magnetic lineation while the foliation is provided by the oblate shaped plagioclase fabric petrofabric studies indicate that the abnormal magnetic fabric is unrelated to flow competition of interstitial magnetite grains crystallizing either along as well as perpendicular to the magma stretching direction seems to account for the weak magnetic anisotropy and the irregular distribution of the ams types on the swarm

magma flow inferred from anisotropy of magnetic susceptibility in the coastal parana etendeka igneous province evidence for rifting before flood volcanism the parana etendeka igneous province is one of the largest flood volcanic provinces in the world peak magmatic activity at 132 ma is believed to have occurred about 5 m y before the birth of south atlantic sea floor and development of rift basins along the brazilian coastal margin anisotropy of magnetic susceptibility ams measurements on 283 samples 28 flows and 3 sills from the etendeka igneous province of namibia and 180 samples 21 flows from the parana province in brazil reveal remarkably consistent fabric orientations with maximum susceptibility k1 axes subhorizontal and parallel to the rifted margin the ams results are most likely due to shape anisotropy reflecting magma flow directions suggesting that lava flows and intrusive conduits near the eventual rifted margin were controlled by structures having topographic expression in existence at the time of peak flood volcanism these results imply that rifting preceded flood volcanism at least in the portion of the magmatic province within 100 km of the nascent mid atlantic ridge

bedload transport in the instrumented catchment of the rio cordon part ii analysis of the bedload rate abstract sediment transport is monitored by a specially designed instrumentation installed on a steep mountain streams the rio cordon the variability of bedload rate and yield reflects the variability in flow discharge bedload and flow data for ordinary low peak flow floods and exceptional sediment transport events are used to test the range of application of the bedload equations proposed for high gradient streams such equations overestimate bedload rate for ordinary events while their reliability increases when used to predict high bedload transport rates like those recorded during the exceptional flood that affected rio cordon on september 14 1994 the best agreement between computed and measured values of cumulated bedload volumes is found by using the bagnold bagnold r a 1956 the flow of cohesionless grains in fluids philos trans r soc london 249a 235 297 smart and jaeggi smart j m jaeggi m n r 1983 sediment transport on steep slopes mitteil 64 versuchsanstalt fur wasserbau hydrologie und glaziologie eth zurich switzerland 191 pp and rickenmann rickenmann d 1991 hyperconcentrated flow and sediment transport at steep slopes j hydraul eng zurig 117 11 1419 1439 formulas the schoklitsch equation schoklitsch a 1962 handbuch des wasserbaues 3rd edn springer wien also provides good estimations for instantaneous bedload rates at high sediment transport intensity and unlimited sediment supply conditions the formal type of the last equation is still valid and can be calibrated for low intensity bedload rates

effect of seasonal snow cover on suspended sediment runoff in a mountainous catchment summary the effect of snow cover and snowmelt on suspended sediment ss runoff at a mountainous catchment in the temperate zone was investigated the observation was carried out from march 1999 to may 2002 3 years at an experimental catchment with the area of 0 347 km 2 ranging from 280 m to 618 m above mean sea level with average stream gradient of 1 4 it was concluded that the snow accumulation and ablation process in the catchment had a significant impact on ss runoff characteristics especially during the snow melting period it was estimated that more than 60 of the annual ss load flowed out during the snow melting period because of the enhanced water discharge the daily average ss flux during the snow melting period was calculated to be 2 54 g s 1 km 2 corresponding to a 6 7 times greater ss flux than that during other periods the c q relation analysis in each runoff event revealed a dynamic change in the ss runoff mechanism during the snow melting period strong clockwise hysteresis in c q relation in the early stage of the snow melting period may be explained by consumption of the bed load by the first flush followed by quick depletion of the material on the stream bed due to suppression of further ss supply by thick snow cover counterclockwise hysteresis in c q relation was observed only in the late stage of the snow melting period ss production at steep slopes beside the stream by avalanches and surface soil slides induced by an abundance of meltwater was considered to be one of the main causes of the counterclockwise loops it would be hypothesized that exposure of other steep slopes or bluffs in the catchment apart from the stream and stream bank failure by repeating surges of the stream water stage could also be other possible ss sources causing counterclockwise hysteresis in the late snow melting period

morpho textural implications to bedload flux and texture in the sand gravel ephemeral poveda gully abstract we report on channel morpho texture and bedload transport in a natural steep sand gravel ephemeral channel draining the small poveda gully watershed in the mining area of the alto tajo natural park spain first ever continuous bedload flux and texture monitoring in a transitional sand gravel environment was undertaken by two independent reid type slot samplers morphological changes in the feeder reach have been quantified by tls terrestrial laser scanning and sfm structure from motion technologies we identified a pattern in channel bed morphology and texture morpho texture when the channel is incised its texture is coarser otherwise sand filling occurs these changes determine bedload flux and texture sand fill brings rise to high fluxes and fine grained bedload whereas incision caused by evacuation of sand leaves a sandy gravel surface with lower bedload fluxes and coarser texture a video camera recording during events allowed identification of dramatic changes in bedload flux and texture owing to the appearance and erosion of bars supplying field evidence to explain the difficulty in the prediction of bedload flux at short time intervals

experimental observations of the mechanics of borehole failure in porous sandstone abstract to investigate borehole failure under hydrostatic stress in sandstone of varying porosity experiments were conducted on three sandstone varieties with 2 5 mm bores tennessee darley dale and penrith sandstone types were selected to represent most of the spectrum of sandstone porosity variations respectively 0 07 0 12 and 0 28 confining pressures ranged up to 500 mpa and pore fluid volumometry was used to detect bore failure failed samples were studied microstructurally using optical and scanning electron microscopy each rock type failed with the development of oriented breakout features normally seen to develop around boreholes loaded under non hydrostatic stress and in tennessee sandstone at least these developed in a consistent orientation with respect to an external reference frame dip direction of foreset beds all of the rock types showed strength and or elastic anisotropy thus the formation of oriented breakouts under hydrostatic loading is attributed to the effects of anisotropy two modes of breakout development were observed in darley dale and penrith sandstones a combination of intergranular shear and extensional fracture produced broad and shallow features with breakout width unaltered during growth in tennessee sandstone a purely extensional mode of intragranular fracture was observed leading to deeper breakout features the samples tested showed higher failure pressures for smaller bore sizes when failure pressure is normalized with respect to grain crushing pressure p i and bore diameter with the product of porosity with grain size all data lie on a single master curve with bore failure pressure approximately 0 15 p i in the regime of bore size independent behaviour

sediment concentration versus water discharge during single hydrologic events in rivers relations between sediment concentration c and water discharge q for a hydrologic event such as a flood are studied qualitatively by analyzing smoothed temporal graphs discharge and concentration vs time in terms of mode spread and skewness comparing cq ratios at a given discharge on the rising and falling limbs of the discharge hydrograph provides a consistent reliable method for categorizing c q relations five common classes of such relations are single valued straight or curved clockwise loop counterclockwise loop single valued plus a loop and figure eight temporal graph mode and skewness influence the type of relation whereas temporal graph spread affects the details of the particular c q relation its graphical breadth shape orientation and plotted location field examples of the various types of relations are given including varieties that heretofore have received little attention such as the figure eight explanations for each type of c q relation are discussed

temporal variability of suspended sediment sources in an alpine catchment combining river rainfall monitoring and sediment fingerprinting influence of the rainfall regime on erosion and transfer of suspended sediment in a 905 km 2 mountainous catchment of the southern french alps was investigated by combining sediment monitoring rainfall data and sediment fingerprinting based on geochemistry and radionuclide concentrations suspended sediment yields were monitored between october 2007 and december 2009 in four subcatchments 22 713 km 2 automatic sediment sampling was triggered during floods to trace the sediment origin in the catchment sediment exports at the river catchment outlet 330 pm 100 t km 2 yr 1 were mainly driven 80 by widespread rainfall events long duration low intensities in contrast heavy local and short duration storms generated high peak discharges and suspended sediment concentrations in small upstream torrents however these upstream floods had generally not the capacity to transfer the sediment down to the catchment outlet and the bulk of this fine sediment deposited along downstream sections of the river this study also confirmed the important contribution of black marls up to 70 to sediment transported in rivers although this substrate only occupies c 10 of the total catchment surface sediment exports generated by local convective storms varied significantly at both intra and inter flood scales because of spatial heterogeneity of rainfall however black marls marly limestones contribution remained systematically high in contrast widespread flood events that generate the bulk of annual sediment supply at the outlet were characterized by a more stable lithologic composition and by a larger contribution of limestones marls quaternary deposits and conglomerates which corroborates the results of a previous sediment fingerprinting study conducted on riverbed sediment

magnetite grain shape fabric and distribution anisotropy vs rock magnetic fabric a three dimensional case study abstract shape fabric and distribution anisotropy of magnetite grains in a highly ferromagnetic s l syenite are determined for three mutually perpendicular planes on about 600 magnetite grains the grains are lenticular with an average aspect ratio of about 2 0 their preferred orientation determined by the inertia tensor method is consistent with the principal directions of the magnetic susceptibility ellipsoid and the axial ratios of the magnetic fabric ellipses are very close to those of the shape fabric ellipses e g 1 41 and 1 39 in the section plane perpendicular to the magnetic foliation and parallel to the magnetic lineation the anisotropic wavelet transform can detect and quantify the anisotropic distribution of the magnetite grains which are located interstitially along the feldspar grain boundaries this anisotropic distribution has no noticeable effect on the rock s anisotropy of magnetic susceptibility ams since only a few percent of grains are close enough to interact magnetically therefore it is realistic to consider that the ams of ferromagnetic granitic rocks originates mainly from the shape fabric of anisotropic magnetite grains and a close correlation between the magnetic fabric and the magnetite grain shape fabric is expected

step pool evolution in the rio cordon northeastern italy the principle that formative events punctuated by periods of evolution recovery or temporary periods of steady state conditions control the development of the step pool morphology has been applied to the evolution of the rio cordon stream bed the rio cordon is a small catchment 5 km2 within the dolomites wherein hydraulic parameters of floods and the coarse bedload are recorded detailed field surveys of the step pool structures carried out before and after the september 1994 and october 1998 floods have served to illustrate the control on step pool changes by these floods floods were grouped into two categories the first includes ordinary events which are characterized by peak discharges with a return time of one to five years 1 8 5 15 m3 s 1 and by an hourly bedload rate not exceeding 20 m3 h 1 the second refers to exceptional events with a return time of 30 50 years a flood of this latter type occurred on 14 september 1994 with a peak discharge of 10 4 m3 s 1 and average hourly bedload rate of 324 m3 h 1 step pool features were characterized primarily by a steepness parameter c h ls s the evolution of the steepness parameter was measured in the field from 1992 to 1998 the results indicate that maximum resistance conditions are gradually reached at the end of a series of ordinary flood events during this period bed armouring dominate the sediment transport response however following an extraordinary flood and unlimited sediment supply conditions the steepness factor can suddenly decrease as a result of sediment trapped in the pools and a lengthening of step spacing the analogy of step spacing with antidune wavelength and the main destruction and transformation mechanism of the steps are also discussed copyright 2001 john wiley sons ltd

integrating borehole breakout dimensions strength criteria and leak off test results to constrain the state of stress across the chelungpu fault taiwan article the paper describes the computation of the maximum horizontal stress h magnitude in the vicinity of the chelungpu fault taiwan host of the slip zone during the chi chi earthquake mw 7 6 1999 the scientific hole b intercepts the chelungpu fault at 1136 m at the depths of logged breakouts 940 1310 m the vertical stress v as estimated from density logs increases linearly with depth from 22 to 31 mpa a series of leak off tests yielded two reliable shut in pressures 23 7 mpa at 1085 m and 29 8 mpa at 1279 m which are lower than the estimated v albeit by only 2 1 and 0 6 mpa respectively in our analysis the shut in pressures were considered to represent estimates of the least horizontal principal stresses h at the respective depths and consequently the test induced fractures were assumed to have been vertical principal stress directions had been previously determined by others 105 155 for the maximum horizontal stress h

40ar 39ar chronology petrology and geodynamic setting of mesozoic to early cenozoic magmatism from the benue trough nigeria the benue trough is a continental scale intraplate tectonic megastructure which is part of mid african rift system this rift initiated in the latest jurassic was related to the opening of the central and south atlantic oceans mesozoic to early cenozoic magmatism accompanied this evolution two principal magmatic domains are evident the northern and southern benue in the northern domain magmatism is characterized by transitional alkaline basalts and transitional tholeiitic basalts acidic magmatism of peralkaline nature is also present in the southern benue several magmatic districts exhibit alkaline or tholeiitic affinities a detailed chronology of emplacement of this volcanism has been established using the 40 ar 39 ar radiometric method which lead to recognition of three periods of magmatic activity 1 147 106 ma well expressed in the northern benue represefited by transitional basaltic types 2 97 81 ma occurring only in the southern benue represented exclusively by alkaline intrusive rocks 3 68 49 ma restricted also to the southern benue with alkaline intrusions followed by tholeiitic subvolcanic rocks in the light of the general geodynamic evolution a scenario is proposed supported by the three chronological periods the late jurassic to albian magmatism occurred when the equatorial atlantic was still closed contemporaneous with the ne brazilian magmatism both magmatism could represent the forerunners of opening of the equatorial atlantic this activity occurred under a general extensional regime during which crustal strike slip faults gave rise to the emplacement of transitional alkaline basalts transitional tholeiitic basalts erupted along normal faults the second period of activity cenomanian to santonian restricted to the southern benue occurred after the opening of atlantic ocean during a period of decreasing extension this period ended with a santonian compressional episode the last period of activity from late maastrichtian to eocene is characterized by subsidence generated as an isostatic response to the early cretaceous crustal thinning and post rift thermal relaxation of the lithosphere expressed by tertiary e w extension

polyaxial strength criteria and their use in estimating in situ stress magnitudes from borehole breakout dimensions abstract we conducted laboratory simulation tests of borehole breakouts and investigated their potential use as an indicator of in situ stress magnitudes in westerly granite and berea sandstone we also carried out simple triaxial tests and used the results to derive several strength criteria for these rocks using the assumption that the state of stress at the breakout boundary on the borehole wall is in a state of limit equilibrium with the rock strength we attempted to determine the appropriate strength criterion for each of the two rocks we concluded that the well known mohr coulomb criterion is not compatible with the condition of stress at breakout failure on the other hand truly triaxial polyaxial strength criteria which incorporate the effect of the intermediate principal stress on failure are much more in agreement with the stress at the breakout boundary one such criterion due to nadai and another due to mogi appear suitable for determining breakout failure in the sandstone and the granite respectively thin section analysis suggests that breakout failure mechanism may play an important role in determining the appropriate strength criterion for a given rock type utilizing the appropriate strength criterion for the corresponding rock type and having knowledge of the breakout span at the borehole wall and the minimum horizontal and vertical principal stresses we were able to estimate the maximum far field principal stress within an average of 14 error

is this magnetic fabric normal a review and case studies in volcanic formations abstract when studying weakly anisotropic rocks non standard relationships between magnetic and expected petrofabric axes are sometimes observed in particular the so called inverse or intermediate fabrics a review of possible explanations for these effects is presented and leads to the conclusion that a majority of abnormal magnetic fabrics often encountered in magnetite rich volcanic rocks are due to abnormal preferred orientations or distributions of magnetite grains through case studies in dikes from skye island yemen and the iberian peninsula and magma and ash flows from the ethiopian traps and southern corsica the various possible origins of such fabrics are examined it is possible to retrieve reliable magma flow directions from these sites provided proper data selection is performed leading to non unique interpretations

evidence of magmatic activity related to middle jurassic and lower cretaceous rifting from northeastern brazil ceara mirim k ar age palaeomagnetism petrology and sr 1bnd isotope characteristics the mesozoic magmatic activity in the easternmost part of ne brazil ceara mirim is mainly represented by two pyroxene tholeiitic dykes only few dykes have alkaline character k ar ages and palaeomagnetism data indicate that ceara mirim dykes are of middle jurassic 175 160 ma and early cretaceous 140 130 ma age both middle jurassic and lower cretaceous dykes have high incompatible element concentrations and tio2 with the lower contents generally confined to the middle jurassic dykes rare tholeiitic dykes low in tio2 and incompatible elements are present sr 1bnd isotopic and other chemical data do not support appreciable crustal contamination and in a 87sr86sr vs 143nd144nd diagram almost all the dykes plot in a narrow area of the enriched quadrant of the mantle array tholeiitic and alkaline ceara mirim dykes are related to different parent magmas probably originating by different degrees of melting of garnet peridotite mantle sources characterized by distinct sr 1bnd isotope compositions and small scale chemical heterogeneities ceara mirim tholeiitic dykes show close mineralogical chemical and isotopic similarities with the lower cretaceous high tio2 tholeiites from maranhao sardinha intrusives and parana northern province basins in general chemical and sr 1bnd isotope data for high and low tio2 brazilian mesozoic tholeiites appear to be related to time integrated enriched and depleted mantle components respectively subcontinental mantle heterogeneity is believed to be due to variable enriched components related to metasomatic processes the ceara mirim jurassic dykes correlate well in terms of composition and tectonic setting with the analogue tholeiitic dyke swarms from the benue trough and can be related to the opening of the central atlantic ocean the lower cretaceous ceara mirim magmatic activity corresponds to the coeval one of the benue trough and can be related to the early rifting events responsible for the opening of the equatorial domain of the south atlantic whose oceanic crust formed between 120 and 100 ma

factors affecting the relative importance of shape and distribution anisotropy in rocks theory and experiments abstract the effect of magnetic interactions has been commonly neglected in the interpretation of the anisotropy of magnetic susceptibility ams of igneous rocks despite the likely occurrence of magnetic interactions due to their relatively high content of ferromagnetic minerals current models of magnetic interactions apply to highly simplified systems and are not directly applicable to natural rocks on this work a model that includes variables previously neglected is used to assess the relative importance of magnetically interactive and non interactive fractions in a rock results of the model show that a variable proportion of magnetically interactive grains the relative values of the bulk susceptibility degree of anisotropy and orientation of the anisotropies characteristic for each fraction all play an important role in controlling the rock ams experimental evidence illustrating the importance of the distribution of the ferromagnetic grains within a specimen is also reported and supports the model predictions both theory and experiments indicate that if a rock has unequant magnetic grains and clusters of magnetic grains the contribution to the ams of the rock will depend on the relative values of all the model variables and not only on the occurrence of magnetic interactions as previously presumed

anti clockwise hysteresis in suspended sediment concentration during individual storms holbeck catchment yorkshire england abstract analysis of the flow sediment hysteresis shape may assist in determining the sediment source area in a small basin a clockwise hysteresis occurs when sediment is derived from the bed and banks of the channel or areas adjacent to the channel whereas an anti clockwise hysteresis occurs when the upper part of the slopes is the sediment source area

spatial scale dependence of sediment dynamics in a semi arid badland drainage basin abstract problems of spatial scale transference are of key interest in drainage basin research the objective of this study was to investigate the spatial scale dependence of sediment dynamics in semi arid badland drainage basins simulated rainfall experiments indicated that on microscale plots runoff generation and sediment entrainment occurred when total rainfall exceeded 0 5 to 6 mm on pediment surfaces 1 5 to 4 mm on sandstone surfaces and 8 to 25 mm on shale surfaces the sediment concentration discharge relationship for two mesoscale basins displayed a change from clockwise to counterclockwise hysteresis when total rainfall exceeded the threshold rainfall for the initiation of flow in deep tunnel systems the initiation of tunnel flow causes counterclockwise hysteresis due to a delayed increase in sediment concentrations during a runoff event this contrasts with the clockwise hysteresis caused by flushing in the early stages of runoff for smaller rainstorms comparison of micro and mesoscale sediment dynamics indicates that microscale thresholds are not by necessity in evidence at the mesoscale in addition at the mesoscale elements exist which are non existent at the microscale e g a deep tunnel system the behaviour of the mesoscale basin is dominated by these elements rather than by the microscale components it contains

erosion quantification in the small marly experimental catchments of draix alpes de haute provence france calibration of the etc rainfall runoff erosion model abstract erosion rates measured for 15 years in the small ranging from 0 13 ha to nearly 1 km2 and steep 30 75 mountainous marly basins of draix south alps france are over 100 tons ha year in a badland area devoid of vegetation in a similar basin reforested at the end of the 19th century the sediment yield is considerably reduced less than 3 tons ha year the analysis of the sediment yield of these torrents reveals the importance of the erosion processes on slopes at the scale of the elementary gully and the influence of deposition transport and scouring processes as soon as the channel network of the basin is developed these processes were modelled by a hydrosedimentologic model developed by cemagref for flood torrent erosion and called etc etc is an integrated spatialized and global model working at the event scale the rainfall runoff component and the solid transport component which involves scouring deposition and armouring are well developed on the other hand the erosion component is not yet a physically based model as the knowledge on the elementary processes is not enough quantitative the etc model was used on a badland basin of 86 ha in area the laval and has shown its ability to simulate both water and sediment flows in mountainous and steep basins the erosion modelling highlighted the need for a better representation of the slope processes and for more information on the storing of sediments in the channel network observations carried out on the influence of the vegetation cover patterns and the links between slopes and channels should be taken into account to improve the model

river loads and modern denudation of the alps a review this paper presents the first comprehensive analysis of sediment and dissolved load across an entire mountain range we investigate patterns and rates of modern denudation of the european alps based on a compilation of data about river loads and reservoir sedimentation from 202 drainage basins that are between ca 1 to 10 000 km2 large the study basins cover about 50 of the total area of the alps modern glaciated basins have the highest sediment yields of up to 7000 t km 2 a 1 which are on average 5 to 10 times higher than in non glaciated basins likewise sediment yield and glacial cover are positively correlated instead relief is a relatively weak predictor of sediment yield the strong glacial impact in the correlations is due to glacier recession since the 19th century as well as due to glacial conditioning during repeated quaternary glaciations which have produced the strong transient state of the alpine landscape we suggest that this is the major cause for ca 3 fold enhanced denudation of the western compared to the eastern alps chemical denudation rates are highest in the external alps dominated by carbonate sedimentary rocks where they make up about one third of total denudation the high rates cannot be explained without anhydrite dissolution we estimated that only 45 of the sediments mobilized in headwaters are exported out off the alps most sediments being trapped in artificial reservoirs the total amount of sediment annually trapped within the alps equates to 43 mt when corrected for sediment storage we obtain an area weighted mean total denudation rate for the alps of about 0 32 mm a 1 the pre dam rate might be as high as 0 42 mm a 1 in total ca 35 plus 23 mt of mass are exported each year out of the alps as solids and solutes respectively these rates are not enough to out pace modern rock uplift nevertheless pattern of sediment yield across the alps coincides roughly with the intensity of glacial conditioning and modern rock uplift supporting the hypothesis of an erosion driven uplift of the alps

the effects of low magnitude flow conditions on bedload mobility in a steep mountain stream abstract the transport of coarse material strongly controls the stability and evolution of mountain fluvial systems but despite this bedload dynamics are not yet fully understood especially in mountain streams in this sense particular attention was paid on the bedload magnitude volume expressed at event scale and on the long term while few studies were focused on when and how the transport of the coarse material occurs the aim of this work was to investigate the bedload mobility in the rio cordon a mountain stream characterized by cascade and step pool morphologies with a rough streambed here the critical conditions for initiation of motion transport distance and virtual velocity expressed by the coarse streambed material were assessed and their relationships with hydraulic forcing conditions and grain size were analyzed to this end a monitoring program based on bedload tracing was maintained over 7 years allowing to analyze the bedload mobility during persistent high frequency low magnitude flow conditions to investigate the bedload mobility 250 tracers were released between 2011 and 2012 and their propagation along study site was monitored until 2018 overall 14 tracer inventories were realized determining 1697 tracer localizations during the study period the bedload dispersion resulted well described by the peak discharge magnitude qp qp and p c while no significant relationships were observed with duration of competent flow tover and effective runoff volume er transport distance and tracer grain size were negatively correlated whereas virtual velocity increased with increasing particle size in this sense the propagation velocity seems to be affected by the high frequency flows that on the one hand triggered mobilization of the coarser tracers only through limited and impulsive events and on the other hand favored a slowdown on the finer particles due to bedforms disturbance compared to other study sites the rio cordon exhibited accentuated threshold conditions with lower transport distance and virtual velocity confirming that steep mountain streams are generally influenced by a reduced transport efficiency due to protruding bedforms and macro roughness that cause a pronounced energy dissipation interestingly such condition seems to have progressively reduced from under to near bankfull flows the results were compared to the bedload mobility observed in the rio cordon during 1993 1998 enabling to quantitatively assess how the bedload dispersion varied between a setting of stable armouring layer with protruding bedforms 2012 2018 and a partial alteration of these 1993 1998 an evident difference was observed in terms of transport distance while critical conditions did not significantly change lastly the long term bedload tracing investigation highlighted that a certain legacy on the transport efficiency was produced by the persistent high frequency flow conditions over the study period a general decrease of transport distance was observed that could be explained by a progressive stabilization of streambed material previous studies suggested that such condition can be interrupted by high magnitude low frequency floods

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

mountain erosion over 10 yr 10 k y and 10 m y time scales we used cosmogenic 10 be to measure erosion rates over 10 k y time scales at 32 idaho mountain catchments ranging from small experimental watersheds 0 2 km 2 t o large river basins 35 000 km 2 these long term sediment yields are on average 17 times higher than stream sediment fluxes measured over 10 84 yr but are consistent with 10 m y erosion rates measured by apatite fission tracks our results imply that conventional sediment yield measurements even those made over decades can greatly underestimate long term average rates of sediment delivery and thus overestimate the life spans of engineered reservoirs our observations also suggest that sediment delivery from mountainous terrain is extremely episodic sporadically subjecting mountain stream ecosystems to extensive disturbance

high flow events and sediment transport in small streams in the tertiary basin area in piedmont northwest italy rainfall peak discharges and suspended sediment transport were surveyed for 280 events in three small 0 8 to 10 km2 catchments in a hilly area derived from neogene marls silts and sands under similar hydrological input conditions stream flow behaviour and sediment delivery differed considerably from one catchment to another depending on topography lithology land use and especially sediment availability analytical treatment of data showed a good fit between sediment yield and peak flow discharge less good although still significant was the correlation between sediment concentration and discharge values for different flow stages rainfall peak basin lag time and rainfall discharge showed poor or no correlation mainly due to strong variations in rainfall distribution sediment concentration in the catchments varied enormously according to season from zero up to 334 g 1 1 sediment yield was 160 900 tonnes km 2 yr 1 in the two major catchments and over 5200 tonnes km 2 yr 1 in the headwater catchment stressing the importance of small tributaries not only in inducing floods in downstream channels but also in sediment supply

pleistocene holocene climate change re establishment of fluvial drainage network and increase in relief in the swiss alps abstract data are presented about modern sediment discharge of the swiss rivers and related to the size of catchments the information reveals that the central alps have experienced denudation rates of 0 15 mm yr 1 in the foreland and 0 5 mm yr 1 in the alpine core mapping however indicates that modern erosion only affects 30 50 of the alpine surface and that fluvial and associated hillslope processes have focused erosion in 50 200 m deep valleys these valleys are incised into the glacial surface if this limited spatial extent of erosion is considered then effective erosion rates are significantly higher than average denudation rates these effective rates equal or locally exceed modern rates of rock uplift this implies that the modification of erosional processes related to the pleistocene holocene climate change has resulted in an increase in the relief at a local scale at a drainage basin scale however the relief appears not to change at present

sediment transfer processes in two alpine catchments of contrasting morphological settings summary coarse sediment transport processes in steep headwater streams may vary between bedload and debris flows events depending on basin geomorphology and sediment supply this paper compares two small catchments drainage area 4 5 km 2 located in the eastern italian alps where the dominant sediment transport processes differ substantially i e debris flows in the moscardo torrent and bedload events in the rio cordon the two basins were selected because they provided the unique opportunity to analyze long term data of debris flow and bedload volumes respectively the two basins are compared in terms of peak discharge event duration and magnitude frequency characteristics of transported sediment volumes additional bedload data from two more alpine experimental basins are also considered the results show that for comparable recurrence intervals debris flow volumes are 2 3 orders of magnitude larger than bedload volumes this contrasting sediment transfer activity can be attributed to different basin and channel morphologies which are analyzed in terms of sediment supply conditions longitudinal profiles and slope area curves

three decades of monitoring in the rio cordon instrumented basin sediment budget and temporal trend of sediment yield this paper investigates nearly 30 years of monitoring of sediment fluxes in an instrumented alpine basin rio cordon italy the collected bedload and suspended sediment transport data allows sediment dynamics to be analyzed at different time scales ranging from short single event to long term three decades the rio cordon monitoring station has been operating since 1986 continuously recording water discharge bedload and suspended load at the flood event scale a good relationship was found between peak discharges qpeak and sediment load bedload and suspended load the inter annual sediment yields were analyzed also assessing the contribution of the single floods to the total sediment budget the annual suspended load ranges from 10 to 2524 t yr 1 while the bedload varies from 0 to 1543 t yr 1 the higher annual yields were recorded in the years when large floods occurred highlighting that the sediment budget in the rio cordon is strongly controlled by the occurrence of high magnitude events investigation of the seasonal suspended load contribution demonstrated that from 1986 to 1993 most fine sediments were transported during the snowmelt summer seasons while autumn and snowmelt were the dominant seasons contributing to sediment yield in the periods 1994 2002 and 2003 2014 respectively the mean annual sediment yield from 1986 to 2014 is equal to 103 t km 2 yr 1 and overall bedload accounts for 21 of the total sediment yield the ratio between the sediment transport and the effective runoff of the events allowed the temporal trends of transport efficiency to be inferred highlighting the existence of periods characterized by different sediment availability in particular despite no significant changes in the hydrological variables i e rainfall nearly a decade 1994 2002 with high transport efficiency appears to have occurred after an exceptional event recurrence interval 100 years this event affected the sediment availability at the basin and channel bed scales and provided a legacy influencing the sediment dynamics in the basin over the long term by increasing the transport efficiency for approximately a decade this work benefits from the long lasting monitoring program undertaken in the rio cordon and is the product of long term data series the quasi unique dataset has provided detailed evidence of sediment dynamics over about three decades in a small alpine basin also enabling the effects triggered by an exceptional event to be analyzed

erosion in the western alps dora baltea basin 2 quantifying sediment yield abstract the present work shows how sediment composition can be used to constrain bed load sediment budgets in mountain catchments a database of high resolution petrographic and dense mineral analyses of detritus carried by the dora baltea river and its tributaries allowed us to partition bed load sediment budgets obtained from data available from a public authority between two different sets of sediment sources major tributaries and major geological units relative and absolute budgets of sediment bed load thus obtained are more robust than those derived from traditional empirical methods alone total detrital flux in the dora baltea drainage basin is 1 000 000 ton year bed load 590 000 ton year suspended load 410 000 ton year with denudation rates of 0 12 mm year data from italian public authority progetto di piano stralcio per l assetto idrogeologico pai parma supplemento straordinario della gazzetta ufficiale 166 more than 75 of the dora baltea total bed load 453 000 9000 ton year is derived from tributaries dora di ferret dora di veny savara grand eyvia buthier lys sourced from the highest granitoid peaks 4000 m a s l m bianco m rosa m cervino gran paradiso massifs which drain 36 of the whole catchment the m bianco massif with its granitoid lithology extreme relief and heavily glaciated drainage basins occupies only 3 of total basin area but it produces 294 000 6000 tons of arkosic sands per year which represents 50 of total dora baltea bed load the dora di veny 2 of total dora baltea mountain catchment exhibits the highest denudation rate of the whole dora baltea mountain basin 0 73 mm year the values calculated in this study compare well with measured modern river loads of partly glaciated mid latitude mountain regions

quartz c axes orientation determination using the rotating polarizer microscope abstract a fast and accurate optical method to calculate quartz c axis orientations using the rotating polarizer stage and standard thin sections is presented c axis orientations are calculated for each pixel and achsenverteilungsanalyse ava can easily be constructed to study problems that would normally require a prohibitive amount of tedious work the computer controlled rotating polarizer stage replaces the polarizer and analyzer of the standard petrographic microscope and allows a thin section to remain fixed while the polarizing filters are rotated by stepper motors data are collected by stepping the polarizers through a 180 rotation capturing a frame at each step and extracting information on the intensity of the pixel and position of the polarizers the position data are used to calculate the trend or trend 180 of the quartz c axes while a simple mathematical relationship between intensity and plunge is derived which allows the plunges of c axes to be calculated

evidence from magnetic fabric for the flow pattern of magma in the mackenzie giant radiating dyke swarm continental flood basalts and their associated swarms of mafic dykes are thought to result from melting in mantle plumes1 3 but the processes by which the resulting magma makes its way from mantle to crust remain obscure here we use magnetic anisotropy measurements to reconstruct the pattern of magma flow in the proterozoic mackenzie dyke swarm our results indicate that magma was injected vertically within 500 km of the focal point of the dyke swarm and then travelled horizontally at all further distances out to at least 2 100 km the sharp transition from vertical to horizontal flow at between 500 and 600 km may correspond to the outer boundary of melt generation in the mantle plume believed to be responsible for the mackenzie igneous events

bedload transport measurements at the erlenbach stream with geophones and automated basket samplers in the erlenbach stream a pre alpine steep channel in switzerland sediment transport has been monitored for more than 25 years near the confluence with the main valley river stream flow is monitored and sediment is collected in a retention basin with a capacity of about 2000 m3 the basin is surveyed at regular intervals and after large flood events in addition sediment transport has been continuously monitored with piezoelectric bedload impact and geophone sensors since 1986 in 2008 2009 the measuring system in the erlenbach stream was enhanced by installing an automatic system to obtain bedload samples movable metal baskets are mounted on a rail at the downstream wall of the large check dam above the retention basin and they can be moved automatically into the flow to take bedload transport samples the wire mesh of the baskets has a spacing of 10 mm to sample all sediment particles coarser than this size which is about the limiting grain size detected by the geophones the upgraded measuring system permits to obtain bedload samples over short sampling periods and to measure the grain size distribution of the transported material and its variation over time and with discharge the analysis of calibration relationships for the geophone measuring system confirms findings from very similar measurements which were performed until 1999 with piezoelectric bedload impact sensors there is a linear relationship between impulse counts and bedload mass passing over the sensors findings from flume experiments are used to discuss the most important factors which affect the calibration of the geophone signal the bedload transport rates as measured by the moving baskets are among the highest measured in natural streams with values of the order of several kilograms per meter per second copyright 2012 john wiley sons ltd

climate scale modelling of suspended sediment load in an alpine catchment debris flow rio cordon northeastern italy abstract pulsing storms and prolonged rainfall can drive hydrological damaging events in mountain regions with soil erosion and debris flow in river catchments the paper presents a parsimonious model for estimating climate forcing on sediment loads in an alpine catchment rio cordon northeastern italian alps hydroclimatic forcing was interpreted by the novel clismssl climate scale modelling of suspended sediment load model to estimate annual sediment loads we used annual data on suspended solid loads monitored at an experimental station from 1987 to 2001 and on monthly precipitation data the quality of sediment load data was critically examined and one outlying year was identified and removed from further analyses this outlier revealed that our model underestimates exceptionally high sediment loads in years characterized by a severe flood event for all other years the clismssl performed well with a determination coefficient r2 equal to 0 67 and a mean absolute error mae of 129 mg y 1 the calibrated model for the period 1986 2010 was used to reconstruct sediment loads in the river catchment for historical times when detailed precipitation records are not available for the period 1810 2010 the model results indicate that the past centuries have been characterized by large interannual to interdecadal fluctuations in the conditions affecting sediment loads this paper argues that climate induced erosion processes in alpine areas and their impact on environment should be given more attention in discussions about climate driven strategies future work should focus on delineating the extents of these findings e g at other catchments of the european alpine belt as well as investigating the dynamics for the formation of sediment loads

the impact of exceptional events on erosion bedload transport and channel stability in a step pool channel sediment transport in the erlenbach a small stream with step pool morphology in the canton of schwyz switzerland has been monitored for more than 20 years during this time three exceptional events events with high sediment yield and long return times that have a large effect on channel morphology have impacted the stream and partly or completely rearranged the existing step pool morphology in the aftermath of the events sediment transport rates at a given discharge and total sediment yield remained elevated for about a year or longer for the last event dated on the 20 june 2007 observations of boulder mobility and step destruction were used to interpret channel stability boulders with median diameters of up to 135 cm and estimated weights of more than 2 5 tons have moved during the 2007 event using hydraulic observations and shear stress calculations boulders up to 65 cm in diameter were predicted to have been fully mobile in peak conditions even if form resistance and increased critical stresses needed for the initiation of motion in steep streams were taken into account for two of the events estimated peak shear stresses at the bed exceeded 1000 pa calculated both from observations of the flow hydraulics and from boulder mobility this suggests that highly energetic flows occur relatively frequently in small steep streams and that large boulders can be transported by fluvial processes in such streams the observations have potential significance for hazard risk mitigation stream engineering and restoration copyright 2009 john wiley sons ltd

patterns and controls of sediment production transfer and yield in the illgraben quantification of the volumes of sediment removed by rock slope failure and debris flows and identification of their coupling and controls are pertinent to understanding mountain basin sediment yield and landscape evolution this study captures a multi decadal period of hillslope erosion and channel change following an extreme rock avalanche in 1961 in the illgraben a catchment prone to debris flows in the swiss alps we analyzed photogrammetrically derived datasets of hillslope and channel erosion and deposition along with climatic and seismic variables for a 43 year period from 1963 to 2005 based on these analyses we identify and discuss 1 patterns of hillslope production channel transfer and catchment sediment yield 2 their dominant interactions with climatic and seismic variables and 3 the nature of hillslope channel coupling and implications for sediment yield and landscape evolution in this mountain basin our results show an increase in the mean hillslope erosion rate in the 1980s from 0 24 0 01 m yr 1 to 0 42 0 03 m yr 1 that coincided with a significant increase in air temperature and decrease in snow cover depth and duration which we presume led to an increase in the exposure of the slopes to thermal weathering processes the combination of highly fractured slopes close to the threshold angle for failure and multiple potential triggering mechanisms means that it is difficult to identify an individual control on slope failure on the other hand the rate of channel change was strongly related to variables influencing runoff a period of particularly high channel erosion rate of 0 74 0 02 m yr 1 1992 1998 coincided with an increase in the frequency and magnitude of intense rainfall events hillslope erosion exceeded channel erosion on average indicative of a downslope directed coupling relationship between hillslope and channel and demonstrating the first order control of rock slope failure on catchment sediment yield and landscape evolution

evolution of stress induced borehole breakout in inherently anisotropic rock insights from discrete element modeling the aim of this study is to better understand the mechanisms controlling the initiation propagation and ultimate pattern of borehole breakouts in shale formation when drilled parallel with and perpendicular to beddings a two dimensional discrete element model is constructed to explicitly represent the microstructure of inherently anisotropic rocks by inserting a series of individual smooth joints into an assembly of bonded rigid discs both isotropic and anisotropic hollow square shaped samples are generated to represent the wellbores drilled perpendicular to and parallel with beddings at reduced scale the isotropic model is validated by comparing the stress distribution around borehole wall and along x axis direction with analytical solutions effects of different factors including the particle size distribution borehole diameter far field stress anisotropy and rock anisotropy are systematically evaluated on the stress distribution and borehole breakout propagation simulation results reveal that wider particle size distribution results in the local stress perturbations which cause localization of cracks reduction of borehole diameter significantly alters the crack failure from tensile to shear and raises the critical pressure rock anisotropy plays an important role on the stress state around wellbore which lead to the formation of preferred cracks under hydrostatic stress far field stress anisotropy plays a dominant role in the shape of borehole breakout when drilled perpendicular to beddings while a secondary role when drilled parallel with beddings results from this study can provide fundamental insights on the underlying particle scale mechanisms for previous findings in laboratory and field on borehole stability in anisotropic rock

evidence from gabbro of the troodos ophiolite for lateral magma transport along a slow spreading mid ocean ridge the lateral flow of magma and ductile deformation of the lower crust along oceanic spreading axes has been thought to play a significant role in suppressing both mid ocean ridge segmentation and variations in crustal thickness direct investigation of such flow patterns is hampered by the kilometres of water that cover the oceanic crust but such studies can be made on ophiolites fragments of oceanic crust accreted to a continent in the oman ophiolite small scale radial patterns of flow have been mapped along what is thought to be the relict of a fast spreading mid ocean ridge here we present evidence for broad scale along axis flow that has been frozen into the gabbro of the troodos ophiolite in cyprus thought to be representative of a slow spreading ridge axis the gabbro suite of troodos spans nearly 20 km of a segment of a fossil spreading axis near a ridge transform intersection we mapped the pattern of magma flow by analysing the rocks magnetic fabric at 20 sites widely distributed in the gabbro suite and by examining the petrographic fabric at 9 sites we infer an along axis magma flow for much of the gabbro suite which indicates that redistribution of melt occurred towards the segment edge in a large depth range of the oceanic crust our results support the magma plumbing structure that has been inferred indirectly from a seismic tomography experiment on the slow spreading mid atlantic ridge

modelling partially emptied compaction bands induced by borehole drilling abstract drilling into rock blocks subjected to critical far field stresses can result in localized failure around the created borehole manifested by the formation of two diametrically opposed breakouts in weakly bonded quartz rich porous sandstones breakouts take the form of narrow tabular slot like openings extending along a plane perpendicular to the maximum applied stress direction sem images strongly suggest that these breakouts are compaction bands cb s that have been emptied to different degrees debonded grains some whole others cracked or crushed within the compaction band are totally or partially removed by the circulating drilling fluid creating the breakout a new analytical model is developed here which computes the stress field around partially emptied cbs and predicts the expected lengths of these defects and their dependence on borehole radius and the extent of the cb emptying by the drilling fluid it is found that boreholes with larger radius generate longer partially emptied cbs the results also demonstrate that when the ratio of the filled to the emptied part of a cb increases addressing a smaller drilling fluid flow rate the resulting total length of partially emptied cb decreases both of these findings are in good agreement with results of drilling experiments conducted by sheets and haimson 2004

impacts of gravel mining and renaturation measures on the sediment flux and budget in an alpine catchment johnsbach valley austria abstract in the johnsbach valley austria a medium size non glaciated torrent catchment enormous amounts of sediment have been made available due to the brittle dolomite bedrock this occurs mainly in the zwischenmauerstrecke zms english translation reach between the walls and presents a major challenge to local river management within a renaturation project which followed several decades of disturbance flood protection and gravel mining in the zms it is of particular importance to understand where the sediments come from and the transport pathways through the system to prepare future forecasts in the present study we investigate the recent sediment cascade in a comprehensive analysis of the zms that was achieved by means of airborne laser scanning campaigns in 2010 and 2015 the current bedload yield at the outlet was measured using an integrative bedload monitoring system historical data from 1954 was used to illustrate the effects of the mining period on the former sediment routing finally we evaluated the expected sediment transport rates in the near future the results show that from the hillslopes sediments are mainly transported via the active side trenches to the main channel 7000 m3 yr 1 the sediment transport in the johnsbach river consists mainly in relocating the periodically occurring sediment entries of the side trenches the bedload transport rates at the outlet sum up to annual bedload yields of 2000 m3 yr 1 to almost 12 000 m3 yr 1 during the observation period especially those areas inside the side trenches that were heavily affected by gravel mining excavated amount of sediment during the mining period 25 000 m3 yr 1 are now accumulating sediment since the end of this period 8000 m3 yr 1 future scenarios will depend heavily on the progress in the mining affected side channels the impacts of this period are continuously being reworked and a natural sediment flow will adjust in the near future the sediment input into the johnsbach river will rise significantly and could lead to a doubling in the annual sediment yield at the outlet compared to now in particular the reaches along the johnsbach river following the confluences with the mining affected side trenches are already showing morphological changes due to the recently imported sediments

morphological effects of local scouring in step pool streams step pool morphology characterizes many high gradient streams in a variety of natural settings but formative processes and evolutionary dynamics are still poorly understood in this paper natural step pool geometry is compared with steep alluvial channels where grade control structures such as check dams and bed sills make the stream profile resemble a natural stepped stream along these channels local scouring due to falling jets forms plunge pools under each structure analogous to natural steps determining the formation of pools in order to test the hypothesis that natural pools are analogous to pools formed below grade control works with respect to their dimensions shape and formative dynamics 37 natural pools and 73 artificial pools were surveyed in 10 mountain streams of the eastern italian alps pools below grade control works featured a transitional zone between the scour hole and the downstream sloping bed marked by a depositional berm when geometric parameters such as maximum pool depth length and step berm distances are normalized to the jet virtual energy no statistically significant differences were detected between natural and artificial systems these results lend support to an upstream forced cascade model for step pool formation where the energy of falling jets controls the geometry of the pools and is therefore regarded as the most important scaling independent variable copyright 2005 john wiley sons ltd

effect of mechanical interactions on the development of shape preferred orientations a two dimensional experimental approach abstract modifications in the development of preferred orientations of rigid particles due to mechanical interactions between particles are studied experimentally in two dimensions experiments in both pure shear and simple shear were performed and the results analysed using an easy and fast new automatic method for increased concentration of rigid particles the rotation of individual particles may be slowed down or even stopped due to collisions or disturbance of the flow in the matrix caused by neighbours in coaxial flow the fabric intensity is consequently reduced in simple shear flow the fabric evolution is no longer cyclic the intensity is on average weaker and the fabric axis rotates asymptotically toward the shear plane in the case of preferred orientations of particles having a low aspect ratio 2 5 the fabric rotates through the shear plane then undergoes a reverse rotation and rotates toward the shear plane again in the light of these experimental results we emphasize that quantification of finite strain based on such fabrics may lead to significant underestimates and calculated values should be taken as minimum estimates the kinematic significance of concentrated rigid particle preferred orientations in rocks is modified by interactions between particles techniques for qualitative or quantitative kinematic analysis may become unreliable for simple shear flows the concentrated population fabrics show an angular behaviour close to that of passive markers they tend to align parallel to the shear plane in simple shear flow