morphology and mechanics of submarine spreading a case study from the storegga slide spreading is a common type of ground failure in subaerial environments however this type of mass movement has hardly been documented in submarine settings in this paper we show that spreading covers at least 25 of the storegga slide scar area a giant submarine slide located offshore mid norway the morphological signature of spreading is a repetitive pattern of ridges and troughs oriented perpendicular to the direction of movement two modes of failure can be identified retrogressive failure of the headwall and slab failure and extension both involving the breakup of a sediment unit into coherent blocks these blocks are displaced downslope along planar slip surfaces limit equilibrium modeling indicates that loss of support and seismic loading are the main potential triggering mechanisms the extent of displacement of the spreading sediment is controlled by gravitationally induced stress angle of internal friction of the sediment pore pressure escape and friction the resulting block movement pattern entails an exponential increase of displacement and thinning of the failing sediment with distance downslope sediment properties explain the remaining spatial variation of ridge and trough morphologies associated with spreading

geological context and vents morphology of the ultramafic hosted ashadze hydrothermal areas mid atlantic ridge 13 n 1 recent rov dives and high resolution bathymetric data acquired over the ashadze fields on the mid atlantic ridge 13 n allow us to derive constraints on the regional and local geological setting of ultramafic hosted hydrothermal fields the active vent fields of ashadze hydrothermal fields are located in the western axial valley wall downslope from the termination of a prominent corrugated surface and in a transitional domain with respect to ridge segmentation the study of the shipboard and rov bathymetry shows that decameter 100 m by 60 m to kilometer scaled rockslides shape the axial valley wall slopes in this region the ashadze 1 vent field occurs on a coherent granular landslide rock mass that is elongated in an e w direction the ashadze 1 vent field comprises hundreds of active and inactive sulfide chimneys the ashadze 2 vent field is located in a nne trending linear depression which separates outcrops of gabbros and serpentinized peridotites active black smokers in the ashadze 2 field are located on ultramafic substratum in a 40 m diameter crater 5 m deep this crater recalls similar structures described at some vents of the logatchev hydrothermal field mid atlantic ridge 15 n we discuss the mode of formation for these craters as well as that for a breadcrust like array of radial fissures identified at ashadze 1 we propose that hydrothermalism at ashadze can be an explosive phenomena associated with geyser like explosions our study also constrains the geological and geophysical context of the ultramafic hosted ashadze hydrothermal system that may use the oceanic detachment fault as a preferred permeability conduit

oceanic corrugated surfaces and the strength of the axial lithosphere at slow spreading ridges abstract we analyse the topography and gravity signature of 39 corrugated surfaces formed over the past 26 myrs in the footwall of axial detachment faults at the eastern southwest indian ridge these corrugated surfaces appear to have formed at a melt supply about half the global melt supply average for mid ocean ridges and we find that their presently elevated topography relative to adjacent non corrugated seafloor was mostly acquired at the end of their formation at the termination stage this configuration which also characterizes many off axis corrugated surfaces in other oceans suggests that the plate flexural rigidity was very low during the formation of the corrugated surface and increased significantly at the termination stage following buck 1988 we hypothesize that stresses related to bending of the plate cause internal deformation and damage in the footwall of the fault which is associated with weakening as a possible mechanism for enhanced footwall weakening while corrugated surfaces form we propose the formation of weak shear zones coated with hydrous minerals such as talc amphibole chlorite and serpentine in mantle derived ultramafics next to gabbro intrusions if this hypothesis is correct the amount of footwall weakening and roll over along axial detachment faults at slow spreading ridges may be controlled both by access to hydrothermal fluids in the footwall of the detachment and by the abundance and distribution of gabbros intrusions in exhumed ultramafics

mid ocean ridges fine scale tectonic volcanic and hydrothermal processes within the plate boundary zone a first order model of spreading centers as idealized linear boundaries of crustal and lithospheric generation provides only a gross understanding of global scale plate kinematics as we attempt to understand the complexity of crustal and lithospheric structure of two thirds of the earth s surface it is becoming increasingly necessary to study the tectonic volcanic and hydro thermal processes within the spreading center plate boundary zone all ocean ic crust bears the imprint of these processes this review focuses on a few selected topics concernining the fine scale tectonics and geophysics of the active axial zone of mid ocean ridges with reference to associated volcanic and hydrothermal processes it draws heavily on recent studies that use deeply towed instrument packages multi beam bathymetric mapping ocean bottom instruments and alvin e g the famous amar rise and galapagos expeditions we begin with a review of the large scale structure of spreading centers we then take a close look at the axial neovolcanic zone and progress away from the axis through the active tectonic zones next we consider the characteristics of the axial magma chamber and associated hydrothermal actvity as well as the generation of magnetic anomaly stripes and their implications for crustal generation one of our findings is that the initial two dimensional model of volcanic and tectonic zones must be expanded upon to allow for variations

experimental study of extreme shear stress for shallow flow under simulated rainfall the raindrop impact and overland flow are two major factors causing soil detachment and particle transportation in this study the turbulent characteristics of the shallow rain impacted water flow were investigated using a 2 d fibre optic laser doppler velocimetry fldv and an artificial rainfall simulator the fluctuating turbulent shear stress was computed using digital data processing techniques the experimental data showed that the reynolds shear stress follows a probability distribution with heavy tails the tail probability increases with an increase of rainfall intensity or raindrop diameter and it decreases with an increase of reynolds number a modified empirical equation was derived using both the raindrop diameter and rainfall intensity as independent variables to provide a better prediction of the darcy weisbach friction coefficient f under rainfall conditions copyright 2009 john wiley sons ltd

spatial and temporal distribution of seismicity along the northern mid atlantic ridge 15 35 n 1 a detailed investigation of the relationship between the spatial and temporal patterns of the seismic activity recorded by six autonomous hydrophones and the structure of the northern mid atlantic ridge between 15 and 35 n is presented two years of monitoring yielded a total of 3485 hydroacoustically detected events within the array recorded by four or more hydrophones the seismically active zone extends 20 km to either side of the ridge axis consistent with earlier results from studies of fault morphology along the axis hydrophone recorded activity shows important variations areas with intense and persistent seismic activity stripes stand in sharp contrast to areas that lack seismicity gaps the regions of persistent activity are a new observation at mid ocean ridges in general the patterns of seismically active inactive regions are also recognized in the 28 year teleseismic record implying that these patterns are maintained at timescales between a few years and a few decades we find no simple relationship between individual segment variables e g length or trend of the segment maximum offset of discontinuities or along axis change in mantle bouguer anomaly mba and water depths and number of hydrophone recorded events there does appear to be a correlation between axial thermal structure and seismicity regions of low and high numbers of events would thus correspond to thinner hotter and thicker colder lithosphere respectively seismicity may reflect thermal structure at short timescales decadal or longer while relief and inferred crustal thickness may integrate this structure over longer periods of time order of 1 myr

non transform offsets along the mid atlantic ridge south of the azores 38 n 34 n ultramafic exposures and hosting of hydrothermal vents ten contiguous non transform offsets ntos along the mid atlantic ridge mar south of the azores between 38 n and 35 40 n have been studied in detail using swath bathymetric acoustic backscatter and deep tow high resolution sidescan sonar tobi data in contrast with discontinuities studied elsewhere at slow spreading ridges these left lateral ntos are consistently broader and larger with complex structural fabrics accommodating the offset they are characterized by a range of elevated and faulted massifs detached from their segment flanks with an irregular acoustic backscatter pattern some of these massifs have been explored and sampled recently during dive cruises revealing that they are composed of upper mantle peridotites and lower crustal rocks and sometimes associated with high temperature hydrothermal venting water column surveys adjacent to these massifs show high ch4 and low tdm total dissolvable manganese concentrations possibly resulting from the process of serpentinization of ultramafic rocks the correlation between the shallow dome like shaped massifs and the high concentrations of ch4 associated with low levels of mn is of particular interest to predict the outcrop of ultramafic rocks within the ntos where no geological data are available the exposure of the ultramafic massifs within the ntos is favored by low magmatic supply and low angle detachment faulting occurring at segment ends the pervasive fracturing and faulting at these discontinuities favor circulation of hydrothermal fluids and occurrence of high temperature vent sites

higher order moments of velocity fluctuations in an open channel flow with large bottom roughness the present study was undertaken to examine the effect of surface roughness on the higher order velocity moments in a turbulent open channel flow the wall roughness is large and the ratio of the roughness size to the depth of flow ranges from 0 1 to 0 15 flow over two types of roughness conditions ribs and dunes are examined and compared with that over a smooth open channel in the case of the rib roughness three different spacings are used p k 4 5 9 and 18 here p distance between the leading edges of two consecutive ribs and k height of a rib with square cross section the shape of the smooth wall dunes was geometrically similar to that commonly used in previous studies in an effort to understand the influence of local wall roughness rough wall dunes are also used in the present study the variables of interest include higher order moments conditional statistics based on a quadrant analysis relationship of higher order moments to the reynolds stress and energy production although there

deformation associated with the denudation of mantle derived rocks at the mid atlantic ridge 13 15 n the role of magmatic injections and hydrothermal alteration 1 outcrops of deeply derived ultramafic rocks and gabbros are widespread along slow spreading ridges where they are exposed in the footwall of detachment faults we report on the microstructural and petrological characteristics of a large number of samples from ultramafic exposures in the walls of the mid atlantic ridge mar axial valley at three distinct locations at lat 13 n and 14 45 n one of these locations corresponds to the footwall beneath a corrugated paleo fault surface bearing in mind that dredging and rov sampling may not preserve the most fragile lithologies fault gouges this study allows us to document a sequence of deformation and the magmatic and hydrothermal history recorded in the footwall within a few hundred meters of the axial detachment fault at the three sampled locations we find that tremolitic amphiboles have localized deformation in the ultramafic rocks prior to the onset of serpentinization we interpret these tremolites as hydrothermal alteration products after evolved gabbroic rocks intruded into the peridotites we also document two types of brittle deformation in the ultramafic rocks which we infer could produce the sustained low magnitude seismicity recorded at ridge axis detachment faults the first type of brittle deformation affects fresh peridotite and is associated with the injection of the evolved gabbroic melts and the second type affects serpentinized peridotites and is associated with the injection of si rich hydrothermal fluids that promote talc crystallization leading to strain localization in thin talc shear zones we also observed chlorite serpentine shear zones but did not identify samples with serpentine only shear zones although the proportion of magmatic injections in the ultramafic rocks is variable these characteristics are found at each investigated location and are therefore proposed as fundamental components of the deformation in the footwall of the detachment faults associated with denudation of mantle derived rocks at the mar

numerical modeling of self channeling granular flows and of their levee channel deposits when not laterally confined in valleys pyroclastic flows create their own channel along the slope by selecting a given flowing width furthermore the lobe shaped deposits display a very specific morphology with high parallel lateral levees a numerical model based on saint venant equations and the empirical variable friction coefficient proposed by pouliquen and forterre 2002 is used to simulate unconfined granular flow over an inclined plane with a constant supply numerical simulations successfully reproduce the self channeling of the granular lobe and the levee channel morphology in the deposits without having to take into account mixture concepts or polydispersity numerical simulations suggest that the quasi static shoulders bordering the flow are created behind the front of the granular material by the rotation of the velocity field due to the balance between gravity the two dimensional pressure gradient and friction for a simplified hydrostatic model competition between the decreasing friction coefficient and increasing surface gradient as the thickness decreases seems to play a key role in the dynamics of unconfined flows the description of the other disregarded components of the stress tensor would be expected to change the balance of forces the front s shape appears to be constant during propagation the width of the flowing channel and the velocity of the material within it are almost steady and uniform numerical results suggest that measurement of the width and thickness of the central channel morphology in deposits in the field provides an estimate of the velocity and thickness during emplacement citation mangeney a f bouchut n thomas j p vilotte and m o bristeau 2007 numerical modeling of self channeling granular flows and of their levee channel deposits

lidar derived morphology of the 1993 lascar pyroclastic flow deposits and implication for flow dynamics and rheology abstract pumice flows are potentially destructive volcanic events that derive from eruption column collapse and whose dynamics are poorly understood the challenges in studying these flows include the lack of constraints on the dynamics kinematics and initial conditions that control their emplacement we present a morphological study of the distal deposits lobes of the pumice flows resulting from the 1993 eruption at lascar chile the surface geometry of the lobes was measured in detail using a lidar device which allowed for detailed characterisation of their morphology consisting of central channel and lateral levees and terminal frontal snout in particular we find that the ratio of channel levee height as a function of the ratio of the distance between levees total width of the lobe has a characteristic curve for these pumice flow lobes our analysis of several of the lascar pumice lobe deposits south east sector identified several dimensionless groups of the available parameters which when compared against published results from both experimental and numerical investigations allowed us to constrain crucial kinematic and dynamic information on the terminal phase of the pumice flows notably we estimate the velocity of the terminal phase of pumice flows to be 5 10 m s froude numbers of 1 5 2 are comparable with values found for experimental granular flows height width aspect ratios for the levee channel section of the pumice lobes are similar to those for experimental flows although these same aspect ratios for the snout are much larger for the natural deposits than their small scale analogues finally we discuss the possible emplacement dynamics of the terminal lascar 1993 pumice flows a pseudo reynolds number based on the velocity estimation is found to be up to 100 times larger for the pumice flows than experimental scale flows this suggests that the flow retarding frictional forces for large scale flows are relatively unimportant compared to flows at smaller scales mechanical effects such as fluidisation mobilisation of material lying on the slopes over which they propagate and lubrication due to polydispersivity could provide an explanation for their ability to propagate on shallow slopes 6 11

long term denudation of ocean crust in the central north atlantic ocean near bottom sidescan bathymetric and visual observations of fault scarps in 4 24 ma sea floor show that basaltic ocean crust undergoes extensive denudation that creates wide complex scarp zones most denudation is caused by mass wasting probably accompanied by abrasion by disaggregated debris in 11 24 ma crust trellis drainage patterns are formed by deep cross scarp canyons and intersecting scarp parallel gullies that appear to follow weak zones of fracturing and intracrustal weathering until stabilized e g by sediment burial fault scarps will continue to degrade with time yielding increasingly distorted representations of apparent fault geometry in remotely sensed morphological data

self consistent rolling hinge model for the evolution of large offset low angle normal faults the nature of the physical processes responsible for the formation of continental and oceanic metamorphic core complexes is widely debated the controversy focuses primarily on whether the low angle normal faults observed in these environments formed and slipped at low angles or were rotated from an original high angle orientation after large offsets we describe a self consistent numerical model for the extension of a brittle layer that can spontaneously produce normal fault structures in our formulation a fault or faults form because strength is locally reduced with increasing strain if the reduction in fault strength is 10 of the total strength of the layer then faults lock after an offset smaller than the layer thickness and new faults form larger strength reduction leads to single faults that continue to slip no matter how large the fault offset if the strength reduction occurs by the loss of cohesion then we see the unlimited offset faults for layers 11 22 km thick for reasonable values of cohesion the key result of this study is that structures very similar to those observed in both oceanic and continental core complexes are produced by rotation of the inactive part of the model fault after very large offset

a simple model for the fault generated morphology of slow spreading mid oceanic ridges we postulate that fluctuations in magmatic activity at mid oceanic ridges perturb the horizontal least principal stress across rift bounding normal faults leading to alternating phases of magmatic accretion which increases valley width and tectonic extension which results in the growth of inner rift wall topography fine scale bathymetrie surveys and earthquake fault plane solutions show that active normal faults at slow spreading ridges are moderately dipping approximately 45 planar features throughout the seismogenic oceanic lithosphere a simple quantitative model that includes flexural deformation of a 10 km thick elastic plate by slippage on 45 dipping normal faults can match the bathymetrie profiles across several slow spreading ridge segments comparison among dip distributions of normal faulting earthquakes at mid ocean ridges in the trench outer rise region and on continents suggests that most events from these three tectonic environments initiated at dips close to 45 raising unanswered questions about the mechanical conditions under which the faults originated

quantifying creep behaviour of clay bearing rocks below the critical stress state for rapid failure mam tor landslide derbyshire england abstract the mam tor landslide derbyshire england slips downhill at up to 0 5 m a 1 and offers an excellent opportunity to study time dependent creep in mudstones under in situ conditions annual surveys show that creep rates increase following heavy rainfall but to establish detailed correlation between creep and pore water pressure required spatially and temporally higher resolution monitoring we acquired 3 years of such data at 3 h intervals from wire creep meters borehole piezometers and rainfall monitoring showing that creep is strongly focused into the winter months and correlates well with pore water pressure summer grass and fern growth strongly influence rainfall infiltration recycling much of the rainfall back to the atmosphere explaining the seasonal variability of creep the dependence of creep rate on pore pressure can be recast as a rheological model relating shear strain rate to shear stress using the friction angle for the creeping mudstone to link effective normal stress to shear stress the creep is very non linear following a power law with a stress exponent of 48 this flow law may apply also to shear failure in poorly consolidated mudrocks under high pore pressure conditions for example within some landslides subglacial sediments tectonic fault zones tectonic melanges and accretionary complexes

sinuous gullies on mars frequency distribution and implications for flow properties recent gullies on mars are suspected to be the result of liquid water bearing flows a formation from wet flows has been challenged by studies invoking granular dry flows our study focuses on the sinuous shapes observed for some of the recent martian gullies sinuous gullies are found in locations and slopes of 10 15 similar to straight gullies and they are therefore related to the same formation processes numerical simulations of granular flows are performed here by introducing topographic variations such as obstacles roughness or slope changes that could possibly generate flow sinuosity none of these simulations was able to reproduce sinuous shapes on a slope lower than 18 with friction angles typical of dry granular material the only way to simulate sinuous shapes is to create small amplitude periodic variations of the topography of the deposit an origin not supported by current martian imagery given the presence of sinuosity in natural terrestrial debris flows we have concluded that sinuous martian gullies are better reproduced by liquid water bearing debris flows sinuous shapes in leveed flows are used to derive mechanical parameters from several martian gullies using photoclinometry values in yield strength of 100 2200 pa velocities of 1 1 3 3 m s 1 and viscosities from 40 to 1040 pa s are found which are all within the range of values for terrestrial debris flows with various proportions of liquid water 20 40

mobility and topographic effects for large valles marineris landslides on mars 1 recent experiments on dry granular flows over horizontal plane bare some similarities with large martian landslides observed in valles marineris vm however martian normalized runout are twice as large as those that observed in dry granular flow experiments numerical simulations on theoretical 2d and real 3d topographies reconstructed from remote sensing data show that slope effects significantly reduce the shift between experimental results and martian observation however topography effects are not strong enough to explain the high mobility of martian landslides as a result other physical and or geological processes should play a key role into the dynamics of martian landslides a new mobility is defined that makes it possible to characterize the dynamics of the flow regardless of the geometry of the released mass and of the underlying topography

erosion and mobility in granular collapse over sloping beds 1 we describe laboratory experiments of granular material flowing over an inclined plane covered by an erodible bed designed to mimic erosion processes of natural flows travelling over deposits built up by earlier events two controlling parameters are the inclination of the plane and the thickness of the erodible layer we show that erosion processes can increase the flow mobility i e runout over slopes with inclination close to the repose angle of the grains r by up to 40 even for very thin erodible beds erosion efficiency is shown to strongly depend on the slope of the topography entrainment begins to affect the flow at inclination angles exceeding a critical angle c r 2 runout distance increases almost linearly as a function of the thickness of the erodible bed suggesting that erosion is mainly supply dependent two regimes are observed during granular collapse a first spreading phase with high velocity followed by a slow thin flow provided either the slope or the thickness of the erodible bed is high enough surprisingly erosion affects the flow mostly during the deceleration phase and the slow regime the avalanche excavates the erodible layer immediately at the flow front waves are observed behind the front that help to remove grains from the erodible bed steep frontal surges are seen at high inclination angles over both rigid or erodible bed finally simple scaling laws are proposed making it possible to obtain a first estimate of the deposit and emplacement time of a granular collapse over a rigid or erodible inclined bed

fault rotation and core complex formation significant processes in seafloor formation at slow spreading mid ocean ridges mid atlantic ridge 13 15 n 1 the region of the mid atlantic ridge mar between the fifteen twenty and marathon fracture zones displays the topographic characteristics of prevalent and vigorous tectonic extension normal faults show large amounts of rotation dome shaped corrugated detachment surfaces core complexes intersect the seafloor at the edge of the inner valley floor and extinct core complexes cover the seafloor off axis we have identified 45 potential core complexes in this region whose locations are scattered everywhere along two segments 13 and 15 n segments steep outward facing slopes suggest that the footwalls of many of the normal faults in these two segments have rotated by more than 30 the rotation occurs very close to the ridge axis as much as 20 within 5 km of the volcanic axis and is complete by 1 my producing distinctive linear ridges with roughly symmetrical slopes this morphology is very different from linear abyssal hill faults formed at the 14 n magmatic segment which display a smaller amount of rotation typically 15 we suggest that the severe rotation of faults is diagnostic of a region undergoing large amounts of tectonic extension on single faults if faults are long lived a dome shaped corrugated surface develops in front of the ridges and lower crustal and upper mantle rocks are exposed to form a core complex a single ridge segment can have several active core complexes some less than 25 km apart that are separated by swales we present two models for multiple core complex formation a continuous model in which a single detachment surface extends along axis to include all of the core complexes and swales and a discontinuous model in which local detachment faults form the core complexes and magmatic spreading forms the intervening swales either model can explain the observed morphology

3 d p wave velocity structure of oceanic core complexes at 13 n on the mid atlantic ridge the mid atlantic ridge at 13 n is regarded as a type locality for oceanic core complexes occs as it contains within 70 km along the spreading axis four that are at different stages of their life cycle the wealth of existing seabed observations and sampling makes this an ideal target to resolve contradictions between the existing models of occ development here we describe the results of p wave seismic tomographic modelling within a 60 60 km footprint containing several occs the ridge axis and both flanks which determines occ crustal structure detachment geometry and occ interconnectivity along axis a grid of wide angle seismic refraction data was acquired along a series of 17 transects within which a network of 46 ocean bottom seismographs was deployed approximately 130 000 first arrival travel times together with sparse moho reflections have been modelled constraining the crust and uppermost mantle to a depth of 10 km below sea level depth slices through this 3 d model reveal several independent structures each with a higher p wave velocity vp than its surrounds at the seafloor these features correspond to the occs adjacent to the axial valley walls at 13 20 n and 13 30 n and off axis at 13 25 n these high vp features display dipping trends into the deeper crust consistent with the surface expression of each occ s detachment implying that rocks of the mid to lower crust and uppermost mantle within the footwall are juxtaposed against lower vp material in the hanging wall the neovolcanic zone of the ridge axis has systematically lower vp than the surrounding crust at all depths and is wider between occs on average throughout the 13 n region the crust is 6 km thick however beneath a deep lava floored basin between axial occs the crust is thinner and is more characteristically oceanic in layering and velocity depth structure thicker crust at the ridge axis suggests a more magmatic phase of current crustal formation while modelling of the sparse moho reflections suggests the crust mantle boundary is a transition zone throughout most of the 13 n segment our results support a model in which occs are bounded by independent detachment faults whose dip increases with depth and is variable with azimuth around each occ suggesting a geometry and mechanism of faulting that is more complicated than previously thought the steepness of the northern flank of the 13 20 n detachment suggests that it represents a transfer zone between different faulting regimes to the south and north we propose that individual detachments may not be linked along axis and that occs act as transfer zones linking areas of normal spreading and detachment faulting along ridge variation in magma supply influences the nature of this detachment faulting consequently not only does magma supply control how detachments rotate and migrate off axis before finally becoming inactive but also how when and where new occs are created

structural control evolution and accumulation rates of massive sulfides in the tag hydrothermal field the trans atlantic geotraverse tag hydrothermal field on the mid atlantic ridge is one of the best studied hydrothermal systems to date however high resolution bathymetric data obtained in 2016 by an autonomous underwater vehicle auv reveal new information about the distribution of active and inactive hydrothermal deposits and their relation to structural features the discovery of previously undocumented inactive vent sites contributes to a better understanding of the accumulation rates and the resource potential of seafloor massive sulfide deposits at slow spreading ridges the interpretation of ship based and high resolution auv based data sets allowed for the determination of the main tectonic stress regimes that have a first order control on the location and distribution of past and present hydrothermal activity the data reveal the importance of cross cutting lineament populations and temporal variations in the prevalent stress regime a dozen sulfide mounds contribute to a substantial accumulation of hydrothermal material 29 mt the accumulation rate of 1 500 t yr is comparable to those of other modern seafloor vent fields however our observations suggest that the tag segment is different from many other slow spreading ridge segments in its tectonic complexity which confines sulfide formation into a relatively small area and is responsible for the longevity of the hydrothermal system and substantial mineral accumulation the inactive and weakly active mounds contain almost 10 times the amount of material as the active high temperature mound providing an important indication of the global resource potential for inactive seafloor massive sulfide deposits

numerical model of turbulent flow over sand dune a two dimensional numerical model based on solution of the reynolds averaged navier stokes equations and the k turbulence model which takes into account sand grain roughness is developed to describe the flow in a fixed dune bed channel the model predicts the velocity and turbulence fields as well as the pressure and friction distributions along the dune the details of the flow in the separation eddy are calculated the model predictions are in general agreement with existing detailed experimental data in a rectangular channel with two dimensional dunes of typical but regular shape the calculated pressure and friction distributions enable determination of the resistance components of the channel without further empiricism however compared to a well known and representative semiempirical engineering formula for the prediction of resistance of natural dune bed channels the two dimensional numerical model predicts significantly different contributions of friction and pressure to the total resista

seafloor slopes at mid ocean ridges from submersible observations and implications for interpreting geology from seafloor topography abstract observations from 145 submersible dives are used to create a database of mid ocean ridge scarp topography and lithology seafloor lithologies are classified into extrusives basaltic talus dykes gabbros and serpentinites and the dive locations are broadly classified according to whether they are close to transform valleys and as a function of ridge spreading rate the database is used to determine whether there is any difference in the maximum slope for each rock type which might relate to differences in rock jointing cohesion or friction properties there is a common perception that lower crustal rocks form steeper slopes than shallower crustal rocks but until now there has been little evidence to support or refute this idea from our analysis we find a tendency for gabbro and dykes to form steeper slopes than serpentinite the 90th percentile of each lithology slope distribution used as a measure of limiting slope is 43 39 and 32 for gabbro dykes and serpentinite respectively lithologic control on slope is weak however compared to overall slope variability in these mid ocean ridge settings so seafloor relief is likely to be a poor guide to underlying geology we speculate on the structure of eroding fault scarps outline the implications for attempts to infer active faults from talus ramp activity and discuss more generally factors affecting the geomorphology of mid ocean ridge slopes

on spreading modes and magma supply at slow and ultraslow mid ocean ridges abstract the ultraslow eastern southwest indian ridge swir offers an opportunity to study the effect of magma supply on an ultraslow mid ocean ridge starting from quasi melt free detachment dominated spreading and transitioning to volcanic spreading as one nears prominent axial volcanos detachments in the quasi melt free mode extend along axis 60 to 95 km and have a lifetime of 0 6 to 1 5 myrs they cut into their predecessor s footwall with an opposite polarity causing part of the footwall lithosphere to experience further deformation hydrothermal alteration sparse magmatism and possibly thermal rejuvenation in a hanging wall position the accretion of the oceanic lithosphere in this context therefore occurs in two distinct stages over the lifetime of two successive detachment faults we examine the transition from this nearly amagmatic detachment dominated mode to the more common volcanic mode of spreading showing that it occurs along axis over distances 30 km it involves a significant thinning of the axial lithosphere and a gradual decrease of the amount of tectonic displacement on faults as the magmatic contribution to the divergence of the two plates increases we develop a conceptual model of this transition in which magma plays a double role it fills the space between the diverging plates thus reducing the need for displacement along faults and it modifies the thermal state and the rheology of the plate boundary affecting its thickness and its tectonic response to plate divergence based on a comparison of the ultraslow eastern swir with the faster spreading mid atlantic ridge we show that the activation of the volcanic or of the detachment dominated modes of spreading is connected with the volume of magma supplied per increment of plate separation over a range of axial lithosphere thickness and therefore over a range of the m ratio defined by buck et al 2005 as the relative contribution of magma and faults to plate divergence m is smaller for a given volume of melt per increment of plate separation if the plate is thicker we therefore propose that m does not fully explain the variability in faulting styles observed at slow and ultraslow ridges and propose that rheological changes induced by magma also play a key role melt itself is weak hydrothermally altered gabbro peridotite mixtures are weak and melt heat sustains more vigorous hydrothermal circulation resulting in contrasted potentials for strain localization footwall flexure on faults and the development of detachment faults

along axis variations in seafloor spreading in the mark area recent investigations with the manned submersible alvin and the angus deep towed camera sled greatly extended the known range of variations in the style of seafloor spreading along the axis of the mid atlantic ridge five transects of the spreading centre at intervals of10 20 km south of the kane fracture zone at 24 n latitude demonstrate dramatic changes in the style and magnitude of tectonic extension development of the neovolcanic zone expression of hydrothermal venting types oflithologic exposures and morphology of the median valley

tectonics of the mid atlantic rift valley between the tag and mark areas 26 24 n evidence for vertical tectonism abstract a segment of the mid atlantic ridge between the tag and mark areas between 26 and 24 n was studied during march april of 1988 from the r v akademik mstislav keldysh using mir submersibles the rift valley is depressed here to depths of 3200 4700 m and includes seven independent magmatic cells which are in different phases of their evolution some of them are now in the constructive phase whereas others are in the destructive phase and are strongly fractured slopes of two types flank the rift valley the normal slopes similar to the famous area are block faulted terrains with small elevations above the neovolcanic ridge crest in the center of the rift valley the abnormal slopes are elevated from 1 to 3 km above the neovolcanic ridge crest an almost undisturbed section of the upper oceanic crust from gabbro through sheeted dikes to pillow lavas outcrops on the abnormal slopes as the dikes are dipping nearly vertically and pillow lavas preserve their initial inclinations no block rotation or back tilting occurred during the development of rift mountains pure vertical uplift was responsible for rift mountain growth speculations are made that serpentinization of the uppermost mantle peridodite can be considered as the main process leading to oceanic crust uplift serpentinization takes place during the nonvolcanic destructive phases when seawater can easily penetrate into the deeper crust and uppermost mantle reaching the peridodites as a result serpentinites are added to the oceanic crust of slow spreading ridges

quantifying tectonic strain and magmatic accretion at a slow spreading ridge segment mid atlantic ridge 29 n high resolution deep towed side scan sonar data are used to characterize faulting and variations in tectonic strain along a segment of the slow spreading mid atlantic ridge near 29 n sonar data allow us to identify individual fault scarps to measure fault widths and spacing and to calculate horizontal fault displacements heave and tectonic strain we find that over long periods of time 1 myr on average tectonic strain is 10 on average and does not vary significantly along axis there is a marked asymmetry in tectonic strain that appears to be linked to asymmetric accretion along the whole segment indicated by 50 lower tectonic strain on the east flank than on the west flank these variations in tectonic strain do not correlate directly with changes in fault spacing and heave fault spacing and heave increase from the center of the segment toward the end inside corner on the west flank and from the outside to the inside corner across the axis these parameters remain relatively constant along the segment on the east flank and across the axis at the segment center tectonic strain appears to be decoupled from magmatic accretion at timescales 1 myr as the decrease in magma supply from the segment center toward the end inferred from variations in crustal thickness along the axis is not correlated with a complementary increase in tectonic strain instead tectonic strain remains relatively constant along the axis at 7 on the east flank and at 15 on the west flank these results indicate that variations in fault development and geometry may reflect spatial differences in the rheology of the lithosphere and not changes in tectonic strain or magma supply along axis

detachment shear zone of the atlantis massif core complex mid atlantic ridge 30 n near bottom investigations of the cross section of the atlantis massif exposed in a major tectonic escarpment provide an unprecedented view of the internal structure of the footwall domain of this oceanic core complex integrated direct observations sampling photogeology and imaging define a mylonitic low angle detachment shear zone dsz along the crest of the massif the shear zone may project beneath the nearby corrugated upper surface of the massif the dsz and related structures are inferred to be responsible for the unroofing of upper mantle peridotites and lower crustal gabbroic rocks by extreme localized tectonic extension during seafloor spreading over the past 2 m y the dsz is characterized by strongly foliated to mylonitic serpentinites and talc amphibole schists it is about 100 m thick and can be traced continuously for at least 3 km in the tectonic transport direction the dsz foliation arches over the top of the massif in a convex upward trajectory mimicking the morphology of the top of the massif kinematic indicators show consistent top to east toward the mar axis tectonic transport directions foliated dsz rocks grade structurally downward into more massive basement rocks that lack a pervasive outcrop scale foliation the dsz and underlying basement rocks are cut by discrete anastomosing normal slip shear zones widely spaced steeply dipping normal faults cut all the older structures and localize serpentinization driven hydrothermal outflow at the lost city hydrothermal field a thin few meters sequence of sedimentary breccias grading upward into pelagic limestones directly overlies the dsz and may record a history of progressive rotation of the shear zone from a moderately dipping attitude into its present gently dipping orientation during lateral spreading and uplift

two dimensional mapping of sea ice keels with airborne electromagnetics airborne electromagnetic aem equipment can be used to sense sea ice thickness by interpreting the aem data to obtain the distance from the towed bird that holds the em system to the ice seawater interface the ice thickness itself is obtained by subtracting from that quantity the distance from the bird to the upper ice surface as determined by a laser altimeter to interpret aem data acquired over sea ice keels we first solve the forward problem using an integral equation approach to the neumann boundary value problem in this approach we assume that sea ice is an insulator and that seawater is a perfect conductor when the ice keel is two dimensional the pertinent equations can be transformed into the wavenumber domain along the strike direction resulting in the rapid numerical computation of the aem response by compiling numerical model results we constructed an interpretation chart that relates the parameters of the observed aem response anomaly to the geometric variables of the ice keel the

tectonic structure evolution and the nature of oceanic core complexes and their detachment fault zones 13 20 n and 13 30 n mid atlantic ridge microbathymetry data in situ observations and sampling along the 13 20 n and 13 20 n oceanic core complexes occs reveal mechanisms of detachment fault denudation at the seafloor links between tectonic extension and mass wasting and expose the nature of corrugations ubiquitous at occs in the initial stages of detachment faulting and high angle fault scarps show extensive mass wasting that reduces their slope flexural rotation further lowers scarp slope hinders mass wasting resulting in morphologically complex chaotic terrain between the breakaway and the denuded corrugated surface extension and drag along the fault plane uplifts a wedge of hangingwall material apron the detachment surface emerges along a continuous moat that sheds rocks and covers it with unconsolidated rubble while local slumping emplaces rubble ridges overlying corrugations the detachment fault zone is a set of anostomosed slip planes elongated in the along extension direction slip planes bind fault rock bodies defining the corrugations observed in microbathymetry and sonar fault planes with extension parallel stria are exposed along corrugation flanks where the rubble cover is shed detachment fault rocks are primarily basalt fault breccia at 13 20 n occ and gabbro and peridotite at 13 30 n demonstrating that brittle strain localization in shallow lithosphere form corrugations regardless of lithologies in the detachment zone finally faulting and volcanism dismember the 13 30 n occ with widespread present and past hydrothermal activity semenov fields while the irinovskoe hydrothermal field at the 13 20 n core complex suggests a magmatic source within the footwall these results confirm the ubiquitous relationship between hydrothermal activity and oceanic detachment formation and evolution

what causes low magnetization at basalt hosted hydrothermal sites insights from inactive site krasnov mar 16 38 n high resolution magnetic surveys acquired near the seafloor show that active basalt hosted hydrothermal sites are associated with zones of lower magnetization this observation may reflect the thermal demagnetization of a hot hydrothermal zone the alteration of basalt affected by hydrothermal circulation and or the presence of thick nonmagnetic hydrothermal deposits in order to discriminate among these inferences we acquired vector magnetic data 50 m above inactive hydrothermal site krasnov using the remotely operated vehicle rov victor this deep hydrothermal site located 7 km east of the mid atlantic ridge mar axis at 16 38 n is dissected by major normal faults and shows no evidence of recent hydrothermal activity it is therefore a perfect target for investigating the magnetic signature of an inactive basalt hosted hydrothermal site krasnov exhibits a strong negative magnetic anomaly which implies that the lower magnetization observed at basalt hosted hydrothermal sites is not a transient effect associated with hydrothermal activity but remains after activity ceases thermal demagnetization plays only a secondary role if any in the observed magnetic low forward models suggest that both the nonmagnetic hydrothermal deposits and an altered zone of demagnetized basalt are required to account for the observed magnetic low the permanence of this magnetic signature makes it a useful tool to explore midocean ridges and detect inactive hydrothermal sites

widespread active detachment faulting and core complex formation near 13 n on the mid atlantic ridge oceanic core complexes are massifs in which lower crustal and upper mantle rocks are exposed at the sea floor1 2 3 they form at mid ocean ridges through slip on detachment faults rooted below the spreading axis2 3 4 5 6 to date most studies of core complexes have been based on isolated inactive massifs that have spread away from ridge axes here we present a survey of the mid atlantic ridge near 13 n containing a segment in which a number of linked detachment faults extend for 75 km along one flank of the spreading axis the detachment faults are apparently all currently active and at various stages of development a field of extinct core complexes extends away from the axis for at least 100 km our observations reveal the topographic characteristics of actively forming core complexes and their evolution from initiation within the axial valley floor to maturity and eventual inactivity within the surrounding region there is a strong correlation between detachment fault morphology at the ridge axis and high rates of hydroacoustically recorded earthquake seismicity preliminary examination of seismicity and seafloor morphology farther north along the mid atlantic ridge suggests that active detachment faulting is occurring in many segments and that detachment faulting is more important in the generation of ocean crust at this slow spreading ridge than previously suspected

emplacement of deep crustal and mantle rocks on the west median valley wall of the mark area mar 23 n abstract exposures of deep crustal and mantle rocks within the axial rift valley characterize accretion processes in the slow spreading mid atlantic ridge nine dives of the submersible nautile explored the western axial valley wall in the northern cell of the mark area mid atlantic ridge kane fracture zone where peridotite and gabbro outcrops had been previously reported in order to constrain the structure and determine emplacement mechanisms the ridge transform intersection massif on the western wall shows a section of gabbros from 6000 to 2500 mbsl locally overlain by metabasalts and metadolerites capped by slightly weathered basalts the morphology is controlled by ridge parallel faults dipping moderately 40 65 to the east transform parallel scarps present in the northernmost dives become rare toward the south brittle deformation along moderately dipping fault scarps produced a dense microcrack network filled with greenschist facies minerals chlorite actinolite epidote quartz locally overprinting high temperature ductile deformation fabrics the small hill located at 23 20 in the western wall shows good exposures of serpentinized peridotite between 3700 and 3100 mbsl above 3100 mbsl the summit of the hill is composed of pillow basalts and sediments the peridotite outerops display a strong schistosity dipping 20 40 to the east parallel to striated normal fault planes some steeper east facing fault scarps truncate the lower dipping fault surfaces the serpentinites deriving from a harzburgitic protolith are cut by rare dikelets of highly differentiated gabbro these new data combined with previous results of alvin dives are used to draw a generalized geological map of the western axial valley wall this map suggests a variation in the thickness of crustal units and composition along strike in the northern cell of the mark area the gabbro body disappears toward the south where basalts appear to directly overlie the mantle peridotites which are cut by isolated gabbroic dikelets low angle stretching affecting this heterogeneous lithosphere is probably responsible for the exposure of gabbros in the intersection massif and of peridotites further south

erosion transport and segregation of pumice and lithic clasts in pyroclastic flows inferred from ignimbrite at lascar volcano chile abstract investigations have been made on the distribution of pumice and lithic clasts in the lithic rich soncor ignimbrite 26 5 ka and the 1993 pumice flow deposits of lascar volcano chile the soncor ignimbrite shows three main lithofacies which grade into one another coarse lithic breccias range from matrix poor stratified varieties irregular shaped sheets and elongate hummocks in proximal environments to breccia lenses with pumiceous ignimbrite matrix massive lithic rich facies comprise the bulk of the ignimbrite pumice rich facies are bimodal with abundant large pumice clasts often with reverse grading rare lithic clasts and occur distally and on high ground adjacent to deep proximal valleys in the 1993 pyroclastic flow deposits lithic rich facies are deposited on slopes up to 14 whereas pumice rich facies are deposited only on slopes

ultramafic and gabbroic exposures at the mid atlantic ridge geological mapping in the 15 n region abstract the outcrops of mantle derived ultramafic rocks in the 15 n region are the most extensive yet reported for the mid atlantic ridge north of the fifteen twenty fracture zone these outcrops form a belt at least 20 km long along the west wall of the axial valley and also crop out on the east axial valley wall ultramafic rocks also crop out extensively south of the fifteen twenty fracture zone based on dredging and on a morphological analysis of the bathymetric map we propose that ultramafic outcrops may be common in the crust formed between 14 30 n and 15 50 n during at least the past 2 4 m y moderately dipping fault planes and large expanses of tectonic breccia have been observed during dives on the ultramafic outcrops diving observations also show that the ultramafic rocks are capped in stratigraphic contact by a thin layer of basalt this suggests that these rocks were tectonically emplaced at the axial seafloor or very close to it then uplifted in the footwall of the faults that bound the axial valley the occurrence of ultramafic rocks on both walls of the axial valley may be due to frequent changes of faulting polarity in the axial region instead of one master shear zone there would be a complex array of cross cutting conjugate faults and shear zones that could jump inward in the axial domain as spreading proceeds

fault structure and detailed evolution of a slow spreading ridge segment the mid atlantic ridge at 29 n we present preliminary results of a detailed near bottom study of the morphology and tectonics of the 29 n broken spur segment on the slow spreading mid atlantic ridge using principally the tobi deep towed instrument the survey covered two thirds of the segment length including all of its southern non transform boundary and extended off axis of 40 km 3 3 ma on either side we obtained nearly complete near bottom sidescan sonar coverage and deep towed three component magnetic observations along 2 km spaced e w tracks sidescan data reveal new details of fault structure and evolution faults grow by along axis linkage in the inside corner they also link in the axis normal direction by curving to meet the next outer older fault this leads to wider spaced faults compared to segment centre or outside corner outward facing faults exist but are rare the non transform offset is characterised by faults that are highly oblique not parallel to the spreading direction and show cross cutting relations with ridge parallel faults to the north suggesting along axis migration of the offset almost all volcanic activity occurs within 5 km of the axis most fault growth is complete within 15 km of the axis 1 2 ma though large scarps continue to be degraded by mass wasting beyond there crustal magnetisation is strongly three dimensional the current neovolcanic zone is slightly oblique to earlier reversal boundaries and its magnetisation rises to a maximum of 30 a m 1 near its southern tip the central magnetisation high tapers southwards and is asymmetric with a sharp western but gradual eastern boundary we infer a highly asymmetric accretion of layer 2 near the segment end older magnetic anomalies are kinked and sometimes missing we interpret these observations as evidence of a rapid 18 km southward migration of the segment boundary during the past 1 8 ma and present a series of reconstructions illustrating this tectonic history

high resolution bathymetry reveals contrasting landslide activity shaping the walls of the mid atlantic ridge axial valley 1 axial valleys are found along most slow spreading mid ocean ridges and are one of the most prominent topographic features on earth in this paper we present the first deep tow swath bathymetry for the axial valley walls of the mid atlantic ridge these data allow us to analyze axial valley wall morphology with a very high resolution 0 5 to 1 m compared to 50 m for shipboard multibeam bathymetry revealing the role played by landslides slow spreading ridge axial valleys also commonly expose mantle derived serpentinized peridotites in the footwalls of large offset normal faults detachments in our map of the ashadze area lat 13 n ultramafic outcrops have an average slope of 18 and behave as sliding deformable rock masses with little fragmentation by contrast the basaltic seafloor in the krasnov area lat 16 38 n has an average slope of 32 and the erosion of the steep basaltic rock faces leads to extensive fragmentation forming debris with morphologies consistent with noncohesive granular flow comparison with laboratory experiments suggests that the repose angle for this basaltic debris is 25 we discuss the interplay between the normal faults that bound the axial valley and the observed mass wasting processes we propose that along axial valley walls where serpentinized peridotites are exposed by detachment faults mass wasting results in average slopes 20 even in places where the emergence angle of the detachment is larger

models of ocean ridge lithospheric deformation dependence on crustal thickness spreading rate and segmentation we use three dimensional 3 d temperature and rheology models to investigate the effects of crustal thickness and ridge segmentation on mid ocean ridge lithospheric structure we find that crustal thickness variations associated with focused magma accretion at a slow spreading ridge segment can cause significant along axis gradients in crustal temperature and a pita pocket shaped weak zone in the lower crust that decouples brittle upper crust from upper mantle in contrast fast spreading ridge segments with little crustal thickness variation are found to be uniformly weak along axis the overthickened crust produced by ridge hotspot interaction alters the heat balance between magma emplacement and hydrothermal cooling creating an extremely weak lithosphere in a steady state model we apply a simple two dimensional 2 d cyclic faulting model to across axis sections of temperature and rheological structure slow spreading segments are predicted to have relatively large along axis variations in fault height and spacing in contrast fast spreading and hotspot affected segments are predicted to have much smaller variations in faulting styles except in the immediate vicinity of a major transform fault the presence or lack of a steady state axial rift valley is also predicted to depend on crustal thickness spreading rate and the ability of rift bounding normal faults to propagate along axis for fast spreading and hotspot affected segments the sizes of axial rift valleys are predicted to be small and may not be distinguishable from those of neovolcanic or magma chamber supported isostatic features this is in contrast to most slow spreading segments where axial rift valleys are predicted to be a dominant morphological feature for a slow spreading segment of great length however the axial rift valley size is predicted to diminish toward the segment center because large faults formed at segment distal ends cannot propagate through a large decoupling zone created by locally thickened crust at the segment center

flow and deposition of pyroclastic granular flows a type example from the 1975 ngauruhoe eruption new zealand small volume pyroclastic density currents pdcs are generated frequently during explosive eruptions with little warning assessing their hazard requires a physical understanding of their transport and sedimentation processes which is best achieved by the testing of experimental and numerical models of geophysical mass flows against natural flows and or deposits to this end we report on one of the most detailed sedimentological studies ever carried out on a series of pristine small volume pdc deposits from the 1975 eruption of ngauruhoe volcano whose emplacement were also witnessed during eruption using high resolution gps surveys a series of lateral excavations across the deposits and bulk sedimentological analysis we constrained the geomorphology internal structure and texture of the deposits with respect to laterally varying modes of deposition deposition from these pdcs began only on slopes at or around the material s angle of repose c 30 in unconfined settings the granular pdcs are interpreted to have been quasi steady forming sheets and lobes around the angle of repose where flows were confined sheet like proximal facies made up around 10 of the deposit volume at the angle of repose but 90 of the material was deposited from apparently unsteady inertial granular pdcs as a distal levee and channel facies on slopes well below the repose angle hence confined pdcs were able to travel up to 50 farther than unconfined flows in the distal facies the deposit width is inversely correlated to the local slope and the height of the levees above the deposit centreline is positively correlated with slope internally the deposits comprise three parts a coarse grained fines free sole layer that laterally connects to levees zone i an ashy matrix supported central body zone ii and an overlying coarse plaster of clasts zone ii trends in grain size data suggests these zones derive from a continuous un mixing of coarse particles from the initial bulk material by granular segregation that preferentially drives large particles to the upper free surface of the flow where they are concentrated at the front of flow before being deposited and overrun by comparison to analogue experiments we suggest a model of flow and deposition where the temporally and spatially varying mode of deposition is determined by the flow velocity the local slope the vertical velocity gradient the velocity gradient at the free surface and the vertical deposition rate using this model estimated vertical deposition rates of c 5 cm s 1 from the ngauruhoe pdcs agree with those determined in laboratory experiments on inertial granular flows

massive submarine rockslide in the rift valley wall of the mid atlantic ridge within the past 450000 yr a section of ocean crust 4 by 5 km was removed from the eastern wall of the mid atlantic rift valley in a massive rockslide that disintegrated to form a debris avalanche slope failure probably occurred along preexisting west dipping faults where hydrothermal metamorphism is inferred to have weakened the crust the debris avalanche flowed more than 11 km into the rift valley and deposited a debris wedge with a volume of 19 x 10 9 m 3 run up and rebound features occur where the leading edge of the avalanche encountered a basement ridge and they suggest rapid transport in an event that lasted only a few minutes this is the first known occurrence of such large scale mass wasting along the tectonically active rift valley of a mid ocean ridge

effect of clay fraction on turbulence characteristics of flow near an eroded bank abstract stream bank erosion in the alluvial channel is a matter of great concern particularly for the irretrievable loss of fertile land this in effect has direct impact on the agriculture environment economy and social issues at large a series of laboratory experiments were carry out to study the turbulence structure over eroded bank topography modulation of mean turbulent flow characteristics and the benefaction of turbulent bursting structures to the total reynolds shear stress due to the changed geometry of the eroded bank wall are described for three different clay fraction variations a side looking micro acoustic doppler velocimeter adv was used to record the detailed high frequency velocity data near the bank wall to understand the coupled dynamics of flow and erosion on sediment water interface the information on clay and fine sand content of natural river bank was obtained from field observation results from the present study indicate that higher turbulence intensities and reynolds shear stress have prominent role in the removal of bank materials from the bank wall and continues the dislodgement of material from the bank face until mass failure quadrant analysis to the random velocity fluctuation in the vicinity of eroded stream bank shows that downstream bank material movement is strongly correlated to the presence of sweep events probability density function pdf kinetic energy fluxes and coefficients of skewness and kurtosis of velocity fluctuations show significant changes with the change in clay fraction of the bank material composition though the velocity spectral densities are in general observed to be similar for all the three different bank undercut depths for different clay fraction of bank however spectral energy shows signature of higher energy peak for lower clay fraction of the bank material

relation between dry granular flow regimes and morphology of deposits formation of levees in pyroclastic deposits experiments on dry granular matter flowing down an inclined plane are performed in order to study the dynamics of dense pyroclastic flows the plane is rough and always wider than the flow focusing this study on the case of laterally unconfined free boundary flows we found that several flow regimes exist depending on the input flux and on the inclination of the plane each flow regime corresponds to a particular morphology of the associated deposit in one of these regimes the flow reaches a steady state and the deposit exhibits a levee channel morphology similar to those observed on small pyroclastic flow deposits the levees result from the combination between lateral static zones on each border of the flow and the drainage of the central part of the flow after the supply stops particle segregation features are created during the flow corresponding to those observed on the deposits of pyroclastic flows moreover the measurements of the deposit morphology thickness of the channel height of the levees width of the deposit are quantitatively related to parameters of the dynamics of the flow flux velocity height of the flow leading to a way of studying the flow dynamics from only measurements of the deposit some attempts to make extensions to natural cases are discussed through experiments introducing the polydispersity of the particle sizes and the particle segregation process