numerical modeling of the mount meager landslide constrained by its force history derived from seismic data we focus on the 6 august 2010 mount meager landslide that occurred in southwest british columbia canada this 48 5 mm3 rockslide that rapidly changed into a debris flow was recorded by over 25 broadband seismic stations we showed that the waveform inversion of the seismic signal making it possible to calculate the time history of the force applied by the landslide to the ground is very robust and stable even when using only data from a single station by comparing this force with the force calculated through numerical modeling of the landslide we are able to support the interpretation of seismic data made using a simple block model however our study gives different values of the friction coefficients involved and more details about the volumes and orientation of the subevents and the flow trajectory and velocity our sensitivity analysis shows that the characteristics of the released mass and the friction coefficients all contribute to the amplitude and the phase of the force despite this complexity our study makes it possible to discriminate the best values of all these parameters our results suggest that comparing simulated and inverted forces helps to identify appropriate rheological laws for natural flows we also show that except for the initial collapse peaks in the low frequency force related to bends and runup over topography changes are associated with high frequency generation possibly due to an increased agitation of the granular material involved

numerical modeling of the emplacement of socompa rock avalanche chile 1 the 7 5 ka socompa sector collapse emplaced 25 km3 of fragmented rock as a thin but widespread 500 km2 avalanche deposit followed by late stage sliding of 11 km3 as toreva blocks most of the avalanche mass was emplaced dry although saturation of a basal shear layer cannot be excluded modeling was carried out using the depth averaged granular flow equations in order to provide information on the flow behavior of this well preserved long run out avalanche results were constrained using structures preserved on the surface of the deposit as well as by deposit outline and run up a proxy for velocity models assuming constant dynamic friction fail to produce realistic results because the low basal friction angles 1 to 3 5 necessary to generate observed run out permit neither adequate deposition on slopes nor preservation of significant morphology on the deposit surface a reasonable fit is obtained however if the avalanche is assumed simply to experience a constant retarding stress of 50 100 kpa during flow this permits long run out as well as deposition on slopes and preservation of realistic depositional morphology in particular the model explains a prominent topographic escarpment on the deposit surface as the frozen front of a huge wave of debris reflected off surrounding hills the result that socompa avalanche experienced a small approximately constant retarding stress during emplacement is consistent with a previously published analysis of avalanche data

effects of near fault seismic loadings on run out of large scale landslide a case study this study presents the run out analysis of the daguangbao landslides subjected to near fault multi direction earthquake forces using discontinuous deformation analysis dda the daguangbao landslide is the largest landslide induced by the 2008 wenchuan earthquake in order to investigate the effects of near fault seismic force on landslide run out kinematic behavior of sliding mass is simulated by a dynamic discrete numerical analysis method called dda in this simulation based on the shape of failure surface and the feature of slope geology the whole slope is divided into three parts base block upper sliding mass and lower sliding mass then two sliding masses are divided into the smaller discrete deformable blocks based on pre existing discontinuities size effect of the huge landslide is also considered baseline corrected real horizontal and vertical ground motions are taken as volume force acting to the base block the results show that seismic force has a significant influence on the landslide progression sliding distance and shape of post failure results of the horizontal and vertical situation are in good agreement with those obtained from post earthquake field investigation remote sensing image and description from the survivors

pyroclastic flows from the 1991 eruption of unzen volcano japan pyroclastic flows from unzen were generated by gravitational collapse of the growing lava dome as soon as the parental lobe failed at the edge of the dome spontaneous shattering of lava occurred and induced a gravity flow of blocks and finer debris the flows had a overhanging tongue like head and cone or rollershaped vortices expanding outward and upward most of the flows traveled from 1 to 3 km but some flows reached more than 4 km burning houses and killing people in the evacuated zone of kita kamikoba on the eastern foot of the volcano the velocities of the flows ranged from 15 to 25 m s on the gentle middle flank observations of the flows and their deposits suggest that they consisted of a dense basal avalanche and an overlying turbulent ash cloud the basal avalanche swept down a topographic low and formed to tongue like lobe having well defined levees it is presumed to have moved as a non newtonian fluid the measured velocities and runout distances of the flows can be matched to a bingham model for the basal avalanche by the addition of turbulent resistance the rheologic model parameters for the 29 may flow are as follows the density is 1300 kg m3 the yield strength is 850 pa the viscosity is 90 pa s and the thickness of the avalanche is 2 m the ash cloud is interpreted as a turbulent mixing layer above the basal avalanche the buoyant portions of the cloud produced ash fall deposits whereas the dense portions moved as a surge separated from the parental avalanche the ash cloud surges formed a wide devastated zone covered by very thin debris the initial velocities of the 3 june surges when they detached from avalanches are determined by the runout distance and the angle of the energy line slope a comparison between the estimated velocities of the 3 june avalanches and the surges indicates that the surges that extended steep slopes along the avalanche path detached directly from the turbulent heads of the avalanches the over running surge that reached kita kamikoba had an estimated velocity higher than that of the avalanche this farther travelled surge is presumed to have been generated by collapse of a rising ash cloud plume

flow of variably fluidized granular masses across three dimensional terrain 2 numerical predictions and experimental tests numerical solutions of the equations describing flow of variably fluidized coulomb mixtures predict key features of dry granular avalanches and water saturated debris flows measured in physical experiments these features include time dependent speeds depths and widths of flows as well as the geometry of resulting deposits three dimensional 3 d boundary surfaces strongly influence flow dynamics because transverse shearing and cross stream momentum transport occur where topography obstructs or redirects motion consequent energy dissipation can cause local deceleration and deposition even on steep slopes velocities of surge fronts and other discontinuities that develop as flows cross 3 d terrain are predicted accurately by using a riemann solution algorithm the algorithm employs a gravity wave speed that accounts for different intensities of lateral stress transfer in regions of extending and compressing flow and in regions with different degrees of fluidization field observations and experiments indicate that flows in which fluid plays a significant role typically have high friction margins with weaker interiors partly fluidized by pore pressure interaction of the strong perimeter and weak interior produces relatively steep sided flat topped deposits to simulate these effects we compute pore pressure distributions using an advection diffusion model with enhanced diffusivity near flow margins although challenges remain in evaluating pore pressure distributions in diverse geophysical flows riemann solutions of the depth averaged 3 d coulomb mixture equations provide a powerful tool for interpreting and predicting flow behavior they provide a means of modeling debris flows rock avalanches pyroclastic flows and related phenomena without invoking and calibrating rheological parameters that have questionable physical significance

a model for the analysis of rapid landslide motion across three dimensional terrain a new numerical model for the dynamic analysis of rapid flow slides debris flows and avalanches has been developed the model is an extension of an earlier algorithm and is implemented using a nu

forensic investigations of the cima salti landslide northern italy using runout simulations abstract over the last decades a movement has begun to reclassify deposits previously misidentified as having origins other than landsliding the reverse problem of incorrectly assigning deposits a mass movement origin however has been addressed less in the landslide community the cima salti landslide in the lake garda region of northern italy is a cautionary tale of assuming source areas and volumes it was traditionally thought to have dammed tenno lake in the middle ages and to have a volume of 20 30 mm3 we show through geological field data and simple runout simulations with the codes dan3d and shaltop which produced comparable results that the volume of the landslide was likely significantly overestimated in the past and that it most likely did not dam tenno lake as has been assumed we propose that a smaller volume landslide 2 5 mm3 was deposited on stagnant ice melting in situ in the lateglacial period a relatively minor event in the complex history of the magnone valley this interpretation emphasizes the importance of careful field investigations and assumption validation at cima salti and in a broader context it also shows the unique capacity of landslide simulation to guide field observation and discriminate mass emplacement processes

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

a morphological stability analysis for a long straight barred coast a morphological stability analysis is carried out for a long straight coast with a longshore bar the situation with oblique wave incidence and a wave driven longshore current is considered the flow and sediment transport are described by a numerical modelling system the models comprise i a wave model with depth refraction shoaling and wave breaking ii a depth integrated model for wave driven currents and iii a sediment transport model for the bed load transport and the suspended load transport in combined waves and current the direction of the sediment transport is taken to be parallel to the depth integrated mean current velocity neglecting the effects of a bed slope and secondary currents an instability is found to develop around the bar crest the instability is periodic in the alongshore direction and tends to form rip channels and to steepen the offshore face of the bar between the rip channels the alongshore wave length of the most unstable perturbation is determined for different combinations of the wave conditions and the geometry of the profile

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

pressures at the base of dry flows of angular rock fragments as a function of grain size and flow volume experimental results geophysical granular flows such as pyroclastic flows and rock avalanches kill people and damage properties worldwide the pressures exerted at their base affect the retarding forces that act on them and for this reason affect also their mobility that is important to foresee when assessing natural hazards in mountain regions here we present the results of experiments obtained by measuring with a load cell the basal pressures exerted by dry and cohesionless granular flows that descend a curved chute in the laboratory the interaction between these flows and the chute surface on which they travel is dominated by collisions of particles and or clusters of particles a dimensional analysis suggests that the energy dissipation of these flows increases as grain size increases and as flow volume decreases all the other features equal therefore the smaller the grain size and the larger the volume the larger is expected to be flow mobility although the longer travel distances of the centre of mass of finer grain size flows are easily discernible in our experiments the effect of volume is probably hidden by additional phenomena such as the deposition first of the frontal portion of longer flows on the less steep more distal part of the slope that prevents the rear portion and the centre of mass of the flows to travel further downhill

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

the statistics and kinematics of transverse sand bars on an open coast abstract ten years 1987 1996 of time exposure video images of the nearshore region at duck nc were used to study transverse sand bars bathymetric features of intermediate length scales 10 200 m oriented oblique or perpendicular to the shoreline these transverse sand bars extend seaward from both the shoreline trough transverse bars and the shore parallel sand bar offshore transverse bars transverse bars had not previously been observed in an energetic coastal environment such as that at duck and their dynamics and role in nearshore processes is unknown frequency of occurrence statistics and length scales of the transverse bars were calculated using the video images trough and offshore transverse bars appeared a mean of 39 and 73 days per year respectively the offshore bars were found to be much larger features than the trough bars with mean wavelengths alongshore spacing between consecutive crests of 79 and 172 m for trough and offshore bars respectively both the trough and offshore bars were found to persist for periods of days to months the alongshore movement of the bars was measured and compared to estimates of surf zone longshore currents which were calculated from wave height and wave angle data both sets of bars were observed to move at rates up to 40 m day at times both trough and offshore bars were observed shifting in the same direction as the current was flowing and at other times both sets of bars remained stationary even under relatively strong longshore currents trough bars were also observed moving against the current an hypothesis proposed by barcilon and lau 1973 j geophys res 78 15 2656 2664 that the transverse bars were created as a sea bed instability under longshore currents was tested by comparing the magnitude of estimated surf zone longshore currents with times of formation or presence of transverse bars there was no evidence to suggest that the bars were formed by this simple longshore current instability mechanism instead it is plausible that the combined effects of waves and currents may drive the formation of these features

self organization mechanisms for the formation of nearshore crescentic and transverse sand bars the formation and development of transverse and crescentic sand bars in the coastal marine environment has been investigated by means of a nonlinear numerical model based on the shallow water equations and on a simplified sediment transport parameterization by assuming normally approaching waves and a saturated surf zone rhythmic patterns develop from a planar slope where random perturbations of small amplitude have been superimposed two types of bedforms appear one is a crescentic bar pattern centred around the breakpoint and the other herein modelled for the first time is a transverse bar pattern the feedback mechanism related to the formation and development of the patterns can be explained by coupling the water and sediment conservation equations basically the waves stir up the sediment and keep it in suspension with a certain cross shore distribution of depth averaged concentration then a current flowing with against the gradient of sediment concentration produces erosion deposition it is shown that inside the surf zone these currents may occur due to the wave refraction and to the redistribution of wave breaking produced by the growing bedforms numerical simulations have been performed in order to understand the sensitivity of the pattern formation to the parameterization and to relate the hydro morphodynamic input conditions to which of the patterns develops it is suggested that crescentic bar growth would be favoured by high energy conditions and fine sediment while transverse bars would grow for milder waves and coarser sediment in intermediate conditions mixed patterns may occur

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

model space exploration for determining landslide source history from long period seismic data the seismic signals generated by two large volcanic debris avalanches montserrat lesser antilles 1997 and mount st helens usa 1980 and a large rock ice avalanche mount steller usa 2005 have been analyzed for the two debris avalanches given the times and locations of such landslides their signals were recorded by only a few seismic stations moreover these signals cover only a very narrow frequency band and include considerable noise the mount steller on the contrary was precisely recorded for each event the source mechanism i e point force has been determined by waveform inversion using at most two broadband seismic stations the resulting force is very difficult to interpret in terms of landslide characteristics a monte carlo inversion was therefore performed by imposing a simple force model associated with the landslide based on the schematic view of an accelerating decelerating mass traveling down the slope the best parameter set of the force model was then found by minimizing misfits and maximizing correlations between data and synthetic signals this model appears to contain the minimum degree of complexity required to well reproduce the seismic data we detail here the method for the montserrat debris avalanche and then present it s validation on the well studied mount st helens debris avalanche and the well recorded mount steller rock ice avalanche the horizontal and vertical components of the resulting force have different source time functions the best force model compares well with the force obtained by waveform inversion finally this simple force model was interpreted using analytical and empirical relations derived from the sliding block model granular flow model and landslide studies this made it possible to estimate the order of magnitude of the mass flow duration and direction initial topography slope mean velocity and travel distance of the avalanches for these three avalanches the calculated characteristics are consistent with former studies

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

dynamic implications of ridges on a debris avalanche deposit at tutupaca volcano southern peru catastrophic volcanic landslides can involve different parts of a volcano that can be incorporated into any resulting debris avalanche the different material properties may influence the mechanical behaviour and hence the emplacement mechanisms of the different avalanche units we present data from a coupled hydrothermal and magmatic related volcanic landslide at tutupaca volcano peru around ad 1802 the hydrothermal system under tutupaca s growing dacite dome failed creating a debris avalanche that triggered a large explosive eruption a typical debris avalanche hummocky unit is found formed out of rock from the dome foot and the underlying hydrothermally altered lavas it is covered by a more widespread and remarkable deposit that contains remnants of the hot dome core and the inner hydrothermal material this deposit has ridges 20 500 m long 10 30 m wide and 1 5 m high regularly spaced and that fan slightly outward cross sections exposed within the ridges reveal coarser cores and finer troughs suggesting grain size segregation during emplacement ridge morphology and granulometry are consistent with fingering known to occur in granular flows the ridges are also associated with large blocks that have evidence of differential movement compared with the rest of the flowing mass the presence of both ridged and hummocky deposits in the same event shows that as different lithologies combine and collapse sequentially materials with different mechanical properties can coexist in one landslide leading to contrasting emplacement dynamics the different structures thus highlight the complexity of such hazardous volcanic events and show the difficulty we face with modelling them

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

formation of recurring slope lineae on mars by rarefied gas triggered granular flows active dark flows known as recurring slope lineae have been observed on the warmest slopes of equatorial mars the morphology composition and seasonality of the lineae suggest a role of liquid water in their formation however internal and atmospheric sources of water appear to be insufficient to sustain the observed slope activity experimental evidence suggests that under the low atmospheric pressure at the surface of mars gas can flow upwards through porous martian soil due to thermal creep under surface regions heated by the sun and disturb small particles here we present numerical simulations to demonstrate that such a dry process involving the pumping of rarefied gas in the martian soil due to temperature contrasts can explain the formation of the recurring slope lineae in our simulations solar irradiation followed by shadow significantly reduces the angle of repose due to the resulting temporary temperature gradients over shaded terrain and leads to flow at intermediate slope angles the simulated flow locations are consistent with observed recurring slope lineae that initiate in rough and bouldered terrains with local shadows over the soil we suggest that this dry avalanche process can explain the formation of the recurring slope lineae on mars without requiring liquid water or co2 frost activity transient streaks on martian slopes have been attributed to liquid water simulations show that a dry avalanche process involving the flow of gas in the martian soil due to temperature contrasts can instead explain these recurring features

modelling the formation of shoreface connected sand ridges on storm dominated inner shelves a morphodynamic model is developed and analysed to gain fundamental understanding of the basic physical mechanisms responsible for the characteristics of shorefaceconnected sand ridges observed in some coastal seas these alongshore rhythmic bed forms have a horizontal lengthscale of order 5 km and are related to the mean current along the coast the seaward ends of their crests are shifted upstream with respect to where they are attached to the shoreface the model is based on the two dimensional shallow water equations and assumes that the sediment transport only takes place during storms the flux consists of a suspended load part and a bed load part and accounts for the eects of spatially non uniform wave stirring as well as for the preferred downslope movement of sediment the basic state of this model represents a steady longshore current driven by wind and a pressure gradient the dynamics of small perturbations to this state are controlled by a physical mechanism which is related to the transverse bottom slope this causes a seaward deflection of the current over the ridges and the loss of sediment carrying capacity of the flow into deeper water the orientation spacing and shape of the modelled ridges agree well with eld observations suspended load transport and spatially non uniform wave stirring are necessary in order to obtain correct e folding timescales and migration speeds the ridge growth is only due to suspended load transport whereas the migration is controlled by bed load transport

martian gullies a comprehensive review of observations mechanisms and insights from earth analogues upon their discovery in 2000 martian gullies were hailed as the first proof of recent i e less than a few million years flowing liquid water on the surface of a dry desert planet many processes have been proposed to have formed martian gullies ranging from liquid water seepage from aquifers melting of snow ice and frost to dry granular flows potentially lubricated by co2 terrestrial analogues have played a pivotal role in the conception and validation of gully formation mechanisms comparison with the terrestrial landscape argues for gully formation by liquid water debris flows originating from surface melting however limited knowledge of sediment transport by sublimation is a critical factor in impeding progress on the co2 sublimation hypothesis we propose avenues towards resolving the debate a laboratory simulations targeting variables that can be measured from orbit b applications of landscape evolution models c incorporation of the concept of sediment connectivity d using 3d fluid dynamic models to link deposit morphology and flow rheology and e a more intense exchange of techniques between terrestrial and planetary geomorphology including quantitative and temporal approaches finally we emphasize that the present may not accurately represent the past and that martian gullies likely formed by a combination of processes

an efficient and stable hydrodynamic model with novel source term discretization schemes for overland flow and flood simulations numerical models solving the full 2 d shallow water equations swes have been increasingly used to simulate overland flows and better understand the transient flow dynamics of flash floods in a catchment however there still exist key challenges that have not yet been resolved for the development of fully dynamic overland flow models related to 1 the difficulty of maintaining numerical stability and accuracy in the limit of disappearing water depth and 2 inaccurate estimation of velocities and discharges on slopes as a result of strong nonlinearity of friction terms this paper aims to tackle these key research challenges and present a new numerical scheme for accurately and efficiently modeling large scale transient overland flows over complex terrains the proposed scheme features a novel surface reconstruction method srm to correctly compute slope source terms and maintain numerical stability at small water depth and a new implicit discretization method to handle the highly nonlinear friction terms the resulting shallow water overland flow model is first validated against analytical and experimental test cases and then applied to simulate a hypothetic rainfall event in the 42 km2haltwhistle burn uk

variability of shore and shoreline evolution shore and shoreline evolution both due to natural and human induced causes or factors can be variable over a wide range of different temporal and or spatial scales our capability to understand and especially predict this variability is still limited this can lead to misinterpretation of coastal change information which hampers informed decision making and the subsequent design and implementation of soft engineering interventions collecting and describing example observations of shore and shoreline variability is one way to support and improve such human intervention this paper describes causes and factors for the variability and the resulting possible evolutions of wave dominated shores and shorelines which are illustrated by a number of case studies the new element of this work is that the variability is described in terms of a range of different time and space scales which helps to structure such analysis however it is difficult to generalise the results for arbitrary situations especially on decadal time scales scientific and engineering improvements require more quantitative insight into the physical mechanisms behind the free and forced shore behaviour responsible for the variability

emplacement of pyroclastic flows during the 1998 1999 eruption of volcan de colima mexico after three years of quiescence volcan de colima reawakened with increasing seismic and rock fall activity that reached its peak on november 20 1998 when a new lava dome forced its way to the volcano s summit the new lava rapidly reached the s sw edge of the summit area beginning the generation of merapi type pyroclastic flows that traveled down la lumbre and the el cordoban western and eastern ravines reaching distances of 3 4 5 and 3 km respectively on december 1 1998 the lava flow split into three fronts that in early 1999 had reached 2 8 3 1 and 2 5 km in length advancing down the el cordoban ravines the lava flow fronts disaggregated into blocks forming pyroclastic flows one of the best examples occurred on december 10 1998 as the lava flow ceased moving in early 1999 activity became more explosive strong blasts were recorded on february 10 may 10 and july 17 1999 the last event developed a 10 km high eruptive column from which a pyroclastic flow developed from the base traveling 3 3 km sw from the summit into the san antonio montegrande ravines regardless of the mechanism of pyroclastic flow generation each flow immediately segregated into a basal avalanche that moved as a granular flow and an upper ash cloud in which particles were sustained in turbulent suspension when the basal avalanche lost velocity and eventually stopped the upper ash cloud continued to move independently as a dilute pyroclastic flow that produced a massive pyroclastic flow deposit and an upper dune bedded surge deposit the dilute pyroclastic flow scorched and toppled maguey plants and trees and sandblasted vegetation in the direction of the flow at the end of the dilute pyroclastic flow path the suspended particles lifted off in a cloud from which a terminal ash fall was deposited the basal avalanche emplaced block and ash flow deposits up to 8 m thick that filled the main ravines and consisted of several flow units each flow unit was massive monolithologic matrix supported and had a clast supported steep front ca 1 5 to 2 m thick composed of boulders up to 1 7 m in diameter the juvenile lithic clasts had an average density of 1800 kg m3 the dilute pyroclastic flow emplaced overbank deposits found on valley margins or beyond the tip of block and ash flow deposits they consist from bottom to top of a massive medium to coarse sand size flow layer 2 4 cm thick a dune bedded surge layer 2 10 cm thick and a massive silt size layer 0 5 cm thick the total estimated volume of the pyroclastic flow deposits produced during the 1998 1999 eruption is 24 105 m3

gravity driven granular free surface flow around a circular cylinder snow avalanches and other hazardous geophysical granular flows such as debris flows lahars and pyroclastic flows often impact on obstacles as they flow down a slope generating rapid changes in the flow height and velocity in their vicinity it is important to understand how a granular material flows around such obstacles to improve the design of deflecting and catching dams and to correctly interpret field observations in this paper small scale experiments and numerical simulations are used to investigate the supercritical gravity driven free surface flow of a granular avalanche around a circular cylinder our experiments show that a very sharp bow shock wave and a stagnation point are generated in front of the cylinder the shock standoff distance is accurately reproduced by shock capturing numerical simulations and is approximately equal to the reciprocal of the froude number consistent with previous approximate results for shallow water flows as the grains move around the cylinder the flow expands and the pressure gradients rapidly accelerate the particles up to supercritical speeds again the internal pressure is not strong enough to immediately push the grains into the space behind the cylinder and instead a grain free region or granular vacuum forms on the lee side for moderate upstream froude numbers and slope inclinations the granular vacuum closes up rapidly to form a triangular region but on steeper slopes both experiments and numerical simulations show that the pinch off distance moves far downstream

infragravity rip current pulsations 1 the origins of rip current pulsations within the infragravity frequency band 0 004 0 04 hz are determined from measurements made with arrays of colocated pressure and velocity sensors deployed on a beach with persistent rip current channels the observations indicate significant energy in cross shore infragravity velocities that varies spatially in the alongshore due to the presence of rip channels infragravity velocities are smaller within the rip channel than on the shore connected shoal owing to differences in water depth rip current pulsations at infragravity frequencies are linked to standing infragravity motions but not to the ponding and subsequent release of water by wave group pumping

constraining landslide characteristics with bayesian inversion of field and seismic data using a fully nonlinear bayesian approach based on forward modelling of granular flow we invert for landslide parameters volume release geometry and rheology from different kinds of observations synthetic tests show that the runout distance and the deposit area by themselves do not constrain landslide parameters better constraints on landslide parameters are obtained from the thickness distribution of the landslide deposits as well as from the force history applied by the landslide to the ground which contains information on the landslide dynamics therefore inverting force histories calculated from seismic broad band records is an important alternative to inverting thickness distributions of landslide deposits which are usually difficult to obtain we test the method on the 1997 boxing day debris avalanche on montserrat island which involved 40 50 mm3 the bayesian inversion and granular flow model provide good estimates for volume release geometry and effective friction coefficient this study thus underlines the value of broad band seismic records as observations to monitor landslides and validation for their numerical flow models

understanding coastal morphodynamic patterns from depth averaged sediment concentration this review highlights the important role of the depth averaged sediment concentration dasc to understand the formation of a number of coastal morphodynamic features that have an alongshore rhythmic pattern beach cusps surf zone transverse and crescentic bars and shoreface connected sand ridges we present a formulation and methodology based on the knowledge of the dasc which equals the sediment load divided by the water depth that has been successfully used to understand the characteristics of these features these sand bodies relevant for coastal engineering and other disciplines are located in different parts of the coastal zone and are characterized by different spatial and temporal scales but the same technique can be used to understand them since the sand bodies occur in the presence of depth averaged currents the sediment transport approximately equals a sediment load times the current moreover it is assumed that waves essentially mobilize the sediment and the current increases this mobilization and advects the sediment in such conditions knowing the spatial distribution of the dasc and the depth averaged currents induced by the forcing waves wind and pressure gradients over the patterns allows inferring the convergence divergence of sediment transport deposition erosion occurs where the current flows from areas of high to low low to high values of dasc the formulation and methodology are especially useful to understand the positive feedback mechanisms between flow and morphology leading to the formation of those morphological features but the physical mechanisms for their migration their finite amplitude behavior and their decay can also be explored

can the collapse of a fly ash heap develop into an air fluidized flow reanalysis of the jupille accident 1961 a fly ash heap collapse occurred in jupille liege belgium in 1961 the subsequent flow of fly ash reached a surprisingly long runout and had catastrophic consequences its unprecedented degree of fluidization attracted scientific attention as drillings and direct observations revealed no water saturated zone at the base of the deposits scientists assumed an air fluidization mechanism which appeared consistent with the properties of the material in this paper the air fluidization assumption is tested based on two dimensional numerical simulations the numerical model has been developed so as to focus on the most prominent processes governing the flow with parameters constrained by their physical interpretation results are compared to accurate field observations and are presented for different stages in the model enhancement so as to provide a base for a discussion of the relative influence of pore pressure dissipation and pore pressure generation these results show that the apparently high diffusion coefficient that characterizes the dissipation of air pore pressures is in fact sufficiently low for an important degree of fluidization to be maintained during a flow of hundreds of meters

transferability of a calibrated numerical model of rock avalanche run out application to 20 rock avalanches on the nuussuaq peninsula west greenland long run out rock avalanches are one of the most hazardous geomorphic processes and risk assessments of the potential threat they pose are often reliant on numerical modelling of their potential run out distance the development of such models requires a thorough understanding of past flow behaviour inferred from deposits emplaced by previous events despite this few records exist of multiple rock avalanches that occurred in conditions sufficiently consistent to develop a set of more generalised and hence transferrable rules we conduct field and imagery based mapping and use numerical modelling to investigate the emplacement of 20 adjacent rock avalanches on the southern flanks of the nuussuaq peninsula west greenland the rock avalanches run out towards the vaigat strait and are sourced from a range of coastal mountains of relatively uniform geology we calibrate a three dimensional continuum dynamic flow code volcflow with data from a modern well constrained event that occurred at paatuut ad 2000 the best fit model assumes a constant retarding stress with a collisional stress coefficient simulating run out to within 0 3 of that observed this calibration was then used to model the emplacement of deposits from five other neighbouring rock avalanches before simulating the general characteristics of a further 14 rock avalanche deposits on simplified topography our findings illustrate that a single calibration of volcflow can account for the observed deposit morphology of a uniquely large collection of rock avalanche deposits emplaced by a series of events spanning a large volume range although the prevailing approach of tuning models to a specific case may be useful for detailed back analysis of that event we show that more generally applied models even using a single pair of rheological parameters can be used to model potential rock avalanches of varied volumes in a region and therefore to assess the risks that they pose

sims u pb rutile age of low temperature eclogites from southwestern chinese tianshan nw china article i nfo the geological evolution in the southwestern chinese tianshan orogen in nw china is poorly understood because of controversial geochronological results of the low temperature eclogites it is likely due to sm nd and rb sr isotopic disequilibrium in different mineral fractions excess 40 ar in the high pressure k bearing minerals and multi stage growths of zircon in u pb system rutile as a typical eclogite facies mineral with high u pb ratio is a feasible candidate to constrain the eclogite facies metamorphic event in this study we measured u pb rutile age data using sims cameca ims 1280 for low temperature eclogites from southwestern chinese tianshan orogen nw china we demonstrate that sims is a powerful technique for in situ u pb dating of rutile with u content as low as 1 ppm sims u pb rutile dating yielded an age of 318 7 ma which may record the time when the rocks cooled down to the closure temperature of pb in rutile ca 500 c but should be very close to the time of eclogite facies metamorphism in terms of common fast exhumation of coesite bearing eclogite this new proof strongly suggests a late carboniferous collision between kazakhstan yili block and central tianshan microcontinent

development of crescentic bars for a periodically perturbed initial bathymetry 1 the development of crescentic bed patterns starting from an undisturbed beach i e one only perturbed so as to simulate background noise and thereby initiate morphological development is compared with that starting from a beach where monochromatic and in some cases bichromatic bed patterns pre exist using a fully non linear model morfo55 a wide range of different lengthscales and amplitudes is investigated the findings suggest that the pre existence of crescentic bed forms can influence the subsequent morphological development of this beach significantly but that this development is related to the undisturbed beach development whether a pre existing bed form remains under certain forcing conditions depends on the position of the pre existing lengthscale along the undisturbed linear growth rate curve if the pre existing mode shows significant linear growth in the undisturbed scenario this pre existing lengthscale remains otherwise the pre existing mode will be replaced by a bed form with a lengthscale closer to the undisturbed fastest growing mode a pre existing lengthscale that is significantly longer than the undisturbed fastest growing mode will be replaced by a higher harmonic of the original lengthscale for shorter pre existing lengthscales this will be the linear fastest growing mode an increased amplitude of the pre existing bed form accelerates the development toward a new stable situation for small initial amplitudes the initial response of the system to pre existing bed forms could theoretically be described using linearized equations alone the migration rates of both the pre existing and newly arising modes correspond to the migration rate of these modes in the undisturbed scenario

observations of nearshore crescentic sandbars 1 the temporal and spatial variability of crescentic sandbars is analyzed with hourly long term months video observations collected at four barred sites and are qualitatively compared to the temporal and spatial variability predicted by hypotheses underpinning existing approaches and models for crescentic bar formation edge wave template model linear stability analysis and nonlinear models the observations coming from the single barred beaches at duck north carolina usa and miyazaki kyushu japan and from the double barred beaches at the northern gold coast queensland australia and noordwijk netherlands show that crescentic sandbar wavelength and amplitude variations over space and time are very common for instance at any moment in time the wavelength of the smallest and longest crescentic bar can differ by a factor of 2 temporal changes in wavelength and amplitude result from merging and splitting of individual crescents causing the final configuration of a crescentic sandbar system to be very different from the initial configuration the gold coast data indicate that these intrinsically nonlinear interactions are an attempt of the crescentic bar system to self organize into a more uniform pattern as splitting is usually confined to the longest crescentic bar observed whereas merging usually combines the smallest crescentic bars into a longer bar the observed spatial and temporal crescentic bar behavior contrasts qualitatively with behavior predicted from the edge wave template model and implies that the predictive skill of linear stability models is limited nonlinear models are potentially better suited for a comparison against these field observations several suggestions to improve these models and hence to facilitate a data model comparison are made

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

the role of viscous particle segregation in forming chromite layers from slumped crystal slurries insights from analogue experiments the question of how the mineral layering in layered intrusions forms has been extensively debated for many decades there are many types of layering and it is of course possible that a number of mechanisms are involved of particular interest is how chromite layers form because these may contain valuable metals such as platinum group elements in addition to cr one model for the formation of these layers is that they formed through slumping of semi consolidated cumulates from the margins of the intrusion into the magma chamber during this slumping the grains are sorted by density and or size differences this study examines the viability of this process using analogue modelling starting materials beads and glycerine were scaled to match the density and size of the minerals chromite orthopyroxene and plagioclase present in layered mafic ultramafic layered intrusions and to match the density and viscosity of the silicate magma a perspex flume tank divided by a removable partition at one end was fully filled with glycerine a homogenized mixture of the beads was placed in the smaller partition of the tank representing the margins of the magma chamber the tank was then inclined between 16 and 45 the partition was removed and the beads flowed into the main part of the box the experiments were recorded by video camera allowing us to follow the dynamics of the flow during each run segregation of the beads was observed in the final deposits the larger less dense beads representing plagioclase concentrated at the top of the flow with the intermediate sized and medium density beads representing orthopyroxene in the middle and the smaller denser beads representing chromite at the bottom thus mimicking natural examples in experiments where the angle of inclination was low long thin layers formed such as those found in the bushveld complex in experiments where the angle of inclination was high thick but short layers formed a dimensionless analysis allows better understanding of the dynamics of the flow at the macroscopic scale the flow regime is strongly influenced by the viscosity of the fluid and is considered macro viscous where the role of the interstitial liquid is non negligible

flow of variably fluidized granular masses across three dimensional terrain 1 coulomb mixture theory rock avalanches debris flows and related phenomena consist of grain fluid mixtures that move across three dimensional terrain in all these phenomena the same basic forces govern motion but differing mixture compositions initial conditions and boundary conditions yield varied dynamics and deposits to predict motion of diverse grain fluid masses from initiation to deposition we develop a depth averaged three dimensional mathematical model that accounts explicitly for solid and fluid phase forces and interactions model input consists of initial conditions path topography basal and internal friction angles of solid grains viscosity of pore fluid mixture density and a mixture diffusivity that controls pore pressure dissipation because these properties are constrained by independent measurements the model requires little or no calibration and yields readily testable predictions in the limit of vanishing coulomb friction due to persistent high fluid pressure the model equations describe motion of viscous floods and in the limit of vanishing fluid stress they describe one phase granular avalanches analysis of intermediate phenomena such as debris flows and pyroclastic flows requires use of the full mixture equations which can simulate interaction of high friction surge fronts with more fluid debris that follows special numerical methods described in the companion paper are necessary to solve the full equations but exact analytical solutions of simplified equations provide critical insight an analytical solution for translational motion of a coulomb mixture accelerating from rest and descending a uniform slope demonstrates that steady flow can occur only asymptotically a solution for the asymptotic limit of steady flow in a rectangular channel explains why shear may be concentrated in narrow marginal bands that border a plug of translating debris solutions for static equilibrium of source areas describe conditions of incipient slope instability and other static solutions show that nonuniform distributions of pore fluid pressure produce bluntly tapered vertical profiles at the margins of deposits simplified equations and solutions may apply in additional situations identified by a scaling analysis assessment of dimensionless scaling parameters also reveals that miniature laboratory experiments poorly simulate the dynamics of full scale flows in which fluid effects are significant therefore large geophysical flows can exhibit dynamics not evident at laboratory scales

a mechanism for the generation of wave driven rhythmic patterns in the surf zone the coupling between topographic irregularities and wave driven mean water motion in the surf zone is examined this coupling occurs because the topographic perturbations produce excess gradients in the wave radiation stress that cause a steady circulation this circulation in turn creates a sediment transport pattern that can reinforce the bottom disturbance and may thereby lead to the growth of large scale bed forms to investigate this coupling mechanism the linearized stability problem with an originally plane sloping beach and normal wave incidence is solved in two different cases first the breaking line is considered to be fixed and second the perturbations in water depth that produce a displacement of the breaker line are accounted for the first case shows that the basic topography can be unstable with respect to two different modes a giant cusp pattern with shore attached transverse bars that extend across the whole surf zone and a crescentic pattern with alternate shoals and pools at both sides of the breaking line showing a mirroring effect in the second case the varying breaker line may have a strong influence on the circulation this is clear for the giant cusp topography whose growth is totally inhibited in contrast the morphology and the growth of the crescentic pattern remains almost unchanged

generation of block and ash flows during the 1990 1995 eruption of unzen volcano japan processes generating block and ash flows by gravitational dome collapse merapi type pyroclastic flow were observed in detail during the 1990 1995 eruption of unzen volcano japan two different types were identified by analysis of video records and observations during helicopter flights most of the block and ash flows erupted during the 1991 1993 exogenous dome growth stage initially involved crack propagation due to cooling and flowage of the dome lava lobes the mass around the crack became unstable locally decreasing in tensile strength finally a slab separated from the lobe front fragmented progressively from the base to the top within a few seconds and became a block and ash flow rock falls immediately followed in response to local instability of the lobe front clasts in these rock falls fragmented and merged with the preceding flow in contrast block and ash flows during the endogenous dome growth stage in 1994 were generated due to local bulge of the dome unstable lava blocks collapsed and subsequently fragmented to produce block and ash flows

the indication of martian gully formation processes by slope area analysis the formation process of recent gullies on mars is currently under debate this study aims to discriminate between the proposed formation processes pure water flow debris flow and dry mass wasting through the application of geomorphological indices commonly used in terrestrial geomorphology high resolution digital elevation models dems of earth and mars were used to evaluate the drainage characteristics of small slope sections data from earth were used to validate the hillslope debris flow and alluvial process domains previously found for large fluvial catchments on earth and these domains were applied to gullied and ungullied slopes on mars in accordance with other studies our results indicate that debris flow is one of the main processes forming the martian gullies that were being examined the source of the water is predominantly distributed surface melting not an underground aquifer evidence is also presented indicating that other processes may have shaped martian crater slopes such as ice assisted creep and solifluction in agreement with the proposed recent martian glacial and periglacial climate our results suggest that within impact craters different processes are acting on differently oriented slopes but further work is needed to investigate the potential link between these observations and changes in martian climate

p t evolution of glaucophane omphacite bearing hp lt rocks in the western tianshan orogen nw china new evidence for alpine type tectonics the late palaeozoic western tianshan high pressure low temperature belt extends for about 200 km along the south central tianshan suture zone and is composed mainly of blueschist eclogite and epidote amphibolite greenschist facies rocks p t conditions of mafic garnet omphacite and garnet omphacite blueschist which are interlayered with eclogite were investigated in order to establish an exhumation path for these high pressure rocks maximum pressure conditions are represented by the assemblage garnet omphacite paragonite phengite glaucophane quartz rutile estimated maximum pressures range between 18 and 21 kbar at temperatures between 490 and 570 c decompression caused the destabilization of omphacite garnet and glaucophane to albite ca amphibole and chlorite the post eclogite facies metamorphic conditions between 9 and 14 kbar at 480 570 c suggest an almost isothermal decompression from eclogite to epidote amphibolite facies conditions prograde growth zoning and mineral inclusions in garnet as well as post eclogite facies conditions are evidence for a clockwise p t path analysis of phase diagrams constrains the p t path to more or less isothermal cooling which is well corroborated by the results of geothermobarometry and mineral textures this implies that the high pressure rocks from the western tianshan orogen formed in a tectonic regime similar to alpine type tectonics this contradicts previous models which favour franciscan type tectonics for the southern tianshan high pressure rocks

an energetics total load sediment transport model for a plane sloping beach bagnold s energetics based total load sediment transport model for streams is used as a basis for the development of a total load model of time varying sediment transport over a plane sloping bed in both the bedload and suspended load the transport rate vectors are found to be composed of a velocity induced component directed parallel to the instantaneous velocity vector and a gravity induced component directed down slope the model is applied to idealized surfzone conditions leading to estimates of the local longshore and onshore offshore sediment transport rates as well as the equilibrium beach slope as a function of the local wave and current conditions the model is combined with a nonlinear longshore current model and spatially integrated to obtain predictions of the total longshore transport rate as a function of the incident wave conditions the results support the general form of the wave power equation except that the wave power coefficient is no longer constant but is instead a complex function of the incident wave and beach characteristics

effects of pore pressure in pyroclastic flows numerical simulation and experimental validation pyroclastic flows are mixtures of volcanic gases and particles that can be very hazardous owing to their fluid like behavior one possible mechanism to explain this behavior is the reduction of particles friction due to the internal gas pore pressure to verify this hypothesis we present a numerical model of a granular flow with high initial pore pressure that decreases with time as the gas particle mixture propagates first we validate the model by reproducing laboratory experiments then the numerical code is applied to pyroclastic flows of lascar volcano 1993 eruption chile the simulation reproduces the runout and the morphological features of the deposits with lateral levees a central channel and a lobate front our results support the hypothesis of the role of gas pore pressure in pyroclastic flows and explain both the fluid like behavior of the flows and the formation of lateral levees

self channelisation and levee formation in monodisperse granular flows dense granular flows can spontaneously self channelise by forming a pair of parallel sided static levees on either side of a central flowing channel this process prevents lateral spreading and maintains the flow thickness and hence mobility enabling the grains to run out considerably further than a spreading flow on shallow slopes since levees commonly form in hazardous geophysical mass flows such as snow avalanches debris flows lahars and pyroclastic flows this has important implications for risk management in mountainous and volcanic regions in this paper an avalanche model that incorporates frictional hysteresis as well as depth averaged viscous terms derived from the rheology is used to quantitatively model self channelisation and levee formation the viscous terms are crucial for determining a smoothly varying steady state velocity profile across the flowing channel which has the important property that it does not exert any shear stresses at the levee channel interfaces for a fixed mass flux the resulting boundary value problem for the velocity profile also uniquely determines the width and height of the channel and the predictions are in very good agreement with existing experimental data for both spherical and angular particles it is also shown that in the absence of viscous second order gradient terms the problem degenerates to produce plug flow in the channel with two frictionless contact discontinuities at the levee channel margins such solutions are not observed in experiments moreover the steady state inviscid problem lacks a thickness or width selection mechanism and consequently there is no unique solution the viscous theory is therefore a significant step forward fully time dependent numerical simulations to the viscous model are able to quantitatively capture the process in which the flow self channelises and show how the levees are initially emplaced behind the flow head both experiments and numerical simulations show that the height and width of the channel are not necessarily fixed by these initial values but respond to changes in the supplied mass flux allowing narrowing and widening of the channel long after the initial front has passed by in addition below a critical mass flux the steady state solutions become unstable and time dependent numerical simulations are able to capture the transition to periodic erosion deposition waves observed in experiments

suitability of simple rheological laws for the numerical simulation of dense pyroclastic flows and long runout volcanic avalanches 1 the rheology of volcanic rock avalanches and dense pyroclastic flows is complex and it is difficult at present to constrain the physics of their processes the problem lies in defining the most suitable parameters for simulating the behavior of these natural flows existing models are often based on the coulomb rheology sometimes with a velocity dependent stress e g voellmy but other laws have also been used here i explore the characteristics of flows and their deposits obtained on simplified topographies by varying source conditions and rheology the coulomb rheology irrespective of whether there is a velocity dependent stress forms cone shaped deposits that do not resemble those of natural long runout events a purely viscous or a purely turbulent flow can achieve realistic velocities and thicknesses but cannot form a deposit on slopes the plastic rheology with e g bingham or without a velocity dependent stress is more suitable for the simulation of dense pyroclastic flows and long runout volcanic avalanches with this rheology numerical flows form by pulses which are often observed during natural flow emplacement the flows exhibit realistic velocities and deposits of realistic thicknesses the plastic rheology is also able to generate the frontal lobes and lateral levees which are commonly observed in the field with the plastic rheology levee formation occurs at the flow front due to a divergence of the driving stresses at the edges once formed the levees then channel the remaining flow mass the results should help future modelers of volcanic flows with their choice of which mechanical law corresponds best to the event they are studying

modeling and analyzing observed transverse sand bars in the surf zone 1 a morphodynamic model has been applied to explain the characteristics of transverse sandbars observed in the inner surf zone of open beaches the model describes the feedback between waves rollers depth averaged currents and bed evolution so that self organized processes can develop the modeled bar characteristics i e wavelength 30 70 m crest orientation up current and the e folding growth time about 12 hr are in good agreement with those of observed transverse bars at noordwijk beach the netherlands but modeled migration speeds tens of meters per day turn out to be a factor 2 larger than those observed the wavelength increases with the distance between the shoreline and the peak of the longshore current and the migration speed is correlated with the maximum longshore current the model also explains why transverse bar formation at noordwijk occurs for obliquely incident waves of intermediate heights realistic positive feedback leading to formation of up current oriented bars like those observed is only obtained if a term related to the turbulence sediment resuspension created by the rollers is included in the transport formula in that case the depth averaged sediment concentration decreases seaward across the inner surf zone enhancing the convergence of sediment transport in the offshore directed flow perturbations that occur over the up current bars this offshore current deflection is mainly caused by frictional torques but the roller radiation stresses also play an important role

new views of granular mass flows concentrated grain fluid mixtures in rock avalanches debris flows and pyroclastic flows do not behave as simple materials with fixed rheologies instead rheology evolves as mixture agitation grain concentration and fluid pressure change during flow initiation transit and deposition throughout a flow however normal forces on planes parallel to the free upper surface approximately balance the weight of the superincumbent mixture and the coulomb friction rule describes bulk intergranular shear stresses on such planes pore fluid pressure can temporarily or locally enhance mixture mobility by reducing coulomb friction and transferring shear stress to the fluid phase initial conditions boundary conditions and grain comminution and sorting can influence pore fluid pressures and cause variations in flow dynamics and deposits

numerical modeling of landquakes the thurwieser landslide that occurred in italy in 2004 and the seismic waves it generated have been simulated and compared to the seismic signal recorded a few tens of kilometers from the landslide source i e landquake the main features of the low frequency seismic signal are reproduced by the simulation topography effects on the flowing mass have a major impact on the generated seismic signal whereas they weakly affect low frequency wave propagation simulation of the seismic signal makes it possible to discriminate between possible alternative scenarios for flow dynamics and to provide first estimates of the rheological parameters during the flow as landquakes are continuously recorded by seismic networks our results provide a new way to collect data on the dynamics and rheology of natural flows

two dimensional tide induced residual sand transport applications to the jiangsu coast china abstract the residual sand d 62 5 m transport rst refers to the tidally averaged rate of horizontal sand transport albeit much smaller than the peak rates it determines the morphological evolution the analytical expression for the tide induced rst has been reported in the condition of one dimensional tidal currents by van de kreeke and robaczewska 1993 here we extended the analytical solution to two dimensional the constituents of the residual m2 and m4 tidal current velocities were used to characterize the collinear tidal current in the orthogonal x and y directions i e cross shore and alongshore respectively while the m2 tidal constituent is dominant in both directions based on the solution rst is controlled by a series of triple interactions of the m2 tidal velocity in the x direction m2 tidal velocity in the y direction and the residual or m4 velocity in the x or y direction the solution was applied to the tide dominated continental shelf of the jiangsu coast china where the alongshore current is much stronger than the cross shore component the results show that the triple interactions of the cross shore m2 tidal velocity um2 the alongshore m2 tidal velocity vm2 and the alongshore residual velocity account for the major parts of both the alongshore and cross shore rst in the nearshore area the rst patterns promote sand accumulation in the shallow nearshore area and generate a narrow and active conduit of coastal alongshore sand transport these findings can be applied in similar marine environments to understand the effects of non linear tidal interactions in rst

constraints on eolian grain flow dynamics through laboratory experiments on sand slopes abstract to illuminate both the dynamics of eolian grain flows and the controls on their geometry we conducted experiments on an inclined platform on which grain flows were initiated by broadcasting sand near the top of the platform in a pattern consistent with wind blown deposition the growing depositional bumps eventually over steepened and failed generating steep headward and laterally migrating scarps mass was fed to the grain flow in this way for approximately 1 4 of the duration of the flow after which the flows were solitary waves spreading both downslope and cross slope the flows abandoned small levees at their widest points and eventually stopped commonly before reaching the base of the platform our grain flows were typically 2 m long by 20 cm wide and slightly less than 1 cm thick the surface velocities at the toe were 15 cm s increased to 20 cm s at the nose and then steadily decreased to 10 cm s towards the tail of the flow the longitudinal velocity gradients created considerable longitudinal strain rates the toe was in compression with mean strain rates of order 0 1 s while the tail was in extension with mean strain rates of order 0 1 s averaged over many seconds the velocities were quite steady over shorter periods however distinct velocity fluctuations dominated the record with variations up to 100 and s andard deviations 10 20 of the mean there were both temporal and spatial correlations in velocity histories of surface tracers we interpret spatial correlations to reflect fixed topographic perturbations at the self defined bottom boundary or ramps and temporal correlations to indicate coherent regions within the flow or rafts ramps were more common than rafts the longitudinal length scales of these features may be up to many times the thickness of the flow and endure up to two seconds based on the average velocity and the magnitude of the velocity response to perturbations at the bed the slightly rate dependent coulomb rheological model proposed by savage and hutter 1991 best describes the general behavior of these flows grain flows stop when the toe either thins below a critical thickness or reaches the toe of the slope the thickness of the nose of a grain flow is controlled by a combination of gradients in longitudinal volume flux and volume losses to the levees at the edge of the flow the nose eventually thins sufficiently to stop the initial spatial distribution of velocities is set by the volume flux history of the evolving scarp within the depositional bump this sets the spatial distribution of strain within the flow which in turn controls the thickness of the nose assuming that the sizes and geometries of depositional bumps are not a function of dune size we expect a minimum flow thickness to occur on dunes whose lee face length equals the natural runout length of a typical grain flow for dunes taller than this grain flow thickness should increase because of coalescence of flow tongues at some mid point on the lee face loading the mid face region with coalescing grain flow tongues that subsequently fail as a single large flow

channeled flow analytic solutions laboratory experiments and applications to lava flows although channeled lava flows are common in basaltic volcanism relationships between channel morphology eruption and emplacement parameters and lava properties are not well understood several models have commonly been used to constrain these relations but they have not been well tested on natural or simulated lava flows over a wide range of parameter space here we test the accuracy and assumptions of a moderately simple analytic rectangular channel solution by comparing the behavior of well controlled laboratory polyethylene glycol peg channeled flows to the analytic solution for isothermal steady newtonian flow in a rectangular channel with constant dimensions this analytic solution agrees well with laboratory measurements volumetric effusion rates q m3 s 1 calculated from the analytical model using measured peg flows as input yield ratios of qcalculated qpumped of 0 2 to 3 6 and flow rates calculated from a best fit surface velocity profile to measured velocities give more accurate ratios of 0 8 to 1 2 we find a very weak dependence of solution accuracy on slope attributable to flow front effects within the laboratory flows we subsequently apply the solution to several subaerial and submarine terrestrial flows as well as extraterrestrial channeled flows over a wide range of flow parameters viscosity ranges and flow rates obtained using measured channel dimensions and assumed lava properties are plausible interestingly the resulting extraterrestrial estimates of viscosities and flow rates tend to fall closer to known terrestrial measurements and estimates of channel flow than to previous planetary estimates we therefore suggest that the analytic newtonian rectangular channel flow model is a more appropriate physical model for many channeled terrestrial and planetary flows than the newtonian infinite sheet flow and approximation to bingham channel flow widely used previously

interpreting rockfall activity on an outcrop talus slope system in the southern japanese alps using an integrated survey approach abstract understanding relationships between meteorological conditions and rockfall activity is important for the management of rockfall risks as well as for the estimation of future rockfall activity under climate change seasonal activity of rockfall on talus slopes depends on the actual triggers of rockfall which in turn may vary as well between outcrops because of different rockfall sources and the influence of topography in this study we interpret spatial and temporal variations in rockfall activity and related sediment transfer processes in an outcrop talus slope system in central japan through monitoring using rock temperature and moisture sensors sediment traps and time lapse cameras in addition tree ring analysis has been added to understand possible changes of rockfall activity over longer time periods results suggest that the frequency of grouped gravel transport i e soil creep was higher than that of individual transport i e rockfall and dry ravel on the talus slope whereas rockfall likely is the predominant process from the outcrops observations from sediment traps showed that coarse gravel is characterized by higher bounce heights and that it travelled longer distances than fine gravel rockfall from the outcrops was most active during dormancy of trees which locally lasts from autumn to early spring and can be related to freeze thaw cycles in contrast rockfall and other sediment transfer processes were monitored on the talus slope all year round secondary movement of gravels on the talus slope such as soil creep during rainfall events likely triggers rockfall during times when the outcrops are not producing rockfall i e from late spring to summer consequently our results suggest that the spatio temporal rockfall activity varies substantially between outcrops and talus slopes and that differences in process behavior should be taken into account in future disaster mitigation measures

shedding dynamics and mass exchange by dry granular waves flowing over erodible beds abstract a continuous exchange of particles between an erodible substrate and the granular flow above it occurs during almost all geophysical events involving granular material such as snow avalanches debris flows and pyroclastic flows the balance between eroded and deposited material can drastically influence the runout distance and duration of the flow in certain conditions a perfect balance between erosion and deposition may occur leading to the steady propagation of material in which the flow maintains its shape and velocity throughout it is shown experimentally how the erosion deposition process in dense flows of sand 160 200 m on an erodible bed of the same material produces steadily propagating avalanches that deposit subtle levees at their lateral extent moreover it is shown in this paper by using two colours of the same sand that although the avalanche is propagating at constant velocity and maintaining a constant shape the grains that are initially released are deposited along the flow path and that the avalanche will eventually be composed entirely of particles that are eroded from the bed different steady travelling wave regimes are obtained depending on the slope angle thickness of the erodible layer and the amount of material released outside of the range of parameters where steady travelling waves form the avalanches loose mass and decay if the initial amount of material released is too small or if the initial release is too large they re adjust to a steadily propagating regime by shedding material and breaking into smaller avalanches at its rear side numerical simulations are performed using a shallow water like avalanche model together with a friction law that captures the erosion deposition process in flowing to static regimes and a transport equation for the interface between layers of the two colours the characteristic behaviours observed in the experiments are qualitatively reproduced specifically the complex processes such as the exchange of particles leading to a change in colour of the avalanche and the formation of lateral levees are captured by the model finally a comparison is made with deposits in lunar craters which are interpreted as closely analogous to the deposits formed in our laboratory experiments

nearshore oblique sand bars 1 the coupling between hydrodynamics and the evolving topography in the surf zone has been theoretically examined for oblique wave incidence it is shown that positive feedback can lead to the initial growth of several types of rhythmic systems of sand bars the bars can be down current oriented or up current oriented which means that the offshore end of the bar is shifted down current or up current with respect to the shore attachment in the limit of strong current compared to wave orbital motion very oblique down current oriented b ars are obtained with a spacing of several times the surf zone width when wave orbital motions are dominant systems of up current oriented bars and crescentic down current oriented bars appear with spacings of the order of the surf zone width the latter feature consists of alternating shoals and troughs at both sides of the break line with the inner shoals being bar shaped and oblique to the coast the growth e folding time of the bars ranges from a few hours to a few days and it is favored by constant wave conditions the range of model parameters leading to growth corresponds to intermediate beach states in between the fully dissipative and the fully reflective situations preliminary comparison with field observations shows qualitative agreement

sand waves along the dutch coast sand waves defined as longshore wave like movements of the shoreline measured in a horizontal plane are described along several stretches of the shoreline of the netherlands they have a celerity in the order of 50 200 m yr a period of 50 150 years and an amplitude of 30 500 m they are found along the whole dutch shoreline analysis of sand waves shows that the assumed effect of groins might be very small along this shoreline there are indications that groins did not have any long term effect on coastal regression

experimental observations of water like behavior of initially fluidized dam break granular flows and their relevance for the propagation of ash rich pyroclastic flows the physics of ash rich pyroclastic flows were investigated through laboratory dam break experiments using both granular material and water flows of glass beads of 60 90 m in diameter generated from the release of initially fluidized slightly expanded 2 5 4 5 columns behave as their inertial water counterparts for most of their emplacement for a range of initial column height to length ratios of 0 5 3 both types of flows propagate in three stages controlled by the time scale of column free fall h0 g 1 2 where h0 denotes column height and g denotes gravitational acceleration flows first accelerate as the column collapses transition to a second constant velocity phase occurs at a time t h0 g 1 2 1 5 the flow velocity is then u equation image gh0 1 2 larger than that for dry initially nonfluidized granular flows transition to a last third phase occurs at t h0 g 1 2 4 granular flow behavior then departs from that of water flows as the former steadily decelerates and the front position varies as t1 3 as in dry flows motion ceases at t h0 g 1 2 6 5 with normalized runout x h0 5 5 6 the equivalent behavior of water and highly concentrated granular flows up to the end of the second phase indicates a similar overall bulk resistance although mechanisms of energy dissipation in both cases would be different interstitial air particle viscous interactions can be dominant and generate pore fluid pressure sufficient to confer a fluid inertial behavior to the dense granular flows before they enter a granular frictional regime at late stages efficient gas particle interactions in dense ash rich pyroclastic flows may promote a water like behavior during most of their propagation

dynamics of pyroclastic density currents conditions that promote substrate erosion and self channelization mount st helens washington usa abstract the may 18th 1980 eruption of mount st helens msh produced multiple pyroclastic density currents pdcs burying the area north of the volcano under 10s of meters of deposits detailed measurements of recently exposed strata from these pdcs provide substantial insight into the dynamics of concentrated currents including inferences on particle particle interactions current mobility due to sedimentation fluidization and internal pore pressure particle support mechanisms the influence of surface roughness and the conditions that promote substrate erosion and self channelization four primary flow units are identified along the extensive drainage system north of the volcano each flow unit has intricate vertical and lateral facies changes and complex cross cutting relationships away from source each flow unit is an accumulation from an unsteady but locally sustained pdc or an amalgamation of several pdc pulses the pdcs associated with units i and ii likely occurred during the pre climactic waxing phase of the eruption these currents flowed around and filled in the hummocky topography leaving the massive to diffusely stratified deposits of units i and ii the deposits of both units i and ii are generally more massive in low lying areas and more stratified in areas of high surface roughness suggesting that surface roughness enhanced basal shear stress within the flow boundary units iii and iv are associated with the climactic phase of the eruption which produced the most voluminous and wide spread pdcs both flow units are characteristically massive and enriched in vent derived lithic blocks these currents flowed over and around the debris avalanche deposits as evidenced by the erosion of blocks from the hummocks unit iii is massive poorly sorted and shows little to no evidence of elutriation or segregation of lithics and pumice suggesting a highly concentrated current where size density segregation was suppressed unit iv shows similar depositional features but typically has a basal lithic rich region is variably fines depleted and contains pumice lobes suggesting density segregation in a less concentrated current relative to unit iii deep erosive channels cut by the unit iii current and thick lithic levee deposits within unit iv occur in an area where debris avalanche relief is limited suggesting self channelization developed as a function of internal flow dynamics an increase in the proportion and size of lithic blocks is found 1 downstream of debris avalanche hummocks suggesting the pdcs were energetic enough to locally entrain accidental lithics from the hummocks and transport them tens of meters downstream and 2 within large channels cut by later pdcs into earlier pdc deposits suggesting self channelization of the flows increased the carrying capacity of the subsequent channelized currents finally the combination of thick massive deposits with a high percentage of fine ash within unit iii and in the medial distal depositional regions of units ii iv suggests that the pdcs developed and maintained a high internal pore pressure during transport and deposition the most important results include our ability to understand the role of internal pore pressure on current mobility the influence of self channelization on carrying capacity of the currents and the influence of surface roughness on substrate erosion these observations have critical consequences for understanding the flow dynamics and hazard potential of pdcs

formation of levees and en echelon shear planes during snow avalanche run out snow avalanches often form levees and en echelon shear planes in the run out zone we describe the formation of these depositional structures using a simple model that accounts for the role of granular fluctuations in avalanche motion a mathematical feature of this model is the existence of a bifurcation saddle point describing how granular fluctuations control the avalanche velocity in the run out zone the saddle point discriminates between a flowing and stopping regime and defines the physical boundary between the flow and non flow regions of the avalanche i e the location of shear planes in the avalanche deposits the formation of a shear plane depends on the interplay between terrain slope and avalanche mass flux which varies from avalanche head to tail levees can form immediately at the avalanche front or for steep slopes and low mass fluxes at the avalanche tail at ravine and gully shoulders the mass flux is restricted thus initiating levee formation we find that the levee lines are parallel to the flow direction when the mass flux is constant en echelon shear lines occur when the mass flux is decreasing we test the model using several case studies where we have accurate laser scans of avalanche deposits our results suggest that avalanche flow parameters can be determined from simple levee measurements or conversely formation of levees and flow fingers can be predicted once the parameters governing the granular fluctuations are known

a mechanism for the formation and maintenance of shore oblique sand ridges on storm dominated shelves a remarkable set of shore oblique sand ridges occupies the inner portion of the storm dominated middle atlantic and south atlantic bights off the east coast of the united states of america a mechanism for present day formation and growth of these distinctive geological features follows from a linearized analysis of the stability of alongshore periodic topographical perturbations based on a depth averaged fluid dynamical model with a simple representation of sediment transport the analysis indicates exponential growth of shore oblique features as a result of offshore deflection of storm driven alongshore flows at ridge crests which leads to a convergence of sediment flux because the effective carrying capacity decreases with increasing distance offshore the analysis indicates a set of conditions required for ridge growth model solutions for topography under conditions favorable for ridge growth are strikingly similar to the observed sand ridges

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

a new depth averaged model for flow like landslides over complex terrains with curvatures and steep slopes abstract flow like landslides are one of the most catastrophic types of natural hazards due to their high velocity and long travel distance they travel like fluid after initiation and mainly fall into the flow movement type in the updated varnes classification hungr et al 2014 in recent years depth averaged models have been widely reported to predict the velocity and run out distance of flow like landslides however most of the existing depth averaged models present different shortcomings for application to real world simulations this paper presents a novel depth averaged model featured with a set of new governing equations derived in a mathematically rigorous way based on the shallow flow assumption and mohr coulomb rheology particularly the new mathematical formulation takes into account the effects of vertical acceleration and curvature effects caused by complex terrain topographies the model is derived on a global cartesian coordinate system so that it is easy to apply in real world applications a godunov type finite volume method is implemented to numerically solve these new governing equations together with a novel scheme proposed to discretise the friction source terms the hydrostatic reconstruction approach is implemented and improved in the context of the new governing equations providing well balanced and non negative numerical solutions for mass flows over complex domain topographies the model is validated against several test cases including a field scale flow like landslide satisfactory results are obtained demonstrating the model s improved simulation capability and potential for wider applications

numerical modeling of the mount steller landslide flow history and of the generated long period seismic waves the rock ice avalanche that occurred in 2005 on mount steller alaska and the resulting long period seismic waves have been simulated for different avalanche scenarios i e flow histories with and without erosion processes taken into account this 40 60 mm3 avalanche traveled about 10 km down the slope mainly on top of a glacier eroding a significant amount of ice it was recorded by 7 broadband seismic stations the simulations were compared with the recorded long period seismic signal and with the inverted flow history the results show that when erosion processes are taken into account the simulations reproduce the observed signal at all the stations over a wide range of azimuths and source station distances 37 623 km this comparison makes it possible to constrain the rheological parameters involved which should help constrain the volume of eroded material because landslides are continuously recorded by seismic networks this method could significantly broaden quantitative insights into natural flow dynamics

debris flows over sand dunes on mars evidence for liquid water 1 this study focuses on the formation and physical properties of the gullies observed over large martian dunes especially those of the russell crater 54 s 347 w geomorphic features like sinuosities and connections of the channels show that gullies over dunes involve flows with a significant proportion of liquid the occurrence of levees implies that these flows are debris flows with a yield strength characteristics of bingham plastic materials we apply terrestrial methods to estimate viscosity and velocity of these flows from levee size and sinuosities we obtain average velocities in the range of 1 to 7 m s 1 and apparent viscosities of 2 8 to 46 000 pa s with an average at 740 pa s compared with the 0 001 pa s of pure water these viscosities and velocities are in the range of terrestrial debris flows with a proportion of 10 to 40 of h2o these properties are typical of water holding debris flows but not of pure water surface runoff or co2 driven flows the debris flows over dunes are oriented on south facing slopes like other recent gullies meltwater from ground ice formed during a recent period of high obliquity is the more likely explanation for the formation of such flows over dunes

modeling of the steady state temperature field in lava flow levees the rationale of lava flow deviation is to prevent major damage and among the possible techniques the opening of the flow levees has often been demonstrated to be suitable and reliable the best way to open the levees in the right point in order to obtain the required effect is to produce an explosion in situ and it is then necessary to map with the highest precision the temperature field inside the levees in order to design a safe and successful intervention the levees are formed by lava flows due to their non newtonian rheology where the shear stress is lower than the yield stress the levees then cool and solidify due to heat loss into the atmosphere in this work we present analytical solutions of the steady state heat conduction problem in a levee using the method of conformal mapping for simple geometrical shapes of the levee cross section triangular or square numerical solutions are obtained with a finite element code for more complex realistic geometries

fine grained linings of leveed channels facilitate runout of granular flows abstract catastrophic dense granular flows such as occur in rock avalanches debris flows and pyroclastic flows move as fully shearing mixtures that have approximately 60 vol solids and tend to segregate to form coarse grained fronts and leveed channels levees restrict spreading of unconfined flows and form as coarse particles that become concentrated in the top of the flow are transported to the front and then advect to the sides in the flow head channels from which most material has drained away down slope are commonly lined with fine grained deposit widely thought to remain from the tail of the waning flow we show how segregation in experimental dense flows of carborundum or sand 300 425 m mixed with spherical fine ballotini 150 250 m on rough slopes of 27 29 produces fine grained channel linings that are deposited with the levees into which they grade laterally maximum runout distance is attained with mixtures containing 30 40 sand just sufficient to segregate and form levees that are adequately robust to restrict the spreading attributable to the low friction fines resin impregnation and serial sectioning of deliberately arrested experimental flows shows how fines lined levees form from the flow head the flows create their own stable conduit entirely from the front which in a geophysical context can play an important mechanistic role in facilitating runout the flow self organization ensures that low friction fines at the base of the segregated channel flow shear over fine grained substrate in the channel thus reducing frictional energy losses we propose that in pyroclastic flows and debris flows which have considerable mobility attributable to pore fluid pressures such fine grained flow contact zones form similarly and not only reduce frictional energy losses but also reduce flow substrate permeability so as to enhance pore fluid pressure retention thus the granular flow self organization that produces fine grained channel linings can be an important factor in facilitating long runout of catastrophic geophysical flows on the low slopes few degrees of depositional fans and aprons around mountains and volcanoes

influence of the scar geometry on landslide dynamics and deposits application to martian landslides received 24 january 2011 revised 23 june 2011 accepted 30 june 2011 published 4 october 2011 1 landslides dynamics prediction remains difficult in spite of a considerable number of studies the runout distance is widely used in analysis of landslide dynamics and in the calibration of the rheological parameters involved in numerical modeling however the unknown impact of the significant uncertainty in the shape of the initial released mass on the runoutdistanceandontheoverallshapeofthedepositraisesquestionsabouttherelevanceof these approaches the impact of the initial scar geometry on flow and distribution of the deposits is studied here using satellite data and numerical modeling of theoretical landslides and martian landslides informed by geomorphological analysis by varying the initial scar geometry from spoon shaped to steep wall geometry our results show that the runout distance is a very robust parameter that is only slightly affected by the change in the geometry of the initial scar on the contrary the lateral extent of the deposit is shown to be controlled by the scar geometry providing unique insights into the initial landsliding conditionsonmarsandmakesitpossibletoaccuratelyrecoverthevolumeinitiallyinvolved an essential ingredient for volume balance calculation a feedback analysis of valles marineris landslides can be drawn showing good agreement between numerical results and geomorphological analysis the geometry of the initial scar inferred from numerical modeling is strongly correlated with the regional tectonic history in valles marineris area

the controls and consequences of substrate entrainment by pyroclastic density currents at mount st helens washington usa evidence in the deposits from the may 18 1980 eruption at mount st helens demonstrates that pyroclastic density currents pdcs produced during the afternoon of the eruption became intermittently erosive using detailed componentry and granulometry we constrain the sources for lithic blocks in the deposits and identify deposits from pdcs that became locally erosive the componentry of the lithics in the fall deposits is used as a proxy for vent erosion and assumed to represent the starting componentry for pdcs prior to entrainment from any other source we find little evidence in the pdc deposits nearest to the base of the volcano for entrainment from the steep flanks however significant evidence indicates that pdcs eroded into the debris avalanche hummocks suggesting that entrainment is favored as pdcs interact with highly irregular topography evidence for locally entrained material downstream from debris avalanche hummocks decreases with height in the outcrop suggesting that less entrainment occurs as local relief decreases and upstream topography is buried the prevalence of lithofacies containing locally entrained material at the base of unit contacts and only 10s of meters downstream from debris avalanche hummocks suggests that the majority of entrainment occurs at or near the head of the current occasionally entrained material is located high above unit contacts and deposited well after the initial head of the current is inferred to have passed indicating that entrainment can occur during periods of non deposition either from the semi sustained body of the current or from a pulsating current additionally self channelization of pdcs either by levee deposition or scouring into earlier pdc deposits occurs independently of interaction with topographic obstacles and can affect carrying capacity and runout distance while we begin to explore the mechanisms and effects of erosion on current dynamics additional laboratory and numerical studies are necessary to fully understand these processes

a sph depth integrated model for popocatepetl 2001 lahar mexico sensitivity analysis and runout simulation abstract lahars are debris flows of volcanic origin which can endanger or even destroy communities located near the flanks of volcanoes lahars are not always triggered by eruptions they can form during heavy rainfall or after hydrothermal alteration and volcanic edifice collapse decision makers need lahar hazard maps to devise hazard prevention measures that will prevent casualties so lahar modelling is an important tool for assessing flow behavior and determining inundation areas the depth integrated numerical model used in this study is derived from the velocity pressure of the biot zienkiewicz model and was discretized using the smoothed particle hydrodynamics sph method to simulate a lahar that occurred at popocatepetl volcano in 2001 in order to investigate the convergence of the model we used a range of different sph mesh resolutions once the optimum mesh resolution was bounded we analyzed the model s sensitivity to the initial lahar volume the density of the geomaterial and the rheological parameter of the bingham fluid the results show that the sph depth integrated model produced a highly accurate simulation of the distribution and velocity of the 2001 lahar the study also shows the effects of sph mesh resolution and the relevant influence of rheological parameters

simulation of tsaoling landslide taiwan based on saint venant equations over general topography the 1999 chi chi earthquake triggered the catastrophic tsaoling landslide in taiwan the geomorphological change measured from the data of the 1989 and 2000 aerial photos reveals that the scar and deposit volumes are about 0 126 km3 and 0 15 km3 respectively the debris material ran over a distance of 1 6 km with 500 m descent in elevation in this paper we use the continuum model of hydraulic flow shaltop2d based on the equations of bouchut and westdickenberg to simulate numerically the landslide dynamics when the mass is moving the flow is assumed hydrostatic with a basal coulomb friction the best fit is obtained using the basal friction angle equal to 6 the only parameter of the simulation uniformly applied in the calculation domain the landslide front reaches the chinshui river valley the foothill of the slope within only about 25 s after initiation and the motion settles in about 113 s the maximum speed is estimated 75 m s the spreading of the deposit agrees well with the field measurement

field observations of pristine block and ash flow deposits emplaced april 16 17 1991 at volcan de colima mexico abstract for the first time since the effusive activity of 1981 1982 volcan de colima extruded scoriaceous andesitic lava on march 1 1991 this followed a period of increasing seismicity summit dome deformation and fumarolic activity that began in february of 1991 growth of the new lava dome proceeded until april 16 at 16 00 hrs local time gmt 6 hours when a series of gravitational failures of the upper edifice and the new lava dome flow triggered the emplacement of successive small volume non glowing block and ash flows to a distance of 4 km within the upper reaches of barranca el cordoban south southwest of the present summit aerial photos taken at the time of the event clearly show the lack of explosions at the summit dome efficient elutriation of the finest silt and clay sized fraction from the main body of the avalanching material produced large reddish yellowish and grayish ash clouds which rose to an altitude of 1 5 2 5 km for several hours and were carried southeast to northeast by predominant winds vegetation in the path of the debris was totally stripped sand blasted and bent in the sense of flowage but was not burnt no fatalities were reported we present a summary of our field observations of the pristine deposits which we studied prior the rainy season on april 20 27 between 2 200 and 2 500 m elevation

morphodynamic instabilities of planar beaches sensitivity to parameter values and process formulations the initial growth of bed perturbations on planar sloping beaches under the forcing of obliquely incident breaking waves is investigated using a state of the art numerical model this allows for a systematic investigation of the sensitivity of the spatial structures of the bed perturbations and their growth and migration rates to different model formulations and parameterizations if the sediment is only transported in the direction of the net current velocity and sediment stirring is taken proportional to the wave height squared growing up current oriented crescentic bars are found with a preferred spacing of 800 m and a down current migration rate of 10 m d 1 varying the angle of wave incidence drag coefficient and bed slope results in qualitatively similar growing bed forms using an engelund and hansen transport formula very oblique down current oriented bars are obtained that grow in time no preferred wavelength however is found using the bailard transport formula results in growing up current oriented bars with a preferred spacing smaller than 300 m for wave angles smaller than 7 when using either the engelund and hansen or bailard sediment transport formulation it is essential to take the transport in the direction of the wave orbital velocity into account in order to have growing bed perturbations

characteristics and dynamics of surfzone transverse finger bars 1 patches of transverse finger bars have been identified in the surf zone of noordwijk beach netherlands they consisted of three to nine elongated accumulations of sand attached to the low tide shoreline the bars extended up to 50 m into the inner surf zone had an oblique orientation with respect to the shore normal and were quasiregularly spaced in the alongshore direction we analyzed nearly 6 years of video data and observed a significant presence of finger bars 14 of the time with good data bars were visible on 193 days gathered in 44 events that persisted from 2 days to 2 months obliquely incident waves of intermediate and approximately constant height were dominant during finger bar presence shore normal incident or more energetic wave fields destroyed the bar patches the underlying bathymetry affected finger bar formation inner surfzone troughs with cross shore areas of 100 m2 and inner surfzone slopes of 0 02 were more conducive to their growth the mean alongshore wavelength of the finger bar patches was 39 m ranging from 21 to 75 m bar crests deviated up to 40 degrees from the shore normal against the alongshore current direction up current orientation and bar patches migrated at rates up to 22 m day in the direction of the alongshore current we used these observations to test existing theoretical self organization mechanisms for transverse bar formation the bed flow mechanism was the most viable explanation for the generation and persistence of noordwijk finger bars our observations were consistent with most of the predictions of two models that included this interaction but migration rates differed by 1 order of magnitude

evaluating titan2d mass flow model using the 1963 little tahoma peak avalanches mount rainier washington the titan2d geophysical mass flow model is evaluated by comparing its simulation results and those obtained from another flow model flow3d with published data on the 1963 little tahoma peak avalanches on mount rainier washington the avalanches totaling approximately 10 10 6 m 3 of broken lava blocks and other debris traveled 6 8 km horizontally and fell 1 8 km vertically h l 0 246 velocities calculated from runup range from 24 to 42 m s and may have been as high as 130 m s while the avalanches passed over emmons glacier titan2d is a code for an incompressible coulomb continuum it is a depth averaged dshallow watert granular flow model the conservation equations for mass and momentum are solved with a coulomb type friction term at the basal interface the governing equations are solved on multiple processors using a parallel adaptive mesh godunov scheme adaptive gridding dynamically concentrates computing power in regions of special interest mesh refinement and coarsening key on the perimeter of the moving avalanche the model flow initiates as a pile defined as an ellipsoid by a height z and an elliptical base defined by radii in the x and y planes flow parameters are the internal friction angle and bed friction angle results from the model are similar in terms of velocity history lateral spreading location of runup areas and final distribution of the little tahoma peak deposit the avalanches passed over the emmons glacier along their upper flow paths but lower in the valley they traversed stream gravels and glacial outwash deposits this presents difficulty in assigning an appropriate bed friction angle for the entire deposit incorporation of variable bed friction angles into the model using gis will help to resolve this issue d 2004 elsevier b v all rights reserved

the emplacement dynamics of pumice lobes ascertained from morphology and granulometry examples from the 1993 deposits at lascar volcano chile abstract the work presented here focuses on lobe shapes and clast populations within lobate termini of the 1993 pumice flow deposits at lascar volcano chile a new method to analyze a coarse tail grain size population with field photographs is presented using this method 33 000 0 5 cm clasts from the pumice lobes of the 1993 pumice flow deposits were measured at 36 sites and the resultant grain size distributions were then related to lobe morphology lobe margins i e levees clefts and snouts were found to contain significantly larger pumice clasts and be more poorly sorted than lobe central channels i e locations away from the margins previous laboratory experiments suggest lobe margins form by the floatation and deflection of larger clasts to the margins of an advancing flow lobe results here indicate that the same sorting process efficiently segregates clasts into two flow regimes 1 a mobile central channel depleted in coarse clasts and 2 friction dominated margins enriched in clasts 15 cm the lobe margins 60 enriched in larger particles with matrix

introduction to special section on marine sand wave and river dune dynamics marine sand waves and river dunes are rhythmic patterns formed at the interface between a sandy bed and turbulent flows driven by tidal and river currents their origin development and dynamics are far from being fully understood to enhance the discussion on this topic we organized the international conference marine sand wave and river dune dynamics marid in april 2004 in enschede netherlands scientific papers that originated from the marid conference are presented in this special section this introduction places these papers in the context of recent progress

influence of slope angle on pore pressure generation and kinematics of pyroclastic flows insights from laboratory experiments the influence of slope angle on pore pressure generation and kinematics of fines rich pyroclastic flows was investigated through laboratory experiments granular flows were generated by the release of a column of fine glass beads d 0 08 mm in an inclined channel 0 30 the granular column could be fluidized while the channel base was either smooth or made rough by glued beads of 3 mm diameter pore pressure measurements reveal that the degree of autofluidization caused by air escaping from the substrate interstices into which flow particles settled was high at all slope angles flow runout increase due to autofluidization however was reduced at slope angle higher than 12 because of the occurrence of a strong deceleration phase that limited the flow duration this is probably caused by the combination of flow head thinning at increased slope angle and settling of particles into the substrate interstices until the flow ran out of mass analysis of high speed videos suggests that ingestion of ambient air at the flow front did not occur even on steep slopes of 30 experiments at inclinations close to 25 or slightly higher 30 than the repose angle of the granular material 28 5 revealed the formation of a thin basal deposit that was then eroded as the flow thickness and velocity gradually decreased our study suggests that air escape from substrate interstices in nature can be a significant external cause of pore pressure generation that favors low energy dissipation and long runout distances of pyroclastic flows on moderate topographies

bars bumps and holes models for the generation of complex beach topography in shallow water any two waves of the same frequency are shown to produce complex patterns of drift velocity above the sea bed if the longshore components hi h of the wave numbers of the two waves are different these steady flow patterns exhibit a longshore periodicity of wave number hi h irrespective of whether the waves propagate in the same direction say hi he positive or in opposite directions he negative the interaction of two edge wave modes is examined in detail the drift velocities are calculated and a simple sediment transport model is used to predict the beach topography that would be in equilibrium with these flow patterns as expected crescentic sand bars are produced by the special case of standing edge waves hi h intriguingly for all other cases a combination of complex transverse bars plus meandering or straight offshore bars result patterns that are surprisingly reminiscent of many published descriptions of complex rhythmic topography the extension of the model to three or more waves produces topography that appears to be very irregular although the pattern should repeat over sufficiently long distances along the beach even with only three waves these distances may be very large compared to the scale of the bars