flow behaviour and runout modelling of a complex debris flow in a clay shale basin identification of debris flow hazard areas necessitates the knowledge of the flow thickness and the runout distance both have been investigated using a numerical runout model on the faucon stream south french alps representative of clay shale basins results of various rheological tests and numerical experiments are presented and discussed the calibration of the model was undertaken using the results of both geomorphological surveys and sedimentological analyses rheological tests using either a parallel plate rheometer a coaxial rheometer slump tests and an inclined plane were carried out on several samples results have shown that the flow behaviour could be described by an herschel bulkley constitutive equation the rheological responses of several natural suspensions collected from surficial deposits sandstones moraines weathered black marls were also investigated in order to model the runout of the flow the model bing was used the model describes well the influence of each type of sediment on the behaviour runout distance deposit thickness of the flow although the velocities were significantly overestimated different risk scenarios are tested and discussed copyright 2005 john wiley sons ltd

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

the influence of slope angle ratio on the dynamics of granular flows insights from laboratory experiments laboratory experiments on granular flows using natural material were carried out in order to investigate the behaviour of granular flows passing over a break in slope sensors in the depositional area recorded the flow kinematics while video footage permitted reconstruction of the deposit formation which allowed investigation of the deposit shape as a function of the change in slope we defined the slope angle ratio as the proportion between slope angle in the depositional area and that of the channel when the granular flow encounters the break in slope part of the flow front forms a bouncing clast zone due to elastic impact with the expansion box floor during this process part of the kinetic energy of the dense granular flow is transferred to elutriating fine ash which subsequently forms turbulent ash cloud accompanying the granular flow until it comes to rest morphometric analysis of the deposits shows that they are all elliptical with an almost constant minor axis and a variable major axis the almost constant value of the minor axis relates to the spreading angle of flow at the end of the channel which resembles the basal friction angle of the material the variation of the major axis is interpreted to relate to the effect of competing inertial and frictional forces this effect also reflects the partitioning of centripetal and tangential velocities which changes as the flow passes over the break in slope after normalization morphometric data provided empirical relationships that highlight the dependence of runout from the product of slope angle ratio and the difference in height between granular material release and deposit the empirical relationships were tested against the runouts of hot avalanches formed during the 1944 ad eruption at vesuvius with differences among actual and calculated values are between 1 7 and 15 velocity measurements of laboratory granular flows record deceleration paths at different breaks in slope when normalized the velocity data show third order polynomial fit highlighting a complex behaviour involving interplay between inertial and frictional forces the theoretical velocity decays were tested against the data published for volcaniclastic debris flows of the 5 6 may 1998 event in the sarno area the comparison is very good for non channelized debris flows with significant differences between actual and calculated velocities for the channelized debris flows

a method for the calculation of the impact parameters of dilute pyroclastic density currents based on deposit particle characteristics 1 a new method for the reconstruction of the physical characteristics of dilute pyroclastic density currents is introduced the velocity density and particle volumetric concentration profiles of the stratified current are calculated together with the profile of dynamic pressure which is a useful parameter for checking resistance of buildings the model links turbulent boundary layer shear flow theory with particle coupling to gas turbulence the working procedure starts with the recognition in the field of the fining upward sequence of layers formed during the time integrated depositional history of an individual current distinct processes of particle transportation and deposition are associated with the different particle modes composing the bedset the system of equations for the solution of the fluid dynamic parameters is implemented in two alternative ways the first one uses data of particles coming from both the basal coarse layer and the overlying laminated layer of the bedset the second uses features of two distinct components of the laminated layer a statistical test is performed for checking model results against experimental data of actual particles model calculations give the average solution as well as solutions corresponding to a range of 68 of probability around the average value the maximum solution can be considered as a safety value for impact parameters the methodology is applied to deposits of recent eruptions of vesuvius and campi flegrei in italy and results are discussed in terms of hazard and expected damage

sorting in grain flows at the lee side of dunes abstract sediment sorting at the lee side of ripples dunes and bars has already been recognized long ago a predictive model of the sorting is necessary but unavailable for implementation in sediment transport models for sediment mixtures relevant processes in sedimentological and physical literature are reviewed and compared to the sparse data of sediment sorting a synthesis is given of the most important variables governing the sorting processes for the benefit of future experimentation and modelling these variables are the sorting standard deviation skewness and bimodality of the sediment mixture delivered to the brink point the height of the dune or bar relative to the average grain size of the mixture the velocity of the flow above the brink point relative to the settling velocity for all grain size fractions and the frequency of the grain flows in addition the initiation mechanism and frequency of the grain flows affect the pattern and effectiveness of sorting

sequential plug formation disintegration by vulcanian explosions and the generation of granular pyroclastic density currents at tungurahua volcano 2013 2014 ecuador following 84 years of repose tungurahua volcano ecuador initiated its present eruptive episode in october 1999 but its pdc activity only began in july 2006 a period of highly energetic vulcanian eruptions started in 2012 those of 14 july 2013 18 october 2013 and 1 february 2014 being the most important these eruptions were well monitored by a 5 station broadband seismic and acoustic array repeated repose intervals of 3 5 months between vulcanian events vei 2 suggest that gases in the ascending juvenile magma experienced sequential pressurization cycles as magma of preceding eruptive events solidified to form plugs that sealed the conduit every 34 months plug failure occurred abrupt decompression followed and the resulting vulcanian explosions are associated with the highest seismic and acoustic energies ever registered anywhere small to moderate sized pdc flows associated with the explosions and fountain collapses were generated and traveled 7 km down the steep n nw and w flanks of tungurahua s cone at velocities of 11 to 18 m s although a small lateral blast and its pdc were clocked at 33 m s descending the n flank the explosive fragmentation of the plugs a dense microcrystalline andesite and the juvenile magma a vesiculated glassy andesite comprise the principal rock fragments of the pdc deposits each deposit typically consisting of two layers a thin upper layer of large segregated and abraded clasts with few fines and a thicker lower layer that is fines rich with few large clasts many deposits were studied and photographed within a few days of their formation which are presented

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

high velocity ring shear tests on sand ring shear tests on sand materials have been carried out to show whether there is a change in the behaviour of these materials at high shearing rates and normal stresses this question is relevant to the problem of the mobility of large rock avalanches sturzstroms but is also of more general academic interest a ring shear apparatus of unusual although simple design has been constructed capable of achieving circumferential velocities of 2 m s at normal stresses of up to 200 kpa tests were carried out on two types of coarse sand wet or dry sand rock flour mixtures and polystyrene beads perfect frictional behaviour was observed in all the tests uninfluenced by either velocity or normal stress over the entire range of these variables change in frictional behaviour due to high rate of shearing therefore cannot be used to explain the high observed mobility of sturzstroms des essais de cisaillement circulaire par torsion ont ete effectes afin de decouvrir si un changement ait lieu dans le comportem

significance of coarse clasts in viscous debris flows abstract debris flows are flowing mixture of water and sediments from clay to boulder sized particles the sediments control both occurrence and characteristics of debris flows however the relevant literature has concentrated mainly on fine debris considering their large fractions in debris flows the significance of coarse clasts 0 005 mm is investigated by comparing the crude debris cd the fractions of aggregation of data collected in 39 tested debris water mixtures leads us to conclude that the coarse clasts can greatly affect the slurrying susceptibility of debris masses and bulk behavior of slurries the debris flow indices id from the cd to rd slurries with maximum grain sizes of 10 and 5 mm decrease by 29 and 17 respectively the cd slurries possess higher yield strength and viscosity than their rd counterparts with the same solid volumetric concentrations cvs the areas inundated by 10 cd slurries with maximum grain sizes of 10 and 5 mm are approximately 17 39 of those of their rd counterparts the excess pore pressures in the rd slurries dissipate more quickly than those in the cd slurries the shape and surface texture of coarse clasts regulate slurrying of debris masses as well as influence their liquefaction potential which in turn has an impact on the mobility and persistence of subsequent slurries the platy flaky debris producing mountain catchments generally experience lower magnitude higher frequency lower cv debris flows of relatively less destructive power and the debris flows dominated by equidimensional clasts are often more powerful and hazardous despite their potentially lower frequency

unravelling the multiphase run out conditions of a slide flow mass movement abstract in this paper an attempt is made to unravel the run out characteristics of a mass movement in the sichuan province sw china by means of 1d numerical modelling and calibration on the topography of run out profiles the dagou mass movement started as a rockslide with an initial volume of 480 000 m3 which transformed into a debris flow increasing in volume due to entrainment of loose material in the upper part of the travelling track the rapid mass movement had a run out distance of 1380 m and a run out time of about 50 s numerical calculations were conducted with the depth average shallow water equation to explain the variation in thickness of the debris flow deposits along the run out track for the calibration of the first run out phase three rheological models were applied namely the bingham voellmy and quadratic rheology calibration was done on 1 the run out distance 2 the run out time and 3 the goodness of fit with the thickness of the deposits along the track in addition the erosion constant in the entrainment equation was calibrated on the observed versus calculated run out volumes sensitivity analyses of the resistance parameters for the different rheologies showed that the viscosity the basal friction the turbulence term and the resistance factor are the most sensitive ones it appeared that the variation in thickness along the run out track can be explained by entrainment of material in the upper part of the track and a change in parametric values during the run out process the three rheologies produced a reasonable fit with the observed geometry of the run out profile run out time and run out volume it was argued that the voellmy rheology seems to give the most appropriate explanation for the difference in resistance along the run out path the main problem in the simulation was to stop the debris flow on a slope with a gradient around 22 a reactivation of the mass movement by frictional sliding of the material half way the run out track was simulated it occurred 30 min after the first run out phase due to an increase in pore pressure the sliding material changed into a slow flowing mass that reached a newly built up area after about 1 h and moved into wangong town over a distance of 80 m

volcanic avalanche fault zone with pseudotachylite and gouge in french massif central abstract structures and textures with sedimentological variations at different scales of the lithofacies assemblage help us to constrain the basal kinematic transition from non depositional to depositional conditions during volcanic avalanche emplacement in the well exposed impact sheared contact along volcanic avalanche fault zone in the french massif central we observe how the granular textures of the pseudotachylite and fault gouge have recorded the propagation of shock wave with granular oscillatory stress sequential events of basal aggradation along avalanche fault zone have been established related to fractal d values temperature pressure regime and oscillatory stress during slow wave velocity a typical lithofacies assemblage with a reverse grading shows the pseudotachylite and fault gouge a cataclastic gradient is characterised by the fractal d values from 2 7 in jigsaw breccias with pseudotachylite partial melt to 2 6 in the polymodal gouge shock brecciation and comminution produce cataclastic shear bands in the pseudotachylite and quartz microstructures along the basal contact of the volcanic debris avalanche deposit gouge microstructures show granular segregation cataclasis with antithetic rotational riedel shear and an arching effect between the riedel shear bands x ray microtomography provided 3d microfabrics along the clastic vein in the sandy gouge from the available statistical dataset a few equations have been developed implicating the same cataclastic origin with a co genetic evolution of lithofacies an impact wave during primary shear propagation may contribute to produce hydroclastic matrix pseudotachylite partial melt and proximal gouge thixotropy with v 50m s and a t

flank collapse at mount wrangell alaska recorded by volcanic mass flow deposits in the copper river lowland an areally extensive volcanic mass flow deposit of pleistocene age known as the chetaslina volcanic mass flow deposit is a prominent and visually striking deposit in the southeastern copper river lowland of south central alaska the mass flow deposit consists of a diverse mixture of colorful variably altered volcanic rocks lahar deposits glaciolacustrine diamicton and till that record a major flank collapse on the southwest flank of mount wrangell the deposit is well exposed near its presumed source and thick continuous stratigraphic exposures have permitted us to study its sedimentary characteristics as a means of better understanding the origin significance and evolution of the deposit deposits of the chetaslina volcanic mass flow in the chetaslina river drainage are primary debris avalanche deposits and consist of two principal facies types a near source block facies and a distal mixed facies the block facies is composed entirely of block supported shattered and fractured blocks with individual blocks up to 40 m in diameter the mixed facies consists of block sized particles in a matrix of poorly sorted rock rubble sand and silt generated by the comminution of larger blocks deposits of the chetaslina volcanic mass flow exposed along the copper tonsina and chitina rivers are debris flow deposits that evolved from the debris avalanche component of the flow and from erosion and entrainment of local glacial and glaciolacustrine diamicton in the copper river lowland the debris flow deposits were probably generated through mixing of the distal debris avalanche with the ancestral copper river or through breaching of a debris avalanche dam across the ancestral river the distribution of facies types and major element chemistry of clasts in the deposit indicate that its source was an ancestral volcanic edifice informally known as the chetaslina vent on the southwest side of mount wrangell a major sector collapse of the chetaslina vent initiated the chetaslina volcanic mass flow forming a debris avalanche of about 4 km 3 that subsequently transformed to a debris flow of unknown volume

granular mass flows and coulomb s friction in shear cell experiments implications for geophysical flows 1 granular mass flows of rock fragments are studied in the lab by means of a high speed video camera at 2000 frames per second these granular flows are generated using beds of pumice fragments positioned on a rough rotating disk whose angular velocity is controlled by a motor the experimental apparatus allows an understanding of the arrangement of the particles in granular mass flows with relatively small and relatively large values of the savage number the savage number represents the ratio between grain collision stresses and gravitational grain contact stresses in particular these flows develop a basal layer of agitated and colliding particles underneath a relatively rigid upper layer our experimental results suggest the validity on average of the coulomb s relationship between shear and normal forces at the base of granular mass flows irrespective of their savage number value in coulomb s equation the shear stresses do not depend on the shear rate we expect the coulomb friction law to be valid also in moving pyroclastic flows our experiments suggest that the collisions and subsequent comminution of pumice fragments in moving pyroclastic flows could provide ash for the overriding ash clouds in our experiments the amount of ash generated by particle particle and particle boundary interactions increases as the value of the savage number increases in nature part of this ash may also simply move toward the base of the flows because of kinetic sieving

coarse tail vertical and lateral grading in pyroclastic flow deposits of the latera volcanic complex vulsini central italy origin and implications for flow dynamics abstract coarse tail vertical and lateral grading are common features of pyroclastic flow deposits of the latera volcanic complex vulsini volcanoes central italy and are described for four representative flow units lithic clasts show normal vertical and lateral grading in all four units pumice clasts show reverse vertical and lateral grading within three flow units normal vertical and lateral grading of scoria clasts has been observed in one flow unit the origin of vertical and lateral grading of lithic and pumice clasts is related to mechanisms operating during the transport process within the high particle concentration basal avalanche of pyroclastic flows vertical grading results from the balance between gravitational and dispersive forces and is transferred to a lateral grading by vertical velocity gradients within a nonturbulent flow zone of pyroclastic flows the pyroclastic flows are modeled as bingham type fluids a framework that explains some of the basic deposit features even though it is a highly simplified treatment of the flows plug flow zones in the flows were a relatively minor part of their thicknesses evidence for the flows having had high densities probably within a factor of two of the final deposit density is presented finally their origin by single pulse or progressive formation is discussed

flow characteristics of 2 phase granular mass flows from model flume tests abstract changes in basal fluid pressure and normal flow depth in 2 phase granular mass flows the equivalent coefficient of friction and the equivalent coefficient of friction between gravity centres before and after failure were investigated for pumiceous gravel and a mixture of pumiceous gravel and volcanic ash by means of large scale model flume tests the proportion of finer soil particles the inclination of slope segments and the width of horizontal segments were selected as the controlled conditions no excess of basal fluid pressure was observed in the pumiceous gravel on the other hand an excess of pressure head was generated in the mixture of pumiceous gravel and volcanic ash this was due to the suspension of the fine particles in the pore fluid increasing its effective density and the quasi undrained shear deformation due to the low permeability of the mixture in the mass of the granular flow during its motion in tests with a slope of 30 both the pumiceous gravel and the mixture of pumiceous gravel and volcanic ash travelled less distance in the narrow flume than in the wide one this was likely because in the wide flume no clogging occurred where the width of the flume changed and less frictional collisions against side walls and resulting grains contact took place in tests with a narrow flume the pumiceous gravel clogged and most of material was deposited around the constriction however the mixture passed through the constriction smoothly this could be because less frictional resistance was generated in the mixture due to the lowering of effective stress between soil particles associated with the excess of pore fluid pressure although the test on a slope of 35 had the largest potential energy before the release of the materials and the test on a slope of 25 had the least the test with the 35 degree slope produced the largest equivalent coefficient of friction and the smallest value was obtained from the test with a 25 degree slope this finding suggests that the dissipation of kinetic energy especially in the vertical direction due to the collisions and the following abrupt deformation around the connection of the flume between the slope and horizontal segments may play an important role in the travel distance

from the source area to the deposit collapse fragmentation and propagation of the frank slide the combination of structural data from the source area and descriptive data from the deposit s carapace as well as remote sensing and statistical analysis allows a better understanding of the collapse fragmentation and propagation processes of the frank slide rock avalanche the in situ observed conservation of the stratigraphic sequence of the turtle mountain anticline s normal limb in the deposit is interpreted as the consequence of the collapse mode involving simple shearing of the mass accompanied by a rotational movement i e a simple shear parallel to the topography and a breakage of the hinge followed by overthrusting of the normal limb on the inverse limb coherence between the block size distributions of the source area and the deposit carapace is interpreted as a demonstration of the primary control of preexisting fracturing on the fragmentation processes remote sensing indexes allow us to uncover a priori hidden morphological features preserved on the surface of the deposit i e longitudinal and compressional features as well as lobes their location on the carapace provides evidence of lateral heterogeneity in the propagation highlighted by three different types of propagation behaviors this comprehensive study not only provides elements that contribute to an understanding of the frank slide rock avalanche but it also provides insight into essential parameters to take into account in further modeling of these types of phenomena

simply pyroclastic currents gravity driven ground hugging gas pyroclast mixtures produced during explosive volcanic eruptions define a full spectrum of particle concentration flow regime and particle support mechanisms to describe these phenomena the term pyroclastic density current pdc has become increasingly popular in the last few tens of years here i question the general application of the term pdc to the whole flow spectrum and instead i propose the simpler term pyroclastic current

combinations of volcanic flank and seafloor sediment failure offshore montserrat and their implications for tsunami generation recent seafloor mapping around volcanic islands shows that submarine landslide deposits are common and widespread such landslides may cause devastating tsunamis but accurate assessment of tsunami hazard relies on understanding failure processes and sources here we use high resolution geophysical data offshore from montserrat in the lesser antilles to show that landslides around volcanic islands may involve two fundamentally different sources of sediment island flank and larger seafloor sediment failures and can occur in multiple stages a combination of these processes produces elongate deposits with a blocky centre associated with island flank collapse surrounded by a smoother surfaced deposit that is dominated by failed seafloor sediment the failure of seafloor sediment is associated with little marginal accumulation and involves only limited downslope motion submarine landslide deposits with similar blocky and smooth surfaced associations are observed in several locations worldwide but the complex emplacement processes implied by this morphological relationship can only be revealed by high resolution geophysical data such complexity shows that the volume of landslide deposits offshore of volcanic islands cannot simply be used in tsunami models to reflect a single stage collapse of primary volcanic material by applying predictive equations for tsunami amplitude to investigate general scenarios of volcanic island landslide generation we show that the tsunami hazard associated with volcanic island collapse remains highly significant volcanic flank failures even if relatively small may generate large local tsunamis but associated seafloor sediment failures even if they have a much greater volume have a substantially lower potential for tsunami generation

analyzing debris flows with the statistically calibrated empirical model laharz in southeastern arizona usa abstract hazard zone delineation for extreme events is essential for floodplain management near mountain fronts in arid and semiarid regions on 31 july 2006 unprecedented debris flows occurred in the santa catalina mountains of southeastern arizona following extreme multiday precipitation recurrence interval 1000 years for 4 day precipitation most mobilized sediment contributing to debris flows was derived from shallow seated failures of colluvium on steep slopes a total of 435 slope failures in the southern santa catalina mountains released 1 34 million mg of sediment into the channels of 10 drainage basins five drainages produced debris flows that moved to the apices of alluvial fans on the southern edge of the mountain front damaging infrastructure and aggrading channels to reduce future flood conveyance using the statistically calibrated empirical debris flow model laharz and modified model coefficients developed to better match conditions in southeastern arizona we predicted the approximate area of deposition and travel distance in comparison to observed depositional areas and travel distance for seven debris flows two of the modeled debris flows represented single slope failures that terminated downslope with no additive influence of other debris flows or streamflow flooding five of the simulated debris flows represented the aggregation of multiple slope failures and streamflow flooding into multiple debris flow pulses because laharz is a debris flow hazard zone delineation tool the complexity of alternating transport and deposition zones in channels with abrupt expansions and contractions reduces the applicability of the model in some drainage basins

quartz arenites of the cambro ordovician kamouraska formation quebec appalachians canada i deep water depositional processes in a continental slope environment the kamouraska formation is an uppermost cambrian lowermost ordovician quartz arenite dominated unit of controversial origin deposited on the southeastern slope of laurentia bordering the iapetus ocean it is exposed in the quebec appalachians on the south shore of the st lawrence estuary the formation consists of basal polymictic conglomerate and overlying massive sheet like quartz arenite the conglomerate beds are reversely and reversely to normally graded the quartz arenite beds are generally massive although they may show coarse tail grading beds containing full or partial bouma sequences are rare paleoflow directions from ripple cross lamination ripple marks on bed surfaces and sole marks point towards southeast south and southwest the clastic sediments of the kamouraska were transported into the deep sea by sediment gravity flows that evolved from hyperconcentrated to concentrated density flows and then to turbidity currents the depositional environment is interpreted to have been a

volcaniclastic debris flows at la fossa volcano vulcano island southern italy insights for erosion behaviour of loose pyroclastic material on steep slopes abstract this paper describes a qualitative model of erosion of loose volcaniclastic material on steep slopes of la fossa cone vulcano island italy that generates small volume debris flows the loose volcaniclastic cover rests on an almost impermeable substratum which comprises a fine grained hydromagmatic tuff morphologically three sectors were distinguished 1 a water supply zone slope 32 where rain water is enriched in mud and concentrated in the initiation zone 2 an initiation zone or source area sensu stricto slope with 30 where debris flows form and 3 a transport and deposition zone where debris flows deposited levees and terminal lobes slope 30 main episodes of erosion of loose volcaniclastic cover and debris flow generation occur in response to thunderstorms the erosion of tuff from superficial water added a significant amount of fines mud fraction to the initiating flows debris flow stoppage on steep slopes was interpreted as the result of a loss of mass estimated between 35 and 53 of total mass to form levees from field and laboratory data the density of debris flows was estimated at about 1950 kg m3 morphological data matrix texture mass number nm and clay content of debris flow deposits suggest that they were deposited by saturated granular slurries

particle velocity fields and depositional processes in laboratory ash flows with implications for the sedimentation of dense pyroclastic flows we conducted laboratory experiments on dam break flows of sub 250 m volcanic ash generated by the release of gas fluidized and variably non expanded to expanded up to 35 beds in order to gain insights into the internal kinematics of pyroclastic flows the flows were typically several cm thick and had frontal speeds of up to 2 m s 1 high speed videos taken through the transparent sidewall of the 3 m long channel were analyzed with a particle tracking algorithm providing a spatial and temporal description of transport and sedimentation the flows deposited progressively as they traveled down the flume being consumed by sedimentation until they ran out of volume deposition commenced 5 20 cm rearward of the flow front and for a given expansion proceeded at a rate independent of distance from the lock gate deposit aggradation velocities were equal to those inferred beneath quasi static bed collapse tests of the same ash at the same initial expansions implying that shear rates of up to 300 s 1 have no measurable effect on aggradation rate the initially non expanded and just fluidized flow deposited progressively at a rate indicative of an expansion of a few percent perhaps due to shear induced reynolds dilation during initial slumping the fronts of the flows slid across the flume floor on very thin basal shear layers but once deposition commenced a no slip condition was established at the depositional interface within the flows the trajectory of the constituent particles was linear and sub horizontal the velocities of the particles increased with height above the depositional interface reached a maximum then declined slightly towards the flow surface perhaps due to air drag at a given location the velocity profiles were translated upwards as the deposit aggraded the results show that even cm thin poorly expanded flows of ash deposit progressively as inferred for many pyroclastic flows the change from frontal slip to rearward no slip conditions at the bases of the laboratory flows are qualitatively consistent with some textural features of pyroclastic flow deposits

a scaling distribution for grain composition of debris flow debris flow is composed of a wide range of grains this study proposes a general form of grain size distribution p d cd mu exp d d c which is satisfied well by various debris flows and by soils and sediments related to debris flows the parameters mu and d c are found to be related to debris flow density in power laws in particular represents some characteristic porosity of soil in a natural condition and controls the variation of soils in developing debris flows and d c defines a characteristic size governing the sediment concentration field observations indicate that debris flows fall into a certain range of parameters mu d c almost all debris flows have mu 0 10 and most debris flows of high density have mu 0 05 moreover experiments show that the exponent p increases during soil failures under rainfall providing an index varying in the course of debris flow initiation finally grain size distribution is used to evaluate the properties of debris flows in different regions the distribution provides a simple but quantitative method of predicting a potential flow through the source soils c 2013 elsevier b v all rights reserved

volcaniclastic sequences at the foot of tacana volcano southern mexico implications for hazard assessment extensive volcaniclastic deposits have originated from the tacana volcanic complex tvc throughout its evolution the valleys of the coatan and cahuacan rivers have been the main routes for descending flows which have occasionally reached the pacific ocean as a result three fans have been deposited or increased their volume the most recent tapachula is 13 km long and covers an area of 48 km2 that has been largely urbanized by the city of tapachula which is located 30 km sw of the tvc the 0 7 km3 fan is bounded by the coatan river to the west and the cahuacan river to the east and is composed of a complex succession of volcaniclastic deposits accumulated between 23 000 and 1 300 years ago in response to remobilization of debris along the coatan river basin collectively the three fans consist of 34 stacked units grouped into five stratigraphic sequences from the oldest to the youngest these sequences are as follows 1 pre tacana chanjale fan comprising five units associated with the remobilization of material produced during the formation of the chanjale caldera 1 myr ago 2 mal paso mal paso fan comprising four units emplaced between 100 000 and 23 000 years ago 3 lower tapachula tapachula fan consisting of two units deposited around 23 000 years ago 4 upper tapachula tapachula fan consisting of 14 units emplaced between 14 300 and 1 300 years ago and 5 the topmost sequence coatan is made up of 11 units deposited during the past 1 300 years inside the valley of the coatan river today 200 000 people live on top of the tapachula fan which makes the city vulnerable to future lahars from the tvc

the influence of debris flow rheology on fan morphology owens valley california we have investigated factors controlling the surface morphology of debris flow fans comprising the bajada along the western slope of owens valley california these fans have average slopes of 4 an extensive network of abandoned boulder lined channels rough undulatory surfaces near the range front and smooth distal surfaces field relationships and mechanical considerations indicate that the channels of the bajada are products of fluvial incision and not debris flow scour this is significant because detailed geomorphic maps indicate that the channels strongly influence the pattern of debris flow deposition the locus of debris flow deposition on a channelized fan surface is set by the interaction of debris flows with the channel system and is controlled by channel size channel gradient flow volume flow hydrograph and flow rheology debris flow behavior is most directly controlled by variations in bulk sediment concentration and its influence on flow rheology whereas low sediment concentration debris flows tend to smooth the surface of the lower fan spreading into thin sheets and filling channels and surface undulations repeated deposition of high sediment concentration debris flows produces the rugged topography of the upper fan the texture of the fan surface rough or smooth is determined by the relative volumetric importance of these two types of debris flow in addition channel avulsions and the associated long term shifting of depositional loci are driven by in channel deposition of debris flows with the highest sediment concentrations these debris flows therefore play a critical role in determining both the structure of the channel network and the long term pattern of deposition on the fan surface as a whole we infer that the frequency distribution of debris flow rheologies set by source terrain geology and hydrology is an important control on fan morphology

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

anatomy of turbidites and linked debrites based on long distance 120 x 30 km bed correlation marnoso arenacea formation northern apennines italy much of our understanding of submarine sediment laden density flows that transport very large volumes ca 1 to 100 km3 of sediment into the deep ocean comes from careful analysis of their deposits direct monitoring of these destructive and relatively inaccessible and infrequent flows is problematic in order to understand how submarine sediment laden density flows evolve in space and time lateral changes within individual flow deposits need to be documented the geometry of beds and lithofacies intervals can be used to test existing depositional models and to assess the validity of experimental and numerical modelling of submarine flow events this study of the miocene marnoso arenacea formation italy provides the most extensive correlation of individual turbidity current and submarine debris flow deposits yet achieved in any ancient sequence one hundred and nine sections were logged through a ca 30 m thick interval of time equivalent strata between the contessa mega bed and an overlying columbine marker bed correlations extend for 120 km along the axis of the foreland basin in a direction parallel to flow and for 30 km across the foredeep outcrop as a result of post depositional thrust faulting and shortening this represents an across flow distance of over 60 km at the time of deposition the correlation of beds containing thick 40 cm sandstone intervals are documented almost all thick beds extend across the entire outcrop area most becoming thinly bedded 40 cm in distal sections palaeocurrent directions for flow deposits are sub parallel and indicate confinement by the lateral margins of the elongate foredeep flows were able to traverse the basin in opposing directions suggesting a basin plain with a very low gradient small fractional changes in stratal thickness define several depocentres on either side of the verghereto high area the extensive bed continuity and limited evidence for flow defection suggest that intrabasinal bathymetric relief was subtle substantially less than the thickness of flows thick beds contain two distinct types of sandstone ungraded mud rich sandstone intervals record evidence of en masse debrite deposition graded mud poor sandstone intervals are inferred to result from progressive grain by grain turbidite deposition clast rich muddy sandstone intervals pinch out abruptly in downflow and crossflow directions in a fashion consistent with en masse debrite deposition the tapered shape of mud poor sandstone intervals is consistent with an origin through progressive grain by grain turbidite deposition most correlated beds comprise both turbidite and debrite sandstone intervals intrabed transitions from exclusive turbidite sandstone to turbidite sandstone overlain by debrite sandstone are common in the downflow and crossflow directions this spatial arrangement suggests either i bypass of an initial debris flow past proximal sections ii localized input of debris flows away from available sections or iii generation of debris flows by transformation of turbidity currents on the basin plain because of seafloor erosion and or abrupt flow deceleration a single submarine flow event can comprise multiple flow phases and deposit a bed with complex lateral changes between mud rich and mud poor sandstone

basal shear stress of debris flow in the runout phase abstract a laboratory device is proposed to assess the basal shear stresses generated by debris flow mixtures during their runout phase the device consists of an inclinable box with a gate facing a deposition plane the box is filled with a selected debris flow mixture and after sudden opening of the gate the features of the dam break deposit can be measured based on some simplified assumptions of the energy balance a methodology is proposed to assess basal shear stresses the device has been tested using sediment samples from debris flow deposits generated by two catchments of the dolomites cortina d ampezzo belluno italy by carrying out runout tests for different sediment concentrations by volume the results show how the static coulomb friction law is valid in the runout phase with friction angles on the order of the angle of repose of the same material in dry conditions the data elaboration also yields an innovative constitutive equation for shear stresses this relation merges the coulomb mixture approach with the concept of a one phase flow with a certain rheology this integration offers a useful insight into the weaknesses of the rheological approach if it is not properly scaled up to the ambient pressure of interest

continuum simulation of flow failures dynamic aspects of several catastrophic slope failures have been evaluated by unsteady flow modelling assuming two dimensional or quasi three dimensional transient flow of an incompressible bivi

constraints on the long term colluvial erosion law by analyzing slope area relationships at various tectonic uplift rates in the siwaliks hills nepal 1 the large database of topographic form and uplift rates that exists for the siwaliks hills central nepal makes possible a thorough analysis of the long term erosion model the study especially focuses on drainage areas larger than 5 10 3 km2 fixed by the database resolution and smaller than 1 km2 above which a fluvial signature is recorded this area range corresponds to colluvial valleys in which the dominant erosion process is likely debris flow we evaluate a phenomenological model wherein erosion is considered to depend on drainage area and slope we test this model by assuming that the uplift rate is in approximate equilibrium with erosion the stream power law model formulated by analogy to river incision and transport problems is found to be consistent with data since an inverse power law relationship between slope and drainage area is systematically observed between 7 10 3 and 1 km2 with little variability on the exponent 0 24 thanks to the range of uplift rates we obtain constraints on the slope dependency of erosion law which appears linear and which predicts a significant erosion threshold the linear dependence on slope in the debris flow zone is consistent with findings by kirby and whipple 2001 in the fluvial downstream zone and with the linear relationship between local relief and uplift rate documented by hurtrez et al 1999 the transition between this colluvial channel regime and the fluvial regime appears quite sharp in contrast with recent studies but the latter regime is not sufficiently documented to derive definite conclusions

effectiveness of exceptional rainstorms on a small mediterranean basin abstract a comprehensive investigation of rainstorms and their consequent impacts on landscape evolution is geomorphologically important but only scant information may be available on exceptional events because parameters on synoptic conditions rainstorm landforms and hydrology for such events may be incomparable with previous knowledge we studied an exceptional storm on april 2 2006 in the ramot menashe region israel our investigation of rainfall landslides debris flows and channel suggests the effectiveness of such an event on the development of basin scale morphology the storm caused damage and casualties although it covered relatively narrow strips neither direct rainfall nor runoff measurements exist for the most severely affected area of ramot menashe but the geomorphologic evidence combined with high resolution meteorological radar data provides the basic understanding of the processes and hazardous conditions which prevailed at the time in the storm core based on estimation from meteorological radar data 263 mm of rain fell within 3 h with a maximum intensity of 220 mm h 1 for 10 min triggering both sporadic landslides at the soil bedrock contact on the upper slopes and widespread landslides at the fractured massive bedrock contact on the lower slopes the 1st order channels on the alternation of chalk and marl also underwent erosion and the produced sediment deposited on alluvial fans at the confluence with the main channel the specific peak discharges for catchment size of 0 3 10 km2 were 11 to 73 m3 s 1 km 2 higher than any recorded floods in the mediterranean climatic region of israel the effectiveness of the flood for geomorphic work represented by shear stress and stream power per unit boundary area reached 87 398 n m 2 and 212 2134 w m 2 respectively this kind of analysis can be applied to hazard prediction in other areas under similar geomorphological conditions

decoding pyroclastic density current flow direction and shear conditions in the flow boundary zone via particle fabric analysis abstract one of the greatest challenges in volcanology is extracting information from volcanic deposits that inform the conditions at the time of emplacement here we explore particle shape fabric within samples from the column collapse pyroclastic density current pdc deposits generated by the 18 may 1980 eruption of mt saint helens msh particle shape fabric is the mutual alignment of particles within a sample which is dependent on shearing conditions at the time of deposition here particle shape fabric is used to address the following hypotheses 1 particle shape fabric will align with bulk flow direction estimates made by previous studies while resolving fine scale flow direction variations 2 samples extracted from pdc deposits immediately above a basal contact will show higher extents of fabric development i e clast alignment relative to samples extracted well above the contact and 3 samples extracted from cross stratified deposits will have higher extents of fabric development relative to samples extracted from the massive facies we find that fabric orientations approximate previous flow direction interpretations of general flow from south to north and channelization due to paleo topography furthermore shape fabric records flow interaction with the substrate created by debris avalanche deposits leading to fine scale variations in flow paths these variations are recorded in samples extracted near the substrate deposit contact moreover these samples do not show a higher measure of clast alignment relative to samples taken well above flow contacts but do exhibit bimodal clast alignment this suggests some degree of traction transport and thus higher shearing conditions relative to when the currents deposited massive lapilli tuffs samples extracted from the cross stratified deposits do not show higher extents of fabric development relative to the massive deposits supporting previous interpretations that these deposits formed from a rapidly sedimenting concentrated flow boundary zone that was thin enough to be frequently interrupted or influenced by the overriding turbulent portion of the flow finally observations of fine scale variability in measured fabric within a single outcrop indicates unsteady flow conditions and step wise aggradation during deposition this work demonstrates that particle shape fabric analyses can aid in decoding pdc flow conditions future complementary experimental work may allow for the extraction of quantitative information regarding the magnitudes of shear and subsequent particle alignments within the flow boundary zone providing further insight into pdc dynamics

estimating the mud depth of debris flow in a natural river channel a theoretical approach and its engineering application mud depth of debris flow is an essential parameter for assessing the hazard magnitude in an event however direct prediction of mud depth in a natural river channel is a scientific challenge because current methods often treat the complex relief of bed surface as a rectangular one which makes the prediction illogical in this paper we propose a new theoretical approach the so called numerical integral method based approach for estimating the maximum mud depth of debris flow at a complex cross section in a natural river channel given a predefined peak discharge of the debris flow event the numerical integral method based iteration algorithm uses the riemann method to search for an approximate mud depth in contrast to the previous methods the presented approach addresses an important issue namely it takes into account the complex shape of the bed surface and superelevation at the bend for natural channels two cases are used to illustrate the performance and advantages of the presented approach one is a well documented event in the previous study and the other is a debris flow event after ms 8 0 wenchuan earthquake an engineering application regarding the rational design of a debris flow canal is subsequently discussed the canal was completely destroyed in a debris flow event in 2008 we used the proposed method to back analyze the mud depth and velocity in the canal it was found that the abrupt decrease of mud depth from the natural channel to the concrete canal significantly reduced the transportation capability thereby causing blockage in the canal the canal was modified and reconstructed in 2009 with suggested improvements from the proposed method and successfully transported subsequent debris flow in 2011

transient quaternary erosion and tectonic inversion of the northern range trinidad abstract cosmogenic 10be measured in sediments from northern range catchments on the island of trinidad reveals low millennial scale rates of erosion average 40 mm ka that increase roughly eightfold from 11 to 92 mm ka eastward across the mountain range these results in conjunction with an analysis of mountain morphometrics are consistent with quaternary east side up tilting of the northern range which has occurred recently 100 ka the highest millennial scale erosion rates coincide spatially with quaternary east side surface uplift albeit not in magnitude high modern rainfall rates low topographic relief and convex longitudinal stream profiles indicating transient quaternary erosion we interpret that hillslope adjustment and erosion of the northern range is buffered from climatic and tectonic forcings by dense tropical vegetation cover thick saprolite and porous regolith compared with longer term thermochronology exhumation rates we document that an order of magnitude deceleration of and reversal in the locus of erosion and exhumation has occurred during the pliocene to the holocene we suggest that these combined data sets highlight distinct syn and post collisional phases of northern range development that are related to a major change in relative caribbean south american plate motion from oblique convergence to transform motion oblique collision during the mid miocene likely caused relatively higher rates of and asymmetric exhumation of the northern range post collisional mountain scale tilting is likely caused by a combination of crustal extension in the gulf of paria and by deep subsurface lithospheric detachment processes that drives dynamic topography

the influence of palaeotopography on facies architecture and pyroclastic flow processes of a lithic rich ignimbrite in a high gradient setting the abrigo ignimbrite tenerife canary islands abstract the late pleistocene 188 19 ka abrigo ignimbrite represents the last major explosive caldera forming eruption on tenerife it consists almost entirely of a moderate volume 1 8 km 3 light grey phonolitic lithic rich ignimbrite deposit although a possible abrigo member thin fall deposit is locally preserved beneath the ignimbrite suggesting an initial short lived stable plinian eruption column the ignimbrite deposit is dispersed radially around the lower flanks of the las canadas edifice and correlates to a clast supported lithic breccia on the eastern and northern caldera wall much of the ignimbrite was probably deposited offshore or within the caldera now buried by more recent lavas two major depositional units separated by a co ignimbrite ash cloud deposit and which display dramatic variations in thickness pyroclastic flows were channelised along and deposited within the same valleys that exist today and were commonly continuous and sheet like across the interfluves the basal zones of pyroclastic flows are envisaged as a bed load of coarse lithic lapilli and blocks transported under their own momentum and with the support of the surrounding fine ash gas granular flow

two unusual type b refractory inclusions in the ningqiang carbonaceous chondrite evidence for relicts xenoliths and multi heating abstract two type b refractory inclusions consisting mainly of melilite fassaite and spinel anorthite were found in the anomalous ningqiang carbonaceous chondrite the composition of melilite varies from ak4 15 near the diopside rims to ak80 90 in the centers of these inclusions in addition melilite exhibits intergrowths with fassaite and or anorthite in the centers of the inclusions these observations suggest that both inclusions were once molten the na2o content of melilite is positively correlated with the ak content for ak beyond crystallization from melts the ningqiang type b refractory inclusions contain possible relict fassaite fragments these fragments are embedded in gehlenitic melilite and have corroded outlines surrounded by highly tio2 enriched fringes as distinguished from the fassaites intergrown with melilite in the centers of the inclusions in inclusion nqj331 most grains of anorthite occur as irregular coarse grained fragments distinct from those intergrown with melilite toward these anorthite fragments melilite shows a steep decrease in ak content we propose that these anorthite fragments are xenoliths and were probably injected into the host while the latter was crystallizing palisades occur only in nqj331 and are probably relicts too distinctly low v2o3 concentrations of the spinels from the palisade bodies and the presence of palisade bodies consisting of one or more corroded crystals of fassaite anorthite are new lines of the evidence for a relict origin of palisades the other type b refractory inclusion nqj354 contains a spherule consisting of a grossite core and a spinel mantle enclosing laths of hibonite the modal abundance and mineral chemistry of the spinel hibonite spherule are distinctly different from the host inclusion we propose that the spinel hibonite spherule crystallized from a sio2 poor melt at a very high temperature and was injected into the type b host before the latter was completely solidified this grossite bearing spinel hibonite spherule may be related to the spinel hibonite spherules in cm2 chondrites

nonhydrostatic granular flow over 3 d terrain new boussinesq type gravity waves understanding granular mass flow is a basic step in the prediction and control of natural or man made disasters related to avalanches on the earth savage and hutter 1989 pioneered the mathematical modeling of these geophysical flows introducing saint venant type mass and momentum depth averaged hydrostatic equations using the continuum mechanics approach however denlinger and iverson 2004 found that vertical accelerations in granular mass flows are of the same order as the gravity acceleration requiring the consideration of nonhydrostatic modeling of granular mass flows although free surface water flow simulations based on nonhydrostatic depth averaged models are commonly used since the works of boussinesq 1872 1877 they have not yet been applied to the modeling of debris flow can granular mass flow be described by boussinesq type gravity waves this is a fundamental question to which an answer is required given the potential to expand the successful boussinesq type water theory to granular flow over 3 d terrain this issue is explored in this work by generalizing the basic boussinesq type theory used in civil and coastal engineering for more than a century to an arbitrary granular mass flow using the continuum mechanics approach using simple test cases it is demonstrated that the above question can be answered in the affirmative way thereby opening a new framework for the physical and mathematical modeling of granular mass flow in geophysics whereby the effect of vertical motion is mathematically included without the need of ad hoc assumptions

geomorphic and sedimentary evidence of a gigantic outburst flood from towada caldera after the 15 ka towada hachinohe ignimbrite eruption northeast japan abstract this study reports on geomorphic and sedimentary evidence for a gigantic breakout flood from towada caldera honshu island northeast japan as observed along the oirase river downstream from the outlet of the caldera lake a number of features of the oirase river are inconsistent with its present discharge including the occurrence of 1 hanging valleys and a horseshoe shaped waterfall in the upstream gorge area 2 boulder bars and scattered flood boulders 3 a dry valley at a high elevation in the gorge and 4 a large fan the sanbongi fan in the downstream area of the river the sanbongi fan is composed of thick lithic rich hyperconcentrated flow deposits that include pumice clasts derived from the 15 ka towada hachinohe ignimbrite and well rounded meter sized and outsized boulders derived from bedrock of welded ignimbrite the deposits are entirely aggradational with no major channels indicating the absence of a major hiatus during sedimentation the depositional facies also indicate that a single sheet like flood event deposited the sediment within the sanbongi fan area based on the age of the sanbongi fan the flood occurred between 15 and 12 ka after eruption of the towada hachinohe ignimbrite the most probable water source for the flood is towada caldera lake as suggested by landforms and sediments along the lake outlet a paleohydrological analysis indicates that at least 6 km 3 of water was released from the caldera at a peak discharge of 2 10 4 to 3 10 5 m 3 s 1 during the breakout flood although the sanbongi fan was previously considered to be a normal alluvial fan that formed during a stage of low stand sea level the present results show that the formation of the fan was closely related to a catastrophic flood from towada caldera rather than perennial fluvial activity climate change or a change in relative sea level

direct measurement of channel erosion by debris flows illgraben switzerland 1 the timing and magnitude of channel bed erosion by three debris flows was measured in 2008 at the illgraben catchment switzerland using a scour sensor which consisted of a vertical array of erodible sensor elements during the largest debris flow sediment was entrained progressively and stepwise at the flow head within 20 s after front arrival and onset of erosion started before maximum values for flow height and normal and shear stress measured nearby were reached erosion in one of the two smaller debris flows also occurred at the head of the flow but the magnitude of erosion was at the detection limit for the sensor for the other small debris flow we were not able to determine the timing of erosion due to the presence of a sediment layer covering the sensors measurements of pressure fluctuations along the channel sidewall which are produced by interparticle collisions within the flow indicate that the entrainment of sediment is coincident with the largest mean and fluctuating pressures suggesting that interparticle collisions may drive the erosion process at the front of debris flows after erosion at the head of the debris flows sediment was deposited on top of the erosion sensor columns indicating that the bed was reworked to a larger depth than directly visible at the surface after the event observations from elsewhere along the channel support our measurements of the magnitude of net debris flow erosion and indicate that significant erosion can be expected on debris fans when the flow is confined to a channel debris flow entrainment and subsequent bulking of the flow influence the flow dynamics and therefore should be considered in debris flow models and hazard assessment

quantifying periglacial erosion insights on a glacial sediment budget matanuska glacier alaska glacial erosion rates are estimated to be among the highest in the world few studies have attempted however to quantify the flux of sediment from the periglacial landscape to a glacier here erosion rates from the nonglacial landscape above the matanuska glacier alaska are presented and compare with an 8 yr record of proglacial suspended sediment yield non glacial lowering rates range from 1 8 0 5 mm yr 1 to 8 5 3 4 mm yr 1 from estimates of rock fall and debris flow fan volumes an average erosion rate of 0 08 0 04 mm yr 1 from eight convex up ridge crests was determined using in situ produced cosmogenic 10be extrapolating these rates based on landscape morphometry to the matanuska basin 58 ice cover it was found that nonglacial processes account for an annual sediment flux of 2 3 1 0 106 t suspended sediment data for 8 years and an assumed bedload to estimate the annual sediment yield at the matanuska terminus to be 2 9 1 0 106 t corresponding to an erosion rate of 1 8 0 6 mm yr 1 nonglacial sources therefore account for 80 45 of the proglacial yield a similar set of analyses were used for a small tributary sub basin 32 ice cover to determine an erosion rate of 12 1 6 9 mm yr 1 based on proglacial sediment yield with the nonglacial sediment flux equal to 10 7 of the proglacial yield it is suggested that erosion rates by nonglacial processes are similar to inferred subglacial rates such that the ice free regions of a glaciated landscape contribute significantly to the glacial sediment budget the similar magnitude of nonglacial and glacial rates implies that partially glaciated landscapes will respond rapidly to changes in climate and base level through a rapid nonglacial response to glacially driven incision copyright 2009 john wiley sons ltd

visualization of dominant stress transfer mechanisms in experimental debris flows of different particle size distribution physical modelling of debris flow in a small scale flume has been carried out to investigate the internal stress transfer mechanisms within unsteady saturated and segregating granular free surfac

experiments on the flow behaviour of granular materials at high velocity in an open channel a series of laboratory flume experiments has been conducted to investigate the flow behaviour of dry sand at high velocities the first incentive for this experimental programme was an attempt to explain the high mobility of apparently dry masses of rapidly moving broken rock during rock avalanches sturzstroms test velocities of over 5 m s and most other parameters of the tests were found to be dimensionally similar to those for a typical rock avalanche yet the conclusion was negative even the most rapid of the experiments indicated flow behaviour which is in conformity with the constant volume uniform coulomb friction relationship as applicable to slow shearing this conclusion was confirmed independently both by direct measurements of base friction and mean density of the flows and by detailed observations of flow uniformity acceleration and velocity profiles the surprising mobility of st umlrzstroms therefore requires a different explanation une serie de tests a canaux a ete entreprise dans le

rheological properties of loose sands subjected to upward flow the objective of this study was to investigate the rheological properties of loose sands subjected to upward flow by using a vane type rheometer that controlled upward flow in the loose sand specim

pyroclastic flow deposits from a kimberlite eruption the orapa south crater botswana abstract the orapa diamond mine republic of botswana exposes a bi lobate kimberlite pipe that erupted during the late cretaceous epoch 93 ma through archaean basement and volcano sedimentary rocks of the karoo supergroup geological mapping of the crater zone of the south pipe has revealed a 15 25 m thick in situ kimberlite pyroclastic flow deposit the pyroclastic deposit fills in the crater and completely drapes lower units indicating that the parent flow originated from an adjacent kimberlite pipe the unit comprises a basal coarse lithic concentration layer exhibiting imbricated clasts which grades upwards into massive poorly sorted lapilli tuff the tuff contains abundant sub vertical degassing structures defined by lithic enrichment and depletion in fine grained material degassing structures commonly emanate from blocks in the basal layer the presence of degassing structures and a coarse basal layer distinguishes this deposit from pipe filling massive volcaniclastic kimberlite which is typically homogeneous in terms of texture and clast size over distances on the order of 100s of metres studies of the thermal remanent magnetism in basalt clasts from the deposit together with serpentine diopside assemblages indicate that it was emplaced at elevated temperatures on the order of 200 440 c consistent with deposition from a pyroclastic flow the lithofacies characteristics can be explained by the interaction of the pyroclastic flow with the complex topography of a pre existing crater

the 2500 yr b p chicoral non cohesive debris flow from cerro machin volcano colombia abstract cerro machin volcano cmv is located in the central part of the colombian andes 2750 m asl 150 km southwest of bogota it is considered the most dangerous active volcano of colombia cmv has experienced at least six major explosive eruptions during the last 5000 years these eruptions have emplaced many types of pyroclastic deposits with associated lahars that have traveled more than 100 km one of these lahars is called chicoral debris flow deposit dfd2 this deposit is exposed as discontinuous terraces 3 20 m thick along the coello and magdalena rivers up to 109 km from the source the dfd2 covers a minimum area of 62 km2 and has a minimum volume of 0 57 km3 it comprises two dacite rich volcaniclastic units grain size analysis reveals that the matrix content and sorting increase with distance while the average grain size decreases the clay content of the dfd2 matrix is approximately 1 thus categorizing it as a non cohesive debris flow radiocarbon dates obtained from underlying and overlying paleosols yielded ages of 2505 65 and 1640 45 yr b p respectively these dates suggest that dfd2 is related to the 2600 yr b p el guaico eruption of cmv this eruption produced a block and ash flow that filled and blocked the toche river up to 5 km from the volcano subsequent remobilization of this loose material by runoff water generated a massive debris flow that traveled 91 km along the toche and coello rivers and continued across the espinal alluvial fan debouching into the magdalena river where it continued another 18 km prior to its transformation into a sediment laden flow because the last eruption of the volcano occurred ca 900 years ago no historic activity of cmv is known among inhabitants of the region hence the region has developed without awareness of volcanic hazards therefore an assessment of volcanic hazards is essential for understanding and evaluating the vulnerability and risk to which people are exposed in case of a future eruption such assessment is critical for urban planning development contingency emergency and education planning

measuring basal force fluctuations of debris flows using seismic recordings and empirical green s functions we present a novel method for measuring the fluctuating basal normal and shear stresses of debris flows by using along channel seismic recordings our method couples a simple parameterization of a debris flow as a seismic source with direct measurements of seismic path effects using empirical green s functions generated with a force hammer we test this method using two large scale 8 and 10 m experimental flows at the u s geological survey debris flow flume that were recorded by dozens of three component seismic sensors the seismically derived basal stress fluctuations compare well in amplitude and timing to independent force plate measurements within the valid frequency range 15 50 hz we show that although the high frequency seismic signals provide band limited forcing information there are systematic relations between the fluctuating stresses and independently measured flow properties especially mean basal shear stress and flow thickness however none of the relationships are simple and since the flow properties also correlate with one another we cannot isolate a single factor that relates in a simple way to the fluctuating forces nevertheless our observations most notably the gradually declining ratio of fluctuating to mean basal stresses during flow passage and the distinctive behavior of the coarse unsaturated flow front imply that flow style may be a primary control on the conversion of translational to vibrational kinetic energy this conversion ultimately controls the radiation of high frequency seismic waves thus flow style may provide the key to revealing the nature of the relationship between fluctuating forces and other flow properties

hyperconcentrated flows and gastroliths sedimentology of diamictites and wackes of the upper cloverly formation lower cretaceous wyoming u s a abstract diamictites and matrix supported wackes of the upper cloverly formation lower cretaceous represent rivers laden with volcaniclastic sediment hyperconcentrated flows the cloverly formation of central wyoming is dominantly fluvial lacustrine and playa deposits the sediments accumulated east of the cordilleran foredeep during the early stages of the sevier orogeny the diamictites and wackes are decimeters thick and stacked vertically forming rock bodies up to 11 m thick pebbles and cobbles within the diamictites and wackes occur as isolated clasts or in poorly defined layers many such clasts exhibit some degree of polish clast lithologies can be correlated to rocks that were exposed in the mountain belt to the west provenance data are consistent with early cretaceous movement on the meade laketown paris willard thrust system the clay fraction of the diamictites and wackes is dominantly illite smectite and smectite characteristic of altered volcanic ash diamictites and matrix supported wackes lack primary sedimentary structures e g cross stratification but do exhibit soft sediment deformation features indicative of dewatering erosional bases and bedding geometries are indicative of channelized flow the diamictites and matrix supported wackes resemble debris flow deposits however maintaining debris flows that behave as bingham plastics on low depositional slopes 200 400 km from the mountain front is improbable rather the diamictites and wackes represent hyperconcentrated flows deposition either en masse by a newtonian or nearly newtonian flow that was turbulent throughout or by progressive sedimentation from a stratified flow with a basal incipient granular mass flow overlain by a turbulent suspension is more consistent with the field data paleohydraulic calculations indicate that grain sizes up to small pebbles could have been transported in suspension with larger clasts transported as bedload consistent with sedimentological evidence much of the finer grained suspended sediment was remobilized volcanic ash likely derived from the idaho batholith to the west northwest the polished extraformational pebbles and cobbles long regarded as dinosaur gastroliths or stomach stones are simply clasts associated with the hyperconcentrated flow deposits the polish exhibited by many of the clasts is attributable to transport in ash laden flows the occurrence of polished extraformational stones in cloverly diamictites and wackes may have implications for presumed gastroliths in other fluvial rocks of the western interior e g the cedar mountain and morrison formations

a semi empirical method to calculate the permeability of homogeneously fluidized pyroclastic material this work postulates that highly polydisperse materials have an effective size distribution that controls permeability existence of such effective distribution implies that not all clasts participate to the permeable network resisting to gas flow and that clasts smaller than the minimal effective size are elutriated when this concept is coupled to a generalized blake kozeny equation the resulting semi empirical law links permeability to material properties only bed void fraction clast sizes and densities after calibration of an experimental constant it is able to replicate within 0 6 log unit experimentally measured permeabilities of both loosely packed and expanded beds made of highly polydisperse from 1 m to 4 mm pyroclastic deposits that were resampled so as to ensure homogeneous fluidization the presence of an experimentally calibrated constant and the necessary absence of segregation during fluidization limit the extrapolation of the proposed law to any pyroclastic bed satisfactory fitting of the experimental values however confirms that the permeability of homogeneously fluidized beds is controlled by a balance between settling and elutriation this balance suggests a first order link between permeability and bed expansion which has implications on the kinetics of dense pyroclastic flows

anatomy of a submarine pyroclastic flow and associated turbidity current july 2003 dome collapse soufriere hills volcano montserrat west indies the 12 to 13 july 2003 andesite lava dome collapse at the soufriere hills volcano montserrat provides the first opportunity to document comprehensively both the sub aerial and submarine sequence of events for an eruption numerous pyroclastic flows entered the ocean during the collapse depositing approximately 90 of the total material into the submarine environment during peak collapse conditions as the main flow penetrated the air ocean interface phreatic explosions were observed and a surge cloud decoupled from the main flow body to travel 2 to 3 km over the ocean surface before settling the bulk of the flow was submerged and rapidly mixed with sea water forming a water saturated mass flow efficient sorting and physical differentiation occurred within the flow before initial deposition at 500 m water depth the coarsest components 60 of the total volume were deposited proximally from a dense granular flow while the finer components 40 were efficiently elutriated into the overlying part of the flow which evolved into a far reaching turbidity current

triggering conditions and mobility of debris flows associated to complex earthflows landslides on black marl slopes of the french alps are in most cases complex catastrophic failures in which the initial structural slides transform into slow moving earthflows under specific hydrological conditions these earthflows can transform into debris flows due to their sediment volume and their high mobility debris flow induced by landslides are far much dangerous than these resulting from continuous erosive processes a fundamental point to correctly delineate the area exposed to debris flows on the alluvial fans is therefore to understand why and how some earthflows transform into debris flow while most of them stabilize in this paper a case of transformation from earthflow to debris flow is presented and analysed an approach combining geomorphology hydrology geotechnics and rheology is adopted to model the debris flow initiation failure stage and its runout postfailure stage using the super sauze earthflow alpes de haute provence france as a case study the objective is to characterize the hydrological and mechanical conditions leading to debris flow initiation in such cohesive material results show a very good agreement between the observed runout distances and these calculated using the debris flow modeling code cemagref 1 d the deposit thickness in the depositional area and the velocities of the debris flows are also well reproduced furthermore a dynamic slope stability analysis shows that conditions in the debris source area under average pore water pressures and moisture contents are close to failure a small excess of water can therefore initiate failure seepage analysis is used to estimate the volume of debris that can be released for several hydroclimatic conditions the failed volumes are then introduced in the cemagref 1 d runout code to propose debris flow hazard scenarios results show that clayey earthflow can transform under 5 year return period rainfall conditions into 1 km runout debris flow of volumes ranging between 2000 to 5000 m 3 slope failures induced by 25 year return period rainfall can trigger large debris flow events 30 000 to 50 000 m 3 that can reach the alluvial fan and cause damage

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

particle size density relationships in pyroclastic deposits inferences for emplacement processes in moving pyroclastic systems particles are sorted as a function of their sizes densities and shapes the analysis of the distribution of these characteristics in particle populations of pyroclastic deposits is a major tool in evaluating properties and regimes of parent transport systems this paper reports a study of size density relationships of component subpopulations from selected quaternary pyroclastic deposits of the latera volcanic complex vulsini italy by means of integrated field and laboratory investigations including grain size and component analyses density measurements and sem crystal morphoscopy three kinds of particle size density relationships characterize the studied deposits as follows 1 a significant correlation of decreasing sizes with increasing component densities exists for direct suspension sedimentation products including plinian fall and pyroclastic surge deposits 2 a wide data dispersion with poor correlation normally occurs for the main zones of deposits from high concentration pyroclastic flows and 3 component subpopulations occur in a narrow size range irrespective of density in granular systems dominated by grain collisions such as traction zones beneath low concentration pyroclastic surges and sheared basal layers of pyroclastic flows the regression coefficients of size density relationships appear as a comparative measure of particle concentration in the parent systems consistent with that inferred from the degree of sorting and abrasion of crystal subpopulations from sequential fragmentation transport analysis of grain size data and quantitative morphoscopy the crystal component becomes less sorted and more abraded as the fit to the size density relationship decreases from plinian fall to pyroclastic surge to pyroclastic flow consistent with increasing particle concentration in the transporting current

the occurrence and origin of prominent massive pumice rich ignimbrite lobes within the late pleistocene abrigo ignimbrite tenerife canary islands abstract the 0 196 ma lithic rich abrigo ignimbrite on tenerife canary islands contains localised massive coarse pumice rich ignimbrite lobes mprils they typically form low ridges up to 2 m high with axes parallel to the flow direction and in cross section they range from symmetrical to asymmetrical and highly skewed lobate bedforms generally with flat bases the major components are rounded pebble to cobble sized phonolitic pumice clasts within an ignimbritic matrix of ash fine lithics and minor crystals which varies from lithic rich to lithic poor commonly there is a vertical increase in pumice concentration from matrix supported texture at the base to clast supported at the top accompanied by an increase in pumice clast size mprils often thin and grade laterally perpendicular to current flow into planar pumice concentration zones they occur at one or more stratigraphic levels as either solitary lobes associated with flat topography or as multiple onlapping lobes or within a laterally complex stratified pumice rich ignimbrite facies lcspis near palaeotopographic highs mprils are original depositional features not erosional in origin and are derived from a larger pyroclastic flow it is likely that pumice was segregated to the upper and outer regions of the parent flow causing a significant rheological contrast with the lower lithic rich zone the more pumice rich parts are interpreted to have detached from the parent flow as it decelerated onto gentler slopes or interacted with topographic highs and raced ahead as mobile derivative pyroclastic flows the flow parallel ridge shape of mprils may be a result of fingering within these flows or concentration of pumice within the intermediary clefts deposition occurred en masse at the termination of the flow front the resultant lobate deposits were then overridden and mantled by normal ignimbrite facies from either a later flow pulse or the following main part of the parent flow

transverse architecture of lahar terraces inferred from radargrams preliminary results from semeru volcano indonesia semeru volcano is the highest mountain of java indonesia and a vulcanian explosion occurs every 15 minutes on average since 1967 thus a constantly renewed stock of material and the heavy monsoon rainfall 3700 mm yr 1 at 1500 m above sea level a s l provide a perfect setting for the study of lahars and their deposits hence we examined the architecture of lahars terraces 9 5 km from the summit in the curah lengkong valley we first used ground penetrating radar gpr over vertical exposures of the lahars cut bank terraces this allowed us to better understand transversal radargrams across terraces which are not visually accessible in the field preliminary results from a single radargram are very instructive since 1 they prove that the lateral architecture does not correspond to that observed from banks only 2 we could observe the presence of lenses and stratigraphic discontinuities 3 the setting of the various units can also help reconstruct deposition processes and the chronology of different units in order to finalize these preliminary results we however need to perform multiple gpr radargrams and provide a complete set of results copyright 2010 john wiley sons ltd

subaqueous density flow processes and deposits of an island volcano landslide stromboli island italy stromboli is a 3000 m high island volcano rising to 900 m above sea level it is the most active volcano of the aeolian archipelago in the tyrrhenian sea italy major large volume 1 km 3 sector collapses four occurring in the last 13 kyr have played an important role in shaping the north western flank sciara del fuoco of the volcano potentially generating a high risk tsunami hazard for the aeolian islands and the italian coast however smaller volume partial collapses of the sciara del fuoco have been shown to be more frequent tsunami generating events one such event occurred on 30 december 2002 when a partial collapse of the north western flank of the island took place the resulting landslide generated 10 m high tsunami waves that impacted the island multibeam bathymetry side scan sonar imaging and visual observations reveal that the landslide deposited 25 to 30 10 6 m 3 of sediment on the submerged slope offshore from the sciara del fuoco two contiguous main deposit facies are recognized i a chaotic coarse grained metre sized to centimetre sized clasts deposit and ii a sand deposit containing a lower cross bedded sand layer and an upper structureless pebbly sand bed capped by sea floor ripple bedforms the sand facies develops adjacent to and partially overlying the coarse deposits characteristics of the deposits suggest that they were derived from cohesionless sandy matrix density flows flow rheology and dynamics led to the segregation of the density flow into sand rich and clast rich regions a range of density flow transitions both in space and in time caused principally by particle concentration and grain size partitioning within cohesionless parent flows was identified in the deposits of this relatively small scale submarine landslide event

vertical segregation in granular mass flows a shear cell study 1 non fluidised dry granular mass flows are obtained with rock fragments located on a rough rotating disk in these flows that develop a quasi rigid upper layer and a basal layer of colliding particles dense clasts sink whereas light ones rise when surrounded by particles with intermediate density our experiments demonstrate that the presence of a quasi rigid upper layer in granular mass flows does not prevent vertical segregation and that the formation of coarse tail grading in pyroclastic flows does not require fluidising gases high speed videos reveal that vertical segregation in granular mass flow of rock fragments is generated by inertia differences between segregating clasts and matrix when they are both pushed upward by collisions with the basal layer coarse tail grading occurs because the average segregation velocity of smaller clasts is smaller than that of larger clasts

grain size segregation and levee formation in geophysical mass flows 1 data from large scale debris flow experiments are combined with modeling of particle size segregation to explain the formation of lateral levees enriched in coarse grains the experimental flows consisted of 10 m3 of water saturated sand and gravel which traveled 80 m down a steeply inclined flume before forming an elongated leveed deposit 10 m long on a nearly horizontal runout surface we measured the surface velocity field and observed the sequence of deposition by seeding tracers onto the flow surface and tracking them in video footage levees formed by progressive downslope accretion approximately 3 5 m behind the flow front which advanced steadily at 2 m s 1 during most of the runout segregation was measured by placing 600 coarse tracer pebbles on the bed which when entrained into the flow segregated upwards at 6 7 5 cm s 1 when excavated from the deposit these were distributed in a horseshoe shaped pattern that became increasingly elevated closer to the deposit termination although there was clear evidence for inverse grading during the flow transect sampling revealed that the resulting leveed deposit was strongly graded laterally with only weak vertical grading we construct an empirical three dimensional velocity field resembling the experimental observations and use this with a particle size segregation model to predict the segregation and transport of material through the flow we infer that coarse material segregates to the flow surface and is transported to the flow front by shear within the flow head coarse material is overridden then recirculates in spiral trajectories due to size segregation before being advected to the flow edges and deposited to form coarse particle enriched levees

assessing entrainment of bed material in a debris flow event a theoretical approach incorporating monte carlo method entrainment of underlying bed sediment by a debris flow can significantly increase the debris flow magnitude to study this phenomenon a theoretical approach to assessing bed sediment entrainment is presented the approach is based on a static approximation that bed sediment entrainment occurs when the shearing stress of the flow is sufficiently high to overcome the basal resistance of the bed sediment in order to delineate erodible zones in a channel we analyze the critical condition of this static equilibrium model and subsequently propose a new concept of a critical line to detect the entrainment reaches in a channel considering the spatial and temporal uncertainties of the input parameter the approach is further incorporated within a monte carlo method and the distribution of entrainment zones and post entrainment volumes can be analyzed this approach is illustrated by back analysis of the 2010 yohutagawa debris flow event japan results from 10 000 trials of monte carlo simulation are compared with the in situ surveys it is shown that the present approach can be satisfactorily used to delineate erodible zones and estimate possible entrainment volume of the event discussion regarding the sensitivities and limitations of the approach concludes the paper copyright 2015 john wiley sons ltd

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

the hypermobility of huge landslides and avalanches abstract catastrophic failure of large land masses which generate landslides rockfalls and debris avalanches can have hazardous consequences extending far beyond the source observations show that the mobility of such events depends strongly on the volume for volumes larger than 10 6 m 3 with many different processes invoked to explain higher mobilities hypermobility for both terrestrial and extraterrestrial events although the mobility of large events has been extensively studied there is no generally accepted mechanism for predicting extreme travel distances because the underlying physical processes are poorly understood here we show using physical and rheological arguments that the wide scatter observed for very large mass wasting events in all environments collapses to a single relationship between event volume or inundation area and mobility hypermobility is defined to be the reciprocal of the effective friction coefficient e where the scale dependent e is derived analytically as a function of the mechanical volumetric and topographical parameters of the flow the dominant term in the coefficient is the degree of fluidization involved in the flow our results show that fluidization is limited in extraterrestrial events that significant fluidization occurs in non volcanic and volcanic events and fluidization dominates submarine events this analysis demonstrates that fluidization is associated with long run out distances and that the degree of fluidization can be predicted by the volume and physical and topographic parameters the methodology is simple physically based and validated with datasets of very large terrestrial and extraterrestrial avalanche events we demonstrate that the effective coulomb friction rheology and the hypermobility function are applicable to avalanche events of any size providing an opportunity to simulate past and or potential huge landslide and debris avalanche events run out distances destructive impact and assessment of risk the model can be used to estimate the overrun area and volume in terms of known mobility data

on pyroclastic flow emplacement in this note i investigate some theoretical characteristics of pyroclastic flow deposits assuming that these flows are bingham fluids probably the simplest non newtonian fluids pyroclastic flows are modeled as laminar debris flows moving on an inclined plane and their physics is discussed within the classical framework of lubrication theory using general hydrodynamics methods i show that the arrestment and emplacement of pyroclastic flows may be seen as the time asymptotic limit of their equations of motion this limit is found to be a nonlinear ordinary differential equation whose solution gives the shape of pyroclastic flow deposits the model suggests that these flows stop when the supply of material from the source is depleted deposit thickness is controlled principally by the flow yield stress z a parameter characteristic of bingham fluids while deposit length a measure of flow mobility depends on z on the source flux q0 and on the slope of the solid substrate even in this simple model theoretical analysis shows a complex correlation between flow parameters and deposit profiles

umbrella structure and channel wall stoping in the cambrian st roch formation quebec appalachians significance for particle support mechanisms and turbulence development in hyper concentrated sediment gravity flows umbrella structure is a newly recognized sedimentary structure associated with large platy clasts in resedimented boulder bearing pebble conglomerate with a sandy matrix it consists of a sand rim that lacks pebbles on parts or the entire underside of platy boulders whereas on the upper side pebbles are in direct contact with the boulders the depositing processes were high to hyper concentrated sediment gravity flows in a submarine channel or canyon on the cambrian continental slope of north america bordering the iapetus ocean the structure occurs predominantly where clasts dip moderately in the down current direction based on the association of the structure with slightly forward dipping slabs it is proposed that these down current dipping slabs may have been in the process of counter clockwise rotation that was aborted and may have generated a pressure shadow on the underside enabling the inrush of fluid and the infiltration of sand into the anomalous low pressure zone the structure has implications for particle support mechanisms in high to hyper concentrated sedimentary gravity flows in that it redirects attention to the much debated mechanism of dispersive pressure and alternatives it provides an observable sediment structure that supports dispersive pressure which so far depended on experimental evidence and theoretical arguments alone vrolijk and southard s 1997 concept of a laminar sheared layer is here for the first time interpreted as having an upward moving free surface layer effect during deposition from hyper concentrated flows channel wall stoping involves unlithified turbiditic spillover sand in the levee sediment of the canyon wall that was washed out by the upper diluted parts of the high concentration flows coming down the channel and leaving a niche in the wall that was filled with coarser channel axis facies by the same flow or later flows when its aggradation reached the level of the niche the contact between turbidite and pebble conglomerate occurs now more than 2 m laterally into the exposed channel wall channel wall stoping tracks turbulence development in hyper concentrated gravity flows

experimental study of bedrock erosion by granular flows 1 field studies suggest that bedrock incision by granular flows may be the primary process cutting valleys in steep unglaciated landscapes an expression has been proposed for debris flow incision into bedrock which posits that erosion rate depends on stresses due to granular interactions at the snout of debris flows here we explore this idea by conducting laboratory experiments to test the hypothesis that bedrock erosion is related to grain collisional stresses which scale with shear rate and particle size we placed granular material in a 56 cm diameter rotating drum to explore the relationship between erosion of a synthetic bedrock sample and variables such as grain size shear rate water content and bed strength grain collisional stresses are estimated as the inertial stress using the product of the squares of particle size and vertical shear rate our uniform granular material consisted of 1 mm sand and quartzite river gravel with means of 4 6 or 10 mm in 67 experimental runs the eroded depth of the bed sample varied with inertial stresses in the granular flow to a power less than 1 0 and inversely with the bed strength the flows tended to slip on smooth boundaries resulting in higher erosion rates than no slip cases we found that lateral wall resistance generated shear across the channel producing two cells whose widths depended on wall roughness while the hypothesized inertial stress dependency is supported with these data wear mechanics needs to account for grain dynamics specifically at the snout and possibly to include lateral shear effects

a fluid dynamics approach to modelling the 18th march 2007 lahar at mt ruapehu new zealand lahars are water sediment mass flows from a volcanic source they can be triggered by a variety of mechanisms and span a continuum of flow rheology and hydraulic properties even within the same event lahars are extremely powerful landscaping agents and represent a considerable hazard potential however this highly dynamic character and a lack of direct measurements has made modelling lahars difficult this study therefore applies a fluid dynamics model delft3d to analyse the 18th march 2007 dam break lahar at mount ruapehu new zealand the modelled lahar routed through the whangaehu gorge in 30 min crossed the whangaehu fan in 60 min and then over a further 3 h travelled an additional 22 km distance along the whangaehu river to the tangiwai bridge the modelled mean frontal velocity was 6 5 m s 1 along the gorge although peak velocity reached up to 19 6 m s 1 the modelled lahar flow front progressively slowed across the fan but along the river it accelerated from 2 1 3 3 m s 1 calculated peak velocity along the river was 4 5 m s 1 these results generally compare well with gauged records with historical records and with other modelling approaches however discrepancies in frontal velocity and time to peak stage arise due to 1 specifying roughness which arises from slope variations between adjacent computational nodes and which is stage dependant and 2 due to rapid topographic changes that produce frequent hydraulic jumps which are inadequately accommodated in the numerical scheme the overall pattern of discharge attenuation and of relationships between topographic and hydraulic variables is similar to that calculated for lahars on other volcanoes this modelling method could be applied at other similar sites where a likely source hydrograph and high resolution topographic data are available these results have important implications for hazard management at ruapehu and for examining geomorphic and sedimentary impacts of this lahar

the influence of variable topography on the depositional behaviour of pyroclastic density currents the examples of the upper pollara eruption salina island southern italy abstract stratigraphic reconstruction of the upper pollara eruption has allowed for the inference of eruptive mechanisms and the distillation of a sedimentological model for pyroclastic density currents pdcs moving across variable topography the pre eruptive topography in the study area was characterised by a tuff ring like morphology with both inward and outward dipping slopes highly viscous moderately porphyritic dacitic to rhyolitic magmas fed the eruption which was characterised by a vulcanian eruptive style the stratigraphic succession was divided into five eruption units eus which result from different phases of the eruption separated by stases sustained columns occurred only during eu1 while pdc generation dominates eu2 5 lithofacies analysis of the pdc deposits indicates the prevalence of massive coarse grained deposits on the inner slopes of the pollara crater which are interpreted as the deposits of a flow boundary zone dominated by granular flow or fluid escape regimes dune bedded massive to stratified lithofacies dominate the outer slopes of the pollara crater and are interpreted as the deposits of pdcs with flow boundary zones in which traction played a major role thin massive pdc deposits are exposed on the sub horizontal malfa terrace and are interpreted as representative of flow boundary zones dominated by a granular flow regime the occurrence of stacked deposits indicates that most of the pdcs were characterised by unsteady pulsatory behaviour with development of trains of pulses during their transport the downcurrent lithofacies transitions observed for the upper pollara deposits have finally been compared with other similar lithofacies associations which have been described for short lived pdcs at tuff rings in order to discuss the influence of pre eruptive topography on lithofacies association