coarse grained debris flow dynamics on erodible beds a systematic set of flume experiments is used to investigate the features of velocity profiles within the body of coarse grained debris flows and the dependence of the transport sediment concentration on the relevant parameters runoff discharge bed slope grain size and form the flows are generated in a 10 m long laboratory flume initially filled with a layer consisting of loose debris after saturation a prescribed water discharge is suddenly supplied over the granular bed and the runoff triggers a debris flow wave that reaches nearly steady conditions three types of material have been used in the tests gravel with mean grain size of 3 and 5 mm and 3 mm glass spheres measured parameters included triggering water discharge volumetric sediment discharge sediment concentration flow depth and velocity profiles the dynamic similarity with full sized debris flows is discussed on the basis of the relevant dimensionless parameters concentration data highlight the dependence on the slope angle and the importance of the quasi static friction angle the effects of flow rheology on the shape of velocity profiles are analyzed with attention to the role of different stress generating mechanisms a remarkable collapse of the dimensionless profiles is obtained by scaling the debris flow velocity with the runoff velocity and a power law characterization is proposed following a heuristic approach the shape of the profiles suggests a smooth transition between the different rheological regimes collisional and frictional that establish in the upper and lower regions of the flow and is compatible with the presence of multiple length scales dictated by the type of contacts instantaneous or long lasting between grains

proglacial deposition and deformation in the upper carboniferous to lower permian wynyard formation tasmania a process analysis abstract the wynyard formation of tasmania australia provides the youngest evidence of grounded ice during the late carboniferous early permian in the tasmania basin of southeastern gondwana during the late paleozoic ice age within the wynyard formation four facies associations are recognized 1 massive diamictite 2 stratified diamictite 3 conglomerate and sandstone and 4 deformed mudstone and fine sandstone a detailed facies analysis was performed in order to interpret the depositional processes and environments the massive diamictite facies association contains massive diamictite and sandstone and was deposited primarily by iceberg rain out in a subaqueous morainal bank setting the stratified diamictite facies association is composed of stratified diamictite sandstone and conglomerate and was deposited by debris flows and iceberg rain out and deformed by glacial pushing the conglomerate and sandstone facies association is made up of cross stratified channelized conglomerate and pebbly sandstone that were deposited by glacial outwash on grounding line fans the deformed mudstone and fine sandstone facies association is composed of pervasively deformed pebbly mudstone and fine grained sandstone that exhibit volcano flame and dyke structures this facies association was deposited by a combination of suspension settling iceberg rain out and soft sediment deformation in a quiet distal proglacial setting the facies analysis supports the interpretation that the wynyard formation was deposited by a wet based tidewater glacier or glaciers the depositing glacier s occupied a 40 km wide trough in northwest tasmania based on the distribution of the wynyard formation and the presence of glacial deposits in other eroded troughs in tasmania glaciation occurred in the region within broadly eroded valleys the wynyard formation and overlying mudstone of the inglis formation provide a glacial postglacial signature similar to those in south africa antarctica and eastern australia during the latest carboniferous early permian therefore the climate warmed in southern gondwana following this glacial interval the continued glaciation in eastern australia was a result of regional topography and oceanographic processes

response of the global ocean to greenland and antarctic ice melting 1 we investigate the transient response of the global ocean circulation to enhanced freshwater forcing associated with melting of the greenland and antarctic ice sheets increased freshwater runoff from greenland results in a basin wide response of the north atlantic on timescales of a few years communicated via boundary waves equatorial kelvin waves and westward propagating rossby waves in addition modified air sea interaction plays a fundamental role in setting up the basin scale response of the atlantic circulation in its subpolar and subtropical gyres in particular the modified ocean dynamics and thermodynamics lead to a depression in the central north and south atlantic that would not be expected from linear wave dynamics moreover the heat content increases on basin and global scales in response to anomalous freshwater forcing from greenland suggesting that the ocean s response to enhanced freshwater forcing would be a coupled problem other parts of the world ocean experience a much slower adjustment in response to greenland freshwater forcing communicated via planetary waves but also involving advective diffusive processes especially in the southern ocean over the 50 years considered here most of the sea level increase associated with freshwater input from greenland remains in the atlantic ocean in contrast ice melting around antarctica has a much reduced effect on the global ocean in both cases none of the basins came to a stationary state during the 50 year experiment

determining rheological parameters of debris flow material abstract a 2 0 m diameter steel 30 inverted cone and plate viscometer rheometer was designed constructed and used to test the behaviour of coarse grained debris flow materials a 1 5 scale model machine was also constructed and used to test the internal flow dynamics of the viscometer rheometer and to obtain results for fluids grain fluid mixtures and debris flow fines for fluids and grain fluid mixes our results were similar to those obtained earlier using standard viscometric systems derived rheological parameters for debris flow materials and clay slurries agreed well with those determined from calculation direct measurement and field observation apparent viscosities were shear rate dependent extremely sensitive to water content and as high as 6000 pa s instantaneous stresses within shearing debris flow material varied over a wide range debris flow materials with bimodal grain size distributions had a dilatant plastic rheology those with a low content of coarse material and unimodal grain size distribution or exceptionally high fines content had a plastic or viscoplastic rheology

depositional settings and evolution of a fjord system during the carboniferous glaciation in northwest argentina abstract fjord systems represented by glacial diamictites and postglacial transgressive shales formed in the basins of western argentina during the late carboniferous gondwana glaciation well exposed fjord deposits of the guandacol formation were studied in the loma de los piojos region protoprecordillera where they fill a 2 9 km wide paleovalley with steep side walls and a relatively flat floor the valley cross cuts lower devonian sandstones and mississippian mudstones and sandstones and provides evidence of glacial abrasion including striated pavements and glacial microtopography grooves ridges and striae based on the analysis of seven sedimentary logs eight sedimentary facies in the valley fill were recognized a massive diamictites b laminated mudstones with dropstones c stratified diamictites d clast supported conglomerates and sandstones e deformed diamictites conglomerates and sandstones f folded diamictites g mudstones interbedded with sandstones and h stacked and amalgamated sandstones these sedimentary facies are grouped into two principal facies assemblages that represent different stages of the paleovalley fill assemblage 1 is composed of diamictites facies a c and f laminated mudstones with dropstones facies b and conglomerates facies d and e which represent glacially influenced sedimentation in the paleovalley assemblage 2 represents the paleovalley fill when glacial influence ceased and comprises laminated mudstones interbedded with sandstones facies g and stacked sandstone beds facies h that mostly record deltaic sedimentation stratigraphic relationships plant fossils found in the paleovalley walls and palynological assemblages recovered in mudstones of facies d help to establish an early pennsylvanian age for both the incision and the filling of the paleovalley the studied paleovalley records an exceptional example of the western gondwanan glacial to postglacial transition due to the continuous stratigraphic succession within the paleovalley as well as palynological megafloristic and radiometric data this example provides a complete framework of the late carboniferous postglacial evolution in western gondwana

surficial patterns of debris flow deposition on alluvial fans in death valley ca using airborne laser swath mapping data debris flows are a common event in mountainous environments they often possess the greatest potential for destruction of property and loss of lives in these regions delimiting the spatial extent of potential damage from debris flows relies on detailed studies of the location of depositional zones current research indicates debris flow fans have two distinct depositional zones however the two zones were derived from studies containing detailed analyses of only a few fans high resolution airborne laser swath mapping alsm data is used to calculate profile curvature and surface gradient on 19 debris flow fans on the eastern side of death valley the relationship between these parameters is assessed to 1 identify if debris flow fans are accurately represented by two depositional zones and 2 to assess how these terrain parameters relate to one another at the individual fan scale the results show at least three zones of deposition exist within the sampled fans these zones do not hold consistent when individual fan morphometry is analyzed in conjunction with localized fan surface gradients fans with consistently shallower gradients exhibit numerous depositional zones with more subtle changes in profile curvature steeper gradient fans exhibit significantly fewer zones with more pronounced local changes in profile curvature the surface complexity of debris flow fans is evident from these analyses and must be accounted for in any type of hazard studies related to these features

field observations rheological testing and numerical modelling of a debris flow event debris flows generated from landslides are common processes and represent a severe hazard in mountain regions due to their high mobility and impact energy we investigate the dynamics and the rheological properties of a 90 000 m3 debris flow event triggered by a rapid regressive landslide with high water content field evidence revealed a maximum flow depth of 7 8 m with an estimated peak discharge of 350 400 m3 s 1 depositional evidence and grain size distribution of the debris pose the debris flow in an intermediate condition between the fluid mud and grain flow behaviour the debris flow material has silt clay content up to 15 per cent the rheological behaviour of the finer matrix was directly assessed with the ball measuring system the measurements performed on two samples at 45 63 per cent in sediment concentration by volume gave values of 3 5 577 pa for the yield strength and 0 6 27 9 pa s for the viscosity based on field evidence we have empirically estimated the yield strength and viscosity ranging between 4000 200 pa and 108 134 pa s respectively we used the flo 2d code to replicate the debris flow event we applied the model with rheological properties estimated by means of direct measurements and back analyses the results of these models show that the rheological behaviour of a debris flow mass containing coarse clasts can not be assessed solely on the contribution of the finer matrix and thus neglecting the effects of direct grain contacts for debris flows composed by a significant number of coarse clasts a back analysis estimation of the rheological parameters is necessary to replicate satisfactorily the depositional extent of debris flows in these cases the back estimated coefficients do not adequately describe the rheological properties of the debris flow copyright 2006 john wiley sons ltd

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

pleistocene debris flow deposition of the hippopotamus bearing collecurti bonebed macerata central italy taphonomic and paleoenvironmental analysis abstract an integrated taphonomic sedimentological study provides insight into the origin preservation biases and paleobiological significance of the latest early earliest middle pleistocene bonebed of collecurti near colfiorito macerata central italy which represents an important benchmark in the european biochronological scale sedimentological evidence indicates that the bonebed is hosted in a debris flow deposit which was emplaced in a shallow lacustrine setting geologic and geomorphic controls on sedimentation in the intermontane colfiorito basin provided an ideal setting for the development of cohesive mass flows due to high relief and poorly integrated catchments along the basin margin and the abundance of detrital fines yielded by mesozoic sedimentary rocks of the local basement the fossil assemblage includes 496 bones with a minimum of 24 individuals representing 9 species and 8 genera dominated by hippopotamus antiquus the hippopotamus remains include partially articulated carcass parts as well as closely associated elements few disarticulated elements which are bones that can be more easily transported hydraulically were involved in pre debris flow winnowing and sorting and then entrained by the debris flows in nearby uplands transported a short distance down into a shallow pond or lake margin where the flow buried hippopotamus carcasses that had accumulated in the pond lake the hippopotamus carcasses were in an advanced state of decomposition when the debris flow entrained them their bones show no evidence of weathering trampling scavenging sorting or transportation prior to debris flow reworking which indicates that the animals were probably lying on the bottom of the pond where they lived or were already partially buried in mud previous palynological investigations have shown that the strata of interest at collecurti were deposited during a climatic trend toward ever increasing cooler conditions the low richness of the fauna confirms long exposure to harsh climatic and environmental conditions two are the plausible causes of the death of the collecurti animals i e severe cold and or drought taphonomic attributes rule out drought indicating that the assemblage accumulated in a short time as the result of a mass mortality event possibly due to a cold snap there are no other reported examples of quaternary debris flow hosted bonebeds in europe probably because this agent of taphonomic accumulation is rarely investigated in high energy paleogeomorphic settings it is likely that more such sedimentary events took place in the area and that similar fossil sites await to be discovered

rheological properties of fine grained sediment the roles of texture and mineralogy rheological properties of fine grained sediments depending on index properties and salinity were examined to characterize flow behaviors as a function of soil type groups were made for convenienc

field observations of a debris flow event in the dolomites a debris flow event occurred in june 1997 in the dolomites eastern alps italy the phenomenon was directly observed in the field and recorded by a video camera near its initiation area the debris flow originated shortly after an intense rainstorm 25 mm in 30 min whose runoff mobilised the loose coarse debris that filled the bottom of the channel in its upper part the analysis of the steep headwater basin indicates a very short concentration time 9 14 min that fits the quick hydrological response observed in the field the debris flow mobilisation was not contemporaneous with the arrival of the peak water discharge in the initiation area probably due to the time required for the saturation of the highly conductive channel bed material channel cross section measurements taken along the flow channel indicate debris flow peak velocity and discharge ranging from 3 1 to 9 0 m s and from 23 to 71 m3 s respectively samples collected immediately after deposition were used to determine the water content and bulk density of the material channel scouring fines enrichment and transported volume increase testify erosion and entrainment of material along the flow channel field estimates of the rheological properties based on open channel flow of bingham fluid indicate a yield strength of 5000 400 pa and relatively low viscosity 60 326 pa s probably due to a high percentage of fines approx 30

laboratory analysis of mudflow properties a rotational viscometer has been designed for laboratory measurements of the rheological properties of natural mudflow deposits in colorado the mudflow matrices comprised of silt and clay particles are sheared under temperature controlled conditions at volumetric sediment concentrations ranging from 0 10 0 45 this study stresses the importance of conducting rheological measurements at low rates of shear because 1 those are the conditions found in natural channels and 2 they avoid the slippage problems observed at large sediment concentrations at low rates of shear the bingham model is fitted to the measured rheograms and both the viscosity and yield stress increase exponentially with the sediment concentration of the fluid matrix both the yield stress and the viscosity increase by three orders of magnitude as the volumetric concentration of sediments in the fluid matrix changes from 10 to 40 the addition of sand particles does not significantly alter the rheological properties of the matrix unless the volumetric concentration of sands exceeds 0 20

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

sediment mass flow processes on a depositional lobe outer mississippi fan abstract seamarc 1a sidescan sonar imagery and cores from the distal reaches of a depositional lobe on the mississippi fan show that channelized mass flow was the dominant mechanism for transport of silt and sand during the formation of this part of the fan sediments in these flows were rapidly deposited once outside of their confining channels the depositional lobe is formed of a series of long narrow sublobes composed of thin bedded turbidites normally graded siliciclastic sand and silt 20 cm thick on average debris flow deposits soft clay clasts up to 5 cm in diameter in a siliciclastic silt matrix 48 cm thick on average and background sedimentation hemipelagic muds the mass flows most likely originated from slope failure at the head of the mississippi canyon or on the outer ontinental shelf and flowed approximately 500 km to the distal reaches of the fan with debris flow being the dominant flow type an analysis that uses the geometry of the confining channels and strength properties of the debris flow material shows that these thin debris flows could have traveled hundreds of kilometers on extremely small sea floor slopes at low velocities if the flowing medium behaved as bingham fluids and were steady state phenomena

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

effects of debris flow composition on runout depositional mechanisms and deposit morphology in laboratory experiments predicting debris flow runout is of major importance for hazard mitigation apart from topography and volume runout distance and area depends on debris flow composition and rheology but how is poorly understood we experimentally investigated effects of composition on debris flow runout depositional mechanisms and deposit geometry the small scale experimental debris flows were largely similar to natural debris flows in terms of flow behavior deposit morphology grain size sorting channel width depth ratio and runout deposit geometry lobe thickness and width in our experimental debris flows is largely determined by composition while the effects of initial conditions of topography i e outflow plain slope and channel slope and width and volume are negligible we find a clear optimum in the relations of runout with coarse material fraction and clay fraction increasing coarse material concentration leads to larger runout however excess coarse material results in a large accumulation of coarse debris at the flow front and enhances diffusivity increasing frontal friction and decreasing runout increasing clay content initially enhances runout but too much clay leads to very viscous flows reducing runout runout increases with channel slope and width outflow plain slope debris flow volume and water fraction these results imply that debris flow runout depends at least as much on composition as on topography this study improves understanding of the effects of debris flow composition on runout and may aid future debris flow hazard assessments

strain signatures of fjord sediment sliding micro scale examples from yakutat bay and glacier bay alaska u s a abstract samples of gravity cores recovered from yakutat bay and glacier bay in southeast alaska were examined in thin section the samples representing rhythmically laminated plume deposits current derived silts and sands and iceberg rafted diamicts exhibit microstructures indicative of vertical deformation such as loading and water escape as well as boudinage and other features which are indicative of simple shear deformation narrow zones in many of the fine grained core intervals show subtle patterns of preferred clay mineral orientations plasmic fabrics we interpret these intervals as being low strain simple shear zones they all show a consistent and regular internal configuration that is formed by sets of conjugate shear planes the setting and conditions in the alaskan fjords allow the assumption that the shear zones are exclusively associated with penecontemporaneous movements of the unconsolidated sediment on subaqueous slopes analyzing characteristics and trends relating to symmetry and strain intensity we argue that these are diagnostic identifiers for sliding mass movements we present a conceptual model in which deformation resulting from gravity driven sliding is described we suggest that strain signatures can be used to recognize types of shear zones and be helpful in distinguishing between for example gravity driven deformation and subglacial deformation in sedimentary records

features and evolution of slip structures in badlands areas se spain abstract slips are little known mud coated structures several centimeters thick produced by gravity driven flows on free vertical surfaces we have differentiated a sequence formed by three main morphologies mud drips slips and pseudo stalactites this study located in the badlands of the guadix and baza basins se spain suggests that formation of muddy morphologies on subvertical walls is determined by the physico chemical characteristics of colloidal suspensions slurries related to rainy periods and does not indicate any substrate decay multiple braided microchannels internally structured like irregular book pages are commonly found each formed by mudflows during rainy episodes these morphologies constitute a temporary sink of fine erosive materials they consist of scarcely sorted mixtures of heterogeneous matter of a detrital cohesive nature with low clay contents which inherit the features of the parent materials the current semiarid environmental conditions appear to favor conservation rather than development the differences observed in the slips of the guadix and baza basins can be determined by the different geomorphological evolution of the two basins and to a lesser extent by the properties of the slurries that fed the slips

magnitude frequency relations in debris flow debris flow occurs frequently in mountainous regions in china because of the difficulties involved in predicting and catching live debris flows an assessment of the potential for debris flow is crucial in hazard mitigation magnitude frequency mf relations are of special significance in such assessments in previous studies mf relations have been inferred by analyzing environmental factors and historical records and using empirical relations this paper is concerned with the derivation of mf relations at regional and valley scales using a large database of statistics at the regional scale it is represented by the distribution of the valley area because the area is often taken to indicate the potential magnitude of debris flow statistics from over 5 000 debris flow valleys in various provinces in china show that a power law holds for the distribution i e p a a n where p a is the percentage of valleys with area a and n varies with region and thus describes regional differences at the valley scale a case study focusing on jiangjia gully jjg was conducted and the mf relations derived from it were expressed by the distributions of discharge and runoff i e the total volume of living debris flows observed over the last 40 years the distributions can be expressed as exponential functions where the exponents vary with the events these mf relations provide not only a potential quantitative reference for practical purposes but also hint at the intrinsic properties of the debris flow

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

the perfect debris flow aggregated results from 28 large scale experiments 1 aggregation of data collected in 28 controlled experiments reveals reproducible debris flow behavior that provides a clear target for model tests in each experiment 10 m3 of unsorted water saturated sediment composed mostly of sand and gravel discharged from behind a gate descended a steep 95 m flume and formed a deposit on a nearly horizontal runout surface experiment subsets were distinguished by differing basal boundary conditions 1 versus 16 mm roughness heights and sediment mud contents 1 versus 7 percent dry weight sensor measurements of evolving flow thicknesses basal normal stresses and basal pore fluid pressures demonstrate that debris flows in all subsets developed dilated coarse grained high friction snouts followed by bodies of nearly liquefied finer grained debris mud enhanced flow mobility by maintaining high pore pressures in flow bodies and bed roughness reduced flow speeds but not distances of flow runout roughness had these effects because it promoted debris agitation and grain size segregation and thereby aided growth of lateral levees that channelized flow grain size segregation also contributed to development of ubiquitous roll waves which had diverse amplitudes exhibiting fractal number size distributions despite the influence of these waves and other sources of dispersion the aggregated data have well defined patterns that help constrain individual terms in a depth averaged debris flow model the patterns imply that local flow resistance evolved together with global flow dynamics contradicting the hypothesis that any consistent rheology applied we infer that new evolution equations not new rheologies are needed to explain how characteristic debris flow behavior emerges from the interactions of debris constituents

recognition classification and mechanical description of debris flows abstract various types of flow or mass movement involving water and sediments occur on steep slopes in mountainous areas among them debris flows are peculiar events during which a large volume of a highly concentrated viscous water debris mixture flows through a stream channel throughout the world these phenomena cause considerable damage but remain poorly understood although a basic knowledge is already available concerning their recognition and propagation firstly a synthesis of the useful practical criteria of recognition is proposed debris flows must be seen as intermediate phenomena between hyperconcentrated flows intense bed load transport and landslides separated from them by sharp transitions of some characteristics celerity deposit nature and flow type two parameters solid fraction and material type thought to be appropriate for a sound and practical classification are brought out and the corresponding complete classification of flow and mass movements in mountain areas is presented two extreme debris flow types are thus distinguished muddy debris flows and granular debris flows a critical review of recent advances in debris flow dynamic is then proposed it is pointed out that adequate work must be carried out in the field of non newtonian fluid mechanics in particular one fundamental rheological property of debris flow materials is the yield stress which explains thick deposits on steep slopes and can be inferred from field measurements furthermore it can be used to estimate viscous dissipation within the bulk during flow relevant models predicting muddy debris flow dynamics are already available whereas further progress is needed concerning granular flows

downstream coarsening in headwater channels 1 field data from four mountain drainage basins in western washington document systematic downstream coarsening of median bed surface grain size d50 and a subsequent shift to downstream fining at a drainage area of about 10 km2 analyses of network wide patterns of unit stream power derived from both channel surveys and digital elevation models reveal maximum unit stream power that in all four study areas roughly corresponds with both the grain size maxima and an inflection in the drainage area slope relation thought to represent the transition from debris flow dominated channels to fluvially dominated channels our results support the hypothesis that basin wide trends in d50 are hydraulically controlled by systematic variations in unit stream power in addition to lag deposits forced by mass wasting processes the similar relations found in our four study areas suggest that the tendency for downstream coarsening may be ubiquitous in headwater reaches of mountain drainage basins where debris flow processes set the channel gradient

geotechnical and rheological characteristics of waste rock deposits influencing potential debris flow occurrence at the abandoned imgi mine korea mass movements associated with abandoned mines are dangerous and destructive local communities near abandoned mine sites are often threatened by the effect of extreme precipitation events on these sites in this study the geotechnical and rheological characteristics of mine deposits were examined to delimit the hazardous areas near abandoned mines waste rock materials were collected from a pyrophyllite mine deposit in the mountainous region of korea and a sieve analysis was performed to determine the grain size distribution the yield stress in the debris flow modeling was determined using fall cone and rheometric tests rheological tests were performed on materials finer than 4 75 mm using a ball measuring system rheometer these samples were mainly composed of gravels and sands with small clay content the waste materials typically exhibited a shear thinning behavior within a given shear rate ranging between 10 5 and 102 s 1 the yield stresses obtained from the rheometric tests agreed well with those obtained from the fall cone tests for the input parameter we selected the yield stresses ranging from 100 to 500 pa as a case study the debris flow mobility associated with the abandoned mine was examined using a one dimensional flow dynamic model the runout distance and velocity of the waste materials are strongly dependent on the yield stress both factors significantly increase with decreasing yield stress however even under the highest yield stress i e 500 pa the failed mass can flow into the mountain stream thus the physico chemical contaminations of areas downslope of abandoned mines may be unavoidable with respect to extreme rainfall events

mid carboniferous deglaciation of the protoprecordillera argentina recorded in the agua de jaguel palaeovalley abstract the agua de jaguel formation near uspallata mendoza province argentina was deposited within a palaeovalley along the southeastern margin of the calingasta uspallata basin adjacent to the protoprecordillera the basal glacigenic sequence of the formation was deposited in the serpukhovian early bashkirian near the beginning of the late palaeozoic ice age the sequence is composed of diamictite conglomerate sandstone and mudrock and records four depositional stages within a palaeofjord 1 morainal bank deposition by a wet based tidewater glacier 2 glacial retreat succession where ice retreated up the fjord out of the immediate area allowing iceberg deposition of dropstones and dump deposits 3 continued glacial retreat with ice receding onto land allowing a shoreface to develop within the palaeovalley and 4 transgression across the shoreface and resumption of iceberg deposition the thickness and facies of this succession are similar to deposits within modern alaskan fjords housing temperate tidewater glaciers comparison of the agua de jaguel formation with alaskan fjords indicates that sequence stratigraphy used for low latitude deposits must be applied with caution as glacimarine ice retreat within a fjord produces strata surfaces that are easily misidentified as flooding surfaces resulting from changes in water depth likewise the transgression during stage 4 is significant as it indicates a rise in sea level that occurred during glaciation of the protoprecordillera thus suggesting that the transgression between stages 3 and 4 was not driven by input of glacial meltwater additionally the sediment geochemistry suggests that the bottom waters of the palaeovalley were anoxic which may help explain the absence of bioturbation in the sequence as well as in other ancient glacimarine palaeovalleys the deglaciation succession and transgression are also recorded in the nearby hoyada verde and tramojo formations so it is proposed that all three formations record one glacial event in the protoprecordillera overlying fluvial and shallow marine strata in the agua de jaguel hoyada verde and tramojo formations show no indication of continued glaciation in the protoprecordillera following stage 4 and equivalent strata the deglaciation succession of the agua de jaguel formation affirms the emerging concept that the late palaeozoic ice age was characterized by alpine glaciers ice caps and small ice sheets that were not massive enough to have driven eustatic fluctuations of 100 m as previously understood and that ice never covered westernmost gondwana during later lpia events

sedimentary and tectonic history of the holowilena ironstone a neoproterozoic iron formation in south australia abstract the holowilena ironstone is a neoproterozoic iron formation in south australia associated with glacial deposits of the sturtian glaciation through a comprehensive field study coupled with optical and scanning electron microscopy x ray fluorescence and x ray diffraction a detailed description of the stratigraphy sedimentology mineralogy and structure of the holowilena ironstone was obtained the holowilena ironstone comprises ferruginous shales siltstones diamictites and is largely made up of hematite and jasper early diagenetic replacement minerals of precursor iron oxyhydroxides and silica these chemical precipitates are variably influenced by turbidites and debris flows contributing clastic detritus to the depositional system structural and stratigraphic evidence suggests deposition within a synsedimentary half graben a model for the holowilena ironstone is proposed in which dense oxic fluids expelled during sea ice formation in the cryogenian pool in the depression of the half graben allowing for long lived mixing with the ferruginous seawater and the deposition of iron oxides this combination of glacial dynamics tectonism and ocean chemistry may explain the return of iron formations in the neoproterozoic

an integrated analysis of the march 2015 atacama floods in march 2015 unusual ocean and atmospheric conditions produced many years worth of rainfall in a 48 h period over northern chile s atacama desert one of earth s driest regions resulting in catastrophic flooding here we describe the hydrologic and geomorphic drivers of and responses to the 2015 atacama floods in the salado river we estimated a flood peak discharge of approximately 1000 m3 s which caused widespread damage and high sediment loads that were primarily derived from valley fill erosion hillslopes remained surprisingly intact despite their lack of vegetation in the coastal city of chanaral flooding of the salado river produced maximum water depths over 4 5 m meters thick mud deposition in buildings and along city streets and coastal erosion the atacama flooding has broad implications in the context of hazard reduction erosion of contaminated legacy mine tailings and the atacama s status as a terrestrial analog for mars

illuminating the plate interface structure beneath cook strait new zealand with receiver functions 1 using teleseismic receiver functions derived from broadband seismic arrays on the north end of the south island and south end of the north island of new zealand we image seismic impedance discontinuities in the upper mantle beneath cook strait using common conversion point ccp and kirchhoff migration methods our primary findings are observations of discontinuities associated with the top of the subducting pacific plate our results suggest that contrary to recent suggestions the plate is continuous under the northern south island through the region of seismicity deeper than 50 km west of cook strait the slab dips steeply to the northwest we find evidence for a low velocity layer at the top of the slab near which much of the seismicity is concentrated we see hints of two crustal discontinuities consistent with observations from previous studies we also see substantial and continuous energy on the transverse receiver function stacks above the mantle wedge extending to the northwestern edge of our stacks which may indicate seismic anisotropy above 50 km depth

applicability of power law for describing the rheology of soils of different origins and characteristics the rate dependent rheological behaviour of soils of different origins and characteristics was studied and the applicability of the power law model was examined the studied soils were divided into

experimental study of the grain flow fluid mud transition in debris flows abstract we have performed a series of laboratory experiments that clarify the nature of the transition between fluid mud and grain flow behavior the surface velocity structure and the speed of the nose of debris flows in channels with semicircular cross sections were measured with several cameras and visual tracers while the mass flow rate was recorded using a load cell at the exit chamber other rheological tests were used to calculate independently the yield strength and matrix viscosity of the debris flow mixture shear rates were varied by nearly an order of magnitude for each mixture by changing the channel radius and slope shear rates were significantly higher than expected 6 55 s 1 given the modest slopes examined 10 7 15 2 the large values were primarily a result of the concentration of shear into narrow bands between a central nondeforming plug and the sidewall as a result the shear rate of interest was calculated by using the width of the shear band and the plug velocity as oppose

analysis of a spectrally unique deposit in the dissected noachian terrain of mars 1 we have analyzed a spectrally anomalous dark intracrater deposit and an adjacent lighter toned fan shaped deposit in the dissected noachian terrain of mars using a combination of high spatial and spectral resolution remote sensing data sets the spatial proximity of these two deposits and their dust free spectral character make these prime targets for 1 determining whether the dark toned deposit is derived from the fan shaped deposit and 2 constraining the nature and mineralogy of the fan shaped deposit stereo observations and derived digital elevation models of the of the fan shaped deposit show a set of three flows lobes calculations of the yield strength based on morphometry of the lobes indicate yield strengths consistent with those of other volcanic flows on mars although an aqueous origin cannot be discounted the dark deposit consists of a mantle that forms dunes at its thickest portions and extends as a thinner veneer we find no obvious morphologic association between the dark deposit and adjacent fan multispectral imaging from the themis vis and ir instruments show that the two deposits have different spectral characteristics probably caused by differences in their mineralogy rather than their physical properties finally modeling of mgs tes spectra of the combined deposits indicates a feldspar rich composition that is possibly complemented by smaller quantities of alteration products such as carbonates and possibly sulfates and clays these results indicate that 1 there is no association between these deposits and 2 the combined deposits have a primarily igneous mineralogy although some aqueous alteration may have occurred

depositional processes in large scale debris flow experiments this study examines the depositional process and characteristics of deposits of large scale experimental debris flows to 15 m3 composed of mixtures of gravel to 32 mm sand and mud the experiments were performed using a 95 m long 2 m wide debris flow flume that slopes 31 following release experimental debris flows invariably developed numerous shallow 10 cm deep surges sediment transported by surges accumulated abruptly on a 3 runout slope at the mouth of the flume deposits developed in a complex manner through a combination of shoving forward and shouldering aside previously deposited debris and through progressive vertical accretion progressive accretion by the experimental flows is contrary to commonly assumed en masse sedimentation by debris flows despite progressive sediment emplacement deposits were composed of unstratified accumulations of generally unsorted debris hence massively textured poorly sorted debris flow deposits are not emplaced uniquely en masse the depositional

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

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