temporal relations between meander deformation water discharge and sediment fluxes in the floodplain of the rio beni bolivian amazonia the andean cordillera and piedmont significantly influence river system and dynamics being the source of many of the important rivers of the amazon basin the beni river whose upper sub catchments drain the andean and sub andean ranges is a major tributary of the madeira river this study examines the river in the south western amazonian lowlands of bolivia where it develops mobile meanders channel migration meander bend morphology and ox bow lakes are analysed at different temporal and spatial scales the first part of this study was undertaken with the aim to link the erosion deposition processes in the active channel with hydrological events the quantification of annual erosion and deposi tion areas shows high inter annual and spatial variability in this study we investigate the conditions of sediment exportation in the river in relation to three hydrological parameters flood intensity date of discharge peak and duration of the bank full stage level the second part of this study focusing on the abandoned meanders analyses the cutoff processes and the post abandonment evolution during 1967 2001 this approach shows the influence of the active channel behaviour on the sediment diffusion and sequestration of the abandoned meanders and allows us to build a first model of the contemporary floodplain evolution

mobility of pyroclastic flows and surges at the soufriere hills volcano montserrat the soufriere hills volcano on montserrat has produced avalanche like pyroclastic flows formed by collapse of the unstable lava dome or explosive activity pyroclastic flows associated with dome collapse generate overlying dilute surges which detach from and travel beyond their parent flows the largest surges partially transform by rapid sedimentation into dense secondary pyroclastic flows that pose significant hazards to distal areas different kinds of pyroclastic density currents display contrasting mobilities indicated by ratios of total height of fall h run out distance l area inundated a and volume transported v dome collapse flow mobilities characterised by either l h or a v2 3 resemble those of terrestrial and extraterrestrial cold rockfalls dade and huppert 1998 in contrast fountain fed pumice flows and fine grained secondary pyroclastic flows travel slower but for comparable initial volumes and heights can inundate greater areas

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

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

the 15 september 1991 pyroclastic flows at unzen volcano japan a flow model for associated ash cloud surges large scale collapse of a dacite dome in the late afternoon of 15 september 1991 generated a series of pyroclastic flow events at unzen volcano pyroclastic flows with a volume of 1 106 m3 as dre descended the northeastern slope of the volcano changing their courses to the southeast due to topographic control after they exited a narrow gorge an ash cloud surge rushed straight ahead detaching the main body of the flow that turned and followed the topographic lows to the east the surge swept the kita kamikoba area which had been devastated by the previous pyroclastic flow events and transported a car as far as 120 m following detachment the surge lost its force after it moved several hundred meters but maintained a high temperature the deposits consist of a bottom layer of better sorted ash unit 1 a thick layer of block and ash unit 2 and a thin top layer of fall out ash unit 3 unit 2 overlies unit 1 with an erosional contact the upper part of unit 2 grades into better sorted ash at distal block and ash flow deposits the bottom part of unit 2 also consists of better sorted ash and the contact with the unit 1 deposits becomes ambiguous video footage of cascading pyroclastic flows during the 1991 1995 eruption traveling over surfaces without any topographic barriers revealed that lobes of ash cloud protruded intermittently from the moving head and sides and that these lobes surged ahead on the ground surface this fact together with the inspection by helicopter shortly after the events suggests that the protruded lobes consisted of better sorted ash and resulted in the deposits of unit 1 the highest ash cloud plume at the oshigadani valley exit and the thickest deposition of fall out ash over kita kamikoba and ohnokoba indicate that abundant ash was also produced when the flow passed through a narrow gorge in the model presented here the ash clouds from the pyroclastic flows were composed of a basal turbulent current of high concentration main body an overriding and intermediate fluidization zone and an overlying dilute cloud release of pressurized gas in lava block pores due to collisions among blocks and the resulting upward current caused a zone of fluidization just above the main body the mixture of gas and ash sorted in the fluidization zone moved ahead and to the side of the main body as a gravitational current where the ash was deposited as surge deposits the main body which had high internal friction and shear near its base then overran the surge deposits partially eroding them when the upward current of gas fluidization waned better sorted ash suspended in the fluidization zone was deposited on block and ash deposits in the distal places of block and ash deposits unit 2 probably was deposited in non turbulent fashion without any erosion of the underlying layer unit 1

origin and mode of emplacement of lithic rich breccias at aso volcano japan geological paleomagnetic and petrological reconstruction abstract takajosan breccia rocks are distributed around the southwestern caldera rim of the aso volcano in japan they are characterized by coarse lithic breccias with a pumiceous matrix the proximal coarse lithic breccias are divided into the lower massive unit and the upper stratified unit the lower massive lithic breccias tend to transform laterally into tuff breccias and pumiceous lapilli tuffs paleomagnetic results showed that all of the deposits were deposited at high temperatures of 175 560 c this was also supported by geological characteristics such as spatter clasts clasts with a bread crust texture and weakly welded parts these features clearly show that the deposits originated from pyroclastic density currents pdcs the dense lithic rich lithofacies low vesicularity of pumice lack of plinian fall deposits and radial distribution indicate that the deposits were derived from boil over pdcs rather than plinian column collapse pdcs the sio2 contents of the matrix glasses of the proximal lower massive breccia showed a progressive decrease from the bottom toward the upper part we interpret that this chemical variation corresponds to chemical zonation of the magma chamber this indicates that the massive deposits aggraded progressively from the base upwards progressive aggradation rather than through en masse freezing the vertical lithofacies changes of the proximal breccias from the lower massive to the upper stratified units indicate that a sustained current in a quasi steady state switched to an unsteady current with the progression of the volcanic activity

how do gravel bed rivers braid sedimentary processes and bed forms leading to the onset of braiding were observed in small scale hydraulic models of gravel bed streams the laboratory streams had a variety of combinations of constant discharge and slope but identical bed material particle size distributions from initially straight channels braiding occurred by four different processes deposition and accumulation of a central bar chute cutoff of point bars conversion of single transverse unit bars to mid channel braid bars and dissection of multiple bars in these experiments the chute cutoff mechanism was the most common but the predominant braiding mechanism depends upon sediment mobility excess bed shear stress and the bed form regime at very low excess bed shear stress the central bar process dominates but at higher excess bed shear stress slip face unit bars are more common bed scour at confluences is more pronounced and propogation of alternate convergence scour and divergence deposition is more likely thus chu

generation of block and ash flows at the onset of silicic volcanism in the parana magmatic province brazil evidence from photoanalysis of caxias do sul breccias in this work we perform textural analysis on volcanic breccias related to the silicic magmatism in the region of sao marcos southern brazil parana magmatic province the breccias are matrix supported coarse grained poorly sorted with angular to rounded fragments in a fine grained matrix juvenile fragments are dense to pumiceous massive to banded dacites lithic fragments were not recognised the analyses were performed on field photographs grain size distribution gsd analysis showed maximum fragment sizes between 8 and 9 5 and smallest recognised sizes between 3 and 1 5 due to the spatial resolution limit of the photographs and the weathered condition of the matrix the fine fragments from the matrix were not analysed the gsd fractality could be quantified by a single power law with low moderate d values of 1 9 2 3 vesicle size distribution vsd and shape parameters of both fragments and vesicles were also measured the fragments are typically low vesicularity with median vesicle area fractions around 5 for all samples but pumiceous fragments with up to 43 area are found vsds exhibit single exponential concave upwards curves with vesicles becoming more deformed complex with increasing size suggesting a single continuous process of nucleation and growth under low degrees of shear regarding the fragments shape parameters all samples have high values of solidity which together with the low vesicularity of the fragments suggest brittle fragmentation of poorly vesicular material and the operation of secondary fragmentation processes during transport that round and smooth the clasts however field evidence for local conduit systems together with the gsd fractality suggest that these may be proximal deposits without substantial transport history based on a comparison of the deposits characteristics with several types of volcanic breccias we propose a block and ash flow source for these breccias that indicate the presence of nearby lava domes providing evidence for high viscosity low flux dacitic volcanism in the parana magmatic province

emplacement mechanisms of contrasting debris avalanches at volcan mombacho nicaragua provided by structural and facies analysis we study the lithology structure and emplacement of two debris avalanche deposits dads with contrasting origins and materials from the quaternary holocene mombacho volcano nicaragua a clear comparison is possible because both dads were emplaced onto similar nearly flat 3 slope topography with no apparent barrier to transport this lack of confinement allows us to study in nature the perfect case scenario of a freely spreading avalanche in addition there is good evidence that no substratum was incorporated in the events during flow so facies changes are related only to internal dynamics mombacho shows evidence of at least three large flank collapses producing the two well preserved debris avalanches of this study one on its northern flank las isletas directed northeast and the other on its southern flank el crater directed south other south eastern features indicate that the debris avalanche corresponding to the third collapse la danta occurred before las isletas and el crater events the materials involved in each event were similar except in their alteration state and in the amount of substrata initially included in the collapse while el crater avalanche shows no signs of substratum involvement and has characteristics of a hydrothermal weakening related collapse the las isletas avalanche involves significant substratum and was generated by gravity spreading related failure the latter avalanche may have interacted with lake nicaragua during transport in which case its run out could have been modified through a detailed morphological and structural description of the mombacho avalanches we provide two contrasting examples of non eruptive volcanic flank collapse we show that remarkably even with two distinct collapse mechanisms the debris avalanches developed the same gross stratigraphy of a coarse layer above a fine layer this fine layer provided a low friction basal slide layer whereas dad layering and the run outs are roughly similar the distribution of structures is different and related to lithology las isletas has clear proximal faults replaced distally by inter hummock depressions where basal unit zones are exhumed whereas el crater has faults throughout but the basal layer is hidden in the distal zone hummocky forms depend on material type with steep hummocks being formed of coherent lava units and low hummocks by matrix rich units in both avalanches extensional structures predominate the upper layers exclusively underwent longitudinal and lateral extension this is consistent with evidence of only small amounts of block to block interactions during bulk horizontal spreading the base of the moving mass accommodated transport by large amounts of simple shear we suggest that contractional structures and inter block collisions seen in many other avalanches are artifacts related to topographic confinement

sedimentology and geomorphology of the deposits from the august 2006 pyroclastic density currents at tungurahua volcano ecuador the deposits of the pyroclastic density currents from the august 2006 eruption of tungurahua show three facies associations depending on the topographic setting the massive proximal cross stratified and distal cross stratified facies 1 the massive facies is confined to valleys on the slopes of the volcano it contains clasts of 1 m diameter to fine ash material is massive and interpreted as deposited from dense pyroclastic flows its surface can exhibit lobes and levees covered with disk shaped and vesicular large clasts these fragile large clasts must have rafted at the surface of the flows all along the path in order to be preserved and thus imply a sharp density boundary near the surface of these flows 2 the proximal cross stratified facies is exposed on valley overbanks on the upper part of the volcano and contains both massive coarse grained layers and cross stratified ash and lapilli bedsets it is interpreted as deposited from a dense pyroclastic flows that overflowed the gentle ridges of valleys of the upper part of the volcano and b dilute pyroclastic density currents created from the dense flows by the entrainment of air on the steep upper flanks 3 the distal cross stratified facies outcrops as spatially limited isolated and wedge shaped bodies of cross stratified ash deposits located downstream of cliffs on valleys overbanks it contains numerous aggrading dune bedforms whose crest orientations reveal parental flow directions a downstream decrease in the size of the dune bedforms together with a downstream fining trend in the grain size distribution are observed on a 100 m scale this facies is interpreted to have been deposited from dilute pyroclastic density currents with basal tractional boundary layers we suggest that the parental flows were produced from the dense flows by entrainment of air at cliffs and that these diluted currents might rapidly deposit through pneumatic jumps three modes are present in the grain size distribution of all samples independently of the facies which further supports the interpretation that all three facies derive from the same initial flows this study emphasizes the influence of topography on small volume pyroclastic density currents and the importance of flow transformation and flow stripping processes

stratigraphic architecture of an experimental basin with interacting drainages abstract the stratigraphic architecture of intracontinental rift basins is defined by a dynamic relationship between depositional processes associated with the basin floor and flanking tributary streams the resulting depositional belts are sensitive to a variety of factors including basin geometry subsidence rate and sediment discharge the experimental earthscape run in 2006 xes06 examined the development of fluvial morphology and alluvial architecture as a function of subsidence and sediment flux in an experimental basin based on the form of a simple half graben sediments from tributary drainages were introduced into the axial stream through toe cutting and realignment of transverse drainage courses to parallel the prevailing axial flow direction transverse sediment contributions to the axial stream were almost equally apportioned over a wide range of sediment discharges tested in the experiments sediment tracers showed a larger contribution of footwall derived sediment into the axial belt probably due to more frequent and aggressive toe cutting by axial streams changes in the axial transverse deposit boundary to external forcing by subsidence and sediment discharge and relatively rapid intrastage stabilization of the depositional belts resembles the large scale self organization observed in moving boundaries that define the morphology of fluviodeltaic systems basin sedimentation was matched to subsidence in order to maintain a constant base level which made the location and width of the axial belt sensitive to the relative sediment fluxes from the transverse systems rather than the axis of maximum subsidence the asymmetrical subsidence pattern and the transverse fan morphology influenced the preservation of sedimentary sequences stage bounding stratigraphic lacunae were well preserved in the hanging wall succession providing a reliable record of basin development

deposit temperature of pyroclastic density currents emplaced during the el chichon 1982 and colima 1913 eruptions new data on the pyroclastic density current pdc deposit temperature t dep are provided for two prominent eruptions of mexican volcanoes of the twentieth century the 1982 eruption of el chichon and the 1913 eruption of colima in spite of similar lithofacies magma composition and pre eruptive conditions the t dep of the pdcs from the 1982 el chichon and 1913 colima eruptions differ significantly with intervals of t dep of 360 420 c and 250 330 c respectively these new data emphasize that a full understanding of the physical mechanisms responsible for equilibrium temperature attainment within a pyroclastic deposit has not yet been realized the t dep measured for el chichon pdc deposits confirm the preliminary data published elsewhere while colima magnetic temperatures provide different values to those published previously

parallel adaptive numerical simulation of dry avalanches over natural terrain high fidelity computational simulation can be an invaluable tool in planning strategies for hazard risk mitigation the accuracy and reliability of the predictions are crucial elements of these tools being successful we present here a new simulation tool for dry granular avalanches using several new techniques to create a highly accurate tool with a combination of good models and numerical methodologies highlights of our methodology are the use of a depth averaged model of the conservation laws and an adaptive grid godunov solver to solve the resulting equations the software is designed to run on distributed memory supercomputers and make use of digital elevation data dynamically i e refine the grid and input data to finer resolutions to better capture flow features as the flow evolves our simulations are validated using quantitative and qualitative comparisons to tabletop experiments and data from field observations our software is freely available and can be used on a range of hardware from inexpensive desktop computers to the largest supercomputers

effect of grain size on mobility of dry granular flows of angular rock fragments an experimental determination abstract rapid mass movements of rock fragments are among the most hazardous natural phenomena they are too dangerous to be approached and studied directly and for this reason experiments are necessary to understand their flow mechanisms here we present the results of experiments on granular flow mobility obtained releasing batches of angular rock fragments down a curved chute our experiments demonstrate that the finer the grain size of the flow the larger its mobility this is accompanied by a decrease of fragments agitation when grain size decreases as shown by particle image velocimetry measurements of high speed video camera images the smaller the agitation the smaller is also the energy dissipated by flows per unit of travel distance this explains the effect of finer grain size on flow mobility these results are an important step towards the prediction of runout distances as a function of the features that characterize the different geophysical flows

the 1902 peleean deposits in the fort cemetery of st pierre martinique a model for the accumulation of turbulent nuees ardentes abstract the ancient fort cemetery located at the northwestern limit of st pierre has been left undisturbed since 1902 and therefore offers a unique opportunity to study the deposits of the eruptions that destroyed the city six eruption units were found overlying the floor of the cemetery leaving an average 1 6 m thick deposit the city was hit by four major nuees which occurred on may 8 20 june 6 and august 30 the may 20 and june 6 eruption units are each made of three beds the basal bed always lacks fines and is generally massive the middle bed is normally graded on which dune type cross bedding is superimposed in the may 20 deposit the upper bed the thinnest has the finest grain size of the eruption unit and is normally graded true parallel laminae were only observed in the upper bed the may 8 eruption unit is essentially made of fines depleted massive lapilli and tuff the evidence strongly suggests that the deposits of the middle and upper beds accumulated from turbulent suspensions the absence of structures in the basal bed is not conclusive evidence of laminar flow deposition and its characteristics are similar to deposits that have accumulated from highly concentrated turbulent suspensions the lack of fines observed only in the basal bed is attributed to gravity segregation helped by vaporization of water present in the underlying deposits and for the may 8 deposit to escaping gas produced by the destruction of the vegetation during or immediately after deposition which could explain the absence of primary structures in the basal bed the fine grained deposits of mt pelee show a primary structure sequence similar to the turbidite sequence and are therefore interpreted in terms of decreasing flow velocity and grain size with time at a fixed site

the anatomy of a pyroclastic density current the 10 july 2015 event at volcan de colima mexico pyroclastic density currents pdcs represent one of the most dangerous phenomena occurring in explosive volcanic eruptions and any advance in the physical understanding of their transport and sedimentation processes can contribute to improving their hazard assessment the 10 11 july 2015 eruption at volcan de colima provided a unique opportunity to better understand the internal behaviour of pdcs based on seismic monitoring data on 10 july 2015 the summit dome collapsed producing concentrated pdcs that filled the main channel of the montegrande ravine a lahar monitoring station installed 6 km from the volcano summit recorded a pdc before being completely destroyed real time data acquisition from a camcorder and a geophone that were part of the station along with field observations and grain size data of the pyroclastic deposits are used here to interpret the internal flow structure and time variant transport dynamics of low volume valley confined concentrated pdcs the pdc that reached the monitoring station moved at a velocity of 7 m s and filled a 12 m deep channel the outcrops show massive block and ash flow deposits with trains of coarse clasts in the middle and towards the top of the depositional units the seismic record gathered with the geophone was analysed for the time window when the flow travelled past the sensor the geophone record was also compared with the recordings of a broadband seismic station located nearby two main frequency ranges were recognised which could be correlated with the basal frictional forces exerted by the flow on the channel bed 10 20 hz and a collisional regime 20 40 hz interpreted to be associated with a clast segregation process i e kinematic squeezing this latter regime promoted the upward migration of large blocks which subsequently deviated towards the margin of the flow where they interacted with the sidewall of the main channel the energy calculated for both seismic components shows that the collisional regime represents 30 of the total energy including an important sidewall stress component these results gathered directly from a moving flow contribute to unravelling the internal behaviour of concentrated pdcs providing information on energy partitioning and particle particle interactions this confirms previous assumptions inferred from field observations and tested by analogue or numerical modelling the nature of the contact between grains is still poorly documented in natural pdcs and there is still much uncertainty and discussion about dominant forces in such currents data reported here may thus be useful to better constrain the physics of low volume valley confined concentrated pdcs and our findings need to be considered in theoretical models in parallel this study shows how geophones can provide a cheap alternative for pdc detection

computer assisted image analysis on clast shape fabric from the orvieto bagnoregio ignimbrite vulsini district central italy implications on the emplacement mechanisms abstract computer assisted image analysis can be succesfully used to derive quantitative information about grain size distribution particle shape and fabric on both consolidated and unconsolidated solid aggregates we have developed a new analytical method that provides a series of quantitative textural parameters from whatever particulate deposits by combining commercial image acquisition system with devoted c software after exhaustive tests of the method we applied it to a widespread quaternary ignimbrite formation in central italy the orvieto bagnoregio formation the results suggest some new aspects of emplacement mechanisms of ignimbrites 1 elongated particles shows variable degrees of flow related preferred orientation both on horizontal and vertical planes 2 vertical variations of flow related preferred particle orientations follow a zig zag pattern that we interpret to result from deposition by progressive aggradation during the passage of a particulate flow the filling up of paleovalleys by means of progressive aggradation proceeds flank to flank due to alternating flow directions induced by the already deposited material 3 the occurrence of vertically spaced peaks on the strength of clast orientation suggests the existence of discrete depositional units deposited by aggradation from an unsteady but persisting flow strong fabrics are inferred to result from the high amount of shear stress imparted to particles at the depositional boundary layer which at the same time can be responsible for the development of the basal inversely graded layer image analysis can also provide useful indications of paleoflow directions paleotopographic details and ignimbrite source areas

pyroclastic flows generated by gravitational instability of the 1996 97 lava dome of soufriere hills volcano montserrat numerous pyroclastic flows were produced during 1996 97 by collapse of the growing andesitic lava dome at soufriere hills volcano montserrat measured deposit volumes from these flows range from 0 2 to 9 106 m flows range from discrete single pulse events to sustained large scale dome collapse events flows entered the sea on the eastern and southern coasts depositing large fans of material at the coast small runout distance 1 km flows had average flow front velocities in the order of 3 10 m s while flow fronts of the larger runout distance flows up to 6 5 km advanced in the order of 15 30 m s many flows were locally highly erosive field relations show that development of the fine grained ash cloud surge component was enhanced during the larger sustained events periods of elevated pyroclastic flow productivity and sustained dome collapse events are linked to pulses of high magma extrusion rates

interaction between meander dynamics and floodplain heterogeneity in a large tropical sand bed river the rio beni bolivian amazon the evolution of meandering river floodplains is predominantly controlled by the interplay between overbank sedimentation and channel migration the resulting spatial heterogeneity in floodplain deposits leads to variability in bank erodibility which in turn influences channel migration and planform development despite the potential significance of these feedbacks few studies have quantified their impact upon channel evolution and floodplain construction in dynamic settings e g locations characterized by rapid channel migration and high rates of overbank sedimentation this study employs a combination of field observations geographic information system gis analysis of satellite imagery and numerical modelling to investigate these issues along a 375 km reach of the rio beni in the bolivian amazon results demonstrate that the occurrence of clay rich floodplain deposits promotes a significant reduction in channel migration rates and distinctive styles of channel evolution including channel straightening and immobilization of bend apices leading to channel narrowing clay bodies act as stable locations limiting the propagation of planform disturbances in both upstream and downstream directions and operate as hinge points around which the channel migrates spatial variations in the erodibility of clay rich floodplain material also promote large scale 10 50 km differences in channel sinuosity and migration although these variables are also likely to be influenced by channel gradient and tectonic effects that are difficult to quantify numerical model results suggest that spatial heterogeneity in bank erodibility driven by variable bank composition may force a substantial c 30 reduction in average channel sinuosity compared to situations in which bank strength is spatially homogeneous copyright 2015 john wiley sons ltd

decoupling of small volume pyroclastic flows and related hazards at merapi volcano indonesia the november 1994 eruption at merapi volcano provided good evidence of decoupling of dome collapse pyroclastic flows and of large scale detachment of an ash cloud surge acs component from the basal block and ash flow baf timing and stratigraphic relationships of the largest 1994 acs indicate that this escaped from the valleys travelled well ahead of the baf arrived at the termination tens of seconds before it and deposited a discrete acs deposit beneath the baf unit this suggests that the acs detachment mostly occurred relatively high on the volcano slope likely at the foot of the proximal cone later pyroclastic flow eruptions in january 1997 and july 1998 also showed evidence of acs detachment although to a lesser extent suggesting that acss could be a frequent hazard at merapi volcano based on an extensive review of the available literature and on field investigations of historical deposits we show here that flow decoupling and acs detachment in the way inferred from the 1994 eruption is a common process at merapi the acs related destructions outside valleys were frequently reported in the recent past activity of the volcano i e in at least 16 pyroclastic flow eruptions since 1927 destruction occurred systematically in eruptions where maximum runout of the bafs was 6 5 km or more and occurred rarely for baf runouts of 4 5 km or less the acs deposits have been recognized beneath some valley filling baf units we attribute to some recent destructive eruptions i e the 1930 1954 1961 and 1969 eruptions topographic conditions at merapi volcano favouring acs detachment include a the high slope 30 of the proximal cone leading to high proximal velocities of the pyroclastic flows and thus to the transfer of large amounts of particles into the ash cloud b the strong break in slope at the foot of the proximal cone where the velocity of the basal baf is strongly reduced and a major acs component is thought to form and detach by shearing over the baf and c the small depth of most valleys in the first kilometres beyond the foot of the cone which allows minor acs components to escape from the valleys during travel of the baf however flow decoupling and acs detachment occur for only some of the numerous pyroclastic flows that follow the same path in a given eruption this indicates that topography alone cannot lead to flow decoupling we suggest two factors that control flow decoupling and its extent the main one is flow volume and thus flux as both are correlated in almost instantaneous dome collapse events as suggested by the observed relationship between flow decoupling and the travel distance of the pyroclastic flows the second factor is the amount of available ash in the flow at its early stage which influences the mass and thus momentum of the ash cloud the amount of ash in the pyroclastic flows of merapi may depend on several factors among which are a the physical and thermal state of the part of the active dome that collapses and b the proportion of older cold rocks incorporated in the flow either by undermining of surrounding summit rocks by the current pyroclastic flow activity or by erosion on the upper slopes

using fractal analysis to quantitatively characterize the shapes of volcanic particles 1 the shapes of volcanic particles reflect numerous eruptive parameters e g magma viscosity volatile content and degree of interaction with water and are useful for understanding fragmentation and transport processes associated with volcanic eruptions however quantitative analysis of volcanic particle shapes has proven difficult because of their morphological complexity and variability here a newly developed procedure for shape analysis based on fractal geometry is described and tested although volcanic particle shapes are not truly fractal their complexity can be effectively characterized in terms of fractal values pseudofractal dimensions reflecting morphological invariance over discrete ranges of scale using fractal data produced by dilation of a particle s two dimensional boundary a spectrum of fractal dimensions is calculated for each particle by taking the first derivative of the dilation data compared with fractal methods that express shape in terms of only one or two fractal dimensions typically derived from the slope of data on a richardson plot this technique results in better discrimination between samples in addition use of multiple fractal values allows incorporation of multivariate statistical analysis further strengthening the differentiating power of the technique this fractal spectrum technique yields promising results for samples of sideromelane shards from iceland and is likely to be effective at characterizing other kinds of volcanic particle shapes

varying discharge controls on timescales of autogenic storage and release processes in fluvio deltaic environments tank experiments 1 changes in external forcing have traditionally been the main areas of interest in understanding sedimentary records while in most stratigraphic interpretation autogenic behavior has been thought of as a noise generator this study aims to investigate autogenic processes in a fluvio deltaic system under a range of discharge conditions and to show that autogenic processes generate distinct signatures rather than random noise a matrix of nine different experiments is presented here to systematically evaluate the effects of sediment and water discharge variations on the timescale of fluvial autogenic processes temporary sediment storage regularly occurs by backfilling of sediment in the fluvio deltaic channels followed by a period of strong channelization that releases the stored sediment these storage and release processes cycle along with changes in the fluvial slope and planform pattern of the flow here we propose that the autogenic behavior of deltaic progradation has a distinct timescale that is controlled by sediment and water discharges an increase in sediment discharge primarily reduces the autogenic timescale as higher sediment supply fills the channels faster in contrast the high sediment discharge causes a morphologic feedback by increasing the magnitude of fluvial slope change between the storage and release events and increasing the size of the temporary sediment storage termed the fluvial envelope this works against the sediment discharge control as the autogenic timescale is increased increasing the water discharge increases the autogenic timescale by improving the fluvial organization toward a strongly channelized system changes in autogenic timescale due to variations in the sediment and water discharges are nonlinear for different sediment to water discharge ratios as the ratio decreases the fluvial system is better organized and the timescale is more linearly related to the change in sediment discharge as the ratio increases deltas develop poorly organized fluvial systems and the associated timescales converge even with different sediment discharges the results presented here provide enhanced interpretation of sedimentary records by better decoupling of autogenic signatures from allogenic products developed across a wide range of discharge conditions

ichthyosaurs reptilia ichthyosauria from the lower and middle triassic sulphur mountain formation wapiti lake area british columbia canada ichthyosaurs are found in the lower and middle triassic members of the sulphur mountain formation in the wapiti lake area british columbia three species are recognized pessosaurus sp in the family shastasauridae from the middle triassic mixosaurus cf m nordenskioeldii in the family mixosauridae from the lower and middle triassic and phalarodon cf p fraasi in the family omphalosauridae from the middle triassic other ichthyosaur material in the lower triassic smithian member is the oldest known from north america and coeval with the oldest known elsewhere but cannot be identified confidently at this time this material provides new information relative to the paleobiogeography of early ichthyosaurs and additional confirmation that ichthyosaurs were already highly specialized and quite diverse by the early triassic

a lower cretaceous ichthyosaur graveyard in deep marine slope channel deposits at torres del paine national park southern chile remnants of ophthalmosaurid ichthyosaurs recently discovered in the vicinity of the tyndall glacier in the torres del paine national park of southern chile are extremely abundant and well preserved after three field campaigns to the area a total of 46 articulated and virtually complete ichthyosaur specimens both adults and juveniles were tentatively assigned to four different species of ophthalmosauridae preservation is excellent and occasionally includes soft tissue and embryos the skeletons are associated with ammonites belemnites inoceramid bivalves and fishes as well as numerous plant remains the enormous concentration of ichthyosaurs is unique for chile and south america and places the tyndall locality among the prime fossil lagerstatten for early cretaceous marine reptiles worldwide the deposit is early cretaceous valanginian hauterivian in age and forms part of a monotonous bathyal to abyssal sequence of the late jurassic to late early cretaceous rocas verdes back arc basin in this region the tyndall ichthyosaur population may have profited from cold upwelling currents that caused abundant life at the shelf edge including masses of belemnites and small fish the preferred diet of ichthyosaurs the abundance of almost completely articulated ichthyosaur skeletons in the tyndall area suggests that some animals fell victim to episodic mass mortality events caused by turbidity currents traveling downslope through a submarine canyon they lost orientation drowned and were dragged into the deep sea by these turbulent high energy gravity flows their bodies ended up in an oxygen deficient basin environment where they were immediately embedded by the fine turbidite suspension fallout the tyndall ichthyosaur locality thus combines characteristics of both concentration and conservation lagerstatten

rheological changes induced by clast fragmentation in debris flows on the basis of rotating drum analogue experiments we describe a fragmentation process acting within debris flows during transport and its influence on rheologic behavior our hypothesis is based on a detailed textural analysis including granulometry clast morphology and rheologic properties of the fluid matrix results of the experiments point out that breakage of certain granulometric classes produces fine particles like fine sand and silt the population growth of fine clasts with time leads to an increase in yield strength and viscosity that progressively modifies the rheologic behavior from a textural point of view this is reflected in a bimodal granulometric distribution up to now this characteristic has been explained as the effect of bulking and or sedimentation processes during transport our experimental results show that the type of fragmentation depends on particle size and is the consequence of strong clast clast interaction and clast fluid interactions coarse particles develop small fractures which cause the loss of sharp edges and asperities medium sized particles develop through going fractures that cause them to break apart the latter process explains why intermediate granulometric classes progressively diminish with time in debris flows analogue experiments enable us to study the efficacy of clast fragmentation in modifying the textural character and flow behavior of debris flows without the influence of external factors such as erosion and sedimentation the obtained results constitute the base of a new approach for modeling debris flow dynamics

can dispersive pressure cause inverse grading in grain flows grain flows in the collisional regime are self regulated in such a way that dispersive pressure at every level tends to balance static pressure and so cannot promote the upward segregation of large particles in a steady flow le roux adds new insights to this analysis by pointing out that dispersive and static pressures would not balance in unsteady flows when shear strain rate increases in a grain flow dispersive pressure which is positively correlated to shear strain rate increases too and the gradient of dispersive pressure becomes higher than the gradient of static pressure as a consequence the grain flow expands thus lowering the dispersive pressure until the two gradients reequilibrate during the

a morphology independent methodology for quantifying planview river change and characteristics from remotely sensed imagery abstract remotely sensed imagery of rivers has long served as a means for characterizing channel properties and detection of planview change in the last decade the dramatic increase in the availability of satellite imagery and processing tools has created the potential to greatly expand the spatial and temporal scale of our understanding of river morphology and dynamics to date the majority of gis and automated analyses of planview changes in rivers from remotely sensed data has been developed for single threaded meandering river systems these methods have limited applicability to many of the earth s rivers with complex multi channel planforms here we present the methodologies of a set of analysis algorithms collectively called spatially continuous riverbank erosion and accretion measurements scream scream analyzes planview river metrics regardless of river morphology these algorithms quantify both the erosion and accretion rates of riverbanks from binary masks of channels generated from imagery acquired at two time periods additionally the program quantifies the area of change between river channels and the surrounding floodplain and area of islands lost or formed between these two time periods to examine variations in erosion rates in relation to local channel attributes and make rate comparisons between river systems of varying sizes the program determines channel widths and bank curvature at every bank pixel scream was developed and tested on rivers with diverse and complex planform morphologies in imagery acquired from a range of observational platforms with varying spatial resolutions validation and verification of scream generated metrics against manual measurements show no significant measurement errors in determination of channel width erosion and bank aspects scream has the potential to provide data for both the quantitative examination of the controls on erosion rates and for the comparison of these rates across river systems ranging broadly in size and planform morphology

the anatomy of a lahar deciphering the 15th september 2012 lahar at volcan de colima mexico abstract volcan de colima is one of the most active volcanoes in mexico where lahars are a common phenomenon since the reactivation of the volcanic activity in 1991 lahars have become more frequent during the june october rainy season in this region therefore volcan de colima represents a natural laboratory ideal for the constant monitoring of lahars and to study factors controlling their origin flow transport and deposition since 2007 the systematic detection of lahars in volcan de colima has been carried out using seismic data from the broadband stations of the resco network the seismological network of colima university along with three rain gauge stations located on the southern ravines of the volcano in 2011 a new monitoring station was built at 2000 m a s l along the montegrande ravine which consists of a geophone a video camera and a rain gauge station coupled with a moisture sensor transmitting in real time to the resco facilities at colima university with all the instrumentation currently installed on the volcano flanks we could monitor and describe the lahar that occurred on 15 th september 2012 along the montegrande ravine and correlate the monitoring data with information gathered by the field campaign conducted two days after the event the high quality of collected data enabled us to describe the anatomy of this lahar the event consisted of a lahar that lasted 40 min triggered by 20 mm of accumulated rainfall with a maximum intensity of 95 mm h the lahar was characterized by three main surges at 4 5 minute intervals that formed an 80 cm thick terrace the first surge was a debris flow with a block rich front followed by the main body that progressively diluted to a hyperconcentrated flow from which a 40 cm thick massive unit was emplaced 33 wt gravel and 60 wt of sand it was followed by a more dilute hyperconcentrated flow that left a massive 10 cm thick sandy layer 80 wt of sand the third surge deposited a 30 cm thick upper massive unit texturally similar to the first laminated layers separate the two first units subsequent surges were confined to the inner portion of the channel by the newly formed terrace based on flow depth estimation and difference in arrival times between geophones a mean velocity of 3 m s and a maximum peak discharge of 48 m 3 s were estimated segregation processes that promote the upwelling of the largest clasts 20 30 cm on the flow surface were also observed resulting in a clast rich levee on top of the depositional units a sedimentation rate of 5 7 cm min was also determined the results here obtained are useful to better understand textural features of lahar deposits from which important information on flow behavior can be interpreted

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

chemical and isotopic composition of fumarolic gases and the so2 flux from volcan de colima mexico between the 1994 and 1998 eruptions volcan de colima is the most active volcano in mexico including a significant effusive eruption in 1991 and a weak explosive event in 1994 geochemical monitoring of the volcano started in january 1996 with collection of fumarolic gases approximately every 3 months from two sites in the summit crater z3 800 c and z2 400 c chemical compositions of volcanic gases from the z2 fumarole showed a peak in s cl in the middle of 1997 14 15 months before the start of the 1998 lava eruption high temperature volcanic vapors from z3 changed progressively in water isotopic composition and showed a weak trend of increasing hcl hf and a peak in s cl at the same time starting from the summer of 1997 the volcanic water became gradually enriched in deuterium which probably indicated an increasing contribution from deep less degassed magma a negative correlation between d and cl content for the z3 fumarolic gases is explained by shallow degassing of the colima hot lava plug this hypothesis is consistent with published data on cl contents and solubilities in magmas and supported by the observed positive trends of s cl and hcl hf with d for the z3 fumarole until september 1998 the so2 flux from the volcano was at a low level 100 tons day and often below the detection limit of the instrument 30 tons day a sharp increase in the so2 flux was recorded 1 month before the eruption started it jumped from 400 50 tons day to 1600 tons day 2 days before new lava emerged on 20 november 1998 the so2 flux correlated well with seismicity

crumbling of dacite dome lava and generation of pyroclastic flows at unzen volcano recent modelling of volcanic eruptions has shown that the efficiency of subsurface degassing of magmas determines whether magma erupts explosively or effuses quietly1 2 slow uprise of magma is often accompanied by effective degassing leading to the extrusion of lava flows and domes although lava dome extrusion is one of the less explosive modes of eruption it is often accompanied by explosive pyroclastic activities3 5 the 1991 eruption of unzen volcano provided an opportunity to observe at close range several types of small scale pyroclastic flow glowing avalanches originating from lava domes most of the pyroclastic flows are of merapi type caused by blocks falling from a collapsing dome others are of pelean type originating in an explosion from the side of a dome the lavas apparently show variable degrees of self explosivity we suggest that variable degrees of degassing of the magma produced a wide range of excess pore pressures in the extruded lava domes resulting in both merapi type and pelean type pyroclastic flows from the domes

channel network extraction from high resolution topography using wavelets 1 the availability of high resolution topography from lidar offers new opportunities for objectively extracting the channels directly from a dem using local topographic information instead of inferring them indirectly based on global criteria such as area or area slope threshold relationships here we introduce the use of wavelet filtering to delineate threshold curvatures for defining valleys and threshold slope direction change for defining probable channeled portions of the valleys this approach exploits the topographic signatures uniquely found in high resolution topography and reveals the fuzzy topographic transition in which local weakly convergent areas lie at the transition between hillslopes and valleys

fluvial morphology and sediment flux steering of axial transverse boundaries in an experimental basin abstract the distinction between depositional belts associated with the basin axis and flanking piedmont streams is a fundamental attribute of the stratigraphic architecture of intracontinental rift basins spatiotemporal distributions of these lithofacies associations are sensitive to a combination of factors including basin geometry subsidence rate and sediment discharge however most studies have focused on one or two controls and one depositional component axial or tributary of the basin fill succession a new perspective on how these depositional belts develop under simple but precisely controlled boundary conditions of steady subsidence sediment flux and water discharge is achieved through the creation of an experimental stratigraphic succession the experimental earthscape run in 2006 xes06 focused on the geomorphic evolution of sedimentary successions within an asymmetrically subsiding basin analogous to a simple half graben containing four interacting supply points of sediment and water under the imposed conditions the experimental system self organized into an axial stream flanked by transverse fans imposition of various combinations of longitudinal and lateral sediment flux showed that the locations and widths of the axial and transverse systems were strongly controlled by relative sediment fluxes flux steering and less influenced by the location of the subsidence maximum and subsidence rate the axial drainage was dominated by transversely sourced sediment through toe cutting of the transverse fans except during the highest axial sediment discharges footwall fans persisted even under conditions of very large axial sediment discharge aided by topographic inheritance of the steeper transverse depositional slopes

can dispersive pressure cause inverse grading in grain flows discussion the concept of dispersive pressure was originally proposed by bagnold 1954 who showed experimentally that sheared granular material develops a dispersive pressure that is proportional to the shear stress and the particle concentration legros 2002 presented a theoretical analysis suggesting that dispersive pressure cannot account for the inverse grading commonly observed in grain flows modified grain flows or traction carpets contrary to what has been accepted for decades by many sedimentologists he pointed out that if the dispersive pressure in a sheared granular mass increases and exceeds the applied normal stress or static pressure the net upward force acting upon the bed causes it to expand as has in fact been observed in experiments bed expansion immediately causes a decrease in particle concentration and consequently in dispersive pressure until the latter balances the static pressure and expansion stops if the dispersive pressure becomes less than the static pressure the net downward force acting upon the granular bed causes compaction thus increasing the particle concentration and dispersive pressure this is an important concept enhancing our understanding of an as yet poorly understood process however legros 2002 went further to state that the dispersive pressure must always equal the applied normal shear stress at every level emphasis mine through the shearing granular bed this implies that the whole sheared bed is in constant equilibrium which is probably not the case in this discussion a modified process is proposed that accounts for the bipartite traction carpet structure proposed by sohn 1997 traction carpets are moving layers of highly concentrated bedload material developed beneath and driven by an overlying turbulent flow dzulynski and sanders 1962 sohn 1997 on the basis of numerical analyses computer simulations field measurements and experimental studies bagnold 1955 1963 hanes and bowen 1985 wan

deposits and physical properties of pyroclastic density currents during complex subplinian eruptions the ad 472 pollena eruption of somma vesuvius italy small scale pyroclastic density currents pdcs associated with the ad 472 pollena eruption of somma vesuvius italy were generated by both magmatic and phreatomagmatic explosive fragmentation the resulting deposits were emplaced under flow boundary conditions dominated by varying combinations of grain interaction fluid escape and traction processes stratigraphic and lithofacies analysis of these pdcs offers a new perspective on the en masse versus progressive aggradation debate for pdc deposition in particular the analyses indicate that pdcs were density stratified with a basal underflow dominated by grain interactions the underflows comprised trains of self organized granular pulses of variable thickness and magnitude depending on the overall particle concentration and fluid turbulence a change in gradient between the upper and lower slopes of the volcano promoted deposition and the different pulses aggraded sequentially stepwise in this model each pulse stops en masse and the whole deposit aggrades progressively particle concentration density mean velocity and flow height were assessed for the studied pdcs using differaent methods for massive and stratified deposits the calculated mobility of the flows was 0 2 to 0 3 in the expected range for small scale pdcs

numerical simulations of block and ash flows using the titan2d flow model examples from the 2006 eruption of merapi volcano java indonesia we present titan2d simulations of two well characterized block and ash flow baf events of the 2006 eruption of merapi java indonesia that affected the gendol valley on the volcano s southern flank and adjacent densely populated interfluve non valley areas 1 a single dome collapse event to the south that generated one of the smaller post june 14 flows and 2 a sustained multiple dome collapse event also directed to the south that produced the largest flows of the 2006 eruption emplaced in the afternoon of june 14 using spatially varying bed friction angles titan2d is capable of reproducing the paths velocities runout distance areas covered and deposited volumes of these flows over highly complex topography the model results provide the basis for estimating the areas and levels of hazards associated with bafs generated during relatively short as well as prolonged dome collapse periods and guidance during future eruptive crises at merapi

merapi central java indonesia an outline of the structural and magmatological evolution with a special emphasis to the major pyroclastic events abstract merapi volcano in the central part of java is regarded as the most active and most dangerous volcano in indonesia on the basis of field studies and geochronological data its history is divided into four periods ancient middle recent and modern merapi according to our preliminary age data the ancient period may have begun around 40 000 y bp and lasted until 14 000 y bp when the middle period begun the recent period begun around 2200 y bp and was replaced by the modern period after the eruption of 1786 during the middle merapi stage a mount st helens type edifice collapse occurred our data suggest that his event is younger than 6700 y bp and older than 2200 y bp during the recent merapi stage violent magmatic to phreatomagmatic eruptions twice interrupted the growth of the volcano the older gumuk phreatoplinian deposits cover the entire cone charcoal found within these deposits gave 14c ages of 2200 and 1470 y bp the overlying sambisari ash deposits were emplaced by violent pyroclastic surges directed towards the south i e to the present location of the town of yogyakarta they buried the shivaitic temple of sambisari at the start of the 15th century modern merapi is characterised by the persistent growth of a summit dome periodically interrupted by partial or total collapse of the dome to generate frequent merapi type nuees ardentes blocks and ash flows and associated surges or more exceptionally fall back st vincent type nuees ardentes scoria flows in contrast previous stages were characterised by effusion of long lava flows alternating with violent explosive phases generating essentially st vincent type nuees ardentes merapi lavas are calc alkaline with a compositional range between 49 5 and 60 5 wt sio2 moreover high k basaltic andesites represent about 90 of merapi lavas disequilibrium features are common in the mineralogical assemblage plagioclase orthopyroxene clinopyroxene olivine amphibole titanomagnetite scarce alkali feldspar macroscopic and microscopic textural heterogeneities are related to magma mixing that may have buffered the compositions of lavas and caused the restricted range of compositions our studies of past activity at merapi provide some insights into future activity and to related volcanic hazards it is clear that merapi has the potential of eruptions much more powerful than observed during the historic period

autocyclic behaviour of fan deltas an analogue experimental study fan deltas are excellent recorders of fan building processes because of their high sedimentation rate particularly in tectonically active settings although previous research focuses mainly on allogenic controls there is clear evidence for autogenically produced storage and release of sediment by flume and numerical modelling that demands further definition of characteristics and significance of autogenically forced facies and stratigraphy analogue experiments were performed on fan deltas with constant extrinsic variables discharge sediment supply sea level and basin relief to demonstrate that fan delta evolution consists of prominent cyclic alternations of channellized flow and sheet flow the channellized flow is initiated by slope induced scouring and subsequent headward erosion to form a channel that connected with the valley while the removed sediment is deposited in a rapidly prograding delta lobe the resulting decrease in channel gradient causes a reduction in flow strength mouth bar formation flow bifurcation and progressive backfilling of the channel in the final stage of channel filling sheet flow coexists for a while with channellized flow semi confined flow although in cycle 1 this phase of semi confined flow was absent subsequent autocyclic incisions are very similar in morphology and gradient however they erode deeper into the delta plain and as a result take more time to backfill the duration of the semi confined flow increases with each subsequent cycle during the period of sheet flow the delta plain aggrades up to the critical gradient required for the initiation of autocyclic incision this critical gradient is dependent on the sediment transport capacity defined by the input conditions these autogenic cycles of erosion and aggradation confirm earlier findings that storage and release of sediment and associated slope variation play an important role in fan delta evolution the erosional surfaces produced by the autocyclic incisions are well preserved by the backfilling process in the deposits of the fan deltas these erosional surfaces can easily be misinterpreted as climate sea level or tectonically produced bounding surfaces

temporal evolution of the minoan eruption santorini greece as recorded by its plinian fall deposit and interlayered ash flow beds the plinian fall deposit of the minoan eruption santorini greece and its interlayered ash flow beds show textural componentry and chemical trends indicative of their temporal evolution and conditions that lead to the ash flow emplacement the deposits have been sampled in detail at a selected locality and the following features have been analyzed i maximum clast size ii grain size distribution iii componentry iv lithic types v pumice morphology vi pumice types and vii pumice crystal abundance stratigraphic variations of these features are assumed to record changes that occurred during the eruption including changes in eruptive plume height nature and relative efficiency of the magma fragmentation process conduit stability and magma flow in the conduit based upon the inferred temporal changes we propose the following eruption reconstruction the sustained plinian column activity reached its climax in terms of mass eruption rate and plume altitude soon after the beginning of the eruption and subsequently began to gradually subside as a result of eruption waning the conduit walls began to collapse causing an increase in the shear stress in the flowing vesicular magma and an increase in the efficiency of the magma fragmentation process eventually the conduit closed or became too narrow to support a high standing eruption column leading to ash flow eruption as a result of the collapse of what was left of the eruptive plume and or directly from emission of an overpressured jet subsequent conduit pressure increases led to conduit re opening and a plinian column with associated pumice fallout began anew the eruptive magma fragmentation process is proposed to have been of a brittle nature and linked to the shear stress generated by conduit wall friction fragmentation efficiency is recorded by grain size distributions and free crystal contents of the deposits

holocene block and ash flows from summit dome activity of citlaltepetl volcano eastern mexico a major eruption produced several block and ash flows about 4 100 years b p at citlaltepetl volcano pico de orizaba an ice capped 5670 m high andesitic active stratovolcano located at the eastern end of the mexican volcanic belt repetitive gravitational collapse of a dacitic dome at the summit crater produced a series of block and ash flows lahars and floods which were channeled through two main river valleys on the west and south flanks of the volcano the total erupted volume is estimated to be at least 0 27 km3 the deposits in both areas are similar in composition and size but they differ in the area covered distribution and structure the western deposits form a large fan cover a larger area and include numerous laharic and fluviatile deposits in contrast the southern deposits form prominent terraces where confined in narrow channels and have associated laharic units in distal areas where the flows reach a maximum distance of 30 km from the vent directed disruptions of a central summit dome occurred possibly first to the west and then to the southeast perhaps due to minor modifications of the summit dome morphology producing the voluminous block and ash flow deposits documented here the flows were strongly controlled by topography influencing the deposition of the moving particles grain size variations along the flow paths are hardly detectable suggesting no evident lateral downstream transformations because sudden changes in dome morphology may cause significant variations in the direction of future dome collapse specific areas of potential affectation cannot be predicted therefore about 350 000 inhabitants living within a radius of 35 km from the vent could be potentially impacted if catastrophic block and ash flows were to recur in the future from similar summit dome activity recognition of these deposits is therefore important for hazard assessment because some seemingly safe areas may be at high risk

pyroclastic flow erosion and bulking processes comparing field based vs modeling results at tungurahua volcano ecuador pyroclastic density currents pdcs are high temperature and high velocity mixtures that threaten populations in the vicinity of many active volcanoes deciphering the cause of their remarkable mobility is essential for volcanic hazard analysis but remains difficult because of the complex processes occurring within the flows here we investigate the effect of bulking on dense pdc mobility by means of a double approach first we estimate the amount of material incorporated into scoria flows emplaced during the august 2006 eruption of tungurahua volcano ecuador for this we carry out a detailed analysis of 3d corrected digital images of well exposed scoria flow deposits componentry analysis indicates that pdc bulking occurs principally on the steep 25 upper slope of the volcano and the deposits typically comprise 40 50 wt of non juvenile i e accessory and accidental material secondly we develop a simple stress related grain by grain equation of erosion combined with two simple depth averaged geophysical mass flow models that compare the bulking mechanism to a non fluidized and a fluidized flow two behaviors based on coulomb and plastic rheologies are used to reproduce on a first order basis the 2006 tungurahua pdcs cross check comparisons between these modeled cases and the erosion pattern inferred from field based data allow us to evaluate the accuracy of our modeling assumptions regardless of the rheological regime the pdc induced erosion pattern of the 2006 tungurahua eruption can only be reproduced by fluctuations of the flow s basal shear stress during emplacement such variations are controlled by flow thinning thickening processes notably through the formation of a thick non erosive flow body that pushes a thin frictional erosive front during pdc emplacement the input volume of juvenile material as well as the thickness of the erodible layer available prior to the eruption are additional key parameters our work highlights complexities in pdc erosion and bulking processes that deserve further study in terms of hazard assessment our findings reveal that incorporation and bulking translate into increased flow mobility i e the augmented flow mass enhances both flow velocity and runout distance up to 20 these outcomes should be considered closely for hazard analysis at many other andesitic volcanoes worldwide where similar pdc events are common

investigation of variable aeration of monodisperse mixtures implications for pyroclastic density currents the high mobility of dense pyroclastic density currents pdcs is commonly attributed to high gas pore pressures however the influence of spatial and temporal variations in pore pressure within pdcs has yet to be investigated theory suggests that variability in the fluidisation and aeration of a current will have a significant control on pdc flow and deposition in this study the effect of spatially heterogeneous gas pore pressures in experimental pdcs was investigated sustained unsteady granular currents were released into a flume channel where the injection of gas through the channel base was controlled to create spatial variations in aeration maximum current front velocity results from high degrees of aeration proximal to the source rather than lower sustained aeration along the whole flume channel however moderate aeration i e 0 5 minimum static fluidisation velocity umf st sustained throughout the propagation length of a current results in greater runout distances than currents which are closer to fluidisation i e 0 9 umf st near to source then de aerating distally additionally although all aerated currents are sensitive to channel base slope angle the runout distance of those currents where aeration is sustained throughout their lengths increases by up to 54 with an increase of slope from 2 to 4 deposit morphologies a primarily controlled by the spatial differences in aeration where there is a large decrease in aeration the current forms a thick depositional wedge sustained gas aerated granular currents are observed to be spontaneously unsteady with internal sediment waves travelling at different velocities

inferring pyroclastic density current flow conditions using syn depositional sedimentary structures the processes occurring in the basal region of concentrated pyroclastic density currents pdcs influence the mobility runout distance and damage potential of a current but directly observing these processes is extremely difficult instead we must investigate the deposits to glean information regarding the conditions of sediment transport and deposition the pdc deposits of the may 18 1980 eruption of mount st helens wa usa contain sedimentary structures consisting of bed material reworked into undulose structures and recumbent flame structures the structures vary over two orders of magnitude in size with lengths ranging from 8 cm to 18 m and heights ranging from 4 cm to 1 8 m despite the large range in sizes the structures remain self similar in form suggesting a common mechanism for formation the structures are interpreted as the record of granular shear instabilities similar to kelvin helmholtz instabilities formed at the interface between a shearing high concentration flow and the substrate in the moments just prior to deposition the morphology of the structures suggests that the basal region of pdcs must be both highly concentrated and also highly mobile in the moments before final deposition likely a result of elevated pore fluid pressures we use a modified instability growth criterion to estimate pdc flow velocities at the time of formation for the mount st helens pdcs the velocity estimates range from 0 2 to 7 5 m s 1 with larger structures requiring higher flow velocities combining the velocity estimates with the dimensions of the structures suggests deposition rates of 4 to 32 cm s 1 such high deposition rates indicate that the deposits likely accumulated in a stepwise manner rather than either progressively or en masse the structures suggest that sections of the deposit accumulated during punctuated periods of high deposition lasting at most a few seconds followed by periods of bypassing i e non deposition or erosion lasting minutes to tens of minutes our findings motivate continued experimental and numerical work to understand how the formation of recumbent flame and similar structures affects subsequent flow behavior in terms of runout distance and hazard potential

volcanic debris avalanche deposits of the upper maronne valley cantal volcano france evidence for contrasted formation and transport mechanisms abstract the deposits of two volcanic debris avalanches vda i and ii that occur in the upper maronne valley northwest sector of cantal volcano france were studied to establish their mechanisms of formation transport and deposition these two volcanic debris avalanches that clearly differ with regard to their structures textures and extensions exemplify the wide spectrum of events associated with large scale sector collapse vda i is voluminous 1 km3 in the upper maronne valley and widespread the deposits comprise two distinct facies the block facies that forms the intermediate and upper part of the unit and the mixed facies that crops out essentially at the base of the unit the block facies consists of more or less brecciated lava block and ash flow breccia and pumice flow tuff megablocks set in breccias resulting from block disaggregation mixing and differential movements are almost absent in this part of the vda the mixed facies consists of breccias rich in fine particles that originate from block disagregation as well as being picked up from the substratum during movement mixing and differential movements are predominant in this zone analysis of fractures on lava megablocks suggests that shear stress during the initial sliding is the principal cause of fracture these data strongly indicate that vda i is purely gravitational and argue for a model in which the initial sliding mass transforms into a flow due to differential in situ fragmentation caused by the shear stress vda ii is restricted to low topography areas its volume in the studied area is about 0 3 km3 the deposits consist of brecciated rounded blocks and megablocks set in a fine grained matrix composed essentially of volcanic glass this unit is stratified with a massive layer that contains all the megablocks at the base and in the intermediate part and in the upper part a normally graded layer that contains only blocks

the milling factory componentry dependent fragmentation and fines production in pyroclastic flows in order to decipher the mobility of hazardous small volume pyroclastic flows pfs we investigate here the role of clast fragmentation and production of fine particles 2 mm in controlling pf dynamics we report a high resolution textural data set i e grain size distribution clast componentry and clast morphology of andesitic scoriaceous pf deposits from tungurahua volcano ecuador based on a unique method and data processing procedure the strong relationship shown between clast size and componentry in pf deposits is quantified through a componentry versus size index csi which varies between 1 and 1 all components in the coarse or fine fractions respectively our results show that the incorporated old lava clasts csi of 0 33 control early grinding of the pristine juvenile bombs csi of 1 which produce smaller scoriaceous andesitic fragments csi of 0 26 these latter interact in the granular assemblage and release fine particles through the abrasion processes as supported by the morphological data the textural maturity of the deposits reveals that the milling factory works before sedimentation begins i e on steep upper slopes and that there is some balance between fines production and loss the process evident here tends to redistribute stress into the moving flow and produces fines that contribute to fluidization of it the milling factory is thus likely to enhance the mobility of geophysical flows which has strong implications for modeling and hazard assessment purposes

preliminary report on the activity at unzen volcano japan november 1990 november 1991 dacite lava domes and pyroclastic flows abstract the eruption of unzen volcano commenced on 17 november 1990 phreatic and phreatomagmatic eruptions occurred by early may 1991 no large scale explosive eruptions preceded the extrusion of lava domes lava domes appeared in a summit crater on 20 may 1991 and they grew on the steep slope of mt fugen at unzen volcano rockfalls from the margins of the domes frequently generated pyroclastic flows major pyroclastic flows occurred on 3 june 8 june and 15 september 1991 the 3 june pyroclastic flow killed forty three persons many of the pyroclastic flows seem to have resulted from the simple rockfalls except one flow on 8 june which was accompanied by an explosion from the crater many of the rockfalls that generated pyroclastic flows were witnessed as of november 1991 unzen volcano was still active with a nearly constant magma supply rate of about 0 3 106 m3 d the total magma output exceeded 45 106 m3 by the beginning of november 1991 the volume of the lava domes is more than 23 106 m3

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

the 1984 nuee ardente deposits of merapi volcano central java indonesia stratigraphy textural characteristics and transport mechanisms for many centuries merapi volcano has generated hot avalanches of blocks lapilli and ashes derived from the destruction of partially solidified viscous lava domes merapi type nuees ardentes on 15 june 1984 at least four nuees ardentes came down the southwest slope of the merapi the first and the last being responsible for more than 99 of the deposits which are now exposed the first nuee ardente a merapi type nuee ardente was produced by the destruction of the dome travelled 7 km from the crater leaving a measured deposit 2 7 m thick 4 km from the crater near its upper depositional limit regularly increasing to a maximum measured thickness of 12 m at the front of the deposit the lower contact is sharp non erosive with pines still rooted in the underlying paleosol the deposit consists of 50 ash 33 lapilli and 17 blocks with two subpopulations one rosin and one normal and is finespoor with less than 4 of fine ash d finer than 4 the deposit displays reverse population grading of both vesiculated and massive clasts and of the maximum grain size the maximum size significantly increases regularly down current over most of the exposed length of unit 1 and bed thickness increases for the entire length of the deposit the deposit of the second nuee ardente is only 6 21 cm thick and of very limited lateral extent it is a normally graded coarse to fine ash with a finespoor base the third unit consists of fines poor normally graded coarse ash exposed in low amplitude 20 40 cm 12 m wavelength dunes the deposit of the fourth nuee ardente rests in sharp erosive contact on the underlying unit increasing in thickness down flow it consists of transitional coarse and fine grained strata 6 130 c cm thick dipping 5 10 down flow the deposit made up of two subpopulations one rosin and one normal is normally graded over the entire bed but coarsegrained strata are reversely graded the relative content of vesiculated clasts increases up bed in both strata types from 12 at the base to 40 at the top the characteristics of unit 1 suggest that it accumulated from a concentrated suspension of cohesionless solids exhibiting non newtonian behavior where dispersive pressure played an important role in the suspension of the clasts units 2 and 3 were probably deposited from dilute turbulent suspensions whereas the upper unit 4 is a classic example of deposition from a high density turbulent suspension leading to the formation of multiple traction carpets driven by the overlying lower density surge the horizontal distance travelled by a hot rock avalanche may be influenced by its transport mechanism debris flows are mobile on very low slopes as low as 1 whereas grain flows even density modified grain flows require relatively high slopes more than 6 at merapi to maintain their mobility if the present merapi dome were to collapse and produce a debris flow its present volume coupled with the minimal 1 5 km vertical drop could travel a distance ranging between 15 and 30 km however if transport were by grain flow mechanisms the mass could come to rest as it reaches a 5 10 slope

mt pelee martinique may 8 and 20 1902 pyroclastic flows and surges abstract the distribution stratigraphic relationships and fragmental components of the may 8 and 20 1902 pyroclastic flows from mt pelee martinique together with eyewitness accounts suggest the following explanation for those eruptions the eruptions were vertically directed magmatic perhaps initiated phreatically and contained abundant juvenile lithics from congealed magma of the dome and neck this resulted in a two part eruption column having 1 a dense lithic charged part which collapsed into the crater and flowed out of a pre existing notch in its side giving rise to pyrochlastic flows and 2 a magmatically derived column containing gases juvenile vitric material and crystals which largely by passed the neck and dome and escaped into the atmosphere all of the energy of the flows was apparently focused through the notch they emerged fully turbulent and flowed down riviere blanche gravity segregation of large and abundant fragments soon resulted in a dense high concentration poorly fluidized block and ash flow confined to the valley leaving above a fully turbulent high energy ash cloud surge as the ash cloud surge moved down the mountain it continued to expand outward the process of gravity segregation continued as the ash cloud surge expanded resulting in secondary block and ash underflows toward st pierre the secondary block and ash flows developed on a gently sloping upland surface 100 m or more above the valley of riviere blanche the turbulent fragment depleted surges above the secondary block and ash flows maintained sufficient energy to devastate the landscape outward to about 3000 m including st pierre the surges refracted around obstacles and in one place moved up a small valley in a direction opposite to the main flows

fragmentation transport and deposition of a low grade ignimbrite the citlaltepetl ignimbrite eastern mexico the citlaltepetl ignimbrite records one of the largest explosive events during the holocene activity of citlaltepetl volcano pico de orizaba multiple pyroclastic flow units a fall deposit and some lahar units were emplaced between 8500 9000 y b p as a result of repetitive but discrete explosive events the whole ignimbrite resulted from discrete fluctuations in eruptive intensity that decreased with time the initial pyroclastic flow pulse was by far the most violent and widespread event and its deposits show conspicuous variations in structure and texture that could be associated with different mechanisms of transport and emplacement subpopulation sequential fragmentation transport sft analyses were carried out in order to determine the physical mechanisms that selectively concentrate or remove particles in the moving flows we suggest that lateral and temporal changes in the flow rheology in which fluidization yield strength entrainment of atmospheric air and sedimentation played a dominant role in flow propagation and emplacement may imprint a unique signature in the grain size spectra the lowermost unit of the citlaltepetl ignimbrite can be envisaged by a model in which progressive aggradation near the vent became replaced by en masse emplacement farther outward

the role of fluidization in the emplacement of pyroclastic flows 2 experimental results and their interpretation abstract although often quoted as being important in the emplacement of pyroclastic flows little relevant experimental fluidization work has been done fluidization processes are first reviewed for a simple system against which ignimbrite samples can be compared results from fluidization experiments on ignimbrite samples show that their behaviour differs radically from any simple system principally because of their extremely poor sorting at a certain gas velocity u ie whose value cannot be predicted some ignimbrite samples begin to expand whilst at a higher gas velocity u mp the samples begin to show segregation structures the minimum fluidization velocity u mf in simple systems is replaced by u mp the value of the latter in pyroclastic materials cannot be easily or reliably predicted from published u mf correlations and a new empirical method for determining u mp is presented from the experimental data during fluidization ignimbrite samples expand much less than more conventional materials due to the bypassing of gas through segregation channels the total amount of expansion is also limited e g a 100 m thick pyroclastic flow will from fairly high gas velocities deflate to form an ignimbrite which is not less than 70 85 m thick during fluidization the poor sorting causes only part of the weight of the ignimbrite samples to be supported by the gas flow the degree of support increasing with an improvement in sorting segregation structures and grain size and compositional variations within fluidized ignimbrite samples show varying behaviour depending on the sorting of the sample after subjecting a sample to high gas velocities the net result is a grain size and compositionally zoned bed which becomes richer upwards in pumice and fine material once formed these features cannot be destroyed under laboratory conditions implying that some segregation structures should be present in any ignimbrite where u mp was exceeded

nature of stress accommodation in sheared granular material insights from 3d numerical modeling active faults often contain distinct accumulations of granular wear material during shear this granular material accommodates stress and strain in a heterogeneous manner that may influence fault stability we present new work to visualize the nature of contact force distributions during 3d granular shear our 3d discrete numerical models consist of granular layers subjected to normal loading and direct shear where gouge particles are simulated by individual spheres interacting at points of contact according to simple laws during shear we observe the transient microscopic processes and resulting macroscopic mechanical behavior that emerge from interactions of thousands of particles we track particle translations and contact forces to determine the nature of internal stress accommodation with accumulated slip for different initial configurations we view model outputs using novel 3d visualization techniques our results highlight the prevalence of transient directed contact force networks that preferentially transmit enhanced stresses across our granular layers we demonstrate that particle size distribution psd controls the nature of the force networks models having a narrow i e relatively uniform psd exhibit discrete pipe like force clusters with a dominant and focussed orientation oblique to but in the plane of shear wider psd models e g power law size distributions d 2 6 also show a directed contact force network oblique to shear but enjoy a wider range of orientations and show more out of plane linkages perpendicular to shear macroscopic friction level is insensitive to these distinct force network morphologies however force network evolution appears to be linked to fluctuations in macroscopic friction our results are consistent with predictions based on recent laboratory observations that force network morphologies are sensitive to grain characteristics such as particle size distribution of a sheared granular layer our numerical approach offers the potential to investigate correlations between contact force geometry evolution and resulting macroscopic friction thus allowing us to explore ideas that heterogeneous force distributions in gouge material may exert an important control on fault stability and hence the seismic potential of active faults 2007 elsevier b v all rights reserved

discrete element simulations of bed force anomalies due to force chains in dense granular flows abstract surficial flows on volcanic edifices are often comprised of high concentrations of granular materials either derived from juvenile eruptive material or material sourced from an unstable edifice although much attention has been given to granular flow mobility the physics that govern flow internal behavior and substrate interaction are still poorly understood recent laboratory experiments have shown that force chains transmit extreme localized forces to the substrates of free surface granular flows in this work we combine computational and experimental approaches to investigate the forces at the bed of a simplified granular flow a photoelastic experimental approach is used to resolve discrete forces in the granular flows we also conduct discrete element model dem simulations using input parameters derived from measureable physical material properties of experimental and natural materials that successfully reproduce the experimental bed forces generated by filamentary force chain structures observed in free surface granular flows the dem results show particular sensitivity to values prescribed for contact stiffness which is in contrast with previous reports indicating that stiffness values have insignificant influence on flow behavior the transient forces at the bed generated by force chain structures can greatly exceed by several 100 the bed forces predicted from continuum approaches and our simulation results imply that natural materials are more prone to excessive bed forces than photoelastic materials due to their larger contact stiffnesses this work suggests that force chain activity may play an important role in the bed physics of dense volcanic flows by influencing substrate entrainment

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

digital elevation model networks demon a model of flow over hillslopes for computation of contributing and dispersal areas current algorithms for computing contributing areas from a rectangular grid digital elevation model dem use the flow routing model of o callaghan and mark 1984 which has two major restrictions 1 flow which originates over a two dimensional pixel is treated as a point source nondimensional and is projected downslope by a line one dimensional moore and grayson 1991 and 2 the flow direction in each pixel is restricted to eight possibilities we show that large errors in the computed contributing areas result for any terrain topography divergent convergent or planar we present a new model called digital elevation model networks demon which avoids the above problems by representing flow in two dimensions and directed by aspect demon allows computation of both contributing and dispersal areas demon offers the main advantage of contour based models e g moore et al 1988 the representation of varying flow width over nonplanar topography while having the convenience of using rectangular grid dems

large scale experiments on the mechanics of pyroclastic flows design engineering and first results 1 a newly designed apparatus for experimental studies of pyroclastic flows consists of a cylindrical conduit that is filled with samples of natural volcanic products tephra blowing nozzles in the base plate of the conduit are connected to a volume of highly pressurized gas opening of fast solenoid valves results in impulse like coupling of the released gas to the sample the system was designed so that the range of mechanical energy transferred to the particle mass in the conduit reflects the mechanical energy observed and measured during fragmentation experiments with melts of similar composition depending on the specific mechanical energy sme of the system which results from pv m where p is gas overpressure i e pressure atmospheric v is gas volume and m is sample mass different behaviors are observed if sme 2 6 kj kg a dilute plume develops and particles are sedimented by fallout exclusively if sme 106 implying that flows are fully turbulent and that particle coupling to gas turbulence of natural pyroclastic flows is replicated by the experiments the measured shear current velocities are proportional to the impact mass flow rate i e the product of mixture density and impact velocity experimental data and grain size analysis of the produced particle deposits suggest that the scale of the experiment is large enough to reproduce the transport dynamics of natural pyroclastic flows

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

pyroclastic flow deposits of the 1991 eruption of volcan de colima mexico the april 16 1991 eruption of volcan de colima represents a classical example of partial dome collapse with the generation of progressively longer runout merapi type pyroclastic flows that traveled up to 4 km along the el cordoban gullies east central and west the flows filled the gullies with block and ash flow deposits up to 10 m thick of which after 7 years of erosion only remnants remained in the el cordoban west and east gullies the el cordoban central gully however provided a well preserved and incised longitudinal section of the 1991 deposits the deposits were emplaced as proximal and distal facies separated by a change in slope angle from 30 to 20 the proximal facies consists of massive clast supported flow units up to 1 m thick with andesite blocks locally supported by a matrix of coarse ash and devoid of segregation structures or grading the distal facies consists of a massive matrix supported deposit up to 8 m thick which contains dispersed andesite blocks in a fine ash matrix in the distal facies a train of blocks marks flow unit upper boundaries and although sorting is poor some grading is present thin finely stratified or dune bedded layers of fine ash material are locally present above or below units of both facies sedimentologic parameters show that the size or fraction of large pyroclasts larger than 1 decreases from proximal to distal facies as the percentage of matrix 0 to 4 increases especially immediately beyond the break in slope we propose that the propagation of the colima pyroclastic flows is critically dependent on local slope angle the presence of erodible slope debris and the decrease in grain size with distance from the vent the progressive fining is probably caused by some combination of erosion clast breakup and deposition of larger pyroclasts and is itself influenced by the slope angle in the proximal region the flows moved as granular avalanches in which interacting grains ground each other and erosion occurred to produce an overriding dilute ash cloud the maximum runout distance of the avalanches was controlled by the angle of repose of the material and the volume and grain size of source and eroded material because the slope angle is close to the repose angle for this debris granular avalanches were not able to propagate far beyond the change in slope if however an avalanche had enough mass in finer grain size fractions at least part of the flow continued beyond the break in slope and across the volcano apron propagating in a turbulent state and depositing surge layers or in an otherwise settling modified state and depositing block and ash flow layers

a conceptual model for block and ash flow basal avalanche transport and deposition based on deposit architecture of 1998 and 1994 merapi flows the 1998 block and ash flow baf deposits on the western flanks of merapi were described both immediately following emplacement and after one and two wet seasons of erosion this afforded a unique combination of data on deposit morphology and internal structure from proximal to distal reaches the deposits of the basal avalanches from individual baf events were classified into three major and two minor facies in channelised reaches primarily resulting from effects of channel confinement and slope termination reaches were classified into three facies related to preevent topography the deposit facies architecture was interpreted to understand particle transport and deposition within the framework of granular flow systematics the transport model we propose for these basal avalanches involves unsteady flow conditions generated by pulses of collapse as the source and or by development of kinetic waves during the granular flow the coarsest clasts along with low density material migrated to the wave pulse fronts within these flows whereas in bulk flow grain dispersive pressures and kinetic sieving result in coarsest clasts being buoyed to the flow top with this tendency being greatest on higher slopes greater kinetic energy and with greater flow confinement maximising particle collisions deposition begins as the flow reaches near its full extent an initial pulse or flow wave freezes rapidly from its base upward and its rear forward as it looses kinetic energy and dispersive pressure such that an upper higher energy part of the flow is still able to move downstream over the frozen base later waves or pulses then accrete progressively horizontally upslope banking up onto or overtopping earlier deposited sediment hence the overall flow freezes from its front to its tail at termination reaches in unconfined areas the overflowing upper part of flow gradually deposits from its base upward resulting in a slightly tapering sheet formed deposit marked by a front made up of wood fragments and large boulders on sudden slope breaks in termination areas piling up of sediment occurs in flat reaches producing whaleback type forms as the flows rapidly lost competence one implication of this model is that each kinetic wave or flow pulse crest developed within the basal avalanche represents a portion of greater flow depth or stage height hence development of these crests control the ability of parts of the basal avalanche to escape from confined channels and generate unexpected hazards

the oldest south american ichthyosaur from the late triassic of northern chile ichthyosaur remains found in late triassic shallow marine limestones in quebrada dona ines chica latitude 26 07 s longitude 69 20 w northern chile are the oldest known ichthyosaur fossils from central and south america the previous oldest south american ichthyosaur was recorded in hettangian rocks also from northern chile the fossils comprise five worn teeth one paddle bone and one scapula or humerus fragment all collected from a single bed at the same locality although the material has not been identified to a generic or specific level its presence alone broadens the knowledge of the distribution and habitat of triassic ichthyosaurs late triassic ammonites and brachiopods in the same stratum provide the age control

stratigraphy sedimentology and inferred flow dynamics from the july 2015 block and ash flow deposits at volcan de colima mexico abstract the july 2015 block and ash flow baf events represent the first documented series of large volume and long runout bafs generated from sustained dome collapses at volcan de colima this eruption is particularly exceptional at this volcano due to 1 the large volume of baf material emplaced 0 0077 0 001 km3 2 the long runout reached by the associated bafs max 10 km and 3 the short period 18 h over which two main long sustained dome collapse events occurred on 10 and 11 july respectively stratigraphy and sedimentology of the 2015 baf deposits exposed in the southern flank of the volcano based on lithofacies description grain size measurements and clast componentry allowed the recognition of three main deposit facies i e valley confined overbank and ash cloud surge deposits correlations and lithofacies variations inside three main flow units from both the valley confined and overbank deposits left from the emplacement of the second series of bafs on 11 july provide detailed information about 1 the distribution volumes and sedimentological characteristics of the different units 2 flow parameters i e velocity and dynamic pressure and mobility metrics as inferred from associated deposits and 3 changes in the dynamics of the different flows and their material during emplacement these data were coupled with geomorphic analyses to assess the role of the topography in controlling the behaviour and impacts of the successive baf pulses on the volcano flanks finally these findings are used to propose a conceptual model for transport and deposition mechanisms of the july 2015 bafs at volcan de colima in this model deposition occurs by rapid stepwise aggradation of successive baf pulses flow confinement in a narrow and sinuous channel enhance the mobility and runout of individual channelized baf pulses when these conditions occur the progressive valley infilling from successive sustained dome collapse events promote the overspill and lateral spreading of the upper and marginal regions of the main flow body generating highly mobile overbank flows that travel outside of the main valley volume and distance dependent critical channel capacities for the generation of overbank flows are used to better estimate the inundation area of these hazardous unconfined pyroclastic flows these results highlight the importance of including and correctly assessing the hazards posed by large volume and long runout bafs associated with frequent small vei sustained dome collapse eruptions

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

reconciling pyroclastic flow and surge the multiphase physics of pyroclastic density currents abstract two end member types of pyroclastic density current are commonly recognized pyroclastic surges are dilute currents in which particles are carried in turbulent suspension and pyroclastic flows are highly concentrated flows we provide scaling relations that unify these end members and derive a segregation mechanism into basal concentrated flow and overriding dilute cloud based on the stokes number s t the stability factor t and the dense dilute condition d d we recognize five types of particle behaviors within a fluid eddy as a function of s t and t 1 particles sediment from the eddy 2 particles are preferentially settled out during the downward motion of the eddy but can be carried during its upward motion 3 particles concentrate on the periphery of the eddy 4 particles settling can be delayed or fast tracked as a function of the eddy spatial distribution and 5 particles remain homogeneously distributed within the eddy we extend these concepts to a fully turbulent flow by using a prototype of kinetic energy distribution within a full eddy spectrum and demonstrate that the presence of different particle sizes leads to the density stratification of the current this stratification may favor particle interactions in the basal part of the flow and d d determines whether the flow is dense or dilute using only intrinsic characteristics of the current our model explains the discontinuous features between pyroclastic flows and surges while conserving the concept of a continuous spectrum of density currents

the fractal and multifractal dimension of volcanic ash particles contour a test study on the utility and volcanological relevance abstract image processing analysis is used to check the ability of the fractal dimension for quantitatively describing the shape of volcanic ash particles digitized scanning electron microscopy images of fine pyroclasts from the eruptions of monte pilato rocche rosse lipari italy are investigated to test the efficiency of the fractal dimension to discriminate between particles of different eruptive processes multivariate analysis of multiple fractal components allows distinction between magmatic particles and phreatomagmatic particles which however is less significant than the discrimination obtained in previous studies by the use of simple adimensional shape parameters approximation of the actual particle boundary and the not rotation invariant nature of the fractal data frequently result in a significant scatter of data points in the mandelbrot richardson plot such behavior obscures in some cases the actual information of particle shape and renders the discriminating power of fractal analysis less effective than classical shape descriptors data less affected by scatter reveal that phreatomagmatic particles of the monte pilato rocche rosse eruptions are true mono fractals whereas magmatic particles are multifractals the textural small scale fractal of magmatic particles is similar to the fractal dimension value of phreatomagmatic particles and is attributed to the rheological behavior of melt upon brittle fragmentation the structural large scale fractal of magmatic particles refers to the walls of ruptured vesicles that lay on the particle outline the high difference between the values of the textural and structural fractals of magmatic particles of the monte pilato rocche rosse eruptions suggests two distinct and independent processes in the formation of such pyroclasts at the scales corresponding to the textural fractal the fragmentation process is independent of vesicles magmatic fragmentation is not simply related to growth expansion interference and explosion of vesicles but to a brittle cracking of the highly viscous melt likely related to rapid decompression

experimental evidence links volcanic particle characteristics to pyroclastic flow hazard abstract pyroclastic flows represent the most hazardous events of explosive volcanism one striking example being the famous historical eruption of vesuvius that destroyed pompeii ad 79 much of our knowledge of the mechanics of pyroclastic flows comes from theoretical models and numerical simulations valuable data are also stored in the geological record of past eruptions including the particles contained in pyroclastic deposits but the deposit characteristics are rarely used for quantifying the destructive potential of pyroclastic flows by means of experiments we validate a model that is based on data from pyroclastic deposits the model allows the reconstruction of the current s fluid dynamic behaviour model results are consistent with measured values of dynamic pressure in the experiments and allow the quantification of the damage potential of pyroclastic flows

the 17 july 1999 block and ash flow baf at colima volcano new insights on volcanic granular flows from textural analysis abstract on july 17 1999 a strong explosion occurred at colima volcano mexico that produced a 10 km high eruptive column the partial column collapse originated a block and ash flow baf that flowed to the south along the san antonio and montegrande ravines travelling 3 3 km from the volcano summit the flow filled the ravines with a volume estimated at 7 9 105 m3 the erosion of these deposits occurred between 1999 and 2002 time of sampling providing excellent longitudinal outcrops that allowed their detailed textural study the study was carried out by means of quantitative textural analysis 1 rosiwal intersections for carrying out vertical granulometric profiles 2 total grain size analysis from 11 to 9 and 3 fourier and fractal analysis of the particle morphology grain size and morphometric parameters obtained with these methods were used to identify vertical and longitudinal variation patterns in the baf deposit the grain size variations allowed to infer the main particle segregation mechanisms that acted during transport and deposition of the studied bafs the two methods used for studying the particle shape morphologies yielded results with different accuracy and reliability in particular fractal analyses have been found to be the most effective in describing the particle support mechanisms that acted during transport and deposition of the studied bafs the results highlight the importance of the information obtained by means of these techniques and provide new insights in transportation and deposition mechanisms of bafs

dome collapse mechanisms and block and ash flow emplacement dynamics inferred from deposit and impact mark analysis mono craters ca abstract characteristics of the panum block and ash flow baf deposit mono craters ca were analyzed to determine the mechanisms of collapse of the parent dome and dynamics of emplacement of the baf granulometry componentry and obsidian water content data were used to define distinct facies of the panum baf deposit these suggest a sequential three stage collapse model for the ancestral dome of the panum vent with destabilization first of its cold brittle outer margins and then of its hot ductile interior to an estimated depth of 260 m below the free air surface impact marks on clast faces that resulted from clast to clast interactions recorded details of the impacting mechanism we analyzed 15 000 marks and report for the first time their size shape and sorting to infer the flow regime of the baf during emplacement to a distance of 2 6 km from the vent clast to clast interactions occurred over a broad spectrum from purely collisional normal to clast faces to purely frictional clasts shearing in a unidirectional flow and recorded a transition to a more frictional flow regime in distal reaches as the sliding head of the baf decelerated and halted finally we briefly differentiate a similar but previously undescribed older deposit that predates the 1325 1350 a d north mono eruptive episode

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

emplacement temperatures of the november 22 1994 nuee ardente deposits merapi volcano java abstract a study of emplacement temperatures was carried out for the largest of the 22 november 1994 nuee ardente deposits at merapi volcano based mainly on the response of plastic and woody materials subjected to the hot pyroclastic current and the deposits and to some extent on eyewitness observations the study emphasizes the turgo kaliurang area in the distal part of the area affected by the nuee ardente where nearly 100 casualties occurred the term nuee ardente as used here includes channeled block and ash flows and associated ash clouds of surge and fallout origins the emplacement temperature of the 8 m thick channeled block and ash deposit was relatively high 550 c based mainly on eyewitness reports of visual thermal radiance emplacement temperatures for ash cloud deposits a few cm thick were deduced from polymer objects collected at turgo and kaliurang most polymers do not display a sharp melting range but polyethylene terephthalate used in water bottles melts between 245 and 265 c and parts of the bottles that had been deformed during fabrication molding turn a milky color at 200 c the experimental evidence suggests that deposits in the turgo area briefly achieved a maximum temperature near 300 c whereas those near kaliurang were

eruptive and magmatic cycles at fuego de colima volcano mexico the fuego de colima volcano displays a pattern of eruptive cyclicity characterized by lava flows and or slow effusions in an open crater alternating with short explosive events historical accounts field investigations and petrological data allow us to refine our understanding of the relationships between recurrent acidic acidic andesite and mafic andesitic products and this eruptive behaviour the second to last 1818 1913 and present 1913 present day cycles are instructive in this respect the short explosive events in 1818 and 1913 correspond to the initial mixing stage of a differentiated magmatic body with a new mafic input mathematical modeling shows that the pyroclastic products of 1913 result from the mixing between an acidic andesite 61 5 sio2 and an olivine andesite 56 sio2 in various ratios the final andesite mixture is made of 38 basaltic andesite and 62 acidic andesite the long effusive extrusive phases correspond to the ensuing differentiation stage of the new magmatic body for example the 1961 lava flows were derived from the final mixed and homogenized magma after the eruption of 1913 by fractionation of 7 plagioclase 9 pyroxene clinopyroxene orthopyroxene and 0 7 titanomagnetite the fractionation of 11 plagioclase 9 pyroxene and 1 4 titanomagnetite is required to produce the composition of the 1986 summit lava dome from the same parent in conclusion at fuego de colima an eruptive cycle begins with a short violent explosive event related to a mixing process and continues with a long effusive phase characterized by magmatic differentiation this scheme differs from others that have been proposed which consider that the eruptive cycles end with an explosive event

channel head location and characteristics using digital elevation models the drainage network is the conduit through which much surface water and sediment are routed within a catchment in a catchment the position of where hillslopes begin and channels end has long been considered the position of transition between diffusive processes upslope and the more incisive fluvial processes downslope consequently understanding channel head location is an important issue in understanding catchment hydrology and geomorphology this study examines channel head position and characteristics in a catchment in arnhem land northern territory australia in this study the position of channel heads was mapped within the catchment and plotted on a reliable digital elevation model of the catchment it was found that the majority of channel heads have relatively small source areas and that graphical catchment descriptors such as the area slope relationship and cumulative area distribution can provide reliable measures of the field position of the heads of first order streams and the transition from hillslope to channel the area slope relationship and cumulative area distribution are also shown to be good tools for determining digital elevation model grid size which can capture hillslope detail and the transition from hillslope to channel copyright 2005 john wiley sons ltd

pore fluid pressure and internal kinematics of gravitational laboratory air particle flows insights into the emplacement dynamics of pyroclastic flows 1 the emplacement dynamics of pyroclastic flows were investigated through noninvasive measurements of the pore fluid pressure in laboratory air particle flows generated from the release of fluidized and nonfluidized granular columns analyses of high speed videos allowed for correlation of the pressure signal with the flow structure the flows consisted of a sliding head that caused underpressure relative to the ambient followed by a body that generated overpressure and at the base of which a deposit aggraded for initially fluidized flows overpressure in the body derived from advection of the pore pressure generated in the initial column and decreased by diffusion during propagation relatively slow diffusion caused the pore pressure in the thinner flow to be larger than lithostatic at early stages furthermore partial auto fluidization revealed in initially nonfluidized flows also occurred and contributed to maintain high pore pressure whereas dilation or contraction of the air particle mixture with associated drag and or pore volume variation transiently led the pressure to decrease or increase respectively the combination of all these processes resulted in long lived high pore fluid pressure in the body of the flows during most of their emplacement in the case of the initially fluidized and slightly expanded 3 4 flows at least 70 100 of the weight of the particles was supported by pore pressure which is consistent with their inertial fluid like behavior dense pyroclastic flows on subhorizontal slopes are expected to propagate as inertial fluidized gas particle mixtures consisting of a sliding head possibly entraining basement derived clasts and of a gradually depositing body

channel planform geometry and slopes from freely available high spatial resolution imagery and dem fusion implications for channel width scalings erosion proxies and fluvial signatures in tectonically active landscapes article i nfo the rapid expansion of high spatial resolution optical sensors and imagery over the last decade presents ex ceptional opportunities for quantifying visible attributes of geomorphic systems in this study we detail a simple robust methodology changeom to extract continuous channel width and centerline datasets for single thread channels using freely available high spatial resolution imagery currently available in google earth and bing maps comparisons with a global dataset of field and lidar derived channel widths indicate minimal errors associated with the imagery and changeom methodology b1 overall while examples from the goriganga river indian himalaya and the yakima river wa usa emphasize the benefit of em pirical width values over established channel width scalings in deciphering fluvial responses to complex landscape forcings in tectonically active regions additionally accurate centerline delineation from the changeom methodology provides improved sinuosity measurements and when fused with coarse resolution digital elevation models dems removes along profile shortening and coincident increases in reach scale channel slope lastly comparisons of aster gdem v2 srtm v4 1 and lidar channel profiles extracted in moderate to high relief regions demonstrate the inferiority of the aster gdem for channel slope calcula tions despite the apparent spatial resolution advantages 9 the methodology presented here will facili tate new discoveries in the fluvial environment that have historically been difficult due to access and imagery resolution issues and provide greater perspective on channel signatures and responses to a host of landscape forcings especially in tectonically active bedrock and lower order drainage systems

emplacement temperature estimation of the 2015 dome collapse of volcan de colima as key proxy for flow dynamics of confined and unconfined pyroclastic density currents abstract the recent 10th 11th of july 2015 volcan de colima eruption involved the collapse of the summit dome that breached to the south generating pyroclastic density currents pdcs along the montegrande ravine on the southern flank of the volcano trees within the valley were buried uprooted and variably transported by the pdcs while the trees on the edges of the valley and on the overbanks were mainly burned and folded the emplacement temperature of valley confined and overbank pdc deposits were reconstructed using partial thermal remanent magnetization ptrm analysis of lithic clasts and charcoal reflectance analysis ro applied to the charred wood a total of 13 sites were sampled for the ptrm study and 39 charcoaled wood fragments were collected for the charcoal optical analysis along the entire deposit length in order to detect temperature variation from proximal to distal zone the result overlap from both data sets display a t max from 345 385 c in valley confined area from 3 5 to 8 5 km from the vent and 170 220 c from 8 0 to 10 5 km from the vent in unconfined distal area the emplacement temperature pattern along the 10 5 km long deposit appears related to the degree of topography confinement valley confined and unconfined in particular the valley confined setting is very conservative in terms of temperature while the major drop occurs in a very narrow space where the pdc expanded over unconfined flat topography just at the exit of the main valley this study represents the first attempt in determining the relationship between pdcs flow dynamics variation and topographic confining using deposit emplacement temperature as key proxy

deposits associated with the 1990 1995 eruption of unzen volcano japan abstract the 1990 1995 eruption of unzen volcano in japan was characterized by lava dome growth and block and ash flows triggered by dome collapse the repeated dome collapse events produced block and ash flow ash cloud surge and fine grained ash fall deposits block and ash flow deposits which are confined to valleys are massive to reversely graded very poorly sorted and contain non vesiculated to poorly vesiculated blocks up to 10 m across the deposits often display finer grained basal parts coarse clast depleted flow units which have intermediate grain size distribution between main flow and surge deposits occur as marginal part of block and ash flow deposits ash cloud surge deposits which spread more widely are finer grained and better sorted than block and ash flow deposits ash fall deposits which were derived from ash clouds of block and ash flows and were dispersed around the volcano are very fine grained and are as well sorted as the surge deposits lahars resulting from remobilization of pyroclastic debris devastated the base of the volcano and their deposits are moderately fines depleted and occasionally display two different lahar facies debris flow and hyperconcentrated flow units

predicting the block and ash flow inundation areas at volcan de colima colima mexico based on the present day february 2010 status abstract maps of areas potentially affected by block and ash flows and associated ash clouds are here presented for the volcan de colima titan2d 2 0 1 code has been used to simulate block and ash flows using as an input volume that of the actual summit dome assessed at 2 10 6 m 3 while the energy cone model has been used to delimit the possible inundated area from associated ash clouds both merapi and soufriere type block and ash flows were generated using different basal friction angles and maintaining fixed the volume and the internal friction angle the setting of the input parameters takes into account some flow characteristics such as the stepwise aggradation of different pulses that piled up to form the total thickness of the block and ash flow deposits the outputs of the computational routines are reported as two maps describing the total thickness of the final deposits they predict that thick deposits will engulf the ravines descending from the main cone to the west south and southeast with expected maximum runouts between 4 5 and 7 km the associated ash clouds have slightly longer runouts and the model predicts they will inundate some higher grounds that are not affected by the concentrate underflows the presented maps represent useful tools for managing the current block and ash flow hazard at volcan de colima

the pulse of calm fan deltas abstract at the heart of interpreting the history of earth surface evolution preserved in the rock record is distinguishing environmental allogenic forcing from internally generated autogenic noise allogenic deposits classically have been recognized by their cyclic nature which apparently results from periodic changes in base level sediment supply or tectonics autogenic deposits which are quite variable in their origin and scale are caused by the nonlinearity of sediment transport and might be expected to have a random or scale free fractal signature here we describe a robust mechanism that generates cyclic deposits by an autogenic process in experimental fan deltas sheet flow over the fan surface induces deposition and an increase in fluvial slope and curvature to a point where the surface geometry is susceptible to a channelization instability similar to channel initiation on hillslopes channelized flow results in incision and degrading of the fan surface to a lower slope releasing a

particle interaction inside debris flows evidence through experimental data and quantitative clast shape analysis abstract results of analytical experiments related to the dynamic behavior of debris flows are presented particle interaction and the amount and type of fines content present in the matrix aspects that govern debris flow behavior are studied via the morphological evolution of constituent particles four different mixtures of water and sediment with compositions resembling debris flows were prepared and put into a rotating drum known as a los angeles standard abrasion machine and studied at different time intervals for each sampling time quantitative shape analysis was performed using three morphological coefficients mc 2 mc 3 8 and mc 30 34 coefficient mc 2 gives information about particle ellipticity mc 3 8 is related to basic irregularities at a macro scale such as roundness mc 30 34 is related to microscale irregularities like surface texture coefficient mc 3 8 was shown to be very sensitive to silt content in the matrix and coefficient mc 30 34 to the presence of clay all three coefficients point to the fact that changes in shape between granulometric classes are gradual and follow a power law coarse granulometric classes acquire more circular and smooth profiles while small particles maintain their irregular profiles this phenomenon is the result of clast interaction processes within mixtures clast collisions between particles produce comminution of the coarsest fractions while finer particles fracture along their entire surface the rate at which these changes occur is related to the type of fine sediment present in the matrix changes in particle shape are an important tool for revealing internal dynamics because they are related to clast interaction and affect sedimentation processes inside these flows this type of experiment although not on a real scale provides important physical information for understanding the phenomena that occur inside debris flows enabling the study of a variety of textural parameters and their changes at regular time intervals the experimental patterns observed offer new insights into clast clast interaction rounding and comminuting theory with important implications for understanding rheological behavior and kinematics of flows and related hazards