run out of cut slope landslides mesh free simulations this study uses an incompressible smoothed particle hydrodynamics isph model to investigate the run out and deposit morphology of granular materials flowing down cut slopes the primary aim is to study the influence of various factors on the run out and to summarise a quantitative relationship for direct use in landslide hazard management in the model the granular materials are modelled as a rigid perfectly plastic material with a coulomb yield surface the coupled continuity equation and momentum equation are solved by a semi implicit algorithm the model is first validated and its results are carefully compared with various controlled experiments regarding granular flows the model reproduces the flows and correctly predicts the deposition profiles under various conditions then the computational results are used to study the run out and mobility of landslides for granular columns collapsing onto a flat surface a normalised run out and a new scaling relationship are proposed which are supported

on crustal corrections in surface wave tomography summary mantle models from surface waves rely on good crustal corrections we investigated how far ray theoretical and finite frequency approximations can predict crustal corrections for fundamental mode surface waves using a spectral element method we calculated synthetic seismograms in transversely isotropic prem and in the 3 d crustal model crust2 0 on top of prem and measured the corresponding time shifts as a function of period we then applied phase corrections to the prem seismograms using ray theory and finite frequency theory with exact local phase velocity perturbations from crust2 0 and looked at the residual time shifts after crustal corrections residuals fall within the uncertainty of measured phase velocities for periods longer than 60 and 80 s for rayleigh and love waves respectively rayleigh and love waves are affected in a highly non linear way by the crustal type oceanic crust affects love waves stronger while rayleigh waves change most in continental crust as a consequence we find that the imperfect crustal corrections could have a large impact on our inferences of radial anisotropy if we want to map anisotropy correctly we should invert simultaneously for mantle and crust the latter can only be achieved by using perturbation theory from a good 3 d starting model or implementing full non linearity from a 1 d starting model

a global view of martian surface compositions from mgs tes thermal emission spectrometer tes data from the mars global surveyor mgs are used to determine compositions and distributions of martian low albedo regions two surface spectral signatures are identified from low albedo regions comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass the distribution of the two compositions is split roughly along the planetary dichotomy the basaltic composition is confined to older surfaces and the more silicic composition is concentrated in the younger northern plains

two dimensional water flood and mudflow simulation flo 2d is a two dimensional finite difference model that simulates clear water flood hazards mudflows and debris flows on alluvial fans and urban floodplains interactive flood or mudflow routing between channel street and floodplain flow is performed using a uniform grid system to describe complex floodplain topography a quadratic rheological model developed from field and laboratory mudflow data enables appropriate simulations of flooding conditions ranging from clear water to hyperconcentrated sediment flows computer aided design cad graphics of predicted time sequenced flood depths automates the delineation of flood hazards replication of the 1983 rudd creek mudflow in utah demonstrates the capability of the model

fragmentation efficiency of explosive volcanic eruptions a study of experimentally generated pyroclasts abstract products of magma fragmentation can pose a severe threat to health infrastructure environment and aviation systematic evaluation of the mechanisms and the consequences of volcanic fragmentation is very difficult as the adjacent processes cannot be observed directly and their deposits undergo transport related sorting however enhanced knowledge is required for hazard assessment and risk mitigation laboratory experiments on natural samples allow the precise characterization of the generated pyroclasts and open the possibility for substantial advances in the quantification of fragmentation processes they hold the promise of precise characterization and quantification of fragmentation efficiency and its dependence on changing material properties and the physical conditions at fragmentation we performed a series of rapid decompression experiments on three sets of natural samples from unzen volcano japan the analysis comprised grain size analysis and surface area measurements the grain size analysis is performed by dry sieving for particles larger than 250 m and wet laser refraction for smaller particles for all three sets of samples the grain size of the most abundant fraction decreases and the weight fraction of newly generated ash particles up to 40 wt increases with experimental pressure potential energy for fragmentation this energy can be estimated from the volume of the gas fraction and the applied pressure the surface area was determined through argon adsorption the fragmentation efficiency is described by the degree of fine particle generation results show that the fragmentation efficiency and the generated surface correlate positively with the applied energy

impact crater formation in icy layered terrains on mars we present numerical simulations of crater formation under martian conditions with a single near surface icy layer to investigate changes in crater morphology between glacial and interglacial periods the ice fraction thickness and depth to the icy layer are varied to understand the systematic effects on observable crater features to accurately model impact cratering into ice a new equation of state table and strength model parameters for h2o are fitted to laboratory data the presence of an icy layer significantly modifies the cratering mechanics observable features demonstrated by the modeling include variations in crater morphometry depth and rim height and icy infill of the crater floor during the late stages of crater formation in addition an icy layer modifies the velocities angles and volumes of ejecta leading to deviations of ejecta blanket thickness from the predicted power law the dramatic changes in crater excavation are a result of both the shock impedance and the strength mismatch between layers of icy and rocky materials our simulations suggest that many of the unusual features of martian craters may be explained by the presence of icy layers including shallow craters with well preserved ejecta blankets icy flow related features some layered ejecta structures and crater lakes therefore the cratering record implies that near surface icy layers are widespread on mars

back analysis of geophysical flows using three dimensional runout model predicting the mobility and delineating the extent of geophysical flows remains a challenge for engineers the accuracy of predictions hinges on the reliability of input parameters of runout models

evidence of liquid water in recent debris avalanche on mars 1 the identification of landforms associated to liquid water on mars is a major goal for the understanding of the geologic and climatic evolution of this planet in the region of reull vallis near hellas basin lobate debris aprons are recent landforms due to the creep of water ice mixed with rocks among these landforms one unusually long debris apron has a tongue shape and gross morphology that indicates a different mechanism of deposition this study demonstrates using topographic data from viking dem and mola mars observer laser altimeter that the geometric parameters of this feature support the presence of liquid water during its flow this landform is therefore comparable in size to the most developed wet debris avalanches on earth its late amazonian age questions the presence of near surface liquid water in the recent geological past of mars

atmospheric effects on ejecta emplacement laboratory experiments allow the investigation of complex interactions between impacts and an atmosphere although small in scale they can provide essential first order constraints on the processes affecting late stage ballistic ejecta and styles of ejecta emplacement around much larger craters on planetary surfaces the laboratory experiments involved impacting different fine grained particulate targets under varying atmospheric pressure and density different gas compositions during crater formation ballistic ejecta form the classic cone shaped profile observed under vacuum conditions as atmospheric density increases for a given pressure however the ejecta curtain bulges at the base and pinches above this systematic change in the ejecta curtain reflects the combined effects of deceleration of ejecta smaller than a critical size and entrainment of these ejecta within atmospheric vortices created as the outward moving wall of ejecta displaces the atmosphere additionally a systematic change in emplacement style occurs as a function of atmospheric pressure largely independent of density contiguous ejecta rampart superposing ballistically emplaced deposits 0 06 to 0 3 bar ejecta flow lobes 0 3 to 0 7 bar and radial patterns 0 8 bar underlying processes controlling such systematic changes in emplacement style were revealed by observing the evolution of the ejecta curtain by changing target materials including layered targets and low density particulates by varying atmospheric density by changing impact angle and by comparing the ejecta run out distances with first order models of turbidity flows three distinct ejecta emplacement processes can be characterized ejecta ramparts result from coarser clasts sorted and driven outward by vortical winds behind the outward moving ejecta curtain this style of wind modified emplacement represents minimal ejecta entrainment and is enhanced by a bimodal size distribution in the ejecta such eddy supported flows are observed to increase in run out distance scaled to crater size with increasing atmospheric pressure by analogy with turbidity flows this scaled distance should increase as r1 2 for a given atmospheric pressure and degree of entrainment ejecta flows with much greater run out distances develop as the turbulent power in atmospheric response winds increase such flows overrun and scour the inner ejecta facies thereby producing distinct inner and outer facies the degree of ejecta entrainment depends on the dimensionless ratio of drag to gravity forces acting on individual ejecta and the intensity of the winds created by the outward moving curtain entrainment increases with increasing atmospheric density and ejection velocity crater size but decreases with ejecta density and size the intensity of curtain generated winds increases with ejection velocity crater size the dimensionless drag ratio characterizing the laboratory experiments can be applied to mars since the reduced atmospheric density is offset by the increased ejection velocities for kilometer scale events for a given crater size ejection velocity and atmospheric conditions a wide range of nonballistic ejecta emplacement styles could occur simply by varying ejecta sizes even without the presence of water alternatively the onset crater diameter for nonballistic emplacement styles can reflect the range of ejecta sizes possible from the diverse martian geologic history massive basalts to fine grained aeolian deposits scaling considerations further predict that ejecta run out distances scaled to crater size on mars should increase as r1 2 hence long run out flows dependent on crater diameter need not reflect depth to a buried reservoir of water on venus however the dense atmosphere maximizes entrainment and results in ejecta flow densities approaching a constant fraction of the atmospheric density under such conditions ejecta run out distances should decrease as r 1 2

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

the ries impact a double layer rampart crater on earth the ejecta blankets of impact craters formed on a planetary body that is free of significant quantities of volatiles show substantial differences from those formed on a volatile rich planetary body craters in volatile rich environments often have layered ejecta blankets with lobe like ramparts and long runout flows as seen for martian impact craters under volatile free conditions present on the moon and mercury radial textures and patterns and a gradational decrease in ejecta thickness with distance can be observed the ries crater in germany is one of the rare impacts on earth with a preserved ejecta blanket this crater was previously regarded as an analogue for impact formation on the moon here we demonstrate for the first time that the recent ries ejecta blanket contains a massive and continuous rampart structure at 1 45 2 12 crater radii from the crater center ejecta distribution and thickness as well as the ejecta fabric indicate the presence of fluids during the emplacement process although mars differs in atmospheric pressure and water distribution from earth the ries crater shows striking similarities to martian craters in particular those with double layered ejecta consequently terrestrial impact craters can be better used as analogues for understanding impact formation on mars than for planetary bodies with volatile free conditions as seen on the moon and mercury

identifying an index of subsurface volatiles on mars through an analysis of impact crater morphometry using principal component analysis layered ejecta craters comprise a significant fraction of the ejecta on mars and may form from the excavation of subsurface volatiles such as ice a recent global catalogue identified extensive numbers of layered ejecta craters and their properties and is examined here in this study over 10 000 single layered and double layered ejecta craters were analyzed by principal component analysis principal component analysis revealed the existence of four significant principal components for single layered ejecta craters and five for double layered ejecta craters which accounted for 73 and 80 of the sample variances respectively the first three pcs were interpreted as indices of impactor energy target volatiles and impactor angle the fourth component for both morphologies was interpreted as a resurfacing index the fifth component for double layered craters was identified as an index of preservation of the impact feature using the putative target volatile index identified through principal component analysis the spatial distribution of potential subsurface volatiles both past and geologically recent is mapped

explosive fragmentation criteria and velocities for vesicular magma abstract we present a new criterion for primary fragmentation of natural rock samples in shock tube experiments and new formulae for the effective strength of natural rock samples for the size of primary fragments and for fragmentation velocities these formulae and the fragmentation criterion are given in terms of the physical properties of the rock and in terms of experimental parameters the formulae and criterion are derived from numerical solutions and asymptotic analytic solutions to a novel recently published mathematical model for the explosive fragmentation of vesicular magma in shock tube experiments this model is singularly successful in accounting for the length scales observed in these experiments the criterion and formulae provide good matches to data from shock tube experiments on natural samples

ries bunte breccia revisited indications for the presence of water in itzing and otting drill cores and implications for the emplacement process we reassessed two drill cores of the bunte breccia deposits of the ries crater germany the objectives of our study were the documentation of evidence for water in the bunte breccia the evaluation of how that water influenced the emplacement processes and from which preimpact water reservoir it was derived the bunte breccia in both cores can be structured into a basal layer composed mainly of local substrate material overlain by texturally and compositionally diverse crater derived breccia units the basal layer is composed of the youngest sediments tertiary clays and upper jurassic limestone and has a razor sharp boundary to the upper breccia units which are composed of older rocks of upper jurassic to upper triassic age sparse material exchange occurred between the basal layer and the rest of the bunte breccia fluids predominantly came from the tertiary and the upper triassic sandstone formation in the basal layer tertiary clays were subjected to intense ductile deformation indicating saturation with water this suggests that water was mixed into the matrix creating a fluidized basal layer with a strong shear localization in the upper units upper triassic sandstones are intensely deformed by granular flow the texture requires that the rocks were disaggregated into granular sand vaporization of pore water probably aided fragmentation of these rocks in the otting core hot suevite t 600 c covered the bunte breccia shortly after its emplacement vertically oriented gas escape pipes in suevite partly emanate directly at the contact to the bunte breccia they indicate that the bunte breccia contained a substantial amount of water in the upper part that was vaporized and escaped through these vents

martian rampart crater ejecta experiments and analysis of melt water interaction abstract viking images of martian craters with rampart bordered ejecta deposits reveal distinct impact ejecta morphology when compared to that associated with similar sized craters on the moon and mercury topographic control of distribution lobate and terraced margins cross cutting relationships and multiple stratigraphic units are evidence for ejecta emplacement by surface flowage it is suggested that target water explosively vaporized during impact alters initial ballistic trajectories of ejecta and produces surging flow emplacement the dispersal of particulates during a series of controlled steam explosions generated by interaction of a thermite melt with water has been experimentally modeled preliminary results indicate that the mass ratio of water to melt and confining pressure control the degree of melt fragmentation ejecta particle size and the energy and mode of melt ejecta dispersal study of terrestrial lobate volcanic ejecta produced by steam blast explosions reveals that particle size and vapor to clast volume ratio are primary parameters characterizing the emplacement mechanism and deposit morphology martian crater ramparts are formed when ejecta surges lose fluidizing vapors and transported particles are deposited en masse this deposition results from flow yield strength increasing above shear stress due to interparticle friction

hydrothermal eruptions at unstable crater lakes insights from the boiling lake dominica lesser antilles abstract the boiling lake a major touristic attraction in the morne trois pitons national park dominica s west indies world heritage site is located in an area of high hydrothermal activity in the southern part of the island this spectacular lake is characterized by unstable behavior which has been interpreted to result from the presence of a water body above a fluctuating gas filled or multi phase vent system the system produces a near boiling lake that occasionally drains and refills with water without any simple periodicity despite the fact that such unstable draining lakes are thought to be non eruptive the boiling lake is known to have sourced occasional small hydrothermal eruptions as well as toxic gas emissions which accompany the refilling phase of these drainage events similar explosive events seem also to be likely after landslide slumped rocks from steep altered crater walls cover the vent area in the lake leading to overpressurized conditions in both cases rock expulsion and gas release continue to pose serious threats for tourists and tour guides while conceptual models exist describing possible mechanisms of the boiling lake drainage itself little information exists to date regarding the trigger mechanisms related to the explosive events further no estimation of the eruption processes and dynamics of these events has previously been attempted to address this knowledge gap we employ here a combined field and laboratory based approach in order to i characterize the properties of the dominant lithologies from the crater walls at boiling lake ii determine how the ongoing alteration may affect their petrophysical properties e g porosity and permeability and iii evaluate how water saturated unconsolidated wall rock materials behave when rapidly decompressed from a slightly elevated pressure and temperature conditions here we propose that it is the petrophysical state of the materials involved e g porosity permeability and alteration related strength which controls the style and energy of these eruptions as well as the potential for landslides from the crater walls the experimentally simulated scenarios included in this study are i decompression from only slightly elevated pressure conditions inferred for small hydrothermal eruptions occurring after lake drainage events and ii decompression from rapidly enhanced pressure conditions produced by the capping and overpressurization of the vent area following landslide episodes ejection velocities obtained from rapid decompression experiments were used as input parameters for ballistic trajectory calculations allowing for estimation of the potential area impacted by ejected debris we anticipate that this study will serve as a contribution to the understanding of the hazard potential of future hydrothermal eruptions at unstable crater lakes in general as well as providing direct insights into the ongoing hydrothermal activity at the boiling lake

experimental constraints on phreatic eruption processes at whakaari white island volcano vigorous hydrothermal activity interspersed by sequences of phreatic and phreatomagmatic eruptions occur at whakaari white island volcano new zealand here we investigate the influence of sample type hydrothermally altered cemented ash tuffs and unconsolidated ash lapilli and fragmentation mechanism steam flashing versus gas expansion on fragmentation and ejection velocities as well as on particle size and shape our rapid decompression experiments show that fragmentation and ejection speeds of two ash tuffs cemented by alunite and amorphous opal increase with increasing porosity and that both are significantly enhanced in the presence of steam flashing ejection speeds of unconsolidated samples are higher than ejection speeds of cemented tuffs as less energy is consumed by fragmentation fragmentation dominated by steam flashing results in increased fragmentation energy and a higher proportion of fine particles particle shape analyses before and after fragmentation reveal that both steam flashing and pure gas expansion produce platy or bladed particles from fracturing parallel to the decompression front neither fragmentation mechanisms nor sample type show a significant influence on the shape our results emphasize that under identical pressure and temperature conditions eruptions accompanied by the process of liquid water flashing to steam are significantly more violent than those driven simply by gas expansion therefore phase changes during decompression and cementation are both important considerations for hazard assessment and modeling of eruptions in hydrothermally active environments

magma fragmentation by rapid decompression the processes leading to magma fragmentation and the generation of pyroclastic debris during explosive volcanic eruptions are of fundamental importance in volcanology observations of explosive eruptions1 3 as well as theoretical analyses of the underlying processes4 have raised the question of whether the rapid decompression of highly viscous vesicular magma that results from the collapse of a lava dome or volcanic edifice can in itself produce explosive magma fragmentation and pyroclast formation here we report the results of a laboratory investigation of pyroclast formation following rapid decompression samples of magma from the 1980 eruption of mount st helens when rapidly depressurized from initial pressures of up to 12 mpa and at temperatures in the range 750 825 c fragmented to form pyroclastic products that are in many respects similar to those formed in real eruptions moreover we observe explosive fragmentation at temperatures well below those normally associated with magmatic processes suggesting that even relatively cool magma bodies can be very hazardous when subjected to rapid unloading events

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

the savage hutter avalanche model how far can it be pushed the savage hutter sh avalanche model is a depth averaged dynamical model of a fluid like continuum implementing the following simplifying assumptions i density preserving ii shallowness of the avalanche piles and small topographic curvatures iii coulomb type sliding with bed friction angle delta and iv mohr coulomb behaviour in the interior with internal angle of friction phi or delta and an ad hoc assumption reducing the number of mohr s circles in three dimensional stress states to one we scrutinize the available literature on information regarding these assumptions and thus delineate the ranges of validity of the proposed model equations the discussion is limited to relatively large snow avalanches with negligible powder snow component and laboratory sand avalanches starting on steep slopes the conclusion of the analysis is that the sh model is a valid model for sand avalanches but its mohr coulomb sliding law may have to be complemented for snow avalanches by a second velocity dependent contribution for very small snow avalanches and for laboratory avalanches starting on moderately steep and bumpy slopes it may not be adequate

experimental investigations on the explosivity of steam driven eruptions a case study of solfatara volcano campi flegrei steam driven eruptions both phreatic and hydrothermal expel exclusively fragments of non juvenile rocks disintegrated by the expansion of water as liquid or gas phase as their violence is related to the magnitude of the decompression work that can be performed by fluid expansion these eruptions may occur with variable degrees of explosivity in this study we investigate the influence of liquid fraction and rock petrophysical properties on the steam driven explosive energy a series of fine grained heterogeneous tuffs from the campi flegrei caldera were investigated for their petrophysical properties the rapid depressurization of various amounts of liquid water within the rock pore space can yield highly variable fragmentation and ejection behaviors for the investigated tuffs our results suggest that the pore liquid fraction controls the stored explosive energy with an increasing liquid fraction within the pore space increasing the explosive energy overall the energy released by steam flashing can be estimated to be 1 order of magnitude higher than for simple argon gas expansion and may produce a higher amount of fine material even under partially saturated conditions the energy surplus in the presence of steam flashing leads to a faster fragmentation with respect to gas expansion and to higher ejection velocities imparted to the fragmented particles moreover weak and low permeability rocks yield a maximum fine fraction using experiments to unravel the energetics of steam driven eruptions has yielded estimates for several parameters controlling their explosivity these findings should be considered for both modeling and evaluation of the hazards associated with steam driven eruptions

hydrothermal alteration of surficial rocks at solfatara campi flegrei petrophysical properties and implications for phreatic eruption processes abstract solfatara crater is located within the campi flegrei caldera to the west of naples italy it is one of the largest fumarolic manifestations known and the rocks hosting the hydrothermal system are affected by intense hydrothermal alteration alteration can result in changes of degassing behavior and in the formation of a cap rock thereby increasing the probability of phreatic eruptions here we investigate the effects of alunitic solfataric alteration on the mineralogy the physical properties porosity density permeability and the mechanical properties strength of the rocks involved as well as its influence on fragmentation and ejection behavior our results show that the pristine mineralogy of deposits from the vicinity of the solfatara cryptodome and from pisciarelli is almost completely replaced by amorphous silica and alunite the differences in the degree of alteration among the samples series are reflected in the investigated properties and behavior as well as in the analysis of the experimentally generated particles alunitic alteration increases porosity and permeability whereas it reduces density elastic wave velocity and strength leading to higher fragmentation and ejection speeds for the sample series examined in this study our results also show that alteration results in the generation of a high fraction of fines particle sizes

experimental estimates of the energy budget of hydrothermal eruptions application to 2012 upper te maari eruption new zealand sudden hydrothermal eruptions occur in many volcanic settings and may include high energy explosive phases ballistics launched by such events together with ash plumes and pyroclastic density currents generate deadly proximal hazards the violence of hydrothermal eruptions or explosive power depends on the energy available within the driving fluids gas or liquid which also influences the explosive mechanisms volumes durations and products of these eruptions experimental studies in addition to analytical modeling were used here to elucidate the fragmentation mechanism and aspects of energy balance within hydrothermal eruptions we present results from a detailed study of recent event that occurred on the 6th of august 2012 at upper te maari within the tongariro volcanic complex new zealand the eruption was triggered by a landslide from this area which set off a rapid stepwise decompression of the hydrothermal system explosive blasts were directed both westward and eastward of the collapsed area with a vertical ash plume sourced from an adjacent existing crater all explosions ejected blocks on ballistic trajectories hundreds of which impacted new zealand s most popular hiking trail and a mountain lodge 1 4 km from the explosion locus we have employed rocks representative of the eruption source area to perform rapid decompression experiments under controlled laboratory conditions that mimic hydrothermal explosions under controlled laboratory conditions an experimental apparatus for 34 by 70 mm cylindrical samples was built to reduce the influence of large lithic enclaves up to 30 mm in diameter within the rock the experiments were conducted in a temperature range of 250 degrees c 300 degrees c and applied pressure between 4 mpa and 6 5 mpa which span the range of expected conditions below the te maari crater within this range we tested rapid decompression of pre saturated samples from both liquid dominated conditions and the vapor dominated field further we tested dry samples at the same pressure and temperature conditions results showed that host rock lithology and state of the interstitial fluid was a major influence on the fragmentation and ejection processes as well as the energy partitioning clasts were ejected with velocities of up to 160 m s as recorded by high speed camera in addition to rare large clasts analogous to ballistics a large amount of fine and very fine 63 mu m ash was produced in all experiments the efficiency of transformation of the total explosive energy into fragmentation energy was estimated between 10 to 15 depending on the host rock lithology while less than 0 1 of this was converted into kinetic energy our results suggest that liquid to vapor flashing expansion provides an order of magnitude higher energy release than steam expansion which best explains the dynamics of the westward and most energetic directed blast at te maari considering the steam flashing as the primary energy source the experiments suggested that a minimum explosive energy of 7 x 10 10 to 2 x 10 12 j was involved in the te maari blast experimental studies under controlled conditions compared closely to a field example are thus highly useful in providing new insights into the energy release and hazards associated with eruptions in hydrothermal areas c 2016 the author s published by elsevier b v

analysis of run up of granular avalanches against steep adverse slopes and protective barriers the purpose of this study was to determine whether run up of rapid landslides or avalanches against protective dykes or walls placed perpendicular to the path can be predicted using a dynamic model based on shallow flow assumptions a series of laboratory experiments were carried out involving rapid flow of dry sand in a flume arrested by a steep adverse slope the barrier slope was varied and included a perpendicular wall a curved transition of varying radius separated the path from the barrier the dynamic internal and basal friction angles of the sand were determined by independent testing the results were analysed using a savage hutter type model a shock wave was observed as the flow approached the barrier toe and the model had to be improved by an original velocity smoothing algorithm to prevent numerical instability the new model is capable of simulating the entire process of run up of the leading edge against the barrier face deposition of the sand behind the barrier and backward migration o

multidisciplinary constraints of hydrothermal explosions based on the 2013 gengissig lake events kverkfjoll volcano iceland hydrothermal explosions frequently occur in geothermal areas showing various mechanisms and energies of explosivity their deposits though generally hardly recognised or badly preserved provide important insights to quantify the dynamics and energy of these poorly understood explosive events furthermore the host rock lithology of the geothermal system adds a control on the efficiency in the energy release during an explosion we present results from a detailed study of recent hydrothermal explosion deposits within an active geothermal area at kverkfjoll a central volcano at the northern edge of vatnajokull on august 15th 2013 a small jokulhlaup occurred when the gengissig ice dammed lake drained at kverkfjoll the lake level dropped by approximately 30 m decreasing pressure on the lake bed and triggering several hydrothermal explosions on the 16th here a multidisciplinary approach combining detailed field work laboratory studies and models of the energetics of explosions with information on duration and amplitudes of seismic signals has been used to analyse the mechanisms and characteristics of these hydrothermal explosions field and laboratory studies were also carried out to help constrain the sedimentary sequence involved in the event the explosions lasted for 40 50 s and involved the surficial part of an unconsolidated and hydrothermally altered glacio lacustrine deposit composed of pyroclasts lavas scoriaceous fragments and fine grained welded or loosely consolidated aggregates interbedded with clay rich levels several small fans of ejecta were formed reaching a distance of 1 km north of the lake and covering an area of approximately 0 3 km2 with a maximum thickness of 40 cm at the crater walls the material volume of approximately 104 m3 has been ejected by the expanding boiling fluid generated by a pressure failure affecting the surficial geothermal reservoir the maximum thermal craterisation and ejection energies calculated for the explosion areas are on the order of 1011 1010 and 109 j respectively comparison of these with those estimated by the volume of the ejecta and the crater sizes yields good agreement we estimate that approximately 30 of the available thermal energy was converted into mechanical energy during this event the residual energy was largely dissipated as heat while only a small portion was converted into seismic energy estimation of the amount of freshly fragmented clasts in the ejected material obtained from sem morphological analyses reveals that a low but significant energy consumption by fragmentation occurred decompression experiments were performed in the laboratory mimicking the conditions due to the drainage of the lake experimental results confirm that only a minor amount of energy is consumed by the creation of new surfaces in fragmentation whereas most of the fresh fragments derive from the disaggregation of aggregates furthermore ejection velocities of the particles 40 50 m s measured via high speed videos are consistent with those estimated from the field the multidisciplinary approach used here to investigate hydrothermal explosions has proven to be a valuable tool which can provide robust constraints on energy release and partitioning for such small size yet hazardous steam explosion events

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

dynamics of explosive volcanism at unzen volcano an experimental contribution knowledge of the dynamics of magma fragmentation is necessary for a better understanding of the explosive behaviour of silicic volcanoes here we have measured the fragmentation speed and the fragmentation threshold of five dacitic samples 6 7 53 5 vol open porosity from unzen volcano kyushu japan the measurements were carried out using a shock tube based fragmentation apparatus modified after alidibirov and dingwell 1996a b the results of the experimental work confirm the dominant influence of porosity on fragmentation dynamics the velocity of the fragmentation front increases and the value of the fragmentation threshold decreases with increasing porosity further we observe that the fragmentation speed is strongly influenced by the initial pressure difference and the texture of the dacite at an initial pressure difference of 30 mpa the fragmentation speed varies from 34 m s for the least porous sample to 100 m s for the most porous sample these results are evaluated by applying them to the 1990 1995 eruptive activity of unzen volcano emplacements of layered lava dome lobes merapi type pyroclastic flows and minor explosive events dominated this eruption the influence of the fragmentation dynamics on dome collapse and vulcanian events is discussed

permeability control on magma fragmentation fragmentation of porous magma that is subject to gas overpressure is considered to be a crucial process in the generation of explosive volcanic eruptions a decompressive event e g rapid magma ascent landslide dome collapse disrupts the stress equilibrium between the gas phase and the surrounding melt when the gas in the pores is exposed to a pressure gradient it may either fragment the surrounding magma or escape from the magma along an existing pathway of cracks and interconnected bubbles therefore magma permeability can be a decisive parameter in determining if an eruption experiences fragmentation i e whether it is explosive or effusive or exhibits a temporal transition between the two eruptive styles despite the central role that gas permeability may play in the fragmentation of volcanic rocks previous studies have not experimentally verified or quantified this influence based on a comprehensive database of combined permeability and fragmentation experiments we show that high permeability substantially increases the overpressure required to fragment porous volcanic rocks our results allow us to deduce a fragmentation criterion that incorporates gas permeability as well as porosity and internal overpressure this criterion implies that the energy required for fragmentation is less dependent on the actual pore geometry than on the way the void space is interconnected and thus on the contribution of permeable gas flow to decompression

an instability mechanism in the formation of the martian lobate craters and the implications for the rheology of ejecta 1 lobate craters are an indication of the existence of fluids in the martian megaregolith the emplacement of the ejecta could be similar to debris flow dynamics in this paper we suggest that the lobate ejecta result of an instability mechanism during the surface flow indeed recent experimental studies on injection of heavy viscous fluid in a lighter one show that the wavelength of the instability depends on the viscosity and density contrast between the two fluids an extension of this 2d experiment to a cylindrical geometry has been carried out in that case we demonstrate that a distribution of wavelengths is related to viscosity contrast those results have been applied to 250 single layer craters in lunae planum and sinai planum to measure the variation of viscosity with depth the results are in agreement with a possible 1 km thick volatile rich layer above a less porous one

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

magma fragmentation speed an experimental determination abstract the propagation speed of a fragmentation front combined with the ascent velocity of magma is in all likelihood a controlling factor in the dynamics of explosive volcanic eruptions direct measurement of the fragmentation speed in natural systems appears to be impossible at present fortunately laboratory experiments can provide information on the propagation speed of the fragmentation front here we present the results of fragmentation speed determinations using a so called fragmentation bomb these are to the best of our knowledge the first in situ fragmentation speed determinations performed on magma natural magma samples merapi basaltic andesite mount st helens dacite and unzen dacite have been investigated in the temperature range of 20 950 c and at pressures up to 25 mpa two techniques have been employed firstly in experiments at 20 c dynamic pressure transducers were placed above and below the magma samples and the fragmentation speed of the magma sample was derived from an analysis of the decompression curves secondly at elevated temperatures an alternative technique was introduced and successfully employed this involved the severing via fragmentation of conducting wires placed within the samples at various heights fragmentation speeds are very low falling in the range of 2 70 m s and increasing with an increase in the magnitude of the decompression step responsible for the fragmentation the first high temperature determination seems consistent with low temperature results implications for explosive volcanism are discussed briefly

the formation of fluidized ejecta on mars by granular flows a simple granular flow model is used to investigate some of the conditions under which ejecta may flow as a granular media the purpose of this investigation is to provide some bounds as to when either volatiles or an atmosphere are required to explain the fluid like morphology of many martian ejecta deposits we consider the ejecta deposition process from when an ejecta curtain first strikes a target surface via ballistics and possibly flows thereafter a new finding is that either hard smooth surfaces or slightly erodible surfaces allow ejecta to flow readily as a granular medium neither volatiles nor an atmosphere are required to initiate flow a low friction coefficient between ejecta grains can also generate flow and would be analogous to adding volatiles to the ejecta the presence of either a rough or a densely packed erodible surface does not permit easy ejecta flow high friction coefficients between ejecta grain also prevent flow while changes in the coefficient of restitution a measure of how much energy is retained after collisions between particles plays a minor role in the flow dynamics of ejecta a hard smooth or a somewhat erodible surface could be generated by past fluvial activity on mars which can either indurate a surface erode and smooth a surface or generate sedimentary terrains that are fairly easy to erode no ramparts or layered ejecta morphologies are generated by our model but this may be because several simplifying assumptions are used in our model and should not be construed as proof that either volatiles or an atmosphere are required to form fluidized ejecta morphologies

water or ice in the martian regolith clues from rampart craters seen at very high resolution abstract very high resolution viking orbiter images 8 17 m per pixel have been used to investigate the morphology of martian rampart crater ejecta blankets and the crater interiors with the objective of identifying the fluidizing medium for the ejecta and the physical properties of the target rock the occurrence of well preserved small scale pressure ridges and scour marks evidence for subsidence around isolated buried blocks in partially eroded ejecta lobes and the stability of crater walls and distal ramparts argue for ground ice being the dominant state for volatiles within the target rocks at the time of impact rare examples of channels 190 650 m wide on the surfaces of ejecta blankets and on the inner walls of the crater cerulli indicate that in some instances liquid water was incorporated into the ejecta during its emplacement no morphological evidence has been found to discount the idea that atmospheric effects were partially responsible for ejecta fluidization but it is clear that these effects were not the sole reason for the characteristic lobate deposits surrounding at least some rampart craters on mars

a hydroclimatic threshold for landslide initiation on the north shore mountains of vancouver british columbia landslides triggered by rainfall are the cause of thousands of deaths worldwide every year one possible approach to limit the socioeconomic consequences of such events is the development of climatic thresholds for landslide initiation in this paper we propose a method that incorporates antecedent rainfall and streamflow data to develop a landslide initiation threshold for the north shore mountains of vancouver british columbia hydroclimatic data were gathered for 18 storms that triggered landslides and 18 storms that did not discriminant function analysis separated the landslide triggering storms from those storms that did not trigger landslides and selected the most meaningful variables that allow this separation discriminant functions were also developed for the landslide triggering and nonlandslide triggering storms the difference of the discriminant scores cs for both groups is a measure of landslide susceptibility during a storm the variables identified that optimize the separation of the two storm groups are 4 week rainfall prior to a significant storm 6 h rainfall during a storm and the number of hours 1 m3 s discharge was exceeded at mackay creek during a storm three thresholds were identified the landslide warning threshold lwt is reached when cs is 1 the conditional landslide initiation threshold ctli is reached when cs is zero and it implies that landslides are likely if 4 mm h rainfall intensity is exceeded at which point the imminent landslide initiation threshold itli is reached the lwt allows time for the issuance of a landslide advisory and to move personnel out of hazardous areas the methodology proposed in this paper can be transferred to other regions worldwide where type and quality of data are appropriate for this type of analysis

cracking of lithosphere north of the galapagos triple junction the galapagos triple junction is a ridge ridge ridge triple junction where the cocos nazca and pacifi c plates meet around the galapagos microplate directly north of the large scarps of the cocos nazca rift a 250 km long and 50 km wide band of northwest southeast trending cracks with volcanics at their western ends crosscuts and blankets the north south trending abyssal hills of the east pacifi c rise it appears that the roughly northeast southwest extension of east pacifi c rise generated seafl oor has been accommodated by a succession of minor rifts that during at least the past 4 m y had their triple junctions with the east pacifi c rise at distances of 50 100 km north of the tip of the propagating cocos nazca rift we propose that the rift locations are controlled by stresses associated with the dominant cocos nazca rift and scaled by the distance of its tip to the east pacifi c rise we speculate that similar ephemeral rifts occurred south of the cocos nazca rift and were instrumental in the origin of the rotating galapagos microplate ca 1 5 ma

two years at meridiani planum results from the opportunity rover the mars exploration rover opportunity has spent more than 2 years exploring meridiani planum traveling 8 kilometers and detecting features that reveal ancient environmental conditions these include well developed festoon trough cross lamination formed in flowing liquid water strata with smaller and more abundant hematite rich concretions than those seen previously possible relict hopper crystals that might reflect the formation of halite thick weathering rinds on rock surfaces resistant fracture fills and networks of polygonal fractures likely caused by dehydration of sulfate salts chemical variations with depth show that the siliciclastic fraction of outcrop rock has undergone substantial chemical alteration from a precursor basaltic composition observations from microscopic to orbital scales indicate that ancient meridiani once had abundant acidic groundwater arid and oxidizing surface conditions and occasional liquid flow on the surface

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

a candidate methane clathrate destabilisation event on mars a model for sub millennial scale climatic change on earth abstract methanogenic explosion of siberian permafrost mounds over the last three years questions whether this new phenomenon is the first sign of cascading release under climatic warming identical mounds occur in their millions on mars but are uniformly interpreted as ancient volcanic structures a geomorphic paradigm whose geological basis continues to escape objective observation here i show that thousands of mars mounds have recently exploded onto overlying aeolian dunes and are thus active and climatogenic the time lag between formation and synchronous explosion naturally explained by a trigger of climatic origin time transgressive mass explosion of a multi billion year aged source has no parallel in rock forming processes and points to regional scale mobilisation of volatiles this abrupt destabilisation event having immediate implications for hypothesised cascading releases from terrestrial clathrate reservoirs whether the siberian explosions are new or simply newly discovered is uncertain but their spatial density is 20 000 times lower than on mars inconsistent with ongoing multi millennial scale process we should therefore consider the possibility that they are just beginning and irrespective of volatile involved we now have a scaleable example of how they might end were the clathrates of the east siberian arctic shelf to degas on the density and frequency of mars then the entire reservoir would be depleted and unstoppable runaway warming initiated

trends in large deformation analysis of landslide mass movements with particular emphasis on the material point method traditional geotechnical analyses for landslides involve failure prediction i e onset of failure and the design of structures that can safely withstand the applied loads the analyses provide limited information on the post failure behaviour modern numerical methods are able to simulate large mass movements and there is an opportunity to utilise such methods to evaluate the risks of catastrophic damage if a landslide occurs in this paper various large deformation analysis methods are introduced and their applicability for solving landslide problems is discussed since catastrophic landslides often involve seepage forces consideration of the coupled behaviour of soil and pore fluid is essential two approaches to model soil pore fluid coupling in large deformation analysis using the material point method mpm are introduced an example simulation is presented for each approach one on a model levee failure and the other on a natural cut slope failure the selborne experiment conducted by cooper and co workers in 1998 in the levee failure case mpm simulation was able to capture a complex failure mechanism including the development of successive shear bands the simulation was also able to predict excess pore pressure generation during the failure propagation and the subsequent consolidation stage the simulations demonstrated the importance of the dilation characteristics of soil as well as changes in geometry for the post failure behaviour in the selborne case mpm was able to simulate the progressive failure of brittle overconsolidated clay the evolution of shear stresses along the failure surface was also captured by the mpm the changes in the pore pressure and the actual shape of the failure surface were simulated by the mpm the importance of accurately modelling the shear band within the mpm framework is highlighted

finite element analysis for rockfall and debris flow mitigation works1 landslide risks arising from boulder falls and debris flows are commonly mitigated using rigid and flexible barriers debris barrier interaction is a complicated process so current design methods

estimating total resisting force in flexible barrier impacted by a granular avalanche using physical and numerical modeling flexible barriers are a promising tool for protection against extremely rapid landslides such as debris flow and debris avalanches with landslide impacts of any size the total force induced withi

experimental volcanology on eruptive products of unzen volcano abstract protracted dome building eruptions may be profitably investigated using laboratory based experiments density distribution studies on the pyroclastic flow deposits of unzen 1990 1995 allow us to apply the results of experimental investigations on unzen samples to the interpretation of the last eruption of unzen here primary laboratory experiments have focused on several aspects of the degassing permeability and the fragmentation behavior threshold speed and efficiency those investigations have been flanked by analyses of flexural strength fracture toughness and seismic velocities to provide new insights into eruption related processes here we present a review of these results and their application to the eruption dynamics of unzen volcano we propose that efforts be made to incorporate routinely such comprehensive experimental analyses into the response to emerging volcanic crises in future

a model for the runout analysis of rapid flow slides debris flows and avalanches runout analyses are used for risk assessment and design of remedial measures against rapid landslides such as debris flows debris avalanches rockslide avalanches large scale liquefaction failure

dynamic analysis of an extraordinarily mobile rock avalanche in the northwest territories canada the pre historic rock avalanche at avalanche lake was a spectacularly mobile rock avalanche that resulted in the largest documented runup of any landslide on earth the runout of the 200 mm3 event was a complex and three dimensional process that created three distinct depositional lobes there is some controversy as to whether the presence of glacial ice played an important role in the dynamics of this event to investigate this hypothesis an advanced three dimensional numerical landslide runout model was used to reconstruct the dynamics of this event it was found that a conventional runout model is able to reproduce the bulk characteristics of this event including its spectacular runup without accounting for glacial ice a sensitivity analysis was performed to determine the factors that control the mobility of this event it was found that low strength in the source zone as well as the presence of significant internal strength is required to reproduce the 600 m runup this has important implication

martian craters viewed by the thermal emission imaging system instrument double layered ejecta craters 1 the thermal emission imaging system themis visible vis images provide new insight into the nature and development of the unique ejecta deposits of martian craters this study focuses on double layered ejecta dle craters to date over 100 dle craters have been examined using mainly themis vis data our observations suggest that emplacement of dle crater ejecta occurred in two stages with the inner ejecta layer emplaced similar to single layered ejecta sle crater ejecta this may have involved both ballistic and flow processes in contrast the outer ejecta layer of dle craters appears to have been emplaced through the high velocity outflow of materials from tornadic winds generated by the advancing ejecta curtain or base surge remarkably dle craters lack secondary craters which suggests that the large ejecta blocks that normally produce such craters may have either been entrained and or crushed by these winds or fragmented as a result of the presence of water in the target materials these observations suggest that volatiles either trapped in the subsurface or in the atmosphere have played a key role in the emplacement of the ejecta of dle craters and leaves open the question as to what role volatiles play in the emplacement of ejecta of other types of fluidized ejecta craters i e sle and mle craters because dle craters are found in many different regions of mars often in close proximity to other types of craters conditions e g atmospheric density that produce dle craters must fluctuate or the martian crust must be unexpectedly heterogeneous laterally and vertically while the degree of heterogeneity has yet to be recognized recent suggestions about possible martian climate change raises the possibility of impact into target materials that are periodically wet or that a significantly higher atmospheric pressure may be periodically present

atmospheric effects on ejecta emplacement and crater formation on venus from magellan the venus cratering record provides a unique environment for assessing the effects of both gravity and an atmosphere on impact crater formation this contribution uses surface signatures of energy partitioning as a framework for testing extrapolations from laboratory experiments and other planetary settings seven general conclusions can be drawn first the dense lower atmosphere of venus takes on the role of a low density target for bodies smaller than about 4 km in diameter air blasts created by cratering in the atmosphere create distinctive surface signatures that allow the derivation of an independent assessment of impactor energy at the limit of break up second dynamic pressures during entry of larger bodies will exceed their strength limit but may not prevent penetration of the atmosphere due to aerodynamic reshaping that minimizes the drag coefficient such a process may account for the formation of unusually small craters 1 3 km third the dense atmosphere of venus preserves signatures of early time cratering processes on the surface that are typically lost on atmosphere free surfaces such signatures not only provide another estimate of impactor energy but also include a distinctive record of the impactor i e comet versus asteroid in distinctive run out flows created before the crater has finished formation strong winds and turbulence associated with the atmospheric disturbance at later times create wind streaks behind topographic barriers fourth ballistic ejection of excavated debris occurs from craters on venus just as it does on planets without an atmosphere thereby underscoring the fundamental mechanical transfer of energy from impactor to target fifth ejecta emplacement is nonballistic due to the large dynamic forces acting on the advancing curtain and its constituent ejecta the outward moving ejecta curtain induces strong response winds that entrain ejecta and drive a ground hugging debris flow outward without returning to the cavity flow separation creates an overriding run out ejecta flow further sustained by atmospheric turbulence and identified as radar dark lobate lobes sixth radar dark parabolas are proposed to be late time fallout deposits created as the downrange fireball evolves aloft perhaps analogous to terrestrial tektite strewn fields and seventh the response of crater formation to the atmosphere is conversely expressed by a reduction in cratering efficiency as revealed by the unusually large central peak complexes and the unexpected diameter depth relations of craters hence surface ages may be significantly underestimated

outwash plains and thermokarst on mars abstract the spatial distribution of different types of rampart craters on mars suggests a hemispheric asymmetry in the distribution of ground ice the northern plains especially major topographic depressions near the terminations of outflow channels have high percentages of rampart craters two of these basins acidalia and utopia planitiae received extraordinarily large amounts of water and sediment from the chryse and elysium outflow channels in both regions the analysis of high resolution viking pictures 12 m pixel indicates a concentration of kilometer scale depressions that are similar in size and form to thermokarstic features in yakutia siberia and parts of the arctic coastal plain of north america accordingly we infer that 1 utopia planitia and acidalia planitia may contain thick laterally continuous ice rich sedimentary deposits related to outflow channel forming floods and 2 these areas of mars may have experienced thermokarstic processes similar to modern thermokarstic processes in some periglacial regions of earth

north polar region craterforms on mars geometric characteristics from the mars orbiter laser altimeter abstract this study focuses on topographic characterization of ice associated north polar region impact craters and several enigmatic polar craterforms using new information from the mars orbiter laser altimeter mola an instrument aboard the mars global surveyor mgs orbiter we find that for ice associated craters the topography reveals several surprising results not previously apparent from orbital images alone first geometric properties for several impact craters associated with ice and frost deposits suggest that cavity infill is as high as 80 of reconstructed preerosion levels second craters associated with ice also demonstrate unique cavity geometries relative to their nonpolar counterparts finally in some cases ice associated impact features are anomalously deep on the basis of depths modeled from the best available scaling laws we suggest that burial of these impact features by either episodic advance of the polar cap margin or by continuous deposition at the highest rates previously estimated for the north polar region of mars has occurred subsequent stripping has exhumed the features leaving behind cavity infill deposits and a few of these display topographic levels above the surrounding preimpact surface in at least one case cavity interior deposits show layering with a typical thickness of 10 m suggesting episodic deposition and ablation of materials as in the polar layered terrain in addition to ice associated craters we investigated the topography of several enigmatic polar craterforms in particular a few craterforms within 150 km of the permanent north polar cap appear to resemble simple effusive lava shield volcanoes found on earth their geometric properties cannot be reconciled with previous suggestions that they were manifestations of martian hydromagmatic processes i e maar volcanism mola s initial measurements of impact craters and other craterforms in the north polar latitudes of mars support the concept of a geologically recent surface with evidence of effusive volcanism and enhanced sedimentation in addition the measured impact crater depths for ice associated craters suggest at least a few cases of enhanced excavation and thus a possibly weaker target relative to the typical northern hemisphere plains

insights into complex layered ejecta emplacement and subsurface stratigraphy in chryse planitia mars through an analysis of themis brightness temperature data layered ejecta craters on mars have been interpreted to indicate the presence of volatiles in the substrate making them important targets for the investigation of sites of astrobiological significance if the ejecta are associated with the presence of water in the substratum specific surface grain size trends are expected in this study we explore the distribution of grain sizes in the layered ejecta of impact craters located in chryse planitia using thermal emission imaging system themis thermal infrared data ejecta grain size trends in conjunction with ejecta mobility and lobateness values are applied to assess the degree of surface flow of the ejecta and in turn to constrain the plausible volatile abundance cohesion and fine particle content of the target materials craters with a larger fraction of small grain sizes in their ejecta showed greater ejecta mobility and lobateness consistent with a water rich and or a low cohesion target craters displaying decreasing grain size with increasing radius had smaller diameters and lower ejecta mobility and lobateness indicating only a minimal component of surface ejecta flow ejecta grain size trends varied with crater diameter from which the presence of vertical compositional stratigraphy in chryse planitia is inferred and interpreted our observations are synthesized into a number of plausible geologic scenarios for chryse planitia

landslide mobility analysis for design of multiple debris resisting barriers multiple debris resisting barriers have been commonly used worldwide to mitigate debris flows in drainage lines however a well developed methodology to assess the mobility of debris flows with co

martian impact craters correlations of ejecta and interior morphologies with diameter latitude and terrain abstract the premise of this study is that global analysis of crater morphologies can discriminate between the effects of impact energy atmosphere and subsurface volatiles based on the correlation between morphology and latitude diameter and terrain this study focuses on seven ejecta and nine interior morphologies associated with 3819 craters 8 km in diameter distributed across the entire martian surface this data set is sufficiently large to provide statistically viable results on a global scale the results of the analyses indicate that changes in ejecta and interior morphology correlate with increases in crater diameter excavation depths corresponding to these diameters are calculated from depth diameter relationships and are compared to the theoretical distribution of subsurface volatiles the different ejecta morphologies can be described by impact into material with varying proportions of volatiles and the latidudinal variations seen for rampart crater morphologies correlate well with the proposed latitude depth relationship for ice and brines across the planet many of the interior structres show distributions indicative of terrain dependent influences for example the concentrations of central pit craters around ancient impact basins and on alba patera suggest that volatiles preferentially collect in these areas however central peak and peak ring interior morphologies show little relationship to planetary properties and probably result from changes in impact energy thus many of the unique morphologies associated with martian impact craters result from the presence of subsurface volatiles

the lawn hill annulus an ordovician meteorite impact into water saturated dolomite the lawn hill impact structure lhis is located 250 km n of mt isa in nw queensland australia and is marked by a highly deformed dolomite annulus with an outer diameter of similar to 18 km overlying low metamorphic grade siltstone sandstone and shale along the ne margin of the georgina basin this study provides detailed field observations from sections of the lawn hill annulus and adjacent areas that demonstrate a clear link between the deformation of the dolomite and the lawn hill impact ar 40 ar 39 dating of impact related melt particles provides a time of impact in the ordovician 472 8 ma when the georgina basin was an active depocenter the timing and stratigraphic thickness of the dolomite sequence in the annulus suggest that there was possibly up to 300 m of additional sedimentary rocks on top of the currently exposed thorntonia limestone at the time of impact the exposed annulus is remarkably well preserved with preservation attributed to postimpact sedimentation the lhis has an atypical crater morphology with no central uplift the heterogeneous target materials at lawn hill were probably low strength porous and water saturated with all three properties affecting the crater morphology the water saturated nature of the carbonate unit at the time of impact is thought to have influenced the highly brecciated nature of the annulus and restricted melt production the impact timing raises the possibility that the lawn hill structure may be a member of a group of impacts resulting from an asteroid breakup that occurred in the mid ordovician 470 6 ma

the effects of water vaporization on rock fragmentation during rapid decompression implications for the formation of fluidized ejecta on mars abstract crater and ejecta morphology provide insight into the composition and structure of the target material fluidized ejecta surrounding martian rampart craters are thought to result from the addition of water to the ejecta during impact into a water rich ice or liquid regolith here we test experimentally an alternate hypothesis we propose that the decompression of a rock water mixture across the water vaporization curve during the excavation stage of impact cratering results in an increased proportion of fines in the ejecta this enables the ejecta to flow with little or no liquid water present to test this hypothesis fragmentation experiments were conducted on sandstone 28 vol open porosity from the northern eldorado mountains nevada using a shock tube apparatus at the lmu munich germany rock samples with 0 92 of their open pore space filled with water were pressurized to 15 mpa at 177 c or 300 c and rapidly decompressed as the water vaporization curve is crossed the water in the pore space rapidly flashes to steam causing together with the expanding gas in the water free pore space the sample to fragment the presence of water has a significant effect on the grain size distribution and grain shape of the fragmented rock samples in comparison with dry control samples samples with water with 15 50 open pore space exhibit much smaller grain sizes the predominant grain shape of dry as well as partially water saturated samples is bladed reflecting fracturing parallel to the decompression front samples with 80 water in open pore space had an increase in fines and larger particles but less intermediate sized particles fragments from experiments with 80 water in open pore space also displayed a more equant grain shape indicating that the decompression of water caused fracturing independent of the orientation of the decompression front these results may provide insight into the morphology of martian rampart craters we propose here that even relatively low water contents in the target 16 may be sufficient to produce a significant increased proportion of fines allowing the ejecta to flow with little or no water present

impact generated winds on mars abstract bright and dark wind streaks across mars record wind patterns related to atmospheric circulation in some cases these streaks represent erosion of a surface veneer in others they indicate sand grains mobilized by strong vortices shed off of positive relief such as crater rims while many streaks change length or orientation over time others not only remain unchanged but also may indicate a completely different wind direction these permanent streaks could reflect past circulation patterns in response to conditions related to orbital forcing e g thomas and veverka 1979 veverka et al 1981 here however we focus on a subset of permanent wind streaks unrelated to global circulation rather to impact generated winds that can extend more than 500 km away from the crater nighttime images from the mars odyssey s thermal emission imaging system themis reveal certain large craters 15 km in diameter having sets of thermally bright streaks that radiate from certain fresh impact craters these streaks extend from pre existing topographic highs crater rims wrinkle ridges beyond the continuous ejecta deposits to more than 6 crater radii unrelated to secondary craters for illustration this contribution primarily focuses on the 20 km diameter santa fe crater in chryse planitia context camera ctx images reveal that these streaks correspond to zones of erosion the thermally bright rays in nighttime images correlate with regions where coarser materials have been exposed not always resolved even in hirise images models of the impact process indicate impact generated vapor most likely generated intense winds that scoured the region well before arrival of secondary craters and later ejecta run out flows pre existing relief such as crater rims disturbed this flow and generated intense cross flow instabilities resulting in long parallel streaks

an improved landslide mobility model a relatively simple and versatile numerical model known as dan developed by oldrich hungr for the assessment of landslide mobility has been enhanced to incorporate the consideration of a trapezoidal shaped flow channel for more realistic modelling purposes this enhanced debris mobility model dmm has been programmed to run on a spreadsheet and has been calibrated against detailed landslide data in hong kong in contrast to previous work the enhanced dmm eliminates the limitations inherited from the assumption of a rectangular flow channel with frictionless side boundaries when using dmm no predefined width of landslide is needed the dmm simulates landslide mobility with the flow resistance on the whole wetted perimeter of the channel calculates the surface width of the landslide based on the cross sectional geometry of the channel and is capable of predicting a lobe shaped debris deposition area this technical note presents details of the enhancement to the dan formulation key words landslides

simulation of interactions between debris flow and check dams on three dimensional terrain abstract debris flows are rapid gravity driven flows of sediment water mixture which can be greatly destructive due to its huge volume high velocity and large impact force check dam is essential protective structure for controlling debris flow however it is a challenging work to assess the interactions between debris flow and check dam especially when involving complex topography and dam destruction a numerical method was developed in this study to investigate the interactions between debris flow and check dam on three dimensional terrain the debris flow and check dam were simulated by smoothed particle hydrodynamics sph method and finite element method fem respectively the method was validated by a dam break problem and a granular flow flume test an actual debris flow event originated from failure of tailings dams on 19 july 1985 in stava italy was simulated as an example the results indicate that the proposed method is a practical tool to simulate the runout characteristics of debris flow e g flow velocity flow depth impact area and interactions between debris flow and check dam e g impact force destruction of check dam interception by check dam given similar total dam volume increasing the number of dams will improve the hazard mitigation effect moreover it is recommended to construct dams in downstream area with straight channel this study will contribute to a better understanding of the flow structure interaction and is helpful for rational design of check dams

modeling damage and deformation in impact simulations numerical modeling is a powerful tool for investigating the formation of large impact craters but is one that must be validated with observational evidence quantitative analysis of damage and deformation in the target surrounding an impact event provides a promising means of validation for numerical models of terrestrial impact craters particularly in cases where the final pristine crater morphology is ambiguous or unknown in this paper we discuss the aspects of the behavior of brittle materials important for the accurate simulation of damage and deformation surrounding an impact event and the care required to interpret the results we demonstrate this with an example simulation of an impact into a terrestrial granite target that produces a 10 km diameter transient crater the results of the simulation are shown in terms of damage a scalar quantity that reflects the totality of fragmentation and plastic strain both total plastic strain the accumulated amount of permanent shear deformation regardless of the sense of shear and net plastic strain the amount of permanent shear deformation where the sense of shear is accounted for damage and plastic strain are both greatest close to the impact site and decline with radial distance however the reversal in flow patterns from the downward and outward excavation flow to the inward and upward collapse flow implies that net plastic strains may be significantly lower than total plastic strains plastic strain in brittle rocks is very heterogeneous however continuum modeling requires that the deformation of the target during an impact event be described in terms of an average strain that applies over a large volume of rock large compared to the spacing between individual zones of sliding this paper demonstrates that model predictions of smooth average strain are entirely consistent with an actual strain concentrated along very narrow zones furthermore we suggest that model predictions of total accumulated strain should correlate with observable variations in bulk density and seismic velocity

investigating the interactions between an atmosphere and an ejecta curtain 1 wind tunnel tests when an asteroid impacts a planetary surface ejecta are excavated along ballistic trajectories whose loci define an inverted cone shape the outward advancing motion of this curtain displaces atmosphere to generate a ring vortex whose winds can entrain transport and deposit ejecta and fine grained surface materials curtain width and velocity particle concentration size distribution and motion parallel to the curtain and the density viscosity and compressibility of the surrounding atmosphere all influence the vortex circulation strength as analogs to an advancing ejecta curtain we tested the effect of inclined solid and porous plates on vortex formation in a low speed wind tunnel we found that hydraulic resistance a measure of energy losses for 1 d porous flow governs the position along a porous plate where it becomes effectively permeable and flow separation occurs the resulting flow field is similar to that over an inclined solid plate of the same effective length energy losses through the top permeable portions of the plate reduce circulation strength by only 7 relative to flow over a solid plate the two parameters needed to estimate circulation strength curtain velocity and impermeable height can thus be determined by coupling an impact model with published hydraulic resistance data these tests also served to calibrate a numerical model which we then applied to investigate the influence of atmospheric compressibility and particle motion parallel to the curtain see part 2 barnouin jha et al this issue these two studies provide a method to predict the curtain induced flow and consequent patterns of debris deposition associated with impacts on planets with atmospheres

experiments on deaerating granular flows and implications for pyroclastic flow mobility 1 granular flows were generated by the release of beds of particles in various fluidized states which then deaerated in a horizontal channel we describe characteristics of the flows and their deposits morphological similarities between deposits in experiments and in the field suggest that pyroclastic flow deposits form from a fluidized mixture the experiments show that slightly expanded fluidized flows are more mobile than non fluidized flows of equivalent volume and material composition they travel to a fixed distance from their source which depends only weakly on their initial degree of fluidization flows of fine particles 100 m deaerate slowly and are highly mobile pyroclastic flows commonly have large amounts of fine ash which may have a controlling influence on their high mobility

new images of the earth s upper mantle from measurements of surface wave phase velocity anomalies 1 the sensitivity of a surface wave to the lateral structure of the earth s mantle depends on the local structure and thickness of the crust particularly at short periods the strong lateral heterogeneity of the crust has a significant nonlinear effect on the surface wave sensitivity functions thus far this effect has not been quantified and tomographic studies of the upper mantle based on surface wave observations have not taken it into account on the basis of a jeffreys wentzel kramers brillouin jwkb description of surface wave propagation we find and discuss the lateral variations of the sensitivity of love and rayleigh waves to mantle seismic anomalies associated with a realistic model of the crust mooney et al 1998 we then use the resulting laterally varying sensitivity kernels to determine a new tomographic image of horizontally and vertically polarized shear velocity in the upper mantle from love and rayleigh wave phase velocity measurements periods from 35 to 300 s in terms of large scale patterns of high and low velocity our model is similar to previously published ones confirming among other features the anomalous anisotropy underlying the central pacific ekstrom and dziewonski 1998 we find however that the lateral dependence of the surface wave sensitivity kernels has a significant effect on the absolute amplitude of the anomalies which should not be neglected as we attempt to obtain higher resolution images of the upper mantle

an experimental facility for the investigation of magma fragmentation by rapid decompression a special experimental facility has been developed to investigate the fragmentation of vesicular magma undergoing rapid decompression the facility operates in a regime similar to that of shock tubes and at temperatures up to 950 c and pressures up to 200 bar cylindrical samples diameter ca 17 mm length ca 50 mm undergo rapid decompression in a high temperature high pressure section of the facility following the disruption of a diaphragm separating that section from a low pressure low temperature section actual vesicular magma samples have been experimentally fragmented at elevated temperatures and pressures corresponding to those observed during explosive volcanic eruptions and the resulting pyroclastics have been photographically resolved in flight and collected for physical characterization the results of these experiments show that the rapid decompression of highly viscous vesicular magma can generate pyroclastic ejecta via rapid and complete fragmentation of magma at high temperature this new fragmentation facility is presented as a tool for experimental volcanology under well constrained conditions