the effect of paleotopography on lithic distribution and facies associations of small volume ignimbrites the wtt cupa roccamonfina volcano italy abstract the distribution of lithic clasts within two trachytic small volume pumiceous ignimbrites are described from the quaternary white trachytic tuff cupa formation of roccamonfina volcano italy the ignimbrites show a downslope grading of lithics with a maximum size where there is a major break in the volcano s slope rather than at proximal locations this is also the location where ignimbrites are thickest and most massive the break in slope is interpreted to have reduced flow capacity and velocity increasing the sedimentation rate so that massive ignimbrite formed by hindered settling sedimentation ignimbrite cc exhibits no vertical grading of lithics though it does show downslope grading with maximum size at the major break in slope and a rapid decrease further downslope ignimbrite cc thins away from the break in slope and shows an upward fining of the grain size within the topmost few decimeters of the unit the ignimbrite is stratified proximally and grades to massive facies at the break in slope and distally to stratified facies with numerous inverse graded beds the simplest mechanism accounting for these downslope variations is progressive aggradation from a quasi steady nonuniform pyroclastic density current the changes in deposit thickness and facies are interpreted to record downcurrent changes in sedimentation rate the upward fining reflects waning flow inversely graded bedded depositional facies in distal areas is interpreted to reflect flow unsteadiness and a decrease in suspended sediment load ignimbrite cd shows vertical as well as downslope grading of lithics this characteristic coupled with the widespread massive facies of the deposit and the tabular unit geometry are features that can be reconciled with both the debris flow plug analogy for pyroclastic flows sparks 1976 and the progressive aggradation model branney and kokelaar 1992 however none of them appears to satisfy completely the field evidences implying that when dealing with massive ignimbrites other evidence than lithic grading needs to be presented to better understand the related transport and depositional processes

erosion by pyroclastic flows on lascar volcano chile pyroclastic flows generated in the 19 20 april 1993 eruption of lascar volcano chile produced spectacular erosion features scree and talus were stripped from the channels and steep slopes on the flanks of the volcano exposed bedrock and boulders suffered severe abrasion producing smoothed surfaces on coarse breccias and striations and percussion marks on bedrock and large boulders erosional furrows developed with wavelengths of 0 5 2 m and depths of 0 1 0 3 m furrows commonly nucleated downstream of large boulders or blocks which are striated on the upstream side and thereby produced crag and tail structures erosive features were produced where flows accelerated through topographic restrictions or where they moved over steep slopes the pyroclastic flows are inferred to have segregated during movement into lithic rich and pumice rich parts lithic rich deposits occur on slopes up to 14 whereas pumice rich deposits occur only on slopes less than 4 and mainly at the margins and distal parts of the 1993 fan the lithic rich deposits contain large up to 1 m lithic clasts eroded from the substrate and transported from the vent whereas pumice rich deposits contain only small typically 2 cm lithic clasts these observations suggest that lithic clasts segregated to the base of the flows and were responsible for much of the erosive phenomena the erosive features distribution of lithic clasts and deposit morphology indicate that the 1993 flows were highly concentrated avalanches dominated by particle interactions in some places the flows slid over the bedrock causing abrasion and long striations which imply that large blocks were locked in fixed positions for periods of about 1 s however shorter striae at different angles impact marks segregation of the deposits into pumice and lithic rich parts and mixing of bedrock derived lithic clasts throughout the deposits indicate that clasts often had some freedom of movement and that jostling of particles allowed internal mixing and density segregation to occur within the flows

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

volume growth of a powder snow avalanche we contrast the frontal dynamics of dilute powder snow avalanches with the behavior of their tail while the former can be regarded as a fast moving eruption current dominated by synergistic material injection into a short head the latter behaves as a nearly arrested dilute cloud of particles expanding by progressive incorporation of ambient air or by entrainment of snow cover material by late avalanches trailing well behind the front

the bi azimuthal scattering distribution of an abyssal hill high resolution bistatic images of a typical abyssal hill on the western flank of the mid atlantic ridge are made with a low frequency towed array system operating remotely at 1 2 convergence zone 33 3 km stand off comparison with modeled images generated from high resolution supporting bathymetry sampled at 5 m intervals roughly the wavelength scale reveals that steep scarps return the strongest echoes because they project the largest area along the acoustic path from the source to receiver prominent returns deterministically image scarp morphology when the cross range axis of the system s resolution footprint runs along the scarp axis statistical fluctuations inherent in the scattered field prevent the system from distinguishing smaller scale anomalies on the scarps such as canyons and gullies 100 200 m scale that would otherwise be resolvable in range in certain bistatic geometries the mean bi azimuthal scattering distributions of the two major scarps on the abyssal hill are identical a

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

quantifying velocity and turbulence structure in depositing sustained turbidity currents across breaks in slope two dimensional experiments investigating sediment transport and turbulence structure in sustained turbidity currents that cross breaks in slope are presented as analogue illustrations for natural flows the results suggest that in natural flows turbulence generation at slope breaks may account for increased sand transport into basins and that the formation of a hydraulic jump may not be necessary to explain features such as the occurrence of submarine plunge pools and the deposition of coarser grained beds in the bottomsets of gilbert type fan deltas experimental flows were generated on 0 3 6 and 9 slopes of equal length which terminated abruptly on a horizontal bed two component velocities were measured on the slope at the slope break and downstream of the slope break flows were depositional and non uniform visibly slowing and thickening with distance downstream one dimensional continuous wavelet transforms of velocity time series were used to produce time period variance maps peaks in variance were tested against a background red noise spectrum at the 95 level a significant period banding occurs in the cross wavelet transform at the slope break attributed to increased formation of coherent flow structures kelvin helmholtz billows variance becomes distributed at progressively longer periods and the shape of the bed normal velocity spectral energy distribution changes with distance downstream this is attributed to a shift towards larger turbulent structures caused by wake stretching mean velocity reynolds shear stress and turbulent kinetic energy profiles illustrate the mean distribution of turbulence through the currents a turbulent kinetic energy transfer balance shows that flow non uniformity arises through the transfer of mean streamwise slowing to mean bed normal motion through the action of reynolds normal stresses net turbulence production through the action of normal stresses is achieved on steeper slopes as turbulence dissipation due to mean bed normal motion is limited at the slope break an imbalance between the production and dissipation of turbulence occurs because of the contrasting nature of the wall and free shear boundaries at the bottom and top of the flows respectively a rapid reduction in mean streamwise velocity predominately affects the base of the flows and steeper proximal slope flows have to slow more at the break in slope the increased turbulent kinetic energy limited bed normal motion and strong mixing imposed by steep proximal slopes means rapid slowing enhances turbulence production at the break in slope by focusing energy into coherent flow structures at a characteristic period thus mean streamwise slowing is transferred into turbulence production at the slope break that causes increased transport of sediment and a decrease in deposit mass downstream of the slope break the internal effects of flow non uniformity therefore can be separated from the external influence of the slope break

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

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

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

performance of rubble mound breakwaters under tsunami attack a case study haydarpasa port istanbul turkey abstract ports are one of the most vulnerable coastal utilities in case of marine natural hazards such as tsunamis and need to be protected against their devastating effects thus studying the effects of tsunamis on protective structures such as breakwaters is critical the sea of marmara is a part of an active earthquake zone that has generated tsunamis in the history in terms of population density coastal utilization and economic potential marmara coastline seems most vulnerable to marine hazards the availability of natural stones allows for wide use of rubble mound breakwaters as coastal protective structures in turkey the stability of these types of structures under the attack of storm waves has already been studied however their stability and performance under the effect of long waves and tsunami attacks have not yet been studied experimentally the present study is a case study focusing on haydarpasa port located at the southern entrance of istanbul bosphorus strait north coast of the sea of marmara it aims to investigate the performance level of the port in case of tsunami attack physical model experiments were conducted in the 105 m long wave flume in the port and airport research institute pari japan with a froude type length scale of 1 30 the experiments conducted to test the stability of rubble mound breakwater were twofold i solitary wave experiments and ii tsunami overflow experiments the heights of incoming tsunami waves were selected from results of simulations were conducted in the same region oyo int co 2007 ayca 2012 yalciner et al 2014 guler et al 2014 aytore 2015 first the incoming solitary wave heights were selected as 5 7 5 and 10 cm using the overflow heights obtained from solitary wave experiments i e wave height at the top of crown wall when the solitary waves are overtopping the crown wall tsunami overflow experiments were conducted ranging from an overflow height of 1 1 cm to 4 6 cm results of these experiments showed that haydarpasa breakwater especially the crown wall of the breakwater is not stable under a moderate tsunami attack therefore an improved cross section was also tested under the same conditions and the improvement proved successful

a comparison of quasi continuous wave and broadband travel time techniques in the prediction of long range reverberation previous work has shown that the general structure of deep ocean reverberation can be reasonably modeled using single frequency propagation techniques recent results indicate that secondary multipath influences can affect reverberation levels significantly primarily these influences are observed in shadow regions of the primary direct path ensonification temporal separation of these paths is required in order to distinguish these effects this suggests that regions of the reverberation signal may not be well predicted by single frequency quasi cw continuous wave methods in this paper a quasi cw method of predicting long range reverberation is compared to an exact two way travel time technique each model assumes a simple constant plane wave scattering strength thereby emphasizing the influence of propagation results from both models are compared to measured reverberation data from an onr srp bottom reverberation experiment conducted near the mid atlantic ridge it is shown that the single frequency method underestimates reverberation levels on the backside of large ridge structures which act as shadow zones for all propagation paths returns from multipaths however begin to fill in these regions in time and may explain the lack of such dramatic signal drop outs from measured data

the influence of large scale seafloor slope and average bottom sound speed on low grazing angle monostatic acoustic scattering variations in large scale seafloor slope and average seabed sound speed account for a significant portion of the variations in scattering intensity observed in low grazing angle monostatic reverberation numerical modeling using a finite difference solution to the elastic wave equation is used to quantify the effect of these large scale parameters in interpretations of reverberation data for hard rough seafloor e g basalt the results of the modeling suggest that the monostatic backscattering strength increases with increasing large scale seafloor slope up to a slope of about 15 dipping toward the incident direction once the grazing angle of the incident wavefield exceeds the critical grazing angle for the flat reference seafloor the backscattering intensity increases only slowly with increasing grazing angle similarly average subseafloor sound speed has a significant effect seafloor with low sound speeds characteristic of soft bottoms e g sediment generate significantly weaker backscatter signals than seafloor with sound speeds characteristic of hard bottoms e g basalt the difference is that the shear waves can always be passed into soft bottoms because even for a flat seafloor there is no shear wave critical grazing angle

pressures on a rubble mound breakwater crown wall for tsunami impact abstract rubble mound breakwaters are commonly constructed with a parapet or crown wall at the crest the design of these superstructures depends on the expected storm wave load history throughout the service life cycle in tsunami prone areas this design must include tsunami actions since their loads can definitely exceed those of storm waves however tsunami loads are rarely accounted for this study aimed at incorporating tsunami actions in the design of crown walls of rubble mound breakwaters for the first time within this scope laboratory experiments on a scaled model of a typical mediterranean rubble mound breakwater typology under tsunami actions were conducted this paper is the continuation of our previous paper aniel quiroga et al 2018 1 in which experiments were presented and a stability analysis of the armor units was conducted this research paper presents the second part of the analysis focused on understanding the pressures that crown walls of rubble mound breakwaters must support due to tsunami like actions these pressures were measured and analyzed providing the horizontal and uplift pressure time series and laws the magnitude and timing of the maximum pressure peaks were identified the maximum horizontal pressure is caused by the first impact of the tsunami by contrast the maximum uplift pressure is prompted by a pressure wave generated by the overtopped water falling into the leeside this pressure wave penetrates the structure from the rear slope as a result of this analysis pressures were characterized allowing the presentation of a new complete methodology that provides for the tested structure the design procedure of the crown wall under tsunami actions a new formulation to calculate the run up of solitary waves on the tested rubble mound breakwater slope is presented here

reverberation at the mid atlantic ridge during the 1993 arsrp experiment seen by r v alliance from 200 1400 hz and some modeling inferences in july 1993 saclantcen participated in an experiment for the acoustic reverberation special research program arsrp the primary objective was to take high resolution measurements to shed light on the detailed physical processes dominating the low frequency scattering from rough topographic features and from deep sediment pond areas a very detailed set of monostatic and bistatic scattering experiments were conducted just west of the mid atlantic ridge near 26 degrees n 47 degrees w results from saclantcen s r v alliance are presented which show monostatic and bistatic scattering from selected bathymetric features using pulsed sources from 200 1400 hz and sus charges area water depths ranged from 3300 to greater than 5200 m the receivers were a horizontal array of 128 elements spaced at 0 5 1 and 2 m source depths varied from 120 to 1200 m and receiver depths ranged from 400 to 500 m received reverberation levels are presented as functions of the estimated scatterer position on area bathymetry maps results show the same high scattering areas from one seamount were observed in three distinct frequency bands centered at 227 350 and 700 hz even at 1350 hz the correlation of scattering highlights with nearby bathymetric features is quite good comparisons of measured reverberation and modeled reverberation are presented which suggest that the dominant longer range scattering from the large features is driven by the steep slopes present above the critical depth but that small scale roughness is also essential for strong backscatter

granular fingering as a mechanism for ridge formation in debris avalanche deposits laboratory experiments and implications for tutupaca volcano peru the origin of subparallel regularly spaced longitudinal ridges often observed at the surface of volcanic and other rock avalanche deposits remains unclear we addressed this issue through analogue laboratory experiments on flows of bi disperse granular mixtures because this type of flow is known to exhibit granular fingering that causes elongated structures resembling the ridges observed in nature we considered four different mixtures of fine 300 400 m glass beads and coarse 600 710 m to 900 1000 m angular crushed fruit stones with particle size ratios of 1 9 2 7 and mass fractions of the coarse component of 5 50 wt the coarse particles segregated at the flow surface and accumulated at the front where flow instabilities with a well defined wavelength grew these formed granular fingers made of coarse rich static margins delimiting fines rich central channels coalescence of adjacent finger margins created regular spaced longitudinal ridges which became topographic highs as finger channels drained at final emplacement stages three distinct deposit morphologies were observed 1 joined fingers with ridges were formed at low 1 9 size ratio and moderate 10 20 wt coarse fraction whereas 2 separate fingers or 3 poorly developed fingers forming series of frontal lobes were created at larger size ratios and or higher coarse contents similar ridges and lobes are observed at the debris avalanche deposits of tutupaca volcano peru suggesting that the processes operating in the experiments can also occur in nature this implies that volcanic and non volcanic debris avalanches can behave as granular flows which has important implications for interpretation of deposits and for modeling such behaviour may be acquired as the collapsing material disaggregates and forms a granular mixture composed by a right grain size distribution in which particle segregation can occur limited fragmentation and block sliding or grain size distributions inappropriate for promoting granular fingering can explain why ridges are absent in many deposits

the contribution of experimental volcanology to the study of the physics of eruptive processes and related scaling issues a review abstract the experimental approach has become a major tool increasingly used by volcanologists in recent decades to investigate the physics of eruptive processes in complement to field and theoretical works researchers have developed various methodologies to study volcanic phenomena at reduced length scale the works involve natural or analogue materials and their types range from first order tests to identify fundamental processes and make qualitative comparison with field observations to more sophisticated experiments in which precise data obtained in a controlled environment can be used to validate outputs of theoretical models scaling is a central issue to ensure dynamic similarity between the small scale experiments and the large scale volcanic phenomena when natural conditions cannot be simulated due to inherent length scale difference and or technical limitations in this respect dimensionless numbers are used to map physical regimes and to define scaling laws which allow experimental results to be extrapolated to natural scale this review presents the variety of experimental studies conducted to investigate subterraneous and aerial volcanic phenomena involving in particular fluid particle mixtures we focus on the major scaling issues and the physical regimes investigated and we also highlight in a historical perspective some of the major advances achieved through experimental studies finally we conclude on some perspectives for future works

explosive activity and generation mechanisms of pyroclastic flows at arenal volcano costa rica between 1987 and 2001 explosive activity at arenal and associated tephra fall that has occurred over the 14 year period from 1987 2001 is described explosions have been notably variable in both frequency and size a marked decrease in both frequency and quantity of tephra fallout occurred in early 1998 until the end of 2001 grainsize distributions of cumulative tephra samples collected once a month are typically bimodal aggregation causing premature fallout of fine ash and possibly fallout from ash plumes produced by pyroclastic flows are considered responsible for the bimodality of fallout scanning electron microscopy of the glass component of tephra from single explosions show predominantly blocky and blocky fluidal clast types interpreted as being the product of vulcanian type explosions fragmentation of a mainly rigid degassed magma body and a minor molten component is inferred for these explosions pyroclastic flows were produced either associated with the larger explosions by a mechanism of column collapse 1987 1990 or unrelated to explosions by partial collapse of the crater wall 1993 1998 2000 2001 pyroclastic flow activity has migrated from west to north during the period reported pyroclastic flow deposits are variable in the quantity of juvenile material and any associated surge component large juvenile blocks were partially molten on emplacement and many have a typical cauliform texture blocks with both juvenile and lithic textures indicate that at the summit magma was in intimate contact with the pre existing edifice rather than as a simple open crater or lava pool crater wall collapse may have been promoted by the reduction in explosive activity which has increased the lava accumulation at the summit and in turn increased instability of the summit region thus although explosive activity has waned if the lava output is maintained the hazard of pyroclastic flows is likely to continue

characteristics and emplacement mechanisms of the coranzuli ignimbrites central andes abstract we present a detailed stratigraphy of the coranzuli caldera forming deposits this caldera located in the altiplano puna volcanic complex central andes generated four ignimbrite deposits with similar field characteristics and facies that differ from each other in above all the nature of the lithic fragments they contain three different lithofacies fine grained cross stratified facies massive lithic breccia facies and massive ignimbrite facies are found in all the ignimbrite deposits which occasionally also contain a lenticular lithic rich facies and or a pumice rich facies these field characteristics and in particular local deposit thicknesses were used to develop a theoretical model of the dynamics and emplacement mode of the coranzuli pyroclastic flows our results show that these ignimbrites were emplaced by dense pyroclastic density currents subjected to high accumulation rates and velocities thereby indicating rapid en masse emplacement that was also influenced by local paleotopography as deduced from facies analysis

numerical analysis of wave overtopping of rubble mound breakwaters abstract the paper describes the results of a two dimensional 2 d numerical modelling investigation of the functionality of rubble mound breakwaters with special attention focused on wave overtopping processes the model cobras uc is a new version of the cobras cornell breaking waves and structures based on the volume averaged reynolds average navier stokes varans equations and uses a volume of fluid technique vof method to capture the free surface the nature of the model equations and solving technique provides a means to simulate wave reflection run up wave breaking on the slope transmission through rubble mounds overtopping and agitation at the protected side due to the combined effect of wave transmission and overtopping also two dimensional experimental studies are carried out to investigate the performance of the model the computations of the free surface and pressure time series and spectra under regular and irregular waves are compared with the experimental data reaching a very good agreement the model is also used to reproduce instantaneous and average wave overtopping discharge comparisons with existing semi empirical formulae and experimental data show a very good performance the present model is expected to become in the near future an excellent tool for practical applications

propagation and analysis issues in the prediction of long range reverberation data collected from the office of naval research special research program onr srp bottom reverberation research cruises consist of various environmental measurements sound speed profiles bottom properties etc extensive bathymetric mapping of the 300 km 150 km natural laboratory and high quality acoustic reverberation data recorded in both monostatic and bistatic geometries the analysis of the acoustic data and the effects of propagation are investigated accurate gps tracking of the participating research vessels provided the precision necessary to attempt to correlate spiky reverberation events with bathymetric features understanding the limitations of our ability to resolve such features due to imperfect signal processing environmental variability and complex multipath structures is the main objective of this work using a simplified time to range conversion the measured reverberation data can be displayed over the local bathymetry this process shows good correlation between large scal

real time experimental forecast of the peruvian tsunami of august 2007 for u s coastlines 1 at 23 41 utc on 15 august 2007 an offshore earthquake of magnitude 8 0 severely damaged central peru and generated a tsunami severe shaking by the earthquake collapsed buildings throughout the region and caused 514 fatalities the tsunami resulted in three casualties and a representative maximum runup height of 7 m in the near field the first real time tsunami data available came from a deep ocean tsunami detection buoy within 1 hour of tsunami generation these tsunami data were used to produce initial experimental forecasts within 2 hours of tsunami generation the far field forecasts indicated that the tsunami would not flood any of the 14 u s communities comparison with real time tide gage data showed very accurate forecasts

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

erosion transport and segregation of pumice and lithic clasts in pyroclastic flows inferred from ignimbrite at lascar volcano chile abstract investigations have been made on the distribution of pumice and lithic clasts in the lithic rich soncor ignimbrite 26 5 ka and the 1993 pumice flow deposits of lascar volcano chile the soncor ignimbrite shows three main lithofacies which grade into one another coarse lithic breccias range from matrix poor stratified varieties irregular shaped sheets and elongate hummocks in proximal environments to breccia lenses with pumiceous ignimbrite matrix massive lithic rich facies comprise the bulk of the ignimbrite pumice rich facies are bimodal with abundant large pumice clasts often with reverse grading rare lithic clasts and occur distally and on high ground adjacent to deep proximal valleys in the 1993 pyroclastic flow deposits lithic rich facies are deposited on slopes up to 14 whereas pumice rich facies are deposited only on slopes

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

a comparison of bistatic scattering from two geologically distinct abyssal hills the bistatic scattering characteristics of two geologically distinct abyssal hills located on the western flank of the mid atlantic ridge known as b and c are experimentally compared using data acquired with low frequency towed array systems at 12 convergence zone 33 km stand off the comparison is significant because the abyssal hills span the two classes of elevated seafloor crust that cover the mid atlantic ridge the highly lineated b feature is representative of abyssal hills composed of outside corner crust the most commonly occurring category whereas the domed c promontory is representative of the rougher low aspect ratio abyssal hills composed of inside corner crust the latter are less common and usually restricted to segment valley margins the mean biazimuthal scattering distributions of the two abyssal hills each exhibit lambertian behavior with comparable albedos suggesting that the distinction between abyssal hills composed of differing crust is not significant in modeling long

migration of backscatter data from the mid atlantic ridge in studies of low frequency reverberation within the marine environment a central concern is the relationship between reverberation events and morphological features of the seafloor a time domain migration algorithm for the reverberation intensity field is developed that produces scattering coefficient maps coregistered with a bathymetry database the algorithm is tailored to broadband transient sources with good range resolution and was developed to analyze an extensive set of reverberation records from a 200 255 hz source collected on the flanks of the mid atlantic ridge the precise sample by sample tracking of wavefronts across elements of the bathymetry database that forms the foundation of the algorithms implementation results in reverberation maps that show a clear and detailed correlation between scattering and morphology with narrow scarp slopes consistently highlighted environmentally induced asymmetries in transmission loss and incidence angle are exploited to break the inherent left righ

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

wave loads on rubble mound breakwater crown walls in deep and shallow water wave conditions abstract the semi empirical formulae by pedersen 1996 for wave loads on vertical front faces of stiff crown walls are based on model tests with deep and intermediate water wave conditions a new series of model tests performed at the same test facility as used by pedersen has revealed that the formulae by pedersen overpredict the loads in shallow water wave conditions this paper presents a modification expansion of the formulae to cover loads in both deep and shallow water wave conditions the modification is based on a series of 162 physical model tests on typical rubble mound breakwaters with crown wall superstructures the implementation of shallow water wave conditions in the formulae is done by modifying the term for wave run up to be dependent on the incident wave height distribution moreover the adjusted formulae provide more accurate estimates of the wave loads on free walls without front armour protection pressure transducers with very high eigen frequencies were used in the present model tests as opposed to the transducers applied by pedersen which in some cases seem to have been affected by dynamic amplifications

wave loads on rubble mound breakwater crown walls abstract crown walls are primarily built to reduce wave overtopping of mound breakwaters several methods have been proposed to calculate wave loads on the crown wall e g iribarren and nogales iribarren r nogales c 1964 obras maritimas dossat ed madrid 376 pp jensen jensen o j 1984 a monograph on rubble mound breakwaters danish hydraulic institute and gunbak and gokce gunbak a r gokce t 1984 wave screen stability of rubble mound breakwaters international symposium of maritime structures in the mediterranean sea athens greece pp 2 99 2 112 in this paper a new method based on those previous results and on further experimental work using monochromatic waves is presented the application of the new method requires waves breaking on the armour layer i e only broken waves will reach the crown wall the method is extended to irregular waves via the hypothesis of equivalence introduced by saville saville t 1962 an approximation of the wave run up frequency distribution proc 8th international conference on coastal engineering mexico city and is applied to the crown walls of gijon and bilbao breakwaters in spain the comparison of the probability force distributions obtained by the present method to that measured by burcharth et al burcharth h f frigaard p berenguer j m gonzalez b uzcanga j villanueva j 1995 design of the ciervana breakwater bilbao in t telford ed proc 4th coastal structures and breakwaters chap 3 institution of civil engineers and jensen 1984 is relatively good

the runup of solitary waves this is a study of the runup of solitary waves on plane beaches an approximate theory is presented for non breaking waves and an asymptotic result is derived for the maximum runup of solitary waves a series of laboratory experiments is described to support the theory it is shown that the linear theory predicts the maximum runup satisfactorily and that the nonlinear theory describes the climb of solitary waves equally well different runup regimes are found to exist for the runup of breaking and non breaking waves a breaking criterion is derived for determining whether a solitary wave will break as it climbs up a sloping beach and a different criterion is shown to apply for determining whether a wave will break during rundown these results are used to explain some of the existing empirical runup relationships

flow and deposition of pyroclastic granular flows a type example from the 1975 ngauruhoe eruption new zealand small volume pyroclastic density currents pdcs are generated frequently during explosive eruptions with little warning assessing their hazard requires a physical understanding of their transport and sedimentation processes which is best achieved by the testing of experimental and numerical models of geophysical mass flows against natural flows and or deposits to this end we report on one of the most detailed sedimentological studies ever carried out on a series of pristine small volume pdc deposits from the 1975 eruption of ngauruhoe volcano whose emplacement were also witnessed during eruption using high resolution gps surveys a series of lateral excavations across the deposits and bulk sedimentological analysis we constrained the geomorphology internal structure and texture of the deposits with respect to laterally varying modes of deposition deposition from these pdcs began only on slopes at or around the material s angle of repose c 30 in unconfined settings the granular pdcs are interpreted to have been quasi steady forming sheets and lobes around the angle of repose where flows were confined sheet like proximal facies made up around 10 of the deposit volume at the angle of repose but 90 of the material was deposited from apparently unsteady inertial granular pdcs as a distal levee and channel facies on slopes well below the repose angle hence confined pdcs were able to travel up to 50 farther than unconfined flows in the distal facies the deposit width is inversely correlated to the local slope and the height of the levees above the deposit centreline is positively correlated with slope internally the deposits comprise three parts a coarse grained fines free sole layer that laterally connects to levees zone i an ashy matrix supported central body zone ii and an overlying coarse plaster of clasts zone ii trends in grain size data suggests these zones derive from a continuous un mixing of coarse particles from the initial bulk material by granular segregation that preferentially drives large particles to the upper free surface of the flow where they are concentrated at the front of flow before being deposited and overrun by comparison to analogue experiments we suggest a model of flow and deposition where the temporally and spatially varying mode of deposition is determined by the flow velocity the local slope the vertical velocity gradient the velocity gradient at the free surface and the vertical deposition rate using this model estimated vertical deposition rates of c 5 cm s 1 from the ngauruhoe pdcs agree with those determined in laboratory experiments on inertial granular flows

stability of rubble mound breakwaters under tsunami first impact and overflow based on laboratory experiments abstract recent tragic tsunami events like those that occurred in the indian ocean in 2004 and in japan in 2011 have revealed the need of further work to reduce tsunami risk in coastal areas an important aspect towards risk reduction is the study of the interaction between tsunami waves and coastal structures as these are the first to receive the tsunami s energy dikes and breakwaters must have an adequate structural behavior and maintain some functionality and operability under tsunami attacks to be able to contribute to the reduction of its consequences within this scope laboratory experiments on scaled models of two typical mediterranean rubble mound breakwater typologies under tsunami waves were conducted for the first time the tsunami s action was split into 2 parts 1 the first impact of solitons was tested by means of large solitary waves and 2 the subsequent overflow was approached by applying a pump driven wave maker the damage on the breakwaters due to these actions was measured and assessed the result is an in deep analysis of the relationships among stability number damage level and number of tsunami waves the outcome of this analysis includes the development of a set of formulae that provide in the range of the conducted tests the value of the damage parameter so that tsunami actions can be taken into account in the design of rubble mound structures finally based on the results of these experiments the threshold values of the damage parameter used to characterize damage in armors initiation of damage initiation of destruction destruction was particularized for tsunami actions

development of lithic breccias in the 1982 pyroclastic flow deposits of el chichon volcano mexico abstract pyroclastic flow deposit f1 volume 0 02 km 3 produced during phase iii of the 1982 eruption of el chichon volcano mexico contains basal lithic breccias the breccia layers are well exposed in el platanar gully between 2 and 4 km east of the volcano crater the lithic breccias are inversely graded as defined by lithics dense juvenile blocks and pumice supported in a coarse sandy matrix composed of the same constituents the contact between the main body of the pyroclastic flow deposit and the lithic breccias is generally sharp and planar but not erosive in some outcrops it is gradational and is only shown by an alignment of lithic clasts the origin of these beds is interpreted to be due to a hydraulic jump in the moving pyroclastic flow formed after a pronounced slope break from 11 to 3 at the site where the flow began to be funnelled into the el platanar gully we have investigated the possible modes of formation of the lithic breccias with analog laboratory experiments the experiments show that coarse localized segregations could form through a number of mechanisms the field observations interpreted with the assistance of the laboratory results suggest that pyroclastic flow 1 which produced deposit f1 moved as a kind of density stratified flow with a basal lithic rich zone transporting larger particles and an upper less dense zone transporting smaller particles in suspension at the slope break flow 1 lost competence and dumped the largest particles forming a piled up breccia downstream somewhat smaller lithic particles may have been deposited as ballistics from a low angle jetlike structure comprising a hydraulic jump this deposit thins with distance downstream once the deposit was sufficiently thick on its upstream end particles may have been re entrained into the jet to be deposited further along the flow in a low angle downstream prograding bouldery dune reverse grading in the dune beds may result from kinetic sieving we suggest that planar contacts between the lithic breccias and the associated pyroclastic flow deposit may be the result of strong density and velocity gradients between the two parts of the flow

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

relation between dry granular flow regimes and morphology of deposits formation of levees in pyroclastic deposits experiments on dry granular matter flowing down an inclined plane are performed in order to study the dynamics of dense pyroclastic flows the plane is rough and always wider than the flow focusing this study on the case of laterally unconfined free boundary flows we found that several flow regimes exist depending on the input flux and on the inclination of the plane each flow regime corresponds to a particular morphology of the associated deposit in one of these regimes the flow reaches a steady state and the deposit exhibits a levee channel morphology similar to those observed on small pyroclastic flow deposits the levees result from the combination between lateral static zones on each border of the flow and the drainage of the central part of the flow after the supply stops particle segregation features are created during the flow corresponding to those observed on the deposits of pyroclastic flows moreover the measurements of the deposit morphology thickness of the channel height of the levees width of the deposit are quantitatively related to parameters of the dynamics of the flow flux velocity height of the flow leading to a way of studying the flow dynamics from only measurements of the deposit some attempts to make extensions to natural cases are discussed through experiments introducing the polydispersity of the particle sizes and the particle segregation process

lessons in reducing volcano risk since 1980 volcanologists have confronted more volcanic crises than any time since the mont pelee catastrophe in 1902 good science alone will not do the job of reducing volcano risk