onset of scour below pipelines and self burial abstract this paper summarizes the results of an experimental study on the onset of scour below and self burial of pipelines in currents waves pressure was measured on the surface of a slightly buried pipe at two points one at the upstream side and the other at the downstream side of the pipe both in the sand bed the latter enabled the pressure gradient which drives a seepage flow underneath the pipe to be calculated the results indicated that the excessive seepage flow and the resulting piping are the major factor to cause the onset of scour below the pipeline the onset of scour occurred always locally but not along the length of the pipeline as a two dimensional process the critical condition corresponding to the onset of scour was determined both in the case of currents and in the case of waves once the scour breaks out it will propagate along the length of the pipeline scour holes being interrupted with stretches of soil span shoulders supporting the pipeline as the span shoulder gets shorter and shorter more and more weight of the pipeline is exerted on the soil in this process a critical point is reached where the bearing capacity of the soil is exceeded general shear failure at this point the pipe begins to sink at the span shoulder self burial it was found that the self burial depth is governed mainly by the keulegan carpenter number the time scale of the self burial process on the other hand is governed by the keulegan carpenter number and the shields parameter diagrams are given for the self burial depth and the time scale of the self burial process

debris jets in continental phreatomagmatic volcanoes a field study of their subterranean deposits in the coombs hills vent complex antarctica abstract the ferrar large igneous province of antarctica contains significant mafic volcaniclastic deposits some of which are interpreted to fill large vent complexes such a complex was re examined at coombs hills to map individual steep sided cross cutting bodies in detail and we found several contrasting types two of which are interpreted to have filled subterranean passageways forcefully opened from below into existing non consolidated debris these transient conduits were opened because of the propagation of debris jets upward moving streams of volcaniclastic debris steam magmatic gases liquid water droplets following explosive magma aquifer interaction some debris jets probably remained wholly subterranean whereas others made it to the surface but the studied outcrops do not allow us to differentiate between these cases the pipes filled with country rock rich lapilli tuff or tuff breccia are interpreted to have formed following phreatomagmatic explosions occurring near the walls or floor of the vent complex causing fragmentation of both magma and abundant country rock material in contrast some of the cross cutting zones filled with basalt rich tuff breccia or lapilli tuff could have been generated following explosions taking place within pre existing basalt bearing debris well away from the complex walls or floor we infer that once focused jets were formed they did not incorporate significant amounts of existing debris while travelling through them instead incorporation of fragments from the granular host took place near explosion sites other basalt rich tuff breccia zones accompanied by domains of in situ peperite and coherent basalt pods are inferred to have originated by less violent processes

vs30 and spectral response from collocated shallow active and passive source vs data at 27 sites in puerto rico shear wave velocity vs and time averaged shear wavevelocity to 30 m depth vs30 are the key parameters used in seismic site response modeling and earth quake engineering design where vs data are limited available data are often used to develop and refine map based proxy models of vs30 for predicting ground motion intensities in this paper we present shallow vs data from 27 sites in puerto rico these data were acquired using a multimethod acquisition approach consisting of noninvasive collocated active source body wave refraction reflection active source surface wave at nine sites and passive source surface wave refraction micro tremor remi techniques vs versus depth models are constructed and used to calculate spectral response plots for each site factors affecting method reliability are analyzed with respect to site specific differences in bedrock vs and spectral response at many but not all sites body and surface wave methods generally determine similar depths to bedrock and it is the difference in bedrock vs that influences site ampli fication the predicted resonant frequencies for the majority of the sites are observed to be within a relatively narrow bandwidth of 1 3 5 hz for a first order comparison of peak frequency position predictive spectral response plots from eight sites are plot ted along with seismograph instrument spectra derived from the time series of the 16 may 2010 puerto rico earthquake we show how a multimethod acquisition approach using collocated arrays compliments and corroborates vs results thus adding confi dence that reliable site characterization information has been obtained

transport and mixing dynamics from explosions in debris filled volcanic conduits numerical results and implications for maar diatreme volcanoes abstract most volcanoes experience some degree of phreatomagmatism during their lifetime however the current understanding of such processes remains limited relative to their magmatic counterparts maar diatremes are a common volcano type that form primarily from phreatomagmatic explosions and are an ideal candidate to further our knowledge of deposits and processes resulting from explosive magma water interaction due to their abundance as well as their variable levels of field exposure which allows for detailed mapping and componentry two conceptual models of maar diatreme volcanoes explain the growth and evolution of the crater maar and subsurface vent diatreme through repeated explosions caused by the interaction of magma and groundwater one model predicts progressively deepening explosions as water is used up by phreatomagmatic explosions while the other allows for explosions at any level in the diatreme provided adequate hydrologic conditions are present in the former deep seated lithics in the diatreme are directly ejected and their presence in tephra rings is often taken as a proxy for the depth at which that particular explosion occurred in the latter deep seated lithics are incrementally transported toward the surface via upward directed debris jets here we present a novel application of multiphase numerical modeling to assess the controls on length scales of debris jets and their role in upward transport of intra diatreme material to determine the validity of the two models the volume of gas generated during a phreatomagmatic explosion is a first order control on the vertical distance a debris jet travels unless extremely large amounts of magma and water are involved it is unlikely that most explosions deeper than 250 m breach the surface other factors such as pressure and temperature have lesser effects on the length scales assuming they are within realistic ranges redistribution of material within a diatreme is primarily driven by subsidence following debris jet passage natural debris jet deposits often contain wall rock material that originated above the explosion site likely this material was first transported downward by subsidence associated with preceding explosions and debris jets the length scales of debris jets decrease with increasing depth all other factors staying equal the characteristics of the domains formed from just one explosion along with the difficulty of erupting deep seated material indicate that erupted material at maar diatreme volcanoes has a complex history before it is erupted and is mostly sourced from the upper most part of the diatreme

water magma interaction some theory and experiments on peperite formation experiments using molten thermite as a magma analog produce peperite when the melt interacts with wet sand these experiments also show explosive behavior developing strombolian and surtseyan like bursts the results demonstrate that the application of fuel coolant interaction fci theory is appropriate for interpretation of peperites the theory described includes discussion of the importance of mass interaction ratios of wet sediment and magma rs which determine thermal equilibrium temperature limits and contact interface dynamics the dynamics of the interface between magma and wet sediments involves heat transfer over a wide range of rates from passive quenching to explosive fragmentation a vapor film layer develops at the interface and acts both as an insulating barrier promoting passive quenching as well as a potential energy reservoir that can cause magma fragmentation mingling of the magma with wet sediments and explosive quenching when the vapor film becomes unstable an important parameter in determining the behavior of the vapor film is the value of rs which controls whether heat can be convectively removed from the layer as more is being added from its contact with magma if rs 1 for fully saturated sediments there is enough water in the sediments to make convective heat flow effective in quenching the magma but below that value there is the potential that the vapor film will be unstable producing highly dynamic phenomena including explosive fragmentation at values of rs 0 1 there is insufficient water to allow the escalation of explosive fragmentation

assessing the reliability of the modified three component spatial autocorrelation technique summary analysis of seismic ambient vibrations is becoming a widespread approach to estimate subsurface shear wave velocity profiles however the common restriction to vertical component wavefield data does not allow investigations of love wave dispersion and the partitioning between rayleigh and love waves in this study we extend the modified spatial autocorrelation technique mspac to three component analysis 3c mspac by determination of love wave dispersion curves this technique provides additional information for the determination of shear wave velocity depth profiles furthermore the relative fraction of rayleigh waves in the total portion of surface waves on the horizontal components is estimated tests of the 3c mspac method are presented using synthetic ambient vibration waveform data different types of surface waves are simulated as well as different modes in addition different spatial distributions of sources are used we obtain rayleigh and love wave dispersion curves for broad frequency bands in agreement with the models used for waveform simulation the same applies for the relative fraction of rayleigh waves dispersion curves are observed at lower frequencies for love waves than for rayleigh waves while 3c mspac has clear advantages for determination of love waves velocities 3c mspac and conventional vertical frequency wavenumber analysis complement each other in estimating the rayleigh wave dispersion characteristics inversions of the dispersion curves for the shear wave velocity depth profile show that the use of love wave velocities confirms the results derived from rayleigh wave velocities in the presence of higher mode surface waves love waves even can improve results application of 3c mspac to ambient vibration data recorded during field measurements pulheim germany show dominance of love waves in the wavefield existing shear wave profiles for this site are consistent with models obtained from inversion of rayleigh and love wave dispersion curves

thermohydraulic explosions in phreatomagmatic eruptions as evidenced by the comparison between pyroclasts and products from molten fuel coolant interaction experiments 1 thermohydraulic explosions were produced by molten fuel coolant interaction mfci experiments using remelted shoshonitic rocks from vulcano italy the fragmentation history and energy release were recorded the resulting products were recovered and analyzed with the scanning electron microscope fine particles from experiments show shape and surface features that result from melt fragmentation in brittle mode these clasts relate to the thermohydraulic phase of the mfci where most of the mechanical energy is released they are here called active particles the total surface area of such particles is proportional to the energy of the respective explosions other particles from experiments show shape and surface features that result from melt fragmentation in a ductile regime these fragments called passive particles form after the thermohydraulic phase during the expansion phase of the mfci in order to verify thermohydraulic explosions in volcanic eruptions we compared experimental products with samples from phreatomagmatic base surge deposits of vulcano ash particles from the experiments show features similar to those from the deposits suggesting that the experiments reproduced the same fragmentation dynamics to achieve discrimination between active and passive particles we calculated shape parameters from image analysis the mass of active particles in base surge deposits was calculated as the material properties for the natural samples are identical to the experimental ones the energy measurements and calculations of the experiments can be applied for a single phreatomagmatic eruption at vulcano a maximum mechanical energy release of 2 75 1013 j was calculated representing a tnt analogue of 6 5 kt

post caldera activity in the alban hills volcanic district italy 40ar 39ar geochronology and insights into magma evolution we present 24 40ar 39ar ages for the youngest volcanic products from the alban hills volcanic district rome combined with petrological data on these products we have attempted to define the chronology of the most recent phase of activity and to investigate the magma evolution of this volcanic district the early mainly explosive activity of the alban hills spanned the interval from 561 1 to 351 3 ka after approximately 50 kyr of dormancy a mainly effusive phase of activity took place accompanied by the strombolian activity of a small central edifice monte delle faete this second phase of activity spanned the interval 308 2 to 250 1 ka after another dormancy period of approximately 50 kyr a new hydromagmatic phase of activity started at 200 ka at several centers located to the southwest of the monte delle faete edifice after an initial recurrence period of approximately 50 kyr which also characterized this new phase of activity the longest dormancy period approximately 80 kyr in the history of the volcanic district preceded the start of the activity of the albano and giuturna centers at 70 1 ka results of our study suggest a quasi continuous magmatic activity feeding hydromagmatic centers with a new acme of volcanism since around 70 ka based on data presented in this paper we argue that the alban hills should not be considered an extinct volcanic district and a detailed re assessment of the volcanic hazard for the area of rome is in order

fracture surface energy of the punchbowl fault san andreas system the energetics of earthquake rupture slip weakening and rupture surface formation are poorly understood by measuring the energy associated with fracture damage along the punchbowl fault in the devil s punchbowl los angeles county park part of the san andreas system chester et al show that the fracture surface energy for rupture along a mature fault of this type accounts for only a small fraction of the energy released during large earthquakes as determined by seismologists this suggests that mechanisms such as melt lubrication and thermal pressurization are responsible for slip weakening fracture energy is a form of latent heat required to create an earthquake rupture surface and is related to parameters governing rupture propagation and processes of slip weakening1 2 3 fracture energy has been estimated from seismological and experimental rock deformation data4 5 6 7 8 yet its magnitude mechanisms of rupture surface formation and processes leading to slip weakening are not well defined8 9 10 here we quantify structural observations of the punchbowl fault a large displacement exhumed fault11 12 in the san andreas fault system and show that the energy required to create the fracture surface area in the fault is about 300 times greater than seismological estimates would predict for a single large earthquake if fracture energy is attributed entirely to the production of fracture surfaces then all of the fracture surface area in the punchbowl fault could have been produced by earthquake displacements totalling 1 km but this would only account for a small fraction of the total energy budget and therefore additional processes probably contributed to slip weakening during earthquake rupture

comparisons of shear wave slowness in the santa clara valley california using blind interpretations of data from invasive and noninvasive methods many groups contributed to a blind interpretation exercise for the deter mination of shear wave slowness beneath the santa clara valley the methods in cluded invasive methods in deep boreholes as well as noninvasive methods using active and passive sources at six sites within the valley with most investigations being conducted at a pair of closely spaced sites near the center of the valley although significant variability exists between the models the slownesses from the various methods are similar enough that linear site amplifications estimated in several ways are generally within 20 of one another the methods were able to de rive slownesses that increase systematically with distance from the valley edge cor responding to a tendency for the sites to be underlain by finer grained materials away from the valley edge this variation is in agreement with measurements made in the boreholes at the sites

effects of explosion energy and depth to the formation of blast wave and crater field explosion experiment for the understanding of volcanic explosion we made field explosion experiments as an analogue of volcanic explosion to understand the relationship between the explosion condition and the resultant surface phenomena the main parameters we employed were explosion depth and explosion energy through the experiments we confirmed that scaled depth which is the depth divided by cube root of energy is the main parameter determining the properties of explosive volcanism the energy assigned to blast wave decreased exponentially against the scaled depth the scaled crater diameter became maximum when the scaled depth was about 4 10 3 m j scaled crater diameters by nuclear chemical subsurface and some volcanic explosions were almost the same from the scaling law the overpressure at crater rim was estimated to be several mpa which corresponded to typical rock strength probably the ground forming materials were broken inside the area where overpressure exceeded their strength

subsurface structure of a large basaltic maar volcano examined using geologically constrained potential field modelling lake purrumbete maar newer volcanics province southeastern australia abstract lake purrumbete maar lpm is situated in the late cenozoic intraplate basaltic newer volcanics province southeastern australia it is one of the largest maar volcanoes in the world with a near circular crater that is up to 2800 m in diameter containing a 45 m deep lake gellibrand marl accidental lithics which occurs to a maximum depth of 250 m below lpm represent the deepest excavated host rock unit present in the volcanic succession irregular clast shapes and peperitic textures observed in marl lithics suggest the host rock was poorly consolidated during the eruption high resolution lake and land based gravity and magnetic data were collected to conduct forward and inverse modelling of the subsurface architecture of the maar this is done to test the assumption based on lithics that the diatreme is limited to 250 m depth and identify the reasons behind lpm s large size the collection of gravity data presented a unique challenge due to the nature of measuring small changes in gravitational forces

energy partition in the 1982 eruption of el chichon volcano chiapas mexico abstract the 1982 eruption of el chichon volcano chiapas mexico has been extensively investigated from various standpoints including seismicity tephra geology atmospheric effects and tectonic structure in this paper the six largest of a series of explosions are isolated considering various sources of information then the seismic energy released by volcanic earthquakes and tremor is estimated using seismograms of low magnification in order to avoid saturation of seismic wave amplitudes the explosion kinetic energy is evaluated by two methods one by the initial velocity of the ejecta and the other by the air wave data recorded at a distance both the results are roughly coincident the thermal energy is classified into two components that transferred by volcanic ejecta and that consumed by convective clouds the thermal energy released by the explosions is very large compared with that of mechanical energy such as the seismic energy and explosion kinetic energy after the last major explosion of april 4 a type volcanic earthquakes swarmed till the end of april their occurrence rate decreased with time in an aftershock like sequence these earthquake swarms may have been due to post eruptive readjustment of the stress field within and near the volcano such seismic activity contrasts with other examples of similar major eruptions which were followed by growth of lava domes in the new craters after the paroxysmal eruptions the 1982 eruption of el chichon volcano has not been followed by the growth of a lava dome within the newly formed crater

generation of fine hydromagmatic ash by growth and disintegration of glassy rinds 1 the deposits of mafic hydromagmatic eruptions are more fine grained and variable in vesicularity than dry magmatic deposits blocky equant shapes of many hydromagmatic clasts also contrast with droplet thread and bubble wall morphology of dry magmatic fragments small 180 m blocky hydromagmatic pyroclasts have traditionally been interpreted to result from discrete vapor explosions although such explosions tend to occur only under certain conditions this paper considers a process of hydromagmatic ash formation that involves repeated growth and disintegration of glassy rinds on pyroclast surfaces as they deform within turbulent flows this process termed turbulent shedding may occur during the expansion phase of vapor explosions or during turbulent but nonexplosive mixing of magma with water steam or water sprays the occurrence of turbulent shedding and the resulting fragment sizes depend on the timescale for rind growth and the timescale between disturbances that remove or disintegrate glassy rinds turbulent shedding is directly observable in some small littoral jets at kilauea calculations suggest that in the presence of liquid water or water sprays glassy rinds having a thickness of microns to millimeters should form in milliseconds to seconds this is similar to the timescale between turbulent velocity fluctuations that can shred lava globules and remove such rinds the fraction of a deposit consisting of fine ash should increase with the duration of this process large scale surtseyan jets generate hundreds or thousands of shedding events bubble bursts or tephra jets at kilauea s coast may produce only a few

constraining depth to basement for mineral exploration using microtremor a demonstration study from remote inland australia abstractwe constrain the depth and seismic structure of stiff sediment cover overlying a prospective basement terrane using a passive seismic technique which uses surface wave energy from microtremor also known as ambient seismic energy or seismic noise this may be applied to mineral exploration under cover to decrease the inherent ambiguity in modeling potential field data for exploration targeting we use data from arrays of portable broadband seismometers processed using both the multimode spatially averaged coherency mmspac method and the horizontal to vertical spectral ratio hvsr method to produce profiles of seismic velocity structure along a 12 km transect we have developed field protocols to ensure consistent acquisition of high quality data in near mine and remote locations and a variety of ground conditions a wavefield approaching the theoretical ideal for mmspac processing is created by combining the energy content of an off road vehicle driven around the seismometer array and ambi

diatreme evolution during the phreatomagmatic eruption of the songaksan tuff ring jeju island korea the songaksan tuff ring jeju island korea which erupted ca 3 7 ka bp in a coastal setting provides an unusual opportunity to study the processes of phreatomagmatic eruption and the formation of a diatreme because of the exceptionally well preserved ejecta beds and well known subsurface geology the tuff sequence can be divided into four units a to d which have distinctly different accidental componentry quartz rich vs quartz poor grain surface features abraded and ash coated vs unabraded and uncoated and chemical compositions of juvenile particles the basal tephra bed of unit a which probably erupted after the removal of the relatively hard shallow level 120 m deep accidental grains suggesting that the early erupted tephra had not yet experienced recycling and pre eruption mixing in the diatreme on the other hand the overlying tephra beds of units a b and d contain an abundance of abraded and ash coated juvenile accidental grains suggesting that the tephra comprised significant proportions of recycled or premixed materials from previous eruptions or subsurface explosions which participated in the explosion driven mixing in the diatreme before eventual ejection from the diatreme unit c is unusual in that it comprises extremely rare accidental grains and ash coated juvenile accidental grains we interpret that the supply of solid materials either accidental or juvenile to the diatreme was greatly reduced because of temporary stabilization of the diatreme and the reduction in magma flux to the diatreme the diatreme is therefore envisaged to have been filled with a water saturated slurry in which particle abrasion and adhesion were inhibited we also infer that the diatreme fill was temporarily removed by a powerful explosion before eruption of unit c on the basis of the near absence of the tephra grains from earlier eruptions throughout the tephra beds of unit c the ratio of tachylite to sideromelane grains generally increases up section of the tuff sequence with two abrupt drops across the tuff unit boundaries these variations are coincident with the changes in the chemical composition of juvenile particles suggesting an overall decrease in magma flux punctuated by brief increases in magma flux associated with the arrival of new magma batches the textural and compositional variations of the songaksan tuff ring suggest that there can be significant variability in diatreme processes even during a purely phreatomagmatic eruption of a tuff ring including removal and renewal of the diatreme fill and that there is still much room for further investigation of the diatreme processes from the ejecta beds in order to make the current diatreme model more robust

revised conceptual model for maar diatremes subsurface processes energetics and eruptive products diatremes are debris filled structures beneath maars that result from many magma water phreatomagmatic explosions during a monogenetic volcano s lifetime a long standing model requires deepening explosions due to water table drawdown that eject progressively deeper seated country rock from the explosion sites while the overlying diatreme and its surface crater widen due to subsidence a revised model is proposed wherein explosions can take place at any level within a diatreme at a given time most effectively venting material from near surface explosions deep seated country rock lithics in tephra deposits record stepwise vertical mixing of material by upward directed debris jets and downward subsidence rather than direct ejection from deep explosions juvenile and lithic clasts erupted during a given explosion may have had a complex history within the diatreme and need not directly reflect fragmentation or brecciation during the explosion that ejects them

sedimentation induced burial of subsea pipelines observations from field data and laboratory experiments abstract sediment transport induced changes to the embedment of three 26 km long sections of subsea pipeline are analysed and subsequently explained using model scale experiments rather than the scour and scour induced sinking and sagging traditionally thought to dominate post lay pipeline spanning and embedment change the change for these pipelines is shown to be caused by sedimentation the pipelines traverse a range of metocean and soil conditions the variation in embedment correlates well with the variation in metocean conditions with most change occurring in an area where multidirectional high velocity short duration flows associated with internal waves propagate at near perpendicular angles to the pipeline to understand the mechanism driving these changes a series of model scale tests in o tube flumes have been completed under flow conditions mimicking those recorded in the field good agreement is found between the field and laboratory results both in terms of the process timescale and the post sedimentation profile the consistency of the embedment changes between the pipelines their correlation with metocean conditions and the ability to replicate these changes in model scale tests suggests that such changes can be accounted for in more effective pipeline design spans are relatively rare along the pipelines but where they do occur fish rather than scour are shown to be the principal agent of span formation

predicting the rate of scour beneath subsea pipelines in marine sediments under steady flow conditions abstract model scale experiments of scour beneath a submarine pipeline coupled with erosion testing have been undertaken using two marine sediments and five artificial sediments having a wide range of grain size the experiments reveal that for both the marine and artificial sediments the time scale of scour beneath the pipeline depends on the erosion properties of the sediment for coarser sediments mobilised mainly in transport along the bed the rate of scour is found to agree well with the existing empirical formula of fredsoe et al 1992 in contrast for finer sediments that are mobilised mainly through entrainment into suspension and can have relatively high erosion resistance the rate of scour is different to that predicted using the same empirical formula to explain this result theoretical arguments are used to relate the rate of scour beneath a pipeline to the fundamental erosion properties of the sediment namely the transport rate along the bed and the true erosion rate of the sediment these arguments lead to two new empirical formulas that may be used to predict the time scale of the scour process beneath subsea pipelines the first formula is appropriate when the sediment scours predominantly via transport of sediment along the bed and is consistent with the empirical formula due to fredsoe et al 1992 the second formula is appropriate when sediment erodes mainly via entrainment into suspension as is often the case for fine or cohesive sediments collectively the two formulas may be used in practice to make predictions of the rate of scour for pipelines in marine sediments and artificial sediments provided erosion testing results are available

the fracture behaviour of volcanic glass and relevance to quench fragmentation during formation of hyaloclastite and phreatomagmatism quench fragmentation is a non explosive process that occurs when molten magma is super cooled to glass upon contact with ambient water this occurs when coherent lavas are erupted subaqueously when they flow into water when magma intrudes into water saturated sediments and when magma and water interact explosively during phreatomagmatism quench fragmentation also occurs alongside explosive phreatomagmatic activity although products of quench fragmentation hyaloclastite sensu stricto have been discussed qualitatively in the volcanological literature compared to explosive fragmentation processes very little is known about the exact dynamics of quench fragmentation of magma and how this relates to the rheology and physical properties of volcanic glass based on literature from materials engineering we present a detailed review of the processes by which glass forms the properties of glass and the fracture mechanics that cause it to fragment non explosively we also consider how this can be applied to understanding the dynamics behind the volcanological processes of in situ glass fragmentation during quenching in wet environments and phreatomagmatism important parameters for the occurrence of quench fragmentation are the temperature difference between the magma and the ambient water and how much the ambient water is superheated above its leidenfrost temperature the geometry of the lava or magma intrusion the thermal conductivity and the thermal expansion are also of great importance the resistance of the magma against fragmentation can be increased with the presence of crystals provided the thermal expansion of the crystals does not greatly exceed that of the glass vesicles have the opposite effect unless the magma is highly vesicular this overview then provides a solid basis for further quantitative study of quench fragmentation and hyaloclastite formation

extrapolation of irregular subsurface structures using the horizontal to vertical spectral ratio of long period microtremors one of the key problems in modeling the 3d subsurface structure of sedimentary basins is extrapolation and or interpolation from 2d models constructed from reflection and refraction surveys the use of microtremor horizontal to vertical h v spectral ratios allowing simple and quick microtremor measurements may be suitable for this purpose the validity and usefulness of long period microtremor h v spectral ratios are investigated as a possible tool for extrapolation in 3d basin structure modeling three component microtremor observations were conducted at 51 stations in the northern section of the osaka basin which encompasses the most complex geological structures in the basin the microtremor h v spectral ratios were measured in the range 1 to 5 sec to reproduce these observations three 2d finite element models have been developed that account for the irregular shape of subsurface structures deduced from seismic reflection studies microtremor array studies and deep drilling data the 3d model obtained by combining the 2d models is consistent with geological information for the area such as surface geology and the location of active faults furthermore compared with the basement structure derived from the gravity prospecting this 3d model is more detailed and offers higher resolution than the gravitational method therefore the microtremor h v spectral ratio represents a useful technique of extrapolation and interpolation for modeling 3d basin structures

experimental craters formed by single and multiple buried explosions and implications for volcanic craters with emphasis on maars 1 craters at many volcanoes including most maars are formed by multiple subsurface explosions experiments compared the crater formed by a single large buried explosion with craters formed by multiple explosions with the same cumulative energy explosive charges were detonated in pads composed of layered aggregates in three configurations 1 a single large charge buried near its optimal crater excavation depth 2 three charges each with 1 3 the energy of the first one buried at approximately the same depth with respect to the original pad surface 3 the same three charges buried successively deeper final crater size in the multiple explosion cases is not a good indicator of the energy of individual explosions however crater morphology and ejecta volume and distribution can be good indicators of explosion energy and depth these results directly impact the estimate of the energy released by past maar eruptions and future hazard assessments

numerical investigation of local scour beneath a sagging subsea pipeline in steady currents abstract two dimensional 2 d numerical simulations are conducted to predict scour below the midsection of the suspended span of a pipeline that sags naturally into a scour pit the deflection of the pipeline is calculated based on the suspension length or span length of the pipeline which is predicted by an empirical formula for the length of the scour pit the general properties of the scour process are investigated for various pipeline properties pipeline embedment depths and shields parameters the effect of each of these parameters on pipeline sagging are combined into one non dimensional sagging parameter a touchdown time is defined as the time when the pipeline touches the bottom of the sand pit empirical formulae are proposed for predicting the final scour depth at touchdown and the time scale required for touchdown it is found that the final sagging depth is a function of the sagging parameter and the shields parameter whilst the touchdown time is only a function of the sagging parameter a formula is also developed for predicting the time history of scour depth prior to touchdown collectively the empirical formulae and numerical simulations are found to be in reasonable agreement with an existing theoretical model available in the literature

on bias and noise in passive seismic data from finite circular array data processed using spac methods the finite nature of typical small seismic arrays used in conjunction with spatial autocorrelation spac processing for observing the microtremor wavefield causes predictable perturbationsofthespacspectrumwhensourcesofseismic noiseareconfinedtoarestrictedrangeofazimuths suchperturbations are especially evident at higher frequencies where wavelengths are on the order of the array radius the effects arereadilymodeledandshowthatthetriangulararraygeometries commonly used for microtremor studies require azimuthal distributions of wave energy on the order of 60 or greatertohaveahighprobabilityofbeingfreeofsuchperturbations the imaginary component of the spac spectrum which is ideally zero for a sufficiently dense circular array and or a sufficiently isotropic wavefield is in practice often nonzero and provides three quality control indicators 1 an indication of insufficient spatial averaging 2 an empirical measure of the level of statistical uncertainty in spac spectralestimates and3anindicationofdeparturesfromplanewavestationarityoftheseismicnoisewavefield

long term multi proxy climate reconstructions and dynamics in south america lotred sa state of the art and perspectives abstract high resolution multi proxy climate reconstructions with a representative spatial coverage over the globe are arguably among the most important tools for the assessment of the responses of the earth climate to natural and anthropogenic forcing whereas hemispheric or regional multi proxy reconstructions for the past 500 1000 years are available for europe and north america the southern hemisphere including south america has remained largely terra incognita in this special issue we present a comprehensive review of previously published and new data sets from a variety of paleoclimate archives across southern south america south of ca 15 s the underlying collaborative research initiative started in 2006 under the umbrella of igbp pages focus 2 regional climate dynamics and aimed to i collate the large number of disperse paleoclimate data sets from various proxies for the last ca 1000 years and ii produce a spatially explicit highly resolved multi proxy climate reconstruction for southern south america the review and research articles in this special issue cover a variety of archives historical documents tree rings ice cores glacier fluctuations and lacustrine sediments and suggest that at least south of ca 18 s the spatial and temporal coverage of the data is adequate to develop synoptic multi proxy reconstructions for the past ca 400 years although additional high quality proxy records are still needed to resolve the finer temporal and spatial structure of past climate variations the currently available data do provide a consistent picture of climate fluctuations at a large scale we have identified two major directions for future research i a dedicated effort to build a comprehensive quality tested and homogenized set of climate data during the early instrumental period in order to calibrate proxy data series to test and extend reanalysis data sets and to explore the multi decadal variability of synoptic scale atmospheric features and ii expansion of the database of robust well calibrated paleoclimate data series of adequate quality temporal resolution and spatial representation currently this is the bottleneck for further improvements of the reconstructions existing older data sets should be updated to include the most recent years while well calibrated tree ring archives and documentary data have restrictions in terms of spatial coverage and or the length of the data series calibration and quantification of proxy series from ice cores glacier fluctuations lake sediments and vegetation records are of utmost concern and require greatest attention

unconventional maar diatreme and associated intrusions in the soft sediment hosted mardoux structure gergovie france a miocene age volcanic hypabyssal structure comprising volcaniclastic deposits and mafic intrusions is exposed with vertical relief of 110 m on the side of gergovie plateau auvergne france three main volcaniclastic facies are 1 fluidal tuff breccia composed of juvenile basalt and sediment clasts with dominantly fluidal shapes with several combinations of basalt and sediment within individual clasts 2 thickly bedded lapilli tuff composed of varying proportions of fine grained sediment derived from oligocene miocene lacustrine marls and mudstones and basaltic lapilli blocks and bombs 3 planar bedded tuff forming thin beds of fine to coarse ash size sedimentary material and basalt clasts intrusive bodies in the thickly bedded lapilli tuff range from irregularly shaped and anastomosing dikes and sills of meters to tens of meters in length to a main feeder dike that is up to 20 m wide and that flares into a spoon shaped sill at 100 m in diameter and 10 20 m thick in the eastern part of the structure volcaniclastic deposits and structural features suggest that ascending magma entrained soft saturated sediment host material into the feeder dike and erupted fluidal magma and wet sediment via weak strombolian like explosions host sediment and erupted material subsided to replace the extracted sediments producing the growth subsidence structure that is similar to upper diatreme facies in typical maar diatremes but lacks evidence for explosive disruption of diatreme fill irregularly shaped small intrusions extended from the main feeder dike into the diatreme and many were disaggregated due to shifting and subsidence of diatreme fill and recycled via eruption the mardoux structure is an unconventional maar diatreme in that it was produced mainly by weak explosive activity rather than by violent phreatomagmatic explosions and is an example of complex coupling between soft sediment and ascending magma

sedimentation from turbulent jets and plumes theoretical models are developed for the sedimentation from the margins of a particle laden axisymmetric turbulent buoyant plume in a still environment and for an axisymmetric turbulent momentum jet the models assume that the mass of each individual size fraction of sediment carried in a parcel of fluid decreases exponentially with time for relatively coarse particles the fallout models predict that the sediment deposition beyond a distance r on the ground expressed in log units should decay linearly with distance away from the vent for the momentum jet and should decrease with r1 3 for the buoyant plume the exponential decay constant j is proportional to the terminal fall velocity vt of the particles in both cases and inversely proportional to the square root of the initial momentum flux m0 for the jet fallout jj vtmo 1 2 and to the third power of the initial buoyancy flux fo for the plume fallout jp vtfo 1 3 smaller particles are affected by reentrainment caused by the turbulent eddies sweeping ambient fluid back into the plume or jet and thus reincorporating some particles that were released from the flow at greater heights this is taken into account by introducing a reentrainment coefficient into the theoretical models with the assumption that the coefficient has a constant value for a plume of given strength in new experiments fallout occurs from the margins of particle laden fresh water buoyant jets and plumes in a tank of salty water and sedimentation is measured on the tank floor two experiments were weakly affected by reentrainment and show excellent agreement with the simple theory for smaller particles and increasingly buoyant plumes and strong jets particle reentrainment is important the experimental data are fitted by the new reentrainment theory confirming that values of the reentrainment coefficient are approximately constant for a given flow a settling number is defined as the ratio of the characteristic velocity of the jet or plume to the particle settling velocity for 1 reentrainment seems to reach an equilibrium state for which the reentrainment coefficient is a constant of value 0 1 for jets and 0 4 for plumes irrespective of flow strength or particle size the plume experiments indicate that the value of the reentrainment coefficient is strongly dependent on plume strength and particle size for slightly less than 1 the general principles of sedimentation from turbulent plumes and jets are applied to the fallout of pumice from volcanic eruption columns and of metalliferous particles from black smokers on the ocean floor for volcanic eruptions the results provide an explanation for the near vent overthickening of tephra fall deposits and imply that lithic and pumice fragments from small lapilli up to at least 1 m diameter blocks are efficiently reentrained into eruption columns the size of particles reentrained in hydrothermal plumes is predicted to vary from less than 100 m in weakly buoyant plumes up to over 1000 m in megaplumes

an experimental study of hydromagmatic fragmentation through energetic non explosive magma water mixing abstract in this paper we report the first experimental investigation of non explosive hydromagmatic fragmentation during energetic mixing with water we mix magma and water by two methods 1 pouring a basaltic melt between two converging water sprays and 2 jetting basaltic melt at high pressure 3 mpa through a nozzle into a tank of stagnant water these experiments involved shear at relative velocities of 5 16 m s and vigorous mixing for less than a second providing sufficient time for glassy rinds to grow but insufficient time for clot interiors to cool in resulting fragments we examined the gross morphology which reflects fluid deformation during mixing and surface textures which reflect the growth and disruption of glassy rinds we find major differences in both fragment morphology and surface texture between experiments water spray experiments produced pele s hair thin bubble shards melt droplets and angular fracture bound droplet pieces melt jet experiments produced mostly coarse 1 mm diameter wavy fluidal fragments with broken ends fluidal surfaces of fragments produced by water spray experiments were generally shiny under reflected light and in microscopic examination smooth down to micron scale implying no disruption of glassy rinds except for a rare flaking on pele s hair that was bent prior to solidification or b cracking and alligator skin textures on segments of melt balls that had expanded before complete cooling in contrast textures of fluidal surfaces on fragments produced by melt jet experiments are dull in reflected light and in scanning electron images exhibit ubiquitous discontinuous skins rinds that are flaked peeled or smeared away in stripes adhering to these surfaces are flakes blocks and blobs of detached material microns to tens of microns in diameter in the water spray fragments we interpret the scarcity of disrupted surface rinds to result from lack of bending after surfaces formed in the melt jet fragments the ubiquity of partially detached rinds and rind debris likely reflects repeated bending scraping impact and other disruption through turbulent velocity fluctuations when extrapolated to jets of surtseyan scale where velocity fluctuations reach tens of meters per second and turbulent mixing persists for tens of seconds rind disintegration could fragment a large fraction of the erupted material

3d scour below pipelines under waves and combined waves and currents this paper presents the results of an experimental investigation on three dimensional local scour below a rigid pipeline subjected to wave only and combined wave and current conditions the tests were conducted in a conventional wave flume the major emphasis of the investigation was on the scour propagation speed free span expansion rate along the pipeline after local scour was initiated at a controlled location the effects of flow ratio steady current velocity vs combined waves current velocity flow incidence angle and pipeline initial embedment depth on free span expansion rate were investigated it was observed that the scour along the pipeline propagated at a constant rate under wave only conditions the scour propagation rate decreased with increasing embedment depth however increased with the increasing keuglegan carpenter kc number under combined wave and current conditions the effect of velocity ratio on scour propagation velocity along the pipeline was quantified empirical relationships between the scour propagation rate vh and key parameters such as the kc number and embedment depth e d were established based on the testing results

using the characteristics of rootless cone deposits to estimate the energetics of explosive lava water interactions during volcanic eruptions the interaction of magma and groundwater can produce thermohydraulic explosions capable of significantly increasing the eruption energy the most well known mechanism by which explosive magma water interactions occur molten fuel coolant interaction mfci is a complex series of macro and microscale processes which have been simulated using laboratory scale experiments as a natural analog for mfci experiments we utilize rootless cone beds formed by lava water explosions to estimate explosion energy the specific mechanical energy of the lava water explosions studied here occurs over a broader range 4 to 178 kj kg than mfci experiments and includes estimates for the highest energy lava water explosions studied to date explosion energy is partitioned similarly over the two systems with kinetic transport and fragmentation energy making up 25 40 and 42 80 of the mechanical energy respectively which overlap the ranges estimated for mfci experiments our study of lava water explosions therefore provides a field scale analog of mfci laboratory experiments for understanding the energetics and therefore hazards of mfci in natural systems

a study of near source effects in array based spac microtremor surveys summary array based methods for exploiting ambient seismic noise are receiving increasing attention in the literature particularly for use in providing shear wave velocity profiles to assist with simulation of site specific earthquake responses many of these microtremor methods such as the spatial autocorrelation technique spac operate under the fundamental assumption of plane wave propagation of surface waves however when there are significant microtremor sources in close proximity to an array wave front curvature becomes significant and the plane wave assumption becomes a tenuous one this paper explains the use of a simplified geometry based approach to examine the effect of source distance on spac spectra for hexagonal six station and triangular three station arrays the results suggest that near source effects are generally minimal provided that most of the sources are located a distance equal to at least two array radii from the centre of the array although this distance increases when attenuation is considered results of a field trial involving the deliberate use of near sources in proximity to a hexagonal six station array support the findings of the theoretical model near source effects generally result in the measured spac curve being offset to lower frequencies for wavenumbers less than the first secondary maximum of the spac curve kr 0 86r resulting in underestimates of shear velocity values in the inverted layered earth model for the field example shear velocity was underestimated by up to approximately 17 per cent studies of near source effects in a number of theoretical source distributions for hexagonal arrays revealed that cyclic variation in the imaginary spac coefficients are indicative of near source effects although field examples indicate this effect is less significant than the geometric modelling suggests modelling of linear microtremor source distributions intended to represent traffic travelling along a road resulted in less severe near source effects than full 360 azimuthal source coverage a result confirmed by field data model and field studies also indicated that in situations of a dominant close microtremor source of limited azimuthal extent use of a hexagonal six station array significantly mitigates near source effects compared with a similarly aligned triangular three station array

using the spac microtremor method to identify 2d effects and evaluate 1d shear wave velocity profile in valleys the requirement of a layered earth geology is a restrictive assumption when using the spatially averaged coherency spectra spac method numerical simulations of microtremors and spac observations recorded in the tamar paleoval ley launceston tasmania australia are used to assess the potential of the spac method to identify two dimensional 2d effects and evaluate one dimensional 1d shear wave velocity swv profile in a valley environment the tamar valley is approximately 250 m deep by 700 1000 m wide it is filled with soft sediments from the tertiary and quaternary periods above hard dolerite bedrock of jurassic age observed coherency spectra of the vertical component are analyzed at two sites in the tamar valley using two 50 m radius centered triangular arrays above the deepest point of the valley at site dbl and above the east flank of the valley at site rgb simulated and observed coherency spectra suggest the propagation of rayleigh waves of first higher mode at the sv frequency of resonance of the tamar valley affects the coherency spectra recorded with pairs of sensors perpendicular to the valley transverse coh simulated and observed coherency spectra recorded above the deepest point of the valley site dbl with pairs of sensors parallel to the valley axis axial coh are not affected by these edge generated rayleigh waves and agree well with the theoretical coherency spectrum computed from the preferred 1d swv profile the simulated and observed results from this paper suggest that differences between the observed axial coh and transverse coh give an indication of the exis tence of the 2d buried valley results also suggest that the observed coherency spectra recorded on pairs of sensors oriented parallel to the valley axis can provide a reliable evaluation of a 1d swv profile above the deepest point of a deep and narrow valley such as the tamar valley

volcanic and stratospheric dustlike particles produced by experimental water melt interactions commercially available thermit al fe sub 3 o sub 4 was ignited forming a molten mixture of al sub 2 o sub 3 fe the subsequent mixing of this melt with water in steel containers produced explosive interactions that were used to model hydrovolcanic activity debris collected from the experiments consisted of quenched thermit particles ranging in size from 1 mu m to centimeters scanning electron microscopy of the debris showed spheroidal irregular aggregates and blocky particle shapes that are very similar to hydrovolcanic ash as well as some types of stratospheric dust and industrial fly ash 27 references 3 figures 1 table

experimental birth of a maar diatreme volcano abstract maar diatreme eruptions are hazardous to people and infrastructure and are also linked to the formation of the kimberlitic variety of diatremes which is important economically processes occurring in the subsurface diatreme and their relation to surface eruptions are not yet well understood we conducted field scale experiments using analog materials to shed more light on these processes especially the formation of the proto diatreme during the first explosions of a maar eruption specifically a series of buried explosions in a prepared layered substrate pad produced craters extra crater deposits and sub crater deposits analogous to volcanic maar craters tephra rings and incipient diatremes post explosion substrate excavation revealed that single large explosions produce sub crater deposits extending nearly to the crater rim crest the same energy divided into three blasts either co located or at different depths with the same epicenter produced narrower and sometimes deeper sub crater deposits even though the final sizes of the craters were similar to that produced by the single large blast the sub crater deposits have an upper zone with domains from different substrate depths and an underlying zone distinguished primarily by being more loosely packed than the original substrate videos show surface motion extending beyond the post shot crater rim and largely vertical ejection and fallback of material into the footprint of these deposits especially for the explosions that occurred below optimal depth of burial we infer that much of the loosely packed material was disassembled vertically transported to different heights during the explosions then fell back without significant relative lateral movement of grains however subvertical fallback did produce apparent cross cutting structures in shallow sub crater deposits one explosion ejected material from the deepest substrate horizon but it was redeposited only within the crater and is unrepresented in the ejecta rim implications of the experiments for maar diatreme volcanoes including some kimberlite pipes are as follows 1 vertical focusing of deep explosions in the diatreme explains the deficit of deep wallrock lithics observed at maar volcanoes 2 direct vertical fallback is possibly an important process forming diatreme deposits especially during the earliest stages and 3 even in our limited simulation the number and scaled depth of explosions clearly affect proto diatreme size and structure

tsunamis generated by subaqueous volcanic explosions in taal caldera lake philippines volcanic subaqueous explosions can generate hazardous tsunamis especially in lakes in this paper we simulate different scenarios of subaqueous explosions and related tsunamis in taal caldera lake luzon philippines taal volcano is one of the most active volcanoes in southeast asia and eruptive processes are mostly explosive we test different energies of explosions at eight different explosion sites in the lake the initial water surface displacement 0 generated by the explosion is estimated as a function of explosion energy at a given depth we estimate the tsunami travel times maximum wave heights and wave periods at the shoreline this type of hazard is typically neglected and our work has important implications for hazard assessment around taal lake due to fast propagation of tsunamis in the lake waves typically crossing the lake in less than 10 min there is only a short time available for issuing a warning for 0 50 m wave heights at the shoreline are less than 2 m with a non dispersive numerical model and less than 0 5 m with a dispersive model whatever the explosion depth and location powerful explosions with 0 100 m generate wave heights greater than 2 m all around the lake and local peaks higher than 10 m

site characterization for urban seismic hazards in lower manhattan new york city from microtremor array analysis 1 we characterize the shear wave velocity vs of soil deposits in lower manhattan at six sites using the spac and hvsr microtremor methods the soil vs ranges from 140 m s to 300 m s over bedrock we believe that bedrock depth is constrained to 15 with these microtremor data but an accurate quantification of bedrock vs is unattainable because of low spectral coherency at frequencies below 3 hz hvsr data corroborate the spac microtremor results at sites based on good alignment of theoretical rayleigh ellipticity peaks 1d sh amplifications and peak hvsr resonant frequencies vary between 1 4 and 5 5 hz between the sites from both observed hvsr and predicted 1d sh amplification shear wave velocities to 30 m classify the sites as c d or e this study demonstrates that given relatively shallow bedrock depth the spac method can work in extremely urbanized areas

a model for calculating eruptive volumes for monogenetic volcanoes implication for the quaternary auckland volcanic field new zealand abstract monogenetic basaltic volcanism is characterised by a complex array of behaviours in the spatial distribution of magma output and also temporal variability in magma flux and eruptive frequency investigating this in detail is hindered by the difficulty in evaluating ages of volcanic events as well as volumes erupted in each volcano eruptive volumes are an important input parameter for volcanic hazard assessment and may control eruptive scenarios especially transitions between explosive and effusive behaviour and the length of eruptions erosion superposition and lack of exposure limit the accuracy of volume determination even for very young volcanoes in this study a systematic volume estimation model is developed and applied to the auckland volcanic field in new zealand in this model a basaltic monogenetic volcano is categorised in six parts subsurface portions of volcanoes such as diatremes beneath phreatomagmatic volcanoes or crater infills are approximated by geometrical considerations based on exposed analogue volcanoes positive volcanic landforms such as scoria spatter cones tephras rings and lava flow were defined by using a light detection and ranging lidar survey based digital surface model dsm finally the distal tephra associated with explosive eruptions was approximated using published relationships that relate original crater size to ejecta volumes considering only those parts with high reliability the overall magma output converted to dense rock equivalent for the post 250 ka active auckland volcanic field in new zealand is a minimum of 1 704 km3 this is made up of 1 329 km3 in lava flows 0 067 km3 in phreatomagmatic crater lava infills 0 090 km3 within tephra tuff rings 0 112 km3 inside crater lava infills and 0 104 km3 within scoria cones using the minimum eruptive volumes the spatial and temporal magma fluxes are estimated at 0 005 km3 km2 and 0 007 km3 ka the temporal volumetric evolution of auckland is characterised by an increasing magma flux in the last 40 ky which is inferred to be triggered by plate tectonics processes e g increased asthenospheric shearing and backarc spreading of underneath the auckland region

site specific issues for strong ground motions during the kocaeli turkey earthquake of 17 august 1999 as inferred from array observations of microtremors and aftershocks array observations of microtremors and aftershocks were carried out near the permanent strong motion observation sites and the damaged areas after the kocaeli turkey earthquake of 17 august 1999 the major objectives were to determine s wave velocity structures at the sites and to understand the site effects on strong motion or damage array observation of microtremors is a useful method for determining the s wave velocity structures in a sedimentary basin with less practical restriction than the other geotechnical methods the spatial autocorrelation method spac was applied to array data of microtremors for determining s wave velocity structures the spac method generally provides an equivalent result with that of the frequency wavenumber method using fewer array sites and a smaller array size most strong motion sites near the fault are classified into stiff and or very hard soils the records cannot directly be used for interpreting damage to buildings in the sedimentary basin records of long durations of strong motion at ats near avcilar west of istanbul are closely related to the low velocity v s 200 m sec of the surface layers the s wave velocity structure at avcilar where there was severe damage during the mainshock is similar to that of the lowland ats and it differs significantly from that of cna located 4 km northeast of avcilar where the strong motion record was obtained from the mainshock the strong ground motion at avcilar during the mainshock is estimated to be similar to that at ats of the strong motion sites sakarya skr is located on very hard soil whereas thick and soft sediments cover downtown adapazari it is plausible that strong ground motions during the mainshock in the damaged area adc were significantly different from those of skr a large difference between the strong motions of a hillside and the lzmit bay area in and around golcuk is also indicated by a comparison of aftershock records

subsoil structure using spac measurements along a line the spac spatial autocorrelation method was proposed almost 50 years ago by aki 1957 this method allows a phase velocity dispersion curve to be obtained from microtremor measurements using an array of stations arranged in a circle the subsoil structure is subsequently derived from the inversion of that dispersion curve in this article we show that it is possible to get similar results using microtremors recorded along a line we use microtremor records obtained by using four broadband seismographs disposed along a line with different interstation spacings 5 10 20 and 40 m our data are precessed by using the standard spac procedure with the exception of the azimuthal average the final subsoil structure as determined from the inversion of the phase velocity dispersion curve shows excellent agreement with previous results at the site of our measurements our results suggest that the use of the spac method is not restricted to a particular geometry of the array provided that the basic requirement of stationarity is fulfilled

maar diatreme geometry and deposits subsurface blast experiments with variable explosion depth basaltic maar diatreme volcanoes which have craters cut into preeruption landscapes maars underlain by downward tapering bodies of fragmental material commonly cut by hypabyssal intrusions diatremes are produced by multiple subsurface phreatomagmatic explosions although many maar diatremes have been studied the link between explosion dynamics and the resulting deposit architecture is still poorly understood scaled experiments employed multiple buried explosions of known energies and depths within layered aggregates in order to assess the effects of explosion depth and the morphology and compaction of the host on the distribution of host materials in resulting ejecta the development of subcrater structures and deposits and the relationships between them experimental craters were 1 2 m wide analysis of high speed video shows that explosion jets had heights and shapes that were strongly influenced by scaled depth physical depth scaled against explosion energy and by the presence or absence of a crater jet properties in turn controlled the distribution of ejecta deposits outside the craters and we infer that this is also reflected in the diverse range of deposit types at natural maars ejecta were dominated by material that originated above the explosion site and the shallowest material was dispersed the farthest subcrater deposits illustrate progressive vertical mixing of host materials through successive explosions we conclude that the progressive appearance of deeper seated material stratigraphically upward in deposits of natural maars probably records the length and time scale for upward mixing through multiple explosions with ejection by shallow blasts rather than progressive deepening of explosion sites in response to draw down of aquifers

three dimensional scour below offshore pipelines in steady currents this paper presents the results of an experimental investigation on three dimensional scour below offshore pipelines subject to steady currents the major emphasis of the investigation is on the scour propagation velocity along the pipeline after the scour initiation physical experiments were conducted to quantify the effects of various parameters on scour propagation velocity along the pipeline in a water flume of 4 m wide 2 5 m deep and 50 m long local scour depths directly below the model pipeline were measured using specifically developed conductivity scour probes effects of various parameters such as pipeline embedment depth incoming flow shields parameter and flow incident angle relative to the pipeline on scour propagation velocity along the pipeline were investigated it was found that scour propagation velocity generally increases with the increase of shields parameter but decreases with the increase of the pipeline embedment depth a general predictive formula for scour propagation velocity is proposed and validated against the experimental results

origins and energetics of maar volcanoes examples from the ultrapotassic sabatini volcanic district roman province central italy maar volcanoes represent a common volcano type which is produced by the explosive interaction of magma with external water here we provide information on a number of maars in the ultrapotassic sabatini volcanic district svd roman province as young as 90 ka the svd maars are characterised in terms of crater and ejecta ring morphologies eruptive successions and magma compositions in light of the local substrate settings with the aim of assessing magma water interaction conditions eruption energetics and genetic mechanisms feeder magmas spanned the whole svd differentiation trend from trachybasalts shoshonites to phonolites from the ejected lithic fragments from aquifer rocks the range of depth of magma water explosive interaction is estimated to have been mostly at 400 600 m below ground level with a single occurrence of surficial interaction in palustrine lacustrine environment in particular the interaction with external water may have triggered the explosive behaviour of poorly differentiated magmas whereas it may have acted only as a late controlling factor of the degree of fragmentation and eruption style for the most differentiated magma batches during low flux ascent in an incipiently fragmented state crater sizes ejecta volumes and ballistic data allow a reconstruction of the energy budget of svd maar forming eruptions erupted tephra volumes from either monogenetic or polygenetic maars ranged 0 004 0 07 km3 during individual maar forming eruptions with corresponding total magma thermal energies of 8 1015 4 1017 j based on energy partitioning and volume balance of erupted magmas and lithic fractions vs crater holes we consider the different contributions of explosive excavation of the substrate vs subsidence in forming the svd maar craters following available models based on crater sizes highly variable fractions 5 50 of the magma thermal energies would have been required for crater excavation it appears that subsidence may have played a major role in some svd maars characterised by low lithic contents whilst substrate excavation became increasingly significant with increasing degrees of aquifer fragmentation

stress induced brittle fragmentation of magmatic melts theory and experiments 1 the release of kinetic energy during explosive volcanic eruptions is a key parameter for hazard assessment and civil defense the explosive production of volcanic ash by intensive fragmentation of magma and host rocks represents a substantial part of this energy for cases of explosive eruption where predominantly host rock was fragmented phreatomagmatic eruptions to form the major part of volcanic ash rock mechanical parameters could be measured and fragmentation energies assigned in cases where most of the produced ash is of juvenile origin magmatic eruptions a general method for the determination of fragmentation energy is still lacking in this article we introduce a thermodynamic approach that relates grain size data of the produced ash deposits to shear rates acting during the deformation of magma with the use of a standardized fragmentation experiment the physical parameters needed to determine the specific fragmentation energy and deformation history were measured the experiment was calibrated and tested with two case histories of the campi flegrei volcanic field southern italy both eruptions are classified as most probable worst case scenarios during the next period of activity to be expected within the next 10 100 years using the experimentally determined specific fragmentation energies the total mass of produced ash of each eruption and assuming an energy dissipation as observed in the experiments the total kinetic energy release of the worst case campi flegrei eruptive events to come were calculated with 25 and 40 kt tnt equivalent

mid distal occurrences of the albano maar pyroclastic deposits and their relevance for reassessing the eruptive scenarios of the most recent activity at the colli albani volcanic district central italy abstract the late pleistocene albano maar hosted the most recent volcanic activity of the colli albani volcanic district represented at near vent sections by a thick pyroclastic succession of seven units clustered in two main eruptive cycles dated at around 70 68 and 41 36 ka b p respectively recent stratigraphic investigations allowed us to recognise a pyroclastic succession comprising four eruptive units widely spread in the northeastern sectors of the colli albani volcano up to 15 km eastward from the albano maar integrated tephrostratigraphic morpho pedostratigraphic archaeological petrological and geochemical analyses enable us to recognise them as distal deposits of the first third fifth and seventh albano maar eruptions enlarging significantly their previously supposed dispersion area further tephrostratigraphic studies in central apennine area allowed us to identify the albano maar products in late pleistocene deposits of several intermountain basins extending still further the dispersion area of distal ash fallout as far as 100 120 km from the vent on the basis of the identification and the study of these previously unrecognised mid distal albano maar deposits a reappraisal of the eruptive scenarios and related energetic parameters is proposed

a new facility for studying ocean structure seabed interactions the o tube abstract this paper describes a unique new physical testing facility for studying ocean structure seabed interactions and in particular pipeline on bottom stability on erodible seabed under hydrodynamic loading the facility named the o tube due to its shape is a fully enclosed flume in which ambient and storm induced near seabed flows are generated by a computer controlled flow pump combined steady and oscillatory flow can be generated by alternating pump flow directions in a controlled manner and computer control also allows irregular flow to be generated the design of the o tube combines the capabilities of a conventional open channel flume which provides steady current with a u tube which provides oscillatory flow the facility is designed to physically model severe storm conditions as well as ambient or tidal flows when studying pipeline stability on erodible seabed under severe hydrodynamic loading conditions tests can be performed at a relatively large scale typically 1 5 for large diameter pipelines e g 40 in gas trunklines and at full scale for small diameter pipelines

scaling multiblast craters general approach and application to volcanic craters most volcanic explosions leave a crater in the surface around the center of the explosions such craters differ from products of single events like meteorite impacts or those produced by military testing because they typically result from multiple rather than single explosions here we analyze the evolution of experimental craters that were created by several detonations of chemical explosives in layered aggregates an empirical relationship for the scaled crater radius as a function of scaled explosion depth for single blasts in flat test beds is derived from experimental data which differs from existing relations and has better applicability for deep blasts a method to calculate an effective explosion depth for nonflat topography e g for explosions below existing craters is derived showing how multiblast crater sizes differ from the single blast case sizes of natural caters radii and volumes are not characteristic of the number of explosions nor therefore of the total acting energy that formed a crater also the crater size is not simply related to the largest explosion in a sequence but depends upon that explosion and the energy of that single blast and on the cumulative energy of all blasts that formed a crater the two energies can be combined to form an effective number of explosions that is characteristic for the crater evolution the multiblast crater size evolution has implications on the estimates of volcanic eruption energies indicating that it is not correct to estimate explosion energy from crater size using previously published relationships that were derived for single blast cases

lifelong embedment and spanning of a pipeline on a mobile seabed abstract seven years of field survey measurements of a subsea pipeline obtained using sonar profilers and underwater video indicate significant lowering of the pipeline into the seabed due to sediment mobility and scour the majority of the lowering occurs within 2 years of pipeline laying and appears to result from sustained ambient tidal and soliton currents as opposed to large storms the lowering results in an increase in pipeline embedment relative to the far field seabed of up to 0 8 times the pipe diameter referenced at a distance 8 d from the pipeline at most locations along the pipeline this increase in far field embedment is uniform and occurs after the formation of many closely spaced scour holes this suggests that the pipeline lowered mainly through sinking into the seabed at span shoulders rather than sagging into widely spaced scour holes for much of the pipeline length a beam bending analysis confirmed the dominance of sinking but did show some evidence of pipeline sagging calculating deflections of up to 0 3 pipeline diameters at the time of surveying in contrast to the traditional conception of span growth and self burial which conceives of complete pipeline burial as an endpoint this pipeline primarily appears to exhibit self lowering towards a mature state that consists of a pseudo static profile of alternating spanning and embedded sections that are distributed at regular intervals the observed changes appear to be predictable given sufficient pipeline setting data which suggests that they can be quantified in the stability design of new pipelines this opens up the possibility of more efficient on bottom stability design as the beneficial shielding and support provided by the self lowering process is not usually accounted for

maar diatreme volcanoes a review maar diatreme volcanoes are produced by explosive eruptions that cut deeply into the country rock a maar is the crater cut into the ground and surrounded by an ejecta ring while the diatreme structure continues downward and encloses diatreme and root zone deposits here we attempt an evenhanded review of maar diatreme volcanology that extends from mafic to kimberlitic varieties and from historical maar eruptions to deeply eroded or mined diatreme structures we conclude that maar diatreme eruptions are episodic ejecta rings provide invaluable insight into eruption processes and sequence but are incomplete records of diatreme formation deposits within the diatreme structure include in varying proportions lower unbedded deposits sometimes typified by subvertical contacts among domains of debris emplaced sequentially and upper bedded deposits formed by sedimentation on surfaces open to the atmosphere a basal root zone comprises the transition from coherent magmatic feeder dike to clastic deposits formed by fragmentation of magma and enclosing country rock root zones are irregular in form and the clastic deposits are typically intruded by contorted dikes irregular root zone like chaotic breccias cut by contorted dikes are also present within diatreme deposits where they represent intra diatreme fragmentation zones and record changes in the location of the explosion locus during eruption

eruptive history and petrologic evolution of the albano multiple maar alban hills central italy a comprehensive volcanological study of the albano multiple maar alban hills italy using i 40ar 39ar geochronology of the most complete stratigraphic section and other proximal and distal outcrops and ii petrographic observations phase analyses of major and trace elements and sr and o isotopic analyses of the pyroclastic deposits shows that volcanic activity at albano was strongly discontinuous with a first eruptive cycle at 69 1 ka producing at least two eruptions and a second cycle with two peaks at 39 1 and 36 1 ka producing at least four eruptions contrary to previous studies we did not find evidence of magmatic or hydromagmatic eruptions younger than 36 1 ka the activity of albano was fed by a new batch of primary magma compositionally different from that of the older activity of the alban hills moreover the ree and 87sr 86sr data indicate that the albano magma originated from an enriched metasomatized mantle according to the modeled liquid line of descent this magma differentiated under the influence of magma limestone wall rock interaction our detailed eruptive and petrologic reconstruction of the albano maar evolution substantiates the dormant state of the alban hills volcanic district

discrete blasts in granular material yield two stage process of cavitation and granular fountaining a discrete blast within granular material such as a single subterranean explosion within a debris filled diatreme structure is typically considered to produce a single uprush of material our experiments demonstrate that apparent debris jet deposits can be formed by a two stage process of cavitation and subsequent granular fountaining bench scale experiments reported here demonstrate that for a range of overpressures and depths individual discrete buried gas blasts open space and expel particles from the blast site in two largely decoupled stages expanding gas initially pierces material nearest the blast source to open a cavity above it then a fountain of grains rises from the source into the cavity this staged motion dynamically segregates source grains from host material grains and the rates of cavity opening versus fountain rise show a power law decay relationship with initial pressure our experimental analysis has implications for maar diatreme systems field scale detonation experiments and underground nuclear testing

a note on maar eruption energetics current models and their application hydromagmatic eruptions convert thermal into mechanical energy via the expansion of ground and or surface water several models address the energetics of these eruptions based on different physical volcanological approaches here we test different models with two case studies in the colli albani volcanic district central italy the monogenetic prata porci and the polygenetic albano maars test results are mutually consistent and show cumulative mechanical energy releases on the order of 1015 1017 j for single maars the fraction of thermal energy turned into mechanical ranges from 0 45 as calculated from the theoretical maximum mechanical energy through 0 1 calculated from country rock fragmentation crater formation and ballistic ejection to 0 03 derived from magma fragmentation by thermohydraulic explosions it appears that the energy released during the most intense hydromagmatic events may account for a dominant fraction of the total mechanical energy released during the whole maar eruptive histories finally we consider the role of magmatic explosive activity intervening during maar eruptions in causing departures from predictions of the models evaluated

comparisons between vs30 and spectral response for 30 sites in newcastle australia from collocated seismic cone penetrometer active and passive source vs data although the time averaged shear wave velocity down to 30 m depth v s 30 can be a proxy for estimating earthquake ground motion amplification significant controversy exists about its limitations when used as a single parameter for the prediction of amplification to examine this question in absence of relevant strong motion records we use a range of different methods to measure the shear wave velocity profiles and the resulting theoretical site amplification factors afs for 30 sites in the newcastle area australia in a series of blind comparison studies the multimethod approach used here combines past seismic cone penetrometer and spectral analysis of surface wave data with newly acquired horizontal to vertical spectral ratio passive source surface wave spatial autocorrelation spac refraction microtremor remi and multichannel analysis of surface wave data the various measurement techniques predicted a range of different afs the spac and remi techniques have the smallest overall deviation from the median af for the majority of sites we show that v s 30 can be related to spectral response above a period t of 0 5 s but not necessarily with the maximum amplification according to the modeling done based on the measured shear wave velocity profiles both v s 30 and af values are influenced by the velocity ratio between bedrock and overlying sediments and the presence of surficial thin low velocity layers 0 5 s do the amplification curves consistently show higher values for soft site classes and lower for hard classes

rapid injection of particles and gas into non fluidized granular material and some volcanological implications in diatremes and other volcanic vents steep bodies of volcaniclastic material having differing properties particle size distribution proportion of lithic fragments etc from those of the surrounding vent filling volcaniclastic material are often found it has been proposed that cylindrical or cone shaped bodies result from the passage of debris jets generated after phreatomagmatic explosions or other discrete subterranean bursts to learn more about such phenomena we model experimentally the injection of gas particulate dispersions through other particles analogue materials glass beads or sand and a finite amount of compressed air are used in the laboratory the gas is made available by rapidly opening a valve therefore the injection of gas and coloured particles into a granular host is a brief 1 s discrete event comparable to what occurs in nature following subterranean explosions the injection assumes a bubble shape while expanding and propagating upwards in reaction the upper part of the clastic host moves upward and outward above the bubble forming a dome the doming effect is much more pronounced for shallow injection depths thin hosts with dome angles reaching more than 45 significant surface doming is also observed for some full scale subterranean blasts e g buried nuclear explosions so it is not an artefact of our setup what happens next in the experiments depends on the depth of injection and the nature of the host material with shallow injection into a permeable host glass beads the compressed air in the bubble is able to diffuse rapidly through the roof meanwhile the coloured beads sediment into the transient cavity which is also closing laterally because of inward directed granular flow of the host depending on the initial gas pressure in the reservoir the two phase flow can erupt or not non erupting injections produce cylindrical bodies of coloured beads whereas erupting runs produce flaring upward or conical deposits changing the particle size of the host glass beads does not have a large effect under the size range investigated 100 200 to 300 400 m doubling the host thickness injection depth requires a doubling of the initial gas pressure to produce similar phenomena such injections whether erupting or wholly subterranean provide a compelling explanation for the origin and characteristics of multiple cross cutting bodies that have been documented for diatreme and other vent deposits

multimethod characterization of the french pyrenean valley of bagneres de bigorre for seismic hazard evaluation observations and models a narrow rectilinear valley in the french pyrenees affected in the past by damaging earthquakes has been chosen as a test site for soil response characteriza tion the main purpose of this initiative was to compare experimental and numerical approaches a temporary network of 10 stations has been deployed along and across the valley during two years parallel various experiments have been conducted in particular ambient noise recording and seismic profiles with active sources for struc ture determination at the 10 sites classical observables have been measured for site amplification evaluation such as spectral ratios of horizontal or vertical motions between site and reference stations using direct s waves and s coda and spectral ratios between horizontal and vertical h v motions at single stations using noise and s coda records vertical shear velocity profiles at the stations have first been obtained from a joint inversion of rayleigh wave dispersion curves and ellipticity they have subsequently been used to model the h v spectral ratios of noise data from synthetic seismograms the h v ratio of s coda waves based on equipartition theory and the 3d seismic response of the basin using the spectral element method general good agreement is found between simulations and observations the 3d simulation reveals that topography has a much lower contribution to site effects than sedimentary filling except at the narrow ridge crests we find clear evidence of a basin edge effect with an increase of the amplitude of ground motion at some distance from the edge inside the basin and a decrease immediately at the slope foot

recurrence of volcanic activity along the roman comagmatic province tyrrhenian margin of italy and its tectonic significance 1 the roman comagmatic province rcp developed along the nw se striking extensional tyrrhenian margin of italy since middle pleistocene and includes ultrapotassic small eruptive centers and large volcanic districts by means of a review and statistical analysis of a large data set of radiometric ages we demonstrate that in the rcp major eruptive cycles occurred at different volcanic districts almost simultaneously and with an almost constant recurrence time our analysis started with the alban hills volcanic district where a detailed 40ar 39ar chronology of the eruptive cycles has been recently achieved and then extended to include a database of 264 radiometric ages of the rcp volcanics published since 1980 statistical treatment of the data set shows a marked non poissonian behavior of volcanic activity through the whole magmatic province with climax of each major eruptive cycle occurring simultaneously at the different districts approximately every 48 kyr the concomitant eruption of many volcanic districts spreading over a 250 km long chain implies a control mechanism acting at a regional scale after discussing the possible relationship between tectonics sea level changes and volcanic activity we hypothesize that constant rates of slab retreat during middle pleistocene could have been a key factor controlling the rate of magma upwelling and the major cycles of recharge of the magma chambers as a working hypothesis we propose that the duration of the cycles may be related to 1 progressive weakening of the crust due to magma underplating or 2 cyclic injection of convective plumes into the mantle wedge

sub surface dynamics and eruptive styles of maars in the colli albani volcanic district central italy protezione civile italy 2004 2006 agreement with istituto nazionale di geofisica e vulcanologia ingv project v3 1

s wave velocity profiling by joint inversion of microtremor dispersion curve and horizontal to vertical h v spectrum a joint inverse analysis using both microtremor dispersion curve and horizontal to vertical h v spectrum is proposed for estimating the s wave velocity vs profiles of subsurface soils in the inversion both microtremor dispersion and h v data are assumed to be the rayleigh wave dispersion curve and the surface both rayleigh and love wave h v spectrum that have been theoretically derived by taking into account the effects of their fundamental and higher modes the proposed joint inversion as well as the conventional one using dispersion data alone is per formed at four sites where shallow vs profiles down to engineering bedrock are available the vs profiles estimated by the proposed joint inversion are more con sistent with available down hole velocity logs than those by the conventional method in particular the proposed inversion shows significant improvement in estimating bedrock vs structures compared to the conventional inversion sensitivity analyses indicate that the surface wave h v ratio is sensitive to the bedrock vs structure more than the rayleigh wave phase velocity confirming that the proposed joint inversion including h v spectrum is promising

fragmentation in the val pola rock avalanche italian alps 1 grain size data from the deposit of the 1987 val pola rock avalanche central italian alps are compared with data concerning rock avalanching rock fragmentation and comminution the weibull distribution fits a small part of the entire particle size distribution of debris samples with a mean value of the curve shape factor of 0 54 0 28 this is typical of multiple comminution or fragmentation with much shearing a fractal distribution fits over a greater size range computed fractal dimensions range between 1 3 and 3 2 within the deposit with average values of about 2 6 2 7 these values cover the range between the theoretical values of the plane of weakness model 1 97 and the pillar of strength model 2 84 and are close to the theoretical value for the constrained comminution model 2 58 these suggest that both texturally mature and immature deposits are present and that more than a single comminution process acted during the rock avalanche motion variation of the grain size distribution within the deposit and grain size segregation show as trends in the fractal dimension and arise from variation in the fragmentation process a variety of different physical and empirical laws suggest that 1 30 of the energy expended in the rock avalanche was consumed in fragmentation

determination of shallow shear wave velocity profiles in the cologne germany area using ambient vibrations summary we have used both single station and array methods to determine shallow shear velocity site profiles in the vicinity of the city of cologne germany from ambient vibration records based on fk analysis we assume that fundamental mode rayleigh waves dominate the analysed wavefield in the frequency range of 0 7 2 2 hz according to this view a close relation exists between h v spectral ratios and the ellipticity of the contributing rayleigh waves the inversion of the shape of h v spectral ratios then provides quantitative information concerning the local shear wave velocity structure however based on tests with synthetic data believed to represent a typical situation in the lower rhine embayment dispersion curves were found to provide stronger constraints on the absolute values of the velocity depth model than the ellipticities the shape of the ellipticities was found to be subject to a strong trade off between the layer thickness and the average layer velocity we have made use of this observation by combining the inversion schemes for dispersion curves and ellipticities such that the velocity depth dependence is essentially constrained by the dispersion curves while the layer thickness is constrained by the ellipticities in order to test this method in practice we have used array recordings of ambient vibrations from three sites where the subsurface geology is fairly well known and geotechnical information is at least partially available in order to keep the parameter space as simple as possible we attempted to fit only a single layer over a half space model however owing to earlier studies from the region we assume a power law depth dependence for sediment velocities for all three sites investigated the inversion resulted in models for which the shear wave velocity within the sediment layer both in absolute value at the surface and in depth dependence are found to be remarkably similar to the results obtained by budny from downhole measurements this is strong support for the interpretation of h v spectral ratios as rayleigh wave ellipticities for all three sites the predicted sh wave site amplification factors at the fundamental frequency are of the order of 5 6 with a slightly smaller value south of cologne

shallow velocity structure and site effects at mt vesuvius italy from hvsr and array measurements of ambient vibrations abstract ambient vibrations were recorded by two dense short period seismic arrays located on mount vesuvius the aim of this study is to derive the surface velocity structure through the application of array techniques and to interpret it in terms of resonance effects mount vesuvius which is located in proximity to the apennines earthquake source zone is one of the most dangerous volcanoes of the world we compared different array techniques to derive the dispersive properties of the surface waves composing the noise wave field the frequency wavenumber f k spectral method applied to the data recorded by array a furnished the rayleigh waves and love waves dispersive functions and proved the time space stationarity of the noise wave field the existence of a stochastic wave field justifies the use of the spatial autocorrelation spac method and the time stationarity autocorrelation tsac method which appear to be most effective at the lowest frequencies the tsac method which time averages is confirmed as the most user friendly because it does not require circular geometries the knowledge of the surface structure is an important goal in site effects studies and is used to determine the frequency response of the near surface geology velocity models have been derived from the dispersion curves using both trial and standard inversion procedure the results are compared with those obtained from array measurements in adjacent areas scarpa et al 2003 revealing similar mechanical properties in the cover deposits and heterogeneities down to 40 m of depth the shear wave velocity profiles derived at the array sites are used to model the 1d transfer functions for vertically incident shear waves the fundamental resonance frequencies agree with the peak frequencies observed in the microtremor horizontal to vertical spectral ratios the frequency band of amplification is also compatible with the results obtained from local earthquakes at sites located at the same elevation on mount vesuvius galluzzo et al 2009

reconstructing the eruption magnitude and energy budgets for the pre historic eruption of the monogenetic 5 ka mt gambier volcanic complex south eastern australia understanding explosive volcanic eruptions especially phreatomagmatic eruptions their intensities and energy budgets is of major importance when it comes to risk and hazard studies with only a few historic occurrences of phreatomagmatic activity a large amount of our understanding comes from the study of pre historic volcanic centres which causes issues when it comes to preservation and vegetation in this research we show that using 3d geometrical modelling it is possible to obtain volume estimates for different deposits of a pre historic complex monogenetic centre the mt gambier volcanic complex south eastern australia using these volumes we further explore the energy budgets and the magnitude of this eruption vei 4 including dispersal patterns eruption columns varying between 5 and 10 km dispersed towards north east to south to further our understanding of intraplate monogenetic eruptions involving phreatomagmatic activity we also compare which thermodynamic model fits best in the creation of the maar crater of mt gambier the major explosion dominated model or the incremental growth model in this case the formation of most of the craters can best be explained by the latter model

physical characteristics of kimberlite and basaltic intraplate volcanism and implications of a biased kimberlite record we assess bias in the record of kimberlite volcanism by using newly acquired size data on more than 900 kimberlite bodies from 12 kimberlite fields eroded to depths of between 0 m and 1200 m and by a comparison with intraplate monogenetic basaltic volcanic fields eroded kimberlite fields are composed of pipes or diatremes and dikes and within any one kimberlite field regardless of erosion level kimberlite bodies vary in area at earth s surface over 2 3 orders of magnitude typically 60 70 of the bodies are

energy and depth of usu 2000 phreatic explosions 1 on 31 march 2000 the usu volcano located in hokkaido japan began erupting after 22 years of dormancy after the first phreato magmatic explosion there were many small scale phreatic explosions at the nishiyama and kompirayama craters in april and may observations were made using a piezo blast sensor and a visible video recorder to get a better understanding of volcanic explosions the data thus obtained were analyzed using the scaling laws that relate surface phenomena to both explosion energy and depth the analysis using the shape of the explosion cloud and the peak over pressure of the volcanic blast wave indicated that the average explosion energy and depth of the phreatic explosions of mid april ranged from 1010 to 1012 j and originated from between just beneath the ground surface to a depth of a few tens of meters

models of maar volcanoes lunar crater nevada usa maar volcanoes are generally understood to be the result of highly energetic explosive interaction between magma and water groundwater or surface water two end member conceptual models have been proposed to explain the dimensions diameter depth of maar craters 1 an incremental growth model where a crater grows due to subsidence and ejection of debris over the course of many explosions and the final size is an integrated result of multiple explosive events 2 a model in which the dimensions of a maar crater are the result of the largest single explosion during the lifetime of the maar major explosion dominated model in the latter case the maar size can be used to estimate the energy and depth of the largest explosion which in turn allows estimation of the magma mass involved this paper describes lunar crater maar nevada usa and tests the two models as explanations for the characteristics of the volcano in particular the major explosion dominated model this model implies magma mass and supply rates that are unrealistic and the tephra at the maar do not contain key features observed in the ejecta at large single explosion craters the incremental growth model seems most suitable based upon geological evidence

a new model for the fracture energy budget of phreatomagmatic explosions the fragmentation of magma and of the hosting country rocks is a major process in explosive eruptions it is important to quantify the mechanical energy needed for fragmentation in order to assess the physical processes of this volcanic phenomenon this paper presents a method to calculate the fragmentation energy of country rock using granulometry data of a typical phreatomagmatic eifel maar volcano explosion the total fracture area of country rock fragments in one tephra layer was quantified and related to the critical fragmentation energy of these country rocks the rock parameters critical shear stress and critical fragmentation energy were determined experimentally whereas the pre volcanic crack inventory was measured in the field the paper concludes with the calculation of the energy balance i e partitioning of thermal energy into kinetical energy and mechanical energy of the fragmentation of one eifel maar volcanic explosion

mass and energy budgets of explosive volcanic eruptions analysis of the frequency size relationship of explosive volcanic eruptions for the past 2000 years reveals that the time averaged eruptive mass flux of tephra from subaerial explosive eruptions is 3 104 kg s 1 this mass flux corresponds to a thermal energy release of 4 1010 w half of the long term 10 year mass and thermal energy release from explosive volcanic eruptions is accounted for by eruptions of 10 km of tephra

thermodynamics of gas and steam blast eruptions eruptions of gas or steam and non juvenile debris are common in volcanic and hydrothermal areas from reports of non juvenile eruptions or eruptive sequences world wide at least three types or end members can be identified 1 those involving rock and liquid water initially at boiling point temperatures boiling point eruptions 2 those powered by gas primarily water vapor at initial temperatures approaching magmatic gas eruptions and 3 those caused by rapid mixing of hot rock and ground or surface water mixing eruptions for these eruption types the mechanical energy released final temperatures liquid water contents and maximum theoretical velocities are compared by assuming that the erupting mixtures of rock and fluid thermally equilibrate then decompress isentropically from initial near surface pressure 10 mpa to atmospheric pressure maximum mechanical energy release is by far greatest for gas eruptions 1 3 mj kg of fluid rock mixture about one half that of an equivalent mass of gunpowder and one fourth that of tnt it is somewhat less for mixing eruptions 0 4 mj kg and least for boiling point eruptions 0 25 mj kg the final water contents of crupted boiling point mixtures are usually high producing wet sloppy deposits final erupted mixtures from gas eruptions are nearly always dry whereas those from mixing eruptions vary from wet to dry if all the enthalpy released in the eruptions were converted to kinetic energy the final velocity v max of these mixtures could range up to 670 m s for boiling point eruptions and 1820 m s for gas eruptions highest for high initial pressure and mass fractions of rock m r near zero for mixing eruptions v max ranges up to 1150 m s all observed eruption velocities are less than 400 m s largely because 1 most solid material is expelled when m r is high hence v max is low 2 observations are made of large blocks the velocities of which may be less than the average for the mixture 3 heat from solid particles is not efficiently transferred to the fluid during the eruptions and 4 maximum velocities are reduced by choked flow or friction in the conduit