laboratory experiments of forced plumes in a density stratified crossflow and implications for volcanic plumes the mass eruption rate feeding a volcanic plume is commonly estimated from its maximum height winds are known to affect the column dynamics causing bending and hence reducing the maximum plume height for a given mass eruption rate however the quantitative predictions including wind effects on mass eruption rate estimates are not well constrained to fill this gap we present a series of new laboratory experiments on forced plumes rising in a density stratified crossflow we identify three dynamical regimes corresponding to increasing effect of wind on the plume rise the transition from one regime to another is governed by two dimensionless velocity scales defined as a function of source and environmental parameters the results are found consistent with the conditions of historical eruptions and provide new empirical relationships to estimate mass eruption rate from plume height in windy conditions leading to valuable tools for eruption risk assessment

extraction algorithm of mining subsidence information on water area based on support vector machine information on subsidence in a water area caused by mining has a great value on the research of the mining subsidence law of a mining area with a high groundwater level in eastern china based on the measured data of the subsidence area without water the data extraction of subsidence in a water area is studied in this paper with a support vector machine as subsidence in such an area is difficult to measure research shows that the training sample number and dimension should be strengthened by increasing the measuring times or using the interpolation method to obtain ideal prediction accuracy the e support vector regression model with three parameters optimized by the genetic algorithm or the particle swarm optimization algorithm is suitable to extract subsidence information in a water area caused by mining and the algorithm is accomplished on matlab data analysis showed that when the water is deeper than 1 8 m and the distance is over 60 m from the measured points the prediction error of test samples will exceed 10 out of all measured results meaning that practicability is relatively poor while water depth is 0 8 m or the distance is lower than 60 m from the measured points the prediction error of test samples will be calculated to 5 of the measured results the prediction results can be used

deformation characteristics of a roadway in steeply inclined formations and its improved support abstract mining roadways in steeply inclined rock layers commonly experience severe deformation in form of large asymmetric deformation roof subsidence and floor heave which significantly threaten the stability of a roadway using a coal exploration roadway in anhui province china as a case study the deformation characteristics of a roadway in steeply inclined rock formations and the corresponding improved support scheme is analysed by numerical simulation the simulation is performed using a cohesive element to consider the influence of geologic bedding plane around the roadway the results show that due to the spatial relationship of the roadway and the two bedding planes i e interfaces rocks above the roadway move downward along the interface while rocks below the roadway move upward along the interface the maximum deformation occurs along the upper left and lower right sides of the roadway surface which accounts for the large leaning asymmetric deformation of the roadway right inclination an improved support scheme for the roadway is proposed using long cables to restrain severe deformation short cables and enclosed u shaped steel sets to improve the ground stress state the proposed scheme can effectively restrain floor heave manage large asymmetrical deformation compared to the original scheme

cavability control by hydraulic fracturing for top coal caving in hard thick coal seams abstract insufficient breaking and falling of top coal is a technical problem in hard thick or super thick coal seams during top coal mining based on top coal weakening by hydraulic fracturing and main roof hydraulic fracturing to induce coal crushing a method of improving the top coal cavability by top coal and roof hydraulic fracturing is proposed more specifically linear multi hole hydraulic fracturing and deep hole retreating hydraulic fracturing methods for top coal control in top coal caving of hard thick coal seams are proposed a set of high pressure 60 mpa hydraulic fracturing devices was developed the hydraulic fracturing technology and devices were applied in the 3 coal seam in the yulin district where the coal is hard the occurrence depth is shallow and the ground pressure is not extreme the top coal begins to fall when the working face advances 20 m from the setup room and begins to cave normally when the working face advances 40 m after the top coal begins to cave normally the recovery ratio in shallow hard thick coal seam conditions reaches over 80 reaching the average level of top coal caving faces these methods ensure efficient and safe top coal caving in the first coal face by control of the top coal and roof without explosive blasting compared to traditional methods of weakening the top coal and roof by blasting hydraulic fracturing is simpler and safer and requires less work and lower costs 10 of the cost of explosive blasting

an integrated model of magma chamber conduit and column for the analysis of sustained explosive eruptions abstract explosive volcanic eruptions comprise a complex series of processes involving withdrawal from the magma chamber magma ascent along the conduit and eruption column dynamics numerous studies have modeled the different sub domains of a volcanic system but their interplay has seldom been analyzed to this end we developed c 3 c cubed that stands for chamber conduit and column a new integrated model that describes the dynamics of an explosive eruption as a series of steady state regimes and as a function of geometry and initial conditions of the magma reservoir we used global sensitivity analysis to quantify the role of the relevant model parameters and describe the interplay between the different volcanic sub domains in particular we analyzed the evolution of a sustained explosive eruption in order to identify the conditions for buoyant super buoyant and collapsing columns input data were based on field reconstructions of quaternary explosive eruptions in the vulsini volcanic district roman province central italy model results show that 1 the column regime although affected by complex interactions among several factors mostly depends on the conduit radius the volatile content i e supersaturation concentration at the top of the chamber and length of the conduit in decreasing level of importance 2 the amount of mass erupted is independent of the conduit radius and depends mostly on volatile supersaturation the radius of the magma chamber the length of the conduit and the overpressure at the conduit inlet 3 the mass flow rate column height and duration of the eruption are largely controlled by the conduit radius 4 the flow pressure and density at the conduit exit are mostly controlled by the conduit inlet overpressure at the onset of the eruption and by the length of the conduit at the end of the eruption 5 the exit velocity from the conduit is mostly controlled by the volatile content the length of the conduit and the inlet overpressure in this model framework and with specific reference to selected plinian events of the vulsini volcanic district simulation results show that column collapse is not achieved for reasonable eruption durations order of hours and conduit widths tens of meters this is consistent with field reconstructions suggesting that column collapse did not likely occur and that pyroclastic flows were therefore generated by independent mechanisms from ring fissures and or multiple vents concomitant to caldera collapse

experimental study of analogue vent erosion towards nozzle shapes abstract volcanic vent shapes evolve over the course of an explosive eruption as the high pressure ejecta erode the solid conduit walls the changing shape affects the fluid behavior of the expelled gases potentially the plume rise column collapse and the type and amount of accidental debris ejected field observations of evolving vent shape are difficult or impossible while the mechanics of this process have been studied numerically almost no laboratory studies have examined these behaviors thus a series of test samples was manufactured using 3d printing techniques which were eroded using high pressure compressed air four material combinations were considered using stainless steel and alumina powders consolidated with binder concentrations of 16 and 38 material properties were evaluated using compression testing while the erosion behavior was studied through high speed visualization and pressure measurements with identical samples at constant inflow conditions in all cases the erosion showed an initial rapid erosion of the vent exit followed by quasi steady state conditions all samples produced converging diverging nozzle shapes with exit areas increasing by 1 5 to 6 times depending on the sample properties behavior correlated strongly with binder concentration as low binder materials had significant increases in nozzle area when using high density particles these weaker samples disintegrated due to particle abrasion from higher kinetic energy impacts the nozzle shapes produced supersonic exit conditions with mach numbers from 1 48 to 2 51 for the various samples however exit pressures were not balanced suggesting that the optimum is not the isentropic pressure balanced shape previously postulated

researching the earth and a few of its neighbors during my career our knowledge of erupting geysers and volcanoes in the solar system has exploded in this prefatory i tell how i became fascinated with high speed processes through studying meteorite impact dynamics and then how my initial idea of studying old faithful geyser as a volcanic analog led me to work not only on the dynamics of eruption of mount st helens in 1980 but also on geysers erupting on io a fiery satellite of jupiter triton a frigid satellite of neptune and enceladus an active satellite of saturn unforeseeably the study of these events also led to work on mineral thermodynamics and the hydraulics and geomorphic evolution of rapids in the grand canyon this is a narrative not a formal review article but the reader can find references in the related resources section to explore topics in more detail

probabilistic modeling using bivariate normal distributions for identification of flow and displacement intervals in longwall overburden abstract gob gas ventholes ggv are used to control methane emissions in longwall mines by capturing it within the overlying fractured strata before it enters the work environment in order for ggvs to effectively capture more methane and less mine air the length of the slotted sections and their proximity to top of the coal bed should be designed based on the potential gas sources and their locations as well as the displacements in the overburden that will create potential flow paths for the gas in this paper an approach to determine the conditional probabilities of depth displacement depth flow percentage depth formation and depth gas content of the formations was developed using bivariate normal distributions the flow percentage displacement and formation data as a function of distance from coal bed used in this study were obtained from a series of borehole experiments contracted by the former us bureau of mines as part of a research project each of these parameters was tested for normality and was modeled using bivariate normal distributions to determine all tail probabilities in addition the probability of coal bed gas content as a function of depth was determined using the same techniques the tail probabilities at various depths were used to calculate conditional probabilities for each of the parameters the conditional probabilities predicted for various values of the critical parameters can be used with the measurements of flow and methane percentage at gob gas ventholes to optimize their performance

an extension of the insar based probability integral method and its application for predicting 3 d mining induced displacements under different extraction conditions underground extraction can be roughly classified into three types i e subcritical critical and supercritical extraction in accordance with the geological conditions in the overburden and the geometry of mined out areas in 2016 we proposed an approach based on the interferometric synthetic aperture radar insar technique and the probability integral method pim for the cost effective prediction of 3 d mining induced displacements abbreviated as insar pim due to the inherent assumption of critical extraction in the pim the insar pim method performs well in predicting the 3 d displacements caused by critical and or supercritical extraction but poorly for subcritical extraction in this paper we first propose a generalized pim gpim by modifying the traditional pim with a simplified boltzmann function we then replace the pim of the insar pim with the proposed gpim to develop an extension of insar pim referred as to insar gpim the insar gpim was tested in the qianyingzi coal mining area china the results show that the insar gpim predicted horizontal and vertical displacements caused by subcritical critical and supercritical extraction agree well with the in situ observations with average root mean square errors of about 0 032 and 0 050 m respectively these accuracies represent improvements of 60 9 and 59 when compared with the accuracies predicted by the insar pim in the horizontal and vertical directions the results indicate that the insar gpim is capable of accurately predicting 3 d mining induced displacements under different extraction conditions i e subcritical critical and supercritical extraction and it performs much better than the insar pim in the case of subcritical extraction it is therefore believed that insar gpim will have a wider scope of applications than the previous insar pim

the ecosystem of the mid atlantic ridge at the sub polar front and charlie gibbs fracture zone eco mar project strategy and description of the sampling programme 2007 2010 the work was supported by the uk natural environment research council consortium grant no ne c512961 1 and the census of marine life

the dynamics of volcanic jets temporal evolution of particles exit velocity from shock tube experiments pyroclast ejection during explosive volcanic eruptions occurs under highly dynamic conditions involving great variations in flux particle sizes and velocities this variability must be a direct consequence of complex interactions between physical and chemical parameters inside the volcanic plumbing system the boundary conditions of such phenomena cannot be fully characterized via field observation and indirect measurements alone in order to understand better eruptive processes we conducted scaled and controlled laboratory experiments by performing shock tube experiments at known conditions we defined the influence of physical boundary conditions on the dynamics of pyroclast ejection if applied to nature we are focusing in the near vent processes where independently of fragmentation mechanism impulsively released gas pyroclast mixtures can be observed these conditions can be met during e g strombolian or vulcanian eruptions parts of plinian eruptions or phreatomagmatic explosions the following parameters were varied 1 tube length 2 vent geometry 3 particle load 4 temperature and 5 particle size distribution gas and particles in the experiments are not coupled st 1 the initial overpressure with respect to atmosphere was always at 15mpa we found a positive correlation of pyroclast ejection velocity with 1 particle load 2 diverging vent walls and 3 temperature as well as a negative correlation with 1 tube length and 2 particle size additionally we found that particle load strongly affects the temporal evolution of particle ejection velocity these findings stress the importance of scaled and repeatable laboratory experiments for a better understanding of volcanic phenomena and therefore volcanic hazard assessment

geochemical time series of hydrothermal fluids from the slow spreading mid atlantic ridge implications of medium term stability abstract time series investigations of hydrothermal fluids from different geological settings at the slow spreading mid atlantic ridge mar indicate a surprising medium term stability of their chemical composition over up to 20 years this does not only apply to tectonically controlled systems with exposure of mantle rocks where magmatic activity is limited such as the logatchev 1 hydrothermal field at 14 45 n we also found the 407 c hot and extremely metal rich fluids at the 5 s site turtle pits 2986 m water depth to discharge at constant composition indicating supercritical phase separation for at least 4 years which contrasts with rather dynamic volcanically driven hydrothermal systems at the fast spreading east pacific rise epr possibly fluid pathways and pressure temperature conditions are more stable in tectonically controlled settings at mar than at the epr where frequent volcanic activity affects permeability within the hydrothermal systems despite some spatial variability hydrothermal fluids discharging at the shallower ca 810 870 m menez gwen hydrothermal field at 37 50 n seem to represent a stable discharge of phase separated vapor type fluids over 16 years this demonstrates that medium term stability of hydrothermal fluid composition seems to be a general feature at slow spreading ridges as a consequence hydrothermal vent organisms at the mar may live in a more stable chemical environment compared to vent systems at fast spreading ridges considering the fact that slow spreading ridges account for more than half of the submarine ridge system such a constant emanation of hydrothermal fluids makes hydrothermal vent systems on slow spreading ridges a medium term stable source of fe and other micronutrients into the ocean

the decompression of volcanic jets in a crater during explosive volcanic eruptions during explosive volcanic eruptions fragmented silicic magma and volatiles exit the vent with pressures typically in the range 10 100 atm and at the speed of sound of the mixture we show that for magmatic volatile contents no in the range 0 03 no 0 06 this has the approximate value 0 95 0 05 nort 12 where r is the gas constant and t is the eruption temperature this speed is nearly independent of the vent pressure and vent radius by assuming there is negligible mixing with the air we have modelled the decompression of such jets following eruption from the vent for free decompression into the atmosphere the velocity of the decompressed jet has the approximate value 1 85 0 05 nort 12 this is nearly independent of the eruption rate for decompression into a crater the process is more complex at low eruption rates with low vent pressure the material becomes underpressured as it rises in the crater a shock then forms in the crater this recompresses the magma volatile mixture which then issues from the crater as a relatively slow subsonic jet at atmospheric pressure as the eruption rate increases such shocks move towards the top of the crater and ultimately cannot form in the crater instead the material issues from the crater as a high speed supersonic jet the upward thrust provided by the crater walls on this high pressure jet then increases the upward velocity above that of a freely decompressing jet the presence of a crater may therfore cause collapse in relatively small eruptions whereas it may promote formation of buoyant eruption columns at higher eruption rates if a crater grows through erosion during an eruption column collapse will typically ensue even if the mass flux remains steady

an experimental study of the flow structure and acoustics of jets implications for volcano infrasound abstract aeroacoustic jet noise theory describes the relationship between acoustic signals and jet operating parameters based on empirical aeroacoustic relationships a link between peak frequency and amplitude and jet diameter and velocity has been used by volcano acousticians to return the operating parameters of column generating volcanic eruptions there are however significant differences between the nozzle geometries and structures of flows studied in the aeroacoustic literature and flows emitted from volcanic vents these differences raise questions as to the validity of applying engineering relationships to volcanic eruptions combining particle image velocimetry and acoustic data we investigated the flow structures acoustic signals and dominant source locations of jet flows emitted from three simple nozzle geometries convergent straight and divergent flows from the straight and divergent nozzles exited in a more developed flow regime than those emitted from convergent nozzles while for the convergent nozzles dominant sound sources were located within the jet flow the dominant signals from the straight and divergent nozzles were located in the region of the nozzle exit consequently for the straight and divergent nozzles it was not possible to differentiate between signals generated by the jet flow and those generated by internal sound sources without beamforming analysis in order to better replicate the volcanic case and in contrast to studies for industrial applications our experimental test section was not engineered to minimise internal noise without acoustic treatment such as screens choke plates and paddles jet noise signals were contaminated by signals generated within the test rig and so even for the convergent nozzles the aeroacoustic relationships derived from engineering studies could not be used to retrieve the jet operating parameters our results indicate that in the volcanic case the raw acoustic spectra will contain signals generated by both in conduit and above vent processes therefore inversions for volcanic jet parameters such as mass eruption rate from standard aeroacoustic relationships may be unreliable

deep sea research part ii topical studies in oceanography editorial note ecomar ecosystems of the mid atlantic ridge at the sub polar front and charlie gibbs fracture zone

an ultrasonic based method for longwall top coal cavability assessment abstract longwall top coal caving ltcc is widely employed in the underground mining of thick coal seams the technique divides a thick coal seam into a lower and an upper section the bottom coal is sheared by a cutting head and transported by a conveyor in front of the support while the top coal fails and caves under mining pressure transported by a conveyor at the rear of the support in an ltcc panel accurate assessment of top coal cavability is critical to the design of mining parameters required to achieve continuous caving of top coal in the present paper an integrated detection system in which fracture development and ultrasonic wave velocity are used to characterize top coal cavability is introduced the cavability is predicted conveniently due to ease of access of the ultrasonic wave velocity in the top coal accordingly an ultrasonic model is established and coupled to the mechanical model previously proposed by the authors to simulate the evolution of the wave velocity in stressed coal the mechanical ultrasonic coupling model is validated by comparison against experimental data and further extended to evaluate top coal cavability in dongzhouyao mine with a finite difference type code the predictions including the excavation damaged zone roof weighting interval stress distribution stress rotation and ultrasonic wave velocity evolution are consistent with the field measurements with the proposed model the influence provided by hydraulic fracturing on top coal cavability is investigated by conducting the finite difference type modeling

coupled fluid and solid evolution in analogue volcanic vents volcanic eruptions emit rock particulates and gases at high speed and pressure which change the shape of the surrounding rock simplified analytical solutions field studies and numerical models suggest that this process plays an important role in the behavior and hazards associated with explosive volcanic eruptions here we present results from a newly developed laboratory scale apparatus designed to study this coupled process the experiments used compressed air jets expanding into the laboratory through fabricated rock analogue material which evolves through time during the experiment the compressed air was injected at approximately 2 5 times atmospheric pressure we fabricated rock analogues from sand and steel powder samples with a three dimensional printing process we studied the fluid development using phase locked particle image velocimetry while simultaneously observing the solid development via a video camera we found that the fluid response was much more rapid than that of the solid permitting a quasi steady approximation in most cases the solid vent flared out rapidly increasing its diameter by 20 to 100 after the initial expansion the vent and flow field achieved a near steady condition for a long duration the new expanded vent shapes permitted lower vent exit pressures and larger jet radii in one experiment after an initial vent shape development and establishment of steady flow behavior rock failure occurred a second time resulting in a new exit diameter and new steady state this second failure was not precipitated by changes in the nozzle flow condition and it radically changed the downstream flow dynamics this experiment suggests that the brittle nature of volcanic host rock enables sudden vent expansion in the middle of an eruption without requiring a change in the conduit flow

investigation of non explosive expansion material in roof caving field application abstract effective roof caving plays a significant role in mining safety a spatiotemporal coupling fracturing method using a non explosive expansion material neem is proposed in this paper this method depends on the high fracturing capacity of the neem and a change from vertical charging to inclined charging aimed at producing new free surfaces step by step until the integrity of the entire rock is destroyed from a space time perspective the expansion stress and water adsorption of the neem were studied to determine the optimum stress increase interval and soak time with respect to the space aspect the charging sequence of boreholes was negatively correlated to their incline angles bringing the neem s superiority into full play based on the generation of new free surfaces in steps with respect to the time aspect the charging intervals of the inclined boreholes were designed to obtain the best stress compensation and highest fracturing efficiency a field trial was carried out in pingdingshan no 2 mine the results of which showed that some radial cracks were produced around the charging boreholes and that they propagated to the pilot boreholes moreover four main cracks were formed and were approximately parallel to the direction of the borehole rows in a fracturing group a fracture network was eventually generated which verified the expansion capacity of the neem and the feasibility of the spatiotemporal coupling fracturing method for field application

field and numerical investigations of gateroad system failure induced by hard roofs in a longwall top coal caving face abstract in longwall mining hard roofs located immediately above the coal seam should not cave and cause ground control problems around the working longwall face in this paper comprehensive field observations and numerical simulations were used to investigate the chain pillar and adjoining gateroad failure during a longwall top coal caving ltcc face retreat at the majialiang coalmine located in shanxi china the results show that hard roof strata did not cave behind the longwall face but overhung to form a cantilever beam above the chain pillar the roof beam concentrated high stress in the chain pillar and caused the pillar failure the concentrated stress moved close to the headgate and the solid side of the next panel causing gateroad damage and rib collapse numerical simulations found that hard roof treatment could fill the space near the goaf edge and deliver support pressure to the roof as well as alleviate the stress concentration in the pillar and the solid side of the next longwall panel simulations suggested that a pillar size of 50 m or larger was feasible without consideration of hard roof treatment a 40 m chain pillar with hard roof treatment could also satisfy the demand on the pillar and supply gateroad safety during the service period field practices verified the numerical results and suggested that hard roof treatment by hydraulic fracturing is a feasible method for overcoming ground control problems in a situation such as that presented in this paper

strategies methods and technologies adopted on the r v g o sars mar eco expedition to the mid atlantic ridge in 2004 abstract the mar eco project aimed to gather information on mid ocean ridge macro and megafaunal assemblages and their distribution patterns in relation to the abiotic environment and the target area extended from iceland to the azores comprising waters associated with the mid atlantic ridge strategies and methods adopted on the 2004 international expedition on the r v g o sars and m s loran were selected in order to maximise data and sample collection in all pelagic and benthic habitats to a maximum depth of 3500 m spanning the organism size range from mm to metres the approach selected was to combine 1 continuous sampling along the ship s track 2 point observations using a pre defined set of samplers at pre determined sites and 3 opportunistic sampling to study particular phenomena or carry out exceptional tasks a wide range of nets and mid water and bottom trawls were mobilised in order to collect biological samples hull mounted lowered and towed optical and acoustical instruments collected data and images two remotely operated vehicles rovs were used for pelagic and demersal studies and moored echosounders and cameras on benthic landers collected vessel independent information observation of whales and seabirds were made from a custom built observation area on top of the wheelhouse using a range of technologies from the same platform efficiently provided comprehensive results and enhanced the potential for new discoveries at the organism community and ecosystem levels

hydraulic conductivity changes and influencing factors in longwall overburden determined by slug tests in gob gas ventholes abstract this study presents the results of core log analyses from the exploration boreholes the analyses of face advance rates and the results of downhole monitoring studies performed in gob gas ventholes for calculation of changes in hydraulic properties in the longwall overburden at a mine site in southwestern sw pennsylvania section of northern appalachian basin in the first part of the study coal measure rocks in overburden strata were analyzed and the locations where possible fractures and bedding plane separations would occur were evaluated in the second part the hydraulic conductivities were computed by two different slug test analyses methods using the water level changes measured in gob gas ventholes as longwall face approached hydraulic conductivities were analyzed with respect to the changes in overburden depth the locations of the borehole and mine face advance rates these data were used to interpret the potential productivities of the gob gas ventholes as a result of fracturing and changes in hydraulic conductivities the general results showed that the probability of fracturing and bedding plane separations in the overburden increase between strong and weak rock interfaces also the probability of bedding plane separations increases as the interface is close to the extracted coal seam evaluation of slug tests showed that the hydraulic conductivity developments in the boreholes and their potential production performances are affected by the underground strata and the roof materials in situations where the roof material is stiff and thick the development of high permeability fractures around the borehole will be less results also indicated that borehole location with respect to face position affects the fracturing time and permeability evolution as well greater overburden depths generally cause earlier fracturing as longwall face approaches but eventually result in lower hydraulic conductivities and potentially less effective boreholes increasing mining rates also resulted in generally lower hydraulic conductivities in the overburden the results of this study were intended to improve the interpretation of gob gas venthole performance and to provide better siting of these boreholes

determination of actual limit angles to the surface and their comparison with the empirical values in the upper silesian basin czech republic abstract this study deals with the determination of the actual limit angles in the long term formed subsidence basin in the czech part of the upper silesian basin the remaining part lays in poland here there was the most extensive underground exploitation of black coal in the north east of the czech republic a limit angle is absolutely decisive in the determination of deep mining influences in relation to the current and future utilisation of this territory the two csm and paskov mine localities on the edge of the subsidence basin were selected for this study since they could not have been affected by mining in neighbouring mines on the grounds of the long term levelling monitoring of points on the surface which started prior to mining the horizontal distance between the mined out area and the undisturbed ground surface was identified the impact of limit angle on the surface was calculated by means of the horizontal distance and the established mining depth such identified actual limit angles reached the values of 36 at the csm mine and 25 for the paskov mine the calculated values are significantly lower when compared with the currently applied empirical values of 57 for the csm mine and 56 for the paskov mine this means that the extent of the undermining effects is unambiguously wider by 611 m at the csm mine and by 883 m at the paskov mine this study thus establishes the existence of a significantly vaster area influenced by coal deep mining than previously expected the identified facts lead to the conclusion that regular revisions and follow up updates of the empirically determined parameters are recommended

seepage prevention of mining disturbed riverbed abstract coal mining under a body of water introduces a potential risk of water inrush to the mine based on the practice of coal mining near the jinsha river in gansu province china and focused on the seepage prevention of the mining disturbed riverbed the surface movement failure characteristics of the overburden strata and water percolation induced by mining underneath the river have been investigated by means of in situ monitoring physical modeling and discrete element numerical simulation a flexible anti seepage scheme four element structure fes is put forward to protect the riverbed from seepage and the structure can harmonize and buffer the mining induced deformation of the surface land upward from the bottom of the riverbed fes is composed respectively of reinforcement layer which plays the roles of strengthening the riverbed buffering the deformation and enhancing the integrity of the riverbed bedding course layer which prevents the anti seepage layer from folding damage due to dislocation and sharpness in the riverbed meanwhile it can absorb localized deformation anti seepage layer which is a major anti seepage texture made by geo membrane with the properties of water proof a high strength good flexibility and ductility protective layer which covers the geo membrane by a layer of precast reinforced concrete bricks to fix and protect the anti seepage layer in addition treatment principles are proposed for reshipping of the river path in plane the stream gradient along the longitude and the shape of cross section of the riverbed and a comprehensive seepage prevention system is established

fluid dynamics in explosive volcanic vents and craters abstract explosive volcanic jets can transition to buoyant plumes or collapse to form pyroclastic density currents depending on their ability to entrain and heat the ambient air recent one dimensional 1d analysis shows that fluid acceleration through volcanic vents and craters changes the velocity and pressures within these jets sufficiently enough to be a first order control on plume dimensions and therefore air entrainment and column stability koyaguchi et al 2010 these 1d studies are only applicable to craters and vents with angles of less than about 30 to vertical using analytical formulations and numerical simulations this study describes 2d effects of shallowly dipping vents and craters on volcanic eruptions the effect of vents on acceleration and expansion of eruptive mixtures of ash and gas is described as a force imparted on the fluid by the vent wall the wall force fw this force is a measure of the momentum coupling between an eruption and the solid earth that takes place in the vent rapid divergence of supersonic eruptive fluid within shallowly dipping vents occurs via prandtl meyer expansion which results in different pressure and velocity fields than those predicted by 1d analysis this expansion decreases fw and the vertical acceleration experienced by the eruptive fluid in the vent for jets predicted by 1d analysis to exit the vent at supersonic velocities and at atmospheric pressure this decrease in fw will cause an increase in the predicted plume area decreasing column stability the complex 2d shape of volcanic vents can change jet structure presence and location of shock waves and preclude the development of jets that exit the vent supersonically with no internal standing shock waves i e perfectly expanded or pressure balanced jets these significant complications in jet structure and increase in plume radius may result in changes to air entrainment plume stability and tephra distribution

numerical analysis and prediction of ground surface movement induced by coal mining and subsequent groundwater flooding abstract ground surface movement shows different features during mining and post mining period if the mine goaf is dry surface subsidence is observed in both periods if the mine goaf is flooded by groundwater however ground surface uplift can be observed although much smaller in amplitude compared to the preceding subsidence a numerical modeling strategy is proposed to predict uplift during the flooding process of an excavated coal mining area under complex geological conditions the modeling approach considers three phases virgin state before mining stage immediately after mine closure flooding phase the model considers elasto plastic material behavior including faults represented by interfaces in situ measurements are used for calibration of the model the oelsnitz abandoned coal mine is used for model validation and prediction the measured subsidences up to 17 m were reproduced as well as the uplift within the last 10 years with values between 0 5 2 0 mm year spatial distribution of uplift areas is well reproduced predictions up to the year 2051 show an increase in uplift velocity between 0 5 3 0 mm year and additional total uplift of up to 300 mm

effects of the crater on eruption column dynamics 1 during explosive eruptions a mixture of pyroclasts and volcanic gas forms a buoyant eruption column or a pyroclastic flow we systematically investigate how the condition that separates these two eruption styles column collapse condition depends on crater shape and magma chamber conditions by integrating the theoretical models for conduit flow flow inside a crater and eruption column dynamics the results show that previous model predictions of column collapse condition based on the relationship between magma discharge rate and water content nf strongly depend on crater shape depth d and opening angle when a crater is present the decompression and or compression of gas pyroclast mixture inside and just above the crater result in two distinct types of column collapse collapse with increasing hm side collapse and that with decreasing lm side collapse hm side collapse is caused by an increase in conduit radius during the waxing stage of an eruption lm side collapse is associated with a decrease in magma chamber pressure during the waning stage the value of for hm side collapse varies by two orders of magnitude depending on crater shape for fixed nf this estimate also depends on assumed models for decompression into the atmosphere the value of for lm side collapse is 108 kg s 1 when d tan 102 m these results are consistent with the field observations from the st helens 1980 and pinatubo 1991 eruptions

blast dynamics at mount st helens on 18 may 1980 at 8 32 a m on 18 may 1980 failure of the upper part of the north slope of mount st helens triggered a lateral eruption the blast that devastated the conifer forests in a sector covering 500 km2 north of the volcano i present here a steady flow model for the blast dynamics and propose that through much of the devastated area the blast was a supersonic flow of a complex multiphase solid liquid vapour mixture the shape of the blast zone pressure temperature velocity mach number and density distributions within the flow positions of weak and strong internal shocks and mass flux energy flux and total energy are calculated the shape of blast zone was determined by the initial areal expansion from the reservoir by internal expansion and compression waves including shocks and by the density of the expanding mixture the pressure within the flow dropped rapidly away from the source of the blast until at a distance of 11 km the flow became underpressured relative to the surrounding atmosphere weak shocks within the flow subparallel to the east and west margins coalesced at about this distance into a strong mach disk shock across which the flow velocities would have dropped from supersonic to subsonic as the pressure rose back towards ambient the positions of the shocks may be reflected in differences in the patterns of felled trees at the limits of the devastated area the temperature had dropped only 20 from the reservoir temperature because the entrained solids thermally buffered the flow the dynamic and thermodynamic effects of the admixture of the surrounding atmosphere and the uprooted forest and soils into the flow are not considered the density of the flow decreased with distance until at the limits of the blast zone 20 25 km from the volcano the density became comparable with that of the surrounding dirty atmosphere and the flow became buoyant and ramped up into the atmosphere according to the model the mass flux per unit area at the source was 0 6 104 g s 1 cm 2 and the energy flux per unit area was 2 5 mw cm 2 from the measured total ejected mass 0 25 1015 g the total energy released during the eruption was 1024 erg or 24 megatons the model triggering of the eruption and the transition from unsteady to steady flow and applications to eyewitness observations and atmospheric effects are discussed in ref 1

investigation of movement and damage of integral overburden during shallow coal seam mining abstract most prediction methods used to calculate mining induced subsidence are empirical which cannot explain the mechanism of fundamental rock strata movement in this paper based on key stratum theory and the mechanical analysis of overburden a new analytical solution the analogous hyperbola subsidence model ahsm was proposed to describe the movement and damage of inner burden mining induced rock strata movement was verified using the distinct element method udec to assess the performance of the theoretical model three subsidence parameters smax t sgoaf smax d h generally used to describe surface subsidence trough agree with statistical field measurements of the south coalfield in australia the surface subsidence and the movement boundary in the overburden are very close to the theoretical predictions additionally the primary key stratum damages the least in the overlying strata its broken length is the smallest the width of subsidence trough and maximum surface subsidence increase as the primary key stratum drops

effect of discontinuity stress shadows on hydraulic fracture re orientation hydraulic fracturing has been applied to the cave mining industry as a pre conditioning method to improve rock mass caveability and fragmentation sizes in theory the hydraulic fracture orientation is dictated by and is perpendicular to the minimum in situ stress orientation such orientations will not always result in the creation of a blocky rock mass to aid caveability the understanding of hydraulic fracture re orientation induced by the stress shadow effect is important for either avoiding the undesirable interaction between multiple transverse hydraulic fractures or taking advantage of this phenomenon to create prescribed hydraulic fractures that result in the creation of blocky rock masses in this paper the existing knowledge of the stress shadow effect around a pre existing discontinuity is reviewed a 3d numerical modelling code rock failure process analysis rfpa is used to investigate factors influencing hydraulic fracture re orientation it is established that hydraulic fractures can be forced to propagate in desired directions if advantage is taken of the stress shadow effect in combination with knowledge of rock mass homogeneity and site far field stress conditions both the differential stresses between 2 and 3 and between 1 and 3 affect the hydraulic fracture re orientation geometry the minimum far field stress magnitude has no direct impact on hydraulic fracture re orientation rock mass homogeneity significantly influences how far a hydraulic fracture propagates along its predefined orientation from its initiation point before re orientation

towards improved understanding of the diversity and abundance patterns of the mid ocean ridge macro and megafauna mid ocean ridges are vast features of all oceans but their fauna and ecological significance remain poorly understood ridge studies in recent decades were understandably biased in favour of the newly discovered chemosynthetic ecosystems investigations of photosynthesis based systems and communities associated with ridges were scattered and few despite their much larger scale and significance for ocean productivity patterns and biogeography and for the management of human activities on the high seas this knowledge gap was recognised by the census of marine life coml programme and led to the initiation of a dedicated field project on non chemosynthetic systems and communities of a mid ocean ridge the present collection of articles highlights results from the project patterns and processes of the ecosystems of the northern mid atlantic mar eco the coml field project that aims to explore the diversity and distribution patterns of photosynthesis based communities of mid ocean ridges by a range of classical and new technologies and methods in 2003 2005 comprehensive investigations were conducted on pelagic and epibenthic macro and megafauna of the mid atlantic ridge between iceland and the azores several research vessels participated in the first field phase of the project but the majority of the results were from a 2 month international expedition on the norwegian vessels r v g o sars and the chartered fishing vessel m s loran in 2004 this introduction explains the background and goals of mar eco summarizes the strategies and sampling efforts and briefly introduces future plans as the project enters a second field phase in 2007 2009

rock deformation models and fluid leak off in hydraulic fracturing summary fluid loss into reservoir rocks during hydraulic fracturing is modelled via a poro elastoplastic pressure diffusion equation in which the total compressibility is a sum of fluid rock and pore space compressibilities inclusion of pore compressibility and porosity dependent permeability in the model leads to a strong pressure dependence of leak off i e drainage rate dilation of the matrix due to fluid invasion causes higher rates of fluid leak off the present model is appropriate for naturally fractured and tight gas reservoirs as well as for soft and poorly consolidated formations whose mechanical behaviour departs from simple elastic laws enhancement of the leak off coefficient by dilation predicted by the new model may help explain the low percentage recovery of fracturing fluid usually between 5 and 50 per cent in shale gas stimulation by hydraulic fracturing

are eruptions from linear fissures and caldera ring dykes more likely to produce pyroclastic flows turbulent volcanic jets are produced by highly energetic explosive eruptions and may form buoyant plumes that rise many tens of kilometres into the atmosphere to form umbrella clouds or collapse to generate ground hugging pyroclastic flows ash injected into the atmosphere can be transported for many hundreds of kilometres with the potential to affect climate disrupt global air travel and cause respiratory health problems pyroclastic flows by contrast are potentially catastrophic to populations and infrastructure close to the volcano key to which of these two behaviours will occur is the extent to which the mechanical entrainment and mixing of ambient air into the jet by large entraining eddies forming the jet edge changes the density of the air ash mixture low entrainment rates lead to pyroclastic flows and high entrainment rates give rise to buoyant plumes recent experiments on particle laden multi phase volcanic jets from flared and straight sided circular openings suggest that the likelihood for buoyant plumes will depend strongly on the shape and internal geometry of the vent region this newly recognised sensitivity of the fate of volcanic jets to the structure of the vent is a consequence of a complex dynamic coupling between the jet and entrained solid particles an effect that has generally been overlooked in previous studies building on this work here we use an extensive series of experiments on multi phase turbulent jets from analogue linear fissures and annular ring fractures to explore whether the restrictive vent geometry during cataclysmic caldera forming ccf eruptions will ultimately lead a relatively greater frequency of pyroclastic flows than eruptions from circular vents on stratovolcanoes our results understood through scaling analyses and a one dimensional theoretical model show that entrainment is enhanced where particle motions contribute angular momentum to entraining eddies however because the size of the entraining eddies scales approximately with vent width the extent of entrainment is reduced as the vent width becomes small in comparison to its length consequently our work shows that for specified mass eruption rates the high length to width ratio vents typical of ccf events are more likely to produce pyroclastic flows we suggest that the enigmatic trend in the geological record for the largest ccf eruptions to produce pyroclastic flows is an expected consequence of their being erupted through continuous or piece wise continuous caldera ring fractures

a user friendly one dimensional model for wet volcanic plumes 1 this paper presents a user friendly graphically based numerical model of one dimensional steady state homogeneous volcanic plumes that calculates and plots profiles of upward velocity plume density radius temperature and other parameters as a function of height the model considers effects of water condensation and ice formation on plume dynamics as well as the effect of water added to the plume at the vent atmospheric conditions may be specified through input parameters of constant lapse rates and relative humidity or by loading profiles of actual atmospheric soundings to illustrate the utility of the model we compare calculations with field based estimates of plume height 9 km and eruption rate 4 105 kg s during a brief tephra eruption at mount st helens on 8 march 2005 results show that the atmospheric conditions on that day boosted plume height by 1 3 km over that in a standard dry atmosphere although the eruption temperature was unknown model calculations most closely match the observations for a temperature that is below magmatic but above 100 c

dynamics of deep submarine silicic explosive eruptions in the kermadec arc as reflected in pumice vesicularity textures abstract despite increasing recognition of silicic pumice bearing deposits in the deep marine environment the processes involved in explosive silicic submarine eruptions remain in question here we present data on bubble sizes and number densities number of bubbles per unit of melt matrix for deep submarine erupted pumices from three volcanoes healy raoul sw and havre along the kermadec arc sw pacific to investigate the effects of a significant 1 km overlying water column and the associated increased hydrostatic pressure on magma vesiculation and fragmentation we compare these textural data with those from chemically similar subaerially erupted pyroclasts from nearby raoul volcano as well as submarine erupted tangaroan fragments derived by non explosive buoyant detachment of foaming magma from macauley volcano also along the kermadec arc deep submarine erupted pumices are macroscopically similar colour density texture to subaerial or shallow submarine erupted pumices but show contrasting microscopic bubble textures deep submarine erupted pyroclasts have fewer small

mechanism and risk assessment of overall instability induced rockbursts in deep island longwall panels abstract an increasing number of mines in china are being subjected to overall instability induced oii rockbursts in extracting deep remnant island longwall panels causing severe damage at far larger scale and intensity compared with common local rockbursts using the island longwall panel lw1305 at zhaolou coal mine as a case example this paper investigates the mechanism of the newly defined oii rockburst by means of stress and microseismic monitoring and then proposes a straightforward risk assessment method for oii rockbursts based on the actual bearing index in an attempt to provide guidelines for making engineering judgement the proposed risk assessment method was successfully applied to lw1305 and the assessment result is supported by the occurrence of an oii rockburst in lw1305 and further verified by numerical modeling and microseismic monitoring

assessment of rock mass characteristics and the excavation disturbed zone in the lingxin coal mine beneath the xitian river china safe production and induced hazard prevention in coal mines mainly concern problems in the excavation disturbed zone edz but coal mining can also make a significant impact on the environment comprehensive techniques using a borehole tv viewer system electrical logging and monitoring of drilling fluid leakage offer the ability to identify changing geological conditions and the location of any nearby abandoned mining workings the inner collapsed zone and the expanding height of the crack zone transmitting water plus their spatial distribution after excavating the superincumbent coal seam stratum are determined at no l3414 workings lingxin coal mine beneath the xitian river china an integrated system of gis based on a stochastic model which has been developed for the prediction of dynamic subsidence coupling the time function and probabilistic integral method is verified through practice at the lingxin coal mine this development has greatly expanded the ability of the mine operator to characterize previously inaccessible areas of the mine providing a reliable basis for safe mining and prevention of induced hazards to ensure high production mining underneath the river bed

a system to mitigate deep mine tremor effects in the design of civil infrastructure deep mining may induce quakes reaching magnitude ml of 4 5 to 5 5 and leading to surface ground motion with modified mercalli intensities up to viii such strong ground motions may cause serious damages in civil infrastructure in the vicinity of mines however any adaptation of a classic seismic code in design faces an impending problem of differences in spectral content and duration between the surface records of the rockbursts and natural earthquakes as well as in their different risk definitions this paper presents a system to define design seismic load based on forecasted surface horizontal particle velocity from the rockbursts expected during the planned mining activities such forecasts are routinely prepared by the geophysical mine services respective seismic load may then be applied in the design of buildings and other structures to mitigate the rockburst induced seismic effects on them for this purpose the european seismic code eurocode 8 is adapted

moist convection and the injection of volcanic ash into the atmosphere if unsaturated water vapor is carried upward by a volcanic eruption column it may eventually become saturated owing to the decrease in temperature of the column as it expands through decompression and transfers heat to entrained air heat released as a result of the subsequent condensation of water vapor causes the air within the column to expand we show that this increases the buoyancy and therefore the total height of rise of the column the increase in height is significant in relatively small sub plinian and strombolian eruptions in which mass eruption rates lie in the range 103 to 106 kg s in such eruptions the latent heat released as the entrained water vapor condenses may provide the main source of heat which drives the ash and clasts upward the height of rise then becomes relatively insensitive to the mass flux erupted at the vent and depends primarily upon the vapor loading of the atmosphere in a moist atmosphere ash may rise several kilomtres higher than in an eruption of comparable strength in a dry environment moist convection leads to much wider ash dispersal particularly from very small eruptions subsequently rain flushing of ash from umbrella clouds may result from the water which forms through the condensation of entrained vapor the ash provides natural condensation nuclei for some of this entrained vapor whose mass may be much greater than that of the ash in small columns 107 kg s the latent heat released by condensation of vapor is relatively small in comparison with the thermal energy provided by the hot clasts and therefore moisture has no significant effect upon the eruption column dynamics furthermore the mass of water vapor originating from the erupted volatiles is usually comparable to or greater than that entrained from the ambient air our model also shows that if the erupting mixture becomes buoyant then the eruption columns associated with phreatomagmatic eruptions ascend nearly as high as plinian columns with the same mass eruption rate this is because the water which is vaporized by the hot ash at the source condenses higher in the column and thereby restores its latent heat to the ascending ash

numerical simulations of volcanic jets importance of vent overpressure journal of geophysical research vol 113 b02204 doi 10 1029 2007jb005133 2008 numerical simulations of volcanic jets importance of vent overpressure darcy e ogden 1 kenneth h wohletz 2 gary a glatzmaier 1 and emily e brodsky 1 received 24 april 2007 revised 5 october 2007 accepted 5 november 2007 published 29 february 2008 1 explosive volcanic eruption columns are generally subdivided into a gas thrust region and a convection dominated plume where vents have greater than atmospheric pressure the gas thrust region is overpressured and develops a jet like structure of standing shock waves using a pseudogas approximation for a mixture of tephra and gas we numerically simulate the effects of shock waves on the gas thrust region these simulations are of free jet decompression of a steady state high pressure vent in the absence of gravity or a crater our results show that the strength and position of standing shock waves are strongly dependent on the vent pressure and vent radius these factors control the gas thrust region s dimensions and the character of vertical heat flux into the convective plume with increased overpressure the gas thrust region becomes wider and develops an outer sheath in which the erupted mixture moves at higher speeds than it does near the column center the radius of this sheath is linearly dependent on the vent radius and the square root of the overpressure the sheath structure results in an annular vertical heat flux profile at the base of the convective plume which is in stark contrast to the generally applied gaussian or top hat profile we show that the magnitude of expansion is larger than that predicted from previous 1d analyses resulting in much slower average vertical velocities after expansion these new relationships between vent pressure and plume expansion may be used with observations of plume diameter to constrain the pressure at the vent citation ogden d e k h wohletz g a glatzmaier and e e brodsky 2008 numerical simulations of volcanic jets importance of vent overpressure j geophys res 113 b02204 doi 10 1029 2007jb005133 1 introduction 2 in large explosive volcanic eruptions the eruptive fluid issues from the vent as a high speed compressible gas with entrained solid particulates it is important to quantify the behavior of this gas thrust region because it provides a connection between the fluid dynamics in the conduit and that of the buoyant column if the eruptive fluid velocity is at or greater than sonic and vent pressure is higher than atmospheric pressure the dynamics will be complicated by the presence of standing shock waves that can drastically alter the distribution of the vertical heat flux necessary for eruption column stability the fluid dynamics and structure of a compressible jet issuing from a sonic nozzle into an ambient atmosphere of lower pressure are well known from experimental analytical and computational studies e g crist et al 1966 young 1975 norman et al 1982 figure 1 although application of compressible jet dynamics to explosive volcanic eruptions was first sug gested over 25 years ago by kieffer 1981 the concept has earth planetary sciences department university of california at santa cruz santa cruz california usa los alamos national laboratory los alamos new mexico usa copyright 2008 by the american geophysical union 0148 0227 08 2007jb005133 09 00 yet to be widely applied in modeling and analysis of explosive eruption columns 3 in this paper we present computational results that quantify the important effects of vent pressure on the fluid dynamics of volcanic jets and show that overpressured jets produce vertical heat flux profiles that are drastically different than those of pressure balanced jets note to avoid confusion here we use the physics convention and consider heat flux the thermal energy transfer per area per unit time j m 2 s 1 and heat flow the thermal energy transfer integrated over an entire area per time j s 1 in volcanology literature the term heat flux is often used to mean either of these things e g woods 1988 mastin 2007 the simulations shown here are time dependent though they assume a steady vent condition through these simulations we quantify the effects of vent pressure and radius on plume radius and heat flux distribution after expansion of the jet this may allow the prediction of major features of the eruptive structure we do not consider the effects of variations in conduit dynamics buoyancy or the presence of a crater in order to focus only on the effects of vent pressure and radius alone this study is not a complete picture of the complicated flow dynamics of a volcanic eruption rather the results presented here could be consid ered the simplest case to which one could compare the dynamics resulting from more complicated simulations and observations of high pressure volcanic jets b02204 1 of 18

vertical structure biomass and topographic association of deep pelagic fishes in relation to a mid ocean ridge system abstract the assemblage structure and vertical distribution of deep pelagic fishes relative to a mid ocean ridge system are described from an acoustic and discrete depth trawling survey conducted as part of the international census of marine life field project mar eco http www mar eco no the 36 station zig zag survey along the northern mid atlantic ridge mar iceland to the azores covered the full depth range 0 to 3000 m from the surface to near the bottom using a combination of gear types to gain a more comprehensive understanding of the pelagic fauna abundance per volume of deep pelagic fishes was highest in the epipelagic zone and within the benthic boundary layer bbl 0 200 m above the seafloor minimum fish abundance occurred at depths below 2300 m but above the bbl biomass per volume of deep pelagic fishes over the mar reached a maximum within the bbl revealing a previously unknown topographic association of a bathypelagic fish assemblage with a mid ocean ridge system with the exception of the bbl biomass per volume reached a water column maximum in the bathypelagic zone between 1500 and 2300 m this stands in stark contrast to the general open ocean paradigm that biomass decreases exponentially from the surface downwards as much of the summit of the mar extends into this depth layer a likely explanation for this mid water maximum is ridge association multivariate statistical analyses suggest that the dominant component of deep pelagic fish biomass over the northern mar was a wide ranging bathypelagic assemblage that was remarkably consistent along the length of the ridge from iceland to the azores integrating these results with those of previous studies in oceanic ecosystems there appears to be adequate evidence to conclude that special hydrodynamic and biotic features of mid ocean ridge systems cause changes in the ecological structure of deep pelagic fish assemblages relative to those at the same depths over abyssal plains lacking terrigenous input of allochthonous organic carbon increased demersal fish diversity and biomass over the mar relative to the abyssal plains may be maintained by increased bathypelagic food resources the aggregation of bathypelagic fishes with mar topographic features was primarily a large adult phenomenon considering the immense areal extent of mid ocean ridge systems globally this strategy may have significant trophic transfer and reproductive benefits for deep pelagic fish populations

reconciling longwall gob gas reservoirs and venthole production performances using multiple rate drawdown well test analysis abstract longwall mining is an underground mining method during which a mechanical shearer progressively mines a large block of coal called a panel in an extensive area during this operation the roof of the coal seam is supported only temporarily with hydraulic supports that protect the workers and the equipment on the coal face as the coal is extracted the supports automatically advance and the roof strata cave behind the supports caving results in fracturing and relaxation of the overlying strata which is called gob due its highly fractured nature gob contains many flow paths for gas migration thus if the overlying strata contain gassy sandstones or sandstone channels gas shales or thinner coal seams which are not suitable for mining then the mining induced changes can cause unexpected or uncontrolled gas migration into the underground workplace vertical gob gas ventholes ggv are drilled into each longwall panel to capture the methane within the overlying fractured strata before it enters the work environment thus it is important first to understand the properties of the gas reservoir created by mining disturbances and second to optimize the well parameters and placement accordingly in this paper the production rate pressure behaviors of six ggvs drilled over three adjacent panels were analyzed by using conventional multi rate drawdown analysis techniques the analyses were performed for infinite acting and pseudo steady state flow models which may be applicable during panel mining dm and after mining am production periods of ggvs these phases were analyzed separately since the reservoir properties due to dynamic subsidence boundary conditions and gas capacity of the gob reservoir may change between these two stages the results suggest that conventional well test analysis techniques can be applicable to highly complex gob reservoirs and ggvs to determine parameters such as skin permeability radius of investigation flow efficiency and damage ratio the insights obtained from well test analyses can be used for a better understanding of the gob and for designing more effective gob gas venthole systems

a numerical study of turbulent mixing in eruption clouds using a three dimensional fluid dynamics model 1 the dynamics of eruption clouds in explosive volcanic eruptions are governed by entrainment of ambient air into eruption clouds by turbulent mixing we develop a new numerical pseudo gas model of an eruption cloud by employing three dimensional coordinates a third order accuracy scheme and a fine grid size in order to investigate the behavior of entrainment due to turbulent mixing the quantitative features of entrainment are measured by a proportionality constant relating the inflow velocity at the edge of the flow to the average vertical velocity i e the entrainment coefficient our model has successfully reproduced the quantitative features of entrainment observed in the laboratory experiments as well as fundamental features of the dynamics of eruption clouds such as the generation of eruption columns and or pyroclastic flows the value of the entrainment coefficient for eruption clouds is estimated from the column height and critical condition for column collapse by comparing results of our model with those of previous one dimensional models it is suggested that the value of the entrainment coefficient for an eruption cloud is approximately constant although the value estimated from the critical condition for column collapse k 0 07 is slightly smaller than that based on the column height k 0 1 this difference reflects the vertical change of flow structure in the eruption cloud the eruption cloud in the upper region exhibits a meandering instability which leads to efficient mixing whereas the cloud near the vent maintains a concentric structure with an inner dense core surrounded by an outer shear region our model is consistent with previous one dimensional models for steady eruption clouds supported by the laboratory experiments and it is also applicable to unsteady and transient features of actual eruption clouds

inter comparison of three dimensional models of volcanic plumes abstract we performed an inter comparison study of three dimensional models of volcanic plumes a set of common volcanological input parameters and meteorological conditions were provided for two kinds of eruptions representing a weak and a strong eruption column from the different models we compared the maximum plume height neutral buoyancy level where plume density equals that of the atmosphere and level of maximum radial spreading of the umbrella cloud we also compared the vertical profiles of eruption column properties integrated across cross sections of the plume integral variables although the models use different numerical procedures and treatments of subgrid turbulence and particle dynamics the inter comparison shows qualitatively consistent results in the weak plume case mass eruption rate 1 5 106 kg s 1 the vertical profiles of plume properties e g vertical velocity temperature are similar among models especially in the buoyant plume region variability among the simulated maximum heights is 20 whereas neutral buoyancy level and level of maximum radial spreading vary by 10 time averaging of the three dimensional 3d flow fields indicates an effective entrainment coefficient around 0 1 in the buoyant plume region with much lower values in the jet region which is consistent with findings of small scale laboratory experiments on the other hand the strong plume case mass eruption rate 1 5 109 kg s 1 shows greater variability in the vertical plume profiles predicted by the different models our analysis suggests that the unstable flow dynamics in the strong plume enhances differences in the formulation and numerical solution of the models this is especially evident in the overshooting top of the plume which extends a significant portion 1 8 of the maximum plume height nonetheless overall variability in the spreading level and neutral buoyancy level is 20 whereas that of maximum height is 10 this inter comparison study has highlighted the different capabilities of 3d volcanic plume models and identified key features of weak and strong plumes including the roles of jet stability entrainment efficiency and particle non equilibrium which deserve future investigation in field laboratory and numerical studies

impact of wind on the condition for column collapse of volcanic plumes the collapse of volcanic plumes has significant implications for eruption dynamics and associated hazards we show how eruptive columns can collapse and generate pyroclastic density currents as a result of not only the source conditions but also of the atmospheric environment the ratio of the potential energy and the kinetic energy at the source quantified by the richardson number and the entrainment efficiency quantified by the radial entrainment coefficient have already been identified as key parameters in controlling the transition between a buoyant and collapsing plume here we quantify how this transition is affected by wind using scaling arguments in combination with a one dimensional plume model air entrainment due to wind causes a volcanic plume to lower its density at a faster rate and therefore to favor buoyancy we identify the conditions when wind entrainment becomes dominant over radial entrainment and quantify the effect of wind on column collapse these findings are framed into a generalized regime diagram that also describes previous regime diagrams for the specific case of choked flows many observations confirm how bent over plumes typically do not generate significant collapses a quantitative comparison with the 1996 ruapehu and the 2010 eyjafjallajokull eruptions shows that the likelihood of collapse is reduced even at moderate wind speeds relative to the exit velocity at the vent

release characteristics of overpressurised gas from complex vents implications for volcanic hazards many explosive volcanic eruptions produce underexpanded starting gas particle jets the dynamics of the accompanying pyroclast ejection can be affected by several parameters including magma texture gas overpressure erupted volume and geometry with respect to the latter volcanic craters and vents are often highly asymmetrical here we experimentally evaluate the effect of vent asymmetry on gas expansion behaviour and gas jet dynamics directly above the vent the vent geometries chosen for this study are based on field observations the novel element of the vent geometry investigated herein is an inclined exit plane 5 15 30 slant angle in combination with cylindrical and diverging inner geometries in a vertical setup these modifications yield both laterally variable spreading angles as well as a diversion of the jets where inner geometry cylindrical diverging controls the direction of the inclination both the spreading angle and the inclination of the jet are highly sensitive to reservoir conduit pressure and slant angle increasing starting reservoir pressure and slant angle yield 1 a maximum spreading angle up to 62 and 2 a maximum jet inclination for cylindrical vents up to 13 our experiments thus constrain geometric contributions to the mechanisms controlling eruption jet dynamics with implications for the generation of asymmetrical distributions of proximal hazards around volcanic vents

transient two dimensional dynamics in the upper conduit of a rhyolitic eruption a comparison of closure models for the granular stress to elucidate the role of particle collisions in redistributing momentum after fragmentation a numerical study was performed comparing the behavior of an inviscid or collision less granular material with a granular material whose viscosity and pressure were modeled using kinetic theory the granular viscosity calculation is sensitive to particle size and three particle sizes were considered 0 0002 m 0 002 m and 0 02 m a critical volume fraction of gas 0 75 identifies the onset of fragmentation dividing the region of rhyolitic magma with dispersed bubbles from the region of turbulent gas with dispersed particles the transient simulations can be divided into two dynamic regimes an initial shock followed by a transition to steady state during the initial shock phase treatment of the granular pressure and viscosity led to greater particle velocities relative to the inviscid calculation due to the development of higher gas pressure at fragmentation however as steady state is approached the viscosity slows the particle phase relative to the inviscid counterpart for particles greater than a millimeter the modeled sub millimeter particle velocity was insensitive to the treatment of the granular pressure and viscosity centimeter scale particles have a much higher granular viscosity up to 10 1 pa s and the kinetic theory calculation is thus relevant in these conditions after reaching steady state the differential velocity between gas and particles at the conduit exit correlates with particle size for both the inviscid and granular viscosity calculations negligible differential velocity develops for sub millimeter particles but centimeter scale particles exit the conduit with 5 differential velocity between phases

first data on benthic and fish communities from the mid atlantic ridge 16 40 17 14 n abstract the first ecological survey in the tropical part of the northern mid atlantic ridge mar was conducted between 17 14 n and 16 40 n in february march 2015 during the 37th cruise of the rv professor logachev significant effort of the survey was aimed at studies of benthic non vent soft sediment fauna at depths from 2270 m to 3900 m samples of this fauna at seven stations revealed 780 specimens and at least 136 species the most common species was the hermit crab parapagurus cf nudus also common were the ophiuroids ophiotypa simplex and ophiomusium cf lymani most benthic organisms were