linking microearthquakes to fracture permeability change the role of surface roughness despite its importance the relation between microearthquakes meqs and changes in hydraulic properties during hydraulic stimulation of a fractured reservoir has rarely been explored and it is still not well understood to investigate this relation we first formulate a plausible scale dependence where fracture length and shear displacement are variables for channeling flow through heterogeneous aperture distributions for joints and faults by combining this formulation with the concept of the seismic moment we derive quantitative relations between the moment magnitude mw of meqs and the fracture permeability change in the directions orthogonal to kfault kjoint and parallel to kfault kjoint the shear displacement in the form kfault kjoint 116 4 100 46mw and kfault kjoint 13 1 100 46mw despite the simplicity of the derivation these relations have the potential to explain the results of field experiments on hydraulic stimulation such as the enhanced geothermal systems at soultz sous foret and basel

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

terrestrial climate evolution in the southwest pacific over the past 30 million years abstract a reconstruction of terrestrial temperature and precipitation for the new zealand landmass over the past 30 million years is produced using pollen data from 2000 samples lodged in the new zealand fossil record electronic database and modern climate data of nearest living relatives the reconstruction reveals a warming trend through the late oligocene to early miocene peak warmth in the middle miocene and stepwise cooling through the late neogene whereas the regional signal in our reconstruction includes a 5 10 northward tectonic drift as well as an increase in high altitude biomes due to late neogene and pliocene uplift of the southern alps the pattern mimics inferred changes in global ice extent which suggests that global drivers played a major role in shaping local vegetation importantly seasonal temperature estimates indicate low seasonality during the middle miocene and that subsequent neogene cooling was largely due to cooler winters we suggest that this may reflect increased subantarctic influence on new zealand vegetation as the climate cooled

a note on induced stress changes in hydrocarbon and geothermal reservoirs abstract earthquakes have been induced by oil and gas production where pore pressures have decreased in some cases by several tens of mpa it has previously been suggested that such earthquakes are caused by poroelastic stressing of crust surrounding the reservoir induced earthquakes are also common in geothermal fields such as the geysers where strong correlations between both steam production and condensate injection and earthquake activity have been observed over the last several decades stress measurements within hydrocarbon reservoirs show that the least horizontal stress decreases with declining reservoir pressure as predicted by poroelasticity for circular disk shaped reservoirs isothermal reduction in pore pressure induces a relative horizontal tension within the reservoir production induced stressing may promote frictional sliding on pre existing faults within the reservoir itself normal faulting is promoted if the regional stress is extensional and the biot coefficient is sufficiently large 0 85 for reasonable coefficients of friction on the other hand dilatant fracturing and normal faulting are always promoted in extensional environments near the edge of the reservoir or in regions of high pore pressure gradient it is suggested that such fracturing could enhance fracture permeability in tight rocks adjacent to portions of the reservoir that experience large reductions in pore pressure due to production in regional compressional environments production modestly favors reverse faulting above and below the reservoir the ratio of thermal to poroelastic stress can be quite large in geothermal reservoirs such as the geysers reservoir wide energy balance considerations suggest that the average temperature has declined at the geysers by 6 c during the past 20 years reservoir average stress changes are thus on the order of 2 mpa and are certainly much larger near injection wells and steam producing fractures

seismicity triggered by fluid injection induced aseismic slip anthropogenic fluid injections are known to induce earthquakes the mechanisms involved are poorly understood and our ability to assess the seismic hazard associated with geothermal energy or unconventional hydrocarbon production remains limited we directly measure fault slip and seismicity induced by fluid injection into a natural fault we observe highly dilatant and slow 4 micrometers per second m s aseismic slip associated with a 20 fold increase of permeability which transitions to faster slip 10 m s associated with reduced dilatancy and micro earthquakes most aseismic slip occurs within the fluid pressurized zone and obeys a rate strengthening friction law 0 67 0 045ln v v with v 0 1 m s fluid injection primarily triggers aseismic slip in this experiment with micro earthquakes being an indirect effect mediated by aseismic creep

vesiculation in magmas from stromboli and implications for normal strombolian activity and paroxysmal explosions in basaltic systems 1 we performed a series of x ray tomographic experiments and lattice boltzmann permeability simulations on pyroclastic products from explosive activity at stromboli between december 2004 and may 2006 we reconstructed the 3 d textures of vesicles to investigate the relationship between the nature of vesiculation in the erupted products and the dynamics of gas transport in the shallow conduit in order to derive implications for the eruptive behavior of basaltic volcanoes scoriae from normal strombolian explosions display remarkably consistent vesicle volume distributions fit by power laws with an exponent of 1 0 2 we ascribe the origin of such distributions to the combined effect of coalescence and continuous nucleation events in the steady state shallow magma system that supplies normal strombolian activity volume distributions and textures of vesicles in pumice clasts from the 5 april 2003 and 15 march 2007 paroxysmal activity are markedly different from those in the scoriae besides a power law function with a higher exponent portions of these distributions can be also fit by an exponential function suggesting the attempt of the system to reach near equilibrium conditions the investigated pumice clasts also lack the large connecting vesicles responsible for the development of degassing pathways in the stromboli magma that erupts the scoriae this testifies to a decreased degassing efficiency of the magma associated with paroxysmal explosions and potential overpressure buildup at depth by comparison with degassing experiments on basaltic melts we derive a time constraint on the order of minutes to hours for the incubation of paroxysms at stromboli

late miocene turnover of molluscan faunas new zealand taxonomic and ecological reassessment of diversity changes at multiple spatial and temporal scales abstract previous estimates of molluscan biodiversity during the neogene in new zealand have revealed a pattern of significant diversity decline during the latest miocene this study uses an occurrence based dataset derived from published literature to examine this pattern in further detail with both traditional synoptic measures and subsequent sampling standardization synoptic analyses of regional scale data reveal diversity trajectories similar to those previously established and rarefaction techniques demonstrate that the inferred pattern of late miocene diversity decline and early pliocene rebound is only somewhat biased by variations in sampling intensity the pattern is also affected by temporal variations in the preservation of shelf paleoenvironments with representation of highly diverse shallow water facies varying considerably between biostratigraphic stages the sampling and corresponding synoptic genus richness of biogeographic areas within the new zealand region is also uneven within a single sedimentary basin sampled at high temporal resolution wanganui basin new data suggest that late miocene faunas were as diverse as those of the early pliocene contrasting with the pattern of diversity decrease and subsequent increase observed at the regional spatial scale in prior studies however an ecological analysis of the new data demonstrates that turnover and restructuring of benthic communities did take place at the end of the late miocene these findings suggest that spatial scale and temporal resolution are important considerations in determining the magnitude of diversity and ecological change observed in paleontologic studies contemporaneous biodiversity may not be similarly expressed at varying spatial or temporal scales in the fossil record rather regional patterns of diversity change are governed by a complex interplay of not only large scale environmental factors e g temperature control but also independent basin scale processes e g basin subsidence and local sampling intensity

what makes hydromagmatic eruptions violent some insights from the keanakāko i ash kilauea volcano hawai i abstract volcanic eruptions at the summit of kilauea volcano hawai i are of two dramatically contrasting types 1 benign lava flows and lava fountains and 2 violent mostly prehistoric eruptions that dispersed tephra over hundreds of square kilometers the violence of the latter eruptions has been attributed to mixing of water and magma within a wet summit caldera however magma injection into water at other volcanoes does not consistently produce widespread tephras to identify other factors that may have contributed to the violence of these eruptions we sampled tephra from the keanak ko i ash the most recent large hydromagmatic deposit and measured vesicularity bubble number density and dissolved volatile content of juvenile matrix glass to constrain magma ascent rate and degree of degassing at the time of quenching bubble number densities 9 10 4 1 10 7 cm 3 of tephra fragments exceed those of most historically erupted kilauean tephras 3 10 3 1 8 10 5 cm 3 and suggest exceptionally high magma effusion rates dissolved sulfur average 330 ppm and water 0 15 0 45 wt concentrations exceed equilibrium saturation values at 1 atm pressure 100 150 ppm and 0 09 respectively suggesting that clasts quenched before equilibrating to atmospheric pressure we interpret these results to suggest rapid magma injection into a wet crater perhaps similar to continuous uprush jets at surtsey estimates of reynolds number suggest that the erupting magma was turbulent and would have mixed with surrounding water in vortices ranging downward in size to centimeters such fine scale mixing would have ensured rapid heat exchange and extensive magma fragmentation maximizing the violence of these eruptions

new evidence for degassing processes during explosive eruptions measurements of pore size distribution in five samples of pumice formed during explosive eruptions of plinian type show three distinct sizes of vesicle the characteristics of the three pore size populations are similar in the samples although they were collected from plinian deposits of five different volcanoes we interpret the pore size populations as representing the degassing of silicic magma on three very different time scales the coarse population 60 m represents slow vesiculation within the magma chamber over periods of weeks months or years at small levels of gas supersaturation the medium sized population 50 5 m represents rapid vesiculation of magma on ascent to the surface during the plinian eruption over periods of minutes to hours the fine population 5 0 5 m represents bubbles formed during explosive disruption of magma and rapid ejection into the atmosphere involving short time scales a few seconds but large decompression rates

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization crystal size distributions csds measured in metamorphic rocks yield quantitative information about crystal nucleation and growth rates growth times and the degree of overstepping t of reactions during metamorphism csds are described through use of a population density function n dn dl where n is the cumulative number of crystals per unit volume and l is a linear crystal size plots of ln n vs l for olivine pyroxene and magnetite in high temperature 1000 c basalt hornfelses from the isle of skye define linear arrays indicating continuous nucleation and growth of crystals during metamorphism using the slope and intercept of these linear plots in conjunction with growth rate estimates we infer minimum mineral growth times of less than 100 years at t 10 c and nucleation rates between 10 4 and 10 1 cm3 s garnet and magnetite in regionally metamorphosed pelitic schists from south central maine have csds which are bell shaped we interpret this form to be the result of two processes 1 initial continuous nucleation and growth of crystals and 2 later loss of small crystals due to annealing the large crystals in regional metamorphic rocks retain the original size frequency distribution and may be used to obtain quantitative information on the original conditions of crystal nucleation and growth the extent of annealing increases with increasing metamorphic grade and could be used to estimate the duration of annealing conditions if the value of a rate constant were known finally the different forms of crystal size distributions directly reflect differences in the thermal histories of regional vs contact metamorphosed rocks because contact metamorphism involves high temperatures for short durations resulting csds are linear and unaffected by annealing similar to those produced by crystallization from a melt because regional metamorphism involves prolonged cooling from high temperatures primary linear csds are later modified by annealing to bell shapes

earthquake nucleation on rough faults earthquake nucleation is currently explained using rate and state stability analysis which successfully models the behavior of laboratory simulated faults with constant thickness gouge layers however roughness is widely observed on natural faults and its influence on earthquake nucleation is little explored here we conduct frictional sliding experiments with different roughness on granite samples at upper crustal conditions 30 200 mpa we observe a wide range of behaviors from stable sliding to stick slip depending on the combination of roughness parameters and normal stress stick slip is repeatedly observed in velocity strengthening regimes and increases in normal stress stabilize slip these features are not fully predicted by current stability analysis we derive a new instability criterion that matches our observations based on fracture energy considerations and the size of weak patches created by fault roughness

a comprehensive study of pumice formation and dispersal the cretaio tephra of ischia italy the cretaio tephra is a small volume 0 02 km3 pumice deposit on the island of ischia in italy it was erupted during historical time and is associated with a tuff ring dome complex extruded along a n s trending normal fault system bordering the east side of the mt epomeo resurgent block 14c ages of the deposit average 1860 a b p which is in agreement with the potsherds found in paleosols underlying and overlying the deposit the eruption sequence consists of 7 members most of these members are pumice fall deposits one is an ash and pumice fallout and another is a surge bed the tephra have a trachytic phonolitic composition all chemical characteristics including major and trace elements and sr isotope composition are homogeneous throughout the sequence the vesicularity of pumice clasts does not show any systematic change the erupted magma had the same amount of volatiles the same flux and vesicle growth behavior throughout the eruption sequence grain size analyses of 90 tephra samples representative of all the members at variable distance from the supposed vent have been processed using the sequential fragmentation transport theory in order to define the effects of eruptive fragmentation and subsequent transport on the particle sizes distribution four significant subpopulations have been identified and related to transport mechanisms

bubble coalescence in basalt flows comparison of a numerical model with natural examples gas accumulation in magma may be aided by coalescence of bubbles because large coalesced bubbles rise faster than small bubbles the observed size distribution of gas bubbles vesicles in lava flows supports the concept of post eruptive coalescence a numerical model predicts the effects of rise and coalescence consistent with observed features the model uses given values for flow thickness viscosity volume percentage of gas bubbles and an initial size distribution of bubbles together with a gravitational collection kernel to numerically integrate the stochastic collection equation and thereby compute a new size spectrum of bubbles after each time increment of conductive cooling of the flow bubbles rise and coalesce within a fluid interior sandwiched between fronts of solidification that advance inward with time from top and bottom bubbles that are overtaken by the solidification fronts cease to migrate the model predicts the formation of upper and lower vesicle rich zones separated by a vesicle poor interior the upper zone is broader more vesicular and has larger bubbles than the lower zone basaltic lava flows in northern california exhibit the predicted zonation of vesicularity and size distribution of vesicles as determined by an impregnation technique in particular the size distribution at the tops and bottoms of flows is essentially the same as the initial distribution reflecting the rapid initial solidification at the bases and tops of the flows many large vesicles are present in the upper vesicular zones consistent with expected formation as a result of bubble coalescence during solidification of the lava flows both the rocks and model show a bimodal or trimodal size distribution for the upper vesicular zone this polymodality is explained by preferential coalescence of larger bubbles with subequal sizes vesicularity and vesicle size distribution are sensitive to atmospheric pressure because bubbles expand as they decompress during rise through the flow the ratio of vesicularity in the upper to that in the lower part of a flow therefore depends not only on bubble rise and coalescence but also on flow thickness and atmospheric pressure application of simple theory to the natural basalts suggests solidification of the basalts at 1 0 0 2 atm consistent with the present atmospheric pressure paleobathymetry and paleoaltimetry are possible in view of the sensitivity of vesicle size distributions to atmospheric pressure thus vesicular lava flows can be used to crudely estimate ancient elevations and or sea level air pressure

the 1983 86 pu u o o eruption of kilauea volcano hawaii a study of dike geometry and eruption mechanisms for a long lived eruption abstract the 1983 1986 pu u o o eruption of kilauea volcano had a very distinctive episodic character which later changed to steady state activity in this paper we present a physical model of episodic activity which explains the process largely in terms of non uniform magma cooling and yield strength development resulting from variable dike width the model is applied to the pu u o o data set and shows that to explain the pressure variations within the summit magma reservoir and the patterns of summit deflation a yield strength of 80 to 200 pa needs to be developed this corresponds to a temperature decrease in the magma of 10 15 c consistent with temperature variations measured in the erupted lavas the model stimulates the variation in volume flux as a function of time through the eruption and produces results which agree well with observed patterns of magma movement gradual evolution of the dike system through the eruptive series is explained by progressive widening of its narrowest sections the loss of the episodic character and the transition to continuous activity is explained by a slight change in the thermal efficiency of the system the change in pattern of gas release from lava fountaining to gas pistoning and strombolian activity which accompanied the change from episodic activity to steady state eruption results from the reduction in magma flow rate at shallow levels in the dike system however we demonstrate that continuous eruptions do not inherently lack lava fountains higher magma supply rates and thus higher flow velocities would allow fountaining to occur during continuous eruption we demonstrate that episodic eruptions result from a fine balance between the effects of cooling of magma within the dike and the generation of pressure within the magma reservoir and thus that thermally episodic eruptions reflect a middle ground between short lived fissure eruptions in which magma cooling dominates and continuous eruption in which cooling is minimised the initial few months of an eruption being critical to establishing the thermal viability of the dike system

explosive volcanic eruptions ix the transition between hawaiian style lava fountaining and strombolian explosive activity the commonest eruption styles of basaltic volcanoes involve hawaiian lava fountaining or intermittent strombolian explosions we investigate the ways in which magma rise speed at depth magma volatile content and magma viscosity control which of these eruption styles takes place we develop a model of the degree of coalescence between gas bubbles in the magma which allows us to simulate the transition between the two extreme styles of activity we find that magma rise speed is the most important factor causing the transition with gas content and viscosity also influencing the rise speed at which the transition occurs counter to intuitive expectations a decrease in gas content does not cause a transition from hawaiian to strombolian activity but instead causes a transition to passive effusion of vesicular lava rather a change from hawaiian to strombolian style requires a significant reduction in magma rise speed

emplacement of the youngest flood lava on mars a short turbulent story abstract recently acquired data from the high resolution imaging science experiment hirise context ctx imager and compact reconnaissance imaging spectrometer for mars crism onboard the mars reconnaissance orbiter mro spacecraft were used to investigate the emplacement of the youngest flood lava flow on mars careful mapping finds that the athabasca valles flood lava is the product of a single eruption and it covers 250 000 km 2 of western elysium planitia with an estimated 5000 7500 km 3 of mafic or ultramafic lava calculations utilizing topographic data enhanced with mro observations to refine the dimensions of the channel system show that this flood lava was emplaced turbulently over a period of only a few to several weeks this is the first well documented example of a turbulently emplaced flood lava anywhere in the solar system however mro data suggest that this same process may have operated in a number of martian channel systems the magnitude and dynamics of these lava floods are similar to the aqueous floods that are generally believed to have eroded the channels raising the intriguing possibility that mechanical erosion by lava could have played a role in their incision

molluscan generic diversity of new zealand neogene stages extinction and biostratigraphic events abstract the molluscan generic diversity histogram of new zealand neogene stages almost parallels the trend of published new zealand paleotemperature curves the major exception is very high diversity during the relatively cool pliocene and pleistocene stages attributed to the good preservation at this time of near shore mollusc rich facies diversity was lowest during kapitean late miocene time and probably particularly during late kapitean messinian time 22 9 of molluscan genera became extinct at the end of the preceding tongaporutuan stage three major events can be recognised in the neogene molluscan fauna 1 a thermal maximum during late early and early middle miocene coeval around much of the pacific 2 the terminal miocene event when the most marked neogene extinction occurred and 3 the arrival of a cold water subantarctic fauna in central north island 2 4 m y ago coeval with the onset of major northern hemisphere glaciation

latest miocene benthic δ 18 o changes global ice volume sea level and the messinian salinity crisis oxygen isotope evidence indicates high but variable 18o values in benthic foraminiferal calcite during the latest miocene and earliest pliocene these high values may represent increases in global ice volume and associated sea level fall the 18o record resembles glacial interglacial cycles but with only one third the amplitude of the late pleistocene signal this variability may reflect instability in the antarctic ice sheet and palaeomagnetic correlation points to an isotopic event coinciding with the isolation and desiccation of the mediterranean basin during the latest messinian

contrasting mechanisms of magma fragmentation during coeval magmatic and hydromagmatic activity the hverfjall fires fissure eruption iceland growing evidence for significant magmatic vesiculation prior to magma water interaction mwi has brought into question the use of diagnostic features such as low vesicularities and blocky morphologies to identify hydromagmatic pyroclasts we address this question by quantifying co variations in particle size shape and texture in both magmatic and hydromagmatic deposits from the hverfjall fires fissure eruption iceland overlapping vesicularity and bubble number density distributions measured in rapidly quenched magmatic and hydromagmatic pyroclasts indicate a shared initial history of bubble nucleation and growth with substantial vesiculation prior to mwi hydromagmatic fragmentation occurred principally by brittle mechanisms where the length scale and geometry of fracturing was controlled by the bubble population this suggests that the elevated fragmentation efficiency of hydromagmatic deposits is driven at least in part by brittle disintegration of vesicular pyroclasts due to high thermal stress generated during rapid cooling in this way the shape and size distributions of hydromagmatic pyroclasts both critical input parameters for ash dispersion models are strongly influenced by the dynamics of vesiculation prior to mwi this result underlines the need to analyse multiple grain size fractions to characterise the balance between magmatic and hydromagmatic processes during the hverfjall fires eruption the external water supply was sufficient to maintain mwi throughout the eruption with no evidence for progressive exhaustion of a water reservoir we suggest that both the longevity and the spatial distribution of mwi were determined by the pre existing regional hydrology and represent continuous interaction between a propagating dike and a strong groundwater flow system hosted within permeable basalt lavas

permeability evolution of slowly slipping faults in shale reservoirs slow slip on preexisting faults during hydraulic fracturing is a process that significantly influences shale gas production in extremely low permeability shale unconventional reservoirs we experimentally examined the impacts of mineralogy surface roughness and effective stress on permeability evolution of slowly slipping faults in eagle ford shale samples our results show that fault permeability decreases with slip at higher effective stress but increases with slip at lower effective stress the permeabilities of saw cut faults fully recover after cycling effective stress from 2 5 to 17 5 to 2 5 mpa and increase with slip at constant effective stress due to asperity damage and dilation associated with slip however the permeabilities of natural faults only partially recover after cycling effective stress returns to 2 5 mpa and decrease with slip due to produced gouge blocking fluid flow pathways our results suggest that slowly slipping faults have the potential to enhance reservoir stimulation in extremely low permeability reservoirs

episode 49 of the pu u o o kupaianaha eruption of kilauea volcano breakdown of a steady state eruptive era the pu u o o kupaianaha eruption 1983 present is the longest lived rift eruption of either kilauea or neighboring mauna loa in recorded history the initial fissure opening in january 1983 was followed by three years of episodic fire fountaining at the pu u o o vent on kilauea s east rift zone 19km from the summit episodes 4 47 these spectacular events gave way in july 1986 to five and a half years of nearcontinuous low level effusion from the kupaianaha vent 3km to the cast episode 48 a 49th episode began in november 1991 with the opening of a new fissure between pu u o o and kupaianaha this three week long outburst heralded an era of more erratic eruptive behavior characterized by the shut down of kupaianaha in february 1992 and subsequent intermittent eruption from vents on the west flank of pu u o o episodes 50 and 51 the events occurring over this period are due to progressive shrinkage of the rift zone reservoir beneath the eruption site and had limited impact on eruption temperatures and lava composition

mega earthquakes rupture flat megathrusts the 2004 sumatra andaman and 2011 tohoku oki earthquakes highlighted gaps in our understanding of mega earthquake rupture processes and the factors controlling their global distribution a fast convergence rate and young buoyant lithosphere are not required to produce mega earthquakes we calculated the curvature along the major subduction zones of the world showing that mega earthquakes preferentially rupture flat low curvature interfaces a simplified analytic model demonstrates that heterogeneity in shear strength increases with curvature shear strength on flat megathrusts is more homogeneous and hence more likely to be exceeded simultaneously over large areas than on highly curved faults

vesiculation of basaltic magma during eruption vesicle size distributions in vent lavas from the pu9u9o9o kupaianaha eruption of kilauea volcano are used to estimate nucleation and growth rates of h 2 o rich gas bubbles in basaltic magma nearing the earth9s surface 120 m depth by using well constrained estimates for the depth of volatile exsolution and magma ascent rate nucleation rates of 35 9 events cm 3 s 1 and growth rates of 3 2 x 10 4 cm s are determined directly from size distribution data the results are consistent with diffusion controlled growth as predicted by a parabolic growth law this empirical approach is not subject to the limitations inherent in classical nucleation and growth theory and provides the first direct measurement of vesiculation kinetics in natural settings in addition perturbations in the measured size distributions are used to examine bubble escape accumulation and coalescence prior to the eruption of magma

shallowly driven fluctuations in lava lake outgassing gas pistoning kīlauea volcano abstract lava lakes provide ideal venues for directly observing and understanding the nature of outgassing in basaltic magmatic systems k lauea volcano s summit lava lake has persisted for several years during which seismic and infrasonic tremor amplitudes have exhibited episodic behavior associated with a rise and fall of the lava surface gas pistoning since 2010 the outgassing regime of the lake has been tied to the presence or absence of gas pistoning during normal behavior no gas pistoning the lake is in a spattering regime consisting of higher tremor amplitudes and gas emissions in comparison gas piston events are associated with an abrupt rise in lava level up to 20 m during which the lake enters a non spattering regime with greatly decreased tremor and gas emissions we study this episodic behavior using long term multidisciplinary monitoring of the lake including seismicity infrasound gas emission and geochemistry and time lapse camera observations the non spattering regime i e rise phase of a gas piston cycle reflects gas bubbles accumulating near the top of the lake perhaps as a shallow foam while spattering regimes represent more efficient decoupling of gas from the lake we speculate that the gas pistoning might be controlled by time varying porosity and or permeability in the upper portions of the lava lake which may modulate foam formation and collapse competing models for gas pistoning such as deeply sourced gas slugs or dynamic pressure balances are not consistent with our observations unlike other lava lakes which have cyclic behavior that is thought to be controlled by deeply sourced processes external to the lake itself we show an example of lava lake fluctuations driven by cycles of activity at shallow depth and close to the lake s surface these observations highlight the complex and unsteady nature of outgassing from basaltic magmatic systems

constraints from fault roughness on the scale dependent strength of rocks principal slip surfaces in faults have measurable roughness generated during slip the roughness both records previous events and poses the boundary conditions for future rupture digital high precision roughness data are now available at the field scale tens of centimeters to tens of meters for at least 22 faults and at the laboratory scale millimeters to tens of centimeters for a subset of these we quantify the slip surface roughness by measuring the aspect ratio which is the average asperity height divided by the profile length higher aspect ratios indicate rougher surfaces from the field studies two major trends have emerged 1 fault surface roughness lies in a restricted range with aspect ratios in the slip parallel direction of 0 07 0 5 for profiles of 1 m length and 2 fault surfaces are rougher at small scales than large ones these features can both be interpreted as fingerprints of scale dependent strength which sets a limit to the aspect ratio of the surface the measurements imply that shear strength scales with the observation scale l as l 0 4 the new understanding of the physical controls on roughness allows generalization of the extant measurements of a wide array of faults

formation of propagation pattern in two phase flow systems with application to volcanic eruptions summary the hydrodynamic behaviour of a two phase system with different densities and viscosities is investigated assuming that both phases are continuous phases and incompressible and that no phase change occurs mass and momentum conservation equations describe the relative motion of the two phases under the gravitational force when the inertia term is not negligible using the derived equations the stability of a spatially constant structure along gravity is examined in the one dimensional case for an infinite system without boundaries where the basic state is taken as constant velocity and volume fractions two special cases are considered the first is a gas liquid system where the density of one of the phases is neglected the second is a deformable solid liquid system where the densities of the two phases are taken to be the same except for the calculation of the buoyancy force the linear stability analysis shows that a small perturbation always generates a propagating wave which grows unstably with a characteristic wavelength since the spatially uniform structure of a two phase system is always unstable the growth pattern should be observed in nature if the growth rate and spatial scale of the system are suitable the dependence of the wavelength and growth rate on parameters is divided intc two regimes in one regime the wavelength which equals the compaction length and growth rate depend on the typical pore size in the other regime on the other hand they do not depend on the typical pore size but only on the kinematic viscosity of the liquid phase and the volume fraction given the frictional law which regime a real system chooses depends on a nondimensional parameter the first case gas liquid system is applied to magma effusion in an eruption style volcano the system consisting of a silicate liquid phase and a gas phase can have a wavelength from metres to tens of metres and a growth rate from the order of less than a second to 1 week depending on viscosities typical pore size and volume fraction as a result the rhythm and discreteness of magma effusion observed at volcanic eruptions may be explained by the mechanism presented here the theory provides a relation between the observed period of the magma effusion rate the mixture exit velocity of gas plus magma and the volume fraction of magma given the frictional law using the relation the mixture exit velocity is estimated from the observed period for the 1986 izu oshima eruption the applicability to partially molten systems in the mantle and the core and basic assumptions are discussed

the structure of basaltic scoria and reticulite and inferences for vesiculation foam formation and fragmentation in lava fountains in this investigation pyroclast structures are used to constrain degassing in basaltic lava fountains vesicle size shape number density interconnectedness and packing character are quantified and related to 1 the kinetics of bubble nucleation and growth 2 the structural evolution of magmatic foams and 3 the influence of vesiculation rate on magma fragmentation measurements made on a diverse suite of pyroclasts from kilauea volcano indicate that basaltic foams evolve through an initially disordered closed celled spherical state to a well ordered open celled polyhedral state as the vesicularity rises from 75 to 98 the structural changes occur rapidly 10 s in the conduit and fountain in response to an intense vesiculation burst vesicle size distribution systematics indicate bubble nucleation rates 2 104 events cm 3s 1 that are approximately three orders of magnitude greater than those found for effusive eruptive activity bubble growth rates 9 10 4 cm s exceed effusive estimates by a factor of 3 the observed runaway rate of bubble production indicates strong supersaturations at the onset of nucleation we speculate that the rise speed of the magma as it reaches the level where significant volatile exsolution begins determines the intensity of the vesiculation burst and hence the vigor of the eruption rapid expansion and acceleration of the magma under these conditions may provide the impetus for fragmentation

dynamics of degassing at kilauea volcano hawaii at kilauea volcano hawaii the recent long lived eruptions of mauna ulu and pu u o o have occurred in two major stages defining a characteristic eruptive pattern the first stage consists of cyclic changes of activity between episodes of fire fountaining and periods of quiescence or effusion of vesicular lava the second stage consists only of continuous effusion of lava we suggest that these features reflect the dynamics of magma degassing in a chamber which empties into a narrow conduit in the volcano chamber gas bubbles rise through magma and accumulate at the roof in a foam layer the foam flows toward the conduit and its shape is determined by a dynamic balance between the input of bubbles from below and the output into the conduit the foam thickness is proportional to lq e2 l g 1 4 where l and l are the viscosity and density of magma e is the gas volume fraction in the foam g is the acceleration of gravity and q is the gas flux the bubbles in the foam deform under the action of buoyancy and the maximum permissible foam thickness is hc 2 e lgr where is the coefficient of surface tension and r is the original bubble radius if this critical thickness is reached the foam collapses into a large gas pocket which erupts into the conduit foam accumulation then resumes and a new cycle begins the attainment of the foam collapse threshold requires a gas flux in excess of a critical value which depends on viscosity surface tension and bubble size hence two different eruption regimes are predicted 1 alternating regimes of foam buildup and collapse leading to the periodic eruption of large gas volumes and 2 steady foam flow at the roof leading to continuous bubbly flow in the conduit the essential result is that the continuous process of degassing can lead to discontinuous eruptive behavior data on eruption rates and repose times between fountaining phases from the 1969 mauna uiu and the 1983 1986 pu u o o eruptions yield constraints on three key variables the area of the chamber roof must be a few tens of square kilometers with a minimum value of about 8 km2 magma reservoirs of similar dimensions are imaged by seismic attenuation tomography below the east rift zone close to the roof the gas volume fraction is a few percent and the gas bubbles have diameters lying between 0 1 and 0 6 mm these estimates are close to the predictions of models for bubble nucleation and growth in basaltic melts as well as to the observations on deep submarine basalts the transition between cyclic and continuous activity occurs when the mass flux of gas becomes lower than a critical value of the order of 103 kg s in this model changes of eruptive regime reflect changes in the amount and size of bubbles which reach the chamber roof

non newtonian flow of bubbly magma in volcanic conduits the dynamics of magma ascent along volcanic conduits toward the earth s surface affects eruptive styles and contributes to volcanic hazard the rheology of ascending magmatic mixtures is known to play a major role on mass flow rate as well as on pressure and exit velocity at the vent even determining effusive versus explosive eruptive behavior in this work we explore the effects of bubble induced non newtonian rheology on the dynamics of magma flow in volcanic conduits we develop a quasi 2 d model of magma ascent that incorporates a rheological constitutive equation describing the strain dependent effect of gas bubbles on the viscosity of the multiphase magma non newtonian magma flow is investigated through a parametric study where the viscosity of the melt and the water content are varied over natural ranges our results show that non newtonian rheology leads to greater exit velocity mass flow and density the pressure distribution along the conduit remains very similar to the newtonian case deviating only at the conduit exit plug like velocity profiles develop approaching the conduit exit when mixture velocity is high and are favored by smaller liquid viscosity since the mass flow rate the density and the velocity of the mixture exiting from the conduit are fundamental for quantifying and assessing the transport and emplacement dynamics neglecting that the non newtonian effect of bubble bearing magmas may result in misinterpretation of the deposit and consequently eruptive behavior

scaling of rock friction constitutive parameters the effects of surface roughness and cumulative offset on friction of gabbro we describe experiments in which large 14 40 cm nominal contact area blocks of gabbro were sheared in a direct shear apparatus at room temperature 5 mpa normal stress and slip velocities from 0 1 to 10 m s the apparatus was servocontrolled using a displacement feedback measurement made directly between the gabbro blocks two surface roughnesses were studied rough produced by sandblasting and smooth produced by lapping with 60 grit and accumulated displacements reached 60 mm measurements of surface topography were used to characterize roughness and asperity dimensions step changes in loading velocity were used to interrogate friction constitutive properties both rough and smooth surfaces showed appreciable displacement hardening the coefficient of friction for rough surfaces was about 0 45 for initial slip and 0 7 after sliding 50 mm smooth surfaces exhibited higher and a greater tendency for unstable slip the velocity dependence of frictiona b and the characteristic friction distanced c show systematic variations with accumulated displacement for rough surfacesa b started out positive and became negative after about 50 mm displacement andd c increased from 1 to 4 m over the same interval for smooth surfaces a b began negative and decreased slightly with displacement andd c was about 2 m independent of displacement for displacements 30 mm rough surfaces exhibit a second state variable with characteristic distance about 20 m the decrease ina b with displacement is associated with disappearance of the second state variable our data indicate thatd c is controlled by surface roughness in a complex way including but not limited to the effect of roughness on contact junction dimensions for bare rock surfaces the data show that simple descriptions of roughness such as rms and peak to trough are not sufficient to inferd c our observations are consistent with a model in whichd c scales with gouge thickness

measurement of bubble size distributions in vesiculated rocks with implications for quantitative estimation of eruption processes abstract this paper outlines methods for determining a bubble size distribution bsd and the moments of the bsd function in vesiculated clasts produced by volcanic eruptions it reports the results of applications of the methods to 11 natural samples and discusses the implications for quantitative estimates of eruption processes the analysis is based on a quantitative morphological stereological method for 2 dimensional imaging of cross sections of samples one method determines with some assumptions the complete shape of the bsd function from the chord lengths cut by bubbles the other determines the 1st 2nd and 3rd moments of distribution functions by measurement of the number of bubbles per unit area the surface area per unit volume and the volume fraction of bubbles comparison of procedures and results of these two distinct methods shows that the latter yields rather more reliable results than the former though the results coincide in absolute and relative magnitudes results of the analysis for vesiculated rocks from eleven subplinian to plinian eruptions show some interesting systematic correlations both between moments of the bsd and between a moment and the eruption column height or the sio2 content of magma these correlations are successfully interpreted in terms of the nucleation and growth processes of bubbles in ascending magmas this suggests that bubble coalescence does not predominate in sub plinian to plinian explosive eruptions the moment moment correlations put constraints on the style of the nucleation and growth process of bubbles the scaling argument suggests that a single nucleation event and subsequent growth with any kind of bubble interaction under continuous depressurization which leads to an intermediate growth law between the diffusional growth r m t 2 3 at a constant depressurization rate and the ostwald ripening r m t 1 3 under a constant pressure where rm and t are the mean radius of bubble and the effective time of diffusion respectively occurred in the eruptions it is emphasized that the bsd in vesiculated rocks from terrestrial volcanoes can be used to estimate quantitatively eruption processes such as the initial saturation pressure and magma ascent velocity in a volcanic conduit

numerical study of nucleation and growth of bubbles in viscous magmas the nucleation and growth processes of bubbles in viscous magmas with a constant decompression rate have been numerically investigated based on a formation which accounts for effects of viscosity as well as diffusivity interfacial tension and decompression rate the numerical solutions show two regimes in the nucleation and growth process a diffusion controlled regime and a viscosity controlled regime mainly depending on the decompression rate initial saturation pressure and viscosity the basic mechanism common to both regimes is that growth governs nucleation through depletion of degassing components in basaltic eruptions the vesiculation is essentially controlled by diffusion and the viscosity controlled regime is limited to very high decompression rate and very small water content when andesitic magma saturated by water at 10 mpa is decompressed through the propagation of rarefraction wave induced by a landslide as took place in the mount st helens 1980 eruption the vesiculation is controlled by the viscosity up to 100 m depth on the other hand in a rhyolitic magma for the same situation vesiculation is controlled by the viscosity over the whole depth of the magma column in the viscosity controlled regime the vesicularity may be 90 or less as seen in silicic pumice whereas in the diffusion controlledmore regime the vesicularity equals or exceeds 98 such as in reticulite in hawaiian basalt an observed variation of the number density of bubbles by several orders of magnitude in plinian eruptions and the correlation with the sio2 content can be attributed approximately to the dependence of diffusivity of viscosity on sio2 content and temperature assuming the apparent correlation between sio2 content and temperature of magma less

crystal size distribution systematics and the determination of magma storage times the 1959 eruption of kilauea volcano hawaii abstract the theory of crystal size distribution csd theory is based on a steady state population balance that monitors the flux of crystals growing into and out of specificed size categories in precipitating solutions the conservation equation describing this balance permits crystal growth and nucleation rates to be determined directly from crystal size distribution data in this investigation it is shown that csd analysis can alternatively be used to calculate the residence time of crystals in the system or in volcanologic terms the magma storage time prior to eruption if the characteristic crystal growth rate can be independently determined or estimated the crystal size data needed for storage time determinations are easily obtained from thin sections of glassy eruption samples and the mathematical calculations are relatively simple analysis of the errors inherent in this new technique predicts storage estimates accurate to within an order of magnitude

petrography and geochemistry of achnelithic tephra from las herrerias volcano calatrava volcanic field spain formation of nephelinitic achneliths and post depositional glass alteration abstract we present the results of a petrographic and geochemical study carried out on a layer of achnelithic tephra outcropping at the base of the volcanic cone of las herrerias miocene quaternary volcanic region of campo de calatrava spain the tephra with a composition of nephelinite and ash 3 of all major elements and notable increase in h 2 o content the elements liberated by this process formed smectite with an average structural formula comprised between those of beidellite and nontronite end terms na 0 01 k 0 03 ca 0 18 mg 0 22 fe 0 16 2 fe 0 48 al 1 02 3 ti 0 18 4 si 3 58 al 0 42 o 10 oh 2 the degree of palagonitization in each achnelith was likely related to the amount of water incorporated by individual clasts at the moment of their deposition in a volcanic maar lake afterwards there was no more water circulation through the achnelithic tephra which was sealed from water by overlying hydrovolcanic tuff deposits it was this isolation that made possible the preservation of glass to the present day

exposed coasts vs sheltered bays contrast between new zealand and japan in the molluscan record of temperature change in plio pleistocene cyclothems abstract cyclothems in the omma formation on the japan sea coast of central honshu each contains two ecostratigraphic datums the appearance and disappearance datums of warm water molluscs cold water molluscs occur both below in early tst and above in late hst and possibly rst warm water ones which occur in late tst and early hst in contrast no new zealand cyclothems in the main plio pleistocene basins contain both cold and warm water faunas in one cycle cyclothems in the petane group central hawke s bay and in the castlecliff section wanganui basin contain entirely eurythermal and warm water molluscs throughout cyclothems in south wairarapa have entirely eurythermal and cold water molluscs throughout the subantarctic zygochlamys delicatula fauna even in hsts of some cycles this contrast demonstrates the importance of exposure of the deposition site to strong coastal currents for the maximum faunal expression of temperature change the omma formation was deposited in an open site on the japan sea coast where currents transported larvae of a wide variety of molluscs northwards and southwards in response to temperature oscillations the main new zealand cyclothemic successions were deposited in large embayments sheltered from the influence of coastal currents the maximum faunal expression within one cyclothem of plio pleistocene temperature change can be expected in only those few deposition sites that satisfy the optimum requirements deposition of reasonably complete sequences at least tsts hsts and rsts preserved in an exposed coastal site influenced by strong currents from both the north and south on the inner shelf in the temperate regions between ca 30 and 60 north and south near the north south oriented coast of a large continent

explosive volcanic eruptions viii the role of magma recycling in controlling the behaviour of hawaiian style lava fountains explosive eruptions of mafic magmas produce lava fountains whose heights are a function of the exsolved volatile content of the magma its erupted mass flux and the geometry of the vent which may be an elongate fissure or a localized near circular conduit the geometry of the initial vent and the eruptive behaviour can be distinctly modified by lava drainback and accumulating ejecta hot pyroclasts landing near the vent may coalesce to form rootless flows some of which may drain back into the vent to be recycled into the eruption products rootless flows may be at least partially confined by pre existing topographic features or by spatter or cinder ramparts being built up by the eruption itself so that they accumulate into a lava pond over and around the vent the erupting jet of magmatic gas and pyroclasts must force its way through such a pond and will entrain some of the pond lava as it does so the energy expended in entraining and accelerating previously erupted materials will reduce the eruption velocity and the lava fountain height by an amount which can be calculated as a function of the eruption conditions and the lava pond depth or lava drainback rate the results of such calculations are presented and are used to assess the influence of this process on attempts to infer magma volatile contents from field observations of lava fountain heights

vesiculation of may 18 1980 mount st helens magma the may 18 1980 eruption of mount st helens washington produced both white and gray pumice similar in composition but varying in phenocryst microlite and vesicle content the white pumice has fewer phenocrysts no microlites and higher vesicularity and is thus less dense than the gray in addition vesicles in the white pumice are larger and more interconnected than those in the gray both white and gray have effective crystal free vesicularities 85 7 and 72 2 respectively close to the traditionally accepted fragmentation vesicularity of 75 77 given that the two pumice types were erupted concurrently for several phases of the eruption and therefore probably had similar eruption paths we suggest that differences in vesicularity and vesicle size distributions result from the presence or absence of microlites the presence of microlites in the gray pumice not only increased the magma viscosity and effective vesicularity but appears to have aided bubble nucleation and hindered bubble expansion and coalescence thus magmas with microlites may fragment at a lower bulk vesicularity than those without microlites fragmented microlite bearing clasts are also likely to expand less after fragmentation and therefore more closely preserve the bubble distribution and structure at the time of magma fragmentation

slip tendency analysis fault reactivation potential and induced seismicity in a deep geothermal reservoir abstract a slip tendency analysis is used to assess the reactivation potential of shear and dilational fractures in a deep geothermal reservoir in the northeast german basin based on the notion that slip on faults is controlled by the ratio of shear to normal stress acting on the plane of weakness in the in situ stress field the reservoir rocks composed of lower permian sandstones and volcanics were stimulated by hydraulic fracturing a surprisingly low microseismic activity was recorded with moment magnitudes mw ranging from 1 0 to 1 8 the slip tendency analysis suggests a critically stressed reservoir exists in the sandstones whereas the volcanic rocks are less stressed rock failure first occurs with an additional pore pressure of 20 mpa presumed failure planes form a conjugate set and strike nw and ne slip failure is more likely than tensional failure in the volcanic rocks because high normal stresses prevent tensional failure these results from slip tendency analysis are supported by the spatial distribution of recorded microseismicity source characteristics indicate slip rather than extension along presumed ne striking failure planes this suggests that slip tendency analysis is an appropriate method that can be used to understand reservoir behavior under modified stress conditions

ring moat dome structures rmdss in the lunar maria statistical compositional and morphological characterization and assessment of theories of origin ring moat dome structures rmdss are positive morphologic features found clustered across many mare regions on the moon of which only a few isolated examples have been previously reported our continuing survey has expanded the known locations of the rmdss from 2 600 to over 8 000 indicating that rmdss are more common geological features than previously thought this work presents a detailed geomorphological analysis of 532 rmdss identified in several mare basins the combination of detailed elemental mapping morphological and morphometric analyses spatial distribution relationships with other geologic structures and comparison with terrestrial analogs lead us to conclude that 1 rmdss represent low circular mounds with diameters of a few hundred meters average about 200 m and a mean height of 3 5 m the mounds are surrounded by moats ranging from tens to over 100 m in width and up to several meters in depth 2 there is a wide variation of titanium abundances although rmdss are more commonly found in mare regions of moderate to high titanium content 3 wt tio2 3 rmdss are found to occur on or around fractures graben and volcanic edifices small shields and cones 4 a spatial association between rmdss and irregular mare patches see braden et al 2014 https doi org 10 1038 ngeo2252 is observed suggesting that both may form from related lava flows 5 comparisons between rmdss and lava inflationary structures on earth support an inflation related extrusive nature and a genetic relationship with host lava flow processes and 6 rmds embayment relationships with craters of different degradation ages superposed on the host mare and regolith development models produces conflicting age relationships and divide theories of rmds origin into two categories 1 synchronous with the emplacement and cooling of the host lava flows 3 4 ga and 2 emplaced substantially after the host mare lava unit in the period 0 3 ga we outline the evidence supporting this age conundrum and implications for the different theories of origin and describe future research avenues to help resolve these outstanding questions 2020 american geophysical union all rights reserved

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization ii makaopuhi lava lake crystal size distribution csd theory has been applied to drill core samples from makaopuhi lava lake kilauea volcano hawaii plagioclase and fe ti oxide size distribution spectra were measured and population densities n were calculated and analyzed using a steady state crystal population balance equation n n0 exp l g slopes on ln n versus crystal size l plots determine the parameter g a product of average crystal growth rate g and average crystal growth time the intercept is j g where j is nucleation rate known temperature depth distributions for the lava lake provide an estimate of effective growth time allowing nucleation and growth rates to be determined that are independent of any kinetic model plagioclase growth rates decrease with increasing crystallinity 9 9 5 4 10 11 cm s as do plagioclase nucleation rates 33 9 1 6 10 3 cm3 s ilmenite growth and nucleation rates also decrease with increasing crystallinity 4 9 3 4 10 10 cm s and 15 2 2 10 3 cm3 s respectively magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus g 2 9 10 10 cm s j 7 6 10 2 cm3 s moments of the population density function were used to examine the change in crystallization rates with time preliminary results suggest that total crystal volume increases approximately linearly with time after 50 crystallization a more complete set of samples is needed for material with 50 crystals to define the entire crystallization history comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling this interpretation is consistent with proposed thermal models of magmatic cooling where heat loss is balanced by latent heat production to maintain equilibrium cooling

pyroclast characteristics of a subaqueous to emergent surtseyan eruption black point volcano california abstract we present the first ever quantitative analysis of pyroclast textures from subaqueous deposits of a surtseyan emergent volcano the volcano black point formed in mono lake s pleistocene precursor lake russell at 13 300 500 bp from an explosive basaltic eruption involving the interaction of shallow lake water 105 m with vesiculating magma the bulk of the edifice comprises unconsolidated tephra and represents submerged stages of eruption thin summit deposits formed during a final phase of emergent eruption and produced a group of low tuff rings lapillus clasts 16 mm to 32 mm and fine ash grains 4 0 0625 mm from the subaqueous deposits have textures that reveal a conduit history of bubble nucleation growth collapse intense microlite crystallisation and magma water interaction lapilli vesicularity ranges broadly to high values up to 89 while vesicle number densities 5 4 102 4 8 104 vesicles per mm3 are comparable to those published for strombolian and plinian basaltic eruptions 1 104 vesicles per mm3 vesicle size and volume distributions suggest continuous bubble nucleation but the suite of data as a whole indicates that a late stage nucleation event played a significant role in shaping the eruption ash grain morphology and surface features indicative of magma water interactions attest to water s role in fragmentation overall the pyroclast textures are consistent with water modification of a rather intense basaltic eruption which might have been of a violent strombolian or plinian style if the eruption had been dry and occurred subaerially

it takes three to tango 2 bubble dynamics in basaltic volcanoes and ramifications for modeling normal strombolian activity this is the second paper in a two part series examining numerical simula tions of buoyancy driven ow in the presence of large viscosity contrasts in the rst pa per we demonstrated that a combination of three numerical tools an extended ghost uid type method the level set approach and the extension velocity technique accurately simulate complex interface dynamics in the presence of large viscosity contrasts in this paper we use this three fold numerical method to investigate bubble dynamics in the conduits of basaltic volcanos with a focus on normal strombolian eruptions strombolian type activity named after the famously episodic eruptions at stromboli volcano is char acterized by temporally discrete fountains of incandescent clasts the mildly explosive nature of normal strombolian activity as compared to more eusive variants of basaltic volcanism is related to the presence of dissolved gas in the magma yielding a complex two phase ow problem we present a detailed scaling analysis allowing identication of the pertinent regime for a given ow problem the dynamic interactions between gas and magma can be clas sied into three non dimensional regimes based on bubble sizes and magma viscosity re solving the uid dynamics at the scale of individual bubbles is not equally important in all three regimes as long as bubbles remain small enough to be spherical their dy namic interactions are limited compared to the rich spectrum of coalescence and breakup processes observed for deformable bubbles in particular once inertia ceases to be neg ligible one key nding in our simulations is that both large gas bubbles and large conduit lling gas pockets slugs are prone to dynamic instabilities that lead to their rapid breakup during buoyancy driven ascent we provide upper bound estimates for the maximum sta ble bubble size in a given magmatic system and discuss the ramications of our results for two commonly used models of normal strombolian type activity the rise speed dependent rsd model and the collapsing foam cf model

textural variation in juvenile pyroclasts from an emergent surtseyan type volcanic eruption the capelas tuff cone sao miguel azores abstract here i present textural data i e vesicularity vesicle size distributions vsd plagioclase crystallinity crystal size distributions csd combined with fractal analyses of particle outlines from a natural succession of alternating fall and surge deposits in the emergent capelas tuff cone azores the textural variation in the capelas succession is surprisingly small considering the wide variety of fragmentation processes vent activity and emplacement mechanisms that are characteristic of emergent eruptions the plagioclase crystal content varies between 24 and 33 vol csd analyses of plagioclase show near linear trends with a slight increase in time for the smallest crystal sizes with surge deposits having more groundmass plagioclase when compared with fall deposits this is consistent with crystallization induced by degassing and decompression at lower eruption rates the vesicularities of the capelas pyroclasts are more variable 18 to 59 vol with vsds displaying kinked trends characteristic of coalescence this is especially evident in the fall deposits and consistent with being formed in continuous uprush jetting with an overall shallow fragmentation level within the conduit bubble coalescence can also be identified in the surge deposits although to a much lesser extent the amount of bubble coalescence is negatively correlated with the amount of groundmass crystallization i e plagioclase in the capelas deposits a relatively broad range of fractal dimensions with average dbox 1 744 and 0 032 for the outlines of pyroclastic fragments emplaced by fall or as surges indicate that there is little difference in the fragmentation process itself at capelas in addition to this the fact that the fractal dimensions for both the fall and surge end members completely overlap suggests that shape modification due to abrasion and chipping of grain edges was minor during emplacement of base surges these results are consistent with emergent eruptions building tuff cones to be a relatively low energy phreatomagmatic landform e g at least when compared with more energetic phreatomagmatic eruptions producing tuff rings and maar volcanoes

globorotalia planktic foraminifera at the miocene pliocene boundary in new zealand abstract mid latitude assemblages of globorotalia in the late miocene and early pliocene of new zealand are dominated by the g miozea complex and its derivative taxa most of which appear rather suddenly in the basal pliocene the most uninterrupted sequence present in dsdp site 284 on the challenger plateau is closely matched in the north island mangapoike river section which is correlated by biostratigraphy geomagnetic polarity and a fission track date with blind river in the south island k ar dates of 5 2 m y and 5 3 m y for basalt associated with basal pliocene fossiliferous deposits in the chatham islands support the location of the miocene pliocene boundary at or close to the gilbert chron 5 boundary the isotopic record indicates that there were one or more periods of oceanic instability accompanied by cooling and polar ice accumulation in the late miocene immediately before the marked phase of evolutionary radiation of globorotalia in the early pliocene

geomorphological reconstruction and morphometric modelling applied to past volcanism accurate and precise morphometric modelling can be extended to past eruptions after a careful palaeogeomorphological reconstruction of volcanic landforms in an oceanic island this reconstruction was used to derive the pre post eruption and present day digital elevation models dem the correct pixel size interpolation method and quality of these dems are discussed the process in a geographical information system framework of the geological information of cone lava flow and tephra fall deposits together and the aforementioned dems allowed the determination of main morphological features of these volcanic landforms and their derivatives the calibration and validation of morphometric modelling were performed on simulated volcanic landforms and verified by a case study a typical holocene monogenetic basaltic eruption at gran canaria island spain

the degassing of hawaiian tholeiite accepting the gerlach and graeber 1985 estimates of the initial co2 and h2o concentrations we have calculated the variation of the concentrations of these gases dissolved and or exsolved in hawaiian tholeiite from the moment it is generated until it solidifies at the earth s surface these computations are extensions of our previous work bottinga and javoy 1989 1990a 1990b on the nucleation growth and ascent of bubbles in mid oceanic ridge basalt the present study is different in that we consider low pressure p 1 bar bubble nucleation and the presence of h2o our results indicate that 1 hawaiian liquid tholeiite is supersaturated with respect to co2 when it erupts 2 degassing of the basaltic liquid takes place during different stages each of which gives rise to a compositionally distinct bubble population which to a large extent is lost before the formation of a new population 3 fumarolic gas compositions are affected by the pressure and temperature at which gas bubbles are released from the lava and the velocity with which lava is ejected from the magma chamber

submarine eruption near socorro island mexico geochemistry and scanning electron microscopy studies of floating scoria and reticulite abstract products of an underwater eruption near socorro island in the ne pacific were observed directly on january 29 1993 ten days after precursors were first recorded by sofar sound fixing and ranging hydrophones located in hawaii and tahiti eruptive activity was noticed from boats and ships as small steam plumes rising from the sea at an area centered at 18 48 n 111 05 w 2 4 km nw of punta tosca and 4 6 km ssw of cape henslow on socorro island the observed steam was produced by 1 3 m large blocks of hot dark grey highly vesiculated basalt rising buoyantly to the surface from two submarine shallow vents at 210 and 30 m depth tens of blocks accompanied by bubbles could be observed rising to the surface in irregular pulses these scoriaceous blocks remained floating at the surface until they would crack into smaller pieces by thermal contraction emitting hissing noises from vapourizing seawater in contact with the hot interior of the blocks steam jets several metres in height were produced and occasionally blocks were propelled laterally by the steam jet depending on vesicularity and permeability blocks remained floating and drifting with the surface current for 1 15 minutes before sinking back floating rocks covered an area of about 6000 m2 this intermittent activity has been observed ever since and has not stopped as of april 1994 buoyant scoria and reticulite are indicative of volatile mostly co2 supersaturation and exsolution in the magma prior to rapid quenching which inhibits loss of volatiles by bubble escape a high velocity ascent of low viscosity magma in a relatively narrow conduit is also required to prevent substantial gas escape and allow formation of reticulite the buoyant scoria is most probably ejected by intermittent lava fountaining at fixed vents as a result of changes in eruption velocities due to changes in the exsolved gas content of the lava between january and july 1993 floating blocks of scoria and reticulite were collected on several occasions from the surface of the sea for chemical and mineralogical analyses major and minor element analyses including ree as well as electron microprobe analyses of different phases revealed that the composition of the emitted lava has not changed through time blocks of basalt sio2 45 47 are highly vitric and vesicular with tabular anorthite phenocrysts up to 3 mm in length and minor grains of forsteritic olivine ree and trace element composition of these rocks suggest an anomalous mantle source for the erupted alkali basalt lava the ongoing eruption will either continue in a similar fashion as described and eventually cease or built up a mound that reaches the surface and forms an island with accompanying change in eruptive style

influence of shear and deviatoric stress on the evolution of permeability in fractured rock 1 the evolution of permeability in fractured rock as a function of effective normal stress shear displacement and damage remains a complex issue in this contribution we report on experiments in which rock surfaces were subject to direct shear under controlled pore pressure and true triaxial stress conditions while permeability was monitored continuously via flow parallel to the shear direction shear tests were performed in a pressure vessel under drained conditions on samples of novaculite arkansas and diorite coso geothermal field california the sample pairs were sheared to 18 mm of total displacement at 5 mm s at room temperature and at effective normal stresses on the shear plane ranging from 5 to 20 mpa permeability evolution was measured throughout shearing via flow of distilled water from an upstream reservoir discharging downstream of the sample at atmospheric pressure for diorite and novaculite initial preshear fracture permeability is 0 5 1 10 14 m 2 and largely independent of the applied effective normal stresses these permeabilities correspond to equivalent hydraulic apertures of 15 20 mm because of the progressive formation of gouge during shear the postshear permeability of the diorite fracture drops to a final steady value of 0 5 10 17 m 2 the behavior is similar in novaculite but the final permeability of 0 5 10 16 m 2 is obtained only at an effective normal stress of 20 mpa

regional biotic turnover dynamics in the plio pleistocene molluscan fauna of the wanganui basin new zealand sampling gaps and variable preservation greatly complicate attempts to interpret patterns of biotic change from the fossil record this study investigates whether observed patterns of first and last occurrences of mollusc species can be explained by poor or uneven sampling of a diverse 800 species plio pleistocene marine fauna from the wanganui basin north island new zealand estimates of sampling completeness are high ranging from 78 to 98 mean 88 despite several sampling gaps in the succession stratigraphic permutation tests suggest that most of the apparent peaks in the local first and last appearances of species are caused by uneven sampling however peaks of last occurrences of species during the late pliocene 2 5 2 0 ma and of first occurrences in the middle pleistocene 0 75 0 5 ma cannot be classified as artefacts and appear to represent real biological events a wide early pleistocene gap in the stratigraphic section in the basin prevents the precise estimation of the magnitude duration or timing of these biotic transitions mechanisms for the biotic change remain elusive better palaeoenvironmental control and detailed ecological study of selected molluscan clades are required to test alternative causal hypotheses however similar turnover episodes have been documented from the temperate and tropical western atlantic suggesting a global biotic perturbation on shallow shelves in response to plio pleistocene global environmental change

frictional stability permeability relationships for fractures in shales there is wide concern that fluid injection in the subsurface such as for the stimulation of shale reservoirs or for geological co2 sequestration gcs has the potential to induce seismicity that may change reservoir permeability due to fault slip however the impact of induced seismicity on fracture permeability evolution remains unclear due to the spectrum of modes of fault reactivation e g stable versus unstable as seismicity is controlled by the frictional response of fractures we explore friction stability permeability relationships through the concurrent measurement of frictional and hydraulic properties of artificial fractures in green river shale grs and opalinus shale ops we observe that carbonate rich grs shows higher frictional strength but weak neutral frictional stability the grs fracture permeability declines during shearing while an increased sliding velocity reduces the rate of permeability decline by comparison the phyllosilicate rich ops has lower friction and strong stability while the fracture permeability is reduced due to the swelling behavior that dominates over the shearing induced permeability reduction hence we conclude that the friction stability permeability relationship of a fracture is largely controlled by mineral composition and that shale mineral compositions with strong frictional stability may be particularly subject to permanent permeability reduction during fluid infiltration

hydraulic mechanical properties of microfaults in granitic rock using the punch through shear test abstract fault zones are key features in crystalline geothermal reservoirs or in other subsurface environments due to the fact that they act as main fluid pathways an adequate experimental description of the evolution of permeability of a realistic microscopic fault zone under in situ reservoir and fracture parallel flow conditions is required to address this topic we demonstrate a novel experimental set up punch through shear test that is able to generate a realistic shear zone microfault under in situ reservoir conditions while simultaneously measuring permeability and dilation three samples of intact granite from the odenwald upper rhine graben were placed into a mts 815 tri axial compression cell where a self designed piston assembly punched down the inner cylinder of the sample creating the desired microfault geometry with a given offset permeability was measured and fracture dilation was inferred from an lvdt extensometer chain as well as the balance of fluid volume flowing in and out of the sample after fracture generation the shear displacement was increased to 1 2 mm and pore pressure changes of 5 or 10 mpa were applied cyclically to simulate injection and production scenarios formation of a microfault increased the permeability of the granite rock by 2 to almost 3 orders of magnitude further shear displacement led to a small increase in permeability by a factor of 1 1 to 4 0 but permeability was reduced by a factor of 2 5 to 4 within 16 h due to compaction and fault healing effective pressure cycling led to reversible permeability changes ct images showed that the fracture network is rather complex but depicts all features commonly observed in larger scale fault zones

stability of foams in silicate melts bubble coalescence and the spontaneous disruption of high porosity foams in silicate melts are the result of physical expulsion of interpore melt syneresis leading to bubble coalescence and diffusive gas exchange between bubbles melt expulsion can be achieved either along films between pairs of bubbles or along plateau borders which represent the contacts between 3 or more bubbles theoretical evaluation of these mechanisms is confirmed by experimental results enabling us to quantify the relevant parameters and determine stable bubble size and critical film thickness in a foam as a function of melt viscosity surface tension and time foam stability is controlled primarily by melt viscosity and time melt transport leading to coalescence of bubbles proceeds along inter bubble films for smaller bubbles and along plateau borders for larger bubbles thus the average bubble size accelerates with time in silicate melts the diffusive gas expulsion out of a region of foam is effective only for water and even then only at small length scales as the diffusion of co2 is negligible the results of our analyses are applicable to studies of vesicularity of lavas melt degassing and eruption mechanisms

simple mathematical model of a rough fracture a simple mathematical model of rough walled fractures in rock is described which requires the specification of only three main parameters the fractal dimension the rms roughness at a reference length scale and a length scale describing the degree of mismatch between the two fracture surfaces fractured samples collected from natural joints and laboratory specimens have been profiled to determine the range of these three parameters in nature it is shown how this surface roughness model can be implemented on a computer allowing future detailed study of the mechanical and transport properties of single fractures and the scale dependence of these properties

collapse of reacted fracture surface decreases permeability and frictional strength five 3d x ray computed tomography images of eagle ford shale rock coupon pairs one for each condition shown in figure 3 in the related publication details of the data in this part are presented in readme txt for more information about the experiments and methodology please refer to related publication