origin of the lethal gas burst from lake monoun cameroun abstract on 15 august 1984 a lethal gas burst issued from a submerged 96 m deep crater in lake monoun in cameroun western africa killing 37 people the event was associated with a landslide from the eastern crater rim which slumped into deep water waters below 50 m are anoxic dominated by high fe 2 600 mg l and hco 3 1900 mg l anoxic and supersaturated with siderite which is a major component of the crater floor sediments the unusually high fe 2 levels are attributed to reduction of laterite derived ferric iron gradually brought into the lake as loess and in river input sulfur compounds are below detection limits in both water and gas gases effervescing from depressurized deep waters are dominantly co 2 with minor ch 4 having 13 c of 7 18 and 54 8 per mil respectively bacterial decomposition of organic matter may account for the methane but 14 c of lake water indicates that only 10 of the carbon is modern giving an apparent age of 18 000 years the dominant source of carbon is therefore attributed to long term emission of co 2 as volcanic exhalation from vents within the crater which led to gradual build up of hco 3 in the lake the density stratification of the lake may have been upset by an earthquake and underwater landslide on 15 august which triggered overturn of the lake and caused nucleation of co 2 in the deep water the resultant ebullition of co 2 from deep lake waters led to a gas burst at the surface and locally generated a water wave up to 5 m high people travelling through the gas cloud were asphyxiated presumably from co 2 and suffered skin discoloration from unidentified components

the geological setting of tourmalinite at rum jungle n t australia genetic and economic implications tourmalinite is a common rock type associated with proterozoic strata bound mineral deposits although common it is often difficult to recognise in the field leading to misidentification it occurs as a conformable banded quartz tourmaline lithological unit comprising at least 15 and as much as 50 of the rock at rum jungle tourmalinite occurs within the oldest sediments arenites and magnesites as distinct lenses as facies equivalents of quartz magnetite units and mafic schists tuffs and distal equivalents of polymetallic sulfides distinct layering slump folding rip up clasts and the association with diagenetic pyrite suggest a sedimentary environment enechelon fracturing of the fine grained light green tourmaline crystals spectacularly supports pre deformation formation the crystals are optically and chemically zoned parallel to the c axis with irregular growth lamellae width which supports a pre regional metamorphic origin analyses show the tourmaline to be the mg rich variety dravite most tourmalinites are interpreted as subaqueous marine deposits it is more likely that they form in lacustrine shallow water evaporitic environments particularly continental rifts suitable b bearing fluids can be generated by hotspring activity and mobilized by co2 rich fluids association with chemical sediments suggests tourmalinites also have a chemical sediment precursor ample evidence at rum jungle supports the notion of a continental rift environment which was the site of deposition of fluvial arenites and alkaline evaporitic lake sediments localised hot spring activity contributed b bearing fluids which precipitated chemical sediments according to the pertaining ph temperature etc diagenetic alteration produced the tourmalinite now present these tourmalinites are comparable to those of similar age elsewhere e g sullivan broken hill they can be genetically modelled upon recent borate concentrations all of which occur in continental rift environments

dynamics of coupled diffusive and decompressive bubble growth in magmatic systems bubble growth in an ascending parcel of magma is controlled both by diffusion of oversaturated volatiles and decompression as the magma rises we have developed a numerical model which explores the processes involved in water exsolution from basaltic and rhyolitic melts rising at a constant rate from magma chamber depths of 4 and 1 km while the model does not attempt to simulate natural eruptions it sheds light on the processes which control eruptive behavior under various conditions ascent rates are defined such that a constant rate of decompression dp dt is maintained a variety of initial ascent rates are considered in the model from 1 m s to 100 m s for basalts and from a few centimeters per second to 10 m s for rhyolite at the base of the conduit the model results indicate that for any reasonable ascent rate basaltic melt degasses at a rate sufficient to keep the dissolved volatile concentration at equilibrium with the decreasing ambient pressure rhyolitic melt reaches the surface at equilibrium if its ascent rate is less than 1 m s but it can erupt with high oversaturation at greater ascent rates the latter may lead to explosive eruptions if the ascent rate of rhyolite is 10 m s or more then melt barely degasses at all in the conduit and erupts with the highest oversaturation possible for the case of slow magma rise bubble growth is limited by decompression for the case of rapid magma rise bubble growth is limited by diffusion the results of our simple model do not accurately simulate natural volcanic eruptions but suggest that subsequent more complex models may be able to simulate eruptions using the insights regarding diffusive and decompressive bubble growth processes explored in this study numerical modeling of volcanic degassing may eventually lead to better prediction of eruption timing energetics and hazards of active volcanoes

origin and significance of tourmaline rich rocks in the broken hill district australia tourmaline rich rocks are widespread minor lithologies within the early proterozoic willyama supergroup in the broken hill district australia tourmaline concentrations occur in strata bound and local stratiform tourmalinites clastic metasedimentary rocks quartz gahnite lode rocks stratiform pb zn ag sulfide ores garnet quartzites strata bound scheelite deposits quartz tourmaline nodules discordant quartz veins and granitic pegmatites most of the tourmaline rich rocks are within the broken hill group that hosts the main pb zn ag ores at the globe mine along the northeast end of the main lodes tourmalinites are closely associated with pb zn ag mineralization and in places are interbedded with mn rich garnet quartzites galena and other ore minerals occur locally in the cores of recrystallized tourmaline grains in these tourmalinites indicating that tourmaline and sulfides were present together prior to deformation and high grade metamorphism electron microprobe analyses of tourmalines intergrown with fe sulfides at the globe mine show mg rich compositions relative to tourmalines in sulfide free assemblages from the same area suggesting early premetamorphic introduction of boron and mg enrichment of tourmaline by sulfide silicate reactions during metamorphism combined field and geochemical data indicate that the district tourmalinites represent normal clastic sediments that were metasomatically altered by boron rich hydrothermal fluids at or below the sediment water interface whole rock chemical analyses of 33 tourmaline rich rocks show linear trends of data for major and trace elements that closely resemble the trends observed for unmineralized elastic metasedimentary rocks of the district average fe al mg al na al and ti al molar ratios of the tourmaline rich rocks and clastic metasediments are very similar the average k al molar ratio of the tourmaline rich rocks is significantly lower than that of the clastic metasediments reflecting the loss of k during tourmalinite formation chondrite normalized patterns of rare earth elements ree in the quartz rich tourmalinites are generally similar to those of the clastic metasediments except for minor depletions of light ree local positive and negative ce anomalies suggest tourmalinite formation in the presence of seawater or a seawater derived pore fluid the geochemical data imply relative immobility of al ti cr and heavy ree during hydrothermal alteration and later metamorphism boron isotope analyses of 52 tourmaline separates show a total range of delta 11 b values from 26 8 to 17 0 per mil fine grained euhedral nonpoikilitic tourmalines from tourmalinites in the andalusite muscovite zone in the northern part of the district e g black prince mine have delta 11 b values from 21 to 17 per mil whereas coarse granoblastic and poikilo blastic tourmalines from the sillimanite and two pyroxene granulite zones in the southern part of the district e g globe mine have delta 11 b values of 24 to 19 per mil tourmalines in strongly retrogressed tourmalinites have delta 11 b values from about 27 to 20 per mil the observed variations in delta 11 b are consistent with prograde and retrograde metamorphic fractionation of boron isotopes in which the fluid phase is preferentially enriched in the heavier isotope 11 b premetamorphic hydrothermal fluids that deposited the black prince tourmalinites had delta 11 b values of 8 to 5 per mil at 200 degrees to 300 degrees c suggesting a boron source from nonmarine evaporite borates tourmalinites in the broken hill district apparently formed by the same submarine hydrothermal processes as the main pb zn ag lodes and the siliceous ferromanganese protoliths of the garnet quartzites in our model the hydrothermal system s acquired abundant boron by leaching evaporitic borates within the thackaringa group the stratigraphic sequence that underlies the broken hill group and most of the tourmaline concentrations we suggest that evaporites of the thackaringa group provided a source of readily extractable boron for formation of the tourmalinites and also the source of the fluoride sulfur and perhaps the carbonate in the main lodes such evaporites may have been critical for increased metal chloride complexing and transport necessary for deposition of the high grade pb zn ag ores the broken hill deposit may have formed contemporaneously with the mount isa and mcarthur river pb zn ag deposits in similar evaporite bearing sequences during widespread early proterozoic continental rifting

energetics of gas driven limnic and volcanic eruptions abstract this paper lays the foundation for the rigorous treatment of the energetics of gas exsolution from a gas containing liquid which powers gas driven volcanic and limnic eruptions various exsolution processes reversible or irreversible slow or rapid are discussed and the maximum amount of kinetic energy derivable from a reversible gas exsolution process is obtained the concept of dynamic irreversibility is proposed for discussing the kinetic energy available from irreversible gas exsolution processes the changes of thermodynamic properties during gas exsolution processes are derived density pressure relations for gas liquid mixtures are presented including empirical relations for irreversible gas exsolution the energetics of gas driven eruptions through both fluid and rigid media including the role of buoyancy and the role of magma chamber expansion work are investigated for reversible processes the energetics can be used to discuss the dynamics of gas driven eruptions leading to maximum erupting velocities and maximum eruptible fractions for irreversible processes empirical relations and parameters must be employed the exit velocities of the lake nyos eruption and the 18 may 1980 eruption of mount st helens are modeled by incorporating possible irreversibility

two step deglaciation of the southeastern barents sea marine geologic evidence from the western barents sea shelf leaves little doubt that theareawascoveredbygroundediceduringthelastglaciation butthepatternandtiming of the subsequent deglaciation were not well determined here we reconstruct the timing and mechanism of ice sheet retreat as constrained by seismic stratigraphy and lithostratigraphy and accelerator mass spectrometer 14 c dating of foraminifera and mollusc shellsinsedimentboringsfromthesoutheasternbarentssea 1000kmfromthewestern shelf edge and former ice sheet margin the deposition of ice proximal glaciomarine sediments upon till began at or shortly before 12 7 ka indicating that the ice sheet retreat whichmostlikelycommencedalongthewesternmarginofthebarentsseashelfat15 14 5 ka reached the southeastern part of the shelf in 2 ka the subsequent accumulation of glaciomarinesedimentstookplaceintwodistinctpulses 12 7 12 1kaand 10 5 9 4ka separatedbyanintervalofnondepositionlasting 1 5ka thetwopulsesofsedimentation were coeval with periods of increasing surface water and air temperatures in the northern atlanticregionandacceleratedeustaticsea levelrise suggestingthattheremainingretreat of the barents shelf ice sheet was paced by these factors

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

on the development of highly viscous skins of liquid around bubbles during magmatic degassing we report experiments which show that the development of high viscosity volatile depleted skins of liquid around bubbles has a major effect on bubble growth rates and thus on volcanic conduit flow dynamics decompression experiments were performed at room temperature in a cylindrical shock tube using viscous solutions of gum rosin and acetone gra after an initial transient the propagation of the flow front follows an empirical exponential law covering most of the final expansion theories of magma flow dynamics that rely on a constant liquid viscosity conclude that most of the degassing takes place in a diffusion limited decelerating bubble growth regime by contrast we assume that viscous resistance to bubble growth is controlled by the high viscosity of the liquid skins around bubbles and find that in both explosive gra and magma flows bubble growth lies mostly in a diffusion driven but viscosity limited accelerating regime we infer that in explosive events diffusion limited degassing is unlikely to occur before fragmentation

experimental simulations of gas driven eruptions kinetics of bubble growth and effect of geometry simulated gas driven eruptions using co2 water polymer systems are reported eruptions are initiated by rapidly decompressing co2 saturated water containing up to 1 0 wt co2 both cylindrical test cells and a flask test cell were used to examine the effect of magma chamber conduit geometry on erup tion dynamics bubble growth kinetics are examined quantitatively in experiments using cylindrical test cells uninhibited bubble growth can be roughly expressed as dr dt ld b 1 gt 1 3 for a co2 water polymer system at 0 22 7c and with viscosities up to 5 pa7s where r is the radius of bubbles l and d are the ostwald solubil ity coefficient and diffusivity of the gas in the liquid b is the degree of saturation decompression ratio and g characterizes how the boundary layer thickness in creases with time and is roughly 1 0 10 5 m s 1 3 in this system unlike the radius of cylindrical test cells which does not affect the eruption threshold and dynamics the shape of the test cells flask vs cylindrical affects the dynamics but not the threshold of eruptions for cylindrical test cells the front motion is characterized by constant acceleration with both dh the height in crease and dv the volume increase being propor tional to t 2 for the flask test cell however neither dh nor dv is proportional to t 2 as the conduit radius var ies test cell geometry also affects foam stability in the flask test cell as it moves from the wider base chamber into the narrower conduit the bubbly flow becomes fragmented affecting the eruption dynamics the frag mentation may be caused by a sudden increase in accel eration induced by conduit shape change or by the presence of obstacles to the bubbly flow this result may help explain the range in vesicularities of pumice and reticulite

shear sense indicators in striped bedding veins striped bedding veins are veins that lie subparallel to bedding and have an internal layering or lineation at a small angle to the veins long axis they form during bedding parallel slip and can be used as shear sense indicators solid inclusion trails produce the visible internal layering or lineation and track the opening direction of the veins elongate quartz crystals however can be oriented at an angle of up to 80 to the opening direction are non tracking and contain almost no information on the shear sense the striped bedding veins can be separated into three types according to the geometry of their internal segmentation veins of type b opened parallel to jogs oriented at a low angle to bedding veins of type j opened parallel to jogs oriented at a high angle to bedding and veins of type o opened orthogonal to bedding and jogs striped bedding veins of types b and j contain crack seal inclusion bands and displacement parallel inclusion trails striped bedding veins of type o feature only crack seal inclusion bands the example of striped bedding veins presented in this paper from the orobic alps of italy belongs to type b the lineation in the veins and the orientation of the inclusion bands and inclusion trails as well as the orientation of steps in the vein wall can be used to determine the sense of shear and the direction and amount of vein opening or bedding parallel slip

methane escape from gas hydrate systems in marine environment and methane driven oceanic eruptions 1 huge quantities of ch4 are stored in marine sediment in the form of methane hydrate bubbles and dissolved ch4 in pore water here i discuss the various pathways for methane to enter the ocean and atmosphere including i methane hydrate dissolution or dissociation as it rises through seawater the dissociation rate can be 2 to 3 orders of magnitude greater than the dissolution rate ii the dissolution and expansion of a bubble with or without a hydrate shell as it rises through seawater there is a critical radius which depends on depth above which a bubble would reach the surface or even become larger as it rises i also propose and model the dynamics of a new type of terrestrial gas driven eruptions methane driven oceanic eruptions such eruptions not only represent a yet unrecognized geohazard but also provide a pathway for ch4 to rapidly enter the atmosphere as a greenhouse gas

evolution of an early permian extensional detachment fault from synintrusive mylonitic flow to brittle faulting grassi detachment fault orobic anticline southern alps italy

the use of a shear thinning polymer as a bubbly magma analogue for scaled laboratory experiments abstract analogue materials are commonly used in volcanology to perform scaled laboratory experiments analogue experiments inform on fundamental fluid dynamic structural and mechanical processes that are typically very difficult to observe and quantify directly in the natural volcanic system here we investigate the suitability of an aqueous solution of hydroxyethyl cellulose polymer hec for use as a lava magma analogue with a particular focus on its rheological behaviour we characterize a range of physical properties as functions of the concentration and temperature of the solution density specific heat capacity thermal diffusivity thermal conductivity surface tension as well as rheology hec has a non newtonian shear thinning rheology that depends on the concentration and temperature of the solution we show that the rheology is well described by the cross model which was originally developed for polymer solutions but has also been applied to bubbly magmas using this similarity an approach for scaling analogue experiments that use shear thinning polymers like hec to bubbly magma is presented a detailed workflow and a spreadsheet are provided to allow experimentalists to investigate the effects of non newtonian behaviour in their existing laboratory set ups this contribution will allow for the more complex but often more realistic case of bubble bearing magmas to be rigorously studied in experimental volcanology

gum rosin acetone system as an analogue to the degassing behaviour of hydrated magmas solutions of gum rosin and acetone reproduce the volatile and temperature dependent viscosity together with the phase behaviour of hydrated magmas a range of experimental exsolution conditions was investigated including the variation of supersaturation rate of decompression solution temperature and volatile content degassing processese were controlled by the formation of an exsolution interface above a supersaturated liquid the end products ranged from a mildly degassed liquid to a solid foam which preserved strained vesicles solutions of gum rosin and acetone are proposed as a suitable analogue system with which to study magma degassing processes

linking co2 degassing in active fault zones to long term changes in water balance and surface water circulation an example from sw turkey abstract calcite veins are commonly found at shallow depth a few metres below the surface in damage zones of active normal fault systems in southwest turkey although earlier studies demonstrated the link between the vein formation and seismicity the association of near surface carbonate precipitation with climate driven hydrological conditions water table amount of precipitation and evaporation and water discharge is poorly understood in this study using the u th dating method we investigate the timing of vein formation and the interrelationship between tectonic and climatic related hydrological processes carbonate precipitation is interpreted to occur as a result of sudden pressure drops and co2 release after earthquake induced fracturing vein formation mostly occurred during glacial periods which coincide with slow growth rates and higher oxygen isotope values of speleothems from the eastern mediterranean region we relate these episodes to reduced winter rainfall due to the decrease in westerly flow in sw turkey these somewhat drier conditions influenced the chemical composition of circulating water creating conditions conducive to carbonate precipitation and sealing of damage zones these conditions also facilitated co2 accumulation and overpressure build up in the rupture zones failure of the faults resulted in the release of large volumes of co2 rich fluids and the generation of shallow carbonate veins it is proposed that during phases of increased winter rainfall co2 is advected to the surface and discharged as passive degassing when meteoric water circulation is enhanced while regional tectonics is the ultimate driver of fault activity and fracture formation climate driven near surface hydrological changes may have played an important role in modulating co2 rich fluid circulation and surface discharge

estimate of pyroclastic flow velocities resulting from explosive decompression of lava domes apparently benign silicic domes or lava flows can travel for several kilometres and then suddenly collapse to generate pyroclastic phenomena capable of causing widespread destruction as happened recently at mount unzen in japan1 two sources have been proposed for the energy that propels such pelean or merapi type2 pyroclastic flows gravitational col lapse supplemented by heating and expansion of air and sudden expansion of pressurized gases from inside the lava flow if gravity controls the energy transfer then areas likely to be affected can be predicted on the basis of topography3 and the resulting deposits will bear a simple relationship to the part of the lava flow from which they issued but if gas pressure adds a significant contribution hazard assessment becomes more difficult because gas decompression adds velocities beyond those acquired by gravitational forces putting much larger areas at risk and forming pyroclastic deposits that are much more difficult to relate to their source here we estimate the initial velocities of pyroclastic flows generated by dome disintegration for a range of lava compositions and volatile contents and offer a conceptual framework for correlating the dynamics of dome front collapse with the resulting sediment record our results indicate that explosive decompression at distal portions of domes can cause velocities comparable to gravitational collapse especially in cases where volatiles become locally concentrated above equilibrium values

cryptocrystalline permian tourmalinites of possible metasomatic origin in the orobic alps northern italy strata bound tourmaline rich rocks or tourmalinites are relatively rare but important rock types that locally are associated with base metal gold tungsten cobalt and uranium deposits e g ethier and campbell 1977 slack 1982 slack et al 1984 plimer 1986 1987 bone 1988 sun and ge 1989 nie et al 1990 modreski and connor 1991 bhattacharya et al 1992 bandyopadhyay et al 1993 although their significance as guides to strata bound mineral deposits is well established the origin of most tourmalinites is still controversial see slack et al 1993 nearly all documented tourmalinites are of proterozoic or early paleozoic age and have undergone at least lower greenschist facies metamorphism that hampers interpretations of their origin because of changes in texture mineralogy and chemistry this paper describes an important occurrence of finegrained tourmalinites from the orobic alps northern italy in which metamorphic onditions did not exceed prehnite pumpellyite grade the orobic tourmalinites are believed to be permian and represent the youngest and most fine grained examples of such rocks known to date

fragmentation of a porous viscoelastic material implications to magma fragmentation fragmentation of vesicular magma by rapid decompression is one of the most likely triggers for explosive eruptions in this phenomenon the decompression rate and the viscoelastic nature of magma are considered to be key factors in order to obtain a clear idea on the effects of these two factors controlled fragmentation experiments have been conducted these experiments have three advantages first the specimen is made of a viscoelastic material with controlled porosity and geometry second the fragmentation process is directly monitored finally both the magnitude and rate of decompression are controlled brittle fragmentation and ductile expansion were both observed in the same porous material at different timescales the various mechanical responses of the specimen elastic flow and fragmentation were correlated with the pressure profile measured at the base of the specimen fragmentation was noted to occur when the decompression exceeded a critical value within a critical time two relevant timescales are discussed in terms of physical mechanisms of relaxation the first is the measured glass transition time the second is the estimated timescale for the onset of viscous bubble expansion the observed phenomena bear several similarities with natural magma fragmentation it is thus considered that the present results are a useful step toward constructing a model for magma fragmentation

experimental observations of the effect of crystals and pre existing bubbles on the dynamics and fragmentation of vesiculating flows the effect of crystals and pre existing gas phases on the dynamic degassing and fragmentation of magmas in a volcanic conduit have been simulated by analogue experiments a series of decompression experiments of viscous solutions of gum rosin and acetone with and without the incorporation of particles silicon carbide glass beads organic seeds or pre existing air bubbles have been performed in a transparent shock tube the addition of internal bubbles or solid particles in the starting solution shifts the fragmentation conditions towards lower acetone volatile contents and lower decompression ratios the effect of solid particles depends on their number density and spatial distribution in the starting solution a small number of sinking particles has little impact on the flow dynamics however a floating layer of particles provides a high concentration of surface bubbles that leads to an early fragmentation pulse the observations also imply that the presence of crystals if able to generate a high number density of bubbles will lead to an earlier and deeper fragmentation of the magma in the volcanic conduit

mathematical models for quantifying eruption velocity in degassing pipes based on exsolution of a single gas and simultaneous exsolution of multiple gases abstract after the limnic eruptions at nyos and monoun in the 1980s degassing pipes were installed to reduce the continuous increase of co2 at the bottom of these lakes the degassing system consists of a vertical pipe from the lake bottom to the surface and a small pump located near the top of the pipe which raises water in the pipe up to a level where it becomes saturated with gas which in turn leads to volume expansion and eruption this paper describes two new mathematical models for predicting eruption velocity in degassing pipes based on exsolution of a single gas and the simultaneous exsolution of multiple gases the models were applied to the degassing system of lakes nyos and monoun which contain two main gases namely co2 and ch4 because the volume proportion of ch4 is significant only in lake monoun the lake nyos test case considered the co2 gas only while as the lake monoun test case considered the simultaneous exsolution of co2 and ch4 good agreement between the results of the models and observed data is found for both test cases the results for the eruption in lake monoun considering the two main gases measured in this lake co2 and ch4 were found to have a better agreement with the measurements compared to the model results obtained considering the main gas only co2

dynamics of lake eruptions and possible ocean eruptions dissolved gas in liquid is able to power violent eruptions two kinds of such gas driven eruptions are known in nature explosive volcanic eruptions driven by dissolved h2o in magma at high temperatures and lake eruptions driven by dissolved co2 in water at low temperatures there are two known occurrences of lake eruptions one in 1984 lake monoun and one in 1986 lake nyos both in cameroon africa the erupted co2 gas asphyxiated 1700 people in the lake nyos eruption and 37 people at lake monoun here we review experimental simulations of co2 driven water eruptions and dynamic models of such eruptions and a bubble plume theory is applied to the dynamics of lake eruptions field evidence experimental results and theoretical models show that lake eruptions can be violent and theoretical calculations are consistent with the high exit velocities and eruption columns inferred from observations furthermore the dynamics of lake degassing experiments are consistent with theoretical models other kinds of gas driven eruptions are possible and may have occurred in nature in the past a concentrated and large release of methane gas or hydrate from marine sediment may result in an ocean eruption furthermore injection of liquid co2 into oceans might also lead to ocean eruptions if care is not taken the various kinetic and dynamic processes involved are examined and quantified

control of impact crater fracture systems on subsurface hydrology ground subsidence and collapse mars 1 noachian layered materials are pervasively exposed throughout the highlands of mars the layered deposits in places many kilometers thick exhibit impact craters of diverse morphologic characteristics ranging from highly degraded to pristine most of which formed during the period of heavy bombardment in addition exhumed impact craters ancient channels and fluvial and alluvial fans are visible in the layered deposits through moc imagery these features are more abundant in noachian terrains which indicates relatively high erosion rates during ancient mars that competed with heavy meteoritic bombardment the noachian layered materials are thus expected to contain numerous buried impact craters in various states of preservation here we propose that impact craters buried and exposed and associated fracture systems dominate the basement structural fabric of the ancient highlands and that they have significantly influenced the hydrogeology diversity in the occurrence of high and low densities of impact craters and associated fracture systems controls the magnitude of the local effects of magmatic driven hydrothermal activity in and surrounding the tharsis region for example the formation of chaotic terrains the source regions of the circum chryse outflow channel system and a large diversity of collapse structures including impact crater moats and pit chains appear to be the result of enhanced hydrothermal activity

gas driven water volcanism and the resurfacing of europa we have analyzed the problem of how pathways are created for the resurfacing by water or volatiles for a europa model in which there is an ocean underlying a thin ice shell 10 km thickness open cracks propagating downward cannot reach the ocean unless the relative tension in the ice is both very high 100 bar and applied very rapidly 10 4 10 5sec there is no known way to satisfy these criteria water filled cracks propagating upward can approach the surface for relative tensions of 5 10 bar comparable to the stresses induced by the eccentricity tide exsolution of plausible gas species co 2 co ch 4 so 2 can then occur at the crack tip the application of linear elastic fracture mechanics shows that the gas filled portion of the crack pinches off from the water filled portion and may rise rapidly to the surface entraining some water many of these cracks may end up as intrusions rather than extrusions because of partial freeze out of co 2 and water on the walls of the crack the resulting eruption is initially gas dominated but may include a subsequent less extended eruption of foam there may not be a direct relationship between the resurfacing process described here and the currently known geologic features observed on the surface the main problem with this or any model for tapping the ocean is the propagation of cracks through the soft ice immediately overlying the ocean

stratiform tourmalinites in metamorphic terranes and their geologic significance stratiform tourmalinites are significant minor rock types in many regional metamorphic terranes of the world tourmalinites are more widespread than previously recognized and are especially common in proterozoic and early paleozoic sequences dominated by clastic metasedimentary rocks they consist of conformable layers made up primarily of quartz and abundant tourmaline the latter typically exceeding 15 to 20 of rock volumes a few tourmalinites display striking sedimentary structures such as graded bedding cross laminations slump and flame structures and rip up clasts these and other geologic features provide important constraints for assessing the origin of these rocks and they suggest that tourmalinites form by the early diagenetic modification of a primary boron rich chemical precipitate tourmalinites are significant in preserving a valuable record of unusual chemical and paleogeographic conditions in clastic sedimentary basins and in their close association with a variety of stratabound mineral deposits

siderite deposits in northern italy early permian to early triassic hydrothermalism in the southern alps abstract we present a minero petrographic geochemical and geochronological study of siderite orebodies from different localities of the southern alps northern italy siderite occurs as veins cutting the variscan basement and the overlying lower permian volcano sedimentary cover collio fm and as both veins and conformable stratabound orebodies in the upper permian verrucano lombardo and bellerophon fms and lower triassic servino and werfen fms sedimentary sequences of the lombardian and the venetian alps all types of deposits show similar major and rare earth ree element patterns suggesting a common iron mineralizing event the compositions of coexisting siderite fe rich dolomite and calcite suggest formation from hydrothermal fluids at relatively high temperature conditions 250 c geochemical modelling supported by ree analyses and by literature and new 1 3 c and 18 o isotopic data suggests that fluids responsible for the formation of siderite in the variscan basement and in the overlying lower permian cover were derived from dominant fresh water which leached fe and c from volcanic rocks mainly rhyolites rhyodacites and organic carbon bearing continental sediments on the basis of u th pb microchemical dating of uraninite associated with siderite in the val vedello and novazza deposits lombardian alps the onset of hydrothermalism is constrained to 275 13 ma early mid permian i e it was virtually contemporaneous to the plutonism and the volcanic sedimentary cycle reported in the same area orobic basin the youngest iron mineralizing event is represented by siderite veins and conformable orebodies hosted in lower triassic shallow marine carbonatic successions in this case the siderite forming fluids contained a seawater component interacted with the underlying permian successions and eventually replaced the marine carbonates at temperatures of 250 c the absence of siderite in younger rocks suggests an early triassic upper limit for the iron pulse in the southern alps which would thus predate the middle triassic magmatism based on the overlap between hydrothermalism extensional tectonics and in part magmatism the genesis of siderite in the southern alps may be related to plutonic activity and or magmatic underplating occurring since the permian in a geodynamic scenario preluding the opening of the neo tethys

large scale thin skinned thrusting in the southern alps kinematic models the tectonics of the southern alps are dominated by thrusting on extensive ramp flat systems and by folding some of which is ramp folding basement slivers are involved that frontally are not thicker than 5 km the most unequivocal section is that of the grigna mountains east of lake como for which kinematic modeling based on material balance considerations results in a shortening of 40 km it is separated from the grona section in the west and the valtorta section in the east by probably pre existing transverse zones that cut through the important decollement horizons and define blocks of different depths to basement local tectonics across these transverse zones change abruptly while over all shortening remains constant in particular both east and west of the grigna section basement ramp folds were wedged into the very incompetent raibl beds provoking back thrusting of the thick hauptdolomit and higher sediments with the substitution of the original cover of the frontal limb of the basement fold this new kinematic interpretation is compatible with the information facilitates the construction of balanced sections and is required for lateral constancy of shortening

economic potential of the rooiberg group volcanic rocks in the floor and roof of the bushveld complex volcanic rocks of the rooiberg group are preserved in the floor and roof of the mafic rustenburg layered suite of the bushveld complex field and geochemical characteristics of these volcanic rocks imply that they are genetically related to the rustenburg layered suite four major ore forming events are identified in the rooiberg group the first phase was accompanied by volcanic hosted fault controlled hydrothermal copper mineralisation which is found in the lowermost portion of the rooiberg group underlying the rustenburg layered suite this type of mineralisation is tentatively linked to initial rustenburg layered suite intrusions stratabound arsenic mineralisation that possibly formed in response to contact metamorphism characterises the second phase and occurred after extrusion of the damwal formation possibly due to shallow granophyric intrusion the third mineralising event occurred in response to contact metamorphism during the final stages of the rustenburg layered suite where especially pb and zn were introduced into the felsite roof rocks this type of mineralisation affected the majority of the rooiberg group but is most pronounced towards the contact with the rustenburg layered suite the fourth phase is restricted to the rooiberg group in the nylstroom area and is linked to the granite intrusions of the lebowa granite suite from which sn and f were introduced into the uppermost felsite succession mineralisation in the rooiberg group appears to be controlled by the character and intrusion level of the associated bushveld magmas different styles of mineralisation in rooiberg group volcanic rocks are encountered at various stratigraphic levels major primary volcanogenic ore deposits appear to be absent

late pleistocene and holocene depositional environments and paleoceanography of the barents sea evidence from seismic and biostratigraphic data abstract on the basis of seismic lithological and biostratigraphic data from the barents sea shelf a spatial correlation of the glacial glaciomarine and marine landforms and deposits is established the stratigraphic boundaries are established on the basis of biostratigraphic and lithostratigraphic data and correspond to the boundaries of seismostratigraphic units thus it is possible to trace reflectors as time lines during the late pleistocene and holocene the barents sea existed as a marine basin in which depositional environments changed from marine mikulino eem interglacial to glaciomarine wurm glaciation and back to marine holocene variations in intensification of the atlantic current seem to be the most significant paleoenvironmental factor in the pleistocene and holocene history of the barents sea the important event during the holocene history of the sea is the period of hydrobiological or marine optimum characterized by high productivity and increase in surface and bottom water temperatures this interval corresponds to the end of the atlantic stage and the beginning of the subboreal stage whose range in the barents sea is estimated as 5 7 3 7 ka bp there is good accordance with data obtained from other arctic eurasian seas

petrological insights into shifts in eruptive styles at volcan llaima chile tephra and lava pairs from two summit eruptions ad 2008 and 1957 and a flank fissure eruption ad 1850 are compared in terms of textures phenocryst contents and mineral zoning patterns to shed light on processes responsible for the shifts in eruption style during typical eruptive episodes at volcan llaima andean southernvolcanic zone chile the mineralogy and whole rock com positions of tephra and lavas are similar within eruptive episodes suggesting a common magma reservoir for strombolian paroxysms and lava effusion the zoning profiles and textures of plagioclase record successive and discrete intrusions of volatile rich mafic magma accompanied by mixing of these recharge magmas with the resident basaltic andesitic crystal mushes that are commonly present at shallow levels in the llaima system each recharge event destabil izes the plagioclase in equilibrium with the resident crystal mush melt and stabilizes relatively an rich plagioclase as is recorded by the numerous resorption zones lavas typically have 15 20 vol more phenocrysts than the tephra differences in plagioclase and olivine textures and zoning combined with different phenocryst contents indicate that a greater volume fraction of recharge magma is present in the explosively erupted magma than in subsequent effu sively erupted magma we propose that strombolian paroxysms at volcan llaima are triggered by interactions with large volume frac tions of recharge magma which decrease the bulk viscosity and in crease the volatile contents of the erupted magmas leading to the conditions required for the fragmentation of basaltic andesite lava effusion ensues from reduced interactions with the recharge magma after it has partially degassed and crystallized thereby impeding rapid ascent this process could be operating at other steady state basaltic volcanoes wherein shallow reservoirs are periodically re filled by fresh volatile rich magmas

dynamics of co2 driven lake eruptions on 21 august 1986 a massive release of carbon dioxide from lake nyos in cameroon killed about 1 700 people a similar event occurred on 15 august 1984 at lake monoun also in cameroon it was suggested1 5 that the co2 released was initially dissolved in the hypolimnion dense lower layer of the lake and was released by eruptive outgassing because of its violence the nyos outburst was at first thought6 to have been volcanic but undisturbed sediments and other evidence indicate that no large volcanic eruption occurred7 9 recent experiments10 11 have shown that decompression of co2 saturated water is able to power explosive eruptions here i analyse the dynamics of co2 driven lake water eruptions by deriving an equation of state for gas liquid mixtures and using it to integrate the bernoulli equation which describes the dynamics of the bubbly flow i find that under certain conditions these eruptions can be violent the lake surface exit velocity of an initially gas saturated water parcel may reach 89m s 1 for lake nyos and 51m s 1 for lake monoun the dynamics are similar to those of water driven volcanic eruptions which are also powered by gas exsolution from a liquid

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes