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

magmatism as a response to exhumation of the priest river complex northern idaho constraints from zircon u pb geochronology and hf isotopes abstract zircon and monazite u pb geochronology and zircon hf isotopes place constraints on the temporal and source relationships between crustal anatexis magmatism and exhumation of the priest river metamorphic core complex northern idaho granitoids that intruded the migmatitic pelitic hauser lake gneiss include the

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

turbulent bubble plumes and co2 driven lake eruptions abstract we examine the motion of turbulent bubble plumes within lakes containing large quantities of dissolved co2 such as lake nyos cameroon first we describe some new laboratory experiments in which we examine the dynamics of turbulent bubbles plumes produced by electrolysis in an aqueous solution these experiments were analysed to determine the entrainment rate into the plume using the experimental results we then develop a model of the motion of a bubble plume through a co2 rich lake the model identifies that for a sufficient amount of dissolved co2 in the lake or a sufficient flux of co2 at the base of the lake a turbulent bubble plume can rise through the lake and erupt at the surface the model predicts that owing to the rapid entrainment of ambient fluid the surface flux of co2 may be 104 105 times greater than that at the base of the lake we also show that the return flow in the lake acts to decrease the co2 content at all depths as the co2 is erupted at the surface and that this eventually leads to termination of the activity the model provides the first quantitative analysis that co2 saturated lakes can overturn convectively and lead to rapid degassing events such as occurred at lake nyos in cameroon in 1986

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

submersible study of mud volcanoes seaward of the barbados accretionary wedge sedimentology structure and rheology abstract in 1992 the nautile went to a mud volcano field located east of the barbados accretionary wedge near 13 50n using nannofossil analysis on cores we determined the sedimentation rate and provided a new estimation of the age of the mud volcanoes 750 000 years for the oldest one six structures have been explored with the submersible nautile and manifestations of fluid venting chimneys carbonate cementation and chemosynthetic communities were observed on all sedimentological analysis identifies two sources of diapiric mud most mud volcanoes expel mud containing late miocene to quaternary faunae that have the same composition as sediments drilled above the barbados wedge decollement one volcano also contains older oligocene taxa with a mud composition corresponding to the sedimentary sequence below the decollement we use diving observations to map the fine scale morphology the distribution of chemosynthetic fauna and define two end member types of structures mud pies flat topped mud volcanoes and conical mounds mud pies atalante and cyclops are characterised by the presence of a lake of highporosity mud 70 to 75 in their central parts chemosynthetic benthic communities calyptogena colonies and sponge bushes are concentrated in the outer parts contrasting morphologies of the two mud pies indicate different stages of activity cyclops is growing whereas atalante is collapsing expulsion of water and methane occurs mostly through the mud lake and may be stronger during the collapse phase on conical mounds there are no mud lakes fluid venting concentrates near the summit and occurs through carbonate cemented chimneys which form within the sediment viscosity measurements have been carried out on mud samples from the two mud pies and one conical mound all mud samples have a plastic fluid behaviour the plastic threshold decreases with porosity and thixotropy is observed for a porosity of more than 70 an analogue experiment shows that for this thixotropic mud shearing in the feeding conduit liquefies the mud which then spreads to form a mud pie conical mounds form when the mud remains plastic we show that the dissociation of methane hydrate is the cause of the high porosity in mud pies and confirm that these structures are a consequence of large scale dissociation of methane hydrate at the base of its stability field dissociation of hydrates before and during ascent is only slightly contributing to the pore fluid in conical mounds but solid hydrates still present in the mud may contribute to its buoyancy

water and gas chemistry of lake nyos and its bearing on the eruptive process abstract the isotopic and chemical composition of water samples collected from lake nyos some two and eight weeks after the eruption of august 21 1986 point to the existence of three distinct mixing regimes involving three water components an essentially homogeneous unmixed body of water at depths 100 m overlain by water increasingly affected by surface evaporation and a 5 10 m layer containing recent but pre eruption rain water the cationic constituents na k mg ca mn fe of the lake water correspond to the dissolution of around 0 1 g of local rock the waters are close to saturation with respect to siderite the composition of the gas dissolved in the deep lake waters 0 65 b w of co2 pco2 4 4b corresponds in mmol mol 1 to 996 co2 2 0 ch4 2 0 n2 0 05 ar 0 004 he 0 0002 h2 0 0001 ne co 2 13 c 3 4 and of he rair 5 5 suggest deep magmatic origins the 13c and 2h content of ch4 organic sedimentary origin the presence of aromatic hydrocarbons indicates very high temperatures of hydrocarbon formation exsolution of gas will first lead to the precipitation of siderite then iron hydroxide the chemistry of the lake waters points to a loss of some 240 000 t of co2 from the upper 100 m of the lake their isotopic composition is consistent with the assumption that the eruption was triggered by the accumulation of cold rain waters at the lake surface prior to the eruption inducing partial convective overturn there is no need to invoke addition of chemical or isotopic constituents from deeper levels during the eruption

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

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

mechanisms of the nyos carbon dioxide disaster and of so called phreatic steam eruptions abstract during the night of august 21 1986 a huge volume of concentrated co 2 was emitted by the crater maar of nyos cameroon it killed more than 1700 people and all animal life as far as 14 km away two hypotheses have been put forward to account for this disaster the chronologically first one imputes it to have been a phreatic eruption exceptionally co 2 rich as had been the case in february 1979 on the dieng plateau in central java indonesia where the erupting crater was lake less the second one claims a limnic origin for the co 2 release through an overturn of the 220 m deep lake nyos the hypolimnium of which was supposed to be oversaturated by dissolved gas of volcanic origin the present paper points to six observed facts for which the eruptive hypothesis easily accounts and which the authors of the limnic one do ignore

mechanism of instantaneous coal outbursts thousands of mine workers die every year from mining accidents and instantaneous coal outbursts in underground coal mines are one of the major killers various models for these outbursts have been proposed but the precise mechanism is still unknown we hypothesize that the mechanism of coal outbursts is similar to magma fragmentation during explosive volcanic eruptions i e it is caused by high gas pressure inside coal but low ambient pressure on it breaking coal into pieces and releasing the high pressure gas in a shock wave hence coal outbursts may be regarded as another type of gas driven eruption in addition to explosive volcanic lake and possible ocean eruptions we verify the hypothesis by experiments using a shock tube apparatus knowing the mechanism of coal outbursts is the first step in developing prediction and mitigation measures the new concept of gas driven solid eruption is also important to a better understanding of salt gas outbursts rock gas outbursts and mud volcano eruptions

lithospheric flexure and gravity spreading of olympus mons volcano mars the structural architecture of large volcanoes is governed substantially by gravity driven deformation that is manifest as distinct processes such as basement flexure or volcanic spreading temporal effects and the mutual interplay of these processes have been investigated only to a limited extent and so we present novel numerical models of the time dependent deformation associated with them the models simulate the combined effects of lithospheric flexure and volcanic spreading during growth increments of an elastoplastic volcanic cone different spreading scenarios are considered by a variable coupling decoupling behavior at the interface between volcano and basement we apply our models to olympus mons on mars which is characterized by upper to middle flank terraces on the shield is encircled by a basal scarp that has an average slope of 30 and is surrounded by distant deposits that resemble large scale slumping features on earth our results are consistent with the interpretation that terraces on olympus mons flanks form by thrust faulting that results from lithospheric flexure the presence and expression of terraces depend on the coupling of volcano and basement on the time of volcano growth relative to mantle relaxation and on the cohesion of the edifice the encircling scarp may be related to a very low friction detachment at the edifice base which leads to a normal fault regime on the lowermost flanks with time and volcano growth predicted stress and faulting regimes migrate only slightly indicating that the structural architecture of volcanoes is largely set in the very early stages of formation

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

methane driven oceanic eruptions and mass extinctions focusing on the permian triassic boundary ca 251 ma i explore the possibility that mass extinction can be caused by an extremely fast explosive release of dissolved methane and other dissolved gases such as carbon dioxide and hydrogen sulfide that accumulated in the oceanic water masses prone to stagnation and anoxia e g in silled basins the mechanism of the explosive release is the same as in the lake nyos disaster of 1986 i e a water column eruption caused by the interplay of buoyancy forces and exsolution of dissolved gas the eruption brings to the surface deep anoxic waters that cause extinctions in the marine realm terrestrial extinctions are caused by explosions and conflagrations that follow the massive release of methane the air methane mixture is explosive at methane concentrations between 5 and 15 and by the eruption triggered floods this scenario accounts well for the available data and may be relevant to other phenomena

a model of overturn of co2 laden lakes triggered by bottom mixing we develop a model for the ascent of a discrete cloud of mixed water from the base of a lake which is saturated in co2 at the lake bed and which becomes progressively under saturated with height above the lake bed we show that for a given co2 profile there is a critical size of cloud which can ascend to the lake surface and that smaller clouds only rise to a finite height within the lake and then intrude at that level the model provides a simplified picture of how disturbances which mix the water in the lower few meters of the lake may lead to release of co2 at the lake surface through the buoyant ascent of discrete parcels of mixed fluid this provides a possible rationalisation of the potential for co2 driven lake overturn to be triggered by a landslide or the lake bottom turbulence associated with a wind driven seiche we consider the relevance of the model to historic eruptions of lake nyos 1986 and lake monoun 1984 in cameroon

liquid carbon dioxide of magmatic origin and its role in volcanic eruptions natural liquid carbon dioxide is produced commercially from a 2 5 km deep well near the 4 500 yr old maar volcano mount gambier south australia the carbon dioxide has accumulated in a dome that is located on the extension of a linear chain of volcanic activity a magmatic origin for the fluid is suggested by the geological setting 13cpdb of 4 0 for the co2 where pdb represents the carbon isotope standard and a relatively high 3he component of the contained helium and high 3he c ratio 6 4 x 10 10 the 3he 4he and he ne ratios are 3 0 and 1 370 times those of air respectively the co2 as collected at the earth s surface at 29 5 c and 75 bar expands more than 300 fold to form a gas at 1 atm and 22 c we suggest that liquid co2 or high density co2 fluid the critical point is 31 1 c 73 9 bar of volcanic origin that expands explosively from shallow levels in the earth s crust may be a major contributor to phreatic volcanic eruptions and maar formation less violent release of magmatic co2 into crater lakes may cause gas bursts with equally disastrous consequences such as occurred at lake nyos cameroon in august 1986

the evolution of thermal structure and water chemistry in lake nyos abstract we collected a time series of physical and chemical data to gain a better understanding of the dynamics of lake nyos measurements of water and gas chemistry and temperature made during january march and may 1987 are compared to data taken in september 1986 just after the initial co 2 gas release there is no pattern of change in overall heat content of the lake although heat input to bottom waters 185 208 m has occurred at a rate of 1600 mw m 2 this increase in heat content translates to a change from 23 38 to 24 12 c at 200 m and can be explained by geothermal heat flow and addition of thermal spring water concentrations of ca 2 mg 2 na k fe 2 and alkalinity have increased only in bottom waters in situ lake processes such as sulfate and iron reduction are unable to account for the changes in alkalinity observed chemical changes are consistent with a scenario where slightly thermal soda water is being input to the bottom of the lake measurements of p co 2 at depth ranged from 18 to 28 of saturation and exhibited horizontal variability overall recharge of co 2 in bottom waters is negligible mainly because of increasing ion concentrations in bottom water total stability of the water column increased 33 from 48 800 j m 2 in september 1986 to 64 700 j m 2 in may 1987 as long as co 2 concentrations remain the same this level of stability is higher than could be disrupted by common limnologic or meteorologic processes there is thermal and chemical evidence that a buildup of dissolved iron and co 2 in bottom waters must have preceded the august 1986 gas release in addition a survey of all crater lakes in cameroon indicates that only lakes nyos and monoun contain high concentrations of dissolved iron and co 2 thus there is a low probability of any other cameroonian lake releasing a substantial volume of co 2

convective crystal dissolution the effect of free and forced convection on crystal dissolution is examined both theoretically and experimentally well established relationships for heat and mass transfer are applied to obtain approximate expressions for the dissolution velocity and the associated thickness of the compositional boundary layer these expressions are found to be in good agreement with experimental observations of the dissolution of quartz crystals in basalt and nacl crystal in water when applied to light felsic crystals in basaltic magmas the expressions predict that forced convection will produce a boundary layer thickness of about 100 m and a dissolution velocity of order 10 6 cm s 1 these velocities are too slow for xenocrysts to be dissolved significantly during magma ascent in dykes but are sufficient for cm size crystals to dissolve in the interior of a convecting magma chamber larger crystals are likely to accumulate at the chamber s roof where free convection is predicted to dissolve them at velocities of order 10 7 cm s 1 in an appendix the dissolution of the chamber s walls is also considered and a velocity of order 10 8cm s 1 is predicted

laboratory simulations of sustained volcanic eruptions many violent eruptions are driven by rapid exsolution of dissolved volatiles within liquid magma the accelerating two phase mixture emerges at the vent as a sustained quasi steady discharge lasting for periods from hours to days refs 1 2 the initial growthin discharge rate commonly observed subsequent fluctuations and discrete pulses and shocks remain largely unexplained we have simulated volcanic conduit flows by producing sustained quasi steady explosions in a liquid undergoing rapid exsolution of a gas this was done by rapidly decompressing large volumes of co 2 saturated water the results reveal fluctuations in discharge rate that reflect heterogeneities in the two phase mixture that form spontaneously as a consequence of the size and geometry of the experimental system an initial transient with a growing discharge rate is observed in experiments in which material is erupted from a spherical flask up a narrow neck that mimics the magma chamber conduit assembly of volcanic systems the fragmentation region propagates down the neck during the initial transient until it reaches a stable position at the top of the flask at which point a quasi steady discharge ensues

gas buildup in lake nyos cameroon the recharge process and its consequences the gases dissolved in lake nyos cameroon were quantified recently december 1989 and september 1990 by two independent techniques in situ measurements using a newly designed probe and laboratory analyses of samples collected in pre evacuated stainless steel cylinders the highest concentrations of co2 and ch4 were 0 30 mol kg and 1 7 mmol kg respectively measured in cylinders collected 1 m above lake bottom probe measurements of in situ gas pressure at three different stations showed that horizontal variations in total dissolved gas were negligible total dissolved gas pressure near the lake bottom is 1 06 mpa 10 5 atm 50 as high as the hydrostatic pressure of 2 1 mpa 21 atm comparing the co2 profile constructed from the 1990 data to one obtained in may 1987 shows that co2 concentrations have increased at depths to below 150 m based on these profiles the average rate of co2 input to bottom waters was 2 6 108 mol a increased deep water temperatures require an average heat flow of 0 32 mw into the hypolimnion over the same time period the transport rates of co2 heat and major ions into the hypolimnion suggest that a low temperature reservoir of free co2 exists a short distance below lake bottom and that convective cycling of lake water through the sediments is involved in transporting the co2 into the lake from the underlying diatreme increased ch4 concentrations at all depths below the oxycline and a high14c content 41 modern in the ch4 4 m above lake bottom show that much of the ch4 is biologically produced within the lake the ch4 production rate may vary with time but if the co2 recharge rate remains constant co2 saturation of the entire hypolimnion below 50 m depth would require 140a given present day concentrations

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

satellite monitoring of the vertical temperature profile of lake nyos cameroon abstract the present contribution to lake nyos studies which have been carried out since 1987 by a team of french geophysicists working in close cooperation with the institut de recherches geologiques et minieres irgm of cameroon involves a continuous long duration remote monitoring of the temperature distribution in the depth of the lake the system which was developed for that purpose essentially includes 1 a vertical chain of temperature probes lifted by an anchored buoy called nyossonde and 2 an associated telemetry relayed by the argos transponder on board the noaa meteorological satellites the telemetered data are collected processed and archived both in france lannion toulouse garchy and cameroun yaounde even though the upper part of the chain was damaged the lower part is still in operation analysis of the telemetered data and comparison with other measurements confirm that the presently described monitoring system is well suited for installation in crater lakes

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

the anecdotal evidence did it help or hinder investigation of the lake nyos gas disaster abstract in the aftermath of the lake nyos disaster it was widely reported that a smell af bad eggs or gunpowder was associated with the cloud of toxic gas in general these reports have been accepted at face value by scientists working on the disaster and used with varying degrees of emphasis to support favoured hypotheses six possible explanations for the reported smell are considered in this paper and three of them are either rejected or regarded as very unlikely 1 1 volcanic gas from beneath the lake very unlikely 2 2 hydrogen sulphide exolved from the lake water rejected 3 3 high concentrations of carbon dioxide causing olfactory hallucinations rejected 4 4 an illusion reflecting the expectation of some of those who questioned the survivors and of stories which subsequently started to circulate most likely 5 5 an illusion reflecting an association between death and the smell of gunpowder in the culture of some of the peoples of the area a possible contributary factor 6 6 confusion between the smell of gas and the taste of lake water in the toxic cloud a probable contributing factor my general conclusion is that an over reliance on anecdotal evidence has seriously hindered investigation of the lake nyos disaster and will continue to do so if hypotheses which rely heavily on such evidence are taken too seriously

extreme efficiency of mud volcanism in dewatering accretionary prisms drilling results from two mud volcanoes on the mediterranean ridge accretionary complex as well as bottom sampling and the wealth of geophysical data acquired recently have provided fundamental knowledge of the 3d geometry of mud extrusions mud volcanism is generally related to buoyancy density inversion and is triggered by the collision of the african and eurasian blocks forcing undercompacted clayey sediments to extrude along faults in the central and hinterlandward parts of the prism volumetric estimates of extruded mud in several well studied areas were based on pre stack depth migrated seismic profiles across the entire up to 150 km wide prism the resulting volumes of mud were combined with ages from mud dome drilling so that rates of mud extrusion were obtained subtracting the solid rock mass from the bulk mud volume using physical property data fluid flux as a function of mud volcanism alone has been quantified for the first time the volume of fluid extruding with the mud is found to be variable but reaches up to 15 km3 fluid per km trench length and ma along cross sections with abundant mud volcanoes such large fluid quantities in a region some 50 150 km behind the deformation front exceed estimates from those elsewhere where undoubtedly the majority of the interstitial fluid is lost due to compaction such fluids near the backstop are likely to result predominantly from mineral dehydration and diagenetic reactions at depth and consequently provide a window to understand deeper processes along the deep decollement more importantly the enormous rates with which such fluids and liquified mud escape along the out of sequence faults alter fluid budget calculations in subduction zones drastically

kinetics of convective crystal dissolution and melting with applications to methane hydrate dissolution and dissociation in seawater abstract large quantities of methane hydrate are present in marine sediment when methane hydrate is exposed or released to seawater it dissolves in seawater or dissociates into methane gas and water there was some confusion in the literature about the kinetics of these processes it is critical to realize that dissolution and dissociation are two different processes dissolution is due to instability in the presence of seawater similar to dissolution of nacl in water and is controlled by mass transfer dissociation is due to inherent instability similar to melting of ice with or without water although presence of warm water may increase the dissociation rate dissociation of methane hydrate into gas and water is similar to ice melting and is controlled by heat transfer hence dissolution is relatively slow and dissociation is rapid in this work we extend previous theory on convective crystal dissolution and melting to greater reynolds numbers we carry out laboratory experiments on the dissolution and descent of nacl kcl nabr and kbr in water to verify the applicability of our theory we then apply our models as well as previous ones to estimate methane hydrate dissolution and dissociation rates for several cases including dissolution of exposed methane hydrate floor dissolution and dissociation of hydrate as it rises through seawater the results show i convective dissolution rate of exposed hydrate floor is of the order 0 07 m yr ii convective dissolution rate of a rising hydrate crystal is 0 2 0 3 m s and a crystal of 5 mm radius is able to survive the rise through an 1800 m seawater column and iii convective dissociation rate is high and depends on the difference between the ambient water temperature and the equilibrium dissociation temperature of hydrate starting from a depth when hydrate just reaches dissociation instability a hydrate sphere of 5 mm radius would survive only a 47 m water column because hydrate is unstable in the surface ocean and would undergo rapid dissociation only very large hydrate chunks greater than about 0 09 m radius would be able to survive a 530 m surface water column

recent ph and co2 profiles at lakes nyos and monoun cameroon implications for the degassing strategy and its numerical simulation abstract in situ ph profiles are reported for the first time for lakes nyos and monoun the ph profiles were converted to co2 profiles using hco3 profiles calculated from conductivity data recent observations 1993 1996 at lake nyos indicates that co2 still accumulates below 180 m depth at a rate of 125 mmol year 1 at lake monoun the majority of co2 is present below a depth of 60 m only 25 m below the saturation depth consequently a potential danger of gas explosion is high at both lakes and artificial degassing of the lakes should be performed as soon as possible a system for industrial degassing of the lakes is proposed the system based on the self sustained gas lift principle consists of multiple pipes 14 cm in diameter with different intake depths 12 pipes for lake nyos four each at 185 195 and 205 m and three pipes for lake monoun at 70 80 and 90 m the stepped degassing at different depths is intended to keep the maximum stability of the lakes the proposed degassing operation was simulated using the dyresm code for both lakes in 5 years approximately 50 of currently dissolved co2 in lake nyos and 90 in lake monoun will be removed the expected changes in the thermal and chemical structures of the lakes as degassing proceeds will be most easily monitored with a carefully calibrated ctd equipped with a ph sensor the simulation indicates that the discharged degassed water will sink to a level of neutral buoyancy i e to a maximum of 70 m at lake nyos and 35 m at lake monoun there would be no possibility of triggering a gas explosion by this plunge of discharged water because the water present there would have already been replaced by water at lower co2 concentration during the degassing from shallower pipes

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

low sea level emplacement of a very large late pleistocene megaturbidite in the western mediterranean sea large volume turbidites termed megaturbidites or megabeds result from catastrophic slope failures and the associated downslope transport of enormous quantities of sediment from continental margins to the deep sea such large sediment failures can generate tsunamis and in terrains underlain by gas hydrates clathrates may be associated with the release of substantial amounts of the greenhouse gas methane it has been proposed that the megaturbidite events may be triggered by seismic activity or may result from gas hydrate release itself caused by a lowering of hydrostatic pressure on clathrates as a result of low sea level previous conclusions on the significance of sea level change however have been conditional because of the lack of absolute times of turbidite emplacement here we use accelerator mass spectrometry radiocarbon dating in five widely spaced cores to constrain the date of emplacement of a large volume 500 km3 bed in the balearic basin of the western mediterranean this turbidite is exceptional in its magnitude and represents the main sedimentation event in the balearic basin over the past 100 kyr our data provide an estimate of 22 000 calendar years before present for emplacement of the megabed a time when sea level stood at its lowest level during the last glacial maximum the coincidence of these dates is consistent with emplacement due to clathrate destabilization caused by low sea level although other triggering mechanisms such as seismic shock cannot be ruled out