the 2005 eruption of sierra negra volcano galapagos ecuador sierra negra volcano began erupting on 22 october 2005 after a repose of 26 years a plume of ash and steam more than 13 km high accompanied the initial phase of the eruption and was quickly followed by a 2 km long curtain of lava fountains the eruptive fissure opened inside the north rim of the caldera on the opposite side of the caldera from an active fault system that experienced an mb 4 6 earthquake and 84 cm of uplift on 16 april 2005 the main products of the eruption were an a a flow that ponded in the caldera and clastigenic lavas that flowed down the north flank the a a flow grew in an unusual way once it had established most of its aerial extent the interior of the flow was fed via a perched lava pond causing inflation of the a a this pressurized fluid interior then fed pahoehoe breakouts along the margins of the flow many of which were subsequently overridden by a a as the crust slowly spread from the center of the pond and tumbled over the pahoehoe the curtain of lava fountains coalesced with time and by day 4 only one vent was erupting the effusion rate slowed from day 7 until the eruption s end two days later on 30 october although the caldera floor had inflated by 5 m since 1992 and the rate of inflation had accelerated since 2003 there was no transient deformation in the hours or days before the eruption during the 8 days of the eruption gps and insar data show that the caldera floor deflated 5 m and the volcano contracted horizontally 6 m the total eruptive volume is estimated as being 150 106 m3 the opening phase tephra is more evolved than the eruptive products that followed the compositional variation of tephra and lava sampled over the course of the eruption is attributed to eruption from a zoned sill that lies 2 1 km beneath the caldera floor

volcanic eruption velocities measured with a micro radar a novel technique to quantitatively assess volcanic eruption dynamics is presented we report on measurements of volcanic eruption velocities with a modified micro radar doppler anemometer on stromboli volcano italy the mean vertical eruption velocity recorded during a four day period in late 1996 was around 10 m s which is somewhat on the small side for strombolian eruptions however the activity of stromboli volcano during this period was very weak explaining the relatively small velocities the technique used is much better in resolution than older techniques based on static photos and allows a continuous monitoring of the volcanic activity in addition to the velocity information recorded by the doppler spectrum it also contains information on the density of the ejected material and the size distribution of the particles in the volcanic jet

lava fountain heights at pu u o o kilauea hawaii indicators of amount and variations of exsolved magma volatiles we review the factors determining lava fountain heights in hawaiian style basaltic eruptions such as those occurring during the recent series of eruptive episodes at the pu u o o vent east rift zone of kilauea volcano hawaii numerical solutions to the equations describing the fluid dynamics of such eruptions predict that lava fountain heights which are indicators of the velocity of magmas in vents should be controlled much more strongly by amounts of exsolved volatiles than by any other factors the next most important factor is the width of the conduit system which determines frictional losses and can be characterized by the volume flux of magma the diameter of the surface vent required to accommodate a given discharge i e instantaneous volume rate of eruption is also a function of exsolved magma volatile content but is less dependent on this factor than is the fountain height we simulate fountain heights for typical discharges at pu u o o and find implied exsolved gas contents very close to those determined by other methods the corresponding predicted vent diameters are comparable with and somewhat smaller than the observed diameter of the pu u o o vent the discrepancy is probably a consequence of processes occurring in the lava pond which is present over the vent during eruptions the variation of fountain height with time during eruptive episodes can be used as a measure of changing exsolved magma volatile content which can be related to processes occurring in the subsurface dike system

desert loess versus glacial loess quartz silt formation source areas and sediment pathways in the formation of loess deposits abstract pathways are presented which show the proposed sequence of events involved in the formation of loess deposits both hypothetical deposits and those of central china hungary nigeria and tunisia these pathways illustrate the potential role of and inter relationships between a variety of silt generating mechanisms in the formation of loess using these pathways the existence of desert loess is discussed and it is concluded that this depends on how the terms glacial loess and desert loess are applied if desert loess is taken either to signify nonglacial mechanisms of silt production or to characterise the environment from which aeolian entrainment took place then desert loess is a very real and widely distributed deposit however if the term glacial loess is used to refer to the global climatic regime under which the loess deposit has formed rather than the geomorphic mechanisms responsible for silt generation then desert loess would not be an appropriate term for the classification of loess deposits it is suggested that classifying loess deposits with reference to the global climatic regime under which they accumulated would facilitate a greater understanding of the role of environmental conditions at all stages in the formation of loess deposits

coupled textural and compositional characterization of basaltic scoria insights into the transition from strombolian to fire fountain activity at mount etna italy strombolian and fire fountain activities represent a common expression of explosive basaltic eruptions however the transition between these two eruptive styles and their source mechanisms are still debated we use textural and compositional studies to characterize pyroclastic material from both the strombolian and hawaiian style fire fountain phases of the january june 2000 etna activity we find that basaltic scoria presents distinctive textural and compositional features that reflect different modes of magma vesiculation and crystallization in the two eruptive regimes overall magma that forms strombolian scoria is far more crystallized less vesicular and more evolved indicating strong volatile depletion and longer residence time before being erupted fire fountain scoria indicates a fast rising magma with evidence of moderate syneruptive volatile exsolution the new textural and compositional data set is integrated with previous volcanological and geophysical investigations to provide further insights into the dynamics of fire fountains and to frame the transition from strombolian explosions to fire fountain activity into a model that may apply to future eruptions at mount etna as well as other active basaltic volcanoes

video monitoring reveals pulsating vents and propagation path of fissure eruption during the march 2011 pu u ō ō eruption kilauea volcano abstract lava fountains are a common eruptive feature of basaltic volcanoes many lava fountains result from fissure eruptions and are associated with the alignment of active vents and rising gas bubbles in the conduit visual reports suggest that lava fountain pulses may occur in chorus at adjacent vents the mechanisms behind such a chorus of lava fountains and the underlying processes are however not fully understood the march 2011 eruption at pu u kilauea volcano was an exceptional fissure eruption that was well monitored and could be closely approached by field geologists the fissure eruption occurred along groups of individual vents aligned above the feeding dyke we investigate video data acquired during the early stages of the eruption to measure the height width and velocity of the ejecta leaving eight vents using a sobel edge detection algorithm the activity level of the lava fountains at the vents was determined revealing a similarity in the eruption height and frequency based on this lava fountain time series we estimate the direction and degree of correlation between the different vents we find that the height and velocity of the eruptions display a small but systematic shift in time along the vents indicating a lateral migration of lava fountaining at a rate of 11 m s from w to e this finding is in agreement with a propagation model of a pressure wave originating at the kilauea volcano and propagating through the dyke at 10 m s from w to e based on this approach from videos only 30 s long we are able to obtain indirect constraints on the physical dyke parameters with important implications for lateral magma flow processes at depth this work shows that the recording and analysis of video data provide important constraints on the mechanisms of lava fountain pulses even though the video sequence is short it allows for the confirmation of the magma propagation direction and a first order estimation of the dyke dimensions

waves of bubbles in basaltic magmas and lavas initially homogeneous suspensions of bubbles in basaltic magmas and lava flows may become unstable and form rising waves or layers of bubbles we derive a set of model equations for the two phase bubble liquid system and present the results of a linear stability analysis and numerical simulations periodic vesicle layers are preserved in columbia liver flows with a spacing of 1 m the prediction of the stability analysis combined with a simple model for solidification of the lava suggests that vesicle layers may represent waves of bubbles formed within the flow the spacing of layers is determined by a balance between the growth of bubbles and hydrodynamic self diffusion vesicular layers preserved in columbia liver flows may thus form by hydrodynamic processes and do not require the repeated injection of fresh volatile rich magma or a periodic nucleation of bubbles waves of bubbles may also develop in magma chambers and conduits and could play a role in eruption dynamics

eruptive processes leading to the most explosive lava fountain at etna volcano the 23 november 2013 episode the 23 november 2013 lava fountain at etna volcano was the most explosive of the last 44 episodes that have occurred at etna in 2011 2013 we infer the total magma volume erupted by thermal images analysis and show that it was characterized by a very high time averaged discharge rate tadr of 360 m3 s 1 having erupted 1 6 106 m3 of dense rock equivalent magma volume in just 45 min which is more than 3 times the tadr observed during previous episodes two borehole dilatometers confirmed the eruption dynamics inferred from the thermal images when compared to the other lava fountains this episode can be considered as the explosive end member however the erupted volume was still comparable to the other lava fountain events we interpret that the 23 november explosive end member event was caused by more primitive and gas rich magma entering the system as demonstrated by the exceptional height reached by the lava fountain

formation of bedding parallel fibrous calcite veins in laminated source rocks of the eocene dongying depression a growth model based on petrographic observations abstract bedding parallel fibrous calcite veins commonly referred to as beefs are widely developed within eocene lacustrine laminated organic rich source rocks in the dongying depression of bohai bay basin east china understanding the formation of this type vein is essential to elucidate the diagenetic evolution and fluid migration in muddy source rocks this study investigates the mechanism s of growth of bedding parallel veins in hydrocarbon source rocks of the es4 upper and the es3 lower units in the dongying depression based on systematic observations of macro and micro scale features both in veins and their wall rocks combined with x ray diffraction and analyses of geochemical indicators the source rocks are heterogeneous in both composition and structure the beefs mainly occur in laminated rocks consisting of organic rich laminae which occur together with horizontally continuous banded lamalginites and rare carbonate rich laminae overall corresponding to high toc low carbonate contents and low maturity average ro 0 57 most beefs are embedded in the neighboring lamalginites of organic rich laminae with low clay mineral contents the beefs are products of diagenesis accompanying burial and both the initial fracture opening and subsequent dilation represent early stages of hydrocarbon generation and expulsion the presence of bedding parallel bituminite veins and the median plane or parting is evidence for horizontally oriented hydrofracturing due to fluid overpressure in turn fluid overpressure reflects the generation and primary migration of hydrocarbon bearing fluids hydrocarbon generation organic matter evolution and clay mineral dehydration illitization of smectite were responsible for the fluid overpressure crystal growth within the beefs was a continuous process with an antitaxial growth direction and there was no growth competition between adjacent fibres these observations indicate that the crystal growth and fracture dilation were synchronous and growth space was limited the force exerted by crystallizing vein fill contributed to the high fluid pressure suggesting that fibrous vein minerals actively promoted further dilation as the veins grew vein dilation accompanied the migration of hydrocarbon bearing fluids evinced by the occurrence of primary hydrocarbon inclusions found in the fibrous calcites therefore the hydrocarbon bearing fluids were present at the time of horizontal fluid flow from the start of fracture opening to the end of the dilation

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

smectite dehydration its relation to structural development and hydrocarbon accumulation in northern gulf of mexico basin a comparison of clay diagenesis data obtained from a study of tertiary shales from the brazos colorado river system of texas the mississippi river system of louisiana and the niger river system of nigeria illustrates significant differences in temperature intervals over which smectite diagenesis occurs the threshold temperature required to initiate diagenesis ranges from about 160 f 71 c in mississippi river sediments to more than 300 f 150 c in the niger delta water expelled from smectite into the pore system of the host shale during the process of diagenesis may migrate out of the shale early or may be totally or partially trapped and released slowly through time in either situation the water can act as a vehicle for hydrocarbon migration p ovided hydrocarbons are present in a form and in sufficient quantities to be transported observations from the northern gulf of mexico basin indicate a close relation between buildup of high fluid pressure and the smectite illite transformation process abnormal pressures exert partial control on the type and quantity of hydrocarbons accumulated because pressure potential determines the direction of fluid flow and overpressuring partly controls the geometry of growth faults and related folds in basins where shale structures are the dominant type formed the depths to which growth faults can penetrate and the angle of dip that these faults assume at depth are largely dependent on fluid pressure in the sedimentary section at the time of faulting dips of some faults in texas have been observed to change abruptly within the interval of smectite diagenesis and some faults formed in the overpressured miocene and younger sections become beddingplane types at depths where the temperature is near that required for thermal generation of petroleum although these faults may be important for fluid redistribution in shallow sandstone shale sections they are a minor factor in moving hydrocarbons out of shale below the faults in much of the texas offshore area fluid movement upward through microfracture systems in the deeply buried overpressured section overlying and extending upward from fault trends in the sub tertiary section is proposed as a mechanism for flushing hydrocarbons from the deeper portion of the northern gulf of mexico basin this flushing process would be enhanced by smectite diagenesis because water derived from smectite that was trapped during basin subsidence would cause the flushing process to continue for longer periods of time and to extend to greater depths than could be attained if only remnants of original pore water were present shale tectonism is also the primary mechanism for structural development in the tertiary section of the niger delta however seismic data indicate that the rate of dip change of seaward dipping listric growth faults is commonly less than that observed in texas where dips as low as 10 15 can occur at depths as shallow as 10 000 15 000 ft 3 048 4 572 m syndepositional faults in nigeria are formed in sandstone shale sections where the clay composition of shale is primarily kaolinite and where little water of smectite diagenesis has been added to the pore system of the host sedimentary section subtle differences in structural styles in the tertiary sections of texas and nigeria are probably the result of differences in clay composition of the shaly sections being deformed

the chinese loess in xifeng i the primary study on magnetostratigraphy of a loess profile in xifeng area gansu province summary 1848 specimens were collected systematically from about 900 horizons in the loess profile of xifeng gansu province china the magnetostratigraphy is established on the basis of the palaeomagnetic results after thermal cleaning usually at 300 c this result has been found to be generally consistent with previous work in luochuan the susceptibility varies regularly with the appearance of loess and palaeosol in the profile and thus could be used as a criterion to classify the loess and palaeosol sequence

location of tremor sources and estimation of lava output using tremor source amplitude on the piton de la fournaise volcano 2 estimation of lava output abstract we propose several relations for estimating the amounts of lava emitted during eruptions of the piton de la fournaise volcano based on the use of tremor source amplitude sources for eruption tremor are located in several frequency bands with a location method based on the use of seismic amplitudes corrected for recording site effects sources are usually found at shallow depth and close to the eruptive vents suggesting that tremor is directly generated by the eruptive activity simultaneously with the location of the tremor sources our program gives the source amplitude of the phenomenon we assume a linear or a quadratic relation between the lava output and the tremor source amplitude both relations are calibrated using data for the march 1998 eruption and tested using the volumes emitted during the july and september 1999 and february 2000 eruptions we found that the 5 10 hz frequency band gives lava output much higher than for lower frequencies suggesting that for that band the tremor generation depends on the eruption site in addition to the lava output or that tremor at those frequencies is not directly caused by the outflow of lava but maybe rather by gas the best estimations are obtained using the quadratic relation for frequencies below 5 hz with an agreement better than 15 with the field observations for the july and september 1999 eruptions and 30 for the february 2000 eruption our results show that the cumulative amplitude of tremor recorded during eruptions of the piton de la fournaise is directly related to the amounts of lava erupted

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

magnetism of chinese loess deposits summary the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene and ascertained a maximum loess age of about 1 2 myr a new collection of nearly 500 samples from a natural outcrop and a borehole section near lochuan lat 35 8 n long 109 2 e shaanxi province has been dated by magnetic stratigraphy thermal cleaning of the natural remanent magnetization nrm removes a strong secondary component of viscous origin along the present geomagnetic field which resides largely in magnetite the characteristic nrm component is due to haematite which is thought to be of chemical origin rhythmical intensity variations of nrm and initial susceptibility depend on the loess lithology and may reflect climatic changes during loess deposition the palaeomagnetic results are consistent between the two sections and yield a clearly defined magnetic polarity zonation the brunhes matuyama boundary and the jaramillo subchron have been positively identified in both outcrops at exactly the same stratigraphic level the olduvai subchron has been found in the borehole section which records the entire loess sequence most probably the formation of chinese loess began shortly after the matuyama gauss polarity transition therefore a late pliocene age of about 2 4 myr is assigned to the oldest loess sediments measured

eruption dynamics of hawaiian style fountains the case study of episode 1 of the kīlauea iki 1959 eruption hawaiian eruptions are characterized by fountains of gas and ejecta sustained for hours to days that reach tens to hundreds of meters in height quantitative analysis of the pyroclastic products from the 1959 eruption of k lauea iki k lauea volcano hawai i provides insights into the processes occurring during typical hawaiian fountaining activity this short lived but powerful eruption contained 17 fountaining episodes and produced a cone and tephra blanket as well as a lava lake that interacted with the vent and fountain during all but the first episode of the eruption the focus of this paper microtextural analysis of hawaiian fountaining products from this opening episode is used to infer vesiculation processes within the fountain and shallow conduit vesicle number densities for all clasts are high 106 107 cm 3 post fragmentation expansion of bubbles within the thermally insulated fountain overprints the pre fragmentation bubble populations leading to a reduction in vesicle number density and increase in mean vesicle size however early quenched rims of some clasts with vesicle number densities approaching 107 cm 3 are probably a valid approximation to magma conditions near fragmentation the extent of clast evolution from low vesicle to melt ratio and corresponding high vesicle number density to higher vesicle to melt ratio and lower vesicle number density corresponds to the length of residence time within the fountain

variations in trace metal and halogen ratios in magmatic gases through an eruptive cycle of the pu u o o vent kilauea hawaii july august 1985 particle and gas samples were obtained before and after eruptive episode 35 in july and august 1985 at the fuming pu u o o vent kilauea volcano hawaii the sampling system employed consisted of a particle filter followed by four sup 7 lioh treated filters to collect acidic gases the filters were analyzed using instrumental neutron activation analysis inaa the results indicate that br cl and re cl ratios do not fluctuate through an eruption cycle but the f cl f br and metal cl ratios in and cd do change through the cycle an inverse relationship between f cl and metal cl was observed the changes are probably due to influxes of relatively undegassed magma during the repose period releasing fume with lower f cl f br and higher metal cl ratios as the magma in the pu u o o conduit gradually degasses either before or several days after an eruptive episode f cl and f br ratios increase and the metal cl ratios decrease one sample collected on july 24 two days before eruptive episode 35 did not follow this general trend this can be explained by a gas pulse from a deeper less degassed portion of magma making its way to the top of the conduit

source rocks in mesozoic cenozoic continental rift basins east china a case from dongying depression bohai bay basin abstract lake basin evolution microscopic and organic geochemistry characteristics are investigated for the paleocene hydrocarbon source rocks of dongying depression bohai bay basin the upper e 2 3 s 4 and the lower e 2 3 s 3 are balanced filled lake basin sediments which show strong climate driven rhythmicity source rocks of these two units have relatively high organic matter content and are dominated by type i kerogen sedimentary and geochemical characteristics indicate there exist persistent lake water stratification and bottom anoxicity during the deposition process by contrast the middle e 2 3 s 3 is an over filled lake deposit dominated by uniform mudstones lacking obvious transgressive regressive cycles it indicates that the lake water lacks stratification and the bottom water is ventilated source rocks of this unit have relatively low organic abundance and are dominated by types ii and iii kerogen thermal evolution studies show that the upper e 2 3 s 4 has a relatively early and multi stage of hydrocarbon generation process and can generate immature oils while the lower e 2 3 s 3 and the middle e 2 3 s 3 have a relatively late and simple hydrocarbon generation process and mainly generate mature oils in addition the persistent increase of eom toc and total hydrocarbons toc indicates that the expelled hydrocarbons from the middle e 2 3 s 3 are in relatively small amounts compared with the other two units the middle e 2 3 s 3 acts as regional caprocks instead of significant source rocks as previously thought the viewpoint will be of great significance in future exploration

interactions between bubbles in magmas and lavas effects of bubble deformation the interactions between two deformable bubbles are studied in order to determine the effects of deformation on bubble dynamics and to determine the limits in which the effects of deformation can be ignored deformation due to hydrodynamic interactions with other bubbles leads to alignment of horizontally offset bubbles and thus an enhanced rate of coalescence bubble alignment may produce spatial inhomogeneities in bubble concentrations in magmas which implies temporal variations in the concentration and size of bubbles in erupting magmas and spatial variations in solidified lavas an approximate quantitative model for the rate of coalescence of deformable bubbles is developed based on a series of experiments the effects of deformation can be ignored if the largest bubbles have radii less than about 5 mm in silicate magmas

radar doppler velocimetry of volcanic eruptions theoretical considerations and quantitative documentation of changes in eruptive behaviour at stromboli volcano italy summary the use of radar doppler velocimetry for the observation of volcanic activity is new we used this method to continuously observe the activity of one vent of stromboli volcano italy from the end of 2000 april until early may during this period we recorded 702 eruptions 132 of which occurred before a strong rain storm passed over the island on april 29 in order to interpret the recorded doppler data we developed a program that simulates different strombolian eruption scenarios for which we then calculate the theoretical doppler spectra comparing our theoretical data with the observed data we are able to show that most of the eruptions are nearly vertical although we did observe only one component of the eruption vector with our doppler radar one of the most interesting features of the data set is a significant change in eruptive behaviour that correlates with the occurrence of the rain storm we find that on average the eruption duration increased by a factor of 2 eruptive velocities were much higher and indirect evidence indicates that the average particle diameter of the erupted material decreased this change may have several causes but the coincidence with the rain storm may be evidence of magma water interaction and feedback on the volcanic activity if the fluid source rain changing the eruptive style is at the surface and in near surface layers then the main control on final eruption dynamics at stromboli volcano must also be in rather shallow regions

a new approach to investigate an eruptive paroxysmal sequence using camera and strainmeter networks lessons from the 3 5 december 2015 activity at etna volcano abstract explosive sequences are quite common at basaltic and andesitic volcanoes worldwide studies aimed at short term forecasting are usually based on seismic and ground deformation measurements which can be used to constrain the source region and quantify the magma volume involved in the eruptive process however during single episodes of explosive sequences integration of camera remote sensing and geophysical data are scant in literature and the total volume of pyroclastic products is not determined in this study we calculate eruption parameters for four powerful lava fountains occurring at the main and oldest mt etna summit crater voragine between 3 and 5 december 2015 these episodes produced impressive eruptive columns and plume clouds causing lapilli and ash fallout to more than 100 km away we analyse these paroxysmal events by integrating the images recorded by a network of monitoring cameras and the signals from three high precision borehole strainmeters from the camera images we calculated the total erupted volume of fluids gas plus pyroclastics inferring amounts from 1 9 10 9 m 3 first event to 0 86 10 9 m 3 third event strain changes recorded during the first and most powerful event were used to constrain the depth of the source the ratios of strain changes recorded at two stations during the four lava fountains were used to constrain the pyroclastic fraction for each eruptive event the results revealed that the explosive sequence was characterized by a decreasing trend of erupted pyroclastics with time going from 41 first event to 13 fourth event of the total erupted pyroclastic volume moreover the volume ratio fluid pyroclastic decreased markedly in the fourth and last event to the best of our knowledge this is the first time ever that erupted volumes of both fluid and pyroclastics have been estimated for an explosive sequence from a monitoring system using permanent cameras and high precision strainmeters during future explosive paroxysmal sequences this new approach might help in monitoring their evolution also to understand when if they are going to finish knowledge of the total gas and pyroclastic fractions erupted during each lava fountain episode would improve our understanding of their processes and eruptive behaviour

introduction to special section on how volcanoes work part 2 the special section on how volcanoes work is a collection of some of the nearly 300 papers presented at the hawaii symposium on how volcanoes work held in hilo in january 1987 tilling 1987a the response of the symposium participants to the invitation to submit their papers for consideration in the special section exceeded expectations in all more than 70 manuscripts were received reviewed and handled following regular jgr editorial procedures part 1 of the special section composed of the papers that were processed and accepted in time to meet the production schedule was published in the december 1987 issue of the journal of geophysical research solid earth and planets tilling 1987a even though part 1 contained only eight papers it nonetheless provided a representative sampling of the multidisciplinary nature of the investigations undertaken to improve our understanding of volcanic systems the papers published in part 1 included ground deformation studies on caldera systems dzurisin and yamashita 1987 mortensen and hopkins 1987 geochemical and observational studies of the lava fountains and of volcanic fume during the 1983 1984 activity of pu u o o in kilauea s east rift zone crowe et al 1987 head and wilson 1987 magmatic crystal stratigraphy and theoretical petrology pearce et al 1987 russell 1987 dynamics of active lava lakes tilling 1987b and seismic evidence for a subcrustal intrusive complex beneath the island of oahu hawaii ten brink and brocher 1987

a detailed geomagnetic record from chinese loess abstract a collection of over 100 individually orientated hand samples was obtained from a 335 m loess section near lanzhou northern china previous studies defined the brunhes matuyama b m boundary and jaramillo normal subchron within the section the position of these magnetic markers led to the suggestion of a basal age for the section of 1 3 ma this disagrees significantly with a date of 2 45 ma for the onset of loess accumulation at lochuan 500 km to the east of lanzhou the present study considers the section in far greater detail and has derived a complex magnetostratigraphy isolating seven normal events within the lower 130 m of the section a simple interpretation of this magnetostratigraphy suggests a basal age for the section in the region of 2 4 ma however the relative chronology of the loess palaeosol sequence although appearing to confirm this basal age has revealed that this simple interpretation of the magnetostratigraphy may not be justified

a plinian treatment of fallout from hawaiian lava fountains a new model is presented which simulates the dispersal and deposition of material from a hawaiian eruption column the model treats the hawaiian column as a coarse grained plinian column and uses a modified version of the wilson and walker wilson l walker g p l 1987 explosive volcanic eruptions vi ejecta dispersal in plinian eruptions the control of eruption conditions and atmospheric properties geophys j r astron soc 89 657 679 plinian pyroclast dispersal model to simulate the fall out of material during a hawaiian eruption the model results are found to be in good agreement with independent estimates of various parameters made for the 1959 kilauea iki eruption of kilauea volcano the close agreement between the model results and these independent estimates shows that dynamically hawaiian eruptions are indistinguishable from plinian eruptions the major differences in the styles and deposits of these two types of eruptions are accounted for by differences in the mass fluxes and gas contents of the erupting magmas and most fundamentally by differences in the grainsize distribution of the erupted clasts plume heights predicted by the model are greater than those found for previous models of hawaiian eruptions this is because previous models did not allow for the progressive fall out of particles from the plume and more importantly made no correction for the velocity disequilibrium between gas and clasts when the grainsize distribution is coarse

age and palaeoclimatic significance of the loess of lanzhou north china extending in a broad arc that abuts the sandy non gobi deserts the loess plateau of northern china1 3 is one of the most massive accumulations of loess in the world the loess sequence is typically characterized by an alternation of silty or sandy loess with more clay rich palaeosols these alternations in conjunction with their enclosed faunas and distinctive mineralogies have been interpreted as reflecting pleistocene glacial interglacial cycles3 8 because it holds implications for the climatic and anthropological history of china9 10 the definition of a reliable chronological framework for loess deposition is of great interest recent palaeomagnetic studies4 5 have indicated that loess deposition in shaanxi province commenced 2 4 myr ago to assess the synchrony of loess accumulation across the loess plateau we have dated a 330 m thick loess sequence near lanzhou gansu province the magnetostrati graphical results reported here indicate that the base of this loess succession dates from 1 3 my r ago this young age in comparison to the shaanxi sequence is attributed to uplift along the northern fringe of the tibetan plateau11 that precluded early pleistocene loess preservation in this mountainous region palaeosols in the basal loess occur on average once every 25 kyr suggesting that climates conducive to soil forming events may have been modulated by orbital precession in the early pleistocene

magma reservoirs and neutral buoyancy zones on venus implications for the formation and evolution of volcanic landforms we examine the production of magma reservoirs and neutral buoyancy zones nbzs on venus and the implications of their development for the formation and evolution of volcanic landforms the high atmospheric pressure on venus reduces volatile exsolution and generally serves to inhibit the formation of nbzs and shallow magma reservoirs for a range of common terrestrial magma volatile contents magma ascending and erupting near or below mean planetary radius mpr should not stall at shallow magma reservoirs such eruptions would be characterized by relatively high total volumes and effusion rates for the same range of volatile contents at 2 km above mpr about half of the cases result in direct ascent of magma to the surface and half in the production of neutral buoyancy zones in general neutral buoyancy zones and shallow magma reservoirs begin to appear as gas content increases and are nominally shallower on venus than on earth for a fixed volatile content nbzs become deeper with increasing elevation over the range of elevations treated here 1 km to 4 4 km depths differ by a factor of 2 4 these analyses reveal several factors that may help to account for the low height of volcanoes on venus larger primary reservoirs cause the wide dispersal of conduits building edifices models of the position of the shallow nbz reservoir during edifice growth show that for earth the magma chamber center remains at a constant depth below the growing edifice summit thus keeping pace with the increasing elevation while on venus the chamber center becomes deeper relative to the summit of the growing edifice because of the major change in atmospheric pressure as a function of altitude therefore neutral buoyancy zones and magma reservoirs on venus will remain in the prevolcano substrate longer and in many cases may not emerge into the edifice at all the lower rate of vertical migration implies that magma reservoirs would tend to stabilize undergo greater lateral growth and become larger on venus than earth the proportion of the available magma going into production of the edifice relative to that intruded into the substrate is smaller on venus than earth large reservoirs would encourage multiple and more widely dispersed source vents and large volumes for individual eruptions in large reservoirs positively buoyant materials are likely to be produced from differentiation substrate remelting and volatile exsolution nonbuoyant materials exsolving volatiles in a shallow reservoir will need higher gas bubble concentrations to produce eruptions than on earth and when this gas enriched melt emerges at the surface it is more likely to retain its bubbles than to undergo explosive disruption due to the high surface atmospheric pressure therefore there is the potential for the production of a range of erupted lavas that have very high gas bubble concentrations leading to anomalous more viscous rheological properties inhibition of disruption of volatile rich magma for both basaltic and more evolved compositions can lead to the production of 1 more bubble rich vesicular flows characterized by higher viscosity and greater thicknesses the venus equivalent of effusions that would have lost much of their volatiles in the fire fountaining process on earth 2 high volume high discharge rate extremely gas rich basaltic effusions that increase viscosity considerably upon surface extrusion and produce domes whose volumes are considerably higher than their dense rock equivalent and 3 more evolved compositions that are gas rich but do not undergo disruption upon effusion and produce domes and flows of high viscosity the venus equivalent of terrestrial ignimbrites on the basis of these analyses we predict that intrusions and dike emplacement should be common particularly around both shallow and deep magma reservoirs and the tops of dikes should be manifested as radial fractures there should be a range of diameters of circular features associated with the presence of both shallow nbz related and deep plumerelated magma reservoirs large volume lava outpourings should be favored at lower elevations and shallow reservoirs and edifices should be more common at intermediate elevations at the highest elevations magma reservoirs are predicted to be large and relatively deep with low associated edifices direct ascent of magma where neutral buoyancy zones are unlikely low elevations and the propensity for relatively larger magma reservoirs on venus when they do form are both factors which will tend to favor high volume eruptions independent of variations in magma temperature or chemistry individual volcanic features should be interpreted in terms of regional geologic setting and the dynamics of elevation changes commonly associated with various scales of mantle processes and magma emplacement in order to assess global crustal growth processes on venus

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

determining paleosol topography using seismic refraction abstract the seismic refraction reversed profiling technique has been used to investigate the topography of the last interglacial soil paleosol s1 within the central chinese loess plateau near xifeng the results suggest an essentially flat lying soil at a depth which varies by only a few meters over an area of more than 10 km2 in addition the results indicate a high velocity layer at 50 60 m depth which is thought to coincide with a layer of carbonate concretions at the base of paleosol s5 the results agree well with the local loess paleosol stratigraphy for this area and indicate that the seismic refraction method is a rapid technique for investigating paleotopography

influence of organic matter on smectite illitization a comparison between red and dark mudstones from the dongying depression china interactions between organic matter om and clay minerals have received considerable attention in previous studies the influence of om on smectite illitization has been analyzed primarily in simulation experiments rather than in diagenetic studies the present study explores the influence of om on smectite illitization during diagenesis thirty red and dark mudstone samples from the dongying depression were analyzed x ray diffraction xrd analyses revealed that the illite percentages in mixed layer illite smectite i s of both types of samples were dispersive above 3100 m and more convergent below this depth the stacking mode of i s in dark mudstones above 3100 m remained primarily at r0 r0 5 ordering with the average number of layers nave dispersively distributed between 2 and 4 5 in red mudstones the i s changed from the r0 to r0 5 mode with the nave increasing from 2 to 5 over this range the smectite illitization in dark mudstones was slower than that in red mudstones below 3100 m the i s stacking mode of dark mudstones changed from r0 5 to r3 ordering with the nave increasing sharply from 4 to 8 in red mudstones the i s displayed r1 5 and r3 ordering with the nave varying between 4 5 and 6 5 over this range the smectite illitization in dark mudstones accelerated rapidly whereas the process in red mudstones was retarded additionally the red mudstone samples contained little om whereas the dark mudstone samples contained abundant total organic carbon 0 17 4 43 thermo xrd near infrared nir as well as mid infrared mir spectroscopy analyses suggested that the om in dark mudstones exhibited a significant transition at 3100 m coincident with the illitization change above 3100 m the smectite illitization in dark mudstones was delayed due to the om pillar effect in the interlayer spaces of smectite below 3100 m the interlayer om became varied and desorbed discharging organic acid this led to the dissolution of smectite structural layers consequently illitization in the dark mudstone was accelerated this study revealed that the existence and occurrence of om could influence the smectite illitization in diagenesis further study on the interactions between om and clay minerals is needed to facilitate our understanding on the mechanism of smectite illitization as well as its geological applications

seismic stratigraphy of chinese loess abstract a loess section near lanzhou china has been investigated using the seismic refraction technique the results show that the method is able to discriminate four distinct seismic boundaries within the section as well as indicating that the loess bedrock contact occurs at a depth of more than 200 m a 30 m deep pit was subsequently dug and revealed that the first two seismic boundaries correspond to soil units sa an intermediate soil within loess unit l1 and s1 the last interglacial soil at the base of l1 these results though preliminary indicate the potential of the technique not only for mapping loess bedrock contacts but also for determining the finer subsurface detail of the loess palaeosol stratigraphy

width change of a planar magma path implication for the evolution and style of volcanic eruptions abstract the width change of a planar path filled with magma is analyzed assuming that the process is controlled by laminar flow of an incompressible viscous magma between movable parallel walls of country rock the analysis shows that the width of a planar path changes at a rate is proportional to the effective opening pressure which is defined as the pressure of the penetrating magma plus the tensile stress component stretching the fluid interface when the opening pressure is a positive constant the fissure widens at an accelerating rate and finally diverges at a critical time constant which depends on the initial size of the fissure and the viscosity of magma as well as on the opening pressure in contrast the fissure gradually narrows under a negative opening pressure this result is applicable to a variety of magmatic processes first the orientation of a volcanic fissure or a dike is such that the tensile stress component is maximized because a fissure with this orientation becomes wider than those at other orientations as it has the minimum value of critical time constant second local irregularities in the geometrical and mechanical conditions of the magma sheet lead to significant variations in fissure width in the widening process this nonuniform increase in width is further exaggerated by mechanical and thermal erosion of the wall rock which makes the irregular surfaces irrecoverable in this manner a planar magma path tends to be split into isolated cylindrical conduits when the magma pressure is reduced and the fissure closes as a whole some actual fissure eruptions such as those at kilauea and izu oshima show evolutionary processes consistent with this prediction another application of the analysis is to explain how the style of a volcanic eruption is determined by the tectonics specifically extensional tectonics which gives a positive opening pressure for any magma pressure allows magma to ascend dispersively along various paths and produces a group of small monogenetic volcanoes in contrast contractional tectonics in which new fissures can be made only for a very high magma pressure concentrates magma into a restricted number of vents and leads to the growth of large polygenetic volcanoes

structural features and genesis of microscopic pores in lacustrine shale in an oil window a case study of the dongying depression the paleogene shale of the dongying depression a continental basin in eastern china is taken as the study subject to examine the microscopic features of lacustrine shale reservoirs in the oil window this study shows that shale pores in this evolutionary stage are present at the micrometer to nanometer scale but fractures commonly have extension distances at the millimeter scale pores and fractures can be divided into three types namely primary pores secondary pores and cracks primary pores commonly have good connectivity at shallow burial depth with the increase of burial depth primary porosity is reduced because of compaction and cementation secondary pores are important in shale including dissolved pores inside grains and at grain edge and dissolution pores inside the hybrid of organic matter om and clay minerals and evaporite minerals including carbonates or sulfates types of cracks were observed bedding fissures dissolution fractures and structural fractures the development of bedding fissures is related to the deposition of shale laminae the formation of dissolution fractures is related to acidic fluids such as organic acids and hydrogen sulfide whereas the formation of structural fractures is jointly controlled by fault development fluid overpressure and lithofacies the pores and fractures in the oil window of lacustrine shale can store and channel oil and gas the hybrid om clay carbonate sulfate and the pores inside are important through the oil window moreover the development of the pores depends not only on hydrocarbon generation but also on the interaction of hydrocarbons and organic acid dissolution this finding has important significance in the accumulation of oil and gas in continental shales

smectite illitization difference of source rocks developed in saline and fresh water environments and its influence on hydrocarbon generation a study from the shahejie formation dongying depression china abstract samples of argillaceous source rocks from three sub members of the shahejie formation es in the dongying depression china were collected to investigate the differences in hydrocarbon generation among the sub members which developed in fresh es32 es33 and saline es41 water environments pyrolysis xrd and thermo xrd analyses were used to compare the characteristics of organic matter om clay minerals and om occurrences total organic carbon and hydrocarbon potential proxies suggest that the samples from es33 were much better than the other two intervals which agrees with previous studies the characteristics of clay minerals suggest that the samples from es41 have the most abundant illite with a maximum illite percentage in mixed layer illite smectite i sm and the best crystallinity of i sm with a main stacking mode of r1 5 however the stacking modes of i sm in es32 and es33 were primarily r0 and r1 respectively and the crystallinity was relatively poor thus the smectite illitization process was faster in es41 than in the other two intervals and a saline environment was a primary cause for the acceleration of the process moreover om occurrence indicates that the samples from es41 had the lowest amount of interlayer om whereas es33 had the largest amount therefore the rapid illitization in es41 caused abundant interlayer om to be desorbed and discharged which in turn caused the amount of residual interlayer om in es41 to be less than that in the other two intervals thus the source rocks of es41 made a more significant contribution to hydrocarbon generation than those of the other two units in conclusion the inconsistent illitization among these intervals was a major cause of the differences in hydrocarbon generation

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

protection of organic matter by mineral matrix in a cenomanian black shale abstract three types of pathways degradation recondensation natural sulphurization and selective preservation are commonly considered for the formation of kerogen dispersed in sedimentary rocks a fourth pathway has been recently put forward however from studies on recent marine sediments the so called sorptive protection mechanism this pathway is based on the adsorption of otherwise labile organic compounds onto minerals thus preventing their diagenetic degradation and promoting their subsequent condensation into kerogen the main results of the present study are derived from a combination of microscopic and pyrolytic methods applied on a cenomanian kerogen they provide i evidence on an ancient material for a crucial role of the mineral matrix both in organic matter om preservation during kerogen formation and in kerogen stability once formed ii indications that the dominant protective process likely involves physical protection by minerals resulting from alternation of organic and clay nanolayers of approximately 100 nm in thickness rather than om adsorption as molecular monolayers and iii observations of the relatively poor stability of an isolated kerogen contrary to the inertness commonly assumed for fossil macromolecular organic matter

europa morphological characteristics of ridges and triple bands from galileo data e4 and e6 and assessment of a linear diapirism model galileo solid state imaging ssi images of europa provide high resolution data on the morphological characteristics of ridges and permit the development of nomenclatural schemes for their description and classification key observations are that ridges 1 are remarkably consistent in their along strike linearity width and height 2 form long linear features in which preexisting structures can sometimes be traced up the outer slopes of the ridges and in other cases appear to be buried 3 contain narrow apical zones of small scale ridge parallel faulting 4 are sometimes flanked by narrow troughs and ridge parallel fractures and 5 often display associated color variations on the basis of the characteristics and associated features of ridges we find that a process in which initial fracturing most plausibly related to tidal deformation of a brittle layer overlying a buoyant ductile substrate leading to linear diapiric upwelling provides a consistent explanation for the observed features in this process the upwelling linear diapir causes flexure bending and faulting of the region marginal to the fracture the deformation and uplift of adjacent plains material and its preexisting structures to form the apical part of the ridge the exposure of the inner walls of the crack and the mass wasting of the inner and outer walls of the ridge to modify but often not completely destroy the preexisting structure of the adjacent plains specifically this mechanism can account for many characteristics of the ridges including their linearity their consistent and regular morphology over their great lateral extent their positive topography the presence of preexisting structure on the outer ridges caused by upbowing of background ridged plains the formation of marginal troughs as diapiric rim synclines the detailed nature of their outer and inner slopes caused largely by faulting and mass wasting processes and their sequential formation with multiple orientations related to tidal deformation processes linear diapirism also provides a possible explanation for color and albedo characteristics related to thermal effects of the upwelling warm ice e g inducing volatile migration and grain size variations as the vast majority of deformation is vertical in this scenario this mechanism minimizes the necessity for complementary compressional deformation required by some other models

an analogue experimental model of depth fluctuations in lava lakes lava lakes consisting of molten degassing lava in summit craters of active basaltic volcanoes sometimes exhibit complex cycles of filling and emptying on time scales of hours to weeks such as recorded at pu u o o in hawaii and oldoinyo lengai in tanzania here we report on a new series of analogue laboratory experiments of two phase flow in a reservoir conduit lava lake system which spontaneously generates oscillations in the depth of liquid within the lake during the recharge phase gas supplied from a subsurface reservoir of degassing magma drives liquid magma up the conduit causing the lake to fill as the magmastatic pressure in the lake increases the upward supply of magma driven by the gas bubbles falls eventually the upflow becomes unstable and liquid drains downwards from the lake driven by the magmastatic pressure of the overlying lake suppressing the ascent of any more bubbles from the chamber at a later stage once the lake has drained sufficiently the descent speed of liquid through the conduit decreases below the ascent speed of the bubbles and the recharge cycle resumes application of a quantitative model of the experiments to the natural system is broadly consistent with field data

effects of smectite on the oil expulsion efficiency of the kreyenhagen shale san joaquin basin california based on hydrous pyrolysis experiments the amount of oil that maturing source rocks expel is expressed as their expulsion efficiency which is usually stated in milligrams of expelled oil per gram of original total organic carbon oil expulsion efficiency can be determined by heating thermally immature source rocks in the presence of liquid water i e hydrous pyrolysis at temperatures between 350 c and 365 c for 72 hr this pyrolysis method generates oil that is compositionally similar to natural crude oil and expels it by processes operative in the subsurface consequently hydrous pyrolysis provides a means to determine oil expulsion efficiencies and the rock properties that influence them smectite in source rocks has previously been considered to promote oil generation and expulsion and is the focus of this hydrous pyrolysis study involving a representative sample of smectite rich source rock from the eocene kreyenhagen shale in the san joaquin basin of california smectite is the major clay mineral 31 wt in this thermally immature sample which contains 9 4 wt total organic carbon toc comprised of type ii kerogen compared to other immature source rocks that lack smectite as their major clay mineral the expulsion efficiency of the kreyenhagen shale was significantly lower the expulsion efficiency of the kreyenhagen whole rock was reduced 88 compared to that of its isolated kerogen this significant reduction is attributed to bitumen impregnating the smectite interlayers in addition to the rock matrix within the interlayers much of the bitumen is converted to pyrobitumen through crosslinking instead of oil through thermal cracking as a result smectite does not promote oil generation but inhibits it bitumen impregnation of the rock matrix and smectite interlayers results in the rock pore system changing from water wet to bitumen wet this change prevents potassium ion transfer and dissolution and precipitation reactions needed for the conversion of smectite to illite as a result illitization only reaches 35 to 40 at 310 c for 72 hr and remains unchanged to 365 c for 72 hr bitumen generation before or during early illitization in these experiments emphasizes the importance of knowing when and to what degree illitization occurs in natural maturation of a smectite rich source rock to determine its expulsion efficiency complete illitization prior to bitumen generation is common for paleozoic source rocks e g woodford shale and retort phosphatic shale member of the phosphoria formation and expulsion efficiencies can be determined on immature samples by hydrous pyrolysis conversely smectite is more common in cenozoic source rocks like the kreyenhagen shale and expulsion efficiencies determined by hydrous pyrolysis need to be made on samples that reflect the level of illitization at or near bitumen generation in the subsurface

deep submarine pyroclastic eruptions theory and predicted landforms and deposits submarine pyroclastic eruptions at depths greater than a few hundred meters are generally considered to be rare or absent because the pressure of the overlying water column is sufficient to suppress juvenile gas exsolution so that magmatic disruption and pyroclastic activity do not occur consideration of detailed models of the ascent and eruption of magma in a range of sea floor environments shows however that significant pyroclastic activity can occur even at depths in excess of 3000 m in order to document and illustrate the full range of submarine eruption styles we model several possible scenarios for the ascent and eruption of magma feeding submarine eruptions 1 no gas exsolution 2 gas exsolution but no magma disruption 3 gas exsolution magma disruption and hawaiian style fountaining 4 volatile content builds up in the magma reservoir leading to hawaiian eruptions resulting from foam collapse 5 magma volatile content insufficient to cause fragmentation normally but low rise speed results in strombolian activity and 6 volatile content builds up in the top of a dike leading to vulcanian eruptions we also examine the role of bulk interaction steam explosivity and contact surface steam explosivity as processes contributing to volcaniclastic formation in these environments we concur with most earlier workers that for magma compositions typical of spreading centers and their vicinities the most likely circumstance is the quiet effusion of magma with minor gas exsolution and the production of somewhat vesicular pillow lavas or sheet flows depending on effusion rate the amounts by which magma would overshoot the vent in these types of eruptions would be insufficient to cause any magma disruption the most likely mechanism of production of pyroclastic deposits in this environment is strombolian activity due to the localized concentration of volatiles in magma that has a low rise rate magmatic gas collects by bubble coalescence and ascends in large isolated bubbles which disrupt the magma surface in the vent producing localized blocks bombs and pyroclastic deposits another possible mode of occurrence of pyroclastic deposits results from vulcanian eruptions these deposits being characterized by the dominance of angular blocks of country rocks deposited in the vicinity of a crater should be easily distinguishable from strombolian and hawaiian eruptions however we stress that a special case of the hawaiian eruption style is likely to occur in the submarine environment if magmatic gas buildup occurs in a magma reservoir by the upward drift of gas bubbles in this case a layer of foam will build up at the top of the reservoir in a sufficient concentration to exceed the volatile content necessary for disruption and hawaiian style activity the deposits and landforms are predicted to be somewhat different from those of a typical primary magmatic volatile induced hawaiian eruption specifically typical pyroclast sizes might be smaller fountain heights may exceed those expected for the purely magmatic hawaiian case cooling of descending pyroclasts would be more efficient leading to different types of proximal deposits and runout distances for density flows would be greater potentially leading to submarine pyroclastic deposits surrounding vents out to distances of tens of meters to a kilometer in addition flows emerging after the evacuation of the foam layer would tend to be very depleted in volatiles and thus extremely poor in vesicles relative to typical flows associated with hawaiian style eruptions in the primary magmatic gas case we examine several cases of reported submarine volcaniclastic deposits found at depths as great as 3000 m and conclude that submarine hawaiian and strombolian eruptions are much more common than previously suspected at mid ocean ridges furthermore the latter stages of development of volcanic edifices seamounts formed in submarine environments are excellent candidates for a wide range of submarine pyroclastic activity due not just to the effects of decreasing water depth but also to 1 the presence of a summit magma reservoir which favors the buildup of magmatic foams enhancing hawaiian style activity and episodic dike emplacement which favors strombolian style eruptions and 2 the common occurrence of alkalic basalts the co2 contents of which favor submarine explosive eruptions at depths greater than tholeiitic basalts these models and predictions can be tested with future sampling and analysis programs and we provide a checklist of key observations to help distinguish among the eruption styles

factors influencing the height of hawaiian lava fountains implications for the use of fountain height as an indicator of magma gas content the heights of lava fountains formed in hawaiian style eruptions are controlled by magma gas content volume flux and the amounts of lava re entrainment and gas bubble coalescence theoretical models of lava fountaining are used to analyse data on lava fountain height variations collected during the 1983 1986 pu u o o vent of kilauea volcano hawaii the results show that the variable fountain heights can be largely explained by the impact of variations in volume flux and amount of lava re entrainment on erupting magmas with a constant gas content of 0 32 wt h2o however the gas content of the magma apparently declined by 0 05 wt during the last 10 episodes of the eruption series and this decline is attributed to more extensive pre eruption degassing due to a shallowing of the sub vent feeder dike it is concluded that variations in lava fountain height cannot be simply interpreted as variations in gas content as has previously been suggested but that fountain height can still be a useful guide to minimum gas contents where sufficient data are available on eruptive volume fluxes and extent of lava entrainment greatly improved estimates can be made of magma gas content from lava fountain height

fluidal clast breccia generated by submarine fire fountaining trooper creek formation queensland australia abstract a distinctive monomictic breccia composed of fluidal and blocky basaltic andesite clasts occurs in a cambro ordovician submarine volcanic succession in northern queensland australia associated with this fluvial clast buccia facies are coherent facies and coarse and fine breccia facies of the same composition the fluidal clast breccia facies is internally massive and 250 m thick varying only in the ratio of fluidal clasts to blocky clasts fluidal clasts range in size from 2 cm to 170 cm and have moderately to highly vesicular cores and thick up to 1 cm non vesicular formerly glassy rims blocky clasts are highly vesicular to non vesicular subaqueous fire fountain breccias are distinguished from subaerial fire fountain breccias by thick glassy margins on fluidal clasts the lack of welding and agglutination and the distinctive association of highly vesicular fluidal clasts with non vesicular angular blocky clasts recognition of submarine fire fountain breccias in volcanic successions constrains the eruption style proximity tens of metres to source and environment of deposition

illite smectite diagenesis in the nanxiang yitong and north china permian carboniferous basins application to petroleum exploration in china the nanxiang basin in henan province and the yitong basin in jilin province located in the eastern part of china are composed mainly of tertiary nonmarine clastic sequences that thicken to more than 4000 5000 m the north china permian carboniferous basin consists of permian carboniferous systems composed of marine and nonmarine coal bearing sequences clay diagenesis in these basins was studied by systematic x ray diffraction analysis the clay mineralogy consists of illite smectite mixed layered illite smectite i s kaolinite and chlorite the major clay reaction is the illitization of smectite with depth and temperature the reactions generally involve discrete smectite stage to smectite plus the randomly interstratified i s r 0 in the reichweite nomenclatur followed by the first rapid change i to the ordered i s of short range stacking r 1 and the second rapid change ii to the metastable stage with the ordered i s of long range stacking r 3 the first rapid change leads to the appearance of i s ordered i s and disappearance of discrete smectite the proportion of smectite layers ps in the i s in the metastable stage remained unchanged 15 20 over a thick burial interval the discrete illite stage finally occurs in highly mature areas potassium feldspar k feldspar in rocks and k ions in present formation waters are available for the i s reactions i s reactions in these areas responded mainly to temperature the i s transition from the randomly interstratified i s r 0 to the ordered i s occurred at 80 95 c and coincided with the onset of the oil window in source rocks and with secondary porosity enhancement of sandstones the transition from the r 1 to r 3 happened around 130 165 c corresponding to the wet gas stage the illite stage corresponds to the dry gas stage of organic materials the duration of burial did not contribute significantly to the reaction integrating the i s reactions with thermal histories hydrological regimes structure sedimentation and sandstone diagenesis of eac basin allows formulation of clay diagenetic models for each specific basin

the genesis and evolution of carbonate minerals in shale oil formations from dongying depression bohai bay basin china abstract shale oil is attracting increasing attention in the petroleum industry as an essential target of unconventional oil and gas exploration recent exploration efforts have indicated that laminar carbonates are closely related to the favorable depositional strata of shale oil this research focused on inter bedded layers of laminar carbonates as well as mudstone and shale in the dongying depression of the bohai bay basin in eastern china and attempted to reveal the genesis and evolution of the carbonates by means of drill core observations thin sections high resolution scanning electron microscopic observations and fluorometric cathodoluminescence and geochemical analyses the results demonstrated that 1 the carbonates could be categorized into two groups crystalline carbonates and micritic carbonates 2 the crystalline carbonates were well crystallized and greenish under fluorescent light and 3 the micritic carbonates were not well crystallized and had biotic textures it was discovered that the crystalline carbonates were mainly developed in the shale layer and were formed from the late filling effects of the diagenetic cracks along the shale fissility planes shale layers with crystalline carbonates are usually favorable for shale oil reserves the micritic carbonates were formed from direct deposition controlled by biological effects in the stratified flows of the seasonal lake basins and are unfavorable for shale oil reserves

nature of local magma storage zones and geometry of conduit systems below basaltic eruption sites pu u o o kilauea east rift hawaii example the fluid dynamics of the well documented eruptive episodes at pu u o o kilauea wolfe et at 1987 are used to investigate quantitativeely the size and shape of the shallow conduit system beneath the vent cooling calculations are employed to study the long term survival of conduits and the consequences of multiple dike injection events we find that the subvent conduit must have a planar geometry at depths greater than a few tens to at most a few hundreds of meters with a width of less than a few meters a length of the order of 100 m and a height of the order of 1 kin this structure is clearly the residue of the preeruption dikes although such a feature can be widened somewhat by repeated dike emplacement events there is no evidence to suggest that a larger and much more equant magma reservoir should develop at shallow depth the extensive degassing often occurring after single eruptions or between repeated eruptions previously thought to imply the presence of a large equidimensional shallow magma chamber can be readily explained by the volume of magma in a dikelike subvent planar magma storage zone on the basis of these observations which we infer to apply commonly to basaltic eruption sites we suggest that the terms chamber or reservoir be used with caution because they most often connote a relatively large equant magma body distinct from the feeder dike lying just below the vent we find that the subvent region has the same basic geometric characteristics as the parental dike and we propose that it be referred to as a planar magma storage zone

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

towards an understanding of the role of clay minerals in crude oil formation migration and accumulation this article reviews progress in the understanding of the role of clay minerals in crude oil formation migration and accumulation clay minerals are involved in the formation of kerogen catalytic cracking of kerogen into petroleum hydrocarbon the migration of crude oil and the continued change to hydrocarbon composition in underground petroleum reservoirs in kerogen formation clay minerals act as catalysts and sorbents to immobilize organic matter through ligand exchange hydrophobic interactions and cation bridges by the mechanisms of maillard reactions polyphenol theory selective preservation and sorptive protection clay minerals also serve as catalysts in acid catalyzed cracking of kerogen into petroleum hydrocarbon through lewis and bronsted acid sites on the clay surface the amount and type of clay mineral affect the composition of the petroleum bronsted acidity of clay minerals is affected by the presence and state of interlayer water and displacement of this water is a probable driver in crude oil migration from source rocks during crude oil migration and accumulation in reservoirs the composition of petroleum is continually modified by interaction with clay minerals the clays continue to function as sorbents and catalysts even while they are being transformed by diagenetic processes the detail of chemical interactions and reaction mechanisms between clay minerals and crude oil formation remains to be fully explained but promises to provide insights with broader application including catalytic conversion of biomass as a source of sustainable energy into the future

volumetric observations during paroxysmal eruptions at mount etna pressurized drainage of a shallow chamber or pulsed supply abstract the october 17 to november 5 1999 eruption of mount etna s bocca nuova crater emplaced a 15 10 6 m 3 flow field the eruption was characterized by 11 paroxysmal events during which intense strombolian and lava fountain activity fed vigorous channelized a a flows at eruption rates of up to 120 m 3 s 1 each paroxysm lasted between 75 and 450 min and was separated by periods of less intense strombolian activity and less vigorous 3 s 1 effusion ground based satellite and model derived volumetric data show that the eruption was characterized by two periods during which eruption rates and cumulative volume showed exponential decay this is consistent with a scenario whereby the system was depressurized during the first eruptive period october 17 23 repressurized during an october 24 pause and then depressurized again during the second period october 25 28 the imbalance between the erupted and supplied volumes mean that the two periods involved the collection of 1 5 5 7 10 6 m 3 and 1 2 3 6 10 6 m 3 respectively or an increase in the time averaged supply to 11 6 13 6 m 3 s 1 and 12 5 14 9 m 3 s 1 two models are consistent with the observed episodic fountaining derived volumetric trends and calculated volume imbalance a magma collection model and a pulsed supply model in the former case depressurization of a shallow reservoir cause the observed volumetric trends and foam collapse at the reservoir roof powers fountaining in the pulsing case variations in magma flux account for pressurization depressurization and supply the excess volume increases in rise rate and volatile flux coupled with rapid exsolution during ascent trigger fountaining limiting equations that define critical foam layer volumes and magma rise rates necessary for hawaiian style fountaining favor the latter model

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

feldspar dissolution authigenic clays and quartz cements in open and closed sandstone geochemical systems during diagenesis typical examples from two sags in bohai bay basin east china feldspar dissolution and precipitation of clays and quartz cements are important diagenetic reactions affecting reservoir quality evolution in sandstones with detrital feldspars we examined two sets of sandstone reservoirs to determine whether the sandstone diagenetic systems were open or closed to the mass transfer of products from feldspar dissolution and its impact on reservoir quality one of the reservoirs is the eocene fan delta sandstone buried 2 5 4 0 km 1 5 2 5 mi below sea level bsl in the gaoliu gl area of the nanpu sag and the other is the eocene subaqueous fan sandstone buried 1 5 4 5 km 1 2 8 mi bsl in the shengtuo st area of the dongying sag both sandstones consist mainly of lithic arkoses and feldspathic litharenites and have secondary porosity formed by dissolution of feldspars in the gl sandstones the absolute amounts of authigenic clays and quartz cements generally 125 c 257 f the low abundance of authigenic clays and quartz cements and low pore water salinity indicate that much of the and released from leached k feldspars were exported from the gl sandstone system and the extensive feldspar dissolution enhanced much porosity and permeability in contrast the st sandstones with secondary pores formed by feldspar dissolution generally contain authigenic clays kaolinite and illite and quartz cements with almost identical volume of secondary pores kaolinite dominates in the st sandstones at shallower depth 3 1 km 2 mi bsl where temperature exceeds 125 c 257 f the presence of abundant clays and quartz cements indicates that and released from leached feldspars were retained in the st sandstone system the dominance of authigenic illite at greater depth indicates that sufficient should have been retained within the sandstones for occurrence of illitization of kaolinite and feldspars secondary porosity in thin sections can be up to 3 but little porosity the diagenetic difference between the gl and the st sandstones can be interpreted by assessing pore water evolution in these two areas the current pore waters with low salinity and negative hydrogen isotopic compositions in the gl sandstone system indicate the significant impact of meteoric water whereas the current pore waters with high salinity and the paleofluids with positive oxygen isotopic compositions in the st sandstone system indicate little trace of meteoric water access of meteoric freshwater to the gl area probably occurred during the late oligocene to neogene through widely developed faults in the paleogene and neogene strata the low salinity water could have been responsible for flushing of solutes derived from feldspar dissolution as such diagenesis in the gl sandstones is considered to have occurred in an open geochemical system whereas with limited faults and high water salinity the st sandstones acted as a closed geochemical system where precipitation of kaolinite illite and quartz cements occurred following dissolution of feldspars

new contributions to chinese plio pleistocene magnetostratigraphy abstract a new collection of over 500 orientated hand samples of which 180 are red clays from a 195 m loess red clay section near xian 109 12 e 34 12 n china has been dated by magnetic stratigraphy biostratigraphic and previous magnetostratigraphic investigations gave a maximum age for the chinese loess of 2 4 ma implying that the underlying red clay formation is pliocene in age the present study yields a clearly defined magnetic polarity stratigraphy in good agreement with a polarity time scale developed by earlier workers an interpretation of this magnetostratigraphy suggests a basal age for the loess series in this region of 2 5 ma and a minimum age for the base of the red clay formation which is also the base of the section of 5 0 ma