shallow vent architecture during hybrid explosive effusive activity at cordon caulle chile 2011 12 evidence from direct observations and pyroclast textures in june 2011 an eruption of rhyolite magma began at the puyehue cordon caulle volcanic complex southern chile by january 2012 explosive activity had declined from sustained pyroclastic plinian to sub plinian fountaining to mixed gas and ash jetting punctuated by vulcanian blasts this explosive activity was accompanied by synchronous effusion of obsidian lava in a hybrid explosive effusive eruption fortuitous climatic conditions permitted ground based observation and video recording of transient vent dynamics as well as real time collection of proximal juvenile ash as it sedimented from the active plume the main eruptive vent complex and site of lava effusion was represented by two loci of vulcanian blasts within a single tephra cone containing a pancake shaped proto lava dome these blast loci each consisted of clusters of sub vents that expressed correlated shifts in eruption intensity indicating the presence of partially connected and or branching zones of high permeability within the upper conduit pyroclast textures were examined by x ray computed microtomography and their permeability was modeled by lattice boltzmann simulations the porosity 39 to 67 and darcian permeability 3 1x10 15 m2 perpendicular to fabric to 3 8x10 11 m2 parallel to fabric of fine ash emitted during ash jetting indicates that the permeable zones comprised highly sheared tube like bubbly magma and contrast with the low porosity 17 and nul permeability of bombs ejected to hundreds of metres from the vent in vulcanian blasts residual h2o content of ash 0 14 wt and two bombs 0 2 0 25 wt determined by karl fischer titration indicate degassing of this pyroclastic material to near atmospheric pressures ash textures and simple degassing vesiculation models indicate the onset of permeability by ductile processes of shear enhanced bubble coalescence in the upper 1 to 1 5 km of the conduit repeated ash jetting and vulcanian blasts indicate that such ductile processes were not sufficiently effective to accommodate all degassing requirements and additional brittle e g fragmentation events transiently assisted in maintaining an open system degassing regime that permitted long lived hybrid explosive effusive activity the eruption at cordon caulle has provided an excellent opportunity to closely observe key processes of silicic volcanism

sandstone vs carbonate petroleum reservoirs a global perspective on porosity depth and porosity permeability relationships plots are presented comparing average porosity vs depth for 30 122 siliciclastic petroleum reservoirs and 10 481 carbonate petroleum reservoirs covering all petroleum producing countries except canada however separate plots cover 5534 siliciclastic and 2830 carbonate reservoirs of the alberta basin in canada average permeability vs average porosity is shown for the non canadian reservoirs key similarities and differences between sandstones and carbonates are noted and implications are discussed regarding the dominant factors controlling reservoir quality in each lithology trends of steadily decreasing median and maximum porosity with increasing depth reflect burial diagenetic porosity loss in response to increasing thermal exposure with depth these trends seem inconsistent with the suggestions that both sandstones and carbonates commonly increase in porosity by dissolution during deeper burial carbonate reservoirs have lower values of median and maximum porosity for a given burial depth probably because of greater chemical reactivity of carbonate minerals relative to quartz and the resulting lower resistance to chemical compaction and associated cementation relative paucity of low porosity 0 8 siliciclastic reservoirs at all depths compared with carbonates may reflect the more common occurrence of fractures in carbonates and the effectiveness of these fractures for facilitating economic flow rates in low porosity rock overall carbonate reservoirs do not have lower permeability for a given porosity compared with sandstones but do have strikingly lower proportions of both high porosity and high permeability values the data presented can serve as a general guide for the distribution of reservoir quality that can reasonably be expected in exploration wells drilled to any given depth in the absence of detailed geologic information such as burial and thermal history

mechanisms for transition in eruptive style at a monogenetic scoria cone revealed by microtextural analyses lathrop wells volcano nevada u s a explosive activity at lathrop wells volcano nevada u s a originated with weak strombolian ws eruptions along a short fissure and transitioned to violent strombolian vs activity from a central vent with lava effusion during both stages the cause for this transition is unknown it does not reflect a compositional change as evidenced by the consistent bulk geochemistry of all the eruptive products however comparison of agglutinate samples from the early ws events with samples of scoria from the later vs events reveal differences in the abundance and morphology of groundmass phases and variable textures in the rims of olivine phenocrysts scanning electron microscope sem examination of thin sections from the ws samples show euhedral magnetite microlites in the groundmass glass and olivine phenocrysts show symplectite lamellae in their rims secondary ion mass spectrometry sims depth profiles of these symplectites indicate they are diffusion controlled the calculated dfe mg allows an estimation of the oxygen fugacity fo2 and indicates an increased fo2 during eruption of the ws products conversely the vs samples show virtually no magnetite microlites in the groundmass glass a lack of symplectites in the olivines and a lower calculated fo2 these microtextural features suggest that the lathrop wells trachybasalt experienced increased oxidation during ws activity as magma ascended through the original fissure exsolved bubbles were concentrated in the wider part s the protoconduit and this bubble flux drove convective circulation that oxidized the magma through exposure to atmosphere and recirculation this oxidation resulted in groundmass crystallization of magnetite within the melt and formation of symplectites within the olivine phenocrysts bubble driven convection mixed magma vertically within the protoconduit keeping it fluid and driving strombolian bursts while microlite crystallization in narrower parts of the fissure helped to focus flow development of a central conduit increased the magma ascent velocity due to a greater product volume in the later eruptive stages and caused the shift in eruption intensity consequently variations in microtextures of the lathrop wells products reveal how a combination of fluid dynamic and crystallization processes in the ascending magma resulted in different styles of activity while the products maintained a consistent bulk composition

combining sedimentary forward modeling with sequential gauss simulation for fine prediction of tight sandstone reservoir abstract a considerable number of tight sandstone gas fields are observed in the xihu depression east china sea the y gas field is at the stage of development it is necessary to describe the reservoir shape and permeability characteristics in detail to deploy development wells the seismic prediction effects of tight sandstone are not good sedimentary forward modeling technology can effectively predict the macroscopic characteristics of sedimentary sand bodies but this technique lacks micro details geostatistical modeling can depict reservoir details but this technique cannot easily reflect macro laws therefore taking h1 layer of the oligocene huagang formation in the y gas field as an example the combination of sedimentary simulation and geostatistical modeling is proposed geostatistical modeling is combined to describe reservoir details by using the sequential gauss simulation method under the control of sedimentary simulation results as macro laws first based on the test data and the sensitivity test results of the adjacent study area five parameters transport capacity of the river sand ratio maximum initial water depth lake level change and tectonic subsidence needed for the simulation are determined a sedimentary forward simulation is carried out and a sand ratio model reflecting macroscopic sedimentary law is obtained second in the geostatistical modeling stage the variogram which has a great influence on the results of geological modeling is discussed the results show that the larger the length and width of the variogram the larger the simulated reservoir scale then considering the characteristics of fewer wells in the study area a reliable variogram is obtained by using the sand ratio results of the sedimentary simulation 2538 m in length and 876 m in width and the main input parameters of geological modeling data probability distribution characteristics and variogram are determined subsequently under the trend of the sediment sand ratio simulation geological modeling research was carried out by using the sequential gauss simulation method and a high precision sand ratio prediction model was established finally the sand ratio model is transformed into a sedimentary microfacies model and the permeability characteristics of different sedimentary microfacies are calculated under the control of sedimentary facies the permeability model is established by the sequential gauss simulation method the model prediction results show that the simulation results can reflect the morphology distribution and permeability of sedimentary microfacies in detail and the macroscopic characteristics of delta sedimentary law the permeability of channels in the study area is 0 3 md and the distribution area is much larger than that of other types of sedimentary microfacies compared with other types of deposits the channel around well a area has better development potential in the front of the delta and is the most favorable oil and gas development area in the study area

morpho structural evolution of the cordon caulle geothermal region southern volcanic zone chile insights from gravity and 40ar 39ar dating the cordon caulle geothermal region 40 5 s is a 13 km 6 km nw se elongate volcano tectonic depression hosting numerous monogenetic volcanic centers fumaroles and hot springs most of which occur spatially associated with the edges of the depression volcanism started at approximately 0 3 ma with dominantly mafic effusions and expressed ultimately in post glacial and historic dacite rhyolite eruptions 1921 1922 and 1960 three ne trending gravimetric profiles were carried out across the depression of cordon caulle yielding a residual negative anomaly with the greatest amplitude 20 mgal at the center of the depression a 2d gravity model given by a 490 m thick shallow body with a density contrast 650 kg m3 interpreted as a shallow package of dacite rhyolite lavas and tephra was found to match the residual anomaly a dense rock equivalent volume of felsic material on the order of 28 km3 25 of the total output of cordon caulle is derived from this thickness previous workers explain the origin of felsic rocks at cordon caulle in terms of the orientation of the borders of cordon caulle relative to the maximum stress direction 1 i e ne trending prevailing during the quaternary according to which nw trending domains were compressional favoring stagnation storage and differentiation of magmas the dominantly monogenetic style of volcanism the plateau like morphology and the negative bouguer anomaly on the contrary are interpreted as an indication of extensional tectonics intra arc extension is proposed to be related to coseismic or postseismic stress relaxation accompanying major thrust events such as the great 1960 chilean earthquake which is consistent at cordon caulle with the direction of propagation of dikes of the 1960 eruption i e coseismic extension and present day subsidence inferred from insar data i e postseismic extension prior to the quaternary 8 2 1 6 ma nearly east west compression prevailed at the intra arc zone a 5 44 0 04 ma old granodiorite intrusion bracketed by two sub parallel branches of the regional margin parallel liquine ofqui fault zone lofz in a prominent pop up structure 15 km to the east of cordon caulle accounts for reverse reactivation of the lofz and rapid fault related exhumation of basement rocks 1 mm year we argue that under compression reverse reactivation of the lofz was facilitated by the combined effect of cyclic increase in fluid pressure induced by magmatic hydrothermal input and removal of lithostatic load induced by glacial erosion 1 5 mm year in the vicinity of cordon caulle

strain localization in vesicular magma implications for rheology and fragmentation the rheology of two or three phase magmas has been the focus of much interest because it controls magma ascent and eruption behavior research on magma rheology has typically considered homogeneous fl ow here we demonstrate based on natural examples that strain resulting from viscous fl ow preceding explosive fragmentation localizes into shear zones at a microscopic scale strain localization affects the rheological behavior of magmas modifying predictions based on experiments localization leads to high strain rate shear zones where elongated sheared vesicles and shear heating have a weakening effect surrounding regions of relatively low strain rate where subequant vesicles have a strengthening effect thus energy is dissipated more effi ciently into localized bands where strain rate increases through feedback effects and can lead to melt fragmentation

frequency dependent p wave polarization and its subwavelength near surface depth sensitivity near surface structure is crucial to assessing seismic hazards and understanding earthquakes and surface processes yet is a major challenge to robustly image recently an approach based on body wave polarization was introduced for constraining shallow seismic structure but the depth sensitivity of the polarization measurement has remained unclear using waveform simulations based on a layer over a half space we find that the depth sensitivity of p wave polarization peaks at the surface and decreases abruptly over a depth range shorter than its wavelength a strong frequency dependence provides constraints on local 1 d structure with frequencies between 0 1 and 10 hz illuminating structure at depths of 10 m to several kilometers applying these results to teleseismic recordings in japan provides constraints on structure at about 120 to 750 m including a distinctive weak zone along the median tectonic line in the kii peninsula and awaji island

complex dynamics of small moderate volcanic events the example of the 2011 rhyolitic cordon caulle eruption chile after decades of repose puyehue cordon caulle volcano chile erupted in june 2011 following a month of continuously increasing seismic activity the eruption dispersed a large volume of rhyolitic tephra over a wide area and was characterized by complex dynamics during the initial climactic phase of the eruption 24 30 h on 4 5 june 11 14 km high plumes dispersed most of the erupted tephra eastward towards argentina reaching as far as the atlantic ocean this first eruptive phase was followed by activity of lower intensity leading to the development of a complex stratigraphic sequence mainly due to rapid shifts in wind direction and eruptive style the resulting tephra deposits consist of 13 main layers grouped into four units each layer was characterized based on its dispersal direction sedimentological features and on the main characteristics of the juvenile fraction texture density petrography chemistry the lowest part of the eruptive sequence unit i corresponding to the tephra emitted between 4 and 5 june is composed of alternating lapilli layers with a total estimated volume of ca 0 75 km3 these layers record the highest intensity phase during which a bent over plume dispersed tephra towards the southeast east with negligible up wind sedimentation products emitted during 5 6 june unit ii signaled an abrupt shift in wind direction towards the north leading to the deposition of a coarse ash deposit in the northern sector ca 0 21 km3 in volume followed by a resumption of easterly directed winds a third phase unit iii began on 7 june and resulted in tephra deposits in the eastern sector and ballistic bombs around the vent area a final phase unit iv started after 15 june and was characterized by the emission of fine grained white tephra from ash charged plumes during low level activity and the extrusion of a viscous lava flow timing and duration of the first eruptive phases were constrained based on comparison of the dispersal of the main tephra layers with satellite images showing that most of the tephra was emitted during the first 72 h of the event the analyzed juvenile material tightly clusters within the rhyolitic field with negligible chemical variations through the eruptive sequence textural observations reveal that changes in eruption intensity and consequently in magma ascent velocity within the conduit and complex interactions between gas rich and gas depleted magma portions during ascent resulted in vesicular clasts with variable degrees of shear localization and possibly in the large heterogeneity of the juvenile material

transition from dome forming to plinian eruptive styles controlled by h2o and cl degassing the transition from a plinian pumice to an effusive dome forming eruptive style is frequently observed in volcanic systems and is generally attributed to the progressive loss of volatiles from magma stored in a superficial reservoir this explosive effusive transition has been explained by the evolution from a closed to an open system of degassing1 2 3 4 but in this context an eruption at mt pelee martinique french west indies dated at 650 years ago which exhibited a rarely observed5 6 succession from dome forming to plinian activity in a short interval of time7 is at odds with such an explanation in this eruption near surface explosions of the dome produced two peleean turbulent pyroclastic flows whose deposits are similar to those of the effusive 1902 eruption and then plinian activity produced pumice fallouts and flows the reconstruction of the degassing paths of both eruptive regimes using the densities and the h2o and cl contents of the clasts shows that the interaction of rising magma with hydrothermal fluids at shallow depth may play a critical role in determining eruptive style

sedimentation of long lasting wind affected volcanic plumes the example of the 2011 rhyolitic cordon caulle eruption chile sedimentation processes and fragmentation mechanisms during explosive volcanic eruptions can be constrained based on detailed analysis of grain size variations of tephra deposits with distance from vent and total grain size distribution tgsd grain size studies strongly rely on deposit exposure and in case of long lasting eruptions can be complicated by the intricate interplay between eruptive style atmospheric conditions particle accumulation and deposit erosion the 2011 cordon caulle eruption chile represents an ideals laboratory for the study of long lasting eruptions thanks to the good deposit accessibility in medial to distal area all layers analyzed are mostly characterized by bimodal grain size distributions with both the modes and the fraction of the coarse subpopulation decreasing rapidly with distance from vent and those of the fine subpopulation being mostly stable due to gradually changing wind direction the two subpopulations characterizing the deposit of the first 2 days of the eruption are asymmetrically distributed with respect to the dispersal axis the tgsd of the climactic phase is also bimodal with the coarse subpopulation representing 90 wt of the whole distribution polymodality of individual samples is related to size selective sedimentation processes while polymodality of the tgsd is mostly related to the complex internal texture e g size and shape of vesicles of the most abundant juvenile clasts the most representative tgsd could be derived based on a combination of the voronoi tessellation with a detailed analysis of the thinning trend of individual size categories finally preferential breakage of coarse pumices on ground impact was inferred from the study of particle terminal velocity

eruptive history geochronology and magmatic evolution of the puyehue cordon caulle volcanic complex chile forty three 40 ar 39 ar age determinations of lava flows domes ignimbrites and dikes plus 14 c dates from seven distal tephra layers combined with stratigraphy geochemistry and sr and th isotope data establish an eruptive chronology for the puyehue cordon caulle volcanic complex at 40 5 s in the andean southern volcanic zone svz the complex preserves 131 km 3 of lava and tephra that erupted from numerous vents widely separated in time and space approximately 80 of the total volume consists of basaltic to andesitic lava that formed two broad shield volcanoes between 314 and 70 ka the modern puyehue stratovolcano was built on the southerly shield during the past 69 k y following a hiatus of 25 k y puyehue has erupted 15 km 3 of basaltic to rhyolitic magma that spans the entire compositional range found in the southern svz and evolved via at least six phases including 1 basaltic andesitic to dacitic lavas between 69 and 32 ka 2 a shift to bimodal magma compositions that is first expressed by a rhyodacite mingled with inclusions of mgo rich basaltic andesite at 34 ka 3 dacitic to rhyolitic flows and domes from 19 to 12 ka 4 basaltic to basaltic andesitic flows between 15 and 12 ka 5 subsequent rhyolitic dome growth in several effusive and explosive stages between 7 and 5 ka followed by 6 a powerful series of phreatomagmatic and sub plinian eruptions at ca 1 1 ka that obliterated the preceding rhyolite domes and formed the present 2 5 km diameter 280 m deep summit crater along the cordon caulle fissure zone 5 km 3 of rhyodacitic to rhyolitic lavas domes and cones have formed during the past 16 5 k y including explosive and effusive eruptions in 1921 1922 and 1960 eruptive rates were nonuniform over time with background growth at 0 04 km 3 k y or less punctuated by spurts at up to 0 90 km 3 k y the time averaged rate 0 42 km 3 k y is nearly double that at the tatara san pedro complex 500 km to the north during the past 300 k y these findings indicate that within a single arc the magmatic and eruptive fluxes at individual frontal volcanoes can be highly variable the last three stratocone building events on puyehue began during periods of deglaciation suggesting a relationship between unloading of ice and ease of magma ascent puyehue basalt exhibits subtle changes in 238 u 230 th 87 sr 86 sr and trace element composition over time that signal shifts in the composition and degree of melting of the mantle wedge or the extent to which basalt was modified by assimilation of heterogeneous crustal melts the complex has become exceptionally bimodal and more explosive over time with recent rhyolites evolving by extreme crystal fractionation of mafic magma and lesser volumes of andesite and dacite created via mixing of rhyolite and basalt despite the high flux of basalt during the past 300 k y no large silicic magma reservoir formed in the upper crust instead 238 u 230 th data favor rapid ascent of several small bodies of basaltic and silicic magma from the lower crust promoted perhaps by conduits that reflect strike slip faulting beneath the complex

estimating the volume of tephra deposits a new simple strategy volume determination of tephra deposits is necessary for the assessment of the dynamics and hazards of explosive volcanoes several methods have been proposed during the past 40 years that include the analysis of crystal concentration of large pumices integrations of various thinning relationships and the inversion of field observations using analytical and computational models regardless of their strong dependence on tephra deposit exposure and distribution of isomass isopach contours empirical integrations of deposit thinning trends still represent the most widely adopted strategy due to their practical and fast application the most recent methods involve the best fitting of thinning data using various exponential segments or a power law curve on semilog plots of thickness or mass area versus square root of isopach area the exponential method is mainly sensitive to the number and the choice of straight segments whereas the power law method can better reproduce the natural thinning of tephra deposits but is strongly sensitive to the proximal or distal extreme of integration we analyze a large data set of tephra deposits and propose a new empirical method for the determination of tephra deposit volumes that is based on the integration of the weibull function the new method shows a better agreement with observed data reconciling the debate on the use of the exponential versus power law method in fact the weibull best fitting only depends on three free parameters can well reproduce the gradual thinning of tephra deposits and does not depend on the choice of arbitrary segments or of arbitrary extremes of integration

locating magma reservoirs using insar and petrology before and during the 2011 2012 cordon caulle silicic eruption abstract we combine petrological and insar observations to probe the origin of deformation of cordon caulle volcano in southern chile before and during the 2011 2012 eruption the erupted rhyodacite is crystal poor and was stored at about 900 c with ca 4 wt h2o and 220 ppm co2 in the melt corresponding to a storage depth of about 6 7 km in addition to a previously documented 2007 2008 deformation episode we find three pre eruptive deformation episodes the first between 2008 and 2009 that covers 400 km2 with a maximum uplift of 18 5 cm the second between february and march 2010 that covers 20 km2 with a maximum uplift of 10 cm and the third between march and may 2011 that covers 40 km2 with a maximum uplift of 6 cm modeling of the 2008 2009 deformation episode suggests source depths of about 5 9 km consistent with the petrologically determined magma storage depth the sum of modeled source volume changes from 2007 to 2009 is about 12 times smaller than the observed erupted volume our calculation of magma compressibility shows that there must have been a significant volume of pre existing magma in the reservoir to account for this difference co eruptive subsidence shows evidence for three distinct magma sources and pre eruptive inflation is seen at two of the three sources modeled deformation sources are located 2 10 km from the 2011 2012 eruptive vent and coincide with the vents from previous historical eruptions 1921 22 1960 and with the neighboring puyehue volcano this implies the existence of an interconnected magma plumbing system that allows for pressure transfer and which covers an area of at least 20 km2 thus the deformation and geochemical characteristics of cordon caulle resemble those of a large silicic caldera system the presence of a mafic crystal clot demonstrates the existence of basaltic melts in the silicic reservoir but we find that the mafic magmas reached the reservoir at least several hundred years before eruption therefore if the pre eruptive deformation was caused by replenishment to a shallow reservoir the new magma was silicic and similar to the pre existing magma and or there was no interaction between the two we find that pre eruptive deformation can occur in pulses and reach its peak years before eruption and thus lack of deformation does not necessarily imply that eruption is not imminent

total grain size distribution and volume of tephra fall deposits on 17 june 1996 ruapehu volcano new zealand produced a sustained andesitic sub plinian eruption which generated a narrow tephra fall deposit extending more than 200 km from the volcano the extremely detailed data set from this eruption allowed methods for the determination of total grain size distribution and volume of tephra fall deposits to be critically investigated calculated total grain size distributions of tephra fall deposits depend strongly on the method used and on the availability of data across the entire dispersal area the voronoi tessellation method was tested for the ruapehu deposit and gave the best results when applied to a data set extending out to isomass values of 1 g m 2 the total grain size distribution of a deposit is also strongly influenced by the very proximal samples and this can be shown by artificially constructing subsets from the ruapehu database unless the available data set is large all existing techniques for calculations of total grain size distribution give only apparent distributions the tephra fall deposit from ruapehu does not show a simple exponential thinning but can be approximated well by at least three straight line segments or by a power law fit on semi log plots of thickness vs area 1 2 integrations of both fits give similar volumes of about 4 106 m3 integration of at least three exponential segments and of a power law fit with at least ten isopach contours available can be considered as a good estimate of the actual volume of tephra fall integrations of smaller data sets are more problematic

tephra stratigraphy and eruptive volume of the may 2008 chaiten eruption chile on may 1st 2008 mount chaiten southern chile interrupted a long period of quiescence generating a sequence of explosive eruptions and causing the evacuation of chaiten town located a few kilometers south of the volcano the activity was characterized by several explosive events each associated with plumes which reached up to about 19 km above sea level the products were dispersed across a wide area with the finest ash reaching the atlantic coast of argentina our field observations in the proximal medial area 3 25 km from the vent indicate that the may 2008 tephra deposit consists of numerous layers most of which can be correlated with individual eruptive events these layers vary from extremely fine grained ash to layers of lapilli and blocks composed of both juvenile and lithic material here we describe the stratigraphy and physical characteristics of the may 2008 deposits and propose a reconstruction of the timing of the may 2008 events the deposits are mainly associated with the three main explosive phases which occurred on 1st 2nd may 3rd 5th may and 6th may with an estimated bulk tephra volume of 0 5 1 0 km3 integration of both exponential and power law fitting for the 6th may event represented by a layer composed mainly of lithic lapilli and blocks 2 mm an isopleth map was compiled from which a 19 km plume height was determined which is in good agreement with satellite observations

dynamics of wind affected volcanic plumes the example of the 2011 cordon caulle eruption chile the 2011 cordon caulle eruption represents an ideal case study for the characterization of long lasting plumes that are strongly affected by wind the climactic phase lasted for about 1 day and was classified as subplinian with plumes between 9 and 12 km above the vent and mass flow rate mfr on the order of 107 kg s 1 eruption intensity fluctuated during the first 11 days with mfr values between 106 and 107 kg s 1 this activity was followed by several months of low intensity plumes with mfr 106 kg s 1 plume dynamics and rise were strongly affected by wind during the whole eruption with negligible upwind spreading and sedimentation the plumes that developed on 4 6 and 20 22 june can be described as transitional i e plumes showing transitional behavior between strong and weak dynamics while the wind clearly dominated the rise height on all the other days resulting in the formation of weak plumes individual phases of the eruption range between volcanic explosivity indices veis 3 and 4 while the cumulative deposit related to 4 7 june 2011 is associated with veis 4 and 5 crosswind cloud and deposit dispersal of the first few days are best described by a linear combination of gravitational spreading and turbulent diffusion with velocities between 1 and 10 m s 1 downwind cloud velocity for the same days is best described by a linear combination of gravitational spreading and wind advection with velocities between 17 and 45 m s 1 results show how gravitational spreading can be significant even for subplinian and small moderate eruptions strongly advected by wind and with low richardson number and low mfr

petrophysical evaluation of a slope fan basin floor fan complex cherry canyon formation ward county texas the cherry canyon formation consists of a 925 ft 280 m thick section of up to 25 different sandstone and siltstone units that were deposited in deep water in the delaware basin lowstand sedimentation by fluid density currents with periodic turbidity currents resulted in a broad migrating channelized slope fan basin floor fan complex exhibiting a complex depositional architecture of reservoir sandstones original depositional fabric modified by diagenetic cements and authigenic clays create a range of petrophysical rock types type i reservoirs are found in channel sandstones beds of lesser reservoir quality type ii are present in laminated overbank interchannel sandstones a practical pore geometry classification scheme based on pore grain shapes and pore throat rad i is used to understand fluid saturations and predict well performance within the context of the depositional framework and structural relief pore geometry factors combine with insufficient structural closure to create high water saturations throughout the oil column type i macroporous reservoirs exhibit oil water transition zones and are interbedded with type ii mesoporous to microporous reservoirs which contain all or mostly water due to high capillarity associated with small pore throat size accurate reservoir water saturations can be derived using archie s equation when combined with a movable oil analysis and drainage relative permeability fractional flow curves initial watercuts can be predicted to maximize deliverability from optimal rock types high original water saturations in the transition zone decrease average water saturations behind the waterflood front resulting in inefficient secondary recovery a combined application of sedimentological petrophysical logging and reservoir engineering technologies is necessary to properly evaluate the cherry canyon reservoirs

quantitative seismic pre stack analysis of potential gas hydrate resources in the makran accretionary prism offshore iran abstract gas hydrates are classified as a major unconventional resource and assumed to be a future potential energy source high pressures low temperature stability conditions of the hydrates restrict their occurrence to the permafrost and deep sea regions from the continental slop to the abyssal in these regions where the well information is most often absent or sparse the amplitude variation with angle ava is a common method of hydrate free gas assessment in this method various linear reflection coefficient equations are fitted to a series of data points to compute some pre stack attributes these attributes have the advantage of being an interface property rather than a layer property which makes them an easy to use characterization tool in lack of well data in recent years rock physics templates nomograms have been presented to estimate the hydrate free gas saturations solely based on these interface properties ava inversion approach was applied to the seismic data in the makran accretionary prism offshore iran to estimate the bottom simulating reflector bsr vicinity hydrate and gas saturations this inversion process included four pre stack attributes of the intercept gradient normal incidence ni and poisson reflectivity pr and was limited to the bsr estimated bsr vicinity saturations were ranged from 7 8 5 for hydrate and 5 6 5 for free gas at three representative locations accuracy of each attribute was analyzed by a synthetic modeling in this modeling the effective medium theory emt was considered to calculate the physical properties of hydrate and gas bearing sediments lithological properties and the acquisition geometry were set to the corresponding values of the field data results of the synthetic ava inversion showed that if the hydrate saturation does not exceed 30 the error of the estimation for pre stack attributes would be in acceptable range the expected estimation errors for actual attributes were derived from this synthetic modeling

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

coupled effect of magma degassing and rheology on silicic volcanism abstract explosive volcanism such as the 1991 mt pinatubo philippines and the 2008 mt chaiten chile eruptions is caused by violent vesiculation of hydrous magma however gas may efficiently separate from magma owing to the enhancement of gas permeability by shear deformation of magma flowing in a volcanic conduit this makes it difficult to maintain the driving force of explosive volcanism although explosive volcanism is actually common here we propose that shear localization in a volcanic conduit controls the eruption style and explosivity based on deformation experiments of vesicular magma linked with synchrotron radiation x ray radiography and computed tomography we observed for the first time in situ that the shear localization caused magma fracturing and formed a slip plane and thus inhibited deformation and outgassing elsewhere we also observed the compaction of vesicular magma into a dense lava as a result of outgassing when shear localization did not occur in a natural setting shear localizes along the edges of a volcanic conduit where the strain rate is high causing a highly permeable fracturing layer to form at the conduit s edge and leaving less sheared and less outgassed magma at its center the less outgassed magma in the center may ascend rapidly and cause explosive volcanism non explosive lava effusion may occur only when shear localization does not occur effectively this new view explains the rapid ascent of viscous magma and the formation of pyroclasts with contrasting vesicularity pyroclastic obsidian and highly vesiculated pumice

storage and eruption of near liquidus rhyolite magma at cordon caulle chile the last three eruptions at the cordon caulle volcanic complex chile have been strikingly similar in that they have started with relatively short pre eruptive warning and produced chemically homogeneous rhyolite to rhyodacite magma with glassy to aphyric texture these characteristics collectively call for an understanding of the storage conditions leading to the rise and extraction of crystal poor silicic magma from volcanoes we have analyzed and experimentally reproduced the mineral assemblage and glass chemistry in rhyolite magma produced in the most recent eruption of cordon caulle and we use these to infer magma storage and ascent conditions fe ti oxide mineral geothermometry suggests that the rhyolite was stored at 870 920 c at these temperatures the phenocryst assemblage plag an37 cpx opx mag ilm can be reproduced under h2o saturated conditions of between 100 and 50 mpa corresponding to crustal depths between about 2 5 and 5 0 km the shallow and relatively hot magma storage conditions have implications for the rapid onset degassing efficiency and progression from explosive to mixed pyroclastic effusive eruption style at cordon caulle

insights into eruption dynamics from textural analysis the case of the may 2008 chaiten eruption the may 2008 chaiten southern chile eruption was characterized by several explosive events each associated with plumes which reached up to about 19 km above sea level on may 6 a study of the textural and physical features of the juvenile clasts erupted during the climactic phase of the 2008 eruption of chaiten is presented pumice clasts show unimodal density distribution main mode at 600 kg m3 average vesicularity of about 69 a glassy groundmass with no microcrystals and vesicles with dimension between 1 m and 2 mm they also show a unimodal vesicle size distribution with most frequent vesicle size in the range 0 05 0 08 mm and an estimated vesicle number density of 1 3 0 5 105 mm 3 related to a rapid nucleation event produced during the late phases of magma rise this is confirmed by the absence of microcrystals that could otherwise have delayed vesicle formation and allowed the magma to maintain a low viscosity and a supersaturation in volatiles vesiculation and fragmentation were triggered by a sudden decompression of the melt associated with the opening of the volcanic conduit 10 mpa s 1

diverse patterns of ascent degassing and eruption of rhyolite magma during the 1 8 ka taupo eruption new zealand evidence from clast vesicularity k lauea hawaii like vesuvius and etna is a frequently active volcano associated with a national park which is a focus for volcano tourism two contrasting summit eruptions at k lauea in 2008 2009 and 1959 emphasize how even small eruptions on populous volcanoes have significant impact on both hawaii volcanoes national park hvnp and the surrounding communities the effects are typically more indirect and social than direct physical but have significant fiscal repercussions the former include both positive benefits and negative impacts as an illustration direct consequences of the 1959 eruption were the rerouting of the major park access road and destruction of a summer camp but benefits included an unprecedented surge in visitor numbers and construction of nature trails that are now the most visited asset in the park both positive and negative impacts have increased in intensity with time due to growth in the resident population and visitor numbers for example the entire park has been evacuated twice during the ongoing 2008 2009 eruption

variability of plinian fall deposits examples from okataina volcanic centre new zealand abstract plinian eruptions are intense sustained open vent volcanic outbursts that produce extensive beds of generally well sorted and generally highly vesicular pumice fallen from eruption plumes up to 55 km high their deposits tend to be almost homogeneous throughout their thickness although inverse grading commonly occurs here we detail departures from this near homogeneity that we observed among the mangaone subgroup a group of 12 plinian pumice fall deposits from okataina volcanic centre one of the dormant rhyolitic volcanoes in the taupo volcanic zone new zealand we propose that plinian eruptions may pass through seven states ranging from inception commencement of activity or renewed activity following a shutdown waxing steady discharge climax and waning leading to column collapse or shutdown decrease to zero intensity some deposits include intercalated water flushed ash rich beds having a bimodal grain size other examples of non homogeneity include phreatoplinian ashes that may alternate with the plinian pumice as though modulated by a delicate balance in water flux and still other eruptions may switch completely from dry to wet conditions when the column wanes towards the latest stages of the eruptions pink pumice occurs in some deposits and is totally absent in others we infer that it oxidized during temporary storage in or around the vent lithics are ubiquitous and concentrations of them may indicate vent wall collapses and explosive ejection of some of the resulting debris some lithic rich horizons neither coincide with apparent variations in the plinian discharge nor interrupt it as is the case with some rain flushed bimodal beds the events that produced these incongruent beds proceeded synchronously with but independent of the main plinian discharge in an isolated portion of the vent system such as a subsidiary vent other variations of density vesicularity and crystallinity among the eruption products record the pre and syn eruptive history of the magma a local inverse relationship between pumice density and crystallinity of one eruptive unit is inferred to reflect a control by crystals on vesiculation and fragmentation

liquid and gas corrected permeability correlation for heterogeneous carbonate reservoir rocks permeability is considered as an efficient parameter for reservoir modelling and simulation in different types of rocks the performance of a dynamic model for estimation of reservoir properties based on liquid permeability has been widely established for reservoir rocks consequently the validated module can be applied into another reservoir type with examination of the validity and applicability of the outcomes in this study the heterogeneous carbonate reservoir rock samples of the tertiary baba formation have been collected to create a new module for estimation of the brine permeability from the corrected gas permeability in addition three previously published equations of different reservoir rock types were evaluated using the heterogenous carbonate samples the porosity and permeability relationships permeability distribution pore system and rock microstructures are the dominant factors that influenced on the limitation of these modules for calculating absolute liquid permeability from the klinkenberg corrected permeability the most accurate equation throughout the selected samples in this study was the heterogenous module and the lowest quality permeability estimation was derived from the sandstone module

magmatic evolution of the puyehue cordon caulle volcanic complex 40 s southern andean volcanic zone from shield to unusual rhyolitic fissure volcanism abstract magmas erupted from quaternary volcanoes of southern andes between 37 and 46 s latitude are mainly basaltic to andesitic however pccvc 40 s shows a singular magmatic evolution due to the abnormal evacuation of rhyolites especially in the last 100 ka in addition pccvc is the result of juxtaposing products from the nw trending alignment of cordillera nevada caldera cordon caulle fissure volcano and the puyehue stratocone using 40 ar 39 ar and 14 c geochronology it can be established that they evolved since ca 500 ka as coeval but separated vents with a first stage of shield volcanism followed by repeated collapses that formed an internal nw elongated graben from ca 100 ka volcanic activity occurred in both a fissure system cordon caulle and a central volcano puyehue holocene explosive eruptions mainly in the puyehue crater accompanied the dome growing along a nw trending fissure system last historical eruptions were in 1921 and 1960 when nw fissures of cordon caulle fed rhyodacitic lava flows in 1960 the fissure eruption was triggered by a remote mw 9 5 thrust earthquake cordillera nevada caldera presents a reduced compositional range 52 63 sio 2 and geochemical features of low pressure magma mixing and assimilation instead cordon caulle and puyehue volcanoes have a wide silica range 48 71 sio 2 and an outstanding affinity which can be modelled with initial high pressure fractional crystallization moderate magma mixing and subsequent low pressure fractional crystallization from a common parental source the exceptional magmatic evolution and eruptive style of pccvc in southern andes could be related with the physics of the plumbing system which in turn can be controlled by external factors as the structure of the continental crust and the ongoing stress regime

the transition from explosive to effusive eruptive regime the example of the 1912 novarupta eruption alaska the shift from explosive to effusive silicic volcanism seen in many historical eruptions reflects a change in the style of degassing of erupted magma this paper focuses on such a transition during the largest eruption of the twentieth century the 1912 eruption of novarupta the transition is recorded in a dacite block bed which covers an elliptical area of 4 km 2 around the vent approximately 700 studied blocks fall into four main lithologic categories 1 pumiceous 2 dense 3 flow banded dacites and 4 welded breccias textural analyses of the blocks indicate portions of the melt underwent highly variable degrees of outgassing vesicle populations show features characteristic of bubble coalescence and collapse a decrease in measured vesicularity and increased evidence for bubble collapse compared with pumice from earlier plinian episodes mark the transition from closed to open system degassing block morphology and textures strongly suggest the magma was first erupted as a relatively gas rich lava dome plug but incomplete out gassing led to explosive disruption heterogeneous degassing of ascending magma began in plinian episode iii and resulted in instability during episode iv dome growth and a series of vulcanian explosion s modeling of the dynamics of explosion initiation and ejecta dispersal indicates that a significant concentration in gas is required to produce the explosions responsible for the observed block field dispersal the amount of gas available in the hot pumiceous dome material appears to have been inadequate to drive the explosion s therefore external water most likely contributed to the destruction

permeability prediction in tight carbonate rocks using capillary pressure measurements abstract the prediction of permeability in tight carbonate reservoirs presents ever more of a challenge in the hydrocarbon industry today it is the aim of this paper to ascertain which models have the capacity to predict permeability reliably in tight carbonates and to develop a new one if required this paper presents i the results of laboratory klinkenberg corrected pulse decay measurements of carbonates with permeabilities in the range 65 nd to 0 7 md ii use of the data to assess the performance of 16 permeability prediction models iii the development of an improved prediction model for tight carbonate rocks and iv its validation using an independent data set initial measurements including porosity permeability and mercury injection capillary pressure measurements micp were carried out on a suite of samples of kometan limestone from the kurdistan region of iraq the prediction performance of sixteen different percolation type and poiseuille type permeability prediction models were analysed with the measured data analysis of the eight best models is included in this paper and the analysis of the remainder is provided in supplementary material some of the models were developed especially for tight gas sands while many were not critically none were developed for tight gas carbonates predictably then the best prediction was obtained from the generic model and the rgpz models r 2 0 923 0 920 and 0 915 respectively with other models performing extremely badly in an attempt to provide a better model for use with tight carbonates we have developed a new model based on the rgpz theoretical model by adding an empirical scaling parameter to account for the relationship between grain size and pore throat size in carbonates the generic model the new rgpz carbonate model and the two original rgpz models have been tested against independent data from a suite of 42 samples of tight solnhofen carbonates all four models performed very creditably with the generic and the new rgpz carbonate models performing well r 2 0 840 and 0 799 respectively it is clear from this study that the blind application of conventional permeability prediction techniques to carbonates and particularly to tight carbonates will lead to gross errors and that the development of new methods that are specific to tight carbonates is unavoidable

characterization and impact on reservoir quality of fractures in the cretaceous qamchuqa formation zagros folded belt abstract reservoir quality in tight fractured carbonate rocks is controlled by the fracture properties the tectonic origin of fractures the relationship of fractures to other sedimentary features within the rockmass and diagenesis in this study fracture analysis porosity and permeability of the qamchuqa formation in the miran west block of the zagros folded belt in kurdistan has been studied this was undertaken using core analysis micro resistivity image logs drill stem tests dst mud logging data repeat formation test rft drilled cutting samples and wireline log data the integrated analysis shows that the qamchuqa formation is characterized by heterogeneous sedimentary and tectonic features the sedimentary features include burial stylolites dissolution seams and some fractures which formed at early stages of burial and diagenesis phase 1 open fractures partially open mineralized fractures veins and tectonic stylolites were formed by later tectonic activity phase 2 the finding of this study highlight that the fracture properties including aperture length frequency and origin play an important role in controlling the reservoir s quality the open fractures and partially open mineralized fractures enhance permeability providing an inter connected fracture network leading to a high fracture permeability that controls fluid flow in this tight carbonate reservoir rock the fracture network had little impact on the volume of hydrocarbon storage which is controlled by the pore matrix in contrast structures including stylolites dissolution seams and veins generally have a negative impact on the reservoir quality by blocking the fluid flow this work emphasizes the importance of understanding the regional geological history and the role of sedimentary and tectonic features when investigating in tight carbonate reservoirs