nonexplosive and explosive magma wet sediment interaction during emplacement of eocene intrusions into cretaceous to eocene strata trans pecos igneous province west texas abstract eocene intrusion of alkaline basaltic to trachyandesitic magmas into unlithified upper cretaceous maastrichtian to eocene fluvial strata in part of the trans pecos igneous province in west texas produced an array of features recording both nonexplosive and explosive magma wet sediment interaction intrusive complexes with 40 ar 39 ar dates of 47 46 ma consist of coherent basalt peperite and disrupted sediment two of the complexes cutting cretaceous strata contain masses of conglomerate derived from eocene fluvial deposits that at the onset of intrusive activity would have been 400 500 m above the present level of exposure these intrusive complexes are inferred to be remnants of diatremes that fed maar volcanoes during an early stage of magmatism in this part of the trans pecos province disrupted cretaceous strata along diatreme margins record collapse of conduit walls during and after subsurface phreatomagmatic explosions eocene conglomerate slumped downward from higher levels during vent excavation coherent to pillowed basaltic intrusions emplaced at the close of explosive activity formed peperite within the conglomerate within disrupted cretaceous strata in the conduit walls and within inferred remnants of the phreatomagmatic slurry that filled the vents during explosive volcanism a younger series of intrusions with 40 ar 39 ar dates of 42 ma underwent nonexplosive interaction with upper cretaceous to paleocene mud and sand dikes and sills show fluidal billowed quenched margins against the host strata recording development of surface instabilities between magma and groundwater rich sediment accentuation of billowed margins resulted in propagation of intrusive pillows into the adjacent sediment more intense disruption and mingling of quenched magma with sediment locally produced fluidal and blocky peperite but sufficient volumes of pore fluid were not heated rapidly enough to generate phreatomagmatic explosions this work suggests that trans pecos texas may be an important locale for the study of subvolcanic phreatomagmatic processes and associated phenomena eocene intrusions in the study area underwent complex interactions with wet sediment at shallow levels beneath the surface in strata as old as maastrichtian which must have remained unlithified and rich in pore water for 20 25 ma

experiments on the heat discharge at the dynamic magma water interface 1 compared to dry atmospheric eruption of magma or dry magma rock contact intensity and time scale of heat discharge from magma to the surroundings is strongly modified by an effective coolant water or water sediment mixes in the case of subaqueous or subglacial eruptions magma water contact must take place and can result in phreatomagmatic explosions even if no explosions occur rapid cooling results in the formation of pyroclasts by thermal granulation to study this process in detail a short term calorimeter was built for the direct measurement of the heat flux from a magmatic melt to a coolant volcanic rocks from recent eruptions in iceland were remelted and used to produce jets of melt poured into a coolant filled container particles could be produced in a non explosive process that are practical identical to those from natural hyaloclastites the process fragmentation energy is about 10 of the total heat transferred from melt to coolant

experimental simulation of phase mingling in a subaqueous lava fountain 1 experimental simulations were carried out to determine hydrodynamic flow structures and phase mingling mechanisms of a completely submerged shallow water volcanic vent with the objective of understanding how flow conditions ultimately affect the character and explosiveness of hydromagmatic eruptions negatively buoyant jets were produced by injecting glycerin water mixtures magma surrogate into silicon oil water surrogate and imaging the flow structure using a laser particle image velocimetry system the experiments were designed to evaluate only the initial mingling processes of magma and water and do not account for subsequent vaporization of water and heat transfer effects the onset of phase mingling is strongly controlled by the richardson number of the jet which governs the flow structure and stability at ri 0 90 an oscillatory collapsing fountain is developed which entrains ambient fluid by vortex rollup and collapsing margins on the basis of the experimental results the incorporation of water into basaltic magma discharged from a submarine vent of the order of 10 m in diameter is predicted to occur when the volume discharge rate is in excess of 460 m3 s

water magma interaction some theory and experiments on peperite formation experiments using molten thermite as a magma analog produce peperite when the melt interacts with wet sand these experiments also show explosive behavior developing strombolian and surtseyan like bursts the results demonstrate that the application of fuel coolant interaction fci theory is appropriate for interpretation of peperites the theory described includes discussion of the importance of mass interaction ratios of wet sediment and magma rs which determine thermal equilibrium temperature limits and contact interface dynamics the dynamics of the interface between magma and wet sediments involves heat transfer over a wide range of rates from passive quenching to explosive fragmentation a vapor film layer develops at the interface and acts both as an insulating barrier promoting passive quenching as well as a potential energy reservoir that can cause magma fragmentation mingling of the magma with wet sediments and explosive quenching when the vapor film becomes unstable an important parameter in determining the behavior of the vapor film is the value of rs which controls whether heat can be convectively removed from the layer as more is being added from its contact with magma if rs 1 for fully saturated sediments there is enough water in the sediments to make convective heat flow effective in quenching the magma but below that value there is the potential that the vapor film will be unstable producing highly dynamic phenomena including explosive fragmentation at values of rs 0 1 there is insufficient water to allow the escalation of explosive fragmentation

models of seismic anisotropy in the deep continental lithosphere seismological observations sks wave polarizations systematic p residual variations azimuthal dependence of pn and surface wave velocities or a dispersion of surface waves are not consistent with isotropic if laterally heterogeneous upper mantle structure therefore an anisotropy should be considered as an a priori aspect of future large scale studies of mantle structure most studies of anisotropy however have assumed horizontal or vertical axes of symmetry but such orientations cannot explain bipolar patterns of spatial variations of p residuals which we have observed at many seismological stations on the basis of the petrophysical properties of real upper mantle rocks we consider anisotropy formed either by hexagonal or by orthorhombic aggregates composed of olivine orthopyroxene and clinopyroxene rotations of the aggregates about vertical and horizontal axes allow us to find the three dimensional orientations of symmetry axes that fit combinations of both p and s seismological observations in central europe and in western north america the orientations with plunging symmetry axes velocity extremes seem to be consistent across large spatially uniform tectonic units and change abruptly at important suture zones

rootless tephra stratigraphy and emplacement processes volcanic rootless cones are the products of thermohydraulic explosions involving rapid heat transfer from active lava fuel to external sources of water coolant rootless eruptions are attributed to molten fuel coolant interactions mfcis but previous studies have not performed systematic investigations of rootless tephrostratigraphy and grain size distributions to establish a baseline for evaluating relationships between environmental factors mfci efficiency fragmentation and patterns of tephra dispersal this study examines a 13 55 m thick vertical section through an archetypal rootless tephra sequence which includes a rhythmic succession of 28 bed pairs each bed pair is interpreted to be the result of a discrete explosion cycle with fine grained basal material emplaced dominantly as tephra fall during an energetic opening phase followed by the deposition of coarser grained material mainly as ballistic ejecta during a weaker coda phase nine additional layers are interleaved throughout the stratigraphy and are interpreted to be dilute pyroclastic density current pdc deposits overall the stratigraphy divides into four units unit 1 contains the largest number of sediment rich pdc deposits units 2 and 3 are dominated by a rhythmic succession of bed pairs and unit 4 includes welded layers this pattern is consistent with a general decrease in mfci efficiency due to the depletion of locally available coolant i e groundwater or wet sediments changing conduit vent geometries mixing conditions coolant and melt temperatures and or coolant impurities may also have affected mfci efficiency but the rhythmic nature of the bed pairs implies a periodic explosion process which can be explained by temporary increases in the water to lava mass ratio during cycles of groundwater recharge

formation of tectonic peperites from alkaline magmas intruded into wet sediments in the beiya area western yunnan china tertiary 3 78 ma to 3 65 ma biotite k feldspar porphyritic bodies intrude tertiary poorly consolidated lacustrine sedimentary rocks in the beiya mineral district in southwestern china the intrusives are characterized by a microcrystalline and vitreous cryptocrystalline groundmass by replacement of some tabular k feldspar phenocrysts with microcrystalline chlorite and calcite and by fe rich rings surrounding biotite phenocrysts peculiar structures such as contemporary contact faults and slickensides ductile shear zones and flow folds foliation and lineations tension fractures and banded and boudin peperites are developed along the contact zones of the intrusives these features are related to the forceful intrusion of the alkaline magmas into the wet tertiary sediments the partially consolidated magmas were deformed and flattened by continued forceful magma intrusion that produced boudinaged and banded peperites these peperites characterized by containing oriented deformation fabrics are classified as tectonic peperites as a new type of peperite and formation of these tectonic peperites was related to fracturing of magmas caused by forceful intrusion and shear deformation and to contemporary migration and injection of fluidized sediments along fractures that dismembered the porphyritic magma emplacement of the magma into the wet sediments in the beiya area is interpreted to be related to a large pressure difference rather than to the buoyancy force

swarms of repeating long period earthquakes at shishaldin volcano alaska 2001 2004 abstract during 2001 2004 a series of four periods of elevated long period seismic activity each lasting about 1 2 months occurred at shishaldin volcano aleutian islands alaska the time periods are termed swarms of repeating events reflecting an abundance of earthquakes with highly similar waveforms that indicate stable non destructive sources these swarms are characterized by increased earthquake amplitudes although the seismicity rate of one event every 0 5 5 min has remained more or less constant since shishaldin last erupted in 1999 a method based on waveform cross correlation is used to identify highly repetitive events suggestive of spatially distinct source locations the waveform analysis shows that several different families of similar events co exist during a given swarm day but generally only one large family dominates a network of hydrothermal fractures may explain the events that do not belong to a dominant repeating event group i e multiple sources at different locations exist next to a dominant source the dominant waveforms exhibit systematic changes throughout each swarm but some of these waveforms do reappear over the course of 4 years indicating repeatedly activated source locations the choked flow model provides a plausible trigger mechanism for the repeating events observed at shishaldin explaining the gradual changes in waveforms over time by changes in pressure gradient across a constriction within the uppermost part of the conduit the sustained generation of shishaldin s long period events may be attributed to complex dynamics of a multi fractured hydrothermal system the pressure gradient within the main conduit may be regulated by temporarily sealing and reopening of parallel flow pathways by the amount of debris within the main conduit and or by changing gas influx into the hydrothermal system the observations suggest that shishaldin s swarms of repeating events represent time periods during which a dominant source is activated

the holocene secche di lazzaro phreatomagmatic succession stromboli italy evidence of pyroclastic density current origin deduced by facies analysis and ams flow directions the edifice of stromboli volcano gravitationally collapsed several times during its volcanic history 100 ka present the largest holocene event occurred during the final stage of the neostromboli activity 13 5 ka and was accompanied by the emplacement of phreatomagmatic and lahar deposits known as the secche di lazzaro succession a stratigraphic and paleomagnetic study of the secche di lazzaro deposits allows the interpretation of the emplacement and the eruptive processes we identify three main units within the succession that correspond to changing eruption conditions the lower unit ua consists of accretionary lapilli rich thinly bedded parallel to cross stratified ash deposits interpreted to indicate the early stages of the eruption and emplacement of dilute pyroclastic density currents upward the second unit ub of the deposit is more massive and the beds thicker indicating an increase in the sedimentation rate from pyroclastic density currents the upper unit uc caps the succession with thick immediately post eruptive lahars which reworked ash deposited on the volcano s slope flow directions obtained by anisotropy of magnetic susceptibility ams analysis of the basal bed of ua at the type locality suggest a provenance of pyroclastic currents from the sea this is interpreted to be related to the initial base surges associated with water magma interaction that occurred immediately after the lateral collapse which wrapped around the shoulder of the sector collapse scar upward in the stratigraphy upper beds of ua and ub paleoflow directions change and show a provenance from the summit vent probably related to the multiple collapses of a vertical pulsatory eruptive column

volcano sedimentary characteristics in the abu treifiya basin cairo suez district egypt example of dynamics and fluidization over sedimentary and volcaniclastic beds by emplacement of syn volcanic basaltic rocks abstract this paper describes the neogene lava sediment mingling from the abu treifiya basin cairo suez district egypt the lava sediment interactions as peperites have been identified for the first time at the study area and can be used as paleoenvironmental indicators the identification of peperite reflects contemporaneous time relationship between volcanism and sedimentation and this finding is of primary importance to address the evolutional reconstruction of the abu treifiya basin characterization of the facies architecture and textural framework of peperites was carried out through detailed description and interpretation of their outcrops the peperites and sedimentary rocks are up to 350 m thick and form a distinct stratigraphic framework of diverse lithology that is widespread over several kilometers at the study area lateral and vertical facies of the peperites vary from sediment intercalated with the extrusive intrusive basaltic rocks forming peperitic breccias to lava sediment contacts at a large to small scales respectively peperites encompass five main facies types ascribed to i carbonate sediments hosted fluidal and blocky peperites ii lava flow hosted blocky peperites iii volcaniclastics hosted fluidal and blocky peperites iv sandstone siltstone rocks hosted blocky peperites and iv debris flows hosted blocky peperites soft sediment deformation structures vesiculated sediments sediments filled vesicles and fractures in lava flows indicate that lava flows mingled with unconsolidated wet sediments all the peperites in this study could be described as blocky or fluidal but mixtures of different clast shapes occur regardless of the host sediment the presence of fluidal and blocky juvenile clasts elucidates different eruptive styles reflecting a ductile and brittle fragmentation the gradual variation from fluidal to blocky peperite texture producing the vertical grading is affected by influencing factors e g the viscosity magma temperature confining pressure sediment fluidization and vapor film at the magma sediment interactions peperites in the study area record deposition within a shallow marine and fluvio lacustrine environment accumulated in a rift related basin developed during pre to syn rift phase respectively the facies transitions peperites in this area resulted from the explosive and sediment depositional processes which were mingled separately by volcanism under contrast geological conditions the development of such contrast in the depositional sequences reflects variation in the accommodation to sediment supply in the same accumulation space inside the depocenters during the rifting of the abu treifiya basin hydrothermal mineralizations comprising quartz and carbonate are restricted to peperites and lava flows

quantitative experiments on phreatomagmatic explosions abstract an experimental set up for controlled generation of thermal explosions fuel coolant interactions has been built by an interdisciplinary research group of volcanologists physicists and engineering scientists the tee haus thermal explosion experiment during the last 3 years more than 500 experimental runs were performed aim of the project was not to build a mini volcano but to produce igniteable mixtures of water and hot melt on a small scale in order to investigate basic physical aspects such small scale mixtures however most probably also occur during phreatomagmatic events in nature mixtures of water and magma on a large scale may be modelled by combination of small elements earlier experimental studies of thermal explosions were carried out with the use of metal melts nearly exclusively therefore a carbonate melt approx 0 3 kg of 1 1 mass ratio na2co3 k2co3 was used for initial experimental series because of easy handling and more magma similarity by injection of water into this melt explosive mixtures were produced and ignited self triggering explosive interactions occurred in a wide melt temperature range 720 to 1040 c at melt temperatures exceeding 1000 c co2 increasingly degassed presence of non condensible gas bubbles in the melt strongly reduced the explosivity the intensity of explosions only slightly increased with higher melt temperatures but strongly increased with higher water injection velocities because of more intensive mixing a minimum injection velocity was found to be approx 0 7 m s 1 experiments with silicate melts derived from diverse remelted volcanic rocks were carried out with a slightly modified set up explosions were ignited by an additional trigger a shock wave of approx 8 j in volcanic systems shock waves of this magnitude are abundant volcanic tremor etc strong explosions with silicate melts were produced at melt temperatures between 1350 and 1750 c the produced explosions exerted repulsion forces of up to 24 000 n with a typical pulse duration of 1 ms carbonate melt resp 1 5 ms silicate melts the ejection velocity was found to be in a range between 200 and 400 m s 1 explosion energy values up to 500 j were calculated the maximum explosion pressure was calculated to be in the range between 10 and 100 mpa only part of the melt so called interactive melt reacts explosively with injected water most of the melt is passively ejected by and after the thermal explosion different fragmentation processes result in specific grain size and grain shape populations that can be distinguished from each other particles resulting from the fine fragmentation process that precedes and causes the thermal explosion are characterized by angular to subrounded shapes and grain sizes ranging from 20 m to 180 m the amount of interactive melt is proportional to the intensity of the explosion the maximum amount of water vapourized at the explosive interaction so called interactive water was estimated thus the water melt mass ratio for explosive interactions could be calculated the values range between 1 25 and 1 35 carbonate melt resp between 1 6 and 1 25 silicate melts

mechanisms of hydrovolcanic pyroclast formation grain size scanning electron microscopy and experimental studies pyroclasts produced by explosive magma water interactions are of various sizes and shapes data from analysis of over 200 samples of hydrovolcanic ash are interpreted by comparison with experimentally produced ash grain size and scanning electron microscopy sem reveal information on the formation of hydrovolcanic pyroclasts strombolian explosions result from limited water interaction with magma and the pyroclasts produced are dominantly centimeter sized with increasing water interaction hydrovolcanism increases in explosivity to surtseyan and vulcanian activity these eruptions produce millimeter to micron sized pyroclasts the abundance of fine ash 63 m diameter increases from 5 to over 30 percent as water interaction reaches an explosive maximum this maximum occurs with interactions of virtually equal volumes of melt and water five dominant pyroclast shape types determined by sem result from hydrovolcanic fragmentation 1 blocky and equant 2 vesicular and irregular with smooth surfaces 3 moss like and convoluted 4 spherical or drop like and 5 plate like types 1 and 2 dominate pyroclasts greater than 100 m in diameter types 3 and 4 are typical of fine ash type 5 pyroclasts characterize ash less than 100 m in diameter resulting from hydrovolcanic fragmentation after strong vesiculation fragmentation mechanisms observed in experimental melt water interactions result from vapor film generation expansion and collapse fragments of congealed melt are products of several alternative mechanisms including stress wave cavitation detonation waves and fluid instability mixing all result in rapid heat transfer these mechanisms can explain the five observed pyroclast shapes stress wave fracturing cavitation of the melt results from high pressure and temperature gradients at the melt water interface simultaneous brittle fracture and quenching produces type 1 pyroclasts type 2 develops smooth fused surfaces due to turbulent mixing with water after fracture and before quenching fluid instabilities promote turbulent mixing of melt and water and produce fine ash this kind of fragmentation occurs during high energy explosions the increased melt surface area due to fine fragmentation promotes high efficiency heat exchange between the melt and water shapes of resulting pyroclasts are determined by maximum surface area type 3 and surface tension effects type 4 type 5 pyroclasts result from nearly simultaneous vesicle burst and melt water fragmentation

deep explosive focal depths during maar forming magmatic hydrothermal eruption baccano crater central italy we describe the eruptive activity of the pleistocene composite baccano maar crater in the sabatini volcanic complex central italy combining stratigraphy grain size componentry and rare earth element and yttrium rey composition of its eruptive products with the stratigraphy and geothermal data derived from deep wells drilled on the baccano structural high the main lithological characteristics of the basal baccano maar pyroclastic deposit composed of more than 60 wt of non thermometamorphosed lithic clasts from the sedimentary basement show that the first eruption was magmatic hydrothermal in nature the lithology of the sedimentary lithic clasts indicates that the fragmentation level was at a depth of 1 000 to 1 200 m with fragment depth verified by deep well stratigraphy the 15 wt juvenile non vesicular glass components suggest that magma played a minor role in powering the eruption assuming that the high salinity hot hydrothermal fluids 365 1 400 m by the aggressive hydrothermal fluids enriched in acid components hf hcl and h2so4 may have contributed to increased co2 partial pressure that helped to drive the hydrofracturing this could have caused rapid vapour separation and pressure drop allowing the almost simultaneous breaking of the aquifer cover and brecciation of the calcareous units down to 1 000 to 1 200 m depth the relative abundance of calcareous lithics in the basal part of the first baccano eruptive unit representing about the upper 200 m of stratigraphy below the top of the baccano structural high reveals the descent of the piezometric surface during the eruption combining deep well information and maar product stratigraphy using also rey data from maar pyroclastic fragments and the basement rocks we draw an interpretative model for the baccano maar forming eruption concluding that a magmatic hydrothermal eruptions may originate deeper than previously thought and b hydrothermal fluids circulating in limestone aquifers may play an important role in triggering such eruptions

subaqueous basaltic magmatic explosions trigger phreatomagmatism a case study from askja iceland abstract sequences of basaltic pillow lavas that transition upward with systematic gradation from pillow fragment breccias to fluidal bomb bearing breccias to bomb bearing lapilli tuffs are common at askja volcano iceland based on the detailed textural investigation of three of these sequences we argue that they record temporally continuous transitions from effusive to explosive products that were erupted from and deposited at or near a single subaqueous vent the recognition of such sequences is important as they provide evidence for controls on the onset of explosive activity in subaqueous environments such investigations are complicated by the interplay of magmatic gas expansion and phreatomagmatic and mechanical granulation fragmentation mechanisms in the subaqueous eruptive environment all of the sequences studied at askja have textural componentry and sedimentological characteristics suggestive of a close genetic and spatial relationship between the pillow lavas and all of the overlying glassy clastic deposits the identification of magma fragmentation signatures in pyroclasts was accomplished through detailed textural studies of pyroclasts within the full range of grain sizes of a given deposit i e bomb blocks lapilli and fine ash these textural characteristics were compared and evaluated as discriminators of fragmentation in pyroclastic deposits the presence of angular vitric clasts within the breccia and lapilli tuff displaying fragile glassy projections indicates little or no post depositional textural modification a shift in vesicle and clast textures between the pillow lavas and the large concentration of fluidal bombs in the breccia indicates that the phreatomagmatic explosions were initially triggered by magmatic vesiculation the initial magmatic gas expansion may have been triggered by depressurization caused by the drainage of the ice confined lake surrounding askja the fuel coolant interactions fcis of the more efficient phreatomagmatic explosions were enabled by the increase in the surface area to volume ratio of the fluidal bombs in the water producing a premix of magma and water the onset and increasing influence of phreatomagmatic fragmentation is preserved in the presence of very fine blocky ash particles and diminished presence of larger particles such as fluidal bombs the textural sedimentological and environmental characteristics of these deposits suggest that phreatomagmatic explosions can be triggered by initial magmatic gas expansion but that it is likely one of many mechanisms for triggering such explosions

a magmatic hydrothermal lacustrine exhalite from the permian lucaogou formation santanghu basin nw china the volcanogenic origin of fine grained clastic sedimentary rocks abstract shales in the middle permian lucaogou formation in the intracontinental santanghu rift basin have been considered as typical organic rich profundal shales for decades our study of well cores using petrographic microscope and scanning electron microscopy suggests an otherwise complex hydrovolcanic and hydrothermal origin this paper describes characteristics of a particular type of the shales composed of fine grained detrital minerals and lithic grains some of them are orthopyroxene calcite peralkaline feldspars and analcime that are interpreted as derived from peralkaline alkaline carbonatite pyroxenite analcime phonolite and andesite whereas others are quartz dolomite ankerite serpentine and calcite that were precipitated from syndepositional or penecontemporary hydrothermal fluids grain size ranges from 0 001 to 2 mm mostly 0 01 0 1 mm well developed laminae are mostly 0 5 3 mm thick and alternate with tuffaceous dolomicrite the rocks are interpreted as sublacustrine hydrovolcanic deposits which had been altered by syndepositional hydrothermal fluids the interpretation is substantiated by abundant cone shaped stratigraphic buildups on seismic sections in the basin this study shows an ancient example of volcanic hydrothermal deposits in a rift basin

olivine basalt and trachyandesite peperites formed at the subsurface surface interface of a semi arid lake an example from the early miocene bigadic basin western turkey abstract miocene successions in western turkey are dominated by lacustrine fluvial and evaporitic sedimentary deposits these deposits include considerable amounts of volcaniclastic detritus derived from numerous ne trending volcanic centres in western turkey as well as in the bigadic region early miocene syn depositional ne trending olivine basalt and trachyandesite bodies that formed as intrusions and lava flows occur within the bigadic borate basin olivine basalts occur as partly emergent intrusions and trachyandesite dykes fed extensive lava flows emplaced in a semi arid lacustrine environment peperites associated with the olivine basalt and trachyandesites appear to display contrasting textural features although all the localities include a large variety of clast morphologies from blocky to fluidal fluidal clasts mainly globular ameboidal and pillow like varieties are widespread in the peperite domains associated with olivine basalts apparently due to large volume sediment fluidisation in contrast fluidal clasts related to trachyandesites are restricted to narrow zones near the margins of the intrusions and have commonly elongate and polyhedral shapes with digitate margins rather than globular and equant varieties blocky and fluidal clasts in the olivine basalt peperite display progressive disintegration suggesting decreasing temperature and increasing viscosity during fragmentation abundance of blocky clasts with respect to fluidal clasts in the trachyandesite peperite indicates that the fluidal emplacement and low volume sediment fluidisation in the early stages were immediately followed by quench fragmentation due to the high viscosity of the magma size texture and abundance of the blocky and fluidal clasts in the olivine basalt and trachyandesite peperites were mainly controlled by sediment fluidisation pulsatory magma injection and magma properties such as composition viscosity vesicularity and size abundance and orientation of phenocrysts variously combining these contrasting features to varying degrees may form diverse juvenile clast shapes in peperitic domains

repeating coupled earthquakes at shishaldin volcano alaska since it last erupted in 1999 shishaldin volcano aleutian islands alaska has produced hundreds to thousands of longperiod 1 2 hz lp earthquakes every day with no other sign of volcanic unrest in 2002 the earthquakes also exhibited a short period 4 7 hz sp signal occurring between 3 and 15 s before the lp phase although the sp phase contains higher frequencies than the lp phase its spectral content is still well below that expected of brittle failure events the sp phase was never observed without the lp phase although lp events continued to occur in the absence of the precursory signal the twophased events are termed bcoupled eventsq reflecting a triggered relationship between two discrete event types both phases are highly repetitive in time series suggestive of stable non destructive sources waveform cross correlation and spectral coherence are used to extract waveforms from the continuous record and determine precise p wave arrivals for the sp phase although depths are poorly constrained the sp phase is believed to lie at shallow b4 km depths just west of shishaldin s summit the variable timing between the sp and lp arrivals indicates that the trigger mechanism between the phases itself moves at variable speeds a model is proposed in which the sp phase results from fluid moving within the conduit possibly around an obstruction and the lp phase results from the coalescence of a shallow gas bubble the variable timing is attributed to changes in gas content within the conduit the destruction of the conduit obstacle on november 21 2002 resulted in the abrupt disappearance of the sp phase published by elsevier b v

peperites and associated pillow lavas subjacent to the oman ophiolite abstract peperites are breccias consisting of a mix of cooled magma and sediment they result from the intrusion of molten rock into water saturated sediments we report an occurrence of peperite in the oman united arab emirates uae border region of khattm al shiklah and characterize samples that have been collected from 6 locations east of al ain uae at jabal um bak jabal hamra and jabal dai in oman geochemical analysis indicates that the magmas represented in these samples are related in addition field relations of the pillow lavas surrounded by limestone with deformed bedding and peperite boundaries between the pillows and the limestone are consistent with the pillow lavas forming directly within carbonate sediments it is likely that the ambient pressure was great enough and cooling of the magma rapid enough to prevent large explosions the fact that the magma also formed pillows is evidence of this the rapid quenching of the magma by water saturated fine unconsolidated sediments likely produced conditions similar to those attending pillow lava formation directly into water

fine grained volcanic hydrothermal sedimentary rocks in permian lucaogou formation santanghu basin nw china implications on hydrocarbon source rocks and accumulation in lacustrine rift basins abstract subaqueous volcanic hydrothermal field is a complex hybrid geological system where sediments originated from volcanic hydrothermal lacustrine terrestrial and biotic sources are mixed recent petrological studies on such sediments have indicated a potential relationship between volcanic hydrothermal activities and oil generation and accumulation here we explore the mechanisms of sedimentation and oil accumulation in well laminated organic rich fine grained sedimentary rocks in permian lucaogou formation deposited in the lacustrine santanghu rift basin nw china we conducted petrographic carbon and oxygen isotopic and organic geochemical analyses of fifty four core samples from three wells forty eight samples from well w1 two from w2 four from w3 designed for tight oil exploration four main observations and interpretations are 1 the fine grained sediments are a mixture of volcanic hydrothermal detrital feldspar grains authigenic quartz crystals and primary lacustrine dolomite forming interbedded tuffaceous shale and dolostone 2 authigenic quartz crystals were precipitated from acidic hydrothermal fluids whereas fine grained angular alkaline feldspars were derived from subaqueous volcanic eruption 3 the toc content and oil generation potential increase with increased mixing of feldspars and carbonate minerals hence the dolomite bearing tuffaceous shale and tuffaceous dolostone are the best source rocks and 4 the fine grained sedimentary rocks are interpreted as a subaqueous volcanic hydrothermal deposit that controls the source potential the sedimentary processes of an ancient sediment hosted geothermal system and its implications on hydrocarbon source rocks and accumulation were first identified algal bloom induced by subaqueous eruptions is the main cause for episodic deposition of organic matter and extreme heterogeneity in both lithofacies and source rock distribution the results suggest that cone shaped buildups on seismic sections which were formed by volcanic hydrothermal deposits and contain highly mixed feldspar and carbonate sediments are the best hydrocarbon reservoirs and demonstrate a strong relationship between volcanic hydrothermal activities and hydrocarbon accumulation in an extensional tectonic setting

variation in peperite textures associated with differing host sediment properties peperites formed by mixing of magma and wet sediment are well exposed along punta china baja california mexico where two sills intrude a section of lava flows limestones and volcaniclastic rocks irregular lobes and dikes extend from the sills several meters into host sediments including highly comminuted flow top breccias lithic lapilli tuff breccias and shelly micrites whereas intrusive contacts with lava flows are sharp and planar where one sill intruded both coarse grained volcaniclastic rock and fine grained limestone textural differences between the hosts produced strikingly different styles of peperite blocky masses of the basaltic intrusions up to 1 m in size were dispersed for distances up to 3 m into host lithic lapilli tuff breccias the blocks consequently underwent in situ fragmentation as they were rapidly quenched the high degree of dispersion resulted from steam explosions as the magma enveloped pockets of water in the coarse grained permeable host elutriation of fine grained material from vertical pipes in tuff breccia above the lower sill provides evidence for meter scale fluidization of the host the contact zone between the basaltic magma and the shelly micrite host resembles a mixture of two viscous immiscible fluids fluidal peperite intrusion occurred behind a stable vapor film which entrained lime mud particles and carried them off grain by grain as magma advanced into the host thin section scale elutriation pipes formed microglobular peperite represents a frozen example of a fuel coolant interaction fci between basaltic magma and fluidized micrite host the intimate intermixing of magma and host at the submillimeter level is attributed to fluid instabilities developed along the magma vapor host interface such intimate intermixing of magma and water bearing fragmental debris is commonly a precursory step toward explosive hydrovolcanism

heat source or heat sink what dominates behavior of non explosive magma water interaction 1 much of the volcanism on earth takes place in subaqueous settings where magma has direct contact with a water reservoir of restricted or quasi unrestricted volume in order to assess the intensity and timescale of non explosive interaction of magmatic melts and water experiments representing these settings were performed natural volcanic samples were remelted and poured as a continuous jet into a water filled calorimeter where the melt interacts with its coolant the rapid cooling results in granulation i e brittle failure of the material granulation needs energy which is taken from the thermal input of the hot melt energy used in granulation was found to require 5 20 of the melt s initial heat content this energy loss fraction is insensitive to variations in coolant and melt temperatures but instead depends on the melt s thermomechanical properties however analysis of the experimentally produced granulate indicates a strong correlation between the initial coolant temperature i e the heat sink and the grain size distribution but also shows variations due to material properties the maximum of the grain size distribution was determined to change from a diameter of 1 mm up to 4 mm due to coolant temperature increase properties of the heat source melt dominate the efficiency of the process whereas both heat sink and source characteristics determine the products

evolution of the submarine subaerial edifice of bogoslof volcano alaska during its 2016 2017 eruption based on analysis of satellite imagery the 2016 2017 eruption of bogoslof volcano involved at least 70 detected eruptive events between mid december 2016 and august 30 2017 acquisition of high resolution satellite imagery throughout the duration of the eruptive period allowed us to document and map the various morphologic changes that occurred on the subaerial part of bogoslof island the emplacement of pyroclastic flow and surge deposits caused the island to increase in area by about 1 5 km2 the dominant volcanic landforms of the eruption were a series of tuff rings emplaced around various submarine vents many of the tuff rings were mantled with surface dunes and impressive amounts of ballistic ejecta likely derived from erupting magma bodies or previously emplaced submarine lava domes debris flow deposits and surface channels extending over tuff ring surfaces apparent in multiple satellite images are evidence for explosive ejection of seawater in most cases erupting vents were initially submarine or began at subaerial lava domes and were largely flooded by seawater suggesting that water magma ratios were likely high under such conditions where water is abundant eruptive products typically reflect a high degree of water involvement and are dominated by the formation of wet tephra jets and flows and associated deposits typically consist of fine ash and lapilli contain accretionary lapilli and ash aggregates and usually form tuff cones and mounds we observed none of these features in our analysis of satellite data or during our examination of eruptive deposits on bogoslof island in 2018 on the contrary the dominant landform associated with the bogoslof eruption was tuff rings the development of tuff rings and surface dunes are commonly associated with the formation of pyroclastic base surges that are by comparison emplaced relatively dry dry base surge deposits can be generated from phreatomagmatic explosions involving superheated steam it is possible that shallow submarine magma wet sediment interactions were a characteristic and possibly a dominant eruptive process of the 2016 2017 bogoslof eruption

the basalt pipes of the tunguska basin siberia russia high temperature processes and volatile degassing into the end permian atmosphere abstract a number of mechanisms have been proposed to explain the end permian crisis many of them explore the link between this catastrophe and the siberian traps we test the hypothesis that eruption of thermogenic gas generated in contact aureoles around igneous sills intruded into evaporite sequences of the tunguska basin triggered the crisis in particular we test the idea that the aspect that breccia pipes represent conduits for voluminous gas migration from the deep basins to the atmosphere this contribution sheds new light on the pipe formation based on new field and borehole observations and electron microscopy analyses of more than three hundred mapped magnetite bearing basalt pipes 43 are classified as diatremes the diatremes are usually circular or elliptical with multiple zones of brecciation reaching the surface sometimes with preserved in filled crater lakes the pipe diameter on the surface varies from a few tens of meters for small single diatremes to about a kilometer the largest crater lake area is 2 7 km 2 we have conducted a detailed study of the breccias in the sholokhovsk basalt pipe located within the nepa potash deposit in the tunguska basin siberia russia about n 59 and e 107 and find that the breccias are cemented by carbonate matrix calcite dolomite and halite breccia clasts are altered at various temperatures evidenced by growth of albite and garnet from basaltic glass and diopside garnet magnetite and chlorine bearing amphibole up to 1 8 cl in altered magmatic clasts these mineral assemblages suggest high temperature interactions with evaporites within the pipe conduits the large number of pipes support that degassing of halogen rich volatiles was a widespread and violent process with implications for the end permian crisis

modeling steam pressure under martian lava flows abstract rootless cones on mars are a valuable indicator of past interactions between lava and water however the details of the lava water interactions are not fully understood limiting the ability to use these features to infer new information about past water on mars we have developed a model for the pressurization of a dry layer of porous regolith by melting and boiling ground ice in the shallow subsurface this model builds on previous models of lava cooling and melting of subsurface ice we find that for reasonable regolith properties and ice depths of decimeters explosive pressures can be reached however the energy stored within such lags is insufficient to excavate thick flows unless they draw steam from a broader region than the local eruption site these results indicate that lag pressurization can drive rootless cone formation under favorable circumstances but in other instances molten fuel coolant interactions are probably required we use the model results to consider a range of scenarios for rootless cone formation in athabasca valles pressure buildup by melting and boiling ice under a desiccated lag is possible in some locations consistent with the expected distribution of ice implanted from atmospheric water vapor however it is uncertain whether such ice has existed in the vicinity of athabasca valles in recent history plausible alternative sources include surface snow or an aqueous flood shortly before the emplacement of the lava flow

the fracture behaviour of volcanic glass and relevance to quench fragmentation during formation of hyaloclastite and phreatomagmatism quench fragmentation is a non explosive process that occurs when molten magma is super cooled to glass upon contact with ambient water this occurs when coherent lavas are erupted subaqueously when they flow into water when magma intrudes into water saturated sediments and when magma and water interact explosively during phreatomagmatism quench fragmentation also occurs alongside explosive phreatomagmatic activity although products of quench fragmentation hyaloclastite sensu stricto have been discussed qualitatively in the volcanological literature compared to explosive fragmentation processes very little is known about the exact dynamics of quench fragmentation of magma and how this relates to the rheology and physical properties of volcanic glass based on literature from materials engineering we present a detailed review of the processes by which glass forms the properties of glass and the fracture mechanics that cause it to fragment non explosively we also consider how this can be applied to understanding the dynamics behind the volcanological processes of in situ glass fragmentation during quenching in wet environments and phreatomagmatism important parameters for the occurrence of quench fragmentation are the temperature difference between the magma and the ambient water and how much the ambient water is superheated above its leidenfrost temperature the geometry of the lava or magma intrusion the thermal conductivity and the thermal expansion are also of great importance the resistance of the magma against fragmentation can be increased with the presence of crystals provided the thermal expansion of the crystals does not greatly exceed that of the glass vesicles have the opposite effect unless the magma is highly vesicular this overview then provides a solid basis for further quantitative study of quench fragmentation and hyaloclastite formation

disappearance of a crater lake implications for potential explosivity at soufriere volcano st vincent lesser antilles soufriere volcano in st vincent west indies is one of the most active volcanoes in the eastern caribbean with at least six eruptions since 1718 ad the latest of which occurred in 1979 prior to the 1979 eruption the active crater hosted deep water lakes during periods of repose which were always replenished within a few years after the eruptions in 1979 the crater was filled with 108 m3 of fragmental material and despite constant precipitation has remained virtually dry ever since with the exception of a small shallow pond a resistivity survey was conducted in july 2006 to investigate groundwater occurrence in the crater results from the resistivity data inversion on several 2 d profiles show a shallow horizontal conductor across the crater floor consistent with a water saturated aquifer they also show that the post 1979 pond currently present in the crater lake is in fact an outcropping part of the groundwater water reservoir the reservoir water table is 28 m above the pre 1979 lake level and reflects mass equilibrium in the system where constant seepage underground balances the meteoric recharge we suggest that the groundwater body extends at depth to the bottom of the pre 1979 crater lake either due to a significant structural discontinuity or because of a reduction of permeability at depth the estimated maximum volume of water stored underground is 10 30 106 m3 and energy considerations indicate that 2 4 7 3 1010 kg of magma would potentially be sufficient to vaporise the whole groundwater body this amount of magma represents only 13 41 of the mass erupted during the last eruption in 1979 which was the smallest of the past 3 eruptions 1902 1971 72 1979 since explosive phreatic or phreatomagmatic eruptions at soufriere seem to be linked to magma water interaction within confined space the results from this survey suggests that phreatic or phreatomagmatic activity is a distinct possibility during future magma intrusion in the summit area despite the apparent disappearance of water in the summit crater

facies architecture of the upper oligocene submarine smrekovec stratovolcano northern slovenia abstract the upper oligocene smrekovec volcanic complex svc represents the remains of a submarine stratovolcano which underwent early miocene tectonic dissection and large scale displacement along the periadriatic line according to the lithofacies architecture abundance and spatial distribution central medial and distal zones of the former volcano edifice have been recognized the zones extend at a distance of 0 2 km 2 5 km and 5 20 km south of the periadriatic line respectively lavas shallow intrusive bodies autobreccia peperite and hyaloclastite deposits occur mainly in the central zone which is extensively altered under hydrothermal conditions characterised by the development of zeolites mainly laumontite prehnite chlorite albite and epidote explosive volcanic activity intensified with the evolution of magma from basaltic andesitic to dacitic gas and water supported eruption fed density flows are assumed their deposits show lithofacies organisation in pyroclastic depositional units pdus similar to either volcaniclastic turbidites type 1 or thin subaqueous ignimbrites type 2 volcaniclastic debris flow deposits are developed as volcaniclastic breccia and sandy debris flow deposits the former occurs in the central and medial zones and the latter occurs in the medial zone only the most widespread lithofacies in the svc are volcaniclastic turbidite deposits three types of sedimentary unit tsu have been distinguished type 1 is 2 5 m thick and dominated by the massive division it mainly occurs in the central zone type 2 is 0 7 3 5 m thick and occurs in the central and medial zones it comprises the massive division bedded fining and thinning upward division and a horizontally wavy and cross laminated division topped by massive fine grained tuff type 3 is 0 1 1 5 m thick and mainly occurs in the distal zone the massive division is absent and thinly bedded and laminated divisions are topped by massive fine grained tuff volcaniclastic turbidites were settled from low density turbidity currents and related suspension clouds mixed volcaniclastic siliciclastic deposits are subordinate in occurrence and restricted to the distal zone they are commonly reworked by bottom currents

complex bombs of phreatomagmatic eruptions role of agglomeration and welding in vents of the 1886 rotomahana eruption tarawera new zealand 1 basaltic bombs ejected from a rotomahana crater during the 1886 tarawera eruption in new zealand are of two fundamental types cored bombs which have single large fragments generally of rhyolite wall rock material as their cores and loaded bombs which contain abundant small fragments dispersed through the bombs similar lithic bearing bombs are common products of other phreatomagmatic eruptions worldwide cored bombs originate when a large wall rock fragment is entrained in basaltic melt and then ejected with an adhering skin of basalt in contrast loaded bombs are constructed by agglomeration of multiple fragments of basalt among which smaller rhyolitic wall rock fragments are dispersed different styles and rates of bomb loading are reflected in the bombs textures and compositions these textures provide insight into the nature of fragmentation during the eruption the processes of recycling that produce multiply ejected clasts versus recapitulated ones those where early formed clasts were reingested in magma and then formed the cores of new bombs the degree and timescale of interaction of magma with vent walls and the timescales over which lithic material from the vent walls is incorporated into complex bombs prior to their ejection because fragments of rhyolitic pumice are readily refused their condition constrains estimates of the timing of fragmentation and agglomeration the presence of nonfused rhyolite pumice within many loaded bombs implies that the processes forming and quenching the bombs cannot have exceeded several seconds in contrast other bombs contain patches of compositionally modified basalt with isolated rhyolite derived feldspar xenocrysts that indicate complete fusing melting and assimilation of entrained rhyolitic debris the bomb population overall indicates that conditions within this rotomahana vent were thermally and physically heterogeneous and that recycling of debris was ubiquitous both as recycling of large individual clasts and by fallback and aggregation of material which was reingested in magma before being reejected as new bombs

detailed topographical distributional and material analyses of rootless cones in myvatn iceland abstract unique types of rootless cones have been found both on earth and on mars they have inner cones inside their summit craters and we call them double cones dcs and multiple cones though previous studies have mentioned their existence there are no quantitative data on their topography distribution or constituent materials having this information available as a comparative reference could promote our understanding of martian cones for this study we conducted a field campaign on terrestrial cones in myvatn iceland to provide high quality reference data about the morphology of rootless cones we performed kinematic global positioning system gps measurements in the study area dcs and multiple cones are located in the vicinity of the lake lake myvatn within 15 km of a fissure vent there are no such cones on the paleo riverbed in crosscut outcrops of dcs on geitey island a clearly recognizable structural boundary between the inner and outer cones shows that the inner cone was formed by a separate explosion episode we propose a probable formation scenario for dcs here we posit that the inner cones of dcs are formed by delayed explosions due to percolation of water through the lacustrine sediments these unique characteristics of rootless cones are useful in the interpretation of martian cones

hyaloclastites peperites and soft sediment deformation textures of a shallow subaqueous miocene rhyolitic dome cryptodome complex palhaza hungary abstract the ne tokaj mountains at palhaza in ne hungary are made up of a complex association of miocene rhyolitic shallow intrusions cryptodomes and endogenous lava domes emplaced into and onto soft wet pelitic sediment in a shallow submarine environment the intrusive extrusive complex shows a range of interaction textures with the host muddy sediment ranging from blocky peperites formed on a 0 1 m scale through to irregular contacts closely resembling globular mega peperites on a 10 m scale the over 200 m thick igneous succession is interpreted to result from the pulsatory growth of shallow cryptodomes through muddy saturated host sediment the intrusions eventually breached the sedimentary cover to build up thick in situ hyaloclastite piles in the shallow subaqueous environment the coherent rhyolitic cryptodome facies is surrounded by intrusive hyaloclastite in the contact zone to the pelitic host sediment in the upper level of the complex rhyolitic dome rock is capped and surrounded by hyaloclastite formed due to quench fragmentation upon contact of the lava surface with sea water

lava penetrating water the different behaviours of pāhoehoe and a ā at the nesjahraun þingvellir iceland the nesjahraun is a basaltic lava flow erupted from a subaerial fissure extending ne along the ingvellir graben from the hengill central volcano that produced p hoehoe lava followed by a the nesjahraun entered iceland s largest lake ingvallavatn along its southern shore during both phases of the eruption and exemplifies lava flowing into water in a lacustrine environment in the absence of powerful wave action this study combines airborne light detection and ranging sidescan sonar and chirp seismic data with field observations to investigate the behaviour of the lava as it entered the water p hoehoe sheet lava was formed during the early stages of the eruption along the shoreline stacks of thin 5 20 cm thick vesicular flows rest upon and surround low 2 m deep 50 m long spaced 50 m apart and have sub horizontal striations on the walls they likely represent channels or collapsed tubes along which lava was delivered into the water a circular rootless cone eldborg formed when water infiltrated a lava tube offshore from the p hoehoe lavas the gradient of the flow surface steepens suggesting a change in flow regime and the development of a talus ramp later the flow was focused into a channel of a lava 200 350 m wide this split into individual flow lobes 20 50 m wide along the shore a clinker is exposed on the water s edge as well as glassy sand and gravel which has been locally intruded by small 1 m irregularly shaped lava bodies the cores of the flow lobes contain coherent but hackly fractured lava mounds consisting predominantly of scoria lapilli and the large paired half cone of gramelur were formed in phreatomagmatic explosions the a flow can be identified underwater over 1 km offshore and the sidescan data suggest that the flow lobes remained coherent flowing down a gradient of 10 the nesjahraun demonstrates that even in the absence of ocean waves phreatomagmatic explosions are ubiquitous and that p hoehoe flows are much more likely to break up on entering the water than a flows which with a higher flux and shallow underlying surface gradient can penetrate water and remain coherent over distances of at least 1 km

peperite a review of magma sediment mingling the study of peperite is important for understanding magma water interaction and explosive hydrovolcanic hazards this paper reviews the processes and products of peperite genesis peperite is common in arc related and other volcano sedimentary sequences where it can be voluminous and dispersed widely from the parent intrusions it also occurs in phreatomagmatic vent filling deposits and along contacts between sediment and intrusions lavas and hot volcaniclastic deposits in many environments peperite can often be described on the basis of juvenile clast morphology as blocky or fluidal but other shapes occur and mixtures of different clast shapes are also found magma is dominantly fragmented by quenching hydromagmatic explosions magma sediment density contrasts and mechanical stress as a consequence of inflation or movement of magma or lava magma fragmentation by fluid fluid shearing and surface tension effects is probably also important in fluidal peperite fluidisation of host sediment hydromagmatic explosions forceful intrusion of magma and sediment liquefaction and shear liquification are probably the most important mechanisms by which juvenile clasts and host sediment are mingled and dispersed factors which could influence fragmentation and mingling processes include magma host sediment and peperite rheologies magma injection velocity volatile content of magma total volumes of magma and sediment involved total volume of pore water heated presence or absence of shock waves confining pressure and the nature of local and regional stress fields sediment rheology may be affected by dewatering compaction cementation vesiculation fracturing fragmentation fluidisation liquefaction shear liquification and melting during magma intrusion and peperite formation the presence of peperite intraclasts within peperite and single juvenile clasts with both sub planar and fluidal margins imply that peperite formation can be a multi stage process that varies both spatially and temporally mingling of juvenile clast populations formed under different thermal and mechanical conditions complicates the interpretation of magma fragmentation and mingling mechanisms

optimization of the horizontal well multiple hydraulic fracturing operation in a low permeability carbonate reservoir using fully coupled xfem model abstract pre analysis of the geometry and deviation of multiple hydraulically induced fractures is a decisive factor in the successful multiple hydraulic fracturing operations besides fracture spacing should be optimal for obtaining desired results such as maintaining sufficient aperture for proppant placement avoiding screen outs and also preventing fracture closure or crossing multiple fractures in fact the final geometry and deviation of multiple hydraulic fractures are dramatically influenced by the interaction of multiple hydraulic fractures on each other known as stress shadow effect which is caused by fracture spacing and pore pressure change predicting the geometry and deviation of multiple hydraulic fractures is a challenging part of conducting this technology in ilam reservoir due to low matrix permeability and naturally fractured nature of the reservoir accordingly a fully coupled stress diffusion xfem model for initiation and propagation of multiple hydraulic fractures with five injection zones was prepared to optimize the effect of fracture spacing and pore pressure change on the multiple hydraulic fractures deviation and geometry additionally the xfem model was verified by three approaches including field data stress intensity factor and kgd zero toughness solution wherein a very good agreement with negligible error was obtained for sif field data and kgd m vertex solution however this study has confirmed that both pore pressure and stress shadows contribute to change the fracture geometry and its deviation significantly in ilam reservoir also increasing pore pressure between fractures may affect the fracture geometry to be tighter in width and shorter in length in addition considering optimized fracture spacing about 75 m resulted in creation of very smooth uniform and deeper multiple hydraulic fractures so there will be no closed fractures in dph 02 horizontal wellbore and the possibility of crossing the furthest fracture by the second fracture significantly reduced when the fracture spacing was higher than 5 m

a late ordovician phreatomagmatic complex in marine soft substrate environment the crozon volcanic system armorican massif france the mafic lavas and the diabases of crozon armorican massif france belong to an anorogenic ordovician volcanic complex emplaced on a rifted passive margin in north gondwana magma passed through syn volcanic soft sedimentary substrate which is today mostly composed of alternating sandstones and mudstones from llanvirn to ashgill in age field observations together with microscopic studies and geochemical analyses of magmatic rocks lead us to propose a model of volcano formation which combines hydromagmatic processes peperitic intrusions a shallow submarine tephra settling eruption fed turbidity currents and a pillow lava effusion the crozon outcrops can be used to reconstruct a complete cross section from the root of the volcanic complex to the lavas and breccias emplaced on the sea floor the sites expose i a hypabyssal breccia containing mud chunks and coarse grained diabase clasts with amoeboidal fine grained magmatic material ii bulbous peperitic sills and pillow like lobes bearing a great quantity of sediment derived enclaves of fluidal morphology iii volcaniclastic breccias containing near spherical magmatic clasts that resulted from the complete fragmentation of sills in the ductile regime iv a rhythmic peperitic breccia interpreted as the product of mingling between thin lava flows and soft calcareous sediment the crozon volcanic form resulting from explosive interaction with subsurface surface water was probably a subaqueous collapsed tuff cone this upper part of the system is synchronous with an ashgill carbonate sedimentation which overlies an ordovician siliciclastic succession deposited in shelf environments

morphology of a crater filling lava lake margin the peninsula tuff cone tule lake national wildlife refuge california implications for formation of peperite textures abstract a crater filling lava lake basalt at the peninsula tuff cone in northeastern california has features on its base formed by interaction of the basalt with wet hydrovolcanic tuff a spectrum of features including elongated streamlined flute shaped lobes and irregular corrugations are exposed on the base of the lava lake flute shaped lobes range in amplitude from several centimeters to 0 5 m plunge downdip with respect to the subjacent layered tuff toward the center of the crater and are better defined at depths more than 3 m below the lava lake surface these may have been formed by growth of rayleigh taylor instability waves caused by the density contrast between the wet tuff and basalt combined with directed stress from flow of the lava lake radially outward from the crater formation of an insulating vapor film at the wet tuff basalt interface and downward pressure exerted by the lava lake allowed the edge of the lava lake to quench gradually and prevented formation of peperite at greater depths in the lake corrugations exposed on the upper 1 5 m of the lava lake margin increase in size from several millimeters to 10 cm in amplitude toward the top of the lava lake and approximately parallel the surface corrugations may be the remnant of fluidal peperite preserved on the edge of the lava lake where the peperite was eroded or may be deformation features formed within an insulating vapor film due to oscillation of the vapor film these were formed higher in the lava lake where the lava lake basalt was thinner wet tuff deposits confining the lava lake were thinner and temperature differences between the wet tuff and lava were greater if corrugations represent deformation of the lava edge within the vapor film rather than peperite formation they preserve an intermediate process that is involved in the formation of peperite this study offers a unique opportunity to evaluate some of the initial mechanisms involved in the formation of peperite based on features preserved in the lava where the host rock in this case hydrovolcanic tuff has been eroded but the properties of the host rock are known from adjacent exposures

shift from magmatic to phreatomagmatic explosions controlled by the lateral evolution of a feeder dike in the suoana kazahaya eruption miyakejima volcano japan abstract explosive phreatomagmatic eruption is one of the most hazardous eruption styles particularly in basaltic systems as the instability of the conduit system can result in a sudden and unexpected shift of eruption style from a mild effusion of lavas to violently explosive activity the geological investigations on the phreatomagmatic activities in the 7th century suoana kazahaya eruption ske of miyakejima reveal that the drop of magmatic overpressure in conduit and the distribution of groundwater controlled the occurrence of phreatomagmatic explosion the dry magmatic eruption in the initial phase of the ske indicates that the positive overpressure of magma in the propagating feeder dike prevents the invasion of external groundwater into the conduit explosive phreatomagmatic eruption occurred at the later phase of the ske from the vents in the higher elevation the drop of magmatic overpressure in the upper part of the feeder dike caused by the downslope propagation of the eruption fissure allowed groundwater inflow to the still hot and molten feeder dikes the limited distribution of phreatomagmatic activities indicated the development of shallow groundwater hosted in the porous pyroclastic deposits within a basin of less permeable older edifice as shifts of eruption style from initial magmatic to later phreatomagmatic explosive eruption style in the top of mafic volcanoes are globally observed in many mafic volcanic systems such as kilauea and mt etna this is probably a far more common eruption mechanism than previously thought and hence it needs to be considered in volcanic hazard scenario descriptions the spatial distributions of phreatomagmatic activities in the ske suggest that the detection of buried caldera structure in a volcanic edifice can indicate a potential site for phreatomagmatic explosion the monitoring of the propagation of eruption fissure and drops of magmatic pressure and flux can indicate the potential of the phreatomagmatic explosion by the invasion of groundwater into the hot conduit

origins and energetics of maar volcanoes examples from the ultrapotassic sabatini volcanic district roman province central italy maar volcanoes represent a common volcano type which is produced by the explosive interaction of magma with external water here we provide information on a number of maars in the ultrapotassic sabatini volcanic district svd roman province as young as 90 ka the svd maars are characterised in terms of crater and ejecta ring morphologies eruptive successions and magma compositions in light of the local substrate settings with the aim of assessing magma water interaction conditions eruption energetics and genetic mechanisms feeder magmas spanned the whole svd differentiation trend from trachybasalts shoshonites to phonolites from the ejected lithic fragments from aquifer rocks the range of depth of magma water explosive interaction is estimated to have been mostly at 400 600 m below ground level with a single occurrence of surficial interaction in palustrine lacustrine environment in particular the interaction with external water may have triggered the explosive behaviour of poorly differentiated magmas whereas it may have acted only as a late controlling factor of the degree of fragmentation and eruption style for the most differentiated magma batches during low flux ascent in an incipiently fragmented state crater sizes ejecta volumes and ballistic data allow a reconstruction of the energy budget of svd maar forming eruptions erupted tephra volumes from either monogenetic or polygenetic maars ranged 0 004 0 07 km3 during individual maar forming eruptions with corresponding total magma thermal energies of 8 1015 4 1017 j based on energy partitioning and volume balance of erupted magmas and lithic fractions vs crater holes we consider the different contributions of explosive excavation of the substrate vs subsidence in forming the svd maar craters following available models based on crater sizes highly variable fractions 5 50 of the magma thermal energies would have been required for crater excavation it appears that subsidence may have played a major role in some svd maars characterised by low lithic contents whilst substrate excavation became increasingly significant with increasing degrees of aquifer fragmentation

fluidization of wet sediments during the emplacement and cooling of various igneous bodies during the emplacement and cooling of igneous bodies fluidization of wet sediment by water vapour may occur by heating or by pressure relief during the opening of fractures momentary fluidization causes sediment reconstitution and local transport continuous fluidization can result in substantial sediment displacement theoretical considerations show that fluidization due to heating is not likely to occur at depths where pressure is much greater than 312 bars studies of the emplacement of sills of andesite ayrshire fluid rhyolite ramsey island and viscous rhyolite moelwyn hills recognize a wide range of phenomena attributable to wet sediment fluidization and in places modify existing interpretations the transgressive bases of the subaqueously welded ash flow tuffs of the capel curig volcanic formation are consistent with emplacement attended by fluidization of the subjacent sediment evidently fluidization is a means by which large volumes of wet sediment can be replaced by igneous material with minimal disturbance of the remaining host also fluidization can result in exceptionally complex contact relationships between sedimentary host and intrusive rocks and can cause fractures formed during cooling to be thoroughly pervaded by sediment fluidization is commonly associated with the formation of peperites

airwaves generated by an underwater explosion implications for volcanic infrasound 1 a shallow explosion in a fluid is one of the fundamental processes of airwave generation in volcanic eruptions to better understand the mechanism of the airwave generation underwater explosion experiments were conducted although the underwater explosions have been intensely studied over the last century airwaves have received little attention in this study pressure waves were measured in air and under water and the corresponding motion of the water surface was captured by a high speed video camera airwaves and associated styles of the surface motion show similarities determined by the scaled depth defined as the depth divided by the cubic root of the explosion energy the air waveforms are quite different from the pressure waves measured in the water and cannot be completely explained by linear transmission of pressure waves from water to air the mechanism of airwave generation is a combination of wave transmission and dynamics of the interface boundary the first mechanism directly reflects the explosion source and the same source is also observed as the underwater pressure waves on the other hand the second is not necessarily visible in the underwater pressure waves but will provide information on the mechanical properties and behavior of the material above the explosion source each mechanism is analyzed in the experiments

explosive lava water interactions ii self organization processes among volcanic rootless eruption sites in the 1783 1784 laki lava flow iceland we have applied quantitative geospatial analyses to rootless eruption sites in the hnuta and hrossatungur groups of the 1783 1784 laki lava flow to establish how patterns of spatial distribution can be used to obtain information about rootless cone emplacement processes and paleo environments this study utilizes sample size dependent nearest neighbor nn statistics and voronoi tessellations to quantify the spatial distribution of rootless eruption sites and validate the use of statistical nn analysis as a remote sensing tool our results show that rootless eruption sites cluster in environments with abundant lava and water resources but competition for limited groundwater in these clusters can cause rootless eruption sites to develop repelled distributions this pattern of self organization can be interpreted within the context of resource availability and depletion topography tends to concentrate lava fuel and water coolant within topographic lows thereby promoting explosive lava water interactions in these regions given an excess supply of lava within broad sheet lobes rootless eruption sites withdraw groundwater from their surroundings until there is insufficient water to maintain analogs to explosive molten fuel coolant interactions rootless eruption sites may be modeled as a network of water extraction wells that draw down the water table in their vicinity rootless eruptions at locations with insufficient groundwater may either fail to initiate or terminate before explosive activity has ceased at nearby locations with a greater supply of water thus imparting a repelled distribution to observed rootless eruption sites

explosive lava water interactions in elysium planitia mars geologic and thermodynamic constraints on the formation of the tartarus colles cone groups 1 volcanic rootless constructs vrcs are the products of explosive lava water interactions vrcs are significant because they imply the presence of active lava and an underlying aqueous phase e g groundwater or ice at the time of their formation combined mapping of vrc locations age dating of their host lava surfaces and thermodynamic modeling of lava substrate interactions can therefore constrain where and when water has been present in volcanic regions this information is valuable for identifying fossil hydrothermal systems and determining relationships between climate near surface water abundance and the potential development of habitable niches on mars we examined the western tartarus colles region 25 27 n 170 171 e in northeastern elysium planitia mars and identified 167 vrc groups with a total area of 2000 km2 these vrcs preferentially occur where lava is 60 m thick crater size frequency relationships suggest the vrcs formed during the late to middle amazonian modeling results suggest that at the time of vrc formation near surface substrate was partially desiccated but that the depth to the midlatitude ice table was 42 m this ground ice stability zone is consistent with climate models that predict intermediate obliquity 35 between 75 and 250 ma with obliquity excursions descending to 25 32 for lava thicknesses ranging from 30 to 60 m and ground ice fractions ranging from 0 1 to 0 3 an ice volume of 4 23 km3 could have been melted and or vaporized by the time the lava solidified and the associated hydrothermal systems could have retained temperatures 273 k for up to 1300 years

azimuthal anisotropy in the earth from observations of sks at geoscope and nars broadband stations abstract we have analyzed observations of low frequency sks waves recorded on horizontal components at several broadband stations of the geoscope and nars arrays splitting of sks is consistently observed and in good agreement with a hypothesis of azimuthal anisotropy due to transverse anisotropy with a horizontal axis in the upper mantle beneath the receivers we have designed an inversion method which takes advantage of observations made simultaneously at different azimuths and which permits us to obtain estimates of the direction of fast axis of anisotropy as well as the time delay between the orthogonal quasi shear waves in general the directions of fast velocity obtained both for stations around the atlantic and around the pacific appear to be related to directions of past and present plate motions

contrasting interactions of two magmas with the same water saturated hosts big bend national park texas abstract rhyolitic and mafic dikes cut lower tertiary sediments tuffs and mafic lavas of the eocene oligocene chisos formation in big bend national park texas two contrasting magmas injected into the same hosts under the same conditions provide a controlled experiment on magma host interaction peralkaline rhyolite dikes are extensive and stand in bold topographic relief on contact surfaces against mudstones close packed spheroids of chilled rhyolite indicate vigorous movement of magma within envelopes of fluid against sandstones the rhyolite dike contacts are more irregular and locally protrude as blunt fingers into the wall rock against mafic lava flows dike contacts are planar and the rhyolite is less altered mafic dikes cut the rhyolite dikes some contacts of these mafic dikes are peperitic indicating intrusion into soft wet sediment and tuff the same hosts of the older rhyolitic dikes must also have been water saturated and unconsolidated higher viscosity and lower temperature prevented rhyolite magma from forming detached bodies or engulfing its host to form peperites estimated pressures and contact temperatures approximate or exceed the critical point of water indicating that the fluid envelopes at rhyolite dike contacts were very unstable because even small temperature fluctuations would have produced wide variations in fluid density around the critical point the resulting volume instability triggered rapid pulsations in the fluid envelope deforming the contacts where permeability of the host was low hot fluid accumulated at contacts but where permeability was high fluid could escape before reaching high temperature

a note on maar eruption energetics current models and their application hydromagmatic eruptions convert thermal into mechanical energy via the expansion of ground and or surface water several models address the energetics of these eruptions based on different physical volcanological approaches here we test different models with two case studies in the colli albani volcanic district central italy the monogenetic prata porci and the polygenetic albano maars test results are mutually consistent and show cumulative mechanical energy releases on the order of 1015 1017 j for single maars the fraction of thermal energy turned into mechanical ranges from 0 45 as calculated from the theoretical maximum mechanical energy through 0 1 calculated from country rock fragmentation crater formation and ballistic ejection to 0 03 derived from magma fragmentation by thermohydraulic explosions it appears that the energy released during the most intense hydromagmatic events may account for a dominant fraction of the total mechanical energy released during the whole maar eruptive histories finally we consider the role of magmatic explosive activity intervening during maar eruptions in causing departures from predictions of the models evaluated

growth of phreatomagmatic explosion craters a model inferred from suoana crater in miyakejima volcano japan abstract a subvertical cross section of a maar diatreme volcano is exposed in the wall of the a d 2000 caldera on miyakejima volcano the maar suoana is one of the lateral vents of this volcano and it was inferred to be formed in the 7th century the subvertical wall of the a d 2000 caldera truncated the suoana maar crater at its center revealing the near comlete cross section of this small maar diatreme volcano exposed in the cross section are a 400 m wide maar crater an associated tuff ring with a maximum thickness of 20 m a diatreme extending vertically to a depth of about 220 m from the floor of the maar crater and a feeder dike connected to the base of the diatreme the depth of the diatreme structure is about 260 m from the original ground surface the outline of the diatreme resembles an upward opening funnel with an almost vertical wall below 560 m asl and an upward flaring wall above 560 m asl coarse grained volcanic breccia fills the diatreme the deposits of which can be divided into 6 units based on lithological and structural characteristics the upper half of the diatreme is filled with landslide deposits mainly derived from the surrounding crater wall the bottom of the diatreme is occupied by massive explosion breccia some coherent blocks were detached from the wall of the diatreme and preserved in the diatreme fill the y shaped cross sectional geometry of the suoana diatreme is the result of a combination of an underground subsidence in the lower part of the diatreme and the surface landslide in its upper part the inwardly inclined stratification of pyroclastic rock units and development of many small faults in the diatreme filling breccia indicate successive collapse and deformation of these materials within the diatreme during the eruption the upper part of the diatreme was formed by the landslides of the crater wall induced by the subsidence of the crater floor discharge of tephra from the bottom of the diatreme caused infill subsidence which induced sliding of the inner wall of the crater as a result the topographic diameter of the crater became much larger than that of the diatreme itself the tephra ring surrounding the crater consists mainly of pyroclastic fall deposits

reconstructing the eruption magnitude and energy budgets for the pre historic eruption of the monogenetic 5 ka mt gambier volcanic complex south eastern australia understanding explosive volcanic eruptions especially phreatomagmatic eruptions their intensities and energy budgets is of major importance when it comes to risk and hazard studies with only a few historic occurrences of phreatomagmatic activity a large amount of our understanding comes from the study of pre historic volcanic centres which causes issues when it comes to preservation and vegetation in this research we show that using 3d geometrical modelling it is possible to obtain volume estimates for different deposits of a pre historic complex monogenetic centre the mt gambier volcanic complex south eastern australia using these volumes we further explore the energy budgets and the magnitude of this eruption vei 4 including dispersal patterns eruption columns varying between 5 and 10 km dispersed towards north east to south to further our understanding of intraplate monogenetic eruptions involving phreatomagmatic activity we also compare which thermodynamic model fits best in the creation of the maar crater of mt gambier the major explosion dominated model or the incremental growth model in this case the formation of most of the craters can best be explained by the latter model

explosive lava water interactions i architecture and emplacement chronology of volcanic rootless cone groups in the 1783 1784 laki lava flow iceland to determine the relationships between rootless cone emplacement mechanisms morphology and spatial distribution we mapped the hnuta and hrossatungur groups of the 1783 1784 laki lava flow in iceland we based our facies maps on differential global positioning system dgps measurements photogeological interpretations and supporting field observations the study area covers 2 77 km2 and includes 2216 explosion sites to establish the timing of rootless cone formation we incorporated tephrochronological constraints from eighty eight stratigraphic sections and determined that the hnuta and hrossatungur groups are composite structures formed by the emplacement of six geographically and chronologically discrete domains rootless eruptions initiated in domain 1 on the first day of the laki eruption june 8 1783 and lasted 1 2 days the second episode of rootless activity began in domain 2 on june 11 and lasted 1 3 days the four domains of the hrossatungur group dominantly formed after june 14 and exhibit a complex emplacement sequence that reflects interactions between the laki lava contemporaneously emplaced rootless cones and an existing topographic ridge in the study area we identify three distinct rootless cone archetypes i e recurring morphological forms that are related to tube channel and broad sheet lobe fed eruptions we assert that emplacement of lava above compressible substrates e g unconsolidated sediments may trigger rootless eruptions by causing subsidence induced flexure and failure of the basal crust thereby allowing molten lava fuel to come into direct contact with groundwater coolant and initiating analogs to explosive molten fuel coolant interactions mfcis

morphometric study of pillow size spectrum among pillow lavas measurements of h and v dimensions in the horizontal and vertical directions of pillows exposed in vertical cross section were made on 19 pillow lavas from the azores cyprus iceland new zealand tasmania the western usa and wales the median values of h and v plot on a straight line that defines a spectrum of pillow sizes having linear dimensions five times greater at one end than at the other basaltic toward the small size end and andesitic toward the large size end the pillow median size is interpreted to reflect a control exercised by lava viscosity pillows erupted on a steep flow foot slope in lava deltas can however have a significantly smaller size than pillows in tabular pillowed flows inferred to have been erupted on a small depositonal slope indicating that the slope angle also exercised a control pipe vesicles generally abundant in the tabular pillowed flows and absent from the flow foot pillows have potential as a paleoslope indicator pillows toward the small size end of the spectrum are smooth surfaced and grew mainly by stretching of their skin whereas disruption of the skin and spreading were important toward the large size end disruption involved increasing skin thicknesses with increasing pillow size and pillows toward the large size end are more analogous with toothpaste lava than with pahoehoe and are inferred from their thick multiple selvages to have taken hours to grow pseudo pillow structure is also locally developed an example of endogenous pillow lava growth that formed intrusive pillows between normal pillows is described from sicily isolated pillow like bodies in certain andesitic breccias described from iceland were previously interpreted to be pillows but have anomalously small sizes for their compositions it is now proposed that they may lack an essential attribute of pillows namely the development of bulbous forms by the inflation of a chilled skin and are hence not true pillows para pillow lava is a common lava type in the flow foot breccias it forms irregular flow sheets that are locally less than 5 cm thick and failed to be inflated to pillows perhaps because of an inadequate lava supply rate or too high a flow velocity

experimental interaction of magma and dirty coolants the presence of water at volcanic vents can have dramatic effects on fragmentation and eruption dynamics but little is known about how the presence of particulate matter in external water will further alter eruptions volcanic edifices are inherently dirty places where particulate matter of multiple origins and grainsizes typically abounds we present the results of experiments designed to simulate non explosive interactions between molten basalt and various coolants ranging from homogeneous suspensions of 0 to 30 mass bentonite clay in pure water to heterogeneous and or stratified suspensions including bentonite sand synthetic glass beads and or naturally sorted pumice four types of data are used to characterise the interactions 1 visual video observations 2 grainsize and morphology of resulting particles 3 heat transfer data from a network of eight thermocouples and 4 acoustic data from three force sensors in homogeneous coolants with 20 sediment heat transfer is by forced convection and conduction and thermal granulation is less efficient resulting in fewer blocky particles larger grainsizes and weaker acoustic signals many particles are droplet shaped or and vesicular containing bubbles filled with coolant both of these particle types indicate significant hydrodynamic magma coolant mingling and many of them are rewelded into compound particles the addition of coarse material to heterogeneous suspensions further slows heat transfer thus reducing thermal granulation and variable interlocking of large particles prevents efficient hydrodynamic mingling this results primarily in rewelded melt piles and inefficient distribution of melt and heat throughout the coolant volume our results indicate that even modest concentrations of sediment in water will significantly limit heat transfer during non explosive magma water interactions at high concentrations the dramatic reduction in cooling efficiency and increase in mingling help to explain globular peperite and provide information relevant to analyses of premixing associated with highly explosive molten fuel coolant interactions in debris filled volcanic vents

paleozoic fluidization folding and peperite formation northern sierra nevada california recognition of peperite is important in establishing broad contemporaneity of magmatism and sedimentation at an occurrence of peperite discovered recently among late paleozoic island arc deposits in the northern sierra nevada it is possible to reconstruct the peperite forming process largely from field observations alone the generally concordant upper margin of a basalt intrusion adjoins thinly laminated basaltic tuff in the taylor formation that was water saturated and unlithified at the time of intrusion the water saturated ash initially was heated by the intrusion at approximately constant essentially hydrostatic pressure concurrently the top of the intrusion was quenched and divided by shrinkage fractures pressure momentarily approached zero as the shrinkage fractures opened abruptly causing vaporization of the pore water and substantial expansion and fluidizing flow of the resulting steam the unlithified ash was swept into the shrinkage fractures and where the downward propagating fractu