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

eruption processes and deposit characteristics at the monogenetic mt gambier volcanic complex se australia implications for alternating magmatic and phreatomagmatic activity the 5 ka mt gambier volcanic complex in the newer volcanics province australia is an extremely complex monogenetic volcanic system that preserves at least 14 eruption points aligned along a fissure system the complex stratigraphy can be subdivided into six main facies that record alternations between magmatic and phreatomagmatic eruption styles in a random manner the facies are 1 coherent to vesicular fragmental alkali basalt effusive hawaiian spatter and lava flows 2 massive scoriaceous fine lapilli with coarse ash strombolian fallout 3 bedded scoriaceous fine lapilli tuff violent strombolian fallout 4 thin medium bedded undulating very fine lapilli in coarse ash dry phreatomagmatic surge modified fallout 5 palagonite altered cross bedded medium lapilli to fine ash wet phreatomagmatic base surges and 6 massive palagonite altered very poorly sorted tuff breccia and lapilli tuff phreato vulcanian pyroclastic flows since most deposits are lithified to quantify the grain size distributions gsds image analysis was performed the facies are distinct based on their gsds and the fine ash to coarse fine ash ratios these provide insights into the fragmentation intensities and water magma interaction efficiencies for each facies the eruption chronology indicates a random spatial and temporal sequence of occurrence of eruption styles except for a magmatic horizon of effusive activity occurring at both ends of the volcanic complex simultaneously the eruption foci are located along nw se trending lineaments indicating that the complex was fed by multiple dykes following the subsurface structures related to the tartwaup fault system possible factors causing vent migration along these dykes and changes in eruption styles include differences in magma ascent rates viscosity crystallinity degassing and magma discharge rate as well as hydrological parameters

drivers of explosivity and elevated hazard in basaltic fissure eruptions the 1913 eruption of ambrym volcano vanuatu sw pacific abstract fissure eruptions along linear structures can extend for several tens of kilometres with distinct separate manifestations of volcanism along their length they typically involve low viscosity mafic magmas forming long lava flows and cinder cones eruptions in 1894 and 1913 on ambrym volcano vanuatu showed how these mildly explosive eruptions can rapidly transform into violent explosive events producing significant hazard and widespread volcanic ash clouds during the 1913 episode a fissure began in the central caldera and basaltic magmas broke out in a series of locations down the island s western flank in all sites over 100 m in elevation fissure outbreaks produced vigorous lava fountains and highly fluid lava flows that travelled rapidly to the shoreline when the outbreaks propagated along the island s axis into coastal plain areas a climactic series of explosive eruptions occurred producing a 1 2 km long by 600 m wide maar and tephra ring a further small tuff ring was formed later creating a temporary island 400 m offshore the onshore tephra ring destroyed a hospital and associated buildings its last evacuating occupants were close witnesses to the eruption processes deposits exposed in the lower portion of the tephra ring show that this part of the eruption began with a mild phreatomagmatic explosive eruption from a narrow vent followed by a magmatic scoria producing phase subsequently a complex sequence of highly explosive phreatomagmatic eruptions occurred producing pyroclastic surges along with repeated distinctive breccia horizons rich in coral and lava country rock these features tally with eye witness accounts to indicate that the main eruption phase was produced by a periodically shifting locus of phreatomagmatic fragmentation and eruption along a single e w fissure the glassy and vesicle poor pyroclasts produced during this eruption phase were dominantly fragmented in a brittle manner by magma water interaction low volatile content of the magma upon fragmentation is confirmed by ftir analysis showing

thermohydraulic explosions in phreatomagmatic eruptions as evidenced by the comparison between pyroclasts and products from molten fuel coolant interaction experiments 1 thermohydraulic explosions were produced by molten fuel coolant interaction mfci experiments using remelted shoshonitic rocks from vulcano italy the fragmentation history and energy release were recorded the resulting products were recovered and analyzed with the scanning electron microscope fine particles from experiments show shape and surface features that result from melt fragmentation in brittle mode these clasts relate to the thermohydraulic phase of the mfci where most of the mechanical energy is released they are here called active particles the total surface area of such particles is proportional to the energy of the respective explosions other particles from experiments show shape and surface features that result from melt fragmentation in a ductile regime these fragments called passive particles form after the thermohydraulic phase during the expansion phase of the mfci in order to verify thermohydraulic explosions in volcanic eruptions we compared experimental products with samples from phreatomagmatic base surge deposits of vulcano ash particles from the experiments show features similar to those from the deposits suggesting that the experiments reproduced the same fragmentation dynamics to achieve discrimination between active and passive particles we calculated shape parameters from image analysis the mass of active particles in base surge deposits was calculated as the material properties for the natural samples are identical to the experimental ones the energy measurements and calculations of the experiments can be applied for a single phreatomagmatic eruption at vulcano a maximum mechanical energy release of 2 75 1013 j was calculated representing a tnt analogue of 6 5 kt

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

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

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

what makes hydromagmatic eruptions violent some insights from the keanakāko i ash kilauea volcano hawai i abstract volcanic eruptions at the summit of kilauea volcano hawai i are of two dramatically contrasting types 1 benign lava flows and lava fountains and 2 violent mostly prehistoric eruptions that dispersed tephra over hundreds of square kilometers the violence of the latter eruptions has been attributed to mixing of water and magma within a wet summit caldera however magma injection into water at other volcanoes does not consistently produce widespread tephras to identify other factors that may have contributed to the violence of these eruptions we sampled tephra from the keanak ko i ash the most recent large hydromagmatic deposit and measured vesicularity bubble number density and dissolved volatile content of juvenile matrix glass to constrain magma ascent rate and degree of degassing at the time of quenching bubble number densities 9 10 4 1 10 7 cm 3 of tephra fragments exceed those of most historically erupted kilauean tephras 3 10 3 1 8 10 5 cm 3 and suggest exceptionally high magma effusion rates dissolved sulfur average 330 ppm and water 0 15 0 45 wt concentrations exceed equilibrium saturation values at 1 atm pressure 100 150 ppm and 0 09 respectively suggesting that clasts quenched before equilibrating to atmospheric pressure we interpret these results to suggest rapid magma injection into a wet crater perhaps similar to continuous uprush jets at surtsey estimates of reynolds number suggest that the erupting magma was turbulent and would have mixed with surrounding water in vortices ranging downward in size to centimeters such fine scale mixing would have ensured rapid heat exchange and extensive magma fragmentation maximizing the violence of these eruptions

the 1732 surtseyan eruption of eggoya jan mayen north atlantic deposits distribution chemistry and chronology the island of jan mayen in the north atlantic ocean is home to the world s northernmost active subaerial volcano beerenberg of the five known historical eruptions on the island the locations of two eruptions 1732 and 1818 have not been accurately located it is known that the 1732 and 1818 eruptions occurred on the south flank of beerenberg and several eruption sites have been proposed for these events here we show that the tuff cone of eggoya on the sw flank of beerenberg was the site of the 1732 eruption based on interpretation of the deposits field relations and historical sources we further describe the deposits from the eruption and show that eggoya is the largest explosive eruption described from jan mayen emplacing at least at least 0 3 0 4 km3 vei 4 of basanitic tephra up to distances of at least 111 km from jan mayen and covering a minimum area of around 500 km2 within the 2 cm isopach we also present our eruption scenario and show that this was an emergent surtseyan eruption with activity shifting between tephra jetting continuous uprush and more magmatic phases

depositional mechanics and sequences of base surges songaksan tuff ring cheju island korea the songaksan mount in the southwestern part of cheju island korea is a taalian tuff ring produced by phreatomagmatic explosions at an aquifer a detailed analysis of proximal to distal facies changes reveals that the tuff ring sequence can be represented by 21 sedimentary facies one lateral facies sequence lfs and three vertical facies sequences vfs the vfs 1 and 2 are representative of facies relationships in horizontal near vent deposits the vfs 1 comprises scour fill bedded tuff inversely graded tuff massive tuff and laminated tuff from base to top the vfs 2 is a variant of the vfs 1 replaced by an inversely graded lapilli tuff unit at the base the sequences suggest traction carpet suspension and minor traction sedimentation from a high concentration near vent base surge the lfs 1 and the vfs 3 are distilled from outward dipping flank deposits both sequences begin with disorganized lapilli tuff followed successively by stratified lapilli tuff dune bedded lapilli tuff very thinbedded tuff and accretionary lapilli they are suggestive of waning base surge which decreases in particle concentration suspended load fall out rate and flow regimes with an increase in traction and sorting these facies sequences suggest that a base surge experiences flow transformation with its flow characters changing with time and space a near vent base surge is turbulent uniformly mixed and highly concentrated and produces scour fill bedded tuff as capacity decreases the surge transforms into a dense and laminar underflow and a dilute and turbulent upper part gravity transformation depositing inversely graded massive and normally graded lapilli tuff ensuing loss of sediment load and mixing of ambient air result in flow dilution surface transformation stratified and dune bedded units are produced by tractional processes of turbulent and low concentration surge further dilution causes deceleration and cooling and results in precipitation of moistened ash and accretionary lapilli from suspension

generation of fine hydromagmatic ash by growth and disintegration of glassy rinds 1 the deposits of mafic hydromagmatic eruptions are more fine grained and variable in vesicularity than dry magmatic deposits blocky equant shapes of many hydromagmatic clasts also contrast with droplet thread and bubble wall morphology of dry magmatic fragments small 180 m blocky hydromagmatic pyroclasts have traditionally been interpreted to result from discrete vapor explosions although such explosions tend to occur only under certain conditions this paper considers a process of hydromagmatic ash formation that involves repeated growth and disintegration of glassy rinds on pyroclast surfaces as they deform within turbulent flows this process termed turbulent shedding may occur during the expansion phase of vapor explosions or during turbulent but nonexplosive mixing of magma with water steam or water sprays the occurrence of turbulent shedding and the resulting fragment sizes depend on the timescale for rind growth and the timescale between disturbances that remove or disintegrate glassy rinds turbulent shedding is directly observable in some small littoral jets at kilauea calculations suggest that in the presence of liquid water or water sprays glassy rinds having a thickness of microns to millimeters should form in milliseconds to seconds this is similar to the timescale between turbulent velocity fluctuations that can shred lava globules and remove such rinds the fraction of a deposit consisting of fine ash should increase with the duration of this process large scale surtseyan jets generate hundreds or thousands of shedding events bubble bursts or tephra jets at kilauea s coast may produce only a few

the role of bubbles in generating fine ash during hydromagmatic eruptions the abundant fine ash produced in the 2011 subglacial eruption of grimsvotn iceland highlights the fragmentation efficiency of mafic hydromagmatic eruptions which is considerably higher than for comparable dry eruptions ash from the 2011 eruption can be divided into three morphological components vesicular particles shards and dense fragments distinguished by the size and abundance of constituent vesicles we use the vesicle characteristics to define a new shape factor the concavity index which provides an unbiased way to classify individual ash particles as either bubbly vesicular particles and shards or dense the relative proportion of bubbly and dense particles varies systematically with grain size with the proportion of bubbly grains decreasing as the particle size approaches the modal bubble diameter measured bubble volume distributions are similar to those of rapidly quenched pyroclasts from hawaiian fountains and suggest a comparable degassing history during magma ascent yet concordance between the size distributions of ash and of bubbles in the grimsvotn samples stands in contrast to the size distributions in hawaiian fountains where pyroclasts are orders of magnitude larger than individual bubbles we propose that the grimsvotn ash formed by brittle disintegration of vesicular pyroclasts and that fragmentation efficiency was amplified by residual thermal stresses in glass quenched by glacial water the strong control of resulting particle sizes and morphologies by the size and spatial distribution of bubbles demonstrates that the bubble population cannot be ignored when modeling hydromagmatic fragmentation

a study of clast size distribution ash deposition and fragmentation in a hawaiian style volcanic eruption ash deposits from hawaiian style eruptions are generally of small volume but are important in understanding the mechanisms of these eruptions an analysis of the ash deposit from the 1959 kilauea iki eruption of kilauea volcano is presented and the whole deposit grain size distribution for the eruption is calculated the grain size distribution is found to be heavily skewed towards the coarsest clast sizes and to differ considerably from size distributions for plinian deposits

physical characterization of explosive volcanic eruptions based on tephra deposits propagation of uncertainties and sensitivity analysis abstract regardless of the recent advances in geophysical monitoring and real time quantitative observations of explosive volcanic eruptions the characterization of tephra deposits remains one of the largest sources of information on eruption source parameters esps i e plume height erupted volume mass mass eruption rate mer eruption duration total grain size distribution tgsd esps are crucial for the characterization of volcanic systems and for the compilation of comprehensive hazard scenarios but are naturally associated with various degrees of uncertainties that are traditionally not well quantified recent studies have highlighted the uncertainties associated with the estimation of esps mostly related to i the intrinsic variability of the natural system ii the observational error and iii the strategies used to determine physical parameters here we review recent studies focused on the characterization of these uncertainties and we present a sensitivity analysis for the determination of esps and a systematic investigation to quantify the propagation of uncertainty applied to two case studies in particular we highlight the dependence of esps on specific observations used as input parameters i e diameter of the largest clasts thickness measurements area of isopach contours deposit density downwind and crosswind range of isopleth maps and empirical constants and wind speed for the determination of mer the highest uncertainty is associated to the estimation of mer and eruption duration and is related to the determination of crosswind range of isopleth maps and the empirical constants used in the empirical parameterization relating mer and plume height given the exponential nature of the relation between mer and plume height the propagation of uncertainty is not symmetrical and both an underestimation of the empirical constant and an overestimation of plume height have the highest impact on the final outcome a 20 uncertainty on thickness measurements area of isopach contours integration limit for the power law fit and deposit density result in esp uncertainties 20 for plume height and erupted volume mass finally a third case study has also been used to explore the sensitivity of the voronoi tessellation strategy for the determination of tgsd and the inversion on both mass area and grain size data for the determination of erupted mass and plume height results confirm the validity of the methods but also the strong dependence on the distribution and number of observations

identifying multiple eruption phases from a compound tephra blanket an example of the ad1256 al madinah eruption saudi arabia complex eruption episodes commonly produce several phases of tephra fall and or concurrent falls from multiple vents phases of eruption are challenging to reconstruct from the geological record especially where there is a lack of distinct physical or chemical variations during an eruption episode a statistical method is proposed for identifying the most likely combination of multiple fall lobes for composite tephra deposits using a new high resolution tephra fall map from the basaltic ad1256 harrat al madinah fissure eruption in saudi arabia this dominantly effusive eruption episode lasted 52 days periodically producing tephra from several vents along the fissure most tephra was produced from high hawaiian fountains and dispersed under differing wind conditions the widest dispersed tephra occurred under phases of the highest fountains at least 500 m high and probably closer to 1000 m these high fountains produced pyroclasts with a broad range of vesicularity similar total versus lobe specific grain size determinations showed little systematic variation of maximum fountain height phases individual tephra lobe properties vesicle form density particle shape and particle size distribution in different sectors around the volcano varied only subtly from the statistical distribution of spot fall thickness measurements a semi empirical tephra fallout model modified to account for weathering wind remobilisation and settling was fitted using maximum likelihood estimation a range of likely eruption event scenarios were evaluated concluding that the ad1256 eruption most likely comprised three separate fall producing eruptions from its northern vent under differing wind conditions the first of these occurred concurrently with high fountaining events from two other major vents southward along the fissure producing overlapping fall lobes applying this method to other similar compound tephra deposits will help elucidate more realistic eruption scenarios and event reconstructions from the geological record

sizing up the bubbles that produce very fine ash during explosive volcanic eruptions explosive volcanic eruptions emit large proportions ofvery fine ash 30 mm into the atmosphere posing hazardsto aviation infrastructure and human health here wepresent an analysis of bubble size distributions at the pointof fragmentation during the 18 may 1980 eruption of mshthrough the examination of simple ash particles in distallydeposited fall samples the external surfaces of individualfine ash grains preserve the morphology of the bubbles thatburst to form the ash so bubble sizes can be measuredusing stereo scanning electron microscopy simple ashparticles are those that allow the measurement of a singlevesicle imprint per individual grain these simple ashparticles are the finest component of the tephra and canthus travel great distances from the source volcano analyses of samples provided bubble volume distributionswith a dominant peak between 560 and 5600 mm

contrasting mechanisms of magma fragmentation during coeval magmatic and hydromagmatic activity the hverfjall fires fissure eruption iceland growing evidence for significant magmatic vesiculation prior to magma water interaction mwi has brought into question the use of diagnostic features such as low vesicularities and blocky morphologies to identify hydromagmatic pyroclasts we address this question by quantifying co variations in particle size shape and texture in both magmatic and hydromagmatic deposits from the hverfjall fires fissure eruption iceland overlapping vesicularity and bubble number density distributions measured in rapidly quenched magmatic and hydromagmatic pyroclasts indicate a shared initial history of bubble nucleation and growth with substantial vesiculation prior to mwi hydromagmatic fragmentation occurred principally by brittle mechanisms where the length scale and geometry of fracturing was controlled by the bubble population this suggests that the elevated fragmentation efficiency of hydromagmatic deposits is driven at least in part by brittle disintegration of vesicular pyroclasts due to high thermal stress generated during rapid cooling in this way the shape and size distributions of hydromagmatic pyroclasts both critical input parameters for ash dispersion models are strongly influenced by the dynamics of vesiculation prior to mwi this result underlines the need to analyse multiple grain size fractions to characterise the balance between magmatic and hydromagmatic processes during the hverfjall fires eruption the external water supply was sufficient to maintain mwi throughout the eruption with no evidence for progressive exhaustion of a water reservoir we suggest that both the longevity and the spatial distribution of mwi were determined by the pre existing regional hydrology and represent continuous interaction between a propagating dike and a strong groundwater flow system hosted within permeable basalt lavas

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

bnd bubble number density decompression rate meter for explosive volcanic eruptions abstract this decade has been witness to substantial progress in the understanding of bubble dynamics and its role in volcanic eruptions a comparison between the results of experiments and a model for bubble nucleation shows that bubble number density bnd can be calculated as a function of decompression rate for given physical properties such as the diffusivity of water in a silicate melt and interfacial tension within an acceptable margin of error conversely in this paper we propose a method hereafter referred to as bnd decompression rate meter to estimate the decompression rate by using bnd data of natural pumice samples from volcanic eruptions as a result of the application of the bnd decompression rate meter to pumice and scoria from explosive eruptions it is found that the decompression rates increase in the range from 10 6 to 10 8 pa s with the eruption column heights these rates are proportional to the 4th power of the eruption column heights and are linear to the discharge rates the absolute values of the estimated decompression rates are very high and cannot be explained by the existing models of conduit flows in order to explain such high rates of decompression and the correlation with discharge rate we propose a possible model according to which the bubble nucleation propagates downward as a rarefaction shock wave in the conduit

identifying magma water interaction from the surface features of ash particles the deposits from explosive volcanic eruptions those eruptions that release mechanical energy over a short time span1 are characterized by an abundance of volcanic ash2 3 this ash is produced by fragmentation of the magma driving the eruption and by fragmenting and ejecting parts of the pre existing crust host rocks interactions between rising magma and the hydrosphere oceans lakes and ground water play an important role in explosive volcanism4 5 because of the unique thermodynamic properties of water that allow it to very effectively convert thermal into mechanical energy although the relative proportion of magma to host rock fragments is well preserved in the pyroclastic rocks deposited by such eruptions it has remained difficult to quantitatively assess the interaction of magma with liquid water from the analysis of pyroclastic deposits2 3 4 5 here we report the results of a study of natural pyroclastic sequences combined with scaled laboratory experiments we find that surface features of ash grains can be used to identify the dynamic contact of magma with liquid water the abundance of such ash grains can then be related to the water magma mass ratios during their interaction

growth of an emergent tuff cone fragmentation and depositional processes recorded in the capelas tuff cone sao miguel azores abstract the capelas tuff cone is an emergent surtseyan type tuff cone that erupted in shallow seawater off the coast of sao miguel azores in this paper we present a detailed stratigraphic study which is used to infer depositional processes and modes of fragmentation for the capelas tuff cone deposits the growth of the tuff cone can be divided into three stages based on variations in depositional processes that are probably related to differences in water magma w m ratios the first stage corresponds well to wet surtseyan type activity where wet fallout is the dominant depositional process with only minor representation of pyroclastic surge deposits the second stage of the eruption is suggested to be the result of alternating wet and slightly drier periods of surtseyan activity with an overall lower w m ratio compared to the first stage the drier surtseyan periods are characterized by the presence of minor grain flow deposits and undulating pyroclastic surge deposits that occasionally display relatively dry structures such as strongly grain segregated layers and brittle behavior when impacted by ballistic ejecta the first deposits of the second stage show an intense activity of pyroclastic surges but fallout commonly modified by surges is still the dominant depositional process during the second stage the third stage represents a final effusive period with the build up of a scoria cone and ponded lava flows inside the tuff cone crater phreatomagmatic fragmentation as seen by studies of the fine ash fraction

the influence of porosity and vesicle size on the brittle strength of volcanic rocks and magma volcanic rocks and magma display a wide range of porosity and vesicle size a result of their complex genesis while the role of porosity is known to exert a fundamental control on strength in the brittle field less is known as to the influence of vesicle size to help resolve this issue here we lean on a combination of micromechanical sammis and ashby s pore emanating crack model and stochastic rock failure and process analysis code modelling the models show for a homogenous vesicle size that an increase in porosity in the form of circular vesicles from 0 to 40 and or vesicle diameter from 0 1 to 2 0 mm results in a dramatic reduction in strength for example uniaxial compressive strength can be reduced by about a factor of 5 as porosity is increased from 0 to 40 the presence of vesicles locally amplifies the stress within the groundmass and promotes the nucleation of vesicle emanating microcracks that grow in the direction of the applied macroscopic stress as strain increases these microcracks continue to grow and eventually coalesce leading to macroscopic failure vesicle clustering which promotes the overlap and interaction of the tensile stress lobes at the north and south poles of neighbouring vesicles and the increased ease of microcrack interaction is encouraged at higher porosity and reduces sample strength once a microcrack nucleates at the vesicle wall larger vesicles impart higher stress intensities at the crack tips allowing microcracks to propagate at a lower applied macroscopic stress larger vesicles also permit a shorter route through the groundmass for the macroscopic shear fracture this explains the reduction in strength at higher vesicle diameters at a constant porosity the modelling highlights that the reduction in strength as porosity or vesicle size increases is nonlinear the largest reductions are observed at low porosity and small vesicle diameters in detail we find that vesicle diameter can play an important role in dictating strength at low porosity but is largely inconsequential above 15 porosity vesicle clustering and stress lobe interaction are implicit at high porosity regardless of the vesicle diameter in the case of an inhomogeneous vesicle size the microcracks grow from the largest vesicles and brittle strength is closer to that of the largest vesicle end member the results of this study highlight the important role of vesicle size and the complex interplay between porosity and vesicle size in controlling the brittle strength of volcanic rocks and magma

vesiculation of basaltic magma during eruption vesicle size distributions in vent lavas from the pu9u9o9o kupaianaha eruption of kilauea volcano are used to estimate nucleation and growth rates of h 2 o rich gas bubbles in basaltic magma nearing the earth9s surface 120 m depth by using well constrained estimates for the depth of volatile exsolution and magma ascent rate nucleation rates of 35 9 events cm 3 s 1 and growth rates of 3 2 x 10 4 cm s are determined directly from size distribution data the results are consistent with diffusion controlled growth as predicted by a parabolic growth law this empirical approach is not subject to the limitations inherent in classical nucleation and growth theory and provides the first direct measurement of vesiculation kinetics in natural settings in addition perturbations in the measured size distributions are used to examine bubble escape accumulation and coalescence prior to the eruption of magma

shallow seated controls on styles of explosive basaltic volcanism a case study from new zealand abstract the pyroclastic deposits of many basaltic volcanic centres show abrupt transitions between contrasting eruptive styles e g hawaiian versus strombolian or dry magmatic versus wet phreatomagmatic these transitions are controlled dominantly by variations in degassing patterns magma ascent rates and degrees of interaction with external water we use crater hill a 29 ka explosive effusive monogenetic centre in the auckland volcanic field new zealand as a case study of the transitions between these end member eruptive styles the crater hill eruption took place from at least 4 vents spaced along a nne trending 600 m long fissure that is contained entirely within a tuff ring generated during the earliest eruption phases early explosive phases at crater hill were characterised by eruption from multiple unstable and short lived vents later dominantly extrusive volcanism took place from a more stable point source most of the crater hill pyroclastic deposits were formed in 3 phreatomagmatic p and 4 dry magmatic m episodes forming in turn the outer tuff ring and maar crater p1 m1 p2 and scoria cone 1 m2 m4 this activity was followed by formation of a lava shield and scoria cone 2 purely wet activity is represented by the bulk of p1 and p2 and purely dry activity by much of m2 m4 however m1 and parts of m2 and m4 show evidence for simultaneous eruptions of differing style from adjacent vents and rapid variations in the extent and timing of magma water interaction at each vent the nature of the wall rock lithics and these rapid variations in inferred water magma ratios imply interaction was occurring mostly at depths of 80 m and the vesicularity patterns in juvenile clasts from these and the p beds imply that rapid degassing occurred at these shallow levels we suggest that abrupt transitions between eruptive styles in time and space at crater hill were linked to changes in the local magma supply rate and patterns and vigour of degassing during the final metres of ascent

cyclic deposits and hummocky cross stratification of probable storm origin in upper cretaceous rocks of the cape sebastian area southwestern oregon abstract cyclic deposits containing hummocky cross stratification occur in the upper part of the cape sebastian sandstone of bourgeois 1980 a shallow marine transgressive sandstone of late cetaceous age on the southern oregon coast the cycles average 1 6 m in thickness and consist where complete of a lower hummocky cross stratified sandstone a middle planar and ripple bedded sandstone with a shale bed in its middle part and an upper bioturbated sandstone noteworthy features of the hummocky cross stratification include the presence of depositional domes in addition to scoured depressions the absence of significant bedform migration and the presence of a small proportion of dip angles greater than the angle of repose 34 in addition to the large proportion of low 15 deg dip angles the lower stratified fining upward part of the cycle up to the top of the shale bed is interpreted as having accumulated under conditions of initially great but gradually decreasing current velocity and deposition rate the currents probably had a strong oscillatory component and the depositional event is inferred to have been a storm the part of the planar and ripple bedded sandstone above the shale bed was probably deposited during relatively fair weather after the storm but before re establishment of a normal benthic fauna the bioturbated sandstone is interpreted to have been deposited during fair weather or during minor storms separated by long intervals of fair weather

tephra ring interpretation in light of evolving maar diatreme concepts stracciacappa maar central italy abstract maar diatreme volcanoes in their simplest form are thought to result primarily from discrete subsurface phreatomagmatic explosions tephra ring deposits around maar craters are commonly interpreted in terms of a framework wherein explosions begin at shallow levels and migrate downward ejecting progressively deeper seated lithic clasts that contribute to the tephra rings additionally variations in grain size of the deposits are sometimes inferred to record different degrees of fragmentation which are in turn related to variations in magma water ratios at the explosion sites recent detailed studies of diatremes and of maar tephra rings suggest a different conceptual model wherein explosions can happen at various vertical and lateral locations within a diatreme during its eruptive lifetime rather than being limited to simple downward migration experiments numerical modeling and field data indicate that most explosions deeper than about 200 250 m will not vent to the surface but instead contribute to mixing within the diatremes arrival of deep seated lithics at the surface is related to this mixing process experiments also indicate that explosion phenomena can result in a range of emplacement mechanisms and grain sizes in tephra rings even in the absence of variations in explosion mechanisms fragmentation efficiency here we document the tephra ring of stracciacappa maar central italy and interpret its eruption and emplacement history in terms of evolving conceptual models along with a comparison to more traditional interpretations because most elements of both conceptual models are viable the work points to an important need to develop criteria to distinguish between the various inferred mechanisms

the structure of basaltic scoria and reticulite and inferences for vesiculation foam formation and fragmentation in lava fountains in this investigation pyroclast structures are used to constrain degassing in basaltic lava fountains vesicle size shape number density interconnectedness and packing character are quantified and related to 1 the kinetics of bubble nucleation and growth 2 the structural evolution of magmatic foams and 3 the influence of vesiculation rate on magma fragmentation measurements made on a diverse suite of pyroclasts from kilauea volcano indicate that basaltic foams evolve through an initially disordered closed celled spherical state to a well ordered open celled polyhedral state as the vesicularity rises from 75 to 98 the structural changes occur rapidly 10 s in the conduit and fountain in response to an intense vesiculation burst vesicle size distribution systematics indicate bubble nucleation rates 2 104 events cm 3s 1 that are approximately three orders of magnitude greater than those found for effusive eruptive activity bubble growth rates 9 10 4 cm s exceed effusive estimates by a factor of 3 the observed runaway rate of bubble production indicates strong supersaturations at the onset of nucleation we speculate that the rise speed of the magma as it reaches the level where significant volatile exsolution begins determines the intensity of the vesiculation burst and hence the vigor of the eruption rapid expansion and acceleration of the magma under these conditions may provide the impetus for fragmentation

satellite observations of a surtseyan eruption hunga ha apai tonga abstract on march 17 2009 a surtseyan eruption occurred around hunga ha apai island tonga a series of observations from the high spatial resolution advanced spaceborne thermal emission and reflection radiometer aster and the high temporal resolution moderate resolution imaging spectroradiometer modis was used to estimate the magnitude location start time and duration of the eruption and measure the evolving characteristics of the new hunga ha apai island the eruption start time was estimated to be between 01 50 and 11 10 local time on march 17 2009 i e between 12 50 and 22 10 utc march 16 the initial explosive phase lasted 3 5 days and consisted of multiple steam and tephra explosions from two distinct vent sources one on the northwest side and another about 100 m off the south shore of the pre existing island the eruption plume reached 4 0 to 7 6 km altitude above sea level and tephra added new land around each of the vents initially tripling the area of the pre existing island the next phase of steaming from newly formed crater lakes around the vents lasted a few days three warm crater lakes formed initially but disappeared with time as the shoreline eroded after 2 months vegetation that was initially buried by tephra was recovering after 10 months the size of the island had eroded down to twice that of the pre existing island and the one remaining crater lake had a temperature of 68 17 c the volume of erupted material was estimated to be 0 0176 km3 and the volcanic explosivity index vei was estimated to be vei 2

3d particle size distributions from 2d observations stereology for natural applications abstract we have developed a general formulation for stereological analysis of particle distributions which is applicable to any particle size or size distribution not limited to log normal unimodal etc we have applied numerical techniques to define intersection probability distributions for any shapes previously only known for spheres and quantified the errors involved in using spherical coefficients for various non spherical particles this stereological technique is based on knowing the probability distribution of random cross sections through various particles so that small circle cross sections can be subtracted from an observed population to provide the 3d size distribution of particles the results indicate that the most important parameter controlling calculated size distribution is particle aspect ratio for a distribution of particles with a specific aspect ratio or range of aspect ratios variations of particle form spherical vs cubic rectangular vs elliptical do not alter the results so the technique can be applied to a range of particle shapes applications can be made in a petrology volcanology and other fields only a few of which can also be treated using expensive x ray techniques

pyroclast textures of the ilchulbong wet tuff cone jeju island south korea abstract jeju island is a quaternary shield volcano situated approximately 95 km south of the korean peninsula comprising holocene late pleistocene phreatomagmatic deposits and shield forming basaltic to trachytic lavas that overlie early mid pleistocene marine sedimentary and hydrovolcanic deposits ilchulbong tuff cone is among the youngest hydrovolcanic centres on the island formed along the shoreline from a surtseyan style eruption involving interaction of magma with external water we have analysed lapilli from selected sites on the volcanic edifice in terms of vesicle population texture shape and size and quantitatively with reference to bulk vesicularity vesicle number density vesicle dimensions and distributions the lapilli range in total vesicularity from low 15 35 to high 50 80 values and show a modest range of vesicle number densities n v number of vesicles per unit rock volume between 2 26 10 3 and 6 97 10 3 vesicles mm 3 such vesicle number densities are higher than those typical of strombolian n v between 9 3 10 1 and 1 3 10 3 vesicles mm 3 stromboli 2002 lautze and houghton 2007 and hawaiian eruptions and more similar to those of plinian n v between 1 5 and 2 5 10 3 vesicles mm 3 tarawera sable et al 2009 eruptions the lapilli studied were not strongly quenched and we infer that the high vesicle number densities reflect a late nucleated bubble population related in origin and formed in response to high levels of microlite growth in the ilchulbong magma prior to final ascent

total grain size distribution of a mafic subplinian tephra tb 2 from the 1986 izu oshima eruption japan an estimation based on a theoretical model of tephra dispersal abstract total grain size distribution was estimated using field data and theoretical modelling isopleth maps of each size were constructed at intervals of 1 phi based on the detailed sampling and analysis of a subplinian deposit tb 2 a product of the climatic phase of the 1986 eruption of the izu oshima volcano japan the umbrella spreading of the eruptive plume is analysed from isopleth maps based on a theoretical model of tephra dispersal bursik m i sparks r s j gilbert j s carey s n 1992 sedimentation of tephra by volcanic plumes i theory and its comparison with a study of the fogo a plinian deposit sao miguel azores bull volcanol 54 329 344 the dispersal of particles in the diameter range of 32 4 mm agrees with the model and the deduced column height is consistent with the visual observation using field data and the theoretical model the erupted mass of each size fraction is estimated and the total grain size distribution and total mass were obtained the observed mass loading decay as a function of the area enclosed by the isopleth is revised using the calculated terminal fall velocity and flux of the plume in the umbrella region the total grain size distribution of tb 2 indicates an intermediate nature between plinian and hawaiian eruption styles

maar diatreme geometry and deposits subsurface blast experiments with variable explosion depth basaltic maar diatreme volcanoes which have craters cut into preeruption landscapes maars underlain by downward tapering bodies of fragmental material commonly cut by hypabyssal intrusions diatremes are produced by multiple subsurface phreatomagmatic explosions although many maar diatremes have been studied the link between explosion dynamics and the resulting deposit architecture is still poorly understood scaled experiments employed multiple buried explosions of known energies and depths within layered aggregates in order to assess the effects of explosion depth and the morphology and compaction of the host on the distribution of host materials in resulting ejecta the development of subcrater structures and deposits and the relationships between them experimental craters were 1 2 m wide analysis of high speed video shows that explosion jets had heights and shapes that were strongly influenced by scaled depth physical depth scaled against explosion energy and by the presence or absence of a crater jet properties in turn controlled the distribution of ejecta deposits outside the craters and we infer that this is also reflected in the diverse range of deposit types at natural maars ejecta were dominated by material that originated above the explosion site and the shallowest material was dispersed the farthest subcrater deposits illustrate progressive vertical mixing of host materials through successive explosions we conclude that the progressive appearance of deeper seated material stratigraphically upward in deposits of natural maars probably records the length and time scale for upward mixing through multiple explosions with ejection by shallow blasts rather than progressive deepening of explosion sites in response to draw down of aquifers

ash from the eyjafjallajokull eruption iceland fragmentation processes and aerodynamic behavior 1 the fragmentation process and aerodynamic behavior of ash from the eyjafjallajokull eruption of 2010 are investigated by combining grain size scanning electron microscopy sem and quantitative particle morphology ash samples were collected on land in iceland at 3 55 km distance from the volcanic vent and represent various phases of the pulsating eruption the grain size is fine even for deposits close to the vent suggesting that the parent particle population at fragmentation consisted of a substantial amount of fine ash sem investigation reveals that ash produced during the first phase of the eruption consists of juvenile glass particles showing key features of magma water interaction suggesting that phreatomagmatism played a major role in the fragmentation of a vesicle poor magma in the last phase of the eruption fragmentation was purely magmatic and resulted from stress induced reaction of a microvesicular fragile melt the shape of ash as determined by quantitative morphology analysis is highly irregular rendering the settling velocity quite low this makes transportation by wind much easier than for other more regularly shaped particles of sedimentary origin we conclude that the combination of magma s fine brittle fragmentation and irregular particle shape was the main factor in the extensive atmospheric circulation of ash from the mildly energetic eyjafjallajokull eruption

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

the role of syn eruptive vesiculation on explosive basaltic activity at mt etna italy abstract we investigated the dynamics of explosive activity at mt etna between 31 august and 15 december 2006 by combining vesicle studies in the erupted products with measurements of the gas composition at the active summit crater the analysed scoria clasts present large connected vesicles with complex shapes and smaller isolated spherical vesicles the content of which increases in scoriae from the most explosive events gas geochemistry reports co 2 so 2 and so 2 hcl ratios supporting a deep derived gas phase for fire fountain activity by integrating results from scoria vesiculation and gas analysis we find that the highest energy episodes of mt etna activity in 2006 were driven by a previously accumulated co 2 rich gas phase but we highlight the lesser role of syn eruptive vesicle nucleation driven by water exsolution during ascent we conclude that syn eruptive vesiculation is a common process in etnean magmas that may promote a deeper conduit magma fragmentation and increase ash formation

amplified hazard of small volume monogenetic eruptions due to environmental controls orakei basin auckland volcanic field new zealand orakei maar and tuff ring in the auckland volcanic field is an example of a basaltic volcano in which the style and impacts of the eruption of a small volume of magma were modulated by a fine balance between magma flux and groundwater availability these conditions were optimised by the pre 85 ka eruption being hosted in a zone of fractured and variably permeable plio pleistocene mudstones and sandstones orakei maar represents an end member in the spectrum of short lived basaltic volcanoes where substrate conditions rather than the magmatic volatile content was the dominant factor controlling explosivity and eruption styles the eruption excavated a crater 80 m deep that was subsequently filled by slumped crater wall material followed by lacustrine and marine sediments the explosion crater may have been less than 800 m in diameter but wall collapse and wave erosion has left a 1 000 m diameter roughly circular basin a tuff ring around part of the maar comprises dominantly base surge deposits along with subordinate fall units grain size texture and shape characteristics indicate a strong influence of magma water and magma mud interactions that controlled explosivity throughout the eruption but also an ongoing secondary role of magmatic gas driven expansion and fragmentation the tuff contains 70 of material recycled from the underlying plio pliestocene sediments which is strongly predominant in the 2 fraction the magmatic clasts are evolved alkali basalt consistent with the eruption of a very small batch of magma the environmental impact of this eruption was disproportionally large when considering the low volume of magma involved dre 0 003 km3 hence this eruption exemplifies one of the worst case scenarios for an eruption within the densely populated auckland city destroying an area of 3 km2 by crater formation and base surge impact an equivalent scenario for the same magma conditions without groundwater interaction would yield a scoria spatter cone with a diameter of 400 550 m destroying less than a tenth of the area affected by the orakei event

linking variable explosion style and magma textures during 2002 at stromboli volcano italy microtextural characteristics of fresh ejecta from stromboli volcano were examined from three periods of differing eruption style and intensity in 2002 activity shifted from relatively weak and infrequent ash charged explosions during january through may into two broad cycles of waxing activity in june through late september and late september through december followed by the onset on 28 december of the 2002 2003 effusive eruption analyzed sets of lapilli from may september october and 28 december show contrasts in the physical properties of magma resident in the shallow conduit during this range of activity three distinct textures are observed among the analyzed pyroclasts low density ld with an abundance of subspherical bubbles the presence of large irregularly shaped bubbles and a light to transparent glass matrix transitional texture tt with an intermediate number of subspherical bubbles a high frequency of large irregularly shaped bubbles and a honey colored glass matrix and high density hd with sparse relatively small bubbles conspicuous large irregular bubbles and a dark glass matrix observational and quantitative data density vesicle size indicate that these textures are linked through variable residence time in stromboli s shallow conduit with an ongoing evolution from ld to hd magma calculations suggest that residual ld magma will evolve to hd texture in a period of hours to days contrasting amounts of the ld tt and hd magmas are present in each sample with the most tt in may the most ld in september october and the most hd in december this implies that the shallow magma had a different rheology at each collection period the viscosity of ld and hd magmas are calculated to be in the range of 2 000 to 2 600 and 3 000 to 5 000 pa s respectively which with their changing proportions must have implications for rates of bubble slug ascent and processes of fragmentation this study suggests that an increasing maturity of magma in stromboli s shallow conduit with resultant increase in viscosity feeds back to reduce the intensity of explosions whereas a steady flux of ld magma favors more powerful explosions

contrasting patterns of vesiculation in low intermediate and high hawaiian fountains a case study of the 1969 mauna ulu eruption abstract hawaiian style eruptions or hawaiian fountains typically occur at basaltic volcanoes and are sustained weakly explosive jets of gas and dominantly coarse juvenile ejecta dense spatter to delicate reticulite almost the entire range of styles and mass eruption rates within hawaiian fountaining occurred during twelve fountaining episodes recorded at mauna ulu k lauea between may and december 1969 such diversity in intensity and style is controlled during magma ascent by many processes that can be constrained by the size and shape of vesicles in the 1969 pyroclasts this paper describes pyroclast vesicularity from high intermediate and low fountaining episodes with eruption rates from 0 05 to 1 3 10 6 m 3 h 1 as each eruptive episode progressed magma ascent slowed in and around the vent system offering extended time for bubbles to grow and coalesce late ejected pyroclasts are thus characterized by populations of fewer and larger vesicles with relaxed shapes this progression continued in the intervals between episodes after termination of fountain activity the time scale for this process of shallow growth coalescence and relaxation of bubbles is typically tens of hours rims and cores of pumiceous pyroclasts from moderate to high fountaining episodes record a second post fragmentation form of vesicle maturation partially thermally insulated pyroclasts can have internal bubble populations evolve more dynamically with continued growth and coalescence on a time scale of only minutes during transport in the fountains reticulite which formed in a short lived fountain 540 m in height underwent late short lived bubble nucleation followed by rapid growth of a uniform bubble population in a thermally insulated fountain and quenched at the onset of permeability before significant coalescence these contrasting patterns of shallow degassing and outgassing were the dominant controls in determining both the form and duration of fountaining episodes at mauna ulu and probably for many other hawaiian style eruptions

eifel maars quantitative shape characterization of juvenile ash particles eifel volcanic field germany abstract the eifel region in western central germany is the type locality for maar volcanism which is classically interpreted to be the result of explosive eruptions due to shallow interaction between magma and external water i e phreatomagmatic eruptions sedimentary structures deposit features and particle morphology found in many maar deposits of the west eifel volcanic field wevf in contrast to deposits in the east eifel volcanic field eevf lack the diagnostic criteria of typical phreatomagmatic deposits the aim of this study was to determine quantitatively the shape of wevf and eevf maar ash particles in order to infer the governing eruption style in eifel maar volcanoes the quantitative shape characterization was done by analyzing fractal dimensions of particle contours 125 250 m sieve fraction obtained from scanning electron microscopy sem and sem micro computed tomography sem micro ct images the fractal analysis dilation method and the fractal spectrum technique confirmed that the wevf and eevf maar particles have contrasting multifractal shapes whereas the low small scale dimensions of eevf particles eppelsberg green unit coincide with previously published values for phreatomagmatic particles the wevf particles meerfelder maar pulvermaar and ulmener maar have larger values indicating more complex small scale features which are characteristic for magmatic particles these quantitative results are strengthening the qualitative microscopic observations that the studied wevf maar eruptions are rather dominated by magmatic processes the different eruption styles in the two volcanic fields can be explained by the different geological and hydrological settings found in both regions and the different chemical compositions of the magmas

pyroclast characteristics of a subaqueous to emergent surtseyan eruption black point volcano california abstract we present the first ever quantitative analysis of pyroclast textures from subaqueous deposits of a surtseyan emergent volcano the volcano black point formed in mono lake s pleistocene precursor lake russell at 13 300 500 bp from an explosive basaltic eruption involving the interaction of shallow lake water 105 m with vesiculating magma the bulk of the edifice comprises unconsolidated tephra and represents submerged stages of eruption thin summit deposits formed during a final phase of emergent eruption and produced a group of low tuff rings lapillus clasts 16 mm to 32 mm and fine ash grains 4 0 0625 mm from the subaqueous deposits have textures that reveal a conduit history of bubble nucleation growth collapse intense microlite crystallisation and magma water interaction lapilli vesicularity ranges broadly to high values up to 89 while vesicle number densities 5 4 102 4 8 104 vesicles per mm3 are comparable to those published for strombolian and plinian basaltic eruptions 1 104 vesicles per mm3 vesicle size and volume distributions suggest continuous bubble nucleation but the suite of data as a whole indicates that a late stage nucleation event played a significant role in shaping the eruption ash grain morphology and surface features indicative of magma water interactions attest to water s role in fragmentation overall the pyroclast textures are consistent with water modification of a rather intense basaltic eruption which might have been of a violent strombolian or plinian style if the eruption had been dry and occurred subaerially

magma water interactions in subaqueous and emergent basaltic in the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of 1 explosive release of magmatic volatiles 2 explosive expansion and collapse of steam formed at magma water contact surfaces 3 explosive expansion of steam following enclosure of water in magma or entrapment of water close to magma and 4 cooling contraction these processes named respectivelymagmatic explosivity contact surface steam explosivity bulk interaction steam explosivity andcooling contraction granulation can be enhanced by mutual interaction and feedback the first three explosive processes are limited at certain water depths hydrostatic pressures and become increasingly vigorous at shallower levels the depth of onset of magmatic explosivity depends largely on juvenile volatile content it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas at the depth where formation of clastic deposits becomes predominant over effusion of lavas magmatic explosivity is subordinate to steam explosivity as a clast forming process the upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it contact surface explosivity commonly requires initiation by a vigorous impact between magma and water and although no certain depth limit is known likelihood of such explosivity decreases rapidly with depth clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water which in sea water is at about 3 km cooling contraction granulation can occur in any depth of water but at shallow levels may be replaced by contact surface explosivity during continuous eruption under water tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur emergent volcanoes are characterized by distinctive steam explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material water and steam the water gets into the vent by flooding across or through the top of the tephra pile and violent explosions cease when this access is sealed the eruptions during emergence of surtsey and capelinhos typify the distinctive explosive activity the style and controls of which are different from those of maar volcanoes

detailed multidisciplinary monitoring reveals pre and co eruptive signals at nyamulagira volcano north kivu democratic republic of congo this paper presents a thorough description of nyamulagira s january 2010 volcanic eruption north kivu democratic republic of congo based on a combination of field observation and ground based and space borne data it is the first eruption in the virunga volcanic province that has been described by a combination of several modern monitoring techniques the 2010 eruption lasted 26 days and emitted 45 5 106 m3 of lava field observations divided the event into four eruptive stages delimited by major changes in effusive activity these stages are consistent with those described by pouclet 1976 for historical eruptions of nyamulagira co eruptive signals from ground deformation seismicity so2 emission and thermal flux correlate with the eruptive stages unambiguous pre eruptive ground deformation was observed 3 weeks before the lava outburst coinciding with a small but clear increase in the short period seismicity and so2 emission the 3 weeks of precursors contrasts with the only precursory signal previously recognized in the virunga volcanic province the short term increase of tremor and long period seismicity which for example were only detected less than 2 h prior to the 2010 eruption the present paper is the most detailed picture of a typical flank eruption of this volcano it provides valuable tools for re examining former mostly qualitative descriptions of historical nyamulagira eruptions that occurred during the colonial period

insights on tephra settling velocity from morphological observations in this study we present a systematic and detailed morphological characterization of tephra particles from different eruptions fontana lapilli masaya nicaragua keanak ko i formation kilauea usa recent dome explosions of soufriere hills volcano montserrat and the calculation of their terminal fall velocity tfv as obtained based on different drag prediction models i e wilson and huang 1979 haider and levenspiel 1989 ganser 1993 and dellino et al 2005 in particular particle sphericity and therefore particle surface area is essential for the calculation of tfv of irregular shape particles but is of complex determination various attempts have been proposed according to our results 2d morphological characterization of volcanic particles is a fast and simple application for a wide range of particle size and provides consistent sphericity and settling velocity values 3d scanning also provides a promising tool for lapilli sized tephra 2 cm in contrast gas adsorption derived surface area is not suitable for the calculation of tfv of volcanic particles mostly because it mainly describes the surface contribution of nanometric pores that are not expected to affect significantly tfv and because bulk sample analysis is representative of neither individual particles nor of the whole particle population settling velocities calculated using values of surface area derived from gas adsorption analyses are up to two orders of magnitude lower than the values obtained through 2d analysis in addition our results also show how the influence of particle shape on tfv increases with particle size in particular calculated tfv converges at small particle sizes 3 regardless of the model applied suggesting that the spherical assumption is appropriate for this size fraction discrepancies with the spherical model are within 10 discrepancies with the spherical model increase with particle size up to about 50 and depend on the choice of both the tfv model and the morphological parameterization used in particular the drag prediction model of ganser 1993 is sensitive to the effect of particle morphology on tfv and is well suited for all sizes and reynolds numbers of typical tephra particles finally our results show how individual size categories whole and half are not associated with individual tfv values but with a range of values which increases with class size nonetheless the half system is associated with a smaller standard deviation than the whole system and is therefore more appropriate for the modeling of tephra dispersal in any case for dispersal modeling purposes it is more appropriate to indicate a range of settling velocities for each size class rather than giving an average value

textural variation in juvenile pyroclasts from an emergent surtseyan type volcanic eruption the capelas tuff cone sao miguel azores abstract here i present textural data i e vesicularity vesicle size distributions vsd plagioclase crystallinity crystal size distributions csd combined with fractal analyses of particle outlines from a natural succession of alternating fall and surge deposits in the emergent capelas tuff cone azores the textural variation in the capelas succession is surprisingly small considering the wide variety of fragmentation processes vent activity and emplacement mechanisms that are characteristic of emergent eruptions the plagioclase crystal content varies between 24 and 33 vol csd analyses of plagioclase show near linear trends with a slight increase in time for the smallest crystal sizes with surge deposits having more groundmass plagioclase when compared with fall deposits this is consistent with crystallization induced by degassing and decompression at lower eruption rates the vesicularities of the capelas pyroclasts are more variable 18 to 59 vol with vsds displaying kinked trends characteristic of coalescence this is especially evident in the fall deposits and consistent with being formed in continuous uprush jetting with an overall shallow fragmentation level within the conduit bubble coalescence can also be identified in the surge deposits although to a much lesser extent the amount of bubble coalescence is negatively correlated with the amount of groundmass crystallization i e plagioclase in the capelas deposits a relatively broad range of fractal dimensions with average dbox 1 744 and 0 032 for the outlines of pyroclastic fragments emplaced by fall or as surges indicate that there is little difference in the fragmentation process itself at capelas in addition to this the fact that the fractal dimensions for both the fall and surge end members completely overlap suggests that shape modification due to abrasion and chipping of grain edges was minor during emplacement of base surges these results are consistent with emergent eruptions building tuff cones to be a relatively low energy phreatomagmatic landform e g at least when compared with more energetic phreatomagmatic eruptions producing tuff rings and maar volcanoes

the krafla fissure swarm iceland and its formation by rifting events fissure swarms at divergent plate boundaries are activated in rifting events during which intense fracturing occurs in the fissure swarm accompanied by intrusion of magma to form dikes that sometimes lead to eruptions to study the evolution of fissure swarms and the behaviour of rifting events detailed mapping was carried out on fractures and eruptive fissures within the krafla fissure swarm kfs fracture densities of dated lava flows ranging from 10 000 years bp to 30 years old were studied and the fracture pattern was compared with data on the historical m vatn rifting episode 1724 1729 and the instrumentally recorded krafla rifting episode 1975 1984 additionally the interaction of transform faults and fissure swarms was studied by analysing the influence of the husavik transform faults on the kfs during the historical rifting episodes eruptions on the fissure swarm occurred within 7 km from the krafla central volcano although faults and fractures were formed or activated at up to 60 70 km distance this is consistent with earlier rifting patterns as holocene eruptive fissures within the kfs are most common closer to the central volcano most fractures within the central krafla caldera are parallel to the overall orientation of the fissure swarm this suggests that the regional stress field is governing in the krafla central volcano while the local stress field of the volcano is generally weak a sudden widening of the graben in the northern kfs and a local maximum of fracture density at the junction of the kfs and the extrapolation of the husavik transform fault zone indicates possible buried continuation of the husavik transform fault zone which extends to the kfs eruptive fissures are found farther away from the krafla central volcano in the southern kfs than in the northern kfs this is either due to an additional magma source in the southern kfs the hei arspor ur volcanic system or caused by the husavik transform faults transferring some of the plate extension in the northern part fracture density within particular lava flow fields increases with field age indicating that repeated rifting events have occurred in the fissure swarm during the last 10 000 years bp the fracture density in the kfs is also generally higher closer to the krafla central volcano than at the ends of the fissure swarm this suggests that rifting events are more common in the parts of the fissure swarm closer to the krafla central volcano

single explosions at stromboli in 2002 use of clast microtextures to map physical diversity across a fragmentation zone abstract a combination of fortuitous eruptive and wind conditions at stromboli volcano in september 2002 enabled the collection of samples of multiple lapilli from individual observed explosions these ejecta present the first opportunity to analyze the vesicularity of material ejected in a single strombolian explosion samples of between 40 and 92 lapilli were collected from each of six sequential explosions on 30 september 2002 and 28 lapilli were obtained from a single explosion 24 h later 1 october density measurements and microtextural observations show that considerable heterogeneity existed within each of the seven samples centimeter to millimeter size bubble rich and bubble poor zones are present and are in places mingled together these data confirm that the shallow conduit at stromboli is a texturally diverse environment at the instant of a single explosion and that a similar range of heterogeneity can persist through closely spaced sequences of explosions on a timescale of hours and probably days despite the dynamic processes of ascent of melt and decoupled gas phases

estimating rates of decompression from textures of erupted ash particles produced by 1999 2006 eruptions of tungurahua volcano ecuador persistent low to moderate level eruptive activity of andesitic volcanoes is difficult to monitor because small changes in magma supply rates may cause abrupt transitions in eruptive style as direct measurement of magma supply is not possible robust techniques for indirect measurements must be developed here we demonstrate that crystal textures of ash particles from 1999 to 2006 vulcanian and strombolian eruptions of tungurahua volcano ecuador provide quantitative information about the dynamics of magma ascent and eruption that is difficult to obtain from other monitoring approaches we show that the crystallinity of erupted ash particles is controlled by the magma supply rate msr ash erupted during periods of high magma supply is substantially less crystalline than during periods of low magma supply this correlation is most easily explained by efficient degassing at very low pressures 50 mpa and degassing driven crystallization controlled by the time available prior to eruption our data also suggest that the observed transition from intermittent vulcanian explosions at low msr to more continuous periods of strombolian eruptions and lava fountains at high msr can be explained by the rise of bubbles through strombolian or trapping of bubbles beneath vulcanian vent capping variably viscous and crystalline magma

maar diatreme volcanoes a review maar diatreme volcanoes are produced by explosive eruptions that cut deeply into the country rock a maar is the crater cut into the ground and surrounded by an ejecta ring while the diatreme structure continues downward and encloses diatreme and root zone deposits here we attempt an evenhanded review of maar diatreme volcanology that extends from mafic to kimberlitic varieties and from historical maar eruptions to deeply eroded or mined diatreme structures we conclude that maar diatreme eruptions are episodic ejecta rings provide invaluable insight into eruption processes and sequence but are incomplete records of diatreme formation deposits within the diatreme structure include in varying proportions lower unbedded deposits sometimes typified by subvertical contacts among domains of debris emplaced sequentially and upper bedded deposits formed by sedimentation on surfaces open to the atmosphere a basal root zone comprises the transition from coherent magmatic feeder dike to clastic deposits formed by fragmentation of magma and enclosing country rock root zones are irregular in form and the clastic deposits are typically intruded by contorted dikes irregular root zone like chaotic breccias cut by contorted dikes are also present within diatreme deposits where they represent intra diatreme fragmentation zones and record changes in the location of the explosion locus during eruption

breaking news on the formation of volcanic ash fracture dynamics in silicate glass abstract in explosive volcanic eruptions magmatic melts behave like brittle solids under rapid loading volcanic ash particles predominantly are generated by brittle fragmentation induced within pre stressed magma in volcanic conduits here we present straightforward measurements of fracture area velocity i e surface generation rates in analog materials under volcanic time and deformation rates using a high resolution high speed camera at up to 2 5 million frames per second surface generation rates are directly linked to energy dissipation and can be related to pyroclast formation during explosive volcanism according to our findings pre existing stress fields play a crucial role for the evolution of cracks control the dynamics of fracture area growths during fragmentation and thus strongly modify the production of volcanic ash

capelinhos 1957 1958 faial azores deposits formed by an emergent surtseyan eruption the 1957 1958 eruption of capelinhos faial island azores involved three periods of surtseyan hydromagmatic activity two in 1957 and one in 1958 deposits from this eruption are exposed both in sea cliffs cut into the flanks of the tuff cone and more distally 1 km from the vent five lithofacies are identified lithofacies i is composed of even thickness beds with laterally continuous internal stratigraphy and is interpreted to have been formed by fallout lithofacies ii consists of beds with internally discontinuous lenses and has sand wave structures that increase in abundance toward the outer margins of the tuff cone this lithofacies is interpreted as having been deposited from pyroclastic surges lithofacies iii is composed of mantle bedded deposits with laterally discontinuous internal stratigraphy this lithofacies is interpreted to have been formed by hybrid processes where fallout of tephra occurred simultaneously with pyroclastic surges in the outer flanks of the tuff cone lithofacies iii grades laterally into fallout beds of lithofacies i lithofacies iv consists of alternating beds of coarse ash aggregates and non aggregated fine ash and is particularly well developed in distal regions some of this facies was formed by fallout alternating beds also occur plastered against obstacles up to 2 km from the vent indicating an origin from wet pyroclastic surges the orientation of plastered tephra indicates that the surges were deflected by topography as they decelerated the distinction between surge and fallout in distal regions is uncertain because wind drifted fallout and decelerating surge clouds can generate similar deposits lithofacies v consists of scoria lapilli beds interpreted to be fallout from hawaiian style fire fountaining in the later stages of the eruption juvenile pyroclasts within hydromagmatic deposits are predominantly poorly vesicular 25 60 of clasts 30 vesicles however on both micro and macroscopic scales there is a wide range in clast vesicularity up to 70 vesicles indicating that although fragmentation was predominantly hydromagmatic vesiculation and magmatic volatile driven fragmentation operated simultaneously

influence of shear and deviatoric stress on the evolution of permeability in fractured rock 1 the evolution of permeability in fractured rock as a function of effective normal stress shear displacement and damage remains a complex issue in this contribution we report on experiments in which rock surfaces were subject to direct shear under controlled pore pressure and true triaxial stress conditions while permeability was monitored continuously via flow parallel to the shear direction shear tests were performed in a pressure vessel under drained conditions on samples of novaculite arkansas and diorite coso geothermal field california the sample pairs were sheared to 18 mm of total displacement at 5 mm s at room temperature and at effective normal stresses on the shear plane ranging from 5 to 20 mpa permeability evolution was measured throughout shearing via flow of distilled water from an upstream reservoir discharging downstream of the sample at atmospheric pressure for diorite and novaculite initial preshear fracture permeability is 0 5 1 10 14 m 2 and largely independent of the applied effective normal stresses these permeabilities correspond to equivalent hydraulic apertures of 15 20 mm because of the progressive formation of gouge during shear the postshear permeability of the diorite fracture drops to a final steady value of 0 5 10 17 m 2 the behavior is similar in novaculite but the final permeability of 0 5 10 16 m 2 is obtained only at an effective normal stress of 20 mpa

contemporaneous phreatomagmatic and effusive activity along the hverfjall eruptive fissure north iceland eruption chronology and resulting deposits abstract the 2500 bp hverfjall eruption in northern iceland produced pyroclastic and effusive deposits of widely different characteristics along the length of the eruptive fissure the southern half of the fissure was located in a shallow lake whereas the northern part of the fissure extended onto dry land this specific setting with overlapping periods of activity at the different vents resulted in various mingling features between fine grained phreatomagmatic deposits and lava flows here we reconstruct the course of events during this eruption based on field observations and granulometric analyses of the resulting deposits the eruption can be divided into three main phases depending on the main depositional characteristics and vent locations the initial phase is dominated by phreatomagmatic fall deposits which are attributed to an overall high eruption rate in a shallow lacustrine setting the second phases involved opening of two new vents on dry ground and deposition of scoria and lava flows the third and final phase of the eruption is associated with a lowering of the eruption rate in the southernmost vent with a shift in the activity from continuous uprush and fall deposits to discrete explosions and emplacement of base surges these surges display features consistent with drying up with increasing distance from the vent suggesting that their dynamics changed during emplacement most wet surges were channelized within a preexisting graben structure close to the vent but some more dilute i e dry surges were able to flow over this obstacle and continued to flow for more than 5 km away from the vent and 100 m uphill before stopping

quantification of vesicle characteristics in some diatreme filling deposits and the explosivity levels of magma water interactions within diatremes abstract vesicles within juvenile fragments in mafic pyroclastic deposits contain important information about the state of the magma at the time of fragmentation there have been few vesicle studies of juvenile pyroclasts from mafic phreatomagmatic deposits however and none we can find from maar diatreme volcanoes in this paper we document the vesicularity and vesicle population characteristics of juvenile fragments sampled from non bedded lithified deposits of the coombs hills diatreme complex part of the ferrar large igneous province antarctica the diatreme filling pyroclastic deposits dominated by lapilli tuffs and tuff breccias contain typically abundant lithic clasts derived mostly from the enclosing sedimentary sequence and several types of juvenile clasts ranging from blocky to fluidal or raggy in the samples measured 77 80 of the juvenile pyroclasts ranging in size from 0 5 mm to fine lapilli is in the non vesicular to incipiently vesicular range fluidal or rag shaped juvenile clasts some circular vesicles and the lack of microlites all suggest that the coombs hills magma had a relatively low viscosity prior to fragmentation despite the basaltic andesite composition this low viscosity allowed parts of the magma to be fragmented in a non brittle fashion during phreatomagmatic explosions and to form fluidal clasts phreatomagmatic explosions in diatremes can therefore produce diverse types of juvenile clasts simultaneously and the proportions of each will depend on the explosivity of the magma water slurry interaction and other factors recycling of fragments is also thought to be an important factor in generating mixtures of different types of juvenile fragments in diatremes

stratigraphy sedimentology and eruptive mechanisms in the tuff cone of el golfo lanzarote canary islands the tuff cone of el golfo on the western coast of lanzarote canary islands is a typical hydrovolcanic edifice along with other edifices of the same age it was constructed along a fracture oriented nee sww that coincides with the main structural trend of recent volcanism in this part of the island we conducted a detailed stratigraphic study of the succession of deposits present in this tuff cone and here interpret them in light of the depositional processes and eruptive dynamics that we were able to infer the eruptive sequence is represented by a succession of pyroclastic deposits most of which were emplaced by flow plus a number of air fall deposits and ballistic blocks and bombs we distinguished five different eruptive depositional stages on the basis of differences in inferred current flow regimes and fragmentation efficiencies represented by the resulting deposits the different stages may be related to variations in the explosive energy eight lithofacies were identified based on sedimentary discontinuities grain size components variations in primary laminations and bedforms the volcanic edifice was constructed very rapidly around the vent and this is inferred to have controlled the amount of water that was able to enter the eruption conduit the sedimentological characteristics of the deposits and the nature and distribution of palagonitic alteration suggest that most of the pyroclastic succession in el golfo was deposited in a subaerial environment this type of hydrovolcanic explosive activity is common in the coastal zones of lanzarote and the other canary islands and is one of the main potential hazards that could threaten the human population of this archipelago detailed studies of these hydrovolcanic eruptions such as the one we present here can help volcanologists understand the hazards that this type of eruption can generate and provide essential information for undertaking risk assessment in similar volcanic environments

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

pele s tears and spheres examples from kilauea iki abstract pele s tears are a well known curiosity commonly associated with low viscosity basaltic explosive eruptions however detailed studies of these pyroclasts are rare and thus there is no full explanation for their formation these intriguing pyroclasts have smooth glassy surfaces vesiculated interiors 30 and fluidal morphologies trending towards teardrops and then spheres as they decrease in size to

origin of the joya honda maar san luis potosi mexico abstract joya honda is a quaternary maar of unusual type from the mexican basin and range province its 300 m deep crater is excavated in cretaceous limestones the surrounding tephra deposit which in places is 100 m thick begins with a series of weakly indurated pyroclastic surge and fall layers that we interpret as dry surge deposits these are overlain by the main sequence of strongly indurated massive tuff breccias that we interpret as wet surge deposits joya honda formed subaerially from the interaction of groundwater with rapidly ascending intraplate type basanitic magma carrying peridotitic mantle xenoliths local aquifer characteristics controlled the style of eruption and the nature of the deposits groundwater in the limestone hosted aquifer beneath joya honda was apparently contained within solution enhanced fractures at the onset of the eruption magma began to interact with a moderate amount of groundwater producing the dry surge deposits which are typical of deposits found at many maars and tuff rings as the eruption continued the crater grew and the hydromagmatic blasts fractured the limestones around the explosion foci a marked increase in the water magma ratio of the system followed when a large fracture or a portion of the limestone with enhanced secondary permeability was intersected by the expanding crater subsequent phreatomagmatic explosions occurred in a system with groundwater flow rates several orders of magnitude larger than in the initial dry surge stage at the maar rim these wet eruptions led to the emplacement of massive tuff breccias through a combination of fallout surges and mudflows these steeply dipping tuff breccias are similar to deposits found at many tuff cones juvenile clasts in the near vent deposits show marked upward increases in both hydration palagonitization and vesicularity the increased palagonitization with height in the section appears to be a consequence of the overall increased wetness of the eruption with time correlating with greater carbonate cementation and lithification in the upper part of the deposit the transition toward higher vesicularity is interpreted as evidence of a gradual reduction in the confining pressure for the ascending magma prior to explosive fragmentation perhaps related to unroofing during progressive excavation of the overlying maar crater thus joya honda does not support maar formation models that invoke downward displacement of explosion foci caused by formation of a cone of depression in the aquifer in order to maintain the confining pressure for the hydromagmatic blasts