shallow magma transport for the 2002 3 mt etna eruption inferred from thermal infrared surveys abstract the 26 october 2002 28 january 2003 eruption of mt etna volcano was characterised by lava effusion and by an uncommon explosivity along a 1 km long eruptive fissure on the southern upper flank of the volcano the intense activity promoted rapid growth of cinder cones and several effusive vents analysis of thermal images recorded throughout the eruption allowed investigation of the distribution of vents along the eruptive fissure and of the nature of explosive activity the spatial and temporal distribution of active vents revealed phases of dike intrusion expansion geometric stabilization and drainage these phases were characterised by different styles of explosive activity with a gradual transition from fire fountaining through transitional phases to mild strombolian activity and ending with non explosive lava effusion here we interpret the mechanisms of the dike emplacement and the eruptive dynamics according to changes in the eruptive style vent morphology and apparent temperature variations at vents detected through thermal imaging this is the first time that dike emplacement and eruptive activity have been tracked using a handheld thermal camera and we believe that its use was crucial to gain a detailed understanding of the eruptive event

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

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

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

pyrolytic assessment of oil generation and expulsion from a suite of vitrinite rich new zealand coals abstract pyrolysis gas chromatography py gc of tara 1 coals great south basin new zealand suggests a mean paraffinic oil potential of 85 kg t c range 70 130 kg t c based on n alkane alkene generation in the c6 c31 range and typical proportions of these compounds in related oils from new zealand this maximum in the depth trend of pyrolysate yield is reached at 0 75 0 80 r0 comparable to the previously reported maximum in hydrogen index hi thermal extraction gc te gc provided higher yields than rock eval s1pyrolysis but without the uniform trend exhibited by s1 c below the 3 0 km below sea floor 0 75 0 80 r0 onset of expulsion in addition the saturates aromatics ratio in the thermal extract decreased with depth indicating preferential retention of aromatics which may affect the expulsion efficiency of paraffins thermal extracts suggest that at most 15 kg t c of paraffinic oil is retained within the tara coals which is lower than previous estimates of saturation threshold however it is likely to be adversely affected lowered by loss of the least volatile components during recovery and storage of cuttings and incomplete recovery of high molecular weight components particularly c40 paraffins using te gc isopimarane generation appears to be restricted to the depth zone corresponding to the early oil window although it is unclear whether this is directly related to the maturity range required for such generation or that only the latest cretaceous coals in tara 1 exhibit particularly high abundances of such gymnosperm derived diterpanes

spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas the eruption of mount etna in 2000 was notable for an exceptional series of 64 periodic lava fountains propelling lava fragments to heights of up to 900 metres it has been difficult to determine which of two suggested sources of power gas release from the magma itself during its rapid ascent or a build up of pressure from gas accumulated at depth is the driving force for these dramatic jets but one of the etna fountains provided volcanologists with the opportunity to use remote sensing not that remote see picture on the following page to determine the infrared spectra of the gas phase this revealed the chemical composition of the gas that powered this fountain as consistent with an origin in an accumulated gas layer lava fountains are spectacular continuous gas jets propelling lava fragments to heights of several hundred metres which occasionally occur during eruptions of low viscosity magmas1 2 3 4 5 whether they are generated by the effervescent disruption of fast rising bubbly melt2 3 4 5 or by the separate ascent of a bubble foam layer accumulated at depth6 7 still remains a matter of debate8 no field measurement has yet allowed firm discrimination between these two models a key insight into the origin of lava fountains may be gained by measuring the chemical composition of the driving gas phase this composition should differ markedly depending on whether the magma degassing occurs before or during eruption9 10 here we report the analysis of magmatic gas during a powerful 250 600 m high lava fountain measured with fourier transform infrared spectroscopy11 12 13 14 on mount etna sicily the abundances of volcanic gas species determined from absorption spectra of lava radiation reveal a fountain gas having higher co2 s and s cl ratios than other etnean emissions14 15 16 17 18 and which cannot derive from syn eruptive bulk degassing of etna basalt19 20 instead its composition suggests violent emptying of a gas bubble layer previously accumulated at about 1 5 km depth below the erupting crater

vesiculation in magmas from stromboli and implications for normal strombolian activity and paroxysmal explosions in basaltic systems 1 we performed a series of x ray tomographic experiments and lattice boltzmann permeability simulations on pyroclastic products from explosive activity at stromboli between december 2004 and may 2006 we reconstructed the 3 d textures of vesicles to investigate the relationship between the nature of vesiculation in the erupted products and the dynamics of gas transport in the shallow conduit in order to derive implications for the eruptive behavior of basaltic volcanoes scoriae from normal strombolian explosions display remarkably consistent vesicle volume distributions fit by power laws with an exponent of 1 0 2 we ascribe the origin of such distributions to the combined effect of coalescence and continuous nucleation events in the steady state shallow magma system that supplies normal strombolian activity volume distributions and textures of vesicles in pumice clasts from the 5 april 2003 and 15 march 2007 paroxysmal activity are markedly different from those in the scoriae besides a power law function with a higher exponent portions of these distributions can be also fit by an exponential function suggesting the attempt of the system to reach near equilibrium conditions the investigated pumice clasts also lack the large connecting vesicles responsible for the development of degassing pathways in the stromboli magma that erupts the scoriae this testifies to a decreased degassing efficiency of the magma associated with paroxysmal explosions and potential overpressure buildup at depth by comparison with degassing experiments on basaltic melts we derive a time constraint on the order of minutes to hours for the incubation of paroxysms at stromboli

a co2 rich gas trigger of explosive paroxysms at stromboli basaltic volcano italy in addition to rhythmic slug driven strombolian activity stromboli volcano occasionally produces discrete explosive paroxysms 2 per year on average for the most frequent ones that constitute a major hazard and whose origin remains poorly elucidated partial extrusion of the volatile rich feeding basalt as aphyric pumice during these events has led to consider their triggering by the fast ascent of primitive magma blobs from possibly great depth here i examine and discuss the alternative hypothesis that most of the paroxysms could be triggered and driven by the fast upraise of co2 rich gas pockets generated by bubble foam growth and collapse in the sub volcano plumbing system data for the so2 and co2 crater plume emissions are used to show that stromboli s feeding magma may originally contain as much as 2 wt of carbon dioxide and early coexists with an abundant co2 rich gas phase with high co2 so2 molar ratio 60 at 10 km depth below the vents compared to 7 in time averaged crater emissions pressure related modelling indicates that the time averaged crater gas composition and output are well accounted for by closed system decompression of the basalt gas mixture until the volcano crust interface 3 km depth followed by open degassing and crystallization in the volcano conduits however both the low viscosity and high vesicularity of the basaltic magma permit bubble segregation and bubble foam growth at deep sill like feeder discontinuities and at shallower physical boundaries such as the volcano crust interface where the gas rich aphyric basalt interacts with the unerupted crystal rich and viscous magma drained back from the volcano conduits gas pressure build up and bubble foam collapse at these boundaries will intermittently trigger the sudden upraise of co2 rich gas blobs that constitute the main driving force of the paroxysms deeper sourced gas blobs driving the most powerful explosions will be the richest in co2 and have highest co2 so2 ratios this mechanism is shown to account well for the dynamic seismic and petrologic features of stromboli s paroxysms and hence to provide a potential alternative interpretation for their genesis and their forecasting enhanced bubble foam leakage prior to a paroxysm or foam emptying in several steps should lead indeed to precursory upstream of co2 rich gas and increasing co2 so2 ratio in crater plume emissions the recent detection of such signals prior to two explosions in december 2006 and march 2007 strongly supports this expectation and the model proposed in this study

infrasound reveals transition to oscillatory discharge regime during lava fountaining implication for early warning 1 we present the analysis of 4 million infrasonic signals which include 39 episodes of lava fountains recorded at 5 5 km from the active vents we show that each eruptive episode is characterized by a distinctive trend in the amplitude waveform and frequency content of the acoustic signals reflecting different explosive levels lava fountain starts with an 93 min long violent phase of acoustic transients at 1 25 hz repeating every 2 5 s infrasound suddenly evolves into a persistent low frequency quasi monochromatic pressure oscillation at 0 4 hz we interpret this shift as induced by the transition from the slug discrete strombolian to churn flow sustained lava fountain regime that is reflecting an increase in the gas discharge rate we calculate that infrasonic transition can occur at a gas superficial velocity of 76 m s and it can be used to define infrasonic based thresholds for an efficient early warning system

vapor phase cristobalite as a durable indicator of magmatic pore structure and halogen degassing an example from white island volcano new zealand vesicles in volcanic rocks are physical records of magmatic degassing however the interpretation of their textures is complicated by resorption coalescence and collapse we discuss the textural significance of vesicle hosted vapor phase cristobalite high t low p sio2 polymorph and its utility as a complement to textural assessments of magmatic degassing using a representative dacite bomb erupted from white island volcano new zealand in 1999 imaging in 2d sem and 3d ct shows the bomb to have 56 bulk porosity almost all of which is connected 99 and devoid of sio2 phases the remaining 1 of porosity is in isolated sub spherical vesicles that have corroded walls and contain small 30 m across prismatic vapor phase cristobalite crystals 98 4 0 4 wt sio2 with diagnostic laser raman spectra halogen degassing models show vapor phase cristobalite to be indicative of closed system chlorine and fluorine partitioning into h2o rich fluid in isolated pores at white island this occurred during shallow 100s of meters ascent and extensive 50 groundmass crystallization associated with slow cooling in a volcanic plug pristine textures in this white island bomb demonstrate the link between pore isolation and vapor phase cristobalite deposition we suggest that because these crystals have higher preservation potential than the bubbles in which they form they can serve as durable qualitative textural indicators of halogen degassing and pre quench bubble morphologies in slowly cooled volcanic rocks e g lava flows and domes even where emplacement mechanisms have overprinted original bubble textures

assessing the depth resolution of tomographic models of upper mantle structure beneath iceland 1 earlier inversions of body wave delay time data recorded during the icemelt portable broadband experiment imaged a cylindrical plume like low velocity anomaly extending to at least 400 km depth beneath iceland but the depth extent of the anomaly resolvable by tomography has recently been called into question we have performed several additional resolution tests to evaluate the depth resolution of tomographic models of the icelandic upper mantle the distribution of paths of body waves recorded by icemelt can distinguish among three different types of models a a wide and shallow anomaly b a narrow and deep anomaly and c a narrow and shallow anomaly while tomographic models contain an element of nonuniqueness these tests illustrate that the depth resolution of passive seismic experiments spanning subaerial iceland is adequate for distinguishing among alternative geodynamic models

explosive volcanic eruptions ix the transition between hawaiian style lava fountaining and strombolian explosive activity the commonest eruption styles of basaltic volcanoes involve hawaiian lava fountaining or intermittent strombolian explosions we investigate the ways in which magma rise speed at depth magma volatile content and magma viscosity control which of these eruption styles takes place we develop a model of the degree of coalescence between gas bubbles in the magma which allows us to simulate the transition between the two extreme styles of activity we find that magma rise speed is the most important factor causing the transition with gas content and viscosity also influencing the rise speed at which the transition occurs counter to intuitive expectations a decrease in gas content does not cause a transition from hawaiian to strombolian activity but instead causes a transition to passive effusion of vesicular lava rather a change from hawaiian to strombolian style requires a significant reduction in magma rise speed

gas driven lava lake fluctuations at erta ale volcano ethiopia revealed by modis measurements the long lived lava lake of erta ale volcano ethiopia is remotely monitored by moderate resolution imaging spectroradiometers modis installed on satellites the normalised thermal index nti wright et al remote sens environ 82 135 155 2002 is shown to be proportional to the volume of the lava lake based on visual observations the lava lake s variable level can be plausibly related to a stable foam i e a mixture composed of densely packed non coalescing bubbles in suspension within a liquid this foam is trapped at the top of the magma reservoir and its thickness changes in response to the gas flux feeding the foam being successively turned on and off the temporal evolution of the foam thickness and the resulting variation of the volume of the lava lake is calculated numerically by assuming that the gas flux feeding the foam initially constant and homogeneous since december 9 2002 is suddenly stopped on december 13 2002 and not restarted before may 2003 the best fit between the theoretical foam thickness and the level of the lava lake deduced from the nti provides an estimate of both the reservoir radius 155 170 m and the gas flux feeding the foam 5 5 10 3 7 2 10 3 m 3 s 1 when existing this is in agreement with previous estimates from acoustic measurements bouche et al earth planet sci lett 295 37 48 2010 the very good agreement between the theoretical foam thickness and that deduced from modis data shows for the first time the existence of a regime based on the behaviour of a stable foam whose spreading towards the conduit wide conduit condition can explain the long lived activity our predictive model which links the gas flux at the vent to the foam spreading could potentially be used on any volcano with a long lived activity the underlying gas flux and the horizontal surface area of the magma reservoir can then be deduced by combining modelling to continuous measurements of gas flux the lava lake when high often shows regular rise and fall of its level we have recognised a minimum of 26 very well marked cycles between january 2001 and december 13 2002 corresponding to a typical return time of 10 8 2 3 days and a gas volume of 8 3 105 2 0 105 m 3 this corresponds to a gas volume fraction in the reservoir equal to 0 023 0 063 the yearly gas flux estimated between december 13 2002 and september 27 2004 varies between 2 3 10 6 and 5 9 10 6 m 3 s 1 at the depth of the reservoir the long time series provided by infra red sensors mounted on satellites could be used on any persistent volcano to detect potential periodic variations in the level of lava lakes or lava columns providing that the vent has a funnel shape as often and is sufficiently large

pele s hairs and tears natural probe of volcanic plume we present a detailed petrographic study of pele s hairs and tears sampled from masaya volcano nicaragua this study provides new observations of these little known pyroclastic objects using both secondary electron images sei and back scattering electron images bsei our work shows that pele s tears can be associated with pele s hairs after their formation tears can be trapped on the walls and or in the cavities of pele s hairs moreover chemical investigations of the pele s hairs and tears highlight the presence of a chemical zonation the edge of these tears and hairs show a siliceous enrichment allowing us to quantify the interaction time of the silicate glass with acid gases in the volcanic plume this study confirms the syneruptive and post eruptive volatile exsolution from pele s hairs and tears

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

poseidic explosive eruptions at loihi seamount hawaii much remains unknown about submarine explosive eruptions their deposits are found to great depths in all the world s oceans but eruptions are typically described by analogy to a subaerial nomenclature that ignores the substantial and inevitable infl uences of hydrostatic pressure and magma water interaction at submerged edifi ces here we explore magmatic volatile exsolution and magma water interaction for a pyroclastic cone forming eruption at 1 km depth on loihi seamount hawaii we examine vesicle textures in lapilli the physical manifestation of degassing dissolved volatiles in matrix glasses and olivine hosted glass inclusions the geochemical record of ascent and volatile exsolution and fi ne ash morphology the evidence for if and how external water assisted in fragmentation this approach allows a submarine explosive eruption style to be defi ned the magma achieved 40 vesicularity through almost perfectly closed system volatile exsolution from 3 km below the vent which accelerated and weakened the melt allowing it to be fragmented by explosive magma water interaction we introduce the name poseidic for this end member style of submarine basalt explosivity poseidic eruptions are identifi able from measurable features in pyroclasts and are possible at all subaqueous basaltic volcanoes

thermo rheological magma control on the impact of highly fluid lava flows at mt nyiragongo 1 in january 2002 mount nyiragongo erupted foiditic lavas that covered the southern volcano flank devastating vast urban areas lava flows originated from vents at different heights on the eruptive fissure displayed different velocities from tens of km h at the highest vents to slow advance 0 1 1 km h in goma town several km away from the volcano to understand the different behavior of lava flows and their threat to the local population we undertook a multidisciplinary study involving textural and rheological measurements and numerical simulations of heat transfer during magma ascent we demonstrate that pre eruptive cooling and syn eruptive undercooling of magma determined the different rheological behavior of lava flows erupted from vents at diverse heights venting at lower altitudes is expected to produce viscous slowly advancing lavas although development of fluid faster flows should be included among possible future eruptive scenarios

vesiculation and fragmentation history in a submarine scoria cone forming eruption an example from nishiizu izu peninsula japan an uplifted 50 m thick half dissected submarine emplaced below wave base scoria cone occurs as dipping beds in coastal outcrops at nishiizu on the izu peninsula in japan concentrically outward dipping weakly stratified ungraded framework supported thin to very thick beds consist of brown coarse tuff to scoria lapilli tuff with outsized fluidal bombs throughout accessory lithic clasts chiefly occur in the lowermost visible beds scoria bombs have quenched margins weak bread crust textures and their vesicle number densities decrease inward which is indicative of fast surface cooling composite textures in the scoria bombs indicate recycling and agglutination of quenched and semi molten pyroclasts at the submarine vent in contrast to weak concentric gradations in vesicle size distribution in the bombs lapilli have asymmetrical gradients in vesicle size distribution indicating that they are fragments of coarser quenched lumps three grain size modes characterise the nishiizu brown scoria with coarse magma lumps ejected during magmatic fragmentation and quench jointed upon contact with seawater to be subsequently fragmented into lapilli and coarse ash by various styles of fragmentation where seawater plays a critical role the cone was constructed by slow moving fallout fed granular flow creep fed directly by suspension settling focused at the crater rim but extending onto the cone flanks with only minor resedimentation by granular flows nishiizu deposits yield an exceptional record of eruption and sedimentation dynamics during submarine cone building activity and in this study we compare their vesiculation and fragmentation mechanisms with those of potential subaerial analogues

explosive volcanic eruptions viii the role of magma recycling in controlling the behaviour of hawaiian style lava fountains explosive eruptions of mafic magmas produce lava fountains whose heights are a function of the exsolved volatile content of the magma its erupted mass flux and the geometry of the vent which may be an elongate fissure or a localized near circular conduit the geometry of the initial vent and the eruptive behaviour can be distinctly modified by lava drainback and accumulating ejecta hot pyroclasts landing near the vent may coalesce to form rootless flows some of which may drain back into the vent to be recycled into the eruption products rootless flows may be at least partially confined by pre existing topographic features or by spatter or cinder ramparts being built up by the eruption itself so that they accumulate into a lava pond over and around the vent the erupting jet of magmatic gas and pyroclasts must force its way through such a pond and will entrain some of the pond lava as it does so the energy expended in entraining and accelerating previously erupted materials will reduce the eruption velocity and the lava fountain height by an amount which can be calculated as a function of the eruption conditions and the lava pond depth or lava drainback rate the results of such calculations are presented and are used to assess the influence of this process on attempts to infer magma volatile contents from field observations of lava fountain heights

relationship between tremor and volcanic activity during the southeast crater eruption on mount etna in early 2000 1 the southeast crater of mount etna italy was characterized by a violent eruptive activity between 26 january and 24 june 2000 this activity produced 64 lava fountain episodes with repose periods from 3 hours to 10 days we estimated a volume of about 15 20 106 m3 lava and at least 2 3 106 m3 of tephra we compared the paroxysmal volcanic activity to its associated seismic signature the high number of events highlighted a strict correlation between tremor and volcanic activity seismic and volcanic characteristics such as the frequency of occurrence the duration of lava fountains and the associated tremor energy suggested the subdivision of the studied period into two stages separated by the 20 february event combining volcanic with seismic data we observed some useful relationships among lava fountain height sustained column height and reduced displacement in addition we found that the entire episode was well correlated with the duration of the amplitude increase computing the tremor energy linked to each event the total energy associated with lava fountains episodes results in 76 of the energy released during the whole period finally the different ratios among the overall spectral amplitude of the seismic signals of the stations located at different altitudes suggested to us the elaboration of a simple qualitative model to explain the dynamic behavior of the tremor source during the whole episode

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

progressive changes in the morphology of fluvial terraces and scarps along the rappahannock river virginia progressive geomorphic changes in the flight of fluvial terraces along the rappahannock river virginia provide a framework for analysing the effect of time on landforms the oldest terrace is probably no younger than early quaternary and the youngest major fill terrace probably correlates with the high sea level of the last major interglacial a uranium series date of 187 000 yr has been obtained on coral from marine sediments related to this terrace indices of terrace preservation especially drainage densities and area to perimeter ratios show systematic changes with terrace age hence these variables appear to satisfactorily indicate relative age and could perhaps be used to estimate actual ages if suitably calibrated the morphology of scarps formed by entrenchment of the fluvial terraces is more variable than analogous morphology of fault scarps and wave cut bluffs however measurements of the fluvial scarps clearly indicate that for a given terrace age higher scarps tend to have steeper slopes and that for a given scarp height older scarps tend to have gentler slopes the terrace forms themselves are preserved for at least several million years depositional features such as bars and channels with l 3m of relief are preserved on terraces on the order of 105 yr old scarps related to the formation of terraces of this age are well preserved and have slopes of about 6 8 degrees where the scarp height is about 5 m the preservation of fluvial landforms and scarps suggests that if fault scarps comparable to these features were commonly formed by earthquakes in low relief areas of the eastern united states many should be recognizable

on the transition from strombolian to fountaining activity a thermal energy based driver since 1999 mount etna s italy south east crater system has been characterised by episodic lava fountaining each episode is characterised by initial strombolian activity followed by transition to sustained fountaining to feed high effusion rate lava flow here we use thermal infrared data recorded by a permanent radiometer station to characterise the transition to sustained fountaining fed by the new south east crater that developed on the eastern flank of the south east crater starting from january 2011 we cover eight fountaining episodes that occurred between 2012 and 2013 we first developed a routine to characterise event waveforms apparent in the precursory strombolian phase this allowed extraction of a database for thermal energy and waveform shape for 1934 events we detected between 66 and 650 events per episode with event durations being between 4 and 55 s in total 1508 78 of the events had short waxing phases and dominant waning phases event frequency increased as climax was approached events had energies of between 3 0 106 and 5 8 109 j with rank order analysis indicating the highest possible event energy of 8 1 109 j to visualise the temporal evolution of retrieved parameters during the precursory phase we applied a dimensionality reduction technique results show that weaker events occur during an onset period that forms a low energy sink the transition towards fountaining occurs at 107 j where subsequent events have a temporal trend towards the highest energies and where sustained fountaining occurs when energies exceed 109 j such an energy based framework allows researchers to track the evolution of fountaining episodes and to predict the time at which sustained fountaining will begin

mineralogical and thermal characterization of a volcanic ash implications for turbine interaction abstract volcanic ash grain size the physico chemical and phase state of ash influences substantially the thermal behavior of volcanic ash and our ability to predict that behavior and therefore depends on reliable characterization of this state here we have investigated the chemical composition and mineralogy phase state of fresh volcanic ash from tungurahua volcano ecuador as a function of grain size below 180 m in order to evaluate differences between ground sampled ash and airborne ash interacting with jet engines for the sieved grain size fractions down to using an optical dilatometer image analysis we have characterized the thermal behavior of the volcanic ash upon heating which we parameterize in terms of four characteristic temperatures using these data the determination of the flow temperature is refined to improve measurement accuracy for fine grained