an experimental study of the kinetics of decompression induced crystallization in silicic melt 1 experiments were conducted to study the temporal evolution of feldspar crystallization kinetics during isothermal decompression pinatubo dacite was held at 780 c 220 mpa fo2 nno 2 h2o saturated conditions for an equilibration period decompressed to final pressures pf ranging from 175 to 5 mpa and then held for 0 3 931 hours according to the plagioclase liquidus curve in ph2o t space for the relevant melt composition these decompressions impose effective undercoolings teff of 34 266 c growth of preexisting phenocrysts and newly formed sparse microlites dominate crystallization at 75 pf 150 mpa teff 34 93 c and equilibrium crystal modes are achieved in 168 hours microlite nucleation is the dominant transformation process for 10 pf 50 mpa teff 125 241 c and chemical equilibrium is not attained by 168 hours under these conditions slow steady decompressions typically produced normally zoned euhedral and planar faceted feldspar crystals although anhedral morphologies were produced at very low pf contrary to expectation slowly decompressed samples were usually further from chemical equilibrium than rapidly decompressed samples after similar durations below the initial pressure although counterintuitive these trends are consistent with new constraints on the relative rates of feldspar nucleation and growth controlled by teff and melt viscosity experienced during each decompression path analysis of liquid to solid transformation kinetics using ttt style diagrams shows that crystallization occurs most rapidly at 100 mpa by a crystal growth mechanism the next most efficient crystallization conditions are at 25 mpa in a crystal nucleation dominated regime

texture and composition of pumices and scoriae from the campi flegrei caldera italy implications on the dynamics of explosive eruptions 1 the campi flegrei cf caldera is one of the most dangerous quiescent volcanic systems in the world its activity mostly resulted in low magnitude explosive eruptions such as that of the monte nuovo tuff cone that represents the last eruptive event within the caldera a d 1538 however there have been more energetic plinian events e g the agnano monte spina eruption 4 1 ka and very highly explosive caldera forming eruptions e g the campanian ignimbrite eruption 39 ka here we integrate new and literature data on the groundmass texture and composition of pyroclastic products from the three above eruptions with the aim of unraveling how volatiles content degassing mechanisms and crystallization processes influence magma explosivity and eruption dynamics at cf previous studies indicate that the investigated rocks share similar major element bulk and phenocryst chemistry also similar is the water content of their trapped melt inclusions these observations suggest that the magmas feeding these eruptions had comparable physicochemical properties during storage in the shallow crust however our investigations indicate that the studied rocks differ in texture and composition of the groundmass and viscosity of the related magmas we ascribe such differences to the variable style of volatile exsolution and outgassing from the melt primarily in response to changes of the rate of magma ascent to the surface we conclude that the magma ascent rate was the key parameter in driving explosive eruptions at cf and we suggest that this parameter may be influenced by magma water interaction and or magma chamber geometry and replenishment

crystallization kinetics in continuous decompression experiments implications for interpreting natural magma ascent processes decompression experiments were performed to study the kinetics of plagioclase crystallization during ascent of hydrous rhyodacite magma these experiments differ from previous studies in that they employ a continuous rather than stepwise pressure time trajectory four series of experiments were performed at rates of 0 5 10mpa h corresponding to ascent rates of 0 007 0 14 m s experiments quenched along each decompression path allow snapshot style monitoring of progressive crystallization as expected rates of plagioclase nucleation and growth depend strongly on decompression rate regardless of decompression rate approximately equal volumes of feldspar crystallize during a given decompression interval even when the observed crystallinity is lower than the equilibrium crystallinity apparently a constant degree of solidification is maintained by a crystallization mechanism striking a shifting balance between nuclei formation and growth of existing crystals other key results pertain to the efficacy with which experimental results allow interpretation of the decompression histories of natural rocks feldspar microlites do not maintain chemical equilibrium with melt they are more anorthite rich than equilibrium plagioclase suggesting that interpretations of magma ascent processes in nature require comparisons with dynamic rather than static phase equilibrium experiments although decompression rate is an important element controlling final textures in volcanic rocks no single compositional or textural parameter uniquely records this rate of the criteria examined microlite number density and morphology are the best indicators of magma decompression rate based on a small number of comparisons between continuous and multi step decompression style at the same time integrated decompression rate 1mpa h decompression path evidently influences crystal texture with stepwise decompression yielding textures correlative with faster decompression than indicated by the time integrated decompression rate thus consideration of magma ascent style in addition to rate will undoubtedly strengthen the interpretive power of experimental studies for constraining natural magma ascent processes

crystallization kinetics of alkali feldspars in cooling and decompression induced crystallization experiments in trachytic melt cooling and decompression experiments have been carried out on trachytic melts in order to investigate crystallization kinetics of alkali feldspar the effect of the degree of undercooling t t liquidus t experimental and time on nucleation and crystal growth process this experimental work gives us new data about crystallization kinetics of trachytic melts and it that will be useful to better understand the natural system of campi flegrei volcanoes experiments have been conducted using cold seal pressure vessel apparatus at pressure between 30 and 200 mpa temperature between 750 and 855 c time between 7 200 and 57 600 s and redox condition close to the nno 0 8 buffer these conditions are ideal to reproducing pre and syn eruptive conditions of the campi flegrei volcanoes where the conditions pertain to the complete range of pressures temperatures and time at which the experiments were performed alkali feldspar is the main phase present in this trachyte and its abundance can strongly vary with small changes in pressure temperature and water content in the melt implying appreciable variations in the textures and in the crystallization kinetics the obtained results show that crystallization kinetics are strictly related to t time final pressure superheating t and water content in the melt t is the driving force of the crystallization and it has a strong influence on nucleation and growth processes in fact the growth process dominates crystallization at small t whereas the nucleation dominates crystallization at large t time also is an important variable during crystallization process because long experiment durations involve more nucleation events of alkali feldspar than short experiment durations this is an important aspect to understand magma evolution in the magma chamber and in the conduit which in turn has strong effects on magma rheology

a 3d imaging textural characterization of pyroclastic products from the 1538 ad monte nuovo eruption campi flegrei italy abstract the explosive volcanic event of the 1538 ad monte nuovo eruption volcanic explosivity index vei 2 in the campi flegrei high risk caldera italy has a strategic significance in the framework of volcanology and volcanic hazard of caldera forming magmatic systems in fact it represents the last and unique historical eruption of the highly populated phlegraean restless caldera and its precursory and eruptive phenomena are well known because they were described in detail by contemporaneous eyewitnesses in this study a set of samples representative of the complete stratigraphic sequence of the monte nuovo eruption was characterized using phase contrast synchrotron radiation computed microtomography and quantitatively investigated through the development of a new protocol for 3d textural analysis of highly vesiculated volcanic rocks previous studies of products from this eruption are available in the literature mostly based on 2d imaging techniques and thus provide a useful data set for comparison the 3d textural measurements allow us to investigate the subvolcanic processes mechanisms and timing of magma degassing that occurred during magma ascent in the conduit for each stage of the eruption and their relationship with the variations in the eruptive style described in the contemporaneous accounts of the eruption this information is fundamental for the definition of a volcanic eruption scenario for such low vei events often recurrent in the history of the caldera and is useful both for hazard assessment and emergency planning

plagioclase nucleation and growth kinetics in a hydrous basaltic melt by decompression experiments isothermal single step decompression experiments at temperature of 1075 c and pressure between 5 and 50 mpa were used to study the crystallization kinetics of plagioclase in hydrous high k basaltic melts as a function of pressure effective undercooling teff and time single step decompression causes water exsolution and a consequent increase in the plagioclase liquidus thus imposing an effective undercooling teff accompanied by increased melt viscosity here we show that the decompression process acts directly on viscosity and thermodynamic energy barriers such as interfacial free energy controlling the nucleation process and favoring the formation of homogeneous nuclei also at high pressure low effective undercoolings in fact this study shows that similar crystal number densities na can be obtained both at low and high pressure between 5 and 50 mpa whereas crystal growth processes are favored at low pressures 5 10 mpa the main evidence of this study is that the crystallization of plagioclase in decompressed high k basalts is more rapid than that in rhyolitic melts on similar timescales the onset of the crystallization process during experiments was characterized by an initial nucleation event within the first hour of the experiment which produced the largest amount of plagioclase this nucleation event at short experimental duration can produce a dramatic change in crystal number density na and crystal fraction triggering a significant textural evolution in only 1 h in natural systems this may affect the magma rheology and eruptive dynamics on very short time scales

magma degassing and crystallization processes during eruptions of high risk neapolitan volcanoes evidence of common equilibrium rising processes in alkaline magmas abstract compositional textural and experimental data on products from explosive and effusive eruptions of neapolitan volcanoes campi flegrei and somma vesuvio allow us to constrain degassing and fragmentation conditions during eruptions of alkaline magmas significant differences in compositional and textural features have been recognized between lavas scoria and pumice resulting respectively from effusive moderately and extremely explosive eruptions pumice samples have highly vesicular glassy matrix low microlite number density and moderate to high water content crystal size distributions csd are steep with high intercept values the narrow microlite size range indicates single nucleation event scoria products are characterized by moderate vesicularity and water content they have high number density of microlites which are bimodal in size csd show distinct inflections that are explained as two crystal populations growing in distinct time lava samples generally have low vesicularities moderate to high microcrystalline groundmass and low glass water content the comparison between textural and compositional features of natural rocks with samples obtained by decompression experiments allows us to conclude that degassing processes during magma ascent occurs in near equilibrium conditions even at high decompression rate moderate to long magma rise times calculated in the order of a few days produce open degassing responsible for moderately explosive to effusive activity short magma rise times calculated in the order of a few hours result in closed system degassing that allow explosive fragmentation when the volume of growing bubble reaches a fixed threshold vesicularity and water content measured on matrix glass of pumice indicate that this process occurs at pressure of 10 30 mpa in these conditions degassing fragmentation and in turn the eruptive style is strongly influenced by initial conditions in the magma chamber volatile content temperature pressure instead of decompression rate in contrast with that observed for rhyolitic melts these differences have important consequences in terms of volcanic hazards and risk the low viscosity alkaline magma is able to maintain efficient degassing even during the final stage of magma ascent favoring in the case of closed system fragmentation and explosive activity

using tree ring analysis to evaluate intra eruptive lahar activity in the nexpayantla gorge popocatepetl volcano central mexico abstract lahar activity is one of the most important processes capable of mobilizing large volumes of sediment and producing devastating effects on human populations and infrastructure estimating the frequency distribution and climatic controls on lahar activity is necessary for understanding how sediment is mobilized from hillslopes to channels and how the landscape is modified by this type of process in this study we evaluate the intra eruptive lahar activity in the nexpayantla gorge nw of popocatepetl volcano central mexico by using a dendrogeomorphological analysis of growth ring records of abies religiosa trees n 100 based on the identification of 322 growth disturbances gd and field evidences we identify 23 intra eruptive lahars that occurred from 1959 to 2013 by analyzing the lahar chronology and climatic data we observed that 83 of lahar activity coincides with moderate to strong cold and dry phases of el nino southern oscillation based on the seasonal timing of gd we explored the intra annual lahar activity we found that 43 of the lahars occurred in the latewood season from july to october when the mean summer monthly rainfall is 120 mm approximately 37 of lahars occurred during the first heavy rainfalls from march to june which corresponds to the earlywood season the remaining 20 of the lahar activity corresponds to the dormancy period winter season when snowmelt and or occasional strong rainfalls 100 mm day 1 occur the gd indicate that in nexpayantla gorge intra eruptive lahar activity takes place around every two years we also found that the effects of lahars are concentrated around the transitional and depositional zone of nexpayantla gorge

dynamics of two phase conduit flow of high viscosity gas saturated magma large variations of sustained explosive eruption intensity the ascent of gas saturated magma in a conduit can lead to the transition from the laminar flow of a bubble rich melt to the turbulent flow of particle rich hot gas in upper part of the conduit this process is investigated with a help of a disequilibrium two phase flow model for steady and unsteady conditions for the description of different gas magma flow regimes in the conduit separated sets of equations are used the main difference from previous conduit flow models is the consideration of the pressure difference between a growing bubble and the surrounding melt for a bubbly liquid to evolve into a gas particle flow a critical overpressure value must be exceeded this transition region is simulated by means of a discontinuity namely by a fragmentation wave the magma flow calculations are carried out for a given conduit length and overpressure between the magma chamber and the atmosphere the steady solution of the boundary problem is not unique and there are up to five distinct steady regimes corresponding to fixed eruption conditions within the framework of the quasi steady approach governing parameters being varied monotonically the transition from one regime to another can take place suddenly and is accompanied by the fundamental restructuring of the conduit flow resulting in rapid or abrupt changes in the intensity of explosive eruptions abrupt intensification of an explosive eruption occurs when the chamber pressure becomes sufficiently less than saturation pressure and therefore corresponds to the case of shallow depth magma chamber and high initial water content a regime with minimum flow rate may relate to the growth of a lava dome following the explosive phase of eruption these models can explain geological observations that imply large and sudden changes of discharge rate in large magnitude explosive eruptions particularly at the transition between plinian phase and ignimbrite formation

development of the 10 11 july 2015 two stage sequence of multiple emplacements of pyroclastic density currents at volcan de colima mexico insight from associated seismic signals abstract the 10 11 july 2015 partial collapses of the lava dome in the crater of volcan de colima mexico were accompanied by a sequence of two stage multiple pdcs separated by a 15 h interval with a total bulk volume of 14 2 10 6 m 3 of fragmentary material and runout distances reaching 9 1 and 10 3 km respectively reyes davila et al 2016 broad band seismic signals associated with the pdcs and recorded at seismic station ez5 installed at a distance of 4 km from the crater were used for analysis of the 20 h eruption process this process included two stages of the multiple pdcs emplacements two one hour periods of preliminary events to each of the stages and the inter stage period analysis of seismic signals allowed us to identify the types of volcanic events composing this eruption episode and estimate their quantitative characteristics and spectral parameters of generated seismic signals it was shown that the seismic signals produced by pdcs emplacements recorded during the two stages were characterized by different characteristics the second stage pdcs had radiated greater seismic energy than the pdcs emplaced during the first stage spectral analysis of the seismic signals produced by pdcs indicates a clearly separation in frequency content at 1 95 hz between the higher frequency events of the first stage and the lower frequency events of the second stage of the pdcs emplacements the obtained difference in the spectral contents of the seismic signals produced by the movement of two multiple pdcs may be supposed as a consequence of the proposed relative difference in the volumes of the pdcs of two multiple sequences due to a difference in the level of radiated seismic energy and a change in bottom conditions of the ravines during their passing along the ravines results of seismic study were used in discussion of the nature of the two stage eruptive process

interpretation of the environmental change of dongting lake middle reach of yangtze river china by 210pb measurement and satellite image analysis abstract the present study examined the recent environmental history of the dongting lake located in the middle yangtze river region central china the sediment was recovered by 22 vibrocores in different lake sectors primarily characterizing subaqueous delta and bay subfacies high sedimentation rates revealed by 210pb measurement in different subfacies of the lake ranged from 0 77 to 2 33 cm year these rates equate to deltaic sedimentation associated with mobile channels resulting from yangtze flood events satellite images confirm that the dongting lake does not contain the biggest yangtze floods moreover comparative bathymetric surveys verify that the dongting lake has lost almost two thirds of its total area in the past century due primarily to siltation by yangtze sediment in the late 19th century a major flood induced channel avulsion resulted in the coupling of the four tributary subbasin to the dongting lake causing a massive increase in the sediment supply into the lake since then hydrological data demonstrate that about 83 of the lake s annual sediment influx are derived from the yangtze in addition pressures from a growing population and associated human activities such as reclamation embanking aquaculture slope modification and deforestation are compounding the loss of the lake surface area and associated storage capacity

effect of stirring on crystallization kinetics of basalt texture and element partitioning isothermal crystallization experiments on basalt have been carried out using an infrared heating furnace to investigate the effect of stirring when stirring was not applied static experiment the results agreed well with previous experiments but when stirring was applied and a flow of reynolds number 10 3 4 was present dynamic experiment considerably different results were obtained especially in respect to the nucleation rate and the morphology of crystals at t 25 c essentially similar results were obtained on the nucleation rates and morphologies of crystals in both static and dynamic experiments however at supercoolings larger than 45 c nucleation density increased drastically in dynamic experiments reaching up to ten times as large as that in static experiments crystals of plagioclase and clinopyroxene were small and adapted acicular morphology regardless of t in dynamic experiments and hyalopilitic textures were formed a ttt diagram shows that the nucleation incubation time is shorter in dynamic experiments than in static experiments no compositional difference in major elements was found in plagioclase and clinopyroxene produced in both static and dynamic experiments however minor element concentrations e g mg in plagioclase and ti al in clinopyroxene were found to increase with both t and flow velocity all these results imply that although chemical diffusion in the melts did not play an important role in the dynamic experiments interface kinetics were important it is suggested that hyalopilitic texture commonly seen in natural basalt is mainly due to flow in magma

stratification at the earth s largest hyperacidic lake and its consequences volcanic lakes provide windows into the interior of volcanoes as they integrate the heat flux discharged by a magma body and condense volcanic gases volcanic lake temperatures and geochemical compositions therefore typically serve as warnings for resumed unrest or prior to eruptions if acidic and hot these lakes are usually considered to be too convective to allow any stratification within their waters kawah ijen volcano featuring the largest hyperacidic lake on earth volume of 27 million m3 is less homogeneous than previously thought hourly temperature measurements reveal the development of a stagnant layer of cold waters 30 c overlying warmer and denser water generally above 30 c and density 1 083 kg m3 examination of 20 yrs of historical records and temporary measurements show a systematic thermal stratification during rainy seasons the yearly rupture of stratification at the end of the rainy season causes a sudden release of dissolved gases below the cold water layer which appears to generate a lake overturn i e limnic eruption and a resonance of the lake i e a seiche highlighting a new hazard for these extreme reservoirs a minor non volcanic event such as a heavy rainfall or an earthquake may act as a trigger the density driven overturn requires specific salinity temperature conditions for the colder and less saline top water layer to sink into the hot saline water spectacular degassing occurs when the dissolved gases progressively stored during the rainy season due to a weakened diffusion of carbon dioxide in the top layer are suddenly released these findings challenge the homogenization assumption at acidic lakes and stress the need to develop appropriate monitoring setups

eruption dynamics inferred from microlite crystallization experiments application to plinian and dome forming eruptions of mt pelee martinique lesser antilles decompression experiments have been conducted to simulate syn eruptive crystallization in volcanic conduits to infer magma ascent rates and conditions during dome forming and plinian eruptions of silicic arc volcanoes the experiments were carried out on starting material with the composition of mt pele e rhyolitic interstitial melt 76 wt sio2 and consisted of three consecutive steps hydration decompression and annealing hydration saturated and undersaturated was performed at 8508c and 200mpa and was followed by isothermal decompression either linearly or stepwise to a final pressure pf of 30 or 5 10mpa decompression rates range from 0 003 to 25mpamin 1 decompression durations of 15 min to 40 days two samples were cooled by 258c and 508c during a 3 day step at pf subsequent to decompression the samples were held for up to 15 days at pf the experiments generated three types of crystals as products of pre syn and post decompression crystallization the experiments basically differ from previous studies in that they are specifically designed to discriminate crystal nucleation from growth and to evaluate the influence of pre decompression crystals on the decompression induced crystallization the effects of pre decompression crystals decompression rate undercooling pf and terminal cooling have been determined on plagioclase nucleation growth morphology and composition the main results suggest a positive correlation between decompression rate and the number density of plagioclase crystals nucleated at pf and highlight the effect of pre decompression crystals in further decompression induced crystallization the relations between the decompression conditions and the plagioclase characteristics have been used to infer mt pele e eruption dynamics suggesting that 1 plinian magmas ascend from the reservoir within less than 1h 1 10 m s 2 dome and block and ash flow magmas ascend within more than 2 5 days giving time for syn decompression crystallization around pre existent microlites 3 dome magmas provide evidence for long stagnation and cooling at low pressure and 4 surge magmas ascend without significant crystallization within less than 4 days and massively nucleate plagioclase at very low pressure the extent and violence of dome destruction may depend on the size or age of the dome with large or old domes favouring mildly explosive block and ash flows whereas small or young protodomes may generate highly explosive surges

the rheology of crystal bearing basaltic magmas from stromboli and etna abstract our ability to forecast volcanic hazards at active volcanoes stems from our knowledge of parameters affecting eruption dynamics persistent activity displayed by basaltic volcanic systems such as etna and stromboli is governed mainly by the textural evolution and rheological properties of eruptive products here we investigate the high temperature 1131 c

oil bearing glacial deposits from permo carboniferous haushi group oman abstract a sequence of glacial and related deposits up to 700 m 2 296 ft thick in the lower part of the haushi group contains significant quantities of oil in several fields in south and central oman and is the main exploration target along the eastern flank of the south oman salt basin more than 300 well penetrations demonstrate that the glacial deposits extend over more than 60 000 km2 23 166 mi2 in outcrop and subsurface the late carboniferous to early permian haushi group dated through palynology unconformably overlies precambrian to devonian rocks of the huqf and haima groups with locally a considerable paleorelief the glacial deposits are overlain by fluvial and shallow marine deposits of the upper haushi group which include a fossiliferous l mestone dated as early permain probably sakmarian the glacial origin of units within the lower part of the haushi group is established from the outcrop area on the west flank of huqf massif where striated pavements of precambrian dolomite have been found one pavement is directly overlain by a 4 m 13 ft thick diamictite interpreted as a basal till in nearby exposures striated boulders have been found both in the outcrops and in the subsurface diamictites with abundant far traveled material granite and volcanic boulders occur they are considered to be mostly debris flow deposits of glacially transported material their common interbedding with varved shales with dropstones is diagnostic of a glaciolacustrine setting the association of varved shales and diamictites is commonly of sealing quality reservoirs in the glacial sequence are formed by sandstones and clast to matrix supported sandy conglomerates which are interpreted as deltaic and fluvial deposits depositional models and paleogeographic reconstructions have been made with the help of core studies and correlation of facies units using wireline logs these correlations demonstrate the limited lateral predictability of reservoirs which is not unexpected in view of the geometrical complexity of many modern glacial deposits the geometry of facies units is however also complicated by syndepositional subsidence due to both progressive dissolution of precambrian salt and to differential erosion at the contact between the glacial sediments and the underlying unconsolidated sands of the haima group end of article last page 429

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization ii makaopuhi lava lake crystal size distribution csd theory has been applied to drill core samples from makaopuhi lava lake kilauea volcano hawaii plagioclase and fe ti oxide size distribution spectra were measured and population densities n were calculated and analyzed using a steady state crystal population balance equation n n0 exp l g slopes on ln n versus crystal size l plots determine the parameter g a product of average crystal growth rate g and average crystal growth time the intercept is j g where j is nucleation rate known temperature depth distributions for the lava lake provide an estimate of effective growth time allowing nucleation and growth rates to be determined that are independent of any kinetic model plagioclase growth rates decrease with increasing crystallinity 9 9 5 4 10 11 cm s as do plagioclase nucleation rates 33 9 1 6 10 3 cm3 s ilmenite growth and nucleation rates also decrease with increasing crystallinity 4 9 3 4 10 10 cm s and 15 2 2 10 3 cm3 s respectively magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus g 2 9 10 10 cm s j 7 6 10 2 cm3 s moments of the population density function were used to examine the change in crystallization rates with time preliminary results suggest that total crystal volume increases approximately linearly with time after 50 crystallization a more complete set of samples is needed for material with 50 crystals to define the entire crystallization history comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling this interpretation is consistent with proposed thermal models of magmatic cooling where heat loss is balanced by latent heat production to maintain equilibrium cooling

magma ascent and eruptive processes from textural and compositional features of monte nuovo pyroclastic products campi flegrei italy geochemical and textural studies were carried out on alkaline products of the ad 1538 monte nuovo eruption due to the integration of the volcanological study with eyewitness reports the dynamics and timing of each phase of the eruption and the volume of emitted magmas are known in detail on this basis unique in campi flegrei the relations between magma chamber mechanisms eruptive styles magma ascent dynamics and volatile exsolution processes have been explored glass and phenocryst compositions indicate that the erupted magma has a homogeneous phono trachytic composition textures and compositions of phenocrysts indicate that they crystallised at equilibrium with the melt in the magma chamber likely as a mushy boundary layer along the chamber wall where the temperature was below the liquidus temperature of the crystal free chamber core the estimated crystallisation temperature is 850 40 c the magma phase relations in petrogeny s residua system suggest that phenocryst crystallisation occurred at text p text h 2 text o between 100 and 200 mpa corresponding to depths ranging from 3 to 8 km the microlite composition and their close genetic relations with vesicles indicate that groundmass crystallisation occurred during the eruption as a consequence of magma degassing and vesiculation induced by decompression during its ascent toward the surface crystal size distributions reveal that microlites grew in two stages of undercooling that we define as 1 magma migration onset upward from the chamber and 2 magma rising through the conduit to the surface possibly lasting tens of days and few days respectively these results provide information on the physical conditions that characterise pre and syn eruptive processes which may be useful in order to define eruptive scenarios and to evaluate short term precursors furthermore the collected data provide for the first time information on degassing induced crystallisation during the eruption of a highly evolved alkaline magma

textural effects of steady state behaviour of the stromboli feeding system abstract the exceptionally persistent activity of stromboli volcano has lasted for at least 1400 years the normal strombolian activity is periodically interrupted by more energetic explosions 1 2 per year and by sporadic effusive episodes every 10 20 years normal activity and effusive episodes are characterized by crystal rich high k to shoshonitic basalts issuing from a volatile poor shallow system crystal poor pumice are emitted only during more violent explosions and are thought to derive from deep pulses of volatile rich magma shallow level degassing induces massive crystallization of deep pulses of feeding magma that continuously mixing with the resident one produces the crystal rich shoshonite of the persistent activity we examined the crystallization history of the crystal rich shallow reservoir using plagioclase crystal size distribution csd analysis of scoriae and lavas emitted in the past twenty years csds show a linear dependence from crystal size in the size interval 0 06 1 2 mm number density of larger crystals is biased by right hand truncation effects csds slopes and intercepts are quite constant during the whole considered time span revealing a system that is close to the equilibrium also from a kinetic point of view the linear crystal size distribution are reached by the system through episodes of growth and resorption respectively occurring in the degassed and undegassed magma during the continuous mixing in the feeding system plagioclase net growth rate 2 10 11 cm s results from a balance of growth 10 10 cm s and resorption episodes which induce spectacular zoning and resorption textures in crystals larger than 200 m csds of mafic phases cannot be accurately acquired on each single sample due to poor counting statistics the evaluation of pyroxene and olivine csd on the whole data set however confirms the conclusions acquired from plagioclase csds

the phlegraean fields structural evolution volcanic history and eruptive mechanisms abstract the main event within the volcanic history of the phlegraean fields was the eruption about 35 000 years ago of a huge alkali trachytic ignimbrite 80 km 3 dre followed by caldera collapse the pre caldera activity evidence from geothermal wells and surface outcrops changed from submarine to subaerial shortly before the ignimbrite eruption the caldera was subsequently invaded by the sea and became progressively filled with tuffites and subordinate submarine flows in its northern half the last submarine explosive activity dates back to 12000 10500 yr with the eruption of mostly hydroplinian yellow tuffs recent mostly subaerial activity consists of a series of explosive eruptions whose volume decreases with time until the last eruption of mt nuovo in 1538 a d two peaks in recent activity occur at 10000 8000 and 4700 3000 years ago during post caldera activity eruptive vents migrated from the caldera rim toward the center where there are two distinct zones of recent vents minor collapses occurred within the caldera after the main eruptions often they are eccentric to the vent and displaced toward the caldera center phlegraean explosive activity is characterized by water magma interaction eruptive events without a hydromagmatic component are extremely rare in most cases the evolved trachytic magmas interacted with surface water either the sea or intracaldera lakes however there is evidence of interaction of magma with deep seated aquifers for some plinian events explosivity i e the efficiency of the transformation of thermal into kinetic energy during magma water interaction is largely controlled by the primary fragmentation of the magmatic melt

rheological properties of magma from the 1538 eruption of monte nuovo phlegrean fields italy an experimental study abstract the rheology of natural partially crystallized samples from monte nuovo 1538 ad eruption have been investigated using a high temperature high pressure internally heated pressure vessel within the temperature interval of investigation the samples exhibited newtonian rheology at deformation strain rates up to 10 4 s 1 at higher strain rates a decrease of viscosity with increasing strain rate shear thinning eventually terminating in a sudden viscosity drop stress weakening was observed stress weakening occurred at higher applied strain rates and stresses with increasing temperature the microstructural analyses of the samples revealed that stress weakening resulted from strain localization which occurred in brittle and viscous regimes at the lowest and highest temperatures investigated respectively the different rheological behaviors of the investigated material is likely responsible for the changes in the dynamics of magma ascent within the volcanic conduit during the eruption of monte nuovo volcano we infer that the occurrence of syn eruptive decompression driven crystallization observed in previous studies induced strong variations in the rheological properties of magma which in turn was responsible for the changes of eruptive style observed during the monte nuovo eruption

magma dynamics beneath kameni volcano thera greece as revealed by crystal size and shape measurements size distributions of plagioclase crystals in series of recent porphyritic dacite lavas from kameni volcano greece can be modelled by mixing two populations of crystals each with overlapping linear crystal size distributions csd termed microlites and megacrysts the magmas bearing the microlites and megacrysts started to crystallise 6 13 and 24 96 years respectively before each eruption the dates of initiation of crystallisation of the megacrysts indicate that they are left overs of earlier injections of new magma into a shallow chamber some magma remains after each eruption and continues to crystallise new magma with few or no crystals is then introduced and the microlites crystallise from the mixed magma eruption followed 6 13 years after mixing such a model would suggest that some porphyritic magmas are products of a shallow magma chamber that is never completely emptied just topped up from time to time

constraining pre eruptive magma conditions and unrest timescales during the monte nuovo eruption 1538 ad campi flegrei southern italy integrating textural and csd results from experimental and natural trachy phonolites we present crystallization experiments representing a broad range of growth conditions of alkali feldspar and sodalite in a trachy phonolite magma composition during later stages of evolution our results include i textural data and mineral assemblages of synthetic samples ii feldspar nucleation kinetics and growth rate estimates and iii textural data mineral abundances and crystal size distribution measurements on samples representative of the monte nuovo eruption 1538 ad the last eruption of campi flegrei southern italy experiments reproduced the texture and feldspar content of natural products indicating that kinetic data can provide insights into processes within the volcanic system shortly before and during this small magnitude eruption and particularly about magma ascent timescale we suggest that the groundmass crystallization of monte nuovo magma started between 4 and 7 km depth 100 200 mpa at a temperature between 825 and 840 c close to the liquidus of alkali feldspar the crystallization kinetics of alkali feldspar and the absence of sodalite in most of the natural samples indicate that magma ascent rate increased in the shallow part of the conduit from about 3 km depth to the quenching level possibly fragmentation point 30 mpa during the first phases of the eruption the crystallization time of the magma requires that it ascended from pre eruptive storage to the quenching level in several hours to a few days we also observe that a small decrease in pressure can induce a dramatic increase in crystallinity with associated rheological changes leading to changes in the eruption style and such changes could occur on timescales of hours to several days the products from the later phases of the monte nuovo eruption are more crystalline and contain sodalite in response to the decrease in magma ascent rate which in turn allowed for more degassing during ascent resulting in more time spent at very shallow depths

the breccia museo formation campi flegrei southern italy geochronology chemostratigraphy and relationship with the campanian ignimbrite eruption the breccia museo is one of the most debated volcanic formations of the campi flegrei volcanic district the deposit made up of six distinctive stratigraphic units has been interpreted by some as the proximal facies of the major caldera forming campanian ignimbrite eruption and by others as the product of several more recent independent and localized events new geochemical and chemostratigraphical data and ar ar age determinations for several units of the breccia museo deposits 39 ka correlate well with the campanian ignimbrite forming eruption the chemical zoning of the breccia museo deposits is interpreted here to be a consequence of a three stage event that tapped a vertically zoned trachytic magma chamber

crystal size distribution analysis of plagioclase in experimentally decompressed hydrous rhyodacite magma article i nfo this study presents crystal size distributions csd of plagioclase forming during decompression experiments of hydrous rhyodacite magma samples were annealed at 130 mpa subjected to continuous decompression at either 2 mpa h 1 or 0 5 mpa h 1 and then quenched along their respective decompression paths at 20 mpa intervals samples display concave up curved csd plots which result from a combination of two crystal populations those which formed during the anneal period and those which formed during decompression the csds also display a decrease in crystal number density at 3 7 m a size range that is easily resolvable with the imaging strategy employed the downturn at small sizes is presumably due to insufficient compensation for the intersection probability effect in converting 2d measurements to 3d size distributions crystal nucleation and growth rates derived from csds using standard assumptions are compared with values obtained using 2d measurements of bulk crystal populations batch methods csd calculated nucleation rates are substantially low relative to the batch values in fact csd derived volumetric nucleation rates may underestimate actual nucleation rates by up to two orders of magnitude in contrast growth rates from csds are consistently higher than batch rates although plagioclase growth rates are relatively constant during decompression at a given rate the average growth rate in the rapidly decompressed series is approximately five times faster than the crystal growth rate in the slowly decompressed series because crystal growth rate depends on decompression rate csds are incapable of revealing decompression timescales or magma ascent rates without independent knowledge of crystal growth rate published by elsevier b v

temperature evolution during magma ascent in basaltic effusive eruptions a numerical application to stromboli volcano the dynamics of magma ascent are controlled by the complex interdependent processes of crystallisation rheological evolution gas exsolution outgassing non ideal gas expansion and temperature evolution temperature changes within the conduit in particular play a key role on ascent dynamics since temperature strongly controls the crystallisation process which in turn has an impact on viscosity and thus on magma ascent rate the cooling produced by gas expansion is opposed by the heat produced by crystallisation and therefore the temperature profile within the conduit is quite complex this complexity means that unravelling the dynamics controlling magma ascent requires a numerical model unfortunately comprehensive integrated models with full thermodynamic treatment of multiple phases and rheological evolution are challenging to produce due to the numerical challenges involved until now models have tended to focus on aspects of the problem without a holistic approach in which petrological thermodynamic rheological and degassing processes and their interactions were all explicitly addressed and quantified here we present a new multiphase steady state model for magma ascent in which the main physical and chemical processes such as crystallisation degassing outgassing rheological evolution and temperature variations are quantitatively calculated basaltic magma s crystallisation and flow are sensitive to initial temperature and volatile content and therefore we investigate temperature variations during magma ascent in a basaltic system with a range of volatile contents as a test case we use one of the most well studied recent basaltic effusive eruptions the 2007 eruption of stromboli italy assuming equilibrium crystallisation and exsolution we compare the solutions obtained both with and without an isothermal constraint finding that temperature variations within the conduit have a significant influence on the ascent dynamics and therefore cannot be ignored when modelling basaltic volcanism furthermore we find good agreement between model results and volcanological observations when the non isothermal condition is assumed we investigate through a sensitivity analysis the role of magma chamber temperature on mass flow rate and crystal content we find that a temperature variation of 30 k at the base of the conduit has a bigger effect on mass discharge rate than an increase of 1 wt in water content finally we find that whilst variations in initial co2 concentration can affect the temperature pressure and viscosity profiles along the conduit they do not alter the macroscopic behaviour of the system c 2015 elsevier b v all rights reserved

kinetics of cooling and decompression induced crystallization in hydrous mafic intermediate magmas article i nfo the crystallization of a hydrous basaltic andesite magma was investigated using cooling and decompression experiments these experiments were designed so that the driving force for crystallization of feldspar the undercooling is equal whether in the direction of cooling or decompression after initial equilibration steps at conditions t 1 025 c and ph2o 150 mpa charges were either cooled or decompressed near instantaneously to final conditions corresponding to undercoolings t 5 2 154 c with dwell times of 12 24 and 48 h at the final p t t his single step experimental strategy ssd for decompression experiments ssc for cooling allowed derivation of kinetic parameters such as nucleation and growth rates as a function of undercooling even though our setup was primarily designed to investigate feldspar crystallization we report kinetic and geochemical data for all phases present glass feldspar clinopyroxene olivine and amphibole at low to intermediate undercoolings the solidification behavior of mafic intermediate magmas is very similar texturally and compositionally whether the crystallization mechanism is cooling or decom pression at high degrees of undercooling feldspar and clinopyroxene nucleation rates are nevertheless higher in ssd compared to ssc runs perhaps due to slower diffusivities or larger nucleation barriers in the cooling runs minerals transition from interface limited growth to diffusion limited growth with increasing undercooling while nucleation regimes shift from homogeneous to heterogeneous crystal morphologies are highly variable but can be used qualitatively to assess the extent of undercooling relative to more silicic melts with similar crystal contents feldspar formed in andesitic melts nucleate at a lower rate but grow to larger sizes published by elsevier b v