high frequency earthquake swarm associated with the may 1991 dome extrusion at unzen volcano japan abstract the 1990 1995 eruption of unzen volcano in southwestern japan was characterized by the extrusion of a dacite lava dome and frequent pyroclastic flows during the dome growth associated with the dome emergence on may 20 1991 an intense swarm of high frequency hf microearthquakes occurred just beneath the crater at very shallow depths we used data from fg3 a seismic station located 500 m ssw of the crater to identify 29 401 hf earthquakes between may 11 and 31 1991 the rate of hf earthquakes increased starting on may 12 and peaked on may 17 the high seismicity continued until may 26 then dropped sharply coinciding with a marked decline in the swelling on the southern upper flank of the volcano the seismicity increased and decreased repeatedly within a 1 to 2 h period which was correlated with tilt cycles observed 680 m west of the crater in such a way that the seismicity increased during uplifting on the craterward side defining an earthquake group as a series of earthquakes with waveforms that are similar or vary only slightly over time we identified 10 such groups each containing more than 300 events the largest group comprised 3 214 events over 18 days seismicity rates of eight groups including the largest increased and decreased repeatedly correlated with the tilt cycles as the waveform data from station fg3 were considerably clipped for relatively large events we analyzed data from two additional stations kra and cja located 3 5 and 8 7 km from the crater respectively and identified a total of five new groups the activity of two groups recorded at kra was correlated with the tilt cycles but those of three groups recorded at cja did not always show such a correlation hypocenters for the groups recorded at kra were distributed to the east side of the conduit and a focal mechanism suggested that the events in this area occurred due to compressional stress produced by the inflation of the conduit the groups recorded at cja occurred to the north side of the dike trending westward from the conduit the focal mechanisms have p axes roughly trending to the dike which can be explained by the compressional stress generated by the increasing thickness of the dike

ground deformation caused by magma ascent in an open conduit this study examines magma ascent processes of three basic types prior to intermittent explosions such as vulcanian or strombolian types specifically their relations to volcano ground deformation such repetitive explosions eject magma from an open conduit at short time intervals consequently magma pressure is expected to decrease at the conduit and or reservoir and thereby deflate the volcano then magma within the conduit rises exerting normal and shear stresses on the conduit wall thereby inflating the volcano diffusive mass transfer of water molecules from the melt to bubbles might occur subject to a sudden depressurization by eruption when magma includes numerous small gas bubbles such gas bubble expansion lifts the magma in the conduit calculations of ground deformation on a semi infinite medium for such rising magma show that vertical and radial displacements and tilt motions recorded in the far fields are proportional to the 1 5 power of time for low viscosity magma gas bubbles might rise in the melt because of buoyancy force the gas bubbles expand rapidly with time because of decreased ambient pressure pushing the magma upward in the conduit consequently the volcano slowly inflates initially then the rate of deformation increases over time eventually engendering a rapid inflation immediately before eruption these temporal changes in ground deformations contrast against cases in which magma does not include gas bubbles in such cases amplitudes of ground deformation increase almost linearly or even decrease with time at far fields these differences which are recognized as basic characteristics of temporal changes of ground deformation enable us to know the driving forces of magma in an open conduit and to evaluate the gas bubble behavior quantitatively in magma before eruption

control on the emplacement of the andesite lava dome of the soufriere hills volcano montserrat by degassing induced crystallization lava solidification is controlled by two mechanisms external cooling and gas exsolution the latter inducing crystallization due to increasing liquidus temperature the andesite lava dome of the soufriere hills volcano montserrat is an extrusion dominated by crystallization caused by gas exsolution where cooling is unimportant in controlling emplacement in the magma chamber the magma has an estimated viscosity of 7 106 pa s during ascent gas exsolution caused the magma to extrude in a highly crystalline state with only 5 15 residual melt viscosities in the range 1013 1014 pa s and mechanical strength 1 mpa deformation can be heterogeneous with extrusion along shear zones rheological stiffening in the upper conduit also causes large overpressures shallow seismicity and cyclic patterns of dome extrusion gas rich porphyritic andesites tend to be the least mobile kind of lava because transition from magma into hot crystalline material was reached during ascent

transitions between explosive and effusive eruptions of silicic magmas water rich silicic magmas may erupt explosively giving rise to massive columns of fragmented ash1 5 or effusively as viscous bubbly lavas to form lava domes6 8 complex cycles of explosive and effusive eruptions are often observed8 12 although these two eruption mechanisms have been modelled independently1 8 the conditions under which a volcano exhibits a particular style of eruption are not known and the transitions between eruption styles are poorly understood by modelling the ascent of magma along a permeable conduit we show here that for small magma chamber overpressures the style of eruption explosive or effusive is dependent on the magma flow rate we also identify a critical overpressure above which only explosive eruptions occur complex eruption sequences follow naturally for example if a shallow magmatic system is supplied with magma at an intermediate flow rate the eruption will be slow and effusive until the chamber over pressure becomes too large an explosive eruption then relieves the overpressure and an effusive eruption style resumes we suggest that monitoring of temporal variations in chamber overpressure for example by measuring ground deformation can be used to assess whether a passively effusing volcano has the potential to erupt explosively

rock fracture as a precursor to lava dome eruptions at mount st helens from june 1980 to october 1986 following its plinian eruption on 18 may 1980 mount st helens washington state usa entered a period of intermittent lava dome extrusion until 1986 renewed extrusion was frequently preceded by accelerating rates of seismicity with more precursory seismicity observed prior to eruptions later in the sequence here the failure forecasting method ffm is used to investigate changes in the observed rate of volcano tectonic vt seismicity the analysis indicates that 1 all vt crises resulted in an eruption within 3 weeks usually less than 10 days 2 the majority of eruptions had vt precursors and 3 patterns of precursory seismicity showed fluctuations about the ideal model trend thus although these seismic events could be used to warn of an impending eruption specific forecasts were subject to an uncertainty of weeks or more it is proposed that 1 increased seismicity prior to later eruptions is a result of a larger and more solidified dome acting as a greater impediment to magma ascent 2 the consistency of seismic swarms resulting in an eruption indicates that stresses high enough to initiate fracturing in the country rock and lava dome carapace were only achieved once the approach to an eruption had already begun and 3 discrepancies between models of accelerating rock fracture and the observed seismicity may arise due to a significant amount of the rocks deforming through ductile mechanisms rather than seismogenic fracture

petrology of the 1991 1995 eruption at unzen effusion pulsation and groundmass crystallization abstract effusive eruption of dacite magma 2 1 108 m3 during 1991 1995 formed a lava dome at the summit of unzen volcano japan the effusion rate was highest at the beginning 4 0 105 m3 day 4 6 m3 s and decreased roughly with time to almost zero before this pattern was repeated with a second pulse of magma supply the whole rock chemistry of lavas shows significant variation attributable to variations in phenocryst abundance the more mafic the more abundant the phenocrysts the pattern of chemical variation with time shows some difference from that of the effusion rate all phenocrysts in dacite plagioclase hornblende biotite quartz and magnetite show evidence of disequilibrium with melt although a glomerophyric aggregation of phenocrysts suggests coexistence with each other phenocrysts are isotopically heterogeneous from species to species the calculated initial melt composition was rhyodacite and was nearly constant throughout the activity in contrast the bulk phenocryst population is andesite a model explaining the textures and the isotopic heterogeneity is the capture of diorite fragments or xenocrysts by parental rhyodacite magma it is suggested that when effusion rate was high less viscous crystal poor magma exited from the reservoir groundmass glass and plagioclase microlite rims show temporal chemical variations correlating with the effusion rate the higher the effusion rate the more evolved the compositions groundmass crystallinity increased with decreasing effusion rate from 33 to 50 textures in dome lavas suggest that groundmass crystallization had been mostly completed when magma reached the conduit top the fe ti oxide temperature 880 780 c was low when the crystallinity was high micropumice erupted before dome growth provided a sample recording magmatic foam in the conduit porosity of dome lavas was lower at lower effusion rates collapse of foam magma and simultaneous escape of volatiles through the conduit top were probably responsible for the accompanying low frequency earthquakes phenocrysts were broken and the breakdown rims on hornblende phenocrysts were torn off during collapse and successive compaction when effusion waned degassing and the resultant crystallization proceeded more completely so that the magma became too viscous to flow in the conduit top and behaved as a plug resulting in a temporary halt of effusion in turn groundmass crystallization in magma below the plug increased excess pressure in the upper parts of conduit due to slow cooling the plug was scavenged when rising excess pressure overcame its effective strength then the second pulse of magma supply began strong endogenous growth and extrusion of a lava spine in the later stage probably occurred for the same reason

oscillatory nature of the okmok volcano s deformation abstract the time dependent deformation of volcanic edifices can help one understand the dynamics of pre eruptive overpressure build up in magma chambers thus geodetic time series recorded at the okmok volcano in alaska show a pattern of fast and short inflations referred to as pulses followed by either slower and longer deflations or time intervals with no deformation this pattern is superimposed onto a longer period inflation a rapid inflation occurred just before the 2008 eruption which suggests that the underlying process may lead to eruptions it is crucial to understand whether such a behavior is driven by external forcing such as melt supply variations or whether it can develop spontaneously within the volcano s plumbing system here we model the observed oscillations 2004 2008 as resulting from the hydraulic interaction between two shallow magma chambers fed by a deeper source region a geometry that is consistent with geochemical petrological and geophysical data the model shows that episodes of periodic fast inflations occur i when a viscosity gradient is present in the vertical pipe for instance as the result of a temperature gradient and ii when the flux supplying the shallower chamber lies between two bounds that we derive analytically the deformation pulses observed at okmok can therewith be fully explained by the internal variability of the magmatic system and do not require time variable external forcing the proposed model can also be seen as an improvement upon the classic hydraulic models regularly used to explain a commonly observed pattern of volcanic deformations i e exponential inflation

an integrated model of magma chamber conduit and column for the analysis of sustained explosive eruptions abstract explosive volcanic eruptions comprise a complex series of processes involving withdrawal from the magma chamber magma ascent along the conduit and eruption column dynamics numerous studies have modeled the different sub domains of a volcanic system but their interplay has seldom been analyzed to this end we developed c 3 c cubed that stands for chamber conduit and column a new integrated model that describes the dynamics of an explosive eruption as a series of steady state regimes and as a function of geometry and initial conditions of the magma reservoir we used global sensitivity analysis to quantify the role of the relevant model parameters and describe the interplay between the different volcanic sub domains in particular we analyzed the evolution of a sustained explosive eruption in order to identify the conditions for buoyant super buoyant and collapsing columns input data were based on field reconstructions of quaternary explosive eruptions in the vulsini volcanic district roman province central italy model results show that 1 the column regime although affected by complex interactions among several factors mostly depends on the conduit radius the volatile content i e supersaturation concentration at the top of the chamber and length of the conduit in decreasing level of importance 2 the amount of mass erupted is independent of the conduit radius and depends mostly on volatile supersaturation the radius of the magma chamber the length of the conduit and the overpressure at the conduit inlet 3 the mass flow rate column height and duration of the eruption are largely controlled by the conduit radius 4 the flow pressure and density at the conduit exit are mostly controlled by the conduit inlet overpressure at the onset of the eruption and by the length of the conduit at the end of the eruption 5 the exit velocity from the conduit is mostly controlled by the volatile content the length of the conduit and the inlet overpressure in this model framework and with specific reference to selected plinian events of the vulsini volcanic district simulation results show that column collapse is not achieved for reasonable eruption durations order of hours and conduit widths tens of meters this is consistent with field reconstructions suggesting that column collapse did not likely occur and that pyroclastic flows were therefore generated by independent mechanisms from ring fissures and or multiple vents concomitant to caldera collapse

magma ascent rates from amphibole breakdown an experimental study applied to the 1980 1986 mount st helens eruptions recent 1980 1986 mount st helens dacites contain the phenocryst assemblage plagioclase amphibole low ca pyroxene magnetite ilmenite and rare high ca pyroxene which indicates that they all originated from an 8 km deep reservoir at 900 20 c with xh2o 0 67 in fluid according to experimental data iron titanium oxide phenocryst compositions indicate that all post may 18 dacitic magmas erupted at 900 20 c except for the final lava extrusion in october 1986 the magma reservoir may have cooled to 866 c by october 1986 amphiboles in the post may 18 1980 magma contain one or more amphibole populations characterized by reaction rims of different thicknesses the development of the amphibole reaction rims in these rocks is a response to water loss from the coexisting melt during an approximately adiabatic ascent from a deep reservoir constant p and t and isothermal decompression experiments show that during a 900 c constant rate decompression from 8 km to the surface no reaction rim develops on amphibole in 4 days a 10 m rim develops in 10 days and a 35 m rim develops in 20 days these experimental data and histograms of rim widths in 1980 1986 mount st helens dacites show that post may 18 eruptions are composed in large part of magma represented by a population of thin rimmed amphiboles magma which ascended from the deep 8 km reservoir in 6 to 10 days the remainder of each sample consists of magma containing amphiboles with reaction rims ranging from 14 to 60 m magma which apparently spent from 8 to 25 days along the conduit margins before being mixed thoroughly millimeter scale into the erupting magma the mixing in a viscous slowly ascending dacite may be enhanced by its flow through partially crystallized magma emplaced earlier and by the evolution and loss of a large vesicle population the experimental calibration of amphibole reaction rim width versus decompression time yields average ascent velocities for post may 18 dacites of about 15 30 m h for magma represented by the thick rimmed amphiboles and from 35 to 50 m hr for magma represented by the thin rimmed crystals an ascent rate of 66 m h is indicated for the may 18 1980 eruption which contains amphiboles with no reaction rims the volume of endogenous dome growth which preceded extrusion of magma newly derived from the deep source region suggests that the effective conduit volume beneath mount st helens in 1981 1982 was equivalent to a cylinder 8 km long and 8 9 m in radius

magma emplacement and remobilization timescales beneath montserrat insights from sr and ba zonation in plagioclase phenocrysts received november 22 2001 accepted december 12 2002since 1995 the soufri ere hills volcano on montserrat lesserantilles island arc has erupted crystal rich andesite magmathat is geochemically very similar to the volcanic products of atleast the last 174 3kyr 1s nomarski images of plagio clase phenocrysts from six andesites erupted between 151 4ka 1s and

paleo surfaces of glacio eustatically forced aggradational successions in the coastal area of rome assessing interplay between tectonics and sea level during the last ten interglacials abstract recently acquired geochronological and stratigraphic data provide new information on the sedimentary successions deposited by the paleo tiber river in the coastal and near coastal area of rome in consequence of the glacio eustatic changes allowing to better define their inner geometry and palaeogeographic spatial distribution in the present work we use this revised sedimentary dataset to provide a geochronologically constrained and tectonically adjusted record of paleo sea level indicators aimed at this scope we review literature data acquired in the last 35 years and using the new geochronological constraints we pinpoint the coastal to fluvial terraces of mis 5 and mis 7 mapping their relic surfaces in an area of 30 km along the coast north and south of the tiber river mouth and 20 km inland of the fluvial valleys of tiber and aniene rivers the geometry of these paleo surfaces provides constraints on the relative elevation of the sea level during the last interglacials and on the uplift rates in this region during the last 200 ka in particular we recognize the previously undetected terraces of mis 5 3 and mis 5 1 interstadials and we assess their spatial relationship with respect to mis 5 5 providing important information on sea level oscillations during this time span comparison with sea level indicators provided by previous aggradational successions deposited during past interglacials spanning mis 9 through mis 21 in the coastal area of rome also allows us to reconstruct the tectonic history and investigate its relationships with the middle pleistocene volcanic activity of the roman comagmatic region along the tyrrhenian sea margin of italy in the last 900 ka

rheology of crystal bearing silicate melts an experimental study at high viscosities the viscosity of partially crystallized mg3al2si3o12 melts has been measured under uniaxial compression in the interval 1010 1013 poise as a function of the volume fraction of crystals these inclusions are well rounded spherulites of aluminous enstatite having the same composition as the melt and whose growth rate is negligible at the temperature of the measurements the viscosity increases by less than 1 order of magnitude for crystal fractions of 40 vol and remains newtonian up to the maximum stress exerted namely 1 kbar the einstein roscoe equation 0 1 m n provides very good fits to the measurements only if either the m or n parameter is allowed to depend on temperature for modeling of magmatic processes however the widely recommended constant values m 0 6 and n 2 5 should be adequate the rheology changes abruptly when the clustered spherulites begin to oppose shear deformation at a crystal fraction of about 40 vol the viscosity becomes non newtonian with yield strengths of a few tens of bars at temperatures at which the viscosity of the melt is higher than 1010 poise as long as the crystal fraction remains lower than 70 vol the deformation proceeds in an irregular manner with a nonuniform distribution of crystals and melt the deformation becomes again regular at low stresses with lower melt fractions but samples undergo extensive fracturation along the direction of uniaxial stress similar rheology changes have been observed during the isothermal crystallization of li2si2o5 melts which produces small ellipsoidal inclusions these results suggest that the influence of solid suspensions on the rheology of magmas is primarily determined by the crystal fraction even though additional measurements would be useful to determine the possible influence of other factors such as the size distribution or the shape of the inclusions

lava flow shapes and dimensions as reflections of magma system conditions abstract the physical conditions producing variation in the shapes of lava extrusions from thin flows to domes to spines are investigated with focus on the influence of the lava thickness the accumulation of lava above the vent acts to increase the vent pressure and reduce the eruption rate in turn the eruption rate determines how the volume and thickness of erupted lava change with time the spreading of lava and the flow of magma from a deep reservoir through a conduit system are therefore coupled a fluid dynamical model is developed to evaluate the influence of magma chamber and conduit dimensions chamber overpressure magma viscosity and dome bulk viscosity on the eruption behaviour and dimensions of the lava flow the model assumes laminar flow of newtonian constant density magma from an overpressured reservoir with elastic walls up a vertical cylindrical conduit and onto a planar horizontal surface on which grows a radially symmetrical lava flow of constant bulk viscosity greater than the magma viscosity two dimensionless numbers characterize the resulting behaviour the ratio of a scale erupted lava volume to the total volume available for eruption and the ratio of the pressure due to a scale thickness of lava to the magma chamber overpressure the dimensionless numbers are used to map the flow behaviours and reveal two extreme extrusion regimes separated by a narrow transition zone one extreme corresponds to thin and voluminous flows and occurs for large deep strongly overpressured magma reservoirs narrow conduits and low viscosity contrasts between the magma and lava the other extreme corresponds to small volume domes and spines and is produced by shallow weakly overpressured chambers wide conduits and high viscosity contrasts near the transitional domain small changes of parameters are sufficient to cause major changes of eruption regime the model provides explanations for the variation in gross morphology of lava extrusions transitions between flow dome and spine eruptions and for long lived episodic extrusion of lava model predictions are consistent with features of the eruptions of montagne pelee 1902 1903 mount st helens 1980 1986 and montserrat 1995 1997 period the model is used to estimate the magnitude of overpressure driving eruptions and suggests that magma buoyancy is important in driving many terrestrial lava dome eruptions the model further suggests that thick extrusions on venus were driven primarily by buoyancy sourced at great depth

terrestrial laser scanning observations of geomorphic changes and varying lava lake levels at erebus volcano antarctica abstract a terrestrial laser scanning tls instrument was used to image the topography of the main crater at erebus volcano each december in 2008 2009 and 2010 our high spatial resolution tls scans provide unique insights into annual and decadal scale geomorphic evolution of the summit area when integrated with comparable data collected by an airborne instrument in 2001 we observe both a pattern of subsidence within the inner crater of the volcano and an 3 m per year drop in the lava lake level over the same time period that are suggestive of decreasing overpressure in an underlying magma reservoir we also scanned the active phonolite lava lake hosted within the inner crater and recorded rapid cyclic fluctuations in the level of the lake these were sporadically interrupted by minor explosions by bursting gas bubbles at the lake surface the tls data permit calculation of lake level rise and fall speeds and associated rates of volumetric change within the lake these new observations when considered with prior determinations of rates of lake surface motion and gas output are indicative of unsteady magma flow in the conduit and its associated variability in gas volume fraction

evolution of volcanic eruption columns 1 the classical steady state model for plinian eruption columns is extended to allow the source conditions at the volcanic vent to change in time it is shown that when the source conditions change rapidly over time scales typically less than approximately 3 4 min this new time dependent volcano model becomes appropriate differences between changes in source velocity and source temperature are also considered qualitatively similar structures are formed when either the source velocity or source temperature is reduced a transient region is formed characterized by a narrowing of the top hat eruption column radius a first attempt to a model a plinian eruption column from its dynamic initiation in a volcanic eruption is made it is shown that the velocity at the front of the eruption column is significantly slower than the velocity at the same height in an established eruption column

physics based models of ground deformation and extrusion rate at effusively erupting volcanoes 1 we present a model of effusive silicic volcanic eruptions which relates magma chamber and conduit physics to time dependent data sets including ground deformation and extrusion rate the model involves a deflating chamber which supplies newtonian magma through a cylindrical conduit solidification is approximated as occurring at fixed depth producing a solid plug that slips along its margins with rate dependent friction changes in tractions acting on the chamber and conduit walls are used to compute surface deformations given appropriate material properties and initial conditions the model predicts the full evolution of an eruption allowing us to examine the dependence of observables on initial chamber volume overpressure and volatile content employing multiple data sets in combination with a physics based model allows for better constraints on these parameters than is possible using kinematic idealizations modeling posteruptive deformation provides an improved constraint on the rate of influx into the magma chamber from deeper sources we compare numerical results to analytical approximations and to data from the 2004 2008 eruption of mount st helens for nominal parameters the balance between magma chamber pressure and frictional resistance of the solid plug controls the evolution of the eruption with little contribution from the fluid magma below the idealized crystallization depth while rate dependent plug friction influences the time dependent evolution of the eruption it has no control on the final chamber pressure or extruded volume

a detailed view into the eruption clouds of santiaguito volcano guatemala using doppler radar 1 using doppler radar technology we are able to show that eruptions at santiaguito volcano guatemala are comprised of multiple explosive degassing pulses occurring at a frequency of 0 2 to 0 3 hz the doppler radar system was installed about 2 7 km away from the active dome on the top of santa maria volcano during four days of continuous measurement 157 eruptive events were recorded the doppler radar data reveals a vertical uplift of the dome surface of about 50 cm immediately prior to a first degassing pulse particle velocities range from 10 to 15 m s in the line of sight of the radar in 80 of the observed eruptions a second degassing pulse emanates from the dome with significantly higher particle velocities 20 25 m s again line of sight and increased echo power which implies an increase in mass flux we carry out numerical experiments of ballistic particle transport and calculate corresponding synthetic radar signals these calculations show that the observations are consistent with a pulsed release of material from the dome of santiaguito volcano

seismic petrologic and geodetic analyses of the 1999 dome forming eruption of guagua pichincha volcano ecuador abstract guagua pichincha located 14 km west of quito ecuador is a stratovolcano bisected by a horseshoe shaped caldera in 1999 after some months of phreatic activity guagua pichincha entered into an eruptive period characterized by the extrusion of several dacitic domes vulcanian eruptions and pyroclastic flows we estimated the three dimensional 3 d p wave velocity structure beneath guagua pichincha using a tomographic inversion method based on finite difference calculations of first arrival times hypocenters of volcano tectonic vt earthquakes and long period lp events were relocated using the 3 d p wave velocity model a low velocity anomaly exists beneath the caldera and may represent an active volcanic conduit petrologic analysis of eruptive products indicates a magma storage region beneath the caldera having a vertical extent of 7 8 km with the upper boundary at about sea level this zone coincides with the source region of deeper vt earthquakes indicating that a primary magma body exists in this region lp swarms occurred in a cyclic pattern synchronous with ground deformation during magma extrusions the correlation between seismicity and ground deformation suggests that both respond to pressure changes caused by the cyclic eruptive behavior of lava domes

periodic behavior in lava dome eruptions lava dome eruptions commonly display fairly regular alternations between periods of high activity and periods of low or no activity the time scale for these alternations is typically months to several years here we develop a generic model of magma discharge through a conduit from an open system magma chamber with continuous replenishment the model takes account of the principal controls on flow namely the replenishment rate magma chamber size elastic deformation of the chamber walls conduit resistance and variations of magma viscosity which are controlled by degassing during ascent and kinetics of crystallization the analysis indicates a rich diversity of behavior with periodic patterns similar to those observed magma chamber size can be estimated from the period with longer periods implying larger chambers many features observed in volcanic eruptions such as alternations between periodic behaviors and continuous discharge sharp changes in discharge rate and transitions from effusive to catastrophic explosive eruption can be understood in terms of the non linear dynamics of conduit flows from open system magma chambers the dynamics of lava dome growth at mount st helens 1980 1987 and santiaguito 1922 2000 was analyzed with the help of the model the best fit models give magma chamber volumes of 0 6 km3 for mount st helens and 65 km3 for santiaguito the larger magma chamber volume is the major factor in explaining why santiaguito is a long lived eruption with a longer periodicity of pulsations in comparison with mount st helens

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

permeability evolution during non isothermal compaction in volcanic conduits and tuffisite veins implications for pressure monitoring of volcanic edifices abstract explosive volcanic eruptions are destructive geological phenomena that pose hazards of significant socioeconomic impact and potential loss of life effective risk mitigation and decision making prior to and during volcanic crises require real time monitoring of gas overpressure the single most important driving force for explosive eruptions development and release of gas overpressure are regulated by gas loss through permeable pathways that are inherently transient here we use geometry dependent conductive cooling models in concert with the most up to date welding and permeability models to assess the potential for freezing in permeability within 1 conduit filling pyroclastic deposits and 2 tuffisite veins within the edifice we find that both geometry and dimension of each deposit dictate its thermal evolution and with that its transient outgassing capacity rapid cooling of thin sheet like tuffisite veins preserves high porosities and permeabilities in contrast wide cylindrical conduit filling deposits cool slowly and permeability is annihilated over a period of minutes to hours this highlights that conduit filling deposits lose their outgassing capacity through welding while tuffisite veins previously thought to rapidly seal can form long lived outgassing features we use the model results to calculate the time dependent gas flow partitioning between both degassing lithologies based on the reconstructed outgassing pattern we outline the potential to use the gas flow balance between the central conduit and distal fumaroles fed by tuffisite veins as a simple tool to monitor gas overpressure within a volcanic edifice

on magma chamber evolution during slow effusive eruptions 1 we explore some of the controls on the evolution of a slow effusive eruption imposed by processes in a shallow magma reservoir we envisage that the emplacement of basaltic magma into a shallow evolved crustal reservoir generates sufficient overpressure to trigger the slow effusive eruption of the overlying layer of evolved magma the subsequent evolution of the system then depends on a number of factors including 1 the volatile contents of the two magmas 2 the rate of any continuing influx of basalt 3 the cooling heating rates of the two layers of magma and 4 the eruption rate of the silicic magma where we assume that the crystals and bubbles remain in the layer in which they formed any exsolved volatiles in the magma increase the compressibility of the magma in a waning system this tends to increase the volume of material which needs to be erupted to relieve a given overpressure by an amount of order 10 100 and hence increases the duration of the eruption typical calculations suggest that eruptions from magma chambers of size 1 10 km3 may persist for times of order 1 10 years if the main body of silicic magma is saturated in volatiles in addition cooling of the basalt leads to formation of dense crystals which lowers the pressure however if the magma becomes saturated exsolution of volatile gases occurs tending to increase the pressure again in a waning system this tends to extend the eruption duration and increase the mass erupted from the chamber for chamber volumes of 1 10 km3 cooling rates of 10 6 k s can increase the eruption volume by a factor of order 10 rapid cooling may also lead to an initial increase in the eruption rate while the chamber pressure is controlled by the rate of production of new bubbles if there is an influx of basalt to the chamber which is maintained during the eruption then the evolution of the eruption is primarily dependent on this input rate although the cooling of the basalt may increase the eruption rate to values in excess of this input rate especially at an early stage in the eruption the complex and nonlinear evolution of the eruption rate predicted by our simple model illustrates the sensitivity of the eruption rate to the magma volatile content and magma cooling rates such understanding is key in developing quantitative models for hazard assessments of slow effusive eruptions

changes in sediment yield of the yellow river basin of china during the holocene this research reconstructs the changes in sediment yield of the yellow river based mainly on a large number of 14 c dates collected from the literature the total volume of sediment yield of the basin during the holocene is estimated to be 8 0 x 10 12 tons the annual sediment yield had an increasing trend over the holocene from 0 68 0 72 0 79 to 1 0 1 x 10 9 tons over each 2500 year period from the early holocene to the present the changes in sediment yield are ascribed to both natural and anthropogenic reasons in which the latter became important in the late holocene the mean rate of increase in natural sediment yield throughout the holocene is estimated to be about 0 027 x 10 6 ton year and the natural annual sediment yield is projected to be 0 95 x 10 9 tons at the present the increasing trend of natural sediment yield is reasoned to be the consequence of evolution of landforms enhanced by tectonic movement and climatic change in the loess plateau the principal sediment source of the river towards a condition favorable to soil erosion comparing the estimated annual natural sediment yield with the current annual sediment load of 1 6 x 10 9 tons of the river it is clear that human activities have augmented natural soil erosion by about 41 in the yellow river basin furthermore an estimate of the overall pattern of anthropogenic sediment yield shows an accelerated increasing trend which is approximately correspondent with that of population in the loess plateau area c 2002 elsevier science b v all rights reserved

controls on conduit magma flow dynamics during lava dome building eruptions 1 lava dome eruptions commonly display fairly regular alternations between periods of high and low or no activity with timescales typically of weeks to years and sudden transitions between effusive and explosive activity we develop a transient model of the magma flow in a volcanic conduit from an open system magma chamber with continuous replenishment the model incorporates gas exsolution bubble growth gas escape through the magma and decompression induced crystallization and considers variations in magma temperature water content conduit diameter phenocryst size chamber volume and magma rheology calculations show the presence of periodic variations in discharge rate due to the transition from a stable regime when discharge rate is low and crystals grow efficiently leading to high magma viscosity to another stable state when discharge rate is high and crystallization is negligible the difference in discharge rates between these regimes can be several orders of magnitude periods are similar to the observed timescales and mainly depend on the chamber volume the system shows strongly nonlinear responses to the variation of governing parameters if magma has a bingham rheology pauses in discharge rate occur between peaks of discharge and the peaks are much higher than for the case of newtonian rheology large changes in discharge rate and eruptive behavior can occur as the consequence of small changes in magma temperature water content phenocryst size distribution or conduit diameter the system can fluctuate between low and high discharge rates with transitions to explosive activity

understanding the timing of eruption end using a machine learning approach to classification of seismic time series abstract the timing and processes that govern the end of volcanic eruptions are not yet fully understood and there currently exists no systematic definition for the end of a volcanic eruption currently end of eruption is established either by generic criteria typically 90 days after the end of visual signals of eruption or criteria specific to a given volcano we explore the application of supervised machine learning classification methods support vector machine logistic regression random forest and gaussian process classifiers and define a decisiveness index d to evaluate the consistency of the classifications obtained by these models we apply these methods to seismic time series from two volcanoes chosen because they display contrasting styles of eruption telica nicaragua and nevado del ruiz colombia we find that for both volcanic systems the end date we obtain by classification of seismic data is 2 4 months later than end dates defined by the last occurrence of visual eruption such as ash emission this finding is in agreement with previous general definitions of eruption end and is consistent across models our classifications have a higher correspondence of eruptive activity with visual activity than with database records of eruption start and end we analyze the relative importance of the different features of seismic activity used in our models e g peak event amplitude daily event counts and find little consistency between the two volcanic systems in terms of the most important features which determine whether activity is eruptive or non eruptive these initial results look promising and our approach may offer a robust tool to help determine when an eruption has ended in the absence of visual confirmation

an experimental study of the surface thermal signature of hot subaerial isoviscous gravity currents implications for thermal monitoring of lava flows and domes received 22 july 2011 revised 23 november 2011 accepted 23 november 2011 published 7 february 2012 1 management of eruptions requires a knowledge of lava effusion rates for which a safe thermal proxy is often used however this thermal proxy does not take into account the flow dynamics and is basically time independent in order to establish a more robust framework that can link eruption rates and surface thermal signals of lavas measured remotely we investigate the spreading of a hot isoviscous axisymmetric subaerial gravity current injected at constant rate from a point source onto a horizontal substrate we performed laboratory experiments and found that the surface thermal structure became steady after an initial transient we develop a theoretical model for a spreading fluid cooled by radiation and convection at its surface that also predicts a steady thermal regime we show that despite the model s simplicity relative to lava flows it yields the correct order of magnitude for the effusion rate required to produce the radiant flux measured on natural lava flows for typical thermal lava properties and an effusion rate between 0 1 and 10 m 3 s 1 the model predicts a steady radiated heat flux ranging from 10 8 to 10 10 w the assessed effusion rate varies quasi linearly with the steady heat flux with much weaker dependence on the flow viscosity this relationship is valid only after a transient time which scales as the diffusive time ranging from a few days for small basaltic flows to several years for lava domes the thermal proxy appears thus less reliable to follow sharp variations of the effusion rate during an eruption

textural and mineral chemistry constraints on evolution of merapi volcano indonesia abstract we analyze and compare the textures of merapi lavas basalts and basaltic andesites ranging in age from proto merapi through modern activity with the goal of gaining insights on the temporal evolution of merapi s magmatic system analysis of textural parameters such as phenocryst and microphenocryst crystallinity coupled with crystal size distribution theory provides information about the storage and transport of magmas we combine textural analyses with geochemical investigations for a comprehensive comparison of erupted lavas over time the chemical analyses identify crystal growth processes in magma chambers and underline differences between sample groups our work suggests the occurrence of two distinct histories presumably associated with at least two generally distinct types of rheological behaviors and storage transport systems these behaviors are associated with different plagioclase growth patterns with both groups influenced by late stage shallow decompression degassing induced microlite crystallization both groups contain amphibole crystals that indicate an early period of mid crustal to deep crustal storage of water rich magmas dome lavas from the 20th century eruptive activity indicate quasi steady state nucleation and growth evolution interspersed with episodes of reheating and textural coarsening suggesting residence in magma storage at multiple depths both 10 km and

on the variations of flow rate in non explosive lava eruptions abstract a physical model is developed to determine factors which influence the dynamics of non explosive lava eruptions in the model magma rises in a laminar regime from an overpressured chamber surrounded by elastic rock and erupts at the surface where the accumulation of lava may alter the vent pressure in a flow rate versus volume diagram an eruption follows a path which is sensitive to relative changes in flow variables such as viscosity conduit dimensions and thickness of lava over the vent the path does not depend on the unknown elastic properties of the country rock or the chamber dimensions with appropriate volcanological data an observed flow rate versus volume path can be interpreted the approach is applied to three well documented eruptions in each case the eruption rate was partially influenced by decreasing chamber pressure the 1988 1990 eruption of lonquimay chile exhibits an early phase of conduit shrinkage which lasted about 100 days probably due to magma solidification against country rock the 1979 eruption of la soufriere de saint vincent west indies was initially affected by lava dome growth and later passed through a phase possibly caused by constriction of the conduit the 1943 1952 eruption of paricutin mexico was affected by changes of lava level in the cinder cone and magma properties in these three eruptions the pre eruptive chamber overpressures were similar 10 20 mpa even though the erupted volumes differed by as much as two orders of magnitude

a new model of volatile bubble growth in a magmatic system isobaric case 1 the nucleation growth and ultimately coalescence of volatile bubbles in a silicate melt magma chamber play a crucial role in the processes leading to volcanic eruptions a new diffusion limited nonlinear growth and nucleation model of volatile bubbles in such a system is proposed here in contrast to previously existing models the present one treats the competitive effects of the other randomly located bubbles on the growth dynamics in presence of a hydrodynamic coupling with the melt advection field through its viscous resistance i consider here cases where the fluid pressure is kept constant numerical results pertaining to a basaltic and a rhyolitic melt suggest that for small volatile supersaturations and for small times bubble growth occurs essentially as in the single bubble problem however for longer times the influence of the other bubbles is important i find that bubble growth rate decreases exponentially with time and propose an approximate expression for the decay rate finally for larger volatile supersaturations the bubble growth is subjected to transitions to and from an inflationary regime whereby the bubble radius increases very rapidly during a small time interval

degassing processes during lava dome growth insights from santiaguito lava dome guatemala abstract eruptions of intermediate magma may be explosive or effusive the development of open system degassing has been proposed as a pre requisite for effusion of intermediate magma however processes leading to open system degassing are poorly understood to better understand degassing processes during lava dome extrusion we report high temporal resolution so2 emission rate measurements collected with an ultra violet imaging camera at santiaguito guatemala santiaguito is an ideal case study as the dome lava is compositionally very similar to products of the 1902 plinian eruption of the parental santa maria volcano we find that degassing is weak 0 4 1 kg s 1 but continuous and explosions are associated with small increases in emission rates up to 2 3 kg s 1 continuous repose degassing occurs through a shallow cap rock which likely represents a proto crust on the block lava flow which is extruded from the same vent the continual permeability of the upper conduit argues against a mechanism of explosion triggering in which gas pressure builds beneath a viscous cap rock or plug rather we consider degassing data better consistent with a model of shear fracturing at the conduit margins using field constraints we model the viscosity of santiaguito magma as a function of depth and show that conditions for shear fracturing are met from 150 600 m to the surface this is in line with independent estimates of explosion initiation depth we show that repose timescales are orders of magnitude longer than the timescale for shear fracture and suggest that explosions are triggered when a continuous network of smaller scale fractures develops at which point decompression occurs and an explosion is triggered fracture healing occurs by viscous relaxation however near to the surface where viscosity is highest an unconsolidated gouge layer may develop our model implies that the observed explosions are a by product of extrusion shear fracturing can drive open system degassing of crystal rich intermediate magma at shallow levels in the conduit as high magma viscosity is able to overcome the low strain rates associated with slow ascent of magma

volatile rich magma injection into the feeding system during the 2001 eruption of mt etna italy its role on explosive activity and change in rheology of lavas the explosive behavior and the rheology of lavas in basaltic volcanoes usually driven by differentiation can also be significantly affected by the kinetics of magma degassing in the upper portion of the feeding system the complex eruption of 2001 at mt etna italy was marked by two crucial phenomena that occurred at the laghetto vent on the southern flank of the volcano 1 intense explosive activity and 2 at the end of the eruption emission of a lava flow with higher viscosity than flows previously emitted from the same vent here we investigate the hypothesis that these events were driven by the injection of volatile rich magma into the feeding system the input and mixing of this magma into a reservoir containing more evolved magma had the twofold effect of increasing 1 the overall concentration of volatiles and 2 their exsolution with consequent efficient vesiculation and degassing this led to an explosive stage of the eruption which produced a 75 m high cinder cone efficient volatile loss and the consequent increase of the liquidus temperature brought about the nucleation of fe oxides and other anhydrous crystalline phases which significantly increased the magma viscosity in the upper part of the conduit leading to the emission of a high viscosity lava flow that ended the eruption the 2001 eruption has offered the opportunity to investigate the important role that input of volatile rich magma may exert in controlling not only the geochemical features of erupted lavas but also the eruption dynamics these results present a new idea for interpreting similar eruptions in other basaltic volcanoes and explaining eruptions with uncommonly high explosivity when only basic magmas are involved

ultra long period seismic signals and cyclic deflation coincident with eruptions at santiaguito volcano guatemala abstract broadband seismic observations made near the active vent at santiaguito provide constraints on changing pressures inside the edifice during january 2009 we recorded episodic ultra long period signals ulps 30 s that were coincident with eruptive activity centered on the active el caliente vent these signals lasted 2 5 min and corresponded to depressurization of a volume beneath the dome coincident shorter period seismic signals 0 5 hz appeared to be associated with shallow level pyroclastic emissions and dome surface motions these shorter period signals varied significantly from event to event unlike the ulp waveforms which were self similar as opposed to the short period signals which were recorded across the network the ulps were only recorded on the horizontal channels of 3 stations that were within 1 1 km of the vent this and other factors suggest that they were a result of long period rotational motion rather than horizontal translation ulp source locations derived from horizontal particle motions point to the northwestern part of el caliente 150 m from the vent axis the general locus of activity from 1967 until flank collapses in 1989 1990 we modeled the ulp signal as a mogi source and solved for three dimensional location and equivalent source strength through analysis of 78 events we identify a mean mogi source that is 200 m west of and 250 m beneath the centre of the vent with the peak volume changes accompanying eruptions ranging from 125 to 1825 m 3 these inferred volume losses coincide with the onset of gas venting and or explosive eruptions at the surface of caliente based upon these observations we develop a model to describe the pre eruptive eruptive and inter eruptive physical processes occurring at the surface and inside santiaguito

effects of gas escape and crystallization on the complexity of conduit flow dynamics during lava dome eruptions 1 we investigated the coupled effects of gas escape and crystallization on the dynamics of lava dome eruptions using a one dimensional conduit flow model the relationship between chamber pressure pch and mass flow rate q for steady conduit flow commonly has a regime of negative differential resistance i e dpch dq 0 5 feedback 1 is the main mechanism that forms negative differential resistance in this case the transition from lava dome to explosive eruption occurs when the magma supply rate exceeds a fixed critical value for low phenocryst content magma volume fraction 0 5 feedback 2 plays a key role so that the transition is controlled by the permeability of the surrounding rocks the critical magma supply rate remarkably decreases with decreasing permeability transition due to feedback 2 is associated with a change in the chemical composition of volcanic gas a drastic increase in magma porosity from nearly 0 to greater than 0 8 and overpressure at a shallower level which can be detected from geochemical and geophysical field observations

control of magma flow in dykes on cyclic lava dome extrusion 1 lava dome eruptions are commonly characterized by large fluctuations in discharge rate with cyclic behaviour on time scalesranging from hours to decades examples include bezymianny volcano russia merapi java santiaguito guatemala mt st helens usa mt unzen japan and soufriere hills volcano montserrat previous models have assumed simple cylindrical conduits for magma transport but extrusions are mainly fed by dykes with cylindrical geometries developing only at shallow levels the widths of dykes embedded in an elastic medium are influenced by local magma pressure affecting flow rates and system dynamics strongly we develop a model for magma flow in dykes which predicts intense pulsations of magma extrusion for the case of a constant source pressure the period time scale is determined by the elastic deformation of the dyke walls and the length to width ratio of the dyke the dyke acts like a volumetric capacitor storing magma as pressure increases and then releasing magma in a pulse of extrusion for the soufriere hills volcano cyclic extrusions with time scales of a few weeks are predicted for dykes 300 500 m long and 3 6 m wide matching observations the model explains the sharp onset of tilt pulsations and seismic swarms citation costa a o melnik r s j sparks and b voight 2007 control of magma flow in dykes on cyclic lava dome extrusion geophys res lett 34 l02303 doi 10 1029 2006gl027466

a 2 ma record of explosive volcanism in southwestern luzon implications for the timing of subducted slab steepening 1 new chemical and isotopic analyses of the tephra layers plus deep sea tephrostratigraphic record from two cores from either side of luzon island philippines have allowed the identification of two periods of explosive volcanic activity originating from the macolod corridor in the southwestern part of the luzon the first period extended from prior to 1355 ka to 1977 ka and the second period extended from 478 ka to the present separated by a period of relative quiescence the time intervals between large explosive eruption events in each period were 31 15 ka and 156 52 ka respectively combined with published chronological and geochemical data from onshore volcanic deposits the tephrostratigraphic record shows that the locus of large explosive eruptions has migrated southwestward from the northeastern section to the middle and southwestern sections of the macolod corridor the period of relative quiescence is characterized by monogenetic volcanism in the central section of the corridor the migration of active volcanism across the southwestern part of luzon during the quaternary is used to infer the evolution of the subducting south china sea crust the period of relative quiescence represents a period of adjustment of the subducted slab by steepening which began around 1355 ka or shortly thereafter and finished at around 478 ka

a stability analysis of a conduit flow model for lava dome eruptions abstract periodic variations in magma discharge rate and ground deformation have been commonly observed during lava dome eruptions we performed a stability analysis of a conduit flow model by barmin et al barmin a melnik o sparks r s j 2002 periodic behavior in lava dome eruptions earth and planetary science letters 199 1 2 173 184 in which the periodic variations in magma flow rate and chamber pressure are reproduced as a result of the temporal and spatial changes of the magma viscosity controlled by the kinetics of crystallization the model is reduced to a dynamical system where the time derivatives of the magma flow rate dq dt and the chamber pressure dp dt are functions of q and p evaluated at a shifted time t t here the time delay t represents the time for the viscosity of fluid particle to increase in a conduit the dynamical system with time delay is approximated by a simple two dimensional dynamical system of q and p where t is given as a parameter the results of our linear stability analyses for these dynamical systems indicate that the transition from steady to periodic flow depends on nonlinearities in the steady state relation between q and p the steady state relation shows a sigmoidal curve in q p phase plane its slope has negative values at intermediate flow rates the steady state solutions become unstable and hence p and q oscillate periodically when the negative slope of the steady state relation dp dq s exceeds a critical value that is dp dq s

sawtooth wave like pressure changes in a syrup eruption experiment implications for periodic and nonperiodic volcanic oscillations this study is based on the observation of sawtooth wave like pressure changes stw observed during repetitive gas emissions in a syrup eruption experiment similar waveforms are observed at many active volcanoes as geodetic signals by studying the physics of such experiments we often find new ideas and insights that are applicable to natural volcanic phenomena we consequently try identifying the features common to both our experimental system and natural volcanic systems we infer that the oscillatory mechanism in our experiment is similar to flow induced oscillation controlled by a coupling between elastic capacitance and variable flow resistance we developed an elementary pipe chamber system to quantitatively test this hypothesis we observed three distinct oscillatory patterns periodic stw non stw and nonperiodic stw a mathematical model is constructed to support the hypothesis and to enable comparison with existing models of volcanic systems models of flow induced volcanic oscillations are mathematically similar to the model derived from our experimental system our results indicate that flow pattern transitions are essential for oscillatory behavior during gas emission an important finding is that cycle periodicity and fluctuation are controlled by interactions between upward and downward flow within the pipe especially during the termination of gas emission and the transition to the next cycle similar interactions occur in natural volcanoes during the termination of an explosive eruption fall back or drain back of ejected materials may modulate the explosivity and periodicity of the next eruption cycle our experimental system may provide a useful tool for understanding the oscillatory behavior of natural volcanic systems this study may also give a proof that the original eruption experiment provides a useful tool for explaining the dynamics of oscillatory and eruptive behaviors of natural volcanic systems in educational e g open day demonstrations

the 2001 2004 dome forming eruption of shiveluch volcano kamchatka observation petrological investigation and numerical modelling there have been three episodes of lava dome growth at shiveluch volcano kamchatka since the plinian explosive eruption in 1964 the episodes in 1980 1981 1993 1995 and 2001 2004 have discharged at least 0 27km 3 of silicic andesite magma a time averaged mean extrusion rate of 0 2m 3 s is thus estimated for the last 40years here the 2001 2004 activity is described and compared with the earlier episodes the recent activity involved three pulses in extrusion rate and a transition to ongoing lava extrusion estimated magma temperatures are in the range 830 to 900 c with 850 c as the best estimate using the plagioclase amphibole phenocryst assemblage and fe ti oxides melt inclusions in amphibole and plagioclase have maximum water contents of 5 1wt implying a minimum pressure of 155mpa for water saturated conditions the magma chamber depth is estimated to be about 5 6km or more a result consistent with geophysical data the thicknesses of opx mt amph reaction rims on olivine xenocrysts are used to estimate the residence time of olivine crystals in the shallow chamber in the range 2 months to 4 years suggesting replenishment of deeper magma into the shallow chamber contemporaneous with eruption the absence of decompression driven breakdown rims around amphiboles indicates ascent times of less than 7days volcanological observations of the start of the 2001 2004 episode suggest approximately 16 days for the ascent time and a conduit equivalent to a cylinder of diameter approximately 53 71m application of a conduit flow model indicates that the magma chamber was replenished during the 2001 2004 eruption consistent with the results of olivine reaction rims and that the chamber has an estimated volume of order 7km 3

the october 1902 plinian eruption of santa maria volcano guatemala abstract the october 1902 eruption of santa maria volcano guatemala was one of the largest this century it was preceded by a great earthquake on april 19 centered at the volcano as well as numerous other major earthquakes the 18 20 hour long plinian eruption on october 25 produced a column at least 28 km high reaching well into the stratosphere the airfall pumice deposit covered more than 1 2 million km2 with a trace of ash and was only two meters thick at the vent white dacitic pumice dark gray scoriaceous basalt with physically and chemically mixed intermediate pumice and loose crystals of plagioclase hornblende hypersthene biotite and magnetite make up the juvenile components of the deposit lithic fragments are of volcanic plutonic and metamorphic origin the plinian deposit is a fine grained crystal rich single pumice fall unit and shows inverse grading mapping of the deposit gives a volume of 8 3 km3 within the one mm isopach crystal concentration studies show that the true volume erupted was at least 20 km3 equivalent to 8 5 km3 of dense dacite and that 90 of the ejecta was less than 2 mm in diameter the plinian volume eruption rate averaged 1 2 105 m3s 1 and the average gas muzzle velocity of the column exceeded 270 ms 1 a total of 8 3 1018 j of energy were released by the eruption a knowledge of both theoretically derived eruption parameters and contemporary information allows a detailed analysis of eruption mechanisms this eruption was the major stratospheric aerosol injection in the 1902 1903 period however mid to low latitude northern hemisphere temperature deviation data for the years following the eruption show no significant temperature decrease this may be explained by the sulfur poor nature of dacite magmas suggesting that volatile composition rather than mass of volatiles is the controlling parameter in climatic response to explosive eruptions