physical models of volcanic eruptions abstract our present understanding of the dynamics of volcanic eruptions is summarized a few important facts about volcanic eruptions are reviewed and outstanding problems are identified current research efforts are aimed at explaining why an eruption may alternate between and pass through different dynamical regimes the basic physics of eruptions are explained from a dynamical point of view with emphasis on the processes acting to fix the gas content of the erupted material the coupling between flow processes and pressure release leads to large changes of decompression rate during ascent in a volcanic conduit the decompression rate may reach very high values which suggests that the kinetics of degassing play an important role accurate values of the solubility of the major magmatic volatile species are required at pressures of

india madagascar paleo fit based on flexural isostasy of their rifted margins the present study contributes new constraints on and definitions of the reconstructed plate margins of india and madagascar based on flexural isostasy along the western continental margin of india wcmi and the eastern continental margin of madagascar ecmm we have estimated the nature of isostasy and crustal geometry along the two margins and have examined their possible conjugate structure here we utilize elastic thickness te and moho depth data as the primary basis for the correlation of these passive margins we employ the flexure inversion technique that operates in spatial domain in order to estimate the spatial variation of effective elastic thickness gravity inversion and flexure inversion techniques are used to estimate the configuration of the moho crust mantle interface that reveals regional correlations with the elastic thickness variations these results correlate well with the continental and oceanic segments of the indian and african plates the present study has found a linear zone of anomalously low te 1 5 km along the wcmi similar to 1680 km which correlates well with the low te patterns obtained all along the ecmm we suggest that the low te zones along the wcmi and ecmm represent paleo rift inception points of lithosphere thermally and mechanically weakened by the combined effects of the marion hotspot and lithospheric extension due to rifting we have produced an india madagascar paleo fit representing the initial phase of separation based on the te estimates of the rifted conjugate margins which is confirmed by a close fit correlation of moho geometry and bathymetry of the shelf margins the matching of tectonic lineaments lithologies and geochronological belts between india and madagascar provide an additional support for the present plate reconstruction c 2014 international association for gondwana research published by elsevier b v all rights reserved

magmatic and hydromagmatic conduit development during the 1975 tolbachik eruption kamchatka with implications for hazards assessment at yucca mountain nv abstract xenoliths in pyroclastic fall deposits from the 1975 tolbachik eruption constrain the timing and development of subsurface conduits associated with basaltic cinder cone eruptions the two largest tolbachik vents contain xenoliths derived from magmatic and hydromagmatic processes which can be correlated with observed styles of eruption activity although many basaltic eruptions progress from early hydromagmatic activity to late magmatic activity transient hydromagmatic events occurred relatively late in the 1975 eruption sequence magmatic fall deposits contain 0 01 0 3 vol xenoliths from 500 m depth into the dry out zone around the conduit disrupting and ejecting 10 5 10 6 m 3 of wall rock through hydromagmatic processes with conduits widening to 8 48 m hydromagmatic falls contain 60 75 vol of highly fragmented xenoliths with juvenile clasts displaying obvious magma water interaction features during the largest hydromagmatic event unusual breccia bombs formed containing a wide range of fresh and pyrometamorphic xenoliths suspended in a quenched basaltic matrix hydromagmatic activity during the 1975 tolbachik eruption occurred below likely fragmentation depths for a basalt containing 2 2 wt magmatic water this activity is more likely related to conduit wall collapse rather than variations in conduit flow pressure in contrast larger volume silicic eruptions may have transient hydromagmatic events in response to conduit flow dynamics above the magma fragmentation depth the 1975 tolbachik volcanoes are reasonably analogous to quaternary basaltic volcanoes in the yucca mountain region and can guide interpretations of their poorly preserved deposits the youngest basaltic volcanoes near yucca mountain have cone deposits characterized by elevated xenolith abundances and distinctive xenolith breccia bombs remarkably similar to 1975 tolbachik deposits extrapolation of 1975 tolbachik data suggests conduits for some yucca mountain basaltic volcanoes may have widened locally on the order of 50 m in response to late stage hydromagmatic events

morphometric analysis of magmatic enclaves a tool for understanding magma vesiculation and ascent abstract the extent of deformation of magmatic enclaves that occur in different portions of the khaggiar endogenous lava dome island of pantelleria italy has been quantified using two morphometric techniques thin plate splines and fractals deformation of enclaves decreases from the outer portions of the dome to the more internal portions defining two exponential trends the amount and distribution of vesicles have also been quantified using image analysis of digital images obtained by a scanning electron microscope the variation of deformation of enclaves correlates with the variation of their vesicle content suggesting that deformation and vesiculation are related we envisaged a continuous feedback system between vesiculation of enclaves and radial forces exerted by the surrounding host magma during the growth of the dome these relationships are used as dynamic markers to infer the eruptive style of the endogenous dome in particular it is suggested that the variation of vesicularity of enclaves is related to the pressure exerted by magma on the extrusion vent this resulted in enclaves being more vesicular and more deformed in the outer portions of the dome that emplaced first and at lower pressure and less vesicular and less deformed in the more internal portions that emplaced later and at higher pressure we interpret the occurrence of the two trends in the variation of deformation and porosity as related to two main eruptive pulses of dome growth

elastic stress transmission and transformation estt by confined liquid a new mechanics for fracture in elastic lithosphere of the earth abstract we report on a new mechanical principle which suggests that a confined liquid in the elastic lithosphere has the potential to transmit a maximum applied compressive stress this stress can be transmitted to the internal contacts between rock and liquid and would then be transformed into a normal compressive stress with tangential tensile stress components during this process both effective compressive normal stress and tensile tangential stresses arise along the liquid rock contact the minimum effective tensile tangential stress causes the surrounding rock to rupture liquid driven fracture initiates at the point along the rock liquid boundary where the maximum compressive stress is applied and propagates along a plane that is perpendicular to the minimum effective tensile tangential stress and also is perpendicular to the minimum principal stress liquid driven fractures and dikes propagate along the axes of cylindrical zones that are perpendicular to the minimum compressive principal stress in rocks in non tectonic regions the minimum depth for liquid driven fracture which is induced by a spherical confined liquid and an isolated magma chamber in the elastic lithosphere ranges from 2 to 6 km whereas dikes with hemi cylinder shaped ends propagate upwards closer to the surface under gravity transmission of pumping pressure i e the pressure differences on the underside of a dike that is connected with a chamber from the source magma chamber to intermediate and shallow chambers increases liquid pressure and also the effective tensile tangential stress and therefore leads to new fractures and dike formation and to upwards transport of magmas that have stagnated in the intermediate chamber tectonic stress alters local stress fields in the surrounding country rocks and therefore synchronously varies the local effective tensile tangential stress and the nature and geometry of the liquid driven fractures

triggering and dynamic evolution of the lusi mud volcano indonesia abstract mud volcanoes are geologically important manifestations of vertical fluid flow and mud eruption in sedimentary basins worldwide their formation is predominantly ascribed to release of overpressure from clay and organic rich sediments leading to impressive build up of mud mountains in submarine and subaerial settings here we report on a newly born mud volcano appearing close to an active magmatic complex in a backarc sedimentary basin in indonesia the location of the mud volcano close to magmatic volcanoes results in a high background temperature gradient that triggers mineralogical transformations and geochemical reactions at shallow depth the eruption of 100 c mud and gas that started the 29th of may 2006 flooded a large area within the sidoarjo village in northeast java thousands of people have so far been evacuated due to the mud flood hazards from the eruption since the initial eruption the flow rate escalated from 5000 to 120 000 m 3 d during the first eleven weeks then the erupted volume started to pulsate between almost zero and 120 000 m 3 d in the period august 14 to september 10 whereas it increased dramatically following swarms of earthquakes in september before reaching almost 180 000 m 3 d in december 2006 sampling and observations were completed during two fieldwork campaigns on the site the eruption of boiling water is accompanied by mud aqueous vapour co 2 and ch 4 based on geochemical and field results we propose a mechanism where the eruptions started following the 27th of may earthquake due to fracturing and accompanied depressurization of 100 c pore fluids from 1700 m depth this resulted in the formation of a quasi hydrothermal system with a geyser like surface expression and with an activity influenced by the regional seismicity

early permian to middle jurassic rifting and sedimentation in east africa and madagascar pre drift sediments of madagascar early permian middle jurassic have been studied palynologically these studies resulted in a more precise dating of individual stratigraphic units and the recognition of minor and major breaks in the succession palynostratigraphic and physical evidence of unconformities have been used to subdivide the pre drift sediments into depositional cycles and to infer rifting events a comparison with equivalent strata of mozambique tanzania kenya ethiopia and somalia shows a general correspondence and provides additional information for the construction of a generalized framework for the east african madagascan region which demonstrates the relationships between rifting and sedimentation and elucidates the prehistory of the break up of gondwana into a western and eastern fragment during the middle jurassic the predrift succession of east africa madagascar can be subdivided into two major sequences a karoo sequence cycles 1 5 asselian early smithian and a transitional sequence cycles 6 9 ladinian early bajocian the two sequences are separeted by a late scythian to anisian hiatus which indicates extensive uplift and erosion before a major rifting event initiated the resumption of sedimentation in the ladinian this middle triassic event marks the transition from the intracratonic rift stage to the pericratonic basin stage and correlates with a significant event in the pangaean history the transition from final coalescence to initial dispersal the onset of the southward drift of madagascar is believed to have occurred about 60 ma later near the aalenian bajocian boundary contemporaneous with or immediately after the deposition of syntectonic sediments of cycle 9

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

sample preparation effects on illite crystallinity measurement grain size gradation and particle orientation abstract specimen thickness is the main experimental factor controlling the results of illite crystallinity ic or crystallite size measurements on sedimentation slides different values obtained from thick and thin preparations are due to grain size gradation effects which may exclude larger and higher ordered grains from contributing to the diffraction orientation effects control the measured peak intensity the change from poor particle orientation in thick slides to high orientation in very thin slides is marked by an increase in specimen density diminishing non basal reflections and by a strong increase in peak intensity a plateau with constant peak breadths is observed if thin slides of well ordered platy illites are used a similar plateau can be recognized for thick preparations of specimens from less ordered materials but not from well ordered ones therefore it is suggested that ic is determined on very thin sedimentation slides with a thickness of 0 25 mg cm2 or less ultrasonic and h2o2 treatments enhance the degree of particle orientation by destruction of grain aggregates and organic compounds leading to smaller peak breadths and higher intensities

corrigendum lusi mud eruption triggered by geometric focusing of seismic waves nature geoscience 6 642 646 2013 published online 21 july 2013 corrected after print 28 august 2014 in our 2013 article1 we adopted a published velocity profile2 described as check shot data which we used as an input constraint for our numerical simulations we were subsequently alerted to artefacts in that velocity profile so below we present revised simulation results based on additional data

evolution and tectonic setting of the malani nagarparkar igneous suite a neoproterozoic silicic dominated large igneous province in nw india se pakistan abstract the neoproterozoic malani igneous suite mis in nw india along with analogous magmatic rocks from the adjoining nagarparkar region in se pakistan can be collectively classified as a silicic dominated large igneous province slip this magmatic event includes bimodal predominantly felsic volcanism granite emplacement and felsic and mafic dyke intrusions felsic rocks have typical a type affinity as indicated by high abundance of silica alkali high field strength and large ion lithophile element concentrations and low cao and mgo contents their nb negative anomalies and zr saturation parameters indicate significant crustal input and high temperature melting mafic volcanics and dykes show geochemical homogeneity and derivation from a depleted continental mantle source without any significant crustal contamination low u and th contents and no visible nb anomaly the region extending from the mount abu batholith in the east to jaswantpura in the west 2700 km2 representing a transition from the metamorphic sirohi terrane to the undeformed mis was evaluated through an integrated structural including satellite image analysis geochemical and geochronological study during the initial stage prior to 760 ma the granitic basement erinpura granites and overlying sirohi metasediments behaved in a brittle manner that led to development of linear fractures and nne trending rift structures and bimodal volcanic activity emplacement of voluminous granitic bodies in response to progressive extension of the crust is inferred during the more evolved second stage younger than 760 ma mirpur granite a representative of this younger granitic suite jalor type pink granite has yielded 753 9 ma zircon u pb crystallization age granitic plutons mark regions of crustal extension as seen in parallel alignment of plutonic bodies jaswantpura granitic belt and parallel mafic dyke swarms 340 transecting the granites structural analysis further identified an episode of crustal convergence which is documented in folding and faulting of the sindreth basin sequence and in tectonic overprint of early stage mafic rocks rifting and bimodal magmatic activity in mis is coeval with similar rock types in nagarparkar in se pakistan further traceable into the seychelles microplate and central madagascar considering the neoproterozoic paleogeography and our observations an extensional setting and an active continental margin position for mis is inferred

the concentration and isotopic composition of carbon in basaltic glasses from the juan de fuca ridge pacific ocean the abundance and 13c12c ratios of carbon were analyzed in basaltic glass from twenty locations along the juan de fuca ridge using a 3 step combustion extraction technique carbon released during the first two combustion steps at 400 500 c and 600 650 c is interpreted to be secondary and only the carbon recovered during a final combustion step at 1200 c is thought to be indigenous to the samples for carbon released at 1200 c glasses analyzed as 1 2 mm chips contained 23 146 ppm c with 13c values of 4 8 to 9 3 whereas samples crushed to 38 63 m or 63 90 m yielded 56 103 ppm c with 13c values of 6 1 to 9 2 the concentrations and isotopic compositions of the primary carbon dissolved in the glasses and present in the vesicles are similar to those previously reported for other ocean ridge basalts the juan de fuca basaltic magmas were not in equilibrium with respect to carbon when they erupted and quenched on the sea floor evidence of disequilibrium includes 1 1 a large range of carbon contents among glasses collected at similar depths 2 2 a highly variable calculated carbon isotopic fractionation between melt and vapor determined by comparing crushed and uncrushed splits of the same sample and 3 3 a lack of correlation between vesicle abundance carbon concentration and depth of eruption variations in carbon concentration and 13c ratios along the ridge do not correlate with major element chemistry the observed relationship between carbon concentrations and 13c values may be explained by late stage variable degrees of open system rayleigh like degassing

u pb geochronology and isotope geochemistry of the archean and proterozoic rocks of north central madagascar abstract new u pb zircon ages and sm nd and rb sr isotopic data are presented for orthogneisses from north central madagascar including ile sainte marie alaotra beforona maevatanana and ambatolampy ambatomarina a migmatite tonalite gneiss from ile sainte marie is dated precisely at documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 3187 pm 2 end document ma and has a sm nd model age tdm of 3204 ma thereby establishing a middle archean age for the oldest juvenile gneisses in northeast madagascar dated orthogneisses int

mayon volcano philippines some insights into stress balance abstract mayon volcano is part of the bicol volcanic chain a peninsula in the south east of luzon island mayon s eruptive history during this century is fairly periodic with eruptions nearly every 10 years during the last two eruptions indications for tidal triggering of activities were found from statistical analyses hints for such a correlation exist for a number of volcanoes the statistical analysis of the seismicity points to a tidal triggering at mayon volcano in order to verify these indications the pressure balance between internal and external forces was computed the computations show that an interrelation between volcanic activities and tides especially ocean loading is probable for this purpose a global ocean model is improved by a regional model and a model of the local areas in order to consider the tidal distribution and the complicated geometry of the coasts the method of farrell w e 1972 deformation of the earth by surface loads rev geophys space physics 10 761 797 is used to calculate the ocean tidal loading the pressure increase in the vent due to vesiculation was tentatively modelled assumed a temperature decrease of 2 c per year the resulting stress is compared to the stress produced by the tidal forces body tides and ocean tidal loading it turns out that during a period of several days the small tidal forces may affect the stress balance considerably if the volcano is already in a critical state using fe modelling we estimate by neglecting all external forces how fast pressure can build up in the vent and to which extent the different physical parameters influence the pressure increase the maximum pressure resulting from the crystallization of the melt is compared with the maximum pressure yielding when in addition tidal forces are acting

physicochemical models of effusive rhyolitic eruptions constrained with insar and dem data a case study of the 2011 2012 cordon caulle eruption abstract the 9 month long 2011 2012 eruption of cordon caulle southern andes chile is the best instrumentally recorded rhyolitic eruption to date and the first time that the effusion of a rhyolitic flow has been observed in detail we use interferometric synthetic aperture radar insar with time lapse digital elevation models dems and numerical models to study the dynamics of coupled magma reservoir deflation and lava effusion insar recorded 2 2 2 5 m of subsidence after the first three days of the eruption which can be modeled using a spheroidal magma reservoir at a depth of 5 km 20 km long and with a pressure drop of 20 30 mpa the source is elongated in the nw se direction and its large dimensions imply a large plumbing system active throughout the eruption and spanning neighboring volcanoes with a slight change in the geometry halfway through the effusive phase tandem x and pleiades dems record the extrusion of both the rhyolitic lava flow and the intrusion of a shallow laccolith around the eruptive vent after the third day of the eruption with a total volume of 1 45 km3 dre the laccolith was emplaced during the first month of the eruption during both the explosive and effusive stages of the eruption both the reservoir pressure drop and the extruded volume time series follow quasi exponential trends and can be explained by a model that couples the reservoir pressure decrease time and pressure dependent variations in the magma properties inside of the reservoir and conduit flow this model predicts both the temporal evolution and amplitude of both time series during the effusive phase and a magma compressibility of 10 10 pa 1 half the reported compressibility of the magma of the sub plinian explosive phase further we estimate that the reservoir contained 1 3 wt dissolved h2o at the onset of lava effusion with no exsolved co2 and h2o in the reservoir throughout the effusive phase this implies that the magma was significantly degassed after the explosive phase the remaining volatiles in the magma after the explosive stage might have caused magma fragmentation consistent with the hybrid explosive effusive style observed during the waning of the eruption

natural hazards triggered mud eruption the indonesian government ruled that the lusi mud eruption was triggered by drilling and held an oil company responsible instead a curved rock layer capping the mud reservoir may have amplified passing seismic waves and the trigger may have been natural

the generation of gas overpressure in volcanic eruptions abstract observations of natural eruption products show that different parts of a single magma batch may experience different degassing histories during ascent in a volcanic conduit in non explosive eruptions lava issuing from a volcanic vent may contain overpressured gas bubbles these important features of volcanic eruptions cannot be accounted for by existing flow models which rely on simplifying hypotheses for the relationship between pressures in the gas phase and in the bulk flow volcanic flows involve highly compressible material which undergoes large viscosity variations as degassing proceeds we show that these properties may lead to large gas overpressures in erupting lava the magnitude of this overpressure depends on the initial volatile content of magma and is largest for relatively volatile poor magmas due to the extreme viscosity variations at water contents less than 1 wt we develop a simple analytical model to illustrate the main features of compressible viscous flows 1 at any level gas pressure is larger near the conduit axis than at the walls 2 gas overpressure is an increasing function of mass discharge rate

energetics of gas driven limnic and volcanic eruptions abstract this paper lays the foundation for the rigorous treatment of the energetics of gas exsolution from a gas containing liquid which powers gas driven volcanic and limnic eruptions various exsolution processes reversible or irreversible slow or rapid are discussed and the maximum amount of kinetic energy derivable from a reversible gas exsolution process is obtained the concept of dynamic irreversibility is proposed for discussing the kinetic energy available from irreversible gas exsolution processes the changes of thermodynamic properties during gas exsolution processes are derived density pressure relations for gas liquid mixtures are presented including empirical relations for irreversible gas exsolution the energetics of gas driven eruptions through both fluid and rigid media including the role of buoyancy and the role of magma chamber expansion work are investigated for reversible processes the energetics can be used to discuss the dynamics of gas driven eruptions leading to maximum erupting velocities and maximum eruptible fractions for irreversible processes empirical relations and parameters must be employed the exit velocities of the lake nyos eruption and the 18 may 1980 eruption of mount st helens are modeled by incorporating possible irreversibility

structural relationships and srnd isotope systematics of polymetamorphic granitic gneisses and granitic rocks from central rajasthan india implications for the evolution of the aravalli craton this paper reviews the state of structural and geochronological knowledge of precambrian cratonic rocks in part of central rajasthan india and contributes new observations and isotopic data on the structural features and age of granitic rocks in the area the granitic rocks comprise plutons of two suites bgc and sendra suites which intrude ortho and paragneisses the archean banded gneiss complex bgc and its inliers as well as the proterozoic delhi supergroup nearly all the plutons show a foliation and a lineation which are mostly the result of solid state deformation although a magmatic component of strain is apparent in some of them the intensity of these structural fabrics varies from weak to extremely strong samples of granitic rocks from the bgc suite yield ages from sm nd isotopic data which scatter around a 2 83 ga reference isochron nd t of 4 1 with depleted mantle model ages ranging from 2 6 to 3 0 ga scatter of the data suggests that the bgc is a composite group of gneisses and confirms the antiquity of the bgc within this part of the aravalli delhi orogenic belt rb sr isotopic data of the bgc suite lie on a 1 7 ga reference isochron indicating a thermal event at that time data from plutons of the sendra suite on the other hand show some scatter but define a model ii isochron with slope equivalent to an age of 0 966 250 ga initial 87sr86sr of 0 70390 0 01889 mswd 311 the scatter of data could reflect open system behavior during a subsequent thermal event malani volcanics although independent evidence for such is lacking in the study area ages calculated from our rb sr data are within the error of published results from previous workers structural observations on granitic rocks within the bgc inlier at ajmer suggest that the inlier could represent a remobilized diapiric ridge emplaced into the delhi supergroup during the 1 7 ga thermotectonic event contemporaneously with formation of d1 structures in the wall rock although the radiometric age of the latter structures is not well constrained microtexture mineralogy and field relations of granitic rocks of the sendra suite point to those plutons being emplaced into the delhi supergroup during the 0 966 ga thermotectonic event late syntectonic relative to d2 indicating that d2 is 0 96 1 0 ga d3 represents retrograde deformation synchronous with cooling of the regional thermal framework and local pluton cooling probably between 0 96 and 0 90 ga further geochronological geochemical and structural work on the plutons and wall rock of both suites is necessary to establish a rigorous thermotectonic chronology by which to accurately model the crustal evolution of this part of central rajasthan

modeling study of growth and potential geohazard for lusi mud volcano east java indonesia abstract the mud volcano known as lusi first erupted in may 2006 in east java indonesia the eruption has continued for over two years and potentially will continue for many years to come impacting an ever larger area an obvious and significant question is how extensive the impacted area will become in the coming years the answer is important for planning scenarios for the relocation of people and infrastructure and for managing the environment and economy to make such a prediction an understanding of the geological processes controlling the mud volcanic evolution is needed a three dimensional simulation model was built to predict the area affected by the mudflow over a ten year period with a special focus on the period from december 2007 until june 2010 the primary model inputs are the mud debit rate the rate of subsidence and the topography the model prediction was validated at the december 2007 time step by comparing the results with satellite images from the same period the simulation was found to provide a good approximation for the mud overflow and growth the results indicate that the mudflow tends to spread to the west and particularly to the east and north from the currently inundated area the model predicts that in june 2010 the peak of the mud volcano will have risen 26 m above the original ground level and the maximum subsidence will have been 63 m below the original ground level the dynamic subsurface condition in the area creates geohazard risks and these are also discussed in this paper

application of wave theoretical seismoacoustic models to the interpretation of explosion and eruption tremor signals radiated by pavlof volcano alaska tremor and explosion signals recorded on september 29 during the fall 1996 pavlof eruption are interpreted using video images field observations and seismic data waveform analysis of tremor and explosions provided estimates of the melt s volcano acoustic parameters and the magma conduit dimensions initial mass fractions of 0 25 water and 0 025 carbon dioxide in the melt can explain the resonance characteristics of the tremor and explosion pulses inferred from seismic data the magma conduit is modeled as a three section rectangular crack we infer that the tremor radiating region consists of the lowermost two sections both with cross sectional areas of 10 m2 the deeper section is 43 m long with magma sound speed of 230 m s density of 2600 kg m3 and viscosity of 1 0 106 pa s the section above it defined by the water nucleation depth is 64 m long with magma sound speed of 91 m s density of 2000 kg m3 and viscosity of 1 4 l06 pa s an average magma flow velocity of 1 2 m s with superposed random oscillations acts as the tremor source explosions are postulated to occur in the uppermost part of the magma conduit after water comes out of solution the explosion source region consists of a 15 m long section with cross sectional area of 20 m2 sound speed of 51 m s density of 1000 kg m3 and viscosity of 1 5 103 pa s a burst pressure of 220 mpa at 14 m depth would generate an acoustic pulse whose amplitude and character match the observed signal waveform analysis of the explosion pulses shows that the explosive event may be preceded by a long period fluid transient which may trigger the metastable magma gas mixture the modeling procedure illustrates the synergy of fluid dynamic seismic and acoustic models and data with geological and visual observations

provenance and tectonic significance of the palaeoproterozoic metasedimentary successions of central and northern madagascar abstract new detrital zircon u pb age data obtained from various quartzite units of three spatially separated supracrustal packages in central and northern madagascar show that these units were deposited between 1 8 and 0 8 ga and have similar aged provenances the distribution of detrital zircon ages indicates an overwhelming contribution of sources with ages between 2 5 and 1 8 ga possible source rocks with an age of 2 5 ga are present in abundance in the crustal segments antananarivo antongil and masora domains either side of a purported neoproterozoic suture betsimisaraka suture zone recently possible source rocks for the 1 8 ga age peak have been recognised in southern madagascar all three supracrustal successions as well as the archaean blocks onto which they were emplaced are intruded by mid neoproterozoic magmatic suites placing a minimum age on their deposition the similarities in detrital pattern maximum and minimum age of deposition in the three successions lend some support to a model in which all of madagascar s archaean blocks form a coherent crustal entity the greater dharwar craton rather than an amalgamate of disparate crustal blocks brought together only during neoproterozoic convergence however potential source terranes exist outside madagascar and on either side of the neoproterozoic sutures so that a model including a neoproterozoic suture in madagascar cannot be dispelled outright

tectonic significance of fissure veins associated with pseudotachylites of the kui chitraseni shear zone aravalli mountain nw india abstract kui chitraseni shear zone of the precambrian aravalli mountain nw india is marked by a nearly 400 m wide ne sw trending belt of cataclasites developed on the granites and metasediments of the delhi supergroup the cataclasites are criss crossed by pseudotachylite and fissure veins while the pseudotachylites are aphanitic to microlitic the fissure veins are characterized by syntaxial bitaxial as well as unitaxial growth of elongate quartz grains textural study of the fissure veins suggests crystallization of quartz grains in a dilational environment in hydrous condition contrarily the pseudotachylites bear the evidence of frictional melting of rocks under anhydrous conditions since in many instances it is observed that the fissure veins have replaced the pseudotachylites following the crack seal mechanism the formation of fissure veins is considered to be latekinematic to pseudotachylites hence it is interpreted that the pseudotachylites and fissure veins were formed in two distinct tectonic events while pseudotachylites were formed in a compressional setting resulted from thrusting along the shear zone the fissure veins have been formed in an extensional setting during a late stage normal faulting in light of this tectonic rejuvenation along the kui chitraseni shear zone various lineaments present within the aravalli mountains need further study for understanding the evolution of the region

experimental studies of collapse calderas we present experiments to investigate the formation of calderas using inflatable balloons in a medium of fused alumina powder this system provides a model of a magma chamber in an homogeneous elastic media which scales to volcanic systems in terms of geometry and strength of the media three kinds of experiment were performed i the balloon was inflated and then deflated simulating pre emption tumescence and caldera collapse ii the balloon was deflated without prior inflation simulating caldera formation without pre eruption tumescence iii three balloons were inflated and deflated in a line simulating multiple magma chambers the influence of magma chamber shape was investigated using different shaped balloons balloon inflation formed a dome with a surface pattern of shallow polygonal fractures centrally and radial fractures peripherally uplift occurs along deep inward dipping concentric reverse faults deflation generated depressions with an outer set of concentric ring fractures surrounding a central funnel formed by sagging along numerous minor faults some of which formed during doming during collapse the concentric reverse faults were converted to normal faults and the radial normally faulted fractures were converted to reverse faults without prior tumescence an outer set of near vertical ring faults surround a flat central depression due to collapse of a coherent block an inner set of outward dipping reverse ring faults also develop the experimental caldera area increased with balloon size and increased as the balloon depth decreased for a given balloon volume and depth collapse area is significantly smaller if doming had occurred prior to collapse arcuate fractures can provide the pathways for magma ascent during pre emption tumescence smith bailey 1968 but the shallow radial and polygonal fracture systems may also influence vent location changes in fault geometry and sense of movement extension to compression and vice versa occur when subsidence initiates and can account for changes in vent location that occur in many eruptions multiple overlapping collapse calderas are associated with magma chamber migration whereas nested calderas can result from the activity of a single magma chamber

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

a 2 5 ga porphyry cu mo au deposit at malanjkhand central india implications for late archean continental assembly abstract eight re os ages from six molybdenite samples representative of the cu mo au mineralization at the giant malanjkhand deposit in madhya pradesh were obtained using id ntims these data provide a clear late archean early paleoproterozoic age for this deposit and by implication for its calc alkaline granitoid host among other diverse models the origin of malanjkhand has been debated as orogenic lode style associated with development of a quartz reef in a shear zone or as porphyry style associated with a pink granitoid intrusion that is conspicuously present in the vicinity of the brittle ductile deformed quartz reef previous models included middle proterozoic ages for the cu mo au mineralization based on poorly constrained rb sr and k ar data direct dating of molybdenite shows that stringer mineralization in the quartz reef and disseminated and vein mineralization in the granite were contemporaneous at 2490 8 ma 2489 5 1 4 ma based on regression without uncertainty in the 187re decay constant mswd 0 5 n 5 additional molybdenite from the quartz reef dated at 2475 and 2450 ma represents at least two pulses of reworking that we suggest configured the elongate and arcuate quartz reef into its present position we suggest that the quartz reef is a high silica stockwork cap embedded in its primary potassic alteration halo and subsequently tilted so that it lies convex to the east with deeper levels exposed to the north petrographic evidence coupled with high re concentrations for molybdenites 400 650 ppm support this scenario and suggest that malanjkhand is a subduction related stockwork porphyry style cu mo au deposit involving mantle malanjkhand geology shares little affinity with three surrounding and tectonically juxtaposed terranes we suggest that the malanjkhand cu mo au deposit and the surrounding batholith containing multiple cu mo au prospects may be the vestiges of a microplate captured along the north margin of the nearly amalgamated southern indian craton at 2 5 ga as the southern craton began to converge with the northern indian craton or other protocontinents now embedded or consumed within the central indian tectonic zone citz this scenario could imply an early paleoproterozoic age for the earliest development of the citz at least in the region of the central indian shear suture cis whose marked ene trend imprints the northwestern part of the malanjkhand batholith and the cu mo au deposit based on a compilation of 2 5 ga events in both the southern and northern indian cratons we suggest that some units in the citz linked an extensive and continuous late archean early paleoproterozoic orogenic belt that may extend to the moyar bavali bhavani attur palghat and cauvery shear zones in southern india and include inboard units of the eastern ghats and the aravalli delhi orogenic belts robust geochronology that can be tied to the early history within these orogenic belts is scarce and extensive reworking during grenvillian and pan african time creates a pervasive overprint at some localities this late archean early paleoproterozoic belt preserves sutures within a coalesced late archean continent that included east antarctica napier and vestfold hills complexes at 2 5 ga

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

experimental fragmentation of crystal and vesicle bearing silicic melts we experimentally investigate the effect of crystals on the fragmentation behavior of a three phase melt gas crystals system under rapid decompression starting materials are cylinders of hydrated haplogranite melts containing alumina crystals that are placed at 6 30 mpa and 600 800 c in a fragmentation bomb for foaming subsequently these bubble and crystal bearing melts are rapidly decompressed within 30 mpa for phenocryst and microlite bearing samples

triggering of the lusi mud eruption earthquake versus drilling initiation abstractthe lusi mud volcano in east java has erupted unabated for almost 2 yr ooding an area of 7 km 2 and displacing more than 25 000 people despite its disastrous impact the mechanism for triggering the lusi eruption remains highly controversial two distinct mechanisms have been proposed one hypothesis suggests that the eruption was triggered by the m w 6 3 earth quake that struck yogyakarta 250 km from lusi two days before the eruption however an examination of static and dynamic stress changes and stress transfer mechanisms indicates that the yogyakarta earthquake was at least an order of magnitude too small to reactivate faults and open uid ow pathways under lusi an alternate theory suggests that lusi was triggered by a blowout following drilling problems in the nearby banjar panji 1 well blowouts result from an inability to control pore uid intakes into the borehole and typically occur when the drilling win dow fracture pressure minus pore pressure is approximately zero and when there is insuf cient protective casing of the well bore pore and fracture pressure data from banjar panji 1 indicate that the well had a narrow drilling window of only 0 2 3 mpa furthermore two planned casing points were skipped during drilling resulting in 1742 m of unprotected borehole the combina tion of hazardously narrow drilling window and long uncased borehole would have made drill ing problems in banjar panji 1 dif cult to control placing the well at high risk of blowing out furthermore well bore pressures following drilling problems in banjar panji 1 reached magni tudes in excess of the fracture pressure and thus were suf cient to create uid ow pathways in the subsurface therefore we suggest that no viable method is known by which the yogyakarta earthquake could have triggered the mud ow and that a blowout in the banjar panji 1 well was the most likely mechanism for triggering the lusi eruption keywords

in situ confirmation of permeability development in shearing bubble bearing melts and implications for volcanic outgassing the ferocity of volcanic eruptions their penchant for either effusive or explosive behaviour is to a large extent a matter of the ease with which volatiles are able to escape the volcanic system of particular importance are the mechanisms by which permeable networks within magma are fabricated and how they permit gas escape thereby diffusing possibly calamitous explosions here we present a series of experiments that confirms sample scale fracture propagation and permeability development during shearing viscous flow of initially impermeable bubble bearing 2 10 4 s 1 at moderate shear strain rates 2 10 4 s 1 3 via en echelon mode i fractures produced by repeated fracture events at high shear strain rates 4 5 10 4 s 1 permeability develops shortly after the onset of inelastic deformation and is again established through a series of en echelon mode i fractures critically strain is not immediately localized on mode i fractures making them long lived and efficient outgassing channels that are ideally oriented for directing volatiles from the central conduit upward and outward toward the conduit rim indeed mode i fracture arrays may prove necessary for dissipating gas overpressures in the central regions of the magma column which are considered difficult to outgas these experiments highlight mechanisms that are likely active along conduit margins and constrain previously postulated processes under truly applicable conditions

present status of the geochronology of the precambrian rocks of rajasthan abstract age determinations mostly by rb sr analyses of the precambrian rocks of rajasthan by us and by others are summarized and discussed broad periods of acid magmatism at 1 3000 2900 m y 2 2600 2500 m y 3 2000 1900 m y 4 1700 1500 m y and 5 850 750 m y were identified the oldest rocks in the area are the yet undated banded gneisses bgc east of udaipur intruded by the untala granite dated at 2950 m y and hence of mid archean age the basal status hitherto attributed to the berach granite dated at 2600 m y is no longer tenable the radiometric control on the beginning and duration of the overlying aravalli supergroup is not yet satisfactory though a lower limit at 2000 m y is indicated heron s original delhi rocks have recorded two magmatic events widely separate in space and time while the earliest granitic activity at 1600 m y is recorded only in the alwar basin in the northeast the younger activity between 850 750 m y is widespread as shown by the nearly concordant ages of erinpura type granites along the aravalli mountain range and the malani rhyolites in the western plains of the aravalli range

nature of magmatism and sedimentation at a columbia active margin insights from combined u pb and lu hf isotope data of detrital zircons from nw india abstract detrital zircons from a palaeoproterozoic quartzite deposited between 1 85 and 1 82 ga in the northern aravalli orogen of nw india show a distinctive age peak of ca 1 85 ga and variable but largely subchondritic ehf1 85 ga between 1 3 and 21 0 corresponding to hafnium model ages of 2 5 to 3 6 ga these data indicate an important period of reworking of ancient eo to neoarchaean strongly heterogeneous continental crust at this time prevalence of ca 1 85 ga subduction related granitoids almost identical u pb age spectra and ehft of detrital zircons in ca 1 85 ga metasedimentary rocks in the aravalli orogen and the inner lesser himalaya indicate similar sediment provenances and thus a geological connection between these two terranes during late palaeoproterozoic all together the data constrain a rapid succession of sedimentation metamorphism and subduction related magmatic activity and support the interpretation of an active geodynamic realm along the entire north indian margin at ca 1 85 ga comparison of detrital zircon data in conjunction with published paleomagnetic data from north india and other crustal blocks of the columbia supercontinent additionally suggest a close affinity of north india with madagascar the cathaysia block of south china and south korea during columbia times

ion microprobe 207pb 206pb ages of zircons from the bundelkhand massif northern india implications for crustal evolution of the bundelkhand aravalli protocontinent abstract 207pb 206pb ages of zircon from gneissic rocks and granitoids representing all major lithological units of the bundelkhand massif northern india have been determined using an ion microprobe the presence of early archaean granitic crust in this region is established from these ages ages for the kuraicha and the mahoba gneisses and associated metabasic enclaves suggest the oldest partial and metamorphic melting event in this region occurred at 3 3 ga the presence of younger gneisses with ages of 2 7 and 2 5 ga suggests the existence of multiple protolith age components within the massif three major granitoid suites hornblende biotite leuco granitoids were emplaced at 2 5 ga within a time span of a few tens of millions of years felsic volcanism also occurred around this time an age of 2 49 ga for the youngest phase of leucogranitoid marks the time of overall stabilization of this massif the geochronological history of the bundelkhand massif appears to be remarkably similar to that of the basement complex of the aravalli delhi orogenic belt another prominent archaean crustal block to the west of this massif geochemical features of the different rock types in these two regions are also very similar we propose that these two apparently discrete blocks evolved as a single crustal unit with stabilization taking place at 2 5 ga

sequential nesting of magmas in marble southwestern grenville province quebec from fracture propagation to diapirism abstract in the southwestern grenville province quebec 1090 1070 my old k rich alkaline equidimensional plutons such as the kensington pluton occur in marble rich country rock but coeval dykes bearing lower crustal xenoliths are found only in a quartzofeldspathic gneiss complex the sequential nesting of magmas the various episodes of skarn formation and the progressively more mafic character of the intruding magmas of the kensington pluton are interpreted in terms of magma ascent through a series of propagating fractures cessation of upward fracturing and pooling of magma in marble rich ductile crust diapirism radial shortening of wall rock and in situ pluton expansion this suite provides evidence that at deep crustal levels the country rock rheology influences the mode of magma ascent and emplacement and that diapirism is a possible mechanism of magma transport through rocks behaving rheologically by a power law model

abrupt transitions during sustained explosive eruptions examples from the 1912 eruption of novarupta alaska plinian ignimbrite activity stopped briefly and abruptly 16 and 45 h after commencement of the 1912 novarupta eruption defining three episodes of explosive volcanism before finally giving way after 60 h to effusion of lava domes we focus here on the processes leading to the termination of the second and third of these three episodes early erupted pumice from both episodes show a very similar range in bulk vesicularity but the modal values markedly decrease and the vesicularity range widens toward the end of episode iii clasts erupted at the end of each episode represent textural extremes at the end of episode ii clasts have very thin glass walls and a predominance of large bubbles whereas at the end of episode iii clasts have thick interstices and more small bubbles quantitatively all clasts have very similar vesicle size distributions which show a division in the bubble population at 30 m vesicle diameter and cumulative number densities ranging from 107 109 cm 3 patterns seen in histograms of volume fraction and the trends in the vesicle size data can be explained by coalescence signatures superimposed on an interval of prolonged nucleation and free growth of bubbles compared to experimental data for bubble growth in silicic melts the high 1912 number densities suggest homogeneous nucleation was a significant if not dominant mechanism of bubble nucleation in the dacitic magma the most distinct clast populations occurred toward the end of plinian activity preceding effusive dome growth distributions skewed toward small sizes thick walls and teardrop vesicle shapes are indicative of bubble wall collapse marking maturation of the melt and onset of processes of outgassing the data suggest that the superficially similar pauses in the 1912 eruption which marked the ends of episodes ii and iii had very different causes through episode iii the trend in vesicle size data reflects a progressive shift in the degassing process from rapid magma ascent and coupled gas exsolution to slower ascent with partial open system outgassing as a precursor to effusive dome growth no such trend is visible in the episode ii clast assemblages we suggest that external changes involving failure of the conduit vent walls are more likely to have effected the break in explosive activity at 45 h

decompression experiments as an insight into ascent rates of silicic magmas an experimental study of h2o exsolution bubble growth and microlite crystallisation during ascent decompression of silicic magmas in the volcanic conduit is presented isobaric and decompression experiments were performed on a rhyolitic melt at 860 c nno 1 h2o saturation and pressures between 15 and 170 mpa two sets of decompression experiments were performed with decompression rates varying between 0 001 and 960 mpa min 1 from 150 to 50 mpa high pressure decompression and 2 from 50 to 15 mpa low pressure decompression the experiments highlight incomplete h2o exsolution for decompression rates 100 mpa min incomplete bubble growth for decompression rates 0 1 mpa min crystal nucleation time lags and incomplete chemical re equilibration to final pressures the observed crystallisation process i e growth versus nucleation depends on the decompression range indeed decompression induced crystallisation during high pressure decompressions is dominated by growth of existing crystals whereas during low pressure decompressions crystal nucleation is the dominating process this study provides a means to infer magma ascent rates in eruptions of silicic magmas through a combined petrologic and experimental approach

volcano deformation and eruption forecasting recent advances in global positioning system gps tilt and interferometric synthetic aperture radar insar have greatly increased the availability of volcano deformation data these measurements combined with appropriate source models can be used to estimate magma chamber depth and to provide information on chamber shape and volume change however kinematic models cannot constrain magma chamber volume and provide no predictive

paleo uplift and cooling rates from various orogenic belts of india as revealed by radiometric ages discussion 1 discussion sur l article de sharma k k bal k d parshad r nard lal nagpaul k k paru dans tectonophysics nld 1980 70 135 158

fragmentation of foamed silicic melts an experimental study we present the first experimental investigation of the fragmentation behavior of two phase melt gas rhyolitic systems under rapid decompression two phase samples have been generated by foaming water oversaturated rhyolitic melts up to 900 c and up to 18 mpa prior to rapid decompression in a fragmentation bomb the fragmented particles or experimental pyroclasts were recovered for analysis several features of naturally foamed pumices have been reproduced including the generation of both isotropic and tube pumices we focus here on the fragmentation behavior fragmentation occurred through a layer by layer process in the brittle regime of melt response we investigated the influence of the magnitude of the decompression 4 to 18 mpa the porosity 0 to 85 vol and the pore morphology tube versus isotropic on the fragment size distribution less vesicular samples porosity 50 vol yield coarser fragments when decompressed below 15 mpa and finer fragments when decompressed above 15 mpa increasing decompression of the vesicular samples results in a decrease in fragment size of 0 2 unit mpa the presence of tubes instead of isotropic pores in vesicular samples generates finer fragments under decompression implications for dome eruptions are discussed

the low viscosities of f h2o bearing granitic melts and implications for melt extraction and transport melt viscosity affects virtually all aspects of igneous petrogenesis although addition of h2o is known to lower melt viscosities addition of fluorine is controversial and may raise them because these two volatiles most commonly reach their highest concentrations in granitic rocks the viscosities of peralkaline strongly peraluminous and weakly peraluminous granitic melts with approximately 1 5 wt f and 6 wt h2o were measured to investigate the combined effects of h2o and f on granitic melt viscosities when those volatiles are present at natural concentration levels viscosities were measured between 800 and 1000 c at 1 0 gpa with the falling sphere technique in a piston cylinder apparatus viscosities of all melts studied behave in an arrhenius manner and can be described by the following equations peralkaline 2 70 0 21 10 6exp 181 9 1 0 rt metalminous 4 54 0 44 10 7exp 213 8 1 0 rt peraluminous 2 60 0 25 10 8exp 242 8 1 0 rt where viscosity is in units of pa s and the activation energy is in kj mol r is the gas constant in j mol 1 k 1 andt is temperature in kelvin uncertainties are 1 standard errors based upon estimated uncertainties 5 relative in the viscosity measurements viscosities of these melts with high volatile contents can be well estimated with existing viscosity models viscosities of the peraluminous melts studied are similar to those of hydrous granitic melts containing water concentrations equal to the total of h2o f in the melts studied all volatile bearing per and metaluminous granitic melts display a rapid 6 to 7 orders of magnitude drop in viscosity with the first 3 wt volatiles added followed by only an additional factor of two decrease in viscosity as the volatile concentration is increased from 3 to 12 wt the peralkaline melt displays viscosities significantly below those of all other volatile bearing per and metaluminous melts previously studied the lower viscosities of peralkaline granitic melts allow them to separate more rapidly from their source regions be transported through conduits at a velocity approximately an order of magnitude faster and experience more efficient crystallization fractionation than per and metaluminous granitic melts

mayon volcano philippines change of monitoring strategy after microgravity and gps measurements from 1992 to 1996 abstract mayon volcano is part of the bicol volcanic chain on the island luzon philippines during this century there were ten activity periods distributed almost regularly because of the density of population about one million people living in the vicinity of the volcano three seismological observatories are in operation measurements of gravity changes started in 1992 just before the eruption of february march 1993 two profiles at the slope were established connected to a regional network around the volcano in order to enable the determination of mass changes between the campaigns the height control was provided by parallel gps measurements in all the network consists of 26 points which were remeasured with three gravimetres at least three times within one campaign during five campaigns within 4 years the differential gps gives no significant changes of the elevation within 4 cm nevertheless the gravity increased significantly by up to 1500 nm s2 equivalent to 150 gal as no significant change of elevation is observed gps no extended shallow magma chamber system below the volcano can be proved this is in accordance with geochemical results indicating a rather undifferentiated magma the youngest lava which is of interest for the eruption dynamics belongs to the medium k basaltic andesite field of the k2o vs sio2 diagram a rather qualitative check of groundwater level changes reveals that these cannot be the sources for the observed gravity changes thus the increase of gravity after the eruption of february 1993 can be explained by a mass redistribution in the volcanic vent from above the level of the gravity points to below practical conclusions of these results lead to changes in the monitoring strategy deformation measurements did not reveal any volcanic activities at least for the eruption of 1993 no significant deformation was observed gravity could be an indicator for long term changes thus repeated gravity measurements gps at selected points could be used in parallel to seismic monitoring to detect slow mass movements prior to changes in seismicity

malani rhyolites a review abstract the late proterozoic malani bimodal volcanics constitute the largest suite of anorogenic acid volcanics in india the volcanism took place during 745 10 ma ago succeeding the granitic activity of abu pluton and ceased before the onset of marwar sedimentation on the basis of field evidences three stages of igneous activity have been recognised volcanics of the first stage are mostly basalt with occasional andesite or trachybasalts these are subsequently covered by the voluminous outpouring of peralkaline and peraluminous rhyolite basalt dacite and trachyte flows the third stage ceased with the outburst of ash flow deposits the dominant felsic volcanics are rhyolites and rhyodacites spread over an area of about 31 000 km 2 the other rock types associated with rhyolite are trachytes dacites pitchstone welded tuff vitric lithic and crystal ash ignimbrite obsidian pyroclastic slates agglomerate volcanic breccia and volcanic conglomerates majority of the acid volcanics are high potassic and a few are calcalkaline or low potassic in composition feldspar geothermometry suggests the temperature of equilibrium to be above 650 c similar results were obtained by magnetite ulvospinel geothermometry oxygen fugacity is estimated to be about 10 18 under fmq ni nio buffer conditions malani volcanism was essentially under terrestrial conditions although deposition by aqueous conditions are also indicated the volcanic eruptions have been through fissures shield volcanoes and central cones the volcanism was triggered in an extensional tectonic regime of continental crust where geotherm was raised by the repeated influx of basic magma the initial basaltic magma was possibly generated at deeper depth by hot spot activity this magma while migrating upwards supplied additional heat for the partial melting of lower sialic crust resulting in the generation of felsic magma the crustal extension has helped in the upward advancement of the felsic magma

the change of eruption styles of martian volcanoes and estimates of the water content of the martian mantle abstract estimated water contents in the martian mantle range from 36 ppm to more than 1 these values are based on the chemical analyses such as hydrous minerals in snc meteorites and formation models of mars this study evaluates the water content of the martian mantle using the change with time of volcanic eruption style on mars as an observational constraint styles of volcanic activity depend on the volatile content of the magma and the atmospheric pressure because a low atmospheric pressure leads to a more explosive volcanic eruption it has been believed that the volcanism on the current martian environment would be very explosive our calculations however show that under the current martian atmospheric conditions erupted magma cannot entrain the ambient air effectively so the decrease in temperature of the magma during ascent is small consequently the erupted magma may form a lava like deposit when it falls back on the ground this effusive like style of eruption is a counterpart of clastogenic lava on mars on the other hand numerical calculations under a thick co 2 atmosphere which may correspond to an ancient martian atmosphere reveal a rather explosive eruption style geological features of earlier stages of martian history in the noachian and hesperian eras suggest that the volcanic eruptions on mars were explosive then effusive eruptions however became dominant in more recent times it has been widely accepted that mars experienced a major climate change in addition the release factor of volatiles on mars has been suggested to be as small as 0 017 0 112 this may imply that the volatile content has been almost constant throughout martian history consequently we assume that this change in eruption style was caused by the change in atmospheric pressure for a given water content of magma a major climatic change may lead to a transition in eruption style if we know the atmospheric pressure at the time of this transition we can calculate the possible range of the volatile content of the mantle using our numerical simulations if the atmospheric pressure on mars around late hesperian era is about 1 bar the estimated values for a typical martian magma are 0 05 0 25 wt which is within the range of the water content of typical terrestrial basaltic magmas

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

anomalous seismic amplitudes measured in the los angeles basin interpreted as a basin edge diffraction catastrophe the los angeles basin passive seismic experiment labpse involved the installation of an array of 18 seismic stations along a line crossing the los angeles basin from the foothills of the san gabriel mountains through the puente hills to the coast at 3 5 km spacing between stations the array has much higher resolution than the permanent network of stations in southern california this resolution was found to be important for analyzing the factors that govern the amplitude variation across the basin we inverted spectra of p and s body wave seismograms from local earthquakes ml 2 1 4 8 for site effects attenuation and corner frequency factor using a standard model that assumes geometric spreading varying as inverse distance exponential attenuation and an x 2 source model the s wave attenuation was sep arable into basin and bedrock contributions in addition to the body wave analysis s wave coda were analyzed for coda q and coda determined site effects we find s wave q qs in bedrock is higher than in the basin high frequency qs is higher than low frequency qs coda q qc is higher than qs p wave q qp was not separable into basement and bedrock values so we determined an average value only the corner frequencies for p and s waves were found to be nearly the same the standard model fit over 97 of the s wave data but data from six clustered events incident along the basin edge within a restricted range of incidence and azimuth angles gen erated anomalous amplitudes of up to a factor of 5 higher than predicted we test whether such basin edge focusing might be modeled by catastrophe theory after ruling out site attenuation and radiation effects we conclude a caustic modeled as a diffraction catastrophe could explain both the frequency and spatial dependence of the anomalous variation

lusi mud eruption triggered by geometric focusing of seismic waves the lusi mud eruption in indonesia has been ongoing since 2006 numerical simulations show that a parabolic shaped layer in the rock surrounding the site of the lusi eruption could have amplified and focussed incoming seismic energy from an earthquake which then triggered the mud eruption

timescales of bubble coalescence outgassing and foam collapse in decompressed rhyolitic melts abstract the timescale of degassing and outgassing in hydrous rhyolitic melts is investigated in a wide range of conditions by means of decompression experiments the evolution of vesicularity bubble diameter and number density is characterized as a function of time either of decompression or spent at final pressure in order to determine the effect of final pressure temperature syn versus post decompression degassing melt composition and microlites on the timescale of bubble growth coalescence and outgassing the result suggests that different bubble evolution and degassing outgassing timescale corresponding to explosive and effusive eruption regimes can be cast in bulk viscosity melt bubbles bulk versus decompression time rather than path space the bulk time relationship defines three domains of i bubble nucleation and growth restricted to short durations and high bulk 0 03 h for bulk 10 5 6 pa s ii equilibrium degassing with coalescence increasing from negligible permeability 10 13 m 2 to extensive permeability 10 11 12 m 2 and iii outgassing restricted to long durations and low bulk 10 h for bulk 10 6 pa s permeability 10 10 m 2 that eventually leads to foam collapse these findings are applied to the case studies of mt pelee and mt pinatubo to infer the transition from pumice to dense pyroclasts in volcanic eruptions and the possibility of evolving from an explosive plinian eruption to an effusive dome growth event by giving the vesicular magma enough time to outgas and collapse i e hundreds to tens of hours for bulk 10 5 to 10 4 pa s respectively we also show the drastic effect of microlites on re arranging preexistent bubbles and potentially triggering a late nucleation event

cover sequences at the northern margin of the antongil craton ne madagascar abstract the island of madagascar is a collage of precambrian generally high grade metamorphic basement domains that are locally overlain by unmetamorphosed sedimentary rocks and poorly understood low grade metasediments in the antalaha area of ne madagascar two distinct cover sequences rest on high grade metamorphic and igneous basement rocks of the archaean antongil craton and the neoproterozoic bemarivo belt the older of these two cover sequences the andrarona group consists of low grade metasedimentary rocks the younger sequence the newly defined ampohafana formation consists of unmetamorphosed sedimentary rocks the andrarona group rests on neoarchaean granites and monzogranites of the antongil craton and consists of a basal metagreywacke thick quartzites and an upper sequence of sericite chlorite meta mudstones meta sandstones and a volcaniclastic meta sandstone the depositional age of the volcaniclastic meta sandstone is constrained in age by u pb laser ablation icp ms analyses of euhedral zircons to 1875 8 ma 2 detrital zircons of archaean and palaeoproterozoic age represent an input from the antongil craton and a newly defined palaeoproterozoic igneous unit the masindray tonalite which underlies the andrarona group and yielded a u pb zircon age of 2355 11 ma 2 thus constraining the maximum age of deposition of the basal part of the andrarona group the andrarona group shows a low grade metamorphic overprint in the area near antalaha illite crystallinity values scatter around 0 17 2 cuk which is within the epizone the ampohafana formation consists of undeformed polymict conglomerate cross bedded sandstone and red mudstone an illite crystallinity value of 0 25 2 cuk obtained from the rocks is typical of the diagenetic zone occurrences of rhyodacite pebbles in the ampohafana formation and the intrusion of a basaltic dyke suggest a deposition in a wsw ene trending graben system during the opening of the indian ocean in the upper cretaceous that was characterized by extensive rhyolitic to basaltic magmatism along madagascar s eastern coast

id tims using the step wise dissolution technique versus ion microprobe u pb dating of metamict archean zircons from ne madagascar abstract a geochronological study using the step wise dissolution technique and in situ ion microprobe analysis is applied to late archean metamict zircons of granitoids from northeastern madagascar basement both techniques provide concordant u pb ages additionally the ion microprobe study provided in situ measurements on the pb isotopic composition of the metamict domains finally pb pb evaporation ages were found to be slightly but systematically younger than the dating obtained by the two other methods based on these data granites from the antongil belt were emplaced during at least three episodes separated by periods of magmatic inactivity of about 10 ma at 2513 2523 and 2532 ma respectively these results are consistent with previous whole rock rb sr and u pb zircon dating from this part of madagascar the occurrence of this late archean basement in northeastern madagascar can be related to southern india where large volumes of contemporaneous granitoids were emplaced

the east java mud volcano 2006 to present an earthquake or drilling trigger abstract on may 29th 2006 a mud volcano later to be named lusi started to form in east java it is still active and has displaced 30 000 people the trigger mechanism for this the world s largest and best known active mud volcano is still the subject of debate trigger mechanisms considered here are a the may 27th 2006 yogyakarta earthquake b the drilling of the nearby banjar panji 1 gas exploration well 150 m away and c a combination of the earthquake and drilling operations we compare the distance and magnitude of the earthquake with the relationship between the distance and magnitude of historical earthquakes that have caused sediment liquefaction or triggered the eruption of mud volcanoes or caused other hydrological responses based on this comparison an earthquake trigger is not expected the static stress changes caused by the rupture of the fault that created the yogyakarta earthquake are a few tens of pascals much smaller than changes in stress caused by tides or variations in barometric pressure at least 22 earthquakes and possibly hundreds likely caused stronger ground shaking at the site of lusi in the past 30 years without causing an eruption the period immediately preceding the eruption was seismically quieter than average and thus there is no evidence that lusi was primed by previous earthquakes we thus rule out an earthquake only trigger the day before the eruption started may 28th 2006 as a result of pulling the drill bit and drill pipe out of the hole there was a significant influx of formation fluid and gas the monitored pressure after the influx in the drill pipe and annulus showed variations typical of the leakage of drilling fluid into the surrounding sedimentary rock strata furthermore we calculate that the pressure at a depth of 1091 m the shallowest depth without any protective steel casing exceeded a critical level after the influx occurred fractures formed due to the excess pressure allowing a fluid gas mud mix to flow to the surface with detailed data from the exploration well we can now identify the specific drilling induced phenomena that caused this man made disaster

waveform analysis of seismoacoustic signals radiated during the fall 1996 eruption of pavlof volcano alaska theoretical modeling of acoustic and seismic signals associated with the 1996 strombolian eruption of pavlof volcano suggests that volcanic tremor at pavlof originates in the deeper part of the magma conduit and is generated by random fluid oscillations in the magma flow explosions are believed to occur in the shallower part of the magma conduit and to be caused by the rapid and violent expansion of metastable magma gas mixtures the effect of increasing the exsolved quantities of h2o and co2 gas with reduced pressure in the melt is to decrease the sound speed and density of the magma gas mixture this causes an acoustic decoupling of the upper and lower parts of the magma conduit the reduced sound speed and density of the melt at shallow depths present a sharp impedance contrast which strongly reflects acoustic energy originating at depth and traps it in the lower part of the magma conduit alternatively acoustic energy originating from the upper part of the conduit remains trapped in the low velocity region formed by the exsolved gas in the melt and hence shallow explosions may preferentially couple into the atmosphere explosion signals may be triggered by an increased flow of melt at depth and may be preceded and accompanied by vigorous mass flux transients

diverse patterns of ascent degassing and eruption of rhyolite magma during the 1 8 ka taupo eruption new zealand evidence from clast vesicularity k lauea hawaii like vesuvius and etna is a frequently active volcano associated with a national park which is a focus for volcano tourism two contrasting summit eruptions at k lauea in 2008 2009 and 1959 emphasize how even small eruptions on populous volcanoes have significant impact on both hawaii volcanoes national park hvnp and the surrounding communities the effects are typically more indirect and social than direct physical but have significant fiscal repercussions the former include both positive benefits and negative impacts as an illustration direct consequences of the 1959 eruption were the rerouting of the major park access road and destruction of a summer camp but benefits included an unprecedented surge in visitor numbers and construction of nature trails that are now the most visited asset in the park both positive and negative impacts have increased in intensity with time due to growth in the resident population and visitor numbers for example the entire park has been evacuated twice during the ongoing 2008 2009 eruption

structure and tectonics of the proterozoic aravalli delhi fold belt in northwestern india from deep seismic reflection studies abstract seismic imaging of the crust along a 400 km long deep seismic reflection profile across the palaeo mesoproterozoic aravalli delhi fold belt in the northwestern indian shield brings into focus its complex structure and provides clues to understand the geological processes involved in the evolution of this belt the reflectivity pattern varies considerably for different crustal units along the profile the deep crustal reflection data image two sets of oppositely dipping strong reflection bands from upper to lower crustal levels these are identified as the signatures of the collision corresponding to aravalli and delhi orogeny the data also exhibit a clear moho and strong lower crustal reflections near the collision boundaries a stack of dipping reflections from the top of the moho to the surface is identified as a major thrust fault indicating that the proterozoic collision and deformation were primarily thick skinned in nature

differentiation and magma mixing on kilauea s east rift zone the lavas of the 1955 east rift eruption of kilauea volcano have been the object of considerable petrologic interest for two reasons first the early 1955 lavas are among the most differentiated ever erupted at kilauea and second the petrographic character and chemical composition of the lava being erupted changed significantly during the eruption this shift from more differentiated mgo 5 0 5 7 to more magnesian mgo 6 2 6 8 lava has been variously interpreted as either due to systematic excavation of a zoned differentiated magma body or to invasion of the differentiated magma by more primitive magma followed by rapid mixing and eruption of the resulting hybrid magmas petrologic examination of several nearvent spatter samples of the late 1955 lavas shows abundant evidence for magma mixing including resorbed and or reversely zoned crystals of olivine augite and plagioclase in addition the compositional ranges of olivine plagioclase and groundmass sulfide are very large implying that the assemblages are hybrid core compositions of olivine phenocrysts range from fo85 to fo77 the most magnesian olivines in these samples must have originally crystallized from a melt containing 8 0 8 5 mgo which is distinctly more magnesian than the bulk composition of the late 1955 lavas the majorelement and trace element data are either permissive or supportive of a hybrid origin for the late 1955 lavas in particular the compositional trends of the 1955 lavas on plots of cao vs mgo and the virtual invariance of al2o3 and sr in these plagioclase phyric lavas are more easily explained by magma mixing than by fractionation the pattern of internal disequilibrium re equilibration in the late 1955 spatter samples is consistent with reintrusion and mixing having occurred at least twice during the latter part of the 1955 eruption plagioclase zonation preserves possible evidence for additional earlier reintrusion events least squares modelling the mixing of early 1955 bulk compositions with various summit lavas olivine pick the 1952 summit lava as most like the primitive component the results also indicate the primitive component had mgo 7 5 8 0 corresponding to liquidus temperatures of 1165 1175 c the absence of fe ti oxide phenocrysts in the late 1955 lavas implies that the cooler component of the hybrid had t 1110 c thus the thermal contrast between the two components may have been as much as 55 65 c sufficient to produce the conspicuous disequilibrium effects visible in the spatter samples

ascent and decompression of viscous vesicular magma in a volcanic conduit during eruption lava domes and flows may become unstable and generate dangerous explosions fossil lava filled eruption conduits and ancient lava flows are often characterized by complex internal variations of gas content these observations indicate a need for accurate predictions of the distribution of gas content and bubble pressure in an eruption conduit bubbly magma behaves as a compressible viscous liquid involving three different pressures those of the gas and magma phases and that of the exterior to solve for these three different pressures one must account for expansion in all directions and hence for both horizontal and vertical velocity components we present a new two dimensional finite element numerical code to solve for the flow of bubbly magma even with small dissolved water concentrations gas overpressures may reach values larger than 1 mpa at a volcanic vent for constant viscosity the magnitude of gas overpressure does not depend on magma viscosity and increases with the conduit radius and magma chamber pressure in the conduit and at the vent there are large horizontal variations of gas pressure and hence of exsolved water content such variations depend on decompression rate and are sensitive to the exit boundary conditions for the flow for zero horizontal shear stress at the vent relevant to lava flows spreading horizontally at the surface the largest gas overpressures and hence the smallest exsolved gas contents are achieved at the conduit walls for zero horizontal velocity at the vent corresponding to a plug like eruption through a preexisting lava dome or to spine growth gas overpressures are largest at the center of the vent the magnitude of gas overpressure is sensitive to changes of magma viscosity induced by degassing and to shallow expansion conditions in conduits with depth dependent radii

the dharwar craton and the assembly of peninsular india peninsular india can be separated into five discrete crustal areas the bhandara singhbhum and aravalli bundelkhand cratons the eastern ghats and a block in southern india containing the dharwar craton and adjoining granulite terrain these areas are separated by four major joins eastern ghats front godavari rift mahanadi rift sukinda thrust and narmada son lineament and associated thrusts all joins except the godavari rift are former orogenic belts where thrusts juxtapose rocks of different metamorphic grade these thrusts and the absence of clear correlation of suites among different cratons suggest that the indian shield formed by accretion of separate continental fragments epicontinental late archean early pro terozoic sediments throughout india however may indicate that the joins are intracontinental formed within a coherent block the term dravidian shield is used for the southernmost of the five crustal blocks including all of india south of the deccan basalts and godavari rift

decompression induced crystallization in hydrated silica rich melts empirical models of experimental plagioclase nucleation and growth kinetics isothermal and isobaric crystallization of plagioclase in a water saturated synthetic rhyolitic melt is investigated through time series of decompression experiments the experimental variables are the rate at which samples are initially decompressed 30 150 and 1200 mpa h from 200 mpa and 875 c final pressure 25 to 160 mpa and holding time at final pressure up to 17 days through textural measurements of the crystals plagioclase crystallization kinetics has been characterized in terms of nucleation lag and rates of nucleation and growth plagioclase crystallization is markedly dependent on effective undercooling teff and holding time at crystallization pressure with teff increasing from 55 to 110 c i nucleation lag decreases from 1 2 days to 15 min ii maximum nucleation rates increase from 10 3 to 10 2 mm 2 s 1 and iii maximum growth rates decrease from 10 6 to 5x10 7 mm s 1 the initial decompression rate 30 150 and 1200 mpa h has no systematic control on crystallization at final pressure except for the 1200 mpa h series in which samples show nucleation difficulties from the experimental data of teff constrained plagioclase number density proportion and morphology we provide means to assess conditions of nucleation and growth of natural plagioclase microlites from rapidly ascended rhyolitic melts through the determination of plagioclase liquidus curve and teff prevailing during crystallization

strike slip faulting as a trigger mechanism for overpressure release through piercement structures implications for the lusi mud volcano indonesia piercement structures such as hydrothermal vent complexes pockmarks and mud volcanoes are found in various geological settings but are often associated with faults or other fluid focussing features this article aims to investigate and understand the mechanisms responsible for the formation of piercement structures in sedimentary basins and the role of strike slip faulting as a triggering mechanism for fluidization for this purpose four different approaches were combined fieldwork analogue experiments and math

dynamics of eruptive phenomena the scope of this chapter is limited to the dynamics of lava and gas rising in a volcanic conduit no mention will be made of the behaviour of eruption columns in the atmosphere which would deserve a chapter on their own some basic knowledge of the main principles of fluid dynamics is assumed the text contains no complex mathematical derivation and save for a few simple points details all the steps required to arrive at a given solution the aim of this chapter is to highlight a few key physical principles using simple problems of relevance to volcanic eruptions true eruptions are of course more complex than the examples given and involve various interactions between the variables

steady state volcanism paleoeffusion rates and magma system volume inferred from plagioclase crystal size distributions in mafic lavas dome mountain nevada abstract the dome mountain dm lavas located in the moat of the timber mountain caldera of the sw nevada volcanic field cap a thick sequence of welded tuffs massive and bedded tuffs and mafic and rhyolitic lava flows these 10 9 m y old flows comprise a pile of some twenty flows with a total thickness of about 300 m individual flows range in thickness from 3 to 20 m and are characterized by a basal vesicular zone a massive central region and an upper vesicular region containing in most cases cooling fractures the flows dip gently away from the summit of dm a prominent topographic feature of the region with an elevation of 2065 m silica contents range from 48 8 wt at the base of the pile to 59 4 wt at the top although most of the flows are andesitic crystal size distributions csds for plagioclase in these comagmatic lavas have been determined to provide information on magma storage times these times when coupled with phase equilibria can be used to infer cooling rates which are indicative of the relative dimensions of magmatic bodies and the vigor of various magmatic cooling processes most of the csds show no sign of crystal fractionation or accumulation assuming a growth rate of 10 10 cm s calculated mean crystal residence times for most lavas cluster in the range of 1 5 to 4 years two of the lower lavas have residence times in the range of 4 to 9 years the residence times correlate inversely with nucleation density and broadly correlate inversely with silica content high residence time low silica lavas occur at the base of the pile whereas low residence time high silica lavas occur at the top of the pile one interpretation of the residence time data is that the lavas are from an open system of more or less constant residence time but varying spatially in system locations e g a magma chamber in which steady state recharge and eruption may have been reached alternatively these lavas may represent small samples closely spaced in time of a slowly cooling large batch or reservoir of magma the greater residence times associated with the lower flows may indicate the increased amount of time necessary to form the conduit of the magma volcano system by the oldest magma or simply that part of the system with the highest liquidus temperature a minimum volume of 1 4 to 2 5 km 3 for the magma chamber is estimated for the dm system using the estimated residence times in a simplified cooling model of a sheet of aspect ratio r the actual system volume depends on r which is strictly unknown and thus the actual system volume may be much larger e g 200 km 3 a mean paleoeffusion rate of 0 05 km 3 yr is obtained for the lavas by assuming that the residence time of each lava corresponds to the amount of time elapsed since the eruption of the underlying flow

textures water content and degassing of silicic andesites from recent plinian and dome forming eruptions at mount pelee volcano martinique lesser antilles arc previous petrological and phase equilibrium experimental studies on recent silicic andesites from mount pelee volcano have evidenced comparable pre eruptive conditions for plinian and dome forming pelean herein eruptions implying that differences in eruptive style must be primarily controlled by differences in degassing behaviour of the mount pelee magmas during eruption to further investigate the degassing conditions of plinian and pelean magmas of mount pelee we study here the most recent mount pelee s products p1 at 650 years b p 1902 and 1929 eruptions which cover a range of plinian and pelean lithologies for bulk rock vesicularities glass water contents glass inclusions in phenocrysts and matrix glasses and microtextures water contents of glass inclusions are scattered in the plinian pumices but on average compare with the experimentally deduced pre eruptive melt water content i e 5 3 6 3 wt whereas they are much lower in the dominant pelean lithologies crystalline poorly vesicular lithics and dome samples this indicates that the glass inclusions of the pelean products have undergone strong leakage and do not represent pre eruptive water contents the water content of the pyroclast matrix glasses are thought to closely represent the residual water content in the melt at the time of fragmentation determination of the water contents of both the pre eruptive melt and matrix glasses allows the estimation of the amount of water exsolved upon syn eruptive degassing we find the amount of water exsolved during the eruptive process to be higher in the pelean products than in the plinian ones typically 90 100 and 65 70 of the initial water content respectively the vesicularities calculated from the amount of exsolved water compare with the measured vesicularities for the plinian pumices consistent with a closed system near equilibrium degassing up to fragmentation by contrast the low residual water contents low groundmass vesicularities and extensive groundmass crystallization of the pelean products are direct evidence of open system degassing microtextural features including silica bearing and silica free voids in the pelean lithologies may represent a two stage vesiculation

the lusi mud volcano triggering controversy was it caused by drilling abstract following the yogyakarta earthquake on may 27th 2006 the subsequent eruption of a mud volcano has been closely observed and analyzed by the geological community the mud volcano known as lusi began erupting near the banjarpanji 1 exploration well in sidoarjo east java indonesia lusi offers a unique opportunity to study the genesis and development of a mud volcano for the first time this paper presents all raw and interpreted drilling data so any interested party can perform their own assessment our study suggests that lusi mud volcano was a naturally occurring mud volcano in an area prone for its mud volcanism pressure analysis done on the banjarpanji well shows that the pressure exerted at the well is lower than the fracture pressure at the last casing shoe and suggests that the well was intact and did not suffer an underground blowout this is further supported by evidence and observation made during drilling such as circulation was done on an open bop and subsequent relief wells sonan and temperature log runs this study offers a different alternative to earlier hypothesis that events at the banjarpanji well were the trigger for the lusi mud volcano more work is needed by the scientific community to study the sequence of events in order to explain and clarify the real trigger of lusi