magmatic precursors to the 18 may 1980 eruption of mount st helens usa perhaps the most difficult task facing volcanologists today is that of distinguishing between low level volcanic restlessness and activity that presages a full scale eruption we illustrate these difficulties by reexamining the sequence of events that led to the 18 may 1980 eruption of mount st helens activity that is often presented as a classic example of early phreatic explosions leading to a magmatic eruption this interpretation is problematic however given the known ascent of juvenile magma to within 250 m of the surface prior to the climactic event reexamination of ash samples from several precursory events shows that small amounts of juvenile material were erupted as early as 28 march 1980 just two weeks after the first seismic signals of reawakening and that the juvenile content of the ash had probably increased by early may the magmatic component of these eruptions was not recognized at the time because of the high crystallinity of the juvenile material a signature of extensive degassing induced crystallization during magma ascent identification of juvenile material in the precursory ash from mount st helens has important implications for initiation of eruptive activity

self similarity properties of seismicity in the southern aegean area we investigate the time self similarity properties of seismicity in the hellenic are which is one of the most rapidly deforming and seismically active regions of the mediterranean area the presence of time scale invariance properties in the shallow and intermediate depth seismicity is revealed in particular 1 f beta fluctuations are detected from the analysis of earthquake sequences using the counting statistics methodology the shallow seismicity is characterized by a time clustering effect and shows a beta value that is a typical fingerprint of self similar behaviours whereas the intermediate seismicity can be considered as a realization of a purely poissonian process the investigations cover instrumentally recorded earthquakes occurring between 1964 and 1996 and the analyses have been carried out selecting different magnitude thresholds the beta value for shallow seismicity decreases from almost 0 5 to 0 2 as the threshold magnitude increases from 3 3 to 4 5 c 2000 elsevier science b v all rights reserved

hydrometeor enhanced tephra sedimentation constraints from the 18 may 1980 eruption of mount st helens 1 uncertainty remains on the origin of distal mass deposition maxima observed in many recent tephra fall deposits in this study the link between ash aggregation and the formation of distal mass deposition maxima is investigated through reanalysis of tephra fallout from the mount st helens 18 may 1980 msh80 eruption in addition we collate all the data needed to model distal ash sedimentation from the msh80 eruption cloud four particle size subpopulations were present in distal fallout with modes at 2 2 4 2 5 9 and 8 3 settling rates of the coarsest subpopulation closely matched predicted single particle terminal fall velocities sedimentation of particles 100 m was greatly enhanced predominantly through aggregation of a particle subpopulation with modal diameter 5 9 0 2 19 3 m mammatus on the msh80 cloud provided a mechanism to transport very fine ash particles with predicted atmospheric lifetimes of days to weeks from the upper troposphere to the surface in a matter of hours in this mechanism ash particles initiate ice hydrometeor formation high in the troposphere subsequently the volcanic cloud rapidly subsides as mammatus develop from increased particle loading and cloud base sublimation rapid fallout occurs as the cloud passes through the melting level in a process analogous to snowflake aggregation aggregates sediment en masse and form the distal mass deposition maxima observed in many recent volcanic ash fall deposits this work provides a data resource that will facilitate tephra sedimentation modeling and allow model intercomparisons

a numerical study of nighttime ionospheric variations in the american sector during 28 29 october 2003 variations of nighttime f2 peak height hmf2 over the american sector during the 28 29 october 2003 storm period were investigated using the national center for atmospheric research thermosphere ionosphere electrodynamics global circulation model the model was generally able to reproduce the ionospheric variations on 28 29 october 2003 observed by the ionosondes a series of controlled model simulations were subsequently undertaken to examine the effects of electric fields and neutral winds on the ionosphere the numerical experiments suggest that the dramatic nighttime increase of hmf2 on the storm day 29 october is mainly caused by traveling atmospheric disturbances tads from the high latitudes of the northern hemisphere however the electric field plays an important role in causing the elevation of hmf2 in the equatorial region the prompt penetration electric field ppef associated with the southward component of the interplanetary magnetic field bz is westward on the nightside whereas when bz reverses and becomes northward the ppef is westward in the premidnight and turns to eastward in the postmidnight these ppefs greatly affect the low latitude ionosphere during storm time on 28 october even though the bz disturbance was weak with a short duration of southward bz the tads from the southern hemisphere can propagate to the northern hemisphere and result in the corresponding oscillations in the nightside hmf2

a review on phreatic eruptions and their precursors abstract an analysis of the reported information on 132 historical phreatic events indicates that most of these 115 were not followed by a magmatic or phreatomagmatic eruption only in 18 cases precursory phenomena are reportedly lacking whereas they are recognized for the majority 72 of the considered cases these precursors have been analyzed as a function of the kind of phreatic event and of its possible triggering mechanism unfortunately the quality of the available information is poor however data suggest that anomalous seismicity ground deformation changes in the output chemistry and temperature of fumaroles and thermal springs are potential mid term precursors whereas seismic tremor is a common short term precursor

using fractal analysis to quantitatively characterize the shapes of volcanic particles 1 the shapes of volcanic particles reflect numerous eruptive parameters e g magma viscosity volatile content and degree of interaction with water and are useful for understanding fragmentation and transport processes associated with volcanic eruptions however quantitative analysis of volcanic particle shapes has proven difficult because of their morphological complexity and variability here a newly developed procedure for shape analysis based on fractal geometry is described and tested although volcanic particle shapes are not truly fractal their complexity can be effectively characterized in terms of fractal values pseudofractal dimensions reflecting morphological invariance over discrete ranges of scale using fractal data produced by dilation of a particle s two dimensional boundary a spectrum of fractal dimensions is calculated for each particle by taking the first derivative of the dilation data compared with fractal methods that express shape in terms of only one or two fractal dimensions typically derived from the slope of data on a richardson plot this technique results in better discrimination between samples in addition use of multiple fractal values allows incorporation of multivariate statistical analysis further strengthening the differentiating power of the technique this fractal spectrum technique yields promising results for samples of sideromelane shards from iceland and is likely to be effective at characterizing other kinds of volcanic particle shapes

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

mechanisms of hydrovolcanic pyroclast formation grain size scanning electron microscopy and experimental studies pyroclasts produced by explosive magma water interactions are of various sizes and shapes data from analysis of over 200 samples of hydrovolcanic ash are interpreted by comparison with experimentally produced ash grain size and scanning electron microscopy sem reveal information on the formation of hydrovolcanic pyroclasts strombolian explosions result from limited water interaction with magma and the pyroclasts produced are dominantly centimeter sized with increasing water interaction hydrovolcanism increases in explosivity to surtseyan and vulcanian activity these eruptions produce millimeter to micron sized pyroclasts the abundance of fine ash 63 m diameter increases from 5 to over 30 percent as water interaction reaches an explosive maximum this maximum occurs with interactions of virtually equal volumes of melt and water five dominant pyroclast shape types determined by sem result from hydrovolcanic fragmentation 1 blocky and equant 2 vesicular and irregular with smooth surfaces 3 moss like and convoluted 4 spherical or drop like and 5 plate like types 1 and 2 dominate pyroclasts greater than 100 m in diameter types 3 and 4 are typical of fine ash type 5 pyroclasts characterize ash less than 100 m in diameter resulting from hydrovolcanic fragmentation after strong vesiculation fragmentation mechanisms observed in experimental melt water interactions result from vapor film generation expansion and collapse fragments of congealed melt are products of several alternative mechanisms including stress wave cavitation detonation waves and fluid instability mixing all result in rapid heat transfer these mechanisms can explain the five observed pyroclast shapes stress wave fracturing cavitation of the melt results from high pressure and temperature gradients at the melt water interface simultaneous brittle fracture and quenching produces type 1 pyroclasts type 2 develops smooth fused surfaces due to turbulent mixing with water after fracture and before quenching fluid instabilities promote turbulent mixing of melt and water and produce fine ash this kind of fragmentation occurs during high energy explosions the increased melt surface area due to fine fragmentation promotes high efficiency heat exchange between the melt and water shapes of resulting pyroclasts are determined by maximum surface area type 3 and surface tension effects type 4 type 5 pyroclasts result from nearly simultaneous vesicle burst and melt water fragmentation

towards fast and routine analyses of volcanic ash morphometry for eruption surveillance applications the morphometry of volcanic ash produced by explosive eruptions yields ample information on fragmentation processes e g magmatic vs magma water interactions and on transport and sedimentation mechanisms most previous works on volcanic clast morphometry focused on the apparent 2d projected shape of ash grains here termed apash to infer processes and eruptive styles however textural analyses of ash grains has remained a long and tedious task that made such approaches inappropriate for eruption surveillance duties in this work we show that new technological advances on automated dispersion of granular materials imaged with a camera coupled microscope and enhanced computer capabilities enable fast and high resolution image acquisition of thousands of ash grains that resolve this limitation with a morpho grainsizer designed for such fast and routine measurements we perform a series of apash analyses on selected ash fractions of tephra deposits from known eruptive styles we record the size aspect ratio circularity and convexity of apash images and assess resolution reproducibility minimum population size and total analytical duration and offer recommendations for the reporting of apash data for inter laboratory comparisons to avoid fractal geometry concerns our analyses are carried out at constant size range 250 300 m and optical magnification 5 on 3000 grains per samples collected from homogenized samples results from the andesitic 1999 ongoing eruption of tungurahua volcano ecuador show that ash particles from the moderate 2001 phase are relatively equant and convex in shape while the stronger 2006 subplinian phase produced ash grains with more elongated less circular and less convex apash signatures ash grains from a basaltic scoria cone forming eruption show even more ragged apash characteristics overall our protocol allows obtaining accurate and reproducible morphometric measurements that reveal subtle variations of the morphological signature and the short duration 1 8 hours of the whole analytical process renders high resolution analyses of ash shape achievable for volcano surveillance applications this research ultimately aims to set up a morphometric database of apash results for well defined eruptive styles in order to interpret on a short term basis any apash data from active volcanoes for monitoring purposes

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

long duration penetration of the interplanetary electric field to the low latitude ionosphere during the main phase of magnetic storms 1 it is well known that the interplanetary electric field can penetrate to the low latitude ionosphere it is generally believed that the penetration of electric fields can last only for 30 min because of the shielding effect in the ring current in this paper we present the observations of the dayside ionospheric electric field enhancements at middle and low latitudes in association with reorientations of the interplanetary magnetic field imf in six cases the eastward electric field in the dayside equatorial ionosphere measured by the jicamarca incoherent scatter radar was enhanced for 2 3 hours after the imf turned southward and remained continuously southward in one case the eastward electric field in the dayside midlatitude ionosphere measured by the millstone hill incoherent scatter radar was continuously enhanced for 10 hours during southward imf since millstone hill is close to the equatorward boundary of the auroral zone during magnetic storms the penetration electric field there may be different from that at the equatorial ionosphere the most striking feature of the measurements is that the enhancements of the ionospheric electric field can last for many hours without significant decay the electric field enhancements in the middle and low latitude ionosphere are closely related to magnetic activity and occur during the main phase of magnetic storms the observations show that the interplanetary electric field can continuously penetrate to the low latitude ionosphere without shielding for many hours as long as the strengthening of the magnetic activity is going on under storm conditions

midlatitude f region peak height changes in response to interplanetary magnetic field conditions and modeling results 1 the response of the electron density peak height of the f2 region hmf2 to geomagnetic storms has been investigated and a characteristic behavior of the peak height disturbance in relation to local time season and conditions of the interplanetary magnetic field has been obtained the experimental results support the storm scenario which the change in the thermospheric wind is the main physical mechanism raising the ionospheric peak height a real time forecasting tool modeling the hmf2 disturbance hmf2 by analytical time dependent functions has been developed the empirical model predicts hmf2 for latitudes of the iberian peninsula with an 86 of success and without false alarms the behavior of the model fits to the experimental observations at other latitudes and longitudes within europe which would allow extending its usefulness at wider latitudinal ranges

furthering the investigation of eruption styles through quantitative shape analyses of volcanic ash particles abstract volcanic ash morphology has been quantitatively investigated for various aims such as studying the settling velocity of ash for modelling purposes and understanding the fragmentation processes at the origin of explosive eruptions in an attempt to investigate the usefulness of ash morphometry for monitoring purposes we analyzed the shape of volcanic ash particles through a combination of 1 traditional shape descriptors such as solidity convexity axial ratio and form factor and 2 fractal analysis using the euclidean distance transform edt method we compare ash samples from the hydrothermal eruptions of iwodake japan in 2013 tangkuban perahu indonesia in 2013 and marapi sumatra indonesia in 2015 the dome explosions of merapi java indonesia in 2013 the vulcanian eruptions of merapi in 2010 and tavurvur rabaul papaua new guinea in 2014 and the plinian eruption of kelud indonesia in 2014 particle size and shape measurements were acquired from a particle size analyzer with a microscope camera attached to the instrument clear differences between dense blocky particles from hydrothermal or dome explosions and vesicular particles produced by the fragmentation of gas bearing molten magma are well highlighted by conventional shape descriptors and the fractal method in addition subtle differences between dense blocky particles produced by hydrothermal explosions dome explosions or quench granulation during phreatomagmatic eruptions can be evidenced with the fractal method the combination of shape descriptors and fractal analysis is therefore potentially able to distinguish between juvenile and non juvenile magma which is of importance for eruption monitoring

fractal approach of the temporal earthquake distribution in the hellenic arc trench system the time clustering of earthquakes occurring in the hellenic arc trench system is quantitatively analyzed by means of the fractal dimension d of their time distribution in the time intervals of 1950 1985 m s 4 5 and 1964 1985 m s 4 0 the results obtained imply that scale invariant clustering holds over very large scale lengths of time t with 22 28 t in min 220 222 depending on the seismotectonic segment considered in all segments a common feature is the relation between thed1 d2 andd3 values found for shallow intermediate depth and all depth shocks respectively d3 d1 d2 thed values found for shallow shocks range between 0 137 and 0 191 with the exception of the ionian islands and cretan segments where anomalously high values d 0 221 0 251 have been determined we discuss possible seismotectonic interpretations of the results

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

quantitative discrimination of magma fragmentation and pyroclastic transport processes using the fractal spectrum technique abstract the morphology of volcanic particles can yield insight into magma fragmentation transport processes and style of eruption however the complexity and variability of volcanic particle shapes make quantitative characterization difficult the technique applied in this study is based on fractal geometry which has been successfully used to characterize a wide variety of particles and shapes here fractal data is produced by dilation of the 2 d particle boundary to produce a full spectrum of fractal dimensions over a range of scales for each particle multiple fractal dimensions which can be described as a fractal spectrum curve are calculated by taking the first derivative of data points on a standard richardson plot use of multiple fractal dimensions results in more effective discrimination than expressions of shape based on one or two fractal dimensions quantitative comparisons are carried out using multivariate statistical techniques such as cluster and principal components analysis applications to samples from well documented eruptions e g mt st helens 1980 tambora 1815 surtsey 1963 64 indicate that the fractal spectrum technique provides a useful means of characterizing volcanic particles and can be helpful for identifying the products of specific fragmentation processes volatile exsolution phreatomagmatic quench granulation and modes of volcanic transport deposition tephra fall pyroclastic flow blast surge

quantitative shape measurements of distal volcanic ash 1 large scale volcanic eruptions produce fine ash 200 m which has a long atmospheric residence time 1 hour or more and can be transported great distances from the volcanic source thus becoming a hazard to aircraft and public health ash particles have irregular shapes so data on particle shape size and terminal velocities are needed to understand how the irregular shaped particles affect transport processes and radiative transfer measurements in this study a methodology was developed to characterize particle shapes sizes and terminal velocities for three ash samples of different compositions the shape and size of 2500 particles from 1 distal fallout 100 km of the 14 october 1974 fuego eruption basaltic 2 the secondary maxima 250 km of the 18 august 1992 spurr eruption andesitic and 3 the miocene ash hollow member nebraska rhyolitic were measured using image analysis techniques samples were sorted into 10 to 19 terminal velocity groups 0 6 59 0 cm s using an air elutriation device grain size distributions for the samples were measured using laser diffraction aspect ratio feret diameter and perimeter measurements were found to be the most useful descriptors of how particle shape affects terminal velocity these measurement values show particle shape differs greatly from a sphere commonly used in models and algorithms the diameters of ash particles were 10 120 larger than ideal spheres at the same terminal velocity indicating that irregular particle shape greatly increases drag gas adsorption derived surface areas are 1 to 2 orders of magnitude higher than calculated surface areas based on measured dimensions and simple geometry indicating that particle shapes are highly irregular correction factors for surface area were derived from the ash sample measurements so that surface areas calculated by assuming spherical particle shapes can be corrected to reflect more realistic values

quantitative scanning electron microscope analysis of volcanic ash surfaces application to the 1982 1983 galunggung eruption indonesia qualitative analyses of volcanic ash are time consuming and subjective whereas quantitative analyses are methodical and automated not only volcanic ash particles but also many natural particles have been widely described and quantified by their outlines the qualitative data of volcanic ash surfaces need to be expressed quantitatively supported by supplementary methods such as statistical analysis and artificial intelligence well defined surface descriptors can be applied to volcanic ash particles in this study roughness and texture descriptors of pyroclastic material from the 1982 1983 eruption of galunggung java indonesia were used to describe the vesicle surfaces of the particles alteration intensity and or fine particle abundance these parameters are important for distinguishing the products of magmatic eruptions from those of phre atomagmatic eruptions further application of this method may allow these descriptors to be easily converted to alteration grade vesicularity index intensity of the fragmentation mechanism and relative proportions of the pyroclast types hence discrimination between products of different fragmentation mechanisms may permit forecasting of volcanic hazards

use of fractal analysis for discrimination of particles from primary and reworked jokulhlaup deposits in se iceland abstract the morphology of sideromelane particles from jokulhlaup deposits in southeastern iceland has been studied by fractal analysis to assess post depositional changes associated with reworking fractal dimensions of particle boundaries were calculated from data obtained by the caliper and dilation methods most particles exhibit multifractal relationships with a textural d1 and structural d2 fractal dimension particles from primary jokulhlaup deposits have significantly greater textural and structural fractal dimensions compared to reworked deposits differences in the fractal dimensions indicate that reworking in the littoral zone has reduced both the amount of fine scale features on particle surfaces and the complexity of the overall particle shapes the caliper and dilation methods yield similar values of textural fractal dimension for each particle for the same particles the dilation method yields higher values of structural fractal dimension reworked particles used in this study can be effectively discriminated from primary particles using a combination of d1 and d2 fractal dimensions the results indicate that fractal analysis provides a useful quantitative characterization of complex volcanic particles and can be utilized to examine aspects of particle origin transport and deposition

a dayside ionospheric positive storm phase driven by neutral winds 1 this paper presents observations and numerical simulations of ionospheric and thermospheric disturbances associated with a moderate geomagnetic storm on 10 september 2005 during the event the incoherent radars located in millstone hill and arecibo observed a dayside positive storm phase as manifested by the enhanced electron density in the f region the universal time ut altitude profile of electron density measured by both radars displayed a structure that closely resembles the greek letter a similar structure is also reproduced by the thermosphere ionosphere electrodynamics general circulation model tiegcm this peculiar electron density distribution is found to be associated with vertical ion drift which initially was upward and then became downward using realistic time dependent ionospheric convection and auroral precipitation as inputs the tiegcm reveals that the primary cause of the positive storm response was the enhanced meridional neutral wind rather than the penetration magnetospheric electric field this study reiterates the importance of neutral wind effects on ionospheric disturbance

juvenile volcanic glass erupted before the appearance of the 1991 lava dome unzen volcano kyushu japan fugen dake the main peak of unzen volcano began to erupt on 17 november 1990 after 198 years of dormancy following a period of steam dominated tephra eruptions a new lava dome appeared at the bottom of jigokuato crater in the summit region on 20 may 1991 non hydrated vesiculated glass was detected in the precursory tephra eruptions beginning 12 february 1991 determination of whether glass pyroclasts are hydrated or not appears to be an effective means of ascertaining whether the tephra contains juvenile material from ascending magma the detection of juvenile pyroclasts at fugen dake more than 3 months before the appearance of the lava dome suggests that monitoring of early tephra emissions is an effective way to help forecast impending magmatic eruptions

merapi 2010 eruption chronology and extrusion rates monitored with satellite radar and used in eruption forecasting abstract despite dense cloud cover satellite borne commercial synthetic aperture radar sar enabled frequent monitoring of merapi volcano s 2010 eruption near real time interpretation of images derived from the amplitude of the sar signals and timely delivery of these interpretations to those responsible for warnings allowed satellite remote sensing for the first time to play an equal role with in situ seismic geodetic and gas monitoring in guiding life saving decisions during a major volcanic crisis our remotely sensed data provide an observational chronology for the main phase of the 2010 eruption which lasted 12 days 26 october 7 november 2010 unlike the prolonged low rate and relatively low explosivity dome forming and collapse eruptions of recent decades at merapi the eruption began with an explosive eruption that produced a new summit crater on 26 october and was accompanied by an ash column and pyroclastic flows that extended 8 km down the flanks this initial explosive event was followed by smaller explosive eruptions on 29 october 1 november then by a period of rapid dome growth on 1 4 november which produced a summit lava dome with a volume of 5 10 6 m 3 a paroxysmal vei 4 magmatic eruption with ash column to 17 km altitude destroyed this dome greatly enlarged the new summit crater and produced extensive pyroclastic flows to 16 km radial distance in the gendol drainage and surges during the night of 4 5 november the paroxysmal eruption was followed by a period of jetting of gas and tephra and by a second short period 12 h of rapid dome growth on 6 november the eruption ended with low level ash and steam emissions that buried the 6 november dome with tephra and continued at low levels until seismicity decreased to background levels by about 23 november our near real time commercial sar documented the explosive events on 26 october and 4 5 november and high rates of dome growth 25 m 3 s 1 an event tree analysis for the previous 2006 merapi eruption indicated that for lava dome extrusion rates 1 2 m 3 s 1 the probability of a large 1872 scale eruption was 10 consequently the order of magnitude greater rates in 2010 along with the explosive start of the eruption on 26 october the large volume of lava accumulating at the summit by 4 november and the rapid and large increases in seismic energy release deformation and gas emissions were the basis for warnings of an unusually large eruption by the indonesian geological agency s center for volcanology and geologic hazard mitigation cvghm and their volcano research and technology development center bpptk in yogyakarta warnings that saved thousands of lives

the fractal and multifractal dimension of volcanic ash particles contour a test study on the utility and volcanological relevance abstract image processing analysis is used to check the ability of the fractal dimension for quantitatively describing the shape of volcanic ash particles digitized scanning electron microscopy images of fine pyroclasts from the eruptions of monte pilato rocche rosse lipari italy are investigated to test the efficiency of the fractal dimension to discriminate between particles of different eruptive processes multivariate analysis of multiple fractal components allows distinction between magmatic particles and phreatomagmatic particles which however is less significant than the discrimination obtained in previous studies by the use of simple adimensional shape parameters approximation of the actual particle boundary and the not rotation invariant nature of the fractal data frequently result in a significant scatter of data points in the mandelbrot richardson plot such behavior obscures in some cases the actual information of particle shape and renders the discriminating power of fractal analysis less effective than classical shape descriptors data less affected by scatter reveal that phreatomagmatic particles of the monte pilato rocche rosse eruptions are true mono fractals whereas magmatic particles are multifractals the textural small scale fractal of magmatic particles is similar to the fractal dimension value of phreatomagmatic particles and is attributed to the rheological behavior of melt upon brittle fragmentation the structural large scale fractal of magmatic particles refers to the walls of ruptured vesicles that lay on the particle outline the high difference between the values of the textural and structural fractals of magmatic particles of the monte pilato rocche rosse eruptions suggests two distinct and independent processes in the formation of such pyroclasts at the scales corresponding to the textural fractal the fragmentation process is independent of vesicles magmatic fragmentation is not simply related to growth expansion interference and explosion of vesicles but to a brittle cracking of the highly viscous melt likely related to rapid decompression

temporal variation in volcanic ash texture during a vulcanian eruption at the sakurajima volcano japan abstract we discuss the process of vulcanian eruptions on the basis of temporal variation of the texture of andesitic volcanic ash ejected from the sakurajima volcano japan falling ash samples were collected every 2 50 min for petrological analysis these ash samples contained juvenile particles altered rock fragments and fragments of crystals here we subdivide the juvenile particles into blocky vesicular and fluidal particles because the crystallinities of the vesicular and fluidal particles are lower than those of the blocky particles we refer to the vesicular and fluidal particles as low crystallinity particles lcps and the blocky particles as high crystallinity particles hcps the temporal variation observed in ash texture reveals that the ratio of lcps to hcps lcp hcp was small at the initiation of the eruption and increased as the eruption progressed the higher microlite crystallinity in the hcps indicates crystallization under lower pressures for longer durations relative to the lcp magma the increase of the lcp hcp ratio during a single vulcanian eruption suggests that the emission of less viscous gas rich magma under a cap rock increases as the eruption progresses such temporal variation in ash texture reflects the transition from a sudden explosion to continuous ash emission during a vulcanian eruption

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

perils in distinguishing phreatic from phreatomagmatic ash insights into the eruption mechanisms of the 6 august 2012 mt tongariro eruption new zealand abstract the weak geophysical precursors of the 6 august 2012 te maari eruption of mt tongariro and a lack of obvious juvenile components in its proximal ballistic deposits imply that the eruption was caused by the sudden decompression of a sealed hot hydrothermal system strong magmatic signals in pre and post eruption gas emissions indicate that fresh magma had intruded to shallow levels shortly before this eruption here we examine the volcanic ash produced during the august eruption with the aim of determining whether juvenile magma was erupted or not the widely applied criteria for identifying fresh juvenile pyroclasts provided inconclusive results the te maari ash sorting and trend towards a unimodal grain size distribution increase with distance along the dispersal axis proximal to intermediate sites showing polymodal grain size distributions can be related to the re fragmentation of different pre existing lithologies overlapped erupted pulses and transport mechanisms and to particle aggregation between 69 and 100 vol of particles coarser than 3 and 45 75 vol of grains finer than 3 were sourced from the pre existing commonly hydrothermally altered vent area lavas and pyroclasts free crystals pyroxene plagioclase magnetite pyrite make up 0 23 vol of particles coarser than 3 and 22 41 vol of grains finer than 3 brown to black fragments of fresh glass are a small 1 15 vol but notable component under sem these blocky glassy particles are poorly vesicular and irregularly shaped some with fluidal or bubble wall surfaces and others with fragmented stepped surfaces and fine adhering ash in thin section they contain variable amounts of microlites within an isotropic groundmass the range in silica content of the microprobe analysed glass is very wide 56 77 wt and cannot be correlated to any specific particle textural type these chemically and texturally diverse glassy fragments are identical to mechanically broken pieces of country rock lavas and pyroclasts both their diversity and their match with vent country rocks argue strongly against a juvenile origin for the glassy fragments we conclude that rising magma provided only heat and gas into the overlying sealed vapour dominated hydrothermal system a landslide from this area led to a rapid decompression and ash was produced by top down hydrothermal explosions careful attention must be paid to the combination of compositions and textures of fine ash particles in such situations as well as to the context of their source vent in order to be confident that new magma has reached the surface

a physical mechanism of positive ionospheric storms at low latitudes and midlatitudes 1 a physical mechanism of the positive ionospheric storms at low latitudes and midlatitudes is presented through multi instrument observations theoretical modeling and basic principles according to the mechanism an equatorward neutral wind is required to produce positive ionospheric storms the mechanical effects of the wind 1 reduce or stop the downward diffusion of plasma along the geomagnetic field lines 2 raise the ionosphere to high altitudes of reduced chemical loss and hence 3 accumulate the plasma at altitudes near and above the ionospheric peak centered at around 30 magnetic latitudes daytime eastward prompt penetration electric field ppef if it occurs also shifts the equatorial ionization anomaly crests to higher than normal latitudes up to approximately 30 latitudes the positive ionospheric storms are most likely in the longitudes where the onset of the geomagnetic storms falls in the ionization production dominated morning noon local time sector when the plasma accumulation due to the mechanical effects of the wind largely exceeds the plasma loss due to the chemical effect of the wind the mechanism agrees with the multi instrument observations made during the supergeomagnetic storm of 7 8 november 2004 with 18 h long initial phase ip and 10 h long main phase mp the observations which are mainly in the japanese australian longitudes where the mp onset was in the morning 0600 lt 2100 ut show 1 strong positive ionospheric storms in ne nmax hmax global positioning system total electron content gps tec and 630 nm airglow intensity in both northern and southern hemispheres started at the morning 0600 lt mp onset and lasted for a day 2 repeated occurrence of strong eastward ppef events penetrated after the mp onset and superposed with westward electric field started before the mp onset and 3 storm time equatorward neutral winds inferred from 1 and 2 repeated occurrence of an unusually strong f3 layer with large density depletions around the equator was also observed during the morning noon mp

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

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

fractal geometry in the san andreas fault system it has been noted that the spatial distribution of earthquakes and the mode of strain release in the san andreas fault system is related to the complexity of fault geometry because of their rough appearance over many length scales faults can be regarded as fractal surfaces direct estimates of fractal dimension d of portions of the san andreas fault system between the northern gabilan range and the salton sea including the postulated extent of the great 1857 fort tejon earthquake are obtained from measured fault lengths analogous to the lengths of coastlines as discussed by mandelbrot regions characterized by complicated fault geometry are associated with larger values of d based on fault traces mapped at a scale of 1 750 000 d is 1 3 for this reach of the fault defined as a 30 km wide band about a main fault trace for that part near parkfield which could be associated with the nucleation of the 1857 earthquake d is 1 1 at this same scale d is 1 4 for the san andreas and related faults near san bernardino where the 1857 rupture stopped compared to 1 2 for the san andreas san juan fault segments near the point of arrest of the 1966 parkfield earthquake at finer map scales 1 24 000 and 1 62 500 critical lengths of 500 m and 1 km are identified which might relate to the extent of off san andreas fault offsets the critical lengths also suggest that fault geometry is not self similar if this fractal geometry persists through the seismic cycle it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault

dynamic variation of the auroral oval during intense magnetic storms the latitudinal variations of the noon sector polar cusp region and the nightside auroral oval were examined to investigate the auroral oval dynamics during three intense geomagnetic storms the variations were compared with the variation in ring current intensity i e dst and with changes of the interplanetary magnetic field bz component to determine the dominant parameter of the large scale polar region configuration changes during magnetic storms deviations of the polar cusp and the midnight auroral oval from their normal quiet time position are also compared to determine the occurrence of the large scale reconfiguration of the polar region geometry it is found that a the large 10 geomagnetic latitude equatorial shift of the auroral oval occurs in coordination with the equatorward motion of the polar cusp region b the polar cusp is displaced by a few degrees more than the nightside auroral oval near the peak of a magnetic storm c the midnight auroral oval recovers more slowly than the polar cusp region during the storm recovery phase and d the midnight oval and the noon sector polar cusp region move coherently with the southward variation of the interplanentary magnetic field bz but not necessarily with the dst intensity variations

two step development of geomagnetic storms using the dst index more than 1200 geomagnetic storms from weak to intense spanning over three solar cycles have been examined statistically interplanetary magnetic field imf and solar wind data have also been used in the study it is found that for more than 50 of intense magnetic storms the main phase undergoes a two step growth in the ring current that is before the ring current has decayed significantly to the prestorm level anew major particle injection occurs leading to a further development of the ring current and making dst decrease a second time thus intense magnetic storms may often be the result of two closely spaced moderate storms the corresponding signature in the interplanetary medium is the arrival of double structured southward imf at the magnetosphere

observations and simulations of the ionospheric and thermospheric response to the december 2006 geomagnetic storm initial phase 1 we have investigated the thermospheric and ionospheric response to the 14 15 december 2006 geomagnetic storm using a coupled magnetosphere ionosphere thermosphere cmit 2 0 model simulation in this paper we focus on observations and simulations during the initial phase of the storm about 8 h when the shock was driving changes in geospace the global ionospheric maps of total electron content tec ionosonde data at four stations and millstone hill incoherent scatter radar isr observations are compared with the corresponding simulation results from the cmit model the observations showed significant positive storm effects occurred in the atlantic sector after the onset of this storm the cmit model is able to capture the temporal and spatial variations of the ionospheric storm effects seen in the gps tec observations although the model slightly underestimates the daytime positive ionospheric storm in the south american sector the simulations are also in agreement with the ionosonde and isr ionospheric measurements term analysis of the ion continuity equation demonstrates that changes in the electric fields play a dominant role in generating the observed ionospheric positive storm effect in the american sector during the initial phase although neutral winds and composition changes also contribute the difference in the strength of the enhancements over north and south america can be explained by the slope of the topside electron density profiles in the two hemispheres in the southern hemisphere electron densities decrease slowly with altitude whereas the decrease is much more rapid in the northern winter hemisphere the electric fields therefore cannot cause large increases in electron density by uplifting the plasma so positive storm effects are small in the southern hemisphere compared with the northern hemisphere even though the increase in hmf2 is greater in the southern hemisphere nighttime changes in electron density in other longitude sectors are small because the topside electron densities also decrease slowly with altitude at night

processes controlling the shape of ash particles results of statistical ipa abstract ash particles have unique morphologies and shapes that are characteristic of certain fracture mechanisms and can be used to identify the type of fragmentation such as magmatic brittle or ductile fragmentation and phreatomagmatic molten fuel coolant interaction type fragmentation identifying these two different fragmentation processes is especially important in complex volcanic systems where both fragmentation processes can occur in this study image parameter analysis and statistical parameter analysis are used to compare ash particles from standardised magma fragmentation experiments with natural ash particles from the pleistocene lake purrumbete maar southeastern australia the pyroclastic lake purrumbete maar sequence containsvarious deposit types that show evidence for changing eruption conditions therefore it is of a main interest to determine the main fragmentation mechanism that formed these deposits a comparison with experimental ash particles revealed that lake purrumbete ash particles show significant differences from experimental samples of magmatic brittle type fragmentation whereas they show no significant differences from phreatomagmatic molten fuel coolant interaction type fragmentation samples indicating a predominance of phreatomagmatic fragmentation during the eruption of lake purrumbete the experiments further show that pre existing stresses also influence the particle shape and may be the reason for the absence of a significant similarity between most of the particle populations

color measurements of volcanic ash deposits from three different styles of summit activity at sakurajima volcano japan conduit processes recorded in color of volcanic ash abstract we measured quantitatively colors of volcanic ash deposits erupted from three different styles of summit activity strombolian activity vulcanian explosions and continuous ash venting activity at sakurajima volcano from 1974 to 1985 colors of strombolian ash samples have larger yellow components of their visible spectra b values than those of explosion and continuous venting ash samples colors of explosion ash samples show larger variation in both red and yellow components of their visible spectra a and b values respectively while colors of continuous venting ash samples are in the narrow ranges within colors of explosion ash samples colors of components with lower densities than 3 1 g cm 3 groundmass and phenocrystic plagioclase obtained by magnetic and heavy liquid separation methods are similar to the unseparated bulk ash samples this result suggests that the color variations of ash deposits are mainly originated from the particles composed of groundmass the particles can be classified into three different types of particles with different vesicularity and crystallinity vesicular particle vp dense particle with vesicles dpv and dense particle without vesicles dp analytical results of component proportions chemical compositions of groundmass glasses ferrous iron contents and surface ferric materials show that 1 vp has larger yellow components of the visible spectrum b values and high ferrous iron content and is less crystallized than the dp and dpv 2 dp has larger red and yellow components of its visible spectrum a and b values respectively and involves ferric materials on the surfaces produced by oxidation process and 3 dpv has smaller red and yellow components of its visible spectrum a and b values respectively and involves less ferric materials on the ash surfaces color differences of ash deposits from three different activity styles can be explained by the different mixing ratios of vp dpv and dp during the strombolian activity the vp is a main component in the ash which is formed from relatively less degassed and crystallized magma in the vulcanian explosion and continuous ash venting activity the proportions of dpv and dp in ash are larger than that in the strombolian activity the highly crystallized dp may correspond to a vent cap and dpv to a magma below the cap the color measurements of ash deposits provide information on the pre eruptive processes at the shallower levels of a conduit

constraining particle size dependent plume sedimentation from the 17 june 1996 eruption of ruapehu volcano new zealand using geophysical inversions weak subplinian plinian plumes pose frequent hazards to populations and aviation yet many key parameters of these particle laden plumes are to date poorly constrained this study recovers the particle size dependent mass distribution along the trajectory of a well constrained weak plume by inverting the dispersion process of tephra fallout we use the example of the 17 june 1996 ruapehu eruption in new zealand and base our computations on mass per unit area tephra measurements and grain size distributions at 118 sample locations comparisons of particle fall times and time of sampling collection as well as observations during the eruption reveal that particles smaller than 250 m likely settled as aggregates for simplicity we assume that all of these fine particles fell as aggregates of constant size and density whereas we assume that large particles fell as individual particles at their terminal velocity mass fallout along the plume trajectory follows distinct trends between larger particles d 250 m and the fine population d 250 m that are likely due to the two different settling behaviors aggregate settling versus single particle settling in addition we computed the resulting particle size distribution within the weak plume along its axis and find that the particle mode shifts from an initial 1 mode to a 2 5 mode 10 km from the vent and is dominated by a 2 5 to 3 mode 10 180 km from vent where the plume reaches the coastline and we do not have further field constraints the computed particle distributions inside the plume provide new constraints on the mass transport processes within weak plumes and improve previous models the distinct decay trends between single particle settling and aggregate settling may serve as a new tool to identify particle sizes that fell as aggregates for other eruptions

causes and consequences of pressurisation in lava dome eruptions abstract high total and fluid pressures develop in the interior of high viscosity lava domes and in the uppermost parts of the feeding conduit system as a consequence of degassing two effects are recognised and are modelled quantitatively first large increases in magma viscosity result from degassing during magma ascent strong vertical gradients in viscosity result and large excess pressures and pressure gradients develop at the top of the conduit and in the dome calculations of conduit flow show that almost all the excess pressure drop from the chamber in an andesitic dome eruption occurs during the last several hundred metres of ascent second microlites grow in the melt phase as a consequence of undercooling caused by gas loss rapid microlite growth can cause large excess fluid pressures to develop at shallow levels theoretically closed system microlite crystallization can increase local pressure by a few tens of mpa although build up of pressure will be countered by gas loss through permeable flow and expansion by viscous flow microlite crystallization is most effective in causing excess gas pressures at depths of a few hundred metres in the uppermost parts of the conduit and dome interior some of the major phenomena of lava dome eruptions can be attributed to these pressurisation effects including spurts of growth cycles of dome growth and subsidence sudden onset of violent explosive activity and disintegration of lava during formation of pyroclastic flows the characteristic shallow level long period and hybrid seismicity characteristic of dome eruptions is attributed to the excess fluid pressures which are maintained close to the fracture strength of the dome and wallrock resulting in fluid movement during formation of tensile and shear fractures within the dome and upper conduit

the cyclic and fractal seismic series preceding an mb 4 8 earthquake on 1980 february 14 near the virgin islands summary seismic activity in the 10 months preceding the 1980 february 14 mb 4 8 earthquake in the virgin islands reported on by frankel in 1982 consisted of four principal cycles each cycle began with a relatively large event or series of closely spaced events and the duration of the cycles progressively shortened by a factor of about 3 4 had this regular shortening of the cycles been recognized prior to the earthquake the time of the next episode of seismicity the main shock might have been closely estimated 41 days in advance that this event could be much larger than the previous events is indicated from time to failure analysis of the accelerating rise in released seismic energy using a non linear time and slip predictable foreshock model examination of the timing of all events in the sequence shows an even higher degree of order rates of seismicity measured by consecutive interevent times when plotted on an iteration diagram of a rate versus the succeeding rate form a triangular circulating trajectory the trajectory becomes an ascending helix if extended in a third dimension time this construction reveals additional and precise relations among the time intervals between times of relatively high or relatively low rates of seismic activity including period halving and doubling the set of 666 time intervals between all possible pairs of the 37 recorded events appears to be a fractal the set of time points that define the intervals has a finite non integer correlation dimension of 0 70 in contrast the average correlation dimension of 50 random sequences of 37 events is significantly higher close to 1 0 in a similar analysis the set of distances between pairs of epicentres has a fractal correlation dimension of 1 52 well defined cycles numerous precise ratios among time intervals and a non random temporal fractal dimension suggest that the seismic series is not a random process but rather the product of a deterministic dynamic system

seismotectonics of the aegean region abstract fault plane solutions neotectonic field observations and in situ stress measurements have been used to determine the stress field associated with the active deformation of the lithosphere in the aegean and surrounding regions a stress gradient and a zonal pattern of different tectonism away from the trench axis has been postulated pure thrust faulting occurs in the fore arc side while the back arc side is mainly dominated by almost n s extensional tectonics a narrow belt of strike slip faults with predominantly thrust component separates these tectonic zones this belt seems to represent a transition from the thrust type faults to normal faults fault plane solutions of the whole region in question indicate that both the large and small magnitude shocks are caused by the same regional stress field a body of 33 focal mechanisms indicates that the intermediate depth shocks along the sinking mediterranean slab are associated with thrust type fracturing orientation of kinematic axes favours the suggestion that shear zones within the descending slab cause these shocks the active crustal shortening along the hellenic consuming boundary and the sinking of the mediterranean lithosphere beneath the south aegean area explain satisfactorily the seismotectonic features of the fore arc and the southern back arc sides on the contrary geophysical evidence concerning the cenozoic geodynamic evolution of the aegean is needed to interpret features of the north back arc area

evolution of the temporal multifractal scaling properties of the chiayi earthquake ml 6 4 taiwan abstract variations in the fractal dimension of earthquakes have been suggested to be a precursor of a large earthquake however the physical characteristics and seismicity are always different along a large fault system and it is difficult to segment a large fault for further investigating therefore the fractal dimension of earthquakes on a given fault only reflects the average seismic characteristics of the area and may be unrelated to precursory activity in this paper the evolution of the temporal generalized fractal dimension dq of a seismic cluster within a small fault system associated with the chiayi earthquake ml 6 4 taiwan is investigated the earthquakes of this sequence are confined in small source volume and reflect the behavior of the local fault system our results show that the dq curve of the background stage is smooth with a low multifractal degree 0 36 and the seismicity is nearly monofractal in the chiayi region during the foreshock stage the seismicity becomes active such that not only the dq curve exhibits greater variability especially for the steep slope of dq curve at q 0 but also the temporal fractal dimension changes from nearly monofractal to multifractal in the aftershock stage the fluctuation of dq is large and the multifractal degree is up to 1 0 the temporal multifractal property becomes more pronounced as well finally when the seismicity returns to the background stage the dq curve becomes smooth and nearly monofractal again therefore the fluctuations in the dq spectrum of an earthquake cluster associated with a large earthquake not only give a clear picture of the temporal alterations in the seismogenic regimes but also illustrate their variability through time for a large earthquake in addition the variation of the slope of dq curve at q 0 in the foreshocks may be used as a precursor of a large earthquake

image processing analysis in reconstructing fragmentation and transportation mechanisms of pyroclastic deposits the case of monte pilato rocche rosse eruptions lipari aeolian islands italy abstract a quantitative study of particle morphology of samples from monte pilato rocche rosse deposits lipari aeolian islands italy shows a significant variability in particle structure and texture the study consisted of image processing techniques and multivariate statistical methods in analysis of the quantitative particle morphology data with the goal of identifying the genetic processes responsible for the formation of the deposits from these investigations we numerically define the form of the clasts thus avoiding subjectivity in the classification of clast morphology starting from this clast definition we then construct diagrams in which clasts due to different genetic processes i e magmatic vs hydromagmatic fragmentation are discriminated based on simple nondimensional parameters the application of the methods used seems to be of general interest in discriminating the fragmentation and transportation dynamics responsible for the formation of pyroclastic deposits