effects of h2o on elastic wave velocities in ultrabasic rocks at 900 c under 1 gpa simultaneous measurements of compressional and shear wave velocities vp and vs in five ultrabasic rocks with hydrous minerals were carried out from room temperature to 900 c under 1gpa in a closed system both vp and vs in all five rocks decreased markedly near 600 c and or 800 c following the dehydration of hydrous minerals in the rocks considering velocities only in the anhydrous matrix which were estimated from the volumetric ratio of forsterite and enstatite in each sample the effects of water produced by the dehydration reactions were estimated the ratio of v at 900 c under 1gpa is represented by the following equation v 1 0 0027 w to both p and s wave where v is the velocity in the rock including the extricated water w kg m 3 and is the velocity in the sample excluding the extricated water the low velocity layer lies between the descending lithosphere and the overlying asthenosphere beneath the japanese island arcs and the ratio of vp drop for the low velocity layer to that of the underlying descending lithosphere is approximately 5 if the observed velocity drop is wholly attributed to the free water produced by dehydration of serpentine minerals in the descending slab the required volumetric ratio of serpentine minerals in the descending slab would be 5 10

lightning associated with the 1992 eruptions of crater peak mount spurr volcano alaska abstract lightning occurred associated with the ash clouds of all three eruptions of mt spurr volcano in 1992 lightning was detected on seismograms as simultaneous spikes and simultaneous gain ranging a feature that normally lowers the gain at a station when the signal level begins to saturate spikes had typical durations of 0 04 0 05 s using uniform criteria we found 28 lightning flashes in the june 27th eruption 29 in the august 18th eruption and three in the september 17th eruption we measured peak voltages on station rso 94 km ssw to determine the relative strengths of lightning and found that the august lightning was strongest june weakest and september intermediate based on relative signal strengths at different stations we found evidence for different lightning geometries between the june and august eruptions during which prevailing winds blew the ash clouds to the north and east respectively for all three eruptions the first lightning was recorded 21 26 min after the onset of the eruption suggesting that charge separation occurred in the convecting cloud rather than at the vent data recorded by a bureau of land management lightning detection system for the august eruption showed negative polarities for the first 12 recorded flashes and a positive polarity for the last this suggests a charge separation based on particle size in which negative charge is found for larger particles which fall first and positive charge remains on smaller particles which remain suspended longer all three eruptions had similar durations of 3 5 4 h and tephra volumes of 44 56 million cubic meters the august eruption however produced stronger volcanic tremor 30 cm2 reduced displacement as compared with 16 cm2 for june and greater gas 400 120 kt so2 for august and 200 60 kt for june thus lightning strength correlates with both tremor amplitude and magmatic gas content the august eruption occurred during the lightest winds so the ash cloud and charge separation were vertically oriented and favored cloud to ground lightning the september eruption occurred during the coldest and driest atmospheric conditions which may explain the small amount of lightning in general volcanic lightning is important because it can help confirm that explosive eruptions are in progress although the value of the information may be limited by the long delay from eruption onset to first lightning and the variability of eruptive and atmospheric conditions

multiparametric observation of volcanic lightning sakurajima volcano japan we recorded volcanic lightning generated by vulcanian explosions at sakurajima volcano using a synchronized multiparametric array physical properties of lightning are related to plume dynamics and associated electromagnetic field variations are revealed by video observations high speed and normal speed together with infrasound and high sampling rate magnetotelluric signals data show that volcanic lightning at sakurajima mainly occurs in the plume gas thrust region at a few hundred meters above the crater rim where the overpressure of the turbulent volcanic jets determines the electrification of particles generating a complex charge structure in the growing plume organization of charges may be achieved at later stages when the plume transitions from the jet phase to the convective phase comparison with atmospheric sounding and maximum plume height data show that the effect of hydrometeors on flash generation at sakurajima is negligible and can be more prudently considered as an additional factor contributing to the electrification of volcanic plumes

migration of fluid phases and genesis of basalt magmas in subduction zones dehydration and hydration reactions in both the downgoing lithosphere and the overlying mantle wedge have been examined in order to understand the role of h2o in the production of magmas at convergent plate boundaries the subduction of oceanic lithosphere occurring with increasing pressures and rising temperatures causes liberation of h2o from the slab amphibole which can be stable to the highest pt conditions among hydrous phases in the slab decomposes at around 90 km depth it follows that the subducted lithosphere is essentially anhydrous beneath volcanic arcs lying more than 110 km above the slab and that the supply of slab derived h2o is not a direct trigger for the production of arc magmas instead the h2o released from downgoing lithosphere reacts with the forearc mantle wedge to crystallize hydrous minerals serpentine talc amphibole chlorite and phlogopite this hydrated peridotite is dragged downward on the slab toward higher pt regions and releases h2o to shallower potential magma source regions in the mantle wedge combining experimental data on the stability of serpentine and talc with the thermal structure in the mantle wedge it is concluded that those minerals decompose beneath the forearc region on the other hand high pt experimental and thermodynamic data suggest that dehydration of amphibole and chlorite in the downdragged hydrated peridotite can take place just beneath a volcanic front phlogopite in the peridotite decomposes to release h2o at a deeper level about 200 km h2o liberated from the hydrated peridotite causes partial melting of overlying mantle wedge peridotites along with the migration of h2o through the above processes subduction components especially large ion lithophile elements can be overprinted on the magma source region which governs the geochemical characteristics of arc magmas

volcanic source for fixed nitrogen in the early earth s atmosphere hot volcanic vents promote the thermal fixation of atmospheric n2 into biologically available forms the importance of this process for the global nitrogen cycle is poorly understood at masaya volcano nicaragua no and no2 are intimately associated with volcanic aerosol such that nox levels reach as much as an order of magnitude above local background in plume hno3 concentrations are elevated above background to an even greater extent 50 mmol m 23 we estimate the production efficiency of fixed nitrogen at hot vents to be 3 3 10 28 mol j 21 implying present day global production of 10 9 mol of fixed n per year although conversion efficiency would have been lower in a preoxygenated atmosphere we suggest that subaerial volcanoes potentially constituted an important source of fixed nitrogen in the early earth producing as much as 10 11 mol yr 21 of fixed n during major episodes of volcanism these fluxes are comparable to estimated nitrogen fixation rates in the prebiotic earth from other major sources such as bolide impacts and thunderstorm and volcanic lightning

the taiwan ryukyu subduction collision complex folding of a viscoelastic slab and the double seismic zone 1 the termination of the ryukyu trench against eurasia and the oblique subduction of the philippine sea plate create a subduction collision complex offshore taiwan which has not previously been elucidated in detail we combine traveltime data from the seismic networks in taiwan and japan to better illuminate how the subducting ryukyu slab deforms in this subduction collision zone more than 5000 events recorded by both networks were relocated with the double difference method using an optimal regional one dimensional velocity model the offshore seismicity indicates that the double seismic zone with a gap of 15 20 km exists in the subducting slab in the depth range of 40 80 km focal mechanisms suggest that the double seismic zone is caused by east west compression resulting from oblique convergence the improved hypocentral locations for the first time reveal folding of the slab into a horizontal curvature larger in magnitude than and opposite in sign to that of the ryukyu trench in the depth range 50 100 km the anomalous curvature together with the focal mechanisms suggests that the slab folds against the eurasian lithosphere and that this deformation cannot be fully elastic we model this deformation mode as the developing instability of a viscoelastic maxwell layer embedded in a viscous medium the characteristic wavelength of the instability i e 250 km is consistent with folding of a slab whose viscosity is 100 times higher than that of the surrounding mantle for an along strike elastic membrane strain as small as 0 01 or more than 3 orders of magnitude higher if 5 elastic strain is allowed

volcanic plume electrification experimental investigation of a fracture charging mechanism although ashfall from particulate volcanic plumes is known to be highly electrically charged little is known about the charging mechanism we describe experiments designed to investigate the particle charges generated from the fracture of pumice small silicate particles were produced in the laboratory during collisions between two samples cut from pumice clasts the net charge magnitudes detected on these particles are similar to those previously measured on ashfall from volcanic plumes 10 5 to 10 6 c kg 1 this net charge is also shown to be the result of a small imbalance between the sums of individual particle charges of both polarities which are up to several orders of magnitude larger than the net charge the magnitude of both the net and single polarity specific charges were only weakly affected by changes of relative humidity but single polarity charges increased steadily with increasing sample impact velocities the dominant charging process during the experiments was that of material fracture the charging mechanism is thus interpreted to be fractoemission the release of nuclear particles from fresh crack surfaces occurring during the production of the silicate particles this implies that the electrification of volcanic plumes could be the result of brittle fragmentation of magma or pumice clasts within the upper regions of the conduit and in the jet region of the plume

subkilometer martian volcanoes properties and possible terrestrial analogs kilometer to subkilometer cones with large central craters are the most numerous volcanic structures in the northern plains of mars based on examination of more than 12 000 high resolution viking orbiter images most of these very small cones are located in parts of eastern acidalia and utopia isidis elysium planitia measurements of base and pit diameter for some 2000 well resolved features show small variations in the histogram of base diameters between and within regions but remarkable similarity in the distribution of crater cone diameter ratios this suggests that the small cones had a similar origin with only minor variations in local conditions the acidalia cones are generally larger more widely distributed and occur on a greater variety of terrains than those in utopia isidis elysium based on morphology distribution and the crater cone ratio histograms the smallest martian cones may be similar to icelandic pseudocraters somewhat larger steeper cones with smaller crater cone ratios which also occur in eastern acidalia may be analogs of terrestrial cinder cones

observations of volcanic lightning during the 2009 eruption of redoubt volcano abstract observations of volcanic lightning during the eruption of redoubt volcano in march and april 2009 were made with the lightning mapping array during the eruption twenty three distinct episodes of volcanic lightning were observed electrical activity occurred as either a volcanic lightning storm with up to thousands of lightning discharges or as a weak electrical event with only a handful of lightning discharges during the volcanic lightning storms we observed two phases of electrical activity the explosive phase and the plume phase the explosive phase consisted of very small discharges on the order of 10 100 m occurring directly above the vent while an explosive eruption was ongoing whereas the plume phase was comprised of discharges occurring throughout the plume subsequent to the explosive eruption the area of discharges during the explosive phase ranged from less than 1 km2 to 50 km2 or more the electrical activity at the beginning of the plume phase was dominated by small discharges over time the horizontal extent of the flashes increased with the largest flashes occurring at the end of the plume phase the distribution of the horizontal size of the discharges over the lifetime of the storm indicate that the charge structure of the plume evolved from a complex and clumpy structure to a more simple horizontally stratified structure plume height was shown to be a key factor in the quantity of lightning in a storm the volcanic lightning storms occurred in plumes with column heights greater than 10 km the tall plumes may contribute to the efficiency of charge generation through ice collisions by providing strong updrafts from the large thermal energy input from the eruption

inferring compressible fluid dynamics from vent discharges during volcanic eruptions observations at numerous volcanoes reveal that eruptions are often accompanied by continual radio frequency crf emissions the source of this radiation however has remained elusive until now through experiments and the analysis of field data we show that crf originates from proximal discharges driven by the compressible fluid dynamics associated with individual volcanic explosions blasts produce flows that expand supersonically generating regions of weakened dielectric strength in close proximity to the vent as erupted materialcharged through fragmentation friction or other electrification processtransits through such a region pyroclasts remove charge from their surfaces in the form of small interparticle spark discharges or corona discharge discharge is maintained as long as overpressured conditions at the vent remain beyond describing the mechanism underlying crf we demonstrate that the magnitude of the overpressure at the vent as well as the structure of the supersonic jet can be inferred in real time by detecting and locating crf sources

subducting oceanic high causes compressional faulting in southernmost ryukyu forearc as revealed by hypocentral determinations of earthquakes and reflection refraction seismic data absolute earthquake hypocenter locations have been determined in the area offshore eastern taiwan at the southernmost ryukyu subduction zone location process is run within a 3d velocity model by combining the taiwanese and neighboring japanese networks and using the 3d maxi technique the study focuses on the most active seismic cluster in the taiwan region that occurs in the forearc domain offshore eastern taiwan earthquakes distribute mainly along 2 active planes the first one aligns along the subduction interface and the second one shallower affects the overriding margin focal mechanisms within the shallow group indicate that nodal planes are either compatible with high angle back thrusts or low angle thrusts the active seismic deformation exclusively indicates reverse faulting revealing that the forearc basement undergoes trench perpendicular strong compression by integrating the seismological image into the regional context we favor the hypothesis in which the dense seismicity occurring offshore marks the activity of en echelon high angle reverse faults accommodating the uplift of a broken piece of ryukyu arc basement called hoping basement rise the uplift is inferred to be caused by the subduction of an oceanic relief either exotic block seamount or oceanic crust sliver our favored solution satisfies the narrowness of epicenter s cluster along the hoping canyon and the observation of high angle active faults on seismic lines crossing the area furthermore this solution is compatible with the active uplift of the hoping rise demonstrated from morphological and sedimentological data we do not exclude the branching of the high angle reverse faults system onto a splay fault connected with the subduction interface but further investigations are needed to map precisely the 3d distribution of active faults that break the margin

the 2010 eruption of eyjafjallajokull lightning and plume charge structure six lightning mapping array lma stations were deployed in april 2010 around eyjafjallajokull volcano in southern iceland single station lma observations were made during the first explosive period 14 18 april and three dimensional lma observations were made during the second explosive period 5 22 may the single station observations revealed that continuous rf electrical activity caused by high rates of small vent discharges occurred during the first explosive period but not the second indicating that the strength of vent charging varied between the first and second explosive periods during the second explosive period very little lightning was detected between 5 and 10 may while moderate rates of lightning were detected between 11 and 21 may signaling that another change occurred on 11 may that affected plume electrification the data do not make clear if it was changing eruptive activity or changing meteorological activity that resulted in the sudden onset of lightning the plume charge structure during the second explosive period was inferred from the three dimensional lightning data showing that the dominant charge structure varied between a positive monopole and a negative over positive dipole the predominance of a low altitude region of positive charge and the observation that electrical activity was concentrated near the vent indicate that net positive vent charging was dominating the electrification

joint vp and vs tomography of taiwan implications for subduction collision orogeny abstract the taiwan orogen sitting at the pre rifted eurasian margin and bracketed by two sub orthogonal subduction systems is subject to complicated geotectonics motivating numerous seismic tomographic studies in local and regional scale most of them obtained p wave velocities vp or with vp vs ratio jointly but few were for s wave velocities vs with unprecedented amount of s wave data in this study a new set of well tuned vp vs and vp vs models were determined by an elaborate joint inversion scheme integrating the data of p and s wave travel times s p times and the borehole logging data for near surface correction into one system this allowed us to revisit the subduction collision process in detail by comparing vp vs and vp vs ratio simultaneously with enhanced slab imaging of philippine sea plate psp under northeast taiwan we are able to discriminate the plausible missing luzon forearc basement along the plate boundary and propose a skateboarding edge model in which the westernmost psp rides on the east subducted forearc basement and subducts northward underneath the eurasian lithosphere the underlain forearc basement along with the psp subduction then results in the anomalous shallow double seismic zone observed only near taiwan island meanwhile at around 121 e the north subducting psp seems dipping west to collide with the deep eurasian lithosphere shaping an irregular corner wedge structure in addition we evaluate our model with previous ones by waveform modeling approach and show the current performance of travel time tomography in taiwan region

correlated high speed video and radio interferometric observations of a cloud to ground lightning flash a six stroke cloud to ground lightning flash has been studied using observations from a high speed video camera 1000 frames s 1 and a vhf radio interferometer 1 s time resolution as well as additional electric magnetic and optical measurements the flash produced strokes along two channels to ground and a long 550 ms continuing current the video observations provided time resolved pictures of stepped and dart leaders short and long continuing currents and m components during the continuing currents and complemented and confirmed the interferometer observations of flash structure and development the m components were initiated by fast negative streamers inside the cloud which propagated into the conducting channel of the continuing current and subsequently brightened the channel to ground we call this sequence an m event dart leaders and the fast streamers of m and k events were found to be significantly brighter than stepped leaders and continuing currents to ground a number of streamers did not initiate m events that were identical to in cloud k streamers analysis of the m and k event occurrences indicated that the conducting channels of the continuing current both expanded and contracted with time an m type event was also observed during a dart leader it is proposed that the channel multiplicity within the flash resulted from cutoff of the channel to ground while charge continued to flow down the channel from the stroke source region stranding negative charge along the channel dart stepped leaders such as occurred during the third stroke are similarly explained because the stranded charge is observed to be greatest for initial strokes new channels to ground of stepped and dart stepped leaders are expected to follow initial strokes as is usually observed the video and electric field observations indicate that all return strokes have at least a short continuing current of the order of one or a few milliseconds the results also reinforce the well known observation that long continuing currents tend to follow relatively weak return strokes

dislocation model for crustal deformation in the longitudinal valley area eastern taiwan abstract three trilateration and leveling networks traversing the longitudinal valley eastern taiwan have been surveyed frequently during 1983 1988 average rates of length change on each line and height difference on each leveling section are used to study the crustal deformation of this area we model the aseismic deformation near the fault as the sum of a steady rigid block motion and the effect of an upper locked crust due to frictional resistance the effect of the locked part is equivalent to that of a negative dislocation on the fault for the northernmost hualien and central yuli networks we simply assume two blocks and one fault patch while the southernmost taitung network is modeled by three blocks and three fault patches the fault aforementioned is presumed to be the main trace of the longitudinal valley fault lvf we invert the geodetic data to determine the block motion and dislocation model parameters by utilizing a bayesian nonlinear inversion method parameters to be estimated include the three components of velocity for each block and the vertical and horizontal dislocation rates dip angle and width of each rectangular fault patch the estimated block motion parameters and fault widths are mostly well resolved by the observed data the fault widths are all very shallow tectonophysics vol 42 is concentrated on a quite narrow zone several kilometers wide centered at the lvf however due to the limited aperture of our geodetic networks the total width of the deformation zone and the velocity of relative plate motion at this active collision boundary are not resolved the new gps satellite survey technique can be used to solve this ambiguity

3d topography of the moho discontinuity in the taiwan area as extracted from travel time inversion of pmp phases abstract the reflective signals are often used to find a particular reflective interface therefore we used the travel time of the pmp phase to investigate the moho depth beneath taiwan in this study we used the directionality and rectilinearity functions to increase the accuracy and the convenience of the pmp phase identification in all we selected 1054 earthquakes with 13 715 travel time data of the pmp phase to invert the attitude of the moho discontinuity from the results we offer these conclusions 1 the distribution of the moho depth in taiwan trends nne ssw which is consistent with the topography 2 the deepest part of the moho discontinuity is beneath the central mountain range 38 km in depth and the depth of the moho discontinuity beneath the peikang basement high is only 26 km 3 the western coastal plain is divided into an active continental margin and a passive continental margin by the peikang basement high 4 the moho depth beneath the northern part of the coastal range is deeper than the southern part because of more vigorous collision activity

crust mantle boundaries in the taiwan luzon arc continent collision system determined from local earthquake tomography and 1d models implications for the mode of subduction polarity reversal abstract in order to better understand the mode of subduction polarity reversal in the taiwan luzon arc continent collision zone we mapped its crust mantle boundaries using local earthquake tomography by contouring surfaces of constant vp 7 5 km s 1 we identified three moho discontinuities and the plate interface that juxtaposes eurasian lower crust against mantle lithosphere of the philippine sea plate the plate interface dips to the east under southeastern taiwan and steepens progressively towards north until it becomes vertical at 23 7 n from there it continues northward in a vertical orientation until the limit of the tomographic model inhibited further mapping for the moho additional depth constraints were derived from 1d models using p wave arrivals of local earthquakes the mohos of the eurasian and philippine sea plates are disconnected across the plate interface beneath southern taiwan the eurasian moho dips to the east at 50 60 following the orientation of the plate boundary and continuous with the benioff zone towards north the eurasian moho steepens into subvertical again together with the plate boundary the philippine sea plate moho exhibits a synform like crustal root interpreted as the base of the magmatic luzon arc towards the north this root deepens from 30 to 70 km underneath the ryukyu trench in northernmost taiwan the hinge of the vertically subducting eurasian slab steps westward out of the thrust belt leaving the deformation front to the east inactive and giving way to the north dipping philippine sea plate a subhorizontal moho at 30 35 km depth overlies the north dipping philippine sea slab and is interpreted as a newly formed moho established after westward rollback and delamination of the subducting eurasian slab in combination these data support a model of progressive subduction polarity reversal in which a tear within the eurasian lithosphere propagated southwestward deactivating the deformation front

toward real time regional earthquake simulation ii real time online earthquake simulation ros of taiwan earthquakes abstract we developed a real time online earthquake simulation system ros to simulate regional earthquakes in taiwan the ros uses a centroid moment tensor solution of seismic events from a real time moment tensor monitoring system rmt which provides all the point source parameters including the event origin time hypocentral location moment magnitude and focal mechanism within 2 min after the occurrence of an earthquake then all of the source parameters are automatically forwarded to the ros to perform an earthquake simulation which is based on a spectral element method sem a new island wide high resolution sem mesh model is developed for the whole taiwan in this study we have improved sem mesh quality by introducing a thin high resolution mesh layer near the surface to accommodate steep and rapidly varying topography the mesh for the shallow sedimentary basin is adjusted to reflect its complex geometry and sharp lateral velocity contrasts the grid resolution at the surface is about 545 m which is sufficient to resolve topography and tomography data for simulations accurate up to 1 0 hz the ros is also an infrastructural service making online earthquake simulation feasible users can conduct their own earthquake simulation by providing a set of source parameters through the ros webpage for visualization a shakemovie and shakemap are produced during the simulation the time needed for one event is roughly 3 min for a 70 s ground motion simulation the ros is operated online at the institute of earth sciences academia sinica http ros earth sinica edu tw our long term goal for the ros system is to contribute to public earth science outreach and to realize seismic ground motion prediction in real time

using lightning observations as a volcanic eruption monitoring tool lightning commonly occurs in the eruption columns produced by explosive volcanic eruptions there are several different kinds of lightning detection instruments that could be employed to help monitor volcanoes each with their own advantages and disadvantages very low frequency vlf instruments have the ability to detect lightning at long ranges but tend to have low sensitivity due to network geometry and typically can provide only the time and 2 d location of a cloud to ground return stroke or similar high amplitude pulse produced by an intracloud discharge low frequency lf and medium frequency mf instruments typically have more sensitivity than a vlf network but can only be used for detection on a regional scale very high frequency vhf lightning mapping instruments also provide only regional coverage but detect all lightning within their range during the 2009 eruption of redoubt volcano alaska usa each of these types of instruments detected lightning from redoubt s ash plume the vhf system consistently detected lightning before the other two during each distinct explosive event and also detected more lightning than the others by one or two orders of magnitude lightning observations could be used to confirm and in some cases detect explosive volcanic activity the rapid response provided by lightning monitoring is a valuable tool for fast identification of potentially hazardous ash clouds

charge mechanism of volcanic lightning revealed during the 2010 eruption of eyjafjallajokull 1 volcanic lightning has intrigued observers through the centuries several likely processes have been proposed to explain the electrification of volcanic plumes including quenching magma water interactions the fracturing or internal friction of fine grained ash and the freezing of plume water at height scarce measurements of volcanic lightning have not been able to distinguish between proposed ideas the eyjafjallajokull volcanic eruption in iceland in april may 2010 may have revealed its charge mechanism during its 39 days the eruption went through a few phases while the conditions of the ambient atmosphere also changed but at different times the most surprising change in the lightning activity occurred on 11 may with no obvious change in the physical eruption character or strength during 3 10 may there was no lightning recorded by long range networks followed by intense activity 11 20 may the change in lightning activity coincided with a change in the conditions of the ambient atmosphere at this time the altitude of the isotherms for droplet freezing about 20 c dropped drastically below the plume top therefore it appears that the atmospheric conditions around the plume were influencing or even controlling some of the lightning activity the critical plume top temperature which appears to have turned on and off the observed lightning activity during the eyjafjallajokull eruption is estimated to be between 20 and 24 c we conclude that a significant charge generation process of the observed volcanic lightning is probably analogous to processes in meteorological thunderclouds

crustal scale seismic profiles across the manila subduction zone the transition from intraoceanic subduction to incipient collision 1 we use offshore multichannel seismic mcs reflection and wide angle seismic data sets to model the velocity structure of the incipient arc continent collision along two trench perpendicular transects in the bashi strait between taiwan and luzon this area represents a transition from a tectonic regime dominated by subduction of oceanic crust of the south china sea west of the philippines to one dominated by subduction and eventual collision of rifted chinese continental crust with the luzon volcanic arc culminating in the taiwan orogeny the new seismic velocity models show evidence for extended to hyperextended continental crust 10 15 km thick subducting along the manila trench at 20 5 n along transect t1 as well as evidence indicating that this thinned continental crust is being structurally underplated to the accretionary prism at 21 5 n along transect t2 but not along t1 to the south coincident mcs reflection imaging shows highly stretched and faulted crust west of the trench along both transects and what appears to be a midcrustal detachment along transect t2 a potential zone of weakness that may be exploited by accretionary processes during subduction an additional seismic reflection transect south of t1 shows subduction of normal ocean crust at the manila trench

the electrification of volcanic jets and controlling parameters a laboratory study abstract lightning is ubiquitous in large ash rich eruptions however the quantification of the link between volcanic and electrical activities is still missing hindering its potential for monitoring explosive eruptions here we focus on vent lightning i e discharges occurring within the ash laden jet we use a shock tube apparatus generating jets with variable mass of ash grain size distribution and initial overpressure the experimental jet is directed inside a faraday cage where the current flux of electrical charges is measured allowing to estimate the total charge of the plume and the number and magnitude of jet to ground discharges three mechanisms control the electrical structure of the jet i the tribocharging of the ash particles against the shock tube walls ii the particle particle tribocharging in the jet flow iii the particle and charge separation according to the particle size leading to the formation of clusters of electrical charges the number and magnitude of discharges mainly rely on the two latter mechanisms while the particle particle interactions define the total charge in all the clusters which is linked to the observed cumulative magnitude of the discharges the jet structure defines the size of the individual clusters and in turn how the cumulative magnitude is partitioned on a number of discharges finally our experimental relationships between eruptive and electrical parameters are compatible with field observations suggesting that the pattern of discharges recorded by electrical monitoring systems can be used to interpret the structure of volcanic jets and their dynamic evolution

preliminary result of magnetotelluric soundings in the fold thrust belt of taiwan and possible detection of dehydration abstract until the magnetotelluric mt soundings were conducted in the last two years there was no systematic view of the deep electric conductivity in the fold thrust belt of the taiwan orogen being a typical example of arc continental collision presented in this paper are the initial results and preliminary interpretation of the mt survey in taiwan the determinant response of the impedance tensor was calculated for inversion and occam s inversion which could generate smooth models was mainly used for interpreting mt data at each site the existence of a conductive zone with depths of 10 20 km beneath the island of taiwan is undoubtedly the most important feature found in this study the depths are well correlated with the inferred depth of dehydration reactions of suppe 1981 and the top of the aseismic lower crust observed by wang et al 1994 thus the authors believe that the cause of this conductive zone is probably the fluids released from dehydration reactions additionally close to the lishan fault the mt data show strong distortions which may be the result of induction in more complex three dimensional structures further multi dimensional analysis of the data is required in the future for delineating a more realistic image of the subsurface heterogeneous structure

short time electrical effects during volcanic eruption experiments and field measurements laboratory experiments on the fragmentation and expansion of magmatic melt have been performed using remelted volcanic rock at magmatic temperatures as magma simulant a specially designed dc amplifier in combination with high speed data recording was used to detect short time electrostatic field effects related to the fragmentation and expansion history of the experimental system as documented by simultaneous force and pressure recording as well as by high speed cinematography it was found that 1 the voltage time ratio of electrostatic field gradients 100 to 104 v s reflects different physical mechanisms of fragmentation and expansion and 2 the maximum voltage measured in 1 m distance 0 1 to 180 v can be correlated with the intensity of the respective processes based on these experimental results a field method was developed and tested at stromboli volcano in italy a 0 8 m rod antenna was used to detect the dc voltage against local ground i e the electrostatic field gradient at a distance of 60 to 260 m from the respective vent upwind position of the detection site was chosen to prevent interference caused by contact of charged ash particles with the antenna a standard 8 hz geophone was used to detect the accompanying seismicity three types of volcanic activity occurred during the surveillance operation two of these could be clearly related to specific electrical and seismical signals a typical delay time was found between the electrical and the seismical signal corresponding to the seismic velocity within the crater deposits using a simple first order electrostatic model the field measurements were recalibrated to the laboratory scale comparison of field and laboratory data at first approximation revealed striking similarities thus encouraging the further development of this technique for real time surveillance operation at active volcanoes

evaluation of the electrical properties of dust storms by multi parameter observations and theoretical calculations abstract dusty phenomena such as wind blown sand dust devils and dust storms play key roles in earth s climate and geological processes dust electrification considerably affects the lifting and transport of dust particles however the electrical properties of dust storms remain poorly understood here we conducted multi parameter measurements and theoretical calculations to investigate the electrical properties of dust storms and their application to dust storm prediction the results show that the vertical electric field e field decreases first then increases and finally decreases with the height above the ground reversing its direction at two heights 8 12 and 24 m this suggests that the charge polarity of dust particles changes from negative to positive and back to negative again as the height increases by carefully analyzing the e field and dust concentration data we further found that there is a significant positive linear relationship between the measured e field intensity and dust concentration at the given ambient conditions in addition measurements and calculations demonstrate that a substantial enhancement in the vertical e field can be observed several hours before the arrival of the external source dust storms indicating that the e field can be used to provide an early warning of external source dust storms

investigating the origin of continual radio frequency impulses during explosive volcanic eruptions volcanic lightning studies have revealed that there is a relatively long lasting source of very high frequency radiation associated with the onset of explosive volcanic eruptions that is distinct from radiation produced by lightning this very high frequency signal is referred to as continual radio frequency crf due to its long lasting nature the discharge mechanism producing this signal was previously hypothesized to be caused by numerous small 10 100m leader forming discharges near the vent of the volcano to test this hypothesis a multiparametric data set of electrical and volcanic activity occurring during explosive eruptions of sakurajima volcano in japan was collected from may to june 2015 our observations show that a single crf impulse has a duration on the order of 160ns giving an upper limit on discharge length of 10m and is distinct from near vent lightning discharges that were on the order of 30m in length crf impulses did not produce discernible electric field changes and occurred in the absence of a net static electric field lightning mapping data and infrared video observations of the eruption column showed that crf impulses originated from the gas thrust region of the column these observations indicate that crf impulses are not produced by small leader forming discharges but rather are more similar to a streamer discharge likely on the order of a few meters in length plain language summary this paper investigates the origin of a radio frequency rf signal previously termed continual rf that has been detected from the ash plumes of explosive volcanic eruptions continual rf had been hypothesized to be caused by many very small lightning like discharges on the order of 100m in length occurring at the vent of the volcano to test this hypothesis we conducted a multiparametric observational experiment at sakurajima volcano in japan we measured continual rf during eruptions of sakurajima in 2015 and found that continual rf is a collection of short duration rf impulses on the order of 160ns in duration these rf impulses are distinct from those typically produced by lightning we also observed small 30 m lightning discharges occurring near the volcanic vent that were distinct from the source of continual rf our observations show that continual rf is caused by an electrical discharge that is more simple than even a very small approximate to 100m lightning discharge we conclude that continual rf is caused by numerous small electrical discharges similar to streamer discharges on the order of a few meters in length

measurements of electric charge distribution in volcanic plumes at sakurajima volcano japan measurements of perturbations in the atmospheric potential gradient around volcanic plumes at multiple from two to five sites and measurements of the charge mass ratio of ash particles falling from volcanic plumes were carried out at sakurajima volcano japan results from 28 and 29 october 1995 show that the nature of the perturbations depends on the intensity of plume activity although plume activity was vigorous on 28 october negative perturbations were predominant as plume activity peaked the magnitude of negative perturbations decreased just below the plume and increased at an off axis site during the peak period positively charged ash particles fell out from the plume this suggests that the active plume dominantly contained negatively charged materials and that positively and negatively charged materials were added to the lower and upper parts of the plume respectively during the peak period on the other hand as plume activity became less vigorous on 29 october the perturbations were characterized by a positive anomaly followed by a negative anomaly because wind velocity increased with altitude that day we infer that positive and negative charges were distributed in the upper and lower parts of the plume respectively the differences in perturbations observed on 28 and 29 october suggest that volcanic plumes are generally composed of three parts an upper part with positively charged gas and aerosol a middle part with negatively charged fine ash particles and a lower part with positively charged coarse ash particles the compilation of present and previous results from sakurajima and other volcanoes indicates that the effect of the negative charge in the middle part was predominant in most cases although positive perturbations caused by the upper part were observed around some weak plumes the effect of positively charged particles in the lower part was observable only when plume activity was sufficiently strong because positively charged coarse particles tended to fall out near the vent

three dimensional p and s wave velocity structures beneath taiwan deep structure beneath an arc continent collision the island of taiwan is a byproduct of one of the few active collisions between a continent represented by the eurasian continental shelf and an island arc represented by the northern extension of the luzon arc on the philippine sea plate to understand better the evolution and current tectonics of this collision we selected 1260 well recorded earthquakes from an initial set of 50 000 located by the taiwan telemetered seismograph network for the determination of one and three dimensional p and s wave velocity structures beneath the island the results for both structures and earthquake relocations reveal that the island is divided tectonically into three distinct zones in the east the philippine oceanic plate is underthrusting the eurasian plate east of a north south boundary that is well defined by both seismic activity and a region of high velocity in the south the eurasian continental plate is underthrusting the philippine sea plate south of an east west boundary at about 23 n that is sharply defined by both subcrustal seismicity and a zone of relatively low velocities the dip of the subducted continent is shallow until it reaches the luzon island arc 50 km east of the main island structure under the main part of the island north of 230n reveals a shallow dipping zone of low velocities in the west above 25 km depth that narrows and steepens below that depth to at least 50 km beneath the central range the dip of this low velocity region is outlined by a narrow zone of seismicity that extends to depths of 100 km this seismic zone lies in a velocity saddle and marks an apparent offset in the central low velocity region at 24 n evidence for the subduction of the eurasian continent beneath taiwan therefore exists everywhere beneath the island and the low velocity regions in the mantle support but do not require the subduction of some 6 16 km of lower continental crust to depths of at least 50 km the distinct change in both the velocity structure and the seismic activity at 23 n and the offset of the low velocity regions at 24 n argue for abrupt changes in the nature of subduction across these latitudes these changes may be caused by an interaction of the luzon island arc with the subducted continental shelf that mimics a similar interaction evident at the surface finally the velocity structure of the subducting philippine sea plate suggests that the earthquakes beneath 70 km depth are not occurring within the highest velocity regions of the plate but are probably located near the upper edge of the plate there is also evidence from earthquake locations and velocity structure that suggests that the subducting plate is segmented and that subduction is presently occurring as far south as 22 n

influence of particle aggregation on deposition of distal tephra from the may 18 1980 eruption of mount st helens volcano the may 18 1980 eruption of mount st helens msh produced an extensive ashfall deposit in washington idaho and montana with a minumum volume of 0 55 km3 tephra an unusual feature of the deposit is the occurrence of a second thickness maximum 325 km ene of msh near ritzville washington grain size and component abundance analysis of samples along the main dispersal axis indicates that ash in this region is very fine grained mean size 22 m poorly sorted polymodal and rich in glass shards and pumice fragments a computer simulation of ash fallout from an atmospherically dispersed eruption plume was developed to evaluate various hypotheses for the origin of the distal ash characteristics particularly the thickness versus distance relationship the model was constrained by observations of the eruption column height elevation of major ash transport lateral spreading of the eruption plume and atmospheric wind structure in the vicinity of msh results of different simulations indicate that the second thickness maximum cannot be attributed to either decreased wind velocities over central washington or injection of fine ash above the horizontal wind velocity maximum near the tropopause for the model to fit the observed characteristics of the deposit significant particle aggregation of ash finer than 63 m must be invoked the best fit occurs when ash less than 63 m is aggregated into particles several hundred microns in diameter with a settling velocity of 0 35 m s support for this process comes from the observation and collection of fragile ash clusters of similar size which fell at pullman washington during the may 18 eruption sorem 1982 the premature fallout of fine ash as particle aggregates is a fundamental process in the origin of the grain size characteristics variations in component abundances and thickness versus distance relationship of the may 18 msh ash fall deposit

geodynamic evolution of the taiwan luzon mindoro belt since the late eocene abstract the structural framework of the taiwan luzon mindoro belt or festoon is described following three major transects the luzon transect with active subduction and active island arc the taiwan transect with active collision the mindoro transect with active subduction and inactive collision based on this geological study and on available geophysical data a model for the geodynamic evolution of this portion of the philippine sea and eurasia plates boundary is proposed in a succession of reconstructions between the late eocene and the present the major geodynamic events are 1 1 beginning of the opening of the south china sea s c s in lower oligocene times contemporaneous with obduction of the zambales and angat ophiolites on luzon 2 2 subduction of a mesozoic oceanic basin along the proto manila trench from the upper oligocene to the lower miocene 3 3 obduction of the south china sea oceanic crust onto the chinese and reed bank calamian passive margins in middle miocene time 14 15 ma related to a major kinematic reorganization end of opening of the s c s 4 4 beginning of collision between the luzon microblock and the two margins of the s c s in the upper miocene 7 ma collision is still active in taiwan whereas it stopped in mindoro during the pliocene

magnetotelluric pulses generated by volcanic lightning at sakurajima volcano japan 1 continuous magnetotelluric mt measurements were conducted at sakurajima volcano japan revealing syn eruption electric pulses and sometimes accompanying geomagnetic pulses movies of the eruptions recorded with timing provided by a gps clock show a large number of volcanic lightning flashes some mt pulses occurred simultaneously with lightning flashes pulses were observed more than 10 seconds after the onset of the eruption and tend to occur during eruptions that emit volcanic ash to high altitudes pulses were more common during mild eruptions rather than during vulcanian eruptions the observations suggest that the dominant mechanism of volcanic lighting is similar to that of lightning in thunderstorms in that it requires the collision of particles and subsequent separation of positive and negative charge

characterization and applications of vlf lf source locations from lightning using the huntsville alabama marx meter array 1 arrays that detect and locate the four dimensional spacetime positions of radiation sources from lightning have largely utilized sensors sensitive to the very high frequency vhf regime with 15 km baselines or very low frequency low frequency vlf lf regime with 100 km baselines this paper details initial results from the newly developed huntsville alabama marx meter array hamma consisting of marx meters electric field change meters sensitive to a frequency band 1 hz to 400 khz the arrival time of hamma waveforms due to radiation sources from lightning are used to determine the spacetime position of these sources the locations are compared with two well documented and operational arrays the national lightning detection network nldn and the north alabama lightning mapping array nalma the standard deviation of the difference between hamma and nldn locations of return strokes is 305 and 266 m in x and y respectively while the standard deviation of the difference between hamma and nalma sources is 237 226 and 688 m in x y and z respectively we further show that nldn intracloud locations differ in horizontal distance from the corresponding hamma locations by a median value of 479 m in addition we use hamma source locations to map several lightning flashes in the vlf lf and show hamma sources largely map out the same electrical extent as vhf sources and provide unique insights to the properties of the discharges occurring finally we show that vlf lf sources can determine the leader polarity in several example flashes but not necessarily whether a flash comes to ground copyright 2013 american geophysical union all rights reserved

size limits for rounding of volcanic ash particles heated by lightning volcanic ash particles can be remelted by the high temperatures induced in volcanic lightning discharges the molten particles can round under surface tension then quench to produce glass spheres melting and rounding timescales for volcanic materials are strongly dependent on heating duration and peak temperature and are shorter for small particles than for large particles therefore the size distribution of glass spheres recovered from ash deposits potentially record the short duration high temperature conditions of volcanic lightning discharges which are hard to measure directly we use a 1 d numerical solution to the heat equation to determine the timescales of heating and cooling of volcanic particles during and after rapid heating and compare these with the capillary timescale for rounding an angular particle we define dimensionless parameters capillary fourier stark biot and peclet numbers to characterize the competition between heat transfer within the particle heat transfer at the particle rim and capillary motion for particles of different sizes we apply this framework to the lightning case and constrain a maximum size for ash particles susceptible to surface tension driven rounding as a function of lightning temperature and duration and ash properties the size limit agrees well with maximum sizes of glass spheres found in volcanic ash that has been subjected to lightning or experimental discharges demonstrating that the approach that we develop can be used to obtain a first order estimate of lightning conditions in volcanic plumes

correlating the electrification of volcanic plumes with ashfall textures at sakurajima volcano japan abstract volcanic lightning detection has become a useful resource for monitoring remote under instrumented volcanoes previous studies have shown that the behavior of volcanic plume electrification responds to changes in the eruptive processes and products however there has not yet been a study to quantify the links between ash textures and plume electrification during an actively monitored eruption in this study we examine a sequence of vulcanian eruptions from sakurajima volcano in japan to compare ash textural properties grain size shape componentry and groundmass crystallinity to plume electrification using a lightning mapping array and other monitoring data we show that the presence of the continual radio frequency crf signal is more likely to occur during eruptions that produce large seismic amplitudes 7 m and glass rich volcanic ash with more equant particle shapes we show that crf is generated during energetic impulsive eruptions where charge buildup is enhanced by secondary fragmentation milling as particles travel out of the conduit and into the gas thrust region of the plume we show that the crf signal is influenced by a different electrification process than later volcanic lightning by using volcanic crf and lightning to better understand the eruptive event and its products these key observations will help the monitoring community better utilize volcanic electrification as a method for monitoring and understanding ongoing explosive eruptions

volcanic lightning global observations and constraints on source mechanisms lightning and electrification at volcanoes are important because they represent a hazard in their own right they are a component of the global electrical circuit and because they contribute to ash particle aggregation and modification within ash plumes the role of water substance water in all forms in particular has not been well studied here data are presented from a comprehensive global database of volcanic lightning lightning has been documented at 80 volcanoes in association with 212 eruptions the volcanic explosivity index vei could be determined for 177 eruptions eight percent of vei 3 5 eruptions have reported lightning and 10 of vei 6 but less than 2 of those with vei 1 2 these findings suggest consistent reporting for larger eruptions but either less lightning or possible under reporting for small eruptions ash plume heights 142 observations show a bimodal distribution with main peaks at 7 12 km and 1 4 km the former are similar to heights of typical thunderstorms and suggest involvement of water substance whereas the latter suggest other factors contributing to electrical behavior closer to the vent reporting of lightning is more common at night 56 and less common in daylight 44 reporting also varied substantially from year to year suggesting that a more systematic observational strategy is needed several weak trends in lightning occurrence based on magma composition were found the bimodal ash plume heights are obvious only for andesite to dacite basalt and basaltic andesite evenly span the range of heights and rhyolites are poorly represented the distributions of the latitudes of volcanoes with lightning and eruptions with lightning roughly mimic the distribution of all volcanoes which is generally flat with latitude meteorological lightning on the other hand is common in the tropics and decreases markedly with increasing latitude as the ability of the atmosphere to hold water decreases poleward this finding supports the idea that if lightning in large deep eruptions depends on water substance then the origin of the water is primarily magma and not entrainment from the surrounding atmosphere seasonal effects show that more eruptions with lightning were reported in winter bounded by the respective autumnal and vernal equinoxes than in summer this result also runs counter to the expectations based on entrainment of local water vapor

tomographic inversion of local earthquake data from the hengill grensdalur central volcano complex iceland parameters is generally low however a quantitative analysis of resolution provides an unambiguous assessment of well resolved volumes within the better resolved regions of the model the averaging volumes are 1 2 km and 2 4 km in vertical and horizontal extent respectively results of tomographic inversion image three distinct bodies of anomalously high velocity two of these extend from near the surface to a depth of about 3 km these high velocity volumes are located directly beneath the surface expressions of the extinct grensdalur volcano and the extinct husmuli basalt shield the third high velocity structure occurs in the depth range of 3 4 km but does not extend to the surface these three high velocity bodies are interpreted to be solidified magmatic intrusions relatively low velocities underlay limited portions of the trace of the present accretionary axis and a low velocity body is imaged in the roots of the active hengill volcano the volume of lower velocities located beneath the surface expression of the hengill volcano is interpreted to be a region of partial melt

physical properties of volcanic lightning constraints from magnetotelluric and video observations at sakurajima volcano japan abstract the lightning generated by explosive volcanic eruptions is of interest not only as a promising technique for monitoring volcanic activity but also for its broader implications and possible role in the origin of life on earth and its impact on the atmosphere and biosphere of the planet however at present the genetic mechanisms and physical properties of volcanic lightning remain poorly understood as compared to our understanding of thundercloud lightning here we present joint magnetotelluric mt data and video imagery that were used to investigate the physical properties of electrical discharges generated during explosive activity at sakurajima volcano japan and we compare these data with the characteristics of thundercloud lightning using two weeks of high sensitivity high sample rate mt data recorded in 2013 we detected weak electromagnetic signals radiated by volcanic lightning close to the crater by carefully inspecting all mt waveforms that synchronized with visible flashes and comparing with high speed 3000 frame s and normal speed 30 frame s videos we identified two types of discharges the first type consists of impulses type a and is interpreted as cloud to ground cg lightning the second type is characterized by weak electromagnetic variations with multiple peaks type b and is interpreted as intra cloud ic lightning in addition we observed a hybrid mt event wherein a continuous weak current accompanied type a discharge the observed features of volcanic lightning are similar to thunderstorm lightning and the physical characteristics show that volcanic lightning can be treated as a miniature version of thunderstorm lightning in many respects the overall duration length inter stroke interval peak current and charge transfer all exhibit values 1 2 orders of magnitude smaller than those of thunderstorm lightning thus suggesting a scaling relation between volcanic and thunderstorm lightning parameters that is independent of the type of charged particles on the other hand the polarities which are estimated by long time 3 4 yrs mt 32 samples s and video 30 frame s observations are different than those of normal thunderstorm lightning these observations are consistent with the notion that charge structures in volcanic ash plumes are highly disordered and are characterized by numerous small charged regions with high charge density

deep structure of japan subduction zone as derived from local regional and teleseismic events we have determined a detailed three dimensional p wave velocity structure of the japan subduction zone to 500 km depth by inverting local regional and teleseismic data simultaneously we used 45 318 p wave arrivals from 1241 shallow and deep earthquakes which occurred in and around the japan islands the arrival times are recorded by the japan university seismic network which covers the entire japan islands densely and uniformly we also used 4211 travel time residuals from 100 teleseismic events which are read from seismograms recorded by seismic stations in northeastern japan in comparison with the previous results obtained from only local and regional events the present result for the area around the lower plate boundary and the mantle below the plate is determined more reliably because of the addition of 7035 data from 100 teleseismic events and 41 very deep earthquakes in the crust and uppermost mantle low velocity zones are clearly visible beneath active volcanoes in the mantle wedge the low velocity zones generally parallel with the slab and exist continuously to a depth of about 200 km which is consistent with the petrological geochemical and geodynamic studies we consider that the existence of volcanism related low velocity anomalies in the mantle wedge is a general seismological characteristic of subduction zones in light of all the available tomographic results for many subduction zones in the world the pacific slab beneath japan is imaged more clearly than in previous studies as a high velocity zone with a thickness of 80 90 km and a p wave velocity 4 6 higher than the normal mantle lower velocity anomalies are found in the mantle below the slab

changes to the turbulent kinematics of a volcanic plume inferred from lightning data the 2009 redoubt volcano eruption produced a series of explosive events the largest of which produced episodes of volcanic lightning similar to thunderstorms flash energy spectra were calculated from lightning mapping data collected during the eruption the spectra were compared to the turbulence characteristics expected from each stage of plume development small flash length scales present at early times were associated with the gas thrust and initial convective stages increases in flash length scales and flash energy as the explosive events progressed were associated with an increase in volume of the plume spectra with a large range in flash length scales 0 2 10 km and a spectral peak at small flash length scales 1 km were associated with a superposition of spectra from gas thrust convective and umbrella ash cloud regions an approximate 5 3 power law slope was observed on the order of 10 min after gas thrust forcing had ended and the transition to a drifting ash cloud was underway which may reflect the dissipating state of the drifting ash cloud

swelling of a lava plug associated with a vulcanian eruption at sakurajima volcano japan as revealed by infrasound record case study of the eruption on january 2 2007 in order to clarify the time relation of the expansion of a gas pocket and failure of its overlying plug of lava during vulcanian eruptions infrasound records and video images of the vulcanian eruption that occurred at sakurajima volcano on january 2 2007 were analyzed with respect to their origin times weak 3 pa and slowly increasing air pressure preceded the impulsive compression phase by 0 25 0 32 s and a longer period rarefaction phase of infrasound waves was recognized at all microphone stations the velocity of the compression phase was assumed to be supersonic ca 400 m s up to 850 m above the crater bottom from other recent explosions on the other hand the propagation velocity of the preceding weak signal was regarded to be similar to the air sound velocity because the lack of impulsiveness is unlikely to be related to the main compression phase therefore the estimated origin time of the main compression phase was delayed by 0 5 0 7 s from the preceding phase the origin time of the preceding phase coincided with the onset of the isotropic expansion process of the pressurized gas pocket which was obtained by the waveform inversion of the explosion earthquake in contrast the origin time of the main impulsive phase coincided with the time when the expansion rate reached its peak this observation suggests that the volumetric increase of the gas pocket caused swelling of the surface of the crater bottom and its subsequent failure when the expansion velocity exceeded a threshold level the main impulsive compression phase radiated with a high velocity by the sudden releases of the pressurized gases the volumetric change at the source was estimated to be 280 560 m3 from the preceding phase of the infrasound this volume change indicates that the vertical displacement of the swelling ground was on the order of 1 0 m assuming the radius of the lava plug was ca 10 m

nitrogen fixation by volcanic lightning in the early earth we examine an unusual mechanism to fix nitrogen in the early earth by lightning discharges occurring inside explosive volcanic clouds containing gases characteristic of hawaiian volcanoes as a model of archean volcanic volatiles the products are predicted on thermodynamic equilibrium assumptions of the chemical species frozen out as the lightning channel rapidly expands and cools to 2400 c volcanic lightning is simulated in the laboratory by flowing the gas mixture into a microwave discharge cavity where the gases are excited and then the products are analyzed downstream by chemical ionization mass spectrometry nitric oxide was found to be the major product formed with an energy yield of 1 1016 molecule j 1 it is estimated that about 1012 1013 g of no could have been produced annually by volcanic clouds occurring about 4 gyr ago

electric potential gradient changes during explosive activity at sakurajima volcano japan we report electric potential gradient measurements carried out at sakurajima volcano in japan during 1 explosions which generated ash plumes 2 steam explosions which produced plumes of condensing gases and 3 periods of ashfall and plume induced acid rainfall sequential positive and negative deviations occurred during explosions which generated ash plumes however no deflections from background were found during steam explosions during periods of ashfall negative electric potential gradients were observed while positive potential gradients occurred during fallout of plume induced acid rain from the same eruption these results suggest that a dipole arrangement of charge develops within plumes such that positive charges dominate in the volcanic gas rich top and negative charges in the following ash rich part of the plume the charge polarity may be reversed for other volcanoes hatakeyama and uchikawa 1952 we suggest that charge is generated by fracto emission donaldson et al 1988 processes probably during magma fragmentation within the vent rather than by frictional effects within the plume

paleomagnetic evidence for a diachronic clockwise rotation of the coastal range eastern taiwan abstract paleomagnetic results obtained from over 2100 cores sampled at 132 early pliocene to late pleistocene sites in the coastal range of eastern taiwan indicate that since the late pliocene the margin of the philippine sea plate has undergone a clockwise rotation of about 30 as a direct consequence of the plio pleistocene collision of this plate with the chinese continental plate the rotation is diachronic and started between 3 and 4 ma ago in the northern coastal range then propagated southward at an average speed of the order of 70 10 km ma this value is in very good agreement with estimates of the southward propagation of the collision between the philippine sea plate and the eurasian margin in taiwan it is suggested that the rotation reflects the deformation of the philippine sea plate at depth and does not results from the shallow deformations involved in the building of the coastal range orogen

a model for the termination of the ryukyu subduction zone against taiwan a junction of collision subduction separation and subduction boundaries 1 the nw moving philippine sea plate psp collides with the eurasian plate eup in the vicinity of taiwan and at the same time it subducts toward the north along sw ryukyu the ryukyu subduction zone terminates against eastern taiwan while the ryukyu trench is a linear bathymetric low about 100 km east of taiwan closer to taiwan it cannot be clearly identified bathymetrically owing to the deformation related to the collision making the location of the intersection of the ryukyu with taiwan difficult to decipher we propose a model for this complex of boundaries on the basis of seismicity and 3 d velocity structures in this model the intersection is placed at the latitude of about 23 7 n placing the northern part of the coastal range on eup as psp gets deeper along the subduction zone it collides with eup on the taiwan side only where they are in direct contact thus the eurasian plate on the taiwan side is being pushed and compressed by the nw moving philippine sea plate at increasing depth toward the north offshore of northeastern taiwan the wedge shaped eup on top of the ryukyu subducting plate is connected to the eup on the ryukyu side and coupled to the nw moving psp by friction at the plate interface the two sides of the eup above the western end of the subduction zone are not subjected to the same forces and a difference in motions can be expected the deformation of taiwan as revealed by continuous gps measurements geodetic movement along the east coast of taiwan and the formation of the hoping basin can be understood in terms of the proposed model

experimental generation of volcanic lightning explosive volcanic eruptions are commonly associated with intense electrical activity and lightning direct measurement of the electric potential at the vent where the electric activity in the volcanic plume is first observed is severely impeded limiting progress in its investigation we have achieved volcanic lightning in the laboratory during rapid decompression experiments of gas particle mixtures under controlled conditions and recorded it using a high speed camera and two antennas we find that lightning is controlled by the dynamics of the particle laden jet and by the abundance of fine particles the relative movement of clusters of charged particles generates the electrical potential which is necessary for lightning the experimental generation of volcanic lightning suggests that rapid progress can now be expected in understanding electrical phenomena in volcanic plumes to implement lightning monitoring systems and the forecasting of volcanic ash emissions

subduction zone thermal structure and mineralogy and their relationship to seismic wave reflections and conversions at the slab mantle interface seismological studies of the interface between downgoing slabs of subducted lithosphere and the overriding mantle provide constraints against which models of mantle and slab temperature and bulk composition can be tested these studies employing waves reflected and converted at the slab mantle interface suggest that a velocity contrast of 5 10 occurs over a distance of 10 20 km to depths of at least 350 km the authors have investigated whether such sharp contrasts can result form thermal structure compositional differences phase changes or other effects such as preferred mineral orientation using a mantle and slab temperature model a petrologic model of mantle and slab mineralogy and a data base of elastic properties of mantle and slab phrases theoretical seismic velocities were calculated and compared with the observed velocity contrast and boundary thickness constraints at 9 6 gpa and 1000c conditions modeled at the slab mantle interface at approximately 280 km depth cooler temperatures in the slab interior produce at constant composition only approximately a 1 75 v sub p increase into the slab in any of the peridotitic and eclogitic mineralogies investigated variation in v sub p among the different bulk compositions is only approximately 0 5 these contrasts are substantially lower than those obtained from the seismological studies andmore indicate that temperature and bulk compositional differences between mantle and slab are inadequate to cause the observed velocity contrasts they propose that phase transformations in mantle and slab mineralogies notably elevation of the olivine spinel phase change normally occurring at 400 km depth are important factors in these sharp contrasts other contributing effects may include preferential mineral orientation near the slab surface and at shallower depths the presence of partial melt or hydrous fluid evolved from dehydration reactions along the interface less

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

electrical activity during the 2006 mount st augustine volcanic eruptions by using a combination of radio frequency time of arrival and interferometer measurements we observed a sequence of lightning and electrical activity during one of mount st augustine s eruptions the observations indicate that the electrical activity had two modes or phases first there was an explosive phase in which the ejecta from the explosion appeared to be highly charged upon exiting the volcano resulting in numerous apparently disorganized discharges and some simple lightning the net charge exiting the volcano appears to have been positive the second phase which followed the most energetic explosion produced conventional type discharges that occurred within plume although the plume cloud was undoubtedly charged as a result of the explosion itself the fact that the lightning onset was delayed and continued after and well downwind of the eruption indicates that in situ charging of some kind was occurring presumably similar in some respects to that which occurs in normal thunderstorms

tomographic imaging of lithospheric structures under taiwan abstract tomographic images of the crustal and mantle velocity structures under taiwan are obtained by simultaneous inversion of local earthquake p wave arrival times for hypocenters and p wave velocity structures in northern taiwan a high velocity zone coinciding with the wadati benioff zone can readily be identified as the subducted philippine sea plate the imaged zone dips toward the north at an angle of 40 from a depth range of 20 55 to 100 130 km an upper mantle low velocity wedge ranging from 40 to 80 km in depth exists above the subducted slab above this wedge is the ilan plain of northern taiwan which lies at the west end of the okinawa trough a well recognized back arc basin the crustal velocities under the plain are also relatively low the well defined high velocity zone and the low velocity wedge provide some constraints on the thermal structures of the subduction system under northern taiwan in tomographic images across the central section of taiwan thickening of the crust and up arching of the lower crustal materials under the central range are commonly observed the crust under the western foothills region is clearly thinner and the near surface low velocity layers are well developed the structures under the central range show that although the taiwan orogeny is quite young a root deeper in the north and shallowing to the south has formed the results of our tomography show that a significant portion of the lithosphere is involved in the taiwan orogeny

nitric acid from volcanoes abstract atmospheric cycling of nitric acid and other nitrogen bearing compounds is an important biogeochemical process with significant implications for ecosystems and human health volcanoes are rarely considered as part of the global nitrogen cycle but here we show that they release a previously unconsidered flux of hno3 vapour to the atmosphere we report the first measurements of nitric acid vapour in the persistent plumes from four volcanoes masaya nicaragua etna italy and villarrica and lascar chile mean near source volcanic plume concentrations of hno3 range from 1 8 to 5 6 mol m 3 an enrichment of one to two orders of magnitude over background 0 1 1 5 mol m 3 using mean molar hno3 so2 ratios of 0 01 0 02 0 05 and 0 07 for villarrica masaya etna and lascar respectively combined with so2 flux measurements we calculate gaseous hno3 fluxes from each of these volcanic systems and extend this to estimate the global flux from high temperature non explosive volcanism to be 0 02 0 06 tg n yr 1 while comparatively small on the global scale this flux could have important implications for regional fixed n budgets the precise mechanism for the emission of this hno3 remains unclear but we suggest that thermal nitrogen fixation followed by rapid oxidation of the product no is most likely in explosive ash rich plumes no may result from or at least be supplemented by production from volcanic lightning rather than thermal n fixation we have calculated no production via this route to be of the order of 0 02 tg n yr 1