ash plume dynamics and eruption source parameters by infrasound and thermal imagery the 2010 eyjafjallajokull eruption during operational ash cloud forecasting prediction of ash concentration and total erupted mass directly depends on the determination of mass eruption rate mer which is typically inferred from plume height uncertainties for plume heights are large especially for bent over plumes in which the ascent dynamics are strongly affected by the surrounding wind field here we show how uncertainties can be reduced if mer is derived directly from geophysical observations of source dynamics the combination of infrasound measurements and thermal camera imagery allows for the infrasonic type of source to be constrained a dipole in this case and for the plume exit velocity to be calculated 54 142 m s based on the acoustic signal recorded during the 2010 eyjafjallajokull eruption from 4 to 21 may exit velocities are converted into mer using additional information on vent diameter 50 10 m and mixture density 5 4 1 1 kg m3 resulting in an average 9 105 kg s mer during the considered period of the eruption we validate our acoustic derived mer by using independent measurements of plume heights icelandic meteorological office radar observations acoustically derived mer are converted into plume heights using field based relationships and a 1d radially averaged buoyant plume theory model using a reconstructed total grain size distribution we conclude that the use of infrasonic monitoring may lead to important understanding of the plume dynamics and allows for real time determination of eruption source parameters this could improve substantially the forecasting of volcano related hazards with important implications for civil aviation safety

the rio caliente ignimbrite analysis of a compound intraplinian ignimbrite from a major late quaternary mexican eruption the rio caliente ignimbrite is a multi flow unit orcompound ignimbrite formed during a major late quaternary explosive rhyolitic eruption of la primavera volcano mexico the eruption sequence of the ignimbrite is complex and it occurs between lower and upper plinian air fall deposits it is therefore anintraplinian ignimbrite air fall layers pyroclastic surge mudflow and fluviatile reworked pumice deposits also occur interbedded between ignimbrite flow units a chaotic near vent facies of the ignimbrite includes co ignimbrite lag breccias segregated from proximal pumice flows the facies locates a central vent but one which could not have been associated with a well defined edifice many of the lithics in the exposed lag breccias and near vent facies of the ignimbrite appear to be fragments of welded rio caliente ignimbrite and indicate considerable vent widening or migration during the eruption nearer vent the ignimbrite is thickest and composed of the largest number of flow units here it is welded and is a simple cooling unit evidence suggests that it was only the larger thicker pumice flows that escaped to the outer parts of the sheet detailed analysis of four flow units indicates that the pumice flows were generally poorly expanded less mobile flows which would be produced by collapse of low eruption columns the analogy of a compound ignimbrite with a compound lava flow is therefore good a compound lava flow forms instead of a simple one when the volumetric discharge rate or intensity is low and in explosive eruptions this predicts lower eruption column heights a corollary is that the ignimbrite has a high aspect ratio

theoretical study of the ionospheric plasma cave in the equatorial ionization anomaly region this paper investigates the physical mechanism of an unusual equatorial electron density structure plasma cave located underneath the equatorial ionization anomaly by using theoretical simulations the simulation results provide important new understanding of the dynamics of the equatorial ionosphere it has been suggested previously that unusual e b drifts might be responsible for the observed plasma cave structure but model simulations in this paper suggest that the more likely cause is latitudinal meridional neutral wind variations the neutral winds are featured by two divergent wind regions at off equator latitudes and a convergent wind region around the magnetic equator resulting in plasma divergences and convergence respectively to form the plasma caves structure the tidal decomposition analysis further suggests that the cave related meridional neutral winds and the intensity of plasma cave are highly associated with the migrating terdiurnal tidal component of the neutral winds

on the relationship between the postmidnight thermospheric equatorial mass anomaly and equatorial ionization anomaly under geomagnetic quiet conditions the equatorial mass anomaly ema in the thermosphere and equatorial ionization anomaly eia in the ionosphere are two interesting phenomena in low equatorial latitude regions previous studies have shown that the ema appears between 1000 and 2000 local time lt and its location of trough is aligned with dip equator indicating the plausible role of the eia structure in the development of ema in this report we conducted a statistical study of the occurrence of postmidnight ema and eia on the basis of the champ in situ measurements during 2002 2008 our results revealed that clear ema and eia structures are sometimes visible in the postmidnight sector 0100 0600 lt during geomagnetic quiet periods kp 3 the postmidnight ema is not necessarily accompanied by the eia signature in both case study and statistics sense being distinct from the daytime situation in addition the occurrence rates of postmidnight ema and eia display contrasting behavior with respect to their local time longitudinal and solar activity dependences the highest occurrence rate for ema is 8 at around 0300 lt while the occurrence rate of the eia decreases gradually from about 30 at around 2300 lt to similar to 5 at 0600 lt longitudinal occurrence of postmidnight eia presents a wave like pattern however no salient feature appears for the longitudinal occurrence of ema postmidnight ema is more likely to occur at lower solar activity whereas an opposite trend presents in the eia on the basis of above results our findings imply that a simple eia ema cause effect relationship does not hold in the postmidnight sector

first detection of the supersonic upward plasma flow structures in the early morning sector we present the first observations of the supersonic updrafting plasma drifts in the predawn sector two dmsp satellites quasi simultaneously detected two fast speed events one of 385 km spatial extension and with the maximum upward velocity of 1683 m s appeared at 3 lt and the other of 1500 km large with maximum speed of 1770 m s occurred at 5 lt both supersonic structures were observed above the eastern pacific region separated by 35 of longitude in space and by 45 min in time the events occurred at the recovery phase of the geomagnetic storm of 19 february 2014 during rapid oscillations of the interplanetary magnetic field b z and the interplanetary electric field e y components which increased the eastward electric field in the equatorial nighttime ionosphere and triggered the generation of plasma irregularities the storm time penetration electric fields seem to be the principal driver of the observed supersonic events

on postmidnight low latitude ionospheric irregularities during solar minimum 2 c nofs observations and comparisons with the equatorial atmosphere radar 1 a detailed comparison between the observations of the communication navigation outage forecasting system c nofs satellite and the 47 mhz equatorial atmosphere radar ear in west sumatra indonesia 10 36 s dip latitude on the postmidnight irregularities is presented the zonal and meridional e b drift velocities measured by the vector electric field instrument on the c nofs are consistent with the westward propagation of backscatter echoes and the line of sight doppler velocities observed with the ear respectively the plasma density depletions are observed in the postmidnight sector for several consecutive orbits which suggests the depletions grow slowly during the premidnight period and reach the spacecraft altitude around local midnight the convergence of the equatorward wind which could be responsible for the midnight temperature maximum may produce a preferable condition for the growth of the rayleigh taylor instability around midnight electric field fluctuations of medium scale traveling ionospheric disturbances may play an important role in seeding the instability both equatorial and midlatitude type plasma instabilities could be operational at the ear latitude sector which together would foster a high occurrence of postmidnight irregularities during solar minimum

episodic growth and homogenization of plutonic roots in arc volcanoes from combined u th and u th he zircon dating abstract tracing the fate of unerupted magma is challenging because plutonic roots of young volcanoes are largely inaccessible here we develop the use of zircon age spectra to determine crystal provenance and source rocks for volcanic products in analogy to detrital crystals in sediments u th zircon crystallization ages for the soufriere volcanic complex saint lucia lesser antilles frequently predate their eruption as determined from combined u th and u th he zircon dating the oldest dated eruptions are 273 15 ka and 264 8 ka 1 uncertainty for morne bonin dacite and bellevue pumice deposit respectively the most recent eruptions formed morphologically pristine domes in the center of the qualibou depression belfond 13 6 0 4 ka terre blanche 15 3 0 4 ka u th u pb zircon crystallization ages determined for crystal rims and interiors range between near eruption ages to 600 ka older xenocrysts are absent zircon crystallization age distributions are complex yet systematic crystal rim ages in the most recently erupted volcanic rocks match those of co erupted plutonic inclusions whereas crystal interiors are equivalent to the cumulative distribution of zircon ages from older eruptions this is evidence that silicic lava domes and pyroclastic flows share a common source that is located underneath the qualibou depression where the intrusive roots of this long lived arc volcanic system became homogenized through thermal and mechanical reprocessing of individual batches of unerupted magma from earlier volcanic episodes within timescales of

seismic excitation by the space shuttle columbia seismic stations in southern california recorded the atmospheric shock waves generated by the space shuttle columbia on its return to the edwards air force base on 13 august 1989 fig 1 in addition to the shock wave the broad band iris terrascope station at pasadena recorded a distinct pulse with a period of 2 3 seconds which arrived 12 5 seconds before the shock wave fig 2 this pulse was also recorded at the university of southern california near downtown los angeles where it arrived 3 seconds after the shock wave the origin of this pulse could not be readily identified we show here that it was a seismic p wave excited by the motion of high rise buildings in downtown los angeles which were hit by the shock wave the proximity of the natural period of the high rise buildings to that of the los angeles basin enabled efficient energy transfer from shock wave to seismic wave

an empirical model of the earth s horizontal wind fields hwm07 1 the new horizontal wind model hwm07 provides a statistical representation of the horizontal wind fields of the earth s atmosphere from the ground to the exosphere 0 500 km it represents over 50 years of satellite rocket and ground based wind measurements via a compact fortran 90 subroutine the computer model is a function of geographic location altitude day of the year solar local time and geomagnetic activity it includes representations of the zonal mean circulation stationary planetary waves migrating tides and the seasonal modulation thereof hwm07 is composed of two components a quiet time component for the background state described in this paper and a geomagnetic storm time component dwm07 described in a companion paper

frequency dependent acoustic seismic coupling of meteor shock waves simultaneous infrasonic and seismic observations of meteor shock waves have been recorded at a collocated array in southwestern ontario canada analysis of signals from seven events that exhibited acoustic seismic coupling representing 0 6 of the meteor flux detected using other systems suggests signifi cant filtering and amplitude enhancement indicative of a frequency dependent acous tic transfer function the acoustic response at the site possesses the properties of an 10 hz high pass filter on incident shock waves with ground motions up to an order of magnitude larger than theoretical predictions in terms of energy the air to ground energy coupling efficiency is measured at 1 3 0 8 above this cutoff overall cou pling efficiencies however are much lower between 0 0007 and 0 071 as the dominant frequencies of the incident shock waves typically 0 1 10 hz are weak or nonexistent in the seismic signals such strong frequency dependent effects suggest that without detailed knowledge of the site and its influences on the subsequent ground motion transformation of seismic data to produce pseudopressure data for the purposes of quantitative source energy estimation may be unreliable for seismom eters located within thick overburden

radiometric dating of three large volume flank collapses in the lesser antilles arc abstract it is now recognised that flank collapses are a recurrent process in the evolution of the lesser antilles arc volcanoes large magnitude debris avalanche deposits have been identified off the coast of dominica martinique and st lucia with associated volumes up to 20 km 3 deplus c le friant a boudon g komorowski j c villemant b harford c segoufin j cheminee j l 2001 submarine evidence for large scale debris avalanches in the lesser antilles arc earth planet sci lett 192 145 157 we present new radiometric dating of three major events using the k ar cassignol gillot technique in the qualibou depression of st lucia a collapse has been constrained by dome emplacement prior to 95 2 ka in dominica where repetitive flank collapse events have occurred le friant a boudon g komorowski j c deplus c 2002 l ile de la dominique a l origine des avalanches de debris les plus volumineuses de l arc des petites antilles c r geoscience 334 235 243 the plat pays event probably occurred after 96 2 ka inside the depression caused by this event scotts head which is interpreted as a proximal megabloc from the subsequent soufriere avalanche event has been dated at 14 1 ka providing an older bound for this event on martinique three different domes within the carbets structure dated at 337 5 ka constrain the age of this high magnitude event finally these results obtained from three of the most voluminous flank collapses provide constraints to estimate the recurrence of these events which represent one of the major hazards associated with volcanoes of the lesser antilles arc

finite difference calculation of travel times the travel times of the first arriving seismic waves through any velocity structure can be rapidly computed on a two or three dimensional numerical grid by finite difference extrapolation from point to point wavefronts rather than the traditional rays are tracked head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 03 per cent are found between the results of this technique and raytracing for a complex two dimensional model this scheme is useful for the windowing of finite difference calculations to increase computing speed and promises to aid in earthquake location tomographic inversion and kirchhoff migration in structures that have strong lateral velocity gradients

preliminary geochemical and thermodynamic assessment of the geothermal resources sulphur springs area st lucia w i abstract a high temperature geothermal resource has been located on the island of st lucia w i which was tapped by means of a well drilled in 1988 to a total depth of 1410 m in the sulphur springs area the well encountered mainly dacitic agglomerates and lava flows and a permeable zone below 1340 m with a maximum temperature of 290 c well productivity decreased from an initial value close to 62 t h to about 33 t h under well head pressures of 1 5 mpa 15 bar a after 255 h of production initial reservoir static pressure was 7 5 mpa 75 bar a a decline in reservoir pressure of about 15 was observed at the end of the production test during the first two days of exploitation the well initially produced a two phase fluid with high steam fraction which then developed into superheated steam with a high content of non condensable gas exceeding 100 1 kg at standard conditions and a computed p co2 of 1 mpa 10 bar the average steam fraction at reservoir conditions computed from gas composition after 120 h of production is 0 3 high hcl concentrations of about 300 ppm are present in the condensate steam indicating the presence of a high concentrated boiling brine to the point of halite saturation all data support the hypthesis of a hydrothermal hot water system prior to drilling that underwent a very rapid drawdown with production

theoretical study of the ionospheric weddell sea anomaly using sami2 1 the ionospheric weddell sea anomaly wsa was first reported more than five decades ago based on ionosonde data near the antarctica peninsula the wsa is an ionospheric structure characterized by a larger nighttime electron density than daytime density recent satellite observations indicate that the wsa can extend from south america and antarctica to the central pacific the major physical mechanisms that have been suggested for the wsa formation are an equatorward neutral wind an electric field the photoionization and the downward diffusion from the plasmasphere on the basis of the theoretical modeling performed in this study using the sami2 model an equatorward neutral wind is identified as the major cause of the wsa while the downward flux from the plasmasphere provides an additional plasma source to enhance or maintain the density of the anomalous structure

a dayside plasma depletion observed at midlatitudes during quiet geomagnetic conditions in this study we investigate a dayside midlatitude plasma depletion dmlpd encountered on 22 may 2014 by the swarm and grace satellites as well as ground based instruments the dmlpd was observed near puerto rico by swarm near 10 lt under quiet geomagnetic conditions at altitudes of 475 520 km and magnetic latitudes of 25 30 the dmlpd was also revealed in total electron content observations by the saint croix station and by the grace satellites 430 km near 16 lt and near the same geographic location the unique swarm constellation enables the horizontal tilt of the dmlpd to be measured 35 clockwise from the geomagnetic east west direction ground based airglow images at arecibo showed no evidence for plasma density depletions during the night prior to this dayside event the c nofs equatorial satellite showed evidence for very modest plasma density depletions that had rotated into the morningside from nightside however the equatorial depletions do not appear related to the dmlpd for which the magnetic apex height is about 2500 km the origins of the dmlpd are unknown but may be related to gravity waves

c nofs observations of deep plasma depletions at dawn 1 the communication navigation outage forecasting system c nofs satellite was launched in 2008 during solar minimum conditions an unexpected feature in the c nofs plasma density data is the presence of deep plasma depletions observed at sunrise at all satellite altitudes ionospheric irregularities are often embedded within these dawn depletions their frequencies strongly depend on longitude and season dawn depletions are also observed in coincident satellite passes such as dmsp and champ in one example the depletion extended 50 14 in the n s and e w directions respectively these depletions are caused by upward plasma drifts observed in c nofs and ground based measurements the reason for these upward drifts is still unresolved we discuss the roles of dynamo electric fields over shielding and tidal effects as sources for the reported depletions

role of large flank collapse events on magma evolution of volcanoes insights from the lesser antilles arc flank collapse events are now recognized as common processes of destruction of volcanoes they may occur several times on a volcanic edifice pulling out varying volumes of material from km3 to thousands of km3 in the lesser antilles arc a large number of flank collapse events were identified here we show that some of the largest events are correlated to significant variations in erupted magma compositions and eruptive styles on montagne pelee martinique magma production rate has been sustained during several thousand years following a 32 ka old flank collapse event basic and dense magmas were emitted through open vent eruptions that generated abundant scoria flows while significantly more acidic magmas were produced before the flank collapse the rapid building of a new cone increased the load on magma bodies at depth and the density threshold magma production rate decreased and composition of the erupted products changed to more acidic compared to the preceding period of activity these low density magma generated plinian and dome forming eruptions up to the present in contrast at soufriere volcanic centre of st lucia and at pitons du carbet in martinique the flank collapses have an opposite effect in both cases the acidic magmas erupted immediately after the flank collapses these magmas are highly porphyritic up to 60 phenocrysts and much more viscous than the magmas erupted before the flank collapses they have been generally emplaced as voluminous and uptight lava domes called the pitons such magmas could not ascent without a significant decrease of the threshold effect produced by the volcanic edifice loading before the flank collapse

volcanic stratigraphy and geochemistry of the soufriere volcanic centre saint lucia with implications for volcanic hazards abstract the soufriere volcanic complex svc saint lucia represents one of the largest silicic centres in the lesser antilles arc it comprises extensive pumiceous pyroclastic flow deposits lava flows as well as pelean style domes and dome collapse block and ash flow deposits these deposits occur within and around the qualibou depression a 10 km diameter wide sector collapse structure to date vent locations for svc pyroclastic deposits and their relationship to the sector collapse have been unclear because of limited stratigraphic correlation and few radiometric ages in this study we reconstruct the geologic history of the svc in light of new and recently published u th he u th and u pb zircon chronostratigraphic data aided by mineralogical and geochemical correlation compositionally svc deposits are monotonous medium k calc alkaline rocks with 61 6 to 67 7 wt sio 2 and display similar trace element abundances combined u th and u th he zircon dating together with 14 c ages and mineral fingerprinting reveals significant explosive eruptions at 640 515 265 104 60 and 40 ka producing deposits previously grouped together as the choiseul unit and at 20 ka belfond unit the mineralogically and geochemically distinct belfond unit is a large valley filling pumiceous pyroclastic flow deposit distributed to the north northeast south and southeast of the qualibou depression that was probably deposited during a single plinian eruption the unit previously referred to as choiseul tuff is much less well defined the typical choiseul unit comprises a series of yellowish white crystal poor non welded pumiceous pyroclastic deposits cropping out to the north and southeast of the qualibou depression however its age is poorly constrained a number of other units previously mapped as choiseul can be distinguished based on age and in some cases mineral and whole rock chemistry pyroclastic deposits at micoud 640 19 ka bellevue 264 8 ka anse john 104 4 ka and la pointe 59 8 2 1 ka anse noir and piaye were all previously grouped with or associated with the choiseul tuff all uncertainties 1 we suggest that these units represent individual periods of activity spanning a range of ages whereas choiseul pumice at the type locality has yielded a u th he zircon age of 515 19 ka their overall geochemical and mineralogical similarities with the choiseul at the type locality suggest that they might have all originated from the same centre morne tabac 532 21 ka is a dome truncated by the depression escarpment whereas morne bonin 273 15 ka gros piton and petit piton 71 3 ka and 109 4 ka resp belfond 13 6 0 4 ka and terre blanche 15 3 0 4 ka are domes within the qualibou depression belfond and terre blanche have whole rock geochemistry and mineral assemblages similar to the belfond pyroclastic flow deposit thus possibly representing late erupted degassed portions of the magma that produced the belfond pyroclastics the geochemical characteristics and similar zircon age distributions of the silicic lava domes and pyroclastics of the svc suggest that these share a common magma source beneath the qualibou depression the distribution of the pyroclastic flows and the wide range in their eruption ages makes it unlikely that these were erupted during caldera forming activity and we instead invoke a series of smaller volume explosive eruptions from the area of the current depression the earliest of which occurred from a large proto qualibou edifice that subsequently underwent sector collapse activity from this proto qualibou centre may have ceased sometime between 38 and 59 ka ago it therefore seems unlikely given our present understanding that there will be another eruption from the southern central highland region however the young dome forming activity in the qualibou depression may have occurred in or close to the holocene and there have been dome collapse events and explosion craters formed since then a new dome eruption or renewed activity at a dome within the depression growing in the style of the ongoing soufriere hills lava dome on the nearby island of montserrat is possible as is a future plinian eruption from this area such an eruption would not only have a devastating impact on saint lucia but would also have significant regional and global impacts

the role of zonal winds in the production of a pre reversal enhancement in the vertical ion drift in the low latitude ionosphere 1 the evolution of the pre reversal enhancement in the vertical ion drift in the equatorialfregion is described via an examination of the current systems determined from a coupled ionosphere thermosphere model we find that the pre reversal enhancement is produced by a reversal in thef region zonal wind that results in an additional upward current where the e region pedersen conductivity is declining across the dusk sector the continuity of the total current is maintained through an enhancement in the eastward zonal current and an associated upward drift of the ions

a two fault model of the 2003 leucas aegean arc earthquake based on topological inversion of gps data the fault pattern of the 2003 m w 6 2 leucas lefkada lefkas earthquake at the northwest edge of the aegean arc an area of very high seismicity rates was modeled using global positioning system gps data the rupture process of this earthquake is a matter of debate because of the complexities in the aftershock distribution and in the waveforms of the mainshock as well as the kinematics of the area are not well understood especially the characteristics of the cephalonia kefalonia keffalinia transform fault and its relationship with major discordant active thrusts representing the tectonic fabric of western greece our analysis was based on the topological inversion topinv algorithm which uses a deterministic hypergrid search to identify one or more clusters of n dimensional points around the true solution of the system of observation equations from these clusters optimal estimators of the variables defining okada type faults and their variance covariance matrices are computed as statistical moments and results are validated by minimum mean misfits faulting of the 2003 seismic sequence was approximated by two stepping essentially strike slip segments with a separation of 10 km this pattern is in agreement with fault rupture models based on inversion of seismological data and their main difference is a thrust component in the major segment well constrained by interferometric synthetic aperture radar and gps observations of uplift this thrust component may reflect either postseismic evaporite salt controlled slip or uncertainties in the inversion models the 2003 and other seismic sequences among them the 1953 m 7 2 cephalonia catastrophic earthquakes that were associated with major uplift seem to confirm previous views for an 100 km wide shear zone superimposed on compression along the edges of the aegean arc online material description of analytical inversion methodology the topological inversion algorithm topinv including a figure showing projection of hypergrids on planes

comparison of penetration electric fields created by the solar wind with jicamarca data using swage 1 swage solar wind acting on the geophysical environment calculates the global ionospheric electric field generated by high latitude electrodynamics drivers determined from the time shifted solar wind data measured at l1 by joining the hill siscoe polar cap potential model with the n c ionospheric potential solver of particular interest are the conditions under which the eastward equatorial penetration electric field near twilight contributes to the pre reversal enhancement pre in the present model it is found that a steeper terminator conductance gradient leads to a more pronounced pre the model is statistically consistent with the jicamarca vertical drift data at twilight during quiet times for eighty two days in the years 1998 2005 the model is also consistent with the jicamarca vertical drift data during the november 2004 magnetic superstorms dst 250 nt and highlights the importance of including the lt dependence of the ionospheric response in this comparison disturbance dynamo dd effects are also included comparison is much better using the conductance model with a shallower terminator gradient and indicates that the conductance lt profile was relatively unchanged throughout the storms

coherent and incoherent scatter radar study of the climatology and day to day variability of mean f region vertical drifts and equatorial spread f

late quaternary explosive silicic volcanism on st lucia west indies many explosive eruptions of dacitic magmas have occurred on st lucia during the late quaternary these have produced widespread aprons and fans of pumice flow and ash flow deposits radiating around the central highlands with co eruptive air fall and surge layers interbedded with palaeosols and epiclastic deposits vents in the highlands have not been located because of the dense tropical jungle but we suspect they are now plugged by lava domes surrounded by aprons of block and ash flow deposits young magmatically related dacitic lava domes have been extruded in the qualibou depression the pumice succession can be divided into older quartz poor deposits forming the choiseul pumice and younger crystal rich deposits with abundant large quartz which are called the belfond pumice the choiseul pumice groups together scattered remnants of the products of many eruptions of different low silica dacitic magma types the belfond pumice is the product of several eruptions of a high silica magma type and 14 c ages have dated these between 20900 to 34200 years b p the pumice flow deposits occur as small volume valley fills a granulometric study of belfond pumice flow deposits shows them to be strongly depleted in finer ash and vitric components it is suggested that the narrow winding and vegetated valleys on the island locally induced turbulence and the flows moved with large highly fluidized and inflated heads resulting in substantial loss of fine vitric ash one ash flow deposit which is extremely rich in crystals and carbonized vegetation is highly depleted in fines and shows enhanced vitric losses this flow may have been a much more violent ash hurricane or blast which surmounted topography ingesting large amounts of lush vegetation ignition of this released the large quantities of gas needed to elutriate most of the fines a model is suggested for the recent volcanic activity on st lucia in which separate batches of silicic magma each having a distinctive petrological and chemical character rose into high level chambers over a large area eruptions of volatile rich magma led to highly explosive pumice forming activity from vents in the central highlands degassed and more crystal rich magma was extruded later from the same vents or in the attenuated flank of the qualibou depression to from lava dome complexes

early morning irregularities detected with spaceborne gps measurements in the topside ionosphere a multisatellite case study we present observations of the equatorial plasma bubbles epb in the topside ionosphere at early morning hours 05 08 lt in the recovery phase of the 18 19 february 2014 geomagnetic storm this rare type of irregularities was detected in the pacific sector using gps measurements on board several low earth orbit leo satellites we use a multisatellite constellation consisted of the three swarm and one terrasar x satellites that on 19 february flew in the same region and at similar altitudes 500 km the epb occurrence in the leo gps data was observed for several consecutive orbits from 11 ut to 16 17 ut on 19 february 2014 which suggests the following 1 rather long duration hours of favorable conditions for epb generation 2 formation and evolution of epb over wide longitude range of the pacific ocean and 3 possible movement of the epb region in the westward direction with dawn registration of the early morning epb in leo gps data was supported by concurrent in situ swarm and dmsp defense meteorological satellite program and ground based ionosonde and gps measurements leo based gps technique is found to be essential and promising data source to study the topside epb over regions with lack of the ground based facilities in addition we use the prompt penetration model and the thermosphere ionosphere electrodynamics global circulation model tie gcm to identify the possible mechanisms responsible for the observed phenomenon the model simulation results indicate the occurrence of the zone with the enhanced vertical plasma drift 40 45 m s owing to the disturbance dynamo action in the predawn dawn sector during 09 17 ut

self consistent modeling of equatorial dawn density depletions with sami3 1 large scale dawn density depletions in the equatorial ionosphere have been observed by instruments on the stpsat1 and champ satellites the naval research laboratory nrl ionosphere model sami3 sami3 is also a model of the ionosphere is used to study this new phenomenon using a self consistent electric field two empirical horizontal wind models hwm are used in the simulation study hwm93 and hwm07 dawn density depletions are found using hwm07 but not with hwm93 the cause of the depletions is a post midnight enhancement of the eastward electric field that generates an upward plasma drift this drift lifts low density plasma to high altitudes i e 600 km we compare our model results to remote sensing data and to in situ satellite data

seismic observations of meteors coupling theory and observations to date coupling of acoustic waves directly with the earth s surface represents the bulk of the observed meteor related seismic signals while precursory and impact related seismic waves remain an observational rarity with proliferation of infrasound and seismic monitoring systems new opportunities exist to explore the relationship between earth s atmosphere andsurface continued studyofmeteorseismologywillleadto new methods to constrain energies sizes and fluxes for moderately cm to m sized meteoroids on earth and potentially on mars

ignimbrite depositional facies the anatomy of a pyroclastic flow a model is presented for the depositional regimes in a pyroclastic flow to explain the origin of facies in the taupo ignimbrite and to compare these with other published examples in this model a pyroclastic flow consists of a head a body and a tail the head which is where fluidization caused by air ingestion occurs generates layer 1 deposits on lithological grounds these are divided into layers 1 p which is fines depleted and rich in pumice and 1 h which is fines depleted and rich in lithics and crystals layer 1 p represents material thrown forwards from the flow head and is termed the jetted deposits layer 1 h represents material sedimented from within the flow head and is termed the ground layer the body represents the bulk of the flow and the tail is its trailing part which is slowed by ground friction these parts generate the layer 2 deposits which include the valley pond ignimbrite and its associated ignimbrite veneer deposit localized depositional modes within the body and tail generate distinctive coarse pumice concentration zones and pumiceous lee side lenses behind obstacles at its outer limits all of the flow on interfluves is affected by air ingestion fluidization producing the distant facies which combines features of both layer 1 and 2 deposits one important conclusion of this work is that the thicknesses and compositions of the various facies are not related in any simple way to the thickness and composition of the parent flow

sources of low latitude ionospheric e b drifts and their variability 1 the complete mechanism of how upward propagating tropospheric tides connect to the upper atmosphere is not yet fully understood one proposed mechanism is via ionospheric wind dynamo however other sources can potentially alter the vertical e b drift gravity and plasma pressure gradient driven current the geomagnetic main field and longitudinal variation in the conductivities in this study we examine the contribution to the vertical drift from these sources and compare them we use march equinox results from the thermosphere ionosphere mesosphere electrodynamics general circulation model we found that the gravity and plasma pressure gradient driven current and the longitudinal variation of the conductivities excluding the variation due to the geomagnetic main field do not change the longitudinal variation of the vertical drift significantly modifying the geomagnetic main field will change the vertical drift at 5 6 lt 18 19 lt and 23 24 lt at almost all longitudes in general the influence of the geomagnetic main field on the vertical drift is larger with respect to the maximum difference at 18 19 lt and 23 24 lt equal at 5 6 lt and smaller at 14 15 lt than the influence due to nonmigrating tidal components in the neutral winds examination of the contribution from e and f region neutral winds to the vertical drift shows that their importance depends on the local time and the solar activity this implies that the vertical drift has to be analyzed at specific local times to examine the relation between the wave number in the vertical drift and in the neutral winds

characteristics of the large scale traveling atmospheric disturbances during geomagnetically quiet and disturbed periods simulated by a whole atmosphere general circulation model 1 we have investigated characteristics of the large scale traveling atmospheric disturbances ls tads generated during geomagnetically quiet and disturbed periods using a whole atmosphere general circulation model gcm the gcm simulations show that various tads appear in association with passages of regions with large temperature gradients near the solar terminator midnight temperature anomaly and auroral oval which move with the earth s rotation these tads which are superimposed on each other appear even when a geomagnetically quiet period the tads generated during a geomagnetically quiet period show structures extending in the longitudinal direction at high latitude and in the latitudinal direction at mid and low latitude these structures disappear after their short range propagations the tads generated during a geomagnetically disturbed period show structures extending widely in the longitudinal direction and propagate from high to low latitude these simulation results suggest the different generation mechanisms and features between the tads generated during geomagnetically quiet and disturbed periods

altitudinal dependence of evening equatorial f region vertical plasma drifts we use jicamarca incoherent scatter radar measurements to study for the first time the altitudinal variations of late afternoon and early night equatorial f region vertical plasma drifts we also present the initial vertical drift measurements over the altitudinal range from about 200 to 2000 km these data show that the afternoon drifts decrease weakly with altitude near their evening prereversal enhancements the vertical drifts generally increase with altitude below about the f layer peak decrease with height near the f layer peak and above and are nearly height independent in the solar flux dependent topside ionosphere the transition altitudes from height decreasing to height independent evening upward drifts decrease with altitude from solar maximum to solar minimum after their reversal to downward the vertical drifts do not change much with height the altitudinal dependence of the evening vertical drifts has large day to day variability and is closely related to the time dependence of the zonal drifts as expected from the curl free electric field condition

numerical study of pyroclastic surges abstract the dynamics of pyroclastic surges accompanied by co ignimbrite plumes is investigated numerically the numerical simulations are performed with a newly developed numerical model which is based on the navier stokes equations for time dependent flows of a compressible fluid in two dimensional cartesian coordinates we regard pyroclastic surges as dilute turbulent suspensions in which hot gases and fine solid particles are homogeneously mixed owing to vigorous turbulence in other words the gas particle mixture is treated as a single phase fluid whose bulk density is represented by averaging the density of each component in the numerical model we focus on the effect of buoyancy forces generated by the thermal expansion of the air mixed into pyroclastic surges from the calm surroundings for our purpose the numerical model is designed to simulate relatively simple flows spreading over a horizontal flat surface topographic irregularity and the sedimentation process of solid particles are neglected in the present simulations the motion of pyroclastic surges is generated by the instantaneous release of a gas particle mixture whose density is initially larger than the ambient air density and changes nonlinearly with the temperature and concentration of suspended solid particles turbulent mixing is evaluated by adopting the smagorinsky model by employing cubic interpolated pseudo particle cip method and c cup method we obtain the fine structure of flows the behavior of calculated flows agrees fairly well with observed pyroclastic surges in nature the current head which remains hot and dense keeps spreading over a horizontal surface at a speed of about 20 m s 1 the spreading speed is of the order of the speed of a gravity current that excludes the influence of thermal expansion besides turbulent mixing between the basal dense layer and the ambient air is enhanced by the successive development of an interfacial less dense layer this results in the formation of a number of buoyant plumes rising above a horizontally spreading current consequently the tails of the current thickens as time progresses a parametric study shows that the initial temperature of a gas particle mixture should be higher than about 600 k when buoyant plumes occur owing to the thermal expansion of mixed air the result is quantitatively interpreted by introducing a diagram that describes the relationship among the bulk density temperature and concentration of solid particles suspended in pyroclastic surges

the behaviour of subaerially produced pyroclastic flows in a subaqueous environment evidence from the roseau eruption dominica west indies abstract the roseau tephra 30 000 yrs b p with its source on the island of dominica represents the largest eruption in the caribbean in the last 200 000 years pyroclastic flows generated by the eruption flowed offshore into the grenada basin giving rise to a widespread layer of sediment gravity flow deposits on land the flow deposits are valley ponded and their granulometric characteristics allow them to be classified as weakly fines depleted ignimbrites offshore the characteristics of the sediment gravity flow deposits are consistent with deposition by numerous small scale events rather than a single large scale event a comparison of the on land and offshore deposits reveals an increase in the crystal lithic ratio in the latter this change can be best explained by the fragmentation of hot pyroclastic material as the subaerial flows mixed with water mixing and fragmentation occurred not at the air water interface but as flows descended the steep submarine slopes of the island of dominica

study of the equatorial and low latitude electrodynamic and ionospheric disturbances during the 22 23 june 2015 geomagnetic storm using ground based and spaceborne techniques we use a set of ground based instruments global positioning system receivers ionosondes magnetometers along with data of multiple satellite missions swarm c nofs dmsp guvi to analyze the equatorial and low latitude electrodynamic and ionospheric disturbances caused by the geomagnetic storm of 22 23 june 2015 which is the second largest storm in the current solar cycle our results show that at the beginning of the storm the equatorial electrojet eej and the equatorial zonal electric fields were largely impacted by the prompt penetration electric fields ppef the ppef were first directed eastward and caused significant ionospheric uplift and positive ionospheric storm on the dayside and downward drift on the nightside furthermore about 45 min after the storm commencement the interplanetary magnetic field imf bz component turned northward leading to the eej changing sign to westward and to overall decrease of the vertical total electron content vtec and electron density on the dayside at the end of the main phase of the storm and with the second long term imf bz southward turn we observed several oscillations of the eej which led us to conclude that at this stage of the storm the disturbance dynamo effect was already in effect competing with the ppef and reducing it our analysis showed no significant upward or downward plasma motion during this period of time however the electron density and the vtec drastically increased on the dayside over the asian region we show that this second positive storm was largely influenced by the disturbed thermospheric conditions

responses in the polar and equatorial ionosphere to the march 2015 st patrick day storm the st patrick day storm of 2015 17 march 2015 occurred at a unique time when there were multiple spacecraft observing the earth s ionosphere between 350 and 885 km observations of the plasma flows and densities from the five operational polar orbiting dmsp spacecraft combined with those from the equatorial orbiting c nofs spacecraft provided a comprehensive global record of the both the polar and equatorial ionosphere regions responses to the storm this paper presents an overview of the data from this suite of spacecraft focusing on the following aspects 1 the polar cap ionosphere s reaction to the storm 2 the change in the penetration electric field in the midlatitude region as a function of time and the solar local time during the storm 3 the equatorial ionosphere s response of the meridional vertical flows to the penetration electric field and the disturbance dynamo during the storm and 4 the creation of a predawn ionospheric bubble system near the equator during the storm s main phase that was observed at low altitudes by c nofs and later at high altitudes by several dmsp examining these phenomenon enable us to trace the dynamic flow of energy from the solar wind input in the polar ionosphere all the way to the equatorial ionosphere

calderas or gravity slide structures in the lesser antilles island arc abstract large arcuate depressions up to about 10 km in diameter on the back arc side of st lucia dominica and st vincent in the lesser antilles arc are discussed the qualibou depression on st lucia has been previously described as a caldera partly because it was believed to be the source of ignimbrites on the island remapping and stratigraphic studies of these ignimbrites show they were not erupted from the depression but from central vents in the highland rainforests and are much younger dominica is geologically similar and has two scarped depressions at the southern end of the island soufriere volcano st vincent has a prominent arcuate scarp opening to the west the southern half of which has been buried under the youngest volcanic products of the volcano we interpret these structures as the root zones of gravity slides perhaps eruption related and triggered by magmatic inflation post slide activity lava domes and fumaroles has occurred within them due to reduction in lithostatic load and pressure release on the flanks of these island volcanic complexes the presence of these structures only on the western coasts is correlated with the steeper 9 slopes into the grenada basin in contrast to the 1 submarine slopes of the atlantic side

u series isotopes and destructive plate margin magma genesis in the lesser antilles high precision tims230th232th isotope ratios are presented from a suite of lavas which span the length of the lesser antilles island arc compositions vary from low k tholeiitic lavas with low87sr86sr in the north to high k calc alkaline to alkalic lavas with higher87sr86sr in the south the northern lavas are characterised by 230th238u 1 a three component model is required for magma genesis in the lesser antilles sediments from the subducting slab melt and variably enrich the mantle wedge while the subducting oceanic crust dehydrates releasing fluids enriched in u ba sr and k but with negligible th and low87sr86sr which promote partial melting in the wedge ta zr increases with87sr86sr southwards along the arc and this is inferred to reflect increasing enrichment of the mantle wedge through the addition of partial melts of subducted sediment mass balance calculations are consistent with a relatively constant fluid flux except for u and little variation in the degree of partial melting 10 15 along the arc and they suggest that the sediment contribution to the arc lavas increases from 2 in the north to 15 in the south in the northern parts of the arc the addition of u by these fluids overprints any increases inth u that might have been caused by partial melting and results in lavas with 230th238u 1 m yr 1 which imply channelled flow through the mantle wedge

observations of dc electric fields in the low latitude ionosphere and their variations with local time longitude and plasma density during extreme solar minimum 1 dc electric fields and associated e b plasma drifts detected with the double probe experiment on the c nofs satellite during extreme solar minimum conditions near the june 2008 solstice are shown to be highly variable with weak to moderate ambient amplitudes of 1 2 mv m 25 50 m s average field or drift patterns show similarities to those reported for more active solar conditions i e eastward and outward during day and westward and inward at night however these patterns vary significantly with longitude and are not always present daytime vertical drifts near the magnetic equator are largest in the prenoon sector observations of weak to nonexistent prereversal enhancements in the vertical drifts near sunset are attributable to reduced dynamo activity during solar minimum as well as seasonal effects enhanced meridional drifts are observed near sunrise in certain longitude regions precisely where the enhanced eastward flow that persisted from earlier local times terminates the nightside ionosphere is characterized by larger amplitude structured electric fields dominated by horizontal scales of 500 1500 km even where local plasma densities appear relatively undisturbed data acquired during successive orbits indicate that plasma drifts and densities are persistently organized by longitude the high duty cycle of the c nofs observations and its unique orbit promise to expose new physics of the low latitude ionosphere

amisr 14 observations of equatorial spread f a new 14 panel advanced modular incoherent scatter radar amisr 14 system was recently deployed at the jicamarca radio observatory we present results of the first coherent backscatter radar observations of equatorial spread f esf irregularities made with the system colocation with the 50 mhz jicamarca unattended long term studies of the ionosphere and atmosphere julia radar allowed unique simultaneous observations of meter and submeter irregularities observations from both systems produced similar range time intensity maps during bottom type and bottomside esf events we were also able to use the electronic beam steering capability of amisr 14 to image scattering structures in the magnetic equatorial plane and track their appearance evolution and decay with a much larger field of view than previously possible at jicamarca the results suggest zonal variations in the instability conditions leading to irregularities and demonstrate the dynamic behavior of f region scattering structures as they evolve and drift across the radar beams

listening to sounds from an exploding meteor and oceanic waves low frequency sound infrasound measurements have been selected within the comprehensive nuclear test ban treaty ctbt as a technique to detect and identify possible nuclear explosions the seismology division of the royal netherlands meteorological institute knmi operates since 1999 an experimental infrasound array of 16 micro barometers here we show the rare detection and identification of an exploding meteor above northern germany on november 8th 1999 with data from the deelen infrasound array dia at the same time sound was radiated from the atlantic ocean south of iceland due to the atmospheric coupling of standing ocean waves called microbaroms occurring with only 0 04 hz difference in dominant frequency dia proved to be able to discriminate between the physically different sources of infrasound through its unique lay out and instruments the explosive power of the meteor being 1 5 kt tnt is in the range of nuclear explosions and therefore relevant to the ctbt

topside ionospheric irregularities as seen from multisatellite observations we use in situ data from champ and dmsp satellites along with data of gps receiver onboard champ satellite and ground based gps receivers to study the occurrence and global distribution of ionospheric irregularities during the main phase of the geomagnetic storm of 29 31 august 2004 minimum dst excursion of a128 nt using the champ gps measurements we created maps of gps phase fluctuation activity and found two specific zones of the most intense irregularities 1 the region of the auroral oval at high latitudes of both hemispheres and 2 the low latitudes equatorial region between africa and south america at high latitudes the topside ionospheric irregularities appeared to be more intensive in the southern hemisphere which is most likely due to seasonal variations in the interhemispheric field aligned currents system an analysis of multi instrumental observations reveals reinforcement of the equatorial ionization anomaly after sunset in atlantic sector on 30 august and formation of the significant plasma depletions and irregularities over a large longitudinal range equatorial irregularities were also found in the morning sector at the recovery phase of the storm in addition to low earth orbit leo gps measurements we analyze the leo in situ measurements and we show that these two techniques cannot be interchangeable in all cases because of the altitudinal extent of plasma irregularities overall we demonstrate that the leo gps technique can serve a useful tool for detection of the topside ionospheric irregularities during space weather events and may essentially contribute to other methods based on various instruments

global equatorial plasma bubble occurrence during the 2015 st patrick s day storm an analysis of the occurrence of equatorial plasma bubbles epbs around the world during the 2015 st patrick s day geomagnetic storm is presented a network of 12 global positioning system receivers spanning from south america to southeast asia was used in addition to colocated vhf receivers at three stations and four nearby ionosondes the suppression of postsunset epbs was observed across most longitudes over 2 days the epb observations were compared to calculations of the linear rayleigh taylor growth rate using coupled thermosphere ionosphere modeling which successfully modeled the transition of favorable epb growth from postsunset to postmidnight hours during the storm the mechanisms behind the growth of postmidnight epbs during this storm were investigated while the latter stages of postmidnight epb growth were found to be dominated by disturbance dynamo effects the initial stages of postmidnight epb growth close to local midnight were found to be controlled by the higher altitudes of the plasma i e the gravity term modeling and observations revealed that during the storm the ionospheric plasma was redistributed to higher altitudes in the low latitude region which made the plasma more susceptible to rayleigh taylor growth prior to the dominance of the disturbance dynamo in the eventual generation of postmidnight epbs

a citizen science approach for monitoring volcanic emissions and promoting volcanic hazard awareness at sulphur springs saint lucia in the lesser antilles arc abstract sulphur springs park ssp saint lucia in the lesser antilles is a popular geothermal area with a vigorous passively degassing hydrothermal field visitors staff and management of the park have raised concerns about the volcanic emissions and their possible effects on their health as part of the responsibility of the university of the west indies seismic research centre uwi src to provide volcanic surveillance through its geothermal monitoring programme a monitoring network was established for quantifying the ambient so2 concentrations at the park to assess the potential risk of unsafe exposure this required the development of a participatory citizen science effort with researchers training local personnel in field sampling and basic analytical techniques to measure so2 concentrations the operation of a citizen science network required engagement and collaboration with local stakeholders in saint lucia to ensure that the research addressed the needs of all partners this participatory approach was an effective option for scientists to engage local stakeholders and the wider community as partners in geoscience hazards education ambient so2 concentrations obtained with handmade active air samplers titrimetric hydrogen peroxide traps showed that when the atmospheric concentrations of so2 was lower the data from the diffusion tubes and the handmade samplers followed a similar pattern the ambient concentrations measured using the handmade samplers cannot be used as absolute values due to uncertainties related to the input parameters needed for the calculation of so2 concentrations however the data may be useful in identifying areas exposed to elevated so2 concentrations of potential concern to public health the samplers proved useful as a tool to promote volcanic hazard awareness and education among the local stakeholders and citizen scientists important lessons learned by the research team from participant surveys were that time constraints and personal motivation of volunteers are key factors in the success of the operations of this monitoring network

the recent isla san luis volcanic centre petrology of a rift related volcanic suite in the northern gulf of california mexico abstract isla san luis one of the most recent eruptive centres in the gulf of california presents a complete magma evolution trend from basaltic andesites to rhyolites the less evolved lavas are palagonite tuffs related to surtseyan type activity which characterized the emergent stage of the island subaerial lava flows and later high energy hydromagmatic eruptions are dacites which make up the tuff rings of the southeastern corner of the island rhyolites are the latest erupted products and the development of the younger dome in the centre of the island was preceded by ash and pumice fallout containing quenched bombs with an obsidian crust and a pumiceous core basaltic andesites contain olivine fo87 80 calcium rich plagioclase and sparse clinopyroxene microphenocrysts the typical mineralogy of dacitic and rhyolitic lavas is plagioclase two pyroxenes major and trace elements vary regularly with mgo taken as a differentiation index isla san luis lavas are enriched in lile and depleted in nb ta and ti their characteristics are intermediate between tholeiitic and calc alkaline lavas they are also lree enriched and the la yb n ratios steepen slightly with differentiation such an evolution is better explained by combined fractional crystallization and assimilation processes

effects of the vertical plasma drift velocity on the generation and evolution of equatorial spread f we use radar observations from the jicamarca observatory from 1968 to 1992 to study the effects of the f region vertical plasma drift velocity on the generation and evolution of equatorial spread f the dependence of these irregularities on season solar cycle and magnetic activity can be explained as resulting from the corresponding effects on the evening and nighttime vertical drifts in the early night sector the bottomside of the f layer is almost always unstable the evolution of the unstable layer is controlled by the history of the vertical drift velocity when the drift velocities are large enough the necessary seeding mechanisms for the generation of strong spread f always appear to be present the threshold drift velocity for the generation of strong early night irregularities increases linearly with solar flux the geomagnetic control on the generation of spread f is season solar cycle and longitude dependent these effects can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance dynamo electric fields the occurrence of early night spread f decreases significantly during equinox solar maximum magnetically disturbed conditions due to disturbance dynamo electric fields which decrease the upward drift velocities near sunset the generation of late night spread f requires the reversal of the vertical velocity from downward to upward for periods longer than about half an hour these irregularities occur most often at 0400 local time when the prompt penetration and disturbance dynamo vertical drifts have largest amplitudes the occurrence of late night spread f is highest near solar minimum and decreases with increasing solar activity probably due to the large increase of the nighttime downward drifts with increasing solar flux

comparative analysis of spread f signature and gps scintillation occurrences at tucuman argentina 1 we analyze data recorded from october 2010 to september 2011 during the ascending phase of the 24th solar cycle from an advanced ionospheric sounder istituto nazionale di geofisica e vulcanologia ionosonde and a gps ionospheric scintillation and total electron content tec monitor scintillation receiver colocated at low latitude in the southern american longitudinal sector tucuman 26 9 s 294 6 e magnetic latitude 15 5 s argentina the site offers the opportunity to perform spread f and gps scintillation statistics of occurrence under the southern crest of the equatorial ionospheric anomaly spread f signatures classified into four types strong range spread f ssf range spread f frequency spread f fsf and mixed spread f the phase and amplitude scintillation index and s4 respectively the tec and the rate of tec parameter marker of the tec gradients that can cause scintillations are considered the seasonal behavior results as follows the occurrence of all four types of spread f is higher in summer and lower in winter while the occurrence of scintillations peaks at equinoxes in the postsunset sector and shows a minimum in winter the correspondence between ssf and scintillations seems to be systematic and a possible correlation between s4 and fsf peaks is envisaged at the terminator the investigation focused also on two particular periods from 12 to 16 march 2011 and from 23 to 29 september 2011 both characterized by the simultaneous presence of ssf signatures and scintillation phenomena allowing to discuss the role of traveling ionospheric disturbances as a strong candidate causing ionospheric irregularities

volcano flank instability in the lesser antilles arc diversity of scale processes and temporal recurrence 1 the 1997 boxing day collapse a remarkable feature of the ongoing eruption of soufriere hills on montserrat has prompted new interest in the study of volcano stability in the lesser antilles building on a few cases documented in the literature we have now identified at least 47 flank collapse events on volcanoes of the caribbean arc where this type of behavior is characteristic and repetitive about 15 events occurred on active volcanoes within the last 12 000 years in the northern part of the arc flank collapses are repetitive do not exceed 1 km3 in volume occur in all directions and are promoted by intense hydrothermal alteration and well developed fracturing of the summit part of the edifices in contrast infrequent but large sector collapses with volumes up to tens of km3 are typical of the southern volcanoes they are always directed to the west as a result of the high overall slopes of the islands toward the deep back arc grenada basin because caribbean islands are small a large part of the resulting debris avalanches have flowed into the sea thus contributing voluminous and sudden inputs of volcaniclastic sediments to the grenada basin deposits from such submarine flows have been identified during the recent aguadomar and caraval oceanographic cruises and traced to their source structures on land edifice collapses have a major influence on subsequent volcanic activity but also are of high concern because of their tsunamigenic potential

revised global model of thermosphere winds using satellite and ground based observations thermospheric wind data obtained from the atmosphere explorer e and dynamics explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground based incoherent scatter radar and fabry perot optical interferometers to generate a revision hwm90 of the hwm87 empirical model and extend its applicability to 100 km comparison of the various data sets with the aid of the model shows in general remarkable agreement particularly at mid and low latitudes the ground based data allow modeling of seasonal diurnal variations which are most distinct at mid latitudes while solar activity variations are now included they are found to be small and not always very clearly delineated by the current data they are most obvious at the higher latitudes the model describes the transition from predominately diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below significant altitude gradients in the wind are found to extend to 300 km at some local times and pose complications for interpretation of fabry perot observations

seismic and acoustic detection of a bolide airburst in the gulf of naples southern italy 1 on 10 september 2005 at 1711 lt 1511 ut a loud boom was heard on the ischia island a clear seismic signal was also recorded by the seismic monitoring network of the neapolitan volcanic areas ischia campi flegrei and mount vesuvius and on a regional station mount massico on the basis of the seismic recordings and on acoustic phenomena reports we relate this event to the atmospheric explosion airburst of a bolide about 15 km sw of ischia at an elevation of about 11 5 km the location has been obtained through nonlinear traveltime inversion in a realistic atmospheric model including wind effects we show using statistical estimators how the traveltime pattern is due to both atmospheric winds and the bolide trajectory using the same reasoning we discard a human origin supersonic jet or sea air missile in addition we also propose a new algorithm for fast acoustic traveltime computation for a supersonic moving source

seismic ground motions from a bolide shock wave 1 an intensely brilliant bolide accompanied by an audible sonic boom occurred on the night of 3 november 2003 2150 lt or 4 november 2003 0350 ut in northeastern arkansas the sonic boom was well recorded by 22 three component stations of the center for earthquake research and information cooperative seismic network arrival times and wave polarizations were used to reconstruct the acoustic wave front propagating across the network and to estimate trajectory parameters of the bolide a grid search location technique constrains the trajectory and gives a reference height of 50 100 km above the southern edge of the network an azimuth of propagation of 270 290 toward the northwest and a plunge of 38 48 downward the trajectory and date of the bolide event are consistent with a taurid shower meteor transient ground motions from the sonic boom were studied using plane wave cagniard dehoop and propagator matrix theory for an incident pressure pulse impinging on a layered elastic earth model general characteristics of the vertical and radial polarization and wave frequency content require acoustic coupling within a thin 10 m near surface layer with low p wave 0 25 km s and s wave 0 125 km s velocities ground motions are generally confined to this near surface layer are not sensitive to deeper earth structure within the mississippi embayment unconsolidated sediments and display both leaky mode pl a type of dispersed p type seismic wave and locked mode rayleigh wave propagation acoustic wave ground motion coupling studies may be a useful way to analyze near surface site responses to determine velocity structure in earthquake shaking hazard studies

radar and satellite global equatorial f region vertical drift model we present the first global empirical model for the quiet time f region equatorial vertical drifts based on combined incoherent scatter radar observations at jicamarca and ion drift meter observations on board the atmospheric explorer e satellite this analytical model based on products of cubic b splines and with nearly conservative electric fields describes the diurnal and seasonal variations of the equatorial vertical drifts for a continuous range of all longitudes and solar flux values our results indicate that during solar minimum the evening prereversal velocity enhancement exhibits only small longitudinal variations during equinox with amplitudes of about 15 20 m s is observed only in the american sector during december solstice with amplitudes of about 5 10 m s and is absent at all longitudes during june solstice the solar minimum evening reversal times are fairly independent of longitude except during december solstice during solar maximum the evening upward vertical drifts and reversal times exhibit large longitudinal variations particularly during the solstices in this case for a solar flux index of 180 the june solstice evening peak drifts maximize in the pacific region with drift amplitudes of up to 35 m s whereas the december solstice velocities maximize in the american sector with comparable magnitudes the equinoctial peak velocities vary between about 35 and 45 m s the morning reversal times and the daytime drifts exhibit only small variations with the phase of the solar cycle the daytime drifts have largest amplitudes between about 0900 and 1100 lt with typical values of 25 30 m s we also show that our model results are in good agreement with other equatorial ground based observations over india brazil and kwajalein

the 2003 kanto large bolide s trajectory determined from shockwaves recorded by a seismic network and images taken by a video camera 1 anomalous loud sounds like booms were heard in a wide area in the kanto region japan on june 16 2003 since the sky was thickly clouded the source of the sounds which was supposed to be a meteoroid penetrating the atmosphere was hardly witnessed and photographed it was recorded by only one video camera we searched the shockwaves from the meteoroid recorded by a dense seismographic network shockwave signals were identified at 40 stations of the network deployed in the region we report here the trajectory of the meteoroid determined by an analysis of seismic data combining the trajectory with the video camera data we determined the precise velocity of the bolide in the atmosphere

eruption transport and deposition of ignimbrite a case study from mexico abstract the acatlan ignimbrite covers 150 km 2 around a vent situated 40 km southwest of guadalajara mexico the upper and main ignimbrite flow unit is compositionally zoned and has white or pink rhyolitic pumice in its lower part and black andesite in its upper these parts are believed to have been erupted continuously from the same magma chamber this zonation has been important in correlating an extremely coarse lithic rich deposit a co ignimbrite lag fall deposit with this ignimbrite the co ignimbrite lag fall deposit indicates that the flow unit formed by continuous collapse of an explosive eruption column and enables the source vent to be located the vertical compositional grading of the flow unit also provides a means of testing the various proposed mechanisms of ignimbrite emplacement turbulent vs high concentration flow the preservation of compositional zonation and other features in the deposit indicate that flow was not turbulent details of the grain size distribution indicate that laminar flow was important early in the flow history when collapsing material from the eruption column was superimposed in stratigraphical sequence initial high gas flow rates associated with flow segregation and formation at the site of column collapse rapidly decayed away from vent and later in its history the flow degassed to a semi rigid plug overriding a sheared basal layer

radiocarbon redating of contaminated samples from a tropical volcano the mansion series of st kitts west indies heavy rainfall and dense vegetation on tropical volcanoes produce abundant carbonized wood in pyroclastic deposits in addition to easy contamination of this wood by root systems and soluble humic material because the physical nature of the charcoal varies some samples are more prone to contamination two independent studies of the same volcano mt liamuiga on st kitts in the lesser antilles sometimes using samples from the same carbonized tree yielded a systematic difference in radiocarbon ages an exchange of samples and a re investigation of three physically distinct types of charcoal yielded the following results rare hard dense charcoal lacking contamination which had yielded a spurious age of 2860 years bp was redated at 1845 58 years bp common soft friable charcoal with good cellular structure proved to be susceptible to contamination a field decontamination technique utilized by one group seems significant as it yields older ages than when only routine laboratory pre treatment was used indicating that the latter technique only partly removes the dried and hard residue produced by the decomposition of modern plant rootlets a previous date of 24870 years bp obtained from powdery charcoal in a horizon beneath the mansion series contradicted ages older than 41000 years bp from common friable charcoal in the lower mansion series the soft powdery charcoal was re investigated using a sample collected a few centimeters from the original although field decontamination of this sample was not possible more extensive laboratory treatment yielded an age of ca 43000 years bp again proving that routine laboratory pretreatments are inadequate a revised geochronology for the mansion series is described and a cautionary discussion is presented for the benefit of investigators using radiocarbon ages to date volcanic deposits

reconnaissance de structures tectoniques et volcaniques sous marines de l arc recent des petites antilles kick em jenny qualibou montagne pelee nordouest de la guadeloupe abstract a multibeam bathymetric survey seacarib 1 was carried out in april 1985 on board the r v conrad lamont doherty geological observatory off the western coasts of several islands of the lesser antilles complementing a previous survey of the same type arcante 2 thermosite 1980 devoted to adjoining areas in guadeloupe martinique and st lucia it allowed us to precisely map submarine volcanoes in a marginal setting behind the recent arc the main volcanic axis of the archipelago emplaced during the neogene the kick em jenny volcano south of the grenadines is the only active submarine volcano of the lesser antilles it is a small and very young cone probably only tens or hundreds of years old which was hydrothermally active during the survey the directeur volcano guadeloupe is the largest submerged volcanic centre thus far detected in the lesser antilles having been formed between 3 3 and 2 9 ma during the 1980 survey two other large volcanoes were discovered off southern basse terre guadeloupe vieux fort volcano 2 5 2 0 ma and in front of fort de france bay martinique schoelcher volcano older than 4 2 ma several other much smaller volcanoes have been mapped off the same coasts particularly the bouillante seapeaks guadeloupe moreover large tectonic structures cut the recent arc transversally and obliquely the well known qualibou depression on the island of st lucia was interpreted in various ways neither the hypothesis of a large caldera the western side of which collapsed offshore nor the suggestion of a huge rotational gravity slide are confirmed the depression seems more likely to have been controlled by tectonic factors shaping a complex graben structure the seaward extension appears to be restricted to a northern channel the soufriere channel the st pierre fault in martinique is a large transverse feature extending seaward down to some 2000 m depth to the south it bounds the mount pelee active volcanic system and the escarpment of the fault forms a dam against subaqueous pyroclastic flows running down from the volcano these flows are responsible for the unusually smooth morphology of the submarine flanks the zombi fault of northwest guadeloupe is part of a first order feature extending along at least 130 km from montserrat in the north to marie galante in the east this curved fracture cuts across the northern central part of the lesser antilles passing progressively from a subparallel to a transverse orientation with respect to the axis of the island arc these types of surveys are important because they provide better understanding of the structure and recent geological evolution of the recent volcanic arc they are also a useful complementary tool for geothermal and seismological studies

the qualibou caldera st lucia west indies abstract recent geological geophysical and hydrogeochemical studies conducted in the qualibou area of st lucia west indies provide new data for reevaluation of the geothermal resource and recommendation of sites for renewed drilling activities this work supports the original hypothesis of tomblin that the qualibou depression is a caldera precaldera volcanic activity was concentrated along faults associated with regional ne and nw trending structures basaltic lavas dated at 5 5 ma crop out along the western coast and are overlain by andesitic composite cones dated at 1 2 and 0 9 ma which form the highest ridges of the island superimposed upon the andesitic cones are dacitic domes 0 25 ma the eroded plugs of two of these form the spectacular pitons the major event in this volcanic field was the intermittent eruption of the choiseul pumice concurrent with the formation of the qualibou caldera 32 000 to 39 000 yrs ago about 6 km3 dense rock equivalent of lithic crystal andesitic tephra was erupted mainly as nonwelded to welded pyroclastic flows and surges some of these tuffs have been identified in geothermal drill holes within the 12 km2 caldera postcaldera eruption of dacitic tephra and dome lava 20 000 to 32 000 yrs ago occurred from vents within the caldera and appear to be a result of magmatic resurgence a 5 2 km long dipole dipole dc resistivity survey measured along a north south trending line through the caldera gave apparent resistivity results similar to those obtained in previous studies these results are compatible with a caldera substructure where low apparent resistivities analysis and interpretation of hydrogeochemical data from the qualibou caldera indicate that a geothermal reservoir underlies the sulphur springs area and consists of three layers 1 an upper steam condensate zone 2 an intermediate two phase vapor zone and 3 a lower brine zone measured temperatures at depth of 212 c are complemented by estimated temperatures of 250 c in the brine layer the water chemistry of various thermal springs indicates upwelling primarily near the caldera center at sulphur springs which feeds steam to steamcondensate hot springs along the northern caldera wall

timing and emplacement dynamics of newly recognised mass flow deposits at 8 12ka offshore soufriere hills volcano montserrat how submarine stratigraphy can complement subaerial eruption histories this contribution describes two mass movement deposits total volume 0 5 km3 identified in seven marine cores located 8 to 15 km offshore southern montserrat west indies the deposits were emplaced in the last 35 ka and have not previously been recognised in either the subaerial or distal submarine records age constraints provided by radiocarbon dating show that an explosive volcanic eruption occurred at ca 8 12 ka emplacing a primary eruption related deposit that overlies a large 0 3 km3 reworked bioclastic and volcaniclastic flow deposit formed from a shelf collapse between 8 and 35 ka the origin of these deposits has been deduced through the correlation of marine sediment cores component analysis and geochemical analysis the 8 12 ka primary volcanic deposit was likely derived from a highly erosive pyroclastic flow from the soufriere hills volcano that entered the ocean and mixed with the water column forming a water supported density current previous investigations of the eruption record suggested that there was a hiatus in activity at the soufriere hills volcano between 16 and 6 ka the ca 8 12 ka eruptive episode identified here shows that this hiatus was shorter than previously hypothesised and thus highlights the importance of obtaining an accurate and complete marine record of events offshore from volcanic islands and incorporating such data into eruption history reconstructions comparisons with the submarine deposit characteristics of the 2003 dome collapse also suggests that the 8 12 ka eruptive episode was more explosive than eruptions from the current eruptive episode

lava dome growth and explosive volcanism in the jemez mountains new mexico evidence from the plio pleistocene puye alluvial fan abstract the plio pleistocene puye formation north central new mexico is a 200 km2 volcanogenic alluvial fan shed eastward from the tschicoma volcanic center part of the jemez mountains volcanic field the fan contains 15km3 of volcaniclastic material derived from closely spaced lava domes in the northeastern portion of the tschicoma center interbedded in the fan sediments are at least 25 primary pyroclastic units from explosive eruptions of dacitic and rhyolitic lava domes tephra occur mainly as pumice falls but include several pumiceous ignimbrites and two thick proximal block and ash pyroclastic flows the upper part of the fan also contains rhyolitic plinian deposits erupted from sources in the central portion of the jemez field and basaltic ash derived from the central rio grande rift fanglomeratic pyroclastic and epiclastic facies exhibit considerable lateral variation primary tephra deposits however provide a stratigraphic framework for reconstruction of the growth of individual lava domes while only volcanic domes and lava flows are exposed in the tschicoma center puye tephra layers show that vulcanian subplinian and plinian activity and block and ash pyroclastic flows accompanied many dome forming events degradation of these lava domes produced coarse grained debris flows dominated by lava and dome carapace clasts from these epiclasts it is possible to identify lithologies of lavas that are either currently buried or have been obliterated by erosion or by collapse of the valles calderas the preservation of puye deposits reflects very high rates of aggradation and gradual down faulting in the espanola basin of the central rio grande rift this record of pyroclastic and epiclastic deposition allows detailed interpretation of the evolution of a volcanic center from its pyroclastic and erosion products and is the first example of a volcanogenic alluvial fan in an intracontinental rift setting to be described in detail this study emphasizes that interpretation of any ancient volcanic terrain based solely upon data derived from mapping radiometric dating and chemical analysis of lavas or existing denuded edifices is likely to greatly underestimate both the role of explosive volcanism in the build up of volcanic centers and subsequent estimates of the volumes of material produced