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

possible causes for the seismic activity observed in cotopaxi volcano ecuador continuous monitoring of cotopaxi volcano from january 1989 to september 1997 shows that it is subject to a steady shallow long period lp activity lp events are concentrated in a column with a diameter of about 3 km and a height of about 12 km between an elevation of 4 km and 8 km depth they do not occur in swarms nor have there been periods of complete calm high frequency volcano tectonic vt events are mostly located on the northeastern side of the lp column with the maximum activity of both types of events coinciding in depth lp activity cannot be related to unrest of the volcano the most likely explanation for the continuous occurrence of lp events beneath cotopaxi is that they are produced by the interaction of glacier thaw water and hot material at shallow depths the relative spatial distribution of both type of events in two adjacent zones suggest that vt and lp activities are interconnected

source process of very long period events accompanying long period signals at cotopaxi volcano ecuador abstract renewed seismic activity of cotopaxi ecuador began in january 2001 with the increased number of long period lp events followed by a swarm of volcano tectonic vt earthquakes in november 2001 in late june 2002 the activity of very long period vlp 2 s events accompanying lp 0 5 1 s signals began beneath the volcano the vlp waveform was characterized by an impulsive signature which was accompanied by the lp signal showing non harmonic oscillations we observed temporal changes of both the vlp and lp signals from the beginning until september 2003 the vlp signal gradually disappeared and the lp signal characterized by decaying harmonic oscillations became dominant assuming possible source geometries we applied a waveform inversion method to the observed waveforms of the largest vlp event our inversion and particle motion analyses point to volumetric changes of a sub vertical crack as the vlp source which is located at a depth of 2 3 km beneath the northeastern flank the spectral analysis of the decaying harmonic oscillations of lp events shows frequencies between 2 0 and 3 5 hz with quality factors significantly above 100 the increased vt activity and deformation data suggest an intrusion of magma beneath the volcano a release of gases with small magma particles may have repetitively occurred due to the pressurization which was caused by sustained bubble growth at the magma ceiling the released particle laden gases opened a crack above the magma system and triggered the resonance of the crack we interpret the vlp and lp events as the gas release process and the resonance of the crack respectively

gas aerosol ash interaction in volcanic plumes new insights from surface analyses of fine ash particles the reactions occurring between gases aerosols and silicate ash particles in volcanic eruption plumes remain poorly understood despite the fact that they are at the origin of a range of volcanic environmental atmospheric and health effects in this study we apply x ray photoelectron spectroscopy xps a surface sensitive technique to determine the chemical composition of the nearsurface region 2 10 nm of nine ash samples collected from eight volcanoes in addition atomic force microscopy afm is used to image the nanometer scale surface structure of individual ash particles isolated from three samples we demonstrate that rapid acid dissolution of ash occurs within eruption plumes this process is favoured by the presence of fluoride and is believed to supply the cations involved in the deposition of sulphate and halide salts onto ash afm imaging also has permitted the detection of extremely thin 10 nm coatings on the surface of ash this material is probably composed of soluble sulphate and halide salts mixed with sparingly soluble fluoride compounds the surface approach developed here offers promising aspects for better appraising the role of gas aerosol ash interaction in dictating the ability of ash to act as sinks for various volcanic and atmospheric chemical species as well as sources for others c 2007 elsevier b v all rights reserved

trajectories of thermospheric air parcels flowing over alaska reconstructed from ground based wind measurements it is widely presumed that the convective stability and enormous kinematic viscosity of earth s upper thermosphere hinders development of both horizontal and vertical wind shears and other gradients any strong local structure over scale sizes of several hundreds of kilometers that might somehow form would be expected to dissipate rapidly air flow in such an atmosphere should be relatively simple and transport effects only slowly disperse and mix air masses however our observations show that wind fields in earth s thermosphere have much more local scale structure than usually predicated by current modeling techniques at least at auroral latitudes they complicate air parcel trajectories enormously relative to typical expectations for tracing air parcels we used wind measurements of an all sky scanning doppler fabry perot interferometer and reconstructed time resolved two dimensional maps of the horizontal vector wind field to infer forward and backward air parcel trajectories over time this is the first comprehensive study to visualize the complex motions of thermospheric air parcels carried through the actual observed local scale structures in the high latitude winds results show that thermospheric air parcel transport is a very difficult observational problem because the trajectories followed are very sensitive to the detailed features of the driving wind field to reconstruct the actual motion of a given air parcel requires wind measurements everywhere along the trajectory followed with spatial resolutions of 100 km or less and temporal resolutions of a few minutes or better understanding such transport is important for example in predicting the global scale impacts of aurorally generated composition perturbations

neutral thermospheric dynamics observed with two scanning doppler imagers 3 horizontal wind gradients 1 this is the third and final article in a series of papers reporting on observations of the 630 0 nm thermospheric airglow emission by two spatially separated scanning doppler imagers sdi s in alaska in this article bistatic winds derived from the combined measurements of both instruments in a region of field of view overlap were used to derive local scale maps of horizontal neutral wind gradients averaged over the bistatic field of view these gradient estimates were compared with the monostatic gradient estimates routinely produced by the two sdi s the key findings to emerge from this study include 1 the bistatic gradient estimate agreed very well with monostatic estimates for the majority of the time which given the very different methods involved in each technique gives us great confidence in our ability to measure f region neutral wind gradients 2 the strongest gradient was that which describes the magnetic meridional shear of the zonal wind which is driven by momentum deposition from convecting ions 3 vortical flow was more often observed than divergent flow and both types of flow showed systematic variations with magnetic local time 4 viscous heating due to non negligible gradients was on the order of 10 11 wm 3 which while small compared to typical f region joule heating rates may be comparable to particle heating and in a time integrated sense may be an appreciable source of heating

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

combining ash analyses with remote sensing to identify juvenile magma involvement and fragmentation mechanisms during the 2018 19 small eruption of peteroa volcano southern andes abstract the planchon peteroa volcanic complex ppvc is located on the border of chile and argentina and is one of the most active volcanic systems in the andes holocene activity has included magma water interaction with an evolving series of crater lakes mainly sourced from peteroa volcano this study examines data from the 2018 19 eruption together with the volcanic history of the ppvc to elucidate the complex interplay between magmatic activity and summit water and ice from february 2016 to mid 2019 three seismic swarms occurred in the ppvc preceding the explosive eruption from september 2018 to april 2019 the activity originated from a small vent nested within the easternmost crater the most active portion of the complex peteroa the explosions interacted with a crater lake producing ash plumes up to 2 km above the crater and building a small tephra cone to investigate the eruption mechanisms we performed remote sensing analysis of plume dispersal thermal anomalies and ground deformation and characterized the volcanic products including grain size componentry morphology internal textures composition and mineralogy our results suggest that the precursory seismicity beginning in 2016 was related to the intrusion of a new magma batch that reached the surface during the 2018 19 eruption the eruption was also preceded by thermal anomalies geomorphic changes and increased hydrothermal activity at the surface though without any ground deformation recognized through radar interferometry insar the eruption initially produced predominantly recycled ash phreatic activity then evolved to increasing proportions of juvenile magma phreatomagmatic by april 2019 the juvenile clasts had a trachyandesite composition 59 wt sio2 with vesicular and dense scoria containing plagioclase and pyroxene the ash surfaces show external quenching cracks and step fractures consistent with phreatomagmatic fragmentation within the active crater lake textural characteristics also point to a slowly ascending batch of magma that was relatively viscous by the time it interacted with water in the crater lake notably these juvenile particles are distinctive from the pre 2018 products ash erupted from 2010 11 did not contain recognizable juvenile material and is inferred to have been a mainly phreatic eruption our findings suggest that the interplay between phreatic and phreatomagmatic eruptions fed by small magma batches intruding at shallow levels characterize much of the eruptive behavior of the ppvc during the last three decades multi parametric assessment is a powerful tool to discriminate between phreatic and phreatomagmatic eruptions

mapping thermospheric winds in the auroral zone a new all sky imaging fabry perot asifp spectrometer has been developed for ground based mapping of upper atmospheric wind and temperature fields in the auroral zone although several other asifp spectrometers exist for atmospheric studies rees et al 1984 sekar et al 1993 biondi et al 1995 these instruments have all operated with etalons of fixed optical gap a method potentially subject to errors in the presence of auroral intensity gradients in this instrument the etalon plate spacing is scanned periodically over one order of interference and each photon detected is assigned to a wavelength interval which is determined from both its arrival location on the detector and the etalon plate spacing prevailing at the detection time spectra accumulated this way are not distorted by spatial intensity gradients preliminary 630 nm observations were made during the winter of 1994 95 from poker flat research range alaska to illustrate some of the features we have observed in this study we present line of sight wind estimates derived for the night of december 7 1994 the background wind matches averages presented previously by sica et al 1986 and is consistent with winds driven principally by momentum deposition from ionospheric plasma convection through ion drag smaller scale curvature and divergence features are also discernable and are discussed

estimating volcanic deformation source parameters with a finite element inversion the 2001 2002 unrest at cotopaxi volcano ecuador deformation at cotopaxi was observed between 2001 and 2002 along with recorded seismicity beneath the northeast ne flank despite the fact that the last eruption occurred in 1942 we use electronic distance meter deformation data along with the patterns of recorded seismicity to constrain the cause of this unrest episode to solve for the optimum deformation source parameters we employ inverse finite element fe models that account for material heterogeneities and surface topography for a range of source shapes the models converge on a shallow reservoir beneath the southwest sw flank the individual best fit model is a small oblate shaped source approximately 4 5 km beneath the summit with a volume increase of roughly 20 10 6 m 3 this sw source location contrasts with the ne seismicity locations subsequently further fe models that additionally account for temperature dependent viscoelasticity are used to reconcile the deformation and seismicity simultaneously comparisons of elastic and viscous timescales allude to aseismic pressurization of a small magma reservoir in the sw seismicity in the ne is then explained through a mechanism of fluid migration from the sw to the ne along fault systems we extend our analyses to further show that if future unrest crises are accompanied by measurable seismicity around the deformation source this could indicate a higher magma supply rate and increased likelihood of a forthcoming eruption

spatial structure in the thermospheric horizontal wind above poker flat alaska during solar minimum a new all sky imaging wavelength scanning fabry perot spectrometer was used to record high resolution r 200 000 spectra of the 630 nm thermospheric optical emission above poker flat alaska these spectra were used to derive spatially resolved maps of the horizontal wind vector at approximately 250 km altitude we describe the procedure used to infer vector winds from line of sight doppler shifts along with its limitations we present the time evolution of the vector wind fields obtained from this method for 6 nights of observation five of the 6 nights contained periods when we inferred the existence of significant curvature divergence or shear in the thermospheric wind across our instrument s 1000 km diameter field of view the sixth night exhibited little spatial structure and is shown for comparison we compare these results with a generic solar minimum winter time run of the national center for atmospheric research s thermosphere ionosphere and electrodynamics general circulation model while agreement was good at the start and end of the night considerable differences were found in the late evening and midnight sectors some possible origins for these discrepancies are proposed in particular we suggest that the f region horizontal wind may be deflected by upwelling vertical winds which are in turn driven by e region heating in the auroral zone we note that both the instrument used and our high latitude implementation of the analysis procedure are new experimental techniques thus the data presented here should be regarded as preliminary and if possible be validated by comparison with results from other techniques

sedimentological analysis of the tephra from the 12 15 august 1991 eruption of hudson volcano the tephra fallout from the 12 15 august 1991 explosive eruption of hudson volcano cordillera de los andes 45 54 s 72 58 w chile was dispersed on a narrow elongated ese sector of patagonia covering an area on land of more than 100 000 km2 the elongated shape of the deposit together with the relatively coarse mean and median values of the particles at a considerable distance from the vent were the result of strong winds blowing to the southeast during the eruption the thickness of the fall deposit decreases up to 250 km ese from hudson volcano where it begins to thicken again secondary maxima are well developed at approximately 500 km from the vent secondary maxima together with grainsize bimodality in individual layers and in the bulk deposit suggest that particle aggregation played an important role in tephra sedimentation the fallout deposit is well stratified with alternating fine grained and coarsegrained layers which is probably a result of strong eruptive pulses followed by relatively calm periods and or changes in the eruptive style from plinian to phreatoplinian the tephra is mostly composed of juvenile material the coarse mode mostly pumice shifts to finer sizes with distance from the volcano the fine mode mostly glass shards is always about 5 6 phi glass shards and pumice are mostly light gray to colorless however considerable amounts of dark poorly vesiculated blocky shards suggest a hydromagmatic component in the eruption a land based tephra volume of 4 35 km3 was estimated and a total volume of 7 6 km3 arose from an extrapolation which took into account the probable volume sedimented in the sea bulk density ranges from 0 9 to 1 10 gr cm3 beyond 110 km from the vent rather uniform density values measured in crushed samples 2 45 2 50 gr cm3 at all distances from the vent reveal a relatively homogeneous composition mean and median sizes decrease rapidly up to 270 km from the vent beyond that point they are more or less constant whereas the maximum size 1 phi shows a steady decrease up to 550 km a concomitant improvement in sorting is observed this is attributed to sorting due to wind transport combined with particle aggregation at different times and distances from the vent the hudson tephra fallout shares some strikingly similar features with the mount st helens 18 may 1980 and quizapu 1932 eruptions

simultaneous fpi and tma measurements of the lower thermospheric wind in the vicinity of the poleward expanding aurora after substorm onset

superficial simplicity of the 2010 el mayor cucapah earthquake of baja california in mexico the geometry of faults is usually thought to be more complicated at the surface than at depth and to control the initiation propagation and arrest of seismic ruptures the fault system that runs from southern california into mexico is a simple strike slip boundary the west side of california and mexico moves northwards with respect to the east however the m w 7 2 2010 el mayor cucapah earthquake on this fault system produced a pattern of seismic waves that indicates a far more complex source than slip on a planar strike slip fault here we use geodetic remote sensing and seismological data to reconstruct the fault geometry and history of slip during this earthquake we find that the earthquake produced a straight 120 km long fault trace that cut through the cucapah mountain range and across the colorado river delta however at depth the fault is made up of two different segments connected by a small extensional fault both segments strike n130 e but dip in opposite directions the earthquake was initiated on the connecting extensional fault and 15 s later ruptured the two main segments with dominantly strike slip motion we show that complexities in the fault geometry at depth explain well the complex pattern of radiated seismic waves we conclude that the location and detailed characteristics of the earthquake could not have been anticipated on the basis of observations of surface geology alone

optical observations of thermospheric dynamics at arecibo observations of thermospheric neutral winds have been made at arecibo puerto rico by using a fabry perot interferometer to measure the doppler shift of the nighttime o d 630 nm emission we have developed a scheme of making observations at eight equally spaced azimuth positions with a constant zenith angle this technique allows us to determine the mean neutral wind velocities in the meridional and zonal directions as well as any horizontal gradients in the wind field it also provides a good means of simultaneously monitoring any spatial variations in neutral temperature and the intensity of the o d emission in general the highest equatorward wind velocity is observed at about 2100 lst the meridional wind velocity usually lessens as midnight approaches and sometimes but by no means always reverses after midnight the magnitude of the equatorward velocity is greater in summer than in winter months for winter and spring months the zonal wind blows eastward throughout the night with the velocity tending to decrease in a fairly regular fashion from about 125 m s 1 at 2100 lst towards zero by 0400 lst in summer the pattern is similar but the eastward flow usually reverses earlier and a westward velocity of some 50 m s 1 may be attained by 0400 lst significant horizontal wind gradients are often observed in the meridional direction but not in the zonal direction near midnight especially during both the equinox and summer months the equatorward wind is often greater to the north of arecibo than to the south we interpret this as being an effect of the passage of the midnight equatorial pressure maximum to the south of the station measurements of neutral temperature with the interferometer do indeed show that between 0100 0200 lst the neutral temperature to the south of arecibo is enhanced by some 40 k over that to the north

assimilated observations of thermospheric winds the aurora and ionospheric currents over alaska we present simultaneous measurements of thermospheric winds auroral emissions and ionospheric currents over alaska obtained from four separate instruments thermospheric f region wind maps were recorded by an all sky imaging fabry perot spectrometer located at poker flat and observing at 630 0 nm auroral images at 557 7 nm were obtained from the low resolution visible imager on board the polar satellite white light all sky auroral images were recorded by ground based all sky cameras located in alaska at poker flat 65 07 n 212 34 e and at kaktovik 70 06 n 217 24 e finally the east west component of the ionospheric f region plasma convection was inferred using the alaskan meridian chain of magnetometers montage images of these four data sets are presented projected onto a geographic map of the alaskan region we examine a 10 hour period during the alaskan local nighttime of february 10 1997 these montages illustrate a close relationship between spatial structures occurring in the aurora in the ionospheric plasma convection and in the f region wind field latitudinal shear of the geomagnetic zonal wind often observed in the premidnight time sector was seen to be associated with both the equatorward and poleward boundaries of the discrete aurora we focus particularly on a period commencing just after 0900 ut when a strong shear in the zonal wind was observed to sweep southward across alaska after magnetic midnight the wind field was dominated by the emergence of the cross polar jet from the polar cap this overwhelmed any wind features associated with local auroral processes

seasonal dependence of northern high latitude upper thermospheric winds a quiet time climatological study based on ground based and space based measurements this paper investigates the large scale seasonal dependence of geomagnetically quiet time northern high latitude f region thermospheric winds by combining extensive observations from eight ground based optical remote sensing and three space based optical remote sensing and in situ instruments to provide a comprehensive picture of the wind morphology data are assimilated into a seasonal empirical vector wind model as a function of season latitude and local time in magnetic coordinates the model accurately represents the behavior of the constituent data sets there is good general agreement among the various data sets but there are some major offsets between goce and the other data sets especially on the duskside the assimilated wind patterns exhibit a strong and large duskside anticyclonic circulation cell sharp latitudinal gradients in the duskside auroral zone strong antisunward winds in the polar cap and a weaker tendency toward a dawnside cyclonic circulation cell the high latitude wind system shows a progressive intensification of wind patterns from winter to equinox to summer the latitudinal extent of the duskside circulation cell does not depend strongly on season zonal winds show a mainly diurnal variation two extrema around polar and middle latitudes and semidiurnal variation four extrema at auroral latitudes meridional winds are primarily diurnal at all high latitudes the strength of zonal winds channeling through the auroral zone on the duskside is strongest in the summer season the vorticity of the wind pattern increases from winter to summer whereas divergence is maximum in equinox in all three seasons divergence is weaker than vorticity

volcanic ash leachate compositions and assessment of health and agricultural hazards from 2012 hydrothermal eruptions tongariro new zealand abstract after almost 80 years of quiescence the upper te maari vent on mt tongariro erupted suddenly at 2352 h nz time on 6 august 2012 the short lived hydrothermal eruption distributed a fine ash of minor volume 5 10 5 m 3 over 200 km from source the threat of further eruptions prompted an investigation of the possible health and agricultural impacts of any future eruptions from this volcano particularly since the most recent large scale ash falls in new zealand in 1995 1996 had generated significant agricultural problems including livestock deaths deposited ash was sampled between 5 and 200 km from the volcano as soon as possible after the eruption two sub lobes of ash were identified from different vent areas and displayed subtly different leaching properties the first was an initial small lobe directed nne likely formed from drifting low level clouds associated with the initial lateral explosive blast and surges the main fall lobe directed eastward was sourced from a short lived vertical plume that rose up to c 8 km ash from the initial fall lobe had higher concentrations of f and al in single step leaches as well as in the totals of three sequential extractions further the initial lobe showed a higher proportion of soluble f and al extracted in the first leach compared to totals a linear relationship between concentrations of al and f in single leaches from the 6 august eruption was highly significant pearson correlation coefficient r 0 987 for 1 20 leaching ratios and r 0 971 for 1 100 suggesting the presence of soluble alumino fluoride complexes alf x 3 x an even more significant 1 1 ratio is displayed for the largest concentration leached ions of ca and so 4 which correspond to the presence of crystalline gypsum throughout the newly excavated hydrothermal system although no fresh magma was erupted in this event a shallow intrusion prior to the hydrothermal explosion apparently provided significant contents of volcanic gas that was dissolved within the hydrothermal fluids and adhering to ejected particles this and the ubiquitous presence of gypsum dominated the soluble components of these ash deposits leading to a complex leaching profile the leaching study carried out here showed that agricultural and human health hazard assessment particularly of f and s is not straightforward particularly because f solubility may be complex and not well characterised by simple leaching studies in the case of s which is agriculturally important saturation effects are apparent using normal leaching protocols and also imply a need for modification of standard methods

estimation of mesoscale thermospheric wind structure using a network of interferometers we introduce a technique for estimating the regional thermospheric wind field from measurements made by a network of interferometers unlike previous work this technique does not make assumptions about the functional form of the wind field and instead uses inverse theory to find the smoothest wind field that agrees with the measurements this technique is general and applies to any network making radial velocity measurements we show reconstructions of the thermospheric wind field over the eastern united states and over eastern brazil using data from two distinct networks of fabry perot interferometers measuring the doppler shift of the 630 0 nm airglow emission in brazil we find direct evidence of a convergent wind field during the period of rapid thermospheric temperature increase associated with the equatorial midnight temperature maximum

seismically induced mass movements and volumetric fluxes resulting from the 2010 mw 7 2 earthquake in the sierra cucapah mexico the observation that sediment flux from mountain ranges struck by high magnitude earthquakes can be strongly influenced by coseismic mass movements brings into question the nature of coseismic deformation as a net contributor to mountain building to better constrain the role of high magnitude earthquakes in orogenesis high resolution data of earthquake induced mass wasting is required for areas of differing tectonic morphological and climatic settings here we compare the erosional flux to the tectonic flux associated with the 2010 mw 7 2 sierra el mayor earthquake in mexico and examine the landslide patterning of coseismic mass movements associated with this event the ruptured fault system has a significant strike slip component with subsidence along the eastern flank and uplift on the western flank of the range peak ground acceleration was highest along the steepest sections of the range such that the frequency of landslide occurrence was strongly correlated to slope gradient both vertical and horizontal coseismic displacement demonstrated a strong control over landslide initiation this result suggests that strike slip systems experience very different landslide patterning to thrust faults during earthquakes based on interferometric analysis of synthetic aperture radar images the earthquake resulted in a total uplifted volume of 41 6 106 m3 and a loss of 95 2 106 m3 due to subsidence this suggests a net tectonic volumetric flux of 53 6 106 m3 sediment mobilisation by coseismic landslides is estimated at 2 7 106 m3 derived from a manually mapped inventory using spot 5 multispectral imagery thus the net volume loss through coseismic subsidence of the mountain range generated a strongly negative mass flux which was only marginally enhanced by mass wasting

relationship between volcanic ash fallouts and seismic tremor quantitative assessment of the 2015 eruptive period at cotopaxi volcano ecuador understanding the relationships between geophysical signals and volcanic products is critical to improving real time volcanic hazard assessment thanks to high frequency sampling campaigns of ash fallouts 15 campaigns 461 samples the 2015 cotopaxi eruption is an outstanding candidate for quantitatively comparing the amplitude of seismic tremor with the amount of ash emitted this eruption emitted a total of 1 2e 9 kg of ash 8 6e 5 m3 during four distinct phases with masses ranging from 3 5e 7 to 7 7e 8 kg of ash we compare the ash fallout mass and the corresponding cumulative quadratic median amplitude of the seismic tremor and find excellent correlations when the dataset is divided by eruptive phase we use scaling factors based on the individual correlations to reconstruct the eruptive process and to extract synthetic eruption source parameters daily mass of ash mass eruption rate and column height from the seismic records we hypothesize that the change in scaling factor through time associated with a decrease in seismic amplitudes compared to ash emissions is the result of a more efficient fragmentation and transport process these results open the possibility of feeding numerical models with continuous geophysical data after adequate calibration in order to better characterize volcanic hazards during explosive eruptions

estimating the volume of tephra deposits a new simple strategy volume determination of tephra deposits is necessary for the assessment of the dynamics and hazards of explosive volcanoes several methods have been proposed during the past 40 years that include the analysis of crystal concentration of large pumices integrations of various thinning relationships and the inversion of field observations using analytical and computational models regardless of their strong dependence on tephra deposit exposure and distribution of isomass isopach contours empirical integrations of deposit thinning trends still represent the most widely adopted strategy due to their practical and fast application the most recent methods involve the best fitting of thinning data using various exponential segments or a power law curve on semilog plots of thickness or mass area versus square root of isopach area the exponential method is mainly sensitive to the number and the choice of straight segments whereas the power law method can better reproduce the natural thinning of tephra deposits but is strongly sensitive to the proximal or distal extreme of integration we analyze a large data set of tephra deposits and propose a new empirical method for the determination of tephra deposit volumes that is based on the integration of the weibull function the new method shows a better agreement with observed data reconciling the debate on the use of the exponential versus power law method in fact the weibull best fitting only depends on three free parameters can well reproduce the gradual thinning of tephra deposits and does not depend on the choice of arbitrary segments or of arbitrary extremes of integration

chronology and dispersal characteristics of recently last 5000 years erupted tephra of cotopaxi ecuador implications for long term eruptive forecasting abstract cotopaxi the highest active volcano on earth and one of the most dangerous of ecuador is constituted by a composite cone made up of lava and tephra erupted from the summit crater the activity of the present volcano begun with large volume plinian eruptions followed by a succession of small volume lava emissions and pyroclastic episodes which led to the edification of a symmetrical cone the growth of the cone was broken by an episode of slope failure the scar of which is now obliterated by recent and historical products volcanic history eruptive frequency and characteristics of the activity were investigated by studying the stratigraphy of tephra and carrying out fifteen new 14 c dating on paleosols and charcoals the investigated period is comprised between the slope failure and the present the deposit of the volcanic landside dry debris avalanche of rio pita previously believed to be between 13 000 and 25 000 yr b p is now considered to have an age slightly older than 5000 yr b p the stratigraphy of tephra of the last 2000 years reveals the existence of 22 fallout layers seven of them were dated with 14 c whereas three were ascribed to the eruptions of 1534 1768 and 1877 on the basis of comparison with historical information maximum clast size distribution isopleths of 9 tephra layers points out that the sustained explosive eruptions of cotopaxi during the last 2000 years are characterized by very high dispersive power plinian plumes with column heights between 28 and 39 km and high intensity peak mass discharges from 1 1 to 4 1 10 8 kg s the magnitude mass of tephra fallout deposits calculated from distribution of thickness isopaches are however moderate from 0 8 to 7 2 10 11 kg the limited volume of magma erupted during each explosive episode is consistent with the lack of caldera collapses small volume pyroclastic flows and surges virtually accompanied all identified tephra fallouts during such an activity large scale snow ice melting of the summit glacier produced devastating mudflows comparable in scale to those of 1877 eruption by assuming a 1 1 correspondence between fallout episodes and generation of large scale lahar we have estimated an average recurrence of one explosive lahartriggering event every 117 years over the last two millennia this value compares well with that calculated by considering the period since spanish conquest the probability of having an eruption like this in 100 or 200 years is respectively of 0 57 and 0 82 such an high probability underscores the need for quick actions aimed at the mitigation of cotopaxi lahar hazard along all the main valleys which originate from the volcano

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

landslides earthquakes and erosion this paper relates landslide inventories to erosion rates and provides quantitative estimates of the landslide hazard associated with earthquakes we do this by utilizing a three parameter inverse gamma distribution which fits the frequency area statistics of three substantially dcompletet landslide event inventories a consequence of this general distribution is that a landslide event magnitude ml lognlt can be introduced where nlt is the total number of landslides associated with the landslide event using this general distribution landslide event magnitudes ml can be obtained from incomplete landslide inventories and the total area and volume of associated landslides as well as the area and volume of the maximum landslides can be directly related to the landslide event magnitude using estimated recurrence intervals for three landslide events and the time span for two historical inventories we estimate regional erosion rates associated with landslides as typically 0 1 2 5 mm year 1 we next give an empirical correlation between the earthquake magnitude associated landslideevent magnitude and the total volume of associated landslides using these correlations we estimate that the minimum earthquake magnitudes that will generate landslides is m 4 3f0 4 finally using gutenberg richter frequency magnitude statistics for regional seismicity we relate the intensity of seismicity in an area and the magnitude of the largest regional earthquakes to erosion rates we find that typical seismically induced erosion rates in active subduction zones are 0 2 7 mm year 1 and adjacent to plate boundary strike slip fault zones are 0 01 0 7 mm year 1

modeling thickness variability in tephra deposition the attenuation of tephra fall thickness is most commonly estimated after contouring isolated and often irregular field measurements into smooth isopachs with varying degrees of subjectivity introduced in the process here we present an explicit description of the variability introduced into a semiempirical tephra attenuation relation this opens the way to fitting models to actual tephra observations through maximum likelihood estimation rather than using weighted least squares estimation on the isopachs the method is illustrated for small scale basaltic explosive eruptions using a simple but typical data set of the actual tephra thickness data published from the 1973 heimaey eruption of the distributions considered to describe variability in these measurements the lognormal performed poorly due to its tendency to predict a small number of greatly over thickened deposits the weibull and gamma distributions fitted the data to a very similar degree and produced very similar estimates for the effective volume mean wind direction and mass thickness attenuation rate the latter can be inverted to obtain an estimate of the mean column height the estimated wind direction and the column height derived from the estimated thickness attenuation parameter agreed very well with the direct observations made during the eruption augmented by a mixture framework allowing for the incorporation of multiple lobes and or vents the model was able to identify the source and direction of tephra deposition for the 1977 ukinrek maars eruptions from only the tephra thickness data

landslide rupture and the probability distribution of mobilized debris volumes 1 landslide driven erosion is controlled by the scale and frequency of slope failures and by the consequent fluxes of debris off the hillslopes in this paper we tackle the magnitude frequency part of the process and develop a theory of initial slope failure and debris mobilization that reproduces the heavy tailed distributions probability density function or pdfs observed for landslide source areas and volumes landslide rupture propagation is treated as a quasi static noninertial process of simplified elastoplastic deformation with strain weakening debris runout is not considered the model tracks the stochastically evolving imbalance of frictional cohesive and body forces across a failing slope and uses safety factor concepts to convert the evolving imbalance into a series of incremental rupture growth or arrest probabilities a single rupture is simulated with a sequence of weighted coin tosses with weights set by the growth probabilities slope failure treated in this stochastic way is a survival process that generates asymptotically power law tail pdfs of area and volume for rock and debris slides predicted scaling exponents are consistent with analyses of landslide inventories the primary control on the shape of the model pdfs is the relative importance of cohesion over friction in setting slope stability the scaling of smaller shallower failures and the size of the most common landslide volumes are the result of the low cohesion of soil and regolith whereas the negative power law tail scaling for larger failures is tied to the greater cohesion of bedrock

regional patterns of earthquake triggered landslides and their relation to ground motion 1 we have documented patterns of landsliding associated with large earthquakes on three thrust faults the northridge earthquake in california chi chi earthquake in taiwan and two earthquakes on the ramu markham fault bounding the finisterre mountains of papua new guinea in each case landslide densities are shown to be greatest in the area of strongest ground acceleration and to decay with distance from the epicenter in california and taiwan the density of co seismic landslides is linearly and highly correlated with both the vertical and horizontal components of measured peak ground acceleration based on this observation we derive an expression for the spatial variation of landslide density analogous with regional seismic attenuation laws in its general form this expression applies to our three examples and we determine best fit values for individual cases our findings open a window on the construction of shake maps from geomorphic observations for earthquakes in non instrumented regions

sulfur as a binding agent of aggregates in explosive eruptions understanding the mechanisms that govern ash aggregation is of critical importance in volcanology aggregation reduces the residence time of ash 2 mm in the atmosphere strongly by enhancing the sedimentation of finer grained material generated during explosive eruptions to date experimental studies have focused on the expectation that water provides the strongest bonds between particles to form spherical to oblate aggregates typically less than or equal to a few mm occasionally up to several cm preserved in pyroclastic deposits under water rich conditions individual accreted particles rarely exceed 1 mm in pyroclastic density current deposits produced during the 1982 eruption of el chichon mexico which emitted 7 5 tg of so2 in the atmosphere aggregate particles one to several millimeters strongly cemented by a s rich film are common they exhibit similarities with aggregates found in sulfur cones at poas volcano costa rica we propose that sulfur is the binder between the silicate grains such a binding capacity implies a relatively fluid behavior of sulfur such as might be expected in the low viscosity temperature regime just above its melting point if so then the explosive ejection of sulfur during eruptions combined with its ability to act as a cement for particles 2 mm would imply that size fractions of lapilli can be efficiently removed from eruptive clouds a few kilometers from the vent such an aggregation mechanism would have important implications for pyroclast dispersal models and hazard assessment

neutral thermospheric dynamics observed with two scanning doppler imagers 2 vertical winds 1 this article is the second in a series of three papers reporting on observations of the 630 0 nm thermospheric airglow emission by two spatially separated scanning doppler imagers sdi s in alaska in this article line of sight wind measurements from these instruments in four common volume regions lying along the great circle joining the two observatories have been used to derive estimates of the vertical wind in those common volumes these estimates are combined with the vertical winds measured directly in each of the station zeniths to resolve both the spatial and temporal variations of the vertical wind field data from four nights are presented as examples of the wave like oscillations and frequently high spatial correlations that are observed a statistical study of data from the full 19 night data set showed that the frequency of observing statistically significant correlation between vertical winds measured at separate locations decreased linearly with increasing separation a linear fit to this trend indicated that for this particular location and orientation the largest separation over which statistically significant correlation would be expected to occur is approximately 540 km

phreatomagmatic ash from the ongoing eruption of etna reaching the greek island of cefalonia on october 26 2002 etna volcano sicily southern italy entered a new eruptive phase characterised by the usual effusive activity from fissure vents located both on the southern and on the northern sector of the summit area in addition explosive events of unusual intensity were recorded at the beginning of the eruption and produced a substantial plume rich in fine ash particles and steam on october 27 fine ash from the plume blown by the wind was reported falling on the island of cefalonia greece which is located approximately 500 km east of the volcano in this communication we report on the study of fine ash from the eruption as collected on cefalonia we elaborate on the nature of the peculiar type of explosion mechanism that led to such an unusual manifestation of etna which is phreatomagmatism this finding draws a new picture of the eruptive scenario of this active volcano and requires a careful evaluation of the hazard that similar events might pose in the future not just the surroundings of the volcano but also the aviation corridors of the southern mediterranean area could be potentially affected

cyclic processes and factors leading to phreatic eruption events insights from the 25 september 2007 eruption through ruapehu crater lake new zealand abstract a dangerous block ash eruption occurred without warning from ruapehu crater lake on 25 september 2007 ending a 6 month period of temperature decline in the lake the northerly directed blast sent ballistics of up to 2 m diameter more than 2 km from the source the ejecta comprised a variety of volcano lacustrine lithologies many showing evidence of intense hydrothermal alteration petrographic studies of the ballistics reveal numerous examples of pores vesicles being filled with assemblages of elemental sulphur anhydrite pyrite and natroalunite and many ballistics exuded liquid sulphur from their pores during cooling at atmospheric pressure up to 5 of the ash was comprised of fine grained juvenile glass material confirming the presence of magma in the shallow vent environment a long recognised characteristic of this volcano is the thermal cycling behaviour of the crater lake behaviour which has remained effectively unchanged through two magmatic eruption events in 1945 and in 1995 96 airborne measurements of co2 and so2 flux from the volcano since 2003 show a strong positive correspondence with temperature cycling in the lake pointing to a definitive link between heat and mass discharge through the system low so2 emission rates and c s mole ratios 30 were typical of the period 2003 to early 2007 and appear to reflect vigorous scrubbing of s gases in the hydrothermal system during this time to better understand the chemical and physical processes operating in this very dynamic volcanic hydrothermal system and its propensity to develop potentially dangerous hydrothermal seals we have developed an integrated finite difference tough2 heat mass transport simulation of the hydrothermal environment the model which is constrained by observed heat and mass flux characteristics of the volcano demonstrates the transient nature of the heating cycles on the vent lake system of particular interest is the role of co2 as a relatively inert pressure transmitting medium in the hydrothermal environment seal formation was simulated using the reactive transport code x1t which showed that condensation of magmatic vapour into a highly porous medium of andesitic composition leads to rapid formation of an elemental sulphur anhydrite natroalunite mineral assemblage and a drastic reduction in permeability we suggest that since the 1995 96 vent clearing eruptions a shroud of elemental sulphur and other alteration phases formed along the margins of the 2 phase liquid vapour region enclosing the conduit this effectively seals the upper portion of the vent from the adjacent hydrostatically controlled environment and allows for development of pressurised vapour static gas columns beneath the northern and central vents

hydrovolcanic ash emission between august 14 and 24 2015 at cotopaxi volcano ecuador characterization and eruption mechanisms abstract cotopaxi is an active hazardous and ice covered stratovolcano 60 km southeast of quito ecuador whose last major eruption occurred in 1877 during 2001 2002 volcanic unrest characterized by volcanic seismicity and deformation ended without eruptive activity on april 2015 a new increase of seismicity so2 emissions thermal anomalies and edifice deformation evolved into the onset of a new eruptive cycle beginning august 14 we sampled and measured the ash fall deposits to the west of cotopaxi between august 14 and 24 2015 the ash collected was analyzed using grain size x ray fluorescence x ray diffraction and scanning electron microscope sem eds revealing the eruptive products to be compound of dense fragments mostly lithics diverse types of scoria pumice free fractured crystals glassy particles and aggregates most of hydrothermal alteration is observed during the initial stage of the eruption 14 15 august including cu oxides and fe minerals in the lithics the glassy particles were blocky morphology and textural changes were recognized over 10 days of eruption varying from null or low vesicularity to low to moderate vesicularity occasionally exhibiting molten or subrounded textures the bulk ash has a basaltic andesitic composition 55 67 wt of sio2 while clusters of selected particles likely juvenile analyzed through sem eds reveal dacitic composition 65 67 and 65 8 wt sio2 plagioclase clinopyroxene and orthopyroxene are the main minerals present with accessory anhydrite melanterite and pyrite these typically observed during the initial stage of eruption these variations in addition to the geophysical background led us to interpret this eruption as the result of the volcano s hydrothermal system disruption due to a shallow low volume magma input which initially evolved into phreatic activity at surface level further activity up to 24 august was triggered by the indirect interaction between magma and the depleted hydrothermal system generating a magmatic hydrothermal eruption the issue is important for evaluating unrest periods at active stratovolcanoes and the impact of their initial low volume ash falls in neighboring communities

source parameters of the 1 october 1995 dinar turkey earthquake from sar interferometry and seismic bodywave modelling abstract the 1 october 1995 m s 6 1 dinar earthquake ruptured a 10 km section of the nw se dinar civril fault there are discrepancies between the published source parameters from seismic data with seismic moments in disagreement by over a factor of two we use both sar interferometry and seismic bodywave modelling to determine earthquake source parameters an interferogram generated from ers 1 2 sar imagery spanning the event and separated by 5 months is used to derive source parameters by a downhill simplex inversion with multiple monte carlo restarts we model the displacements in the satellite line of sight initially using uniform slip on a rectangular dislocation in an elastic half space the resultant model fault plane agrees in strike and location with the observed surface break but systematic residuals exist in the line of sight deformation field resulting in a r m s residual of 20 mm in the interferogram the residuals are reduced if the depth distribution of slip is allowed to vary spatially in four segments along a continuous fault plane our best fitting solution with a r m s misfit of 8 mm reveals two distinct areas of slip on the fault plane strike 145 dip 49 rake 270 a main rupture slipping by 1 44 m between depths of 1 and 8 km becoming deeper to the se and matching the observed surface rupture and an along strike continuation to the nw of the same fault plane but between depths of 8 and 13 km and not associated with a surface break the total geodetic moment 4 5 0 1 10 18 nm is more than twice as large as published seismic moments based on the inversion of p waveforms alone but close to the harvard cmt moment 4 7 10 18 nm we use sh waveforms in addition to the p waves used previously to determine an alternative seismic source mechanism sh waves constrain the depth to be shallower than solutions based on p waves alone agreeing with the depths from the interferometric inversion and resulting in a larger moment 3 1 0 4 10 18 nm than the previous bodywave estimates 2 2 1 10 18 nm the cmt moment reduces in magnitude to a similar size 3 3 10 18 nm if the centroid depth and fault dip are constrained to the values determined from bodywave modelling and interferometry thus the geodetic moment is 40 bigger than the moment determined from seismology

statistical analysis of an earthquake induced landslide distribution the 1989 loma prieta california event the 1989 loma prieta california earthquake moment magnitude m 6 9 generated landslides throughout an area of about 15 000 km2 in central california most of these landslides occurred in an area of about 2000 km2 in the mountainous terrain around the epicenter where they were mapped during field investigations immediately following the earthquake the distribution of these landslides is investigated statistically using regression and one way analysis of variance anova techniques to determine how the occurrence of landslides correlates with distance from the earthquake source slope steepness and rock type the landslide concentration defined as the number of landslide sources per unit area has a strong inverse correlation with distance from the earthquake source and a strong positive correlation with slope steepness the landslide concentration differs substantially among the various geologic units in the area the differences correlate to some degree with differences in lithology and degree of induration but this correlation is less clear suggesting a more complex relationship between landslide occurrence and rock properties

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

juvenile magma recognition and eruptive dynamics inferred from the analysis of ash time series the 2015 reawakening of cotopaxi volcano forecasting future activity and performing hazard assessments during the reactivation of volcanoes remain great challenges for the volcanological community on august 14 2015 cotopaxi volcano erupted for the first time in 73 years after approximately four months of precursory activity which included an increase in seismicity gas emissions and minor ground deformation here we discuss the use of near real time petrological monitoring of ash samples as a complementary aid to geophysical monitoring in order to infer eruption dynamics and evaluate possible future eruptive activity at cotopaxi twenty ash samples were collected between august 14 and november 23 2015 from a monitoring site on the west flank of the volcano these samples contain a range of grain types that we classified as hydrothermal altered lithic juvenile and free crystals the relative proportions of theses grains evolved as the eruption progressed with increasing amounts of juvenile material and a decrease in hydrothermally altered material in samples from the initial explosion juvenile grains are glassy microlite poor and contain hydrothermal minerals opal and alunite the rising magma came in contact with the hydro thermal system under confinement causing hydro magmatic explosions that cleared the upper part of the plumbing system subsequently the magmatic column produced a thermal aureole in the conduit and dried out the hydrothermal system allowing for dry eruptions magma ascent rates were low enough to allow for efficient outgassing and microlite growth constant supply of magma from below caused quasi continuous disruption of the uppermost magma volume through a combination of shear deformation and gas expansion the combination of increasing crystallinity of juvenile grains and high measured so2 flux indicate decreasing integrated magma ascent rates and clearing of the hydrothermal system along transport pathways in a system open to gas loss the near real time monitoring of ash samples combined with traditional geophysical monitoring techniques during the reawakening of cotopaxi allowed us to gain a much clearer understanding of events than when using traditional geophysical monitoring alone c 2016 elsevier b v all rights reserved

spatial sampling of the thermospheric vertical wind field at auroral latitudes 1 results are presented from two nights of bistatic doppler measurements of neutral thermospheric winds using fabry perot spectrometers at mawson and davis stations in antarctica a scanning doppler imager sdi at mawson and a narrow field fabry perot spectrometer fps at davis have been used to estimate the vertical wind at three locations along the great circle joining the two stations in addition to the vertical wind routinely observed above each station these data were obtained from observations of the 630 0 nm airglow line of atomic oxygen at a nominal altitude of 240 km low resolution all sky images produced by the mawson sdi have been used to relate disturbances in the measured vertical wind field to auroral activity and divergence in the horizontal wind field correlated vertical wind responses were observed on a range of horizontal scales from 150 to 480 km in general the behavior of the vertical wind was in agreement with earlier studies with strong upward winds observed poleward of the optical aurora and sustained though weak downward winds observed early in the night the relation between vertical wind and horizontal divergence was seen to follow the general trend predicted by burnside et al 1981 whereby upward vertical winds were associated with positive divergence and vice versa however a scale height approximately 3 4 times greater than that modeled by nrlmsise 00 was required to best fit the data using this relation

assessment of environmental controls on acid sulfate alteration at active volcanoes in nicaragua applications to relic hydrothermal systems on mars 1 a variety of secondary mineralogies has been detected on mars from both orbiters and landers indicating widespread aqueous alteration of the crust many of these locales exhibit sulfates which in some cases imply acidic fluids at present there are few constraints on the paleoenvironmental conditions that existed during formation of the widespread and diverse classes of secondary minerals on mars we investigated hydrothermal systems at three active acidic volcanic systems in nicaragua including cerro negro momotombo and telica the recently erupted materials are similar in composition to the martian crust and are undergoing extensive acid sulfate alteration predominately in gas dominated settings fumaroles we characterized the secondary mineralogy and local variables including temperature ph rock and gas composition and fluid rock ratio we find that these environmental parameters exhibit strong controls on the alteration mineralogy the environments studied include ph that ranged from 1 to 6 temperatures from ambient to hundreds of degrees celsius and fumaroles to hot springs the hottest and most acidic systems contained sulfur silica and minor gypsum while moderately acidic and cooler fumaroles included abundant silica gypsum and other hydrated sulfates and phyllosilicates a setting with a higher fluid rock ratio but similar temperature and acidity was dominated by phyllosilicates and to a lesser degree sulfates the characterization of aqueous alteration of basalts under a variety of environmental conditions provides a conceptual framework for interpretation of similar relic environments on mars finally while identification of phyllosilicates on mars is generally thought to require neutral to alkaline fluids we documented significant formation of these minerals in the acidic volcanic systems

representing the landslide magnitude frequency relation capilano river basin british columbia we use magnitude frequency analysis as a statistical tool to quantify the erosion caused by landslides and debris ows using air photo and ground derived data we show that the departure from power law distribution customarily observed for small magnitude is an artefact of sampling de ciencies nonetheless the total distribution is not sensitive to the frequency of small slides and total erosion remains adequately represented in the air photo derived data our data also demonstrate a real departure from simple scaling at much larger magnitudes the cause of which is not de nitively established copyright 2004 john wiley sons ltd

the enormous chillos valley lahar an ash flow generated debris flow from cotopaxi volcano ecuador the chillos valley lahar cvl the largest holocene debris flow in area and volume as yet recognized in the northern andes formed on cotopaxi volcano s north and northeast slopes and descended river systems that took it 326 km north northwest to the pacific ocean and 130 km east into the amazon basin in the chillos valley 40 km downstream from the volcano depths of 80 160 m and valley cross sections up to 337 000 m2 are observed implying peak flow discharges of 2 6 6 0 million m3 s the overall volume of the cvl is estimated to be 3 8 km3 the cvl was generated approximately 4500 years bp by a rhyolitic ash flow that followed a small sector collapse on the north and northeast sides of cotopaxi which melted part of the volcano s icecap and transformed rapidly into the debris flow the ash flow and resulting cvl have identical components except for foreign fragments picked up along the flow path juvenile materials including vitric ash crystals and pumice comprise 80 90 of the lahar s deposit whereas rhyolitic dacitic and andesitic lithics make up the remainder the sand size fraction and the 2 to 10 mm fraction together dominate the deposit constituting 63 and 15 wt of the matrix respectively whereas the silt size fraction averages less than 10 wt and the clay size fraction less than 0 5 wt along the 326 km runout these particle size fractions vary little as does the sorting coefficient average 2 6 there is no tendency toward grading or improved sorting limited bulking is recognized the cvl was an enormous non cohesive debris flow notable for its ash flow origin and immense volume and peak discharge which gave it characteristics and a behavior akin to large cohesive mudflows significantly then ash flow generated debris flows can also achieve large volumes and cover great areas thus they can conceivably affect large populated regions far from their source especially dangerous therefore are snow clad volcanoes with recent silicic ash flow histories such as those found in the andes and alaska

the respiratory health hazards of volcanic ash a review for volcanic risk mitigation studies of the respiratory health effects of different types of volcanic ash have been undertaken only in the last 40 years and mostly since the eruption of mt st helens in 1980 this review of all published clinical epidemiological and toxicological studies and other work known to the authors up to and including 2005 highlights the sparseness of studies on acute health effects after eruptions and the complexity of evaluating the long term health risk silicosis non specific pneumoconiosis and chronic obstructive pulmonary disease in populations from prolonged exposure to ash due to persistent eruptive activity the acute and chronic health effects of volcanic ash depend upon particle size particularly the proportion of respirable sized material mineralogical composition including the crystalline silica content and the physico chemical properties of the surfaces of the ash particles all of which vary between volcanoes and even eruptions of the same volcano but adequate information on these key characteristics is not reported for most eruptions the incidence of acute respiratory symptoms e g asthma bronchitis varies greatly after ashfalls from very few if any reported cases to population outbreaks of asthma the studies are inadequate for excluding increases in acute respiratory mortality after eruptions individuals with pre existing lung disease including asthma can be at increased risk of their symptoms being exacerbated after falls of fine ash a comprehensive risk assessment including toxicological studies to determine the long term risk of silicosis from chronic exposure to volcanic ash has been undertaken only in the eruptions of mt st helens 1980 usa and soufriere hills montserrat 1995 onwards in the soufriere hills eruption a long term silicosis hazard has been identified and sufficient exposure and toxicological information obtained to make a probabilistic risk assessment for the development of silicosis in outdoor workers and the general population a more systematic approach to multi disciplinary studies in future eruptions is recommended including establishing an archive of ash samples and a website containing health advice for the public together with scientific and medical study guidelines for volcanologists and health care workers

neutral thermospheric dynamics observed with two scanning doppler imagers 1 monostatic and bistatic winds 1 doppler shift measurements of the thermospheric 630 0 nm emission recorded by two spatially separated imaging fabry perot spectrometers in alaska have been combined to infer f region horizontal wind vectors at approximately 75 locations across their overlapping fields of view these bistatic horizontal wind estimates rely only on an assumption regarding the local vertical wind and assume a common observing volume and thus represent a more direct measurement of the wind than do the monostatic single station vector wind fields routinely inferred by these instruments here we present comparisons between both the independently derived monostatic wind fields from each instrument and the bistatic wind estimates inferred in their common observing volumes data are presented from observations on three nights during 2010 two principal findings have emerged from this study first the monostatic technique was found to be capable of estimating the actual large scale wind field reliably under a large range of geophysical conditions and is well suited to applications requiring only a large scale big picture approximation of the wind flow secondly the bistatic or tristatic technique is essential for applications requiring detailed knowledge of the small scale behavior of the wind as for example is required when searching for gravity waves

the rhyolitic andesitic eruptive history of cotopaxi volcano ecuador at cotopaxi volcano ecuador rhyolitic and andesitic bimodal magmatism has occurred periodically during the past 0 5 ma the sequential eruption of rhyolitic 70 75 sio2 and andesitic 56 62 sio2 magmas from the same volcanic vent over short time spans and without significant intermingling is characteristic of cotopaxi s holocene behavior this study documents the eruptive history of cotopaxi volcano presenting its stratigraphy and geologic field relations along with the relevant mineralogical and chemical nature of the eruptive products in order to determine the temporal and spatial relations of this bimodal alternation cotopaxi s history begins with the barrancas rhyolite series dominated by pumiceous ash flows and regional ash falls between 0 4 and 0 5 ma which was followed by occasional andesitic activity the most important being the ample andesitic lava flows 4 1 km3 that descended the n and nw sides of the edifice following a 400 ka long repose without silicic activity cotopaxi began a new eruptive phase about 13 ka ago that consisted of seven rhyolitic episodes belonging to the holocene f and colorado canyon series the onset of each episode occurred at intervals of 300 3 600 years and each produced ash flows and regional tephra falls with dre volumes of 0 2 3 6 km3 andesitic tephras and lavas are interbedded in the rhyolite sequence the colorado canyon episode 4 500 years bp also witnessed dome and sector collapses on cotopaxi s ne flank which with associated ash flows generated one of the largest cohesive debris flows on record the chillos valley lahar a thin pumice lapilli fall represents the final rhyolitic outburst which occurred at 2 100 years bp the pumices of these holocene rhyolitic eruptions are chemically similar to those of older rhyolites of the barrancas series with the exception of the initial eruptive products of the colorado canyon series whose chemistry is similar to that of the 211 ka ignimbrite of neighboring chalupas volcano since the colorado canyon episode andesitic magmatism has dominated cotopaxi s last 4 400 years characterized by scoria bomb and lithic rich pyroclastic flows infrequent lava flows that reached the base of the cone andesitic lapilli and ash falls that were carried chiefly to the w and large debris flows andesitic magma emission rates are estimated at 1 65 km3 dre ka for the period from 4 200 to 2 100 years bp and 1 85 km3 dre ka for the past 2 100 years resulting in the present large stratocone