atmospheric sulfur dioxide measurements during the 2005 and 2007 eruptions of the piton de la fournaise volcano implications for human health and environmental changes abstract piton de la fournaise is an active volcano located in the south eastern part of reunion island a tiny island found in the south western indian ocean 21 s 55 5 e this volcano erupts regularly at least once a year with notable amount of degassing concerning the volcanic eruptions the regulation of the french ministry of environment on the air quality is mainly focussed on the standards applicable for the sulfur dioxide so 2 in terms of public health and environmental changes air samples have been collected continuously every 10 days on passive diffusion tubes of so 2 an atmospheric tracer of volcanic plumes by ora observatoire reunionnais de l air at 10 sites which have been located around the volcano since september 2005 the mean so 2 concentrations measured over a 10 day period in the absence of any volcanic eruption range between very low values 1 15 g m 3 for all 10 sites however during the december 2005 eruption notable so 2 concentrations factor 5 25 have been measured at the locations situated on the north west flanks of the volcano the so 2 degassing reached concentrations of 65 379 g m 3 which is mainly caused by the volcanic activity when coupled with the local to regional atmospheric circulations land sea breezes easterlies etc a wide range of atmospheric measurements was performed in the vicinity of piton de la fournaise in order to characterize the gaseous and particle emissions during the april may 2007 eruption so 2 concentrations were also measured continuously by sf 2000 analyser at several coastal locations in the vicinity of the volcano during and off eruption activities in the absence of any volcanic eruption the so 2 concentrations showed day to day variations with hourly mean concentrations varying between 1 and 20 g m 3 these values correspond to the background concentrations for this coastal rural location and might as well come in part from non volcanic origin the so 2 concentrations however were increased by a factor 10 30 with a maximum hourly mean concentration of 2486 g m 3 during the april may 2007 eruption hereby several statutory thresholds were exceeded particularly at the tremblet location indeed the information and recommendation threshold 350 g m 3 h as well as the alert threshold 500 g m 3 on 3 h consecutively were exceeded 32 and 5 times respectively at this site these measurements point out that during the times of eruptions with significant amounts of degassing the threshold values for protecting the ecosystems and the air quality for human health were exceeded at several inhabited locations with implications for human health and environmental changes on local to regional scale

the 1982 el chichon volcano eruptions a satellite perspective abstract the march 28 april 3 and april 4 1982 eruptions of el chichon volcano were detected and monitored using the goes and noaa 6 environmental satellites the satellite data provided information about the height and dispersal of the eruption plume and subsequent ash cloud on each of these dates based on the satellite data it was concluded that the march 28 eruption the second of two eruptions on april 3 and the april 4 eruption injected material into the stratosphere at heights between 17 and 31 km

ice nucleation and overseeding of ice in volcanic clouds 1 water is the dominant component of volcanic gas emissions and water phase transformations including the formation of ice can be significant in the dynamics of volcanic clouds the effectiveness of volcanic ash particles as ice forming nuclei in is poorly understood and the sparse data that exist for volcanic ash in have been interpreted in the context of meteorological rather than volcanic clouds in this study single particle freezing experiments were carried out to investigate the effect of ash particle composition and surface area on water drop freezing temperature measured freezing temperatures show only weak correlations with ash in composition and surface area our measurements together with a review of previous volcanic ash in measurements suggest that fine ash particles equivalent diameters between approximately 1 and 1000 m from the majority of volcanoes will exhibit an onset of freezing between 250 260 k in the context of explosive eruptions where super micron particles are plentiful this result implies that volcanic clouds are in rich relative to meteorological clouds which typically are in limited and therefore should exhibit distinct microphysics we can expect that such overseeded volcanic clouds will exhibit enhanced ice crystal concentrations and smaller average ice crystal size relative to dynamically similar meteorological clouds and that glaciation will tend to occur over a relatively narrow altitude range

plume tracker interactive mapping of volcanic sulfur dioxide emissions with high performance radiative transfer modeling abstract we describe the development of plume tracker an interactive toolkit for the analysis of multispectral thermal infrared observations of volcanic plumes and clouds plume tracker is the successor to map so2 and together these flexible and comprehensive tools have enabled investigators to map sulfur dioxide so 2 emissions from a number of volcanoes with tir data from a variety of airborne and satellite instruments our objective for the development of plume tracker was to improve the computational performance of the retrieval procedures while retaining the accuracy of the retrievals we have achieved a 300 improvement in the benchmark performance of the retrieval procedures through the introduction of innovative data binning and signal reconstruction strategies and improved the accuracy of the retrievals with a new method for evaluating the misfit between model and observed radiance spectra we evaluated the accuracy of plume tracker retrievals with case studies based on modis and airs data acquired over sarychev peak volcano and aster data acquired over kilauea and turrialba volcanoes in the sarychev peak study the airs based estimate of total so 2 mass was 40 lower than the modis based estimate this result was consistent with a 45 reduction in the airs based estimate of plume area relative to the corresponding modis based estimate in addition we found that our airs based estimate agreed with an independent estimate based on a competing retrieval technique within a margin of 20 in the kilauea study the aster based concentration estimates from 21 may 2012 were within 50 of concurrent ground level concentration measurements in the turrialba study the aster based concentration estimates on 21 january 2012 were in exact agreement with so 2 concentrations measured at plume altitude on 1 february 2012

volcanic ash clusters tephra rafts and scavengers abstract much of the volcanic ash deposited in the vicinity of pullman washington from the may 18th eruption of mt st helens in 1980 fell in the form of composite ash clusters 0 25 to 0 5 mm in diameter particles in the clusters ranged from sub micron to more than 40 microns in size the porous clusters rafted large ash particles great distances and scavenged particles of all sizes as the wind blew them eastward the result is poorly sorted ash deposits as far as 644 km east missoula within individual clusters textural relationships suggest that both mechanical interlocking and electrostatic attraction played a role in cluster formation the clusters are very fragile and may never be preserved in the stratigraphic record but it is suggested that this kind of ash transport may well have occurred in the geologic past documentation of this ash cluster fall will promote a better understanding of the physical aspects of the downwind distribution of fine grained volcanic ash the poor size sorting in some ancient ash deposits may thus be explained

satellite analysis and puff simulation of the eruptive cloud generated by the mount etna paroxysm of 22 july 1998 1 we applied the puff algorithm searcy et al 1998 to simulate the space time evolution of the eruptive cloud generated by one of the main paroxysms to have occurred this past century at etna volcano namely the 22 july 1998 explosive event at the voragine summit crater the comparison of puff simulations to satellite images of the ash cloud at different times allowed us to estimate several parameters of the eruptive event such as onset time duration ash cloud height and shape and pyroclast size based on this analysis we concluded that the paroxysm started around 1645 gmt lasted between 20 and 40 min and generated a poissonian shaped ash column nearly 13 km high and composed of particles with a mean diameter md of 10 3 m and size logarithmic standard deviation lsd equal to 1 5 the puff simulations using horizontal and vertical diffusivity values of 5000 and 10 m2 s 1 respectively provided the best agreement to the eruption clouds observed on satellite images the results were compared to the information available in the literature concerning the eruption e g volcanological video camera and volcanic tremor data the analysis showed that the method of simulating the eruptive clouds and comparing simulations to satellite images can give a contribution to the study of paroxysmal events generated by the etna volcano also the degree of accuracy of the cloud simulation leads us to be optimistic about the potential of using this method as a tool for hazard mitigation in the etna region with particular applications to air traffic

evaluation of sulfur dioxide emissions from explosive volcanism the 1982 1983 eruptions of galunggung java indonesia abstract galunggung volcano java awoke from a 63 year quiescence in april 1982 and erupted sporadically through january 1983 during its most violent period from april to october the cikasasah volcano observatory reported 32 large and 56 moderate to small eruptions from april 5 through september 19 the total ozone mapping spectrometer toms carried on nasa s nimbus 7 satellite detected and measured 24 different sulfur dioxide clouds an estimated 1730 kilotons kt of so2 were outgassed by these explosive eruptions the trajectories and rapid dispersion rates of the so2 clouds were consistent with injection altitudes below the tropopause an additional 300 kt of so2 were estimated to have come from 64 smaller explosive eruptions based on the detection limit of the toms instrument for the first time an extended period of volcanic activity was monitored by remote sensing techniques which enabled observations of both the entire so2 clouds produced by large explosive eruptions using toms and the relatively lower levels of so2 emissions during non explosive outgassing using the correlation spectrometer or cospec based on cospec measurements from august 1982 to january 1983 and on the relationship between explosive and non explosive degassing approximately 400 kt of so2 were emitted during non explosive activity the total sulfur dioxide outgassed from galunggung volcano from april 1982 to january 1983 is calculated to be 2500 kt 30 from both explosive and non explosive activity while galunggung added large quantities of sulfur dioxide to the atmosphere its sporadic emissions occurred in relatively small events distributed over several months and reached relatively low altitudes and are unlikely to have significantly affected aerosol loading of the stratosphere in 1982 by volcanic activity

on some radiative features of the el chichon volcanic stratospheric dust cloud and a cloud of unknown origin observed at mauna loa we present some results of our initial optical observations of the el chichon volcanic cloud these observations were made at the geophysical monitoring for climatic change mauna loa observatory hawaii and consist of lidar profiles optical thickness spectral variation in optical thickness and changes in global and direct solar broadband fluxes particle size distribution and cloud mass information contained in the optical thickness observations are discussed it is clear that the atmospheric radiative effects of the el chichon cloud far exceed the effects of all other volcanic clouds observed at mauna loa since observations were begun in 1958

injection of gases into the stratosphere by explosive volcanic eruptions 1 explosive eruptions can inject large amounts of volcanic gases into the stratosphere these gases may be scavenged by hydrometeors within the eruption column and high uncertainties remain regarding the proportion of volcanic gases which eventually reach the stratosphere these are caused by the difficulties of directly sampling explosive volcanic eruption columns and by the lack of laboratory studies in the extreme parameter regime characterizing them using the nonhydrostatic nonsteady state plume model active tracer high resolution atmospheric model atham we simulated an explosive volcanic eruption we examined the scavenging efficiency for the climatically relevant gases within the eruption column the low concentration of water in the plume results in the formation of relatively dry aggregates more than 99 of these are frozen because of their fast ascent to low temperature regions consideration of the salinity effect increases the amount of liquid water by one order of magnitude but the ice phase is still highly dominant consequently the scavenging efficiency for hcl is very low and only 1 is dissolved in liquid water however scavenging by ice particles via direct gas incorporation during diffusional growth is a significant process the salinity effect increases the total scavenging efficiency for hcl from about 50 to about 90 the sulfur containing gases so2 and h2s are only slightly soluble in liquid water however these gases are incorporated into ice particles with an efficiency of 10 to 30 despite scavenging more than 25 of the hcl and 80 of the sulfur gases reach the stratosphere because most of the particles containing these species are lifted there sedimentation of the particles would remove the volcanic gases from the stratosphere hence the final quantity of volcanic gases injected in a particular eruption depends on the fate of the particles containing them which is in turn dependent on the volcanic and environmental conditions

el chichon the genesis of volcanic sulfur dioxide monitoring from space the 1982 eruption of el chichon inspired a new technique for monitoring volcanic clouds data from the total ozone mapping spectrometer toms instrument on the nimbus 7 satellite were used to measure sulfur dioxide in addition to ozone for the first time precise data on the sulfur dioxide mass in even the largest explosive eruption plumes could be determined the plumes could be tracked globally as they are carried by winds magmatic eruptions could be discriminated from phreatic eruptions the data from el chichon are reanalyzed in this paper using the latest version of the toms instrument calibration v8 they show the shearing of the eruption cloud into a globe circling band while still anchored over mexico in three weeks the measured sulfur dioxide mass in the initial march 28 eruption was 1 6 tg the april 3 eruption produced 0 3 tg more and the april 4 eruptions added 5 6 tg for a cumulative total of 7 5 tg in substantial agreement with estimates from prior data versions toms aerosol index absorbing aerosol data show rapid fallout of dense ash east and south of the volcano in agreement with advanced very high resolution radiometer avhrr ash cloud positions

particle sedimentation and diffusive convection in volcanic ash clouds 1 understanding the longevity of volcanic ash clouds generated by powerful explosive eruptions is a long standing problem for assessing volcanic hazards and the nature and time scale of volcanic forcings on climate change it is well known that the lateral spreading and longevity of these clouds is influenced by stratospheric winds particle settling and turbulent diffusion observations of the recent 2010 eyjafjallajokull and 2011 grimsvotn umbrella clouds as well as the structure of atmospheric aerosol clouds from the 1991 mt pinatubo event suggest that an additional key process governing the cloud dynamics is the production of internal layering here we use analog experiments on turbulent particle laden umbrella clouds to show that this layering occurs where natural convection driven by particle sedimentation and the differential diffusion of primarily heat and fine particles give rise to a large scale instability where umbrella clouds are particularly enriched in fine ash this particle diffusive convection strongly influences the cloud longevity more generally cloud residence time will depend on fluxes due to both individual settling and diffusive convection we develop a new sedimentation model that includes both sedimentation processes and which is found to capture real time measurements of the rate of change of particle concentration in the 1982 el chichon 1991 mt pinatubo and 1992 mt spurr ash clouds a key result is that these combined sedimentation processes enhance the fallout of fine particles relative to expectations from individual settling suggesting that particle aggregation is not the only mechanism required to explain volcanic umbrella longevity

did ice charging generate volcanic lightning during the 2016 2017 eruption of bogoslof volcano alaska the 2016 2017 shallow submarine eruption of bogoslof volcano in alaska injected plumes of ash and seawater to maximum heights of 12 km more than 4550 volcanic lightning strokes were detected by the world wide lightning location network wwlln and vaisala s global lightning dataset gld360 over 9 months lightning assisted monitoring efforts by confirming ash producing explosions in near real time but only 32 out of the 70 explosive events produced detectable lightning what led to electrical activity within some of the volcanic plumes but not others and why did the lightning intensity wax and wane over the lifetime of individual explosions we address these questions using multiparametric observations from ground based lightning sensors satellite imagery photographs acoustic signals and 1d plume modeling detailed time series of monitoring data show that the plumes did not produce detectable lightning until they rose higher than the atmospheric freezing level approximated by 20 c temperatures for example on 28 may 2017 event 40 the delayed onset of lightning coincides with modeled ice formation in upper levels of the plume model results suggest that microphysical conditions inside the plume rivaled those of severe thunderstorms with liquid water contents 5 g m 3 and vigorous updrafts 40 m s 1 in the mixed phase region where liquid water and ice coexist based on these findings we infer that thunderstorm style collisional ice charging catalyzed the volcanic lightning however charge mechanisms likely operated on a continuum with silicate collisions dominating electrification in the near vent region and ice charging taking over in the upper level plumes a key implication of this study is that lightning during the bogoslof eruption provided a reliable indicator of sustained ash rich plumes and associated hazards above the atmospheric freezing level

goes weather satellite observations and measurements of the may 18 1980 mount st helens eruption we demonstrate the use of geostationary operational environmental satellite goes images of the may 18 1980 mount st helens volcanic plume in providing details of the dynamics and changing character of this major explosive eruption visible and thermal infrared ir data from a sequence of images at 30 min intervals from 0850 to 1720 local time lt give information on dispersal and plume top temperature initial visible and ir images at 0850 show the top of a spreading co ignimbrite like umbrella plume and an overshooting column emerging from it both rising off the ground hugging pyroclastic gravity flow generated by the opening directed blast the overshooting column had a minimum temperature significantly colder than local ambient atmosphere indicating substantial undercooling and a maximum altitude of 31 2 km at 0920 this large plume system then formed a high velocity radially spreading gravitationally driven current before becoming advected in the wind field at an average downwind velocity of 29 m s within 30 to 60 min the undercooled plume adjusted to ambient temperatures after this initial event the eruption column fluctuated over the next 8 hours between stable plinian column rise and unstable conditions favoring column collapse leading to pyroclastic flows and further development of co ignimbrite ash columns over this period of observation profiles of plume top temperatures derived from ir data versus distance along the downwind axis have distinctive patterns with steep slopes associated with co ignimbrite plumes and shallower slopes associated with plinian plumes moreover reflectance values from visible goes data change from lower to higher during periods of transition from darker toned plinian to lighter toned coignimbrite plumes indicating that in this case satellite data resolved changes in eruptive style from plumes with a coarser to a finer dominant particle size

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

the 1982 eruptions of el chichon volcano mexico stratigraphy of pyroclastic deposits abstract following a repose period of 500 to 600 years el chichon volcano in se mexico erupted explosively during the months of march and april 1982 three major eruptions involving trachyandesite magma injected ash into the stratosphere on 29 march at 0515 gmt and on 4 april at 0139 and 1110 gmt the first major eruption generated only tephra fall which was dispersed ene in the troposphere over the yucatan peninsula and wsw in the stratosphere towards the pacific ocean the second eruption produced tephra fall and pyroelastic surges and pyroclastic flows by repeated collapse of a lithicrich eruption column the surge and flow activity devastated a roughly circular area 153 km 2 around el chichon to a distance of about 6 km from the vent nine villages within the zone were either partially or completely destroyed and loss of human life was perhaps as high as 2000 pyroclastic flows and surges were also generated during the third eruption although ash fall was the primary activity as a result of both the second and third eruptions tephra was transported ene in the troposphere and wsw in the stratosphere the total volume of material ejected during the three major eruptions 0 50 km 3 d r e is represented by tephra fall 0 37 km 3 pyroclastic surges 0 09 km 3 and pyroclastic flows and debris flows 0 04 km 3 as a result of the eruptions a new 1 km wide and 300 m deep crater was formed by the disruption and excavation of a pre existing summit dome

theoretical study on volcanic plume hbox so _ 2 and ash retrievals using ground tir camera sensitivity analysis and retrieval procedure developments in this paper a sensitivity analysis and procedure development for volcanic plume sulfur dioxide and ash retrievals using ground thermal infrared camera have been carried out the semiconductor device camera considered as a reference has a spectral range of 8 14 m with noise equivalent temperature difference that is better than 100 mk at 300 k the camera will be used to monitor and assess the hazards of mt etna volcano to mitigate the risk and impact of volcanic eruptions on the civil society and transports a minimum number of filters have been selected for sulfur dioxide so2 and volcanic ash retrievals the sensitivity study has been carried out to determine the so2 and volcanic ash minimum concentration detectable by the system varying the camera geometry and the atmospheric profiles results show a meaningful sensitivity increase considering high instrument altitudes and low camera elevation angles for all geometry configurations and monthly profiles the sensitivity limit varies between 0 5 and 2 g m 2 for so2 columnar abundance and between 0 02 and 1 for ash optical depth two procedures to detect so2 and ash based on the least square fit method and on the brightness temperature difference btd algorithm respectively have also been proposed results show that high concentration of atmospheric water vapor columnar content significantly reduces the ash plume effect on the btd a water vapor correction procedure introduced improves the ash retrievals and the cloud discrimination in every season considering all the camera geometries

simulating the dispersal of tephra from the 1991 pinatubo eruption implications for the formation of widespread ash layers abstract puff and hazmap two tephra dispersal models developed for volcanic hazard mitigation are used to simulate the climatic 1991 eruption of mt pinatubo puff simulations indicate that the majority of ash was advected away from the source at the level of the tropopause 17 km several eruptive pulses injected ash and so2 gas to higher altitudes 25 km but these pulses represent only a small fraction 1 of the total erupted material released during the simulation comparison with toms images of the so2 cloud after 71 and 93 h indicate that the so2 gas originated at an altitude of 25 km near the source and descended to an altitude of 22 km as the cloud moved across the indian ocean hazmap simulations indicate that the pinatubo tephra fall deposit in the south china sea was formed by an eruption cloud with the majority of the ash concentrated at a height of 16 18 km results of this study demonstrate that the largest concentration of distal ash was transported at a level significantly below the maximum eruption column height 40 km and at a level below the calculated height of neutral buoyancy 25 km simulations showed that distal ash transport was dominated by atmospheric circulation patterns near the regional tropopause in contrast the movement of the so2 cloud occurred at higher levels along slightly different trajectories and may have resulted from gas particle segregations that took place during intrusion of the pinatubo umbrella cloud as it moved away from source

the 1982 eruptions of el chichon volcano mexico 2 observations and numerical modelling of tephra fall distribution tephra fallout from the a 1 march 29 0532 ut b april 4 0135 ut and c april 4 1122 ut 1982 explosive eruptions of el chichon produced three tephra fall deposits over southeastern mexico bidirectional spreading of eruption plumes as documented by satellite images was due to a combination of tropospheric and stratospheric transport with heaviest deposition of tephra from the ene tropospheric lobes maximum column heights for the eruptions of 27 32 and 29 km respectively have been determined by comparing maximum lithic clast dispersal in the deposits with predicted lithic isopleths based on a theoretical model of pyroclast fallout from eruption columns these column heights suggest peak mass eruption rates of 1 1 108 1 9 108 and 1 3 108 kg s maximum column heights and mass eruption rates occured early in each event based on the normal size grading of the fall deposits sequential satellite images of plume transport and the production of a large stratospheric aerosol plume indicate that the eruption columns were sustained at stratospheric altitudes for a significant portion of their duration new estimates of tephra fall volume based on integration of isopach area and thickness yield a total volume of 2 19 km3 1 09 km3 dre dense rock equivalent or roughly twice the amount of the deposit mapped on the ground up to one half of the erupted mass was therefore deposited elsewhere as highly dispersed tephra

fluid venting in the eastern aleutian subduction zone fluid venting has been observed along 800 km of the alaska convergent margin the fluid venting sites are located near the deformation front are controlled by subsurface structures and exhibit the characteristics of cold seeps seen in other convergent margins the more important characteristics include 1 methane plumes in the lower water column with maxima above the seafloor which are traceable to the initial deformation ridges 2 prolific colonies of vent biota aligned and distributed in patches controlled by fault scarps over steepened folds or outcrops of bedding planes 3 calcium carbonate and barite precipitates at the surface and subsurface of vents and 4 carbon isotope evidence from tissue and skeletal hard parts of biota as well as from carbonate precipitates that vents expel either methane or sulfide dominated fluids a biogeochemical approach toward estimating fluid flow rates from individual vents based on oxygen flux measurements and vent fluid analysis indicates a mean value of 5 5 0 7 l m 2 d 1 for tectonics induced water flow wallmann et al 1997b a geophysical estimate of dewatering from the same area von huene et al 1997 based on sediment porosity reduction shows a fluid loss of 0 02 l m 2 d 1 for a 5 5 km wide converged segment near the deformation front our video guided surveys have documented vent biota across a minimum of 0 1 of the area of the convergent segment off kodiak island hence an average rate of 0 006 l m 2 d 1 is estimated from the biogeochemical approach the two estimates for tectonics induced water flow from the accretionary prism are in surprisingly good agreement

constraints on unroofing rates in the high himalaya eastern nepal thermobarometric data for samples across the main central thrust zone in eastern nepal show an inversion in temperature but not in pressure these data have been interpreted to represent a portion of the paleogeotherm at the time of main central thrust deformation a 40ar 39ar age on hornblende closure temperature tc 500 50 c constrains the timing of this deformation to be 21 0 2 ma the 40ar 39ar ages of other minerals muscovite tc 350 c age t 12 0 0 2 ma k feldspar tc 220 c t 8 0 0 2 ma from the same location further constrain the cooling history of this region together the geochronologic and thermobarometric data yield an average unroofing rate of 1 2 0 6 mm yr for the high himalaya of eastern nepal simple thermal models show that these geochronologic and thermobarometric data are consistent with a wide range of different initial geotherms applied boundary conditions and magnitude of radiogenic heat production the variation through time of the unroofing rates can only be poorly constrained however the unroofing histories were found to be largely insensitive to the details of the assumed initial geotherm fairly sensitive to the magnitude of radiogenic heat production and extremely sensitive to the nature of the boundary conditions applied below the fault zone this study underscores the difficulty in constraining uplift histories on the basis of cooling rates even when thermobarometric data are available to supplement geochronologic constraints on the cooling history of the region

experiments on gas ash separation processes in volcanic umbrella plumes abstract we present a series of analogue laboratory experiments which simulate the separation of ash and gas and the formation of secondary intrusions from finite volcanic umbrella plumes we examined the lateral spreading of mixtures of freshwater and particles released into a laboratory tank containing a uniformly stratified aqueous solution for times smaller than the sedimentation time of particles through the intrusion the current remains coherent and intrudes laterally as some of the particles settle into the underlying ambient fluid a layer of particle depleted fluid develops below the upper surface of the current and the density of the residual fluid is reduced over longer times the intrusion ceases to be coherent with small fingers of relatively buoyant particle depleted fluid rising from the upper part of the intrusion into the overlying fluid meanwhile the lateral motion of the injected solution induces a return flow in the ambient fluid which sweeps some of the particles sedimenting from the lower surface of the intrusion inwards as a result relatively dense particle laden fluid collects below the intrusion and then sinks into the underlying fluid eventually this fluid reaches a new neutral buoyancy height where it intrudes to form a second laterally spreading current below the original intrusion the process then repeats to form further weaker intrusions below these results of the separation of the ash and volcanic gas in an umbrella plume are consistent with field observations at sakurajima volcano where positively charged plumes thought to consist of volcanic gas have been observed above negatively charged plumes of ash this work also suggests that volcanic aerosols may form up to a kilometer above the original injection height of the ash in a strong wind shear this could result in very different trajectories of the ash and gas and so be important for evaluating the impact of ash plumes on both aviation safety and volcanic aerosol formation the separation of the ash from the umbrella plume after a time of order 10 3 10 4 s corroborates recent models of the may 18 1980 eruption at mount st helens that after a few hours the motion of the ash was simply controlled by wind dispersal and gravitational settling the complex motion of the sedimenting ash may also explain some of the observations of multiple intrusions in short lived umbrella plumes such as observed at redoubt alaska in april 1990

the el chichon stratospheric cloud solid particulates and settling rates sampling of the el chichon stratospheric cloud in early may and in late july 1982 showed that a significant proportion of the cloud consisted of solid particles between 2 m and 40 m size in addition many particles may have been part of larger aggregates or clusters that ranged in size from 50 m the majority of individual grains were angular aluminosilicate glass shards with various amounts of smaller adhering particles surface features on individual grains include sulfuric acid droplets and larger 0 5 m to 1 m sulfate gel droplets with various amounts of na mg ca and fe the sulfate gels probably formed by the interaction of sulfur rich gases and solid particles within the cloud soon after eruption ca sulfate laths may have formed by condensation within the plume during eruption or alternatively at a later stage by the reaction of sulfuric acid aerosols with ash fragments within the stratospheric cloud a wilson huang formulation for the settling rate of individual particles qualitatively agrees with the observed particle size distribution for a period at least four months after injection of material into the stratosphere this result emphasizes the importance of particle shape in controlling the settling rate of volcanic ash from the stratosphere

the 1980 eruptions of mount st helens physical and chemical processes in the stratospheric clouds we investigate the physical and chemical properties of the stratospheric clouds produced by the recent eruptions of the mount st helens volcano the large and diverse set of observational data collected in the high altitude plumes of the may 18 may 25 and june 13 1980 eruptions is organized and analyzed for evidence of the processes at work the data are used to guide and constrain detailed model simulations of the volcanic clouds for this purpose a comprehensive one dimensional model of stratospheric sulfate aerosols sulfur precursor gases and volcanic ash and dust is utilized the model accounts for gas phase and condensed phase heterogeneous chemistry in the clouds aerosol nucleation and growth and cloud expansion computational results are given for the time histories of the gaseous species concentrations aerosol size distributions and ash burdens of the eruption clouds the long term buildup of stratospheric aerosols in the northern hemisphere and the persistent effects of injected chlorine and water vapor on stratospheric ozone are also investigated we conclude that so2 water vapor and ash were probably the most important substances injected into the stratosphere by the mount st helens volcano both with respect to their widespread effects on composition and their impact on climate despite the seemingly large magnitude of the mt st helens eruption we also find that the volcano had little influence on the climate 0 05 k surface cooling in the northern hemisphere or on stratospheric ozone 0 2 maximum hemispherical depletion the remaining problems in the field of volcanic cloud physics and chemistry and the requirements for future experimental work are also discussed

the mysteries of mammatus clouds observations and formation mechanisms mammatus clouds are an intriguing enigma of atmospheric fluid dynamics and cloud physics most commonly observed on the underside of cumulonimbus anvils mammatus also occur on the underside of cirrus cirrocumulus altocumulus altostratus and stratocumulus as well as in contrails from jet aircraft and pyrocumulus ash clouds from volcanic eruptions despite their aesthetic appearance mammatus have been the subject of few quantitative research studies observations of mammatus have been obtained largely through serendipitous opportunities with a single observing system e g aircraft penetrations visual observations lidar radar or tangential observations from field programs with other objectives theories describing mammatus remain untested as adequate measurements for validation do not exist because of the small distance scales and short time scales of mammatus modeling studies of mammatus are virtually nonexistent as a result relatively little is known about the environment formation mechanisms properties microphysics and dynamics of mammatus this paper presents a review of mammatus clouds that addresses these mysteries previous observations of mammatus and proposed formation mechanisms are discussed these hypothesized mechanisms are anvil subsidence subcloud evaporation sublimation melting hydrometeor fallout cloud base detrainment instability radiative effects gravity waves kelvin helmholtz instability rayleigh taylor instability and rayleigh benard like convection other issues addressed in this paper include whether mammatus are composed of ice or liquid water hydrometeors why mammatus are smooth what controls the temporal and spatial scales and organization of individual mammatus lobes and what are the properties of volcanic ash clouds that produce mammatus the similarities and differences between mammatus virga stalactites and reticular clouds are also discussed finally because much still remains to be learned research opportunities are described for using mammatus as a window into the microphysical turbulent and dynamical processes occurring on the underside of clouds

early evolution of a stratospheric volcanic eruption cloud as observed with toms and avhrr this paper is a detailed study of remote sensing data from the total ozone mapping spectrometer toms and the advanced very high resolution radiometer avhrr satellite detectors of the 1982 eruption of el chichon mexico the volcanic cloud atmosphere interactions in the first four days of this eruption were investigated by combining ultraviolet retrievals to estimate the mass of sulfur dioxide in the volcanic cloud krueger et al 1995 with thermal infrared retrievals of the size optical depth and mass of fine grained 1 10 m radius volcanic ash wen and rose 1994 our study provides the first direct evidence of gravitational separation of ash from a stratospheric gas rich plinian eruption column and documents the marked differences in residence times of volcanic ash and sulfur dioxide in volcanic clouds the eruption column reached as high as 32 km carey and sigurdsson 1986 and was injected into an atmosphere with a strong wind shear which allowed for an observation of the separation of sulfur dioxide and volcanic ash the upper more sulfur dioxide rich part of the cloud was transported to the west in the stratosphere while the fine grained ash traveled to the south in the troposphere the mass of sulfur dioxide released was estimated at 7 1 109 kg with the mass decreasing by approximately 4 1 day after the peak the mass of fine grained volcanic ash detected was estimated at 6 5 109 kg amounting to about 0 7 of the estimated mass of the ash which fell out in the mapped ash blanket close to the volcano over the following days 98 of this remaining fine ash was removed from the volcanic cloud and the effective radius of ash in the volcanic cloud decreased from about 8 m to about 4 m

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

retrieval of volcanic ash particle size mass and optical depth from a ground based thermal infrared camera abstract volcanoes can emit fine sized ash particles 1 10 m radii into the atmosphere and if they reach the upper troposphere or lower stratosphere these particles can have deleterious effects on the atmosphere and climate if they remain within the lowest few kilometers of the atmosphere the particles can lead to health effects in humans and animals and also affect vegetation it is therefore of some interest to be able to measure the particle size distribution mass and other optical properties of fine ash once suspended in the atmosphere a new imaging camera working in the infrared region between 7 14 m has been developed to detect and quantify volcanic ash the camera uses passive infrared radiation measured in up to five spectral channels to discriminate ash from other atmospheric absorbers e g water molecules and a microphysical ash model is used to invert the measurements into three retrievable quantities the particle size distribution the infrared optical depth and the total mass of fine particles in this study we describe the salient characteristics of the thermal infrared imaging camera and present the first retrievals from field studies at an erupting volcano an automated ash alarm algorithm has been devised and tested and a quantitative ash retrieval scheme developed to infer particle sizes infrared optical depths and mass in a developing ash column the results suggest that the camera is a useful quantitative tool for monitoring volcanic particulates in the size range 1 10 m and because it can operate during the night it may be a very useful complement to other instruments e g ultra violet spectrometers that only operate during daylight

simultaneous retrieval of volcanic ash and so2 using msg seviri measurements 1 volcanic ash and sulphur dioxide masses from the november 2005 eruption of karthala volcano comoros islands are simultaneously retrieved using rapid scan multispectral infrared measurements from the spin enhanced visible and infrared imager on board the meteosat second generation geosynchronous satellite retrievals are made every 15 min which show that the ash and so2 separate in the vertically sheared atmosphere producing a fast moving upper level 12 km so2 cloud a slower moving middle level 8 km ash cloud and a boundary layer 3 km so2 plume the total mass of fine ash is 0 1 0 05 tg sio2 the upper level so2 mass is 0 19 0 01 tg s while the boundary layer so2 mass is 0 009 0 01 tg s these are the first simultaneous satellite measurements of ash and so2 from an erupting volcano and confirm previous ideas about vertical separation we suggest care must be exercised when using so2 as a tracer for volcanic ash in aviation hazard warning systems

remote sensing of active volcanoes the synoptic coverage offered by satellites provides unparalleled opportunities for monitoring active volcanoes and opens new avenues of scientific inquiry thermal infrared radiation can be used to monitor levels of activity which is useful for automated eruption detection and for studying the emplacement of lava flows satellite radars can observe volcanoes through clouds or at night and provide high resolution topographic data in favorable conditions radar inteferometery can be used to measure ground deformation associated with eruptive activity on a centimetric scale clouds from explosive eruptions present a pressing hazard to aviation therefore techniques are being developed to assess eruption cloud height and to discriminate between ash and meterological clouds the multitude of sensors to be launched on future generations of space platforms promises to greatly enhance volcanological studies but a satellite dedicated to volcanology is needed to meet requirements of aviation safety and volca

failures in detecting volcanic ash from a satellite based technique abstract immediate and accurate detection of airborne volcanic ash is an operational imperative of the aviation industry especially jet aircraft ash encounters place passengers aboard these aircraft at severe risk and significantly impact via forced rerouting both the safety and profit margins of freight carriers due to their limited fuel supply moreover the airlines can suffer high economic costs for repair and replacement of equipment operational detection and tracking of volcanic ash by most national weather services has relied heavily on a split window differencing technique of thermal longwave infrared channels on currently operational satellites unfortunately prior work on volcanic ash detection has not emphasized the dynamical interaction between the erupting volcano and the effects of overlying atmospheric water vapor phreatic and phreatomagmatic water sources six volcanic ash eruptions from around the globe were chosen for study because they have wide variation in ambient atmospheric water vapor available ground and surface water and different magma types results show that the present differencing technique is not uniformly effective in properly classifying volcanic ash pixels in the satellite scene and often falsely interprets meteorological clouds as volcanic ash clouds and conversely moreover it is not always a robust early detector an operational aviation requirement seasonal variability in global integrated atmospheric water vapor coupled with the geographical distribution of currently active volcanoes suggests the concerns discussed herein with regard to six specific eruptions have applicability to the global aviation industry operational implications are discussed and a strategic proposal is presented on necessary steps to improve detection

tephra sedimentation during the 2010 eyjafjallajokull eruption iceland from deposit radar and satellite observations the april may 2010 eruption of eyjafjallajokull volcano iceland was characterized by a nearly continuous injection of tephra in the atmosphere that affected various economic sectors in iceland and caused a global wide interruption of air traffic eruptive activity during 4 8 may 2010 was characterized based on short duration physical parameters in order to capture transient eruptive behavior of a long lasting eruption i e total grainsize distribution erupted mass and mass eruption rate averaged over 30 minute activity resulting 30 minute total grainsize distribution based on both ground and msg seviri satellite measurements is characterized by mdphi of about 2 phi and a fine ash content of about 30wt accumulation rate varied by two orders of magnitude with an exponential decay away from the vent whereas mdphi shows a linear increase until about 18 km from vent reaching a plateau of about 4 5 phi between 20 56 km associated mass eruption rate is in between 0 6 1 2 x 10 5 kg s 1 in situ sampling showed how fine ash mainly fell as aggregates of various typologies about 5 to 9 wt of the erupted mass remained in the cloud up to 1000 km from the vent suggesting that nearly half of the ash 7 phi settled as aggregates within the first 60 km particle sphericity and shape factor varied between 0 4 and 1 with no clear correlation with size and distance from vent our experiments also demonstrate how satellite retrievals and doppler radar grainsize detection can provide real time description of the source term but for a limited particle size range

combined effects of total grain size distribution and crosswind on the rise of eruptive volcanic columns abstract the maximum height of an explosive volcanic column h depends on the 1 4th power of the eruptive mass flux q and on the 3 4th power of the stratification of the atmosphere n expressed as scaling laws this relationship has made h a widely used proxy to estimate q two additional effects are usually included to produce more accurate and robust estimates of q based on h particle sedimentation from the volcanic column which depends on the total grain size distribution tgsd and the atmospheric crosswind both coarse tgsd and strong crosswind have been shown to decrease strongly the maximum column height and tgsd which also controls the effective gas content in the column influences the stability of the column however the impact of tgsd and of crosswind on the dynamics of the volcanic column are commonly considered independently we propose here a steady state 1d model of an explosive volcanic column rising in a windy atmosphere that explicitly accounts for particle sedimentation and wind together we consider three typical wind profiles uniform linear and complex with the same maximum wind velocity of 15 m s 1 subject to a uniform wind profile the calculations show that the maximum height of the plume strongly decreases for any tgsd the effect of tgsd on maximum height is smaller for uniform and complex wind profiles than for a linear profile or without wind the largest differences of maximum heights arising from different wind profiles are observed for the largest source mass fluxes 107 kg s 1 for a given tgsd compared to no wind conditions the field of column collapse is reduced for any wind profile and tgsd at the vent an effect that is the strongest for small mass fluxes and coarse tgsd provided that the maximum plume height and the wind profile are known from real time observations the model predicts the mass discharge rate feeding the eruption for a given tgsd we apply our model to a set of eight historical volcanic eruptions for which all the required information is known taking into account the measured wind profile and the actual tgsd at the vent substantially improves by 30 the agreement between the mass discharge rate calculated from the model based on plume height and the field observation of deposit mass divided by eruption duration relative to a model taking into account tgsd only this study contributes to the improvement of the characterization of volcanic source term required as input to larger scale models of ash and aerosol dispersion

the structure of the polar vortex reconstruction of the airborne antarctic ozone experiment and airborne arctic stratosphere expedition aircraft constituent observations radiative heating rate computations and trajectory calculations are used to generate comparative pictures of the 1987 southern hemisphere sh late winter and 1989 northern hemisphere nh mid winter lower stratospheric polar vortices overall both polar vortices define a region of highly isolated air where the exchange of trace gases occurs principally at the vortex edge through erosional wave activity aircraft measurement showed that 1 between 50 and 100 mbar horizontally stratified long lived tracers such as n20 are displaced downward 2 3 km on the cyclonic poleward side of the jet with the meridional tracer gradient sharpest at the jet core 2 eddy mixing rates computed using parcel ensemble statistics are an order of magnitude or more lower on the cyclonic side of the jet compared to those on the anticyclonic side 3 poleward zonal mean meridional flow on the anticyclonic side of the jet terminates in a descent zone at the jet core despite the similarities between the sh and nh winter vortices there are important differences during the aircraft campaign periods the sh vortex jet core was located roughly 8 o 10 o equatorward of its nh counterpart after pole centering as a result of the arger size of the sh vortex the dynamical heating associated with the jet core descent zone is displaced further from the pole the sh polar vortex can therefore approach radiative equilibrium temperatures over a comparatively larger area than the nh vortex the subsequent widespread formation of polar stratospheric clouds within the much colder sh vortex core gives rise to the interhemispheric differences in the reconstructed h20 noy c10 and 03 species which are affected by polar stratospheric clouds

the possible effects of large 19th and 20th century volcanic eruptions on zonal and hemispheric surface temperatures abstract the contribution of volcanic material to the stratosphere from major eruptions within the last two centuries has been estimated using volcanological criteria including eruption type eruption column height volume and duration of eruption and composition and degree of fragmentation of magma the chronology of major explosive volcanic eruptions is compared with a record of mean surface temperature deviation t for the same interval constructed from all available temperature data the temperature records are divided into 6 latitudinal zones allowing analysis for individual zones where temperature changes induced by aerosol perturbation might be intensified we focus on the explosive volcanic events which by our estimates injected the most material into the stratosphere these include tambora 1815 krakatau 1883 santa maria 1902 katmai 1912 and quizapu 1932 such eruptions appear to have produced a consistent but small temperature decrease on the order of 0 2 to 0 5 c on a hemispheric scale for periods ranging from one to five years although these changes are similar to background temperature variations the maximum change in t after some of these explosions appears to lag by up to three years in going from equatorial to polar latitudes somewhat smaller eruptions e g agung 1963 and possibly cosiguina 1835 seem to have produced about the same perturbation in t as the larger eruptions this suggests either a limiting mechanism on loading of the aerosol layer after a volcanic eruption or that the composition of injected material i e the ratio of silicate dust to volatiles and composition of the volatiles may significantly effect stratospheric optical depth perturbation temperatures do not remain depressed for a longer period after a series of closely timed eruptions e g the 1881 1889 or the 1902 1903 sequences than after single events

wind driven dispersal of volcanic ash plumes and its control on the thermal structure of the plume top the dispersal of an ash plume as it propagates downwind with the ash settling under gravity is presented it is shown that wind shear the initial plume height and the plume grain size distribution have an important role in the dispersal of the ash in particular in determining the evolution of the upper surface and the leading edge of the ash cloud once the ash has thermally equilibrated with the atmosphere the temperature of the upper surface of the ash plume is directly related to its altitude as a result we can use the model to interpret satellite images of the temperature of the upper surface of ash plumes these calculations are compared with new analyses of satellite data from the 18 may 1980 eruptions of mount st helens in which both thermal infra red and visible goes satellite data were examined in accord with the data the model is able to predict the rate at which the mount st helens ash plume propagated downwind through a combination of the wind shear and gravitational settling of different size particles the model is also able to explain the observed thermal structure of the upper surface of the ash plume in which the temperature initially decreases but then increases with downwind distance as the ash falls through the tropopause