the cowichan fold and thrust system vancouver island southwestern british columbia the cowichan fold and thrust system is a southwest verging linked thrust system formed by northeast southwest large scale crustal contraction involving the upper cretaceous nanaimo group and its wrangellian basement the geometry of the thrust system from plan and profile perspectives illustrates its thick skinned structural style the thrust system is interpreted to be a leading imbricate fan thrusting was most likely in sequence creating an estimated minimum 20 30 shortening at the basement cover interface both fault propagation and fault bend folding are evident the former being more common kinematic indicators and the geometry of the thrust system show no evidence of significant transpressional or transtensional displacement fields contraction postdates deposition of the nanaimo group and is indirectly dated as late eocene the sole fault of the thrust system is interpreted to rise from northwest to southeast on a series of deep lateral to oblique ramps and merge with the san juan fault system this explains the rapidly westward thickening wedge of thrusted wrangellian basement in the study area in the east the sole fault is interpreted to have locally permitted the nanaimo group to overthrust the san juan terrane investigation of the cowichan fold and thrust system reveals how shortening during westward progressing terrane accretion is accommodated in a forearc region dominated by a large slab of rigid semicontinental crust

accurate stratospheric particle size distributions from a flat plate collection surface the first representative chemical structural and morphological analysis of the solid particles from a single collection surface has been performed this collection surface sampled the stratosphere between 17 and 19 km in altitude in the summer of 1981 and therefore before the 1982 eruptions of el chichon a particle collection surface was washed free of all particles with rinses of freon and hexane and the resulting wash was directed through a series of vertically stacked nucleopore filters the size cutoff for the solid particle collection process in the stratosphere is found to be considerably less than 1 m the total stratospheric number density of solid particles larger than 1 m in diameter at the collection time is calculated to be about 2 7 10 1 particles per cubic meter of which approximately 95 are smaller than 5 m in diameter previous classification schemes are expanded to explicitly recognize low atomic number material with the single exception of the calcium aluminum silicate cas spheres all solid particle types show a logarithmic increase in number concentration with decreasing diameter the aluminum rich particles are unique in showing bimodal size distributions in addition spheres constitute only a minor fraction of the aluminum rich material about 2 3 of the particles examined were found to be shards of rhyolitic glass this abundant volcanic material could not be correlated with any eruption plume known to have vented directly to the stratosphere the micrometeorite number density calculated from this data set is 5 10 2 micrometeorites per cubic meter of air an order of magnitude greater than the best previous estimate at the collection altitude the maximum collision frequency of solid particles 5 m in average diameter is calculated to be 6 91 10 16 collisions per second which indicates negligible contamination of extraterrestrial particles in the stratosphere by solid anthropogenic particles

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

el chichon volcanic ash in the stratosphere particle abundances and size distributions after the 1982 eruption volcanic ash particles collected from the stratosphere after the march april 1982 explosive eruption of el chichon volcano mexico were mostly 2 40 m vesicular shards of silicic volcanic glass that varied in abundance at 16 8 19 2 km altitude from 200 m 3 30 49 n lat in may to 1 3 m 3 45 75 n in october at the minimum the ash cloud covered latitudes 10 60 n in july and 10 s 75 n in october in may and july ash particles were mostly free individual shards and clusters of shards but by october were intimately associated with liquid droplets presumably sulfuric acid in may 1982 the total stratospheric burden of ash was at least 240 tons 2 2 108 g although the total ash injected into the stratosphere by the eruption was probably 480 8400 tons

extraction algorithm of mining subsidence information on water area based on support vector machine information on subsidence in a water area caused by mining has a great value on the research of the mining subsidence law of a mining area with a high groundwater level in eastern china based on the measured data of the subsidence area without water the data extraction of subsidence in a water area is studied in this paper with a support vector machine as subsidence in such an area is difficult to measure research shows that the training sample number and dimension should be strengthened by increasing the measuring times or using the interpolation method to obtain ideal prediction accuracy the e support vector regression model with three parameters optimized by the genetic algorithm or the particle swarm optimization algorithm is suitable to extract subsidence information in a water area caused by mining and the algorithm is accomplished on matlab data analysis showed that when the water is deeper than 1 8 m and the distance is over 60 m from the measured points the prediction error of test samples will exceed 10 out of all measured results meaning that practicability is relatively poor while water depth is 0 8 m or the distance is lower than 60 m from the measured points the prediction error of test samples will be calculated to 5 of the measured results the prediction results can be used

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

multiple deformation episodes at myra falls volcanic hosted massive sulfide camp central vancouver island british columbia canada a detailed deformation history for central vancouver island was determined at myra falls volcanic hosted massive sulfide camp with early ductile deformation overprinted by several distinct episodes of brittle deformation brittle structures were subdivided into separate groups based on their morphology geometry kinematics and crosscutting relations the central location of this study provides a link between previous deformation studies in northem and southem vancouver island late paleozoic northeast southwest compression d i produced open upright folds with variably developed north northwest striking axial planar cleavage zones si and subhorizontal stretching lineations li subparallel to fi fold axes renewed northeast southwest compression during the collision of wrangellia and north america produced a second foliation s2 in localized shear zones slightly oblique to the dominant si foliation these two events are recorded throughout vancouver island wherever the basement is exposed mid cretaceous northeastsouthwest compression during d3 produced early steep conjugate strike slip faults d3a overprinted by northeast and southwest dipping thrust faults and bedding parallel shears d3b d3 structures have been previously recognized in northem vancouver island but not as far south as myra falls north south extension d4 produced east north and east southeast striking normal faults these faults consistently crosscut earlier d i d3 structures and reactivate steep d3a faults normal faulting is correlated with the development of the upper cretaceous nanaimo basin but no faults of this age have previous been reported from onshore studies the youngest structures at myra falls are large northweststriking northeast dipping tbrust faults and steep west to west northwest striking sinistral strike slip faults formed during the ds event these faults are gouge rich wavy anastomosing structures with cleaved wall rock zones up to several metres wide the ds faults are correlated with eocene deformation caused by the accretion of the pacific rim and crescent terranes along the southwestern margin of vancouver island myra falls is the northemmost location to have been reported at which the structures formed as part of the cowichan fold and tbrust belt

mineralogy of chondritic interplanetary dust particles from a mineralogical survey of approximately 30 chondritic micrometeorites collected from the lower stratosphere and studied in detail using current electron microscopy techniques it is concluded that these particles represent a unique group of extraterrestrial materials these micrometeorites differ significantly in form and texture from components of carbonaceous chondrites and contain some mineral assemblages which do not occur in any meteorite class electron microscope investigations of chondritic micrometeorites have established that these materials 1 are extraterrestrial in origin 2 existed in space as small objects 3 endured minimal alteration by planetary processes since formation and 4 can suffer minimal pulse heating 600 c on entering earth s atmosphere the probable sources for chondritic interplanetary dust particles idps are cometary and asteroidal debris and perhaps to a lesser extent interstellar regions these sources have not been conclusively linked to any specific mineralogical subset of idp although the chondritic porous cp aggregate is considered of likely cometary origin chondritic idps occur in two predominant mineral assemblages 1 carbonaceous phases and phyllosilicates and 2 carbonaceous phases and nesosilicates or inosilicates although particles with both types of silicate assemblages are observed olivines pyroxenes layer silicates and carbon rich phases are the most commonly occurring minerals in many chondritic idps other phases often observed in variable proportions include sulphides spinels metals metal carbides carbonates and minor amounts of sulphates and phosphates individual mineral grain sizes range from micrometers primarily pyroxenes and olivines to nanometers with the predominant size for all phases less than 100 nm specific mineral characteristics for particular chondritic idps provide an indication of processes which may have occurred prior to collection in the earth s stratosphere for example pyroxene mineralogy in some chondritic aggregates is consistent with condensation from a vapor phase and we consider with condensation in a turbulent solar nebula at relatively low temperatures 1000 c carbonaceous phases present in other cp aggregates have been used to imply low temperature formation processes such as fischer tropsch synthesis 530 c or carbonization and graphitization 315 c alteration processes have been implicated in the formation of some layer silicates in cp aggregates and may have involved hydrocryogenic alteration at 0 c in general interpretations of transformation processes on submicrometer size minerals in chondritic idps are consistent with formation at a radius equivalent to the asteroid belt or greater during the later stages of solar nebula evolution using currently available models

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

assessing hydrothermal alteration intensity in volcanic hosted massive sulfide systems using portable x ray fluorescence analysis of drill core an example from myra falls canada current portable x ray fluorescence pxrf technology can rapidly and inexpensively yield concentrations of geologically significant elements typically with instrument detection limits below several tens of parts per million based on conventional xrf whole rock geochemical data both the ishikawa alteration index and the chlorite carbonate pyrite index increase with proximity to sulfide mineralization at myra falls however available pxrf technology is typically unable to detect all the elements required to calculate these alteration indices as a result there is a need to utilize the elements that are readily detectable using pxrf and apply these to hydrothermal alteration assessment we propose that rb sr ratios provide a robust proxy for the ishikawa alteration index and demonstrate that conventional whole rock xrf analytical results for rb and sr can be reproduced using pxrf analysis from drill core surfaces at myra falls the rb sr ratios vary from 2 0 for intensely altered rocks downhole profiles of alteration intensity generated from systematic pxrf analysis of drill core surfaces can be used to inform drilling and targeting decisions the application of the rb sr ratio as a proxy for alteration intensity extends beyond this case study and can be applied to other hydrothermal systems that produce phyllosilicate minerals as alteration products of feldspar

the mount st helens volcanic eruption of 18 may 1980 minimal climatic effect an energy balance numerical climate model was used to simulate the effects of the mount st helens volcanic eruption of 18 may 1980 the resulting surface temperature depression is a maximum of 0 1 c in the winter in the polar region but is an order of magnitude smaller than the observed natural variability from other effects and will therefore be undetectable

effect of the eruption of el chichon on stratospheric aerosol size and composition dominant effects of the el chichon eruption on stratospheric aerosols at 19 8 to 20 7 km are 1 vapor depositional growth of the small aerosol background mode 2 development of a large particle mode by sedimentation from the highest altitudes in the cloud 3 a change in the large particle mode from sulfate coated silicates to sulfate aerosols some with silicate cores 4 a 100 fold increase in sulfate mass in the large particle mode terminal velocities of large silicate particles maximum r 2 3 m sampled 1 month after eruption and calibrated with the aid of lidar data indicate initial injection to 26 to 27 km smaller velocities of sulfate aerosols median r 0 5 m are compatible with major growth in 2 to 3 months at 27 to 28 km aerosol settling accounts for the descent of the main lidar return to 26 5 km in august and to 20 to 21 km in december additional growth by condensation and or coalescence during descent is required to explain the largest aerosols r 0 5 to 0 9 m although sedimentation is the dominant cause of bimodality mixing of air from low and high latitudes can produce bimodal or trimodal distributions

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

morphology of ash aggregates from wet pyroclastic surges of the 1982 eruption of el chichon volcano mexico the detailed stratigraphic study of the pyroclastic surge units s1 iu and s3 produced during the most violent phases of the 1982 eruption of el chichon volcano contains a complex succession of hydromagmatic events triggered by the interaction of different proportions of magma and external water component analyses of the horizons within single units reveal that almost all wet and cohesive horizons contain ash aggregates based on their morphology and internal structure four different types of aggregates were distinguished a accretionary lapilli b armored lapilli c irregular aggregates and d cylindrical aggregates the first three types have been described in the volcanological literature field and experimental studies cylindrical forms are reported here for the first time these hollow cylindrical aggregates consist of concentric layers of crystals and glass fragments set in a finer grained matrix they formed around millimeter size foliage fragments that are locally preserved in the interior of the aggregates as scorched or completely carbonized vestiges sem analyses suggest different mechanisms of formation for the four types of aggregates irregular aggregates and armored lapilli formed nearly instantaneously whereas accretionary lapilli and cylindrical aggregates resulted from progressive aggregation of ash in different regions of the eruptive cloud

layer silicates in a chondritic porous interplanetary dust particle analytical electron microscopy on individual grains from a portion of a chondritic porous interplanetary dust particle aggregate w7029c1 from the nasa johnson space center cosmic dust collection shows that layer silicates compose 50 percent of the silicate fraction examined these layer silicates can be classified into two distinct crystallochemical groups 1 fine grained polycrystalline smectite minerals and 2 well ordered single crystals of kaolinite and mg poor talc the layer silicates in this portion of sample w7029 asterisk a are dissimilar to those described in other chondritic porous aggregates the predominant layer silicate assemblage in w7029 asterisk a indicates that heating of the aggregate during atmospheric entry was brief and probably to a temperature less than 300c comparison with terrestrial phyllosilicate occurrences suggests that some layer silicates in aggregate w7029 asterisk a may have been formed by alteratiton from preexisting silicate minerals at low temperatures less than 25c after aggregate formation

bismuth oxide nanoparticles in the stratosphere platey grains of cubic bi2o3 bi2o3 and bi2o2 75 nanograins were associated with chondritic porous interplanetary dust particles w7029c1 w7029e5 and 2011c2 that were collected in the stratosphere at 17 19 km altitude similar bi oxide nanograins were present in the upper stratosphere during may 1985 these grains are linked to the plumes of several major volcanic eruptions during the early 1980s that injected material into the stratosphere the mass of sulfur from these eruptions is a proxy for the mass of stratospheric bi from which we derive the particle number densities p m 3 for average bi2o3 nanograins due to this volcanic activity and those necessary to contaminate the extraterrestrial chondritic porous interplanetary dust particles via collisional sticking the match between both values supports the idea that bi2o3 nanograins of volcanic origin could contaminate interplanetary dust particles in the earth s stratosphere copyright 1997 by the american geophysical union

northward translation of baja british columbia along the late cretaceous to paleocene margin of western north america paleomagnetic data suggest that a large part of british columbia and southern alaska was at the latitude of baja california mexico in early late cretaceous time this allochthonous block baja bc includes the insular talkeetna in alaska and intermontane composite terranes the miniterranes between them and possibly part of the omineca metamorphic belt assuming that baja bc was adjacent to north america by middle cretaceous an analysis using plate kinematics of the pacific basin produces a model of northward movement of baja bc which is compatible with the known geology of the reconstructed margin of western north america baja bc moved north 2400 km as part of the kuia plate along a transform margin with north america from 85 to 66 ma this time interval is marked by the cessation of igneous activity in the sierra nevada development of wrench faults and basins along coastal california and initiation of laramide style tectonics to the east within baja bc diminished igneous activity to the west was coeval with possible wrench tectonic basins along its eastern margin by the end of the cretaceous baja bc was positioned from oregon to northern british columbia between 66 and 56 ma baja bc became attached to north america in a dextral transpressive stage during which the kula north america plate boundary expanded to encompass the whole block with a series of northwest trending strike slip faults a fold and thrust belt in the east and large scale uplifts and the formation of an incipient volcanic arc on the west southern alaska was the site of convergence during the whole of the period of northward translation of baja bc a late cretaceous subduction zone in alaska evolved into a major compressional belt as the basin and miniterranes on the northern margin of baja bc collided with interior alaska the collision culminated in the paleocene with formation of the mckinley granites and coeval dextral slip on the denali fault system

capture of an olivine micrometeoroid by spacecraft in low earth orbit particulates associated with an impact feature in the solar maximum satellite meb thermal control blanket are identified as magnesium rich mg mg fe2 0 66 0 83 olivine and confirm that the impact feature was caused by an olivine micrometeoroid at a relative impact velocity of 7 km s a considerable portion of the micrometeoroid was lost due to back splattering analytical electron microscope analysis of recovered particulates show several degrees of mineralogical and chemical degradation such as mechanical fragmentation melting loss of sulfur and iron and formation of fe ni grains the results indicate that recovery of information is sufficient to establish the character of the impacted micrometeoroid

stratospheric dust loading from early 1981 to september 1985 based on the twilight sounding method and stratospheric dust collections stratospheric aerosol loading from early 1981 to late 1985 was investigated by remote optical measurements using the twilight sounding method and by in situ mineral dust collections both experiments tracked the decay of aerosol abundances after the el chichon eruption a comparison between the remote optical observations and dust samplings suggests that aerosol maxima in 1985 were probably associated with a minor eruption of the bezymianny volcano considering the different dynamical behavior of volcanic ash and condensed sulfuric acid aerosol we traced the origin of collected dust to a minor eruption of una una volcano this collected dust that could not be detected by remote sensing techniques against the high background level due to condensed aerosol from el chichon highlights the complimentary nature of stratospheric dust collections and the twilight sounding method

volcanic particle aggregation in explosive eruption columns part ii numerical experiments abstract the goal of this paper is to determine the parameters that control the aggregation efficiency and the growth rate of volcanic particles within the eruption column numerical experiments are performed with the plume model atham active tracer high resolution atmospheric model in this study we employ the parameterizations described in a companion paper this issue the presence of hydrometeors promotes the aggregation of ash particles which strongly increases their fall velocities and thus their environmental impact the tephra mass is about two orders of magnitude greater than that of hydrometeors during typical plinian eruptions without interaction of external water ice is highly dominant in comparison to liquid water 99 by mass this is caused by the fast column rise 100 m s 1 on average to very cold altitudes most particles occur in the form of frozen aggregates with low ice content the collection efficiency is governed by the availability of hydrometeors acting as adhesives at the particles surface in our study and wet ash particles have a higher sticking capacity than icy ones therefore aggregation is fastest during the eruption within the column when limited regions of liquid water exist and when particle concentrations are very high of the order of 10 5 cm 3 increased humidity in the background atmosphere generally leads to enhanced ice formation but shows only a weak influence on the aggregation process first sensitivity studies showed however a significant increase of the liquid water fraction when considering salinity effects the availability of water or ice at the particles surfaces is also governed by the surface properties the porosity and permeability of ash which are not well established to date particle growth is significantly enhanced for greater differences in the sizes and fall velocities among particles as gravitational capture becomes more efficient our experiments indicate a major influence of the erupted particle size distribution first sensitivity studies show that electrostatic forces result in a significant enhancement of aggregated particles the present exploratory study provides new insights into the sensitivity of the ash aggregation process to a number of key parameters our results indicate the need of further constraining particle composition size porosity permeability and surface properties at low temperatures by in situ observations in the laboratory and in the field in addition further research on electrostatic aggregation would be desirable

enhanced residence of submicron si rich volcanic particles in the lower stratosphere abstract abundant submicron si rich grains were collected in the lower stratosphere between may 1981 and january 1982 analytical electron microscopy shows that the morphology surface features and chemical compositions of these platey grains are consistent with keatite keatite forms by devitrification of amorphous si rich grains that condensed in ascending volcanic eruption clouds low settling rates for platey grains should cause concentration of si rich grains in the stratosphere during extended periods of volcanic activity such a concentration is not observed probably because the grains were present as small aggregates with greater settling rates aggregation did not occur in the atmosphere because collision frequencies are too low thus aggregation took place in the volcanic cloud the faster settling rates for the aggregates is still sufficiently slow to increase the amount of small volcanic particles in the stratosphere thereby enhancing the amount of sites for heterogeneous aerosol nucleation

evidence for cretaceous paleogene boundary bolide impact winter conditions from new jersey usa abrupt and short lived impact winter conditions have commonly been implicated as the main mechanism leading to the mass extinction at the cretaceous paleogene k pg boundary ca 66 ma marking the end of the reign of the non avian dinosaurs however so far only limited evidence has been available for such a climatic perturbation here we perform high resolution tex86 organic paleothermometry on three shallow cores from the new jersey paleoshelf northeastern usa to assess the impact provoked climatic perturbations immediately following the k pg impact and to place these short term events in the context of long term climate evolution we provide evidence of impact provoked severe climatic cooling immediately following the k pg impact this so called impact winter occurred superimposed on a long term cooling trend that followed a warm phase in the latest cretaceous

natural occurrence of keatite precipitates in uhp clinopyroxene from the kokchetav massif a tem investigation we report the first natural occurrence of keatite also known as silica k discovered as a precipitate in the core of ultrahigh pressure uhp clinopyroxene cpx within garnet pyroxenite from the kokchetav massif kazakhstan high resolution transmission electron microscopy and electron diffraction demonstrate that sub micrometer and nano scale keatite precipitates have a definite crystallographic relationship with the host pyroxene diopside di 90 cpx 100 keatite 100 and cpx 010 keatite 001 clinopyroxene provides a template for keatite nucleation due to the close structural relationship and excellent lattice match between the diopside and keatite we propose that keatite micro precipitates are formed in localized low pressure micro environments produced as a result of exsolution of extra silica and vacancies held within uhp host diopside and stabilized by the pyroxene lattice low density metastable keatite and its relationship to the host pyroxene likely reflects the important influence of pyroxene precipitate interfacial energy on the micro and nano scales in controlling the nature of exsolved phases in exhumed uhp minerals

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

collection of microparticles at high balloon altitudes in the stratosphere we report the collection of stratospheric particles at 34 36 km using balloon borne collectors the concentration of particles on the collection surfaces and element concentrations were measured on the majority of the particles using scanning electron microscope sem and proton induced x ray emission pixe analysis respectively particle morphologies elemental composition and electron diffraction data were obtained on a small number of the collected particles using transmission electron microscope tem techniques the concentration of particles between 0 045 lower imaging limit and 1 m in radius is several orders of magnitude above the blank levels on the collection surfaces while the concentration of particles above 1 m is near blank levels more than 106 submicron particles were collected the concentration of submicron particles is between 10 and 50 times the concentration expected at the sampling altitude based on models using the measured flux of extraterrestrial particles to the atmosphere the higher concentration of submicron particles may be due to contributions from volcanic particles inaccuracies in the influx of particles of this size to the earth or breakup of larger particles analysis of the elemental composition using pixe showed cl s ti fe br ni zr zn sr and cu in decreasing order of concentration elements below s could not be detected in the analysis cl s and br are believed to be present due to reaction of the collection surfaces and particles with atmospheric gases while the other elements are present in the particles the elemental composition of the particles does not allow an unequivocal origin to be assigned because particles from several of the possible sources listed above contain the measured elements tem analysis of 23 of the submicron particles showed 16 to be non graphitic the particles ranged from al rich silicates to almost pure fe to one containing almost exclusively ba and s none were definitely chondritic in composition this collection of particles complements existing collections obtained by aircraft they were colleted at much higher altitude and are predominantly submicron in size collection and analysis of particles at high altitudes using balloons presents unique challenges and opportunities in understanding the particle population in the stratosphere

historic eruptions of tambora 1815 krakatau 1883 and agung 1963 their stratospheric aerosols and climatic impact abstract decreases in surface temperatures after the eruptions of tambora 1815 krakatau 1883 and agung 1963 were of similar magnitude even though the amount of material dust and volatiles injected into the stratosphere by these three events differed greatly large amounts of fine ash and volatiles were dispersed into the upper atmosphere by krakatau and tambora the agung eruption in 1963 was a much smaller vulcanian type eruption which injected dust and volatiles into the stratospheric aerosol layer more directly analyses of magmatic volatiles indicate that the agung eruption was proportionately richer in so 2 and cl than either tambora or krakatau relative amounts of fine ash produced by the tambora krakatau and agung eruptions are estimated at about 150 20 1 whereas the masses of atmospheric sulfate aerosols produced were on the order of 7 5 3 1 decreases in surface temperature of a few tenths of a degree c for several years following volcanic eruptions are primarily a result of the sulfate aerosols rather than of the silicate dust the similarity in the atmospheric response after these three eruptions supports the idea of limiting mechanisms on volcanic stratospheric aerosol loading which is suggested by microphysical processes of aerosol particles fluctuations in stratospheric aerosol optical depth seem to be controlled to a large degree by high intensity sulfur rich eruptions e g agung 1963 which may however be relatively small in total ejecta volume such eruptions leave little geologic record but appear as acidity peaks in polar ice cores

new constraints for indentation mechanisms in arcuate belts from the jura mountains france the mechanism of indentation in arcuate belts is discussed using the jura mountains as an example using fault inversion analysis from numerous sites the miocene pliocene stress pattern is reconstructed two superimposed compressional stress fields have been recognized considering the theoretical distribution of compression in front of a rigid indenter we interpret the complex stress pattern in the jura mountains as a result of a major change in the mechanism of indentation of the jura by its hinterland initially the indenter was narrower and limited in the southwest by the vuache transfer fault with time it expanded to the southwest and included the entire molasse basin this evolution highlights the importance of decoupling along faults which here controlled the indenter shape

the 1883 eruption of krakatau the 1883 eruption of krakatau was a modest ignimbrite forming event the deposits are primarily coarse grained dacitic non welded ignimbrite large explosions produced pyroclastic flows that entered the sea generating destructive tsunami grain size studies of the ignimbrite suggest that these explosions were not driven by magma seawater interaction the total bulk volume of pyroclastic deposits including co ignimbrite ash is estimated to be 18 21 km3

volcanic and structural reconstruction of the deformed and metamorphosed ming volcanogenic massive sulfide deposit canada implications for ore zone geometry and metal distribution

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

volcanic dust in the stratosphere between 34 and 36 km altitude during may 1985 abstract the morphology mineralogy chemistry and size distribution of nonspherical particles collected in the stratosphere between 34 and 36 km altitude during may 1985 were determined by analytical electron microscope analysis the single crystal grains are between a few nanometers in diameter and 14 m in length and occur as single particles and in mono and polymict clusters about 70 of all particles are tridymite cristobalite keatite and anorthite that delineate cotectic plagioclase mullite and tridymite mullite crystallisation in order of decreasing abundance the particles further include orthopyroxene olivine barite and metal oxides all particle properties including salt microcrystals and sulfuric acid droplets on their surface uniquely support a volcanic origin the abundance of ca al silicate and silica particles could indicate fractionation in ascending volcanic plumes or be an artifact of lacking data for ash fall deposits at comparable size fractions the observed upper size limit of nonspherical particles is accurately predicted by the wilson huang settling law when particle diameters are equal to or larger than the gas mean free path of the atmosphere the abundance of particles m in size at collection altitude suggests that nonspherical particles smaller than the gas mean free path behave as spherical particles with faster settling rates settling rate modelling the mineralogical and chemical properties of the nonspherical particles support that they could be from the top of the 1982 el chichon eruption plume that reached an altitude similar to the 1985 collection altitude

the northern cascadia subduction zone at vancouver island seismic structure and tectonic history the structure and tertiary tectonic history of the northern cascadia subduction zone have been delineated by a series of new multichannel seismic lines acquired across the continental shelf to the

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

recent glacier variations and volcanic eruptions the injection of volcanic dust and gases into the atmosphere during major eruptions has been advanced to explain short term variations of climate1 4 a calculated global cooling of 1k during episodes of intense volcanic activity3 could lead to a snowline depression sufficient to cause glacier advances equivalent to those of the last several centuries the hypothesis would therefore be strengthened if a close relationship could be demonstrated between global volcanicity and the pattern of recent glacier variations glacier activity in the northern hemisphere during much of the past 100 yr shows a lack of synchrony with that in the southern hemisphere but in each hemisphere the sequence of glacier variations matches the acidity record in polar ice cores and the frequency of volcanic eruptions in successive latitude belts this suggests that glaciers fluctuate in response to atmospheric build up of volcanic aerosols produced during large eruptions and that explosive volcanism may therefore be a major factor in modulating climate on the decadal scale

the eocene southern vancouver island orocline a response to seamount accretion and the cause of fold and thrust belt and extensional basin formation abstract a deflection of the fault controlled southwestern coastline of vancouver island suggests the presence of a minor orocline with a southern crustal block south of barkley sound alberni inlet rotated 20 counterclockwise relative to a northern fixed crustal block about a pole of rotation located northeast of port alberni in this paper two models of orocline development one of pure block rotation and one of pure bending are proposed the predictions of these models are tested against available geological maps structural orientation data identified regions of extension and contraction and paleomagnetic data structural orientation and paleomagnetic data are consistent with 18 of post late cretaceous counter clockwise rotation of the southern crustal block relative to the northern fixed crustal block a southward increase in the magnitude of rotation evident in the structural orientation data argues for a model of bending both bending and block rotation models predict the development of a zone of contraction along the northeast margin of the southern crustal block coincident with the location of the eocene cowichan fold and thrust belt that diminishes northward toward the pole of rotation as predicted the fold and thrust belt is characterized by a northerly decrease in the amount of shortening from 30 at the south end of the thrust belt to 0 shortening north of port alberni the northerly decrease in shortening is complemented by a north to south change in structural style from cylindrical to conical folds and finally to planar undeformed strata the model of block rotation predicts the presence of a zone of extension extending southwest from the zone of rotation coincident with the location of eocene extensional structures within barkley sound and with horst and graben structures in the offshore eocene to miocene tofino basin extension is less than predicted by a model of pure block rotation and suggests that much of the oroclinal rotation was accommodated by bending timing constraints indicate that orocline development was coeval with and resulted from the eocene accretion of seamounts of the crescent terrane these findings demonstrate that oroclinal orogeny the buckling of a linear crustal beam about vertical axes of rotation can significantly impact the geometry structure and character of an orogenic belt even where the buckles are minor

aqueous alteration in five chondritic porous interplanetary dust particles abstract analytical electron microscope analysis of stratospheric micrometeorites show that layer silicates are common albeit minor constituents in five particles of the nominally anhydrous subclass of chondritic porous cp interplanetary dust particles idps these layer silicates are single crystal na k rich smectite minerals illite kaolinite and less common pyrophyllite mica and rare talc rare non stoichiometric crystalline feldspars of probable authigenic origin occur in cp idp w7029e5 the feldspars are low anorthite and undetermined na k alkali feldspar polymorphs similar al2o3 al2o3 sio2 ratios and alkali content of feldspars and layer silicates suggest a genetic relationship between these minerals whereby layer silicates form during aqueous alteration in the case of cp idp w7029e5 alteration occurred in a mildy acidic ph 5 7 fluid at 175 195 c if cp idps are solid debris from short period comets the observations give evidence for mineralogical and chemical activity in nuclei of short period comets if an asteroidal origin for these cp idps can be established these observations provide a window to the processes that may ultimately lead to fully hydrated carbonaceous chondrite matrices

geology lithogeochemistry and alteration of the battle volcanogenic massive sulfide zone buttle lake mining camp vancouver island british columbia volcanogenic polymetallic massive sulfide deposits within the buttle lake mining camp occur within the felsic volcanic and volcaniclastic rocks of the myra formation that immediately overlies price formation andesite these units comprise the lower exposed part of the paleozoic sicker group in the buttle lake uplift in central vancouver island the sicker group represents a volcanic island arc that forms the base of the allochthonous wrangell terrane the battle main zone contains 2 3 million tons mt of proven and probable reserves grading 1 3 g t au 25 3 g t ag 2 5 percent cu 0 5 percent pb and 13 2 percent zn overall the buttle lake camp hosts geologic reserves of about 12 5 mt the battle main massive sulfide zone occurs within the h w horizon the lowest member of the myra formation immediately above the price formation andesite price formation andesite is over 300 m thick in the vicinity of the camp and consists of feldspar or pyroxene porphyritic basaltic andesite flows synvolcanic block faulting of this unit formed the regional scale buttle lake camp basin with a strike length of at least 10 km local sub basins in this major structure contain the sulfides and felsic volcanic rocks of the h w horizon the h w horizon is a 15 to 200 m thick felsic package that extends throughout the basin it consists of eight members three of which represent periods of massive sulfide deposition from the stratigraphic base to the top of these members are 1 the battle main massive sulfide lens 2 fine rhyolitic tuffaceous deposits 3 h w mafic sills 4 gap massive sulfide lens 5 coarse rhyolite pyroclastic deposits 6 rhyolite tuffaceous and cherry sediments 7 battle upper massive sulfide lenses and 8 a tripartite rhyolite flow dome complex consisting of quartz porphyritic rhyolite quartz feldspar porphyritic rhyolite and green quartz feldspar porphyritic rhyolite volcaniclastic units in the felsic package evolved with interfingering of subaerial and submarine pyroclastic processes flow dome units evolved by fractionation of quartz and feldspar alteration evaluated petrographically and with pearce element ratios is most intense close to synvolcanic and synmineral feeder faults that channeled solutions through the price formation andesite proximal to the battle main massive sulfide lens envelopes to the feeder faults have distinctive mg addition anomalies and contain the mineral assemblage pyrite sericite quartz chlorite discharge feeder stockworks immediately below the battle main massive sulfide lens contain varying proportions of sericite quartz and pyrite but lack significant chlorite deposition of the h w horizon rhyolitic units on top of the battle main massive sulfide lens did not halt mineralization rather fluids continued to percolate upward through the newly deposited rhyolitic units and deposited the battle upper lenses close to the new sediment water interface alteration below the battle upper lenses consists of quartz sericite and pyrite with minor galena sphalerite and tennantite overall hydrolysis of feldspar in both the price formation and the h w horizon resulted in a halo surrounding the ore lenses marked by addition of k and concomitant na and ca depletion

ground subsidence observations and a modified influence function method for complete subsidence prediction abstract the results of surface subsidence investigations carried out in different coal fields in india are presented in this paper important differences are seen to exist between the subsidence norms given in the subsidence engineers handbook uk and those obtained in indian conditions differences also exist for extraction below unfractured or uncaved rock and below pre existing caved goaf s the subsidence is higher in the latter case and also in the slopes and strains consequently separate equations and guidelines have been given for these two conditions of mining since indian coal mining is mostly under shallow to moderate cover several cases of discontinuous subsidence have been observed a demarcation limit for discontinuous subsidence is given seeing that discontinuous subsidence causes severe surface damage since room and pillar mining is the principal underground method of extraction panels of irregular shapes often occur making complete subsidence prediction difficult the influence function method with a new function and additional functions for modelling subsidence asymmetry and the effect of extraction edges are given in this paper the method for extraction below goaf s is also examined four cases are given for the comparison of observed and predicted subsidence contours and two cases for comparison of the slopes and strains

changes in stratospheric composition chemistry radiation and climate caused by volcanic eruptions the primary effect of a volcanic eruption is to alter the composition of the stratosphere by the direct injection of ash and gases on average there is a stratospherically significant volcanic eruption about every 5 5 years the principal effect of such an eruption is the enhancement of stratospheric sulphuric acid aerosol through the oxidation and condensation of the oxidation product h2804 following the formation of the enhanced aerosol layer observations have shown a reduction in the amount of direct radiation reaching the ground and a concomitant increase in diffuse radiation this is associated with an increase in stratospheric temperature and a decrease in global mean surface temperature although the spatial pattern of temperature changes is complex in addition the enhanced aerosol layer increases heterogeneous processing and this reduces the levels of active nitrogen in the lower stratosphere this in turn gives rise to either a decrease or an increase in stratospheric ozone levels depending on the level of chlorine loading

volcanic particle aggregation in explosive eruption columns part i parameterization of the microphysics of hydrometeors and ash abstract the aggregation of volcanic ash particles within the eruption column of explosive eruptions has been observed at many volcanoes it influences the residence time of ash in the atmosphere and the radiative properties of the umbrella cloud however the information on the processes leading to aggregate formation are still either lacking or very incomplete we examine the fate of ash particles through numerical experiments with the plume model atham active tracer high resolution atmospheric model in order to determine the conditions that promote ash particle aggregation in this paper we describe the microphysics and parameterization of ash and hydrometeors in a companion paper this issue we use this information in a series of numerical experiments the parameterization includes the condensation of water vapor in the rising eruption column the formation of liquid and solid hydrometeors and the effect of latent heat release on the eruption column dynamics are considered the interactions of hydrometeors and volcanic ash within the eruption column that lead to aggregate formation are simulated for the first time within a rising eruption column the microphysical parameterization follows a modal approach the hydrometeors are described by two size classes each of which is divided into a liquid and a frozen category by analogy with the hydrometeor classification we specify four categories of volcanic ash particles we imply that volcanic particles are active as condensation nuclei for water and ice formation ash can be contained in all categories of hydrometeors thus forming mixed particles of any composition reaching from mud rain to accretionary lapilli collisions are caused by gravitational capture of particles with different fall velocity coalescence of hydrometeor ash aggregates is assumed to be a function of the hydrometeor mass fraction within the mixed particles the parameterization also includes simplified descriptions of electrostatics and salinity effects

small particles in plumes of mount st helens particles in the size range of 0 1 25 micrometers were sampled by aircraft carrying a quartz crystal microcascade in the mount st helens plume on three dates in august and september 1980 two of the sampling dates represented typical emissions of the volcano between plinian eruptions one sampling flight was made 1 4 hours before the small plinian eruption of august 7 1980 when the plume had become discontinuous and visibly darker size distributions were determined and individual particles were studied by using scanning electron microscopy the plume sampled on august 7 before the eruption contained mainly approximately 2 micrometer diameter silicic glass particles fragments of the mount st helens magma the typical plumes sampled on september 22 and august 6 had much smaller concentrations of particles trimodal size distributions with peaks at 10 0 4 and 0 1 micrometers the particles were largely nonsilicate and apparently represented cu zn oxide 10 micrometer peak al sulfate chloride and oxide and sulfuric acid smallest size peak the characterization of small particles in the plume may give information about approaching activity and possibly about changing conditions in the subsurface magma body

the impact of particle shape on fall velocity implications for volcanic ash dispersion modelling abstract modelling atmospheric volcanic ash dispersion is a critical tool in mitigating the impact of large explosive eruptions it is also useful for understanding and reconstructing past events most atmospheric dispersion models include a sedimentation velocity term that is sensitive to the physical properties of the particle but many do not use particle shape as an input parameter instead particles are assumed to be spherical there are many empirical and semi empirical shape dependent drag laws we measure the velocity of scaled analogue particles over the range of flow conditions anticipated for volcanic ash dispersion to test published formulae against an independent dataset we use a semi empirical formula we determined to be accurate for non spheres to investigate the sensitivity of the modelled transport of an ash cloud to particle shape using the atmospheric dispersion model name and a shape parameter we measure for non spherical ash particles from katla volcano iceland we find that model particle trajectories are sensitive to particle shape for particles 1 3 m diameter the sedimentation velocity of smaller particles is low compared to atmospheric vertical velocities sensitivity to shape increases with size such that 100 m particles can travel 44 further from the source when they are highly non spherical sphericity 0 5 despite the sensitivity of the fall velocity of large particles to their shape however forecasts of distal ash concentration using particle size distributions of 0 1 100 m and 0 1 250 m show relatively good agreement between a spherical and non spherical case for the first 36 h after an eruption the vertical structure of an ash cloud is more sensitive to particle shape than the horizontal extent model particle trajectories are also sensitive to particle size and we find a discrepancy between different particle size parameters for non spherical ash particle long axis l used in cryptotephra studies was on average twice the equivalent volume sphere diameter dv used in dispersion modelling for tephra samples from katla volcano iceland this discrepancy in size measurements could explain the observed travel distance of large distal cryptotephra shards

satellite limb scanning thermal infrared observations of the el chichon stratospheric aerosol first results the infrared radiometer experiment on the solar mesosphere explorer satellite has been continuously measuring the 6 8 m thermal emission from the stratospheric aerosol from the el chichon volcano since the time of eruption in early april 1982 inversion results for the zonally averaged infrared extinction coefficient in height latitude and time show that the aerosol increased in mass to a maximum of 8 tg 8 1012gm about 15 weeks after the april 4 eruption it descended in height with an average speed consistent with the gravitational settling time of particles with a diameter of about 1 4 m

rapid short term cooling following the chicxulub impact at the cretaceous paleogene boundary the mass extinction at the cretaceous paleogene boundary 66 ma is thought to be caused by the impact of an asteroid at chicxulub present day mexico although the precise mechanisms that led to this mass extinction remain enigmatic most postulated scenarios involve a short lived global cooling a so called impact winter phase here we document a major decline in sea surface temperature during the first months to decades following the impact event using tex86 paleothermometry of sediments from the brazos river section texas we interpret this cold spell to reflect to our knowledge the first direct evidence for the effects of the formation of dust and aerosols by the impact and their injection in the stratosphere blocking incoming solar radiation this impact winter was likely a major driver of mass extinction because of the resulting global decimation of marine and continental photosynthesis

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