observations of volcanic clouds in their first few days of atmospheric residence the 1992 eruptions of crater peak mount spurr volcano alaska abstract satellite so2 and ash measurements of mount spurr s three 1992 volcanic clouds are compared with ground based observations to develop an understanding of the physical and chemical evolution of volcanic clouds each of the three eruptions with ratings of volcanic explosivity index three reached the lower stratosphere 14 km asl but the clouds were mainly dispersed at the tropopause by moderate to strong 20 40 m s tropospheric winds three stages of cloud evolution were identified first heavy fallout of large 500 m pyroclasts occurred close to the volcano 25 km from the vent during and immediately after the eruptions and the cloud resembled an advected gravity current second a much larger highly elongated region marked by a secondary mass maximum occurred 150 350 km downwind in at least two of the three events this was the result of aggregate fallout of a bimodal size distribution including fine 25 m ash that quickly depleted the solid fraction of the volcanic cloud for the f

magnetization of 0 26 5 ma seafloor at the ultraslow spreading southwest indian ridge 61 67 e 1 we investigate the magnetic signature of volcanic and nonvolcanic seafloor areas along the southwest indian ridge between 61 e and 67 e and analyze their relationship with crustal thickness variations and past to present ridge segmentation this part of the southwest indian ridge is an end member for the global ridge system in terms of low melt supply thin crust and ultraslow spreading rates it is characterized by large expanses of seafloor that show no evidence for a volcanic upper crustal layer we find that variations of intrinsic magnetization and thickness of the basaltic extrusive layer where it is present dominate the present day along axis crustal magnetization off axis the magnetization contrast is on average higher for volcanic seafloor than for smooth nonvolcanic topography indicating that the contribution of the basaltic upper crustal layer to the production of magnetic anomalies remains important however magnetic anomalies that record past magnetic polarity events are found almost everywhere in the survey area even over domains that lack a volcanic upper crustal layer arguing thus for the contribution of other sources we propose that both gabbros and serpentinized peridotites contribute to these anomalies although not systematic and weak over most parts of the survey area an induced component of magnetization is clearly present in some nonvolcanic seafloor domains serpentinized peridotites are the likely carriers of this induced magnetization component

paleoenvironmental changes across the cretaceous tertiary boundary at koshak kazakhstan based on planktic foraminifera and clay mineralogy abstract the koshak section of the mangyshlack peninsula kazakhstan is one of the most complete cretaceous tertiary k t transitions known from the boreal paratethys cretaceous species richness is low 11 to 13 species except for a peak of 20 species near the k t boundary in the uppermost maastrichtian top 50 cm that represents the temporary incursion of low latitude taxa this maximum species richness occurred during climatic warming associated with increased humidity as suggested by clay mineral analyses biofacies analysis suggests external platform conditions at this time followed by a more humid climate a sea level transgression and deepening basinal facies in the lower danian subzone p1a shallower platform conditions resumed in danian subzones p1b and p1c accompanied by a cooler and probably more arid climate no abrupt mass extinction occurred at the koshak k t boundary which is marked by an ir anomaly a clay layer and the first appearance of tertiary planktic foraminifera the influx of lower latitude species ends at or before the k t boundary whereas the majority of the indigenous cretaceous assemblage survived into the danian these data suggest that long term climatic changes may have been the principal factors in the progressive demise of the cretaceous planktic foraminifera in the eastern boreal paratethys

87sr 86sr test of the degree of impact induced slope failure in the maastrichtian of the western north atlantic analyses of 8 7 sr 8 6 sr in foraminifera and sedimentological observations suggest that the chicxulub impact was not the trigger for slumps or a hiatus within the maastrichtian section recovered at ocean drilling programsites 1049 1050 and 1052 subtropical western north atlantic the slumps and hiatus occur within a sequence dominated by pelagic chalk the 8 7 sr 8 6 sr measurements show a general increase through the maastrichtian at each site but suggest chronostratigraphic gaps on the order of 10 6 yr across the slumps some of the slumps have burrowed upper surfaces and are composed of material that is older and coarser grained than the bounding chalks pelagic deposition punctuated by gravity flows easily explains the maastrichtian record on blake nose whereas an impact based explanation for slumping is difficult to reconcile with sedimentological and geochemical observations

strontium isotopic evidence for extensive reworking in sediments spanning the cretaceous tertiary boundary at odp site 738 the maastrichtian and danian intervals of ocean drilling program odp hole 738c contain numerous microfossils above the level of their putative extinction suggesting either 1 persistence of local communities long after species turnover occurred across the rest of the globe or 2 large scale reworking these interpretations have very different paleoenvironmental implications but discriminating between them has proved difficult to test the competing hypotheses we measured the 87 sr 86 sr ratios of taxon specific separates from a number of samples and compared these values both to each other and to expected seawater values at the time of deposition our results indicate extensive and pervasive reworking throughout maastrichtian and lower danian strata in odp hole 738c we estimate that up to 30 of the mass of foraminifers in any sample can be contributed by individuals that have been reworked

continuous exhumation of mantle derived rocks at the southwest indian ridge for 11 million years the global mid ocean ridge system where tectonic plates diverge is traditionally thought of as the largest single volcanic feature on the earth yet wide expanses of smooth sea floor in the easternmost part of the southwest indian ridge in the indian ocean lacks the hummocky morphology that is typical for submarine volcanism at other slow spreading ridges the sea floor can extend by faulting the existing lithosphere along only one side of the ridge axis however the smooth sea floor in the easternmost southwest indian ridge also lacks the corrugated texture created by such faulting instead the sea floor is smooth on both sides of the ridge axis and is thought to be composed of altered mantle derived rocks here we use side scan sonar to image the sea floor and dredge samples to analyse the composition of two sections of the southwest indian ridge between 62 050 e and 64 400 e where the sea floor formed over the past 11 million years we show that the smooth floor is almost entirely composed of seawater altered mantle derived rocks that were brought to the surface by large detachment faults on both sides of the ridge axis faulting accommodates almost 100 of plate divergence and the detachment faults have repeatedly flipped polarity we suggest that this tectonic process could also explain the exhumation of mantle derived rocks at the magma poor margins of rifted continents

geochemistry of fluids associated with the 1995 1996 eruption of mt ruapehu new zealand signatures and processes in the magmatic hydrothermal system abstract the 1995 1996 eruption of mt ruapehu has provided a number of insights into the geochemical processes operating within the magmatic hydrothermal system of this volcano both pre eruption degassing of the rising magma and its eventual intrusion into the convective zone of the hydrothermal system beneath the lake were clearly reflected in lake water compositions the eruptions of september october 1995 expelled the lake and provided the first ever opportunity to characterise gas discharges from this volcano the fumarolic discharges revealed compositions typical of andesite volcanoes and strong interaction with the enclosing meteoric and hydrothermal system fluids some 1 1 mt of so 2 gas was released from the volcano between september 1995 and december 1996 whereas ca twice this amount 2 2 mt equivalent so 2 was erupted as soluble i e leachable oxyanions of sulphur significantly more sulphur was released from the volcano over this period than can be accounted for from the magma volume actually erupted the evidence suggests that a sizable component of the evolved sulphur was remobilised from the long lived hydrothermal system within the volcano during the 1995 1996 activity

rainwater and ash leachate analysis as proxies for plume chemistry at soufriere hills volcano montserrat chloride and sulphate concentrations in rainwater and water soluble leachates from volcanic ash samples track the compositions of gas emissions at the soufriere hills volcano montserrat from 1996 to 2001 there are both systematic spatial and temporal variations in the chloride sulphate ratio expressed as the equivalent hcl so2 mass ratio in rainwater and ash leachates temporal variations reflect changes in eruption rate and eruptive style mass ratios of hcl so2 in ash leachates correspond closely with those obtained by open path fourier transform infrared op ftir spectroscopy and reflect changes in volatile emissions throughout the eruption both leachate and op ftir spectroscopic analyses show mass ratios of hcl so2 1 during dome growth and hcl so2 1 during non eruptive periods the hcl so2 mass ratios in rainwater samples from 1996 and 1997 show temporal variations that correlate with changes in extrusion rate the hcl so2 ratios in plume affected rainwater and ash leachates from june and july 2001 correlate positively with increasing rockfall energy and with increasing eruption rate prior to a dome collapse event the hcl so2 mass ratios in water soluble ash leachates and rainwater samples collected at the same time and from the same sites are linearly correlated with rainwater hcl so2 ratios systematically two to three times higher than ash leachate ratios spatial patterns of rainwater ph and hcl so2 in rainwater and ash leachates are principally influenced by the proximity of the sampling sites to the active dome and to the typical pattern of dispersion of the plume by tropospheric winds these results demonstrate that rainwater chemistry and ash leachate analysis provides a useful indicator of volcanic activity and represents a valuable supplement to volcano surveillance efforts

the effect of volcanic eruptions on the chemistry of surface waters the 1991 and 2000 eruptions of mt hekla iceland abstract the mt hekla eruptions in 1991 and 2000 have provided a unique opportunity to study the local environmental effects of high latitude volcanic eruptions in the middle of winter both eruptions started around sunset at sub zero temperatures in order to define better these effects we studied the chemistry of surface waters in the vicinity of the volcano additionally we describe and predict the environmental consequences of these volcanic eruptions on the chemistry of surface waters on land and in the ocean several dissolved elements in the polluted snow melt from the 2000 eruption cl f al fe mn as cd pb zn and u exceeded the limits for water intended for human consumption the volcanic ash the primary minerals and secondary mineral phases that commonly form in the weathering environment of iceland were undersaturated in the polluted snow melts with the exception of fluorite barite goethite and amorphous feooh these minerals can constrain the maximum initial concentration of the respective dissolved constituents in the meltwaters it took few days after the first rainfall on the volcanic ash to flush out the readily soluble constituents in the vicinity of the headwaters of the ytri ranga river the polluted river waters were oversaturated with respect to several secondary minerals resulting in precipitation of amorphous al hydroxide and feooh and further scavenging of some trace elements on the al and fe surfaces dissolved al and f were the main contaminants in the ytri ranga river water previous studies have shown that combined al f toxicity is directly related to the predominance of specific al f species in solution model calculations for mixing of a hekla type volcanic cloud with 4 surface water end members shows al f species to be most important in rain and dilute river waters this makes al and f phyto available but diminishes the concentration of the al 3 species the most toxic al species mixing with high alkalinity river waters or seawater results in the domination of non toxic al oh 4 species at dilutions greater than 800 thus hindering al toxicity and bioavailability this study indicates that h 2 so 4 contamination from volcanic eruptions is time and place dependent volcanic eruptions that take place during winter at high latitudes result in relatively high global sulfur contamination and relatively low local sulfur contamination due to the low oxidation rate of so 2 into h 2 so 4 because of the low solar radiation

ash storms impacts of wind remobilised volcanic ash on rural communities and agriculture following the 1991 hudson eruption southern patagonia chile tephra fall from the august 1991 eruption of volcan hudson affected some 100 000 km 2 of patagonia and was almost immediately reworked by strong winds creating billowing clouds of remobilised ash or ash storms the immediate impacts on agriculture and rural communities were severe but were then greatly exacerbated by continuing ash storms this paper describes the findings of a 3 week study tour of the diverse environments of southern patagonia affected by ash storms with an emphasis on determining the impacts of repeated ash storms on agriculture and local practices that were developed in an attempt to mitigate these impacts ash storms produce similar effects to initial tephra eruptions prolonged for considerable periods these have included the burial of farmland under dune deposits abrasion of vegetation and contamination of feed supplies with fine ash these impacts can then cause problems for grazing animals such as starvation severe tooth abrasion gastrointestinal problems corneal abrasion and blindness and exhaustion if sheep fleeces become laden with ash in addition ash storms have led to exacerbated soil erosion human health impacts increased cleanup requirements sedimentation in irrigation canals and disruption of aviation and land transport ash deposits were naturally stabilised most rapidly in areas with high rainfall 1 500 mm year through compaction and enhanced vegetation growth stabilisation was slowest in windy semi arid regions destruction of vegetation and

seismic properties of subducting oceanic crust constraints from natural lawsonite bearing blueschist and eclogite in sivrihisar massif turkey abstract investigating the seismic properties of natural lawsonite lws bearing blueschist and eclogite is particularly important for constraining the seismic interpretation of subducting oceanic crust based on seismological observations to achieve this end we analyzed in detail the mineral fabrics and seismic properties of foliated lws blueschist and lws eclogites from sivrihisar massif in turkey in both blueschists and eclogites the lawsonite fabric is characterized by three different patterns 0 0 1 axes aligning sub normal to foliation and 0 1 0 axes aligning sub parallel to lineation normal type 0 0 1 axes aligning sub parallel to lineation and 1 0 0 axes aligning sub normal to foliation with a girdle sub normal to lineation abnormal type and 0 0 1 axes aligning both sub normal to foliation and sub parallel to lineation 0 1 0 axes aligning sub parallel to lineation and 1 0 0 axes aligning sub normal to foliation transitional pattern in contrast glaucophane and omphacite mostly present consistent axial fabrics with the 0 0 1 axes aligning to lineation these mineral fabrics produce whole rock seismic anisotropies with similar patterns however the variations in seismic anisotropies are mainly controlled by the rock type to a lesser extent are determined by the lawsonite fabric type and to only a small extent are affected by mineral fabric strength despite the constructive abnormal type lawsonite fabric on whole rock seismic anisotropies because of their weaker mineral fabric strength or deformation degree the abnormal type lws blueschist still exhibit comparatively lower seismic anisotropies than those normal type lws blueschist from other localities based on the calculated seismic anisotropies and velocities we estimated that when oceanic crust transforms from lws blueschist to lws eclogite with increasing subduction depth 1 p wave and max s wave polarization anisotropies reduce about 70 and 40 respectively and 2 variations of vp and vs contrasts relative to mantle peridotites are about 7 to 3 and 8 to 6 respectively these results corroborate the important roles of lws bearing blueschist and eclogite in interpreting the existence and gradual weakening of low velocity layers in subducting oceanic crust during the subduction process

glaciological response to distal tephra fallout from the 1947 eruption of hekla south iceland glacier responses to tephra deposition are shown to be highly variable where wind transported eruption plumes produce narrow distal fallout zones with steep lateral thickness gradients significant but short lived advances of faster flowing glaciers can be triggered by deposition from modest eruptions the 1947 eruption of hekla south iceland covered nearby glaciers with variable thicknesses of tephra causing dramatic spatial variations in ablation rate relative snow ablation increased by an estimated 80 at the eastern margin of eyjafjallajokull but decreased by 54 at the western margin relative ice ablation increased by only 4 in the east but decreased by 75 at the western margin only 15 km distant the effect on mass balance therefore depends on tephra distribution as well as on the nature of the glacier surface on gigjokull retardation of ablationwas greatest at the terminus associated with an anomalous advance of 328 m between 1947 and 1954 other glaciers in the fallout zone show either no recognizable response or accelerated retreat advances will be short lived due to the rapid redistribution of supraglacial tephra in a maritime climate and the potential for discriminating between volcanically and climatically forced advances in the glacio geomorphological record is low the long term glaciological effect of volcanism is to create thin low albedo covers after reworking which make conditions less favourable for glaciation

tectonics mantle spread across the sea floor the sea floor around mid ocean ridges is often carpeted by hummocky lava flows images from the southwest indian ridge sea floor however show a smooth texture created by exhumation and widespread exposure of altered mantle rocks

pattern and forcing of northern hemisphere glacier variations during the last millennium time series depicting mountain glacier fluctuations in the alps display generally similar patterns over the last two centuries as do chronologies of glacier variations for the same interval from elsewhere in the northern hemisphere episodes of glacier advance consistently are associated with intervals of high average volcanic aerosol production as inferred from acidity variations in a greenland ice core advances occur whenever acidity levels rise sharply from background values to reach concentrations 1 2 equiv h kg above background a phase lag of about 10 15 yr equivalent to reported response lags of alpine glacier termini separates the beginning of acidity increases from the beginning of subsequent ice advances a similar relationship but based on limited and less reliable historical data and on lichenometric ages is found for the preceding 2 centuries calibrated radiocarbon dates related to advances of non calving and non surging glaciers during the earlier part of the little ice age display a comparable consistent pattern an interval of reduced acidity values between about 1090 and 1230 a d correlates with a time of inferred glacier contraction during the medieval optimum the observed close relation between noothern hemisphere glacier fluctuations and variations in greenland ice core acidity suggests that sulfur rich aerosols generated by volcanic eruptions are a primary forcing mechanism of glacier fluctuations and therefore of climate on a decadal scale the amount of surface cooling attributable to individual large eruptions or to episodes of eruptions is simlar to the probable average temperature reduction during culminations of little ice age alacier advances ca 0 5 1 2 c as inferred from depression of equilibrium line altitudes

a study of clast size distribution ash deposition and fragmentation in a hawaiian style volcanic eruption ash deposits from hawaiian style eruptions are generally of small volume but are important in understanding the mechanisms of these eruptions an analysis of the ash deposit from the 1959 kilauea iki eruption of kilauea volcano is presented and the whole deposit grain size distribution for the eruption is calculated the grain size distribution is found to be heavily skewed towards the coarsest clast sizes and to differ considerably from size distributions for plinian deposits

fluvial sediment transport and deposition following the 1991 eruption of mount pinatubo the 1991 eruption of mount pinatubo generated extreme sediment yields from watersheds heavily impacted by pyroclastic flows bedload sampling in the pasig potrero river one of the most heavily impacted rivers revealed negligible critical shear stress and very high transport rates that reflected an essentially unlimited sediment supply and the enhanced mobility of particles moving over a smooth fine grained bed dimensionless bedload transport rates in the pasig potrero river differed substantially from those previously reported for rivers in temperate regions for the same dimensionless shear stress but were similar to rates identified in rivers on other volcanoes and ephemeral streams in arid environments the similarity between volcanically disturbed and arid rivers appears to arise from the lack of an armored bed surface due to very high relative sediment supply in arid rivers this is attributed to a flashy hydrograph whereas volcanically disturbed rivers lack armoring due to sustained high rates of sediment delivery this work suggests that the increases in sediment supply accompanying massive disturbance induce morphologic and hydrologic changes that temporarily enhance transport efficiency until the watershed recovers and sediment supply is reduced d 2002 elsevier science b v all rights reserved

impact and extinction in remarkably complete cretaceous tertiary boundary sections from demerara rise tropical western north atlantic ocean drilling program odp leg 207 on the demerara rise in the western tropical north atlantic recovered multiple cretaceous paleogene boundary sections containing an ejecta layer sedimentological geochemical and paleontological changes across the boundary closely match patterns expected for a mass extinction caused by a single impact a normally graded 2 cmthick bed of spherules that is interpreted as a primary air fall deposit of impact ejecta occurs between sediments of the highest cretaceous plummerita hantkeninoides foraminiferal zone and the lowest paleogene p0 foraminiferal zone there are no other spherule layers in the section in addition to extinction of cretaceous taxa foraminiferal abundance drops from abundant to rare across the boundary ir concentrations reach a maximum of 1 5 ppb at the top of the spherule bed and the ir anomaly is associated with enrichment in other siderophile elements we attribute the unusually well preserved and relatively simple stratigraphy to the fact that demerara rise was close enough 4500 km to the chicxulub impact site to receive 2 cm of ejecta yet was far enough away and perhaps sheltered by the curve of northern south america to have been relatively unaffected by impact induced waves

investigation of the environmental impact of remote volcanic activity on north mayo ireland during the mid holocene seven layers of microscopic tephra have been detected in ombrotrophic peat from western ireland a radiocarbon chronology suggests that two of the tephra layers were deposited around 4000 bp pollen fungal spores and testate amoebae have been analyzed from the peat immediately above and below the tephra layers these analyses provide information of changes in the landscape surrounding the bog and as well as conditions on the bog surface analysis of rates of change in these data has been employed to investigate the relative magnitude of environmental changes at the time of tephra deposition tephra deposition occurred at least 100 years after a major decline in pinus pollen and coincides with fairly stable conditions in the terrestrial environ ment more significant changes on the bog surface indicative of wetter conditions are associated with the timing of tephra deposition

nonvolcanic seafloor spreading and corner flow rotation accommodated by extensional faulting at 15 n on the mid atlantic ridge a structural synthesis of odp leg 209 drilling during odp leg 209 dredging and submersible dives have delineated an anomalous stretch of the mid atlantic ridge north and south of the 15 20 n fracture zone the seafloor here consists dominantly of mantle peridotite with gabbroic intrusions that in places is covered by a thin discontinuous extrusive volcanic layer thick lithosphere 10 20 km in this region inhibits magma from reaching shallow levels beneath the ridge axis thereby causing plate accretion to be accommodated by extensional faulting rather than magmatism the bathymetry and complex fault relations in the drill core suggest that mantle denudation and spreading are accommodated by a combination of high displacement rolling hinge normal faults and secondary lower displacement normal faults these extensional faults must also accommodate corner flow rotation up to 90 of the upwelling mantle within the shallow lithosphere consistent with remnant magnetic inclinations in denuded peridotite and gabbro from leg 209 core that indicate up to 90 of sub curie temperature rotation

high levels of particulate matter in iceland due to direct ash emissions by the eyjafjallajokull eruption and resuspension of deposited ash 1 the dangers to people living near a volcano due to lava and pyroclastic flows and on glacier or snow covered volcanoes jokulhlaups are well known the level of risk to human health due to high concentrations of ash from direct emission and resuspension from the ground is however not as well known the eruption at eyjafjallajokull 14 april to 20 may 2010 produced abundant particulate matter due to its explosive eruption style even after the volcanic activity ceased high particulate matter pm concentrations were still measured on several occasions due to resuspended ash the 24 hour mean concentration of pm10 in the small town of vik 38 km se of the volcano reached 1230 g m 3 which is about 25 times the health limit on 7 may 2010 with 10 min average values over 13 000 g m 3 even after the eruption ceased values as high as 8000 g m 3 10 min and 900 g m 3 24 h were measured because of resuspension of freshly deposited fine ash in reykjavik 125 km wnw of the volcano the pm10 concentration reached over 2000 g m 3 10 min during an ash storm on 4 june 2010 which should have warranted airport closure summarizing our study reveals the importance of ash resuspension compared to direct volcanic ash emissions this likely has implications for air quality but could also have detrimental effects on the quality of ash dispersion model predictions which so far generally do not include this secondary source of volcanic ash

flexural rotation of normal faults a conceptual model is proposed for the generation of low angle normal faults in metamorphic core complexes the model is based on three assumptions 1 the isostatic response to normal fault motion is of regional extent 2 when a fault segment is significantly rotated from the optimum angle of slip relative to the crustal stress field it is replaced by a new planar fault oriented in the optimum direction and 3 the fault cuts the entire upper crust and fault motion always nucleates in the same region at the base of the upper crust the stress field is considered to be uniform through the crust and the regional isostatic response of the crust to loads is computed using the thin plate flexure approximations active low angle normal faults are difficult to reconcile with rock mechanics theories earthquake focal mechanism studies and geochronologic results indicating rapid cooling of core complex rocks the model does not require active fault slip on low angle faults the flexural response to normal faulting is shown to be significantly affected by anelastic behavior of the crust and by loading due to sedimentation the anelastic response to large bending stresses results in significant reduction in the effective elastic rigidity of the upper crust this can explain the observed short wavelength of topographic response to normal fault loads the model results in 1 a nearly flat lying abandoned normal fault or detachment below slices of upper plate rocks and sedimentary infill 2 a strong contrast in metamorphic grade across the abandoned detachment 3 rapid movement of lower plate rocks from midcrustal depths to shallower depths these results are qualitatively in agreement with geologic observations for core complexes

opening of the central atlantic ocean implications for geometric rifting and asymmetric initial seafloor spreading after continental breakup study of the deep structure of conjugate passive continental margins combined with detailed plate kinematic reconstructions can provide constraints on the mechanisms of rifting and formation of initial oceanic crust in this study the central atlantic conjugate margins are compared based on compilation of wide angle seismic profiles from nw africa nova scotian and u s passive margins the patterns of volcanism crustal thickness geometry and seismic velocities in the transition zone suggest symmetric rifting followed by asymmetric oceanic crustal accretion conjugate profiles in the southern central atlantic image differences in the continental crustal thickness while profiles on the eastern u s margin are characterized by thick layers of magmatic underplating no such underplate was imaged along the african continental margin in the north two wide angle seismic profiles acquired in exactly conjugate positions show that the crustal geometry of the unthinned continental crust and the necking zone are nearly symmetric a region including seismic velocities too high to be explained by either continental or oceanic crust is imaged along the canadian side corresponding on the african side to an oceanic crust with slightly elevated velocities these might result from asymmetric spreading creating seafloor by faulting the existing lithosphere on the canadian side and the emplacement of magmatic oceanic crust including pockets of serpentinite on the moroccan margin after isochron m25 a large scale plate reorganization might then have led to an increase in spreading velocity and the production of thin magmatic crust on both sides

the short term influence of the mount st helens volcanic eruption on surface temperature in the northwest united states abstract the surface temperature effects of the 18 may 1980 eruption of the mount st helens volcano were examined for the two days immediately following the eruption the volcanic signal was investigated by examining regional maps of surface temperature 24 h surface temperature differences and model output statistics mos errors as well as the detailed temporal evolution of surface temperature and mos errors at selected stations the analysis was simplified by the presence of a large anticyclone which dominated the synoptic situation both before and after the eruption during the daytime hours immediately after the eruption temperatures in eastern washington state were up to 8 c colder because of the volcanic plume that night because of low level volcanic dust temperatures were up to 8 c warmer in idaho and montana these effects caused by large aerosols in the troposphere quickly diminished the following day as the volcanic dust cloud dissipated and moved toward the east this is believed to be

environmental assessment of 1991 hudson volcano eruption ashfall effects on southern patagonia region argentina the august 1991 eruption of the hudson volcano in the southern andean volcanic zone affected an area of 1000 km in radius to the east in the argentine patagonic meseta the thickness of ash ranged from 20 cm in the andean area to less than 1 mm in the atlantic coast zone wind storms reactivated the ash deposits together with terrigenous material more than one year after the eruption in order to assess the potential risk of the ash analyses of concentration size mineralogical composition toxic elements and irritating effects of gases were performed in all samples the percentage of particles of the 2 to 5 m range is below the toxic threshold level trace elements are below the toxic threshold concentration for humans and animals the major impact of the ashfall was on sheep herds about one third of them were lost in the areas close to the volcano soil incorporated the ash layers and a fast recovery of orchards was reported two years later rivers were loaded with sediment in the immediate aftermath but one year later returned to previous conditions along the shores of the buenos aires lake a fresh tephra layer can be distinguished

subduction zone volcanic ash can fertilize the surface ocean and stimulate phytoplankton growth evidence from biogeochemical experiments and satellite data volcanoes confront earth scientists with new fundamental questions can airborne volcanic ash release nutrients on contact with seawater thereby excite the marine primary productivity mpp and most notably can volcanoes through oceanic fertilization affect the global climate in a way that is so far poorly understood here we present results from biogeochemical experiments showing that 1 volcanic ash from subduction zone volcanoes rapidly release an array of nutrients co limiting algal growth in vast oceanic areas 2 at a speed much faster minute scale than hitherto known and that marine phytoplankton from low iron oceanic areas can swiftly within days utilize iron from volcanic sources we further present satellite data possibly indicating an increase of the mpp due to the seaward deposition of volcanic particulate matter our study supports the hypothesis that oceanic iron fertilization with volcanic ash may play a vital role for the development of the global climate

record of volcanism since 7000 b c from the gisp2 greenland ice core and implications for the volcano climate system sulfate concentrations from continuous biyearly sampling of the gisp2 greenland ice core provide a record of potential climate forcing volcanism since 7000 b c although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions only about 30 percent of the events from 1 to 7000 b c were matched to such events several historic eruptions may have been greater sulfur producers than previously thought there are three times as many events from 5000 to 7000 b c as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions this increased volcanism in the early holocene may have contributed to climatic cooling

fallout and distribution of volcanic ash over argentina following the may 2008 explosive eruption of chaiten chile 1 the major explosive eruption of chaiten volcano chile in may 2008 provided a rare opportunity to track the long range dispersal and deposition of fine volcanic ash the eruption followed 10 000 years of quiescence was the largest explosive eruption globally since hudson chile in 1991 and was the first explosive rhyolitic eruption since novarupta alaska in 1912 field examination of distal ashfall indicates that 1 6 1011 kg of ash dense rock equivalent volume of 0 07 km3 was deposited over 2 105 km2 of argentina during the first week of eruption the minimum eruption magnitude estimated from the mass of the tephra deposit is 4 2 several discrete ashfall units are identifiable from their distribution and grain size characteristics with more energetic phases showing a bimodal size distribution and evidence of cloud aggregation processes ash chemistry was uniform throughout the early stages of eruption and is consistent with magma storage prior to eruption at depths of 3 6 km deposition of ash over a continental region allowed the tracking of eruption development and demonstrates the potential complexity of tephra dispersal from a single eruption which in this case comprised several phases over a week long period of intense activity

the immediate environmental effects of tephra emission the earth s history is punctuated by large explosive eruptions that eject large quantities of magma and silicate rock fragments into the atmosphere these tephra particles can sometimes be dispersed across millions of square kilometres or even entire continents the interaction of tephra with or in receiving environments may induce an array of physical chemical and biological effects the consequences for affected systems and any dependent communities may be chronic and localised in the event of frequent small eruptions while larger and rarer events may have acute regional scale impacts it is therefore necessary to document the range of possible impacts that tephra may induce in receiving environments and any resulting effects in interconnected systems we collate results from many studies to offer a detailed multidisciplinary and interdisciplinary review of the immediate post eruptive effects of tephra emission into the atmosphere onto vegetation soil or ice snow surfaces and in aquatic systems we further consider the repercussions that may be induced in the weeks to years afterwards in the atmosphere tephra can influence cloud properties and air chemistry by acting as ice nuclei in or by offering sites for heterogeneous reactions respectively tephra on vegetation causes physical damage and sustained coverage may elicit longer term physiological responses tephra deposits on soils may alter their capacity to exchange gas water and heat with the atmosphere or may have a specific chemical effect such as nutrient input or acidification on sensitive soils tephra deposition onto snow or ice may affect ablation rates rivers and lakes may experience turbidity increases and changes in their morphology as a result of fallout and prolonged months or years erosion from the tephra covered catchment in the first weeks after deposition tephra leaching may affect river chemistry the abundance and speciation of phytoplankton populations in lakes may be altered by tephra induced changes in water chemistry or sediment water nutrient cycling in the oceans tephra deposition may fertilise fe limited waters with potential impacts on the global carbon cycle embracing the full complexity of environmental effects caused by tephra fall demands a renewed investigative effort drawing on interdisciplinary field and laboratory studies combined with consideration of the interconnectivity of induced impacts within and between different receiving environments

hygroscopic properties of volcanic ash 1 limited observational data exists on the physical interactions between volcanic ash particles and water vapor yet it is thought that these interactions can strongly impact the microphysical evolution of ash with implications for its atmospheric lifetime and transport as well as formation of water and ice clouds in this study we investigate for the first time the hygroscopic properties of ultra fine volcanic ash 125 m diameter from the eruptions of mt st helens in 1980 el chichon in 1982 tungurahua in 2006 chaiten in 2008 mt redoubt in 2009 and eyjafjallajokull in 2010 the hygroscopicity of the ash particles is quantified by their ability to uptake water and nucleate into cloud drops under controlled levels of water vapor supersaturation evidence presented strongly suggests that ash uptakes water efficiently via adsorption and a simple parameterization of ash hygroscopicity is developed for use in ash plume and atmospheric models

ice cores as an index of global volcanism from 1850 to the present to evaluate an important cause of past climate change climate researchers need reliable estimates of volcanic aerosol loading in the atmosphere previous indices the dust veil index volcanic explosivity index and those by mitchell 1970 sato et al 1993 and khmelevtsov et al unpublished manuscript 1993 all have drawbacks ice core acidity and sulfate records because they contain physical evidence of atmospheric loading are a promising source of information on past volcanic aerosols but these records contain large nonvolcanic signals as well we have compared northern hemisphere nh and southern hemisphere sh annual average versions of five indices with eight nh and six sh ice core records for the period 1850 to the present in an attempt to identify the volcanic signal common to all records the indices are all highly correlated with each other for the nh although the individual ice core records are in general not well correlated with each other or with any of the indices a composite derived from averaging the cores the ice core volcano index ivi shows promise as a new index of volcanic aerosol loading this new index correlates well with the existing non ice core volcanic indices and with high frequency temperature records for the sh the individual ice cores and indices are better correlated the shivi is again highly correlated with all indices and individual ice cores but not with high frequency temperature records for both hemispheres the southern oscillation index shows no significant correlation with the volcanic indices ice cores or the ivi thus providing no evidence for the impact of volcanic eruptions on el nino southern oscillation events

sediment yield from disturbed earth systems changes of sediment yield rates through time reflect evolutionary changes within a landscape when a drainage basin is perturbed significantly by base level climatic or tectonic change sediment yields increase dramatically but with no further disturbance they decline rapidly these sediment yield changes have been documented at all scales from small experimental studies to incised channels to the colorado river basin and to the himalaya mountains thus the shape of the sediment yield curve can be used to estimate future sediment yields and to interpret past tectonic events

insights on tephra settling velocity from morphological observations in this study we present a systematic and detailed morphological characterization of tephra particles from different eruptions fontana lapilli masaya nicaragua keanak ko i formation kilauea usa recent dome explosions of soufriere hills volcano montserrat and the calculation of their terminal fall velocity tfv as obtained based on different drag prediction models i e wilson and huang 1979 haider and levenspiel 1989 ganser 1993 and dellino et al 2005 in particular particle sphericity and therefore particle surface area is essential for the calculation of tfv of irregular shape particles but is of complex determination various attempts have been proposed according to our results 2d morphological characterization of volcanic particles is a fast and simple application for a wide range of particle size and provides consistent sphericity and settling velocity values 3d scanning also provides a promising tool for lapilli sized tephra 2 cm in contrast gas adsorption derived surface area is not suitable for the calculation of tfv of volcanic particles mostly because it mainly describes the surface contribution of nanometric pores that are not expected to affect significantly tfv and because bulk sample analysis is representative of neither individual particles nor of the whole particle population settling velocities calculated using values of surface area derived from gas adsorption analyses are up to two orders of magnitude lower than the values obtained through 2d analysis in addition our results also show how the influence of particle shape on tfv increases with particle size in particular calculated tfv converges at small particle sizes 3 regardless of the model applied suggesting that the spherical assumption is appropriate for this size fraction discrepancies with the spherical model are within 10 discrepancies with the spherical model increase with particle size up to about 50 and depend on the choice of both the tfv model and the morphological parameterization used in particular the drag prediction model of ganser 1993 is sensitive to the effect of particle morphology on tfv and is well suited for all sizes and reynolds numbers of typical tephra particles finally our results show how individual size categories whole and half are not associated with individual tfv values but with a range of values which increases with class size nonetheless the half system is associated with a smaller standard deviation than the whole system and is therefore more appropriate for the modeling of tephra dispersal in any case for dispersal modeling purposes it is more appropriate to indicate a range of settling velocities for each size class rather than giving an average value

use of paleo records in determining variability within the volcanism climate system abstract volcanic eruptions that inject large quantities of sulfur rich gases into the stratosphere have the capability of cooling global climate by 0 2 0 3 c for several years after the eruption equatorial eruptions will impact global climate whereas mid latitude eruptions can cool climate in the hemisphere of origin magnitude of cooling varies by latitude and it is possible for warming to occur in certain regions primarily during the winter although instrumental records have been used to quantify the volcanic impact on climate they are limited in their temporal and spatial coverage and the style and magnitude of eruptions occurring over the two centuries of instrumental records is limited a thorough evaluation of the range of variability in the volcanism climate system requires a multidisciplinary approach that includes the analysis of ice core records geological data atmospheric measurements and visual phenomena tree ring records and other proxy data evaluation of these longer time series indicates that multiple volcanic eruptions have the potential to force climate over decadal to multi decadal time frames especially when these eruptions enhance or extend pre existing cool conditions on the other hand a lack of climatically significant eruptions may result in warmer average temperatures over decadal time frames because the volcanic cooling component within the climate system is absent mega eruptions like the toba eruption of 71 000 73 000 yr ago may impact climate on centennial time frames through positive feedback mechanisms evidence exists which indicates that environmental changes associated with rapid climatic fluctuations such as crustal loading unloading with glaciation deglaciation and variability in glacial meltwater loading on ocean basins may cause an increase in volcanic activity

the aerodynamic behaviour of volcanic aggregates a large proportion of solid material transported within the atmosphere during volcanic eruptions consists of particles less than 500 m in diameter the majority of these particles become incorporated into a wide range of aggregate types the aerodynamic behaviour of which has not been determined by either direct observation or in the laboratory in the absence of such data theoretical models of fallout from volcanic plumes make necessarily crude assumptions about aggregate densities and fall velocities larger volcanic ejecta often consists of pumice of lower than bulk density experimental data are presented for the fall velocities of porous aggregates and single particles determined in systems analogous to that of ejecta falling from a volcanic plume it is demonstrated that the fall of aggregates may be modelled in identical fashion to single particles by using a reduced aggregate density dependent on the porosity and a size corresponding to an enclosing sphere particles incorporated into aggregates attain a substantially higher fall velocity than single particles this is due to the larger physical dimensions of the aggregate which overcomes the effect of lower aggregate density additionally the internal porosity of the aggregate allows some flow of fluid through the aggregate and this results in a small increase in fall velocity the increase in fall velocity of particles incorporated into aggregates rather than falling individually results in the enhanced removal of fine material from volcanic plumes

icelandic volcanic ash and the mid holocene scots pine pinus sylvestris pollen decline in northern scotland a volcanic ash layer in peat from northern scotland has been identified and coincides exactly with an abrupt decline in pinus sylvestris l scots pine pollen frequencies this provides an isochrone time equivalent marker horizon with which to investigate the timing of the holocene pine decline furthermore two possible causes of the southward shift of the range of pinus in scotland c 4000 bp are suggested a direct effect of acid pollution by chemicals produced by the eruption of hekla h 4 or a volcanically induced climatic perturbation these possibilities have wider implications for the influence of volcanism on postglacial environmental change

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

resuspension of volcanic ash from mount st helens measurements are presented of the size spectra of ash particles previously deposited on the ground from the may 18 1980 eruption of mount st helens that were resuspended into the air in eastern washington it is concluded that winds of just a few meters per second were capable of resuspending most of the smaller ash particles and that this caused dramatic reductions in visibility

volcanic dilemma flow or blow volcanic eruptions can be either slow outpourings of lava or explosive ejections of fragmented rock in his perspective dingwell discusses the physical and chemical properties of magma that lead to these two styles of eruption new experiments and computer simulations are pointing to the involvement of solidlike behavior of liquid magma when it makes a transition to a glass

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

sedimentation from strong volcanic plumes 1 we develop descriptions of the key processes influencing tephra dispersal from strong volcanic plumes these are characterized by the development of a subvertical eruption column in the atmosphere that forms a spreading current at a level of neutral buoyancy we describe the propagation of the spreading current due to both gravity and wind advection using scaling arguments and a simplified geometry to model particle sedimentation in a windy as well as a wind free environment new parameterizations are used to describe the wind field below the spreading current particle aggregation and particle density variations we conducted a broad study to investigate the effects of these processes and made comparisons with field observations the greatest variations resulted from wind advection below the spreading current which shifts the plume corner mass accumulation and the position of transitions in fallout regimes downwind particle aggregation strongly depends on the initial grain size distribution and significantly affects deposit thinning depending on the aggregate size and density and on the relative amount of aggregating particles small aggregates can reproduce secondary maxima of mass accumulation when sedimenting in a wind field variation of particle density also affects the resulting thinning trend the model provides acceptable reproduction of observations of the propagation of the spreading current tested with the plinian phase of the 18 may 1980 eruption of mount st helens and of observed thinning of tephra fallout deposits tested with deposits from mount st helens 1980 askja d 1875 quizapu 1932 minoan eruption 3 6 ka b p novarupta a 1912 and hudson 1991

evidence for a small 0 000 030 but resolvable increase in seawater 87sr 86sr ratios across the cretaceous tertiary boundary previous studies of 87 sr 86 sr patterns across the cretaceous tertiary k t boundary have generated inconsistent results analyses of samples from ocean drilling program hole 1049c provide better taphonomic and diagenetic control than has been previously achieved and indicate 1 that there was a rapid increase of 0 000 030 in seawater 87 sr 86 sr ratios across the k t boundary 2 that post k t cretaceous foraminifera at this site are reworked and 3 that subtle diagenetic overprinting affects the basal 15 cm of the danian ooze these conclusions are consistent with the asteroid impact hypothesis reworking rather than survivorship confirms nearly complete extinction of cretaceous tethyan planktic foraminifera the 87 sr 86 sr excursion can be explained by enhanced continental weathering perhaps related to acid rain in the aftermath of the k t impact

lacustrine responses to tephra deposition examples from mexico one of the major problems with palaeoclimate investigations in volcanic regions is that tephra inputs to lakes can cause changes in proxies analogous to those of climate forcing we review the range of impacts thought to be associated with tephra deposition distinguishing between direct effects on lake ecosystems and indirect changes to catchment nutrient cycles to achieve better understanding of these complex responses we have used high resolution diatom analysis from around 17 tephra layers in three mexican lakes a positive response to the tephra inputs has been identified for over half of these layers the most common response was for diatom concentrations to increase after tephra deposition also in plankton dominated systems fragilaria spp replaced stephanodiscus spp and aulacoseira spp an increase in the supply of silica to the lakes through their catchments is probably the cause of the diatom changes in the lakes studied direct effects of the tephra inputs to these lakes can be excluded as they would not generate changes of sufficient longevity the impact of these tephras which lasted for several decades was insufficient to perturb the underlying long term climate forcing of these lake systems c 2004 elsevier ltd all rights reserved