preliminary sensitivity study of eruption source parameters for operational volcanic ash cloud transport and dispersion models a case study of the august 1992 eruption of the crater peak vent mount spurr alaska abstract ash clouds are one of the major hazards that result from volcanic eruptions once an eruption is reported volcanic ash transport and dispersion vatd models are used to forecast the location of the ash cloud these models require source parameters to describe the ash column for initialization these parameters include eruption cloud height and vertical distribution particle size distribution and start and end time of the eruption further if downwind concentrations are needed the eruption mass rate and or volume of ash need to be known upon notification of an eruption few constraints are typically available on many of these source parameters recently scientists have defined classes of eruption types each with a set of pre defined eruption source parameters esp we analyze the august 18 1992 eruption of the crater peak vent at mount spurr alaska which is the example case for the medium silicic eruption type we have evaluated the sensitivity of two of the esp the grain size distribution gsd and the vertical distribution of ash on the modeled ash cloud hysplit and puff vatd models are used to simulate the ash clouds from the different sets of source parameters we use satellite data processed through the reverse absorption method as reference for computing statistics that describe the modeled to observed comparison with the grain size distribution the three options chosen 1 an estimated distribution based on past eruption studies 2 a distribution with finer particles and 3 the national oceanic and atmospheric administration hysplit gsd have little effect on the modeled ash cloud for the initial vertical distribution both linear uniform concentration throughout the vertical column and umbrella shapes were chosen for hysplit the defined umbrella distribution no ash below the umbrella apparently underestimates the lower altitude portions of the ash cloud and as a result has a worse agreement with the satellite detected ash cloud compared to that with the linear vertical distribution for this particular eruption the puff model with a poisson function to represent the umbrella cloud gave similar results as for a linear distribution both having reasonable agreement with the satellite detected cloud further sensitivity studies of this eruption as well as studies using the other source parameters are needed

development of a subvolcanic structure by the interaction of liquid filled cracks abstract the interaction of liquid filled cracks may be an important process for magma accumulation and the development of subvolcanic structures the horizontal interaction was studied through the stress analyses around pressured cracks in various regional stress fields the vertical interaction was studied using gelatin experiments buoyaney driven cracks coalesce more easily than pressure cracks the theory of the three dimensional crack interaction was discussed there are two types of crack interaction the interaction between liquid filled cracks may cause coalescence of cracks the interaction between a liquid filled crack and a solid filled crack never causes coalescence the stress relaxation by ductile or brittle behavior or by the driving out of magma decreases the local stress field generated by the accumulation of magma filled cracks as the regional differential stress increases and the minimum compressive principal stress becomes tensile magma filled cracks become parallel to each other as the supply rate of magma filled cracks becomes relatively large or as the regional differential stress decreases and the minimum compressive stress increases the arrangement of magma filled cracks varies from an offset pattern to a radial one because the local compressive stress field cannot be decreased this process leads to the development of subparallel or radial dikes in two dimensions or a dike sheet complex in three dimensions a large magma chamber such as a sphere or a cylinder is not always necessary for the development of a basaltic volcano in case of the interaction between liquid filled cracks magma filled cracks coalesce easily into one large crack and diminish the local compressive stress field last the theory of the crack interaction is applied to developments of various volcanoes the fissure pattern of hekla volcano iceland is explained in terms of the variation of the stress relaxation the difference in fissure pattern between izu oshima and miyakejima volcanoes japan is interpreted by the variation of the differential stress the local stress balance including the stress relaxation is kept in the developments of etna volcano italy and kilauea volcano hawaii

estimating volcanic ash hazard in european airspace abstract the widespread disruption of european air traffic in late april 2010 during the eruption of eyjafjallajokull showed the importance of early assessment of volcanic hazard from explosive eruptions in this study we focus on the short term hazard of airborne ash from a climatological perspective focusing on eruptions on iceland by studying eruptions of different intensity and frequency we estimate the overall probability that ash concentration levels considered hazardous to aviation are exceeded over different parts of europe the method involves setting up a range of eruption scenarios based on the eruptive history of icelandic volcanoes and repeated simulation of these scenarios for 2 years worth of meteorological data simulations are conducted using meteorological data from the era interim reanalysis set which is downscaled using the weather research and forecasting wrf model the weather data are then used to drive the lagrangian particle dispersion model flexpart wrf for each of the eruption scenarios a set of threshold values commonly used in volcanic ash advisories are used to analyze concentration data from the dispersion model we see that the dispersion of ash is highly dominated by the mid latitude westerlies and mainly affect northern uk and the scandinavian peninsula the occurrence of high ash levels from icelandic volcanoes is lower over continental europe but should not be neglected for eruptions when the release rate of fine ash m is in the order of 10 7 kg s 1 or higher there is a clear seasonal variation in the ash hazard during the summer months the dominating dispersion direction is less distinct with some plumes extending to the northwest and greenland in contrast during the winter months the strong westerly winds tend to transport most of the emissions eastwards the affected area of a winter time eruption is likely to be larger as high concentrations can be found at a further distance downwind from the volcano effectively increasing the probability of hazardous levels of ash reaching the european continent the concentration thresholds for aviation which were adopted after the eyjafjallajokull eruption in 2010 have strong influence on the hazard estimates for weaker eruptions but is less important for larger eruptions thus ash forecasts for weaker eruptions are likely more uncertain in comparison to larger eruptions

late quaternary vegetation dynamics and hydro climate in the drakensberg south africa abstract a multi proxy study of a sediment sequence from braamhoek wetland covering the last c 16 000 years reveals a record of regional climate and vegetation dynamics in the drakensberg region south africa including signals from both the organic sediment fraction fossil pollen charcoal n alkane abundance n alkane 13c toc and the inorganic fraction mineral magnetic properties the reconstruction supported by a robust chronology indicates two major periods of increased regional wetness during the late pleistocene to early holocene phase c 13 800 12 600 cal yr bp c 10 200 8500 cal yr bp and one during the late holocene c 2000 cal yr bp to present drier conditions are recorded during the younger dryas c 12 600 11 300 cal yr bp and mid holocene c 7000 2000 cal yr bp a major decline in fynbos vegetation during the early holocene suggests a shift towards warmer temperatures and possibly towards less pronounced winter rains in eastern south africa from c 8500 cal yr bp comparison with records from interior of south africa show relatively high inter site variability however the braamhoek moisture proxies do co vary with the speleothem isotope records from makapansgat suggesting a similar hydro climate evolution in eastern and interior parts of the summer rainfall region during the studied period on multi millennial time scales an inverse hydro climatological pattern is evident between these two south african records and reconstructions from tropical locations in southeast africa such a rainfall dipole between eastern tropical and southern africa has previously been identified on shorter time scales i e on inter annual to millennial scales the braamhoek study suggests that a similar dipole pattern is acting also on a multi millennial perspective these long term precipitation anomalies are tentatively coupled to teleconnections from multi millennial changes in the dynamics of the indian ocean dipole iod and el nino southern oscillation enso

magma buoyancy and volatile ascent driving autocyclic eruptivity at hekla volcano iceland volcanic eruptions are typically accompanied by ground deflation due to the withdrawal of magma from depth and its effusion at the surface here based on continuous high resolution borehole strain data we show that ground deformation was absent during the major effusion phases of the 1991 and 2000 eruptions of hekla volcano iceland this lack of surface deformation challenges the classic model of magma intrusion withdrawal as source for volcanic ground uplift subsidence we incorporate geodetic and geochemical observables into theoretical models of magma chamber dynamics in order to constrain quantitatively alternative co and inter eruptive physical mechanisms that govern magma propagation and system pressurization we find the lack of surface deformation during lava effusion to be linked to chamber replenishment from below whilst magma migrates as a buoyancy driven flow from the magma chamber towards the surface we further demonstrate that inter eruptive pressure build up is likely to be generated by volatile ascent within the chamber rather than magma injection our model explains the persistent periodic eruptivity at hekla throughout historic times with self initiating cycles and is conceptually relevant to other volcanic systems

toothpaste lava characteristics and origin of a lava structural type transitional between pahoehoe and aa toothpaste lava an important basalt structural type which illustrates the transition from pahoehoe to aa is particularly well displayed on the 1960 kapoho lava of kilauea volcano its transitional features stem from a viscosity higher than that of pahoehoe and a rate of flow slower than that of aa viscosity can be quantified by the limited settling of olivine phenocrysts and rate of flow by field observations related to the low angle slope on which the lava flowed much can be learned about the viscosity rheologic condition and flow velocity of lavas long after solidification by analyses of their structural characteristics and it is possible to make at least a semiquantitative assessment of the numerical values of these parameters

volcanic ash hazard climatology for an eruption of hekla volcano iceland abstract ash produced by a volcanic eruption on iceland can be hazardous for both the transatlantic flight paths and european airports and airspace in order to begin to quantify the risk to aircraft this study explored the probability of ash from a short explosive eruption of hekla volcano 63 98 n 19 7 w reaching european airspace transport dispersion and deposition of the ash cloud from a three hour explosive eruption with an initial plume height of 12 km was simulated using the met office s numerical atmospheric dispersion modelling environment name the model used operationally by the london volcanic ash advisory centre eruptions were simulated over a six year period from 2003 until 2008 and ash clouds were tracked for four days following each eruption results showed that a rapid spread of volcanic ash is possible with all countries in europe facing the possibility of an airborne ash concentration exceeding international civil aviation organization icao limits within 24 h of an eruption an additional high impact low probability event which could occur is the southward spread of the ash cloud which would block transatlantic flights approaching and leaving europe probabilities of significant concentrations of ash are highest to the east of iceland with probabilities exceeding 20 in most countries north of 50 n deposition probabilities were highest at scottish and scandinavian airports there is some seasonal variability in the probabilities ash is more likely to reach southern europe in winter when the mean winds across the continent are northerly ash concentrations usually remain higher for longer during summer when the mean wind speeds are lower

geophysical evaluation of effectiveness of blasting for roof caving during longwall mining of coal seam deep longwall mining of coal seams is made in the upper silesian coal basin uscb under complicated and mostly unfavourable geological and mining conditions usually it is correlated with rockburst hazard mostly at a high level one of the geological factors affecting the state of rockburst hazard is the presence of competent rocks in the roof of extracted coal seams so rock falling behind the longwall face does not occur and hanging up of roof rocks remains the long lasting absence of caving may lead to an occurrence of high energy tremor in the vicinity of the longwall face roof caving behind the longwall face may be forced by blasting the column of explosives is then located in blastholes drilled in layers of roof rocks e g sandstones behind the longwall face in this article a characterization of tremors initiated by blasts for roof caving during underground extraction of coal seam no 507 in one of the collieries in the uscb has been made using three independent methods by the basic seismic effect method the effectiveness of blasting is evaluated according to the seismic energy of incited tremors and mass of explosives used according to this method selected blasts gave extremely good or excellent effect an inversion of the seismic moment tensor enables determining the processes happening in the source of tremors in the foci of provoked tremors the slip mechanism dominated or was clearly distinguished the expected explosion had lesser significance or was not present by the seismic source parameters analysis among other things an estimation of the stress drop in the focus or its size may be determined the stress drop in the foci of provoked tremors was in the order of 105 pa and the source radius according to the brune s model varied from 44 3 to 64 5 m the results of the three mentioned methods were compared with each other and observations in situ in all cases the roof falling was forced

hekla 1947 1845 1510 and 1158 tephra in finland challenges of tracing tephra from moderate eruptions

a multidisciplinary effort to assign realistic source parameters to models of volcanic ash cloud transport and dispersion during eruptions during volcanic eruptions volcanic ash transport and dispersion models vatds are used to forecast the location and movement of ash clouds over hours to days in order to define hazards to aircraft and to communities downwind those models use input parameters called eruption source parameters such as plume height h mass eruption rate duration d and the mass fraction m63 of erupted debris finer than about 4 or 63 m which can remain in the cloud for many hours or days observational constraints on the value of such parameters are frequently unavailable in the first minutes or hours after an eruption is detected moreover observed plume height may change during an eruption requiring rapid assignment of new parameters this paper reports on a group effort to improve the accuracy of source parameters used by vatds in the early hours of an eruption we do so by first compiling a list of eruptions for which these parameters are well constrained and then using these data to review and update previously studied parameter relationships we find that the existing scatter in plots of h versus yields an uncertainty within the 50 confidence interval of plus or minus a factor of four in eruption rate for a given plume height this scatter is not clearly attributable to biases in measurement techniques or to well recognized processes such as elutriation from pyroclastic flows sparse data on total grain size distribution suggest that the mass fraction of fine debris m63 could vary by nearly two orders of magnitude between small basaltic eruptions 0 01 and large silicic ones 0 5 we classify eleven eruption types four types each for different sizes of silicic and mafic eruptions submarine eruptions brief or vulcanian eruptions and eruptions that generate co ignimbrite or co pyroclastic flow plumes for each eruption type we assign source parameters we then assign a characteristic eruption type to each of the world s 1500 holocene volcanoes these eruption types and associated parameters can be used for ash cloud modeling in the event of an eruption when no observational constraints on these parameters are available

holocene vegetation history of the kotihi lagoon northwest peloponnesus greece abstract pollen diagrams are presented from two sediment cores from the area of kotihi lagoon in the northwestern peloponnesus greece radiocarbon dates indicate that the analyzed sediments accumulated during the last 7000 years six pollen assemblage zones are recognized the oldest zone middle neolithic in age is characterized by dominance of herbaceous types nap the second zone dated to the late and final neolithic shows a considerable increase in the abundance of arboreal types ap and a decrease in herbaceous taxa the third zone from the bronze age did not register any substantial change in the vegetation but the various communities changed considerably in the fourth zone from the iron age to roman period the abundance of arboreal types varied in the fifth zone medieval in age and in the sixth zone corresponding to the ottoman period arboreal pollen abundances continued to prevail during the last 3000 years human activity was the main factor influencing the vegetation in the study area

the roza member columbia river basalt group a gigantic pahoehoe lava flow field formed by endogenous processes we present studies on the physical volcanology of the 15 ma roza member of the wanapum formation in the columbia river basalt group the roza member represents a compound pahoehoe flood basalt lava flow field with an area of 40 300 km 2 and a volume of 1300 km 3 it consists of 4 major lava flows each composed of numerous decimeter to kilometer long pahoehoe lobes roza lavas feature a wide range of pahoehoe surface structures such as lava rise plateaus tumuli and surface breakouts and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas an integral component of the roza flow field is the sheet lobe with internal structures identical to those of inflated pahoehoe sheet lobes from hawaii and iceland both at the same scale and at much larger scales we identify a three part division of the sheet lobes into basal crust lava core and lava crust which are interpreted as the equivalent to the bottom crust the liquid lava core and the surface crust of an active inflating pahoehoe lobe the upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling this relationship is used to calculate the emplacement time for individual roza sheet lobes and to derive a first order estimate on the duration of the roza eruption the results indicate that the emplacement of individual roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years we propose that the roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth as the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of 0 1 c km and allowed for efficient transport of lava over distances up to 300 km

trace element degassing and enrichment in the eruptive plume of the 2000 eruption of hekla volcano iceland during its last eruption in february 2000 hekla volcano iceland emitted a sub plinian plume that was condensed and scavenged down to the ground by heavy snowstorms offering the unique opportunity to study the chemistry of the gaseous plume released during highly explosive eruptions in this paper we present results on trace element and minor volatile species sulfates chlorides and fluorides concentrations in snow samples collected shortly after the beginning of the eruption the goal of this study is to better constrain the degassing and mobility of trace elements in gaseous emissions trace element volatility at hekla is quantified by means of enrichment factors ef relative to be well known volatile trace elements e g transition metals heavy metals and metalloids are considerably enriched in the volcanic plume of hekla their abundances are governed by the primary magmatic degassing of sulfate and or halide compounds which are gaseous at magmatic temperature their volatility is however slightly lower than in basaltic systems most likely because of the lower magma temperature and higher magma viscosity at hekla more surprisingly refractory elements e g ree th ba and y are also significantly enriched in the eruptive plume of hekla where their apparent volatility is two orders of magnitude higher than in mafic systems in addition ree patterns normalized to the hekla 2000 lava composition show a significant enrichment of hree over lree suggesting the presence of ree fluorides in the volcanic plume such enrichments in the most refractory elements and ree fractionation are difficult to reconcile with primary degassing processes since ree fluorides are not gaseous at magma temperature ree enrichments at hekla could be attributed to incongruent dissolution of tephra grains at low temperature by f rich volcanic gases and aerosols within the eruptive plume this view is supported by both leaching experiments performed on hekla tephra and thermodynamic considerations on ree mobility in hydrothermal fluids and modeling of glass dissolution in f rich aqueous solutions tephra dissolution may also explain the observed enrichments in other refractory elements e g th y and ba and could contribute to the degassing mass balance of some volatile trace elements provided they are mobile in f rich fluids it thus appears that both primary magmatic degassing and secondary tephra dissolution processes govern the chemistry of eruptive plumes released during explosive eruptions

satellite detection long range transport and air quality impacts of volcanic sulfur dioxide from the 2014 2015 flood lava eruption at barðarbunga iceland the 2014 2015 bar arbunga vei ivotn fissure eruption at holuhraun produced about 1 5 km3 of lava making it the largest eruption in iceland in more than 200 years over the course of the eruption daily volcanic sulfur dioxide so2 emissions exceeded daily so2 emissions from all anthropogenic sources in europe in 2010 by at least a factor of 3 we present surface air quality observations from across northern europe together with satellite remote sensing data and model simulations of volcanic so2 for september 2014 we show that volcanic so2 was transported in the lowermost troposphere over long distances and detected by air quality monitoring stations up to 2750 km away from the source using retrievals from the ozone monitoring instrument omi and the infrared atmospheric sounding interferometer iasi we calculate an average daily so2 mass burden of 99 49 kilotons kt of so2 from omi and 61 18 kt of so2 from iasi for september 2014 this volcanic burden is at least a factor of 2 greater than the average so2 mass burden between 2007 and 2009 due to anthropogenic emissions from the whole of europe combining the observational data with model simulations using the united kingdom met office s numerical atmospheric dispersion modelling environment model we are able to constrain so2 emission rates to up to 120 kilotons per day kt d during early september 2014 followed by a decrease to 20 60 kt d between 6 and 22 september 2014 followed by a renewed increase to 60 120 kt d until the end of september 2014 based on these fluxes we estimate that the eruption emitted a total of 2 0 0 6 tg of so2 during september 2014 in good agreement with ground based remote sensing and petrological estimates although satellite derived and model simulated vertical column densities of so2 agree well the model simulations are biased low by up to a factor of 8 when compared to surface observations of volcanic so2 on 6 7 september 2014 in ireland these biases are mainly due to relatively small horizontal and vertical positional errors in the simulations of the volcanic plume occurring over transport distances of thousands of kilometers although the volcanic air pollution episodes were transient and lava dominated volcanic eruptions are sporadic events the observations suggest that i during an eruption volcanic so2 measurements should be assimilated for near real time air quality forecasting and ii existing air quality monitoring networks should be retained or extended to monitor so2 and other volcanic pollutants

the seismic source parameters of tremors provoked by long hole destress blasting executed during the longwall mining of a coal seam under variable stress conditions the underground mining of coal seams in the upper silesian coal basin is carried out at great depths and mostly in the presence of remnants or edges of other surrounding coal seams i e under the condition of high stress level in the rock mass therefore this mining is accompanied by rockburst hazard and suitable preventive action is required long hole destress blasting plays an important role and is commonly applied in rockburst prevention in underground hard coal mines estimated blasting effectiveness is important when designing rockburst prevention it is commonly estimated on the basis of the seismic energy of a provoked tremor the seismic source parameters have already been considered for this purpose additional information about the effects of long hole destress blasting could be contemplated in the planning of active rockburst prevention the seismic source parameters of tremors provoked by long hole destress blasting have been calculated and are presented in this article destress blasts were performed during the longwall mining of coal seam no 506 in one of the hard coal mines in the upper silesian coal basin they were executed from the longwall face in order to destress the rock mass ahead of it parameters of the blasts were variable and they were modified according to geological and mining conditions and the observed level of rockburst hazard the seismic source parameters have been determined for tremors provoked directly after firing explosives and for tremors occurring in the waiting time and they have been compared with each other

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

earthquake activity related to the 1991 eruption of the hekla volcano iceland the 1991 eruption of the hekla volcano started unexpectedly on 17 january no long term precursory seismicity was observed the first related activity was a swarm of small earthquakes that began approximately half an hour before the eruption intensive seismicity both earthquakes and volcanic tremor accompanied the violent onset of the eruption almost 400 events up to ml magnitude 2 5 were recorded during the first few hours during the later phases of the eruption the earthquake activity was modest and the main volcano related seismic signal was the persistent volcanic tremor the tremor died away together with the eruption on 11 march and hekla was seismically quiet until the beginning of june 1991 when a sudden swarm of numerous small shallow earthquakes occurred this activity is atypical for hekla and is interpreted to be a failed attempt to resume the eruption

iceberg rafted tephra as a potential tool for the reconstruction of ice sheet processes and ocean surface circulation in the glacial north atlantic ice rafted tephra deposits of marine isotope stage 6 mis 6 age from site u 1304 on the gardar drift north atlantic were examined for their shard size distribution and major element composition the heterogeneous composition large shard sizes and association with ice rafted debris ird indicate that these late mis 6 deposits were transported by iceberg rafting from iceland to site u 1304 comparison of individual shard geochemistry with the geochemistry of holocene volcanic systems from iceland allows the identification of different potential volcanic source regions this detailed geochemical analysis when combined with icelandic ice sheet iis flow models for the last glacial maximum lgm suggests that the iis had calving margins to both the north and south during the late mis 6 and that icebergs could have been transported to the site u 1304 by following surface ocean circulation patterns similar to those that prevailed during the lgm we demonstrate that the descriptive concept of icelandic glass in the characterization of tephra components within north atlantic ird can be significantly improved through quantitative characterization and that such data hold the potential to help constrain surface ocean circulation models while also potentially yielding new information about the iis during earlier glacial periods supplementary material statistical tests major element concentrations of analysed shards primary and secondary standards are available at http www geolsoc org uk sup18716

a half century of geologic and geothermic investigations in iceland the legacy of kristjan saemundsson abstract one of the world s premier field geologists kristjan saemundsson led immense geological mapping programs and authored or co authored nearly all geological maps of iceland during the past half century including the first modern bedrock and tectonic maps of the whole country these monumental achievements collectively yield the most inclusive view of an extensional plate boundary anywhere on earth when kristjan began his work in 1961 the relation of iceland to sea floor spreading was not clear and plate tectonics had not yet been invented kristjan resolved key obstacles by demonstrating that the active rifting zones in iceland had shifted over time and were linked by complex transforms to the mid ocean spreading ridge thus making the concept of sea floor spreading in iceland acceptable to those previously skeptical further his insights and vast geological and tectonic knowledge on both high and low temperature geothermal areas in iceland yielded a major increase in knowledge of geothermal systems and probably no one has contributed more than he to icelandic energy development kristjan s legacy is comprised by his numerous superb maps on a variety of scales the high quality papers he produced the impactful ideas generated that were internationally diffused and the generations of colleagues and younger people he inspired mentored or otherwise positively influenced with his knowledge and generous attitude

subaerial submarine evidence of structures feeding magma to stromboli volcano italy and relations with edifice flank failure and creep abstract structural field data including parameters of 109 sheets strike mostly n10 55 e average dip angle mostly 70 90 average thickness two peaks at 1 2 m and 4 2 m and of 14 eruptive fissures and vents as well as bathymetric and numerical data suggest that stromboli experienced the development of a volcanic rift zone across the cone summit with a tendency to widen towards the lower submarine flanks during the last 100 ka inside this rift zone intrusive sheets mostly strike ne and become more abundant more steeply dipping and thicker on approaching the rift axis this rift persistence reflects the edifice s state of stress with a nw se horizontal least principal stress on the magma intrusion paths after 13 ka ago sheets mainly intruded with a horseshoe shaped geometry in plan view along the boundaries of the northwestern unstable volcano flank where four main lateral collapses occurred during the last 13 ka they also intruded with a ne strike across the volcano summit and the northeastern volcano flank the horseshoe shaped geometry is influenced by the lateral creep of the volcano flank which provides space for intrusion along the transtensional boundaries of the unstable sector where thinner sheets were emplaced when the collapse depression was filled up by new deposits ne striking thicker dykes emplaced across the northwestern volcano flank indicating a rapid re establishment of regional tectonic forces across the cone unbuttressing due to the present sciara del fuoco depression and ongoing flank creeping can account for intrusions also inside the sciara del fuoco the latter in 2007

pollen corrected leaf wax d h reconstructions of northeast african hydrological changes during the late miocene abstract plant leaf wax hydrogen isotope dwax reconstructions are increasingly being used to reconstruct hydrological change this approach is based upon the assumption that variations in hydroclimatic variables and in particular the isotopic composition of precipitation dp dominate dwax however modern calibration studies suggest that offsets between plant types may bias the dwax hydrological proxy at times of vegetation change in this study i pair leaf wax analyses with published pollen data to quantify this effect and construct the first vegetation corrected hydrogen isotopic evidence for precipitation dcorrp in marine sediments from deep sea drilling program site 231 in the gulf of aden spanning 11 4 3 8 ma late miocene and earliest pliocene i find 77 swings in dwax that correspond to pollen evidence for substantial vegetation change similarities between dp and dcorrp imply that the hydrological tracer is qualitatively robust to vegetation change however computed vegetation corrections can be as large as 31 indicating substantial quantitative uncertainty in the raw hydrological proxy the resulting dcorrp values quantify hydrological change and allow us to identify times considerably wetter than modern at 11 09 7 26 5 71 and 3 89 ma more generally this novel interpretative framework builds the foundations of improved quantitative paleohydrological reconstructions with the dwax proxy in contexts where vegetation change may bias the plant based proxy the vegetation corrected paleoprecipitation reconstruction dcorrp represents the best available estimate as proof of concept for an approach that i hope will be refined and more broadly applied

reconstructing middle to late holocene palaeogeographies of the lower messenian plain southwestern peloponnese greece coastline migration vegetation history and sea level change abstract the glacio eustatic sea level rise after the last glacial maximum lgm led to a worldwide flooding of shelf areas and the evolution of marine embayments and indentations its significant deceleration in mid holocene times resulted in the overcompensation by sediment yields and shoreline progradation in many areas at the southeastern part of the lower messenian plain southwestern peloponnese greece detailed investigations of the holocene stratigraphy revealed a maximum landward shoreline displacement around 3000 bc subsequently aggradational processes started to form a prominent beach ridge in the late 3rd millennium bc this is the substratum on which the early iron age poseidon sanctuary of akovitika was founded approx 900 850 bc palaeogeographic reconstructions based on 18 corings in the sanctuary and its surroundings revealed the later extension of adjacent marshland and gradual surface levelling due to seasonal inundations these findings represent probable reasons for the abandonment of the ceremonial site around 380 350 bc palynological studies of the vegetational changes provide evidence for early land use and reflect regional settlement activities initial degradation and burning of woodland during late neolithic times c 3500 3100 bc as well as significantly reduced human impact during the protogeometric dark ages c 1060 900 bc are proven additionally local relative mean sea level rsl change since 5000 bc was reconstructed based on 14c dated paralic peats

biomarker hydrogen isotope composition δd as proxy for holocene hydroclimatic change and seismic activity in sw peloponnese greece we present a 6000 year long record tracing hydroclimate changes in sw greece based on hydrogen isotope composition of aquatic plant derived n c 23 alkanes d c23 in a sediment core from the messe

a diverse ecosystem response to volcanic aerosols unexpectedly high aluminium concentrations beside fluoride and essential elements are released from metal salts adsorbed to volcanic ash through simulation of the mixing of pristine volcanic ash leachate with fresh water and seawater using phreeqc we found an increased potential toxicity in fresh waters through the combination of high aluminium and fluoride concentrations owing to the mixing of acid ash leachate with fresh water aluminofluoride complexes alfx 3 x persist in aqueous systems with low turnover rates and could be toxic to both plants and animals in contrast due to the well buffered and relatively high ph in seawater the speciation of the ash leachate seawater mixture shows that complexes of fluoride and aluminium i e alfx 3 x will not dominate in a well mixed marine system instead al oh x 3 x species will occur at greatest concentration consequently compared with fresh water environments the mixing of ash leachate with seawater indicates reduced toxic effects due to decreased formation of alfx 3 x complexes and the low solubility of al hydroxides in addition the deposition of volcanic aerosols may enhance biological activity in the marine environment by providing micronutrients as some oceanic phytoplankton species tolerates extreme concentrations of fluoride f

the spatial distribution of holocene cryptotephras in north west europe since 7 ka implications for understanding ash fall events from icelandic eruptions abstract we present distribution maps for all cryptotephras distal volcanic ash layers younger than 7 ka that have been reported from three or more lakes or peatlands in north west europe all but one of the tephras originates from iceland the exception has been attributed to jan mayen we find strong spatial patterning in tephra occurrence at the landscape scale most but not all of the tephra occurrences are significantly spatially clustered which likely reflects atmospheric and weather patterns at the time of the eruptions contrary to expectations based on atmospheric modelling studies tephras appear to be at least as abundant in ireland and northern scotland as in scandinavia rhyolitic and other felsic tephras occur in lakes and peatlands throughout the study region but andesitic and basaltic tephras are largely restricted to lake sites in the faroe islands and ireland explanations of some of these patterns will require further research on the effects of different methodologies for locating and characterizing cryptotephras these new maps will help to guide future investigations in tephrochronology and volcanic hazard analysis

n alkane parameters from a deep sea sediment transect off southwest africa reflect continental vegetation and climate conditions abstract an isobathic transect of marine surface sediments from 1 n to 28 s off southwest africa was used to further evaluate the potential of the chain length distribution and carbon stable isotope composition of higher plant n alkanes as proxies for continental vegetation and climate conditions we found a strong increase in the n c 29 33 weighted mean average 13 c values from 33 near the equator to around 26 further south additionally c 25 35 n alkanes reveal a southward trend of increasing average chain length from 30 0 to 30 5 the data reflect the changing contribution of plants employing different photosynthetic pathways c 3 and c 4 and or being differently influenced by the environmental conditions of their habitat the c 4 plant proportions calculated from the data ca 20 for rivers draining the rainforest to ca 70 at higher latitude correspond to the c 4 plant abundance in continental catchment areas postulated by considering prevailing wind systems and river outflows furthermore the c 4 plant contribution to the sediments correlates with the mean annual precipitation and aridity at selected continental locations in the postulated catchment areas suggesting that the c 4 plant fraction in marine sediments can be used to assess these environmental parameters

plant wax δd values record changing eastern mediterranean atmospheric circulation patterns during the 8 2 kyr b p climatic event abstract throughout the holocene the climate of the mediterranean region has been strongly influenced by variability in the atmospheric circulation of the high and low latitudes a prominent example for such holocene climate perturbations is the 8 2 kyr b p climatic event reorganization of northern hemisphere atmospheric circulation patterns resulted in variations of temperature and precipitation distribution across the mediterranean the effects of changing high and low latitude atmospheric circulation on mediterranean climate in relation to the 8 2 kyr b p climatic event are however not well understood here we present a high resolution record of stable hydrogen isotope composition of plant wax n alkanes dwax across the 8 2 kyr b p climatic event from the tenaghi philippon peat deposit ne greece in order to characterize patterns of precipitation and changes in atmospheric circulation in the eastern mediterranean region our record reveals pronounced changes in dwax that correlate closely with previously published palynological data a long term decline in dwax values characterizes the lower part of the section the 8 2 kyr b p climatic event itself is connected to two distinct positive dwax excursions a minor shift in dwax around 8 2 kyr b p and a major shift in dwax between ca 8 1 and 8 0 kyr b p the upper part of the section shows a progressive trend towards higher dwax values we link shifts in dwax to changes in mediterranean air mass trajectories supplying precipitation to ne greece caused by variations in the relative contributions of northerly derived d depleted moisture and southerly derived d enriched moisture possible control mechanisms for alternating air mass trajectories include changes in the influence of the siberian high and differences in the influence of the african and asian monsoon circulation on anticyclonic conditions in the mediterranean region as well as regional inflow of moist air masses from the aegean sea

non climatic factors and the environmental impact of volcanic volatiles implications of the laki fissure eruption of ad 1783 studies of the potential of icelandic volcanic eruptions to modify the environment of the british isles have primarily concentrated on the degree of induced climate change but models and temperatu

stratospheric volcanic ash emissions from the 13 february 2014 kelut eruption mount kelut indonesia erupted explosively around 15 50 ut on 13 february 2014 sending ash and gases into the stratosphere satellite ash retrievals and dispersion transport modeling are combined within an inversion framework to estimate the volcanic ash source term and to study ash transport the estimated source term suggests that most of the ash was injected to altitudes of 16 17 km in agreement with space based lidar data modeled ash concentrations along the flight track of a commercial aircraft that encountered the ash cloud indicate that it flew under the main ash cloud and encountered maximum ash concentrations of 9 3 mg m 3 mean concentrations of 2 1 mg m 3over a period of 10 11 min of the flight giving a dosage of 1 2 0 3 g s m 3 satellite data could not be used directly to observe the ash cloud encountered by the aircraft whereas inverse modeling revealed its presence

operational prediction of ash concentrations in the distal volcanic cloud from the 2010 eyjafjallajokull eruption 1 during the 2010 eruption of eyjafjallajokull improvements were made to the modeling procedure at the met office uk enabling peak ash concentrations within the volcanic cloud to be estimated in this paper we describe the ash concentration forecasting method its rationale and how it evolved over time in response to new information and user requirements the change from solely forecasting regions of ash to also estimating peak ash concentrations required consideration of volcanic ash emission rates the fraction of ash surviving near source fall out and the relationship between predicted mean and local peak ash concentrations unresolved by the model to validate the modeling procedure predicted peak ash concentrations are compared against observations obtained by ground based and research aircraft instrumentation this comparison between modeled and observed peak concentrations highlights the many sources of error and the uncertainties involved despite the challenges of predicting ash concentrations the ash forecasting method employed here is found to give useful guidance on likely ash concentrations predicted peak ash concentrations lie within about one and a half orders of magnitude of the observed peak concentrations a significant improvement in the agreement between modeled and observed values is seen if a buffer zone accounting for positional errors in the predicted ash cloud is used sensitivity of the predicted ash concentrations to the source properties e g the plume height and the vertical distribution of ash at the source is assessed and in some cases seemingly minor uncertainties in the source specification have a large effect on predicted ash concentrations

the 1989 1990 eruption of redoubt volcano alaska impacts on aircraft operations abstract the december 1989 june 1990 eruption of redoubt volcano affected commercial and military air operations in the vicinity of anchorage alaska these effects were due to the direct impact of volcanic ash on jet aircraft as well as to the rerouting and cancellations of flight operations owing to eruptive activity between december and february five commercial jetliners were damaged from ash encounters the most serious incident took place on december 15 1989 when a boeing 747 400 aircraft temporarily lost power of all four engines after encountering an ash cloud as the airplane descended for a landing in anchorage while there were no injuries to passengers the damage to engines avionics and aircraft structure from this encounter is estimated at 80 million four additional encounters between jet aircraft and redoubt ash clouds occurred in the anchorage area on december 15 and 16 1989 and february 21 1990 none resulted in engine failure two additional encounters took place on december 17 1989 when jet airliners encountered the redoubt cloud over west texas at the time of these encounters the cloud was up to 55 hours old and had traveled in excess of 2 900 nautical miles 5 300 km following the december 15 encounters anchorage international airport remained open however most airline companies canceled operations for up to several days as communications between federal agencies and airlines improved and as a better understanding of the nature and behavior of ash rich eruption clouds was achieved most airlines resumed normal service by early january 1990 the resulting loss of revenue at anchorage international airport during several months following the eruption is estimated to total 2 6 million the impact on general aviation and military operations consisted mostly of cancellation and rerouting of flights

volcanic tremor related to the 1991 eruption of the hekla volcano iceland volcanic tremor at the hekla volcano is directly related to eruptive activity it starts simultaneously with the eruptions and dies down at the end of them no tremor at hekla has been observed during non eruptive times the 1991 hekla eruption began on 17 january after a short warning time local seismograph stations recorded small premonitory earthquakes from 16 30 gmt on at 17 02 gmt low frequency volcanic tremor became visible on the seismograph records marking the onset of the eruption the initial plinian phase of the eruption was short lived during the first day several fissures were active but by the second day the activity was already limited to a segment of one principal fissure the eruption lasted almost 53 days at the end of it during the early hours of 11 march volcanic tremor disappeared under the detection threshold and was followed by a swarm of small earthquakes at the start of the eruption the tremor amplitude rose rapidly and reached a maximum in only 10 min the tremor was most vigorous during the first hour and started to decline sharply during the next hour and later on more gently during the eruption as a whole the tremor had a continuous declining trend with occasional increases lasting up to about 2 days spectral analysis of the tremor during the first 7 h of the eruption shows that it settled quickly within a couple of minutes to its characteristic frequency band 0 5 1 5 hz the spectrum had typically one dominant peak at 0 7 0 9 hz and a few subdominant peaks hekla tremor likely has a shallow source particle motion plots suggest that it contains a significant component of surface waves the tremor started first when the connection of the magma conduit with the atmosphere was reached suggesting that degassing may contribute to its generation

in situ observations of volcanic ash clouds from the faam aircraft during the eruption of eyjafjallajokull in 2010 1 during april may 2010 the uk facility for airborne atmospheric measurements faam bae 146 aircraft flew 12 flights targeting volcanic ash clouds around the uk the aircraft observed ash layers between altitudes of 2 8 km with peak mass concentrations typically between 200 2000 g m3 as estimated from a cloud and aerosol spectrometer cas a peak value of 2000 5000 g m3 was observed over scotland on 14 may 2010 although with considerable uncertainty due to the possible contamination by ice aerosol size distributions within ash clouds showed a fine mode 0 1 0 6 m associated with sulphuric acid and or sulphate and a coarse mode 0 6 35 m associated with ash the ash mass was dominated by particles in the size range 1 10 m volume equivalent diameter with a peak typically around 3 5 m electron microscope images and scattering patterns from the sid 2h small ice detector probe showed the highly irregular shape of the ash particles ash clouds were also accompanied by elevated levels of so2 10 100 ppbv strong aerosol scattering 50 500 10 6 m 1 and low angstrom exponents 0 5 to 0 4 from the 3 wavelength nephelometer coarse mode mass specific aerosol extinction coefficients kext based on the cas size distribution varied from 0 45 1 06 m2 g a representative value of 0 6 m2 g is suggested for distal ash clouds 1000 km downwind from this eruption

new insights into volcanic activity from strain and other deformation data for the hekla 2000 eruption abstract hekla is one of iceland s most active volcanoes its eruptions characterized by surface fissuring and repeated lava flows during its post glacial activity have built up an 800 m high elongated mountain since 1970 it has erupted every 10 years the previous repose interval averaged 60 years for the last eruption in 2000 we constrain the magma geometry by using a wide variety of deformation data campaign gps an insar interferogram dry tilt data and borehole strain data the dike that causes surface fissuring extends no more than 0 5 km in depth and the reservoir depth is 10 km these are connected by a conduit of small lateral extent data for previous eruptions are consistent with this model we propose that the marked change in eruption interval is because this conduit remains liquid during the short interval between recent eruptions only a small pressure increase is required to rupture the thin crustal seal such a state is consistent with precursory seismicity being confined to very shallow depths and may be applicable to other volcanoes that undergo abrupt changes in eruption interval

seismic activity related to the 2000 eruption of the hekla volcano iceland the 2000 hekla eruption took place from february 26 to march 8 its seismic expressions were a swarm of numerous small earthquakes related to its onset and low frequency volcanic tremor that continued throughout the eruption a swarm of small earthquakes was observed some 80 min before the onset of the eruption and the size of the events increased with time low frequency volcanic tremor with a characteristic frequency band of 0 5 1 5 hz and dominant spectral peak s at 0 7 0 9 hz became visible at 18 19 gmt on february 26 marking the onset of the eruption the tremor amplitude rose quickly and was very high in the beginning of the eruption however it soon began to decrease after about an hour in general the seismic activity related to the 2000 hekla eruption was very similar to what was observed in the previous eruption in 1991 based on knowledge gained from seismicity and strain observations from 1991 this was the first time that a hekla eruption was predicted

late postglacial paleoenvironmental change in the northeastern mediterranean region combined palynological and molecular biomarker evidence three gravity cores collected from the ne mediterranean nemr across a transect from the northern aegean sea north skyros basin to the south cretan margin scm were investigated for pollen and terrestrial biomarkers derived from epicuticular waxes of vascular plants during the last 20 ky pollen data show diversified mixed temperate forest in the northern borderlands and enhanced mediterranean vegetation in the southern areas documenting an n s climatic trend terrestrial plant biomarkers and their diagnostic geochemical indices exhibit latitudinal patterns which are interpreted in terms of the different delivery pathways fluvial runoff vs atmospheric transport resulting from the climate conditions during different periods during the late glacial and early deglaciation periods 20 14 ka bp relatively increased humidity h index is recorded in the north aegean sea while in the south drier climate was the limiting factor for vegetation development during this interval terrestrial n alkanes showed increased accumulation rates suggesting massive transport of terrestrial organic matter through runoffs and rivers followed by weaker input after 14 ka bp after 11 ka bp a major expansion of forest cover is evidenced in the nemr accompanied by a higher h index because of the climatic amelioration the forest vegetation exhibited regionally different characteristics with cool temperate taxa being more abundant in the aegean cores while the scm record is being featured by mediterranean elements at the onset of the holocene and throughout the holocene climatic optimum the delivery of terrestrial biomarkers increased and became more significant in the aegean sites compared to the scm site within the holocene the average chain length acl of long chain n alkanes exhibits lower values in the northern aegean than in the southeastern aegean and scm indicating the predominance of warmer species southwards finally the h index records a conspicuous humidity increase between 5 4 and 4 3 ka bp in the south aegean that coincides with an increase in the terrestrial biomarker supply and the deposition of a distinct sapropel like layer smh sapropel mid holocene similar trends in t temperature and h indices are slightly delayed and attenuated in the northern aegean and are accompanied by an increase in the acl index a noticeable increase in the accumulation rates ars of terrestrial biomarkers and the hpa index values during this period are clearly recorded in all three cores indicative of enhanced terrigenous inputs of organic matter along with higher in situ preservation

effect of wind on the rise height of volcanic plumes a theoretical model of a volcanic plume based on applying the equations of motion in a plume centered coordinate system suggests that the interaction between a volcanic plume and wind causes enhanced entrainment of air and horizontal momentum plume bending and a decrease in plume rise height at constant eruption rate because of rapid dilution in the high windspeeds of the polar jet plumes that vary over more than one order of magnitude in mass eruption rate 106 to 107 108 kg s if injected into the polar jet may all attain rise heights only slightly different from that of the core of the jet 10 km as opposed to 17 33 km in a still atmosphere

moment magnitude m w and local magnitude m l relationship for earthquakes in northeast india an attempt has been made to examine an empirical relationship between moment magnitude mw and local magnitude ml for the earthquakes in the northeast indian region some 364 earthquakes that were recorded during 1950 2009 are used in this study focal mechanism solutions of these earthquakes include 189 harvard cmt solutions mw 4 0 for the period 1976 2009 61 published solutions and 114 solutions obtained for the local earthquakes 2 0 ml 5 0 recorded by a 27 station permanent broadband network during 2001 2009 in the region the mw ml relationships in seven selected zones of the region are determined by linear regression analysis a significant variation in the mw ml relationship and its zone specific dependence are reported here it is found that mw is equivalent to ml with an average uncertainty of about 0 13 magnitude units a single relationship is however not adequate to scale the entire northeast indian region because of heterogeneous geologic and geotectonic environments where earthquakes occur due to collisions subduction and complex intra plate tectonics

the krafla spreading segment iceland 1 three dimensional crustal structure and the spatial and temporal distribution of local earthquakes the geothermal seismicity of the krafla volcanic system ne iceland was monitored for 3 months in 1985 using a dense local seismometer network the seismicity was continuous and the spatial and temporal distributions were roughly known prior to monitoring the instruments could thereby be deployed in a well positioned array a total of 489 locatable events were recorded within the network and 1771 arrival times were inverted to calculate the three dimensional p wave velocity structure and hypocentral locations low velocity volumes were imaged beneath the krafla and namafjall geothermal areas and indicate zones of hydrothermal alteration high velocity bodies beneath the krafla caldera rim are interpreted as gabbroic intrusions using a three dimensional velocity structure instead of a refraction based one dimensional model to locate the hypocenters significantly improves their location quality and illustrates the shortcomings of using refraction based models to locate earthquakes in local anomalous areas seismic activity was concentrated within the krafla and namafjall geothermal areas and in a narrow zone where dike injections had occurred 8 and 5 years earlier the activity occurred in the depth range 0 3 km the seismic rate for the whole area was one magnitude 3 2 event per year and the b value was 0 77 0 10 most of the seismicity appears to result from geothermal processes in the manner proposed for other icelandic areas foulger and long 1984 foulger 1988b seismicity directly beneath the bjarnarflag well field within the namafjall area is probably induced partly by geothermal exploitation considerable seismicity also occurred immediately below leirhnjukur a site of intense geothermal activity in the center of the krafla caldera that overlies a roof pendant in the magma chamber below this volume of high seismicity is probably highly fractured and may provide a conduit for magma escaping from the magma chamber

the hekla eruption 1980 1981 the sixteenth eruption of hekla since 1104 began on august 17th 1980 after the shortest repose period on record only ten years the eruption started with a plinian phase and simultaneously lava issued at high rate from a fissure that runs along the hekla volcanic ridge the production rate declined rapidly after the first day and the eruption stopped on august 20th a total of 120 million m3 of lava and about 60 million m3 of airborne tephra were produced during this phase of the activity in the following seven months steam emissions were observed on the volcano activity was renewed on april 9th 1981 and during the following week additional 30 million m3 of lava flowed from a summit crater and crater rows on the north slope

speleothem evidence for late holocene climate variability and floods in southern greece abstract we present stable isotope data 18o 13c from a detrital rich stalagmite from kapsia cave the peloponnese greece the cave is rich in archeological remains and there are reasons to believe that flooding of the cave has directly affected humans using the cave using a combination of u th and 14c dating to constrain a site specific correction factor for 232th 238u detrital molar ratio a linear age model was constructed the age model shows that the stalagmite grew during the period from ca 950 bc to ca ad 830 the stable oxygen record from kapsia indicates cyclical changes of close to 500 yr in precipitation amount with rapid shifts towards wetter conditions followed by slowly developing aridity superimposed on this signal wetter conditions are inferred around 850 700 500 and 400 100 bc and around ad 160 300 and ad 770 and driest conditions are inferred to have occurred around 450 bc ad 100 150 and ad 650 detrital horizons in the stalagmite indicate that three major floods took place in the cave at 500 bc 70 bc and ad 450 the stable carbon isotope record reflects changes in biological activity being a result of both climate and human activities

seismic constraints on magma chambers at hekla and torfajokull volcanoes iceland hekla and torfajokull are active volcanoes at a rift transform junction in south iceland despite their location next to each other they are physically and geologically very different hekla is an elongate stratovolcano built mainly of basaltic andesite torfajokull is a prominent rhyolitic centre with a 12 km diameter caldera and extensive geothermal activity the scope of this study is to examine the propagation of body waves of local earthquakes across the hekla torfajokull area and look for volumes of anomalous s wave attenuation which can be evidence of magma chambers so far the magma chamber under hekla has been modelled with various geophysical means and its depth has been estimated to be 5 9 km a data set of 118 local earthquakes providing 663 seismic rays scanning hekla and torfajokull was used in this study the major part 650 seismograms did not show evidence for s wave attenuation under these volcanoes only six seismograms had clear signs of s wave attenuation and seven seismograms were uncertain cases the data set samples hekla well at depths of 8 14 km and south part of it also at 4 8 km and 14 16 km western torfajokull is sampled well at depths of 4 14 km eastern and southern torfajokull at 6 12 km conclusions cannot be drawn regarding the existence of magma beyond these depth ranges also magma volumes of smaller dimensions than about 800 m cannot be detected with this method if a considerable molten volume exists under hekla it must be located either above 4 km or below 14 km the former possibility seems unlikely because hekla lacks geothermal activity and persistent seismicity usually taken as expressions of a shallow magma chamber an aseismic volume with a diameter of 4 km at the depth of 8 km in the west part of torfajokull has been inferred in earlier studies and interpreted as evidence for a cooling magma chamber our results indicate that this volume cannot be molten to a great extent because s waves travelling through it are not attenuated intense geothermal activity and low frequency earthquakes are possibly signs of magma in the south part of torfajokull but a magma chamber was not detected there in the areas sampled by this study

climate variability and socio environmental changes in the northern aegean ne mediterranean during the last 1500 years abstract we provide new evidence on sea surface temperature sst variations and paleoceanographic paleoenvironmental changes over the past 1500 years for the north aegean sea ne mediterranean the reconstructions are based on multiproxy analyses obtained from the high resolution decadal to multi decadal marine record m2 retrieved from the athos basin reconstructed ssts show an increase from ca 850 to 950 ad and from ca 1100 to 1300 ad a cooling phase of almost 1 5 c is observed from ca 1600 ad to 1700 ad this seems to have been the starting point of a continuous sst warming trend until the end of the reconstructed period interrupted by two prominent cooling events at 1832 15 ad and 1995 1 ad application of an adaptive kernel smoothing suggests that the current warming in the reconstructed ssts of the north aegean might be unprecedented in the context of the past 1500 years internal variability in atmospheric oceanic circulations systems as well as external forcing as solar radiation and volcanic activity could have affected temperature variations in the north aegean sea over the past 1500 years the marked temperature drop of approximately 2 c at 1832 15 yr ad could be related to the 1809 d unknown and the 1815 ad tambora volcanic eruptions paleoenvironmental proxy indices of the m2 record show enhanced riverine continental inputs in the northern aegean after ca 1450 ad the paleoclimatic evidence derived from the m2 record is combined with a socio environmental study of the history of the north aegean region we show that the cultivation of temperature sensitive crops i e walnut vine and olive co occurred with stable and warmer temperatures while its end coincided with a significant episode of cooler temperatures periods of agricultural growth in macedonia coincide with periods of warmer and more stable ssts but further exploration is required in order to identify the causal links behind the observed phenomena the black death likely caused major changes in agricultural activity in the north aegean region as reflected in the pollen data from land sites of macedonia and the m2 proxy reconstructions finally we conclude that the early modern peaks in mountain vegetation in the rhodope and macedonia highlands visible also in the m2 record were very likely climate driven

predicting regions susceptible to high concentrations of airborne volcanic ash in the north pacific region abstract airborne ash probability distribution aapd maps have been generated to show the distribution of airborne volcanic ash in the north pacific nopac region by simulating volcanic eruption clouds from 22 of the 100 most historically active volcanoes in the region the puff ash dispersion model was run daily using archived wind field data between 1994 1995 and 1997 2001 for low and high aircraft flight levels subsequent statistics are generated representing the distribution of simulated airborne ash at 6 and 24 h intervals defining the regions most likely to contain airborne ash and the direction and distance a volcanic ash cloud may propagate from a given volcano the aapd maps show the extent of ash from a given volcano can encompass all of alaska most of the north pacific ocean portions of northwestern north america regions as far south as 35 n regions over the western arctic ocean and portions of eastern russia in general low altitude atmospheric regions 3 8 km asl are more susceptible to airborne volcanic ash when compared to regions above 8 km asl due to the eruption characteristics of volcanoes in the north pacific and the region s atmospheric profile the results indicate that the paths of many nopac air traffic routes coincide with airborne ash distribution probability maxima the upper atmospheric region most likely to contain airborne ash is located off the eastern coast of the kamchatkan peninsula and is generally centered over the heavy air traffic flight corridor of the nopac although this paper focuses on the nopac region the technique can be directly applied to other regions characterized by active volcanism

long hole destress blasting for rockburst control during deep underground coal mining abstract the lazy colliery in the ostrava karvina coalfield of the upper silesian coal basin adopted modern longwall technology for an underground extraction of coal seam no 504 this coal seam is located at a cover depth of around 700 m the seam thickness varied from 3 1 m to 5 0 m in the selected longwall panel two overlying coal seams nos 512 and 530 experienced mining at average heights of 58 m and 75 m respectively from the planned working horizon of the seam no 504 the proposed longwall panel was adversely situated below goaf edges of the workings in these two overlying extracted seams an analysis of the inter burden rock mass among these coal seams showed the presence of strong massive strata of sandstones and conglomerates with uniaxial compressive strength values between 70 mpa and 120 mpa the stress is measured at different mining stages by compact conical ended borehole monitoring ccbm a simple laboratory test of the coal sample found a high value of the ratio of the elastic deformation to the total deformation 0 8 indicating the energy storing characteristic prone to burst bump of the coal seam under the existing geo mining conditions of the site a suitable destress blasting long hole drilling and blasting design is adopted to pre fracture the identified competent strata from both gate roads in advance the total length of the panel could be extracted without any bump rockburst after the destress blasting the efficiency of the adopted destress blasting at the different mining stages is evaluated in terms seismic effect se which is calculated through the available seismic monitoring data and weight of the charged explosive a systematic adoption of the destress rock blasting led the 300 m long longwall panel to be smoothly extracted without any further rockbursts

are flood basalt eruptions monogenetic or polygenetic a fundamental classification of volcanoes divides them into monogenetic and polygenetic we discuss whether flood basalt fields the largest volcanic provinces are monogenetic or polygenetic a polygenetic volcano whether a shield volcano or a stratovolcano erupts from the same dominant conduit for millions of years excepting volumetrically small flank eruptions a flood basalt province built from different eruptive fissures dispersed over wide areas can be considered a polygenetic volcano without any dominant vent however in the same characteristic a flood basalt province resembles a monogenetic volcanic field with only the difference that individual eruptions in the latter are much smaller this leads to the question how a flood basalt province can be two very different phenomena at the same time individual flood basalt eruptions have previously been considered monogenetic contrasted by only their high magma output and lava fluidity with typical small volume monogenetic volcanoes field data from hawaiian shield volcanoes iceland and the deccan traps show that whereas many feeder dykes were single magma injections and the eruptions can be considered large monogenetic eruptions multiple dykes are equally abundant they indicate that the same dyke fissure repeatedly transported separate magma batches feeding an eruption which was thus polygenetic by even the restricted definition the same magma conduit this recognition helps in understanding the volcanological stratigraphic and geochemical complexity of flood basalts the need for clear concepts and terminology is however strong we give reasons for replacing monogenetic volcanic fields with diffuse volcanic fields and for dropping the term polygenetic and describing such volcanoes simply and specifically as shield volcanoes stratovolcanoes and flood basalt fields

analysis of exceptionally large tremors in two gold mining districts of south africa an investigation of ground motion recorded using broad band wide dynamic range digital seismographs of large mine tremors from two south african mining districts with different geologic settings reveals some essential differences in both seismic source and ground motion parameters in the klerksdorp district where the strata are offset by major throughgoing normal faults the largest tremors with magnitudes ranging as high as 5 2 tend to be associated with slip on these pre existing faults moreover the seismic source and ground motion parameters are quite similar to those of natural crustal earthquakes in the carletonville district by contrast where substantial faults do not exist the large magnitude tremors appear to result from the failure of relatively intact rock and cause seismic stress drops and ground motion parameters higher than normally observed for natural shocks additionally there appears to be an upper magnitude limit of about 4 in the carletonville district detailed analyses of an exceptionally large event recorded locally from each of these districts serve to highlight these contrasts

high resolution environmental reconstruction in sw peloponnese greece covering the last c 6000 years evidence from agios floros fen messenian plain a paleolimnological record from the central messenian plain southwestern peloponnese southern greece indicates rapid changes in the water level and chemistry of a transient lake on the flanks of the taygetos mountains during the last c 6000 years the analyses are based on diatoms as well as carbon and nitrogen isotopes from bulk sediments in a 7 5 m long sediment core retrieved from the drained fen of agios floros at the northern banks of the ancient river pamisos the sequence consists of fen peat in the uppermost section underlain by lacustrine sediments which are punctuated by two layers of clay with diatomaceous silt bands high accumulation rate is recorded in the oldest part of the section up to 23 mm yr particularly during two decadal long periods centered at c 5700 and c 5300 cal bp the diatom record reveals pronounced peaks in the planktonic taxon cyclotella distinguenda which correspond to the laminated sequences reflecting the rapid development of a deep lake with an open water

late glacial holocene climate variability at the south eastern margin of the aegean sea abstract new micropaleontological palynological and geochemical results from a relatively shallow 500 m sediment core ns 14 in the south eastern aegean sea provide a detailed picture of the regional expression of sapropel s1 formation in this sub basin of the eastern mediterranean sea specifically freshwater input during 10 6 10 0 ka bp has preceded the deposition of s1 further decrease in surface water salinity is evidenced between 10 0 and 8 5 ka bp at the lower part of s1a which in respect to s1b is featured by warmer 19 5 c and more productive surface waters associated with dysoxic bottom conditions a series of coolings detected within the s1 depositional interval may be linked to outbursts of cold northerly air masses and relevant pulses in the deep intermediate water ventilation that caused the s1 interruption between 7 9 and 7 3 ka bp and culminated during the deposition of s1b with the decline of deep chlorophyll maximum dcm at 6 5 ka bp the climate instability and the relevant absence of anoxia weakened the organic matter preservation in the shallow south eastern aegean margin during the s1 times ns 14 record provides evidence for a distinct mid holocene warm up to 25 c and wet phase associated with the deposition of the sapropel like layer smh sapropel mid holocene between 5 4 and 4 3 ka bp the smh layer could represent evidence of on going albeit weak african monsoon forcing only expressed at the south eastern edge of the aegean sea its end is associated with the 4 2 ka bp northern hemisphere mega drought event and the termination of the african humid period at 3 8 ka bp

distal deposition of tephra from the eyjafjallajokull 2010 summit eruption the 2010 eyjafjallajokull lasted 39 days and had 4 different phases of which the first and third 14 18 april and 5 6 may were most intense most of this period was dominated by winds with a northerly component that carried tephra toward europe where it was deposited in a number of locations and was sampled by rain gauges or buckets surface swabs sticky tape samples and air filtering in the uk tephra was collected from each of the phases 1 3 with a combined range of latitudes spanning the length of the country the modal grain size of tephra in the rain gauge samples was 25 mu m but the largest grains were 100 mu m in diameter and highly vesicular the mass loading was equivalent to 8 218 shards cm 2 which is comparable to tephra layers from much larger past eruptions falling tephra was collected on sticky tape in the english midlands on 19 20 and 21st april phase 2 and was dominated by aggregate clasts mean diameter 85 mu m component grains 10 mu m sem eds spectra for aggregate grains contained an extra peak for sulphur when compared to control samples from the volcano indicating that they were cemented by sulphur rich minerals e g gypsum caso4 center dot h2o air quality monitoring stations did not record fluctuations in hourly pm10 concentrations outside the normal range of variability during the eruption but there was a small increase in 24 hour running mean concentration from 21 24 april phase 2 deposition of tephra from phase 2 in the uk indicates that transport of tephra from iceland is possible even for small eruption plumes given suitable wind conditions the presence of relatively coarse grains adds uncertainty to concentration estimates from air quality sensors which are most sensitive to grain sizes 10 mu m elsewhere tephra was collected from roofs and vehicles in the faroe islands mean grain size 40 mu m but 100 mu m common from rainwater in bergen in norway 23 91 mu m and in air filters in budapest hungary 2 6 mu m a map is presented summarizing these and other recently published examples of distal tephra deposition from the eyjafjallajokull eruption it demonstrates that most tephra deposited on mainland europe was produced in the highly explosive phase 1 and was carried there in 2 3 days

the millennium eruption of hekla in february 2000 the 18th historic eruption of hekla started on 26 february 2000 it was a short lived but intense event emitting basaltic andesitic 55 5 wt sio2 pyroclastic fragments and lava during the course of the eruption monitoring was done by both instruments and direct observations together providing unique insight into the current activity of hekla during the 12 day eruption a total of 0 189 km3 dre of magma was emitted the eruptive fissure split into five segments the segments at the highest altitude were active during the first hours while the segments at lower altitude continued throughout the eruption the eruption started in a highly explosive manner giving rise to a subplinian eruptive column and consequent basaltic pyroclastic flows fed by column collapses after the explosive phase reached its maximum the eruption went through three more phases namely fire fountaining strombolian bursts and lava effusion in this paper we describe the course of events of the eruption of hekla and the origin of its magma and then show that the discharge rate can be linked to different style of eruptive activity which are controlled by fissure geometry we also show that the eruption phases observed at hekla can be linked with inferred magma chamber overpressure prior to the eruption

evaluating the structure and magnitude of the ash plume during the initial phase of the 2010 eyjafjallajokull eruption using lidar observations and name simulations 1 the eyjafjallajokull volcano in iceland erupted explosively on 14 april 2010 emitting a plume of ash into the atmosphere the ash was transported from iceland toward europe where mostly cloud free skies allowed ground based lidars at chilbolton in england and leipzig in germany to estimate the mass concentration in the ash cloud as it passed overhead the uk met office s numerical atmospheric dispersion modeling environment name has been used to simulate the evolution of the ash cloud from the eyjafjallajokull volcano during the initial phase of the ash emissions 14 16 april 2010 name captures the timing and sloped structure of the ash layer observed over leipzig close to the central axis of the ash cloud relatively small errors in the ash cloud position probably caused by the cumulative effect of errors in the driving meteorology en route result in a timing error at distances far from the central axis of the ash cloud taking the timing error into account name is able to capture the sloped ash layer over the uk comparison of the lidar observations and name simulations has allowed an estimation of the plume height time series to be made it is necessary to include in the model input the large variations in plume height in order to accurately predict the ash cloud structure at long range quantitative comparison with the mass concentrations at leipzig and chilbolton suggest that around 3 of the total emitted mass is transported as far as these sites by small 100 m diameter ash particles

the 1991 eruption of hekla iceland the eruption that started in the hekla volcano in south iceland on 17 january 1991 and came to an end on 11 march produced mainly andesitic lava this lava covers 23 km2 and has an estimated volume of 0 15 km3 this is the third eruption in only 20 years whereas the average repose period since 1104 is 55 years earthquakes as well as a strain pulse recorded by borehole strainmeters occurred less than half an hour before the start of the eruption the initial plinian phase was very short lived producing a total of only 0 02 km3 of tephra the eruption cloud attained 11 5 km in height in only 10 min but it became detached from the volcano a few hours later several fissures were active during the first day of the eruption including a part of the summit fissure by the second day however the activity was already essentially limited to that segment of the principal fissure where the main crater subsequently formed the average effusion rate during the first two days of the eruption was about 800 m3 s 1 after this peak the effusion rate declined rapidly to 10 20 m3 s 1 then more slowly to 1 m3 s 1 and remained at 1 12 m3 s 1 until the end of the eruption site observations near the main crater suggest that the intensity of the volcanic tremor varied directly with the force of the eruption a notable rise in the fluorine concentration of riverwater in the vicinity of the eruptive fissures occurred on the 5th day of the eruption but it levelled off on the 6th day and then remained essentially constant the volume and initial silica content of the lava and tephra the explosivity and effusion rate during the earliest stage of the eruption as well as the magnitude attained by the associated earthquakes support earlier suggestions that these parameters are positively related to the length of the preceeding repose period the chemical difference between the eruptive material of hekla itself and the lavas erupted in its vicinity can be explained in terms of a density stratified magma reservoir located at the bottom of the crust we propose that the shape of this reservoir its location at the west margin of a propagating rift and its association with a crustal weakness all contribute to the high eruption frequency of hekla

the impact of the atmosphere on the eyjafjallajokull 2010 eruption plume 1 the eruption of eyjafjallajokull volcano in 2010 lasted 39 days 14 april 23 may the eruption had two explosive phases separated by a phase with lava formation and reduced explosive activity during the explosive phases there were episodes of strong winds that advected ash to the south and southeast leading to widespread disruptions in air traffic the height of the eruption plume was monitored with a weather radar and with web cameras mounted with a view of the volcano three different types of the impact of the ambient atmosphere on the eruption plume are described first the weather situation throughout the eruption has been analyzed the frequency of northerly wind component is found to be unusually high or 71 in comparison to 49 on average in spring secondly during the effusive phase of the eruption diurnal variation was observed in the plume altitude and there is evidence that suggest that nocturnal inversions may have played a role limiting the rise of the weak plume thirdly images from a web camera were analyzed and the rise of individual cloud heads associated with explosions at the volcano vent mapped the velocity profiles obtained largely agree with conceptual models of volcanic plumes

source parameters of mining induced seismic events an evaluation of homogeneous and inhomogeneous faulting models for assessing damage potential source parameter estimates based on the homogeneous and inhomogeneous source models have been examined for an anomalous sequence of seven mine induced events located between 640 and 825 m depth at strathcona mine ontario and having magnitudes ranging betweenmn 0 8 and 2 7 the derived brune static stress drops were found to be similar to those observed for natural earthquakes 30 bars whereas dynamic stress drops were found to range up to 250 300 bars source radii derived from madariaga s model better fit documented evidence of underground damage these values of source radii were similar to those observed for the inhomogeneous model the displacement at the source based on the observed attenuation relationship was about 60 mm for three magnitude 2 7 events this is in agreement with slip values calculated using peak velocities and assuming the asperity as a brune source within itself 72 mm by using madariaga s model for the asperity the slip was over 3 times larger than observed peak velocity and acceleration scaling relations with magnitude were investigated by incorporating available south african data appropriately reduced to canadian geophysical conditions the dynamic stress drop scaled as the square root of the seismic moment similar to reported results in the literature for crustal earthquakes this behavior suggests that the size of the asperities responsible for the peak ground motion with respect to the overall source size follow distributions that may be similar over a wide range of magnitudes measurements of source rupture complexity ranging from 2 to 4 were found to agree with estimates of overall source to asperity radii suggesting together with the observed low rupture velocities 0 3 to 0 6 that the sources were somewhat complex validation of source model appropriateness was achieved by direct comparison of the predicted ground motion level to observed underground damage in creighton mine located within the same regional stress and geological regime as strathcona mine close to the source 100 m corresponding to relatively higher damage levels a good agreement was found between the predicted peak particle velocities for the inhomogeneous model and velocities derived based on established geomechanical relationships the similarity between asperity radii and the regions of the highest observed damage provided additional support for the use of the inhomogeneous source model in the assessment of damage potential

temporal development of the 1999 intrusive episode in the eyjafjallajokull volcano iceland derived from insar images eyjafjallajokull volcano located in southern iceland is characterized by its quiet nature only about a handful of earthquakes associated with the volcanic system had been detected prior to the 1990s earthquake swarms did however occur in 1994 and 1999 here we investigate the spatio temporal evolution of a magmatic intrusion associated with the 1999 earthquake swarm via analysis of produced surface deformation a series of interferometric synthetic aperture radar insar images spanning various periods of the intrusion show that in 1999 surface deformation occurred mainly on the southern flanks of the volcano the deformation amounts to more than 20 cm of range change inverse modeling resolves the deformation source to be a sill intrusion at 6 3 km depth sill opening was up to 1 m and the total intruded volume amounts to 0 03 km3 the insar data display a migration of the center of deformation through time enabling us to create time dependant sill opening models furthermore we investigate the spatio temporal distribution of earthquakes and find that the distribution supports the insar derived model and additionally provides indications for a possible site of a feeder channel magmatic flow rate estimates indicate an initial intrusion rate of 4 6 m3 s declining over a few weeks

location of a magma reservoir beneath hekla volcano iceland hekla situated on the western boundary of the eastern volcanic zone in south iceland is one of the most active volcanoes in iceland having erupted 16 times since 1104 repeated electronic distance measurements since its eruption in 1980 81 show significant changes in crustal movement in the aftermath of the eruption such movement on and around volcanoes can be used to monitor movement of magma within and below volcanoes1 3 we show here that these measurements can be interpreted in terms of inflating magma reservoirs with a centre at 8 km depth below the volcano over a period of 10 months the volume of the inflation amounted to 55 106 m3

seismicity associated with the 1995 1996 eruptions of ruapehu volcano new zealand narrative and insights into physical processes abstract seismicity associated with the 1995 1996 eruptions of ruapehu reflects processes associated with the intrusion of magma to shallow depth in the volcanic edifice its subsequent eruption and changes in the volcanic plumbing system resulting from the eruptions the sequence consisted of two distinct periods of eruptive activity the first lasting from september 17 1995 until late october or early november 1995 and the second from june 16 1996 until late july 1996 immediately prior to and during the early stages of the 1995 eruptions seismicity was similar to that recorded at ruapehu during the previous 25 years with the exception of the occurrence between september 17 and 25 1995 of sub 1 hz tremor which is thought to represent magmatic intrusion in early october a new pattern of seismicity was established with the disappearance of the 2 hz tremor resonator source and a change to wideband 2 10 hz tremor and wideband volcanic earthquakes this change coincided with the ejection of the last vestiges of crater lake and the change in eruptive style from phreatomagmatic to magmatic seismicity associated with the 1996 eruptions was very similar to that which accompanied the later part of the 1995 activity implying the same eruption processes and that no significant changes had occurred in the volcanic plumbing system during the intervening period geochemical geodetic and seismic precursors to the 1995 eruptions were both minor and inconsistent highlighting the difficulty in forecasting these eruptions furthermore deep volcano tectonic earthquakes were extremely rare throughout the 1995 and 1996 eruptive sequences suggesting that stresses associated with magmatic intrusion were minor this most likely resulted from the existence of either an open or a ductile pathway from the deep magma source to the surface prior to the eruptions and because the volume of magma intruded and subsequently erupted was relatively small 3

δd values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record abstract the compound specific hydrogen isotope composition d of sedimentary n alkanes is increasingly used as a palaeoclimate proxy to explore the origin of the hydrogen isotope signal of n alkanes from higher terrestrial plant biomass in sedimentary organic matter of small lakes we have analysed the n alkane composition and d values of 31 plant biomass samples birch betula beech fagus oak quercus alder alnus hornbeam carpinus and myrtle myrtus as well as non stomata containing sphagnum cladonia and moss from 14 sites along a climatic gradient from northern finland to southern italy eleven of the sites were previously investigated for the n alkane d values in adjacent lake sediments and are compared to the leaf wax n alkane d values the distribution of terrestrial n alkanes in lake sediments was not found to be characteristic of the dominant vegetation around the lake evidently n alkane distributions within the same species at different sites were found to be variable these findings complicate the use of certain n alkane distributions in sediments as a palaeoenvironmental indicator d values of plant biomass n alkanes show a significant positive correlation with the precipitation d values biomass n alkane d values are in general less negative than the associated sedimentary n alkanes of terrestrial origin possibly due to the stronger evapotranspiration during the summer when sampling took place this suggests that n alkanes in leaves show seasonal variations and the sedimentary organic matter receives the lighter isotope signal of the autumn when most leaves are incorporated into the sediment the variability of the d values from non stomata containing plants is much higher than for broadleaf trees since stomata can regulate water loss through evapotranspiration the average chain length acl of n alkanes from deciduous tree leaves increases from north to south with increasing acl the hydrogen isotopic fractionation e between source water and n alkanes also increases our results prove that terrestrial n alkane d values record the d value of precipitation modified by the amount of isotope enrichment in the leaf water due to plant anatomy stomata vs no stomata and site specific meteorological conditions such as evapotranspiration relative humidity and soil moisture therefore terrestrial n alkanes in lake sediments can deliver information on changes in these parameters over geological timescales in lake sediments where aquatic n alkanes such as n c 17 record the lake water d value the isotopic difference between terrestrial and aquatic n alkanes could therefore be used to reconstruct changes in evapotranspiration

response of seismic activity in mines to the stress changes due to mining induced strong seismic events the influence of the static stress transfer due to two stronger seismic events from one mine section on subsequent seismicity linked to the same section is studied the first strong tremor was provoked by destressing blasting the static stress transfer caused by this tremor had apparently a triggering effect for the occurrence of the second strong event this second event occurred in less than three weeks after the first one and on the area of simultaneous enhancement of both shear and normal components of the coulomb stress change caused by the first event it appears also that in the next few months the cumulative stress change due to both the events influenced significantly the location and rate of smaller subsequent events interestingly contrary to the results of previous analyses the negative coulomb stress changes turn out to have a major role in this respect the coseismic stress change impact even seems to prevail over the influence of time varying stress alteration caused by advancement of the mining front

tephrostratigraphical evidence for the timing of pleistocene explosive volcanism at jan mayen wavelength dispersive wds electron microprobe analysis of glass shards recovered from pleistocene sediments at ocean drilling program hole 907a leg 151 has been used to define key pleistocene tephrochronostratigraphical markers for the greenland iceland norwegian gin seas two tephras have particularly distinctive geochemistry making them useful as marker horizons in cores from the iceland plateau and potentially further afield these tephras enable the construction of a sedimentation rate history that indicates reduced sediment deposition in the mid brunhes magnetochron possibly through reduced carbonate preservation no significant geochemical weathering of the iceland plateau tephra sequence has occurred the geochemical signature of a key tephra dated to 577 640 ka can be attributed to the jan mayen rock suite demonstrating unambiguously the explosive potential of jan mayen and its potential to contribute to the north atlantic tephra record copyright 2004 john wiley sons ltd

lateral magma flow caldera collapse and a mechanism of large eruptions in iceland abstract lateral magma flow from shallow magma chambers and associated caldera collapse has frequently been invoked as a mechanism of fissure eruptions in iceland this mechanism is examined from the point of view of fluid dynamics and rock mechanics it is found that if the magma from a shallow chamber is to flow laterally rather than vertically towards the surface the density of the roof of the chamber must be much less than the density of the magma and also less than the density of the crust along the pathway of the resulting dike it is concluded that formation or reopening of caldera fractures has no effect on the magmatic pressure in the chamber and thus does not lead to magma being squeezed out of it it is also found that most shallow magma chambers in iceland are too small to give rise to large fissure eruptions of the order of several km3 a different mechanism is proposed of which the salient features are the following large eruptions are fed by partially molten magma reservoirs with an average magma fraction of 0 25 located at the boundary of the crust and upper mantle at depths of 8 10 km beneath the volcanic zones if the magmatic pressure in a reservoir increases the crustal layers above may bend slightly and thereby develop high compressive stresses for a while the reservoir may thus contain magma with excess pressure much greater than the tensile strength of the crust subsequently when an eruption occurs the eruptive volume may be abnormally large compared with the reservoir volume it is estimated that the ratio of reservoir volume to eruptive volume may then be as little as about 200 compared with an ordinary ratio of about 5000 this mechanism is applied to the lakagigar eruption of 1783 which lasted about 8 months and produced some 12 km3 of lava it is concluded that if this eruption was fed by the grimsvotn reservoir only the uppermost few km of that reservoir supplied magma during the eruption

the tephrochronology of iceland and the north atlantic region during the middle and late quaternary a review the tephrochronology of iceland and the north atlantic region is reviewed in order to construct a unified framework for the last 400 kyr bp nearly all of the tephra layers described are also characterised geochemically a number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre holocene tephra layers have been given an informal denotation the tephrostratigraphy of ash zone ii is highlighted where possible the rhyolitic tephra layers found outside iceland have been correlated to known icelandic tephra layers or to the volcanic source area the application of tephra fallout in various depositional environments is described and discussed copyright 2000 john wiley sons ltd

holocene changes in biome size and tropical cyclone activity around the northern south china sea abstract the south china sea scs characterized by a large continental shelf is located at the edge of the asian monsoon domain in this study two marine sediment cores from the northern scs nscs continental slope were investigated to construct composite vegetation and precipitation isotopic composition records based on the 13c and d values of plant wax n alkanes throughout the holocene last 11 200 years i e 11 2 ka the composite 13cwax record indicates an overall predominance of c3 vegetation over the last 11 2 ka before 8 ka bp higher 13cwax values are attributed to preferential wax input from grassland and wetland biomes on the exposed continental shelf after the inundation of the shelf by eustatic sea level rise until ca 8 ka bp grassland and wetland biomes suffered a major size reduction and arboreal vegetation became better represented in the 13cwax record the composite temperature corrected dwax t record suggests that moisture source variability drove precipitation isotopic composition changes during the holocene lower dwax t values before 8 3 ka bp are interpreted as a larger moisture contribution by pacific ocean tropical cyclones whereas higher dwax t values after 8 5 ka bp are interpreted as a larger moisture contribution from the indian ocean summer monsoon higher incidence of tropical cyclones in the nscs during the early holocene was related to a temporary westward shift of the western pacific warm pool and enhanced insolation over the northern hemisphere both external and internal forcing mechanisms regulated moisture source changes in east asia during the holocene

the socio environmental history of the peloponnese during the holocene towards an integrated understanding of the past published archaeological palaeoenvironmental and palaeoclimatic data from the peloponnese in greece are compiled discussed and evaluated in order to analyse the interactions between humans and the environment over the last 9000 years our study indicates that the number of human settlements found scattered over the peninsula have quadrupled from the prehistoric to historical periods and that this evolution occurred over periods of climate change and seismo tectonic activity we show that societal development occurs both during periods of harsh as well as favourable climatic conditions at some times some settlements develop while others decline well known climate events such as the 4 2 ka and 3 2 ka events are recognizable in some of the palaeoclimatic records and a regional decline in the number and sizes of settlements occurs roughly at the same time but their precise chronological fit with the archaeological record remains uncertain local socio political processes were probably always the key drivers behind the diverse strategies that human societies took in times of changing climate the study thus reveals considerable chronological parallels between societal development and palaeoenvironmental records but also demonstrates the ambiguities in these correspondences and in doing so highlights some of the challenges that will face future interdisciplinary projects we suggest that there can be no general association made between societal expansion phases and periods of advantageous climate we also propose that the relevance of climatic and environmental regionality as well as any potential impacts of seismo tectonics on societal development need to be part of the interpretative frameworks

origins and variations of fluoride in greenland precipitation summit greenland firn and ice core sections have been analyzed to determine the fluoride background level of high northern latitude precipitation and to investigate its temporal variations over various time periods a continuous profile covering the last century and a discontinuous study of the last 27 000 years spanning the entire holocene time period 0 to 11 500 years b p and the late part of the last glaciation have been achieved this first detailed study of the fluoride content of polar ice help us obtain a better understanding of the atmospheric cycle of inorganic fluoride in remote atmospheres first our data suggest that blown dust is among the nonvolcanic sources that contributed to the natural fluoride background level of this high latitude precipitation primary sea salt emissions represent an insignificant contribution our study also indicates that high latitude biomass burning debris which sometimes reaches the greenland ice cap represents an additional weak source of fluoride for greenland precipitation second this work provides useful information for evaluating the impact of the volcanic activity on the fluoride budget of these high northern latitude regions indeed our data demonstrate that although the natural background fluoride content of greenland snow is very often sporadically disturbed by volcanic emissions from iceland numerous hekla eruptions and the 1783 laki eruption for instance located relatively close to the greenland ice cap large explosive eruptions tambora in 1815 for instance only weakly disturb this background level our data suggest that even in the case of significant input within the stratosphere fluoride is rapidly scavenged probably along with ash particles finally our study of recent snow layers suggests that man made sources mainly coal burning represent an important contribution which has dominated this high northern hemisphere fluoride budget for the three last decades furthermore over the last 10 years a possible influence of the stratospheric reservoir builded up from the chlorofluorocarbons degradation cannot be ruled out and in the future this growing contribution may represent a significant part of the anthropogenic fluoride input compared to the input derived from coal burning

effect of tensile stress concentration around magma chambers on intrusion and extrusion frequencies what controls the intrusion and extrusion frequencies associated with volcanoes is still poorly understood i propose that for volcanoes at divergent plate boundaries these frequencies may be largely determined by the tensile stress concentration around the magma chambers that feed them this stress concentration is mainly a function of the applied tensile stress associated with spreading and the aspect height width ratios of the chambers high spreading rates and or aspect ratios lead to high rates of tensile stress concentration around the chambers and to an increase in their intrusion frequencies it is found that for chambers at the same depth in a volcanic zone the one of the highest aspect ratio will normally intrude magma most frequently also if the chambers are of equal aspect ratios the one at the greatest depth will intrude magma most frequently because the extrusion frequency of a volcano is a fraction of its intrusion frequency the extrusion frequency may also be largely determined by the rate of tensile stress concentration around the magma chamber that feeds the volcano these results are applied to the divergent plate boundary in iceland where many of the volcanoes appear to be fed by double chambers that is shallow chambers fed by deep seated chambers it is found that except when the aspect ratio of the deep seated chamber is much less than that of the shallow chamber the intrusion frequency of the shallow chamber is normally largely controlled by that of the deep seated chamber it is concluded that whereas the short term i e 103 yrs extrusion frequencies of volcanoes at the plate boundary in iceland may be similar to the dike intrusion frequencies of the source chambers the long term i e 104 yrs extrusion frequencies may be about ten times lower than the intrusion frequencies

chemotaxonomy in some mediterranean plants and implications for fossil biomarker records the increasing utilization of n alkanes as plant derived paleo environmental proxies calls for improved chemotaxonomic control of the modern flora in order to calibrate fossil sediment records to m

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

seismic anisotropy in the crust at the mid atlantic plate boundary in south west iceland summary seismograms of microearthquakes recorded on stations of the sil network in south western iceland exhibit strong shear wave splitting and are consistent with being caused by aligned parallel cracks in the uppermost crust splitting times of 0 1 0 3 s are observed with the larger values 0 2 0 3 s occurring beneath stations in the highly heated western volcanic zone and the smaller values 0 1 s in the younger less fractured south iceland seismic zone five of the stations have a fast shear wave polarization azimuth of n30 e n40 e7 parallel to the axis of the western volcanic zone i e the mid atlantic ridge in iceland and in the direction of maximum horizontal compression defined by fault dyke and fissure strikes and microearthquake focal mechanisms station gyg in the north western part of the network has the significantly different azimuth of n70 e this is parallel to one of the local strike slip fault trends and is probably due to a heated rock fabric caused by those faults

disruption of tephra fall deposits caused by lava flows during basaltic eruptions observations in the usa iceland and tenerife canary islands reveal how processes occurring during basaltic eruptions can result in complex physical and stratigraphic relationships between lava and proximal tephra fall deposits around vents observations illustrate how basaltic lavas can disrupt dissect spatially and temporally and alter sheet form fall deposits complexity arises through synchronous and alternating effusive and explosive activity that results in intercalated lavas and tephra deposits tephra deposits can become disrupted into mounds and ridges by lateral and vertical displacement caused by movement including inflation of underlying p hoehoe lavas and clastogenic lavas mounds of tephra can be rafted away over distances of 100 s to 1 000 s m from proximal pyroclastic constructs on top of lava flows draping of irregular topography by fall deposits and subsequent partial burial of topographic depressions by later lavas can result in apparent complexity of tephra layers these processes deduced from field relationships have resulted in considerable stratigraphic complexity in the studied proximal regions where fallout was synchronous or alternated with inflation of subjacent lava sheets these mechanisms may lead to diachronous contact relationships between fall deposits and lava flows such complexities may remain cryptic due to textural and geochemical quasi homogeneity within sequences of interbedded basaltic fall deposits and lavas the net effect of these processes may be to reduce the usefulness of data collected from proximal fall deposits for reconstructing basaltic eruption dynamics