imaging the inner core under africa and europe abstract the inner core under africa is thought to be a region where the nature of inner core texture changes from the strongly anisotropic western part of the inner core to the weakly anisotropic or isotropic eastern part of the inner core additionally observations of a difference in isotropic velocity between the two hemispheres have been made a very large new dataset of simultaneous pkpdf and pkpbc observations on which differential travel times have been measured is used to examine the upper 360 km of the inner core under europe africa and the surrounding oceans inversion of the differential travel time data for laterally varying inner core anisotropy reveals that inner core anisotropy is stronger under central africa and the atlantic ocean than under the western indian ocean no hemispherical pattern is present in voigt isotropic velocities indicating that the variation in anisotropy is due to differing degrees of crystal alignment in the inner core not material differences when anisotropy is permitted to change with depth the upper east most part of the study region shows weaker anisotropy than the central and western regions when depth dependence in the inner core is neglected the hemisphere boundary is better represented as a line at 40 e than one at 10 e however it is apparent that the variation of anisotropy as a function of depth means that one line of longitude cannot truly separate the more and less anisotropic regions of the inner core the anisotropy observed in the part of the inner core under africa which lies in the western hemisphere is much weaker than that under central america showing that the western hemisphere is not uniformly anisotropic as the region of low anisotropy spans a significant depth extent it is likely that heterogeneous heat fluxes in the core which may cause variations in inner core anisotropy have persisted for several hundred million years

continuous monitoring of fumarole temperatures at mount etna italy abstract in this paper we present the first data of temperature continuously recorded in two fumarole fields designated vor and hor located in the summit area of mount etna volcano italy the time series embraces two distinct periods 1 october 2007 to november 2009 during which an effusive eruption occurred from may 2008 to july 2009 and 2 november 2011 to june 2012 characterized by the occurrence of strong paroxysms fire fountains and lava flow the analysis of the temperature signal in both the time and frequency domains and its comparison with meteorological observations allowed us to separate the exogenous influences from the effects of variations in the activity state of the volcano the acquired data were weakly affected by seasonal cycles of the air temperature and strongly affected by the rainfall optimization of site conditions i e sensor depth and soil permeability markedly reduced meteorological disturbances the distance from the main degassing and or eruptive fractures was crucial to maximizing the probability of the technical survival of the monitoring apparatus which was seriously affected by the emission of acidic gases tephra fallout and lava flows apart from the exogenous influences the most appreciable variation was observed at vor where a huge increase in fumarole temperature was detected immediately after the onset of the 2008 2009 eruption such an anomalous increase was attributed to the rapid ascent of magma feeding the eruptive fracture another abrupt increase in temperature was recorded at hor in march and april 2012 during this period the frequency of paroxysm occurrence increased markedly and this led us to hypothesize that the thermal anomaly was due to the intrusion of a new batch of magma in the conduits of the southeast crater medium to long term monitoring weeks to months of fumarole temperatures revealed variations that were attributed to pressurization depressurization phases of the shallow volcanic system which varied between the various monitored sectors of the volcano our observations suggest that continuous monitoring of fumarole temperature can give useful information about the activity of mount etna moreover due to the complexity of its shallow plumbing system we conclude that the monitoring systems should be extended to cover the entire fumarole network of the summit area

inner core structure behind the pkp core phase triplication the structure of the earth s inner core is not well known between depths of 100 200 km beneath the inner core boundary this is a result of the pkp core phase triplication and the existence of strong precursors to pkp phases which hinder the measurement of inner core compressional pkikp waves at epicentral distances between roughly 143 and 148 consequently interpretation of the detailed structure of deeper regions also remains difficult to overcome these issues we stack seismograms in slowness and time separating the pkp and pkikp phases which arrive simultaneously but with different slowness we apply this method to study the inner core s western hemisphere beneath south and central america using paths travelling in the quasi polar direction between 140 and 150 epicentral distance which enables us to measure pkikp pkikp differential traveltimes up to greater epicentral distance than has previously been done the resulting pkikp pkikp differential traveltime residuals increase with epicentral distance which indicates a marked increase in seismic velocity for polar paths at depths greater than 100 km compared to reference model ak135 assuming a homogeneous outer core these findings can be explained by either i inner core heterogeneity due to an increase in isotropic velocity or ii increase in anisotropy over the studied depth range although this study only samples a small region of the inner core and the current data cannot distinguish between the two alternatives we prefer the latter interpretation in the light of previous work

the 1995 1998 eruption of the soufriere hills volcano montserrat wi eruption of the soufriere hills volcano began on 18 july 1995 after three years of elevated seismic activity four months of increasingly vigorous phreatic activity culminated in mid november 1995 with the initiation of dome growth growth rates increased unevenly through early march 1996 with fluctuations on time scales from hours to months since march 1996 gravitational collapse of the unstable dome flank has affected an ever increasing area with pyroclastic flows surges and ashfalls major collapse of the eastern flank on 17 september 1996 resulted in a sub plinian explosive eruption later that day by february 1997 the dome had outgrown the confines of the crater and begun to spill into the surrounding valleys a large collapse on 25 june 1997 caused pyroclastic flows and surges on the northern flanks and resulted in the only deaths of the eruption in august september and october 1997 vulcanian explosions followed further collapses on the western and northern flanks the largest event of the eruption occurred on 26 december 1997 with failure of the southwestern flank of the volcano producing a debris avalanche and large dome collapse pyroclastic flows dome growth ceased in early march 1998 but residual volcanic activity has continued and consists of ash venting mild explosions and dome collapse pyroclastic flows

large variations in travel times of mantle sensitive seismic waves from the south sandwich islands is the earth s inner core a conglomerate of anisotropic domains 1 cylindrical anisotropy in earth s inner core has been invoked to account for travel times of pkp core sensitive seismic waves such as from the south sandwich islands ssi earthquakes observed in alaska which depart from predictions newly collected travel time residuals from seismic waves from the ssi region that sample only earth s mantle pcp and p waves have a comparable range to the pkp differential travel time residuals yet they are insensitive to core structure this observation suggests that mantle structure affects pkp travel time residuals more than previously acknowledged and challenges the existing conceptual framework of a uniform inner core anisotropy the inner core could be a conglomerate of anisotropic domains and the pkp travel times are most likely influenced by the geometry of inner core sampling and inhomogeneous mantle structure this concept reconciles observed complexities in travel times while preserving a net inner core anisotropy that is required by observations of earth s free oscillations

multiproxy evidence of little ice age palaeoenvironmental changes in a peat bog from northern poland little ice age lia climatic deteriorations have been abundantly documented in various archives such as ice lake sediments and peat bog deposits palaeoecological analyses of peat samples have identified these climatic deteriorations using a range of techniques for example palynology plant macrofossils testate amoebae or carbon isotopic analyses the use of inorganic geochemistry and the reconstruction of dust fluxes has remained a challenge in tracing the nature of lia climatic changes although the idea of enhanced erosion conditions and storminess is commonly discussed the conditions for dust deposition in peatlands over europe during the lia are rarely favourable because the natural forest cover over europe was much more important than nowadays preventing dust deposition this intense forest canopy masks the deposition of dust in peatlands in northern poland near the baltic shore the slowin skie blota area was deforested around ad 1100 ie just before the lia and therefore constitutes a key area for the reconstruction of lia climatic change with the support of a well constrained chronology climatic fluctuations are recorded in an ombrotrophic bog using inorganic geochemistry plant macrofossils and carbon isotopic analyses the reconstruction of lia climatic changes is in good agreement with other records from poland and ne europe however a c 50 year discrepancy can be observed between various records this discrepancy is possibly due to progressive time dependent cooling gradient from north to south europe

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

historical and present day human impact on fluvial systems in the old polish industrial district poland abstract the increase of intensive anthropopression since the middle ages has been recorded in numerous anthropogenic forms embankments dumps canals pits etc and sediments changes of sedimentation type buried soils slags charcoals geochemical changes of the valleys of the holy cross mountains the development of small scale water retention systems associated with functioning forges and mills on the watercourses resulted in changes in river patterns anthropogenic anastomoses and the reduction of the flood stage maximum during the little ice age on the kamionka river in the twentieth century after the disappearance of the small scale retention system caused by economic changes on the kamionka and czarna konecka rivers hydrotechnical failures appeared that led to the formation of catastrophic flash floods previously unknown during the holocene the geomorphological effects of these floods exceeded by many times the effects of secular processes

magma production and growth of the lava dome of the soufriere hills volcano montserrat west indies november 1995 to december 1997 from november 1995 to december 1997 a total volume of 246 106 dre m of andesite magma erupted partitioned into 93 106 m of the dome 125 106 m of pyroclastic flow deposits and 28 106 m of explosive ejecta in the first 11 weeks magma discharge rate was low 0 5 m s from february 1996 to may 1997 discharge rates have averaged 2 1 m s but have fluctuated significantly and have increased with time three pulses lasting a few months can be recognised with discharge rates reaching 3 to 8 m s short term pulsations in growth lasting a few days reach discharge rates of over 10 m s and there are periods of days to a few weeks when dome growth is 0 5 m s discharge rate increased from may 1997 with an average rate of 7 5 m s to december 1997 the observations indicate an open magmatic system

continuous gas monitoring at galeras volcano colombia first evidence abstract this paper describes a system of instruments for continuously monitoring fumarolic gases which is installed at galeras volcano colombia several parameters such as the concentration of co2 and rn in the fumarolic emissions as well as the temperature of the gases and their pressure are measured every 6 s we report variations in these parameters which were observed during a short flurry of seismic activity at the volcano at this stage it is uncertain whether the changes in the parameters are directly associated with volcanic processes from the data presented here we can conclude that ambient air can enter the fumarolic vent system in consequence the fumarole may be influenced by the direction and strength of the wind

remobilization of andesite magma by intrusion of mafic magma at the soufriere hills volcano montserrat west indies the 1995 1999 eruption of the soufriere hills volcano montintroduction serrat has produced a crystal rich andesite containing quenchthe soufriere hills volcano montserrat located in the textured mafic inclusions which show evidence of having been molten lesser antilles island arc in the west indies began to when incorporated into the host magma individual crystals in the erupt on 18 july 1995 after about 350 years of dormancy andesite record diverse histories amphibole phenocrysts vary from young et al 1998b the eruption was preceded by a pristine and unaltered to strongly oxidized and pseudomorphed by period of seismic swarms which began in january 1992 anhydrous reaction products plagioclase phenocrysts are commonly previous earthquake crises have occurred on montserrat reverse zoned often with dusty sieve textures reverse zoned rims are in 1896 1897 1932 1935 and 1966 1967 powell 1938 also common on orthopyroxene phenocrysts pyroxene geothermometry shepherd et al 1971 initial phreatic and phregives an average temperature of 858 20 c for orthopyroxene atomagmatic activity was followed by extrusion of an phenocryst cores whereas reverse zoned rims record temperatures andesitic lava dome in november 1995 pyroclastic flows from about 880 to 1050 c the heterogeneity in mineral rim generated by gravitational collapse of the unstable dome compositions zoning patterns and textures is interpreted as reflecting have been the dominant form of activity throughout the non uniform reheating and remobilization of the resident magma eruption but periods of explosive activity producing body by intrusion of hotter mafic magma convective remobilization pumice flows and falls have also occurred robertson et results in mixing together of phenocrysts that have experienced al 1998 young et al 1998b dome growth ceased different thermal histories depending on proximity to the intruding suddenly in march 1998 and further activity up to may mafic magma the low temperature and high crystallinity are 1999 has mainly involved gravitational collapses of the interpreted as reflecting the presence of a cool highly crystalline dome and periods of ash venting with some small scale magma body beneath the soufriere hills volcano the petrological vulcanian explosive events observations in combination with data on seismicity extrusion rate the soufriere hills volcano is the only active centre and so2 fluxes indicate that the current eruption was triggered by on montserrat the volcano is a composite of at least recent influx of hot mafic magma five andesitic lava domes flanked by pyroclastic deposits rea 1974 identified four other volcanic centres all

chlorine variations in the magma of soufriere hills volcano montserrat insights from cl in hornblende and melt inclusions the soufriere hills volcano in montserrat erupts a cl rich porphyritic andesite hcl degassing accompanies eruption and is dependent on the growth rate of the lava dome the magma contains hornblende phenocrysts that show repetitive zoning in most elements including cl on the basis of the zoning data cl oh ratios in the melt calculated from partitioning data increase rimward through each zone indicating that the phenocrysts formed under conditions of varying cl oh m an empirical relationship between a site occupancy in the hornblende and temperature implies that crystallisation of each zone is also accompanied by increasing temperature each zone ends at a resorption horizon and crystallisation recommences at lower temperature and cl oh m melt inclusion h2o and cl contents for the 8th january 2007 explosive eruption can be explained by closed system degassing with dclfl m between 5 and 30 or by open system degassing accompanied by a small amount of crystallisation however neither simple closed system degassing nor convective circulation of magma can explain the positive correlation of cl oh m with temperature we suggest that the zoning can be caused by accumulation of co2 rich vapour in the andesite probably as a result of mafic magma injection into the chamber decreasing h2o fugacity and or increasing clm result in increasing cl oh m while heat transferred with the volatiles causes the rise in temperature intermittently the accumulated fluid is lost to the surface possibly as a result of renewed eruptive activity this model requires the co2 rich fluid to be decoupled from the magma consistent with previous observations of continuous co2 emissions at the surface

scatter and bias in differential pkp travel times and implications for mantle and core phenomena differential travel times commonly used to eliminate unwanted near source and near receiver heterogeneity from travel time studies can be affected by slabs and hypocentral errors when phase pair slownesses differ greatly in particular d and core structure studies can be biased if differential pkp times are used here we present differential pkp travel time measurements having significant azimuthal travel time anomalies consistent both in size and pattern with a near source slab effect and explore other sources of error in differential times

gas emissions and crustal deformation from the krýsuvik high temperature geothermal system iceland abstract the kr suvik volcanic system is located on the oblique spreading reykjanes peninsula sw iceland since early 2009 the region has been undergoing episodes of localized ground uplift and subsidence from april november 2013 we operated near real time monitoring of gas emissions in kr suvik using a multi component gas analyzer system multi gas collecting data on gas composition from a fumarole h2o co2 so2 h2s the dataset in this study comprises a near continuous gas composition time series the quantification of diffuse co2 gas flux analytical results for direct samples of dry gas seismic records and gps data gas emissions from the kr suvik geothermal system were examined and compared with crustal deformation and seismicity the gas emissions from the kr suvik system are h2o dominated with co2 as the most abundant dry gas species followed by smaller concentrations of h2s the average subsurface equilibrium temperature was calculated as 278 c this is consistent with previous observations made through sporadic spot sampling campaigns in addition the semi continuous multi gas dataset reveals higher variations in gas composition than previously reported by spot sampling the diffuse soil co2 flux is found to be variable between the three studied degassing areas in kr suvik ranging from 10 9 70 9 t day with the highest flux in hveradalir where the multi gas station is located the total flux is estimated as 101 t day comparison between multi gas and geophysical data shows that peaks of h2o rich emissions appears to follow crustal movements coinciding with the h2o rich peaks so2 is detected in minor amounts 0 6 ppmv allowing for calculations of h2o so2 co2 so2 and h2s so2 ratios this is the first time so2 has been detected in the kr suvik area the large variations in h2o co2 and h2o h2s ratios are considered to reflect variable degassing activity in the fumarole the activity of the fumarole appears less intense during intervals of low or no recorded seismic events the h2o co2 and h2o h2s ratios are lower presumably due to h2o condensation affecting the steam jet before reaching the multi gas inlet tube

retrieval and intercomparison of volcanic so2 injection height and eruption time from satellite maps and ground based observations abstract syneruptive gas flux time series can in principle be retrieved from satellite maps of so 2 collected during and immediately after volcanic eruptions and used to gain insights into the volcanic processes which drive the volcanic activity determination of the age and height of volcanic plumes are key prerequisites for such calculations however these parameters are challenging to constrain using satellite based techniques here we use imagery from omi and gome 2 satellite sensors and a novel numerical procedure based on back trajectory analysis to calculate plume height as a function of position at the satellite measurement time together with plume injection height and time at a volcanic vent location we applied this new procedure to three etna eruptions 12 august 2011 18 march 2012 and 12 april 2013 and compared our results with independent satellite and ground based estimations we also compare our injection height time series with measurements of volcanic tremor which reflects the eruption intensity showing a good match between these two datasets our results are a milestone in progressing towards reliable determination of gas flux data from satellite derived so 2 maps during volcanic eruptions which would be of great value for operational management of explosive eruptions

pkp travel times at near antipodal distances implications for inner core anisotropy and lowermost mantle structure abstract previous studies from pkp ab df differential travel times at large distances suggest that the central part of the inner core is very anisotropic these differential times however can be affected greatly by strong heterogeneity in the lowermost mantle here we examine a unique data set of pkp travel times from global digital and analog stations at near antipodal distances where the effects of both inner core anisotropy and mantle heterogeneity are the greatest our results show that the ab df residuals for the polar paths are consistently larger than those of the equatorial paths by over 3 4 standard deviations we also measured df and ab absolute times and found that the df residuals are negatively correlated with the ab df residuals while the ab residuals have a much weaker correlation with the ab df residuals we compare several mantle models with the data our results suggest that the mantle structure can explain part of the residuals of the equatorials paths but cannot explain the polar path anomalies these results strongly suggest that most of the ab df anomalies for the polar paths are likely from the inner core anisotropy and not from mantle heterogeneity assuming a uniform cylindrical anisotropy model the average inner core anisotropy amplitude is about 2 5 on the other hand equatorial paths from events in the west pacific and recorded at south america show a steep azimuthal change in ab df times about 4 s over a 60 azimuthal range the sharp change is well predicted by existing p and s tomographic models the azimuthal change occurs as the ab paths sweep across the great slow anomaly in the central pacific the high correlation between the p and s velocities suggests that the central pacific slow anomaly may be of thermal origin

fluid dynamics of the 1997 boxing day volcanic blast on montserrat west indies 1 directed volcanic blasts are powerful explosions with a significant laterally directed component which can generate devastating high energy pyroclastic density currents pdcs such blasts are an important class of eruptive phenomena but quantified understanding of their dynamics and effects is still incomplete here we use 2 d and 3 d multiparticle thermofluid dynamic flow codes to examine a powerful volcanic blast that occurred on montserrat in december 1997 on the basis of the simulations we divide the blast into three phases an initial burst phase that lasts roughly 5 s and involves rapid expansion of the gas pyroclast mixture a gravitational collapse phase that occurs when the erupted material fails to mix with sufficient air to form a buoyant column and thus collapses asymmetrically and a pdc phase that is dominated by motion parallel to the ground surface and is influenced by topography we vary key input parameters such as total gas energy and total solid mass to understand their influence on simulations and we compare the simulations with independent field observations of damage and deposits demonstrating that the models generally capture important large scale features of the natural phenomenon we also examine the 2 d and 3 d model results to estimate the flow mach number and conclude that the range of damage sustained at villages on montserrat can be reasonably explained by the spatial and temporal distribution of the dynamic pressure associated with subsonic pdcs

problems of dating alluvium using buried subfossil tree trunks lessons from the black oaks of the vistula valley central europe dating of alluvia of large rivers based on subfossil tree trunks is discussed using examples from the vistula valley near krakow and from literature referring to central europe the method which has been used hitherto for dating alluvia based exclusively on single trunks or single generations has led usually to erroneous results because the majority of trunks in the alluvia were redeposited den drochronology is helpful in solving problems of dating alluvia which should use only in situ trunks i e trunks with bark sapwood and branches equally suitable materials are stumps in growth position which were cut down with an axe and which are preserved by an aggradating river these stumps possess well preserved root systems with roots of a lower order redeposition of trunks in alluvia is associated with lateral migration of a river channel channel migration leads to the washing out of subfossil trunks of different ages from older alluvia these trunks heavier than water are redeposited at the level

three dimensional structure at the base of the mantle beneath the central pacific forward modeling of differential travel times of phases sensitive to lowermost mantle beneath the central pacific reveals lateral heterogeneity that is higher in amplitude than predicted by tomographic models a broad zone of low s velocity 4 percent with respect to standard models which may correspond to the base of a thermal plume narrows and is deflected as it extends to about 1000 kilometers above the core mantle boundary to the east of this zone a localized region of fast s velocity 5 percent suggests strong heterogeneity or anisotropy related to the presence of high pressure and temperature assemblages which may or may not involve core material its presence could also explain the observation of precursors to core reflected phases in this region

so2 bro ratios studied in five volcanic plumes abstract the distribution of bromine monoxide bro and sulphur dioxide so2 was measured by ground based max doas scattered light multi axis differential optical absorption spectroscopy in the plume of five volcanoes soufriere hills volcano on montserrat in may 2002 masaya volcano in nicaragua in march 2003 etna volcano on sicily in september october 2003 and august october 2004 stromboli volcano in italy in september 2003 and villarica in chile in november 2004 maximum slant column densities scds of several 1014 molecules cm2 of bro were observed bromine monoxide sulphur dioxide ratios of 10 0 10 4 0 8 10 4 4 8 10 4 2 1 10 4 2 1 10 4 and 1 3 10 4 were found in the plumes of soufriere hills masaya etna 2003 etna 2004 stromboli and villarica respectively causes for the differences in the bro so2 ratios for the various volcanic sites are discussed

anomalous emissions of so2 during the recent eruption of santa ana volcano el salvador central america santa ana volcano in western el salvador central america had a phreatic eruption at 8 05 am local time on october 1 2005 101 years after its last eruption however during the last one hundred years this volcano has presented periods of quiet degassing with fumarolic activity and an acidic lake within its crater this paper presents results of frequent measurements of so2 degassing using the minidoas differential optical absorption spectroscopy system and a comparison with the volcanic seismicity prior to the eruption during and after the eruption vehicle measurements of so2 flux were taken every hour during the first nine days of the eruption and daily after that the period of time reported here is from august to december 2005 three periods of degassing are distinguished pre eruptive eruptive and post eruptive periods the intense activity at santa ana volcano started in july 2005 during the pre eruptive period up to 4306 and 5154 ton day of so2 flux were recorded on october 24 and september 9 2005 respectively these values were of the same order of magnitude as the recorded values just after the october 1st eruption 2925 ton day at 10 01 am hourly measurements of so2 flux taken during the first nine days after the main eruptive event indicate that explosions are preceded by an increase in so2 flux and that this parameter reaches a peak after the explosion took place this behavior suggests that increasing accumulation of exsolved magmatic gases occurs within the magmatic chamber before the explosions increasing the pressure until the point of explosion a correlation between so2 fluxes and rsam real time seismic amplitude measurements is observed during the complete sampling period periodic fluctuations in the so2 and rsam values during the entire study period are observed one possible mechanism explaining these fluctuations it that convective circulation within the magmatic chamber can bring fresh magma periodically to shallow levels allowing increasing degasification and then decreasing degasification as the batch of magma lowers its gas content becomes denser and sinks to give space to a new magma pulse these results illustrate that the measurements of so2 flux can provide important warning signals for incoming explosive activity in active volcanoes

a phenomenological model for precursor volcanic eruptions intense explosions of relatively short duration frequently precede large explosive and effusive volcanic eruptions by as much as weeks to months in the case of very viscous magmas1 2 3 4 5 6 in some cases such pre eruption activity has served as a sufficient warning to those living in the vicinity to evacuate and avoid calamity1 precursor events seem to be related to the formation of a magma pathway to the surface but their precise interpretation is a long standing puzzle it has been inferred from theoretical studies that exsolution of volatiles might create an almost separate gas pocket at the tip of a propagating dyke7 8 9 here we explain the role that such a process may have using a laboratory study of the transient propagation of a liquid filled crack with a gas pocket at its tip that grows with time we show that once the gas pocket acquires sufficient buoyancy to overcome the fracture resistance of the host solid the dynamics of the gas pocket rather than those of the liquid determine the velocity of the crack tip furthermore we find that the gas can ultimately separate from the liquid we propose that fast moving gas rich pockets reaching the surface ahead of the main liquid filled fissure could be the origin of many precursor eruptions

so2 emissions to the atmosphere from active volcanoes in guatemala and el salvador 1999 2002 ground based and aircraft correlation spectrometer cospec measurements at the principal active volcanoes in guatemala pacaya santiaguito fuego and tacana and el salvador santa ana and san miguel were carried out at intervals during the period 1999 2002 as part of an attempt to measure baseline so2 emissions of potentially dangerous volcanoes and to better understand their eruption mechanisms we discuss some of the uncertainties involved in interpreting intermittent gas data together with possible improvements other problems pertaining to current monitoring of so2 and implications for future studies are also discussed santa ana volcano is proposed to be a venting hydrothermal system while santiaguito fuego pacaya and san miguel all exhibit open vent characteristics data for tacana volcano are presented but are not enough to make descriptions of its characteristics and activity pacaya is emitting high fluxes of so2 1000 tonnes day while the other vents are much lower emitters 20 300 tonnes day in general so2 emissions at pacaya suggest a large circulating and convecting high level chamber the most recent emission rates at fuego were measured during its current active phase since january 2002 average so2 emission rates during 1999 2002 are 1350 tonnes day for pacaya 340 tonnes day for fuego 120 tonnes day for santiaguito 260 tonnes day for san miguel 140 tonnes day for santa ana and 30 tonnes day for tacana these volcanoes account for about 6 to 12 of the estimated annual global volcanic output of so2

using earthquake doublets to study inner core rotation and seismicity catalog precision 1 we report our search for doublets in the south sandwich islands ssi region among 906 earthquakes from january 1982 to december 1998 event pairs with source separation less than 40 km which was calculated using pde locations were checked using vertical component short period and broadband digital records cross correlation coefficients of p or pkp waveforms were computed for similarity comparison whole waveforms of those event pairs with correlation coefficients larger than 0 8 were checked by eye by this process 17 doublets were found some of which form multiplets however only one doublet event pair 14 august 1995 and 28 march 1987 has clear pkp df phases on both records at college alaska col the pkp df travel time change measured by cross correlation is a decrease by 0 15 s with standard deviation 0 02 s over a time period of about 8 years this result strongly supports differential rotation of the earth s inner core relative to the mantle and the crust the estimated rotation rate ranges from 0 4 to 1 per year eastward the special case of a locked inner core can then be ruled out we also checked the precision of pde and isc locations using the 17 doublets results show that both catalogs have relatively high location precision standard deviations in latitude longitude and depth are less than 4 km 6 km and 10 km respectively supporting prior claims of detection of inner core rotation song and richards 1996

pre and syn eruptive geochemistry of volcanic gases from soufriere hills of montserrat west indies soufriere hills fumaroles contained magma derived volatiles before and during the eruption initiated in 1995 but also preserved a typical and quite steady hydrothermal composition chemical changes due to increased boiling and a greater input of oxidizing magmatic gas occurred only at galway s soufriere the most active fumarolic field hydrothermal buffering of the fumaroles has been favoured by their remote location 1 2 km from the eruptive vents and by a preferential degassing of the uprising magma through intrusive conduits under the crater high temperature 720 c gas collected from the extruding lava dome in feb 1996 was chemically and isotopically representative of the magmatic gas stream its composition allows assessment of average eruptive fluxes of h2o co2 and hcl which require the degassing of only 2 5 3 times more magma than erupted

changes to the volcanic outgassing mechanism and very long period seismicity from 2007 to 2011 at mt asama japan abstract volcanic gases can provide significant information on the state of magma which is important for interpreting and predicting volcanic activity we present a study of the seismicity and volcanic gases from mt asama japan from 2007 to 2011 to elucidate the change in the mechanism of volcanic gas supply for very long period vlp seismic events two types of degassing occur at mt asama persistent degassing and a gas burst ash free eruption following a vlp seismic event we used the linear relationship between the seismic moment and sulfur dioxide so 2 emissions and seismic records to estimate the quantity of so 2 gas in the ash free eruption which causes the vlp seismic events the amount of so 2 and volcanic gas composition data were used to calculate the amount of volcanic gases including h 2 o co 2 and other species we compared the volcanic gas emission rates of ash free eruptions eruptive gas emission rates and total volcanic gas emission rates including the persistent degassing the ratio of the eruptive gas emission rate to the total gas emission rate eruptive total gas ratios showed a drastic change with eruption an increase occurred immediately before the 2008 and after the 2009 eruptions the vlp seismic events are likely caused by sudden outgassing at a shallow depth that is induced by the propagation of the gas phase expansion and rupture we suggest that the rates of sudden outgassing are controlled by the distribution of gas phases in the conduit the variability of the eruptive gas emission rates suggests changes in the gas phase distribution in the conduit

the explosive eruption of soufriere hills volcano montserrat west indies 17 september 1996 on 17 september 1996 the soufriere hills volcano started a 9 hour period of dome collapse involving 11 7 106 m dre of lava after 2 5 hours of quiescence a sustained explosive eruption began estimated eruption parameters are plume height at least 11 3 km and a maximum of 15 km 180 m s for launch velocities of ballistic clasts peak explosion pressure of 27 5 mpa magma water contents of 2 5 5 magma discharge rates from 2300 to 4300 m s ejecta volume of 3 2 0 9 106 m dre ejecta consists of pumice 1160 kg m higher density vesiculated ejecta 1300 to 2000 kg m dense glassy clasts 2600 kg m breccias cut by tuffisite veins and hydrothermally altered lithics the ejecta are interpreted as a conduit assemblage with evacuation of the conduit down to depths of about 3 to 5 km the eruption was triggered by unloading of a gas pressurised conduit due to dome collapse

when did the anthropocene begin a mid twentieth century boundary level is stratigraphically optimal abstract we evaluate the boundary of the anthropocene geological time interval as an epoch since it is useful to have a consistent temporal definition for this increasingly used unit whether the presently informal term is eventually formalized or not of the three main levels suggested an early anthropocene level some thousands of years ago the beginning of the industrial revolution at 1800 ce common era and the great acceleration of the mid twentieth century current evidence suggests that the last of these has the most pronounced and globally synchronous signal a boundary at this time need not have a global boundary stratotype section and point gssp or golden spike but can be defined by a global standard stratigraphic age gssa i e a point in time of the human calendar we propose an appropriate boundary level here to be the time of the world s first nuclear bomb explosion on july 16th 1945 at alamogordo new mexico additional bombs were detonated at the average rate of one every 9 6 days until 1988 with attendant worldwide fallout easily identifiable in the chemostratigraphic record hence anthropocene deposits would be those that may include the globally distributed primary artificial radionuclide signal while also being recognized using a wide range of other stratigraphic criteria this suggestion for the holocene anthropocene boundary may ultimately be superseded as the anthropocene is only in its early phases but it should remain practical and effective for use by at least the current generation of scientists

tomographic inversion for three dimensional anisotropy of earth s inner core abstract seismological studies generally suggest that the earth s inner core is anisotropic and the anisotropic structure changes significantly both laterally and with depth previous body wave studies of the inner core have relied on ray tracing or waveform modeling using one dimensional 1d models here we present non linear tomographic inversions of the inner core anisotropy using three dimensional 3d ray tracing spline parameterization and a large collection of pkp differential travel times we adapt a pseudo bending ray tracing pbr method in spherical coordinates for seismic rays that traverse the inner core pkp df phase the method iteratively perturbs each discontinuity point and continuous segment of the ray through 3d earth structure so that its travel time is minimum the 3d anisotropic structure of the inner core is approximated to the first order as 3d heterogeneous but isotropic structure for a given ray the data are corrected using a scaled mantle tomographic model the inner core anisotropy model obtained has the following major features 1 the model has strong hemispherical and depth variation the isotropic velocity in the topmost inner core is greater in quasi eastern hemisphere qeh 40 160 e than in quasi western hemisphere qwh other longitudes the anisotropy is weak in qeh to the depth of 600 700 km below the inner core boundary icb while in qwh the anisotropy increases at much shallower depth about 100 200 km below the icb to about 3 4 then remains at about 2 4 throughout the rest of the inner core 2 the anisotropy form changes abruptly over a depth range of about 150 km at the radius of about 600 km slightly less than half of the inner core radius forming a distinct inner inner core iic the velocity in the iic has maximums at equatorial and polar directions and minimum at an angle of about 40 from the equatorial plane the velocity in the outer inner core oic however changes little for ray directions 0 40 from the equatorial plane 3 despite large variation of the anisotropy the isotropic velocity voigt average throughout the inner core is nearly uniform the results suggest that the oic is likely composed of the same type of iron crystals with uniform chemistry but the iic may be composed of a different type of crystal alignment a different iron phase or a different chemical composition our tests on model parameterization mantle correction and linear and non linear inversion suggest the main features of our model are very robust however fine scale structures are likely to differ particularly in the major transition zones e g in the topmost qwh isotropy to anisotropy between oic and iic change in the form of anisotropy and between qeh and qwh in oic difference in anisotropy strength searches for possible waveform complications from these boundaries need to be aware of the directional dependence and geographical variation to be successful

monitoring so2 emission at the soufriere hills volcano implications for changes in eruptive conditions correlation spectrometer measurements of sulfur dioxide so2 emission rates during the current eruption of the soufriere hills volcano montserrat have contributed towards identifying different phases of volcanic activity so2 emission rate has increased from 550 td 1 6 4 kgs 1 after july 1996 with the uncertainty associated with any individual measurement ca 30 significantly enhanced so2 emission rates have been identified in association with early phreatic eruptions 800 td 1 9 3 kgs 1 and episodes of vigorous dome collapse and pyroclastic flow generation 900 to 1500 td 1 10 4 to 17 4 kgs 1 so2 emission rate has proved a useful proxy measurement for magma production rate observed so2 emission rates are significantly higher than those inferred from analyses of glass inclusions in phenocrysts implying the existence of a s rich magmatic vapour phase

inner core rotation rate from small scale heterogeneity and time varying travel times the time it takes seismic waves to propagate from south atlantic earthquakes through the inner core to station col in alaska has decreased systematically over the past 30 years travel times from three earthquakes in 1991 to an array of 37 seismometers in alaska suggest that lateral gradients in seismic wavespeeds are steep in this part of the inner core this combination of observations can be explained by postulating that the inner core is rotating 0 2 to 0 3 per year faster than the mantle

excess volatiles supplied by mingling of mafic magma at an andesite arc volcano we present the results of a study of volcanic gases at soufriere hills volcano montserrat which includes the first spectroscopic measurements of the major gas species co2 and h2s at this volcano using a multisensor gas analyzer system multigas sensor the fluxes of co2 and h2s were 640 2750 t d and 84 266 t d respectively during july 2008 during a prolonged eruptive pause the flux of co2 is similar to estimates for the entire arc from previous geochemical studies while the measured h2s flux significantly alters our interpretation of the sulphur budget for this volcano the fluxes of both sulphur and carbon show considerable excesses over that which can be supplied by degassing of erupted magma we demonstrate using thermodynamic models and published constraints on preeruptive volatile concentrations that the gas composition and fluxes are best modeled by mixing between 1 gases derived from isobaric quenching of mafic magma against cooler andesite magma at depth and 2 gases derived from shallower rhyolitic interstitial melt within the porpyritic andesite the escape of deep derived gases requires pervasive permeability or vapor advection extending to several kilometers depth in the conduit and magma storage system these results provide more compelling evidence for both the contribution of unerupted mafic magma to the volatile budget of this andesitic arc volcano and the importance of the intruding mafic magma in sustaining the eruption from a broader perspective this study illustrates the importance and role of underplating mafic magmas in arc settings these magmas play an important role in triggering and sustaining eruptions and contribute in a highly significant way to the volatile budget of arc volcanoes copyright 2010 by the american geophysical union

the relationship between degassing and ground deformation at soufriere hills volcano montserrat we examine the correlations between so2 emission rate seismicity and ground deformation in the month prior to the 25 june 1997 dome collapse of the soufriere hills volcano montserrat during this period the volcano exhibited a pattern of cyclic inflation and deflation with an 8 14 h period we find that so 2 emission rates measured by cospec correlate with the amplitude of these tilt cycles and that higher rates of so 2 emission were associated with stronger ground deformation and enhanced hybrid seismicity within tilt cycles degassing peaks coincide with maximum deformation gradients increases in the amount of gas in the magma conduit feeding the dome probably due to increases in volatile content of ascending magma volume can account for the observed increases in tilt amplitude hybrid seismicity and so2 emission rate q 2000 elsevier science b v all rights reserved

seismological and mineralogical constraints on the inner core fabric 1 under the assumption of lattice preferred orientation of iron hcp crystals the seismic anisotropy of the inner core is related to single crystal elastic properties by a fabric model this model is able to explain a new seismological constraint the constant behaviour of the ratio k of two anisotropy coefficients despite radial and lateral variations of the anisotropy level in the inner core the relevance of the theoretical calculations of iron single crystal elastic properties at inner core conditions are tested by a comparison between seismic estimates and computed values of this ratio k taking into account the error bar of the seismic estimate iron hcp structures presenting fast and slow c axis could fit the data equally well

gas and particle emissions from soufriere hills volcano montserrat west indies characterization and health hazard assessment the soufriere hills volcano montserrat erupting since 18 july 1995 intensified its degassing in early 1996 with the continuing growth of the lava dome inside the summit crater during this period of increased activity between 11 and 18 march 1996 we measured gases and particles within the visible plume to determine whether at that time it posed a health risk to the population of plymouth the capital town which is 5 km southwest downwind and was then still occupied gravimetric measurements were made of total suspended particles tsp and particles having an aerodynamic diameter of less than 10 m pm10 measurements were made of sulphur dioxide so2 hydrochloric acid hcl hydrofluoric acid hf nitric acid hno3 acetic acid ch3cooh formic acid hcooh and particulate sulphate so4 2 chloride cl nitrate no3 fluoride f methanesulphonate ch3so3 acetate ch3coo formate hcoo ammonium nh4 sodium na and acidity h trace metals having human health implications chromium cr nickel ni cobalt co copper cu zinc zn arsenic as selenium se cadmium cd tin sn mercury hg and lead pb were also determined mean concentrations of hcl so2 and hf obtained in the town of plymouth were 14 0 5 9 and 0 8 ppbv respectively corresponding concentrations in the mixed plume on the crater edge were 533 168 and 22 ppbv there were no direct emissions of hno3 although nitrate was detected in coarse particles at the source higher concentrations of ch3cooh and hcooh were measured close to the crater mean tsp and pm10 were 64 and 15 g m 3 in plymouth and 455 and 47 g m 3 on the upper volcano slope aerosols were highly acidic at the source but rapidly neutralised during transport trace metals were enriched in the aerosol relative to crater surface material the concentrations of the acid gases sulphur dioxide in particular and particles were found to be too small to pose a health hazard at the time of these measurements when relatively modest volcanic activity was occurring

insights into the behaviour of s f and cl at santiaguito volcano guatemala from apatite and glass abstract the mineral apatite can incorporate all of the major magmatic volatile species into its structure where melt inclusions are not available magmatic apatite may therefore represent an opportunity to quantify volatile concentrations in the pre eruptive melt we analysed apatites and matrix glasses from andesites and dacites erupted from santiaguito volcano guatemala between the 1920s and 2002 x ray mapping shows complex zoning of sulphur in the apatite grains but typically with sulphur rich cores and sulphur poor rims apatite microphenocrysts are enriched in f and depleted in cl relative to inclusions matrix glasses are dacite to rhyolite and contain low f but up to 2400 ppm cl overall the data are consistent with progressive depletion of cl in the most evolved melts due to crystallisation and degassing in the absence of pristine melt inclusions we used apatite together with published partitioning data to reconstruct the likely volatile contents of the pre eruptive melt and hence estimate long term average gas emissions of so 2 hf and hcl for the ongoing eruption the data indicate time averaged so 2 emissions of up to 157 tonnes day hcl of 74 1382 tonnes day and up to 196 tonnes day hf apatite may provide a useful measure of long term volatile emissions at volcanoes where direct emissions measurements are unavailable or for comparison with intermittent gas sampling methods however significant uncertainty remains regarding volatile distribution coefficients for apatite and their variations with temperature and pressure

three years of so2 flux measurements of mt etna using an automated uv scanner array comparison with conventional traverses and uncertainties in flux retrieval 1 sviluppo di sistemi di monitoraggio dipartimento di protezione civile della regione sicilia 2 ingv istituto nazionale di geofisica e vulcanologia sezione di catania italy 3 novac network for observation of volcanic and atmospheric change eu funded sixth framework programme project 18354 4 uk nerc national centre for earth observation via the dynamic earth and geo hazards

pkp bc df travel time residuals and short scale heterogeneity in the deep earth differential pkp bc pkp df travel time residuals for quasi polar paths in the earth present large excursions from the trends predicted by simple models of inner core anisotropy we analyze a set of such paths classified according to specific source and station regions and show that observations are compatible with a constant anisotropy model of at most 1 5 in the outer 400 km of the inner core to explain local departures of up to 3 sec from the predictions of such a model strong lateral variations on scale lengths shorter than a few hundred km need to be invoked either in the core or in the mantle independent results of d modelling argue in favor of an important contribution from the latter

traveltime sensitivity kernels for pkp phases in the mantle abstract we investigate the finite frequency effects of perturbations of compressional wave velocity on the traveltimes of pkp phases owing to their long paths in the mantle pkp phases have a large fresnel zone at the cmb and thus sample a large volume of the d layer we compute traveltime frechet derivatives of the three pkp phases in the mantle with respect to the ak135 reference model taking into account the coupling between the different branches pkp kernels do not have a simple banana doughnut shape because the different pkp branches interfere with each other and because of the presence of shadow zones and caustics in addition we compute the differential kernels ab bc bc df and ab df the geometry of pkp differential kernels in d show significant qualitative differences from those predicted by simple ray tracing this suggests that the tomographic techniques commonly used to image lower mantle structures could be improved by using 3d frechet kernels

core structure re examined using new teleseismic data recorded in antarctica evidence for at most weak cylindrical seismic anisotropy in the inner core we present a significant addition to the data set of traveltimes of seismic pkp waves that sample the earth s lowermost mantle and core along the earth s rotation axis recorded at permanent global seismic network gsn and temporary sscua deployment broad band seismographic stations in antarctica the new data improve the previously poor and biased coverage that underlies the seismic constraints on recent models of inner core structure and anisotropy on the one hand new differential pkp traveltime measurements improve the sampling of predominantly the eastern inner core hemisphere pkpab df and pkpbc df differential traveltime residuals with respect to the spherically symmetric model ak135 are consistently smaller than two seconds along the north south paths sampled axially symmetric models of inner core seismic anisotropy with fast axis parallel to the earth s rotation axis require a weak anisotropy of 0 7 0 1 per cent to be consistent with our pkpbc df observations pkpbc df residuals from the quasi eastern hemisphere indicate 0 4 0 1 per cent anisotropy if only pkpbc df observations from the top 200 km of this hemisphere are considered this is reduced to 0 1 0 2 per cent consistent with an isotropic layer on the other hand new absolute pkp traveltime measurements add to the sampling of both hemispheres of the inner core but it is difficult to use them with more confidence to assess structure of the core since they are affected by crustal and mantle structure and source uncertainties the newly collected data set also increases constraints on d structure beneath the south pole in contrast to previous inferences based on data from northern stations we find no evidence of a velocity heterogeneity in the outer core near the inner core boundary associated with the cylinder tangent to the inner core in the southern hemisphere

overview of the eruption of soufriere hills volcano montserrat 18 july 1995 to december 1997 the onset of phreatic volcanic activity at the soufriere hills volcano montserrat on 18 july 1995 followed a three year period of heightened volcano seismic activity beneath the island phreatic explosions gave way to continuous eruption of juvenile andesitic magma in the form of a lava dome on or around 15 november 1995 magma production rate has varied leading to changes in eruptive style an explosive eruption on 17 september 1996 followed a period of enhanced dome growth and large scale gravitational collapses from its eastern flank increasing dome volume led to stressing and overtopping of the confining crater walls to the southwest north and west during early 1997 sustained high magma production rate since june 1997 has led to three periods of major gravitational dome collapses followed by vulcanian explosive eruptions dome growth re started immediately after the cessation of the latest of these explosive phases in october 1997 and continues as of december 1997

petrologic evidence for pre eruptive pressure temperature conditions and recent reheating of andesitic magma erupting at the soufriere hills volcano montserrat w i the recent eruption of the soufriere hills volcano in montserrat july 1995 to present september 1997 has produced an andesitic dome sio 2 59 61 wt the eruption has been caused by invasion of mafic magma into a preexisting andesitic magma storage region p 130 mpa 5 km depth the composition of the andesite has remained essentially constant throughout the eruption but heating by the mafic magma increased the andesite temperature from 830 c to 880 c prior to being heated the stable mineral assemblage in the andesite was plagioclase amphibole orthopyroxene titanomagnetite ilmenite quartz the rise in temperature from 830 c to 880 c fo 2 1 log unit above nno has caused quartz to become unstable and has also caused changes in silicate and fe ti oxide mineral compositions the andesitic magma is likely saturated with an h 2 o rich vapor phase in the upper part of the magma storage region melt h 2 o content is 4 7 wt

global scale observations of scattered energy near the inner core boundary seismic constraints on the base of the outer core abstract we have collected a global dataset of several thousands of high quality records of pkpdf pkpbc pkpbc diff and pkpab phase arrivals in the distance range 149 178 within this collection we have identified an energy packet that arrives 5 20 s after the pkpbc or pkpbc diff and represents a phase that is not predicted by 1d reference seismic models we use array analysis techniques to enhance the signal of these scattered phases and show that they originate along the great circle path in a consistent range of arrival times and narrow range of ray parameters we therefore refer to this scattered energy the m phase using the cross correlation technique to detect and measure the scattered energy arrival times we compiled a dataset of 1116 records of this m phase there are no obvious variations with source or station location nor with the depth of the source after exploration of possible location for this m phase we show that its origin is most likely in the vicinity of the inner core boundary a tentative model is found that predicts an m like phase and produces good fits to its travel times as well as those of the main core phases in this model the p velocity profile with depth exhibits an increased gradient from about 400 km to 50 km above the icb i e slightly faster velocities than in ak135 or prem and a 50 km thick lower velocity layer right above the icb

inner core anisotropy in three dimensions the purpose of this paper is the investigation of cylindrical anisotropy in the inner core based on the travel time anomalies of the pkikp phase we use the arrival times reported in the international seismological centre bulletins for years 1964 1990 we select only earthquakes which have a good azimuthal coverage and a sufficiently large number of reporting stations the earthquakes are relocated using corrections for lateral heterogeneity computed for our most recent three dimensional mantle model we use a total of 313 422 observations of the df branch of pkp travel time anomalies within the epicentral distance ranges of 120 140 and 150 180 reported by 2335 stations for 26 377 earthquakes we process the data using an averaging procedure which we call cylindrical anisotropy stacking that enhances the effects of anisotropy but is expected to suppress those due to lateral heterogeneity and random errors the processed residuals show a remarkably consistent pattern this confirms the dominance of the cylindrical elastic anisotropy in the inner core with approximately a constant axis of symmetry this axis of symmetry is found to be tilted 10 5 1 from the earth s rotation axis in the direction 160 e 5 in the northern hemisphere in this new coordinate system we determine a four layer axisymmetric model of transverse anisotropy with each layer approximately 300 km thick the model shows that the anisotropy is strongest 3 within the innermost part of the core the travel time anomalies show significant 1 5 s longitudinal variations even when the tilt of the axis of symmetry is considered there is a substantial increase in the amplitude of the longitudinal variations which are dominated by the second and fourth harmonics for rays with bottoming depths exceeding 400 km below the inner core boundary the measurable tilt of the axis of symmetry and the presence of significant nonaxisymmetric signal may provide important clues with respect to the possible causes of anisotropy the increase in the anisotropy in the innermost part of the core departs from earlier inferences that anisotropy may be limited to the outermost 200 300 km of the earth s inner core

automated high time resolution measurements of so2 flux at soufriere hills volcano montserrat we report here the first results from an automated telemetered uv scanning spectrometer system for monitoring so2 emission rates at soufriere hills volcano montserrat two spectrometers receive light by way of a motor driven stepping prism and telescope in order to make vertical scans of the volcanic plume spectral data from these spectrometers situated 2 800 m apart and 4 500 m from the volcano are relayed back to the observatory every 4 5 s via radio modems a full scan of the plume is accomplished every 1 6 min by the time synchronised spectrometers and a so2 emission rate is calculated using the so2 slant concentrations scan angles and plume speeds estimated from the wind speed from a telemetered weather station near to the volcano the plume s position and dimensions are calculated using the angular data from the two spectrometers the plume height varies significantly diurnally and seasonally and is important in order to minimise the error on so2 emission rates the new scanning system scanspec provides so2 emission rates from 08 00 to 16 00 h local time every day preliminary results highlight a number of features of the so2 time series and plume dynamics and give our first indications of the errors and limits of detection of this system so2 emission rates vary widely on all time scales minutes days months this new system has already provided the first real and consistent indication that so2 emission rates vary on a minutes to hours basis which can be correlated with volcanic activity for example rockfall and pyroclastic flow activity it is anticipated that this system at soufriere hills will yield information on shallow processes occurring on short time scales periods of minutes to hours as well as deep processes relating to magma supply rates which will be associated with longer wavelength so2 signals of weeks to months

results from the broadband seismic network on montserrat a digital broadband seismic network has been installed around soufriere hills volcano on montserrat while several distinctive types of seismic events with frequencies ranging from 0 5hz to 30hz could be identified the emphasis is on two types of low frequency events which indicate the involvement of a fluid phase in the source mechanism the so called long period events and the hybrid events the latter occur in swarms with distinct periodicities of 4 to 12 hours and preceed major dome collapses and explosions the swarms correlate very well with the tilt observed at the flanks of the volcanic edifice and hence can be linked to the pressurization of the magmatic system occasionally separate hybrid events merge and form harmonic tremor which sometimes has a shifting spectral content this reveals temporary changes in the source parameters low frequency seismic signals on montserrat are considered to be key parameters for the monitoring of the internal dynamics of the volcano

late quaternary geomorphology and geoarchaeology in the rivers of the holy cross mountains region central europe late quaternary terraces and sediments in the holy cross mountain region of poland emplaced within an environment that had evolved following multiple pleistocene glaciations provide evidence of increasing anthropogenic influence on landscape development since the middle ages as revealed by research in the kamionka kamienna czarna konecka and nida valleys the development of the anthropogenic small scale water retention system aswrs including numerous artificial ponds channels and forges and mills along the watercourses resulted in changes in river patterns with additional anthropogenic channels which in turn reduced the maximum flood stage levels during the little ice age with the collapse of the industries and the disappearance of the aswrs several major flood events took place unknown in the earlier holocene and caused by hydrotechnical failures the geomorphic effects of these catastrophic flash floods significantly exceeded those of natural processes

the effect of d on pkp ab df travel time residuals and possible implications for inner core structure abstract the hypothesis that the deep inner core is anisotropic is based on pkp travel time observations at large distances and relies on a small number of very anomalous measurements for paths quasi parallel to the earth s rotation axis here we analyze a global dataset of pkp ab df travel times residuals and discuss their significant dispersion 2 s and coherent large scale patterns we show that the trends observed for quasi equatorial paths are consistent with predictions from recent tomographic mantle models when the latter are modified to account for strong heterogeneity at the base of the mantle under the pacific ocean and africa as documented in several recent studies likewise for polar paths we show that a large part of the signal could be explained by deep mantle structure the effects of complex structure in the deep mantle on pkp ab df travel times should be carefully considered in order to reliably estimate the anisotropic structure of the central part of the inner core

pkp bc versus pkp df differential travel times and aspherical structure in the earth s inner core pkp bc versus pkp df differential travel times show coherent patterns of residuals indicating aspherical structure within the earth s inner core using a waveform correlation method we measure 318 differential pkp bc versus pkp df travel times from 5 years of global digital seismograph network gdsn short period data at ranges between 145 and 155 in addition we obtain 19 470 probable bc versus df travel times at these ranges by searching through 23 years of the international seismological centre isc catalog plots of residuals versus turning point location and residuals versus ray direction show clear patterns which indicate that the differential travel times are highly correlated along similar ray paths this pattern is robust with respect to range and source depth these anomalies are almost certainly due to aspherical inner core structure since pkp bc and pkp df have nearly coincident ray paths in the mantle and outer core the gdsn and isc residual patterns are in general agreement but the isc residuals underpredict the gdsn residuals by about a factor of 2 the isc data have better spatial coverage particularly for n s ray paths within the inner core these n s ray paths show positive residuals of about 0 5 s indicating faster inner core p velocities in this direction a result consistent with previous studies of absolute pkp df travel times but derived from an independent data set due to the sparse ray coverage of our data either heterogeneity or anisotropy within the inner core with about 1 velocity variations could explain these residual patterns however inversions of the isc data for heterogeneity require many more free parameters to achieve the same variance reduction as a simple two parameter anisotropy model

evidence for strong shear velocity reductions and velocity gradients in the lower mantle beneath africa we present data which indicate that the broad low shear velocity anomaly beneath southern africa is stronger and more extensive than previously thought recordings of earthquakes in the southwestern atlantic ocean at an array of broadband seismic stations in eastern africa show anomalously large propagation time delays of the shear phases s scs and sks which vary rapidly with epicentral distance by forward modeling we estimate that the low velocity anomaly extends from the core mantle boundary about 1500 km up into the mantle and that the average shear velocity within this structure is 3 lower than in standard models such as prem strong velocity contrasts exist at its margins 2 over about 300 km these seismic characteristic are consistent with recent numerical simulations of lower mantle mega plume formation

convection and anisotropy of the inner core estimation of the rayleigh number of the inner core suggests that this region is convecting the flow pattern is likely to produce crystallographic preferred orientation of the elastically anisotropic hexagonal closest packed phase of iron such that compressional wave velocities would be greater in the axial relative to the equatorial direction by roughly 1 percent this result is in agreement with seismological evidence that the inner core is elastically anisotropic

holocene floodplain deposition and scale effects in a typical european upland catchment a case study from the ambleve catchment ardennes belgium this study quantifies holocene alluvial sediment deposition in the belgian ambleve catchment 1080 km2 situated in the ardennes uplands an extended coring data set is used for a quantitative description and a quantification of the alluvial depositions the floodplains fall into three main types the upper and lower floodplains and the steep reaches total holocene alluvial sediment deposition amounts to 32 tg or 0 029 tg km2 dating of sediments using iron slag as tracer shows that on average 42 of contemporary storage was accumulated during the last 600 years radiocarbon dating of fluvial deposits at eight sites in the catchment confirms that the majority of the sediment is relatively recent the increased sedimentation rates for this period are related to anthropogenic land use possibly enhanced by climatic variations a fluvial sediment budget was constructed for this 600 yr time period and shows that export from the catchment has about the same importance as storage in the floodplains while la

catchment scale cumulative impact of human activities on river channels in the late anthropocene implications limitations prospect abstract evidence for the proposed anthropocene epoch in fluvial geomorphology hinges on the influence of human activities relative to natural forcing however research on cause effect understanding in river channel evolution has rarely focused on the cumulative impact of multiple drivers for change limiting insights systematic review of 25 recent studies professing to explain reach scale channel responses to cumulative impacts of human activities and natural forcing over the recent past ca 1880 2005 reveals some consistencies in spatio temporal response across various catchment sizes median 3000 km2 in mostly industrialized nations common drivers for change include changing flood and flow regimes dam construction changing land uses and forest cover bank protection and instream aggregate mining recent channel evolution has predominantly involved narrowing incision and terrace development reduced bed sediment storage lower activity rates and simplified channel geometries rates of channel change frequently peaked 1955 1990 providing some support for the anthropocene great acceleration evidence here suggests that many river systems are now in morphologically novel configurations coinciding temporally with dramatic recent declines in global freshwater aquatic biodiversity sustainable approaches to freshwater management must acknowledge these configurations placing emphasis on process based approaches to river ecosystem health in which sediment cascades are reconceived to reflect altered longitudinal and lateral connectivity however the reviewed studies are driven largely by expert judgment depicting cause effect associations through summary conceptual models based on spatial proximity and temporal synchronicity providing insufficient scientific proof for the anthropocene based on the overwhelming impact of human factors more conclusive cause effect statements will require hypothetic deductive approaches explicit functional criteria and best practice environmental model building geomorphologists should now move beyond the phase of discovery and develop rigorous proofs for cause effect relationships of cumulative impact this may be enhanced by developing an avowedly anthropocene perspective in which rivers are viewed critically as socio biophysical systems co evolving with human activity

volcanic plume monitoring at mount etna by diffusive passive sampling 1 this paper reports the use of diffusive tubes in determining hf hcl and so2 in the volcanic plume of mount etna in an attempt to highlight the potential of this method in studying volcanoes in a first application a network of 18 diffusive tubes was installed on etna s flanks aimed at evaluating the atmospheric dispersion of the volcanic plume on a local scale results showed a monotonic decrease in volatile air concentrations with distance from the craters hf from 0 15 to 0 003 mol m 3 hcl from 2 to 0 01 mol m 3 and so2 from 11 to 0 04 mol m 3 revealing the prevalently volcanic contribution matching of so2 hcl and hcl hf volatile ratios with contemporaneous measurements at the summit craters validated the use of diffusive tubes in tracing the chemical features of a volcanic plume from remote locations a first tentative assessment of dry deposition rates of volcanogenic acidic gases was also made yielding 2 5 74 t d 1 so2 0 6 17 t d 1 hcl and 0 02 0 6 t d 1 hf and revealing the potential environmental impact of gas emissions in a second experiment carried out during the recent october 2002 to february 2003 eruption of etna diffusive tubes provided a continuous record of the chemical composition of the eruptive plume from a safe distance of 1 km from the vents thus considerably decreasing the risks involved in sampling this highlighted a clear time decrease in so2 concentrations and so2 hcl ratios which was interpreted as due to progressive exhaustion of volatile degassing and eruption energy

seismic evidence for an inner core transition zone seismic waves that traverse earth s inner core along north south paths produce unusually broad pulse shapes at long periods compared with waves along east west paths and reflections from below the inner core boundary at short periods the observations provide compelling evidence for a seismic velocity discontinuity along north south paths about 200 kilometers below the inner core boundary separating an isotropic upper inner core from an anisotropic lower inner core the triplication associated with such a structure might be responsible for reported waveform complexity of short period inner core arrivals along north south paths and if the depth of the boundary is laterally variable their large travel time variation

constraints on inner core anisotropy using array observations of p p author s frost da romanowicz b abstract 2017 american geophysical union all rights reserved recent studies of pkpdf travel times suggest strong anisotropy 4 or more in the quasi western inner core hemisphere however the availability of paths sampling at low angles to the earth s rotation axis the fast axis is limited to augment this sampling we collected a travel time data set for the phase p p df pkppkpdf for which at least one inner core leg is quasi polar at two high latitude seismic arrays we find that the inferred anisotropy is weak on the order of 0 5 to 1 5 confirming previous results based on a much smaller p p data set while previous models of inner core anisotropy required very strong alignment of anisotropic iron grains our results are more easily explained by current dynamic models of inner core growth we observe large travel time anomalies when one leg of p p df is along the south sandwich to alaska path consistent with pkpdf observations and warranting further investigation

natural and anthropogenic channel pattern changes in the mid mountain valley during the late glacial and holocene polish uplands the purposes of this study are to describe the channel patterns of the czarna nida river quantitatively and to determine the factors that have had the greatest influence on the development of these patterns among the factors considered were natural climatic and anthropogenic prehistoric metallurgy river development was examined with a focus on valley floor formations channel geometry changes and depositional changes river widths and channel patterns were measured on aerial photographs and longitudinal profiles were prepared from topographic maps within the bottom of the valley in a single morphological level a row of inserts of various ages appears these inserts were formed by the river of different development of the channel macromeanders late glacial multichannel systems early holocene subatlantic small meanders holocene general tendencies of the late glacial and holocene erosion accumulation cycle are related to the well known principles for valleys of central europe and described in numerous studies they encompass dissection from the turn of the younger pleniglacial and late glacial younger dryas straightening and braiding of channels as well as holocene phases of intensified fluvial activity in the czarna nida river valley distinct traces of higher fluvial activity linked with development of prehistoric iron metallurgy in the roman period were recognised