regimes of magma recharge and their control on the eruptive behaviour during the period 2001 2005 at mt etna volcano mount etna volcano italy during the period 2001 2005 has undergone a period of intense eruptive activity marked by three large eruptions 2001 2002 2003 and 2004 2005 these eruptions encompassed diverse eruptive styles and regimes from intensely explosive during 2001 and 2002 2003 eruptions to exclusively effusive in the 2004 2005 event in this work we put forward the idea that these three eruptions are the response of the progressive arrival into the uppermost segment of the open conduit system of a new magma which was geochemically distinct in terms of trace element and sr nd pb isotope signature from the products previously emitted by the etnean volcano the magma migrated upwards mainly through a peripheral tectonic system which can be considered as eccentric in spite of its relative proximity to the main system the ingress of the new magma and its gradual displacement from the eccentric system into the uppermost sector of the open conduit gave rise to different eruptive behaviours at the beginning the ascent of the undegassed magma able to exsolve a gas phase at depth and its interaction with closed system magma reservoirs less than 10 km deep gave rise to the explosive events of 2001 and 2002 2003 later when the same magma entered into the open conduit system it took part in the steady state degassing and partially lost its volatile load leading to a totally effusive eruption during the 2004 2005 event one further consideration highlighted here is that in 2001 2005 migration of the feeding axis from an eccentric and peripheral position towards the main open conduit has led to the development of a new vent south east crater 2 located at the eastern base of the south east crater through which most of the subsequent etnean activity occurred

drivers of explosivity and elevated hazard in basaltic fissure eruptions the 1913 eruption of ambrym volcano vanuatu sw pacific abstract fissure eruptions along linear structures can extend for several tens of kilometres with distinct separate manifestations of volcanism along their length they typically involve low viscosity mafic magmas forming long lava flows and cinder cones eruptions in 1894 and 1913 on ambrym volcano vanuatu showed how these mildly explosive eruptions can rapidly transform into violent explosive events producing significant hazard and widespread volcanic ash clouds during the 1913 episode a fissure began in the central caldera and basaltic magmas broke out in a series of locations down the island s western flank in all sites over 100 m in elevation fissure outbreaks produced vigorous lava fountains and highly fluid lava flows that travelled rapidly to the shoreline when the outbreaks propagated along the island s axis into coastal plain areas a climactic series of explosive eruptions occurred producing a 1 2 km long by 600 m wide maar and tephra ring a further small tuff ring was formed later creating a temporary island 400 m offshore the onshore tephra ring destroyed a hospital and associated buildings its last evacuating occupants were close witnesses to the eruption processes deposits exposed in the lower portion of the tephra ring show that this part of the eruption began with a mild phreatomagmatic explosive eruption from a narrow vent followed by a magmatic scoria producing phase subsequently a complex sequence of highly explosive phreatomagmatic eruptions occurred producing pyroclastic surges along with repeated distinctive breccia horizons rich in coral and lava country rock these features tally with eye witness accounts to indicate that the main eruption phase was produced by a periodically shifting locus of phreatomagmatic fragmentation and eruption along a single e w fissure the glassy and vesicle poor pyroclasts produced during this eruption phase were dominantly fragmented in a brittle manner by magma water interaction low volatile content of the magma upon fragmentation is confirmed by ftir analysis showing

quantifying tropospheric volcanic emissions with airs the 2002 eruption of mt etna italy 1 the atmospheric infrared sounder airs is a hyperspectral ir spectrometer orbiting on the eos aqua spacecraft since may 2002 in late october 2002 airs detected lower tropospheric sulfur dioxide and ash emitted by an eruption of mt etna italy in plumes which could be tracked over 1000 km from the volcano into north africa we report retrievals of so2 and ash column amounts and ash particle size in the etna plumes airs total so2 compares favorably with contemporaneous ground based correlation spectrometry cospec measurements retrieval of ash cloud parameters in the eruption plumes permits quantitative studies of distal ash fallout the etna data demonstrate the potential of airs to improve measurements of volcanic so2 and ash loading in the troposphere and to refine our understanding of volcanic cloud composition structure and evolution

thermohydraulic explosions in phreatomagmatic eruptions as evidenced by the comparison between pyroclasts and products from molten fuel coolant interaction experiments 1 thermohydraulic explosions were produced by molten fuel coolant interaction mfci experiments using remelted shoshonitic rocks from vulcano italy the fragmentation history and energy release were recorded the resulting products were recovered and analyzed with the scanning electron microscope fine particles from experiments show shape and surface features that result from melt fragmentation in brittle mode these clasts relate to the thermohydraulic phase of the mfci where most of the mechanical energy is released they are here called active particles the total surface area of such particles is proportional to the energy of the respective explosions other particles from experiments show shape and surface features that result from melt fragmentation in a ductile regime these fragments called passive particles form after the thermohydraulic phase during the expansion phase of the mfci in order to verify thermohydraulic explosions in volcanic eruptions we compared experimental products with samples from phreatomagmatic base surge deposits of vulcano ash particles from the experiments show features similar to those from the deposits suggesting that the experiments reproduced the same fragmentation dynamics to achieve discrimination between active and passive particles we calculated shape parameters from image analysis the mass of active particles in base surge deposits was calculated as the material properties for the natural samples are identical to the experimental ones the energy measurements and calculations of the experiments can be applied for a single phreatomagmatic eruption at vulcano a maximum mechanical energy release of 2 75 1013 j was calculated representing a tnt analogue of 6 5 kt

marine carbonate cements biofilms biomineralization and skeletogeneis some bivalves do it all recent years have seen a growing interest in the direct and indirect roles of organisms and more explicitly of organic matter in the crystallization of minerals in sediments two bivalve genera form extensive biofilms that are apparently responsible for the growth of a variety of isolated crystals together with a marine cement granicorium indutum and samarangia quadrangularis are infaunal species that cover their shells with a cemented coating of sand sculpted to mimic the surface ornament typical of many bivalves granicorium has an exceptionally mobile mantle margin that produces large volumes of mucus harboring a diverse microbial community the sand grains surrounding both species are initially bound by a biofilm that provides structural integrity but also acts like others as a template for the crystallization of a variety of carbonate polymorphs these include varied prismatic crystals rice grain and wheatsheaf forms and more importantly large volumes of acicular crystals indistinguishable from typical marine cements the distribution of these crystals is related to positions accessible to the mantle of the animal and in samarangia appears to result from the active emplacement of grains and mucus several times a year summing the evidence it seems that these species are responsible not only for the biomineralization involved in the formation of their shells but also for crystallization mediated through biofilms and for the generation of cements that are morphologically indistinguishable from typical marine cements the boundaries between these three strategies may be closer than we think

the 1245 yr bp asososca maar eruption the youngest event along the nejapa miraflores volcanic fault western managua nicaragua abstract the asososca tephra comprises the asymmetrically distributed well stratified phreatomagmatic products of the 1245 125 120 yr bp asososca maar eruption west of managua nicaragua it is the youngest eruptive unit related to the monogenetic volcanism concentrated along the n s trending nejapa miraflores active fault and intersecting e w to ne sw and nw se minor faults the close relationship between monogenetic volcanism and the structural local tectonic framework is evidenced by the lineament domains and vent alignment patterns identified by remotely sensed images and dems of the research area the asososca maar lake bathymetry suggests that the crater was formed by coalescing vents migrating during the eruptive event the asososca tephra dominantly consists of accidental lithics disrupted from the underlying stratigraphic units observed inside and around the maar crater dry base surge bedsets are dominant throughout the eruptive unit showing facies variation from proximal cross stratified beds to mid distal plane parallel and wavy parallel beds grain size analyses indicate that base surges transported dominantly 1 0 and 1 sized particles at the bedload in form of traction carpets while fine ash material in continuous suspension was minimal juvenile fragments were only identified in the finer fractions varying from vesiculated scoriae to dense sideromelane fragments sem analyses suggest that the asososca eruption resulted from a highly efficient fuel coolant interaction between a tholeiitic basaltic melt and an aquifer hosted in a shallow level between 50 and 200 m of olivine bearing scoria ash and lapilli beds the explosion triggered the country rock comminution and the production of moss like fused shaped and blocky ash shards with stepped surfaces quenching cracks pitting alteration skins and adhered particles all indicative of phreatomagmatic fragmentation the very recent age of the asososca maar eruption confirms that the densely inhabited managua area is volcanically active and that hazard studies should focus on the potential for phreatomagmatic eruptions

mechanisms of hydrovolcanic pyroclast formation grain size scanning electron microscopy and experimental studies pyroclasts produced by explosive magma water interactions are of various sizes and shapes data from analysis of over 200 samples of hydrovolcanic ash are interpreted by comparison with experimentally produced ash grain size and scanning electron microscopy sem reveal information on the formation of hydrovolcanic pyroclasts strombolian explosions result from limited water interaction with magma and the pyroclasts produced are dominantly centimeter sized with increasing water interaction hydrovolcanism increases in explosivity to surtseyan and vulcanian activity these eruptions produce millimeter to micron sized pyroclasts the abundance of fine ash 63 m diameter increases from 5 to over 30 percent as water interaction reaches an explosive maximum this maximum occurs with interactions of virtually equal volumes of melt and water five dominant pyroclast shape types determined by sem result from hydrovolcanic fragmentation 1 blocky and equant 2 vesicular and irregular with smooth surfaces 3 moss like and convoluted 4 spherical or drop like and 5 plate like types 1 and 2 dominate pyroclasts greater than 100 m in diameter types 3 and 4 are typical of fine ash type 5 pyroclasts characterize ash less than 100 m in diameter resulting from hydrovolcanic fragmentation after strong vesiculation fragmentation mechanisms observed in experimental melt water interactions result from vapor film generation expansion and collapse fragments of congealed melt are products of several alternative mechanisms including stress wave cavitation detonation waves and fluid instability mixing all result in rapid heat transfer these mechanisms can explain the five observed pyroclast shapes stress wave fracturing cavitation of the melt results from high pressure and temperature gradients at the melt water interface simultaneous brittle fracture and quenching produces type 1 pyroclasts type 2 develops smooth fused surfaces due to turbulent mixing with water after fracture and before quenching fluid instabilities promote turbulent mixing of melt and water and produce fine ash this kind of fragmentation occurs during high energy explosions the increased melt surface area due to fine fragmentation promotes high efficiency heat exchange between the melt and water shapes of resulting pyroclasts are determined by maximum surface area type 3 and surface tension effects type 4 type 5 pyroclasts result from nearly simultaneous vesicle burst and melt water fragmentation

the last 40 ka tephrostratigraphic record of lake ohrid albania and macedonia a very distal archive for ash dispersal from italian volcanoes abstract a 1075 cm long core lz1120 was recovered in the south eastern part of the lake ohrid republics of macedonia and albania and sampled for identification of tephra layers magnetic susceptibility investigations show rather high magnetic values throughout the core with peaks unrelated to the occurrence of tephra layers but instead to the relative abundance of detrital magnetic minerals in the sediment naked eye inspection of the core allowed us to identify of two tephra layers at 896 897 cm and 1070 1075 cm laboratory inspection of the grain size fraction 125 m allowed for the identification of a third cryptotephra at 310 315 cm major element analyses on glass shards of the tephra layers at 896 897 cm and 1070 1075 cm show a trachytic composition and indicate a correlation with the regionally dispersed y 3 and y 5 tephra layers dated at ca 30 and 39 cal ka bp the cryptotephra at 310 315 cm has a mugearitic benmoreitic composition and was correlated with the fl eruption of mt etna dated at 3370 70 cal yr bp these ages are in agreement with five 14 c ams measurements carried out on plant remains and macrofossils from the lake sediments at different depths along the core the recognition of distal tephra from italian volcanoes allows us to link the lake ohrid succession to other archives located in the mediterranean area and in eastern europe the benmoreitic mugearitic tephra layer at 310 315 cm is the first recognition in the balkan area of a distal ash deposit from a mid intensity explosive eruption of mt etna as far as 600 km from the source

first evidence of hydromagmatism at colima volcano mexico abstract here we report for the first time evidences of hydromagmatism at colima volcano western sector of trans mexican volcanic belt the studied location exposes 9 m of fine ash deposits dated at around 15 cal kyr bp by 14 c measurement on organic matter collected at the very base of the stratigraphic succession the ash deposits rest directly on the top of a debris avalanche deposit the morphology and grain size distribution of ash samples from the basal part of the stratigraphic succession testify for an explosive magma water interaction which produced finely bedded layers with blocky fragments characterized by adhering particles quenching cracks and chemical pitting the availability of ground water was hypothesized to be in close relationship with the amelioration of climate conditions at the end of the last glacial period with rising temperatures that induced melting of glaciers and snow previously accumulated on the volcano summit slopes this recognition demonstrates how even a dry volcano like colima can experience hydromagmatism under adequate climatic conditions

shifting styles of basaltic explosive activity during the 2002 03 eruption of mt etna italy abstract the 2002 03 flank eruption of etna was characterized by two months of explosive activity that produced copious ash fallout constituting a major source of hazard and damage over all eastern sicily most of the tephra were erupted from vents at 2750 and 2800 m elevation on the s flank of the volcano where different eruptive styles alternated the dominant style of explosive activity consisted of discrete to pulsing magma jets mounted by wide ash plumes which we refer to as ash rich jets and plumes similarly ash rich explosive activity was also briefly observed during the 2001 flank eruption of etna but is otherwise fairly uncommon in the recent history of etna here we describe the features of the 2002 03 explosive activity and compare it with the 2001 eruption in order to characterize ash rich jets and plumes and their transition with other eruptive styles including strombolian and ash explosions mainly through chemical componentry and morphology investigations of erupted ash past models explain the transition between different styles of basaltic explosive activity only in terms of flow conditions of gas and liquid our findings suggest that the abundant presence of a solid phase microlites may also control vent degassing and consequent magma fragmentation and eruptive style in fact in contrast with the strombolian or hawaiian microlite poor fluidal sideromelane clasts ash rich jets and plumes produce crystal rich tachylite clasts with evidence of brittle fragmentation suggesting that high groundmass crystallinity of the very top part of the magma column may reduce bubble movement while increasing fragmentation efficiency

identifying magma water interaction from the surface features of ash particles the deposits from explosive volcanic eruptions those eruptions that release mechanical energy over a short time span1 are characterized by an abundance of volcanic ash2 3 this ash is produced by fragmentation of the magma driving the eruption and by fragmenting and ejecting parts of the pre existing crust host rocks interactions between rising magma and the hydrosphere oceans lakes and ground water play an important role in explosive volcanism4 5 because of the unique thermodynamic properties of water that allow it to very effectively convert thermal into mechanical energy although the relative proportion of magma to host rock fragments is well preserved in the pyroclastic rocks deposited by such eruptions it has remained difficult to quantitatively assess the interaction of magma with liquid water from the analysis of pyroclastic deposits2 3 4 5 here we report the results of a study of natural pyroclastic sequences combined with scaled laboratory experiments we find that surface features of ash grains can be used to identify the dynamic contact of magma with liquid water the abundance of such ash grains can then be related to the water magma mass ratios during their interaction

controls on the explosive emplacement of diamondiferous kimberlites new insights from hypabyssal and pyroclastic units in the diavik mine canada abstract kimberlites are mantle derived magmas that either crystallise as hypabyssal intrusions erupt explosively after rapid ascent to the surface or less commonly form lava lakes and flows thereby creating texturally distinct kimberlite units efforts to fully understand the processes responsible for the explosive eruption of kimberlite magmas have been hindered by the widespread alteration and crustal contamination of most volcaniclastic kimberlites to address this issue we have undertaken a detailed petrographic and mineral chemical study of fresh i e minimally altered pyroclastic and hypabyssal kimberlites hk from the ca 55 56 ma a154 north and south kimberlite pipes in the diavik mine lac de gras canada these localities host exceptionally fresh kimberlites and are therefore ideally suited to this study kimberlite emplacement at a154 north and south initiated with the intrusion of hypabyssal kimberlite external dykes and was followed by the explosive formation of kimberlite pipes and volcaniclastic kimberlite infill subsequent kimberlite magmas intruded the volcaniclastic kimberlite units forming multiple cross cutting internal dykes the studied volcaniclastic units feature abundant rounded magmaclasts and massive textures suggestive of primary deposits these units are classified as pyroclastic kimberlites pk pyroclastic and hypabyssal kimberlite units at diavik exhibit subtle mineral compositional differences samples from both internal hk units and pk units feature identical compositions for liquidus olivine rims mg 90 5 0 1 and 90 7 0 2 respectively with a marginally lower mg of 90 2 0 2 in olivine rims from the external hk dykes similarly early formed chromite compositions are the same for internal hk and pk units cr 79 1 3 4 and 78 3 5 7 mg 60 0 1 3 and 60 0 2 2 but differ in the external hk units cr 86 9 2 7 mg 52 8 1 9 the internal hk and pk units also exhibit lower carbonate contents than the internal hk units these compositional differences indicate that the external dykes were probably derived from slightly different primitive melt compositions to those parental to the internal hk and pk units spinel evolutionary trends from chromite to magnesian ulv spinel magnetite mum compositions are indistinguishable in internal hk and pk samples fe3 47 2 5 8 and 49 7 9 3 cr 25 7 11 0 and 17 0 14 0 these results demonstrate that the primitive melt compositions and early magmatic evolution processes are identical for the internal kimberlite units regardless of whether the kimberlite melts erupted explosively or were emplaced as shallow intrusions however magmaclasts in the pk units contain higher abundances of phlogopite

fragmentation versus transportation mechanisms in the pyroclastic sequence of monte pilato rocche rosse lipari italy abstract monte pilato is a rhyolitic pumice cone formed about 1400 years ago during the last volcanic activity which occurred at lipari its activity consisted of numerous explosive episodes ending with the extrusion of the rocche rosse obsidian lava flow we have identified nine different pyroclastic lithofacies of which four main lithofacies represent 90 of the erupted products they include 1 deposits consisting of decimeters to meters thick well sorted graded beds of pumice lapilli which are of fall origin 2 massive deposits consisting of decimeters thick beds of pumice lapilli in an ash matrix interpreted as being of pyroclastic flow origin 3 deposits of centimeters thick ash beds of surge origin 4 decimeter thick fine ash layers with scattered subcentimetric accretionary lapilli of turbulent flow origin the complex grain size distributions of the main lithofacies were distinguished using a multivariate statistic analysis r mode factor analysis variations of the grain size characteristics in relation to the distance from the vent area have been investigated in order to discriminate the roles played by fragmentation and transportation processes in the lithofacies 1 fall deposits the grain size distribution is always unimodal and varies from a rosin type distribution near the vent to a gaussian one in the distal outcrops this is caused by the transport process and the different particle trajectories in lithofacies 2 3 and 4 the grain size distributions are always polymodal the polymodality is not caused by preferential processes occurring during transportation but seems rather to be connected with the original fragmentation of the pyroclastic material the pumice lapilli present both in lithofacies 1 and 2 have mean vesicularity index values always in excess of 65 and the value is homogeneous throughout the sample these data suggest that for these two lithofacies the pumice lapilli originated from exsolution of magmatic gases in contrast the fine ash particles in lithofacies 2 and also the main mode of lithofacies 3 and 4 deposits show typical features of hydromagmatic fragmentation processes the grain size population is always centered at 4 5 0 032 0 064 mm and interestingly the same grain size has been obtained recently zimanowski et al 1991 for fragments produced by experimental magma water interaction field and laboratory data suggest that during monte pilato rocche rosse eruptions magmatic and hydromagmatic mechanisms were frequently operative at the same time

cyclostratigraphy and high frequency carbon isotope fluctuations in upper cretaceous shallow water carbonates southern italy a detailed carbon isotope study has been carried out on a santonian upper cretaceous carbonate platform succession that crops out at monte sant erasmo southern italy previous centimetre scale studies on this succession have shown that high frequency eustatic changes resulting from the earth s orbital fluctuations controlled the hierarchical organization of the depositional and early diagenetic features in elementary cycles bundles groups of three to five elementary cycles and superbundles groups of three or four bundles the elementary cycles which correspond to single beds suggest a control caused by earth s precession the bundles and superbundles record the short 100 kyr and long 400 kyr eccentricity periodicity respectively the 1 3 c signal of the monte sant erasmo succession is cyclic in nature and may be considered to be a reliable proxy for the sedimentary evolution and related sea level history of the analysed sequence the carbon isotope cyclicity is recorded at bundle and superbundle level but it is not evident at the scale of the elementary cycles at least with the sampling interval used in this study spectral analysis of the 1 3 c record shows two main peaks corresponding to the short and long eccentricity periodicity whereas the precession signal is not evident in the power spectrum in addition lithofacies analysis shows that in each bundle and superbundle higher c isotope values occur in sediments characterized by marine cements whereas lower values are normally found in more restricted deposits overprinted by early meteoric diagenesis early diagenesis driven by periodic sea level fluctuations developed in either shallow subtidal marine diagenesis or subaerial exposed meteoric overprint sedimentary environments and directly influenced the carbon isotope signature as a consequence the 1 3 c record at monte sant erasmo reflects high frequency climatic oscillations controlling both environmental and early diagenetic changes the long term isotopic record is similar to that of contemporaneous pelagic sections in england and elsewhere in italy it is concluded that the 1 3 c signature of shallow water carbonates such as those of monte sant erasmo offers great potential for correlation with coeval sections including those of the pelagic realm

statistical analysis of textural data from complex pyroclastic sequences implications for fragmentation processes of the agnano monte spina tephra 4 1 ka phlegraean fields southern italy the agnano monte spina eruption 4 1 ka generated pyroclastic deposits with complex internal stratigraphy that reflects variations in eruptive style to obtain constraints on the fragmentation processes we analysed grain size and scanning electron microscopy sem data by means of multivariate statistical techniques of the cluster and factor analysis types the results allow the identification of end member deposits related to either pure magmatic activity or pure phreatomagmatic activity in addition some deposits show evidence of the contemporaneous operation of both end member fragmentation modes the presence of the two contrasting fragmentation processes during the various phases of explosive activity is tentatively interpreted to be a function in inhomogeneities in gas exsolution processes within the magma column that feeds the eruption

rapidity of freshwater calcite cementation implications for carbonate diagenesis and sequence stratigraphy abstract in less than 10 years subaerially exposed holocene oolitic sand on eleuthera island bahamas was completely case hardened by freshwater vadose calcite cementation this phenomenon demonstrates the rapidity of freshwater carbonate diagenesis and explains in part why carbonate platforms preferentially shed unconsolidated sediment during highstands and not during lowstands when they are subaerially exposed it further proves contrary to what the exxon conceptual sequence stratigraphic models imply that carbonate deposits do in fact respond differently to subaerial exposure than siliciclastic deposits case hardening of unconsolidated carbonate sediment in response to subaerial exposure and early near surface freshwater diagenesis helps explain why shallow water platform sediments are preferentially shed into adjacent basins during highstands of sea level and not during lowstands during lowstands rapid subaerial lithification of carbonate sediments retards their reworking by wind or water once lithified these deposits are further stabilized by vegetation and karstification inhibiting their transport as unconsolidated sediment into adjacent deeper water basins observations from eleuthera island also document the reciprocal processes associated with freshwater carbonate diagenesis calcium carbonate released by partial dissolution of aragonitic ooids was locally reprecipitated as pore filling low magnesian calcite cement this reciprocity is confirmed by the confinement of freshwater dissolution and cementation to the upper 10 20 cm of the subaerially exposed body of oolitic sand below this case hardened surface oolitic sands remained unconsolidated only very minor amounts of calcite cement were required for effective casae hardening

perils in distinguishing phreatic from phreatomagmatic ash insights into the eruption mechanisms of the 6 august 2012 mt tongariro eruption new zealand abstract the weak geophysical precursors of the 6 august 2012 te maari eruption of mt tongariro and a lack of obvious juvenile components in its proximal ballistic deposits imply that the eruption was caused by the sudden decompression of a sealed hot hydrothermal system strong magmatic signals in pre and post eruption gas emissions indicate that fresh magma had intruded to shallow levels shortly before this eruption here we examine the volcanic ash produced during the august eruption with the aim of determining whether juvenile magma was erupted or not the widely applied criteria for identifying fresh juvenile pyroclasts provided inconclusive results the te maari ash sorting and trend towards a unimodal grain size distribution increase with distance along the dispersal axis proximal to intermediate sites showing polymodal grain size distributions can be related to the re fragmentation of different pre existing lithologies overlapped erupted pulses and transport mechanisms and to particle aggregation between 69 and 100 vol of particles coarser than 3 and 45 75 vol of grains finer than 3 were sourced from the pre existing commonly hydrothermally altered vent area lavas and pyroclasts free crystals pyroxene plagioclase magnetite pyrite make up 0 23 vol of particles coarser than 3 and 22 41 vol of grains finer than 3 brown to black fragments of fresh glass are a small 1 15 vol but notable component under sem these blocky glassy particles are poorly vesicular and irregularly shaped some with fluidal or bubble wall surfaces and others with fragmented stepped surfaces and fine adhering ash in thin section they contain variable amounts of microlites within an isotropic groundmass the range in silica content of the microprobe analysed glass is very wide 56 77 wt and cannot be correlated to any specific particle textural type these chemically and texturally diverse glassy fragments are identical to mechanically broken pieces of country rock lavas and pyroclasts both their diversity and their match with vent country rocks argue strongly against a juvenile origin for the glassy fragments we conclude that rising magma provided only heat and gas into the overlying sealed vapour dominated hydrothermal system a landslide from this area led to a rapid decompression and ash was produced by top down hydrothermal explosions careful attention must be paid to the combination of compositions and textures of fine ash particles in such situations as well as to the context of their source vent in order to be confident that new magma has reached the surface

fall vs flow activity during the 1991 climactic eruption of pinatubo volcano philippines six years after the 1991 mt pinatubo eruption deep erosion incisions into the pyroclastic deposits accumulated around the volcano enabled us to investigate the stratigraphy of the climactic deposits both in valley bottoms and on contiguous ridges stratigraphic relationships between fall flow and surge deposits in the marella drainage system indicate that during the climactic eruption a progressive shift occurred from an early convective regime to a transitional regime feeding both the plinian convective column and mostly dilute density currents to a fully collapsing regime producing mostly dense pyroclastic flows syn plinian dilute density currents surges propagated up to 10 km from the crater both along valley bottoms and on contiguous ridges of the marella valley whereas post plinian pyroclastic flows had greater runout 13 km were confined to valleys and were not associated with significant surges stratigraphic study and grain size analyses allow the identification of three types of intra plinian deposits a lower and often coarse grained surge deposits emplaced during the accumulation of the coarsest portion of the fallout bed at time intervals of 16 24 min b upper fine grained surge deposits interstratified with the fine grained portion of the fall bed and emplaced at shorter time intervals of 3 13 min and c small volume channel confined massive pumiceous flow deposits interbedded with the upper surges in the upper fine grained fall bed maximum clast size isopleths of 1 6 and 0 8 cm for lithics ml and 2 0 and 4 0 cm for pumices mp show almost symmetrical distribution around the vent indicating that the passing of the typhoon yunya during the climactic eruption had little effect on trajectories of high reynold number clasts significant distortion was however observed for the 3 2 cm ml and 6 0 cm mp proximal isopleths whose patterns were probably influenced by the interaction of the clasts falling from column margins with the uprising co ignimbrite ash plumes application of the carey and sparks 1986 model to the undisturbed isopleths generated by the umbrella cloud yields a maximum column height of 42 km in good agreement with satellite measurements systematic stratigraphic and vertical grain size studies of the plinian fall deposit in the marella valley combined with satellite data and eyewitness accounts reveal that the carrying capacity of the convective column and related fallout activity peaked in the early phase of the eruption beginning slightly before 13 41 and gradually declined until its cessation 3 h later most of the pumiceous pyroclastic flow deposits were emplaced after the end of the fallout activity at 16 30 but before the summit caldera collapse at approximately 19 11 only a small volume of pumiceous flow deposits accumulated after the final caldera collapse in contrast to the previous reconstruction of holasek et al 1996 which interpreted the progressive lowering of the column documented by satellite data as due to a decreasing mass eruption rate we suggest that a progressive shift from a plinian column to a large co ignimbrite column could also account for such a variation

fractionation of benzocarbazoles between source rocks and petroleums the concentrations of the a and c isomers of benzocarbazoles in a number of crude oils and source rock bitumens were obtained by in house methods and from reported published data the changes in benzocarbazole concentrations and the benzocarbazole a a c ratio relating to source maturity facies and migration are described with increasing source maturity in north sea oils and source rocks up to 0 85 vitrinite reflectance equivalent benzocarbazole concentrations increase due to generation followed by a decrease above 0 85 vitrinite reflectance equivalent due to expulsion dilution by newly generated hydrocarbons comparison of benzocarbazole concentrations between reservoired petroleum and related source petroleum revealed a concentration bias in favour of source petroleum where concentrations of benzocarbazoles reached up to 10 times that found in equivalent reservoired petroleum the differences in benzocarbazole concentrations between related oils and source rocks indicate that the major fractionation is introduced during primary migration and expulsion because when secondary migration is limited as in the miller field we see extensive benzocarbazole fractionation between reservoired petroleum and associated source petroleum the relationships between source rock toc content and petroleum benzocarbazole concentrations and a a c ratios indicate that source organic matter exerts a strong influence on benzocarbazole distributions the introduction of a reservoir source fractionation parameter rsfp defined as the ratio between the concentrations of benzo a benzo c carbazole in reservoired petroleum versus the concentration of benzo a benzo c carbazole in source petroleum enables description of the relationship between reservoired petroleum and source petroleum from different petroleum systems petroleum deriving from clastic source rocks demonstrated high levels of benzocarbazole fractionation between reservoired petroleum and source petroleum during primary and secondary migration compared to petroleum deriving from carbonate systems the rsfp parameter may also be used to examine fractionation effects during migration between different compound types the more polar benzocarbazoles are fractionated more strongly than dibenzothiophene and phenanthrene between reservoired petroleum and source petroleum whereas sometimes source maturity signals do dominate the benzocarbazole signals in migrated oils in other circumstances often associated with clastic source rocks no clear maturity signal is transferred to migrated oils

modeling eruption source parameters by integrating field ground based and satellite based measurements the case of the 23 february 2013 etna paroxysm

phreatomagmatic ash from the ongoing eruption of etna reaching the greek island of cefalonia on october 26 2002 etna volcano sicily southern italy entered a new eruptive phase characterised by the usual effusive activity from fissure vents located both on the southern and on the northern sector of the summit area in addition explosive events of unusual intensity were recorded at the beginning of the eruption and produced a substantial plume rich in fine ash particles and steam on october 27 fine ash from the plume blown by the wind was reported falling on the island of cefalonia greece which is located approximately 500 km east of the volcano in this communication we report on the study of fine ash from the eruption as collected on cefalonia we elaborate on the nature of the peculiar type of explosion mechanism that led to such an unusual manifestation of etna which is phreatomagmatism this finding draws a new picture of the eruptive scenario of this active volcano and requires a careful evaluation of the hazard that similar events might pose in the future not just the surroundings of the volcano but also the aviation corridors of the southern mediterranean area could be potentially affected

hydrovolcanic ash emission between august 14 and 24 2015 at cotopaxi volcano ecuador characterization and eruption mechanisms abstract cotopaxi is an active hazardous and ice covered stratovolcano 60 km southeast of quito ecuador whose last major eruption occurred in 1877 during 2001 2002 volcanic unrest characterized by volcanic seismicity and deformation ended without eruptive activity on april 2015 a new increase of seismicity so2 emissions thermal anomalies and edifice deformation evolved into the onset of a new eruptive cycle beginning august 14 we sampled and measured the ash fall deposits to the west of cotopaxi between august 14 and 24 2015 the ash collected was analyzed using grain size x ray fluorescence x ray diffraction and scanning electron microscope sem eds revealing the eruptive products to be compound of dense fragments mostly lithics diverse types of scoria pumice free fractured crystals glassy particles and aggregates most of hydrothermal alteration is observed during the initial stage of the eruption 14 15 august including cu oxides and fe minerals in the lithics the glassy particles were blocky morphology and textural changes were recognized over 10 days of eruption varying from null or low vesicularity to low to moderate vesicularity occasionally exhibiting molten or subrounded textures the bulk ash has a basaltic andesitic composition 55 67 wt of sio2 while clusters of selected particles likely juvenile analyzed through sem eds reveal dacitic composition 65 67 and 65 8 wt sio2 plagioclase clinopyroxene and orthopyroxene are the main minerals present with accessory anhydrite melanterite and pyrite these typically observed during the initial stage of eruption these variations in addition to the geophysical background led us to interpret this eruption as the result of the volcano s hydrothermal system disruption due to a shallow low volume magma input which initially evolved into phreatic activity at surface level further activity up to 24 august was triggered by the indirect interaction between magma and the depleted hydrothermal system generating a magmatic hydrothermal eruption the issue is important for evaluating unrest periods at active stratovolcanoes and the impact of their initial low volume ash falls in neighboring communities

an unloading foam model to constrain etna s 11 13 january 2011 lava fountaining episode 1 the 11 13 january 2011 eruptive episode at etna volcano occurred after several months of increasing ash emissions from the summit craters and was heralded by increasing so2 output which peaked at 5000 megagrams day several hours before the start of the eruptive activity the eruptive episode began with a phase of strombolian activity from a pit crater on the eastern flank of the se crater explosions became more intense with time and eventually became transitional between strombolian and fountaining before moving into a lava fountaining phase fountaining was accompanied by lava output from the lower rim of the pit crater emplacement of the resulting lava flow field as well as associated lava fountain and strombolian phases was tracked using a remote sensing network comprising both thermal and visible cameras thermal surveys completed once the eruptive episode had ended also allowed us to reconstruct the emplacement of the lava flow field using a high temporal resolution geostationary satellite data we were also able to construct a detailed record of the heat flux during the fountain fed flow phase and its subsequent cooling the dense rock volume of erupted lava obtained from the satellite data was 1 2 106 m3 this was emplaced over a period of about 6 h to give a mean output rate of 55 m3 s 1 by comparison geologic data allowed us to estimate dense rock volumes of 0 85 106 m3 for the pyroclastics erupted during the lava fountain phase and 0 84 1 7 106 m3 for lavas erupted during the effusive phase resulting in a total erupted dense rock volume of 1 7 2 5 106 m3 and a mean output rate of 78 117 m3 s 1 the sequence of events and quantitative results presented here shed light on the shallow feeding system of the volcano

clinker formation in basaltic and trachybasaltic lava flows clinker is a term used to describe massive or scoriaceous fragments commonly associated with a lava flows clinker is generally considered to form by fragmentation of an upper vesiculated crust due to an increase in apparent viscosity and or to an increase in shear strain rate surface clinker is considered to be transported to the flow front and incorporated at the base by caterpillar motion clinker that we have observed on a variety of lava flows has very variable textures which suggests several different mechanisms of formation in order to study clinker formation we examined several lava flows from the chaine des puys central france where good sections surface morphology and surface textures are widespread and clearly visible we observed basal and surface a clinker that has fragmentation textures similar to those observed in ash formed in eruptions under dry conditions in two p hoehoe flows we have observed basal clinker that formed in situ two other flows display clinker features identical to those commonly observed in phreatomagmatic ash such as adhering particles blocky shapes spherical glass and attached microphenocrysts another p hoehoe flow has a flakey angular basal breccia with microfaulted and abraded clasts these were probably formed at a cooled lava base by large amounts of simple shear and consequent intra lava brittle faulting using these observations we propose three different ways of fragmentation 1 clinker can form at the surface and eventually produce roll over basal breccia 2 water lava interactions can form basal clinker by phreatomagmatic fragmentation water lava ratio variations may produce different clinker structures in a manner similar to observed textural changes in phreatomagmatic eruptions 3 clinker can be formed by brittle brecciation during basal simple shear the different clinker can provide information about the mechanisms and environmental conditions during lava flow emplacement

what controls diffuse fractures in platform carbonates insights from provence france and apulia italy abstract fractures are widespread in rocks and regional opening mode arrays are commonly ascribed to major tectonic events however fractures occur in otherwise undeformed rocks some of these are early developed features independent of tectonics and forming a background network at regional scale to overcome this lack of understanding two hydrocarbon reservoir analogues from platform carbonates have been targeted the provence se france and the apulian platform se italy in both areas an early fracturing stage has been observed made of high angle to bedding opening mode fractures and bed parallel stylolites these features developed synchronously during the first burial stages and prior to major tectonic events the fracture sets are not genetically related to the present day layering contrarily fractures developed in a brittle media where facies transitions were not sharp and did not act as mechanical discontinuities carbonate facies distribution and early diagenetic imprint constrained the mechanical stratigraphy when fractures occurred in addition we observed that fractures related to late tectonic inversion were partly inhibited indeed rock mechanical properties change through time characterizing the temporal evolution of carbonate rocks has revealed that diagenesis and sedimentary facies are the prime actors for brittleness and mechanical layering in carbonates

rapidity of marine carbonate cementation implications for carbonate diagenesis and sequence stratigraphy perspective abstract lithification is a rapid process but how rapid is rapid a year after one of my visits to joulter s cay bahamas i found a sardine can from my previous visit the cementation of carbonate particles in and around the can was surprising 382 g of ooids and skeletal material had filled the can and lithified therein or had become cemented to the outside of the can the rapidity of marine carbonate cementation implies that during highstand of sea level shallow water platform carbonate sediments are subject to marine lithification which retards erosion this conclusion is at variance with that of other workers who rely on freshwater cementation during lowstands to generate cement which retards reworking clearly the historical debate over highstand versus lowstand of shallow water marine carbonates is not yet over