features of some paleosols on the flanks of etna volcano italy and their origin abstract volcano flanks are usually covered by deposits of fine materials tephra with variable thickness originated by the explosive activity the deposits form bedded sequences of tephra layers often alternated with paleosols pyroclastic successions on etna volcano italy are composed of scoria or pumice lapilli and ash deposits representing separate eruptions and volcanogenic sediments developed between eruptions the origin of paleosols cropping out in three pyroclastic successions on mt etna is here discussed on the basis of stratigraphic pedological chemical and mineralogical data the results suggest that the sequences originated from the accumulation of primary volcanic materials produced by explosive events together with material of secondary origin derived from wind transported materials originated by the alteration of the pyroclastic deposits formed at higher elevations the vegetation present at the surface at any time would have favoured the aggrading of the soil by exerting a trapping effect on the wind blown materials at the same time the presence of plants would have favoured enrichment in organic c and mineral alteration in the studied paleosols the pedogenetic processes were not sufficiently intense or did not act for a sufficient time to favour neogenesis of mineralogical phases either crystalline or amorphous

stratigraphy and dispersal of the mangaone subgroup pyroclastic deposits okataina volcanic centre new zealand abstract the mangaone subgroup from the okataina volcanic centre consists of silicic plinian pyroclastic units that lie between the oruanui deposit from the taupo volcanic centre corrected 14 c calendar age 26 5 ka and the rotoiti flow rotoehu fall deposits from okataina volcanic centre k ar age 64 ka in this study we present a new stratigraphy for the subgroup that is significantly revised from the earlier work and was developed after extensive field mapping and laboratory study we now recognize and describe a total of 12 rhyolitic units as opposed to the 8 that had been recognized previously with a total bulk eruptive volume of approximately 81 km 3 the vents for all the mangaone subgroup units were within the haroharo caldera and possibly migrated through time first within a roughly north south trending zone in the central part of the caldera and then toward the eastern part of the caldera we present new radiometric ages suggesting that the whole sequence was erupted in a relatively short time span possibly 10 15 ka our findings of more eruptions in a shorter time span than in previous work underscores the utility of detailed field studies particularly when volcanic hazards are being assessed all the fall units have plinian dispersals but show various degrees of magma water interaction the majority of the eruptions were large and intense enough to generate pyroclastic flows yet flows were observed in only 2 units and is volumetrically small

ultrahigh temperature metamorphism and decompression history of sapphirine granulites from rajapalaiyam southern india implications for the formation of hot orogens during gondwana assembly sapphirine bearing mg al granulites from rajapalaiyam in the southern part of the madurai block provide critical evidence for late neoproterozoic cambrian ultrahigh temperature uht metamorphism in southern india poikiloblastic garnet in quartzo feldspathic and pelitic granulites contain inclusions of fine grained subidioblastic to xenoblastic sapphirine associated with quartz suggesting that the rocks underwent t 1000 c peak metamorphism quartz inclusions in spinel within garnet are also regarded as clear evidence for a uht condition inclusions of orthopyroxene within porphyroblastic garnet in the sapphirine bearing rocks show the highest al 2 o 3 content of up to 10 3 wt suggesting t 1050 1070 c and p 8 5 9 5 kbar temperatures estimated from ternary feldspar and other geothermometers t 950 1000 c further support extreme thermal metamorphism in this region xenoblastic spinel inclusions in sapphirine coexisting with quartz suggest that the spinel quartz assemblage pre dates the sapphirine quartz assemblage probably implying a cooling from t 1050 c or an anticlockwise p t path the fmas reaction sapphirine quartz garnet orthopyroxene sillimanite indicates a cooling from the sapphirine quartz stability field after the peak metamorphism corona textures of orthopyroxene cordierite sapphirine orthopyroxene sapphirine cordierite and cordierite spinel around garnet suggest subsequent near isothermal decompression followed by decompressional cooling toward t 650 750 c and p 4 5 5 5 kbar the sapphirine quartz association and related textures described in this study have an important bearing on the uht metamorphism and exhumation history of the madurai block as well as on the tectonic evolution of the continental deep crust in southern india our study provides a typical example for extreme metamorphism associated with collisional tectonics during the late neoproterozoic cambrian assembly of the gondwana supercontinent

understanding multi vent plinian eruptions at mt tongariro volcanic complex new zealand the andesitic tongariro volcanic complex in the central north island of new zealand comprises tens of vents along an actively extending graben past work has hypothesised that multiple vents may operate during a single explosive eruption episode providing an unprecedented hazard challenge for this region the stratigraphic record suggests an irregular clustering of eruption episodes over time including an unusual 200 year long period from 11 3 11 1 ka when several large explosive eruptions occurred we carried out new field mapping stratigraphy and sedimentology of the resulting pyroclastic deposits to identify seven episodes during this period locating the vent sites and calculating their climactic dynamic properties five of the episodes involved two or more vent locations that produced separate sub plinian plinian eruption columns eruption columns ranged between 16 and 24 km high and erupted volumes of 0 05 to 0 76 km3 indicating magnitudes of 4 to 5 each of these episodes show north to south unzipping of the tongariro graben with episodes beginning in northerly vents before being joined by vents south of these this included two scenarios northern edifice vents followed by central edifice ones or central edifice vents followed by southern ones in both cases the northerly vents generally display the greatest peak eruption magnitudes and the steadiest eruptions by contrast the southernmost vents formed along a fault controlled fissure like system these produced unsteady plumes and pyroclastic density currents the northward widening tectonic graben structure thus influences the pattern and style of these plinian style eruptions this study highlights a real possibility for an extreme hazard scenario involving successive large scale eruptions at volcanic systems in slowly rifting environments and sheds new light on the volcano tectonic interaction in such settings

degassing behaviour at basaltic volcanoes new insights from experimental investigations of different conduit geometry and magma viscosity abstract understanding gas magma dynamics in volcanic conduits and linking them with the associated geophysical signals at the surface is of fundamental importance in monitoring active volcanoes in the past a significant number of studies have been devoted to this topic addressing the onset the key factors governing each degassing regime and the related markers at the surface particularly at basaltic volcanoes here we first review such a broad and increasing literature focusing on the main approaches used in the attempt of deciphering conduit dynamics by indirect observations 1 analogue laboratory experiments and 2 seismo acoustic measurements then we combine the two techniques into a novel set of experiments addressing a crucial yet unexplored issue the irregularity i e the departure from an ideal smooth cylindrical shape of the conduit surface we built a set of epoxy conduits with various fractal dimensions dc i e irregularity of the internal surface using silicone oil as a proxy for magma different degassing patterns bubbly slug and churn annular flow were reproduced by changing systematically 1 injected gas flux 5 to 180 10 3 l s 2 analogue magma viscosity 10 to 1000 pas 3 fractal dimension dc of the conduit surface i e dc 2 dc 2 18 and dc 2 99 the experiments were monitored by means of a video camera and a set of sensor aimed to detect the seismic and acoustic signals results show that viscosity strongly influences the transition among degassing patterns and the recurrence rate of slug bursts at the surface moreover we observed an increase of the exponent of the power law equation linking squared seismic amplitude to gas flow rate with conduit roughness the opposite trend was noticed with increasing liquid viscosity these results have important implications for linking seismic tremor to eruption source parameters such as the volume discharge rate at different volcanoes or for investigating its temporal evolution at a single vent

satellite analysis and puff simulation of the eruptive cloud generated by the mount etna paroxysm of 22 july 1998 1 we applied the puff algorithm searcy et al 1998 to simulate the space time evolution of the eruptive cloud generated by one of the main paroxysms to have occurred this past century at etna volcano namely the 22 july 1998 explosive event at the voragine summit crater the comparison of puff simulations to satellite images of the ash cloud at different times allowed us to estimate several parameters of the eruptive event such as onset time duration ash cloud height and shape and pyroclast size based on this analysis we concluded that the paroxysm started around 1645 gmt lasted between 20 and 40 min and generated a poissonian shaped ash column nearly 13 km high and composed of particles with a mean diameter md of 10 3 m and size logarithmic standard deviation lsd equal to 1 5 the puff simulations using horizontal and vertical diffusivity values of 5000 and 10 m2 s 1 respectively provided the best agreement to the eruption clouds observed on satellite images the results were compared to the information available in the literature concerning the eruption e g volcanological video camera and volcanic tremor data the analysis showed that the method of simulating the eruptive clouds and comparing simulations to satellite images can give a contribution to the study of paroxysmal events generated by the etna volcano also the degree of accuracy of the cloud simulation leads us to be optimistic about the potential of using this method as a tool for hazard mitigation in the etna region with particular applications to air traffic

the masaya triple layer a 2100 year old basaltic multi episodic plinian eruption from the masaya caldera complex nicaragua the masaya caldera complex has been the site of three highly explosive basaltic eruptions within the last six thousand years a plinian eruption ca 2 ka ago formed the widespread deposits of the masaya triple layer we distinguish two facies within the masaya triple layer from each other la concepcion facies to the south and managua facies to the northwest these two facies were previously treated as two separated deposits la concepcion tephra and the masaya triple layer of perez and freundt 2006 because of their distinct regional distribution and internal architectures however chemical compositions of bulk rock matrix and inclusion glasses and mineral phases demonstrate that they are the product of a single basaltic magma batch additionally a marker bed containing fluidal shaped vesicular lapilli allowed us to make a plausible correlation between the two facies also supported by consistent lateral changes in lithologic structure and composition thickness and grain size we distinguish 10 main subunits of the masaya triple layer i to x with bulk volumes ranging between 0 02 and 0 22 km3 adding up to 0 86 km3 0 4 km3 dre for the entire deposit distal deposits identified in two cores drilled offshore nicaragua at a distance of 170 km from the masaya caldera complex increase the total tephra volume to 3 4 km3 or 1 8 km3 dre of erupted basaltic magma isopleth data of five major fallout subunits indicate mass discharges of 106 to 108 kg s and eruption columns of 21 to 32 km height affected by wind speeds of 2 m s to 20 m s which increased during the course of the multi episodic eruption magmatic plinian events alternated with phreatoplinian eruptions and phreatomagmatic explosions generating surges that typically preceded breaks in activity while single eruptive episodes lasted for few hours the entire eruption probable lasted weeks to months this is indicated by changes in atmospheric conditions and ash layer surfaces that had become modified during the breaks in activity the masaya triple layer has allowed to reconstruct in detail how a basaltic plinian eruption develops in terms of duration episodicity and variable access of external water to the conduit with implications for volcanic hazard assessment

volcanological evolution of mount erciyes stratovolcano and origin of the valibaba tepe ignimbrite central anatolia turkey abstract mount erciyes 3917 m is the largest stratovolcano of central anatolia turkey the volcanological evolution of mount erciyes from pliocene quaternary to historical times exhibits two distinct stages 1 koc dag and 2 erciyes during the koc dag stage basaltic and andesitic lava flows were emitted from the cinder cones of kizil tepe and topakkaya tepe then koc dag pyroclastics were emplaced leading to a caldera collapse of 14 18 km in diameter with a volume estimated at 110 km3 two eruption phases separated by scoria fall and mud flow deposits are recognised associated with the caldera forming event during phase 1 plinian fall and pumice flows were emplaced on the eastern part of the volcano plinian fall deposits occur more than 50 km away from the source area the volume of tephra is estimated at 63 3 km3 16 km3 dense rock equivalent dre including 62 km3 of plinian fall and 1 3 km3 pumice flow deposits phase 2 mainly consists of pyroclastic flow deposits two pumiceous flow units and valibaba tepe ignimbrite vti the pumiceous flow deposits 4 2 km3 dre extend 30 km from the inferred source area towards the north and northeast the final pyroclastic flows of phase 2 occurred 2 8 ma ago and produced the vti the vti is a low aspect ratio welded ignimbrite and its volume is estimated at 40 km3 dre plinian fall deposits 0 8 km3 dre preceded the vti and are only observed on the eastern part of the volcano covering an area of 1500 km2 during the erciyes stage two eruptive cycles are defined the first cycle 2 6 0 17 ma is characterised by effusive extrusive and weakly explosive activity with emplacement of andesitic lava flows dacitic dome flows basaltic andesite lava flows and andesitic cones the second cycle involved dacitic extrusive and explosive activity located at the summit area and produced block and ash flows derived from rhyodacitic domes plinian fall surge and pumice flow deposits were emplaced prior to rhyodacitic dome extrusions the last event was the emplacement of debris avalanche deposits related to sector collapse caldera

long and short term magma differentiation at mt etna as revealed by sr nd isotopes and geochemical data abstract mt etna in sicily italy produces effusive and explosive eruptions from summit craters and flanks petrology of erupted products has proved fundamental to explore the relationship between magma dynamics within the plumbing system and eruptive styles data of sr nd isotopes are quite scarce if compared with the great number of chemical analyses carried out in products of last decades we measure sr nd isotopes major and trace elements in products emitted from 2001 to 2012 and consider also published analyses of the 1995 2001 eruptions because carried out in the same laboratories of 2001 2012 ones furthermore we take into account other published analyses extending back to the 14th century even if performed by different facilities based on this dataset magma dynamics operating at different timescales inside the volcano s plumbing system have been explored our analyses evidence that from 2001 2012 three magma types are present in the volcano s plumbing system i a deep and poorly evolved basaltic and k trachybasaltic magma enriched in radiogenic sr and lile erupted during the 2001 and 2002 03 flank activity ii a shallower more evolved k trachybasaltic magma less enriched in radiogenic sr feeding both summit and flank eruptions and iii an uncommon and scarcely radiogenic hawaiitic magma lile poor emitted exclusively from a small sector of the 2002 03 eruptive fissures by considering a broader time scale from 14th to 21st century we conclude that i different magmatic components are present in the deep volcano s plumbing system at about 10 12 km b s l ii a decoupling of geochemical and isotopic features in magmas stored at different depths is observed after the 1974 flank eruption up to date iii mixing between different magmas is an efficient magmatic process to produce magma differentiation at mt etna regardless of the investigated temporal scale

relating vesicle shapes in pyroclasts to eruption styles vesicles in pyroclasts provide a direct record of conduit conditions during explosive volcanic eruptions although their numbers and sizes are used routinely to infer aspects of eruption dynamics vesicle shape remains an underutilized parameter we have quantified vesicle shapes in pyroclasts from fall deposits of seven explosive eruptions of different styles using the dimensionless shape factor omega a measure of the degree of complexity of the bounding surface of an object for each of the seven eruptions we have also estimated the capillary number ca from the magma expansion velocity through coupled diffusive bubble growth and conduit flow modeling we find that omega is smaller for eruptions with rm ca ll 1 than for eruptions with ca gg 1 consistent with previous studies we interpret these results as an expression of the relative importance of structural changes during magma decompression and bubble growth such as coalescence and shape relaxation of bubbles by capillary stresses among the samples analyzed strombolian and hawaiian fire fountain eruptions have rm ca ll 1 in contrast to vulcanian plinian and ultraplinian eruptions interestingly the basaltic plinian eruptions of tarawera volcano new zealand in 1886 and mt etna italy in 122 bc for which the cause of intense explosive activity has been controversial are also characterized by rm ca gg 1 and larger values of omega than strombolian and hawaiian style fire fountain eruptions we interpret this to be the consequence of syn eruptive magma crystallization resulting in high magma viscosity and reduced rates of bubble growth our model results indicate that during these basaltic plinian eruptions buildup of bubble overpressure resulted in brittle magma fragmentation

a unique 4000 year long geological record of multiple tsunami inundations in the augusta bay eastern sicily italy abstract we present the geological evidence for a 4000 year long record of multiple tsunami inundations along the coast of the augusta bay eastern sicily and discuss its implications the research was carried out through a multi theme approach which benefited from an extraordinarily long historical record that we used to guide detailed geomorphologic and geologic surveys coring campaigns and laboratory analyses two sites named the augusta hospital and priolo reserve were selected and investigated in detail along the 25 km long coastline of augusta bay we found evidence for six possibly seven tsunami deposits three of them may be tentatively associated with the 1693 and 365 ad ionian sea historical tsunamis and the 3600 bp santorini event the other three possibly four deposits are evidence for unknown paleo inundations dated at about 650 770 ad 600 400 bc and 975 800 bc at augusta hospital site and 800 600 bc at priolo reserve site we use these ages to extend further back the historical record of tsunamis available for this coastal area the exceptional number of tsunami deposits found with this study allowed us to derive an average geologic tsunami recurrence interval in the augusta bay of about 600 years for the past 4 ka conversely the historical tsunami data for the past millennium suggest an average tsunami recurrence interval of about 250 years this difference in the average recurrence intervals suggests that only the strongest inundations may leave recognizable geological signatures at the investigated sites i e the evidence for the 1908 and 1169 tsunamis is missing but also that the geomorphological setting of the site and its erosional depositional history are critical aspects for the data recording thus an average recurrence interval derived from the geological record should be considered as a minimum figure the identification and age estimation of tsunami deposits represent a new and independent contribution to tsunami scenarios and modeling for coastal hazard assessment in civil protection applications furthermore our study cases provide new elements on tsunami deposit recognition related to exceptionally large events that occurred in the aegean sea

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

morphometry of scoria cones located on a volcano flank a case study from mt etna italy based on high resolution lidar data abstract by using new high resolution 2 m digital elevation model derived from the 2005 lidar survey of mt etna volcano italy our study measured the classical morphometrical parameters for scoria cones i e w co cone width w cr crater diameter h cone height as well as volume inclination of cone slope and substrate and a number of other parameters for 135 scoria cones of mt etna volume and age distribution of cones shows that there is no direct structural control on their emplacement in terms of etna s rift zones the cones are progressively smaller in size toward summit which can be explained by the large volcano s feeding system and progressively frequent lava burial toward top a careful analysis of h w co ratio determined as 0 18 for other volcanic fields worldwide shows that this ratio strongly depends on 1 the calculation method of h and 2 lava burial of cone for etnean cones applying an improved method for calculating h relative to the dipping substrate results in a significantly lowered standard h w co ratio 0 137 which in turn questions the validity of the classical value of 0 18 in the case of large central volcanoes the reduction of the ratio is not only due to methodology but also to the common lava burial this can be expressed even better if h mean is used instead of h max h mean w co 0 098 using this measure at etna well formed cones have higher ratios than structurally deformed e g double or rifted cones furthermore although the sampled scoria cones at etna have formed in a relatively narrow time interval h w co corresponding to erosional changes detected globally h w co 0 143 0 135 and 0 115 for three age classes of etna s scoria cones corresponding to average slopes of 26 6 23 9 and 23 7 because the morphometrical effect of position on a dipping substrate as well as lava burial exceeds the effect of erosion we call attention to use caution in simply using the h w co ratio of scoria cones for detecting age especially on large active volcanoes

the ilopango tierra blanca joven tbj eruption el salvador volcano stratigraphy and physical characterization of the major holocene event of central america abstract the ilopango caldera is the source of the large tierra blanca joven tbj eruption that occurred about 1 5 ka years ago between ca ad270 and ad535 the eruption dispersed volcanic ash over much of the present territory of el salvador and pyroclastic density currents pdcs extended 40 km from the volcano in this study we document the physical characteristics of the deposits from all over el salvador to further constrain the eruption processes and the intensity and magnitude of the different phases of the eruption the succession of deposits generated by the tbj eruption is made of 8 units the eruption started with pdcs of hydromagmatic origin unit a0 followed by fallout deposits units a and b that are

unusual magma storage conditions at mt etna southern italy as evidenced by plagioclase megacryst bearing lavas implications for the plumbing system geometry and summit caldera collapse at mt etna volcano the emission of plagioclase megacryst bearing lavas known locally as cicirara has occurred rarely and generally in association with unusual volcanological phenomena in this work we interpret the magma chamber processes and the structural features of the plumbing system that led to the production of these peculiar volcanic rocks based on a detailed study of plagioclase megacrysts including their oscillatory zoning sieve textures and fluid inclusions patchy zoning suggests limited ascent in the deep levels of the plumbing system based on the plagioclase nucleation threshold and the volatile saturation depth at intermediate water undersaturated levels of the plumbing system ascent is faster as indicated by crystals with coarse sieve textures storage at shallow water saturated levels less than 6 km deep is associated with oscillatory zoning with very small changes in an slightly larger an variations coupled with different wavelengths provide evidence of convection of crystals across distinct zones of the chamber stripes of melt inclusions formed at steps of magma ascent and volatile loss whereas layers of fluid inclusions may be related to episodes of volatile flushing into the magma chamber in contrast strongly sieve textured envelopes with an increase and constant feo may be related to mixing with more volatile rich magmas of similar composition we interpret the repeated occurrence of cicirara lavas as evidence that the shallow portion of the plumbing system underwent a progressive coalescence of a complex network of dykes and sills in response to increasing rates of magma supply from depth major magma withdrawals from this larger reservoir may be linked to episodes of summit instability associated with major caldera collapses

the late holocene tephra record of the central mediterranean sea mapping occurrences and new potential isochrons for the 4 4 2 0 ka time interval five cores from the southern tyrrhenian and ionian seas were studied for their tephra and cryptotephra content in the 4 4 2 0 ka time interval the chronological framework for each core was obtained by accelerator mass spectrometry 14c dating the occurrence of distinct marker tephra and stratigraphic correlation with adjacent records tephrochronology allowed us to correlate the analyzed deposits with tephra markers associated with somma vesuvius 79 ad ischia island cretaio mt etna fg fl and fs and campi flegrei astroni agnano monte spina events for the first time in the marine setting a large single glass data set is provided for the late holocene etnean marker beds including the fs tephra ca 4 3 ka moreover unknown deposits from lipari ca 2 2 2 0 ka and vulcano 3 6 3 3 ka are also recognized at more distal sites than previously reported these results contribute to improve the high resolution tephrostratigraphic framework of the central mediterranean sea they also provide new insights into the chemical composition and dispersal pattern of tephras that can be used as inter archive tools for regional and local stratigraphic correlations and for addressing paleoclimate research

the 18 7 ka phreatomagmatic flank eruption on etna italy relationship between eruptive activity and sedimentary basement setting this paper documents a phreatomagmatic flank eruption that occurred 18 700 100 a bp on the lower north eastern slope of etna during the ellittico volcano activity which produced fall and surge deposits this type of eruption is connected to a sedimentary basement ridge at etna the interaction between the rising magma and the shallow groundwater hosted in the volcanic pile overlying the impermeable sediments resulted in phreatomagmatic instead of strombolian activity three eruptive phases are distinguished based on field and analytical data i an explosive phreatomagmatic opening ii a main phase producing coarse lithic rich fallout and a strombolian deposit and iii the final pulsating surge forming phase the discovery of this phreatomagmatic flank eruption which occurred at lower altitude raises important issues for previous hazard assessments at etna

preeruptive magma viscosity an important measure of magma eruptibility 1 using a compilation of melt compositions meltwater contents temperatures and phenocryst contents the preeruptive viscosities under magma reservoir conditions are calculated for 83 erupted magmas the basaltic to rhyolitic magmas have preeruptive viscosities over the range 101 to 108 pa s although bulk sio2 content has often been used as a qualitative measure of preeruptive magma viscosity the bulk sio2 content shows a weak correlation with magma viscosity correlation coefficient r 0 5 because of a wide range of phenocryst contents from 0 to 50 vol andesitic magmas have viscosities ranging from 102 to 107 pa s which are lower or higher than those of phenocryst poor rhyolitic magmas with 105 to 106 pa s focusing on andesitic to rhyolitic magmas the r between bulk sio2 contents and magma viscosities changes to 0 1 in contrast the melt only sio2 content from a basaltic to rhyolitic melt shows a good linear correlation with melt only viscosity r 0 9 although most of the calculated viscosities of erupted magmas fall below 106 pa s as consistent with the previous compilation study this paper describes 20 examples of highly viscous magmas with 106 pa s in most cases composed of mixtures of high silica rhyolitic melt 75 79 wt sio2 and abundant phenocrysts 30 55 vol in these highly viscous magmas 9 examples have erupted following the precursory eruption of less viscous magma suggesting that precursory dike propagation and conduit formation by the less viscous magma with 106 pa s induced the following eruption of less eruptible highly viscous magmas

climate forcing of volcano lateral collapse evidence from mount etna sicily in this study we present evidence for early holocene climatic conditions providing circumstances favourable to major lateral collapse at mount etna sicily the volcano s most notable topographic feature is the valle del bove a 5 x 8 km cliff bounded amphitheatre excavated from the eastern flank of the volcano its origin due to prehistoric lateral collapse is corroborated by sturtzstrom deposits adjacent to the amphitheatre s downslope outlet but the age nature and cause of amphitheatre excavation remain matters for debate cosmogenic 3 he exposure ages determined for eroded surfaces within an abandoned watershed flanking the valle del bove support channel abandonment ca 7 5 ka bp as a consequence of its excavation in a catastrophic collapse event watershed development was largely dictated by pluvial conditions during the early holocene which are also implicated in slope failure a viable trigger is magma emplacement into rift zones in the eastern flank of a water saturated edifice leading to the development of excess pore pressures consequent reduction in sliding resistance detachment and collapse such a mechanism is presented as one potential driver of future lateral collapse in volcanic landscapes forecast to experience increased precipitation or melting of ice cover as a consequence of anthropogenic warming

temperature control of continental lithosphere elastic thickness te vs vs article i nfo the elastic thickness of the continental lithosphere is closely related to its total strength and therefore to its susceptibility to tectonic deformation and earthquakes recently it has been questioned whether the lithosphere thickness and strength are dependent on crustal and upper mantle temperatures and compositions as predicted by laboratory data we test this dependence regionally by comparison in northwestern north america of the effective elastic thickness te from topography gravity coherence with upper mantle temperatures mapped by shear wave tomography velocities vs and other temperature indicators the te values are strongly bimodal as found globally less than 20 km for the hot cordillera backarc and over 60 km for the cold stable craton these te correspond to low vs beneath the cordillera and high vs beneath the craton model temperature depth profiles are used to estimate model te for comparison with those observed only limited areas of intermediate thermal regimes i e thermotectonic ages of 300 ma have intermediate te that suggest a weak lower crust over a stronger upper mantle there are large uncertainties in model te associated with composition water content strain rate and decoupling stress threshold however with reasonable parameters model yield stress envelopes correspond to observed te for thermal regimes with 800 900 c at the cordillera moho and 400 500 c for the shield in agreement with temperatures from vs and other estimators our study supports the conclusion that lithosphere elastic thickness and strength are controlled primarily by temperature and that laboratory based rheology generally provides a good estimate of the deformation behaviour of the crust and upper mantle on geological time scales

large volume basaltic hyaloclastite eruption along a propagating land lake lithosphere fracture at lake van eastern anatolia impact of volcanism on the evolution of lake van v the incekaya hyaloclastite cone eastern anatolia turkey the focal point along a major eruptive fissure was the main source of an unusually large explosive basaltic eruption the ca 80 ka old eruption began onshore with scoria cones from a 5 km n s fracture propagating toward lake van surface area of 3755 km2 at the intersection with the fault bounded lake basin a ca 400 m high subaerial hyaloclastite edifice formed which can be crudely subdivided into a main lower massive bulk of hydrothermally altered lithic rich hyaloclastites cl topped unconformably by a 30 m thick well bedded fallout tephra cu the cu tephras are correlated with 1 widespread onshore hyaloclastite fallout deposits mostly west southwest of the cone and 2 a ca 2 m thick ca 80 ka old bedded hyaloclastite v 60 part of a 220 m icdp international continental scientific drilling program core drilled in lake van 27 km n of incekaya the hyaloclastite unit was seismically identified as being the most widespread and well defined reflector throughout much of western lake van a minimum volume of 9 km3 fallout hyaloclastite tephra is estimated when the area of the seismic reflector is extrapolated to the coast and 2 km inland seismic reflectors also suggest at least two hyaloclastite intralake cones rising up to 388 m above the lake sediment surface 1 5 km nw off incekaya cone and were possibly erupted along the same fracture the total volume of hyaloclastites includes a subaerial incekaya cone b the inferred subaqueous continuation of the cone s c the bedded intralake and onshore deposits and tentatively d a widespread seismically defined mass flow deposits directly beneath incekaya reflector of roughly 20 km3 and may represent the deposits of explosively erupted basaltic magma sideromelane shards the main clast type are dominantly angular and most show 50 vol vesicles less common tachylite clasts are poorly vesicular 50 vol structural transitions and interlayering between tachylite and sideromelane are ubiquitous fluidal and pumiceous lapilli are present in the basal massive facies bulk rock and glass compositions indicate constant composition of the slightly evolved al rich basalt magma olivine fo78 82 and plagioclase an70 80 microphenocrysts many skeletal with growth features and microlites make up 1 vol and suggest rapid magma ascent the high explosive energy of the eruption is interpreted to be due to 1 high magma discharge rates and shearing in the eruptive jet and 2 magma water interaction conditions approximate temporal coincidences with the incekaya eruption include the following a an abrupt cessation in the supply of evolved tephra from the adjacent suphan volcano to the lake sediments which ended abruptly for ca 60 ky b an extreme fall in lake level by ca 150 m and c a drastic increase in pore water salinity na and cl g l and ph

possible tsunami signatures from an integrated study in the augusta bay offshore eastern sicily italy abstract twelve anomalous layers marked by a high concentration of displaced epiphytic foraminifera species growing in vegetated substrates like the posidonia oceanica and subtle grain size changes were found in a 6 7 m long fine sediment core ms 06 sampled 2 km off the shore of the augusta harbor eastern sicily at a depth of 72 m recording the past 4500 yrs of deposition because concentrations of epiphytic foraminifera are quite common in infralittoral zones but not expected at 72 m we believe that these anomalous layers might be related to the occurrence of tsunamis causing substantial uprooting and seaward displacement of p oceanica blades with their benthic biota our approach involved the study of geophysical data morphobathymetry seismic reflection and seafloor reflectivity and sediment samples including x ray imaging physical properties isotopic dating tephrochronology grain size and micropaleontology correlations between anomalous layers and tsunami events have been supported by a multivariate analysis on benthic foraminifera assemblage and dates of historical tsunami records we found that four out of the eleven layers were embedded in age intervals encompassing the dates of major tsunamis that hit eastern sicily 1908 1693 and 1169 and the broader eastern mediterranean santorini at about bp 3600 one more layer even if less distinct than the others was also defined and may be the evidence for the ad 365 crete tsunami

confort 15 model of conduit dynamics applications to pantelleria green tuff and etna 122 bc eruptions numerical simulations are useful tools to illustrate how flow parameters and physical processes may affect eruption dynamics of volcanoes in this paper we present an updated version of the conflow model an open source numerical model for flow in eruptive conduits during steady state pyroclastic eruptions mastin and ghiorso in a numerical program for steady state flow of magma gas mixtures through vertical eruptive conduits u s geological survey open file report 00 209 2000 in the modified version called confort 15 the rheological constraints are improved incorporating the most recent constitutive equations of both the liquid viscosity and crystal bearing rheology this allows all natural magma compositions including the peralkaline melts excluded in the original version to be investigated the crystal bearing rheology is improved by computing the effect of strain rate and crystal shape on the rheology of natural magmatic suspensions and expanding the crystal content range in which rheology can be modeled compared to the original version conflow is applicable to magmatic mixtures with up to 30 vol crystal content moreover volcanological studies of the juvenile products crystal and vesicle size distribution of the investigated eruption are directly incorporated into the modeling procedure vesicle number densities derived from textural analyses are used to calculate through toramaru equations maximum decompression rates experienced during ascent finally both degassing under equilibrium and disequilibrium conditions are considered this allows considerations on the effect of different fragmentation criteria on the conduit flow analyses the maximum volume fraction criterion porosity criterion the brittle fragmentation criterion and the overpressure fragmentation criterion simulations of the pantelleritic and trachytic phases of the green tuff pantelleria and of the plinian etna 122 bc eruptions are performed to test the upgrades in the confort 15 modeling conflow and confort 15 numerical results are compared analyzing the effect of viscosity decompression rate temperature fragmentation criteria critical strain rate porosity and overpressure criteria and equilibrium versus disequilibrium degassing in the magma flow along volcanic conduits the equilibrium simulation results indicate that an increase in viscosity a faster decompression rate a decrease in temperature or the application of the porosity criterion in place of the strain rate one produces a deepening in fragmentation depth initial velocity and mass flux of the mixture are directly correlated with each other inversely proportional to an increase in viscosity except for the case in which a faster decompression rate is assumed taking into account up to date viscosity parameterization or input faster decompression rate a much larger decrease in the average pressure along the conduit compared to previous studies is recorded enhancing water exsolution and degassing disequilibrium degassing initiates only at very shallow conditions near the surface brittle fragmentation i e depending on the strain rate criterion in the pantelleritic green tuff eruption simulations is mainly a function of the initial temperature in the case of the etna 122 bc plinian eruption the viscosity strongly affects the magma ascent dynamics along the conduit using confort 15 and therefore incorporating the most recent constitutive rheological parameterizations we could calculate the mixture viscosity increase due to the presence of microlites results show that these seemingly low viscosity magmas can explosively fragment in a brittle manner mass fluxes resulting from simulations which better represent the natural case i e microlite bearing are consistent with values found in the literature for plinian eruptions 106 kg s the disequilibrium simulations both for green tuff and etna 122 bc eruptions indicate that overpressure sufficient for fragmentation if present occurs only at very shallow conditions near the surface

new physical characterization of the fontana lapilli basaltic plinian eruption nicaragua the fontana lapilli deposit was erupted in the late pleistocene from a vent or multiple vents located near masaya volcano nicaragua and is the product of one of the largest basaltic plinian eruptions studied so far this eruption evolved from an initial sequence of fluctuating fountain like events and moderately explosive pulses to a sustained plinian episode depositing fall beds of highly vesicular basaltic andesite scoria sio2 53 wt samples show unimodal grain size distribution and a moderate sorting that are uniform in time the juvenile component predominates 96 wt and consists of vesicular clasts with both sub angular and fluidal elongated shapes we obtain a maximum plume height of 32 km and an associated mass eruption rate of 1 4 108 kg s 1 for the plinian phase estimates of erupted volume are strongly sensitive to the technique used for the calculation and to the distribution of field data our best estimate for the erupted volume of the majority of the climactic plinian phase is between 2 9 and 3 8 km3 and was obtained by applying a power law fitting technique with different integration limits the estimated eruption duration varies between 4 and 6 h marine core data confirm that the tephra thinning is better fitted by a power law than by an exponential trend

mass budget partitioning during explosive eruptions insights from the 2006 paroxysm of tungurahua volcano ecuador how and how much the mass of juvenile magma is split between vent derived tephra pdc deposits and lavas i e mass partition is related to eruption dynamics and style estimating such mass partitioning budgets may reveal important for hazard evaluation purposes we calculated the volume of each product emplaced during the august 2006 paroxysmal eruption of tungurahua volcano ecuador and converted it into masses using high resolution grainsize componentry and density data this dataset is one of the first complete descriptions of mass partitioning associated with a vei 3 andesitic event the scoria fall deposit near vent agglutinate and lava flow include 28 16 and 12 wt of the erupted juvenile mass respectively much 44 wt of the juvenile material fed pyroclastic density currents i e dense flows dilute surges and co pdc plumes highlighting that tephra fall deposits do not depict adequately the size and fragmentation processes of moderate pdc forming event the main parameters controlling the mass partitioning are the type of magmatic fragmentation conditions of magma ascent and crater area topography comparisons of our dataset with other pdc forming eruptions of different style and magma composition suggest that moderate andesitic eruptions are more prone to produce pdcs in proportions than any other eruption type this finding may be explained by the relatively low magmatic fragmentation efficiency of moderate andesitic eruptions these mass partitioning data reveal important trends that may be critical for hazard assessment notably at frequently active andesitic edifices this article is protected by copyright all rights reserved

hazards from pyroclastic density currents at mt etna italy abstract despite the recent recognition of mount etna as a periodically violently explosive volcano the hazards from various types of pyroclastic density currents pdcs have until now received virtually no attention at this volcano large scale pyroclastic flows last occurred during the caldera forming ellittico eruptions 15 16 ka ago and the risk of them occurring in the near future is negligible however minor pdcs can affect much of the summit area and portions of the upper flanks of the volcano during the past 20 years small pyroclastic flows or base surge like vapor and ash clouds have occurred in at least 8 cases during summit eruptions of etna four different mechanisms of pdc generation have been identified during these events 1 collapse of pyroclastic fountains as in 2000 and possibly in 1986 2 phreatomagmatic explosions resulting from mixing of lava with wet rock 2006 3 phreatomagmatic explosions resulting from mixing of lava with thick snow 2007 4 disintegration of the unstable flanks of a lava dome like structure growing over the rim of one of the summit craters 1999 all of these recent pdcs were of a rather minor extent maximum runout lengths were about 1 5 km in november 2006 and march 2007 and thus they represented no threat for populated areas and human property around the volcano yet events of this type pose a significant threat to the lives of people visiting the summit area of etna and areas in a radius of 2 km from the summit craters should be off limits anytime an event capable of producing similar pdcs occurs the most likely source of further pdcs in the near future is the southeast crater the youngest most active and most unstable of the four summit craters of etna where 6 of the 8 documented recent pdcs originated it is likely that similar hazards exist in a number of volcanic settings elsewhere especially at snow or glacier covered volcanoes and on volcano slopes strongly affected by hydrothermal alteration

pyroclastic density currents resulting from the interaction of basaltic magma with hydrothermally altered rock an example from the 2006 summit eruptions of mount etna italy after 16 months of quiescence mount etna began to erupt again in mid july 2006 the activity was concentrated at and around the southeast crater sec one of the four craters on the summit of etna and eruptive activity continued intermittently for 5 months during this period numerous vents displayed a wide range of eruptive styles at different times virtually all explosive activities took place at vents at the summit of the sec and on its flanks eruptive episodes which lasted from 1 day to 2 weeks became shorter and more violent with time volcanic activity at these vents was often accompanied by dramatic mass wasting processes such as collapse of parts of the cone highly unusual flowage processes involving both old rocks and fresh magmatic material and magma water interaction the most dramatic events took place on 16 november when numerous rockfalls and pyroclastic density currents pdcs were generated during the opening of a large fracture on the se flank of the sec cone the largest pdcs were clearly triggered explosively and there is evidence that much of the energy was generated during the interaction of intruding magma with wet rocks on the cone s flanks the most mobile pdcs traveled up to 1 km from their source this previously unknown process on etna may not be unique on this volcano and is likely to have taken place on other volcanoes it represents a newly recognized hazard to those who visit and work in the vicinity of the summit of etna

theoretical modeling of eruption plumes on mars under current and past climates we have used a combined conduit transport eruption column model to explore the evolution of volcanic eruption plumes on mars under different atmospheric conditions in the calculations we consider a volatile phase composed of h2o co2 and so2 and take into account that the magmatic water erupted at the vent may condense as the eruption column rises into the martian atmosphere as two end member models we explore the eruption of rhyolitic and basaltic melt compositions containing different amounts of volatiles as well as having different eruption temperatures under current martian atmospheric conditions eruption plumes are found to rise as high as 100 km for a mass eruption rate of 5 107 kg s 1 which is consistent with model calculations by wilson and head 1994 in contrast under a dense atmosphere 105 pa on the martian surface which may have existed earlier in martian history the same eruption plume reaches only about 25 km height all magmatic water released during the eruption is found to freeze as it rises in the eruption column which means that fallout from the plume will contain water ice which can be subsequently deposited in near surface layers this ice may then suddenly melt due to higher surface heat flow or shallow intrusions leading to rapid release of water on the flanks of volcanoes only if the atmosphere were hotter in the past could the water in the eruption plume condense and produce rain rather than ice furthermore the calculations show that smaller micron size particles would be distributed globally from eruption plumes under current martian conditions but would not have been as widely dispersed from plumes erupted into an earlier dense atmosphere

active tectonic features and structural dynamics of the summit area of mt etna italy revealed by soil co2 and soil temperature surveying project cgl2005 07509 cli ministry of education and science of spain dpc ingv project flank istituto nazionale di geofisica e vulcanologia osservatorio etneo sezione di catania

development and spatial distribution of soils on an active volcano mt etna sicily abstract as a large active volcano mt etna presents a complex soil forming environment with a spatial diversity of lava flow age tephra deposition local climate and agriculture following a review of previous published research on etna s soils this paper analyses physical and chemical data for 23 profiles between 120 m and 1030 m elevation on all flanks of the volcano with the aim of characterising the soils and determining the extent to which the chief controls on their nature and geography may be identified soils are sampled across a chronosequence of lava flows dating from 72 yr to between 28 ka and 42 ka bp which occur in conditions of diverse land use and local climate ages of flows 3000 yr are only broadly constrained the majority of soils comprise mostly tephra chief soil processes inferred have been identified in previous published research on mt etna accumulation of soil organic matter rapid loss of na and production of fine grained materials particularly those inferred to be of short range order other developments are soil structural formation and evidence of increasing soil mesofaunal activity despite the complexity of environmental diversity and spatial variation in tephra deposition a number of soil properties including material

origin of the term nuees ardentes and the 1580 and 1808 eruptions on sao jorge island azores abstract in this paper we provide a brief account of the 1580 and 1808 eruptions on sao jorge in the azores which produced pyroclastic density currents pdcs discuss the first recorded use of the term nuees ardentes to describe these pdcs trace how this term was introduced into the scientific literature and discuss its adoption by alfred lacroix 1863 1948 to describe the glowing clouds produced by mt pelee martinique in 1902 the 1580 and 1808 eruptions on sao jorge are important because they provide early descriptions of pdcs documentary evidence of the eruptions and their impacts suggest that the 1580 pdc was a hotter flow whereas the 1808 pdcs were cooler and more moist contemporary accounts describe the 1580 pdc as a globe of fire mixed with caustic smoke and moving at speed towards the bottom of the slope in contrast the 1808 pdcs comprised humid ash were not incandescent and it is likely that the flows were cooler than that produced in 1580 since the eruption of mt pelee in 1902 it has been widely accepted that the term nuees ardentes was introduced by lacroix 1904 being based on his description of the pyroclastic flows that he witnessed lacroix acknowledges that the portuguese expression nuvem ardente was first used in contemporary accounts of the sao jorge pdcs this was first translated as nuee ardente and introduced into the scientific by the french geologist ferdinand fouque 1828 1904 who was also lacroix s father in law indeed lacroix provides an account of the 1580 and 1808 eruptions of sao jorge in his 1904 work la montagne pelee et ses eruptions the seminal work of frank alvord perret 1867 1943 on the 1929 32 eruptions of mt pelee and his description of nuees ardentes probably helped reinforce the association between the term and mt pelee

experimental and analytical modeling of basaltic ash explosions at mount etna italy 2001 1 the summer 2001 flank eruption of mount etna ended with repeated basaltic ash explosions the explosions were similar to small scale vulcanian blasts and probably originated when a plug of magma at the top of the conduit became overpressurized we use three independent methods to estimate the overpressure in the plug 1 to determine the pressure differential required to fragment the plug we use a shock tube apparatus to heat and pressurize ballistic blocks at temperature t up to 900 c and pressure p up to 25 mpa and rapidly decompress them to ambient conditions 2 we apply a model to determine the overpressure generated by microlite growth at depth because pyroclasts from the explosions have 35 vol more microlites than preceding strombolian product and 3 we relate the range of ballistic blocks to their exit velocity and with models for vulcanian eruptions the exit velocity to pressure in the conduit experiments and ejecta range bracket the overpressure driving the explosions between 3 and 5 mpa below 2 5 mpa the blocks would not reach the observed range but above 5 mpa the existing blocks with 20 porosity would not survive the explosions crystallization of 35 vol microlites at a depth of 100 m increases the pressure in the plug to 6 mpa above atmospheric enough to drive the explosions with a possible contribution from deeper volatiles combining the different methods we also constrain the exsolved water at fragmentation at 0 05 wt and provide inferences on how the explosions came to an end

determination of the largest clast sizes of tephra deposits for the characterization of explosive eruptions a study of the iavcei commission on tephra hazard modelling the distribution of clasts deposited around a volcano during an explosive eruption typically contoured by isopleth maps provides important insights into the associated plume height wind speed and eruptive style nonetheless a wide range of strategies exists to determine the largest clasts which can lead to very different results with obvious implications for the characterization of eruptive behaviour of active volcanoes the iavcei commission on tephra hazard modelling has carried out a dedicated exercise to assess the influence of various strategies on the determination of the largest clasts suggestions on the selection of sampling area collection strategy choice of clast typologies and clast characterization i e axis measurement and averaging technique are given mostly based on a thorough investigation of two outcrops of a plinian tephra deposit from cotopaxi volcano ecuador located at different distances from the vent these include 1 sampling on a flat paleotopography far from significant slopes to minimize remobilization effects 2 sampling on specified horizontal area sections with the statistically representative sampling area depending on the outcrop grain size and lithic content 3 clast characterization based on the geometric mean of its three orthogonal axes with the approximation of the minimum ellipsoid lithic fragments are better than pumice clasts when present and 4 use of the method of the 50th percentile of a sample of 20 clasts as the best way to assess the largest clasts it is also suggested that all data collected for the construction of isopleth maps be made available to the community through the use of a standardized data collection template to assess the applicability of the new proposed strategy on a large number of deposits and to build a large dataset for the future development and refinement of dispersal models

micro porous pyroclasts reflecting multi vent basaltic andesite plinian eruptions at mt tongariro new zealand abstract mt tongariro is a multi vent volcanic complex in the central north island of new zealand constructed along the axis of an active graben its five largest known explosive eruption episodes occurred 11 000 years ago during a 200 year long paroxysm during these stable plinian and collapsing sub plinian columns erupted from multiple sequential and synchronous vents along the graben axis we examined the spatially varying eruption dynamics during the 200 year paroxysm through the lens of pyroclastic textures each eruption episode produced micro vesicular basaltic andesitic juvenile lapilli with high vesicle number densities and high groundmass crystallinity textural characteristics indicate that pressurisation via second boiling drove eruptions and rhyolite like melt viscosities promoted brittle failure highly variable and mingled textures within individual juvenile lapilli evidence diverse conditions developed across the conduit during the eruption foamy magma rose rapidly through the conduit core driving explosive vigour and dragged and sheared gas poor crystallised magma from the conduit margins consistent with the northward widening graben the most stable plinian eruptions occurred at northern vents under highest extensional stresses and possibly widest most stable conduits by contrast collapsing unstable eruption columns occurred at southern vents where mainly degassed and crystalline magma erupted at lower ejection rates through narrower unstable and shifting conduits these data collectively show how spatial variations in structure and tectonics may strongly influence explosive eruption style

complex magma dynamics at mount etna revealed by seismic thermal and volcanological data 1 three eruptive episodes during the 2006 summit eruptions of mount etna were exceptionally well documented by visual seismic and thermal monitoring the first 16 november was strongly explosive with vigorous strombolian activity and ash emission from multiple vents lava emission and phreatomagmatic explosions generating pyroclastic density currents pdcs the second episode 19 november had a rather weakly explosive component with mild strombolian activity but more voluminous lava emission the third 24 november was a moderately explosive paroxysm with intermittent lava fountaining and generation of a tephra column as well as lava emission and pdcs data recorded by a thermal monitoring camera clearly document the different phases of each paroxysm weather clouds occasionally hampering thermal monitoring the images show a rapid onset of the volcanic activity which during each of the paroxysms reached a peak in eruptive and thermal intensity and then decreased gradually the stronger phreatomagmatic explosions and pdcs on 16 and 24 november did not yield any seismic signature linked to the opening of new vents nor were they associated with peculiar characteristics of the seismic signal nevertheless eruptive styles strombolian activity lava emission and different levels in the intensity of explosive activity were generally well reflected in the amplitude and frequency content of the seismic signal and in the source location of the volcanic tremor centroid throughout the three eruptive episodes this multidisciplinary study therefore not only provides a key to distinguish between endogenous and exogenous origins of the phenomena observed but also documents the complex magma dynamics within the volcano

three years 2011 2013 of eruptive activity at mt etna working modes and timescales of the modern volcano plumbing system from micro analytical studies of crystals abstract tracking magma dynamics at active volcanoes by using the compositional and textural records of minerals is becoming an important aspect of modern volcanology to solve key issues such as temporal relationships between magma recharge and eruption duration of magma storage and final ascent upward to the surface these issues are relevant at mt etna where the style of volcanic activity during the last years showed drastic variations in duration and intensity the paroxysmal activity between 2011 and 2013 at the volcano summit has given the opportunity to investigate the chemical physical processes driving the activity and to fix their spatial temporal relationships into the plumbing system an extensive compositional dataset of plagioclase and olivine crystals from lavas emitted between the 2011 and 2013 at mt etna has been used to constrain modes and timescales of magma storage and transfer to the surface plagioclase crystals display either near equilibrium or disequilibrium textures at the core and rim that indicate complex histories of magma crystallization under variable chemical and physical conditions crystals with different textures have been characterized for major an minor fe and mg and trace elements sr ba textural relationships at the plagioclase cores support the idea that crystals undergo variable decompression rates in the deep parts of the plumbing system fe and mg zoning vs anorthite in correspondence of plagioclase sieve textures at the rim suggest that processes of gas flushing have a dominant role in triggering paroxysmal eruptions determining a sudden intensification of the eruptive activity up to the fountaining phase the sr ba ratio in oscillatory zoned plagioclase revealed the dominant presence into the plumbing system of high sr magma volumes coexisting with low sr magma batches that preserve a geochemical signature similar to that of magmas feeding the pre 1971 activity through sr diffusion modeling in plagioclase the maximum time of magma storage during the considered eruptive period has been evaluated timescales of crystal residence in the plumbing system are short five years to three decades suggesting limited magma storage and faster transfer dynamics to the surface chemical zoning of olivine crystals highlights processes of multi step magma transfer and residence at different levels of the plumbing system the upward migration of magmas occurred primarily through multiple episodes of injection and mixing between five compositionally distinct magmatic environments m i whose p t o 2 characteristics and concentrations in dissolved volatiles were constrained by thermodynamic modeling on the basis of the forsterite contents found at the olivine cores from a deepest reservoir located at depth of 600 mpa the most primitive magma m00 fo 84 moved along dominant pathways intercepting the m0 fo 80 82 at 390 mpa and or m1a fo 78 250 mpa m1b fo 75 140 mpa and finally the shallow m2 fo 70 73 40 mpa storage zones for some eruptive episodes olivine zoning highlights a preferential route of transfer connecting the m00 and m2 storage zones that facilitated the fast migration of primitive magma at shallow depth fe mg diffusion modeling on olivine normal and reverse zoning defines the timescales of magma transfer and storage across these magmatic environments which vary from 1 to 18 months whereas intrusion and mixing by more basic magma into the shallowest reservoir occurred always within 5 months before the eruption relevance of this study mainly relies on the quantification of volcanic processes at depth that may have considerable consequences in development of unusual high energy eruptions at basaltic volcanoes generally acknowledged for their weak to mild explosive activity

the influence of conduit processes on changes in style of basaltic plinian eruptions tarawera 1886 and etna 122 bc basaltic volcanism is most typically thought to produce effusion of lava with the most explosive manifestations ranging from mild strombolian activity to more energetic fire fountain eruptions however some basaltic eruptions are now recognized as extremely violent i e generating widespread phreatomagmatic subplinian and plinian fall deposits we focus here on the influence of conduit processes especially partial open system degassing in triggering abrupt changes in style and intensity that occurred during two examples of basaltic plinian volcanism we use the 1886 eruption of tarawera new zealand the youngest known basaltic plinian eruption and the only one for which there are detailed written eyewitness accounts and the well documented 122 bc eruption of mount etna italy and present new grain size and vesicularity data from the proximal deposits these data show that even during extremely powerful basaltic eruptions conduit processes play a critical role in modifying the form of the eruptions even with very high discharge and presumably ascent rates partial open system behaviour of basaltic melts becomes a critical factor that leads to development of domains of largely stagnant and outgassed melt that restricts the effective radius of the conduit the exact path taken in the waning stages of the eruptions varied in response to factors which included conduit geometry efficiency and extent of outgassing and availability of ground water but a relatively abrupt cessation to sustained high intensity discharge was an inevitable consequence of the degassing processes

pyroclast characteristics of a subaqueous to emergent surtseyan eruption black point volcano california abstract we present the first ever quantitative analysis of pyroclast textures from subaqueous deposits of a surtseyan emergent volcano the volcano black point formed in mono lake s pleistocene precursor lake russell at 13 300 500 bp from an explosive basaltic eruption involving the interaction of shallow lake water 105 m with vesiculating magma the bulk of the edifice comprises unconsolidated tephra and represents submerged stages of eruption thin summit deposits formed during a final phase of emergent eruption and produced a group of low tuff rings lapillus clasts 16 mm to 32 mm and fine ash grains 4 0 0625 mm from the subaqueous deposits have textures that reveal a conduit history of bubble nucleation growth collapse intense microlite crystallisation and magma water interaction lapilli vesicularity ranges broadly to high values up to 89 while vesicle number densities 5 4 102 4 8 104 vesicles per mm3 are comparable to those published for strombolian and plinian basaltic eruptions 1 104 vesicles per mm3 vesicle size and volume distributions suggest continuous bubble nucleation but the suite of data as a whole indicates that a late stage nucleation event played a significant role in shaping the eruption ash grain morphology and surface features indicative of magma water interactions attest to water s role in fragmentation overall the pyroclast textures are consistent with water modification of a rather intense basaltic eruption which might have been of a violent strombolian or plinian style if the eruption had been dry and occurred subaerially

petrologic evidence of a complex plumbing system feeding the july august 2001 eruption of mt etna sicily italy after the major 1991 1993 eruption mt etna resumed flank activity in july 2001 through a complex system of eruptive fissures cutting the ne and the s flanks of the volcano and feeding effusive activity fire fountains strombolian and minor phreatomagmatic explosions throughout the eruption magmas with different petrography and composition were erupted the vents higher than 2 600 m a s l hereafter upper vents uv erupted porphyritic plagioclase rich trachybasalt typical of present day summit and flank activity differently the vents located at 2 550 and 2 100 m a s l hereafter lower vents lv produced slightly more primitive trachybasalt dominated by large clinopyroxene olivine and uncommon minerals for etna such as amphibole apatite and orthopyroxene and containing siliceous and cognate xenoliths petrologic investigations carried out on samples collected throughout the eruption provided insights into one of the most intriguing aspects of the 2001 activity namely the coeval occurrence of distinct magmas we interpret this evidence as the result of a complex plumbing system it consists in two separate magma storage systems a shallow one feeding the activity of the uv and a deeper and more complex storage related to the activity of lv in this deep storage zone which is thermally and compositionally zoned the favourable conditions allow the crystallization of amphibole and the occurrence of cognate xenoliths representing wall cumulates throughout 2001 eruption uv and lv magmas remain clearly distinct and ascended following different paths ruling out the occurrence of mixing processes between them furthermore integrating the 2001 eruption in the framework of summit activity occurring since 1995 we propose that the 2001 magma feeding the vents lower than 2 600 m a s l is a precursor of a refilling event which reached its peak during the 2002 2003 etna flank eruption

a late holocene explosive mafic eruption of villarrica volcano southern andes the chaimilla deposit abstract villarrica chile is one of the most active volcanoes in south america having erupted about 60 times in the last 460 years although its historical eruptive activity has been mainly effusive and weakly explosive it had strong explosive behaviour in postglacial times chaimilla

ash bearing transgressive coastal dune on sao vincente cape verde islands dune history and evidence of explosive volcanic activity around 35 ka climbing transgressive dunes are developed at the relief controlled narrow desert coast of praia grande on sao vicente cape verde islands and this paper describes one of these spectacular coastal dunes the dune was initiated during a low sea level in the late pleistocene the dune migrated landwards presumably during the influence of persistent northeasterly trade winds and it reached the present coast of the island some time before 35 ka when it was covered with volcanic ash volcanic activity in the cape verde archipelago is presently limited to the island of fogo or is submarine however late pleistocene eruptions have been identified on many of the islands but few eruptions younger than 100 ka have been absolutely dated the revelation of a 35 ka pyroclastic deposit on sao vicente is evidence for the continued activity in the northern part of the archipelago the praia grande ash is not readily reconciled with the young strombolian or effusive sao vicente volcanism which is also geochemically different the geochemical composition of the fractionation corrected praia grande ash is compared to a large database for volcanic rocks of the northern part of the cape verde archipelago major and trace elements as well as incompatible element ratios in combination allow identification of the likely source for the praia grande ash as the monte gordo volcano at the island sao nicolau 70 km to the se and the eruption possibly was of vei 5

paleo earthquake signatures from the south wagad fault swf wagad island kachchh gujarat western india a potential seismic hazard abstract in last 500 years kachchh experienced several large magnitude earthquakes 6 0 m 7 8 however not all accompanied surface rupture the 1819 allah bund earthquake mw7 8 accompanied surface rupture whereas the 2001 bhuj event mw7 6 occurred at a depth of 23 km on e w striking south dipping thrust fault remained blind discontinuities between the denser brittle basement and overlying ductile softer mesozoic tertiary quaternary succession resulted in a different geometry of faulting normal faults associated with rift were reactivated as reverse faults during inversion tectonics propagated in sedimentary succession and arrested thrust ramps developed along the discontinuities accompanied surface ruptures folded structures along the south wagad fault swf an active thrust exhibits lateral propagation of fold segments and linkage suggestive of fault related fold growth paleoseismic investigations revealed evidence of at least three paleo earthquakes event i occurred before bce 5080 event ii between bce 4820 and 2320 and was probably responsible for a massive damage at dholavira harappan site event iii was between bce 1230 and 04 most likely caused severe damage to dholavira archaeo seismological quality factor aqf of 0 5 suggests that the dholavira is vulnerable to earthquakes from nearby active faults with 1500 2000 yr of recurrence interval occurrence of a large magnitude earthquake on swf cannot be ruled out

the onset of an eruption selective assimilation of hydrothermal minerals during pre eruptive magma ascent of the 2010 summit eruption of eyjafjallajokull volcano iceland abstract the complex processes occurring in the initial phases of an eruption are often recorded in the products of its opening stage which are usually characterized by small volume and limited dispersal and thus generally poorly studied the 2010 eruption of eyjafjallajokull iceland represents a unique opportunity for these investigations thanks to the good preservation of tephra deposits within the ice snow pack a detailed geochemical investigation on the glassy groundmass of single ash clasts disclosed a population of fragments with unusual high 87 sr 86 sr up to 0 70668 for icelandic magmatism and anomalous elemental composition with respect to most of the juvenile material of the eruption this suggests that during its rise before intruding into the ice cover magma at a dyke tip selectively assimilated hydrothermal minerals with seawater related high sr isotopic ratios zeolites silica phases anhydrite hosted in altered volcanic epiclastic rocks according to the observed precursory seismicity only restricted to few hours before the onset of the eruption this process could have accompanied subcritical aseismic fracture opening during the days before the eruption possibly related to stress corrosion cracking processes which enhanced the partial dissolution melting and subsequent selective assimilation of the host rocks

mechanisms for ground surface fracturing and incipient slope failure associated with the 2001 eruption of mt etna italy analysis of ephemeral field data abstract during the july august 2001 eruption of mt etna development of extensional fractures faults and grabens accompanied magma intrusion and subsequent volcanic activity during the first days of the eruption we performed an analysis of attitude displacement and propagation of fractures and faults exposed on the ground surface in two sites torre del filosofo and valle del leone located along the same fracture system in the region surrounding the valle del bove depression on the eastern flank of mt etna fractures and faults formed as the consequence of a shallow intruding dyke system that fed the several volcanic centres developed along the fracture system the investigated sites differ in slope attitude and in geometrical relationships between fractures and slopes in particular the fracture system propagated parallel to the gentle slope

airborne i doas measurements at mt etna bro and oclo evolution in the plume abstract spatial distributions of bromine monoxide bro chlorine dioxide oclo and sulfur dioxide so 2 were determined in the volcanic emissions of mt etna on 8th and 9th of july 2011 by airborne imaging differential optical absorption spectroscopy ai doas slant column densities scds in units of molec cm 2 of up to 4 2 10 14 for bro 1 5 10 14 for oclo and 4 6 10 18 for so 2 were detected assuming so 2 to be a stable tracer to overcome dilution effects measurements of bro so 2 and oclo so 2 ratios from distances of 1 19 km to the summit crater region were used to investigate the evolution of bro and oclo within corresponding plume ages of 2 34 min along the centerline of the plume relatively constant bro so 2 ratios of 1 4 10 4 and 2 0 10 4 were detected on 8th and 9th of july 2011 respectively furthermore the bro so 2 ratio was investigated along several cross sections of the volcanic plume on both days significant increases by a factor of 2 3 in the bro so 2 ratio from the center to the edge of the plume were seen from simultaneous measurements of bro and oclo the mixing ratios of clo could be inferred to range from about 80 to 300 ppt in addition decreases in the bro so 2 ratio with time could be observed by measurements three to four hours before the culmination of a paroxysm at mt etna on 9th july 2011

modeling the effects of eruptive and seismic activities on flank instability at mount etna italy 1 the identification and evaluation of trigger mechanisms for volcano flank instabilities and or collapse represent a key issue for risk assessment in densely populated volcanic areas as well as in long distance settings particularly in case of island or coastal volcanoes here we address quantitatively the effects of external seismic and inner magmatic forcing on the stress strain state associated to flank instabilities at mount etna sicily southern italy by means of a 2 d finite difference method numerical modeling modeled seismic actions include strong near field strong far field and low magnitude near field earthquakes magmatic actions consider the inner pressure changes induced by energetic lava fountains in the summit crater area and subvertical and oblique dike ascent below the summit area model results are validated in light of available monitoring data and recent eruptive activity numerical results show that the main strain effects are produced by high magnitude near field earthquakes expected return time of 103 yrs and by vertical uprise of a magma dike below the volcano summit area maximum displacements in the order of tens of centimeters may involve the summit area up to some 106 m3 m over some kilometers laterally stress releases up to 107 pa may affect a limited portion of the magmatic conduit thus favoring major effusive flank eruptions major catastrophic events such as volcano flank collapse should not be expected by applying either individually or combined the aforementioned actions

tephrostratigraphy and provenance from iodp expedition 352 izu bonin arc tracing tephra sources and volumes from the oligocene to recent provenance studies of widely distributed tephras integrated within a well defined temporal framework are important to deduce systematic changes in the source scale distribution and changes in regional explosive volcanism here we establish a robust tephro chronostratigraphy for a total of 157 marine tephra layers collected during iodp expedition 352 we infer at least three major phases of highly explosive volcanism during oligocene to pleistocene time provenance analysis based on glass composition assigns 56 of the tephras to a japan source including correlations with 12 major and widespread tephra layers resulting from individual eruptions in kyushu central japan and north japan between 115 ka and 3 5 ma the remaining 101 tephras are assigned to four source regions along the izu bonin arc one of exclusively oligocene age is proximal to the bonin ridge islands two reflect eruptions within the volcanic front and back arc of the central izu bonin arc and a fourth region corresponds to the northern izu bonin arc source first order volume estimates imply eruptive magnitudes ranging from 6 3 to 7 6 for japan related eruptions and between 5 5 and 6 5 for ibm eruptions our results suggest tephras between 30 and 22 ma that show a subtly different izu bonin chemical signature compared to the recent arc after a 11 m y gap in eruption tephra supply from the izu bonin arc predominates from 15 to 5 ma and finally a subequal mixture of tephra sources from the palaeo honshu and izu bonin arcs occurs within the last 5 ma

a continuous palaeosecular variation record of the last four millennia from the augusta bay sicily italy summary we present a high resolution palaeomagnetic and rock magnetic study of two cores ms06 and ms06 sw 6 7 and 1 1 m long respectively collected at 72 m below sea level in the augusta bay shelf eastern sicily ionian sea italy about 2 3 km from the coastline geophysical surveying carried out in the sampling area highlighted the presence of a homogeneous sedimentary sequence that most likely was deposited after the last glacial maximum and was not affected by anthropogenic disturbances the two cores penetrated a monotonous mud sedimentary sequence interrupted at 3 m depth by a 3 4 cm thick volcanic sandy layer that is correlated with the tephra fallout deposit produced by the 122 bc plinian eruption of mt etna this tephra along with radiocarbon dating of nine marine shells and with radioactive tracers for the uppermost 0 3 m 210pb and 137cs provide the chronological constraints for the stratigraphic sequence that resulted younger than 4500 yr bp palaeomagnetic and rock magnetic data show that the sample sequence is magnetically homogeneous a single peak of high magnetic mineral concentration is present and corresponds to the volcanic sandy layer palaeomagnetic data allowed the identification of a well defined characteristic remanent magnetization that provides a high resolution record of palaeosecular variation psv at the sampling site the reconstructed psv curve is in good agreement with the available regional reference psv curves and with the prediction from recent psv modelling for europe the palaeomagnetic data obtained in this study on the one hand support and refine the age model for the cores derived from other independent constraints and on the other hand provide an original high resolution psv curve that can serve as a reference for the central mediterranean over the last 4 ka

explosive eruption of a picrite the 3930 bp subplinian eruption of etna volcano italy 1 we report on a subplinian eruption fed by a picritic magma that occurred 3930 60 bp at etna volcano the eruption produced a fallout deposit of 0 183 km3 0 055 km3 dre widely dispersed eastward which represents a marker bed for the holocene stratigraphy of the volcano tephra have a composition of nearly primary magma owing to their high mg 72 79 glass geothermometry indicates eruptive temperatures 1159 1171 c 100 higher than those measured in recent eruptions high volatile content and unusual enrichment of lil elements in feeding magma both suggest addition of fluids in the source zone accounting for a large production of highly buoyant fast rising melt vigorous degassing of volatile rich picritic magma is responsible for the explosive nature of this eruption

discovery of a plinian basaltic eruption of roman age at etna volcano italy basaltic plinian eruptions are rare and poorly known volcanic phenomena etna is an active basaltic volcano the activity of which is dominated by effusive eruptions that represent a continuous threat to a large populated area we report on a plinian eruption of basaltic composition that occurred in 122 b c lapilli fallout caused extensive damage to the southern flank of the volcano the discovery of this large explosive eruption raises important issues for previous hazard assessment at etna and other basaltic volcanoes an effusive basaltic volcano generally nonhazardous for humans can become very dangerous

geological and geomorphological evolution of the etna volcano ne flank and relationships between lava flow invasions and erosional processes in the alcantara valley italy abstract in this paper the interrelationships between volcanic activity and fluvial events in the alcantara valley are investigated based on the correlation between the stratigraphy of the ne flank of mt etna and subsurface data the geological and geomorphological evolutions of the valley are reconstructed new 1 10 000 scale geological mapping shows that the bulk of this sector of the volcano is made up of the ellittico volcano lava flows though they are widely covered by the products of the eruptive activity of the last 15 ka the present day morphological setting of the alcantara valley is the result of two main evolutionary phases initiated during the activity of the ellittico volcano only one lava flow invasion of the valley floor occurred in the first phase this phenomenon was followed by a long period of erosional processes leading to the entrenchment of the drainage pattern and the erosion of the ellittico lava flow about 20 25 ka ago an important change in the frequency of the lava flow invasions into the valley occurred associated with the final stage of the ellittico volcano activity marking the beginning of the second phase during this phase volcanic processes became predominant with respect to other morphogenetic processes in the alcantara valley lava flows coming from the ne flank of the ellittico volcano caused a radical modification of the morphological setting of this area even though only one lava flow emitted by an eruptive fissure located within the valley partially filled the riverbed during the eruptive activity of the last 15 ka the complete filling of the alcantara valley floor occurred in particular between 15 and 7 ka a lava flow originated from the mt moio scoria cone filled the valley floor for a distance of about 9 km following a short period of erosion an eruptive fissure located within the valley generated a 20 21 km long lava flow that was channelled along the full extent of the alcantara valley and stretches for about 3 km offshore in the ionian sea in the last 7 ka lava flows originating from the ne rift zone produced only temporary damming of the riverbed without any important contribution to the filling of the alcantara valley

magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallization basaltic eruptions are the most common form of volcanism on earth and planetary bodies the low viscosity of basaltic magmas inhibits fragmentation which favours effusive and lava fountaining activity yet highly explosive hazardous basaltic eruptions occur the processes that promote fragmentation of basaltic magma remain unclear and are subject to debate here we used a numerical conduit model to show that a rapid magma ascent during explosive eruptions produces a large undercooling in situ experiments revealed that undercooling drives exceptionally rapid in minutes crystallization which induces a step change in viscosity that triggers magma fragmentation the experimentally produced textures are consistent with basaltic plinian eruption products we applied a numerical model to investigate basaltic magma fragmentation over a wide parameter space and found that all basaltic volcanoes have the potential to produce highly explosive eruptions the critical requirements are initial magma temperatures lower than 1 100 c to reach a syn eruptive crystal content of over 30 vol and thus a magma viscosity around 105 pa s which our results suggest is the minimum viscosity required for the fragmentation of fast ascending basaltic magmas these temperature crystal content and viscosity requirements reveal how typically effusive basaltic volcanoes can produce unexpected highly explosive and hazardous eruptions volcanoes that typically erupt effusively can generate highly explosive eruptions of basaltic lava under specific temperature and viscosity conditions suggest crystallization experiments combined with numerical models of magma fragmentation

degassing driven crystallisation in basalts abstract syn eruptive crystallisation can drastically increase magma viscosity with profound implications for conduit dynamics lava emplacement and volcanic hazards there is growing evidence that crystallisation is not only cooling driven but can also occur almost isothermally during decompression induced degassing on ascent from depth here we review field and experimental evidence for degassing driven crystallisation in a range of magma compositions we then present new results showing for the first time experimental evidence for this process in basaltic magma our experiments use simultaneous thermogravimetric analysis and differential scanning calorimetry coupled with mass spectrometry tga dsc ms to monitor degassing patterns and thermal events during heating and cooling of porphyritic basaltic samples from mt etna italy the partly degassed samples which contained 0 39 0 81 wt total volatiles in the glass fraction were subjected to two cycles of heating from ambient to 1250 c on the first heating tga data show that 30 60 of the total volatiles degassed slowly at

abnormal carbonate diagenesis in holocene late pleistocene sapropel associated sediments from the eastern mediterranean evidence from emiliania huxleyi coccolith morphology in studying the holocene late pleistocene record of the eastern mediterranean considerable emiliania huxleyi size shape variation not clearly assignable to primary or secondary calcification was observed accordingly different morphotypes were distinguished by light microscope lm a subsequent scanning electron microscope sem analysis of selected samples has indicated that emiliania huxleyi coccoliths are variably affected by carbonate diagenesis in these sediments a series of diagenetic stages were qualitatively defined comprising well preserved specimens three overgrowth og1 to og3 and one etching e1 stage comparing sem and lm observations a tentative correlation between the e huxleyi calcified lm morphotypes and e huxleyi sem overgrowth stages is proposed here our study not only indicates that emiliania huxleyi coccoliths are strongly influenced by carbonate diagenesis but also that they show effects of carbonate precipitation and dissolution much more clearly than other coccoliths the relative abundances of the different lm morphotypes were used to define an e huxleyi overgrowth index exo that qualitatively estimates carbonate precipitation dissolution on coccoliths in this sediment this resulted in definition of five diagenetic intervals d1 to d5 deposition of sapropel s1 was a time of good preservation with variable dissolution and no overgrowth of e huxleyi coccoliths whereas calcite overgrowth was high during the last glacial maximum lgm and interglacial period and to a lesser extent during the younger dryas and through the last 5 ka d 2004 elsevier b v all rights reserved

reconstructing eruptions from historical accounts makaturing c 1765 philippines abstract for some volcanoes the only evidence for past eruption is provided by historical accounts when interpreted carefully these have the potential to be a rich source of information and yet they have so far been under utilised in reconstructing eruption histories the navigator thomas forrest describes a large eruption at makaturing volcano southern philippines in approximately 1765 that he considers the catalyst for the local iranun population transitioning from an agrarian society to long distance piracy and slave raiding within the historical literature the eruption is attributed to large scale physical impacts around the volcano and disruptions to trading routes and livelihoods that ultimately changed the course of southeast asia s history however no such eruption or impacts are recognised in the scientific literature or in eruption databases and fieldwork to the region remains difficult here we reinterpret the account of forrest from a multi disciplinary perspective with a historian and physical volcanologists working together to incorporate the greatly needed local context into identifying credible volcanic processes and impacts associated with the reported activity we used a novel approach to eruption reconstruction by cross referencing deposits and impacts inferred from the historical record with stochastic tephra dispersal modelling that considered multiple eruption sources and characteristics we found that forrest s account was best characterised by an eruption of vei 4 between may and october with plume heights in the range of 12 to 16 km while at least one eruption of this size was required to reproduce the impacts described in the historical record it may have formed part of a longer sequence of multiple repeated eruptions in this way such an eruption could have acted as a tipping point for a local population already on the verge of socio political and economic collapse disproportionately affecting regions on a much larger scale than the reported deposits suggest there remains a disconnect between the eruption characteristics recorded in historical accounts and those reproduced by numerical modelling for which we propose alternative interpretations of the historical record unfortunately given the minimal details available about the eruption this discordance is unlikely to be resolved even when geological studies are possible however a valuable benefit of the probabilistic modelling approach presented here is that it highlights the likely direction of tephra dispersal and deposition during a future eruption of makaturing supporting rapid tephra hazard assessment in the event of future unrest

buoyancy controlled eruption of magmas at mt etna buoyancy controls the ability of magma to rise its ascent rate and the style of the eruptions geophysical geological and petrological data have been integrated to evaluate the buoyancy of magmas at mt etna the density difference between host rocks and magmas is mainly related to the amount of h2o dissolved in the magma and to the bubble liquid separation processes in the depth interval 22 2 km b s l highly hydrated h2o 3 basaltic magmas or mixtures of bubbles liquid have positive buoyancy and rise rapidly conversely bubble depleted liquids with an intermediate h2o content 1 5 having neutral buoyancy will spread out and form magmatic reservoirs at different depths until cooling crystallization further modify composition and density these different processes account for the magma compositions location of magmatic reservoirs as determined by geophysical methods and the complex eruptive cycles slow effusions fire fountains and plinian eruptions that have been observed in the history of the volcano