has the ozone hole contributed to increased antarctic sea ice extent 1 since the 1970s sea ice extent has decreased dramatically in the northern hemisphere and increased slightly in the southern hemisphere a difference that is potentially explained by ozone depletion in the southern hemisphere stratosphere in this study we consider the impact of stratospheric ozone depletion on antarctic sea ice extent using a climate model forced with observed stratospheric ozone depletion from 1979 to 2005 contrary to expectations our model simulates a year round decrease in antarctic sea ice due to stratospheric ozone depletion the largest percentage sea ice decrease in our model occurs in the austral summer near the coast of antarctica due to a mechanism involving offshore ekman sea ice transport the largest absolute decrease is simulated in the austral winter away from the coast of antarctica in response to an ocean warming that is consistent with a poleward shift of thc large scale pattern of sea surface temperature our model results strongly suggest that processes not linked to stratospheric ozone depletion must be invoked to explain the observed increase in antarctic sea ice extent

lava fountain heights at pu u o o kilauea hawaii indicators of amount and variations of exsolved magma volatiles we review the factors determining lava fountain heights in hawaiian style basaltic eruptions such as those occurring during the recent series of eruptive episodes at the pu u o o vent east rift zone of kilauea volcano hawaii numerical solutions to the equations describing the fluid dynamics of such eruptions predict that lava fountain heights which are indicators of the velocity of magmas in vents should be controlled much more strongly by amounts of exsolved volatiles than by any other factors the next most important factor is the width of the conduit system which determines frictional losses and can be characterized by the volume flux of magma the diameter of the surface vent required to accommodate a given discharge i e instantaneous volume rate of eruption is also a function of exsolved magma volatile content but is less dependent on this factor than is the fountain height we simulate fountain heights for typical discharges at pu u o o and find implied exsolved gas contents very close to those determined by other methods the corresponding predicted vent diameters are comparable with and somewhat smaller than the observed diameter of the pu u o o vent the discrepancy is probably a consequence of processes occurring in the lava pond which is present over the vent during eruptions the variation of fountain height with time during eruptive episodes can be used as a measure of changing exsolved magma volatile content which can be related to processes occurring in the subsurface dike system

seasonal relationships between large scale climate variability and antarctic sea ice concentration abstractthe observed relationships between anomalous antarctic sea ice concentration sic and the leading patterns of southern hemisphere sh large scale climate variability are examined as a function of season over 1980 2008 particular emphasis is placed on 1 the interactions between sic the southern annular mode sam and el nino southern oscillation enso and 2 the contribution of these two leading modes to the 29 yr trends in sea ice regression composite and principal component analyses highlight a seasonality in sh sea ice atmosphere interactions whereby antarctic sea ice variability exhibits the strongest linkages to the sam and enso during the austral cold season months as noted in previous work a dipole in sic anomalies emerges in relation to the sam characterized by centers of action located near the bellingshausen weddell and amundsen eastern ross seas the structure and magnitude of this sic dipole is found to vary considerably as a function of season consistent with the season

antarctic sea ice climatology variability and late twentieth century change in ccsm4 abstracta preindustrial control run and an ensemble of twentieth century integrations of the community climate system model version 4 ccsm4 are evaluated for antarctic sea ice climatology modes of variability trends and covariance with related physical variables such as surface temperature and sea level pressure compared to observations the mean ice cover is too extensive in all months this is in part related to excessively strong westerly winds over 50 60 s which drive a large equatorward meridional ice transport and enhanced ice growth near the continent and also connected with a cold bias in the southern ocean in spite of these biases in the climatology the model s sea ice variability compares well to observations the leading mode of austral winter sea ice concentration exhibits a dipole structure with anomalies of opposite sign in the atlantic and pacific sectors both the el nino southern oscillation and the southern annular mode sam project onto this mode in twentieth century inte

the 1891 submarine eruption offshore pantelleria island sicily channel italy identification of the vent and characterization of products and eruptive style high resolution bathymetry and seafloor sampling have been used to characterize the 1891 submarine eruption of the pantelleria volcanic complex this submarine eruption has been documented mainly by historical reports describing basaltic scoria bombs floating on the sea surface i e lava balloons in this study the 1891 eruptive vent has been identified as a small cone volume of 700 000 m3 rising 90 m from 350 m w d and located within a newly discovered submarine volcanic field covering a wide area offshore from the nw coast of pantelleria recently kelly et al 2012 confirmed this location by a multibeam and rov survey pyroclasts from the 1891 eruption crop out directly on the seafloor and are fresh scoria clasts i e small bombs bomb fragments and lapilli and glass ash sized grains both have been characterized in their morphology textures and geochemistry the distinctive vesicularity and crystallization characteristics displayed by the scoriaceous pyroclasts reflect modes of degassing in both syn and posteruptive regimes these characteristics along with the distribution of deposits suggest for the strongest eruptive phase of the 1891 eruption a style analogous to hawaiian fountaining glass grains from a buoyant plume were dispersed northward from the vent up to distances of 1 5 km redirected by the levantine intermediate water the identification of the 1891 submarine eruptive vent offshore pantelleria as well as the features of erupted pyroclasts improve our knowledge of submarine explosive eruptions that occur at shallow intermediate depths and among these of the rare eruptions producing lava balloons

spatial patterns of variability in antarctic surface temperature connections to the southern hemisphere annular mode and the southern oscillation 1 the 17 year 1982 1998 trend in surface temperature shows a general cooling over the antarctic continent warming of the sea ice zone with moderate changes over the oceans warming of the peripheral seas is associated with negative trends in the regional sea ice extent effects of the southern hemisphere annular mode sam and the extrapolar southern oscillation so on surface temperature are quantified through regression analysis positive polarities of the sam are associated with cold anomalies over most of antarctica with the most notable exception of the antarctic peninsula positive temperature anomalies and ice edge retreat in the pacific sector are associated with el nino episodes over the past two decades the drift towards high polarity in the sam and negative polarity in the so indices couple to produce a spatial pattern with warmer temperatures in the antarctic peninsula and peripheral seas and cooler temperatures over much of east antarctica

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

externally triggered renewed bubble nucleation in basaltic magma the 12 october 2008 eruption at halema uma u overlook vent kīlauea hawai i usa 1 from october 2008 until present dozens of small impulsive explosive eruptions occurred from the overlook vent on the southeast side of halema uma u crater at k lauea volcano usa these eruptions were triggered by rockfalls from the walls of the volcanic vent and conduit onto the top of the lava column here we use microtextural observations and data from clasts erupted during the well characterized 12 october 2008 explosive eruption at halema uma u to extend existing models of eruption triggering we present a potential mechanism for this eruption by combining microtextural observations with existing geophysical and visual data sets we measure the size and number density of bubbles preserved in juvenile ejecta using 2d images and x ray microtomography our data suggest that accumulations of large bubbles with diameters of 50 m to at least millimeters existed at shallow levels within the conduit prior to the 12 october 2008 explosion furthermore a high number density of small bubbles 50 m is measured in the clasts implying very rapid nucleation of bubbles visual observations combined with preexisting geophysical data suggest that the impact of rockfalls onto the magma free surface induces pressure changes over short timescales that 1 nucleated new additional bubbles in the shallow conduit leading to high number densities of small bubbles and 2 expanded the preexisting bubbles driving upward acceleration the trigger of eruption and bubble nucleation is thus external to the degassing system

subaqueous basaltic magmatic explosions trigger phreatomagmatism a case study from askja iceland abstract sequences of basaltic pillow lavas that transition upward with systematic gradation from pillow fragment breccias to fluidal bomb bearing breccias to bomb bearing lapilli tuffs are common at askja volcano iceland based on the detailed textural investigation of three of these sequences we argue that they record temporally continuous transitions from effusive to explosive products that were erupted from and deposited at or near a single subaqueous vent the recognition of such sequences is important as they provide evidence for controls on the onset of explosive activity in subaqueous environments such investigations are complicated by the interplay of magmatic gas expansion and phreatomagmatic and mechanical granulation fragmentation mechanisms in the subaqueous eruptive environment all of the sequences studied at askja have textural componentry and sedimentological characteristics suggestive of a close genetic and spatial relationship between the pillow lavas and all of the overlying glassy clastic deposits the identification of magma fragmentation signatures in pyroclasts was accomplished through detailed textural studies of pyroclasts within the full range of grain sizes of a given deposit i e bomb blocks lapilli and fine ash these textural characteristics were compared and evaluated as discriminators of fragmentation in pyroclastic deposits the presence of angular vitric clasts within the breccia and lapilli tuff displaying fragile glassy projections indicates little or no post depositional textural modification a shift in vesicle and clast textures between the pillow lavas and the large concentration of fluidal bombs in the breccia indicates that the phreatomagmatic explosions were initially triggered by magmatic vesiculation the initial magmatic gas expansion may have been triggered by depressurization caused by the drainage of the ice confined lake surrounding askja the fuel coolant interactions fcis of the more efficient phreatomagmatic explosions were enabled by the increase in the surface area to volume ratio of the fluidal bombs in the water producing a premix of magma and water the onset and increasing influence of phreatomagmatic fragmentation is preserved in the presence of very fine blocky ash particles and diminished presence of larger particles such as fluidal bombs the textural sedimentological and environmental characteristics of these deposits suggest that phreatomagmatic explosions can be triggered by initial magmatic gas expansion but that it is likely one of many mechanisms for triggering such explosions

phreatomagmatic vs magmatic eruptive styles in maar diatremes a case study at twin peaks hopi buttes volcanic field navajo nation arizona the hopi buttes volcanic field hbvf is located on the colorado plateau northern arizona in this miocene volcanic field the erosion level increases southward allowing the study of maar diatreme volcanoes from top posteruptive crater infill and ejecta ring to bottom lower diatreme the twin peaks volcanic complex consists mostly of two hills north peak and south peak with thick lavas at their summits and pyroclastic rocks underneath in the hbvf such volcanic remnants have received little scientific attention so far despite their relative abundance our field observations allow us to interpret the north and south peaks as remnants of two maar diatreme volcanoes which evolved into lava lakes filling the craters within the complex we distinguish four volcanic units from unit 1 at the bottom to unit 4 at the top on the basis of the field description of the deposits and the componentry measurements we suggest that unit 1 is phreatomagmatic unit 2 is phreato strombolian with mixed phreatomagmatic and strombolian characteristics unit 3a is phreato hawaiian with mixed phreatomagmatic and hawaiian characteristics unit 3b is hawaiian formed by lava fountains and unit 4 consists of lava lakes filling the maar craters there is therefore a progressive evolution from a purely phreatomagmatic eruptive style which excavated the craters and diatremes and partly filled them to magmatic explosive to nonexplosive eruptive styles which filled the maar craters up to the pre eruptive surface we discuss traditional criteria used to distinguish phreatomagmatic from magmatic eruptive styles in ultramafic to mafic maar diatreme volcanoes

what makes hydromagmatic eruptions violent some insights from the keanakāko i ash kilauea volcano hawai i abstract volcanic eruptions at the summit of kilauea volcano hawai i are of two dramatically contrasting types 1 benign lava flows and lava fountains and 2 violent mostly prehistoric eruptions that dispersed tephra over hundreds of square kilometers the violence of the latter eruptions has been attributed to mixing of water and magma within a wet summit caldera however magma injection into water at other volcanoes does not consistently produce widespread tephras to identify other factors that may have contributed to the violence of these eruptions we sampled tephra from the keanak ko i ash the most recent large hydromagmatic deposit and measured vesicularity bubble number density and dissolved volatile content of juvenile matrix glass to constrain magma ascent rate and degree of degassing at the time of quenching bubble number densities 9 10 4 1 10 7 cm 3 of tephra fragments exceed those of most historically erupted kilauean tephras 3 10 3 1 8 10 5 cm 3 and suggest exceptionally high magma effusion rates dissolved sulfur average 330 ppm and water 0 15 0 45 wt concentrations exceed equilibrium saturation values at 1 atm pressure 100 150 ppm and 0 09 respectively suggesting that clasts quenched before equilibrating to atmospheric pressure we interpret these results to suggest rapid magma injection into a wet crater perhaps similar to continuous uprush jets at surtsey estimates of reynolds number suggest that the erupting magma was turbulent and would have mixed with surrounding water in vortices ranging downward in size to centimeters such fine scale mixing would have ensured rapid heat exchange and extensive magma fragmentation maximizing the violence of these eruptions

a new method for identifying the pacific south american pattern and its influence on regional climate variability abstractthe pacific south american psa pattern is an important mode of climate variability in the mid to high southern latitudes it is widely recognized as the primary mechanism by which el nino southern oscillation enso influences the southeast pacific and southwest atlantic and in recent years has also been suggested as a mechanism by which longer term tropical sea surface temperature trends can influence the antarctic climate this study presents a novel methodology for objectively identifying the psa pattern by rotating the global coordinate system such that the equator a great circle traces the approximate path of the pattern the identification algorithm utilizes fourier analysis as opposed to a traditional empirical orthogonal function approach the climatology arising from the application of this method to era interim reanalysis data reveals that the psa pattern has a strong influence on temperature and precipitation variability over west antarctica and the antarctic peninsula and on sea i

monitoring the cooling of the 1959 kīlauea iki lava lake using surface magnetic measurements lava lakes can be considered as proxies for small magma chambers offering a unique opportunity to investigate magma evolution and solidification repeated magnetic ground surveys over more than 50 years each show a large vertical magnetic intensity anomaly associated with k lauea iki crater partly filled with a lava lake during the 1959 eruption of k lauea volcano island of hawai i the magnetic field values recorded across the k lauea iki crater floor and the cooling lava lake below result from three simple effects the static remnant magnetization of the rocks forming the steep crater walls the solidifying lava lake crust and the hot but shrinking paramagnetic non magnetic lens 540 c we calculate 2d magnetic models to reconstruct the temporal evolution of the geometry of this non magnetic body its depth below the surface and its thickness our results are in good agreement with the theoretical increase in thickness of the solidifying crust with time using the 2d magnetic models and the theoretical curve for crustal growth over a lava lake we estimate that the former lava lake will be totally cooled below the curie temperature in about 20 years this study shows the potential of magnetic methods for detecting and monitoring magmatic intrusions at various scales

eruption dynamics of the 23 february 2013 event at mt etna abstract volcanic activity at mt etna in the last decade has mostly been manifested by sequences of short paroxysmal episodes characterised by powerful lava fountains and high eruption columns on the 23 february 2013 an exceptionally intense episode occurred at the new south east crater producing a fountain 800 m high among the highest ever recorded at etna and a 9 km eruption column that dispersed ash 400 km from the vent textural and petrographic analyses of lapilli revealed that magma erupted during the high intensity phase is characterised by low microlite contents

a zonal wave 3 index for the southern hemisphere 1 in this study 500 hpa geopotential heights from the ncar ncep reanalysis are used to calculate an index describing the spatial and temporal characteristics of zonal wave three zw3 in the high latitude southern hemisphere atmosphere the index spans the period 1958 2001 wavelet analysis of the index shows the strong interannual variation which is characteristic of zw3 and also reveals significant high amplitude decadal scale variation this interannual variation takes the form of marked fluctuation in sign and magnitude of the index it appears to occur when there are rapid changes from strongly meridional to strongly zonal flow or vice versa initial indications are that some of this variability may be associated with enso events

subplinian monogenetic basaltic eruption of sunset crater arizona usa sunset crater volcano located 25 km northeast of downtown flagstaff arizona usa in the san francisco volcanic field represents an interesting case of highly explosive monogenetic volcanism sunset crater is a young ca 1085 ce scoria cone 290 m high that produced 0 52 km3 dense rock equivalent dre of basaltic magma 0 16 0 12 and 0 24 km3 dre for the scoria cone lava flows and tephra deposit respectively the activity developed in three distinct phases an initial fissure phase followed by a highly explosive phase and a final low explosivity waning phase the first phase was characterized by the opening of a 10 kmlong fissure which produced the gyp crater spatter mounds and the vent 512 lava flow 10 km se of the main scoria cone followed by lava fountaining activity that produced the first tephra layer unit 1 0 01 km3 dre during the second highly explosive phase the activity migrated to the northwest to evolve into a single vent eruption which formed the main scoria cone the central vent activity was initially characterized by variable eruptive styles which started the process of cone building including deposition of a second tephra layer unit 2 0 01 km3 dre and the effusion of the two main lava flows bonito and kana a following the initiation of effusive activity the eruption increased in explosivity to produce three subplinian tephra layers from the central vent units 3 4 and 5 which emitted more than 0 22 km3 dre of basalt with associated eruption columns 20 km high by the end of this phase the kana a lava flow was almost completely emplaced but the bonito flow continued to grow forming a 3 km diameter flow field a final waning phase produced several tephra units commonly discontinuous and reworked with 0 01 km3 dre cumulative volume the comparatively large volume of tephra the high eruptive columns and high mass eruption rates make sunset crater the most explosive monogenetic eruption studied to date volcano explosivity index vei 3 4 sunset crater volcano represents an interesting case of monogenetic volcanism in that its activity was characterized by highly explosive eruptive phases up to subplinian in scale and intermittent episodes of lava effusion that heavily affected prehistoric communities in the area explosive basaltic volcanism should be considered when assessing volcanic hazards in continental settings such as in the western united states

vapor phase cristobalite as a durable indicator of magmatic pore structure and halogen degassing an example from white island volcano new zealand vesicles in volcanic rocks are physical records of magmatic degassing however the interpretation of their textures is complicated by resorption coalescence and collapse we discuss the textural significance of vesicle hosted vapor phase cristobalite high t low p sio2 polymorph and its utility as a complement to textural assessments of magmatic degassing using a representative dacite bomb erupted from white island volcano new zealand in 1999 imaging in 2d sem and 3d ct shows the bomb to have 56 bulk porosity almost all of which is connected 99 and devoid of sio2 phases the remaining 1 of porosity is in isolated sub spherical vesicles that have corroded walls and contain small 30 m across prismatic vapor phase cristobalite crystals 98 4 0 4 wt sio2 with diagnostic laser raman spectra halogen degassing models show vapor phase cristobalite to be indicative of closed system chlorine and fluorine partitioning into h2o rich fluid in isolated pores at white island this occurred during shallow 100s of meters ascent and extensive 50 groundmass crystallization associated with slow cooling in a volcanic plug pristine textures in this white island bomb demonstrate the link between pore isolation and vapor phase cristobalite deposition we suggest that because these crystals have higher preservation potential than the bubbles in which they form they can serve as durable qualitative textural indicators of halogen degassing and pre quench bubble morphologies in slowly cooled volcanic rocks e g lava flows and domes even where emplacement mechanisms have overprinted original bubble textures

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

explosive volcanic eruptions ix the transition between hawaiian style lava fountaining and strombolian explosive activity the commonest eruption styles of basaltic volcanoes involve hawaiian lava fountaining or intermittent strombolian explosions we investigate the ways in which magma rise speed at depth magma volatile content and magma viscosity control which of these eruption styles takes place we develop a model of the degree of coalescence between gas bubbles in the magma which allows us to simulate the transition between the two extreme styles of activity we find that magma rise speed is the most important factor causing the transition with gas content and viscosity also influencing the rise speed at which the transition occurs counter to intuitive expectations a decrease in gas content does not cause a transition from hawaiian to strombolian activity but instead causes a transition to passive effusion of vesicular lava rather a change from hawaiian to strombolian style requires a significant reduction in magma rise speed

contrasting mechanisms of magma fragmentation during coeval magmatic and hydromagmatic activity the hverfjall fires fissure eruption iceland growing evidence for significant magmatic vesiculation prior to magma water interaction mwi has brought into question the use of diagnostic features such as low vesicularities and blocky morphologies to identify hydromagmatic pyroclasts we address this question by quantifying co variations in particle size shape and texture in both magmatic and hydromagmatic deposits from the hverfjall fires fissure eruption iceland overlapping vesicularity and bubble number density distributions measured in rapidly quenched magmatic and hydromagmatic pyroclasts indicate a shared initial history of bubble nucleation and growth with substantial vesiculation prior to mwi hydromagmatic fragmentation occurred principally by brittle mechanisms where the length scale and geometry of fracturing was controlled by the bubble population this suggests that the elevated fragmentation efficiency of hydromagmatic deposits is driven at least in part by brittle disintegration of vesicular pyroclasts due to high thermal stress generated during rapid cooling in this way the shape and size distributions of hydromagmatic pyroclasts both critical input parameters for ash dispersion models are strongly influenced by the dynamics of vesiculation prior to mwi this result underlines the need to analyse multiple grain size fractions to characterise the balance between magmatic and hydromagmatic processes during the hverfjall fires eruption the external water supply was sufficient to maintain mwi throughout the eruption with no evidence for progressive exhaustion of a water reservoir we suggest that both the longevity and the spatial distribution of mwi were determined by the pre existing regional hydrology and represent continuous interaction between a propagating dike and a strong groundwater flow system hosted within permeable basalt lavas

eruption dynamics of hawaiian style fountains the case study of episode 1 of the kīlauea iki 1959 eruption hawaiian eruptions are characterized by fountains of gas and ejecta sustained for hours to days that reach tens to hundreds of meters in height quantitative analysis of the pyroclastic products from the 1959 eruption of k lauea iki k lauea volcano hawai i provides insights into the processes occurring during typical hawaiian fountaining activity this short lived but powerful eruption contained 17 fountaining episodes and produced a cone and tephra blanket as well as a lava lake that interacted with the vent and fountain during all but the first episode of the eruption the focus of this paper microtextural analysis of hawaiian fountaining products from this opening episode is used to infer vesiculation processes within the fountain and shallow conduit vesicle number densities for all clasts are high 106 107 cm 3 post fragmentation expansion of bubbles within the thermally insulated fountain overprints the pre fragmentation bubble populations leading to a reduction in vesicle number density and increase in mean vesicle size however early quenched rims of some clasts with vesicle number densities approaching 107 cm 3 are probably a valid approximation to magma conditions near fragmentation the extent of clast evolution from low vesicle to melt ratio and corresponding high vesicle number density to higher vesicle to melt ratio and lower vesicle number density corresponds to the length of residence time within the fountain

mechanisms forcing an antarctic dipole in simulated sea ice and surface ocean conditions abstract the mechanisms forcing variability in southern ocean sea ice and sea surface temperature from 600 years of a control climate coupled model integration are discussed as in the observations the leading mode of simulated variability exhibits a dipole pattern with positive anomalies in the pacific sector associated with negative anomalies in the atlantic it is found that in the pacific ocean circulation changes associated with variable wind forcing modify the ocean heat flux convergence and sea ice transport resulting in sea surface temperature and sea ice anomalies the pacific ice and ocean anomalies persist over a number of years due to reductions in ocean shortwave absorption reinforcing the initial anomalies in the atlantic sector no single process dominates in forcing the anomalies instead there are contributions from changing ocean and sea ice circulation and surface heat fluxes while the absorbed solar radiation in the atlantic is modified by the changing surface albedo the anomalies

time scales of magma transport and mixing at kīlauea volcano hawai i modeling of volcanic processes is limited by a lack of knowledge of the time scales of storage mixing and final ascent of magmas into the shallowest portions of volcanic plumbing systems immediately prior to eruption it is impossible to measure these time scales directly however micro analytical techniques provide indirect estimates based on the extent of diffusion of species through melts and crystals we use diffusion in olivine phenocrysts from the a d 1959 k lauea iki hawai i usa eruption to constrain the timing of mixing events in the crustal plumbing system on time scales of months to years before eruption the time scales derived from zonation of fe mg in olivines combined with contemporaneous geophysical data suggest that mixing occurred on three time scales 1 as much as 2 yr prior to eruption in the deep storage system 2 in a shallow reservoir between incoming hot melts and resident melt for several weeks to months prior to eruption and 3 in the conduit and summit reservoir between the resident magma and cooled surface lava draining back into the vent on time scales of hours to several days during pauses between episodes synchronous inflation of the shallow reservoir with deep earthquake swarms and mixing suggests an intermittently open transcrustal magmatic system

the mechanism of volcanic eruptions a steady state approach a theory of a volcanic eruption as a steady magma flow from a magma chamber to the surface is described magma is considered as a two component two phase medium and magma flow is steady one dimensional and isothermal mass and momentum exchange between condensed and gaseous phases is assumed to be in equilibrium with nucleation of bubbles as a fast process at small oversaturations three basic flow structures in a conduit are recognized and three resulting types of eruption are described 1 in the discrete gas separation dgs flow melt with discrete gas bubbles erupts this type includes lava eruptions and strombolian activity 2 in the dispersion regime there is continuous eruption of a gas pyroclastic suspension catastrophic explosive eruptions are included in this type 3 here a partly destroyed foam is erupted with permeable structure that allows gas escape near the surface this structure evolves with an increase in permeability and a decrease in the total porosity this type corresponds to lava dome extrusions a criterion dividing dgs flow from the other two regimes is obtained di u n1 3a c0 where u is the magma ascent velocity is magma viscosity n is number of bubble nuclei in a unit mass of magma a is the solubility coefficient for volatiles in magma and c0 is the volatile content the boundary between the dispersion regime and the partly destroyed foam regime depends on u c0 and particle size dp for the dispersion regime the basic governing parameters are magma chamber depth h conduit conductivity b2 b is the characteristic cross dimension of the conduit and excess pressure in the magma chamber instability of the dispersion regime is investigated numerically the dependence of magma discharge rate on the governing parameters is described as a combination of equilibrium surfaces with cusp catastrophes magma chamber depth is a splitting parameter in most cusps and controls the existence of unstable magma flow with sharp regime changes catastrophic rise of eruption intensity is possible if h hcr the critical chamber depth hcr depends approximately linearly on c0 and is about 15 km at c0 0 05 some scenarios of eruption evolution are described in a steady state approximation and the mechanism of catastrophic explosive eruptions is proposed the theory is applied to well documented eruptions tolbachik 1975 1976 and mount st helens 1980 the theory can also describe changes in a volcanic system such as destruction of the conduit or chamber walls destruction of the edifice changes in magma composition and caldera subsidence due to magma evacuation

fragmentation of magma during plinian volcanic eruptions the ratio of the volume of vesicles gas to that of glass liquid in pumice clasts v g v l reflects the degassing and dynamic history experienced by a magma during an explosive eruption v g v l in pumices from a large number of plinian eruption deposits is shown here to vary by two orders of magnitude even between pumices at a given level in a deposit these variations in v g v l do not correlate with crystallinity or initial water content of the magmas or their eruptive intensities despite large ranges in these variables gas volume ratios of pumices do however vary systematically with magma viscosity estimated at the point of fragmentation and we infer that pumices do not quench at the level of fragmentation but undergo some post fragmentary evolution on the timescale of plinian eruptions pumices with viscosities 109 pa s can expand after fragmentation as long as their bubbles retain gas at a rate inversely proportional to their viscosity once the bubbles connect to form a permeable network and lose their gas expansion halts and pumices with viscosities 105 pa s can collapse under the action of surface tension textural evidence from bubble sizes and shapes in pumices indicates that both expansion and collapse have taken place the magnitudes of expansion and collapse therefore depend critically on the timing of bubble connectivity relative to the final moment of quenching we propose that bubbles in different pumices become connected at different times throughout the time span between fragmentation and quenching after accounting for these effects we derive new information on the fragmentation process from two characteristics of pumices the most important is a relatively constant minimum value of v g v l of 1 78 64 vol vesicularity in all samples with viscosities 105 pa s this value is independent of magma composition and thus reflects a property of the eruptive mechanism the other characteristic is that highly expanded pumices 85 vol vesicularities are common which argues against overpressure in bubbles as a mechanism for fragmenting magma we suggest that magma fragments when it reaches a vesicularity of 64 vol but only if sheared sufficiently strongly the intensity of shear varies as a function of velocity in the conduit which is related to overpressure in the chamber so that changes in overpressure with time are important in controlling the common progression from explosive to effusive activity at volcanoes

multiparametric study of the february april 2013 paroxysmal phase of mt etna new south east crater european fp7 med suv mediterranean supersite volcanoes grant number 308665 european research council european fp7 fp 2007 2013 erc grant number 279802 sigma sistema integrato di sensori in ambiente cloud per la gestione multirischio avanzata

arrested diatreme development standing rocks east hopi buttes navajo nation usa abstract maar diatreme volcanoes defined by their relatively large pyroclastic debris filled subsurface structures and craters that cut into the pre eruptive land surface are typically found in small volume mafic to ultramafic monogenetic volcanic fields diatremes are associated with strong explosions throughout most of their development focused along feeder dikes and generally attributed to magma water interaction or high magmatic volatiles detailed mapping of the magnificently exposed standing rocks east sre diatreme shows evidence of additional eruptive complexity and offers new insights into how the plumbing and vent structures of small volume volcanoes evolve during an eruption sre is part of a larger basanitic volcanic complex that includes several diatremes formed along a series of irregular offset nw se trending dikes exposed 300 m below the pre eruptive land surface its similarly oriented elliptical shaped diatreme structure comprises predominantly country rock lithic rich breccia of coarse inhomogeneously mixed wall rock blocks sourced from above and below the current surface plus sparse juvenile material domains of pyroclastic deposits crosscut the country rock breccia deposits and the best exposed is the nw massif rising 35 m above the current erosional surface it represents a cross section of an evolving crater floor and comprises matrix rich lapilli tuff and spatter deposits cut by irregularly distributed dikes some with very complex textures the most significant deposit in terms of volume is an unbedded lapilli tuff that is poorly sorted and has a well mixed population of wall rock and juvenile clast varieties thus resembling deposits typical of diatremes it is overlain by and locally intercalated with spatter deposits and this irregular contact demarcates the base of what was during eruption an uneven evolving crater floor the generally massive variably welded spatter deposits constitute mostly lapilli sized juvenile clasts with fluidal folded over shapes and ropy surfaces subordinate thermally altered wall rock and variegated domains of lapilli tuff sre shows a progressive transition from fissure to diatreme and overall evolution from more explosive to weakly explosive eruption styles recorded at the conduit crater transition diatreme development was initiated by deep quarrying explosive eruptions along a fissure to form the country rock rich breccia only parts of the fissure remained active as magma feeding the highly explosive eruptions along the fissure localized into discrete point sources forming the matrix rich lapilli tuff deposits these superimposed deposits record the passage of multiple debris jets and subvertical fallback from shallow cratering arising from explosions triggered by magma water interaction at numerous discrete sites however instead of continuing to build a well formed diatreme the system switched to weak spattering with intermittent explosive activity and near surface dike emplacement into the unconsolidated anisotropic pyroclastic debris of the crater floor dominant spatter from strombolian style bursts accumulated on the topographically varied evolving unstable syn eruptive crater floor and led to local failure and remobilization this study demonstrates how the combination of fissure behavior and sensitivity of the shallow plumbing system to local conditions during an eruption can lead to a decrease in eruptive footprint within the diatreme structure and an overall decrease in explosivity resulting in the arrested development of an immature diatreme

vesiculation of basaltic magma during eruption vesicle size distributions in vent lavas from the pu9u9o9o kupaianaha eruption of kilauea volcano are used to estimate nucleation and growth rates of h 2 o rich gas bubbles in basaltic magma nearing the earth9s surface 120 m depth by using well constrained estimates for the depth of volatile exsolution and magma ascent rate nucleation rates of 35 9 events cm 3 s 1 and growth rates of 3 2 x 10 4 cm s are determined directly from size distribution data the results are consistent with diffusion controlled growth as predicted by a parabolic growth law this empirical approach is not subject to the limitations inherent in classical nucleation and growth theory and provides the first direct measurement of vesiculation kinetics in natural settings in addition perturbations in the measured size distributions are used to examine bubble escape accumulation and coalescence prior to the eruption of magma

vesiculation and quenching during surtseyan eruptions at hunga tonga hunga ha apai volcano tonga surtseyan eruptions are shallow to emergent subaqueous explosive eruptions that owe much of their characteristic behavior to the interaction of magma with water the difference in thermal properties between water and air affects the cooling and postfragmentation vesiculation processes in magma erupted into the water column here we study the vesiculation and cooling processes during the 2009 and 2014 2015 surtseyan eruptions of hunga tonga hunga ha apai volcano by combining 2 d and 3 d vesicle scale analyses of lapilli and bombs and numerical thermal modeling most of the lapilli and bombs show gradual textural variations from rim to core the vesicle connectivity in the lapilli and bombs increases with vesicularity from fully isolated to completely connected and also increases from rim to core in transitional clasts we interpret the gradual textural variations and the connectivity vesicularity relationships as the result of postfragmentation bubble growth and coalescence interrupted at different stages by quenching in water the measured vesicle size distributions are bimodal with a population of small and large vesicles we interpret this bimodality as the result of two nucleation events one prefragmentation with the nucleation and growth of large bubbles and one postfragmentation with nucleation of small vesicles we link the thermal model with the textural variations in the clasts showing a dependence on particle size leidenfrost effect and initial melt temperature in particular the cooling profiles in the bombs are consistent with the gradual textural variations from rim to core in the clasts likely caused by variations in time available for vesiculation before quenching

a plinian treatment of fallout from hawaiian lava fountains a new model is presented which simulates the dispersal and deposition of material from a hawaiian eruption column the model treats the hawaiian column as a coarse grained plinian column and uses a modified version of the wilson and walker wilson l walker g p l 1987 explosive volcanic eruptions vi ejecta dispersal in plinian eruptions the control of eruption conditions and atmospheric properties geophys j r astron soc 89 657 679 plinian pyroclast dispersal model to simulate the fall out of material during a hawaiian eruption the model results are found to be in good agreement with independent estimates of various parameters made for the 1959 kilauea iki eruption of kilauea volcano the close agreement between the model results and these independent estimates shows that dynamically hawaiian eruptions are indistinguishable from plinian eruptions the major differences in the styles and deposits of these two types of eruptions are accounted for by differences in the mass fluxes and gas contents of the erupting magmas and most fundamentally by differences in the grainsize distribution of the erupted clasts plume heights predicted by the model are greater than those found for previous models of hawaiian eruptions this is because previous models did not allow for the progressive fall out of particles from the plume and more importantly made no correction for the velocity disequilibrium between gas and clasts when the grainsize distribution is coarse

the structure of basaltic scoria and reticulite and inferences for vesiculation foam formation and fragmentation in lava fountains in this investigation pyroclast structures are used to constrain degassing in basaltic lava fountains vesicle size shape number density interconnectedness and packing character are quantified and related to 1 the kinetics of bubble nucleation and growth 2 the structural evolution of magmatic foams and 3 the influence of vesiculation rate on magma fragmentation measurements made on a diverse suite of pyroclasts from kilauea volcano indicate that basaltic foams evolve through an initially disordered closed celled spherical state to a well ordered open celled polyhedral state as the vesicularity rises from 75 to 98 the structural changes occur rapidly 10 s in the conduit and fountain in response to an intense vesiculation burst vesicle size distribution systematics indicate bubble nucleation rates 2 104 events cm 3s 1 that are approximately three orders of magnitude greater than those found for effusive eruptive activity bubble growth rates 9 10 4 cm s exceed effusive estimates by a factor of 3 the observed runaway rate of bubble production indicates strong supersaturations at the onset of nucleation we speculate that the rise speed of the magma as it reaches the level where significant volatile exsolution begins determines the intensity of the vesiculation burst and hence the vigor of the eruption rapid expansion and acceleration of the magma under these conditions may provide the impetus for fragmentation

non newtonian flow of bubbly magma in volcanic conduits the dynamics of magma ascent along volcanic conduits toward the earth s surface affects eruptive styles and contributes to volcanic hazard the rheology of ascending magmatic mixtures is known to play a major role on mass flow rate as well as on pressure and exit velocity at the vent even determining effusive versus explosive eruptive behavior in this work we explore the effects of bubble induced non newtonian rheology on the dynamics of magma flow in volcanic conduits we develop a quasi 2 d model of magma ascent that incorporates a rheological constitutive equation describing the strain dependent effect of gas bubbles on the viscosity of the multiphase magma non newtonian magma flow is investigated through a parametric study where the viscosity of the melt and the water content are varied over natural ranges our results show that non newtonian rheology leads to greater exit velocity mass flow and density the pressure distribution along the conduit remains very similar to the newtonian case deviating only at the conduit exit plug like velocity profiles develop approaching the conduit exit when mixture velocity is high and are favored by smaller liquid viscosity since the mass flow rate the density and the velocity of the mixture exiting from the conduit are fundamental for quantifying and assessing the transport and emplacement dynamics neglecting that the non newtonian effect of bubble bearing magmas may result in misinterpretation of the deposit and consequently eruptive behavior

the rheology of two phase magmas a review and analysis abstract we consider the current state of our understanding of the rheology of two phase magmas that is suspensions of either bubbles or crystals in a viscous silicate melt the discussion is restricted to strain rates at which the suspending melt can be considered newtonian we start by considering the range of textures found in magmas and the bubble deformation and particle motions caused by shearing we then review proposed models for suspensions focussing on those functions of the form r f or f that have been most widely used to describe magmatic systems r is the relative apparent viscosity of the suspension is the volume fraction of the suspended phase is the driving stress and is the strain rate both theoretical and empirical methods are presented and then compared against the available analogue i e non magmatic and magmatic data the paper contains new data and significant re analysis of previously published data we present a new semi empirical constitutive model for bubble bearing magmas that is valid for steady and unsteady flow and large strains and strain rates this equation utilises a new parameter the capillarity cx that encapsulates the combined effect of shearing and unsteadiness on bubble suspensions we also present a new scheme for dealing with polydispersivity of bubble suspensions new data on the rheology of particle suspensions undergoing forced oscillations are presented these data show that the cox merz rule only holds for dilute particle suspensions 0 25 a re analysis of all available experimental data that relate rheology to particle aspect ratio provides distinct curves of maximum packing as a function of aspect ratio for smooth and rough particles with magmatic data lying on the curve appropriate for rough particles we analyse several rheological datasets of crystal bearing basaltic magmas and find that they are in good agreement with the constitutive equations derived from analogue data by contrast the same equations do not agree well with data for high viscosity haplogranitic melts this may be an effect of fracturing or viscous dissipation within these samples the paper concludes with a practical rheological recipes section giving a step by step method for calculating a constitutive equation for a two phase magmatic suspension and assessing its likely accuracy

the influence of atmospheric zonal wave three on antarctic sea ice variability 1 the study examines the relationship between atmospheric zonal wave three and antarctic sea ice variability using an index of zonal wave three and sea ice concentration the net sensible heat flux and the surface air temperature are used to explain the apparent atmosphere sea ice interaction the results show that zonal wave three forces an alternating pattern of equatorward colder and poleward warmer flow which influences the temperature difference between the atmosphere and the ocean the net sensible heat flux is positive ocean heat loss is greater and sea ice growth and expansion is greater in regions of colder air the reverse is true in regions of warmer air this influence of zonal wave three on sea ice concentration appears greatest in the southern fall and early winter it is most clearly seen in the ross and weddell seas outflows and off the amery iceshelf

seasonal zonal asymmetries in the southern annular mode and their impact on regional temperature anomalies abstractthe southern hemisphere annular mode sam is the dominant mode of climate variability in the extratropical southern hemisphere representing variations in pressure and the corresponding changes to the circumpolar zonal flow it is typically thought of as an annular or ringlike structure however on seasonal time scales the zonal symmetry observed in the sam in monthly or annual mean data is much less marked this study further examines the seasonal changes in the sam structure and explores temperature signals across the southern hemisphere that are strongly tied to the asymmetric sam structure the sam asymmetries are most marked in the pacific sector and in austral winter and spring related to changes in the jet entrance and exit regions poleward of 30 s depending on the season the asymmetric sam structure explains over 25 of the variance in the overall sam structure and has strong connections with enso or zonal wavenumber 3 in austral summer and autumn the sam has been becoming more zona

grain shape of basaltic ash populations implications for fragmentation here we introduce a new quantitative method to produce grain shape data of bulk samples of volcanic ash and we correlate the bulk average grain shape with magma fragmentation mechanisms the method is based on automatic shape analysis of 2d projection ash grains in the size range 125 63 m loose bulk samples from the deposits of six different basaltic eruptions were analyzed and 20 000 shape measurements for each were obtained within 45 min using the particle insight dynamic shape analyzer pidsa we used principal component analysis on a reference grain dataset to show that circularity rectangularity form factor and elongation best discriminate between the grain shapes when combined the grain population data show that the studied eruptive environments produce nearly the same range of grain shapes although to different extents our new shape index the regularity index ri places an eruption on a spectrum between phreatomagmatic and dry magmatic fragmentation almost vesicle free surtseyan ash has an ri of 0 207 0 002 2 whereas vesiculated hawaiian ash has an ri of 0 134 0 001 2 these two samples define the end member ri while two subglacial one lacustrine and another submarine ash sample show intermediate ris of 0 168 0 002 2 0 175 0 002 2 0 187 0 002 2 and 0 191 0 002 2 respectively the systematic change in ri between wet and dry eruptions suggests that the ri can be used to assess the relative roles of magmatic vs phreatomagmatic fragmentation we infer that both magmatic and phreatomagmatic fragmentation processes played a role in the subglacial eruptions

abrupt transitions during sustained explosive eruptions examples from the 1912 eruption of novarupta alaska plinian ignimbrite activity stopped briefly and abruptly 16 and 45 h after commencement of the 1912 novarupta eruption defining three episodes of explosive volcanism before finally giving way after 60 h to effusion of lava domes we focus here on the processes leading to the termination of the second and third of these three episodes early erupted pumice from both episodes show a very similar range in bulk vesicularity but the modal values markedly decrease and the vesicularity range widens toward the end of episode iii clasts erupted at the end of each episode represent textural extremes at the end of episode ii clasts have very thin glass walls and a predominance of large bubbles whereas at the end of episode iii clasts have thick interstices and more small bubbles quantitatively all clasts have very similar vesicle size distributions which show a division in the bubble population at 30 m vesicle diameter and cumulative number densities ranging from 107 109 cm 3 patterns seen in histograms of volume fraction and the trends in the vesicle size data can be explained by coalescence signatures superimposed on an interval of prolonged nucleation and free growth of bubbles compared to experimental data for bubble growth in silicic melts the high 1912 number densities suggest homogeneous nucleation was a significant if not dominant mechanism of bubble nucleation in the dacitic magma the most distinct clast populations occurred toward the end of plinian activity preceding effusive dome growth distributions skewed toward small sizes thick walls and teardrop vesicle shapes are indicative of bubble wall collapse marking maturation of the melt and onset of processes of outgassing the data suggest that the superficially similar pauses in the 1912 eruption which marked the ends of episodes ii and iii had very different causes through episode iii the trend in vesicle size data reflects a progressive shift in the degassing process from rapid magma ascent and coupled gas exsolution to slower ascent with partial open system outgassing as a precursor to effusive dome growth no such trend is visible in the episode ii clast assemblages we suggest that external changes involving failure of the conduit vent walls are more likely to have effected the break in explosive activity at 45 h

tropical connections to climatic change in the extratropical southern hemisphere the role of atlantic sst trends abstractthe austral spring relationships between sea surface temperature sst trends and the southern hemisphere sh extratropical atmospheric circulation are investigated using an atmospheric general circulation model agcm a suite of simulations are analyzed wherein the agcm is forced by underlying sst conditions in which recent trends are constrained to individual ocean basins pacific indian and atlantic allowing the impact of each region to be assessed in isolation when forced with observed global sst the model broadly replicates the spatial pattern of extratropical sh geopotential height trends seen in reanalyses however when forcing by each ocean basin separately similar structures arise only when atlantic sst trends are included it is further shown that teleconnections from the atlantic are associated with perturbations to the zonal walker circulation and the corresponding intensification of the local hadley cell the impact of which results in the development of atmospheric rossby w

an analysis of the atmospheric processes driving the large scale winter sea ice variability in the southern ocean the response of the sea ice in the southern ocean to the variability of the atmosphere on the period 1979 2004 is investigated using both model and observational data on the one hand our results show that in line with previous investigations the classical modes of atmospheric variability do not explain a large part of the winter sea ice extent variability integrated over the entire southern ocean on the other hand the regression between the ice extent and the atmospheric pressure displays a pattern with low pressure areas over the south atlantic over the indian ocean and on the southwestern part of the pacific ocean and a high pressure area over the antarctic region extending toward both the southeastern pacific and the region south of australia this pattern which does not correlate significantly with any of the known modes of atmospheric variability induces changes in the sea ice extent by influencing the air temperature the ice production and both the meridional and the zonal ice velocity however there is no clear link between the different centers of action of this pattern furthermore the correlation of the sea ice extent between the different sectors is generally low as a conclusion we must consider that the sea ice extent in the southern ocean over the last 30 years does not behave as a single entity its variability is the result of the combination of regional sea ice changes each sector should thus be examined separately

magma decompression rates during explosive eruptions of kīlauea volcano hawaii recorded by melt embayments the decompression rate of magma as it ascends during volcanic eruptions is an important but poorly constrained parameter that controls many of the processes that influence eruptive behavior in this study we quantify decompression rates for basaltic magmas using volatile diffusion in olivine hosted melt tubes embayments for three contrasting eruptions of k lauea volcano hawaii incomplete exsolution of h2o co2 and s from the embayment melts during eruptive ascent creates diffusion profiles that can be measured using microanalytical techniques and then modeled to infer the average decompression rate we obtain average rates of 0 05 0 45 mpa s 1 for eruptions ranging from hawaiian style fountains to basaltic subplinian with the more intense eruptions having higher rates the ascent timescales for these magmas vary from around 5 to 36 min from depths of 2 to 4 km respectively decompression exsolution models based on the embayment data also allow for an estimate of the mass fraction of pre existing exsolved volatiles within the magma body in the eruptions studied this varies from 0 1 to 3 2 wt but does not appear to be the key control on eruptive intensity our results do not support a direct link between the concentration of pre eruptive volatiles and eruptive intensity rather they suggest that for these eruptions decompression rates are proportional to independent estimates of mass discharge rate although the intensity of eruptions is defined by the discharge rate based on the currently available dataset of embayment analyses it does not appear to scale linearly with average decompression rate this study demonstrates the utility of the embayment method for providing quantitative constraints on magma ascent during explosive basaltic eruptions

vesiculation and fragmentation history in a submarine scoria cone forming eruption an example from nishiizu izu peninsula japan an uplifted 50 m thick half dissected submarine emplaced below wave base scoria cone occurs as dipping beds in coastal outcrops at nishiizu on the izu peninsula in japan concentrically outward dipping weakly stratified ungraded framework supported thin to very thick beds consist of brown coarse tuff to scoria lapilli tuff with outsized fluidal bombs throughout accessory lithic clasts chiefly occur in the lowermost visible beds scoria bombs have quenched margins weak bread crust textures and their vesicle number densities decrease inward which is indicative of fast surface cooling composite textures in the scoria bombs indicate recycling and agglutination of quenched and semi molten pyroclasts at the submarine vent in contrast to weak concentric gradations in vesicle size distribution in the bombs lapilli have asymmetrical gradients in vesicle size distribution indicating that they are fragments of coarser quenched lumps three grain size modes characterise the nishiizu brown scoria with coarse magma lumps ejected during magmatic fragmentation and quench jointed upon contact with seawater to be subsequently fragmented into lapilli and coarse ash by various styles of fragmentation where seawater plays a critical role the cone was constructed by slow moving fallout fed granular flow creep fed directly by suspension settling focused at the crater rim but extending onto the cone flanks with only minor resedimentation by granular flows nishiizu deposits yield an exceptional record of eruption and sedimentation dynamics during submarine cone building activity and in this study we compare their vesiculation and fragmentation mechanisms with those of potential subaerial analogues

the influence of the large scale atmospheric circulation on antarctic sea ice during ice advance and retreat seasons antarctic sea ice a key component of the southern hemisphere climate system is influenced by several large scale modes of the atmospheric circulation antarctic sea ice variability is spatially heterogeneous and links between the atmospheric circulation modes and the sea ice variability are unclear using the observed sea ice concentration data this research isolates distinct regions of sea ice variability around antarctica and determines the advance and retreat periods for each of them the latter are then statistically linked with the observed geopotential height data to determine the atmospheric circulation pattern associated with the variability in the sea ice for each period and region the results clarify which circulation mechanism is of primary importance to sea ice variability during critical periods of the ice lifecycle in the different regions around antarctica and have potential for making estimates of past sea ice extent using the observed geopotential height data

petrography and geochemistry of achnelithic tephra from las herrerias volcano calatrava volcanic field spain formation of nephelinitic achneliths and post depositional glass alteration abstract we present the results of a petrographic and geochemical study carried out on a layer of achnelithic tephra outcropping at the base of the volcanic cone of las herrerias miocene quaternary volcanic region of campo de calatrava spain the tephra with a composition of nephelinite and ash 3 of all major elements and notable increase in h 2 o content the elements liberated by this process formed smectite with an average structural formula comprised between those of beidellite and nontronite end terms na 0 01 k 0 03 ca 0 18 mg 0 22 fe 0 16 2 fe 0 48 al 1 02 3 ti 0 18 4 si 3 58 al 0 42 o 10 oh 2 the degree of palagonitization in each achnelith was likely related to the amount of water incorporated by individual clasts at the moment of their deposition in a volcanic maar lake afterwards there was no more water circulation through the achnelithic tephra which was sealed from water by overlying hydrovolcanic tuff deposits it was this isolation that made possible the preservation of glass to the present day

the vertical fingerprint of earthquake cycle loading in southern california vertical crustal motions during the earthquake cycle are poorly constrained for strike slip faults analysis of gps data from the san andreas fault shows that the crust flexes over hundreds of kilometres due to locking of the fault at depth

relation between annular modes and the mean state southern hemisphere summer abstract the annular modes emerge as the leading mode of extratropical month to month climate variability in both hemispheres here the influence of the background state on the structure and dynamics of the southern hemisphere annular mode sam during the austral summer when the climatology is characterized by a single well defined eddy driven jet is studied subsets of the climatology are constructed for early and late summer and for contrasting polarities of the enso cycle the analysis is based both on observations and on perpetual state gcm experiments the main differences between the subsets involve variations of the latitude of the mean jet it is found that in all the cases the sam is characterized by latitudinal shifts of the jet about its mean position reinforced by a positive momentum flux feedback from baroclinic waves this result is consistent with previous studies of the dynamics of the zonally averaged circulation but is found here to hold over all longitudes and for different positi

links between the amundsen sea low and sea ice in the ross sea seasonal and interannual relationships previous studies have shown that sea ice extent in the southern ocean is influenced by the intensity and location of the amundsen sea low asl through their effect on the meridional winds however the inhomogeneous nature of the influence of the asl on sea ice as well as its influence during critical periods of the sea ice annual cycle is not clear in this study we do a spatio temporal analysis of links between the asl and the sea ice during the advance and retreat periods of the ice over the period 1979 2013 focusing on the role of the meridional and zonal winds we use the era interim monthly averaged 500 mb geopotential height and 10 m wind data along with monthly passive microwave sea ice concentrations sic to examine the seasonal and interannual relationships between the asl and sic in the ross amundsen sea ice sector to characterize the state of the asl we use indices that describe its location and its intensity we show that the asl has preferred locations and intensities during ice advance and retreat seasons the strength and direction of the influence of the asl are not spatially homogeneous and can change from advance to retreat season and there are strong significant relationships between the characteristics of the asl and sic within and across seasons and interannually

linked trends in the south pacific sea ice edge and southern oscillation index previous work have shown that sea ice variability in the south pacific is associated with extratropical atmospheric anomalies linked to the southern oscillation so over a 32 year period 1982 2013 our study shows that the trend in southern oscillation index soi is also able to quantitatively explain the trends in sea ice edge drift and surface winds in this region on average two thirds of the winter ice edge trend in this sector linked to ice drift and surface winds could be explained by the positive soi trend thus subjecting the ice edge to strong decadal so variability if this relationship holds the negative soi trend prior to the recent satellite era suggests that ice edge trends opposite to that of the recent record over a similar time scale significant low frequency ice edge trends linked to the natural variability of so are superimposed upon any trends expected of anthropogenic forcing

linking variable explosion style and magma textures during 2002 at stromboli volcano italy microtextural characteristics of fresh ejecta from stromboli volcano were examined from three periods of differing eruption style and intensity in 2002 activity shifted from relatively weak and infrequent ash charged explosions during january through may into two broad cycles of waxing activity in june through late september and late september through december followed by the onset on 28 december of the 2002 2003 effusive eruption analyzed sets of lapilli from may september october and 28 december show contrasts in the physical properties of magma resident in the shallow conduit during this range of activity three distinct textures are observed among the analyzed pyroclasts low density ld with an abundance of subspherical bubbles the presence of large irregularly shaped bubbles and a light to transparent glass matrix transitional texture tt with an intermediate number of subspherical bubbles a high frequency of large irregularly shaped bubbles and a honey colored glass matrix and high density hd with sparse relatively small bubbles conspicuous large irregular bubbles and a dark glass matrix observational and quantitative data density vesicle size indicate that these textures are linked through variable residence time in stromboli s shallow conduit with an ongoing evolution from ld to hd magma calculations suggest that residual ld magma will evolve to hd texture in a period of hours to days contrasting amounts of the ld tt and hd magmas are present in each sample with the most tt in may the most ld in september october and the most hd in december this implies that the shallow magma had a different rheology at each collection period the viscosity of ld and hd magmas are calculated to be in the range of 2 000 to 2 600 and 3 000 to 5 000 pa s respectively which with their changing proportions must have implications for rates of bubble slug ascent and processes of fragmentation this study suggests that an increasing maturity of magma in stromboli s shallow conduit with resultant increase in viscosity feeds back to reduce the intensity of explosions whereas a steady flux of ld magma favors more powerful explosions

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

vesiculation of high fountaining hawaiian eruptions episodes 15 and 16 of 1959 kīlauea iki the 1959 summit eruption of k lauea volcano produced the highest recorded hawaiian fountain in hawai i quantitative analysis of closely spaced samples from the final two high fountaining episodes of the eruption result in a fine scale textural study of pyroclasts and provide a record of postfragmentation processes as clast vesicularity increases the vesicle number density decreases and vesicle morphology shifts from small and round to larger and more irregular the shift in microtexture corresponds to greater degrees of postfragmentation expansion of clasts with higher vesicularity we suggest the range of clast morphologies in the deposit is related to thermal zonation within a hawaiian fountain where the highest vesicularity clasts traveled in the center and lowest traveled along the margins vesicle number densities are greatest in the highest fountaining episode and therefore scale with intensity of activity major element chemical analyses and fasciculate crystal textures indicate microlite rich zones within individual clasts are portions of recycled lava lake material that were incorporated into newly vesiculating primary melt

contrasting patterns of vesiculation in low intermediate and high hawaiian fountains a case study of the 1969 mauna ulu eruption abstract hawaiian style eruptions or hawaiian fountains typically occur at basaltic volcanoes and are sustained weakly explosive jets of gas and dominantly coarse juvenile ejecta dense spatter to delicate reticulite almost the entire range of styles and mass eruption rates within hawaiian fountaining occurred during twelve fountaining episodes recorded at mauna ulu k lauea between may and december 1969 such diversity in intensity and style is controlled during magma ascent by many processes that can be constrained by the size and shape of vesicles in the 1969 pyroclasts this paper describes pyroclast vesicularity from high intermediate and low fountaining episodes with eruption rates from 0 05 to 1 3 10 6 m 3 h 1 as each eruptive episode progressed magma ascent slowed in and around the vent system offering extended time for bubbles to grow and coalesce late ejected pyroclasts are thus characterized by populations of fewer and larger vesicles with relaxed shapes this progression continued in the intervals between episodes after termination of fountain activity the time scale for this process of shallow growth coalescence and relaxation of bubbles is typically tens of hours rims and cores of pumiceous pyroclasts from moderate to high fountaining episodes record a second post fragmentation form of vesicle maturation partially thermally insulated pyroclasts can have internal bubble populations evolve more dynamically with continued growth and coalescence on a time scale of only minutes during transport in the fountains reticulite which formed in a short lived fountain 540 m in height underwent late short lived bubble nucleation followed by rapid growth of a uniform bubble population in a thermally insulated fountain and quenched at the onset of permeability before significant coalescence these contrasting patterns of shallow degassing and outgassing were the dominant controls in determining both the form and duration of fountaining episodes at mauna ulu and probably for many other hawaiian style eruptions

dynamics of an open basaltic magma system the 2008 activity of the halema uma u overlook vent kīlauea caldera on march 19 2008 a small explosive event accompanied the opening of a 35 m wide vent overlook vent on the southeast wall of halema uma u crater in k lauea caldera initiating an eruptive period that extends to the time of writing the peak of activity in 2008 consisted of alternating background open system outgassing and spattering punctuated by sudden short lived weak explosions triggered by collapses of the walls of the vent and conduit near daily sampling of the tephra from this open system along with exceptionally detailed observations allow us to study the dynamics of the activity during two eruptive sequences in late 2008 each sequence includes background activity preceding and following one or more explosions in september and october 2008 respectively componentry analyses were performed for daily samples to characterise the diversity of the ejecta nine categories of pyroclasts were identified in all the samples including wall rock fragments the six categories of juvenile clasts can be grouped in three classes based on vesicularity 1 poorly 2 uniformly highly to extremely and 3 heterogeneously highly vesicular the wall rock and juvenile clasts show dissimilar grainsize distributions reflecting different fragmentation mechanisms the wall rock particles formed by failure of the vent and conduit walls above the magma free surface and were then passively entrained in the eruptive plume the juvenile componentry reveals consistent contrasts in degassing and fragmentation processes before during and after the explosive events we infer a crude layering developed in the shallow melt in terms of both rheology and bubble and volatile contents beneath a convecting free surface during background activity a tens of centimetres thick viscoelastic surface layer was effectively outgassed and relatively cool while at depths of less than 100 m the melt remained slightly supersaturated in volatiles and actively vesiculating decoupled metre sized bubbles rising through the column burst through the free surface frequently ejecting fragments of the outgassed upper layer when the surface was abruptly perturbed by the rock falls existing mm sized bubbles expanded leading to the acceleration of adjacent melt upward and consecutive explosions while renewed nucleation created a minor population of 10 micron sized bubbles after each explosive event in september october 2008 this layering was re established but with decreasing vigour suggesting that the magma batch as a whole was becoming progressively depleted in dissolved volatiles

extraterrestrial lava lakes abstract active lava lakes are rare on earth with only ten documented examples all formed by lavas of basaltic composition and housed inside summit craters or calderas the existence of lava lakes on other planetary bodies may imply similarities in either composition or volcano tectonic settings and so has important implications for understanding the link between melt production and volcanism we review lava lakes on earth and other planets particularly active caldera like features interpreted to be currently containing active lava lakes on jupiter s moon io and features interpreted as remnants of lava lakes on venus and mars mercury and the moon do not boast the major calderas or shield volcanoes of their larger rocky neighbors partly due to a horizontally compressive tectonic regime arising from global contraction that makes it difficult to move melts through the upper crust we discuss the evidence for active lava lakes on io and show how modeling based on terrestrial lava lakes can reveal how these phenomena differ on both bodies the superficial similarities do not necessarily imply that the plumbing is similar observations of the largest lava lake on io loki patera provide insight into the nature of ionian lava lakes in general which may be more similar to eruptive episodes on the east pacific rise on earth which lead to temporary lava lakes although temporal data for io s lava lake activity are scarce studies of temporal variability of lava lakes on earth are useful for providing ground truth for comparisons future studies of earth by remote sensing and field observations and of io by both ground based observations and future missions are needed to answer many questions including why lava lakes rare on earth appear to be common on io

synchronous variability in the southern hemisphere atmosphere sea ice and ocean resulting from the annular mode zonally symmetric fluctuations of the midlatitude westerly winds characterize the primary mode of atmospheric variability in the southern hemisphere during all seasons this is true not only in observations but also in an unforced 15 000 yr integration of a coarse resolution r15 coupled ocean atmosphere model here it is documented how this mode of atmospheric variability known as the southern annular mode sam generates ocean circulation and sea ice variations in the model integration on interannual to centennial timescales that are tightly in phase with the sam the positive phase of the sam is associated with an intensification of the surface westerlies over the circumpolar ocean around 608s and a weakening of the surface westerlies farther north this induces ekman drift to the north at all longitudes of the circumpolar ocean and ekman drift to the south at around 308s through mass continuity the ekman drift generates anomalous upwelling along the margins of the antarctic continent and downwelling around 458s the anomalous flow diverging from the antarctic continent also increases the vertical tilt of the isopycnals in the southern ocean so that a more intense circumpolar current is also closely associated with positive sam in addition the anomalous divergent flow advects sea ice farther north resulting in an increase in sea ice coverage finally positive sam drives increases in poleward heat transport at about 308s while decreases occur in the circumpolar region ocean and sea ice anomalies of the opposite sign occur when the sam is negative the ocean and sea ice fluctuations associated with the sam constitute a significant fraction of simulated ocean variability poleward of 308s year round the robustness of the mechanisms relating the sam to oceanic variability suggests that the sam is likely an important source of large scale variability in the real southern hemisphere ocean

fragmentation mechanisms associated with explosive lava water interactions in a lacustrine environment rootless cones form when partially outgassed lava interacts explosively with external water the explosions represent an end member system that can elucidate mechanisms of explosive magma water interactions in the absence of magmatic fragmentation induced by outgassing the proportion of finely fragmented ejecta i e ash generated in rootless explosions may contribute significantly to the energy of the explosion even if the ash volume is small relative to coarser ejecta laboratory experiments indicate that the degree of melt water mixing and energy release are proportional to the abundance of blocky grains fragmented by brittle disintegration which effectively contribute thermal energy to the system to constrain the mechanisms and dynamics of rootless explosive activity we assess the nature and modes of fragmentation and ejecta characteristics through morphological textural and density analysis of rootless tephra associated with a p hoehoe lava flow in a lacustrine lake basin environment we observe strong correlations between the mean grain size and the mass percentage of both blocky negative power law trend and fluidal positive logarithmic tephra clasts of all sizes we interpret these trends as scale dependent fragmentation behavior due to the decreasing efficacy of hydrodynamic fragmentation as it occurs over finer scales especially over the ash size range additionally all analyzed beds contain fine ash sized blocky and mossy clasts which are thought to be diagnostic of a high transfer rate of thermal to mechanical energy characteristic of molten fuel coolant interactions these results agree with a recent model of rootless cone formation prior fragmentation theory and scaled laboratory experiments and therefore provide a field based analog for future experimental and modeling efforts

atmospheric forcing of antarctic sea ice on intraseasonal time scales abstractintraseasonal relationships between antarctic sea ice and atmospheric circulation have been investigated using a 29 yr record of pentad mean antarctic sea ice concentration and southern hemisphere 500 hpa height fields analyses were carried out for four sea ice seasons minimum extent growth maximum extent and decay interannual variability was removed from both datasets to focus on intraseasonal variations patterns of sea ice variability and linkages to the atmospheric circulation varied markedly with season the strongest and most coherent relationships were evident during the maximum ice extent period and to a lesser degree during the growth period at those times of year the strongest relationships were associated with atmospheric circulation anomalies leading sea ice anomalies by 4 or 5 days suggesting that variations in the atmospheric circulation force changes in the sea ice field ice decreases are generally found in regions of poleward flow and ice increases are found in regions of

intricate episodic growth of a hawaiian tephra deposit case study of the 1959 kīlauea iki eruption the 1959 k lauea iki eruption on hawai i generated a succession of fountains most reaching hundreds of meters high the 16 episodes of fountaining persisted intermittently with repose periods of between 7 h and 4 days for 36 days they produced tephra deposits that were dispersed several kilometers downwind of the vent and a much larger volume of clastogenic lava which drained into the k lauea iki crater to form a 100 m deep lava lake field data from 211 tephra sample pits downwind of the vent reflect imperfectly the episodic nature of the fountaining behavior only five composite stratigraphic subunits from the total of 16 fountaining episodes can be mapped in the field however isopach maps of these subunits were generated and by the application of empirical deposit thinning relationships volumes of each subunit were estimated in combination with detailed observations made in 1959 our field data allow us to assign stratigraphic subunits to either single or aggregates of several fountaining episodes the most voluminous subunits are linked with the highest fountaining not with the longest in duration in fact significant downwind dispersal was possible only if the top part of the fountains reached above the crater rim which was located about 100 m above the vent the end of high fountaining episodes produced ash rich partings which are found on top of the lapilli sized products of some episodes however the ash rich intervals are strongly attenuated by wind advection and so are only present along the dispersal axes the subunits follow slightly different dispersal axes the maximum spread of 28 degrees between various dispersal axes is predominantly controlled by changing wind directions and spatter cone collapse into the vent which modified its geometry this study outlines the dependency of tephra dispersal on fountain height and emphasizes the capability of an episodic hawaiian fountaining eruption to generate a seemingly monotonous downwind tephra deposit

a novel approach to diagnosing southern hemisphere planetary wave activity and its influence on regional climate variability abstractsouthern hemisphere mid to upper tropospheric planetary wave activity is characterized by the superposition of two zonally oriented quasi stationary waveforms zonal wavenumber 1 zw1 and zonal wavenumber 3 zw3 previous studies have tended to consider these waveforms in isolation and with the exception of those studies relating to sea ice little is known about their impact on regional climate variability a novel approach is taken to quantifying the combined influence of zw1 and zw3 using the strength of the hemispheric meridional flow as a proxy for zonal wave activity the methodology adapts the wave envelope construct routinely used in the identification of synoptic scale rossby wave packets and improves on existing approaches by allowing for variations in both wave phase and amplitude while zw1 and zw3 are both prominent features of the climatological circulation the defining feature of highly meridional hemispheric states is an enhancement of the zw3 component composites of the mea

textural studies of vesicles in volcanic rocks an integrated methodology abstract vesicles in volcanic rocks are frozen records of degassing processes in magmas for this reason their sizes spatial arrangements numbers and shapes can be linked to physical processes that drive magma ascent and eruption although numerous techniques have been derived to describe vesicle textures there is no standard approach for collecting analyzing and interpreting vesicular samples here we describe a methodology for techniques that encompass the entire data acquisition process from sample collection to quantitative analysis of vesicle size and number carefully chosen samples from the lower mean and higher density vesicularity endmembers are characterized using image nesting strategies we show that the texture of even microvesicular samples can be fully described using less than 20 images acquired at several magnifications to cover efficiently the range of existing vesicle sizes a new program foams was designed to perform the quantification stage from vesicle measurement to distribution plots altogether this approach allows substantial reduction of image acquisition and processing time while preserving enough user control to ensure the validity of obtained results we present three cameo investigations on basaltic lava flows scoria deposits and pumice layers to show that this methodology can be used to quantify a wide range of vesicle textures which preserve information on a wide range of eruptive conditions

drivers of antarctic sea ice volume change in cmip5 models antarctic sea ice trends have to date been linked to surface winds through sea ice motion and atmospheric thermal advection this paper analyzes sea ice volume in 10 cmip5 model configurations under pre industrial and historical climate forcings to compare the relative importance of ice motion and thermodynamic processes we find that the models responses to historical forcings is dependent on their sea ice motion formulation models with low magnitude sea ice motion tend to have historical trends that are dominated by thermodynamic processes whilst sea ice models with higher magnitude motion have more spatially variable relative contributions from dynamic and thermodynamic processes trends at the sea ice edge during the season of sea ice advance are generally dominated by dynamic processes whereas during retreat thermodynamic trends dominate the models show more disagreement in the sea ice interior this analysis highlights the different estimates and patterns of sea ice volume among global climate models and offers insight into the drivers of sea ice volume change as well as the subsequent implications for simulated atmosphere sea ice ocean interactions

regions of rapid sea ice change an inter hemispheric seasonal comparison this bi polar analysis resolves ice edge changes on space time scales relevant for investigating seasonal iceocean feedbacks and focuses on spatio temporal changes in the timing of annual sea ice retreat and advance over 1979 80 to 2010 11 where arctic sea ice decrease is fastest the sea ice retreat is now nearly 2 months earlier and subsequent advance more than 1 month later compared to 1979 80 resulting in a 3 month longer summer ice free season in the antarctic peninsula and bellingshausen sea region sea ice retreat is more than 1 month earlier and advance 2 months later resulting in a more than 3 month longer summer icefree season in contrast in the western ross sea antarctica region sea ice retreat and advance are more than 1 month later and earlier respectively resulting in a more than 2 month shorter summer ice free season regardless of trend magnitude or direction and at latitudes mostly poleward of 70 n s there is strong correspondence between anomalies in the timings of sea ice retreat and subsequent advance but little correspondence between advance and subsequent retreat these results support a strong ocean thermal feedback in autumn in response to changes in spring sea ice retreat further model calculations suggest different net ocean heat changes in the arctic versus antarctic where autumn sea ice advance is 1 versus 2 months later ocean atmosphere changes particularly in boreal spring and austral autumn i e during march may are discussed and compared as well as possible inter hemispheric climate connections

the pacific south american modes and tropical convection during the southern hemisphere winter abstract atmospheric circulation features and convection patterns associated with two leading low frequency modes in the southern hemisphere sh are examined in multiyear global reanalyses produced by ncep ncar and nasa dao the two leading modes referred to as the pacific south american psa modes are represented by the first two eof patterns the two patterns are in quadrature with each other and are dominated by wavenumber 3 in midlatitudes with large amplitudes in the pacific south american sector in the pacific anomalies in the subtropics and in the midlatitudes are opposite in phase taken together the two psa modes represent the intraseasonal oscillation in the sh with periods of roughly 40 days the evolution of the psa modes shows a coherent eastward propagation a composite analysis was conducted to study the evolution of tropical convection and the corresponding circulation changes associated with the psa modes outgoing longwave radiation olr anomaly composites during the mature phase

influence of the southern annular mode on the sea ice ocean system 1 the global sea ice ocean model orca2 lim driven by the ncep ncar national centers for environmental prediction national center for atmospheric research reanalysis daily 2 m air temperatures and 10 m winds and by monthly climatologies for precipitation cloud cover and relative humidity is used to investigate the impact of the southern annular mode sam on the antarctic sea ice ocean system our results suggest that the response of the circumpolar southern ocean consists of an annular and a nonannular component for the sea ice cover the non annular component seems to be the most important the annular component strongly affects the overall patterns of the upper ocean circulation when the sam is in its positive phase a northward surface ekman drift a downwelling at about 45 degreess and an upwelling in the vicinity of the antarctic continent are simulated the non annular component has a significant impact at the regional scale especially in the weddell ross amundsen and bellingshausen seas in those regions the pressure pattern associated with the sam induces meridional winds which advect warmer air in the weddell sea and around the antarctic peninsula and colder air in the amundsen and ross seas this implies a dipole response of sea ice to the sam with on average a decrease in ice area in the weddell sea and around the antarctic peninsula and an increase in the ross and amundsen seas during years with a high sam index the long term trend in the observed sea ice area does not appear to be related to the trend in the sam index

variability of ash deposits at piton de la fournaise la reunion island insights into fragmentation processes at basaltic shield volcanoes 25 it is commonly accepted that effusive activity emplaces the main emitted magmatic volume in basaltic 26 shield volcanoes at piton de la fournaise la reunion island france eruptive activity occurs mostly within the 27 non populated enclos fouque caldera and generally does not pose any risk to the population however historical 28 observations recent monitoring data and field work on tephra deposits suggest that some eruptions have produced 29 unusual and unexpected explosive phases a comprehensive sampling of tephra from major historical and recent 30 eruptions on this volcano allowed us to perform systematic componentry grain size chemical and morphological 31 analyses in order to characterize the eruptive dynamics involved in these explosive basaltic eruptions this 32 integrative approach reveals highly variable characteristics of the studied tephra reflecting different fragmentation 33 efficiencies and multiple associated mechanisms primary ductile and partially brittle fragmentation of various 34 intensity of juvenile magma emitted during hawaiian fountaining or mild strombolian explosions were identified 35 as the most common fragmentation mechanisms in particular during the 2014 2018 dominantly effusive eruptive 36 sequence in parallel we distinguished more efficient short lived fragmentation events related to i plug 37 pressurization and brittle fragmentation enhanced by syn eruptive crystallization ii magma water interactions 38 iii rare phreatic explosions and iv secondary fragmentation producing fine ash during caldera collapse we 39 conclude that textural geochemical and morphological analysis make it possible to identify and characterize the 40 variability in eruptive processes with the grain size and the componentry of the ash particles being probably the 41 most important parameters to quantify both the efficiency and the nature of the fragmentation 42 43

textural and geophysical characterization of explosive basaltic activity at villarrica volcano 1 villarrica volcano chile is one of the most active volcanoes in south america its activity is currently characterized by continuous degassing from a summit lava lake vent punctuated by explosive events during november 2004 a multidisciplinary experiment was deployed for a 10 d period to define the style of emission and infer shallow conduit dynamics at this basaltic center this involved collection of thermal seismic and infrasonic data to describe the background activity confined inside the crater and use of samples to texturally and chemically characterize the ejecta from more energetic explosions able to attain the crater rim the background activity was characterized by gas bursting with a frequency of 9 events per minute this involved emission of gas puffs fed by bubble bursting with larger bursts emplacing sheets of magma onto the lower crater walls the ejecta population from the more energetic events was characterized by the coexistence of both scoriae and golden pumice these two types of clasts have different textures but identical glass compositions suggesting that they underwent different conduit histories the golden pumice is interpreted as the expanding inner part of a short lived jet fed by a rapidly ascending magma batch the scoria forms the outer portion of the jet and comprises degassed material entrained during passage of the fresh batch through material residing in the upper most portion of the conduit we thus have a largely degassed upper column that feeds persistent bubble bursting through which fresh batches occasionally rise to feed events of relatively higher energy

insights into eruption dynamics from textural analysis the case of the may 2008 chaiten eruption the may 2008 chaiten southern chile eruption was characterized by several explosive events each associated with plumes which reached up to about 19 km above sea level on may 6 a study of the textural and physical features of the juvenile clasts erupted during the climactic phase of the 2008 eruption of chaiten is presented pumice clasts show unimodal density distribution main mode at 600 kg m3 average vesicularity of about 69 a glassy groundmass with no microcrystals and vesicles with dimension between 1 m and 2 mm they also show a unimodal vesicle size distribution with most frequent vesicle size in the range 0 05 0 08 mm and an estimated vesicle number density of 1 3 0 5 105 mm 3 related to a rapid nucleation event produced during the late phases of magma rise this is confirmed by the absence of microcrystals that could otherwise have delayed vesicle formation and allowed the magma to maintain a low viscosity and a supersaturation in volatiles vesiculation and fragmentation were triggered by a sudden decompression of the melt associated with the opening of the volcanic conduit 10 mpa s 1

eruption and fountaining dynamics of selected 1985 1986 high fountaining episodes at kīlauea volcano hawai i from quantitative vesicle microtexture analysis abstract tephra from the early hawaiian fountaining episodes of the ongoing eruption of pu u in the east rift zone erz of k lauea provides an opportunity to study the vesicle microtextures of pyroclasts erupted from a single vent over a prolonged period of time we report the results of microtextural analysis of pyroclasts from five of pu u s high 200 m hawaiian fountaining episodes episodes 32 37 40 44 and 45 erupted during 1985 1986 this analysis was carried out to constrain the parameters that led to large variations in fountain height at pu u o and the extent to which pyroclast residence times in the fountain modified microtextures our results confirm the finding of stovall et al 2011 stovall et al 2012 that pyroclasts from a single hawaiian fountain can vary greatly in texture from bubbly to foamy and have vesicle volume densities nmv and vesicle to melt ratios vg vl that vary by an order of magnitude this range in vesicle texture and population is due to extensive growth and coalescence of vesicles within the fountain after fragmentation only one pyroclast from four of five episodes was found to have textures interpreted as indicative of the vesicle population near the moment of fragmentation bubbly texture high density typically 500 kg m 3 high nmv 2 2 106 to 4 4 106 and low vg vl of 2 06 to 4 65 we demonstrate a linear correlation between vg vl and peak fountain height across a range of hawaiian fountains from kilauea this correlation could be used to infer peak heights of unobserved hawaiian fountaining eruptions after further testing using well recorded events

on the transition from strombolian to fountaining activity a thermal energy based driver since 1999 mount etna s italy south east crater system has been characterised by episodic lava fountaining each episode is characterised by initial strombolian activity followed by transition to sustained fountaining to feed high effusion rate lava flow here we use thermal infrared data recorded by a permanent radiometer station to characterise the transition to sustained fountaining fed by the new south east crater that developed on the eastern flank of the south east crater starting from january 2011 we cover eight fountaining episodes that occurred between 2012 and 2013 we first developed a routine to characterise event waveforms apparent in the precursory strombolian phase this allowed extraction of a database for thermal energy and waveform shape for 1934 events we detected between 66 and 650 events per episode with event durations being between 4 and 55 s in total 1508 78 of the events had short waxing phases and dominant waning phases event frequency increased as climax was approached events had energies of between 3 0 106 and 5 8 109 j with rank order analysis indicating the highest possible event energy of 8 1 109 j to visualise the temporal evolution of retrieved parameters during the precursory phase we applied a dimensionality reduction technique results show that weaker events occur during an onset period that forms a low energy sink the transition towards fountaining occurs at 107 j where subsequent events have a temporal trend towards the highest energies and where sustained fountaining occurs when energies exceed 109 j such an energy based framework allows researchers to track the evolution of fountaining episodes and to predict the time at which sustained fountaining will begin

quantification of vesicle characteristics in some diatreme filling deposits and the explosivity levels of magma water interactions within diatremes abstract vesicles within juvenile fragments in mafic pyroclastic deposits contain important information about the state of the magma at the time of fragmentation there have been few vesicle studies of juvenile pyroclasts from mafic phreatomagmatic deposits however and none we can find from maar diatreme volcanoes in this paper we document the vesicularity and vesicle population characteristics of juvenile fragments sampled from non bedded lithified deposits of the coombs hills diatreme complex part of the ferrar large igneous province antarctica the diatreme filling pyroclastic deposits dominated by lapilli tuffs and tuff breccias contain typically abundant lithic clasts derived mostly from the enclosing sedimentary sequence and several types of juvenile clasts ranging from blocky to fluidal or raggy in the samples measured 77 80 of the juvenile pyroclasts ranging in size from 0 5 mm to fine lapilli is in the non vesicular to incipiently vesicular range fluidal or rag shaped juvenile clasts some circular vesicles and the lack of microlites all suggest that the coombs hills magma had a relatively low viscosity prior to fragmentation despite the basaltic andesite composition this low viscosity allowed parts of the magma to be fragmented in a non brittle fashion during phreatomagmatic explosions and to form fluidal clasts phreatomagmatic explosions in diatremes can therefore produce diverse types of juvenile clasts simultaneously and the proportions of each will depend on the explosivity of the magma water slurry interaction and other factors recycling of fragments is also thought to be an important factor in generating mixtures of different types of juvenile fragments in diatremes

the influence of recent antarctic ice sheet retreat on simulated sea ice area trends 1 observations indicate that dynamic mass loss from the antarctic ice sheet has been accelerating over recent decades leading to a freshening of the southern ocean here we quantify the effect of several rates and spatial distributions of freshwater forcing on simulated sea ice area trends in contrast to a previous study our simulations show that the freshwater effect on sea ice trends over the historical period is small and fails to reproduce the observed regional pattern of trends when using observationally consistent rates of freshwater forcing the coupled model intercomparison project phase 5 cmip5 models do not represent this dynamic ice sheet mass loss and it has been suggested that this deficiency may significantly influence the simulated sea ice trends we show that when accounting for internal variability the average cmip5 sea ice area trend is statistically consistent with the observed trend and accounting for ice sheet derived freshwater forcing has little influence

pele s tears and spheres examples from kilauea iki abstract pele s tears are a well known curiosity commonly associated with low viscosity basaltic explosive eruptions however detailed studies of these pyroclasts are rare and thus there is no full explanation for their formation these intriguing pyroclasts have smooth glassy surfaces vesiculated interiors 30 and fluidal morphologies trending towards teardrops and then spheres as they decrease in size to