the 25 september 2007 eruption of mount ruapehu new zealand directed ballistics surtseyan jets and ice slurry lahars abstract at 20 26 nzdt on 25 september 2007 a moderate gas driven eruption beneath the summit crater lake of mt ruapehu new zealand generated a directed ballistic fallout apron and surtseyan jet that impacted an area of c 2 5 km2 to the north of the vent two climbers were caught in the blast at a hut 600 m from the vent primary ice slurry lahars were generated in two catchments draining the summit region including a flow that entered a commercial ski field the ejecta consists of blocks of andesitic lava and scoria erupted during previous volcanic episodes a variety of mineral cemented lake floor sediments vent fill debris and rare glassy material interpreted to be derived from a fresh batch of magma a minority of clasts contain formerly molten elemental sulphur indicating that vent temperatures at the base of the lake were in excess of 119 c the ballistic deposit is confined to a c 40 wide swath directed northwards that extends up to 2 km from the inferred vent location beneath crater lake the strong directionality of the jetted deposits and ballistic free shadow zones sheltered by intervening topography all point to a relatively low angle directed blast previous similar eruptions at ruapehu also show preferred deposit orientations that are here correlated with an inclined and off centre vent beneath crater lake the 25 september 2007 eruption appears to have resulted from failure of a relatively shallow hydrothermal seal composed of elemental sulphur and other mineral precipitates developed in the vent breccia which breached following overpressurization by a pulse of magmatic gases released from deeper in the conduit this event highlights the potential hazard from relatively minor gas driven eruptions at ruapehu that can occur with little or no warning improved understanding of the eruption mechanism for this style of eruption will inform future risk assessments for ruapehu and other similar volcanoes worldwide

seasonal variations of sea ice motion in the canada basin and their implications ice velocities and sea level pressure data from arctic drifting buoys for 1979 85 are used to examine the seasonal variation of sea ice drift in the canada basin a recurring reversal of the mean anticyclonic gyre is demonstrated in late summer in response to changes in atmospheric forcing the identification of this reversal of ice motion is significant for numerical modeling of arctic atmosphere ocean ice interactions

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

atmospheric controls on sea ice motion in the southern beaufort sea 1 the beaufort sea ice gyre is characterized in winter months by an anticyclonic regime associated with sea level pressure slp highs previous studies have shown instances of a reversal in this regime in summer months with the arrival of slp lows over the beaufort sea while also demonstrating a link to variations in lower stratospheric potential vorticity in this study we examine the role of relative vorticity in describing dynamic variability on weekly timescales from the surface to the middle stratosphere results from this analysis show that the beaufort gyre is characterized predominantly by anticyclonic activity throughout the year for the time interval considered from 1979 to 2000 with a summer reversal to cyclonic activity whose strength and duration varies between years these reversals coincide with reversals in slp based on a correlation analysis comparison of ice and atmospheric relative vorticity fields in the beaufort sea region bsr for all weeks from 1979 to 2000 indicates that sea ice and lower tropospheric processes are anticorrelated at zero time lag this is in contrast to relative vorticity fields at 10 mbar which exhibit maximum correlation between stratospheric and sea ice responses when 10 mbar leads ice relative vorticity by 2 6 weeks

furthering the investigation of eruption styles through quantitative shape analyses of volcanic ash particles abstract volcanic ash morphology has been quantitatively investigated for various aims such as studying the settling velocity of ash for modelling purposes and understanding the fragmentation processes at the origin of explosive eruptions in an attempt to investigate the usefulness of ash morphometry for monitoring purposes we analyzed the shape of volcanic ash particles through a combination of 1 traditional shape descriptors such as solidity convexity axial ratio and form factor and 2 fractal analysis using the euclidean distance transform edt method we compare ash samples from the hydrothermal eruptions of iwodake japan in 2013 tangkuban perahu indonesia in 2013 and marapi sumatra indonesia in 2015 the dome explosions of merapi java indonesia in 2013 the vulcanian eruptions of merapi in 2010 and tavurvur rabaul papaua new guinea in 2014 and the plinian eruption of kelud indonesia in 2014 particle size and shape measurements were acquired from a particle size analyzer with a microscope camera attached to the instrument clear differences between dense blocky particles from hydrothermal or dome explosions and vesicular particles produced by the fragmentation of gas bearing molten magma are well highlighted by conventional shape descriptors and the fractal method in addition subtle differences between dense blocky particles produced by hydrothermal explosions dome explosions or quench granulation during phreatomagmatic eruptions can be evidenced with the fractal method the combination of shape descriptors and fractal analysis is therefore potentially able to distinguish between juvenile and non juvenile magma which is of importance for eruption monitoring

experimental investigations on the explosivity of steam driven eruptions a case study of solfatara volcano campi flegrei steam driven eruptions both phreatic and hydrothermal expel exclusively fragments of non juvenile rocks disintegrated by the expansion of water as liquid or gas phase as their violence is related to the magnitude of the decompression work that can be performed by fluid expansion these eruptions may occur with variable degrees of explosivity in this study we investigate the influence of liquid fraction and rock petrophysical properties on the steam driven explosive energy a series of fine grained heterogeneous tuffs from the campi flegrei caldera were investigated for their petrophysical properties the rapid depressurization of various amounts of liquid water within the rock pore space can yield highly variable fragmentation and ejection behaviors for the investigated tuffs our results suggest that the pore liquid fraction controls the stored explosive energy with an increasing liquid fraction within the pore space increasing the explosive energy overall the energy released by steam flashing can be estimated to be 1 order of magnitude higher than for simple argon gas expansion and may produce a higher amount of fine material even under partially saturated conditions the energy surplus in the presence of steam flashing leads to a faster fragmentation with respect to gas expansion and to higher ejection velocities imparted to the fragmented particles moreover weak and low permeability rocks yield a maximum fine fraction using experiments to unravel the energetics of steam driven eruptions has yielded estimates for several parameters controlling their explosivity these findings should be considered for both modeling and evaluation of the hazards associated with steam driven eruptions

multidisciplinary constraints of hydrothermal explosions based on the 2013 gengissig lake events kverkfjoll volcano iceland hydrothermal explosions frequently occur in geothermal areas showing various mechanisms and energies of explosivity their deposits though generally hardly recognised or badly preserved provide important insights to quantify the dynamics and energy of these poorly understood explosive events furthermore the host rock lithology of the geothermal system adds a control on the efficiency in the energy release during an explosion we present results from a detailed study of recent hydrothermal explosion deposits within an active geothermal area at kverkfjoll a central volcano at the northern edge of vatnajokull on august 15th 2013 a small jokulhlaup occurred when the gengissig ice dammed lake drained at kverkfjoll the lake level dropped by approximately 30 m decreasing pressure on the lake bed and triggering several hydrothermal explosions on the 16th here a multidisciplinary approach combining detailed field work laboratory studies and models of the energetics of explosions with information on duration and amplitudes of seismic signals has been used to analyse the mechanisms and characteristics of these hydrothermal explosions field and laboratory studies were also carried out to help constrain the sedimentary sequence involved in the event the explosions lasted for 40 50 s and involved the surficial part of an unconsolidated and hydrothermally altered glacio lacustrine deposit composed of pyroclasts lavas scoriaceous fragments and fine grained welded or loosely consolidated aggregates interbedded with clay rich levels several small fans of ejecta were formed reaching a distance of 1 km north of the lake and covering an area of approximately 0 3 km2 with a maximum thickness of 40 cm at the crater walls the material volume of approximately 104 m3 has been ejected by the expanding boiling fluid generated by a pressure failure affecting the surficial geothermal reservoir the maximum thermal craterisation and ejection energies calculated for the explosion areas are on the order of 1011 1010 and 109 j respectively comparison of these with those estimated by the volume of the ejecta and the crater sizes yields good agreement we estimate that approximately 30 of the available thermal energy was converted into mechanical energy during this event the residual energy was largely dissipated as heat while only a small portion was converted into seismic energy estimation of the amount of freshly fragmented clasts in the ejected material obtained from sem morphological analyses reveals that a low but significant energy consumption by fragmentation occurred decompression experiments were performed in the laboratory mimicking the conditions due to the drainage of the lake experimental results confirm that only a minor amount of energy is consumed by the creation of new surfaces in fragmentation whereas most of the fresh fragments derive from the disaggregation of aggregates furthermore ejection velocities of the particles 40 50 m s measured via high speed videos are consistent with those estimated from the field the multidisciplinary approach used here to investigate hydrothermal explosions has proven to be a valuable tool which can provide robust constraints on energy release and partitioning for such small size yet hazardous steam explosion events

genesis and evolution of the cerro prieto volcanic complex baja california mexico the cerro prieto volcanic complex cpvc located in northwestern mexico is the only surface manifestation of the cerro prieto geothermal field the third largest producer of geothermal energy in the world this geothermal field and the salton sea in the usa sit in a pull apart basin that belongs to the trans tensional tectonic zone that includes the san andreas fault system and the salton trough basin to the nw and the east pacific rise to the se in spite of its strategic importance in the generation of geothermal energy the origin of cerro prieto and its relationship with the geothermal reservoir were unknown in this contribution we discuss the origin evolution and mechanisms of formation of this small monogenetic volcano and the magmas that fed the system the volcanic complex is located on top of the cerro prieto left lateral fault to the northwest of the cerro prieto geothermal field the complex consists of a lava cone and a series of domes 0 15 km3 protruding from tertiary sandstones and recent unconsolidated sediments of the alluvial plain of the colorado river the cerro prieto volcanic complex consists of seven stratigraphic units emplaced in a brief time span around 78 81 ka its activity began with the extrusion of a dacitic lava that came into contact with water saturated sediments causing brecciation of the lava the activity continued with the emplacement of dacitic domes and a dyke that were destroyed by a phreatic explosion emplacing a lithic rich breccia this phreatic explosion formed a 300 m wide and 40 m deep circular crater the activity then migrated 650 m to the sw where three dacitic lava domes were extruded and ended with the emplacement of a fissure fed lava flow subsequent remobilization of the rocks in the complex has generated debris and hyperconcentrated flow deposits interbedded with fluviatile sediments in the surrounding terrain all rocks of the cpvc are dacites with phenocrysts of plagioclase orthopyroxene and fe ti oxides and minor quartz gabbro dioritic dykes intruded in tertiary sandstones and siltstones of the local basement contain phenocrysts of plagioclase clinopyroxene fe ti oxides and olivine all cpvc rocks are chemically homogeneous suggesting discrete modifications by crustal assimilation fractional crystallization or magma mixing processes during upper crustal residence aeromagnetic results suggest that the depth of the magmatic source in the area is located below 3 5 km cpvc rocks contain chemical anomalies typical of subduction zones which suggests that all cpvc magmas could have been generated by partial melting of the remains of the subducted farallon plate

mechanisms of the nyos carbon dioxide disaster and of so called phreatic steam eruptions abstract during the night of august 21 1986 a huge volume of concentrated co 2 was emitted by the crater maar of nyos cameroon it killed more than 1700 people and all animal life as far as 14 km away two hypotheses have been put forward to account for this disaster the chronologically first one imputes it to have been a phreatic eruption exceptionally co 2 rich as had been the case in february 1979 on the dieng plateau in central java indonesia where the erupting crater was lake less the second one claims a limnic origin for the co 2 release through an overturn of the 220 m deep lake nyos the hypolimnium of which was supposed to be oversaturated by dissolved gas of volcanic origin the present paper points to six observed facts for which the eruptive hypothesis easily accounts and which the authors of the limnic one do ignore

seismic signature of a phreatic explosion hydrofracturing damage at karthala volcano grande comore island indian ocean karthala volcano is a basaltic shield volcano with an active hydrothermal system that forms the southern two thirds of the grande comore island off the east coat of africa northwest of madagascar since the start of volcano monitoring by the local volcano observatory in 1988 the july 11th 1991 phreatic eruption was the first volcanic event seismically recorded on this volcano and a rare example of a monitored basaltic shield from 1991 to 1995 the vt locations 0 5 ml 4 3 show a crack shaped pattern 3 km long 1 km wide within the summit caldera extending at depth from 2 km to 2 km relative to sea level this n s elongated pattern coincides with the direction of the regional maximum horizontal stress as deduced from regional focal mechanism solutions this brittle signature of the damage associated with the 1991 phreatic eruption is a typical pattern of the seismicity induced by controlled fluid injections such as those applied at geothermal fields in oil and gas recovery or for stress measurements it suggests the 1991 phreatic eruption was driven by hydraulic fracturing induced by forced fluid flow we propose that the extremely high lp and vt seismicity rates relative to other effusive volcanoes during the climax of the 1991 phreatic explosion are due to the activation of the whole hydrothermal system as roughly sized by the distribution of vt hypocenters the seismicity rate in 1995 was still higher than the pre eruption seismicity rate and disagrees with the time pattern of thermo elastic stress readjustment induced by single magma intrusions at basaltic volcanoes we propose that it corresponds to the still ongoing relaxation of pressure heterogeneity within the hydrothermal system as suggested by the few lp events that still occurred in 1995

a phreatic explosion model inferred from a very long period seismic event at mayon volcano philippines during a phreatic explosion at mayon volcano philippines on 7 may 2013 a very long period seismic event with a peak frequency of 0 4 hz was observed our frequency domain waveform inversion solution of the event in the frequency range 0 1 0 6 hz is consistent with a subhorizontal tensile crack and a vertical single force at a shallow location beneath the summit crater the source time functions obtained by the waveform inversion are band passed forms we estimated the deconvolved forms of the source time functions dstfs which are source time functions corrected for the effects of the band pass filter the dstf of the crack can be approximated by an impulse type function composed of inflation followed by deflation whereas the dstf of the single force can be approximated by a downward impulse the inflation of the crack may be attributed to boiling of underground water and its deflation can be attributed to discharge of water vapor whereas the downward force may be understood as the counterforce of the explosion our results suggest that only a portion of the crack wall was destroyed by the explosion we could not find clear precursors in seismic thermography geothermal geodetic and meteorological data we present a model of repeated explosions in which an explosion can occur once the fragmented portion of the crack is sealed by precipitation of clay minerals or hydrothermal secondary deposits this model may explain the absence of clear precursory signals before the 2013 explosion

a pleistocene pyroclastic poor maar from central anatolia turkey influence of a local fault on a phreatomagmatic eruption in central anatolia the late pleistocene narkoy maar formed on a fault zone a 5 m thick pyroclastic succession erupted from a crater 900 m in diameter the presence of gas fumeroles hot springs and hydrothermal alteration zones indicates that the area is geothermally active the products of the maar are large blocks and lapilli to coarse ash planar bedding and cross stratification are well developed within coarse ash beds the maar deposits were generated by a single period of phreatomagmatic explosion with two episodes the first episode produced wet eruption clouds while the second one was relatively dry in nature the estimate of the volume of pyroclastic ejecta compared with the dimensions of the maar demonstrates a material deficiency which is attributed to a large volume of gas emanated during the phreatomagmatic explosion along a fault presently cross cutting the maar in addition a relatively small volume of magma intruded along the fault and mixed with meteoric water in the fault zone to produce the phreatomagmatic eruption the existence of a hydrothermal system in the fault zone is important in affecting the eruption style and evolution of narkoy maar

some consequences of volcanic edifice destruction for eruption conditions abstract destruction of a volcanic edifice by landslides or phreatic explosions unloads the upper crust induced changes of stress field around and of magmatic pressure within a magma reservoir are investigated with an analytical model for the deformation of a liquid filled cavity within an elastic half space unloading affects the reservoir pressure and hence the net result depends on how the liquid filled reservoir responds to a change of remote stress magma compressibility is taken into account and may dampen changes of internal pressure in small volatile rich reservoirs the main consequence of edifice destruction is a decrease of magmatic pressure and stresses on the reservoir walls in some cases this may be responsible for dyke closure at the reservoir walls which stops magma withdrawal and may prevent eruption if an eruption does occur edifice destruction affects the volume of magma erupted depending on edifice size magma reservoir size and depth the erupted volume may be smaller or larger than that which would be erupted with no damage to the edifice these results suggest that major phreatic explosions may prevent magmatic eruptions

variety and sustainability of volcanic lakes response to subaqueous thermal activity predicted by a numerical model we use a numerical model to investigate the factors that control the presence or absence of a hot crater lake at an active volcano we find that given a suitable pair of parameters e g the enthalpy of subaqueous fumaroles and the ratio of mass flux of the fluid input at the lake bottom to lake surface area hot crater lakes can be sustained on relatively long timescales neither a high rate of precipitation nor an impermeable layer beneath the lake bottom are always necessary for long term sustainability the two controlling parameters affect various hydrological properties of crater lakes including temperature chemical concentrations and temporal variations in water levels in the case of low temperature crater lakes increases in flux and enthalpy which are a common precursor to phreatic or phreatomagmatic eruptions result in an increase in both temperature and water level in contrast a decrease in water level accompanied by a rise in temperature occurs at high temperature lakes furthermore our model suggests that crater geometry is a key control on water temperature for lakes with a conical topography a perturbation in the water level due to trivial non volcanic activity such as low levels of precipitation can cause persistent increases in water temperature and chemical concentrations and a decrease in the water level even though subaqueous fumarolic activity does not change such changes in hot crater lakes which are not caused by changes in volcanic activity resemble the volcanic unrest that precedes eruptions

volcanic earthquakes and their relationship to eruptions at ruapehu and ngauruhoe volcanoes abstract crustal earthquakes near ruapehu and ngauruhoe fall into two classes each of which can be subdivided on the one hand there are high frequency events 3 hz with sharp well defined phases mainly concentrated beneath ruapehu crater lake low frequency events the low frequency events resemble minakami s b type and explosion earthquakes but sometimes occur where no vent exists and rather deeper than his formal definition difficulty in applying minakami s classification rigorously and the fact that low frequencies may be due to abnormal attenuation of higher frequencies along the path rather than to their suppression or absence at the source has led to reclassification of earthquakes near the volcanoes into two broad groups tectonic and volcanic the former includes all high frequency earthquakes and those discrete events in which dominant low frequencies are due to path effects the latter includes multiple and emergent events which show evidence of prolonged or repetitive source mechanism dominant low frequencies are ascribed to occurrence in heat weakened material and high frequencies to instantaneous source mechanisms operating in competent rock the term volcano tectonic describes tectonic earthquakes within some arbitrary distance of a volcano at ngauruhoe and ruapehu volcanic earthquakes accompany explosive vent clearing eruptions subsequent open vent degassing and ash emission however although often powerful and prolonged usually occurs without earthquakes such activity is however frequently accompanied by volcanic tremor at ruapehu under closed vent conditions when lake temperature is low low frequency earthquakes up to magnitude ml 3 4 have occurred without any eruption five types of phreatic eruptions are identified at ruapehu each having a distinctive seismic pattern the three most explosive types appear to be generated by a chain reaction process and all involve flashing of water to steam the first by failure of the roof with little precursory seismicity after a closed vent period during which lake temperature decreases the second after prolonged heating of the lake and much preliminary volcanic tremor interpreted as due to rising magma and the third under open vent conditions in the wake of one of the two preceding types a fourth probably occurs in wet sediments near the base of the lake as a result of upward migration of hot gas and a fifth aseismic or accompanied by very weak volcanic tremor is associated with convective overturn within crater lake

are the ashes from the latest eruptions 2010 2016 at turrialba volcano costa rica related to phreatic or phreatomagmatic events abstract the initial eruptive episodes of explosive eruptions are classified as phreatic if the amount of juvenile material scoria glass pumice is null and the amount of fresh accidental lithics and hydrothermally altered lithics is substantial phreatic eruptions have been in some cases recognized as precursory events preceding phreatomagmatic and magmatic eruptive phases usually the lithological features of tephra deposits are investigated and sampled in the field investigation of ash samples under binocular microscope or by back scattered electron bse microscope images of polished sections is usually considered sufficient to typify the fragmentation mechanism of the eruption the opening eruptive phases at turrialba volcano together with the formation of new intracraters i e 2010 2012 2014 and the enlargement of the western crater 29 october 2014 to present were classified in previous papers and internal reports as phreatic we studied a series of ash samples erupted from 2010 to 2016 with the aim of understanding the fragmentation processes characterizing the vent opening phases we used sem eds analyses in addition to field and microscopic investigation results showed a composition of accidental lithics of fresh to hydrothermally altered clasts and secondary minerals 82 98 besides juvenile andesite fragments 2 18 which leads us to revisit the classification of the initial eruptive phases of turrialba as phreatomagmatic our method allowed the detection of a juvenile component directly involved in an effective magma water interaction which was possible only by a scrutinous examination of the glass surface textures by sem in the range size between 3 and 3 5 phi we recommend such a type of investigation when the identification of fresh magma in a new eruption is crucial for the preparedness and hazard evaluation at active volcanoes

short period volcanic gas precursors to phreatic eruptions insights from poas volcano costa rica abstract volcanic eruptions involving interaction with water are amongst the most violent and unpredictable geologic phenomena on earth phreatic eruptions are exceptionally difficult to forecast by traditional geophysical techniques here we report on short term precursory variations in gas emissions related to phreatic blasts at poas volcano costa rica as measured with an in situ multiple gas analyzer that was deployed at the edge of the erupting lake gas emitted from this hyper acid crater lake approaches magmatic values of so2 co2 1 6 days prior to eruption the so2 flux derived from magmatic degassing through the lake is measureable by differential optical absorption spectrometry sporadic campaign measurements which allows us to constrain lake gas output and input for the major gas species during eruptive and non eruptive periods we can further calculate power supply to the hydrothermal system using volatile mass balance and thermodynamics which indicates that the magmatic heat flux into the shallow hydrothermal system increases from 27 mw during quiescence to 59 mw during periods of phreatic events these transient pulses of gas and heat from the deeper magmatic system generate both phreatic eruptions and the observed short term changes in gas composition because at high gas flux scrubbing of sulfur by the hydrothermal system is both kinetically and thermodynamically inhibited whereas co2 gas is always essentially inert in hyperacid conditions thus the so2 co2 of lake emissions approaches magmatic values as gas and power supply to the sub limnic hydrothermal system increase vaporizing fluids and priming the hydrothermal system for eruption our results suggest that high frequency real time gas monitoring could provide useful short term eruptive precursors at volcanoes prone to phreatic explosions

pigeonholing pyroclasts insights from the 19 march 2008 explosive eruption of kīlauea volcano we think conventionally of volcanic explosive eruptions as being triggered in one of two ways by release and expansion of volatiles dissolved in the ejected magma magmatic explosions or by transfer of heat from magma into an external source of water phreatic or phreatomagmatic explosions we document here an event where neither magma nor an external water source was involved in explosive activity at k lauea instead the eruption was powered by the expansion of decoupled magmatic volatiles released from deeper magma which was not ejected by the eruption and the trigger was a collapse of near surface wall rocks that then momentarily blocked that volatile flux mapping of the advected fall deposit a day after this eruption has highlighted the difficulty of constraining deposit edges from unobserved or prehistoric eruptions of all magnitudes our results suggest that the dispersal area of advected fall deposits could be miscalculated by up to 30 of the total raising issues for accurate hazard zoning and assessment eruptions of this type challenge existing classification schemes for pyroclastic deposits and explosive eruptions and in the past have probably been interpreted as phreatic explosions where the eruptive mechanism has been assumed to involve flashing of groundwater to steam

evolution of volcanic gas composition during repeated culmination of volcanic activity at kuchinoerabujima volcano japan abstract chemical and isotopic compositions of low to medium temperature fumarolic gasses were measured at various fumaroles of kuchinoerabujima volcano from 1993 to 2009 by the combination of fumarolic gas sampling and multi gas measurement of volcanic plumes repeated culmination of the volcanic activity was observed as contemporaneous occurrence of seismic swarms summit inflation and demagnetization almost every two years after 1999 fumarolic activity also increased parallel with these activities new fumarolic fields of low temperature fumaroles at boiling point formed at the southern and western rims of the summit crater in 2003 and intense degassing activity started at medium temperature fumaroles inside the summit crater in 2008 the low temperature fumarolic gasses have peculiar composition with high h2 h2o co co2 and so2 h2s ratios typical features of high temperature volcanic gasses but also with low hcl and total s contents typical features of low temperature gasses these features indicate that the gasses are formed by low temperature differentiation of high temperature gasses variation of h and o isotopic ratios of the low temperature gasses indicates that the gasses are formed by isoenthalpic processes of vapor liquid separation at 100 c of a high temperature gas and meteoric water mixture implying that the high temperature gas was injected into a shallow aquifer without cooling temperatures of the high temperature gasses were estimated as 550 700 c based on the equilibrium temperature calculation with considering the low temperature differentiation the medium temperature fumarolic gasses from the summit crater have typical compositions of high temperature volcanic gasses and are estimated as the source gas of the boiling point fumaroles the h2 h2o and co2 st ratios of the low temperature fumaroles increased from 2004 to 2009 which is interpreted to be caused by the evolution of thermal structure of a shallow gas storage region of a few hundred meters deep increase of magmatic gas supply caused enlargement of a high temperature zone of the gas storage region widening the surrounding temperature transit zone with smaller temperature gradient the enlargement of the high temperature zone also reduces the overlying low temperature aquifer which caused the decrease of co2 st ratio by reduction of sulfur removal reaction the enlargement of the high temperature zone resulted in the leakage of the high temperature gasses directly to the surface as the medium temperature gasses from the summit crater

introducing the volcanic unrest index vui a tool to quantify and communicate the intensity of volcanic unrest accurately observing and interpreting volcanic unrest phenomena contributes towards better forecasting of volcanic eruptions thus potentially saving lives volcanic unrest is recorded by volcano observatories and may include seismic geodetic degassing and or geothermal phenomena the multivariate datasets are often complex and can contain a large amount of data in a variety of formats low levels of unrest are frequently recorded causing the distinction between background activity and unrest to be blurred despite the widespread usage of these terms in unrest literature including probabilistic eruption forecasting models and in volcanic alert level val systems frequencies and intensities of unrest episodes are not easily comparable over time or between volcanoes complex unrest information is difficult to communicate simply to civil defence personnel and other non scientists the volcanic unrest index vui is presented here to address these issues the purpose of the vui is to provide a semi quantitative rating of unrest intensity relative to each volcano s past level of unrest and to that of analogous volcanoes the vui is calculated using a worksheet of observed phenomena ranges for each phenomenon within the worksheet can be customised for individual volcanoes as demonstrated in the companion paper for taupo volcanic centre new zealand potter et al 2015 the vui can be determined retrospectively for historical episodes of unrest based on qualitative observations as well as for recent episodes with state of the art monitoring this enables a long time series of unrest occurrence and intensity to be constructed and easily communicated to end users the vui can also assist with val decision making we present and discuss two approaches to the concept of unrest

hydrothermal fluid flow disruptions evidenced by subsurface changes in heat transfer modality the la fossa cone of vulcano italy case study detecting volcanic unrest is of primary importance for eruption forecasting especially on volcanoes characterized by highly dangerous and often seemingly unpredictable phreatic or phreatomagmatic eruptions we present a simple and innovative analysis of shallow vertical temperature profiles to depths of 70 cm these data were recorded at la fossa cone of vulcano aeolian islands italy during an episode of increased hydrothermal and seismic activities that occurred between september and december 2009 this work involves the use of the coefficient of determination r 2 on vertical temperature profiles in order to identify changes in conductive versus convec tive heat transfer modality the increase in convective heat transfer can be related to the disruption of the hydrothermal system due to its pressurization and or variation of ground permeability between the hydrothermal system and the surface while raw temperature data do not evidence any significant variation during the period investigated and the classic temperature gradient is highly influenced by seasonal variations the fluctuation of r 2 displayed striking spikes that coincided with the seismic swarm inside the volcanic edifice such a low cost device associated with easy real time data processing could constitute a very promising yet deceptively simple technique to monitor hydrothermal systems in order to assess the hazard posed by high energy eruptions for populations living close to active volcanoes

magma hydrothermal system interaction inferred from volcanic gas measurements obtained during 2003 2008 at meakandake volcano hokkaido japan phreatic eruptions occurred at the meakandake volcano in 1988 1996 1998 2006 and 2008 we conducted geochemical surveillance that included measurements of temperature so2 emission rates and volcanic gas composition from 2003 to 2008 at the nakamachineshiri nm northwest nw and akanuma ak fumarolic areas and the 96 1 vent where historical eruptions had occurred the elemental compositions of the gases discharged from the different areas are similar compared with the large variations observed in volcanic gases discharged from subduction zones all the gases showed high apparent equilibrium temperatures suggesting that all these gases originated from a common magmatic gas the gases discharged from each area also exhibited different characteristics which are probably the results of differences in the conditions of meteoric water mixing quenching of chemical reactions and vapor liquid separation the highest apparent equilibrium temperatures about 500 c were observed in the case of nw fumarolic gases despite the low outlet temperature of about 100 c at these fumaroles since the nw fumaroles were formed as a result of the 2006 phreatic eruption the high temperature gas supply to the nw fumarole suggests that the phreatic eruption was caused by the ascent of high temperature magmatic gases the temperatures compositions and emission rates of the nm and 96 1 gases did not show any appreciable change after the 2006 eruption indicating that each fumarolic system had a separate magmatic hydrothermal system the temperatures compositions and emission rates of the nm fumarolic gases were apparently constant and these fumaroles are inferred to be formed by the evaporation of a hydrothermal system with a constant temperature of about 300 c the 96 1 gas compositions showed large changes during continuous temperature decrease from 390 to 190 c occurred from 2003 to 2008 but the sulfur gas emission rates were almost constant at about four tons day at the 96 1 vent the so2 h2s ratio decreased while the h2 h2o ratio remained almost constant this was probably caused by the rock buffer controlled chemical reaction during the temperature decrease

probable dynamic triggering of phreatic eruption in the tatun volcano group of taiwan abstract on 16 march 2014 utc a small phreatic eruption occurred in the tatun volcano group tvg of taiwan although it was not reported until analysis of both seismic and acoustic data revealed that the source was in the vicinity of the hsiaoyukeng fumarole a replay of the acoustic data accelerated 60 fold reveals that the gradual decrease in frequency that was recorded produces a volcanic whistle similar to the jet of steam released from a heating kettle the phreatic eruption may have been dynamically triggered by a m6 7 earthquake in chile a similar phenomenon occurred on 5 january 2015 when a phreatic eruption was recorded in the tvg immediately after the generation of dynamic seismic waves by an m5 0 earthquake in japan this is the first scientific report of a phreatic eruption detected in the tvg indicating that these volcanoes are still active as a result it is important to monitor their volcanic activity and identify volcanic reservoirs beneath the tvg to mitigate future possible volcanic impact

chemical and isotopic characteristics of geothermal fluids from sulphur springs saint lucia abstract sulphur springs is a vigorous geothermal field associated with the active soufriere volcanic centre in southern saint lucia lesser antilles island arc the sulphur springs park is an important tourist attraction touted as the world s only drive through volcano with some of the hot pools being developed into recreational pools some 200 000 people visit the park each year since 2001 the hydrothermal fluids of sulphur springs have been sampled as part of an integrated volcanic monitoring programme for the island gas and water samples were analysed to characterise the geochemistry of the hydrothermal system and to assess the equilibrium state and subsurface temperatures of the reservoir this has also enabled us for the first time to establish baseline data for future geochemical monitoring the gases are of typical arc type composition with n2 excess and low he and ar content the dry gas composition is dominated by co2 ranging from 601 993 mmol mol with deeper magmatic sourced h2s rich vapour undergoing boiling and redox changes in the geothermal reservoir to emerge with a hydrothermal signature in the fumarolic gases fluid contributions from magmatic degassing are also evident mainly from the moderate to high contents of hcl and deeply sourced h2s gas respectively sulphur springs hydrothermal waters have acid sulphate type compositions so4 78 4008 mg l ph 3 7 and are of primarily meteoric origin which have been affected by evaporation processes based on the enrichment in both 18o and d 18o 1 to 15 and d 9 to 14 respectively in relation to the global meteoric water line gmwl these waters are steam heated water typically formed by absorption of h2s rich gases in the near surface oxygenated groundwaters reservoir temperatures calculated from the evaluation of gas equilibria in the co2 ch4 h2 system reveal higher temperatures 190 to 300 c than those derived from quartz geothermometry 95 to 169 c which appeared to be affected by dilution with meteoric waters generally no significant variations in fluid geochemistry of the hydrothermal system were observed between 2001 and 2006 and we propose that there were no changes in the state of volcanic activity during this period

the miwah high sulphidation epithermal au ag deposit aceh indonesia geology and spatial relationships of gold with associated metals and structures abstract geological mineralogical and whole rock geochemical studies of the plio pleistocene miwah high sulphidation au ag deposit in aceh indonesia revealed evidence of a complex and dynamic interplay between structural development and mineralisation the mineralisation occurs in a zone of predominantly phreatic breccias measuring 1 1 km long by 400 m wide and 200 350 m deep within a fault bounded calc alkaline andesite ridge within this zone low grade disseminated au ag has superimposed narrow high grade au ag zones hydrothermal alteration and mineralisation in three mineralised centres the miwah bluff in the west and the west block m and east block m in the east are controlled by steeply dipping 60 and northerly trending pre to syn mineral feeders this alteration displays an outward sequence of vuggy silica i alunite silica advanced argillic and kaolinite illite argillic a distal chlorite smectite propylitic zone may precede or constitute the end product of the above alteration late silica flooding converted parts of the vuggy silica i and the alunite quartz zone into variably sulphide rich massive silica and vuggy silica ii containing pyrophyllite alunite respectively penecontemporaneous with the massive silicification main stage mineralisation initially deposited intergrowths of pyrite enargite quartz followed by scattered enargite and pyrite and finally rapidly precipitated ag bearing native gold dendrites in vugs with lesser amounts of sulphides the crack seal texture of the host rocks paragenetic variation in precious and base metal mineral species and selective dissolution fracturing and shearing of most of the metallic and gangue minerals are interpreted to reflect transient pulses of fluid flows and mineralisation within zones of structural deformation high grade au zones and associated metals formed clusters along the feeders whereas low grade disseminations of the same metals were spread across the deposit these metals are zoned along the feeders from apical au ag to deep cu as sb te and sn are variably distributed laterally the zonation is from au ag in the feeders through cu as sb bi te and sn and finally to pb or zn in the periphery while these bulk rock metal abundances indicate the efficacy of certain physico chemical conditions of the fluids to accumulate the metals their ratios point to an upward paleo flow path of the fluids along the northerly striking faults and related fractures combining all of the above data we propose that miwah developed in fault fracture networks beneath paleo solfataras in a volcanic crater where the ascending acidic magmatic gas or gas fluids vapours transformed the phreatic breccia host rocks first into vuggy silica and advanced argillic rocks which were subsequently resilicified and mineralised into au and base metal rich massive silica during the depressurisation and condensation of the gas fluid phases mineralisation processes terminated with limited ag enrichment by late stage fluids in the upper segment of the deposit and in deep fractures

organic control on shoreface stacking patterns bogged down in the mire in ever wet climates raised mires that are elevated several metres above flood levels can cover significant portions of coastal plains because peat accumulation may keep pace with moderate rates of base level rise the development of raised mires may reduced the areal extent of marine transgressions thick low ash coals are present immediately landward of many vertically stacked shoreface parasequences in cretaceous state of the western interior of north america we suggest that these coals formed in raised mires that stabilized shorelines for long periods of time in such settings the rate of sediment supply including peat accumulation to the coastal environment is partly a function of the rate of change in base level

eruptive activity at turrialba volcano costa rica inferences from 3he 4he in fumarole gases and chemistry of the products ejected during 2014 and 2015 a new period of eruptive activity started at turrialba volcano costa rica in 2010 after almost 150 years of quiescence this activity has been characterized by sporadic explosions whose frequency clearly increased since october 2014 this study aimed to identify the mechanisms that triggered the resumption of this eruptive activity and characterize the evolution of the phenomena over the past 2 years we integrate 3he 4he data available on fumarole gases collected in the summit area of turrialba between 1999 and 2011 with new measurements made on samples collected between september 2014 and february 2016 the results of a petrological investigation of the products that erupted between october 2014 and may 2015 are also presented we infer that the resumption of eruptive activity in 2010 was triggered by a replenishment of the plumbing system of turrialba by a new batch of magma this is supported by the increase in 3he 4he values observed since 2005 at the crater fumaroles and by comparable high values in september 2014 just before the onset of the new eruptive phase the presence of a number of fresh and juvenile glassy shards in the erupted products increased between october 2014 and may 2015 suggesting the involvement of new magma with a composition similar to that erupted in 1864 1866 we conclude that the increase in 3he 4he at the summit fumaroles since october 2015 represents strong evidence of a new phase of magma replenishment which implies that the level of activity remains high at the volcano this article is protected by copyright all rights reserved

turmoil at turrialba volcano costa rica degassing and eruptive processes inferred from high frequency gas monitoring eruptive activity at turrialba volcano costa rica has escalated significantly since 2014 causing airport and school closures in the capital city of san jose whether or not new magma is involved in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material here we use high frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions pulses of deeply derived co2 rich gas co2 s total 4 5 precede explosive activity providing a clear precursor to eruptive periods that occurs up to 2weeks before eruptions which are accompanied by shallowly derived sulfur rich magmatic gas emissions degassing modeling suggests that the deep magmatic reservoir is similar to 8 10km deep whereas the shallow magmatic gas source is at similar to 3 5km two cycles of degassing and eruption are observed each attributed to pulses of magma ascending through the deep reservoir to shallow crustal levels the magmatic degassing signals were overprinted by a fluid contribution from the shallow hydrothermal system modifying the gas compositions contributing volatiles to the emissions and reflecting complex processes of scrubbing displacement and volatilization h2s so2 varies over 2 orders of magnitude through the monitoring period and demonstrates that the first eruptive episode involved hydrothermal gases whereas the second did not massive degassing 3000t d so2 and h2s so2 1 followed suggesting boiling off of the hydrothermal system the gas emissions show a remarkable shift to purely magmatic composition h2s so2 0 05 during the second eruptive period reflecting the depletion of the hydrothermal system or the establishment of high temperature conduits bypassing remnant hydrothermal reservoirs and the transition from phreatic to phreatomagmatic eruptive activity

evidences of volcanic unrest on high temperature fumaroles by satellite thermal monitoring the case of santa ana volcano el salvador on october 1st 2005 santa ana volcano el salvador underwent a vei 3 phreatomagmatic eruption after approximately one century of rest casualties and damages to some of the local infrastructures and surrounding plantations were followed by the evacuation of the nearby communities the analysis of modis moderate resolution imaging spectroradiometer infrared data reveals that the main explosion was preceded by a one year long thermal unrest associated to the development of a fumaroles field located at the western rim of the summit crater lake by combining space based thermal flux and ground based measurements seismicity sulfur emissions and lake temperatures we suggest that the activity observed at santa ana between 2004 and 2005 was driven by the gradual intrusion of an undegassed magma body at a very shallow depth magma injection induced thermal anomalies associated with sustained degassing from the fumaroles field and promoted the interaction between the magmatic hydrothermal system and the overlying water table this process culminated into the vei 3 phreatomagmatic eruption of october 2005 that strongly modified the shallow structure of the crater area the subsequent three years long activity resulted from self sealing of the fracture system and by the opening of a new fracture network directly connecting the deeper hydrothermal system with the crater lake our results show that satellite based thermal data allow us to detect the expansion of the high temperature fumarolic field this may precede an explosive eruption and or a lava dome extrusion in particular we show that thermal records can be analyzed with other geochemical i e so2 emissions and geophysical seismicity data to track a shallow magmatic intrusion interacting with the surrounding hydrothermal system this provides a remarkable support for volcano monitoring and eruption forecasting particularly in remote areas where permanent ground data acquisition is hazardous expensive and difficult

the gas cloud of lake nyos cameroon 1986 results of the italian technical mission abstract on august 21 1986 a gas cloud issued from lake nyos in cameroon killed over 1700 people an italian technical mission reached the area seven days later and obtained the first field evidences of the catastrophe on the basis of observations and measurements in the field and of samples collected the origin of the gas outburst is attributed to a phreatic explosion from beneath the bed of the lake this interpretation appears to fit well the observed and reported phenomena and seems perfectly consistent with the geological geothermal conditions of the area

relationship between volcanic activity and shallow hydrothermal system at meakandake volcano japan inferred from geomagnetic and audio frequency magnetotelluric measurements abstract hydrothermal activity at meakandake volcano japan from 2004 to 2014 was investigated by using long term geomagnetic field observations and audio frequency magnetotelluric amt surveys the total intensity of the geomagnetic field has been measured around the summit crater ponmachineshiri since 1992 by kakioka magnetic observatory we reanalyzed an 11 year dataset of the geomagnetic total intensity distribution and used it to estimate the thermomagnetic source models responsible for the surface geomagnetic changes during four time periods 2004 2006 2006 2008 2008 2009 and 2013 2014 the modeled sources suggest that the first two periods correspond to a cooling phase after a phreatic eruption in 1998 the third one to a heating phase associated with a phreatic eruption in 2008 and the last one to a heating phase accompanying minor internal activity in 2013 all of the thermomagnetic sources were beneath a location on the south side of ponmachineshiri crater in addition we conducted amt surveys in 2013 and 2014 at meakandake and constructed a two dimensional model of the electrical resistivity structure across the volcano combined the resistivity information and thermomagnetic models revealed that the demagnetization source associated with the 2008 eruptive activity causing a change in magnetic moment about 30 to 50 times greater than the other sources was located about 1000 m beneath ponmachineshiri crater within or below a zone of high conductivity a few ohm meters whereas the other three sources were near each other and above this zone we interpret the conductive zone as either a hydrothermal reservoir or an impermeable clay rich layer acting as a seal above the hydrothermal reservoir along with other geophysical observations our models suggest that the 2008 phreatic eruption was triggered by a rapid influx of heat into the hydrothermal reservoir through fluid rich fractures developed during recent seismic swarms the hydrothermal reservoir remained hot after the 2008 eruption and heat was sporadically transported upward through its low permeability ceiling

source mechanism of a very long period event at mt ontake central japan response of a hydrothermal system to magma intrusion beneath the summit abstract a very long period vlp volcanic event which occurred on 25 january 2007 beneath mt ontake central japan was recorded by nearby broadband seismometers as well as the japanese nationwide hi net and f net seismic networks the vlp waveforms show a pulse like shape with a duration of approximately 1 min the vlp event was accompanied by a burst sequence of long period lp events we carried out waveform inversion to determine the source mechanism and location of the vlp event our analysis indicates volumetric changes in an inclined crack seismic moment of 10 14 nm at the vlp source which is located at 0 6 km above sea level beneath the summit of mt ontake and above dikes determined from gps data the source time functions of the vlp event showed a pulse like triangular shape indicating inflation followed by deflation of the crack at the source we interpreted the result of the waveform inversion as follows gases released from the intruded magma heated an aquifer system beneath the summit of mt ontake a break of unstable superheated water in a hydrothermal crack in the system caused vaporization of water and associated crack inflation which was followed by discharge of steam from the crack resulting in its collapse these processes caused the vlp event which may have been a precursor of a small phreatic eruption that occurred in late march 2007

seismic precursors of the february 10 1990 eruption of kelut volcano java abstract kelut volcano eastern java indonesia erupted on february 10 12 1990 seismic activity and an increase of temperature and acoustic noise in the crater lake appeared three months before the eruption and were the main precursory signs of this eruption during the pre eruptive stage the number of events was eight per day on average and the cumulative seismic energy released was 5 6 10 15 erg these low values are uncommon for an andesitic volcano seismic activity mainly consisted of swarms of very shallow volcano tectonic earthquakes many of which were part of seismic multiplets in the last three weeks before the eruption seismic activity remained at a very low level this quiescent period was followed 24 hours prior to the eruption initiation by an intense swarm of low energy events which progressively became continuous spasmodic tremor most of the data obtained during the pre eruptive stage are consistent with a process of fracturation of a shallow and low strength plug blocking the eruptive conduit before the eruption several observations suggest that water is an important element in the preeruptive and eruptive phenomena at kelut volcano in particular the monochromatic events observed at kelut are characterized by one narrow peak in their spectra the estimations of q value and impedance contrast for these events suggest that the fluid which fills the source resonator could be water

a record minimum arctic sea ice extent and area in 2002 1 arctic sea ice extent and area in september 2002 reached their lowest levels recorded since 1978 these conditions likely resulted from 1 anomalous warm southerly winds in spring advecting ice poleward from the siberian coast 2 persistent low pressure and high temperatures over the arctic ocean in summer promoting ice divergence and rapid melt

dynamic fluid recycling at laguna caliente poas costa rica before and during the 2006 ongoing phreatic eruption cycle 2005 10

locally distributed ground deformation in an area of potential phreatic eruption midagahara volcano japan detected by single look based insar time series analysis abstract although it is difficult to monitor the spatial extent and temporal evolution of local and small magnitude ground inflation this information is vital to assess the potential for phreatic eruption herein we demonstrate the detection of locally distributed ground deformation preceding the enhancement of geothermal activity in the midagahara volcano japan through the application of single look based interferometric synthetic aperture radar analysis in the jigoku dani geothermal area the ground deformation proceeded at a low speed of 4 cm year at most with a spatial extent of 500 m in the east west direction and 250 m in the north south direction the deformation can be recognized to progress from 2007 at the latest to 2010 after which the geothermal activity increased with the collapse of sulfur towers and the appearance of active fumaroles and boiling water on the ground surface the most deformed area corresponds to the geothermal area with the highest activity observed on the ground surface assuming a sill opening model the deformation source is estimated to be located at a depth of 50 m from the surface with a speed of 7 cm year at most which is consistent with the depth of the highly conductive medium inferred from magnetotelluric analyses this may suggest that volcanic fluid and or heat was injected into the fluid rich medium from depth and caused the ground inflation our results demonstrate that high spatial resolution deformation data can be an effective tool to monitor subsurface pressure conditions with pinpoint spatial accuracy during the build up to phreatic eruptions

variability of fram strait ice flux and north atlantic oscillation we estimate the winter sea ice export through the fram strait using ice motion from satellite passive microwave data sea ice motion october may is obtained by tracking the displacement of common features in sequential 85 and 37 ghz brightness temperature fields the average winter area flux over the 18 year record 1978 1996 is 670 000 km2 7 of the area of the arctic ocean the winter area flux ranges from a minimum of 450 000 km2 in 1984 to a maximum of 906 000 km2 in 1995 the daily monthly and interannual variabilities of the ice area flux are high there is an upward trend in the ice area flux over the 18 year record the average winter volume flux over the winters of october 1990 through may 1995 is 1745 km3 ranging from a low of 1375 km3 in the 1990 flux to a high of 2791 km3 in 1994 the sea level pressure gradient across the fram strait explains more than 80 of the variance in the ice flux over the 18 year record we use the coefficients from the regression of the time series of area flux versus pressure gradient across the fram strait and ice thickness data to estimate the summer area and volume flux the average 12 month area flux and volume flux are 919 000 km2 and 2366 km3 we find a significant correlation r 0 86 between the area flux and positive phases of the north atlantic oscillation nao index over the months of december march correlation between our 5 years of volume flux estimates and the nao index gives r 0 56 during the high nao years a more intense icelandic low increases the gradient in the sea level pressure by almost 1 mbar across the fram strait thus increasing the atmospheric forcing on ice transport correlation is reduced during the negative nao years because of decreased dominance of this large scale atmospheric pattern on the sea level pressure gradient across the fram strait

late pleistocene hansel valley basaltic ash northern lake bonneville utah usa abstract the hansel valley ash bed lies within 5 cm of the base of deposits of lake bonneville 28 ka in the vicinity of great salt lake and provides a useful stratigraphic marker for this area of the lake basin however it has not been matched to an eruptive edifice presumably because such an edifice was eroded by waves of lake bonneville we present data for the chemical composition of the tephra and for possible matching lavas and tephras of the region as well as grain size data for the tephra in an attempt to identify the location of the eruption matches with other tephras are negative but lavas near the coarsest ash deposits match well with the distinctive high values of tio2 and p2o5 of the ash neither chemistry nor grain size data points uniquely to a source area but an area near the northwest shore of great salt lake and within curlew valley is most likely the hansel valley ash is an example of an ash that has no direct numerical date from proximal deposits despite considerable study yet nonetheless is useful for stratigraphic studies by virtue of its known stratigraphic position and approximate age basaltic tephras commonly are not as widespread as their rhyolitic counterparts and in some cases apparently are produced by eruptive sources that are short lived and whose edifices are not persistent

pyroclastic density current from the 1888 phreatic eruption of bandai volcano ne japan abstract the great eruption of july 15 1888 at bandai volcano produced large phreatic explosions and a major debris avalanche toward the northern foot this eruption is characterized as follows 1 there was no significant precursor 2 the eruption and collapse of the volcanic edifice were triggered by an earthquake with a magnitude of about 5 3 the initial explosions were accompanied with a pyroclastic density current 4 the main explosive eruption quickly ceased a few minutes after the eruption began 5 a subsequent late stage plume rose buoyantly to a height of 5000 m falling with a heavy warm rain which generated a lahar and 6 ejected materials were made up wholly of pre existing rock fragments with no juvenile glass shards the main branch of the pyroclastic density current cascaded from the summit for a distance of 6 km along the biwazawa valley on the southeast flank the heim coefficient of the reconstructed energy line slope for the density current is 0 223 to 0 296 the estimated velocity using these values is less than 100 m s the density current deposit consists of normally graded parallel bedded or scour fill cross bedded thin layers of coarse ash and lapilli except for coarse massive breccia near the vent the sedimentary structures and grain size data suggest that the pyroclastic materials were transported in traction saltation and true suspension the estimated velocity is competent for transportation of the deposit the time sequence suggests that the seismic shocks and subsequent collapse of the edifice broke the confined hydrothermal system and caused the phreatic explosions the pressurized hydrothermal fluids had been presumably stored due to self sealing of the system because hydrothermal activities had been vigorous at the summit region until the july 15 seismic shocks collapse of the dry and dense initial eruption column generated the density current which spilled toward the opposite side of the crater along the topographic lows the change from the collapse to the late stage ascending plume results from a decrease in the rock fragment contents which made the plume light and wet this is because that a decrease in the fraction of rock fragments causes an increase in the fraction of steam produced within the plume the occurrence of the water flushed ash fall and lahar during the late stage eruption is consistent with this model

numerical model of crater lake eruptions we present results from a numerical investigation of subaqueous eruptions involving superheated steam released through a lake mimicking the volcanic setting at mt ruapehu the simulations were conducted using an adaptive mesh multi material hydrodynamics code with thermal conduction sage simple adaptive grid eulerian parameters investigated include eruption pressure lake level and mass of superheated vapor the simulations produced a spectrum of eruption styles from vapor cavities to radial jets that resulted in hazards that ranged from small scale waves to high amplitude surges that reached and cascaded over the edge of the crater rim there was an overall tendency for lake surface activity to increase including wave amplitude with increasing mass of superheated vapor and eruption pressure surface waves were induced by the formation and collapse of a gas cavity the collapse of the cavity is considered to play a major role in the characteristic features observed during a subaqueous eruption the additional mass of superheated vapor produced a larger cavity that displaced a larger area of the lake surface resulting in fast moving surges upon the collapse of the cavity high lake levels 90 m appear to suppress the development of explosive jetting activity when eruption pressures are 10 mpa vertical jets and radial ejections of steam and water can occur in water depths 90 m less explosive eruption styles can produce hazardous events such as lahars by the outward movement of surface waves over the crater rim

cyclic processes and factors leading to phreatic eruption events insights from the 25 september 2007 eruption through ruapehu crater lake new zealand abstract a dangerous block ash eruption occurred without warning from ruapehu crater lake on 25 september 2007 ending a 6 month period of temperature decline in the lake the northerly directed blast sent ballistics of up to 2 m diameter more than 2 km from the source the ejecta comprised a variety of volcano lacustrine lithologies many showing evidence of intense hydrothermal alteration petrographic studies of the ballistics reveal numerous examples of pores vesicles being filled with assemblages of elemental sulphur anhydrite pyrite and natroalunite and many ballistics exuded liquid sulphur from their pores during cooling at atmospheric pressure up to 5 of the ash was comprised of fine grained juvenile glass material confirming the presence of magma in the shallow vent environment a long recognised characteristic of this volcano is the thermal cycling behaviour of the crater lake behaviour which has remained effectively unchanged through two magmatic eruption events in 1945 and in 1995 96 airborne measurements of co2 and so2 flux from the volcano since 2003 show a strong positive correspondence with temperature cycling in the lake pointing to a definitive link between heat and mass discharge through the system low so2 emission rates and c s mole ratios 30 were typical of the period 2003 to early 2007 and appear to reflect vigorous scrubbing of s gases in the hydrothermal system during this time to better understand the chemical and physical processes operating in this very dynamic volcanic hydrothermal system and its propensity to develop potentially dangerous hydrothermal seals we have developed an integrated finite difference tough2 heat mass transport simulation of the hydrothermal environment the model which is constrained by observed heat and mass flux characteristics of the volcano demonstrates the transient nature of the heating cycles on the vent lake system of particular interest is the role of co2 as a relatively inert pressure transmitting medium in the hydrothermal environment seal formation was simulated using the reactive transport code x1t which showed that condensation of magmatic vapour into a highly porous medium of andesitic composition leads to rapid formation of an elemental sulphur anhydrite natroalunite mineral assemblage and a drastic reduction in permeability we suggest that since the 1995 96 vent clearing eruptions a shroud of elemental sulphur and other alteration phases formed along the margins of the 2 phase liquid vapour region enclosing the conduit this effectively seals the upper portion of the vent from the adjacent hydrostatically controlled environment and allows for development of pressurised vapour static gas columns beneath the northern and central vents

wovodat an online growing library of worldwide volcanic unrest abstract the world organization of volcano observatories wovo with major support from the earth observatory of singapore is developing a web accessible database of seismic geodetic gas hydrologic and other unrest from volcanoes around the world this database wovodat is intended for reference during volcanic crises comparative studies basic research on pre eruption processes teaching and outreach data are already processed to have physical meaning e g earthquake hypocenters rather than voltages or arrival times and are historical rather than real time ranging in age from a few days to several decades data from 900 episodes of unrest covering 75 volcanoes are already accessible users can visualize and compare changes from one episode of unrest or from one volcano to the next as the database grows more complete users will be able to analyze patterns of unrest in the same way that epidemiologists study the spatial and temporal patterns and associations among diseases wovodat was opened for station and data visualization in august 2013 and now includes utilities for data downloads and boolean searches many more data sets are being added as well as utilities interfacing to new applications e g the construction of event trees for more details please see www wovodat org

resistivity structure and geochemistry of the jigokudani valley hydrothermal system mt tateyama japan abstract this study clarifies the hydrothermal system of jigokudani valley near mt tateyama volcano in japan by using a combination of audio frequency magnetotelluric amt survey and hot spring water analysis in order to assess the potential of future phreatic eruptions in the area repeated phreatic eruptions in the area about 40 000 years ago produced the current valley morphology which is now an active solfatara field dotted with hot springs and fumaroles indicative of a well developed hydrothermal system the three dimensional 3d resistivity structure of the hydrothermal system was modeled by using the results of an amt survey conducted at 25 locations across the valley in 2013 2014 the model suggests the presence of a near surface highly conductive layer of 2 o isotopic ratios all hot spring waters had low ph and could be categorized into three types on the basis of the cl so 4 2 concentration ratio with all falling largely on a mixing line between magmatic fluids and local meteoric water lmw the geochemical analysis suggests that the hydrothermal system includes a two phase zone of vapor liquid a comparison of the resistivity structure and the geochemically inferred structure suggests that a hydrothermal reservoir is present at a depth of approximately 500 m from which hot spring water differentiates into the three observed types the two phase zone appears to be located immediately beneath the cap rock structure these findings suggest that the hydrothermal system of jigokudani valley exhibits a number of factors that could trigger a future phreatic eruption

an example of health hazard people killed by gas during a phreatic eruption dieng plateau java indonesia february 20th 1979 on february 20th 1979 142 inhabitants of dieng plateau indonesia were asphyxiated by poisonous gases during a mild phreatic eruption from later fields gas collection and analysis the casualties are considered to be due to co2 rich volcanic gases

debris flow evolution and the activation of an explosive hydrothermal system te maari tongariro new zealand abstract analysis of the pre and post eruption topography together with observations of the avalanche deposition sequence yields a triggering mechanism for the 6 august 2012 eruption of upper te maari the avalanche was composed of a wedge of c 683 000 774 000 m 3 of coarse breccia spatter and clay rich tuffs and diamictons which slid from the western flanks of the upper te maari crater the failure plane is considered to be a hydrothermally altered clay layer this landslide led to a pressure drop of up to 0 5 mpa enough to generate an explosive eruption from the hydrothermal system below which had been activated over the months earlier by additional heat and gas from a shallow intrusion the landslide transformed after c 700 m into a clay rich cohesive debris flow eroding soils from steep narrow stretches of channel before depositing on intermediate broad flatter reaches after each erosive reach the debris flow contained greater clay and mud contents and became more mobile at c 2 km flow distance however the unsaturated flow stopped due to a lack of excess pore pressure this volume controlled flow deposited thick steep sided lobes behind an outer levee accreting inward and upward to form a series of curved surface ridges

a heating process of kuchi erabu jima volcano japan as inferred from geomagnetic field variations and electrical structure since august 2000 we have recorded the total intensity of the geomagnetic field at the summit area of kuchi erabu jima volcano where phreatic eruptions have repeatedly occurred a time series analysis has shown that the variations in the geomagnetic field since 2001 have a strong relationship to an increase in volcanic activity these variations indicate thermal demagnetization of the subsurface around the presently active crater the demagnetization source for the early variations until summer 2002 was estimated at about 200 m below sea level for the variations since 2003 the source was modeled on the basis of the expansion of a uniformly magnetized ellipsoid the modeling result showed that the source is located at 300 m above sea level beneath the crater we carried out an audio frequency magnetotelluric survey with the aim of obtaining a relation between the demagnetization source and the shallow structure of the volcano a two dimensional inversion applied to the data detected two good conductors a shallow thin one which is restricted to a region around the summit area while the other extends over the edifice at depths between 200 and 800 m these conductors are regarded as clay rich layers with low permeability which were assumed to be generated through hydrothermal alteration the demagnetization source for the early variations was possibly located at the lower part of the deep conductor and the source after 2003 lies between the two conductors where groundwater is considered to be abundant based on these results as well as on seismological geodetic and geochemical information we propose a heating process of the kuchierabu jima volcano in the initial stage high temperature volcanic gases supplied from the deep seated magma remained temporarily at the level around the lower part of the less permeable deep conductor since the ascent path had not yet been established then when the pathway developed as a result of repeated earthquakes it became possible for a massive flux of volcanic gases to ascend through the conductor the high temperature gases reached the aquifer located above the conductor and the heat was efficiently transported to the surrounding rocks through the groundwater as a consequence an abrupt increase of the gas flux and di ffusion of the heat through the aquifer occurred and the high temperature zone expanded since the high temperature zone is located beneath another conductor which acts as caprock we assume that the energy of the phreatic explosion is accumulated there

a review on phreatic eruptions and their precursors abstract an analysis of the reported information on 132 historical phreatic events indicates that most of these 115 were not followed by a magmatic or phreatomagmatic eruption only in 18 cases precursory phenomena are reportedly lacking whereas they are recognized for the majority 72 of the considered cases these precursors have been analyzed as a function of the kind of phreatic event and of its possible triggering mechanism unfortunately the quality of the available information is poor however data suggest that anomalous seismicity ground deformation changes in the output chemistry and temperature of fumaroles and thermal springs are potential mid term precursors whereas seismic tremor is a common short term precursor

dynamics of shallow hydrothermal eruptions new insights from vulcano s breccia di commenda eruption understanding the dynamics and effects of hydrothermal eruptions is crucial to the hazard assessment in both volcanic and geothermal areas eruptions from hydrothermal centres may occur associated with magmatic phases but also as isolated events without magmatic input with the most recent examples being those of te maari tongariro new zealand in 2012 and ontake japan in 2014 the most recent caldera of the island of vulcano southern italy hosts in its centre the la fossa cone active since 5 5 ka and now characterised by continuous fumarolic degassing in historical times la fossa cone has experienced several hydrothermal eruptions with the most violent event being the breccia di commenda eruption that occurred during the thirteenth century ad based on analysis of 170 stratigraphic logs we show that the breccia di commenda eruption occurred in three main phases after an opening low intensity ash emission phase phase 1 the eruption energy climaxed during phase 2 when a series of violent explosions produced an asymmetric shower of ballistic blocks and the contemporaneous emplacement of highly dispersed lithic rich blast like pyroclastic density currents pdcs the tephra units emplaced during phase 2 ranging in volume from 0 2 to 2 7 105 m3 were covered in turn by thin ash fall deposits phase 3 the dynamics of the most violent and intense stage of the eruption phase 2 was investigated by numerical simulations a three dimensional numerical model was applied describing the eruptive mixture as a eulerian eulerian two phase non equilibrium gas particle fluid plus a one way coupled lagrangian ballistic block fraction at the initial simulation time a mass of about 109 kg with initial overpressure above 10 mpa and a temperature of 250 c was suddenly ejected from a 200 m long eastward inclined nne ssw trending fissure the mass release formed blast like pdcs on both sides of the fissure and launched ballistic blocks eastwards field investigations and numerical simulations confirm that hydrothermal explosions at la fossa cone include intense ballistic fallout of blocks emission of pdcs potentially travelling beyond the la fossa caldera and significant ash fallout the hazard associated with both ballistic impact and pdc ingress as associated with hydrothermal eruption is significantly larger with respect to that associated with vulcanian type events of la fossa

first estimates of fumarolic so2 fluxes from putana volcano chile using an ultraviolet imaging camera abstract putana is a stratovolcano in the central andes volcanic zone in northern chile on the border with bolivia fumarolic activiy has been visible at its summit crater at 5890 m altitude from long distances since the early 1800s however due to its remote location neither detailed geological studies have been made nor gas fluxes have been monitored and therefore its evolution remains unknown on november 28 2012 an ultraviolet uv imaging camera was transported to putana and for about 30 min images of the fumaroles were recorded at 12 hz these observations provide the first measurements of so2 fluxes from the fumarolic field of putana and demonstrate the applicability of the uv camera to detect such emissions the measurement series was used to assess whether the sampling rate of the data influences the estimate of the gas flux the results suggest that measurements made at 10 s and 1 min intervals capture the inherent turbulent variability in both the plume wind speed and so2 flux relatively high so2 fluxes varying between 0 3 kg s 1 and 1 4 kg s 1 which translates to 26 t day and 121 t day assuming constant degassing throughout the day were observed on november 28 2012 furthermore we demonstrate how an optical flow algorithm can be integrated with the so2 retrieval to calculate so2 fluxes at pixel level average values of 0 64 kg s 1 0 20 kg s 1 and 0 70 kg s 1 0 53 kg s 1 were retrieved from a classical transect method and the advanced optical flow based retrieval respectively assuming constant emissions throughout all times these values would results in an average annual so2 burden of 20 22 kt

experimental estimates of the energy budget of hydrothermal eruptions application to 2012 upper te maari eruption new zealand sudden hydrothermal eruptions occur in many volcanic settings and may include high energy explosive phases ballistics launched by such events together with ash plumes and pyroclastic density currents generate deadly proximal hazards the violence of hydrothermal eruptions or explosive power depends on the energy available within the driving fluids gas or liquid which also influences the explosive mechanisms volumes durations and products of these eruptions experimental studies in addition to analytical modeling were used here to elucidate the fragmentation mechanism and aspects of energy balance within hydrothermal eruptions we present results from a detailed study of recent event that occurred on the 6th of august 2012 at upper te maari within the tongariro volcanic complex new zealand the eruption was triggered by a landslide from this area which set off a rapid stepwise decompression of the hydrothermal system explosive blasts were directed both westward and eastward of the collapsed area with a vertical ash plume sourced from an adjacent existing crater all explosions ejected blocks on ballistic trajectories hundreds of which impacted new zealand s most popular hiking trail and a mountain lodge 1 4 km from the explosion locus we have employed rocks representative of the eruption source area to perform rapid decompression experiments under controlled laboratory conditions that mimic hydrothermal explosions under controlled laboratory conditions an experimental apparatus for 34 by 70 mm cylindrical samples was built to reduce the influence of large lithic enclaves up to 30 mm in diameter within the rock the experiments were conducted in a temperature range of 250 degrees c 300 degrees c and applied pressure between 4 mpa and 6 5 mpa which span the range of expected conditions below the te maari crater within this range we tested rapid decompression of pre saturated samples from both liquid dominated conditions and the vapor dominated field further we tested dry samples at the same pressure and temperature conditions results showed that host rock lithology and state of the interstitial fluid was a major influence on the fragmentation and ejection processes as well as the energy partitioning clasts were ejected with velocities of up to 160 m s as recorded by high speed camera in addition to rare large clasts analogous to ballistics a large amount of fine and very fine 63 mu m ash was produced in all experiments the efficiency of transformation of the total explosive energy into fragmentation energy was estimated between 10 to 15 depending on the host rock lithology while less than 0 1 of this was converted into kinetic energy our results suggest that liquid to vapor flashing expansion provides an order of magnitude higher energy release than steam expansion which best explains the dynamics of the westward and most energetic directed blast at te maari considering the steam flashing as the primary energy source the experiments suggested that a minimum explosive energy of 7 x 10 10 to 2 x 10 12 j was involved in the te maari blast experimental studies under controlled conditions compared closely to a field example are thus highly useful in providing new insights into the energy release and hazards associated with eruptions in hydrothermal areas c 2016 the author s published by elsevier b v

subsurface geology ancient hydrothermal systems and crater excavation processes beneath lake rotomahana evidence from lithic clasts of the 1886 ad rotomahana pyroclastics abstract the craters associated with the 1886 ad phreatomagmatic rotomahana eruption okataina volcanic centre new zealand and the near vent geology are now hidden beneath lake rotomahana and its post eruptive sediment fill lithic clasts from the near vent lithic lapilli ash deposits of the rotomahana pyroclastics are used in this study to trace geological and geothermal conditions before the eruption as well as vent excavation dynamics near vent deposit characteristics were described in the field representative lithic clasts were documented petrographically and unaltered clasts were analysed for major and trace element compositions the majority of the lithic clasts were rhyolites with subordinate ignimbrites and hydrothermally altered clasts and trace siltstone and silicified clasts the rhyolites were classified into four petrographic groups according to phenocryst content and assemblage and were more diverse with respect to geochemical compositions most of the rhyolite lithics in the rotomahana pyroclastics did not match the rhyolite domes exposed subaerially around the lake but did have affinities with the pre matahina caldera wairua rhyolite and potentially other older non exposed domes ignimbrites most likely correlated either to the matahina ignimbrite or older non exposed units hydrothermally altered rhyolite and ignimbrite lithic clasts are common and suggest that there has been a long lived hydrothermal system in this sector possibly dating back to early activity of the okataina volcanic centre the diversity in lithic types indicate a spatial variation in country rock lithology and strength which probably contributed to the vent position and morphology along the rotomahana fissure

heat source of the 2014 phreatic eruption of mount ontake japan we present petrological evidence of the shallow magmatic processes that may have supplied heat and gas to the eruption of mount ontake japan on 27 september 2014 which resulted in 63 fatalities ash from the eruption comprises primarily hydrothermally altered white toned rock fragments however the ash contains trace amounts 0 7 wt of vitreous less altered particles laps which are only altered on their surfaces suggesting rapid ascent through the hydrothermal system the laps are classified into two categories glassy and crystalline glassy laps comprise high silica rhyolitic glass 74 83 wt sio2 with rounded quartz chalcedony free vesicles and reversely zoned plagioclase cores 47 mol an rims 70 mol an indicating magma re heating crystalline laps have a groundmass like texture that suggests eutectic crystallization at shallow depths thermodynamic calculations indicate that the pre eruptive temperatures of the glassy and crystalline laps were 700 1300 c and 700 c respectively and that the storage depth was 4 km pressure 100 mpa the observed petrological features suggest that the laps were sourced from a magma recently intruded at shallow depths although crustal deformation i e the volume change associated with magmatic intrusion was insignificant prior to the 2014 eruption a clear signature of crustal deformation was observed in 2007 the source of which was located 3 km below the summit we suggest that the magma that was intruded 3 km below the summit in 2007 supplied the heat and gas for the 2014 phreatic eruption

high frequency field auto sampling of volcanic waters discharged near craters of active volcanoes temporal changes in volcanic water chemistry are reliable indicators of changes in volcanic activity conventionally volcanic water discharges are monitored through repetitive sampling and subsequent laboratory analysis samples are usually taken at intervals ranging between weekly and annually due to the campaign style of observations however samples collected in this way to track chemical changes were insufficient in terms of number frequency and temporal coverage completeness to allow quantitative tracking of volcanic activity in this study we thus developed a field auto sampling tool for collecting volcanic waters discharged near craters to improve the frequency of water sampling the basis of the developed tool is a commercially available xy plotter a drawing robot which can be controlled by a computer numerical control cnc operator code called g code to collect the water in the arranged sampling bottles the drawing pen of the xy plotter was replaced with a plastic drip pipe connected to a peristaltic pump a field test using the g code operated field auto sampling tool gofat was conducted at a hot spring at a crater area of hakone volcano in japan samples were collected at three hour intervals for 40 consecutive days the gofat successfully operated without stopping and collected a total of 332 water samples using the high temporal resolution samples obtained by the gofat we observed short term significant positive so4 peaks that endured for approximately a day which had not been detected by a repetitive sampling carried out in previous studies at this volcano our results clearly show the importance of high temporal resolution sampling even during quiescent periods to clarify the characteristics of the observed hot spring

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

phreatomagmatic and phreatic eruptions in locally extensive settings of southern central andes the tocomar volcanic centre 24 10 s 66 34 w argentina abstract two pleistocene eruptions are studied linked to an increment in the tectonic activity of an extensive system related to calama olacapato el toro fault cot fault the first one consisting of dense pyroclastic flows and pyroclastic surges interbedded with fall deposits was caused by a phreatoplinian eruption the second one consisting of a succession of pyroclastic surges derived from a phreatic eruption both eruption vents have been located in en echelon normal faults with an nne trend and conjugated to strike faults following an nnw trend in both episodes pyroclastic deposits and ballistic blocks follow an e sse trend the direction to which the fault planes and topographical slope lean the obsidianic deposit filling the first eruption vent has the same trend and dip as the main fault plane and provides preliminary evidences of syntectonic emplacement on the other hand pyroclastic surge deposits linked to the second episode offer evidences of syndepositional faulting with listric growth faults it is concluded that this local horizontal area linked to the cot fault was intensely active during the pleistocene and triggered both eruptions

hydrothermal eruptions at el humazo domuyo geothermal field argentina insights into the eruptive dynamics and controls abstract hydrothermal eruptions are explosive events driven by the sudden and violent vaporization of the water present in many hot water geothermal fields worldwide over recent years thermodynamical conditions of fluids and petrophisical geomechanical features of host rocks were mentioned as responsible of the wide range of eruptive styles and deposits of hydrothermal eruptions nevertheless geological and historical records show that pdc and fallout processes are underestimated as common processes linked to hydrothermal eruptions this paper analyzes from a multi disciplinary approach virtual outcrops modeling sedimentology petrographic and xdr studies facies modeling eye witness source analysis and stratigraphy the pristine holocene historic hydrothermal eruptive record of el humazo manifestation domuyo geothermal field patagonia argentina different eruptive scenarios are characterized by ballistic ejection pdc and or fallout mechanisms with discernible tefra composition and granulometry associated with both excavational and or aggradational landforms we show how diverse eruptive dynamics are controlled by pre eruptive internal and external factors such as reservoir energy depth of the explosion fragmentation levels physical properties and structural anisotropy of the host rocks and eruptive center migrations we consider that this case study may be useful not only for the application in the assessment of the volcanic hazard associated with the domuyo geothermal field but also contributes to the knowledge of the eruptive dynamics in other geothermal systems with similar characteristics

a baroclinic mechanism for the eddy feedback on the zonal index a baroclinic mechanism for the positive eddy feedback on the zonal index is proposed the author considers the quasigeostrophic response of the zonally averaged flow to forcing by baroclinic eddies the transient response to eddy forcing is a largely barotropic acceleration of the westerly flow and a reduction of the baroclinicity at the latitudes of eddy generation but over time the action of surface drag leads to enhanced baroclinicity at these latitudes the steady state response has positive baroclinicity at the latitude of eddy generation if the eddies propagate away from this latitude before they dissipate this reinforcement of the low level baroclinicity provides a positive feedback if it is assumed that baroclinic eddies are generated more vigorously in regions of stronger low level baroclinicity the proposed mechanism explains observed and modeled features of zonal index variations the frequency and drag dependence of eddy feedback the bandedness in latitude of zonal wind variations and the tendency for anomalies in the zonally averaged zonal wind to drift poleward over time

mechanisms of unrest and eruption at persistently restless volcanoes insights from the 2015 eruption of telica volcano nicaragua many of earth s volcanoes experience well defined states of quiescence and unrest with unrest occasionally culminating in eruption some volcanoes however experience an unusually protracted i e decades long period of noneruptive unrest and are thus categorized as persistently restless volcanoes prvs the processes that drive persistently restless volcanism are poorly understood as our knowledge of prvs is currently based on a small number of case studies here we examine multidisciplinary observations of the 2015 eruptive episode at telica volcano nicaragua in the context of its long term behavior we suggest that the latter phases of the 2015 eruption were ultimately driven by destabilization of its shallow magma reservoir based on previous geodetic seismic studies of telica geirsson et al 2014 https doi org 10 1016 j jvolgeores 2013 11 009 rodgers et al 2013 https doi org 10 1016 j jvolgeores 2013 08 010 and 2015 https doi org 10 1016 j jvolgeores 2014 11 012 and on multiparameter observations at telica over a 7 year period we propose that three distinct states of unrest occur at telica over decadal timescales a stable open state involving steady conduit convection and two distinct unstable states that may lead to eruptions in the weak sealing state phreatic explosions result from steady conduit convection underlying a weak seal in the destabilized state destabilization of the top of the convecting magma in the conduit leads to rapid accumulation of high pressures leading to strong impulsive phreatomagmatic explosions our observations and interpretations suggest that continuous seismic ground based deformation gas emission and thermal monitoring and interpretation of these data within a paradigm of sustained conduit convection modulated by episodes of sealing and destabilization of shallow magma reservoirs may allow robust forecasting of eruption potential energy and duration at telica and similar prvs worldwide

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

a numerical model simulation of a summer reversal of the beaufort gyre abstract ice drift derived from the polar ice prediction system pips is used to study the sea ice circulation of the beaufort and chukchi seas in the late summer model simulations for the years 1983 1986 and 1987 show that the anticyclonic beaufort gyre reverses to cyclonic circulation in the late summer this result is due to a change in the mean atmospheric surface pressure drifting buoys from 1983 confirm this reversal of the beaufort gyre sea ice models ice drift beaufort gyre

volcanic hazards from bezymianny and bandai type eruptions major slope failures are a significant degradational process at volcanoes slope failures and associated explosive eruptions have resulted in more than 20 000 fatalities in the past 400 years the historic record provides evidence for at least six of these events in the past century several historic debris avalanches exceed 1 km3 in volume holocene avalanches an order of magnitude larger have traveled 50 100 km from the source volcano and affected areas of 500 1500 km2 historic eruptions associated with major slope failures include those with a magmatic component bezymianny type and those solely phreatic bandai type the associated gravitational failures remove major segments of the volcanoes creating massive horseshoe shaped depressions commonly of caldera size the paroxysmal phase of a bezymianny type eruption may include powerful lateral explosions and pumiceous pyroclastic flows it is often followed by construction of lava dome or pyroclastic cone in the new crater bandai type eruptions begin and end with the paroxysmal phase during which slope failure removes a portion of the edifice massive volcanic landslides can also occur without related explosive eruptions as at the unzen volcano in 1792 the main potential hazards from these events derive from lateral blasts the debris avalanche itself and avalanche induced tsunamis lateral blasts produced by sudden decompression of hydrothermal and or magmatic systems can devastate areas in excess of 500km2 at velocities exceeding 100 m s 1 the ratio of area covered to distance traveled for the mount st helens and bezymianny lateral blasts exceeds that of many pyroclastic flows or surges of comparable volume the potential for large scale lateral blasts is likely related to the location of magma at the time of slope failure and appears highest when magma has intruded into the upper edifice as at mount st helens and bezymianny debris avalanches can move faster than 100 ms 1 and travel tens of kilometers when not confined by valley walls avalanches can affect wide areas beyond the volcano s flanks tsunamis from debris avalanches at coastal volcanoes have caused more fatalities than have the landslides themselves or associated eruptions the probable travel distance l of avalanches can be estimated by considering the potential vertical drop h data from a catalog of around 200 debris avalanches indicates that the h l rations for avalanches with volumes of 0 1 1 km3 average 0 13 and range 0 09 0 18 for avalanches exceeding 1 km3 h l ratios average 0 09 and range 0 5 0 13 large scale deformation of the volcanic edefice and intense local seismicity precede many slope failures and can indicate the likely failure direction and orientation of potential lateral blasts the nature and duration of precursory activity vary widely and the timing of slope faliure greatly affects the type of associated eruption bandai type eruptions are particularly difficult to anticipate because they typically climax suddenly without precursory eruptions and may be preceded by only short periods of seismicity

volcanic hazard assessment for ruapehu composite volcano taupo volcanic zone new zealand ruapehu is a very active andesitic composite volcano which has erupted five times in the past 10 years historical events have included phreatomagmatic eruptions through a hot crater lake and two dome building episodes ski field facilities road and rail bridges alpine huts and portions of a major hydroelectrical power scheme have been damaged or destroyed by these eruptions destruction of a rail bridge by a lahar in 1953 caused the loss of 151 lives other potential hazards with holocene analogues include strombolian and sub plinian explosive eruptions lava extrusion from summit or flank vents and collapse of portions of the volcano the greatest hazards would result from renewed phreatomagmatic activity in crater lake or collapse of its weak southeastern wall three types of hazard zones can be defined for the phreatomagmatic events inner zones of extreme risk from ballistic blocks and surges outer zones of disruption to services from fall deposits and zones of risk from lahars which consist of tongues down major river valleys ruapehu is prone to destructive lahars because of the presence of 107 m3 of hot acid water in crater lake and because of the surrounding summit glaciers and ice fields the greatest risks at ruapehu are to thousands of skiers on the ski field which crosses a northern lahar path three early warning schemes have been established to deal with the lahar problems collapse of the southeastern confining wall would release much of the lake into an eastern lahar path causing widespread damage this is a long term risk which could only be mitigated by drainage of the lake

hydrothermal activity and subsoil complexity implication for degassing processes at solfatara crater campi flegrei caldera the solfatara area and its fumaroles are the main surface expression of the vigorous hydrothermal activity within the active campi flegrei caldera system at depth a range of volcanic and structural processes dictate the actual state of the hydrothermal system below the crater the presence of a large variety of volcanic products at shallow depth including pyroclastic fallout ash beds pyroclastic density current deposits breccias and lavas and the existence of a maar related fault system appears to exert major controls on the degassing and alteration behavior adding further to the complexity of this environment variations in permeability and porosity due to subsoil lithology and alteration effects may further influence fluid flow towards the surface here we report results from a field campaign conducted in july 2015 that was designed to characterize the in situ physical temperature humidity and mechanical permeability strength stiffness properties of the solfatara crater subsoil the survey also included a mapping of the surficial hydrothermal features and their distributions finally laboratory measurements porosity granulometry of selected samples were performed our results enable the discrimination of four main subsoils around the crater 1 the fangaia domain located in a topographic low in the southwestern sector 2 the silica flat domain on the western altered side 3 the new crust domain in the central area and 4 the crusted hummocks domain that dominates the north east and south parts these domains are surrounded by encrusted areas reworked material and vegetated soil the distribution of these heterogeneous subsoils suggests that their formation is mostly related to i the presence of the fangaia domain within the crater and ii a system of ring faults bordering it the subsoils show an alternation between very high and very low permeabilities a fact which seems to affect both the temperature distribution and surficial degassing a large range of surface temperatures from 25 up to 95 degrees c has been measured across these surfaces with the hottest spot corresponding to the mud pools the area of new crust formation and the crusted hummocks in the subsoil the distribution of temperature is more complex and controlled by the presence of coarser and more permeable sandy pebbly levels these act as preferential pathways for hot hydrothermal fluid circulation in contrast low permeability fine grained levels act as thermal insulators that remain relatively cold and hinder fluid escape to the surface hot gases reach the surface predominantly along vertical fractures when this occurs mound like structures can be formed by a cracking and healing process associated with significant degassing it is anticipated that the results presented here may contribute to an improved understanding of the hazard potential associated with the ongoing hydrothermal activity within the solfatara crater at this site the permeability of the near surface environment and its changes in space and time can affect the spatial and temporal distribution of gas and heat emission particularly in areas where reduction in permeability occurs it can produce pore pressure augmentation that may result in explosive events

water and gas chemistry of lake nyos and its bearing on the eruptive process abstract the isotopic and chemical composition of water samples collected from lake nyos some two and eight weeks after the eruption of august 21 1986 point to the existence of three distinct mixing regimes involving three water components an essentially homogeneous unmixed body of water at depths 100 m overlain by water increasingly affected by surface evaporation and a 5 10 m layer containing recent but pre eruption rain water the cationic constituents na k mg ca mn fe of the lake water correspond to the dissolution of around 0 1 g of local rock the waters are close to saturation with respect to siderite the composition of the gas dissolved in the deep lake waters 0 65 b w of co2 pco2 4 4b corresponds in mmol mol 1 to 996 co2 2 0 ch4 2 0 n2 0 05 ar 0 004 he 0 0002 h2 0 0001 ne co 2 13 c 3 4 and of he rair 5 5 suggest deep magmatic origins the 13c and 2h content of ch4 organic sedimentary origin the presence of aromatic hydrocarbons indicates very high temperatures of hydrocarbon formation exsolution of gas will first lead to the precipitation of siderite then iron hydroxide the chemistry of the lake waters points to a loss of some 240 000 t of co2 from the upper 100 m of the lake their isotopic composition is consistent with the assumption that the eruption was triggered by the accumulation of cold rain waters at the lake surface prior to the eruption inducing partial convective overturn there is no need to invoke addition of chemical or isotopic constituents from deeper levels during the eruption

changes in the thickness distribution of arctic sea ice between 1958 1970 and 1993 1997 1 submarine sonar data collected in the central arctic basin during middle and late summer were used to examine differences in the sea ice thickness distribution function g h between the periods 1958 1970 and 1993 1997 cruises during the former period were made in july and august whereas the 1993 1997 cruises were made in september and october seasonal correction was applied to adjust for the differences in thickness while ice drafts were from only seven submarine cruises and somewhat spatially limited results indicate that the fractional area covered by open water and first year ice increased from 0 19 to 0 30 during the time interval this was balanced by an 11 reduction of level multiyear and ridged ice substantial losses occurred in ice thicker than 2 m with an increase in the amount of 1 2 m ice the volume of ice less than 4 m thick remained nearly the same and the total volume decreased about 32 losses in the volume of thicker ice increased with increasing thickness part of the change in g h is likely caused by increased ice area export through fram strait in the late 1980s and early 1990s because decadal variations in the north atlantic oscillation and arctic oscillation indices correlate with ice export anomalies export induced changes in g h probably tend to be cyclical in nature however a substantial shift in the peak of g h suggests that changes in thermal forcing were also a major factor in the observed thinning

echo resonance and hydraulic perturbations in magma cavities application to the volcanic tremor of etna italy in relation to its eruptive activity a study is presented of spectral features of volcanic tremor recorded at mount etna sicily italy following the methods of analysis suggested by the resonant scattering formalism of gaunaurd and uberall 1978 1979a 1979b and the model for hydraulic origin of seidl et al 1981 the periods investigated include summit and flank eruptions that occurred between 1984 and 1993 recordings from a permanent station located near the top of the volcano were used and the temporal patterns associated with a the average spacing bar delta between consecutive spectral peaks in the frequency range 1 6 hz b the spectral shape and c the overall spectral amplitude were analyzed bar delta values are thought to depend on the physical properties of magma such as its density which in turn is controlled by the degree of gas exsolution variations in the spectral shape are tentatively attributed to changes in the geometrical scattering from the boundary of resonant conduits and magma batches finally the overall amplitude at the station should essentially reflect the state of turbulence of magma within the superficial ascending path a limit in the application of the resonant scattering formalism to the study of volcanic tremor is given by the fact that the fundamental modes and integer harmonics are difficult to identify in the frequency spectra as tremor sources are likely within cavities of very complex geometry rather than in spherical or cylindrical chambers as expected by theory this study gives evidence of some correlations between the analyzed temporal patterns and the major events in the volcanic activity related to both lava flow and explosions at the summit vents in particular relatively high values of bar delta have been attained during the se crater eruption of 1984 the complex eruptive phases of september october 1989 and the 1991 1993 flank eruption suggesting the presence of a relatively dense magma for all of these events conversely very low values have been recorded in coincidence with the december 1985 activity and the paroxysmal explosions at the summit craters of early 1990 which are interpreted here as fed by fluid vesiculated magma appreciable modifications in the spectral shape have been observed in relation to changes of the volcanic activity that probably preceded the opening and disactivation of shallow dykes or magma batches finally the overall amplitude seems to be a sensitive indicator of the state of gas turbulence within the shallow conduits as is suggested by the high values attained during phases of intense volcanic activity

stable hydrogen and oxygen isotopic compositions of water vapor in volcanic plumes sampled in glass bottles using cavity ring down spectroscopy abstract the isotopic compositions 2h and 18o of fumarolic h2o emitted during volcanic eruptions can distinguish the type of eruption magmatic or phreatic but direct sampling of fumarolic h2o in eruptive volcanoes is often neither practical nor safe in this study we developed a new analytical system to safely determine the isotopic compositions of fumarolic h2o from the volcanic plume samples taken in glass bottles the system consisted of stainless steel gas introduction line and a cavity ring down spectroscopic unit in the 1 l glass sample bottles analytical precision 1 was estimated to be better than 2 and 0 3 respectively when 3400 ppmv of h2o was introduced and better than 3 2h and 0 4 18o when 1800 ppmv of h2o was introduced the h2o concentration accuracy was better than 5 using this in situ collection method and the analytical system we determined the isotopic compositions of h2o in volcanic plume samples taken at iwo yama in the kirishima volcano group japan and deduced the isotopic composition of fumarolic h2o from the volcanic plume the reciprocal of the h2o concentration in the plume samples showed a good linear relationship with the isotopic composition the isotopic composition of fumarolic h2o from iwo yama estimated from the plume samples directly corresponded to the determined fumarolic h2o this method improves upon previous analyses to obtain the isotopic compositions of fumarolic h2o particularly by reducing tedious time consuming and dangerous sampling of water vapor at volcanic fumaroles

likelihood of basaltic eruptions as a function of volatile content and volcanic edifice size a simple physical model is used to link eruption likelihood in continental regions to the size and shape of the volcanic edifice as well as to magma density and volatile content a volcanic edifice acts as a surface load and modifies the stress field in upper crustal levels including the magma chamber it affects the critical magma overpressure for reservoir failure as well as the conditions of dyke ascent from reservoir to surface calculations are made for dyke ascent in the stress field due to an overpressured reservoir beneath an edifice different edifice shapes are investigated from shield volcanoes with gentle slopes to stratovolcanoes with steeper flanks beneath a mature volcanic edifice magmatic overpressures required for reservoir failure are large but not large enough for a dyke to reach the central vent area at the summit thus basaltic summit eruptions can only occur if the amount of dissolved volatiles exceeds some threshold value which increases with edifice size and hence must be in explosive regimes unless magma is able to degas at shallow depths for mature volcanic systems edifice collapse or destruction may lead to renewed basaltic activity through the central vent area

initial processing of volcanic seismic signals using hidden markov models nevado del huila colombia abstract volcanic eruptions are commonly preceded by seismic signals that carry important information about the underlying physical processes driving the eruptive activity the manual classification of this seismicity is often difficult during seismic crises and timely responses in volcanic surveillance depend upon on how fast this work is performed automatic classification programs are an excellent alternative because they can classify seismic signals in near real time although these programs have been successfully tested for many volcanoes they have not yet been applied to the monitoring of volcanic crises we automated the initial processing of the seismic activity recorded at nevado del huila volcano in colombia using hidden markov models the technique consists of classifying seismic signals extracting the main characteristics of each classified signal and deriving important physical parameters that are important in volcanic surveillance continuous seismic data from 2007 to 2012 were used to develop this project a total of 2142 events were selected to train the program the best characteristic model obtained during the training had an accuracy of 91 25 and a similar pattern in volcanic behavior to that from manual classification was modeled the encouraging results demonstrate that automatic classification programs are a powerful tool that can be used in surveillance and monitoring of active volcanoes as they provide timely information for the proper management of volcanic crises and subsequent hazards mitigation

migration of seismic activity associated with phreatic eruption at merapi volcano indonesia abstract phreatic activity of merapi started after nearly 2 years of quiescence following the october november 2010 eruption which was the largest in more than 100 years a dozen eruptions identified by visual and or seismic observations took place between august 2012 and april 2014 we present in this work the results of a detailed analysis of the april 20 2014 phreatic eruption we attempted to reconstruct the eruptive process which lasted for over 30 min to this end we determined the wavefield composition by polarization analysis located high frequency earthquakes occurring in the initial part of the eruption process and then determined the seismic source migration of low frequency part of the tremor like signal 0 3 3 hz over time source depth of low frequency signal was obtained by comparing the slowness vector calculated using 3 stations of the seismic antenna with a slowness vector model obtained by ray tracing in the structure taking into account the topography and a 1d velocity model obtained by spatial auto correlation analysis the results allow to distinguish 3 different phases 1 high frequency transients interpreted as the result of a sudden decompression caused by the transition of the volcanic fluid to a gaseous phase that occurred approximately 1 5 km deep this decompression process in the hydrothermal system generated a migration of the low frequency seismic source from 900 m to 1800 m above sea level 2 a second decompression process revealed by high frequency micro seismicity and associated to the migration of the low frequency tremor source which is marked first by a descent phase followed by a sharp ascent until reaching the surface the evolution of the back azimuth during the migration process indicates a slight inclination of the conduit presumably in the orientation of the dome fracture in the nw se direction this direction is consistent with the alignment of regional tectonic structures and with the directivity of eruption deposits 3 the seismic source then remains positioned at the altitude of the dome for over 10 min this phase probably corresponds to the ash emission process the average migration speed of the low frequency seismic source from the starting eruptive process to ash emission is about 5 m s

meteorological forcing of sea ice concentrations in the southern beaufort sea over the period 1979 to 2000 1 northern hemisphere sea ice areal extent and perhaps thickness have shown a detectable reduction over the past several decades this situation is particularly apparent in the southern beaufort sea the region encompassing the mackenzie shelf the cape bathurst polynya and the canada basin mobile pack ice all occur in a region referred to here as the canadian arctic shelf exchange study area cases in this paper we present results from an analysis of atmosphere sea ice and ocean coupling over the period 1979 to 2000 as a means of setting a physical science context for the cases research network operating over the period 2001 2005 results show that the cape bathurst polynya complex can be considered as a recurrent polynya particularly the flaw leads associated with the early opening of the polynya the polynya appears to be a consequence of the beaufort sea gyre acting like an ice bridge and a series of flaw leads creating conditions conducive to oceanic upwelling the sea ice average areal extent has been decreasing in this region over the period 1979 to 2000 large regional reductions are found i north of the yukon and alaska coasts in the region between the canada basin pack ice and the landfast sea ice and 2 at the eastern limit of the cape bathurst polynya in amundsen gulf the meteorological forcing of sea ice anomalies occurs through a full range of timescales and space scales at hemispheric scales a statistical cross correlation analysis between weekly sea ice concentration anomalies and the arctic oscillation accounts for a maximum of about 25 percent of the explained variance and show a surprising spatial coherence in correlation magnitudes both within the study area and northward along the canadian archipelago coast at local scales positive and negative concentration anomaly periods can be explained through local scale advective processes associated with regional scale sea level pressure 500 hpa geopotential heights and surface temperature anomalies

three dimensional p wave velocity structure of bandai volcano in northeastern japan inferred from active seismic survey the three dimensional p wave velocity structure of the bandai volcano has been revealed by tomographic inversion using approximately 2200 travel time data collected during an active seismic survey comprising 298 temporary seismic stations and eight artificial shots the key result of this study is the delineation of a high velocity anomaly vp 4 6 km s at sea level immediately below the summit peak this feature extends to depths of 1 2 km below sea level the near surface horizontal position of the high velocity anomaly coincides well with that of a positive bouguer gravity anomaly geological data demonstrate that sector collapses have occurred in all directions from the summit and that the summit crater has been repeatedly refilled with magmatic material these observations suggest that the high velocity region revealed in this study is a manifestation of an almost solidified magmatic plumbing system we have also noted that a near surface low velocity region vp 3 0 km s at sea level on the southern foot of the volcano corresponds to the position of volcanic sediments including ash and debris avalanche material in addition we have made use of the tomographic results to recompute the hypocenters of earthquake occurring during seismic swarms beneath the summit in 1988 and 2000 relocating the earthquakes using the three dimensional velocity model clearly indicates that they predominantly occurred on two steeply dipping planes low frequency earthquakes observed during the swarms in 2000 occurred in the seismic gap between the two clusters the hypocentral regions of the seismic swarms and the low frequency earthquakes are close to the higher velocity zone beneath the volcano s summit these observations suggest that the recent seismic activity beneath the summit is likely associated with thermal energy being released within the solidifying magmatic plumbing system

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

first detection of precursory ground inflation of a small phreatic eruption by insar abstract phreatic eruptions are caused by pressurization of geothermal fluid sources at shallow levels they are relatively small compared to typical magmatic eruptions but can be very hazardous however owing to their small magnitudes their occurrences are difficult to predict here we show the detection of locally distributed ground inflation preceding a small phreatic eruption at the hakone volcano japan through the application of interferometric synthetic aperture radar analysis the ground inflation proceeded the eruption at slow speed of 5 mm month with a spatial size of 200 m in the early stage and then it accelerated 2 months before the eruption that occurred for the first time in 800 900 yrs the ground uplift reached 30 cm and the eruption occurred nearby the most deformed part the deformation speed correlated well with inflation of spherical source located at 4 8 km below sea level thus suggesting that heat and or volcanic fluid supply from the spherical source maybe magma reservoir directly drove the subsurface hydrothermal activity our results demonstrate that high spatial resolution deformation data can be a good indicator of subsurface pressure conditions with pinpoint spatial accuracy during the preparatory process of phreatic eruptions

mass and heat flux balance of la soufriere volcano guadeloupe from aerial infrared thermal imaging abstract la soufriere of guadeloupe is an active volcano of lesser antilles that is closely monitored due to a high eruptive hazard potential since 1992 it exhibits a medium level but sustained background hydrothermal activity with low energy and shallow seismicity hot springs temperature increase and high flux acidic gas fumaroles at the summit the problem of estimating the heat balance and quantifying the evolution of hydrothermal activity has become a key challenge for surveillance this work is the first attempt of a global mapping and quantification of la soufriere thermal activity performed in february 2010 using aerial thermal infrared imagery after instrument calibration and data processing we present a global map of thermal anomalies allowing to spot the main active sites the summit area including the fumaroles of tarissan pit and south crater the ty fault fumarolic zone and the hot springs located at the vicinity of the dome in a second step we deduce the mass and the energy fluxes released by the volcano in particular we propose a simple model of energy balance to estimate the mass flux of the summit fumaroles from their brightness temperature and size in february 2010 tarissan pit had a 22 8 8 1 kg s 1 flux 1970 704 tons day 1 while south crater vents had a total of 19 5 4 0 kg s 1 1687 348 tons day 1 once converted into energy flux summit fumaroles represent 98 of the 106 30 mw released by the volcano the 2 remaining being split between the hot springs and the thermal anomalies at the summit and at the ty fault fumarolic zone these values are in the high range of the previous estimations highlighting the short term variability of the expelled fluxes such a heat flux requires the cooling of 1500 m 3 of magma per day in good agreement with previous geochemical studies

evolution of a small hydrothermal eruption episode through a mud pool of varying depth and rheology white island nz white island volcano new zealand was a host to multiple hydrothermal eruptive episodes within a mud sulphur pool in 2013 although hydrothermal activity is common at white island past events have largely gone undescribed in favour of the larger phreatomagmatic and magmatic eruptions here we detail the first and longest hydrothermal episode of 2013 lasting from 15 january to 7 february using video and photo analysis from tour operators and staff responsible for monitoring the volcano differences in the dominant bubble burst style across this episode led to the classification of four distinct eruption regimes 1 multiple irregular bursts on the pool surface 2 larger distinct symmetric hemispheres with starbursts and or followed by mud heaves 3 no initial pool surface deformation but a vertical steam jet followed by a sometimes large directed mud heave and 4 no lake and continuous pulsating dry ash and block venting the progression through these regimes is associated with a lowering lake level and a concomitantly increasing viscosity of the pool which initially comprises a low viscosity muddy water and partially evaporates to yield a shallow layer of high viscosity mud that ends with the complete drying up of the mud pool formation of primary mud hemispheres or gas jets is followed by heaves or secondary upheaval events the heights of these heaves are used as a measure of explosivity heights increase from 8 m during regime 1 on 15 january to 102 m during regime 3 on 28 january venting of dry mud during regime 4 developed on 29 january before a regression back to regime 1 took place on 7 february as the pool re established through observations of the shapes of ejected mud clots we propose that the increasing explosivity of higher number regimes is primarily due to increasing slug bubble lengths teamed with increasing mud pool viscosity we attribute a lesser control to the decreasing depth of the pool during its progressive desiccation which may in turn influence the bubble burst depth occasionally visible yellowing of the steam gas plume led us to suggest that elemental sulphur may also be present in the conduit and may also play a role in regulating bubble release dynamics although evidence for magmatic phreatomagmatic eruptions was present during eruptions later in 2013 we found no evidence for juvenile magma in the january february eruption episode described here however we concur with other investigators that magma was probably intruded to shallow levels and may have driven heat and gas flux our explanation for the correlation of pool depth mud viscosity and eruption regime is based on a conceptual model in which a pool is perched above a two phase hydrothermal system and is sensitive to changes in the heat and gas flux from shallow magma the variable release of gas and thermal perturbations in the course of the january february eruptive episode impacted the pool level the water to sediment ratio in the pool and thus its viscosity and in turn modulated the eruption regime the varying degree of explosivity throughout this episode calls for a new consideration of pool properties in assessing eruption hazards at this frequently visited volcano we additionally emphasise that ballistic hazards from small eruptions exist coupled with a range of seismic signals and that the hazard was greatest during infrasound tremor

pyroclastic deposits of san diego maar central colombia an example of a silicic magma related monogenetic eruption in a hard substrate