plinian eruptions at glacier peak and newberry volcanoes united states implications for volcanic hazards in the cascade range several fall deposits from glacier peak and newberry volcanoes both located in the cascade range united states have been studied to determine eruptive column heights intensities and volumes the late pleistocene eruptions of glacier peak ranged from small phreatic explosions to two plinian eruptions that each erupted more than 1 km 3 of magma at intensities 10 8 kg s generating plumes with heights 30 km at newberry volcano the last plinian eruption ca 1300 14 c yr b p had an intensity of 2 8 10 7 kg s and a plume height of 18 to 21 km about 0 1 km 3 of magma was erupted in the plinian phase followed by eruption of a pyroclastic flow and an obsidian lava flow combined with similar data from mount st helens mount rainier and mount mazama crater lake these eruptions define the range of plinian events that have occurred in the cascade volcanic arc in the past 12 k y during this period there have been plinian eruptions with plume heights between 11 and 55 km intensities between 10 6 and 10 9 kg s and volumes between 0 01 and 5 km 3 of magma all eruptions with intensities greater than or equal to 10 8 kg s also produced large volume pyroclastic flows and surges monitoring column height intensity during eruptions could help mitigate hazards because it may indicate pending generation of pyroclastic flows in the cascade range there have been at least 12 eruptions of 1 km 3 of tephra in the past 12 k y suggesting that eruptions of such magnitude occur about once every 1 k y although such frequencies vary greatly at each volcano the volume of magma erupted in each event correlates with both column height intensity and magma composition suggesting that eruptions of these volcanoes relate to the accumulation rate of magma in their reservoirs

structure and dynamics of decadal anomalies in the wintertime midlatitude north pacific ocean atmosphere system the structure and dynamics of decadal anomalies in the wintertime midlatitude north pacific ocean atmosphere system are examined in this study using the ncep ncar atmospheric reanalysis hadisst sst and simple ocean data assimilation data for 1960 2010 the midlatitude decadal anomalies associated with the pacific decadal oscillation are identified being characterized by an equivalent barotropic atmospheric low high pressure over a cold warm oceanic surface such a unique configuration of decadal anomalies can be maintained by an unstable ocean atmosphere interaction mechanism in the midlatitudes which is hypothesized as follows associated with a warm pdo phase an initial midlatitude surface westerly anomaly accompanied with intensified aleutian low tends to force a negative sst anomaly by increasing upward surface heat fluxes and driving southward ekman current anomaly the sst cooling tends to increase the meridional sst gradient thus enhancing the subtropical oceanic front as an adjustment of the atmospheric boundary layer to the enhanced oceanic front the low level atmospheric meridional temperature gradient and thus the low level atmospheric baroclinicity tend to be strengthened inducing more active transient eddy activities that increase transient eddy vorticity forcing the vorticity forcing that dominates the total atmospheric forcing tends to produce an equivalent barotropic atmospheric low pressure north of the initial westerly anomaly intensifying the initial anomalies of the midlatitude surface westerly and aleutian low therefore it is suggested that the midlatitude ocean atmosphere interaction can provide a positive feedback mechanism for the development of initial anomaly in which the oceanic front and the atmospheric transient eddy are the indispensable ingredients such a positive ocean atmosphere feedback mechanism is fundamentally responsible for the observed decadal anomalies in the midlatitude north pacific ocean atmosphere system

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

structure and emplacement of the nandurbar dhule mafic dyke swarm deccan traps and the tectonomagmatic evolution of flood basalts flood basalts such as the deccan traps of india represent huge typically fissure fed volcanic provinces we discuss the structural attributes and emplacement mechanics of a large linear tholeiitic dyke swarm exposed in the nandurbar dhule area of the deccan province the swarm contains 210 dykes of dolerite and basalt 1 km in length exposed over an area of 14 500 km2 the dykes intrude an exclusively basaltic lava pile largely composed of highly weathered and zeolitized compound pahoehoe flows the dykes range in length from 1 km to 79 km and in thickness from 3 to 62 m almost all dykes are vertical with the others nearly so they show a strong preferred orientation with a mean strike of n88 because they are not emplaced along faults or fractures they indicate the regional minimum horizontal compressive stress 3 to have been aligned n s during swarm emplacement the dykes have a negative power law length distribution but an irregular thickness distribution the latter is uncommon among the other dyke swarms described worldwide dyke length is not correlated with dyke width using the aspect ratios length thickness of several dykes we calculate magmatic overpressures required for dyke emplacement and depths to source magma chambers that are consistent with results of previous petrological and gravity modelling the anomalously high source depths calculated for a few dykes may be an artifact of underestimated aspect ratios due to incomplete along strike exposure however thermal erosion is a mechanism that can also explain this whereas several of the nandurbar dhule dykes may be vertically injected dykes from shallow magma chambers others particularly the long ones must have been formed by lateral injection from such chambers the larger dykes could well have fed substantial 1 000 km3 and quickly emplaced a few years flood basalt lava flows this work highlights some interesting and significant similarities and contrasts between the nandurbar dhule dyke swarm and regional tholeiitic dyke swarms in iceland sudan and elsewhere

postshield volcanism and catastrophic mass wasting of the waianae volcano oahu hawaii the 3 9 to 2 9 ma waianae volcano is the older of two volcanoes making up the island of oahu hawaii exposed on the volcanic edifice are tholeiitic shield lavas overlain by transitional and alkalic postshield lavas the postshield alkalic cap consists of aphyric hawaiite of the palehua member of the waianae volcanics overlain unconformably by a small volume of alkalic basalt of the kolekole volcanics kolekole volcanics mantle erosional topography including the uppermost slopes of the great lualualei valley on the lee side of the waianae range twenty new k ar dates combined with magnetic polarity data and geologic relationships constrain the ages of lavas of the palehua member to 3 06 2 98 ma and lavas of the kolekole volcanics to 2 97 2 90 ma the geochemical data and the nearly contemporaneous ages suggest that the kolekole volcanics do not represent a completely independent or separate volcanic event from earlier postshield activity thus the kolekole volcanics are reduced in rank becoming the kolekole member of the waianae volcanics magmas of the palehua and kolekole members have similar incompatible element ratios and both suites show evidence for early crystallization of clinopyroxene consistent with evolution at high pressures below the edifice however lavas of the kolekole member are less fractionated and appear to have evolved at greater depths than the earlier palehua hawaiites postshield primary magma compositions of the palehua and kolekole members are consistent with formation by partial melting of mantle material of less than 5 10 relative to waianae shield lavas within the section of palehua member lavas an increase with respect to time of highly incompatible to moderately incompatible element ratios is consistent with a further decrease in partial melting by approximately 1 2 this trend is reversed with the onset of eruption of kolekole member lavas where an increase in extent of partial melting is indicated the relatively short time interval between the eruption of palehua and kolekole member lavas appears to date the initial formation of lualualei valley which was accompanied by a marked change in magmatic conditions we speculate that the mass wasting event separating lavas of the palehua and kolekole members may be related to the formation of a large submarine landslide west and southwest of waianae volcano enhanced decompression melting associated with removal of the equivalent volume of this landslide deposit from the edifice is more than sufficient to produce the modeled increase of 1 2 in extent of melting between the youngest palehua magmas and the posterosional magmas of the kolekole member the association between magmatic change and a giant landsliding event suggests that there may be a general relationship between large mass wasting events and subsequent magmatism in hawaiian volcano evolution

late holocene hydrous mafic magmatism at the paint pot crater and callahan flows medicine lake volcano n california and the influence of h2o in the generation of silicic magmas this paper characterizes late holocene basalts and basaltic andesites at medicine lake volcano that contain high pre eruptive h2o contents inherited from a subduction related hydrous component in the mantle the basaltic andesite of paint pot crater and the compositionally zoned basaltic to andesitic lavas of the callahan flow erupted approximately 1000 14c years before present 14c years b p petrologic geochemical and isotopic evidence indicates that this late holocene mafic magmatism was characterized by h2o contents of 3 to 6 wt h2o and elevated abundances of large ion lithophile elements lile these hydrous mafic inputs contrast with the preceding episodes of mafic magmatism from 10 600 to 3000 14c years b p that was characterized by the eruption of primitive high alumina olivine tholeiite haot with low h2o 0 2 wt lower lile abundance and different isotopic characteristics thus the mantle derived inputs into the medicine lake system have not always been low h2o primitive haot but have alternated between haot and hydrous subduction related calc alkaline basalt this influx of hydrous mafic magma coincides temporally and spatially with rhyolite eruption at glass mountain and little glass mountain the rhyolites contain quenched magmatic inclusions similar in character to the mafic lavas at callahan and paint pot crater the influence of h2o on fractional crystallization of hydrous mafic magma and melting of pre existing granite crust beneath the volcano combined to produce the rhyolite fractionation under hydrous conditions at upper crustal pressures leads to the early crystallization of fe mg silicates and the suppression of plagioclase as an early crystallizing phase in addition h2o lowers the saturation temperature of fe and mg silicates and brings the temperature of oxide crystallization closer to the liquidus these combined effects generate sio2 enrichment that leads to rhyodacitic differentiated lavas in contrast low h2o haot magmas at medicine lake differentiate to iron rich basaltic liquids when these fe enriched basalts mix with melted granitic crust the result is an andesitic magma since mid holocene time mafic volcanism has been dominated primarily by hydrous basaltic andesite and andesite at medicine lake volcano however during the late holocene h2o poor mafic magmas continued to be erupted along with hydrous mafic magmas although in significantly smaller volumes

simple fluid dynamic models of volcanic rift zones the dynamics of magma flow through a reservoir connected to a fissure in an elastic medium is investigated magma is supplied to the reservoir at a rate which may vary with time the distribution of fluid pressure the elastic deformation of the reservoir walls and the characteristics of dyke intrusion are calculated for a range of reservoir sizes and supply rates magma is stored in the reservoir whilst magma is intruded in the fissure at high supply rates the reservoir pressure increases by large amounts and only small amounts of magma flow into the fissure conversely at low supply rates most of the magma supplied to the system is injected into the fissure for a given supply rate the amount stored depends weakly on the reservoir size and is largest for small reservoirs the delay between the onset of reservoir inflation i e the start of magma input and the opening of the fissure decreases with increasing reservoir size rapid deflation of the reservoir occurs if the supply rate decreases with time all else being equal the largest reservoir pressures are reached for high supply rates which suggests that these conditions lead to summit eruptions rift zone intrusions are most extensive at low supply rates

wind driven ocean currents and ekman transport oceanographic engineering of the woods hole oceanographic institution and the massachusetts institute of technology woods hole ma 02543 oceanographers have long sought to verify the theoretical ekman transport relation which predicts that a steady wind stress acting together with the coriolis force will produce a transport of water to the right of the wind in situ measurements of wind and ocean currents provide a detailed view of this phenomenon by separating the wind driven current from the measured total current and by averaging over a long record it is found that the observed transport is consistent with theoretical ekman transport to within about 10 percent in this case the wind driven transport is strongly surface trapped with 95 percent occurring in the upper 25 meters as a result of fair summer weather

seismic activity and ground deformation associated with 1995 phreatic eruption of kuju volcano kyushu japan abstract kuju volcano lies near aso caldera in central kyushu after a few hundred years of dormancy a phreatic eruption began with the ejection of about 20 000 m 3 ash on 11 october 1995 a number of new vents have opened on a series of lines striking east west on the eastern slope of mt hossho one of the domes of the kuju complex a few hundred meters from a pre existing fumarolic area after the eruption there has been continuous steam emission from the new vents there was the second ash eruption in december 1995 before these eruptions seismic events were rarely observed either near the site of the new vents or elsewhere under kuju volcano in the nearly 2 years since the first eruption several thousand earthquakes have been recorded these events have been very horizontally concentrated just to the north of the new vents vertically between 800 m above sea level and 1000 m below sea level very few earthquakes have been located on the southern side of the new vents there was clearly a strong high frequency attenuation affecting the seismic waves which passed through the region beneath the new vents to the seismometers south of mt hossho this evidence possibly indicates a thermal fluid content beneath the new vents suggesting that there is a seismic attenuating zone in the feeding area of the new vents nearly all the earthquake spectra were of dominantly high frequency but the percentage of earthquakes with predominantly low frequency spectra increased at times of enhanced volcanic activity volcanic tremors were also observed around the times of peak activity slope distance measurements have been made since the eruption the main results of these measurements are a contraction of more than 200 ppm in distances between mt hossho and points further north the significant distance changes occurred during seismic swarms this indicated that the seismic activities influenced ground deformation even though some of these swarms were 3 or 5 km from mt hossho the slope distance changes indicate that an area near the top of mt hossho has been moving to the northeast

dynamics of an interhemispheric teleconnection across the critical latitude through a southerly duct during boreal winter abstractin this study an interhemispheric teleconnection pattern across the critical latitude from southern africa through south asia to the north pacific was revealed in boreal winter monthly averaged 250 hpa streamfunction fields obtained from both the 40 yr ecmwf re analysis era 40 and the ncep ncar reanalysis data from 1957 58 to 2001 02 classical rossby wave theory for zonally varying flow in which the effects of the basic state meridional wind are ignored predicts that stationary rossby waves cannot propagate across easterlies to elucidate the underlying mechanisms responsible for this interhemispheric teleconnection the theoretical basis for stationary wave propagation across the critical latitude is considered taking into account meridional ambient flow the theoretical results suggest that the southerly flow over east africa the western indian ocean and south asia creates a path for the northward propagation of stationary waves across the critical latitude stationary wavenumber and grou

modulation of the tibetan plateau snow cover on the enso teleconnections from the east asian summer monsoon perspective theeastasiansummermonsoon easm mayexhibitratherlargevariabilitybetweenyearscharacterized by the same enso phase such inconsistency reduces the easm predictability based on enso results in this study show that the tibetan plateau snow cover tpsc exerts a modulating effect on enso teleconnections and enso significantly correlates with the easm only during the reduced tpsc summers three dimensional circulation structures are examined to manifest that the typical enso signals in reduced tpsc summers tend to be stronger than in excessive tpsc summers numerical and theoretical evidences indicate that the anomalously reduced tpsc can force positive geopotential height anomalies at the upper troposphereandweakenthejetstreamsacrosseasternasiaandnorthwesternpacific governedbysuchbasic state zonal flows the extratropical rossby wave response to the enso forcing usually has a larger amplitude and pronounced westward development in such case enso extends its influences to eastern asia and enhances its connection with the easm

quaternary volcanic stratigraphy of managua nicaragua correlation and source assignment for multiple overlapping plinian deposits a tephrochronological study that began as an active fault mapping program in managua nicaragua following the 1972 earthquake has yielded information with broader geologic relevance seven principal widespread quaternary air fall deposits the managua sequence have been defined the deposits are basaltic or rhyodacitic span probably 11 km 3 dense rock equivalent and are classified as plinian or phreatoplinian regardless of chemical composition two of the units were radiocarbon dated at 6 600 yr b p and 21 000 yr b p as a result of this study ages of the other layers are not as well constrained but are estimated on the basis of soil development and position in the section correlation and source assignment were particularly difficult because of incomplete exposure and similarity of physical and chemical features but they were accomplished with a combination of detailed measurement and sampling at managua reconnaissance mapping and sampling at potential vent areas and application of petrographic mineralogic and chemical correlation methods the close similarity among the rhyodacite pumices posed the greatest difficulty for correlation cluster analysis applied to multielement xrf chemical analyses of pure glass separates gave the best results the clarification of the managua sequence has revealed the local geologic history of managua has characterized the average largest recent nicaraguan eruptions and has defined time stratigraphic markers used for archaeologic and engineering purposes additionally it has provided a regional framework within which to interpret and correlate more detailed studies of individual nicaraguan volcanoes

tectonic stress controls on ascent and emplacement of magmas abstract the tectonic stresses can significantly affect the propagation of a magma filled crack it has been pointed out that the rheological boundaries control the emplacement of magmas through the effect of stress however it has not been clarified how the role of rheological boundaries depends on the regional tectonic and thermal states we have evaluated the role of rheological boundaries under various tectonic and thermal conditions and found that the level of magma emplacement may jump according to the changes in the tectonic force or the surface heat flow the stress profiles were estimated by a simple model of lithospheric deformation we employed a three layer model of the lithosphere the upper crust the lower crust and the upper mantle have different rheological properties a constant horizontal force is applied to the lithosphere and the horizontal strain is assumed to be independent of depth when realistic tectonic forces 10 11 n m are applied the rheological boundaries mainly control the emplacement of magma the emplacement is expected at the moho the upper lower crust boundary and the brittle ductile boundary for lower tectonic forces 11 n m the tectonic stress no longer plays an important role in the emplacement of magmas when the tectonic stress controls the emplacement the roles of rheological boundaries strongly depend on the surface heat flow when the surface heat flow is relatively high 80 mw m 2 the stress in the mantle is quite low and the moho cannot trap ascending magmas for relatively low heat flow 2 on the other hand the moho acts as a magma trap and the upper lower crust boundary acts as a magma trap only when the magma supply rate is sufficiently high our results suggest that the emplacement depth can change responding to the change in the tectonic force and or that in the surface heat flow this may provide us a key to understand the relation between the evolution of a volcanic region and its tectonic and or thermal history

on the mechanisms of decadal variability of the north pacific gyre oscillation over the 20th century the decadal variability of the north pacific gyre oscillation npgo over the 20th century is examined from a long term integration of the simple ocean data assimilation soda reanalysis the npgo is reflected by the second dominant pattern of sea surface height ssh variability in soda with a north south dipole structure over the northeast pacific ssh anomalies in this region exhibit distinct decadal variability with a significant spectrum peak at approximately 18 years the upper ocean heat budget reveals that this dipole structure associated with the npgo is predominantly due to the anomalous ekman pumping and ekman advection induced by the surface wind the npgo mode in soda reanalysis originates from atmosphere stochastic noise north pacific oscillation which has a meridional dipole pattern but no preferred time scale the oceanic planetary wave particularly the advective baroclinic mode integration of atmospheric stochastic noise leads to a spatial resonance with preferred decadal time scale the limitation of current study is also discussed

origin of bimodal volcanism southern basin and range province west central arizona miocene volcanic rocks in the castaneda hills area west central arizona are interbedded with continental clastic sedimentary rocks minor limestone gravity glide blocks of precambrian and paleozoic rocks and monolithologic megabreccia the sedimentary and volcanic units dip to the southwest and are offset by northwest trending listric and high angle normal faults the listric faults coalesce at the rawhide detachment fault which overlies mylonitic gneiss the volcanic suite is strongly bimodal rocks with 55 to 71 wt sio 2 are rare on the basis of age geomorphic position and petrography five volcanic units can be distinguished older basalts 18 7 and 16 5 m y old quartz bearing basalts 13 7 and 12 4 m y old rhyolite lavas and tuffs 15 1 to 10 3 m y old mesa forming basalts 13 1 to 9 2 m y old and megacryst bearing basalts 8 6 to 6 8 m y old most of the basalts contain groundmass olivine and titanaugite phenocrysts and are alkali olivine basalts many rhyolites contain more than 75 wt sio 2 the initial whole rock sr isotopic composition of the basalts indicates that they are partial melts of an isotopically vertically heterogenous mantle the chemical composition of some of the megacrysts in megacryst bearing basalts with 87 sr 86 sr i equal to 7035 and 7038 supports a high pressure mantle origin the low 7034 sr ratio and lack of evidence for mixing with young rocks indicate that the quartz bearing basalts were also derived from the mantle other basalts with 87 sr 86 sr i 0 705 probably were derived from old lithospheric mantle with a high rb sr ratio and do not appear to be contaminated with old upper crustal material the rhyolites have initial sr isotopic ratios of 0 7093 and 0 7141 these ratios indicate that the rhyolites were not differentiated from the basalts partial melting of 1 3 b y old lower crustal material with rb sr 0 10 to 0 19 satisfactorily explains the isotopic ratios of the rhyolites granulite which may constitute the lower crust in this part of arizona has rb sr ratios similar to those required to produce the rhyolites k substituted for na during cooling and devitrification in some of the rhyolites partial melting of upper mantle peridotite and old lower crustal granulite from 19 to 7 m y ago in the castaneda hills area produced the bimodal volcanic suite the nearly contemporaneous production of basaltic and rhyolitic magma from the earth9s crust and mantle requires extremely heterogenous source regions asthenospheric upwelling associated with basin range extensional tectonism probably produced the heating event that caused partial melting and basaltic magma generation at different levels in the mantle partial melting in the lower crust to produce rhyolitic magmas probably was caused by the intrusion of basalt magma the basaltic and rhyolitic magmas formed in separate source regions rose independently and erupted at the same time and place

methane concentration profiles in a lake with a permanently anoxic hypolimnion lake lugano switzerland italy methane concentrations were measured in the water column of the northern basin of lake lugano in 1993 and 1994 methane profiles show three distinct zones 1 low concentrations generally below 0 1 mmol m 3 from the surface to 80 90 m depth 2 a sharp rise in concentration up to 50 mmol m 3 from 80 90 to not vert similar 150 m depth and 3 from not vert similar 150 m depth to the bottom with a lower concentration gradient and with the highest methane concentrations in near bottom water was not vert similar 80 mmol m 3 these profiles result from a combination of several factors such as fluxes from sediments spatially variable vertical mixing and aerobic and anaerobic bacterial oxidation in the water column 13c values indicate a biogenic origin for the methane the methane inventory in the anoxic hypolimnion is not vert similar 2000 metric tonnes yet its transfer to the surface water is almost completely cancelled by oxidation at the permanent redox interface situated at not vert similar 90 m water depth increased methane concentrations in near surface water are not related to the deep water methane reservoir but probably result from bacterial production of methane in the photic zone surface water is over saturated with methane in respect to the atmosphere anthropogenic eutrophication in temperate zone lakes has affected the carbon budget and methane production and storage the potential impact of these changes on global emissions to the atmosphere should be evaluated

location and variation of the summertime upper troposphere temperature maximum over south asia the upper troposphere temperature maximum uttm over south asia is a pronounced feature in the northern hemisphere summer its formation mechanism is still unclear this study shows that the latitude location of the upper tropospheric warm center t coincides with the subtropical anticyclone and its longitude location is determined by the zonal distribution of vertical gradient of heating cooling q z q z which is different from the gill s model since both convective heating and radiation cooling decrease with height in the upper troposphere the heating cooling generates vertical northerly southerly shear leading to a warm cold center being developed between heating in the east west and cooling in the west east the location of the uttm coincides with the south asian high sah and is between a radiation cooling in the west and the asian monsoon convection heating source in the east the uttm is sensitive to this convective heating increased heating in the source region in a general circulation model causes intensification of both the sah and uttm and imposing periodic convective heating there results in oscillations in the sah uttm and vertical motion to the west with the same period diagnoses of reanalysis indicate that such an inherent subtropical t q z relation is significant at interannual timescale during the end of the twentieth century rainfall increase over south china is accompanied by an increasing northerly flow aloft and intensification in the sah and uttm to the west results demonstrate that the feedback of atmospheric circulation to rainfall anomalies is an important contributor to the regional climate anomaly pattern

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

eruptive response of oceanic islands to giant landslides new insights from the geomorphologic evolution of the teide pico viejo volcanic complex tenerife canary large sector collapses are a major component of oceanic islands evolution here we show that voluminous events such as the icod landslide on tenerife canary islands cause dramatic changes on the magma feeding system and control the subsequent volcanic and geomorphologic evolution of the eruptive complex over a period of more than 150 kyr instantaneous unloading by the icod landslide is marked by the development of a large phonolitic explosive eruption dated at 175 3 ka and interpreted as reflecting the immediate emptying of a shallow pre existing magma chamber geochronological geomorphological and geochemical analyses carried out on the post landslide volcanic succession sampled in a 4 4 km long underground water recovery gallery provide further evidence for an enhanced extrusion of primitive lavas starting in the 10 kyr time interval following the failure rapid construction 40 kyr of a thick basaltic volcano in the landslide scar at high eruptive rates up to 8 km3 kyr 1 increased the lithostatic pressure which then favored the intermittent storage of basic magma under the edifice this resulted in more episodic construction evidenced by a significant decrease in output rates and the increasing occurrence of lavas with intermediate composition from 117 7 to 52 7 ka an apparent volcanic gap is observed between 52 7 and 18 1 ka after which highly differentiated lavas have been dominantly erupted we propose that part of the gap can be explained by the individualization of a shallow magma reservoir a few kilometers below the base of the teide volcano during recent periods vertical and lateral extrusions of trachytic and phonolitic viscous bodies from this storage area contributed to increase the slope of the main edifice up to 35 overall favoring its present day instability

structure and emplacement of the coastal deccan tholeiitic dyke swarm in goa on the western indian rifted margin mafic dyke swarms when controlled by a regional stress field are emplaced perpendicular to the minimum principal compressive stress direction however mafic dyke swarms may also exploit pre existing structural fabric in their host rocks distinguishing between the two scenarios is important for correct geodynamic understanding of magmatic events continental flood basalt provinces such as the deccan traps of india represent huge fissure eruptions produced by swarms of mafic dykes the coastal dyke swarm of the deccan along the western indian rifted margin is one of its three major dyke swarms we present a field study of the goa dykes part of the coastal swarm the dykes are typical dolerites and basalts exposed in proterozoic age basement lava flows which these dykes may have once fed have been stripped away by erosion though exposed in the western ghats escarpment 100 km to the east the goa dyke swarm contains 60 dykes some of which form larger multiple injection dykes the dykes are short compared to typical kilometers or tens of kilometers long dykes in flood basalt provinces such as the deccan or iceland and range in length from 15 to 220 m and in thickness from 3 cm to 20 m most dykes are vertical and the others dip steeply in various directions their structural attributes and internal features such as vesicular zones and columnar jointing provide clues to the processes of magma flow and solidification in the dykes field measurements yield an average crustal dilation of 8 due to dyke emplacement calculations of magmatic overpressures and magma chamber depths generally yield unrealistic values owing to the low aspect ratios of the dykes based on comparisons between the dyke trends and the host rock joint trends we consider that a few of the goa dykes were emplaced along pre existing fractures but the orientations of the great majority of the dykes reflect contemporaneous stress fields based on crosscutting relationships we infer that the regional minimum horizontal compressive stress 3 changed over time from a e w orientation to a ne sw orientation and finally to a n s direction

a rotated eigenanalysis of the correlation between 700 mb heights and sea surface temperatures in the pacific and atlantic abstract associations between pacific and atlantic sea surface temperature sst and the 700 mb circulation were studied using 30 years 1949 78 of gridded monthly data the monthly data were grouped into four nonstandard seasons for the analysis the linear correlation between the two fields sst and 700 mb heights was analyzed by finding the eigenvalue solution of the mean product matrix of the cross correlations this technique introduced by prohaska was modified through the use of a varimax rotation the result is a set of pairs of patterns one pattern for each medium which explains part of the linear correlation between the two fields the number of significant modes pairs was determined by a monte carlo simulation one well known atmospheric teleconnections pattern referred to as the pacific north american pna pattern by wallace and gutzler was found in all seasons however seasonal differences were noted during the warm season the pna pattern manifests itself as the great plains g

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

petrology of aoso volcano northeast japan arc temporal variation of the magma feeding system and nature of low k amphibole andesite in the aoso osore volcanic zone the aoso volcano is a member of the newly defined volcanic front of northeast japan characterized by the occurrence of low k and hornblende andesites its activity can be divided into three stages the early caldera forming and late stages while petrographic and geochemical data show all products underwent magma mixing or co mingling sr and nd isotopic ratios indicate that all are consanguineous the end member magmas are basaltic and andesitic in the early stage but basaltic and dacitic in the late stage in the caldera forming stage hornblende free and hornblende rich andesites co mingled which triggered an explosive eruption leading to caldera formation hornblende occurs also in the dacite from the early part of the late stage these hornblende andesites and dacites are lower in magmatic temperature compared to hornblende free andesites the estimated basaltic end member is low k and high in magmatic temperature and can be derived by a high degree of partial melting of mantle under the volcanic front the estimated andesitic and dacitic end members cannot be derived from the basaltic end member magma through fractional crystallization but can be derived from partial re melting of the solidified low k basalt leaving amphibolitic and gabbroic residues respectively

handbook of environmental isotope geochemistry vol 1 the terrestrial environment a p fritz and j ch fontes editors elsevier amsterdam 1980 xii 532 pp u s 90 25 dfl 185 00

potassium argon geochronology of a basalt andesite dacite arc system the mount adams volcanic field cascade range of southern washington high precision k ar dating and detailed mapping have established an eruptive chronology for a cascade stratovolcano and its surrounding array of coeval basaltic centers mount adams is a 200 km 3 andesitic cone that stands at the center of a coeval 1250 km 2 quaternary volcanic field that contains 60 discrete vents k ar ages were measured for 74 samples from 63 of the 136 volcanic units defined in the course of the mapping within analytical error there are no discrepancies between k ar ages and stratigraphic sequence major activity began in the area ca 940 ka and inception of the central stratovolcano took place at ca 520 ka a plot of cumulative volume erupted versus time shows that between 940 and 520 ka the eruptive rate was 3 k y and 80 of the products were basaltic andesites are volumetrically dominant and were emplaced in three main cone building episodes centered at 500 450 and 30 ka at eruptive rates of 1 6 5 km 3 k y at a lower rate of 0 05 0 1 km 3 k y the magmatic system remained almost continuously active between the main pulses although breaks in activity as long as 30 k y are permitted by the k ar data andesitic dacitic activity in the focal region and dominantly basaltic activity on the periphery have coexisted for 520 k y and their products are interstratified the last main episode of cone construction occurred ca 40 10 ka the oldest andesite identifiably derived from within the present day edifice having an age of 33 14 ka andesites forming the south summit rim and the true summit have ages of 13 8 ka and 15 8 ka respectively the time volume composition data bear upon several fundamental questions concerning the long term behavior of arc volcanoes stratovolcanoes commonly grow in spurts but can stay active between the widely spaced episodes of peak productivity large stratocone systems may remain active for half a million years subdivision of complex stratovolcanoes into eruptive or constructional stages without detailed mapping geochronology and compositional data should be treated skeptically discussion of volumetric eruptive rates can be misleading without an adequate time scale stratovolcanoes need never develop large upper crustal magma chambers basalt erupts peripherally but its ascent is suppressed beneath stratovolcanoes by deep crustal domains of magma storage and hybridization that form where concentrated injection of basalt amplifies crustal melting

role of the tibetan plateau thermal forcing in the summer climate patterns over subtropical asia the mechanism of the tibetan plateau tp thermal forcing in influencing the summer climate patterns over subtropical asia is investigated by means of ncep ncar reanalysis diagnosis results show that since the tp is a huge elevated heating source with the strongest heating in the surface layers in summer the thermal adaptation results in a shallow cyclonic circulation near the surface and a deep anticyclonic circulation above it according to the steady barotropic vorticity equation for large scales airflow must converge in the lower layers and diverge in the higher layers over the eastern side of the tp however the western side of the tp is characterized by a reversed structure i e divergence in lower layers but convergence in higher layers hence pumping and sucking processes bring in upward and downward movement over the east and west sides of the tp respectively such a circulation is embedded in the large scale circulation that is forced by the eurasian continental heating because the tp together with iran plateau are located at the central and eastern parts of the continent and because the orography induced circulation is in phase with the continental scale circulation the role of the tp thermal forcing is to intensify the east asian monsoon to its east and the dry and hot desert climate in mid asia to its west the summertime thermal forcing of the rockies and andes can generate similar circulations along the two subtopics as the tp does since they are located near the western coasts but the lower troposphere poleward flow that is induced by orographic thermal forcing does not coincide with the poleward flows over the eastern coastal region that is induced by continental heating and the monsoon rainfall in north and south america is not as strong as in east asia however the equatorward flow and the associated subsidence induced by the two mountain ranges along the western coasts of both north and south america are in phase with those induced by continental heating these contribute to the formation of the stable low stratus clouds and strong long wave radiative cooling over the eastern subtropical pacific regions just off the western coast of the continent

petrological study of nasu chausudake volcano ca 16 ka to present northeastern japan chausudake volcano is representative of the active volcanoes in northeastern japan and has a record of many historical eruptions because its 16 ky eruptive history is well documented chausudake is well suited for examining the temporal change of magma chamber processes and for assessing potential hazards the activity of the chausudake volcano can be divided into six magmatic units ch1 ch6 most of its products have similar characteristics but those from unit ch1 show wider variation most rocks are andesite and have plagioclase clinopyroxene orthopyroxene and fe ti oxides as phenocrysts with or without olivine or quartz mafic inclusions which are observed in most products are basaltic andesites that have various combinations of the same phenocryst species petrographic features observed in host rocks and mafic inclusions such as disequilibrium phenocrysts and resorbed textures suggest magma mixing co mingling whole rock compositions of both host rocks and mafic inclusions show linear trends in variation diagrams which suggest that the rocks are derived from the mixing co mingling between mafic and felsic end members bulk silica content of the mafic end member magma is estimated to be ca 52 and contains mg rich olivine and an rich plagioclase the temperature of this end member is estimated to have been higher than 1 100 c bulk silica content of the felsic end member magma is estimated to be 66 and contains mg poor pyroxenes an poor plagioclase and quartz phenocrysts with a temperature of between 800 and 900 c trace element compositions show that the end members have different origins but have changed little over the entire 16 ky of activity the mafic end member magmas might come from a lower crustal homogeneous large magma chamber whereas the felsic end member magmas may be partial melts of crustal materials produced by the heat of the mafic end member felsic end member magma may have accumulated in the middle crust before ch1 activity the mixing ratio of the felsic to mafic end members was 0 5 0 5 to 0 4 0 6 for the ch1 unit and ca 0 4 0 6 for the other units considering that ca 75 of the total volume of the eruptive products form the first unit its wider compositional variation is attributed to more heterogeneous mixing ratios

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

effects of volcano loading on dike propagation in an elastic half space we use laboratory experiments and numerical models to examine the effects of volcano loading on the propagation of buoyant dikes in a two dimensional elastic half space in laboratory experiments we simulate the propagation of buoyant dikes in an isotropic regional stress field by injecting air into tanks of solidified gelatin a weight resting on the surface of the gelatin represents a volcanic load a numerical model is used to simulate these experiments both experiments and numerical simulations show that as a dike ascends it begins to curve toward the load in response to the local stress field imposed by the load the lateral distance over which dikes curve to the load increases with the ratio of average pressure at the base of the load to the dike driving pressure for realistic volcano and dike dimensions this pressure ratio is going to be large suggesting that dikes can converge to a volcano over lateral distances several times the load width numerical calculations involving an anisotropic regional stress field however predict that the lateral extent of dike attraction shrinks as the regional horizontal compressive stress decreases relative to the vertical compressive stress dike focusing will be substantial if the regional differential stresses are less than the average pressure at the base of the load if this is the case then our models predict a positive feedback between the size of volcanoes and the area of dike attraction this feedback may promote the development of large discrete volcanoes and also predicts a positive correlation between the spacing and sizes of adjacent volcanoes to test this prediction we examine nearest neighbor pairs of the 21 largest volcanoes in the cascade range the 14 pairs examined show a large range in volcano spacing 6 115 km and a statistically significant correlation between spacing and average volcano height this result is consistent with our model results and suggests that the local compressive stress induced by these volcanoes may be an important factor in controlling magma transport in the lithosphere

observed influence of north pacific sst anomalies on the atmospheric circulation abstract a lagged maximum covariance analysis mca of monthly anomaly data from the ncep ncar reanalysis shows significant relations between the large scale atmospheric circulation in two seasons and prior north pacific sea surface temperature sst anomalies independent from the teleconnections associated with the enso phenomenon regression analysis based on the sst anomaly centers of action confirms these findings in late summer a hemispheric atmospheric signal that is primarily equivalent barotropic except over the western subtropical pacific is significantly correlated with an sst anomaly mode up to at least 5 months earlier although the relation is most significant in the upper troposphere significant temperature anomalies are found in the lower troposphere over north america the north atlantic europe and asia the sst anomaly is largest in the kuroshio extension region and along the subtropical frontal zone resembling the main mode of north pacific sst anomaly variability in late winter

geologic evidence for a magma chamber beneath newberry volcano oregon at newberry volcano central oregon more than 0 5 m y of magmatic activity including caldera collapse and renewed caldera filling volcanism has created a structural and thermal chimney that channels magma ascent holocene rhyolitic eruptions 1 have been confined mainly within the caldera in an area 5 km in diameter 2 have been very similar in chemical composition phenocryst mineralogy and eruptive style and 3 have occurred as recently as 1300 years ago with repose periods of 2000 3000 years between eruptions holocene basaltic andesite eruptions are widespread on the flanks but are excluded from the area of rhyolitic volcanism basaltic andesite in fissures at the edge of the rhyolite area has silicic inclusions and shows mixed basalt rhyolite magma relations these geologic relations and the high geothermal gradient that characterizes the lower part of a drill hole in the caldera u s geological survey newberry 2 indicate that a rhyolitic magma chamber has existed beneath the caldera throughout the holocene its longevity probably is a result of intermittent underplating by basaltic magma

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

cold tongue and warm pool enso events in cmip5 mean state and future projections abstractthe representation of the el nino southern oscillation enso under historical forcing and future projections is analyzed in 34 models from the coupled model intercomparison project phase 5 cmip5 most models realistically simulate the observed intensity and location of maximum sea surface temperature sst anomalies during enso events however there exist systematic biases in the westward extent of enso related sst anomalies driven by unrealistic westward displacement and enhancement of the equatorial wind stress in the western pacific almost all cmip5 models capture the observed asymmetry in magnitude between the warm and cold events i e el ninos are stronger than la ninas and between the two types of el ninos that is cold tongue ct el ninos are stronger than warm pool wp el ninos however most models fail to reproduce the asymmetry between the two types of la ninas with ct stronger than wp events which is opposite to observations most models capture the observed peak in enso

plinian airfall deposits of basaltic composition two widespread scoria fall deposits locally known as the fontana lapilli and san judas formation are demonstrated to have issued from masaya caldera complex nicaragua and to be the first documented plinian airfall deposit of basaltic composition data from maps of median grain size average maximum pyroclast diameter and average maximum diameter of lithic fragments provide conclusive evidence of the plinian nature of both deposits the volume within the 1 mm isopach of the fontana lapilli is 12 km3 3 4 km3 dense rock equivalent and within the san judas formation it is 1 2 km3 0 35 km3 dre theoretical eruption parameters calculated for the fontana lapilli and san judas formation respectively include muzzle velocity 170 m s and 150 m s column height 50 km and 18 km volume eruption rate 2 105 m3 s and 1 104 m3 s and duration 2 h and 10 h these are all similar to the calculated parameters for silicic plinian eruptions basaltic magmas are generally considered incapable of erupting in the manner characteristic of plinian eruptions recognition of them argues that factors other than high viscosity may be of fundamental importance

volcanic and geochemical evolution of the teno massif tenerife canary islands some repercussions of giant landslides on ocean island magmatism large scale catastrophic mass wasting is a major process contributing to the dismantling of oceanic intraplate volcanoes recent studies however have highlighted a possible feedback relationship between flank collapse or incipient instability and subsequent episodes of structural rearrangement and or renewed volcano growth the teno massif located in northwestern tenerife canary islands is a deeply eroded miocene shield volcano that was built in four major eruptive phases punctuated by two lateral collapses each removing 20 25 km3 of the volcano s north flank in this paper we use detailed field observations and petrological and geochemical data to evaluate possible links between large scale landslides and subsequent volcanism magmatism during teno s evolution inspection of key stratigraphic sequences reveals that steep angular unconformities relics of paleolandslide scars are marked by polymict breccias near their base these deposits typically include abundant juvenile pyroclastic material otherwise scarce in the region while some of teno s most evolved low density magmas were produced just before flank collapses early postlandslide lava sequences are characterized by anomalously high proportions of dense ankaramite flows extremely rich in clinopyroxene and olivine crystals a detailed sampling profile shows transitions from low mg lavas relatively rich in sio2 to lavas with low silica content and comparatively high mg after both landslides long term variations in zr nb normative nepheline and la lu are coupled but do not show a systematic correlation with stratigraphic boundaries we propose that whereas loading of the growing precollapse volcano promoted magma stagnation and differentiation the successive giant landslides modified the shallow volcano tectonic stress field at teno resulting in widespread pyroclastic eruptions and shallow magma reservoir drainage this rapid unloading of several tens of km3 of near surface rocks appears to have upset magma differentiation processes while facilitating the remobilization and tapping of denser ankaramite magmas that were stored in the uppermost mantle degrees of mantle melting coincidently reached a maximum in the short time interval between the two landslides and declined shortly after probably reflecting intrinsic plume processes rather than a collapse induced influence on mantle melting our study of teno volcano bears implications for other oceanic volcanoes where short term compositional variations may also directly relate to major flank collapse events

marginal stability of atmospheric eruption columns and pyroclastic flow generation explosive volcanic eruptions frequently generate fall and flow deposits simultaneously which can be attributed to a marginally stable atmospheric column in transitional conditions between the buoyant and collapse regimes this behavior is reproduced by laboratory experiments and numerical simulations ten well documented eruptions are used to test theoretical models of explosive eruptions three types of deposits fall flow and composite deposits made of intercalated flow and fall units are observed in these eruptions estimates of mass discharge rate and initial volatile concentration in the magma are available for each eruptive phase using the simple assumptions that 1 the mass fraction of gas in the mixture is equal to the initial volatile content of magma and 2 jet expansion outside the vent is unconstrained by crater dimensions theoretical predictions are not consistent with the data agreement between data and theory may be achieved by appealing to imperfect degassing of pyroclasts which lowers the gas content of the erupted mixture the effective amount of continuous gas phase carrying pyroclasts in suspension depends on the size distribution of pyroclasts in coarse pyroclast populations a large amount of magmatic gas remains trapped in bubbles within the pyroclasts and is not involved in the bulk volcanic flow a new regime diagram based on estimates of the effective gas content in the erupted mixture allows good agreement with the observations for given mass flux and initial dissolved volatile content changes of the size distribution of pyroclasts may have a strong effect on atmospheric column behavior

pelagic boundary conditions affect the biological formation of iron rich particles iron snow and their microbial communities we studied the formation of iron rich particles at steeply opposing gradients of oxygen and fe ii within the redoxcline of an acidic lignite mine lake ph 2 9 particles formed had a diameter of up to 380 m showed high sedimentation velocity 2 m h 1 and were dominated by the iron mineral schwertmannite although the particles were highly colonized by microbial cells 1010 cells g dry weight 1 the organic carbon content was below 11 bathymetry and the inflow of less acidic fe ii rich groundwater into the northern basin of the lake results in two distinct mixing regimes in the same lake the anoxic monimolimnion of the northern basin had higher ph fe ii dissolved organic carbon and co2 values compared with the more central basin particles formed in the northern basin differed in color were smaller had higher organic carbon contents but were still dominated by schwertmannite microcosm incubations revealed the dominance of microbial fe ii oxidation comparison of bacterial clone libraries suggested that ph was a major driving force shaping the microbial communities responsible for the oxidation of fe ii in both basins acidophilic ferrovum spp and chlorobia related bacteria were present in the central basin whereas neutrophilic sideroxydans spp dominated the northern basin snow like particles had a high sinking velocity and acted as a carrier for organic carbon microorganisms trace metals and fe iii to the sediment because these particles are fundamentally different from organic rich snows from lakes rivers and oceans we propose a new term iron snow

h2o in rhyolitic glasses and melts measurement speciation solubility and diffusion dissolved h2o in silicate melts and glasses plays a crucial role in volcanic eruptions on terrestrial planets and affects glass properties and magma evolution in this paper major progress on several aspects of the h2o melt or glass system is reviewed consistency among a variety of data is investigated discrepancies are evaluated and confusion is clarified on the infrared measurement of total h2o and species concentrations calibration for a variety of glasses has been carried out at room temperature the measurements for h2o in rhyolitic glasses have undergone the most scrutiny resulting in the realization that absorptivities for the near infrared bands depend on total h2o content although the variation of the absorptivities does not seem to significantly affect the determination of total h2o it does affect the determination of molecular h2o and oh species concentrations calibration of the infrared technique for h2o in rhyolitic glasses still needs much improvement especially at high total h2o furthermore it is now almost certain that the molar absorptivities also depend on the measurement temperature in in situ studies hence it will be necessary to carry out calibrations in situ at high temperatures on h2o speciation results from two experimental approaches the quench technique and the in situ technique are very different leading to controversy in our understanding of true speciation a solution is presented to reconcile this controversy it is almost certain that the quench technique does not suffer from a quench problem but interpretation of in situ results suffered from ignoring the dependence of the molar absorptivities on measurement temperature accurate calibration at high temperatures is necessary for the quantitative application of the in situ technique to h2o speciation in silicate melts and glasses on h2o solubility in silicate melts recent experimental work has significantly expanded the t p range of solubility measurements and recent solubility models fill a gap for predicting solubility for a wide range of melt compositions i present a solubility model for rhyolitic and quasi rhyolitic melts over a wide range of t and p 500 1350 c 0 8 kbar by incorporating the role of speciation the solubility model is able to recover the experimental solubility data and has extrapolative value although the partial molar volume of h2o derived from the solubility model differs from that derived from density measurements on h2o diffusion recent studies on h2o diffusion in a quasi rhyolitic melt at 800 1200 c 0 5 5 kbar and up to 7 total h2o not only provide important new diffusion data but are also challenging earlier understanding of h2o diffusion based on data in rhyolitic glasses at 400 550 c 1 bar and 0 2 1 8 total h2o a comparison between the earlier model and recent data is made the recent high temperature diffusivities at total h2o 2 can be predicted by the earlier model however at higher total h2o the earlier model fails new work is under way to understand the diffusion mechanisms at high h2o contents

composition and origin of organic matter in surface sediments of lake sarbsko a highly eutrophic and shallow coastal lake northern poland abstract we present an organic geochemical study of surface sediments of lake sarbsko a shallow coastal lake on the middle polish baltic coast the aim was to provide evidence concerning the origin of the organic matter om and its compositional diversity in surface deposits of this very productive highly dynamic water body the content and composition of the om in the bottom sediments were investigated at 11 sampling stations throughout the lake basin om sources were assigned on the basis of bulk indicators total organic carbon toc total nitrogen tn 13 c toc and 15 n and extractable om yield biomarker composition of extractable om and compound specific c isotope signatures the source characterization of autochthonous compounds was verified via phytoplankton analysis the distribution of gaseous hydrocarbons in the sediments as well as temporal changes in lake water ph the concentration of dic dissolved inorganic carbon and 13 c dic were used to trace om decomposition the sedimentary om is composed mainly of well preserved phytoplankton compounds and shows minor spatial variability in composition however the presence of ch 4 and co 2 in the bottom deposits provides evidence for microbial degradation of sedimentary om the transformation of organic compounds in surface bottom and pore waters via oxidative processes influences carbonate equilibrium in the lake and seasonally favours precipitation or dissolution of caco 3 the data enhance our understanding of the relationships between the composition of sedimentary om and environmental conditions within coastal ecosystems and shed light on the reliability of om proxies for environmental reconstruction of coastal lakes

spring arctic oscillation east asian summer monsoon connection through circulation changes over the western north pacific in the present study the links between spring arctic oscillation ao and east asian summer monsoon easm was investigated with focus on the importance of the north pacific atmospheric circulation and sea surface temperature sst to reduce the statistical uncertainty we analyzed high pass filtered data with the inter annual time scales and excluded the el nino southern oscillation signals in the climate fields using a linear fitting method the significant relationship between spring ao and easm are supported by the changes of multi monsoon components including monsoon indices precipitation and three dimensional atmospheric circulations following a stronger positive spring ao an anomalous cyclonic circulation at 850 hpa appears in southeastern asia and the western north pacific in summer with the easterly anomalies spanning from the pacific to asian continent along 25 n 30 n and the westerly anomalies south of 15 n at the same time the summer western north pacific subtropical high becomes weaker consistently the positive precipitation anomalies are developed over a broad region south of 30 n stretching from southern china to the western pacific and the negative precipitation anomalies appear in the lower valley of the yangtze river and southern japan the anomalous cyclone in the western north pacific persisting from spring to summer plays a key role in modulating easm and monsoon precipitation by a positive air sea feedback mechanism during spring the ao associated atmospheric circulation change produces warmer ssts between 150 e 180 near the equator the anomalous sensible and latent heating in turn intensifies the cyclone through a gill type response of the atmosphere through this positive feedback the tropical atmosphere and sst patterns sustain their strength from spring to summer that consequently modifies the monsoon trough and the western north pacific subtropical high and eventually the easm precipitation moreover the sst response to ao circulation is supported by the numerical simulations of an ocean model and the anomalous atmospheric circulation over the western north pacific is also reproduced by the dedicated numerical simulations using the coupled atmosphere ocean model the observation evidence and numerical simulations suggest the spring ao can impact the easm via triggering tropical air sea feedback over the western north pacific

shallow open system evolution of basaltic magma beneath a subduction zone volcano the masaya caldera complex nicaragua abstract lavas and pyroclastic material from the masaya caldera complex have a number of distinctive geochemical features relative compositional homogeneity low al2o3 and high feo contents a tholeitic differentiation trend and elevated large ion lithophile lil element concentrations e g ba 800 ppm on cmas projections their compositions always fall on or near low pressure cotectics in addition the basalts of masaya have unusually high 87sr 86sr and 10be masaya has exhibited medium term compositional cycles best exhibited by the sawtoothed changes in tio2 and feo mgo there are also a number of longer term compositional changes which are abrupt and generally coincide with caldera formation many of the geochemical characteristics of masaya coupled with a number of volcanological observations indicate masaya is underlain by a large shallow open system magma chamber perhaps on the order of 10 km3 in size although fractional crystallization is a significant magmatic process in masaya s open system chamber magma mixing contamination is equally important magma mixing is necessary to explain the discontinuous stratigraphic changes in magma composition observed at masaya and crustal contamination is necessary to explain their generally elevated 87sr 86sr and lil element concentrations two components therefore have been admixed into the magma chamber of masaya a lil poor basaltic component such has been erupted from the nearby nejapa and granada cinder cones and a lil rich acidic component such has been erupted from the nearby calderas of apoyo and apoyeque admixtures of the former have dominated admixtures of the latter ended with caldera formation ironically open system behavior has exerted fundamental control on the maintenance of relative compositional homogeneity

relationship between the tibetan plateau heating and east asian summer monsoon rainfall 1 this study reveals the close correspondence between the interannual variability of the dominant east asian summer rainfall pattern and the diabatic heating over the tibetan plateau in both spring and summer the heating fluctuation over the tibetan plateau is associated with two wave like circulation patterns which bear the characteristics of forced rossby wave emanating away from the deep heating the wave like pattern in turn affects the east asian summer rainfall because of the persistent heating over the tibetan plateau from spring to summer and its possible effect on the surrounding areas the heating index defined in this study can be used as a good predictor for the jja heating and precipitation distributions evidences shown suggest that external conditions other than the sst anomaly must be considered to understand the interannual variability of the east asian summer rainfall

origin of silicic magma and magma feeding system of the shirataka volcano ne japan abstract stratovolcanoes in ne japan produce mixed andesites dacites with a silicic end member the petrologic features of this end member remained uncertain and its origin has long been debated here we suggest how the silicic magma is generated and interpret the magma feeding system for one such stratovolcano the shirataka 0 9 0 7 ma the rocks of the shirataka are divided into six petrologic groups g1 6 mafic inclusions are observed in g1 g2 g5 and g6 silica poor inclusions have tschermakitic hornblende in the groundmass while the others are hornblende free the detailed petrologic study revealed that all products were formed by magma mixing mingling between mafic and silicic end members mafic end members 1150 c 47 52 wt sio2 have magnesian olivine magnesian clinopyroxene and an rich plagioclase phenocrysts whereas silicic end members 750 900 c 63 68 wt sio2 have an poor plagioclase low mg pyroxenes hornblende and quartz the phenocryst compositions an mg and temperature of silicic end members have changed among the groups over time the trends defined by such mafic and silicic end members of each group are systematically parallel except for g3 and g4 which have distinct specific bulk compositions suggesting that the two end members for each group have co genetic relationships the trace element model calculations indicate that each estimated silicic end member can be produced through partial remelting of the corresponding solidified mafic end member leaving a gabbroic residue the presence of groundmass hornblende in silica poor mafic inclusions suggests that volatile rich mafic magmas ascended settled and solidified as gabbroic bodies in the lower or middle crust silicic magmas were then produced by partial remelting of these bodies and ascended to the shallower part of the crust to form chambers leaving the gabbro finally wet mafic magmas newly supplied along the marginal part of the gabbroic bodies and injected into the chambers triggered the eruption and the mixing mingling took place during ascent to the surface two distinct silicic magmas were simultaneously formed by this mechanism and they mixed with corresponding mafic magmas in g3 and g4 giving rise to two discrete mixed magmas finally these magmas erupted contemporaneously mingling with each other and forming pyroclastic flows

interhemispheric influence of indo pacific convection oscillation on southern hemisphere rainfall through southward propagation of rossby waves tropical indo western pacific convection anomalies influence atmospheric circulation impacting climate far beyond the tropics here we present observational and modelling evidence for an interhemispheric effect of the boreal summer june august indo pacific convection oscillation ipco which is characterized by a zonal seesaw pattern between the north indian ocean nio and the western north pacific wnp it is found that the ipco is significantly correlated with simultaneous rainfall over many parts of the southern hemisphere sh including western australia and western brazil these interhemispheric connections in rainfall remain significant when then el nino southern oscillation the indian ocean dipole and the sh annular mode related signals are excluded simultaneously which may help to improve the sh seasonal predictions the physical mechanism that underlies this interhemispheric connection is investigated using observations rossby wave diagnostics and a series of atmospheric model experiments results suggest that convective heating anomalies associated with the ipco excite two distinct southward propagating equivalent barotropic wave trains that propagate into the extratropics in the sh the south africa mid latitudes wave train excited by the heat sink over the nio and the maritime continent subtropical australia wave train excited by the heat source over the wnp we further demonstrate that upper tropospheric northerlies over tropical africa and the indian ocean are responsible for the southward propagation of stationary rossby waves across the easterlies these equivalent barotropic waves then modulate the moisture transport baroclinicity and mid latitude storminess and thus affect rainfall anomalies in the sh the new wave train patterns provide novel insight into the teleconnection pathways of convective heating over the tropical indian ocean and western pacific

interannual variability of the north pacific mixed layer associated with the spring tibetan plateau thermal forcing abstractby using multisourced data and two sets of sensitivity runs from the coupled general circulation model cesm1 2 0 we investigated the effects of the spring march april and may mam sur

petrogenesis of mafic inclusions in rhyolitic lavas from narugo volcano northeastern japan mafic inclusions present in the rhyolitic lavas of narugo volcano japan are vesiculated andesites with diktytaxitic textures mainly composed of quenched acicular plagioclase pyroxenes and interstitial glass when the mafic magma was incorporated into the silicarich host magma the cores of pyroxenes and plagioclase began to crystallize 1000 c in a boundary layer between the mafic and felsic magmas phenocryst rim compositions and interstitial glass compositions average 78 wt sio2 in the mafic inclusions are the same as those of the phenocrysts and groundmass glass in the host rhyolite this suggests that the host felsic melt infiltrated into the incompletely solidified mafic inclusion and that the interstitial melt composition in the inclusions became close to that of the host melt c 850 c infiltration was enhanced by the vesiculation of the mafic magma finally hybridized and density reduced portions of the mafic magma floated up from the boundary layer into the host rhyolite we conclude that the ascent of mafic magma triggered the eruption of the host rhyolitic magma

interhemispheric propagation of stationary rossby waves in a horizontally nonuniform background flow abstractsignificant interhemispheric teleconnections are identified that span the tropical easterlies in the boreal summer 300 hpa streamfunction such as the north africa antarctic naa and the north pacific south america npsa patterns these patterns are not supported by traditional wave theory since stationary waves in a basic state without meridional wind would be trapped in the easterlies to describe the interhemispheric responses more realistically two dimensional spherical rossby wave theory in a horizontally nonuniform basic state is considered conditions sufficient for the existence of one propagating wave are obtained and the meridional group velocity of the wave is shown to have the same direction as the meridional basic wind at the traditional critical latitude it is concluded that stationary waves with a specific wavelength can propagate across the easterlies from south north to north south via southerly northerly flows hence energy transport by stationary waves on a horizont

decadal evolution of a degassing magma reservoir unravelled from fire fountains produced at etna volcano italy between 1989 and 2001 between 1989 and 2001 five eruptions at etna displayed a regular alternation between repose periods and episodes rich in gas termed quasi fire fountains and consisting of a series of strombolian explosions sometimes leading to a fire fountain this behaviour results from the coalescence of a foam layer trapped at the top of the reservoir which was periodically rebuilt prior to each episode vergniolle and jaupart j geophys res 95 2793 2809 1990 visual observations of fire fountains are combined with the foam dynamics to estimate the five degassing parameters characteristic of the degassing reservoir i e the number of bubbles gas volume fraction bubble diameter reservoir thickness and reservoir volume the study of decadal cycles of eruptive patterns allard et al earth sci rev 78 85 114 2006 suggests that the first eruption with fire fountains occurred in 1995 while the last one happened in 2001 the number of bubbles and the gas volume fraction increase smoothly from the beginning of the cycle 1995 to its end 2001 the increasing number of bubbles per cubic metre from 0 61 20 105 to 0 1 3 4 109 results from cooling of the magma within the reservoir the simultaneously decreasing bubble diameter from 0 67 0 43 to 0 30 0 19 mm is related to the decreasing amount of dissolved volatiles meanwhile the thickness and the volume of the degassing reservoir diminish from values typical of the magma reservoir to values characteristic of a very thin bubbly layer marking the quasi exhaustion of volatiles the magma reservoir has a slender vertical shape with a maximum thickness of 3 300 8 200 m and a radius of 240 m vergniolle 2008 making its detection from seismic studies difficult its volume at most 0 58 1 4 km3 is in agreement with geochemical studies 0 5 km3 le cloarec and pennisi j volcanol geotherm res 108 141 155 2001 the time evolution of both the total gas volume expelled per eruption and the inter eruptive gas flux results from the competition between the increasing number of bubbles and the decreasing bubble diameter the smooth temporal evolution of the five degassing parameters also points towards bubbles being produced by a self induced mechanism within the magma reservoir rather than by a magmatic reinjection prior to each eruption the decadal cycles are therefore initiated by a magmatic reinjection in agreement with a typical return time of 14 80 years albarede 1993 hence the 1995 eruption results from a fresh magma being newly emplaced while the magma from the following eruptions is progressively depleted in volatiles species until reaching a state of quasi exhaustion in 2001 a magmatic reinjection of 0 13 0 6 km3 every few decades is sufficient to explain the expelled gas volume including so2 a scenario is also proposed for the alternation between gas rich summit eruptions and gas poor flank eruptions which are observed during decadal cycles the scenario proposed for etna could also be at work at piton de la fournaise and erta ale volcanoes

volcano growth mechanisms and the role of sub volcanic intrusions insights from 2d seismic reflection data abstract temporal and spatial changes in volcano morphology and internal architecture can determine eruption style and location however the relationship between the external and internal characteristics of volcanoes and sub volcanic intrusions is often difficult to observe at outcrop or interpret uniquely from geophysical and geodetic data we use high quality 2d seismic reflection data from the ceduna sub basin offshore southern australia to quantitatively analyse 56 pristinely preserved eocene age volcanogenic mounds and a genetically related network of sub volcanic sills and laccoliths detailed seismic mapping has allowed the 3d geometry of each mound to be reconstructed and distinct seismic facies within them to be recognised forty six continental basaltic shield volcanoes have been identified that have average flank dips of 3 parallel seismic reflections within the shield volcanoes are interpreted to represent interbedded volcanic and clastic material suggesting that a series of temporally separate eruptions emanated from a central vent the shield volcanoes typically overlie the lateral tips of sills and we suggest that the intermittent eruption phases correspond to the incremental emplacement of discrete magma pulses within the laterally extensive sill complex eight volcanogenic hydrothermal vents which are also associated with the lateral tips of sills were also recognised and these appear to have formed from the seepage of intrusion related hydrothermal fluids onto the seafloor via emplacement induced fractures this work highlights that deformation patterns preceding volcanic eruptions may i be offset from the eruption site ii attributed to intrusions with complex morphologies and or iii reflect magma movement along pre existing fracture systems these complexities should therefore be considered in eruption forecasting models that link pre eruption ground deformation to subterranean magma emplacement depth and volume more generally our study highlights the key role that seismic reflection data can play in understanding the geometry distribution and evolution of ancient and modern volcanic systems

volcano load control on dyke propagation and vent distribution insights from analogue modeling 1 the spatial distribution of eruptive vents around volcanoes can be complex and evolve as a volcano grows observations of vent distribution at contrasting volcanoes from scoria cones to large shields show that peripheral eruptive vents concentrate close to the volcano base we use analogue experiments to explore the control of volcano load on magma ascent and on vent location results show that the local loading stress field favors eruption of rising magma away from the volcano summit if a central conduit is not established or is blocked two sets of scaled experiments are developed with contrasting rheological properties to analyze similarities and differences in simulated magma rise below a volcano 1 golden syrup magma analogue is injected into a sand plaster mixed layer crust analogue under a cone 2 water or air magma analogues is injected into gelatin under a sand cone rising dykes approaching the cone stress field are stopped by the load compressive stress with continued intrusion dyke overpressure builds up dykes extend laterally until their tips are able to rise vertically again and to erupt in the flank or at the base of the volcano lateral offset of the extrusion point relative to the edifice summit depends on substratum thickness volcano slope and dyke overpressure the 3d geometry of golden syrup intrusions varies with experimental parameters from cylindrical conduits to dyke and sill complexes experimental results are compared with illustrative field cases and with previously published numerical models this comparison enables applications and limitations of the analogue models to be highlighted and allows us to propose a conceptual model for the evolution of vent distribution with volcano growth

geology of the saucer shaped sill near mahad western deccan traps india and its significance to the flood basalt model an 22 m thick saucer shaped sill occurs near mahad and is exposed as a curvilinear miniature ridge within the deccan traps the sill has variable dips 42 55 it has a 7 1 km long axis and 5 3 km short axis aspect ratio of 1 4 and is larger than the mv sill of the golden valley sill complex south africa and the panton sill australia the sill has distinct glassy upper and lower chilled margins with a coarse grained highly jointed core the samples from the margin are invariably fractured and iron stained because of deuteric alteration the rock from the sill is plagioclase phyric basalt at least three thick sill like apophyses emanate from the base of the main sill the apophyses change direction because of bending and thinning from a horizontal concordant sheet at the top to a discordant inclined form that bends again to pass into a lower horizontal concordant sheet we interpret such features as nascent saucer shaped sills that did not inflate to form nested sills geochemically the sill consists of poorly differentiated tholeiitic basalt that has a restricted geochemical range critical trace element ratios and primitive mantle normalised trace and ree patterns indicate that the sills have geochemical affinities to the poladpur chemical type and that the pahoehoe flow they intrude belongs to the bushe formation calculated magmatic overpressures during sill emplacement range from 8 4 to 11 3 mpa for young s modulus e 5 gpa and 16 7 to 22 5 mpa for e 10 gpa and depth to magma chamber ranges from 8 5 to 11 5 km e 5 gpa and 17 1 to 22 9 km e 10 gpa consistent with petrological and gravity modelling the volume of the mahad sill is approximately 276 km3 and is constant irrespective of the variations in the values of host rock young s modulus in 1980 cox j petrol 21 629 650 1980 proposed a conceptual model of the crust mantle section beneath the karoo cfb which is considered as the fundamental model for flood basalt volcanism our paper confirms the presence of a sill plus the inferred substructure beneath mahad that are compatible with predictions of that model in lips saucer shaped sills are formed in areas experiencing extensional tectonics where processes such as the cook gordon delamination and dundurs elastic extensional mismatch between layered sedimentary rocks or lava flows are responsible for the deflection of dykes into sills a similar process is envisaged for the formation of the mahad sill