palynology dacryoconarids and the lower eifelian middle devonian basal chotec event case studies from the prague and appalachian basins

magmatic processes revealed by textural and compositional trends in merapi dome lavas syn eruptive degassing of volcanoes may lead to syn eruptive crystallization of groundmass phases we have investigated this process using textural and compositional analysis of dome material from merapi volcano central java indonesia samples included dome lavas from the 1986 88 1992 93 1994 and 1995 effusive periods as well as pyroclastic material deposited by the november 1994 dome collapse with total crystallinities commonly in excess of 70 phenocrysts 1 microlites the liquids present in merapi andesites are highly evolved rhyolitic at the time of eruption feldspar microlites in dome rocks consist of plagioclase cores ab63an29or8 surrounded by alkali feldspar rims ab53an5or42 compositional pairs which are not in equilibrium a change in the phase relations of the ternary feldspar system caused by degassing best explains the observed transition in feldspar composition a small proportion of highly vesicular airfall tephra grains from the 1994 collapse have less evolved glass compositions than typical dome material and contain rimless plagioclase microlites suggesting that the 1994 collapse event incorporated less degassed partially liquid magma in addition to fully solidified dome rock as decompression drives volatile exsolution rates of degassing and resultant microlite crystallization may be governed by magma ascent rate microlite crystallinity is nearly identical among the 1995 dome samples an indication that similar microlite growth conditions ph2 o and temperature were achieved throughout this extrusive period however microlite number density varied by more than a factor of four in these samples and generally increased with distance from the vent low vent ward microlite number densities and greater microlite concentrations down flow probably reflect progressively decreasing rates of undercooling at the time of crystal nucleation during extrusion of the 1995 dome comparison between dome extrusion episodes indicates a correlation between lava effusion rate and microlite number density suggesting that extrusion slowed during 1995 crystal textures and compositions in the 1992 93 and 1994 domes share the range exhibited by the 1995 dome suggesting that transitions in crystallization conditions i e rates of undercooling determined by effusion rate are cyclic q 2000 elsevier science b v all rights reserved

fracture patterns at lava ice contacts on kokostick butte or and mazama ridge mount rainier wa implications for flow emplacement and cooling histories abstract cooling lava commonly develop polygonal joints that form equant hexagonal columns such fractures are formed by thermal contraction resulting in an isotropic tensional stress regime however certain linear cooling fracture patterns observed at some lava ice contacts do not appear to fit the model for formation of cooling fractures and columns because of their preferred orientations these fracture types include sheet like ladder like rectangular fracture pattern intermediate pseudo aligned individual column bounding fractures and pseudopillow straight to arcuate fractures with perpendicular secondary fractures caused by water infiltration fractures that form the edges of multiple columns along a single linear fracture despite the relatively common occurrence of these types of fractures at lava ice contacts their significance and mode of formation have not been fully explored this study investigates the stress regimes responsible for producing these unique fractures and their significance for interpreting cooling histories at lava ice contacts data was collected at kokostick butte dacite flow at south sister or and mazama ridge andesite flow at mount rainier wa both of these lava flows have been interpreted as being emplaced into contact with ice and linear fracture types have been observed on their ice contacted margins two different mechanisms are proposed for the formation of linear fracture networks one possible mechanism for the formation of linear fracture patterns is marginal bulging melting of confining ice walls will create voids into which flowing lava can deform resulting in margin parallel tension causing margin perpendicular fractures if viewed from the ice wall these fractures would be steeply dipping linear fractures another possible mechanism for the formation of linear fracture types is gravitational settling pure shear during compression and settling can result in a tensional environment with similar consequences as marginal inflation in addition to this horizontally propagating cooling fractures will be directly influenced by viscous strain caused by the settling of the flow this would cause preferential opening of fractures horizontally resulting in vertically oriented fractures it is important to note that the proposed model for the formation of linear fractures is dependent on contact with and confinement by glacial ice the influence of flow or movement on cooling fracture patterns has not been extensively discussed in previous modeling of cooling fractures rapid cooling of lava by the interaction with water and ice will increase the ability to the capture and preserve perturbations in the stress regime

local influences of geothermal anomalies on permafrost distribution in an active volcanic island deception island antarctica abstract this study aims at understanding the spatial distribution and characteristics of the frozen and unfrozen terrain in an alluvial fan on deception island which is an active strato volcano located in the bransfield strait south shetland islands with recent eruptions in 1967 1969 and 1970 the alluvial fan is dominated by debris flow run off and rock fall processes and permafrost occurs in several parts in the vicinity of anomalous geothermal heat flux the aim is to assess the ways volcanic activity controls permafrost development and associated geomorphic dynamics using shallow subsurface surface and air temperature measurements as well as thaw depth and electrical resistivity tomography ert surveys results show a temperature increase with depth in the lower part of the fan reaching 13 c at 0 80 m depth without the presence of permafrost the shallow borehole located at this site showed a stable thermal stratification all year round with only the upper 0 20 m reacting to meteorological forcing in the upper part of the alluvial fan and debris cones c 100 m from the coast frozen ground is present at c 0 70 m depth there the shallow borehole shows a good coupling with air temperatures and the thermal regime favours the presence of permafrost ert shows the lowest resistivity values in the lower part of the alluvial fan and a highly resistivity zone in the upper sector of the fan and in the debris cones these large variations in resistivity mark the presence of a saline water wedge from the sea into the fan reaching frozen ground conditions about 100 m inland it can be shown that the volcano hydrothermal activity only inhibits frost development very locally with frozen ground conditions occurring about 100 m away

the formation of helgafell southwest iceland a monogenetic subglacial hyaloclastite ridge sedimentology hydrology and volcano ice interaction abstract helgafell a little eroded basaltic hyaloclastite ridge in southwest iceland formed in a single eruption under a pleistocene ice sheet the ice thickness at the eruption site was at least 500 m and it was probably located some 15 km from the glacier s snout the eruption created a 2 km long 0 8 km wide and initially 300 m high ridge gravity modelling indicates that helgafell has a bulk density of 1800 kg m 3 and that holocene lavas around it are 40 80 m thick this confirms that helgafell is predominantly made of hyaloclastite with pillow lavas and intrusions only making up a few percent of the total volume the southeast side is made of unsorted eruption fed hyaloclastites considered to have been piled up against an ice wall while moderately to well sorted water transported material is found on the northwest side glacier flow and meltwater drainage was towards the northwest the absence of basal pillow lavas suggests that magma fragmentation occurred from the onset of the eruption until its end the lithofacies preserved indicate a fully subglacial eruption although a final subaerial eruptive phase may have taken place through an ice chimney the volatile contents h 2 o 0 26 0 37 wt of several glass samples from the southeast side of the mountain indicate water pressures of 1 mpa throughout the eruption efficient syn eruptive drainage of meltwater coupled with rapid ice subsidence probably led to partial dynamic support of the ice causing water pressure in the vault to be much lower than the static load of the overlying ice observed lack of correlation between elevation and volatile content may be a consequence of gradual reduction in dynamic support as the eruption rate declined and the edifice grew higher helgafell demonstrates that explosive activity may occur under 500 m thick ice and it may be an analogue to the ridge formed in the gjalp eruption in 1996

will present day glacier retreat increase volcanic activity stress induced by recent glacier retreat and its effect on magmatism at the vatnajokull ice cap iceland an area of 8000 km 2 has been continuously retreating losing about 10 of its mass during last century present day uplift around the ice cap is as high as 25 mm yr we evaluate interactions between ongoing glacio isostasy and current changes to mantle melting and crustal stresses at volcanoes underneath vatnajokull the modeling indicates that a substantial volume of new magma 0 014 km 3 yr is produced under vatnajokull in response to current ice thinning ice retreat also induces significant stress changes in the elastic crust that may contribute to high seismicity unusual focal mechanisms and unusual magma movements in nw vatnajokull citation pagli c and f sigmundsson 2008 will present day glacier retreat increase volcanic activity stress induced by recent glacier retreat and its effect on magmatism at the vatnajokull ice cap iceland geophys res lett 35 l09304 doi 10 1029 2008gl033510

multiple climatic changes around the permian triassic boundary event revealed by an expanded palynological record from mid norway here we present the palynological record from two shallow core holes 6611 09 u 01 and 02 from the trondelag platform offshore mid norway consisting of 750 m of upper permian and lower triassic sediments the relatively homogeneous assemblages recovered from the upper permian deposits are dominated by gymnosperm pollen mainly pteridosperms at the base of the griesbachian numerous spore species appear in the record leading to an increased diversity the change at this boundary is also marked by the massive reduction of one group of pteridosperm pollen vittatina together with other typical permian elements e g lueckisporites virkkiae this group is rare but consistently present in the lower part of the griesbachian and it gradually disappears in its upper part the distribution of other groups such as taeniate and non taeniate bisaccate gymnosperm pollen pteridosperms and conifers shows no significant change across the boundary whereas spores and other gymnosperm pollen increase in diversity and abundance these changes coincide with the formational change between the schuchert dal formation upper permian and the wordie creek formation griesbachian equivalents late permian and griesbachian palynomorph assemblages display different patterns the former show a homogeneous composition of low diversity whereas the latter reflect diverse and variably composed floras the data suggest that the arid phase of the late permian was followed by a humid phase at the base of the griesbachian in the griesbachian section a succession of six distinct palynological assemblages phase ii vii can be inferred comparable changes have been described from east greenland the variations in the palynological record are interpreted to reflect changing ecological conditions e g changing humidity comparable variations in the distribution of 13 c isotope values reported from various sections from greenland and china showing stable values during the late permian and highly variable values during the griesbachian suggest common causes for the observed fluctuations multiphase volcanic activity of the siberian traps seems to be the most likely candidate to have caused the variations in the 13 c isotope as well as in the palynological record in contrast to the common claim that marine and terrestrial biota both suffered a mass extinction related to the permian triassic boundary event the studied material from the norwegian midlatitudinal sites shows no evidence for destruction of plant ecosystems the presence of diverse microfloras of griesbachian age supports the idea that the climate in this area allowed most plants to survive the permian triassic boundary event

geochemistry and petrology of the galeras volcanic complex colombia abstract the galeras volcanic complex gvc has erupted lavas and pyroclastic flows ranging from basaltic andesites to dacites during the last million years the chemical composition of the volcanic products has been fairly constant characterized by calc alkaline high silica medium potassium andesites variations from basaltic andesites to dacites have occurred during individual stages but overall composition and petrographic characteristics are quite constant the guaca cinder cone is the exception being more alkaline rather than calc alkaline the trace element and ree contents of the gvc samples suggest that sediments or fluids from the subducted sediments are involved in the generation of the magmas at the source region although high sr and ba contents are also present in the upper continental crust the high b levels are consistent with the contribution of sediment related elements small degrees of partial melting of a hydrated mantle wedge are consistent with the observed distribution of ree plus the addition of highly soluble elements from the subducted sediments crystal fractionation at depths of about 36 km approximately 12 kbar of a hydrated tholeiitic basalt melt can produce andesites and basaltic andesites having a phase assemblage of amphibole plagioclase clinopyroxene magnetite ilmenite and apatite the magma then re equilibrates at higher levels reaching levels as shallow as 10 km about 2 5 to 3 kbar and crystallizing orthopyroxene and large amounts of plagioclase at these shallow levels amphibole is no longer stable and re equilibrates to oxides pyroxene and plagioclase the melts become saturated with respect to most volatiles by depressurization and crystallization in the gvc we observe that it is not necessary to have large volumes of highly differentiated magma to cause caldera forming eruptions

long period events the most characteristic seismicity accompanying the emplacement and extrusion of a lava dome in galeras volcano colombia in 1991 abstract since its reactivation in 1988 the principal eruptions of galeras volcano occurred on may 4 9 1989 july 16 1992 and january 14 march 23 april 3 april 14 and june 7 1993 the initial eruption was a phreatic event which clearly marked a new period of activity a lava dome was extruded within the main crater in october 1991 and subsequently destroyed in an explosive eruption on july 16 1992 the eruptions that followed were all vulcanian type explosions the seismicity accompanying the emplacement extrusion and destruction of the lava dome was dominated by a mix of long period lp events and tremor displaying a variety of waveforms repetitive lp events with dominant periods in the range 0 2 1 s were observed in october and november 1991 and visually correlated with short energetic pulses of gas venting through a crack bisecting the dome surface each lp event was characterized by a weak precursory signal with dominant periods in the range 0 05 0 1 s lasting roughly 7 s using the fluid driven crack model of chouet 1988 1992 we infer that two distinct cracks may have acted as sources for the lp and precursor signals spectral analyses of the data yield the following parameters for the lp source crack length 240 360 m crack width 130 150 m crack aperture 0 5 3 4 mm crack stiffness 100 500 sound speed of fluid 880 m s and excess pressure 0 01 0 19 mpa similar analyses yield the parameters of the precursor source crack length 20 30 m crack width 15 25 m crack aperture 2 3 8 7 mm crack stiffness 5 15 sound speed of fluid 140 m s and excess pressure 0 06 0 15 mpa combined with geologic and thermodynamic constraints obtained from field observations these seismic parameters suggest a gas release mechanism in which the episodic collapse of a foam layer trapped at the top of the magma column subjacent to the dome releases a slug of pressurized gas which escapes to the surface while dilating a preexisting system of cracks in the dome structure accordingly the fracture observed on the crystallized dome body is the surface extension of the lp source crack where lp activity is induced by the rapid emission and expansion of gas flowing through this conduit the width and aperture of the crack estimated in the model are in good agreement with the length and aperture of the fracture estimated from visual observations the source parameters of the precursor signal are suggestive of a nozzle like conduit connecting the lp source crack to the underlying magma reservoir excitation of this conduit segment is attributed to the rapid emission and acceleration of the frothy fluid resulting from the collapse of the foam layer at the top of the reservoir the calculated periodicity of foam collapse events is in agreement with the observed average rate of thirteen lp events per hour

effect of the volcanic front migration on helium nitrogen argon and carbon geochemistry of hydrothermal magmatic fluids from hokkaido volcanoes japan abstract active volcanoes from hokkaido are distributed along the sw ne trending volcanic front where the subducting pacific plate changes direction from n s to wsw ese one exception is the tokachi volcano which is located approximately 50 km to the north west of the current volcanic front the tokachi oki slab cracking zone represents the transitional zone between the honshu and kurile trenches this change is responsible for the rapid lateral variation of the subduction angle and slab shape we investigate the consequence of this change on the chemical and isotopic compositions from hydrothermal magmatic fluids and mineral separates collected from three volcanoes of hokkaido northern japan namely tarumae tokachi and meakan our data show that these volcanoes have a distinct range of he n and c isotopic compositions meakan fumaroles have a 3he 4he ratio that ranges from 4 46ra to 6 88ra 15n from 2 2 to 3 5 and 13c co2 from 8 47 to 9 81 consistent with subducted sediment contribution tarumae fumaroles have a particularly low 3he 4he ratio 3 08ra in comparison with their hot springs up to 5 24ra and are associated with high co2 3he ratios 2 2 5 3 1011 hydrothermal crustal interactions from the dome or from a deeper hydrothermal system are the main mechanisms that control the 3he 4he and co2 3he ratios in tarumae fumaroles the 15n and 13c co2 values for tarumae volcano range from 0 6 to 3 1 and from 6 34 to 6 43 respectively tokachi fumaroles are characterized by high 3he 4he up to 7 38ra low 15n 2 4 0 1 and low 13c co2 up to 5 32 consistent with mantle contribution and minor subducted sediment contribution the limestone sediment mantle ratio shows a decreasing contribution from subducted sediments starting from tokachi 1 9 to meakan 3 4 and finally tarumae 5 3 this change of isotopic compositions from the sw ne of hokkaido is the result of the tokachi oki slab cracking zone slab dehydration under tokachi occurs at a deeper level 150 200 km than in other hokkaido volcanoes 100 km which produces the migration of the volcanic front therefore we argue that the isotopic signature of tokachi is the result of i a lower sediment contribution from the slab ii a deeper dehydration of the slab and iii a lower degree of partial melting

molybdenum tungsten and manganese partitioning in the system pyrrhotite fe s o melt rhyolite melt impact of sulfide segregation on arc magma evolution abstract experiments were performed to determine the partitioning of molybdenum tungsten and manganese among a rhyolitic melt melt pyrrhotite po and an immiscible fe s o melt fe s o sulfide phases such as these may be isolated from a silicate melt along with other crystallizing phases during the evolution of arc magma and partition coefficients are required to model the effect of this process on molybdenum and tungsten budgets we developed an experimental design to take advantage of properties of the phases under study careful control of temperature allowed pyrrhotite and magnetite to be stable along with an fe s o melt and this phase assemblage allowed the composition of run product pyrrhotite to be used to calculate both fs2 and fo2 for the experiments at run temperature 1042 2 c a rhyolitic melt can be formed at low pressure under nominally dry conditions which removed the need for confining pressure as well as externally imposed fugacities the silica saturated melt allowed the charges to be contained in sealed evacuated silica tubes without danger of reaction and with closed system behavior for molybdenum and tungsten experiments were run for durations up to 2000 min molybdenite mb and wolframite wo were added to the experiments as sources for molybdenum and tungsten respectively manganese was added to the system as both a component of the starting rhyolitic pumice and of mn bearing wolframite oxygen fugacity in these experiments was fixed at the ni nio oxygen fugacity buffer sulfur fugacity was 10 1 bar run products were analyzed by epma and la icp ms analysis of the run products yielded d i a b 1 x standard deviation of the mean d mo fe s o si melt 90 10 d w fe s o si melt 9 3 d mo po si melt 35 3 and d w po si melt 0 0012 0 0006 the partition coefficients for manganese in this system are d mn fe s o si melt 2 9 0 3 and d mn po si melt 1 1 0 1 simple rayleigh fractionation modeling suggests that oxidized felsic melts produced through fractional crystallization may have lost as much as 14 of their initial molybdenum but only 2 of their initial tungsten through the removal of an fe s o melt along with crystalline phases modeling consistent with conditions of oxygen and sulfur fugacity influenced by assimilation of sulfide with low concentrations of molybdenum and tungsten from for example sedimentary rock results in evolved magmas significantly depleted in molybdenum but only moderately depleted in tungsten the molybdenum tungsten ratio can vary by two orders of magnitude these systematics may help to explain some of the variability in metal ratios of intrusion related hydrothermal ore deposits

stratigraphical and palaeogeographical significance of the continental sedimentary transition across the permian triassic boundary in spain abstract the permian triassic transition a time of phenomenal palaeoenvironmental and palaeogeographical change represents the largest episode of mass extinctions known to palaeontologists this episode is however very poorly understood and a lack of sediments and palaeontological data particularly in the continental record is a feature common to every basin despite compelling information on the continental permian triassic boundary ptb emerging from recent efforts evaluating vertebrate evolution fungal events and isotope curves results are still insufficient to make any valuable correlations among continental basins and are even less appropriate for relating sediments of continental to those of marine origin the present report discusses and attempts to locate the ptb in the basins of iberia and balearic islands through an analysis of the palaeontological and sedimentary record across the permian triassic transition the aim of the paper is to contribute to our present knowledge of the palaeogeographical and stratigraphical significance of the permian and triassic continental units of western europe the present day iberian ranges catalonian ranges and balearic islands hold the most complete late permian early triassic sedimentary record in iberia this record consists of alluvial sediments mainly of braided fluvial systems corresponding to the saxonian and buntsandstein facies all the units examined so far have been dated through palynological associations the two saxonian facies formations are of thuringian age although the lower one shows some palynological elements of autunian affinities the buntsandstein units range from thuringian to anisian in age there being no evidence up to now of the scythian in iberia the exact position of the ptb in iberia is up to now impossible to pinpoint with the precision of the marine series sedimentary characteristics and palynological data in the iberian ranges point that it lies at the sedimentary interval 10 to 30 m thick formed by the upper member of the la hoz del gallo formation and the lowermost beds of the canizar formation or its time equivalent the prades and eramprunya units in the catalonian ranges and the asa and b 1 in the balearic islands we compare a normalized standard late permian middle triassic column of the iberian ranges with standards from western and central europe and the southern urals using recent permian time scales a palaeogeographic essay map of the permian triassic transition is provided for the iberian plate the plate was located in a northern subtropical position 200 400 km from the westernmost tethys coast as part of the central pangean mountain range comprised of the appalachian mauretanide variscan orogenic belts of estimated altitudes 2000 4000 m based on this palaeogeographic location sedimentary characteristics and the main wind flows established for the tethys we can infer conditions of high precipitation dominated by monsoon and seasonal regimes with isolated semiarid areas for the iberian plate during the transition

structures and facies associated with the flow of subaerial basaltic lava into a deep freshwater lake the sulphur creek lava flow north cascades washington abstract the ca 8800 14c yrs bp sulphur creek lava flowed eastward 12 km from the schriebers meadow cinder cone into the baker river valley on the southeast flank of mount baker volcano the compositionally zoned basaltic to basaltic andesite lava entered crossed and partially filled the 2 km wide and 100 m deep early holocene remnant of glacial lake baker the valley is now submerged beneath a reservoir but seasonal drawdown permits study of the distal entrant lava as a lava volume that may have been as much as 180 106 m3 entered the lake the flow invaded the lacustrine sequence and extended to the opposite east side of the drowned baker river valley the volume and mobility of the lava can be attributed to a high flux rate a prolonged eruption or both basalt exposed below the former level of the remnant glacial lake is glassy or microcrystalline and sparsely vesicular with pervasive hackly or blocky fractures together with pseudopillow fractures these features reflect fracturing normal to penetrative thermal fronts and quenching by water a fine grained hyaloclastite facies was probably formed during quench fragmentation or isolated magma water explosions although the structures closely resemble those developed in lava ice contact environments establishing the depositional environment for lava exhibiting similar intense fracturing should be confirmed by geologic evidence rather than by internal structure alone the lava also invaded the lacustrine sequence forming varieties of peperite including sills that are conformable within the invaded strata and resemble volcaniclastic breccias the peperite is generally fragmental and clast or matrix supported fine grained and rounded fluidal margins occur locally the lava formed a thickened subaqueous plug that as the lake drained in the mid holocene was exposed to erosion the baker river then cut a 52 m deep gorge through the shattered highly erodible basalt

evidence for a fungal event methane hydrate release and soil erosion at the permian triassic boundary in southern israel abstract the transition between the permian and the triassic systems in israel is evident only in the subsurface two cores from the makhtesh qatan 2 core 9 and avedat 1 core 5 drillholes in which the permian triassic boundary was found marked by a fungal event were sampled at close intervals and analysed for palynological petrographical mineralogical chemical and isotopic properties three palynozones were recorded lueckisporites virkkia zone late permian fungal event and endosporites papillatus zone early triassic the fungul event occurs in a narrow interval of 1 m and contains almost exclusively fungal remains and recycled woody particles the two cores consist of laminated sediments mainly siliciclastic that were deposited in very shallow to restricted marine environments with a minor presence of evaporites and no bioturbation green glauconitic material and framboidal pyrite suggest suboxic conditions even in the shallow waters reddish brown particles and plant fragments derived from nearby soils now outcropping on the northeast side of the dead sea these materials as well as recycled brown glauconitic grains suggest a drop in sea level and intense erosion before sedimentation which was apparently continuous major and trace element compositions including rare earth elements do not exhibit any particular pattern that might be related to the fungul event or to other core intervals the rare earth element patterns are basically normal and their concentration correlates with the clay content reflecting the provenance of the arabo nubian massif and its sedimentary rims iridium results were mostly at the background level and therefore the two distinct anomalous values are inconclusive microspherules mainly of 2 m size and al si composition were observed in a few samples in both cores their origin could not be determined though they are considered to be natural there was no evidence for shocked quartz 13corg excursion exhibits a marked negative shift in both cores just below the fungal event the lowest values 37 and 42 are among the lowest ever recorded near the permian triassic boundary and suggest large scale release of methane hydrates

ice dynamical constraints on the existence and impact of subglacial volcanism on west antarctic ice sheet stability 1 subglacial volcanism in west antarctica may play a crucial role in the dynamics and stability of the west antarctic ice sheet wais evidence supporting the existence of an individual subglacial volcanic center mt casertz in the upper catchments of whillans and kamb ice stream wis and kis comes from a comparison of ice sheet modeling results with measured ice velocities lubrication of an area which otherwise should be frozen to its bed is best explained by basal melt water generated in the vicinity of mt casertz the estimated melt water production of mt casertz corresponds to 8 of the total melt water production in the two catchments this would be sufficient to offset basal freezing in the dormant kis relubricating its bed and potentially causing a restart near future volcanic activity changes are speculative but would have far reaching implications on the dynamics and stability of the wais requiring further investigation

will subglacial rhyolite eruptions be explosive or intrusive some insights from analytical models simple analytical models of subglacial eruptions are presented which simulate evolving subglacial cavities and volcanic edifices during rhyolitic eruptions beneath temperate glaciers they show that the relative sizes of cavity and edifice may strongly influence the eruption mechanisms intrusive eruptions will occur if the edifice fills the cavity with rising magma quenched within the edifice and slow melting of ice explosive magma water interaction may occur if a water or steam filled gap develops above the edifice meltwater is assumed to drain away continuously but any gap above the edifice will be filled by meltwater or steam ductile roof closure will occur if the glacier weight exceeds the cavity pressure and is modelled here using nye s law the results show that the effusion rate is an important control on the eruption style with explosive eruptions favoured by large effusion rates the models are used to explain contrasting eruption mechanisms during various quaternary subglacial rhyolite eruptions at torfaja kull iceland although the models are simplistic they are first attempts to unravel the complex feedbacks between subglacial eruption mechanisms and glacier response that can lead to a variety of eruptive scenarios and associated hazards

a synthesis of the recent activity of galeras volcano colombia seven years of continuous surveillance 1989 1995 abstract the current period of re activation since 1988 at galeras volcano colombia has been characterized mainly by the following events 1 a semi continuous series of vulcanian eruptions during 5 9 may 1989 2 emplacement of an andesitic lava dome at the bottom of the main crater in october november 1991 3 six vulcanian eruptions during 1992 1993 the first of which destroyed most of the dome on 16 july 1992 and 4 three volcano tectonic seismic crises in april 1993 november december 1993 and march 1995 during much of this seven year period several small ash and gas emissions also have taken place the 4 9 may 1989 eruptions originated from the secondary crater el pinta and deposited ash lapilli and blocks in the crater area the 1992 1993 eruptions originated from the main crater and were associated with obstruction of the conduit by magma from dome emplacement in late 1991 causing overpressurization of the system for the 1992 1993 eruptions pre eruptive seismicity deformation and so2 flux all exhibited very low levels the eruptions were characterized by their sudden initiation low intensity vei 1 small eruption columns and small volumes of erupted material the source of the volcano tectonic seismic crises is located approximately 3 km north and northeast of the crater some of these events were felt in pasto and other towns located around the volcano on one occasion causing loss of life injuries and damage to buildings

late permian flora and vegetation changes near the permian triassic boundary in the landete section of the alcotas formation se iberian ranges spain on the basis of rich and diverse thuringian palynomorph samples gathered from successive levels of the landete section alcotas formation se iberian ranges the succession of palynofloras and the vegetation dynamics have been studied in detail with the aid of quantitative analysis the aim of this study is to elucidate the timing and scenario of the biotic crisis during the latest permian before the actual permian triassic boundary and to determine the shape of the extinction at the local level four successive associations have been recognized through time the oldest a klausipollenites lueckisporites association this was followed by a klausipollenites falcisporites an alisporites lueckisporites and finally a re establishment of a klausipollenites lueckisporites association it is worth noting the scarcity or lack of fungal remains which indicates that in this area the fungal spike event cannot be demonstrated the palynomorph associations are dominated by non striate bisaccate pollen and verrucate spores in contrast with other palynofloras from western europe north america and continental series in eurasia the study indicated the absence of transitional floras and a dieback of diversity that ranges from 35 to 67 depending on the group population density of the 27 taxa identified underwent a significant decline ca 75 average indicating that at least at a local level the biotic crisis occurred prior to the p t boundary futhermore the quantitative analysis of the successive palynomorph assemblages allowed us to locally recognize the evolution of vegetation in which competitive exclusion and competitive release events took place

three dimensional velocity structure of the galeras volcano colombia from passive local earthquake tomography abstract a three dimensional estimation of the vp vs and vp vs ratio structure at galeras volcano was conducted by means of passive local earthquake tomography 14 150 volcano tectonic events recorded by 58 stations in the seismological network established for monitoring the volcanic activity by the colombian geological survey pasto volcano observatory between the years 1989 and 2015 were inverted by using the lotos code the seismic events are associated with shear stress fractures in solid rock as a response to pressure induced by magma flow tomography resolution tests suggest a depth of imaging that yield 10 km from the summit of the main crater illuminating a large portion of the volcanic structure and the interaction of tectonic features like the buesaco and silvia pijao faults full catalog tomographic inversion that represents the stacked image of the volcanic structure or the most permanent features underneath the volcano shows vertical structures aligned with seismicity beneath the main crater we hypothesize that these structures correspond to a system of ducts or fractures through which magma and fluid phases flow up from deeper levels toward the top and related with the intersection of the surface traces of the silvia pijao and buesaco faults

preliminary report on the activity at unzen volcano japan november 1990 november 1991 dacite lava domes and pyroclastic flows abstract the eruption of unzen volcano commenced on 17 november 1990 phreatic and phreatomagmatic eruptions occurred by early may 1991 no large scale explosive eruptions preceded the extrusion of lava domes lava domes appeared in a summit crater on 20 may 1991 and they grew on the steep slope of mt fugen at unzen volcano rockfalls from the margins of the domes frequently generated pyroclastic flows major pyroclastic flows occurred on 3 june 8 june and 15 september 1991 the 3 june pyroclastic flow killed forty three persons many of the pyroclastic flows seem to have resulted from the simple rockfalls except one flow on 8 june which was accompanied by an explosion from the crater many of the rockfalls that generated pyroclastic flows were witnessed as of november 1991 unzen volcano was still active with a nearly constant magma supply rate of about 0 3 106 m3 d the total magma output exceeded 45 106 m3 by the beginning of november 1991 the volume of the lava domes is more than 23 106 m3

intrusive and extrusive growth of the mount st helens lava dome lava domes grow by a combination of endogenous intrusive and exogenous extrusive addition of magma either as single continuous events1 2 or through a series of relatively small pulses which together build a larger construct3 evaluating the hazards that attend growth of a dome requires an assessment of the processes controlling whether lava is added to its interior or surface because many of these dangers depend on how volatiles are admitted to or released from hot magma if the volatile pressure inside an inflating dome becomes high enough sudden exposure provided by flow front slumping can lead to explosive decompression and the generation of pyroclastic flows4 5 on the other hand lava erupted on the oversteepened surface of a dome may collapse fragment and mix with snow or ice to form pyroclastic flows surges and mudflows6 7 here we provide a quantitative assessment of the partitioning of magma into endogenous intrusions and exogenous lobes using high resolution digital topographic maps of the mount st helens dome derived from aerial photographs taken periodically between 1980 and 1986 endogenous exogenous and total volume production rates follow distinct trends which provide important clues about the nature of eruption mechanisms calculating endogenous and exogenous components for active domes like those recently formed at redoubt volcano may help quantify magma chamber processes and provide another tool for understanding the re equilibration of shallow magmatic systems

the chemical and isotopic composition of fumarolic gases and spring discharges from galeras volcano colombia abstract galeras fumarole discharges have been collected since its reactivation in 1988 through december 1995 the gases are dominated by h2o co2 s as so2 and h2s and hcl the relative proportions of these gases classify them as magmatic thermodynamic equilibrium temperatures of the gases range from 260 to 600 c the relative abundance of inert gases n2 ar and he can be used as tracers to identify the source of the fumarole discharges at galeras the majority of the samples have a composition characteristic of gases originating from arc related magmas with relatively high n2 contents and minor he and ar during 1993 the year of frequent eruptions the gas composition changed to basaltic or mantle derived gases with significantly higher he contents this is interpreted to be the result of injection of volatiles from a basaltic magma body at depth prior to and during the increased eruptive activity of 1993 the 13c values for co2 in fumarole discharges are typical of andesitic volcanoes and may indicate addition of morb derived co2 the 15n values for n2 may indicate significant contribution of n2 from marine sediments and only minor contribution of morb derived n2 the d and 18o values of the discharging steam lie on a mixing trend between the isotopic composition of arc related magmatic water and18o shifted meteoric water the most magmatic discharges have d values of 30 to 35 while the most meteoric discharges have values of 70 to 75 similar to galeras thermal spring waters galeras thermal water discharges consist of acid sulfate and bicarbonate waters s cl ratios in the acid sulfate waters are similar to fumarole ratios suggesting direct absorption of magmatic gases into shallow ground waters this is supported by the essentially meteoric d and 18o values of the discharges and by elevated3he 4he ratios of thermal spring waters the absorption of acid s and cl rich gases yield acid waters which are capable of dissolving rocks the thermal waters however are far from equilibrium with galeras lavas and pyroclastic rocks providing evidence of the immaturity of the galeras hydrothermal system the so4 and cl content as well as the o and h isotopic composition of galeras thermal springs vary with the activity of the volcano the 7 year sampling program at galeras revealed intriguing results concerning the activity of galeras its magmatic hydrothermal system and the origin of the volatiles despite decreasing outlet temperatures since 1992 deep temperatures remain high implying continued unrest in the galeras magmatic system

tuyas a descriptive genetic classification we present a descriptive genetic classification scheme and accompanying nomenclature for glaciovolcanic edifices herein defined as tuyas positive relief volcanoes having a morphology resulting from ice confinement during eruption and comprising a set of lithofacies reflecting direct interaction between magma and ice melt water the combinations of lithofacies within tuyas record the interplay between volcanic eruption and the attending glaciohydraulic conditions although tuyas can range in composition from basaltic to rhyolitic many of the characteristics diagnostic of glaciovolcanic environments are largely independent of lava composition e g edifice morphology columnar jointing patterns glass distributions pyroclast shapes our classification consolidates the diverse nomenclature resulting from early isolated contributions of geoscientists working mainly in iceland and canada and the nomenclature that has developed subsequently over the past 30 years tuya subtypes are first recognized on the basis of variations in edifice scale morphologies e g flat topped tuya then on the proportions of the essential lithofacies e g lava dominated flat topped tuya and lastly on magma composition e g basaltic lava dominated flat topped tuya these descriptive modifiers potentially supply additional genetic information and we show how the combination of edifice morphologies and lithofacies can be directly linked to general glaciohydraulic conditions we identify nine distinct glaciovolcanic model edifices that potentially result from the interplay between volcanism and glaciohydrology detailed studies of tuya types are critical for recovering paleo environmental information through geological time including ice sheet locations extents thicknesses and glaciohydraulics such paleo environmental information represents a new innovative underutilized resource for constraining global paleoclimate models

impacts of global warming on permo triassic terrestrial ecosystems geologists and palaeontologists have expressed mixed views about the effects of the end permian mass extinction on continental habitats and on terrestrial life current work suggests that the effects on land were substantial with massive erosion following the stripping of vegetation associated with long term aridification and short term bursts of warming and acid rain wildfires at the permo triassic boundary contributed to the removal of forests and the prolonged absence of forests from the earth s surface for up to 10 myr these physical crises on land impinged on the oceans suggesting tight interlocking of terrestrial and marine crises levels of extinction on land may well have been as high as in the sea and this is certainly the case for tetrapods the mass extinction seems to have been less profound for plants and insects but it is hard at present to disentangle issues of data quality from reductions in abundance and diversity several killing agents have been proposed and of these tetrapods may have succumbed primarily to acid rain mass wasting and aridification plants may have been more affected by the sudden effects of heating and wildfires and the crisis for insects has yet to be explored

emplacement and petrological evolution of the andesitic dome of galeras volcano 1990 1992 abstract since the reactivation of galeras volcano in 1988 the emplacement of a lava dome in the main crater of the volcano has been its most significant magmatic activity changes leading to the emplacement of the dome were present as early as june july 1990 when the trend of degassing for the major species mainly so 2 and co 2 in the summit fumaroles changed drastically and small vulcanian explosions become more frequent moreover after august 1990 an inflationary trend as measured by an electronic tiltmeter was observed to increase over background levels and the temperature of a newly formed fumarole besolima increased from 130 to 738 c within a month the dome was seen for the first time in early october 1991 at the base of the main crater the dome grew for about a month to a total volume of 4 10 5 m 3 during this time the growth rate was calculated to be 12 10 3 m 3 day or 0 14 m 3 s an explosive eruption on 16 july 1992 destroyed most of the dome the chemical composition of the dome ranges from 59 4 to 61 1 wt sio 2 anhydrous the presence of 1 large plagioclase phenocrysts with strongly inversely zoned rims and 2 small euhedral plagioclase crystals with normal zoning and ca rich cores indicates that a magma mixing event occurred early in the history of dome emplacement large amounts of crystal fractionation then took place about 70 fractionation can explain the mineral suite and the major and trace element compositions of the glasses the uppermost part of the dome degassing freely at the surface for ten months was able to isolate the magmatic system producing a highly evolved melt in the dome interior the july 1992 eruption tapped not only the uppermost part of the dome but also a deeper h 2 o saturated magma analyses from these samples show that most of the h 2 o was degassed while cl and b contents were higher than in the uppermost part of the dome however the f content is lower in this deeper part of the conduit while it increases in the matrix glass of the degassed upper part of the dome

the carbon and sulfur cycles and atmospheric oxygen from middle permian to middle triassic the results of a theoretical isotope mass balance model are presented for the time dependence of burial and weathering plus degassing fluxes within the combined long term carbon and sulfur cycles averaged data for oceanic 13c and 34s were entered for every million years from 270 to 240 ma middle permian to middle triassic to study general trends across the permian triassic boundary results show a drop in the rate of global organic matter burial during the late permian and a predominance of low values during the early to middle triassic this overall decrease with time is ascribed mainly to epochs of conversion of high biomass forests to low biomass herbaceous vegetation resulting in a decrease in the production of terrestrially derived organic debris additional contributions to lessened terrestrial carbon burial were increased aridity and a drop in sea level during the late permian which led to smaller areas of low lying coastal wetlands suitable for coal and peat deposition mirroring the drop in organic matter deposition was an increase in the burial of sedimentary pyrite and a dramatic increase in the calculated global mean ratio of pyrite s to organic c high s c values resulted from an increase of deposition in marine euxinic basins combined with a decrease in the burial of low pyrite associated terrestrial organic matter the prediction of increased oceanic anoxia during the late permian and early triassic agrees with independent studies of the composition of sedimentary rocks weathering plus burial fluxes for organic carbon and pyrite sulfur were used to calculate changes in atmospheric oxygen the striking result is a continuous drop in o2 concentration from 30 to 13 over a twenty million year period this drop was brought about mainly by a decrease in the burial of terrestrially derived organic matter but with a possible contribution from the weathering of older organic matter on land it must have exerted a considerable influence on animal evolution because of the role of o2 in respiration some examples are the extinction of many vertebrates loss of giant insects and amphibians and the restriction of animals to low elevations it is concluded that the extinction of plants may have contributed to the extinction of animals

pre eruptive water content of rhyolitic magmas as determined by ion microprobe analyses of melt inclusions in phenocrysts abstract the ion microprobe was used to analyze trapped melt inclusions in phenocrysts from two rhyolitic eruptions for h2o f and incompatible trace elements eleven melt inclusions from phenocrysts in air fall tephra from obsidian dome near long valley usa gave an average of 4 1 1 2 wt h2o and showed large variations in f and incompatible trace elements reflecting a complex history reported to involve mixing of at least two magma types eight inclusions in phenocrysts from the taupo ultraplinian event new zealand gave 4 5 0 8 wt h2o with small variations in the other elements analyzed measured water contents are similar to earlier estimates of the pre eruptive water contents of these and similar rhyolites and major and trace element analyses of inclusions compare closely with bulk analyses suggesting that the analyses of inclusions represent the chemistry of the magma at the time of entrapment

the terminal paleozoic fungal event evidence of terrestrial ecosystem destabilization and collapse because of its prominent role in global biomass storage land vegetation is the most obvious biota to be investigated for records of dramatic ecologic crisis in earth history there is accumulating evidence that throughout the world sedimentary organic matter preserved in latest permian deposits is characterized by unparalleled abundances of fungal remains irrespective of depositional environment marine lacustrine fluviatile floral provinciality and climatic zonation this fungal event can be considered to reflect excessive dieback of arboreous vegetation effecting destabilization and subsequent collapse of terrestrial ecosystems with concomitant loss of standing biomass such a scenario is in harmony with predictions that the permian triassic ecologic crisis was triggered by the effects of severe changes in atmospheric chemistry arising from the rapid eruption of the siberian traps flood basalts

the emplacement of an obsidian dyke through thin ice hrafntinnuhryggur krafla iceland an eruption along a 2 5 km long rhyolitic dyke at krafla volcano northern iceland during the last glacial period formed a ridge of obsidian hrafntinnuhryggur the ridge rises up to 80 m above the surrounding land and is composed of a number of small volume lava bodies with minor fragmental material the total volume is 0 05 km3 the lava bodies are flow or dome like in morphology and many display columnar jointed sides typical of magma ice interaction quench fragmented lower margins indicative of interaction with meltwater and pumiceous upper surfaces typical of subaerial obsidian flows the fragmental material compromises poorly sorted perlitic quench hyaloclastites and poorly exposed pumiceous tuffs lava bodies on the western ridge flanks are columnar jointed and extensively hydrothermally altered at the southern end of the ridge the feeder dyke is exposed at an elevation 95 m beneath the ridge crest and flares upwards into a lava body using the distribution of lithofacies we interpret that the eruption melted through ice only 35 55 m thick which is likely to have been dominated by firn hrafntinnuhryggur is therefore the first documented example of a rhyolitic fissure eruption beneath thin ice firn the eruption breached the ice leading to subaerial but ice firn contact lava effusion and only minor explosive activity occurred the ridge appears to have been well drained during the eruption aided by the high permeability of the thin ice firn which appears not to have greatly affected the eruption mechanisms we estimate that the eruption lasted between 2 and 20 months and would not have generated a significant jokulhlaup 70 m3s 1

isotopic and geochemical investigation of two distinct mars analog environments using evolved gas techniques in svalbard norway the 2010 arctic mars analog svalbard expedition amase investigated two distinct geologic settings on svalbard using methodologies and techniques to be deployed on mars science laboratory msl amase related research comprises both analyses conducted during the expedition and further analyses of collected samples using laboratory facilities at a variety of institutions the sample analysis at mars sam instrument suite on msl includes pyrolysis ovens a gas processing manifold a quadrupole mass spectrometer qms several gas chromatography columns and a tunable laser spectrometer tls an integral part of sam development is the deployment of sam like instrumentation in the field during amase 2010 two parts of sam participated as stand alone instruments a hiden evolved gas analysis mass spectrometer ega qms system represented the ega qms component of sam and a picarro cavity ring down spectrometer ega crds represented the ega tls component of sam a field analog of chemin the xrd xrf on msl was also deployed as part of this field campaign carbon isotopic measurements of co2 evolved during thermal decomposition of carbonates were used together with ega qms geochemical data mineral composition information and contextual observations made during sample collection to distinguish carbonates formation associated with chemosynthetic activity at a fossil methane seep from abiotic processes forming carbonates associated with subglacial basaltic eruptions carbon and oxygen isotopes of the basalt hosted carbonates suggest cryogenic carbonate formation though more research is necessary to clarify the history of these rocks

1989 1995 earthquake sequences in the galeras volcano region sw colombia and possible volcano earthquake interactions abstract the galeras volcanic complex located in the narino department sw colombia includes the most historically active volcano in the country galeras a 4276 m high stratovolcano located 9 km west of the city of san juan de pasto 400 000 inhabitants the area is also affected by the continental faulting represented by the buesaco aranda and pasto faults belonging to one of the most seismically active structures in colombia the romeral fault system several moderate to strong shallow earthquakes affected the city of san juan de pasto and its neighbouring region since the xvii century the coexistence of an active volcanic complex and an active fault system complicates the study and interpretation of the different processes taking place in the region as well as the identification of any connection or interaction among them the reactivation of the volcano in 1989 was characterized by three main magmatic events 1 a series of vulcanian eruptions during 4 9 may 1989 with semi continuous ash emissions from a secondary crater 2 the emplacement of an andesitic lava dome at the bottom of the main crater from september 1990 until december 1991 and 3 six vulcanian eruptions from the main crater during 1992 1993 with destruction of most of the dome during the first one on 16 july 1992 during the same period four earthquake sequences were located in a limited area n and ne of galeras volcano on august september 1989 aug1989 april june 1993 apr1993 november december 1993 nov1993 and march august 1995 mar1995 the last one included a ml4 7 main shock on 4 march 1995 producing moderate to high damage in the epicentral region msk maximum intensity viii and in the city of san juan de pasto vi vii the last damaging earthquake in the region was a msk intensity viii ix in 1947 a detailed analysis of the spatio temporal characteristics of the four earthquake sequences allowed identifying their different origin and suggesting some interrelationship between the reactivated eruptive process and the contemporaneous seismic activity the aug1989 sequence presents a typical volcanic swarm like pattern most probably related with the process of magma intrusion from depth at the beginning of the volcano s reactivation the apr1993 the nov1993 and the mar1995 sequences show a clear tectonic origin with events occurring on rupture planes almost vertical that can be associated to the active faults in the area the seismogenic process of these three sequences could have been activated or accelerated by the main eruptions during 1992 1993 these results suggest that constrains provided by improved relocations and the detailed analysis of the space time characteristics of earthquake sequences in galeras volcanic environment allow to establish the different generation mechanisms involved and to suggest feasible explanations on the possible interrelationships of the magmatic volcanic processes and the seismicity observed

phanerozoic large igneous provinces lips heatt haline euxinic acidic thermal transgression episodes and mass extinctions abstract the phanerozoic consists of three mutually exclusive climate states icehouse greenhouse and hothouse the greenhouse is the default state representing 70 of the phanerozoic it is characterized by a weak thermal mode pole driven deep water formation with little or no continental sea ice and weakly oxic cool water sinking near the poles nitrogen limitation characterizes greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen the steady state greenhouse default must be forced to produce either of the other two states continent continent collision produces the intense chemical weathering that draws down atmospheric co2 and results in the icehouse state that comprises 20 25 of the phanerozoic icehouses have ice caps in contact with the ocean that produce icebergs and foster sea ice formation sea ice formation fills the ocean with highly oxic phosphorus limited icewater except for a thin layer of warm surface water in the tropics of the 23 most conspicuous mass extinctions of the phanerozoic including the late ediacaran 4 are associated with ice volume related regressions and 3 are problematic we suggest that the other 16 mass extinctions occurred when greenhouse climate was forced to hothouse climate large igneous provinces lips can trigger the heatt haline euxinic acidic thermal transgression mechanism which can force greenhouse climate to a hothouse climate state the rapid voluminous co2 emissions of lips cause a series of events that result in very slow but pronounced haline mode circulation mid latitude driven deep water formation that produces warm saline bottom water at very dry hot subtropical and middle latitudes this water upwells at the poles causing warm and moist equable climate hothouse development promotes deep sea anoxia that is generated in concert with co2 buildup and warming the spread of anoxia favors reduced nitrogen over nitrate and limited iron dust curtails nitrogen fixation this leads to dominance of primary productivity by primitive green algae and or cyanobacteria progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning even as availability of usable nitrogen plummets the result is eukaryotic mass extinction we suggest that the 16 phanerozoic mass extinctions referred to above resulted at least in part from the heatt process evidence for this relationship at 11 of the most severe extinctions is convincing data sets for the other 5 are strongly suggestive of heatt related mass extinction but do not yet have enough documentation to reliably characterize them as heatt episodes

morphological changes of the active cone of galeras volcano colombia during the last century abstract the morphology of the active cone of galeras volcano is a consequence of the complex interplay between effusive and explosive processes and erosion the main crater several secondary craters and zones of fumarolic activity were formed on the active cone as a result of these processes analysis of detailed descriptions from observations that began in 1989 indicates that volcanic activity led to the formation of many fissures in the main crater and on the active cone which appear to show an important relationship with the volcano s structure the fractures and fissures are associated with a tangential system generally aligned with the crater rim and a radial system that tends to intersect the crater rim at high angles the intersections of the tangential and radial systems have generated zones of weakness some of which have developed into eruptive centers thus certain fumaroles have evolved into small craters and these craters have contributed to the growth of the main crater on the active cone

palynology and vegetation dynamics across the permian triassic boundary in southern tibet abstract the end permian mass extinction epme is regarded as the most severe biotic crisis in earth history which is particularly well documented in the marine fossil record despite compelling evidence that dramatic global environmental changes probably drove this extinction event its effects on terrestrial plants are still highly controversial here we present changhsingian latest permian to late smithian latest early triassic composite palynological successions from the lagoonal to open marine qubu and tulong sections in southern tibet quantitative analyses of palynomorph distributions range charts and relative abundance data allow us to differentiate five distinct informal palynofloral assemblages in ascending order the scheuringipollenites ovatus vitreisporites pallidus op assemblages the reduviasporonites catenulatus assemblage the endosporites papillatus pinuspollenites thoracatus pt assemblages the lundbladispora brevicula densoisporites nejburgii bn assemblages and the falcisporites nuthallensis alisporites landianus nl assemblages these palynological assemblage intervals and the associated ammonoid and conodont biostratigraphy resolve vegetation changes across the permian triassic boundary ptb on the northern tethyan margin of gondwanaland in great detail and high resolution principal component analysis pca of palynological data indicates that the op assemblages which are dominated by non taeniate bisaccate pollen represent a vegetation in a cool and dry climate during the changhsingian in the qubu section the palynological turnover from the op assemblages to the c assemblage 0 81 m below the ptb coincides with abrupt sea level fluctuations in the latest permian as this turnover further coincides with an extreme negative 13corg shift a great abundance of amorphous organic matter aom and marine acritarchs as well as the frequent occurrence of reduviasporonites catenulatus the c assemblage is tentatively interpreted to represent the fungal spike reported worldwide at the onset of the epme in southern tibet the epme appears to result only in a short term disturbance and range contraction of land plant communities surprisingly the early dienerian pt assemblages postdating the epme by about 500kyrs closely resemble the late changhsingian op assemblages suggesting a resurgence of those land plant groups that were dominant during the late changhsingian this recovery was disrupted with the onset of the late dienerian bn assemblages in the qubu section which is represented by a peak abundance of cavate trilete spores reflecting large scale deforestation for nearly one million years the regional vegetation appears to have been dominated by pioneer communities of quillworts and spike mosses only towards the end of the smithian bisaccate gymnosperm pollen regained dominance with the onset of the nl assemblages in the tulong section integrating the results of the principal component analysis on our new palynological data and conodont apatite oxygen isotope data from neighbouring sections in pakistan the contraction of gymnosperm forests during the early dienerian smithian in southern tibet is interpreted to be accompanied by an abrupt change to an episode with a warmer and more humid climate this observation supports the hypothesis that the secondary eruptions of the siberian large igneous province during the induan led to long term global warming and as a side effect to more humid conditions in the southern temperate zone as a result of altered precipitation and evaporation patterns

evolution of an englacial volcanic ridge pillow ridge tindar mount edziza volcanic complex ncvp british columbia canada abstract glaciovolcanic deposits are critical for documenting the presence and thickness of terrestrial ice sheets and for testing hypotheses about inferred terrestrial ice volumes based on the marine record deposits formed by the coincidence of volcanism and ice at the mount edziza volcanic complex mevc in northern british columbia canada preserve an important record for documenting local and possibly regional ice dynamics pillow ridge located at the northwestern end of the mevc formed by ice confined fissure fed eruptions it comprises predominantly pillow lavas and volcanic breccias of alkaline basalt composition with subordinate finer grained volcaniclastic deposits and dykes the ridge is presently 4 km long 1000 m in maximum width and 600 m high fifteen syn and post eruptive lithofacies are recognized in excellent exposures along the glacially dissected western side of the ridge we recognize five lithofacies associations 1 poorly sorted tuff breccia and dykes 2 proximal pillow lava dykes and tuff breccia 3 distal pillow lava poorly sorted conglomerate and well sorted volcanic sandstone 4 interbedded tuff lapilli tuff and tuff breccia units and 5 heterolithic volcanogenic conglomerate and sandstone given the abundance of pillow lavas and the lack of surrounding topographic barriers capable of impounding water we agree with souther souther j g 1992 the late cenozoic mount edziza volcanic complex geol soc can mem vol 420 320 pp that the bulk of the edifice formed while confined by ice but have found evidence for a more complex and variable eruption history than that which he proposed preliminary estimates of water ice depths derived from ftir analyses of h2o give ranges of 300 to 680 m assuming 0 ppm co2 and 857 to 1297 m assuming 25 ppm co2 variations in depth estimates among samples may indicate that water ice depths changed during the evolution of the ridge which is consistent with our interpretations for the origins of different lithofacies associations given that the age of the units are likely to be ca 0 9 ma souther j g 1992 the late cenozoic mount edziza volcanic complex geol soc can mem vol 420 320 pp pillow ridge may be the best documentation of a regional high stand of the cordilleran ice sheet cis in the middle pleistocene and an excellent example of the lithofacies and stratigraphic complexities produced by variations in water levels during a prolonged glaciovolcanic eruption

deformation associated with the extrusion of a dome at galeras volcano colombia 1990 1991 abstract during 1989 1992 two electronic tilt meters named crater and peladitos and a short level line named las piedras were used for monitoring galeras volcano the two tilt meters detected considerable changes of uplift mainly from june to november 1991 the crater station showed cumulative values of more than 600 microradians while the peladitos station exhibited values of more than 100 microradians the short level line showed inflationary tilt of more than 20 microradians in 1989 this behavior was related to increases in the daily occurrence of long period seismic events during july november 1991 caused by the rise and extrusion of a lava dome which was subsequently destroyed in july 1992 at the end of 1990 the deformation source was located at a depth of 2 3 km by december 1991 the source had migrated to less than 500 m in depth the magma ascent rate was 1 4 m day during this period the dome emplaced in the crater had a volume between 300 000 to 400 000 m 3 using a hydrodynamic model and the tilt changes registered by the peladitos station the volume of the magma body is estimated at approximately 2 8 10 6 m 3

hydrogen isotope evidence for extrusion mechanisms of the mount st helens lava dome from october 1980 to october 1986 the dacite lava dome at mount st helens grew through the accumulation of more than 15 separate lobes during extrusive episodes that lasted from 1 to 24 days except for an anomalous period of continuous growth throughout most of 19831 over these six years the growth rate was generally volume predictable that is the amount of lava added to the dome in a given eruption was roughly proportional to the time since the preceding extrusion2 these well documented eruptions were separated by repose intervals lasting from several months to more than a year2 in an attempt to identify the triggering mechanisms for these periodic eruptions we have used hydrogen isotope analyses to determine water content and deuterium content for 18 samples of the mount st helens dome dacite these isotope data the first ever collected from an active lava dome suggest a steady state process of magma evolution combining crystallization induced volatile production in the chamber with three different degassing mechanisms closed system volatile loss in the magma chamber open system volatile release during ascent and kinetically controlled degassing upon eruption at the surface the data suggest that future dome building eruptions may require a new influx of volatile rich magma into the chamber

mid to late permian microfloristic evidence in the metamorphic successions of the northern apennines insights for age constraining and palaeogeographical correlations recent studies on the stratigraphy of paleozoic successions belonging to key sectors of the inner northern apennines provide data that can be used to propose new hypotheses about the palaeogeography of the western mediterranean domain during post hercynian times we report here the first evidence of mid to late permian guadalupian lopingian palynomorphs in the chronostratigraphically highly debated metamorphic units of the northern apennines the rio marina formation the mt calamita formation and the le cetine formation and consider the stratigraphic implications for the tuscan basement to which the study rocks belong and their palaeogeographical attribution considering their gondwana affinity these results agree with the interpretation that the alpine tethyan sedimentary cycle was already active during the mid to late permian thematic collection this article is part of the apennines and tyrrhenian system collection available at https www lyellcollection org cc the apennines tyrrhenian system

the spatial nearshore offshore distribution of latest permian phytoplankton from the yangtze block south china abstract in order to analyze the spatial paleoecological distribution of the organic walled microphytoplankton in the late permian five sections from the yangtze block south china displaying different sediment facies types from neritic to offshore paleoenvironments including basinal facies have been investigated palynologically based on the diversity and relative abundance of acritarch species and genera the new data from the permian provide similar patterns as those described from other geological periods 1 low diversities with 2 to 4 acritarch species occur in nearshore environments whereas the higher diversities more than ten acritarch species appear in the offshore environments 2 at the generic level the genera leiosphaeridia reduviasporonites and micrhystridium are distributed widely from nearshore facies corresponding to shallow water environments to offshore facies corresponding to deeper water settings whereas some genera such as dictyotidium and veryhachium have a narrower distribution occurring on the continental shelf and towards the basin indicating open marine environments 3 the genus schizosporis only occurs around the permian triassic boundary ptb when the sea level declined probably indicating nearshore environments with shallow water settings 4 at the specific level the species micrhystridium breve displaying short spines and leiosphaeridia minutissima are indicative of neritic facies whereas the other species of micrhystridium and veryhachium with longer spines e g micrhystridium stellatum and veryhachium hyalodermum and leiosphaeridia microgranifera indicate more open marine environments big spherical acritarch species over 80 m in diameter such as dictyotidium reticulatum indicate shallow water environments and 5 in the ptb strata the relative abundance of the enigmatic reduviasporonites interpreted by some authors as a fungal spore is not higher than 14 in every sample indicating that a spike of reduviasporonites does not occur in the yangtze area reduviasporonites chalastus 40 m in length obviously dominates in shelf environments of shallow water whereas the smaller reduviasporonites catenulatus 15 m in length are more common in deeper water

twenty years 1990 2010 of geodetic monitoring of galeras volcano colombia from continuous tilt measurements abstract galeras an andesitic stratovolcano part of the galeras volcanic complex is one of the most active volcanoes in colombia historic activity is centered on a small volume cone inside the youngest amphitheater which breaches the west flank of the volcano at least 30 confirmed eruption periods have been recorded in the past 480 years with episodes of unrest ranging from weak fumarolic activity and ash emissions to larger explosive events the most recent eruption periods recorded instrumentally since 1988 have been characterized by minor explosive eruptions and the emplacement of three crater domes and small pyroclastic flow deposits in this paper we discuss the evolution of volcanic activity using a 20 year long record of tilt measurements in particular we focus on three episodes of unrest occurred in 1991 2006 and 2008 when the deformation was clearly associated with shallow magma intrusions and the emplacement and destruction of crater domes the depth of the intrusions varied from a few hundred meters august 2005 to two kilometers january 2009 while the volume change ranged from 10 4 m 3 may october 2009 to 10 6 m 3 january 2009 a comparison with seismic data indicates that the deformation sources were located within the cloud of hypocenters of the volcano tectonic events the lack of a clear correlation between the volume change and depth of the sources and the total so 2 flux could indicate that the unrest at galeras was related to a larger intrusive event with only a small part of the magma erupted in the form of tephra and lava domes

massive volcanism at the permian triassic boundary and its impact on the isotopic composition of the ocean and atmosphere abstract bulk carbonate and conodonts from three permian triassic p t boundary sections at guryul ravine kashmir abadeh central iran and pufels bula bulla italy were investigated for 13 c and 18 o carbon isotope data highlight environmental changes across the p t boundary and show the following features 1 a gradual decrease of 4 to more than 7 starting in the late permian changhsingian c bachmanni zone with two superimposed transient positive excursions in the c meishanensis h praeparvus and the m ultima s mostleri zones 2 two 13 c minima the first at the p t boundary and a higher occasionally double minimum in the lower i isarcica zone it is unlikely that the short lived phenomena such as a breakdown in biological productivity due to catastrophic mass extinction a sudden release of oceanic methane hydrates or meteorite impact s could have been the main control on the latest permian carbon isotope curve because of its prolonged 0 5 ma duration gradual decrease and the existence of a 1 positive shift at the main extinction horizon the p t boundary 13 c trend matches in time and magnitude the eruption of the siberian traps and other contemporaneous volcanism suggesting that volcanogenic effects such as outgassed co 2 from volcanism and even more thermal metamorphism of organic rich sediments as the likely cause of the negative trend

interactions between lava and snow ice during the 2010 fimmvorðuhals eruption south central iceland 1 the 20 march 12 april basaltic effusive eruption at fimmvor uhals southern iceland was an important opportunity to directly observe interactions between lava and snow ice the eruption site has local perennial snowfields and snow covered ice and at the time of eruption it was covered with an additional 1 3 m of seasonal snow syn eruption observations of interactions between lava and snow ice are grouped into four categories 1 lava advancing directly on top of snow 2 lava advancing on top of tephra covered snow 3 snow ice melting at lava flow margins and 4 lava flowing beneath snow based on syn and post eruption observations in 2010 11 we conclude that the features seen in the lava flow field show only limited and localized evidence for the influence of snow ice presence during the eruption estimated melting rates from radiant and conductive heating at the flow fronts are too slow on the order of 5 m hr to allow for complete melting of snow ice ahead of the advancing lava flows at least during periods of observed rapid lava advance rates 15 55 m hr thus we conclude that during those periods which largely established the aerial extent of the lava flow field lava advanced on top of snow that this likely was the predominant mode of lava emplacement for much of the eruption is supported by many syn eruption field observations examination of the lava flows subsequent to the eruption has so far only found subtle evidence for interactions between lava and snow ice for example locally lava flows have fractured and are collapsing or have developed marginal rubble aprons from melting of snow banks that were partly covered by lava flow margins

explosive activity associated with the growth of volcanic domes abstract domes offer unique opportunities to measure or infer the characteristics of magmas that at domes and elsewhere control explosive activity a review of explosive activity associated with historical dome growth shows that 1 1 explosive activity has occurred in close association with nearly all historical dome growth 2 2 whole rock sio 2 content a crude but widely reported indicator of magma viscosity shows no systematic relationship to the timing and character of explosions 3 3 the average rate of dome growth a crude indicator of the rate of supply of magma and volatiles to the near surface enviornment shows no systematic relationship to the timing or character of explosions and 4 4 new studies at arenal and mount st helens suggest that water content is the dominant control on explosions from water rich magmas whereas the crystal content and composition of the interstitial melt and hence magma viscosity are equally or more important controls on explosions from water poor magmas new efforts should be made to improve current rather limited techniques for monitoring pre eruption volatile content and magma viscosity and thus the explosive potential of magmas

tephra deposition on glaciers and ice sheets on mars influence on ice survival debris content and flow behavior we examine the consequences of pyroclastic deposits being emplaced onto ice layers on mars both those in the polar caps and those forming glaciers on the flanks of some of the large shield volcanoes we show that layers of pyroclasts greater than a few meters in thickness whether emplaced cold as fall deposits or hot as pyroclastic density current deposits act almost exclusively to protect ice layers beneath them from sublimation irrespective of whether they are emplaced at high or low elevations or high or low latitudes layers less than about 2 m thick on the other hand can cause significant ice loss by raising the surface temperature due to their low albedo and then transmitting that increased temperature to the underlying ice especially on a diurnal time scale this can have a significant bearing on the emplacement history of polar water ice and on the survival time of glacial ice on shield volcano flanks a key factor in the latter case is the timing of the episodic volcanic activity relative to the cycles of climate change driven by mars obliquity and eccentricity variations

coeval strombolian and vulcanian type explosive eruptions at panarea aeolian islands southern italy in this paper we document the evolution of the emergent panarea dome in the aeolian islands southern italy placing particular emphasis on the reconstruction of the explosive events that occurred during the final stage of its evolution two main pyroclastic successions exposing fall deposits with different compositions have been studied into detail the andesitic palisi succession and the basaltic punta falcone succession the close in time deposition of the two successions the dispersal area and grain size distribution of the deposits account for their attribution to vents located in the western sector of the present island and erupting almost contemporaneously vents could have been aligned along nne trending regional fracture systems controlling the western flank of the dome and possibly its collapse laboratory analyses have been devoted to the characterization of the products of the two successions that have been ascribed to vulcanian and to strombolian type eruptions respectively the vulcanian eruption started with a vent clearing phase that occurred by sudden decompression of a pressurized magma producing ballistic bombs and a surge blast and the development of a vulcanian plume vulcanian activity was almost contemporaneous to strombolian type fall out eruptions the coeval occurrence of basaltic and andesitic eruptions from close vents and the presence of magmatic basaltic enclaves in the final dacitic lava lobe of the dome allow us to speculate that the intrusion of a basaltic dyke played a major role in triggering explosive eruptions the final explosive episodes may have been caused by extensional tectonics fracturing the roof of a zoned shallow magma chamber or by the intrusion of a new basaltic magma into a more acidic and shallow reservoir intrusion most likely occurred through the injection of dykes along the western cliff of the present panarea island inducing the collapse of the western sector of the dome

significance of polycyclic aromatic hydrocarbons pahs in permian triassic boundary sections abstract in this study the abundances of several polycyclic aromatic hydrocarbons pahs table 1 i xxi have been measured throughout three permian triassic p tr sections from meishan south china kap stosch area east greenland and peace river basin western canada dibenzothiophene i and dibenzofuran ii were found to decrease in abundance just before or shortly after the p tr transition in all three sections while perylene iii was observed to increase in abundance at the onset of the main extinction horizon bed 25 in meishan perylene has been attributed to a wood degrading fungal source and therefore it seems possible these phenomena are related to the demise of land plants further distinct patterns of various combustion derived pahs occurring in each section imply that forest fire events occurred within the late permian and early triassic in the meishan section high amounts of combustion derived pahs pyrene iv fluoranthene v benzo a anthracene vi benzofluoranthenes sum i e vii benzo a pyrene viii benzo e pyrene ix and coronene x occur within bed 25 also containing ash attributed to the fallout from massive volcanic eruptions in siberia and or china

a model of vulcanian eruptions at galeras volcano colombia abstract a series of six vulcanian eruptions at galeras volcano colombia occurred during 1992 1993 these eruptions followed the emplacement of a lava dome in late 1991 which was accompanied by cooling crystallizing and partial solidification of the column of magma plugging the conduit five of the eruptions were preceded by episodes of monochromatic long period seismicity suggesting cyclic pressurization of the magma the quiescent intervals between eruptions generally decreased with each successive eruption we propose a model of gas release from magma into confined stationary pore spaces by 5 10 crystallization of anhydrous minerals causing repeated overpressurization of the magmatic system using initial lithostatic pressures of 20 100 mpa 800 3900 m depth gas buildup by crystallization indicates overpressures of 3 17 mpa which is the approximate fracture criterion for a magma chamber our galeras data suggest two models of pressurization 1 gas exsolution may have occurred at similar depths but with progressively smaller overpressures being developed before each successive eruption according to this model the comparatively long quiescent periods between the first eruptions resulted in relatively large amounts of gas exsolution from the magma and accumulation in pore spaces whereas the shorter quiescent periods for the later eruptions exsolved less gas the decrease in overpressure with time may have resulted from progressive fracturing of partly solidified magma during the eruptions which progressively decreased the tensile strength and increased the permeability of the magma 2 since overpressures are smaller at shallower depths for a given amount of crystallization the first eruptions of 1992 1993 were caused by gas exsolution at shallow depths while the last eruptions having shorter quiescent intervals resulted from a greater amount of gas exsolution at greater depths in this case the rate of gas exsolution varied as a function of depth the two scenarios for pressurization may be combined into a more general model involving edifice weakening and the development of a shallow hydrothermal system from continued degassing of the magma plug as weakening of the edifice formed an extensive system of fractures the shallow hydrothermal system deepened due to meteoric water input and magmatic degassing with time a greater number of fractures were filled and partly sealed by hydrothermal minerals at progressively deeper levels as a result the source of the overpressure also deepened with time

volatiles in basaltic glasses from a subglacial volcano in northern british columbia canada implications for ice sheet thickness and mantle volatiles

temporal change of the magma plumbing system at galeras volcano colombia revealed by repeated seismic tomography in 2009 2018 abstract we performed repeated three dimensional seismic tomography in 2009 2018 for the area influenced by the intersection of the silvia pijao buesaco and cauca almaguer fault systems beneath galeras volcano colombia we analyzed two periods 2009 2012 and 2013 2018 which were characterized by explosive eruptive activity and relative quiescence at galeras respectively we used p and s wave arrival times of 2848 2009 2012 and 2289 2013 2018 earthquakes that occurred beneath the volcano p and s wave velocity vp and vs respectively anomalies and their changes between the two periods were interpreted to be associated with magma movement in the volcanic plumbing system which was controlled by the intersection of the faults two possible pathways of magma ascent and accumulation were identified in the fault systems one located sw of the active crater consisted of areas with high vp vs values 1 9 at depths of 2 to 4 km below sea level and the other located ne of the active crater with high and low vp vs values the low vp vs

subglacial to emergent basaltic volcanism at hloðufell south west iceland a history of ice confinement abstract hlo ufell is a familiar 1186 m high landmark located about 80 km northeast of reykjavik and 9 km south of the langkjokull ice cap in south west iceland this is the first detailed study of this well exposed and easily accessible subglacial to emergent basaltic volcano eight coherent and eleven volcaniclastic lithofacies are described and interpreted and its evolution subdivided into four growth stages i iv on the basis of facies architecture vents for stages i ii and iv lie along the same fissure zone which trends parallel to the dominant nne ssw volcano tectonic axis of the western volcanic zone in this part of iceland but the stage iii vent lies to the north and is probably responsible for the present n s elongation of the volcano the basal stage i is dominated by subglacially erupted lava mounds and ridges which are of 240 m maximum thickness were fed from short fissures and locally display lava tubes some of the stage i lavas preserve laterally extensive flat to bulbous steep glassy surfaces that are interpreted to have formed by direct contact with surrounding ice and are termed ice contact lava confinement surfaces these surfaces preserve several distinctive structures such as lava shelves pillows that have one flat surface and mini pillow

a model of degassing at galeras volcano colombia 1988 1993 galeras volcano reactivated in early 1988 as evidenced by increased seismicity gas emissions and fumarole temperatures and had a series of explosive eruptions in may 1989 during 1989 1990 the volcano was characterized by high so 2 flux reaching 5000 t metric tons day this period of strong degassing was followed by upward movement of magma july september 1991 and the emplacement of a lava dome october november 1991 since november 1991 long period seismicity and so 2 flux have decreased indicating that the conduit has partially sealed itself probably by crystallization and solidification of the magma on july 16 1992 the dome was destroyed by an explosion consistent with pressurization due to sealing and degassing in a nonporous medium continued pressurization beneath the volcano is indicated by eruptions on january 14 march 23 april 4 april 13 and june 7 1993 glass inclusion and matrix glass analyses support a hypothesis of significant magma degassing at depth in the magma chamber and in the conduit this degassing has reduced the h 2 o s and cl contents of the magma but the f content appears to have increased due to crystallization of anhydrous mineral phases and to the low fluid melt partition coefficient for f despite its degassed state galeras is currently a dangerous volcano because the sealing process forces gas saturated magma to release volatile components into confined spaces thereby causing pressurization and explosive eruptions

basaltic subglacial sheet like sequences evidence for two types with different implications for the inferred thickness of associated ice abstract subglacially erupted volcanic sequences provide proxies for a unique range of palaeo ice parameters and they are potentially highly useful archives of palaeoenvironmental information particularly for pre quaternary periods they can thus be incorporated by climate and ice sheet modellers in the same way as other environmental proxies yet they remain largely under utilised basaltic volcanic sequences erupted subglacially consist empirically of two major types corresponding to eruptions under thick and thin ice respectively the latter are called subglacial sheet like sequences and only one generic type of sequence has been described so far however there is now evidence that there are at least two generic types with significantly different implications for interpretations of associated palaeo ice sheet thicknesses one type which is relatively well described is believed to be a diagnostic product of eruptions associated with a relatively thin glacial cover 1000 m eruptions that form the dalsheidi type of sequence commence with the injection and inflation of a sill along the ice bedrock interface such interface sills were predicted theoretically but had no known geological example until now subsequent evolution commonly involves floating of the ice cover catastrophic meltwater drainage and emplacement of widespread sheets of hyaloclastite as cohesionless mass flows and hyperconcentrated flows the water saturated hyaloclastite is characteristically intruded by apophyses sourced in the underlying interface sill eruptions are commonly not explosive until their later stages dalsheidi type deposits are outflow sequences probably linked to subglacial pillow volcanoes which in iceland were erupted along fissures they only provide an indication of minimum thicknesses of the associated overlying ice although theoretical considerations suggest substantial ice thicknesses in excess of 1000 m however they are likely to be characteristic products of eruptions under the thick west antarctic ice sheet but are currently inaccessible such eruptions may be capable of destabilising that ice sheet

anisotropic stress accumulation in cooling lava flows and resulting fracture patterns insights from starch water desiccation experiments abstract desiccation of starch water slurries is a useful analog for the production of polygonal fractures columnar joints in cooling lava flows when left to dry completely a simple mixture of 1 1 starch and water will produce columns that appear remarkably similar to natural columnar joints formed in cooled lava flows columns form when the accumulation of isotropic stress exceeds the tensile strength of a material at which point a fracture forms and advances through the material perpendicular to the desiccating surface individual fractures will initially form orthogonal to the desiccation surface but will quickly evolve into a hexagonal fracture network that advances incrementally through the material however some fracture patterns found within natural lava flows are not hexagonal lodge and lescinsky 2009 this issue but rather have fracture lengths that are much longer than the distance to adjacent fractures these fractures are commonly found at lava flows that have interacted with glacial ice during emplacement the purpose of this study is to utilize starch analog experiments to better understand the formation of these fractures and the stress regimes responsible for their non hexagonal patterns to simulate anisotropic conditions during cooling the starch slurry was poured into a container with a movable wall that was attached to a screw type jack the jack was then set to slowly extend or retract while the slurry desiccated this resulted in either a decrease or increase in the chamber cross sectional area thus creating compressional or extensional regimes decreasing chamber area dca experiments resulted in fractures with larger lengths parallel to the direction of wall movement also direction of compression it also caused localized thrust faulting and curved column development increasing chamber area ica experiments produced a zone of horizontal column development along the expanding margin produced when the wall detached from the sample within this zone vertical fracture traces were observed that extended beyond individual columns the viscoelastic rheology of both starch water slurries and cooling lava flows aid in the production of these long and continuous fractures during desiccation cooling the total strain in the material is divided into elastic strain stress accumulating and viscous strain stress relaxing during isotropic conditions the viscous component is also isotropic therefore stress is relaxed equally in all directions however if there is an existing viscous strain such as in the dca and ica experiments stress can be preferentially relaxed in a single direction resulting in fracture development with preferred orientations

secular variations of helium and carbon isotopes at galeras volcano colombia copyright c 1997 elsevier science b v all rights reserved we have measured 3 he 4 he 4 he 20 ne and co 2 4 he ratios and d 13 c values of co 2 in eighteen samples from crater fumaroles of galeras volcano colombia and seven samples of bubbling gases of the pandiaco mineral spring located about 8 km east of the volcano from april 1988 to july 1995 the 3 he 4 he ratios of crater fumaroles corrected for atmospheric contamination increased significantly from 5 47 r atm in december 1989 to 7 93 r atm in august 1990 and reached a maximum of 8 84 r atm in may 1992 the ratio then decreased gradually until july 1995 overall variation of helium isotopes appears to be related to the current activity of the volcano the 3 he 4 he ratios of pandiaco mineral spring were constant between april 1988 and november 1991 and increased in april 1993 although experimental error is large the d 13 c values of co 2 of crater fumaroles show negative correlation to the helium isotopes while those of pandiaco are relatively constant based on the d 13 c values and co 2 3 he ratios it is possible to estimate fractions of upper mantle carbon in these samples calculated mantle fractions are 3 10 in crater fumaroles while those in pandiaco spring are negligibly small

excitation of a buried magmatic pipe a seismic source model for volcanic tremor recent observations of seismic events at various volcanoes suggest that harmonic tremor results from the sustained occurrence of so called long period or low frequency events accordingly we can view the long period volcanic event as the elementary process of tremor and interpret it as the impulse response of the tremor generating system we present a seismic model in which the source of tremor is the acoustic resonance of a fluid filled volcanic pipe triggered by excess gas pressure the model consists of three elements namely a triggering mechanism a resonator and a radiator for simplicity we assume a hemispherical trigger cylindrial resonator and circular radiator set in a vertical configuration with the trigger capping the top of the pipe and the disk shaped radiator shutting off its bottom considering the simple case of a source buried in a homogeneous half space we then apply the discrete wave number method to obtain a complete representation of the ground motion response at near and intermediate distances the results demonstrate that the displacement attributed to the pipe dominates the near field motion while that due to the disk is representative of the intermediate and far fields the trigger itself has a smaller contribution mainly limited to the field in the proximity of the source the characteristics displayed by the free surface response evolve from a strong impulsive signature in the immediate vicinity of the epicenter to a well developed harmonic wave train dominated by rayleigh waves at larger distances no clear shear arrival can be detected in the synthetic seismograms the displacement spectrum reflects the organ pipe modes of the conduit and the bandwidth associated with the dominant spectral peak of motion is controlled by the combined losses due to viscous attenuation in the fluid and elastic radiation into the solid in the case of the cylindrical magma column considered the radiation loss is proportional to the square of the pipe radius while the loss related to viscous damping is inversely proportional to the same factor indicating that the relative importance of the two loss mechanisms is critically dependent on the geometry of the magma reservoir the relative importance of the pipe and disk elements likewise is a function of the conduit cross section this suggests the possibility of determining the geometry of the source as well as the radiation loss and in situ magma viscosity from a comparison of near and far field observations

catastrophic soil erosion during the end permian biotic crisis organic geochemical analyses of sedimentary organic matter from a marine permian triassic transition sequence in northeastern italy reveal a significant influx of land derived diagenetic products of polysaccharides this unique event reflects massive soil erosion resulting from destruction of land vegetation due to volcanogenic disturbance of atmospheric chemistry the excessive supply of soil materials to the oceans provides a direct link between terrestrial and marine ecological crises suggesting that ecosystem collapse on land could have contributed to the end permian marine extinctions

response of glacier basal motion to transient water storage the speed of a glacier is affected most by sudden jumps in the water supply to the glacier but it goes back to previous levels if high water inputs are sustained because the glacier s plumbing system adjusts

the table a flat topped volcano in southern british columbia revisited more than 65 years ago w h mathews published a seminal paper in american journal of science describing the table an iconic flat topped volcano in southern british columbia canada the table is recognized as the type example of a glaciovolcanic lava dominated tuya we use field mapping 3 d photogrammetry lithofacies identification and 40ar 39ar geochronology to re examine the emplacement origins of this unique volcanic edifice the table is a steep sided flat topped mass of dense porphyritic andesite preserving a near original outer surface of hackly fractured aphanitic material the age of the edifice is 100 12 ka a new model for the emplacement involves dike injection and endogenous inflation within an overlying ice mass that is estimated to have been 250 to 350 m thick the model assumes that the edifice expanded outwardly as an elliptical cylinder endogenously inflating and melting an equal volume of ice the thermal exchange between the expanding massif and the melting ice operates across a subvertical well drained enveloping carapace of quench breccia for effusion rates of 0 5 to 2 m3 s 1 marginal heat fluxes are 43 to 186 w m 2 implying low overall heat transfer coefficients 0 04 to 0 18 w m 2 k 1 the total volume of ice melted serves as a calorimeter and constrains the average thickness 3 m and properties thermal conductivity 0 1 0 4 w m 1 k 1 of the breccia carapace the heat transfer efficiency of intermediate lava dominated tuyas is significantly lower 2 than reported for other glaciovolcanic systems commonly 45 77 but similar to that found for block lava flows and lava tubes

permian triassic boundary in the central transantarctic mountains antarctica the permian triassic boundary occurs within a relatively complete terrestrial sequence in the shackleton glacier area of the central transantarctic mountains the boundary is within a 7 to 10 m thick interval between the permian glossopteris flora and the lower triassic lystrosaurus fauna this interval representing on the order of 200 k y records some of the events that occurred in the transition from the permian to triassic in the best documented section at graphite peak in the beardmore glacier region protohaploxypinus microcorpus zone palynomorphs which we assign to the latest permian record the declining glossopteris flora and occur near the top of the buckley coal measures just below a previously reported major negative 13c excursion in the shackleton glacier area the permian glossopteris flora including fossil wood roots and leaves occurs within the lower part of the fremouw formation the antarctic lystrosaurus assemblage of early triassic age has several species in common with the south african fauna that lived 20 to 35 closer to the equator the migration of vertebrates from southern africa into antarctica in the early triassic supports hypotheses of runaway greenhouse warming possibly related to co2 emissions from siberian flood basalts and large methane gas releases changes in flora bracketing the first of the major negative 13c anomalies near the boundary in antarctica and in east greenland support the hypothesis that a global event perhaps through mutations caused by enhanced ultraviolet radiation may have played a role in the destruction of floras

observations on lava snowpack and their interactions during the 2012 13 tolbachik eruption klyuchevskoy group kamchatka russia abstract observations made during january and april 2013 show that interactions between lava flows and snowpack during the 2012 13 tolbachik fissure eruption in kamchatka russia were controlled by different styles of emplacement and flow velocities a a lava flows and sheet lava flows generally moved on top of the snowpack with few immediate signs of interaction besides localized steaming however lavas melted through underlying snowpack 1 4 m thick within 12 to 24 h and melt water flowed episodically from the beneath flows pahoehoe lava lobes had lower velocities and locally moved beneath within the snowpack even there the snow melting was limited snowpack responses were physical including compressional buckling and doming and thermal including partial and complete melting maximum lava temperatures were up to 1355 k 1082 c type k thermal probes and maximum measured meltwater temperatures were 335 k 62 7 c theoretical estimates for rates of rapid e g radiative and slower conductive snowmelt are consistent with field observations showing that lava advance was fast enough for a a and sheet flows to move on top of the snowpack at least two styles of physical interactions between lava flows and snowpack observed at tolbachik have not been previously reported migration of lava flows beneath the snowpack and localized phreatomagmatic explosions caused by snowpack failure beneath lava the distinctive morphologies of sub snowpack lava flows have a high preservation potential and can be used to document snowpack emplacement during eruptions

effects of volcanic eruptions on the co2 content of the atmosphere and the oceans the 1996 eruption and flood within the vatnajokull glacier iceland abstract the october 1996 eruption within the vatnajokull glacier iceland provides a unique opportunity to study the net effect of volcanic eruptions on atmospheric and oceanic co2 volatile elements dissolved in the meltwater that enclosed the eruption site were eventually discharged into the ocean in a dramatic flood 35 days after the beginning of the eruption enabling measurement of 50 dissolved element fluxes the minimum concentration of exsolved co2 in the 1 1012 kg of erupted magma was 516 mg kg s was 98 mg kg cl was 14 mg kg and f was 2 mg kg the ph of the meltwater at the eruption site ranged from about 3 to 8 volatile and dissolved element release to the meltwater in less than 35 days amounted to more than one million tonnes equal to 0 1 of the mass of erupted magma the total dissolved solid concentration in the floodwater was close to 500 mg kg ph ranged from 6 88 to 7 95 and suspended solid concentration ranged from 1 to 10 according to h o c and s isotopes most of the water was meteoric whereas the c and s were of magmatic origin both c and s went through isotopic fractionation due to precipitation at the eruption site creating short cuts in their global cycles the dissolved fluxes of c ca na si s and mg were greatest ranging from 1 4 1010 to 1 4 109 mol the dissolved c flux equaled 0 6 million tonnes of co2 the heavy metals ni mn cu pb and zn were relatively mobile during condensation and water rock interactions at the eruption site about half of the measured total carbon flood flux from the 1996 vatnajokull eruption will be added to the long term co2 budget of the oceans and the atmosphere the other half will eventually precipitate with the ca and mg released thus for eruptions on the ocean floor one can expect a net long term c release to the ocean of less than half that of the exsolved gas this is a considerably higher net c release than suggested for the oceanic crust by staudigel et al geochim cosmochim acta 53 1989 3091 in fact they suggested a net loss of c therefore magma degassed at the ocean floor contributes more c to the oceans and the atmosphere than magma degassed deep in the oceanic crust the results of this study show that subglacial eruptions affecting the surface layer of the ocean where either mn fe si or cu are rate determining for the growth of oceanic biomass have a potential for a transient net co2 removal from the ocean and the atmosphere for eruptions at high latitudes timing is crucial for the effect of oceanic biota eruptions occurring in the wintertime when light is rate determining for the growth of biota have much less potential for bringing about a transient net negative co2 flux from the ocean atmosphere reservoir

rhyolitic volcano ice interactions in iceland iceland contains an abundance and diversity of rhyolitic edifices produced during volcano ice interactions glaciovolcanism that is unmatched by any other volcanic province with an estimated 350 km3 erupted during the past 0 8 ma from at least fifteen volcanic systems this review summarises research undertaken during the past decade and provides a new summary of the distribution of rhyolitic glaciovolcanic rocks erupted during the past 0 8 ma descriptions of effusion dominated edifices focus on the two best studied edifices the c 0 6 km3 and 570 m high prestahnukur edifice and the smaller volume 0 1 km3 drape of blahnukur both show little or no evidence of magmatic fragmentation i e driven by volatile exsolution but both show abundant evidence of quench fragmentation and meltback of ice walls a particular feature of prestahnukur is its sheet like lava bodies which are interpreted as sills that intruded the ice edifice interface rhyolitic tuyas are products of sustained eruptions into thick ice and form distinctive steep sided edifices with flat or broad dome like tops they are 300 700 m high with volumes up to 2 km3 though 0 5 1 0 km3 is more typical initial vigorous phreatomagmatic eruptions within well drained ice vaults build steep sided piles of tephra confined by ice walls gradual upwards increases in inflated clasts point to the decreasing involvement of meltwater and the increasing ability of the magma to vesiculate as the eruption progresses and terminates non explosive degassing produces lava caps up to 300 m thick oraefajokull is a stratovolcano illustrating complex volcano ice interactions generated when rhyolitic lavas erupt onto steeper slopes and encounter ice of variable thickness and properties e g fracturing eruptive units record dramatic ice thickness fluctuations of up to 500 m in valley glaciers between eruptions which emphasises that useful palaeoenvironmental information can be gleaned from detailed studies of volcano ice interactions considerable value is added when palaeoenvironmental information is combined with ar ar dating for example ar ar dating of two rhyolitic tuyas at torfajokull reveal that they erupted prior to the last glacial maximum when temperatures were at least 4 c cooler than the present day ar ar dating of prestahnukur suggests it erupted during the last interglacial glacial transition into over 700 m of ice which corroborates studies arguing for rapid accumulation of land based ice during global cooling

constraints on the dynamics of subglacial basalt eruptions from geological and geochemical observations at kverkfjoll ne iceland the kverkfjoll area ne iceland is characterised by subglacial basalt pillow lavas erupted under thick ice during the last major glaciation in iceland the water contents of slightly vesiculated glassy rims of pillows in six localities range from 0 85 0 03 to 1 04 0 03 wt the water content measurements allow the ice thickness to be estimated at between 1 2 and 1 6 km with the range reflecting the uncertainty in the co2 and water contents of the melt the upper estimates agree with other observations and models that the ice thickness in the centre of iceland was 1 5 2 0 km at the time of the last glacial maximum many of the pillows in the kverkfjoll area are characterised by vesiculated cores 40 60 vesicles surrounded by a thick outer zone of moderately vesicular basalt 15 20 vesicles the core contains 1 mm diameter spherical vesicles distributed uniformly this observation suggests a sudden decompression and vesiculation of the still molten core followed by rapid cooling the cores are attributed to a jokulhlaup in which melt water created by the eruption is suddenly released reducing the environmental pressure mass balance and solubility relationships for water allow a pressure decrease to be calculated from the observed change of vesicularity of between 4 4 and 4 7 mpa depressurization equivalent to a drop in the water level in the range 440 470 m consideration of the thickness of solid crust around the molten cores at the time of the jokulhlaup indicates an interval of 1 3 days between pillow emplacement and the jokulhlaup upper limits for ice melting rates of order 10 3 m s are indicated this interpretation suggests that jokulhlaups can reactivate eruptions

chemical constitution of a permian triassic disaster species one of the most controversial biological proxies of environmental crisis at the close of the permian is the organic microfossil reduviasporonites the proliferation of this disaster species coincides with the mass extinction and numerous geochemical disturbances originally reduviasporonites was assigned to fungi opportunistically exploiting dying end permian forests but subsequent geochemical data have been used to suggest an algal origin we have used high sensitivity equipment partly designed to detect interstellar grains in meteorites to reexamine the geochemical signature of reduviasporonites organic chemistry carbon and nitrogen isotopes and carbon nitrogen ratios are consistent with a fungal origin the use of this microfossil as a marker of terrestrial ecosystem collapse should not be merely discounted unequivocally diagnostic data however may have been precluded by post burial replacement of its organic constituents

subglacial intermediate volcanism at kerlingarfjoll iceland magma water interactions beneath thick ice the products of andesite and dacite glaciovolcanism at kerlingarfjoll are unlike others previously described in the literature three sequences of lithofacies are described and interpreted here the andesitic deposits at campsite gully are divided into massive vitriclastic lapilli tuff with intrusions fluidal clast bearing vitriclastic lapilli tuff and stratified pumice rich vitriclastic lapilli tuff at tindur andesitic eruptions produced contorted pillow fragment breccia and the clast supported lithic breccia finally pillow lava with intrusions and crudely bedded vitriclastic lapilli tuff of dacitic composition are described at haraldur abundant vitriclasts the presence of pillow lavas hackly fracturing of lava bodies and lack of oxidation of clasts demonstrate that each of these lithofacies formed in the presence of abundant water this contrasts with all other descriptions of subglacially erupted intermediate magmas which are characterised by jointed and glassy lava flows and domes with a marked scarcity of fragmental material the kerlingarfjoll sequences therefore demonstrate that it is possible for intermediate magmas to generate and interact with significant volumes of water at the base of a glacier preliminary estimates of volatile contents in glassy clasts correspond to quenching pressures equivalent to 500 m water or 550 m ice this is consistent with eruption beneath an ice sheet that was thick enough to overwhelm the underlying topography and where meltwater drainage was controlled by the morphology of the glacier surface it is argued that the drainage of water due to steep topography and or thin and fractured ice as opposed to thermodynamic considerations is the most likely explanation for the absence of evidence for significant magma water interaction in previously described instances of intermediate glaciovolcanism the apparent low viscosity of the kerlingarfjoll magmas may relate to relatively high eruption temperatures and or the inhibition of degassing of the magma due to high ambient pressures and the consequent limitation of groundmass crystallisation

anomalous hopane distributions at the permian triassic boundary meishan china evidence for the end permian marine ecosystem collapse abstract molecular and carbon isotopic geochemistry of hopanes in marine sediments of the meishan section in changxing county zhejiang province of china were studied to reveal biotic and environmental changes across the permian triassic boundary ptb and the wuchiapingian changhsingian boundary wcb the hopane distribution at the ptb is characterized by high ratios of moretane hopane tm ts tm c 30 hopane c 31 c 32 hopane and hopane sterane this hopane distribution is anomalous for these marine sediments but it is typical of coal measure strata and soils two possible genetic mechanisms for such an anomaly are suggested 1 these hopanes were terrigenous and most probably originated from acidified soil and peat this mechanism implies that the marine primary production and aerobic bacteria production at the ptb were extremely low 2 this hopane distribution was possibly caused by freshening and acidification of the upper water column during the end permian to early triassic marine stagnation and stratification this hopane anomaly which coincides with the end permian mass extinction and carbon isotope excursion may signal the end permian mass extinctions and marine and terrigenous ecosystem collapse the 13 c enriched hopanes with the fingerprint of typical anoxic marine shales coupled with an n c 15 n c 17 dominated distribution of n alkanes strongly indicate that the organic matter around the wcb at meishan originated mainly from cyanobacteria the corresponding positive 13 c carbonate and higher total organic carbon and hydrocarbon index hi values strongly suggest that high marine primary production and marine anoxia caused by intermittent cyanobacterial blooms resulted in the local mass extinction at meishan

dome growth and destruction during the 1989 1990 eruption of redoubt volcano abstract much of the six month long 1989 1990 eruption of redoubt volcano consisted of a dome growth and destructive phase in which 14 short lived viscous silicic andesite domes were emplaced and 13 subsequently destroyed the life span of an individual dome ranged from 3 to 21 days and volumes are estimated at 1 10 6 to 30 10 6 m 3 magma supply rates to the vent area averaged about 5 10 5 m 3 day for most of the dome building phase and ranged from a high of 2 2 10 6 m 3 per day initially to a low of 1 8 10 5 m 3 per day at the waning stages of the eruption the total volume of all domes is estimated to be about 90 10 6 m 3 and may represent as much as 60 70 of the volume for the entire eruption the site of 1989 1990 dome emplacement like that in 1966 was on the margin of a north facing amphitheatre like summit crater the domes were confined on the east and west by steep cliffs of pre eruption cone building volcanic rocks and thus were constrained to grow vertically rapid upward growth in a precarious site caused each dome to spread preferentially to the north resulting in eventual gravitational collapse as long as the present conduit remains active at redoubt volcano any dome formed in a new eruption will be confined to a narrow steeply sloping gorge leading to rapid vertical growth and a tendency to collapse gravitationally repetitive cycles of dome formation and failure similar to those seen in 1989 1990 are probably the norm and must be considered in future hazard analyses of redoubt volcano

gravity changes and internal processes some results obtained from observations at three volcanoes temporal gravity changes provide information about mass and or density variations within and below the volcano edifice three active volcanoes have been under investigation each of them related to a plate boundary mayon luzon philippines merapi java indonesia and galeras colombia the observed gravity changes are smaller than previously expected but significant for the three volcanoes under investigation and within the observation period mainly the increase of gravity is observed ranging from 1 000 nm 2 to 1 600 nms 2 unexpectedly the gravity increase is confined to a rather small area with radii of 5 to 8 km around the summit at mayon and merapi the parallel gps measurements yield no significant elevation changes this is crucial for the interpretation as the internal pressure variations do not lead to significant deformation at the surface thus the classical mogi model for a shallow extending magma reservoir cannot apply to confine the possible models the attraction due to changes of groundwater level or soil moisture is estimated along the slope of merapi exemplarily by 2 d modelling mass redistribution or density changes were evaluated within the vent as well as deeper fluid processes to explain the gravity variations the results are compared to the model incorporating the additional effect of elastic deformation

carbon isotope excursions and microfacies changes in marine permian triassic boundary sections in hungary abstract several permian triassic boundary sections occur in various structural units within hungary these sections represent different facies zones of the western palaeotethys margin the gardony core in the ne part of the transdanubian range typically represents the inner ramp while the balvany section in the bukk mountains of northern hungary represents an outer ramp setting the two sections have different patterns for their 13 c values the balvany section shows a continuous change towards more negative 13 c values starting at the first biotic decline followed by a sharp quasi symmetric negative peak at the second decline the appearance of the 13 c peak has no relationship to the lithology and occurs within a shale with low overall carbonate content indicating that the peak is not related to diagenesis or other secondary influences instead the shift and the peak reflect primary processes related to changes in environmental conditions the continuous shift in 13 c values is most probably related to a decrease in bioproductivity whereas the sharp peak can be attributed to an addition of c strongly depleted in 13 c to the ocean atmosphere system the most plausible model is a massive release of methane hydrate the quasi symmetric pattern suggests a rapid warming cooling cycle or physical unroofing of sediments through slope failure and releasing methane hydrate the gardony 1 core shows a continuous negative 13 c shift starting below the p t boundary however the detailed analyses revealed a sharp 13 c peak in the boundary interval just below the major biotic decline although its magnitude doesn t reach that observed in the balvany section based on careful textural examination and high resolution stable isotope microanalyses we suggest that the suppression of the 13 c peak that is common in the oolitic boundary sections is due to combined effects of condensed sedimentation sediment reworking and erosion as well as perhaps diagenesis

two episodes of 13c depletion in organic carbon in the latest permian evidence from the terrestrial sequences in northern xinjiang china new analyses reveal two intervals of distinctly lower 13c values in the terrestrial organic matter of permian triassic sequences in northern xinjiang china the younger negative 13corg spike can be correlated to the conspicuous and sharp 13c drops both in carbonate carbon and organic carbon near the permian triassic event boundary pteb in the marine section at meishan the geochemical correlation criteria are accompanied by a magnetic susceptibility pulse and higher abundances of distinctive chain like organic fossil remains of reduviasporonites the older negative 13corg spike originates within a latest permian regression significant changes in organic geochemical proxies are recorded in the equivalent interval of the marine section at meishan these include relatively higher concentrations of total organic carbon isorenieratane c14 c30 aryl isoprenoids and lower ratios of pristane phytane that together indicate the onset of anoxic euxinic and restricted environments within the photic zone the massive and widespread oxidation of buried organic matter that induced these euxinic conditions in the ocean would also result in increased concentrations of 13c depleted atmospheric co2 the latest permian environmental stress marked by the older negative 13corg episode can be correlated with the distinct changeover of ostracod assemblages and the occurrences of morphological abnormalities of pollen grains these observations imply that biogeochemical disturbance was manifested on the land at the end of the permian and that terrestrial organisms responded to it before the main extinction of the marine fauna