steep sided domes on venus characteristics geologic setting and eruption conditions from magellan data a survey of more than 95 percent of the venus surface reveals 145 steep sided domes which can be subdivided into a variety of morphologic forms the most common being shaped like inverted bowls or flat topped domes results of a preliminary analysis of the distribution and geologic setting of the domes are presented the relation of the domes to analogous terrestrial features is examined and possible models for their mode of emplacement are outlined

volcanic conduit controls on effusive explosive transitions and the 2010 eruption of merapi volcano indonesia abstract individual volcanoes can produce both effusive and explosive eruptions a transition between these two eruption styles dramatically changes the hazards and can occur either between distinct eruption events or within one eruption episode the causes of these transitions are difficult to determine due to the number of system parameters that can influence whether or not magma fragments in a runaway process we apply a numerical model of magma ascent in a volcanic conduit to isolate and test the effects of key parameters related to magma rheology and system geometry we find that for a given volcanic system parameters that control magma viscosity such as initial water mass fraction initial crystal volume fraction and temperature have the greatest influence on whether or not magma fragments during ascent and erupts explosively we also define a critical condition for the full set of initial parameters under which a transition in eruption style from effusive to explosive or the reverse is more likely to occur under these conditions small heterogeneities in the water or crystal content of the magma or small perturbations to the conduit pressure gradient due to magma chamber overpressure or dome growth or collapse can disrupt the magmatic conditions and cause a transition in eruption style the 2010 vei 4 eruption of merapi volcano included both effusive and explosive phases and was larger by an order of magnitude than its eruptions during the previous century we constrain our model for the merapi system using published literature values and show that between the previous eruption in 2006 and the 2010 eruption the shallow magmatic system at merapi reached critical conditions due to the ascent from depth of a large hotter more volatile rich magma under these critical conditions and according to our model results small changes in the volatile content of the magma small dome collapses subtle changes in degassing rate or the addition of co2 to the magma through decarbonation of the bedrock are all feasible mechanisms for triggering rapid transitions between effusive and explosive activity during the 2010 eruption period

middle permian cephalopods from central peninsular malaysia implications for faunal migration through the southern tethys abstract a wordian middle permian cephalopod fauna consisting of four ammonoid species tauroceras aff scrobiculatum gemmellaro agathiceras sp bamyaniceras orientale n sp and pronoritidae gen and sp indet and two nautiloid species tainoceras sp and orthocerida fam indet were recovered from the bera south area southern pahang peninsular malaysia the outcrop represents the southernmost extent of the bera formation bamyaniceras and tainoceras are recorded in malaysia for the first time the presence of t aff scrobiculatum suggests a regional correlation with an ammonoid bearing bed of sungai cheroh western pahang and permits global correlations with strata of northeastern iraq northern oman and sicily italy a possible eastwards faunal migration through the southern tethys is suggested

digital topography of volcanoes from radar interferometry an example from mt vesuvius italy a new airborne radar technique can generate digital topographic data for volcanoes at a scale of 10 m spatial and 1 5 m vertical with a swath width of 6 4 km called topsar the intrument is an interferometric radar flown on the nasa dc 8 aircraft topsar data permit the quantification of volcano slopes volumes and heights and as such will be valuable for the analysis of lava flows domes and lahar channels this instrument will be flown over several volcanoes in the near future providing volcanologists with valuable data sets for the analysis of high resolution topography we briefly illustrate the potential use of topsar data through examples from mt somma and vesuvius italy

effects of eruption history and cooling rate on lava dome growth to better understand the factors controlling the shapes of lava domes laboratory simulations measurements from active and prehistoric flows and dimensional analysis were used to explore how effusion history and cooling rate affect the final geometry of a dome fifty experiments were conducted in which a fixed volume of polyethylene glycol wax was injected into a tank of cold sucrose solution either as one continuous event or as a series of shorter pulses separated by repose periods when the wax cooling rates exceeded a critical minimum value the dome aspect ratios height diameter increased steadily with erupted volume over the course of a single experiment and the rate at which height increased with volume depended linearly on the time averaged effusion rate thus the average effusion rate could be estimated from observations of how the dome shape changed with time our experimental results and dimensional analyses were compared with several groups of natural lava flows the recently emplaced mount st helens and soufriere domes which had been carefully monitored while active three sets of prehistoric rhyolite domes that varied in eruptive style and shape and two sets of holocene domes with similar shapes but different compositions geometric measurements suggest that dome morphology can be directly correlated with effusion rate for domes of similar composition from the same locality and that shape alone can be related to a dimensionless number comparing effusion rate and cooling rate extrapolation to the venusian pancake domes suggests that they formed from relatively viscous lavas extruded either episodically or at average effusion rates low enough to allow solidified surface crust to exert a dominating influence on the final morphology

rock fracture as a precursor to lava dome eruptions at mount st helens from june 1980 to october 1986 following its plinian eruption on 18 may 1980 mount st helens washington state usa entered a period of intermittent lava dome extrusion until 1986 renewed extrusion was frequently preceded by accelerating rates of seismicity with more precursory seismicity observed prior to eruptions later in the sequence here the failure forecasting method ffm is used to investigate changes in the observed rate of volcano tectonic vt seismicity the analysis indicates that 1 all vt crises resulted in an eruption within 3 weeks usually less than 10 days 2 the majority of eruptions had vt precursors and 3 patterns of precursory seismicity showed fluctuations about the ideal model trend thus although these seismic events could be used to warn of an impending eruption specific forecasts were subject to an uncertainty of weeks or more it is proposed that 1 increased seismicity prior to later eruptions is a result of a larger and more solidified dome acting as a greater impediment to magma ascent 2 the consistency of seismic swarms resulting in an eruption indicates that stresses high enough to initiate fracturing in the country rock and lava dome carapace were only achieved once the approach to an eruption had already begun and 3 discrepancies between models of accelerating rock fracture and the observed seismicity may arise due to a significant amount of the rocks deforming through ductile mechanisms rather than seismogenic fracture

generation of pyroclastic flows and surges by hot rock avalanches from the dome of mount st helens volcano usa several hot rock avalanches have occurred during the growth of the composite dome of mount st helens washington between 1980 and 1987 one of these occurred on 9 may 1986 and produced a fan shaped avalanche deposit of juvenile dacite debris together with a more extensive pyroclastic flow deposit laterally thinning deposits and abrasion and baking of wooden and plastic objects show that a hot ash cloud surge swept beyond the limits of the pyroclastic flow plumes that rose 2 3 km above the dome and vitric ash that fell downwind of the volcano were also effects of this event but no explosion occurred all the facies observed originated from a single avalanche erosion and melting of craterfloor snow by the hot debris caused debris flows in the crater and a small flood that carried juvenile and other clasts north of the crater a second broadly similar event occured in october 1986 larger events of this nature could present a significant volcanic hazard

exogenous and endogenous growth of the unzen lava dome examined by satellite infrared image analysis abstract phase 1 of the most recent eruption of unzen volcano japan occurred between 1991 and 1993 and involved the endogenous and exogenous addition of magma to a growing summit lava dome the temporal variation between endogenous and exogenous styles of dome growth has an important bearing on the hazard posed by dome collapse and explosive events however such data are difficult to acquire and have previously only been obtained in a fully quantitative manner for the mount st helens dome in that case using detailed photogrammetry here we investigate these competing dome growth processes at unzen via analysis of their thermal emission signals present in shortwave infrared swir satellite imagery we find that both the endogenous and exogenous growth styles exhibit identifiable swir signatures whose magnitude can be related to their respective magma supply rates we find that the swir radiant area corresponding to endogenous growth is around four times larger than that corresponding to exogenous growth at the same magma discharge rate analysis of time series imagery indicates that like mount st helens unzen experienced a temporally decreasing magma discharge rate during phase 1 as time progressed and the discharge rate fell the growth style of the unzen dome changed from exogenous only through exogenous decreasing and endogenous increasing to endogenous only thus relative growth rates at the endogenous and exogenous areas of the unzen dome appear to be at least partly controlled by the overall magma discharge rate as with mount st helens the cause of this relationship was most likely the formation and strengthening of a brittle crust at the surface vent which impeded exogenous growth more effectively as time elapsed and the discharge rate fell these results suggest the similarity of the processes operating at the unzen and mount st helens domes though important differences remain in that dome growth was basically continuous at unzen whilst at mount st helens growth episodes were interspersed by significant periods of repose

petrology of the 1991 1995 eruption at unzen effusion pulsation and groundmass crystallization abstract effusive eruption of dacite magma 2 1 108 m3 during 1991 1995 formed a lava dome at the summit of unzen volcano japan the effusion rate was highest at the beginning 4 0 105 m3 day 4 6 m3 s and decreased roughly with time to almost zero before this pattern was repeated with a second pulse of magma supply the whole rock chemistry of lavas shows significant variation attributable to variations in phenocryst abundance the more mafic the more abundant the phenocrysts the pattern of chemical variation with time shows some difference from that of the effusion rate all phenocrysts in dacite plagioclase hornblende biotite quartz and magnetite show evidence of disequilibrium with melt although a glomerophyric aggregation of phenocrysts suggests coexistence with each other phenocrysts are isotopically heterogeneous from species to species the calculated initial melt composition was rhyodacite and was nearly constant throughout the activity in contrast the bulk phenocryst population is andesite a model explaining the textures and the isotopic heterogeneity is the capture of diorite fragments or xenocrysts by parental rhyodacite magma it is suggested that when effusion rate was high less viscous crystal poor magma exited from the reservoir groundmass glass and plagioclase microlite rims show temporal chemical variations correlating with the effusion rate the higher the effusion rate the more evolved the compositions groundmass crystallinity increased with decreasing effusion rate from 33 to 50 textures in dome lavas suggest that groundmass crystallization had been mostly completed when magma reached the conduit top the fe ti oxide temperature 880 780 c was low when the crystallinity was high micropumice erupted before dome growth provided a sample recording magmatic foam in the conduit porosity of dome lavas was lower at lower effusion rates collapse of foam magma and simultaneous escape of volatiles through the conduit top were probably responsible for the accompanying low frequency earthquakes phenocrysts were broken and the breakdown rims on hornblende phenocrysts were torn off during collapse and successive compaction when effusion waned degassing and the resultant crystallization proceeded more completely so that the magma became too viscous to flow in the conduit top and behaved as a plug resulting in a temporary halt of effusion in turn groundmass crystallization in magma below the plug increased excess pressure in the upper parts of conduit due to slow cooling the plug was scavenged when rising excess pressure overcame its effective strength then the second pulse of magma supply began strong endogenous growth and extrusion of a lava spine in the later stage probably occurred for the same reason

identification of structural controls in an active lava dome with high resolution dems volcan de colima mexico monitoring the topography of active lava domes is critical for detecting changes that may trigger or influence collapse or explosive activity internal dome structure and conditions are more difficult to elucidate but also play vital roles here we describe the exposure following an explosion of significant scarps in the active dome at volcan de colima mexico that are interpreted as evidence of brittle failure planes and a complex internal dome morphology in the first use of automated 3d computer vision reconstruction techniques structure from motion and multi view stereo sfm mvs on an active volcanic dome we derive high resolution surface models from oblique and archive photographs taken with a consumer camera the resulting 3d models were geo referenced using features identified in a web sourced orthoimage no ground based measurements were required in december 2010 the dome 2 14 106 m3 had a flat upper surface reflecting an overall ductile emplacement regime between then and may 2011 a period of low explosivity was accompanied by a small volume loss 0 4 105 m3 and arcuate steps appeared in the dome surface suggesting the presence of localized planes of weakness the complex array of summit scarps was exposed following a significant explosion in june 2011 and is interpreted to be the surface expression of fault planes in the dome the 1 m resolution dems indicated that the region of greatest volume loss was not coincident with the assumed location of the conduit and that heterogeneity within the dome may have been important during the june explosion

rhyolite magma degassing an experimental study of melt vesiculation the vesiculation of a peralkaline rhyolite melt initially containing 0 14 wt h2o has been investigated at temperatures above the rheological glass transition tg 530 c by a in situ optical observation of individual bubble growth or dissolution and b dilatometric measurements of the volume expansion due to vesiculation the activation energy of the timescale for bubble growth equals the activation energy of viscous flow at relatively low temperatures 650 790 c but decreases and tends towards the value for water diffusion at high temperatures 790 925 c the time dependence of volume expansion follows the avrami equation

using a discrete element approach to model lava dome emplacement and collapse abstract lava dome collapses can lead to explosive activity and pyroclastic flow generation which makes them one of the most deadly consequences of volcanic activity the mechanisms linked to a collapse are however still poorly understood and very few numerical models exist that investigate the actual collapse of a lava dome after emplacement we use a discrete element method implemented in the modelling software particle flow code to investigate lava dome growth but also go further to test the stability of the dome under the following conditions increased internal pressure switch in extrusion direction caused by partial cooling of the dome and extrusion of lava onto variable underlying topography we initially show the morphology development of a growing lava dome and how the rheological boundary between core and talus evolves throughout the lifetime of a dome and with varied solidus pressures through visualisation of strain accumulation within the lava dome we show superficial rockfall development due to interaction with topography whereas large deep seated failures occur when the dome is exposed to internal overpressures we find that a switch in extrusion direction promotes a transition from endogenous to exogenous dome growth and leads to lava lobe formation we demonstrate that lava dome collapse exhibits many features similar to common landslides and by investigating strain patterns within the dome we can use numerical modelling to understand features that elude field observations

infrared image analysis of volcanic thermal features lascar volcano chile 1984 1992 fifteen landsat thematic mapper tm images of lascar volcano chile recorded between december 1984 and april 1992 document the evolution of a lava dome within the summit crater four of the scenes were acquired at night in every image the two short wavelength infrared bands 5 and 7 have detected thermal radiation from the volcano as a consequence of the planck distribution function the relative response of these two channels depends on the proportions of very hot 600 c surfaces occupying tiny pixel areas and broader regions at moderate temperatures 280 c intercomparison of bands 5 and 7 thereby provides a means for interpreting tm thermal anomalies even in the absence of ground observations pronounced changes in the configuration and intensity of the lascar anomaly suggest that the volcano has experienced at least two cycles of lava dome activity since 1984 the first of these progressed through a cooling period possibly reflecting a reduced flux of magmatic volatiles at the surface and culminated in an explosive eruption on september 16 1986 which appears to have completely destroyed the inferred lava dome the tm data indicate that a new dome had been emplaced by november 1987 more than 15 months before it was first discovered by local observers lascar s style of cyclical effusive and explosive activity is typical of many volcanoes and the remote sensing techniques presented herein could be applied elsewhere

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

groundmass crystallization of mount st helens dacite 1980 1986 a tool for interpreting shallow magmatic processes the 1980 1986 eruption of mount st helens volcano provides an unprecedented opportunity to observe the evolution of a silicic magma system over a short time scale groundmass plagioclase size measurements are coupled with measured changes in matrix glass plagioclase and fe ti oxide chemistry to document increasing groundmass crystallinity and thus to better constrain proposed physical models of the post may 18 1980 magmatic reservoir measurements of plagioclase microlite and microphenocryst sizes demonstrate that relatively rapid growth approximately 10 9 cm s of groundmass plagioclase occurred immediately subsequent to may 18 relatively rapid plagioclase growth continued through the end of 1980 at an average rate of 3x10 11 cm s plagioclase growth rates then decreased to 1x10 11 cm s through 1986 changes in groundmass crystallinity are reflected in changes in both matrix glass and plagioclase microphenocryst rim chemistry although the matrix glass composition appears to have remained approximately constant from 1981 1986 after a rapid compositional change from may 18 until the end of 1980 plagioclase microphenocrysts show increasingly more complex zoning patterns with time microphenocryst core compositions are commonly positively correlated with crystal size both of these observations indicate continuous groundmass plagioclase growth through 1986 magmatic temperatures estimated from fe ti oxide pairs are approximately constant through 1981 at eruption temperatures of 930 c and at log fo2 of 10 8 by 1985 1986 oxide temperatures decreased to 870 c chemical and textural changes can be explained by 1 rapid degassing and crystallization in response to the intrusion of magma into a shallow 4 5 km reservoir toward the end of the may 18 1980 eruption 2 continued crystallization at a much reduced rate through 1986 due to slow cooling of the shallow magma reservoir growth rates and consequent chemical changes appear to decrease at the end of 1980 this is coincident with the change in eruption style from explosive eruptions sometimes followed by dome growth to solely extrusive dome building events and can be explained by the expected viscosity increase of both degassing and increasing crystallinity the model of twostage crystallization of magma in a shallow reservoir is consistent with conclusions from gas studies casadevall et al 1983 gerlach and casadevall 1986 a b patterns of crater deformation chadwkck et al 1988 and post 1980 seismicity endo et al 1990 although it does not explain the experimental data of hill and rutherford 1989 on the growth rate of amphibole reaction rims textural measurements on mount st helens dacite can also be used to evaluate crystallization kinetics in silicic magmas systems for which experimental data is almost non existent plagioclase growth rates are 5 10 times slower than estimated plagioclase growth rates in basaltic systems a result consistent with the higher viscosity of a more silicic melt furthermore patterns of textural change both average crystal size and number density are similar to those observed during the 1984 mauna loa eruption by lipman and banks 1987 suggesting that the only modification to the crystallization behavior of plagioclase required in extrapolation from basaltic systems is a moderate decrease in rates such that the rate of crystallization scales with the melt viscosity

the emplacement of the active lava flow at sinabung volcano sumatra indonesia documented by structure from motion photogrammetry abstract an effusive eruption at sinabung volcano in indonesia began in december 2013 we use structure from motion sfm photogrammetric techniques to create digital elevation models dems of the active lava flow we build dems from photographs taken during two separate time periods and from two separate low cost handheld cameras and compare them with a pre eruption dem to assess the quality and accuracy of photogrammetric dems created using different cameras calculate flow volume and long term average effusion rate and document changes in flow morphology on september 22nd 2014 the lava flow was 2 9 km long and had a volume of 1 03 0 14 108 m3 leading to an estimated time averaged discharge rate of 4 8 0 6 m3 s 1 differencing the photogrammetric dems shows that during the two week field campaign topographic changes of the flow occurred in zones along the flow front and on the upper flank a finding supported by relatively high temperatures in corresponding thermal images the deformation can be explained by active advance at the flow front and development of instabilities and collapse on the upper flanks large pyroclastic density currents associated with gravitational collapse of upper flank instabilities in october 2014 and june 2015 were caused by lava growing over ridges that had initially confined the flow to a pre existing channel this work demonstrates the ability of sfm photogrammetry to measure or identify the lava flow volume time averaged discharge rate flow emplacement rate and style as well as the development of gravitational instabilities our results show the potential of sfm photogrammetry as a cost and time effective method of repeatedly measuring active volcanic features and monitoring hazards at sinabung and during similar eruptions

characteristics and consequences of lava dome collapse at ruawahia taupo volcanic zone new zealand the eruption of large rhyolitic lava domes may be accompanied by the formation of large block and ash flows this may be linked to the style of dome extrusion whether it forms a series of individual lobes flows or spines exogenous or grows by internal inflation endogenous lava domes can transition from one extrusive style to another as a result of a change in extrusion rate or the formation of facilitating structures such as shear zones how this change can affect large rhyolitic lava domes is unclear as there are few historically recorded rhyolitic dome eruptions here we present structures at ruawahia lava dome a well exposed 700 year old lava dome how these facilitating structures enable exogenous extrusion at ruawahia dome and link this to collapse episodes along the fringes of the dome during growth ruawahia dome is part of the tarawera dome complex a chain of domes running parallel to regional structures across the okataina caldera complex in the taupo volcanic zone new zealand ruawahia dome consists of 1 a high porosity 44 52 crystalline 65 dre locally brecciated carapace facies with rare bread crusting and ropey flow textures 2 a core facies of dominantly low to moderate porosity 20 25 with elongate vesicles that mark weak flow bands and 3 thin 5 m thick interior breccia zones flow bands at ruawahia are complex and do not fit with hypothesised flow band orientations attributed to a single phase of exogenous or endogenous dome growth inward dipping flow bands on ramp structures on the flow surface suggest a flow like coulee morphology however steeply dipping and multidirectional flow bands on the edges of the dome challenge this hypothesis widespread block and ash flow deposits have been sourced from the leading dome fronts to the nw and se these collapse events left behind inflated and bread crusted outcrops on these dome fronts suggesting syn eruption collapse events that led to expansion of a hot pressurised dome interior we consider ruawahia erupted from multiple aligned vents either as lobes confined within the crater of a pyroclastic cone formed during the initial plinian phase of the eruption or those able to flow down the cone flank the confined lobes formed steep internal breccia zones as individual dome lobes extruded past one another lobes that were able to overcome the pyroclastic cone rim or where the vent was outside the crater were able to flow down the flanks as bulldozing thickening flows with dominantly ductile interiors and brittle exteriors these flows collapsed as the front thickened possibly due to a decrease in gradient producing widespread block and ash flows the removal of lava associated with collapse generated a decompression event which resulted in fragmentation cracking and vesiculation in the hot interior of the lava flows these events left behind a re vesiculated and bread crusted lava flow front and produced block and ash flows with abundant breadcrust bombs that reached the base of tarawera

insights into lava dome and spine extrusion using analogue sandbox experiments abstract lava dome formation is a common process at stratovolcanoes involving the shallow intrusion or extrusion of viscous lava and may lead to the rise of spines spines are protrusions observed to extrude episodically during lava dome growth yet the structural and mechanical factors controlling their formation are only partially understood here we provide new detailed insight into lava dome growth and the production of spines using a novel set of analogue experiments extruding sand plaster mixtures from a fixed diameter conduit under isothermal conditions we trace displacement and strain with photogrammetric methods for precise and detailed monitoring of the extrusion process results show initial dome growth forming a steep sided and flat topped shape through extrusion of new material leading to slumping of oversteepening slopes forming a talus spines are found to protrude at a later stage through the dome surface along discrete circular faults that originate from the conduit walls starting a cycle of spine growth and collapse as our spines only appear after prolonged extrusion we relate their appearance to the compaction and strengthening of material within the conduit we find that spine diameter height and volume are positively correlated with increasing cohesion and therefore material strength the spine diameter was also observed to be smaller or equal to the diameter of the underlying conduit as shear extrusion occurs along vertical to outward dipping fault planes for natural domes our findings imply that spine growth may be the consequence of compaction and densification via porosity loss shearing and or outgassing of conduit magma during ascent more efficient compaction will yield wider and taller spines as a result of increasing rock strength our study further highlights the relevance of analogue experiments in the study of lava domes and spines which remain one of the most hazardous and unpredictable features at dome forming volcanoes worldwide

middle permian brachiopods from the tumenling formation in the wuchang area southern heilongjiang ne china and their palaeobiogeographical implications abstract this paper describes nine brachiopod species in eight genera from the tumenling formation in the wuchang area southern heilongjiang northeast china the tumenling fauna is constrained to a wordian capitanian guadalupian middle permian age based on the correlation of the faunas and previously published data from the same horizons in the same area this middle permian brachiopod fauna is characterized by an admixture of elements of boreal affinity kochiproductus sp yakovlevia sp stenoscisma margaritovi gypospirifer volatilis spiriferella keilhavii spiriferella lita and alispiriferella neimongolensis with palaeoequatorial forms spinomarginifera sp vediproductus sp and leptodus nobilis the wuchang fauna as a whole is comparable to several contemporaneous faunas described from inner mongolia in northern china jilin in northeast china south primorye in eastern russia and the hida gaien belt of japan in terms of its index elements and its boreal palaeoequatorial mixture during the middle permian these areas or blocks were referred to the inner mongolia japan transition zone or the northern transition zone between the palaeoequatorial and boreal realms the overwhelming majority of the boreal elements reveal that the wuchang area was probably situated in the northern subzone of this transitional zone which belongs to the southern margin of the bureya block these east and northeast asian blocks acted as migratory stepping stones bridging faunal migration between the palaeoequatorial and boreal realms during the middle permian

growth process of the lava dome flow complex at sinabung volcano during 2013 2016 abstract mount sinabung north sumatra indonesia erupted for the first time in 2010 and reactivated again in 2013 the eruption started with a phreatic phase changed to phreatomagmatic and then andesite lava appeared at the summit crater in late december 2013 lava effusion continued and has been associated with partial to complete collapses of the lava complex which successively generated pyroclastic density currents pdcs the lava complex grew first as a lava dome and then developed into a lava flow lava extension stage it extended up to about 3 km in horizontal runout distance by late 2014 when the front of the lava complex moved onto the middle and lower slope of the volcano pdc events were initially replaced by simple rock falls inflation of the upper part of the lava complex began in mid 2014 when the movement of the lava flow front stagnated the inflation was associated with hybrid seismic events and frequent partial collapses of the upper part of the lava complex generating pdc events with long travel distances from mid september 2014 new lobes repeatedly appeared near the summit and collapsed cyclic vulcanian events began in august 2015 when hybrid events peaked and continued 1 5 years vulcanian stage these events sometimes triggered pdcs whose deposits contained vesiculated lava fragments the distribution of pdc deposits which extended over time mostly overlapped in areal extent with that of the 9th 10th century eruption eruption volumes were estimated based on measurements with a laser distance meter during 6 periods digital surface model dsm analysis of satellite images during one period and the cumulative number of seismically detected pdc events assuming a constant volume of each pdc event the total volume of eruption products reached about 0 16 km 3 dre as of the end of 2015 the lava discharge rate was largest during the initial stage 7 m 3 s and decreased exponentially over time the discharge rate during the vulcanian stage was 1 m 3 s the trend of decreasing discharge rate is in harmony with that of ground deflation recorded by a gps measurement the chemical composition of lava slightly evolved with time cyclic vulcanian events may have been triggered by limited degassing conditions in the upper conduit and by unloading of the conduit by lava dome collapses

monitoring lava dome growth during the 2004 2008 mount st helens washington eruption using oblique terrestrial photography abstract we present an analysis of lava dome growth during the 2004 2008 eruption of mount st helens using oblique terrestrial images from a network of remotely placed cameras this underutilized monitoring tool augmented more traditional monitoring techniques and was used to provide a robust assessment of the nature pace and state of the eruption and to quantify the kinematics of dome growth eruption monitoring using terrestrial photography began with a single camera deployed at the mouth of the volcano s crater during the first year of activity analysis of those images indicates that the average lineal extrusion rate decayed approximately logarithmically from about 8 m d to about 2 m d 2 m d from november 2004 through december 2005 and suggests that the extrusion rate fluctuated on time scales of days to weeks from may 2006 through september 2007 imagery from multiple cameras deployed around the volcano allowed determination of 3 dimensional motion across the dome complex analysis of the multi camera imagery shows spatially differential but remarkably steady to gradually slowing motion from about 1 2 m d from may through october 2006 to about 0 2 1 0 m d from may through september 2007 in contrast to the fluctuations in lineal extrusion rate documented during the first year of eruption dome motion from may 2006 through september 2007 was monotonic 0 10 m d to gradually slowing on time scales of weeks to months the ability to measure spatial and temporal rates of motion of the effusing lava dome from oblique terrestrial photographs provided a significant and sometimes the sole means of identifying and quantifying dome growth during the eruption and it demonstrates the utility of using frequent long term terrestrial photography to monitor and study volcanic eruptions

discrimination of lava dome activity styles using satellite derived thermal structures abstract thermal imaging from satellites is one methodology used for the monitoring and scientific investigation of volcanoes including those characterised by active lava domes to be most effective the remote sensing techniques employed must allow the cause of any observed thermal anomaly to be identified ideally using information contained within the remote sensing data itself whilst using any ancillary field data to guide analysis and the necessary assumptions this study investigates a method by which such discrimination maybe accomplished for activity at lava domes for this purpose we use three landsat thematic mapper tm scenes of unzen volcano japan to determine the temperature structure of the active lava dome existing during 1991 1993 these data are of particularly high quality since the tm scenes were obtained during night time overpasses and a large amount of supplementary data are available to parameterise the model used to retrieve the subpixel temperature structure of the dome surface the results are matched to near contemporaneous geological sketch maps of the then current situation in order to identify the tm pixel groupings corresponding to the different styles of dome activity namely fumarolic degassing exogenous and endogenous dome growth and collapse deposits resulting from block and ash flows small scale pyroclastic flows and rockfalls the spatial and statistical characteristics of the resultant tm derived temperature distributions are then investigated to determine rule based criteria that may be used to differentiate the activity styles of lava domes based on their thermal structure within the remote sensing data results indicate that fumarolically active locations regions of active dome growth and areas of collapse deposition on the unzen dome can be differentiated using only the statistical distribution of the hotspot temperatures and fractional areas identified via analysis of tm imagery the statistics derived for hotspots at the fumarolically active areas show them to be in general significantly hotter and smaller than those found at the areas of active dome growth whereas hotspots retrieved on the areas of collapse deposition are cooler and larger we find that the frequency distributions of hotspot temperatures extracted for the areas of endogenous and exogenous dome growth exhibit statistically inseparable means but that discrimination between these two dome growth styles is possible using analysis of the spatial arrangement of the retrieved hotspots specifically the exogenous lobes are characterised by structures interpreted to be the effusing vent of new magma and the collapsing lobe front these features are absent at locations showing only endogenous growth it is hoped that the criteria developed here will prove useful during future quantitative analysis of the extended tm time series available for unzen and for identification of thermal anomalies of uncertain origin at other active domes observed via satellite remote sensing

crystallization of mount st helens 1980 1986 dacite a quantitative textural approach quantitative measurements of crystal size distributions csds have been used to obtain kinetic information on crystallization of industrial compounds randolph and larson 1971 and more recently on hawaiian basalts cashman and marsh 1988 the technique is based on a population balance resulting in a differential equation relating the population densityn of crystals to crystal sizel i e at steady staten no exp l itg whereno is nucleation density g is the average crystal growth rate is the average growth time and the nucleation ratej nog csd inn vsl plots of plagioclase phenocrysts in 12 samples of mount st helens blast dacite and 14 samples of dacite from the 1980 1986 mount st helens dome are similar and averageg 9 6 1 1 10 3 cm andno 1 2 106 cm 4 reproducibility of the measurements was tested by measuring csds of 12 sections cut from a single sample in three mutually perpendicular directions precision of the size distributions is good in terms of relative but not necessarily absolute values 10 growth and nucleation rates for plagioclase have been calculated from these measurements using time brackets of 30 150 years growth ratesg are 3 10 10 12cm s and nucleation ratesj are 5 21 10 6 cm3 s g andj for fe ti oxides calculated from csd data areg 2 13 10 13 cm sec andj 7 33 10 5 cm3 s respectively the higher nucleation rate and lower growth rate of oxides resulted in a smaller average crystal size than for plagioclase sizes of plagioclase microlites 0 01 mm in the blast dacite groundmass have been measured from backscatter sem photographs nucleation of these microlites was probably triggered by intrusion of material into the cone of mount st helens in spring 1980 this residence time of 52 days gives minimum crystallization estimates ofg 1 3 10 11 cm s andj 9 16 1o3 cm3 s the skeletal form of the microlites provides evidence for nucleation and growth at high values of undercooling t relative to the phenocrysts a comparison of nucleation and growth rates for the two crystal populations phenocrysts vs microlites suggests that while growth rate seems to be only slightly affected by changes in t nucleation rate is a very strong function of undercooling a comparison of plagioclase nucleation and growth rates measured in the mount st helens dacite and in basalt from makaopuhi lava lake in hawaii suggests that plagioclase nucleation rates are not as dependent on composition groundmass textures suggest that plagioclase microphenocrysts crystallized at depth rather than in the conduit in the dome or after extrusion onto the surface most of this crystallization appears to be in the form of crystal growth coarsening of groundmass microphenocrysts at small degrees of undercooling rather than extensive nucleation of new crystals this continuous crystallization in a shallow magmatic reservoir may provide the overpressurization needed to drive the continuing periodic domebuilding extrusions which have been the pattern of activity at mount st helens since december 1980

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

influence of extrusion rate and magma rheology on the growth of lava domes insights from particle dynamics modeling abstract lava domes are structures that grow by the extrusion of viscous silicic or intermediate composition magma from a central volcanic conduit repeated cycles of growth are punctuated by collapse as the structure becomes oversized for the strength of the composite magma that rheologically stiffens and strengthens at its surface here we explore lava dome growth and failure mechanics using a two dimensional particle dynamics model the model follows the evolution of fractured lava with solidification driven by degassing induced crystallization of magma the particle dynamics model emulates the natural development of dome growth and rearrangement of the lava dome which is difficult in mesh based analyses due to mesh entanglement effects the deformable talus evolves naturally as a frictional carapace that caps a ductile magma core extrusion rate and magma rheology together with crystallization temperature and volatile content govern the distribution of strength in the composite structure this new model is calibrated against existing observational models of lava dome growth results show that the shape and extent of the ductile core and the overall structure of the lava dome are strongly controlled by the infusion rate the effects of extrusion rate on magma rheology are sensitive to material stiffness which in turn is a function of volatile content and crystallinity material stiffness and material strength are key model parameters which govern magma rheology and subsequently the morphological character of the lava dome and in turn stability degassing induced crystallization causes material stiffening and enhances material strength reflected in non newtonian magma behavior the increase in stiffness and strength of the injected magma causes a transition in the style of dome growth from endogenous expansion of a ductile core to stiffer and stronger intruding material capable of punching through the overlying material and resulting in the development of a spine or possibly inducing dome collapse simulation results mimic development of a megaspine upon the influx of fresh magma which leads to the re direction of magma flow creating a new shear zone and the switching of dome growth from one side to the other our model shows similar dome growth dynamics as observed at soufriere hills volcano montserrat indicating a strong correlation between extrusion rate and its subsequent effect on mechanical properties and variations in magma rheology

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

distribution and characteristics of mixed transitional mid permian late artinskian ufimian marine faunas in asia and their palaeogeographical implications abstract the permian marine biogeography of the asian region is characterised by the development of three broad realms boreal tethyan and gondwanan in the early early permian asselian to early artinskian there seems to have existed sharp biogeographical boundaries with no transitional zones between the realms presumably due to the effect of gondwanan glaciation and sharp climatic zonation the mid permian late artinskian to ufimian of the asian region is distinguished by the rise of two broad transitional zones in which mixed marine faunas flourished the northern transitional zone north and northeast china sikhote alin central and northeast japan is characterised by an admixture of both warm water cathaysian and cold temperate boreal genera the southern transitional zone arabian peninsula iran afghanistan the karakorum southeast and central pamir salt range central and northwest tibet shan thai terrane timor and western irian jaya on the other hand is distinguished by incorporating faunal elements of both gondwanan and cathaysian origin the mixed faunas of both transitional zones share several antitropically distributed genera e g monodiexodina lytvolasma and spiriferella and are succeeded by palaeotropical tethyan faunas of late permian age it has been postulated that the mixed mid permian fauna of the northern transitional zone was probably formed in an epicontinental sea which was connected to both the asian tethys and the arctic which facilitated the migration of cathaysian and boreal forms into the epicontinental sea and subsequent faunal mixing the formation of the mixed faunas of the southern transitional zone on the other hand is probably related to the breaking off of the cimmerian blocks from northern gondwana and subsequent drifting into a lower latitudinal zone with geographical proximity to both gondwana and cathaysia during the mid permian

fracturing of volcanic systems experimental insights into pre eruptive conditions conditions for fracturing are a primary control on the behaviour of volcanic systems especially during the approach to eruption we here present the results of deformation experiments under simulated volcanic conditions on a porhyritic andesite from ancestral mount shasta andesite was chosen as a representative material because it is common at subduction zone volcanoes among both erupted products and country rock we deformed the lava in tension and triaxial compression tests at strain rates of 10 5 s 1 confining pressures from 0 to 50 mpa and temperatures up to 900 degrees c we also concurrently recorded acoustic emissions ae in order to monitor cracking activity the results show that deformation behaviour changes significantly in the temperature range 600 750 degrees c thus as temperatures increased across this interval the tensile fracture toughness increased from 2 5 0 5 mpa m 1 2 to 3 5 1 mpa m 1 2 the compressive strength decreased from 110 30 mpa to 55 35 mpa at 900 degrees c and the corresponding young s modulus decreased from 20 4 gpa to 6 4 gpa the changes occur when the deformation of the sample changes from elastic brittle to brittle ductile behaviour which we attribute to the blunting of crack tips due to melting of the glass phase and enhanced crystal plasticity at high temperature ae activity was observed in all experiments indicating that earthquakes can be generated not only in country rock but also in hot magma such as may be found in lava domes and at the margins of magma conduits in addition the trends in accelerating ae event rates before sample failure were comparable to those seen in earthquakes before some volcanic eruptions and a minimum in the seismic b value coincided with sample failure applied to volcanic systems the results suggest that 1 andesite strength and elasticity will not be affected by temperature or pressure beyond similar to 10 100 m from active magma 2 before eruptions fractures propagate preferentially through weaker horizons in a mechanically heterogeneous volcano and 3 volcanic rocks have characteristic seismic b values that are perturbed during the approach to bulk failure each of these conditions provides quantitative constraints on models for seismic precursors to eruption or intrusion c 2009 elsevier b v all rights reserved

clastic and core lava components of a silicic lava dome the formation of a lava dome involves fractionation of the lava into core and clastic components we show that for three separate successive andesitic lava domes that grew at soufriere hills volcano montserrat between 1999 and 2007 the volumetric proportion of the lava converted to talus or pyroclastic flow deposits was 50 90 of the lava extruded currently only 8 of the total magma extruded during the 1995 2007 eruption remains as core lava the equivalent representation in the geological record will probably be even lower most of the lava extruded at the surface flowed no further than 150 300 m from the vent before disaggregation resulting in a lava core whose shape tends to a cylinder moderate to high extrusion rates at the soufriere hills domes may have contributed to the large clastic fraction observed creating talus dissipates much of the energy that would otherwise be stored in the core lava of domes the extreme hazards from large pyroclastic flows and blasts posed by wholesale collapse of a lava dome depend largely on the size of the lava core and hence on the aggregate history of the partitioning process not on the size of the dome

ballooning emplacement and alteration of the chah musa subvolcanic intrusion ne iran inferred from magnetic susceptibility and fabric the porphyritic diorite chah musa subvolcanic intrusion is located in the toroud chah shirin magmatic arc in the northern central iranian structural zone the elliptical chah musa body hosts a copper deposit and intrudes an eocene sequence of volcanic breccia agglomerate and red tuffaceous sediment high magnetic susceptibility values are attributed to the presence of magnetite as a magnetic carrier changes in bulk magnetic susceptibility correlate with zonation of alteration in the intrusion although the degree of anisotropy of magnetic susceptibility decreases due to hydrothermal alteration the field observations confirm that this parameter can be used as a strain marker strongly oblate magnetic ellipsoids are found in the eastern half of the intrusion where isolated outcrops of flat lying tuffaceous host cover dioritic rocks roof zone stations with prolate ellipsoids mostly belong to the centre of the intrusion where the magnetic lineations plunge steeply they are interpreted as indicating the main feeder zone the concentric fabric pattern at the periphery of intrusion the oblate magnetic ellipsoids at the roof the highest anisotropy degree along the small diameter of the intrusion and an intense deformation of the host rocks especially at the western margin all are evidence that the intrusion was ballooning during the late stages of its emplacement ascent and emplacement of the chah musa body is ascribed to the tensional space provided by a dextral shear zone created by the regional left lateral movement on the bounding anjilow and toroud strike slip faults

grand sarcoui volcano chaine des puys massif central france a case study for monogenetic trachytic lava domes abstract the grand sarcoui is a prominent trachytic volcano of the intraplate quaternary volcanic field of chaine des puys massif central france which fulfills basic requirements for being qualified as monogenetic grand sarcoui looks like a simple axisymmetric lava dome but close observation reveals a complex and dissymmetric structure and composition the construction of the dome about 12 5 ka ago combined both endogenous and exogenous growth which resulted in variable modes of emplacement and textures of the lava one of its most interesting features is a large 0 29 106 m2 fan of deposits bearing hummocks and secondary hydro eruption craters cross sections of these deposits demonstrate that they originated from a sector collapse accompanied by a blast like event the dome is covered by a thin layer of lapilli and ash attributed to a delayed summit eruption which occurred about 10 6 ka ago surprisingly late after its construction so this volcano has at a reduced scale features that are more usually observed in large composite volcanoes however some of these features differ slightly from those that have been documented to date and they remain partly unexplained this shows that monogenetic well preserved trachytic lava domes are uncommon and poorly known unlike rhyolitic andesitic and dacitic domes

numerical modelling of the growth dynamics of a simple silicic lava dome 1 two dimensional axisymmetrical computational models have been developed using finite element techniques to represent the rheological stiffening due to degassing induced crystallisation and the effects of a brittle carapace within a simple lava dome the dome is modelled numerically considering the effects of temperature pressure and rate of extrusion using these state variables the bulk viscosity is derived from empirical equations and the bulk rheology approximated using a solidification viscosity dividing the dome into solid dominated and fluid dominated domains elastoplastic equations for the solid component and fluid mechanical equations for the fluid domain are solved simultaneously allowing continuous stress across the fluid solid interface to ensure the two components move in unison we apply this model a hookean solid carapace model and a purely fluid lava dome model to the case of the october 1980 lava dome at mount st helens the results show that dynamic growth models involving a solid carapace are required to simulate this lava dome

endogenous growth of a miocene submarine dacite cryptodome rebun island hokkaido japan momo iwa rebun island hokkaido japan is a dacite cryptodome 200 300 m across and 190 m high the dome is inferred to have intruded wet poorly consolidated sediment in a shallow marine environment the internal structure of the dome is concentric with a massive core banded rim and narrow brecciated border all of which are composed of compositionally uniform feldspar phyric dacite boundaries between each of the zones are distinct but gradational the massive core consists of homogeneous coherent unfractured dacite and is characterized by radial columnar joints 60 200 cm across the banded rim encircles the massive core and is 40 m wide it is characterized by large scale flow banding parallel to the dome surface the flow banding comprises alternating partly crystalline and more glassy bands 80 150 cm thick the outermost brecciated border is up to 80 cm thick and consists of in situ breccia and blocky peperite the in situ breccia comprises polyhedral dacite clasts 5 20 cm across and a cogenetic granular matrix the blocky peperite consists of polyhedral dacite clasts 0 5 2 cm across separated by the host sediment mudstone the internal structures of the dome suggest endogenous growth involving a continuous magma supply during a single intrusive phase and simple expansion from the interior although much larger the internal structures of momo iwa closely resemble those of lobes in subaqueous felsic lobe hyaloclastite lavas

morphology and growth style of a miocene submarine dacite lava dome at atsumi northeast japan abstract a miocene submarine lava dome at tate iwa atsumi yamagata japan displays well preserved primary morphological features the dome currently rises above a wave cut coastal platform and is 55 m high and 90 180 m across it comprises a massive core and a lava lobe hyaloclastite rim both of which are composed of compositionally uniform feldspar phyric dacite sio2 64 wt the boundary between these two zones is distinct but gradational the massive core consists of homogeneous coherent dacite and is characterized by flow banding along the margin and by columnar joints radiating from the centre to the margin the lava lobe hyaloclastite rim encircles the massive core and consists of a complex of 80 90 dacitic lava lobes and 10 20 hyaloclastite the lava lobes are 1 6 m thick 3 12 m wide and more than 5 m long each lobe consists of a radially columnar jointed core and a glassy rim 10 30 cm thick the hyaloclastite comprises polyhedral dacite clasts 5 100 cm across in a matrix of dacite fragments up to 5 mm across the lava lobes and hyaloclastite have gradational contacts in places paleobathymetric studies based on foraminifera in sediment beneath the dome and the k ar age of the dome suggest that it was extruded in a middle bathyal environment 1500 2000 m below sea level at 12 9 0 6 ma the internal structures of the dome suggest that it formed by a combination of exogenous growth involving extrusions of small dacite lobes and endogenous growth involving a continuous magma supply and simple expansion from the interior the presence of small lava lobes along the rim suggests that the magma had relatively low viscosity at the time of extrusion in spite of its high silica content magma temperatures calculated by two pyroxene and fe ti oxide geothermometers were 999 1042 and 957 1005 c respectively the inferred low viscosity may be attributed to the high temperature of the magma and or a high confining pressure resulting from the deep sea environment

hydrogen isotope investigation of amphibole and glass in dacite magmas erupted in 1980 1986 and 2005 at mount st helens washington in active shallow sub volcanic magma conduits the extent of the dehydrogenation oxidation reaction in amphibole phenocrysts is controlled by energetic processes that cause crystal lattice damage or conditions that increase hydrogen diffusivity in magmatic phases amphibole phenocrysts separated from dacitic volcanic rocks erupted from 1980 to 1986 and in 2005 at mount st helens msh were analyzed for dd water content and fe3 fe2 and fragments of glassy groundmass were analyzed for dd and water content changes in amphibole dd values through time are evaluated within the context of carefully observed volcanic eruption behavior and published petrological and geochemical investigations driving forces for amphibole dehydrogenation include increase in magma oxygen fugacity decrease in amphibole hydrogen fugacity or both the phenocryst amphibole dd value c 57o and 2 wt h2o in the white fallout pumice of the may 18 1980 plinian eruptive phase is probably little modified during rapid magma ascent up an 7 km conduit younger volcanic rocks incorporate some shallowly degassed dacitic magma from earlier pulses based on amphibole phenocryst populations that exhibit varying degrees of dehydrogenation pyroclastic rocks from explosive eruptions in june october 1980 have elevated abundances of mottled amphibole phenocrysts peaking in some pyroclastic rocks erupted on july 22 1980 and extensive amphibole dehydrogenation is linked to crystal damage from vesiculation and pyroclastic fountain collapse that increased effective hydrogen diffusion in amphibole multiple amphibole dd populations in many 1980 pyroclastic rocks combined with their groundmass characteristics e g mixed pumice textures support models of shallow mixing prior to or during eruption as new volatile rich magma pulses blended with more oxidized degassed magma amphibole dehydrogenation is quenched at the top surface of msh dacite lava lobes but the diversity in the ddamph populations in original fresh lava flow surfaces may occur from blending magma domains with different ascent histories in the sub volcanic environment immediately before eruption multi stage open system magma degassing operated in each parcel of magma rising toward the surface whereas the magma below 7 km was a relatively closed system at least to the october 1986 eruption based on the large population of minimally dehydrogenated rim free amphibole in the lavas magma degassing and possibly h isotope exchange with low dd fluids around the roof zone may have accompanied the 1 5 km upward migration of the 1980 magma body the low ddamph c 188 to 122o oxy amphibole phenocrysts in lava spines extruded in may 2005 reflect dehydrogenation as ascending viscous magma degassed and crystallized and fractures that admitted oxygen into the hot solidified lava spine interior facilitated additional iron oxidation

a possible brine reservoir beneath occator crater thermal and compositional evolution and formation of the cerealia dome and vinalia faculae abstract the dawn spacecraft has imaged several putative cryovolcanic features on ceres and several lines of evidence point to past cryovolcanic activity at occator crater it is therefore possible that cryovolcanism played a key role in delivering sodium carbonate and chloride enriched brines to ceres surface in recent geological times the detection of a 200 km 200 km negative bouguer anomaly beneath occator suggests the presence of a low density region beneath the crater if this region is a residual partially crystallized cryomagma chamber excess pressures caused by its gradual freezing or stresses produced by the occator forming impact could have facilitated the delivery of cryolavas to the surface in the geologically recent past here the progressive solidification of a cryomagma chamber beneath occator and implications for the delivery of cryolavas to the surface has been explored models for the behavior of cryolavas at ceres surface and for the formation of the cerealia dome and vinalia faculae are also presented minimal crystallization of a subsurface fluid reservoir located at the crust mantle boundary could have driven cryolavas enriched in chloride salts and nh3 to ceres surface however cryolavas enriched in sodium carbonates would have had to have existed at shallower levels in the crust in order to be delivered to the surface via pressure driven ascent depending on the size of the reservoir cryolavas could have been driven to ceres surface for tens to hundreds of millions of years after cooling of the cryomagma chamber commenced the mineralogy at occator is suggestive of subsurface cryomagma reservoirs enriched in sodium carbonate and chloride salts aqueous solutions enriched in chloride salts and or ammonia would have arrived at the surface at warm enough temperatures to erupt if transported in propagating fractures that traveled at least 10 5 m s additionally if the cerealia dome was formed from viscous cryolava extrusions bulk kinematic lava viscosities may have been between 106 108 m2 s at the onset of relaxation plausible relaxation times to form the dome which are linked to bulk cryolava rheology are found to have ranged from 2 5 to 273 days moreover the low volatile content necessary to drive explosive eruptions on ceres supports the possibility that cerealia and vinalia faculae were emplaced as a consequence of ballistic eruptions the enigmatic geology of occator crater is consistent with a diversity of exchange processes operating on ceres in the geologically recent past further the processes that have occurred at occator could shed light on the changing geology associated with a relic ocean world future studies of occator and ceres should be undertaken with these results in mind

structural analysis and vein episode of the penjom gold deposit malaysia implications for gold mineralisation and tectonic history in the central belt of malaysia abstract gold mineralisation at the penjom gold deposit in the central belt of peninsular malaysia is dominantly hosted in structurally controlled quartz carbonate veins that display a variable degree of overprinting events under a ductile brittle regime mineralised veins are categorised into two main episodes fold and thrust related veins mainly comprised of bedding and penjom thrust parallel shear veins and associated extension veins developed during a d2 event in addition ne to nne trending splays and penjom thrust parallel reverse dextral and locally nnw to ns reverse sinistral faults overprint earlier vein events forming a new episode of extensional veins during d3 event mostly at the fault contacts of intrusives either as shallow dipping or vertical sheeted stockwork or brecciated veins at least two episodes of faulting d4 d5 are evident which postdates the main episodes of veining and mineralisation this is indicated by a series of late episodes ns trending sinistral and oblique to normal faults which transect and displace the penjom thrust and the folded footwall sequence at low angles and responsible for intensive vein deformation along the penjom thrust and displacement of ore body structural interpretations of mineralised veins suggest that the veins were formed under a compressional to transpressional regime with later post vein displacement in a transtensional to extensional regime vein formation in response to deformation observed at penjom reflects regional structural deformation within the central belt of peninsular malaysia and specifically along the bentong raub suture zone

internal structure and emplacement of an upper pliocene dacite cryptodome milos island greece the upper pliocene kalogeros cryptodome is exposed on the northeastern part of milos greece the dacite cryptodome is 800 1300 m across and at least 120 m high it is inferred to have intruded wet unconsolidated pumiceous sediments in a shallow marine environment the kalogeros cryptodome includes five facies the coherent dacite facies 80 vol consists of massive non vesicular dacite and is characterised by radial columnar joints 20 250 cm across the banded dacite facies 15 vol encircles the coherent core and is up to 40 m thick it comprises alternating bands 0 5 4 m thick of pale grey and black dacite the fractured dacite facies less than 1 vol forms an irregular zone 1 3 m thick at the outer margin of the cryptodome the outermost massive dacite breccia facies less than 2 vol consists of blocky to polyhedral dacite clasts 1 40 cm in diameter and is characterised by domains of jigsawfit and clast rotated breccia the stratified dacite breccia 2vol is clast to matrix supported monomictic poorly sorted and composed of dacite clasts up to several metres in diameter the facies association collectively records endogenous growth of a cryptodome that involved a continuous magma supply during a single intrusive phase and simple expansion inflation during emplacement the margins of the kalogeros cryptodome were quench fragmented forming an outer domain of intrusive hyaloclastite and intensely fractured dacite the near solid outer carapace insulated the hotter less viscous interior laminar shear accompanied inflation generating large scale flow banding around the outer part of the core once stagnant concentric isotherms were established within the cryptodome and controlled the orientation of columnar joints cryptodomes are characterised by a well developed internal concentric distribution of distinctive textural domains modest autoclastic breccia and the absence of redeposited autoclastic facies

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

temporal trends in lava dome extrusion at santiaguito 1922 2000 we present a means of extracting lava dome extrusion rates from data provided by the thematic mapper and enhanced thematic mapper plus instruments flown on the landsat satellites extrusion rates derived from the landsat data for santiaguito dome complex guatemala during november 1987 and january 2000 of 0 72 0 08 and 0 48 0 09 m3 s 1 compare favorably with ground based estimates of 0 63 0 28 and 0 48 0 17 m3 s 1 a satellite data derived set of 18 extrusion rate estimates between 1987 and 2000 along with ground based volume estimates prior to 1987 allow us to infer volumes of magma erupted since 1922 these data reveal cyclic extrusion at santiaguito each cycle begins with a 3 6 year long phase of high extrusion rate 0 5 2 1 m3 s 1 followed by a longer 3 11 years phase of low extrusion rate 0 2 m3 s 1 the 8th cycle began in 1996 and was still in its high extrusion rate phase during january 2000 with time however the durations of the low extrusion rate phases have increased peak extrusion and time averaged extrusion rates for each cycle have decreased and the difference between extrusion rates during the high and low extrusion rate phases of each cycle has decreased these trends may be the result of depressurization and exhaustion of the source in this case the current eruption may be expected to end around 2020 alternatively santiaguito may be entering a period of persistent activity maintained by a stable magma supply in this case we may expect extrusion to become less cyclic and to stabilize at 0 2 0 4 m3 s 1 however a 2 wt decrease in sio2 content of erupted products since 1970 appears to be consistent with chamber exhaustion as well as an increase in block lava flow lengths during 1970 2000

mount st helens and santiaguito lava domes the effect of short term eruption rate on surface texture and degassing processes in order to assess the effect of eruption rate on the surface morphology and degassing mechanisms of silicic lava flows we studied surface characteristics and obtained water content and hydrogen isotopic values of samples from flows at the mount st helens and santiaguito lava domes we compared the surface textures and inferred degassing processes to short term extrusion rates and found that when domes are small and eruption rates are high lava will not completely degas in transit to the surface allowing additional volatile loss through surface vesiculation which results in the formation of a scoriaceous carapace when domes exceed a critical size and or their cooled crusts reach a critical strength emergence of new magma is impeded short term eruption rates decline and more thorough degassing can take place leading to smooth textured flows lacking scoria development at mount st helens this transition occurred during the dome s third year when it grew from 31 8 to 53 2 106 m3 santiaguito attained a comparable state after 2 3 years of growth and for most of its 70 year history has produced non vesicular lava degassing patterns that combine closed open and kinetic processes can be distinguished using isotope data obtained from samples whose positions on a flow and emplacement histories are well constrained evidence for these patterns is most clearly preserved in lavas erupted during early rapid stages of dome growth petrologists and volcanologists seeking to infer magma chamber conditions from the volatile contents of extruded lavas thus need to sample flows early in their emplacement while paying attention to surface texture position relative to the vent and flow front and time of emergence

airborne photogrammetry and geomorphological analysis of the 2001 2012 exogenous dome growth at molodoy shiveluch volcano kamchatka abstract in 2001 after a six year pause in extrusive activity lava dome growth resumed at molodoy shiveluch volcano the new period of dome growth 2001 present has morphological features that were uncommon during the previous periods of the dome formation 1980 1981 1993 1995 numerous lava lobes and crease structures thus the current dome growth is mostly of an exogenous type with short periods of endogenous growth that occurred in 2003 2005 and 2010 geomorphological interpretation of stereo photo images has revealed elements of the dome that are hardly distinguishable in single photographs we have made detailed descriptions of the dome morphology covering all the dates of the available images by using photogrammetric processing of aerial photographs we created digital terrain models and topographic maps of the lava dome and defined its volumes for 2001 0 19 km 3 2003 0 47 km 3 2005 0 48 km 3 2010 0 54 km 3 and 2012 0 63 km 3 we also defined other morphometric characteristics absolute and relative heights as well as the dimensions of the dome and its elements for the investigated period taking into account large partial failures of the dome in 2005 0 11 km 3 and 2010 0 28 km 3 we suggest that the volume of the extruded material for the whole 1980 2012 period was no less than 1 02 km 3 the average extrusion rate over the 2001 2012 period exceeded 225 000 m 3 day the transition from endogenous to exogenous dome growth was possibly caused by change in extruded material physical properties due to an increase of sio 2 on the basis of geomorphological analysis of the current lava dome features we suggest the possible process of the exogenous dome formation at molodoy shiveluch the crease structures detected at molodoy shiveluch were classified into three groups according to their shapes radial bilaterally symmetrical and irregular these crease structures are morphologically similar to those formed at unzen volcano during the 1990 1995 eruption some revealed morphological features of the crease structures show that the role of gravity is insignificant in their formation we assume that the crease structures at molodoy shiveluch were formed by inner stresses due to thermal and solidification gradients

the bentong raub suture zone abstract it is proposed that the bentong raub suture zone represents a segment of the main devonian to middle triassic palaeo tethys ocean and forms the boundary between the gondwana derived sibumasu and indochina terranes palaeo tethyan oceanic ribbon bedded cherts preserved in the suture zone range in age from middle devonian to middle permian and melange includes chert and limestone clasts that range in age from lower carboniferous to lower permian this indicates that the palaeo tethys opened in the devonian when indochina and other chinese blocks separated from gondwana and closed in the late triassic peninsular malaysia segment the suture zone is the result of northwards subduction of the palaeo tethys ocean beneath indochina in the late palaeozoic and the triassic collision of the sibumasu terrane with and the underthrusting of indochina tectonostratigraphic palaeobiogeographic and palaeomagnetic data indicate that the sibumasu terrane separated from gondwana in the late sakmarian and then drifted rapidly northwards during the permian triassic during the permian subduction phase the east malaya volcano plutonic arc with i type granitoids and intermediate to acidic volcanism was developed on the margin of indochina the main structural discontinuity in peninsular malaysia occurs between palaeozoic and triassic rocks and orogenic deformation appears to have been initiated in the upper permian to lower triassic when sibumasu began to collide with indochina during the early to middle triassic a type subduction and crustal thickening generated the main range syn to post orogenic granites which were emplaced in the late triassic early jurassic a foredeep basin developed on the depressed margin of sibumasu in front of the uplifted accretionary complex in which the semanggol formation rocks accumulated the suture zone is covered by a latest triassic jurassic and cretaceous mainly continental red bed overlap sequence

internal fabric development in complex lava domes abstract viscous lava extrusions were modeled using plaster of paris with admixed magnetite dust which served as a tracer of the internal anisotropy of magnetic susceptibility fabric in model lava domes used analogue material showed pseudoplastic behavior and yield strength level proportional to increasing mixing ratio of plaster powder and water a series of models ranging from simple gravity flows to complex lava domes showing combined endogenous and exogenous growth were created by intrusion of plaster into a sandbox the similarity of model bodies is compared with natural lava domes on the basis of dynamic scaling analysis growth dynamics exogenous growth and internal fabric development in natural lava domes is critically discussed using the experimental results

progressive growth of the cerro bayo cryptodome chachahuen volcano argentina implications for viscous magma emplacement cryptodome and dome collapse is associated with volcanic hazards such as explosive eruptions pyroclastic flows and volcanic edifice collapse study of the growth and evolution of volcanic domes

structural mapping using palsar data in the central gold belt peninsular malaysia abstract the central gold belt cgb of peninsular malaysia has been investigated to map structural elements associated with gold mineralization using the phased array type l band synthetic aperture radar palsar satellite remote sensing data gold mineralization in this belt is structurally controlled and associated with steeply dipping faults and fold hinges adaptive local sigma and directional filters were applied to palsar data for tracing structural elements associated with gold mineralization structural features along the bentong raub suture zone have been identified as highly potential areas for gold prospecting four sets of lineaments trending n s ne sw nnw sse and ese wnw were identified results of this study demonstrate the applicability of palsar remote sensing data to assist gold exploration in the cgb particularly in reducing costs related to exploration for epithermal and polymetallic vein type mineralization in tropical environments

an unusual volcano on venus materials that issued from an unusual venusian volcano produced 1 a complex domical structure about 100 km across with thick broad flow lobes up to 41 km wide 2 an extensive sheet of thick flows and 3 radar bright surfaces that extend to 360 400 km from the volcano altimetry indicates that the relief of the domical structure is about 0 5 1 1 km the lobes and flows have prominent regularly spaced ridges 686 820 m apart thick flows with large ridge separations and broad lobes are rare on venus we suggest that the viscosities these flows were larger than those of most lava flows on venus comparisons of the dimensions of the volcano s lobes with lava flows on earth suggest that the venusian lavas may have large silica contents radar bright surfaces around the volcano may represent the result of an explosive eruption or very thin deposits of low viscosity lavas thus we suggest that the radar bright surfaces and lavas of the volcano were derived from a magma that differentiated within the crust or mantle of venus the differentiation produced 1 a gas rich low viscosity phase 2 high viscosity lavas and 3 a residual primary magma

lava effusion rate definition and measurement a review measurement of effusion rate is a primary objective for studies that model lava flow and magma system dynamics as well as for monitoring efforts during on going eruptions however its exact definition remains a source of confusion and problems occur when comparing volume flux values that are averaged over different time periods or spatial scales or measured using different approaches thus our aims are to 1 define effusion rate terminology and 2 assess the various measurement methods and their results we first distinguish between instantaneous effusion rate and time averaged discharge rate eruption rate is next defined as the total volume of lava emplaced since the beginning of the eruption divided by the time since the eruption began the ultimate extension of this is mean output rate this being the final volume of erupted lava divided by total eruption duration whether these values are total values i e the flux feeding all flow units across the entire flow field or local i e the flux feeding a single active unit within a flow field across which many units are active also needs to be specified no approach is without its problems and all can have large error up to 50 however good agreement between diverse approaches shows that reliable estimates can be made if each approach is applied carefully and takes into account the caveats we detail here there are three important factors to consider and state when measuring giving or using an effusion rate first the time period over which the value was averaged second whether the measurement applies to the entire active flow field or a single lava flow within that field and third the measurement technique and its accompanying assumptions

the chanthaburi terrane of southeastern thailand stratigraphic confirmation as a disrupted segment of the sukhothai arc a permo triassic volcanic arc system the sukhothai arc is recognised between the indochina and sibumasu continental blocks the chanthaburi terrane is here interpreted as a fault detached highly disrupted southern segment of the sukhothai arc occupying part of southeastern thailand and extending into cambodia the klaeng tectonic line is defined as the boundary between the chanthaburi terrane and sibumasu block the stratigraphy of the chanthaburi terrane is compared with that of the sukhothai terrane in northern thailand the late palaeozoic mesozoic sequences of these two volcanic arc terranes in the sukhothai zone share important similarities but show marked contrasts to those of the sibumasu and indochina blocks where the late permian triassic is largely absent due to the indosinian i unconformity western indochina or is dominantly carbonates with little terrigenous clastic input sibumasu there is no clear evidence of pre carboniferous sedimentary rocks for either the sukhothai or chanthaburi terranes late permian lyttoniid brachiopod shale near klaeng in the chanthaburi terrane was revisited the brachiopod previously reported as leptodus is re identified to oldhamina the genus previously known elsewhere in southeast asia only in the huai tak formation of the sukhothai terrane oldhamina in thailand is confined to the sukhothai arc the marine stratigraphy of the sukhothai arc is represented by a permian triassic lithological succession of mixed carbonates and siliciclastics with common volcanic material the late permian and triassic litho and biostratigraphy of the chanthaburi terrane are comparable with the upper ngao and lampang groups of the sukhothai terrane in particular they share similar successions from oldhamina brachiopod bearing shale to palaeofusulina colaniella foraminifer bearing limestone in the latest permian marine depositional conditions were terminated on the sukhothai arc by end triassic times later than on the indochina block late permian but earlier than on the sibumasu block jurassic cretaceous

digital photogrammetry as a tool in analogue modelling applications to volcano instability abstract three techniques of digital photogrammetry have been applied successfully to laboratory analogue models to study surface displacements caused by various volcano deformation types firstly side perspective videos are used to differentiate profile displacements between cryptodome intrusion models and models deforming by ductile inner core viscous flow both models show similar morphologic features including a bulged flank and an asymmetric upper graben however differences in displacement trajectories of the bulge crest reflect upward intrusion push contrasting with essentially downward displacement vectors of weak core models the other two techniques use vertical views correlated automatically either as time sequence monoscopic views or as coeval stereoscopic pairs this exploits to a maximum the method s potential by imaging surface displacements over the whole model successive monoscopic photograms because they suffer only moderate numerical processing for topographic effect removal can detect very small displacements occurring early in deformation processes as illustrated by analysis of intrusion models the monoscopic method allows prediction of fault locations and main displacement locations it can also anticipate the principal strain directions and separate different deformation stages on the other hand the stereo photogrammetry technique although more complicated provides topography and volume changes as well as pictures of surface displacements in three dimensions results are presented for the spreading of volcano models on a ductile substratum and viscous cored cones we have found digital photogrammetry to be a useful tool for analogue modelling because it provides quantitative data on surface displacements including movement invisible to the eye as well as topographic changes it is a good method for investigating and comparing different deformation mechanisms it is especially useful for interpretation of displacement patterns obtained from monitoring of natural active volcanoes in fact results of the methods used in the laboratory can be directly compared with field data from geodetic or photogrammetric surveys as at mount st helens in 1980

a review of the origins of subparallel ridges and troughs generalized morphological predictions from terrestrial models the morphologies of ridges and troughs on earth and the processes involved in their formation are reviewed for application to sets of subparallel ridges and troughs on outer planet satellites we consider tension fracturing normal faulting thrust faulting buckle folding strike slip tectonism fissure eruption wall diapirism surface folding of a flow and near surface laccolithic intrusion the landform characteristics and geologic associations predicted of each process are generalized to be independent of planet specific parameters we find that the combinations of landforms derived from each process are unique making each distinguishable in the idealized case morphological parameters most diagnostic of formational process are ridge and trough cross sectional shape termination style and incipient character the characteristics described are useful in constraining the origin of ridge and trough terrains observed in voyager images and will aid in analysis of high resolution images from the galileo and cassini spacecraft

the impact of the appalachian mountains on cyclonic weather systems part i a climatology abstract a climatological study of cold fronts and cyclones crossing the appalachian mountains from the west through northwest has been performed a sample size of 50 fronts and 40 cyclones was derived from the seven winter seasons december through march between 1979 and 1986 the analysis revealed that initially linear cold fronts are slowed and deformed by the mountains with the mean frontal speed decreasing 40 and the fronts developing a pronounced kink just east of the southern appalachians furthermore over the mountains the cross front thermal and pressure gradients are enhanced by about 25 and 63 respectively once past the mountains fronts are weaker and often difficult to locate in particular the cyclonic wind shift is very ill defined and the cross front pressure gradient is reduced to 38 of the premountain value finally small scale 500 km diameter lee lows form on more than half of the fronts though typically benign some of these disturbances may play a role in offshore c

transient effects of magma ascent dynamics along a geometrically variable dome feeding conduit abstract the transient dynamics of magma ascent during dome forming eruptions were investigated and the effects of magma chamber pressure perturbations on eruption rate are illustrated the numerical model domeflow developed by the authors for this work is applied to the problem domeflow is a transient 1 5d isothermal two phase flow model of magma ascent through an axisymmetric conduit of variable radius which accounts for gas exsolution bubble growth crystallization induced by degassing permeable gas loss through overlying magma and through conduit walls as well as viscosity changes due to crystallization and degassing for runs in which chamber pressure increases the time required to reach the new steady state transition time is a complex function of the pressure perturbation while for decreasing chamber pressure transition time is a monotonic function of the magnitude of the pressure perturbation the transition to the new steady state is mainly controlled by magma compressibility travel time time required for one parcel of magma to travel from chamber to surface and the time over which the pressure perturbation occurs results of many runs 300 were analyzed using dimensional analysis to reveal a general relationship which predicts the temporal evolution of magma effusion rate for a given sudden increase in chamber pressure the product of the change in steady state extrusion rate and the time required to reach the new steady state is linearly proportional to the normalized change in chamber pressure the volume of the conduit and the ratio of top and bottom conduit radii and inversely proportional to the cubic root of volatile fraction this relationship is used to interpret observed variations in two ongoing dome building eruptions the soufriere hills volcano montserrat and merapi volcano indonesia

cooling rate and thermal structure determined from progressive magnetization of the dacite dome at mount st helens washington our study of a magnetic anomaly associated with the recently active dacite dome at mount st helens suggests that the dome consists of a hot nonmagnetized core surrounded by a cool magnetized carapace and flanking talus the talus does not contribute to the anomaly because its constituent blocks are randomly oriented temporal changes in the magnetic anomaly indicate that the magnetized carapace thickened at an average rate of 0 03 0 01 m d from 1984 to 1986 petrographic and rock magnetic properties of dome samples indicate that the dominant process responsible for these changes is magnetization of extensively oxidized rock at progressively deeper levels within the dome as the rock cools through its blocking temperature rather than subsequent changes in magnetization caused by further oxidation newly extruded material cools rapidly for a short period as heat is conducted outward in response to convective heat loss from its surface the cooling rate gradually declines for several weeks and thereafter the material cools at a relatively constant rate by convective heat loss from its interior along fractures that propagate inward the rate of internal convective heat loss through fractures varies with rainfall snowmelt and large scale fracturing during subsequent eruptive episodes in accordance with a model for solidification of the 1959 lava lake at kilauea iki hawaii we picture the dome s magnetized carapace as being a two phase porous convective zone separated from the nonmagnetized core of the dome by a thin single phase conductive zone as a consequence of the heat balance between the conductive and convective zones the blocking temperature isotherm migrates inward at a relatively constant rate if the dome remains inactive the time scale for its complete magnetization is estimated to be 18 36 years a forecast which can be refined by shallow drilling into the dome and by continuing studies of its growing magnetic anomaly

on lava dome growth with application to the 1979 lava extrusion of the soufriere of st vincent abstract a theoretical analysis is presented for the spread of a viscous liquid flowing under its own hydrostatic pressure on a horizontal surface in order to model lava dome formation two situations are considered in detail the spreading of a constant volume of liquid and the case where the amount of liquid is continually increased experiments with silicone liquids show close agreement with theory the formation of a basaltic andesite lava extrusion in 1979 on the crater floor of the soufriere of st vincent west indies provided the motivation for and an application of the model the extrusion reached a diameter of 868 m and a height of 133 m over a period of 150 days over the first 90 days the growth relationships were consistent with those predicted by theory application of the theory to the soufriere dome suggests an effective viscosity of 2 x 10 12 poise for the basaltic andesite lava the large effective viscosity calculated for the lava may be attributed to the dominant influence of a high viscosity skin which forms at the margins of the flow as it cools after 70 days the rate of growth of the extrusion markedly decreased because a substantial collar of rubble accumulated at the flow front due to this collar the growth of the extrusion ceased after 150 days from approximately two weeks after the initiation of the extrusion the discharge rate of lava decreased approximately linearly with increasing dome height this observation suggests that the lava ascended under a decreasing hydrostatic driving pressure and that extrusion ceased when the lava column reached hydrostatic equilibrium

the leptodus shales of central peninsular malaysia distribution age and palaeobiogeographical affinities the terms leptodus shales and leptodus beds have been used to describe a rich brachiopod bearing unit within the permian argillaceous facies of the central belt of peninsular malaysia to date there has been no formal description of this unit regarding its age spatial distribution or faunal composition a review of previous literature backed by recently collected data from our field surveys and biostratigraphical studies reveals that there is a sequence of fossiliferous assemblages within the leptodus shales which range in age from middle permian to possibly early late permian and extend geographically from southern kelantan to southern pahang peninsular malaysia these assemblages are found in argillaceous sediments which are often highly tuffaceous and in northern pahang are associated with pyroclastic volcanics of probable island arc origin the faunas are of palaeo equatorial affinity and are taxonomically close to faunas in indochina such as the sisophon fauna in cambodia typical elements include vediproductus cf punctatiformis chao transennatia gratiosa waagen t termierorum sone leman and shi uncuninellina timorensis beyrich leptodus richthofeni kayser l cf tenuis waagen leptodus nobilis waagen gubleria aff ninglangensis fang and jiang and spyridiophora gubleri termier and termier

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

middle permian brachiopods from central peninsular malaysia faunal affinities between malaysia and west cambodia a moderately diverse permian brachiopod fauna is described from a new rock unit the bera formation in the bera district central pahang peninsular malaysia the fauna consists of 19 taxa including 14 genera and 17 both identified and unidentified typically tethyan species the fauna appears to be correlative on the basis of brachiopods with the neoschwagerina yabeina fusulinid zones in indochina and south china in particular it has strong linkage to member c yabeina beds of the sisophon limestone west cambodia this is indicated by three of the bera species urushtenoidea chaoi ching spyridiophora gubleri termier and termier and transennatia termierorum sp nov being shared with the cambodian fauna a possible early capitanian middle permian age is proposed for the bera brachiopod fauna

high effusion rates of the cordon caulle 2011 2012 eruption southern andes and their relation with the quasi harmonic tremor high effusion rates of intermediate to high silica lavas seem to be less uncommon than previously thought in particular during their initial eruptive stages in this study we report satellite based time averaged discharge rates for the 2011 2012 effusive phase at cordon caulle which are well correlated with the evolution of the quasi harmonic tremor the most significant seismic signal after the initial explosive stage such a correspondence could become a key method for detection of the onset of effusive phases especially in remote and or very cloudy areas supplying an additional tool for effective warnings and near real time hazards appraisal

the transition from explosive to effusive eruptive regime the example of the 1912 novarupta eruption alaska the shift from explosive to effusive silicic volcanism seen in many historical eruptions reflects a change in the style of degassing of erupted magma this paper focuses on such a transition during the largest eruption of the twentieth century the 1912 eruption of novarupta the transition is recorded in a dacite block bed which covers an elliptical area of 4 km 2 around the vent approximately 700 studied blocks fall into four main lithologic categories 1 pumiceous 2 dense 3 flow banded dacites and 4 welded breccias textural analyses of the blocks indicate portions of the melt underwent highly variable degrees of outgassing vesicle populations show features characteristic of bubble coalescence and collapse a decrease in measured vesicularity and increased evidence for bubble collapse compared with pumice from earlier plinian episodes mark the transition from closed to open system degassing block morphology and textures strongly suggest the magma was first erupted as a relatively gas rich lava dome plug but incomplete out gassing led to explosive disruption heterogeneous degassing of ascending magma began in plinian episode iii and resulted in instability during episode iv dome growth and a series of vulcanian explosion s modeling of the dynamics of explosion initiation and ejecta dispersal indicates that a significant concentration in gas is required to produce the explosions responsible for the observed block field dispersal the amount of gas available in the hot pumiceous dome material appears to have been inadequate to drive the explosion s therefore external water most likely contributed to the destruction

seismic signals of rockfalls as indicators of the origin of lava fragments emplaced during the 2010 endogenous and exogenous growth in the crater of volcan de colima mexico the 2010 2011 exogenous emplacement of a lava lobe during the 2007 2011 lava dome growth at andesitic volcan de colima mexico interrupted the previous endogenous regime and allowed us to obtain seismic signals associated with rockfalls triggered by both exogenous and endogenous growth we analyzed a total of 410 seismic signals of rockfalls with durations from 50 to 150 s recorded during january april 2010 two characteristic populations of seismic signal peak frequencies were identified a low frequency lf group mean 1 76 0 44 hz and a high frequency hf group mean 3 13 0 63 hz associated respectively with rockfalls caused by endogenous and exogenous growth in the crater application of the kolmogorov smirnov test showed at the 0 01 significance level that the databases of lf and hf seismic signals of rockfalls belong to different groups of signals and may be considered as having different origins the results show that the spectral properties of the seismic signals produced by rockfalls may serve as indicators of the origin of falling lava fragments and thus can be used to monitor effusive volcanic activity

conduit degassing and thermal controls on eruption styles at mount st helens abstract the explosivity of silicic eruptions depends on the interplay between magma rheology exsolution kinetics and degassing magma degassing is governed by the competing effects of vertical transport within the conduit and the lateral flux of gas out of the conduit diller et al 2006 jaupart and allegre 1991 we combine a simplified treatment of these degassing processes with thermodynamic modeling to examine the conditions present at mount st helens during the spine extruding eruption from 2004 to 2008 we find that two parameters are primarily responsible for controlling the eruptive style the magma chamber temperature and a dimensionless parameter that gauges the efficiency of lateral degassing together these parameters determine whether and where magma can solidify at depth to form a dense solid plug that is gradually extruded as a volcanic spine we show that the small 50 oc decrease in magma chamber temperature between eruptive activity in the 1980s and that of 2004 2008 combined with a modest increase in degassing efficiency associated with lower volumetric flux can explain the observed change in erupted material from viscous lava flows to solidified spines more generally we suggest that similar threshold behavior may explain observed abrupt transitions in effusive eruptive styles at other intermediate composition volcanoes finally we extrapolate our results to suggest that the increase in degassing efficiency accompanying decreasing magma supply rates may have caused the transition from explosive to effusive activity in late 1980

venus volcanism initial analysis from magellan data magellan images confirm that volcanism is widespread and has been fimdamentally important in the formation and evolution of the crust of venus high resolution imaging data reveal evidence for intrusion dike formation and cryptodomes and extrusion a wide range of lava flows also observed are thousands of small shield volcanoes larger edifices up to several hundred kilometers in diameter massive outpourings of lavas and local pyroclastic deposits although most features are consistent with basaltic compositions a number of large pancake like domes are morphologically similar to rhyolite dacite domes on earth flows and sinuous channels with lengths of many hundreds of kilometers suggest that extremely high effusion rates or very fluid magmas perhaps komatiites may be present volcanism is evident in various tectonic settings coronae linear extensional and compressional zones mountain belts upland rises highland plateaus and tesserae volcanic resurfacing rates appear to be low less than 2 km 3 yr but the significance of dike formation and intrusions and the mode of crustal formation and loss remain to be established