shallow vent architecture during hybrid explosive effusive activity at cordon caulle chile 2011 12 evidence from direct observations and pyroclast textures in june 2011 an eruption of rhyolite magma began at the puyehue cordon caulle volcanic complex southern chile by january 2012 explosive activity had declined from sustained pyroclastic plinian to sub plinian fountaining to mixed gas and ash jetting punctuated by vulcanian blasts this explosive activity was accompanied by synchronous effusion of obsidian lava in a hybrid explosive effusive eruption fortuitous climatic conditions permitted ground based observation and video recording of transient vent dynamics as well as real time collection of proximal juvenile ash as it sedimented from the active plume the main eruptive vent complex and site of lava effusion was represented by two loci of vulcanian blasts within a single tephra cone containing a pancake shaped proto lava dome these blast loci each consisted of clusters of sub vents that expressed correlated shifts in eruption intensity indicating the presence of partially connected and or branching zones of high permeability within the upper conduit pyroclast textures were examined by x ray computed microtomography and their permeability was modeled by lattice boltzmann simulations the porosity 39 to 67 and darcian permeability 3 1x10 15 m2 perpendicular to fabric to 3 8x10 11 m2 parallel to fabric of fine ash emitted during ash jetting indicates that the permeable zones comprised highly sheared tube like bubbly magma and contrast with the low porosity 17 and nul permeability of bombs ejected to hundreds of metres from the vent in vulcanian blasts residual h2o content of ash 0 14 wt and two bombs 0 2 0 25 wt determined by karl fischer titration indicate degassing of this pyroclastic material to near atmospheric pressures ash textures and simple degassing vesiculation models indicate the onset of permeability by ductile processes of shear enhanced bubble coalescence in the upper 1 to 1 5 km of the conduit repeated ash jetting and vulcanian blasts indicate that such ductile processes were not sufficiently effective to accommodate all degassing requirements and additional brittle e g fragmentation events transiently assisted in maintaining an open system degassing regime that permitted long lived hybrid explosive effusive activity the eruption at cordon caulle has provided an excellent opportunity to closely observe key processes of silicic volcanism

d h ratios and h2o contents record degassing and rehydration history of rhyolitic magma and pyroclasts abstract volcanic eruptions of rhyolitic magma often show shifts from powerful vulcanian to plinian explosive episodes to a more gentle effusion of viscous lava forming obsidian flows another prevailing characteristic of these eruptions is the presence of pyroclastic obsidians intermingled with the explosive tephra this dense juvenile product is similar to the tephra and obsidian flow in composition but is generally less degassed than its flow counterpart the formation mechanism s of pyroclastic obsidians and the information they can provide concerning the extent to which magma degassing modulates the eruptive style of rhyolitic eruptions are currently subject to active research porous tephra and pyroclastic and flow obsidians from the 1060ce glass mountain rhyolitic eruption at medicine lake volcano california were analyzed for their porosity water content h2o and hydrogen isotopic composition d h2o in porous pyroclasts is correlated negatively with d and positively with indicating that the samples were affected by post eruptive rehydration numerical modeling suggests that this rehydration occurred at an average rate of 10 23 5 0 5 m2 s 1 during the 960 years since the eruption causing some pyroclasts to gain up to 1 wt of meteoric water pyroclastic and flow obsidians were not affected by rehydration due to their very low porosity comparison between modeled d h2o relationships in degassing magma and values measured in the glass mountain samples supports the idea that rhyolitic magma degasses in closed system until its porosity reaches a value of about 65 5 beyond which degassing occurs in open system until quench during the explosive phase rapidly ascending magma fragments soon after it becomes permeable creating porous lapilli and ash that continue to degas in open system within an expanding gas phase as suggested by recent studies some ash may aggregate and sinter on the conduit sides at different depths above the fragmentation level partly equilibrating with the continuously fluxing heavier magmatic vapor explaining the wide range of h2o contents and high variability in d measured in the pyroclastic obsidians using only h2o and d it is impossible to rule out the possibility that pyroclastic obsidians may also form by permeable foam collapse either syn explosively near the conduit sides below the fragmentation level or during more effusive periods interspersed in the explosive phase during the final effusive phase of the eruption slowly ascending magma degasses in open system until it reaches the surface creating flows with low h2o and d this study shows that h2o measured in highly porous pyroclasts of a few hundred years or more cannot be used to infer syn eruptive magma degassing pathways unless careful assessment of post eruptive rehydration is first carried out if their mechanism of formation can be better understood detailed analysis of the variations in texture and volatile content of pyroclastic obsidians throughout the explosive phase may help decipher the reasons why rhyolitic eruptions commonly shift from explosive to effusive phases

petrologic and experimental evidence for the movement and heating of the pre eruptive minoan rhyodacite santorini greece hydrothermal experiments combined with petrologic observations form the basis for a new two stage model for the evolution of the pre eruption minoan magma chamber at santorini greece ninety nine percent of the erupted volume is two pyroxene rhyodacitic magma that had been stored at a temperature of 885 c based on magnetite ilmenite and quilf geothermometry the rest of the volume is basaltic to andesitic magma which occurs as 200 mpa in addition the composition of the plagioclase hosts an56 6 of the inclusions require temperatures of 825 25 c at pressures 200 mpa this demonstrates that the minoan rhyodacitic magma underwent a two stage evolution first crystallizing at 825 c and 200 mpa and then rinsing to a shallow 50 mpa storage region with a concomitant rise in temperature to 885 c we suggest that the episodic intrusion of mafic magmas provided the necessary heat and perhaps contributed to the ascent of the magma to shallow crustal depths where it reequilibrated before the cataclysmic eruption phase equilibria suggest that much of the heating of the rhyodacite occurred in the shallow storage region thermal budget calculations suggest that the rhyodacite magma could have been heated by intrusions of basalt rising at reasonable upwelling rates and injected into the storage zone over several hundred years preservation of amphibole in the mafic scoria indicate that injection of mafic magma continued up until days before the cataclysmic eruption perhaps triggering the event

possible structural control on the 2011 eruption of puyehue cordon caulle volcanic complex southern chile determined by insar gps and seismicity

recent volcanism in the puyehue cordon caulle region southern andes chile 40 5 s petrogenesis of evolved lavas

geochemical constraints on the role of tuffisite veins in degassing at the 2008 09 chaiten and 2011 12 cordon caulle rhyolite eruptions abstract hybrid activity during the rhyolitic eruptions of chaiten 2008 09 and cordon caulle 2011 2012 in chile has offered unprecedented insights into the enigmatic and complex degassing processes occurring during eruptions of silicic magma highly permeable transient fracture networks within the conduit can act as outgassing channels their interaction with deeper volatile rich melt can account for both punctuated explosive activity and large scale degassing of the system leading towards predominantly effusive behaviour in this study we characterise trace element concentrations and 210pb 226ra systematics within pyroclastic material from the recent eruptions at chaiten and cordon caulle volcanoes results reveal how gas fluxing from deep volatile rich reservoirs to the surface within magmatic conduits can be recorded by trace elements and 210pb 226ra disequilibria in tuffisite veins tuffisite veins particle filled fracture networks are present in volcanic bombs from both eruptions trace element heterogeneity associated with tuffisites preserves evidence for degassing at chaiten enrichments e g cu and depletions e g mo li and bi are identified in vein material and clasts transported within veins and record multiple degassing events at cordon caulle enrichments of volatiles in an early vein e g tl and bi and depletions in a later vein e g cd in pb and tl reflect interactions between glassy clasts and the carrier gas phase that transported them in contrast 210pb and 226ra which can be fractionated during degassing are mostly in secular equilibrium modelling suggests that the disparity between the signals preserved in these two types of chemical signatures reflects the brevity of degassing events and the relative volumes of tuffisite veins and the bodies of degassing magma that they source gas from the lack of preserved 210pb enrichments in tuffisite veins at both volcanoes places an upper limit on the mass of deeper bubble rich magma outgassed via tuffisites during their lifetime this study shows that both the presence and absence of sample scale geochemical heterogeneity can be used to place constraints on syn eruptive physical processes and underlines the value of analysing a wide suite of trace element species

the origin and evolution of breakouts in a cooling limited rhyolite lava flow understanding lava flow processes is important for interpreting existing lavas and for hazard assessments although substantial progress has been made for basaltic lavas our understanding of silicic lava flows has seen limited recent advance in particular the formation of lava flow breakouts which represent a characteristic process in cooling limited basaltic lavas but has not been described in established models of rhyolite emplacement using data from the 2011 2012 rhyolite eruption of puyehue cordon caulle chile we develop the first conceptual framework to classify breakout types in silicic lavas and to describe the processes involved in their progressive growth inflation and morphological change by integrating multiscale satellite field and textural data from cordon caulle we interpret breakout formation to be driven by a combination of pressure increase from local vesiculation in the lava flow core as well as from continued supply via extended thermally preferential pathways and a weakening of the surface crust through lateral spreading and fracturing small breakouts potentially resulting more from local vesiculation than from continued magma supply show a domed morphology developing into petaloid as inflation increasingly fractures the surface crust continued growth and fracturing results in a rubbly morphology with the most inflated breakouts developing into a cleft split morphology reminiscent of tumulus inflation structures seen in basalts these distinct morphological classes result from the evolving relative contributions of continued breakout advance and inflation the extended nature of some breakouts highlights the role of lava supply under a stationary crust a process ubiquitous in inflating basalt lava flows that reflects the presence of thermally preferential pathways textural analyses of the cordon caulle breakouts also emphasize the importance of late stage volatile exsolution and vesiculation within the lava flow although breakouts occur across the compositional spectrum of lava flows the greater magma viscosity is likely to make late stage vesiculation much more important for breakout development in silicic lavas than in basalts such late stage vesiculation has direct implications for hazards previously recognized from silicic lava flows enhancing the likelihood of flow front collapse and explosive decompression of the lava core

complex dynamics of small moderate volcanic events the example of the 2011 rhyolitic cordon caulle eruption chile after decades of repose puyehue cordon caulle volcano chile erupted in june 2011 following a month of continuously increasing seismic activity the eruption dispersed a large volume of rhyolitic tephra over a wide area and was characterized by complex dynamics during the initial climactic phase of the eruption 24 30 h on 4 5 june 11 14 km high plumes dispersed most of the erupted tephra eastward towards argentina reaching as far as the atlantic ocean this first eruptive phase was followed by activity of lower intensity leading to the development of a complex stratigraphic sequence mainly due to rapid shifts in wind direction and eruptive style the resulting tephra deposits consist of 13 main layers grouped into four units each layer was characterized based on its dispersal direction sedimentological features and on the main characteristics of the juvenile fraction texture density petrography chemistry the lowest part of the eruptive sequence unit i corresponding to the tephra emitted between 4 and 5 june is composed of alternating lapilli layers with a total estimated volume of ca 0 75 km3 these layers record the highest intensity phase during which a bent over plume dispersed tephra towards the southeast east with negligible up wind sedimentation products emitted during 5 6 june unit ii signaled an abrupt shift in wind direction towards the north leading to the deposition of a coarse ash deposit in the northern sector ca 0 21 km3 in volume followed by a resumption of easterly directed winds a third phase unit iii began on 7 june and resulted in tephra deposits in the eastern sector and ballistic bombs around the vent area a final phase unit iv started after 15 june and was characterized by the emission of fine grained white tephra from ash charged plumes during low level activity and the extrusion of a viscous lava flow timing and duration of the first eruptive phases were constrained based on comparison of the dispersal of the main tephra layers with satellite images showing that most of the tephra was emitted during the first 72 h of the event the analyzed juvenile material tightly clusters within the rhyolitic field with negligible chemical variations through the eruptive sequence textural observations reveal that changes in eruption intensity and consequently in magma ascent velocity within the conduit and complex interactions between gas rich and gas depleted magma portions during ascent resulted in vesicular clasts with variable degrees of shear localization and possibly in the large heterogeneity of the juvenile material

the role of unsteady effusion rates on inflation in long lived lava flow fields abstract the emission of volcanic gases and particles can have global and lasting environmental effects but their timing tempo and duration can be problematic to quantify for ancient eruptions where real time measurements are absent lava flows for example may be long lasting and their impact is controlled by the rate tempo and vigor of effusion these factors are currently difficult to derive from the geologic record but can have large implications for the atmospheric impact of an eruption we conducted a set of analogue experiments on lava flow inflation aiming at connecting lava morphologies preserved in the rock record to eruption tempo and dynamics through pulsating effusion rates inflation a process where molten material is injected beneath the crust of an active lava flow and lifts it upwards is a common phenomenon in basaltic volcanic systems this mechanism requires three components a a coherent insulating crust b a wide spread molten core and c pressure built up beneath the crust from a sustained supply of molten material inflation can result in a lava flow growing tens of meters thick even in flow fields that expand hundreds of square kilometers it has been documented that rapid effusion rates tend to create channels and tubes isolating the active part of the flow from the stagnant part while slow effusion rates may cause crust to form quickly and seize up forcing lava to overtop the crust however the conditions that allow for inflation of large flow fields have not previously been evaluated in terms of effusion rate by using peg 600 wax and a programmable pump we observe how by pulsating effusion rate inflation occurs even in very low viscosity basaltic eruptions we show that observations from inflating hawaiian lava flows correlate well with experimental data and indicate that instantaneous effusion rates may have been 3 times higher than average effusion rates during the emplacement of the 23 january 1988 flow at k lauea hawai i the identification of a causal relationship between pulsating effusion rates and inflation may have implications for eruption tempo in the largest inflated flows flood basalts

eruptive history geochronology and magmatic evolution of the puyehue cordon caulle volcanic complex chile forty three 40 ar 39 ar age determinations of lava flows domes ignimbrites and dikes plus 14 c dates from seven distal tephra layers combined with stratigraphy geochemistry and sr and th isotope data establish an eruptive chronology for the puyehue cordon caulle volcanic complex at 40 5 s in the andean southern volcanic zone svz the complex preserves 131 km 3 of lava and tephra that erupted from numerous vents widely separated in time and space approximately 80 of the total volume consists of basaltic to andesitic lava that formed two broad shield volcanoes between 314 and 70 ka the modern puyehue stratovolcano was built on the southerly shield during the past 69 k y following a hiatus of 25 k y puyehue has erupted 15 km 3 of basaltic to rhyolitic magma that spans the entire compositional range found in the southern svz and evolved via at least six phases including 1 basaltic andesitic to dacitic lavas between 69 and 32 ka 2 a shift to bimodal magma compositions that is first expressed by a rhyodacite mingled with inclusions of mgo rich basaltic andesite at 34 ka 3 dacitic to rhyolitic flows and domes from 19 to 12 ka 4 basaltic to basaltic andesitic flows between 15 and 12 ka 5 subsequent rhyolitic dome growth in several effusive and explosive stages between 7 and 5 ka followed by 6 a powerful series of phreatomagmatic and sub plinian eruptions at ca 1 1 ka that obliterated the preceding rhyolite domes and formed the present 2 5 km diameter 280 m deep summit crater along the cordon caulle fissure zone 5 km 3 of rhyodacitic to rhyolitic lavas domes and cones have formed during the past 16 5 k y including explosive and effusive eruptions in 1921 1922 and 1960 eruptive rates were nonuniform over time with background growth at 0 04 km 3 k y or less punctuated by spurts at up to 0 90 km 3 k y the time averaged rate 0 42 km 3 k y is nearly double that at the tatara san pedro complex 500 km to the north during the past 300 k y these findings indicate that within a single arc the magmatic and eruptive fluxes at individual frontal volcanoes can be highly variable the last three stratocone building events on puyehue began during periods of deglaciation suggesting a relationship between unloading of ice and ease of magma ascent puyehue basalt exhibits subtle changes in 238 u 230 th 87 sr 86 sr and trace element composition over time that signal shifts in the composition and degree of melting of the mantle wedge or the extent to which basalt was modified by assimilation of heterogeneous crustal melts the complex has become exceptionally bimodal and more explosive over time with recent rhyolites evolving by extreme crystal fractionation of mafic magma and lesser volumes of andesite and dacite created via mixing of rhyolite and basalt despite the high flux of basalt during the past 300 k y no large silicic magma reservoir formed in the upper crust instead 238 u 230 th data favor rapid ascent of several small bodies of basaltic and silicic magma from the lower crust promoted perhaps by conduits that reflect strike slip faulting beneath the complex

rhyolite lava emplacement dynamics inferred from surface morphology abstract the morphology of a silicic lava is created by the fluid dynamic conditions that operated during flow careful analysis of these features can thus be used to reconstruct emplacement processes we used unoccupied aerial system and structure from motion photogrammetry techniques to collect centimeter scale spatial resolution imagery of the surfaces of south coulee and obsidian dome rhyolite lavas mono inyo craters usa we supplement the newly acquired orthomosaics and digital elevation models with existing imagery of other holocene rhyolite lavas from across the western usa including rock mesa dome south sister or newberry flow south sister or obsidian flow newberry or interlake flow newberry or and banco bonito flow valles caldera nm although many morphologic features exist we restrict our quantitative analyses to the recurrent ridges and blocks of loose rubble that are common to the flows ridge spacing and ridge vergence indicate the ridges are likely folds produced by compression during emplacement pressure ridge spacings range from 27 to 45 m at south coulee and 18 to 34 m on obsidian dome spacing generally decreases with distance from the vent across both lavas ridge amplitudes range from 4 to 17 m at both lavas and show little correlation with distance from the vent the vergence of the crest of the ridges in the flow interiors points back to the source vent which provides strong evidence for endogenous flow and the backward rotation of folds produced by undertow of the underlying lava ridges near flow margins verge towards the flow front demonstrating that exogenous flow becomes increasingly important at the point of advance in both south coulee and obsidian dome block sizes are largest near the vent and gradually decrease towards the flow front the gradual decrease in block size with increasing distance from the vent likely reflects decreasing effusion rates from the conduit we interpret our high resolution field measurements under the lens of analytical solutions to fluid dynamic models to estimate emplacement timescales and associated rates we calculate relatively abbreviated eruptive timescales ranging from 1 month to

cummingtonite and the evolution of the mount st helens washington magma system an experimental study hydrothermal experiments have been conducted on the 3 5 ka cummingtonite bearing yn tephra from mount st helens washington to determine the stability field of cummingtonite in volcanic rocks and to gather additional data on the evolutionary history of the mount st helens magmatic system cummingtonite is not stable in experiments conducted at or above 810 c at pressures 2 o analyses of melt inclusions that yield preeruption melt h 2 o contents of 6 4 wt the yn tephra belongs to a series of cummingtonite bearing dacites that erupted early in the history of mount st helens these early dacites have relatively homogeneous compositions and are characterized by low temperature 800 c high water pressure and high oxygen fugacity nno 1 phenocryst crystallization silicic magmas that erupted after eruption of basaltic andesite at mount st helens 2 3 ka are more heterogeneous in composition and last equilibrated under higher temperatures 900 c lower water pressures and lower oxygen fugacities than the early dacites these changes in the magma chamber conditions appear to have been related to the intrusion of mafic magma into an upper crustal dacitic magma chamber

european and mediterranean hydroclimate responses to tropical volcanic forcing over the last millennium nasa modeling analysis and prediction program noaa climate change data and detection program na10oar4310123 national science foundation division of atmospheric and geospace sciences nsf ags 15 02224 ldeo climate center and climate and life initiatives ags 12 03818 ags 13 03976

time dependent permeability evolution in compacting volcanic fracture systems and implications for gas overpressure abstract volcanic eruptions are driven by the ascent of volatile laden magma the capacity of a volcano system to outgas these volatiles its permeability controls the explosive potential and fractures at volcanic conduit margins play a crucial role in tempering eruption explosivity by acting as outgassing pathways however these fractures are often filled with hot volcanic debris that welds and compacts over time meaning that these permeable pathways have a finite lifetime while numerous studies emphasize that permeability evolution is important for regulating pressure in shallow volcanic systems how and when this occurs remains an outstanding question in volcanology in this contribution we show that different pressure evolution regimes can be expected across a range of silicic systems as a function of the width and distribution of fractures in the system the timescales over which they can outgas a function of depth and temperature and the permeability of the host material we define outgassing diffusive relaxation and pressure increase regimes which are distinguished by comparing the characteristic timescales over which they operate moreover we define a critical permeability threshold which determines in concert with characteristic timescales of diffusive mass exchange between the pore and melt phases whether systems fracture and outgas efficiently or if a volcano will be prone to pressure increases incomplete healing and explosive failure

late holocene lava flow morphotypes of northern harrat rahat kingdom of saudi arabia implications for the description of continental lava fields a lava morphotype refers to the recognizable and distinctive characteristics of the surface morphology of a lava flow after solidification used in a similar way to a sedimentary facies this classification method is explored on an example volcanic field in the kingdom of saudi arabia where copious lava outpourings may represent an important transition between monogenetic and flood basalt fields here young and well preserved mafic lava fields display a wide range of surface morphologies we focussed on four post 4500 yrs bp lava flow fields in northern harrat rahat 10 ma and propose a framework for describing systematic changes in morphotypes down flow the morphotypes give insight into intrinsic and extrinsic parameters of emplacement rheology and dominant flow behavior as well as the occurrence and character of other lava structures the harrat rahat lava flow fields studied extend up to 23 km from the source and vary between 1 2 m and 12 m in thickness areas of the lava flow fields are between 32 and 61 km2 with individual flow field volumes estimated between 0 085 and 0 29 km3 they exhibit shelly slabby and rubbly pahoehoe platy cauliflower and rubbly a a and blocky morphotypes morphotypes reflect the intrinsic parameters of composition temperature crystallinity and volatile content vesicularity along with external influences such as emission mechanism effusion rate topography and slope control of flow velocity one morphotype can transition to another in individual flow units or lobes and they may dominate zones not all morphotypes were found in a single lava flow field pahoehoe morphotypes are related to the simple mechanical disaggregation of the crust whereas a a morphotypes are related to the transitional emergence and subsequent transitional disappearance of clinker blocky morphotypes result from fracturing and auto brecciation a a morphotypes i e platy cauliflower rubbly a a dominate the lava flow field surfaces in northern harrat rahat which suggests that core dominated flows were predominant during flow movement lava structures are well developed and well preserved and some may be related to some morphotypes down flow changes exhibit key illustrative and easy recognizable features in the lava flow fields and might provide insights into real time monitoring of future flows in this region

slope stability models for rainfall induced lahars during long lasting eruptions abstract in this study we analyse the spatial distribution of potential lahar sources during long lasting eruptions using two slope stability models shalstab and trigrs the analysis is based on observed deposit grain size and thickness rainfall data and slope angle of the lahar events in the area surrounding the cordon caulle volcano chile that occurred during the 2011 eruption the main phase of the eruption 4 7 june was characterized by eruptive plumes from 7 to 11 km high which dispersed most of the tephra eastward toward argentina with a total estimated volume of about 1 km3 tephra fallout blanketed the region from ese to ene of the volcano with the thickness of the tephra fallout layers between approximately 1 m 15 km from vent and 0 06 m 240 km from the vent on 10 june 2011 a major lahar occurred close to the argentina chile border that reached the national road 231 28 km from the vent three field campaigns were undertaken to collect samples and data from tephra fallout deposits and triggering mechanisms in the lahar source area model input parameters were obtained from geotechnical tests and field measurements several metrics were used for model evaluation and best fit to the data were obtained for simulations considering non cohesive ash layers for shalstab and a cohesion of 0 5 kpa for trigrs both models are sensitive to the physical properties of the tephra fallout deposit and the hydraulic and materiel strength properties of the study area they both also show good agreement with field data but provide different information trigrs provides an estimate of the timing based on a storm event and location of a potentially unstable area while shalstab simulations result in landslide susceptibility classes based on critical rainfall value these outcomes provide fundamental insights into lahar triggering during long lasting volcanic eruptions and are crucial to the compilation of lahar hazard maps and emergency management plans in the south andes volcanic region

spherulite crystallization induces fe redox redistribution in silicic melt rhyolitic obsidians from krafla volcano iceland record the interaction between mobile hydrous species liberated during crystal growth and the reduction of ferric iron in the silicate melt we performed synchrotron ftir and xanes measurements along a transect extending from a spherulite into optically distinct colorless and brown glass zones measurements show that the colorless glass is enriched in oh groups and depleted in ferric iron while the brown glass shows the opposite relationship the color shift between brown and clear glass is sharp suggesting that the colorless glass zone was produced by a redox front that originated from the spherulite margin and moved through surrounding melt during crystallization we conclude that the most likely reducing agent is hydrogen produced by magnetite crystallization within the spherulite the krafla obsidians dramatically capture redox disequilibrium on the micoscale and highlight the importance of hydrous fluid liberation and late stage crystallization to the redox signature of glassy lavas

cristobalite in the 2011 2012 cordon caulle eruption chile cristobalite is a low pressure high temperature polymorph of sio2 found in many volcanic rocks its volcanogenic formation has received attention because 1 pure particulate cristobalite can be toxic when inhaled and its dispersal in volcanic ash is therefore a potential hazard and 2 its nominal stability field is at temperatures higher than those of magmatic systems making it an interesting example of metastable crystallization we present analyses by xrd sem epma laser raman and synchrotron ct of representative rhyolitic pyroclasts and of samples from different facies of the compound lava flow from the 2011 2012 eruption of cordon caulle chile cristobalite was not detected in pyroclasts negating any concern for respiratory hazards but it makes up 0 23 wt of lava samples occurring as prismatic vapour deposited crystals in vesicles and or as a groundmass phase in microcrystalline samples textures of lava collected near the vent which best represent those generated in the conduit indicate that pore isolation promotes vapour deposition of cristobalite mass balance shows that the sio2 deposited in isolated pore space can have originated from corrosion of the adjacent groundmass textures of lava collected down flow were modified during transport in the insulated interior of the flow where protracted cooling additional vesiculation events and shearing overprint original textures in the most slowly cooled and intensely sheared samples from the core of the flow nearly all original pore space is lost and vapour deposited cristobalite crystals are crushed and incorporated into the groundmass as the vesicles in which they formed collapse by strain and compaction of the surrounding matrix holocrystalline lava from the core of the flow achieves high mass concentrations of cristobalite as slow cooling allows extensive microlite crystallization and devitrification to form groundmass cristobalite vapour deposition and devitrification act concurrently but semi independently both are promoted by slow cooling and it is ultimately devitrification that most strongly contributes to total cristobalite content in a given flow facies our findings provide a new field context in which to address questions that have arisen from the study of cristobalite in dome eruptions with insight afforded by the fundamentally different emplacement geometries of flows and domes

a high resolution benthic stable isotope record for the south atlantic implications for orbital scale changes in late paleocene early eocene climate and carbon cycling abstract the late paleocene and early eocene were characterized by warm greenhouse climates punctuated by a series of rapid warming and ocean acidification events known as hyperthermals thought to have been paced or triggered by orbital cycles while these hyperthermals such as the paleocene eocene thermal maximum petm have been studied in great detail the background low amplitude cycles seen in carbon and oxygen isotope records throughout the paleocene eocene have hitherto not been resolved here we present a 7 7 million year myr long high resolution orbitally tuned benthic foraminiferal stable isotope record spanning the late paleocene and early eocene interval 52 5 60 5 ma from ocean drilling program odp site 1262 south atlantic this high resolution 2 4 kyr record allows the changing character and phasing of orbitally modulated cycles to be studied in unprecedented detail as it reflects the long term trend in carbon cycle and climate over this interval the main pacemaker in the benthic oxygen isotope 18 o and carbon isotope 13 c records from odp site 1262 are the long 405 kyr and short 100 kyr eccentricity cycles and precession 21 kyr obliquity 41 kyr is almost absent throughout the section except for a few brief intervals where it has a relatively weak influence during the course of the early paleogene record and particularly in the latest paleocene eccentricity paced negative carbon isotope excursions 13 c cies and coeval negative oxygen isotope 18 o excursions correspond to low carbonate caco 3 and coarse fraction cf values due to increased carbonate dissolution suggesting shoaling of the lysocline and accompanied changes in the global exogenic carbon cycle these negative cies and 18 o events coincide with maxima in eccentricity with changes in 18 o leading changes in 13 c by 6 5 kyr in the 405 kyr band and by 3 1 kyr in the higher frequency 100 kyr band on average however these phase lags are not constant with the lag in the 405 kyr band extending from 4 5 kyr to 21 2 kyr from the late paleocene to the early eocene suggesting a progressively weaker coupling of climate and the carbon cycle with time the higher amplitude 405 kyr cycles in the latest paleocene are associated with changes in bottom water temperature of 2 4 c while the most prominent 100 kyr paced cycles can be accompanied by changes of up to 1 5 c comparison of the 1262 record with a lower resolution but orbitally tuned benthic record for site 1209 in the pacific allows for verification of key features of the benthic isotope records which are global in scale including a key warming step at 57 7 ma

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

crystal poor rhyolites and rhyodacites from volcan tepetiltic mexico evidence for melt formation crystallization and eruption over short timescales abstract a detailed petrologic study is presented for six rhyolite and rhyodacite pumices that erupted from volcan tepetiltic in western mexico to determine the pre eruptive conditions of the magma reservoir as the volcano exited a 180 kya hiatus of activity rhyolite pumices are crystal poor 6 7 and minimally saturated in seven mineral phases plagioclase titanomagnetite ilmenite apatite quartz orthopyroxene clinopyroxene hornblende zircon in all samples plagioclase is the most abundant phenocryst phase and spans a range of composition of 20 30 mol an in each sample pre eruptive temperatures determined from two fe ti oxide geo thermometry range from 703 to 857 c maximum pre eruptive h2o contents determined from plagioclase hygrometry range from 5 0 8 9 wt where the most calcic plagioclase compositions correspond to the highest water contents comparison of compositions textures and sr and ba concentrations in plagioclase are used to determine phenocrysts from xenocrysts through comparison with experiments xenocrysts are identified in one sample comp 48 comparison of plagioclase abundances textures and sizes with those grown in the run products of experiments from the literature reveals that 1 the pumices were all likely super heated prior to crystallization 2 they experienced a low degree of undercooling induced by either degassing or cooling and 3 four of the pumices those with

explosive origin of silicic lava textural and δd h2o evidence for pyroclastic degassing during rhyolite effusion a long standing challenge in volcanology is to explain why explosive eruptions of silicic magma give way to lava a widely cited idea is that the explosive to effusive transition manifests a two stage degassing history whereby lava is the product of non explosive open system gas release following initial explosive closed system degassing direct observations of rhyolite eruptions indicate that effusive rhyolites are in fact highly explosive as they erupt simultaneously with violent volcanic blasts and pyroclastic fountains for months from a common vent this explosive and effusive overlap suggests that pyroclastic processes play a key role in rendering silicic magma sufficiently degassed to generate lava here we use precise h isotope and magmatic h2o measurements and textural evidence to demonstrate that effusion results from explosion s lavas are the direct product of brittle deformation that fosters batched degassing into transient pyroclastic channels tuffisites that repetitively and explosively vent from effusing lava our measurements show specifically that d h ratios and h2o contents of a broad suite of explosive and effusive samples from chaiten volcano hydrous bombs plinian pyroclasts tuffisite veins and lava define a single and continuous degassing trend that links wet explosive pyroclasts 1 6 wt h2o d 76 4 to dry obsidian lavas 0 13 wt h2o d 145 7 this geochemical pattern is best fit with batched degassing model that comprises small repeated closed system degassing steps followed by pulses of vapour extraction this degassing mechanism is made possible by the action of tuffisite veins which by tapping already vesicular or brecciated magma allow batches of exsolved gas to rapidly and explosively escape from relatively isolated closed system domains and large tracts of conduit magma by giving them long range connectivity even though tuffisite veins render magma degassed and capable of effusing they are nonetheless the avenues of violent gas and particle transport and thus have the potential to drive explosions when they become blocked or welded shut thus the effusion of silicic lava traditionally thought to be relatively benign process presents a particularly hazardous form of explosive volcanism

rheology of bubble bearing magmas the rheology of bubble bearing suspensions is investigated through a series of three dimensional boundary integral calculations in which the effects of bubble deformation volume fraction and shear rate are considered the behaviour of bubbles in viscous flows is characterized by the capillary number ca the ratio of viscous shear stresses that promote deformation to surface tension stresses that resist bubble deformation estimates of ca in natural lava flows are highly variable reflecting variations in shear rate and melt viscosity in the low capillary number limit e g in carbonatite flows bubbles remain spherical and may contribute greater shear stress to the suspension than in high capillary number flows in which bubble deformation is significant at higher ca deformed bubbles become aligned in the direction of flow and as a result contribute less shear stress to the suspension calculations indicate that the effective shear viscosity of bubbly suspensions at least for ca 0 5 is a weakly increasing function of volume fraction and that suspensions of bubbles are shear thinning field observations and qualitative arguments however suggest that for sufficiently large ca ca greater than about 1 the effective shear viscosity may be less than that of the suspending liquid bubbles reach their quasi steady deformed shapes after strains of order one for shorter times the continuous deformation of the bubbles results in continual changes of rheological properties in particular for small strains the effective shear viscosity of the suspension may be less than that of the liquid phase even for small ca results of this study may help explain previous experimental theoretical and field based observations regarding the effects of bubbles on flow rheology

analysing the topographic form of stratovolcanoes abstract the goal of this study is to explore ideal analytic functional forms that best fit the topographic shape of n 190 isolated stratovolcanoes from around the world using a stochastic model for the piling of lava flows to demonstrate one set of physical processes that give rise to a stratovolcano s topography we find that although the ideal form fits well for many stratovolcanoes there exist deviations from this shape particularly where the edifice is more protuberant than expected we explore sub surface factors such as the emplacement of magma beneath a volcano edifice that may be responsible for these deviations and estimate the relative contribution of dyke intrusions on the height and shape of a volcanic edifice versus the constructional piling of lava from this comparison we are able to gain more insight into the role of important subsurface physical factors such as chamber depth and total intruded volume we find that low basal ellipticity is a characteristic of nearly all volcanoes that fit the ideal stratovolcano form by fitting along each quadrant bisected by either a semi major or semi minor ellipse axis we find that the volcanoes chosen in this study fall into four groups 1 volcanoes that are axisymmetric and fit the ideal form well 2 volcanoes that are not axisymmetric but may be fit to the ideal form using different fitting parameters in each quadrant 3 volcanoes that have axisymmetric protuberant deviations in all quadrants and 4 volcanoes that have non axisymmetric protuberant deviations that are only present in a couple of quadrants we show that in some cases the non axisymmetry of volcanoes in category 2 may be understood as the result of the piling of eruptive products along a regional planar trend for edifices in categories 3 and 4 we model protuberant deviations as the result of a statistical distribution of elastic tensile dislocations representing dykes which emanate from a magma reservoir and cause uplift at the surface we support this interpretation of the excess topography in a few case studies where independent geologic and geophysical data corroborate our model results

rigid migration of unzen lava rather than flow abstract we have reassessed the mode of advance of lava erupted in the 1990s from unzen fugen dake volcano in northwestern kyushu japan the apparent viscosity of unzen lava had been estimated to be 0 9 4 2 1010 pa s from the observed lava surface velocity in 1991 using jeffreys model based on the assumption that the lava was a newtonian or bingham fluid in contrast the viscosity of synthetic groundmass glass derived from unzen lava had been measured in the laboratory at expected lava temperatures 780 c 880 c to be 1011 1013 pa s considerably higher than the viscosity based on field observation if the suspension effect of crystals is taken into consideration for groundmass glass several orders of magnitude higher viscosity than observed should be expected for unzen lava to seek the source of the disparity in viscosity estimates we first performed uniaxial compression viscometry on natural unzen lava samples collected in 1991 and thereby confirmed that the lava viscosity was actually higher than determined by field observations and equal to or higher than the fluid solid threshold viscosity 1012 pa s this suggests that the observational viscosity had been underestimated from reanalysis of the lava migration using video and photographs contemporaneous with the field based viscosity estimation we found that the lava behavior was far from that of a fluid apparently the lava lobe lost its fluidity at the flow front and instead advanced rigidly thereby indicating that the application of jeffreys model had incorrectly led us to underestimate viscosity although we used only the 1991 lava samples and image data we infer that rigid migration was common for all exogenous lava lobes during the 1991 1995 activity our comparative study demonstrates that cooled and or degassed lavas could show higher mobility than expected from experiment or model based viscosity apparently this occurs when the frictional force is smaller between lobe base and underlying slope than the viscous resistance inherent in lava

physicochemical models of effusive rhyolitic eruptions constrained with insar and dem data a case study of the 2011 2012 cordon caulle eruption abstract the 9 month long 2011 2012 eruption of cordon caulle southern andes chile is the best instrumentally recorded rhyolitic eruption to date and the first time that the effusion of a rhyolitic flow has been observed in detail we use interferometric synthetic aperture radar insar with time lapse digital elevation models dems and numerical models to study the dynamics of coupled magma reservoir deflation and lava effusion insar recorded 2 2 2 5 m of subsidence after the first three days of the eruption which can be modeled using a spheroidal magma reservoir at a depth of 5 km 20 km long and with a pressure drop of 20 30 mpa the source is elongated in the nw se direction and its large dimensions imply a large plumbing system active throughout the eruption and spanning neighboring volcanoes with a slight change in the geometry halfway through the effusive phase tandem x and pleiades dems record the extrusion of both the rhyolitic lava flow and the intrusion of a shallow laccolith around the eruptive vent after the third day of the eruption with a total volume of 1 45 km3 dre the laccolith was emplaced during the first month of the eruption during both the explosive and effusive stages of the eruption both the reservoir pressure drop and the extruded volume time series follow quasi exponential trends and can be explained by a model that couples the reservoir pressure decrease time and pressure dependent variations in the magma properties inside of the reservoir and conduit flow this model predicts both the temporal evolution and amplitude of both time series during the effusive phase and a magma compressibility of 10 10 pa 1 half the reported compressibility of the magma of the sub plinian explosive phase further we estimate that the reservoir contained 1 3 wt dissolved h2o at the onset of lava effusion with no exsolved co2 and h2o in the reservoir throughout the effusive phase this implies that the magma was significantly degassed after the explosive phase the remaining volatiles in the magma after the explosive stage might have caused magma fragmentation consistent with the hybrid explosive effusive style observed during the waning of the eruption

equilibration scales in silicic to intermediate magmas implications for experimental studies experimental phase equilibrium studies are increasingly being used for the determination of intensive variables p t fh2o fo2 in silicic to intermediate magmas in contrast silicic igneous bodies are now perceived as open periodically recharged systems involving only limited chemical equilibration thus the use of laboratory determined crystal liquid equilibrium data needs clarification here we review the field petrological and geochemical evidence concerning states and scales of chemical equilibrium in silicic magma bodies it is concluded that total chemical equilibrium is generally not the rule however a subsystem in local equilibrium the reactive magma can be identified equilibration scales in silicic magmas are rate limited either by diffusive flux in crystals dicl regime or by diffusive flux in the melt md regime the recognition that equilibrium in magmas is limited to a reactive subsystem requires phase equilibrium studies to be chemically scaled experiments either of total or partial equilibrium type should aim at a close reproduction of equilibrium states specific to natural systems the laboratory reconstruction of the natural equilibrium states guarantees a precise determination of the pre eruptive parameters and a reliable application of the experimental data to active volcanic systems

palaeoclimate evidence of vulnerable permafrost during times of low sea ice climate change in the arctic is occurring rapidly and projections suggest the complete loss of summer sea ice by the middle of this century1 the sensitivity of permanently frozen ground permafrost in the northern hemisphere to warming is less clear and its long term trends are harder to monitor than those of sea ice here we use palaeoclimate data to show that siberian permafrost is robust to warming when arctic sea ice is present but vulnerable when it is absent uranium lead chronology of carbonate deposits speleothems in a siberian cave located at the southern edge of continuous permafrost reveals periods in which the overlying ground was not permanently frozen the speleothem record starts 1 5 million years ago ma a time when greater equator to pole heat transport led to a warmer northern hemisphere2 the growth of the speleothems indicates that permafrost at the cave site was absent at that time becoming more frequent from about 1 35 ma as the northern hemisphere cooled and permanent after about 0 4 ma this history mirrors that of year round sea ice in the arctic ocean which was largely absent before about 0 4 ma ref 3 but continuously present since that date the robustness of permafrost when sea ice is present as well as the increased permafrost vulnerability when sea ice is absent can be explained by changes in both heat and moisture transport reduced sea ice may contribute to warming of arctic air4 6 which can lead to warming far inland7 open arctic waters also increase the source of moisture and increase autumn snowfall over siberia insulating the ground from low winter temperatures8 10 these processes explain the relationship between an ice free arctic and permafrost thawing before 0 4 ma if these processes continue during modern climate change future loss of summer arctic sea ice will accelerate the thawing of siberian permafrost a reconstruction of permafrost dynamics using speleothems from a siberian cave indicates that siberian permafrost is robust to warming when arctic sea ice is present but vulnerable when it is absent

the association of lava dome growth with major explosive activity vei 4 domehaz a global dataset investigation of the global eruptive records of particular types of volcanoes is a fundamental and valuable method of understanding what style of activity can be anticipated in the future and can highlight what might be expected or unusual in particular settings this paper investigates the relationship between large explosions volcanic explosivity index vei 4 and lava dome growth from 1000 ad to present and develops the domehaz database domehaz contains information from 397 dome forming episodes including duration of dome growth duration of pauses in extrusion extrusion rates and the timing and magnitude vei of associated large explosions major explosive activity when associated with dome growth is more likely to occur before dome growth rather than during or at the end of dome forming eruptions in most cases where major explosive activity has been associated with dome growth the eruptions occurred at basaltic andesite to andesitic volcanoes the most common type of dome forming volcano but a greater proportion of dacitic and rhyolitic dome growth episodes were associated with large explosions high extrusion rates 10 m3 s 1 seem to be associated with large explosions and may inhibit degassing or destabilize existing domes leading to explosive decompression large explosions may alternatively be followed by dome growth which represents the clearing of residual magma from the conduit relationships extracted from the global record can be used to construct probability trees for new and ongoing dome forming eruptions or can be used in conjunction with other types of event trees to aid in forecasting volcanic hazards during a crisis especially for volcanoes where data are sparse

sedimentation of long lasting wind affected volcanic plumes the example of the 2011 rhyolitic cordon caulle eruption chile sedimentation processes and fragmentation mechanisms during explosive volcanic eruptions can be constrained based on detailed analysis of grain size variations of tephra deposits with distance from vent and total grain size distribution tgsd grain size studies strongly rely on deposit exposure and in case of long lasting eruptions can be complicated by the intricate interplay between eruptive style atmospheric conditions particle accumulation and deposit erosion the 2011 cordon caulle eruption chile represents an ideals laboratory for the study of long lasting eruptions thanks to the good deposit accessibility in medial to distal area all layers analyzed are mostly characterized by bimodal grain size distributions with both the modes and the fraction of the coarse subpopulation decreasing rapidly with distance from vent and those of the fine subpopulation being mostly stable due to gradually changing wind direction the two subpopulations characterizing the deposit of the first 2 days of the eruption are asymmetrically distributed with respect to the dispersal axis the tgsd of the climactic phase is also bimodal with the coarse subpopulation representing 90 wt of the whole distribution polymodality of individual samples is related to size selective sedimentation processes while polymodality of the tgsd is mostly related to the complex internal texture e g size and shape of vesicles of the most abundant juvenile clasts the most representative tgsd could be derived based on a combination of the voronoi tessellation with a detailed analysis of the thinning trend of individual size categories finally preferential breakage of coarse pumices on ground impact was inferred from the study of particle terminal velocity

fayalite oxidation processes in obsidian cliffs rhyolite flow oregon this study investigates the oxidation of fayalite fe22 sio4 that is present in lithophysae from a rhyolite flow obsidian cliffs oregon textural chemical and structural analyses of the successive oxidation zones are used to constrain 1 the oxidation processes of olivine and 2 the role of temperature chemical diffusion and meteoric infiltration petrologic analyses and thermodynamic modeling show that the rhyolite flow emplaced at 800 950 c fayalite bearing lithophysae formed only in the core of the lava flow variations in the gas composition inside the lithophysae induced the oxidation of fayalite to a laihunite 1 m zone fe12 fe23 1 sio4 2 this zone is made of nano lamellae of amorphous silica sio2 and laihunite 3 m fe2 1 6fe3 1 6 0 8 sio4 2 hematite fe2o3 it probably formed by a nucleation and growth process in the fayalite fractures and defects and at fayalite crystal edges the laihunite 1 m zone then oxidized into an oxyfayalite zone with the composition fe2 0 52fe3 2 32 1 16 sio4 2 this second oxidation zone is made of lamellae of amorphous silica sio2 and hematite fe2o3 with a possible small amount of ferrosilite fe2 sio3 a third and outer zone composed exclusively of hematite is also present the successive oxidation zones suggest that there may be a mineral in the olivine group with higher fe3 content than laihunite 1 m the transformation of laihunite 1 m to this oxyfayalite phase could occur by a reaction such as formula 1 this would imply that fe3 can also be incorporated in the m1 site of olivine 1 embed mml math 1 gif

color change processes of a plinian pumice and experimental constraints of color change kinetics in air of an obsidian colors of plinian pumices were measured by spectrocolorimetry and their quantitative color parameters in the l a b color space were determined a series of heating experiments of obsidian was conducted to simulate the color change processes of rhyolitic glasses in these experiments following three stages of color change processes were observed stage i showed a rapid b yellowishness increase associated with fast dehydration controlled by water diffusivity dwater in stage ii a reddishness increase was accompanied by fe2 decrease both a increase and fe2 decrease can be simulated by a diffusion model obtained diffusivity doxidation were about two orders of magnitude smaller than dwater the a value increase after the oxidation in stage iii appeared to be quasi linear with time indicating the zeroth order reaction corresponding to the formation of hematite like structures in rhyolitic glasses the diffusion limited a increase model in stage ii was applied to a natural plinian pumice fall unit to evaluate time periods of color change processes through oxidation by air of fragmented rhyolitic materials

dynamics of wind affected volcanic plumes the example of the 2011 cordon caulle eruption chile the 2011 cordon caulle eruption represents an ideal case study for the characterization of long lasting plumes that are strongly affected by wind the climactic phase lasted for about 1 day and was classified as subplinian with plumes between 9 and 12 km above the vent and mass flow rate mfr on the order of 107 kg s 1 eruption intensity fluctuated during the first 11 days with mfr values between 106 and 107 kg s 1 this activity was followed by several months of low intensity plumes with mfr 106 kg s 1 plume dynamics and rise were strongly affected by wind during the whole eruption with negligible upwind spreading and sedimentation the plumes that developed on 4 6 and 20 22 june can be described as transitional i e plumes showing transitional behavior between strong and weak dynamics while the wind clearly dominated the rise height on all the other days resulting in the formation of weak plumes individual phases of the eruption range between volcanic explosivity indices veis 3 and 4 while the cumulative deposit related to 4 7 june 2011 is associated with veis 4 and 5 crosswind cloud and deposit dispersal of the first few days are best described by a linear combination of gravitational spreading and turbulent diffusion with velocities between 1 and 10 m s 1 downwind cloud velocity for the same days is best described by a linear combination of gravitational spreading and wind advection with velocities between 17 and 45 m s 1 results show how gravitational spreading can be significant even for subplinian and small moderate eruptions strongly advected by wind and with low richardson number and low mfr

3d gravity inversion and thermodynamic modelling reveal properties of shallow silicic magma reservoir beneath laguna del maule chile abstract active large volume silicic magma systems are potentially the most hazardous form of volcanism on earth knowledge of the location size and physical properties of silicic magma reservoirs is therefore important for providing context in which to accurately interpret monitoring data and make informed hazard assessments accordingly we present the first geophysical image of the laguna del maule volcanic field magmatic system using a novel 3d inversion of gravity data constrained by thermodynamic modelling the joint analysis of gravity and thermodynamic data allows for a rich interpretation of the magma system and highlights the importance of considering the full thermodynamic effects on melt density when interpreting gravity models of active magmatic systems we image a 30 km 3 low density volatile rich magma reservoir at around 2 km depth containing at least 85 melt hosted within a broader 115 km 3 body interpreted as wholly or partially crystallised 70 crystal cumulate mush our model suggests a magmatic system with shallow crystal poor magma overlying deeper crystal rich magma even though a large density contrast 600 kg m 3 with the surrounding crust exists the lithostatic load is 50 greater than the magma buoyancy force suggesting buoyancy alone is insufficient to trigger an eruption the reservoir is adjacent to the inferred extension of the troncoso fault and overlies the location of an intruding sill driving present day deformation the reservoir is in close proximity to the 2 0 km 3 nieblas rln eruption at 2 3 ka which we calculate tapped approximately 7 of the magma reservoir however we suggest that the present day magma system is not large enough to have fed all post glacial eruptions and that the location or size of the system may have migrated or varied over time with each eruption tapping only a small aliquot of the available magma the presence of a shallow reservoir of volatile rich near liquidus magma in close proximity to regional scale faulting has important implications for volcano monitoring and hazard mitigation

the origin of volcano tectonic earthquake swarms volcano tectonic vt seismicity is commonly recorded prior to and during eruptions vt seismicity may reflect stresses induced by dike propagation as indicated by propagating hypocenters and fault plane solutions fps reflecting regional stresses or stresses induced by dike inflation indicated by randomly distributed hypocenters and fps with pressure axes rotated 90 to regional maximum compression although numerical models of dike induced stresses indicate that both regimes should occur during dike emplacement this has not yet been observed according to published seismic data instead 90 rotated fps are observed in some cases while propagating hypocenters mark dike formation in other cases we suggest that differences in the seismic expression of upper crustal magma migration may result from differences in the regional tectonic setting and in the nature of magma wall rock interactions ultimately it may be possible to use information contained in vt seismicity to forecast changes in a volcano s behavior by establishing the characteristic stress field response for a given volcano or through a deeper understanding of the complex relationships between vt seismicity local crustal stresses and the physical mechanisms of magma migration

elastic internal multiple analysis and attenuation using marchenko and interferometric methods abstractconventional seismic processing aims to create data that contain only primary reflections whereas real seismic recordings also contain multiples as such it is desirable to predict identify and attenuate multiples in seismic data this task is more difficult in elastic solid media because mode conversions create families of internal multiples not present in the acoustic case we have developed a method to predict prestack internal multiples in general elastic media based on the marchenko method and convolutional interferometry it can be used to identify multiples directly in prestack data or migrated sections as well as to attenuate internal multiples by adaptively subtracting them from the original data set we developed the method on two synthetic data sets the first composed of horizontal density layers and constant velocities and the second containing horizontal and vertical density and velocity variations the full elastic method is computationally expensive and ideally uses data co

measuring effusion rates of obsidian lava flows by means of satellite thermal data abstract space based thermal data are increasingly used for monitoring effusive eruptions especially for calculating lava discharge rates and forecasting hazards related to basaltic lava flows the application of this methodology to silicic more viscous lava bodies such as obsidian lava flows is much less frequent with only few examples documented in the last decades the 2011 2012 eruption of cordon caulle volcano chile produced a voluminous obsidian lava flow 0 6 km3 and offers an exceptional opportunity to analyze the relationship between heat and volumetric flux for such type of viscous lava bodies based on a retrospective analysis of modis infrared data mirova system we found that the energy radiated by the active lava flow is robustly correlated with the erupted lava volume measured independently we found that after a transient time of about 15 days the coefficient of proportionality between radiant and volumetric flux becomes almost steady and stabilizes around a value of 5 106 j m 3 this coefficient i e radiant density is much lower than those found for basalts 1 108 j m 3 and likely reflects the appropriate spreading and cooling properties of the highly insulated viscous flows the effusion rates trend inferred from modis data correlates well with the tremor amplitude and with the plume elevation recorded throughout the eruption thus suggesting a link between the effusive and the coeval explosive activity modelling of the eruptive trend indicates that the cordon caulle eruption occurred in two stages either incompletely draining a single magma reservoir or more probably tapping multiple interconnected magmatic compartments

short magmatic residence times of quartz phenocrysts in patagonian rhyolites associated with gondwana breakup a key parameter in the study of magma evolution is the time scale on which magmatic processes occur using nanoscale secondary ion mass spectrometry nanosims sims and cathodoluminescence cl analyses we have measured titanium ti diffusion profiles in quartz phenocrysts from a jurassic rhyolite of the el quemado complex patagonia argentina providing new insights into the time scales of the associated volcanic processes cl imaging of quartz phenocrysts reveals oscillatory magmatic zoning we determined ti concentrations with sims and acquired multiple nanosims profiles across growth zones from core to rim all transects show sharp changes in the ti 48 si 29 ratio which correlate reasonably well with changes in cl intensity diffusion modeling of ti in quartz yields a surprisingly short time scale for quartz crystallization of 5 6 2 2 yr and a rapid crystal growth rate of 2 3 x 10 12 m s based on the observed quartz textures we suggest that the rhyolite erupted shortly after initial onset of crystallization followed by decompression driven quartz dissolution during fast magma ascent we further argue that the observed oscillatory zoning and the variation of the ti concentration of the quartz phenocryst does not reflect temperature pressure or titanium activity a ti changes of the magmatic system but rather is the result of growth kinetics which has important implications for the ti in quartz thermometry

the iugs systematics of igneous rocks in order to create a sustainable classification of igneous rocks which all geologists might use an international body was set up by the iugs the iugs subcommission on the systematics of igneous rocks in the course of creating the classification the subcommission has established ten principles for its construction and for defining an appropriate nomenclature the principles are 1 use descriptive attributes 2 use actual properties 3 ensure suitability for all geologists 4 use current terminology 5 define boundaries of rock species 6 keep it simple to apply 7 follow natural relations 8 use modal mineralogy 9 if mode not feasible use chemistry 10 follow terminology of other iugs advisory bodies these principles and their rationale have not previously been enunciated the classification separates and individually classifies the pyroclastic carbonatitic melititic lamprophyric and charnockitic rocks before entering the main qapf classification for plutonic and volcanic rocks which is based on the modal mineral proportions of quartz q alkali feldspar a and plagioclase p or of alkali feldspar a plagioclase p and feldspathoids f rocks with mafic content 90 have their own classification if the mineral mode cannot be determined as is often the case for volcanic rocks then a chemical classification of total alkalis versus silica tas is used the nomenclature for these classifications necessitates only 297 rock names out of the c 1500 that exist

magma ascent rates volcanoes can erupt explosively generating high columns of ash and occasional pyroclastic flows or they can erupt slowly forming lava flows and domes this variation reflects significant differences in mass eruption rate e g wilson et al 1980 mass eruption rates in turn are controlled by the rates of magma ascent through the volcanic conduit and the conduit size the magma ascent rate itself is a function of the pressure in the magma storage region the physical properties of the magma such as its density viscosity and crystallinity and the resistance to flow in the conduit that connects the magma storage zone to the surface papale and dobran 1994 mastin and ghiorso 2001 pinkerton et al 2002 sparks et al 2006 a number of important characteristics of volcanic eruptions are affected or controlled by the rate at which magma ascends from depth for example the bubble content i e vesicularity and the degree of crystallization that develop in the melt phase can be significantly different in rapidly vs slowly ascended magma in fact the inability of rapidly ascending magma to effectively lose exsolved gas may be one factor causing an eruption to change from effusive to explosive behavior as recently documented for the soufriere hills eruption on montserrat in the west indies sparks et al 1998 therefore in order to better understand the processes involved and the changes that occur in volcanic eruptions it is important to quantify the rates at which different magmas rise to the surface the fact that the rate of magma ascent controls a number of reactions that occur in volatile rich magmas suggests several ways to study magma ascent rates using reaction data and theoretical flow models one reaction that is a direct result of magma ascent is the exsolution of volatiles from the melt

did magma ascent rate control the explosive effusive transition at the inyo volcanic chain california rhyolitic eruptions often begin explosively and then shift to extrusions of lava it is widely believed that the style of eruption is dependent on magma flow rate within the conduit fast ascent leading to explosive eruption and slow ascent favoring effusive behavior currently the velocity of rhyolite magma flowing in a conduit is unknown and therefore eruption models remain untested against geologic evidence of magma ascent we show that explosively erupted rhyolite magma from the inyo volcanic chain ascended slowly centimeters per second at same rates as the dome building phases we propose that the explosive effusive transition sub plinian rhyolite eruptions is governed by the alleviation of exsolved volatile pressure in the shallow conduit rather than the magma flow rate

an experimental study of the kinetics of decompression induced crystallization in silicic melt 1 experiments were conducted to study the temporal evolution of feldspar crystallization kinetics during isothermal decompression pinatubo dacite was held at 780 c 220 mpa fo2 nno 2 h2o saturated conditions for an equilibration period decompressed to final pressures pf ranging from 175 to 5 mpa and then held for 0 3 931 hours according to the plagioclase liquidus curve in ph2o t space for the relevant melt composition these decompressions impose effective undercoolings teff of 34 266 c growth of preexisting phenocrysts and newly formed sparse microlites dominate crystallization at 75 pf 150 mpa teff 34 93 c and equilibrium crystal modes are achieved in 168 hours microlite nucleation is the dominant transformation process for 10 pf 50 mpa teff 125 241 c and chemical equilibrium is not attained by 168 hours under these conditions slow steady decompressions typically produced normally zoned euhedral and planar faceted feldspar crystals although anhedral morphologies were produced at very low pf contrary to expectation slowly decompressed samples were usually further from chemical equilibrium than rapidly decompressed samples after similar durations below the initial pressure although counterintuitive these trends are consistent with new constraints on the relative rates of feldspar nucleation and growth controlled by teff and melt viscosity experienced during each decompression path analysis of liquid to solid transformation kinetics using ttt style diagrams shows that crystallization occurs most rapidly at 100 mpa by a crystal growth mechanism the next most efficient crystallization conditions are at 25 mpa in a crystal nucleation dominated regime

a compositional tipping point governing the mobilization and eruption style of rhyolitic magma measurements of the composition dependent viscosity of rhyolitic magma reveal a tipping point that changes the physical properties of the melt and controls the transition between effusive and explosive eruptions calcalkaline rhyolites produce the largest explosive volcanic eruptions but these eruptions can switch repeatedly between being effusive and explosive this is difficult to attribute to the rheological effects of magma water content or crystallinity danilo di genova and co authors report the viscosity of a series of melts spanning the compositional range of the yellowstone rhyolitic volcanic system they find that within a narrow compositional zone melt viscosity increases by up to two orders of magnitude which they propose to be the consequence of melt structure reorganization the authors confirm that such a compositional tipping point exists in the global geochemical record of rhyolites which separates effusive from explosive deposits they conclude that the anhydrous water free composition of calcalkaline rhyolites is decisive in determining mobilization and eruption dynamics of the earth s largest volcanic systems the most viscous volcanic melts and the largest explosive eruptions1 on our planet consist of calcalkaline rhyolites2 3 these eruptions have the potential to influence global climate4 the eruptive products are commonly very crystal poor and highly degassed yet the magma is mostly stored as crystal mushes containing small amounts of interstitial melt with elevated water content5 it is unclear how magma mushes are mobilized to create large batches of eruptible crystal free magma further rhyolitic eruptions6 7 8 can switch repeatedly between effusive and explosive eruption styles and this transition is difficult to attribute to the rheological effects of water content or crystallinity9 10 here we measure the viscosity of a series of melts spanning the compositional range of the yellowstone volcanic system and find that in a narrow compositional zone melt viscosity increases by up to two orders of magnitude these viscosity variations are not predicted by current viscosity models11 12 and result from melt structure reorganization as confirmed by raman spectroscopy we identify a critical compositional tipping point independently documented in the global geochemical record of rhyolites at which rhyolitic melts fluidize or stiffen and that clearly separates effusive from explosive deposits worldwide this correlation between melt structure viscosity and eruptive behaviour holds despite the variable water content and other parameters such as temperature that are inherent in natural eruptions thermodynamic modelling demonstrates how the observed subtle compositional changes that result in fluidization or stiffening of the melt can be induced by crystal growth from the melt or variation in oxygen fugacity however the rheological effects of water and crystal content alone cannot explain the correlation between composition and eruptive style we conclude that the composition of calcalkaline rhyolites is decisive in determining the mobilization and eruption dynamics of earth s largest volcanic systems resulting in a better understanding of how the melt structure controls volcanic processes

emplacement of the rocche rosse rhyolite lava flow lipari aeolian islands the rocche rosse lava flow marks the most recent rhyolitic extrusion on lipari island italy and preserves evidence for a multi stage emplacement history due to the viscous nature of the advancing lava 108 to 1010 pa s indicators of complex emplacement processes are preserved in the final flow this study focuses on structural mapping of the flow to highlight the interplay of cooling crust formation and underlying slope in the development of rhyolitic lavas the flow is made up of two prominent lobes small 0 2 m scale folding and a channelled geometry foliations dip at 2 4 over the flatter topography close to the vent and up to 30 50 over steeper mid flow topography brittle faults tension gashes and conjugate fractures are also evident across flow heterogeneous deformation is evident through increasing fold asymmetry from the vent due to downflow cooling and stagnation a steeper underlying topography mid flow led to development of a channelled morphology and compression at topographic breaks resulted in fold superimposition in the channel we propose an emplacement history that involved the evolution through five stages each associated with the following flow regimes 1 initial extrusion crustal development and small scale folding 2 extensional strain stretching lineations and channel development over steeper topography 3 compression at topographic break autobrecciation lobe development and medium scale folding 4 progressive deformation with stagnation large scale folding and re folding and 5 brittle deformation following flow termination the complex array of structural elements observed within the rocche rosse lava flow facilitates comparisons to be made with actively deforming rhyolitic lava flows at the chilean volcanoes of chaiten and cordon caulle offering a fluid dynamic and structural framework within which to evaluate our data

deposition of the 2011 2012 cordon caulle tephra chile 40 s in lake sediments implications for tephrochronology and volcanology tephras preserved in lake sediments are commonly used to synchronize sedimentary archives of climate and environmental change and to correlate them with terrestrial environments they also provide opportunities to reconstruct volcanic explosive activity e g eruption frequency and tephra dispersal although sedimentary processes may affect the record of tephras in lakes lake sediments are generally considered as one of the best archives of tephra stratigraphy the 2011 2012 eruption of cordon caulle volcano chile 40 degrees s offered an ideal opportunity to study the processes affecting tephra deposition in lakes although the prevailing westerlies transported the erupted pyroclastic material away from nearby puyehue lake the tephra was identified within this relatively large lake with a thickness ranging from 1 to 10cm this is in contrast with smaller lakes where tephra thickness was in agreement with ashfall distribution maps geomorphological observations and sedimentological analyses provide evidence that the tephra deposited in puyehue lake entirely consists of material reworked from the upper watershed transported by rivers and distributed by lake currents according to particle size and density our results have important implications for tephrochronology and volcanology they suggest that 1 lakes do not act as passive tephra traps 2 lakes with large watersheds record more eruptions than smaller lakes which only register direct ashfalls affecting conclusions regarding the recurrence of volcanic eruptions and 3 using lakes with large watersheds for isopach mapping systematically leads to an overestimation of erupted tephra volumes smaller lakes with limited drainage basins are generally better suited for volcanological studies

northern european summer temperature variations over the common era from integrated tree ring density records tree ring chronologies of maximum latewood density are most suitable to reconstruct annually resolved summer temperature variations of the late holocene the two longest such chronologies have been developed in northern europe stretching back to the 2nd century bc and the 5th century ad we show where similarities between the two chronologies exist and combine portions of both into a new summer temperature reconstruction for the common era to minimize the transfer of potential biases we assess the contribution of the candidate reconstructions measurements and exclude data i from exceptionally young and old trees and ii produced by different laboratory technologies our new composite reconstruction reveals warmer conditions during roman medieval and recent times separated by prolonged cooling during the migration period and little ice age twentieth century warmth as indicated in one of the existing density records is reduced in the new reconstruction also affecting the overall millennial scale cooling trend over the late holocene 0 30uc per 1000 years due to the reduced biological memory typical for tree ring density measurements the new reconstruction is most suitable for evaluating the rate and speed of abrupt summer cooling following large volcanic eruptions copyright 2014 john wiley sons ltd

late quaternary tephrostratigraphy of southern chile and argentina abstract the southern and austral volcanic zones of the andes comprise 74 volcanic centres with known post glacial activity at least 21 of these have had one or more large explosive eruptions in the late quaternary dispersing tephra over vast areas these tephra layers therefore have great potential as tephrochronological marker horizons in palaeoenvironmental studies in southern chile and argentina a region that is particularly useful to study climate dynamics of the southern hemisphere however to date tephrochronology has rarely been fully utilised in this region as a correlation and dating tool here we review the existing post glacial tephrostratigraphic record of the southern and austral volcanic zones and compile a database of known occurrences of tephra from these volcanoes in ice and lacustrine marine peat and cave sediment records we address the inconsistencies in and revisions of the tephrostratigraphies presented in prior literature and discuss the challenges in correlating tephras and the limitations of the tephrostratigraphic record in this area this study highlights the many gaps that still exist in our knowledge of the eruptive histories of these volcanoes but also reveals the largely under utilised potential of tephra as a correlation tool in this region this is exemplified by the severe lack of adequate geochemical analysis of tephra layers preserved in many lacustrine and peat sediment sections which are particularly important tephrostratigraphic records in southern chile and argentina due to the paucity of surface preservation

a comparison of the sedimentary records of the 1960 and 2010 great chilean earthquakes in 17 lakes implications for quantitative lacustrine palaeoseismology seismically induced event deposits embedded in the sedimentary infill of lacustrine basins are highly useful for palaeoseismic reconstructions recent well documented great megathrust earthquakes provide an ideal opportunity to calibrate seismically induced event deposits for lakes with different characteristics and located in different settings this study used 107 short sediment cores to investigate the sedimentary impact of the 1960 mw 9 5 valdivia and the 2010 mw 8 8 maule earthquakes in 17 lakes in south central chile i e lakes negra lo encanado aculeo vichuquen laja villarrica calafquen pullinque pellaifa panguipulli neltume rinihue ranco maihue puyehue rupanco and llanquihue a combination of image analysis magnetic susceptibility and grain size analysis allows identification of five types of seismically induced event deposits i mass transport deposits ii in situ deformations iii lacustrine turbidites with a composition similar to the hemipelagic background sediments lacustrine turbidites type 1 iv lacustrine turbidites with a composition different from the background sediments lacustrine turbidites type 2 and v megaturbidites these seismically induced event deposits were compared to local seismic intensities of the causative earthquakes eyewitness reports post earthquake observations and vegetation and geomorphology of the catchment and the lake megaturbidites occur where lake seiches took place lacustrine turbidites type 2 can be the result of i local near shore mass wasting ii delta collapse iii onshore landslides iv debris flows or mudflows or v fluvial reworking of landslide debris on the contrary lacustrine turbidites type 1 are the result of shallow mass wasting on sublacustrine slopes covered by hemipelagic sediments due to their more constrained origin lacustrine turbidites type 1 are the most reliable type of seismically induced event deposits in quantitative palaeoseismology because they are almost exclusively triggered by earthquake shaking moreover they most sensitively record varying seismic shaking intensities the number of lacustrine turbidites type 1 linearly increases with increasing seismic intensity starting with no lacustrine turbidites type 1 at intensities between v and vi and reaching 100 when intensities are higher than vii combining different types of seismically induced event deposits allows the reconstruction of the complete impact of an earthquake

eruption mechanisms and short duration of large rhyolitic lava flows of yellowstone abstract large volume effusive rhyolite lava flows are a common but poorly understood occurrence from silicic volcanic centers we integrate characterization of lava flow topographic morphology and petrographic textures and zoning of crystals with physical models of viscous fluid flow in order to interpret the eruption durations and discharge rates for the most recent effusive volcanic eruptions from yellowstone these large volume 10 70 km3 crystal poor rhyolite lavas erupted within the yellowstone caldera as 100 200 m thick flows and have a cumulative erupted volume of 650 km3 that is similar to less frequent caldera forming events but occur as individual eruptions spread over 100 ka most of this work is focused on the axisymmetric 124 ka 50 km3 summit lake flow we examined crystallinity major and trace element concentrations oxygen and hydrogen isotopic values and quartz morphology and zoning in samples from the center to margin of this flow water contents down to 0 1 wt and d values of 110 are low and require closed system degassing until near surface lithostatic pressure while major elements are consistent with water undersaturated pre eruptive storage and crystallization at 4 8 km depth we found some evidence for subtle km scale zoning within the lavas but describe significant microscopic scale compositional diversity including sharp boundaries between high ti cores and 200 m thick rims on quartz phenocrysts embayed quartz external morphology and rim growth may be the result of undercooling during coalescence of magma bodies during shallow transport between dikes and sills modeling the emplacement of the lava flow as a simple viscous fluid suggests that emplacement of rhyolite lava at 800 c occurred over 2 to 5 yrs with high discharge rates 100 m3 s such high magma discharge rates are accommodated through 6 km long fissures that allow for slower magma ascent velocities of 10 yr flow durations and significant cooling of the flow front that should result in a more complex compound flow morphology than observed higher temperatures require unrealistically wide 50 m dike widths to accommodate large discharge rates petrographic and isotopic evidence from crystals suggests recharge and merger of individual magma batches occurs on a similar timescale to the eruption duration and may directly cause overpressure and emplacement of these rhyolite lava flows from a shallow ephemeral magma chamber large volume rhyolitic lavas are able to erupt effusively through elongate fissures that utilize preexisting zones of crustal weaknesses such as ring fractures less common explosive eruptions at yellowstone may result when ascending magmas are forced through narrower conduits or when recharge rates are especially high the results of this study provide a unique top down constraint on effusive eruption rates make new interpretations of common petrographic textures and presents a comprehensive model for eruption control

locating magma reservoirs using insar and petrology before and during the 2011 2012 cordon caulle silicic eruption abstract we combine petrological and insar observations to probe the origin of deformation of cordon caulle volcano in southern chile before and during the 2011 2012 eruption the erupted rhyodacite is crystal poor and was stored at about 900 c with ca 4 wt h2o and 220 ppm co2 in the melt corresponding to a storage depth of about 6 7 km in addition to a previously documented 2007 2008 deformation episode we find three pre eruptive deformation episodes the first between 2008 and 2009 that covers 400 km2 with a maximum uplift of 18 5 cm the second between february and march 2010 that covers 20 km2 with a maximum uplift of 10 cm and the third between march and may 2011 that covers 40 km2 with a maximum uplift of 6 cm modeling of the 2008 2009 deformation episode suggests source depths of about 5 9 km consistent with the petrologically determined magma storage depth the sum of modeled source volume changes from 2007 to 2009 is about 12 times smaller than the observed erupted volume our calculation of magma compressibility shows that there must have been a significant volume of pre existing magma in the reservoir to account for this difference co eruptive subsidence shows evidence for three distinct magma sources and pre eruptive inflation is seen at two of the three sources modeled deformation sources are located 2 10 km from the 2011 2012 eruptive vent and coincide with the vents from previous historical eruptions 1921 22 1960 and with the neighboring puyehue volcano this implies the existence of an interconnected magma plumbing system that allows for pressure transfer and which covers an area of at least 20 km2 thus the deformation and geochemical characteristics of cordon caulle resemble those of a large silicic caldera system the presence of a mafic crystal clot demonstrates the existence of basaltic melts in the silicic reservoir but we find that the mafic magmas reached the reservoir at least several hundred years before eruption therefore if the pre eruptive deformation was caused by replenishment to a shallow reservoir the new magma was silicic and similar to the pre existing magma and or there was no interaction between the two we find that pre eruptive deformation can occur in pulses and reach its peak years before eruption and thus lack of deformation does not necessarily imply that eruption is not imminent

six hundred thirty eight years of summer temperature variability over the bhutanese himalaya high resolution tree ring reconstructions from the himalaya provide essential context for assessing impacts of future climate change on regional water reserves and downstream agriculture here we e

ash production and dispersal from sustained low intensity mono inyo eruptions recent rhyolitic volcanism has demonstrated that prolonged low intensity ash venting may accompany effusive dome formation we examine the possibility and some consequences of episodes of extended weak ash venting at the rhyolitic mono inyo chain in eastern california we describe ash filled cracks within one of the youngest domes panum crater which provide a textural record of ash venting during dome effusion we use synchrotron based x ray computed tomography to characterize the particles in these tuffisites particle sizes in well sorted tuffisite layers agree well with grain size distributions observed during weak ash venting at soufriere hills volcano montserrat and yield approximate upper and lower bounds on gas velocity and mass flux during the formation of those layers we simulate ash dispersal with ash3d to assess the consequences of long lived mono inyo ash venting for ash deposition and the accompanying volcanic hazards our results highlight the sensitivity of large scale outcomes of volcanic eruptions to small scale processes

h2o content and temperature limit the explosive potential of rhyolite magma during plinian eruptions abstract recent rhyolite eruptions on earth have demonstrated their capacity to produce a multitude of hazards including ash formation lasting months and impacting the large reaches of the southern hemisphere nevertheless the underlying mechanisms driving these eruptions are not yet fully understood magmatic volatiles especially h2o dictate whether volcanic eruptions proceed explosively or effusively experimental evidence for the role played by h2o in driving explosive fragmentation is rare in particular in the eruption of rhyolitic magma here we show that when hydrous rhyolitic obsidians from chaiten volcano chile are experimentally heated above their glass transition temperatures at ambient 1 atm conditions two different behaviors result depending on starting h2o concentration and temperature obsidians vesiculate to stable or quasi steady state foams when h2o is 1 wt for a wide range of temperatures 728 1032 c but will explode within just tens of seconds 874 c explosive activity occurs above chaiten s estimated eruption temperature but for lower temperatures only foaming occurs whether a foaming sample remains coherent or explodes depends on two interrelated factors the peclet number pe a dimensionless ratio of diffusive and viscous timescales and the timescale or rate of decompression which is dictated in part by the h2o vapor pressure gradient between bubbles and atmosphere at or above 1 4 wt h2o and for a range of permissible chaiten eruption temperatures 780 825 c pe is large 10 meaning viscous deformation aiding vapor expansion is the dominant mode of growing bubbles consequently vesiculation can proceed rapidly due to high initial overpressure and low melt viscosity until the point is reached that the melt deforms at a rate greater than its relaxation rate resulting in fragmentation below 1 4 wt h2o and for temperatures equal to or lower than chaiten s eruption decompression and deformation rates inferred from experimental clast expansion and bubble growth behavior are at least an order of magnitude smaller than the explosive cases which is insufficient for critical melt rupturing pe estimations highlight the first order influence of temperature and h2o content on physical degassing behavior since the starting h2o content and temperature dictate many the parameters that govern bubble growth pressure gradient melt viscosity and chemical diffusivity our experiments shed light on what limits fragmentation in natural eruptions and offer an alternative explanation for h2o contents measured in plinian fall deposits from chaiten and other rhyolite centers in essence pyroclastic obsidian h2o contents could reflect temperature and p h2o limitations on fragmentation furthermore since foam expansion under low p high t h2o conditions can foster strain rates in excess of the melt s relaxation rate and thus drive fragmentation we contend that in addition to rapid magma ascent and high magma supply rates rapid clast expansion under low pressure conditions may also be important for explosive magma fragmentation

coupled effect of magma degassing and rheology on silicic volcanism abstract explosive volcanism such as the 1991 mt pinatubo philippines and the 2008 mt chaiten chile eruptions is caused by violent vesiculation of hydrous magma however gas may efficiently separate from magma owing to the enhancement of gas permeability by shear deformation of magma flowing in a volcanic conduit this makes it difficult to maintain the driving force of explosive volcanism although explosive volcanism is actually common here we propose that shear localization in a volcanic conduit controls the eruption style and explosivity based on deformation experiments of vesicular magma linked with synchrotron radiation x ray radiography and computed tomography we observed for the first time in situ that the shear localization caused magma fracturing and formed a slip plane and thus inhibited deformation and outgassing elsewhere we also observed the compaction of vesicular magma into a dense lava as a result of outgassing when shear localization did not occur in a natural setting shear localizes along the edges of a volcanic conduit where the strain rate is high causing a highly permeable fracturing layer to form at the conduit s edge and leaving less sheared and less outgassed magma at its center the less outgassed magma in the center may ascend rapidly and cause explosive volcanism non explosive lava effusion may occur only when shear localization does not occur effectively this new view explains the rapid ascent of viscous magma and the formation of pyroclasts with contrasting vesicularity pyroclastic obsidian and highly vesiculated pumice

magmatic evolution of the puyehue cordon caulle volcanic complex 40 s southern andean volcanic zone from shield to unusual rhyolitic fissure volcanism abstract magmas erupted from quaternary volcanoes of southern andes between 37 and 46 s latitude are mainly basaltic to andesitic however pccvc 40 s shows a singular magmatic evolution due to the abnormal evacuation of rhyolites especially in the last 100 ka in addition pccvc is the result of juxtaposing products from the nw trending alignment of cordillera nevada caldera cordon caulle fissure volcano and the puyehue stratocone using 40 ar 39 ar and 14 c geochronology it can be established that they evolved since ca 500 ka as coeval but separated vents with a first stage of shield volcanism followed by repeated collapses that formed an internal nw elongated graben from ca 100 ka volcanic activity occurred in both a fissure system cordon caulle and a central volcano puyehue holocene explosive eruptions mainly in the puyehue crater accompanied the dome growing along a nw trending fissure system last historical eruptions were in 1921 and 1960 when nw fissures of cordon caulle fed rhyodacitic lava flows in 1960 the fissure eruption was triggered by a remote mw 9 5 thrust earthquake cordillera nevada caldera presents a reduced compositional range 52 63 sio 2 and geochemical features of low pressure magma mixing and assimilation instead cordon caulle and puyehue volcanoes have a wide silica range 48 71 sio 2 and an outstanding affinity which can be modelled with initial high pressure fractional crystallization moderate magma mixing and subsequent low pressure fractional crystallization from a common parental source the exceptional magmatic evolution and eruptive style of pccvc in southern andes could be related with the physics of the plumbing system which in turn can be controlled by external factors as the structure of the continental crust and the ongoing stress regime

petrologic indicators of preeruption magma dynamics new phase equilibria experiments on dacite from the june 1991 eruption of mount pinatubo philippines allow calibration of a geobarometer for matrix glass at pressures of 160 220 mpa comparison with natural glass compositions suggests equilibration at lower water fugacity mathit f h 2 o than inferred from al in hornblende geobarometry the disparity between geobarometric techniques may be explained by a decrease in mathit f h 2 o and consequent crystallization several weeks before eruption a time period too short for hornblende reequilibration reduced mathit f h 2 o could have resulted from processes associated with basalt magma injection including 1 late stage magma ascent under h 2 o saturated conditions or 2 influx of other volatiles co 2 so 2 into the dacite magma system

transitions between explosive and effusive eruptions of silicic magmas water rich silicic magmas may erupt explosively giving rise to massive columns of fragmented ash1 5 or effusively as viscous bubbly lavas to form lava domes6 8 complex cycles of explosive and effusive eruptions are often observed8 12 although these two eruption mechanisms have been modelled independently1 8 the conditions under which a volcano exhibits a particular style of eruption are not known and the transitions between eruption styles are poorly understood by modelling the ascent of magma along a permeable conduit we show here that for small magma chamber overpressures the style of eruption explosive or effusive is dependent on the magma flow rate we also identify a critical overpressure above which only explosive eruptions occur complex eruption sequences follow naturally for example if a shallow magmatic system is supplied with magma at an intermediate flow rate the eruption will be slow and effusive until the chamber over pressure becomes too large an explosive eruption then relieves the overpressure and an effusive eruption style resumes we suggest that monitoring of temporal variations in chamber overpressure for example by measuring ground deformation can be used to assess whether a passively effusing volcano has the potential to erupt explosively

sulfur budget and global climate impact of the a d 1835 eruption of cosiguina volcano nicaragua large explosive volcanic eruptions can inject massive amounts of sulfuric gases into the earth s atmosphere and in so doing affect global climate the january 1835 eruption of cosiguina volcano nicaragua ranks among the americas largest and most explosive historical eruptions but whether it had effects on global climate remains ambiguous new petrologic analyses of the cosiguina deposits reveal that the eruption released enough sulfur to explain a prominent ca ad 1835 sulfate anomaly in ice cores from both the arctic and antarctic a compilation of temperature sensitive tree ring chronologies indicates appreciable cooling of the earth s surface in response to the eruption consistent with instrumental temperature records we conclude that this eruption represents one of the most important sulfur producing events of the last few centuries and had a sizable climate impact rivaling that of the 1991 eruption of mount pinatubo

explosive to effusive transition during the largest volcanic eruption of the 20th century novarupta 1912 alaska silicic volcanic eruptions commonly show abrupt shifts between powerful and dangerous plinian explosive episodes and gentle effusion of lava whether the onset of magma permeability and ensuing gas loss controls these transitions has been a subject of debate we measured porosities and permeabilities in samples from the a d 1912 eruption of novarupta volcano alaska and analyzed them within the context of a well constrained eruptive sequence that encompasses sustained explosive and effusive activity for the explosive samples we find that the degree of vesicle interconnectivity measured as the ratio of connected to total porosity decreases with phenocryst content and with increasing eruption intensity permeabilities of explosive samples show a weak dependence on porosity dome samples are not significantly different in permeability but are of lower porosity which together with abundant flattened vesicles is consistent with bubble collapse by permeable outgassing quantitative analysis indicates that outgassing alone was insufficient to affect the transition to effusive activity rather the change from explosive to effusive activity was probably a consequence of high versus low magma ascent rates

evidence for explosive silicic volcanism on the moon from the extended distribution of thorium near the compton belkovich volcanic complex we reconstruct the abundance of thorium near the compton belkovich volcanic complex on the moon using data from the lunar prospector gamma ray spectrometer we enhance the resolution via a pixon image reconstruction technique and find that the thorium is distributed over a larger 40km 75 km area than the 25km 35 km high albedo region normally associated with compton belkovich our reconstructions show that inside this region the thorium concentration is 14 26ppm we also find additional thorium spread up to 300km eastward of the complex at 2 ppm the thorium must have been deposited during the formation of the volcanic complex because subsequent lateral transport mechanisms such as small impacts are unable to move sufficient material the morphology of the feature is consistent with pyroclastic dispersal and we conclude that the present distribution of thorium was likely created by the explosive eruption of silicic magma

thermogenic methane release as a cause for the long duration of the petm the paleocene eocene thermal maximum petm 56 ma was a 170 000 y 170 kyr period of global warming associated with rapid and massive injections of 13c depleted carbon into the ocean atmosphere system reflected in sedimentary components as a negative carbon isotope excursion cie carbon cycle modeling has indicated that the shape and magnitude of this cie are generally explained by a large and rapid initial pulse followed by 50 kyr of 13c depleted carbon injection suggested sources include submarine methane hydrates terrigenous organic matter and thermogenic methane and co2 from hydrothermal vent complexes here we test for the contribution of carbon release associated with volcanic intrusions in the north atlantic igneous province we use dinoflagellate cyst and stable carbon isotope stratigraphy to date the active phase of a hydrothermal vent system and find it to postdate massive carbon release at the onset of the petm crucially however it correlates to the period within the petm of longer term 13c depleted carbon release this finding represents actual proof of petm carbon release from a particular reservoir based on carbon cycle box model i e long term ocean atmosphere sediment carbon cycle reservoir loscar model experiments we show that 4 12 pulses of carbon input from vent systems over 60 kyr with a total mass of 1 500 pg of c consistent with the vent literature match the shape of the cie and pattern of deep ocean carbonate dissolution as recorded in sediment records we therefore conclude that ch4 from the norwegian sea vent complexes was likely the main source of carbon during the petm following its dramatic onset

cooling and crystallization of rhyolite obsidian lava insights from micron scale projections on plagioclase microlites abstract to reveal the cooling process of a rhyolite obsidian flow we studied the morphology of plagioclase microlites in the tokachi ishizawa lava of shirataki northern hokkaido japan where the structure of the lava can be observed from obsidian at the base of the flow to the innermost rhyolite needle like micron scale textures known as projections occur on the short side surfaces of the plagioclase microlites using fe sem we discovered a positive correlation between the lengths and spacings of these projections on the basis of the instability theory of an interface between melt and crystal and to understand the length and spacing data we developed a model that explains the positive correlation and allows us to simultaneously estimate growth rates and growth times applying the model to our morphological data and the estimated growth rates and growth times we suggest that the characteristics of the projections reflect the degree of undercooling which in turn correlates with lava structure the obsidian at the margin of the flow experienced a higher degree of undercooling than the interior rhyolite the newly developed method provides insights into the degree of undercooling during the final stages of crystallization of a rhyolitic lava flow

storage conditions of the 29 ka rhyolitic guangoche white pumice sequence los azufres volcanic field central mexico abstract rhyolitic magmas in occasions can be related to explosive eruptions in active volcanoes that may not exhibit precursory signals making them very dangerous for the surrounding communities to understand the pre eruptive conditions of such magmas it is important to decipher the mechanisms capable to produce these explosive events in this study we analyzed the pre eruptive conditions of guangoche stratovolcano located to the southwest of the los azufres volcanic field in the central part of the trans mexican volcanic belt during the late pleistocene guangoche generated three plinian subplinian eruptions and some effusive eruptions all of them involving high silica rhyolitic magmas one of these plinian events vei 5 occurred 29 ka and deposited the white pyroclastic sequence wps this eruption ejected 0 7 km3 dre volume of rhyolitic magma and deposited a pumice fallout followed by three pumice rich pyroclastic density currents petrography combined with mineral composition melt inclusions and water saturated phase equilibria experiments were used to determine the evolution of the magma storage of the wps event prior to the eruption the magma was a crystal poor 14 vol rhyolite containing the following mineral assemblage biotite fe ti oxides amphibole sanidine and quartz set in a rhyolitic matrix 77 3 wt sio2 with low ba 121 16 7 ppm eu 0 15 0 02 ppm and sr 37 7 ppm based on fe ti oxythermometers and phase equilibria experiments we determine that the magma was stored between 75 and 100 mpa 3 4 km depth at a temperature of 769 8 c moreover h2o co2 dissolved in quartz melt inclusions and the textural features of the mineral assemblage of the wps products provided insights of the presence of a quartzo feldspathic crystal mush located at minimum depths between 4 3 and 9 5 km 98 218 mpa large sanidine quartz plagioclase and amphibole phenocrysts and mineral clots in the wps rocks represent assimilated parts from this mush by a melt extraction process probably triggered by the arrival of a relatively hotter magma at the base of the crystal mush which in turn caused reheating and partial melting of the quartzo feldspathic crystal mush generating the 29 ka rhyolitic wps magma

holocene tephra succession of puyehue cordon caulle and antillanca casablanca volcanic complexes southern andes 40 41 s abstract puyehue cordon caulle and antillanca volcanic complexes are two of at least 50 active frontal arc volcanoes that define the 1400 km long southern volcanic zone of chile holocene tephra deposits in chile and argentina 40 41 s up to 100 km east of these volcanoes comprise at least five voluminous 1 to 8 km 3 pyroclastic fall layers that preceded several recently deposited cordon caulle pumice fallouts field observations of proximal medium and distal facies of the deposits in conjunction with geochronology and geochemistry of the volcanic complexes indicate that three fall layers are derived from puyehue volcano puyehue 1 and 2 and mil hojas whereas two are sourced from the antillanca complex playas blanca negra and nahuel huapi tephra 20 km to the south the oldest tephra calibrated 14 c age 10 49 0 12 ka 2 found only at medium distal facies is deposited directly on granitic moraine boulders and consists of deeply weathered orange dacitic pumice lapilli the next prominent tephra at 7 ka comprises dacitic pumice and its age is equivalent to a rhyodacitic dome exposed in the puyehue summit crater above these deposits there are phases of a complex eruption consisting of a conspicuous compositionally zoned tephra it also comprises a pyroclastic density current together with lithic rich and scoriaceous fallout deposits mineralogical geochemical and sr isotope evidence plus the isopach maps confirm that this sequence of eruptive events is sourced from antillanca at 1932 68 yrbp the total volume of this eruptive sequence exceeds 8 km 3 making it the largest holocene eruption from either volcanic complex this eruption was likely responsible for the destruction of an ancestral antillanca volcano and the formation of a 4 5 km diameter caldera a distinctive younger unit in the region is a voluminous rhyodacitic pumice fall calibrated 14 c age 1 11 0 07 ka above which a series of several alternating dark lithic and pumice lapilli beds accumulated correlation with proximal deposits indicates that the 1 11 ka eruption was derived from puyehue and destroyed 3 km 3 of rhyodacitic domes at this volcano summit historic explosive activity at the nascent casablanca volcano and along cordon caulle including the 2011 2012 eruption 1 km 3 of uncompacted pumice the largest from this fissural zone emphasizes an increased risk for volcanic hazards in central chile and argentina

magma fragmentation by rapid decompression the processes leading to magma fragmentation and the generation of pyroclastic debris during explosive volcanic eruptions are of fundamental importance in volcanology observations of explosive eruptions1 3 as well as theoretical analyses of the underlying processes4 have raised the question of whether the rapid decompression of highly viscous vesicular magma that results from the collapse of a lava dome or volcanic edifice can in itself produce explosive magma fragmentation and pyroclast formation here we report the results of a laboratory investigation of pyroclast formation following rapid decompression samples of magma from the 1980 eruption of mount st helens when rapidly depressurized from initial pressures of up to 12 mpa and at temperatures in the range 750 825 c fragmented to form pyroclastic products that are in many respects similar to those formed in real eruptions moreover we observe explosive fragmentation at temperatures well below those normally associated with magmatic processes suggesting that even relatively cool magma bodies can be very hazardous when subjected to rapid unloading events

the permeability evolution of tuffisites and implications for outgassing through dense rhyolitic magma there is growing evidence that outgassing through transient fracture networks exerts an important control on conduit processes and explosive effusive activity during silicic eruptions indeed the first modern observations of rhyolitic eruptions have revealed that degassed lava effusion may depend upon outgassing during simultaneous pyroclastic venting the outgassing is thought to occur as gas and pyroclastic debris are discharged through shallow fracture networks within otherwise low permeability conduit plugging lava domes however this discharge is only transient as these fractures become clogged and eventually blocked by the accumulation and sintering of hot melt rich pyroclastic debris drastically reducing their permeability and creating particle filled tuffisites in this study we present the first published permeability measurements for rhyolitic tuffisites using samples from the recent rhyolitic eruptions at chaiten 2008 2009 and cordon caulle 2011 2012 in chile to place constraints on tuffisite permeability evolution we combine 1 laboratory measurements of the porosity and permeability of tuffisites that preserve different degrees of sintering 2 theoretical estimates on grainsize and temperature dependent sintering timescales and 3 h2o diffusion constraints on pressure time paths the inferred timescales of sintering driven tuffisite compaction and permeability loss spanning seconds in the case of compaction driven sintering to hours surface tension driven sintering coincide with timescales of diffusive degassing into tuffisites observed vent pulsations during hybrid rhyolitic activity extrusive behaviour coincident with intermittent explosions and more broadly timescales of pressurisation accompanying silicic lava dome extrusion we discuss herein the complex feedbacks between fracture opening closing and sintering and their role in outgassing rhyolite lavas and mediating hybrid explosive effusive activity

rheology of crystal bearing silicate melts an experimental study at high viscosities the viscosity of partially crystallized mg3al2si3o12 melts has been measured under uniaxial compression in the interval 1010 1013 poise as a function of the volume fraction of crystals these inclusions are well rounded spherulites of aluminous enstatite having the same composition as the melt and whose growth rate is negligible at the temperature of the measurements the viscosity increases by less than 1 order of magnitude for crystal fractions of 40 vol and remains newtonian up to the maximum stress exerted namely 1 kbar the einstein roscoe equation 0 1 m n provides very good fits to the measurements only if either the m or n parameter is allowed to depend on temperature for modeling of magmatic processes however the widely recommended constant values m 0 6 and n 2 5 should be adequate the rheology changes abruptly when the clustered spherulites begin to oppose shear deformation at a crystal fraction of about 40 vol the viscosity becomes non newtonian with yield strengths of a few tens of bars at temperatures at which the viscosity of the melt is higher than 1010 poise as long as the crystal fraction remains lower than 70 vol the deformation proceeds in an irregular manner with a nonuniform distribution of crystals and melt the deformation becomes again regular at low stresses with lower melt fractions but samples undergo extensive fracturation along the direction of uniaxial stress similar rheology changes have been observed during the isothermal crystallization of li2si2o5 melts which produces small ellipsoidal inclusions these results suggest that the influence of solid suspensions on the rheology of magmas is primarily determined by the crystal fraction even though additional measurements would be useful to determine the possible influence of other factors such as the size distribution or the shape of the inclusions

effusive silicic volcanism in the parana magmatic province south brazil evidence for locally fed lava flows and domes from detailed field work abstract lava flows and dome complexes of silicic composition were identified in the lower cretaceous parana magmatic province pmp at rio grande do sul state southern brazil detailed mapping and image analysis reveals significant volumes of effusive deposits aligned according to main lineaments likely representing the fissural systems that fed the three palmas type silicic units different structures indicative of effusive emplacement lava domes lobated flows sheet flows and autobreccias are very common in the study area and are probably also more abundant than previously thought in whole pmp silicic magmatism in fact effusive deposits seem predominant in the three distinct silicic units identified in the area since no remnants of pyroclastic components have been identified the vitreous dacites that make up the upper flows of the basaltic andesite to dacite barros cassal sequence are clearly effusive as indicated by their occurrence as thin sheet flows the much thicker early caxias do sul dacites occur mostly as lava flow lobes and pancake like of low to moderate viscosity and lava domes the younger high sio2 santa maria rhyolite unit shows unequivocal examples of effusive deposits at its lower portion as lobated flows formed by vesicle rich obsidian in spite of higher viscosities relative to the previous units 106 pa s it is probable that the very low h2o contents 1 wt of these rhyolite melts associated with high discharge rates resulted in an effusive nature in most to this unit

a rheological investigation of vesicular rhyolite abstract the rheology of vesiculating rhyolitic systems exerts a strong control on the transport of silicic magmas in the subvolcanic to volcanic environments we present here an investigation of vesiculating and vesiculated rhyolites using dilatometric methods this study examines the effect of vesicle content on the viscosity of a natural supercooled rhyolitic liquid with 0 70 vesicles the experimental samples of rhyolitic glass are derived from fusion of a natural obsidian from little glass butte oregon crystal free rhyolite glasses of varying porosity were prepared by fusing obsidian powder in a pt crucible differing porosities were obtained by varying the temperature 1300 1650 c and duration 0 5 6 h of the fusions cylindrical samples of the resulting vesiculated rhyolites were cored from the crucible using diamond tools and their ends were ground flat and parallel for dilatometry the porosity of each sample was determined from archimedean buoyancy density determinations and comparison with bubble free rhyolite 2 331 g cm 3 porosity 1 p p o the density of foamed samples was determined using their mass volume and regular geometry viscosities were determined in the parallel plate mode at stresses of 5 10 3 to 10 5 pa the viscosimeter was calibrated using nbs 711 glass the bubble contents were microscopically investigated using a video reflected light system and image analysis software distribution functions of the size orientation aspect ratio and surface porosity were obtained the viscosity of rhyolite decreases with increasing bubble content a general relationship of the form 0 1 c describes the effect of porosity in volume fraction on the viscosity where c is a dimensionless constant 22 4 2 9 and log 10 0 10 94 0 04 pa s at 850 c

co eruptive subsidence and post eruptive uplift associated with the 2011 2012 eruption of puyehue cordon caulle chile revealed by dinsar abstract the 2011 2012 eruption of the puyehue cordon caulle volcanic complex southern andes chile was associated with complex surface deformation affecting an area of roughly 50 by 50 km we report here differential sar interferometry dinsar results of pre co and post eruptive deformation from envisat asar cosmo skymed and alos 2 palsar scenes acquired between early 2011 and early 2017 no clear pre eruptive deformation is observed during five months before the eruption although some patterns could be interpreted as showing inflation occurring between april and may 2011 co eruptive interferograms show a complex deformation pattern consisting in a major deflation lobe 120 cm los lengthening centered 10 km nw of the eruption vent accompanied by smaller uplift and subsidence regions in the vicinity of the vent re inflation began immediately after the end of the eruption a first pulse lasted 3 years between 2012 and 2015 accumulating 70 cm uplift we detect here a second pulse beginning in june 2016 and still ongoing in february 2017 reaching 12 cm in half a year inverse modeling with spherical cavity and spheroidal sources locates re inflation sources at a depth ranging between 8 and 11 km under the surface it suggests re filling of the reservoir occurring after the draining of a shallow magma chamber during the 2011 2012 eruption

rapid reinflation following the 2011 2012 rhyodacite eruption at cordon caulle volcano southern andes imaged by insar evidence for magma reservoir refill cordon caulle is a large fissural volcano that has erupted rhyodacitic magma of the same composition in its past three historical eruptions in 1921 1960 and 2011 2012 there was significant ground deformation observed before and during the 2011 2012 eruption here we use c and x band insar time series results to document post eruptive uplift up to 0 8 m between march 2012 and may 2015 with los rates up to 45 cm yr that have been largely aseismic along with subsidence in the 2011 2012 lava flow the 2012 uplift rate is one of the largest for silicic systems and was likely produced by the intrusion of 0 125 km3 of magma in the same tectonically controlled plumbing system that has been active during the historical eruptions nevertheless the uplift ended before the reservoir refilled with the erupted volume maybe due to a change in the pressure gradient produced by the 2011 2012 eruption

a melt viscosity scale for preeruptive magmas a simplified method to estimate preeruptive melt viscosity by using only melt sio2 content groundmass sio2 content is proposed for sub alkaline magmas melt viscosity is controlled by many magmatic properties e g melt composition melt water content and temperature however these properties are linked by phase equilibrium in preeruptive magmas in this study the magmatic properties were investigated by compiling data of phase equilibria experiments performed under preeruptive conditions negative correlations are found between melt sio2 contents and liquidus temperatures and between liquidus temperatures and melt water contents both increasing melt sio2 content and decreasing liquidus temperature have the effect of increasing the melt viscosity producing a linear positive correlation between logarithmic values of melt viscosity and linear values of melt sio2 content for a specific melt sio2 content an increase in liquidus temperature causes a decrease in melt viscosity whereas a decrease in water content causes an increase in melt viscosity as a result of this opposing effect the melt viscosity is strongly correlated with the melt sio2 content the correlation coefficient of 1 based on this relationship an empirical equation predicting logarithmic values of preeruptive melt viscosity is proposed as a linear function of melt sio2 content referred to as the melt viscosity scale the equation reproduces melt viscosities for compiled experimental melts and natural melts with root mean square deviation of 0 4 and 0 5 log units respectively this method provides order of magnitude estimates for preeruptive melt viscosity its strength is in being applicable to examples for which a full dataset of preeruptive magmatic properties is lacking or has large uncertainties e g slowly cooled lavas the simplicity of this method enables us to easily and promptly estimate preeruptive melt viscosity combined with rheological models for multiphase magmas the present method can be applied widely and thus greatly increase the number of case studies which include evidence based estimates of preeruptive magma viscosity

estimation of the refractive index of volcanic ash from satellite infrared sounder data abstract we investigated the spectral refractive indices ris of volcanic ash materials in the wavenumber range of 700 1100 cm 1 using satellite infrared sounder measurements and radiative transfer calculations the ash ris of 10 ash clouds from eight volcanoes were evaluated bezymianny on 2 september 2012 chaiten on 3 may 2008 kelut on 14 february 2014 kirishimayama on 27 january 2011 kliuchevskoi on 30 june 2007 and 18 october 2013 puyehue cordon caulle on 5 june 2011 sangeang api on 31 may 2014 and sheveluch on 28 october 2010 and 18 september 2012 we elaborated on a dataset of volcanic ash measurements made by the atmospheric infrared sounder airs onboard the aqua satellite the measured brightness temperatures in the ash cloud data revealed silicate absorption features at around 10 m by applying atmospheric profiles from results of a global data assimilation system and using ash cloud properties ash optical depth effective radius and ash cloud height as parameters for radiative transfer calculations least squares analyses for the observed and calculated brightness temperatures were conducted using airs channels in the wavenumber range of 700 1100 cm 1 except for the o3 absorption channels in the range of 980 1070 cm 1 using the ris for typical volcanic rocks in the ascending order of sio2 content basalt andesite and rhyolite a mixture of basalt and rhyolite and a mixture of andesite and rhyolite for the ash material were considered the volume fraction of the mixture was used as a retrieval parameter and as the ash cloud parameter using the estimated ash cloud parameters as fixed values and under the assumption that the ri from the estimated volume fraction had some accuracy in the wavenumber ranges of 850 980 cm 1 and 1070 1100 cm 1 the ri imaginary part of each eruptive ash cloud captured by airs was then determined from iterative calculations at wavenumbers between 750 cm 1 and 980 cm 1 in the wavenumber range of 850 980 cm 1 the observed brightness temperatures could be approximately simulated using the reported ris from pollack toon and khare 1973 for andesite basalt and rhyolite and their combinations furthermore some estimated ris were consistent with the reported rock types of the volcanoes which had been previously classified by compositional analyses in the literature our analysis also identified weak absorptions around 750 850 cm 1 which could not be reproduced by the reported ris these weak absorptions were likely due to si o and or al o vibrations which have been proposed in reports from previous laboratory experiments for some silicate glass samples our results suggest that the detailed ri of volcanic ash can be determined from an analysis of satellite infrared sounder data the ri of the ash material estimated from satellite infrared sounder data can be used to improve the ash retrieval algorithms of other satellite measurements furthermore an ri retrieved by sounder measurements may provide diagnostic information regarding volcanic activity from comparisons with the ash ris from past eruptions

rheology of bubble bearing magmas abstract the physical effects of air or argon bubbles on the rheology of a calcium aluminosilicate melt have been measured at temperatures ranging from 830 to 960 c at 1 bar pressure the melt composition is sio 2 64 al 2 o 3 23 and cao 13 wt while bubble volume fractions are 0 0 06 0 13 0 32 0 41 and 0 47 measured newtonian viscosities range from 10 10 to 10 14 dpa s melts with bubble fractions of 0 06 and 0 13 show with increasing temperature t an increasing relative viscosity for t t 850 c for all bubble fractions the viscosity decreases markedly with temperature the observed maximum decrease of the relative viscosity is 75 for a bubble fraction of 0 47 at 907 c at all bubble fractions the viscosity is independent of the applied stress which ranged from 11 to 677 bars no clear indications were observed of non newtonian rheological behavior under our experimental conditions the relative viscosity of the two phase liquid depends primarily on the bubble fraction physical and volcanological implications of these measurements are discussed

petrological architecture of a magmatic shear zone a multidisciplinary investigation of strain localisation during magma ascent at unzen volcano japan shearing of magma during ascent can promote strain localisation near the conduit margins anymechanical and thermal discontinuities associated with such events may alter the chemical physicaland rheological stability of the magma and thus its propensity to erupt lava spines can record suchprocesses preserving a range of macroscopic and microscopic deformation textures attributed toshearing and friction as magma ascends through the viscous brittle transition here we use a multi disciplinary approach combining petrology microstructures crystallography magnetics and experi mentation to assess the evidence role and extent of shearing across a marginal shear zone of the1994 1995 lava spine at unzen volcano japan our results show that crystals can effectively moni tor stress conditions during magma ascent with viscous remobilisation crystal plasticity and com minution all systematically increasing towards the spine margin accompanying this we find anincrease in mineral destabilisation in the form of pargasitic amphibole breakdown displaying tex tural variations across the shear zone from symplectitic to granular rims towards the spine margin in addition the compaction of pores chemical and textural alteration of interstitial glass and mag netic variations all change systematically with shear intensity the strong correlation between thedegree of shearing crystal deformation and disequilibrium features together with distinct magneticproperties implies a localised thermal input due to shear and frictional processes near the conduitmargin during magma ascent this was accompanied by late stage or post emplacement fluid andgas induced alteration of the gouge as well as oxidation and glass devitrification understandingand recognising evidence for strain localisation during magma ascent may therefore be vital whenassessing factors that regulate the style of volcanic eruptions which may provide insights into thecryptic shifts from effusive to explosive activity as observed at many active lava domes

storage and eruption of near liquidus rhyolite magma at cordon caulle chile the last three eruptions at the cordon caulle volcanic complex chile have been strikingly similar in that they have started with relatively short pre eruptive warning and produced chemically homogeneous rhyolite to rhyodacite magma with glassy to aphyric texture these characteristics collectively call for an understanding of the storage conditions leading to the rise and extraction of crystal poor silicic magma from volcanoes we have analyzed and experimentally reproduced the mineral assemblage and glass chemistry in rhyolite magma produced in the most recent eruption of cordon caulle and we use these to infer magma storage and ascent conditions fe ti oxide mineral geothermometry suggests that the rhyolite was stored at 870 920 c at these temperatures the phenocryst assemblage plag an37 cpx opx mag ilm can be reproduced under h2o saturated conditions of between 100 and 50 mpa corresponding to crustal depths between about 2 5 and 5 0 km the shallow and relatively hot magma storage conditions have implications for the rapid onset degassing efficiency and progression from explosive to mixed pyroclastic effusive eruption style at cordon caulle

lava rise plateaus and inflation pits in the mccartys lava flow field new mexico an analog for pāhoehoe like lava flows on planetary surfaces

reconstruction of total grain size distribution of the climactic phase of a long lasting eruption the example of the 2008 2013 chaiten eruption the 2008 2013 eruption of chaiten volcano chile was a long lasting eruption whose climactic phase may 6 2008 produced a sub plinian plume with height ranging between 14 and 20 km that dispersed to the ne reaching the atlantic coast of argentina the erupted material was mainly of lithic origin 77 wt resulting in a unimodal total grain size distribution tgsd dominated by coarse ash 77 wt with md of 2 7 and of 2 4 lapilli clasts 2 mm dominate the proximal deposit within 20 km of the vent while coarse 63 m 2 mm and fine ash 400 km do not significantly affect the determination of the tgsd in contrast gaps in data sampling in the medial deposit in particular the gap between 50 and 350 km from vent that coincides with shifts in sedimentation regimes have large impacts on estimates of tgsd particle number distribution for this deposit is characterized by a high power law exponent 3 0 following a trend very similar to the vesicle size distribution in the juvenile pyroclasts although this could be taken to indicate a bubble driven fragmentation process we suggest that fragmentation was more likely the result of a shear driven process because of the predominance of non vesicular products lithics and obsidians and the large fraction of coarse ash in the tgsd

rhyodacite magma storage conditions prior to the 3430 ybp caldera forming eruption of aniakchak volcano alaska this study presents a pre eruptive magma storage model for the rhyodacite and andesite magmas erupted during the 3430 ybp caldera forming eruption of aniakchak volcano alaska derived from phase equilibria experiments and petrological data the compositions of fe ti oxide pairs from the early erupted plinian rhyodacite pumice yield core temperatures of 871 900 c with rims up to 942 c and fo2 from 10 6 to 11 8 log units melt inclusions entrapped in plagioclase phenocrysts have h2o contents between 3 and 5 wt estimated by ftir and electron microprobe volatiles by difference methods with no detectable co2 assuming water saturation this corresponds to entrapment pressures between 65 and 150 mpa phase equilibria results reproduce the natural phase assemblages at p text h 2 text o of 95 150 mpa at 870 880 c assuming water saturation a mismatch in experimental versus natural glass sio2 and al2o3 and melts models for h2o undersaturated conditions indicate that the rhyodacite may not have been h2o saturated melts models with x text h 2 text o 0 8 and ptotal of 125 150 mpa at 870 880 c reproduce the natural groundmass glass al2o3 composition best indicating the magma may have been slightly h2o undersaturated those pressures correspond to storage at 4 5 5 4 km depth in the crust melts models and vbd estimates from melt inclusions in titanomagnetite grains from the andesite indicate pre eruptive conditions of 1 000 c and 110 mpa corresponding to a minimum residence depth of 4 1 km assuming water saturation or greater if the magma was h2o undersaturated previous geochemical studies indicate separate histories of the two magmas though they retain some evidence that they are ultimately related through fractional crystallization processes analogous to the 1912 novarupta magmas the rhyodacite and andesite presumably originated within the same crystal mush zone beneath the edifice yet were separated laterally and underwent different degrees of crustal assimilation the andesite must have resided in close proximity with ascent occurring in response to movement of the rhyodacite and resulting in extensive syn eruptive mingling