viscosity of microlite bearing rhyolitic obsidians an experimental study to investigate the influence of microlites on lava flow rheology the viscosity of natural microlite bearing rhyolitic obsidians of calc alkaline and peralkaline compositions containing 0 1 0 4 wt water was measured at volcanologically relevant temperatures 650 950 c stresses 103 105 pa and strain rates 10 5 to 10 7 s 1 the glass transition temperatures t g were determined from scanning calorimetric measurements on the melts for a range of cooling heating rates based on the equivalence of enthalpic calorimetric and shear viscosity relaxation we calculated the viscosity of the melt in crystal bearing samples from the t g data the difference between the calculated viscosity of the melt phase and the measured viscosity for the crystal bearing samples is interpreted to be the physical effect of microlites on the measured viscosity the effect of 45 vol crystals for both of these samples a connectivity factor is apparent with for the latter a close packing framework of crystals which is interpreted to influence the apparent viscosity

impact of tropical pacific precipitation anomaly on the east asian upper tropospheric westerly jet during the boreal winter abstractthe leading mode of boreal winter precipitation variability over the tropical pacific for the period 1980 2010 shows a west east dipole pattern with one center over the western north pacific wnp and maritime continent and the other center over the equatorial central pacific cp observational evidence shows that the variability of the east asian upper tropospheric subtropical westerly jet eaj has a significant correlation with precipitation anomalies over the wnp and cp and that tropical precipitation anomalies over wnp and cp have a distinct influence on the variation of the eaj a series of numerical experiments based on a linear baroclinic model are performed to confirm the influence of the heating anomalies associated with precipitation perturbations over the wnp and cp on the eaj the results of numerical experiments indicate that a heat source over the wnp can excite a northward propagating rossby wave train in the upper troposphere over east asia and facilitate a poleward eddy momentum

the giant lavas of kalkarindji rubbly pāhoehoe lava in an ancient continental flood basalt province the kalkarindji continental flood basalt province of northern australia erupted in the mid cambrian c 511 505 ma it now consists of scattered basaltic lava fields the most extensive being the antrim plateau volcanics apv a semi continuous outcrop c 50 000 km2 reaching a maximum thickness of 1 1 km cropping out predominately in the sw of the apv close to the top of the basalt succession lies the blackfella rockhole member brm originally described as basaltic agglomerate the brm has in recent years been assumed to be explosive tephra of phreatomagmatic origin thus providing a potent vehicle for volatile release to the upper atmosphere our detailed field investigations reveal that this basaltic agglomerate is in reality giant rubble collections 15 20 m thick forming the upper crusts of rubbly p hoehoe lava units 25 40 m thick covering 18 000 72 000 km2 and an estimated volume of 1 500 19 200 km3 these flows rheologically but not chemically distinct from the majority of kalkarindji lavas indicate a fundamental change in eruption dynamics a low volatile content induced high amounts of pre eruptive degassing causing super cooling and an increase in crystal nucleation and viscosity a more viscous lava and a consistently faster rate of effusion analogous to that of laki iceland created the flow dynamics necessary to disturb the lava crust to the extent seen in the brm volatile release is estimated at 1 65 x 104 2 11 x 105 tg total co2 at a rate of 867 tg a 1 and 9 07 x 103 1 16 x 105 tg so2 at 476 50 tg a 1 these masses accounted for 0 5 of cambrian atmospheric conditions whilst limiting factors reduced the effect of volatile delivery to the atmosphere thus any potential global impact caused by these flows alone was minimal

repeated fracture and healing of silicic magma generate flow banding and earthquakes textures in an exceptionally preserved effusive rhyolite conduit at torfajokull iceland indicate that rising magma repeatedly fractured and healed at shallow levels in the conduit rfh process anastomosing tuffisite veins filled by fine grained juvenile clasts were generated by shear fracture of highly viscous magma in the glass transition interval welding of the particulate material during subsequent deformation led to thorough healing of veins allowing repeated fracture of the same body of magma we propose that the rfh process is a rechargeable trigger mechanism for hybrid seismicity and show that the time scale of the process and the fractures formed by it are consistent with the repeat time and magnitude of hybrid earthquakes during silicic eruptions the rfh process may also form the flow banding that is nearly ubiquitous in obsidian

volcanic drumbeat seismicity caused by stick slip motion and magmatic frictional melting during volcanic eruptions solidifying magma ascends through the volcanic conduit often accompanied by repetitive drum beat seismicity laboratory experiments on magma samples from soufriere hills volcano montserrat and mount st helens volcano usa show that viscous melt formed at the surface between the rising magma and conduit walls can temporarily halt magma ascent accentuating the cyclical seismicity

modelling the lava dome extruded at soufriere hills volcano montserrat august 2005 may 2006 part i dome shape and internal structure lava domes comprise core carapace and clastic talus components they can grow endogenously by inflation of a core and or exogenously with the extrusion of shear bounded lobes and whaleback lobes at the surface internal structure is paramount in determining the extent to which lava dome growth evolves stably or conversely the propensity for collapse the more core lava that exists within a dome in both relative and absolute terms the more explosive energy is available both for large pyroclastic flows following collapse and in particular for lateral blast events following very rapid removal of lateral support to the dome knowledge of the location of the core lava within the dome is also relevant for hazard assessment purposes a spreading toe or lobe of core lava over a talus substrate may be both relatively unstable and likely to accelerate to more violent activity during the early phases of a retrogressive collapse soufriere hills volcano montserrat has been erupting since 1995 and has produced numerous lava domes that have undergone repeated collapse events we consider one continuous dome growth period from august 2005 to may 2006 that resulted in a dome collapse event on 20th may 2006 the collapse event lasted 3 h removing the whole dome plus dome remnants from a previous growth period in an unusually violent and rapid collapse event we use an axisymmetrical computational finite element method model for the growth and evolution of a lava dome our model comprises evolving core carapace and talus components based on axisymmetrical endogenous dome growth which permits us to model the interface between talus and core despite explicitly only modelling axisymmetrical endogenous dome growth our core talus model simulates many of the observed growth characteristics of the 2005 2006 shv lava dome well further it is possible for our simulations to replicate large scale exogenous characteristics when a considerable volume of talus has accumulated around the lower flanks of the dome model results suggest that dome core can override talus within a growing dome potentially generating a region of significant weakness and a potential locus for collapse initiation

estimation of entrainment rate in simple models of convective clouds a method for estimating lateral entrainment rate in clouds is suggested linking its magnitude to buoyant production of vertical kinetic energy within a cloud updraught in single column model studies the formulation captures the high values of entrainment seen in shallow convection and the values an order of magnitude lower in cases of deep convection as suggested by observational studies and large eddy model simulations together with a realistic vertical variation comparison is made with other recent attempts to parametrize entrainment

air sea interaction effects in the lower troposphere across the north wall of the gulf stream abstract significant atmospheric and oceanographic differences have often been observed in the regions lying on either side of the north wall of the gulf stream satellite visible range sensors have revealed changes in reflectivity across the gulf stream believed to be due to changes in sea state that are related to these atmospheric and oceanic differences in addition lines of low level cloud paralleling the edge of the gulf stream have been observed to persist in satellite imagery for several days at a time anomalous radar propagation also has been noted to occur in these same regions in an attempt to document the interrelation of these phenomena the lower atmosphere over the north wall of the gulf stream was studied on two separate occasions sea state photography and measurements of sea surface temperature air temperature dew point temperature and atmospheric pressure were made by an instrumented rp 3a aircraft flying at various altitudes from the gulf stream across the north wall and onto

quasi stationary extratropical wave trains associated with distinct tropical pacific seasonal mean convection patterns observational and amip model results in this paper mechanisms for the formation of quasi stationary extratropical wave trains associated with four distinct winter patterns of seasonal mean tropical pacific convection anomalies including the western cp w cp pattern la nina ln pattern cp el nino cpen pattern and ep el nino epen pattern are investigated by utilizing observational and six atmospheric model intercomparison project phase 5 amip5 high skilled models access1 0 canam4 ccsm4 cmcc cm hadgem2 a mpi esm lr datasets the observational results show that tropical pacific forcing induces upper level anomalous rossby wave source that force vorticity over the central north pacific through modulating the local hadley circulation then excite eastward propagation of quasi stationary planetary waves penetrating into the north atlantic and finally establish the associated teleconnections in mid and high latitudes by local synoptic eddy mean flow interaction different structures of wave trains may be explained by evident differences in intensity and scale of the extratropical vorticity forcing originating from distinct convection anomalies over the tropical pacific the mme results further confirm the possible physical processes obtained from observations but there still exist some significant differences these cover the north pacific and north america and can possibly be attributed to the models simulation ability of extratropical vorticity forcing and local storm track intensity in addition the stratosphere troposphere interaction plays an important role for extratropical atmospheric circulation anomalies the stratospheric polar vortex not only modulates the underlying wave train especially for the north atlantic europe sector but is also affected by the upper tropospheric disturbance in high latitudes through the upward wave activity flux

strain partitioning during partial melting and crystallizing felsic magmas abstract the rheology of partly molten felsic systems changes dramatically during the onset of melting and through crystallization solid to liquid and liquid to solid transitions are not rheologically identical contradicting the concept of a unique rheological critical melt percentage we use four thresholds separating the successive stages according to the melt fraction for the melting transition 1 the liquid percolation threshold connects the melt pockets at about 8 of melt thus allowing local magma displacement at the metric scale and 2 for greater melt percentages 20 25 a melt escape threshold corresponds to the onset of transport over large distances of the melt and part of the residual solid phase leading ultimately to granitic bodies for the solidification transition 3 the first formation of a rigid framework of crystals which can accumulate stress although the melt can still flow corresponds to the rigid percolation threshold 55 solids and 4 the system becomes totally locked at about 72 75 solid which corresponds to the particle locking threshold the present paper focuses on strain partitioning induced by the coexistence of two contrasting rheological phases between these thresholds on a variety of scales non coaxial deformation is preferentially accommodated by the lower viscosity melt which increases the vorticity in the melt phase and reinforces asymmetries in the flow pattern strain partitioning also increases the scale length of the weakest phase during melting and magma ascent whereas strain partitioning decreases the scale length during crystallizing strain partitioning also affects the migration of melt by raising the particle locking threshold and lowering the melt escape threshold for three dimensional deformations such as transpression the direction of melt segregation e g horizontal may differ from the direction of melt migration e g vertical

viscosity of the dome of mount st helens abstract a sample of dacite from the dome of mt st helens has been studied experimentally and found to have a viscosity that declines from about 10 15 at 800 c to 10 3 poise at 1500 c its yield strength declines from about 2 10 6 dynes cm 2 at 800 c to less than the precision of our measurements 10 4 dynes cm 2 above 1050 c the geometrical form of the dome is approximately consistent with these properties if the internal temperature of the dome is between 900 and 1000 c the melting behavior of the crystalline dacite has been determined between 1000 and 1225 c data on the composition of the liquid fraction and sizes and proportion of crystals have been used to derive a set of equations for predicting the effective viscosity of crystal bearing magmas below their liquidus temperatures although of the bulk composition of the magma has changed little the increasing crystallinity and viscosity appear to have influenced eruptive behavior of the volcano during its most recent periods of activity

application of a textural geospeedometer to the late stage magmatic history of mil 03346 dynamic crystallization experiments performed on fe rich al poor basalt are employed as a textural calibration set to quantify the late stage igneous history of nakhlite miller range mil 03346 the ratio of crystal melt surface area to volume typifying morphologically distinct populations of ca pyroxene has been shown to vary as a strong function of cooling rate hammer 2006 furthermore a texture of phenocrysts surrounded by finer grained groundmass crystals arises by sequential nucleation events during constant rate cooling but multiple populations nucleate only if the cooling rate is 72 c h 1 textural analysis of meteorite mil 03346 reveals at least two distinct populations the ca pyroxene phenocryst and microphenocryst three dimensional 3d aspect ratios are 112 8 3 and 1530 160 mm 1 respectively by comparison with the calibration set the range of cooling rates consistent with 3d aspect ratios of both populations in mil 03346 is 20 c h 1 an additional experiment was performed approximating a conductive heat transfer profile in order to interpret and apply results of constant rate cooling experiments to the natural cooling of magma results suggest that the textures of constant rate experiments parallel the initial period of rapid cooling in natural magma initial cooling rates of 20 c h 1 in the lava hosting mil 03346 occur in conductively solidifying lava at depths of 0 4 m constraining the minimum total thickness to 0 8 m crystal accumulation beginning in a subsurface reservoir and continuing after lava emplacement as an inflated pahoehoe sheet satisfies all textural constraints on the late stage igneous history of mil 03346

rheological change and degassing during a trachytic vulcanian eruption at kilian volcano chaine des puys france magma ascent during silicic dome forming eruptions is characterized by significant changes in magma viscosity permeability and gas overpressure in the conduit these changes depend on a set of parameters such as ascent rate outgassing and crystallization efficiency and magma viscosity which in turn may influence the prevailing conditions for effusive versus explosive activity here we combine chemical and textural analyses of tephra with viscosity models to provide a better understanding of the effusive explosive transitions during vulcanian phases of the 9 4 ka eruption of kilian volcano chaine des puys france our results suggest that effusive activity at the onset of vulcanian episodes at kilian volcano was promoted by i rapid ascent of initially crystal poor and volatile rich trachytic magma ii a substantial bulk and melt viscosity increase driven by extensive volatile loss and crystallization and iii efficient degassing outgassing in a crystal rich magma at shallow depths trachytic magma repeatedly replenished the upper conduit and variations in the amount of decompression and cooling caused vertical textural stratification leading to variable degrees of crystallization and outgassing outgassing promoted effusive dome growth and occurred via gas percolation through large interconnected vesicles fractures and tuffisite veins fostering the formation of cristobalite in the carapace and talus regions build up of overpressure was likely caused by closing of pore space bubbles and fractures in the dome through a combination of pore collapse cristobalite formation sintering in tuffisite veins and limited pre fragmentation coalescence in the dome or underlying hot vesicular magma sealing of the carapace may have caused a transition from open to closed system degassing and to renewed explosive activity we generalize our findings to propose that the broad spectrum of eruptive styles for trachytic magmas may be inherited from a combination of characteristics of trachytic melts that include high water solubility and diffusivity rapid microlite growth and low melt viscosity compared to their more evolved subalkaline dacitic and rhyolitic equivalents we show that trachytes may erupt with a similar style e g vulcanian but at significantly higher ascent rates than their andesitic dacitic and rhyolitic counterparts this suggests that the periodicity of effusive explosive transitions at trachytic volcanoes may differ from that observed at the well monitored andesitic dacitic and rhyolitic volcanoes which has implications for hazard assessment associated with trachytic eruptions

the impact of convection on enso from a delayed oscillator to a series of events abstract the ncar community climate system model version 3 ccsm3 exhibits persistent errors in its simulation of the el nino southern oscillation enso mode of coupled variability the amplitude of the oscillation is too strong the dominant 2 yr period too regular and the width of the sea surface temperature response in the pacific too narrow with positive anomalies extending too far into the western pacific two changes in the parameterization of deep convection result in a significant improvement to many aspects of the enso simulation the inclusion of convective momentum transport cmt and a dilution approximation for the calculation of convective available potential energy cape are used in development integrations and a striking improvement in enso characteristics is seen an increase in the periodicity of enso is achieved by a reduction in the strength of the existing short circuited delayed oscillator mode the off equatorial response is weaker and less tropically confined largely as a

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

physical properties of the 1980 mount st helens cryptodome magma physical properties of cryptodome and remelted samples of the mount st helens grey dacite have been measured in the laboratory the viscosity of cryptodome dacite measured by parallel plate viscometry ranges from 10 82 to 9 94 log10 pa s t 900 982 c and shrinkage effects were dilatometrically observed at t 900 c the viscosity of remelted dacite samples measured by the micropenetration method is 10 60 9 25 log10 pa s t 736 802 c and viscosities measured by rotational viscometry are 3 22 1 66 log10 pa s t 1298 1594 c comparison of the measured viscosity of cryptodome dacitic samples with the calculated viscosity of corresponding water bearing melt demonstrates significant deviations between measured and calculated values this difference reflects a combination of the effect of crystals and vesicles on the viscosity of dacite as well as the insufficient experimental basis for the calculation of crystal bearing vesicular melt viscosities at low temperature assuming that the cryptodome magma of the 18 may 1980 mount st helens eruption was residing at 900 c with a phenocryst content of 30 vol a vesicularity of 36 vol and a bulk water content of 0 6 wt we estimate the magma viscosity to be 1010 8 pa s

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

dynamics of seismogenic volcanic extrusion at mount st helens in 2004 05 the 2004 05 eruption of mount st helens exhibited sustained near equilibrium behaviour characterized by relatively steady extrusion of a solid dacite plug and nearly periodic shallow earthquakes here we present a diverse data set to support our hypothesis that these earthquakes resulted from stick slip motion along the margins of the plug as it was forced incrementally upwards by ascending solidifying gas poor magma we formalize this hypothesis with a dynamical model that reveals a strong analogy between behaviour of the magma plug system and that of a variably damped oscillator modelled stick slip oscillations have properties that help constrain the balance of forces governing the earthquakes and eruption and they imply that magma pressure never deviated much from the steady equilibrium pressure we infer that the volcano was probably poised in a near eruptive equilibrium state long before the onset of the 2004 05 eruption

a connection between the tropical pacific ocean and the winter climate in the asian pacific region the impact of the tropical pacific sea surface temperature sst anomaly on the winter mean surface air temperature sat in the asian pacific region is investigated during the period from 1948 to 2008 using both observations and a linear baroclinic model lbm a singular value decomposition svd analysis is conducted between the 500 hpa geopotential height z500 over the northern hemisphere and the sst over the tropical pacific ocean to obtain the large scale atmospheric patterns related to tropical pacific sst focus is given to the second pair of svd mode svd2 which bears some similarities in the z500 field to the arctic oscillation over the north atlantic sector and can impact the sat over a larger area of asian pacific in the winter of a positive svd2 the sat over the midlatitude to high latitude asian continent the arctic ocean the indian ocean and the western subtropical pacific ocean tends to be warmer than normal while the north pacific ocean around the bering strait is abnormally cold and vice versa examination of the associated surface general circulation shows that a positive svd2 tends to shift the siberian high southward and the aleutian low eastward resulting in anomalous weak pressure gradient between the asian continent the north pacific anomalous positive sea level pressure anomalies around japan and southerly wind along the east coast of the asian continent are observed at the same time the east asian trough at midtroposphere becomes weaker than normal and the east asian westerly jet stream is increased in magnitudes and shifted northward the analysis of the wave activity flux and result of idealized numerical experiments show a possible influence of the western tropical pacific sst forcing on the svd2

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

rheology of granitic magmas during ascent and emplacement flow abstract considerable progress has been made over the past decade in under standing the static rheological properties of granitic magmas in the continental crust changes in h2o content co2 content and oxidation state of the interstitial melt phase have been identified as important compositional factors governing the rheodynamic behavior of the solid fluid mixture although the strengths of granitic magmas over the crystallization interval are still poorly constrained theoretical investigations suggest that during magma ascent yield strengths of the order of 9 kpa are required to com pletely retard the upward flow in meter wide conduits in low bagnold number magma suspensions with moderate crystal contents solidosities 0 1 0 3 viscous fluc tuations may lead to flow differentiation by shear enhanced diffusion ams and mi crostructural studies support the idea that granite plutons are intruded as crystal poor liquids 50 with fabric and foliation development restricted to the final stages of emplacement if so then these fabrics contain no information on the ascent verti cal transport history of the magma deformation of a magmatic mush during pluton emplacement can enhance significantly the pressure gradient in the melt resulting in a range of local macroscopic flow structures including layering crystal alignment and other mechanical instabilities such as shear zones as the suspension viscosity varies with stress rate it is not clear how the timing of proposed rheological transitions formulated from simple equations for static magma suspensions applies to mixtures undergoing shear new theories of magmas as multiphase flows are required if the full complexity of granitic magma rheology is to be resolved

new approaches to inferences for steep sided domes on venus abstract new mathematical approaches for the relaxation and emplacement of viscous lava domes are presented and applied to steep sided domes on venus a similarity solution approach is applied to the governing equation for fluid flow in a cylindrical geometry for two distinct scenarios in the first scenario dome relaxation is explored assuming a constant volume of fluid i e lava has been rapidly emplaced onto the surface cooling of lava is represented by a time variable viscosity and singularities inherent in previous models for dome relaxation have been eliminated at the onset of relaxation bulk dynamic viscosities lie in the range between 10 10 10 16 pa s consistent with basaltic andesite to rhyolitic compositions plausible relaxation times range from 5 to 5000 years depending on initial lava viscosity the first scenario however is only valid during the final stages of dome relaxation and does not consider the time taken for lava to be extruded onto the surface in the second scenario emplacement and growth of a steep sided dome is considered when the volume of lava on the surface increases over time i e time variable volume approach the volumetric flowrate may depend on an arbitrary power of the dome thickness thus embracing newtonian as well as other rheologies for describing terrestrial and planetary mass flows the approach can be used to distinguish between basic flowrate models for fluid emplacement the formalism results in radial expansion of a dome proportional to t 1 2 consistent with the diffusive nature of the governing equation the flow at the front is shown to thicken as the front advances for a constant rate of lava supply emplacement times are intimately correlated with the bulk rheology comparison of the theoretical profiles with the shape of a typical dome on venus indicates that a newtonian bulk rheology is most appropriate consistent with prior studies however results here suggest a bulk dynamic viscosity of 10 12 10 13 pa s and emplacement times of approximately 2 16 years both scenarios investigated give emplacement times significantly less than prior estimates and compositions consistent with basaltic andesite

rock and soil avalanches theory and simulation 1 we present a 2 d contact dynamics discrete element model for simulating initiation and motion of rock avalanches integrating hillslope geometry mohr coulomb rock behavior pore pressure before avalanche triggering and avalanche trigger avalanche motion is modeled as a dense granular flow of dry frictional and cohesive particles on the basis of granular physics and shear experiments we review some of the theories for the unexpectedly long runout of rock avalanches different causes are evoked according to the strength strong or weak of the slip surface relative to the bulk mechanical fluidization and acoustic fluidization theories state that agitation of rock particles reduces frictional strength increasing runout conversely granular mechanics suggests that as shear strain rate increases granular material becomes more agitated more dissipative and more resistant another theory states that dynamic fragmentation of clasts creates an isotropic pressure that drives longer runout in contrast granular mechanics suggests that fragmentation may induce fluidization and strengthening of the granular material while particle size reduction among others induces weakening of the granular flow and enhances long runout runout is also enhanced for column like rock masses collapsing from steep hillslopes long runout may also be linked to thermal weakening mechanisms at the slip surface e g thermal pressurization and shear melting which may lower drastically the shear strength the model is illustrated with a hypothetical example of a rain triggered avalanche mobilizing shallowly dipping layers several phases are identified including slope failure avalanche triggering resulting from slip weakening and avalanche motion in which rocks are folded and sheared

distinct winter patterns of tropical pacific convection anomaly and the associated extratropical wave trains in the northern hemisphere in this paper distinct patterns of boreal winter convection anomalies over the tropical pacific and associated wave trains in the extratropics are addressed the first leading mode eof1 of convection anomalies as measured by outgoing longwave radiation demonstrates an east west oscillation of deep convection with centers over the equatorial central pacific cp and over the tropical western north pacific and the maritime continent the second leading mode eof2 is also a dipole pattern with opposite centers straddling 170 w possibly modifying eof1 to some extent combining the first two leading modes five major categories of tropical convection anomalies can be identified for the period 1979 80 2012 13 the comparison between these five categories and the corresponding sst anomaly patterns indicates a nonlinear relationship between convection and sst the combination of eof1 and eof2 with in phase pcs exhibits an east west dipole pattern with opposite signs over west of the dateline and the maritime continent the negative phase of the two pcs named la nina pattern induces a negative pacific north american positive north atlantic oscillation teleconnection in the extratropics approximately opposite responses can be detected in its positive phase named cp el nino pattern the negative pc2 superposing positive pc1 named ep el nino pattern shows the strongest convection anomalies with enhanced depressed convection over the eastern western pacific and leads to a tropical northern hemisphere like teleconnection pattern and an anomalous anticyclone extending from the north pacific to the north atlantic the positive pc2 with neutral pc1 named western cp pattern shows weakly enhanced convection to the west of the dateline as a response to local sst warming around the dateline this convection anomaly pattern although weak is important and excites a northeastward wave train from the tropics to greenland resulting in surface air temperature cooling covering the northeastern north america and warmer and wetter conditions over western europe

the influence of porosity and vesicle size on the brittle strength of volcanic rocks and magma volcanic rocks and magma display a wide range of porosity and vesicle size a result of their complex genesis while the role of porosity is known to exert a fundamental control on strength in the brittle field less is known as to the influence of vesicle size to help resolve this issue here we lean on a combination of micromechanical sammis and ashby s pore emanating crack model and stochastic rock failure and process analysis code modelling the models show for a homogenous vesicle size that an increase in porosity in the form of circular vesicles from 0 to 40 and or vesicle diameter from 0 1 to 2 0 mm results in a dramatic reduction in strength for example uniaxial compressive strength can be reduced by about a factor of 5 as porosity is increased from 0 to 40 the presence of vesicles locally amplifies the stress within the groundmass and promotes the nucleation of vesicle emanating microcracks that grow in the direction of the applied macroscopic stress as strain increases these microcracks continue to grow and eventually coalesce leading to macroscopic failure vesicle clustering which promotes the overlap and interaction of the tensile stress lobes at the north and south poles of neighbouring vesicles and the increased ease of microcrack interaction is encouraged at higher porosity and reduces sample strength once a microcrack nucleates at the vesicle wall larger vesicles impart higher stress intensities at the crack tips allowing microcracks to propagate at a lower applied macroscopic stress larger vesicles also permit a shorter route through the groundmass for the macroscopic shear fracture this explains the reduction in strength at higher vesicle diameters at a constant porosity the modelling highlights that the reduction in strength as porosity or vesicle size increases is nonlinear the largest reductions are observed at low porosity and small vesicle diameters in detail we find that vesicle diameter can play an important role in dictating strength at low porosity but is largely inconsequential above 15 porosity vesicle clustering and stress lobe interaction are implicit at high porosity regardless of the vesicle diameter in the case of an inhomogeneous vesicle size the microcracks grow from the largest vesicles and brittle strength is closer to that of the largest vesicle end member the results of this study highlight the important role of vesicle size and the complex interplay between porosity and vesicle size in controlling the brittle strength of volcanic rocks and magma

confort 15 model of conduit dynamics applications to pantelleria green tuff and etna 122 bc eruptions numerical simulations are useful tools to illustrate how flow parameters and physical processes may affect eruption dynamics of volcanoes in this paper we present an updated version of the conflow model an open source numerical model for flow in eruptive conduits during steady state pyroclastic eruptions mastin and ghiorso in a numerical program for steady state flow of magma gas mixtures through vertical eruptive conduits u s geological survey open file report 00 209 2000 in the modified version called confort 15 the rheological constraints are improved incorporating the most recent constitutive equations of both the liquid viscosity and crystal bearing rheology this allows all natural magma compositions including the peralkaline melts excluded in the original version to be investigated the crystal bearing rheology is improved by computing the effect of strain rate and crystal shape on the rheology of natural magmatic suspensions and expanding the crystal content range in which rheology can be modeled compared to the original version conflow is applicable to magmatic mixtures with up to 30 vol crystal content moreover volcanological studies of the juvenile products crystal and vesicle size distribution of the investigated eruption are directly incorporated into the modeling procedure vesicle number densities derived from textural analyses are used to calculate through toramaru equations maximum decompression rates experienced during ascent finally both degassing under equilibrium and disequilibrium conditions are considered this allows considerations on the effect of different fragmentation criteria on the conduit flow analyses the maximum volume fraction criterion porosity criterion the brittle fragmentation criterion and the overpressure fragmentation criterion simulations of the pantelleritic and trachytic phases of the green tuff pantelleria and of the plinian etna 122 bc eruptions are performed to test the upgrades in the confort 15 modeling conflow and confort 15 numerical results are compared analyzing the effect of viscosity decompression rate temperature fragmentation criteria critical strain rate porosity and overpressure criteria and equilibrium versus disequilibrium degassing in the magma flow along volcanic conduits the equilibrium simulation results indicate that an increase in viscosity a faster decompression rate a decrease in temperature or the application of the porosity criterion in place of the strain rate one produces a deepening in fragmentation depth initial velocity and mass flux of the mixture are directly correlated with each other inversely proportional to an increase in viscosity except for the case in which a faster decompression rate is assumed taking into account up to date viscosity parameterization or input faster decompression rate a much larger decrease in the average pressure along the conduit compared to previous studies is recorded enhancing water exsolution and degassing disequilibrium degassing initiates only at very shallow conditions near the surface brittle fragmentation i e depending on the strain rate criterion in the pantelleritic green tuff eruption simulations is mainly a function of the initial temperature in the case of the etna 122 bc plinian eruption the viscosity strongly affects the magma ascent dynamics along the conduit using confort 15 and therefore incorporating the most recent constitutive rheological parameterizations we could calculate the mixture viscosity increase due to the presence of microlites results show that these seemingly low viscosity magmas can explosively fragment in a brittle manner mass fluxes resulting from simulations which better represent the natural case i e microlite bearing are consistent with values found in the literature for plinian eruptions 106 kg s the disequilibrium simulations both for green tuff and etna 122 bc eruptions indicate that overpressure sufficient for fragmentation if present occurs only at very shallow conditions near the surface

long period seismicity during magma movement at volcan de colima during the period from february to september 2005 volcan de colima produced 30 vulcanian explosions of sufficient magnitude to produce pyroclastic flows of variable size with a total volume of at least 2 5 106 m3 swarms of long period events were associated with each event their duration ranging from about 6 h to 3 days and each swarm containing up to 886 events the characteristics of the swarms have been studied to understand the source mechanism and their relationship with the vulcanian explosions in total 12 548 long period events were analysed using various comparative and statistical methods patterns were not apparent in the data with no correlation between different properties of the swarms duration magnitude or frequency of occurrence of lp events and the magnitude of the associated vulcanian explosion whether recorded by seismicity volume of pyroclastics or altitude of the eruption column this along with other characteristics of the swarms such as the continuation of the swarm after the explosion with an increase in long period event amplitude in some cases suggests that the mechanism is not merely associated with the pressurization under an impermeable cap and resulting pressure differentials between adjacent volumes within the system it is more likely that the production of long period events is dominated by brittle fracturing on the margins of an ascending magma body a model is proposed whereby the unloading above the ascending magma column produced by a vulcanian explosion resulted in an increase in ascent rate reflected in the increasing amplitude of long period events the results reflect the complexity of non linear processes involved during magma ascent degassing crystallization and rupture of the impermeable plug during the vulcanian process at volcan de colima as at many volcanoes long period events represent a useful precursor for eruptive activity for monitoring this paper highlights some useful analyses that can be carried out which could illustrate certain characteristics of an eruptive episode a preliminary model is presented of the conduit processes at work during the cyclic extrusive and explosive activity during 2005

two key parameters for the el nino continuum zonal wind anomalies and western pacific subsurface potential temperature this is the author accepted manuscript the final version is available via springer at http link springer com article 10 1007 2fs00382 015 2550 0

rheological properties of basaltic lavas at sub liquidus temperatures laboratory and field measurements on lavas from mount etna models of many magmatic processes require accurate data on the rheological properties of lava at sub liquidus temperatures laboratory measurements of the rheological properties of basalts erupted on mount etna in 1983 were made at various crystal concentrations in a specially designed furnace using a haake rotovisco viscometer attached to a spindle designed to eliminate slippage at the melt spindle interface measurements were made at strain rates between 0 3 and 5 s 1 over the range of eruption temperatures on mount etna 1084 1125 c at temperatures above 1120 c the 1983 lava behaves as a newtonian fluid at lower temperatures the lava is a thixotropic pseudoplastic fluid with a maximum yield strength of 78 pa at a temperature of 1087 c in view of its low yield strength over this temperature range the theological behaviour of the lava approximates to that of a power law fluid apparent viscosities at unit shear strain rates increase from 150 pa s at 1125 c to 3000 pa s at 1084 c unit strain rate apparent viscosities measured in the field using a rotating vane viscometer range from 1385 pa s to 1630 pa s these values are in close agreement with those measured at the same temperature in the laboratory and with those calculated theoretically from the physico chemical properties of the lava

rheological properties of dome lavas case study of unzen volcano abstract transitions between effusive and explosive styles of lava dome eruptions are likely accompanied by changes in lava rheology the common presence of crystals in dome lavas produces a complex non newtonian rheology thus models of such complex rheology are essential for volcanic eruption models here we have measured the rheology of natural unzen lavas with a compressive uniaxial press operating at stresses between 1 and 70 mpa and temperatures between 940 and 1010 c crystal rich unzen lavas are characterised by two essential rheological features which produce non newtonian effects the first is an instantaneous response of the apparent viscosity to applied stress which requires that the magma be described as a visco elastic fluid that exhibits shear thinning the second effect takes the form of a time dependence of the viscosity at moderate to high stress 10 mpa in this regime the apparent viscosity slowly decreases as increasing fracturing of the phenocrysts and the groundmass occurs fragmentation of crystals and alignment of crystal fragments are observed to produce flow banding effects which in turn lower the apparent viscosity of natural dome lavas ultimately deformation may lead to complete rupture of the lava if the stress is sufficient cracking thus stands as an important process in natural dome lava rheology the ubiquitous non newtonian rheology of dome lavas observed experimentally here needs to be adequately treated in order to generate appropriate eruption models

experimental generation of volcanic pseudotachylytes constraining rheology volcanic systems are highly dynamic environments that comprise rocks and magmas which in the process of strain localisation e g in catastrophic flank collapse or dome building events are candidate materials for the occurrence of frictional melting and the formation of pseudotachylytes we evaluate the frictional behaviour of a plagioclase two pyroxene and glass bearing andesite and introduce an approach to constrain the rheology of frictional melts frictional slip at a rate of 1 3 m s under an axial stress of 1 5 mpa induces heating at a rate approximating 130 c per meter of slip and frictional melting of the andesite occurs at 1000 c which corresponds to a peak in shear stress with continuing displacement the shear stress decreases by 25 from the peak strength and stabilises while the temperature equilibrates to 1230 1290 c the shear stress for the system is congruent with a non arrhenian temperature dependent frictional melt rheology exhibiting a non newtonian viscosity evolving from approximately 104 2 to 103 4 pa s post experiment analysis show a gradation from 1 the host rock to 2 an extraordinary zone of unmelted yet viscously deformed material to 3 a thin outer region of chemically heterogeneous protomelts and to 4 an inner region of chemically homogeneous frictionally generated modified melt in the core of the slip zone we discuss the role and identification of frictional melting in volcanic systems and the implication of viscous remobilisation of magmatic plugs during frictional slip of glass bearing volcanic materials

frictional melt homogenisation during fault slip geochemical textural and rheological fingerprints abstract volcanic environments often represent structurally active settings where strain localisation can promote faulting frictional deformation and subsequent melting along fault planes such frictional melting is thermodynamically a disequilibrium process initiated by selective melting of individual mineral phases and softening of volcanic glass at its glass transition as a response to rapid frictional heating the formation of a thin melt layer on a fault plane surface can drastically accelerate or terminate slip during fault motion a comprehensive understanding of the physical and chemical properties of the frictional melt is required for a full assessment of slip mechanisms as frictional rheology depends on the contributions from selectively melted mineral and glass phases as well as the physical effects of restite fragments suspended in the frictional melt here we experimentally investigate the impact of host rock mineralogy on the compositional and textural evolution of a frictional melt during slip high velocity rotary shear hvr experiments were performed under controlled volcanically relevant coseismic conditions 1 m s 1 slip rate and 1 mpa normal stress using three intermediate dome lavas with contrasting mineral assemblages sampled from volcanic systems where fault friction is evident 1 an amphibole bearing andesite soufriere hills volcano montserrat 2 an amphibole poor dacite santiaguito dome complex guatemala and 3 an amphibole free andesite volcan de colima mexico for each sample five hvr experiments were terminated at different stages of frictional melt evolution namely 1 at the onset of melting 2 upon formation of a steady state melt layer and 3 after 5 m 4 10 m and 5 15 m of slip at steady state conditions progressive mixing and homogenisation of selective single phase melts within the frictional melt layer through double diffusion convection demonstrates the control of melt composition on slip behaviour amphiboles melted preferentially leading to consistently lower shear stress 1 mpa less than amphibole poor samples and pronounced shear weakening during the frictional melting of amphibole bearing lavas the results highlight the implications of mineral assemblages on fault slip including conduit flow processes which may influence the style of eruptions and run out distances of rapid granular flows

the rheology of two phase magmas a review and analysis abstract we consider the current state of our understanding of the rheology of two phase magmas that is suspensions of either bubbles or crystals in a viscous silicate melt the discussion is restricted to strain rates at which the suspending melt can be considered newtonian we start by considering the range of textures found in magmas and the bubble deformation and particle motions caused by shearing we then review proposed models for suspensions focussing on those functions of the form r f or f that have been most widely used to describe magmatic systems r is the relative apparent viscosity of the suspension is the volume fraction of the suspended phase is the driving stress and is the strain rate both theoretical and empirical methods are presented and then compared against the available analogue i e non magmatic and magmatic data the paper contains new data and significant re analysis of previously published data we present a new semi empirical constitutive model for bubble bearing magmas that is valid for steady and unsteady flow and large strains and strain rates this equation utilises a new parameter the capillarity cx that encapsulates the combined effect of shearing and unsteadiness on bubble suspensions we also present a new scheme for dealing with polydispersivity of bubble suspensions new data on the rheology of particle suspensions undergoing forced oscillations are presented these data show that the cox merz rule only holds for dilute particle suspensions 0 25 a re analysis of all available experimental data that relate rheology to particle aspect ratio provides distinct curves of maximum packing as a function of aspect ratio for smooth and rough particles with magmatic data lying on the curve appropriate for rough particles we analyse several rheological datasets of crystal bearing basaltic magmas and find that they are in good agreement with the constitutive equations derived from analogue data by contrast the same equations do not agree well with data for high viscosity haplogranitic melts this may be an effect of fracturing or viscous dissipation within these samples the paper concludes with a practical rheological recipes section giving a step by step method for calculating a constitutive equation for a two phase magmatic suspension and assessing its likely accuracy

influence of non newtonian rheology on magma degassing 1 many volcanoes exhibit temporal changes in their degassing process from rapid gas puffing to lava fountaining and long lasting quiescent passive degassing periods this range of behaviors has been explained in terms of changes in gas flux and or magma input rate we report here a simple laboratory experiment which shows that the non newtonian rheology of magma can be responsible alone for such intriguing behavior even in a stationary gas flux regime we inject a constant gas flow rate q at the bottom of a non newtonian fluid column and demonstrate the existence of a critical flow rate q above which the system spontaneously alternates between a bubbling and a channeling regime where a gas channel crosses the entire fluid column the threshold q depends on the fluid rheological properties which are controlled in particular by the gas volume fraction or void fraction when increases q decreases and the degassing regime changes non newtonian properties of magma might therefore play a crucial role in volcanic eruption dynamics

imaging the 2013 explosive crater excavation and new dome formation at volcan de colima with terrasar x time lapse cameras and modelling abstract the summit region of steep volcanoes hosting lava domes often displays rapid geomorphologic and structural changes which are important for monitoring the source region of hazards explosive crater excavation is often followed by new lava dome growth which is one of the most dynamic morphometric changes that may occur at volcanoes however details of these crater formations and the ensuing new dome growth remain poorly studied a common problem is the lack of observational data due to hazardous field access and the limited resolution of satellite remote sensing techniques this paper describes the destructive constructive crater activity at volcan de colima mexico which occurred between january and march 2013 the crater geometry and early dome formation were observed through a combination of high resolution terrasar x spotmode satellite radar images and permanently installed monitoring cameras this combined time lapse imagery was used to identify ring shaped gas emissions prior to the explosion and to distinguish between the sequential explosion and crater excavation stages which were followed by dome growth by means of particle image velocimetry the digital flow field is computed from consecutive camera images showing that vertical dome growth is dominant at the beginning the upward growth is found to grade into spreading and a lateral growth domain after approximately two months of gradually filling the excavated craters with new magma the dome overflows the western margin of the crater and develops into a flow that produces block and ash flow hazards we discuss and compare the observations to discrete element models allowing us to mimic the vertical and lateral growth history of the dome and to estimate the maximum strength of the bulk rock mass moreover our results allow a discussion on the controls of a critical dome height that may be reached prior to its gravitational spreading

interannual seesaw between the aleutian and icelandic lows part ii its significance in the interannual variability over the wintertime northern hemisphere abstract through analysis of observational data for the period of 1973 94 the late winter formation of an interannual seesaw between the surface aleutian and icelandic lows al and il respectively is shown to significantly impact the covariance structure of the leading mode of the interannual variability in the geopotential height field over the extratropical northern hemisphere the tropospheric leading mode for early winter november january is characterized by a polar midlatitude dipole over the euro atlantic sector with a high degree of the annularity coupled with the anomalous lower stratospheric polar vortex over the north pacific no significant anomalies are associated with this mode after the formation of the al il seesaw however the dipole no longer dominates in the upper tropospheric variability the dipole signature is masked in late winter february april by the predominant combined signature of the so called pacific north american pattern and a meridional dipole over the northweste

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

an expanded non arrhenian model for silicate melt viscosity a treatment for metaluminous peraluminous and peralkaline liquids we present new viscosity measurements for melts spanning a wide range of anhydrous compositions including rhyolite trachyte moldavite andesite latite pantellerite basalt and basanite micropenetration and concentric cylinder viscometry measurements cover a viscosity range of 10 1 to 10 12 pas and a temperature range from 700 to 1650 c these new measurements combined with other published data provide a high quality database comprising 800 experimental data on 44 well characterized melt compositions this database is used to recalibrate the model proposed by giordano and dingwell giordano d dingwell d b 2003a non arrhenian multicomponent melt viscosity a model earth planet sci lett 208 337 349 for predicting the viscosity of natural silicate melts the present contribution clearly shows that 1 the viscosity temperature relationship of natural silicate liquids is very well represented by the vft equation log a b t c over the full range of viscosity considered here 2 the use of a constant high t limiting value of melt viscosity e g a is fully consistent with the experimental data 3 there are 3 different compositional suites peralkaline metaluminous and peraluminous that exhibit different patterns in viscosity 4 the viscosity of metaluminous liquids is well described by a simple mathematical expression involving the compositional parameter sm but the compositional dependence of viscosity for peralkaline and peraluminous melts is not fully controlled by sm for these extreme compositions we refitted the model using a temperature dependent parameter based on the excess of alkalies relative to alumina e g ae sm the recalibrated model reproduces the entire database to within 5 relative

viscous flow behavior of tholeiitic and alkaline fe rich martian basalts abstract the chemical compositions of martian basalts are enriched in iron with respect to terrestrial basalts their rheology is poorly known and liquids of this chemical composition have not been experimentally investigated here we determine the viscosity of five synthetic silicate liquids having compositions representative of the diversity of martian volcanic rocks including primary martian mantle melts and alkali basalts the concentric cylinder method has been employed between 1500 c and the respective liquidus temperatures of these liquids the viscosity near the glass transition has been derived from calorimetric measurements of the glass transition although some glass heterogeneity limits the accuracy of the data near the glass transition it was nevertheless possible to determine the parameters of the non arrhenian temperature dependence of viscosity over a wide temperature range 1500 c to the glass transition temperature at superliquidus conditions the martian basalt viscosities are as low as those of the fe ti rich lunar basalts similar to the lowest viscosities recorded for terrestrial ferrobasalts and 0 5 to 1 order of magnitude lower than terrestrial tholeiitic basalts comparison with empirical models reveals that giordano et al 2008 offers the best approximation whereas the model proposed by hui and zhang 2007 is inappropriate for the compositions considered the slightly lower viscosities exhibited by the melts produced by low degree of mantle partial melting versus melts produced at high degree of mantle partial melting likely corresponding to the early history of mars is not deemed sufficient to lead to viscosity variations large enough to produce an overall shift of martian lava flow morphologies over time rather the details of the crystallization sequence and in particular the ability of some of these magmas to form spinifex texture is proposed to be a dominant effect on the viscosity during martian lava flow emplacement and may explain the lower range of viscosities 10 2 10 4 pa s inferred from lava flow morphology further the differences between the rheological behaviors of tholeiitic vs trachy basalts are significant enough to affect their emplacement as intrusive bodies or as effusive lava flows the upper range of viscosities 10 6 10 8 pa s suggested from lava flow morphology is found consistent with the occurrence of alkali basalt documented from in situ analyses and does not necessarily imply the occurrence of basaltic andesite or andesitic rocks

impact of heating anomalies associated with rainfall variations over the indo western pacific on asian atmospheric circulation in winter observational data show that the dominant mode of the boreal winter rainfall anomalies in the tropical indo western pacific iwp is a west east dipolar pattern which is called the indo western pacific dipole iwpd mode and is related to el nino southern oscillation it is found that corresponded to the iwpd mode is a new atmospheric teleconnection pattern a wave train pattern emitted from the iwp toward asia and the northwest pacific in winter during the positive negative phase of the iwpd the teleconnection pattern features the negative positive anomalies of 200 hpa geopotential height h200 centered at 30 n 110 e and the positive negative anomalies of h200 centered at 45 n 140 e the teleconnection pattern represents the dominant mode of the boreal winter h200 anomaly over asia a series of simple atmospheric model experiments are performed to confirm that this winter teleconnection pattern is induced by the heating anomalies associated with the iwpd and the heating anomalies over the equatorial central pacific are not important to this teleconnection pattern from the iwp toward asia and the northeast pacific the iwpd is strengthened after the climate regime shift of the 1970s which leads to a stronger teleconnection pattern

a new parameterization for shallow cumulus convection and its application to marine subtropical cloud topped boundary layers part i description and 1d results abstract a new parameterization of shallow cumulus convection is presented the parameterization consists of a mass flux scheme based on a buoyancy sorting entrainment detrainment plume model the mass flux scheme is coupled to a 1 5 order turbulence closure model with an entrainment closure for convective boundary layers model performance is verified using single column model simulations at relatively high vertical resolution of pure trade cumulus convection and a cumulus to stratocumulus transition mixing rates cloud cover and vertical flux profiles as deduced from previously published large eddy simulation studies are well reproduced by the parameterization the model is used to demonstrate that height variations of lateral mixing rates can be successfully captured by a simple implementation of a buoyancy sorting mechanism in the updraft cloud model a companion paper describes the implementation of the scheme in a mesoscale model

the effect of particle shape on suspension viscosity and implications for magmatic flows 1 the rheology of crystal bearing magma and lava depends on both the shape and volume fraction of the suspended crystals we present the results of analogue rheometric experiments on monodisperse suspensions of solid particles in a newtonian liquid in which particle volume fraction and aspect ratio rp are varied systematically we find that the effect of on viscosity is well captured by the maron pierce model and that this model is valid across the range of particle aspect ratios investigated 0 04 rp 22 i e strongly oblate to strongly prolate when the maximum packing fraction m is treated as a fitting parameter the value of m derived from fitting to our experimental data depends strongly and systematically on particle aspect ratio hence m represents an effective proxy for the influence of particle shape on suspension rheology we present a simple relationship for m rp which allows the viscosity of a suspension to be calculated as a function of and rp only we investigate the impact of accounting for crystal shape when modelling volcanic flows by simulating the eruption of magma carrying crystals of different aspect ratio and conclude that the effect of crystal shape should not be neglected

seismological analysis of conduit dynamics in fragmentation experiments we simulate gas burst and volcanic explosions under controlled laboratory conditions inducing fragmentation of volcanic rocks by rapid depressurization a series of experiments were performed in a shock tube apparatus at room temperature and a pressure range of 4 to 20 mpa using argon ar gas and particles or pumice samples of different porosities the instrumentation of this system with high precision piezoelectric sensors enabled us to capture elastic waves and to recognize their characteristic signatures by relating these signals to physical processes in the wave field we have been able to characterize the conduit mechanism and the source dynamics we compare and discuss conspicuous features of the waveforms and frequency spectra of these experimental signals with those of volcanic origin despite the fact that these signals are different in amplitude resulting from different scale conditions our observations indicate that the physical processes that occur during simulated explosions and those that occur during volcanic eruptions yield comparable signatures in their respective records the effects of the source receiver configuration and resonance also have significant implications all this suggests that the physical processes e g pressurization and depressurization of a system involve a system response that causes similar distinctive effects independent of the system size reflecting its intrinsic dynamics these similarities imply that powerful constraints on the source mechanisms of volcanic seismicity can emerge from seismic investigations of experimental simulations of volumetric sources such constraints may yield significant advances in the understanding of volcanic conduit dynamics and in the interpretation of seismic unrest at volcanic centers

non newtonian rheological law for highly crystalline dome lavas volcanic eruption models are hampered by the lack of multiphase magmatic flow laws most rheological models estimate the viscosity of multiphase lavas via the einstein roscoe equation but this simplification cannot be used for high crystallinity and it does not consider the non newtonian strain rate dependence of viscosity we carried out parallel plate experiments on natural samples to simulate multiphase lava deformation under various stresses and strain rates multiphase lavas exhibit an important component of shear thinning and appear to invalidate the adequacy of einstein roscoe based formulations for highly crystalline lava rheology the remarkable singular dependence of viscosity on strain rate yields a novel universal rheology law at eruptive temperatures t i e log 0 993 8974 t 0 543 log our work reveals the importance of considering microcracking and viscous dissipation at very high strain rate 10 3 s 1 explaining the occurrence of seismic swarms along the conduit margins and consequently supporting plug like magma ascent models

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

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

the fragmentation threshold of pyroclastic rocks in response to rapid decompression porous magma may fragment explosively this occurs when the melt can no longer withstand forces exerted upon it due to the overpressure in included bubbles this occurs at a critical pressure difference between the bubbles and the surrounding magma in this study we have investigated this pressure threshold necessary for the fragmentation of magma here we present the first comprehensive high temperature experimental quantification of the fragmentation threshold of volcanic rocks varying widely in porosity permeability crystallinity and chemical composition we exposed samples to increasing pressure differentials in a high temperature shock tube apparatus until fragmentation was initiated experimentally we define the fragmentation threshold as the minimum pressure differential that leads to complete fragmentation of the pressurized porous rock sample our results show that the fragmentation threshold is strongly dependent on porosity high porosity samples fragment at lower pressure differentials than low porosity samples the fragmentation threshold is inversely proportional to the porosity of the other factors permeability likely affects the fragmentation threshold at high porosity values whereas chemical composition crystallinity and bubble size distribution appear to have minor effects the relationship for fragmentation threshold presented here can be used to predict the minimum pressure differential necessary for the initiation or cessation of the explosive fragmentation of porous magma

patterns of tropical pacific convection anomalies and associated extratropical wave trains in amip5 in this paper the performance of 18 coupled model intercomparison project phase 5 cmip5 models forced by observational ssts in simulating the tropical pacific convective variation and the atmospheric responses in the extratropics are assessed the multi model ensemble mean results of 18 cmip5 models show that five major patterns of tropical pacific convection anomaly in winter can indeed be well reproduced however the simulation of the corresponding extratropical responses for each pattern exists some deficiency except for the la nina pattern compared with observations we defined an optimized subset of well performing models access1 0 canam4 ccsm4 cmcc cm hadgem2 a mpi esm mr in tropical pacific deep convection according to the ranking of model skill score these models exhibit approximately identical convection anomaly patterns in both amplitude and spatial structure to the observation which potentially might improve the representation of extratropical teleconnections with the tropical pacific especially for the cp el nino cpen ep el nino epen and western cp w cp patterns both evident atmospheric anomalies of cpen and epen patterns over the na e sector and the northeastward propagating wave trains of w cp pattern can be quite well simulated in the high skilled models

the impact of tropical western pacific convection on the north pacific atmospheric circulation during the boreal winter in this study we investigate the impact of atmospheric convection over the western tropical pacific 100 145 e 0 20 n on the boreal winter north pacific atmosphere flow by analyzing national center for environmental prediction reanalysis 1 extended reconstructed sea surface temperature and global precipitation climatology project data the western tropical pacific convection is not only the main energy source driving the local hadley and walker circulations but it also significantly influences north pacific circulation by modifying a mid latitude jet stream through the connection with the local hadley circulation on the one hand this strong convection leads to a northward expansion of local hadley cells simultaneous with a northward movement of the western north pacific jet because of the close correlation between the jet and hadley circulation boundaries on the other hand this strong convection also intensifies tropical pacific walker circulation which reduces the eastern pacific sea surface temperature resembling a la nina state through the enhanced equatorial upwelling the cooling of the eastern tropical pacific has an inter tropical convergence zone located further north thus the local hadley circulation moves northward as a result the jet axis over the eastern north pacific which also corresponds to the boundary of the local hadley circulation moves to higher latitude consequently this northward movement of the jet axis over the north pacific is reflected as a northwest southeast dipole sea level pressure slp pattern the composite analysis of slp over the north pacific against the omega pa s at 500 hpa over the western tropical pacific actually reveals that this northwest southeast dipole structure is attributed to the intensified tropical western pacific convection which pushes the pacific jet to the north finally we also analyzed south pacific for the austral winter as did previously to north pacific and found that the results were consistent

a density current parameterization coupled with emanuel s convection scheme part i the models abstract the aim of the present series of papers is to develop a density current parameterization for global circulation models this first paper is devoted to the presentation of this new wake parameterization coupled with emanuel s convective scheme the model represents a population of identical circular cold pools the wakes with vertical frontiers the wakes are cooled by the precipitating downdrafts while the outside area is warmed by the subsidence induced by the saturated drafts the budget equations for mass energy and water yield evolution equations for the prognostic variables the vertical profiles of the temperature and humidity differences between the wakes and their exterior they also provide additional terms for the equations of the mean variables the driving terms of the wake equations are the differential heating and drying due to convective drafts the action of the convection on the wakes is implemented by splitting the convective tendency and attributing the effect of the precip

anomalous winter climate conditions in the pacific rim during recent el nino modoki and el nino events present work compares impacts of el nino modoki and el nino on anomalous climate in the pacific rim during boreal winters of 1979 2005 el nino modoki el nino is associated with tripole dipole patterns in anomalies of sea surface temperature precipitation and upper level divergent wind in the tropical pacific which are related to multiple boomerangs of ocean atmosphere conditions in the pacific zonal and meridional extents of those boomerangs reflect their independent influences which are seen from lower latitudes in the west to higher latitudes in the east in the central pacific more moisture is transported from the tropics to higher latitudes during el nino modoki owing to displacement of the wet boomerang arms more poleward toward east discontinuities at outer boomerang arms manifest intense interactions between tropical and subtropical extratropical systems the pacific north american pattern and related climate anomalies in north america found in earlier studies are modified in very different ways by the two phenomena the seesaw with the dry north and the wet south in the western usa is more likely to occur during el nino modoki while much of the western usa is wet during el nino the moisture to the southwestern usa is transported from the northward shifted itcz during el nino modoki while it is carried by the storms traveling along the southerly shifted polar front jet during el nino the east asian winter monsoon related anticyclone is over the south china sea during el nino modoki as compared to its position over the philippine sea during el nino causing opposite precipitation anomalies in the southern east asia between the two phenomena

hot pressing in conduit faults during lava dome extrusion insights from mount st helens 2004 2008 abstract rhyodacitic volcanoes such as mount st helens msh soufriere hills mount unzen and mount pelee erupt spines mantled by layers of magma derived cataclasite and fault gouge msh produced seven lava spines from 2004 2008 composed of low porosity compositionally uniform crystalline dacite dome extrusion was attended by continuous drumbeat seismicity derived from faulting along the conduit margin at 0 5 1 km depth and evidenced by the enveloping gouge layers we describe the properties of the gouge derived fault rocks including laboratory measurements of porosity and permeability the gouge varies from unconsolidated powder to lithified low porosity low permeability fault rocks we reconstruct the subsurface ascent of the msh magma using published field observations and create a model that reconciles the diverse properties of the gouge with conditions in the conduit during ascent i e velocity temperature we show lithification of the gouge to be driven by hot pressing processes wherein the combination of elevated temperature confining pressure and dwell time cause densification and solid state sintering of the comminuted crystal rich glass poor gouge the degree of gouge lithification corresponds with residence time in the conduit such that well lithified materials reflect extended times in the subsurface due to slower ascent rates with this insight we suggest that gouge competence can be used as a first order estimate of lava ascent rates furthermore we posit gouge lithification which reduces porosity and permeability inhibits volcanic outgassing thereby increasing the potential for explosive events at spine producing volcanoes

tracking the permeable porous network during strain dependent magmatic flow abstract rheological variations have been postulated as the cause of transitions from effusive to explosive volcanic eruption style rheology is integrally linked to the composition and textural state porosity crystallinity of magma as well as the stress temperature and strain rate operative during flow this study characterises the rheological behaviour and importantly the evolution of physical properties of two magmas with different crystallinity and porosity from volcan de colima mexico a volcanic system known for its rapid fluctuations in eruption style magma samples deformed in a uniaxial press at a constant stress of 2 8 12 or 24 mpa a constant temperature of 940 945 c comparable to upper conduit or lava dome conditions to strains of 20 or 30 displayed different mechanical behaviour and significant differences in measured strain rates 10 2 10 5 s 1 the evolution of porosity permeability dynamic young s modulus and dynamic poisson s ratio illustrate a complex evolution of the samples manifested as strain hardening visco elastic constant rate and strain weakening deformation both magmas behave as shear thinning non newtonian liquids and viscosity decreases as a function of strain we find that strain localisation during deformation leads to the rearrangement and closure of void space a combination of pores and cracks followed by preferentially aligned fracturing in the direction of the maximum principal stress to form damage zones as well as densification of other areas in a dome setting highly viscous low permeability magmas carry the potential to block volcanic conduits with a magma plug resulting in the build up of pressures in the conduit above a certain threshold of strain dependent upon stress strain rate the initiation propagation and coalescence of fractures leads to mechanical degradation of the magma samples which then supersedes magmatic flow and crystal rearrangement as the dominant form of deformation this results in lower apparent viscosities than those anticipated for magma of such crystallinity especially at high strain rates in a lava dome this could result in dome collapse and the concomitant depressurisation could trigger an explosive eruption

enhanced crystal fabric analysis of a lava flow sample by neutron texture diffraction a case study from the castello d ischia dome 1 the crystal fabric of a lava has been analyzed for the first time by neutron texture diffraction in this study we quantitatively investigate the crystallographic preferred orientation of feldspars in the castello d ischia ischia island italy trachytic exogenous dome the crystallographic preferred orientation was measured with the monochromatic neutron texture diffractometer sv7 at the forschungszentrum julich in germany and a rietveld refinement was applied to the sum diffraction pattern the complementary thin section analysis showed that the three dimensional crystal shape and the corresponding shape preferred orientation are in agreement with the quantitative orientation distributions of the neutron texture data the 0k0 crystallographic planes of the feldspars are roughly parallel to the local flow bands whereas the other corresponding pole figures show that a pivotal rotation of the anorthoclase and sanidine crystals was active during the emplacement of this lava dome in combination with scanning electron microscopy investigations electron probe microanalysis xrf and x ray diffraction the rietveld refinement of the neutron diffraction data indicates a slow cooling dynamic on the order of several months during their crystallization under subaerial conditions results attained here demonstrate that neutron texture diffraction is a powerful tool that can be applied to lava flows

volcanic dilemma flow or blow volcanic eruptions can be either slow outpourings of lava or explosive ejections of fragmented rock in his perspective dingwell discusses the physical and chemical properties of magma that lead to these two styles of eruption new experiments and computer simulations are pointing to the involvement of solidlike behavior of liquid magma when it makes a transition to a glass

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

the strength of heterogeneous volcanic rocks a 2d approximation abstract volcanic rocks typically contain heterogeneities in the form of crystals and pores we investigate here the influence of such heterogeneity on the strength of volcanic rocks using an elastic damage mechanics model in which we numerically deform two dimensional samples comprising low strength elements representing crystals and zero strength elements representing pores these circular elements are stochastically generated so that there is no overlap in a medium representing the groundmass our modelling indicates that increasing the fraction of pores and or crystals reduces the strength of volcanic rocks and that increasing the pore fraction results in larger strength reductions than increasing the crystal fraction the model also highlights an important weakening role for pore diameter but finds that crystal diameter has a less significant influence for strength to account for heterogeneity pores and crystals we propose an effective medium approach where we define an effective pore fraction p v p v p v g where v p and v g are the pore and groundmass fractions respectively highly heterogeneous samples containing high pore and or crystal fractions will therefore have high values of p and vice versa when we express our numerical samples more than 200 simulations spanning a wide range of crystal and pore fractions in terms of p we find that their strengths can be described by a single curve for a given pore diameter to provide a predictive tool for the strength of heterogeneous volcanic rocks we propose a modified version of 2d solution for the sammis and ashby 1986 pore emanating crack model a micromechanical model designed to estimate strength using microstructural attributes such as porosity pore radius and fracture toughness the model reformulated to include p and therefore crystal fraction captures the strength curves for our numerical simulations over a sample heterogeneity range relevant to volcanic systems we find that published experimental data for which the porosity and crystal fraction is known correlate well with our modelled curves adding validity to our approach we present herein a 2d analytical tool to estimate the strength of volcanic rock that can be used when the porosity crystal fraction and maximum pore diameter are known

crystallization kinetics and rheology of leucite bearing tephriphonolite magmas from the colli albani volcano italy abstract we have investigated the rheology of liquid and crystal bearing tephriphonolite magmas from the colli albani volcanic district high 1124 1569 c and low 690 800 c temperature anhydrous liquid viscosities were determined by a combination of concentric cylinder 101 0 to 103 6 pa s and micropenetration 109 2 to 1012 1 pa s viscometry comparison with literature data reveals that at high temperatures viscosity seems to be related to the melts degree of polymerization nbo t while at low temperatures the dependency is not linear with values of viscosity higher than expected subliquidus isothermal crystallization experiments and viscosity determinations were carried out at high temperature 1150 1240 c in air using a concentric cylinder apparatus at constant shear strain rate 0 1 s 1 the overall crystal fraction varies between 0 06 at 1240 c leucite and 0 34 at 1150 c leucite 0 32 plagioclase 0 02 with a direct linear increase of crystal content with decreasing temperature which parallels the viscosity increase the inspection of products quenched at the end of the crystallization stage defined when viscosity reaches a constant value reveals strong evidence of leucite clustering after the first segment of the experiment performed at a constant shear rate a second stage of experiments at variable shear rate was performed comprised of an up ramp 0 1 s 1 0 9 s 1 and a down ramp 0 9 s 1 0 1 s 1 segment at the end of the down ramp leucite crystals appear sub spherical and unclustered for the same applied shear rate the viscosity values of the up ramp are not recovered within the experimental time scale indicating strain and strain rate dependent rheology for these suspensions while the down ramp viscosity data are shown to be in perfect agreement with literature models discrepancies between the up ramp data and pre existing predicting models have been observed we suggest that this complex behavior is related to the clustering of leucite crystals during the crystallization process and their breakage during the higher shear rate viscosity measurements the kinetics of crystallization in terms of nucleation and growth rates seems to be strongly affected by the degree of undercooling and dynamic stirring conditions we conclude that any modeling of tephriphonolite magma flow either in conduit or subaerial should take into account the effects of strain strain rate and internal textures i e clustering

analysis of the nonlinearity of el nino southern oscillation teleconnections abstractel nino southern oscillation enso has significant variations and nonlinearities in its pattern and strength enso events vary in their position along the equator with some located in the central pacific cp and others in the east pacific ep to study how these variations are reflected in global enso teleconnections both observations and idealized atmospheric general circulation model agcm simulations are analyzed clear nonlinearities exist in observed teleconnections of sea level pressure slp and precipitation however it is difficult to distinguish if these are caused by the different signs strengths or spatial patterns of events strong el nino events mostly being ep events and strong la nina events mostly being cp events or by combinations of these therefore sensitivity experiments are performed with an agcm forced with idealized ep and cp enso sea surface temperature sst patterns with varying signs and strengths the response is generally stronger for warm events than for c

atmospheric circulation cells associated with the el nino southern oscillation abstract atmospheric circulation cells associated with the el nino southern oscillation enso are described and examined using the ncep ncar reanalysis field and the ncep sea surface temperature sst from january 1950 to december 1999 the divergent wind and pressure vertical velocity are employed for the identification of atmospheric circulation cells the warm phase of enso shows positive sst anomalies in the equatorial eastern pacific and along the east coast of asia and the west coast of north america and negative sst anomalies in the off equatorial western pacific and in the central north pacific associated with this sst anomaly distribution are variations of atmospheric zonal and meridional circulation cells over the pacific the equatorial zonal walker circulation cell is weakened consistent with previous schematic diagrams the anomalous meridional hadley circulation cell in the eastern pacific shows the air rising in the tropics flowing poleward in the upper troposphere sinking in the subt