topographic and boundary effects on steady and unsteady flow through straits an overview of topographic and boundary effects in flows through straits is presented the emphasis is on the various types of interaction of uniform and stratified flow with the topography of straits especially the interaction with sills the interaction of a single layer flow in a channel with a sill obstacle depends on the froude number of the flow and the relative height of the sill two classification schemes one steady and one pseudo steady are given for single layer flow in straits where the effects of rotation are important a further parameter the ratio of the channel width to a rossby radius is needed and a similar classification scheme as for the non rotating flows can be obtained unsteady flows often result in bores for single layer flows and internal bores in stratified flows and the behaviour of these is discussed the flow of stratified flow past sills may generate lee waves while the increased flow speeds at the sill may allow deep water to be drawn up and over the sill aspiration features of the strait topography away from the sill including slopes at the side of the channel and also downstream of the sill channel curvature and channel widening have important effects on the character of the flow and on mixing

unsteady draining of reservoirs over weirs and through constrictions the gravitationally driven flow of fluid from a reservoir following the partial collapse of its confining dam or the partial opening of its confining lock is modelled using the nonlinear shallow water equations coupled to outflow conditions in which the drainage is modelled as flow over a constricted broad crested weir the resulting unsteady motion reveals systematic draining on which strong and relatively rapid oscillations are imposed the oscillations propagate between the outflow and the impermeable back wall of the reservoir this dynamics is investigated utilising three methods hodograph techniques to yield quasi analytical solutions asymptotic analysis at relatively late times after initiation and numerical integration of the governing equations the hodograph transformation is used to find exact solutions at early times revealing that from initially quiescent conditions the fluid drains and yet repeatedly generates intervals during which there are regions of constant depth and velocity adjacent to the boundaries a novel modified multiscale asymptotic analysis designed for late times is employed to determine the limiting rate of draining and wave structure it is shown that the excess height drains as t 2 and when the obstacle has finite height the velocity field decays as t 3 and exhibits a wave structure that tends towards a constant and relatively rapid phase speed in the case of a pure constriction for which all the fluid ultimately drains out of the reservoir the motion adjusts to a self similar state in which the velocity field decays as t 1 oscillations around this state have an exponentially increasing period numerical simulations with a novel implementation of boundary conditions are performed they confirm the hodograph solution and provide data for the asymptotic results

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

unusual fluidal behavior of a silicic magma during fragmentation in a deep subaqueous eruption havre volcano southwestern pacific ocean magma responds to applied stresses in either a viscous or elastic manner depending on the time scales over which strain is accommodated for silicic magmas high strain rates of explosive volcanism cause brittle fragmentation and produce abundant small particles ash the a d 2012 havre kermadec arc southwestern pacific ocean eruption at 900 m water depth deposited a unit of silicic ash with features indicative of syn and or post fragmentation viscous deformation viscously deformed ash makes up 3 35 of the two main ash subunits s1 and s2 with the remaining ash formed by brittle fragmentation viscous behavior of melt during production of fine ash is unexpected for the silicic havre magma and for the high strain rates typical of fine fragmentation the occurrence together of viscous and brittle ash grains suggests local and or short term variations in eruption conditions we infer an explosive eruption mechanism modified by magma water interaction during which multi source steam veiled fragmentation sites permitted rapid viscous deformation of ash prior to contact with water

magmatic architecture of dome building eruptions at volcan de colima mexico changes in the physical chemical and rheological properties of ascending magma regulate the style of volcanic eruptions volcan de colima s eruptive cycles of lava dome growth and explosions have been thoroughly monitored during the period 1998 2010 and provide a remarkable opportunity for deepening our understanding of the underlying processes responsible for the evolution of magma properties here we integrate direct observation with analytical and experimental data to 1 constrain the configuration of the shallow plumbing system and its influence on eruptive activity 2 describe the rheological behaviour of the magma and 3 assess the conditions that lead to fragmentation and ultimately to explosive eruptions the configuration of the shallow plumbing system was inferred from direct observation of extrusion sites and porosity of the erupted products during the ongoing eruptive phase magma was never extruded from a central vent both explosive and effusive activities were restricted to discrete vents inside the crater extensive field based density measurements on 500 blocks in pyroclastic flow deposits reveal a bimodality of porosity at values of 12 and 26 vol the least porous rocks tend to be altered whereas the more porous rocks are pristine this bimodal distribution combined with the lack of a central vent suggests the presence of a central dense altered plug the fragments of which are entrained during explosive eruptions during effusive periods the plug appears to deflect the ascent of magma at a shallow depth and consequently the site of lava extrusion the rheological properties and deformation induced seismogenic behaviour of the magmas were investigated using a uniaxial deformation apparatus instrumented with acoustic sensors the homogeneity in the physicochemical properties of the erupted magma permits the description of a flow law at eruptive temperature and strain rate conditions the crystal rich magma of volcan de colima exhibits a shear thinning rheology and becomes increasingly brittle at higher strain rates complete failure of magma can be predicted using the material failure forecast method which integrates the acceleration of released acoustic energy throughout the deformation rapid decompression experiments of samples pressurised with argon were performed to assess the fragmentation conditions under which explosive eruptions progress in the absence of gas loss due to permeable flow the pore pressure required to fragment volcanic products is inversely proportional to the porosity at volcan de colima a rapid decompression of 6 mpa is required to fragment magma averaging 26 vol pores and to thereby instigate an explosive eruption analysis of ballistic impacts 4 6 km away from the vent from recent explosive eruptions further requires decompression as great as 20 mpa which is sufficient to disrupt the more porous material as well as a fraction of the denser plug the continuing growth of a lava dome and of a larger more impermeable plug could have consequences for the stability of the edifice and development of stronger and more erratic explosive activity at volcan de colima

role of conduit shear on ascent of the crystal rich magma feeding the 800 year b p plinian eruption of quilotoa volcano ecuador we have characterized pumice products belonging to the climactic phase of the 800 year b p quilotoa eruption bulk rock compositions petrography mineral and glass chemistry and textural investigations were performed on the three end member pumice types namely white gray and mingled pumices all the investigated pumice clasts are dacites characterized by the same bulk rock composition and mineralogical assemblage but glass compositions and bulk textures change according to different pumice types white pumice has higher crystallinity 48 wt abundant euhedral pheno microphenocrysts no groundmass microlites the most evolved glass compositions 74 78 wt sio2 and heterogeneous vesicle populations marked by deformed and highly coalesced vesicles with thin walls gray pumice exhibits lower crystallinity 29 36 wt abundant broken and or resorbed crystals ubiquitous groundmass phenocryst fragments and microlites the widest range of glass compositions 69 78 wt sio2 and quite homogeneous poorly deformed and coalesced vesicles with thicker walls mingled pumices are characterized by the alternation of bands or patches with white and gray pumice compositional and textural characteristics we attribute heterogeneities in glass compositions and crystal and vesicle textures to processes occurring within volcanic conduits as magma is ascending to the surface in particular the above observations and results are consistent with an origin of a gray magma by heating of the original white magma in a strongly sheared region of the conduit because of a mechanism of viscous dissipation and crystal grinding and resorption at the conduit walls the less viscous gray magma therefore would enable the onset and preservation of a high mass flux of the eruption otherwise difficult to explain for highly viscous crystal rich dacitic magmas

thermal vesiculation during volcanic eruptions a textural examination of volcanic ash erupted from santiaguito volcano in guatemala coupled with an analysis of the geophysical signals indicates that rapid heating during fault friction can cause melting and vesiculation development of bubbles of hydrated silicic magma thus strongly affecting magma strength and eruptive behaviour

rheological transitions in high temperature volcanic fault zones silicic magma experiences shear induced brittle fracturing during its ascent resulting in the formation of a magmatic fault at the conduit margin once the fault is formed frictional behavior of the fault controls the magma ascent process we observed torsional deformation of a magmatic fault gouge in situ at temperatures of 800 and 900 c using synchrotron radiation x ray radiography the torsional deformation rate was set at 0 1 10 rpm corresponding to equivalent slip velocities of 2 27 10 5 1 74 10 3 m s 1 and shear strain rates of 0 014 1 16 s 1 the normal stresses used were 1 5 and 10 mpa the magmatic fault showed frictional sliding as well as viscous flow even above the glass transition temperature the transition between frictional sliding and viscous flow depends on temperature deformation rate and normal stress on the fault at 900 c the fault showed viscous deformation at a normal stress of 10 mpa while frictional sliding was predominant at 800 c we propose the ratio of timescales of fault healing and deformation as a criterion for transition between frictional sliding and viscous flow the experimentally calibrated criterion infers that frictional sliding is predominant from 500 m in depth during explosive eruption this may explain rapid magma ascent without efficient outgassing frictional heating would in turn enhance fault healing resulting in the reverse transition from frictional sliding to viscous flow followed by deceleration of magma ascent therefore cyclic transitions between frictional sliding and viscous flow are a possible explanation for the cyclic behavior of lava effusion

in situ thermal characterization of cooling crystallizing lavas during rheology measurements and implications for lava flow emplacement abstract transport properties of natural silicate melts at super liquidus temperatures are reasonably well understood however migration and transport of silicate melts in the earth s crust and at its surface generally occur at sub liquidus temperatures and in settings where the melts undergo crystallization under various cooling and or decompression conditions in such dynamic situations the occurrence of processes such as the release of latent heat during phase changes viscous heating thermal advection and inertia and changing heat capacity all represent potential influences on the state and thereby on the physico chemical behavior of the system to date rheological data at sub liquidus temperatures are scarce and cooling rate dependent disequilibrium rheological data are virtually absent in fact no in situ thermal characterization of liquid or multiphase mixtures during rheological experiments under either static or dynamic thermal conditions has been presented to date here we describe a new experimental setup for in situ thermal characterization of cooling crystallizing lavas during viscosity measurement at temperatures up to 1600 c we use this device to recover in situ real time observations of the combined rheological and thermal evolution of natural re melted lava samples during the transient disequilibrium conditions characteristic of lava flows and shallow crustal magma migration and storage systems in nature we present the calibration procedure and the method employed to recover the thermal evolution of an experimental sample during flow in varying shear regimes assess the experimental uncertainty and show the ability of the apparatus to measure the release of latent heat of crystallization during transient rheological experiments we further report the results from a first experimental study on the rheological and thermal evolution of a basaltic lava undergoing continuous cooling at a series of different cooling rates and discuss the implications of the results for magma migration and lava flow emplacement

lock exchange gravity currents with a low volume of release propagating over an array of obstacles the study discusses based on high resolution 3 d large eddy simulation results the evolution of lock exchange boussinesq gravity currents with a low volume of release lvr propagating over an array of identical two dimensional 2 d obstacles large roughness features in the form of dunes and ribs corresponding to eroded substrates in a rectangular horizontal channel the study analyzes the effect of the shape and height of the roughness elements and scale effects between reynolds numbers at which most laboratory experiments of lock exchange currents are conducted and reynolds numbers closer to field scale currents in geophysical applications on the temporal variation of the front velocity mixing and flow structure within the gravity current the temporal evolution of the flow instabilities e g kelvin helmholtz billows forward and backward propagating interfacial waves forming as a result of the interaction of the front of the current with the obstacles and bed friction velocity distributions are analyzed during the different stages of the evolution of the current the focus is on the later stages of the propagation of lvr currents after the transition to the self similar drag dominated regime has started the differences between the evolution and structure of gravity currents with a low and a high volume of release are highlighted

gravity current flow over obstacles when a gravity current meets an obstacle a proportion of the flow may continue over the obstacle while the rest is reflected back as a hydraulic jump there are many examples of this type of flow both in the natural and man made environment e g sea breezes meeting hills dense gas and liquid releases meeting containment walls two dimensional currents and obstacles where the reflected jump is in the opposite direction to the incoming current are examined by laboratory experiment and theoretical analysis the investigation concentrates on the case of no net flow so that there is a return flow in the finite depth upper layer the theoretical analysis is based on shallow water theory both a rigid lid and a free surface condition for the top of the upper layer are considered the flow may be divided into several regions the inflow conditions the region around the hydraulic jump the flow at the obstacle and the flow downstream of the obstacle both theoretical and empirical inflow conditions are examined the jump conditions are based on assuming that the energy dissipation is confined to the lower layer and the flow over the obstacle is described by hydraulic control theory

thermal and dynamical regimes of single and two phase magmatic flow in dikes finite element calculations of magma flow in dikelike channels with length to width ratios of 1000 1 or more have been used to investigate the coupling between thermal and dynamical regimes due to temperature dependent viscosity and dissipation steady state solutions with realistic thermal and dynamical parameter values have been obtained the models show that the onset of solidification on the boundaries of a basaltic or andesitic dike as predicted by idealized laminar flow models can be prevented or significantly delayed by a small amount of transverse flow induced by rising bubbles boundary roughness or turbulence this effect will reduce the critical initial widths of dikes estimated by bruce and huppert 1989 in the absence of transverse flow the bulk temperature of the magma may actually increase slightly with distance along the dike as a result of viscous dissipation even while solidification is occurring on the walls of the dike with converging or necking dike walls it is found that boundary temperatures fall to a minimum and then increase with distance along a dike even if viscous heating is neglected for viscous heating to offset significant rates of heat loss 2 kw m2 in a plane parallel 1 m wide basaltic dike an average flow velocity of 2 7 m s driven by a pressure gradient of 1 7 mpa km is required a 7 void fraction caused by exsolution of volatiles or chamber gas in the magma will produce this pressure gradient the ease of producing such a gradient by reducing the density of the magmatic column with addition of a gas phase makes it likely that flows of basaltic magma could be maintained in dikes tens of kilometers long furthermore a gas phase may be important for the propagation of the fracture prior to the initial injection of magma during dike emplacement rapid transport of more silicic magmas through dikes is inhibited by the requirement of large driving pressure gradients exceeding several hundred megapascals per kilometer however the pressure gradient can be substantially reduced if the magma is a heterogenous mixture of a predominantly silicic component with a more mafic component pipe flow experiments involving molten polymers that exhibit dynamical similarity to magmas strongly suggest that unmixing occurs when a two component magma mixture in which the components have different viscosities rises within a dike within a few dike widths of the inlet the less viscous mafic component encapsulates the more viscous silicic part effectively lubricating the passage of the more viscous component compositional variations in the obsidian dome volcano support the occurrence of this pressure reduction or self lubrication mechanism such a self lubrication process often may be necessary to permit very viscous magmas to reach earth s surface if so chemical and lithologic zoning would be anticipated as a common feature of near surface intrusions or lava flows that are characterized by a high silica and or high crystal content such as at deadman dome in long valley california

preeruptive magma viscosity an important measure of magma eruptibility 1 using a compilation of melt compositions meltwater contents temperatures and phenocryst contents the preeruptive viscosities under magma reservoir conditions are calculated for 83 erupted magmas the basaltic to rhyolitic magmas have preeruptive viscosities over the range 101 to 108 pa s although bulk sio2 content has often been used as a qualitative measure of preeruptive magma viscosity the bulk sio2 content shows a weak correlation with magma viscosity correlation coefficient r 0 5 because of a wide range of phenocryst contents from 0 to 50 vol andesitic magmas have viscosities ranging from 102 to 107 pa s which are lower or higher than those of phenocryst poor rhyolitic magmas with 105 to 106 pa s focusing on andesitic to rhyolitic magmas the r between bulk sio2 contents and magma viscosities changes to 0 1 in contrast the melt only sio2 content from a basaltic to rhyolitic melt shows a good linear correlation with melt only viscosity r 0 9 although most of the calculated viscosities of erupted magmas fall below 106 pa s as consistent with the previous compilation study this paper describes 20 examples of highly viscous magmas with 106 pa s in most cases composed of mixtures of high silica rhyolitic melt 75 79 wt sio2 and abundant phenocrysts 30 55 vol in these highly viscous magmas 9 examples have erupted following the precursory eruption of less viscous magma suggesting that precursory dike propagation and conduit formation by the less viscous magma with 106 pa s induced the following eruption of less eruptible highly viscous magmas

thin skinned deformation of sedimentary rocks in valles marineris mars deformation of sedimentary rocks is widespread within valles marineris characterized by both plastic and brittle deformation identified in candor melas and ius chasmata we identified four deformation styles using hirise and ctx images kilometer scale convolute folds detached slabs folded strata and pull apart structures convolute folds are detached rounded slabs of material with alternating dark and light toned strata and a fold wavelength of about 1 km the detached slabs are isolated rounded blocks of material but they exhibit only highly localized evidence of stratification folded strata are composed of continuously folded layers that are not detached pull apart structures are composed of stratified rock that has broken off into small irregularly shaped pieces showing evidence of brittle deformation some areas exhibit multiple styles of deformation and grade from one type of deformation into another the deformed rocks are observed over thousands of kilometers are limited to discrete stratigraphic intervals and occur over a wide range in elevations all deformation styles appear to be of likely thin skinned origin crism reflectance spectra show that some of the deformed sediments contain a component of monohydrated and polyhydrated sulfates several mechanisms could be responsible for the deformation of sedimentary rocks in valles marineris such as subaerial or subaqueous gravitational slumping or sliding and soft sediment deformation where the latter could include impact induced or seismically induced liquefaction these mechanisms are evaluated based on their expected pattern scale and areal extent of deformation deformation produced from slow subaerial or subaqueous landsliding and liquefaction is consistent with the deformation observed in valles marineris

oblique reflection of turbidity currents turbidity currents meeting obstacles for example the margins of a confined basin are subject to reflection the consequent change in flow direction is expressed in the sequence of depositional structures of the resulting bed of sediment putative examples of orthogonal reflection have been described based on 180 opposed current directions we present field evidence for the more general case of oblique reflection of turbidites and we report the results of flume experiments indicating a mechanism involving generation of internal solitary waves at an oblique ramp these propagate normal to the ramp regardless of the angle of incidence flow directions in reflected turbidites may indicate the orientation of reflecting surfaces such as basin margin slopes and thus may be of considerable help in paleogeographic and tectonic reconstructions

the influence of viscous and latent heating on crystal rich magma flow in a conduit the flow dynamics of crystal rich high viscosity magma is likely to be strongly influenced by viscous and latent heat release viscous heating is observed to play an important role in the dynamics of fluids with temperature dependent viscosities the growth of microlite crystals and the accompanying release of latent heat should play a similar role in raising fluid temperatures earlier models of viscous heating in magmas have shown the potential for unstable thermal runaway flow as described by a gruntfest number using an arrhenius temperature dependence for the viscosity but have not considered crystal growth or latent heating we present a theoretical model for magma flow in an axisymmetric conduit and consider both heating effects using finite element method techniques we consider a constant mass flux in a 1 d infinitesimal conduit segment with isothermal and adiabatic boundary conditions and newtonian and non newtonian magma flow properties we find that the growth of crystals acts to stabilize the flow field and make the magma less likely to experience a thermal runaway the additional heating influences crystal growth and can counteract supercooling from degassing induced crystallization and drive the residual melt composition back towards the liquidus temperature we illustrate the models with results generated using parameters appropriate for the andesite lava dome forming eruption at soufriere hills volcano montserrat these results emphasize the radial variability of the magma both viscous and latent heating effects are shown to be capable of playing a significant role in the eruption dynamics of soufriere hills volcano latent heating is a factor in the top two kilometres of the conduit and may be responsible for relatively short term days transients viscous heating is less restricted spatially but because thermal runaway requires periods of hundreds of days to be achieved the process is likely to be interrupted our models show that thermal evolution of the conduit walls could lead to an increase in the effective diameter of flow and an increase in flux at constant magma pressure

the controlling effect of viscous dissipation on magma flow in silicic conduits nearly all volcanic conduit models assume that flow is newtonian and isothermal such models predict that during high flux silicic eruptions gradients in pressure with depth increase upward as magma accelerates and becomes more viscous leading to extremely low pressure and fragmentation at a depth of kilometers below the surface in this paper i show that shear heating also known as viscous dissipation dramatically reduces the pressure gradient required for flow and concentrates shear in narrow zones along the conduit margin the reduction in friction may eliminate the zone of low pressure predicted by isothermal models and move the fragmentation level up to the surface

strain offsets with monotonous damped oscillations during the 1986 izu oshima volcano eruption the sequential process of the 1986 izu oshima volcano eruption japan was recorded by a volumetric strain meter near the erupted summit the records show occasional strain offsets accompanying long period damped oscillations which we interpret as responses of the volcanic system to perturbations in magmatic pressure the polarities of strain offsets were contractive for all events before the enormous ground deformation of november 21 due presumably to the intensive dike intrusion on the contrary all events after that had expansive polarities the characteristic frequencies of oscillations were 42 6 mhz for the events before changing abruptly to half that after the ground deformation in our model which is a one dimensional magma filled conduit the boundary condition at the top of the conduit changed from a closed to an open end upon a void formation at the top of the magma head due to its descent immediately after the dike intrusion before the magma escape from the reservoir as a dike magma was episodically supplied from the reservoir to the conduit and thus contraction events were generated after the magma escape magma left in the conduit was episodically drained back to the reservoir to generate expansion events this episodic magma supply or drainage was modeled by a prescribed pressure change at the bottom of the conduit we solved the free oscillation problem of the conduit pipe with an elastic sidewall to calculate the resultant volumetric strain outside the pipe physical properties of the magma and the excitation mechanism are inferred from the application of our formulation to the observation the conduit length and fluid acoustic velocity are estimated to be 10 km and 430 m s respectively suggesting that the fluid is composed of a gas liquid mixture if the conduit radius is taken to be 40 m and if the damping of oscillation occurred by viscous dissipation the fluid viscosity is 108 109 pa s a reasonable estimate for the basaltic magma the applied pressure changes at the bottom of the conduit are in a range from 105 to 106 pa with risetimes of the order of 4 to 100 s

shear deformation experiments on vesicular rhyolite implications for brittle fracturing degassing and compaction of magmas in volcanic conduits 1 shear induced brittle fractures in vesicular magmas are thought to be possible pathways for open system degassing that controls the explosivity of volcanic eruptions to investigate the detailed processes involved in the shear induced degassing we performed torsional deformation experiments on columnar rhyolites with water contents and averaged vesicularities of 0 4 0 5 wt and 20 41 vol respectively at temperatures of 780 930 c and strain rates of 0 03 s 1 the experimental conditions such as viscosity and vesicularity of the sample strain rate and total strain simulated those of typical natural dehydrated rhyolites in shallow volcanic conduits at relatively high temperatures 855 c the columnar samples were homogeneously twisted and deformed on the other hand at temperatures of 830 c the deformation was localized and finally resulted in brittle failure into a column and a disk followed by a slip at the fractured interface this slip prevented further brittle failure and shear induced bubble coalescence in the remaining parts of the sample a permeable fragmented zone was formed near the interface while in the rest of the sample the bubbles remained isolated and permeability did not increase from this we infer that a single event of magma fracturing may enhance open system degassing locally near a fracture but repeated fracturing and healing processes are necessary for the effective degassing of the entire magma that leads to nonexplosive eruptions

impact of synsedimentary metre scale normal fault scarps on sediment gravity flow dynamics an example from the gres d annot formation se france abstract synsedimentary faults result in the direct interaction between tectonic and sedimentary processes at similar spatio temporal scales sedimentological analysis of sediment laden gravity flows in the northern part of the gres d annot formation sanguiniere sub basin col de la moutiere tete ronde has revealed the presence of fault scarps of metre scale height these synsedimentary fault scarps were sufficient to disturb the sediment gravity flow dynamics resulting in i a strong variation of the erosive behaviour of a concentrated flow and ii the transformation of a strongly stratified laminar hyperconcentrated flow into a turbulent flow in short distance less than 500 m these disturbances develop without the flows being deviated by the fault scarps but produce great facies heterogeneity the least homogeneous facies mixing sand and clay being localized on the upstream obstacle side the most homogeneous massive sand downstream

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

gravity current propagation up a valley the authors gratefully acknowledge the national science foundation grant oce 0824636 and the office of naval research grant n00014 09 1 0844 for their support of the 2013 whoi geophysical fluid dynamics summer school where much of the research presented in this paper was performed

melt fracturing and healing a mechanism for degassing and origin of silicic obsidian we present water content transects across a healed fault in pyroclastic obsidian from lami pumice cone lipari italy using synchrotron fourier transform infrared spectroscopy results indicate that rhyolite melt degassed through the fault surface transects define a trough of low water content coincident with the fault trace surrounded on either side by high water content plateaus plateaus indicate that obsidian on either side of the fault equilibrated at different pressure temperature p t conditions before being juxtaposed the curves into the troughs indicate disequilibrium and water loss through diffusion if we assume constant t melt equilibrated at pressures differing by 0 74 mpa before juxtaposition and the fault acted as a low p permeable path for h2o that diffused from the glass within time scales of 10 and 30 min assuming constant p instead melt on either side could have equilibrated at temperatures differing by as much as 100 c before being brought together water content on the fault trace is particularly sensitive to post healing diffusion its preserved value indicates either higher temperature or lower pressure than the surroundings indicative of shear heating and dynamic decompression our results reveal that water contents of obsidian on either side of the faults equilibrated under different p t conditions and were out of equilibrium with each other when they were juxtaposed due to faulting immediately before the system was quenched degassing due to faulting could be linked to cyclical seismic activity and general degassing during silicic volcanic activity and could be an efficient mechanism of producing low water content obsidian

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

bouncing internal bores of ardmucknish bay scotland propagating fronts and internal waves have been observed in the sea using bottom mounted side scan sonar1 in ardmucknish bay north of oban on the west coast of scotland the fronts between brackish water and seawater are generated when less saline and so less dense water discharges tidally into the sea from the mouth of a sea loch the fronts appear to propagate from the direction of the loch as might be expected but the internal waves were found to propagate almost at right angles to this direction a time lapse cine camera was mounted on a nearby hill and was used to investigate the phenomena which are visible on the surface because of their effect on surface waves and hence on the brightness of the sea surface the internal waves are found to be generated when the fronts reflect from the coastline on one side of the bay and this explains then direction of propagation the movement of fronts influence the horizontal transfer of say nutrients from the sea loch into the surrounding coastal water

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

fault textures in volcanic conduits evidence for seismic trigger mechanisms during silicic eruptions it is proposed that fault textures in two dissected rhyolitic conduits in iceland preserve evidence for shallow seismogenic faulting within rising magma during the emplacement of highly viscous lava flows detailed field and petrographic analysis of such textures may shed light on the origin of long period and hybrid volcanic earthquakes at active volcanoes there is evidence at each conduit investigated for multiple seismogenic cycles each of which involved four distinct evolutionary phases in phase 1 shear fracture of unrelaxed magma was triggered by shear stress accumulation during viscous flow forming the angular fracture networks that initiated faulting cycles transient pressure gradients were generated as the fractures opened which led to fluidisation and clastic deposition of fine grained particles that were derived from the fracture walls by abrasion fracture networks then progressively coalesced and rotated during subsequent slip phase 2 developing into cataclasite zones with evidence for multiple localised slip events fluidisation and grain size reduction phase 2 textures closely resemble those formed on seismogenic tectonic faults characterised by friction controlled stick slip behaviour increasing cohesion of cataclasites then led to aseismic distributed ductile deformation phase 3 and generated deformed cataclasite zones which are enriched in metallic oxide microlites and resemble glassy pseudotachylite continued annealing and deformation eventually erased all structures in the cataclasite and formed microlite rich flow bands in obsidian phase 4 overall the mixed brittle ductile textures formed in the magma appear similar to those formed in lower crustal rocks close to the brittle ductile transition with the rheological response mediated by strain rate variations and frictional heating fault processes in highly viscous magma are compared with those elsewhere in the crust and this comparison is used to appraise existing models of volcano seismic activity based on the textures observed it is suggested that patterns of long period and hybrid earthquakes at silicic lava domes reflect friction controlled stick slip movement and eventual healing of fault zones in magma which are an accelerated and smaller scale analogue of tectonic faults

temperature distribution inside and around a lava tube abstract we propose a model describing the thermal effects of a lava tube the tube is a circular cylinder embedded in a solid medium and filled with a newtonian liquid flowing under the gravity force steady state conditions are considered the velocity field in the tube evaluated by the navier stokes equation is introduced into the heat equation taking into account the viscous dissipation the temperature distribution is evaluated both inside the tube and in the surrounding solid medium under the assumption that the lava tube is embedded in a solid half space the surface heat flow due to the presence of the tube is calculated it is shown that heat flow measurements at the earth s surface can give information on the depth size and temperature of the buried lava tube

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

viscous heating in rhyolite an in situ experimental determination viscous heating during magmatic flow may play a major role in eruption dynamics in order to document viscous heating during deformation of magma we have conducted a series of rheological experiments where viscous heating is directly monitored via thermocouples in high viscosity magmas we observe experimentally the strain rate dependence of viscous heating viscous heating becomes rheologically significant in the highly viscous lavas investigated at strain rates above ca 10 3 s 1 a simple analysis shows that the temperature increase generated through viscous heating during deformation of melts with viscosities ranging from 108 to 1012 pa s can account for their apparent non newtonian rheology in these experiments this thermal correction transforms apparent non newtonian strain rate dependent rheology of magma to a newtonian behavior over the range of conditions accessed in this work in this manner this study provides an experimental basis for separating the relative roles of structural relaxation and viscous heating in the generation of apparent non newtonian rheology at high strain rates here viscous heating dominates and the observation of the structural onset of non newtonian behavior is precluded by a viscous heating induced lowering of the newtonian viscosity the interplay of viscous heating and structural relaxation in melts in nature is discussed briefly

experimental and numerical study of topographic effects on deposition from two dimensional particle driven density currents abstract topographic effects on deposition from particle driven density current were investigated the laboratory experiments were carried out on topography consisting of a ramp and a series of humps the results show a localized increase in deposit distribution downstream of the slope break and on the upslope of a hump a numerical model is developed to predict the topographic effects on deposit distribution the model based on layer averaged navier stokes equations is applied to the experiments and the process of the topographic influence is analyzed the preferential deposition downstream of the slope break is interpreted to result from deceleration of the flow which increases deposit distribution through loss of capacity of the flow and longer duration of the flow passage the former effect is more influential than the latter while additional effects of a hydraulic jump may be imposed increased deposit on the upslope of a hump is attributed to partial blocking of the flow at the hump crest as well as to the differential deposition due to deceleration on the upslope

viscous dissipation in explosive volcanic flows 1 most models for magma flow in volcanic conduits during explosive eruptions assume isothermal ascent conditions due to the high heat capacity of the magma here we present a non isothermal axisymmetrical flow model that accounts for the temperature dependent viscosity of magma and viscous dissipation of heat significant changes in velocity and temperature profiles result in strong reduction of the conduit friction leading to an order of magnitude increase in discharge rate in comparison with the isothermal case this allows high intensity eruptions to occur from significantly narrower volcanic conduits and so helps to resolve inconsistencies between conduit dimensions inferred from models and observations for a given conduit diameter fragmentation can occur at much shallow depths than for an isothermal model

timescales of bubble coalescence outgassing and foam collapse in decompressed rhyolitic melts abstract the timescale of degassing and outgassing in hydrous rhyolitic melts is investigated in a wide range of conditions by means of decompression experiments the evolution of vesicularity bubble diameter and number density is characterized as a function of time either of decompression or spent at final pressure in order to determine the effect of final pressure temperature syn versus post decompression degassing melt composition and microlites on the timescale of bubble growth coalescence and outgassing the result suggests that different bubble evolution and degassing outgassing timescale corresponding to explosive and effusive eruption regimes can be cast in bulk viscosity melt bubbles bulk versus decompression time rather than path space the bulk time relationship defines three domains of i bubble nucleation and growth restricted to short durations and high bulk 0 03 h for bulk 10 5 6 pa s ii equilibrium degassing with coalescence increasing from negligible permeability 10 13 m 2 to extensive permeability 10 11 12 m 2 and iii outgassing restricted to long durations and low bulk 10 h for bulk 10 6 pa s permeability 10 10 m 2 that eventually leads to foam collapse these findings are applied to the case studies of mt pelee and mt pinatubo to infer the transition from pumice to dense pyroclasts in volcanic eruptions and the possibility of evolving from an explosive plinian eruption to an effusive dome growth event by giving the vesicular magma enough time to outgas and collapse i e hundreds to tens of hours for bulk 10 5 to 10 4 pa s respectively we also show the drastic effect of microlites on re arranging preexistent bubbles and potentially triggering a late nucleation event

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

maximal two layer exchange over a sill and through the combination of a sill and contraction with barotropic flow the analysis of two layer exchange flow through contractions with a barotropic component treated by armi farmer 1986 is extended to include exchange flows over sills and through a combination of a sill and contraction it is shown that exchange over a sill is fundamentally different from exchange through a contraction control at the sill crest acts primarily through the deeper layer into which the sill projects and only indirectly controls the surface layer this asymmetry in the control results in asymmetrical flows the interface depth above the crest is not one half the total depth as assumed in other studies by analogy with flow through contractions but is somewhat deeper the maximal exchange rate is less than for flow through a contraction of equal depth when both a sill and a contraction are present the contraction influences control at the sill crest only if it lies between the sill and the source of denser water the response to barotropic flow is also asymmetrical the transition to single layer flow occurs at much lower speeds for a barotropic component in one direction than the other results of the analysis are applied to exchange flow through the strait of gibraltar which includes both a sill and a contraction it is shown that maximal exchange conditions apply throughout part of the tidal cycle and observations illustrate several of the analytical predictions for barotropic flows including the formation of fronts single layer flow submaximal exchange and reverse flow

clinker formation in basaltic and trachybasaltic lava flows clinker is a term used to describe massive or scoriaceous fragments commonly associated with a lava flows clinker is generally considered to form by fragmentation of an upper vesiculated crust due to an increase in apparent viscosity and or to an increase in shear strain rate surface clinker is considered to be transported to the flow front and incorporated at the base by caterpillar motion clinker that we have observed on a variety of lava flows has very variable textures which suggests several different mechanisms of formation in order to study clinker formation we examined several lava flows from the chaine des puys central france where good sections surface morphology and surface textures are widespread and clearly visible we observed basal and surface a clinker that has fragmentation textures similar to those observed in ash formed in eruptions under dry conditions in two p hoehoe flows we have observed basal clinker that formed in situ two other flows display clinker features identical to those commonly observed in phreatomagmatic ash such as adhering particles blocky shapes spherical glass and attached microphenocrysts another p hoehoe flow has a flakey angular basal breccia with microfaulted and abraded clasts these were probably formed at a cooled lava base by large amounts of simple shear and consequent intra lava brittle faulting using these observations we propose three different ways of fragmentation 1 clinker can form at the surface and eventually produce roll over basal breccia 2 water lava interactions can form basal clinker by phreatomagmatic fragmentation water lava ratio variations may produce different clinker structures in a manner similar to observed textural changes in phreatomagmatic eruptions 3 clinker can be formed by brittle brecciation during basal simple shear the different clinker can provide information about the mechanisms and environmental conditions during lava flow emplacement

shallow water analysis of gravity current flows past isolated obstacles the flow of a partial depth lock exchange gravity current past an isolated bottom mounted obstacle is studied by means of two dimensional direct numerical simulations and steady shallow water theory the simulations indicate that the flux of the current downstream of the obstacle is approximately constant in space and time this information is employed to extend the shallow water models of rottman et al j hazard mater vol 11 1985 pp 325 340 and lane serff beal hadfield j fluid mech vol 292 1995 pp 39 53 in order to predict the height and front speed of the downstream current as functions of the upstream froude number and the ratio of obstacle to current height the model predictions are found to agree closely with the simulation results in addition the shallow water model provides an estimate for the maximum drag that lies within 10 of the simulation results for obstacles much larger than the boundary layer thickness

tail structure and bed friction velocity distribution of gravity currents propagating over an array of obstacles the bed friction velocity distribution and sediment entrainment potential of boussinesq compositional gravity currents propagating over a series of obstacles and over a smooth surface respectively are analysed based on high resolution three dimensional large eddy simulations the investigation focuses on the parameter regime for which currents with a high volume of release go through an extended slumping phase with approximately constant front velocity tokyay constantinescu meiburg j fluid mech vol 672 2011 570 605 under these conditions a quasi steady regime is reached between consecutive obstacles that is similar to the steady regime observed for constant density channel flows over bottom obstacles at a given location this quasi steady regime is reached in the tail of the current after the passage of the front and the associated hydraulic jumps reflected from the first few downstream obstacles a double averaging procedure is employed to characterize the global changes in the structure of the tail region between currents with a high volume of release propagating over smooth surfaces and over obstacles reynolds number induced scale effects on the flow and turbulence structure within the tail region are discussed in some detail the presence of this quasi steady regime is significant since the simulations with obstacles show that most of the sediment is entrained by the tail of the current rather than by its front a detailed analysis of the effects of the obstacle shape on the quasi steady mean flow and turbulence structure is presented which provides insight into why gravity currents over dunes can entrain more sediment than gravity currents over ribs of comparable size finally the bed friction velocity distributions and the potential to entrain sediment are compared for a compositional current with a high volume of release during the slumping phase and a current with a low volume of release for which transition to the buoyancy inertia phase occurs a short time after the release of the lock gate

semi brittle deformation of granitoid gouges in shear experiments at elevated pressures and temperatures abstract the physical and chemical processes acting in the brittle to plastic transition are of great interest for a better understanding of fault rheology we performed a series of experiments on granitoid gouge material under high confining pressures pc 500 1500 mpa temperatures t 300 c and 500 c and fast shear strain rates 1 8 10 4 s 1 where the material deforms by semi brittle flow samples deformed at 500 c are systematically weaker than samples deformed at 300 c over the whole examined confining pressure range indicating a non frictional component of the deformation all samples develop an s c fabrics and deformation localizes in slip zones containing amorphous feldspar material with an intermediate composition na ca and k rich further we observe changes in composition of feldspars enrichment in the albite component in the highly fragmented but crystalline regions with increasing finite shear strain our results indicate that mass transfer processes keep pace with frictional deformation even at high strain rates and together with viscous flow of the amorphous material are responsible for the observed strength difference

pseudopillow fracture systems in lavas insights into cooling mechanisms and environments from lava flow fractures abstract detailed field observations of structures within the flow front of a holocene trachyandesite lava from snaefellsnes iceland are presented the lava provides exceptional three dimensional exposure of complex brittle and ductile deformation textures that record processes of lava fracture and quenching driven by external water the flow front interior is characterised by structures consisting of a large metre scale curviplanar master fracture with many smaller centimetre scale subsidiary fractures perpendicular to the master fracture such structures have previously been recognised in a range of lava compositions from basalt to dacite and called pseudopillows or pseudopillow fractures we propose the term pseudopillow fracture systems to emphasise the consistent package of different fracture types occurring together all documented occurrences of pseudopillow fracture systems are in lavas that have been inferred to interact with an aqueous coolant i e liquid water ice or snow we use fracture surface textures and their orientation in relation to flow banding to identify three distinct types of master fracture and two types of subsidiary fractures master fracture surface textures used to identify fracture mechanisms include chisel marks striae cavitation dimples river lines and rough smooth fracture surface textures these indicate both brittle and ductile fracture happening on different types of master fracture chisel marks on subsidiary fractures indicate comparative cooling rates cooling directions and isotherm orientations at the time of fracture we propose a model for pseudopillow fracture system formation taking into account all the various fracture types textures and fracture propagation mechanisms and discuss their implications for interaction mechanisms between lava flows and external coolants

insights into volcanic conduit flow from an open source numerical model 1 numerical models that calculate the fluid dynamics of explosive volcanic eruptions have been used with increasing frequency to understand volcanic processes and evaluate volcanic hazards yet those who develop such models rarely make them publicly available so that they can be verified used and possibly improved by other scientists in this paper i present a visual interactive open source numerical model that calculates steady state flow of magma and gas in vertical eruptive conduits and contains user friendly utilities for quickly determining physical thermodynamic and transport properties of silicate melts h2o gases and melt gas crystal mixtures the model represents an advance over previously published conduit models by incorporating a non arrhenian viscosity relation for hydrous silicate melts a relation between viscosity and volume fraction of gas that depends on capillary number and adiabatic temperature changes in the mixture using established thermodynamic relations for melts and h2o gas respectively volcanologists who have not had access to conduit models have frequently approximated conduit flow using an analytical equation for incompressible laminar newtonian pipe flow which predicts that the mass flux is proportional to the fourth power of conduit radius and inversely proportional to mixture viscosity the model presented here which is not much more difficult to use than a back of the envelope calculation shows that the pipe flow approximation significantly overestimates the sensitivity of mass flux to both conduit radius and mixture viscosity results from the model also show that viscous heating in the lower conduit which is not considered in most other models may increase the mass flux of large silicic eruptions by several percent and decrease the viscosity of the mixture at the fragmentation depth by a few tens of percent

cellular automata model of density currents abstract cellular automata ca represent an interesting approach to the modelling of dynamical systems evolving on the basis of local interactions and internal transformations the ca model specially developed for simulating density currents is described the objective is to predict the formation and evolution of channels and the structure of deposits associated to the flow path for simulation purposes currents are represented as a dynamical system subdivided into elementary parts whose state evolves as a consequence of local interactions and internal transformations within a spatial discrete domain the model is developed for unsteady two dimensional depth averaged particle laden turbulent underflows driven by gravity acting on density gradients created by non uniform and non cohesive sediment ca is defined as a tessellation of finite state automata cells the attributes of each cell substates describe physical characteristics the natural phenomenon is decomposed into a number of elementary processes with a particular composition that makes up the transition function of the ca by applying this function to all the cells simultaneously the evolution of the phenomenon can be simulated in terms of modification of the substates the transition function includes the effects of water incorporation at the suspension ambient fluid interface a transport equation for the particle volume concentration and a toppling rule for the deposited sediments simple and flexible the obtained model constitutes a first step toward quantitative comprehension of the impact of external parameters on the turbidity current dynamics and on the organisation of the subsequent depositional sequences

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 hit and run giant impact scenario abstract the formation of the moon from the debris of a slow and grazing giant impact of a mars sized impactor on the proto earth cameron and ward 1976 lunar planet sci conf canup and asphaug 2001 nature 412 708 is widely accepted today we present an alternative scenario with a hit and run collision asphaug 2010 chem erde 70 199 with a fractionally increased impact velocity and a steeper impact angle

control of turbidity currents in reservoirs by solid and permeable obstacles turbidity currents are often the main process for the transport and deposition of the sediments in narrow alpine reservoirs these underwater avalanches with high concentration of suspended sediments follow the thalweg of the lake to the deepest area near the dam where the sediments can affect the operation of the bottom outlet and the intake structures to control the sedimentation within the reservoir the effects of solid and permeable obstacles on the turbidity current were investigated with physical experiments and numerical simulations in the physical experiments the velocity distributions as well as the spatial and temporal evolution of the deposits were measured the investigated measures were also simulated by means of a two dimensional numerical model based on the flow solver cfx 4 4 the investigations showed that turbidity currents can be influenced effectively by properly designed constructive measures based on the results of the physical experiments and numerical simulations some design recommendations for solid and permeable obstacles are proposed

two layer hydraulics a functional approach a new approach for investigating two layer hydraulic exchange flows in channels is introduced the approach is based on the functional formalism of gill 1977 and applied to the flow through a contraction in width and to flow over a simple sill the sill geometry is an extension of that looked at by earlier workers in particular farmer armi 1986 who used a froude number plane approach in the present paper a simple relationship between the composite froude number and the hydraulic functional is derived though the functional approach may also be applied to channels where a froude number is not readily defined the ability to trace roots of this functional from one reservoir to the other is a prerequisite for the flow to be realizable two hydraulic transitions are required for the flow to be fully controlled and the exchange flow rate to be maximal if only one hydraulic transition is present the flow is governed by the conditions in one of the reservoirs and the exchange flow rate is found to be submaximal the flow along a channel is found to be very sensitive to small departures from symmetry about a horizontal plane the response of the interface to the introduction of a net barotropic flow is found to be a discontinuous function of the strength of the forcing for some range of sill heights

potential causes for the non newtonian rheology of crystal bearing magmas experimental studies indicate that crystal bearing magma exhibits non newtonian behavior at high strain rates and solid fractions we use a zero dimensional 0 d inversion model to reevaluate rheological parameters and shear heating effects from laboratory data on crystal bearing magma the results indicate non newtonian behavior with power law coefficients of up to n 13 5 it has been speculated that finite strain effects shear heating power law melt rheology or plasticity are responsible for this non newtonian behavior we use 2 d direct numerical crystal scale simulations to study the relative importance of these mechanisms these simulations demonstrate that shear heating has little effect on aggregate bulk rheologies finite strain effects result in both strain weakening and hardening but the resulting power law coefficient is modest maximum n 1 3 for simulations with spherical crystals the strain weakening and hardening behavior is related to rearrangement of crystals rather than strain rate related weakening finite strain effects were insignificant in a numerical simulation with naturally shaped crystals strain partitioning into the melt phase may induce microscopic stresses that are adequate to provoke a nonlinear viscous response in the melt large differential stresses and low effective stresses revealed by the simulations are sufficient to cause crystals to fail plastically numerical experiments that account for plastic failure show large power law coefficients n 50 in some simulations we conclude that this effect is the dominant cause of the strong nonlinear viscous response of crystal bearing magmas observed in laboratory experiments

subaqueous basaltic lava dome and carapace breccia on king george island south shetland islands antarctica on king george island during latest oligocene earliest miocene time submarine eruptions resulted in the emplacement of a small ca 500 m estimated original diameter basalt lava dome at low head the dome contains a central mass of columnar rock enveloped by fractured basalt and basalt breccia the breccia is crystalline and is a joint block deposit lithic orthobreccia interpreted as an unusually thick dome carapace breccia cogenetic with the columnar rock it was formed in situ by a combination of intense dilation fracturing and shattering caused by natural hydrofracturing during initial dome effusion and subsequent endogenous emplacement of further basalt melt now preserved as the columnar rock muddy matrix with dispersed hyaloclastite and microfossils fills fractures and diffuse patches in part of the fractured basalt and breccia lithofacies the sparse glass rich clasts formed by cooling contraction granulation during interaction between chilled basalt crust and surrounding water together with muddy sediment they were injected into the dome by hydrofracturing local steam fluidisation and likely explosive bulk interaction the basalt lava was highly crystallised and degassed prior to extrusion together with a low effusion temperature and rapid convective heat loss in a submarine setting these properties significantly affected the magma rheology increased the viscosity and shear strength and influenced the final dome like form of the extrusion conversely high heat retention was favoured by the degassed state of the magma minimal undercooling a thick breccia carapace and viscous shear heating which helped to sustain magmatic eruption temperatures and enhanced the mobility of the flow