on the shape and velocity of fluid filled fractures in the earth summary in this paper i present a model to estimate the shape and velocity of slowly ascending buoyancy driven fluid filled fractures the model considers elastic deformation linear fracture mechanics and fluid flow an attempt is made to incorporate the effect ofthe 2 d fluid pattern on the viscous pressure drop most other models assume that the viscous pressure drop can be approximated by flow through a channel with constant width although the form of the fracture is known to deviate from such a simple shape the 2 d flow in my model has an important consequence for the mechanism of buoyancy driven fracture propagation it predicts a large pressure gradient at the tail of the propagating fracture indicating that the tail of the fracture is most important in hindering the fracture propagation a singularity at the tail of the fracture can be avoided when a small amount of fluid trails in the channel left behind the propagating fracture the trailing and decoupling of fluids at the tail seems to be accompanied by small flow and shape instabilities which is indicated by the jerky movement of the tail observed in propagating air filled fractures in solidified gelatine and by numerical boundary element solutions of the coupled flow deformation fracturing problem by comparing the predictions for propagation velocities with laboratory observations of buoyancy driven fracture propagation in gelatine i derive a non dimensional effective thickness at the tail of the fracture for which trailing of fluids may occur the model is applied to earth relevant problems such as oil and water filled fractures in pressurized sediments or magma filled dykes in the lithosphere which are discussed in the paper

development of a subvolcanic structure by the interaction of liquid filled cracks abstract the interaction of liquid filled cracks may be an important process for magma accumulation and the development of subvolcanic structures the horizontal interaction was studied through the stress analyses around pressured cracks in various regional stress fields the vertical interaction was studied using gelatin experiments buoyaney driven cracks coalesce more easily than pressure cracks the theory of the three dimensional crack interaction was discussed there are two types of crack interaction the interaction between liquid filled cracks may cause coalescence of cracks the interaction between a liquid filled crack and a solid filled crack never causes coalescence the stress relaxation by ductile or brittle behavior or by the driving out of magma decreases the local stress field generated by the accumulation of magma filled cracks as the regional differential stress increases and the minimum compressive principal stress becomes tensile magma filled cracks become parallel to each other as the supply rate of magma filled cracks becomes relatively large or as the regional differential stress decreases and the minimum compressive stress increases the arrangement of magma filled cracks varies from an offset pattern to a radial one because the local compressive stress field cannot be decreased this process leads to the development of subparallel or radial dikes in two dimensions or a dike sheet complex in three dimensions a large magma chamber such as a sphere or a cylinder is not always necessary for the development of a basaltic volcano in case of the interaction between liquid filled cracks magma filled cracks coalesce easily into one large crack and diminish the local compressive stress field last the theory of the crack interaction is applied to developments of various volcanoes the fissure pattern of hekla volcano iceland is explained in terms of the variation of the stress relaxation the difference in fissure pattern between izu oshima and miyakejima volcanoes japan is interpreted by the variation of the differential stress the local stress balance including the stress relaxation is kept in the developments of etna volcano italy and kilauea volcano hawaii

buoyancy driven fracture ascent experiments in layered gelatine laboratory experiments on air filled fracture propagation in solidified homogeneous and layered gelatine have been carried out providing an analogue model for magma filled dikes ascending in the crust the effects of layering on fracture velocity and shape have been analyzed in detail the free surface is found to accelerate approaching fractures layering accelerates or decelerates fractures approaching discontinuities of the elastic parameters depending on the value of the rigidity contrast the shape of fractures are strongly influenced as they pass from one layer to another the observed cross sectional shape when crossing a layer interface and the acceleration with decreasing rigidity can be explained with theoretical models our experiments also reproduce the arrest of fractures in proximity of joints and the formation of sills in the layer below the interface these findings could help in the interpretation of accelerated seismicity and deformation rates observed in volcanic areas

tomographic images and 3d earthquake locations of the seismic swarm preceding the 2001 mt etna eruption evidence for a dyke intrusion 1 on july 12 2001 mt etna experienced a sudden increase of seismic activity heralding one of the most intense eruptions of the past 30 years between july 12 and july 18 when the eruption started thousands of small magnitude earthquakes occurred and were recorded by a dense seismic network run by the istituto nazionale di geofisica e vulcanologia sezione di catania ingv ct hypocentral depths of earthquakes were very shallow mostly located above 3 km b s l and clustered near the summit area the high quality seismic dataset gives us the unique opportunity to study the process of magma migration before the eruption in this study we present the three dimensional earthquake locations and the velocity structure obtained by a tomographic inversion the shallowness of seismicity allowed us to enhance the details of the structure beneath the summit craters in a volume poorly defined by previous tomographic studies the presence of a high vp body previously observed at mt etna is confirmed at shallow depth beneath the southeastern part of the summit area the earthquakes preceding the eruption onset concentrated at its western border a low vp vs anomaly is found at 0 1 km depth just at the top of the volume where the magma intruded before the eruption this anomalous zone can be considered as molten material wealthy in gas the relocated seismicity occurs in a cylinder below the vents activated along the fracture system and exhibited an upward migration until the eruption all these results show evidence for the emplacement of a near vertical dyke striking about n s and a few kilometres south of the summit craters

controls on sill and dyke sill hybrid geometry and propagation in the crust the role of fracture toughness abstract analogue experiments using gelatine were carried out to investigate the role of the mechanical properties of rock layers and their bonded interfaces on the formation and propagation of magma filled fractures in the crust water was injected at controlled flux through the base of a clear perspex tank into superposed and variably bonded layers of solidified gelatine experimental dykes and sills were formed as well as dyke sill hybrid structures where the ascending dyke crosses the interface between layers but also intrudes it to form a sill stress evolution in the gelatine was visualised using polarised light as the intrusions grew and its evolving strain was measured using digital image correlation dic during the formation of dyke sill hybrids there are notable decreases in stress and strain near the dyke as sills form which is attributed to a pressure decrease within the intrusive network additional fluid is extracted from the open dykes to help grow the sills causing the dyke protrusion in the overlying layer to be almost completely drained scaling laws and the geometry of the propagating sill suggest sill growth into the interface was toughness dominated rather than viscosity dominated we define kic as the fracture toughness of the interface between layers relative to the lower gelatine layer kicint kicg our results show that kic influences the type of intrusion formed dyke sill or hybrid and the magnitude of kicint impacted the growth rate of the sills kicint was determined during setup of the experiment by controlling the temperature of the upper layer tm when it was poured into place with tm

transient shallow reservoirs beneath small eruptive centres constraints from mg fe interdiffusion in olivine abstract small eruptive centres commonly have more primitive lavas than those associated with stratovolcanoes an observation that has been taken to indicate a short magma residence in the crust relative to those reservoirs below stratovolcanoes the caburgua cones of the andean southern volcanic zone from a basaltic small eruptive centre where this can be tested here we use melts simulations and the available thermobarometry data to determine the conditions of olivine crystal rim formation and the mg fe diffusion modelling to determine the magma residence times of those rims in the crust results yield timescales varying from a few days to dozens of days and if freezing is to be avoided can only be explained by some form of storage or slow transport through at least one shallow magma body the longest durations of magma residence seen in the olivine rim zones are up to 471 days these timescales are shorter than those estimated decadal from the nearby more differentiated and well established stratovolcano villarrica which has a dominantly basaltic andesite composition for caburgua cones we propose the existence of a transient reservoir in contrast to a long lived reservoir such as that inferred beneath the adjacent villarrica stratovolcano

dynamic dyke propagation deduced from tilt variations preceding the march 9 1998 eruption of the piton de la fournaise volcano during the hour preceding the march 9 1998 eruption of the piton de la fournaise volcano the deformation network of the observatory recorded some large deformations in the summit area a broadband seismic station of the geoscope global network rer is located about 8 km away from the summit of the volcano signals from that station may be interpreted as tilt changes the combination of the above two kinds of signals allows by using a tensile fault model to constrain the geometry as well as some characteristics volume propagation velocity of the dyke that intruded the summit area during the hour preceding the beginning of eruptive activity

deformation around a rising diapir modeled by creeping flow past a sphere a new experimental method for determining the pattern of flow and three dimensional progressive finite deformation of fluid elements in low reynolds number re viscous flow has been applied to creeping flow past a rigid sphere falling in a cylinder this is intended as a model analogue of natural rock deformation associated with magmatic and solid state diapirs rising through ductile crust the kinematics of finite strain in such analogue experiments may give useful information on the development of natural structures the experiment and a new method for quantifying the progressive finite deformation of fluid volumes in the transparent newtonian test fluid used sgm36 are discussed in detail the progressive finite deformation of fluid flowing along specific streamlines passing the sphere appears to be complex and largely a function of the initial distance of fluid volumes and the particular streamlines which they follow from the flow axis the progressive deformation history in the material surrounding a rising spherical diapir is characterized by progressive flattening and rotation of material above and progressive stretching below the sphere the results compare favorably with the external strain pattern associated with post tectonic mesozonal diapiric intrusions

dike propagation through layered rocks 1 dike penetration through a succession of upper crustal layers with different densities is studied with a new numerical code for an individual layer to significantly affect dike ascent its thickness must be of order 1 when scaled to the characteristic length scale for the inflated nose region that develops below the dike tip this characteristic length is l q 1 6 g 1 1 2 g 2 3 where and are the viscosity and buoyancy of magma g and are elastic moduli for the encasing rocks q is the magma flow rate and g gravity for basaltic dikes l is 1 km which is of the same order of magnitude as the typical thickness of sedimentary strata and volcanic deposits in such conditions dike ascent proceeds irregularly with large changes of velocity and width at an interface scaling laws for the ascent rate and dike width are derived penetration through low density layers is determined by a local buoyancy balance in the inflated nose region of the dike independently of the total buoyancy of the magma column between source and tip in such conditions a dike develops an internal overpressure that may be large enough to generate a horizontally propagating sill for this to occur the thickness of the low density layers must exceed a threshold value which depends only on the rock strength and on the average negative buoyancy of magma for basaltic melt we estimate that this threshold thickness cannot be less than about 700 m and is 2 km on average

the mechanics of sill inception propagation and growth experimental evidence for rapid reduction in magmatic overpressure abstract a model of magma propagation in the crust is presented using a series of analogue experiments where dyed water is injected at a constant flux into layers of solidified gelatine the gelatine layers are transparent and when intruded deform in an almost ideal elastic manner under the experimental conditions low gelatine concentration 2 5 or 3 wt and low temperature 5 10 c the upper gelatine layer was 1 0 to 1 5 times stiffer than the lower layer with either a weak or strong interface strength between the gelatine layers the gelatine is seeded with 20 50 m diameter pmma rhb neutrally buoyant particles that are fluoresced by a pulsed vertical laser sheet centred on the injection point digital image correlation dic is used to calculate incremental strain and finite strain in the deforming host material as it is intruded this is mapped in 2d for the developing experimental volcanic plumbing system that comprises a feeder dyke and sill since the gelatine deforms elastically strain measurements correlate with stress our results indicate that for constant magma flux the moment of sill inception is characterised by a significant magmatic pressure decrease of up to 60 this is evidenced by the rapid contraction of the feeder dyke at the moment the sill forms sill propagation is then controlled by the fracture properties of the weak interface with fluid from the feeder dyke extracted to help grow the sill pressure drops during sill inception and growth are likely to be important in volcanic systems where destabilisation of the magmatic plumbing system could trigger an eruption

effects of crustal scale mechanical layering on magma chamber failure and magma propagation within the venusian lithosphere understanding the connection between shallow subsurface magmatism and related surface expressions provides first order insight into the volcanic and tectonic processes that shape a planet s evolution when assessing the role of flexure previous investigations assumed homogeneous host rock but planetary lithospheres typically include crust and mantle material and the mechanical response of a layered lithosphere subjected to flexure may influence both shallow magma reservoir failure and intrusion propagation to assess the formation of giant radial dike systems such as those observed on venus we create axisymmetric elastic finite element models of a spherical reservoir centered at the contact between stiff dense mantle overlain by softer lighter crust we analyze magma chamber stability overpressure at rupture and resulting intrusion types for three distinct environments lithostatic upward flexure and downward flexure in the lithostatic case reservoir failure at the crust mantle contact favors lateral sill injection in the flexure cases we observe that failure location depends upon the crust lithosphere thickness ratio and at times will favor radial dike intrusion specifically upward flexure can promote the formation of giant radiating dike swarms a scenario consistent with a plume derived origin our results present a mechanical explanation for giant radial dike swarm formation showing that both the stability of magma chambers on venus and the type of intrusions that form are influenced by lithospheric layering furthermore where dike swarms occur our approach provides a powerful new way to constrain local crust mantle layering characteristics within the lithosphere at the time the swarm was forming

steep rock lake sedimentology and geochemistry of an archean carbonate platform abstract the 2800 ma mosher carbonate formation at steep rock lake in south central canada is one of earth s oldest limestone deposits it is both thick up to 500 m and relatively well preserved and was one of the first precambrian successions to be noted for evidence of early life it continues to provide information on the antiquity of such processes as photosynthesis the carbonate contains a variety of fabrics and facies from apparently fine grained bedded limestones with domal and columnar stromatolites atikokania radial fans and sheet cracks to closely packed metric scale hybrid domes of originally aragonite seafloor crust interlayered with fenestral fabric here we review previous work provide new observations concerning these sediments and their geochemistry and discuss the inception overall development and ultimate demise of the steep rock platform we divide the mosher carbonate into the lower hogarth member and upper elbow point member these units constitute a shallow water carbonate platform succession the hogarth member overlies eroded 3000 ma tonalite and is at least 120 m thick thin horizons of domal pseudocolumnar columnar and fenestral stratiform stromatolites and occasional layers of atikokania radial crystal fans occur within relatively fine grained thin bedded limestone with iron carbonate horizons in the upper part meter scale domes occur locally with sheet cracks and stromatactis the irregular laminae that build the small domal and columnar stromatolites are interpreted to be lithified mats and biofilms presumably cyanobacteria dominated fine grained well bedded facies of the lower hogarth member and its varied association of small stromatolites is interpreted to have accumulated in a relatively protected inner platform environment numerous very thin horizons of iron carbonate in the lower and upper parts of the hogarth member suggest temporally limited influence of iron rich offshore waters vertical trends in fe mn ba sr ce and 13 c probably reflect progressive restriction of circulation with at least one abrupt but short lived change back to more open seawater conditions the upper hogarth member with large banded domes and fenestral crusts and stromatolites is interpreted as back margin facies the overlying elbow point member is at least 70 m thick and appears to be entirely composed of innumerable juxtaposed elongate smooth and thickly layered domes lacking intervening sediment each dome is typically several meters across and composed of centimetric alternations of cuspate fenestral fabric possibly microbial and crystal fan fabric that is probably abiotic seafloor aragonite precipitate adjacent cuspate fenestral and crystal fan fabric show significant differences in concentration of 13 c sr ba fe and mn this giant dome facies is interpreted as a platform margin deposit in which alternating calcite aragonite mineralogies within each dome reflect a laterally fluctuating offshore redox boundary negative ce anomalies positive gd anomalies and reduced positive eu anomalies relative to laterally correlative deep water iron formation occur in the majority of crystal fan samples and in some cuspate fenestral fabric samples ca carbonate precipitation at the margin of an anoxic iron rich sea would have been promoted by oxygenic removal of iron from seawater otherwise fe carbonate would have been favored over ca carbonate precipitation the mosher carbonate formation is interpreted as an early marine oxygen oasis a shallow platform that favored cyanobacterial productivity was sufficiently isolated from open marine circulation for the seawater to become relatively oxygenated and where carbonate sediment aggradation was a positive feedback that sustained these shallow water conditions limestone accumulation terminated as transgressive suboxic and anoxic seawater deposited first manganese oxide rich and then manganese oxide poor iron formation sediments

propagation regimes of buoyancy driven hydraulic fractures with solidification this study investigates the propagation of a semi infinite buoyancy driven hydraulic fracture in situations when the fluid is able to solidify along the crack walls such problems occur when hot magma ascends from a chamber due to buoyancy forces and solidifies by interacting with colder rock in the model the solidification rate is calculated assuming a one dimensional heat transfer problem in which case it becomes mathematically equivalent to carter s leak off model which is commonly used to describe the fluid leak off from a hydraulic fracture into a porous rock formation in order to construct a mathematical model for a buoyancy driven hydraulic fracture with solidification the aforementioned thermal problem is combined with i linear plane strain elasticity to ensure equilibrium of the rock surrounding the fracture ii linear elastic fracture mechanics to determine the fracture propagation iii lubrication theory to capture the viscous fluid flow inside the crack and to account for the effect of buoyancy and iv volume balance of the magma to address the problem the governing equations are first rewritten in terms of one integral equation with a non singular kernel which significantly simplifies the analysis and the procedure for obtaining a numerical solution the latter solution is shown to obey a multiscale behaviour near the fracture tip that is fully resolved by the numerical scheme in order to understand the structure of the solution and to quantify the regimes of propagation and the associated transitions a thorough analysis of the problem has been performed finally the developments are applied to investigate the non steady propagation of a buoyancy driven fracture that is fed by a constant flux

a model for radial dike emplacement in composite cones based on observations from summer coon volcano colorado usa we mapped the geometry of 13 silicic dikes at summer coon an eroded oligocene stratovolcano in southern colorado to investigate various characteristics of radial dike emplacement in composite volcanoes exposed dikes are up to about 7 km in length and have numerous offset segments along their upper peripheries surprisingly most dikes at summer coon increase in thickness with distance from the center of the volcano magma pressure in a dike is expected to lessen away from the pressurized source region which would encourage a blade like dike to decrease in thickness with distance from the center of the volcano we attribute the observed thickness pattern as evidence of a driving pressure gradient which is caused by decreasing host rock shear modulus and horizontal stress both due to decreasing emplacement depths beneath the sloping flanks of the volcano based on data from summer coon we propose that radial dikes originate at depth below the summit of a host volcano and follow steeply inclined paths towards the surface near the interface between volcanic cone and basement which may represent a neutral buoyancy surface or stress barrier magma is transported subhorizontally and radially away from the center of the volcano in blade like dikes the dikes thicken with increasing radial distance and offset segments and fingers form along the upper peripheries of the intrusions eruptions may occur anywhere along the length of the dikes but the erupted volume will generally be greater for dike fed eruptions far from the center of the host volcano owing to the increase in driving pressure with distance from the source observed eruptive volumes vent locations and vent area intrusions from inferred post glacial dike fed eruptions at mount adams washington usa support the proposed model hazards associated with radial dike emplacement are therefore greater for longer dikes that propagate to the outer flanks of a volcano

forced stationary planetary waves in mars s winter atmosphere abstract mariner 9 and viking spacecraft observations provided evidence for planetary scale wavelike disturbances in the mars winter atmosphere possible sources of the wave activity are dynamical instabilities for example barotropic and or baroclinic instabilities other candidate sources are forced quasi stationary planetary waves waves that arise predominantly via zonally asymmetric surface properties the authors attempt to model aspects of the wave activity focusing on forced planetary waves in representative wintertime atmospheres for mars by applying a spherical linear primitive equations model basic states representing relatively nondusty and highly dusty conditions near winter solstice allow wavenumber 1 and 2 disturbances to propagate meridionally and vertically about the jet higher wavenumbers are strongly vertically trapped stationary waves during winter in the northern and southern extratropics differ strongly in amplitude phase and dominant horizontal wave pattern northern

the role of rift zone storage in controlling the site and timing of eruptions and intrusions of kilauea volcano hawaii repeated eruptive and intrusive activity on the east rift zone of kilauea volcano allows dikes to exist within the rift zone for extended periods of time leakage of magma from the summit storage region into the rift zone can cause inflation of a rift zone dike inflation raises the excess pressure at the dike centre and increases the stress intensity at the dike edges if the inflation is sufficiently large the stress intensity may exceed the fracture toughness of the country rocks and allow vertical or lateral dike emplacement to occur theoretical modelling can be used to predict the conditions under which vertical or lateral dike propagation and hence eruptive or intrusive activity may occur over typical ranges of dike half height and regional tension gradient vertical propagation and hence eruption are favored by high fracture toughness relatively low dike half heights and low regional tension gradients lateral propagation can occur when the fracture toughness is low when dike half height is higher and when the regional tension gradient is high the results of from the model constrain the fracture toughness within the east rift zone to be 100 110 mpa m and the regional tension gradient to be 1000 pa m

rock interface strength influences fluid filled fracture propagation pathways in the crust abstract rock interface strengths have often been assumed to be zero in numerical and analogue models of fracture propagation and magma intrusion in the crust rock strength tests were performed to explore the role that rock interfaces have on the geometry and propagation dynamics of fluid filled fractures in the crust we used a 1 kn test machine to study 5 mm thick cuboidal specimens cut from a sandstone siltstone rock core where the strata were known to host magma intrusions and the rock interface between the units was intact by measuring the load required to grow a crack running along the lithological contact between the layers we calculate its fracture toughness k c the siltstone had an average k c of 0 56 0 03 mpa m 1 2 compared to the sandstone at 0 42 0 02 mpa m 1 2 the rock interface had intermediate average fracture toughness to the parent units at 0 45 0 03 mpa m 1 2 these results have important implications on fracture propagation pathways through rocks as well as for the geometry and propagation dynamics of magma intrusions in the crust

control of pore fluid pressure on depth of emplacement of magmatic sills an experimental approach article in sedimentary basins the emplacement of magmatic sills tends to occur within rock of low mechanical competence and permeability such as shale this often contains pore fluids at abnormally high pressure we first theoretically show that in anisotropic media the higher the pore fluid pressure the deeper the sill emplacement then we introduce a new technique for analogue modelling of such intrusive bodies under conditions of fluid overpressure greater than hydrostatic which corroborate the theoretical analysis as an analogue of brittle sediment we use a diatomite powder this material is a dry fine grained frictional cohesive and permeable material as an analogue for magma we take a silicone putty rtv silicone which is at first newtonian but then solidifies at room temperature we use compressed air as a pore fluid under these experimental conditions we investigate the intrusion of magma into the host powder under various fluid overpressures in homogeneous diatomite powder having uniform cohesion intrusive bodies are segmented dykes these become feeders to sills if the fluid overpressure exceeds the weight of overburden where the sedimentary column has a horizontal discontinuity in strength the transition from dyke to sill occurs at a smaller overpressure hydrostaticb exb1 as a possible illustration of these results we consider sills within source rocks of the neuquen basin and of the parana basin both in south america where overpressure may have resulted from maturation of organic material

volcanic history geologic analysis and map of the prometheus patera region on io data from jupiter s moon io returned by the galileo spacecraft have been used to create a geologic map of prometheus patera its associated flow field and nearby features we have identified the location of the vent that fed the prometheus flow field during the galileo epoch in the north eastern portion of the main prometheus flow field this vent is the probable source of a small sulphur rich plume previous studies suggested that the vent may be atop a tectonic fault but we find that the vent is offset from the putative fault it is plausible that in the past magma exploited the fault to reach the surface at prometheus patera but subsequent magma cooling in the conduit could have caused an obstruction preventing further eruptions from providing significant contributions to the prometheus flow field we also speculate on how a new prometheus plumbing system may be fed by mafic magmas after melt stalls in magma reservoirs during its ascent through the lithosphere from the mantle

propagation and arrest of dikes under topography models applied to the 2014 bardarbunga iceland rifting event dikes along rift zones propagate laterally downslope for tens of kilometers often becoming arrested before topographic reliefs we use analogue and numerical models to test the conditions controlling the lateral propagation and arrest of dikes exploring the presence of a slope in connection with buoyancy and rigidity layering a gentle downslope assists lateral propagation when combined with an effective barrier to magma ascent e g gelatin stiffness contrasts while antibuoyancy alone may be insufficient to prevent upward propagation we also observe that experimental dikes become arrested when reaching a plain before opposite reliefs our numerical models show that below the plain the stress field induced by topography hinders further dike propagation we suggest that lateral dike propagation requires an efficient barrier rigidity to upward propagation assisting antibuoyancy and a lateral pressure gradient perpendicular to the least compressive stress axis while dike arrest may be induced by external reliefs

gelatins as rock analogs a systematic study of their rheological and physical properties abstract in a laboratory model the behavior of the selected analog material must be properly scaled to nature here we systematically investigate both rheological and physical properties of a wide range of gelatins as functions of temperature composition concentration ageing and applied strain rate results show that gelatins behavior changes gradually from purely elastic to visco elasto brittle to purely viscous nonlinear rheology going from the gel to the sol state the rheological variability of gelatins appears promising for the potential use of these analog materials to simulate crustal and lithospheric rheological behavior in particular we found that pig skin 2 5 wt at 10 c has the required rheological properties for a suitable experimental set up to model crustal deformation

challenging dyke ascent models using novel laboratory experiments implications for reinterpreting evidence of magma ascent and volcanism volcanic eruptions are fed by plumbing systems that transport magma from its source to the surface mostly fed by dykes here we present laboratory experiments that model dyke ascent to eruption using a tank filled with a crust analogue gelatine which is transparent and elastic that is injected from below by a magma analogue dyed water this novel experimental setup allows for the first time the simultaneous measurement of fluid flow sub surface and surface deformation during dyke ascent during injection a penny shaped fluid filled crack is formed intrudes and traverses the gelatine slab vertically to then erupt at the surface polarised light shows the internal stress evolution as the dyke ascends and an overhead laser scanner measures the surface elevation change in the lead up to dyke eruption fluorescent passive tracer particles that are illuminated by a laser sheet are monitored and the intruding fluid s flow dynamics and gelatine s sub surface strain evolution is measured using particle image velocimetry and digital image correlation respectively we identify 4 previously undescribed stages of dyke ascent stage 1 early dyke growth the initial dyke grows from the source and two fluid jets circulate as the penny shaped crack is formed stage 2 pseudo steady dyke growth characterised by the development of a rapidly uprising central single pseudo steady fluid jet as the dyke grows equally in length and width and the fluid down wells at the dyke margin sub surface host strain is localised at the head region and the tail of the dyke is largely static stage 3 pre eruption unsteady dyke growth an instability in the fluid flow appears as the central fluid jet meanders the dyke tip accelerates towards the surface and the tail thins surface deformation is only detected in the immediate lead up to eruption and is characterised by an overall topographic increase with axis symmetric topographic highs developed above the dyke tip stage 4 is the onset of eruption when fluid flow is projected outwards and focused towards the erupting fissure as the dyke closes a simultaneous and abrupt decrease in sub surface strain occurs as the fluid pressure is released our results provide a comprehensive physical framework upon which to interpret evidence of dyke ascent in nature and suggest dyke ascent models need to be re evaluated to account for coupled intrusive and extrusive processes and improve the recognition of monitoring signals that lead to volcanic eruptions in nature

rheology of pig skin gelatine defining the elastic domain and its thermal and mechanical properties for geological analogue experiment applications abstract gelatine is a viscoelastic polymer that has been employed widely in geological analogue experiments to study processes related to the elastic behaviour of rocks such as tensile fracturing seismicity and magma intrusion however the elastic domain of this material has not yet been clearly defined by rheological tests here we describe the rheology and define the elastic domain of 250 bloom 20 mesh pigskin gelatine at concentrations 10 wt and temperatures of 5 25 c however these results are strongly comparable with gelatine of 245 260 bloom new equations are given for the shear and elastic moduli in relationship to temperature and gelatine concentration it is found that at concentrations 3 wt the tested gelatine is best described by a rheological model composed of a combination of kelvin voight and maxwell elements and therefore is not suitable to model elastic behaviour in geological analogue experiments at higher concentrations it is best described by a simpler viscoelastic model comprising a single maxwell element in order to ensure that geological analogue experiments remain within the elastic domain where the elastic component is far greater than the viscous component strain rates should range between 0 1 and 10 s 1 and temperature values should be 3 wt analogue experiments using gelatine approximate the elastic behaviour of natural rocks more closely than previously assumed

stability of bubbles in a linear elastic medium implications for bubble growth in marine sediments 1 methane bubbles in muddy fine grained sediments grow initially through a process of elastic expansion punctuated by discrete fracture events lefm growth the ability of the surrounding sediments to support a stress and actively resist expansion can under conditions of low gas production or high sediment toughness result in the cessation of growth and the presence of stable bubbles thus it is possible for a bubble to stop growing despite the presence of a source in the sediments that continues to produce gas this contrasts with growth of bubbles in a fluid medium which cannot support a stress and so will continue to grow as long as a surrounding source provides gas this no growth condition is the result of the coupling between gas supply methane production or supersaturation and the sediment mechanics here we quantify this condition and present a criterion for the switch between no growth and the lefm growth regimes we apply this theory to the sediments of eckernforde bay in the kiel bight germany and despite the absence of measurements for the key sediment mechanical properties we can provide a qualitative explanation for the sizes and shapes of the observed bubble population with depth in the sediment we also show how the release of hydrostatic pressure can stimulate growth by pushing otherwise stable bubbles into the lefm growth regime this could provide a mechanism for the release of bubbles during periods of low water such as during low tide or wave events