late stage water eruptions from ascraeus mons volcano mars implications for its structure and history abstract ascraeus mons was one of the first of the martian volcanoes to be imaged by the high resolution stereo camera hrsc experiment onboard the esa mars express spacecraft these images show much of the volcano at a higher resolution than previously and details of its lava flows sinuous rilles flank vents and tectonic features indicate an unexpected origin for some of these features we establish the time stratigraphic sequence for these features and use a numerical model on hrsc stereo dtms of the sinuous rilles and conclude that they were formed by water erosion terrestrial analogues for such features are found at reunion island and other volcanoes we then examine the overall structure of the volcano which is dissimilar to that of large terrestrial volcanoes in important respects and perform laboratory analogue experiments of its deformation concluding that the tectonic features were formed by sinking of the volcano into a substratum that was much weaker than the volcanic edifice an ice rich substratum melted by a combination of pressure melting and magmatic heating seems the most likely mechanism analogous water escape structures in a similar volcanic situation have been identified at mt haddington in the antarctic the possible role of a hydrological cycle and a hydrothermal system within the volcano are discussed based on field evidence we propose that much of the broad aprons of lobate flows issuing from the ne and ssw foot of ascraeus mons are composed of mudflows rather than lava flows these different approaches are linked into a coherent history of this volcano the similarity of ascraeus mons to pavonis mons and arsia mons though ascraeus is younger suggests that some of our conclusions may apply to these volcanoes too

integrated electrical resistivity tomography ert and self potential sp techniques for assessing hydrological processes within glacial lake moraine dams moraine dams can be inherently unstable but effective assessment strategies remain poorly identified we integrate electrical resistivity tomography ert with electrical self potential sp and lake level measurements to investigate the structure of and hydrological processes within a moraine dam complex adjacent to miage glacier italy this complex separates two meltwater lakes characterized by an efficient subterranean hydraulic connection our ert data reveal a continuous free surface within the complex whose morphology reflects the topography of the moraine complex akin to unconfined groundwater aquifers sp data were corrected for spatial changes in the thickness of the upper unsaturated layer using principles of electrography the residual streaming potential map is consistent with darcian flow of lake waters through the moraine complex characterized by a negative to positive potential change from 70 mv these electrical signatures are consistent with those generated by water seepage through earth dams in various non glacial settings integrated electrical geophysical methods thus provided an inexpensive and unobtrusive evaluation of the hydrological properties of and processes within the moraine complex since spatio temporal patterns of subsurface water flow critically affect the strengths of moraine sediments such methods promise to be powerful in assessing the long term stability of moraine dammed glacial lakes

experimental modelling of ground deformation associated with shallow magma intrusions abstract active volcanoes experience ground deformation as a response to the dynamics of underground magmatic systems the analysis of ground deformation patterns may provide important constraints on the dynamics and shape of the underlying volcanic plumbing systems nevertheless these analyses usually take into account simplistic shapes sphere dykes sills and the results cannot be verified as the modelled systems are buried in this paper i present new results from experimental models of magma intrusion in which both the evolution of ground deformation during intrusion and the shape of the underlying intrusion are monitored the models consisted of a molten vegetable oil simulating low viscosity magma injected into cohesive fine grained silica flour simulating the brittle upper crust oil injection resulted is sheet intrusions dykes sills and cone sheets the initial topography in the models was flat while the oil was intruding the surface of the models slightly lifted up to form a smooth relief which was mapped through time after an initial symmetrical development the uplifted area developed asymmetrically at the end of the experiments the oil always erupted at the steepest edge of the uplifted area after the experiment the oil solidified the intrusion was excavated and the shape of its top surface mapped the comparison between the uplifted zone and the underlying intrusions showed that 1 the complex shapes of the uplifted areas reflected the complex shapes of the underlying intrusions 2 the time evolution of the uplifted zone was correlated with the evolution of the underlying intrusion and 3 the early asymmetrical evolution of the uplifted areas can be used to predict the location of the eruption of the oil the experimental results also suggest that complex intrusion shapes inclined sheet cone sheet complex sill may have to be considered more systematically in the analyses of ground deformation patterns on volcanoes

numerical modelling of self potential signals associated with a pumping test experiment summary the study of electrical signals associated with groundwater flow is a powerful method to determine in a non invasive way the distribution of hydraulic heads in aquifers hence the distribution of the hydraulic conductivity and storativity experimental hydraulic heads and electrical self potential sp signals associated with a pumping test in an unconfined aquifer were reproduced with a numerical model based on the finite difference method for simplicity we assumed axial symmetry around the pumping well we assessed the equivalent hydraulic conductivity and specific storage of the aquifer by fitting the piezometric levels obtained in the course of the pumping against synthetic hydraulic heads produced by the model the current coupling coefficient is obtained from the best fit between the experimental and modelled sp signals at the end of the pumping phase then keeping the previously determined hydraulic parameters the relaxation of both the hydraulic heads and the sp signals were modelled and found to be consistent with the measured values the data show almost linear relationships between the hydraulic heads in the aquifer and the electrical signals recorded at the ground surface these results show that sp signals allow monitoring subsurface flow in the course of pumping experiments

field evidence for flank instability basal spreading and volcano tectonic interactions at mt cameroon west africa the mt cameroon volcano is the highest and most active volcano of the cameroon volcanic line little geological information is available for improving the understanding of the structure of this large volcanic system and its relationship to regional tectonics after reviewing the tectonic evolution of the region the analysis of a digital elevation model and results from a field campaign dedicated to mapping geological structures in the summit area and at the se base of mt cameroon are presented mt cameroon is a lava dominated volcano with long steep over 30 flanks it is elongate parallel to its well defined rift zone the summit plateau is bordered by 10 m high cliffs formed by summit subsidence along normal faults geological profiles were measured along rivers cutting through a topographic step at the se base of mt cameroon this step is associated with deformed miocene sediments from the douala basin that are overlain by volcanic products weak sediments of this area are deformed by 050 060 and 020 030 trending asymmetrical folds verging toward the se and thrusts faults related to the spreading of the volcano over its mechanically weak substratum combined remote sensing and field observations suggest that spreading is accommodated by summit subsidence and flanks sliding both slow spreading movements and catastrophic collapses of the steep flanks are interpreted to result from complex interactions between the growing edifice repeated dyke intrusions the weak sedimentary substratum and tectonic structures

a sagging spreading continuum of large volcano structure gravitational deformation strongly infl uences the structure and eruptive behavior of large volcanoes using scaled analog models we characterize a range of structural architectures produced by volcano sagging and volcano spreading these arise from the interplay of variable basement rigidity and volcano basement de coupling from comparison to volcanoes on earth la reunion and hawaii and mars elysium and olympus montes the models highlight a structural continuum in which large volcanoes throughout the solar system lie

gravity driven deformation of damavand volcano iran detected through insar time series the detection and monitoring of gravity driven volcano deformation are vital for understanding volcanic hazards such as landslides lateral blasts and debris avalanches although deformation has been detected at several large active volcanoes e g mount etna vesuvius kilauea these systems also exhibit persistent magmatic activity obscuring the gravity driven signals of ground motion in this study we present a first interferometric synthetic aperture radar insar deformation time series at the dormant damavand volcano in northern iran over the period a d 2003 2008 the high resolution data show a lateral extension of the volcano at the relative rate of as much as 6 mm yr accompanied by subsidence at the rate of as much as 5 mm yr at the volcano summit we find that lateral motion of the east flank is more significant than that of the west flank on the basis of past understanding and modeling of deforming volcanoes elsewhere we interpret this new evidence to reveal long term slow gravity driven deformation possibly in the form of gravitational spreading at damavand this persistent deformation activity is well expressed although no volcanic activity was ever reported in history this finding shows that magmatic activity is not required for spreading and highlights the importance of identifying long lived gravity driven deformation for hazard assessment at dormant or inactive volcanoes

structural analysis of the early stages of catastrophic stratovolcano flank collapse using analogue models many major volcanic flank collapses involve the failure of low angle strata in or under the edifice such failures produce voluminous destructive debris avalanches that are a major volcanic hazard at socompa las isletas mombacho and parinacota volcanoes field studies have shown that during catastrophic flank collapse a significant segment of their substrata was detached and expelled from beneath the volcanic edifice and formed a mobile basal layer on which the sliding flanks were transported previous studies have proposed that gravitational flank spreading was likely involved in the onset of sudden substrata failure the early stages of this particular type of flank collapse can be modelled under laboratory conditions using analogue models this allows us to study the development of structures accommodating early deformation of the sliding flank during catastrophic collapse in the experiments the detached substratum segment low viscosity basal layer was modelled with a silicone layer and the overlying stratovolcano with a layered sand cone the first structure developed in the models is a graben rooted in the low viscosity basal layer this graben forms the limits of the future avalanche amphitheatre and divides the sliding flank into a toreva domain upper sliding flank and a hummock domain lower sliding flank these domains display distinctive structural patterns and kinetic behaviour normal faults develop in the toreva domain and inside the graben while the hummock domain is characterised by transtensional structures the hummock domain also over thrusts the lower amphitheatre sides which allows subsequent sideways avalanche spreading measurements show that horizontal speeds of the hummock domain are always higher than that of the toreva domain during model collapse the main role played by the low viscosity basal layer during this type of collapse is to control the size shape and structural complexity of the sliding flank it also transmits mass and momentum from the toreva to the hummock domain

directional flank spreading at mount cameroon volcano evidence from analogue modeling mount cameroon is characterized by an elongated summit plateau steep flanks and topographic terraces around its base although some of these features can be accounted for by intrusion induced deformation we here focus on the contribution of edifice scale gravitational spreading in the structure of mount cameroon we review the existing geological and geophysical data and morphostructural features of mount cameroon and surrounding sedimentary basins volcanic ridge gravitational spreading is then simulated by scaled analogue models on which fault formation is recorded using digital image correlation three sets of models are presented i models recorded in cross section type i ii models recorded from above with a uniform type iia and iii nonuniform ductile layer type iib type i models illustrate the formation of faults accommodating summit subsidence and lower flank spreading type iia models favor displacement perpendicular to the long axis with formation of a summit graben and basal folds but fail to reproduce the steep flanks type iib models investigate the effect of spatial variations in sediment thickness and or properties consistent with geological evidence directional spreading of the volcano s central part perpendicular to the long axis is accounted for by a sediment layer with restricted lateral extent and increasing thickness away from the volcano axis the later model closely reproduces key features observed at mount cameroon steep upper flanks are accounted for by enhanced lateral spreading of the lower flanks relative to the summit the relevance of these findings for understanding flank instabilities at large oceanic volcanoes is finally highlighted

repeat ridge jumps and microcontinent separation insights from ne arabian sea abstract microcontinents separate due to ridge jumps associate either asymmetric sea floor spreading or plume ridge interactions india separated from seychelles at 64 ma by asymmetric sea floor spreading initially when the spreading centre in the mascarene basin jumped towards the indian sub continent between magnetic chrons c29 and c28 the subsequent tectonics is difficult to comprehend since laxmi ridge another microcontinent formed during the later phase most of the studies considered the laxmi ridge as a sliver others considered it to be oceanic crust high resolution deep 25 km seismic data reveals that i the ridge possesses 15 km deep sea ward dipping reflector sdr packages ii normal faulted rift valleys devoid of syn rift sedimentary packages and iii axial magma chambers 5 7 km beneath the ridge top additionally from 2d forward gravity models we deduce that the ridge most possibly comprises of high density oceanic crust we conclude the laxmi ridge to be indeed composed of oceanic crust and a fossil spreading centre we thus identified the ridge jumps and their relation to the seychelles microcontinent separation previous numerical models suggest that the time required for a ridge jump is controlled by magmatic heating spreading rate at the ridge and plate ages for repeated ridge jumps the additional factor is the dynamic relation between the plume and lithosphere in terms of melt transfer and heating we find that the medium spreading rates and high magmatic heating due to the reunion plume and young plates favoured rapid and repeated ridge jumps towards the plume

catastrophic collapse at stratovolcanoes induced by gradual volcano spreading unlike ordinary mountains which are formed by slow uplift and erosion volcanoes are constructed rapidly as a consequence many are liable to massive flank failures leading to debris avalanches for example at mount st helens in 1980 such failures occur worldwide about once every 25 years ref 1 and even small ones can present a major hazard in particular if far reaching tsunamis are generated as at mayu yama in 1792 ref 2 previous work has tended to emphasize differences in eruption style associated with flank failure2 but here we focus on the fundamental structural causes of failure most volcanic failures are generated by magmatic intrusion and flank spreading3 we present evidence however that mombacho volcano in nicaragua experienced a previously unrecognized type of failure triggered by sub volcanic basement spreading notably collapses related to basement spreading do not require that the volcano be magma tically active and thus flank failure may pose a significant risk even at inactive volcanoes which are rarely monitored

alluvial fans on volcanic islands a morphometric perspective sao vicente cape verde abstract the distribution morphology and development of volcanic island alluvial fans are investigated using sao vicente from the cape verde volcanic chain east central atlantic ocean this is a tectonically and volcanically inactive dryland setting comprising an eroded plio pleistocene composite volcano overlying a submarine shield volcano we mapped 228 alluvial fans quantifying fan f and catchment c morphological properties area a gradient g relief r length l fans and catchments of varying size and gradient are distributed around the island coastal margins 6 and along interior valley sides 94 regression results i e ve ve slopes of best fit lines conformed to broader fan research but with weak correlations and coefficient exponent values outside or at the lower end of values reported from non volcanic settings analysis of fan area and gradient vs catchment area regression residuals revealed fans were dominated by small steep gradient 28 and large low gradient forms 39 fan building space is a fundamental control specifically linked to volcano structure but with interplay between rock strength base level and climate fans around the volcanic edifice flanks are uncommon due to steep flank slopes where flank margin fans occur they are typically small and steep forms due to marine erosion fans along flank incised valleys are common large low gradient fans are associated with a major volcanic rift aligned valley structure with extensive erosion into altered and weathered edifice core lithologies small steep gradient fans are associated with edifice flank valleys steeper and narrower valley forms reflect incision into stronger lithologies of the composite volcano flanks restricting fan building space fans located within the volcano central depression are amongst the largest and lowest gradient types building into the eroded and unconfined edifice core space coalescence apex toe incision toe erosion and catchment stream channel backfilling displayed by most fans suggest landscape erosion dominates during more arid periods e g interglacials with the dryland setting generating limited sediment and insufficient flood runoff for transport and fan deposition fan building likely occurs during wetter periods linked to quaternary climate variability quaternary eustatic variations are relevant for the volcano edifice margins where sea level changes control fan building space and erosion

the interaction between volcanoes and strike slip transtensional and transpressional fault zones analogue models and natural examples regional strike slip faulting can control magma movements deform volcanoes and may destabilise their flanks the aim of this study is to address this problem by comparing two natural examples basse terre island volcanoes lesser antilles and maderas volcano nicaragua with analogue experiments the field and remote sensing analyses of their structures reveal that guadeloupe volcanoes which developed in a1 45 striking sinistral transtensional fault zone are dominantly fractured in a 090 e120 direction which is parallel to the maximum principal horizontal stress and to the elongation direction of the summit graben of analogue models this graben is bordered by the sigmoid i fault or y shear structure and has facilitated the formation of the beaugendre and vieux habitants valleys by faulting erosion or collapse this structure has also influenced the injection of dykes and the transport of hydrothermal fluids the comparison of maderas volcano with the analogue models confirms that the volcano has developed parallel to a 135

hybrid collapse mechanism at piton de la fournaise volcano reunion island indian ocean 1 recent studies have shown that hydrothermal alteration in the core of volcanoes may weaken the edifice and trigger sector collapse lopez and williams 1993 day 1996 voight and elsworth 1997 van wyk de vries et al 2000 reid et al 2001 alteration of volcanic products must take place over long periods of times before collapse can occur so this process is considered to be less frequent than volcanic failure generated by magmatic intrusion and flank spreading however acceleration of this slow process may occur along one direction as a result of a weak lateral confinement following outward gravitational sliding of a flank of the volcano we present here evidence that the enclos fouque depression of piton de la fournaise volcano results from such a hybrid mechanism seaward sliding of the grand brule trough on top of an ancient hypovolcanic complex led to a lateral unconfined boundary along which collapse of the altered core of the edifice took place the result is a caldera like structure breached on the grand brule slide scaled experiments to simulate this process of pseudocaldera formation reveal tectonic features remarkably similar to those encountered in the field and demonstrate the mechanical consistency of the model similar processes may have played a role in the evolution of other volcanoes

application of open source photogrammetric software micmac for monitoring surface deformation in laboratory models quantifying deformation is essential in modern laboratory models of geological systems this paper presents a new laboratory monitoring method through the implementation of the open source software micmac which efficiently implements photogrammetry in structure from motion algorithms critical evaluation is provided using results from two example laboratory geodesy scenarios magma emplacement and strike slip faulting micmac automatically processes images from synchronized cameras to compute time series of digital elevation models dems and orthorectified images of model surfaces micmac also implements digital image correlation to produce high resolution displacements maps the resolution of dems and displacement maps corresponds to the pixel size of the processed images using 24 mp cameras the precision of dems and displacements is 0 05 mm on a 40 40 cm surface processing displacement maps with matlab scripts allows automatic fracture mapping on the monitored surfaces micmac also offers the possibility to integrate 3 d models of excavated structures with the corresponding surface deformation data the high resolution and high precision of micmac results and the ability to generate virtual 3 d models of complex structures make it a very promising tool for quantitative monitoring in laboratory models of geological systems

the volcano tectonic evolution of concepcion nicaragua we describe the evolution of concepcion volcano by integrating regional geology eruptive activity morphology stratigraphy petrology structure and active deformation data this nicaraguan volcano is set close to the back limb of the northwest trending tertiary rivas anticline a regional structure that bounds the southwest side of lake nicaragua concepcion rises 1 600 m above a 1 km thick sequence of quaternary lacustrine mud stones there is no record of volcanism in the lake prior to concepcion in addition the only nearby volcano maderas volcano has not deposited material on concepcion because of the trade winds thus concepcion and made ras too can be considered as pristine volcanic environments unaffected by other centres a topographic rise forms an annulus 20 km in diameter around the cone the rise is created by thrust related folds at the western base where the trade winds have accumulated a thick sequence of tephra and by mud diapirs at the eastern base where only lake mudstones are present four magmatic eruptive episodes exist in the stratigraphic record the first begins with primitive low alumina basalt and subsequently evolves to dacitic compositions the following three episodes begin with high alumina basalts and evolve only to silicic andesites the occurrence of the high alumina basalt after the first episode is indicative of crystal fractionation at lower crustal depths the first episode may be associated with a compressive phase of volcano evolution in this phase the edifice load compresses substrata allowing a longer magma residence time and differentiation in a shallow reservoir possibly located at the density contrast between the lake sediments and the tertiary flysch during the next three episodes the weak sediments below the volcano started to rupture and yield under its increasing load beginning a thrusting diapiring phase of volcano evolution because of outward thrusting vertical and horizontal stresses above the chamber were reduced allowing magma to erupt more easily and to reach a lesser degree of evolution if we consider the future evolution of concepcion the differentiation in the shallow reservoir has probably generated a cumulitic complex which eventually will start to deform and spread beginning another this time plutonic spreading phase this phase which may be beginning now could allow less evolved magmas to be erupted again four components influence the phases of volcano evolution 1 the regional geology that is the boundary condition of the environment 2 the substrata rheology that controls deformation 3 the load of the volcanic edifice and 4 the magma which provides the input of mass and energy our model of volcanic evolution suggests that concepcion is a complex geologic environment the volcanic activity tectonics and hazards can only be constrained through a complete knowledge of the many components of this environment

near n s paleo extension in the western deccan region india does it link strike slip tectonics with india seychelles rifting this is the first detailed report and analyses of deformation from the w part of the deccan large igneous province dlip maharashtra india this deformation related to the india seychelles rifting during late cretaceous early paleocene was studied and the paleostress tensors were deduced near n s trending shear zones lineaments and faults were already reported without significant detail an e w extension was envisaged by the previous workers to explain the india seychelles rift at 64 ma the direction of extension however does not match with their n s brittle shear zones and also those faults sub vertical ne sw nw se and few n s we report and emphasize in this work slickenside bearing fault planes brittle shear zones and extension fractures in meso scale enabled us to estimate the paleostress tensors directions and relative magnitudes the field study was complemented by remote sensing lineament analyses to map dykes and shear zones dykes emplaced along pre existing n s to ne sw nw se shears fractures this information was used to derive regional paleostress trends a nw se ne sw minimum compressive stress in the oldest kalsubai subgroup and a n s direction for the younger lonavala wai and salsette subgroups were deciphered thus a nw ne to n s extension is put forward that refutes the popular view of e w india seychelles extension paleostress analyses indicate that this is an oblique rifted margin field criteria suggest only ne sw and nw se with some n s strike slip faults brittle shear zones we refer this deformation zone as the western deccan strike slip zone wdsz the observed deformation was matched with offshore tectonics deciphered mainly from faults interpreted on seismic profiles and from magnetic seafloor spreading anomalies these geophysical findings too indicate oblique rifting in this part of the w indian passive margin we argue that the seychelles microcontinent separated from india only after much of the dlip erupted further studies of magma rich passive margins with respect to timing and architecture of deformation and emplacement of volcanics are required

numerical simulation of electrokinetic potentials associated with subsurface fluid flow a postprocessor has been developed to calculate space time distributions of electrokinetic potentials resulting from histories of underground conditions pressure temperature vapor saturation concentrations of dissolved species flow rate etc computed by unsteady multidimensional geothermal reservoir simulations electrokinetic coupling coefficients are computed by the postprocessor using formulations based on experimental work reported by ishido and mizutani 1981 the postprocessor was applied to both numerical modeling of natural self potential sp anomalies in geothermal fields and production induced sp changes the essential features of the sp anomalies and sp changes which have actually been observed in real geothermal fields are reproduced reasonably well in these calculations for both single phase liquid and two phase vapor liquid geothermal reservoirs the postprocessor was also applied to predicting the magnitude of electrical earthquake precursory signals caused by dilatant strains taking place within a narrow vertical fault zone if the rate of porosity increase is high enough to induce substantial pore pressure decrease two phase flow develops in the fault zone and produces observable signals at the ground surface if a high conductivity channel connects the near surface region and the deep fault zone

the 18 7 ka phreatomagmatic flank eruption on etna italy relationship between eruptive activity and sedimentary basement setting this paper documents a phreatomagmatic flank eruption that occurred 18 700 100 a bp on the lower north eastern slope of etna during the ellittico volcano activity which produced fall and surge deposits this type of eruption is connected to a sedimentary basement ridge at etna the interaction between the rising magma and the shallow groundwater hosted in the volcanic pile overlying the impermeable sediments resulted in phreatomagmatic instead of strombolian activity three eruptive phases are distinguished based on field and analytical data i an explosive phreatomagmatic opening ii a main phase producing coarse lithic rich fallout and a strombolian deposit and iii the final pulsating surge forming phase the discovery of this phreatomagmatic flank eruption which occurred at lower altitude raises important issues for previous hazard assessments at etna

electrokinetic spontaneous polarization in porous media petrophysics and numerical modelling abstract the behaviour of streaming potential is directly related to movement of groundwater the responses for typical subsurface flows are modelled to investigate possibilities of spontaneous polarization sp when performing quantitative data interpretation the physical properties of geomaterials related to streaming potential are described a magnitude range of streaming current coefficient is assessed for geomaterials and found to be from 10 10 to 10 8 a pa m depending on water salinity and rock composition the electrical sources of sp caused by groundwater flow in saturated media are theoretically described it is shown that sp is completely defined by three types of electrical sources situated 1 on boundaries where water enters or quits porous media 2 in areas with transient regime and 3 on the boundaries of rocks with different properties hydraulic conductivity streaming current coefficients and electrical conductivity a 2d computer program based on the method of finite difference was created to provide numerical successive modelling of both groundwater flow and sp using sill s geophysics 48 1983 76 approach first the water heads are calculated then electrical sources of sp are obtained on the basis of the calculated heads and coefficient of streaming current finally the sp is obtained on the basis of calculated electrical sources and subsurface electrical conductivity numerical examples illustrating sp responses of infiltration of barrage with different electrical conductivity and of well pumping are discussed field data obtained at the site containing the dam between superficial artificial reservoir and the river are interpreted on the basis of numerical modelling the discussed method can be mainly used for additional calibration of groundwater flow models

rapid deformation of the south flank of kilauea volcano hawaii the south flank of kilauea volcano has experienced two large magnitude m 7 2 and m 6 1 earthquakes in the past two decades global positioning system measurements conducted between 1990 and 1993 reveal seaward displacements of kilauea9s central south flank at rates of up to about 10 centimeters per year in contrast the northern side of the volcano and the distal ends of the south flank did not displace significantly the observations can be explained by slip on a low angle fault beneath the south flank combined with dilation deep within kilauea9s rift system both at rates of at least 15 centimeters per year

an example of river pattern evolution produced during the lateral growth of a central polygenic volcano the case of the alcantara river system mt etna italy abstract analysis of numerous geognostic soundings and geophysical investigation data indicates the presence of a wide depression identifiable as the ancient valley of the alcantara river below the northern flank of mt etna surface and subsurface data were used to reconstruct the complex stratigraphic succession filling the paleo alcantara valley consisting of superimposed lava flows interlayered with thick lentiform clastic bodies the evolution of the alcantara river system was defined with reference to the different phases of growth of mt etna the first correlation between volcanic activity and the drainage system refers to the initial phases of alkaline volcanism 170 100 ka during this period the southern watershed of the paleo alcantara valley acted as a morphological barrier to the products of the various volcanoes which gradually grew in the sector now occupied by the valle del bove the paleo alcantara riverbed was sporadically invaded by lava flows generated by peripheral activity of the central edifice a radical modification of the hydrographic pattern of the region began about 45 40 ka as a consequence of the growth of the ellittico volcano the main eruptive centre of the etnean edifice the gradual expansion of this volcano led over a period between about 30 and 25 ka to the northward deviation of the paleo alcantara riverbed the consequent erosion of a section of the watershed with the adjacent hydrographic basin of the paleo s paolo river resulted in the capture of the latter from then on the hydrographic pattern of the area gradually took on the characteristics it has today a water circulation system developed within the thick volcanic pile filling the paleo alcantara valley with the formation of an aquifer which is today one of the most important hydro structures of the whole volcanic edifice and is in part exploited in the eastern side of sicily

volcanic spreading forcing and feedback in geothermal reservoir development amiata volcano italia abstract we made a stratigraphic structural and morphologic study of the amiata volcano in italy we find that the edifice is dissected by intersecting grabens that accommodate the collapse of the higher sectors of the volcano in turn a number of compressive structures and diapirs exist around the margin of the volcano these structures create an angular drainage pattern with stream damming and captures and a set of lakes within and around the volcano we interpret these structures as the result of volcanic spreading of amiata on its weak substratum formed by the late triassic evaporites burano anhydrites and the middle jurassic to early cretaceous clayey chaotic complexes ligurian complex regional doming created a slope in the basement facilitating the outward flow and spreading of the ductile layers forced by the volcanic load we model the dynamics of spreading with a scaled lubrication approximation of the navier stokes equations and numerically study a set of solutions in the model we include simple functions for volcanic deposition and surface erosion that change the topography over time scaling indicates that spreading at amiata could still be active the numerical solution shows that as the central part of the edifice sinks into the weak basement diapiric structures of the underlying formations form around the base of the volcano deposition of volcanic rocks within the volcano and surface erosion away from it both enhance spreading in addition a sloping basement may constitute a trigger for spreading and formation of trains of adjacent diapirs as a feedback the hot hydrothermal fluids decrease the shear strength of the anhydrites facilitating the spreading process finally we observe that volcanic spreading has created ideal heat traps that constitute todays exploited geothermal fields at amiata normal faults generated by volcanic spreading volcanic conduits and direct contact between volcanic rocks which host an extensive fresh water aquifer and the rocks of the geothermal field constitute ideal pathways for water recharge during vapour extraction for geothermal energy production we think that volcanic spreading could maintain faults in a critically stressed state facilitating the occurrence of induced and triggered seismicity

determination of the permeability of seepage flow paths in dams from self potential measurements abstract the flow of the pore water in porous media generates an electrical current known as the streaming current this current is due to the drag of the excess of charges contained in the electrical diffuse layer coating the surface of the grains this current is associated with an electric field called the streaming potential field the fluctuations of this field can be remotely measured using a set of non polarizable electrodes located at the ground surface or in wells and a sensitive voltmeter the self potential method sp aims at passively measuring the streaming potential anomalies associated with ground water flow we present a stochastic numerical framework for inverting self potential data in order to localize seeps in dams and characterize their permeability and darcy velocity our approach is based on the use of markov chains monte carlo mcmc method for solving the inverse problem we performed first a validation of the method on a synthetic case study and then on large scale field surveys on three different dams our approach is successful in localizing seeps and determining their permeability a sensitivity study is performed on each of these three dams to better define the hydraulic and electrical parameters influencing the self potential signal and the uncertainties associated with the estimation of those parameters our results show that the self potential method can provide quantitative hydrogeological information for the characterization of seeps in dams and dikes

the influence of edifice slope and substrata on volcano spreading gravitational volcano spreading is caused by flow of weak substrata due to volcanic loading and is now a process known to affect many edifices the process produces extension in the upper edifice evidenced by graben and normal faults and compression at the base seen in strike slip faults and thrusts where spreading is identified host volcanoes have a range of fault densities variable rift and graben shapes and different degrees of structural asymmetry previous studies have suggested a link between edifice shape and structure and the proportion of brittle to ductile material in the substrata or lower edifice we study this link using refined sand cone analogue models standing on a brittle ductile sand silicone substrata two scenarios have been investigated the first mainly represents oceanic volcanoes with a ductile layer within the edifice type i where there is an outer ductile free surface the second represents most continental volcanoes that have ductile substrata type ii we apply the model results to natural examples and develop quantitative relationships between slope brittle ductile ratio fault density spreading rate and structural style displacement fields calculated from stereophotogrammetry show significant differences between different slope models we find that more faults are produced when the cone is initially steeper or when the brittle substratum is thinner however the effect of the brittle layer dominates over that of slope the strike slip movements are found to be an essential feature in the spreading mechanism and the graben are in fact transtensional features strike slip and graben faults make a conjugate flower pattern the structures produced are well organised for type ii edifices but they are poorly organised for type i models type i models represent good analogues for oceanic volcanoes that are commonly affected by large slumps bounded by an extensional zone and lack of well formed sector graben the well observed connection between oceanic volcano rifts and large landslide slumps is confirmed to be a consequence of spreading

fault propagation folds induced by gravitational failure and slumping of the central costa rica volcanic range implications for large terrestrial and martian volcanic edifices long sublinear ridges and related scarps located at the base of large volcanic structures are frequently interpreted as normal faults associated with extensional regional stress in contrast the ridges bordering the central costa rica volcanic range ccrvr are the topographic expression of hanging wall asymmetric angular anticlines overlying low angle thrust faults at the base of the range these faults formed by gravitational failure and slumping of the flanks of the range due to the weight of the volcanic edifices and were perhaps triggered by the intrusion of magma over the past 20 000 years the thrust fault underlying alajuela ridge rises from a depth of 700 m at a dip of 15 over a distance of a few kilometers it ramps up at 600 m depth on a 40 slope and terminates in the axis of the forward syncline 400 m below the surface the hanging wall of this fault has been thrusted about 200 m away from the volcanic range axis thrusting on the lower flanks of the ccrvr is compensated by extension on the range axis with formation of summit grabens shallow seismicity in the volcanic range suggests that thrusting is still active we postulate that at kilauea volcano hawaii the gravity and magma induced slumping of the southern flank on low angle thrust faults generates hanging wall anticlines similar to those observed in costa rica these anticlines are hypothesized to occur along the base of the volcano where the thrust faults ramp up toward the sea bottom ridges and scarps between 2000 and 5000 m below sea level are interpreted as the topographic expression of these folds we further suggest that the scarps of the ccrvr and kilauea are valid scaled terrestrial analogs of the perimeter scarp of the martian volcano olympus mons we suggest that the crust below olympus mons has failed under the load of the volcano triggering the radial slumping of the flanks of the volcano on basal thrusts the thrusting would have in turn formed the anticlinal ridges and scarps that surround the edifice the thrusting seems to be preferential toward the northwest and southeast and a northeast southwest rift zone seems to have developed perpendicular to the regional topographic gradient the thrust faults may extend all the way to the base of the martian crust about 40 km and they may have been active until almost the end of the volcanic activity we suggest that gravitational failure and slumping of the flanks of volcanoes is a process common to most large volcanic edifices in the ccrvr and at kilauea this slumping of the flanks is a slow intermittent process but it could evolve to rapid massive avalanching leading to catastrophic eruptions thus monitoring of uplift and displacement of the folds related to the slump tectonics could become an additional effective method for mitigating volcanic hazards

magnetic studies of basement off the coast of bombay west of india abstract bathymetric and total magnetic intensity data along 45 closely spaced profiles in 20 100 m of water totalling 2400 line km were collected on the continental shelf off bombay west of india magnetic intensity anomaly maps were prepared the anomalies show prominent trends in e w nnw sse and ene wsw directions correlations of the anomaly signatures with the geology known from the drill well logs and seismic results infer 1 1 the mostly basaltic nature of the basement overlain by the tertiary sediments except in the murud depression and isolated patches of the bombay high and inner shelf where granites are interpreted 2 2 the lateral extent of the two nnw sse trending regional faults between longitudes 70 50 e and 71 40 e 3 3 the outlines of the magnetic signatures associated with the structural highs and depressions two dimensional model and spectral studies of the anomalies under numerical constraints have revealed the structure of the basement overlain by 1 5 5 0 km thick sediments a crustal section along a transect across the inner shelf the bassein high structure and the offshore basin in the middle shelf the bombay high structure in the middle outer shelf and further west is interpreted the section depicts the structure of the tertiary sediments the late cretaceous early tertiary basalts and the archaean precambrian granites thick basalt constructs occur in the paleoslopes of the archaean precambrian basement down faulting of parts of the western indian peninsula into the arabian sea along the regional faults is suggested due to the lithologically similar sequences of the tertiary sediments the basalts deccan traps and granitic gneisses of the study and onshore areas therefore the area is considered to be divided into three structural blocks consisting of the inner shelf the offshore basin and the bombay high separated by nnw sse trending deep seated faults which result from rifting of the crust the basement faults mostly extending to the overlying young sediments and the tectogenes indicate a continued stress regime the continued subsidence both mechanical and thermal of the crust in the study area under increased sediments the drift of the indian continent from the south to the present latitudes and the dynamic interaction of the oceanic continental lithospheres appear to deform the crust by thinning and shearing

landslides and spreading of oceanic hot spot and arc shield volcanoes on low strength layers lsls an analogue modeling approach during their growth and evolution oceanic hot spot and arc shield volcanoes are destabilized and often dismantled by landslides the origin of these phenomena can be found in the structure of volcanic islands marked by several low strength horizons such as a marine substratum hyaloclastites hydrothermally altered rocks or volcaniclastic deltas that weaken the edifice we have tested the role of these low strength layers lsls with analogue modeling we conclude that destabilization on these levels can lead to landslides or gravitational spreading in our experiments slides generated are only slump type events but they can evolve in nature into debris avalanches through mechanisms that could not be modeled in the laboratory the role of fan shaped volcaniclastic deltas included in the edifice structure is critical to slump formation this process is more efficient if deltas are associated with another upper lsl such as weak hyaloclastites or hydrothermally altered rocks in this case recurrent events generating collapses with increasing width are observed gravitational spreading of a volcanic island occurs when it is underlain by a ductile marine substratum or includes an intra edifice unconstrained hyaloclastic layer 1 3 as thick as the height of the subaerial edifice spreading is characterized by edifice stretching and subsidence and does not generate major landslides we also show that gravitational spreading on a marine substratum tends to inhibit slide generation especially when the thickness of the sedimentary layer is larger than 1 10 of the edifice total height however if this value is lower spreading occurs later and slumps can develop initially we describe natural examples of oceanic hot spot or arc shield volcanoes affected by both spreading and landslides such as reunion island hawaii island james ross island antarctica and martinique island antilles the main structural features on these volcanoes can be explained solely by deformation on lsls we therefore propose a general model for the destabilization of volcanic islands that is applicable to all shield like edifices

self potential signals associated with localized leaks in embankment dams and dikes abstract the self potential method can be used to detect and monitor anomalous seepages in dams and embankments in such a case an electrical field of electrokinetic nature i e associated with pore water flow can be measured using a set of non polarizable electrodes typically located at the ground surface or in some wells this field can be in turn related to the pattern of groundwater flow we built an experimental dam to investigate to which extent the self potential method can help characterizing seepages in dams we first use the finite element method to simulate the ground water flow in a heterogeneous porous and permeable material by solving the groundwater flow equation the resulting groundwater flow solution is then used to compute the electrical potential distribution by solving the corresponding elliptic partial differential equation in a preliminary experiment we could not measure any self potential anomaly associated with the infiltration of water in the dam our numerical simulations showed that the magnitudes of the self potential anomalies were controlled by 1 the nature of the flow regime viscous laminar versus inertial laminar flow regimes and 2 the presence of insulating polyvinyl chloride pvc tubes located at the end of the preferential flow channels in the structure of the dam thanks to these numerical simulations we added sand at the entrance of the infiltration area in order to reduce the effects of the pvc tubes and to restrain the flow regime to the viscous laminar flow regime new experiments allowed for detecting a self potential anomaly with an amplitude of around 9 mv consistent with that obtained through numerical modelling with a finite element simulator this comparison was used to test the accuracy of the modelling approach and define the strengths and weaknesses of the self potential method to determine preferential seepages in earth dam structures

influences of holocene sea level regional tectonics and fluvial gravity and slope currents induced sedimentation on the regional geomorphology of the continental slope off northwestern india abstract regional geomorphology derived from echosounding and bathymetric data lines of a total of 12 000 km depth to basement regional deep seated tectonic features surficial sediment distribution and holocene sedimentation rates of the continental margin off northwestern india are presented results indicate that the shelf edge over most of the region shelf break between 80 and 154 m water depth is covered with relict carbonate facies and partially buried bioherms of holocene age particularly off bombay and saurashtra regions significant changes in the depth and orientation of the shelf edge adjacent to saurashtra and the bombay high areas in relict carbonate facies are recorded at locations shelf edge depth is much more up to 150 m than the early holocene eustatic sea level still stand in this region about 100 m the upper boundary of the slope also varies considerably in depth about 1450 m in the vicinity of the indus fan having high sedimentation and 2900 m further southwards the gradient of the slope off the kachchh is steepest and some regional notches are observed at the upper slope the gentler slope off saurashtra and the bombay high area has large benches at depths of 180 230 m width 2 10 km and 650 780 m well below the holocene sea level the bombay high area has slope breaks between 400 and 600 m whereas off saurashtra steep breaks in the slope occur between 560 and 960 m depth further southwards at the foot of the slope elevations and depressions are present variations in the geomorphology of the slope off the northwestern continental margin of india are attributed to 1 late pleistocene holocene sea levels 2 regional tectonics 3 fluvial sedimentation and 4 gravity and slope currents induced sediment dynamics the locations under influences of slumping turbidity and tectonic movements with altered in situ sequence of sedimentations are delineated

emplacement mechanisms of contrasting debris avalanches at volcan mombacho nicaragua provided by structural and facies analysis we study the lithology structure and emplacement of two debris avalanche deposits dads with contrasting origins and materials from the quaternary holocene mombacho volcano nicaragua a clear comparison is possible because both dads were emplaced onto similar nearly flat 3 slope topography with no apparent barrier to transport this lack of confinement allows us to study in nature the perfect case scenario of a freely spreading avalanche in addition there is good evidence that no substratum was incorporated in the events during flow so facies changes are related only to internal dynamics mombacho shows evidence of at least three large flank collapses producing the two well preserved debris avalanches of this study one on its northern flank las isletas directed northeast and the other on its southern flank el crater directed south other south eastern features indicate that the debris avalanche corresponding to the third collapse la danta occurred before las isletas and el crater events the materials involved in each event were similar except in their alteration state and in the amount of substrata initially included in the collapse while el crater avalanche shows no signs of substratum involvement and has characteristics of a hydrothermal weakening related collapse the las isletas avalanche involves significant substratum and was generated by gravity spreading related failure the latter avalanche may have interacted with lake nicaragua during transport in which case its run out could have been modified through a detailed morphological and structural description of the mombacho avalanches we provide two contrasting examples of non eruptive volcanic flank collapse we show that remarkably even with two distinct collapse mechanisms the debris avalanches developed the same gross stratigraphy of a coarse layer above a fine layer this fine layer provided a low friction basal slide layer whereas dad layering and the run outs are roughly similar the distribution of structures is different and related to lithology las isletas has clear proximal faults replaced distally by inter hummock depressions where basal unit zones are exhumed whereas el crater has faults throughout but the basal layer is hidden in the distal zone hummocky forms depend on material type with steep hummocks being formed of coherent lava units and low hummocks by matrix rich units in both avalanches extensional structures predominate the upper layers exclusively underwent longitudinal and lateral extension this is consistent with evidence of only small amounts of block to block interactions during bulk horizontal spreading the base of the moving mass accommodated transport by large amounts of simple shear we suggest that contractional structures and inter block collisions seen in many other avalanches are artifacts related to topographic confinement

lithospheric flexure and gravity spreading of olympus mons volcano mars the structural architecture of large volcanoes is governed substantially by gravity driven deformation that is manifest as distinct processes such as basement flexure or volcanic spreading temporal effects and the mutual interplay of these processes have been investigated only to a limited extent and so we present novel numerical models of the time dependent deformation associated with them the models simulate the combined effects of lithospheric flexure and volcanic spreading during growth increments of an elastoplastic volcanic cone different spreading scenarios are considered by a variable coupling decoupling behavior at the interface between volcano and basement we apply our models to olympus mons on mars which is characterized by upper to middle flank terraces on the shield is encircled by a basal scarp that has an average slope of 30 and is surrounded by distant deposits that resemble large scale slumping features on earth our results are consistent with the interpretation that terraces on olympus mons flanks form by thrust faulting that results from lithospheric flexure the presence and expression of terraces depend on the coupling of volcano and basement on the time of volcano growth relative to mantle relaxation and on the cohesion of the edifice the encircling scarp may be related to a very low friction detachment at the edifice base which leads to a normal fault regime on the lowermost flanks with time and volcano growth predicted stress and faulting regimes migrate only slightly indicating that the structural architecture of volcanoes is largely set in the very early stages of formation

a new model for the evolution of la reunion volcanic complex from complete marine geophysical surveys results from recent marine geophysical surveys offer a new perspective for characterizing the evolution processes of volcanic islands in 2006 cruises forever and eroder 1 investigated the submarine flanks and the surrounding abyssal plain of la reunion indian ocean to obtain for the first time a complete geophysical survey of the area combined analyses of these data reveal major differences in the evolution of the two emerged volcanoes piton des neiges and piton de la fournaise we show that debris avalanche deposits extend on the abyssal plain only offshore the active piton de la fournaise volcano attesting the occurrence of large flank collapse events the absence of such deposits offshore piton des neiges and the presence of compressive structures within the sedimentary unit below the edifice support a mechanism of slow deformation of this volcano such as sliding or spreading the slow deformation of piton des neiges has led to numerous secondary submarine slope instabilities and favored some unconfined turbidity flows which generated large sediment waves running downward all around the island this study proposes a new model using the most complete marine data set available slow deformation controls the evolution of piton des neiges whereas piton de la fournaise formed on the flanks of a pre existing edifice experienced catastrophic large flank collapse events

three dimensional modelling of streaming potential summary the self potential sp method responds to the electrokinetic phenomenon of streaming potential and has been applied to hydrogeologic and engineering investigations to aid in the evaluation of subsurface hydraulic conditions to enable the study of variably saturated flow problems of complicated geometry a 3 d finite volume algorithm is developed to evaluate the sp distribution resulting from subsurface fluid flow the algorithm explicitly calculates the distribution of streaming current sources and solves for the sp given a model of hydraulic head and prescribed distributions of the streaming current cross coupling conductivity and electrical conductivity the forward solution is verified by comparing it with an analytical solution for a point source of flow and measured data taken at the surface of a homogeneous embankment we apply the forward model to a synthetic pumping well example to illustrate that heterogeneous physical property distributions can result in significant charge accumulation the sign and magnitude of this secondary charge is determined by the physical property and potential gradients at the interface and can complicate the interpretation of sp data when a single primary flow source is assumed the 3 d character of the sp response to seepage through an embankment and foundation is illustrated in a preliminary study of sp data collected at a dam site in british columbia

scaled experiments of volcanic spreading experiments were conducted to study the spreading of volcanic constructs volcanoes are simulated by a sand cone and the volcanic substratum is simulated by a sand layer brittle substratum overlying a silicone layer ductile substratum similarity conditions between natural volcanoes and experimental prototypes led to the definition of dimensionless numbers experiments determine values which predict whether or not spreading takes place of particular importance are the ratio between the thickness of the brittle substratum and the height of the volcano 2 and the brittle ductile ratio of the substratum 3 2 indicates that the volcano must be large enough to break the substratum before spreading occurs whereas 3 controls the style of deformation during spreading these dimensionless numbers change with time reaching values that tend toward those observed for stable configurations experimental values are compared with those from well constrained natural examples it is found that an essential requirement for volcanic spreading is the presence of a low viscosity layer within the substratum flow of the weak layer away from the excess load is responsible for the spreading the overlying edifice displays radial intersecting grabens due to concentric stretching dissected summit areas concentric zones of thrusts and folds form in the substratum around the edifice and diapirs of the ductile substratum rise within the fault zones

volcanotectonic interactions between mauna loa and kilauea insights from 2 d discrete element simulations abstract numerical simulations using the discrete element method dem are carried out to examine the dynamics and internal deformation of overlapping volcanoes constructed upon a weak decollement horizon as analogs to the kilauea mauna loa system of volcanoes in hawaii employing a frictional rheology the dem simulations capture much of the complex deformation behavior of mauna loa and kilauea volcanoes here referred to as the primary and secondary edifices respectively the models demonstrate incremental displacements of the outer flanks of the volcanoes and concurrent summit subsidence leading to characteristic low slopes and inward dipping strata slip discontinuities that develop within the piles define steeply dipping normal faults along the upper flanks and beneath the edifice summits that accommodate subsidence and flank spreading edifice overlap influences dynamic behavior significantly even small topographic perturbations restrict the internal deformation and spreading of the confined flanks the degree of buttressing depends on the relative positions of the two edifices if the secondary edifice grows high upon the flanks of the primary edifice outward spreading of the underlying flank is enhanced if the secondary edifice is built low upon the primary flanks spreading of the underlying flank is effectively prevented or possibly reversed furthermore as the second edifice grows it subsides into the underlying flank partitioning it into a mobile downslope region entrained by spreading of the second edifice and a comparatively stable upper flank region these results suggest that much of the mass of kilauea volcano may lie deeply buried within the underlying flank of mauna loa while older mauna loa rocks may lie far from their source beneath the mobile flank of the younger volcano

self potential modeling from primary flows this paper discusses a new method for the investigation of self potentials sp based on induced current sources the induced current sources are due to divergences of the convection current which is driven in turn by a primary flow either heat or fluid as a result of using this approach there is a shift in emphasis toward the vector flow field and its interaction with current cross coupling structure when compared with the total potential approach of nourbehecht 1963 which emphasized the primary flow potential and the voltage cross coupling this shift in emphasis is advantageous because it is analogous to the actual physical processes for example fluid flow in the ground gives rise to drag convection currents and the interaction of the convection currents with the electrical structure gives rise to the electrical potentials sp this simple physical picture should aid in developing a better intuitive understanding of the generation of sp effects the convective current approach is easily ada

fracture mode analysis and related surface deformation during dyke intrusion results from 2d experimental modelling surface deformation analysis in volcanic edifices in response to shallow magma intrusion is crucial for assessing volcanic hazards in this paper we discuss the effect of dyke propagation mode on surface deformation through 2d laboratory models our experimental setup consists of a hele shaw cell in which a model magma is injected into a cohesive model crust using an optical image correlation technique particle imaging velocimetry we measured the surface deformation the displacements and the strain field induced by magma emplacement within the country rock we identify two types of intrusion morphologies types a and b which exhibit two evolutional stages during the first stage both types resulted in a vertical dyke at depth its propagation was controlled by both shear deformation and tensile opening the model surface lifted up to form a smooth symmetrical dome resulting in tensile cracks during the second stage types a and b experiments differ when the dyke reaches a critical depth in type a the intrusion gradually rotates forming an inclined sheet dipping between 451 and 651 this rotation results in asymmetrical surface uplift and shear failure upon the tip of the dyke in type b the dyke tip interacts with tensile cracks formed during the first stage this fracture controls the subsequent propagation of the dyke toward the surface in both types of experiments intrusions result in surface uplift which can be accommodated by reverse faults our study suggests that dykes propagate as viscous indenters rather than linear elastic fracturing

relationships between volcano gravitational spreading and magma intrusion volcano spreading with its characteristic sector grabens is caused by outward flow of weak substrata due to gravitational loading this process is now known to affect many present day edifices a volcano intrusive complex can form an important component of an edifice and may induce deformation while it develops such intrusions are clearly observed in ancient eroded volcanoes like the scottish palaeocene centres or in geophysical studies such as in la reunion or inferred from large calderas such as in hawaii the canaries or galapagos volcanoes volcano gravitational spreading and intrusive complex emplacement may act simultaneously within an edifice we explore the coupling and interactions between these two processes we use scaled analogue models where an intrusive complex made of golden syrup is emplaced within a granular model volcano based on a substratum of a ductile silicone layer overlain by a brittle granular layer we model specifically the large intrusive complex growth and do not model small scale and short lived events such as dyke intrusion that develop above the intrusive complex the models show that the intrusive complex develops in continual competition between upward bulging and lateral gravity spreading the brittle substratum strongly controls the deformation style the intrusion shape and also controls the balance between intrusive complex spreading and ductile layer related gravitational spreading in the models intrusive complex emplacement and spreading produce similar structures to those formed during volcano gravitational spreading alone i e grabens folds en echelon fractures therefore simple analysis of fault geometry and fault kinetic indicators is not sufficient to distinguish gravitational from intrusive complex spreading except when the intrusive complex is eccentric from the volcano centre however the displacement fields obtained for 1 a solely gravitational spreading volcano and for 2 a gravitational spreading volcano with a growing and spreading intrusive complex are very different consequently deformation fields like those obtained from geodetic monitoring can give a strong indication of the presence of a spreading intrusive complex we compare the models with field observations and geophysical evidence on active volcanoes such as la reunion island indian ocean ometepe island nicaragua and eroded volcanic remnants such as ardnamurchan scotland and suggest that a combination between gravitational and intrusive complex spreading has been active

growth and evolution of an emergent tuff cone considerations from structural geology geomorphology and facies analysis of sao roque volcano sao miguel azores abstract the syn eruptive and post eruptive history of sao roque tuff cone its geological setting and volcanological features were studied in detail to understand the role played by the different factors that contributed to the morphological evolution of this relatively simple and small volcanic edifice in addition attention was also focused on the series of natural changes that affected the tuff cone during the course of the years and that finally led to its structural disassembly a novel model is proposed to explain this process the sao roque volcanic centre located on the island of sao miguel azores consists of two well consolidated bodies and numerous small islets that formed more than 4700 years ago during the hydromagmatic activity that took place along an intruding dyke whose nnw sse trend is in agreement with the regional tectonic pattern the eruptive vents probably migrated progressively from sse to nnw forming small edifices through the rapid accumulation of sediments during alternating phases of dry and wet magmatic emissions syn eruptive partial collapses greatly modified the original morphological structure of these edifices probably allowing sea water to continuously flow into the vents the complex interaction of these factors controlled the depth of magma fragmentation producing different types of deposits in which the ash lapilli ratio varies considerably the high water saturation degree of these deposits caused syn eruptive and post eruptive remobilization which resulted in collapses and some small scale landslides post eruptive wnw ese trending transtensional and extensional tectonic activities operated during the initial dissection of the cone generating instability furthermore the rapid accumulation of wet tephra and its following consolidation caused selective collapses that favoured the fragmentation of the deposit and caused the formation of numerous islets separated by radially arranged channels collapses also involved the lava units emplaced in more recent times around the tuff cone which show that brittle deformation has been significant in the area for a prolonged period

crustal structure from deep seismic soundings along the koyna ii kelsi loni profile in the deccan trap area india abstract the crustal depth section obtained from deep seismic soundings along the koyna ii kelsi loni profile which lies near latitude 18 n roughly in the east west direction in that part of the deccan trap maharashtra state india shows a number of reflection segments below the deccan traps down to the moho discontinuity a deep fault below the deccan traps 13 km east of mahad divides the entire cross section including the moho boundary into two crustal blocks the reflection segments show updip towards the west coast in the western block the moho discontinuity which is at a depth of 39 km near the deep fault starts rising towards the coast reaching a depth of 31 5 km at the west coast the eastern block is thrown up by 1 5 km with respect to the western block along the deep fault a structural contour map of the moho discontinuity for the koyna reservoir area has been prepared from the present results and the crustal information obtained along the koyna i profile kaila et al 1979a shows that the deep fault in the koyna area is aligned in the nnw sse direction refraction seismic data analysis by the wave front method reveals that the thickness of the deccan trap increases towards the west coast the deccan trap is 600 700 m thick in the eastern region between nira sp 130 and loni sp 200 and attains a thickness of 1500 m at 10 km east of the west coast the longitudinal wave velocity in the deccan traps along the profile varies from 4 8 to 5 0 km sec and in the crystalline basement from 6 0 to 6 15 km sec a tentative isopach contour map of the deccan traps and a tentative structural contour map of the pre deccan trap contact have been prepared for the koyna reservoir area from the results along the koyna ii and koyna i profiles a flexure aligned in a nnw sse direction in the pre deccan trap contact which is an expression of the deep fault into the basement has been clearly brought out the flexure coincides in general with the orientation of the deccan volcanic scarp in this area

dynamic basis of volcanic spreading the established models of the structure and dynamics of a typical hawaiian volcano lead inevitably to a paradox finite element viscoelastic calculations using tecton melosh and raefsky 1980 1981 predict that a compressional stress field should characterize their upper flanks instead extension is observed the paradox is solved by postulating that volcanic evolution is determined by feedback processes related to growth and spreading of the volcanic edifice many examples of the process of spreading are documented in the geologic literature on volcanoes of a very broad size range and very different geologic settings the process is similar across many orders of magnitude in size the deformation of the substratum related to magma intrusion during lava dome building events is at the lower end of the scale the spreading of seafloor at oceanic ridges is at the higher end of the scale volcanoes may evolve from small constructs into huge shield volcanoes and perhaps into ocean plates key elements for volcanic spreading are 1 the existence of a weak basal layer and 2 a sufficiently high mass and magma influx to drive the process as the mass of a volcano grows it passes through five phases which may overlap repeat or be omitted building compressing thrusting intruding and spreading during the building phase the mass of a volcano does not significantly affect the stress field of the substratum primitive magmas are likely to be erupted as the mass increases the volcano subsides and becomes characterized by a compressional stress field which inhibits any further intrusion of magma into the volcanic edifice magma may differentiate in the crust allowing for large caldera forming eruptions to occur in the next phase thrusting begins on a decollement usually located at the foot of the edifice while the stress field on the upper slopes of the volcano remains compressional the stress at the base close to the center becomes extensional allowing the magma to intrude and differentiate at the base of the edifice a basal intrusive complex begins to grow explosive eruptions may be expected finally spreading of this complex creates an extensional stress field on the upper flanks of the volcano confining compression to the lower slopes of the edifice the extension allows primitive magma to erupt again at the summit the process of spreading seems to have a fundamental influence on the structural and magmatic evolution of volcanoes at every scale this process results from coupling and feedback between the gravitational and thermal fields thus studying this process may improve our understanding of the relation between structural dynamics and magma evolution and of the origin and evolution of volcanic seismicity and eruptions

the effect of volcanic constructs on rift fault patterns volcanoes in rift situations often show distinctive hour glass fault patterns with increased fault throw as the volcano is approached we present analogue models that show that this is caused by an interaction of the regional stress field with that set up by the volcano mass for faults to be reorientated there must be a ductile layer below the volcano this can be hot crust at mid ocean ridges continental rifts or weak sedimentary strata increased volcano size or mass and lower brittle ductile ratios lead to increased fault curvature whereas an increased regional extension rate decreases the effect volcanoes on one side of a rift may capture it forming the axis of a new rift with curved or en echelon zones on either side by concentrating extension magma is more easily erupted so volcanoes may erupt more magma of less evolved composition a positive feedback between increased extension and magma eruption rate will lead to rift narrowing which can favor the formation of oceanic crust

gravity anomalies and crustal structure of the western continental margin off goa and mulki india abstract bathymetric and gravity data totalling 2000 line kilometres on the continental margin off goa and mulki india have been studied and prominent nnw sse and ene wsw trending free air gravity anomalies varying between 60 and 25 mgal have been identified using constraints from seismic refraction and reflection and well log results the thicknesses of the layers are estimated by computing two dimensional crustal structure models for the free air gravity anomalies the study suggests that 1 there are three layers varying in thickness from 0 5 to 4 0 km 0 5 to 12 0 km and from 14 0 to 26 0 km with densities of 2 3 2 6 and 2 9 g cm 3 which are interpreted as sedimentary granitic and mafic basaltic layers respectively that 2 there is a maximum thickness of 4 0 km of sediment over the shelf margin basin and that 3 the moho occurs at a depth of 24 30 km

analogue modelling of volcano flank terrace formation on mars of the features that characterize large shield volcanoes on mars flank terraces remain the most enigmatic several competing mechanisms have been proposed for these laterally expansive topographically subtle landforms here we test the hypothesis that horizontal contraction of a volcano in response to the down flexing of its underlying basement leads to flank terracing we performed a series of analogue models consisting of a conical sand plaster load emplaced on a basement comprising a layer of brittle sand plaster atop a reservoir of viscoelastic silicone our experiments consistently produced a suite of structures that included a zone of concentric extension distal to the conical load a flexural trough adjacent to the load base and convexities terraces on the cone s flanks the effects of variations in the thickness of the brittle basal layer as well as in the volume slope and planform eccentricity of the cone were also investigated for a given cone geometry we find that terrace formation is enhanced as the brittle basement thickness decreases but that a sufficiently thick brittle layer can enhance the basement s resistance to loading such that terracing of the cone is reduced or even inhibited altogether for a given brittle basement thickness terracing is reduced with decreasing cone slope and or volume our experimental results compare well morphologically to observations of terraced edifices on mars and so provide a framework with which to understand the developmental history of large shield volcanoes on the red planet

combined application of surface geoelectrical methods for groundwater flow modeling a case history electrical methods electrical profiling and sounding induced polarization ip and self potential sp combined with geochemical and hydrochemical surveys were applied to characterize shallow sediments at a site contaminated by oil related brines the site is located within the romashkinskoye oil field tatarstan republic russian federation results of geochemical and hydrochemical surveys as well as those of electrical profiling revealed no individual haloes of contaminant in the soil and groundwater which suggests that the entire site is contaminated vertical electrical ip soundings ves ip allowed us to obtain the stratigraphic characteristics of the site and to distinguish a shallow aquifer among clayey aquitards interpretation of sp data on the basis of forward numerical modeling helped us to develop a groundwater flow model of the site to reduce ambiguities we kept fixed the values of layer resistivity derived from the inverted ves ip data boundary conditions on water head and water flow were based on drilling and sampling data we varied only the values of hydraulic conductivity to fit the calculated sp values to the measured sp values we found a strong misfit between the measured and calculated sp values for the one aquifer model by inferring a second deeper seated aquifer we computed a two aquifer model that produced a satisfactory sp fit

rifting recurrent landsliding and miocene structural reorganization on nw tenerife canary islands we studied mechanisms of structural destabilization of ocean island flanks by considering the linkage between volcano construction and volcano destruction exemplified by the composite teno shield volcano on tenerife canary islands during growth tenerife episodically experienced giant landslides genetically associated with rifting and preferentially located between two arms of a three armed rift system the deeply eroded late miocene teno massif allows insights into the rifting processes the failure mechanisms and related structures the semicircular geometry of palaeo scarps and fracture systems breccia deposits and the local dike swarm reconfigurations delineate two clear landslide scarp regions following an earlier collapse of the older los gigantes formation to the north the rocks around the scarp became fractured and intruded by dikes substantial lava infill and enduring dike emplacement increased the load on the weak scarp and forced the flank to creep again finally resulting in the collapse of the younger carrizales formation once more the changing stress field caused deformation of the nearby rocks a fracture belt formed around the scarp and dikes intruded into new concentric directions the outline size and direction of the second failed flank of teno very much resembles the first collapse we suggest structural clues concerning mechanisms of recurrent volcano flank failure verifying the concept that volcano flanks that have failed are prone to collapse again with similar dimensions

styles of volcano induced deformation numerical models of substratum flexure spreading and extrusion the gravitational deformation of volcanoes is largely controlled by ductile layers of substrata using numerical finite element modelling we investigate the role of ductile layer thickness and viscosity on such deformation to characterise the deformation we introduce two dimensionless ratios a volcano radius ductile layer thickness and b viscosity of ductile substratum failure strength of volcano we find that the volcanic edifice spreads laterally when underlain by thin ductile layers a 1 while thicker ductile layers lead to inward flexure a 1 the deformation style is related to the switch from predominantly horizontal to vertical flow in the ductile layer with increasing thickness increasing a structures produced by lateral spreading include concentric thrust belts around the volcano base and radial normal faulting in the cone itself in contrast flexure on thick ductile substrata leads to concentric normal faults around the base and compression in the cone in addition we show that lower viscosities in the ductile layer low b lead to faster rates of movement and also affect the deformation style considering a thin ductile layer if viscosity is high compared to the failure strength of the volcano high b then deformation is coupled and spreading is produced however if the viscosity is low low b substratum is effectively decoupled from the volcano and extrudes from underneath it in this latter case evidence is likely to be found for basement compression but corresponding spreading features in the volcano will be absent as the cone is subject to a compressive stress regime similar to that produced by flexure at volcanoes where basement extrusion is operating high volcano stresses and outward substratum movement may combine to produce catastrophic sector collapse an analysis of deformation features at a volcano can provide information about the type of basement below it a useful tool for remote sensing and planetary geology also knowledge of substratum geology can be used to predict styles of deformation operating at volcanoes where features have not yet become well developed or are obscured

from gradual spreading to catastrophic collapse reconstruction of the 1888 ritter island volcanic sector collapse from high resolution 3d seismic data abstract volcanic island flank collapses have the potential to trigger devastating tsunamis threatening coastal communities and infrastructure the 1888 sector collapse of ritter island papua new guinea in the following called ritter is the most voluminous volcanic island flank collapse in historic times the associated tsunami had run up heights of more than 20 m on the neighboring islands and reached settlements 600 km away from its source this event provides an opportunity to advance our understanding of volcanic landslide tsunami hazards here we present a detailed reconstruction of the 1888 ritter sector collapse based on high resolution 2d and 3d seismic and bathymetric data covering the failed volcanic edifice and the associated mass movement deposits the 3d seismic data reveal that the catastrophic collapse of ritter occurred in two phases 1 ritter was first affected by deep seated gradual spreading over a long time period which is manifest in pronounced compressional deformation within the volcanic edifice and the adjacent seafloor sediments a scoria cone at the foot of ritter acted as a buttress influencing the displacement and deformation of the western flank of the volcano and causing shearing within the volcanic edifice 2 during the final catastrophic phase of the collapse about 2 4 km3 of ritter disintegrated almost entirely and traveled as a highly energetic mass flow which incised the underlying sediment the irregular topography west of ritter is a product of both compressional deformation and erosion a crater like depression underlying the recent volcanic cone and eyewitness accounts suggest that an explosion may have accompanied the catastrophic collapse our findings demonstrate that volcanic sector collapses may transform from slow gravitational deformation to catastrophic collapse understanding the processes involved in such a transformation is crucial for assessing the hazard potential of other volcanoes with slowly deforming flanks such as mt etna or kilauea

an integrated field numerical approach to assess slope stability hazards at volcanoes the example of pacaya guatemala pacaya is an active stratovolcano located 30 km south of guatemala city guatemala a large 0 65 km3 sector collapse of the volcano occurred 0 6 1 6 ka b p producing a debris avalanche that traveled 25 km sw of the edifice the current cone has since rebuilt within the scarp of this ancestral collapse the structural setting of the volcano along with two recent smaller volume collapses in 1962 and 2010 suggests gravitational instability of this volcano to assess pacaya s stability and potential for another large lateral collapse of the active cone standard engineering methodologies for studying non volcanic slopes were used to examine the sw flank of the edifice a geomechanical model was developed based on the physical mechanical material properties of pacaya s intact rocks and rock mass characteristics found through field observations and laboratory tests slope stability was analyzed in several scenarios with the limit equilibrium method lem and finite element method fem including static conditions i e under gravity forces only and considering the application of magma pressure and seismic force as triggering mechanisms for slope failure results show that the edifice remains stable under gravity alone however a large scale collapse could be triggered by reasonable ranges of magma pressure 7 7 mpa if constant along a dyke or peak ground acceleration 460 cm s2 results also suggest that a layer of pyroclastics beneath the edifice could have controlled the ancestral sector collapse structural analysis shows that a transtensional stress regime is causing a nw se orientation of aligned features at the surface and may be a controlling mechanism for the direction of a future collapse fem results are concordant with those from lem and reveal that maximum shear strain patterns within the edifice may account for long lava flows erupted from lower vent elevations

gravitational spreading and formation of new rift zones on overlapping volcanoes large volcanic edifices are often shaped by the coalescence of adjacent volcanoes as well as intrusive rift zones and gravitational spreading to better understand the structure of such volcanoes we designed analogue experiments simulating gravitational spreading of an edifice made by overlapping cones of different age and examined the formation of rift zones the results allow distinction of two main rift geometries i spreading edifices of similar age that partly overlap tend to develop a rift zone approximately perpendicular to the boundary of both volcanoes such a rift zone causes two volcanoes to grow together and form an elongated topographic ridge ii partly overlapping volcanoes of different age are spreading at different rates and thus form a rift zone parallel to the boundary of both volcanoes such a rift zone causes two volcanoes to structurally separate the results are widely applicable for large volcanoes subject to rifting and flank spreading which we demonstrate for reunion island and for southern hawaii

deformed symmetrical volcanoes analog modeling of volcanic cones traversed by strike slip faulting was conducted and the cones were analyzed for deformation characteristics the study shows that symmetrical volcanoes that have undergone basal strike slip offset may be deformed internally without manifesting any change in their conical shape volcanoes deformed by strike slip faulting may already have well developed fractures in their interior yet still appear as a symmetrical cone exhibiting concentric contours when viewed on a topographic map moreover slight changes in the basal shape of the cone induced by strike slip movement can be restored by the relatively faster resurfacing and reshaping processes from the deposition of younger eruptive products these findings pose a subtle but significant point in the assessment of volcanic landslide hazards not all perfect cones are undisturbed the detection of concealed deformation is important because fractures induce further instability in volcanoes and act as slip planes during volcano collapse events there are many examples of symmetrical volcanoes in nature the faultless appearance of such perfect cones can be misleading which requires careful attention in hazards assessment

modeling of streaming potential responses caused by oil well pumping the occurrence of streaming potentials is directly related to movement of fluids in the subsurface to investigate whether streaming potential measurements in boreholes and at the surface can be used to monitor subsurface flow and detect subsurface flow patterns in oil reservoirs we model streaming potential responses caused by oil well pumping in monitoring wells and at the earth s surface since the model parameters permeabilities cross coupling properties and electric conductivities depend on a few basic rock physics parameters such as brine conductivity amount of water saturation and porosity the model parameters are evaluated self consistently using rock physics models using a threedimensional 3 d finite difference algorithm the governing differential equations that are drawn from nonequilibrium thermodynamics are solved numerically in three self consistent steps solution of the hydraulic problem computation of the streaming current sources based on the principle of conservation of char

marine magnetic anomalies off ratnagiri western continental shelf of india abstract total magnetic intensity and bathymetric surveys were carried out in the offshore area of ratnagiri on the western continental shelf of india and an isomagnetic anomalies map at a contour interval of 50 nt was prepared which reveals n s trends of magnetic anomalies two dimensional model and spectral studies of these anomalies were carried out and subsurface models of the geology in the area have been derived from anomalies at a number of places the results suggest that the anomalies occur over a magnetic crystalline basement at a depth of 1 1 2 km which is similar in magnetization to onshore basalts of northwest india these anomalies are believed to be an expression of a considerable thickness around 1 7 km of basalt underlain by sediments identification of these basalts in offshore areas along the northwestern continental shelf of india would support 1 the idea that the onshore deccan basalts of western india and the rhyolitic tuffs at the laccadive ridge system dsdp site 210 are related to the same volcanic events and 2 subsequent downfaulting of onshore deccan basalts into the arabian sea and submergence below the tertiary sediments

catastrophic sector collapse at usu volcano hokkaido japan failure of a young edifice built on soft substratum catastrophic sector collapse is a destructive volcanic process that occurs during the growth history of a volcano understanding the timing and causal mechanisms of sector collapse at individual volcanoes is essential for evaluating long term volcano evolution and associated hazards this paper describes the lithofacies tephrostratigraphy and radiocarbon dating of a debris avalanche deposit at usu volcano japan based on detailed field geological surveys and proposes that uplift of soft substratum played an important role in destabilizing the young volcanic edifice usu is a quaternary basaltic to andesitic stratovolcano that has an amphitheater at the summit the basement of the volcano has been uplifted by 300 400 m relative to the surrounding area the debris avalanche deposit is 0 3 km3 in volume and displays well preserved hummocky topography the hummocks are composed of andesite blocks derived from the stratovolcano and non welded pyroclastic flow and fluvial deposits derived from the basement of the stratovolcano tephrostratigraphy and radiocarbon dating of charcoal samples from the debris avalanche deposit indicate that the sector collapse occurred at 16 ka the age of sector collapse combined with previous geochronological data enables reconstruction of the eruptive history of usu as follows 1 andesitic explosive eruption at 18 19 ka 2 stratovolcano growth between 18 and 16 ka 3 sector collapse at 16 ka 4 hiatus in volcanic activity for 15 000 years 5 rhyolitic plinian eruption in ad 1663 and 6 dacitic dome forming eruptions after ad 1663 this eruptive history indicates that the sector collapse occurred within 3000 years of the onset of stratovolcano growth much sooner than at other volcanoes where the timing of sector collapse is known we infer that the sector collapse of such a young volcanic edifice was caused by a combination of dome like uplifting tilting forced folding of soft substratum overloading of the volcanic edifice on the soft substratum a ne sw trending fault system that deeply cuts the substratum and possible magma intrusion within the edifice and associated earthquakes usu provides an excellent example of edifice instability that is characterized by uplift of soft substratum our new view of causal mechanisms of the sector collapse provides invaluable information for hazard assessment of quaternary volcanoes

an eruptive history of maderas volcano using new 40ar 39ar ages and geochemical analyses maderas volcano is a small andesitic stratovolcano located on the island of ometepe in lake nicaragua nicaragua with no record of historic activity twenty one samples were collected in 2010 from lava flows of maderas the selected samples were analyzed for whole rock geochemistry using icp aes and or were dated using the 40ar 39ar method the results of these analyses were combined with previously collected data from maderas as well as field observations to determine the eruptive history of the volcano and create a geologic map the results of the geochemical analyses indicate that maderas has higher concentrations of alkalies than most nicaraguan and costa rican volcanoes including its nearest neighbor concepcion volcano it is also different from concepcion in that it displays higher incompatible elements determined age dates range from 179 2 16 4 ka to 70 5 6 1 ka based on these ages and the geomorphology of the volcano which is characterized by a bisecting graben it is proposed that maderas experienced two generations of development initial build up of the older cone including pre graben lava flows followed by post graben lava flows the ages also indicate that maderas is markedly older than concepcion which is historically active volcanic hazards were also assessed the 40ar 39ar ages indicate that maderas has likely been inactive for tens of thousands of years and future volcanic eruptions are not considered an immediate hazard however earthquake and lahar hazards exist for the communities around the volcano the steep slopes of the eroded older cone are the most likely sources of lahar hazards

streaming potential properties of westerly granite with applications this paper reports on laboratory measurements of the streaming potential properties of common minerals and in particular of westerly granite data are presented for these solids in contact with simple electrolytic solutions and in one case for temperature variation in the range 5 70 c for 1 1 electrolytes the ratio of the streaming potential coupling coefficient to fluid resistivity was approximately 4 mv atm m and for 2 1 electrolytes 2 mv atm m the effect of temperature was small 0 05 mv c temperature increase and indicates that the zeta potential was independent of temperature preliminary experimental results using mixed electrolytic solutions nacl cacl2 and two phase fluid flow are also described two phase flow can enhance streaming potentials by as much as a factor of 3 or 4 the laboratory data are used to interpret streaming potentials in geological problems such as earthquake prediction geothermal prospecting using the self potential method and surface conductivity contribution to the electrical resistivity of rocks

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

fault volcano interactions with broadly distributed stretching in rifts abstract areas undergoing pure extension are typically characterized by the formation of faults and fractures orthogonal to the maximum principal stress in these conditions the presence of a volcano and its magmatic system perturbs the local stress field leading to changes in faulting magnitude and attitude this process has been analyzed in many previous modeling works in which fault volcano interaction have been reproduced with set ups that create extension over a single discontinuity by use of a standard base plate however many natural rifts display broadly distributed extension between main border faults with no discrete discontinuities driving deformation to account for these conditions in this study we improve the previous works by reproducing and analyzing the interaction of tectonic stresses with volcanic edifices in areas characterized by broadly distributed extension in particular we run a set of analogue models which are extended by stretching a basal elastic sheet with this improved set up models are generally consistent with previous ones but better reproduce the geometry and architecture of faulting in rifts leading to improved and more rigorously results to compare with real cases we confirmed that the presence of a volcano and or an intrusive body locally modifies the fault pattern concentrating faulting and curving faults notably the rheological contrast between the intrusion and the host rock leads to faults that follow the outline of the body favoring concentric faults in contrast radial faults are developed by the volcano load the combination of intrusion host rock contrast and volcano loading creates both types of faulting which are recognized in natural examples the geometry of the resulting faults is dependent on the coexistence or not of intrusion and edifice and on their dimensions the results indicate that volcanic edifices have a stronger influence on fault attitude with respect to the presence of intrusions experimental results are compared with some natural cases from the east african rift system finally we suggest that using faulting geometries as a foundation geodetic monitoring and more precise modeling could be used to assess the rift evolution of such extensional magmatic systems

pointcatcher software analysis of glacial time lapse photography and integration with multitemporal digital elevation models terrestrial time lapse photography offers insight into glacial processes through high spatial and temporal resolution imagery however oblique camera views complicate measurement in geographic coordinates and lead to reliance on specific imaging geometries or simplifying assumptions for calculating parameters such as ice velocity we develop a novel approach that integrates time lapse imagery with multi temporal digital elevation models to derive full 3d coordinates for natural features tracked throughout a monoscopic image sequence this enables daily independent measurement of horizontal ice flow and vertical ice melt velocities by combining two terrestrial laser scanner surveys with a 73 day sequence from solheimajokull iceland variations in horizontal ice velocity of 10 were identified over timescales of 25 days an overall surface elevation decrease of 3 0 m showed rate changes asynchronous with the horizontal velocity variations demonstrating a temporal disconnect between the processes of ice surface lowering and mechanisms of glacier movement our software pointcatcher is freely available for user friendly interactive processing of general time lapse sequences and includes monte carlo error analysis and uncertainty projection onto dem surfaces it is particularly suited for analysis of challenging oblique glacial imagery and we discuss good features to track both for correction of camera motion and for deriving ice velocities

flexural and stratigraphic development of the west indian continental margin subsidence curves for 27 wells from the western continental margin of india show a characteristic late oligocene to early miocene 24 5 ma rapid increase in subsidence rate superposed on the long lived slow subsidence typical of the thermal subsidence phase of passive continental margins by subtracting a best fit negative exponential subsidence from the observed subsidence curves we obtain an estimate of the distribution and magnitude of the excess subsidence affecting the neogene development of the west indian margin the magnitude of this excess subsidence increases seaward from the coast ranging from a few meters to 2000 m near the shelf edge we examine the following hypotheses to explain the distribution and timing of this excess subsidence 1 modification of basin stratigraphy due to the effects of lithospheric in plane compression 2 creation of accommodation space on the margin by flexural effects associated with indus fan loading and 3 rapid growth of the continental margin and associated flexural effects of the three hypotheses tested the least important mechanism to account for the observed excess subsidence is that of variations of lithospheric in plane force principally because maximum in plane compression within the indo australian plate was only achieved in the late miocene because indus fan sediment deposition began in the late oligocene to early miocene we investigated three dimensional flexural effects associated with fan loading as a cause of the excess subsidence beginning at 24 ma the distribution and magnitude of modeled flexural deflection however are not consistent with the observed excess subsidence interpretation of seismic reflection data indicates that the margin has aggraded and prograded by 100 km basin ward since the oligocene therefore we evaluate the flexural effects of this margin growth by estimating the amount of space infilled by margin progradation and aggradation since 24 ma and computing the resulting deflection this deflection matches the distribution and magnitude of observed excess subsidence along the margin in addition the distribution of the flexural bulge predicted from the combined deflections due to indus fan and margin loading is spatially coincident with the distribution of exposed marine terraces and drainage divides in the saurastra peninsula and the regions surrounding the gulfs of cambay and kutch respectively available gravity seismic reflection refraction and well data are consistent with our prediction of a 4000 to 5000 m thick sediment load developed during the neogene along the outer margin we propose that flexural deformation due to sedimentary loading provides a potential tectonic feedback mechanism that affects coastal and fluvial depositional processes as regions in close proximity to the load are depressed regions farther from the load experience uplift i e the peripheral bulge which is sufficient to cause subaerial exposure of large portions of the shelf and to modify existing drainage networks this feedback represents a mechanism for inducing relative sea level changes without invoking glacial eustasy

conduction phenomena from theory to geotechnical practice virtually all geotechnical problems involve the flow of fluids chemicals and energy a current review of the types of direct and coupled flow through soil is given and assessment of their significance in geotechnical practice is made darcy s fourier s ohm s and fick s laws provide a suitable practical basis for the analysis of water heat electrical and chemical flows due to gradients of the same type prolonged application of gradients of the different types can cause significant changes in the state and properties of a soil and flows through it the quantification of coupled flows is most easily done by direct measurement of coupling coefficients when only two types of flow are important the application of irreversible thermodynamics is useful for quantification of flows in more complex systems relationships are provided for the expression of coupling coefficients in terms of directly measurable soil parameters such as hydraulic conductivity coupled fluid flows due to electrical and chemical gr

geological and geomorphological evolution of the etna volcano ne flank and relationships between lava flow invasions and erosional processes in the alcantara valley italy abstract in this paper the interrelationships between volcanic activity and fluvial events in the alcantara valley are investigated based on the correlation between the stratigraphy of the ne flank of mt etna and subsurface data the geological and geomorphological evolutions of the valley are reconstructed new 1 10 000 scale geological mapping shows that the bulk of this sector of the volcano is made up of the ellittico volcano lava flows though they are widely covered by the products of the eruptive activity of the last 15 ka the present day morphological setting of the alcantara valley is the result of two main evolutionary phases initiated during the activity of the ellittico volcano only one lava flow invasion of the valley floor occurred in the first phase this phenomenon was followed by a long period of erosional processes leading to the entrenchment of the drainage pattern and the erosion of the ellittico lava flow about 20 25 ka ago an important change in the frequency of the lava flow invasions into the valley occurred associated with the final stage of the ellittico volcano activity marking the beginning of the second phase during this phase volcanic processes became predominant with respect to other morphogenetic processes in the alcantara valley lava flows coming from the ne flank of the ellittico volcano caused a radical modification of the morphological setting of this area even though only one lava flow emitted by an eruptive fissure located within the valley partially filled the riverbed during the eruptive activity of the last 15 ka the complete filling of the alcantara valley floor occurred in particular between 15 and 7 ka a lava flow originated from the mt moio scoria cone filled the valley floor for a distance of about 9 km following a short period of erosion an eruptive fissure located within the valley generated a 20 21 km long lava flow that was channelled along the full extent of the alcantara valley and stretches for about 3 km offshore in the ionian sea in the last 7 ka lava flows originating from the ne rift zone produced only temporary damming of the riverbed without any important contribution to the filling of the alcantara valley

stress field interactions between overlapping shield volcanoes borehole breakout evidence from the island of hawai i usa acknowledgments this pta2 borehole investigation was funded by the international continental scientific drilling program icdp and by vmapp volcanic margin petroleum prospectivity project vbpr dougalearth tgs in collaboration with the humu ula groundwater research project d a j and s p are partly funded through a norwegian research council centres of excellence project project number 223272 ceed we thank marco groh for the logging operations we thank two anonymous reviewers for the comments and suggestions we are particularly grateful to the associate editor mike poland for his valuable comments and his critical review that greatly improved the manuscript

influence of water pressure dynamics and fluid flow on the streaming potential response for unsaturated conditions streaming potentials are produced by electrokinetic effects in relation to fluid flow and are used for geophysical prospecting the aim of this study is to model streaming potential measurements for unsaturated conditions using an empirical approach a conceptual model is applied to streaming potential measurements obtained from two drainage experiments in sand the streaming potential data presented here show a non monotonous behaviour with increasing water saturation following a pattern that cannot be predicted by existing models a model involving quasi static and dynamic components is proposed to reproduce the streaming potential measurements the dynamic component is based on the first time derivative of the driving pore pressure the influence of this component is investigated with respect to fluid velocity which is very different between the two experiments the results demonstrate that the dynamic component is predominant at the onset of drainage in experiments with the slowest water flow on the other hand its influence appears to vanish with increasing drainage velocity our results suggest that fluid flow and water distribution at the pore scale have an important influence on the streaming potential response for unsaturated conditions we propose to explain this specific streaming potential response in terms of the behaviour of both rock water interface and water air interfaces created during desaturation processes the water air interfaces are negatively charged as also observed in the case of water rock interfaces both the surface area and the flow velocity across these interfaces are thought to contribute to the non monotonous behaviour of the streaming potential coefficient as well as the variations in its amplitude the non monotonous behaviour of air water interfaces created during the flow was highlighted as it was measured and modelled by studies published in the literature the streaming potential coefficient can increase to about 10 to 40 when water saturation decreases such an increase is possible if the amount of water air interfaces is increased in sufficient amount which can be the case

sheet intrusions and deformation of piton des neiges and their implication for the volcano tectonics of la reunion abstract to understand the volcano tectonic history of piton des neiges the dormant volcano of la reunion we measured in the field the orientation of sheeted intrusions and deformation structures and interpreted the two datasets separately with a paleostress inversion results show that the multiple proposed rift zones may be simplified into three trends 1 a n30 e 5 km wide linear rift zone running to the south of the edifice active in the shield building 2 48 0 43 ma and terminal stages 190 22 ka 2 a curved n110 to n160 e rift zone widening from 5 km to 10 km toward the nw flank essentially active during the early emerged shield building 1 3 ma and 3 two sill zones 1 km thick in total in the most internal parts of the volcano active in the shield building and terminal stages in parallel deformation structures reveal that the tectonics of the edifice consisted in three end member stress regimes sharing common stress axes 1 nw se extension affecting in priority the south of the edifice near the n30 e rift zone 2 nne ssw extension on the northern half of the volcano near the n110 160 e rift zone 3 compression occurring near the sill zones with a ne sw or nw se maximum principal stress these three stress regimes are spatially correlated and mechanically compatible with the injection trends combined together our data show that the emerged piton des neiges underwent sector spreading delimited by perpendicular rift zones as observed on piton de la fournaise the active volcano of la reunion analogue experiments attribute such sector spreading to brittle edifices built on a weaker substratum we therefore conclude that la reunion volcanoes are both brittle as opposed to hawaiian volcanoes or mount etna whose radial spreading is usually attributed to a ductile body within the edifices

tectonic patterns and regional stresses near venusian coronae abstract many venusian coronae exhibit distinctive patterns of faults in particular we find the tectonic patterns of one such corona similar to the striking patterns of the grabens surrounding alba patera on mars pursuing this similarity we perform a stress analysis analogous to one that successfully explained the alba patera pattern and in so doing determined a value for the local regional stress local stress fields of venusian coronae are assumed to be created by either a gaussian axially symmetric upwarp or a cylindrical load due to accumulation of volcanic materials on an elastic lithosphere the local coronal stresses are combined with varying amounts of a uniform regional stress field for different elastic lithospheric thicknesses from the magnitudes and orientations of the resultant principal stresses the predicted patterns of surface tectonic features i e graben and thrust fault chains are plotted these patterns are compared to those of coronae on magellan images matching the patterns thus determines the regional stress and elastic lithospheric thickness about the coronae comparison of predicted to observed tectonic patterns for three specific coronae leads to estimated regional stresses of approximately 0 1 0 6 kbar and effective elastic lithospheric thicknesses consistent with 10 5 km although one area may have had a lithosphere as thin as 2 km during corona formation

streaming potential and permeability of saturated sandstones under triaxial stress consequences for electrotelluric anomalies prior to earthquakes the streaming potential due to fluid circulation in rock was measured on saturated sediments fontainebleau sandstones the electrokinetic coupling coefficient which is the ratio of the streaming potential and the excess pore pressure is proportional to the fluid resistivity additionally for a fluid conductivity of 10 3 s m the electrokinetic coupling coefficient varies from 10 to 6642 mv 0 1 mpa for sample permeability in the range of permeabilities from 0 15 10 15 to 1220 10 15 m2 the different values of the electrokinetic coupling coefficient have been explained by the effect of increasing surface conductivity which becomes nonnegligible compared to fluid conductivity for low permeability when the sample is deformed under triaxial stress up to failure the vertical permeability along the principal stress drops by about 0 20 0 1 mpa when failure occurs the typical variation of the electrokinetic coupling coefficient is a large increase beginning with the onset of the localization of the shear band at about 75 of the yield stress and stopping at the failure this increase of the electrokinetic coupling coefficient is due to an increase of potential in the shear zone when new surfaces are created and connected possible consequences of our results are given concerning the electrical fields which could appear during the preparation of an earthquake it is shown that in some cases self potential anomalies reported in the deformed zone preceding an earthquake occurrence could be due to an increase of the electrokinetic coupling coefficient from 75 of the yield stress to rupture in the vicinity of one of the electrodes any variation of fluid resistivity or permeability in the vicinity of one electrode could change the electrokinetic coupling coefficient inducing a surface electrokinetic potential anomaly in regard to the interpretation of the electrokinetic effect which occurs at large distance from the epicenter a larger electrokinetic potential anomaly could be measured between electrodes situated along a vertical fluid flow for instance in a shallow borehole an electrokinetic potential anomaly up to 30 mv for a fluid conductivity of 0 01 s m and a rock permeability of 10 12 m2 could be observed with a change of the underground water table level as slight as 50 cm 50 mbar moreover if the permeability between the electrodes is increased by a factor of 8 103 the electrokinetic coupling coefficient could be enhanced by a factor up to 650

the panvel flexure along the western indian continental margin an extensional fault structure related to deccan magmatism abstract on the basis of field observations aided by remote sensing data a new model for the western indian panvel flexure is proposed the model involves normal motion on east dipping faults and westward tilting of fault blocks the flexuring occurred by attenuation and foundering of continental crust due to crustal thinning and loading by a dyke swarm following a period of massive magmatic discharge accompanying the continental break up and opening of indian ocean during early tertiary times

holocene eruptions of mt popa myanmar volcanological evidence of the ongoing subduction of indian plate along arakan trench in the western part of myanmar the geodetic and seismic data indicate the ongoing highly oblique subduction of indian plate under eurasian plate volcanoes of burma arc however did not produce eruptions in the recorded history and are considered extinct such perception questions the ongoing subduction as well as keeping local officials unaware of possibility of future volcanic eruptions in the country we have investigated the youngest lava flows and pyroclasts of mt popa which is the best preserved polygenetic volcanic edifice in myanmar the ar ar dating of the youngest products of the volcano provided very young radiometric ages which were unable to be measured accurately the radiocarbon dating of paleosols intercalated with the most recent ash layers of the volcano has shown that mt popa produced several eruptions in the beginning of holocene the youngest eruption occurred 8000 bp and included the 1 3 km3 gravitational collapse of the volcanic cone with deposition of the 11 km long debris avalanche immediately followed by emplacement of 0 1 km3 of pyroclastic flow of calc alkaline basaltic andesite composition the collapse direction as well as complex morphology of the resulted crater were prearranged by geometry of the listric fault which was formed during the pre collapse asymmetric gravitational spreading of the volcanic cone the recently erupted products are geochemically similar to products of young monogenetic volcanoes of monywa area located 150 km north mt popa and both display patterns consistent with magma generation at an active subduction system low magma production rate of mt popa 3 10 5 km3 year averaged for the 1 ma of the volcano history is in agreement with the highly oblique angle and slow rate of the subduction the fact of the holocene eruptions of calc alkaline composition in burma arc represents volcanological evidence of the ongoing subduction in this part of the collision zone between india and asia

vertical axis rotation of the upper portions of the north east rift of tenerife island inferred from paleomagnetic data abstract paleomagnetic sampling sites were established in 82 dykes along an 8 km long section of the north east rift zone nerz of tenerife canary islands spain of the 70 interpretable sites 16 are of normal polarity and 54 of reversed polarity four normal polarity sites and fifteen reverse polarity sites were excluded from the grand mean calculation for statistical reasons after inverting the reverse polarity sites through the origin the in situ grand mean yields a declination d 023 8 an inclination i 42 3 95 3 2 39 0 n 51 that is discordant to the expected late miocene to pleistocene field direction d 357 6 i 38 8 95 4 7 this discordance can be explained as either a 26 clockwise vertical axis rotation or a 28 wnw side down tilt about an average 009 horizontal tilt axis the sampled section is composed of numerous semi vertical dykes cutting mainly lava flow units that are sub horizontal and cross cut by steeply dipping faults 70 90 field evidence is therefore more compatible with a vertical axis rotation rather than a horizontal axis tilt of the drilled units we argue that this clockwise vertical axis rotation is likely related to strike slip movements that occurred along the edges of the collapse scars and accommodate the emplacement and growth of the underlying intrusive core and associated dykes six new 40ar 39ar age determinations constrain the main interval of dyke emplacement within the nerz between 0 99 ma and 0 56 ma the intrusive activity in the sampled section of the rift appears to have been almost continuous with several intrusion pulses that are probably related to flank destabilisation event s during the mid pleistocene our study thus demonstrates a long lived multi faceted history that shaped the nerz

volcano spreading controlled by dipping substrata most volcanoes grow on slopes and some tend to fail catastrophically on the downslope side many volcanoes also deform by volcano spreading which may lead to failure we look at the effect of dipping substrata on the potential for spreading and collapse with analogue models the dip is found to strongly control the spreading style rate and direction a distinct change from purely radial spreading occurs even with small 1 substrata tilt structures on the cone and surrounding area are modified according to the underlying dip direction spreading becomes concentrated on downslope sectors where movement is predominantly in the dip direction the degree of structural realignment is a function of the slope angle our models are applied to previously known and new examples of volcano spreading the effect of dipping substrata in confining spreading to sectors increases the potential for deep seated sector collapses this finding provides a mechanism for failure on the downslope side the incorporation of substrata can create very large volume collapses