complete dynamic modeling calibration for the thurwieser rock avalanche italian central alps abstract few rock avalanches have been witnessed and no exact real time description is available the 2 5 m m 3 punta thurwieser rock avalanche september 2004 italian central alps is a unique event for which many quantitative observations have been gathered this is the first case ever of a natural rock avalanche being recorded on video and for which an almost exact value of the total time duration from initial detachment to final deposition is available the landslide travelled over 2 9 km from its source partially in a glacial environment the initial failure and the time for the complete evacuation of the source area were studied and assessed by a series of photos the mean front velocities along the path have been estimated from the video the final geometry and the characteristics of the deposit have been obtained by gps measurements aerial photos field surveys and laboratory tests a quasi 3d continuum dynamic analysis of the landslide motion has been performed assuming both a voellmy and a frictional rheology in the model dan 3d for the first time the landslide front velocities have been used for back analyses and calibration of the rheological parameters together with the final shape and thickness of the deposit and its developing extension the dynamic flow resistance parameters initially calibrated with dan were adopted and validated in dan 3d showing good consistency they are consistent with the existing database for calibrated landslides of similar type and scale flow velocities on the path segment underlain by glacial deposits up to 55 65 m s 1 are more accurately predicted by adopting a frictional rheology up to 50 55 m s 1 with zero pore pressure and a 26 friction angle than by a voellmy rheology up to 40 45 m s 1 both observations and modelling show that glacial ice plays a substantial role in increasing the rock avalanche mobility

variscan tectonics of central europe postaccretionary intraplate deformation of weak continental lithosphere the area occupied by the variscan belt of central europe forms part of gondwana derived microplates essentially avalonia and armorica that according to paleomagnetic data juxtaposed baltica and laurentia from the upper ordovician to the lower devonian the actual structure of this area is a puzzle of rather small fault bounded crustal blocks different in p t t histories which was created by later tectonic processes at around 360 to 320 ma according to a common view and by contrast to paleomagnetic data the structural record of fault bounded blocks is interpreted in terms of mid devonian to lower carboniferous amalgamation of narrow continental plates represented by the fault bounded blocks themselves however this is not supported in this article instead it will be shown that fault systems and fault bounded blocks were created by intraplate deformation of a weak domain of gondwana derived continental lithosphere significantly after its accretion deformation was partitioned into newly formed deep seated strike slip and kinematically connected reverse or normal detachment systems large translation magnitudes caused juxtaposition of crustal areas of variable thickness until they were emplaced along the fault systems the various categories of fault bounded complexes record different tectonic events category 1 metamorphic complexes represent deep seated parts of thickened crust some time before unroofing on the detachment systems between about 340 360 and 320 ma however the record of subduction and extreme crustal thickening during earlier stages of the collision history was erased to a high degree and is only preserved by mineral and structural relics strike slip and detachment systems propagated across and dismembered tectonic boundaries formed during these early events category 2 metamorphic complexes and the barrandian basin recording predominant pre late devonian metamorphic or stratigraphic events represent the brittle upper crustal parts during continuing metamorphism in the category 1 complexes weakly or unmetamorphosed lower paleozoic category 3 basins represent areas of thinned continental crust and record subsidence before and to some degree during activity of detachment systems the complex overall kinematic pattern of block bounding strike slip and detachment systems indicates compression and extension acting simultaneously this probably reflects the effects of continuing oblique plate convergence rotation and wsw extrusion of fault bounded blocks in addition to heating and extensional flow of previously thickened crustal areas

settling driven gravitational instabilities associated with volcanic clouds new insights from experimental investigations downward propagating instabilities are often observed at the bottom of volcanic plumes and clouds these instabilities generate fingers that enhance the sedimentation of fine ash despite their potential influence on tephra dispersal and deposition their dynamics is not entirely understood undermining the accuracy of volcanic ash transport and dispersal models here we present new laboratory experiments that investigate the effects of particle size composition and concentration on finger generation and dynamics the experimental set up consists of a plexiglas tank equipped with a removable plastic sheet that separates two different layers the lower layer is a solution of water and sugar initially denser than the upper layer which consists of water and particles particles in the experiments include glass beads as well as andesitic rhyolitic and basaltic volcanic ash during the experiments we removed the horizontal plastic sheet separating the two fluids particles were illuminated with a laser and filmed with a hd camera particle image velocimetry piv is used to analyse finger dynamics results show that both the number and the downward advance speed of fingers increase with particle concentration in the upper layer while finger speed increases with particle size but is independent of particle composition an increase in particle concentration and turbulence is estimated to take place inside the fingers which could promote aggregation in subaerial fallout events finally finger number finger speed and particle concentration were observed to decrease with time after the formation of fingers a similar pattern could occur in volcanic clouds when the mass supply from the eruptive vent is reduced observed evolution of the experiments through time also indicates that there must be a threshold of fine ash concentration and mass eruption rate below which fingers do not form this is also confirmed by field observations

strombolian explosions 1 a large bubble breaking at the surface of a lava column as a source of sound strombolian activity consists of a series of explosions caused by the breaking of large overpressurized bubbles at the surface of the magma column acoustic pressure has been measured for 36 explosions at stromboli we propose that sound is generated by the vibration of the bubble before it bursts oscillations are driven by an initial overpressure inside the bubble assumed to be initially at rest just below the magma air interface inertia effects cause the bubble to overshoot its equilibrium radius then the bubble becomes underpressurized and contracts because of gas compressibility these oscillations are only slightly damped by viscous effects in the magma layer above the bubble the bubble cannot complete more than one cycle of vibration because of instabilities developing on the magma layer that lead to its breaking near the minimum radius assuming a simple geometry we model this vibration and constrain the radius and length of the bubble and the initial overpressure by fitting a synthetic waveform to the measured acoustic pressure the fit between synthetic and observed waveforms is very good both for frequency 60 rad s 1 and amplitude the initial bubble radius is 1 m and the length varies between several and a few tens of meters from the initial overpressure approximately 105 pa we calculate the maximum radial velocity of ejecta 30 m s 1 the generally good agreement between data and predictions of our model leads us to suggest that acoustic measurements are a powerful tool for the understanding of eruption dynamics

lessons from ontake san a comparative analysis of debris avalanche dynamics abstract dynamic aspects of the long runout ontake san debris avalanche are evaluated by a comparison of several models an unsteady numerical model assumes two dimensional flow of an incompressible biviscous or newtonian fluid represented as a continuum with a free surface internal deformation of the flowing mass is considered as well as boundary resistances thus flow thinning and deposit shape as well as flow kinematics may be modeled parameters are adjusted to match observed runout with additional constraints on velocity and emplacement time with abundant constraints for ontake san from careful field investigations by japanese research teams our analysis indicates that a substantial decrease in flow resistance occurred as a function of displacement constant property models that match runout tend to overestimate the peak velocities and to underestimate the emplacement times a staged increase in mobility in both constant volume and variable volume models leads to results consistent with field data runout in a channel overflow area was also modeled qualitatively similar results have been obtained by other researchers using simple sliding block models with empirical parameters a slide block model with rational parameter selection a modified flood simulation and a multi element frictional slide model the relative merits of these models are compared the field mechanisms associated with this mobility increase with displacement are poorly understood but the question is now identified as a target for future research at debris avalanche sites and some plausible mechanisms are considered the main reason probably involves the entrainment of river water and saturated sediment leading to enhanced efficiency of fluid pressure mechanisms with undrained shear in addition progressive shearing reduced the mean particle size and angularity and the cohesion and friction and apparent viscosity of avalanche debris near the wetted perimeter hydroplaning the shearing of water films and slurries may have occurred locally

friction and dynamics of rock avalanches travelling on glaciers rock avalanches travelling on glaciers often exhibit effective friction coefficient lower than those on a rocky terrain after briefly considering some data of rock avalanches on glaciers the physics of sliding of solid objects on icy surfaces is reviewed and a model is put forward for the mechanics of rock avalanche sliding on ice accounting for the formation of a natural lubricating layer it is suggested that at the beginning of the flow of a rock avalanche friction results from rocky blocks ploughing on ice as the erosion continues a gouge of ice particles results which clogs the interstices between blocks and may partially melt as a consequence of the production of frictional heat this conceptual model is numerically investigated for a slab travelling on ice the results show an increase in mobility as a function of slab thickness travelled length and the gravity field in agreement with case studies the results are useful to interpret the peculiar features of rock avalanches travelling on icy surfaces such as digitations out runner blocks and longitudinal furrows the lubrication theory for landslides on ice proposed here may provide a framework for understanding landslides on earth and for future modelling in addition it may help elucidate the presence of similar landslide deposits on the surface of mars

the evolution of volcanic plume morphology in short lived eruptions the details of volcanic plume source conditions or internal structure cannot readily be revealed by simple visual images or other existing remote imaging techniques for example one predominant observable quantity the spreading rate in steady or quasi steady volcanic plumes is independent of source buoyancy flux however observable morphological features of short duration unsteady plumes appear to be strongly controlled by volcanic source conditions as inferred from our recent work here we present a new technique for using simple morphological evolution to extract the temporal evolution of source conditions of short lived unsteady eruptions in particular using examples from stromboli italy and santiaguito guatemala volcanoes we illustrate simple morphologic indicators of 1 increasing injection rate during the early phase of an eruption 2 onset of source injection decline and 3 the timing of source injection cessation combined these observations indicate changes in eruption discharge rate and injection duration and may assist in estimating total mass erupted for a given event in addition we show how morphology may provide clues about the vertical mass distribution in these plumes which may be important for predicting ash dispersal patterns

the angle of reach as a mobility index for small and large landslides the relations between the angle of reach fahrboschung and other indexes expressing the mobility of landslides and vertical drop horizontal reach and volume of landslide mass have been analyzed by means of simplified plots and regression equations results for 204 landslides of all sizes show that whatever the mechanism of motion all kinds of landslides experience a continuous reduction of the angle of reach with volume increase this reduction starts from the smallest sizes scattering in this relation is mostly due to mechanisms of motion and to both obstacles and topographic constraints on the path this synthesis indicates that small landslides less than 0 5 106 m3 in relative terms display excesses of travel distance similar to large landslides since most small landslides are not expected to develop any change in the mechanism of progression while moving the decrease in the reach angle with volume suggests that scale effects should be taken into account the angle of reach is found to be

physical models of rock avalanche spreading behaviour with dynamic fragmentation the dynamic fragmentation of rock during avalanche motion has been postulated as a mechanism explaining the long runout of large rock avalanches or sturzstrome this paper investigates whether test

geodynamic model for the palaeozoic crustal consolidation of western and central europe abstract the crystalline basement of western and central europe consists of a mosaic of crustal elements which were consolidated during pre grenvillian the grenvillian dalslandian morarian cadomian caledonian and hercynian orogenic cycles contemporaneous with the caledonian suturing of the precambrian laurentia greenland and fennosarmatian shields a number of gondwana derived cadomian micro cratons were accreted to the southern margin of laurasia following the late caledonian paroxysm the devonian and early carboniferous evolution of europe was dominated by continued northward subduction of the proto tethys plate at an arc trench system parallelling the southern margin of laurasia the accretion of additional gondwana derived continental fragments back arc rifting and a sinistral translation of major proportions between the laurentia greenland and the fennosarmatian sub plates the acadian and bretonian orogenies were of the pacific type the visean collision of gondwana with laurasia marked the onset of the himalayan type variscan orogeny during which collision related compressive stresses overpowered the devonian early carboniferous back arc rift systems and caused the development reactivation of a subduction zones the central armorican and saxothuringian successor basins became folded and destroyed during the latest visean whilst the variscan foredeep became scooped out in part by nappes involving the basement during the late westphalian major crustal shortening during the variscan diastrophism was accompanied by the anatectic remobilisation of subducted crustal and upper mantle material and a widespread syn and late orogenic magmatism the latest carboniferous early permian reorientation of the convergence direction between gondwana and laurasia induced the development of a complex wrench fault system transecting the variscan fold belt and an extensive post orogenic volcanism the hypotheses summarised here require confirmation by further palaeomagnetic and radiometric data and faunal analyses

the avalanche lake rock avalanche mackenzie mountains northwest territories canada description dating and dynamics at avalanche lake located in the backbone ranges of the mackenzie mountains about 200 106 m3 of massive devonian carbonate rock slid down remarkably planar bedding surfaces dipping at 30 and c

time evolution of transient volcanic plumes insights from fractal analysis abstract transient volcanic plumes are time dependent features generated by unsteady eruptive sources having similar eruption duration and plume development timescales their morphological evolution reflects both the discharge history at the vent and air entrainment crucial parameters controlling volcanic ash dispersal and impact on the environment and human activities however despite its importance transient plume morphology has been scarcely quantified due to both observational and analytical hindrances in this study we introduce new tools to quantify the initial morphological evolution of transient volcanic plumes by applying fractal analysis and plume s perimeter measurements to thermal high speed and visible light high resolution videos of eruptions eruptive plumes from sakurajima japan stromboli italy and fuego guatemala volcanoes were recorded during several field campaigns in 2012 2016 the eruption dataset has been complemented by the fractal analysis of three 2d numerical gas jet simulations at different reynolds number 2 103 5 103 and 10 103 in order to provide reference configurations to compare with the natural cases the two shape analysis methods used show different sensitivities the ratio between plume and bounding box perimeters appears to be more perceptive of punctual dynamical variations while fractal analysis reflects the overall plume evolution both methods highlight that plume shape complexity increases over time and is related to the formation and development of smaller scale vortexes the variability of the rate of fractal dimension increase over time d effectively captures plume evolution it also appears that d correlates with the ash eruption rate aer evolution and the instability of the source this study shows that discharge history and intensity at the vent are the first order control on plume s shape evolution and by inference on its air entrainment ability

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

the dynamics of volcanic jets temporal evolution of particles exit velocity from shock tube experiments pyroclast ejection during explosive volcanic eruptions occurs under highly dynamic conditions involving great variations in flux particle sizes and velocities this variability must be a direct consequence of complex interactions between physical and chemical parameters inside the volcanic plumbing system the boundary conditions of such phenomena cannot be fully characterized via field observation and indirect measurements alone in order to understand better eruptive processes we conducted scaled and controlled laboratory experiments by performing shock tube experiments at known conditions we defined the influence of physical boundary conditions on the dynamics of pyroclast ejection if applied to nature we are focusing in the near vent processes where independently of fragmentation mechanism impulsively released gas pyroclast mixtures can be observed these conditions can be met during e g strombolian or vulcanian eruptions parts of plinian eruptions or phreatomagmatic explosions the following parameters were varied 1 tube length 2 vent geometry 3 particle load 4 temperature and 5 particle size distribution gas and particles in the experiments are not coupled st 1 the initial overpressure with respect to atmosphere was always at 15mpa we found a positive correlation of pyroclast ejection velocity with 1 particle load 2 diverging vent walls and 3 temperature as well as a negative correlation with 1 tube length and 2 particle size additionally we found that particle load strongly affects the temporal evolution of particle ejection velocity these findings stress the importance of scaled and repeatable laboratory experiments for a better understanding of volcanic phenomena and therefore volcanic hazard assessment

characterization and interpretation of volcanic activity at karymsky volcano kamchatka russia using observations of infrasound volcanic emissions and thermal imagery 2 a multiparameter data set including measurements of infrasound volcanic emissions and thermal imagery is used to characterize and interpret diverse volcanic activity observed during field campaigns in august 2011 and july 2012 at karymsky volcano kamchatka russia four activity types are visually identified and characterized according to so2 emission rate ash mass event duration peak temperature thermal radiation energy infrasound onset and frequency reduced infrasonic pressure and acoustic energy these activity types include 1 ash explosions 2 pulsatory degassing 3 gas jetting and 4 explosive eruption unique infrasound signals are associated with all four activity types suggesting that infrasound can be used to help remotely and continuously detect and characterize volcanic activity at karymsky and other similar volcanoes our observations suggest that so2 is emitted continuously though in varying abundance while ash is emitted discontinuously and is only associated with certain types of activity our data set supports previous models that attribute variations in surface activity to changes in conduit permeability at karymsky volcano evidence for a decrease in conduit permeability as a trigger for ash explosions and explosive eruption activity types is supported by weakened but still detectable so2 emission rates prior to eruption along with the highly impulsive infrasonic onset and large reduced infrasound pressure indicating high pressure at the vent we speculate that changes in conduit permeability at karymsky volcano result from changes in magma supply from the shallow crustal storage region though additional measurements are required to validate this hypothesis

quantification of the gas mass emitted during single explosions on stromboli with the so2 imaging camera we performed measurements using an so2 imaging camera of the so2 gas mass emitted during five discrete explosive events on stromboli volcano on 3 october 2006 the so2 gas mass released during discrete explosions was 15 40 kg per explosion producing 3 8 of the total daily so2 gas emission demonstrating that in terms of gas flux strombolian explosions are a second order phenomenon compared with quiescent degassing using the typical gas composition measured with op ftir allows us to determine the total gas mass released during an explosion as 360 960 kg with a volume of 1500 4100 m 3 at 1 bar at the probable source pressure of gas slug formation of 75 mpa this gas amount would occupy a volume equivalent to a sphere with a radius of 0 8 1 m comparable with estimates of stromboli s conduit geometry c 2009 elsevier b v all rights reserved

palaeozoic terranes and their lithospheric boundaries within the trans european suture zone tesz a review the trans european suture zone tesz is a broad and complex zone of terrane accretion separating ancient lithosphere of the baltic shield and east european craton eec from the younger lithosphere of western and southern europe there is debate about the number of terranes involved and their origins the most significant terrane boundaries originally oceanic sutures are poorly exposed and are defined using faunal provinciality prominent geophysical lineaments may represent sub terrane boundaries within composite terranes the avalonia composite terrane was amalgamated to baltica in latest ician time the provenance of the malopolska and moravo silesian terranes whose neoproterozoic basement is suspect with respect to baltica but with which they nonetheless share faunal affinities is still debated the extent of the variscide rhenohercynian zone defines the southern limit of the early palaeozoic accreted terranes terranes within the bohemian massif exhibit hp metamorphism recording subduction driven collision prior to incorporation in the tesz collage itself associated with a hp event in romania the saxothuringian zone and rheic suture are directly juxtaposed with the eec and the crustal structure of the tesz has been much modified by post palaeozoic tectonism deep seismic reflection data where available show that the oceanic sutures are frequently associated with inclined reflectivity zones irz in the lithospheric mantle here inferred to mark relict subduction zones interpreting the age of subduction is complicated by offset of originally coplanar mantle and crustal segments of the irz resulting from early orogenic lithospheric delamination at the moho interface and or post orogenic reordering processes the mantle irz appear to indicate a n directed polarity for early palaeozoic subduction apparently incompatible with the geological evidence which indicates subduction of the tornquist sea beneath avalonia and a large amount of underthrusting of avalonia by baltica possible explanations for these apparently incompatible observations are evaluated

chitinozoan contribution to the ordovician and lower silurian paleobiogeography relationships between various lower silurian chitinozoan assemblages are established using statistical methods such as calculation of the number of species in common and similarity coefficient conclusions clearly indicate that eastern canadian chitinozoan fauna are distinct from those of the north gondwana margin the proposed relationships are refined by the use of more rigorous analytical techniques such as correspondence analysis and cluster analysis the results are compared to the paleogeographic reconstructions available for the ordovician and the lower silurian they show that chitinozoans are useful not only for stratigraphic correlations but also as their paleogeographic distribution seems to be linked to paleolatitudes they can be used to document plate tectonic dynamics

accretionary history and crustal evolution of the variscan belt in western europe abstract the variscan belt of western europe is part of a large intra paleozoic belt extending on both sides of the atlantic from the ouachitas in the us and the mauritanides in west africa to the bohemian massif in czechoslovakia and poland the belt was constructed between 500 and 250 ma as a result of convergence and collision between two main continents laurentia baltica and africa after the closure of various oceanic basins iapetus rheic and galicia massif central now recorded as discrete in part cryptic sutures which form the roots of large crystalline nappes in which are found dismembered remnants of oceanic crust and mantle the accretionary history of the variscan belt in western europe is related to the progressive closure of probably two oceanic basins the rheic in the north and another the galicia massif central in the south by respectively southward and northward intraoceanic subduction followed by obduction and intracontinental lithospheric subduction the result is a broad 700 800 km fan like divergent belt which must be considered as a classical obduction collision orogen with a long intracontinental history of about 100 150 ma its arcuate shape is probably due to the northwestward impingement of a promontory of the african continent into laurentia baltica

the zymoetz river rock avalanche june 2002 british columbia canada abstract on june 8 2002 the pacific northern gas pipeline in the zymoetz river valley was severed by a large debris flow the event initiated as a rock avalanche in glen falls creek a tributary of the zymoetz river the rock avalanche involved 1 106 m3 of volcaniclastic bedrock and travelled through a complex flow path to finally deposit a large fan in the main zymoetz river approximately half of the debris volume was deposited in the cirque basin at the head of the valley with the rest deposited in the channel and the fan examination of the initiation zone showed a very persistent slightly curved joint set that forms the main sliding surface for the failed block with a dip of 45 and dip direction of 300 a geographic information system gis was used to examine the event and allowed for further interpretation of field data preliminary dynamic analysis indicates that the event reached velocities of up to 34 m s comparison of the zymoetz river rock avalanche zrra with other similar events from the literature indicates that it exhibited similar mobility and velocities as evidenced from the literature these long runout events can cause significant damage and have the potential to be a very high risk as forestry and recreation activities spread further into remote areas

experiments on a turbulent plume shape analyses 1 we report the results of laboratory experiments on a turbulent plume a simplified model of a positively buoyant volcanic plume with a small content of fine ash to study how the shape of the plume changes as a function of time to model such plumes we continuously inject a dense fluid downward at a constant exit velocity and study how the plume shape changes with time as vortices develop from flow instability and entrainment here a series of experiments are conducted with exit velocity and the density difference as the changeable parameters and the jet plume transition is realized in the laboratory initially the plume has a finger like shape which becomes unstable and forms a plume head and later transforms into a cone like self similar shape we also find that when the buoyancy becomes sufficiently large compared to inertia there is a temporary deviation from the cone like shape to form a headed cone we devise new methods to quantitatively characterize these changes of shape and define four regimes as a function of time we find that the onset times of the flow instability and the regimes have negative power law dependence on the initial re or the exit velocity and that buoyancy causes the regime transitions to become earlier our experiments suggest that monitoring the change of the shape of the rising volcanic plumes and analyzing the regime onset times can be used as a measure to constrain their buoyancy

rise dynamics of unsteady laboratory jets with implications for volcanic plumes a b s t r a c t geophysical observations of discrete volcanic eruptions suggest their eruption rates vary rapidly in time to learn how such variations may impact the initial stages of plume rise we conducted a laboratory study of neutrally buoyant jets generated by unsteady source conditions analogous to the volcanic case turbulent jets were generated by quickly injecting a finite volume of water into a large volume of still water the mass injection rates evolved over time with a gaussian like history producing jets with peak reynolds numbers ranging from 10 4 to 10 5 consistent with values estimated for small discrete eruptions except during very early and late times jet heights show a logarithmic dependence on time this trend contrasts with the power law dependence for jets produced by steady state or instantaneous discharge conditions we show that this logarithmic dependence is the similarity form appropriate for impulsive releases from a time varying source and found characteristic length and time scales that consolidate the non dimensional jet heights as functions of non dimensional times from a range of experimental conditions onto a single trend the rise of unsteady volcanic plume fronts from short duration eruptions mori and burton 2009 patrick 2007 s how the same trend as that observed in the laboratory variations in mass eruption rate strongly influence the initial phases of plume rise and may impact related processes such as mixing entrainment and eruption column collapse consequently source unsteadiness must be accounted for in physical plume models before they will reliably estimate trajectory dilution and stability for volcanic plumes from discrete eruptions 2014 elsevier b v all rights reserved

dynamics of strombolian ash plumes from thermal video motion morphology and air entrainment 1 imaging volcanic plumes is essential to provide an observational basis for understanding and modeling plume dynamics during june july 2004 150 strombolian ash plumes were imaged at stromboli volcano italy with a forward looking infrared radiometer flir thermal video camera 30 hz of these 25 80 plumes were suited for different levels of quantitative analyses in this study some simple analyses are applied to constrain basic parameters for the dynamics of strombolian plumes during their initial ascent 130 m plume rise rates covered both gas thrust 15 m s 1 and buoyant regimes 15 m s 1 which in turn controlled lateral spreading rates and air entrainment rates the half angle of lateral spreading of the plume front averaged 7 3 1 6 for gas thrust regimes and 13 5 1 6 for buoyant regimes equating to mean air entrainment coefficients of 0 06 0 12 for gas thrust regimes and 0 22 0 03 for buoyant regimes these factors were also linked to plume morphologies which included jets starting plumes and thermals a rooted thermal form was observed and presumed as an intermediary between starting plumes and discrete thermals plume rise could be approximated by a power law dependence with time rooted thermals spread and entrained air at rates approaching those of a discrete thermal but rose at a rate similar to that of a starting plume phenomena including helical motion and sedimentation were visible in the flir imagery these results demonstrate that emergent plume behavior is progressive and highly transient furthermore this study offers empirical reinforcement that entrainment dynamics are intrinsically different in 1 gas thrust versus buoyantly driven regimes and 2 plume fronts versus steady plumes

the flow structure of jets from transient sources and implications for modeling short duration explosive volcanic eruptions we used laboratory experiments to examine the rise process in neutrally buoyant jets that resulted from an unsteady supply of momentum a condition that defines plumes from discrete vulcanian and strombolian style eruptions we simultaneously measured the analog jet discharge rate the supply rate of momentum and the analog jet internal velocity distribution a consequence of momentum transport and dilution then we examined the changes in the analog jet velocity distribution over time to assess the impact of the supply rate variations on the momentum driven rise dynamics we found that the analog jet velocity distribution changes significantly and quickly as the supply rate varied such that the whole field distribution at any instant differed considerably from the time average we also found that entrainment varied in space and over time with instantaneous entrainment coefficient values ranging from 0 to 0 93 in an individual unsteady jet consequently we conclude that supply rate variations exert first order control over jet dynamics and therefore cannot be neglected in models without compromising their capability to predict large scale eruption behavior these findings emphasize the fundamental differences between unsteady and steady jet dynamics and show clearly that i variations in source momentum flux directly control the dynamics of the resulting flow ii impulsive flows driven by sources of varying flux cannot reasonably be approximated by quasi steady flow models new modeling approaches capable of describing the time dependent properties of transient volcanic eruption plumes are needed before their trajectory dilution and stability can be reliably computed for hazards management

the rand granite in the southern schwarzwald and its geodynamic significance in the variscan belt of sw germany the rand granite is a heterogeneous metamorphosed granitoid rock complex with numerous wallrock inclusions situated in the moldanubian zone at the southern margin of the central schwarzwald gneiss complex it is a largely mylonitized elongated body and is thrust over the badenweiler lenzkirch zone forming a nappe with shear zones along its northern and southern boundaries it comprises meta granites meta trondhjemites and biotite augen gneisses derived from monzogranites to granodiorites mineral behaviour indicates that the magmatic body has been deformed under upper greenschist facies conditions nappe thrusting which also affected the south schwarzwald gneiss complex occurred in visean time during high temperature low pressure metamorphism kinematic indicators in the mylonites document e to ese directed nappe transport highly transpressive relative to the trend of the nappe boundaries and the foliation the trondhjemites formed at 351 5 4 ma predating the variscan ht metamorphism they have initial end values of 6 6 to 6 7 and relatively low initial 87sr 86sr ratios 0 7042 to 0 7063 indicating a predominant mantle origin the granites and protoliths of the biotite augen gneisses probably crystallised between 436 and 377 ma suggested by u pb zircon model ages they are different from the trondhjemites with low initial end values 4 7 to 3 3 and higher initial 87sr 86sr ratios 0 7068 0 7077 indicating that large part of the rand granite originated from anatexis of continental crust internal structure of zircons from the rand granite reveals mixing of magmas derived from both mantle and crust sources these new data support an interpretation that the rand granite developed along an active continental margin and therefore represents a possible root of a variscan magmatic arc

particle transport in subaqueous eruptions an experimental investigation abstract subaqueous volcanic eruptions are natural events common under the world s oceans here we report results from bench scale underwater explosions that entrain and eject particles into a water tank our aim was to examine how particles are transferred to the water column and begin to sediment from it and to visualize and interpret evolution of the eruption cloud understanding particle transfer to water is a key requirement for using deposit characteristics to infer behaviour and evolution of an underwater eruption for the experiments here we used compressed argon to force different types of particles under known driving pressures into water within a container and recorded the results at 1 mpx frame and 1000 fps three types of runs were completed 1 particles within water were driven into a water filled container 2 dry particles were driven into water 3 dry particles were driven into air at atmospheric pressure across the range of particles used for all subaqueous runs we observed a initial doming b a main expansion of decompressing gas and c a phase of necking when a forced plume separated from the driving jet phase c did not take place for the subaerial runs a key observation is that none of the subaqueous explosions produced a single simple open cavity in all cases multiphase mixtures of gas bubbles particles and water were formed explosions in which the expanding argon ejects particles in air analogous to delivery of particles created in an explosion produce jets and forced plumes that release particles into the tank more readily than do those in which particles in water are driven into the tank the latter runs mimic propulsion of an existing vent slurry by an explosion explosions with different particle types also yielded differences in behaviour controlled primarily by particle mass particle density and particle population homogeneity particles were quickly delivered into the water column during plume rise following necking with minor transfer along initial jet margins and for breaching explosions additional delivery from splashdown of tephra jets plume rise after necking also draws upward and re entrains some groups of particles most delivered particles participate in initiating vertical sediment gravity flows some of which reached the tank floor and began lateral flow within the short duration of our experiments particles transferred from plume margins locally were sufficiently well separated to settle independently from suspension

rb sr and u pb isotope studies on migmatites from the schwarzwald germany constraints on isotopic resetting during variscan high temperature metamorphism mineral and isotope studies were undertaken on migmatites from the schwarzwald moldanubian zone of the variscan belt the aims of the study were to date the migmatite formation and to determine the processes involved in migmatization in order to evaluate their influence on isotopic resetting textural evidence and the comparison of mineral compositions from leucosomes and mesosomes of two centimetre scale migmatite profiles respectively suggest that migmatitic textures and mineral assemblages were formed by metamorphic segregation deformation enhanced mass transport rather than by partial melting anatexis the results of rb sr thin slab dating on these profiles indicate that sr isotopes were not completely reset during migmatization no true isochron ages but ages of approximate isotopic homogenization were obtained on the thin slabs by calculating 87sr 86sr ratios back to various stages in their evolution the coincidence of these rb sr data with u pb ages of monazites from migmatites and non migmatitic gneisses shows that gneisses and migmatites were formed during the same high temperature event in the carboniferous 330 335 ma the observation that high temperature metamorphism failed to equilibrate sr isotopes on the centimetre scale imposes limitations on the use of conventional whole rock isochron techniques in dating migmatites

determining sedimentation ages of high grade metamorphic gneisses by their palynological record a case study in the northern schwarzwald variscan belt germany in the northern schwarzwald moldanubian zone of the variscan belt paragneisses drilled from approximately 2500 m depth at the buhl 1 drilling site have experienced amphibolite facies metamorphism and were later partly transformed to mylonites under greenschist facies conditions completely graphitised acritarchs and chitinozoans were recovered from these paragneisses and mylonitic gneisses whereas both groups of palynomorphs give evidence of a marine depositional environment only the chitinozoans are stratigraphically useful in this case and indicate a paleozoic age previous findings of acritarchs in a different high grade metamorphic gneiss unit within the schwarzwald indicate an upper proterozoic marine sedimentation age the spectrum of palynomorphs found thus far in the schwarzwald in combination with petrological data suggests that within the moldanubian domain of the armorican microplate rocks with different sedimentary records later experienced diverging prograde metamorphic histories in general the results reveal that palynological studies in combination with petrological data are a promising tool for reconstructing pre orogenic settings in collisional belts

an algorithm for the detection and characterisation of volcanic plumes using thermal camera imagery volcanic plumes are turbulent mixtures of particles and gas which are injected into the atmosphere during a volcanic eruption depending on the intensity of the eruption plumes can rise from a few tens of metres up to many tens of kilometres above the vent and thus present a major hazard for the surrounding population currently however few if any algorithms are available for automated plume tracking and assessment here we present a new image processing algorithm for segmentation tracking and parameters extraction of convective plume recorded with thermal cameras we used thermal video of two volcanic eruptions and two plumes simulated in laboratory to develop and test an efficient technique for analysis of volcanic plumes we validated our method by two different approaches first we compare our segmentation method to previously published algorithms next we computed plume parameters such as height width and spreading angle at regular intervals of time these parameters allowed us to calculate an entrainment coefficient and obtain information about the entrainment efficiency in strombolian eruptions our proposed algorithm is rapid automated while producing better visual outlines compared to the other segmentation algorithms and provides output that is at least as accurate as manual measurements of plumes

relationship between infrasound derived and buoyancy derived eruption plume volume estimates volume estimations for discrete plumes accompanying short lived eruptions are potentially possible using infrasound signals plumes emitted during short lived discrete eruptions have been modeled as discrete thermals or rooted thermals based on the one dimensional model for the rise of a discrete thermal the initial buoyancy f0 of a spherical thermal can theoretically be estimated from the maximum plume height and a vertical profile of ambient air density we here examine the relationship between infrasound derived volume vinf and the buoyancy derived volume vb as derived from f0 which depends on gravity acceleration and the difference in density between the thermal and surrounding air to understand how vinf relates to the dynamics of the eruption plume we analyze infrasound data accompanying vulcanian and phreatic eruptions at aso shinmoedake and lokon empung volcanoes to estimate vinf and consider vinf from other volcanoes we obtain a representative ratio of vb vinf of 16 by examining 53 events because the analyzed infrasound signals share a prominent pressure pulse at the onset we regard vinf as the volume of the plume at initiation i e as a jet instead we consider vb as the thermal volume when it has entrained a sufficient amount of the surrounding air and obtains f0 comparison of the bulk density of the jet and the discrete thermal yields a rate of volume change between both regimes by a factor of 1 8 32 which is consistent with the ratio of vb vinf our result provides an effective index to constrain erupted plume volume using infrasound data with real time monitoring systems

oblique crustal detachment in the variscan schwarzwald southwestern germany the schwarzwald is part of the central polymetamorphic crystalline belt of the variscan orogen moldanubian belt from north to south it consists of four terranes the metasedimentary zone of baden baden the polymetamorphic central schwarzwald gneiss complex the sedimentary metamorphic zone of badenweiler lenzkirch and the hotzenwald complex the largest of these terranes is the central schwarzwald gneiss complex csgc whose rocks record a history of protracted regional metamorphism and anatectic melt generation during variscan convergence between 350 and 325 ma the csgc became detached from a high temperature lower crustal substratum and was emplaced southeastward over paleozoic clastics volcanic rocks and crystalline slivers of the zone of badenweiler lenzkirch and the hotzenwald complex kinematic indicators suggest that these early convergent movements on retrograde shear zones and the concomitant crustal thickening were superseded by movements on divergent shear zones the ascent of voluminous granitic plutons from a mid crustal zone of melt generation into the upper crust was probably triggered by a change in the crustal kinematics from overall convergence to overall divergence at about 325 ma in detail this process was probably diachronous detachment of upper crust and large scale melt generation in the middle crust of the schwarzwald was probably facilitated by the tectonic stacking of water rich pelitic clastics and gneiss slivers with relatively even proportions of crystalline and pelitic materials

a global chitinozoa biozonation for the silurian a global chitinozoan biozonation for the silurian period is proposed each biozone is an interval range defined by the first occurrence of an index species selected from well defined species with a relatively short biostratigraphic range to be included in the scheme index species must have been recorded from at least two major silurian palaeocontinents where usable chitinozoa assemblages have been studied that is avalonia baltica which had already undergone collision by the silurian laurentia gondwana and southern china seventeen biozones are identified with seven in the llandovery the fragilis postrobusta electa maennili alargada dolioliformis and longicollis biozones four in the wenlock the margaritana cingulata pachycephala and lycoperdoides biozones three in the ludlow the elongata philipi and barrandei biozones and three in the p idoli the kosovensis elegans and superba biozones chronostratigraphic calibration is partly provided by reference to the range of the appropriate chitinozoa index species in the global stratotype sections and points gssp of the silurian series e g in bohemia czech republic for the p idoli and the welsh borderland in england for the ludlow and part of the wenlock when this information was not available independent biostratigraphic control was provided by calibration with graptolite biozones or in a few cases conodont or trilobite biozonal schemes the index and most characteristic species of each biozone are illustrated and their total stratigraphie range provided

aspects of problematic acid resistant organic walled microfossils acritarchs in the upper proterozoic of the north atlantic region abstract proterozoic acritarchs are a heterogeneous group of acid resistant organic walled microfossils of obscure biological affinities the acritarch record is regarded as strongly baised by a combination of mechanisms such as the character of the original ecosystems depositional conditions diagenetic history and thermal and tectonic events three distinctive acritarch assemblages are recognized in upper proterozoic sequences in scandinavia and greenland they can be compared with upper proterozoic upper riphean and vendian assemblages previously reported from the russian and siberian platforms china and elsewhere substantial taxonomic changes characterize these assemblages and are usually connected with the existence of major unconformities in the investigated rock sequences the acritarch assemblages can be traced over vast areas and are considered as constituting a promising tool for the biostratigraphic correlation of the upper proterozoic and lower cambrian

rock avalanche mobility the role of path material abstract rock avalanches are high velocity flows of fragmented rock that can dramatically alter landscapes and impact people and infrastructure far from their source these catastrophic events have been studied for over a century however a consensus regarding the mechanism s that govern their motion has yet to emerge this work details the results of the back analysis of 45 rock avalanche case histories using a semi empirical runout model that simulates motion over 3d terrain these simulations account for topographic effects and bulk basal shear resistance variation during motion for a subset of the cases we find that a volume dependent mechanism appears to influence basal resistance in the source zone however once the material has vacated the source zone our results suggest that the character of the path material strongly controls mobility and appears to dominate over other potentially volume dependent mechanisms that may also be at work the results presented in this paper support the longstanding hypothesis that the interaction of flowing debris with the underlying substrate is an important consideration in rock avalanche runout prediction and that this mechanism warrants further research

a model for the runout analysis of rapid flow slides debris flows and avalanches runout analyses are used for risk assessment and design of remedial measures against rapid landslides such as debris flows debris avalanches rockslide avalanches large scale liquefaction failure

explosive volcanic eruptions v observations of plume dynamics during the 1979 soufriere eruption st vincent summary during the 1979 eruption of the soufritre of st vincent west indies a 14min period of explosive activity occurred on april 22 the first three minutes of this activity were filmed five individual explosions formed distinct plumes which fed an eruption column which eventually ascended to a height of over 18 km the ascent velocities of the fronts of these plumes ranged from 8 5 to 61 7m s the half angle of spreading of the plume fronts ranged from 21 5 to 24 one of the plumes was observed to 8 km height and decelerated steadily from 5 1 5 to 23 m s l the main column fed by individual explosions was however observed to accelerate from 8 5 to 58 m s l in the same height interval a theoretical treatment of volcanic plume motion is presented measurements of dimensions velocities and spreading rates from the film are used to estimate plume parameters such as temperature particle content and volume discharge rate of magma from the theoretical relationships these calculations show that the individual plumes became hotter and richer in juvenile ash with time the acceleration of the main eruption column was the result of being fed by increasingly hotter and more ash rich explosions an average volume discharge rate of 12600m3s is estimated from the analysis of the plume motions this value agrees closely with an estimate of discharge rate based on the heat flux required to form an 18 km high column this agreement suggests that theories of convective motions in plumes can be successfully adapted to the volcanic case as long as the effect of hot entrained ash particles is considered

insights into rock ice avalanche dynamics by combined analysis of seismic recordings and a numerical avalanche model 1 rock ice avalanches larger than 1 106 m3 are high magnitude low frequency events that may occur in all ice covered high mountain areas around the world and can cause extensive damage if they reach populated regions the temporal and spatial evolution of the seismic signature from two events was analyzed and recordings at selected stations were compared to numerical model results of avalanche propagation the first event is a rock ice avalanche from iliamna volcano in alaska which serves as a natural laboratory with simple geometric conditions the second one originated on aoraki mt cook new zealand southern alps and is characterized by a much more complex topography a dynamic numerical model was used to calculate total avalanche momentum total kinetic energy and total frictional work rate among other parameters these three parameters correlate with characteristics of the seismic signature such as duration and signal envelopes while other parameters such as flow depths flow path and deposition geometry are well in agreement with observations the total frictional work rate shows the best correlation with the absolute seismic amplitude suggesting that it may be used as an independent model evaluation criterion and in certain cases as model calibration parameter the good fit is likely because the total frictional work rate represents the avalanche s energy loss rate part of which is captured by the seismometer deviations between corresponding calculated and measured parameters result from site and path effects which affect the recorded seismic signal or indicate deficiencies of the numerical model the seismic recordings contain additional information about when an avalanche reaches changes in topography along the runout path and enable more accurate velocity calculations the new concept of direct comparison of seismic and avalanche modeling data helps to constrain the numerical model input parameters and to improve the understanding of rock ice avalanche dynamics

zircon and garnet geochronology of eclogites from the moldanubian zone of the black forest germany abstract the moldanubian zone of the black forest germany part of the internal zone of the central european variscan belt exposes high pressure metamorphic rocks as small eclogite lenses in host gneisses we report zircon u pb and pb pb ages and garnet sm nd and pb pb ages for five eclogites the less mobile trace element contents of these eclogites are similar to those of mid ocean ridge basalts but have moderate to highly fractionated concentrations of the rare earth elements enrichments in the incompatible elements and negative anomalies in the high field strength elements initial nd values range from documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfon

thermal imaging and analysis of short lived vulcanian explosions at volcan de colima mexico abstract vulcanian explosions present a major hazard at many active volcanoes but they also provide useful insights into the underlying behaviour of the volcanic system and therefore require close monitoring thermal infrared cameras are an effective tool for imaging vulcanian explosion plumes since they capture detailed temperature information and can reveal the internal dynamics of the plume forming explosions high spatial resolution thermal images of 200 small to moderate sized vulcanian explosions from the summit crater of volcan de colima mexico recorded between 2006 and 2011 were analysed to distinguish different event types and develop an explosion classification scheme explosions display a broad spectrum of sizes and characteristics ranging between two typical end members large impulsive events producing rapidly ascending explosion plumes up to heights of 600 1600 m above the crater rim and small diffusive events with plumes restricted to heights 1 to 29 m s 1 a time series of thermal imagery throughout the period 2006 2011 reveals a weak relationship between apparent plume temperatures and lava dome extrusion with the highest explosion temperatures coinciding with the onset of dome growth in early 2007 temporal variations in the source locations of explosions across the summit crater are also identified and appear to show a close relationship to the patterns of lava dome growth and thermal evolution with explosion source locations associated with the highest temperature thermal features

an analytical model for gas overpressure in slug driven explosions insights into strombolian volcanic eruptions strombolian eruptions common at basaltic volcanoes are mildly explosive events that are driven by a large bubble of magmatic gas a slug rising up the conduit and bursting at the surface gas overpressure within the bursting slug governs explosion dynamics and vigor and is the main factor controlling associated acoustic and seismic signals we present a theoretical investigation of slug overpressure based on magma static and geometric considerations and develop a set of equations that can be used to calculate the overpressure in a slug when it bursts slug length at burst and the depth at which the burst process begins we find that burst overpressure is controlled by two dimensionless parameters v which represents the amount of gas in the slug and a which represents the thickness of the film of magma that falls around the rising slug burst overpressure increases nonlinearly as v and a increase we consider two eruptive scenarios 1 the standard model in which magma remains confined to the vent during slug expansion and 2 the overflow model in which slug expansion is associated with lava effusion as occasionally observed in the field we find that slug overpressure is higher for the overflow model by a factor of 1 2 2 4 applying our model to typical strombolian eruptions at stromboli we find that the transition from passive degassing to explosive bursting occurs for slugs with volume 24 230 m 3 depending on magma viscosity and conduit diameter and that at burst a typical strombolian slug with a volume of 100 1000 m 3 has an internal gas pressure of 1 5 bars and a length of 13 120 m we compare model predictions with field data from stromboli for low energy puffers mildly explosive strombolian eruptions and the violently explosive 5 april 2003 paroxysm we find that model predictions are consistent with field observations across this broad spectrum of eruptive styles suggesting a common slug driven mechanism we propose that paroxysms are driven by unusually large slugs large v

crustal scale thrusting and extension in the hercynian schwarzwald and vosges central europe the hercynian outcrop areas in the schwarzwald of sw germany and vosges of easternmost france consist from north to south of three major lithotectonic complexes very low to medium grade metamorphics of the saxothuringian belt the polymetamorphic central gneiss complex and the tectonic melange of the southern complex juxtaposition of these three complexes occurred by oblique convergent motions in early carboniferous time the saxothuringian belt is part of a major se dipping accretionary wedge that consists of lower paleozoic meta sedimentary and metaigneous rocks and superimposed upper devonian to lower carboniferous synorogenic volcanics and elastics the central gneiss complex consists of polymetamorphic paragneisses orthogneisses metabasites and meta ultramafics dipping to the nw the southern complex consists of an imbricated melange of north to nw dipping synorogenic elastics volcanics and blocks of ultramafics and gneissic basement the central gneiss complex cgc experienced pervasive hercynian low pressure high temperature metamorphisrn before it was emplaced against and thrust over the sedimentary and volcanic fill of the adjacent synorogenic basins this convergence 340 330 ma produced mylonitic cataclastic shear zones in the cgc the most significant shear zones are the se verging todtnau fault zone between the cgc and the southern complex and the nw verging lubine fault zone between the central gneiss complex and the rocks of the saxothuringian belt these two fault zones enclose a bivergent pop up of the polymetamorphic basement the todtnau fault zone probably extends for more than 100 km along strike and can be traced to a depth of 10 km by deep seismic reflection studies detachment probably occurred along a mid crustal zone of anatexis expressed by a domain of low seismic reflectivity between about 10 and 15 km crustal thickening during early carboniferous convergence led to an extensional phase of crustal reordering between about 330 and 280 ma that was accompanied by the massive rise of posttectonic granitic plutons from middle to high crustal levels simultaneous creation of a structural lamination in the refractory lower crust neglected the main convergent tectonic boundaries it produced a basin and range type lower crust and mantle crust transition in early permian time and involved a major advective input of heat

ordovician and silurian protolith ages of metamorphosed clastic sedimentary rocks from the southern schwarzwald sw germany a palynological study and its bearing on the early palaeozoic geotectonic evolution sedimentation ages of metamorphosed clastic sedimentary rocks in the southern schwarzwald were determined by associations of palynomorphs in the northern subunit of the badenweiler lenzkirch zone two lithostratigraphic assemblages could be discerned in low grade metamorphic units by their facies and age thus revealing a more complex internal structure of this zone than previously assumed lower ordovician metagreywackes and metapelites were discerned from silurian metasiltstones in the cataclastically overprinted metasiltstones and phyllites of the southern subunit of the badenweiler lenzkirch zone only poorly preserved microfossil remains could be detected these show that the sedimentation ages must be ordovician or younger but still probably early palaeozoic high grade metapelitic rocks of the south schwarzwald gneiss complex contain chitinozoans in lenses and layers of schists that are rich in biotite and graphite they yielded mid silurian ages and show that this crystalline complex does not represent an older basement unit but was the result of marine sedimentation at that time the new age determinations have a bearing on geodynamic reconstructions of the internal variscides in early palaeozoic time they show that sedimentation in the oceanic realm of the badenweiler lenzkirch zone or its margins did not occur before the ordovician after transformation of the northern passive into an active continental margin younger greywackes not older than middle devonian received detritus from a volcanic arc forming above the subduction zone

the birth of the rheic ocean early palaeozoic subsidence patterns and subsequent tectonic plate scenarios abstract new plate tectonic reconstructions of the gondwana margin suggest that the location of gondwana derived terranes should not only be guided by the models but should also consider the possible detrital input from some asian blocks hunia supposed to have been located along the cambrian gondwana margin and accreted in the silurian to the north chinese block consequently the gondwana margin has to be subdivided into a more western domain where the future avalonian blocks will be separated from gondwana by the opening rheic ocean whereas in its eastern continuation hosting the future basement areas of central europe different periods of crustal extension should be distinguished instead of applying a rather cylindrical model it is supposed that crustal extension follows a much more complex pattern where local back arcs or intra continental rifts are involved guided by the age data of magmatic rocks and the pattern of subsidence curves the following extensional events can be distinguished during the early to middle cambrian a back arc setting guided the evolution at the gondwana margin contemporaneous intra continental rift basins developed at other places related to a general post pan african extensional phase affecting africa upper cambrian formation of oceanic crust is manifested in the chamrousse area and may have lateral cryptic relics preserved in other places this is regarded as the oceanisation of some marginal basins in a context of back arc rifting these basins were closed in a mid ordovician tectonic phase related to the subduction of buoyant material mid ocean ridge since the early ordovician a new phase of extension is observed accompanied by a large scale volcanic activity erosion of the rift shoulders generated detritus armorican quartzite and the rift basins collected detrital zircons from a wide hinterland this phase heralded the opening of palaeotethys but it failed due to the silurian collision eo variscan phase of an intra oceanic arc with the gondwana margin during this time period at the eastern wing of the gondwana margin begins the drift of the future hunia microcontinents through the opening of an eastern prolongation of the already existing rheic ocean the passive margin of the remaining gondwana was composed of the galatian superterranes constituents of the future variscan basement areas remaining under the influence of crustal extension they will start their drift to laurussia since the earliest devonian during the opening of the palaeotethys ocean

catastrophic detachment and high velocity long runout flow of kolka glacier caucasus mountains russia in 2002 abstract in september 2002 a catastrophic geomorphic event occurred in the caucasus mountains southern russia in which almost the entire mass of kolka glacier detached from its bed accelerated to a very high velocity max 65 80 m s and traveled a total distance of 19 km downstream as a glacier debris flow based on the interpretation of satellite imagery obtained only 8 5 h before the event occurred the analysis of seismograms from nearby seismic stations and subsequent detailed field observations and measurements we suggest that this remarkable event was not a response to impulse loading from a rock avalanche in the mountainside above the glacier or to glacier surging but due entirely to the static and delayed catastrophic response of the kolka glacier to ice and debris loading over a period of months prior to the september 20 detachment we reconstruct the glacier debris flow using field observations in conjunction with the interpretation of seismographs from nearby seismic stations and successfully simulate the behaviour runout velocity and deposition of the post detachment glacier debris flow using a three dimensional analytical model our demonstration of a standing start hypothesis in the 2002 kolka glacier detachment has substantial implications for glacier hazard assessment and risk management strategies in valleys downstream from unstable debris covered glaciers in the mountain regions of the world

runout of dry granular avalanches laboratory experiments on granular avalanching of dry sands and gravels reveal a consistent pattern of runout distance varying with fall height fall slope and volume of material for volumes rangi

the palaeozoic evolution in the alps from gondwana to pangea more than 50 of the alps expose fragments of palaeozoic basement which were assembled during the alpine orogeny although the tectonic and metamorphic history of the basement units can be compared to that of the variscan crust in the alpine foreland most of the basement pieces of the alps do not represent the direct southern continuation of variscan structural elements evident in the massif central the vosges black forest or the bohemian massif the basement units of the alps all originated at the gondwana margin they were derived from a precambrian volcanic arc suture fringing the northern margin of gondwana from which they were rifted during the cambrian ordovician and silurian a short lived ordovician orogenic event interrupted the general rifting tendency at the gondwana active margin after the ordovician the different blocks drifted from the gondwana margin to their pangea position colliding either parallel to armorica with laurussia or with originally peri gondwanan blocks assembled presently in armorica from the devonian onwards many basement subunits underwent the complex evolution of apparently oblique collision and nappe stacking docking started in the external massifs the penninic and lower and middle austroalpine units in approximately devonian early carboniferous times followed by the upper austroalpine and the south alpine domains in the visean and the namurian times respectively wrenching is probably the best mechanism to explain all syn and post collisional phenomena since the visean followed by post orogenic collapse and extension it explains the occurrence of strike slip faults at different crustal levels the formation of sedimentary troughs as well as the extrusion and intrusion of crustal and mantle derived magmas and allows for contemporaneous rapid uplift of lower crustal levels and their erosion from the stephanian onwards all regions were deeply eroded by large river systems

a fragmentation spreading model for long runout rock avalanches based on the observation that deposits of large rock avalanches consist predominantly of intensely fragmented rock debris it is proposed that the processes of rock fragmentation are significant ca