the uwekahuna ash member of the puna basalt product of violent phreatomagmatic eruptions at kilauea volcano hawaii between 2800 and 210014c years ago abstract kilauea volcano s reputation for relatively gentle effusive eruptions belies a violent geologic past including several large phreatic and phreatomagmatic eruptions that are recorded by holocene pyroclastic deposits which mantle kilauea s summit area and the southeast flank of adjacent mauna loa volcano the most widespread of these deposits whose original distribution can be reconstructed is the uwekahuna ash member of the puna basalt a basaltic surge and fall deposit emplaced during two or more eruptive episodes separated by a few decades to several centuries the first episode occurred between 2770 70 and 2265 50 14 c yr ago it included two major pyroclastic surges each preceded by unusually vigorous lava fountaining from a vent near the volcano s summit before the second eruptive episode 2110 120 14 c yr ago plants had re colonized the rainforest environment northeast of the summit and at least two lava flows from mauna loa had buried parts of the first episode deposits the second episode also began with vigorous lava fountaining followed by widespread lithic ashfall a third major surge and finally a fourth fountaining event before the final pumice deposit could be significantly reworked it was partly buried by picritic basalt flows that are unusual in kilauea s summit area in proximal areas the uwekahuna ash member is more than 1 m thick locally 5 m and includes lithic blocks up to 0 8 m in diameter coarse primarily lithic debris was deposited around the vent by laterally expanding surges fallout deposits accumulated preferentially to the northeast under the influence of high altitude counter tradewinds the area devastated by surges and originally buried by at least 15 cm of the uwekahuna was about 420 km 2 the bulk volume of the deposits was approximately 0 3 km 3 including less than 0 1 km 3 of juvenile material juvenile constituents are olivine tholeiitic basalts similar in major element composition to typical kilauea summit lava flows but variations in both major elements and trace elements suggest that the eruptions tapped more than a single uniform source region we infer that the eruptions which produced the uwekahuna were driven by water interacting with a fluctuating magma column magma withdrawal episodes may have been accompanied by large volume submarine effusive eruptions and by summit collapse the volume extent and character of the uwekahuna deposits underscore the hazards posed by relatively infrequent but potentially devastating explosive eruptions at kilauea as well as at other basaltic volcanoes

decrypting silicic magma plug fragmentation at azufral crater lake northern andes insights from fine to extremely fine ash morpho chemistry azufral sw colombia is a dangerous silicic volcano hosting a crater lake which serves as an excellent example of an incipient plug disruption through phreatomagmatism we studied the youngest succession of dilute pyroclastic density currents pdcs onlapping the north eastern crater rim scanning electron microscopy coupled with energy dispersive x ray spectroscopy was used to carry out an automated single particle analysis of fine to extremely fine ash we were able to obtain fast and accurate chemical analysis and imaging of 15 098 particles within the 250 63 m and the 63 32 m size ranges the 2d form and roughness parameters were determined for 4895 juvenile glassy particles and validated by 3d micro x ray computer tomography there are two end members of high group 1 and low group 2 roughness juvenile glassy particles group 1 comprises high roughness glass particles with solidity values as low as 0 34 in 2d and 0 33 in 3d and convexity values as low as 0 33 in 2d and 0 26 in 3d group 2 comprises low roughness glass particles with 2d solidity values 0 79 and 3d solidity values typically 0 58 in this group 2d convexity values are 0 68 and 3d convexity values are 0 71 both end members are mostly discriminated by the 2d concavity index 0 14 to 0 77 in group 1 vs 0 05 0 35 in group 2 the remaining group 3 comprises particles of intermediate roughness values in this study we show how an incipient plug developed over a short repose time might be subjected to only a few cycles of vesicle nucleation collapse and densification retaining the characteristics of juvenile glass each glassy juvenile ash type defined by a particular morphology roughness and microtexture can be linked to a density stratified conduit model in azufral the capping and conduit lining dense regions and the permeable zones of the incipient plug likely cracked the newly formed cracks could allow hydraulic forcing caused by external water and induce phreatomagmatic interaction this interaction favoured the fine fragmentation of the plug while enhancing ongoing magmatic processes finally the variations of bulk componentry provided clues on dilute pyroclastic density current transport and physical fractionation processes by secondary fragmentation elutriation and interaction with the crater rim

stratigraphy of the pleistocene phonolitic cao grande formation on santo antao cape verde highlights two new phonolitic tephra units complementing the two previously known first radiometric ages of the cgf contemporaneously evolution of the cgf and the tope de coroa marine correlations improve tephra volume estimations for cg i and ii abstract the cao grande formation cgf on the western plateau of santo antao island is part of the younger volcanic sequence that originated from both basanitic and nephelinitic magmatic suites respectively called cova and coroa suites based on our detailed revised stratigraphy of the cgf including two yet unknown tephra units we can show that both suites produced multiple highly differentiated eruptions over a contemporaneous period correlations of cgf tephras with marine ash layers provide distal dispersal data for cao grande i cg i and also identify two highly explosive phonolitic eruptions that pre date the cgf tephra deposits known on land within the cgf the lowermost 220 7 ka old unit canudo tephra ct cova suite comprises phonolitic fall deposits and ignimbrites it is partly eroded and overlain by debris flow deposits marking a hiatus in highly differentiated eruptions the phonolitic cg i tephra coroa suite consists of an initial major plinian fall deposit and associated ignimbrite and terminal surge deposits this is immediately overlain by the phonolitic to phono tephritic cao grande ii cg ii cova suite a complex succession of numerous fallout layers and density current deposits cg i and cg ii have radiometric ages of 106 3 ka and 107 15 ka respectively that are identical within their error limits the youngest cgf unit the furninha tephra ft coroa suite consists of three foidic phonolitic fall deposits interbedded with proximal scoria deposits from a different vent the phonolitic eruptions switched to and fro between both magmatic suites in each case with a stronger first followed by a weaker second eruption each eruption evolved from stable to unstable eruption columns during their terminal phases both magma systems also leaked evolved dome forming lavas next to the tephras distal ashes increase the cg i tephra volume to 10 km3 about twice the previously published estimate the tephra volume of cg ii is 3 km3 ct and ft are too poorly exposed for volume estimation the characteristics of the cgf tephra units outline hazard conditions that may be expected from future evolved explosive eruptions on the western plateau of santo antao

observation and analysis of near surface pore pressure measurements in clay shales slopes clay shales largely outcrop in the northern apennines of italy where they are associated with frequent and widespread landslide activity the paper presents the results of monitoring activities carried out in two field sites and focused on the hydrology of clay shales prone to landsliding in the monitored slopes the water table is close to the ground surface throughout the year with seasonal fluctuations of tens of centimetres to a couple of metres shallow weathered soils or clay cover and unaltered material exhibit a much different behaviour although responses to single rainfalls are clearly identifiable as pressure pulses in the clay cover they are never observed in the underlying parental clay shales where downward gradients indicate recharge and only long term seasonal fluctuations are recorded short term variations of pressure head in the clay cover are ruled by downward propagation of a pressure wave in saturated conditions more than 400 pore pressure responses collected in the two sites are analysed in terms of lag time rate and amount of pressure increase and timing of pressure peaking it emerges that the linear diffusion theory can satisfactorily explain the observed behaviour in deeper unaltered material the barometric effect influences the measures similarly to what is observed in confined aquifers after its removal the corrected data exhibit regular seasonal fluctuations which are used to estimate the diffusivity of the material based on phase lag and attenuation of the downward propagating long term periodic pulse copyright 2011 john wiley sons ltd

sea cliff erosion as a function of beach changes and extreme wave runup during the 1997 1998 el nino abstract over time scales of hundreds to thousands of years the net longshore sand transport direction along the central california coast has been driven to the south by north pacific winter swell in contrast during the el nino winter of 1997 1998 comparisons of before and after airborne lidar surveys showed sand was transported from south to north and accumulated on the south sides of resistant headlands bordering pocket beaches this resulted in significant beach erosion at the south ends of pocket beaches and deposition in the north ends coincident with the south to north redistribution of sand shoreline morphology became prominently cuspate with longshore wavelengths of 400 700 m the width and elevation of beaches were least where maximum shoreline erosion occurred preferentially exposing cliffs to wave attack the resulting erosional hotspots typically were located in the embayments of giant cusps in the southern end of the pocket beaches the observed magnitude of sea cliff retreat which reached 14 m varied with the number of hours that extreme wave runup exceeded certain thresholds representing the protective capacity of the beach during the el nino winter a threshold representing the width of the beach performed better than a threshold representing the elevation of the beach the magnitude of cliff erosion can be scaled using a simple model based on the cross shore distance that extreme wave runup exceeded the pre winter cliff position cliff erosion appears to be a balance between terrestrial mass wasting processes which tend to decrease the cliff slope and wave attack which removes debris and erodes the cliff base increasing the cliff slope

ignimbrites of the roque nublo group gran canaria canary islands non welded lithic rich ignimbrites hereintermed the roque nublo ignimbrites are the most distinctive deposits of the pliocene roque nublo group which forms the products of second magmatic cycle on gran canaria they are very heterogeneous with 35 55 volume lithic fragments 15 30 mildly vesiculated pumice 5 7 crystals and 20 30 ash matrix the vitric components pumice fragments and ash matrix are largely altered and transformed into zeolites and subordinate smectites the roque nublo ignimbrites originated from hydrovolcanic eruptions that caused rapid and significant erosion of vents thus incorporating a high proportion of lithic clasts into the eruption columns these columns rapidly became too dense to be sustained as vertical eruption columns and were transformed into tephra fountains which fed high density pyroclastic flows the deposits from these flows were mainly confined to palaeovalleys and topographic depressions in distal areas close to the coast line where these palaeovalleys widened most of the pyroclastic flows expanded laterally and formed numerous thin flow units the combined effect of the magma water interaction and the high content of lithic fragments is sufficient to explain the characteristic low emplacement temperature of the roque nublo ignimbrites this fact also explains the transition from pyroclastic flows into lahar deposits observed in distal facies of the roque nublo ignimbrites the existence of hydrovolcanic eruptions generating high density pyroclastic flows unable to efficiently separate the water vapour from the vitric components during transport also accounts for the intense zeolitic alteration in these deposits

fogo volcano cape verde islands seismicity derived constraints on the mechanism of the 1995 eruption seismic data recorded in the vicinity of the active vent of the 1995 fogo eruption global volcanism network bulletin 1995 20 3 2 4 is used to constrain the associated stress field and deformation using the frequency content of the seismograms to distinguish between brittle fracture of cold host rock and deformation in the vicinity of the intruding magma a sub vertical dyke with 060 strike is identified as the feeder of the eruption and delineated down to a depth of about 4 km the local stress field during the eruption is estimated from composite focal mechanisms besides the expected 3 direction normal to the dyke a group of focal solutions point to a stress field with nearly dyke parallel 3 which is interpreted as a re adjustment of the edifice following the eruption maybe partially controlled by gravity this effect may have increased the instability of the steep eastern flank of the island since the deformation detected during the magma drainback is compatible with predominantly dip slip motion on east dipping surfaces

volcano sedimentary characteristics in the abu treifiya basin cairo suez district egypt example of dynamics and fluidization over sedimentary and volcaniclastic beds by emplacement of syn volcanic basaltic rocks abstract this paper describes the neogene lava sediment mingling from the abu treifiya basin cairo suez district egypt the lava sediment interactions as peperites have been identified for the first time at the study area and can be used as paleoenvironmental indicators the identification of peperite reflects contemporaneous time relationship between volcanism and sedimentation and this finding is of primary importance to address the evolutional reconstruction of the abu treifiya basin characterization of the facies architecture and textural framework of peperites was carried out through detailed description and interpretation of their outcrops the peperites and sedimentary rocks are up to 350 m thick and form a distinct stratigraphic framework of diverse lithology that is widespread over several kilometers at the study area lateral and vertical facies of the peperites vary from sediment intercalated with the extrusive intrusive basaltic rocks forming peperitic breccias to lava sediment contacts at a large to small scales respectively peperites encompass five main facies types ascribed to i carbonate sediments hosted fluidal and blocky peperites ii lava flow hosted blocky peperites iii volcaniclastics hosted fluidal and blocky peperites iv sandstone siltstone rocks hosted blocky peperites and iv debris flows hosted blocky peperites soft sediment deformation structures vesiculated sediments sediments filled vesicles and fractures in lava flows indicate that lava flows mingled with unconsolidated wet sediments all the peperites in this study could be described as blocky or fluidal but mixtures of different clast shapes occur regardless of the host sediment the presence of fluidal and blocky juvenile clasts elucidates different eruptive styles reflecting a ductile and brittle fragmentation the gradual variation from fluidal to blocky peperite texture producing the vertical grading is affected by influencing factors e g the viscosity magma temperature confining pressure sediment fluidization and vapor film at the magma sediment interactions peperites in the study area record deposition within a shallow marine and fluvio lacustrine environment accumulated in a rift related basin developed during pre to syn rift phase respectively the facies transitions peperites in this area resulted from the explosive and sediment depositional processes which were mingled separately by volcanism under contrast geological conditions the development of such contrast in the depositional sequences reflects variation in the accommodation to sediment supply in the same accumulation space inside the depocenters during the rifting of the abu treifiya basin hydrothermal mineralizations comprising quartz and carbonate are restricted to peperites and lava flows

topographic controls on a phreatomagmatic maar diatreme eruption field and numerical results from the holocene dotsero volcano colorado usa we analyze the eruptive products of holocene dotsero volcano colorado usa 4 15 ka which record evidence of a progression from effusive magmatic activity through explosive phreatomagmatic maar forming activity to a final explosive magmatic phase the nature of the deposits suggests that the irregular and mountainous pre eruptive topography strongly influenced the formation of directed pyroclastic density currents pdcs during the phreatomagmatic phase where the topographically high northern crater rim acted as a barrier and promoted transport to the south furthermore the crater shape strongly controlled the grain size of the final deposits providing further evidence that deposit grain size can be a misleading proxy for fragmentation or explosion intensity we test these hypotheses as gleaned from fieldwork by implementing a multiphase numerical model to simulate discrete explosions and their resulting pdcs at maar diatreme volcanoes we confirm that a crater shape where one rim is higher than the other promotes multiple pulses of particle transport in the direction of the lower rim the initial pdcs contain both coarse and fine particles whereas pdcs generated by later pulses contain predominately finer particles this mechanism provides an alternative explanation to the formation of lapilli tuff tuff couplets often found at maar diatreme tephra rings including dotsero volcano additional modeling shows how the crater depth can control grain size of the resulting pdc deposits in the case of a deep crater and a relatively weak explosion it is possible that only the fine particles escape following collapse of the eruptive column resulting in a fine grained deposit this work allows us to improve models developed to describe emplacement of pdcs for different crater geometries and informs on the dynamics of maar diatreme eruptions but also highlights the limitations of our knowledge of key parameters especially those related to the processes of magma water interaction and syn eruptive hydrogeology during such events

subsurface structure of a large basaltic maar volcano examined using geologically constrained potential field modelling lake purrumbete maar newer volcanics province southeastern australia abstract lake purrumbete maar lpm is situated in the late cenozoic intraplate basaltic newer volcanics province southeastern australia it is one of the largest maar volcanoes in the world with a near circular crater that is up to 2800 m in diameter containing a 45 m deep lake gellibrand marl accidental lithics which occurs to a maximum depth of 250 m below lpm represent the deepest excavated host rock unit present in the volcanic succession irregular clast shapes and peperitic textures observed in marl lithics suggest the host rock was poorly consolidated during the eruption high resolution lake and land based gravity and magnetic data were collected to conduct forward and inverse modelling of the subsurface architecture of the maar this is done to test the assumption based on lithics that the diatreme is limited to 250 m depth and identify the reasons behind lpm s large size the collection of gravity data presented a unique challenge due to the nature of measuring small changes in gravitational forces

slope stability and groundwater flow system in the area of lizzano in belvedere northern apennines italy abstract in northern apennines landslides involving weak rocks such as clay shales are widespread and often cause damage to public infrastructure and private properties these landslides mostly classifiable as earthflows generally exhibit continuous slow movements with temporary increases of velocity controlled both by groundwater and rainfall regime although the relationship between precipitation groundwater flow and displacement rate is evident its quantitative description remains problematic we use piezometric and slope movement continuous monitoring to investigate the groundwater flow system in the vicinity of the contact between clay shales and overlying more permeable units where the village of lizzano in belvedere is located our aim is to describe the groundwater flow and its relation to slope deformation in order to simulate the effect of possible drainage measures both on piezometric levels and expected displacement rates timing and magnitude of piezometric responses at different depths are related to observed deformations and used to calibrate a transient 3d groundwater flow model groundwater modeling validates the conceptual hydrogeological scheme and allows simulation of the impact of surface and deep drainages on piezometric levels results indicate that horizontal drains are more effective than infiltration reduction measures both in terms of drawdown and time effectiveness of action simulated hydraulic heads are then used to produce a probabilistic prediction of the expected displacement rates by means of an empirical method in the case of lizzano in belvedere according to our results the lowering of hydraulic heads operated by horizontal drains can reduce the velocity of slope movements from centimeters per year to millimeters per year

an experimental facility for investigating hydromagmatic eruptions at high pressure and high temperature with application to the importance of magma porosity for magma water interaction an experimental facility has been developed to investigate magma water interaction mwi the facility operates in a high pressure and high temperature environment with temperatures up to 1 200 c and pressures up to 200 mpa cylindrical sample holders 20 by 180 mm in size are heated conductively to yield a three phase melt crystals and gas system and then water or other fluid is injected into the sample through a capillary tube diameter 0 5 mm length ca 1 000 mm under controlled conditions pressure volume and temperature changes are continuously recorded during every phase of the experiments to test this facility mwi is studied at subliquidus temperatures 800 and 900 c and pressure 8 mpa using a leucite tephrite sample with two different initial grain sizes because of the grain size dependence of sintering the two starting materials produce magmas with different textures at the same temperature porous magma for large initial grain sizes and dense magma for small initial grain sizes in these experiments 1 5 g of water at room temperature is injected into 6 0 g of partially molten sample at velocities ranging from 1 to 3 m s we find that the extent of fragmentation and transport caused by mwi are mainly controlled by the texture of the interacting sample with explosive interaction occurring only for porous magmas

eruptive mechanisms of the puig de la garrinada volcano olot garrotxa volcanic field northeastern spain a methodological study based on proximal pyroclastic deposits abstract an ephemeral and proximal outcrop at the quaternary basaltic puig de la garrinada cinder volcano was studied in order to decipher eruptive mechanism variations in the course of a single eruption once the volcanostratigraphy was established and recorded by photographs a very detailed sampling of underlying lava flows bombs and a large number of fine sized lapilli and ash beds was carried out an ad hoc description card was elaborated for study under stereo microscope in order to identify the different types of materials that form the volcanic cone ten material types were recognised sedimentary accidental clasts massive lava accidental clasts bombs xenoliths xenocrysts and phenocrysts oxidised scoria scoria with oxidised film fluidal pyroclasts non fluidal pyroclasts and coatings subsequent studies under sem eds and basic chemical characterization of the samples whole rock xrf for major and trace elements and empa were conducted all these studies make possible the reconstruction of the eruptive history of the la garrinada volcano which shows a transition from initial strombolian activity to gradually incorporated phreatomagmatic activity this permits the calculation of magma eruption rates magma column oscillations and aquifer interactions with magma column since our general conclusions agree well with the discrimination of eruptive episodes obtained from the stereo microscope description card macroscopic volcanostratigraphy and chemical results it is proposed that a similar study protocol quick volcanostratigraphy logging photographic record detailed sampling description following this card might be useful in the reconstruction of eruptive activity of other cinder cones in the garrotxa region and elsewhere and therefore can provide a good and quick methodological tool especially when rapid field description and sampling is required ephemeral outcrops risky sampling during active eruptive episodes etc moreover the conducted sampling allows for subsequent studies on the same set of pyroclasts

collapse at the eastern eiger flank in the swiss alps on 13 june 2006 parts of the eastern flank of the eiger peak in the swiss alps collapsed leading to a major rock fall the unstable spur on this flank is made up of several blocks that move relative to one another instability was initiated by a block at the rear that acted as a wedge and triggered motion of the other blocks landslides are a significant natural hazard in mountainous regions1 and are often triggered by external factors such as earthquakes rainfall permafrost melting or retreat of glaciers2 a large landslide occurred in the swiss alps on 13 july 2006 when portions of an immense rock spur on the eastern flank of the eiger peak3 collapsed here we use field observations and terrestrial laser scanning data to record and quantify the relative motion along the various blocks of rock that form this spur the data show that during the year of observation the blocks moved relative to one another by up to tens of metres along fractures that can be related to pre existing planes of weakness rates of motion and deformation were high throughout july 2006 particularly in the northern part of the spur that partially collapsed on 13 july the rates decreased considerably during the subsequent months although a slight increase was noted in june and july 2007 these observations are consistent with instability of the spur initiated by subsidence of a single block at the rear which acted as a wedge and disintegrated over time owing to loss of lateral confinement

the basalt pipes of the tunguska basin siberia russia high temperature processes and volatile degassing into the end permian atmosphere abstract a number of mechanisms have been proposed to explain the end permian crisis many of them explore the link between this catastrophe and the siberian traps we test the hypothesis that eruption of thermogenic gas generated in contact aureoles around igneous sills intruded into evaporite sequences of the tunguska basin triggered the crisis in particular we test the idea that the aspect that breccia pipes represent conduits for voluminous gas migration from the deep basins to the atmosphere this contribution sheds new light on the pipe formation based on new field and borehole observations and electron microscopy analyses of more than three hundred mapped magnetite bearing basalt pipes 43 are classified as diatremes the diatremes are usually circular or elliptical with multiple zones of brecciation reaching the surface sometimes with preserved in filled crater lakes the pipe diameter on the surface varies from a few tens of meters for small single diatremes to about a kilometer the largest crater lake area is 2 7 km 2 we have conducted a detailed study of the breccias in the sholokhovsk basalt pipe located within the nepa potash deposit in the tunguska basin siberia russia about n 59 and e 107 and find that the breccias are cemented by carbonate matrix calcite dolomite and halite breccia clasts are altered at various temperatures evidenced by growth of albite and garnet from basaltic glass and diopside garnet magnetite and chlorine bearing amphibole up to 1 8 cl in altered magmatic clasts these mineral assemblages suggest high temperature interactions with evaporites within the pipe conduits the large number of pipes support that degassing of halogen rich volatiles was a widespread and violent process with implications for the end permian crisis

phreatomagmatic explosions of rhyolitic magma experimental and field evidence 1 experimental studies on explosive molten fuel coolant interaction mfci using basaltic melt compositions and water as the coolant have provided insight into the physical processes of basaltic and andesitic phreatomagmatic volcanism abundant field evidence indicates that rhyolitic and dacitic phreatomagmatism occurs in nature but it has not been possible until now to generate laboratory mfci explosions from the interaction between high silica melts and water under laboratory conditions the high viscosity of these melts apparently prevents formation of an effective hydrodynamic premix of melt and water the documented precursor of experimental explosive mfci caused by mafic melts our new experiments utilized samples from a rhyolitic tuff ring volcano in mexico tepexitl an experimental approach was developed in which premixing conditions were generated by mechanical deformation of the melt leading to brittle type fragmentation at the melt water interface physical measurements recorded during laboratory explosion provide quantitative evidence for rhyolitic explosive mfci additionally a comparison of experimentally produced particles with natural ones from tepexitl deposits show nearly identical chemical mineralogical composition grain size and grain morphology detailed textural analysis confirmed the presence of phreatomagmatically produced particles in both experimental and natural analog particles the results from this series of experiments indicate that under natural conditions stress induced magma fracturing can lead to a critical magma water interface growths and trigger phreatomagmatic explosions of high silica magma the water source for these eruptions may include shallow aquifers surface water bodies strong precipitation and intrusion into ice or wet unconsolidated sediments

centrifuge modeling of failure behaviors of sandy slope caused by gravity rainfall and base shaking abstract this study focused on slope stability behaviors under different conditions including gravity rainfall and earthquake the slope models were prepared by mixing sand 80 and clay kaolinite 20 and compacting at optimum water content under the gravitational condition the model tests were performed with three different directions of a gravel layer embedded into the slope during the test the artificial acceleration was gradually increased until slope failure occurred to observe the slope behaviors under rainfall and earthquake the results indicated that the direction of the gravel layer affected the distribution of water content additionally it was found that the inclination angle was a key factor influencing slope stability rainfall intensity played an important role in infiltration water with regard to the failure wedge among the three conditions examined the earthquake condition generated the most significant effect on slope stability herein for evaluating the stability of slopes the bishop s method incorporating an inclination angle of a gravel layer and apparent cohesion is introduced

3d effects of permeability and strength anisotropy on the stability of weakly cemented rock slopes subjected to rainfall infiltration abstract weakly cemented sedimentary rocks with pronounced stratification exhibit permeability and strength anisotropy the influence of permeability and strength anisotropy on the groundwater flow and slope stability depends on the orientation of the bedding planes the stability of slopes with different orientations of bedding planes under rainfall infiltration was evaluated in this study using three dimensional finite element modeling the groundwater table and pore water pressure in slopes before and after rainfall were simulated and the calculated pore pressure corresponding to the initial and highest groundwater tables was used for slope stability analyses the results showed that in comparison with gently dipping bedding planes a slope with steeply dipping bedding planes exhibits a greater rise of the groundwater table and a greater increase of pore pressure leading to a larger reduction in the factor of safety also a shorter time is required to reach the highest groundwater table and the maximum pore pressure at a certain position in consideration of the anisotropic behavior and the groundwater table rise during rainfall unfavorable conditions were identified for the slope stability the four unfavorable conditions where the bedding planes and the slope face approximately strike in the same direction are 1 the daylight condition of the bedding planes 2 the coincidence of the bedding planes and the slope face and 3 steep bedding planes dipping out or 4 into the slope slopes with the unfavorable orientations of bedding planes need additional attention in order to ensure a safe land development in the mountainous areas

premixing of magma and water in mfci experiments experimental studies have been performed to evaluate pre explosive water melt mixes with respect to explosive volcanic molten fuel coolant interaction mfci i e phreatomagmatic explosion remolten ultrabasic volcanic rock was used as a magma simulant measurement of the explosion intensity was used to determine optimal premixing conditions a well defined optimal range was found for the hydrodynamic mixing energy differential flow speed of 4 2 m s as well as for the water melt mass ratio 0 03 to 0 04 under experimental conditions the mass flux of water had a minor influence on the explosion intensity additionally transparent mixing experiments with silicon oil and inked water were carried out they indicate a direct dependence of the pre explosive water melt interface area on the explosion intensity the experimental results show that the contact conditions of water and melt required for explosive mfci may easily be established in natural volcanic systems thus explosive mfci is a probable mechanism of explosive volcanism

an experimental study of hydromagmatic fragmentation through energetic non explosive magma water mixing abstract in this paper we report the first experimental investigation of non explosive hydromagmatic fragmentation during energetic mixing with water we mix magma and water by two methods 1 pouring a basaltic melt between two converging water sprays and 2 jetting basaltic melt at high pressure 3 mpa through a nozzle into a tank of stagnant water these experiments involved shear at relative velocities of 5 16 m s and vigorous mixing for less than a second providing sufficient time for glassy rinds to grow but insufficient time for clot interiors to cool in resulting fragments we examined the gross morphology which reflects fluid deformation during mixing and surface textures which reflect the growth and disruption of glassy rinds we find major differences in both fragment morphology and surface texture between experiments water spray experiments produced pele s hair thin bubble shards melt droplets and angular fracture bound droplet pieces melt jet experiments produced mostly coarse 1 mm diameter wavy fluidal fragments with broken ends fluidal surfaces of fragments produced by water spray experiments were generally shiny under reflected light and in microscopic examination smooth down to micron scale implying no disruption of glassy rinds except for a rare flaking on pele s hair that was bent prior to solidification or b cracking and alligator skin textures on segments of melt balls that had expanded before complete cooling in contrast textures of fluidal surfaces on fragments produced by melt jet experiments are dull in reflected light and in scanning electron images exhibit ubiquitous discontinuous skins rinds that are flaked peeled or smeared away in stripes adhering to these surfaces are flakes blocks and blobs of detached material microns to tens of microns in diameter in the water spray fragments we interpret the scarcity of disrupted surface rinds to result from lack of bending after surfaces formed in the melt jet fragments the ubiquity of partially detached rinds and rind debris likely reflects repeated bending scraping impact and other disruption through turbulent velocity fluctuations when extrapolated to jets of surtseyan scale where velocity fluctuations reach tens of meters per second and turbulent mixing persists for tens of seconds rind disintegration could fragment a large fraction of the erupted material

peperite a review of magma sediment mingling the study of peperite is important for understanding magma water interaction and explosive hydrovolcanic hazards this paper reviews the processes and products of peperite genesis peperite is common in arc related and other volcano sedimentary sequences where it can be voluminous and dispersed widely from the parent intrusions it also occurs in phreatomagmatic vent filling deposits and along contacts between sediment and intrusions lavas and hot volcaniclastic deposits in many environments peperite can often be described on the basis of juvenile clast morphology as blocky or fluidal but other shapes occur and mixtures of different clast shapes are also found magma is dominantly fragmented by quenching hydromagmatic explosions magma sediment density contrasts and mechanical stress as a consequence of inflation or movement of magma or lava magma fragmentation by fluid fluid shearing and surface tension effects is probably also important in fluidal peperite fluidisation of host sediment hydromagmatic explosions forceful intrusion of magma and sediment liquefaction and shear liquification are probably the most important mechanisms by which juvenile clasts and host sediment are mingled and dispersed factors which could influence fragmentation and mingling processes include magma host sediment and peperite rheologies magma injection velocity volatile content of magma total volumes of magma and sediment involved total volume of pore water heated presence or absence of shock waves confining pressure and the nature of local and regional stress fields sediment rheology may be affected by dewatering compaction cementation vesiculation fracturing fragmentation fluidisation liquefaction shear liquification and melting during magma intrusion and peperite formation the presence of peperite intraclasts within peperite and single juvenile clasts with both sub planar and fluidal margins imply that peperite formation can be a multi stage process that varies both spatially and temporally mingling of juvenile clast populations formed under different thermal and mechanical conditions complicates the interpretation of magma fragmentation and mingling mechanisms

simplified stability analysis of strain softening slopes under drawdown conditions the progressive failure of slopes is often induced by drawdown and strain softening of the soil thus the stability level of a strain softening slope under drawdown conditions should be evaluated while considering progressive failure a simplified method was developed to analyze the stability of a strain softening slope based on a new algorithm for determining the subsidiary shear deformation under drawdown conditions the parameters of the method could be easily determined the predictions of the failure behavior of the slope that were obtained using the proposed method were close to the observations of centrifuge model tests under drawdown conditions thus the method was confirmed to be effective in analyzing the stability evolution of the strain softening slopes induced by the drawdown of water level this proposed method was used to evaluate the stability of a real world slope under drawdown conditions the results showed that there is a significant evolution in the safety factor of the slope as the water level decreases the safety factor of a slope is overestimated if the progressive failure behavior is not considered the strain softening behavior and initial water level have a significant effect on the safety factor and critical slip surface of the slope

eifel maars quantitative shape characterization of juvenile ash particles eifel volcanic field germany abstract the eifel region in western central germany is the type locality for maar volcanism which is classically interpreted to be the result of explosive eruptions due to shallow interaction between magma and external water i e phreatomagmatic eruptions sedimentary structures deposit features and particle morphology found in many maar deposits of the west eifel volcanic field wevf in contrast to deposits in the east eifel volcanic field eevf lack the diagnostic criteria of typical phreatomagmatic deposits the aim of this study was to determine quantitatively the shape of wevf and eevf maar ash particles in order to infer the governing eruption style in eifel maar volcanoes the quantitative shape characterization was done by analyzing fractal dimensions of particle contours 125 250 m sieve fraction obtained from scanning electron microscopy sem and sem micro computed tomography sem micro ct images the fractal analysis dilation method and the fractal spectrum technique confirmed that the wevf and eevf maar particles have contrasting multifractal shapes whereas the low small scale dimensions of eevf particles eppelsberg green unit coincide with previously published values for phreatomagmatic particles the wevf particles meerfelder maar pulvermaar and ulmener maar have larger values indicating more complex small scale features which are characteristic for magmatic particles these quantitative results are strengthening the qualitative microscopic observations that the studied wevf maar eruptions are rather dominated by magmatic processes the different eruption styles in the two volcanic fields can be explained by the different geological and hydrological settings found in both regions and the different chemical compositions of the magmas

processes of coastal bluff erosion in weakly lithified sands pacifica california usa abstract coastal bluff erosion and landsliding are currently the major geomorphic processes sculpting much of the marine terrace dominated coastline of northern california in this study we identify the spatial and temporal processes responsible for erosion and landsliding in an area of weakly lithified sand coastal bluffs located south of san francisco california using the results of a five year observational study consisting of site visits terrestrial lidar scanning and development of empirical failure indices we identify the lithologic and process controls that determine the failure mechanism and mode for coastal bluff retreat in this region and present concise descriptions of each process bluffs composed of weakly cemented sands unconfined compressive strength ucs between 5 and 30 kpa fail principally due to oversteepening by wave action with maximum slope inclinations on the order of 65 at incipient failure periods of significant wave action were identified on the basis of an empirical wave run up equation predicting failure when wave run up exceeds the seasonal average value and the bluff toe elevation the empirical relationship was verified through recorded observations of failures bluffs composed of moderately cemented sands ucs up to 400 kpa fail due to precipitation induced groundwater seepage which leads to tensile strength reduction and fracture an empirical rainfall threshold was also developed to predict failure on the basis of a 48 hour cumulative precipitation index but was found to be dependent on a time delay in groundwater seepage in some cases

on the volcanic waveguide an analytical solution for the sound field in a resonant magma conduit with depth dependent magma properties provides a versatile interpretative tool for the analysis of seismoacoustic signals generated by fluid processes in active volcanoes expressions are given for the acoustic field in the atmosphere and the seismic field in the ground radiated through the magma conduit vent and walls respectively a new source model allows the resonance in the conduit to be excited by the vertical fluid velocity at the bottom of the conduit this source model represents acoustic excitation induced by low frequency fluid oscillations or large volume fluctuations originating at depth the magma conduit is modeled as a three section duct with each section having a different density sound speed viscosity and dimension the modal structure of the coupled resonant system is retained as the sound field in the conduit propagates into the surrounding bedrock and the overlying atmosphere the source time function permits estimates of the total mass injected or removed from the magmatic system and the source spectrum acts as a band pass filter on the resonant modes of the conduit theoretical or empirical source functions can be used to drive the seismoacoustic wave field and the amplitude of the source velocity may be constrained by the ballistics of pyroclasts and the height of ash plumes the acoustic properties of the melt may be predicted from the temperature composition and flow conditions of the magma as a function of depth comparisons of synthetic waveforms and spectra with those of seismic and acoustic signals recorded on active volcanoes permit estimates of the conduit geometry density sound speed and attenuation properties of the melt and characterize the temporal and spectral features of the source function the ability to extract this information accurately and efficiently from seismic and acoustic data streams may permit near real time modeling of fluid driven processes in active volcanoes

models of ice melting and edifice growth at the onset of subglacial basaltic eruptions 1 models of the early stages of basaltic eruptions beneath temperate glaciers are presented that consider the evolving sizes of volcanic edifices emplaced within subglacial cavities the cavity size reflects the competing effects of enlargement by melting and closure by downward ductile deformation of the ice roof which occurs when the cavity pressure is less than glaciostatic due to meltwater drainage eruptions of basaltic magma from fissures and point sources are considered which form either hemicylindrical or hemispherical cavities the rate of roof closure can therefore be estimated using nye s law the cavity size edifice size and depth of meltwater above the edifice are predicted by the model and are used to identify two potential eruption mechanisms explosive and intrusive when the cavity is considerably larger than the edifice hydroclastic fragmentation is possible via explosive eruptions with deposition of tephra by eruptionfed aqueous density currents when the edifice completely fills the cavity rising magma is likely to quench within waterlogged tephra in a predominantly intrusive manner the models were run for a range of magma discharge rates ice thicknesses and cavity pressures relevant to subglacial volcanism in iceland explosive eruptions occur at high magma discharge rates when there is insufficient time for significant roof closure the models correctly predict the style of historic and pleistocene subglacial fissure eruptions in iceland and are used to explain the contrasting sedimentology of basaltic and rhyolitic tuyas the models also point to new ways of unraveling the complex coupling between eruption mechanisms and glacier response during subglacial eruptions

time and space variations in magmatic and phreatomagmatic eruptive processes at easy chair lunar crater volcanic field nevada usa the products of monogenetic volcanoes often record complex sequences of eruptive processes easy chair volcano lunar crater volcanic field nevada usa was formed by a monogenetic eruption along a 2 5 km long series of en echelon fissure vents hawaiian to strombolian fountains along the fissures dominated initial activity producing a series of agglomerate ramparts focusing of eruptive activity to two central vents and the formation of two overlapping scoria cones followed the early phase fountain fed lavas from those cones merged to form a channel that fed lava onto a flow field at the foot of the cones focusing of subsurface magma flow toward the central conduits may have reduced magma flux in the remaining fissures and the southern segment s entered a phase of phreatomagmatic explosions that destroyed the early agglomerate rampart and formed a maar and tephra ring composed of lapilli tuff rich in clasts derived from pre easy chair lavas and early agglomerates the eruption closed with a minor phase of magmatic activity that deposited scoria lapilli and bombs on top of the phreatomagmatic deposits the eruptive sequence indicates that relatively low hazard strombolian to hawaiian activity can be replaced by more hazardous phreatomagmatic explosions well into a monogenetic eruption

shear wave velocity drop prior to clayey mass movement in laboratory flume experiments abstract clay slopes are susceptible to suddenly liquefy into rapidly accelerating landslides thereby threatening people and facilities in mountainous areas because the shear wave velocity v s characterizes the medium stiffness this parameter can potentially be used to investigate the rheological behavior of clay materials before and during the solid to fluid transition associated to such landslide failures previous rheometrical studies performed on clay samples coming from trieves landslides french alps have established that this material behaves as a yield stress fluid with a marked viscosity bifurcation when the applied stress reaches a critical level the viscosity decreases abruptly along with v s which tends to zero in the fully fluidized material here we monitor the rayleigh wave velocity v r variations in a saturated clay layer placed in a flume and progressively brought to failure by tilting the device experiments performed on clay samples with different water contents show a significant relative drop in v r values and hence in v s before the onset of the mass movement additional rheometrical analyses point out that this precursory drop in v s is presumably due to a complex transient rheological response of the clay these new results confirm that v s variations constitute a good indicator for monitoring clay slope stability

crystallization of microlites and degassing during magma ascent constraints on the fluid mechanical behavior of magma during the tenjo eruption on kozu island japan bubble and crystal textures provide information with regard to the kinetics of the vesiculation and crystallization processes they also provide insights into the fluid mechanical behavior of magma in a conduit we performed textural bubble and crystal and compositional analyses of pyroclasts that were obtained from the tenjo pyroclastic flow which resulted on account of the eruption in 838 a d on kozu island about 200 km south of tokyo japan pyroclasts in one flow unit 300 2 060 kg m3 average density 1330 kg m3 can be classified into three types on the basis of vesicle textures type i pyroclasts have small isolated spherical bubbles with higher vesicularities 67 77 vol and number density 10 8 11 7 log m 3 type ii pyroclasts have vesicularities similar to type i 61 69 vol but most bubbles exhibit evidences of bubble coalescence and lower number densities than type i 8 9 9 5 log m 3 type iii pyroclasts contain highly deformed bubbles with lower vesicularities 16 34 vol and number densities 8 2 9 0 log m 3 the microlite volume fraction dre converted also changes consistently across type i type ii and type iii as 0 06 0 08 and 0 10 0 15 respectively however the number density of the microlites remains nearly invariant in all the pyroclast types these facts indicate that the variation in the microlite volume fraction is controlled not by the number density i e nucleation process but by the size i e growth process the growth history of each type of microlite was different water content determinations show that the three types of pumices have similar h2o contents 2 6 0 2 wt this fact implies that all three types were quenched at nearly the same depth 35 5 mpa assuming that the magma was water saturated in the conduit if the crystal sizes are limited only by growth time a variation in this parameter can be related to the residence time which is attributed to the flow heterogeneity in the conduit by assuming a laminar poiseuille type flow these textural observations can be explained by the difference in ascent velocity and shearing motion across the conduit which in turn results in the differences in growth times of crystals degrees of deformation and bubble coalescence consequently for crystals in the inner part of the conduit the crystal growth time from nucleation to quenching is shorter than that near the conduit wall the vesicle texture variation of bubbles in types i ii and iii results from the difference in the deformation history implying that the effect of degassing occurred primarily towards the conduit wall

decompression rate of magma at fragmentation inference from broken crystals in pumice of vulcanian eruption abstract decompression rate of magma at fragmentation immediately before or after fragmentation was determined using broken crystals found in the pumices ejected during the vulcanian explosion of sakurajima volcano japan the combined analysis of textural data obtained from the natural pumice samples and a simple model for the crystal fracturing in vesiculating viscous magma indicated a decompression rate 7 0 10 3 7 8 10 4 pa s for the ejecta produced during the later phase of vulcanian explosion this result suggests that the short duration of the vulcanian explosion is controlled by the rapid decrease of the magma ascent rate to a vent an understanding of the control mechanism of the termination of an eruption by precise prediction of the eruption process is essential for both volcanology and hazard mitigation

field evidence of pore pressure diffusion in clayey soils prone to landsliding 1 the hydrologic behavior of shallow weathered soils commonly determines the propensity for slope failure here we use laboratory data and field data collected by an automated monitoring system to assess the character of pore water pressure responses in a natural clay slope subject to intermittent rainfall although we did not measure pore pressure distributions that triggered slope failure we obtained three years of field data that provided reliable and largely reproducible documentation of transient pore pressure responses at depths of tens of centimeters to a few meters below the ground surface moisture and pressure sensors recorded relatively fast transient responses to precipitation the speeds of pore pressure pulses advancing downward in the saturated zone were much larger than those of advective fronts driven by gravity and the amplitudes of the pulses attenuated with depth statistical assessment of 129 pressure head responses demonstrates that this behavior is consistent with predictions of a linear one dimensional pore pressure diffusion model however the model best simulates measurements if diffusivity is treated as a calibration parameter and if initial moisture conditions match model assumptions for regional assessment of slope stability the predictive accuracy of the linear diffusion model is limited by inherent uncertainties in defining the initial conditions and in assigning the values of hydraulic parameters

maar diatreme volcanoes a review maar diatreme volcanoes are produced by explosive eruptions that cut deeply into the country rock a maar is the crater cut into the ground and surrounded by an ejecta ring while the diatreme structure continues downward and encloses diatreme and root zone deposits here we attempt an evenhanded review of maar diatreme volcanology that extends from mafic to kimberlitic varieties and from historical maar eruptions to deeply eroded or mined diatreme structures we conclude that maar diatreme eruptions are episodic ejecta rings provide invaluable insight into eruption processes and sequence but are incomplete records of diatreme formation deposits within the diatreme structure include in varying proportions lower unbedded deposits sometimes typified by subvertical contacts among domains of debris emplaced sequentially and upper bedded deposits formed by sedimentation on surfaces open to the atmosphere a basal root zone comprises the transition from coherent magmatic feeder dike to clastic deposits formed by fragmentation of magma and enclosing country rock root zones are irregular in form and the clastic deposits are typically intruded by contorted dikes irregular root zone like chaotic breccias cut by contorted dikes are also present within diatreme deposits where they represent intra diatreme fragmentation zones and record changes in the location of the explosion locus during eruption

an empirical conceptual gully evolution model for channelled sea cliffs incised coastal channels are a specific form of incised channel that are found in locations where stream channels flowing to cliffed coasts have the excess energy required to cut down through the cliff to reach the outlet water body the southern coast of the isle of wight southern england comprises soft cliffs that vary in height between 15 and 100 m and which are retreating at rates 1 5 m a 1 due to a combination of wave erosion and landslides in several locations river channels have cut through the cliffs to create deeply 45 m incised gullies known locally as chines the chines are unusual in that their formation is associated with dynamic shoreline encroachment during a period of rising sea level whereas existing models of incised channel evolution emphasise the significance of base level lowering this paper develops a conceptual model of chine evolution by applying space for time substitution methods using empirical data gathered from chine channel surveys and remotely sensed data the model identifies a sequence of evolutionary stages which are classified based on a suite of morphometric indices and associated processes the extent to which individual chines are in a state of growth or decay is estimated by determining the relative rates of shoreline retreat and knickpoint recession the former via analysis of historical aerial images and the latter through the use of a stream power erosion model

dynamic mingling of magma and liquefied sediments abstract hydrodynamic mingling of magma and liquefied sediments is generally accepted to represent the key process in the formation of some peperites experimental studies on simulant liquids and calculations based on recent empirical findings in the field of polymer research were undertaken to investigate the effectiveness of this process these studies show that for a wide range of shear rates a laminar flow behaviour of the system magma liquefied sediment can be expected i e turbulent mingling is not a realistic scenario formation of peperitic fabrics with grain sizes on a cm scale can hydrodynamically be explained under realistic intrusion velocities in addition to the hydrodynamics cooling processes must also be considered during peperite formation calculations of the cooling history of the juvenile magmatic component under realistic cooling conditions demonstrate a significant limitation of the hydrodynamic mingling time the consequence for peperite formation under normal intrusion conditions is that domains of magmatic melt and domains of liquefied sediment smaller than 10 cm are not probable however as smaller domain sizes peperitic grain sizes exist in nature we conclude that either those peperites represent the products of explosive events or that hydrodynamic mingling was accompanied by additional fragmentation processes

chilled margin fragmentation as a trigger for transition from strombolian to phreatomagmatic explosive activity at cova de paul crater santo antao cape verde islands sudden transitions from effusive or mildly explosive eruptions to violent phreatomagmatic explosive activity can occur at high elevation vents on oceanic island volcanoes here we describe near vent deposits around the large cova de paul crater on santo antao cape verde islands which provide insights into the transition from strombolian magmatic to violently explosive phreatomagmatic activity during one such eruption the strombolian deposits change from welded spatter to bedded clinkery scoria to angular blocky scoria and contain a distinct population of strongly banded low vesicularity angular sub glassy clasts with strongly prolate vesicles these sub glassy clasts also form a discrete layer of larger blocks at the transition to the overlying phreatomagmatic deposits they are compositionally identical to the strombolian scoria and are interpreted to be fragments of flow banded chilled margins from the walls of the eruptive conduit the layer of large sub glassy blocks records disintegration and expulsion of the chilled margins at the transition to phreatomagmatic activity we interpret the sequence from spatter through clinkery scoria to blocky scoria as recording an increase in groundwater inflow into the conduit from pressurised aquifers but at coolant input ratios below those required for explosions the shattering of the chilled margins to produce the bed of large sub glassy blocks appears to have allowed a much greater water flow into the conduit leading to the phreatomagmatic explosive phase of the eruption

progressive failure behavior of cohesive soil slopes under water drawdown conditions as the number of large reservoirs has grown rapidly drawdown of water level has become a major factor in inducing landslides a new simulator was developed to simulate the in flight drawdown in a centrifuge model test a series of centrifuge model tests was conducted on slopes with different gradients under drawdown conditions the failure mechanism was obtained via an integrated analysis of deformation and failure processes according to the displacement histories of the slopes measured by the image capture and displacement measurement system the slip surface with slippage failure was developed from the top downwards due to the drawdown the displacement histories of the sliding body could be divided into three stages with the increase rate changing from small to large and finally becoming negligible the deformation of the slope only appeared within a limited zone with a nearly invariable boundary surface during the drawdown the boundary surface moved closer to the slope surface with the deceasing slope gradient the drawdown caused a significant coupling process of local failure and deformation localization which developed from the upper part to the lower part the upper part of the sliding body behaved as a rigid body and the lower parts exhibited significant deformation after the slip surface formed which should be reasonably captured in a stability analysis of a slope under drawdown conditions

discussion of use of terrestrial laser scanning for the characterization of retrogressive landslides in sensitive clay and rotational landslides in river banks appears in the canadian geotechnical journal 46 12 1379 1390

formation of composite pyroclasts by welding inside a lithic rich mafic eruption column los marteles caldera canary islands abstract the tuff ring of the los marteles phreatomagmatic maar gran canaria canary islands includes a particular unit that comprises abundant composite spheroidal clasts however these clasts differ from cored clasts elsewhere that consist of erupted lithic pyroclasts with an adhering rim of coherent chilled magma the composite clasts here studied range from lapilli to bombs and are cored or concentrically banded among the welded components several types of primary clasts are discerned that include i juvenile clasts resultant of the magma inertial fragmentation and ii cognate or accessory lithic clasts juvenile clasts include glass spheres nano and microachneliths and crystals lithic clasts include lava fragments scoriae and olivine xenocrysts primary clasts are interpreted to have been produced by the explosion of a partially crystallized mafic sio 2 50 55 magma that erupted into a maar filled up with scoriae plus lava fragments the explosion would have originated as a dense and turbulent gas thrust into which the repeated collisions of melt droplets with solid clasts generated droplet coated crystals lithic clasts and single glass spheres we interpret the cored and concentrically banded pyroclasts to be made of coalesced and or agglutinated particles coated with a melt rim to the rest of the components these composite clasts developed spheroidal shapes during transport within a violent strombolian eruption column due to spin effect and finally landed in solid state

pliocene and pleistocene exhumation and uplift of two key areas of the northern apennines application of different thermochronological methods to two areas of pronounced relief apuane alps and mt falterona of the northern apennines chain documents an average exhumation rate of about 0 7m m yr this result suggests that the general exhumation of the chain is driven mainly by erosion nevertheless the long term exhumation trend seems to be perturbed by shortterm events at higher exhumation rates the time of increased exhumation rates coincides with onset of intramontane sedimentation documenting a contribution of tectonics local normal faulting to the surface uplift the data indicate an eastward shifting of the onset of topographic relief early pliocene in the apuane alps and early pleistocene in the mt falterona area r 2002 elsevier science ltd and inqua all rights reserved

determining flow type shear rate and shear stress in magmas from bubble shapes and orientations we interpret the shear environments that produced bubble textures in obsidian samples using the results of theoretical numerical and experimental studies on the deformation of bubbles in shear flows in particular we use the shapes and orientations of bubbles vesicles in obsidian to estimate shear rates and shear stresses and assess flow type simple vs pure shear this technique can be used to determine shear rates in volcanic conduits the origin of pyroclastic obsidian and the emplacement history and dynamics of obsidian flows a spherical bubble in a viscous fluid subjected to a low reynolds number steady flow field deforms until it reaches a steady shape and orientation bubble deformation is governed by the competing stresses from shearing that deforms and surface tension that rerounds the ratio of these stresses is the capillary number ca because the relationships among ca bubble orientation and shape differ for pure and simple shear we can distinguish between these flow types using preserved bubble geometries furthermore because ca is a function of shear rate we can use relationships between ca and the magnitude of deformation to calculate shear rates when melt viscosity and surface tension are known to demonstrate the potential of the technique we examine three obsidian samples chosen for diversity of origin and texture two of the samples have low crystallinities and banding defined by layers of different vesicularity bubble geometries in a spatter fed obsidian flow sample record deformation by pure shear whereas a juvenile obsidian clast from a pyroclastic fall deposit records predominantly simple shear a third sample from an obsidian flow has banding marked by variable concentrations of microlites and shows bubble deformation most consistent with dominantly simple shear and some bubble relaxation the highest shear rate and shear stress are recorded by the pyroclastic obsidian shear rate 0 01 s 1 shear stress 60 kpa the spatter fed obsidian flow sample deformed by pure shear records the lowest shear stress 4 9 kpa the obsidian flow sample deformed by simple shear records the lowest shear rates 10 6 6 10 6 9 s 1 despite high shear stresses 22 36 kpa because of the high viscosity of the degassed rhyolite 0 13 wt water

numerical modelling of the hydrogeological and geomechanical behaviour of a large slope movement the triesenberg landslide liechtenstein using advanced hydrogeological and geomechanical finite element modelling it has been possible to model the mechanical behaviour of a large slope movement the triesenberg landslide this slope is located along the rhine valley in the principality of liechtenstein and covers an area of around 5 km 2 which includes two villages pore water pressure fields calculated by the hydrogeological model were used as input for the geomechanical model the results obtained through numerical simulation agree fairly well with field measurements of peak velocity spatial and temporal distribution of velocity and total displacements such results were obtained using a modified cam clay elastoplastic constitutive model for which the required material parameters were obtained through careful geotechnical tests these finite element models were carried out in two and three dimensions to gradually improve the understanding of the physical phenomena governing the hydrogeological conditions and the movements of the slope