radiocarbon studies of latest pleistocene and holocene lava flows of the snake river plain idaho data lessons interpretations abstract latest pleistocene holocene basaltic lava fields of the snake river plain idaho have been dated by the radiocarbon method backhoe excavations beneath lava flows typically yielded carbon bearing charred eolian sediment this material provided most of the samples for this study the sediment typically contains less than 0 2 carbon charcoal fragments were obtained from tree molds but only from a few backhoe excavations contamination of the charred sediments and charcoal by younger carbon components is extensive the effects of contamination were mitigated but appropriate pretreatment of samples using acid and alkali leaches twenty of the more than 60 lava flows of the craters of the moon lava field have been dated their ages range from about 15 000 to about 2000 yr b p the ages permit assignment of the flows to eight distinct eruptive periods with an average recurrence interval of about 2000 yr the seven other latest pleistocene holocene lava fields were all emplaced in short eruptive bursts their 14 c ages yr b p are kings bowl 2222 100 wapi 2270 50 hells half acre 5200 150 shoshone 10 130 350 north robbers and south robbers 11 980 300 and cerro grande 13 380 350

flow processes near smooth and rough concave outer banks in curved open channels flow processes near the concave outer bank in curved river reaches are investigated in a laboratory flume with focus on the influence of the bank roughness an outer bank cell of reversed secondary flow occurs for all the investigated roughness configurations of the outer bank the cell widens the outer bank boundary layer which reduces the flow forcing on the bank but also advects high momentum fluid toward the lower part of the bank which enhances the flow forcing on the bank increasing the roughness of the outer bank causes a considerable widening and strengthening of the outer bank cell which amplifies both effects on the flow forcing the widening of the outer bank boundary layer induced by the outer bank cell reduces the effective width of the channel i e the width where most of the discharge is conveyed which increases significantly the sediment transport capacity in the central part of the channel the near bank processes are qualitatively similar but show considerable quantitative variations around the bend the outer bank cell reaches its maximum strength in the zone that is most vulnerable to bed scour and bank erosion which corroborates its morphological relevance the outer cell is mainly generated by reversed near surface gradients in the profile of the streamwise velocity the anisotropy of the cross stream turbulence is the major mechanism opposed to the outer bank cell increasing roughness of the outer bank amplifies all dominant mechanisms but does not modify their relative importance the relevance of the experimental results for natural curved river configurations is discussed

numerical modeling of flow processes over gravelly surfaces using structured grids and a numerical porosity treatment this article describes the development and validation of a method for representing the complex surface topography of gravel bed rivers in high resolution three dimensional computational fluid dynamic models this is based on a regular structured grid and the application of a porosity modification to the mass conservation equation in which fully blocked cells are assigned a porosity of zero fully unblocked cells are assigned a porosity of one and partly blocked cells are assigned a porosity of between 0 and 1 according to the percentage of the cell volume that is blocked the model retains an equilibrium wall function and an rng type two equation turbulence model the model is combined with a 0 002 m resolution digital elevation model of a flume based water worked gravel bed surface acquired using two media digital photogrammetry and with surface elevations that are precise to 0 001 m the model is validated by comparison with velocity data measured using a three component acoustic doppler velocimeter adv model validation demonstrates a significantly improved level of agreement than in previous studies notably in relation to shear at the bed although the resolution of model predictions was significantly higher than the adv measurements making model assessment in the presence of strong shear especially difficult a series of simulations to assess model sensitivity to bed topographic and roughness representation were undertaken these demonstrated inherent limitations in the prediction of 3 d flow fields in gravel bed rivers without high resolution topographic representation they also showed that model predictions of downstream flux were more sensitive to topographic smoothing that to changes in the roughness parameterization reflecting the importance of both mass conservation i e blockage and momentum conservation effects at the grain and bed form scale model predictions allowed visualization of the structure of form flow interactions at high resolution in particular the most protruding bed particles exerted a critical control on the turbulent kinetic energy maxima typically observed at about 20 of the flow depth above the bed

the origins of s forms form similarity process analogy and links to high energy subglacial meltwater flows abstract this paper first presents the history of ideas on s form formation with an emphasis on meltwater models the main approach is based on form similarity between modern erosional marks and subglacial s forms form similarity is then extended to process similarity which promotes understanding of s forms three classes of erosional marks are identified obstacle scours basin shaped erosional marks and landforms related to escarpment flow identification is based on form with recognition of elements though it mainly depends on recognition of the whole form in much the same way as we recognize family members or familiar flowers flow conditions related to the various flow features are determined by flow visualization and computational fluid dynamics some s forms are produced in flume models though most are natural features observed in the field examples from beneath past ice sheets are seen in the field and illustrated by air and ground photographs satellite images and dem digital elevation model the results of this work show remarkable similarity between modern erosional marks and ancient subglacial s forms consequently established processes are attributed to ancient forms in turn s forms may be used abductively to interpret subglacial hydrological conditions the lack of waning stage bedforms scoured into primary forms suggests that erosional marks form under abruptly terminating catastrophic flow

mapping exposed and buried lava flows using synthetic aperture and ground penetrating radar in craters of the moon lava field the craters of the moon com lava field has a multiple eruptivehistory burialofolderflowshasresultedincomplex subsurface stratigraphy for the older eruptive periods the locations of source vents and the extension of lava flows are eitherspeculativeorunknown becausetheyareburiedunder more recent pyroclastics in this study we used surface and subsurface backscatter characteristics of the p and l band polarimetric airborne synthetic aperture radar airsar data and ground penetrating radar gpr soundings to resolve different exposed and buried lava flows our primary objective is to define the most effective polarization and frequency for mapping resolving and characterizing different lavatypesinthevolcanicfield polarimetricanalysisofairsar images from com allows a clear recognition of the aa and pahoehoe lava types as a result of the variability in their roughness our results suggest that the hv cross polarized airsar l band is capable of producing a detailed map delineating surface lava with different surface backscattering properties an accuracy assessment utilizing the geological map of the inferno cone area was performed to quantify the reliability of differentiating lava types and mapping the lava flows extension below loose pyroclastics using airsar data results shows an ability of p band sar to map buried structures up to 3 meters deep under loose cinder and ash deposits resolvingburiedfissures outcrops andlavaflowsthat were validated with ground truth gpr surveys the techniquesusedinthisstudyprovideatooltoassessvolcanichazardsinremoteandinaccessibleplaces alsoitcouldbeanaid in the study of other planets and planetary bodies in the solar system

fracture patterns at lava ice contacts on kokostick butte or and mazama ridge mount rainier wa implications for flow emplacement and cooling histories abstract cooling lava commonly develop polygonal joints that form equant hexagonal columns such fractures are formed by thermal contraction resulting in an isotropic tensional stress regime however certain linear cooling fracture patterns observed at some lava ice contacts do not appear to fit the model for formation of cooling fractures and columns because of their preferred orientations these fracture types include sheet like ladder like rectangular fracture pattern intermediate pseudo aligned individual column bounding fractures and pseudopillow straight to arcuate fractures with perpendicular secondary fractures caused by water infiltration fractures that form the edges of multiple columns along a single linear fracture despite the relatively common occurrence of these types of fractures at lava ice contacts their significance and mode of formation have not been fully explored this study investigates the stress regimes responsible for producing these unique fractures and their significance for interpreting cooling histories at lava ice contacts data was collected at kokostick butte dacite flow at south sister or and mazama ridge andesite flow at mount rainier wa both of these lava flows have been interpreted as being emplaced into contact with ice and linear fracture types have been observed on their ice contacted margins two different mechanisms are proposed for the formation of linear fracture networks one possible mechanism for the formation of linear fracture patterns is marginal bulging melting of confining ice walls will create voids into which flowing lava can deform resulting in margin parallel tension causing margin perpendicular fractures if viewed from the ice wall these fractures would be steeply dipping linear fractures another possible mechanism for the formation of linear fracture types is gravitational settling pure shear during compression and settling can result in a tensional environment with similar consequences as marginal inflation in addition to this horizontally propagating cooling fractures will be directly influenced by viscous strain caused by the settling of the flow this would cause preferential opening of fractures horizontally resulting in vertically oriented fractures it is important to note that the proposed model for the formation of linear fractures is dependent on contact with and confinement by glacial ice the influence of flow or movement on cooling fracture patterns has not been extensively discussed in previous modeling of cooling fractures rapid cooling of lava by the interaction with water and ice will increase the ability to the capture and preserve perturbations in the stress regime

the eruptive rate and history of kuju volcano in japan during the past 15 000 years abstract the eruptive history of kuju volcano on kyushu japan during the past 15 000 years has been determined by tephrochronology and 14c dating kuju volcano comprises isolated lava domes and cones of hornblende andesite together with aprons of pyroclastic flow deposits on its flanks kuju volcano produced tephras at roughly 1000 yr intervals during the past 5000 years and 70 of the domes and cones have formed during the past 15 000 years the youngest magmatic activity of kuju volcano was the 1 6 km3 andesite eruption about 1600 years ago which emplaced a lava dome and block and ash flow kuju volcano shows a nearly constant long term eruption rate 0 7 0 4 km3 for 1000 years during the past 15 000 years this rate is within the range of estimated average eruption rates of late quaternary volcanoes in the japanese arc but is about one order of magnitude higher than the eruption rate of unzen volcano kuju volcano has been in phreatic eruption since october 1995 the late quaternary history of kuju indicates that it poses a significant volcanic hazard primarily due to block and ash flows from collapsing lava domes

kinematic analysis of fractures in the great rift idaho implications for subsurface dike geometry crustal extension and magma dynamics 1 extension across the southern great rift of the eastern snake river plain esrp idaho was measured to calculate the dimensions of underlying dikes and interpret magmatic and extensional processes cumulative rift perpendicular extension ranges from 0 64 to 4 50 m along the 14 km long kings bowl segment from 1 33 to 4 41 m along the 14 km long new butte segment and from 0 74 to 1 57 m along the 4 km long minidoka segment along strike of each segment extension increases toward coeval vents each rift segment is interpreted to be underlain by a subsurface dike whose dimensions are calculated using buoyancy equilibrium and boundary element models dikes are calculated to have tops that are 950 530 m deep bottoms that are 23 31 km deep and widths that taper to zero from a maximum of 2 21 m modeling suggests that the kings bowl dike has a maximum probable width of 8 m and a volume of 2 km3 about 400 times the volume of its coeval lava flow dike widths and ages at the southern great rift provide evidence for a holocene esrp strain rate of about 1 to 3 10 16 s 1 which is as much as an order of magnitude slower than strain rates in the adjacent seismically active basin and range province eruptive fissures are present where rift width is 1650 m this corresponds to a depth to dike top of 700 m which we propose was the depth where vesiculation initiated thus increasing magma pressure and inducing eruption

fracture and surface crust development in a holocene pahoehoe lava flow on the island of tenerife canaries abstract an almost horizontal pahoehoe surface in a holocene plagioclase basanite lava on tenerife displays three scales of fracture within the surface crust an early formed set of large scale fractures divides up the surface into an orthogonal set of rectangular slabs with dimensions of several metres and depths of 10 12 cm the shortest slab dimension is parallel to the flow emplacement direction inferred from a strong surface lineation the slabs are domed with the centre an average of 9 6 cm with range 4 19 6 cm above the edges of the slabs profiles of the slabs normal and perpendicular to the margins and through the crest indicate that they can be described by a power law in which the deflection of the slab h is related to the distance from the crest x with an exponent between 2 and 3 analysis of joints within the slabs indicates two smaller scale networks an intermediate scale joint network bounds blocks with rectilinear to polygonal shapes in plan view and has a characteristic mean spacing of 24 2 cm range 10 5 48 cm the major fractures in this set are normal and parallel to the slab margins a smaller scale joint network bounds polygonal equant blocks in plan view and has characteristic spacing of 6 4 cm range 3 7 10 5 cm a model of cooling from the pahoehoe surface is used to constrain the growth of the crust and timing of fracture development the large scale slabs are attributed to localised accumulation of gas beneath the growing crust causing buoyant forces the tensile stresses caused by uplift are sufficient to form the large scale fractures after 2 or 3 h of cooling the intermediate scale fracture network is attributed to the flexure of the slab crust the smaller scale polygonal joint network is related to the build up of isotropic tensile stresses in the cooling slab crust due to thermal contraction with fracture development being promoted by the flexure of the slabs an analysis of the slab deformation indicates that lava crust is weak the weakness is explained by division of the crust into three zones an outer zone with small scale joints that cause negligible strength a middle zone of elastic behaviour in which stress can build up and a lower zone of plastic deformation the crustal slabs display profiles similar to that expected in a bending elastic plate the deformation of the 10 cm thick crust can be explained if the elastic zone was about 2 cm thick this result agrees with an independent calculation of elastic zone thickness based on the position of the brittle ductile transition being located at the 600 c isotherm at a depth of about 2 cm when the crustal slabs were rifted apart

tumulus development on lava flows insights from observations of active tumuli and analysis of formation models here we use observations of active flows along with detailed morphometric field measurements of more than 70 tumuli on flows at mount etna italy kilauea and hualalai us volcanoes to constrain a previously published model that estimates the pressure needed to form tumuli in an attempt to discover the nature and magnitude of pressure variations within active lava flow interiors we then consider how tumuli differ from idealized circular plates we incorporate observations of active tumuli and find that they may grow asymmetrically yet produce a symmetrical tumulus and can form where the flow path significantly changes direction bending models of clamped edges provide the most reasonable head estimates for the tumuli in our study tumulus formation requires the proper combination of cooling and effusion rate if cooling is too extensive and effusion rate too low the crust will provide too much resistance to bending if cooling is too limited and effusion rates too high crusts will not develop or have insufficient strength to resist fracture and subsequent breakouts we do not find it surprising that tumuli are rarely found over well established lava tubes that typically have rigid walls overlying crusts that exceed 2 m in thickness and provide too much resistance to bending silicic flows lack tumuli because the viscosity gradients within the flow are insufficient to concentrate stress in a localized area

three dimensional numerical model for flow and bed deformation around river hydraulic structures this paper describes a numerical model developed to simulate flow and bed deformation around river hydraulic structures the model solved the fully three dimensional reynolds averaged navier stokes equation expressed in a moving boundary fitted coordinate system to calculate the flow field with water and bed surfaces varying in time a nonlinear k e turbulence model was employed in order to predict flow near the structure where three dimensional flow is dominant the temporal change in bed topography was calculated by coupling a stochastic model for sediment pickup and deposition using a momentum equation of sediment particles in order to account for the effect of nonequilibrium sediment transport in validating the numerical model a spur dike and a bridge pier which are considered to be typical river engineering structures were selected by comparing the numerical results with observed laboratory experimental data the model was found to reproduce flow and scour geometry around these structures with

an investigation of the flow and scour mechanisms around isolated spur dikes in a shallow open channel 1 conditions corresponding to the initiation of the erosion and deposition process 1 the present study investigates the flow physics and the role played by the main coherent structures in the scouring processes around a vertical spur dike in a straight channel at conditions corresponding to the start flat bed of the scouring process large eddy simulation les is performed at a relatively low channel reynolds number re 18 000 in the range where most flume studies with clear water scour conditions are conducted similar to these studies the incoming flow is fully turbulent and contains realistic turbulence fluctuations visualization experiments are conducted to better understand the nature of the interactions between the dominant coherent structures playing a role in the erosion process it is found that the structure of the horseshoe vortex hv system at the base of the spur dike changes considerably in time and in vertical sections perpendicular to the trajectory defined by the axis of the main necklace vortex however its intensity is the largest at vertical sections situated around the tip of the spur dike it is in this region that the core of the main necklace vortex oscillates aperiodically between two preferred modes in one of them zero flow mode the necklace vortex is closer to the spur dike and more compact and the near bed jet flow beneath it is weak in the other one back flow mode a strong near bed jet flow convects the primary necklace vortex away from the spur dike and its core is more elongated and less compact this explains the large amplification by about 1 order of magnitude compared to the surrounding turbulent flow of the turbulent kinetic energy and pressure fluctuations inside the hv system in the region situated around the tip of the spur dike and the double peak distribution of the turbulent kinetic energy past the spur dike in the legs of the necklace vortex the intensity of the bimodal oscillations decreases such that they are not observed in spanwise sections situated at more than one channel depth behind the spur dike it is found that the legs of the horseshoe vortices can interact at times with the vortex tubes shed in the detached shear layer dsl and with the tip of the spur dike these events typically result in a significant change in the coherence of the hv system the largest bed shear stress values in the mean flow are present in the strong acceleration region near the tip of the spur dike but high bed shear stress values are also observed beneath the upstream part of the dsl the bed shear stress fluctuations around the local mean values can be very high especially in the region situated beneath the upstream part of the dsl at random times some of the vortices shed in the dsl merge or interact with eddies from the recirculation region this leads to an increase in their strength and to a large increase of the bed shear stress along their path

crease structures indicators of emplacement rates and surface stress regimes of lava flows crease structures are features commonly found on lava flow surfaces and consist of a fracture with curved walls that extend outward from a linear valley these crease structures are found on flows of nearly all compositions and crystallinities we have mapped the distributions of crease structures on many flows in the western united states and found that 1 axial length is not dependent upon composition and crystallinity 2 adjacent crease structures are generally aligned in an en echelon pattern 3 crease structures located adjacent to flow margins are generally perpendicular to these margins and 4 at mount st helens washington large lobe bisecting crease structures are found on lobes situated on slopes of less than 20 degrees a primary surface feature found on many crease structures is striations striations are sets of long stripes on the walls of the crease structure that extend approximately parallel to the axis of the central valley and they appear to be analogous to those found on the faces of cyclically fractured basalt columns observations of developing crease structures on 6 of the nearly 20 mount st helens dome lobes show that they form throughout the extrusion of flows situated on slopes of less than 20 degrees but only at the very beginning and or end of extrusion of flows on steeper slopes these observations imply that crease structures form when the lava flow is forced to spread laterally either as the flow advances over a flat area or as the down slope movement stagnates near the end of extrusion causing the rate of spreading to exceed the downslope rate of flow this lateral spreading of lava results in the concentration of tensile stress along a line oriented perpendicular to the direction of spreading the cooled crust of the extrusion is therefore torn apart about this line of tensile stress concentration forming a central valley that exposes hot ductile material from the flow interior to the atmosphere the presence of striations on many crease structure walls implies that the emplacement mechanism is similar to that suggested for columnar basalts where each striation is produced by incremental fracturing the stress responsible for crease structure formation is due to both cooling and lateral spreading of lava calculations show that stress due to spreading is three orders of magnitude higher than that due to cooling fracture advance times were calculated using a simple one dimensional conductive cooling model adjusted for the special geometry of the crease structure the model closely approximates measured crease structure emplacement times at mount st helens and gives reasonable estimates for crease structures found on older silicic lava flows we then used this model to calculate emplacement times of entire domes that consist of a single crease structure by dividing the dome volume by the formation time we are able to calculate extrusion rates for these older domes these values which include the first flow rate estimates reported for rhyolitic lavas 0 03 106 m 3 s similar to average flow rates of 0 7 40 m 3 s calculated for mount st helens dacite lobes from detailed topographic maps

nature of flow and turbulence structure around an in stream vertical plate in a shallow channel and the implications for sediment erosion 1 detailed knowledge of the dynamics of large scale turbulence structures is needed to understand the geomorphodynamic processes around in stream obstacles present in rivers detached eddy simulation is used to study the flow past a high aspect ratio rectangular cylinder plate mounted on a flat bed relatively shallow channel at a channel reynolds number of 2 4 105 similar to other flows past surface mounted bluff bodies the large amplification of the turbulence inside the horseshoe vortex system is because the core of the main necklace vortex is subject to large scale bimodal oscillations the presence of a sharp edge at the flanks of the obstruction fixes the position of the flow separation at all depths and induces the formation and shedding of very strong wake rollers over the whole channel depth compared with the case of a circular cylinder where the intensity of the rollers decays significantly in the near bed region because the incoming flow velocity is not sufficient to force the wake to transition from subcritical to supercritical regime in the case of a high aspect ratio rectangular cylinder the passage of the rollers was found to induce high bed shear stresses at large distances 6 8 d behind the obstruction also the nondimensional values of the pressure root mean square fluctuations at the bed were found to be about 1 order of magnitude higher than the ones predicted for circular cylinders overall this shows that the shape of the in stream obstruction can greatly modify the dynamics of the large scale coherent structures the nature of their interactions and ultimately their capability to entrain and transport sediment particles and the speed at which the scour process evolves during its initial stages

structural and petrophysical characterization of the upper basement crustal section at odp iodp site 1256 east pacific ocean 1 new ocean crust is constantly being formed from mid ocean ridge axis voluminous flows of lava are emplaced also away from the ridge axis adding off axis crustal layers to the crustal pile research on deep sea is of great importance to better understand the mechanisms and the nature of the crust forming and evolution in this work we decipher the first stages of the postmagmatic evolution of an intact volcanic section from the upper oceanic crust at ocean drilling program integrated ocean drilling program odp iodp site 1256 eastern pacific ocean using for the first time an innovative core log integration technique to match direct core related and indirect borehole related data by depth shifting and reorienting individual core pieces recovered by drilling we are able to identify the clusterization of structures and physical properties within distinct downdeep strong and weak lava zones reflecting the cooling and tectonic evolution of lavas rather than lithological variations we define the evolution of the structural zones that typically affect lava flows colonnades and entablature zones studying an off axis lava flow encountered in present day upper ocean crust for the same off axis flow we are also able to suggest the lava flow direction nw se and its relationships with the paleoridge axis despite the environmental difficulties in the study of the subseafloor under deep water and using only one dimensional data deriving from ocean drilling this work shows how an array of diverse data can be integrated into a coherent interpretation of lava flow history obtaining detailed information on the mechanism of submarine lava emplacement and flow

architecture and emplacement of flood basalt flow fields case studies from the columbia river basalt group nw usa the physical features and morphologies of collections of lava bodies emplaced during single eruptions known as flow fields can be used to understand flood basalt emplacement mechanisms characteristics and internal features of lava lobes and whole flow field morphologies result from the forward propagation radial spread and cooling of individual lobes and are used as a tool to understand the architecture of extensive flood basalt lavas the features of three flood basalt flow fields from the columbia river basalt group are presented including the palouse falls flow field a small 8 890 km2 190 km3 unit by common flood basalt proportions and visualized in three dimensions the architecture of the palouse falls flow field is compared to the complex ginkgo and more extensive sand hollow flow fields to investigate the degree to which simple emplacement models represent the style as well as the spatial and temporal developments of flow fields evidence from each flow field supports emplacement by inflation as the predominant mechanism producing thick lobes inflation enables existing lobes to transmit lava to form new lobes thus extending the advance and spread of lava flow fields minimum emplacement timescales calculated for each flow field are 19 3 years for palouse falls 8 3 years for ginkgo and 16 9 years for sand hollow simple flow fields can be traced from vent to distal areas and an emplacement sequence visualized but those with multiple layered lobes present a degree of complexity that make lava pathways and emplacement sequences more difficult to identify

evoluton of polygonal fracture patterns in lava flows cooling induced fractures also known as columnar joints divide basaltic lava flows into prismatic columns with polygonal cross sections the regularity and symmetry of the fracture patterns have long fascinated naturalists in view of the recent selection of two candidate nuclear waste sites in areas where polygonally fractured volcanic rocks are located a better understanding of the fracture patterns is required field data indicate that the tetragonal networks at flow surfaces evolve systematically to hexagonal networks as the joints grow inward during solidification of lava this evolution occurs by the gradual change of most orthogonal intersections to nonorthogonal intersections of about 120 degrees the surface features and intersection geometries of columnar joints show that joint segments at any given level form sequentially yet harmoniously

conceptual model of the geometry and physics of water flow in a fractured basalt vadose zone a conceptual model of the geometry and physics of water flow in a fractured basalt vadose zone was developed based on the results of lithological studies and a series of ponded infiltration tests conducted at the box canyon site near the idaho national engineering and environmental laboratory the infiltration tests included one 2 week test in 1996 three 2 day tests in 1997 and one 4 day test in 1997 for the various tests initial infiltration rates ranged from 4 1 cm d 4 75 10 7 m s to 17 7 cm d 2 05 10 7 m s and then decreased with time presumably because of mechanical or microbiological clogging of fractures and esicular basalt in the near surface zone as well as the effect of entrapped air the subsurface moisture redistribution was monitored with tensiometers neutron logging time domain reflectrometry and ground penetrating radar a conservative tracer potassium bromide was added to the pond water at a concentration of 3 g l to monitor water flow with electrical resistivity probes and water sampling analysis of the data shows evidence of preferential flow rather than the propagation of a uniform wetting front we propose a conceptual model describing the saturation desaturation behavior of the basalt in which rapid preferential flow occurs through the largest vertical fractures followed by a gradual wetting of other fractures and the basalt matrix fractures that are saturated early in the tests may become desaturated thereafter which we attribute to the redistribution of water between fractures and matrix lateral movement of water takes place within horizontal fracture and rubble zones enabling development of perched water bodies

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

column on column structures as indicators of lava ice interaction ruapehu andesite volcano new zealand abstract lava flows of the mangawhero formation ca 15 60 ka on ruapehu volcano erupted during the last glaciation in a distal flow lobe at tukino on the east side of the mountain small secondary columns 10 20 cm thick have formed on the sides of large rectangular primary 0 5 3 m thick cooling columns thick 10 m zones of such small columns form a lateral and basal outer rind of the lobe as they do not mark glassy zones of quenching these secondary columns are interpreted as being formed by a second cooling event at temperatures below the boundary between the low creep and elastic regimes 600 c by rapid influx of copious amounts of water temperature drops deduced from extensional strains of the two sets of columns were used to gauge the viability of such a two stage process absence of reliable data on andesite contraction coefficients was overcome by using a sliding scale to assess a large range of values the estimates indicate that two stage chilling is feasible after flowing across relatively ice poor terrain the lava flow must have interacted with a valley glacier that provided water for further chilling the already formed primary columns and formation of the outer rind small columns given this evidence for lava ice interaction it is likely that prominent thick flows elsewhere in the mangawhero formation may have been constrained to their ridge top locations by ice conditions similar to those described by lescinsky and sisson lescinsky d t sisson t w 1998 ridge forming ice bounded lava flows at mount rainier washington geology 26 351 354

contrasting magma types and steady state volume predictable basaltic volcanism along the great rift idaho the great rift is an 85 km long 2 to 8 km wide volcanic rift zone in the snake river plain idaho three latest pleistocene to holocene basaltic lava fields craters of the moon kings bowl and wapi are located along the great rift the craters of the moon lava field is a composite of more than 60 lava flows 25 cinder cones and at least 8 eruptive fissure systems it covers 1 600 km2 and contains 30 km3 of lava flows and associated pyroclastic deposits field radiocarbon and paleomagnetic data show that the craters of the moon lava field formed in eight eruptive periods each of which was typically several hundred years or less in duration and was separated from others before and after by intervals of several hundred to several thousand years the first eruptive period began 15 000 yr b p and the latest eruptive period ended 2100 yr b p the small kings bowl lava field 3 3 km2 0 01 km3 and the larger wapi lava field 330 km2 6 km3 both formed 2250 yr b p three magma types have fed flows along the great rift the types are 1 a contaminated type that has a sio2 range of 49 64 and commonly shows petrographic evidence of contamination 2 a fractionated type that has a sio2 range of 44 54 and shows no evidence of contamination and whose chemical and mineralogical variation can be accounted for mainly by crystal fractionation and 3 a snake river plain type that has a sio2 range of 45 48 shows little evidence of fractionation and is represented by kings bowl wapi flows and olivine basalts of the snake river plain the contaminated and fractionated magma types were erupted at the craters of the moon lava field and the snake river plain magma type was erupted at the kings bowl and wapi lava fields these relations imply that the magma reservoirs are spatially isolated the magma output rate for the craters of the moon segment of the great rift was constant at 1 5 km3 1 000 yr for the period from 15 000 to 7000 yr b p the rate increased to 2 8 km3 1 000 yr from 7000 to 2000 yr b p mainly as a result of the addition of contaminated magma to the nearly constant output rate of fractionated magma the craters of the moon segment of the great rift has experienced quasi steady state volume predictable volcanism for the last 15 000 yr the recurrence interval of eruptive activity for the craters of the moon lava field ranges from several hundred to 3 000 yr because the present interval has lasted 2 100 yr another eruptive period seems likely to occur within the next 1 000 yr the steady state volume predictable relationship suggests that 5 6 km3 of lava will be erupted in the next eruptive period

experimental measurements of the diffusion parameters of light hydrocarbons in water saturated sedimentary rocks i a new experimental procedure an automatic experimental set up has been developed for the determination of diffusion parameters of hydrocarbon gases through water saturated rock samples diffusive flow of hydrocarbons through rock slices is monitored by gas chromatography experiments are carried out according to the time lag method yielding diffusion coefficients solubility coefficients and diffusion permeabilities diffusion coefficients down to 10 12 m2 s 1 10 8 cm 2 s 1 may be determined routinely on rock samples of 2 10 mm thickness maximum errors in diffusion coefficients are estimated around 20 and reproducibility was found to range between 10 and 20 specific features of this set up are automatic sampling and data acquistion high sampling frequency and maintenance of water saturation of the rock samples throughout the experiment

the effect of oriented microcracks on seismic velocities in an ultramylonite the influence of oriented microcracks on the directional dependence of p and s wave velocities has been investigated in an epidote muscovite ultramylonite optical and sem studies revealed that the fabric of the mylonite is characterized by oriented intragranular and grain boundary cracks comparison of orientation patterns of cracks with calculated elastic properties voigt average of a model rock isotropic matrix ultramylonite crack geometry and laboratory seismic data indicates that wave propagation is particularly affected by oriented grain boundary cracks microcracks are most effective at low pressure and largely closed above about 200 300 mpa the residual part of velocity anisotropy observed above this crack closing pressure is mainly due to preferred mineral orientation in particular of mica maximum concentration of poles to 001 mica planes corresponds to the maximum of poles to oriented grain boundary cracks so that the effects of texture and oriented cracks on wave velocities line up giving rise to extreme values of velocity anisotropy and shear wave splitting at low pressure conditions

localized rotation during paleogene extension in east central idaho paleomagnetic and geologic evidence we collected paleomagnetic data from 137 sites in middle eocene volcanic rocks of the northeastern basin and range province in order to characterize the three dimensional kinematics of continental extension in the lost river and lemhi ranges idaho and to test previous block rotation models statistically significant flattening of directions at three of 10 localities reflects either insufficient averaging of paleosecular variation or erroneous tilt corrections five of the seven remaining locality means are statistically indistinguishable from the middle eocene reference direction this indicates that vertical axis rotation did not accompany post 50 ma normal faulting discordant declinations from two localities in the northern lost river range indicate 30 40 of counterclockwise rotation of a large domain of nnw striking volcanic rocks inclination flattening at one of the two rotated localities is moderate but statistically significant f f 9 9 6 5 in total the paleomagnetic data conflict with earlier predictions of uniform clockwise rotation in response to right lateral transtension adjacent to the eastern snake river plain there is a close correspondence between counterclockwise rotated localities and domains of nnw striking volcanic rocks and between unrotated localities and domains of north striking volcanic rocks new mapping shows that counterclockwise rotated localities are all in the hanging wall of a major west dipping low angle normal fault the donkey fault named for the first time this fault loses displacement southwards was active in eocene oligocene time and is probably a tilted high angle fault the spatial distribution of rotated and unrotated localities is best explained by counterclockwise rotation of the hanging wall of the donkey fault during opening of a southward tapering half graben according to this hanging wall rotation model the footwall of the donkey fault remained fixed relative to its rotating hanging wall our proposed kinematic model is generally applicable to extending continental lithosphere and provides a mechanism for coeval crustal thinning and vertical axis rotation thus vertical axis rotation may occur in the absence of strike slip faults in extensional orogens

flow and turbulence structure around a spur dike in a channel with a large scour hole 1 the flow and turbulence structure around a vertical wall spur dike that extends over the whole depth of a straight channel are investigated using detached eddy simulation des the channel reynolds number in des and the corresponding experiment is red 2 4 105 which is typical of applications in small rivers and outside the range where well resolved large eddy simulation les can be conducted the bathymetry at equilibrium scour conditions is obtained from a loose bed experiment this paper discusses the main mechanisms which drive the growth of the scour hole upstream and downstream from the spur dike during the later stages of the scour process and how these mechanisms change between the initial flat bed conditions and later stages of the scour process scale effects are investigated by comparing simulation results at red 2 4 105 with those from simulations performed at a much lower reynolds number red 18 000 results show that while the structure of the horseshoe vortex hv system changes with respect to the case in which the bed is flat the main necklace vortex of the hv system is still subject to large scale aperiodic oscillations similar to the ones observed in flows past in stream bluff body obstacles mounted on a flat surface present results show that the amplification of the horizontal vorticity within the lower part of the separated shear layer ssl and the associated formation of streaks of high bed shear stress below the region where the ssl eddies are convected in the near bed region is a general feature of high reynolds number flow past a vertical wall spur dike placed in a loose bed channel at all stages of the scour process

thermo mechanical model for incremental fracturing in cooling lava flows abstract this study presents an idealized quantitative model of stress development and incremental fracturing in cooling lavas it appears that columnar jointing forms in lavas by a process of incremental fracturing driven by thermal stresses the fractures progress inward from the cooling surfaces as time increases the cooling of a horizontal layer of lava has been modeled analytically for three cooling regimes conductive cooling with liquid magma present conductive cooling after total solidification and hydrothermal cooling horizontal thermal stresses develop and cause vertical fractures at the upper and lower surfaces of the lava as the lava cools layer after layer becomes elastic thermal stresses develop in these thin layers between previously fractured lava where it is assumed stresses have been released and the hot interior lava where temperatures exceed the elastic temperature limit stresses are analyzed by treating each unfractured elastic layer as a slab restrained in bending unrestrained from contraction the stress level at which incremental fracturing occurs extending previous fractures and the effect of stress and temperature conditions on fracture penetration are discussed our analysis yields values for the length of incremental fracture as a function of time and material strength for both a thin lava flow cooling conductively incremental fracture lengths increase with time and for a thicker lava flow in which hydrothermal convection is important incremental fracture lengths are constant with time our results are compared to observed striae widths measured from the base of basaltic lava columns striae represent successive incremental fractures the comparison shows agreement in magnitude and trend after some amount of cooling i e striae and incremental fracture lengths increase with time at an accelerating rate

dating aboriginal stone walled fishtraps at lake condah southeast australia abstract direct dating of stone walled fishtraps has been a methodological challenge in archaeology and is generally considered insurmountable dating is usually associative linking traps to local archaeological sites and geomorphological features of known age limited excavation of sediments burying the lower sections of stone walled fishtrap features has been previously undertaken with limited success recent fine grained excavation and comprehensive ams dating and analysis of channel in fill sediments associated with an elaborate freshwater fishtrap complex at lake condah western victoria yields reliable insights into the phased construction and use of the feature an early phase of basalt bedrock removal to create a bifurcated channel was subsequently in filled with flood sediments incorporating stone artefacts and charcoal dated to c 6600 cal bp after a hiatus basalt blocks were added to the sides of the channel to create multi tiered walls within the past 600 800 years this site provides the first direct insights into the antiquity of the elaborate fishtrapping and aquaculture system developed by aboriginal people in the lake condah region and may represent one of the world s oldest known fishtraps

use of joint growth directions and rock textures to infer thermal regimes during solidification of basaltic lava flows abstract thermal contraction joints form in the upper and lower solidifying crusts of basaltic lava flows and grow toward the interior as the crusts thicken lava flows are thus divided by vertical joints that by changes in joint spacing and form define horizontal intraflow layers known as tiers entablatures are tiers with joint spacings less than about 40 cm whereas colonnades have larger joint spacings we use structural and petrographic methods to infer heat transfer processes and to constrain environmental conditions that produce these contrasting tiers joint surface morphology indicates overall joint growth direction and thus identifies the level in a flow where the upper and lower crusts met rock texture provides information on relative cooling rates in the tiers of a flow lava flows without entablature have textures that develop by relatively slow cooling and two joint sets that usually meet near their middles which indicate mostly conductive cooling entablature bearing flows have two main joint sets that meet well below their middles and textures that indicate fast cooling of entablatures and slow cooling of colonnades entablatures always occur in the upper joint sets and sometimes alternate several times with colonnades solidification times of entablature bearing flows constrained by lower joint set thicknesses are much less than those predicted by a purely conductive cooling model these results are best explained by a cooling model based on conductive heat transfer near a flow base and water steam convection in the upper part of an entablature bearing flow calculated solidification rates in the upper parts of such flows exceed that of the upper crust of kilauea iki lava lake where water steam convection is documented use of the solidification rates in an available model of water steam convection yields permeability values that agree with measured values for fractured crystalline rock we conclude therefore that an entablature forms when part of a flow cools very rapidly by water steam convection flooding of the flow top by surface drainage most likely induces the convection colonnades form under conditions of slower cooling by conductive heat transfer in the absence of water

insights into pāhoehoe lava emplacement using visible and thermal structure from motion photogrammetry we present the evolution over 3 months of a 2016 2017 p hoehoe flow at k lauea as it changed from a narrow sheet flow into a compound lava field fed by a stable system of tubes the portion of the flow located on k lauea s coastal plain was characterized using helicopter based visible and thermal structure from motion photogrammetry to construct a series of georeferenced digital surface models and thermal maps on eight different days results reveal key influences on the emplacement and evolution of such long lived p hoehoe flows this region of the flow grew by 12 10 6 m 3 with a near constant time average discharge rate of 1 2 2 7 m 3 s the development of two tube systems is captured and shows an initial nascent tube enhanced by a narrow topographic confinement which later inflated and created a topographic inversion that modulated the emplacement of a second flow lobe with its own tube system the analysis of breakouts at various stages of the field s life suggests that the evolution of the thermal and morphological properties of the flow surface reflect its maturity thermal properties of breakouts were used to expand the empirical relationship of breakout cooling to longer timescales this study contributes to the long term development and validation of more accurate predictive models for p hoehoe required during the management of long lasting lava flow crises in hawai i and elsewhere

emergence of coherent flow structures over a gravel surface a numerical experiment 1 gravel bed rivers have complex porous and irregular surfaces characterized by a range of morphological forms these topographical structures determine the flow structures that develop over the river bed primarily by the shedding of vortices in the downstream wake of protruding clasts previous research into these flow structures has come from experimental studies which have used either flow visualization or single point measurements techniques here we present a numerical experiment where large eddy simulation les is used to study the generation evolution and destruction of these flow structures over a naturally water worked gravel surface the numerical simulations reported in this paper show that there are two distinct scales of boundary influence upon the shallow flow and emphasize that the measured flow variability at any one point in a natural river will contain both locally derived and upstream inherited flow structures according to the range of scales of bed topography present

hydrodynamics of mountain river confluences and its relationship to sediment transport mountain confluences are characterized by narrow and steep tributaries that provide important sediment load to the confluence whereas themain channel supplies the dominant flow discharge this results in a marked bed discordance between the tributary and main channel which induces key differences in the hydromorphodynamics of the confluence when compared to concordant bed and some common types of discordant bed confluences the processes of initiation and maintenance of the morphology of confluences are still unknown and research linking morphodynamics and hydrodynamics of river confluences is required to understand these phenomena in this paper eddy resolving simulations based on laboratory experiments made in a live bed model of a mountain river confluence are used to provide a detailed description of flow hydrodynamics and implications for morphodynamics the test case study corresponds to a confluence with an angle of 70 numerical simulations are performed for two extreme bathymetric conditions those at the start of the experiment and when equilibriummorphological conditions are reached results of the simulations and experimental observations are used tomake inferences on erosion mechanisms during the initial and final states of the erosion deposition process the relationship between the coherent structures present in the near bed region in the instantaneous and mean flow fields and sediment entrainment transport is described the present paper demonstrates the critical role played by large scale turbulence generated in the shear layers forming on the side of the tributary flow as it enters the main channel by the main vortex forming over the discordant bed region surrounding the downstream end of the tributary as well as by several near bed vortices induced by the deflection of the tributary flow by the incoming flow in the main channel the predicted patterns of bed shear stress are linked to pathways of sediment movement

post depositional intrusion and extrusion through a scoria and spatter cone of fountain fed nephelinite lavas las herrerias volcano calatrava spain the effusion of lava flows from the base of volcanic cones is a common process in continental monogenetic basaltic fields however there are no descriptions in the literature of the structures that channel the lava output through the cone the pliocene quaternary las herrerias volcano calatrava spain was constructed from the superposition of a nephelinite spatter and scoria cone and related lavas over a maar different eruptive styles contributed to the construction of the current volcanic cone phreatomagmatic hawaiian strombolian and violent strombolian quarrying has exposed a lava pond inside the volcanic cone the intrusion of lava through cone forming pyroclastic deposits and the ponding of associated lava flows within the maar crater low fire fountaining activity formed a lava pond that stagnated within the crater protected by the cone s highly welded spatter deposits at its base and overlying scoria deposits once the pressure exerted by ponding lava and overlying pyroclastic deposits exceeded the yield strength of the damming rock walls the melt oozed out through fractures to form an intricate network of dikes and sills and extruded through the lower part of the volcanic cone forming lava flows we propose that lava intrusions similar to those here described may represent the final stage of feeding systems for lava flows associated with scoria and spatter cones

the origin of ina evidence for inflated lava flows on the moon 1 ina is an enigmatic volcanic feature on the moon known for its irregularly shaped mounds the origin of which has been debated since the apollo missions three main units are observed on the floor of the depression 2 9 km across 64 m deep located at the summit of a low shield volcano irregularly shaped mounds up to 20 m tall a lower unit 1 to 5 m in relief that surrounds the mounds and blocky material analyses of lunar reconnaissance orbiter camera images and topography show that features in ina are morphologically similar to terrestrial inflated lava flows comparison of these unusual lunar mounds and possible terrestrial analogs leads us to hypothesize that features in ina were formed through lava flow inflation processes while the source of the lava remains unclear this new model suggests that as the mounds inflated breakouts along their margins served as sources for surface flows that created the lower morphologic unit over time mass wasting of both morphologic units has exposed fresh surfaces observed in the blocky unit ina is different than the terrestrial analogs presented in this study in that the lunar features formed within a depression no vent sources are observed and no cracks are observed on the mounds however lava flow inflation processes explain many of the morphologic relationships observed in ina and are proposed to be analogous with inflated lava flows on earth

spatial and temporal structure of shear layer turbulence at a stream confluence 1 the shear layer that develops at the interface between converging flows is a prominent but poorly understood hydrodynamic feature at stream confluences to examine the spatial and temporal characteristics of turbulence and coherent turbulent structures within a shear layer three dimensional velocity measurements were obtained at a small stream confluence in illinois using two acoustic doppler velocimeters spaced at various separation distances results indicate that coherent structures can be readily identified through cross correlation analysis of the velocity time series for different measurement locations maximum correlations decrease relatively slowly over short separation distances but decrease rapidly for separation distances greater than about 2 times the flow depth convective velocities of coherent structures derived from the correlation analysis differ from local mean velocities and from spatially averaged mean velocities indicating that coherent structures evolve as they are transported along the shear layer a finding consistent with dye tracing experiments despite this evolution correlation and spectral analyses indicate that the frozen turbulence hypothesis holds for frequencies corresponding to length scales of at least some shear generated coherent vortices a domain of quasi two dimensional turbulence energy at low frequencies appears to be associated with large scale intrusions of fluid from one stream into the other along the mixing interface

pulsed inflation of pahoehoe lava flows implications for flood basalt emplacement abstract dilated fractures in hawaiian pahoehoe lava flows contain three zones that show the kinematics of inflation the upper columnar zone forms through thermal contraction prior to inflation the middle planar zone reflects inflation induced tension and the lower banded zone contains evidence of brittle and ductile deformation the formation of the lower banded zone requires varying strain rates during fracture propagation and is best explained by a model where small pulses of lava inject beneath the cooled flow crust through a network of preferred pathways we demonstrate via simple models of pipe flow that this inflation mechanism is incapable of producing areally extensive continental flood basalts on earth although it may explain related features on large martian volcanoes

conductive cooling of lava columnar joint diameter and stria width as functions of cooling rate and thermal gradient abstract much evidence exists that column diameter and stria width of columnar joints in lava flows vary inversely with cooling rate t t and thermal gradient t x at the point of fracture as the flow cools some evidence suggests that lava flows cool conductively a conductive cooling model yields cooling rate and thermal gradient through space and time for cooling igneous bodies both for extrusive and intrusive settings thermal gradient and cooling rate are then linked to stria width and column diameter with faster cooling leading to narrower columns and steeper gradients to narrower striae this model shows large regions within a body where the ratio of thermal gradient to cooling rate is nearly constant and predicts that the ratio of stria width to column diameter is also nearly constant this prediction is consistent with field observations both in this and other works the model also suggests that if conductive cooling dominates then joint spacing i e column diameter should increase inward from the margins of the body as should stria width

physical constraints on geologic co2 sequestration in low volume basalt formations deep basalt formations within large igneous provinces have been proposed as target reservoirs for carbon capture and sequestration on the basis of favorable co 2 water rock reaction kinetics that suggest carbonate mineralization rates on the order of 10 2 10 3 d although these results are encouraging there exists much uncertainty surrounding the influence of fracture controlled reservoir heterogeneity on commercial scale co 2 injections in basalt formations this work investigates the physical response of a low volume basalt reservoir to commercial scale co 2 injections using a monte carlo numerical modeling experiment such that model variability is solely a function of spatially distributed reservoir heterogeneity fifty equally probable reservoirs are simulated using properties inferred from the deep eastern snake river plain aquifer in southeast idaho and co 2 injections are modeled within each reservoir for 20 yr at a constant mass rate of 21 6 kg s 1 results from this work suggest that 1 formation injectivity is generally favorable although injection pressures in excess of the fracture gradient were observed in 4 of the simulations 2 for an extensional stress regime as exists within the eastern snake river plain shear failure is theoretically possible for optimally oriented fractures if s h 0 70s v and 3 low volume basalt reservoirs exhibit sufficient co 2 confinement potential over a 20 yr injection program to accommodate mineral trapping rates suggested in the literature

the theoretical foundations and potential for large eddy simulation les in fluvial geomorphic and sedimentological research abstract large eddy simulation les is a method for resolving the time dependent structure of high reynolds number turbulent flows with les it is possible to model and track the behaviour of coherent turbulent structures and study their effect on the flow field hence les is potentially an important research tool in the fluvial sciences where flow mixing sediment entrainment and sediment transport are all affected by the presence of coherent vortices and their interactions with channel boundaries and other flow structures this paper introduces the les methodology discusses a variety of ways for representing small scale processes within les the subgrid scale modelling problem and provides some examples of early work into the use of les in a fluvial context a number of advances in computational power and numerical methods are required before les can be effectively applied at the river reach scale this paper considers some recent developments and their potential for providing validated large eddy simulations of river flow at the channel scale

morphology of rubbly pahoehoe simple flows from the deccan volcanic province implications for style of emplacement abstract lava flows with preserved bases and brecciated upper crusts constitute a morphological type that differs in character from typical pahoehoe and a a such flows have been reported from many provinces around the world previous studies had referred to these flows informally as pahoehoe flows with rubbly tops broken top pahoehoe and rubbly pahoehoe recent studies have formally applied the latter term to describe parts of the well studied laki flow in iceland as well as flows from the columbia river basalt province rubbly pahoehoe flows are abundant in the upper stratigraphic formations of the deccan volcanic province dvp and are more commonly known as simple flows this study presents detailed observations of such flows from various parts of the dvp and discusses their implications for understanding flow emplacement these flows which appear to be single units at the outcrop scale are generally much thicker and significantly more extensive than individual pahoehoe lobes that dominate the lower formations of the deccan stratigraphy they are characterised by preserved gently undulating tachylitic bases but variably disrupted crustal zones that grade into flow top breccias the breccias are constituted of highly vesicular and oxidised fragments of varying sizes that appear to have been derived from previously formed pahoehoe crusts previous work has indicated that the morphology of these flows might be related to initial inflation accompanied by rapid volatile exsolution and an increase in effusion rate and or viscosity with time this agrees reasonably well with the qualitative and quantitative models of emplacement developed for the laki flow the abundance of such flows in the upper formations of the deccan stratigraphy clearly hints at a significant shift in the nature of the deccan eruptions this could be indicative of higher eruption rates during this period this in turn raises the possibility of hazardous impact on the climate during the eruption of these flows which is also discussed in the paper

flow field at a vertical wall abutment experiments were conducted to measure the three dimensional turbulent flow field using the acoustic doppler velocimeter at a short vertical wall abutment ratio of abutment length to approach flow depth less than unity before and after the development of a scour hole under a clear water scour condition in the upstream the presentation of flow field through vectors at vertical sections shows a primary vortex associated with the downflow in the downstream the upward flow is comprised of with irregularities owing to the vortex shedding the flow separation near the bed and within the scour hole is evident from the turbulent kinetic energy distribution using reynolds stresses the bed shear stresses are calculated

modelling the evolution of columnar joints abstract cooling cracks developing from the margins of solidifying lava flows or intrusive dykes or sills often propagate inward and divide the rock into prismatic columns it has been shown that 1 the initial crack pattern that forms at the surface of the body is not as regular as the pseudo hexagonal pattern which evolves later 2 columnar structures develop by repeated step wise crack advances forming cm to dm transverse bands on the column faces 3 even within well developed colonnades the polygonal outlines continue to shift slightly from one crack advance to the next we propose that each new crack should propagate parallel to the highest thermal gradient ahead of the current crack tip when adjacent columns are of unequal size the local asymmetry of the isotherms drives the new crack toward the biggest and hottest column we present a geometrical model and algorithm that follows this rule and mimics the successive crack advances as the cooling front migrates into the lava sheet or dyke the model polygonal pattern obtained consists of convex irregular polygons with a variable number of sides but in which pentagons and hexagons predominate the algorithm successfully reproduces the rapid evolution from an initial immature crack pattern to a pseudo hexagonal mature one in which the average number of sides approaches six it predicts also the predominance of y type crack junctions the rapid evolution toward columns of approximately equal sizes and the persistent changes in length and diverging orientation of growth steps observed along the sides of columns the model polygonal patterns exhibit geometrical properties which are very similar to those observed in well developed columnar jointed flows such as the giant s causeway

structures textures and cooling histories of columbia river basalt flows flood basalt flows of the columbia river basalt group commonly exhibit well developed colonnade and entablature structures formed during cooling of individual flows the colonnade refers to the well defined columnar structure of many flows which appears in the lowermost 10 to 30 and in places the uppermost 10 to 20 entablature refers to those parts of a flow that have smaller column diameters and more irregular pattern fractures than those of colonnade entablature commonly occupies the central 60 to 70 of a flow in some cases however the entablature is interrupted by colonnade in such cases the entablature and colonnade may be repeated once or twice within a single flow in other cases flows may lack an entablature entirely petrographic examination reveals a pronounced correlation between structural and textural features thin sections of colonnade basalt have relatively coarse cruciform or octahedral fe ti oxide crystals and 20 glassy mesostasis the central entablature basalt in contrast has much more mesostasis as much as 60 and has textural features such as feathery fe ti oxide crystals indicative of more rapid cooling these features are the reverse of what might be expected for normal conductive cooling because cooling rates at the flow margins should be greater than those in the flow interior we reconciled the observed basalt textures with thermal models by taking into account rainfall and deranged drainage during crystallization of the flow downward migration of water through cracks would cause convective cooling of underlying unsolidified lava this effect and its consequences have been modeled numerically in order to clarify the physical constraints on the mechanism by which the central part of the lava can be quenched we have found that a water infiltration front can explain the presence of a thick quenched flow interior provided that the infiltration front moves downward just behind the lava solidification front despite heavy rainfall on hawaii for example 250 cm yr at kilauea iki exposed prehistoric lava flows on that island exhibit only colonnades we deduce from this that heavy rainfall alone is inadequate to quench flow interiors extensive flooding by deranged drainage or perhaps extremely heavy rainfall 250 cm yr is apparently required to produce entablatures the model also can be used to explain the occurrence of repeated entablature and colonnade by considering the effects of intermittent inundation the imposition of boundary conditions that mimic the removal and reoccurrence of flooding yields cooling histories that are consistent with the development of multiple colonnades and entablatures

numerical and experimental investigation of flow and scour around a circular pile the flow around a vertical circular pile exposed to a steady current is studied numerically and experimentally the numerical model is a three dimensional model the model validation was achieved against new experimental data which include two component laser doppler anemometry lda flow measurements and the hot film bed shear stress measurements and reported in the present paper and the data of others and a k w turbulence model was used for closure the model does not have a free surface facility and therefore is applicable only to cases where the froude number is small fr 0 0 2 the flow model was used to study the horseshoe vortex and lee wake vortex flow processes around the pile the influence on the horseshoe vortex of three parameters namely the boundary layer thickness the reynolds number and the bed roughness was investigated in the latter investigation the steady solution of the model was chosen a study of the influence of the unsteady solution on the previously mentioned flow processes was also carried out the ranges of the parameters covered in the numerical simulations are the boundary layer thickness to pile diameter ratio is varied from 2 x 10 2 to 10 2 the pile reynolds number from 10 2 to 2 10 6 and the pile diameter to roughness ratio from 2 to about 10 3 the amplification of the bed shear stress around the pile including the areas under the horseshoe vortex and the lee wake region was obtained for various values of the previously mentioned parameters the steady state flow model was coupled with a morphologic model to calculate scour around a vertical circular pile exposed to a steady current in the case of non cohesive sediment the morphologic model includes i a two dimensional bed load sediment transport description and ii a description of surface layer sand slides for bed slopes exceeding the angle of repose the results show that the present numerical simulation captures all the main features of the scour process the equilibrium scour depth obtained from the simulation agrees well with the experiments for the upstream scour hole some discrepancy up to 30 was observed however for the downstream scour hole the calculations show that the amplification of the bed shear stress around the pile in the equilibrium state of the scour process is reduced considerably with respect to that experienced at the initial stage where the bed is plane

duration of eruption at the giant crater lava field medicine lake volcano california based on paleomagnetic secular variation nearly 500 cores were collected from the postglacial giant crater lava field on the south flank of medicine lake volcano the basaltic lavas form a continuous set of lava flows which display strong chemical zonation from initially erupted calc alkaline basaltic andesite to final primitive basalt of tholeiitic affinity six chemical stratigraphic groups have been recognized and mapped the eruptive sequence was sampled at numerous sites both to determine the characteristic paleomagnetic direction of each chemical group and to estimate the duration of the eruption inferred from secular variation of the geomagnetic field well grouped mean directions of magnetization were obtained for 41 sites in the giant crater lava field mean directions of magnetization determined for the lava field are nearly identical the likelihood of any extended time interval for the eruption of the different lava types is extremely small and the data suggest an eruptive event of less than 30 years duration analogous to historic hawaiian eruptions however the average of groups 1 4 which cannot be distinguished paleomagnetically from each other is slightly different statistically from that of the average of groups 5 and 6 which have similar directions a time gap of 10 5 years is inferred between eruption of group 4 and 5 lavas based on analysis of the probability of the observed angular difference of 1 27 0 84 between their mean directions and by comparison of this angular difference to calculated field directions with similar declination and inclination determined from spherical harmonic models of the geomagnetic field for the time period 1945 1990 about 200 oriented cores were also collected from predecessor and successor basaltic lava flows on the upper flanks of the volcano together with remanent directions from lavas of the snake river plain the data define a clockwise loop of secular variation

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

coherent structures in the flow field around a circular cylinder with scour hole large eddy simulation les and laboratory flume visualizations were used to investigate coherent structures present in the flow field around a circular cylinder located in a scour hole the bathymetry corresponds to equilibrium scour conditions and is fixed in les the flow parameters in the simulation correspond to the experimental conditions in which the approach flow is fully turbulent detailed consideration is given to the interaction of the horseshoe vortex hv system within the scour hole with the detached shear layers formed from the cylinder and the near bed turbulence it is found that the overall structure of the hv system varies considerably in space and time though a large relatively stable primary necklace vortex is present at practically all times inside the scour hole the simulation captures the presence of bimodal chaotic oscillations inside the hv system as well as the sharp increase in the resolved turbulent kinetic energy levels and pressure fluctuations reported in prior experimental investigations high levels of the mean bed shear stress are observed beneath the primary necklace vortex especially over the region where the bimodal oscillations are strong as well as beneath the small junction vortex at the base of the cylinder it is also found that the detachment and advection of patches of vorticity from the downstream part of the legs of the necklace vortices can induce large instantaneous bed shear stress values when the critical bed shear stress value for sediment entrainment on a flat surface is adjusted for bed slope effects the les simulation correctly predicts that the distribution of the mean bed shear stress is consistent with equilibrium scour conditions

tectonic analysis of fracturing associated with occator crater abstract occator crater a ceres crater that hosts multiple bright spots on its floor has several sets of fractures associated with it a tectonic analysis of each of these fracture sets suggests that the concentric and radial fractures around the central pit and the concentric fractures high on the crater wall near the rim most likely formed due to well known impact cratering processes uplift of the crater floor due to magmatic injection is suggested to have resulted in the concentric floor fractures at the base of the crater wall as well as the cross cutting fractures in the lower part of the southwestern wall a mathematical analysis shows that a cryomagmatic plume diapir could have both reached the height necessary to cause fracturing within occator and that the stresses required are reasonable expansion a lobate flow from beneath is proposed to have formed those linear fractures associated with the vinalia faculae circumferential fractures surrounding occator appear to have formed due to the volumetric compaction of the ejecta blanket over the buried pre existing topography

3d calculations of equilibrium conditions in loose bed open channels with significant suspended sediment load the flow sediment transport and bathymetry at equilibrium conditions in loose bed open channels are predicted using a fully three dimensional 3d reynolds averaged navier stokes model that was validated for cases in which the bed load transport is dominant the paper focuses on two test cases corresponding to laboratory experiments performed in an s shaped channel in which the suspended sediment load is comparable to the bed load a modified version of the original model that accounts for gravitational force effects due to the total sediment load is proposed it is shown that the way bed slope effects are accounted for plays a major role in improving the predictive capabilities of the model for a case in which the equilibrium bathymetry is characterized by relatively large values and sharp variations of the transverse slope the model is then used to qualitatively and quantitatively analyze the distributions of several flow variables that are difficult to measure in the laboratory they include the dis

structure and origin by injection of lava under surface crust of tumuli lava rises lava rise pits and lava inflation clefts in hawaii tumuli are positive topographic features that are common on hawaiian pahoehoe lava flow fields particularly on shallow slopes and 75 measured examples are presented here to document the size range tumuli form by up tilting of crustal plates without any crustal shortening and are thus distinguished from pressure ridges which are up buckled by laterally directed pressure the axial or star like systems of deep clefts that characterize tumuli are defined here as lava inflation clefts their tips advanced into red hot lava and they widened as uplift proceeded and while the lava crust was thickening flat surfaced uplifts formed like tumuli by injection of lava under a surface crust were previously called pressure plateaus but lava rise is proposed instead the pits that abound among lava rises previously attributed to collapse or subsidence are generally formed because the lava around them rose and the name lava rise pit is proposed unique examples of tumuli and lava rises from which lava drained out under a surface crust 1 5 to 2 5 m thick are described from kilauea caldera these examples show that in tumuli and lava rises the crust floats on considerable bodies of fluid lava and is able to do so because of its higher vesicle content the fluid lava loses many of its gas bubbles during residence beneath the crust the bulk densities of samples from tumuli show a general downward increase the form of the density profile is consistent with the relationship that for any given crustal thickness the density of fluid lava closely matched the average density of that crust suggesting that the lava was stably density stratified it is inferred that stable stratification was regulated by out flows of the more vesicular lava fractions loss of bubbles through the lava inflation clefts and entry of injected lava at its level of neutral buoyancy below the uppermost meter the downward decrease in vesicularity closely conforms with that expected by compression of a uniform mass of gas per unit mass of lava

timing of basaltic volcanism along the mesa butte fault in the san francisco volcanic field arizona from 40ar 39ar dates implications for longevity of cinder cone alignments using high precision stepwise heating 40ar 39ar methods we dated volcanic products of at least 12 vents cropping out along the northern segment of the mesa butte fault in the san francisco volcanic field arizona where the relationship between fault and vent alignment is unambiguous the 40ar 39ar isochron dates indicate that the mesa butte fault hosted five episodes of volcanism over a 1 million year interval from 1400 to 300 ka the first episode occurred 1 km northwest of the trace of the mesa butte fault whereas the next two episodes were centered near the intersection of the mesa butte and cedar ranch faults the final two episodes produced red mountain 750 100 ka and shadow mountain 300 100 ka respectively ages of vents representing the third mesa butte episode of volcanism 760 50 ka to 900 80 ka indicate a systematic southwestward shift in the locus of volcanism along the mesa butte fault that contrasts sharply with overall eastward younging of volcanism within the field these data demonstrate that structures in basaltic volcanic fields are capable of hosting multiple episodes of volcanism over periods of time comparable to duration periods of composite volcanoes 106 years but at significantly lower recurrence intervals these results suggest that probability models of spatiotemporal recurrence of volcanism within basaltic volcanic fields should incorporate mapped structures particularly where these structures have either hosted previous volcanic activity or are proximal to population centers or sensitive installations such as nuclear power plants or waste repositories

lava rise plateaus and inflation pits in the mccartys lava flow field new mexico an analog for pāhoehoe like lava flows on planetary surfaces

k ar geochronology of a quaternary monogenetic volcano group in ojika jima district southwest japan an unspiked k ar dating method using a mass fractionation correction procedure was applied to a quaternary independent group of monogenetic volcanoes ojikajima volcano group located in northwestern kyushu in southwest japan in order to clarify in detail secular variations in eruptive volume locations of eruptive vents and magma compositions in a single monogenetic volcano group the major results were as follows a k ar ages of monogenetic volcanoes distribute from 1 08 to 0 30 ma with voluminous peaks at approximately 1 0 and 0 6 ma b the volcanic activity commenced in the central part of the field expanded to the whole field at approximately 0 6 ma and then shrank to the central area 3 concentrations of incompatible elements such as ba k and nb increase with decreasing age whereas p y and zr concentrations remain constant these concentrations suggest gradual decrease in the degree of partial melting from an identical mantle source with residual garnet

characterization and evolution of fractures in low volume pahoehoe lava flows eastern snake river plain idaho we characterize fracture evolution in pahoehoe lava flows of the eastern snake river plain idaho and highlight significant differences to flood basalt sheet flows and implications for hydrologic models there are four distinct fracture types in east ern snake river plain flows 1 column bounding 2 column normal 3 entablature and 4 inflation fractures types 1 3 are driven by thermal stress whereas type 4 is induced by lava pressure from within the flow thermal stress distribution in a flow is dictated by its aspect ratio width height which controls the shape of isotherms isotherms control column bounding fracture orientations resulting in increasingly radial fracture patterns as the aspect ratio approaches unity column normal fractures form in response to thermal stress and fracture induced stress within basalt columns overlap in the timing of column bounding and column normal fracture growth has resulted in complex fracture relationships column normal fracture growth is strongly influenced by vesicular layers which act as mechanical heterogeneities creating preferential pathways for fracture growth as well as causing jogs or terminations along column bounding fractures eastern snake river plain entablatures which preserve the shape of the central lava core during the final stages of cooling have distinctly different origins and fracture styles compared to sheet flows entablatures formed by penetration of the edges of pressurized lava cores by inflation fractures causing rapid convective cooling in addition inflation fractures significantly perturb isotherm shapes in lava flows affecting flow scale fracture patterns and densities the overall effect of all these processes is a complex pattern of fracturing that attests to a strong impact by each fracture type on the growth behavior of all other fracture types

tectonic analysis and paleo stress determination of the upper lava section at odp iodp site 1256 east pacific ocean abstract research on the deep sea is of great importance for a better understanding of the mechanism of magma emplacement and the tectonic evolution of oceanic crust however details of the internal structure in the upper levels of the oceanic crust are much less complete than that of the more fully studied sub aerial areas for the first time this study proposes a dynamic analysis using the inversion method on core data derived from the drilled basement of the present day intact oceanic crust at odp iodp site 1256 in the cocos plate the research is based on an innovative core reorientation process and combines different stress hypothesis approaches for the analysis of heterogeneous failure slip data via exploitation of two distinct techniques from the analysis of the failure slip data both techniques produce 5 distinct subsystem datasets all calculated subsystems are mechanically and geometrically admissible interpretation of the results allows the researchers to note a complex local and regional tectonic evolution deriving from the interplay of 1 the ridge push and rotation of both the east pacific rise and the cocos nazca spreading center 2 the effect of the slab pull of the middle america trench 3 the influence of lava emplacement mechanisms and 4 intra plate deformation

a sinuous tumulus over an active lava tube at klauea volcano evolution analogs and hazard forecasts abstract inflation of narrow tube fed basaltic lava flows tens of meters across such as those confined by topography can be focused predominantly along the roof of a lava tube this can lead to the development of an unusually long tumulus its shape matching the sinuosity of the underlying lava tube such a situation occurred during k lauea volcano s hawai i usa ongoing east rift zone eruption on a lava tube active from july through november 2010 short lived breakouts from the tube buried the flanks of the sinuous ridge like tumulus while the tumulus crest its surface composed of lava formed very early in the flow s emplacement history remained poised above the surrounding younger flows at least several of these breakouts resulted in irrecoverable uplift of the tube roof confined sections of the prehistoric carrizozo and mccartys flows new mexico usa display similar sinuous ridge like features with comparable surface age relationships we contend that these distinct features formed in a fashion equivalent to that of the sinuous tumulus that formed at k lauea in 2010 moreover these sinuous tumuli may be analogs for some sinuous ridges evident in orbital images of the tharsis volcanic province on mars the short lived breakouts from the sinuous tumulus at k lauea were caused by surges in discharge through the lava tube in response to cycles of deflation and inflation di events at k lauea s summit the correlation between di events and subsequent breakouts aided in lava flow forecasting breakouts from the sinuous tumulus advanced repeatedly toward the sparsely populated kalapana gardens subdivision destroying two homes and threatening others hazard assessments including flow occurrence and advance forecasts were relayed regularly to the hawai i county civil defense to aid their lava flow hazard mitigation efforts while this lava tube was active

thermal mechanical modeling of cooling history and fracture development in inflationary basalt lava flows abstract thermal mechanical analyses of isotherms in low volume basalt flows having a range of aspect ratios agree with inferred isotherm patterns deduced from cooling fracture patterns in field examples on the eastern snake river plain idaho and highlight the caveats of analytical models of sheet flow cooling when considering low volume flows our field observations show that low volume lava flows have low aspect ratios width divided by thickness typically

generation of nitrogen and methane from sedimentary organic matter implications on the dynamics of natural gas accumulations nitrogen n2 contents of natural gases in rotliegend and buntsandstein reservoirs of the north german basin regionally approach 100 a review is given of the various hypotheses primordial origin volcanic or magmatic origin radiogenic origin atmospheric origin organic origin inorganic nitrogen in sedimentary rocks presented to account for nitrogen anomalies in this area and other parts of the world the objective of the present study was to investigate sedimentary organic matter in particular coals as a potential source of molecular nitrogen in the subsurface comparison of reservoir sizes and gas generation potentials indicates that carboniferous coal measures which are considered as the source of the natural gas in the north german basin can readily account for the nitrogen quantities found in present day reservoirs laboratory pyrolysis experiments were carried out to investigate the kinetics of generation of methane and molecular nitrogen from coals of different type and rank under experimental conditions nitrogen is formed at higher temperatures than methane supporting the concept of a fractional generation of methane and nitrogen in natural systems based on the kinetic parameters derived from laboratory experiments methane and nitrogen generation rates from coals were calculated for geologic heating rates gas containing more than 50 nitrogen is generated under these conditions at temperatures in excess of 300 c nitrogen rich gases are thus formed only in the final stage of gas generation after methane generation has practically ceased it is concluded that the amounts of gas encountered in nitrogen rich gas accumulations represent only a small fraction possibly 1 of the total gas generation potential of this area while the bulk of the generated gas has escaped to the atmosphere the present day composition of the reservoir gases reflects the composition of only the most recently generated gas on a geologic time scale

long lived shield volcanism within a monogenetic basaltic field the conundrum of rangitoto volcano new zealand drilling through the edifice of rangitoto the youngest and largest volcano in the monogenetic auckland volcanic field reveals the multistage eruptive and magmatic history of a small basalt shield volcano activity commenced calendar year cal 6000 cal yr b p involving minor effusive and pyroclastic volcanism until 650 cal yr b p this period either represents an early less productive phase of a single polygenetic volcano or alternatively rangitoto is better described as a volcanic complex that includes one or more buried edifices concealed by the main structure a voluminous shield building phase occurred 650 550 cal yr b p erupting isotopically uniform subalkalic basalts mg 60 64 four batches of magma distinguished by trace element chemistry were erupted sequentially but they lack genetic connection via fractional crystallization or assimilation two of the magma batches display linear trends of decreasing incompatible trace element abundance and increasing ratios of moderately incompatible to highly incompatible elements with decreasing age this is consistent with cycles of progressive partial melting at the source the final phase of activity ca 550 500 cal yr b p was explosive and less voluminous producing scoria cones at the summit this phase involved more diversity in magma compositions including more mafic subalkalic basalt and alkali basalt pointing to sourcing of magmas simultaneously from different depths in the mantle rangitoto volcano contributes to a growing body of evidence showing that major periods of volcanism in monogenetic basalt fields occur at centers that have experienced multiple eruption episodes changes in magma composition accompany changes in eruption style but a lack of an obvious shared pattern in magmatic evolution at various volcanoes points to the localized mantle heterogeneity and conduit systems hazard scenarios for regions traditionally classified as monogenetic need to encompass the possibility of prolonged episodes of activity and reawakening of volcanoes a significant implication where infrastructure is built on such regions

surface morphology of columnar joints and its significance to mechanics and direction of joint growth columnar joints in basaltic lava flows display conspicuous bands oriented normal to column axes new observations show that each band contains a single plumose structure and thus represents an individual crack or joint segment formed during a discrete growth event analysis of plumose structure and intersections of cracks leads to a new kinematic model of columnar jointing and provides the first direct proof that columnar joints grow incrementally from exterior to interior regions of solidifying magma bodies columnar joints form by nucleation and growth of new cracks on the edges of older cracks each new crack begins at a point and propagates mostly normal to column axes and along the leading edge of a developing column face where thermal stress is concentrated inward propagation of cracks toward hotter regions is limited by a decrease of thermal stress and by the brittle ductile transition of lava outward and lateral propagation is limited by mechanical interaction with previous cracks and by low thermal stress in already fractured lava cracks often diverge slightly from the planes of previous cracks probably because of spatial and temporal changes in directions of local principal stresses mechanical interaction causes a diverging crack to overlap curve toward and usually intersect the previous crack behind its edge leaving a blind tip that points in the overall growth direction of the columnar joints this and other directional criteria are applied to determine joint growth patterns in several lava flows of the western united states in two tiered and multi tiered flows downward growing columnar joints usually meet upward growing joints well below the middle of the flows which indicates very rapid cooling of upper portions relative to lower portions this supports the idea that convection of water in columnar joints connected to the surface may be an important mechanism for cooling the upper portions of these flows whereas conduction is probably the dominant cooling mechanism at the bases

longevity of a small shield volcano revealed by crypto tephra studies rangitoto volcano new zealand change in eruptive behavior of a basaltic field abstract the life span of small volcanoes in terrestrial basaltic fields commonly considered monogenetic can be difficult to assess due to a paucity of datable materials capable of providing a 102 103 year age resolution we have used microscopic tephra layers crypto tephra in lake sediments to determine the longevity of rangitoto volcano a small shield that represents the most recent volcanism in the auckland volcanic field avf new zealand previous studies suggested construction in a relatively short interval at 550 500 cal yrs bp in contrast the tephra record shows evidence of intermittent activity from 1498 140 to at least 504 6 cal yrs bp a longevity of 1000 years rangitoto volcano is thought to represent about half the magma erupted in the 250 ka history of avf thus the avf has experienced a dramatic shift to prolonged and voluminous central vent volcanism in its most recent history this demonstrates the difficulty in determining time erupted volume relationships in such fields previous avf hazard risk modeling based on isolated short lived

viscoelastic thermal stress in cooling basalt flows polygonal fractures commonly form in basaltic lava flows during cooling of the molten lava a transient thermomechanical model is constructed to apply the temperature history in a cooling basalt flow as a boundary condition in a mechanical model of viscoelastic stress in cooling basalt nearly all past modeling of stress in cooling basalt has treated the material as purely elastic below a well defined glass transition temperature an important distinction of this model is that the viscosity of the material is allowed to be temperature dependent and the effects of viscoelastic relaxation are included on the basis of this research faster cooling and higher strain rates lead to markedly higher effective glass transition temperatures consistent with previous observations by researchers the total thermal strain in the system is constant yet the percentage of strain that is not relaxed by viscous flow varies with position relative to the cooling surface this elastic strain partition is the portion of the total strain that creates stress in the material and it is directly dependent on cooling rate thus a genetic link between cooling rate and magnitude of stress is identified

the snake river plain idaho representative of a new category of volcanism studies of the volcanic geology of the snake river plain idaho and comparison with other basaltic regions suggest a new category of volcanic activity termed basaltic plains volcanism typified by the snake river plain this style of volcanism is intermediate between basaltic flood or plateau eruptions and hawaiian volcanism characteristics that are common to both hawaiian and plains volcanism are multiple lava flow units which erupt primarily from point sources formation of low shields and frequent emplacement through lava tubes or channels characteristics that are common to both flood basalts and plains volcanism are high volume flows vents aligned along rift zones and planar surfaces the recognition of plains volcanism in other areas provides a means to interpret the style of eruption and volcanic history

structural evolution of a world class epithermal orebody the martha hill deposit waihi new zealand we describe the complex structure in the highest now mined out levels of the world class martha hill gold silver deposit coromandel peninsula which is hosted in late miocene andesitic rocks a northeast striking block of rock 360 m long and up to 100 m wide was occupied by a complex vein network dominated by northeast striking gold silver lodes up to 30 m thick gold production was entirely from quartz veins the mineralization is embedded in the following geological history 1 deposition of the host volcanic rocks 2 initial tectonic fracturing 3 intrusion of clastic dikes and sills 4 start of hydrothermal alteration 5 main phase of faulting 6 main phase of veining 7 erosion and deep oxidation 8 11 deposition of further volcanic material including prominent rhyolites and formation of present topography veins occupied fractures but also followed a network of preexisting mostly normal faults with a small to medium amount of displacement faulting involved northwest southeast north south and east west extension implying complex 3 d strain clastic dikes of carbonaceous sandstone intruded during the faulting phase fault rocks were mostly brittle cataclasites or breccias but some clay rich zones displayed ductile structures many veins overprinted faults with a change from shear mode to opening mode deformation stockwork veins formed a mesh composed of two orthogonal sets one with northeast southwest and northwest southeast striking veins including the dominant mineralized lodes and the other with north south and east west striking veins although northwest striking veins were earliest during the main vein phase opening oscillated between all the vein directions with the two main lodes in the open pit area the martha and the welcome capturing most of the strain a variety of vein and breccia textures indicate repeated structurally controlled vein opening events that were associated with changes in the physical and chemical conditions of the mineralizing fluid a special concentration of structural features facilitated focusing of fluid flow to produce this world class deposit which contrasts with the less well endowed vein systems around it the overall tectonic control was dominated by northwest southeast extension and dip slip deformation the 3 d strain in this area was not only due to local interference of differently oriented structural features but also to the superposition of regional tectonic north northwest and northeast trends associated with migration of a subduction zone past the coromandel peninsula this demonstrates that structural control in an epithermal mineral deposit may originate from a number of different tectonic controls at different scales

the morphology and formation of flow lobe tumuli on icelandic shield volcanoes three types of tumuli are recognized on monogenetic shield volcanoes in iceland namely 1 lava coated tumuli 2 upper slope tumuli and 3 flow lobe tumuli flow lobe tumuli grade into lava rises which are larger inflation structures but both structures have a similar mode of emplacement the areal distribution of flow lobe tumuli in the flow field differs from that of lava coated tumuli and upper slope tumuli flow lobe tumuli are frequent in the medial and distal parts of pahoehoe flow fields whereas the other two tumulus types are more frequent in the proximal parts of the flow fields the flow lobe tumuli also differ from the two other tumulus types as regards their morphology they are significantly larger have shallower flanks and do not have extensive outflows from the cracks the vesicle distribution within the flow lobe tumuli is similar to that of p type flow lobes a fairly dense zone is situated between the upper and lower vesicular zones each flow lobe tumulus is an individual lobe that inflates and forms tension cracks in the lava crust major lava tubes are mostly absent from the areas where flow lobe tumuli form and therefore the emplacement of flow lobe tumuli must be related to secondary short lived pathways of lava the flow lobe tumuli inside the flow fields of icelandic shield volcanoes are morphologically identical to those flow lobe tumuli that are found in the margins of flow fields of other icelandic volcanoes these observations allow us to model the flow lobe tumuli as morphological variants of p type flow lobes forming along terminating secondary lava paths flow lobe tumuli form at low lava supply rates of the order of 10 2 10 5 m3 s and are generated by inflation of the lava crust as a result of magmatic overpressure in the associated lava core we model the tumulus as a circular elastic plate that becomes uplifted inflated and fractured by a uniform magmatic overpressure at its bottom we conclude that 1 the effective thickness of the lava crust that is subject to bending is 0 2 0 4 m and remains essentially constant during the formation of the tumulus and 2 for flow lobe tumuli that are supplied with magma from tubes that originate in overflow from the lava lake of a shield volcano the elevation difference between the tumuli and the surface of the source lava lake is commonly around 100 m this elevation difference can give rise to a static magmatic overpressure of 2 5 mpa in the tumulus whereas the overpressure needed to form a typical flow lobe tumulus is only 0 2 1 mpa

physical characteristics of kimberlite and basaltic intraplate volcanism and implications of a biased kimberlite record we assess bias in the record of kimberlite volcanism by using newly acquired size data on more than 900 kimberlite bodies from 12 kimberlite fields eroded to depths of between 0 m and 1200 m and by a comparison with intraplate monogenetic basaltic volcanic fields eroded kimberlite fields are composed of pipes or diatremes and dikes and within any one kimberlite field regardless of erosion level kimberlite bodies vary in area at earth s surface over 2 3 orders of magnitude typically 60 70 of the bodies are

eruption recurrence rates in a basaltic volcanic field based on tephra layers in maar sediments implications for hazards in the auckland volcanic field long term eruption recurrence rates in monogenetic basaltic volcanic fields are difficult to assess because of low eruption frequencies but they are important because of the spread of human infrastructure into such fields auckland city new zealand is built on the auckland volcanic field a young 250 ka basaltic volcanic field in the absence of abundant material for radiocarbon and isotopic dating an eruptive chronology based on basalt tephra layers deposited in maar lakes was developed interbedded well dated tephra layers from silicic volcanoes some 220 270 km to the south were used as age constraints the basalt tephra layers reveal a pattern of activity not evident from the temporal spatial distribution of volcanic landforms twenty four basalt tephra layers over the last 80 k y represent an average frequency of one per 3 5 k y recurrence times vary from 0 5 k y to 20 k y and show no temporal trend the tephra record shows a major flare up in explosive activity at 32 2 ka during heightened activity at 34 24 ka this was related to a period of simultaneous eruptions from several volcanoes across the field revealed by paleomagnetic and isotopic ages in contrast the field has been relative quiet during the last 20 k y punctuated by the construction of a shield volcano at 0 7 ka thus the surface manifestation of magmatism varies greatly with time complicating long term volcanic hazard forecasting despite the high risk from future basalt activity because of proximity ash fall from distant andesite volcanoes is the most frequently occurring volcanic hazard in auckland city

controls on volcanism at intraplate basaltic volcanic fields a broad range of controlling mechanisms is described for intraplate basaltic volcanic fields ibvfs in the literature these correspond with those relating to shallow tectonic processes and to deep mantle plumes accurate measurement of the physical parameters of intraplate volcanism is fundamental to gain an understanding of the controlling factors that influence the scale and location of a specific ibvf detailed volume and geochronology data are required for this however these are not available for many ibvfs in this study the primary controls on magma genesis and transportation are established for the pliocene recent newer volcanics province nvp of south eastern australia as a case study for one of such ibvf the nvp is a large and spatio temporally complex ibvf that has been described as either being related to a deep mantle plume or upper mantle and crustal processes we use innovative high resolution aeromagnetic and 3d modelling analysis constrained by well log data to calculate its dimensions volume and long term eruptive flux our estimates suggest volcanic deposits cover an area of 23 100 530 km2 and have a preserved dense rock equivalent of erupted volcanics of least 680 km3 and may have been as large as 900 km3 the long term mean eruptive flux of the nvp is estimated between 0 15 and 0 20 km3 ka which is relatively high compared with other ibvfs our comparison with other ibvfs shows eruptive fluxes vary up to two orders of magnitude within individual fields most examples where a range of eruptive flux is available for an ibvf show a correlation between eruptive flux and the rate of local tectonic processes suggesting tectonic control limited age dating of the nvp has been used to suggest there were pulses in its eruptive flux which are not resolvable using current data these changes in eruptive flux are not directly relatable to the rate of any interpreted tectonic driver such as edge driven convection however the nvp and other ibvfs used for comparison have long term eruptive fluxes that are considerably less than definitive plume related volcanic systems along with their spatio temporal patterns and other analysis it is suggested that the nvp and the vast majority of low and high flux ibvfs appear to be the result of tectonic processes without requiring additional thermal input from a deep mantle source considering a control on volcanism by tectonic processes the range of eruptive flux of ibvfs is related to variations in the rate of the effecting tectonic process mantle composition and the size of the mantle source zone where melt generation and accumulation is taking place

a deterministic methodology for prediction of fracture distribution in basaltic multiflows the fracture distribution in basalt flows is a direct result of thermal processes thus basalt flows present a unique opportunity to characterize a nearly perfect deterministic system with its fundamental physical parameters fracture distribution data collected on cliff exposures of basalt flows near the idaho national engineering and environmental laboratory ineel are combined with calculations of cooling rate and temperature distribution from a finite element model to construct a predictive methodology for fracture spacing the methodology is based on an empirical power law relationship between inverse cooling rate and fracture spacing the methodology may be applied to unexposed basalt flows of approximately elliptical cross section whose thickness and width are constrained only by geophysical or borehole data if sufficient fracture data on nearby exposed flows are available the methodology aids waste remediation efforts at sites involving contaminant transport through fractured basalt such as the ineel and the hanford site in washington as well as involving transport and fluid flow through volcanic or intrusive rocks where thermal processes are responsible for fracturing

local scour at vertical wall abutments under clear water flow conditions 1 new clear water tests on abutment scour are presented thirty one tests with sand bed and nine tests with lightweight pumice bed were carried out in a 28 m long 4 m wide flume tests typically lasted for 1 week or more vertical wall abutments with length to depth l d ratios from 9 up to 36 were used other test campaigns in the literature are added to the data focusing on abutments with 2 l d 100 the critical flow for scour inception at the abutment nose is found to decrease as l d increases the whole data are analyzed for searching the equilibrium scour depths with different methods the slope change in the plot of scour depth against the logarithm of time is the method selected for the group of tests run close to the threshold condition some trends regarding the dimensionless equilibrium scour depth are 1 dependence on the bed material specific gravity in the sense that pumice tests produce less scour and 2 increase of the scour depth as l d increases finally the morphology of the scour area in terms of volume and plan dimensions is given by new regression equations