localization of a coal seam fire using combined self potential and resistivity data abstract the remediation of coal seam fires requires as a first step the precise localization of the burning front various geophysical methods can be employed for this purpose but not all of them can provide an unambiguous localization of this type of target we propose a combined inversion of self potential and resistivity data and the use of joint attributes characterizing the target to localize the burning front of a coal seam fire this new methodology is applied to the 3d reconstruction of a shallow coal seam fire in boulder colorado the coal seam fire is located in the gorham subbituminous coal formation at a depth comprised between 10 and 15 m the self potential survey comprises 160 stations 5 profiles and 32 stations per profile located at the ground surface with self potential anomalies amounting 70 to 50 mv with respect to an arbitrary reference located further away from the burning front the resistivity survey comprises 5 resistivity profiles with 118 measurements per profile 590 measurements in total the burning front is associated with very low value of the electrical resistivity

the crystallization of lava lakes thermal convection driven by the kinetic undercooling of solidification can produce compositional and textural variations in an initially uniform lava flow that is cooled predominantly from above we show that such kinetic undercooling is sufficient to drive convection at high rayleigh numbers even in shallow lava lakes we then employ a theoretical model that includes the effects of convection at high rayleigh number to make predictions of the complete evolution of the lava we show that predictions of the rate of growth of solid crust at the surface of the lake do not differ much from predictions made by ignoring effects due to convection however convective motions do shorten the time for complete solidification because when they are driven by kinetic undercooling there is internal crystallization in addition to that occurring near the cooled upper boundary of the lava this important effect which is absent from purely conductive models predicts stratification and zonation of the lava in agreement with field observations we also examine the effect of taking into account the heat transfer to the country rock below the lava lake and determine how the evolution of the lava lake varies with the viscosity of the lava

flowgo a kinematic thermo rheological model for lava flowing in a channel we present a kinematic self adaptive numerical model to describe the down flow thermal and rheological evolution of channel contained lava as our control volume of lava advances down a channel it cools and crystallizes an increasingly thick and extensive surface crust grows and its heat budget and rheology evolve by estimating down flow heat and velocity loss our model calculates the point at which the control volume becomes stationary giving the maximum distance lava flowing in the channel can extend modeled effusion rates velocities widths surface crust parameters heat budget cooling temperature crystallinity viscosity and yield strength all compare well with field data collected during eruptions at mauna loa k lauea and etna modeled lengths of 25 27 2 5 5 7 and 0 59 0 83 km compare with measured lengths of 25 27 4 and 0 75 km for the three flows respectively over proximal flow portions we calculate cooling crystallization viscosity and yield strength of 1 10 c km 1 0 001 0 01 volume fraction km 1 103 104 pa s and 10 3 102 pa respectively at the flow front cooling crystallization viscosity and yield strength increase to 100 c km 1 0 1 volume fraction km 1 106 107 pa s and 103 104 pa respectively all of which combine to cause the lava to stop flowing our model presents a means of a analyzing lava flow thermo rheological relationships b identifying important factors in determining how far a channel fed flow can extend c assessing lava flow hazard and d reconstructing flow regimes at prehistoric unobserved or remote flows

surf zone currents over irregular bathymetry drifter observations and numerical simulations 1 surf zone currents over irregular bathymetry were observed with gps tracked drifters and modeled with the depth integrated nonlinear shallow water equations trajectories of drifters released in 1 2 m depth sometimes defined rip currents and surf zone eddies features that have been difficult to resolve with fixed instruments the drifter delineated surf zone circulation evolved as the tidal level changed during each 4 6 hour deployment in one case as the tide dropped a shore normal rip current present for the first 2 hours evolved to a more shore parallel flow in a second case on a rising tide a well developed bifurcated rip current was replaced by a weak amorphous circulation rip current velocities were strongest near the surf zone edge and decayed by an order of magnitude within 2 surf zone widths from the shoreline an eddy was observed to persist over a bathymetric depression within the surf zone for at least 1 hour observed and numerically simulated drifter trajectories define similar flow features but the observed and modeled velocities differed by roughly a factor of 2 and flow evolution observed during roughly 0 5 m changes in tidal level were reproduced only if the simulated water levels varied by about 1 m the alongshore momentum balance was spatially variable with wave forcing balanced by pressure gradient friction and advective terms the cross shore momentum balance was everywhere dominated by wave forcing and pressure gradient terms of about equal magnitude in the vicinity of a simulated rip current the residual of the cross shore wave forcing and pressure gradient increased and was balanced by advection terms

formation of lava tubes and extensive flow field during the 1991 1993 eruption of mount etna detailed mapping during the 1991 1993 eruption of mount etna has shown that there is a relationship between tumuli ephemeral vents lava tubes and their parent lava flows during this eruption many tubes formed in stationary inflated a a lava flows ephemeral vents at the fronts of these stationary flows and above lava tubes fed secondary lava flows many of which subsequently developed new tubes the resulting complex network of tubes ephemeral vents and secondary flows was responsible for most of the widening thickening and lengthening of the 1991 1993 etna lava flow field the supply of relatively uncooled lava via tubes to distal parts of this flow field allowed lava to flow 3 km farther from the vent than the longest channel fed lava flow our observations suggest that lava tubes play a more important role in the formation of extensive a a flow fields on etna than has previously been recognized

heat transfer in magma in situ heat transfer rates in a basaltic magma were measured under typical magma chamber conditions and a numerical model of the experiment was used to estimate magma viscosity the results are of value for assessing methods of thermal energy extraction from magma bodies in the upper crust as well as for modeling the evolutionary track of these systems

coupling mechanisms in double sandbar systems part 1 patterns and physical explanation crescentic sandbars and rip channels along wave dominated sandy beaches are relevant to understand localized beach and dune erosion during storms in recent years a paradigm shift from hydrodynamic template models to self organization mechanisms occurred to explain the formation of these rhythmic features in double sandbar systems both the inner and outer bar rip channels and crescentic planshapes are now believed to be free instabilities of the nearshore system arising through self organization mechanisms alone however the occasional occurrence of one or two inner bar rip channels within one outer bar crescent suggests a forced morphologically coupled origin here we use a nonlinear morphodynamic model to show that alongshore variability in outer bar depth and the relative importance of wave breaking versus wave focussing by refraction across the outer bar is crucial to the inner bar rip channel development the coupling patterns simulated by our model are similar to those observed in the field morphological coupling requires a template in the morphology outer bar geometry which through the positive feedback between flow sediment transport and the evolving morphology that is self organization enforces the development of coupling patterns we therefore introduce a novel mechanism that blurs the distinction between self organization and template mechanisms this mechanism may also be extended to explain the dynamics of other nearshore patterns such as beach cusps the impact of this novel mechanism on the alongshore variability of inner bar rip channels is investigated in the companion paper copyright 2010 john wiley and sons ltd

toothpaste lava characteristics and origin of a lava structural type transitional between pahoehoe and aa toothpaste lava an important basalt structural type which illustrates the transition from pahoehoe to aa is particularly well displayed on the 1960 kapoho lava of kilauea volcano its transitional features stem from a viscosity higher than that of pahoehoe and a rate of flow slower than that of aa viscosity can be quantified by the limited settling of olivine phenocrysts and rate of flow by field observations related to the low angle slope on which the lava flowed much can be learned about the viscosity rheologic condition and flow velocity of lavas long after solidification by analyses of their structural characteristics and it is possible to make at least a semiquantitative assessment of the numerical values of these parameters

pahoehoe and aa in hawaii volumetric flow rate controls the lava structure the historical records of kilauea and mauna loa volcanoes reveal that the rough surfaced variety of basalt lava called aa forms when lava flows at a high volumetric rate 5 10 m3 s and the smooth surfaced variety called pahoehoe forms at a low volumetric rate 5 10 m3 s this relationship is well illustrated by the 1983 1990 and 1969 1974 eruptions of kilauea and the recent eruptions of mauna loa it is also illustrated by the eruptions that produced the remarkable paired flows of mauna loa in which aa formed during an initial short period of high discharge rate associated with high fountaining and was followed by the eruption of pahoehoe over a sustained period at a low discharge rate with little or no fountaining the finest examples of paired lava flows are those of 1859 and 1880 1881 we attribute aa formation to rapid and concentrated flow in open channels there rapid heat loss causes an increase in viscosity to a threshold value that varies depending on the actual flow velocity at which when surface crust is torn by differential flow the underlying lava is unable to move sufficiently fast to heal the tear we attribute pahoehoe formation to the flowage of lava at a low volumetric rate commonly in tubes that minimize heat loss flow units of pahoehoe are small usually 1 m thick move slowly develop a chilled skin and become virtually static before the viscosity has risen to the threshold value we infer that the high discharge rate eruptions that generate aa flows result from the rapid emptying of major or subsidiary magma chambers rapid near surface vesiculation of gas rich magma leads to eruptions with high discharge rates high lava fountains and fast moving channelized flows we also infer that long periods of sustained flow at a low discharge rate which favor pahoehoe result from the development of a free and unimpeded pathway from the deep plumbing system of the volcano and the separation of gases from the magma before eruption achievement of this condition requires one or more episodes of rapid magma excursion through the rift zone to establish a stable magma pathway

a morphological stability analysis for a long straight barred coast a morphological stability analysis is carried out for a long straight coast with a longshore bar the situation with oblique wave incidence and a wave driven longshore current is considered the flow and sediment transport are described by a numerical modelling system the models comprise i a wave model with depth refraction shoaling and wave breaking ii a depth integrated model for wave driven currents and iii a sediment transport model for the bed load transport and the suspended load transport in combined waves and current the direction of the sediment transport is taken to be parallel to the depth integrated mean current velocity neglecting the effects of a bed slope and secondary currents an instability is found to develop around the bar crest the instability is periodic in the alongshore direction and tends to form rip channels and to steepen the offshore face of the bar between the rip channels the alongshore wave length of the most unstable perturbation is determined for different combinations of the wave conditions and the geometry of the profile

numerical modeling of lava flow cooling applied to the 1997 okmok eruption approach and analysis 1 throughout february and march of 1997 okmok volcano in the eastern aleutian islands of alaska erupted a 6 km long lava flow of basaltic a a within its caldera a numerical model for lava flow cooling was developed and applied to the flow to better understand the nature of its cooling radiation and convection from the surface as well as conduction to the ground were used to transport the flow s heat to its surroundings in the model internally a conduction only approach moved heat from the interior outward vesiculation latent heat generation and thermal conductivity changes with temperature are among the other factors that were dynamically accounted for results indicate that ambient temperature fluctuations on the scale of days to weeks must be taken into account to create an accurate short term prediction of lava surface temperature daily data of rainfall and ambient temperature as opposed to yearly averages greatly increased the accuracy of the model furthermore convective cooling of the lava surface was observed to be a dominant heat loss process during the first 200 days indicating the convective heat transfer coefficient is a prime determinant of the accuracy of the model for predicting surface temperatures over a longer cooling period 2 years thermal conductivity and porosity proved to be among the dominating factors for heat loss because of the limiting role of conductive heat flow in the interior the model s flexibility allows application to flows other than the 1997 okmok eruption

calculation of lava effusion rates from landsat tm data we present a thermal model to calculate the total thermal flux for lava flowing in tubes on the surface or under shallow water once defined we use the total thermal flux to estimate effusion rates for active flows at kilauea hawaii on two dates input parameters were derived from landsat thematic mapper tm field and laboratory measurements using these parameters we obtain effusion rates of 1 76 0 57 and 0 78 0 27 m3 s 1 on 23 july and 11 october 1991 respectively these rates are corroborated by field measurements of 1 36 0 14 and 0 89 0 09 m3 s 1 for the same dates kauahikaua et al 1996 using weather satellite avhrr data of lower spatial resolution we obtain similar effusion rates for an additional 26 dates between the two tm derived measurements we assume that although total effusion rates at the source declined over the period the shut down of the ocean entry meant that effusion rates for the surface flows alone remained stable such synergetic use of remotely sensed data provides measurements that can a contribute to monitoring flow field evolution and b provide reliable numerical data for input into rheological and thermal models we look forward to being able to produce estimates for effusion rates using data from high spatial resolution sensors in the earth observing system eos era such as landsat 7 the hyperspectral imager the advanced spaceborne thermal emission spectrometer and the advanced land imager

development of lava tubes in the light of observations at mauna ulu kilauea volcano hawaii during the 1969 1974 mauna ulu eruption on kilauea s upper east rift zone lava tubes were observed to develop by four principal processes 1 flat rooted crusts grew across streams within confined channels 2 overflows and spatter accreted to levees to build arched roofs across streams 3 plates of solidified crust floating downstream coalesced to form a roof and 4 pahoehoe lobes progressively extended fed by networks of distributaries beneath a solidified crust still another tube forming process operated when pahoehoe entered the ocean large waves would abruptly chill a crust across the entire surface of a molten stream crossing through the surf zone these littoral lava tubes formed abruptly in contrast to subaerial tubes which formed gradually all tube forming processes were favored by low to moderate volume rates of flow for sustained periods of time tubes thereby became ubiquitous within the pahoehoe flows and distributed a very large proportionof the lava that was produced during this prolonged eruption tubes transport lava efficiently once formed the roofs of tubes insulate the active streams within allowing the lava to retain its fluidity for a longer time than if exposed directly to ambient air temperature thus the flows can travel greater distances and spread over wider areas even though supply rates during most of 1970 1974 were moderate ranging from 1 to 5 m3 s large tube systems conducted lava as far as the coast 12 13 km distant where they fed extensive pahoehoe fields on the coastal flats some flows entered the sea to build lava deltas and add new land to the island the largest and most efficient tubes developed during periods of sustained extrusion when new lava was being supplied at nearly constant rates tubes can play a major role in building volcanic edifices with gentle slopes because they can deliver a substantial fraction of lava erupted at low to moderate rates to sites far down the flank of a volcano we conclude therefore that the tendency of active pahoehoe flows to form lava tubes is a significant factor in producing the common shield morphology of basaltic volcanoes

rip currents mega cusps and eroding dunes abstract dune erosion is shown to occur at the embayment of beach mega cusps o 200 m alongshore that are associated with rip currents the beach is the narrowest at the embayment of the mega cusps allowing the swash of large storm waves coincident with high tides to reach the toe of the dune to undercut the dune and to cause dune erosion field measurements of dune beach and rip current morphology are acquired along an 18 km shoreline in southern monterey bay california this section of the bay consists of a sandy shoreline backed by extensive dunes rising to heights exceeding 40 m there is a large increase in wave height going from small wave heights in the shadow of a headland to the center of the bay where convergence of waves owing to refraction over the monterey bay submarine canyon results in larger wave heights the large alongshore gradient in wave height results in a concomitant alongshore gradient in morphodynamic scale the strongly refracted waves and narrow bay aperture result in near normal wave incidence resulting in well developed persistent rip currents along the entire shoreline the alongshore variations of the cuspate shoreline are found significantly correlated with the alongshore variations in rip spacing at 95 confidence the alongshore variations of the volume of dune erosion are found significantly correlated with alongshore variations of the cuspate shoreline at 95 confidence therefore it is concluded the mega cusps are associated with rip currents and that the location of dune erosion is associated with the embayment of the mega cusp

role of morphological variability in the evolution of nearshore sandbars abstract computations using a depth averaged morphological process based model of a double nearshore bar system have been used to test the hypothesis that bathymetries with small variability adapt more easily to new hydrodynamic conditions than bathymetries with distinctly imprinted crescentic patterns the computations are used to investigate the assumption that nearshore bathymetries tend to evolve toward a rip channelled pattern matching concurrent constant hydrodynamic forcing if these conditions prevail for an extended period of time in each computation an initially alongshore uniform double barred bathymetry seeded with a small random bed level perturbation was forced by two sequential constant hydrodynamic conditions for each set of conditions four different computations show the effect of a later transition moment and thus more distinctly evolved patterns on the level of adaptation to the second condition after the transition to the second condition different hydrodynamic circulations occur due to differences in the bathymetry at the transition moments depending on how pronounced the existing features were at the moment of transition these circulations either reinforce the existing bathymetric pattern or allow the bathymetry to evolve to a new rip chanelled pattern with a spacing similar to the one that occurs if the second condition had been applied from the start as hydrodynamic conditions generally change more rapidly than the adaptation time which is at least in the order of days it is highly unlikely that observed rip channel distances match length scales expected for concurrent hydrodynamic conditions consistent with field observations e g holman et al 2006 it is therefore concluded that nearshore patterns are formed by a combination of both the antecedent morphology and thus antecedent hydrodynamics and the current local hydrodynamic conditions next to factors like sediment characteristics

generation and nonlinear evolution of shore oblique transverse sand bars the coupling between topography waves and currents in the surf zone may self organize to produce the formation of shore transverse or shore oblique sand bars on an otherwise alongshore uniform beach in the absence of shore parallel bars this has been shown by previous studies of linear stability analysis but is now extended to the finite amplitude regime to this end a nonlinear model coupling wave transformation and breaking a shallow water equations solver sediment transport and bed updating is developed the sediment flux consists of a stirring factor multiplied by the depth averaged current plus a downslope correction it is found that the cross shore profile of the ratio of stirring factor to water depth together with the wave incidence angle primarily determine the shape and the type of bars either transverse or oblique to the shore in the latter case they can open an acute angle against the current up current oriented or with the current down current oriented at the initial stages of development both the intensity of the instability which is responsible for the formation of the bars and the damping due to downslope transport grow at a similar rate with bar amplitude the former being somewhat stronger as bars keep on growing their finite amplitude shape either enhances downslope transport or weakens the instability mechanism so that an equilibrium between both opposing tendencies occurs leading to a final saturated amplitude the overall shape of the saturated bars in plan view is similar to that of the small amplitude ones however the final spacings may be up to a factor of 2 larger and final celerities can also be about a factor of 2 smaller or larger in the case of alongshore migrating bars the asymmetry of the longshore sections the lee being steeper than the stoss is well reproduced complex dynamics with merging and splitting of individual bars sometimes occur finally in the case of shore normal incidence the rip currents in the troughs between the bars are jet like while the onshore return flow is wider and weaker as is observed in nature

a mechanism for the generation of wave driven rhythmic patterns in the surf zone the coupling between topographic irregularities and wave driven mean water motion in the surf zone is examined this coupling occurs because the topographic perturbations produce excess gradients in the wave radiation stress that cause a steady circulation this circulation in turn creates a sediment transport pattern that can reinforce the bottom disturbance and may thereby lead to the growth of large scale bed forms to investigate this coupling mechanism the linearized stability problem with an originally plane sloping beach and normal wave incidence is solved in two different cases first the breaking line is considered to be fixed and second the perturbations in water depth that produce a displacement of the breaker line are accounted for the first case shows that the basic topography can be unstable with respect to two different modes a giant cusp pattern with shore attached transverse bars that extend across the whole surf zone and a crescentic pattern with alternate shoals and pools at both sides of the breaking line showing a mirroring effect in the second case the varying breaker line may have a strong influence on the circulation this is clear for the giant cusp topography whose growth is totally inhibited in contrast the morphology and the growth of the crescentic pattern remains almost unchanged

coupling mechanisms in double sandbar systems part 2 impact on alongshore variability of inner bar rip channels double sandbar systems are common morphological features along sandy wave dominated micro to meso tidal coastlines in the companion paper we demonstrated how various alongshore inner bar rip channel patterns can develop through morphological coupling to an alongshore variable outer bar the simulated coupling patterns are however scarcely observed in the field instead inner bar rip channels more often possess remarkably smaller and more variable alongshore length scales suggesting that coupling mechanisms do not play a substantial role in the overall double sandbar dynamics here we use a numerical model to show that the relative importance of self organization and morphological coupling changes in favour of the latter with an increase in waterdepth variability along the outer bar crest furthermore we find that the typical alongshore variability in inner bar rip channel scale is indicative of a mixture of self organization and morphological coupling rather than self organization alone morphological coupling may thus be more important to understanding and predicting the evolution of inner bar rip channels than previously envisaged copyright 2010 john wiley and sons ltd

observations and conceptual modelling of morphological coupling in a double sandbar system nearshore sandbars located in 10 m water depth can contain remarkably periodic alongshore undulations in both cross shore position and depth in a double sandbar system the alongshore spacing of these morphological patterns in the inner sandbar may be identical to those in the outer sandbar although this morphological coupling has been observed previously its frequency and predominance remain unclear in this paper we use a 9 3 year dataset of daily low tide time exposure images from the double barred beach at surfers paradise gold coast australia to analyse the temporal and spatial characteristics of morphological coupling within a double sandbar system we distinguish five types of morphological coupling between the inner and outer sandbars of which four coincide with a downstate progression of the outer bar coupling is either in phase with a landward perturbation of the inner bar facing an outer bar horn or out of phase with a seaward perturbation of the inner bar facing an outer bar horn where the coupled inner bar features either consist of rip channels or predominantly perturbations of the low tide terrace cross correlation of the image derived inner and outer bar patterns shows coupling to be a common phenomenon in the double sandbar system studied here with coupling in 40 of the observations in contrast to previous observations of sandbar shoreline coupling at single barred beaches in phase coupling 85 of all coupled bar patterns predominates over out of phase coupling 15 based on our observations and bathymetries assimilated from the images for a restricted set of coupling events we hypothesize that the angle of offshore wave incidence wave height and depth variations along the outer sandbar determine the type of flow pattern cell circulations versus meandering currents above the inner bar and hence steer the type of coupling copyright 2012 john wiley sons ltd

an energetics total load sediment transport model for a plane sloping beach bagnold s energetics based total load sediment transport model for streams is used as a basis for the development of a total load model of time varying sediment transport over a plane sloping bed in both the bedload and suspended load the transport rate vectors are found to be composed of a velocity induced component directed parallel to the instantaneous velocity vector and a gravity induced component directed down slope the model is applied to idealized surfzone conditions leading to estimates of the local longshore and onshore offshore sediment transport rates as well as the equilibrium beach slope as a function of the local wave and current conditions the model is combined with a nonlinear longshore current model and spatially integrated to obtain predictions of the total longshore transport rate as a function of the incident wave conditions the results support the general form of the wave power equation except that the wave power coefficient is no longer constant but is instead a complex function of the incident wave and beach characteristics

an empirical function to estimate the depths of linear hot sources laboratory modeling and field measurements of lava tubes estimating depths of buried lava tubes is important for determining the thermal budgets and effusion rates of basaltic volcanic systems this research used a laboratory experiment scaled to a lava tube system to measure the 3d temperature field surrounding a hot viscous fluid flowing through a buried glass tube while varying conditions such as flow rate and temperature the depth of the glass tube was changed for different experimental runs numerical techniques were applied to model the laboratory experiment the surface thermal distributions from 166 thermal traverses constrained to a depth to width ratio of 0 6 to 1 6 were analyzed to empirically derive a depth estimation function using regression techniques this linear anomaly surface transect last depth function is a scaleable depth estimation technique which can be solved with thermal imaging data alone the minimum temperature maximum temperature and width of a lorentzian distribution fit to a surface thermal transect are the only inputs required for the last function to estimate the depths of the hot source the input parameters were then applied to non laboratory situations including the kuhio lava tube system in hawai i the last function produced depth estimates of 0 3 m for the kuhio lava tube in hawai i which did not agree with observations on the ground this is the result of the complex composition and geometry of an actual lava tube where heat transfer is controlled by more than a simple fluid filling a tube but also by convection of gasses and fluids in a partially filled passage though not effective for lava tubes at this time the model provides promising results for simple cases applied to engineering and underground coal fires

double bar beach dynamics on the high energy meso macrotidal french aquitanian coast a review the french aquitanian coast is an approximately 250 km long straight low coast exposed to high energy conditions in a mesomacrotidal setting offshore wave conditions are seasonally modulated predominantly with a wnw incidence with offshore significant wave height likely to reach 10 m during winter truc vert beach representative of most of the aquitanian coast beaches commonly exhibitstwodistinctsandbarsystems theinnerbarcangothroughallthestateswithintheintermediateclassificationandusuallyexhibitsa tansversebarandripmorphology afterafewweeksoflowerenergyconditionsduringsummer theinnerbarcommonlybecomesalow tideterracewithameanwavelengthof400mandameansoutherlymigrationrateofabout2 3m day crescenticbarshavebeenreported in the literature in nontidal to microtidal settings long term persistent crescentic patterns are however exhibited at a narrow range of wavelength mean of 700m by the outer bar at the meso macrotidal truc vert beach most of the time the outer bar is inactive and stagnates as offshore waves ofhsn3 m are required to induce a significant morphological change the crescent shape varies from a symmetric shape to a strongly asymmetric shape likely to be the result of a long period of nw wave conditions a strong and rarely observed elsewhere morphological coupling between the inner and outer bars can sometimes be observed and may be the result of the combined effectsof the initial presence of a well developed outer crescentic bar and a long period of shore normal low energy conditions a synthesis of all the data available on the area combined with observations on other environments leads to a truc vert beach state model ranging from a modal double bar configuration to an occasional triple bar configuration this work also identifies knowledge gaps to be explored by further numerical and field studies in tidal double sandbar environments 2007 elsevier b v all rights reserved

flow and convective cooling in lava tubes tube fed basaltic lava flows with lengths ranging from 10 to 200 km are inferred to exhibit similar amounts of cooling to explain the wide range of implied cooling rates we consider forced convection as a dominant cooling process in lava tubes and present solutions that express mean temperature versus distance down the tube as a function of flow rate and flow cross section our models treat forced convective thermal losses in steady laminar flow through a lava tube with constant temperature walls and constant material properties we explore the effects of different wall temperature and heat flux rate boundary conditions for circular tube and parallel plate flows over a range of tube sizes plate spacings eruption temperatures and volume flow rates results show that nonlinear cooling rates over distance are characteristic of constant wall temperature for a piecewise parallel plate circular tube model this provides the best fit to temperature observations for hawaiian tubes such a model may also provide an explanation for the very low 10 c cooling observed in 10 km long hawaii tube flows and inferred in longer 50 to 150 km tube fed flows in queensland the forced convective cooling model may also explain similar flow morphologies for long tube fed basaltic lava flows in a wide variety of locations since small variations in eruption temperature or flow rate can accommodate the entire range of flow lengths and cooling rates considered our results are consistent with previous suggestions that long basaltic flows may be a reflection of low slopes a particularly steady moderate eruption rate and well insulated flow rather than of high discharge rates

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

the initial cooling of pahoehoe flow lobes in this paper we describe a new thermal model for the initial cooling of pahoehoe lava flows the accurate modeling of this initial cooling is important for understanding the formation of the distinctive surface textures on pahoehoe lava flows as well as being the first step in modeling such key pahoehoe emplacement processes as lava flow inflation and lava tube formation this model is constructed from the physical phenomena observed to control the initial cooling of pahoehoe flows and is not an empirical fit to field data we find that the only significant processes are a heat loss by thermal radiation b heat loss by atmospheric convection c heat transport within the flow by conduction with temperature and porosity dependent thermal properties and d the release of latent heat during crystallization the numerical model is better able to reproduce field measurements made in hawai i between 1989 and 1993 than other published thermal models by adjusting one parameter at a time the effect of each of the input parameters on the cooling rate was determined we show that a the surfaces of porous flows cool more quickly than the surfaces of dense flows b the surface cooling is very sensitive to the efficiency of atmospheric convective cooling and c changes in the glass forming tendency of the lava may have observable petrographic and thermal signatures these model results provide a quantitative explanation for the recently observed relationship between the surface cooling rate of pahoehoe lobes and the porosity of those lobes jones 1992 1993 the predicted sensitivity of cooling to atmospheric convection suggests a simple field experiment for verification and the model provides a tool to begin studies of the dynamic crystallization of real lavas future versions of the model can also be made applicable to extraterrestrial submarine silicic and pyroclastic flows

extended cooling and viscous flow of large hot rhyolite lavas implications of numerical modeling results abstract a common misconception about rhyolite lava flows is that they cannot advance far from their vents and are constrained to be small due to their high viscosities although a high viscosity lava will indeed flow quite slowly it may advance a great distance if the lava efficiently retains heat and thus mobility and if the available magma supply is large to evaluate this possibility a finite difference numerical model was used to determine the rate of heat loss from units interpreted to be large rhyolite lavas cooling of such 100 300 m thick units is very slow and is further retarded by a vesicular carapace and by evolution of latent heat thermal history alone suggests that large thick lava flows could remain active for several decades to constrain the duration of flow advance of these units their inferred apparent viscosities are compared with those of active lava flows mean flow velocity of some large rhyolites in southwestern idaho usa was estimated based on the observation that the units must still have been advancing by viscous flow at the start of spherulite crystallization indicating perhaps a 10 to 18 year flow duration based on studies of obsidian dome california mean flow velocities would have been roughly 0 59 to 2 5 km yr and calculated average apparent viscosities of the flows ranged from 1 8 to 3 6 orders of magnitude greater than the viscosity of the lava itself this relationship also holds for active andesite and basaltic andesite block lava flows which have apparent viscosities 2 7 to 4 orders of magnitude greater than lava viscosities this implies that large rhyolites may indeed have been emplaced in the same manner as less silicic block lavas and that long distance viscous flow is not unrealistic for rhyolite lavas a good example of a large volume lava is the 15 km 3 rhyolite of the badlands sw idaho where vent relations show that lava effused from a fissure and advanced up to 9 km more extensive rhyolites could also be emplaced solely by effusion extended flow of these lavas may lead to the remelting and removal of basal crumble breccias and to the formation of welded shard textures in their margins both processes tending to obscure the lava flow origin of the units the great dimensions of lava like rhyolitic units with volumes of 10 to at least 200 km 3 are not a sufficient reason to assume they erupted as ignimbrites

nearshore circulation over transverse bar and rip morphology with oblique wave forcing there is a paucity of field data to describe the transition in nearshore circulation between alongshore meandering and rip current systems a combination of in situ current meters and surf zone drifters are used to characterize the nearshore circulation over a transverse bar and rip morphology at pensacola beach florida in the presence of relatively low energy oblique waves current speeds vary in response to the relative wave height ratio hs h which defines the degree and extent of breaking over the shoal in the absence of wave breaking the nearshore circulation was dominated by an alongshore current driven by the oblique waves as waves begin to break across the shoal 0 2 0 5 the meandering current is replaced by an unsteady rip circulation that moves offshore between the shoals before turning alongshore in the direction of wave advance outside the surf zone the increase in wave dissipation is associated with an increase in very low frequency vlf variations in the current speed across the shoal and in the rip channel that caused the circulation to oscillate between an offshore and an alongshore flow the unsteady nature of the nearshore circulation is responsible for 55 of all surf zone exits under these more dissipative conditions in contrast only 29 of the drifters released from the shoal exited the surf zone and bypassed the adjacent shoal with the alongshore meandering current while the currents had a low velocity maximum of 0 4 m s 1 and would not pose a significant hazard to the average swimmer the results of this study suggest that the transverse bar and rip morphology is sufficient to create an alongshore variation in wave dissipation that forces alongshore meandering and low energy rip circulation systems under oblique wave forcing copyright 2013 john wiley sons ltd

a mechanism for sandbar straightening by oblique wave incidence 1 breaker bars in the surf zone of sandy beaches generally evolve between straight bars parallel to the shore and meandering crescentic bars associated with intense dangerous currents flowing seaward through rip channels understanding the behavior of such systems is fundamental as they control the entire surf zone dynamics the shape of the coastline and the exchange of floating material with the shoreface although the mechanisms behind the meandering of an originally straight bar have been studied extensively a clear physical explanation on the crescentic bar straightening was missing recent field observations have highlighted that this morphological reset can be due to wave obliquity by using a two dimensional horizontal morphological model we show that the bar straightening by oblique waves occurs because the rip current is both weakened in intensity and shifted downdrift from the channel deepest section the technique employed is useful for the study of other types of bed forms

coupled and noncoupled behavior of three dimensional morphological patterns in a double sandbar system 1 eight weeks of daily low tide time exposure images of the gold coast australia were used to analyze the development of three dimensional morphological patterns in a double sandbar system under continued low energy wave conditions following a morphological reset storm event the patterns in both the inner and outer bar evolved albeit at different spatial and temporal scales through the accretionary sequence commonly observed at single barred beaches continuous wavelet transforms cwt of the inner bar and outer bar breaker lines show that after a storm the patterns developed at a wide range of alongshore wavelengths and that variations in wavelength over space and time were common with the bivariate extension of cwt continuous cross wavelet transforms it is found that the initial inner bar and outer bar three dimensional patterns were spatially noncoupled however over time the inner bar morphology appeared to couple with that of the outer bar with the inner bar patterns developing in response to the increasingly three dimensional onshore propagating outer bar the wavelet analysis suggests that the outer bar geometry and the distance between the inner and outer bars are critical parameters governing the morphological evolution of the composite double sandbar system

morphodynamics of intermediate beaches a video imaging and numerical modelling study four years of time exposure images of palm beach sydney australia are used to a develop a phenomenological scheme based on surf zone properties for the classification of the four intermediate beach states low tide terrace ltt transverse bar rip tbr rhythmic bar beach rbb and longshore bar trough lbt identified by wright l d short a d 1984 morphodynamic variability of surf zones and beaches marine geology 56 93 118 and b determine environmental conditions associated with the different beach states the overall agreement between beach state classifications obtained by visual classifications of images and those predicted by the phenomenological scheme exceeds 90 analysis of time series of intermediate beach states and wave data indicates that the nearshore morphology continuously cycles through the four beach states in response to variations in the incident wave energy the results also indicate that lbt morphology is produced by high energy wave conditions erosive while the progression towards ltt occurs under lower waves accretive a depth averaged morphodynamic model is employed to determine the morphodynamic processes governing the rbb to tbr and tbr to ltt transitions model results indicate that the rbb to tbr transition is governed by the erosion of the original longshore bars in the initial rbb morphology and the formation and subsequent welding of shoals in the lee of the original longshore bars model results also indicate that rbb to tbr transitions can occur under shore normal and oblique wave conditions the tbr to ltt model simulations indicate that under obliquely incident waves progressive erosion of the transverse shoals and deposition of the eroded sediment in rip channels gradually diminishes the longshore variability in morphology resulting in an ltt morphology

alongshore rip channel migration and sediment transport abstract the relationship between alongshore rip channel migration and sediment transport is investigated using time averaged video images to identify the positions of rip channels at three sites along southern monterey bay california over 1 3 year periods daily migration rates are calculated for each site the basic coastal engineering research center cerc formula for bulk alongshore sediment transport is used to estimate alongshore transport rates at each site based on hourly input of directional wave spectra measured at an offshore buoy and shoaled and refracted to the nearshore the wave transformation model is validated by comparison with measured nearshore directional wave spectra in 13 m water depth an expanded cerc formulation that accounts for the additional forcing of alongshore wave height gradients is also tested but rejected correlation coefficients between daily rates of calculated alongshore transport and rip channel migration are low 0 01 0 44 and 0 38 at the sand city stilwell and marina sites respectively the problem of digitization noise associated with video based rip channel identification is discussed and several filtering methods are used to increase the signal to noise ratio and obtain improved correlations results indicate that higher frequency migration events on time scales shorter than 8 days will likely be obscured below the digitization noise floor but that longer period oscillations such as tidal and seasonal cycles show up clearly in both rip migration and sediment transport datasets daily rates are cumulatively summed to generate time series of representative overall rip migration distance and net alongshore transport and the cumulative summing procedure is shown to be similar to applying a low pass filter mean migration is demonstrated to lag behind net transport in the summertime suggesting that a minimum level of alongshore forcing is required to generate detectable rip migration rip channel migration and net alongshore transport have correlation coefficients that range from 0 76 to 0 94 at the three sites

development of the 1990 kalapana flow field kilauea volcano hawaii the 1990 kalapana flow field is a complex patchwork of tube fed pahoehoe flows erupted from the kupaianaha vent at a low effusion rate approximately 3 5 m3 s these flows accumulated over an 11 month period on the coastal plain of kilauea volcano where the pre eruption slope angle was less than 2 the composite field thickened by the addition of new flows to its surface as well as by inflation of these flows and flows emplaced earlier two major flow types were identified during the development of the flow field large primary flows and smaller breakouts that extruded from inflated primary flows primary flows advanced more quickly and covered new land at a much higher rate than breakouts the cumulative area covered by breakouts exceeded that of primary flows although breakouts frequently covered areas already buried by recent flows lava tubes established within primary flows were longer lived than those formed within breakouts and were often reoccupied by lava after a brief hiatus in supply tubes within breakouts were never reoccupied once the supply was interrupted during intervals of steady supply from the vent the daily areal coverage by lava in kalapana was constant whereas the forward advance of the flows was sporadic this implies that planimetric area rather than flow length provides the best indicator of effusion rate for pahoehoe flow fields that form on lowangle slopes

observations on basaltic lava streams in tubes from kilauea volcano island of hawai i from 1986 to 1997 the pu u o o kupaianaha eruption of kilauea produced a vast pahoehoe flow field fed by lava tubes that extended 10 12 km from vents on the volcano s east rift zone to the ocean within a kilometer of the vent tubes were as much as 20 m high and 10 25 m wide on steep slopes 4 10 a little farther away from the vent some tubes formed by roofing over of lava channels lava streams were typically 1 2 m deep flowing within a tube that here was typically 5 m high and 3 m wide on the coastal plain 1 tubes within inflated sheet flows were completely filled typically 1 2 m high and several tens of meters wide tubes develop as a flow s crust grows on the top bottom and sides of the tubes restricting the size of the fluid core the tubes start out with nearly elliptical cross sectional shapes many times wider than high broad flat sheet flows evolve into elongate tumuli with an axial crack as the flanks of the original flow were progressively buried by breakouts temperature measurements and the presence of stalactites in active tubes confirmed that the tube walls were above the solidus and subject to melting sometimes the tubes began downcutting progressive downcutting was frequently observed through skylights a rate of 10 cm d was measured at one skylight for nearly 2 months

coupled sandbar patterns and obliquely incident waves 1 in double sandbar systems the alongshore variability in the inner bar often resembles that of the outer bar suggesting that the outer bar acts as a morphological template for the inner bar earlier observations have indicated that this resemblance also termed coupling may take several forms here we apply a nonlinear 2dh morphodynamic model with time invariant forcing to show that the angle of wave incidence is crucial for the alongshore variable morphodynamic evolution of the inner bar for a given crescentic outer bar in contrast to previous modeling efforts of double barred systems which mostly used highly idealized boundary conditions we force our model with realistic hydrodynamics and bathymetrical data derived from video observations at the double barred gold coast australia the results show that for small angles of wave incidence 10 over a crescentic outer bar cell circulation patterns govern the flow at the inner bar giving rise to rip channels that incise the inner bar at the locations of the landward perturbations in the outer bar horns on the other hand for obliquely incident waves 10 20 over a crescentic outer bar the circulatory nature of the flow disappears and gives way to a meandering alongshore current the offshore directed sections of this meandering alongshore current erode the inner bar downdrift of the outer bar horns leading to landward perturbations of the inner bar that are coupled to the outer bar horns an observed coupling type that had not been reproduced as yet oblique wave incidence thus proves to be crucial to the development of this type of sandbar coupling as previously hypothesized from sandbar coupling observations at the gold coast additional simulations including tidal water level variations and bar depth variations demonstrate the robustness of our findings

the morphological response of a nearshore double sandbar system to constant wave forcing results of 2dh morphodynamic computations are presented to quantify the temporal evolution of the crescentic patterns emerging in a double nearshore bar system in response to constant wave boundary forcing sixteen different conditions varying both offshore wave height and angle of wave incidence were applied the mean length scales of the emerging irregular crescentic patterns are linearly proportional to the local longshore velocity over the inner and outer bars for similar longshore velocities the length scales of the outer bar are larger than of the inner bar this is explained by accounting for the difference in water depth above the bar crest the variable morphological response times can be explained by including additional bathymetrical parameters the active volume of the bar defined by the breaker index plays an important role in this response time with larger active volumes the bar responds more rapidly to identical boundary conditions also bars with a smaller total volume respond more quickly this faster response is due to the steeper active volume of the bars different initial perturbations resulted in different locations of the emerging features showing that their location is sensitive to the initial bathymetry however the range in length scales and response times due to the different perturbations was significantly smaller than those obtained for the different hydrodynamic conditions based on the present findings we hypothesize that morphological length scales in the field are rarely in equilibrium with the concurrent offshore wave height and angle of incidence owing to the slow response of the sandbars under constant conditions relative to the stochastic nature of natural wave forcing

mean lagrangian flow behavior on an open coast rip channeled beach a new perspective article i nfo the accepted view of rip currents is that they are an efficient mechanism for transporting material out of the surf zone previous rip current campaigns on natural beaches have focused on eulerian measurements with sparse in situ pressure and current meter arrays here for the first time spatially synoptic estimates of rip current flow patterns vorticity and lagrangian transport behavior are measured in the field using a fleet of 30 position tracking surfzone drifters during multiple rip current occurrences on an open coast beach in monterey ca contrary to the classic view shepard et al 1941 the rip current flow field consisted of semi enclosed large scale vortices that retained the drifters and resulted in a high number of lagrangian observations that are temporally and spatially repeated approximately 19 of the drifters deployed in the rip currents exited the surf zone per hour on average during the experiments the observed surf zone retention of drifters is consistent with measurements from different open coast beach rip current systems 14 at meso macrotidal truc vert france and 16 at macrotidal perranporth united kingdom the three hour average cross shore rip current velocity at monterey was 30 cm s with peak time averaged velocities of 40 60 cm s depending on wave and tidal conditions drifters that episodically exited the surf zone were transported approximately 2 surf zone widths offshore at 20 cm s published by elsevier b v

bar morphology of dissipative beaches an empirical model this study of 150 examples of nearshore bar morphology along the highly dissipative beaches 33 of the southeast mediterranean shoreline employs 32 years of aerial photography and wave data aided by detailed short term field studies three major bar types were delineated non rhythmic parallel meandering bars inner single crescentic bars and double crescentic bars each of these bar families includes variations the bars were related to daily ship and shore wave data including wave spectra from the day of observation back to 60 days prior to the observation the increase in total bar occurrence during summer is related to crossing of a major wave energy threshold in the spring when significant wave heights 1 m sharply increase to 70 85 in april may the bar morphology wave comparisons further indicate that as the significant wave heights decrease and remain below 1 m non rhythmic bars form within 7 10 days single crescentic bars require 15 days and double crescentic bars require 20 30 days this adjustment period of the bars to wave power causes a delayed response which accounts for lack of coincidence between wave energy and bar occurrence the formation of the initial double crescentic bar and its transformation to the mature double crescentic type requires a short pulse of wave energy 0 5 h13 1 5 m some bar families occur throughout the year the aseasonal occurrence is best shown by the mature double crescentic type which apparently is the final stage in the crescenticbar development sequence however other bar families show a tendency for a seasonal distribution which reflects their sensitivity to wave energy inner single crescentic and initial double crescentic bars are largely restricted to the calmest wave months of may april to october november there is an antiphase relationship between the frequencies of non rhythmic and crescentic bars

observations of the effect of wind on the cooling of active lava flows 1 we present the first direct observations of the cooling of active lava flows by the wind we confirm that atmospheric convective cooling processes i e the wind dominate heat loss over the lifetime of a typical pahoehoe lava flow in fact the heat extracted by convection is greater than predicted especially at wind speeds less than 5 m s and surface temperatures less than 400 c we currently estimate that the atmospheric heat transfer coefficient is about 45 50 w m 2 k 1 for a 10 m s wind and a surface temperature 500 c further field experiments and theoretical studies should expand these results to a broader range of surface temperatures and wind speeds

distribution de l uranium du thorium du zirconium du hafnium et des terres rares tr dans des grains de phosphates sedimentaires abstract u th zr hf and ree contents have been determined in phosphate grains from central tunisia southern france montagne noire and the southeastern pacific and in organic fractions humic acids kerogens and stable residues separated in paleocene eocene phosphates of the gafsa metlaoui basin central tunisia due to adsorption phosphatic pellets concentrate high zr ree and th contents and fish debris takes up considerable amounts of zr but not of hf a separation of zr from hf related to the adsorption of zr preferred to hf in apatite and a clear positive correlation between zr and ree contents are found we also note a more or less pronounced fractionation between light and heavy ree which is influenced mainly by organic complexes as shown from the clear enrichment of the heavy ree in each of all of the organic fractions

quasi three dimensional modelling of the morphology of longshore bars a morphological quasi three dimensional q3d area model for barred coasts has been developed the model combines a two dimensional depth integrated model for wave driven currents with a model for undertow circulation currents the combined model makes a simultaneous simulation of the bar forming processes associated with the undertow and the horizontal wave driven circulation currents which may cause instabilities of the bar and the formation of rip channels situations with normal and oblique wave incidence are considered compared to the depth integrated approach the q3d model produces less pronounced alongshore irregularities for obliquely incident waves for normal incident waves the q3d model produces a crescentic bar while the depth integrated model predicts almost straight sections of the bar interrupted by rip channels the sensitivity to variation of wave angle and beach slope is further investigated

thermal anomaly at the earth s surface associated with a lava tube abstract lava tubes are frequently encountered in volcanic areas the formation of lava tubes has strong implications on the volcanic hazard during effusive eruptions the thermal dissipation of lava flowing in a tube is reduced in respect to the lava flowing in an open channel so the lava may threaten areas that would not be reached by flows in open channels for this reason it is important to detect the presence of lava tubes in this work we propose a model to detect the presence and the characteristics of lava tubes by their thermal footprint at the surface we model numerically the temperature distribution and the heat flow both in the steady and the transient state and we take into account the principal thermal effects due to the presence of an active lava tube i e the conduction to the ground and the atmosphere the convection and the radiation in the atmosphere we assume that lava fluid is at high temperature in motion inside a sloping tube under the gravity force the thermal profile across the tube direction in particular the width of the temperature curve allows to evaluate the depth of the tube the values of maximum temperature and of tube depth allow to estimate the area of the tube section the shape of the temperature curve and its asymmetry can give information about the geometry of the tube if we observe volcanic areas at different times by thermal cameras we can detect anomalies and evaluate their causes during an eruption in particular we can evaluate whether they are due to active lava flows or not and what is their state for lava tubes we can connect thermal anomalies with lava tube position characteristics and state

a model for the formation of lava tubes by roofing over a channel the formation of lava tubes is a common phenomenon on some basaltic volcanoes such as etna a model for tube formation by roofing of a channel is proposed and involves first describing lava as a bingham liquid flowing down a slope it is further assumed that lava flows in a channel with rectangular cross section as a result of heat loss into the atmosphere a crust is gradually formed on the upper surface of the flow and this crust eventually welds to the channel levees we assume that a lava tube is formed when such a crust is sufficiently thick to resist the drag of the underlying flow and to sustain itself under its own weight the minimum thickness of the crust satisfying such conditions depends on the tensile strength and shear strength of the crust itself assuming that the growth of the crust produces a downflow linear increase of the shear stress at the interface between flowing lava and the crust the distance is evaluated between the eruption vent and the point where the tube is formed the model predicts that if the flow rate is constant the thickness of the flow increases as the crust fragments grow and weld to each other and the velocity of the crust decreases to zero once the lava tube is formed the initial flow rate can be achieved by a flow thickness smaller than the vertical size of the tube with the same viscous dissipation this may explain why under steady state conditions the lava level inside a tube is frequently lower than the roof of the tube itself