flow of variably fluidized granular masses across three dimensional terrain 2 numerical predictions and experimental tests numerical solutions of the equations describing flow of variably fluidized coulomb mixtures predict key features of dry granular avalanches and water saturated debris flows measured in physical experiments these features include time dependent speeds depths and widths of flows as well as the geometry of resulting deposits three dimensional 3 d boundary surfaces strongly influence flow dynamics because transverse shearing and cross stream momentum transport occur where topography obstructs or redirects motion consequent energy dissipation can cause local deceleration and deposition even on steep slopes velocities of surge fronts and other discontinuities that develop as flows cross 3 d terrain are predicted accurately by using a riemann solution algorithm the algorithm employs a gravity wave speed that accounts for different intensities of lateral stress transfer in regions of extending and compressing flow and in regions with different degrees of fluidization field observations and experiments indicate that flows in which fluid plays a significant role typically have high friction margins with weaker interiors partly fluidized by pore pressure interaction of the strong perimeter and weak interior produces relatively steep sided flat topped deposits to simulate these effects we compute pore pressure distributions using an advection diffusion model with enhanced diffusivity near flow margins although challenges remain in evaluating pore pressure distributions in diverse geophysical flows riemann solutions of the depth averaged 3 d coulomb mixture equations provide a powerful tool for interpreting and predicting flow behavior they provide a means of modeling debris flows rock avalanches pyroclastic flows and related phenomena without invoking and calibrating rheological parameters that have questionable physical significance

high velocity ring shear tests on sand ring shear tests on sand materials have been carried out to show whether there is a change in the behaviour of these materials at high shearing rates and normal stresses this question is relevant to the problem of the mobility of large rock avalanches sturzstroms but is also of more general academic interest a ring shear apparatus of unusual although simple design has been constructed capable of achieving circumferential velocities of 2 m s at normal stresses of up to 200 kpa tests were carried out on two types of coarse sand wet or dry sand rock flour mixtures and polystyrene beads perfect frictional behaviour was observed in all the tests uninfluenced by either velocity or normal stress over the entire range of these variables change in frictional behaviour due to high rate of shearing therefore cannot be used to explain the high observed mobility of sturzstroms des essais de cisaillement circulaire par torsion ont ete effectes afin de decouvrir si un changement ait lieu dans le comportem

granular mass flows and coulomb s friction in shear cell experiments implications for geophysical flows 1 granular mass flows of rock fragments are studied in the lab by means of a high speed video camera at 2000 frames per second these granular flows are generated using beds of pumice fragments positioned on a rough rotating disk whose angular velocity is controlled by a motor the experimental apparatus allows an understanding of the arrangement of the particles in granular mass flows with relatively small and relatively large values of the savage number the savage number represents the ratio between grain collision stresses and gravitational grain contact stresses in particular these flows develop a basal layer of agitated and colliding particles underneath a relatively rigid upper layer our experimental results suggest the validity on average of the coulomb s relationship between shear and normal forces at the base of granular mass flows irrespective of their savage number value in coulomb s equation the shear stresses do not depend on the shear rate we expect the coulomb friction law to be valid also in moving pyroclastic flows our experiments suggest that the collisions and subsequent comminution of pumice fragments in moving pyroclastic flows could provide ash for the overriding ash clouds in our experiments the amount of ash generated by particle particle and particle boundary interactions increases as the value of the savage number increases in nature part of this ash may also simply move toward the base of the flows because of kinetic sieving

flow of variably fluidized granular masses across three dimensional terrain 1 coulomb mixture theory rock avalanches debris flows and related phenomena consist of grain fluid mixtures that move across three dimensional terrain in all these phenomena the same basic forces govern motion but differing mixture compositions initial conditions and boundary conditions yield varied dynamics and deposits to predict motion of diverse grain fluid masses from initiation to deposition we develop a depth averaged three dimensional mathematical model that accounts explicitly for solid and fluid phase forces and interactions model input consists of initial conditions path topography basal and internal friction angles of solid grains viscosity of pore fluid mixture density and a mixture diffusivity that controls pore pressure dissipation because these properties are constrained by independent measurements the model requires little or no calibration and yields readily testable predictions in the limit of vanishing coulomb friction due to persistent high fluid pressure the model equations describe motion of viscous floods and in the limit of vanishing fluid stress they describe one phase granular avalanches analysis of intermediate phenomena such as debris flows and pyroclastic flows requires use of the full mixture equations which can simulate interaction of high friction surge fronts with more fluid debris that follows special numerical methods described in the companion paper are necessary to solve the full equations but exact analytical solutions of simplified equations provide critical insight an analytical solution for translational motion of a coulomb mixture accelerating from rest and descending a uniform slope demonstrates that steady flow can occur only asymptotically a solution for the asymptotic limit of steady flow in a rectangular channel explains why shear may be concentrated in narrow marginal bands that border a plug of translating debris solutions for static equilibrium of source areas describe conditions of incipient slope instability and other static solutions show that nonuniform distributions of pore fluid pressure produce bluntly tapered vertical profiles at the margins of deposits simplified equations and solutions may apply in additional situations identified by a scaling analysis assessment of dimensionless scaling parameters also reveals that miniature laboratory experiments poorly simulate the dynamics of full scale flows in which fluid effects are significant therefore large geophysical flows can exhibit dynamics not evident at laboratory scales

influence of the barotropic mean flow on the width and the structure of the atlantic equatorial deep jets a representation of an equatorial basin mode excited in a shallow water model for a single high order baroclinic vertical normal mode is used as a simple model for the equatorial deep jets the model is linearized about both a state of rest and a barotropic mean flow corresponding to the observed atlantic equatorial intermediate current system we found that the eastward mean flow associated with the north and south intermediate counter currents nicc and sicc respectively effectively shields the equator from off equatorial rossby waves the westward propagation of these waves is blocked and focusing on the equator due to beta dispersion is prevented this leads to less energetic jets along the equator on the other hand the westward barotropic mean flow along the equator reduces the gradient of absolute vorticity and hence widens the cross equatorial structure of the basin mode increasing lateral viscosity predominantly affects the width of the basin modes kelvin wave component in the presence of the mean flow while the rossby wave is confined by the flanking nicc and sicc independent of the presence of the mean flow the application of sufficient lateral mixing also hinders the focusing of off equatorial rossby waves which is hence an unlikely feature of a low frequency basin mode in the real ocean

depressurization of fine powders in a shock tube and dynamics of fragmented magma in volcanic conduits abstract samples of fine glass beads mean grain size equal to 38 and 95 m have been depressurized within a vertical shock tube these short lived rapid decompressions resemble discrete cannon like vulcanian explosions and produce two phase flows that are inhomogeneous in density in both vertical and horizontal directions because of the presence of bubble like heterogeneities we suggest that also volcanic flows may present similar inhomogeneities in density in the experimental apparatus the flow velocities increase from approximately 1 to 13 m s when the pressure drop increases from approximately 200 to 900 mbar a physical model of the initial velocities of expansions in the shock tube has been applied to a range of volcanic overpressures between 0 1 and 20 mpa suggesting initial velocities of volcanic flows caused by the removal of a rock plug in volcanic conduits between 25 and 400 m s during the experiments at large pressure drops as the mixture expands and moves up the tube the flow front becomes highly irregular and bubble like heterogeneities form the shape of these bubbles becomes distorted and stretched in the turbulent flow during the experiments at relatively small pressure drops the sample oscillates when the particles after the expansion flow back and bounce upward again jets with diameter smaller than that of the tube are ejected from the oscillating samples generating independent pulses large bubble like heterogeneities whose diameter is a significant fraction of the tube diameter can also discretize the flows similar mechanisms in real volcanoes may produce pulse like ejections of gas particle mixtures out of the vent

upper and intermediate circulation in the western equatorial pacific ocean in october 1999 and april 2000 1 the upper and intermediate circulation 0 1200 m in the western equatorial pacific ocean is examined thanks to lowered acoustic doppler current profiler ladcp measurements carried out during two cruises in october 1999 and april 2000 several new features of the equatorial circulation are discussed it is shown that the secondary south subsurface countercurrent ssscc laying at 6 s 400 m depth had a deep extension at 165 e with a maximum core velocity around 5 s 1000 m furthermore the equatorial intermediate current eic and the lower eic leic displayed a strong temporal variability between 165 e and 180 as these two westward currents were replaced by eastward flow along the equator on the second cruise finally during the april 2000 cruise the zonal velocity profile carried out at the equator east of the gilbert island around 175 e broke into small vertical scales possibly reflecting topographic effect and or destabilization mechanism that leads to the formation of long zonal jet like structures

basin wavelength equatorial deep jet signals across three oceans equatorial deep jets edjs are equatorially trapped stacked zonal currents that reverse direction every few hundred meters in depth throughout much of the water column this study evaluates their structure observationally in all three oceans using new high vertical resolution argo float conductivity temperature depth ctd instrument profiles from 2010 to 2014 augmented with historical shipboard ctd data from 1972 to 2014 and lower vertical resolution argo float profiles from 2007 to 2014 the vertical strain of density is calculated from the profiles and analyzed in a stretched vertical coordinate system determined from the mean vertical density structure the power spectra of vertical strain in each basin are analyzed using wavelet decomposition in the indian and pacific oceans there are two distinct peaks in the power spectra one kelvin wave like and the other entirely consistent with the dispersion relation of a linear first meridional mode equatorial rossby wave in the atlantic ocean the first meridional mode rossby wave signature is very strong and dominates in all three ocean basins rossby wave like signatures are coherent across the basin width and appear to have wavelengths the scale of the basin width with periods of about 5 yr in the indian and atlantic oceans and about 12 yr in the pacific ocean their observed meridional scales are about 1 5 times the linear theoretical values their phase propagation is downward with time implying upward energy propagation if linear wave dynamics hold

the vertical structure of the zonal pressure gradient in the eastern equatorial pacific ctd data from the epocs and norpax experiments were used to construct a mean zonal pressure gradient profile between 110 w and 150 w for the 1979 to 1981 pre el nino time period the mean zonal pressure gradient referenced to 100 dbar had a value of 4 5 10 7 m s 2 at the surface and decreased to within two standard errors of zero at 200 dbar below this depth the mean was not significantly different from zero deviations from this mean were not related to fluctuations of the zonally averaged zonal wind stress between 150 w and 110 w rather the largest deviations in the boreal springs of 1979 and 1980 appeared to be associated first with vertical mode kelvin wave pulses propagating eastward along the equator the 1979 81 mean profile was also used as a reference to examine variations in zonal pressure gradient during the 1982 83 enso event the sea surface was more sharply sloped upward from the east to west in april and september 1982 before arid near the beginning of the event the surface slope was below normal in april and october 1983 vertical profiles of the zonal pressure gradient deviations showed large high vertical mode contributions during the vent than in the prevent samples

atlantic equatorial deep jets space time structure and cross equatorial fluxes the so called equatorial stacked jets are analyzed with ship board observations and moored time series from the atlantic ocean the features are identified and isolated by comparing vertical wavenumber spectra at the equator with those a few degrees from the equator mode filtering gives clear views of the jets in meridional sections the typical extent being 618 in latitude the vertical structure can be well described explaining 82 of the variance by n21 stretched cosines with a gaussian amplitude tapering in the vertical the stretched wavelengths are somewhat variable fitting jets of a fixed stretched wavelength to four moored sensors in the depth range 1300 1900 m allows one to track the vertical phase of the jets with an rms error of 308 458 the resulting fit from a 20 month moored time series shows long periods of unchanging jet conditions and intermittent times of high variability there is no significant vertical propagation on these timescales nor a seasonal reversal using a composite from many different experiments interannual variability is visible however a possible mechanism for the stacked jets is inertial instability resulting from background meridional shears at the equator a condition is that the ertel potential vorticity becomes zero somewhere due to meridional asymmetries in the zonal flows the ship board observations show that this may be approximately fulfilled by the instantaneous zonal low mode flows at various depths resulting from an excess of zonal momentum south of the equator most of the time inertial instability should act to redistribute this zonal momentum and our mooring data show indeed persistent northward momentum flux but not at the depth levels expected the momentum transport might suggest that the jets can also flux or mix other properties across the equator

temporal and spatial structure of the equatorial deep jets in the pacific ocean abstract the spatial and temporal structure of the equatorial deep jets edjs in the pacific ocean is investigated using ctd station data taken on the equator from 1979 through 2001 the edjs are revealed in profiles of vertical strain z estimated from the ctd data in a stretched vertical coordinate system the majority of synoptic meridional sections were occupied over an 8 yr span west of the date line two decade equatorial time series are available at both 110 w and 140 w analysis shows the expected equatorial trapping of z but yields little new detailed information about the edj meridional structure analysis of the equatorial data yields novel results the edjs are most easily seen in the eastern pacific at and east of 140 w there they may be isolated from the influence of higher frequency rossby waves generated by surface forcing spectral analysis of equatorial z profiles shows a significant and coherent peak at 400 sdbar vertical wavelength with no 1 56 10 3 s 1 from 95 w to 142

results from a velocity transect along the equator from 125 to 159 w abstract during march april 1980 a velocity and ctd transect was made in the pacific along the equator from 110 to 180 w the horizontal baroclinic pressure gradient was observed to be primary confined between 160 and 130 w direct velocity profiles between 125 and 159 w showed the equatorial undercurrent to be a continuous feature maximum eastward transport per unit width in the undercurrent was 2 5 108 cm2 s 1 at 150 w and decreased both westward and eastward to about 1 5 108 cm2 s 1 at 159 w and at 125 w despite these variations the maximum speeds along the transect remained 150 cm s 1 beneath the undercurrent the velocities decreased and were of the order of 25 cm s 1 they exhibited small scale variation in the vertical as has recently been observed at other equatorial locations above 1600 m the vertical wavelength of these variations in the zonal component was 300 m small scale features in these zonal velocities were identifiable over 10 of longitude 1000 km the small vertical an

the deep currents in the eastern equatorial atlantic ocean 1 in the atlantic ocean equatorial deep jets have been observed in the central and western equatorial basin here we present three meridional velocity sections carried out in boreal summer 2000 in the eastern equatorial atlantic at that time the deep equatorial jets were observed to weaken or to vanish in the gulf of guinea toward the african coast at 10 w the comparison with currents measured one year before in boreal summer 1999 along with tracer distributions confirm the existence of an eastward route along the equator of part of the north atlantic deep water

experiments on the flow behaviour of granular materials at high velocity in an open channel a series of laboratory flume experiments has been conducted to investigate the flow behaviour of dry sand at high velocities the first incentive for this experimental programme was an attempt to explain the high mobility of apparently dry masses of rapidly moving broken rock during rock avalanches sturzstroms test velocities of over 5 m s and most other parameters of the tests were found to be dimensionally similar to those for a typical rock avalanche yet the conclusion was negative even the most rapid of the experiments indicated flow behaviour which is in conformity with the constant volume uniform coulomb friction relationship as applicable to slow shearing this conclusion was confirmed independently both by direct measurements of base friction and mean density of the flows and by detailed observations of flow uniformity acceleration and velocity profiles the surprising mobility of st umlrzstroms therefore requires a different explanation une serie de tests a canaux a ete entreprise dans le

deep jets in the equatorial atlantic ocean deep velocity profiles taken in the equatorial atlantic ocean show equatorially trapped deep jets with similar features to those of the indian and pacific oceans a zonal velocity of the order of 10 to 20 cm s 1 and a meridional scale of 1 in the pacific and indian oceans the zonal extent of the jets is at least 15 of longitude owing to the lack of synoptic measurements we have no information on the zonal scale in the atlantic ocean but we present here zonal velocity profiles made at a 16 month interval that have identical baroclinic structure in the western 35 w and central basin 13 w the atlantic jets have a vertical scale larger 400 600 m than those observed in the pacific ocean 250 400 m our measurements confirm the opposite directions of the jets for different seasons in the atlantic ocean furthermore for a given season the vertical profiles of zonal velocity at 35 w 0 are astonishingly similar at a 5 year interval as in the pacific and indian oceans the jets are embedded in a large vertical scale current that changes direction with time the few profiles available in the equatorial atlantic ocean suggest a seasonal reversal of the jets but neither this nor the temporal variability of the large scale current has been adequately resolved

the foundation of a 40 storey tower in jointed basalt abstract a 132 70 m high tower above foundation has been successfully completed at tenerife island the foundation of the tower a 2 m thick reinforced concrete slab is supported by jointed vesicular and weathered basalt and scoria a three dimensional elastic finite element program has permitted to calculate the displacements of the tower and the stresses in the slab the installation of rod extensometers at different depths below the slab and clinometers at the lower basement has provided comparison between measured and calculated displacements and the estimation of in situ deformation moduli a first stage prediction before construction has allowed establishment of an upper limit based upon pressuremeter modulus and a lower limit based upon bieniawski s equation the geomechanics classification in rock engineering applications in proceedings of the fourth cong isrm congress montreux vol 2 1979 p 41 48 of the settlements of the tower slab the geometric mean of these values comes close to the measured settlement the moduli deduced from the simple empirical equation proposed by gokceoglu et al predicting the deformation modulus of rock masses a comparative study int j rock mech min sci 2003 40 701 10 and hoek and brown practical estimates of rock mass strength int j rock mech min sci 1997 40 701 10 as a function of gsi provide a good fit with the measured settlements in this type of rock a good correlation is also obtained with the empirical equation presented by verman et al effect of tunnel depth on modulus of deformation of rock mass rock mech rock eng 1997 30 3 121 7 that incorporates the influence of the confining stress in the deformation modulus

forcing of the atlantic equatorial deep jets derived from observations the equatorial deep jets edjs are an ubiquitous feature of the equatorial oceans in the atlantic ocean they are the dominant mode of interannual variability of the zonal flow at intermediate depth on the basis of more than 10 years of moored observations of zonal velocity at 23 w the vertically propagating edjs are best described as superimposed oscillations of the 13th to the 23th baroclinic modes with a dominant oscillation period for all modes of 1650 days this period is close to the resonance period of the respective gravest equatorial basin mode for the dominant vertical modes 16 and 17 it is argued that since the equatorial basin mode is composed of linear equatorial waves a linear reduced gravity model can be employed for each baroclinic mode driven by spatially homogeneous zonal forcing oscillating with the edj period the fit of the model solutions to observations at 23 w yields a basin wide reconstruction of the edjs and the associated vertical structure of their forcing from the resulting vertical profile of mean power input and vertical energy flux on the equator it follows that the edjs are locally maintained over a considerable depth range from 500 2500 m with the maximum power input and vertical energy flux at 1300 m the strong dissipation closely ties the apparent vertical propagation of energy to the vertical distribution of power input and together with the edjs prevailing downward phase propagation require the phase of the forcing of the edjs to propagate downward

annual reversal of the equatorial intermediate current in the pacific observations and model diagnostics abstract a large reversal of zonal transport below the thermocline was observed over a period of 6 months in the western pacific ocean between 2 s and the equator from 26 2 sv 1 sv 106 m3 s 1 eastward in october 1999 to 28 6 sv westward in april 2000 to document this reversal and assess its origin an unprecedented collection of adcp observations of zonal currents 2004 06 together with a realistic ogcm simulation of the tropical pacific was analyzed the results of this study indicate that this reversal is the signature of intense annual variability in the subsurface zonal circulation at the equator at the level of the equatorial intermediate current eic and the lower equatorial intermediate current l eic in this study the eic and the l eic are both shown to reverse seasonally to eastward currents in boreal spring and winter for the l eic over a large depth range extending from 300 m to at least 1200 m the peak to peak amplitude of the annual cycle of subthermocline zonal currents at

new views of granular mass flows concentrated grain fluid mixtures in rock avalanches debris flows and pyroclastic flows do not behave as simple materials with fixed rheologies instead rheology evolves as mixture agitation grain concentration and fluid pressure change during flow initiation transit and deposition throughout a flow however normal forces on planes parallel to the free upper surface approximately balance the weight of the superincumbent mixture and the coulomb friction rule describes bulk intergranular shear stresses on such planes pore fluid pressure can temporarily or locally enhance mixture mobility by reducing coulomb friction and transferring shear stress to the fluid phase initial conditions boundary conditions and grain comminution and sorting can influence pore fluid pressures and cause variations in flow dynamics and deposits

stacked jets in the deep equatorial atlantic ocean 1 middepth current measurements in the equatorial atlantic are characterized by elevated levels of energy contained in zonal flows of high baroclinic mode number these alternating zonal flows often called equatorial stacked jets have amplitudes up to 20 cm s 1 and vertical wavelengths of 600 m the jets are most pronounced in the depth range between 500 and 2500 m repeated direct velocity observations at 35 w indicate that the jets are coherent within 1 of the equator individual jets can persist for 1 2 years but they appear and decay rather irregularly the equatorial stacked jets are also found in realistic general circulation model simulations the features grow in amplitude with increasing horizontal and vertical model resolution however even at very high model resolutions their amplitudes are still underestimated in all model simulations high levels of energy related to the stacked jets are found in the vicinity of the western boundary currents wbcs depth range and strength of the wbcs in different experiments are related to depth range and strength of the jets in the interior stacked jets are characterized by eastward wave propagation suggesting that high baroclinic mode kelvin waves radiate energy generated in the wbc into the interior and form the stacked jets

sole marks at the base of the late pleistocene abrigo ignimbrite tenerife implications for transport and depositional processes at the base of pyroclastic flows sole marks which are common in turbidites have been observed as casts at the base of the abrigo ignimbrite on tenerife canary islands they have been engraved by pebble to cobble sized lithic tools in a soft cohesive fine grained substrate the casts range from long parallel groove marks often with the tool embedded at their termination to short elongate impact marks and are useful as a flow direction marker they were formed from a highly energetic pyroclastic flow pulse and were almost immediately infilled with ash after rapid waning of flow large lithic tools which formed groove marks were held in place under high gas and grain dynamic pressures and moved forward by their own momentum and the drag force exerted by a highly concentrated granular flow impact marks were formed by smaller lithic tools which had more freedom of movement within the agitated chaotic flow scour structures on the lee side of stationary lithic tools may have formed by local turbulence in their wake

observed tracer fields structuration by middepth zonal jets in the tropical pacific abstractthe middepth ocean circulation in the tropical pacific is dominated by sets of alternating eastward and westward jets the origin and transport properties of these flow features remain in m