high pressure phases in shock induced melt veins of the umbarger l6 chondrite constraints of shock pressure we report a previously undocumented set of high pressure minerals in shock induced melt veins of the umbarger l6 chondrite high pressure minerals were identified with transmission electron microscopy tem using selected area electron diffraction and energy dispersive x ray spectroscopy ringwoodite fa30 akimotoite en11fs89 and augite en42wo33fs25 were found in the silicate matrix of the melt vein representing the crystallization from a silicate melt during the shock pulse ringwoodite fa27 and hollandite structured plagioclase were also found as polycrystalline aggregates in the melt vein representing solid state transformation or melting with subsequent crystallization of entrained host rock fragments in the vein in addition fe2sio4 spinel fa66 fa99 and stishovite crystallized from a feo sio2 rich zone in the melt vein which formed by shock melting of feo sio2 rich material that had been altered and metasomatized before shock based on the pressure stabilities of the high pressure minerals ringwoodite akimotoite and ca clinopyroxene the melt vein crystallized at approximately 18 gpa the fe2sio4 spinel stishovite assemblage in the feo sio2 rich melts is consistent with crystallization of the melt vein matrix at the pressure up to 18 gpa the crystallization pressure of 18 gpa is much lower than the 4590 gpa pressure one would conclude from the s6 shock effects in melt veins stffler et al 1991 and somewhat less than the 25 30 gpa inferred from s5 shock effects schmitt 2000 found in the bulk rock

a numerical study of intermittent sediment concentration under breaking waves in the surf zone a three dimensional large eddy simulation les model is presented together with a sediment pickup advection module for the study of spatial and temporal variation of sediment concentration due to three dimensional fluid motion under breaking waves on a sloping beach the les flow module calculates the turbulent flow due to wave breaking where a large scale turbulence can be directly solved by the governing flow equations and a small scale turbulence can be evaluated using a sub grid scale sgs model in the sediment pickup advection module the sediment pickup rate is estimated by a sediment pickup function using the shield s number at the bottom of the fluid layer and suspended sediment particles are assumed to move with the ambient fluid the numerical results show that the flow field including the wave breaking is represented well by the les model and the sediment pickup advection module is able to simulate spatial and temporal intermittency of the sediment suspension three noticeable sediment pickup areas are defined namely around the breaking point break impact area and run up zone in the inner region of the surf zone the sediment concentration distribution shows strong three dimensionality the calculated results of the time averaged and the equi phase averaged sediment concentration distributions are compared to earlier laboratory experiment results the sediment concentration distribution and advection calculated by the model show general correspondence to the experimental results but the averaged sediment concentration is approximately 1 5 times greater than the experimental value

frictional melting processes in planetary materials from hypervelocity impact to earthquakes frictional melting is the result of the conversion of mechanical deformation to heat under adiabatic conditions of slip within planetary materials which are mainly natural ceramics frictional melting occurs at high strain rates typically 10 2 s 1 and at slip velocities greater than 0 1 m s 1 t he pathway to friction melting is controlled by the mechanical properties of a rock s constituent minerals especially fracture toughness minerals with the lowest fracture toughnesses and breakdown temperatures are preferentially comminuted and fused to form the melt the product is a polyphase suspension comprising mineral and rock fragments enclosed in a liquid matrix this cools to form the rock type known as pseudotachylyte and at even higher strain rates it forms shock veins in meteorites and in impact craters which may contain high pressure mineral polymorphs the generation of melt on sliding surfaces can lubricate earthquake faults facilitate the post shock modification of impact craters and make landslides more hazardous

turbulence transport vorticity dynamics and solute mixing under plunging breaking waves in surf zone plunging breaking waves generate turbulence and vorticity which are of great importance for the solute and sediment transport in surf zone in this paper the complex breaking processes are simulated by using an accurate numerical model that solves the reynolds equations for the mean flow and modified k e equations for the turbulence field a solute transport model is employed to investigate the solute mixing under plunging waves after validation of the numerical model by comparing numerical results with available experimental data the numerical model is further utilized to study the detailed mechanisms of turbulence transport and vorticity dynamics the differences between spilling and plunging breaking waves are discussed the impact of the wave breaking on solute mixing in the surf zone is also examined

lithification mechanisms for planetary regoliths the glue that binds it is understood how rocks are made on earth however on the moon mercury and to a lesser extent mars and venus there are distinct rock forming processes that we do not fully comprehend the surfaces and crusts of the inner planetary bodies may retain a history of disruption by hypervelocity impact resulting in the generation of disaggregated materials to several kilometers depth the uppermost component of this is called regolith typically 20 m thick on the moon which is part of a more extensive megaregolith that is up to tens of kilometers thick and which in places may pervade the entire crust of a planetary body it is from these pulverized materials that new rocks are reaggregated to form so called breccias this work reviews regolith and megaregolith structure for the inner planetary bodies and investigates how extraterrestrial breccias are produced three principal formation mechanisms are explored thermal sintering shock sintering and the dynamic interaction of impact generated melt w

vertical fluxes of sediment in oscillatory sheet flow time series of vertical sediment fluxes are derived from concentration time series in sheet flow under waves while the concentrations c z t vary very little with time for z 10d50 the measured vertical sediment fluxes qzs z t vary strongly with time in this vertical band and their time variation follows to some extent the variation of the grain roughness shields parameter 2 5 t thus sediment distribution models based on the pickup function boundary condition are in some qualitative agreement with the measurements however the pickup function models are only able to model the upward bursts of sediment during the accelerating phases of the flow they are so far unable to model the following strong downward sediment fluxes which are observed during the periods of flow deceleration classical pickup functions which essentially depend on the shields parameter are also incapable of modelling the secondary entrainment fluxes which sometimes occur at free stream velocity reversal the measured vertical fluxes indicate that the effective sediment settling velocity in the high 0 3 c z t 0 4 concentration area is typically only a few percent of the clear water settling velocity while the measurements of richardson and jeronimo chem eng sci 34 1979 1419 from a different physical setting lead to estimates of the order 20 the data does not support gradient diffusion as a model for sediment entrainment from the bed that is detailed modelling of the observed near bed fluxes would require diffusivities that go negative during periods of flow deceleration an observed general trend for concentration variability to increase with elevation close to the bed is also irreconcilable with diffusion models driven by a bottom boundary condition

volcanic avalanche fault zone with pseudotachylite and gouge in french massif central abstract structures and textures with sedimentological variations at different scales of the lithofacies assemblage help us to constrain the basal kinematic transition from non depositional to depositional conditions during volcanic avalanche emplacement in the well exposed impact sheared contact along volcanic avalanche fault zone in the french massif central we observe how the granular textures of the pseudotachylite and fault gouge have recorded the propagation of shock wave with granular oscillatory stress sequential events of basal aggradation along avalanche fault zone have been established related to fractal d values temperature pressure regime and oscillatory stress during slow wave velocity a typical lithofacies assemblage with a reverse grading shows the pseudotachylite and fault gouge a cataclastic gradient is characterised by the fractal d values from 2 7 in jigsaw breccias with pseudotachylite partial melt to 2 6 in the polymodal gouge shock brecciation and comminution produce cataclastic shear bands in the pseudotachylite and quartz microstructures along the basal contact of the volcanic debris avalanche deposit gouge microstructures show granular segregation cataclasis with antithetic rotational riedel shear and an arching effect between the riedel shear bands x ray microtomography provided 3d microfabrics along the clastic vein in the sandy gouge from the available statistical dataset a few equations have been developed implicating the same cataclastic origin with a co genetic evolution of lithofacies an impact wave during primary shear propagation may contribute to produce hydroclastic matrix pseudotachylite partial melt and proximal gouge thixotropy with v 50m s and a t

sediment transport on dissipative intermediate and reflective beaches abstract in this paper we review and synthesize field measurements of suspended sediment transport on the shoreface of dissipative intermediate and reflective beach states the morphodynamic beach state continuum was originally established in the 1970s but at the time only hydrodynamic processes and morphologies in these various states were described since the early 1980s when sensors capable of resolving suspended sediment concentration at intra wave time scale became available many studies have examined suspended sediment transport by waves and currents on the shoreface the synthesis of this work shows that the two end states in the morphodynamic continuum which are the dissipative and reflective states exhibit relatively small rates of cross shore sediment transport and weak gradients in that transport which both ensure that the nearshore morphology is relatively stable the intervening intermediate beach states typically exhibit prominent bar topographies and in these states strong morphodynamic feedbacks between hydrodynamic processes and morphology create locally large transport rates and sharp transport gradients which is the reason for the dynamic nature of these beach states transport processes driving sediment onshore and offshore within beach states are discussed as well as the transport processes responsible for state transitions

turbulence measurements in the surf zone abstract velocity measurements within 1 m of the bottom in approximately 4 5 m water depth on a sand beach provide estimates of turbulent reynolds shear stress using a dual sensor technique that removes contamination by surface waves and inertial range estimates of dissipation when combined with wave measurements along a cross shore transect and nearby wind measurements the dataset provides direct estimates of the terms in simplified equations for alongshore momentum and turbulence energetics and permits examination of semiempirical relationships between bottom stress and near bottom velocity the records are dominated by three events when the measurement site was in the outer part of the surf zone near bottom turbulent shear stress is well correlated with squared correlation coefficient r2 0 63 but smaller than regression coefficient b 0 51 0 03 at 95 confidence wind stress minus cross shore gradient of wave induced radiation stress indicating that estimates of one or more of these ter

mineralogy microtexture and composition of shock induced melt pockets in the los angeles basaltic shergottite analytical electron microscopy of shock features in the basaltic shergottite los angeles stone 1 reveals 1 shock recorded in the bulk sample and 2 localized pressure and temperature excursions that have generated melt pockets up to 4 mm in diameter bulk shock effects include microfaulting offsets 1 200 mm mosaicism deformed exsolution lamellae and planar fracturing in pyroxene undulose extinction in whitlockite mechanical twinning in titanomagnetite and ilmenite and the transformation of plagioclase to maskelynite 4 remnant reduced birefringence the pressure estimates for bulk shock are 35 40 gpa localized shock excursions have generated three types of discrete melt zones 0 07 1 3 mm to 3 0 3 5 mm apparent diameter possessing glassy to microcrystalline groundmasses these melt pockets are differentiated on the basis of size clast volume and degree of crystallization and vesiculation melt veins and melt dikelets emanate from the melt pockets up to 3 mm into the host rock but do not necessarily connect with other melt pockets the melt pockets were generated by pressure temperature excursions of 60 80 gpa and 1600 2000 c resulting in discrete melting of adjacent host rock minerals at grain boundary margins concentric zoning in the margins of clinopyroxenes coincides with a progressive reduction in birefringence as melt pockets are approached this suggests that the shock excursions were focused as point sources in the wake of the shock front that induced bulk damage

nearshore sandbar migration field observations suggest that onshore sandbar migration observed when breaking wave driven mean flows are weak may be related to the skewed fluid accelerations associated with the orbital velocities of nonlinear surface waves large accelerations both increases and decreases in velocity magnitudes previously suggested to increase sediment suspension occur under the steep wave faces that immediately precede the maximum onshore directed orbital velocities weaker accelerations occur under the gently sloping rear wave faces that precede the maximum offshore directed velocities the timing of strong accelerations relative to onshore flow is hypothesized to produce net onshore sediment transport the observed acceleration skewness a measure of the difference in the magnitudes of accelerations under the front and rear wave faces is maximum near the sandbar crest the corresponding cross shore gradients of an acceleration related onshore sediment transport would cause erosion offshore and accretion onshore of the bar crest consistent with the observed onshore migration of the bar crest furthermore the observations and numerical simulations of nonlinear shallow water waves show that the region of strongly skewed accelerations moves shoreward with the bar suggesting that feedback between waves and evolving morphology can result in continuing onshore bar migration

shocking rocks by cavitation and bubble implosion cavitation is proposed as a mechanism for the discrete generation of high pressure high temperature polymorphs in veins within meteorites and hypervelocity impact structures cavitation involves the inception isothermal growth and adiabatic implosion of bubbles their collapse has the potential of generating ultrahigh temperatures and pressures the formation of pseudotachylytic melt veins within the shocked target is critical to the cavitation process these veins facilitate bubble growth on decompression and subsequent bubble collapse on relaxation within the liquid asymmetric bubble implosion can lead to the rapid inrush of liquid to form a supersonic jet if the liquid jet strikes a solid surface i e melt vein walls or suspended clasts at high velocities then temperatures of several thousand kelvin and pressures of 10 gpa or more can be realized in the area of jet impact these conditions are capable of generating high pressure phases such as ringwoodite the spinel structured polymorph of olivine which requires formation pressures of 50 gpa these extreme effects are transient and localized being restricted to microscopic regions of liquid solid impact within the cavitating melt vein the presence of high pressure polymorphs in meteorites and impact structures does not necessarily imply that the primary shock event attained the conditions necessary for polymorph formation instead the presence of polymorphs may be the result of extreme pressure temperature excursions due to cavitation

cross shore suspended sand and bed load transport on beaches simple formulas are developed to predict the time averaged rates of cross shore suspended sand and bed load transport the net suspended sand transport rate is expressed as the product of the depth averaged current and the suspended sediment volume per unit bottom area with a reduction factor that accounts for the correlation between the time varying fluid velocity and sediment concentration the net bed load transport rate under nonlinear waves is assumed to be onshore and proportional to u3 where u is the standard deviation of the horizontal velocity the probabilities of sediment movement and suspension are introduced to account for the initiation of sediment movement and suspension simple functions are proposed to account for the effects of a steep bottom slope on the bed load and suspended sediment transport rates the proposed formulas are found to be in agreement with three data sets within a factor of about 2 the proposed formulas are shown to be consistent with existing simple formulas the formulas are incorporated into a time averaged wave model and the continuity equation of bottom sediment to predict the beach profile evolution the numerical model is compared with seven small scale tests including berm erosion tests and seven large scale tests including dune erosion tests the numerical model predicts the overall beach profile evolution including the berm and dune erosion but does not always predict the fairly subtle profile changes including bar migration accurately

sediment transport near the break point associated with cross shore gradients in vertical eddy diffusivity sediment clouds entrained and mixed vertically into the water column at the breakpoint were observed to advect offshore with the return current following wave breaking at a natural beach an advection diffusion model is applied to this phenomenon providing for cross shore gradients in vertical eddy diffusivity within and beyond the surf zone which result in differential entrainment and settlement near the break point results indicate that the horizontal gradient in turbulent vertical sediment mixing can provide a significant mechanism for bar generation even if the surface gravity and infra gravity waves remain uncoupled quantitative estimates of the rate of bar accretion are obtained after calibrating the sediment transport model using field measurements of currents and suspended sediment loads in the absence of other processes accretion rates of order 20 mm hour associated with the horizontal gradient in vertical diffusivity are predicted on the offshore bar

bar trough generation on a natural beach mechanisms for bar trough generation are examined using velocities measured in the field applied to the bowen 1980 bailard 1981 energetics based sediment transport model measurements consist of a cross shore array of nine electromagnetic current meters spanning the surf zone and daily bathymetric surveys during a 10 day period during which two storms occurred when the bathymetry evolved from a three dimensional terrace to a well developed linear bar the model predicts bed and suspended load transport separately based on various velocity moments the velocities are partitioned into mean currents low frequency infragravity and shear instabilities 0 05 hz to determine the relative importance of various mechanisms to the total transport velocity moments are computed over 90 min intervals to resolve tidal fluctuations tidal signatures were apparent in all modes of transport predicted transport rates are integrated and compared with daily cross shore bathymetric profiles averaged over a 400 m length of beach the suspended load terms were an order of magnitude greater than bed load terms owing to the low fall velocity of the fine grain sand within the surf zone model results for this experiment indicate the dominant mechanism for bar development was sediments mobilized by the strong longshore current and incident short waves within the surf zone and transported offshore by the mean undertow and shoreward transport onshore due to short wave velocity skewness using standard coefficients the model correctly predicted the first order movement of the bar during storms but underpredicted trough development and did not always perform well during mild wave conditions

a stereoscopic method for rapid monitoring of the spatio temporal evolution of the sand bed elevation in the swash zone abstract a stereoscopic technique is developed in order to measure the sand bed elevation in the swash zone at the wave time scale the present technique allows one to perform highly resolved measurements both in time and in space an accuracy and a precision of less than 300 m and 600 m respectively are obtained in each direction this technique has been used during a large scale wave flume experiment where an erosive process of a plane beach is studied the stereoscopic technique allows one to accurately measure the long term evolution of the beach profile in addition spatially dependent variability on shorten time scales is observed featuring accretion as well as erosion at the wave time scale

shock implantation of martian atmospheric argon in four basaltic shergottites a laser probe 40ar 39ar investigation spatially resolved argon isotope measurements have been performed on neutron irradiated samples of two martian basalts los angeles and zagami and two martian olivine phyric basalts dar al gani dag 476 and north west africa nwa 1068 with a similar to 50 mu m diameter focused infrared laser beam it has been possible to distinguish between argon isotopic signatures from host rock matrix minerals and localized shock melt products pockets and veins the concentrations of argon in analyzed phases from all four meteorites have been quantified using the measured j values ar 40 ar 39 ratios and k2o wt in each phase melt pockets contain on average 10 times more gas 7 24 ppb ar 40 than shock veins and matrix minerals 0 3 3 ppb ar 40 the ar 40 ar 36 ratio of the martian atmosphere estimated from melt pocket argon extractions corrected for cosmogenie ar 36 is los angeles similar to 1852 zagami similar to 1744 and nwa 1068 similar to 1403 in addition los angeles shows evidence for variable mixing of two distinct trapped noble gas reservoirs 1 martian atmosphere in melt pockets and 2 a trapped component possibly martian interior ar 40 ar 16 480 490 in matrix minerals average apparent ar 40 ar 39 ages determined for matrix minerals in the four analyzed meteorites are 1290 ma los angeles 692 ma zagami 515 ma nwa 1068 and 1427 ma dag 476 these ar 40 ar 39 apparent ages are substantially older than the similar to 170 0474 ma radiometric ages given by other isotope dating techniques and reveal the presence of trapped 40ar cosmic ray exposure cre ages were measured using spallogenic ar 16 and ar 38 production los angeles 3 1 0 2 ma zagami 2 9 0 4 ma and nwa 1068 2 0 0 5 ma yielded ages within the range of previous determinations dag 476 however yielded a young cre age 0 7 0 25 ma attributed to terrestrial alteration the high spatial variation of argon indicates that the incorporation of martian atmospheric argon into near surface rocks is controlled by localized glass bearing melts produced by shock processes in particular the larger mm size melt pockets contain near end member martian atmospheric argon based on petrography composition and argon isotopic data we conclude that the investigated melt pockets formed by localized in situ shock melting associated with ejection three processes may have led to atmosphere incorporation 1 argon implantation due to atmospheric shock front collision with the martian surface 2 transformation of an atmosphere filled cavity into a localized melt zone and 3 shock implantation of atmosphere trapped in cracks pores and fissures

suspended sand transport in surf zones 1 three tests were conducted in a wave flume to investigate time averaged suspended sediment transport processes under irregular breaking waves on equilibrium beaches consisting of fine sand free surface elevations were measured at ten locations for each test velocities and concentrations were measured in the vicinity of the bottom at 94 elevations along 17 vertical lines the relations among the three turbulent velocity variances are found to be similar to those for the boundary layer flow the vertical variation of the mean velocity which causes offshore transport is fitted by a parabolic profile fairly well the vertical variation of the mean concentration is fitted by the exponential and power form distributions equally well the ratio between the concentration standard deviation c and the mean varies little vertically the correlation coefficient uc between the horizontal velocity and concentration which results in onshore transport is of the order of 0 1 and decreases upward linearly the offshore and onshore transport rates of suspended sediment are estimated and expressed in terms of the suspended sediment volume per unit area a time averaged numerical model is developed to predict as well as the mean and standard deviation of the free surface elevation and horizontal velocity the bottom slope effect on the wave energy dissipation rate db due to wave breaking is included in the model the computation can be made well above the still water shoreline with no numerical difficulty reflected waves from the shoreline are estimated from the wave energy flux remaining at the shoreline the numerical model is in agreement with the statistical data except that the undertow current is difficult to predict accurately the measured turbulent velocities are found to be more related to the turbulent velocity estimated from the energy dissipation rate df due to bottom friction the suspended sediment volume expressed in terms of db and df can be predicted only within a factor of about 2 the roller effect represented by the roller volume flux does not necessarily improve the agreement for the three tests

breaker turbulence and sediment suspension in the surf zone field measurements of fluid velocities and suspended sediment concentrations were used to investigate the relative role of coherent vortices related to wave breaking in suspended sediment dynamics the measurements were obtained from a barred intermediate type beach and the instrument rig was exposed to a range of wave types during the experiment including shoaling waves and both spilling and plunging breakers the time scale of the observed breaker vortices was 5 hz and thus in the frequency range of wave orbital motion coherent breaker vortices were separated from wave orbital motions and incoherent higher frequency turbulence using a threshold magnitude for the vertical velocity component plunging breakers displayed the largest root mean square rms and maximum vertical velocities the latter reaching approximately 1 m s 1 these measurements were made at an elevation of 0 15 m above the bed given the observed scale of the breaker vortices and the phase match between suspended sediment concentrations and fluid velocities the turbulence injected into the water column by the plunging breakers played a significant role in suspending bed sediment on the other hand the role of coherent vortex structures in suspending sediment under spilling breakers and shoaling waves is more limited rms vertical velocities under the spilling breakers and shoaling waves in this experiment were respectively a factor 2 and 4 smaller than for plunging breakers different phase relationships were observed between the horizontal fluid velocity and vortex induced sediment suspension for each of the wave types which may contribute to an explanation of net offshore and onshore sediment transport observed during episodes of beach erosion and recovery respectively

fluid acceleration effects on suspended sediment transport in the swash zone 1 suspended sediment concentrations and fluid velocities measured in the swash zone of a high energy steep beach were used to investigate the importance of fluid accelerations to suspended sediment transport swash flow acceleration was nearly constant at about one half downslope gravitational acceleration with two important exceptions we observed strong short lived periods of accelerating uprush at the beginning of the swash cycle and decelerating backwash at the end of the swash cycle magnitudes of both approximately twice that of the expected downslope gravitational acceleration interestingly spikes in suspended load followed the anomalies in acceleration in a way that was not apparent from the nearly symmetric in magnitude ensemble averaged velocity time series suspended load values were largest during accelerating uprush associated with the shoreward propagating turbulent bore or swash front during backwash suspended loads were generally not as large correspondingly suspended sediment transport rates obtained from the sediment concentration and velocity measurements showed best comparisons with a modified sediment transport model that includes a physical mechanism for enhancing transport rates due to flow acceleration the modified sediment transport model reduced the overall root mean square prediction error by up to 35 and shifted the predicted peak in uprush sediment transport rate earlier in the swash cycle resulting in a better fit to the observations these findings suggest that the inclusion of the acceleration term may account for physical mechanisms that include bore turbulence and horizontal pressure gradients typically associated with the accelerating portion of uprush

the predictability of cross shore bed evolution of sandy beaches at the time scale of storms and seasons using process based profile models deterministic and probabilistic profile models have been compared with hydrodynamic and morphodynamic data of laboratory and field experiments on the time scale of storms and seasons the large scale laboratory experiment is a pure 2d case and offers and ideal test case for cross shore profile models as disturbing alongshore non uniformities are absent the field experiments are performed at the egmond site the netherlands during the eu coast3d project and represent storm time scale oct nov 1998 as well as seasonal time scale conditions may 1998 sep 1999 the objective of the paper is to present information of coastal processes on these time scales and to assess the predictive capabilities coastal process based profile models with respect to hydrodynamics and morphodynamics at sandy beaches on the time scales of storms and seasons profile models can quite accurately errors smaller than 10 represent the cross shore significant wave height distribution in the surf zone if the wave breaking model is properly calibrated the wave breaking coefficient should be a function of local wave steepness and bottom slope for most accurate results profile models can reasonably represent the cross shore and longshore currents undertow in a pure 2d case and in 3d field conditions profile models including cross shore mixing effects and breaker delay effects do not produce better predictions of the longshore and cross shore current velocities profile models using default settings can quite reasonably simulate the behaviour of the outer and inner bars on the storm time scale the behaviour of the beach cannot be modelled with sufficient accuracy on the storm time scale profile models can reasonably simulate the post storm onshore bar migration provided that the near bed orbital velocities and wave asymmetry related sand transport are represented in a sufficiently accurate way using non linear wave theories profile models cannot simulate the beach recovery processes on the post storm time scale because these essentially 3d processes are not sufficiently known to be included in the models profile models using default settings cannot simulate the behaviour of the outer and inner bars and the beach on the seasonal time scale the behaviour of the outer bar on the seasonal time scale can only be represented properly after tuning using measured bed profiles the simulation of the inner bar and beach morphology on the seasonal time scale could not be improved by tuning

shock veins in the central uplift of the manicouagan impact structure context and genesis we describe the development of shock veins that penetrate the anorthositic central uplift of the manicouagan impact structure they occur as thin 2 5 mm wide linear micro fault systems that can be traced for several meters in length and which predominantly trend radially from the point of impact the shock veins are distinguished by the development of maskelynite along vein margins and stishovite in vein matrices which are otherwise absent in non veined regions these phases define a shock excursion of up to 30 gpa in contrast to bulk shock effects of 12 gpa defined by development of shatter cones planar fractures and planar deformation features in various minerals the shock veins at manicouagan share many similarities with vein systems developed in meteorites they also provide an in situ context with which to better understand meteoroid source and lofting conditions in addition to containing high pressure phases the shock veins exhibit evidence for high temperature partial melting of host silicate clasts with the generation of flow textured fragments and glasses the formation of microcrystallites and dendrites from some melts indicates rapid cooling we propose a two stage generation mechanism comprising an initial high pressure shock excursion estimated to last 0 5 s based on projectile size considerations followed by a longer high temperature pulse of a few seconds duration we suggest that the shock excursion is initiated by target heterogeneities that cause distortions in the hemispherically propagating shock front this results in radially oriented tearing and vein formation with shock amplification occurring via intra vein shock reverberation high speed displacement along the veins is driven by stress release on rarefaction which results in frictional melting via adiabatic heating

identification of intense intermittent coherent motions under shoaling and breaking waves laboratory measurements of the instantaneous horizontal and vertical turbulent velocities u and w induced by regular waves spilling on a rough impermeable slope were analyzed to elucidate the nature of turbulence generated in the bottom boundary layer and by wave breaking the analyses focused on the instantaneous turbulent events such as the absolute shear stress u w and turbulent kinetic energy k u 2 w 2 2 below trough level inside the surf zone the horizontal and vertical velocity records showed intense intermittent turbulent events that did not occur with the passing of each wave and the instantaneous quantities of and k could not be explained in terms of the phase averaged quantities the intermittent turbulent events extended into the bottom boundary layer inside the surf zone and in this region the infrequent but intense turbulence generated by wave breaking was an order of magnitude larger than the turbulence generated locally at the boundary two techniques were used to analyze the turbulent motions a quadrant analysis technique showed that although the large turbulent motions did not occur with each wave they were phase dependent near trough level and less so near the bottom a conditional sampling technique quantified the intensity and duration of the turbulent motions indicating that coherent events intense events occurred for 10 2 of the record and accounted for approximately 50 20 of the turbulent motion it is likely that the exactitude of these statistics will differ depending on breaker type nevertheless these statistics indicated that large turbulent motions are infrequent but contribute significantly to the turbulence intensity and possibly the suspension of bottom sediments

analysis of surf zone turbulence measurements of turbulent kinetic energy k under surf zone waves are analyzed to show how k varies over depth between breaker point and shoreline and how k depends on the beach slope it is found that the variation of k over depth is remarkably weak large values being measured a few percent of the depth above the bottom a simple model for the dissipation mechanism makes it possible to derive an empirical formula for the time averaged k that accurately describes all the data considered reliable

geological and hydrological controls on the producibility of coalbed methane geological and hydrological comparison of two united states coalbed methane basins the prolific san juan basin and the marginally producing sand wash basin indicates that coal distribution and rank gas content permeability ground water flow and depositional and structural setting are critical controls on coalbed methane producibility a complex interplay and moreover a synergy amongst these controls determines high productivity this paper proposes a basin scale explanation for the prolific and marginal production in the two basins and that can be applied to evaluation of coalbed methane potential in coal basins worldwide high productivity is governed by 1 thick laterally continuous coals of high thermal maturity 2 basinward flow of ground water through coals of high rank and gas content orthogonally toward no flow boundaries regional hingelines fault systems facies changes and or discharge areas and 3 conventional trapping along those boundaries to provide additional gas beyond that sorbed on the coal surface

observations of turbulence within the surf and swash zone of a field scale sandy laboratory beach abstract current coastal evolution models generally lack the ability to accurately predict bed level change in shallow

turbulence in the swash and surf zones a review this paper reviews mainly conceptual models and experimental work in the field and in the laboratory dedicated during the last decades to studying turbulence of breaking waves and bores moving in very shallow water and in the swash zone the phenomena associated with vorticity and turbulence structures measured are summarised including the measurement techniques and the laboratory generation of breaking waves or of flow fields sharing several characteristics with breaking waves the effect of air entrapment during breaking is discussed the limits of the present knowledge especially in modelling a two or three phase system with air and sediment entrapped at high turbulence level and perspectives of future research are discussed

localized shock melting in lherzolitic shergottite northwest africa 1950 comparison with allan hills 77005 the lherzolitic martian meteorite northwest africa nwa 1950 consists of two distinct zones 1 low ca pyroxene poikilically enclosing cumulate olivine fo70 75 and chromite and 2 areas interstitial to the oikocrysts comprised of maskelynite low and high ca pyroxene cumulate olivine fo68 71 and chromite shock metamorphic effects most likely associated with ejection from the martian subsurface by large scale impact include mechanical deformation of host rock olivine and pyroxene transformation of plagioclase to maskelynite and localized melting pockets and veins these shock effects indicate that nwa 1950 experienced an equilibration shock pressure of 35 45 gpa large millimeter size melt pockets have crystallized magnesian olivine fo78 87 and chromite embedded in an fe rich al poor basaltic to picro basaltic glass within the melt pockets strong thermal gradients minimum 1 c m existed at the onset of crystallization giving rise to a heterogeneous distribution of nucleation sites resulting in gradational textures of olivine and chromite dendritic and skeletal olivine crystallized in the melt pocket center has a nucleation density 1 0 x 10 3 crystals mm 2 that is two orders of magnitude lower than olivine euhedra near the melt margin 1 6 x 10 5 crystals mm 2 based on petrography and minor element abundances melt pocket formation occurred by in situ melting of host rock constituents by shock as opposed to melt injected into the lherzolitic target despite a common origin nwa 1950 is shocked to a lesser extent compared to allan hills alh 77005 45 55 gpa assuming ejection in a single shock event by spallation this places nwa 1950 near to alh 77005 but at a shallower depth within the martian subsurface extensive shock melt networks the interconnectivity between melt pockets and the ubiquitous presence of highly vesiculated plagioclase glass in alh 77005 suggests that this meteorite may be transitional between discreet shock melting and bulk rock melting

observations of swash zone velocities a note on friction coefficients 1 vertical flow structure and turbulent dissipation in the swash zone are estimated using cross shore fluid velocities observed on a low sloped fine grained sandy beach raubenheimer 2002 with two stacks of three current meters located about 2 5 and 8 cm above the bed the observations are consistent with an approximately logarithmic vertical decay of wave orbital velocities within 5 cm of the bed the associated friction coefficients are similar in both the uprush and downrush as in previous laboratory results turbulent dissipation rates estimated from velocity spectra increase with decreasing water depth from o 400 cm2 s3 in the inner surf zone to o 1000 cm2 s3 in the swash zone friction coefficients in the swash interior estimated with the logarithmic model and independently estimated by assuming that turbulent dissipation is balanced by production from vertical shear of the local mean flow and from wave breaking are between 0 02 and 0 06 these values are similar to the range of friction coefficients 0 02 0 05 recently estimated on impermeable rough nonerodible laboratory beaches and to the range of friction coefficients 0 01 0 03 previously estimated from field observations of the motion of the shoreward edge of the swash run up

experimental generation of shock induced pseudotachylites along lithological interfaces to understand the mechanism of formation of shock induced pseudotachylites and particularly the role that rock heterogeneities and interfaces play in their formation shock recovery experiments were carried out on samples consisting of two distinct lithologies dunite and quartzite it was possible to generate melt veins of 1 6 m width along lithological interfaces at moderate shock pressures 6 to 34 gpa the magnitudes of displacement along the interface strain rate and the kinetic heat production indicate that friction is an important heat source that largely contributes to the energy budget of the melt veins the experimentally produced veins resemble natural s type pseudotachylites the geometry of the veins depends on the orientation of the interface with respect to the shock front and includes strong variations in thickness formation of melt pockets and injection veins sudden changes in vein orientation and sharp vein margins two types of melt were observed vesicle free and vesicular melts dense vesicle free melt rock is likely to represent high pressure melts vesicular melts were also generated during shock compression but they remained in a molten state during pressure release and continued shearing intermingling of comminuted olivine and melt suggests that ultracataclasis of olivine induced by a dynamic tensile failure is a precursor stage to frictional melting shock wave interferences at the lithological interface provide the necessary stress conditions to start dynamic failure of olivine the composition of the frictional melts ranges from olivine normative to enstatite normative and is thus largely determined by olivine melting the validity of the sequence of friction melting susceptibilities of rock forming minerals inferred from tectonically produced pseudotachylites is confirmed and can now be applied to ultra high strain rates during shock compression

cross shore sand transport by infragravity waves as a function of beach steepness two field data sets of near bed velocity pressure and sediment concentration are analyzed to study the influence of infragravity waves on sand suspension and cross shore transport on the moderately sloping sand motor beach 1 35 the local ratio of infragravity wave height to sea swell wave height is relatively small hig hsw 0 4 most sand is suspended during negative infragravity velocities and qig is offshore directed the infragravity contribution to the total sand flux is considerably larger and reaches up to 60 during energetic conditions on the whole hig hsw is a good indicator for the infragravity related sand suspension mechanism and the resulting infragravity sand transport direction and relative importance

mineralogy petrology and thermal evolution of the benton ll6 chondrite the benton ll6 chondrite is a brecciated meteorite that was observed to fall on january 16 1949 in benton new brunswick canada internally the meteorite comprises light colored subangular to subrounded clasts embedded in a dark grey colored matrix clasts comprise the same mineral phases as the matrix as well as chondrules and larger 50 100 m single mineral grains mainly olivine and orthopyroxene composite polyphase clasts can be serveral millimeters in length numerous examples of post brecciation and post annealing sheraring and displacement at the micron to millimeter scale occur in the form of shock veins benton is a shock stage s3 chondrite which experienced shock pressures on the order of 15 20 gpa with an estimated post shock temperature increase of 100 150 c benton s history comprises a sequence of events as follows 1 chondrule formation and initial assembly 2 brecciation 3 thermal metemorphism and 4 shock veining events 2 and 4 can be equated with distinct impact events the former representing bombardment of target material that remained in situ or collisionally fragmented during metamorphism and then gravitationally reassembled the latter probably with release from the source body to yield a meteorite thermal metamorphism post dates brecciation the mean equilibration temperature recorded in the benton ll6 chondrite is 890 c obtained using the two pyroxene geothermometer

sediment suspension and turbulence in the swash zone of dissipative beaches abstract this paper investigates mechanisms for stirring and transport of suspended sediment by infragravity scale swash using high frequency field measurements of horizontal and vertical flow velocities water depths and sediment concentration profiles the field data suggest that vertical velocity fluctuations generated by coherent eddies can be important to the process of sediment suspension and can contribute to asymmetrically distributed sediment transport rates between the uprush and backwash phases of the swash cycle this result indicates that the traditional and often used proxy for bed shear stress based solely on measurements of the horizontal component of flow u i e b fu 2 where is the water density and f is a friction factor may be inadequate when used in energetics type sediment transport models applied to the swash which is indeed the case we demonstrate that a bed shear stress formulation which is more consistent with the physics leads to improved predictive capability for energetics type transport models this formulation is based on the correlation between the horizontal and turbulent vertical components of the flow i e b uw despite the improvement it is evident that considerable amounts of calibration data are still required before each application of this model type moreover our data shows that the issue of calibration coefficients is more problematic than generally appreciated the calibration coefficients for energetics type models on a given beach not only differ between uprush and backwash but also vary with position within the swash zone particularly on the uprush phase

calving seismicity from iceberg sea surface interactions 1 iceberg calving is known to release substantial seismic energy but little is known about the specific mechanisms that produce calving icequakes at yahtse glacier a tidewater glacier on the gulf of alaska we draw upon a local network of seismometers and focus on 80 hours of concurrent direct observation of the terminus to show that calving is the dominant source of seismicity to elucidate seismogenic mechanisms we synchronized video and seismograms to reveal that the majority of seismic energy is produced during iceberg interactions with the sea surface icequake peak amplitudes coincide with the emergence of high velocity jets of water and ice from the fjord after the complete submergence of falling icebergs below sea level these icequakes have dominant frequencies between 1 and 3 hz detachment of an iceberg from the terminus produces comparatively weak seismic waves at frequencies between 5 and 20 hz our observations allow us to suggest that the most powerful sources of calving icequakes at yahtse glacier include iceberg sea surface impact deceleration under the influence of drag and buoyancy and cavitation numerical simulations of seismogenesis during iceberg sea surface interactions support our observational evidence our new understanding of iceberg sea surface interactions allows us to reattribute the sources of calving seismicity identified in earlier studies and offer guidance for the future use of seismology in monitoring iceberg calving

the formation of the sudbury breccia in the north range of the sudbury impact structure abstract in the north range of the ca 1 85 ga sudbury impact structure massive bodies of sudbury breccia cut across the archean levack gneiss complex and early proterozoic matachewan diabase dykes the complex underlies the sudbury igneous complex sic which represents an impact melt sheet that lined the floor of the impact crater the breccia occurs as 1 100 m wide irregular bodies that contain rounded clasts of diabase and tonalitic and dioritic levack gneiss within a fine grained to aphanitic black to dark grey matrix mineral chemical analyses and rietveld analyses based on x ray diffraction patterns show that the breccia matrix contains microclasts of magnesiohornblende oligoclase and quartz surrounded by metamorphic andesine laths actinolite kfeldspar albite and chlorite which crystallized during cooling of the sic on binary oxide sio2 diagrams breccia values plot on a compositional mixing line between those of the more felsic tonalitic gneiss and the more mafic dioritic gneiss and diabase the breccia has concentrations in rare earth elements rees intermediate between those of the dioritic and tonalitic gneisses and a ree pattern with a negative slope that is less pronounced than those of the gneisses this is due to the addition of a minor diabase component that has a slightly negative ree slope suggesting that the breccia is a mix of comminuted tonalitic gneiss dioritic gneiss and minor diabase comminution and cataclasis of these source rocks occurred along pre existing anisotropies and fractures that formed and were reactivated during the growth and collapse of the transient crater the comminuted materials mixed together as large bodies of breccia that were injected in dilational sites that opened during the upward expansion and collapse of the crater