steep beach morphology changes due to energetic wave forcing abstract the three dimensional variability of the sub aerial beach is examined for waimea bay hawaii a steep slope pocket beach subject to energetic winter swell events the beach is mapped using 32 real time kinematic global positioning system rtk gps surveys collected from march 1996 to july 1997 the survey method provides 4 m horizontal spacing and 2 3 cm vertical accuracy the primary morphology change is the episodic removal and re establishment of a foreshore dune during the winter swell season the average sand volume flux between surveys reaches 8 and 4 m 2 day during peak erosion and accretion periods the sand volume of the sub aerial beach is found to be highly correlated 0 96 with the position of the shoreline longshore variations in morphology include beach cusps with typical peak to trough amplitudes of 0 5 1 5 m and longshore wavelengths of 30 70 m the relationships between the energetic swell forcing and the volume and flux of sand on the sub aerial beach are examined the highest correlation 0 88 is found between the total sand volume and the wave energy flux after the latter is filtered following wright et al wright l d short a d green m o 1985 short term changes in the morphodynamic states of beaches and surf zones an empirical predictive model mar geol 62 339 364 the filter is effective at capturing slow accretion phases following energetic erosion events

environmental and morphologic controls on wave induced dune response abstract the pacific northwest of the united states exhibits complex spatial patterns of storm induced coastal foredune erosion using oceanographic and morphologic data from three field sites encompassing a range of subaqueous and subaerial coastal profile configurations a relationship is found between morphologic characteristics and dune volume changes during storm events producing high water levels the data suggest that dune erosion increases with increasing backshore beach slope and that under particular oceanographic forcing conditions wave driven processes can grow the lower portion of dunes on low sloping dissipative beaches these observations of environmental and morphologic controls on storm induced dune impacts are further explored using xbeach a state of the art numerical model capable of simulating interactions between hydrodynamics and morphology consistent with the field data model simulations indicate that wave driven dune growth may occur on low sloping beaches in cases where the dynamic still water level still water level plus wave setup is lower than the dune toe however these accretional processes are restricted to events where limited incident wave energy impacts the dune cases with steep backshore beach slopes or dynamic still water levels exceeding the dune toe instead typically result in dune erosion additionally the model simulations suggest that morphologic properties of the shelf nearshore and the dune itself influence storm induced dune volume change therefore morphologic features far from the dune face including shelf geometries shaped in part by the regional historical sediment budget may have important implications on the susceptibility of coastal foredunes systems to storm impacts

a simple ice ocean model for the greenland sea abstract a steady coupled model of the upper ocean circulation and ice cover in a meridional channel is presented and applied to the greenland sea the main ocean gyre is driven by wind stress however a nonzero boundary condition on meridional velocity is applied at the western side to produce a southward flowing coastal current representative of the east greenland current egc to match the egc to the interior sverdrup solution a munk type western boundary layer is introduced the upper ocean temperature is governed by an advection diffusion equation which is forced at the boundaries and by heat exchange with the atmosphere the ice model is purely thermodynamic and the ice edge position is determined iteratively since the streamfunction and temperature fields depend on the ice cover and in turn the ice cover is determined by both the ocean and air temperature the range of behavior of the temperature field and ice edge position is studied as a function of the ice ocean drag the wind stress tra

storm induced response of a nearshore bar system abstract a nearshore bar system was surveyed periodically through a storm and the following recovery period the data showed a very rapid response of morphology to changing wave conditions and allowed various models on bar formation to be tested under low energy conditions prior to the storm a small bar was surveyed 13 m offshore both the high reflectivity of the beach and the cross shore distance to the bar are consistent with a model of sediment convergence at the node or antinode of a standing wave of incident period such a small scale bar may be a common feature on beaches with steep foreshores and more gentle offshore slopes with the increase in wave height during the storm the bar became better developed and migrated offshore at rates up to 2 2 m h 1 the bar maintained its form in that the ratio of trough depth to crest depth h t h c remained roughly constant the bar was in no way related to processes which would cause the convergence of sediment in the breaker zone through most of the storm the bar crest distance offshore was typically only 10 of the surf zone width analysis of the bar distance offshore in terms of a standing wave motion showed that the causative wave period must have been much longer than that of incident waves probably on the order of a minute surf zone wave data showed significant energy in the infragravity band at these periods although no definite link has been made after the height of the storm the bar had a crescentic morphology the development of this morphology occurred very rapidly with parts of the bar migrating onshore at rates up to 1 2 m h 1 in contrast to the storm during the recovery period h t h c varied by nearly a factor of three analysis of the offshore and longshore length scales showed the bar to be similar to one which would be generated by a standing mode 1 edge wave of period on the order of one minute

multi scale morphodynamics of an estuarine beach adjacent to a flood tide delta assessing decadal scale erosion abstract estuarine beaches are ubiquitous yet understudied coastal systems the mixed hydrodynamic processes such as combined tidal and wave forcing and the influence of adjacent sedimentary features such as flood tide deltas ftds leads to complex morphodynamic processes as such the dynamics and evolution of these important coastal systems are poorly understood this study synthesises a set of analyses conducted on an estuarine beach in southeast australia over multiple temporal scales nearshore waves and currents were measured and used to determine the processes driving seasonal to yearly beach change between 2007 and 2010 these results were compared to decadal scale beach change determined from aerial photos between 1963 and 2006 we found the westward transport of sediment towards the inner estuary was the dominant nearshore process leading to erosion in the eastern regions of the beach near the estuary entrance and accretion in the west over yearly time scales cross shore sediment transport occurred during winter storm swell conditions leading to erosion in more exposed sites and some limited accretion in sheltered zones most likely due to sediment input from the flood tide delta however severe storm swell events that propagated into the estuary led to a loss of sediment and erosion across the entire beach which was not recovered during the study period it is likely that the erosion processes observed in the short to medium term days to years analyses are the conditions that led to the long term shoreline retreat observed in the aerial photograph record the long term shoreline retreat since 1963 is likely a result of a negative sediment balance due to movement of the ftd and a lack of sediment input in the eastern regions of shoal bay shoreline retreat will likely continue unless increased sediment input occurs from marine sources or shoreline interventions are maintained

seasonal changes in beach morphology along the sheltered coastline of perth western australia abstract seasonal change in beach morphology is traditionally ascribed to a variation in the incident wave energy level with calm conditions in summer resulting in wide beaches with pronounced subaerial berms and energetic conditions in winter causing narrow beaches with nearshore bar morphology the coastline of perth western australia is characterised by a large seasonal variation in the incident wave height and local beaches exhibit a distinct seasonal change in morphology however these morphological changes are better explained by a seasonal reversal in the littoral drift direction than by variations in the incident wave energy conditions in summer when northward sediment transport prevails due to sea breeze activity beaches located south of coastal structures headlands or rocky outcrops become wider due to the accumulation of sediment against the obstacle these beaches will subsequently erode in winter during storms when the longshore sediment transport is toward the south in contrast beaches located north of obstacles will become narrower during summer and wider during winter the usefulness of the dimensionless fall velocity h b w s t where hb is the breaker height ws is the sediment fall velocity and t is the wave period as a predictor of presence absence of bar morphology and beach type was investigated it was found that fluctuates around the threshold of bar formation 1 5 2 over a variety of time scales daily weekly and seasonally these temporal variations in in conjunction with the relatively low wave energy level that characterises the coast negates the development of beach and nearshore morphology that is in equilibrium with the hydrodynamic conditions as a result bar occurrence and beach type can not be readily predicted using along the perth coast

a simplified ice ocean coupled model for the antarctic ice melt season abstract in the antarctic ocean sea ice melts mostly by warming of the ocean mixed layer through heat input mainly solar radiation in open water areas a simplified ice upper ocean coupled model is proposed in which sea ice melts only by the ocean heat supplied from the air the model shows that the relationship between ice concentration i e fraction c and mixed layer temperature t converges asymptotically with time c t relationship which agrees with observed c t plots during summer in the sector 25 45 e this relationship can be used for estimating the bulk heat transfer coefficient between ice and ocean by fitting to observations and a value of 1 2 10 4 m s 1 is obtained the model shows that the ratio of the heat used for melting to the heat input through open water is inclined to be determined as a function of ice concentration for typical conditions in the antarctic ice melt season the ratio ranges mostly between 0 7 and 0 9 when the model is extended to two dimensions in the meri

morphometric classification of swell dominated embayed beaches abstract globally embayed beaches are common to hilly and mountainous coastlines they are typically characterised by two headlands that are a primary control on incident wave exposure and beach morphodynamics embayed beaches exist under a range of headland morphologies and degree of embaymentisation here we present a generalised embayment morphometric parameter e which classifies the geomorphological setting of embayed beaches based on the embayment indentation and area we apply this to 168 swell dominated embayed beaches from 6 regions using open access imagery the embayment morphometric parameter e was subjected to k means cluster analysis to identify 4 classes of embayed beaches with increasing e indicating greater headland influence and impact on incident wave exposure the classes range from 1 to 4 with increasing degree of embayment the most common is class 2 43 n 73 which represents embayed beaches that have moderate embayment indentation and headland influence there are clear trends in embayment geometry regardless of location wave climate or tidal regimes within the embayments there were 6 possible headland orientations types h1 h6 the most common 58 n 97 is when both headlands are orientated outwards from the beach h6 and may result in greater morphological beach response from less headland shadowing compared with headlands orientated inwards onto the beach h1 in summary we have developed a simple classification scheme for embayed beaches based on degree of indentation and headland orientation that can be applied to any embayed beach globally

holocene evolution of a rock bounded barrier lagoon system cies islands northwest iberia coastal geomorphology results from the combined effects of contemporary dynamics sea level rise and the inherited geological framework yet the relative importance of these driving mechanisms may change throughout the evolutionary history of coastal deposits in this contribution we analyse the depositional history of the cies islands barrier lagoon system based on lithofacies radiocarbon ages and pollen analysis our results reveal a sedimentary sequence that provides evidence for striking changes in the dynamical functioning of this complex since the mid holocene the sedimentary sequence commenced about 7700 cal years bp by fresh water ponding of an upland depression located about 4 m below present mean sea level fresh water ponds were infilled by aeolian sediments following a gradual lowering of the water table 4000 cal years bp post 3600 cal years bp sea level rise allowed water oscillations to reach the elevation of the bedrock causing the inundation of fresh water ponds and subsequent lagoonal and marine sedimentation subsequently landward and upward migration of a sand barrier led to overwash and deposition of sand in the newly formed lagoon the resultant sedimentary sequence suggests that climatic conditions played an important role controlling the sedimentation regime during the entire history of the basin changing water table levels during early stages of evolution and increasing storminess during more recent times in addition background sea level rise related to the holocene transgression was a key factor in controlling the evolution of the system yet its influence depended to an extent on the relative elevation of the bedrock topography copyright 2009 john wiley sons ltd

strain memory of 2d and 3d rigid inclusion populations in viscous flows what is clast spo telling us abstract we model the development of shape preferred orientation spo of a large population of two and three dimensional 2d and 3d rigid clasts suspended in a linear viscous matrix deformed by superposed steady and continuously non steady plane strain flows to investigate the sensitivity of clasts to changing boundary conditions during a single or superposed deformation events resultant clast spos are compared to one developed by an identical initial population that experienced a steady flow history of constant kinematic vorticity and reached an identical finite strain state allowing examination of spo sensitivity to deformation path rotation paths of individual triaxial inclusions are complex even for steady plane strain flow histories it has been suggested that the 3d nature of the system renders predictions based on 2d models inadequate for applied clast based kinematic vorticity gauges we demonstrate that for a large population of clasts simplification to a 2d model does provide a good approximation to the spo predicted by full 3d analysis for steady and non steady plane strain deformation paths predictions of shape fabric development from 2d models are not only qualitatively similar to the more complex 3d analysis but they display the same limitations of techniques based on clast spo commonly used as a quantitative kinematic vorticity gauge our model results from steady superposed and non steady flow histories with a significant pure shearing component at a wide range of finite strain resemble predictions for an identical initial population that experienced a single steady simple shearing deformation we conclude that individual 2d and 3d clasts respond instantaneously to changes in boundary conditions however in aggregate the spo of a population of rigid inclusions does not reflect the late stage kinematics of deformation nor is it an indicator of the unique mean kinematic vorticity experienced by a deformed rock volume

longshore variability of beach states and bar types in a microtidal storm influenced low energy environment beach classification models are widely used in the literature to describe beach states in response to environmental conditions these models were essentially developed for sandy barred to barless beaches in micro to mesotidal environments subject to moderate to high wave energy conditions and have been based on field studies over limited stretches of coast here we further interrogate the performance of the australian beach classification scheme by analysing beach states and corresponding bar types on a regional scale in a storm influenced low wave energy microtidal environment using a large and unique spatial and temporal dataset of supra and subtidal beach morphology and sedimentology the 200 km long coast of the gulf of lions in themediterranean consists of quasi continuous sandy beaches with a well developed double sandbar system all the reported classical beach stateswere observed on this coast from reflective to dissipative alongwith two more unusual states the rock platform constrained beach state which is associated with bedrock outcrops and the non barred dissipative beach statewhich ismore commonly found in large tidal range settings lidar bathymetry shows that the transitions between beach state zones are marked mainly headlands but transitions also occur progressively along stretches of continuous sandy beach the longshore distribution of beach states and associated bar types on a regional scale can be related to the variability of hydrodynamic conditions wave incidence and energy and sediment characteristics particle size however the influence of these parameters on beach state seems to be largely controlled by the geological context such as the presence of a river mouth headland or rock platform finally we assessed the ability of the parameter commonly used to characterise beach states which combines wave characteristics and sediment fall velocity to predict the observed beach states and bar types using a very large set of hydrodynamic and sedimentary data our results based on high frequency spatial sampling show that the fall velocity of the subtidal sediment coupled with wave statistics one month prior the observed beach state strongly improved the predictive power of the parameter

a kinematic model for deformation within brittle shear zones textural analysis of fault gouge indicates that displacement of particles within brittle shear zones occurs by three diaerent modes synthetic riedel shears antithetic riedel shears and shearing particulate flow a kinematic model is developed which incorporates these three slip modes and constrains the combined deformation to be simple shear parallel to the shear zone boundaries penetrative fabric p foliation and shape preferred orientation of survivor grains commonly observed in foliated fault gouge is assumed to be a result of the shearing particulate flow only the model which relates penetrative fabric orientation to the relative shear rates on riedel shears and shearing particulate flow reconciles inclined p foliation and high g 10 shear strain 1999 elsevier science ltd all rights reserved

morphological changes in a cuspate sandy beach under persistent high energy swells renaca beach chile abstract the present work proposes a morphological evolution model for sandy cuspate beaches which depends on two parameters swash excursion s and offshore wave steepness h0 l0 the model was derived from observations of morphology and wave climate at renaca beach in central chile comprising in situ instrumentation topographic surveys wave modeling and optical imagery it was found that wave steepness alone was unable to explain the morphological changes observed on the beach rather results indicate that swash excursion is better to distinguish between erosive and accretionary events with swash excursion exceeding 29 5 m for more than 12 h being indicative of erosive events while morphological changes are led by s wave steepness correlates with the erosive potential of waves especially when h0 l0 is greater than 0 017 although derived for a specific beach under a limited range of conditions this work adds to the understanding of the dynamic behavior of beaches exposed to persistent high energy swells

a box model study of the greenland sea norwegian sea and arctic ocean we develop a simple dynamical system model of the arctic ocean and marginal seas by applying the martinson killworth and gordon box model of a high latitude two layer ocean to four regions connected together the greenland sea the norwegian sea the arctic ocean and the greenland gyre the latter is a small convective region embedded in the northwest corner of the norwegian sea the model for each region consists of a thermodynamic ice layer that covers two layers of saline water which can under specific conditions become statically unstable and hence create a state of active overturning the system is forced by monthly mean atmospheric temperatures in the four regions by continental runoffs and by inflows from adjacent oceans the model predicts the ice thickness and the temperature and salinity of the water in the upper layer of the four regions also determined are the water temperature and salinity of the lower layer in the arctic ocean box the convective state of any given region i e whether it is in an active overturning mode or not is also determined as a continuous function of time the different output variables of the model which are the response to climatological forcing conditions compare favourably with observed data in the control run the arctic ocean region is characterized by continuous ice cover the greenland sea and greenland gyre have ice cover only during winter and the norwegian sea region never forms an ice cover another feature of the control run is the winter time occurrence of convective overturning in the upper 200 m in the greenland gyre region the model is also used for different anomaly experiments a positive air temperature anomaly which represents a global warming of the earth a negative salt anomaly in the norwegian sea which simulates the great salinity anomaly of the 1960s and 1970s and an increase in the ice flux through fram strait which parameterizes anomalous ice production in the arctic

an evaporite bearing accretionary complex in the northern front of the betic rif orogen the guadalquivir accretionary complex forms a largely oblique prism at the northern edge of the betic rif orogen where miocene sediments plus allochthonous evaporite bearing units were accreted during the displacement of the alboran domain towards the west traditional interpretations end the tectonic structuring of the betic cordillera at the present topographic front beyond which gravitational and or diapiric processes would predominate however this study shows pervasive tectonic deformation in the outer prism with coherent oblique shortening kinematics which is achieved through an alternation of roughly n s arcuate thrust systems connected by e w transfer fault zones these structures accord well with the geophysical models that propose westward rollback subduction the main stage of tectonic activity occurred in the early middle miocene but deformation lasted until the quaternary with the same kinematics evaporite rocks played a leading role in the deformation as evidenced by the suite of ductile structures in gypsum distributed throughout the area s and l gypsum tectonites scaly clay fabrics and brittle fabrics coexist and consistently indicate westward motion top to 290 with subordinate n s contraction almost perpendicular to the transfer zones this work reveals ductile tectonic fabrics in gypsum as a valuable tool to elucidate the structure and deformational history of complex tectonic melanges involving evaporites above the decollement level of accretionary wedges

low energy sandy beaches in marine and estuarine environments a review this review was undertaken to identify locations where low energy beaches may occur and their diagnostic forms and process controls including waves tides and water levels examples are drawn from the sheltered coastline of western australia near perth and fetch limited estuarine environments on the northeast coast of the united states we suggest that the term low energy be used in locations where 1 non storm significant wave heights are minimal e g 0 25 m 2 significant wave heights during strong onshore winds are low e g 0 50 m 3 beachface widths are narrow e g 20 m in microtidal environments and 4 morphologic features include those inherited from higher energy events micro topographic features can persist in the swash zone of low energy beaches under non storm wave conditions there is little evidence of cyclic cross shore sediment exchange bars excepting transverse forms located seaward of low still water level do not appear to be part of the sediment exchange system with the foreshore developing a better definition of the term low energy requires understanding the occurrence and duration of morphological characteristics and the type magnitude and frequency of hydrodynamic controls that are responsible for these characteristics efforts also should be directed toward 1 discriminating between processes generated within basins in true fetch limited environments and processes generated outside basins that affect sheltered environments 2 identifying the relative contributions of tide and surge related water level fluctuations on low energy beach shape and 3 estimating thresholds for beach change

the eigenvalues of steady flow in mohr space abstract the eigenvalues of the velocity gradients tensor and of the position gradients tensor describing instantaneous flow or incremental deformations are easily determined in mohr space as the points of intersection between a mohr circle and the horizontal mohr axis intersections occur only if the tensor has real eigenvalues eigenvectors associated with the eigenvalues are directions of no rotation a line of material particles under an eigenvector does not rotate during steady flow although the line is instantaneously stretching at a rate equal to its corresponding eigenvalue for non spinning steady sub simple shearing there will always be two eigenvectors the angle between the eigenvectors is dependent on the ratio of pure to simple shearing rates this angle decreases as the pure shearing component decreases relative to the simple shearing component superimposed increments of pure shear and simple shear produce an equivalent set of non rotated material lines but the deformation histories of these lines are rotational the influence of eigendirections on geological structures is constrained by the rheology of a rock during deformation in homogenous steady flow no influence may be obvious spatially periodic material softening along eigenvectors during bulk hardening may result in a complex fabric of intersecting shear zones the geometry of the fabric elements provides important information on the bulk deformation of the rock particularly on the bulk shear sense

sliding behavior and deformation textures of heated illite gouge abstract the run products of a series of triaxial friction experiments on an illite rich gouge have been examined petrographically to study the relationship between textural development and sliding mode the samples show a complete range of textures from ones in which the entire gouge layer is deformed to ones in which the deformation is concentrated along narrow subsidiary shears and the rest of the gouge layer is massive the samples with a pervasively developed deformation fabric slide stably whereas the samples containing shear bands show stick slip motion if the intersection angles between boundary parallel and cross cutting riedel shears are also relatively high these textural differences suggest that localization of shear combined with higher angle riedel shears are somehow involved in stick slip motion the orientation of riedel type shears in natural fault zones may also have potential as a paleoseismological tool

evaluation of transtension and transpression within contractional fault steps comparing kinematic and mechanical models to field data abstract rock deformation often is investigated using kinematic and or mechanical models here we provide a direct comparison of these modeling techniques in the context of a deformed dike within a meter scale contractional fault step the kinematic models consider two possible shear plane orientations and various modes of deformation simple shear transtension transpression while the mechanical model uses the finite element method and assumes elastoplastic constitutive behavior the results for the kinematic and mechanical models are directly compared using the modeled maximum and minimum principal stretches the kinematic analysis indicates that the contractional step may be classified as either transtensional or transpressional depending on the modeled shear plane orientation suggesting that these terms may be inappropriate descriptors of step related deformation while the kinematic models do an acceptable job of depicting the change in dike shape and orientation they are restricted to a prescribed homogeneous deformation in contrast the mechanical model allows for heterogeneous deformation within the step to accurately represent the deformation the ability to characterize heterogeneous deformation and include fault slip not as a prescription but as a solution to the governing equations of motion represents a significant advantage of the mechanical model over the kinematic models

an example of inversion in a brittle shear zone abstract a useful tool to document structural inversion inside a shear zone is the identification of overprinted structures which can increase the complexity of the internal fabric of shear zones in the case of thrust faults shear zones can also be problematic due to the occurrence of structures connected to flexural slip along bedding in the recumbent forelimb therefore identification of superimposition among different structures can help to distinguish among these configurations inside a shear zone in central apennines italy favourable conditions along the outcrop of mt tancia s thrust allowed the discovery of two sets of superimposed fabric elements referring to two opposite senses of shear the first is related to thrusting top to e ne whereas the second is likely associated to reactivation in normal sense top to w sw the fabric elements have been mapped and their distribution inside a semi brittle shear zone has been defined high angle extensional shear planes occurring only in the uppermost part of the shear zone closest to the main thrust plane have been interpreted as a new generation of c planes connected to negative reactivation instead of riedel shear planes the overprinting relationship defined inside the shear zone helps in discriminating whether the observed structures developed in the footwall of the main thrust or on the recumbent limb of the hanging wall s anticline the deformation inside the shear zone can be described using a simple shear model at the outcrop scale where reoccurrence of fibrous calcite on shear c planes should control rotation of s planes these are dissolution planes parallel to the xy plane of the local strain ellipsoid at thin section scale instead veins maintaining the same orientation suggest a coaxial deformation due to repeated crystallization events controlled by fluid pressure and differential stress variation

on the mechanics of earthquake afterslip we propose a model for earthquake afterslip based on rate and state variable friction laws in the model afterslip is attributed to the interaction of a velocity weakening region at depth within which earthquakes nucleate with an upper region of velocity strengthening frictional behavior the existence of this upper region is supported by independent seismologic observations and the results of laboratory friction experiments in our model afterslip is the result of relaxation of a stress perturbation within the velocity strengthening region which arises when an earthquake propagates into that region from below we derive the stress perturbation and its decay from the friction constitutive law using a simple 1 degree of freedom approximation for the elastic interaction between the fault and its surroundings this approximation is based on thickness averaged displacements and slip velocities within the velocity strengthening region which is assumed to slip as a rigid block coseismic and postseismic slip are coupled through the thickness averaged stiffness k of the velocity strengthening region we assume k to be inversely proportional to the thickness of this region which means that thicker velocity strengthening regions have a greater tendency to arrest coseismic slip we model the afterslip time histories of the 1966 parkfield and 1987 superstition hills earthquakes and relate the model parameters to physical parameters which may govern the rheologic behavior of the faults in accord with field observations our model predicts 1 that afterslip on some faults scales with the thickness of the unconsolidated sedimentary cover and 2 that proportionally more afterslip occurs for earthquakes in which coseismic surface slip is small compared with coseismic slip at depth velocity strengthening frictional behavior is to be expected for faults within poorly consolidated sediments and for those that contain significant gouge zones about 500 m within their shallow regions 3 5 km combining our results with those of recent laboratory friction studies indicates that relatively young faults with little accumulated fault gouge should exhibit little afterslip

catastrophic emplacement of the heart mountain block slide wyoming and montana usa the mechanism that allowed many tens of km of movement of the enormous block slide floored by the rootless heart mountain detachment fault in nw wyoming has long been a puzzle carbonat rich microbreccia that is widespread along the fault and in dikes in the upper plate contains accreted grains indistinguishable from those observed as fallout from volcanic eruption clouds accretionary lapilli and impact ejecta clouds and in intrusive diatremes in these settings and also in industrial processing accreted grains form when particles in a turbulent gaseous suspension containing limited water adhere to a nucleating grain or to each other elongate grains in thick microbreccia have strong but diverse shap preferred orientations unlike those reported from other fault rocks but instead suggestive of turbulent flow and the microbreccia contains layering and other features of sedimentary character that appear to record deposition from suspension rather than frictional processes along a fault we suggest that frictional heating led to dissociation of carbonate rock along the fault producing supercritical co 2 as the suspending medium high co 2 pressure drastically reduced friction along the fault and allowed continuation of catastrophic movement probably initiated by a volcanic or phreatomagmatic explosion resulting in very large displacement on a low dipping surface earlier slower sliding may have occurred but final emplacement was rapid minutes and spectacular

implications of coulomb plasticity for the velocity dependence of experimental faults simulated fault gouges often deform more stably than initially bare surfaces of the same composition it is important to understand why the sliding stability is enhanced because the presence of gouge on natural faults may have the same effect as seen in experiments and thus explain the absence of earthquakes at shallow depths gouge stabilization in experiments has been attributed to positive contributions to velocity dependence within gouge layers from either dilation maroneet al 1990 or grain fracture biegelet al 1989 in this study we test the hypothesis that some aspects of gouge and initially bare surface velocity dependence are identical by measuring the time dependent constitutive parameterb an important result follows however from stress analysis if both sample configurations are frictional in the mohr coulomb sense each configuration is required to deform on planes of distinctly different orientation the measured strength and velocity dependence will reflect this geometric difference our observed values ofb for simulated granite and quartz gouge are two to two and a half times smaller thanb for initially bare surfaces this difference is completely accounted for if gouge is represented as a cohesionless coulomb plastic material the analysis demonstrates the following points 1 gouge deformation is fully consistent with coulomb plasticity 2 observed gouge velocity dependence is a function of observed strength and 3 the constitutive parameterb is the same for both bare surfaces and gouge furthermore the results suggest that there is no time dependent strengthening associated with stabilizing effects in gouge these observations provide a framework for understanding how slip on initially bare surfaces and gouge deformation are related

a thermodynamic coupled ice ocean model of the marginal ice zone abstract a coupled ice ocean model for thermodynamic growth of sea ice suitable for coupling with a similar dynamic model is considered the model is balanced locally in that no horizontal or vertical advection or diffusion of properties are considered furthermore the emphasis is on short time scales and focusing on applicability to the marginal ice zone a main assumption is the inclusion of lateral growth and decay only in that imbalances in the vertical heat fluxes give rise to a change in compactness rather than thickness of ice the vertical heat fluxes are simply parameterized to be proportional to the temperature difference across thin boundary layers adjacent to the ice atmosphere and ice ocean interfaces the ocean is treated as a two layer model in which the lower deep layer acts as a heat source the temperature of the upper mixed layer is predicted the model exhibits time scale for freezing 2 days and melting 6 5 days which are of the same order of magnitude as for similar dyna

principal fault zone width and permeability of the active neodani fault nobi fault system southwest japan the internal structure and permeability of the neodani fault which was last activated at the time of the 1891 nobi earthquake m8 0 were examined through field survey and experiments a new exposure of the fault at a road construction site reveals a highly localized feature of the past fault deformation within a narrow fault core zone the fault of the area consists of three zone units towards the fault core a protolith rocks b 15 to 30 m of fault breccia and c 200 mm green to black fault gouge within the fault breccia zone cataclastic foliation oblique to the fault has developed in a fine grained 2 m wide zone adjacent to the fault foliation is defined by subparallel alignment of intact lozenge shaped clasts or by elongated aggregates of fine grained chert fragments the mean angle of 20 between the foliation and the fault plane suggests that the foliated breccia accommodated a shear strain of 5 assuming simple shear for the rotation of the cataclastic foliation previous trench surveys have revealed that the fault has undergone at least 70 m of fault displacement within the last 20 000 years in this locality the observed fault geometry suggests that past fault displacements have been localized into the 200 mm wide gouge zone gas permeability analysis of the gouges gives low values of the order of 10 20 m2 water permeability as low as 10 20 m2 is therefore expected for the fault gouge zone which is two orders of magnitude lower than the critical permeability suggested for a fault to cause thermal pressurization during a fault slip

how geometrical constraints contribute to the weakness of mature faults increasing evidence that the san andreas fault has low shear strength1 has fuelled considerable discussion regarding the role of fluid pressure in controlling fault strength byerlee2 3 and rice4 have shown how fluid pressure gradients within a fault zone can produce a fault with low strength while avoiding hydraulic fracture of the surrounding rock due to excessive fluid pressure it may not be widely realised however that the same analysis2 4 shows that even in the absence of fluids the presence of a relatively soft gouge layer surrounded by harder country rock can also reduce the effective shear strength of the fault as shown most recently by byerlee and savage5 as the shear stress across a fault increases the stress state within the fault zone evolves to a limiting condition in which the maximum shear stress within the fault zone is parallel to the fault which then slips with a lower apparent coefficient of friction than the same material unconstrained by the fault here we confirm the importance of fault geometry in determining the apparent weakness of fault zones by showing that the apparent friction on a sawcut granite surface can be predicted from the friction measured in intact rock given only the geometrical constraints introduced by the fault surfaces this link between the sliding friction of faults and the internal friction of intact rock suggests a new approach to understanding the microphysical processes that underlie friction in brittle materials

persistence of storm induced morphology on a modal low energy beach a case study from nw iberian peninsula abstract the morphology of low energy beaches is inherited from high energy events showing a non equilibrium state with the prevailing conditions an example of a sheltered low energy beach rodas beach nw iberian peninsula is examined in this paper the evolution of six beach profiles was analysed during three years in order to investigate the response of this beach under fair weather and storm conditions the beach presented significant morphological differences alongshore due to its geographical location with respect to the wave approach these differences determined the sediment transfer pattern longshore or cross shore sediment transport from the emerged beach towards the adjacent inner shoreface zone significant morphological changes at each profile seem to be related to the incidence of sea waves along the beach superimposed on persistent swell during winter morphological changes were recorded under high energy storms during winter whereas the recovery to prestorm conditions occurred under prevailing fair weather conditions during summer the traditional beach classification parameter relative tidal range rtr which takes into account the effect of the tide range was found unsuitable to properly classify such a mesotidal low energy beach therefore a new parameter the relative tidal range maximum rtrmax was introduced which is a modification of the commonly used rtr rtrmax uses the highest wave breaking height observed during high energy storm conditions instead of the modal wave breaking height by using this parameter the studied beach could be properly classified into the traditional beach classification models taking into account the tide range since low energy beaches generally show a morphology that is inherited from higher energy conditions than the prevailing conditions it is expected that the rtrmax will be applicable for the classification of other low energy sheltered beaches

a convective model for the weddell polynya abstract mechanisms are considered which may induct the large over 105 km2 area of open water or polynya which frequently occurs within the weddell sea winter sea ice we propose that when surface cooling and ice formation decrease the temperature and increase the salinity of the surface water the latter by salt rejection during ice formation in a preconditioned area static instability with intense vertical mixing can occur the upwelled warm salty deep water can then supply enough heat to melt the ice or prohibit its formation even in the middle of winter a simple two level model is derived to test this theory and is found to agree well with observations the process is found to be irregular due to different times of ice onset from one year to the next and to a lesser extent from variations in surface heating and cooling further it is shown that unless the freshwater input exactly balances the increased salinity from the overturn each year the system will either gain or lose salt yearly an

trends in research on beaches and dunes on sandy shores 1969 2019 abstract trends in research on morphologic changes on beaches and foredunes on sandy shores are identified from the 1960s to the present research during this period evolved from early descriptive explanation and classification of profile change to instrumented field investigations to modelling of landform change at larger scales research efforts have become increasingly more collaborative with increasing use of field instrumentation data acquisition systems and remote sensing rich datasets are resulting in more comprehensive computational models human altered systems are of increasing interest but knowledge of these systems lags far behind knowledge of natural systems research is becoming more relevant to societal needs as the vulnerability of coastal populations increases the need for investigation of understudied or unexplored environments including human altered ones is ongoing many basic research issues remain but future studies would profit from the development of new models rather than validating or reconfiguring old models collaboration between geomorphologists and engineers may open up research opportunities particularly in modifying beaches and dunes built for shore protection to provide natural values in restricted space application of models to enhance knowledge of effects of sea level rise and coastal storms would be useful to managers developing resiliency plans

sea ice anomalies observed in the greenland and labrador seas during 1901 1984 and their relation to an interdecadal arctic climate cycle two independent ice data sets from the greenland and labrador seas have been analyzed for the purpose of characterizing interannual and decadal time scale sea ice extent anomalies during this century sea ice concentration data for the 1953 1984 period revealed the presence of a large positive anomaly in the greenland sea during the 1960s which coincided with the great salinity anomaly an upper ocean low salinity water mass that was observed to travel cyclonically around the northern north atlantic during 1968 1982 this ice anomaly as well as several smaller ones propagated into the labrador sea and then across to the labrador and east newfoundland coast over a period of 3 to 5 years a complex empirical orthogonal function analysis of the same data also confirmed this propagation phenomenon an inverse relation between sea ice and salinity anomalies in the greenland labrador sea region was also generally found an analysis of spring and summer ice limit data obtained from danish meteorological institute charts for the period 1901 1956 indicated the presence of heavy ice conditions i e positive ice anomalies in the greenland sea during 1902 1920 and in the late 1940s and generally negative ice anomalies during the 1920s and 1930s only limited evidence of the propagation of greenland sea ice anomalies into the labrador sea was observed however probably because the data were from the ice melt seasons on the other hand several large ice anomalies in the greenland sea occurred 2 3 years after large runoffs in the early 1930s and the late 1940s from northern canada into the western arctic ocean similarly a large runoff into the arctic during 1964 1966 preceded the large greenland sea ice anomaly of the 1960s these facts together with recent evidence of climatic jumps in the northern hemisphere tropospheric circulation suggest the existence of an interdecadal self sustained climate cycle in the arctic in the greenland sea this cycle is characterized by a state of large sea ice extent overlying an upper layer of cool relatively fresh water that does not convectively overturn which alternates every 10 15 years with a state of small sea ice extent and relatively warm saline surface water that frequently overturns

strain insensitive preferred orientation of porphyroclasts in mont mary mylonites abstract the shape preferred orientation spo of porphyroclasts was determined in high temperature mylonites the porphyroclasts approach rhomboidal sillimanite or elliptical garnet plagioclase sillimanite shapes and exhibit aspect ratios r as high as 11 particles with r 3 are dominantly rhomboidal the long axis of the best fit ellipse defines a very strong spo inclined at 5 10 to the mylonitic foliation in an antithetic sense with respect to the shear direction this angle is independent of r the inclination of the long sides of rhomboidal sillimanite increases from 10 to 20 with decreasing r in contrast the short sides have a constant orientation of 15 to 17 irrespective of r and are parallel to extensional crenulation cleavage low aspect ratio mainly elliptical objects show low intensity spo close to the shear plane the two spos appear strain insensitive in the case of r r 3 a stable position is acquired this is not explained by any of the current theoretical and experimental models of spo

lidar based detection of the post typhoon recovery of a meso macro tidal beach in the beibu gulf china abstract because of global sea level rising with frequent storm activities most beaches in the world experience widespread erosion which poses a significant hazard to beach management the morphodynamic process of the evolution of a beach in response to storm activities is of increasing concern using a terrestrial laser scanner the topography of yintan beach was continuously observed for 33 days with a 25 cm spatial resolution digital elevation model dem of that covered an area of 15 ha before and after typhoon rammasun the short term beach recovery was explored using a comprehensive approach which included grey relational analysis terrain analysis gaussian fitting gamma fitting and delft3d wave simulation methods the results show that the yintan beach recovery process can be divided into three stages with two transition points stage one began at the end of rammasun which indicated a weakly stable state with an average daily net erosion of 588 m 3 a mean beach slope that ranged from 0 96 to 1 28 and a landform with no obvious alterations after the vast accretion of 6874 m 3 of first transition stage two which was characterized by oscillations occurred in the region with an average daily net erosion of 396 m 3 and a conspicuous beach slope reconstruction in the range of 0 94 2 16 during this stage sandbar reconstruction played a key role the second transition event arose at the end of stage two with a vast accretion of 5762 m 3 afterwards the daily net accretion of 200 m 3 and the beach slope range of 0 93 1 74 dominated the region during stage three and the beach surface became similar to that of the pre rammasun within the entire observation period intense beach elevation changes that ranged from 15 cm to 6 cm and 6 cm to 15 cm mainly occurred in the sandbar and foreshore zones respectively additionally slight elevation changes ranging from 4 cm to 4 cm were densely distributed in the backshore and dunes and moderate elevation changes ranging from 6 cm to 4 cm and 4 cm to 6 cm emerged along the entire beachface it was concluded that the spatial distribution of the bottom shear stress that was induced by wave action was responsible for the reconstruction of the foreshore and sandbar after rammasun whereas the short term beach recovery process was affected by the beach states in various wave breaking conditions

empirical model of morphodynamic beachface behaviour for low energy mesotidal environments abstract four years of monthly monitoring were carried out on a south atlantic beach in spain in a low energy mesotidal environment where beaches change slowly from reflective to dissipative states following a typical seasonal behaviour in this work a two dimensional study of beach morphological variations has been made related to the incident wave variations after applying several morphodynamic parameters to the field data poor or null representative results were obtained it was then necessary to design other type of characterisation of the incident wave energy in this sense the intertidal normalised beach slope was compared with the erosive potential of the incident waves expressed as a combination of the dimensionless grain fall velocity parameter and the energy density of waves median grain size did not vary significantly during the surveys for this reason a new parameter named wave erosivity factor was introduced by considering the fall velocity of grains as a constant in the parameter the resulting ratio between normalised beach slope and wave erosivity expresses the equilibrium state of the beach for any given energy level the departure from the equilibrium curve is largest in the intermediate situations while at the extremes the points are better adjusted to asymptotic tendencies towards equilibrium on reflective states small increases in the wave erosivity will produce important beach changes on dissipative beaches important increases in the wave erosivity will not produce significant morphological modifications the resulting equilibrium curve is presented as a function of the natural range of morphological variation of this beach

winter atmospheric circulation in the arctic basin and possible relationships to the great salinity anomaly in the northern north atlantic variations in synoptic activity are assessed in terms of potential influences on ice transport and indicators of shifts in the arctic atmospheric circulation related to the great salinity anomaly of the northern north atlantic winter pressure anomalies suggest an increased contribution to the fram strait sea ice flux by multiyear ice from along the northern coasts of greenland and ellesmere island this may be related to a teleconnection involving changes in anticyclonicity over the central arctic ocean and canadian arctic archipelago

contour mapping of arctic basin ice draft and roughness parameters a data base of ice draft and roughness parameters has been constructed for selected portions of the arctic ocean based upon analysis of under ice draft distribution data acquired by inverted echo sounder systems on submarines from the voyages of 12 submarines which traversed the alaskan canadian and central arctic regions of the arctic ocean during the summer and winter seasons a series of mean ice draft and deep draft keel statistics was calculated for 50 km segments along each submarine track contour maps of the mean ice draft its standard deviation the mean keel draft and the spatial frequency of ice keels were constructed they show that the greatest ice drafts the roughest ice and the greatest number of deep draft keels are found off the north coasts of the canadian archipelago and greenland due to ice convergence on these land barriers

the black mountains turtlebacks rosetta stones of death valley tectonics the black mountains turtlebacks expose mid crustal rock along the western front of the black mountains as such they provide keys to understanding the tertiary structural evolution of death valley and because of the outstanding rock exposure they also provide valuable natural laboratories for observing structural processes there are three turtlebacks the badwater turtleback in the north the copper canyon turtleback and the mormon point turtleback in the south although important differences exist among them each turtleback displays a doubly plunging antiformal core of metamorphic and igneous rock and a brittle fault contact to the northwest that is structurally overlain by miocene pleistocene volcanic and or sedimentary rock the turtleback cores contain mylonitic rocks that record an early period of top southeastward directed shear followed by top northwestward directed shear the earlier formed mylonites are cut by and locally appear concurrent with 55 61 ma pegmatite we interpret these fabrics as related to large scale basement involved thrust faults at the turtlebacks now preserved as areally extensive metamorphosed basement over younger cover contacts the younger and far more pervasive mylonites record late tertiary extensional unroofing of the turtleback footwalls from mid crustal depths available geochronology suggests that they cooled through 300 8c at different times 13 ma at badwater 6 ma at copper canyon 8 ma at mormon point at mormon point and copper canyon turtlebacks these dates record cooling of the metamorphic assemblages from beneath the floor of an 11 ma tertiary plutonic complex collectively these relationships suggest that the turtlebacks record initiation of ductile extension before 14 ma followed by injection of a large plutonic complex along the ductile shear zone ductile deformation continued during extensional uplift until the rocks cooled below temperatures for crystal plastic deformation by 6 8 ma subsequent low angle brittle fault slip led to final exposure of the igneous and metamorphic complex the turtleback shear zones can constrain models for crustal extension from map view as well as cross sectional perspectives in map view the presence of basement involved thrust faults in the turtlebacks suggest the black mountains were a basement

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

structural geology and kinematic history of rocks formed along low angle normal faults death valley california several late cenozoic low angle normal or detachment faults on the western flank of the black mountains are each characterized by the following in descending structural order 1 a hanging wall of upper tertiary to quaternary sedimentary and volcanic strata that displays little evidence for fault related damage other than widely spaced planar or listric normal faults 2 a sharp planar and locally striated principal slip plane forming the lower boundary of the hanging wall 3 an upper zone zone i of very fine grained fault generated rocks composed dominantly of gouge 4 a lower zone zone ii of coarser grained fault rocks consisting chiefly of foliated breccia and 5 a variably damaged footwall consisting of partly mylonitic precambrian units or tertiary plutonic rocks that has been exhumed from depths of 10 12 km since late miocene time the fault rocks which were mostly derived from the footwalls preserve evidence for cataclastic and particulate flow fault rocks contain authigenic minerals but lack the cyclically deformed mineral filled syntectonic veins that are abundant in some other late cenozoic high angle and strike slip faults meso and microscale fabrics in zones i and ii indicate that finite shear strains increase progressively upward toward the principal slip plane in a conceptual kinematic model of a shear box displacements of the hanging wall produced a shearing flow in the fault rocks below some of the slip on the principal slip plane was also partitioned into localized slip on discrete sliding surfaces in zones i and ii since 770 ka during the latest stages of incremental deformation in the brittle shear zones distributed flow in the fault rocks alternated with slip that was chiefly localized on the principal slip planes in this respect the detachment faults differ from inactive segments of the san andreas system along which displacements were progressively and irreversibly localized onto a single principal slip surface the strain gradients and corresponding changes in grain size in the shear zones resemble those in mylonitic shear zones except in their symmetry strain gradients in the black mountains are notably asymmetric they are present only below the principal slip planes not above

magnetic and clast fabrics as measurements of grain scale processes within the death valley shallow crustal detachment faults 1 the rock product of shallow crustal faulting includes fine grained breccia and clay rich gouge many gouges and breccias have a fabric produced by distributed deformation the orientation of fabric elements provides constraints on the kinematics of fault slip and is the structural record of intrafault strain not accommodated by planar and penetrative surfaces however it can be difficult to quantify the deformational fabric of fault rocks especially the preferred orientations of fine grained minerals or to uniquely determine the relationship between fabric geometry and finite strain here we present the results of a fabric study of gouge and breccia sampled from low angle normal detachment faults in the black mountains death valley ca we measured a preferred orientation of the long axes of the clasts inherited from the crystalline footwall of the fault and compared the shape preferred orientation to the anisotropy of magnetic susceptibility of the fault rocks the two measurements of fabric exhibit systematic similarities and differences in orientation and anisotropy that are compatible with the large scale kinematics of fault slip the dominant carriers of the magnetic susceptibility are micron and sub micron scale iron oxides and clay minerals therefore even the finest grains in the fault rock were sensitive to the distributed deformation and the micro mechanics of particle interaction must have departed from those assumed by the passive marker kinematic model that best explains the fabric

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part ii rock mechanics and microscopic scale abstract characterising large shale thrust zone behaviour down to the diagenetic metamorphic boundary is both simple and complex the task in critical taper analogue and numerical models has been successfully approximated using simple material parameters yet the weakness of shales thrusts on a case by case basis show great variability in key factors across a wide range of scales understanding of these variables and their relationships to different tectonic settings is patchy due to the different objectives of workers studying the various systems e g seismic hazards hydrocarbon exploration structural geology research and the types of available geological and geophysical data early research recognized that megathrusts feature creeping and locked patches which may be described using the rate and state formalism in addition to temperature differential stress and strain rate key controlling factors on thrust weakness are mineralogy amount of weak phase present structure localization mechanisms grain size and shapes porosity permeability and pore fluid pressure the smectite illite transition has been a focus of seismic hazard research due to its coincidence with the top of the seismogenic zone while there may be a relationship other factors such as pore fluid pressure variations or structure localization are also important the critical taper model is a simple means of determining whether basic rock mechanics data e g frictional strength pore fluid pressure is appropriate for natural wedges for example aseismic basal detachments of gravity driven systems smaller critical taper wedges appear to retain higher pore fluid pressures along the basal detachment than seismogenic basal detachments higher critical taper wedges in many continental and deltaic fold and thrust belts high organic carbon content is a very important factor in shale weakness due to 1 the overall more ductile and well cleaved nature of the shale when organic content is high 2 the presence of high overpressures due to maturation of organic material and 3 metamorphism of carbon to low friction graphite this multifaceted influence of organic carbon content is just one example of the diversity of potential influences on shale thrust zone weakness which enable shales to be weak despite considerable lateral deposition related and vertical burial related changes in composition some key variations between different types of fold and thrust belt gravity driven accretionary prism andean himalayan type lie in systematic variations in clay mineralogy magnitudes and origins of overpressures seismic versus aseismic detachments and different structural localization mechanisms further research is required to explore the viability of such distinctions and their impact on structural styles

a comparison of the post storm recovery of two sandy beaches on hong kong island southern china abstract typhoon hagupit was one of six tropical cyclones that affected hong kong in 2008 when the typhoon made landfall the combined effect of the waves storm surge and seasonal high tides resulted in a maximum sea level of 3 53 m at the nearest tide gauge to the study site the highest since 1962 the event caused considerable damage to coastal infrastructure and large scale erosion on many sandy beaches in hong kong to study the degree of erosion and recovery of hong kong beaches we surveyed two sandy beaches tai long wan tlw a relatively high energy exposed beach system and to tei wan ttw a relatively low energy sheltered beach system we examined the two beaches for changes in their beach profiles and sediment properties tlw recovered quickly with significant post storm accretion of fine to medium grained sand within four months after the typhoon tlw regained 700 m 3 sand forming a new 1 0 m high berm with the beach face prograding approximately 5 0 m seaward in contrast within the same four months after the typhoon ttw showed little evidence of sand accretion or recovery with only minor changes in the beach profile in fact instead of post storm sand accretion the landward migration of the high tide mark shown in the pre and post storm satellite images suggested that the post storm beach elevation at ttw decreased the results which reflect the different background energy regimes of each beach indicate that different coastal management strategies should be applied in the case of relatively high energy beaches of hong kong we suggest not interfering with their natural state in contrast in the case of relatively low energy beaches of hong kong which appear unlikely to recover rapidly from erosion during storms we suggest further investigation before applying any long to medium term management strategies

frictional slip of granite at hydrothermal conditions sliding on faults in much of the continental crust likely occurs at hydrothermal conditions i e at elevated temperature and elevated pressure of aqueous pore fluids yet there have been few relevant laboratory studies to measure the strength sliding behavior and friction constitutive properties of faults at hydrothermal conditions we slid laboratory granite faults containing a layer of granite powder simulated gouge velocity stepping experiments were performed at temperatures of 23 to 600 c pore fluid pressures ph2o of 0 dry and 100 mpa wet effective normal stress of 400 mpa and sliding velocities v of 0 01 to 1 m s 0 32 to 32 m yr conditions were similar to those in earlier tests on dry granite to 845 c by lockner et al 1986 the mechanical results define two regimes the first regime includes dry granite up to at least 845 and wet granite below 250 c in this regime the coefficient of friction is high 0 7 to 0 8 and depends only modestly on temperature slip rate and ph2o the second regime includes wet granite above 350 c in this regime friction decreases considerably with increasing temperature temperature weakening and with decreasing slip rate velocity strengthening these regimes correspond well to those identified in sliding tests on ultrafine quartz we infer that one or more fluid assisted deformation mechanisms are activated in the second hydrothermal regime and operate concurrently with cataclastic flow slip in the first cool and or dry regime is characterized by pervasive shearing and particle size reduction slip in the second hot and wet regime is localized primarily onto narrow shear bands adjacent to the gouge rock interfaces weakness of these boundary shears may result either from an abundance of phyllosilicates preferentially aligned for easy dislocation glide or from a dependence of strength on gouge particle size major features of the granite data set can be fit reasonably well by a rate and temperature dependent three regime friction constitutive model chester this issue we extrapolate the experimental data and model fit in order to estimate steady state shear strength versus depth along natural slipping faults for sliding rates as low as 31 mm yr we do this for two end member cases in the first case pore pressure is assumed hydrostatic at all depths shallow crustal strength in this case is similar to that calculated in previous work from room temperature friction data while at depths below about 9 13 km depending on slip rate strength becomes less sensitive to depth but sensitive to slip rate in the second case pore pressure is assumed to be near lithostatic at depths below 5 km strength is low at all depths in this case 20 mpa in agreement with observations of weak faults such as the san andreas the predicted depth of transition from velocity weakening to velocity strengthening lies at about 13 km depth for a slip rate of 31 mm yr in rough agreement with the seismic aseismic transition depth observed on mature continental faults these results highlight the importance of fluid assisted deformation processes active in faults at depth and the need for laboratory studies on the roles of additional factors such as fluid chemistry large displacements higher concentrations of phyllosilicates and time dependent fault healing

the concept of steady state foliation abstract a steady state foliation is thought of as a foliation with constant orientation and intensity in a rock undergoing steady state flow the problem discussed is whether such straininsensitive foliations exist in rocks and how they might be distinguished from the more familiar strain sensitive foliations steady state foliations would be useful indicators of stress or of strain rate yet misleading if used as indicators of finite strain one requirement for maintenance of steady state foliations is operation of processes that locally weaken grain shape preferred orientation or reduce grain aspect ratios or destroy lithological layering during flow these are the inverses of the processes normally discussed in connection with foliation development many such processes are known though the details of how and when they operate efficiently enough to stabilize a foliation are unknown there is however a tendency for some of them to operate more efficiently at high strains high temperatures and in flow regimes with high vorticity natural and experimental high temperature shear zones are accordingly one environment in which steadystate foliations may be encountered an experiment is described in which a thin specimen of para dichlorobenzene was given a large shearing deformation at 90 of its absolute melting point a steady state foliation was not produced but the technique is a promising one for further microstructural studies where in situ observation of material undergoing large deformations is desirable

secondary cleavages in ductile shear zones abstract secondary cleavages developed at late stages in ductile shear zones show several features that are inconsistent with progressive simple shear in the zone these are the orientation of a single secondary cleavage oblique to the shear zone boundaries conjugate sets with opposite senses of shear and multiple sets with the same sense of shear these features can be explained if the bulk flow is partitioned into slip along discrete failure planes parallel to the primary foliation s coaxial stretching along the foliation and spin

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

morphodynamic characteristics and classification of beaches in england and wales abstract the use of beach classification models has become widespread in literature in recent years beach classification models that recognise distinct modal beach states in response to environmental conditions are most widely used these models were developed largely in high energy micro to meso tidal sandy environments and subsequent attention has focussed on extending their use into other beach environments here the applicability of these traditional beach classification models to the highly diverse coastline of england and wales was assessed through collection of detailed morphodynamic characteristics of 92 beaches yielding a comprehensive multi variate data set containing morphological sedimentological and hydrodynamic information the complex and diverse study region incorporates beach morphology covering the full spectrum from reflective to dissipative and non barred to multi barred cluster analysis supplemented by mds ordination resulted in the identification of 9 distinct beach types traditional morphodynamic indices and rtr were found to be effective in discriminating between beach groups providing some support for the beach state models derived using information from australian beaches it was found that absolute wave energy wave power is important as well in controlling beach type for intermediate beaches a wave energy flux p h 2 t value of 3 kw m 1 was found to differentiate between beaches with p 3 kw m 1 and without p 1 three dimensional bar rip morphology a key component controlling recreational beach hazard levels observations presented here inform a beach classification model to be used as the basis for a national beach risk assessment programme beach classification models based on environmental parameters are by necessity simplifications and should be used as tools for understanding morphodynamic systems rather than beach type prediction

beach morphodynamics in a strong wind bay a low energy environment abstract the morphodynamic behaviour of a multibarred beach in a fetch limited strong wind bay seaford beach se australia was examined during both high and low energy conditions and considered in the context of a definition of low energy provided in the literature measurements of nearshore waves currents and morphology revealed a bimodal behaviour under initial low energy conditions the beach exhibited a low tide terrace state and waves and currents were of very low magnitude during subsequent high energy conditions the beach demonstrated dynamic behaviour through the formation of a transitional transverse bar and rip rhythmic bar and beach and migration of the middle bar with the morphology remaining in an arrested high energy state during intervening low energy periods although broadly conforming to the morphodynamic model the beach did exhibit some distinct characteristics attributable to its fetch limited location limited progression through the morphodynamic model and the importance of wind direction and magnitude in governing morphodynamic behaviour furthermore rip currents were not significant in driving beach change through intermediate states the presence of infragravity energy in the storm wave spectra a dissipative multibarred surf zone dynamic inner and middle bars and the attainment of a transitional transverse bar and rip rhythmic bar and beach state during rising wave conditions underline seaford beach as bimodal exhibiting process and morphologic features of both higher and lower energy beaches as an example of a beach in a strong wind bay seaford illustrates that not all fetch limited beaches are low energy furthermore the presence of infragravity energy in a highly fetch limited environment indicates that infragravity energy may occur commonly in fetch limited environments that are subject to periodic strong winds a process that has remained largely unrecognised

magnetic fabric of sheared till a strain indicator for evaluating the bed deformation model of glacier flow wet based portions of ice sheets may move primarily by shearing their till beds resulting in high sediment fluxes and the development of subglacial landforms this model of glacier movement which requires high bed shear strains can be tested using till microstructural characteristics that evolve during till deformation here we examine the development of magnetic fabric using a ring shear device to deform two wisconsin age basal tills to shear strains as high as 70 hysteresis experiments and the dependence of magnetic susceptibility of these tills on temperature demonstrate that anisotropy of magnetic susceptibility ams develops during shear due to the rotation of primarily magnetite particles that are silt sized or smaller at moderate shear strains 6 25 principal axes of maximum magnetic susceptibility develop a strong fabric s 1 eignevalues of 0 83 0 96 without further strengthening at higher strains during deformation directions of maximum susceptibility cluster strongly in the direction of shear and plunge up glacier consistent with the behavior of pebbles and sand particles studied in earlier experiments in contrast the magnitude of ams does not vary systematically with strain and is small relative to its variability among samples this is because most magnetite grains are contained as inclusions in larger particles and hence do not align during shear although processes other than pervasive bed deformation may result in strong flow parallel fabrics ams fabrics provide a rapid and objective means of identifying basal tills that have not been sheared sufficiently to be compatible with the bed deformation model

classification of beach response to extreme storms abstract extreme storms are responsible for rapid changes to coastlines worldwide during the 2013 14 winter the west coast of europe experienced a sequence of large storm induced wave events representing the most energetic period of waves in the last 60 years the southwest coast of england underwent significant geomorphological change during that period but exhibited a range of spatially variable and complex morphological responses despite being subjected to the same storm sequence here we use the 2013 14 storm response along the southwest coast of england as a natural field laboratory and explain this variability in storm response through the introduction and evaluation of a new classification of how sandy and gravel beaches respond to extreme storms cluster analysis was conducted using an unique data set of pre and post storm airborne light detection and ranging lidar data from 157 beach sites based on the net volumetric change dqnet and a novel parameter the longshore variation index lvi which quantifies the alongshore morphological variability in beach response four main beach response types were identified 1 fully exposed beaches that experienced large and alongshore uniform sediment losses dqnet 100 m3 m 1 2 semi exposed beaches that experienced medium alongshore uniform sediment losses dqnet 50 m3 m 1 3 sheltered short beaches that experienced limited net sediment change and alongshore variability in beach response and 4 sheltered long beaches that experienced considerable alongshore variability in beach response and large gross sediment change but limited net sediment change the key factors in determining the type of beach response are exposure to the storm waves angle of storm wave approach and the degree to which the beach is embayed these factors are universally applicable on many exposed coastlines worldwide so the response classification presented here is expected to be widely applicable

shear zones in clay rich fault gouge a laboratory study of fabric development and evolution abstract clay rich fault rocks have long been recognized to host distinctive fabric elements and fault rock fabric is increasingly thought to play a fundamental role in fault mechanical behaviour in the brittle regime although the geometries of fabric elements in fault gouges have been described for almost a century the genesis and evolution of these elements during shear and their links to bulk mechanical properties remain poorly understood we characterize the development and evolution of fabric elements with increasing shear in a variety of clay rich experimental gouges over shear strains of 20 and at normal stresses of 2 150 mpa in the double direct shear configuration in addition to sem observations of experiment products at a variety of shear strains we quantified clay fabric intensity and the degree of grain size reduction using x ray texture goniometry xtg and particle size distribution psd measurements we also measured p and s wave velocities during shear to further probe the evolution of shear fabric and gouge properties we find that clay fabric elements develop in a systematic manner regardless of the gouge material riedel shears in the r1 orientation and boundary parallel shears are the dominant fabric elements riedel shears nucleate at layer margins and propagate into the layer shortly after reaching yield stress clay particles rotate into the p orientation shortly after riedels propagate through the layer the riedel shears are through going but are 10 thinner than similar zones observed in coarser granular materials our results suggest that the weakness of clay rich fault gouge may be less a function of anisotropic crystal structure as has been suggested previously and more a consequence of very thin shear surfaces permitting deformation in clay rich materials with minimal dilation or cataclasis the very thin shear surfaces are a function of the fine grain size of the materials and possibly polymodal psd s

a coupled dynamic thermodynamic model of an ice ocean system in the marginal ice zone wind driven ice ocean processes in the marginal ice zone are studied when thermodynamics is included into a coupled ice ocean model the ocean is considered to be a two layer ocean where a fresh and cold freezing mixed layer is lying above the stagnant warm and saline lower layer the essential part of the thermodynamics is the entrainment between the mixed layer and the lower layer which is parameterized using the frictional velocity at the ocean surface a kraus turner type parameterization it is shown that upwelling at the ice edge which is generated by the difference in the air ice and air water surface stresses will give rise to a strong entrainment by bringing the pycnocline nearer to the surface furthermore the entrainment is negligible outside the areas affected by the ice edge upwelling when cooling at the top is included the heat and salt exchange are further enhanced in the upwelling areas because the entrainment depends inversely on the density difference between the layers new ice formation occurs in the area which is not affected by ice edge upwelling that is no entrainment of the warm lower layer fluid so the mixed layer temperature stays at the freezing point the ice growth will give rise to a large salt flux to the upper layer but the subsequent salinity change is not as large as that due to the entrainment of the lower layer fluid the mixed layer in the areas affected by the ice edge upwelling is only slightly less saline than the lower layer it is suggested that these high salinity mixed layer regions with a scale of a few rossby radii of deformation 10 km will overturn due to cooling possibly as a plume and may this contribute to the formation of deep water

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

an observational and numerical study of wind stress variations within marginal ice zones published studies of ocean mesoscale processes in marginal ice zones mizs using numerical coupled ice ocean models usually assume that the surface wind speed is constant over the model domain and that wind stress variations are simply proportional to surface roughness variations we show that this assumption is not realistic in most situations because the surface wind stress is also significantly affected by mesoscale pressure variations by changes in the surface wind vector and by changes in surface layer stability two numerical case studies utilizing detailed surface and atmospheric measurements examine the factors affecting small scale 5 km variations in wind stress within mizs these case studies and surveyed observational and modeling results demonstrate that wind stress fields are qualitatively different from the surface roughness fields a realistic wind stress scenario consists of a maximum just inside the ice edge and another maximum in the open ocean stress minima occur within the pack ice region away from the miz and over grease ice if present the effect of the rougher miz ice is counteracted when wind stresses over the open ocean are enhanced by large surface heat fluxes over the ocean by a strong low level inversion over the ice or by a sharp atmospheric front with surface winds paralleling the ice edge such situations are common in miz regions some simple methods for including first order atmospheric effects on wind stress variations which could be incorporated into current ice ocean mesoscale models of miz regions are suggested

experimental investigation of incipient shear failure in foliated rock abstract it has long been known that rock fabric plays a key role in dictating rock strength and rheology throughout earth s crust however the processes and conditions under which rock fabric impacts brittle failure and frictional strength are still under investigation here we report on laboratory experiments designed to analyze the effect of foliation orientation on the mechanical behavior and associated microstructures of simulated fault rock sheared at constant normal stress of 50 mpa intact samples of pennsylvania slate were sheared with a range of initial fabric orientations from 0 to 165 with respect to the imposed shear direction foliation orientations of 0 30 produce initial failure at the lowest shear stress while samples oriented at higher angles are less favorable resulting in higher peak failure strength in all samples post peak development of through going deformation zones in the r1 riedel orientation results in a residual strength that is lower than that observed for powdered gouge from the same material as shear strain increases all samples approach a residual apparent friction defined by the ratio of shear strength to normal stress of 0 4 however the final deformation microstructure depends strongly on the orientation of the pre existing foliation when fabric is oriented at low angles to the shear direction

a one dimensional time dependent model for the vertical stratification of the upper arctic ocean abstract a one dimensional time dependent model of the upper arctic ocean is presented it describes the circulation above a dynamically passive reservoir of atlantic water the model is driven by freshwater runoff from land ice production and export bering strait inflow and wind the mixed layer thickness is controlled by the shortest among the following three length scales the depth to the upper pycnocline the ekman length and the monin obukov length the outflow is assumed to occur as geostrophically controlled coastal currents four integral quantities are defined in order to make objective comparisons between model generated and observed salt and temperature profiles the model generates a seasonally varying mixed layer in qualitative agreement with measurements a halocline with water near the freezing temperature is also generated this structure is sustained by the water coming from the bering strait by comparing the model result with the observed freshwater content in the basin likely value

strain and kinematic analysis in general shear zones we present a unifying theory for the development and distribution of strain markers and kinematic indicators in zones of general shear and thus provide a framework in which data previously considered contradictory may be understood rigid and deformable porphyroclast systems including and complex grains are potential indicators of both strain and flow the shapes and distribution of such porphyroclast systems may be used to distinguish among different tectonic regimes general shear is divided into two fields sub simple shear in which the rotational component of the strain is less than that for simple shear and super simple shear in which the rotational component is greater than for simple shear sub simple shear may involve narrowing or broadening of shear zones super simple shear regimes are possible in local regions such as the vicinities of deformable porphyroclasts but must be enclosed by regimes of sub simple shear the polar mohr constructions for finite deformation and flow are useful to analyze general shear in theory the hyperbolic net is employed for practical plotting of real data and derivation of the kinematic vorticity number wn this number represents the relative contributions of pure and simple shear in steady flow in nature deformation is thought to build up and decay by processes that may invalidate the assumption of constant flow regime we therefore introduce the concept of accelerating deformation and analyze the implications of non steady flow for the shearing histories of deformed objects

cyclical evolution of a modern transgressive sand barrier in northwestern spain elucidated by gpr and aerial photos abstract the internal structure of a modern baymouth barrier is analyzed in detail including its historical evolution and the factors controlling it historical evolution was reconstructed using available aerial photographs from 1956 to 2003 detailed geophysical data were acquired using ground penetrating radar gpr and analyzed along with airphotos to reconstruct the recent evolution of a barrier located in northwestern spain the gpr data reveal the internal architecture of the barrier which consists of two main radar facies 1 washover deposits associated with landward barrier migration and vertical aggradation and 2 beach deposits associated with seaward barrier progradation the reconstruction of the stratigraphic sequence indicates the occurrence of two erosive periods followed by an accretionary period the erosion along the barrier is outlined by the presence of three well defined bounding surfaces the stratigraphic record of the subsequent recovery phase depends on the impact level of the erosive phase which is controlled by the presence of ephemeral inlets along the barrier this alternating behavior implies a discontinuous shoreline trajectory in spite of a net landward migration this trend is consistent with regional sea level rise albeit being intensified locally by the interplay of sediment starvation and storm regime landward barrier retreat occurs by overwash and inlet breaching which permits barrier preservation of volume due to a continuous constructive destructive cycle the results acquired from this example expand our understanding of the internal structure and evolutionary trends of transgressive sand barriers

large scale gravity sliding in the miocene shadow valley supradetachment basin eastern mojave desert california abstract the miocene shadow valley basin in the eastern mojave desert of california developed above the active west dipping kingston range halloran hills extensional detachment fault system between 13 5 and ca 7 mybp although mass wasting processes are common phenomena in supradetachment basins the shadow valley basin is an exceptional locale for the study of such processes especially rock avalanches and gravity sliding a score of megabreccias interpreted as rock avalanche deposits and half that number of very large 1 km 2 up to 200 m thick internally intact gravity driven slide sheets are interbedded with various sedimentary facies the slide sheets variably composed of proterozoic crystalline rocks and proterozoic paleozoic and tertiary sedimentary strata moved across both depositional and erosional surfaces in the basin although the majority consist of paleozoic carbonate rocks the largest slide sheet the eastern star crystalline allochthon contains proterozoic gneisses and their sedimentary cover and is now preserved as klippen atop miocene lacustrine and alluvial fan deposits over an area 40 km 2 estimates of slide sheet runouts into the basin from higher eastern and northern source terranes range from approximately a few km to 10 km in most cases the exact provenances of the slide blocks are not known the basal contacts of shadow valley slide sheets are characteristically knife sharp show few signs of lithologic mixing of upper and lower plate rocks and locally exhibit slickensided and striated planar fault like bases pronounced folding of overridden miocene lacustrine and fan deposits beneath the eastern star allochthon extends to depths up to 40 m at widely scattered localities we conclude that this slow moving slide sheet encountered isolated topographic asperities hills and that stress transfer across the basal slide surface produced folding of footwall strata synkinematic gypsum veins in footwall playa sediments with fibers up to 12 cm long have trends and shear senses compatible with the direction and sense of displacement of the overriding crystalline allochthon the undisturbed veins which closely parallel the base of the slide sheet attest to high fluid presence and pressure in the playa sediments factors facilitating allochthon movement across them the long length of the fibers indicative of a protracted dilational process is incompatible with a catastrophic rate of emplacement we believe that the only explanation for slow displacement of this allochthon and other gravity driven slide sheets across the landscape is that they formed as slumps on high steep bedrock slopes and that their elevated heads drove their toes across lower fan and playa deposits initial detachments from bedrock sources were facilitated by pre existing structural and stratigraphic anisotropies detachment of the eastern star allochthon from the bedrock of shadow mountain likely occurred by inversion along the playa ward dip of a preexisting mesozoic thrust fault within proterozoic rock units

a two dimensional thermodynamic model for sea ice advance and retreat in the newfoundland marginal ice zone a time dependent two dimensional ice ocean coupled thermodynamic model is developed to study the ice edge advance and retreat development of the oceanic mixed layer and oceanic response to ice movement ice melt and heat balance in the newfoundland marginal ice zone the model domain is a vertical section of the ocean along the direction of the ice velocity initially the ocean is free of ice and has a deep mixed layer formed by winter surface cooling an ice sheet then moves into the domain from the upstream boundary at constant velocity it melts from the bottom and a shallow mixed layer beneath the ice is developed heat and buoyancy fluxes at the air sea and ice water interfaces and at the bottom of the mixed layer determine the melt rate and change of the mixed layer properties the ice edge reaches a maximum distance and starts to retreat when the ice is being melted by the warm water faster than it is being advected into the area the oceanic properties change with the ice movement during the advancing phase of the ice movement the heat loss to the ice bottom from ice melting exceeds the heat gain by surface heating and entrainment causing the mixed layer temperature to drop but since the buoyancy created by the melting is not sufficient to overcome the effect of wind mixing the mixed layer deepens rapidly during the retreating phase the mixed layer becomes shallower and warmer because of the increasing surface heating and buoyance production by ice melting the most important factors controlling the melt rate and the excursion distance are the air temperature and the ambient water temperature higher wind speeds increase the mixed layer depth but do not have a strong effect on the melt rate

implications for mechanical properties of brittle faults from observations of the punchbowl fault zone california field observations of the punchbowl fault zone an inactive trace of the san andreas are integrated with results from experimental deformation of naturally deformed punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting the punchbowl fault zone consists of a single continuous gouge layer bounded by zones of extensively damaged host rock fault displacements were not only localized to the gouge layer but also to discrete shear surfaces within the gouge deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms textural data also suggest that significant amounts of pore fluids were present during faulting and that fluid assisted mechanisms such as dissolution diffusion and precipitation were operative the experimental data on specimens collected from the fault zone suggest that there is a gradual decrease in strength and elastic modulus and an increase in relative ductility and permeability toward the main gouge zone the gouge layer has fairly uniform mechanical properites and it has significantly lower strength elastic modulus and permeability than both the damaged and the undeformed host rock for the punchbowl fault and possibly other brittle faults the variations in loading of the gouge zone with time are primarily governed by the morphology of the fault and the mechanical properties of the damaged host rock in addition the damaged zone acts as the permeable unit of the fault zone and surrounding rock it appears that the gouge primarily governs whether displacements are localized and it therefore may have a significant influence on the mode of slip

pocket beach hydrodynamics the example of four macrotidal beaches brittany france during several field experiments measurements of waves and currents as well as topographic surveys were conducted on four morphologically contrasted macrotidal beaches along the rocky iroise coastline in brittany france these datasets provide new insight on the hydrodynamics of pocket beaches which are rather poorly documented compared to wide and open beaches the results notably highlight a cross shore gradient in the magnitude of tidal currents which are relatively strong offshore of the beaches but are insignificant inshore despite the macrotidal setting the hydrodynamics of these beaches are thus totally wave driven in the intertidal zone the crucial role of wind forcing is emphasized for both moderately and highly protected beaches as this mechanism drives mean currents two to three times stronger than those due to more energetic swells when winds blow nearly parallel to the shoreline moreover the mean alongshore current appears to be essentially wind driven wind waves being superimposed on shore normal oceanic swells during storms and variations in their magnitude being coherent with those of the wind direction we also found evidence for the contribution of infragravity waves to the formation of an intertidal sand bar through prolonged duration of swash processes at the same beach level and to the development of beach cusps but not to their initiation for which the observed standing edge wave pattern may have been enhanced by the enclosed pocket beach setting the paper highlights some of the specificities of pocket beach with regards to their hydrodynamics and morphodynamics more detailed observations would be needed however prior to a more comprehensive review

southern ocean winter mixed layer austral winter 1986 observations from the polarstern along the greenwich meridian from the ice edge to the antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation incorporation of weddell deep water wdw into the winter mixed layer responsible for this undersaturation also introduces heat and salinity into the surface layer which strongly influences the mixed layer sea air exchanges and sea ice formation processes the total wdw transfer into the mixed layer averages 45 myr 1 implying a residence time for the surface water of 2 5 years the associated winter heat flux is 41 w m 2 which limits ice thickness to about 0 55 m agreeing quite well with observations the air temperatures during the cruise are just sufficient to remove the wdw heat input in the presence of observed ice thickness and concentration this suggests that the sea ice cover and wdw heat input into the mixed layer are in approximate balance by midwinter the annual heat flux from wdw to the surface layer and hence into the atmosphere is estimated as 16 w m 2 extrapolation of the greenwich meridian wdw entrainment value to the full circumpolar 60 70 s belt yields total up welling of 24 106 m3 s 1 similar extrapolation of the heat flux value gives a circumpolar total of 2 8 1014 w as a consequence of circulation topography interaction the maud rise water column stands out as an anomaly relative to the surrounding region with a significantly more saline and dense mixed layer below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m this uplifting is believed to be a response of the upstream flow encountering the rise increased upstream flow would be expected to increase maud rise upwelling and the dependent salinity density of the mixed layer slight increases in the mixed layer density could trigger a convective mode and generation of a polynya it is hypothesized that spin up of the weddell gyre s barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over maud rise

a two dimensional coupled ice ocean model of the bering sea marginal ice zone a two dimensional coupled ice ocean model has been formulated and applied to the wintertime bering sea marginal ice zone the oceanic component is a multilevel model that incorporates second moment closure for turbulent mixing in the water column the ice cover is modeled as a viscous plastic continuum melting at the ice ocean interface is computed using well known lawof the wall concepts in a turbulent boundary layer with particular attention to the disparate momentum and scalar transfer resistance coefficients over rough walls the thermodynamic and dynamical interactions between the ocean and the ice cover and the energy balances at the air ice and air sea interfaces are modeled according to the companion paper mellor and kantha this issue the model incorporates barotropic tides both diurnal and semidiurnal for application to the bering shelf double diffusive fluxes across the interface between the colder fresher layer beneath the melting ice and the warmer more saline water underneath are prescribed from laboratory data on double diffusive convection during winter sea ice in the central bering sea is transported toward the shelf break by off ice winds where it encounters northward flowing warmer north pacific waters and melts it is this situation to which the two dimensional model has been applied by neglecting all variations in the along ice edge direction the water conditions downstream of the ice edge the ice conditions upstream and the wind stress are the primary inputs to the model the model simulates transition from ice covered to open ocean conditions and the associated ice edge front and the two layer circulation underneath the ice cover sensitivity studies indicate that the density structure and the circulation beneath the ice and the position of the ice edge are rather sensitive to the parameters affecting the dynamics and the thermodynamics of the coupled ice ocean system even small changes in the relevant parameters can cause a substantial retreat or advance of the ice edge which may help explain why marginal ice zones are such dynamically active regions

minor storm impact on the beachface of a sheltered sandy beach abstract during a squall at sorrento western australia winds exceeded 50 km h 1 for 6 5 h and gusted up to 80 km h 1 at the storm peak profiles of adjacent cusp horn and cusp embayment locations were surveyed half hourly for over 40 h spanning onset and passage of the storm in conjunction with measurement of water table fluctuation and swash ranging the sequence of beach changes followed the storm structure although with lag effects related to tide groundwater and swash interaction with the local morphology four phases of beachface adjustment were apparent these were 1 a period of adjustment to rising tide and energy conditions during which the cusp horn was eroded and sediment was deposited in the embayment 2 beachface erosion as storm tide and watertable approached their peak 3 a period of adjustment to declining energy conditions falling tide and watertable levels that began immediately after the storm peak on the cusp horn and at mid ebb tide in the embayment and 4 steady beachface accretion through mid to low tide conditions in the latter part of storm passage beach responses on the cusp horn and embayment hence were dissimilar with net erosion resulting on one and net deposition on the other

space time variation of mixed layer properties heat and salt fluxes and ice melt in the newfoundland marginal ice zone oceanographic data collected in the newfoundland marginal ice zone in march 1992 are analyzed to study the variation of mixed layer properties across the ice zone the mixed layer depth decreases from 80 m in the interior of the pack ice to 25 m at the eastern ice edge over a distance of 120 km in the open ocean without ice cover the depth is considerably greater 150 200 m the temperature under the pack ice is near freezing a sharp increase in both the temperature and salinity occurs across the ice edge the variation of the mixed layer properties is simulated by integrating a one dimensional bulk mixed layer model coupled to sea ice from november 1991 to march 1992 the initial ocean conditions are obtained from an objective analysis of archived data of november 1991 the forcings are 6 hourly meteorological data from the european centre for medium range weather forecasts ice concentration and thickness are treated as prescribed functions of time extracted from daily ice maps since ice in the area is not locally formed the model simulation is in good agreement with the observations from the model results a detailed analysis of the roles of wind stress ice melt surface cooling and shortwave radiation in the water mass transformation of the upper ocean is carried out there are large differences in the melt rate and water ice heat flux between the times when ice enters the shelf and after the water has been cooled by the ice to near freezing 15 20 cm d 1 and 500 700 wm 2 and 0 2 cm a 1 and 20 50 wm 2 respectively a large portion of the heat in the water column is expended for ice melting from january to march calculations that use surface data such as surface wind and sea surface temperature without considering ice melt can underestimate the net ocean to air heat flux especially at the eastern ice edge in march

sheltered sandy beaches of southwestern australia four beach types were identified from field surveys of beach profiles on low energy sandy beaches in cockburn sound a micro tidal semi enclosed basin in southwestern australia these were delineated by an exposure factor ef which provided a surrogate for the relationship between incident wave energy and attenuation as a result of structures banks and shoals the four beach profiles identified were exponential segmented concave curvilinear and convex curvilinear in form whether the different profile shapes occurred in environments subject to different degrees of sheltering and protection under the same tidal regime was open to question beach profiles were examined for como beach and princess royal harbour in western australia and compared with observations from cockburn sound to test this proposition cockburn sound and princess royal harbour are subject to minimal penetration of swell waves whereas como beach in the swan river estuary is wholly fetch limited profile forms identified in each environment were consistent with those described from cockburn sound similar profile types had similar exposure values for all sites such that ef 2 of convex curvilinear although this approach requires further testing in low energy environments subject to different tidal ranges and fluctuations in sea level use of the exposure factor for delineation of low energy sheltered beach types appears to be a robust procedure

applicability of parametric beach morphodynamic state classification on embayed beaches abstract use of parametric classification of beach morphodynamic state has been steadily increasing in coastal research despite identification of several shortcomings of their representativeness as elementary beach descriptors in this paper we analyse the parametric classification of beach morphodynamic state in a set of six embayed beaches in southwestern portugal exposed to diverse settings from high energy dissipative to intermediate to low energy intermediate to reflective conditions applicability of parametric approaches considered within the dimensionless space defined by dimensionless fall velocity and rtr relative tidal range according to averaged wave tide and sediment characteristics of beaches was assessed in association with a probabilistic analysis implemented through a bayesian network model that considered the full range of wave tide and sediment conditions at each site both parametric approaches were compared to field based beach state classification implemented using a novel hierarchical framework for beach state analysis the classification obtained within a probabilistic framework provided an innovative approach for analysis of beach state and mobility extending the insights on beach morphodynamic behaviour obtained from averaged environmental parameters reflective to lower intermediate beach conditions showed better agreement with parametric approaches while poor beach state differentiation was achieved for intermediate beach types limitations in the application of beach classification models result from i an inadequacy of existing beach state types in differentiating beaches particularly within the intermediate domain and for geologically controlled embayed beaches and ii shortcomings involved in the parametric approaches the beach state models disregard the major role of geological control in embayed beach morphodynamic behaviour in modulating beach shape and segmentation influencing sediment size and availability causing alongshore variations in the wave field and creating topographically induced nearshore circulations existing beach state models are unable to adequately represent the widely variable conditions observed in embayed beaches

determining glacier flow direction from till fabrics abstract field and experimental data indicate that fabrics of sheared basal tills based on particle orientations and on anisotropy of magnetic susceptibility are inclined relative to the macroscopic plane of shear as a result if this plane is tilted with a transverse component one of the longest standing axioms of glacial geology that particles in basal till are preferentially oriented parallel to the direction of shear is not strictly true the resultant correction to the shearing direction increases with the transverse and longitudinal components of shear plane inclination and with the magnitude of the fabric inclination relative to the shear plane azimuthal corrections calculated herein range from being negligible to a few tens of degrees for reasonable ranges of shear plane tilt the past success of fabric azimuths as indicators of flow direction despite the absence of this correction likely reflects the clustering of shear planes about the horizontal in basal tills however on the flanks of accreting subglacial bedforms shear plane attitudes may well conform to the local bedform slope as illustrated with hypothetical fabrics of drumlins and flutes azimuthal corrections can in that case be sufficiently large and systematic to seriously affect interpretations of bedform genesis