vertical averages of rheology of the continental lithosphere relation to thin sheet parameters abstract we calculate vertically averaged rheologies for continental lithosphere subject to biaxial states of stress corresponding to extensional compressional and strike slip regimes we assume that brittle deformation occurs by byerlee s law and that ductile deformation occurs by steady state creep mechanisms under these conditions the vertically averaged rheology may be approximated by a single power law over the range of strain rates from 10 13 to 10 17 s 1 this is true not only when either brittle or ductile behavior dominates the strength of the lithospere but also when the contributions of brittle and ductile behavior are comparable the value of the power law exponent n and the strength of the lithosphere depend on the depth and stress difference at the brittle ductile transition the temperature at the moho and the geothermal gradient in the range of vertically integrated stress between 1012 and 1013 n m 1n reaches a minimum of between 5 and 10 under other circumstancesn increases rapidly as brittle behavior dominates over ductile behavior the strength of the lithosphere depends most strongly on the thermal state of the upper mantle but also is influenced by the stress supported in brittle portions of the lithosphere

beach ridges and prograded beach deposits as palaeoenvironment records abstract beach ridges are landforms commonly developed on prograded coasts with beach shorelines a sequence of beach ridges coupled with their subsurface deposits can be regarded as a time series of coastal evolution methodological advances in field surveying and chronology applicable to beach ridges have led to detailed palaeoenvironmental reconstructions to be derived from such sequences this paper reconsiders the basic aspects of beach ridges and deposits which need to be properly understood for their comprehensive interpretation in a palaeo environmental context it also reviews case studies in which beach ridge sequences have been used to unveil past sea level history catastrophic events and climate changes proposed formative processes of beach ridges include 1 progradation of sandy beach and berm formations in relation to fairweather waves coupled with aeolian foredune accumulation 2 building of gravel ridges by storm waves 3 welding of longshore bars beach ridge formation through sea level oscillation is thought to be questionable and caution is suggested for this process when undertaking palaeoenvironmental reconstruction beach deposit stratification is known to dip either landwards or seawards but landward dips are uncommon seaward dipping stratification is formed in relation to beachface progradation and is usually dissected in places by erosion surfaces resulting from episodic beach retreat the boundary between the foreshore and the underlying shoreface is well defined only in the case that longshore bars lead to complex bedding structure relative to that of the foreshore reliable chronology of beach ridges can be determined by radiocarbon and optically stimulated luminescence osl dating radiocarbon dating of articulated shells which are considered not to be extensively reworked provides robust results but osl dating is more useful as it enables direct dating of sediment grains it is noted that there are restrictions in chronological resolution and continuity inherent to beach ridge and beach deposits the plan view geomorphic expression of beach ridges typically consists of ridge sets with multi decadal intervals whereas their internal sedimentary structures define shorter time scales records of beach sedimentation and erosion are likely to be reworked by episodic high magnitude beach retreat and the resultant record of the net progradation is likely to be sporadic and discontinuous the height of sandy beach ridges is often variable due to differing degrees of aeolian sand accumulation and they are thus not used as sea level indicators unless purely wave built gravel ridge height is a relatively reliable indicator of sea level but can vary in response to storminess fluctuations subsurface sediment facies boundaries are preferred as sea level indicators and those proposed include boundaries of aeolian beach foreshore shoreface and upper lower shorefaces catastrophic events are expressed in both erosional and depositional records erosion surfaces or scarp imprints revealed in a cross section of beach deposits indicate storm or tsunami events however erosional events are likely to rework previous records of sedimentation and even other erosional events and thus the apparent history decoded from the resultant deposits tends to be biased several attempts for estimating the frequency and intensity of prehistoric cyclones rely on assumed relationships between the level of coarse sand beach ridges and cyclone inundation the formative process of coarse sand ridges remains uncertain and needs to be clarified as it constitutes the fundamental basis of these attempts the growth rates of beach ridge systems are expected to reflect fluctuations in river sediment discharge to the coast and in aeolian sand flux due to onshore winds both of which are affected by climate change assessment of the growth rate is potentially improved by ground penetrating radar survey of subsurface structure and by detailed chronology orientation of beach ridges reflects long term trends in wave direction inferred relationships between beach ridges and cyclic fluctuations of sea level and climate rely on weak assumptions and are not substantiated by rigid chronological evidence and thus remain highly questionable correlation between the inherently decadal signal of beach ridge intervals and possible climate cycles such as sunspot activity is probably coincidental as it lacks causal explanations

classification of washover dynamics in barrier islands abstract this study systematically classifies washover dynamics with reference to coastal changes along the ria formosa barrier islands southern portugal identification of washovers using a sequence of 11 sets of aerial photographs dated between 1947 and 2001 allowed a classification to be developed based on 1 overwash evolution increasing decreasing or constant overwash processes 2 the mechanisms promoting washover formation exceptional to infrequent oceanographic conditions washout processes structural erosion inlet dynamics and human interventions and 3 the mechanisms promoting washover cessation berm development structural erosion dune development inlet dynamics and human interventions a total of 369 different washovers were observed along the ria formosa barriers during the study period with 209 washovers being formed in various types of dune morphology and 303 being obliterated the number of washovers was relatively stable from 1947 to 1972 and increased dramatically between 1972 and 1976 probably as a result of the development of immature inlet margins and downdrift starvation from 1976 to 2001 washover occurrences declined and their spatial dimensions decreased leading to a decrease in overwash activity over this time overall the dominant formation mechanisms of washovers in the ria formosa were inlet dynamics accounting for 57 of washovers formed and structural erosion 20 with human intervention mechanisms accounting for 12 the cessation of washovers was dominated by dune development 33 of the washovers obliterated followed by inlet dynamics 24 and structural erosion 19 while human intervention mechanisms accounted for 13 the classification should be of use for the coastal management of barrier systems including the definition of overwash prone areas and the determination of the relative importance of the mechanisms contributing to washover formation and cessation

quantifying rates of coastal progradation from sediment volume using gpr and osl the holocene fill of guichen bay south east south australia guichen bay on the south east coast of south australia faces west towards the prevailing westerly winds of the southern ocean the bay is backed by a 4 km wide holocene beach ridge plain with more than 100 beach ridges the morphology of the guichen bay strandplain complex shows changes in the width length height and orientation of beach ridges a combination of geomorphological interpretation shallow geophysics and existing geochronology is used to interpret the holocene fill of guichen bay six sets of beach ridges are identified from the interpretation of orthorectified aerial photographs the ridge sets are distinguished on the basis of beach ridge orientation and continuity a 2 25 km ground penetrating radar gpr profile across the beach ridges reveals the sedimentary structures and stratigraphic units the beach ridges visible in the surface topography are a succession of stabilized foredunes that overlie progradational foreshore and upper shoreface sediments the beach progrades show multiple truncation surfaces interpreted as storm events the gpr profile shows that there are many more erosion surfaces in the subsurface than beach ridges on the surface the width and dip of preserved beach progrades imaged by gpr shows that the shoreface has steepened from around 2 9 to around 7 5 the changes in beach slope are attributed to increasing wave energy associated with beach progradation into deeper water as guichen bay was infilled at the same time the thickness of the preserved beach progrades increases slightly as the beach prograded into deeper water using the surface area of the ridge sets measured from the orthophotography and the average thickness of upper shoreface foreshore and coastal dune sands interpreted from the gpr profile the volume of holocene sediments within three of the six sets of beach ridge accretion has been calculated combining optically stimulated luminescence osl ages and volume calculations rates of sediment accumulation for ridge sets 3 4 and 5 have been estimated linear rates of beach ridge progradation appear to decrease in the mid holocene however the rates of sediment accumulation calculated from beach volumes have remained remarkably consistent through the mid to late holocene this suggests that sediment supply to the beach has been constant and that the decrease in the rate of progradation is due to increasing accommodation space as the beach progrades into deeper water changes in beach ridge morphology and orientation reflect environmental factors such as changes in wave climate and wind regime

block rotation by strike slip faulting structural and paleomagnetic evidence geometric analysis shows that motion of sets of strike slip faults should cause block rotation otherwise the distorted fault domain would not fit with its surrounding the sense of the block rotation depends on the sense of fault slip and the spacing and orientation of the faults all of which can be obtained from structural data the predictions of the geometric model can then be independently tested by paleomagnetic measurements the model was tested in northern israel structural data reveal several domains of contemporaneous right and left lateral strike slip faults paleomagnetic measurements show that in a domain of nnw trending left lateral faults blocks rotated 23 3 8 2 clockwise and in a domain of right lateral faults blocks rotated 22 4 9 0 anticlockwise these results are in agreement with the prediction of the geometric analysis of the structure the combined results of the heterogenous deformation of the area resembles a pure shear which allows n s extension by about 1 3 in other domains rotations of 34 6 9 1 and 53 1 11 0 were found in their original orientation the left and right lateral faults intersected at angles of 60 70 enclosing the principal axis of shortening in accordance with theories of brittle failure as a result of block rotations this angle is now larger and may reach 110 the results demonstrate large block rotations in different senses in domains of strike slip faults the independent structural and paleomagnetic data can be interpreted within the framework of a simple geometric model northern israel is considered to be a good model for this efficient mechanism of intraplate deformation which is expected to occur in similar tectonic settings elsewhere

extreme value statistics for wave run up on a natural beach abstract statistics of wave run up maxima have been calculated for 149 35 minutes data runs from a natural beach during the experiment incident wave height varied from 0 4 to 4 0 m incident wave period from 6 to 16 s and beach face slope from 0 07 to 0 20 four extreme statistics were calculated the maximum run up height during each run the 2 exceedence level of shoreline elevation the 2 exceedence height for individual run up peaks and the 2 exceedence level for swash height as determined by the zero upcrossing method these statistics were best parameterized when normalized by the incident significant wave height and plotted against the iribarren number h l 0 1 2 the swash data with set up removed showed less scatter than total run up with set up included for iribarren number greater than 1 5 the run up was dominated by the incident frequencies for lower iribarren number longer period motions dominated the swash a reasonable value of wave steepness for a fully developed storm sea is 0 025 so that a storm iribarren number can be estimated as 6 3 times the beach slope using this and an offshore design wave height the included graphs may provide guidance in determining a design run up height

barrier island resilience assessment applying the ecological principles to geomorphological data abstract applying the ecological resilience principles to barrier island geomorphological evolution requires approaches that perceive and interpret resilience far from predefined barrier characteristics and static views accepting that barrier islands like all natural systems are dynamic and adaptively changing in response to external disturbances is fundamental to the formulated approach to this aim geomorphological units and dimensions were used to describe barrier island stability landscape as an actively shifting topography reshaping in response to exogenous events and in relation to intrinsic properties the structure of the subaerial barrier was characterised using the environmental units of beach dune and marsh or bdm where different combinations of bdm structure define distinct barrier stable states under a simplified framework that is applicable over a wide range of barrier structures the methodology is based on reconstructing resilience trajectories of barrier islands through identifying the distinct bdm states and related shifts thresholds crossed and assessing resilience dimensions latitude resistance and precariousness defined as barrier width and height and proximity to mainland respectively that jointly define the shape of the stability domain the approach was applied to the ria formosa barrier island system s portugal using multi decadal geomorphological data and gradually decreasing spatial discretisation passing from individual barrier transects to sectors and to entire barriers the joint evolution of two inland migrating barriers cabanas island and cacela peninsula was used as an exemplar of adaptive capacity in barrier geomorphic change and therefore of resilient response to external pressures resilience pathways showed that the ria formosa barriers have been resilient over the studied timeframe with a tendency for maintaining or increasing bdm structural complexity in general the stability domain tends to shift from low latitude and high resistance forms narrow deep basins of attraction in the west part of the barrier chain to higher latitudes and lower resistance ones wide shallow basins towards the east precariousness peaks near the edges of the system low lagoon width and minimises towards the central part most detached barriers scaling issues regarding smoothing of longshore variability and potential consequences on masking thresholds and critical dimensions are highlighted and discussed along with the key role of the meaning of specified resilience of what in the assessment the methodology is a novel approach easily transferable to different systems and spatiotemporal scales of analysis representing a step forward in interpreting and assessing barrier island resilience

a 1500 yr record of north atlantic storm activity based on optically dated relict beach scarps understanding of long term dynamics of intense coastal storms is important for determining the frequency and impact of these events on sandy coasts we use optically stimulated luminescence osl dates on relict scarps within a prograded barrier sequence to reconstruct the chronology of large magnitude erosional events in the western gulf of maine osl dates obtained on quartz rich sediments immediately overlying relict scarps indicate severe beach erosion and retreat due to erosional events ca 1550 390 290 and 150 cal yr b p our data provide new evidence of increased storm activity most likely frequency and or intensity of extratropical storms during the past 500 yr which was preceded by a relatively calm period lasting 1000 yr the width of the coastal sequence preserved between successive paleoscarps shows strong correlation with the time interval elapsed between storms our fi ndings indicate that diagnostic geophysical and sedimentological signatures of severe erosional events offer new opportunities for assessing the impact and timing of major storms along sandy coasts

evolution of a large baltic beach ridge plain neudarss ne germany a continuous record of sea level and wind field variation since the homeric minimum

hydrodynamics and equilibrium of a multiple inlet system although it is generally acknowledged that most multiple inlets are unstable and cannot coexist there is evidence to suggest that such inlets can indeed be stable over decadal time scales multiple inlet systems servicing a single embayment in contrast to single inlet systems confer particular hydrodynamic characteristics such as the potential existence of residual discharges and currents between the inlets this paper presents detailed measurements of hydrodynamic variables obtained over complete spring and neap tidal cycles in a multiple inlet system in southern portugal ria formosa the results indicate that the two main interconnected inlets servicing an embayment can coexist at least over a time scale of several decades however their coexistence cannot be explained simply using empirical equilibrium relations or inlet hydraulics although residual flow between the inlets appears to play an important role enhancing their stability it is the availability of sediment stored in the ebb tidal deltas and its capacity to be carried into the inlets during storm events that ultimately dictates the overall equilibrium independently of the flushing capability provided by the hydraulics such movement of sediment leads to the obstruction of the inlet channels thereby affecting the hydraulic efficiency and eventually leading to inlet closure in the long term the results augment existing knowledge concerning multiple inlet systems and improve understanding of their short to medium term stability

role of wave forcing storms and nao in outer bar dynamics on a high energy macro tidal beach abstract outer sand bar dynamics on a high energy macro tidal beach were investigated using long term multi year field datasets of intertidal morphology and offshore bathymetry utilising a 15 year time series of argus video images five distinct outer bar types were identified mega rip longshore crescentic crescentic attached and welded the most common classification was crescentic attached with the outer bar oscillations being out of phase with the inner bar oscillations as would be expected for the shore normal wave approach at this site the outer bar had a typical amplitude of 0 5 1 m and a longshore wavelength of 600 m changes in outer bar morphology were related to measured and modelled nearshore wave data however the outer bar morphology changed over a much longer timescale monthly to annual than the daily to weekly variations in wave height and period an extended duration of energetic wave action was required to bring about an upstate bar transition to the longshore or mega rip state where the bar then remained arrested for a significant amount of time requiring several months of low wave conditions to induce a down state transition through crescentic to welded this slow morphological response is explained by extended relaxation times attributed to the large tidal range at the study site where the outer bar morphology is only active for part of the tidal cycle several hours around low tide the configuration and position of the outer bar were related the more upstate downstate bar types being associated with a more offshore onshore bar position the detrended outer bar position was significantly related to a forcing term based on wave power and disequilibrium of the dimensionless fall velocity with offshore onshore bar migration occurring when wave conditions were more less energetic that the antecedent conditions the upstate end member longshore or mega rip was attained sometime during the winter months for 14 out of the 16 years of monitoring the outer bar remained attached to the low tide shoreline over the winter 2005 2006 and 2010 2011 these two winters with incomplete upstate cycles were characterised by the lowest winter wave conditions and negative winter north atlantic oscillation nao indices suggesting that the winter nao is correlated with both beach state and nearshore bar configuration

foredunes and blowouts initiation geomorphology and dynamics this paper reviews the initiation dynamics geomorphology and evolution of incipient foredunes established foredunes and blowouts incipient foredunes may be initiated in a variety of ways leading to the formation of ramps terraces or ridges depending on progradation rates vegetation type and cover sediment transport rates and scale of erosional processes vegetation cover morphology growth rates and types combine with aerodynamic processes to determine dune and swale morphology established foredunes are classified into five morpho ecological types and the flow behaviour over two types is detailed a new model of foredune evolutionary paths at various possible time scales is presented blowout initiation dynamics and sediment transport and evolution is examined throughout the review the gaps in present understanding of dune processes and a range of ideas for new research possibilities are provided

sandy berm and beach ridge formation in relation to extreme sea levels a danish example in a micro tidal environment abstract the formation of berms and their transformation into beach ridges in a micro tidal environment is coupled to wave run up and overtopping during extreme sea levels a straight forward comparison between extreme sea levels due to storm surges and active berm levels is impossible in the semi enclosed bays along the baltic sea quite often the maximum water levels do not coincide with the maximum intensity of the wave driven processes because of seiches in the baltic in this paper we look into the joined distribution of extreme water levels and high energetic wave conditions at feddet a sandy prograding spit on the south eastern baltic shores of zealand denmark the modern sandy beach at this location consists of a beachface with a shallow incipient berm a mature berm and a dune covered beach ridge it borders a beach ridge plain to the west where more than 20 n s oriented beach ridges and swales are present measured water level data from 1991 to 2012 and topographical observations carried out during fair weather period and during a storm event provided the basis for a conceptual model exhibiting berm formation and transformation into the local beach ridge system the character of extreme sea level events is identified using thirty three well described extreme events throughout a period of 15 years analysis of the meteorological conditions during these events revealed that berm formation only occurred during 20 of all extreme events when onshore winds high energy wave action and elevated water coincided these berm forming events had a mean return period of once every three years the average age between successive beach ridges on the beach ridge plain was about 180 years which means that the transformation of a berm into a single beach ridge is the result of a large number of storm episodes with high energy waves and extreme water levels

impacts of human interventions on the evolution of the ria formosa barrier island system s portugal abstract human interventions on sandy barriers disturb natural barrier dynamics to the extent of having become key forces in modifying geomorphological evolution this work identifies natural and human induced drivers and analyses their importance to the multi decadal evolution of the ria formosa barrier island system in south portugal aerial photographs from the last six decades and historical maps are used to assess changes in cross shore rates morphological characteristics barrier and dune widths inlet morphology and migration and barrier areas through systematic methods that can be easily transferred to other barrier systems interventions and especially hard engineering ones jetties inlet stabilisations affected barrier evolution trends shore perpendicular works increased shoreline progradation updrift and initiated coastal retreat downdrift with strongest erosive impacts along the edges of the system inlet stabilisations changed tidal inlet hydrodynamics and initiated ebb shoal attachment to the barriers on either side of a non migrating inlet that experienced loss of tidal prism this shoal attachment was the main factor for the increase in total barrier area of ria formosa during the 60 years of analysis barrier growth after 2005 was slower which could indicate that the system is reaching morphodynamic stability

integrating millennial and interdecadal shoreline changes morpho sedimentary investigation of two prograded barriers in southeastern australia abstract prograded barriers are distinctive coastal landforms preserving the position of past shorelines as low relief shore parallel ridges composed of beach sediments and commonly adorned with variable amounts of dune sand prograded barriers have been valued as coastal archives which contain palaeoenvironmental information however integrating the millennial timescale geological history of barriers with observed inter decadal modern beach processes has proved difficult technologies such as airborne lidar ground penetrating radar gpr and optically stimulated luminescence dating osl were utilised at boydtown and wonboyn in southeastern australia and combined with previously reported radiocarbon dates and offshore seismic and sedimentological data to reconstruct the morpho sedimentary history of prograded barrier systems these technologies enabled reconstruction of geological timescale processes integrated with an inter decadal model of ridge formation explaining the gpr imaged subsurface character of the barriers both the boydtown and wonboyn barriers began prograding 7500 8000 years ago when sea level attained at or near present height along this coastline and continued prograding until the present day with an initially slower rate of shoreline advancement sources of sediment for progradation appear to be the inner shelf and shoreface with a large shelf sand body likely contributing to progradation at wonboyn the towamba river seems to have delivered sediment to twofold bay during flood events after transitioning to a mature estuarine system sometime after 4000 cal yr bp some of this material appears to have been reworked onto the boydtown barrier increasing the rate of progradation in the seaward 50 of the barrier deposited over the past 1500 years the gpr imaged beachfaces are shown to have similar geometry to beach profiles following recent storm events and a model of ridge formation involving cut and fill of the beachface and dune building in the backshore explains the character of the preserved beachface record and the morphology of the ridges this model is applicable to future management of individual beaches where such beaches are subject to ongoing cut and fill dune building processes and inherited sediment budget conditions

the origin of centennial to millennial scale chronological gaps in storm emplaced beach ridge plains recent studies of tropical cyclone surge and wave emplaced beach ridge plains have shown that these sequences often contain centennial to millennial scale gaps in their chronologies two explanations for the gaps exist they are due to erosion or alternatively a cessation or substantial slowing of depositional processes suggestive of a quieter phase in intense storm activity differentiating between the two is important for uncovering reliable long term storm histories from these sequences we use landform morphology sediment texture and luminescence chronology to determine the origin of substantial chronological gaps in a plain containing more than 100 shore parallel ridges composed of fine grained sand located in northeast australia we identify and describe the characteristics associated with both erosional and non erosional gaps the erosional gaps are associated with changes in orientation between ridge sets and often a high ridge with hummocky topography that appears to have been disturbed by aeolian activity river floods likely caused the partial erosion of ridge sets non erosional gaps do not display these morphological characteristics and are likely associated with quiescence in severe tropical cyclone activity these geomorphic and chronological signatures can be used to identify different sorts of gaps in other ridge plains and are an important tool in the reconstruction of long term storm histories from these coastal landforms the data also suggests that fine grained ridges can like their coarse grained counterparts be predominantly deposited by storm waves and surge and their texture need not necessarily be indicative of the processes responsible for ridge development

sediment supply from shoreface to dunes linking sediment transport measurements and long term morphological evolution a significant problem in current coastal research is the understanding of linkages between morphological phenomena occurring on different temporal and spatial scales morphodynamic processes in the nearshore typically exhibit nonlinear behaviour and consequently phenomena which occur on short temporal event scales as e g observed during field experiments have generally been difficult to upscale to provide an understanding of the long term behaviour of the coast on the time scale of seasons or decades this paper documents a persistent onshore migration of nearshore bar features over a period of 3 decades using a set of cross shore profile surveys from a barrier on the danish north sea coast the observed behaviour is consistent with experimental data obtained during weeklong field campaigns when sediment transport and bar migration were found to be landward directed during high energy dissipative conditions hydrodynamic and sediment transport processes leading to onshore bar migration and eventually welding of the bars are documented to provide an explanation for the observed long term evolutionary trends in addition bar welding and the resulting intertidal bar formation represent an onshore sediment storage which is subsequently available for aeolian transport observations on aeolian sediment transport indicate that transport rates and sediment supply to the foredunes critically depend on the presence of dry sand sources as represented by well drained intertidal bars measurements of long term accretion rates in foredunes indicate that volumes deposited on the crest and lee slope of the dunes are in reasonable correspondence with volumes supplied to the subaerial beach through the process of bar welding hence the data suggest that a persistent onshore directed sediment supply occurs from the shoreface across the surf and intertidal zones and into the dunes of the investigated barrier

assessment of tidal inlet evolution and stability using sediment budget computations and hydraulic parameter analysis abstract research into the response of coastlines to the opening and stabilisation of inlets has been limited by the availability of suitable data the shortcomings of existing formulae when applied to different inlets and the difficulties particular to multi inlet situations our appraisal of methodologies for studying inlet dynamics leads us to formulate a new approach for investigating inlet evolution and stability based on combining sediment budget computations using best estimates and uncertainty analysis and inlet hydraulic parameter analysis the approach developed is applied to a stabilised inlet located within a multi inlet system faro olhao inlet ria formosa southern portugal which was opened starting 1929 and has since been dredged periodically to maintain navigability a series of digital maps was produced based on multi year data acquired from charts surveys and aerial photos the maps were used to compute sediment volumes for six coastal cells delineated on the basis of the morphological features of the inlet cell volumes and fluxes were calculated for three periods 1929 1962 1962 1978 and 1978 2001 and overall sediment budgets were calculated for the latter two periods inlet hydraulic parameters measured included tidal prism inlet channel cross sectional area and hydraulic radius and maximum depth of the inlet throat and were tracked over 9 bathymetric surveys from 1947 2004 the computed budget reveals that the inlet is only at present reaching volumetric equilibrium however the analysis of channel cross sectional area and radius indicates parameter stability around 1978 1985 20 25 years before the inlet started to reach volumetric equilibrium it is hypothesised that the observed stability in parameters for the inlet post 1978 is related to the presence of fixed jetties and to a stratigraphic control that prevents further deepening and not to the achievement of a dynamic equilibrium the findings indicate that the coupling of sediment budget computation and inlet parameter analysis is useful for understanding historical sediment pathways and magnitudes and for analysing the evolution of an inlet towards equilibrium although the analysis of inlet parameter evolution is valuable for examining the locational geometrical stability of an inlet it needs to be used in conjunction with sediment budget computations in order to properly infer inlet equilibrium moreover existing formulae used to infer inlet stability which relate cross sectional area to tidal prism should be reviewed with a view to including other external variables e g stratigraphic controls and to making their application more flexible to cope with the range of different inlet conditions for multi inlet systems the coupling of morphology and hydrodynamics analysis should be extended to all inlets in order to infer the stability of the overall system based on the distribution of the tidal prism through time and the patterns of inlet circulation and sediment transport

a general framework for modeling sediment supply to coastal dunes including wind angle beach geometry and fetch effects a series of spatially explicit equations are derived that form the foundation of a modeling framework that provides insight into how the interaction of the fetch effect and angle of wind approach leads to tradeoffs that govern the magnitude of aeolian sediment transport across beaches of different geometry the spatial distribution of sediment transport rate per unit width at any point on the beach is shown to vary predictably as a function of wind angle critical fetch and beach geometry and this has evident implications for the total volume and distribution of sediment transport into the dunes behind the beach as well as the proportion of sediment lost from the beach dune system at the downwind margin as the wind field shifts from onshore shore perpendicular to oblique shore parallel approach angle total sediment transport rate across a dune line segment will reflect a tradeoff between transport reduction because of the cosine effect and transport enhancement because of potentially longer fetch distances traversed by the wind prior to encountering the dune line this tradeoff is most evident on long narrow beaches when beach width is less than the critical fetch for such beaches and with onshore winds the total sediment transport rate across the dune line will be less than that predicted for a wide beach because of the constraint imposed by the fetch effect however as the angle of wind approach becomes oblique the available fetch becomes progressively longer transport limitations imposed by the fetch effect are negated and transport enhancement across the dune line is to be expected with very large angles of wind approach the cosine effect dominates the interaction and transport reductions across the dune line occur until the wind is shore parallel and sediment supply to the dunes ceases altogether this sequence of adjustments and tradeoffs were only partially understood prior to this study and yet they form the foundation of coastal dune modeling the framework proposed in this paper serves to place future studies of process form interaction in beach dune systems on a robust theoretical foundation it also facilitates the testing of various alternative hypotheses regarding the uneven spatial and temporal distribution of dune height and growth rate in coastal environments

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

average regional strain due to slip on numerous faults of different orientations if a region is cut by faults with different orientations and if the faults intersect the boundaries of the region of interest then the average finite rotational strain eij ui xj is given by eij mij v where is the shear modulus v is the volume of the region and mij represents the sum of asymmetric moment tensors mij for each fault mij m0 u n where m0 is the scalar seismic moment and u and n are the unit vectors parallel to the slip vector and perpendicular to the fault plane this result is applicable when the average regional strain occurs primarily by displacements of essentially rigid blocks that together compose the region of interest and hence when both elastic strains and inelastic strains due to folding and bending are small

finite strain calculations of continental deformation 1 method and general results for convergent zones a finite element method is used to calculate stresses and strain rates in a thin viscous sheet representing the continental lithosphere that is bordered in one part by an indenting boundary we calculate solutions for velocity fields crustal thickness distributions strain rates rotation time integrated vorticity and finite strain ellipsoids to show the dependence of these quantities on the controlling parameters the stress strain exponent n and the strength of the sheet relative to the gravitational forces which may be expressed as a dimensionless number the argand number ar for n 3 and ar between 1 and 10 a plateau of thickened crust is formed in front of the indenter the strain histories of individual elements within the viscous sheet may be quite complex and the finite strain at the end of deformation may bear no obvious relation to the principal stress orientations during the deformation the strain rate fields are interpreted in terms of the style of faulting that would be expected in the brittle upper crust if it were coupled to the ductile but stronger upper mantle in general the length scale of deformation increases with ar and time since the start of the collision and decreases with n for ar 3 the increase in length scale is accompanied by a change in the style of deformation from predominantly crustal thickening with thrust faulting in the brittle layer to predominantly transcurrent deformation strike slip faulting in the brittle layer

thresholds for storm impacts on an exposed sandy coastal area in southern portugal abstract storms are one of the most important phenomena responsible for coastal erosion their destructive power presents major challenges for coastal management and knowledge of their characteristics and associated consequences is therefore of paramount importance in this study thresholds for storm impacts are defined for a sandy coast in southern portugal faro beach ria formosa using two different approaches i hydrodynamic conditions associated with historical storm impacts i e infrastructural damage and ii computed maximum wave run up values r high compared with beach morphology damage thresholds are defined as limits above which the action of a storm exceeds beach front response capability and starts to act directly on human infrastructures according to method i four different thresholds were defined for individual storms directed from the sw the threshold is a significant wave height of 4 7 m with a storm duration of 2 days and for storms directed from the se is a significant wave height of 6 m with a storm duration of at least 2 days regarding storm groups for those directed from the sw the threshold is 2 storms lasting at least 2 days each with significant wave heights greater than 3 5 m whilst for those directed from the se the threshold is 3 short storms lasting 1 day each with significant wave height over 3 9 m the return period for the sw storm group threshold is just 1 7 years for method ii beach morphological parameters d high highest elevation of the frontal dune d low elevation of the dune base and tan f foreshore slope were determined for five chosen cross shore profiles along the study area and r high computed for different hydrodynamic conditions results were validated through field observations of storm impacts the lowest thresholds for overwash are along the central part of the study area where a dune crest is absent due to human occupation the highest thresholds for overwash are on those profiles where a frontal dune is well developed or a foredune ridge is present western and eastern parts of the study area this study presents a methodological strategy to compute realistic thresholds for storm impacts along faro beach based on historical datasets of hydrodynamics and storm impacts information the approach could be implemented in other coastal areas to provide a comprehensive assessment of the storm impact requiring only simple information like offshore storm hydrodynamics characteristics beach morphology and reports of coastal infrastructure damage

extracting storm surge data from coastal dunes for improved assessment of flood risk future changes in climate and sea level are likely to increase the threat from storm surges in many coastal regions mitigation of this threat requires an understanding of storm surge magnitude and frequency and the relationship of these variables to climate parameters this understanding is currently limited by the brevity of instrumental records which rarely predate the twentieth century however evidence of former storm surges can be recorded in coastal dunes because the dune topography may trap high magnitude deposits at elevated locations here we combine a range of techniques to extract storm surge data from coastal dune sediment the sediment is tracked in the subsurface with ground penetrating radar to assess its height and extent and its age is determined with good precision through optically stimulated luminescence dating the probable age of the sediment a d 1775 or 1776 is within a period of increased storminess in northwest europe and the local magnitude of the event is likely to be greater than any on instrumental record by utilizing coastal dunes for storm surge analysis our approach provides a valuable new source of information for understanding storm surge risk which is vital for the protection of coastal regions

vegetation and sedimentation on coastal foredunes on a timescale of years to decades vegetated foredunes may show various modes of morphological development vegetation is one of the factors that determine the sedimentation pattern and thus morphology on the foredune in turn the vegetation pattern may be controlled by the sedimentation pattern although these effects have been quantified for short timescales there is relatively little information on the interaction between vegetation and sedimentation for timescales of over a year for the island of ameland the netherlands elevation measurements and aerial photographs between 2002 and 2012 were used to derive changes in elevation and vegetation patterns on a year to year basis this was done for a range of stable to accreting foredunes sedimentation increases from the beach to a maximum halfway up the seaward slope of the foredune and then decreases again when going landward this trend is further modified by the vegetation s spatial pattern on a timescale of years there is no correlation between the density of vegetation cover and the amount of accretion however by accounting for the gradual depletion of the sand load over the foredune a relationship can be defined between vegetation cover and its trapping efficiency foredune vegetation spreads mainly by lateral expansion of existing patches no strong effect was found of the sedimentation balance on the expansion of vegetation it is suggested that other growth limiting factors are of similar importance masking any possible dependency of vegetation growth on sand accretion

vegetation control allows autocyclic formation of multiple dunes on prograding coasts we investigate the formation of multiple dunes using a 15 yr record of dune growth from long beach peninsula washington state usa and a recently published coastal dune model modified to include a feedback between vegetation growth and local dune slope in the presence of shoreline progradation we find that multiple dune ridge formation can be autocyclic arising purely from internal dune dynamics rather than requiring variations in external conditions our results suggest that the ratio of the shoreline progradation rate and the lateral dune growth rate is critical in determining the height number and form of multiple dunes allowing the development of testable predictions our findings are consistent with observations and imply that caution is required when using dune ridges as proxies for past changes in climate sea level land use and tectonic activity because the relationship between external events and the formation of multiple dunes may not be one to one as previously thought

aeolian beach ridges and their significance for climate and sea level concept and insight from the levant coast east mediterranean abstract relict beach ridges of aeolian origin and associated soils are often used for inferring relative sea level and climate with contrasting results most studies link the aeolian coastal deposits to regressive phases some to high sea level stands and a few to intermediate relative sea level positions we interpret the apparent contradictions as indicating the lack of an over arching concept and the inconsistent usage of sea level related terms in this paper we present an integrated morpho sedimentological concept for a microtidal mid latitudinal coast and review existing data from the levant east mediterranean coast to evaluate the concept and to eliminate nomenclatural confusion a coastal depositional environment in a semi arid environment consists of shallow marine aeolian and alluvial facies which together form an aeolian beach ridge complex as a package of strata which respond simultaneously to sea level change a transgressive complex forms through reworking or overstepping of the coastal foredune and a regressive complex forms by downstepping under transgression the aeolian beach ridge represents the highstand deposit and its adjacent shallow marine sediment is the transgressive deposit under regression the complex represents the falling stage and the associated downdip surface marks the lowstand on the levant coast we find chronologically well constrained offlapping aeolian beach ridges as parts of six downstepping beach ridge complexes formed between 200 ka and 10 ka the complexes represent the falling stage systems tract fsst of a short lived 5th order depositional sequence when the shoreline shifted from a position close to the modern coastline to the shelf or below the shelf edge three of these fssts and their up dip and down dip super bounding surface together form the 4th order 100 ka sequence of the last interglacial glacial cycle the absence of transgressive highstand and lowstand systems tract is explained by the poor preservation potential due to the small sediment budget of the complex the falling stage complex has a high preservation potential because sediment source area increases while the sand drift potential remains above the local threshold on the levant coast sand delivery to the backshore continued during relative sea level falls for distances of up to 10 km between dune and coastline which is unprecedented in most modern analogues the significance of the dune soil succession for climate is limited because the dunes are governed by relative sea level change the vegetation response to changes in precipitation is non linear and the dune dynamics are characterised by low resilience and hysteresis

reconstruction of holocene coastal foredune progradation using luminescence dating an example from the świna barrier southern baltic sea nw poland abstract two sandy spits on the wina barrier wolin and uznam provide a very detailed succession of holocene coastal foredunes and dunes and are regarded as key sites along the southern baltic sea coast optically stimulated luminescence osl dating is proven to be a powerful tool for the reconstruction of holocene coastal spit evolution and foredune accretion quartz extracted from the coastal sediments in the study area provides excellent properties for osl dating the osl age from the innermost dune indicates that spit development of the wina barrier started immediately after rapid sea level rise of the littorina transgression decelerated at 6 6 ka a significant change in the foredune progradation rate occurred during the late subatlantic transgression at 1 2 ka 800 ad when migration rates decreased from 2 6 0 7 m a 1 to 1 3 0 4 m a 1 progradation accelerated again during the little ice age between 1550 and 1850 ad the systematic dating of 28 samples reveals six hiatuses during foredune succession at 2100 bc 900 bc 200 bc 200 ad 600 ad 1000 ad and 1600 ad the timing of these hiatuses correlates with the phases of transgressive dune development in the surrounding area troszyn and wina and with phases of increased aeolian activity in other parts of north and west europe we conclude that four of these phases of foredune erosion instability and aeolian sediment mobilisation were caused by general climate shifts to cooler and stormier conditions at 2200 bc 900 bc 600 ad and at 1600 ad the latter corresponding to the little ice age the period of increased aeolian activity around 1000 ad is probably to a phase of intensive forest clearance in central europe in contrast the systematic foredune accretion and foredune plain growth correlates to periods of positive sediment budget milder and calmer climate and an intact vegetation cover

length scales for continental deformation in convergent divergent and strike slip environments analytical and approximate solutions for a thin viscous sheet model the deformation of a thin viscous layer that has a moving boundary is investigated for comparison with zones of deformation in the continental lithosphere exact analytical solutions for the case of a newtonian fluid and approximate solutions for the case of fluid with power law rheology show that when the imposed velocity vector is normal to the boundary congressional or extensional regime the deformation field decays away from the boundary with a characteristic length scale 1 3 to 1 10 the wavelength of the imposed boundary velocity distribution for n between 1 and 10 where n is the stress strain exponent in the rheology in contrast when the imposed velocity vector is parallel to the boundary transcurrent regime the length scale of the deformation field is approximately 4 times smaller in each case these length scales decrease approximately as n the difference in length scales arises even in the absence of any buoyancy forces acting on thickened or thinned crust such forces would modify the ratio of length scales but not sufficiently to affect this result

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

beach ridges definitions and significance abstract beach ridges frequent components of quaternary coastal plains and other coastal landforms have been cited as indicators of the positions of ancient seashores and associated sea levels numerous authors utilized the term beach ridge for active and relict usually wave built supratidal and or intertidal forms wind built ridges have been only occasionally included in the definition the term was applied also to submerged landward shifting eventually stranded bars a consistent redefinition of the term is highly desirable beach ridges should include all relict strandplain ridges whether dominated by wave swash built or by eolian lithosomes all active ridge like shore features regardless of dimensions morphology and origin are excluded because of the resistance of coarse clastic ridges to wave and wind erosion swash built gravel or coarse shell storm ridges may build several meters above the level of high tide swash built high berms even on pure sandy beaches exceed the highest tides during episodes of wind induced record water levels frequently but not always burying underlying low relief berm ridges of berm lithosomes sequences of relatively steep multiple foredunes are commonly named beach ridge plains the narrow subparallel relict foredunes that form these strandplains presently are designated as eolian beach ridges beach ridges thus are defined as relict semiparallel multiple wave and wind built landforms that originated in the inter and supratidal zones until separated from the shoreline by progradation sandy pebbly or shell enriched backshore berm ridges behind an active foreshore should not be considered beach ridges strandplain progradation is either continuous or with the inclusion of subtidal cat s eye ponds discontinuous contrary to claims transgressive cheniers do not represent true cheniers alone within their overall progradational context cheniers a special category of beach ridges bracketed by subtidal intertidal mudflats may be transgressive or regressive in character landward driven transgressive ridges should be designated beach ridges only after they are stabilized on intertidal flats when recognizable between clearly identifiable intertidal and overlying eolian intervals the horizontal interface between these lithosomes in beach ridges may help the reconstruction of ancient tide lake levels diagnostic sedimentary textures structures and fossils however often may be unavailable in the deposits along with various types of elevated terraces composed of raised marine deposits and certain coastal landforms of erosional origin that occur worldwide beach ridges of clearly proven wave built origin may also serve as indicators of ancient higher than present sea levels

coarse sand beach ridges at cowley beach north eastern australia their formative processes and potential as records of tropical cyclone history storm surges generated by tropical cyclones have been considered a primary process for building coarse sand beach ridges along the north eastern queensland coast australia this interpretation has led to the development of palaeotempestology based on the beach ridges to better identify the sedimentary processes responsible for these ridges a high resolution chronostratigraphic analysis of a series of ridges was carried out at cowley beach queensland a meso tidal beach system with a 3 m tide range optically stimulated luminescence ages indicate that 10 ridges accreted seaward over the last 2500 to 2700 years the ridge crests sit 3 5 to 5 1 m above australian height datum ca mean sea level a ground penetrating radar profile shows two distinct radar facies both of which are dissected by truncation surfaces hummocky structures in the upper facies indicate that the nucleus of the beach ridge forms as a berm at 2 5 m australian height datum equivalent to the fair weather swash limit during high tide the lower facies comprises a sequence of seaward dipping reflections beach progradation thus occurs via fair weather wave accretion of sand with erosion by storm waves resulting in a sporadic sedimentary record the ridge deposits above the fair weather swash limit are primarily composed of coarse and medium sands with pumice gravels and are largely emplaced during surge events inundation of the ridges is more likely to occur in relation to a cyclone passing during high tide the ridges may also include an aeolian component as cyclonic winds can transport beach sand inland especially during low tide and some layers above 2 5 m australian height datum are finer than aeolian ripples found on the backshore coarse sand ridges at cowley beach are thus products of fair weather swash and cyclone inundation modulated by tides knowledge of this composite depositional process can better inform the development of robust palaeoenvironmental reconstructions from the ridges this article is protected by copyright all rights reserved

the structure and development of foredunes on a locally prograding coast insights from ground penetrating radar surveys norfolk uk the internal structure of coastal foredunes from three sites along the north norfolk coast has been investigated using ground penetrating radar gpr which provides a unique insight into the internal structure of these dunes that cannot be achieved by any other non destructive or geophysical technique combining geomorphological and geophysical investigations into the structure and morphology of these coastal foredunes has enabled a more accurate determination of their development and evolution the radar profiles show the internal structures which include foreslope accretion trough cut and fill roll over and beach deposits foredune ridges contain large sets of low angle cross stratification from dune foreslope accretion with trough shaped structures from cut and fill on the crest and rearslope foreslope accretion indicates sand supply from the beach to the foreslope while troughs on the dune crest and rearslope are attributed to reworking by offshore winds bounding surfaces between dunes are clearly resolved and reveal the relative chronology of dune emplacement radar sequence boundaries within dunes have been traced below the water table passing into beach erosion surfaces these are believed to result from storm activity which erodes the upper beach and dunes in one example at brancaster a dune scarp and erosion surface may be correlated with erosion in the 1950s possibly the 1953 storm results suggest that dune ridge development is intimately linked to changes in the shoreline with dune development associated with coastal progradation while dunes are eroded during storms and where beaches are eroding a stable coast provides more time for dune development resulting in higher foredune ridges a model for coastal dune evolution is presented which illustrates stages of dune development in response to beach evolution and sand supply in contrast to many other coastal dune fields where the prevailing wind is onshore on the north norfolk coast the prevailing wind is directed along the coast and offshore which reduces the landward migration of sand dunes

fault friction regional stress and crust mantle coupling in southern california from finite element models ongoing deformation of southern california is simulated in a set of 63 models in an attempt to empirically determine fault friction to a previous code for simulation of anelastic crustal strain we introduce a new finite element to represent a curved fault of arbitrary rheology we also add several selfconsistent patterns of horizontal drag on the base of the crust caused by independent upper mantle flow a grid of isoparametric finite elements represents the regional fault geometry and the known variations in elevation and heat flow plate tectonic velocity boundary conditions are applied solutions include the time averaged flow velocities and fault slip rates and vertically averaged stresses each model is scored by comparing its slip rate predictions with 56 rates from dated offset geologic features in membrane stress models the optimal fault friction is 0 4 0 6 frictional self heating of faults is not a major factor determining strength addition of crust mantle coupling improves results if convergence of north american and pacific lithospheres is assumed to occur under the transverse ranges among such models those with fault friction of about 0 3 score best by most norms of the prediction error these have over 80 of regional strain in faults and only a small amount of block deformation however one model with friction of 0 85 scores better by the percent of correct predictions norm this model has only half the regional strain as fault slip and matches slow rates well but underpredicts slip rates over 1 cm yr furthermore its predictions are degraded considerably if hydraulic lubrication of thrust faults is assumed the low friction models are unaffected we conclude that some source of variation in fault friction remains unmodeled but that at least the fastslipping faults in california have low friction similar to that of hydrated clay gouges appendix is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 001 2 50 payment must accompany order