rapid water exchange between the lagoon and the open ocean at majuro atoll due to wind waves and tide current measurements and conductivity temperature depth surveys of the lagoon and ocean at majuro atoll the republic of the marshall islands were made from january 10 to 24 1997 a vertically integrated tidal current model reproduced qualitatively well tidal ellipses calculated from the observed current measurements by fourier transform a three dimensional robust diagnostic residual current model explained the major features observed in the current measurements averaged over the dominant tidal cycles we used the diagnostic model to examine the effects of wind stress radiation stress density gradients and tidal stress on the exchange of water between the lagoon and the ocean wind effectively mixes the lagoon water in approximately 2 weeks tidal flushing appears to be restricted to a small area near the main channels connecting the lagoon to the ocean cross reef flat currents induced by radiation stress and flowing to the deep channels in the center of the northern boundary form the dominant mechanism for exchange between the lagoon and the open ocean causing water to exchange completely with the ocean in about 15 days computer generated particles tracked through the lagoon showed that radiation stress is also the main forcing mechanism for particle export from the lagoon however the coupling of tidal exchange through the calalin channel and wind stress induced mixing in the lagoon could also provide a significant export mechanism particularly for particles originating uniformly inside the lagoon

the effect of fluid composition on the behavior of well cemented quartz rich sandstone during faulting abstract previous studies o kane a onasch c m farver j 2007 the role of fluids in low temperature fault related deformation of quartz arenite journal of structural geology 29 819 836 cook j dunne w m onasch c m 2006 development of a dilatant damage zone along a thrust relay in a low porosity quartz arenite journal of structural geology 28 776 792 found that quartz arenite within two fault zones in the appalachian foreland thrust belt displays very different structural styles and histories despite deforming at similar pressures and temperatures during the alleghanian orogeny a comparison of the grain scale deformation and fluid histories using transmitted and cathodoluminescence microscopy and fluid inclusion microthermometry shows that fluid composition was a controlling factor for causing these differences the cove fault zone deformed in the presence of aqueous fluids first a cacl 2 brine and then an iron rich fluid the precipitation of quartz cement from the brine kept pace with brittle deformation maintaining overall rock cohesion in the fault zone the introduction of iron rich fluids caused a switch from precipitation to dissolution of quartz along with precipitation of goethite in a damage zone along a backthrust in the cave mountain anticline early deformation occurred in the presence of an aqueous fluid from which quartz was precipitated the latest deformation however occurred in the presence of a methane rich fluid which inhibited the precipitation of quartz cement producing porous breccias and open fractures despite deformation at 6 km depth fluid composition not only affected cementation in the fault zones but also the selection of grain scale deformation mechanisms therefore it is a controlling factor in determining the behavior and strength of these fault zones

geophysical studies of large blind thrust valley and ridge province central appalachians possible thrust sheet geometries in the unexposed cambrian ordovician lithotectonic unit in the nittany anticlinorium of the valley and ridge province in west virginia are defined through analysis of geophysical data calculated gravity for different subsurface interpretations is compared with observed gravity comparisons of model calculations to terrain corrected bouguer gravity indicate that a large blind thrust of the cambrian ordovician lithotectonic unit extending across the entire width of the anticlinorium is an acceptable subsurface interpretation a seismic line across the anticlinorium is also presented the seismic line reveals that a large part of the area is underlain by a double thickness of the cambrian ordovician lithotectonic unit data can be interpreted many ways however the gravity data require that an acceptable model have only minor lateral density contrasts across the anticlinorium so that effectively a double thickness of the cambrian ordovician lithotectonic unit exists across it both the gravity and seismic data indicate that the presence of separate horses beneath the major silurian devonian structures exposed at the surface is unlikely

a numerical study of circulation in a coastal reef lagoon system 1 a coupled wave circulation numerical model was used to simulate the distribution of wave energy as well as the circulation induced by wave breaking wind and tidal forcing within a coral reef system in kaneohe bay oahu hawaii modeled wave current and wave setup fields were compared with field measurements collected on the forereef reef flat and reef channels and in the lagoon over a 4 week period the predicted wave height transformation across the reef lagoon system was in good agreement with field observations using single parameter spatially uniform values to describe both wave breaking and frictional dissipation the spatial distribution of the resulting wave setup field drove a persistent wave driven flow across the reef flat that returned to the ocean through two deeper channels in the reef both the magnitude and direction of these currents were well described using a spatially uniform hydraulic roughness length scale notably the model lends support to field observations that setup within the coastally bounded lagoon was a substantial fraction of the maximum setup on the reef 60 80 which generated relatively weak cross reef wave driven flows 10 20 cm s 1 compared with reefs having mostly unbounded lagoons e g many atolls and barrier reefs numerical experiments conducted using lagrangian particle tracking revealed that residence times within kaneohe bay are extremely heterogeneous typically ranging from 1 month within its sheltered southern lagoon

remagnetization and orogenic fluids testing the hypothesis in the central appalachians summary palaeomagnetic and geochemical studies on devonian sedimentary rocks in the valley and ridge province in west virginia indicate that the hypothesized relationship between orogenic fluids and remagnetization is not straightforward the helderberg group an aquitard and the oriskany formation a palaeoaquifer both contain similar synfolding late palaeozoic chemical remanent magnetizations crms residing in magnetite the results from the oriskany formation are consistent with remagnetization by orogenic fluids because the unit contains geochemical evidence for the migration of such fluids in contrast there is no geochemical evidence for the widespread migration of orogenic fluids into the helderberg group and thus the crm cannot be related to such fluids another remagnetization mechanism which remains elusive must be responsible for the crm in the helderberg group

holocene glacier fluctuations a global overview of glacier advances and retreats grouped by regions and by millennia for the holocene is compiled from previous studies the reconstructions of glacier fluctuations are based on 1 mapping and dating moraines defined by 14 c tcn osl lichenometry and tree rings discontinuous records time series and 2 sediments from proglacial lakes and speleothems continuous records time series using 189 continuous and discontinuous time series the long term trends and centennial fluctuations of glaciers were compared to trends in the recession of northern and mountain tree lines and with orbital solar and volcanic studies to examine the likely forcing factors that drove the changes recorded a general trend of increasing glacier size from the earlyemid holocene to the late holocene in the extra tropical areas of the northern hemisphere nh is related to overall summer temperature forced by orbitally controlled insolation the glaciers in new zealand and in the tropical andes also appear to follow the orbital trend i e they were decreasing from the early holocene to the present in contrast glacier fluctuations in some monsoonal areas of asia and southern south america generally did not follow the orbital trends but fluctuated at a higher frequency possibly triggered by distinct teleconnections patterns during the neoglacial advances clustered at 4 4e4 2 ka 3 8e3 4 ka 3 3e2 8 ka 2 6 ka 2 3e2 1 ka 1 5e1 4 ka 1 2e1 0 ka 0 7e0 5 ka corresponding to general cooling periods in the north atlantic some of these episodes coincide with multidecadal periods of low solar activity but it is unclear what mechanism might link small changes in irradiance to widespread glacier fluctuations explosive volcanism may have played a role in some periods of glacier advances such as around 1 7e1 6 ka coinciding with the taupo volcanic eruption at 232 5 ce but the record of explosive volcanism is poorly known through the holocene the compilation of ages suggests that there is no single mechanism driving glacier fluctuations on a global scale multidecadal variations of solar and volcanic activity supported by positive feedbacks in the climate system may have played a critical role in holocene glaciation but further research on such linkages is needed the rate and the global character of glacier retreat in the 20th through early 21st centuries appears unusual in the context of holocene glaciation though the retreating glaciers in most parts of the northern hemisphere are still larger today than they were in the early and or mid holocene the current retreat

three dimensional structural interrelationships within cambrian ordovician lithotectonic unit of central appalachians a block diagram of the cambrian ordovician lithotectonic unit illustrates three dimensional structural relationships within that sequence along the length of the central appalachian valley and ridge and high plateau provinces the diagram shows that the valley and ridge province is divisible into areas within which shortening is relatively constant in the cambrian ordovician lithotectonic unit these areas are bounded by zones across which significant differences in shortening occur these transition zones contain major cross strike structural discontinuities in surface structure in some instances these discontinuities extend across the valley and ridge province and into the high plateau province increases in fold amplitude and number occur in the cover of the plateau across strike from the more intensely deformed areas of the valley and ridge where shortening within the cambrian ordovician unit is significantly greater than elsewhere within that province structurally controlled gas accumulations are more prevalent in these areas of the plateau

synfolding remagnetization and deformation results from palaeozoic sedimentary rocks in west virginia summary palaeomagnetic analysis was conducted at 27 sites from two stratigraphically adjacent palaeozoic units along two transects meldey and rig of the patterson creek anticline in the appalachian orogen of west virginia to better understand the relationship between deformation and remagnetization while no primary directions were observed we isolated identical well defined secondary late palaeozoic magnetizations in carbonates from the late silurian tonoloway formation and the early devonian helderberg group standard application of conventional palaeomagnetic fold tests suggests that the magnetizations are synfolding in the helderberg group and pre folding to early synfolding in the tonoloway formation a fold test on all data combined indicates a synfolding magnetization best grouping at 60 65 per cent unfolding but the resulting distributions are not circular an alternative interpretation based on optimal differential unfolding at the site mean level yields one group with a nearly pre folding or early synfolding magnetization 70 per cent unfolding that is both circular and concordant with north america s apparent polar wander path the second group has a variable synfolding magnetization that is elliptical at the optimum unfolding level and falls off the path differences in either the age of remagnetization or viscous partial thermoremanent magnetization contamination cannot account for this result the sites falling into the pre folding group are biased towards the tonoloway formation the medley transect the northwest limb away from small folds and lower dip angle relative to the sites in the synfolding group the two groups defined by the fold test results also have a relationship with both total strain and strain partitioning the rocks containing the early synfolding remanence exhibit less total strain and in particular less pressure solution strain relative to grain boundary sliding and calcite twinning it is likely that the remagnetization in the entire area was coincident and occurred prior to folding even though some sites reveal synfolding directions the variation in the behaviour of the remagnetization relative to folding is unclear at present but it indicates that pressure solution and stylolite formation are important processes in remagnetization in any event the relationship between deformation and magnetization is not simple apparently identical magnetizations from adjacent sites may have very different histories and or responses to deformation while the exact relationship between remagnetization and deformation remains elusive this study demonstrates that significant variation in behaviour can exist at a very local scale

the lackawanna synclinorium pennsylvania a salt collapse structure partially modified by thin skinned folding the lackawanna synclinorium is a 110 km long structural trough in the appalachian foreland of northeastern pennsylvania in map view its hinge displays a concave to the foreland i e concave toward the west curve historically the entire synclinorium was thought to be an alleghanian thin skinned contractional structure that formed similarly to the fold trains of the central appalachian valley and ridge province interpretation of seismic reflection data across the structure however suggests that the synclinorium formed primarily by the removal of salt the trend of the central and northern synclinorium reflects the location of upper silurian salina salt in the southern synclinorium the salt collapse structure translated northwestward over a thrust ramp joining detachments in the cambrian waynesboro formation and the salina group interpretation of seismic reflection data also suggests that the basement cover contact deepens westward and that basement penetrating reverse faults and a neoproterozoic rift basin are present beneath the synclinorium we speculate that 1 partial barriers due to sedimentation and or reef formation and 2 localized subsidence over a neoproterozoic rift zone may have formed a late silurian restricted basin that allowed thick accumulations of salina salt regional scale salt shale flow and or foreland directed i e westward fluid migration during the alleghanian orogeny might have removed as much as 700 m of salt the removal of this salt caused the overlying strata to collapse downward and form the synclinorium only in the southern synclinorium was the collapse structure modified significantly by decollement tectonics thus the map view curvature of the structure reflects greater tectonic shortening and westward translation toward the foreland in the southern synclinorium compared to the northern synclinorium

strain paths of three small folds from the appalachian valley and ridge maryland structural analysis indicates that for a given set of conditions subtle differences in layer configuration and rheology can result in major differences in fold kinematics we studied three hand sample scale folds from the maryland valley and ridge province in an effort to understand the accommodation of folding on meso and microscopic scales and to constrain the deformation histories of the folds sampled two single layer folds and one multilayer fold were taken from two nearby outcrops of the wills mountain anticline and are therefore interpreted to have developed under virtually identical pressure and temperature conditions although all three folds are dominated by carbonate material structural fabrics are unique for each fold indicating rheological contributions to and local structural control of fabric development both single layer folds have asymmetric vein distributions that are consistent with strain directions expected from asymmetric flexural flow slickenlines on one sample and cleavage in an adjacent layer in the other sample support this interpretation the first of these folds appears to have undergone late stage hinge tightening as evidenced by the development of crosscutting bed normal stylolites in contrast veins stylolites and the intracrystalline deformation in the multilayer fold are suggestive of symmetric tangential longitudinal strain followed by heterogeneous sub horizontal flattening the three folds are interpreted to be buckle folds with differing mechanisms accommodating strain within the competent layers

spectral wave dissipation over a barrier reef 1 a 2 week field experiment was conducted to measure surface wave dissipation on a barrier reef at kaneohe bay oahu hawaii wave heights and velocities were measured at several locations on the fore reef and the reef flat which were used to estimate rates of dissipation by wave breaking and bottom friction dissipation on the reef flat was found to be dominated by friction at rates that are significantly larger than those typically observed at sandy beach sites this is attributed to the rough surface generated by the reef organisms which makes the reef highly efficient at dissipating energy by bottom friction results were compared to a spectral wave friction model which showed that the variation in frictional dissipation among the different frequency components could be described using a single hydraulic roughness length scale surveys of the bottom roughness conducted on the reef flat showed that this hydraulic roughness length was comparable to the physical roughness measured at this site on the fore reef dissipation was due to the combined effect of frictional dissipation and wave breaking however in this region the magnitude of dissipation by bottom friction was comparable to wave breaking despite the existence of a well defined surf zone there under typical wave conditions the bulk of the total wave energy incident on kaneohe bay is dissipated by bottom friction not wave breaking as is often assumed for sandy beach sites and other coral reefs

displacement transfer at thrust terminations the saltville thrust and sinking creek anticline virginia u s a abstract the saltville thrust terminates in the core of the sinking creek anticline changes in the amplitude of the anticline may preserve profile shortening as the thrust displacement decreases towards the fault termination consequently thrust displacement would be transferred into the fold we combine newly published maps and new strain and mesostructural data from the tuscarora sandstone to argue that the sinking creek anticline did perform this kinematic role we propose that the anticline developed as a fault propagation fold that experienced both decollement and anticlinal breakthrough by the saltville thrust thrust displacement was accommodated by the development of the modified fault propagation fold and by transfer to a roof flat from the decollement breakthrough new strain and mesostructural data indicate no fixed pin lines in either the hinge or backlimb throughout folding consequently layer slip occurred through the hinge during folding and the forelimb deformed internally during breakthrough towards the plungeout of the sinking creek anticline the displacement on the saltville thrust is transferred to a floor thrust we apply this interpretation to the termination of the st clair thrust which has a similar surface geometry where the thrust terminates into an anticline a testable implication of this proposed interpretation for the st clair thrust is that the appalachian plateau must absorb over 20 km of thrust displacement as horizontal shortening

fluid control of localized mineral domains in limestone pressure solution structures grain to grain and stylolitic solution structures in two central appalachian siluro devonian limestone macroscale folds contain one of four distinct mineral assemblages that are characterized by the dominant iron phase mineral present 1 chloritegillitegpyritegcalciteg quartzgtio2ggoethite 2 chloritegillitegpyrite altered to iron oxide hydroxidegcalcite gquartzgtio2 3 chloritegilliteg magnetitegcalcitegquartz and 4 chloritegilliteggoethitegcalcitegquartzgtio2 optical reflectance microscopy and sem eds was used to characterize the mineralogy and mineral morphology of these structures geochemical modeling was used to constrain the conditions of formation and preservation the primary control on solution structure mineral assemblage was the redox conditions present in the solution structures during burial and deformation the redox conditions on the microscale may have been controlled by the local fluid chemistry and the presence absence of hydrocarbons and organic acids within the formation fluids and the influx of externally derived fluids by fracture formation during the folding process the wide variation in mineralogy of the solution structures shows that they were chemical factories where a variety of chemical reactions took place during rock dissolution in particular the formation of authigenic magnetite in solution structures has significant implications for paleomagnetic applications and use of anisotropy of anhysteretic remanent magnetization and anisotropy of magnetic susceptibility fabrics q 2005 elsevier ltd all rights reserved

calculation of shortening due to outcrop scale deformation and its relation to regional deformation patterns abstract the objectives of this study are to assess the regional contribution of outcrop scale structures in well exposed rocks of a tectonic province and evaluate how failure to measure this scale of structure affects the assessment of regional deformation the contribution of outcrop scale structures to regional deformation has not been quantified previously because of the need for long continuous exposures to regionally characterize the structures this study used 18 6 km of semi continuous roadcut and streambed exposures in well exposed devonian clastic rocks to construct 1 200 scale profiles to address the objectives key results are 1 outcrop scale structures contribute about 1 6 to 1 4 of total regional shortening 2 submapscale shortening components from microscale and outcrop scale structures equal mapscale shortening that would be interpreted from a regional cross section 3 analysis of submapscale structures in the target blind thrust belt is needed to identify that the roof sequence deformation preceded and continued through duplex formation 4 the kinematic response of the roof sequence would be incorrectly identified as backthrusting if the shortening contribution of outcrop scale structures is ignored 5 although measured outcrop scale shortening does not match that predicted by the fractal analysis of other workers the fractal approach to predicting deformation as a function of scale may still be valid

spatial arrangement of decollements as a control on the development of thrust faults abstract we used two dimensional finite element models to explore different configurations of weak layers in undeformed sedimentary sequences to investigate the occurrence of three characteristic types of thrust configurations ramp flat imbricate and duplex in our models we embedded two low friction weak layers with a finite spatial extent in a sequence of stronger rock these two weak layers were initially horizontal were separated vertically by 1 km and were arranged in three different relative positions to each other when the models were deformed and these weak layers developed into decollements they interacted to produce one of the three types of thrust faults as a function of their initial configurations when the tips of weak layers were separated by a large gap 10 km only the lower level decollement became active producing imbricate thrusts when the two weak layers overlapped for a large distance 10 km they simultaneously became active decollements producing duplexes in the overlapped zone when the gap or overlap was small

field observations of wave driven setdown and setup wave driven setdown and setup observed for 3 months on a cross shore transect between the shoreline and 5 m water depth on a barred beach are compared with a theoretical balance between cross shore gradients of the mean water level and the wave radiation stress the observed setdown the depression of the mean water level seaward of the surf zone is predicted well when radiation stress gradients are estimated from the observations using linear theory at each location along the transect the observed setdown also agrees with analytical predictions based on offshore wave observations and the assumption of linear dissipationless normally incident waves shoaling on alongshore homogeneous bathymetry the observed setup the superelevation of the mean water level owing to wave breaking is predicted accurately in the outer and middle surf zone but is increasingly underpredicted as the shoreline is approached similar to previous field studies setup at a fixed cross shore location increases with increasing offshore wave height and is sensitive to tidal fluctuations in the local water depth and to bathymetric changes numerical simulations and the observations suggest that setup near the shoreline depends on the bathymetry of the entire surf zone and increases with decreasing surf zone beach slope defined as the ratio of the surf zone averaged water depth to the surf zone width a new empirical formula for shoreline setup on nonplanar beaches incorporates this dependence

structure and tectonics of central and southern appalachian valley and ridge and plateau provinces west virginian and virginia the valley and ridge and eastern allegheny plateau from pennsylvania into tennessee is subdivided into distinct allochthonous sheets emplaced over an essentially featureless precambrian basement surface sheet development is related to variations in stratigraphic thickness and lithology as well as regional basement configuration three sheets control central appalachian structural style the massanutten blue ridge sheet is easternmost and is bounded on the west by the little north mountain pulaski fault system continuing westward into the plateau the martinsburg sheet contains anticlinoria and synclinoria uncut by major thrust faults both massanutten blue ridge and martinsburg sheets are seated in upper ordovician martinsburg reedsville shales the underlying waynesboro sheet is rooted in lower cambrian waynesboro rome shales and its imbrication has controlled the locations of major anticlinoria and synclinoria in the upper sheet within the southern appalachians greater imbrication of the lower sheet and increased thrust fault displacement at longitudinal ramps have destroyed the lateral continuity along strike of the central appalachian waynesboro and overlying martinsburg sheets there imbrication to the surface has formed the saltville sheet continuous into alabama as well as the st clair narrows copper creek cove mountain and st paul honaker sheets southwest of the trend change the holston stone mountain sheet adjacent to the blue ridge is rooted primarily in lower and middle cambrian strata and is underlain by the pulaski sheet in the westernmost sector of this region the pine mountain and richlands sheets are seated in devonian shales the pulaski and massanutten blue ridge sheets rooted primarily in upper ordovician shales form a continuous structural unit and include blue ridge and piedmont rocks

field observations of wave driven water level gradients across a coral reef flat 1 field measurements of still water surface elevations were obtained across a narrow leeward reef flat on lady elliot island great barrier reef australia in june 2003 stilling wells were deployed from the reef crest landward to the island beach and waves and mean water levels were monitored over both rising and falling tides during low to moderate wave energy conditions wave setup of up to 13 8 cm above still water level occurred in the presence of incident waves of 0 4 m yielding maximum water surface slopes greater than 6 results show that the magnitude of wave setup varies both temporally and spatially across the reef with changing water depth setup is dominant on the reef edge at low tide evolving into a dual setup system at both the reef edge and shoreline at midtide and finally a dominant shoreline setup at high tide on lady elliot island the dual setup system is considered to result from spatial differences in transformation and breaking of swell and wind waves at midtide stages the presence of a dual setup system across a reef flat has not been previously identified in field or modeling studies and has potentially significant implications for reefal current development sediment transport and the stability of reef island shorelines

wave generated flow on coral reefs an analysis for two dimensional horizontal reef tops with steep faces waves breaking on the seaward rim of a coral reef generate a flow of water from the exposed side of the reef to the sheltered side and or to either channels through the reef rim or lower sections of the latter this wave generated flow is driven by the water surface gradient resulting from the wave set up created by the breaking waves this paper reviews previous approaches to modelling wave generated flows across coral reefs and discusses the influence of reef morphology and roughness upon these flows laboratory measurements upon a two dimensional horizontal reef platform with a steep reef face provide the basis for extending a previous theoretical analysis for wave set up on a reef in the absence of a flow gourlay m r 1996b wave set up on coral reefs 2 set up on reefs with various profiles coastal engineering 28 1755 to include the interaction between a unidirectional flow and the wave set up the laboratory model results are then used to demonstrate that there are two basic reef top flow regimes reef top control and reef rim control using open channel flow theory analytical relationships are derived for the reef top current velocity in terms of the offreef wave conditions the reef top water depth and the physical characteristics of the reef top topography the wave set up and wave generated flow relationships are found to predict experimental values with reasonable accuracy in most cases the analytical relationships are used to investigate wave generated flows into a boat harbour channel on heron reef in the southern great barrier reef c 2005 elsevier b v all rights reserved

morphological constraints to wave driven circulation in coastal reef lagoon systems a numerical study 1 the response of the wave driven circulation within coastally bounded reef lagoon systems to varying lagoon and channel morphology was investigated using a two dimensional coupled wave circulation numerical model numerical experiments were conducted using a series of coastal reefs that incorporated a wide range of different lagoon depths and channel widths with the morphology of both the reef forereef and reef flat and incident wave forcing held constant the wave driven circulation was found to increase substantially as dimensionless reef morphology parameters characterizing the relative lagoon depth and channel width were each independently increased analysis of the wave setup fields revealed that this increased flow was due to an enhancement of the cross reef water level gradient resulting from a sharp reduction in the lagoon setup as the frictional resistance on the lagoon channel return flow was diminished this follows similar trends observed in existing field and laboratory studies of wave driven reef flows analysis of flushing time scales computed for each reef lagoon geometry predicted the existence of optimal dimensionless lagoon depths and channel widths for a reef system to establish maximal coastal flushing overall the circulation and flushing of coastal reef lagoon systems was found to be largely controlled by the particular morphology of the lagoon and channel region rather than solely by the morphology of the forereef and reef flat that has been the primary focus of analytical models developed to predict wave setup and circulation on reefs

a simplified model of rip currents systems around discontinuous submerged barriers although in the last years several numerical models have been shown to be able to reproduce rip currents around discontinuous submerged barriers only few simple methods of practical use are available for estimating main flow parameters like the current intensity and the mean water levels in terms of geometrical barrier and gap dimensions parameters and wave characteristics the aim of this paper is to present a simplified model to be used for an easy estimate of these important rip currents parameters the model which is based on rough simplifications considers the area between the shoreline and the barrier as a reservoir in which water is pumped by breaking short waves across the barrier and from which water flows out at the gap four equations mass and momentum conservation across the barrier free discharge at the gap and balance of water pumped towards the shore and freely flowing offshore are used to derive one single model equation that can be solved for the wave set up and subsequently used for rip current velocity calculation two free parameters appear in this equation which respectively account for energy losses at the gap cv and bed friction the proposed model is validated against available laboratory experiments to show its ability in providing reasonable estimates of the desired parameters that may be considered by engineers adequate at the preliminary design stage of submerged breakwaters and that can be used for evaluating hydrodynamics on barred beaches

wave driven flow over shallow reefs long term 1 month observations of waves and currents over a natural reef are presented which show a strong correlation between offshore rms incident wave height and cross reef currents at subtidal frequencies the energy spectrum of the cross reef currents shows a significant peak at twice the semidiurnal tidal frequency while the spectrum of sea surface elevation over the reef flat shows no corresponding peak furthermore experimental results reported by gourlay 1993 show setup over the reef occurs in the absence of a beach and the cross reef transport decreases with an increase in the sea surface slope across the reef flat due to an increase in setup at the top of the reef face analytic solutions for flow forced by wave breaking over an idealized reef explain the above features of cross reef flows in the absence of a beach through the surf zone on the reef face the cross reef gradient in the radiation stress due to wave breaking is partitioned between balancing an offshore pressure gradient associated with setup over the reef and forcing a mean flow across the reef over the reef flat where the depth is constant there is no forcing due to wave breaking and the flow is driven by a pressure gradient which results from the setup through the surf zone the magnitude of the setup through the surf zone is such that the transport across the reef flat matches the transport through the surf zone which is forced by the gradient in the radiation stress solutions are presented for general reef geometry defined by the reef width and slope of the seaward reef face and incident wave forcing defined by the depth at the breakpoint and the depth of water over the reef as the depth over the reef goes to zero the solutions converge to the plane beach solutions described by longuet higgins and stewart 1964 wave setup is maximized and the cross reef transport is zero in other cases the relative magnitudes of the setup and the cross reef transport depend on the geometry of the reef and the incident wave forcing

modeling flow in coral communities with and without waves a synthesis of porous media and canopy flow approaches both canopy flow and porous media theories have been developed independent of one another to predict flow through submerged porous structures these approaches are very similar albeit with some key differences in how canopy resistance forces are parameterized canopy models provide a means of parameterizing the shear stresses that occur at the top of the canopy whereas porous media models can often provide a simpler and more tractable way of parameterizing turbulent form drag based on simple morphological metrics and empirical relationships already in the hydrology literature we developed a set of equations combining aspects of both models and applied this hybridized model to predict the flow structure within an experimental canopy formed by the branching coral porites compressa using model parameter values obtained from the literature results from the model predictions agreed well with direct measurements of flow speed and flow forces derived from particle image velocimetry under conditions of both unidirectional and wave driven oscillatory flow

wave breaking hydrodynamics within coral reef systems and the effect of changing relative sea level this paper considers the hydrodynamics of wave driven flow across a coral reef and the resultant flushing of its lagoon current depth coefficients are introduced that describe the fractional change of across reef and lagoonal current with change in the relative local sea level i e the depth of water over the reef flat the coefficients are derived from an analytical hydrodynamic model and compared with data from two reefs the first is ningaloo reef in northwest australia which is a typical barrier reef with a narrow coastal lagoon and the second is kaneohe bay in oahu hawaii where the reef is both unusually deep and wide the current depth coefficients are shown to be sensitive to the form of the frictional law on the reef flat and can be deduced from measurements of the astronomical tidal currents in the lagoon both quadratic and linear friction laws are considered for the reef flat and good agreement obtained with a linear law based on the high frequency motion due to surface gravity waves

wave driven circulation of a coastal reef lagoon system abstract the response of the circulation of a coral reef system in kaneohe bay hawaii to incident wave forcing was investigated using field data collected during a 10 month experiment results from the study revealed that wave forcing was the dominant mechanism driving the circulation over much of kaneohe bay as predicted theoretically wave setup generated near the reef crest resulting from wave breaking established a pressure gradient that drove flow over the reef and out of the two reef channels maximum reef setup was found to be roughly proportional to the offshore wave energy flux above a threshold root mean square wave height of 0 7 m at which height setup was negligible on the reef flat the wave driven currents increased approximately linearly with incident wave height however the magnitude of these currents was relatively weak typically 20 cm s 1 because of i the mild fore reef slope of kaneohe bay that reduced setup resulting from a combination of frictional wave damping and its re

experimental study of nearshore dynamics on a barred beach with rip channels 1 wave and current measurements are presented from a set of laboratory experiments performed on a fixed barred beach with periodically spaced rip channels using a range of incident wave conditions the data demonstrate that the presence of gaps in otherwise longshore uniform bars dominates the nearshore circulation system for the incident wave conditions considered for example nonzero cross shore flow and the presence of longshore pressure gradients both resulting from the presence of rip channels are not restricted to the immediate vicinity of the channels but instead are found to span almost the entire length of the longshore bars in addition the combination of breaker type and location is the dominant driving mechanism of the nearshore flow and both are found to be strongly influenced by the variable bathymetry and the presence of a strong rip current the depth averaged currents are calculated from the measured velocities assuming conservation of mass across the measurement grid the terms in both the cross shore and longshore momentum balances are calculated and their relative magnitudes are quantified the cross shore balance is shown to be dominated by the cross shore pressure and radiation stress gradients in general agreement with previous results however the rip current is shown to influence the wave breaking and the wave induced setup in the rip channel analysis of the longshore balance shows that the overall strength of the longshore feeder currents is governed by a balance between longshore pressure gradient forcing and an opposing radiation stress gradient in addition the longshore feeder currents show maxima in the bar trough region providing experimental evidence that longshore pressure gradients can shift longshore current maxima shoreward from the bar crest finally since the longshore radiation stress gradient in the surf zone is governed by the amount of wave dissipation on the rip current there exists a positive feedback mechanism whereby a strong rip current can weaken the radiation stress gradient opposing the feeder currents and lead to even stronger feeder currents and rips

broad top thrust sheet an extensive blind thrust in the central appalachians interpretation of seismic data from the central appalachians valley and ridge province reveals that a large blind thrust the broad top thrust is much more extensive than previously realized this thrust sheet extends across the 15 mi 24 km width of the nittany anticlinorium a dominate structural element that lies along the western margin of the valley and ridge province adjacent to the plateau province in the appalachian foreland it extends for a distance along strike of at least 100 mi 160 km and duplicates a 7800 ft 2380 m thick sequence of cambrian and ordovician limestone and dolomite referred to as the cambrian ordovician lithotectonic unit thinning of the duplicated cambrian ordovician sequence along the length of the nittany anticlinorium by as much as 2500 ft 760 m observed on seismic lines is attributed to removal of less brittle intervals from the base of the upper sheet and top of the lower sheet the missing section from this inter sheet detachment zone may have been transported toward the foreland and incorporated into the leading parts of the thrust sheet the tectonic thinning solves space problems associated with duplication of the lithotectonic unit beneath what have previously been considered abnormally deep synclines of the anticlinorium the abnormal depth of these synclines occurs where tectonic thinning is located on the seismic lines structural traps in a triangle zone along the allegheny structural front have been attributed to the intense shortening associated with emplacement of the broad top thrust sheet the presence of the thrust sheet along the length of the structural front in west virginia and virginia enhances the probability of successful exploration for triangle zone structures along the entire length of the structural front structures produced by variable tectonic thinning in the inter sheet detachment zone may also produce additional traps within the anticlinorium in the form of closure or associated fracture systems

strain partitioning of deformation mechanisms in limestones examining the relationship of strain and anisotropy of magnetic susceptibility ams abstract in order to investigate the relationship between rock strain and anisotropy of magnetic susceptibility ams strain partitioning and ams analysis was conducted at 35 sites from two stratigraphically adjacent paleozoic limestone units in the patterson creek and wills mountain anticlines in the central appalachian orogen of west virginia in addition anisotropy of anhysteretic remanent magnetization aarm was conducted on selected samples to examine the role of preferentially oriented magnetite on the ams fabric strain is partitioned into bed normal shortening due to compaction solution strain 35 0 shortening bed parallel shortening due to tectonic solution strain 13 3 shortening calcite twinning strain 5 8 shortening and grain boundary sliding 26 7 shortening the ams fabrics in the rocks were found to be a result of a complex interaction between rock lithology deformation mechanisms and strain magnitude although all the rocks have experienced the same deformation conditions six different ams fabrics are exhibited each of the different ams fabrics is a composite fabric resulting from the overprinting of three components 1 an inherent primary depositional ams fabric that is attributed to preferentially oriented phyllosilicates in the rock matrix 2 a diagenetic and or compaction ams fabric formed during burial that is due to preferentially oriented phyllosilicates in solution structures and in the rock matrix and 3 a tectonic ams fabric that was imparted on the rocks by layer parallel shortening deformation prior to folding and is also attributed to preferentially oriented phyllosilicates in solution structures and in the rock matrix as well as twinning of ferroan calcite

wave set up on coral reefs 1 set up and wave generated flow on an idealised two dimensional horizontal reef wave set up may be significant in determining water levels on coral reefs particularly in microtidal environments and hence is an important factor for the design of reef top structures and for the stability of reef top islands laboratory experiments have been made on a two dimensional model of an idealised horizontal reef under two different conditions corresponding to a fringing reef or closed lagoon situation and a platform reef or open lagoon situation both wave set up on the reef top and the wave generated flow across the reef were measured and related to wave and tide level conditions all other factors being the same wave set up is greatest at low tide levels whereas wave generated flow is greater at higher tide levels the magnitude of the set up on a platform reef with a wave generated flow is less than on a fringing reef without any net flow by an amount equal to the velocity head of the flow across the reef dimensionless parameters ghrt o and q gho3 are found to be functions of relative submergence parameters hrho or r hr ho for values of ghr hr ho 1 waves break on the reef top and radiation stress theory can be used to calculate set up for ghr hr ho 0 7 waves break on the reef face and set up is determined by broadcrested weir control at the reef edge the symbols are defined as follows g is gravitational acceleration hr is still water depth over horizontal reef top ho is offreef wave height equivalent deep water value q is discharge per unit length of reef edge t is wave period and ghr is maximum wave set up on reef top

deformation behavior during blind thrust translation as a function of fault strength deformation partitioning between translation and distortion for a thrust sheet and for the roof sequence above a moving thrust horse were analyzed in terms of the role of fault strength using finite element models greater frictional resistance on the thrust decollement decreased fault translation increased distortion of the thrust sheet and roof sequence and increased the ratio of backthrusting to forethrusting for the roof sequence in all models with weak decollements 0 35 the ratio of tip line propagation to thrust displacement is very high during initial thrust movement but decreases significantly during later fault motion this observation supports interpretations in natural thrust systems where thrust faults propagate large distances before accumulating significant displacements the tip lines for weak decollements also propagated into the foreland well in advance of the distortion front in the overlying thrust sheet or roof sequence this result does not support interpretations from natural systems for the existence of ductile beads in front of propagating thrusts but rather suggests that recent models for fault arrest or displacement gradient folds may be mechanically valid in addition no model for roof sequences yielded a simple end member response of only backthrusting or forethrusting suggesting that the many blind thrust belts where only one response has been interpreted may need to be re examined finally in those cases where more than one thrust flat moves simultaneously in the models partitioning of displacement and distortion in space and time changes significantly this result supports interpretations from natural systems where more than one thrust is thought to move at once

deformation history of the roanoke recess appalachians usa the evolution of the roanoke recess is controversial because agreement is lacking about the timing and continuity of deformation increments because it may or may not have behaved like an adjacent salient and recess because while many salients have been investigated few recesses have and because the role of blind thrusts is unclear to gain insight into these controversies we estimated shortening directions shortening magnitudes and relative timing in the recess from map scale folds outcrop scale stylolites and grain scale solution structures and twins the key results from combining these new data with previous work are as follows 1 the deformation history around the roanoke recess is most simply described as temporally continuous with deformation migrating northeastward while the primary shortening direction rotated counterclockwise from n directed to almost w directed 2 consequently the roanoke recess did not deform in the symmetrical manner of the adjacent pennsylvania salient nor with the two step history of the kingston recess further to the north in the appalachians 3 the timing and magnitude of shortening increments are sufficient to necessitate a blind thrust under the present surface rocks of the inner recess throughout the deformation history

roof sequence response to emplacement of the wills mountain duplex the roles of forethrusting and scales of deformation abstract this paper focuses on the behavior of a roof sequence in the appalachian plateau of west virginia u s a and emplacement of the wills mountain duplex with 17 5 km of displacement unlike the plateau along strike in pennsylvania and new york where forethrusting was previously documented this roof sequence lacks an underlying salt dominated roof decollement kinematic analyses reveal that the roof sequence in the west virginian plateau accommodated about two thirds of the 17 5 km of shortening by the adjacent wills mountain duplex as a forethrusting kinematic response the remaining shortening imbalance of about 5 km between the duplexes and younger roof sequence rocks is accommodated by additional forethrusting further into the foreland and local compensation this kinematic response matches that along strike in the central appalachians despite the loss of the salt decollement we interpret that an ordovician shale dominated formation was sufficiently weak to substitute for the salt horizon thus a weak mechanical unit rather than specifically a salt decollement is a necessary prerequisite for forethrusting a contributing factor to forethrusting may be the subvertical front of the wills mountain duplex which inhibited other responses by the roof sequence mesoscale and smaller processes including grain to grain pressure solution twinning and cleavage formation account for over 75 of the shortening in the roof sequence and if ignored would result in an erroneous interpretation of backthrusting or local compensation this result suggests that failure to consider all deformation scales could lead to incorrect kinematic conclusions in other tectonic systems

fractal interrelationships between topography and structure fractal interrelationships between topography and structure are investigated in two areas of the north american central appalachian mountains one in the intensely deformed valley and ridge province and the other in the relatively undeformed foreland area of the appalachian plateau province in the valley and ridge province the fractal dimensions of topographic and structural relief vary systematically along the strike of major folds following a second order polynominal trend cross correlation of the fractal dimensions of topography to structure indicates that there is a significant positive correlation between the two fractal analysis of topography in the relatively undeformed foreland area of the appalachian plateau revealed no significant variation in the fractal characteristics of topography across the study area consistent with the lack of near surface structure however fractal analysis of deeper structures beneath the plateau area undertaken using reflection seismic data revealed step wise increases in fractal dimension from the deeply buried precambrian basement to the near surface these vertical changes in fractal dimension can be related to the tectonic history of the area taken together these studies indicate that fractal analysis provides a means to quantify and compare the influence of near surface structure on topographic development and lateral and vertical structural variability fractal analysis provides a means to characterize the systematic changes in the complex patterns formed by topography and structure and the interrelationships between them similarity in their fractal characteristics implies similarity in the relative amplitude and abundance of different wavelength features in the topographic or structural profile 1998 john wiley sons ltd

wave driven circulation across the coral reef at bamburi lagoon kenya abstract sea level current and wave measurements were carried out within and outside an open ended bar reef lagoon on the east african coast the oceanic tides in this area are semidiurnal with a tidal range varying from 3 m at spring to 1 m at neap reef submergence relative to the mean sea level is 0 7 m waves with significant wave height of typically 0 5 m and periods of 8 10 s continuously break on the reef top and on the reef edge during most of the tidal cycle this results in a wave set up on the reef top and a lagoon ward flow across the reef the set up drives a time dependent circulation which is larger during neap tide when the reef is moderately submerged than during spring tide the wave driven circulation though small compared to the tidally driven circulation is still important because it hinders inflow of polluted water from tidal creeks that enter the ocean north and south of the lagoon itself

changing fluid conditions during folding an example from the central appalachians abstract fluids inclusion microthermometry and stable isotope analyses of vein minerals in the central appalachian patterson creek anticline record dynamic changes in fluid temperature pressure and chemistry during folding these changes resulted from variations in fracture connectivity and fluid communication between stratigraphically restricted fluid reservoirs minerals in early formed bed parallel and ene nnw striking cross fold veins show that prior to folding fluids in silurian through lower upper devonian rocks were well stratified based temperature salinity and isotopic composition stable isotopes data indicates that the fluid systems were essentially closed with no communication between layers as folding commenced early minerals in ne nw striking veins in the siluro devonian carbonate rocks record 2 km of burial by syn tectonic sedimentation with corresponding increases in fluid temperature and pore fluid pressure an additional 2 km of burial along with the influx of low salinity methane saturated brines into the middle and upper devonian clastic rock sequence is recorded by later quartz in the ne nw striking veins at some point during folding stable isotope data indicate that fluid communication increased along fracture and faults between major stratigraphic fluids reservoirs the culmination of this process was the breaching of the stratigraphic seal at the base of the devonian shales allowing fluid infiltration from the devonian shale sequence into the upper portion of the helderberg group this resulted in the local precipitation of quartz and possibly the enhancement of solution structures