sea cliffs their processes profiles and classification general concavity or convexity of sea cliff profiles is controlled by relative rates of erosion by marine and subaerial processes as well as by positions of more resistant strata in the cliffs profiles supplemented by on site examination can establish the activity and dominance of erosional processes and indicate changes in regimen a sharp angle at the sea cliff base generally indicates active marine erosion whereas a smooth curve at the base means that subaerial erosion may dominate talus shows absence of marine erosion studies of profiles can be useful for estimating stability for residences railroads and highways at the top face and base of sea cliffs generally increased erosion and retreat of sea cliffs are in prospect because of projected regionally wetter and stormier climate rising sea level and increased human activities

wave energy gradients across a maldivian atoll implications for island geomorphology exposure to wave energy has been used to account for a range of ecological geological and geomorphic processes in coral reef systems but few attempts have been made to quantify spatial variations in energy at the atoll scale this study presents results of measurements of wave energy on reef platforms across south maalhosmadulu atoll maldives and their implications for island geomorphology the atoll has a perforated rim 37 effective aperture and experiences predictable shifts in monsoon winds from the west 8 months and northeast 4 months results show that wave energy affecting the atoll is considerably greater during the westerly monsoon atoll structure promotes significant changes in wave energy and wave characteristics across the atoll short period 3 8 s monsoon driven wave energy which is significant on windward reefs is dissipated on the peripheral reef network and the density of lagoonal patch reefs limits development of locally generated wind wave energy across the lagoon however longer period swell 8 20 s propagates through the lagoon to leeward reefs a windward to leeward decay in wave energy is evident in the westerly monsoon but not in the northeast monsoon when long period swell from the southwest remains significant on western reefs net energy calculations that account for seasonal changes in wave energy across the atoll identify a steep west east gradient that has geomorphic significance for island building western reefs are dominated by westerly flowing energy that is 4 5 7 times the total energy input elsewhere in the atoll wave energy on central reefs is balanced whereas net energy on eastern reef platforms is dominated by eastward propagating waves this steep energy gradient provides a physical explanation for the presence and distribution of islands on reef platforms across the atoll and provides quantitative support for the theory of gardiner gardiner j s 1903 the fauna and geography of the maldives and laccadives archipelagoes cambridge university press london to explain the prevalence of islands on the eastern atoll reef rim

on processes controlling the distribution and fluxes of boron in natural waters and air along transects across the south island of new zealand abstract the concentrations of boron were measured in rain air and soil water along transects across the southern alps new zealand during southern autumn and early winter 1999 estimates of wet deposition dry deposition and flux of boron leaving the soil in soil water are presented at the main divide of the southern alps strong and constant orographic effects on rain bearing fronts resulted in low concentrations and little variation of boron in rain areas with less orographic influence received varying boron concentrations in the rain depending on the origin and character of the fronts concentrations of boron in air were greater near the sea than in the intramontane basin high mean concentrations in air go together with large variations caused by changes of wind direction and speed during frontal passages air reaching the intramontane basin was depleted of boron because of washout over the eastern and western ranges and by dry deposition after a long dry summer spell the first autumn flush of soil water contained high concentrations of boron at low soil water flow later as the soil wetted up the soil water concentration approached that of rain water at all sites wet deposition was least at sites away from the coast where there was little rain and less boron in it high rainfall with low boron concentrations or mean rainfall with high boron concentrations occurred near the eastern and western divides dry deposition varied over shorter time intervals and distances than wet deposition it was high near the coastlines during onshore winds and low in the intramontane basin especially with weak convective turbulence the concentrations of boron in springs resembled those in rain and soil water increasing from the western coastal plain eastwards across the southern alps

development and morphodynamics of beaches on horizontal shore platforms on the microtidal southeast coast of brazil abstract the differences between beaches completely composed of sand and beaches underlain or fronted seaward by hard structures have been well addressed in the current literature considering their morphological and morphodynamic particularities trenhaile 2004 modeled the accumulation and dynamics of beaches on shore platforms on mesotidal and macrotidal coast although this model had not been verified or tested in the field it can be useful to understand coastal geomorphology therefore this study aims to apply the trenhaile 2004 model to beaches on horizontal shore platforms located on the microtidal coast of espirito santo brazil and validate it using local data for this the morphological and morphodynamic particularities of the studied beaches were considered when applying and interpreting the model results besides the trenhaile 2004 model variables the role of wave runup was considered in the upward growth of the berm and then in the beach height the model results and field data showed that the gradients and elevations of shore platforms in the study area are suitable to form the beaches while wider shore platforms seem to contribute to the development of wider beaches the platforms in the study area also influence accommodation space cross shore sediment exchanges and beach mobility field data was used to test the applicability of trenhaile s 2004 model in the study area the model was found to be a potentially useful tool in coastal management helping to understand coastal geomorphology

hydrodynamic constraints and storm wave characteristics on a sub horizontal shore platform few studies of wave processes on shore platforms have addressed the hydrodynamic thresholds that control wave transformation and energy dissipation especially under storm conditions we present results of a field experiment conducted during a storm on a sub horizontal shore platform on the east coast of auckland new zealand small 2 5 times the gravity wave height 0 05 0 33 hz is necessary for waves to propagate onto the platform without breaking on the platform surface the wave height is a direct function of water depth with limiting maximum wave height to water depth ratios of 0 55 and 0 78 at the centre of the platform and cliff toe respectively a relative platform edge submergence water depth water height ratio threshold of 1 1 is identified below which infragravity 0 05 hz wave energy dominates the platform energy spectra and above which gravity waves are dominant infragravity wave height transformation across the platform is governed by the relative platform edge submergence finally the paper describes the first observations of wave setup on a shore platform during the peak of the storm wave setup on the platform at low tide 0 21 m is consistent with measurements from planar sandy beaches but at higher tidal stages the ratio between incident wave height and maximum setup was lower than expected copyright 2014 john wiley sons ltd

modeling the development of wave cut shore platforms abstract a mathematical model was used to investigate the development of wave cut shore platforms with constant sea level the model considered the effects of deep water wave height spectra period and wavelength breaker height and depth breaker type the width and bottom roughness of the surf zone the gradient of the submarine slope an erosional threshold related to the strength of the rocks the number of hours each year in which the water level is at each intertidal elevation and the amount and persistence of the debris at the cliff foot intertidal erosion rates were calculated according to the force of the surf reaching the shoreline whereas submarine erosion rates were determined using a depth decay variable each of the two hundred and fifty model runs consisted of 300 000 iterations platform width increased and gradient progressively decreased through model runs and states of static equilibrium were attained by the end of one hundred and nine runs when the wave induced force at each point in the intertidal zone had became too weak to continue eroding the rock runs with mesotidal spring tidal range 3 m generally produced subhorizontal platforms with cliff platform junctions at the mean low water neap tidal level a greater variety of profiles was produced in runs with macrotidal spring tidal ranges 9 m although almost 30 of these runs produced gently sloping platforms with average gradients of only 0 3 about two thirds of the simulated profiles had average gradients ranging from about 1 to 3 simulated platform width increased with tidal range and decreased with the rate of submarine erosion rock resistance the roughness or irregularity of the platform surface the amount and persistence of the cliff foot debris and wave period because higher waves break in deeper water than lower waves there was no consistent relationship between simulated platform width and wave height

seasonal variations in wave characteristics around a coral reef island south maalhosmadulu atoll maldives synchronous measurements of waves were made at six locations around a small reef platform island in the maldives during both westerly and northeast monsoon conditions summary statistics of wave records indicated similar hs values propagating onto windward and leeward reef surfaces and a distinct growth in wave height as waves shoal toward island shorelines waves up to 0 78 m were recorded impacting the island shoreline wave energy on the reef platform was strongly modulated by seasonal winds with wave energy during the westerly monsoon an order of magnitude larger than wave conditions in the northeast monsoon spectral analysis of wave records highlighted spatial differences in wave energy around the island windward reefs and shorelines are dominated by waves at wind and swell frequencies whereas wind wave energy is absent from leeward shorelines consequently windward shorelines have up to twice the gross energy input than leeward shorelines results have significant implications for geomorphic processes longer duration and greater incident wave energy during the westerly monsoon has promoted higher growth of the western reef flat 0 2 m and more energetic shoreline runup processes have produced markedly higher western island ridges 0 7 m incident shoreline wave processes are sufficient to entrain beach sediments during both monsoon periods although periods of active sediment mobilisation are constrained to mid to high tide stages the windward leeward gradient in shoreline wave energy is likely to drive littoral sediment flux seasonal modulation of the shoreline wave energy gradients account for observed oscillations in beach position around island shorelines large differences in incident wave energy between monsoons is considered to affect the rate of beach change around island shorelines rather than the total volumetric movement of island beaches

sea level sediment supply and coastal changes examples from the coast of ireland abstract sediment supply and pre existing shoreline morphology are crucial factors in controlling coastal changes due to sea level rise using examples from both southeast and northeast ireland it can be shown that sea level change may trigger a sequence of events which leads to both static and dynamic shoreline equilibrium cliff erosion and longshore sediment movement in east co wexford has led to injection of sediment onto the shelf and the growth under both wave and tide regimes of linear offshore shoals these shoals now control the pattern of shoreline erosion and provide a template for possible stepwise evolution of the coast under any future sea level rise in contrast the nearby coast of south co wexford comprises a series of coarse clastic barriers moving monotonously onshore via overwash processes here the behavior of the barrier is conditioned by the antecedent morphology of both the beach face and stream outlet bedforms finally the rock platform coast of co antrim presents a far more resistant shoreline to incident marine processes yet even here there is strong evidence of present process control over so called raised platforms and embayments it is concluded that coastal sediment supply and dynamics together with coastal morphology and its interaction with waves present a far more complex variety of sea level indicators than is normally acknowledged

micro erosion meter measurements of rock wear on the otway coast of southeast australia abstract the use of the micro erosion meter mem has been refined by providing 1 a base plate on which to check the relationship of legs and probe and 2 a micrometer level to check the relationships of the three studs countersunk in the rock at each site along 50 km of the otway coast lines of mem stations were installed across shore platforms normal to the shore and surveyed to mean low water readings were made bimonthly from 1978 to 1980 average site downwear ranged from 0 02 to 1 8 mm yr 1 according to rock type and the amount of exposure to the almost continuous swell waves the results of this study combined with other information available are used to discuss the origin and evolution of otway coastal morphologies

development of shore platforms on kaikoura peninsula south island new zealand ii the role of subaerial weathering the role of subaerial weathering in the development of shore platforms on kaikoura peninsula is investigated evidence for weathering came from a number of distinctive surface morphologies on platforms salt crystal growth water layer weathering and slaking schmidt hammer test data showed that weathering had occurred and that rock strength was reduced through weathering by as much as 50 weathering processes on shore platforms rely on repeated wetting and drying and for this reason the number of wetting and drying cycles was estimated it was found that the number of wetting and drying cycles depend not only on the pattern of tidal water levels but also on algae growth and desiccation the number of cycles ranged from 104 to 379 per year at elevations low in the tide range fewer cycles occurred the greatest number occurring between the peaks of spring and neap tides and where rainfall adds to the number the zone of most cycles was estimated to occur between 0 6 and 0 9 m above mean sea level on the more landward margins of platforms it is at these elevations that the highest rates of erosion occur based on these results it is argued that the development of shore platforms at kaikoura results from subaerial weathering caused by repeated wetting and drying this is contrary to the view that shore platforms result from marine erosion

new insights on the relative contributions of coastal processes and tectonics to shore platform development following the kaikōura earthquake we describe the immediate impact of the 14 november 2016 kaikoura magnitude 7 8 mw earthquake on shore platforms and cliffs around kaikoura peninsula the earthquake caused an instantaneous uplift of 1 01 m of the peninsula we resurveyed 7 profiles previously used for erosion monitoring and observed changes in the configuration of the shoreline the coseismic uplift has fundamentally changed the process regime operating on the platforms and altered the future trajectory of shore platform and cliff development our observations highlight the interplay of waves weathering biology and tectonics at this location tectonism strongly modulates the process regime driving instantaneous changes in morphology and altering rates and patterns of erosion finally the uplift of the kaikoura coast has implications for changing resilience to climate change and sea level rise

dynamics of a high energy dissipative surf zone vright l d guza r t and short a d 1982 dynamics of a high energy dissipative surf zone mar geol 45 41 62 pressure and horizontal current u v time series were measured at different positions across the inner 150 m of a wide 500 m surf zone of a microtidal high wave energy beach incident waves had average heights of 3 4 m with maxima of 5 m and periods of 12 to 15 sec bores of broken waves diminished in height at a nearly constant rate as they progressed across the surf zone the ratio of bore height h to local water depth h was everywhere less than 1 for even the highest bores and was on the order of 0 40 for the significant bores at incident wave frequencies rip circulation was weak or absent but a moderate longshore current was present shore normal flows were vertically segregated with strong net onshore flows prevailing just below the surface accompanied by weaker net seaward flows near the bed spectra of water surface oscillations as determined from pressure u and v reveal that most of the energy in the inner surf zone was at infragravity frequencies periods greater than 30 sec shoreward decay of wave energy at incident wave frequencies was accompanied by shoreward growth of infragravity energy near the beach the infragravity oscillations had heights on the order of 1 m cross spectra show that the infragravity oscillations were standing in the shore normal direction from the relative magnitudes of infragravity versus incident wave currents it is inferred that the surf beat may be an order of magnitude more important than incident waves to the transport of sediment in the inner surf zone

spatial and temporal variations in wave characteristics across a reef platform warraber island torres strait australia a field experiment was conducted at warraber island torres strait australia to investigate spatial and temporal variations in wave characteristics and energy across a mesotidal coral reef platform measurements of water depth were obtained using five pressure sensors deployed across a 2 7 km section of reef flat from july 3 5 2001 the reef surface was uneven and consisted of an outer reef flat a central reef flat depression an inner reef ramp a palaeo reef surface and the shoreline water levels decreased landward across the platform with tide ranges at the shoreline being almost 50 lower than at the outer reef flat rising and falling tides were characterised by a bimodal energy distribution with both short period 0 3 s and wind 3 8 s waves present higher water levels were dominated by wind waves the highest waves occurred at high tides associated with nocturnal tidal cycles with hs decreasing from 0 5 to 0 2 m from the outer reef flat to the shoreline wave energy at swell 8 20 s and infragravity 20 s frequencies was negligible across the reef platform although there was evidence of wave groups at higher water levels reef geometry and changes in water level determine the magnitude of wave energy on the reef platform up to 85 95 of incident wave energy is attenuated by the central reef flat depression at high and low tide respectively and strong linear relationships exist between hs and h at all locations both wave height and wave type are strongly depth dependent critical reef rim depths required to produce hs of a given size vary spatially across the reef rim due to variations in reef topography a distinct depth related threshold exists at which short period and wind wave dominance reverses over a 14 day spring neap tidal cycle the time of occurrence of wave action diminishes across the reef platform to the shoreline larger waves hs 0 2 m occur for only 9 of time at the outer reef flat and for less than 0 5 over the remaining reef platform this implies that on mesotidal reef platforms sediment entrainment and transport are severely constrained under normal wave energy conditions and significant change is likely restricted to extreme events

modelling the effect of waves weathering and beach development on shore platform development a mathematical model was used to study shore platform development mechanical wave erosion was dependent on such variables as tidal range wave height and period breaker height and depth breaker type surf zone width and bottom roughness submarine gradient rock resistance and the elevational frequency of wave action within the intertidal zone also included were the effects of sand and pebble accumulation cliff height and debris mobility and downwearing associated with tidal wetting and drying the occurrence location and thickness of beaches often depended on initially quite minor variations in platform morphology but owing to their abrasive or protective effect on underlying rock surfaces they were able to produce marked differences in platform morphology generalizations are difficult but the model suggests that platform gradient increases with tidal range platform width also increases with tidal range with slow downwearing but it decreases with fast downwearing platform gradient decreases and width increases with wave energy and decreasing rock resistance and platform roughness with low tidal range platform gradient is generally lower and platform width greater with beaches of fine sand than with gravel but the relationship is more variable with a high tidal range platform width increases and platform gradient decreases with the rate of downwearing on bare surfaces particularly in low tidal range environments but the pattern is less clear on beach covered platforms platforms with large amounts of beach sediment tend to be narrower and steeper than bare platform surfaces platform gradient increases and platform width decreases with increasing cliff height and with decreasing cliff debris mobility copyright 2005 john wiley sons ltd

estuarine shore platforms in whanganui inlet south island new zealand abstract whanganui inlet is a low mesotidal environment where wave energy at the shoreline is limited due to a small fetch a narrow entrance and tidal flat accretion to intertidal elevations wave energy is therefore only an erosive force at high tide and under storm conditions despite this low energy environment extensive shore platforms occur within the inlet they are sub horizontal and range in width from 4 1 to 185 2 m with an average of 44 9 m all the platforms are formed in sandstone of low resistance mean n type schmidt hammer rebound value of 17 8 and have their seaward edges buried by intertidal sediment flats the majority of platforms occur at around mhwn level corresponding to the elevation of those flats where wave energy is highest opposite the inlet s entrance and at those sites with the largest fetch platforms develop to 0 5 1 0 m below msl a higher platform level is also found at mhws elevations however it appears to be relict with active erosion of its seaward edge occurring and therefore is most likely related to a higher mid holocene sea level apart from the location of the lowest platforms little correspondence is found between platform morphology and wave energy platform evolution appears to be intrinsically linked to the intertidal sediment flats which determine the degree of surface saturation of the bedrock and hence the number of wetting and drying cycles the platforms may undergo as the seaward edge is buried platform development is primarily through retreat of the landward cliff this process can however be complicated by the migration of intertidal water channels onto the seaward edge of the platforms or relative sea level fall which may rejuvenate landward retreat of the low tide cliff

decadal scale micro erosion rates on shore platforms abstract knowledge of the long term rates of erosion of shore platforms are needed to assist modeling platform development understand rates and modes of development and decipher issues of inheritance from former sea level few studies report rates from more than 2 years of monitoring we report decadal scale erosion rates using both a micro erosion meter and a traversing micro erosion meter with measurements from 30 years and 10 years respectively gross mean surface lowering rates measured over 10 years with a traversing micro erosion meter were 0 901 s e 0 116 mm yr compared with 1 130 s e 0 217 mm yr over two years over thirty years 1973 2003 12 micro erosion meter sites provide a mean surface lowering rate of 1 09 s e 0 126 mm yr compared to 1 43 s e 0 128 mm yr calculated over twenty years 1973 1993 from 15 bolt sites and 1 53 s d 1 45 mm yr from 31 bolt sites rates calculated over longer time periods are reduced compared to short term rates as a result of faster eroding bolt sites being removed from the data set comparison of means between short and long time periods for existing bolts show no significant difference that is short term measurements over two years are representative of decadal scale erosion rates in fact decadal scale rates may under represent rates of platform development because of the loss of faster eroding bolt sites the loss of such bolts means that obtaining long term erosion rates is problematic future modeling of shore platform development can use mem rates with more certainty but we recommend using higher rates from shorter term studies unless longer records are complete

wave height variation across beaches of arbitrary profile an intuitive expression for the spatial change in energy flux associated with waves breaking in the surf zone is developed using shallow water linear wave theory analytical solutions for wave height transformation due to shoaling and breaking on a flat shelf a plane slope and an equilibrium beach profile are derived and then compared to laboratory data with favorable results the effect of beach slope on wave decay is included explicitly while wave steepness effects are included implicitly by specification of the incipient conditions set down set up in the mean water level bottom friction losses and bottom profiles of arbitrary shape are introduced and solutions are obtained numerically the model is calibrated and verified using laboratory data with very good results for the wave decay but not so favorable results for set up a test run on a prototype scale profile containing two bar and trough systems demonstrates the model s ability to describe the shoaling breaking and wave re forming process commonly observed in nature bottom friction is found to play a negligible role in wave decay in the surf zone when compared to shoaling and breaking

the morphodynamics of shore platforms in a micro tidal setting interactions between waves and morphology abstract the interactions between waves and morphology on shore platforms were investigated at four platforms located at kaikoura peninsula new zealand and the otway coast victoria australia waves were measured over six tidal peaks of a spring tidal sequence at each site during a six month period february 2007 july 2007 this paper reports the results of an investigation into the research question how are waves modified by platform morphology in a micro tidal setting through the investigation of wave interactions on shore platforms it was found that complex hydrodynamic patterns formed on the shore platforms studied through direct measurement of waves on the platforms it was found that wave attenuation was not dependent on platform width but rather influenced by platform gradient and depth of water on the platform spectral analysis was used to assess how wave energy was transformed across the platforms at three of the four platforms investigated energy gradients formed across the platform with wave energy recorded within the infragravity range

development of shore platforms on kaikoura peninsula south island new zealand abstract the role of waves in shore platform development has been investigated on kaikoura peninsula by direct measurement of waves in deep water and on platforms at high tide this showed that the deepwater wave environment off the kaikoura peninsula is very energetic but the amount of energy delivered to platforms is very low in deep water wave power ranged from 5900 to 106 700 n m s 1 per m of crest when calculated from mean significant wave height and when calculated from maximum wave height it ranged from 31 400 to 5 370 000 n m s 1 per m of crest a comparison of deep water wave energy flux with wave energy flux at the high tide cliff of platforms showed that there was a reduction by as much as five orders of magnitude during storm conditions an analysis of the role of breaking waves revealed that these are ineffective as an erosional agent because the depth of water offshore causes breaking before waves arrive on platform surfaces depth of water controlling wave breaking causes larger storm waves to break further from shore preventing direct attack at the cliff base shear stresses and dynamic forces under waves were calculated from waves measured on shore platforms this showed that these forces never exceeded the compressive strength of the platform rocks at kaikoura it is concluded that wave forces are not directly capable of causing erosion on shore platforms at kaikoura

modelling the effect of pliocene quaternary changes in sea level on stable and tectonically active land masses a mathematical model was used to examine the effect of pliocene and quaternary changes in sea level on the development of tectonically active and inactive rock coasts the model calculated rates of mechanical wave erosion according to such factors as the deep water wave regime bottom topography and surface roughness and the resistance of the rocks subaerial terraces were truncated or eliminated by subsequent terrace formation at lower elevations especially on steeply sloping landmasses experiencing slow rates of uplift submarine terraces formed during glacial stillstands were best preserved when rapid subsidence quickly carried them below the level of wave action on slowly subsiding landmasses submarine terraces formed during interglacials and glacial periods experienced repeated erosional modification during subsequent periods of rising and falling sea level and were generally less distinctive on rapidly rising or subsiding 5 mm yr 1 landmasses terraces that formed during interglacial stages alternated above and below present sea level with terraces formed during glacial stages despite some differences in terrace occurrence and elevational distribution it may be difficult to distinguish profiles cut during accelerating or decelerating uplift the amount of erosion during sea level oscillations increases with oscillation amplitude and the larger oscillations in the middle to late quaternary were therefore more conducive to erosion than the smaller oscillations of the pliocene and early quaternary the effect of oscillation amplitude may have been countered during the earlier stages of profile development however by steeper submarine gradients and reduced rates of wave attenuation copyright 2014 john wiley sons ltd

rock coasts with particular emphasis on shore platforms rock coasts are one of the most common elements of the world s littoral zone and they are often important sources of sediment for estuaries and beaches economic development growing populations and the potential effects of rising sea level provide a practical need to understand the dynamics of these coasts although there have been significant advances in our understanding of rocky coastal systems further progress has been hindered by a lack of researchers and by the often imperceptible changes that generally occur within human time scales this paper reviews rock coast processes and landforms in a variety of morphogenic environments one of our most fundamental challenges is to determine the degree to which rock coasts are contemporary rather than inherited features from the quaternary when changes in sea level and climate were responsible for marked variations in the nature intensity and elevational distribution of the marine and subaerial processes that sculpture rock coasts

energy saturation and phase speeds measured on a natural beach field measurements of wave height and speed from 7 m depth shoreward are described the experiment plan consisted of a shore normal transect of closely spaced compared to a dominant wave length velocity pressure and elevation sensors on an almost plane profile having an inshore slope of 1 50 as the waves shoal and begin to break the dominant dissipative mechanism is due to turbulence generated at the crest and wave heights become increasingly depth controlled as they progress across the surf zone wave heights in the inner surf zone are strongly depth independent the envelope of the wave heights is described by h sub rms 0 42 h the depth dependence of the breaking wave height is shown to be related to the kinematic instability criterion celerity spectra were measured by using phase spectra calculated between pairs of adjacent sensors inshore of 4 m depth the celerity was found distant over the energetic region of the spectrum a mean celerity was compared with linear theory and was within 20 and 10 showing good agreement for such a nonlinear dissipative region

shore platform development around lord howe island southwest pacific this paper describes the morphology of near horizontal basalt and calcarenite shore platforms around lord howe island as well as the lithological and process environment in which they occur the morphology of platforms around the island is highly varied for instance they occur at a wide range of elevations between low tide level and several metres above the highest tides and their width ranges between just a few metres to over 100 m however common to most platforms is that they have near horizontal surfaces that terminate abruptly in a steep scarp at their seaward edge correlations indicate that the variability in platform elevation and width is attributable to variability in key parameters of erosion such as rock resistance and shoreline water depth whereas wider platforms occur in rocks of lesser resistance platform elevation is shown to increase both as rock resistance and the depth of water at the shoreline increases wave exposure has a significant control on platform width in some instances but an over arching relationship was not detected most platforms around the island appear to have developed over the holocene and a conceptual model is proposed to account for the varied morphology of platforms that have developed over this period resistant plunging cliffs occur along about 18 of the rocky coastline of lord howe island and represent the starting point for the model where cliffs have yielded to wave erosion platforms have been initiated at an elevation controlled predominantly by rock resistance and shoreline water depth at lord howe island narrow platforms up to about 20 m wide in exposed locations generally occur about 4 to 6 m above high tide level and have apparently been subject to very infrequent erosion shore platforms about 20 to 40 m wide have generally formed in less resistant rocks are somewhat lower at about 2 to 3 m above high tide level and have been subject to more frequent erosion over the holocene most basalt platforms around the island fall within these first two categories but there are some instances of platforms about 50 m wide these platforms have formed in rocks of comparatively low resistance and are relatively low in elevation occurring close to the level of high tide an interesting feature of some of these wide platforms is that unlike the morphology of narrower platforms raised ramparts sometimes occur on their outer edge

rock coast geomorphology recent advances and future research directions there have been considerable advances in rock coast research in the past decade as measured in terms of the number of active researchers and in the number of research papers being produced this review although not exhaustive highlights many of the improvements that have been made in our ability to identify and measure the processes shaping rock coasts at a range of spatial and temporal scales we review how researchers are experimenting with new techniques grappling with quantifying the effects of multiple processes on resultant landforms and exploring how well rock coast systems relate to wider geomorphological and earth science debates recent research including those in this special issue aptly demonstrate the scientific benefits that can be accrued by studying rock coasts at a variety of spatial and temporal scales by considering the effect of the wide range of processes that operate on them and by the application of new measurement techniques and approaches despite these advances there is ample scope for future research which could profit from increasing collaboration with other coastal geomorphologists and allied earth science disciplines in order to identify and quantify linkages between rock coasts and other coastal systems it is also important that new research considers how rock coasts will respond to extreme events and to risks associated with changing climate and to how rock coast geomorphology might contribute beyond coastal science to wider debates in theoretical geomorphology

the formation of beaches on shore platforms in microtidal environments beaches are common features of many rocky shorelines and can be considered to be constrained by the underlying geology in mesotidal to macrotidal areas the slope of the substrate and sediment supply are the primary factors in constraining the size and development of beaches on shore platforms in microtidal settings it is not known if these factors are wholly responsible for determining the presence of beaches on shore platforms nor the contribution of other factors such as hydrodynamics the microtidal coast of victoria australia is surveyed in this study in order to quantify the morphological boundary conditions that constrain beach development on semi horizontal shore platforms an ample sediment supply indicates that the underlying geology is controlling the presence and absence of beaches where beaches occur they always overlie a rock ramp which is the steepest part of the platform the two most important morphological constraints were platform width and height both of which significantly correlated with beach volume an elevational threshold exists at just over 1 0 m where beaches cannot accumulate below this threshold platform width appears to be the principle constraining factor in beach accumulation an evolutionary model is inferred which suggests that dissipation of wave energy associated with platform widening plays an important role in allowing beaches to accumulate the model suggests beaches on platforms will be particularly sensitive to sea level rise copyright 2014 john wiley sons ltd

sedimentology of rocky shorelines 3 hydrodynamics of megaclast emplacement and transport on a shore platform oahu hawaii abstract megaclasts of well cemented coralgal limestone have been emplaced onto a shore platform by large waves on the north shore of oahu hi emplacement and movements of the largest ca 96 ton megaclast have been dated using aerial photographs hydrodynamic forces at the low submerged shoreline cliff are computed using design wave characteristics based on linear wave theory and experimental results considering the local wave climate and near shore bottom topography force exerted by a tsunami has been estimated based on the 1946 aleutian tsunami the computed forces are evaluated in terms of the initial fracturing along a given failure plane that is required in order for the detachment to occur the analysis shows that tsunami as well as large swell waves are capable of quarrying the megaclast provided that sufficient initial fracturing is present dislodgement and emplacement most likely occurred in a sequence during impact of a single wave on the shoreline cliff swell waves however are seldom capable of emplacing large blocks onto the platform due to their rapid disintegration after breaking so that most blocks quarried from the cliff edge fall back onto the submarine terrace emplacement of large boulders seems to require extreme sea waves with periods longer than storms or north pacific swells usually produce transport mechanisms on the shore platform vary depending on megaclast shape sliding is a common mechanism of transport for larger and irregular megaclasts whereas somewhat smaller and platy megaclasts are occasionally found in overturned positions