micro seismic measurements of cliff motion under wave impact and implications for the development of near horizontal shore platforms abstract few high resolution measurements of process form interactions have been taken on rock coasts but recent studies in california have shown that portable seismometers enable useful proxy measurements of wave energy delivery to cliffs here we describe measurements over 20 days of high frequency ground motion of cliffs formed in sedimentary flysch rocks at okakari point north of auckland new zealand three sensors were located in a shore normal array inland from the cliff top and a fourth sensor was bolted to a ledge 2 m above the cliff toe the nearshore wave field in front of the cliff and shore platform was monitored using a shore normal array of 5 wave gauges the instrumentation provided measurements of wave energy delivery and consequent ground motion including the first observations of motion at the top and bottom of cliffs results showed that horizontal ground motion is dominant at the cliff top whereas vertical motion is dominant at the cliff toe power spectra show that several high frequency peaks occur in data from the cliff toe whereas a single broader peak frequency occurs at the cliff top resulting from signal modification as seismic waves pass through tens of metres of cliff rock a 100 m wide shore platform at the cliff toe fundamentally controls the patterns of observed energy delivery the shore platform is nearly horizontal elevated close to high water level and abruptly plunges into water 10 m deep at its seaward edge as expected the magnitude of ground motion at all sensors is greatest during larger waves measurements further show that ground motion both at the bottom and top of the cliff is strongest at low tide and weakest at high tide this observation is opposite to that noted at santa cruz where ground motion was greatest at high tide at okakari point the most significant high frequency ground motions occur at low tide when waves are forced to break sometimes violently against the seaward edge of the shore platform four distinctive frequency peaks between 1 and 50 hz increase in magnitude as tidal stage drops implying that wave breaking against the outside edge of the shore platform represents an important source of vibration a detailed understanding of the energy source e g short duration shock pressures and rock resonance is not provided by this study however quantifying the spatial and temporal patterns of energy delivery places strong emphasis on the important role of shore platform geometry in filtering wave energy delivery to the cliff during the 20 day experiment most wave energy was delivered to the outside edge of the shore platform not the cliff toe the geomorphic role of high frequency shaking from wave impacts remains to be clearly demonstrated but if wave impacts are capable of eroding rock then the data from this study imply that under present conditions the outside edge of the shore platform may be subject to higher erosion rates than the cliff toe it is possible that the shore platform is currently being destroyed rather than created but a longer programme of measurements is required to test this notion

microseismic measurement of wave energy delivery to a rocky coast rocky coasts are attacked by waves that drive sea cliff retreat and etch promontories and embayments into the coastline understanding the evolution of such coastlines requires knowledge of the energy supplied by waves which should depend upon both the deep water waves and the coastal bathymetry they cross we employ microseismic measurements of the wave induced shaking of sea cliffs near santa cruz california as a proxy for the temporal pattern of wave energy delivery to the coast during much of the winter 2001 storm season visual inspection of the time series suggests that both deep water wave heights and tide levels exert considerable control on the energy delivered we test this concept quantitatively with two models in which synthetic time series of wave power at the coast are compared with the shaking data in the first model deep water wave power is linearly scaled by a fitting parameter because this model fails to account for the strong tidal signal it fits poorly in the second model the wave transformation associated with shoaling and refraction diminishes the nearshore wave power and dissipation associated with bottom drag and wave breaking is parameterized by exponential dependencies on two length scales this model reduces the variance by 32 45 and captures the essence of the full signal shoaling and refraction greatly modulate the wave power delivered to the coast energy dissipated by bottom drag across the shelf is relatively small the dissipation length scale is many times the path length across the shelf in contrast much energy is dissipated in the surf zone the tidal dissipation depth scale is of the same order as the tidal range 1 2 m which accounts for the strong dependence of the cliff shaking on the tide

aminostratigraphy and faunal correlations of late quaternary marine terraces pacific coast usa recent studies using the extent of racemization of amino acids to date fossil mollusc shells in the arctic1 the british isles2 and on the atlantic3 4 and pacific5 13 coasts of north america have relied mainly on theoretical kinetic models of racemization ages generated in this fashion are highly model dependent and require estimates of integrated long term diagenetic temperatures we present here an alternative empirical approach to aminostratigraphy in which we plot amino acid enantiomeric ratios versus latitude for localities along the pacific coast of the united states and generate isochronal correlations by connecting data points of geographically proximal localities that have similar d l ratios and zoogeographic aspect isochrons are calibrated at a few localities by independent radiometric dates the diagenetic temperature effect on racemization is reflected in the slope of the isochrons but the need to quantify temperature is eliminated

ground motions on rocky cliffed and sandy shorelines generated by ocean waves 1 we compare ground motions observed within about 100 m of the waterline on eight sites located on shorelines with different morphologies rock slope cliff and sand beaches at all sites local ocean waves generated ground motions in the frequency band 0 01 40 hz between about 0 01 and 0 1 hz foreshore loading and gravitational attraction from ocean swell and infragravity waves drive coherent in phase ground flexing motions mostly oriented cross shore that decay inland at higher frequencies between 0 5 and 40 hz breaking ocean waves and wave rock impacts cause ground shaking overall seismic spectral shapes were generally consistent across shoreline sites and usually within a few orders of magnitude despite the diverse range of settings however specific site response varied and was influenced by a combination of tide level incident wave energy site morphology ground composition and signal decay flexing and shaking increased with incident wave energy and was often tidally modulated consistent with a local generation source flexing magnitudes were usually larger than shaking and flexing displacements of several mm were observed during relatively large incident wave conditions hs 4 5 m comparison with traffic noise and earthquakes illustrate the relative significance of local ocean generated signals in coastal seismic data seismic observations are not a simple proxy for wave cliff interaction

alongshore variability in wave energy transfer to coastal cliffs abstract the alongshore distribution of wave energy is believed to be an important control on the spatial variability of coastal erosion there is however a lack of field data quantifying the alongshore variability in wave energy on rock coasts whereby the relative control of coastline geometry versus foreshore characteristics on wave energy delivery remains unclear a number of studies have identified high frequency cliff top ground shaking to be generated by wave impacts at the cliff toe during high tides ht to capture the variability of wave cliff impact energy along coast we installed an array of cliff top seismometers along a 1 km stretch of coastline in north yorkshire uk our aim is to constrain how wave energy transfer to the cliff toe varies and to examine the relative energy transfer around typical coastline features including a bay and headlands whilst the greatest ht ground motion energy is recorded at a headland and the lowest at the centre of the bay 5 of that observed at the headland we identify no systematic alongshore variation in the ht ground motion energy that can be related to coastline morphology we also note considerable variation between features of similar form the total ht ground motion energy at one headland is only 49 of the next headland 1 km alongshore between neighbouring sites within the bay separated by only 100 m we observe up to an order of magnitude difference in ground motion energy transfer our results demonstrate the importance of the foreshore in driving the variations in energy delivery that we observe local alterations in water depth and foreshore topography control the alongshore distribution of wave energy available to generate cliff ht ground motions importantly this apparently local effect overrides the influence of macroscale coastal planform morphology which has previously been assumed to be the dominant control the results show that foreshore characteristics that hold influence over wave energy transfer vary significantly over short 100 m distances and so we expect erosion controlled by wave impacts to vary over similar scales

quaternary sea level events on northern san clemente island california abstract global sea level changes are expressed in the coastal landforms and deposits of northern san clemente island stratigraphic radiometric amino acid and pedologic dating techniques have allowed the development of a chronology of sea level changes for about the last 500 000 yr a uranium series date on coral of about 127 000 yr for the 2nd terrace serves as a calibration point for amino acid age estimates of four other mapped terraces two of these terraces have age estimates of about 80 000 105 000 yr another has an age estimate of about 127 000 yr and the 5th terrace on the west side of the island is estimated to be about 415 000 575 000 yr old these dates correlate reasonably well with marine terraces dated elsewhere and with stages of the oxygen isotope record that are thought to represent high stands of the sea weakly cemented calcareous dune sands eolianites are moderately extensive on northern san clemente island and appear to represent low stands of the sea since calcareous shelf sands were the most likely source a radiocarbon date of about 22 000 yr suggests that the youngest eolianite was deposited during the last glacial maximum an older eolianite is estimated to be about 140 000 195 000 yr old based on stratigraphic relations and degree of soil development the suggested ages for the eolianites also correlate well with oxygen isotope estimates of low sea levels

the subtidal morphology of microtidal shore platforms and its implication for wave dynamics on rocky coasts abstract the subtidal portions of shore platforms are important geomorphic features as they can modify deep water wave energy before it impacts the intertidal platform edge in this study an integrated marine and terrestrial aerial lidar dataset is used to analyse the morphology of the subtidal portion of shore platforms semi horizontal intertidal platforms on an 85 km along stretch of microtidal open ocean rocky coast in victoria australia are investigated and described quantitatively three distinct types of subtidal morphology occur i a steep cliff with a mean slope of 8 18 ii a gently sloping ramp with a mean slope of

seismic precursory patterns before a cliff collapse and critical point phenomena 1 we analyse the statistical pattern of seismicity before a 1 2 103 m3 chalk cliff collapse on the normandie ocean shore western france we show that a power law acceleration of seismicity rate and energy in both 40 hz 1 5 khz and 2 hz 10khz frequency range is defined on 3 orders of magnitude within 2 hours from the collapse time simultaneously the average size of the seismic events increases toward the time to failure these in situ results are derived from the only station located within one rupture length distance from the rock fall rupture plane they mimic the critical point like behavior recovered from physical and numerical experiments before brittle failures and tertiary creep failures our analysis of this first seismic monitoring data of a cliff collapse suggests that the thermodynamic phase transition models for failure may apply for cliff collapse

a review of amino acid racemization studies in quaternary mollusks stratigraphic and chronologic applications in coastal and interglacial sites pacific and atlantic coasts united states united kingdom baffin island and tropical islands abstract amino acid racemization aar studies of quaternary mollusks mostly marine mollusks from coastal deposits are reviewed data obtained in regional studies from the u s atlantic and pacific coasts baffin island the united kingdom and tropical islands are discussed as they relate to method evaluation kinetic model development and aminostratigraphic applications u s pacific coast studies have been employed for estimating tectonic deformation rates study of molluscan zonation patterns in the late pleistocene and in kinetic model evaluation u s atlantic coast studies have identified multiple aminostratigraphic zones in areas with complex morphostratigraphic relationships and have also revealed some important conflicts between aminostratigraphic temperature concepts and radiometric data studies in the united kingdom involving coastal sites and non marine interglacial sites identify some stratigraphic and kinetic conflicts but provide a preliminary chronostratigraphic model for the classical interglacial terminology of the u k middle to late pleistocene baffin island studies involving aar data and u th dating of shells have resulted in some significant revisions of previous chronologic models the arctic environment has also stimulated some novel approaches in the collection and interpretation of aar results tropical island studies though few in number aid in calibration of observed racemization and also aid in correlation of coastal deposits with late pleistocene isotopic ice volume records

uranium series age of the eel point terrace san clemente island california uranium series analysis of the coral allopora californica verrill from the 2nd 32 m eel point terrace on san clemente island california has yielded an age of 127 000 7 000 yr the eel point terrace is thus correlative with numerous terrace localities on the southern california mainland with coral reefs on barbados and new guinea dated about 120 000 yr and with substage 5e of the marine oxygen isotope record a tectonic uplift rate of about 0 20 m 1 000 yr has been calculated assuming a sea level slightly higher than the present one at the time of terrace formation extrapolation of this uplift rate allows age estimates to be made for other terraces on the island

coastal cliff ground motions from local ocean swell and infragravity waves in southern california 1 ground motions atop a southern california usa coastal cliff are compared with water level fluctuations observed at the cliff base and with ground motions observed 10 km inland at high tide cliff top ground motions in three frequency bands were generated locally by ocean waves at the cliff base 1 high frequency 0 3 hz shaking caused by waves impacting the cliff and 2 gravitational loading induced swaying at the frequency of the incident sea swell waves 0 05 0 1 hz and 3 slow swaying at infragravity frequencies 0 006 0 05 hz at high tide at infragravity and incident sea swell wave frequencies cliff top vertical ground displacement and cliff base water level fluctuations are coherent and oscillate in phase with occasional deviation at sea swell frequencies and spectral levels at the cliff top are much higher than at the inland seismometer in contrast at double frequencies 0 1 0 3 hz spectral levels of vertical motions are nearly identical inland and at the cliff top consistent with a common distant or spatially distributed source at low tide when ocean waves did not reach the cliff base power levels of vertical ground motions at the cliff top decreased to inland levels at incident wave frequencies and higher and only infragravity band motions were noticeably forced by local ocean waves

the role of beach morphology on coastal cliff erosion under extreme waves erosion of hard rock coastal cliffs is understood to be caused by a combination of both marine and sub aerial processes beach morphology tidal elevation and significant wave heights especially under extreme storm conditions can lead to variability in wave energy flux to the cliff toe wave and water level measurements in the nearshore under energetic conditions are difficult to obtain and in situ observations are rare here we use monthly cliff face volume changes detected using terrestrial laser scanning alongside beach morphological changes and modelled nearshore hydrodynamics to examine how exposed cliffs respond to changes in extreme wave conditions and beach morphology the measurements cover the north atlantic storms of 2013 2014 and consider two exposed stretches of coastline porthleven and godrevy uk with contrasting beach morphology fronting the cliffs a flat dissipative sandy beach at godrevy and a steep reflective gravel beach at porthleven beach slope and the elevation of the beach cliff junction were found to influence the frequency of cliff inundation and the power of wave cliff impacts numerical modelling xbeach g showed that under highly energetic wave conditions i e those that occurred in the north atlantic during winter 2013 2014 with hs 5 5 m dissipative site and 8 m reflective site the combination of greater wave height and steeper beach at the reflective site led to amplified wave run up subjecting these cliffs to waves over 4 times as powerful as those impacting the cliffs at the dissipative site 39 kwm 1 compared with 9 kwm 1 this study highlighted the sensitivity of cliff erosion to extreme wave conditions where the majority over 90 of the annual value of cliff face erosion ensued during the winter the significance of these short term erosion rates in the context of long term retreat illustrates the importance of incorporating short term beach and wave dynamics into geomorphological studies of coastal cliff change

an evaluation of uranium series dating of fossil echinoids from southern california pleistocene marine terraces abstract fossil sea urchins strongylocentrotus from pleistocene marine terraces on the southern california channel islands have been dated by the uranium series method in order to test the suitability of echinoids for dating marine terraces results indicate that urchin plates and spines do not behave as closed systems with respect to both uranium and thorium calculated ages based on these data do not agree with uranium series ages 120 000 and 127 000 yrs obtained previously from corals from the same localities thus fossil sea urchins strongylocentrotus are not considered suitable for uraniumseries dating of pleistocene marine terrace deposits

amino acid age estimates of marine terraces and sea levels on san nicolas island california fourteen marine terraces rising to an elevation of 274 m have been mapped on san nicolas island california the lowest terrace is 105 000 yr old on the basis of amino acid ratios in fossil mollusks slightly lower than those from the 120 000 yr old uranium series dated second terrace the age estimate and present elevation of the lowest terrace along with an assumption of constant uplift rate indicate a paleo sea level estimate of 10 to 12 m at about 105 000 b p supporting the general barbados model of sea level history the fourth and fifth terraces probably represent separate high sea level stands during the same interglacial complex 400 000 b p the eight and tenth terraces have amino acid ratios near equilibrium and imply ages of 600 000 yr collectively the data suggest long term average quaternary uplift rates of 0 2 0 3 m 1000 yr

coastal cliff ground motions and response to extreme storm waves coastal cliff erosion from storm waves is observed worldwide but the processes are notoriously difficult to measure during extreme storm wave conditions when most erosion normally occurs limiting our understanding of cliff processes over january february 2014 during the largest atlantic storms in at least 60 years with deepwater significant wave heights of 6 8 m cliff top ground motions showed vertical ground displacements in excess of 50 100 m an order of magnitude larger than observations made previously repeat terrestrial laser scanner surveys over a 2 week period encompassing the extreme storms gave a cliff face volume loss of 2 orders of magnitude larger than the long term erosion rate the results imply that erosion of coastal cliffs exposed to extreme storm waves is highly episodic and that long term rates of cliff erosion will depend on the frequency and severity of extreme storm wave impacts

directional spreading of waves in the nearshore observations of surface gravity waves shoaling between 8 m water depth and the shoreline on a barred beach indicate that breaking results in an increase in the directional spread of wave energy in contrast to the directional narrowing with decreasing depth predicted by refraction theory snell s law during low energy wave conditions when breaking induced wave energy losses over the instrumented transect are small the observed mean propagation direction and spread about the mean both decrease with decreasing depth consistent with the expected effects of refraction nonlinearity causes high frequency components of the spectrum to become directionally aligned with the dominant incident waves during high energy wave conditions with significant wave breaking on the sand bar the observed mean directions still decrease with decreasing depth however the observed directional spreads increase sharply nominally a factor of 2 for values integrated over the swell sea frequency range between the outer edge of the surf zone and the crest of the sand bar followed by a decrease toward the shoreline observations on a nonbarred beach also show directional broadening with spreads increasing monotonically from the outer edge of the surf zone to a maximum value near the shoreline although the mechanism is not understood these spatial patterns of directional broadening suggest that wave breaking causes significant scattering of incident wave energy into obliquely propagating components

observing calving generated ocean waves with coastal broadband seismometers jakobshavn isbrae greenland we use time lapse photography modis satellite imagery ocean wave measurements and regional broadband seismic data to demonstrate that icebergs that calve from jakobshavn isbrae greenland can generate ocean waves that are detectable over 150 km from their source the waves which are recorded seismically have distinct spectral peaks are not dispersive and persist for several hours on the basis of these observations we suggest that calving events at jakobshavn isbrae can stimulate seiches or basin eigenmodes in both ilulissat icefjord and disko bay our observations furthermore indicate that coastal land based seismometers located near calving termini e g as part of the new greenland ice sheet monitoring network glisn can aid investigations into the largely unexplored oceanographic consequences of iceberg calving

nearshore wave induced cyclical flexing of sea cliffs 1 evolution of a tectonically active coast is driven by geomorphically destructive energy supplied by ocean waves wave energy is episodic and concentrated sea cliffs are battered by the geomorphic wrecking ball every 4 25 s we measure the response of sea cliffs to wave assault by sensing the ground motion using near coastal seismometers sea cliffs respond to waves in two distinct styles high frequency motion 20 hz reflects the natural frequency of the sea cliff as it rings in response to direct wave impact low frequency motion in the 0 1 0 05 hz 10 20 s band consistently agrees with the dominant nearshore wave period integrating microseismic velocities suggests 50 m and 10 m displacements in horizontal and vertical directions respectively displacement ellipsoids exhibit simultaneous downward and seaward sea cliff motion with each wave video footage corroborates the downward sea cliff flex in response to the imposed water load on the wave cut platform gradients in displacement amplitudes documented using multiple seismometers suggest longitudinal and shear strain of the flexing sea cliff on the order of 0 5 4 strains during each wave loading cycle as this sea cliff flexure occurs approximately 3 million times annually it has the potential to fatigue the rock through cyclical loading local sea cliff retreat rates of 10 cm yr imply that a given parcel of rock is flexed through roughly 109 cycles of increasing amplitude before exposure to direct wave attack at the cliff face

comparison of uranium series radiocarbon and amino acid data from marine molluscs baffin island arctic canada uranium series and sup 14 c dates and the extent of amino acid racemization are reported for 24 marine shell samples from three areas of baffin island arctic canada when the radiometric dates are plotted against the ratio of d alloisoleucene l isoleucene in the shells five broad age groups are recognized the uranium series data indicate that sup 231 pa is incompletely retained in most fossil shells and that sup 230 th is lost from some of the samples therefore their apparent ages are minimum however a few dated samples in each group have yielded useful age results and the minimum ages of the five groups of samples are estimated as 7 000 to 11 000 greater than or equal to70 000 greater than or equal to136 000 greater than or equal to190 000 and 300 000 yr calculated integrated thermal histories based on the epimerization reaction in the mollusc hiatella arctica linne give paleotemperature estimates of around 5 sup o c compared to the present mean annual air temperature of about 11 sup o c

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

cross shore decay of cliff top ground motions driven by local ocean swell and infragravity waves 1 ground motions at the frequencies between 0 01 and 0 1 hz of ocean infragravity and swell waves were observed on a cross shore transect extending landward from the edge of a southern california coastal cliff cliff top ground motions are coherent and in phase with water level fluctuations at the cliff base vertical ground motions at infragravity and single frequencies decay rapidly with inland distance from the cliff edge e folding scale is about 12 m and at the edge decrease by several orders of magnitude between high tide when waves reach the cliff base and low tide when the waterline is about 50 m from the cliff base the observed cross shore decay scales are qualitatively consistent with gravitational loading and attraction of water waves at tidally modulated distances from the cliff base at approximately constant distance from the waterline ground motions vary roughly linearly with nearshore swell wave energy in contrast to these locally forced ground motions double frequency band 0 1 0 2 hz cliff top vertical ground motions are remotely generated with spatially uniform magnitudes approximately equal to those observed 14 km inland near the cliff edge ground tilt dominates the observed large relative to vertical cross shore acceleration at infragravity frequencies contributes significantly to cross shore acceleration at swell frequencies and is a small fraction of cross shore acceleration at higher frequencies

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

where is the seaward edge a review and definition of shore platform morphology abstract shore platforms are erosional coastal landforms that have attracted scientific attention since the mid 19th century the defining element of a platform is width that is used in many calculations such as determining a platform s evolutionary state or inferring how wave energy is distributed along the shore although a critical variable there are no uniform criteria for defining the seaward edge quantification of platform width has been driven by site specific variables with the seaward edge defined on the basis of tides morphology biology processes and sediment coverage the lack of a uniform definition has meant that comparative studies are difficult and results are possibly spurious as widths derived from very different criteria can vary by an order of magnitude just on the basis of which criteria is used to determine its edge in this review a combination of morphologic and process elements is used to define the seaward edge of a shore platform the development of strict criteria is especially needed in an environment of rising sea levels if measurements of landscape change are to be made in addition the advent of seamless datasets that cross the land sea boundary means that the delineation of platform morphology is no longer limited by physical access this review concludes that the seaward edge of a shore platform will occur at or landward of wave base and should be defined as the point where active erosion of the bedrock ceases characterised by erosional features such as notches and block plucking scars or the deposition of sediment of such a thickness that the underlying bedrock is not exposed during storm events

sea cliff retreat and shore platform widening steady state equilibrium we challenge the notion of steady state equilibrium in the context of progressive cliff retreat on micro tidal coasts ocean waves break at or close to the abrupt seaward edge of near horizontal shore platforms and then rapidly lose height due to turbulence and friction conceptual models assume that wave height decays exponentially with distance from the platform edge and that the platform edge does not erode under stable sea level these assumptions combine to a steady state view of holocene cliff retreat we argue that this model is not generally applicable recent data show that 1 exponential decay in wave height is not the most appropriate conceptual model of wave decay 2 by solely considering wave energy at gravity wave frequencies the steady state model neglects a possible formative role for infragravity waves here we draw attention to possible mechanisms through which infragravity waves may drive cliff retreat over much greater distances and longer timescales than imaginable under the established conceptual model copyright 2013 john wiley sons ltd

field observations of infragravity waves and their behaviour on rock shore platforms infragravity wave igw transformation was quantified from field measurements on two shore platforms on new zealand s east coast making this the first study to describe the presence characteristics and behaviour of igws on rock platform coasts data was collected using a cross shore array of pressure transducers during a 22 hour experiment on oraka shore platform and a 36 hour experiment at rothesay bay shore platform a low pass fourier filter was used to remove gravity wave frequency oscillations allowing separate analysis of igws and the full wave spectrum offshore igw heights were measured to be 7 cm oraka and 9 cm rothesay bay which were 21 oraka and 7 5 rothesay bay the height of incident wave height at the cliff toe significant igw height averaged 15 cm at oraka and 13 cm at rothesay bay this increase in igw height over the platform during both experiments is attributed to shoaling of 40 to 55 over the last 50 60 m before the cliff toe respectively shoaling across the platform was quantified as the change in igw height from the platform edge to cliff toe resulting in a maximum increase of 1 88 and 2 63 on rothesay bay and oraka platforms igw height at the cliff toe showed a strong correlation with incident wave height the proportional increase in igw height shows a strong correlation to water level on each platform the rate of shoaling of long period waves on the shallow horizontal platforms increased at higher water levels resulting in a super elevation in water level at the cliff toe during high tide greater igw shoaling was also observed on the wider oraka shore platform results from this study show the first measurements of igws on shore platforms and identify long wave motion a significant process in a morphodynamic understanding of rock coast copyright 2011 john wiley sons ltd

analytical and approximate solutions to radial dispersion from an injection well to a geological unit with simultaneous diffusion into adjacent strata analytical and approximate solutions are developed for radial dispersion in aquifers with simultaneous diffusion into adjacent strata contaminants from the injection well are transported within the main aquifer by advection and mechanical dispersion assuming a steady state and radially diverging ground water flow field the leakage of contaminants from the main aquifer to the aquitards is accounted for by molecular diffusion a mathematical model consisting of two coupled differential equations is proposed to investigate concentration distributions in the main aquifer as well as in the adjacent aquitards by making use of laplace transforms analytical solutions valid for small time periods are obtained without difficulty to complement these analytical solutions concentration distributions for intermediate and large time intervals are determined approximately by numerically inverting the appropriate transformed solution in the laplace domain with the stehfest algorithm excellent agreement exists between analytical solutions and approximate solutions for small time intervals supporting the validity of approximate solutions for intermediate and large time periods it is shown that the diffusive leakage may significantly delay contaminant movement within the main aquifer at relatively large time periods the solutions can be applied to study radial dispersion in granular aquifers bounded by relatively low permeability aquitards or in planar fractures contained in porous formations

identifying and removing tilt noise from low frequency 0 1 hz seafloor vertical seismic data low frequency 0 1 hz vertical component seismic noise can be reduced by 25 db or more at seafloor seismic stations by subtracting the coherent signals derived from 1 horizontal seismic observations associated with tilt noise and 2 pressure measurements related to infragravity waves the reduction in effective noise levels is largest for the poorest stations sites with soft sediments high currents shallow water or a poorly leveled seismometer the importance of precise leveling is evident in our measurements low frequency background vertical seismic spectra measured on a seafloor seismometer leveled to within 1 10 4 radians 0 006 degrees are up to 20 db quieter than on a nearby seismometer leveled to within 3 10 3 radians 0 2 degrees the noise on the less precisely leveled sensor increases with decreasing frequency and is correlated with ocean tides indicating that it is caused by tilting due to seafloor currents flowing across the instrument at low frequencies this tilting generates a seismic signal by changing the gravitational attraction on the geophones as they rotate with respect to the earth s gravitational field the effect is much stronger on the horizontal components than on the vertical allowing significant reduction in vertical component noise by subtracting the coherent horizontal component noise this technique reduces the low frequency vertical noise on the less precisely leveled seismometer to below the noise level on the precisely leveled seismometer the same technique can also be used to remove background noise due to the seafloor pressure field up to 25 db noise reduction near 0 02 hz and possibly due to other parameters such as temperature variations

observations of coastal cliff base waves sand levels and cliff top shaking concurrent observations of waves at the base of a southern california coastal cliff and seismic cliff motion were used to explore wave cliff interaction and test proxies for wave forcing on coastal cliffs time series of waves and sand levels at the cliff base were extracted from pressure sensor observations programmatically and used to compute various wave impact metrics e g significant cliff base wave height wave cliff interaction was controlled by tide incident waves and beach sand levels and varied from low tides with no wave cliff impacts to high tides with continuous wave cliff interaction observed cliff base wave heights differed from standard normal and rayleigh distributions cliff base wave spectra levels were elevated at sea swell and infragravity frequencies coastal cliff top response to wave impacts was characterized using microseismic shaking in a frequency band 20 45 hz sensitive to wave breaking and cliff impacts response in the 20 45 hz band was well correlated with wave cliff impact metrics including cliff base significant wave height and hourly maximum water depth at the cliff base r2 0 75 with site specific calibration relating wave impacts and shaking and acceptable anthropogenic traffic noise levels cliff top seismic observations are a viable proxy for cliff base wave conditions the methods presented here are applicable to other coastal settings and can provide coastal managers with real time coastal conditions copyright 2016 john wiley sons ltd

quantifying the environmental controls on erosion of a hard rock cliff linking hard rock coastal cliff erosion to environmental drivers is challenging with weak relationships commonly observed in comparisons of marine and subaerial conditions to the timing and character of erosion the aim of this paper is to bring together datasets to explore how best to represent conditions at the coast and to test relationships with erosion which on this coast is primarily achieved via rockfalls on the n yorkshire coast in the uk we compare a continuously monitored microseismic dataset regionally monitored coastal environmental conditions modelled at cliff conditions and periodic high resolution 3d monitoring of changes to the cliff face over a 2 year period cliff top microseismic ground motions are generated by a range of offshore nearshore and at cliff sources we consider such ground motions as proxies for those conditions that promote the occurrence of rockfalls and erosion both these data and modelled at cliff water levels provide improved insight into conditions at and wave energy transfer to the cliff the variability in microseismic modelled and regionally monitored environmental data derives statistically significant relationships with increases in the occurrence of rockfalls the results demonstrate a marine control on the total volume and size characteristics of rockfalls the strongest relationships found are with rockfalls sourced from across the entire cliff rather than just at the toe indicating that the marine influence albeit indirectly extends above and beyond the area inundated these results identify failure mechanisms driving erosion where a range of processes unique to the coast trigger failure but in a manner beyond purely wave action at the cliff toe greater erosion occurs at the cliff toe however comparing water level inundation frequency microseismic energy transfer and erosion we observe that heights up the cliff that correspond with water levels associated with low frequency high energy storms or more frequent inundation do not experience increased erosion our results describe the relationship between inundation duration energy transfer and erosion of hard rock cliffs and illustrate the relative intensity of erosion response to variations in these conditions implicitly our data suggests that in future cliffed rocky coasts may be relatively quick to respond to changes in environmental forcing