lithological control on the elevation of shore platforms in a microtidal setting the shore platforms on shag point southern new zealand are quasi horizontal surfaces and are developed between supratidal and low water spring levels a range of morphologies occur with more exposed platforms having a distinct low tide cliff in contrast to low tide surfaces where the seaward edge is buried beneath rubble and macro algal growth the platforms range in width from 20 to 80 m and are eroded into late cretaceous early tertiary fine marine sandstones and mudstones shore platforms have formed in two principal lithological units a homogeneous unit that is characterized by few discontinuities and a fractured unit with joints spaced about 0 5 m apart rock hardness is low in both units l type schmidt hammer rebound values of 31 4 and there is little systematic variation in values between the two units in which platforms have developed case hardened concretions within the sandstone are significantly harder than surrounding rock and cause local relief of metre scale as the spherical diagenetic features are eroded from the bedrock they do not however appear to affect broad scale platform geometry joints within the bedrock are a primary control on platform elevation platforms formed in jointed rock occur at the lower portion of the intertidal zone in contrast to platforms formed in unjointed bedrock in which horizontal surfaces occur at or above mean high water spring tide level rock structure therefore appears to be the primary determinant factor of platform geometry at shag point copyright 2006 john wiley sons ltd

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

deriving mechanisms and thresholds for cliff retreat in soft rock cliffs under changing climates rapidly retreating cliffs of the suffolk coast uk abstract understanding changing thresholds and mechanisms for retreat in soft rock cliffs is important under changing climates this can be achieved through combining detailed field observation long term process and morphological monitoring and numerical modelling the cliffs of the suffolk coast southern north sea have exhibited long term 1883 2010 recession rates of 3 5 m a 1 rising to 4 7 m a 1 in the period 1993 2010 annual to biannual ground survey data and the application of gis techniques to digitised records of changing shoreline position from historic maps and aerial photography reveal considerable decadal scale variations in cliff recession within which are nested inter annual fluctuations in rates of retreat archival datasets on significant periods of onshore winds and their interaction with high water levels including the incidence of storm surges and rainstorm events are used to determine thresholds for cliff base erosion and its propagation upwards through the cliff profile in addition the geo slope dynamic coupled hydrology stability model is used to establish thresholds for cliff face failures driven by variations in rainfall inputs retreat mechanisms are complex governed by cliff geology both as a primary control on suction loss and through its interaction with basal marine conditions the study allows a general model of cliff retreat for soft rock cliffs to be put forward whereby a resistant basal platform is overlain by more erodible weakly and moderately cemented sands and gravels in this model the varying balance between marine and terrestrial forcing factors are reflected in low 7 m a 1 modes of cliff retreat

estimating long term cliff recession rates from shore platform widths coastal cliff erosion is a problem in many coastal areas however often only very limited data are available to quantify the rates of recession for the development of coastal management strategies in the soft flysch deposits of the waitemata group auckland new zealand coastal cliffs are associated with shore platforms two models exist for the profile evolution of shore platforms and associated cliffs the first suggests that an equilibrium profile develops in response to erosive processes and this profile subsequently migrates landward the second model suggests that the seaward margin of the shore platform is relatively static and the profile extends landward through a combination of cliff recession and platform lowering physical simulations and field measurements for mudstone and limestone lithologies indicate that the second model is more likely for soft flysch deposits a eustatic sea level curve for the weiti estuary auckland suggests that up to 7120f70 years have been available for shore platform development since sea level reached the present seaward margins of shore platforms shore platform widths were measured using gps at two sites in waitemata group rocks the north shore of auckland and the southern side of the tawharanui peninsula north auckland the long term cliff recession rates estimated from shore platform widths 1 4f0 1 to 14 3f0 1 mm y 1 are consistent with the lower end of the average range of cliff top and face recession rates published for waitemata group rocks using different methods 11 75 mm y 1 and in agreement with cliff base recession estimates 3 5 mm y 1 shore platform widths were qualitatively related to the rock mass characteristics of the associated cliffs and therefore platform widths could provide a method of identifying regions of potential hazard d 2005 elsevier b v all rights reserved

a methodology for the study of the relation between coastal cliff erosion and the mechanical strength of soils and rock masses abstract a methodology is proposed to make approximate estimates of the destructive force of waves at the bottoms of cliffs where no accurate bathymetric data are available by means of correlation between the erosion rate of rocky coasts and the mechanical strength of soils and rock masses the correlation used makes it possible to obtain a linear semi logarithmic expression between the long term average erosion rate from an engineering standpoint of coasts consisting of different lithologies wave energy and the uniaxial compressive strength of soils and rock masses forming the cliffs the uniaxial compressive strength of soils consisting of landslide debris was measured using a pocket penetrometer and the rock mass index rmi method was used for rock masses these methods were chosen after critical analysis of the methodologies currently available the proposed approach was tested in the cilento area of southern italy and in particular along a 6 km stretch of coast typified by rock masses and landslide debris that are particularly susceptible to erosion this coastline is exposed to south westerly waves which in deep water reach significant heights between 1 and 3 m and significant wave periods between 4 and 7 s estimates of the coastal erosion rates were made by studying the variations especially in restricted headland areas occurring over two time spans 30 and 45 years respectively by comparing topographic maps and aerial photographs taken at different times these comparisons give approximate indications of retreats of 15 m over the time span of 30 years average erosion rate of 0 5 m year 1 and of 35 m over the time span of 45 years average erosion rate of ca 0 8 m year 1 these data do have a local significance but clearly show how quick these processes sometimes are lastly the study of a notch incised by wave action on a concrete sea wall built to protect a terrace made it possible to quantify the impact of erosion on concrete it was possible to obtain rmi values through field observations furthermore it was possible to obtain the constants of the hoek and brown failure criterion using rmi on the basis of rmi values the rock masses studied were defined as moderately strong to strong and according to the hoek and brown criterion as poor to fair a semilogarithmic linear relation was found between the strength of landslide debris rock masses and concrete as well as their respective long term erosion consequently a rough estimate of the destructive force of waves ca 24 mpa was calculated this value is given by the product of the mean value of their hydraulic pressure for a non dimensional constant which in turn takes into account the sandy pebbly beach sediment at the foot of the cliffs that acts as an abrasive on the rock mass

sea cliff erosion as a function of beach changes and extreme wave runup during the 1997 1998 el nino abstract over time scales of hundreds to thousands of years the net longshore sand transport direction along the central california coast has been driven to the south by north pacific winter swell in contrast during the el nino winter of 1997 1998 comparisons of before and after airborne lidar surveys showed sand was transported from south to north and accumulated on the south sides of resistant headlands bordering pocket beaches this resulted in significant beach erosion at the south ends of pocket beaches and deposition in the north ends coincident with the south to north redistribution of sand shoreline morphology became prominently cuspate with longshore wavelengths of 400 700 m the width and elevation of beaches were least where maximum shoreline erosion occurred preferentially exposing cliffs to wave attack the resulting erosional hotspots typically were located in the embayments of giant cusps in the southern end of the pocket beaches the observed magnitude of sea cliff retreat which reached 14 m varied with the number of hours that extreme wave runup exceeded certain thresholds representing the protective capacity of the beach during the el nino winter a threshold representing the width of the beach performed better than a threshold representing the elevation of the beach the magnitude of cliff erosion can be scaled using a simple model based on the cross shore distance that extreme wave runup exceeded the pre winter cliff position cliff erosion appears to be a balance between terrestrial mass wasting processes which tend to decrease the cliff slope and wave attack which removes debris and erodes the cliff base increasing the cliff slope

a wave tank experiment on the erosional mechanism at a cliff base a laboratory experiment using a two dimensional wave tank was designed to investigate the mechanism of erosion at a cliff base by waves armed with rock fragments the experiment was performed under constant wave conditions by systematically changing the amount of beach sand at the foot of steep model cliffs of the same slope and strength cliff erosion occurred when the beach material at the cliff beach junction was moved by waves turbulence created by bores rushing up on the beach mobilized the sand and exerted a mechanical shearing force on the cliff face using the sand as an abrasive the analysis of results indicated that the effect of the abrasive doubled when the cliff beach junction was located above still water level swl as compared to when it was below swl the assailing force of the sediment laden water masses was proportional to the square of the bore speed immediately in front of the cliff face the factor of proportionality is related to the quantity of beach sand entrapped in the turbulent fluid

coastal cliff behaviour observations on the relationship between beach levels and recession rates abstract beaches dissipate wave energy and regulate the frequency that the cliff foot is subject to wave attack the relationship between beach levels and cliff recession rates has been established for pleistocene soft rock cliffs along the north norfolk and suffolk coasts uk the results suggest that over a decadal timescale there is a non linear increase in the average recession rate as the beach profile area above high water mark hwm decreases small changes in beach level can result in significant differences in the recession rates the impact of a unit change in beach level on the recession rate depends on the initial beach level on a year by year basis it is possible to divide the beach level and recession relationship into a series of zones with characteristic types of behaviour at low beach levels there is high to extremely high recession with considerable variability whereas at high beach levels there is almost zero recession with limited variability it is concluded that historical recession rates are the product of both the past forcing events and changes in cliff beach state extrapolation of historical rates can be extremely unreliable unless it is supported by an understanding of the dynamic behaviour of the cliff beach system and the energy inputs over the observation period

decadal scale coastal cliff retreat in southern and central california abstract airborne lidar data collected in 1998 and 2009 2010 were used to measure coastal cliff erosion and retreat between the mexico california border and bodega head california cliff erosion was detected along 44 of the 595 km of shoreline evaluated while the remaining cliffs were relatively stable the mean cliff top retreat rate was 0 12 m yr while mean retreat averaged over the entire cliff face was 0 04 m yr the maximum cliff top and face retreat rates were 4 2 and 3 8 m yr respectively historical 1930s to 1998 and recent retreat rates were significantly inversely correlated for areas with large historical or recent cliff retreat such that locations with elevated historical retreat had low levels of recent retreat and locations with elevated recent retreat were preceded by low rates of historical retreat the strength of this inverse correlation increased with cliff change magnitudes up to r2 of 0 91 for cliff top retreat rates 2 9 m yr mean recent retreat rates were 52 83 lower than mean historical retreat rates although beaches can protect cliffs against wave driven erosion cliffs fronted by beaches retreated 49 more than cliffs without beaches on average unarmored cliff faces retreated 0 05 m yr between 1998 and 2009 2010 about three times faster than artificially armored cliffs alongshore metrics of wave cliff impact precipitation and cliff hardness were generally not well correlated with recent cliff changes a cliff hazard metric is used to detect cliff steepening and areas prone to future cliff top failures

coastline retreat via progressive failure of rocky coastal cliffs despite much research on the myriad processes that erode rocky coastal cliffs accurately predicting the nature location and timing of coastline retreat remains challenging and is confounded by the apparently episodic nature of cliff failure the dominant drivers of coastal erosion marine and subaerial forcing are anticipated to increase in the future so understanding their present and combined efficacy is fundamental to improving predictions of coastline retreat we captured change using repeat laser scanning across 2 7 104 m2 of near vertical rock cliffs on the uk north sea coast over 7 yr to determine the controls on the rates patterns and mechanisms of erosion for the first time we document that progressive upward propagation of failure dictates the mode and defines the rate at which marine erosion of the toe can accrue retreat of coastline above this is a failure mechanism not conventionally considered in cliff stability models propagation of instability and failure operates at these sites at 10 yr time scales and is moderated by local rock mass strength and the time dependence of rock fracture we suggest that once initiated failure propagation can operate ostensibly independently to external environmental forcing and so may not be tightly coupled to prevailing subaerial and oceanographic conditions our observations apply to coasts of both uniform and complex lithology where failure geometry is defined by rock mass strength and structure and not intact rock strength alone and where retreat occurs via any mode other than full cliff collapse

assimilating coastal wave observations in regional swell predictions part i inverse methods abstract inverse methods are used to assimilate wave observations into numerical predictions of ocean swell 0 04 0 12 hz surface waves propagating over complex continental shelf bathymetry model predictions of swell on the shelf can be degraded by the limited accuracy and resolution of the initializing offshore unsheltered deep water frequency directional spectra so usually derived from buoy measurements or meteorological hindcasts the authors use a spectral refraction wave propagation model to find improved estimates of so that are consistent with both unsheltered and sheltered altered by coastal bathymetry observations and vary smoothly in direction and time in part i linear and nonlinear inverse assimilation methods are developed their potential and limitations are illustrated qualitatively using a scenario where no a priori knowledge of so is used in the inverse estimates inverse estimates of so based solely on sheltered wave data routinely collected in the southern california bight are

temporal and spatial variations in recession rates and sediment release from soft rock cliffs suffolk coast uk high rates of coastal retreat characterise the weakly cemented plio pleistocene rocks and sediments which form much of the cliffed coastline of east anglia southern north sea the accurate establishment of sediment losses from these cliffs has a regional significance as these sediments are important in maintaining beaches and nearshore bank systems and in feeding nearshore sediment transport pathways however the high spatial and temporal variability of cliff failure processes in such materials necessitates fine scale integration of alongshore variations in cliff retreat over a series of well established time periods to accurately define cliffline recession rates and sediment volume inputs to the nearshore system this study applied the dsas digital shoreline analysis system within the gis software package arcmap to digitised georeferenced positions of former shorelines obtained from historic maps and aerial photographs after 1992 for the sections of benacre southwold and dunwich minsmere on the suffolk coast of east anglia uk transects were cast every 10 m alongshore producing very high spatial resolution upon which to assess shoreline retreat over 1000 transects along 11 km of shoreline long term 1883 2008 mean shoreline retreat rates varied between 2 3 3 5 m a 1 benacre southwold and 0 9 m a 1 dunwich minsmere for six cliffed subunits within these larger coastal sections spatial variations in cliffline recession rates for shorter time intervals at ca 20 year intervals within this longer 125 year period were established the combination of recession rates with photogrammetric methods of obtaining cliff top elevation at the same spatial resolution available using aerial photographs and digital terrain models along with cliff sediment composition allowed the calculation of sediment volumetric inputs from cliff retreat in the period 1992 2008 re assessment of the magnitude and location of sediment inputs into the nearshore zone their interaction with regional sediment transport and the growth of inshore bank systems as well as the implications for contemporary and near future coastal management strategies are discussed with reference to this section of the suffolk coast

retreat rates modalities and agents responsible for erosion along the coastal chalk cliffs of upper normandy the contribution of terrestrial laser scanning in order to follow all the changes affecting the coastal chalk cliff face in upper normandy and improve knowledge about cliff erosion repeated terrestrial laser scanning tls surveys were carried out frequently between 2010 and 2013 every 4 5 months they were conducted at two sites with similar lithostratigraphic characteristics but different exposures to marine actions the former being an abandoned cliff and the latter an active cliff they provide a quantification of the production of debris with centimeter precision from 0 01 to 0 04 m these surveys provided three major outcomes 1 cliff retreat rates were measured at high spatial resolution with retreat values unsurprisingly 3 4 times higher for an active cliff than for an abandoned cliff this result highlights that marine actions should be seen as not only a transport agent but also a particularly effective erosion agent 2 a significant proportion of debris fall production about 25 in the total active cliff retreat was identified and 3 one of the modalities of retreat was visualized as the creation of a basal notch which propagates instability towards the upper part of the cliff face later this instability generates rock falls coming from the whole cliff face

characteristics of sea cliff erosion induced by a strong winter storm in the eastern mediterranean abstract changes in sea cliff morphologies along the 30 km long sharon escarpment segment of israel s weakly cemented mediterranean eolianite cliff line were analyzed to gain quantitative insights into erosion characteristics associated with a high energy winter storm 10 20 year return interval ground based repeat lidar measurements at five sites along the cliff line captured perturbations of cliff stability by basal wave scouring during the storm subsequent post storm gravity driven slope failures in the cliff face above and return of the system to transient stability within several months post storm erosion which amounted to 70 of the total volume of cliff erosion documented resulted in dramatic local effects of up to 8 m of cliff top retreat and yet at the larger scale of the 30 km cliff line examined erosion during the storm and the year that followed affected less than 4 of the cliff length and does not appear to be above the average cliff length annual erosion implied by previously published decadal scale retreat rates along this sea cliff our results do not support a direct association between strong storm events and elevated erosion and retreat at the cliff line scale

dike complexes in american samoa abstract coherent dike complexes in which dikes make up more than 50 of the total rock occur in american samoa in two volcanoes on tutuila and in ofu olosega volcano in the manu a islands the dikes are remarkably narrow median width 0 24 0 36 m average width 0 46 0 56 m based on 860 measured dikes significantly narrower than dikes in the koolau volcano oahu hawaii the most closely comparable volcano for which quantitative data are available the vesicularity of these narrow dikes indicates that they were injected at shallow depths below the land surface depths of 200 900 m are inferred from the topography many dikes have prominent bands of vesicles parallel with their margins they tend to form clusters where the weakness of the vesicular rock favored center injection of one dike up the center of another examples are found of center injection repeated up to eight times local breccias often composed largely of dike fragments evidently brecciated in situ occur where irregular dikes were accommodated by deforming the host rocks we see evidence for two dike facies 1 narrow and vesicle banded early formed and shallow injected clustered dikes in the dike complexes which are cut by 2 scattered broad and almost nonvesicular deep injected solitary dikes surface eruptions were fed by solitary dikes the ene trending dikes and elongation of tutuila island contrast with the wnw trend of rift zones and island elongation elsewhere in samoa tutuila is nearly in line with the north fiji transform fracture zone suggesting that at 1 5 1 0 ma when tutuila was formed the volcanism of tutuila was guided by a temporary extension of this fault zone into the pacific plate fault movement offset the samoan hotspot trace by 45 km the en echelon arrangement of dike exposures on tutuila is consistent with left lateral transcurrent motion above this concealed fracture zone

influence of el nino southern oscillation enso events on the evolution of central california s shoreline significant sea cliff erosion and storm damage occurred along the central coast of california during the 1982 1983 and 1997 1998 el nino winters this generated interest among scientists and land use planners in how historic el nino southern oscillation enso winters have affected the coastal climate of central california a relative enso intensity index based on oceanographic and meteorologic data defines the timing and magnitude of enso events over the past century the index suggests that five higher intensity relative values 4 6 and 17 lower intensity relative values 1 3 enso events took place between 1910 and 1995 the enso intensity index correlates with fluctuations in the time series of cyclone activity precipitation detrended sea level wave height sea surface temperature and sea level barometric pressure wave height sea level and precipitation which are the primary external forcing parameters in sea cliff erosion increase nonlinearly with increasing relative enso event intensity the number of storms that caused coastal erosion or storm damage and the historic occurrence of largescale sea cliff erosion along the central coast also increase nonlinearly with increasing relative event intensity these correlations and the frequency distribution of relative enso event intensities indicate that moderate to high intensity enso events cause the most sea cliff erosion and shoreline recession over the course of a century

evidence of nao control on subsurface ice accumulation in a 1200 yr old cave ice sequence st livres ice cave switzerland mid latitude ice caves are assumed to be highly sensitive to climatic changes and thus represent a potentially interesting environmental archive establishing a precise chronology is however a prerequisite for the understanding of processes driving the cave ice mass balance and thus allows a paleoenvironmental interpretation at st livres ice cave jura mountains switzerland subfossil trees and organic material are abundant in the cave ice deposit therefore allowing the dating of individual ice layers the dendrochronological analysis of 45 subfossil samples of norway spruce picea abies l karst from the overhanging front of the ice outcrop as well as the dating of seven wood samples with 14c dating allowed for a reconstruction of the st livres cave ice sequence and for the determination of periods of ice accumulation and ablation results suggest a maximal age of 1200 50 14c yr bp for the observed ice sequence and indicate the presence of four major deposition gaps dated to the 14th 15th mid 19th and late 19th century which can be related with periods of positive north atlantic oscillation anomalies nao over the winter half year and or anthropogenic cave ice abstraction similarly there is evidence that periods of cave ice accumulation as observed between ad 1877 1900 and ad 1393 1415 would correspond with phases of negative nao indices cave ice represents therefore an original climate archive for the winter half year and is complementary to other continental proxies recording preferentially summer conditions e g tree rings varves

statistical analysis of factors influencing cliff erosion along a section of the west wales coast u k cliff erosion along a section of the west wales coastline is described rockfalls mudslides and retreating fencelines are evidence of current activity measurements over a two year period 1983 85 gave mean annual recession figures of up to 0 25 m yr 1 for glacial embayments wave refraction modelling and longshore beach surveys confirmed the existence of high and low beaches factors influencing variation in recession rates were identified and measured regression analysis suggested that the volume of beach face material was the dominant explanatory variable in short term cliff erosion

a shoreline evolution model considering the temporal variability of the beach profile sediment volume sediment gain loss abstract the prediction of shoreline variability along sandy coastlines is a valuable skill for a broad range of coastal engineering applications currently there are multiple proposals in the literature for equilibrium cross shore shoreline evolution models based on a constant equilibrium condition correlated with the shoreline position the aim of this paper is to present an extension of an existing equilibrium shoreline evolution model adding a rate of change component which in turn modifies the relationship between the equilibrium shoreline position and the incident wave energy as a function that advances or retreats over time the proposed model is applied to two study sites on the spanish coast on the one hand one and a half years of shoreline position data obtained from a video camera system at nova icaria beach catalonia are used to evaluate the shoreline evolution during a period of sediment contribution which is attributed to a sand bypass coming from bogatell beach on the other hand 16 years of shoreline position data acquired from beach profile surveys in campo poseidon huelva are used to reproduce the shoreline evolution taking into account the trend of sediment loss due to sediment drift alongshore the results obtained from both study sites using the proposed model show overall good performance the model successfully represents the general shoreline erosion accretion oscillations and the progressive trend of sediment gains or losses through the evolutionary relationship between the equilibrium shoreline position and the incident wave energy

rain waves and short term evolution of composite seacliffs in southern california abstract a four year time series of nine airborne lidar surveys were used to assess the roles of wave attack and rainfall on the erosion of 42 km of southern california seacliffs nine continuous seacliff sections separated by coastal lagoon mouths all show maximum seacliff erosion in the rainiest time period when wave energy was not particularly elevated and in most sections the squared correlations between rainfall and erosion time series exceeded 0 8 although rain and associated subaerial mechanisms such as groundwater seepage triggered most of the observed seacliff failures wave attack accelerated seacliff erosion with erosion rates of cliffs exposed to wave attack five times higher than at adjacent cliffs not exposed to waves the results demonstrate the importance of both waves and rain in the erosion of southern california seacliffs and suggest that the combined influences of marine and subaerial processes accelerate the erosion rate through positive feedbacks

systematic analysis of rocky shore platform morphology at large spatial scale using lidar derived digital elevation models abstract much of the existing research on rocky shore platforms describes results from carefully selected field sites or comparisons between a relatively small number of selected sites here we describe a method to systematically analyse rocky shore morphology over a large area using lidar derived digital elevation models the method was applied to 700 km of coastline in southwest england a region where there is considerable variation in wave climate and lithological settings and a large alongshore variation in tidal range across shore profiles were automatically extracted at 50 m intervals around the coast where information was available from the coastal channel observatory coastal classification routines were developed to automatically remove non platform profiles the remaining 612 shore platform profiles were then subject to automated morphometric analyses and correlation analysis in respect to three possible environmental controls wave height mean spring tidal range and rock strength as expected considerable scatter exists in the correlation analysis because only very coarse estimates of rock strength and wave height were applied whereas variability in factors such as these can locally be the most important control on shoreline morphology in view of this it is somewhat surprising that overall consistency was found between previous published findings and the results from the systematic automated analysis of lidar data platform gradient increases as rock strength and tidal range increase but decreases as wave height increases platform width increases as wave height and tidal range increase but decreases as rock strength increases previous studies have predicted shore platform gradient using tidal range alone a multi regression analysis of lidar data confirms that tidal range is the strongest predictor but a new multi factor empirical model considering tidal range wave height and rock strength yields better predictions of shore platform gradient root mean square error of predictions reduced by 5 the key finding of this study is that large scale semi automated morphometric analyses have the potential to reveal dominant process controls in the face of small scale local variability

patterns of precursory rockfall prior to slope failure in this paper we examine data generated using high resolution three dimensional laser scanning monitoring of coastal rock cliffs these data are used to identify spatial and temporal patterns in rockfall activity behavior prior to slope failure analysis of the data suggests that given sufficient measurement precision precursory behavior here manifest as the rate of rockfall activity prior to failure can be detected measured and monitored environmental conditions appear to have a diminishing influence on the occurrence of increasingly large slope failures the monitoring data implies a time dependent sequence in the occurrence of smaller rockfalls in the period leading to the largest failures recorded this behavior is attributed to the mechanisms of strain accumulation in the rock mass resulting from brittle failure of the slope the implication is that combining these data with models of failure mechanisms may allow failure time to be forecast from wide area monitoring of precursory behavior these findings have implications for the management of potentially unstable slopes the understanding of slope failure mechanisms and the generation of a new type of slope failure warning systems

a signature of transience in bedrock river incision rates over timescales of 10 4 10 7 years measured rates of river incision into bedrock are commonly interpreted as proxies for rates of rock uplift see refs 1 and 2 for example and indices of the strength of climatic forcing of erosion over time see refs 3 and 4 for example this approach implicitly assumes that river incision rates are in equilibrium with external forcings over a wide range of timescales here we directly test this assumption by examining the temporal scaling of bedrock river incision from 155 independent measurements of river incision compiled from 14 sites of these sites 11 exhibit a negative power law dependence of bedrock river incision rate on measurement interval a relationship that is apparent over timescales of 10 4 10 7 years and is independent of tectonic and geomorphic setting thus like rates of sediment accumulation rates of river incision into bedrock exhibit non steady state behaviour even over very long measurement intervals non steady state behaviour can be explained by episodic hiatuses in river incision triggered by alluvial deposition if such hiatuses have a heavy tailed length distribution regardless of its cause the dependence of incision rate on measurement interval complicates efforts to infer tectonic or climatic forcing from changes in rates of river incision over time or from comparison of rates computed over different timescales

the unsteady nature of sea cliff retreat due to mechanical abrasion failure and comminution feedbacks sea cliff retreat is often linked to large waves heavy precipitation and seismic events but the specific operative mechanics have not been well constrained in particular what is the role of mechanical abrasion by beach sediments in cliff platform evolution and how does it relate to the episodic nature of cliff retreat observed at certain locations here we present a simple numerical model of sea cliff retreat that incorporates mechanical abrasion of a basal notch threshold controlled failure of the cantilevered block and a feedback mechanism wherein retreat is dependent on the rate of sediment comminution within the surf zone using shore platform and cliff characteristics found in two coastal settings the central california coast and the english north sea coast the model produces retreat rates comparable to those observed via field measurements the highest retreat rates coincide with the steepest shore platforms and increasing wave height steeper platforms promote wave access to the cliff toe and correspondingly the receding cliff face produces additional accommodation space for the platform beach preserving the erosive efficacy of the beach sediments when exposed to energetic wave forcing the slope of the inner platform segment controls retreat rates for concave platforms whereas the slope of the outer platform segment exerts greater control for convex platforms platform beaches approached a long term dynamic equilibrium on the concave profiles leading to more consistent and steady retreat platform beaches were ephemeral on convex profiles mirroring observed sand wave ord migration on the holderness coast uk these findings agree with previous field observations and support mechanical abrasion as a viable cause of temporal heterogeneity in cliff retreat rate for both coastlines

comparison of short term seacliff retreat measurement methods in del mar california article i nfo seacliff retreat has been variously characterized as the recession rate of the cliff top of the cliff base and as the bulk recession rate based on volumetric changes of the entire cliff face here these measures of retreat are compared using nine semi annual airborne lidar light detection and ranging surveys of southern california seacliffs changes in the cliff base location where the steeply sloping cliff face intersects the beach include cliff retreat owing to basal erosion but also reflect changes in beach sand level and basal talus deposits averaged over the 2 5 km alongshore study span the cliff base actually prograded seaward about 12 cm during the 4 year study cliff top change was dominated by few relatively large several meters localized retreats cliff face changes that include failures and deposits anywhere on the cliff profile had a relatively small mean magnitude compared to cliff top changes and were more widely distributed alongshore however the similar alongshore averaged cumulative cliff top and net bulk cliff face end point retreat 14 and 19 cm respectively suggest that mean cumulative cliff top retreat can potentially be a viable surrogate for mean net cumulative cliff wide erosion and vice versa over relatively short time periods cliff face erosion occurred repeatedly at some locations confirming the presence of seacliff erosion hot spots during the study period

processes of coastal bluff erosion in weakly lithified sands pacifica california usa abstract coastal bluff erosion and landsliding are currently the major geomorphic processes sculpting much of the marine terrace dominated coastline of northern california in this study we identify the spatial and temporal processes responsible for erosion and landsliding in an area of weakly lithified sand coastal bluffs located south of san francisco california using the results of a five year observational study consisting of site visits terrestrial lidar scanning and development of empirical failure indices we identify the lithologic and process controls that determine the failure mechanism and mode for coastal bluff retreat in this region and present concise descriptions of each process bluffs composed of weakly cemented sands unconfined compressive strength ucs between 5 and 30 kpa fail principally due to oversteepening by wave action with maximum slope inclinations on the order of 65 at incipient failure periods of significant wave action were identified on the basis of an empirical wave run up equation predicting failure when wave run up exceeds the seasonal average value and the bluff toe elevation the empirical relationship was verified through recorded observations of failures bluffs composed of moderately cemented sands ucs up to 400 kpa fail due to precipitation induced groundwater seepage which leads to tensile strength reduction and fracture an empirical rainfall threshold was also developed to predict failure on the basis of a 48 hour cumulative precipitation index but was found to be dependent on a time delay in groundwater seepage in some cases

subaerial weathering versus wave processes in shore platform development reappraising the old hat island evidence one of the longest standing debates in rocky coast geomorphology is whether subaerial weathering or wave processes dominate shore platform evolution the origins of this debate date to the mid nineteenth century when the first descriptions of old hat islands were provided from northern new zealand old hat islands are surrounded by a broad near horizontal shore platform their formation was inferred to relate to subaerial weathering of bedrock to a level of permanent saturation with wave processes acting only to remove the weathered debris to date no detailed topographic surveys have been conducted on the old hat islands in new zealand that initiated this debate in this study we provide the first quantitative data on the original field sites topographical surveying and schmidt hammer hardness testing were conducted on 25 profiles of varying wave exposure in contrast to the classic descriptions platform elevation varies from just above mean high water spring mhws at the most exposed sites to mean high water neap mhwn at the most protected sites or mean sea level msl where beaches occur on the platform surface there is no significant difference between the hardness of the cliffs and the platforms fronting them and no clear relationship between wave exposure and platform width rather than being exclusively dominated by subaerial process the formation of microtidal sheltered old hat island platforms is considered to be a function of i the rate of weathering ii exposure to wave energy iii nearshore water depth and iv rock resistance shore platform elevation in the study area is thought to be a function of the level at which waves erode cliff rock and the action of weathering which lowers platform surfaces the width of platforms is strongly influenced by the ability of waves to dissect the platform edge along vertical joint lines copyright 2010 john wiley sons ltd

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

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

recent deep seated coastal landsliding at san onofre state beach california abstract airborne lidar collected during the period 1998 2010 and differential gps surveys conducted over 2008 2013 show recent reactivation and movement of a large deep seated coastal landslide at san onofre state beach san diego county california the overall slide complex extends about 700 m alongshore 150 m inland and an unknown distance offshore differencing digital elevation models and tracking field monuments benchmarks provide time series of quantitative topographic landslide changes and new insight in to the slide motion sequences and mechanics the slide contains several distinct primary and secondary regions moving and deforming at different rates primary slide motion includes slow seaward translational motion rotational slipping and upward offshore movement secondary processes of basal wave erosion and new inland cliffline failures contribute to primary landslide destabilization the landslide exhibits lithologic and structural controls is driven by a combination of marine and subaerial processes influences local beach morphology and deviates from typical southern california coastal cliff processes which mostly involve shallow landslides and topples large scale cross shore slide rotation has recently created new nearshore reefs eroded cliff sediments provide a local beach sand source and probably influence local nearshore ecosystems all known time periods of major historical landslide activity were preceded by elevated seasonal rainfall and analysis suggests elevated rainfall generated primary slide motion as opposed to wave action as of spring 2013 landslide activity has slowed but continued positive feedbacks including toe removal by wave activity suggest that future landsliding will probably threaten coastal infrastructure

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

temporal and spatial variations of chalk cliff retreat in east sussex 1873 to 2001 spatial and temporal variations of chalk cliff retreat rates over a 130 yr period are examined for 22 km of the east sussex chalk coastline between brighton and belle toutetout lighthouse england data are derived from maps surveyed between 1873 and 1925 28 and air photographs dating from 1973 and 2001 the long term average cliff retreat rate over the period 1873 to 1973 is 0 36 m y 1 and from 1873 to 2001 is 0 35 m y 1 over the whole 23 km study area rates calculated over shorter time slices indicate a decline in cliff retreat 0 37 m y 1 between 1873 and 1925 28 0 35 m y 1 between 1925 28 and 1973 0 27 m y 1between 1973 and 2001 temporal variations are unlikely to be due to variations in precipitation and frost days though the relationship remains uncertain due to the resolution of available cliff retreat and climatic data changes in wave climate are small and cannot be responsible for the decline in cliff retreat the study suggests that the most important factors causing the measured decline in cliff retreat rates are firstly the loss of cliff toe beaches over time and secondly widening of the rocky shore platforms that front the cliffs some of the spatial variability in retreat rates can be explained by local variations in lithology

measuring erosion rates using the micro erosion meter 20 years of data from shore platforms kaikoura peninsula south island new zealand abstract fifteen micro erosion meter sites giving 42 individual readings of erosion were remeasured twenty years after installation on mudstone and limestone shore platforms on the kaikoura peninsula south island new zealand the mean annual surface lowering rate was calculated to be 1 43 mm yr longer term data were compared to shorter term data collected over a two year period between 1973 and 1975 to test the validity of extrapolating average erosion rates from shorter term data it was found that the average lowering rate for the shorter term data were in statistically acceptable agreement with those for the longer term data extrapolation of short term micro erosion meter data is therefore acceptable in this particular environment in previous work it has been suggested that measurements from as few as thirty individual micro erosion meter positions are required to calculate a mean annual lowering rate on shore platforms measurements from 30 mem positions provided an statistically acceptable mean annual lowering rate for shore platforms on the kaikoura peninsula

fifty years of coastal erosion and retrogressive thaw slump activity on herschel island southern beaufort sea yukon territory canada abstract patterns of coastal erosion in the arctic differ dramatically from those coasts in more temperate environments thick sea ice and shore fast ice limit wave based erosional processes to a brief open water season however despite this permafrost coasts containing massive ice ice wedges and ice bonded sediments tend to experience high rates of erosion these high rates of erosion reflect the combined thermal mechanical processes of thawing permafrost melting ground ice and wave action climate change in the arctic is expected to result in increased rates of coastal erosion due to warming permafrost increasing active layer depths and thermokarst rising sea levels reduction in sea ice extent and duration and increasing storm impacts with the most ice rich permafrost in the canadian arctic the southern beaufort sea coast between the tuktoyaktuk peninsula and the alaskan border is subject to high rates of erosion and retrogressive thaw slump activity under many climate change scenarios this area is also predicted to experience the greatest warming in the canadian arctic this paper presents results of a remote sensing study on the long term patterns of coastal erosion and retrogressive thaw slump activity for herschel island in the northern yukon territory using orthorectified airphotos from 1952 and 1970 and an ikonos image from 2000 corrected with control points collected by kinematic differential global positioning system and processed using softcopy photogrammetric tools mean coastal retreat rates of 0 61 m yr and 0 45 m yr were calculated for the periods 1952 1970 and 1970 2000 respectively the highest coastal retreat rates are on north west facing shorelines which correspond to the main direction of storm related wave attack during the period 1970 2000 coastal retreat rates for south to south east facing shorelines displayed a distinct increase even though these are the most sheltered orientations however south to south east facing shorelines correspond to the orientations where the highest densities of retrogressive thaw slumps are observed differences in rates of headwall retreat of retrogressive thaw slumps and coastal erosion results in the formation of larger thermokarst scars and the development of polycyclic thaw slumps on south to south east exposures the number and the total area of retrogressive thaw slumps increased by 125 and 160 respectively between 1952 and 2000 as well the proportion of active retrogressive thaw slumps increased dramatically polycyclic retrogressive thaw slumps appear to develop in a periodic fashion related to retrogressive thaw slump stage and maximum inland extent

the california coastal wave monitoring and prediction system abstract a decade long effort to estimate nearshore 20 m depth wave conditions based on offshore buoy observations along the california coast is described offshore deep water directional wave buoys are used to initialize a non stationary linear spectral refraction wave model model hindcasts of spectral parameters commonly used in nearshore process studies and engineering design are validated against nearshore buoy observations seaward of the surfzone the buoy driven wave model shows significant skill at most validation sites but prediction errors for individual swell or sea events can be large model skill is high in north san diego county and low in the santa barbara channel and along the southern monterey bay coast overall the buoy driven model hindcasts have relatively low bias and therefore are best suited for quantifying mean e g monthly or annual nearshore wave climate conditions rather than extreme or individual wave events model error correlation with the incident offshore wave energy and between neighboring validation sites may be useful in identifying sources of regional modeling errors

short term patterns and processes of coastal cliff erosion in santa barbara california abstract sequential terrestrial lidar scans and 3d volumetric change were used to document coastal cliff erosion at several sites along the coast of santa barbara california retreat rates along the base middle and cliff top were calculated for six different scans throughout the el nino of 2015 16 to quantitatively link wave action to cliff base erosion and two seasonal scans were taken during 2017 to investigate patterns in erosion and retreat rates retreat rates along the cliff base middle and top converged over the course of the study period and observations and patterns in erosion help characterize the fundamental mechanisms that govern the retreat of soft shale cliffs the base and middle of the cliff preferentially eroded during high energy swell events and are strongly coupled whereas cliff top erosion is temporally variable and retreat rates increased with higher seasonal rainfall totals we observe that the cliff base experiences erosion from both abrasion and mechanical wave action but the dominant processes is segregated by elevation above the cliff toe abrasion was found to be the dominant processes at elevations up to 0 8 m above the cliff toe whereas block removal from mechanical wave action was dominant at elevations above 0 8 m threshold behavior was observed for cliff base retreat rates and spearman correlation coefficients suggest strong relationships with the sum of the wave energy flux imparted to the cliff base r2 0 84 the sum of the wave energy flux 35 000 w m r2 0 82 and the average total water level above the cliff toe r2 0 85 threshold behavior and maximum retreat rates occurred when average total water levels were 0 8 m above the cliff toe seasonal schmidt hammer measurements suggest that energy thresholds are modulated by weathering rates which remain poorly understood these thresholds when exceeded produced the highest cliff base retreat rates during the study period and reinforce the expectation that coastal cliff retreat rates will increase with rising sea levels

coastal erosion and mass wasting along the canadian beaufort sea based on annual airborne lidar elevation data abstract erosion of permafrost coasts has received increasing scientific attention since 1990s because of rapid land loss and the mobilisation potential of old organic carbon the majority of permafrost coastal erosion studies are limited to time periods from a few years to decades most of these studies emphasize the spatial variability of coastal erosion but the intensity of inter annual variations including intermediate coastal aggradation remains poorly documented we used repeat airborne light detection and ranging lidar elevation data from 2012 and 2013 with 1 m horizontal resolution to study coastal erosion and accompanying mass wasting processes in the hinterland study sites were selected to include different morphologies along the coast of the yukon coastal plain and on herschel island we studied elevation and volume changes and coastline movement and compared the results between geomorphic units results showed simple uniform coastal erosion from low coasts up to 10 m height and a highly diverse erosion pattern along coasts with higher backshore elevation this variability was particularly pronounced in the case of active retrogressive thaw slumps which can decrease coastal erosion or even cause temporary progradation by sediment release most of the extremes were recorded in study sites with active slumping e g 22 m of coastline retreat and 42 m of coastline progradation coastline progradation also resulted from the accumulation of slope collapse material these occasional events can significantly affect the coastline position on a specific date and can affect coastal retreat rates as estimated in long term by coastline digitalisation from air photos and satellite imagery these deficiencies can be overcome by short term airborne lidar measurements which provide detailed and high resolution information about quickly changing elevations in coastal areas

modeling cohesive clay coast evolution and response to climate change a model was used to study the evolution of cohesive clay coasts under different environmental and geological conditions and the effect of future climate change the model considered wave impact on the bluff and in the intertidal zone and bottom generated shear stresses and the protective and abrasive action of beach sediment in the intertidal and subtidal zones quasi equilibrium conditions developed in model runs with parallel slope retreat in the upper portion of the profiles and slope decline in the lower portions profile gradient below the low tidal level increased with the threshold shear stress for bottom erosion therefore rates of wave attenuation were lower in resistant than in weak materials and the intertidal zones were wider and more gently sloping the widest and gentlest intertidal zones developed in runs that had no sediment the largest waves played little role in platform development in part because of low frequency but mainly because they expend most of their energy in crossing wide turbulent surf zones the model suggested that rising sea level will usually result in accelerated rates of bluff recession especially if the rise is rapid simultaneous increases in the frequency of moderately large waves as opposed to the largest waves may also generate marked increases in erosion on bluffs and in intertidal and supratidal zones although erosion may be reduced at some elevations where there is beach sediment positive or negative changes in beach volume can increase or decrease rates of bluff erosion

rocky coasts their role as depositional environments abstract the role of rocky coasts as depositional environments has been generally neglected by rock and depositional coast workers although rock coasts can be hostile sedimentary environments they frequently host a variety of deposits consisting of mixes of boulders and megaclasts to sand and cobbles these deposits include pockets of sand and pebble trapped in topographic depressions or at the foot of scarps and cliffs isolated boulders pocket beaches trapped between headlands and sand to boulder beaches in shallow bays exposed to strong wave action the tectonic setting which is reflected in the degree of geological heterogeneity alongshore together with the wave regime and other elements of the morphogenic environment help to determine the amount and mobility of the sediment and consequently whether it plays an essentially abrasional or protectional role many beaches have a resistant rock foundation which will modulate their response to rising sea level and possibly increased storminess during this century wave refraction and temporal and spatial changes in sediment abrasional and protectional efficacy influence the development of crenulated planforms on coasts with a high degree of geological heterogeneity and possibly on more geologically homogeneous coasts with longshore variations in cliff height or in the amount of sediment theory suggests that these coasts may develop equilibrium planforms with uniform rates of erosion in bays and on headlands or they may undergo a series of cyclical transformations involving alternating increases and decreases in the depth of the bays relative to the headlands

sediment contribution from israel s coastal cliffs into the nile s littoral cell and its significance to cliff retreat mitigation efforts abstract we quantify the volumetric erosion of israel s actively retreating mediterranean coastal cliffs between 2006 and 2015 with airborne lidar our results reveal annual sand contribution of 45 000 m3 from the coastal cliffs into the nile s littoral cell nlc which amounts to 50 of the annual long shore sand transport previously measured at the northern termination of the nlc accordingly we find that implementation of cliff retreat mitigation engineering efforts planned for israel s coastline can lead to a sand deficit in the nlc that may result in increased beach erosion