Sea Cliffs Research Articles

Sea cliff instability susceptibility considering nearby human occupation and predictive capacity assessment

Slope mass movements are the dominant process of sea cliff evolution and are a threat to occupation and human activities located nearby. This fact is compounded with the rapidly increasing human occupation and concentration of economic activities in coastal areas, making cliff hazard assessment a relevant topic. This study was made to assess the effectiveness of a statistically based approach to cliff failure susceptibility assessment in the slowly receding sea cliffs of Mafra County (western coast of Portugal), using the logistic regression method and considering the possible influence of human occupation near the cliffs top, and also to test the true predictive capacity of the susceptibility models produced.The susceptibility assessment was made using number of cliff failure predisposing factors related with geology, geomorphology, wave power and human occupation, which were correlated with a multi-temporal inventory of sea cliff failures for the period 1947–2012, and also with the temporal partition of the cliff failure inventory for the periods 1947 to 1980 and 1980 to 2012, which were used as training and validation sets to test the real predictive capacity of the models generated.The susceptibility models were validated using standard “Receiver Operating Characteristic Curves” (ROC) and the respective “Area Under the Curve” (AUC) which provided encouraging results when compared with the records of past instabilities. However, the predictive capacity computed by the temporal partition of the inventory data was weak, indicating that further studies are required to: 1) assess the monitoring time periods required to provide statistically representative cliff failure inventories in low retreat cliffs, with implication on hazard assessment and long term evolution modeling; 2) cliff failure predisposing factors and their variation along time, namely those related with the human activities and occupation, and also on the cliff failure conditioning and triggering external factors.In spite of this problem, the results obtained with the global inventory data of 1947–2012, which showed good adjustment to the input data, but also on the validation against the time partitions of the inventory, suggest that the selected techniques are viable tools to map sea cliff instability susceptibility and to predict the location of the most critical areas where future instabilities are more likely to occur.

Reliability Analysis of Sea Cliff Slope Stability by Point Estimate Method

The paper presents a reliability analysis of a sea cliff slope. The cliff, located in Jastrzębia Góra, is characterised by a complicated geological structure. Although currently stable, it is in fact close to the limit state. The objective of this paper is to present the point estimate method (PEM) of determining the mean value and standard deviation of the safety factor of the slope. Assuming its normal distribution, these statistical parameters make it possible to determine the probability of failure pf and the reliability index β. In order to reduce the number of random variables, a sensitivity analysis was performed. The results were verified by the Monte Carlo simulation method. The main advantage of this approach is to minimize the number of sample calculations required to obtain estimators of the parameters investigated.

Pleistocene fauna of the Cape south coast revealed through ichnology at two localities

East of Still Bay on the Cape south coast of South Africa lies a rugged, remote stretch of sea cliffs that expose Late Pleistocene aeolianites. A zone of dense concentration of fossil tracks occurs within this area. Two large rocks, which we call Roberts Rock and Megafauna Rock, were identified ~400 metres apart. These rocks contained a variety of trackways, individual tracks, burrow traces and invertebrate trace fossils on multiple bedding planes. Both rocks were found ex situ, but their context could be determined. Roberts Rock has subsequently slid into the ocean, and Megafauna Rock lies at the base of a coastal cliff. Probable trackmakers include elephant, long-horned buffalo, giant Cape horse, rhinoceros, medium and small artiodactyls, golden mole, birds and invertebrates. Dating studies at an adjacent site, which is comparable to the stratigraphy described here, indicate that both rocks were most likely deposited in Marine Isotope Stage 5e (~128–116 ka). Analysis and description of these tracksites confirms the potential of ichnology to complement the skeletal fossil record and to enhance the understanding of Pleistocene life in southern Africa. The ephemeral nature of such tracksites makes repeated visits to this coastline desirable, both to monitor the fate of known sites and to search for newly exposed trace fossil surfaces.
 Significance:
 
 Roberts Rock and Megafauna Rock are two remarkable fossil tracksites on the Cape south coast, which contain tracks of four members of the Late Pleistocene megafauna. They provide a glimpse of Pleistocene dune life and suggest an area teeming with large mammals.
 These tracks were made on dune surfaces near an interface between the grassland of the Palaeo-Agulhas Plain and the inland Fynbos–Strandveld–Renosterveld. Faunal assemblages from both vegetation zones might therefore be recorded.
 The trace fossil record and body fossil record both have inherent biases, but have the potential to independently provide complementary information on palaeofaunal composition.
 The two rocks have provided the first South African records of fossil elephant tracks (as first described by Dave Roberts and colleagues in 2008), the first rhinoceros track and the first extinct giant Cape horse track, and track evidence of the extinct long-horned buffalo.
 Roberts Rock has slumped into the ocean, and it provides an example of the fate of many exposed tracksites. Conversely, new sites frequently become exposed. This scenario stresses the need for regular ichnological surveys along this track-rich coastline to monitor existing sites and to search for new sites.

Detection and analysis of mass wasting events in chalk sea cliffs using UAV photogrammetry

Coastal cliff recession represents a significant risk to both people and infrastructure, it is therefore important that we are able to efficiently monitor these environments to inform future management decisions. Through the use of UAV digital photogrammetry, we obtain point clouds to develop monthly models of the sea cliffs at Telscombe, East Sussex, UK between August 2016 and July 2017. The models captured were accurate to 0.05 m and had an average point density of 351 pts./m2. Using the methodology presented we were able to automatically detect rockfalls by undertaking a 2.5D surface change detection which populated monthly inventories through volumetric estimations. A total of 10,085 failures were observed with an estimated volumetric flux of 3889.4 m3 over the 12 month period of data collection. Due to the high frequency of data capture, successive block failures in the Newhaven Chalk formation were observed. The largest failure within the 12 month period was estimated at 2546.8 m3 and followed significant toe erosion due to wave action. The steepening of the cliff face was modelled through limit equilibrium analysis to determine the reduction in factor of safety for the months preceding failure. We then present a magnitude-frequency analysis using negative power laws from the monthly rockfall inventories for the entire study area. The negative power law models produced a strong correlation across all months with r2 values ranging from 0.97 to 0.99. The normalised power law scaling parameters ranged from 1.421 to 1.955 for β and from 33.79 to 904.14 for s. The observed rollover in power laws presented in previous research matches the resolution of the data presented in this study. Our results show that this method of data capture is comparable to existing methods whilst offering significant benefits in field surveying time and cost.

A Survey of Culturable Fungal Endophytes From Festuca rubra subsp. pruinosa, a Grass From Marine Cliffs, Reveals a Core Microbiome.

Festuca rubra subsp. pruinosa is a perennial grass that inhabits sea cliffs of the Atlantic coasts of Europe. In this unhospitable environment plants grow in rock crevices and are exposed to abiotic stress factors such as low nutrient availability, wind, and salinity. Festuca rubra subsp. pruinosa is a host of the fungal endophyte Epichloë festucae, which colonizes aerial organs, but its root mycobiota is unknown. The culturable endophytic mycobiota of FRP roots was surveyed in a set of 105 plants sampled at five populations in marine cliffs from the northern coast of Spain. In total, 135 different fungal taxa were identified, 17 of them occurred in more than 10% of plants and in two or more populations. Seven taxa belonging to Fusarium, Diaporthe, Helotiales, Drechslera, Slopeiomyces, and Penicillium appeared to be constituents of the core microbiome of Festuca rubra subsp. pruinosa roots because they occurred in more than 20% of the plants analyzed, and at three or more populations. Most fungal strains analyzed (71.8%) were halotolerant. The presence of Epichloë festucae in aboveground tissue was detected in 65.7% of the plants, but its presence did not seem to significantly affect the structure of the core or other root microbiota, when compared to that of plants free of this endophyte. When plants of the grass Lolium perenne were inoculated with fungal strains obtained from Festuca rubra subsp. pruinosa roots, a Diaporthe strain significantly promoted leaf biomass production under normal and saline (200 mM NaCl) watering regimes. These results suggest that the core mycobiome of Festuca rubra subsp. pruinosa could have a role in host plant adaptation, and might be useful for the improvement of agricultural grasses.

Coastal dune hydrology and its influence on maritime occupation sites (12–0.2 ka) in a semiarid island, San Miguel, California, USA

AbstractMaritime occupation sites in upland dune settings (10–150 m elevation mean sea level) in San Miguel Island (37 km2 in size), located 40 km offshore of the south‐central California mainland, were analyzed for reported ages, component types, and distances from paleo‐shorelines around the island’s shelf platform. The occupation sites (dated ~12,200 to 200 cal B.P.) include numerous shell middens and lithic scatters. Some sites contain Paleocoastal stemmed points and chipped stone crescents, the latter believed to be used for hunting waterfowl. What prompted the site occupations in the semiarid dune‐covered coastal bluffs and interior‐plateaus that were located 10–150 m above and 1–4 km distant from age‐correlative paleo‐shorelines? Eolianite dune settings in San Miguel include ephemeral freshwater sources from: (a) vernal pond/wetlands in interior plateaus; (b) gullies or creeks in the dune‐covered bluff slopes; (c) springs exposed in current sea cliffs or canyons; and (d) pond/wetlands barraged by sand ramps on the windward bluff slopes and gully drainages. These freshwater features are proposed to have attracted humans and their hunting, shellfish processing, and plant gathering activities to upland localities, as now preserved above the island’s shelf platform that was submerged by the Holocene marine transgression.

Morphodynamics of beach-cliff systems in the Santa Barbara littoral cell

A better understanding of the main factors and mechanisms that shape the long-term cliff morphology is essential for effective responses to future coastal cliff erosion threats and occurrences. In this study, the interactions among sea cliff morphology, beach morphology, and coastal hydrodynamics were investigated for eight coastal sites near Santa Barbara, California. This investigation utilizes Digital Elevation Model data, and historical shoreline and cliff edge survey data. It was found that, for the study sites with similar meteorological characteristics, the cliff slope is negatively correlated with the beach width and height, and the cliff slope is governed by the inundation number, which is the ratio of the effective wave run-up height and beach-cliff junction height. Distinct shoreline erosion or accretion trends were not observed for most of the eight sites. Buffer zones of beach-cliff systems, however, have been widening mainly due to cliff erosion. Among the study sites, the widening of the buffer zone was larger for wider beaches, where cliff slopes were gentler. Our analysis indicated that long-term cliff erosion in Southern California may be estimated by using adequate wave-induced cliff erosion models.

Structural variation and the development of thick rhyolite lava: A case study of the Sanukayama rhyolite lava on Kozushima Island, Japan

Geological studies of ancient rhyolite lavas are required for understanding flow dynamics because rhyolite lava eruption is an infrequent event. The Pleistocene Sanukayama rhyolite lava is about 130 m thick and located on Kozushima Island, Japan. Vertical sections of the lava are well exposed in the sea cliff and in a dissected valley, providing a good opportunity for the elucidation of the internal structural variations. The vertical lithofacies variations are classified into three zones of pumiceous, obsidian, and crystalline from the top to the base, respectively. The exposed area is considered to correspond to the upper half of the lava. In the boundaries between each zone, the lithofacies are mingled rather than exhibiting gradual change. This indicates that rheological contrasts are arisen within the lava due to differences of vesicularity and/or crystallinity. Various heterogeneous structures are recognized throughout the lava such as obsidian and reddish layers in the pumiceous zone, strongly deformed white-colored bands and a clastic layer in the obsidian zone, and dark-colored bands in the crystalline zone. We demonstrate on the basis of geological evidences and magnetic studies that these heterogeneous structures originated mostly from shear-induced fracturing within the advancing lava. This study indicates that brittle lava fracturing during ductile-brittle transition likely governs the acceleration of rhyolite lava heterogeneity.

The new V&A, Dundee: Dundee's new cliff.

In addressing the assembled media, the rather poetic metaphor first used by the architect Kengo Kuma as he described the building was that of a sea cliff; something that strove to mediate between land and water, city and landscape. An abstract reference but one that has clearly provided a rich seam for exploration in architectural form. On a more prosaic but nevertheless equally aspirational note, he also wished the museum to provide a new ‘living room’ for the city. This latter is something that, if successfully realised, might perhaps offer more tangible benefits to the good people of Dundee. John Alexander, the (astonishingly young) leader of the City Council, also made play on the idea and went further to suggest that the coming of this new institution put ‘new fire in the belly of Dundonians’ . High aspirations indeed but exactly the kind of social and sensual mixture that an architect of good conscience and ability will seek to combine in a coherent whole. This is perhaps …

The Misery Point cliff, Mayaguana Island, SE Bahamas: a unique record of sea-level highstands since the Early Pleistocene

We describe in detail a unique succession of Lower Pleistocene shallow-water carbonates exposed at the Misery Point sea cliff along the northern shoreline of Mayaguana Island (SE Bahamas). This km-scale outcrop comprises a record of seven past sea-level highstands that occurred between ca. 1.3 Ma and 125 ka ago, and reached relative elevations from 3 to possibly 14 m above modern sea level. Considering the tectonic stability of the Mayaguana platform in the Quaternary, the amplitudes of the recorded events could be fairly close to the corresponding glacio-eustatic changes, and thus provide calibration points for sea-level proxies derived from the deep-sea oxygen-isotope records and ice-sheet models. Moreover, our study traces the evolution of the Mayaguana bank over the past 1.3 million years, provides some insight on the birth of possibly the first island of the Bahamas archipelago, and emphasizes that the shift from bioclastic to oolitic-peloidal carbonates (i.e. the transition from the pre-Lucayan to the Lucayan limestones) occurred much later on this platform than on the northern Bahamian banks, which raises questions about the origin of this transition.

Overestimation of short‐term coastal cliff retreat rates in the eastern Mediterranean resolved with a sediment budget approach

AbstractOur understanding of sea‐cliff erosion processes and their response to recent and/or projected environmental changes such as sea‐level rise, climate change and anthropogenic development hinges on our ability to quantify sea‐cliff retreat rates and their variability through time. Here, we focus on Israel's Mediterranean ‘Sharon’ sea‐cliff as a case study for examining the significance of recent short‐term (i.e. annual to decadal) cliff‐top retreat rates that appear to exceed longer‐term rates of ‘background’ (i.e. centennial to millennial) retreat by 1–2 orders of magnitude. We demonstrate that an inherent sampling bias in rate estimates inferred from observation intervals shorter than process episodicity can also explain such a pattern. This potential ambiguity leads to a striking paradox where despite highly accurate and robust documentation of recent cliff‐top retreat, such as that obtained from aerial photographs and/or instrumental surveys, the short‐term retreat rates of episodically retreating sea cliffs remain poorly constrained. To address this key data gap along the Sharon sea cliff we employed a sediment budget approach that focuses on quantifying the continuous wave scouring of cliff‐collapsed material from the shore platform as a rate‐limiting process for episodic retreat of the cliff above. We used four high‐resolution (0.5 m/pixel) airborne LiDAR data sets acquired between 2006 and 2015 to determine short‐term maximum retreat rates of up to ~0.08 m/yr during this nine‐year period. These modern retreat rates compare to the cliff's background retreat rate of 0.03 to 0.09 m/yr since the mid‐Holocene, as determined herein from multiple geologic and archeological observations. Our results demonstrate that previously reported twentieth century cliff‐top retreat rates for this sea cliff, which range up to values of several meters per year, are biased and that sea‐cliff erosion rates have not yet been significantly impacted by recent environmental changes in the eastern Mediterranean basin, such as the restriction of sediment supply following emplacement of the Nile's Aswan dam system. © 2018 John Wiley & Sons, Ltd.

Terrestrial Gastropoda from the Pleistocene of Beni Saf, NW Algeria

A study of the terrestrial gastropods of the Pliocene-Quaternary succession of the Beni Saf sea cliff, NW Algeria, at the Playa Port locality, is presented herein. The sedimentary succession is subdivided into four lithostratigraphic units, on the basis of their lithologic and biogenic contents: the three first units (A, B and C) are of marine origin; the last unit (D) is of continental origin and includes three beds yielding terrestrial gastropod fossils, which form laterally traceable horizons. Herein, we describe the section's lithology, present stratigraphical considerations regarding its age and thoroughly described its terrestrial gastropod fossil fauna. In total, 13 species are reported here from Beni Saf: 2 caenogastropods (family Pomatiidae) and 11 stylommatophorans (family Achatinidae and superfamily Helicoidea). The sedimentological data indicate that the depositional setting at Beni Saf was a dune system flanked by wadi floodplains deposits (snail levels); the ecological preferences of the gastropods largely agrees with this scenario.

Headland or stack? Paleogeographic reconstruction of the coast at the Faraglioni Middle Bronze Age Village (Ustica Island, Italy)

The Faraglioni Village at volcanic island of Ustica (Palermo, Sicily) is one of the best preserved coastal Middle Bronze Age site of the Mediterranean area. It was built on a marine terrace overlooking the sea. Although the southern border of the Village is well defined, many doubts concern its past extent toward the sea. Around 3250-3200 BP the inhabitants suddenly abandoned the site, leaving all their belongings. This sudden flight could be related to a natural disaster that induced the population to find a safer place, or to a hostile invasion from the sea. The coast is formed by 20 m-high sea cliffs, which are often subject to collapses. A small platform develops at the cliff toe and it is locally covered by a beach with pebbles, cobbles and rounded blocks. Off-shore, in front of the archaeological village, a stack, called Colombaio, occurs. It is 17 m x 11 m wide at the top, roughly at the same elevation above the sea level of the terrace on which is located the Faraglioni Village, and it lies about 60 m from the sea cliffs. The latter are cut in columnar basalts, roughly 1 meter in size. A sea cave, 14 m long, 6 m large and 9 m high was discovered inside the stack during the field surveys. There are many submerged or slightly emerged rocks in the canal between the stack and the mainland. Since archaeological remains have been found on the top of the stack, archaeologists suppose that there was a connection with the mainland. Literature suggested that most probably a natural bridge connected the stack and the coast; and that it collapsed as a result of a natural catastrophic event, such as an earthquake. Bathymetric data compared to the sea level change models suggest that the area of the village was largest than nowadays, but the retreat rate is unknown, so it is impossible to estimate the Bronze Age extent of the village and assert that it was certainly connected with the stack. The separation of the stack from the coast could have happened long time before the Bronze Age. Probably, only the so-called Nerone stack was connected during the Bronze Age. However, it is not necessary to hypothesize the occurrence of a natural “bridge” or a human -made connection with the stack from the mainland at the same elevation of the village, because during the Middle Bronze Age, about 3400-3200 BP, the sea level was 3 meter lower than today and the path between the mainland and the stack was about 1 m above the past sea level. The stack was isolated from the village only during severe storms.

A model for calculating the erosion distance of soft sea cliff under wave loading

A model for calculating the erosion distance of soft sea cliff under wave loading is established based on the erosion mechanism of soft sea cliff under wave loading and for considering wave hydrodynamic and sea cliff material parameters. The model is verified, and the parameters are regressed using an indoor flume experiment. The erosion distances of the sea cliff in the northeast of the Pingtan Island are calculated by the model, and the results are compared with the measured data. The maximum erosion occurs in static water level, the location of the maximum erosion moves up as the wave continues, and the erosion stops when the wave lasts for a period of time. The erosion does not occur until the wave height exceeds a critical value; however, the contribution of large waves to the erosion is not relatively substantial. The calculated erosion distances at two places in the northeast of Pingtan Island are 0.32 m and 0.26 m.

A Model Ensemble for Projecting Multidecadal Coastal Cliff Retreat During the 21st Century

AbstractSea cliff retreat rates are expected to accelerate with rising sea levels during the 21st century. Here we develop an approach for a multimodel ensemble that efficiently projects time‐averaged sea cliff retreat over multidecadal time scales and large (>50 km) spatial scales. The ensemble consists of five simple 1‐D models adapted from the literature that relate sea cliff retreat to wave impacts, sea level rise (SLR), historical cliff behavior, and cross‐shore profile geometry. Ensemble predictions are based on Monte Carlo simulations of each individual model, which account for the uncertainty of model parameters. The consensus of the individual models also weights uncertainty, such that uncertainty is greater when predictions from different models do not agree. A calibrated, but unvalidated, ensemble was applied to the 475‐km‐long coastline of Southern California (USA), with four SLR scenarios of 0.5, 0.93, 1.5, and 2 m by 2100. Results suggest that future retreat rates could increase relative to mean historical rates by more than twofold for the higher SLR scenarios, causing an average total land loss of 19–41 m by 2100. However, model uncertainty ranges from ±5 to 15 m, reflecting the inherent difficulties of projecting cliff retreat over multiple decades. To enhance ensemble performance, future work could include weighting each model by its skill in matching observations in different morphological settings.

Variations in volumetric erosion rates of bedrock cliffs on a small inaccessible coastal island determined using measurements by an unmanned aerial vehicle with structure-from-motion and terrestrial laser scanning

We conducted topographic measurements using unmanned aerial vehicles and by terrestrial laser scanning at inaccessible sea cliffs with an overhanging complex shape in eastern Japan. From the repeated measurements, we constructed multitemporal three-dimensional point clouds of the sea cliffs to quantitatively evaluate the volumetric changes in the cliffs with a high spatial resolution (in centimeter). As potential main triggers of rockfalls and slope failures, high sea waves and strong earthquakes were examined with the time series of eroded volumes. It is suggested that sea waves have a greater impact than earthquakes on sea-cliff erosion. The approaches provided in this study have great potential for a wide range of applications including high spatial monitoring of other inaccessible, complex-shaped sea cliffs with high data accuracy and low acquisition and operational costs.

Landslide Interpretation of the Northeast Flank of Kohala Volcano, Hawaii

AbstractThe Hawaiian Island volcanic edifices have shed at least 15 giant submarine landslides, each classified as either a slump or debris avalanche. Controversy exists regarding the number, size, and type of landslides on the northeast flank of Kohala Volcano. This study provides a new interpretation for the Kohala flank based on contour and balanced cross-section analysis. Specifically, contours indicate that there is a landslide extending from the summit to the coast between Pololu and Waipio Valleys. The contour evidence also shows that the slide plane is planar and dips less steeply than the topographic slope. Balanced cross sections show the slide plane to be approximately 950 m deep immediately downhill from the zone of depletion, and the slide plane presumably reaches the surface at the base of the coastal cliffs on the northeast coast of Kohala mountain. The lower part of the landslide once extended from the coast to approximately 10 km offshore, but this portion now has been completely removed, apparently as a debris avalanche. Removal of this distal landslide mass created a 200 to 450 m headwall that is now topographically represented by sea cliffs. This newly identified slide/debris avalanche is informally named the “Kohala landslide.” Based on cross-cutting relations of landslide faults with Hawi series lava flows, the upper slide part of the landslide moved sometime between 270 and 60 ka. The age of the lower, debris avalanche part is even less certain and depends on whether canyons cut in the seafloor after the avalanche movement were eroded in the subaerial or submarine environment.

Evaluation of geomorphic changes and retreat rates of a coastal pyroclastic cliff in the Campi Flegrei volcanic district, southern Italy

Geomorphic evolution of sea cliffs has significant impact on coastal settlements worldwide, so that evaluation of cliff instability processes, failure factors, and retreat rates involves a growing number of scientists for coastal risk and management purposes. Aerial photogrammetry and lidar are among the most used techniques for topographic characterization and geomorphic monitoring of coastal environments. A crucial role in the combined use of such techniques is the evaluation of different spatial accuracy and co-registration between derived terrain models, so that a robust error analysis is required. In this study, we present a change detection analysis of the Torrefumo coastal cliff, in the Campi Flegrei volcanic area (Southern Italy). Aerial images taken in 1956 and 1974, processed through digital photogrammetry, and an airborne lidar point cloud acquired in 2008 were used to produce Digital Elevation Models of the cliff. The analysis was based on the multi-temporal comparison of these models and included the calculation of volumetric changes and average retreat rates of the cliff face with reference to the 1956–1974 and 1974–2008 time intervals. The spatially variable elevation uncertainty of each Digital Elevation Model was evaluated with a probabilistic approach based on the fuzzy set theory. The results of this study showed significant eroded volumes during the period 1956–1974 and relatively smaller volumes in the 1974–2008 time span, with mean annual retreat rates of 1.2 m/year and 0.17 m/year, respectively. We infer that the significant decrease of erosion characterizing the second period was induced by the sheltering effect at the base of the cliff produced by the construction of a seawall in the early 80’s.

Marine control over negative power law scaling of mass wasting events in chalk sea cliffs with implications for future recession under the UKCP09 medium emission scenario

AbstractCoastal cliff erosion represents a significant geohazard for people and infrastructure. Forecasting future erosion rates is therefore of critical importance to ensuring the resiliency of coastal communities. We use high precision monitoring of chalk cliffs at Telscombe, UK to generate monthly mass movement inventories between August 2016 and July 2017. Frequency–magnitude analysis of our inventories demonstrate negative power law scaling over 7 orders of magnitude and, for the first time, we report statistically significant correlations between significant wave height (Hs) and power law scaling coefficients (r2 values of 0.497 and 0.590 for β and s respectively). Applying these relationships allows for a quantitative method to predict erosion at the site based on Hs probabilities and sea level forecasts derived from the UKCP09 medium emission climate model (A1B). Monte‐Carlo simulations indicate a range of possible erosion scenarios over 70 years (2020–2090) and we assess the impact these may have on the A259 coastal road which runs proximal to the cliffs. Results indicate a small acceleration in erosion compared with those based on current conditions with the most likely scenario at the site being 21.7 m of cliff recession by 2090. However, low‐probability events can result in recession an order of magnitude higher in some scenarios. In the absence of negative feedbacks, we estimate an ~11% chance that the A259 will be breached by coastal erosion by 2090. Copyright © 2018 John Wiley & Sons, Ltd.

Quaternary sealevel changes and coastal evolution of the Island of Trindade, Brazil

The present work presented the first dated paleosealevel indicators and new paleogeographic reconstructions of the Island of Trindade. All evidence for Holocene sealevels point to the elevations higher than the present in the age interval between 5.06 ka and 0.55 ka. The altitude and ages of the reconstructions are in good agreement with hindcast model curves and the empirical sealevel envelope for the mainland eastern and northeastern Brazilian coast. However, the position of paleo vermetid-reef indicates that sealevel was lower than eustatic elevation, suggesting an effect of island subsidence. In contrast to the Brazilian mainland coastal zone, where conspicuous evidences of Pleistocene highstands were recorded, no evidence of sealevels predating the Holocene has ever been observed on the island. This could be attributed to intense coastal erosion and log-term island subsidence.A volcanic edifice rising more than 5500 m above the ocean floor was built by magmatic activity that extended over the late Pliocene and early Pleistocene. After the cessation of volcanic build up, the island started to shrink due to subaerial and marine erosion. During Pleistocene sealevel lowstands, alluvial fans were formed beyond the present limits of emerged areas. They were enclosed within and preserved from erosion by the Middle to Late Pleistocene lava flows and pyroclastic deposits. During Late Pleistocene sealevel highstand, intense coastal erosion removed the distal parts of the alluvial fans. It is very likely that at that time the entire coast of the island experienced intense erosion and subsidence as deduced from the absence of Pleistocene coastal deposits, which are widespread along mainland Brazilian coast.The east coast of the island was dominated by high sea cliffs sculpted into volcanic rocks. A volcanic cone was subsequently formed, when the sealevel was lower than present during the Late Pleistocene to early Holocene. During the mid to late Holocene sealevel highstand the volcanic cone was partially eroded and a bay formed, where vermetid-reefs grow and sand beach deposits prograded until the bay was infilled. During the sealevel maximum, wave-cut terraces were formed and sea cliffs were active. During the lowering of the sealevel, cliffs became inactive and vermetid-reefs were eroded. Beach erosion and aeolian deflation presently prevails, indicating a low sediment supply.