Cliff Profiles Research Articles

Revealing geomorphic changes after the occurrence of a seismic event on the south coast of Puerto Rico (2020)

A coastal geomorphological study was conducted to assess the impact of seismic events on the southern coast of Puerto Rico (PR). The goal of this study was to provide new information related to the state of the coast and its geomorphic changes associated with the seismic sequence of 28 December 2019 and the 6.4-magnitude earthquake of 7 January 2020. Coastal geomorphic changes and damage to infrastructure were documented using a combination of a geographic information system (GIS), remote sensing techniques (e.g. unmanned aircraft system [UAS] images), ground-penetrating radar (GPR), high-resolution aerial photos, and field inspection techniques. A geospatial analysis was performed to evaluate the effect of the earthquake events and understand its associated effect on coastal communities’ exposure to this hazard. The findings indicate that the 6.4-magnitude earthquake caused remarkable geomorphic changes, generating a new shape for the southern coast of PR. Coastal changes were characterized by localized coastal subsidence, coastal landslides (e.g. rockslides and rockfalls), the collapse of natural arch-forming sea stacks, changes in cliff profiles, lateral spreading, the destruction of coastal infrastructure, inland shoreline migration, and coastal flooding. This information will be useful for designing new management tools and recontextualizing existing coastal planning instruments in post-earthquake scenarios. These findings clarify the importance of seismic events and their influence on coasts within active tectonic settings.

Proposing a new conceptual model for the reconstruction of ice dynamics in the SW sector of the Scandinavian Ice Sheet (SIS) based on the reinterpretation of published data and new evidence from optically stimulated luminescence (OSL) dating

Abstract. We propose a new concept of the Weichselian ice dynamics in the south-western sector of the Baltic Sea depression. The review of existing geochronological data from Germany, Denmark and southernmost Sweden in combination with new optically stimulated luminescence (OSL) data from the German Oder Lobe area is the basis for a reassessment and an improvement of previous ice dynamic models. Factors like the pre-existing topography, glaciotectonic features and the occurrence of till beds and inter-till deposits of varying origin are also taken into consideration for our process-based reconstruction of the sedimentary environments close to the ice margin and hence the ice dynamics of the Scandinavian Ice Sheet (SIS). During the early MIS 3 (marine isotope stage), the late MIS 3 and MIS 2, the SIS advanced into present-day terrestrial areas around the south-western Baltic Sea Basin. The first ice advance during the warming phase in early MIS 3 is poorly documented as the Ellund–Warnow Advance in Germany but may be correlated with the numerically dated Ristinge Advance in Denmark and Sweden. The late MIS 3 advance in contrast is reliably documented. It shaped the landforms of the Brandenburg Advance and the maximum Weichselian ice extent in the Oder Lobe area in north-eastern Germany and occurred contemporaneously with the Klintholm Advance in southern Sweden and Denmark. The lack of a corresponding till in various cliff profiles along the Baltic Sea coastline between southern Schleswig-Holstein and the island of Rügen can be explained by the distinct lobate structure of this ice advance, which was strongly guided by the pre-existing low-lying topography. We propose the horst of Bornholm, Denmark, acting as an ice divide, with ice-dammed lakes existing on the lee side between two glacier lobes. This lobate structure had not been considered in previous conceptual models, which led to seemingly conflicting chronological and stratigraphical interpretations. Our introduction of the lobate structure for the first time resolves these contradictions and integrates the data in a coherent model. The dynamics of the MIS 2 readvance to the Last Glacial Maximum (LGM) extent were clearly different to the previous advance and were most likely characterized by a more uniformly advancing ice front with a less lobate structure which also overrode the horst of Bornholm and the island of Rügen. This advance reached the maximum Weichselian ice extent in some parts of the south-western SIS, but, in the Oder Lobe area, it is proven to have terminated at a lesser extent than the early MIS 3 advance, but it did shape the most prominent morphological landform record of the last glacial cycle. In order to advance the reconstruction of Weichselian ice dynamics in the future, we strongly suggest using both an MIS-based terminology and a process-based approach in the interpretation of geochronological data to live up to the dynamic nature of continental ice sheets.

Erosion status of a sea cliff promontory bounding an ecologically important beach

The study attempts to assess the retreat of a section of a bounding sea cliff promontory, exposed to wave forcing from both sides, of an important Mediterranean sea-turtle nesting beach, within a Mediterranean marine protected area (Gerakas, Zakynthos Island, Greece). Morphological changes were monitored within a 2-year period using a terrestrial laser scanner and the findings were compared with those from historical ortho-photographs to estimate sea cliff erosion the last 20 years. An advanced wave model supplemented by a model for cliff notch evolution, as well as an analytical model were also used to estimate cliff erosion due to wave attack. Comparisons of sea cliff profiles and calculations of volumetric changes using the collected and historical topographic data showed an average annual recession of about 0.16 m for the period 1997–2016. By comparison, coastal modeling estimated a retreat of about 0.23 m/yr, whereas a 0.14–0.3 m/y recession was assessed by the analytical approach; this reasonable discrepancy with the empirical results, is probably caused, amongst others, by the fact that the models does not account for the protection of cliff toes by a constant supply of erosion debris from above. The wave model was also used to estimate sea cliff retreat rates under a 0.5 m sea level rise and showed a fourfold increase compared with the current recession rate. On the basis of these results, as well as considerations related to the seismicity of the study area, it appears that the factors responsible for the sea cliff retreat are wave action, precipitation-induced surface flows, and earthquake-related instabilities that may cause rapid, large-scale erosion. The outcomes of this study are highlighting the critical interplay of several natural factors and climatic change effect on driving coastal erosion, which consequently results in the loss of ecologically critical habitats, thereby challenging conservation goals and management effectiveness.

The Effect of Basal Erosion on Sea Cliff Stability

Barbosa, N.; Taquez, D.; Santos Jr, O.; Freitas Neto, O.D., and Scudelari, A., 2020. The effect of basal erosion on sea cliff stability. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 362–366. Coconut Creek (Florida), ISSN 0749-0208.Coastal areas attract substantial interest from the general population, and development is quite common in these regions. Therefore, it is necessary to study coastal erosive processes to provide a better understanding of the factors that influence the stability of sea cliffs and consequently their safety. In this paper, two typical cliff profiles were studied: a vertical cliff section and another with a lower slope. Both profiles are representative of slopes existing on the northeastern coast of Brazil. Basal incisions of 1 m, 2 m and 3 m were evaluated. The cliffs considered are not subjected to anthropogenic activities, and thus, only natural conditions influence their stability. The stability of the cliffs was investigated through a comparative analysis between the tensile stresses acting on the slopes and the tensile strengths of the materials considered. For the cliff with a lower slope, it was verified that the tensile stresses obtained presented low values, whereas in the vertical cliff, the tensile stresses were significantly higher. The main mechanism responsible for triggering instability processes is the partial increase in the degree of soil saturation caused by rainfall, which decreases the soil strength and triggers landslides. From the tests carried out, it was observed that the cohesion intercept of the saturated soils is approximately 26% of the value obtained for the soils with natural moisture content. However, the angles of internal friction in both cases suffer negligible variations. The study of the stability analysis presented in this paper effectively represents the types of failures observed in cliffs on the Brazilian coast. The analysis by tensile stress is much more coherent than the failure surfaces obtained by traditional methods of analysis.

Multi-Temporal Cliff Erosion Analysis Using Airborne Laser Scanning Surveys

Rock cliffs are a significant component of world coastal zones. However, rocky coasts and factors contributing to their erosion have not received as much attention as soft cliffs. In this study, two rocky-cliff systems in the southern Baltic Sea were analyzed with Airborne Laser Scanners (ALS) to track changes in cliff morphology. The present contribution aimed to study the volumetric changes in cliff profiles, spatial distribution of erosion, and rate of cliff retreat corresponding to the cliff exposure and rock resistance of the Jasmund National Park chalk cliffs in Rugen, Germany. The study combined multi-temporal Light Detection and Ranging (LiDAR) data analyses, rock sampling, laboratory analyses of chemical and mechanical resistance, and along-shore wave power flux estimation. The spatial distribution of the active erosion areas appear to follow the cliff exposure variations; however, that trend is weaker for the sections of the coastline in which structural changes occurred. The rate of retreat for each cliff–beach profile, including the cliff crest, vertical cliff base, and cliff base with talus material, indicates that wave action is the dominant erosive force in areas in which the cliff was eroded quickly at equal rates along the cliff profile. However, the erosion proceeded with different rates in favor of cliff toe erosion. The effects of chemical and mechanical rock resistance are shown to be less prominent than the wave action owing to very small differences in the measured values, which proves the homogeneous structure of the cliff. The rock resistance did not follow the trends of cliff erosion revealed by volume changes during the period of analysis.

Influence of wave force direction on cliff profiles: formulation and observation in a case of horizontally layered cliffs in the northern coast of Gulf of Oman

Many parameters can affect the profile of rocky coastlines. One of these parameters is wave orientation with respect to coastline direction which has been considered to be assessed mathematically in this study. Wave force can be resolved into two components, in a manner that one of them is perpendicular to the coastline. It was supposed that the perpendicular force of wave is responsible for hammer destroyer effect which makes cracks inside cliffs especially in parallel direction to coastline. Cliffs start to slide from these cracks and consequently the unstable slide zone increases. Hence, an inverse relation between the gradient of cliffs and perpendicular component of waves is expected. Perpendicular force, itself, depends on wave parameters and coastline direction with respect to coming wave orientation. Based on this conception, in this paper, a mathematical formulation was developed to correlate the wave orientation and the gradient of cliff on rocky coastlines. The conceptions and formulations were validated in horizontally layered cliffs in the northern coastline of Gulf of Oman.

Wave Runup Over Steep Rocky Cliffs

AbstractWave runup is known to depend on offshore wave conditions and coastal morphology. While most field studies on wave runup have focused on low‐to‐mild‐sloping sandy beaches, runup measurements on steep and irregular rocky cliff profiles are still very scarce. Here we investigate the physical processes controlling wave runup in such environments and the range of applicability of empirical runup formula. This study focuses on the steep rocky cliffs (0.1 < tanβ < 0.4) of Banneg Island, a small island located in the Molène archipelago, Brittany, France, occasionally flooded during extreme water level events. A statistical parameter for extreme runup is derived from the measurements of pressure sensors deployed in the intertidal zone. Deep water wave parameters are used to force a high‐resolution wave model, and nearshore wave parameters and high‐resolution topographic data are analyzed concurrently with runup time series in order to assess the dependence of the runup on hydrodynamic conditions and morphological parameters. The wave runup is shown to be strongly related to the square root of the offshore significant wave height times the offshore wavelength. The measurements also reveal the depth dependence of the runup, which is mainly attributed to the curvature of the foreshore profile. In comparison to empirical relation obtained for a mild‐sloping beach, the present data show a significant reduction in normalized wave runup, that is attributed to enhanced bottom friction over the rocky bottom.

Innovative use of GIS and drone photogrammetry for cliff stability modelling

Evaluating the condition and stability of coastal cliffs and assessing longevity of significant overhangs and undercuts in an active marine environment is a challenge. As part of cliff management studies undertaken for the Coastal Zone Management Unit of the government of Barbados, a programme of innovative cliff profile mapping was conducted around the island of Barbados. A combination of land-based field mapping information and fixed wing aircraft collected high-resolution LiDAR imagery was utilised for cliff geometry assessments, supplemented for specific cliff profiles by fill-in high-precision three-dimensional (3D) digital terrestrial imagery, captured by low level wide wingspan UAV drone flights. Comprehensive photogrammetric processing of this imagery, combined with detailed geographic information system software evaluation of the collected point cloud data, allowed generation of full 3D wireframe digital terrain and digital elevation models (DTMs and DEMs). Multiple representative cliff areas around the island were identified, allowing thorough 3D stability assessment to be accomplished of key problematic areas using Flac3D. Vertical cross-section profiles were also cut so that undercut and notched cliffs could be analysed in detail in two dimensions using Voronoi tessellation approaches applied within the universal distinct element code UDEC as a means to replicate the characteristics of the vuggy coralline limestone cliffs.

A New Approach of Coastal Cliff Monitoring using Mobile Laser Scanning

Abstract The article proposes a new approach of coastal cliff monitoring which bases on a new comprehensive monitoring system, being a combination of mobile scanning from the sea with the geotechnical stability analysis. Mobile laser scanning is an innovative solution for 3D data collection which allows the monitored object geometry to be precisely measured, thus providing opportunities for series of analyses contributing to the development of an improved monitoring system. The authors present selected cliff profiles obtained from mobile scanning in the area of Jastrzebia Gora, complemented by relevant geotechnical analyses. The analysis of current cliff geometry is accompanied by calculations of hypothetical cliff profile changes resulting from possible action of nature forces. Finally, a comprehensive strategy for coastal cliff monitoring is proposed.

Quaternary paleosols and sediments on the Balearic Islands as indicators of climate changes

Paleosols and sediments are suitable objects for reconstructing paleoclimate. To obtain a high climatostratigraphic resolution in the Western Mediterranean, we investigated geoarchives with paleosols and sediment layers in cliff profiles of two alluvial fans on Mallorca, their pedostratigraphy covered the Late Pliocene, Pleistocene and Holocene. The sites were analysed in terms of colour, CaCO3, δ13C and δ18O isotopes, and micromorphology.The sequence of El Toro (SW Mallorca) comprises 44 partly polygenetic paleosols and sediment layers, where redness is mostly pronounced in Late Pliocene and Early Pleistocene layers, but also partly in younger periods. The Eemian to Würmian sequence of Colonia de Sant Pere (NE Mallorca) consists of yellowish–red beach sand deposits and fine red sediments, while the overlying brunified Holocene soil on loess follows shorter dry periods under moderate climate conditions with a declined pedogenetic intensity. Apart from iron weathering and hematite formation processes, soil reddening also requires polygenesis with frequent secondary climatic oscillations under distinctly alternating moisture conditions. Consequently, the current Mediterranean climate alone is not sufficient for soil reddening.Polygenetic development of the respective paleosols and sediments was underlined by micromorphological studies, showing an alternation of carbonate-rich sediments with predominantly decalcified, brunified and partly recalcified paleosols. Shrink–swell cracks reflect seasonal Mediterranean climate conditions already during the Early Pleistocene.Altogether, pedogenesis was most intense during the Late Pliocene and Early Pleistocene as enhanced by comparatively humid Mediterranean conditions, but then gradually decelerated. The sediments developed under comparatively drier and partly cooler climate conditions with a reduced open or even absent vegetation cover enhancing surface erosion. Paleosols and sediments on the Balearic Islands thus reflect a pronounced climatic cyclicity in the Western Mediterranean since the Late Pliocene.

A new hazard zonation methodology applied to residentially developed sea-cliffs with very low erosion rates, East Coast Bays, Auckland, New Zealand

A new hazard zonation methodology is applied to the East Coast Bays area of North Shore City, one of the most residentially developed cliffed shorelines in New Zealand. It is based on a series of geotechnical cliff profiles from three pilot study areas (George Gair Lookout, Rahopara Reserve–Kennedy Memorial Park, and Mairangi Bay–Rothesay Bay) which detail many of the variables that influence overall cliff stability.

Glacial-interglacial history of the Skaftafell region, southeast Iceland, 0–5 Ma

Volcanic strata in the Skaftafell region, southeast Iceland, record a sequence of at least 16 glacial and interglacial intervals since 5 Ma. Two composite sections of 2 to 2.8 km thickness have been constructed from multiple, overlapping, cliff profiles. The timing of alternating sequences of subaerial lava flows, pillow basalts, and hyaloclastite deposits is provided by magnetostratigraphic mapping and K-Ar radiometric dating. We find that the frequency and intensity of glaciations increased significantly at ca. 2.6 Ma, and particularly since 0.8 Ma, amplifying topographic relief in this area from

Influence of ground ice and permafrost on coastal evolution, Richards Island, Beaufort Sea coast, N.W.T.

A long-term sediment budget (1947−1985) for northern Richards Island shows that, when ground ice and offshore erosion are accounted for, there is a near balance between headland erosion and coastal deposition. Excess ice constitutes about 20% of the total volume of eroded material from the headlands, with massive ground ice contributing nearly 9% and segregated ice lenses and ice wedges making up the remainder. Coastal response to major storms in 1987 and 1993 suggests that erosion is episodic, with short periods of intense disruption followed by readjustment of cliff profiles. Processes characteristic of this environment include mechanical erosion of ice-bonded sediments creating unstable erosional niches, mechanical failure of niches along ice-wedge planes, and longer term thermal erosion of ice-bonded sediments. Where ice contents are high, localized thaw slumps initiated by coastal erosion may retreat at rates substantially higher than those observed at other sections of the coast. Cliff-top retreat rates may be out of phase with storm-event chronology.

Cliff stability evaluation using geomorphological maps based on oblique aerial photographs

Abstract Geomorphological mapping is a well established tool in terrain evaluation. A case record is presented in which high-oblique aerial photography from a light aircraft has been used for basic mapping of a 3 km length of coastline with the purpose of assessing relative landslide hazard. The cliffs at Budleigh Salterton, East Devon, are formed in a succession of Permo-Triassic mudstone, conglomerate and sandstone which dip gently eastwards along the coast. The coastline is divided into five units based on changes in the stratigraphic succession exposed in the cliff face; each unit correlating with distinctive geomorphological features and cliff profiles. Groundwater discharges, wave attack and weathering ensure that there is continuing geomorphological activity. This necessitates frequent updating of local hazard assessment. Overlapping aerial photographs of the cliff face have been taken at intervals during the past six years. With limited ground inspection these photographs provide adequate data for basic geomorphological mapping of the principal forms represented in the cliff. Successive series of photographs are used to follow the development of individual features and to identify the hazards present in each section of the cliff. Data from early Ordnance Survey maps, old photographs and personal reminiscences extend parts of the history of the coast back into the last century. The positions of landslides are controlled largely by geological and hydrological factors whereas the timing of events is often a function of external environmental triggering mechanisms such as weather, tide or waves. A classification of the relative hazard of cliff-top instability has been used to map hazard zones for the coastline. Together with the system of photographic data acquisition advocated, this provides a rapid and economic method to assist planning authorities in determining development strategy.

ON THE RETREAT OF THE SEA CLIFFS ALONG THE PACIFIC COAST AT HARANOMACHI, JAPAN

In order to investigate the cause of local variation in sea cliff retreat, the author surveyed the sea cliffs along the Pacific coast of Ohmika, Haranomachi City in Fukushima Prefecture, Japan (Fig. 1). Throughout this coast of 3 kilometers in length, we find sea cliffs with a height of 5 to 25 meters. Most of them are 20 meters high cutting a marine terrace, but some of them at the northern part are found on a side of another lower fluvial terrace, which is about 5 meters high. An obtuse angled cape divides this coast into two: northern and southern parts (Fig. 2). Judging from the old (1912) and the recent (1959) maps of this area, it is possible to recognize a clear difference of the land area lost between the northern and southern parts (Fig. 4). The southern part showed more loss than the northern one, though the former has a wider beach in general. Moreover, there is a difference in type between the northern and southern cliff profiles (Fig. 3). The northern cliffs are almost everywhere characterized by a vertical bluff just like a wall showing a smooth face. Deep sea-caves at their foot and narrow stepped platforms in the middle of the cliff profiles also can be seen at some places in thenorthern part. On the other hand, the southern cliffs are rough and vertical at the lower part and also quite steep, but not vertical, at the upper. There are no sea-caves but shallow notches at their foot. Wave-cut benches could be seen at the foot of the cliffs in the southern part. As regards to the fallen debris at the foot of these cliffs in the southern part, a large amount of all sizes having fresh faces and sharp edges are to be found. On the contrary, in northern part, there are less debris but most of them are larger and well-rounded. As for the geology of this coast, they consist generally of sand and gravel deposits at the upper, a sandy mudstone layer at middle and lower (Fg.5). At the southern part, this sandy mudstone layer is divided into two by an inserted unconsolidated stratum of sand, and this sandy stratum locates just at the foot of the southern cliffs, The middle and lower parts of the northern cliffs consist of only homogeneous mudstones. To know one of the resisting powers of these strata against wave attack, the author measured hardness for every stratum on the southern and northern cliffs by using a penetrometer, an instrument for measuring soil consistency (Tab.2). The strikes and intervals of the joints in the mudstone layers are also important factors for destruction of the cliffs by storm waves. In the southern part, the strikes are oblique to the present shoreline. On the contrary, the strikes of the northern cliffs are parallel to the shoreline. Other factors concerned with destruction of these cliffs such as wave, wind (Fig.7) and shallow water topography (Fig.6) were also examined, but the author considered that they are not so much concerned with the difference of cliff retreat as geological factors in this coast are. Finally it was proven that the main cause of local variation in cliff retreat, and cliff profiles between the northern and southern parts on this coast depend mainly upon the geological factors, such as differences in stratigraphy, joints in mudstone layers and hardness of strata on this coast.

Recent Papers on the Coast of England and Wales

A considerable amount of interest has been taken in the coast and adjacent sea-floor of Great Britain s c the w r. It seems therefore worthwhile to call attention to papers concerned more particularly with the geographical and geological aspects of coastal morphology, which are scattered through very different types of journals, and so may easily escape the notice of those for whom they are intended. In our own Journal Miss M. A. Arber gave an account of the cliff profiles in Devon and Cornwall,1 and thus extended the observa? tions made known by her father in fThe Coast Scenery of North Devon' (1911). Recently W. G. V. Balchin, continuing his work on Cornwall has given us a paper on the high level surfaces and their relation to the coast of North Devon. J. Challinor added a chapter to his earlier work on the Cardigan coast in the form of a note on convex erosion slopes in North Cardiganshire,2 and E. H. Brown 3 has analysed comprehensively the erosion surfaces of the same area. These three papers are however only incidentally concerned with the coast. C. A. Cotton 4 discusses our south-western coasts, and thinks the morvan theory, slightly modified, explains their structure better than the fault theory outlined by Suess. He regards the English and St. George's Channels as old features. The deepening of the valleys, later drowned by the Flandrian transgression, took place in times of glaciation. He thinks the tempo of coastal erosion has been slow owing to the great width of the continental shelf. Thus shoreline details survive from an interglacial age. His explanation of the bevelled form of some of the cliffs depends on two cycles of erosion, and so differs from Miss Arber who regards the distribution of bevelled cliffs as being controlled by structure, especially jointing. Other differences of opinion arise over the rate of cliff retreat in relation to valley truncation and the preservation of raised beaches.5 Cotton also alludes to The Needles of the Isle of Wight 6 and regards them as the surviving remnants of a plunging cliff which has been subjected to lateral erosion by the sea. Cotton's treatment of these two problems is theoretical, and scarcely takes local details sufficiently into consideration.

Cliff Profiles of Devon and Cornwall

The coast scenery of North Devon and of North and West Cornwall con? sists mainly of rugged cliffs, ranging in profile from the hog's-back slopes around Lynmouth to the sheer precipices of Morwenstow. The loftiest hog'sback cliffs (Plate i) are those in north-east Devon between Combe Martin and Foreland Point, extending still farther east across the Somerset border. The Great Hangman near Combe Martin has a crest 1044 feet above sealevel about 300 yards inland, whence a straight vegetated slope of gradient approaching 1 in 1 descends to the very base, which alone is now subject to wave attack. The clifTs between Hartland Point and Widemouth afford a complete contrast. An inland plateau sloping gently towards the sea is cut clean by an almost vertical cliff face, 400 feet high near Morwenstow and nearly 300 feet high at Hartland Quay (Plate 2). Where the profile, as at the Lizard and the Land's End, does not conform to either of these two extremes, a vegetated slope curves in a bevel from the level surface above to the vertical cliff face below. The curve may be concave (Plate 3) or convex (Plate 4). The greater part of the area considered in this paper (see map) consists of Devonian and Carboniferous rocks. Along the coast the commonest of these are hard grits, shales, sandstones and slates; there are also small outcrops of Devonian igneous rocks. At the end of the Carboniferous period the region was evidently subjected to severe pressure along Armorican lines, resulting in a series of folds with east and west strike. The north of the area is occupied by a great synclinorium, so that in North Devon the regional dip is to the south while along the coast, roughly from Boscastle to Morwenstow, it is to the north. During the same orogeny the great granite domes of Devon and Cornwall were intruded, which outcrop on the mainland coast at the Land's End.