Coastal Cliffs Research Articles

Assessment of long-term structural movements in a historic cliffside construction through Lomb-Scargle spectral analysis of unevenly spaced time records: the Punta Begoña Galleries (Getxo, Spain)

Long-term monitoring of structural movements in historic buildings and heritage sites allows assessing their stability and recognizing damages that require intervention. The Punta Begoña Galleries, built in the earlier part of the twentieth century, present pioneering techniques in the use of reinforced concrete in building construction. They stand directly over a coastal cliff, and their recovery requires first to guarantee their stability, while maintaining their historic and patrimonial values. Thus, with the goal of analyzing their global stability, as well as the extent of the observed damages, we implemented a motion monitoring network that includes three boreholes for extensometric control, an inclinometer, and five crack gauges (crackmeters). This monitoring was complemented with the recording of hydrometeorological variables at the surface and in four piezometers. The spectral analysis of the signals of movements was performed by introducing the use of the Lomb-Scargle (LS) periodogram, which is particularly well-suited for the analysis of unevenly spaced time series. This analysis allowed us to differentiate the reversible seasonal elastic components of the records and to recognize the irreversible long-term plastic displacements, which highlight the sectors with active instability. In our case, the identified damages are related to two local problems of building support. Even though the irreversible component of the displacement after seasonal sinusoidal detrending is small (with maximums up to 0.12 mm/year), it does imply a dynamic plastic deformation, which calls for the need to adopt structural stabilization measures.

Late Pleistocene earthquakes imprinted on glaciolacustrine sediments on Gnitz Peninsula (Usedom Island, NE Germany)

Oscillation of an ice sheet can be accompanied by earthquakes due to local reactivation of pre-existing faults related to the ice loading. A sufficiently large magnitude of an earthquake can trigger seismic waves that may strongly deform susceptible sediment layers and can cause the development of soft-sediment deformation structures (SSDS). Morphological and structural features of SSDS within a glaciolacustrine succession exposed at the coastal cliff on Gnitz Peninsula (Usedom Island) in NE Germany indicate that they must have developed due to glacial isostatic adjustment, which was suggested earlier by Hoffmann and Reicherter (2012).Here we present detailed micro- and meso-scale SSDS within internally deformed layers interpreted as seismites, liquefaction and re-liquefaction sedimentological imprints on Gnitz Peninsula. New optically stimulated luminescence dating results indicate that the most probable time span of corresponding earthquake occurrence is between 23.2 and 14.6 ka. The interpretation of SSDS ‘trapped’ in layers as seismites is strongly supported by modelling of glacially induced Coulomb failure stress changes in this region. Our results point to a set of probably pre-Quaternary faults which were locally reactivated in the area of Gnitz Peninsula during the last glacial maximum.

Mineralogy of interior jewellery ammonites of the Samara region

Background. Ammonite products are increasingly gaining in popularity. Ammonites are characterised by a variety of colour shades, shapes and sizes, making them suitable for manufacturing a wide range of souvenir and jewellery products. Russia enjoys significant resources of ammonites of interior and jewellery-ornamental quality; however, these materials remain insufficiently studied from the mineralogical point of view. This article presents the mineral composition and gemological characteristics of the Upper Jurassic interior jewellery ammonites of the Samara region for the first time.Aim. To describe the stratigraphic position and mineral composition of interior jewellery ammonites of the Samara region.Materials and methods. Late Jurassic ammonites (45 samples) were collected from a number of their main locations. The characteristic types of ammonites of interior-jewellery quality were distinguished and studied. Experiments included the determination of microhardness (25 determinations), density (12 determinations), luminescence features (10 samples), optical and petrographic analysis (5 thin sections), as well as the quantitative determination of mineral and chemical composition (3 samples), and electron probe studies (2 samples).Results. Ammonites are characterized by the presence of a mother-of-pearl layer with multi-coloured iridescence. The ammonites under study consist mainly of apatite (21—70 wt. %) and calcite (21—87 wt. %) along with quartz, aluminosilicates, gypsum, pyrite, zeolites, goethite, ilmenite and organic matter. The chambers of ammonite shells are made of phosphorite and calcite. The walls and partitions of shells have completely lost their original aragonite composition and consist of apatite and calcite with pyrite inclusions. The increased content of Sr (up to 0.17 wt. %) and Ba (up to 0.01 wt. %) are recorded as trace elements in ammonites. Calcite contains the following trace elements (wt. %): Mg — 0.17, Mn — 0.17, Fe — 1.14, Sr — 0.11, and Y — 0.17.Conclusion. The mineral and chemical (including microinclusions and trace elements) composition of interior-jewellery ammonites was established for the first time. The ammonites of the Samara region are of commercial interest as interior samples. Their shell fragments can be used in jewellery production. The ammonites under study can be collected along the coastal cliffs and beach area of the Volga river, thereby requiring no capital investments and producing no environmental pollution.

New Unexpected Species of Acheta (Orthoptera, Gryllidae) from the Italian Volcanic Island of Pantelleria

In late April 2022, while listening to audio files from an unsupervised bioacoustic assessment of the shearwater populations (Aves, Procellariiformes) on the coast of Pantelleria island (Sicily, Italy), a cricket song of unknown attribution was heard. The first bioacoustic analyses, including FFT-based spectrograms and sound pressure envelopes, confirmed that it could not be attributed to the known sound of any Italian nor Mediterranean species of cricket. In the ensuing weeks, field research at the original station and further localities on the southern coast of Pantelleria provided photographs, living specimens, and further audio records. As soon as the photos were shared among the authors, it became clear the species belonged to the genus Acheta. Further bioacoustic analyses and morphological comparison with type specimens of Mediterranean and North-African congenerics in relevant collections and the scientific literature were conducted: they confirmed that the findings could only be attributed to a still undescribed species that escaped detection due to its impervious and unfrequented habitat. Acheta pantescus n. sp. is apparently restricted to the effusive coastal cliffs of the island of Pantelleria, a habitat whose scant extension and vulnerability require environmental protection actions such as the inclusion in a special Red List by the IUCN Italian Committee.

An integrated approach for coastal cliff susceptibility: The case study of Procida Island (southern Italy)

Procida Island, located in the Gulf of Naples (southern Italy), is characterized by steep cliffed coasts, articulated in a succession of headlands and small embayments with narrow pocket beaches, such as Ciraccio and Chiaia, often characterized by instability.In this study, a methodology for coastal cliff susceptibility assessment has been conceived based on hydraulic and geomorphological characteristics, which supported the construction of a Cliff Stability Index (CSI). The geomorphological characteristics are related to the whole cliff face, the cliff material resistance, and the cliff failure mechanisms. The hydraulic actions on the cliff are related to the wave impact which is exerted by the breaking waves once the wave run-up distance exceeds the beach width. The index takes into account the slope of the cliff, the rock strength, the wave energy at the cliff base produced by the broken wave and the presence of defence structures at the cliff base. The resulting index classification, obtained by addition of the partial sub-indices, has been compared with the observed coastal cliff evolution from 1954 to 2021.

Identificación de tipos de deslizamientos en la zona de acantilados entre Ancón y Anconcito, Santa Elena, Ecuador

On the Ecuadorian coasts, landslides are frequent that occur on cliffs that correspond to an instability maintained by the mechanical characteristics of soils and rocks in which there are discontinuities, fault planes that are activated by precipitation or coastal erosion; for this reason, this research was focused on identifying the different types of landslides found in the coastal cliff areas of Ancón and Anconcito in the province of Santa Elena, this study was carried out by photogrammetric flights with UAV technology, carried out by three flights in the study area. It was found that the study sector corresponds to an inclined rocky coast, where mass landslides (soils) and rockslides were found, such as: rotational, earth flows, erosion gullies, falling blocks, sinkholes, planar breaks, and wedge breaks. The results identified in the studied areas highlight the importance of knowing how susceptible they are to different types of movements due to high coastal erosion due to wave incidence and other factors, on the other hand, research should be carried out to show how much the coastal retreat is (m/year) produced by landslides in these areas.

Ground-based visible–near infrared hyperspectral imaging for monitoring cliff weathering of a volcanic island in Dokdo, South Korea

Coastal cliffs undergo erosion and weathering more rapidly under the influence of strong waves and sea winds, leading to stability and environmental conservation issues. Ground-based hyperspectral imaging is useful for the identification and geological interpretation of minerals or rocks in vertical outcrops that are difficult to confirm from an aerial view or through in situ investigation for safety reasons. High spatial and spectral resolutions of visible–near infrared (VNIR) sensors can be advantageous for detecting weathering in cliffs made of volcanic rocks; however, their potential is not well known. In this study, two classification techniques, mixture-tuned matched filtering (MTMF) and support vector machine (SVM), were applied to VNIR hyperspectral data of the cliff face of a volcanic island in Dokdo, South Korea, and the classification results were compared. Results show that SVM is superior to MTMF for the classification of volcanic rocks and weathering minerals. The distinction between volcanic rocks with similar compositions and textures deteriorated using both methods. The shading of the surface owing due to unevenness and stratification also affected the accuracy of classification. This study shows that ground-based VNIR hyperspectral image analysis is a powerful and an effective approach to predict possible geomorphological changes and safety on volcanic islands, as it can explore the weathering of sea cliffs and highlight potentially vulnerable locations.

Новое местонахождение наскального искусства на береговых скалах Оглахты (Хакасия)

The article presents the results of investigation of the rock art site discovered in 2014 on riverside rocks in the Oglakhty mountain range (Republic of Khakasia, left bank of the Yenisei River). One of the largest rock art complexes of the Minusinsk Basin is located in these mountains; the best known in archaeology are the tremendous concentrations of petroglyphs which were located on coastal cliff s before they were fl ooded by the reservoir of the Krasnoyarsk hydroelectric power station. Most of them are irretrievably lost, but some are still preserved and becoming relatively accessible in periods of lower water level. In the process of searching for and redocumenting the petroglyphs at the locations already known (Oglakhty I and II according to Ya. A. Sher’s inventory) new decorated panels have been revealed, and not only in the fl ooded levels, but also on inaccessible rocks above the highest water level. Th is new location is situated upstream from the known ones, within the southernmost section of the riverside cliff s. Several years of regular inspections of this section from a boat at various water levels and with binoculars made it possible to fi nd and document 24 panels, containing about 50 complete and partially preserved fi gures of wild animals (elk, red deer, roe deer, aurochs, arkhar, horse and others). Several stylistic groups of images are distinguished; almost all of them have analogies at known sites, which allows us to confi dently attribute them as a whole to the earliest phase of Minusinsk Basin rock art which undoubtedly predates the Bronze Age, although the specifi c period of its existence has not yet been determined.

Lava deltas, a key landform in oceanic volcanic islands: El Hierro, Canary Islands

Marine and subaerial erosion of volcanic ocean islands form coastal cliffs and shore platforms, particularly during stable sea levels. Posterosional lava flows can spill over these coastal cliffs and fill the platforms, leading to the progradation of lava deltas. This work aims to analyze this volcanic rocky coast setting at the island scale and to assess the volcanic constructional and erosive degradational effects on the coast at the scale of one volcanic edifice. El Hierro Island, Canary Islands, exemplifies a rocky coast with an active sea-cliff profile, reflecting its early evolutionary stage as a young ocean volcanic island with no fringing reef. The occurrence of a contemporary insular shelf formed during the Holocene sea-level highstand (<7 ka) allows constraining the ages of those eruptions forming lava deltas affecting this geomorphological landform. A detailed bathymetry around the island allowed us to distinguish 17 eruptions fulfilling this criterion. The Montaña del Tesoro, which occurred about 1050 years BP, is one of these eruptions and was selected as a case study for morphometric modeling integrating subaerial and submarine data at the scale of a volcanic edifice. This eruption was a Strombolian basaltic volcanic event that produced a scoria cone, pyroclastic fall deposits, and lava flows that reached the ocean in the eastern rift zone of El Hierro island. We combine field-based observations with topographic and bathymetric data analysis to reconstruct the pre- and post-eruption Digital Elevation Models (DEMs) and, comparing with present-day DEM, to analyze morphometrically the influence of volcanism on the coastal landscape's development. The resulting landform complexity required the discretization of the lava field according to the coastline evolution and lava front sectors, and the subaerial or submarine lava placement. The pyroclastic materials' total erupted bulk volume (12,829,578 m3) corresponds to a volcanic eruption index (VEI) of 3. This event was primarily effusive. From a dense rock equivalent (DRE) volume of 25,615,424 m3, 87 % flowed as lava, 10 % formed the cinder cone, and 3 % the tephra fall deposits. We quantitatively demonstrate that dominant degradation occurs in the lava field, mainly disturbed by marine erosion. Marine erosion removed 9 % of the erupted volume of lava flows against 1 % by fluvial erosion. This work provides methods and results of great interest with different implications in oceanic volcanic islands, among which we can mention coastal planning (e.g., rock coast evolution) and volcanic risk assessment (e.g., the importance of Holocene sea-level rise on the development of shore platforms facilitating the progradation of lava deltas).

Geomorphological and Structural Assessment of the Coastal Area of Capo Faro Promontory, NE Salina (Aeolian Islands, Italy)

Capo Faro Promontory, located in Salina (Aeolian Islands, southern Italy), is a popular summer destination due to its volcanic morphologies, seaside, and enogastronomy. A flat area, right behind the scarp edge of a coastal cliff, hosts the Capo Faro Estate, one of the most renowned vineyards and residences on Salina Island. The promontory has been characterised in terms of geomorphological features. Remote sensing analysis, after nadir and off–nadir UAV flights, supports the field activities to explore the hazard to which the area is subjected. In particular, the coastal cliff turns out to be affected by a rapid retreat inducing landslides. Therefore, the cliff area has been investigated through a detailed stratigraphic and structural field survey. Using the generated high–resolution Digital Elevation Model, bathymetric–topographic profiles were extracted along the coastline facing the cliff. The thickness of volcanic deposits was evaluated to obtain a geological model of it. The main rock mass discontinuities have been characterised to define the structural features affecting the stability of the rock wall. The obtained results prove the contribution of such research fundamental in planning risk mitigation measures.

Crowd-sourced SfM: Best practices for high resolution monitoring of coastal cliffs and bluffs

Structure from motion (SfM) photogrammetry is an increasingly common technique for measuring landscape change over time by deriving 3D point clouds and surface models from overlapping photographs. Traditional change detection approaches require photos that are geotagged with a differential GPS (DGPS) location, which requires expensive equipment that can limit the ability of communities and researchers to perform frequent (i.e. daily, weekly, and/or monthly) surveys. Crowd-sourced photos can lower the barrier to entry and substantially increase the frequency of surveys, although such photos often lack accurate location information and can vary in quality. This paper presents a SfM approach for monitoring environmental change in high relief coastal environments that does not require all photos have DGPS location information and does not require field survey data. A 1.5 km section of coastal bluffs near the Elwha River Delta (Washington state) is used to demonstrate the efficacy of this approach. Photos of the bluff were collected with a digital SLR camera or phone camera while either on foot along the beach or from a boat as part of monitoring following removal of two large dams along the Elwha River during 2011–2013. Only 33% of photos had DGPS location information, whereas most photos had no location information or locations that were accurate to a couple of meters. All photos were processed using 3D, 4D, and fixed-floating (FF) SfM alignment methods and the resulting dense point clouds are used to compare the different alignment approaches with crowd-sourced photo sets. Results demonstrate that 4D and FF approaches are more likely to reconstruct and are more accurate than the 3D approach. While the 4D and FF have comparable accuracies, the FF approach is several orders of magnitude more efficient, as this method can leverage camera location information from relatively few photos to improve the accuracy of all aligned and derived products. Effectively utilizing crowd-sourced photos in SfM change detection can improve the frequency of surveying a landscape in a more cost-effective approach that also has potential for citizen-science engagement and communication. This is especially important for data-poor environments such as high-relief coastal cliffs and bluffs, where near-nadir imagery and LIDAR may fail to accurately capture near-vertical cliffs or bluff faces. Based on the analysis of different photo alignment and filtering approaches, we present suggested best practices for engaging citizen scientists in coastal cliff and bluff monitoring efforts through collecting photos amenable for SfM reconstruction.

How to Include Crowd-Sourced Photogrammetry in a Geohazard Observatory—Case Study of the Giant’s Causeway Coastal Cliffs

The Causeway Coast World Heritage Site (Northern Ireland) is subject to rockfalls occurring on the coastal cliffs, thus raising major safety concerns given the number of tourists visiting the site. However, such high tourist frequentation makes this site favorable to implement citizen science monitoring programs. Besides allowing for the collection of a larger volume of data, better distributed spatially and temporally, citizen science also increases citizens’ awareness—in this case, about risks. Among citizen science approaches, Structure-from-Motion photogrammetry based on crowd-sourced photographs has the advantage of not requiring any particular expertise on the part of the operator who takes photos. Using a mock citizen survey for testing purposes, this study evaluated different methods relying on crowd-sourced photogrammetry to integrate surveys performed by citizens into a landslide monitoring program in Port Ganny (part of the touristic site of the Giant’s Causeway). Among the processing scenarios that were tested, the Time-SIFT method allows the use of crowd-sourced data in a very satisfactory way in terms of reconstruction quality, with a standard deviation of 8.6 cm.

Assessment of Moraine Cliff Spatio-Temporal Erosion on Wolin Island Using ALS Data Analysis

The aim of the article is to present the temporal and spatial variability of the cliff coast erosion of the Wolin Island in 2012–2020 in three time periods (2012–2015, 2015–2018, 2018–2020). The research used data from airborne laser scanning (ALS), based on which DEM models were made. Based on the differences between the models, the amount of sediment that was eroded by the sea waves was determined. The conducted research showed that, in the analyzed period, the dynamics of the Wolin cliffs were characterized by high variability. The greatest erosion was observed on sandy cliffs, and the smallest on clay cliffs and on cliffs that are densely covered with vegetation. In the sediment budget studies, two seashore erosivity indicators were proposed: length-normalized sediment budget (LB) (m3/m) and area-normalized sediment budget (AB) (m3/m2). The average annual dynamics of the cliff edge erosion on the Wolin Island was found to be LB = 6.6 ± 0.3 m3/m/a, AB = 0.17 ± 0.01 m3/m2/a. The results obtained are comparable with other postglacial cliffs. The use of the differential analysis of DEM models allows for the determination of the dynamics of the cliff coast and may be used in spatial development and planning of seashore protection zones.

Rocky coastal cliffs reinforced by vegetation roots and potential collapse risk caused by sea-level rise

Evaluation of the effect of vegetation roots on the stability of rocky coastal cliffs is necessary to understand geomorphological, environmental and ecological changes in coastlines caused by sea-level rise (SLR). To better understand these topics, coastal cliffs with and without vegetation were investigated. Study cliffs were selected on Taketomi-jima Island and Kuro-shima Island, both in Okinawa, southwestern Japan, because their environmental settings are similar except for the vegetation cover: the islands are only 10 km away from each other and comprise uplifted coral limestone, with an elevation below 5 m. Pandanus odoratissimus (PO) covers the seaward edge of the top surface of the coastal cliffs in Taketomi-jima but is absent in Kuro-shima. Field investigations were conducted on both islands to map the distribution of blocks with the dimension of one side exceeding 1 m to obtain the parameters required for stability analysis. The results indicate that the actual coastal cliff elevation is higher in Taketomi-jima than that in Kuro-shima by approximately 1 m, which results in the presence of PO on the seaward edge of the coastal cliffs in Taketomi-jima and its absence in Kuro-shima. The PO root system likely reinforces the cliffs in Taketomi-jima because the stability analysis results revealed that these cliffs are unstable in terms of their dimensions. Therefore, the possible disappearance of PO in Taketomi-jima caused by an SLR of 1 m in the following several decades or hundred years can increase the apparent frequency of cliff collapses by approximately tenfold.

Seismic signatures of individual wave impacts on a coastal cliff

AbstractThe mechanisms through which wave action induces cliff erosion are not well quantified, which limits our ability to model future cliff erosion. Previous studies have investigated using seismic measurements of cliff‐top ground motion from wave impacts as a proxy for potential wave driven cliff erosion. However, most attention has focussed on averaged hourly statistics, rather than at the individual wave impact scale. Higher temporal resolution studies are needed to determine the extent to which frequent, low magnitude impacts transfer wave energy into cliff rock, compared to violent impacts that occur much less frequently. We carried out fieldwork in Taranaki, New Zealand on a cliff that is exposed to broken, breaking, and unbroken wave impacts at different tidal stages. Synchronized seismometer, wave gauge, and video data were collected to observe a range of wave impact types under different marine conditions. Approximately 7500 wave impacts were manually classified into eight groups according to the stage of wave transformation at impact using video data. Corresponding seismic signals were then analysed to compare ground motion and impact types. The greatest peaks in ground motion were associated with impact classes identifiable by the wave breaking just in front of, or onto the cliff face. Waves classed as broken and unbroken had a median displacement of 4.2 μm and 5.1 μm, respectively, whereas breaking wave impact classes had a median displacement value of 25.8 μm. Spectral analyses of impact types suggest that different impacts produce peaks in energy at different frequency bands, and the total energy transfer is higher for breaking wave impact classes. This research provides a first step in assessing the spectral signature of wave impacts at an individual wave scale, providing a new method to investigate wave–cliff interaction.

Итальянский пейзаж в творчестве Константина Горбатова

Based on the first widely presented in Russia exhibition of works by the Russian emigrant artist Konstantin Ivanovich Gorbatov (1876–1945) organized in 2021 by the State Museum of History and Art ‘New Jerusalem’ with the participation of museum and private collections, the author analyzes a part of the master’s pictorial heritage dedicated to Italy. A graduate of the Imperial Academy of Arts and a follower of the Russian impressionist tradition, Gorbatov first came to Italy during his retirement trip in 1912. There he was able to feel the power of color and the influence of the light and aerial environment on the transformation of color, and forever remained faithful to the Italian landscape. Having left their homeland in 1922, Gorbatov and his wife settled in Berlin but made numerous journeys to Italy, where he always worked a lot. While staying in Capri, he would travel along the Italian coast, creating his chronicle of charming towns scattered on the coastal cliffs and poetic landscapes inspired by the emerald color of the sea and the bright sun. The subject of the research is the paintings by K.I. Gorbatov dedicated to Italy and his Notes on Art and Life that provide comments on the peculiarities of the master’s perception of nature, vision of color and balance of colors, and his work with color. The research aims to study K.I. Gorbatov’s works in the context of life and work of the Russian artistic emigration in Europe in the second quarter of the 20th century through the analysis of his Italian landscapes, and to analyze the master’s creative method using archival materials. This will contribute to raising understanding and awareness of his art among Russian viewers who were deprived of the opportunity to familiarize themselves with the artist’s work for a long time. The development of the declared research topic involves the application of the interdisciplinary approach, archival, empirical, and iconographic methods, and comparative, artistic and stylistic analyses.

The Tertiary sequence of Varkala coastal cliffs, southwestern India: An ideal site for Global Geopark

Varkala, along the southwestern coast of Peninsular India, has a unique place in Indian geology and geomorphology due to the presence of coastal lateritic cliffs, which exposes the entire Mio-Pliocene sequence of Warkalli Formation, and is declared as the type area. Stratigraphically, this formation exposes carbonaceous clay with lenses of lignite and sticks of marcasite, followed by variegated clays and sandstone. The presence of variegated lithounits endows beauty to these cliffs. Varkala cliffs, edging the Arabian Sea, run for a length of 7.5 km. These cliffs, together with confined beaches, made Varkala a popular tourist destination. Several geodiversity spots within the Varkala Cliff geoheritage site make Varkala geologically unique, just like the vestiges of the last separation of Indian subcontinent from the Mascarene Plateau; showcasing lateritization and distribution of beach placers, and jarosite, formed as a diagenetic replacement mineral from marcasite and considered as a Martian analog, are distinctiveness of the cliff. Additionally, Varkala is an internationally acclaimed beach tourist destination. Furthermore, there are several geoheritage sites as well as socio-cultural-historical sites in the hinterland of Varkala Cliff geoheritage site, which are within the proposed Varkala Global Geopark jurisdiction. Thus, this area fulfills all the criteria to be a Global Geopark. The socio-economic-environmental analysis showcases the changes that have occurred in these 3-end members. When the economic sphere was unaffected, the social scenario was slightly affected (25%) whereas the environmental aspect then drastically deteriorated by 75%. But, the SWOT analysis still elects Varkala as a potential Global Geopark. The concept of geopark contributes to at least one of the 17 goals in Agenda 2030 Sustainable Development Goals (SDG) of the United Nations (UN). Consequently, this work also aims at propagating, not only the need for converting the geologically prominent areas to a geopark, but also attaining SDG, whatever is possible through geoparks.

Spatial and temporal trends in California coastal cliff retreat

Airborne LiDAR datasets were used to measure erosion and retreat along 866 km of California coastal cliffs between 2009–2011 and 2016. Erosion exceeding the level of detection was observed at 55% of cliffs. State-averaged cliff face and top retreat rates were both 0.06 m yr−1, and varied alongshore, with more erosion in northern California compared to southern and central California. Retreat rates were higher for unarmored cliffs and cliffs fronted by sandy beaches. Mean cliff top retreat rates were lower than in previous studies conducted between the 1920s–1930s and 1998/2002, and between 1998 and 2009–2011. However, the average cliff face retreat rates and statistical distributions were similar (r2 = 0.99) for the 1998 to 2009–2011 and 2009–2011 to 2016 time periods. No significant correlation was found between cliff erosion rates and environmental factors such as rock hardness, rainfall, groundwater, waves, and relative sea level change. However, the highest cliff face retreat rates (>1 m yr−1) occurred at locations with weak rocks.

Geomorphological evolution of the calcareous coastal cliffs in North Iberia (Asturias and Cantabria regions)

This paper presents an analysis of the main morphologies observed in the coastal cliffs of northern Spain (Asturias and Cantabria regions). The objective of this contribution is to establish a hypothesis on the origin and evolution of this rocky coast, as well as to present a detailed inventory, to characterise quantitatively and qualitatively singular morphologies and to highlight the geological heritage of this protected coast. The evolution process starts with the formation of an ancient coastal planation surface characterised by a flat morphology caused by regional mainly uplift and to relative sea level falls. Afterwards, wave erosion processes would have started eroding the cliff foot and simultaneously, karst activity produced some exokarst morphologies (sinkholes, karren, etc.) through stratification and fracturing network, while the underground drainage systems produced some caves and chasms. In the following step, corresponding to the last glaciation from the paleoclimatic point of view, sea level fall together with a deepening of the fluvial network caused the preservation of the existing caves and chasms and the generation of new ones at a lower level. On the other hand, dissolution processes on limestones created sinkholes in those areas characterised by alternating layers of limestones and marls, generating collapses. When the sea level reached the maximum height during the Holocene a new erosion cycle of the coastal cliffs began. As a consequence, new landforms and processes were produced, like bays, caves fillings, and intrusion of new sediments in small confined estuaries. In these areas, other types of morphologies associated with the last sea level rise can be observed, such as closed beaches, uncommon closed estuaries developed inside a sinkhole, blowholes produced by mixed wave action and widening of prevailing vertical pipes inside the limestones (including the second largest in the world), total or partial sedimentary filling of small confined estuaries, as well as a tombolo deposit. It is important to point out, that some sites described are included in the Spanish Inventory of Sites of Geological Interest (IELIG). Due to the evolution model here proposed, a portion of the coastal sector described are included in the Global Geosites Project.

CLIFF CHANGE DETECTION USING SIAMESE KPCONV DEEP NETWORK ON 3D POINT CLOUDS

Abstract. Mainly depending on their lithology, coastal cliffs are prone to changes due to erosion. This erosion could increase due to climate change leading to potential threats for coastal users, assets, or infrastructure. Thus, it is important to be able to understand and characterize cliff face changes at fine scale. Usually, monitoring is conducted thanks to distance computation and manual analysis of each cliff face over 3D point clouds to be able to study 3D dynamics of cliffs. This is time consuming and inclined to each one judgment in particular when dealing with 3D point clouds data. Indeed, 3D point clouds characteristics (sparsity, impossibility of working on a classical top view representation, volume of data, …) make their processing harder than 2D images. Last decades, an increase of performance of machine learning methods for earth observation purposes has been performed. To the best of our knowledge, deep learning has never been used for 3D change detection and categorization in coastal cliffs. Lately, Siamese KPConv brings successful results for change detection and categorization into 3D point clouds in urban area. Although the case study is different by its more random characteristics and its complex geometry, we demonstrate here that this method also allows to extract and categorize changes on coastal cliff face. Results over the study area of Petit Ailly cliffs in Varengeville-sur-Mer (France) are very promising qualitatively as well as quantitatively: erosion is retrieved with an intersection over union score of 83.86 %.