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The Rocky Coasts of Northwest Spain: Dynamic Processes, Sediments and Management
Abstract
The coastline of Galicia is more than 2100 km long (POL Galicia 2010) (Fig. 2.1). Two broad types of coast can be differentiated in the region: zones with rías and zones without rías. Marine inlets dominate in the former, whereas rectilinear stretches dominate in the latter and only small coves or estuaries occur. The megaforms of coastal relief in northwest Spain are clearly determined by the tectonic structure, whereas lithological differentiation has played a predominant role in the genesis of meso and microforms (Pérez-Alberti and Blanco-Chao 2005). In general, different factors are involved in shaping the coastline: the overall structure is determined by tectonic processes; the lithology causes differential erosional processes that define the broad features of the coastal front; and, finally, the succession of geomorphological processes that have taken place over time have determined the specific forms and distribution of the different environments. In addition, human activity has affected many areas, particularly the low-lying coastline.
... Shore platforms are plains, generally narrow, located in the intertidal zone. They are not very abundant and are found both inside the estuaries and outside them (Pérez-Alberti and Gómez-Pazo 2019), both in high and low energy sectors, being modeled on metamorphic rocks (Fig. 21a), or on granitic rocks (Fig. 21b). In some places, the platforms are barely 5 m wide. ...
... The variety of typologies of block beaches is high (Pérez-Alberti and López-Bedoya 2004;Pérez-Alberti and Gómez-Pazo 2019). Within them, there are those that are the result of washing the granite alteration layer, those resulting from the dismantling of the granite platforms, or those resulting from the remobilization of the deposits generated by mass movements that have occurred on the façade, or those resulting from cliffs or from the destruction of ancient deposits, mostly of periglacial or snowy origin. ...
Galicia is a complex territory from the environmental (lithology, relief, climate) and socio-economic (population, distribution of productive activities) perspectives. Its geographical position has determined its paleoenvironmental dynamics throughout the last glacial cycle (Würm), in whose final phase a large part of the territory was under glacio-nival conditions, and has favored the emergence of favorable conditions for the domain of deciduous forests throughout the last two thirds of the Holocene. However, as a result of human colonization of most of this territory over the last 5,000 years, its vegetation cover has been greatly homogenized, first favoring the expansion of agricultural crops and scrublands (particularly heaths) and, already in recent times, forest plantations with introduced species (pines and Eucalyptus). The best examples of the characteristic vegetation of this territory take refuge in the steepest mountains, certain slightly altered coastal stretches, and some wetlands. Nonetheless, Galicia still harbors important elements (species, habitats) for the maintenance of biodiversity on a European scale. Its long-term persistence requires territorial planning and management of land use consistent with this singularity and in line with the evolving scientific knowledge and environmental regulations.KeywordsCurrent vegetationResidual forestsHeathsCoastal complexesWetlandsBiodiversity threats
... The number of Iberian Peninsula studies are focused on cliff retreat describing some coastal evolution models based on the features and processes observation is very scares, such as those providing information on cliff behaviour in Algarve (Portugal) by Moura et al. (2006) and Oliveira et al. (2019) and in Spain in the cost of Cádiz (Del Río and Gracia, 2009;Anfuso et al., 2007), Catalonia (Montoya-Montes et al., 2019) or in Galicia (Blanco-Chao et al., 2003;Pérez-Alberti and Gómez-Pazo, 2019). Fewer still are those that present a global and general vision of the functioning of the northern coast of the Iberian Peninsula, considering the different morphologies together with the karstic processes and that, therefore, define the bases for a general evolution coastal model. ...
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 characterized 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 characterized 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.
... As Rías Baixas, caso de Vigo, Pontevedra, Arousa e Muros e Noia, están claramente vencelladas coa dinámica tectónica. Nas Rías Altas, ao anterior hai que sumarlle o papel xogado pola existencia dun bandeado litolóxico, orientado en sentido N-S, que potenciou procesos de disección diferencial e favoreceu a incisión fluvial (Pérez-Alberti & Gómez Pazo, 2019). ...
Coídos are beaches composed of cobbles and boulders that are usually found in association with cliffs and rock platforms, particularly in granite-dominated areas. They consist of accumulations of heterometric, predominantly boulder-sized clasts, often between 1 and 2 m and even with their main axis exceeding 2 m in some areas. The best examples of coídos are found in the area known as Costa da Morte, located north of Cape Vilan (Camariñas, A Coruña); in the Corrubedo area (Ribeira, A Coruña), and along the stretch of coastline located between Cape Silleiro and the Miño river estuary (Baiona, Oia, O Rosal, and A Guarda, in Pontevedra).
According to their shape from top view, five broad types have been defined: longitudinal, double-pointed, arched, corridor-like, and single-pointed. Genetically, four types can also be distinguished: those derived from granite exhumation processes; those generated by the dislodgement of rock fragments from shore platforms and sea cliffs; those produced by rockslides, and those originated by glacial deposition. Their genesis is often of multiple origin.
In order to study boulder mobility, a micro-drone was flown at low heights over two coídos, one in Laxe Brava (Ribeira, A Coruña) and the other in Oia (Pontevedra). Flights were carried out in July 2012, May 2013, and April 2014. These flights yielded ortophotographs and high-resolution digital terrain models (DTM), which were integrated in a GIS and used to monitor thousands of cobbles and boulders for changes in their position. Maximum storm wave height was greater during winter 2013-2014 than during winter 2012-2013, resulting in an increase in the proportion of moved boulders from 17 % to almost 48 % in Laxe Brava and from 53 % to almost 88 % in Oia.
Understanding the external and internal geodynamical processes shaping the Earth is challenging. Physical, chemical, and biological processes form the ground surface over time. Erosion, weathering, transporting, and sedimentation are the natural processes that shape landscapes. However, the continuous interactions of external geodynamic drivers, such as water, wind, and biota, play vital roles in shaping the Earth’s surface. These complex and interconnected processes impact the landscape and environment, making it essential to comprehend them to predict evolution, variability, and changes. This Topical Collection (TC) is a comprehensive set of over 54 articles (to date, it has over 16,500 accesses and 119 citations) focused on Earth’s processes and environment in a changing world. It was grounded in paying tribute to the legacy of the outstanding Spanish geomorphologist, geographer, and honorific Professor Augusto Pérez-Alberti, whose thoughtful contributions have significantly advanced the understanding of earth processes, particularly glacial and periglacial processes, sedimentary dynamics, hydromorphology, and coastal geomorphology. Understanding the geodynamics of the processes that shape Earth systems is critical to protecting and preserving ecosystems, landscapes, natural resources, and communities’ well-being.
The Moroccan coastline extends for 2,130,80 km on the East Atlantic an Western Mediterranean coasts. It shows a high diversity of estuaries, bays, beaches and steep coasts. Despite its ecological, economic, and recreational importance, Morocco does not have a comprehensive inventory of its coastal landscapes. This study attempts to develop a primary classification of Moroccan steep coasts, based on a descriptive inventory of these landscapes, using 12 morphodynamic criteria that we mainly measured on satellite images. To achieve the said classification, we organized the steep coasts and the criteria in a binary matrix, which we treated with the hierarchical ascending classification method (CAH) and Factorial Correspondence Analysis. The results of this treatment provides a clustering scheme where we distinguish six different groups of cliffs, each of them being subdivided to 2 or 3 subgroups. Three categories of criteria appear as determinant in this classification: morphometric (length, area, and elevation), geologic (dominant rock and geologic eras), hydrodynamic (swells), and aerodynamic (wind). However, the two first criteria have the most significant influence on the classification.
This classification, mainly based on satellite data, remains preliminary and requires improvements such using some field data. Finally, the raw and compiled data collected in this study constitute database composed of 175 cliffs, described using parametric criteria; this database is a contribution to the national wetlands inventory and is essential to promoting their conservation as well as management.
Nowadays, a traditional image of Galicia still survives showing the country as a uniform territory, but in fact there is a very different reality that materializes in a wide set of spaces with numerous contrasting landscapes. This is due to several factors: (a) firstly, the existence of an extensive coastal strip and a wide continental territory; (b) secondly, the existence of altitudinal contrasts, linked from the coast to the interior; (c) thirdly, different climatic and biogeographic environments that can be found both on the coast and inland; (d) and, fourthly, a long geomorphological and anthropic evolution affecting to this geographic area.
The contrast between the coast and the interior is, without a doubt, a first element that explains the diversity of Galicia’s landscapes. The length of its coasts-more than 2000 km-and its sinuous profile, with numerous inlets and outlets, due to the chaining of estuaries, bays, inlets, and capes, favored the genesis of contrasting spaces, with linked rocky coasts, beaches, lagoons, estuaries and rías and dune systems. In addi-tion, from the coast inland, a clear staggering of terrain levels is observed. On the same seashore stands a set of mountains, which reach 500/600 m of altitude. This is the case of A Capelada and Montes da Candieira, between the Ortigueira and Cedeira estuaries; O Barbanza, between those of Muros/Noia and Arousa; the Montes do Castrove, between those of Arousa and Pontevedra, or the Montes da Groba and O Galiñeiro, situated in the south of the Vigo estuary.
The above commented staggering becomes more relevant towards the interior. If a west–east cut is made, it is seen that the terrain rises to 1100 m in the western sierras, descends to 400/500 m in the interior of Lugo and Ourense, and reaches 2000 m again in the eastern sierras, in the limits with Asturias and Castilla y León. Also to add the existence of a wide and diverse fluvial network that is intensely embedded, with a large number of narrow and deep valleys that give rise to hills with a diversity of slopes. If lithological diversity is also added to this, it is easier to understand the reasons for the visible differences in the landscapes. From west to east, igneous and metamorphic rocks and, to a lesser extent, sedimentary rocks, are situated in a linking chain. On the Atlantic façade, granites and granodiorites are dominant. In the central regions, mafic and ultramafic rocks are present (as peridotites, eclogites, or gabbro). In the north, schists. In the center and in the south, again granites. In the eastern regions, there are slate, quartzite, limestone and dolomite bands, with small granitic intrusions.
This diversity of lithology, topography and endogenous or exogenous processes, that took place in Galicia over millions of years, has given rise to the presence of landscapes marked by geological factors and that are visible in different places in the Iberian northwest.
Keywords: Geomorphology Landscape, Galicia, Northwestern Iberian Peninsula
Biodiversity loss is considered one of the main threats to marine ecosystems. In this framework of biodiversity decline, organisms that provide biogenic habitat play a relevant role by their capacity to structure assemblages and influence ecological processes. The Mediterranean mussel Mytilus galloprovincialis is considered an ecosystem engineer because it alters local environmental conditions maintaining habitat suitability for other organisms, and enhancing local biodiversity. Although it is widely recognized that mussel beds increase diversity, the drivers shaping these assemblages are poorly explored. We investigate whether mussel size homogenisation shapes the abundance, richness and structure of macrobenthic assemblages associated with mussel beds in two shores of the Galician coast (NW Spain). At each shore, two sites, 10 m apart, were selected and at each site, faunal assemblages were compared between mussel clumps showing shells of various sizes (control), and mussel clumps with closely similar-sized mussels, considered as homogenised. Homogenised clumps showed, in general, higher values in total number of individuals and species than control clumps. Regarding the effect of mussel size homogenisation on the multivariate structure of the assemblages, significant differences between control and homogenised clumps were found in three out of the four sites. Most relevant associated species usually reached higher abundances in homogenised clumps than control ones. Therefore, mussel size homogenisation influenced the structure of the macrofaunal assemblages associated with mussel beds but, its effect was context dependent (i.e., varied with sites). Information about the species contribution to dissimilarities among homogenised and control clumps was provided and the potential influence of sediment and algae on mussel clumps was discussed.
There are several coastal classifications. Most of them have been elaborated worldwide using tectonic, climatic, topographic, or oceanographic criteria. Other classifications have been generated on a larger scale and focused on classifying the coastal forms, as cliffs, beaches, estuaries, lagoons, or dune complexes in different places.
This project analyzes the types of coastlines, understanding as such each sector that presents certain topographic conditionsmarked by the elevation and slope, and that wasmodeled on a concrete type of rock in a specific climatic and marine environment. This paper describes a methodological approach for a detailed scale classification. This approach based on the delimitation of the different coastal systems, exemplified in cliffs and boulder beaches, sandy beaches, and dunes. In this case the shore platforms, marshes and lagoons have not been considered for the technical problems derived from the LiDAR data source, from which the 2 m spatial resolution digital terrain models (DTM) are derived.
The first step in the classification was a manual delimitation combining DTMs and orthophotographs. Subsequently, other typification has been carried out through the automatic creation of Coastal Topographic Units (CTU). This index is the combination of two variables: coastal elevation and slope. The possible integration of others, such as orientation or lithology, is possible, but generate a very high number of units and make it difficult to interpret. For this reason, this study did not consider more variables.
In this project 30 CTUs was generated, and then selecting only those that appear in the cliffs, boulder beaches, sandy beaches, and coastal dunes sectors. The possibility of viewing one or several CTUs in any sector of the coast allows to know more accurately the conditions of each sector and these categories could be improve the coastal management plans. PAPER ACCEPTED. PREPRINT VERSION
Recent technological advances have made it possible to improve the accuracy of coastal studies through devices such as RFID (Radio Frequency IDentification). These sensors allow the monitoring of elements of the
environment at any time since its placement and offer a great level of detail. This research is developed in a boulder beach in Oia (Pontevedra), where 80 RFID sensors were installed in the natural boulders, without changing their position. The sensors were placed in lines of 5 elements perpendicular to the coastline. After the first winter, there is a general movement of the boulders. Of the 48 recovered, 81% have displaced more than 50 cm, minimum value to consider that there was movement. The greater displacements have occurred in boulders whose axes didn’t exceed 100 cm, with a maximum distance of 20,47 meters. As for the areas of greater mobility, it is clearly perceived that the central sector of the study area present greater variations in the position of the boulders, while the north and the lower part of the beach, where it is located coastal platform, are the most stable areas.
Resúmen: Trabajos recientes han demostrado que, en plataformas litológicamente homogéneas, el esclerómetro puede registrar cambios en la resistencia de la superficie de la roca en función de la alteración mareal, de forma que, en ausencia de procesos de erosión mecánica, fundamentalmente de abrasión, la alteración tiende a incrementarse hacia las cotas de marea alta. En este trabajo hemos empleado una metodología semejante, para estudiar un sector de la costa cantábrica gallega en donde afloran dos pequeñas plataformas rocosas. Las plataformas que afloran en Punta Gallín se han desarrollado sobre materiales metamórficos cámbrico-ordovícicos de la Serie de los Cabos, y en su parte posterior están fosilizadas por un depósito complejo en el que alternan niveles de origen continental y marino. El análisis estadístico de los datos de resistencia obtenidos con el esclerómetro en estas plataformas ha demostrado que las diferencias morfológicas en las mismas no responden a diferencias litológicas, sino a los efectos combinados de la alteración mareal, la erosión mecánica actual y procesos de erosión mecánica y alteración heredados. Abstract: Recent research in Galician Coast demonstrated that, in shore platforms with homogeneous lithology, the Schmidt Hammer is able to identify changes in the rock strength caused by tidal weathering. In absence of mechanical erosion processes, weathering degree tends to increase towards the levels of high tide. In this work we have used a similar methodology, to study two small rocky platforms in the Cantabrian Galician coast that have developed on metamorphic rocks and with a cliff deposit in which levels of continental and marine origin alternate. The statistical analysis of the strength data obtained in these platforms has demonstrated that the morphological are not directly controlled by lithological differences but by the combined effects of the tidal weathering, and the inherited processes of mechanical erosion and weathering.
A boulder-strewn rock platform on an Atlantic-facing coastline in Gweebarra Bay, NW Ireland, is examined using an integrated geomorphological, ecological and geotechnical methodology. Here, a steep granite shore platform is cut by intersecting subvertical and subhorizontal fractures and shows a clear biological and geomorphological zonation associated with level within the tidal frame. Minimum surface strength values of the bedrock platform (as derived from Schmidt hammer tests) corresponds to the supralittoral zone, which is dominated by Ramalina siliquosa. Bedrock surface strength increases into the littoral zone, which is characterized by a succession through Verrucaria maura, Semibalanus balanoides and Mytilus edulis communities. Granite boulders in the upper intertidal zone are clustered and stacked into ridges that have a consistent spacing and northeast-southwest alignment. Boulders within the ridges are imbricated, stacked, and have west-facing dips. Boulder surface strength is higher on northwest-facing ridge sides than on southeast-facing sides, and is higher at the landward than seaward ridge end. Variations in surface weathering across the platform show where blocks have been recently removed by storms. Pulverized bedrock and boulder surfaces show where boulders have knocked into each other and been dragged across the platform by backwash. It is likely that such boulder features are formed and destroyed on decadal or shorter time scales.
The main characteristic of the NW Iberian coast is the presence of the “Rias”. Its origin is tectonic, fluvial and marine. The high regional relief is the result of a long crustal uplift since the middle Eocene which controlled the morpho-structural characteristics of the coastline. However, the substratum lithology and the regional landscape evolution are responsible for the more detailed geomorphic features. This study presents the first sedimentological and OSL dating results of a coastal reach located in the right margin of the Pontevedra Ria mouth..
More specifically, the site is located at a small embayment near Sanxenxo (Pontevedra, Spain). The rocky substratum is dominated by intensively fractured Precambrian-Silurian mica schists. Along the coast, a wave-cut platform, about 500 m long and 100 m wide, is subdivided into an eastern and western sector by a rocky headland. One can distinguish a modern wave-cut platform (only exposed at low tide) from an older wave-cut platform (rocky terrace) which has a slope of 4o and is exposed at an altitude of 1.8m to 4.5-5m above sea level. In the western sector the old wave-cut platform is overlain by a 2 m- thick reddish gravelly beach deposit having its base cemented by iron oxides. This beach deposit is erosively covered by a 4 m-thick colluvium, comprising debris flow deposits alternating with gravel pavements that are parallel to the slope. In the eastern sector, the 5 m-thick coastal terrace consists of a sandy-gravelly beach deposit grading upwards into aeolian yellowish medium sands. Locally, a lenticular bed of a greyish green silt was found interbedded in the aeolian sands. At the top, the aeolian sand unit is disconformably capped by a heterometric gravel containing angular clasts of quartz and mica schists inbedded in a sandy matrix. This coastal sedimentary succession is interpreted to represent a time interval of high sea-level, more elevated than the present one, during which the littoral platform was cut and later covered by gravelly beach sands (MIS5). Later, during MIS4, the climatic conditions and the progressive sealevel lowering lead to the accumulation of aeolian sands in the eastern sector. The rocky headland (40 m high) prevented sand deposition in the western sector indicating a prevalence of southwestern winds. Finally, the colluvium unit that disconformably covers the aeolian sands in the eastern sector and the beach deposits in the west - ern sector, points to a cold and humid environment (MIS3 to MIS2) as suggested by the debris flow deposits and associated slumping features. The altitude of the MIS5 wave-cut platform is an indication for regional tectonic stability. Preliminary quartz OSL dating results seem to confirm our interpretation of the different sedimentary units; the final ages will be presented at the conference.
This is the first book to deal comprehensively with Spain's tectonic and sedimentary history over the past sixty or so million years. During Tertiary times, Spain had suffered compressional collision between France and Africa, and its Atlantic and Mediterranean coasts had been further modified by extensional rifting. This study will therefore be of interest to earth scientists generally because of the insights it provides into continental crustal deformation. Spain contains some of the best exposed outcrop geology in Europe. Because it includes sectors of two separate foreland basins, and an intervening craton with basins that have been influenced by extensional and strike-slip deformation, it provides excellent material for the development and testing of theories on the study of sedimentary basin formation and filling.
This is a comprehensive reference text for senior undergraduates, graduate students, and instructors and working professionals in the coastal field. It provides a thorough survey of a present state of geomorphological knowledge across a very broad spectrum of coastal types, including topics, such as the form and processes operating on cold coasts, deltas, cohesive cold coasts, and coral reefs, that have rarely been included in general coastal texts. There is also a detailed discussion on the nature, origin, and transport of beach sediment, and the possible effects of future sea-level changes on coastal environments. Anthropological influences and managerial implications are discussed in several of the chapters. All the material draws upon up-to-date research and scientific findings.
Two models were devised to investigate the development of wave-cut shore platforms, and in particular, how platform width changes through time. One model considers the rates of erosion at the high and low tide levels; whereas the other is concerned with the way in which the tide distributes wave energy within the tidal range. Despite these differences, both models indicate that platforms eventually attain states of dynamic equilibrium. Using data from a variety of morphogenic environments, the models suggest that sufficient time has been available since the sea reached its present level, for shore platforms to be at, or close to their equilibrium states.
The text begins with an introduction to concepts and terminology, and the factors that have affected coastal evolution and coastline changes (Chapter 1). This is followed by a discussion of waves, tides, currents and other nearshore processes (Chapter 2), and a study of the effects of land and sea level changes, notably the Holocene marine transgression, which has played a major part in shaping modern coastlines and can be regarded as a unifying theme in coastal geomorphology (Chapter 3). Cliffs are discussed in Chapter 4 and the shore platforms that border them in Chapter 5. Chapter 6 deals with the origin of beaches and the changes taking place on them, and Chapter 7 with the beach erosion problem. Spits, barriers and bars are discussed in Chapter 8 and the formation of coastal dunes in Chapter 9. Intertidal wetlands, including mudflats, salt marshes and mangroves are dealt with in Chapter 10, followed by estuaries and lagoons, including other inlets (rias, fiords, fiards, calanques, sharms and sebkhas) in Chapter 11. Chapter 12 considers deltas produced by deposition at river mouths, and Chapter 13 reviews coral and algal reefs. Chapter 14 deals with future coasts. There are 187 illustrations and 15 tables. Details of articles cited are given in the References section, which includes many pre-2000 publications that remain relevant.
Significant advances have been made in our understanding of rock coast morphodynamics and evolution as a result, in part, of the use of specialized field and laboratory equipment, mathematical modeling, and remote-sensing techniques to measure rates of erosion. Problems remain in determining the age and mode of development of rock coasts, the possible role of inheritance, the effect of rising sea level, and the relative importance in time and space of the myriad processes that operate according to climatic and geological conditions.
Variations in the width of shore platforms were investigated within southern Wales, Gaspe in eastern Canada, and southern Japan. The strong, positive linear relationship between platform gradient and tidal range implies that platform width may be largely independent of tidal range, although regional negative correlations between platform gradient and width suggest that platforms become narrower with increasing tidal range. Platform width increases with wave intensity, and the widest platforms are oriented toward the dominant waves. The width of the platforms also decreases with increasing rock dip. A structural classification, based upon combinations of rock dip and strike, relative to the orientation of the cliff face, helped to explain variations in platform width in Canada and Japan. Changes in structural class induced by variations in coastal orientation may partially account for differences in the width of platforms on headlands and in embayments. Platform width is also influenced by the presence and type of cliff-foot deposits.
Platform gradient was investigated in three areas of England and Wales, providing a wide range of morphogenic and geological conditions. A correlation coefficient of 0.92 (n = 36) was obtained for platform gradient against tidal range and one of -0.60 (n = 36) for fetch perpendicular to coastal orientation; analysis of covariance demonstrated that there was little difference in the regression for Liassic limestones and shales and chalk. A further correlation coefficient of 0.79 (n = 23) was noted between platform gradient and cliff height for the chalk exposures. It is proposed that platform gradient in these areas is being maintained in dynamic equilibrium, at least in the early period of development.
Differences in slope between Australasian and southern British shore platforms may be explained by morphogenic conditions, the high slopes of platforms in England and Wales being related to high tidal range, storm waves, large and abundant erosional debris, and climatic conditions unsuitable for effective waterlayer levelling. Other typical Australasian features such as the low tide cliff and true platform ramps are, however, generally absent from southern Britain. A classification of contemporary and 'raised' shore platforms and ledges is proposed for England and Wales, in which lithologically controlled storm ledges are distinguished from shore platforms. The relevance of detailed studies of contemporary shore platforms to investigations of 'raised' planation surfaces is emphasized.
Two models were devised to investigate the development of wave-cut shore platforms, and in particular, how platform width changes through time. One model considers the rates of erosion at the high and low tide levels; whereas the other is concerned with the way in which the tide distributes wave energy within the tidal range. Despite these differences, both models indicate that platforms eventually attain states of dynamic equilibrium. Using data from a variety of morphogenic environments, the models suggest that sufficient time has been available since the sea reached its present level, for shore platforms to be at, or close to their equilibrium states.
This reference text deals with the geomorphology of rock coasts. It brings together the results of research conducted by coastal engineers, biologists, geologists and physical geographers from many parts of the world. The first section of the book discusses changes in sea level and the effects of mechanical wave action, chemical weathering, solution, bio-erosion, frost, and mass movement on rock coasts. The second section is concerned with the major landforms which result from these processes. These include cliffs, shore platforms, coastal karst, bays, headlands, and elevated marine terraces.
Low altitude flights by a micro-drone were made in 2012 and 2013 over two boulder beaches in northwestern Spain. Geographical information system software was used to map the data. Boulder outlines from the first flight were recorded on 4796 clasts at Laxe Brava and 2508 clasts at Oia. Changes in location were identified by overlaying these outlines on the 2013 images. About 17.5 % of the boulders (mean surface area 0.32 m2) moved at Laxe Brava and about 53 % (mean surface area 0.23 m2) at Oia. Most movement on both beaches was between the mid-tide to about 2 m above the high tidal level. The location and elevation of the highest points were also recorded on the 2012 images on 4093 boulders at Laxe Brava and 3324 boulders at Oia. These elevations were compared with the elevations at the same locations in 2013. The occurrence and scale of the elevational changes were generally consistent with changes in the boulder outlines. The study confirmed that boulder beaches can be cheaply and effectively monitored using high resolution, micro-drone technology. This article is protected by copyright. All rights reserved.
In this paper we investigate how geological contingency causes variations in scales of erosion within a single study site as opposed to variations between sites. Discontinuity data were collected on different layers of Blue Lias limestone on a shore platform in Wales, United Kingdom. Significant differences in block size were found between stratigraphic layers exposed on the surface of the platform. Evidence of geological contingency from this study illustrates that erosion susceptibility is dependent on which layer of limestone is at the surface, as different layers provide variations in resistance to erosion. Since the size of blocks varies between layers depending on the depth of beds and joint spacing, variations occur in the magnitude of wave energies required to remove blocks. Therefore the rate at which the shore platform and cliff develops is geologically contingent and variable through time and space. The findings of this research: 1) highlights how rock control influences processes and rates of environmental change of a coastal landform; 2) illustrates the critical importance of local scale contingency in shaping/controlling environmental processes and resultant landforms and; 3) demonstrates that greater detail and quantification of geological parameters is required by geomorphologists in all aspects of rock geomorphology.
This paper is the first review of coastal boulder studies; it serves as a peer-reviewed introduction to a special issue on the topic of ‘Boulders as a signature of storms on rock coasts’. Since 2004 and the Indian Ocean tsunami, most coastal boulder research has been focused on using boulders as sedimentary signatures of palaeo-tsunami events and the most commonly used transport equations typically suggest that large boulder deposits are products of tsunami rather than storms. There is growing empirical evidence demonstrating (on inter-annual to century timescales) that storm waves are capable of transporting and depositing boulders of significant size at elevations well above sea level. Current process studies of how boulders are eroded, transported and deposited have not received wide attention by rock coast geomorphologists or palaeoenvironmental reconstruction scientists. This special issue is framed around the goal of highlighting our current understanding of the role of storm waves as a driving mechanism for boulder erosion, transport and deposition. Here, we review the current state of knowledge about boulder dynamics, boulder responses to storms and boulders as sedimentary signatures of storm events. We identify gaps in our conceptual and quantitative understanding. Lastly, we propose means of addressing research gaps, improving consistency between researchers and collecting multi-purpose data. This review and the papers contained within the special issue provide an improved understanding of coastal dynamics; particularly the role storms can play in influencing erosion rates and depositional patterns of coarse material (i.e. boulders or larger), which has hitherto been under represented in the literature.
In this paper we examine the sedimentological properties and morphodynamic evolution of a boulder beach at Huayanpeng Cape on Putuo Island off the southeast China coast. Focus is given to the formation of the boulder beach (256–2000mm diameter) and resulting morphology in relation to high-energy storms and seasonal typhoon. Holocene sea level rise to the present position at ca. 7000–6000yrs BP provides a long term window for the formation of the beach. The beach is primarily characterized from east to west by: 1) the convex to concave beach morphology, 2) reduced longest axis of the skeleton boulders, 3) decreased flatness of the skeleton boulders, and 4) greater sphericity of the skeleton boulders. Infilling cobbles/pebbles in the beach demonstrate a bi-modal distribution, corresponding to dominant sizes of 100–250mm and 50–100mm in diameter, on the eastern beach and western beach, respectively. This reflects changed intensity of storm waves alongshore. Multiple-peaks of the distributions of infilling clasts for the western beach (supratidal) probably reflect storm and calm weather sedimentation. Statistically, both the skeleton boulders and infilling clasts follow a β-distribution, reflecting the high-energy control of beach formation and the dominance of crushing in boulder size reduction. A boulder transport model applied in the present study further reveals that boulders with an a-axis length of 500–1000mm (the dominant component on the beach) move under a wide range of wave conditions depending on wave height and wave period with a cluster of critical wave heights in the range 2–6m and wave periods of 5–15s.
Summarises some of the general features of sea cliff profiles and shows that studies of profiles can be useful for estimating stability for residences, railroads, and highways at the top, face, and base of sea cliffs. Generally increased erosion and retreat of sea cliffs are in prospect because of projected regionally wetter and stormier climate, rising sea level, and increased human activities.-after Author
Erosion rates are 15–18.5 times higher in places where there is a beach at the cliff foot compared with those where there is no beach. The zone of intense erosion associated with a beach of sand and pebbles was below a height of about 10 cm above the surface, maximum erosion being at 14.5 cm below the surface. Erosion was by corrasion and wedging, a previously unrecognised process which is the quarrying of rock aided by fine-grained particles from the beach. Wedging, perhaps with some corrasion, had a median erosion rate of 11.05 · 10−3 cm tide−1 in Upper Lias shale while the rate for corrasion was 5.79 · 10−3 cm tide−1. A smooth, notched cliff foot may be produced by these processes. Where there was no beach, erosion of the cliff foot was by the sporadic quarrying of blocks of rock and the more continuous micro-quarrying of shale fragments. The cliff foot was dominated by structural planes and had a rough surface. The horizontal erosion rate due to quarrying at one cliff foot was 2.3 cm year−1. Quarrying acts on the cliff foot above the intense zone of erosion at a beach surface. The median erosion rate for this quarrying was 0.91 · 10−3 cm tide−1.
Processes of platform development include mechanical wave erosion, weathering and bio-erosion. Form is strongly influenced by lithology and structure. Contrasts between British and Australian forms are noted. These seem to be opposite ends of a tidally regulated wave erosional spectrum of forms. Rates of platform development raise questions of inheritance. -Jennifer Clayton
The rock coast of northwest Ireland comprises steep cliffed headlands and more open coastal sections where bedrock shore platforms are developed. Many shore platforms are overlain by boulders; the locations on the platform from which boulders are derived are marked by ‘holes’ of fresh and unweathered rock surfaces that are not, or are poorly, covered by lichen. These areas of boulder detachment are termed sockets. This paper examines the mapped distributions and physical properties of boulders, sockets and shore platform context of an Atlantic-facing granite shore in County Donegal, northwest Ireland. Results from Schmidt hammer rebound tests show statistically-significant differences in rebound values between areas inside and outside of sockets and between sockets and boulders. Based on their distributions and physical properties, relationships between sockets and boulders are explored. We calculate that sockets are formed rapidly by winter storms but are also rapidly weathered over c. 5years, becoming indistinguishable from the surrounding bedrock platform. We argue that, in contrast to some studies, boulders here were formed during recent winter storms (episodically during the last 150–200years) rather than by more ancient waves or by tsunamis. However, a significant proportion of boulders (c. 20%) are morphometrically dissimilar to sockets; we argue that these were formed by infrequent and unusually-powerful waves that stripped whole bedrock sheets off the platform surface and which detached boulders from the lower shoreface.
The Schmidt Rock Test Hammer was used to study the effect of abrasion on shore platforms in Galicia, northwestern Spain. On platforms where tidally-induced weathering (salt, wetting and drying, etc.) is dominant, rock strength is significantly lower than in areas where abrasion is, or has been active in the recent past. This suggests that abrasion removes weathered surface material, exposing the stronger, less weathered rock below. Abrasion downwearing, measured with a transverse micro-erosion meter, ranged between 0.13 and 1.8 mm yr− 1 over the last year. Most active abrasion occurs in the upper part of the intertidal zone, but weathering is slowly destroying formerly abraded surfaces at lower elevations. These abandoned surfaces were abraded by materials supplied by erosion of fluvio-nival and periglacial slope deposits that covered, or partially covered, parts of the Galician coast during the middle and late Weichselian. During the Holocene, rising sea level and erosion of the slope deposits caused the abrasion zone to gradually migrate up to its present position near the high tidal level. The spatial and temporal role of abrasion on this coast is, therefore, closely associated with the exhumation and inheritance of ancient platform surfaces from beneath Weichselian deposits.
This paper is concerned with the effect of sediment accumulation on shore platform development. Boulder accumulations are common on the granitic shore platforms of Galicia, northwestern Spain. Boulders are produced by erosion of shore platforms and of cliffs consisting of cold-climate deposits from the last glacial period. Measurements were made of the long axis length of more than 800 boulders, and additionally of the short and intermediate axes of 340 of these boulders, as well as of their orientation and gradient. There were two study areas. The boulders on the Barbanza Peninsula are generally a little smaller than those in southern Galicia with, respectively; mean long axis lengths of 0.98 and 1.14, and masses of 1.06 and 1.59 t. There are also some isolated, very coarse boulders and megaclasts in southern Galicia. The distribution and extent of the deposits and boulder imbrication and orientation testify to the high levels of wave energy produced by northwesterly and westerly storms in this region. Although the boulders, as well as the underlying shore platforms, were inherited, in part, from previous interglacial stages, some boulder detachment and movement is occurring today during storms, when significant deep water wave heights exceed 8 to 10 m. Despite some abrasion of the shore platforms, the primary effect of large boulder accumulations is protective. The role of sediment on shore platforms has been neglected, but this study suggests that because of arrested development under thick accumulations, platform gradient in areas with abundant sediment increases with the grain size of the material. The occurrence and type of sediment on shore platforms may therefore help to explain the distribution of sloping and subhorizontal platforms under different morphogenic and geological conditions.
Four types of shore platform are recognised in northeast Yorkshire: 1.Class 1 — the platform is a sub-horizontal plane which has erosion rates of the order of 0.01–0.20 cm year−1 though these are exceeded near the cliff foot. Erosion rates increase with altitude but the platform develops by landward extension of the plane.2.Class 2 — the platform has a ramp, a slope greater than 2.5°, at the cliff foot and a plane seaward of this. The ramp is covered by a beach of debris that can be moved by waves. Erosion rates are of the order of 0.10–3.00 cm year−1, the grain size and thickness of the beach and its altitude being important determinants of these. The plane encroaches on the base of the ramp which moves landward as the cliff foot is eroded. Development of the ramp increases the height of the cliff foot which rises at an angle of up to 2° as it retreats. The high erosion rates lead to this being the widest type of platform.3.Class 3 — the platform is a ramp throughout its width. It may be overlain by large boulder beaches which protect it from wave action and allow almost negligible erosion rates. This is the narrowest type of platform.Changes in the size or nature of the debris on these three types of platform may lead to changes in their morphological class.4.Class 4 — the platform is affected by geological factors and so the ramp and plane cannot be easily recognised.
Abstract Five boulder beaches located along the coast of New South Wales, Australia, were examined in order to determine if beaches composed of boulders differ in basic sedimentological structure and behavior from beaches composed of cobbles or pebbles. Each beach is aligned obliquely to the approaching waves and is composed of locally derived sediment. Investigation of beach-particle size, morphology, and roundness, along with foreshore slope, reveals consistent up-beach particle fining, positive size skewness, absence of shape zoning, absence of sphericity grading, and low foreshore slope. These characteristics of the five studied boulder beaches contrast markedly with the known characteristics of beaches composed of finer sediment, which suggests that boulders appear to form fundamentally distinct coastal sedimentary assemblages.
ABSTRACT The morphometry of shore platforms is determined by their morphogenic environments. Gaspé, Québec is a mesotidal storm wave environment. Shore platforms are cut into steeply dipping flysch, consisting of shale, graywackes, and argillites. The platforms are quasihorizontal, with a low-tide cliff or low-tide ramp at their seaward termini, and a high-tide ramp at the cliff base. Platform gradient is determined by tidal range, mean platform elevation by midtide level, and the cliff platform junction by level of the high tides; lithological and structural factors play a secondary role. Platform width is a function of wave intensity and rock hardness. Most elements of platform morphometry are determined by the elevational distribution of wave action, particularly during storms.
Very large boulders (mega-clasts) are found on some coasts. The size and position of the boulders has been used to suggest that contemporary marine processes, acting within their normal spatial and energy range, are unlikely to have moved them. Explanations for the presence of such boulders include transport by infrequent very high-energy marine processes (storms or tsunamis), mass movement from backing cliffs, transport by ice, or exhumation from glacial deposits. This paper advances an alternative explanation which does not involve transport by any of the marine or glacial processes, or gravity. It is proposed that, in a very specific geological and topographic setting, large boulders are exhumed in situ by storm waves acting on heavily weathered jointed basalts. Eventually wave action liberates residual blocks from the deeply weathered matrix. These liberated boulders will be mobile only if they lie within wave competence, and the larger ones will remain as stationary residuals. The same in situ weathering processes, followed by removal of the friable matrix material debris by wave action, also progressively round the boulders. Consequently, despite their appearance of being transport-rounded, the larger boulders have not transported at all. In specific locations, the assumption that the presence, and rounding, of such large clasts in the shore zone can be attributed to marine transport can lead to erroneous interpretations of very high-energy storm wave (or tsunami) activity.
Understanding the distribution of wave energy on shore platforms is important for models of the long term development of both shore platforms and backing cliffs. Little is known, however, of the magnitude of the wave currents generated on shore platforms in storms. This study uses the distribution of boulders of different sizes on a shore platform on the North Sea coast of Scotland to investigate patterns of storm wave current velocities. In storms over the last 40–240 yr, blocks as large as 9 m 3 have been quarried from the rock step at LWMS and boulders of N 0.5 m 3 have been moved landward over extensive areas of the platform. In earlier storms, boulders N1 m 3 have been moved widely. Wave current velocities in storms have likely reached 3–4 m/s on many parts of the platform, especially in the slightly deeper water along smooth-floored strike canals developed in marl beds. Attenuation of velocities across the platform is limited. Storm wave action is a key process in erosion across large parts of this shore platform. Wave impacts quarry large blocks at or near LWMS and wave current velocities in storms are sufficient to transport landwards large clasts and smaller debris. Weathering of soft marl beds also contributes directly and indirectly to development of the shore platform. Lowering of marl beds at long term rates of ~ 1 mm/yr in response to recent sea-level fall leads to the undercutting and eventual collapse of overlying, more competent rock beds, releasing blocks for wave transport. Deepening of strike canals, by both water-layer weathering and wave action, allows faster wave currents to reach and erode cliffs at the rear of the platform. On this exposed, macro-tidal coast, shore platforms are eroded by both wave action and weathering processes operating over various spatial and temporal scales.
A shore platform on the western coast of Galicia in northwestern Spain has been inherited from interglacial stages when sea level was similar to today. The wide, gently sloping intertidal platform is backed in places by supratidal rock ledges, and in other places by a steeper and narrower supratidal ramp. The gradient of the intertidal platform is consistent with the relationship between platform gradient and tidal range, but the slope of the ramp is much too high. The abandoned and degraded sea cliff is grass-covered along most of this coast, and the ledges and the ramp, which extend up to several metres above the highest tides, are covered by lichen and, in places, by salt-tolerant plants. Radiocarbon-dated sediments in the cliff, which range up to 36 000 years in age, lie on top of an ancient beach deposit. The former beach, remnants of which are found in situ on the ramp and rock ledges, as well as two caves that are filled with the dated sediments, are probably last interglacial in age. The morphological and sedimentary evidence suggests that the supratidal ramp and ledges were also formed during the last interglacial stage, whereas the wider intertidal platform is probably the product of several older interglacials, when sea level was generally similar to today. A general model is proposed for the inheritance of shore platforms in macro- and microtidal environments. Copyright © 1999 John Wiley & Sons, Ltd.
Megaclasts of well cemented coralgal limestone have been emplaced onto a shore platform by large waves on the North Shore of Oahu, HI. Emplacement and movements of the largest, ca. 96 ton megaclast have been dated using aerial photographs. Hydrodynamic forces at the low submerged shoreline cliff are computed using design wave characteristics based on linear wave theory and experimental results, considering the local wave climate and near-shore bottom topography. Force exerted by a tsunami has been estimated based on the 1946 Aleutian Tsunami. The computed forces are evaluated in terms of the initial fracturing along a given failure plane that is required in order for the detachment to occur. The analysis shows that tsunami, as well as large swell waves, are capable of quarrying the megaclast, provided that sufficient initial fracturing is present. Dislodgement and emplacement most likely occurred in a sequence during impact of a single wave on the shoreline cliff. Swell waves, however, are seldom capable of emplacing large blocks onto the platform due to their rapid disintegration after breaking, so that most blocks quarried from the cliff edge fall back onto the submarine terrace. Emplacement of large boulders seems to require extreme sea waves with periods longer than storms or North Pacific swells usually produce. Transport mechanisms on the shore platform vary, depending on megaclast shape. Sliding is a common mechanism of transport for larger and irregular megaclasts, whereas somewhat smaller and platy megaclasts are occasionally found in overturned positions.
Hypotheses advanced concerning the origin of the Pleistocene Hulopoe Gravel on Lanai include mega-tsunami, abandoned beach, ‘multiple event,’ rocky shoreline, and for parts of the deposit, Native Hawaiian constructions and degraded lava flow fronts. Uplift of Lanai shorelines has been suggested for deposits occurring up to at least 190 m. These conflicting hypotheses highlight problems with the interpretation of coarse gravel deposits containing marine biotic remains. The geological records of the processes implied by these hypotheses should look very different. Discrimination among these or any other hypotheses for the origins of the Hulopoe Gravel will require careful study of vertical and lateral variations in litho- and biofacies, facies architecture, contact relationships and stratal geometries of this deposit.
The recent evolution and the present coastal dynamic in middle Atlantic latitudes, as the coast of Galicia, can be considered in a paraglacial context. The fossilization of Eemian coastal landforms by deposits developed under cold conditions, followed by a paraglacial environment during the Holocene transgression. The characteristics of the different types of deposits and the rising sea-level curve controlled the evolution of the coastline, showing the co-existence of bluff-retreat and continental sedimentation.
The tsunami hypothesis proposes that prehistoric tsunamis may have been larger than historic ones along coasts normally (historically) not associated with major tsunamis. The evidence for the hypothesis rests with the types of unusual sedimentary deposits and erosional forms along coasts where the largest historic and prehistoric storm waves do not appear capable of forming the features. This is especially the case at locations where boundary conditions, i.e. offshore water depth, coastal geomorphology and meteorological limitations, are not conducive to the propagation of sufficiently large storm waves at the shore. The tsunami hypothesis has been barely debated in the literature. This is despite the view of some, who suggest that storms have been overlooked, or underestimated, as a cause. Few comparisons have been made of the supposed tsunami generated features and the impacts on coasts of extreme intensity storms. Four of the most powerful tropical cyclones anywhere in the world in recent times struck the Western Australian coast between 1999 and 2002. The results of post-event surveys of these storms showed that none of them produced the enigmatic forms attributed elsewhere to tsunamis.
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