Article

Shore platform abrasion in a para-periglacial environment, Galicia, northwestern Spain

January 2007
Geomorphology 83

DOI:10.1016/j.geomorph.2006.06.028

Authors:

Ramon Blanco-Chao

University of Santiago de Compostela

Augusto Pérez-Alberti

University of Santiago de Compostela

Manuela Costa-Casais

University of Santiago de Compostela

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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.

Coastal Retreat and Sedimentation during the Last 3000 Years. Atlantic Coast of NW Spain

Article

Full-text available

Sep 2019

During the last glaciation, thick nival and periglacial sediments buried large sectors of the NW coast of Spain. The sediments were mostly eroded by the rising sea level during the Holocene, but in several places they remain, forming sedimentary cliffs. Radiocarbon dates obtained at the topmost layers of these cliffs prove that continental sedimentation was active until very recent times, followed by a retreat of the cliffs. During the first stages of the transgression, the erosion of the cliffs and the changes in the coastal system were controlled by the rising sea-level. Once the sea-level stabilized, the exhumation of inherited landforms, the supply of sediments, and a continuous continental sedimentation became the main factors. The last stages of cliff retreat were almost synchronous with the sedimentation of the upper layers of the deposits.

Identifying mechanisms of shore platform erosion using Structure‐from‐Motion (SfM) photogrammetry

Article

Jan 2019

Shore platforms control wave energy transformation which, in turn, controls energy delivery to the cliff toe and nearshore sediment transport. Insight into shore platform erosion rates has conventionally been constrained at mm‐scales using micro‐erosion metres, and at m‐scales using cartographic data. On apparently slowly eroding coasts, such approaches are fundamentally reliant upon long‐term observation to capture emergent erosion patterns. Where in practise timescales are short, and where change is either below the resolution or saturates the mode of measurement, the collection of data that enables the identification of the actual mechanisms of erosion is hindered. We developed a method to monitor shore platform erosion at millimetre resolution within metre‐scale monitoring plots using Structure‐from‐Motion photogrammetry. We conducted monthly surveys at 15 0.25 m2 sites distributed across the Hartle Loup platform in North Yorkshire, UK, over one year. We derived topographic data at 0.001 m resolution, retaining a vertical precision of change detection of 0.001 m. We captured a mean erosion rate of 0.528 mm yr‐1, but this varied considerably both across the platform and through the year. We characterised the volume and shape of eroded material. The detachment volume‐frequency and shape distributions suggest that erosion happens primarily via removal of shale platelets. We identify that the at‐a‐point erosion rate can be predicted by the distance from the cliff and the tidal level, whereby erosion rates are higher closer to the cliff and at locations of higher tidal duration. The size of individual detachments is controlled by local micro‐topography and rock structure, whereby larger detachments are observed on more rough sections of the platform. Faster erosion rates and larger detachments occur in summer months, rather than in more energetic winter conditions. These results have the potential to form the basis of improved models of how platforms erode over both short‐ and long‐timescales.

Análisis comparativo de los distintos tipos de paisaje costeros de Galicia

Chapter

Nov 2018

En este estudio se pretende clasificar distintas zonas del litoral gallego para así poder visualizar con claridad sus diferencias y analizar las razones que marcan los distintos paisajes. Para alcanzar este objetivo inicialmente se realizó un análisis cuantitativo en el que se han considerado la altitud del sector costero (6 categorías) y la rugosidad del terreno (4 categorías), calculando ambas variables con una resolución espacial de 2 metros. De este análisis se obtuvieron un total de 24 tipologías litorales. A partir de los tipos de costa generados se realizó un análisis interpretativo en el que se tuvieron en consideración las características paisajísticas de cada sector, como la litología o los usos de suelo presentes. Como resultado de este trabajo se han evidenciado las grandes diferencias existentes en el litoral gallego, desde zonas como la costa sur donde destacan las altitudes bajas con rugosidades elevadas hasta áreas como la costa lucense donde dominan las altitudes medias y rugosidades moderadas. La variedad de tipos de costa determina junto con la diversidad de usos del suelo la configuración de los distintos paisajes presentes en el litoral gallego, en el que se encuentran zonas muy diferenciadas en espacios muy próximos.

Tracking clast mobility using RFID sensors on a boulder beach in Galicia, NW Spain

Article

Nov 2020
GEOMORPHOLOGY

Previous studies using unmanned aerial vehicles and remote sensing techniques have provided data on group sediment dynamics and overall mobility of a boulder beach at Oia in Galicia, northwestern Spain. They recorded changes in the location and disposition of hundreds of clasts but were unable to trace the intermittent movement of individual boulders. Radio Frequency IDentification (RFID) sensors were used in the present study to identify and record the long-term trajectories of boulders in this area. Sensors were installed in 80 boulders (mean intermediate axes approximately 55 cm) in September 2016 and were used to locate and record their displacement on five occasions, terminating in December 2019. Although burial and other factors prevented data being collected from every tagged boulder during these periods, recovery rates ranged from approximately 50%–75% of the original population. There was considerable variability in the displacement of the boulders, with maxima of >20 m and mean values >5 m. The distance of travel tended to decrease during the course of this study, despite a corresponding increase in storm frequency and intensity. Patterns of movement, including transport distance and direction were essentially chaotic in nature, reflecting the complex interaction and compound effect of a multitude of controls related to such factors as the location of boulders on the beach, their relationship to surrounding boulders, including the effects of sheltering, interlocking, and burial, and their size, shape, and other physical characteristics. The unpredictable behaviour and high transport thresholds of boulder beaches are in contrast to sand and gravel beaches that are characterized by more uniform and predictable patterns of sediment transport and morphological change.

Experimental quantification of bedrock abrasion under oscillatory flow

Article

Jun 2020
GEOLOGY

Although wave-driven abrasion of submarine bedrock affects the evolution of rocky coasts and reefs globally, the dependence of the abrasion rate on wave forcing and sediment availability remains poorly quantified. We performed experiments in which an artificial substrate was abraded by varying amounts of coarse-grained sediment subjected to oscillatory flows. In these experiments, the bedrock incision rate scaled by the square of bedrock tensile strength (I, m yr–1 MPa2) varied with mean root-mean-square (rms) velocity ( , m s–1) according to a power law, I = 1.0 4.2 (angle brackets indicate time-averaging over an entire experiment). Additionally, the relationship between sediment load and bedrock incision rate demonstrates tools and cover effects similar to abrasion in fluvial environments, such that incision is fastest at intermediate sediment loads. However, because oscillatory flows accumulate sediment into bedforms, the increased bedrock exposure reduces the efficiency of the cover effect for high sediment loads relative to unidirectional flow. Our results provide an empirical model that can be used to predict bedrock incision rates in nearshore environments based on wave forcing.

Wave-driven geomorphology of Pacific carbonate coastlines: from landscape to wavelength scale

Book

Full-text available

Jan 2020

James F Bramante

Bedrock hardness values and morphological zonation of a shore platform in South Africa

Article

Oct 2019

Shore platforms found along rock coasts worldwide are often interpreted as wave abrasion acting on uniform bedrock surfaces. Whilst this viewpoint may apply at the macroscale, there are complex feedbacks among bedrock properties (rock type, mineralogy, rock structures), weathering and erosion processes and rates, and microtopography at the meso- to microscale. In turn, these influence wave runup, backwash processes, and the extent of wave-splash and physical, chemical, and biological weathering processes that result. This study investigates the relationships among bedrock hardness properties, microtopography, and shore platform denudation processes from a site on the Indian Ocean-facing coast of South Africa. Three shore-normal transects (45–57 m in length) were surveyed across the sandstone platform using a differential global positioning system (GPS). These data were integrated with rock surface hardness measurements along the transects taken using a Proceq Equotip instrument. Results show that platform morphology and hardness values vary considerably, corresponding to the most dominant denudation processes found at different positions in the tidal frame. The lowest hardness values (most extensive rock weathering) are found on the landward third of the platform but away from the land margin. The highest and greatest variability of hardness values are found on bedrock highs immediately above the highest astronomical tide level, in the lower third of the profile. This position suggests a dominant role of wave-splash and wetting/drying. Variations in hardness values and microtopography through the transects were used to develop an evolutionary model linking rock hardness values to specific weathering and erosion processes of the rocky shore platform.

Evolución de un sector costero durante la Alta Edad Media en el NW de la Península Ibérica

Article

Full-text available

Jul 2015

En el presente trabajo se estudia la evolución de un tramo costero de la Ría de Vigo (NW de la península Ibérica) desde época romana hasta el siglo XVII, prestando particular atención a la Alta Edad Media. Desde el punto de vista arqueológico, la importancia del sector radica en la presencia de una salina de época romana, en uso desde los siglos II BC a III-IV AD, y su abandono para dar paso a la instauración de una iglesia y una necrópolis en la Alta Edad Media (a partir de los siglos IV-V AD). Se muestrearon, con alta resolución, tres secuencias edafo-sedimentarias y se analizaron diversas propiedades físico-químicas (pH, granulometría, contenido en C, N, S, P, Fe, As) y la composición mineralógica, con el fin de determinar la naturaleza de las distintas facies presentes, los procesos implicados y las causas asociadas. Los resultados indican modificaciones en la costa entre finales del periodo romano y comienzos de la Alta Edad Media, con unaevolución del medio desde una dinámica costera, con formaciones de marisma-lagoon costero, a una dinámica eólica, con dunas. Dicho cambio es coincidente con el cese de la explotación romana de sal y el inicio del periodo Frío Altomedieval. Estos resultados son similares a los encontrados en otros puntos de la Ría de Vigo. En los tres sectores comparados (Rosalía de Castro, Toralla y Hospital), a la par que se produce la progradación de las formaciones de marisma y duna, el uso antrópico del sector cambia. Aunque la pauta climática presenta un papel importante en la evolución de este sector, los cambios en la línea de costa que se detectan entre ambos periodos culturales pudo estar determinada también por causas socioecómicas. Evolution of a coastal area during the early Middle Ages in the NW of the Iberian Peninsula - This paper focuses on the evolution of a coastal stretch of the Ria de Vigo (NW Iberian Peninsula) during the early Middle Ages, which presents an important archaeological site with a roman salt mine. Salt exploitation in the Roman period ceased around the AD 3rd-5th centuries, and was followed by the establishment of a churcheand a cemetery during the Middle Ages. The properties (pH, grain size, C, N, S, P, Fe and As, and mineralogicalcomposition) of three pedo-sedimentary sequences were analysed in order to identify the different environmental changes that affected this sector. The results suggest signifcant changes occurred in the coast from the late Roman period (AD 3rth-5th centuries) into the early Middle Ages (AD 5th-6th centuries), with an evolution from a marine-continental dynamics, with formation of salt marshes, to a wind dynamics, with dune formations. This change is consistent with the abandonment of the Roman salt exploitation and the beginning of Cold Dark Ages. These results are similar to those found in other areas of the Ría de Vigo. In the three sectors compared (Rosalia de Castro, Toralla and Hospital) land use changed while the progradation of marsh and dune formations occurred. Although climate may have played a major role in the evolution of this sector, the changes in the coastline between the two cultural periods could be also related to socio-economic causes.

The Rocky Coasts of Northwest Spain: Dynamic Processes, Sediments and Management

Chapter

Jan 2019

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.

Shoreline advance due to the 2024 Noto Peninsula earthquake

Article

Full-text available

Nov 2024

Large earthquakes can instantaneously reshape coastal landforms owing to fault zone ruptures that uplift the Earth’s surface. On January 1, 2024, in the north of the Noto Peninsula, central Japan, an Mj7.6 (Mw7.5) earthquake occurred, triggering coastal uplift of up to 4 m. To measure the resulting shoreline advance, we analyzed orthophotos taken before and after the earthquake, focusing on two bays in the northwest of the Noto Peninsula where the largest uplift occurred. In response to the uplift, the shoreline advanced by up to 200 m, increasing the total area of the coastal plains by 0.46 km². The maximum shoreline extension occurred in the midsection of both bays, while the extension at the edges was less than 20 m, possibly reflecting the shoreface topography and bathymetry existing before the uplift. The uplift exposed previously undersea rocks, forming new coastal plains and extending river channels. Our results indicate that coastal landforms such as sandy beaches, coastal plains, shore platforms, and the sediment budgets of feeding drainage systems were substantially altered by this earthquake, and a long recovery period is anticipated. Our findings serve as a crucial benchmark for tracking future changes in shorelines in response to coastal landform adjustments.

Shore platform lowering on a Pacific coast of Japan: Present, past, and future — Applications of a weathering-controlled erosion model and a long-term platform surface evolution model

Article

Full-text available

Oct 2022
GEOMORPHOLOGY

In order to investigate the lowering process of a shore platform in a tectonically active region along the Pacific microtidal coast of Japan, MEM measurements were carried out seven times during 5.8 years (2004–2010). Four measuring sites were installed on a nearly horizontal, smooth platform in the upper intertidal zone, two sites on the platform surface composed of lapilli tuff and the remaining two on that of sandstone. A time- and space-averaged lowering rate of the lapilli-tuff surface is 0.46 mm/yr and 0.35 mm/yr on the sandstone surface. Evaluations for the assailing force of waves on the platform surface, FA, and the resisting force of unweathered bedrock, FR, indicate that FA ≪ FR, which leads to a conclusion that weathering-induced rock-strength reduction is necessary for the occurrence of platform erosion. A weathering-controlled erosion model is constructed with the aid of results from laboratory experiments on rock disintegration by salt weathering. The field application of the model enables us to determine unknown coefficients included in the model. By use of the coefficient values weathering properties of lapilli tuff and sandstone are explored: lapilli tuff is more susceptible to weathering than sandstone, and weathering rates of both rock types are found to be highly time-dependent. A second model is built to examine the long-term evolution of the platform surface. The model calculations are based on the assumption that downward erosion will cease at the Mean Low Water Spring level (1.0 m below the present MSL) and that both lapilli tuff and sandstone surfaces started to erode immediately after a coseismic uplift event of 1.6 m, estimated to have occurred at 880 CE on the basis of ¹⁴C dating of fossil assemblages. It is modeled that the platform will continue to lower toward a steady state in approximate 13,000 years after the present time. Because long-term platform downwearing shows a strong nonlinearity, it is suggested that a linear extrapolation of decadal time scale erosion data to millennial and further to Holocene time scales will lead to inaccurate results. The relationship between platform lowering rates and elevations, derived from the model, indicates that the maximum rates occur in the upper to middle intertidal zone; the result is almost consistent with the previous elevational pattern reported from Canada and Australia.

Using UAV and Structure-From-Motion Photogrammetry for the Detection of Boulder Movement by Storms on a Rocky Shore Platform in Laghdira, Northwest Morocco

Article

Full-text available

Aug 2022

The detachment and mobilization of boulders from rocky shore platforms by waves involves complex geomorphic and hydrodynamic processes. Understanding these processes requires precise information on the rates and patterns of movement of these megaclasts scaled against the wave conditions that generate boulder mobility. Repeat photogrammetry and structure-from-motion (SfM) models commonly used in geomorphic analyses are an interesting option for monitoring boulder dynamics. In this study, we used unmanned aerial vehicle (UAV)-based digital photogrammetry and SfM differential models to identify recent boulder movements over a rocky shore platform in Laghdira, Morocco. Combining these results with data on storm occurrence in the study area allowed us to identify storm waves as the unique driver of the dislodged and mobilized boulders. The identified storm event had a significant wave height of 5.2 m. The UAV models were built from imagery captured in September and December 2019 using a DJI MAVIC PRO PLATINUM, and we used QGIS to produce 2D and 3D model outputs. The exploitation of the 2D model differentials allowed us to appreciate the response of the boulders to the storm waves and to determine platform volumetric changes and, therefore, boulder mobility. The 3D models were valuable in determining the mode of transport of the boulders. Mobility patterns included sliding, overturning with no further mobility, and rotation and saltation, as well as boulder breakup. Storm waves did not have a preferential impact on any particular boulder shape, size category, or position at the outer edge of the platform. These results highlight the utility of combining UAV surveys with identified storm events, which are much more frequent than tsunamis, in determining observed boulder initiation and mobility.

Understanding the retreat of the Jurassic Cantabrian coast (N. Spain): Comprehensive monitoring and 4D evolution model of the Tazones Lighthouse landslide

Article

Full-text available

May 2022
MAR GEOL

Forecasting coastal dynamics and sea cliff retreat under different sea level rise scenarios requires a good understanding of the conditioning factors and their relative contribution to cliff stability. The so-called Jurassic Cantabrian Coast extends along 76 km of the coastline of the Asturias region (N Spain) and is well-known worldwide due to its paleontological heritage, in particular the presence of dinosaur remains and footprints. The abundance of stratigraphic, paleontological and tectonic studies contrasts with the scarcity of studies focused on the stability of this rocky coastline where cliffs predominate, sometimes exceeding 120 m in height. In fact, evidence of current and recent instability processes can be observed along the entire coastline. In this regard, continuous monitoring is crucial to understand ongoing instabilities in rocky coastlines, as in these settings some instabilities might initiate as slow movements that induce subtle topographic changes whose detection from either satellite or aerial imagery is problematic due to the spatial and temporal resolutions. This contribution presents a 4D evolution model of a key site, the Tazones Lighthouse landslide, located on the Cantabrian Coast of Asturias (N Spain), which affects subvertical rocky cliffs sculpted in the Jurassic bedrock made of alternating sandstone and marl. A high resolution multiapproach methodology was developed in order to understand its structure and kinematic characteristics, including: i) interpretation of aerial photographs and unmanned aerial photogrammetric surveys (UAV); ii) 22 monthly monitoring campaigns by total station; iii) 5 manual boreholes; iv) geomechanical characterization of the cliff bedrock; v) geomorphological evidence mapping; vi) analysis of landscape deformations obtained from UAV; and vii) precipitation, soil moisture and significant wave height (Hs) data analysis. The results show that the slope evolves by means of a complex-type mass movement, which combines translational and sliding mechanisms, and occupies tens of thousands of square meters. DTM and fieldwork analysis indicate that mass movement is mainly controlled by bedrock discontinuities (S0, 360/15-17; J1, 262/85; J2 166/75). The most important accelerations of slope movement correlate very well with rainfall, soil moisture and waves. Thus, the largest displacements occurring in January and October–November 2019, coincide with 2 periods of storms (maximum 24-h rainfall of 64.5 mm and 82.1 mm and maximum Hs of 6.54 and 9.09, respectively) and soil moisture values above 90%. Half of the markers moved more than 1 m and one of them exceeded 15 m. The 4D model obtained after the interpretation of the Tazones Lighthouse slope whole dataset, allows an understanding of how the surrounding cliffs have evolved in the past, fundamental to predicting their future behaviour.

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

Article

Full-text available

May 2022
ESTUAR COAST SHELF S

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.

The bioprotective properties of the blue mussel (Mytilus edulis) on intertidal rocky shore platforms

Article

Feb 2022
MAR GEOL

Biogeomorphological processes are an important component in the geomorphic evolution of rocky coasts. Sessile organisms, including those which form dense biological covers, enhance and/or retard weathering and erosion. The common blue mussel (Mytilus edulis) is found on rocky shores in many parts of the world, typically forming extensive beds several centimetres thick. Yet, unlike other canopy forming marine organisms (e.g., seaweeds), the influences of mussels on processes of rock breakdown lack quantitative analysis. This study assesses the potential of M. edulis to act as a biogeomorphic agent through weathering experiments and field trials on a mudstone shore platform in Wales, UK. Monitoring on the shore platform showed that daily near-surface temperature maxima, range and short-term variability were lower on surfaces colonised by M. edulis compared to those that were bare. This was supported by laboratory simulations which showed that (artificial) mussel beds consistently reduced the internal (subsurface) temperature of rock samples during ‘low-tide’ periods. As mechanical rock weathering processes are influenced by surface and subsurface temperature regimes, it is inferred that these stabilising effects may translate to a reduction in the efficiency of particular rock breakdown processes. Rock hardness (Equotip Piccolo) measurements collected from the shore platform support this assertion as mussel-colonised surfaces were found to be significantly harder than bare surfaces, indicating they had experienced less breakdown during exposure to intertidal weathering and erosion. A supplementary field experiment based on the disintegration of gypsum ‘domes’ as an indirect measure of water/wave motion both within and outside of mussel beds further indicates that mussels may act as bioprotective agents by reducing turbulence at the rock surface. Overall, this study presents the first empirical evidence of mechanisms by which mussels may protect intertidal rocks from weathering and erosional processes through the moderation of near-surface microclimate regimes and water motion in temperate environments. Importantly, compared to other canopy forming species, such as seaweeds, the observed dampening effects of M. edulis are likely only small in magnitude. However, as mussels can dominate the surfaces of rocky shores at certain tidal heights, they may act as locally important geomorphic agents that warrant further consideration as one component of the collective effect of bioprotective and bioerosive species in these environments. Further work is now needed to examine the geomorphic roles of mussel beds on a variety of other rock types, and the extent to which their impacts vary in time and space in relation to other biological, chemical and physical agents of change.

Mapping diamondiferous palaeo-shorelines in complicated terrain: seismic and GIS-based methods from the inner shelf of southern Namibia

Article

Full-text available

Sep 2021
GEO-MAR LETT

The inner shelf of Namibia’s southwestern coastline comprises the submerged extension of the world’s largest diamond placer deposit. The onshore raised beach deposits, which are constrained by wave-cut cliffs and platforms, bevelled into the schist bedrock during palaeo-sea level stillstands, are largely mined out. As land-based operations near their practical limit, spatially accurate resource estimation of the inner shelf becomes increasingly critical to extend the life of mine of this extensive but low-grade resource. This study analyses a comprehensive seismic-reflection dataset, to produce a 50-m cell size bedrock morphology surface for the inner shelf. The data reinforce previous results and show that inherited structural influence exerts the overarching control on bedrock morphology at the scale of the study area. However, within this framework, the detailed data have now facilitated the zonation of the study area into discrete structural zones from which subtle coast-parallel bedrock gradient changes, that we interpret to represent submerged palaeo-shoreline morphologies (i.e. bedrock gradient changes associated with wave-cut cliffs and platforms), have been extracted. These bedrock gradient variations are contextualised within areas of similar glacial isostatic adjustment (GIA) response, which lends weight to the GIS-based palaeo-shoreline interpretation. Although these may be considered composite features that are the product of 42 million years of shoreline transgression and regression, the more recent occupation of the shoreline at these depth intervals, during the late Pleistocene/Holocene, forms a critical upgrading component to the offshore resource. Our study proposes a − 20 msl shoreline, the most recent occupation of which we link to the peak of marine isotope stage (MIS) 5c, and a − 30 msl shoreline that is linked to the time shortly after MIS 5c and the peak of MIS 5a. The most recent period of shoreline occupation for the deepest shoreline at − 40 msl is attributed to slowly rising sea level between 10.8 and 10.6 ka. This information is critical to the development of the resource estimation philosophy for the offshore extension of mining operations.

What Controls Bedrock Shore Platform Hardness? A Field Study from South Africa

Article

May 2020

Knight, J. and Burningham, H., 2020. What controls bedrock shore platform hardness? A field study from South Africa. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 537-541. Coconut Creek (Florida), ISSN 0749-0208. Bedrock shore platforms are common features along the Indian Ocean coast of South Africa but their properties and controls have not been well reported. This study presents high-resolution evidence for rock surface properties and hardness values from a sandstone platform at Morgan's Bay (Eastern Cape, South Africa) where the relative roles of environmental versus lithological factors on bedrock surface hardness can be evaluated. Results show that there is very little correspondence between rock hardness and either absolute platform elevation or distance from low water position of sea level. Two contrasting conceptual models are proposed to explain these results. One model proposes that a uniform geological control dominates, despite variations in environmental forcing. The alternative model considers that environmental controls such as waves and subaerial weathering do not significantly vary over the platform, despite any differences in platform relief and microenvironment. These different models can be used as testable hypotheses to evaluate the relative controls on, and thus interpretations of, measurements of rock surface hardness on shore platforms.

Do artificial structures cause shifts in epifaunal communities and trophic guilds across different spatial scales?

Article

May 2020
MAR ENVIRON RES

In the current frame of proliferation of artificial structures in the sea, the ecological effects of those artificial substrates on marine environments and their associate biota become a topic of great scientific and conservation-ist interest. This study was focused on the amphipod communities from western Mediterranean Sea and tested, using the same secondary substrate, Ellisolandia elongata, if the community and trophic structure differ between artificial (two concrete-based: cubes and tetrapods, and one natural rock-based: rip-raps) and natural substrates. Results usually showed lower taxa number and diversity in artificial substrates, as well as differences in composition and trophic structure of the amphipod community. However, patterns were not consistent for all localities, evidencing the importance of local scale. Other potential factors, besides the substrate type, should be considered to understand particularities of each locality in management and conservation strategies.

Cosmogenic 10Be and 26Al exposure dating of Nam Co lake terraces since MIS 5, southern Tibetan Plateau

Article

Feb 2020
QUATERNARY SCI REV

Lake paleo-shorelines can be used to reconstruct lake level fluctuations, which serve as sensitive indicators of climate change. The Tibetan Plateau (TP) contains the highest areal proportion of lakes in China, and dramatic past lake level changes have led to the formation of numerous relict shorelines. Here, we present 24 10Be and 26Al exposure-ages for five of seven lake terraces situated north of Nam Co, on the southern TP. The ages of four high stands marked by terraces (T7, T6, T5, and T4) are 81.5 ± 9.0 ka, 33.6 ± 1.9 ka, 19.9 ± 1.9 ka, and 15.2 ± 0.4 ka. The topographically highest terrace, T7, correlates with periods of enhanced Indian summer monsoon (ISM) and supports an MIS 5 maximum lake expansion on the TP, as opposed to MIS 3. Ages of two lower terraces (T5 and T4) possibly correspond to Melt Water Pulse (MWP) events. We also evaluate different possible sources of uncertainty from geologic processes on 10Be exposure ages of lake terraces. Subaerial erosion following terrace exposure has the most significant influence on 10Be exposure ages on ancient high terraces (for example > 80 ka), while inherited 10Be from prior exposure and partial shielding by shallow water, beach or talus are the most important geological source error of 10Be exposure ages for relatively low and young terraces (for example < 15 ka).

Caracterización e dinámica dos coídos nas costas de Galicia Characterization and dynamics of boulder beaches in Galician coast

Article

Full-text available

Dec 2019

Augusto Pérez-Alberti

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.

Arctic rock coast responses under a changing climate

Article

Full-text available

Nov 2019
REMOTE SENS ENVIRON

It has been widely reported that Arctic sea ice has decreased in both extent and thickness, coupled with steadily rising mean annual temperatures. These trends have been particularly severe along the rock coast of southern Svalbard. Concerns have been raised over the potential for higher energy storms and longer ice-free open water seasons to increase the exposure of Arctic coasts, and consequently the concentration of infrastructure critical to Arctic community survival, to enhanced rates of erosion. Here we present and apply innovative remote sensing, monitoring and process analyses to assess the impact of recent coastal climatic changes. High resolution analyses demonstrate that the small scale (< 0.001 m 3) changes that are rarely considered quantitatively exhibit geo-morphic responses distinct from those of larger, more readily detected cliff failures. We monitor temperature depth profiles in both the shore platform and the cliff face to show rock sensitivity over time to both global and local influences. The results demonstrate the efficacy of thermal processes on Arctic rock cliffs relative to platforms, and may hold implications for understanding strandflat development rates. New three-dimensional thermography (thermal mapping) and process zone characterisation has been used to spatially assess the sensitivity of Arctic rock coast responses to contemporary processes on deglaciating coasts. Through the spatial and temporal analyses of key geomorphic behaviour zones and comparison over a range of sites, the complex and changing interplay between subaerial weathering and cryogenic and intertidal processes has been highlighted. These data challenge long standing assumptions over the future of Arctic rock coasts and identify new, focused lines of enquiry on the decline in cryogenic processes and understanding the sensitivity of Arctic rock coasts to climatic changes.

Wave impacts on coastal cliffs: Do bigger waves drive greater ground motion?

Article

Full-text available

Jul 2019

Coastal cliff erosion is caused by a combination of marine forcing and sub‐aerial processes, but linking cliff erosion to the environmental drivers remains challenging. One key component of these drivers is energy transfer from wave‐cliff interaction. The aim of this study is to directly observe cliff ground motion in response to wave impacts at an individual wave scale. Measurements are described from two coastal cliff sites: a 45‐minute pilot study in southern California, USA; a 30‐day deployment in Taranaki, New Zealand. Seismometers, pressure sensors, and video are used to compare cliff top ground motions with water depth, significant wave height (Hs), and wave impact types to examine and cliff ground motion response. Analyses of the dataset demonstrate that individual impact events can be discriminated as discrete events in the seismic signal. Hourly mean ground motion increases with incident Hs, but the largest hourly peak ground motions occurred across a broad range of incident Hs (0.9 m to 3.7 m), including during relatively calm conditions. Mean hourly metrics therefore smooth the short‐term dynamics of wave‐cliff interaction; hence, to fully assess wave impact energy transfer to cliffs, it is important also to consider peak ground motion. Video analyses showed that the dominant control on peak ground motion magnitude was wave impact type rather than incident Hs. Wave‐cliff impacts where breaking occurs directly onto the cliff face consistently produced greater ground motion compared to broken or unbroken wave impacts: breaking, broken, and unbroken impacts averaged peak ground motion of 287 μm/s, 59 μm/s, and 38 μm/s respectively. The results illustrate a novel link between wave impact forcing, cliff ground motion response using individual wave field measurements, and highlights the influence of wave impact type on peak energy transfer to coastal cliffs.

Identification of plate-forme à vasques on a temperate shore platform? Quantitative analysis of morphology and relationships at Bembridge, Isle of Wight

Article

Jun 2019
Z GEOMORPHOL

Enigmatic shallow vasques-type pools are identified for the first time on a temperate limestone shore platform. Like their counterparts found in tropical and Mediterranean climatic regions the pools occupy the intertidal zone and are separated from each other by raised ridges that facilitate the retention of tidal water. Ebb tidal water drains via low points in the ridges flowing through an interconnected network of pools towards the platform edge. The formative processes associated with ridge formation are generally attributed to bioconstruction or bioerosion. We assert that the adopted ridge forming processes differ between geographic location based primarily on regional climate which restricts the presence of bioconstructing organisms. Additionally, the direction of water flow through the pool network is predetermined by the shore platform gradient which in turn shapes pool morphology via the process of coalescence. Further interpretation and relationships are drawn from field observations and the analysis of a comprehensive set of morphometric measurements of 24 pools derived from field surveys using Differential Global Positioning Navigation Satellite System (DGNSS) and aerial image analysis. The paper quantifies the morphology, geometry and distribution of the pools providing a baseline protocol to inter-compare similar landforms. We attempt to define the relationships governing form and occurrence and identify surface topography and water flow as key components in defining the geomorphology at the site. We propose a theory for pool network evolution which highlights the respective recession rates of the landward cliff and platform edge as significant in maintaining this unique and valuable intertidal habitat with national and European conservation designations.

Late Quaternary Glacial Phases in the Iberian Peninsula

Article

Mar 2019
EARTH-SCI REV

The only glaciers existing today in the Iberian Peninsula are small features located in the Pyrenees, though their number and extension has undergone significant changes over the Late Quaternary. The wide range of glacial landforms and deposits distributed across different Iberian ranges suggests the occurrence of several past periods with larger glacial systems. The objective of this research is to summarize the current knowledge on the spatial and temporal patterns of glacial activity in the Iberian mountains during the Late Quaternary. To this purpose, the chronological framework was divided in six periods: glaciations prior to the Last Glacial Cycle (Middle Pleistocene), Last Glacial Cycle (Late Pleistocene), Termination-1, Holocene, Little Ice Age (LIA) and present-day. The data were geographically divided considering the mountain systems where glacial evidence exists: Pyrenees, Cantabrian Range, NW ranges, Central Range, Iberian Range and Sierra Nevada. During Quaternary cold stages, ice accumulated in the head valleys of these mountain ranges and glaciers flowed down-valleys. In all cases, glaciers remained confined within the mountain systems and did not reach the surrounding lowlands. Depending on the combination of temperatures and moisture conditions, more or less ice was stored. In some ranges, there is evidence of Middle Pleistocene glaciations, one potentially correlating with marine isotope stage (MIS) 12 and another correlating with MIS 6 with glaciation dated to ca. 130-170 ka. However, most of the glacial records correspond to the Last Glacial Cycle and subsequent Termination. The maximum glacial expansion of this last Pleistocene glaciation stage occurred well before the global Last Glacial Maximum (LGM) between 30 and 60 ka in the Cantabrian Mountains and Pyrenees, at ca. 30 ka in Sierra Nevada and NW ranges, and (almost) synchronously to the LGM in the Central Range and Iberian Range. A massive glacial retreat occurred in all ranges at 19-20 ka, but the long-term deglaciation process was interrupted by cold intervals, such as the Oldest and Younger Dryas, which favoured glacial expansion in the highest mountains. Temperature increase recorded during the Holocene conditioned the melting of glaciers, which only reappeared in the highest massifs during the coldest periods, such as the LIA. However, post-LIA warming led to glacier disappearance in the Cantabrian Mountains, Sierra Nevada and most massifs of the Pyrenees, together with an accelerated shrinkage of the small glaciers still existing in this range at elevations near 3000 m.

Recording inter‐annual changes on a boulder beach in Galicia, NW Spain using an Unmanned Aerial Vehicle

Article

Nov 2018

An unmanned aerial vehicle (UAV) was flown over a boulder beach (area 20,000 m²) on the southern coast of Galicia (northwestern Spain) in May 2016, continuing earlier work based on flights over the same beach in July 2012, May 2013, and late March 2014. Digital Surface Models (DSMs) with 1.8 cm resolution were constructed from the 2014 and 2016 data to identify changes in beach morphology over the intervening period. Analyses were conducted using a Limit of Detection (LoD) of 0 cm and 3.71 cm. In both cases, the analyses showed that erosion dominated over 19 % of the beach area. Accretion occurred over the rest of the beach, which acquired an additional 1500 m³ of material over the study period. Re‐analysis of the data from earlier flights suggested that erosion dominated on the beach in 2012‐2013 and deposition in 2013‐2014. Without any clear relationship between beach behaviour and storm severity during each winter period, it is proposed that gravitationally induced erosion and storm‐wave induced deposition are the result of perturbations about an equilibrium beach gradient. The UAV data also suggested that an essentially random component modulates regional patterns of movement.

Seeking the Shore: Evidence for Active Submarine Canyon Head Incision Due to Coarse Sediment Supply and Focusing of Wave Energy

Article

Nov 2018

Submarine flows carve canyons into continental shelves, yet the conditions and events responsible for canyon incision are incompletely understood. Coarse sediment flux has been shown to promote terrestrial bedrock incision via abrasion in rivers, but similar processes in submarine canyons have yet to be systematically documented. We use repeat bathymetry, provenance analysis, wave modeling, and channel network analysis to show that longshore sheltering and wave focusing by the Delgada submarine canyon induce sediment accumulation and elevated wave shear stresses in its headwall region that frequently mobilize coarse bed material. These mobilizations scour bedrock in the headwall and generate abrasive turbidity currents that work to carve the canyon's active channel into bedrock. These findings highlight an important positive feedback between submarine canyons, waves, and sediment supply and suggest that submarine canyons adjacent to wave-dominated, coarse sediment-rich coastlines seek the shoreline through headward incision.

A fundamental equation for describing the rate of bedrock erosion by sediment-laden fluid flows in fluvial, coastal, and aeolian environments: Formula for the rate of bedrock erosion by sediment-laden fluid flows

Article

Aug 2018

Tsuguo Sunamura

A major physical process shaping bedrock landforms in fluvial, coastal, and aeolian environments is abrasion by sediment‐carrying fluid flows. A unifying formula to describe the rate of abrasion occurring in these environments has not been presented, the exploration of which is the purpose of this study. Considering the threshold concept the formulation is made including erosivity of fluid flows and erodibility of bedrock. The formula is described as dΓ/dt = C [(FA/FR) – 1], where Γ is the amount of erosion, i.e. eroded length (distance), volume, mass, or weight, t is the time, dΓ/dt is the erosion rate, FA (= A x [fluid force]) is the assailing force of sediment‐laden fluid flows used as an index of the flow erosivity, FR (= B x [bedrock strength]) is the resisting force representing the bedrock erodibility, C is a coefficient with the same unit as that of dΓ/dt, and A and B are dimensionless coefficients. The equation is confirmed by existing laboratory abrasion data and its applicability is examined using existing laboratory data of fluvial and aeolian abrasion experiments and field data from a coastal area. Examinations applying fluvial and aeolian abrasion data indicate that the coefficient C is found to represent the amount of sediment working as abrasives in fluid flows and the hardness of sediment relative to bedrock; and A is presented to reflect the particle size of the sediment. The coefficient B is a conversion factor from conventional mechanical strength of rocks to the resisting force. Selecting appropriate physical quantities for FA and FR enables the application of this equation to abrasion studies on various landforms in these environments. © 2018 John Wiley & Sons, Ltd.

Clast abrasion of a rock shore platform on the Atlantic coast of Ireland.: Clast abrasion of a rock shore platform

Article

Full-text available

May 2018

The abrasion of coastal rock platforms by individual or clusters of clasts during transport has not been quantitatively assessed. We present a study which identifies the types of abrasion and quantifies erosion due to the transport of clasts during three storms in February and March 2016. We explore relationships between platform roughness, determined by the Fractal Dimension (D) of the topographic profiles, geomorphic controls and the type and frequency of abrasion feature observed. Clast transport experiments were undertaken in conjunction with the measurement of wave energy to assess transport dynamics under summer and winter (non‐storm) conditions. Platform abrasion occurred extensively during the storms. We identify two types of clast abrasion trails: simple and complex. In addition, we find two forms of erosion occur on these trails: Scratch marks and Percussion marks. An estimated 13.6 m² of the platform surface was eroded by clast abrasion on simple abrasion trails during the three storms. We attribute approximately two thirds of this to scratch‐type abrasion. The total volume of material removed by abrasion was 67,808 cm³. Despite the larger surface area affected by scratch marks, we find that the volume of material removed through percussion impact was almost seven times greater. We also find that the type and frequency of abrasion features is strongly influenced by the effect of platform morphometry on transport mode, with impact‐type abrasion dominating areas of higher platform roughness. Results of the clast transport experiments indicate that abrasion occurs under non‐storm wave energy conditions with observable geomorphological effects. We suggest that abrasion by clasts is an important component of platform erosion on high energy Atlantic coastlines, particularly over longer time scales, and that the morphogenetic link between the cliff and the platform is important in this context as the sediment supplied by the cliff is used to abrade the platform.

Structural inheritance and coastal geomorphology in SW Brittany, France: An onshore/offshore integrated approach

Article

Full-text available

Jan 2018
GEOMORPHOLOGY

The Variscan crystalline basement exposed along the SW Brittany coast recorded extensive long-term planation processes during Mesozoic times. Detailed onshore-offshore mapping (600 km²) in the Penmarc'h-Concarneau granitic coastal area reveals a km-scale, deeply fractured submarine rocky shelf. High-resolution offshore imagery (bathymetry and seismic reflection dataset), combined to structural field investigations, on these surfaces allow us to identify a preserved network of both ductile and brittle structures. The inherited fault pattern is dominated by the N160°E-trending and long-lived Concarneau-Toulven fault zone (CTFS) that separates two distinct morphostructural blocks, and strongly influences the seaward limit of the Concarneau submarine rocky shelf, as well as the linear coastline of the Concarneau embayment. The structural imprint of the CTFS decreases progressively westwards with respect to a composite network of large-scale N50°E- and N140°E-oriented faults bounding the seaward edge of the Penmarc'h rocky shelf. The latter in turn splits into three large-scale blocks along N50°E- (La Torche Fault - LTF), N140°E- (Saint Guénolé Fault - SGF), and N160°E-trending normal faults. The morphostructural evolutionary model applied here to the Penmarc'h-Concarneau granitic coastal area resulted from the combined effects of structural Variscan inheritance and post-Variscan tectonics. Paleo-stress analysis of striated fault planes indicates three main Cenozoic tectonic events, inferred to have operated from Eocene to post -Oligocene times. The 3D-architecture of the Concarneau embayment, as a rocky shelf partially sealed with quaternary sediments, chiefly resulted from the reactivation of the CTFS during Eocene and Oligocene times. Further west, the surface of the Penmarc'h rocky shelf was tilted southeastward by the brittle reactivation of the LTF, and dissected by a horst-graben network post-Oligocene in age. The present-day morphology of the Penmarc'h and Concarneau domains depends on distinct driving processes: the Concarneau N160°E coastline is clearly controlled by tectonic processes via the CTFS, while the Penmarc'h headland land-sea contact appears to have been shaped by post-Cenozoic eustatism.

Quaternary geomorphological evolution of a granitic shore platform constrained by in situ 10 Be concentrations, Penmarc’h, SW Brittany, France

Article

Sep 2017
MAR GEOL

The Penmarc’h granitic coastal domain, SW Brittany (Western France), offers the opportunity to address the little investigated issue of erosional processes in a granitic coastal context. From land to sea, the granitic coast is composed of 1) an aerial marine terrace ( <4 km), 2) a large shore platform ( <800 m), 3) an extensive submarine rocky platform ( <7 km), corresponding to the inner shelf, and 4) an outer shelf. Our geomorphological study, further completed by cosmogenic nuclide (¹⁰Be) analyses, supplies new constraints on the weathering and denudation processes recorded by the Penmarc’h platform in Quaternary times. The role of at least two denudation events is emphasized: (i) a >1.8 m-thick level of granitic material is assumed to have been removed by erosion during the MIS5 sea-level highstand, both in the offshore domain and in the low part of the marine terrace; (ii) an additional 0.6 m-thick level of the granitic substratum was later removed during the last Holocene transgression, mainly in the marine domain. The lack of any morphological step between the subaerial marine terrace and the shore platform is here attributed to the combined effect of multiple factors, including (i) a Quaternary tectonic quiescence, (ii) a major eustatic transgression (MIS5) shaping both the shore platform and the low part of the marine terrace, (iii) the mechanically strong behaviour of the granitic basement with regard to erosion, and (iv) the moderate influence of the Holocene sea-level stillstand (since 6 ka) on the shore platform. Thanks to ¹⁰Be content analysis, a range of vertical erosion rates of ca. 3–6 m⋅Ma −1 is obtained for the onshore domain, showing no discernable difference between the intertidal and aerial erosion rates. From that result, it is thus determined that the long-term development of the Penmarc’h granitic shore platform was mainly driven by marine erosive processes during the MIS5 and Holocene marine transgressions, whereas subaerial erosive processes prevailed after the MIS5 event.

Ephemeral geomorphodiversity: Conceptual debate, valuation, and heritage management

Article

Dec 2024
GEOMORPHOLOGY

Cliffs and Rock Coasts

Chapter

Jan 2011

Alan S. Trenhaile

Trapping of fine-grained sediment on a supply-limited intertidal shore platform at Kaikōura, New Zealand

Article

Oct 2023
GEOMORPHOLOGY

tendencia y atributos del concepto epistémico “Galicia” tras el Estatuto de Autonomía: el caso Scopus

Article

May 2023

Javier Seijo Villamizar

Galicia destaca por ser un referente clave para la nueva producción científica más avanzada. Este logro, tras un dilatado período de ostracismo político y cultural, conllevó un proceso político y social de acción por un bien común social: el reconocimiento de la cultura gallega, la generación de instituciones propias y un marco político-administrativo de gobernanza multinivel. Actualmente, el término de Galicia se interrelaciona con un conocimiento científico interdisciplinar incremental y de primer nivel. Scopus, en el proceso autonómico gallego, ha sido un aliado para la proyección internacional del conocimiento científico de la comunidad gallega. Conforme a este marco, el estudio presenta un análisis y divulgación de parte de la principal producción científica que referencia a Galicia con títulos expresos.

Cross-scale erosion on shore platforms using the micro-erosion meter and Structure-from-Motion (SfM) photogrammetry

Article

May 2023
GEOMORPHOLOGY

Changes in shore platform wetting and drying cycles following the 2016 Kaikōura earthquake: Implications for incipient marine terrace evolution

Article

Jun 2022

Co‐seismic uplift of Kaikōura Peninsula in 2016 has substantially reduced the number of wetting and drying cycles that occur on the shore platforms and the newly uplifted incipient marine terraces. A simple empirical model incorporating field and laboratory measurements was used to determine the number and frequency of wetting and drying cycles. The mudstone supratidal terraces are vulnerable to material disintegration and slaking through sustained drying, and occasional sweeping by storm waves. Overall, wetting and drying cycles have decreased on six of eight field transects, between ‐8% and ‐148%, resulting in prolonged drying of the supratidal terraces following uplift (upwards of a 29% increase in annual drying hours). We conclude that accelerated rates of denudation due to enhanced drying post‐uplift are likely to return sections of the incipient mudstone terraces to their former intertidal pre‐uplift state, potentially removing evidence of the co‐seismic uplift event. Terrace preservation, however, will likely be highly variable between locations depending on its inherited morphology, lithological vulnerability, and the timing of any future tectonism.

Aplicación de novas tecnoloxías no estudo da costa de Galicia dirixidas a unha nova xestión no contexto do cambio global

Thesis

Full-text available

Feb 2022

Alejandro Gómez-Pazo

The aim of this research is to deepen the knowledge of rocky coasts in general, and the Galician coasts in particular. This project carries out an analysis in different scales using the new technologies as the base to improve the coastal knowledge. Devices such as the Equotip are used at the microscale, in the mesoscale this project used RFID (Radio Frequency IDentification) sensors to analyze the displacements in boulder beaches, and lastly, UAV flights data are used in the macroscale to understand the behavior of different coastal typologies, as boulder beaches or cliff areas. Based on the obtained results and from the literature review, we proceed to analyze the risks associated with each type of coast, with particular emphasis in their vulnerability in the global change context. Thus, we developed the necessary recommendations for the existing risks, to improve the coastal management, reviewing the coastal management plans evolution and their possible future.

Intertidal cohesive foreshores: Erosion rates and processes illustrated by a shore platform at Warden Point, Kent, UK

Article

Oct 2021
MAR GEOL

Data are presented from a 9-year monitoring period, using a Traversing Erosion Beam (TEB), of erosional lowering of an inter-tidal shore platform developed in cohesive London Clay at Warden Point, Isle of Sheppey, Kent, UK. Over the monitoring period, average lowering decreased from >30 mm a⁻¹ at 30 m down-platform from the MHW line to <15 mm a⁻¹ at 75 m down-platform and <8.0 mm a⁻¹ at the lowest measured point 120 m seaward of MHW, giving an overall average 17–18.0 mm a⁻¹ across the measured section of platform. Differences in lowering rates recorded between the three down-platform measuring stations were statistically significant, as were differences between average annual rates and between seasons. It is suggested that these differences in recorded rates of lowering result from variation in the relative importance over space and time of sub-aerial versus marine processes of weathering and erosion. Adding the local relative sea-level rise of 2.23–2.36 mm a⁻¹ the average annual rise in mean water level over the platform surface was ~20 mm a⁻¹ and at the cliff-platform junction >32 mm a⁻¹. Backed by cliffs 48 m tall retreating at a long-term average > 1.0 m a⁻¹ the maximum contribution of platform lowering to the long-term erosional budget of the study site was ~7.4%. The significant differences in recorded annual and seasonal erosion rates indicate that extrapolation of average rates based on data collected for two years or less on such rapidly eroding platforms should be treated with caution because they may not be representative of the longer-term average rate either for the entire platform or for individual monitoring points.

Hydrogeology and groundwater management in a coastal granitic area with steep slopes in Galicia (Spain)

Article

Full-text available

May 2021

Groundwater availability, management and protection are great challenges for the sustainability of groundwater resources in the scattered rural areas of the Atlantic regions of Europe where groundwater is the only option for water supply. This report presents a hydrogeological study of the coastal granitic area of Oia in northwestern Spain, which has unique geomorphological and hydrogeological features with steep slopes favoring the erosion of the weathered granite. The hydrogeological conceptual model of the study area includes: (1) the regolith layer, which is present only in the flat summit of the mountains; (2) the slope debris and the colluvial deposits, which are present in the intermediate and lowest parts of the hillside; (3) the marine terrace; and (4) the underlying fractured granite. Groundwater recharge from rainfall infiltration varies spatially due to variations in terrain slope, geology and land use. The mean annual recharge estimated with a hydrological water balance model ranges from 75 mm in the steepest zone to 135 mm in the lowest flat areas. Groundwater flows mostly through the regolith and the detrital formations, which have the largest hydraulic conductivities. Groundwater discharges in seepage areas, springs, along the main creeks and into the sea. The conceptual hydrogeological model has been implemented in a groundwater flow model, which later has been used to select the best pumping scenario. Model results show that the future water needs for domestic and tourist water supply can be safely provided with eight pumping wells with a maximum pumping rate of 700 m3/day.

High resolution mapping and analysis of shore platform morphology in Galicia, northwestern Spain

Article

Mar 2021
MAR GEOL

Most research on shore platforms has been at fairly large spatial scales over distances ranging from hundreds to thousands of metres. Other work at much smaller scales, ranging from one to several decimetres, often corresponds to the dimensions of micro-erosion meter stations. Few studies have been concerned with platform morphology in which the basic data are acquired at intermediate or meso-scales ranging up to a few metres. This is due, in part, to terrestrial surveying at meso-scales being time-consuming while aerial surveys using LiDAR are expensive. A meso-scale study was made on three shore platforms in western Galicia, northwestern Spain using data from an Unmanned Aerial Vehicle (UAV) to produce high resolution Digital Surface Models (DSMs) and to calculate local surface elevation, roughness, slope, and joint density at a 0.5 m pixel scale, and joint orientation and length. This was supplemented by Equotip field measurements of rock hardness. A granitic platform was higher and had rougher surfaces and steeper slopes than two platforms in schist. The relationship between platform morphology and rock hardness and joint density was complex, however, reflecting in part the role of schistosity in accounting for the formation of low, regular platforms in hard schists with low joint density. The study suggested that while tidal range, inheritance, and other environmental and evolutionary factors can be dominant in determining platform morphology at the macro- or regional scale, geological, and particularly structural, factors become increasingly important in Galicia as the scale diminishes, and they are generally dominant at the local or meso-scale.

Spatial Impacts of Climate Change on Periglacial Environments

Chapter

Apr 2021

Periglacial areas are subject to paraperiglacial erosion crises caused by the melting of the permafrost, which are geomorphologically materialized by large scale ground deformations, affecting loose formations such as rocky substrates, slope areas as well as flat areas. In the context of current climate change, knowledge of periglacial processes and the degradation of permafrost are challenges for a global understanding of our planet, the consequences of which do not solely affect periglacial areas. These periglacial spaces are characterized by low temperatures and are often associated with areas of permafrost. This chapter explores the present and past spatial extent of periglacial environments. The processes and forms associated with the paraperiglacial dynamics can be analyzed as a cascading paraperiglacial geosystem. Gravity dynamics increase with global warming and the melting of permafrost walls; they may even affect outdoor tourism activities, particularly mountaineering or the practice of downhill skiing.

Rock Coasts

Chapter

Jan 2021

Rock coasts constitute the majority of the world's shorelines and result largely from erosive processes. Rates of erosion vary from almost nil to tens of meters per year. Cliff and shore platforms are the most common landform types but even these display significant variations in morphology depending on sea-level history, tidal range, the relative contributions of marine and subaerial processes, and geological properties of the rock. Smaller scale features such as stacks and arches are important elements and contribute significantly to landscape values and subsequently, tourism economies. The evolutionary history of rock coasts is difficult to reconstruct because of their erosional origin but modeling and cosmogenic nuclide age dating has revealed much about how such coastlines have developed over the latter part of the Pleistocene and Holocene.

Modelling the development of dynamic equilibrium on shore platforms

Article

May 2020
MAR GEOL

Alan S. Trenhaile

A numerical model was used to determine whether the landward migration of shore platforms at the low tidal level, due to downwearing and possibly other mechanisms, can match the recession caused by wave erosion at the high tidal level. The hybrid model calculated the time required to undercut a cliff face and to remove the debris, and the amount of recession accomplished at the low tidal level during that time. These iterations were repeated over the equivalent of a 40,000 year period. The rates of high tidal erosion calculated during model runs were representative of cliff recession rates recorded in the field, and downwearing rates, specified for each run, were based on data recorded on shore platforms with micro-erosion meters. Almost all runs demonstrated that platform gradients decline asymptotically to a state of dynamic equilibrium that is strongly related to tidal range and rock resistance, although its relationship to wave height varies according to attenuation rates in the surf zone. Periodic changes in rock resistance and continuous changes in cliff height can introduce perturbations that delay equilibrium or, depending on their severity, prevent its occurrence. The conclusion that platforms trend towards dynamic, as opposed to static, equilibrium is contrary to other models which have considered only the effect of wave erosion. The results of this work have important implications for coastal modelling and the estimation of platform lowering for cosmogenic dating.

Late Paleozoic gravity flow depositional systems in the Mandula Basin of the Solonker Belt, Inner Mongolia, China: towards a volcanic-associated submarine environment

Article

Apr 2020

The Solonker Belt is an important tectonic unit of the Central Asian Orogenic Belt in Inner Mongolia, China and the sediments in the Solonker Belt record the paleogeographic evolution of the Paleo-Asian Ocean. This study characterizes the spatial distribution of the lithofacies and lithofacies associations, and environment variations in the Mandula Basin. The Upper Carboniferous to Lower Permian Amushan Formation shows typical features of slump deposits occurred in the lower slope environments. The Lower to Middle Permian Baotege Formation develops the channelized lobes, channel–levee–overbank, and hemipelagic/pelagic deposits that are formed in the base of slope to basin floor environments. The Lower to Middle Permian Dashizhai Formation represents volcanic edifice and volcaniclastic aprons in the basin floor. The Middle Permian Zhesi Formation includes the shallow water reefs, deep-water biogenetic limestones, and volcaniclastic aprons developed in the abyssal slopes of the volcanic edifice. The sedimentary facies in the Mandula Basin constitute two depositional systems: the continental slopes adjacent to marginal carbonate platform and the volcaniclastic aprons associated with volcanic edifice in the basin floor. The Mandula Basin is an extensional deep-water basin and akin to the marginal sea of an ocean.

Periglacial deposits as indicators of paleotemperatures. A case study in the Iberian Peninsula: The mountains of Galicia

Article

Sep 2019

In this study, we provide a paleotemperature reconstruction based on periglacial deposits and landforms from the northwest Iberian Peninsula. We describe different types of periglacial deposits and landforms which were considered as paleoenvironmental archives. The occurrence of these landforms and deposits suggests that mean annual air temperatures must have been of ≤ −2°C for formation of block fields, block slopes and rock glaciers and ≥ 2°C for formation of stratified slope deposits, as indicated by their modern‐day analogs. The information obtained was used to construct paleotemperature maps by estimating temperature in relation to a standard altitudinal gradient. Two phases were differentiated. During the first phase, associated with the Maximum Glacial Advance (MGA) before 30 ka cal BP, the prevailing snow conditions favored the formation of stratified slope deposits and genesis of glaciers in all of the mountain systems, without the presence of permafrost. During the second phase, associated with the Glacial Maximum (GM) between 21 and 25 ka cal BP, colder conditions favored the presence of permafrost and genesis of block fields, block slopes and rock glaciers at elevations above 700 m. Temperature estimations ranged between around +6°C and − 6°C at an elevation of 2,000 m for the first phase, and between +2°C and − 10°C for the second phase. Due to limitations in estimating past climate conditions, the results should be considered as a first approximation to define northwest Iberian Peninsula paleotemperatures for the Late Pleistocene.

Gold-bearing Plio-Quaternary deposits: Insights from airborne LiDAR technology into the landscape evolution during the early Roman mining works in north-west Spain

Article

Mar 2019
JASR

This article focuses on the characterization of auriferous deposits, identification of hitherto unknown Roman mining infrastructure remains, and the early attempts of exploitation carried out in north-west Iberia. The research has combined airborne laser scanning (LiDAR) and field prospection to explore the geomorphological signature and landscape transformation resulting from Roman mining works in two unknown sectors of the western Duero Meseta. The integration of geological and remote sensing information contributed to extend the Roman's mining domains, traditionally focused on the river headwaters of the north-west. The article explores the complex hydraulic system developed in the Jamuz and lower sector of the Eria river valleys, as well as the evidence of open-cast mining and their relationship with the Roman army. The results suggest that the highly dispersed and reduced dimensions of the mining sites correspond to a selected method of gold prospection, employed for the identification of viable exploitation sectors. Thus, the initiation of the mining works could have started in the Jamuz valley and developed systematically in this area, to subsequently spread towards the upstream sectors and nearby valleys. This research contributes to gain new insights into the extension and complexity of the mining infrastructure, indicating the importance of the gold-bearing raña deposits within the framework of Roman gold mining in north-west Spain.

Exploring carbonate reef flat hydrodynamics and potential formation and growth mechanisms for motu

Article

Mar 2019
MAR GEOL

Atolls, which develop as reef-building coral platforms extend to near sea level, typically consist of a shallow reef flat encircling a central lagoon. Often, sub-aerial islets, known as motu or reef islands, consisting of sand, gravel, and coral detritus, can be found perched atop the reef flat. Here, we use hydrodynamic numerical modeling (XBeach) to better understand the role of waves and wave-driven currents on the reef flat and the processes driving motu formation and evolution. By differing representative reef-flat geometry (e.g. width and water depth), we investigate the effects of varying wave climate on hydrodynamics and resultant bed shear stresses across the reef flat. Model results suggest that as a reef flat shallows, bed shear increases, then, after passing a critical value, decreases again. Using these results, we hypothesize that reef flats should attain a critical water depth just at the threshold for sediment mobilization, resulting in a constant depth reef flat in both abrasional and depositional settings. As reef flats widen, prograding into the back-reef lagoon, shear stress decreases across the flat, with a minimum in shear stress arising approximately midway on the reef flat. Motu formation would be expected to initiate at this mid-flat nucleation site, either from a storm, when coarse sediment is mobilized and deposited, or gradually as the reef flat widens. A mid-flat deposit need not be subaerial to form a motu—sediment piled shallower than the critical depth would continue to accumulate. Once a motu is present, reef-flat shear stress directions reverse and the motu shoreline should prograde seawards until reaching a relatively narrow critical reef-flat width (~200 m). Together, these results suggest that reef flats and motu spatially self-organize through a series of morphodynamic feedbacks.

How water, wind, waves and ice shape landscapes and landforms: Historical contributions to geomorphic science

Article

Feb 2019
GEOMORPHOLOGY

James Gardner

Research over approximately 200 yr on the geomorphic effects of the force of water, wind, waves and ice is reviewed. In a changed scientific, technological, institutional and socio-political context, several trends emerge. Increased focus on measurement of processes from the 1930s onwards was facilitated by new technologies, leading eventually to a blurring of disciplinary boundaries and the emergence of geomorphology as an Earth system science. Human impact research and applications have blossomed and are contributing to an emerging understanding of the Anthropocene. Absolute dating techniques have reinvigorated landform and landscape evolution research, while remote sensing and geospatial science generally have enhanced observation, measurement and modeling of terrestrial and planetary surface and subsurface forms and processes. The historical record demonstrates that geomorphology has attained scientific vigour and societal relevance through fascinating journeys of curiosity, exploration, mapping, measurement, modeling and explanation.

Beaches of Galicia

Chapter

Jan 2019

Ramon Blanco-Chao

The coast of Galicia corresponds to the NW end of the Iberian Penninsula and extends from the estuary of the Eo River, in the north, to the mouth of the Miño River in the border with Portugal. This coast has distinctive characteristics compared with the rest of the Atlantic Iberian coasts given the importance of geological and structural controls that define the deeply indented coastline. Although is a coast exposed to a energetic storm and swell wave regime, at different scales there are great variations in the orientation of the coastline that causes a high variability in the exposition and the energetic regime.

Shore platform erosion and evolution: Implications for cosmogenic nuclide analysis

Article

May 2018
MAR GEOL

Alan S. Trenhaile

Determining rates and modes of shore platform development and the age of associated elements are among the greatest challenges facing rock coast researchers today. These coasts generally lack dateable deposits but cosmogenic nuclide analysis (CNA) can be applied directly to bare rock surfaces to estimate erosion rates or the time that a surface has been exposed over millennial timescales. Therefore this technique has the potential to revolutionize current theories on rock coast evolution and modes of development. Because environmental and geomorphological factors affect rates of nuclide accumulation and retention, however, the results of CNA analysis are dependent on the validity of the theoretical models that have to be employed according to the particular application. Among the important assumptions that may be made are those concerned with shading, tidal immersion, beach sediment covers, and other factors that influence rates of nuclide accumulation, and with possible spatial and temporal patterns in shore platform erosion, primarily by wave-generated backwearing and weathering-induced downwearing, that reduce nuclide concentrations. Our lack of understanding of the factors that control these variables, and in particular shore platform erosion, which is the subject of this review, has important implications for modelling rock coast evolution, assessing the possible contribution of inheritance, and dating, especially by CNA, the occurrence of important, formative events.

Shore platform downwearing and cliff retreat in the Portuguese west coast

Conference Paper

Full-text available

Jan 2002

F. Marques

Rates and patterns of bedrock denudation by coastal salt spray weathering: A seven‐year record

Article

Full-text available

Aug 1989
EARTH SURF PROC LAND

D.N. Mottershead

Rapid surface lowering of bedrock is taking place in the supratidal zone by salt spray weathering. A seven-year run of data demonstrates a mean rate of lowering of 0·625 mm a−1. Considerable variation exists in annual point lowering values within measurement sites, although between-site variation is not significant. Aggregate year to year variations in surface lowering are not significant. Spatial variation in individual point values may be compensated by temporal variation over an 11-year period. There is a marked summer maximum in surface lowering rate, and this is strongly correlated with monthly air temperature. Spatially and temporally episodic swelling of the rock surface is demonstrated. This does not correlate statistically with any available climatic variable and is deemed to be a real and largely stochastic phenomenon. It is interpreted as rock bursting at the granular scale due to haloclasty. The processes most likely to be responsible for the observed rapid denudation are crystallization and thermal expansion of halite, both of which are enhanced by high summer temperatures.

Coast line evolution in Portugal since the Last Glacial Maximum until present — a synthesis

Article

Full-text available

Oct 2000
MAR GEOL

An effort has been made to assemble a data set on the evolution of coastal morphology of the West Iberian Continental Margin in Portugal, which has occurred since the Last Glacial Maximum. In this integrated review a particular attention was given to the analyses of coastline shaping phenomena on different time scales. Several overlapping processes such as shore erosion, local sediment supply rate, climatic changes, anthropic impacts and mean sea level rise (MSLR) were identified and their combined effects assessed. The eustatic see level rise appears as a principal factor in shaping the shore line contour until mid Holocene. Since then, the non eustatic factors namely the terrigenous sediment supply rate and the dynamics of barriers and spits systems became dominant in the evolution of the near shore morphology. Since the 15th century AD, the anthropogenic activities, namely deforestation and land cultivation contributed decisively to the positive sedimentary balance in the Portuguese coastal zone. Finally, the multiple damming of the major rivers in 20th century and exploitation of sand and gravel from the river beds led to the sediment starving of the coastal zone and generalized shore line retreat.

Shore platform research: a progress report

Article

A.S. Trenhaile

Influencia de formas y depósitos antiguos en la dinámica litoral: un ejemplo de la costa sur de Pontevedra (Galicia)

Article

Jan 2001

Coastal rock platforms and Quaternary sea-levels in the Baie d'Audierne, Brittany, France

Article

Dec 1998
Z GEOMORPHOL

Along the coast between Plage de Mezpeurleuch and Plage de Guendrez in the Baie d'Audierne (Brittany, France), a suite of three seaward descending rock platforms have been identified. The high platform lies at c. 4 m NGF and extends from the base of low cliffs, underlying unconsolidated Pleistocene deposits, including an extensive raised beach deposit which rests directly on the high platform. This raised beach and high platform have previously been assigned an Eemian (last interglacial, oxygen isotope substage 5e) age. Between this high platform and the modern (low) wave-cut platform at c. 0 m NGF, an intermediate platform occurs at c. 2.5 m NGF. It is important to establish the relative age of this intermediate platform, because if it is younger than the high platform, then an Eemian age for the high platform and associated raised beach deposits is doubtful, as it is unlikely that Weichselian interstadial sea-levels exceeded the Holocene sea-level maxima. A number of hypotheses describing the chronological development of the rock platforms were tested through studies of rock weathering (Schmidt hammer test), and empirical geomorphological and stratigraphical observations. The results indicate that the intermediate platform is more weathered (mean R = 36) than the high platform (mean R = 50.02), and that the morphological boundary between the two is marked by a ramp rather than a vertical wave-cut cliff, such as characterises the boundary between the intermediate and low platform. Also, Pleistocene deposits are seen to rest only on the high platform. This evidence suggests that the intermediate platform represents Holocene weathering of the high platform (unrelated to a palaeo-sea-level high-stand) and, therefore, does not preclude an Eemian (minimum) age for the high platform and associated raised beach deposits.

Field assessment of rock hardness using the Schmidt test hammer

Article

Jan 1977

Shore Platform Processes in Eastern Canada

Article

Jan 2006

This research is conducted on a mesotidal, argillite shore platform at Mont Louis in Gaspé, Québec, and on macrotidal platforms in the basalts of Scots Bay and the sandstones of Burncoat Head in Nova Scotia. Rock samples have been subjected to wetting and drying and to salt weathering cycles. The platforms were surveyed; rock hardness was determined with a Rock Test Hammer; waves were recorded in the field; and downwearing rates were measured at 56 micro-erosion meter stations over 1 to 3 years. Weathering is the dominant process at Mont Louis, although the horizontal platform may have been cut by waves at the high tidal level. Wave backwearing was much more important than downwearing by weathering during the Holocene at Scots Bay. Wave quarrying only occurs on a few scarps today, however, and without much abrasive material, slow downwearing now dominates over most of the platform surface. Waves probably help to remove loosened sand grains at Burncoat Head, thereby contributing to platform downwearing. Abrasion is also important in places, but the data suggest that backwearing by wave quarrying and probably frost has been a little more important than downwearing by abrasion and weathering during the Holocene.

Paraglacial coasts

Chapter

Jan 1994

The shoreline is a rapidly changing interface between the land and the sea, where much of the world's population lives. Coasts are under threat from a variety of natural and anthropogenic impacts, such as climate or sea-level change. This 1995 book assesses how coastlines change, and how they have evolved over the last few thousand years. It introduces concepts in coastal morphodynamics, recognising that coasts develop through co-adjustment of process and form. Particular types of coast, such as deltas, estuaries, reefs, lagoons and polar coasts, are examined in detail with conceptual models developed on the basis of well-studied examples. Coastal Evolution is written for undergraduates who are studying coastal geomorphology, geologists who are mapping coastal sedimentary sequences and environmental scientists, engineers, planners and coastal managers who need to understand the natural processes of change which occur on shorelines.

Modeling the accumulation and dynamics of beaches on shore platforms

Article

May 2004
MAR GEOL

Alan S. Trenhaile

A mathematical model was used to study the development and dynamics of beaches on shore platforms. The model was based on assumptions that: the gradient of the beachface at its seaward edge must be greater than platform gradient; beach sediment tends to move landwards; and beach occurrence and extent depends upon the amount of sediment available. Equilibrium beachface gradient was related to breaker height, wave period, and sediment grain size. Three grain sizes were used, representing fine and coarse sand and pebble; two deep-water wave sets, representing storm wave and west coast swell wave environments; and two tidal ranges of 9.1 and 3.3 m. Runs were made using linear, concave, and convex platform profiles, with gradients ranging between about 0.6° and 8°. Because platform and beachface gradients are normally quite similar, shore platforms are unable to store much sediment. For a linear platform with a lower gradient than the beachface, sediment first accumulates at the cliff base and then, depending on the sediment available, extends increasingly seawards. Beach development first occurs on the gently sloping seaward portions of concave platforms and on the more landward portions of convex profiles. The amount of available material partly determines the landward and seaward extent of these beaches, respectively, although it is also controlled by beachface and platform gradients. Beaches on shore platforms become thinner and more gently sloping during storms, and they may disappear completely, depending on such factors as: sediment grain size, platform gradient, the amount of sediment that can be stored during calm conditions, wave characteristics, and the duration of the storm. The response of beaches on rocky coasts to rising sea level will be different from those on sedimentary coasts, and will depend, in part, on the morphology of the rocky foundation.

The Role of Wave Erosion on Sloping and Horizontal Shore Platforms in Macro and Mesotidal Environments

Article

Mar 2007

Waves were measured over tidal cycles on a sloping, basaltic shore platform at Scots Bay in the macrotidal Bay of Fundy (large tidal range 13.5 m), and on a horizontal, argillite platform at Mont Louis in Gaspe, Quebec (large tidal range 3 m). Video cameras were used to record the height and period of the waves against a series of graduated metal poles anchored along surveyed, shore-normal profiles. Field measurement and theoretical considerations suggest that wave height increases with elevation at Scots Bay, reflecting the occurrence of a gently sloping tidal flat below the midtidal level and higher gradients on the upper than on the lower parts of the platform. Calculated pressures generated within the rock along joints and other discontinuities suggest that wave conditions are suitable for mechanical-wave erosion at Scots Bay. Waves generally break on the low tide cliff at the seaward edge of the platform at Mont Louis, preventing any wave action on the shallow, flooded platform surface behind. During high spring tides, greater water depths allow fairly large waves to cross the platform, but a beach generally protects the cliff foot and, apart from a few upstanding ridges, there is no rock exposed to wave action at the water surface at this elevation. Downwearing by weathering dominates on the horizontal Mont Louis platform, but waves would still attack the cliff during high tides if there were no protective beach, which suggests that the platform may have been cut by waves near the high tidal level and subsequently lowered by weathering to its present elevation.

Shore Processes and Shoreline Development

Article

Jan 1920

Douglas Wilson Johnson

Tidal wetting and drying on shore platforms: An experimental assessment

Article

Aug 2005
GEOMORPHOLOGY

Rocks were subjected to wetting and drying cycles with de-ionized water under real time conditions. Using tidal simulators, one-third of the samples experienced 11 h of exposure and 1 h of inundation over a 12-h tidal cycle (representing high tidal conditions), one-third experienced 6 h of exposure and 6 h of inundation (representing mid-tidal conditions), and one-third experienced 1 h of exposure and 11 h of inundation (representing low tidal conditions). We obtained 324 cores from igneous, metamorphic, and sedimentary rocks from Ontario, which were exposed to more than 930 wetting and drying cycles over 16 months. We obtained 675 cores and cubes from basalts, sandstones, and argillites from shore platforms in eastern Canada, which were exposed to about 700 cycles over 12 months. Many of the cores and cubes experienced very little to no breakdown, particularly those from the igneous and metamorphic rocks of Ontario. Sandstones from a sloping platform in the macrotidal Bay of Fundy and argillites from a horizontal, mesotidal platform in Gaspé, Québec, were the most susceptible rock types, with equivalent surface downwearing rates ranging from 0 to 4 mm year−1. The results suggest that downwearing rates decrease with elevation within the intertidal zone, probably because rocks require much longer to desorb than to absorb water. The experiments demonstrated that wetting and drying can be an important process on shore platforms in some types of rock, helping to lower the height and reduce the gradient of sloping macrotidal platforms and to reduce the height of horizontal micro- and mesotidal platforms.

Micro-erosion meter measurements of rock wear on the Otway Coast of Southeast Australia

Article

Jun 1983
MAR GEOL

The use of the Micro-Erosion Meter (MEM) has been refined by providing: (1) a base plate on which to check the relationship of legs and probe; and (2) a micrometer level to check the relationships of the three studs countersunk in the rock at each site. Along 50 km of the Otway coast, lines of MEM stations were installed across shore platforms normal to the shore, and surveyed to mean low water. Readings were made bimonthly from 1978 to 1980. Average site downwear ranged from 0.02 to 1.8 mm yr−1 according to rock type and the amount of exposure to the almost continuous swell waves. The results of this study, combined with other information available, are used to discuss the origin and evolution of Otway coastal morphologies.

Marine erosive processes at the cliff foot

Article

Mar 1977
MAR GEOL

L.A. Robinson

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.

Article

Jun 1993
Int J Rock Mech Min Sci Geomech Abstr

In this Technical Note, a statistical method which allows the integration of scattered data obtained during Schmidt hammer testing is brought to the attention of those researchers and engineers who work in the area of rock excavation. It is thought that such an integration method will have the advantage of objectively recording the characteristic variations in rock texture and micro-structure which predominantly affect the performance of excavating machinery. However, it is emphasized that there is a need for further research work involving case studies in order to check its practical validity. (A)

Erosive processes on the shore platform of northeast Yorkshire Shore Platform

Article

Apr 1977
MAR GEOL

L.A. Robinson

Different processes erode the plane and ramp, the two morphological elements of the shore platform. On the plane, desiccation of the shale causes contraction of the clay lattices in intertidal periods but wetting by the flood tides produces expansion. These movements crack the shale bedding laminae into polygons about 2 cm in diameter which are removed by waves. Desiccation is enhanced in well-drained areas and there is a positive correlation between altitude and erosion rate producing the smooth-sub-horizontal plane. Erosion is highest during summer. It averages 0.1 cm year−1 but ranges from 0.0 to 0.9 cm year−1.Corrasion is the main erosive process on the ramp. It is most active during winter, the stormy season, but is influenced by beach depth and possibly grain size. A shallow sand and pebble beach less than 5 cm deep allows erosion at all times. Beach depth is the most important influence on corrasion if it brings the ramp within 5 cm of the surface at some times and buries it more than 13.5 cm deep at others. Wave energy is the most important variable if the beach is usually more than 13.5 cm deep. Erosion rates for the zones of 0–5 cm depth, 5–13.5 cm depth, and greater than 13.5 cm depth were respectively 3.94 · 10−3 cm tide−1, 3.26 · 10−3 cm tide−1 and 1.13 · 10−3 cm tide−1.

Tidal wetting and drying on shore platforms: An experimental study of surface expansion and contraction

Article

Jun 2006
GEOMORPHOLOGY

Alan S. Trenhaile

Laboratory experiments have been conducted to measure rock expansion and contraction induced by wetting and drying on intertidal shore platforms in eastern Canada. Almost 800 rock cores and cubes were subjected to between 800 and 1000 tidal cycles. The rocks were put into tidal simulators and inundated in de-ionized water for 1, 6, or 11 h of each 12 h cycle, replicating conditions at the high, mid-, and low tidal levels, respectively. Micro-erosion meter (MEM) stations were also installed in slabs of argillite, sandstone, and basalt. The slabs were subjected to conditions at the high, mid-, and low tidal levels, and a traversing MEM was used to measure rock expansion and contraction as the slabs dried in air with variable temperature and humidity during low tide. The slabs were also exposed for long periods to air with variable humidity. Cores and cubes often gained in weight when they absorbed or adsorbed water and retained it for periods ranging from 1 month to 1 year or more, although this did not appear to be a prelude to rock breakdown. Tidal wetting and drying and exposure to humid air caused the argillite and basalt slabs to expand and contract by up to 0.14 and 0.04 mm, respectively. Wetting and drying did not induce expansion or contraction of the sandstone, but the sandstone did respond slightly to changes in air humidity. The greatest amount of expansion and contraction was at the high tidal level in the argillite and at the mid-tidal level in the basalt, which is consistent with previously measured rates of downwearing.

Depósitos sedimentarios antiguos en la costa atlántica gallega: tipología, localización y área fuente. Un análisis comparativo

Article

Jan 1998

Lateglacial and Holocene environmental changes in Portuguese coastal lagoons 1: The sedimentological and geochemical records of the Santo André coastal area

Article

May 2003

The sedimentological and geochemical study of a core corresponding to sedimentation in the Santo André lowland since 14 000 BP allowed the reconstruction of environmental changes of this area and discussion of the relative importance of local versus global forcing factors responsible for its evolution. The pre-Holocene section of the core represents terrestrial sedimentation in a uviatile environment, contemporaneous of a low sea level and a distal shoreline. Sediment inputs were terrestrial and resulting from intensive weathering and high erosion rate in the adjacent watershed. During the Early Holocene (c. 10 020 to 5380 BP) the sea invaded this lowland and dee ned an open marine shallow environment corresponding to a wide gulf which has been disturbed by multiple terrestrial inputs that might have been induced by massive episodes of uvial discharge. The rst symptoms of conn nement were noticed close to 5400 BP, and c. 5380 BP a major environmental threshold occurred (possibly ree ecting the marked deceleration of the sea-level rise rate) corresponding to the establishment of an eff cient detrital barrier that completely isolated the bay and changed this lowland into a closed coastal lagoon. After 5380 BP, the lagoonal environment evolved as a function of local forcing factors, among which the frequency and eff ciency of exchanges with the ocean predominate: until c. 3570 BP the lagoon was restricted, fed by fresh water and terrestrial sediment inputs; a second episode of lagoonal sedimen-tation lasts until c. 1620 BP, ree ecting brackish conditions and increase in marine in uence due to a reduced eff ciency of the barrier. The upper section of the core represents the nal stages of lling of the lagoonal margin by uvial activity. Human settling and intervention in the barrier are possible causes of a short-lived return to brackish conditions recorded in the uppermost sediment unit of the core and of the dramatic increase of the sedimentation rates.

Holocene environmental development of the Bilbao estuary, northern Spain: Sequence stratigraphy and foraminiferal interpretation

Article

Apr 2004
Mar Micropaleontol

The foraminiferal assemblages recorded in the sedimentary successions of nine boreholes drilled in the Bilbao estuary have been analyzed. Palaeoenvironmental interpretation of these and other previously studied assemblages defines the Bilbao estuary sedimentary infill as a depositional sequence within a fourth-order eustatic cycle (Holocene). This sedimentary sequence comprises a wide range of foraminiferal assemblage zones (FAZ) that are organized into three systems tracts. Each systems tract is composed by a distinct suite of FAZs separated by continuous stratigraphic surfaces. During Lateglacial low sea-level conditions, sedimentation was represented by fluviatile gravels and coarse sands barren of foraminifera (lowstand systems tract). During marine transgression (transgressive systems tract, 8500-3000 cal years BP), great volumes of mainly near-marine sediments were deposited in the lower estuary, alternation of brackish and near-marine sediments were accumulated in the middle estuary, and brackish materials sedimented in the upper estuary. The highstand systems tract deposited during the upper Holocene (3000 cal years BP-19th century human reclamation) represented brackish intertidal and supratidal conditions as the sedimentary infill was taking place under stabilized sea-level. Comparison of these results with other sedimentary sequences from different coastal areas in the Bay of Biscay indicates that, following postglacial sea-level rise, modem estuaries in the region began to develop around 8500 cal years BP. A final transgressive event was dated at around 33000 cal years BP when sea level reached approximately its present position after a second upward-shallowing sequence commenced. (C) 2003 Elsevier B.V. All rights reserved.

Separating eustatic from local environmental effects: A late-Holocene record of coastal change in Albufeira Lagoon, Portugal

Article

Apr 1999

Diatom and sedimentological analyses of a 7.6-m core of the Albufeira coastal lagoon, western Portugal, provide information about the forcing factors and environmental history of the evolution of this lagoon during the last 2500 years. At this timescale, eustasy is considered to be a minor environmental control on the dynamics of the barrier-lagoonal system. Instead, these dynamics are forced by local factors, such as changes in the sand-barrier permeability. Lithological and diatom facies are compared with present-day environ ments and show that the lagoon evolved essentially as a slightly brackish water body with a salinity of around 1‚Ä∞. This pattern was disturbed by three major episodes of sedimentation associated with threshold responses in the permeability of the barrier. The first (c. 2370 BP) did not produce a specific lithological signal and is characterized by a peak in freshwater euplanktonic diatoms, implying an almost permanent isolation of the basin and freshwater flooding. A second episode was identified at c. 1600 BP, when a dramatic opening of the tidal inlet provoked a significant change in the sedimentation regime, which became dominated by inorganic, minerogenic sediments and allowed marine/brackish epiphytic diatoms to flourish together with allochthonous marine planktonic species. Finally, a third threshold occurred at c. 1225 BP corresponding to the establishment of the present-day muddy or sandy-muddy sedimentation pattern. Both the sedimentological features and the diatom assemblages indicate the establishment of a more tidally influenced environment. This reflects regular artificial breaching of the barrier associated with increasing anthropogenic intervention in the system.

Stacks and notches at Hopewell Rocks, New Brunswick, Canada

Article

Nov 1998
EARTH SURF PROC LAND

Spectacular rock formations have developed in coarse, poorly sorted conglomerates and arkosic sandstones at Hopewell Rocks in the Bay of Fundy, which has the largest tidal range in the world. The average gradient of the shore platform is 3.2°, although it varies because of slight differences in rock hardness. Schmidt Rock Test Hammer measurements show that the rock is generally no more resistant in 16 stacks and in one stack-arch than in the adjacent platform and cliff. Most stacks, arch-tunnels and caves in this area result from dissection of the rock mass along prominent, well-spaced joint planes. Old photographs suggest that the stacks at Hopewell Rocks may have developed in the last 100 to 250 years. Notches are ubiquitous at the cliff foot, and they are responsible for the characteristic mushroom-shaped appearance of the stacks. Although there is no consistent relationship between the depth of notches on the seaward and landward sides of the stacks, the notches are at higher elevations on the seaward side. The deepest part of most notches is a little below the mean high tidal level, although several are up to 1 or 2 m below it, especially on the landward side of stacks. Stack morphology and notch depth change in a fairly predictable manner through time, as the stacks become increasingly isolated from the cliff. © 1998 John Wiley & Sons, Ltd.

Shore platform morphology on a rapidly uplifting coast, Wellington, New Zealand

Article

Jul 2005
EARTH SURF PROC LAND

The coast of Wellington, New Zealand, is tectonically active and contains a series of uplifted and contemporary shore platforms that are developed in Triassic Greywacke. The platform profiles are rugged with relief of metre scale common. The surveyed platforms were formed at, and at two distinct levels 1–1·5 and 2–2·5 m above, mean sea level. They range in width up to 70 m and are highly fractured with fracture densities in excess of 20[sol ]m2 common. The rate of development of these platforms is rapid, with lateral erosion rates of up to 0·15 m[sol ]yr calculated, allowing platform development to occur over centennial scales. Even given this rapid development, continued instantaneous uplift of the coast has meant they are unable to reach an equilibrium state, whereby the effectiveness of wave processes in removing material is reduced by platform extension. The co-seismic uplift means that the rear of the platforms is raised beyond the limits of marine process and has become an area of deposition. Although no direct process measurements were made the highly fractured nature of the bedrock appears to play a major role in platform evolution, with wave processes being easily able to pluck blocks as evidenced by fresh erosion scars and active gravel beaches at the rear of many platforms. This coast therefore represents an extremely dynamic youthful shore platform environment, where the processes of marine abrasion can be observed over historical timescales. Copyright © 2005 John Wiley & Sons, Ltd.

The influence of rock resistance on coastal morphology around Lord Howe Island, Southwest Pacific

Article

May 2004
EARTH SURF PROC LAND

An Erratum has been published for this article in Earth Surface Processes and Landforms 27(7) 2004, 931. Lord Howe Island, in the northern Tasman Sea, is a remnant of a much larger Late Miocene basaltic shield volcano. Much of the island's coastline is exposed to waves that have unlimited fetch, but a marked contrast is provided by a fringing coral reef and lagoon that very effectively attenuate wave energy along a portion of the western coastline. The geology of the island is varied, with hard and resistant basalt lavas, breccias and tuffs of intermediate resistance, and highly erodible eolianites. This variability provides an excellent opportunity to examine the inﬂuence of rock resistance on the development of the spectacular rock coast landforms that occur around the island. The hardness of rocks and the extent of weathering around the coastline were assessed using a Schmidt hammer, and statistical analysis was undertaken to remove outlying values. On all but one occasion, higher mean rebound values were returned from fresh surfaces than weathered surfaces, but only half of these differences were statistically signiﬁcant. Shore platforms with two distinct levels are juxtaposed along two stretches of coastline and Schmidt hammer results lend support to hypotheses that the raised surfaces may be inherited features. Relative rock resistance was assessed through a combination of Schmidt hammer data and measurements of joint density, and constrained on the basis of morphological data. This approach formed a basis for examining threshold conditions for sea‐cliff erosion at Lord Howe Island in the context of the distribution of resistant plunging cliffs and erosional shore platforms. Copyright © 2004 John Wiley & Sons, Ltd.

Evolution and inheritance of a rock coast: Western Galicia, Northwestern Spain

Article

Jul 2003
EARTH SURF PROC LAND

There is increasing evidence that shore platforms and other elements of rock coasts may be inherited, at least in part, from interglacial stages when sea level was similar to today's. Most of this evidence, which includes ancient beaches and datable terrestrial deposits, has been obtained from areas of resistant, slowly eroding rock, where the platforms often appear to be much too wide to have developed since the sea reached its present level. It is much more difﬁcult to demonstrate that inheritance has occurred in areas of weaker rock, which generally lack any datable material. The coast of western Galicia in northwestern Spain has shore platforms in igneous and metamorphic rocks that were deeply weathered during the Tertiary. These platforms are closely associated with ancient beaches from the last interglacial stage, and associated periglacial and ﬂuvio-nival deposits that covered and fossilized most of the Eemian platforms and cliffs during the late middle and late Weichselian glacial stage. The sedimentary processes and the thickness and facies of the sediments were determined by the height, aspect and gradient of the coastal mountains, and their distance from the coast. Radiocarbon dating, sedimentary analysis and platform morphology indicate that the shore platforms of Galicia have been inherited from at least the last interglacial stage. They were fossilized in places beneath thick Weichselian deposits and then exhumed during the Holocene transgression. The abundant evidence for inheritance in Galicia has important implications for other coasts in fairly weak rocks where such evidence is generally lacking. Copyright © 2003 John Wiley & Sons, Ltd.

Modelling the effect of waves, weathering and beach development on shore platform development

Article

May 2005
EARTH SURF PROC LAND

Alan S. Trenhaile

A mathematical model was used to study shore platform development. Mechanical wave erosion was dependent on such variables as tidal range, wave height and period, breaker height and depth, breaker type, surf zone width and bottom roughness, submarine gradient, rock resistance and the elevational frequency of wave action within the intertidal zone. Also included were the effects of sand and pebble accumulation, cliff height and debris mobility, and downwearing associated with tidal wetting and drying. The occurrence, location and thickness of beaches often depended on initially quite minor variations in platform morphology, but owing to their abrasive or protective effect on underlying rock surfaces, they were able to produce marked differences in platform morphology. Generalizations are difficult, but the model suggests that platform gradient increases with tidal range. Platform width also increases with tidal range with slow downwearing but it decreases with fast downwearing. Platform gradient decreases and width increases with wave energy, and decreasing rock resistance and platform roughness. With low tidal range, platform gradient is generally lower and platform width greater with beaches of fine sand than with gravel, but the relationship is more variable with a high tidal range. Platform width increases and platform gradient decreases with the rate of downwearing on bare surfaces, particularly in low tidal range environments, but the pattern is less clear on beach-covered platforms. Platforms with large amounts of beach sediment tend to be narrower and steeper than bare platform surfaces. Platform gradient increases and platform width decreases with increasing cliff height and with decreasing cliff debris mobility. Copyright © 2005 John Wiley & Sons, Ltd.

Chapter 14 Modeling shore platforms: present status and future developments

Chapter

Dec 2003

Alan S. Trenhaile

This chapter discusses a model shore platform evolution, and the modifications that need to be made to increase its general utility. Platform models consider erosive conditions within the inter-tidal zone, and are flexible enough to encompass the wide range of wave, tidal, and geological conditions that occur in the field, as well as changes in sea level and climate. The model use basic wave equations to simulate the erosion of rock coasts in the inter-tidal zone. In its present form it can be used to study the long-term evolution of wave-dominated coasts with geological conditions that facilitate the formation of seaward-facing scarps or other upstanding irregularities. Field calibration of the constants in the model permit its use to predict platform and cliff erosion in specific areas with rising sea level, over much shorter time scales. The model does not consider the effect of bio-erosion, weathering or other down wearing mechanisms, although micro-erosion meter data suggest that they are important and in some cases dominant factors on some platforms. The model is modified to allow down wearing processes to operate in conjunction with wave generated back wearing.

Rates and patterns of erosion on inter-tidal shore platforms, Kaikoura Peninsula, South Island, New Zealand

Article

Dec 1998
EARTH SURF PROC LAND

This paper presents measured rates of erosion on shore platforms at Kaikoura Peninsula, South Island, New Zealand. Surface lowering rates were measured with a micro-erosion meter and traversing micro-erosion meter. The mean lowering rate for all shore platforms was 1·130 mm a−1. Differences in lowering rates were found between different platform types and lithologies. The rate of surface lowering on Type A (sloping) mudstone platforms was 1·983 mm a−1, and 0·733 mm a−1 on Type B mudstone platforms (subhorizontal). On limestone platforms the lowering rate was 0·875 mm a−1. A previously reported cross-shore pattern of surface lowering rates from Kaikoura was not found. Rates were generally higher on the landward margins and decreased in a seaward direction. Season is shown statistically to influence erosion rates, with higher rates during summer than winter. The interpretation given to this is that the erosive process is subaerial weathering in the form of wetting and drying and salt weathering. This is contrary to views of shore platform development that have favoured marine processes over subaerial weathering. Copyright © 1998 John Wiley & Sons, Ltd.

Rock coast inheritance: An example from Galicia, northwestern Spain

Article

Jul 1999
EARTH SURF PROC LAND

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.

Development of shore platforms on Kaikoura Peninsula, South Island, New Zealand - II: The role of subaerial weathering

Article

Feb 2000
GEOMORPHOLOGY

The role of subaerial weathering in the development of shore platforms on Kaikoura Peninsula is investigated. Evidence for weathering came from a number of distinctive surface morphologies on platforms: salt crystal growth, water layer weathering, and slaking. Schmidt Hammer test data showed that weathering had occurred and that rock strength was reduced through weathering by as much as 50%. Weathering processes on shore platforms rely on repeated wetting and drying, and for this reason the number of wetting and drying cycles was estimated. It was found that the number of wetting and drying cycles depend not only on the pattern of tidal water levels but also on algae growth and desiccation. The number of cycles ranged from 104 to 379 per year. At elevations low in the tide range, fewer cycles occurred; the greatest number occurring between the peaks of spring and neap tides, and where rainfall adds to the number. The zone of most cycles was estimated to occur between 0.6 and 0.9 m above mean sea level on the more landward margins of platforms. It is at these elevations that the highest rates of erosion occur. Based on these results, it is argued that the development of shore platforms at Kaikoura results from subaerial weathering caused by repeated wetting and drying. This is contrary to the view that shore platforms result from marine erosion.

Development of shore platforms on Kaikoura Peninsula, South Island, New Zealand: Part One: The role of waves

Article

Feb 2000
GEOMORPHOLOGY

The role of waves in shore platform development has been investigated on Kaikoura Peninsula by direct measurement of waves in deep water and on platforms at high tide. This showed that the deepwater wave environment off the Kaikoura Peninsula is very energetic, but the amount of energy delivered to platforms is very low. In deep water, wave power ranged from 5900 to 106 700 N m s−1 per m of crest when calculated from mean significant wave height and when calculated from maximum wave height it ranged from 31 400 to 5 370 000 N m s−1 per m of crest. A comparison of deep water wave energy flux with wave energy flux at the high tide cliff of platforms showed that there was a reduction by as much as five orders of magnitude during storm conditions. An analysis of the role of breaking waves revealed that these are ineffective as an erosional agent because the depth of water offshore causes breaking before waves arrive on platform surfaces. Depth of water controlling wave breaking causes larger storm waves to break further from shore, preventing direct attack at the cliff base. Shear stresses and dynamic forces under waves were calculated from waves measured on shore platforms. This showed that these forces never exceeded the compressive strength of the platform rocks at Kaikoura. It is concluded that wave forces are not directly capable of causing erosion on shore platforms at Kaikoura.

Holocene evolution on Galician coast (NW Spain): An example of paraglacial dynamics

Article

Jul 2002
QUATERN INT

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.

Coarse Clastic Barrier Beaches: A Discussion of the Distinctive Dynamic and Morphosedimentary Characteristics

Article

Aug 1984
MAR GEOL

Coarse clastic barriers are common on mid- and high-latitude coasts. They possess a morphosedimentary and dynamic distinctiveness which sets them apart from sandy fineclastic barrier forms. The reflective nature of the seaward barrier favors the development of zero mode, sub-harmonic edge waves particularly during long period swells (10–20 s), manifest in the formation of high level cusps. In some circumstances the pattern of recent overwashing of the barrier is related to cusps. Lack of distinct tidal passes, due partly to the high seepage potential of coarse barriers, means that very little sediment is transported seaward. Thus the barriers roll steadily onshore, and sections show a variety of washover facies, related to the volume of overwash surges.

Rates and patterns of downwearing of chalk shore platforms of the Channel: Comparisons between France and England

Article

Jan 2006

Two micro-erosion meters were used to measure the surface downwearing of chalk shore platforms developed on either side of the Channel (La Manche). Measurements made along cross-shore profiles indicate that, during the sample period 1999-2002, mean annual rates of surface erosion across all platforms was 3.65 mm y-1 but there were significant differences in rates both down platform and between platforms. The greatest erosion rates were recorded in an abrasion zone scoured by mobile shingle that lies towards the top of the platforms, but there was a secondary maximum which lies mid-platform. The erosion measured on the French platforms was significantly greater than on the English platforms. This contrasts with long-term retreat rates of the chalk cliffs that are much greater on the English coast than the French. Erosion is greatest in autumn and winter, but there is considerable variation between years according to the incidence of stormy weather.

ShoreplatformdownwearingandcliffretreatinthePortuguese west coast

423-431

C Andrade
F Marques
M C Freitas
R Cardoso
P Madureira

Andrade, C., Marques, F., Freitas, M.C., Cardoso, R., Madureira, P., 2002.ShoreplatformdownwearingandcliffretreatinthePortuguese west coast. In: Požar-Domac, A. (Ed.), Littoral 2000, The Changing Coast. EUROCOAST/EUCC, Porto, Portugal, pp. 423–431

An N-type Hammer Fig. 4. Corrubedo. A: Corrubedo East. A1: rugged surfaces at the low tide level; A2: rugged surfaces near the high tide level

Jan 2002

Stephenson
Kirk
Andrade

Stephenson and Kirk, 2000a,b; Andrade et al., 2002; Dickson et al., 2004; Trenhaile and Kanyaya, 2004; Kennedy and Beban, 2005). An N-type Hammer Fig. 4. Corrubedo. A: Corrubedo East. A1: rugged surfaces at the low tide level; A2: rugged surfaces near the high tide level; A3: the zone of abrasion.

L'importance des processes d'origine froide sur la cote Atlantique de la Galice (nord-ouest de la peninsule Iberique) Environnements 150 R

Jan 1998
136-151

Pérez Alberti
Costa Casais
Blanco Chao

Pérez Alberti, A., Costa Casais, M., Blanco Chao, R., 1998a. L'importance des processes d'origine froide sur la cote Atlantique de la Galice (nord-ouest de la peninsule Iberique). Environnements 150 R. Blanco-Chao et al. / Geomorphology 83 (2007) 136–151 Périglaciaires. Bulletin de l'Association Française du Périglaciaire, vol. 5, pp. 21–32.

An Outline of Geomorphol-ogy

Jan 1959

S W Wooldridge
R S Morgan

Wooldridge, S.W., Morgan, R.S., 1959. An Outline of Geomorphol-ogy, 2nd edition. Longmans, London.

Caracterización físco-química do depósito de Mougás (Pontevedra): implicacións morfoxenéticas

Jan 1996
417-430

M Domínguez
C Martínez-Cortizas

Costa-Casais, M., Moares-Domínguez, C., Martínez-Cortizas, A., 1996. Caracterización físco-química do depósito de Mougás (Pontevedra): implicacións morfoxenéticas. In: Pérez Alberti, A., Martínez Cortizas, A. (Eds.), Dinámica y Evolución de Medios Cuaternarios. Xunta de Galicia, Santiago de Compostela, pp. 417–430.

Evolución paleoambiental inferida por diatomeas de la laguna costera de Traba (A Coruña, NO de España) durante los últimos 5000 años. Actas de la XI Reunión Nacional del Cuaternario

Jan 2003
347-352

C Delgado
R Bao
J L Pages

Delgado, C., Bao, R., Pages, J.L., 2003. Evolución paleoambiental inferida por diatomeas de la laguna costera de Traba (A Coruña, NO de España) durante los últimos 5000 años. Actas de la XI Reunión Nacional del Cuaternario. Principado de Asturias, Concejo de Candamo, Cajastur, Oviedo, pp. 347–352.

B1: rugged surfaces at the low tide level; B2: rugged surfaces, even at the edge of blocks and boulders, at the high tidal level Shore platform downwearing and cliff retreat in the Portuguese west coast

Jan 2000
423-431

B Corrubedo
West Andrade
C Marques
F Freitas
M C Cardoso
R Madureira

B: Corrubedo West. B1: rugged surfaces at the low tide level; B2: rugged surfaces, even at the edge of blocks and boulders, at the high tidal level. References Andrade, C., Marques, F., Freitas, M.C., Cardoso, R., Madureira, P., 2002. Shore platform downwearing and cliff retreat in the Portuguese west coast. In: Požar-Domac, A. (Ed.), Littoral 2000, The Changing Coast. EUROCOAST/EUCC, Porto, Portugal, pp. 423–431.

Bulletin de l'Association Française du Périglaciaire

21-32

Périglaciaires

Périglaciaires. Bulletin de l'Association Française du Périglaciaire, vol. 5, pp. 21–32.

L'importance des processes d'origine froide sur la cote Atlantique de la Galice (nord-ouest de la peninsule Iberique

Jan 1998
136-151

Pérez Alberti
Costa Casais
M Blanco Chao
R Environnements
R Blanco-Chao

Pérez Alberti, A., Costa Casais, M., Blanco Chao, R., 1998a. L'importance des processes d'origine froide sur la cote Atlantique de la Galice (nord-ouest de la peninsule Iberique). Environnements R. Blanco-Chao et al. / Geomorphology 83 (2007) 136–151

L'importance des processes d'origine froide sur la cote Atlantique de la Galice (nord-ouest de la peninsule Iberique). Environnements Périglaciaires

Jan 1998
21

Pérez Alberti

Caracterización físco-química do depósito de Mougás (Pontevedra): implicacións morfoxenéticas

Jan 1996
417

Costa-Casais

Evolución paleoambiental inferida por diatomeas de la laguna costera de Traba (A Coruña, NO de España) durante los últimos 5000 años

Jan 2003
347

Delgado

Shore platform downwearing and cliff retreat in the Portuguese west coast

Jan 2002
423

Andrade

Shore platform abrasion in a para-periglacial environment, Galicia, northwestern Spain

Abstract

No full-text available

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