Beach Ridges Research Articles

Relative sea-level changes during the Holocene in the Río de la Plata, Argentina and Uruguay: A review

This study critically reviews the relative sea-level (RSL) data from the Río de la Plata (RDP) (Argentina and Uruguay) in order to analyze the Holocene RSL changes in this region and thus capture the general trend illustrated by both the data and the high-degree polynomial regression analyses which show good agreement with the ICE-6G_C (VM6) model. The previously inferred Holocene sea-level histories reconstructed from palynological and diatom records from the northern and the southern RDP are also compared to the RSL curves proposed in this work. Analysis of the RSL database revealed that the RSL rose to reach the present level at or before c. 7000 cal yr BP, with the peak of the sea-level highstand c. +4 m between c. 6000 and 5500 cal yr BP (depending on the statistical method used) or at c. 7000 cal yr BP according to the ICE-6G model prediction, gradually falling after this time to the present position. The subaerial data tell a consistent story for the last 6000 years for the RDP but the subsurface data are not in agreement with these data or with the glacial isostatic adjustment (GIA) predictions. Since much of the subaerial data come from shells on beaches, beach ridges and storm beaches, they cannot be strictly interpreted as RSL index points. It seems likely that the predicted curves are somewhat high and could be overestimated. The “smooth” model of the late Holocene sea-level decline is in close agreement with both the GIA model predictions and the reconstruction of RSL from palynological and diatom records. The models provide no evidence to suggest that there has been a significant trend of change in the speed of sea-level fall or oscillations during the falling stage system tract. The non-parametric regression model, the GIA predictions and the trend inferred by palynological and diatom data trace out a slow sea-level fall for the last c. 6000 cal yr BP. We critically assessed published Holocene sea-level data from the RDP to produce a Holocene RSL curve of sufficient quality to provide a location in this area for testing theoretical models for the Atlantic coast of South America.

Formation of Danube delta beach ridge plains and signatures in morphology

Danube delta, as most of the large deltas, favours complex interactions between river sediment supply and marine dispersing forces which create complex configurations with concurrent morphologies (i.e. river-versus wave-influenced) or processes (accretion versus erosion) and even distinct landscapes for the same accretionary features: strandplains with low monotonous beach ridges or covered by transgressive dunefields. Beach ridge plains (BRPs) are a common feature of the wave-influenced deltaic lobes, that are created by juxtaposition of succesive berms on the prograding sandy coasts with different shapes and sizes depending on the accretionary mechanisms and the accomodation space.This study reports the formation and dynamics of Danube delta BRPs based on numerical age determination (OSL and AMS) of the paleoshorelines, topographic and geophysical (GPR) surveys and stratigraphic records by cores. A chronological framework is established for all deltaic BRPs which points to the importance of formation timespan and growth rate (as a consequence of sediment supply) on the resultant morphology varying inter-site from small BRP (formation time < 300 years) to large quasi-equilateral triangle-shaped BRP (1400–3000 years) and intra-site from low ridgesets with subparallel beach ridges (progradation rates of 3.5–12 m/yr) to high ridgesets where the original configuration was replaced by massive parabolic dunes or transgressive dunefields (progradation rates ≤ 3.5 m/yr). A six-type morphogenetic classification of BRPs is discussed in respect with the various spatial patterns of progradation – from the large strandplains developed on the updrift side of asymmetric lobes to the small ones accommodating the prograding sectors of the river mouths spits – and with the progradation types encountered: i) beach face accretion during fair-weather, ii) nearshore bar welding, and iii) berm crest building during storms. Although the last is building ca. 1.5% from deltaic BRPs, this is the only case when the visible beach ridges are made by wave processes. For the other two, the aspect of “beach ridges” is the result of aeolian processes that create either unitary foredune or thin eolian sheets (incipient foredune) tens of centimeters higher than adjacent berms.

Testing versions of the Bruun rule for low energy macro-tidal tropical beaches against a theoretical late Holocene sea-level high-stand and beach ridge evidence of late Holocene beach faces

Kerans, A.J., and Cartwright, N., 2016. Testing versions of the Bruun rule for low energy macro-tidal tropical beaches against a theoretical late Holocene sea-level high-stand and beach ridge evidence of late Holocene beach faces. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 740–744. Coconut Creek (Florida), ISSN 0749-0208.Significant evidence of late Holocene beach faces is presented in beach ridges along the North Queensland coast between Mackay and the Daintree region. The ages of these ridges has in some cases been dated giving confidence that the rearmost ridges are the result of a combination of cyclone activity and a late Holocene sea level high-stand. The height of this high-stand is the subject of debate, however the level may be confidently predicted through careful and extensive measurement of relict oyster beds in the region. Using pre-existing beach ridge research together with existing and new measurements of oyster beds on Magnetic Island, North Queensland a value for the late Holocene sea level high-stand is proposed which can be compared to the position of the coast on certain beaches during this period. These measurements are a good basis to test the applicability of the Bruun rules and some proposed modifications for the low energy beach systems of tropical North Queensland. This paper firstly examined the late Holocene sea level evidence stored in relict oyster beds and from that proposes a sea level to be used in the analysis. This sea level is then used to test the Bruun rule and variants and examine the differences between dated Holocene beach faces and the recession predicted by these models.

Geomorphology of the Pinios River delta, Central Greece

ABSTRACTThis paper presents the results of geomorphological investigations carried out on the Pinios River delta, which is a Late Holocene arcuate type delta, located in the southern Thermaikos Gulf (Central Greece). Digital elevation model (DEM) analysis and the study of maps of the last two centuries, accompanied by field survey and aerial photo interpretation have led to the production of a geomorphological map at 1:15,000 scale which outlines the features of the deltaic plain and coastal zone. The evolution and the associated morphology of the delta are the result of the complex interplay of fluvial sedimentation, wave activity and prevailing longshore currents. The dominant landforms of the delta are the numerous abandoned meandering channels, as the river has changed its course several times, and a series of sub-parallel linear sandy beach ridges (cheniers) occupy the lower delta plain. The shoreline of the delta is generally retreating due to marine processes, especially where former river mouths occur whereas the presently active mouth of the river and its immediate surrounds are prograding.

Geomorfologia e arquitetura deposicional de uma planície de cordões litorâneos na margem NE da Lagoa dos Quadros, RS, Brasil

Cordões litorâneos regressivos do tipo dunas frontais (foredune ridges) e do tipo praia (beach ridges) são elementos morfológicos muito comuns em margens de lagoas e lagunas costeiras, embora ainda pouco estudados. Neste trabalho, são apresentados resultados do estudo de uma planície de cordões litorâneos regressivos arenosos que se formou na margem NE da Lagoa dos Quadros, no litoral norte do Rio Grande do Sul. A partir da análise de fotografias aéreas, levantamentos altimétricos, perfis de georadar (GPR), testemunhos de sondagem e amostras superficiais, foram investigadas a morfologia da planície de cordões e o arcabouço estratigráfico de seus respectivos depósitos sedimentares. A planície é composta por 20 cordões contínuos e semi-contínuos, de baixa amplitude e espaçados de 5 a 50 m. Sobre uma fácies basal de fundo lagunar que se formou aproximadamente entre 7 e 6 ka, desenvolveu-se uma sequência regressiva de modo agradacional e progradacional composta por depósitos de antepraia, de pós-praia/face de praia, dunas frontais e depósitos de leque de sobrelavagem. Dunas transgressivas adentrando na lagoa a partir da barreira holocênica IV (barreira de Curumim) podem ter sido uma importante fonte de areia para o desenvolvimento da planície de cordões.

Effect of plant growth on the occurrence and stability of palygorskite, sepiolite and saponite in salt-affected soils on limestone in South Australia

The Mg-rich clay minerals, palygorskite, sepiolite and also Mg-smectites are generally rare in soils. When they occur they are usually concentrated in subsurface horizons and become replaced by other minerals, e.g., dioctahedral smectites in near-surface horizons. Salt-affected soils on limestone in a flat landscape in southern Australia showed patchy pasture growth, including areas in which almost no growth occurred. Chemical and mineralogical analyses of deep profiles of the soils revealed two main types and that the extent of plant growth reflected their mineralogical composition. The soil type in which plants grow well (‘Chromosol’, an Alfisol) contains dioctahedral smectite (montmorillonite and/or beidellite) but only in substantial amounts at depth. The soil type in which little or no plants grew (‘Vertosol’, a Vertisol) has substantial concentrations of a trioctahedral Mg-smectite, saponite, in its surface horizons along with dioctahedral smectite in lower horizons. Both soil types contain sepiolite and palygorskite, largely in the lower horizons of the Chromosol, but also in near-surface horizons of the Vertosol. Both types of soil also contain illite and kaolinite, which are each concentrated in the upper horizons of the soils and are considered to be detrital. The genesis of the two main types of soils can be explained by the depositional history of the basin. On the eastern side of the basin, palustrine limestone formed when the sediments became exposed, possibly from uplift. The Chromosol formed on this material. On the western side, by contrast, lacustrine sediments on lowland adjacent to a stranded beach ridge, experienced prolonged seasonal inundation by water leading to the formation of the Vertosol. This soil is strongly sodic and strongly alkaline throughout and it is concluded that the high concentration of saponite in the surface swells and thereby ensures that the soil remains wet. Together with its high pH, this soil has very poor conditions for plant growth. The persistence of the Mg-rich clay minerals, especially saponite, at the surface of the Vertosol, suggests that the relative lack of plants has preserved these minerals throughout the profile.

Demarcating saline water intrusion pathways using remote sensing, GIS and geophysical techniques in structurally controlled coastal aquifers in Southern India

Application of remote sensing and geographical information system (GIS) with the help of ground truth studies like vertical electrical soundings (VES) and water quality measurements gave a comprehensive picture on saline water intrusion pathways in the structural controlled aquifers of Uppanar and Cauvery River systems located in Sirkazhi and Mannanpandal coastal areas of Southern India. The detailed geomorphic units and lineaments were mapped using IRS LISS-III (1:50,000 Scale) and SRTM Elevation Digital data under GIS environment. The area is mainly alluvial deposits of Holocene Age and classified into three major geomorphic units (i.e., fluvial, fluviomarine, and marine geomorphic units). The identified lineaments are mostly trending North-northeast (NNE)–South-southwest (SSW), Northeast (NE)–Southwest (SW), Northwest (NW)–Southeast (SE), East–West (EW) and East-Northeast (ENE)–West-Southwest (WSW) directions. Some of them are potential for fresh groundwater occurrence and movement. The lineaments trending NE–SW, NNE–SSW, and ENE–WSW act as pathways for saline water intrusion to the inland. The lineament L1 (NNE–SSW trending) conformed as a sinisterly shifted fault played a significant role in saline water intrusion. The area within the parallel lineaments L2 and L3 oriented ENE–WSW direction indicates low topography, beach ridges, paleo-channel sinuosity, large aerial extent of tidal flats, and backwater inundation. All the above geomorphic units gave indirect evidence of land subsidence, which was confirmed with the help of sub-surface geo-electrical signals obtained through VES and in situ groundwater quality measurements. Integrating all the above results, the saline water spread and fresh water pockets were identified.

Soil development on a beach ridge chronosequence in the Gulf of Mexico coastal plain and its relation to the ancient land use

A soil chronosequence study is presented in a beach ridge system at the mouth of the Usumacinta and Grijalva Rivers, Mexico, formed since a strong decrease in the rate of sea level rise some 6000 years ago. Four sites were selected for the chronosequence study: Simón Sarlat (SS), Rancho Magdaleno 1 and 2 (RM1, RM2), Cocoteros (CC), and Playa Cocoteros (PC), located on beach ridges that range in age between 5000 years old to recently formed. The soils show poor to moderate degree of development, and the change in the pedogenic properties has been clearly evaluated. The most pronounced changes are the following, from the older (SS, RM2) to the younger soils (PC, CC): color (becoming yellowish brown in the better developed soils); an increase in the amount of organic matter, clay, and Fed (iron extracted with dithionite solution); a better structure with more stable aggregates; a decrease in the Feo proportion (Fe extracted with oxalate solutions); and an increase in the content of fine magnetic particles (formed by pedogenesis). This area was densely populated and thus affected by human activities since the pre-Classic period (800–300 BC), as many archaeological sites have been registered. We evaluated soil agronomic quality, in order to understand the ancient land use. The results show that the soils in this area, no matter their age, have low agronomic quality, which must have limited their use by ancient population. However, the strategic position near main trade routes, near rich aquatic resources, and a low susceptibility to flooding were favorable for human settlement on the beach ridges.

Continuous record of Holocene sea-level changes and coastal development of the Kattegat island Læsø (4900 years BP to present)

Læsø is the largest island of the Kattegat–Skagerrak region and exposes a vast array of relative sealevel (RSL) indicators, mainly raised beach ridges, swales, lagoons and saltmarshes. The physical environment of continuous glacial rebound, excessive supply of sediment, shallow surrounding waters, low amplitudes of near-shore waves, and micro-tidal conditions produced numerous sealevel proxies of both barrier coasts and saltmarshes. About 1200 RSL/age index points reflect not only short-term sea-level highstands as in most other parts of Europe, but also short-erm sea-level lowstands, which in less regressive environments have normally been removed by coastal erosion or obscured by berms from subsequent highstands. Based on a high-precision lidar digital terrain model, the beach ridges have been mapped, typified, levelled and correlated relative to their order of appearance. Transformation of this relative chronology to a robust absolute age model of the RSL changes has been made on the basis of 119 optically stimulated luminescence (OSL) datings, 14C datings, and tree-ring datings. By ground penetrating radar (GPR) and terrain analyses, the height of the swash zone (run-up) has been determined in order to transform the ridge elevations to a detailed curve of the RSL/age relation. The curve reveals eight centennial sea-level oscillations of 0.5–1.1 m superimposed on the general trend of the RSL curve, including a Little Ice Age lowstand of 0.6 m at 1300 AD. The island grew from now eroded landscapes of Weichselian glacio-marine deposits, including the oldest known post-Weichselian forested area in Scandinavia. During the last 4900 years new coastal landscapes have formed continuously, resulting in around 4000 km of still visible, raised palaeo-shorelines in mostly uncultivated landscapes. After formation of the oldest preserved beach-ridge complex, numerous sea-level proxies formed in a strongly regressive environment caused by glacial rebound supplemented with local uplift due to extensive erosion during Boreal and Atlantic time of the 1700 km2 glacio-marine platform upon which the island is still being built. The combined uplift produced a relative sea-level fall of 10.3 m, corresponding to a mean vertical regression rate of 2.1 mm/year and a mean horizontal regression rate of 2 m/year, and formed eight distinct types of raised coastal landscapes where well separated beach ridges and saltmarshes developed continuously. The oldest preserved part of Læsø appeared 4900 years BP as the eastern tip of a 10 km long barrier-spit system growing from a raised glacio-marine landscape, now represented only by boulder reefs west and north-west of the present island. Around 4000 years BP another barrier-spit system appeared to the south, growing northwards from another raised glacio-marine landscape at the raised boulder reefs in the town of Byrum and the abrasion landscapes of Rønnerne. Around 3000 years BP these two inital barrier-spit systems united and formed one major barrier between the present towns Vesterø and Byrum. To the north-east, a third glacio-marine landscape provided materials for the development of the eastern end of the island. Thus, around 2500 BP the island had become one triangular, completely detached island (’the old triangle’) between Vesterø, Byrum and Bansten Bakke. From this detached stage, nine subsequent barrier-spit systems grew to the east and formed the present Østerby peninsula, while a series of nine barrier-island complexes developed south-west of ’the old triangle’. To the south and south-east, low-energy coasts developed and formed low beach ridges and saltmarsh landscapes.

Late quaternary sea level changes of Gabes coastal plain and shelf: Identification of the MIS 5c and MIS 5a onshore highstands, southern Mediterranean

The continental shelf of the Gulf of Gabes is outlined, during the MIS 5c and MIS 5a onshore highstands, by the genesis of forced regressive beach ridges situated respectively at –19 m b.s.l/100 ka and –8 m b.s.l/80 ka. This area, considered as a stable domain since at least the last 130 ka (Bouaziz et al. 2003), is a particular zone for the reconstruction of the late quaternary sea-level changes in the region. Shuttle Radar Topography Mission (SRTM) data and field observations are highlighted to deduce interaction between hydrodynamic factors and antecedent topography. Variations in geomorphology were attributed to geological inheritance. Petrography and sedimentary facies of the submerged coastal ridges reveal that the palaeocoastal morphology was more agitated than today and the fluvial discharges are consistent. Actual morphologic trend deduced from different environment coasts (sandy coasts, sea cliffs and tidal flat) is marked by accumulation of marine sands and progradation.

Recent shoreline changes in the Volta River delta, West Africa: the roles of natural processes and human impacts

The Volta River delta developed as an asymmetric lobe in a tectonic offset on the coast of Ghana. The delta comprises a large curvilinear spit that widens in its central portion due to the adjunction of successive sandy beach ridges. The appearance of a distinct spit, in lieu of a continuous barrier from the present mouth of the Volta River to the Bight of Benin coast, may be an outgrowth of a natural change in the location of the mouth of the Volta. The spit marks a segmentation of the unique sand drift cell that hitherto prevailed on this bight coast. Spit growth has been accompanied by a wave of erosion over the last century of the immediate downdrift sector of the bight coast, endangering the town of Keta. Erosion since the 1960s may have been aggravated by the construction of the Akosombo hydropower dam. The tip of the spit has recently welded to the shoreline, thus assuring resumption of sand supply from the Volta towards the rest of this formerly sand-starved sector of the bight coast. Blocking of sediment by the Akosombo Dam is, in due course, likely to become the overarching factor in delta shoreline stability.

GIS-based geomorphologic study of Presque Isle Peninsula, a compound lacustrine barrier-spit system along the south-central Lake Erie margin

Abstract The Presque Isle peninsula is a sandy barrier-spit system situated along the south-central Lake Erie coast. This investigation focuses on landform succession along its eastern terminus, where nautical charts and aerial images chronicle morphologic change over the last century. A conceptual framework of this recent terrain evolution provides a blueprint for understanding the process–landform interactions responsible for constructing the compound peninsula over the late Holocene. Presque Isle is compartmentalized into four distinct en echelon strandplains, each comprised of multiple beach ridges of similar orientations, heights and spacing. These strandplain segments are separated by topographically prominent ridgelines that extend across the width of the peninsula and obliquely truncate landward paleoshorelines. The processes responsible for this landform juxtaposition are exemplified by recent spit growth and decay along Presque Isle's eastern terminus, where net lateral accretion has extended the peninsula by ~ 0.8 km 2 since the early 1900s. Truncation of newly formed ridge morphologies here since the 1990s provides a reference frame for understanding broader peninsular evolution, as reflected in Presque Isle's morphological segmentation. Episodes of spit accretion and low-elevation beach-ridge formation sequentially construct strandplains with little internal heterogeneity in way of beach-ridge spacing and height. Net-depositional episodes are subsequently punctuated by extensive erosion and the formation of high-elevation ridgelines at oblique angles to paleoshorelines. While this process is demonstrated over the recent ~ 100 years as a function of human-altered coastal hydrodynamics and sediment-supply reductions, potential linkages between older erosive landforms and major lake-level transgressions are inferred and could potentially be elucidated upon continued research.

Beaches under pressure – effects of human access on vegetation at Baltic Sea beaches

AbstractQuestionsHow do cover, richness and composition of plant species vary according to different levels of beach access? What shifts in plant traits occur along gradients of tourism intensity? What recommendations regarding the sustainable management of Baltic Sea beaches can be proposed?LocationSouthern Baltic Sea beaches in Germany.MethodsIn this study, the species composition of vascular plants on beaches with differing accessibility to tourists was analysed at the southwest Baltic Sea coast. In total, 894 vegetation plots were evaluated in order to determine vegetation changes along the sea–inland gradient due to different levels of human accessibility at beaches. Relevés were conducted as repeated transects from the beach ridge to the shore. Shifts in vegetation characteristics due to different levels of tourism access were analysed at the level of plant communities and plant species traits.ResultsSpecies richness did not differ significantly between the levels of accessibility. Vegetation cover significantly increased with distance to the shore and was highest in the upper shore area of closed beaches (52.0 ± 2.7%). Corresponding to the increase in beach access, we observed an increase in ruderal species and a decrease in typical beach species of the vegetation class Honckenyo‐Elymetea. Tourism access and distance to the shoreline had a decisive influence on the distribution of plants with selected plant traits. In particular, at accessible sites, a loss of plants with leaves having high scleromorphy was recorded.ConclusionsIncreased beach access results in a loss of typical beach plant species. Changes in vegetation characteristics are considered to alter the function of the beach ecosystem. Based on these results, we derived spatially differentiated management measures for excluding the most sensitive beach areas from tourism.

津波浸水域の土地利用履歴にもとづく土地活用の方向性

This study focuses on land use in the tsunami inundation area caused by the Great East Japan Earthquake, particularly land use history in the tsunami-affected area. Hanagama District, Yamamoto City, Miyagi prefecture, was selected as the study area. Land use were examined using aerial photographs taken in 1975, 2010 and 2013. Relationships between land use change and the disaster hazard areas, natural land conditions were analyzed with GIS. As a result of land use analysis, in 1975, land use base on natural land conditions (Residences, Dry fields and Forests- Beach ridge, Paddy fields- Back swamp) were consisted. These land uses were greatly changed by urbanization and tsunami damage.

Facies evolution and depositional model of an arid microtidal coast: example from the coastal plain at the mouth of Wadi Al-Hamd, Red Sea, Saudi Arabia

This study describes the subsurface sedimentary facies of a modern Red Sea coastal plain at the mouth of Wadi Al-Hamd, northern Saudi Arabia, in an attempt to infer the influence of aridity and limited tidal range on facies characteristics. The study provides criteria to delineate the fluviomarine transition in a setting where tidal signatures and other marine influences are weak. Six manually collected cores (1.4 to 1.75 m long) from the channels at the wadi mouth, beach ridge, intertidal flat, strandplain, and supratidal flat enabled the identification of 23 sedimentary facies. The sediments displayed rapid and tremendous variability in facies both within and among cores. They were deposited generally under low energy conditions occasionally punctuated by short-lived high energy events. The sediments in the channel exhibit features characterizing deposition under an arid and semiarid climate, such as rapid and intermittent discharge and short-lived rapidly abandoned channels. The sediments and depositional settings on both sides of the wadi mouth are different. A low gradient intertidal flat influenced by wave and tidal processes develops to the south, whereas a relatively high energy wave dominated strandplain occurs to the north. The deposition in the supratidal flat was accomplished by a short-lived high energy washover event. The facies stacking pattern indicates that the depositional systems are in a state of transgression, with a regime of gradually increasing accommodation possibly during the rising of relative sea level and diminishing of sedimentation. The turnaround from regressive to transgressive stage that coincides with the fluviomarine transition in channel fill deposits is placed at a level of increased soft sediment deformation because the tidal influence is weak in this microtidal setting. Though the plane view shows a deltaic shoreline, the depositional system is interpreted as estuarine. The findings of this study can be applied to similar recent and ancient settings.

Evolution of coastal landforms during the Holocene Epoch along the west and southeast coasts of Sri Lanka

Holocene sea-level reconstructions are of broad interest in the island of Sri Lanka as it provides mainly information on the history of coastal systems. In addition, it is critical to predicting future human-induced sea-level changes on the island. This study deals with the regional correlation of evolution stage of coastal landforms with respect to the Holocene sea-level changes in Sri Lanka. Mud dominant sediments in the wet zone and relatively sand particles dominant sediments in the dry zone reveal that sediment distribution in coastal terrestrial archives are prominently controlled by climatic characteristics. The lower sedimentary succession (Facies 2) can probably indicate the time of mid-Holocene highstands. It is followed by expansion of beach ridges and headlands since marine transgression. The upper sedimentary succession (Facies 1) can probably suggest semi-closed or closed brackish to terrestrial systems after the mid-Holocene highstands.

浜松平野西部における完新世後期の浜堤列の地形発達過程

浜松平野西部における完新世後期の浜堤列の地形発達過程

Geologic records of Holocene typhoon strikes on the Gulf of Thailand coast

Washover sedimentation resulting from modern typhoon strikes on the Gulf of Thailand coast forms anomalous sand layers in low-energy coastal environments including marshes, ponds and swales. The primary diagnostic for recognizing prehistoric typhoon-deposited sand layers in the geologic record are sharp upper and lower contacts between coarser-grained transported sand layers and finer-grained in-situ sediments. In this first paleotempestology study in Thailand, cores from two low-energy settings on the Gulf of Thailand coast – a coastal marsh near Cha-am and beach ridge plain swales near Kui Buri – reveal geologic evidence of up to 19 typhoon strikes within the last 8000years. The sand layers have sharp upper and lower contacts with enclosing finer sediments. Some sand layers also contain other evidence of a sudden powerful landward-directed surge of ocean water, including gravel-sized clasts, offshore foraminifera, abundant shell fragments, plant debris and mud rip-up clasts. Sand layers record eleven typhoon strikes at Cha-am, ranging in age from AD 1952 to 7575cal.yr. BP, and eight typhoon strikes at Kui Buri, ranging in age from 4075 to 7740cal.yr. BP. Bayesian age–depth models, derived from eight AMS radiocarbon dates, suggest that the frequency of typhoon strikes was 2–5 times greater from 3900 to 7800cal.yr. BP compared to 0–3900cal.yr. BP. Possible explanations for this variability in the typhoon record are that typhoons were more frequent and/or more intense in Southeast Asia in the mid-Holocene because of climatic changes associated with the Mid-Holocene Warm Period or that the record reflects site sensitivity changes resulting from a mid-Holocene sea-level highstand. The preliminary finding of a possible link between warmer conditions and a greater frequency of intense typhoon strikes could have important societal implications, given possible consequences of ongoing global warming.

Coastal lagoons and beach ridges as complementary sedimentary archives for the reconstruction of Holocene relative sea‐level changes

AbstractCoastal lagoons and beach ridges are genetically independent, though non‐continuous, sedimentary archives. We here combine the results from two recently published studies in order to produce an 8000‐year‐long record of Holocene relative sea‐level changes on the island of Samsø, southern Kattegat, Denmark. The reconstruction of the initial mid‐Holocene sea‐level rise is based on the sedimentary infill from topography‐confined coastal lagoons (Sander et al., Boreas, 2015b). Sea‐level index points over the mid‐ to late Holocene period of sea‐level stability and fall are retrieved from the internal structures of a wide beach‐ridge system (Hede et al., The Holocene, 2015). Data from sediment coring, georadar and absolute dating are thus combined in an inter‐disciplinary approach that is highly reproducible in micro‐tidal environments characterised by high sediment supply. We show here that the commonly proximate occurrence of coastal lagoons and beach ridges allows us to produce seamless time series of relative sea‐level changes from field sites in SW Scandinavia and in similar coastal environments.

Anthropogenic disruption to the seismic driving of beach ridge formation: The Sendai coast, Japan

The expected geomorphic after-effects of the Mw 9.0 Tōhoku-oki earthquake of 11 March 2011 (eastern Japan) are summarized by a schematic model of seismic driving, which details seismogenic disturbances to sediment systems that affect the rate or timing of sediment delivery to coastlines over timescales of 102–104years. The immediate physical environmental responses to this high-magnitude earthquake included a large tsunami and extensive region-wide slope failures. Normally, slope failures within mountain catchments would have significant impacts on Japan's river and coastal geomorphology in the coming decades with, for example, a new beach ridge expected to form within 20–100years on the Sendai Plain. However, human activity has significantly modified the rate and timing of geomorphic processes of the region, which will have impacts on likely geomorphic responses to seismic driving. For example, the rivers draining into Sendai Bay have been dammed, providing sediment traps that will efficiently capture bedload and much suspended sediment in transit through the river system. Instead of the expected ~1km of coastal progradation and formation of a ~3m high beach ridge prior to the next large tsunami, it is likely that progradation of the Sendai Plain will continue to slow or even cease as a result of damming of river systems and capture of river sediments behind dams. The resulting reduction of fluvial sediment delivery to the coast due to modification of rivers inadvertently makes seawalls and other engineered coastal structures even more necessary than they would be otherwise.