internal structure of aeolian dunes in abu dhabi determined using ground penetrating radar a ground penetrating radar survey of aeolian dunes in the al liwa area of abu dhabi reveals a variety of dipping reflectors which are interpreted as primary sedimentary structures the interpretation of the radar profiles has been confirmed by bulldozing trenches through the study area and comparing logged sections in the trenches with the radar profiles nnw sse orientated radar profiles approximately parallel to the prevailing wind direction show two sets of dipping reflectors which are interpreted as sets of cross stratification and second and third order bounding surfaces radar profiles orientated wsw ene across the prevailing wind direction are dominated by concave up reflectors which are interpreted as trough shaped scours and sets of trough cross stratification produced by oblique progradation of barchanoid dunes nested troughs with small sets of trough cross stratification within larger troughs may be due to reactivation following wind reversal or the superposition of small dunes on larger dunes and the fill of large dune troughs by smaller dunes convex upwards reflectors are interpreted as linear spurs on the convex portions of sinuous dunes or erosional remnants between troughs overall there is a tendency for the larger second order bounding surfaces to dip downwind which confirms brookfield s ideas of the relative migration paths of dunes and draa

proxy records of holocene storm events in coastal barrier systems storm wave induced markers abstract extreme storm events in the coastal zone are one of the main forcing agents of short term coastal system behavior as such storms represent a major threat to human activities concentrated along the coasts worldwide in order to better understand the frequency of extreme events like storms climate science must rely on longer time records than the century scale records of instrumental weather data proxy records of storm wave or storm wind induced activity in coastal barrier systems deposits have been widely used worldwide in recent years to document past storm events during the last millennia this review provides a detailed state of the art compilation of the proxies available from coastal barrier systems to reconstruct holocene storm chronologies paleotempestology the present paper aims i to describe the erosional and depositional processes caused by storm wave action in barrier and back barrier systems i e beach ridges storm scarps and washover deposits ii to understand how storm records can be extracted from barrier and back barrier sedimentary bodies using stratigraphical sedimentological micro paleontological and geochemical proxies and iii to show how to obtain chronological control on past storm events recorded in the sedimentary successions the challenges that paleotempestology studies still face in the reconstruction of representative and reliable storm chronologies using these various proxies are discussed and future research prospects are outlined

beach ridges and prograded beach deposits as palaeoenvironment records abstract beach ridges are landforms commonly developed on prograded coasts with beach shorelines a sequence of beach ridges coupled with their subsurface deposits can be regarded as a time series of coastal evolution methodological advances in field surveying and chronology applicable to beach ridges have led to detailed palaeoenvironmental reconstructions to be derived from such sequences this paper reconsiders the basic aspects of beach ridges and deposits which need to be properly understood for their comprehensive interpretation in a palaeo environmental context it also reviews case studies in which beach ridge sequences have been used to unveil past sea level history catastrophic events and climate changes proposed formative processes of beach ridges include 1 progradation of sandy beach and berm formations in relation to fairweather waves coupled with aeolian foredune accumulation 2 building of gravel ridges by storm waves 3 welding of longshore bars beach ridge formation through sea level oscillation is thought to be questionable and caution is suggested for this process when undertaking palaeoenvironmental reconstruction beach deposit stratification is known to dip either landwards or seawards but landward dips are uncommon seaward dipping stratification is formed in relation to beachface progradation and is usually dissected in places by erosion surfaces resulting from episodic beach retreat the boundary between the foreshore and the underlying shoreface is well defined only in the case that longshore bars lead to complex bedding structure relative to that of the foreshore reliable chronology of beach ridges can be determined by radiocarbon and optically stimulated luminescence osl dating radiocarbon dating of articulated shells which are considered not to be extensively reworked provides robust results but osl dating is more useful as it enables direct dating of sediment grains it is noted that there are restrictions in chronological resolution and continuity inherent to beach ridge and beach deposits the plan view geomorphic expression of beach ridges typically consists of ridge sets with multi decadal intervals whereas their internal sedimentary structures define shorter time scales records of beach sedimentation and erosion are likely to be reworked by episodic high magnitude beach retreat and the resultant record of the net progradation is likely to be sporadic and discontinuous the height of sandy beach ridges is often variable due to differing degrees of aeolian sand accumulation and they are thus not used as sea level indicators unless purely wave built gravel ridge height is a relatively reliable indicator of sea level but can vary in response to storminess fluctuations subsurface sediment facies boundaries are preferred as sea level indicators and those proposed include boundaries of aeolian beach foreshore shoreface and upper lower shorefaces catastrophic events are expressed in both erosional and depositional records erosion surfaces or scarp imprints revealed in a cross section of beach deposits indicate storm or tsunami events however erosional events are likely to rework previous records of sedimentation and even other erosional events and thus the apparent history decoded from the resultant deposits tends to be biased several attempts for estimating the frequency and intensity of prehistoric cyclones rely on assumed relationships between the level of coarse sand beach ridges and cyclone inundation the formative process of coarse sand ridges remains uncertain and needs to be clarified as it constitutes the fundamental basis of these attempts the growth rates of beach ridge systems are expected to reflect fluctuations in river sediment discharge to the coast and in aeolian sand flux due to onshore winds both of which are affected by climate change assessment of the growth rate is potentially improved by ground penetrating radar survey of subsurface structure and by detailed chronology orientation of beach ridges reflects long term trends in wave direction inferred relationships between beach ridges and cyclic fluctuations of sea level and climate rely on weak assumptions and are not substantiated by rigid chronological evidence and thus remain highly questionable correlation between the inherently decadal signal of beach ridge intervals and possible climate cycles such as sunspot activity is probably coincidental as it lacks causal explanations

annual layers revealed by gpr in the subsurface of a prograding coastal barrier southwest washington u s a abstract the southwest washington coastline has experienced extremely high rates of progradation during the late holocene subsurface stratigraphy preserved because of progradation and interpreted using ground penetrating radar gpr has previously been used successfully to document coastal response to prehistoric storm and earthquake events new gpr data collected at ocean shores washington suggest that the historic stratigraphy of the coastal barrier in this area represents a higher resolution record of coastal behavior than previously thought gpr records for this location at 200 mhz reveal a series of gently sloping seaward dipping reflections with slopes similar to the modern beach and spacings on the order of 20 45 cm field evidence and model results suggest that thin 1 10 cm possibly magnetite rich heavy mineral lags or low porosity layers left by winter storms and separated by thick 20 40 cm summer progradational sequences are responsible for generating the gpr reflections these results indicate that a record of annual progradation is preserved in the subsurface of the prograding barrier and can be quantified using gpr such records of annual coastal behavior where available will be invaluable in understanding past coastal response to climatic and tectonic forcing

transgressive and regressive deposits forming the barriers and beachplains of the columbia river littoral cell usa abstract holocene transgression of the columbia river littoral cell crlc led to ravinement of the lowstand topography and the subsequent formation of a transgressive sequence of deposits during the late holocene sea level rise slowed and then stabilized leading to the deposition of a regressive sequence that was expressed geomorphically as beachplains and barrier spits the major focus of this study was to describe the architecture of the transgressive and regressive deposits of the crlc this was facilitated by the use of drill core radiocarbon dates and geomorphic information a generalized stratigraphic sequence for the crlc sand bodies consists of a ravinement overlain by a coarse transgressive lag which is overlain by transgressive and regressive beachface and shoreface deposits that are covered in places by aeolian sand throughout the holocene sediment discharge from the columbia river was so high that accommodation space was rapidly occupied and beach progradation occurred as sea level was still rising today even as areas close to the columbia river are experiencing highstand regressive conditions in the most northerly part of the littoral cell transgressive conditions still exist and a ravinement is being cut due to insufficient sediment input to fill available accommodation space ravinement under the oldest crlc barrier spit near the southern end of long beach peninsula began at about 7 8 ka while ravinement of the northern portion of the clatsop plains was initiated at approximately 5 ka the ravinement surface was formed at about 4 ka in the grayland plains sub cell and

distribution geometry and origin of heavy mineral placer deposits on oregon beaches abstract beach segments 0 5 3 km in length enriched in heavy minerals 20 100 by weight abundance are located south of six prominent headlands that interrupt the 175 km coastline between cape lookout and cape perpetua oregon beach face retreat in the winter of 1982 83 exposed underlying placers containing the economic minerals garnet zircon ilmenite and chromite in each case the highest concentration of placer minerals occurs in an area of maximum shoreline curvature at a distance south of the north bounding headland that is proportional to seaward extent of the headland cross sections and magnetic surveys of one 8 km coastal section otter rock to yaquina head define a small placer body heavy minerals 50 some 0 75 km in length and 80 103 m3 in volume that comprises 10 of the total beach sand between the bounding headlands mineral grain size analyses of winter beach samples along this coastal section confirm earlier models of mineral segregation by entrainment processes the light minerals are more susceptible to fluid shear stress than the heavy minerals maximum segregation and heavy mineral enrichment occur in the backshore and at shoreline inflection points where decreasing flow velocities produce gradients of fl id shear stress allowing light minerals to be winnowed from more stable heavy minerals development of placer deposits is controlled by shoreline configuration as the first order factor and seasonal variations of wave climate and longshore currents as second order factors that delineate shape and concentration of heavy minerals in placer bodies

sudden probably coseismic submergence of holocene trees and grass in coastal washington state growth position plant fossils in coastal washington state imply a suddenness of holocene submergence that is better explained coseismic lowering of the land than be decade or century long rise of the sea these fossils include western red cedar and sitka spruce whose death probably resulted from estuarine submergence close to 300 years ago rings in eroded bark free trunks of the red cedar show that growth remained normal within decades of death rings in buried bark bearing stumps of the spruce further show normal growth continuing until the year of death other growth position fossils implying sudden submergence include the stems and leaves of salt marsh grass entombed in tide flat mud close to 300 years ago and roughly 1 700 and 3 100 years ago the preservation of these stems and leaves shows that submergence and initial burial outpaced decomposition which appears to take just a few years in modern salt marshes in some places the stems and leaves close to 300 year old are surrounded by sand left by an extraordinary landward directed surge probably a tsunami from a great thrust earthquake on the cascadia subduction zone

pedogenic and early diagenetic processes in palaeogene alluvial fan and lacustrine deposits from the sado basin s portugal abstract the palaeogene deposits of the sado basin were deposited in a continental basin that shows a typical pattern with alluvial fans system in the margins of the basin passing towards distal areas of mudflat facies where in some areas the installation of shallow water bodies favoured the development of palustrine conditions the deposits of this basin vary form coarse conglomerates and sandstones to palustrine carbonates these sediments were affected by pedogenesis and early diagenetic processes that promoted important modifications on their primary features these modifications have been studied by the analyses of four profiles developed on proximal middle and distal fan deposits and the fourth one on lacustrine deposits the overall analyses of the sedimentological pedogenic diagenetic features and their relationships indicate that three main processes took place throughout the basin soil formation palygorskite neoformation and dolomitization soil formation processes led to illuviation of clays and carbonate precipitation mostly around roots pedogenic carbonates increase towards distal areas whereas hydromorphic features are present throughout the basin palygorskite neoformation was partially diagenetic being maximum in proximal areas and palustrine deposits this neoformation is attributed to the percolation of alkaline mg rich soil and groundwaters through smectitic rich sediments promoting important clay transformation dolomitization was an early diagenetic process that occurred mainly in carbonate rich deposits of distal and lacustrine environments as a result of the increasing mg ca ratio of the percolating groundwaters in all these processes there has been a close spatial and temporal interplay between pedogenesis and diagenesis driven by the chemistry of soil particles and groundwaters

the architecture of prograding sandy gravel beach ridges formed during the last holocene highstand southwestern british columbia canada this study was conducted to establish the sedimentary architecture of a beach ridge system that developed in response to rising and then stabilizing sea level in a macrotidal setting the beach ridges document a shift from transgressive to highstand depositional conditions a beach ridge complex is being deposited on the boundary bay tidal flats that flank the fraser river delta in southwestern british columbia the delta onlapped an offshore island during the holocene and partially incorporated it into its delta plain sand and gravel eroded from this island is the sediment source for the beach ridges four depositional geomorphic environments are identified beach ridges lagoon and swales washover fans and tidal flats the beach ridges prograded over the tidal flats of the fraser delta when sea level stabilized and the late holocene highstand was established the very earliest beach ridges were deposited about 5200 to 4800 years bp but most were formed after 2250 years bp with the establishment of the holocene highstand beach ridge progradation rates varied between 1 6 m a 1 to 0 48 m a 1 ground penetrating radar gpr was used to provide continuous two and three dimensional images of the facies in order to delineate the depositional architecture of the sandy gravel beach ridges we supplemented the customary use of well logs and cores for ground truthing gpr lines with cone penetration testing cpt which provided a detailed suite of logs invaluable for correlating radar reflections with subtle lithologic variations unidentifiable in core a synthesis of geomorphic environments lithologic logs and radar facies is used to construct a depositional model of the beach ridge complex

sea level variation during the holocene deduced from the morphologic and stratigraphic evolution of morgan peninsula alabama u s a abstract recent gulf of mexico shoreline studies interpret middle to late holocene sea level as falling from a level above present elevation or stable at present elevation however the architecture of morgan peninsula alabama does not support this morgan peninsula is a beach ridge strandplain composed of two obliquely aligned holocene beach ridge sets ground penetrating radar profiles discriminate between parallel even to wavy reflectors of the eolian dune environment and the underlying seaward dipping complex sigmoidal oblique reflectors of the foreshore and upper shoreface environment the contact between foreshore and eolian facies in beach ridges can be used as a sea level indicator the average elevation of this contact in morgan peninsula rises throughout shoreline accretion which occurred throughout the last 5 4 ka suggesting that there was continual sea level rise during this time morgan peninsula is a useful modern analog to ancient shoreface shelf parasequences and demonstrates the significant internal complexities that can exist in these deposits erosional discontinuities imaged in the holocene foreshore upper shoreface environment are laterally continuous extend to elevations above mean sea level and correlate to beach ridges and the transition between beach ridge sets an increase in the wave regime or fluctuations in sediment supply appear to be likely mechanisms for forming erosional discontinuities below beach ridges the erosional surface separating beach ridge sets may have formed by increased storm activity and associated barrier breaching or a reconfiguration of the mobile bay tidal delta complex superimposed on a gradual rate of sea level rise this boundary is recognized by a change in beach ridge orientation at the surface and an increase in the aggradational component of shoreline accretion

sedimentary architecture of a spit end salisbury beach massachusetts the imprints of sea level rise and inlet dynamics abstract in the vicinity of tidal inlets the facies architecture of barrier islands is largely controlled by inlet channel shifting and the transfer of sand between the ebb tidal delta and the adjacent shore including processes of inlet sediment bypas sing merrimack river inlet is situated in a mixed energy setting and is characterized by episodic shifting of the ebb channel prior to being stabilized in 1881 here we delineate the internal structure and evolution of the updrift barrier spit terminus by integrating data obtained from ground penetrating radar transects and sediment cores to document the effects of inlet associated sedimentation processes our results document complex radar and sedimentological facies which define two distinctive associations of facies the inlet distal and proximal within the core of the present barrier these facies are associated with three phases of barrier terminus evolution i barrier retrogradation characterized by the preservation of washover and backbarrier marsh facies deposited during sea level rise ii downdrift barrier progradation characterized by channel fill and swash platform deposits overlain by foreshore deposits generated by long shore currents and swash bars migrating to the foreshore from the swash platform and iii foreshore seaward progradation characterized by cross beds this study illustrates the highly complex nature of inlet associated spit ends of barriers likewise our results shed light on the mechanisms of spit elongation and recurving in a setting where the estuary opening is narrowing

landform characterization using geophysics recent advances applications and emerging tools abstract this paper presents an overview of the strengths and limitations of existing and emerging geophysical tools for landform studies the objectives are to discuss recent technical developments and to provide a review of relevant recent literature with a focus on propagating field methods with terrestrial applications for various methods in this category including ground penetrating radar gpr electrical resistivity er seismics and electromagnetic em induction the technical backgrounds are introduced followed by section on novel developments relevant to landform characterization for several decades gpr has been popular for characterization of the shallow subsurface and in particular sedimentary systems novel developments in gpr include the use of multi offset systems to improve signal to noise ratios and data collection efficiency amongst others and the increased use of 3d data multi electrode er systems have become popular in recent years as they allow for relatively fast and detailed mapping novel developments include time lapse monitoring of dynamic processes as well as the use of capacitively coupled systems for fast non invasive surveys em induction methods are especially popular for fast mapping of spatial variation but can also be used to obtain information on the vertical variation in subsurface electrical conductivity in recent years several examples of the use of plane wave em for characterization of landforms have been published seismic methods for landform characterization include seismic reflection and refraction techniques and the use of surface waves a recent development is the use of passive sensing approaches the use of multiple geophysical methods which can benefit from the sensitivity to different subsurface parameters is becoming more common strategies for coupled and joint inversion of complementary datasets will once more widely available benefit the geophysical study of landforms three cases studies are presented on the use of electrical and gpr methods for characterization of landforms in the range of meters to 100 s of meters in dimension in a study of polygonal patterned ground in the saginaw lowlands michigan usa electrical resistivity tomography was used to characterize differences in subsurface texture and water content associated with polygon swale topography also a sand filled thermokarst feature was identified using electrical resistivity data the second example is on the use of constant spread traversing cst for characterization of large scale glaciotectonic deformation in the ludington ridge michigan multiple cst surveys parallel to an 60 m high cliff where broad 100 m synclines and narrow clay rich anticlines are visible illustrated that at least one of the narrow structures extended inland a third case study discusses internal structures of an eolian dune on a coastal spit in new zealand both 35 and 200 mhz gpr data which clearly identified a paleosol and internal sedimentary structures of the dune were used to improve understanding of the development of the dune which may shed light on paleo wind directions

dating of late holocene beach shoreline positions by regional correlation of coseismic retreat events in the columbia river littoral cell usa abstract beaches and barrier spits of the columbia river littoral cell crlc 160 km in length experienced substantial progradation 0 5 2 5 km in width during the late holocene the accreted beach plains and barriers preserved evidence of episodic catastrophic retreat that was forced by coseismic subsidence the abrupt subsidence events 0 5 1 5 m submergence are associated with slip on the underlying cascadia megathrust with a mean recurrence interval of 500 yr ground penetrating radar gpr profiles taken across the barriers and beach plains show high angle beach retreat scarps 3 15 m vertical relief and foredune ridge slump scarps 5 15 m vertical relief the upper shoreface retreat features are correlated throughout the littoral cell by radiocarbon age position relative to abandoned foredune ridges and distinct sequences of large and small scarps particularly large retreat scarps 10 15 m in height are associated with the first oldest and fourth oldest prehistoric scarps a and d respectively a maximum of 10 retreat scarps in the long beach subcell date from 216 211 calrcybp to 4756 114 calrcybp the youngest seven scarps a g are correlated between all four subcells showing a regional response to the coseismic strain cycles backshore disturbance features 1 3 m vertical relief are observed in the gpr profiles but they are not identified here due to their discontinuities between adjacent profiles at 5 km longshore spacing the seven regional scarps a g are directly correlated to seven coseismic subsidence events reported to date between 0 3 and 3 2 ka the correlation of scarps to earthquake events provides high resolution proxy ages for shoreline positions in late holocene time the proxy shoreline positions are dated at 0 3 1 1 1 3 1 7 2 5 2 8 and 3 2 ka based on buried wetland sequences from adjacent tidal basins the paleoshoreline dating demonstrates that the onset of net shoreface progradation between 4 7 and 0 3 ka was delayed with increasing distance 0 100 km from the columbia river sand source the history of beach progradation reflects the sequential filling of bay and shoreface accommodation spaces located down drift of the columbia river mouth these late holocene shoreline changes portend future redistributions of existing sand within the littoral system as the limited sand reserves continue to migrate away from the columbia river mouth source

the evolution of chabahar beach ridge system in se iran in response to holocene relative sea level changes abstract the chabahar strandplain chs stretches along the chabahar bay at a width of more than 5 km along the northern coast of the gulf of oman and se iran an area that has been subjected to tectonic uplift as a part of the makran accretionary prism the chs comprises of beach ridges inter ridge swales sand dunes tidal channels and fluvial deposits we present the first documentation of the spatial distribution and the internal architecture of the chs based on topographic surveys sediment percussive coring trenching and ground penetrating radar gpr transects radiocarbon dating on marine shells from foreshore deposits of 8 representative beach ridges yielded ages between 4800 and 270 cal years bp at respective distances of 4800 to 670 m from the present shoreline we interpret the boundary between the foreshore beach and the foredune deposits as indicator of past sea levels by analogy to present shore processes this boundary is readily recognizable in sediment profiles from cores and trenches as well as gpr reflectors based on the age model and depositional features we estimate relative sea level fall of up to 15 m over the past 4800 years considering that the eustatic sea level changes for this period are negligible for the makran coast this relative sea level fall is related to tectonic uplift across the coastal makran the elevation of palaeo shorelines with similar ages decrease from east to west of the chs which suggest that alongshore variations in uplift rates are likely related to different movements of coastal fault blocks

ground penetrating radar profiles of holocene raised beach deposits in the kujukuri strand plain pacific coast of eastern japan abstract ground penetrating radar gpr profiles of holocene beach deposits were documented from the kujukuri strand plain pacific coast of japan to examine a marker of past sea level recognized in these profiles the kujukuri strand plain has been uplifted over the last 6000 years with a total relative sea level fall of about 5 m suggested by seaward lowering of the lithologic boundary between the foreshore and upper shoreface facies a gpr survey was performed on a modern aeolian dune and beach ridges of the strand plain using a pulseekko100 system with 100 mhz antennae the profiles obtained contain five vertically stacked radar units r1 r5 with characteristic reflections ground truthing using sediment cores and the morphology of the modern beach suggest that these radar units correspond to aeolian dune r1 small scale swale r2 backshore and foreshore r3 upper shoreface r4 and lower shoreface r5 deposits in descending order the backshore and foreshore radar unit shows a sequence of continuous reflections dipping seaward at an angle consistent with the modern beach whereas the underlying upper shoreface radar unit represents complicated and less continuous reflections the boundary between these two units is a downlap surface of the foreshore reflections and is thought to have formed at about 1 m below the mean sea level at the time of deposition the lateral tracing of the boundary in radar profiles across the strand plain indicates a total fall in relative sea level of 5 m which is consistent with the drill core results radar profiles of the foreshore and upper shoreface deposits in the kujukuri strand plain thus provide a past sea level indicator that is available without drilling sediment cores

evidence for eight great earthquake subsidence events detected with ground penetrating radar willapa barrier washington a new approach to detect holocene subduction zone earthquakes combines the results from ground penetrating radar gpr vibracores and accelerator mass spectrometry ams dates from a barrier spit located west of willapa bay southwest washington gpr data show a 10 m thick facies of beach sand within which we identify and vibracores confirm beach parallel wave eroded buried scarps mantled with multiple beds of magnetite the eight gpr detected buried scarps are interpreted to be eroded by minor transgressions caused by instantaneous barrier subsidence during earthquakes associated with the juan de fuca plate subducting under the north american plate of these scarps four have been ams dated at 300 1110 2540 and 4250 radiocarbon yr b p no datable material has yet been found for the other four radar detected scarps but we interpolate and extrapolate dates of 1800 3400 5000 and 5800 yr b p

identifying causes of ground penetrating radar reflections using time domain reflectometry and sedimentological analyses ground penetrating radar gpr is a geophysical technique widely used to study the shallow subsurface and identify various sediment features that reflect electromagnetic waves however little is known about the exact cause of gpr reflections because few studies have coupled wave theory to petrophysical data in this study a 100 and 200 mhz gpr survey was conducted on aeolian deposits in a quarry time domain reflectometry tdr was used to obtain detailed information on the product of relative permittivity er and relative magnetic permeability lr which mainly controls the gpr contrast parameter in the subsurface combining tdr data and lacquer peels from the quarry wall allowed the identification of various relationships between sediment characteristics and erlr synthetic radar traces constructed using the tdr logs and sedimentological data from the lacquer peels were compared with the actual gpr sections numerous peaks in erlr which are superimposed on a baseline value of 4 for dry sand are caused by potential gpr reflectors these increases in erlr coincide with the presence of either organic material having a higher water content and relative permittivity than the surrounding sediment or iron oxide bands enhancing relative magnetic permeability and causing water to stagnate on top of them sedimentary structures as reflected in textural change only result in possible gpr reflections when the volumetric water content exceeds 0ae055 the synthetic radar traces provide an improved insight into the behaviour of radar waves and show that gpr results may be ambiguous because of multiples and interference

holocene coastal response to monsoons and relative sea level changes in northeast peninsular malaysia abstract sedimentological geomorphic and ground penetrating radar gpr data are combined with optically stimulated luminescence data to define the holocene evolution of a coastal system in peninsular malaysia the setiu coastal region of northeast malaysia comprises five geological and geomorphic units representing distinct evolutionary phases of this coastline estimated marine limiting point elevations indicate deposition of an early aggradational shoreline associated with a sea level elevation of 0 1 to 1 7 m mslpmvgd datum between 6 8 ka and 5 7 ka in agreement with previous sea level studies from the malay thai peninsula a hiatus occurs in the record between 5 7 ka and 3 0 ka possibly due to a relative sea level oscillation and shoreline erosion long term relative sea level fall and possible still stands created strandplains that are interrupted by aggradational to transgressive paleo barrier and estuary formation corresponding with brief episodes of rsl rise analyses of gpr facies and osl ages suggest annual clinoform deposition with geometries dictated by variations in enso these data demonstrate the utility of high resolution studies of coastal facies as useful proxy indicators for paleoclimate studies at subdecadal to millennial time scales

transition of a regressive to a transgressive barrier island due to back barrier erosion increased storminess and low sediment supply bogue banks north carolina usa abstract although back barrier erosion is a prevalent process of island narrowing it is often overlooked in conceptual models of barrier island evolution in many wave dominated barrier island settings the absence of overwash precludes landward movement of the back barrier shoreline and hence the island as a whole from sustaining its width typically regressive barriers are wide and exhibit high elevations with the most seaward dune ridge possessing the highest elevation this morphology may prevent overwash and inlets from breaching the barrier and therefore the associated sediment from reaching the back barrier shoreline for millennia back barrier shoreline erosion from sea level rise and storms can be permanent in the absence of sediment supply from rivers overwash and inlet processes with continued narrowing and lowering of the island regressive barriers may reach a critical state making overwash and inlet formation imminent and transitioning the island to a transgressive barrier the modern day morphologic variability along the 40 km long island of bogue banks north carolina includes both regressive and transgressive segments making this setting ideal for examining whether the transition between these barrier island types is gradual or threshold driven bogue banks consists of two discrete segments characterized by high elevation beach ridges large island widths and stratigraphy consistent with regressive barrier islands these regressive island segments are separated by a broad narrow section of the island devoid of any washover fans flood tide deltas or other transgressive elements analyses of seismic data from the inner continental shelf reveal paleochannels intersecting the wide sections of the island while the narrow central part of the island occupies an inter fluvial area reworking of fluvial sediment from paleochannels was an important sediment source for the barrier during regression optically stimulated luminescence osl dates from the most landward beach ridges constrained initiation of island regression at 3000 cal yr bp close to when there was a significant decrease in the rate of relative sea level rise from 5 mm yr to 0 8 mm yr transects of cores seismic data ground penetrating radar data and radiocarbon and osl dates show that prior to 1500 cal yr bp the central narrow section of the island was wide and progradational similar to adjacent areas back barrier erosion of the central part of the barrier primarily caused island narrowing as a result of increased storminess which occurred around the medieval climate anomaly 1100 cal yr bp this part of the island was more vulnerable to erosion than adjacent areas due to increased bay ravinement bogue sound is widest there and its lower elevation farther away from paleochannel sediment source relict inlet channels exist along the central portion of the island formed within the last 250 yr and likely closed shortly after formation the presence of historical inlets along the narrow central section of the island indicates bogue banks may be nearing a critical width threshold and will subsequently transition to a transgressive barrier because the change in barrier morphology associated with back barrier erosion occurred over a period of time when the rate of sea level rise was relatively low low sediment supply and increased storm frequency are shown to be the main forcing mechanisms of island narrowing these impacts in addition to a predicted increase in sea level rise rates and human modifications e g maintenance of a high elevation foredune closing of inlets prevention of island overwash and associated sediment delivery to the back barrier shoreline will likely promote rapid transition of regressive barrier islands to those dominated by transgressive processes

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

how did the ad 1755 tsunami impact on sand barriers across the southern coast of portugal idl pest oe cte la0019 2013 plani2c ed481b 2014 132 0 post doc eu fp7 research project risc kit ga 2013 603458 e fct investigator program ref if 01047 2014

the structure and development of foredunes on a locally prograding coast insights from ground penetrating radar surveys norfolk uk the internal structure of coastal foredunes from three sites along the north norfolk coast has been investigated using ground penetrating radar gpr which provides a unique insight into the internal structure of these dunes that cannot be achieved by any other non destructive or geophysical technique combining geomorphological and geophysical investigations into the structure and morphology of these coastal foredunes has enabled a more accurate determination of their development and evolution the radar profiles show the internal structures which include foreslope accretion trough cut and fill roll over and beach deposits foredune ridges contain large sets of low angle cross stratification from dune foreslope accretion with trough shaped structures from cut and fill on the crest and rearslope foreslope accretion indicates sand supply from the beach to the foreslope while troughs on the dune crest and rearslope are attributed to reworking by offshore winds bounding surfaces between dunes are clearly resolved and reveal the relative chronology of dune emplacement radar sequence boundaries within dunes have been traced below the water table passing into beach erosion surfaces these are believed to result from storm activity which erodes the upper beach and dunes in one example at brancaster a dune scarp and erosion surface may be correlated with erosion in the 1950s possibly the 1953 storm results suggest that dune ridge development is intimately linked to changes in the shoreline with dune development associated with coastal progradation while dunes are eroded during storms and where beaches are eroding a stable coast provides more time for dune development resulting in higher foredune ridges a model for coastal dune evolution is presented which illustrates stages of dune development in response to beach evolution and sand supply in contrast to many other coastal dune fields where the prevailing wind is onshore on the north norfolk coast the prevailing wind is directed along the coast and offshore which reduces the landward migration of sand dunes

internal structure of mixed sand and gravel beach deposits revealed using ground penetrating radar mixed sand and gravel beaches are a distinctive type of coarse clastic beach ground penetrating radar gpr and photographic records of previous excavations are used to investigate the stratigraphy and internal sedimentary structure of mixed beach deposits at aldeburgh in suffolk south east england the principles of radar stratigraphy are used to describe and interpret migrated radar reflection profiles obtained from the study site the application of radar stratigraphy allows the delineation of both bounding surfaces radar surfaces and the intervening beds or bed sets radar facies the deposits of the main backshore berm ridge consist of seaward dipping bounding surfaces that are gently onlapped by seaward dipping bed sets good correspondence is observed between a sequence of beach profiles which record development of the berm ridge on the backshore and the berm ridge s internal structure the beach profile data also indicate that backshore berm ridges at aldeburgh owe their origin to discrete depositional episodes related to storm wave activity beach ridge plain deposits at the study site consist of a complex progradational sequence of foreshore berm ridge overtop and overwash deposits relict berm ridge deposits separated by seaward dipping bounding surfaces form the main depositional element beneath the beach ridge plain however the beach ridges themselves are formed predominantly of vertically stacked overtop overwash units which lie above the berm ridge deposits consequently beach ridge development in this progradational mixed beach setting must have occurred when conditions favoured overtopping and overwashing of the upper beachface interannual to decadal variations in wave climate antecedent beach morphology shoreline progradation rate and sea level are identified as the likely controlling factors in the development of such suitable conditions