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

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

punctuated progradation of the seven mile beach holocene barrier system southeastern tasmania abstract prograded barriers are depositional coastal landforms which preserve past shoreline locations and have been studied in order to understand the fundamental drivers of barrier formation this paper reconstructs the holocene history of the seven mile beach prograded barrier in tasmania australia using optically stimulated luminescence osl dating ground penetrating radar gpr light detection and ranging lidar elevation models and sedimentological analyses shoreline progradation of the barrier commenced around 7300 years ago and continued to near present despite a 3000 pause in deposition between 6700 and 3600 years ago indicative of substantial changes in sediment availability gpr imaged subsurface structures contain a record of seaward dipping reflectors preserved as sediment supplied beaches and dunes leading to shoreline progradation in the past 500 years a large transgressive dune has formed built from reworked barrier sands and now dominates the eastern portion of the barrier implying that shoreline progradation has ceased this study reaffirms the notion that relict foredune ridges are strongly aligned with modal wave refraction patterns in planform and emphasises the importance of sediment delivery as a key driver of shoreline progradation through beachface and dune accretion the substantial pause in shoreline progradation on this barrier system as observed on others around the world requires further explanation although changes in sediment delivery have been inferred it may also be appropriate to reopen the debate on holocene sea level change in tasmania

gpr in sediments advice on data collection basic processing and interpretation a good practice guide within sedimentological studies ground penetrating radar gpr is being used with increasing frequency because it yields images of the shallow subsurface that cannot be achieved by any other non destructive method the purpose of this paper is to provide an introduction to the collection processing and interpretation of gpr data so that future sedimentary studies can be improved with gpr equipment now being lightweight robust and portable proper data collection and survey design methods need to be followed in order to acquire high resolution subsurface digital data various factors are discussed including reflection profiling velocity soundings test surveys topography logistics data quality and extreme environments basic data processing and visualization are then reviewed followed by a discussion on gpr interpretation strategies including a background to radar stratigraphy for the sedimentary geologist or geomorphologist gpr offers unique data of the shallow subsurface including stratigraphy geometry architecture and structure

a combined study of radar facies lithofacies and three dimensional architecture of an alpine alluvial fan illgraben fan switzerland alluvial fans serve as useful archives that record the history of depositional and erosional processes in mountainous regions and thus can reveal the environmental controls that influenced their development economically they play an important role as groundwater reservoirs as well as host rocks for hydrocarbons in deeply buried systems the interpretation of these archives and the evaluation of their reservoir architecture however are problematic because marked heterogeneity in the distribution of sedimentary facies makes correlation difficult this problem is compounded because the accumulated sedimentary deposits of modern unconsolidated fan systems tend to be poorly exposed and few such systems have been the focus of investigation using high resolution subsurface analytical techniques to overcome this limitation of standard outcrop analogue studies a geophysical survey of an alpine alluvial fan was performed using ground penetrating radar to devise a scaled three dimensional subsurface model radar facies were classified and calibrated to lithofacies within a fan system that provided outcropping walls and these were used to derive a three dimensional model of the sedimentary architecture and identify evolutionary fan stages the illgraben fan in the swiss alps was selected as a case study and a network of ca 60 km sections of ground penetrating radar was surveyed seven radar facies types could be distinguished which were grouped into debris flow deposits and stream flow deposits assemblages of these radar facies types show three depositional units which are separated by continuous fan wide reflectors they were interpreted as palaeo surfaces corresponding to episodes of sediment starvation that affected the entire fan an overall upward decline in the proportion of debris flow deposits from ca 50 to 15 and a corresponding increase in stream flow deposits were identified the uppermost depositional unit is bounded at its base by a significant incision surface up to 700 m wide which was subsequently filled up mostly by stream flow deposits the pronounced palaeo surfaces and depositional trends suggest that allocyclic controls governed the evolution of the illgraben fan making this fan a valuable archive from which to reconstruct past sediment fluxes and environmental change in the alps the results of the integrated outcrop geophysical approach encourage similar future studies on fans to retrieve their depositional history as well as their potential reservoir properties

discharges of turbid water during mini surges of variegated glacier alaska u s a discharges of water sediment and dissolved impurities from variegated glacier ala ska were monitored in the early summers of 1980 and 1981 during the occurrence of mini surg es sea sonal trends weat her related eve nts and diurnal variat ions similar to behavior of other temperat e gl acier streams were found the prin cipal effect in the stream associated with mini surge occurrence was a brief discharge of extremely turbi d water the turbidity is assumed to be introduced into the basal hydraulic system by initiation of the fast motion of a mini surge at a time and locat ion on the upper glacier known from oth er meas ure ments the mean water velocity in the hydraulic system over the int erven ing distance is thereby determined 0 3 m s i the mean water velocity together with the water discharge 16 m3 s 1 at the terminus places con straints on the distribution of water velocity u and total cros s sectional area at of the flow paths along the gl acier base this leads to the con clusion that within the zone of mini surge occurrence in its unpe rturbed state u is about 0 1 m s 1 or possibly less at is about 10 2 m2 or possibly more and it must be divided into a very large number of small passag eways be blocked by constrict ions or both the total water cro ss se ction corresponds to a layer 0 1 2 m thick when spr ead unifo rmly over the glacier width the water velocity is clos e to or less than the propa gation velo city of the mini s urges bet ween the zone affected by mini surges and the stream a dyna mically less active lower section of the glacier is proba bly underlain by a small number of conduits in which the water velocity may be very high 2 m s i water di scharge follo wing the mini surges puts an upper limit on water storage changes ass ociated with the anomalous ice motion

quantifying rates of coastal progradation from sediment volume using gpr and osl the holocene fill of guichen bay south east south australia guichen bay on the south east coast of south australia faces west towards the prevailing westerly winds of the southern ocean the bay is backed by a 4 km wide holocene beach ridge plain with more than 100 beach ridges the morphology of the guichen bay strandplain complex shows changes in the width length height and orientation of beach ridges a combination of geomorphological interpretation shallow geophysics and existing geochronology is used to interpret the holocene fill of guichen bay six sets of beach ridges are identified from the interpretation of orthorectified aerial photographs the ridge sets are distinguished on the basis of beach ridge orientation and continuity a 2 25 km ground penetrating radar gpr profile across the beach ridges reveals the sedimentary structures and stratigraphic units the beach ridges visible in the surface topography are a succession of stabilized foredunes that overlie progradational foreshore and upper shoreface sediments the beach progrades show multiple truncation surfaces interpreted as storm events the gpr profile shows that there are many more erosion surfaces in the subsurface than beach ridges on the surface the width and dip of preserved beach progrades imaged by gpr shows that the shoreface has steepened from around 2 9 to around 7 5 the changes in beach slope are attributed to increasing wave energy associated with beach progradation into deeper water as guichen bay was infilled at the same time the thickness of the preserved beach progrades increases slightly as the beach prograded into deeper water using the surface area of the ridge sets measured from the orthophotography and the average thickness of upper shoreface foreshore and coastal dune sands interpreted from the gpr profile the volume of holocene sediments within three of the six sets of beach ridge accretion has been calculated combining optically stimulated luminescence osl ages and volume calculations rates of sediment accumulation for ridge sets 3 4 and 5 have been estimated linear rates of beach ridge progradation appear to decrease in the mid holocene however the rates of sediment accumulation calculated from beach volumes have remained remarkably consistent through the mid to late holocene this suggests that sediment supply to the beach has been constant and that the decrease in the rate of progradation is due to increasing accommodation space as the beach progrades into deeper water changes in beach ridge morphology and orientation reflect environmental factors such as changes in wave climate and wind regime

structure and development of shell cheniers in essex southeast england investigated using high frequency ground penetrating radar abstract the stratigraphy and internal structure of contemporary shell cheniers on the southern essex coast england were investigated using a high frequency 900 mhz ground penetrating radar gpr system the cheniers lie on the seaward edge of laterally eroding saltmarshes at the junction with the tidal flats four main types of chenier are recognised each with a characteristic morphology and dynamic status migrated radar reflection profiles obtained from each of the chenier types achieved a sub decimetre vertical resolution ground truthing data demonstrate that the radar profiles accurately delineate the subsurface stratigraphy and sedimentary structure of the cheniers interpretation of the radar stratigraphy derived from the radar reflection profiles allows various deposits to be identified these have resulted from overwashing overtopping sedimentation across the whole of a seaward dipping beachface or berm ridge welding onto the upper beachface each chenier is characterised by a different spatial arrangement of these four basic depositional units the results from the gpr surveys support the hypothesis that each of the chenier types represents a distinct phase in the development of these contemporary coastal landforms however a simple model involving a linear progression through chenier types 1 4 with time appears inappropriate instead two main evolutionary pathways are proposed with the sequence of development being principally controlled by the nature of the cheniers longer term sediment budgets

internal structure of the aeolian sand dunes of el fangar spit ebro delta tarragona spain this paper presents an analysis of the dune field dynamics of el fangar spit in the ebro delta spain associating it with the internal structure of dunes carried out with ground penetrating radar and supported by data from topographic dgps these analyses are of great importance to ascertain the state of the internal structure of dunes as an important element in their stability and therefore in their evolution the internal structure shows accretion and progradation sequences of dunes over beach deposits which depend on dune morphology height crest orientation and location as well as the processes acting on them

sea level controls on carbonate beaches and coastal dunes eolianite lessons from pleistocene bermuda 2015 geological society of america coastal dune accumulations at locations around the world have formed during sea level highstands rising sea levels falling sea levels and fluctuating sea levels initially episodes of maximum pleistocene dune activity in bermuda which is the type location for eolianite were correlated with glacio eustatic regressions this model had been abandoned by the 1970s in favor of a rising sea level model for bermuda s north shore and autogenic sediment supply model for the south shore we report the results of a detailed investigation of the intercalated mid late pleistocene beach and coastal dune deposits on the islands of bermuda and we test the existing models for these deposits we contend that the north shore model is invalidated by past misidentification of eoliandeposits as transgressive beach deposits on the south shore facies analysis of the marine isotope stage 7 mis 7 belmont formation reveals that coastal deposition was divided into two phases s1 which includes foreshore and shoreface progradation is predominantly marine and coincided with rising relative sea level s2 which commenced with protosol development on top of the marine section prior to burial by advancing dunes is nonmarine we conclude that the two successions s1 and s2 resulted from forcing by glacio hydro isostatic relative sea level change spanning a highstand rising and then falling rather than from transgressive or autogenic processes the finding that in bermuda the construction of protective coastal dunes depends on a falling relative sea level has potential implications for many vulnerable shorelines that face rising relative sea levels associated with climate change

oceanic internal waves in the sulu celebes sea under sunglint and moonglint moonglint and sunglint satellite imagery acquired from moderate resolution imaging spectroradiometer modis and visible infrared imaging radiometer suite viirs satellite sensors were used to study the characteristics of internal waves iws and their relationship to tides and stratification in the sulu celebes sea tidally generated iws propagate northwestward and southeastward into the sulu and celebes seas showing a spring neap tidal cycle behavior with larger smaller iws occurring under spring neap tides respectively the length of iw crests their wavelength and phase speed derived from the sunglint moonglint image pairs were observed to decrease from spring to neap tides iws in the sulu celebes sea which are correlated with oceanic stratification display seasonal and regional fluctuations in the celebes sea iws were less frequently observed but propagated with faster phase speeds and larger scales compared to those in the sulu sea comparisons of stratification and barotropic tidal transport among the iws generation sites indicate that the shallowing maximum brunt vaisala frequency and strongest tidal transport around pearl bank are major factors contributing to greater iw activity compared to other generation sites iws generated near pangutaran island and pearl bank further merge into one dynamical system creating longer wave crests of 200 km that travel at faster phase speed sim 2 5 text m cdot text s 1 in the sulu sea this paper demonstrates a new application using a combination of sunglint moonglint imagery in tracking an important oceanic phenomenon

late holocene syngenetic ice wedge polygons development bylot island canadian arctic archipelago the initial configuration of the syngenetic ice wedge polygons that developed in the outwash plain of glacier c 79 after 6000 bp was modified by the accumulation of wind blown and organic sediments that began after 3670 110 bp the late holocene sedimentation led to an increase in the thermal contraction coefficient of the soil and the formation of third and fourth order contraction cracks partially explaining the current configuration of the polygonal network the upturning of the sedimentary strata bordering the ice wedges was associated with the summer thermal expansion and resulting internal creep of the soil the mean annual soil displacement coefficient was in the order of 2 5 2 7 10 5 c at the thousand year scale the late holocene sedimentary strata under the centre of the polygons were undisturbed which will make it possible to use this sedimentary record in further studies to attempt paleoenvironmental reconstructions from cores

combining ground penetrating radar surveys and optical dating to determine dune migration in namibia ground penetrating radar gpr profiles across a complex linear dune in the namib sand sea have been used to image sets of cross stratification and their bounding surfaces a combination of radar facies analysis and radar stratigraphy has been used to interpret the radar profiles and define a relative chronology thick sets of cross stratification indicate when the dune was most active whereas thin sets of cross stratification are interpreted to indicate the increased prevalence of wind reversals and lower rates of dune migration with bounding surfaces formed during periods of stabilization non deposition or erosion a drilling and dating campaign was designed on the basis of the dune stratigraphy as defined by the gpr survey sampling was targeted at large sets of cross stratification formed when the dunes were most active and avoiding bounding surfaces formed when the dune was stable or even eroded the results from optical dating give ages between 0 34 0 02 ka and 1 57 0 07 ka indicating a time averaged dune migration rate of 0 12 m a 1 over the past 1600 years

unveiling past aeolian landscapes a ground penetrating radar survey of a holocene coastal dunefield system thy denmark abstract the southern part of the hvidbjerg coastal dunefield and the adjacent part of the lodbjerg coastal dunefield system in northwestern denmark has been mapped using ground penetrating radar coastal cliff exposures and 14 c datings indicate that the presently stabilized dunefield is underlain by a 10 15 m thick succession of holocene aeolian sand deposits and interbedded peaty palaeosols this succession is superimposed on a weichselian till towards the south and a mid holocene beach ridge and swash bar complex towards the north the peaty palaeosols represent preceding periods of dunefield stabilization these palaeosols reveal ages about ad 1100 1200 700 bc and 2100 bc and act as marker horizons in the study area more than 16 km of high resolution gpr data covering an area of 6 km 2 were collected in the near coastal part of the dunefields and enabled a correlation of these marker horizons across the dunefields these data allowed the elaboration of topographic subsurface and isopach maps and enabled an interpretation of the accumulation history of the aeolian system since about 2200 bc this accumulation history tells of alternating periods with a stabilization of the dunefields and periods with high sand accumulation basically a perched ground water level and the morphology of the previous stabilized dunefield made it possible to generate an accumulation space large enough to preserve the sand during periods with stronger winds and marked aeolian activity this 3d mapping of the stabilized dunefield subsurfaces has made it possible to unveil the development of the past aeolian landscape

archean to recent aeolian sand systems and their sedimentary record current understanding and future prospects the sedimentary record of aeolian sand systems extends from the archean to the quaternary yet current understanding of aeolian sedimentary processes and product remains limited most preserved aeolian successions represent inland sand sea or dunefield erg deposits whereas coastal systems are primarily known from the cenozoic the complexity of aeolian sedimentary processes and facies variability are under represented and excessively simplified in current facies models which are not sufficiently refined to reliably account for the complexity inherent in bedform morphology and migratory behaviour and therefore cannot be used to consistently account for and predict the nature of the preserved sedimentary record in terms of formative processes archean and neoproterozoic aeolian successions remain poorly constrained palaeozoic ergs developed and accumulated in relation to the palaeogeographical location of land masses and desert belts during the triassic widespread desert conditions prevailed across much of europe during the jurassic extensive ergs developed in north america and gave rise to anomalously thick aeolian successions cretaceous aeolian successions are widespread in south america africa asia and locally in europe spain and the usa several eocene to pliocene successions represent the direct precursors to the present day systems quaternary systems include major sand seas ergs in low lattitude and mid latitude arid regions pleistocene carbonate and holocene modern siliciclastic coastal systems the sedimentary record of most modern aeolian systems remains largely unknown the majority of palaeoenvironmental reconstructions of aeolian systems envisage transverse dunes whereas successions representing linear and star dunes remain under recognized research questions that remain to be answered include i what factors control the preservation potential of different types of aeolian bedforms and what are the characteristics of the deposits of different bedform types that can be used for effective reconstruction of original bedform morphology ii what specific set of controlling conditions allow for sustained bedform climb versus episodic sequence accumulation and preservation iii can sophisticated four dimensional models be developed for complex patterns of spatial and temporal transition between different mechanisms of accumulation and preservation and iv is it reasonable to assume that the deposits of preserved aeolian successions necessarily represent an unbiased record of the conditions that prevailed during episodes of earth history when large scale aeolian systems were active or has the evidence to support the existence of other major desert basins been lost for many periods throughout earth history

holocene evolution of the ninety mile beach sand barrier victoria australia the role of sea level sediment supply and climate abstract the ninety mile beach nmb barrier system in southeastern australia is the largest active barrier island system in australia the response of a sandy barrier system to a warming climate is dependent on the boundary conditions of sediment supply and sea level deposition during the holocene can therefore provide an indication of how these barriers may change in the future in this study airborne lidar ground penetrating radar and subsurface coring were combined with 46 optically stimulated luminescence and 32 radiocarbon ages to provide a detailed understanding of sedimentation of nmb through the holocene the barrier complex formed in three distinct phases dating back to the earliest stabilisation of sea level after the postglacial marine transgression first restriction of the flooded open ocean embayment that had formed around a last interglacial beach barrier sequence occurred with accretion of an island complex at around 8000 years bp sourced from transgressive sands reworked from the shelf in the second phase at around 6000 years bp a second barrier island formed seaward of the last interglacial barrier but disconnected from the earlier holocene barrier islands by a large tidal inlet waning sediment supply from the shelf meant that aggradation of these islands slowed by 4000 years bp the third and final phase occurred after 3000 years with the initiation of sediment supply at the southwestern end of the barrier the island system which formed seaward of the last interglacial barrier then prograded by several hundred metres and elongated in a northeasterly direction by tens of kilometres infilling the tidal inlet and enclosing the earliest holocene barrier landward of a newly created lake sediment supply appears to be the primary limiting factor in the development of nmb with indications of a change in wave climate and sea level have an influence on barrier evolution

geometry and flow conditions of subglacial water at south cascade glacier washington state u s a an analysis of tracer injections tracers were injected into south cascade glacier to determine the flow condition and geometry of the subglacial water system results indicate that two distincts drainage basins on the glacier feed the two main streams flowing from the glacier in the largest basin two parallel drainage networks exist one englacial and the other subglacial

hydraulics of subglacial cavities modele theorique du comportement a l etat stationnaire des cavites remplies d eau et interconnectees sur le lit du glacier

stratigraphy and internal structure of wind dominated barrier islands dune and machair of the outer hebrides scotland stratigraphy and internal structure of wind dominated barrier islands

the sedimentary architecture of a holocene barrier spit sylt german bight swash bar accretion and storm erosion abstract the southern german north sea coast was shaped by the last post glacial sea level rise that caused a significant retreat of the coastline approximately 5 ka bp the rate of sea level rise decreased providing space for the formation of the frisian islands which line the coast this study is focused on the island of sylt located at the german north sea coast close to the danish border here two sandy spit systems developed during the holocene combining ground penetrating radar studies and sedimentological investigations based on shallow cores new aspects on the sedimentary history of this holocene spit system have been revealed the data indicate that strong erosional events alternated with phases of progradation and growth the welding of swash bars is shown to be the predominant process during progradational phases of the spit system during these periods progradation was not restricted to linear growth along the spit axis but also included a seaward directed component major erosion surfaces which delimit progradational sediment packages are interpreted to reflect exceptionally severe storms the fossilization potential of this sedimentary record was controlled by a positive net long term sediment balance and the position of the ground water table which controlled eolian deflation only with a stable or rising sea level and associated ground water table position are sediments protected from deflation the proposed sedimentary model may serve as a template for interpretation of comparable settings in the geological record

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

can sand dunes be used to study historic storm events knowing the long term frequency of high magnitude storm events that cause coastal inundation is critical for present coastal management especially in the context of rising sea levels and potentially increasing frequency and severity of storm events coastal sand dunes may provide a sedimentary archive of past storm events from which long term frequencies of large storms can be reconstructed this study uses novel portable optically stimulated luminescence posl profiles from coastal dunes to reconstruct the sedimentary archive of storm and surge activity for norfolk uk application of posl profiling with supporting luminescence ages and particle size analysis to coastal dunes provides not only information of dunefield evolution but also on past coastal storms in this study seven storm events two major were identified from the dune archive spanning the last 140 years these appear to correspond to historical reports of major storm surges dunes appear to be only recording at least at the sampling resolution used here the highest storm levels that were associated with significant flooding as such the approach seems to hold promise to obtain a better understanding of the frequency of large storms by extending the dune archive records further back to times when documentation of storm surges was sparse

the origin of centennial to millennial scale chronological gaps in storm emplaced beach ridge plains recent studies of tropical cyclone surge and wave emplaced beach ridge plains have shown that these sequences often contain centennial to millennial scale gaps in their chronologies two explanations for the gaps exist they are due to erosion or alternatively a cessation or substantial slowing of depositional processes suggestive of a quieter phase in intense storm activity differentiating between the two is important for uncovering reliable long term storm histories from these sequences we use landform morphology sediment texture and luminescence chronology to determine the origin of substantial chronological gaps in a plain containing more than 100 shore parallel ridges composed of fine grained sand located in northeast australia we identify and describe the characteristics associated with both erosional and non erosional gaps the erosional gaps are associated with changes in orientation between ridge sets and often a high ridge with hummocky topography that appears to have been disturbed by aeolian activity river floods likely caused the partial erosion of ridge sets non erosional gaps do not display these morphological characteristics and are likely associated with quiescence in severe tropical cyclone activity these geomorphic and chronological signatures can be used to identify different sorts of gaps in other ridge plains and are an important tool in the reconstruction of long term storm histories from these coastal landforms the data also suggests that fine grained ridges can like their coarse grained counterparts be predominantly deposited by storm waves and surge and their texture need not necessarily be indicative of the processes responsible for ridge development

holocene evolution of the chan may coastal embayment central vietnam changing coastal dynamics associated with decreasing rates of progradation possibly forced by mid to late holocene sea level changes abstract southeast asian coastal environments are undergoing massive transformations with unprecedented population and infrastructure development these transformations are occurring on a backdrop of intense natural and anthropogenic environmental change which are increasing the risk to the burgeoning coastal population little is known about how central vietnamese coastal environments have changed naturally since the mid holocene sea level highstand and how recent anthropogenic change and sea level variation have affected the coastal system the chan may embayment in central vietnam allows us to examine how recent changes in both anthropogenic development and sea level change have affected the coastline the embayment preserves a series of prograding beach ridges and is subject to intense human pressures with the construction of a large economic and industrial park and expansion of tourist facilities using ground penetrating radar and quartz optical dating we identify a switch from 6000 years of prograding beach ridges to transgressive dunes within the past century resulting in a decreasing rate of beach ridge progradation possibly in the last 100 years the recent modes of sediment deposition through washovers and a transgressive dune indicates that coastal progradation has slowed and might have stopped

subglacial hydrology for an ice sheet resting on a deformable aquifer glissements et deformation de la calotte de glace en relation avec le materiau de l aquifere et la densite des chenaux de drainage

character of the englacial and subglacial drainage system in the lower part of the ablation area of storglaciaren sweden as revealed by dye trace studies

holocene coastal evolution of the transition from transgressive to regressive barrier in southern brazil abstract in this study the evolution of a holocene coastal barrier was determined based on a basal transgressive unit followed by a regressive unit standard penetrating test vibrocore and ground penetrating radar profiles were used to acquire stratigraphic data sedimentological paleontological and geochronological analyses were performed to describe and interpret the sedimentary facies the base of the holocene record indicates the existence of pre transgression continental and coastal environments basal peat which resulted from the initial flooding of the antecedent topography pleistocene substrate due to rising sea levels during this period the continental environments were flooded by lagoon environments that occupied the landward displacement of the transgressive barrier which had channels that connected the lagoon and the ocean at this time the coastal barrier had a transgressive configuration indicated by its morphology and characterized by washover fans as the backbarrier accommodation space decreased due to the displacement of the barrier transgressive maximum the transition of the transgressive regressive record began at approximately 7 200 years bp restricting the overwash events and the dynamics of the inlets however before the highest level eustatic maximum of the postglacial marine transgression pmt was reached this transgressive barrier stopped its migration toward the continent causing an inversion of the depositional record which became a normal regression later at the end of the pmt sea levels began to fall causing a forced regression that persists to the present day

evidence for and geomorphologic consequences of a reptilian ecosystem engineer the burrowing cascade initiated by the gopher tortoise abstract physical ecosystem engineers often make major durable physical constructs that can provide living space for other species and can structure local animal communities over evolutionary time in florida a medium sized chelonian the gopher tortoise gopherus polyphemus will excavate extensive subterranean chambers that can endure for long periods of time the tortoise starts a burrowing cascade by first excavating a larger burrow that may extend 10 m which is then re engineered by florida mice podomys floridanus and other rodents that dig smaller side burrows and pockets this sequence is often followed by an invertebrate the camel cricket ceuthophilus labibuli which is reported to excavate even smaller chambers our first aim was to quantify the zoogeomorphic impact of this burrowing cascade by measuring the amount of soil excavated in a large sample of burrows in two communities secondly we hypothesized that the high biodiversity reported for these structures might be related to the quasi fractal nature of the geometry following the work of frontier 1987 to visualize this underground geometry we used high resolution 3d ground penetrating radar gpr which provided images and insights previously unobtainable using excavations or 2d gpr our images verified that the active tortoise burrow had a spiraling shape but also showed splits in the larger burrow apparently dug by tortoises for the first time the smaller florida mouse burrows were imaged showing side loops that exit and re renter the tortoise burrow this study also presents new information by making the discovery of numerous remnants of past tortoise burrows underground in the sampling grid surrounding the active burrow our third aim was to interpret our field results with previous ecological field studies to evaluate the strength of evidence that this species ranks as an ecosystem engineer

stratigraphic and chronologic analysis of the warren beach northwest ohio usa the current understanding of lake warren as a proglacial lake stage in the lake erie basin during the last deglaciation is based on limited stratigraphic information from strandlines and a wide range of radiocarbon ages the purpose of this study is to use ground penetrating radar gpr and optically stimulated luminescence osl dating to reconstruct the stratigraphy depositional environment and age of the oak openings ridge oor a former strandline of lake warren in northwestern ohio both sedimentary exposures and 4 km of gpr data were used to demonstrate that the oor is a barrier spit that migrated from the northeast to the southwest and is currently blanketed by an aeolian sheet sediments observed in exposures show a shallowing up sequence attributed to the retreat of proglacial lakes from the area corresponding gpr data reveal three distinct gpr facies the lowermost radar facies 1 rf1 is a sandy barrier spit platform of a lower beach face prograding across finer grained lacustrine mud or

annual to decadal morphodynamics of the foredune system at greenwich dunes prince edward island canada the purpose of this study was to quantify relationships between season sediment availability sediment transport pathways and beach foredune morphology at greenwich dunes pei this was done for periods ranging from a few days to multiple decades using erosion pins bedframe measurements annual surveys and digital photogrammetry using historical aerial photographs the relative significance of seasonal annual processes versus response of the foredune system to broader geomorphic controls e g relative sea level rise storms etc was also assessed the data show that there are clear seasonal differences in the patterns of sand supply from the beach to the foredune at greenwich and that there are differences in sediment supply to the foredune between the east and west reaches of the study area resulting in ongoing differences in foredune morphology they also demonstrate that models that incorporate wind climate alone or even models that include other factors like beach moisture would not be able to predict the amount of sediment movement from the beach to the foredune in this environment unless there were some way to parameterize system morphology especially the presence or absence of a dune ramp finally the data suggest that the foredune can migrate landward while maintaining its form via transfers of sediment from the stoss slope over the crest and onto the lee slope although the rate of foredune development or recovery after disturbance changes over time due to morphological feedback the overall decadal evolution of the foredune system at greenwich is consistent with and supports the davidson arnott 2005 conceptual model of dune transgression under rising sea level copyright 2012 john wiley sons ltd

investigation of large scale washover of a small barrier system on the southeast australian coast using ground penetrating radar abstract prehistoric depositional signatures for large scale washover involving marine inundation events such as storms and tsunami have been the subject of considerable research over the last 15 years much of this research has focused on the identification of sandsheets in back barrier environments as depositional records for extreme washover events all these deposits must have a sediment source and by their nature the most likely source of sediment for washover into back barrier environments is the barrier itself this study identifies an erosional signature for large scale washover from a small coastal barrier on the southeast australian coast a distinct lens of marine sand up to 90 cm thick confined vertically by peat is found in the upper fill of a closed freshwater back barrier lagoon sequence this sand lens is attributed to a large scale washover event during the last 800 years and was possibly deposited by a tsunami the hypothesis for this study was that any event that breached the dune system must have caused considerable geomorphic change to the dunes and hence may have left an erosional signature ground penetrating radar transects of the system show an erosional contact between a series of truncated pre event dunes and several small overlying post event dunes this study outlines a relatively simple non invasive method for the identification of an erosional signature for prehistoric large scale washovers caused by storm surge exceptionally large waves or tsunami

comments on the use of chemically based mixing models in glacier hydrology the assumptions involved in the use of chemically based mixing models for analysis of flow routing of meltwaters in glacierized basins are critically evaluated the assumption that glacial drainage systems consist of only two primary flow components is arbitrary and must be supported by independent evidence recent studies of the processes by which meltwaters acquire solute indicate that the assumption that flow components have unique and constant chemical compositions is unlikely to lie correct source water composition and weathering potential will vary over the course of a melt season and the extent of subglacial weathering is strongly dependent upon such factors as meltwater residence time and the availability of reactive sediment both of which are known to vary on diurnal to seasonal time scales mixing of flow components does not appear to be confined to the terminal regions of glaciers and is therefore unlikely to be conservative as assumed a multi parameter mixing model is applied to the analysis of data on the chemistry of waters sampled from bureholes drilled through haut glacier d arolla switzerland to demonstrate the range of dissolved species for which the assumption of conservative mixing is violated the consequences of this violation for quantitative hydrograph separation are shown to be highly significant the utility of mixing models as a tool for the investigation of glacier hydrological systems is questionable and the results of previous studies are unreliable

extracting storm surge data from coastal dunes for improved assessment of flood risk future changes in climate and sea level are likely to increase the threat from storm surges in many coastal regions mitigation of this threat requires an understanding of storm surge magnitude and frequency and the relationship of these variables to climate parameters this understanding is currently limited by the brevity of instrumental records which rarely predate the twentieth century however evidence of former storm surges can be recorded in coastal dunes because the dune topography may trap high magnitude deposits at elevated locations here we combine a range of techniques to extract storm surge data from coastal dune sediment the sediment is tracked in the subsurface with ground penetrating radar to assess its height and extent and its age is determined with good precision through optically stimulated luminescence dating the probable age of the sediment a d 1775 or 1776 is within a period of increased storminess in northwest europe and the local magnitude of the event is likely to be greater than any on instrumental record by utilizing coastal dunes for storm surge analysis our approach provides a valuable new source of information for understanding storm surge risk which is vital for the protection of coastal regions

ground penetrating radar stratigraphy and dynamics of megaflood gravel dunes ground penetrating radar was used to elucidate the stratigraphy of late pleistocene gravel dunes in the altai mountains of southern siberia that formed when a lake emptied as a result of ice dam failure survey lines across dunes had a resolution of decimetres with depth penetration of 20 m the reflections identify bounding surfaces and radar facies two classes of unconformities are identified 1 an erosional unconformity at the base of the dunes 2 steeply inclined unconformities that truncate underlying inclined reflections and are downlapped by overlying inclined reflections within the dunes unconformities define six radar facies rf rf 1 basal subhorizontal discordant reflections rf 2 poorly defined discordant reflections rf 3 planar inclined reflections rf 4 sigmoidal inclined reflections rf 5 trough fills rf 6 low angle inclined reflections the basal unconformity represents the flood cut surface across which the dunes migrated the inclined unconformities may be interpreted in two ways 1 erosional surfaces induced by unsteady flow within one flood or 2 erosional surfaces developed by a series of floods reactivating dunes left stranded by previous floods the evidence favours the latter model which is consistent with the occurrence of several dune forming events within the basin the broader implications of the study are considered with respect to investigations of megaflood bedforms worldwide

depositional controls on a hypertidal barrier spit system architecture and evolution pointe du banc spit north western france physical stratigraphy architecture and evolution of barrier systems in hypertidal environments tidal range above 6 m are understudied and depositional controls are poorly understood compared with wave dominated barrier systems and barrier spits in microtidal mesotidal and macrotidal settings based on vibracores ground penetrating radar radiocarbon and optically stimulated luminescence age data the formation and evolution of the hypertidal barrier system of pointe du banc north western france has been reconstructed the study shows that the barrier spit has a complex composite sedimentary architecture consisting of wave dominated and tide dominated sedimentary bodies a morpho sedimentary model is presented that demonstrates how barrier spit progradation resulting from littoral drift was the main manner of spit elongation whereas sediment convergence caused by landward migration of swash bars and seaward migration of tidal dunes caused the spit terminus to grow in height and width these results suggest that long term accretion rates varied considerably in response to changes in sediment supply variations in storminess together with the large scale topography of the coast controlled the sediment supply and thus the evolution of the barrier system during latest holocene despite architectural complexity hypertidal barrier systems preserve records of past climate changes

impact of atmospheric circulation patterns on coastal dune dynamics nw spain article i nfo dunes in temperate latitudes have experienced a significant stabilization in recent times essentially as a conse quence of the expansion of dense vegetation cover yet the causes for this gradual stabilization as well as the causes promoting antecedent aeolian mobilization remainpoorlyunderstood the traba coastal dune field located in nw spain was examined to explore the causes inducing aeolian activity and subsequent stabilization since 1940 morphological changes were identified through the combination of aerial photographs and geophysical techniques local wind field regimes were simulated using a regional climate model to obtain the variability of the most relevant modes of atmospheric circulation in the north atlantic and european regions north atlantic oscillation nao eastern atlantic ea and scandinavian scand this allows us to identify the impact of these circulation modes over dune dynamics results document an episode of aeolian activity during the 1950s followed by a gradual stabilization and fixation of the dune coincident with a decrease on storm and wind inten sity yet aeolian sand movement remained active insmall areas blowouts occurring mainly during the summer ne winds associated with a negative phase of the ea explain the movement of sand within the dune field under favorable conditions of sand supply on the other hand sand supply to the dune field from the beach was promoted by nw winds coincident with the summer negative phase of nao during winter the negative nao favored frequent sw winds associated with the passage of intense storms which in turn explain sand remobilization from the beach making sediment available for the nw winds to blow inland with this work it is proven that to understand past and future aeolian activity requires critical consideration of the variability and impact of the two principal modes of atmospheric circulation in the north atlantic nao and ea the scand mode explaining alowerpercentageofthelocalwind fieldvariabilitywasalsoincludedtoachievehigher significance levels of explained variance

internal structure of a trough blowout determined from migrated ground penetrating radar profiles ground penetrating radar gpr was used to investigate the relationship between the geomorphological development of a large aeolian trough blowout and the stratigraphy and internal sedimentary structure of its associated deposits although analogous many of the data processing techniques routinely applied in seismic reflection are very rarely applied in gpr studies in this study a simple migration program was used that significantly enhanced the quality of gpr images from a large trough blowout at raven meols on the sefton coast northwest england these improvements aided subsequent data interpretation which was achieved through application of the principles of radar stratigraphy gpr shows the pre blowout dunes to have a complex internal structure that suggests they were formed in the presence of at least a partial vegetation cover subsequent to stabilization of these dunes a thin soil developed this dune soil forms an important radar sequence boundary and delineates a complex topography beneath the depositional lobe of the blowout the internal structure of the depositional lobe of the blowout does not conform to a model of simple radial foreset deposition as derived from contemporary process studies reported in the literature instead the pattern of deposition has been extensively modified by the antecedent dune topography and by varying spatial and temporal exposure to important sand transporting winds that is partly controlled by interactions between the regional wind pattern and local dune morphology trough blowout deposits in coastal aeolian sedimentary sequences are likely to be recognized by the presence of laterally continuous packets of relatively high angle cross strata which often display a spatially variable radial dip pattern that is only very poorly or partially developed in addition a soil or other surface representing a significant hiatus in dune deposition is likely to underlie the blowout deposits the topography of which will show a clear relationship to the dip and orientation of the overlying cross strata

ground penetrating radar evaluation of the internal structure of fluvial tufa deposits devanos anavieja system ne spain an approach to different scales of heterogeneity

evolution of the internal drainage system in the lower part of the ablation area of storglaci aren sweden during the 1989 melt season ten tracer experiments were conducted to investigate seasonal diurnal and spatial variations in the internal drainage system in the ablation area of storglaciaren sweden dye was injected into moulins and dye concentration and discharge were monitored in two streams at the glacier terminus sydjakk and nordjakk dye emerged only in sydjakk transit velocities ranged from 0 07 to 0 29 m s implying that drainage was through a well defined conduit system velocity and discharge relations suggest that these conduits are part of a multi branched arborescent network of individually braided wide low passages a progressive decline in dispersivity during the early part of the melt season reflects structural changes in these conduits presumably including a decrease in the degree of braiding and an increase in size the system reached its late season configuration in early august by which time the energy dissipated by the flowing water would have sufficed to melt between 0 7 and 21 m 3 of ice per meter of conduit length depending on conduit size potential closure rates exceed melt rates on conduit walls throughout most of the drainage system and so conduits are probably full of water during periods of higher daily discharge with water pressures exceeding atmospheric pressure variations in tracer return curves and dispersivity on a diurnal time scale also appear to reflect changes in the degree of braiding in this case resulting from drowning of low divides between channels as discharge increases

internal structure of a barrier beach as revealed by ground penetrating radar gpr chesil beach uk abstract chesil beach dorset is one of the most famous coastal landforms on the british coast the gravel beach is over 18 km long and is separated for much of its length from land by a tidal lagoon known as the fleet the beach links the isle of portland in the east to the mainland in the west despite its iconic status there is little available information on its internal geometry and evolutionary history here we present a three fold model for the evolution of chesil beach based on a series of nine ground penetrating radar gpr traverses located at three sites along its length at abbotsbury langton herring and at ferry bridge the gpr traverses reveal a remarkably consistent picture of the internal structure of this barrier beach the first phase of evolution involves the landward transgression of a small sand and gravel beach which closed upon the coast leading to deposition of freshwater peat between 5 and 7 k yr bp the second evolutionary phase involves the bulking out of the beach during continued sea level rise but in the presence of abundant gravel supplied by down drift erosion of periglacial slope deposits this episode of growth was associated with a series of washover fans which accumulated on the landward flank of the barrier increasing its breadth and height but without significant landward transgression of the barrier as a whole the final phase in the evolution of chesil beach involves the seaward progradation of the beach crest and upper beach face associated with continued sediment abundance but during a still stand or slight fall in relative sea level this phase may provide further evidence of a slight fall in relative sea level noted elsewhere along the south coast of britain and dated to between 1 2 and 2 4 k yr bp subsequently the barrier appears to have become largely inactive except for the reworking of sediment on the beach face during storm events the case study not only refines the evolutionary picture of chesil beach but illustrates the importance of the subtle interplay between relative sea level and sediment supply in the evolution of a barrier system in addition it also illustrates the potential of gpr in resolving the evolutionary history of gravel rich coastal landforms such as chesil beach

beach dune morphological relationships and erosion accretion an investigation at five sites in england and wales using lidar data abstract the critical relationships between beach and nearshore parameters and the erosion accretion status of frontal dunes have been investigated using lidar data complemented by data obtained from conventional topographic and bathymetric surveys at five dune systems in england and wales morphometric parameters calculated from the lidar data demonstrate the presence of a general relationship between beach morphology dune morphology and erosion accretion eroding dunes were found to be associated with narrower steeper beaches whilst accreting dunes were associated with wider low angle beaches however the critical beach width mean slope angle separating eroding dunes from stable or accreting dunes was found to vary between sites at any given site changes in beach width slope over time can be used to provide an early warning of changes in frontal dune erosion accretion behaviour

review of electromagnetic induction for mapping barrier island framework geology abstract the geologic framework controls on modern barrier island transgression and the relationship of these controls to subsurface structure hydrology and island geomorphology are not well understood recent evidence suggests that alongshore variations in pre holocene geology of barrier islands modify nearshore hydrodynamic processes and sediment transport ultimately affecting how barrier islands will respond to relative sea level rise explorations of holocene barrier island geology are usually based on cores to supplement bathymetric onshore offshore seismic and or ground penetrating radar gpr surveys the advantages and limitations of these methods with respect to barrier island investigations are briefly described in this review alternative near surface geophysical methods including electromagnetic induction emi sensors are increasingly being used for coastal research because they are non invasive provide continuous subsurface information across a variety of sub environments and are capable of characterizing large areas in a short time although these emi sensors have shown promise in coastal applications a number of issues primarily related to subsurface hydrology need to be addressed to fully assess the limitations of this technique this paper reviews the theory methodology and applications of emi in support of geologic framework studies with particular reference to barrier islands resolution of these issues will allow emi sensors to complement and offer significant advantages over traditional methods in support of an improved understanding of large scale barrier island evolution

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

hydropedological investigations with ground penetrating radar gpr estimating water table depths and local ground water flow pattern in areas of coarse textured soils in coarse textured soils ground penetrating radar gpr can provide continuous high resolution records that chart the depth to water tables the use of this information can increase confidence in hydropedological site assessments and reduce the number of wells needed for water table depth and ground water flow determinations ground penetrating radar was used to map spatial and temporal variations in water table depths and ground water flow patterns within an unconfined aquifer located beneath an eolian landscape in northwestern indiana compared with the data collected at a limited number of wells the greater number of observations with gpr provided more comprehensive site coverage and mapped more intricate local ground water flow patterns over a 2 year period gpr revealed systematic temporal and spatial variations in water table depths and local ground water flow patterns

a hydrological approach to estimating daily glacier ablation reduced meltwater discharge owing to glacier retreat can have severe impacts on downstream water users to assess these impacts it is essential to differentiate between water from glacier melt and other sources we propose a method for doing this on a daily time scale by applying a mixing law to electrical conductivity and proglacial discharge measurements daily ablation is then estimated by applying a recession law to the glacier melt component testing this method on summer hydrology and meteorology measurements from the baounet glacier france taken over six consecutive years 2008 2013 allowed us to reconstruct daily ablation during the ablation period mean ablation rates ranged from 20 to 30 mm day 1 air temperature measurements showed that periods of low ablation during the summer were linked to cooler days and snowfall periods comparisons for three consecutive summers showed that the ablation rates obtained by summing calculated daily ablation were statistically similar to the rates recorded

anatomy and sedimentary model of a hooked spit sylt southern north sea a sedimentary model for hooked spit depositional systems based on ground penetrating radar and sedimentological data is presented the recurved main spit of sylt island southern north sea is dominated by migrating sand dunes the investigated hooked spit exhibits a system of foredune ridges oriented perpendicular to the dunes of the recurved spit the development of the hooked spit is related closely to the presence of an adjacent tidal inlet where strong tidal currents and a steep bathymetry prevent a further northward progradation of the main spit and trigger a deflection from northerly directed to easterly directed net sediment transport ground penetrating radar data and shallow sediment cores reveal the sedimentary architecture of the hooked spit in high resolution and allow the proposition of a genetic stratigraphic model it is shown that the growth of the hooked spit is controlled by the interplay of alongshore migrating foreshore beach drifts under fair weather conditions and strong erosional events interpreted as the result of rare severe storms these storms may excavate scarps in the backshore which play an important role in the development of foredune ridges accelerator mass spectrometry 14c ages indicate an absolute age of at least 1300 years for the hooked spit which possibly correlates with strengthened erosion of the main spit in contrast to the main spit where the sediment budget is negative nowadays growth of the hooked spit beach accelerated significantly during the last decades this effect can probably be attributed to enhanced beach nourishments updrift along the main spit and makes the investigated hooked spit a natural laboratory to study the influence of increasing sediment supply into a system developing under the conditions of sea level rise the study shows that the same external forces lead to distinct progradational processes along one barrier spit system

chemical models of solute acquisition in glacial melt waters chemical models for the evolution of bulk melt waters can be constructed by assuming that rock mineral weathering and solute acquisition are controlled by carbonate equilibria different open and closed system models are defined by variations in the rates of weathering relative to the rate of hydrogen ion supply by the dissolution and dissociation of co2 and can be recognized by characteristic ph and relationships the observed and inferred compositions of englacial and subglacial melt suggest that mixing is unlikely to be conservative and that closed system conditions result where post mixing weathering reactions occur the final composition of bulk melt waters is determined by the mixing ratio between englacial and subglacial melt the extent of post mixing evolution and opportunity for mixing with ground waters or re equilibration with the atmosphere

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

investigation of the age and migration of reversing dunes in antarctica using gpr and osl with implications for gpr on mars gpr provides high resolution images of aeolian strata in frozen sand in the mcmurdo dry valleys of antarctica the results have positive implications for potential gpr surveys of aeolian strata on mars within the lower victoria valley seasonal changes in climate and a topographically constrained wind regime result in significant wind reversals as a consequence dunes show reversing crest lines and flattened dune crests ground penetrating radar gpr surveys of the dunes reveal sets of cross strata and low angle bounding surfaces produced by reversing winds summer sand transport appears to be dominant and this is attributed to the seasonal increase in solar radiation solar radiation which heats the valley floor melts ice cements making sand available for transport at the same time solar heating of the valley floor generates easterly winds that transport the sand contributing to the resultant westward dune migration the location of the dune field along the northern edge of the lower victoria valley provides some shelter from the powerful foehn and katabatic winds that sweep down the valley topographic steering of the winds along the valley and drag against the valley wall has probably aided the formation migration and preservation of the dune field optically stimulated luminescence osl ages from dune deposits range from 0 to 1 3 kyr showing that the dune field has been present for at least 1000 yr the osl ages are used to calculate end point migration rates of 0 05 to 1 3 m yr which are lower than migration rates reported from recent surveys of the packard dunes and lower than similar sized dunes in low latitude deserts the relatively low rates of migration are attributed to a combination of dune crest reversal under a bimodal wind regime and ice cement that reduces dune deflation and restricts sand entrainment

evidence for dune reactivation from gpr profiles on the maputaland coastal plain south africa the maputaland area of northeastern south africa is characterized by extensive dune fields which developed during polyphase reworking of regional aeolian cover sand from the mid pleistocene to the holocene extended parabolic dunes many preserved only as wind rift trailing limbs as well as areas of sinuous crested dunes hummocky dune systems and the high composite accretionary coastal barrier dune cordon are the dominant dune forms there are few natural sections exposing the stratigraphic succession and unequivocal relative age relationships between dune systems are uncommon a ground penetrating radar gpr survey of dunes and representative aeolian sand stratigraphic units was undertaken in order to investigate the internal structure of the different dune forms and identify stratigraphic relationships between buried sedimentary units the gpr profiles revealed that the trailing limbs of almost all the parabolic dunes that were surveyed comprise stacked sand units separated by low angle reflections interpreted as bounding surfaces which accumulated through polyphase vertical accretion most extended parabolic dunes are aligned north south and the upper parts of the dunes are characterized by inclined reflections in gpr profile interpreted as large scale sets of cross stratification with apparent dips toward the west a hummocky dune revealed cross stratified aeolian sand superimposed on a truncated dune form and probably formed through deflation of pre existing dunes using 100 mhz and 200 mhz antennae it is clear that gpr is capable of imaging very fine sedimentary structures and buried erosional surfaces in the homogeneous aeolian sand of maputaland at some of the sites investigated the buried sand units identified were sampled by hand augering for infrared stimulated luminescence dating the age determinations on these samples suggest that vertical accretion of up to 7 m of sand occurred intermittently over variable time scales up to 25 000 years on some parabolic dune limbs during the late pleistocene in some complex dunefields adjacent dunes were mobilized at different times suggesting that remobilization was localized the implications of the complex internal structure and vertical accretion of extended parabolic dunes are discussed in the context of changes in vegetation cover and water table due to seasonal and short term cyclical climate variations as well as long term climate change patterns during the last glacial cycle and the holocene

the composition of the englacial and subglacial component in bulk meltwaters draining the gornergletscher switzerland a new method of hydrograph separation for bulk meltwaters draining alpine glaciers is proposed it is based on the two component subglacial and englacial mixing model of collins 1978 but allows the composition of the subglacial component to vary between ascending and descending lines of the hydrograph the mean englacial component can be derived from linear relationships between sulphate concentrations and other ions in bulk meltwaters on certain occasions during the ablation season the maximum concentration of ions in the subglacial component can be determined from the linear relationship between bulk meltwater sulphate concentrations and discharge the bulk discharge is then a direct measure of the mass fraction of the englacial component at maximum discharge the contribution of the subglacial component approaches zero which has implications for the storage and mixing of waters in subglacial reservoirs further the subglacial component is not of constant composition and may itself be a mixture of dilute supraglacial and concentrated subglacial water

airflow and sand transport variations within a backshore parabolic dune plain complex ne graham island british columbia canada onshore aeolian sand transport beyond the beach and foredune is often overlooked in the morphodynamics and sediment budgets of sandy coastal systems this study provides detailed measurements of airflow sand transport via saltation and modified suspension vegetation density and surface elevation changes over an extensive 325 30 m swath of a backshore foredune parabolic dune plain complex near surface 30 cm wind speeds on the backshore ranged from 4 3 to 7 3 m s 1 gusting to 14 0 m s 1 oblique onshore flow is steered alongshore near the incipient foredune then landward into a trough blowout where streamline compression flow acceleration to 1 8 times the incident speed and increasing steadiness occur highest saltation rates occur in steady topographically accelerated flow within the blowout as such the blowout acts as a conduit to channel flow and sand through the foredune into the foredune plain beyond the blowout flow expands vegetation roughness increases and flow decelerates over the foredune plain localized flow steering and acceleration to 1 6 times the incident speed occurs followed by a drop to 40 of incident flow speed in a densely vegetated zone upwind of an active parabolic dune at 250 m from the foredune sediment properties reflect variations in near surface flow and transport processes well sorted fine skewed backshore sands become more poorly sorted and coarse skewed in the blowout due to winnowing of fines sorting improves and sands become fine skewed over the foredune plain toward the parabolic dune due to grainfall of finer sands winnowed from the beach and foredune during the fall winter season significant amounts of sand up to 110 kg m 2 are transported via modified suspension and deposited as grainfall up to 300 m landward of the foredune no distinct trend in grainfall was found although most fell on the depositional lobe of the blowout and at 200 m near an isolated active parabolic dune grainfall amounts may reflect several transporting events over the measurement period and the transport process is likely via localized modified suspension from the crest of the foredune and other compound dune features in the foredune plain this evidence suggests that the process of grainfall delivery though often overlooked in coastal research may be a key process in maintaining active dunes hundreds of metres from the shoreline in a densely vegetated foredune plain the effectiveness of this process is controlled by seasonal changes in vegetation cover and wind strength as well as shorter term e g tidally controlled variations in sand availability from the beach

cyclical evolution of a modern transgressive sand barrier in northwestern spain elucidated by gpr and aerial photos abstract the internal structure of a modern baymouth barrier is analyzed in detail including its historical evolution and the factors controlling it historical evolution was reconstructed using available aerial photographs from 1956 to 2003 detailed geophysical data were acquired using ground penetrating radar gpr and analyzed along with airphotos to reconstruct the recent evolution of a barrier located in northwestern spain the gpr data reveal the internal architecture of the barrier which consists of two main radar facies 1 washover deposits associated with landward barrier migration and vertical aggradation and 2 beach deposits associated with seaward barrier progradation the reconstruction of the stratigraphic sequence indicates the occurrence of two erosive periods followed by an accretionary period the erosion along the barrier is outlined by the presence of three well defined bounding surfaces the stratigraphic record of the subsequent recovery phase depends on the impact level of the erosive phase which is controlled by the presence of ephemeral inlets along the barrier this alternating behavior implies a discontinuous shoreline trajectory in spite of a net landward migration this trend is consistent with regional sea level rise albeit being intensified locally by the interplay of sediment starvation and storm regime landward barrier retreat occurs by overwash and inlet breaching which permits barrier preservation of volume due to a continuous constructive destructive cycle the results acquired from this example expand our understanding of the internal structure and evolutionary trends of transgressive sand barriers

ground penetrating radar as a tool to detect rock heterogeneities channels cemented layers and fractures in the luxembourg sandstone formation grand duchy of luxembourg a combined study of radar profiles and thin section analysis supported by modelling of synthetic radar traces reveals that ground penetrating radar gpr reflections generated in diagenetically altered sandstones cannot always be interpreted unequivocally this is illustrated in the luxembourg sandstone formation which has been altered diagenetically by selective carbonate cementation and fracturing cemented lenses and concretions developed along the bedding planes especially at places with high primary carbonate content cementation resulted in the alternation of cemented carbonate rich sandy layers thickness 30 50 cm and variable length and uncemented carbonate poor sandstone layers the ability of gpr to detect the geometry of these lenses and vertical fractures with centimetre apertures has been tested at several antenna frequencies 100 200 250 and 500 mhz relative dielectric permittivity calculations were carried out to assess variations of this electric property within the cemented and uncemented layers as a function of porosity calcite and water content in the pores two dimensional full waveform modelling was also carried out to study the effect of conductivity in the sandstones and the effect of interlayer clay seams at the penetration depth of the radar 7 m with 250 mhz cemented lenses and concretions could only be detected with gpr when the porosity contrast was sufficiently high which is not always the case this conclusion is supported by the modelling the data also proved the ability of radar to detect large open vertical fractures along which sandstones are weathered the study has implications for investigations which will use gpr to detect three dimensional distribution of diagenetic pore filling precipitates as well as secondary porosity development along fractures

parabolic dune reactivation and migration at napeague ny usa insights from aerial and gpr imagery abstract observations from mapping since the 19th century and aerial imagery since 1930 have been used to study changes in the aeolian geomorphology of coastal parabolic dunes over the last 170 years in the walking dune field napeague ny the five large parabolic dunes of the walking dune field have all migrated across or are presently interacting with a variably forested area that has affected their migration stabilization and morphology this study has concentrated on a dune with a particularly complex history of stabilization reactivation and migration we have correlated that dune s surface evolution as revealed by aerial imagery with its internal structures imaged using 200 mhz and 500 mhz ground penetrating radar gpr surveys both 2d transect and high resolution 3d gpr imagery image downwind dipping bedding planes which can be grouped by apparent dip angle into several discrete packages of beds that reflect distinct decadal scale episodes of dune reactivation and growth from aerial and high resolution gpr imagery we document a unique mode of reactivation and migration linked to upwind dune formation and parabolic dune interactions with forest trees this study documents how dune dune and dune vegetation interactions have influenced a unique mode of blowout deposition that has alternated on a decadal scale between opposite sides of a parabolic dune during reactivation and migration the pattern of recent parabolic dune reactivation and migration in the walking dune field appears to be somewhat more complex and perhaps more sensitive to subtle environmental pressures than an idealized growth model with uniform deposition and purely on axis migration this pattern believed to be prevalent among other parabolic dunes in the walking dune field may occur also in many other places where similar observational constraints are unavailable

internal architecture of a raised beach ridge system anholt denmark resolved by ground penetrating radar investigations abstract the internal architecture of raised beach ridge and associated swale deposits on anholt records an ancient sea level the holocene beach ridges form part of a progradational beach ridge plain which has been interpreted to have formed during an isostatic uplift and a relative fall in the sea level over the past 7700 years the ridges are covered by pebbles and cobbles and commonly show evidence of deflation material presumably removed from the beach ridges and adjacent swales form the present dune forms on anholt ground penetrating radar gpr reflection lines have been collected with 250 mhz shielded antennae across the fossil ridge and swale structures the signals penetrate the subsurface to a maximum depth of 10 m below the fossil features the gpr data resolve the internal architecture of the beach ridges and swales with a vertical resolution of about 0 1 m gpr mapping indicates that the holocene beach ridges are composed of seaward dipping beachface deposits as well as minor amounts of inland dipping deposits of wash over origin the beachface deposits downlap on underlying shoreface deposits and we use these surfaces as markers of a relative palaeo sea level the new data indicate that the highest relative sea level at about 8 5 m was reached 6500 years ago 700 years later the relative sea level had dropped 0 7 m indicating a change in the relative sea level around 1 mm year this fall in the relative sea level most likely records the influence of an isostatic rebound causing younger beach ridge deposits to indicate lower sea levels

investigations of glacier hydrological systems using dye tracer techniques observations at pasterzengletscher austria a l aide de traceurs colores on a mis en evidence une division laterale du drainage dans le bas de la langue qui n est pas determinee par la direction des crevasses obliques la reapparition de l eau dans les differents moulins est complexe bien qu elle reste constante dans le temps

coarse sand beach ridges at cowley beach north eastern australia their formative processes and potential as records of tropical cyclone history storm surges generated by tropical cyclones have been considered a primary process for building coarse sand beach ridges along the north eastern queensland coast australia this interpretation has led to the development of palaeotempestology based on the beach ridges to better identify the sedimentary processes responsible for these ridges a high resolution chronostratigraphic analysis of a series of ridges was carried out at cowley beach queensland a meso tidal beach system with a 3 m tide range optically stimulated luminescence ages indicate that 10 ridges accreted seaward over the last 2500 to 2700 years the ridge crests sit 3 5 to 5 1 m above australian height datum ca mean sea level a ground penetrating radar profile shows two distinct radar facies both of which are dissected by truncation surfaces hummocky structures in the upper facies indicate that the nucleus of the beach ridge forms as a berm at 2 5 m australian height datum equivalent to the fair weather swash limit during high tide the lower facies comprises a sequence of seaward dipping reflections beach progradation thus occurs via fair weather wave accretion of sand with erosion by storm waves resulting in a sporadic sedimentary record the ridge deposits above the fair weather swash limit are primarily composed of coarse and medium sands with pumice gravels and are largely emplaced during surge events inundation of the ridges is more likely to occur in relation to a cyclone passing during high tide the ridges may also include an aeolian component as cyclonic winds can transport beach sand inland especially during low tide and some layers above 2 5 m australian height datum are finer than aeolian ripples found on the backshore coarse sand ridges at cowley beach are thus products of fair weather swash and cyclone inundation modulated by tides knowledge of this composite depositional process can better inform the development of robust palaeoenvironmental reconstructions from the ridges this article is protected by copyright all rights reserved

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

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