quantitative roundness analysis of coastal boulder deposits abstract the sedimentology of coastal boulder deposits cbd is little known these deposits and especially the largest clasts within them which commonly weigh many 10s of tonnes are of increasing interest because they attest to extreme energy wave events acting well above the high tide mark in some cases 40 m above high water and 100 m inland recent observations have made clear that storm waves rather than tsunami are important in both creating and activating these deposits but beyond that we know little about their hydrodynamics or the relative frequency of boulder movement and how this might vary with topographic setting roundness is a first order characteristic that preserves a record of deposit reworking it can tell us whether clasts move around much after they have been created from bedrock or whether they are emplaced into cbd with little or no subsequent transport but because roundness has historically been difficult to measure most roundness estimates in the literature are based on qualitative visual assessment and are therefore of limited analytical value fully reproducible roundness measurements are possible however and in the case of boulders they can be acquired quite easily using the kirkbride 2005 device in combination with a trigonometric formula presented here cbd at locations in ireland and scotland provide a test case demonstrating the utility of quantitative boulder roundness measurements the 567 clasts we measured are generally angular but a substantial proportion shows some degree of rounding most importantly there are demonstrable consistent patterns relating topography and roundness there is a strong and unsurprising inverse correlation between clast roundness and deposit elevation there is no first order relationship between roundness and inland distance but there is a power law inverse relationship between rounding and steepness ratio of elevation to distance inland the greatest degree of rounding is found in cbd located at the back of gentle coastal platforms with gradual slopes these relationships provide new insights into cbd sedimentology which we hope will be probed and tested in future studies

impressive abrasion rates of marked pebbles on a coarse clastic beach within a 13 month timespan abstract in this paper the abrasion rate on a coarse clastic beach was evaluated by calculating the volume loss recorded on indigenous pebbles within a 13 month timespan the experiment was carried out at marina di pisa italy on an artificial beach that was built to counteract the erosion processes affecting this sector of the coast a total of 240 marble pebbles 120 rounded and 120 angular were marked using the rfid technology and injected on the beach the volume loss measured after consecutive recovery campaigns was progressively increasing reaching the maximum value after 13 months 61 overall the average volume loss is consistent between rounded and angular pebbles at any time 59 3 and 64 2 after 13 months respectively meaning that the roundness is not a primary control factor on abrasion rate the pebbles that did not reach such abrasion rates after 8 and 10 months volume loss less than 20 were found at heights equal or greater than 2 m above mean sea level on the crest of the storm berm that formed during the strongest storms this implies that the highest wearing is achieved in the lower portion of the backshore which is also the area that underwent major topographic modifications here sea water action might also exert chemical influence on the pebbles adding to the mechanical abrasion the main result of this research indicating an impressive volume loss on beach pebbles in a short timespan could be of key importance for coastal managers the optimization of coarse sediment beach nourishments is also relevant taking into right consideration that the volume loss due to sediment abrasion might exceed 50 of the original fill volume just after 1 year in the most dynamic portion of the beach

geomorphology and weathering characteristics of erratic boulder trains on tierra del fuego southernmost south america implications for dating of glacial deposits abstract erratic boulder trains ebts are a useful glacial geomorphological feature because they reveal former ice flow trajectories and can be targeted for cosmogenic nuclide exposure dating however understanding how they are transported and deposited is important because this has implications for palaeoglaciological reconstructions and the pre exposure and or erosion of the boulders in this study we review previous work on ebts which indicates that they may form subglacially or supraglacially but that large angular boulders transported long distances generally reflect supraglacial transport we then report detailed observations of ebts from tierra del fuego southernmost south america where their characteristics provide a useful framework for the interpretation of previously published cosmogenic nuclide exposure dates we present the first comprehensive map of the ebts and analyse their spatial distribution size and physical appearance results suggest that they were produced by one or more supraglacial rock avalanches in the cordillera darwin and were then transported supraglacially for 100 s of kilometres before being deposited rock surface weathering analysis shows no significant difference in the weathering characteristics of a sequence of ebts previously hypothesized to be of significantly different age i e different glacial cycles we interpret this to indicate that the ebts are much closer in age than previous work has implied this emphasises the importance of understanding ebt formation when using them for cosmogenic nuclide exposure dating

boulders as a signature of storms on rock coasts this paper is the first review of coastal boulder studies it serves as a peer reviewed introduction to a special issue on the topic of boulders as a signature of storms on rock coasts since 2004 and the indian ocean tsunami most coastal boulder research has been focused on using boulders as sedimentary signatures of palaeo tsunami events and the most commonly used transport equations typically suggest that large boulder deposits are products of tsunami rather than storms there is growing empirical evidence demonstrating on inter annual to century timescales that storm waves are capable of transporting and depositing boulders of significant size at elevations well above sea level current process studies of how boulders are eroded transported and deposited have not received wide attention by rock coast geomorphologists or palaeoenvironmental reconstruction scientists this special issue is framed around the goal of highlighting our current understanding of the role of storm waves as a driving mechanism for boulder erosion transport and deposition here we review the current state of knowledge about boulder dynamics boulder responses to storms and boulders as sedimentary signatures of storm events we identify gaps in our conceptual and quantitative understanding lastly we propose means of addressing research gaps improving consistency between researchers and collecting multi purpose data this review and the papers contained within the special issue provide an improved understanding of coastal dynamics particularly the role storms can play in influencing erosion rates and depositional patterns of coarse material i e boulders or larger which has hitherto been under represented in the literature

modification of clast shape in high arctic glacial environments abstract clast shape data from a range of different glacial environments at several high arctic valley glaciers in svalbard are presented these data add to the growing body of reference information about clast shape in modern glacial environments and is used to explore the role of lithology in clast morphogenesis and to evaluate the different methodological approaches to the analysis of clast shape data the following conclusions are drawn 1 it is possible to distinguish clasts transported subglacially from those moved supraglacially 2 it is not possible to differentiate among different types of subglacial sediment or to distinguish them collectively from glaciofluvial samples 3 lithology has some influence on clast shape although not as much as previously suggested and 4 covaria t plots of the ra percentage of angular and very angular clasts versus c40 percentage of clasts with c to a axial ratio 0 4 index give superior data visualization and discriminate more effectively among different glacial sediments than sphericity and roundness plots

patterns and rates of erosion produced by high energy wave processes on hard rock headlands the grind of the navir shetland scotland abstract the grind of the navir is an ignimbrite headland on the exposed atlantic coast of the shetland islands scotland during storms offshore wave heights exceed 20 m and deep water close inshore allows high energy waves to impact on these cliffs the cliff top at 15 m above sea level is awash with wave water when wave heights exceed 8 m a condition met in storms in most years detailed mapping ground photography and patterns of lichen colonisation and growth allow the processes patterns and rates of erosion to be assessed on different parts of the headland over the past 100 years recent fractures in the rock of the cliff face and top indicate that wave impact forces exceed the 1 5 kpa tensile strength of the rock and fresh sockets low on the cliff face record the removal of fracture bounded blocks that are lost to seaward on the upper part of the cliff face upward moving water flow is capable of removing blocks from both vertical faces and stepped overhangs clefts in the cliff face are extended inwards and upwards by crack propagation and block removal leading to the development of slot caves the movement of waves across the cliff top in fast moving bores quarries blocks from the cliff face close to the edge and from rock steps on the cliff top promoting further rock fracturing socket sizes and block characteristics indicate that blocks of 1 m 3 are rotated from sockets on the cliff top platform and carried landwards for up to 60 m to be deposited in a series of boulder ridges on the cliff top multiple boulder movements during a storm in january 2005 generated impact marks and orientated striations that allow the pattern of water movement to be reconstructed across considerable areas of cliff top the average rate of erosion at the grind is estimated at 1 3 6 0 mm yr on the cliff face and 5 mm yr on the cliff top although erosion rates vary in both time and space although block movement on the cliff top occurs in most years erosion of rock by block removal is most active during major storms nevertheless some parts of the cliff top and face remain blackened by lichen and so have experienced little recent erosion over the last 70 years or so although erosion occurs at the base of the cliffs in recent decades it has been concentrated on upper part of the cliff face and top cliff top erosion is most intense where stepped geos act as channels for waves to access the cliff top the most active features on the cliff top are the boulder ridges where substantial changes can be traced to storms over the past century unlike conventional models of cliff erosion where erosion is concentrated by wave attack at the waterline wave impacts on this headland may occur on any part of cliff face and top and appear particularly effective on the upper cliff and cliff top platform

cliff top storm deposits on banneg island brittany france effects of giant waves in the eastern atlantic ocean this study is based on the morphosedimentary analysis of the cliff top storm deposits accumulated on the coast of banneg island located in the archipelago of molene brittany france these ctsds comprise large tabular clasts quarried from the upper part of the cliff and the backing scoured platform by giant oceanic storm waves impacting directly the western coast of the island an analysis of the distribution and the geomorphology of these accumulations were carried out using the dgps topographic surveys most of the clasts are organised into imbricate boulder clusters or ridges deposited between 7 5 and 14 5 masl 52 accumulations were inventoried from the north to the south of the island representing a global volume of 1000 m3 the median size of the clasts calculated is equivalent to 0 8 0 6 0 4 m and a weight of 0 6 t the largest one measuring 5 3 3 9 0 5 m 32 t is located in the centre of the island ridge 28 it has been deposited 14 m inland from the edge of the cliff at the elevation of 9 m sediment analysis shows that clast sizes become smaller with increasing distance from the shoreline but there is no relationship between the sorting and the distance inland a study of the hydrodynamic conditions inducing clast transport was undertaken by an analysis of the wave data from the 1989 to the 1990 winter storms models of wave runup indicate that their highest water levels may have reached up to 19 masl 5 to 10 m higher than the top of the cliff submersion by giant storm waves has been more important and frequent in the centre and the south of the island wave data over the 1979 to the 2007 period shows that no events as powerful as those of the 1989 to the 1990 winter were recorded during the last 30 years yet it appears that the 1979 1990 decade was characterized by important morphogeneous events while the following period 1990 2007 has experienced a sharp decrease in storm events these variations could be attributed to the inversion from a negative towards a positive phase in the north atlantic oscillation index

the shape of beach gravels in 1970 dobkins and folk demonstrated that isotropic beach gravels possess distinctive shapes this characteristic has allowed beach gravels to be distinguished from fluvial gravels providing a valuable tool for determining the conditions under which ancient conglomerates were deposited however two of the beaches investigated worldwide by dobkins and folk possessed gravels whose shapes differed from those found elsewhere detailed reinvestigation of one of these anomalous sites at batemans bay in new south wales australia has shown the shape of the gravels to be indistinguishable from that of beach gravels found elsewhere in the world this result confirms the value of gravel shape measurement as an aid in the determination of the depositional environment of conglomerates

cliff top megaclast deposits of ireland a record of extreme waves in the north atlantic storms or tsunamis past occurrences of major tsunami in the global record have often been inferred from the presence of megaclast accumulations at significant heights above sea level which sometimes exhibit a pronounced seaward directed imbricate fabric the aran islands off the west coast of ireland exist in a marine environment which is totally unprotected from the most extreme sea states encountered in the north atlantic spectacular megaclast accumulations are found along the tops of vertical cliffs on these islands the elevation of these deposits varies from 0 m to 50 m above mean sea level and they include clasts weighing 250 tonnes at sea level over 117 tonnes at 12 m and 2 9 tonnes at 50 m above sea level imbrication measurements on these megaclasts indicate a well defined and consistent mean direction from the southwest for the emplacing waves one that is consistent with the prevalent storm wind direction for the area the megaclast accumulations are subject to episodic and on going erosion by cliff retreat but the existing accumulations are estimated to record events since at least 1839 recent emplacement and reworking is evidenced by trapped plastic detritus within the deposits and eyewitness accounts of large storms during which clasts have been emplaced similar deposits are found on the exposed coasts of the shetland and orkney islands off scotland there is at present no evidence of any tsunami in recorded history affecting the western irish and scottish coasts other than those generated by the lisbon earthquake of 1755 where the wave effects were slight thus the presence of megaclast accumulations at significant heights above sea level on exposed coasts and exhibiting imbrication should not be used as a definitive criterion for the past occurrence of tsunami these deposits attest to extreme wave conditions occasionally encountered in the north atlantic and act as a record of such events extending back at least 160 years such data on extreme wave conditions are essential for the prediction of the effects of deepwater waves on structures such as offshore drilling platforms

relative sea level curves for the south shetland islands and marguerite bay antarctic peninsula this paper presents preliminary relative sea level curves for the marguerite bay region and for the south shetland islands the marguerite bay curve is constrained by both new and previously published 14c dates on penguin remains and shells and on two isolation basins dating back to 6500 14c yr bp extrapolation back to the marine limit yields a minimum deglaciation date for marguerite bay of ca 9000 14c yr bp analysis of beach clasts suggests that there was a period of increased wave activity perhaps related to a reduction in summer sea ice extent between ca 3500 and ca 2400 14c yr bp the curve for the south shetland islands is derived entirely from published 14c dates from isolation basins and on whalebone penguin bone and seal bone the curve shows an initial relative sea level fall which was interrupted by a period in the mid holocene when relative sea level rose to a highstand of between 14 5 and 16 m above mean sea level amsl before falling again

reservoir continuity logging using connectivity mapping while drilling it is widely recognized that reservoir flow heterogeneities dramatically affect oil recovery and fluid flow thus to improve reservoir management it is necessary to map a reservoir s geologic characteristics in greater detail for example resolution on the order of a few feet is needed to optimize injection and production processes

stable imbrication and delicate unstable settings in coastal boulder deposits indicators for tsunami dislocation abstract medium sized and coarse debris pebbles and boulders can exhibit patterns of setting particularly if they are elongated or tabular these patterns such as imbrication indicate certain transport processes mostly as to direction and character many years of observation and measuring of coarse coastal deposits are the basis for the conclusions presented here on environmental transport processes their character and their energy beside imbrication special emphasis is given to unstable or delicate settings of large boulders that evidently have remained in these positions from hundreds to thousands of years this deserves an explanation to how they arrived at these positions and why they have not changed into a more stable position given an environment of constant energy input along coastlines the discussion lays emphasis on whether both settings of mega boulders can be indicative of tsunami transport processes

evaluation of image analysis methods used for quantification of particle angularity angularity is an important parameter in the characterization of particle morphology that is used to interpret the transport history of particles in sedimentary deposits in the past visual classification using silhouette charts was widely used to determine particle angularity but this approach is subjective and time consuming with advances in modern image analysis techniques and low cost software packages it is possible to rapidly quantify particle angularity more objectively than using visual classification methods this study re examines the performance of three existing image analysis methods and one new image analysis procedure applied to six rock and sediment samples that were visually different in angularity to facilitate comparison between the angularity results measurements were reduced to rankings for each aggregate sample these results show that the four image analysis methods rank the angularity of the samples differently and that none rank the mean angularity index in the same order as the angularity ranking using visual classification therefore further research is needed to develop an image analysis method that can quantify the angularity of sedimentary particles more precisely

magnitude and frequency of extra tropical north atlantic cyclones a chronology from cliff top storm deposits cliff top storm deposits ctsds are known to occur on cliffs at elevations of up to 50 m above sea level at exposed sites on the deep water coasts of the british isles eye witness accounts and time series field mapping of ctsds demonstrate their formation over the historical period and their continued modification during major storms with ctsds burying a range of modern human derived debris older deposits show surface lichen growth and weathering effects that relate to the relative age of ctsds over longer time spans buried sand and peat deposits provide dates on phases of ctsd emplacement and mobilisation and so provide an indication of the frequency and timing of the most severe storms two adjacent sites in shetland provide a combination of 14c dates on peat buried beneath storm deposited boulders 14c dates on marine shells buried inside ctsd boulder ridges and optically stimulated luminescence osl ages on sands intercalated with storm derived boulders although the precision is low this evidence identifies phases of exceptional storm activity spanning approximately 400 550 700 1050 1300 1900 and since 1950 ad by the very nature of cliff top erosion and deposition these records are fragmentary yet the timeline of major storms recorded in the shetland cliffs matches fairly well with the more general record of storminess in the north atlantic derived from the sea salt record in the gisp2 ice core as such ctsds represent an overlooked archive of storm sedimentation with the potential to elucidate local storm chronologies as well as informing debate surrounding the palaeo tempestology and impact of major cyclones and hurricanes

wave emplaced coarse debris and megaclasts in ireland and scotland boulder transport in a high energy littoral environment abstract many coastlines of the world particularly those at higher latitudes and those located in tropical cyclone belts are regularly battered by strong storm waves drowning of low lying areas by storm surges and storm floods has been thoroughly recorded however storm deposits at rocky shorelines or on cliffs have been underrepresented in the literature this article presents observations of extraordinary wave deposits along the high wave energy coastlines of western ireland and the northern scottish isles and discusses possible wave event types and time windows of the processes responsible we used archaeological geomorphological and geochronological disciplines to compare our findings with earlier results published for these areas and to contribute to the debate on whether large clasts found well above sea level and or a considerable distance inland were deposited by storms or by tsunamis

styles of sedimentation beneath svalbard valley glaciers under changing dynamic and thermal regimes glacier beds provide crucial information concerning past and present ice dynamics and thermal regime in this paper we present structural and sedimentological data from four valley glaciers austre lovenbreen midtre lovenbreen vestre lovenbreen and austre broggerbreen on broggerhalvoya nw spitsbergen the main focus of this paper is midtre and austre lovenbreen two typical high arctic land based polythermal valley glaciers the former has a long record of documentation regarding its response to twentieth century climatic warming structural mapping on the glacier surface and analysis of sediments in the proglacial area of midtre lovenbreen indicate that the dynamic regime and thermal structure of the glacier have changed through time dynamically midtre lovenbreen was once heavily crevassed and relatively fast moving but now is virtually crevasse free and slow moving the sedimentary record indicates that extensive areas of this glacier were wet based when it was in a more advanced state probably at its neoglacial maximum late nineteenth early twentieth centuries during this advance a thin deforming layer of diamicton commonly fluted was draped over the existing morphology in the presently exposed proglacial area this morphology consisted of large streamlined ridges aligned parallel to ice flow erosion of the underlying bedrock appears to have been limited radio echo soundings of the glacier show that at present it is characterized by a polythermal basal thermal regime with wet based subglacial conditions only beneath its thicker parts modification of the bed is limited under this thermal regime and as a result the supraglacial environment dominates modern sedimentation comparative studies on austre lovenbreen which also is probably polythermal indicate similar sedimentary characteristics and facies associations although here there are much more extensive areas of striated bedrock indicative of former basal sliding in contrast both austre broggerbreen and by analogy vestre lovenbreen are known to be predominantly cold based collectively these four glaciers suggest a trend of glacier recession and thinning accompanied by a change in thermal regime from predominantly wet based through partly frozen to completely frozen this study suggests that svalbard valley glaciers have several dynamic modes and that glaciers switch between these modes largely as a reaction to changes in mass balance

wave emplaced coarse debris and megaclasts in ireland and scotland boulder transport in a high energy littoral environment a discussion scheffers et al 2009 describe a reconnaissance survey of boulder accumulations along parts of the atlantic coasts of the british isles a substantial part of their report concerns the characteristics of wave transported boulder deposits found high above sea level on cliffs these boulder deposits reach perhaps their ultimate development along the coasts of the aran islands galway bay western ireland and eshaness shetland northern scotland where evidence of wave action reaches elevations of 50 m above sea level a s l we have previously investigated in detail these and numerous other similar localities and concluded that the boulder deposits are cliff top storm deposits ctsds part of an assemblage of features found on certain cliffs on these very high energy coasts that relate to the impacts of extreme waves during major storms williams and hall 2004 hall et al 2006 2008 hansom et al 2008 hansom and hall 2009 however scheffers et al 2009 p 571 claim that at these and other sites no evidence exists for storm wave dislocation of boulders found at altitudes of 120 m a s l indeed no calculations of possible storm wave heights storm wave physics or ages of the deposits and no descriptions of extraordinary storms are sufficient to explain these displacements p 568 and alternative explanations such as tsunamis should be considered p 571 here we rebut these claims by briefly restat

boulder ridges on the aran islands ireland recent movements caused by storm waves not tsunamis abstractireland s aran islands are an excellent place to test whether coastal boulder deposits including individual rocks weighing several tens of tonnes near sea level and clasts weighing several tonnes transported at tens of meters above sea level require a tsunami for emplacement or whether storm waves can do this work elongate deposits of cobbles boulders and megagravel are strung along the atlantic coasts of the aran islands no tsunamis have affected this region in recent centuries so if these deposits are forming or migrating at the present time they must be storm activated we find a diverse range of evidence for recent ridge activity first shells of hiatella arctica subtidal rock boring bivalves preserved in life position within ridge boulders yield radiocarbon ages from 200 ad to modern post 1950 ad second recent motion is attested to by eyewitness accounts that pin the movement of several individual 40 80 t blocks to a specific 1991 storm and by repeat photography over the last fe

from fine sand to boulders examining the relationship between beach face slope and sediment size abstract it is a long standing maxim that coarser sediment sizes are associated with steeper beach face slopes but because most work has focused on sandy beaches few data are available for the pebble cobble or boulder size ranges little is known therefore about how beach morphology and grain size relate at the coarser size grades we compiled data from the literature 2144 measurements of beach face slope with associated grain sizes covering the range from very fine sand to boulders this meta analysis shows that beach faces do tend to steepen as average grain size increases at least up to the cobble size range but the trend is not simple although previous studies suggested a simple power law relationship between grain size and beach face slope in fact the data distribution is best fit by a curve that is steep at the finer grain sizes but is much more gentle as grain size coarsens and may trend downward for boulders fine and medium sands have the greatest range of reported slopes and the data support the importance of effective weight modification and boundary layer dynamics as primary controls on beach face steepness at these fine size grades around the very coarse sand size grade a plateau marks a shift in beach dynamics as hydraulic conductivity increases beaches switch to being infiltration dominated the trend toward steeper slopes continues but at a lower and steady rate from granules through cobbles there appears to be a falloff in slope for the coarsest boulder deposits but we note that this is based on very few locations so should be considered preliminary the overall data distribution is described by a power law function tan a d 50 0 125 b c the broadness of each transition zone also shows that a range of factors other than grain size governs where that tipping point occurs in the cobble and boulder size ranges there are two deposit categories boulder beaches and supratidal boulder ridges although not commonly thought of as beaches boulder ridges record long term storm deposition and reworking on the highest energy coasts supratidal ridges and boulder beaches seem to show different slope grain size relationships with the steepest slopes occurring in boulder ridges and with boulder beaches showing more gentle gradients than other coarse clastic beaches but our data set reveals how little quantitative information exists about the coarsest end of the beach spectrum and invites further work to investigate the sedimentology of cobble and boulder dominated systems

how does wave impact generate large boulders modelling hydraulic fracture of cliffs and shore platforms abstract boulder quarrying by large waves along steep high energy coastlines contributes to erosion both by causing inland migration of cliff faces and by vertical lowering of coastal platform surfaces it also leads to the formation of coastal boulder deposits cbd above and inland of the high water mark we describe mechanisms by which hydraulic fracture creates boulders from cliffs and bedrock platforms intense fluid pressures are induced by wave impact on the base of overhanging ledges and also along interior surfaces as cracks fill with water during wave runup and overtopping these processes impose large loads on the overlying rock and bending stresses thus induced can create or propagate microcracks in the rock repeated loading leads to complete fracture and detachment of bedrock slabs which are liberated as boulders we consider these processes using the aran islands ireland as a type locality both because cbd there are well documented and because flat lying strata and orthogonal joint patterns yield tabular bedrock geometry which lends itself to modelling the loaded rock is modelled as a beam with a microcrack that is fractured by a bending stress from an applied hydrodynamic load this simple approach allows us to examine general scalings and dependencies we determine a condition for fracture relating the fluid pressure loaded area fracture stress microcrack position and geometry in some situations the fluid pressure need only be a fraction of the fracture stress fracture is most likely to occur during extreme wave conditions and when the exposed rock has a large eroded area for loading the balance of forces suggests that larger beams break more easily facilitating the creation of large boulders

linkages between 200 mb tropical and extratropical circulation anomalies during the 1986 1989 enso cycle abstract nmc operational wind analyses have been used to document the 200 mb circulation anomalies during the solstice seasons of the 1987 1989 enso cycle using the one level vorticity balance diagnostic approach the 200 mb rossby wave anomalous source distribution was derived as departures from a three year mean for the single warm phase season january march 1987 the effective rossby wave anomaly sources were found to be generally quite small within 15 of the equator poleward of about 15 the anomalous 200 mb divergence through the planetary vorticity divergence anomaly stretching term is the dominant factor in determining the anomalous 200 mb vorticity source distribution its jfm standard deviation around 30 35 n was an order of magnitude larger than that found in the deep tropics the january march and june august 200 mb circulation differences between the warm and cold phase of the 1987 1989 enso cycle are described the enso cycle linkages between the equatorial pacific convection anomali

distribution geomorphology and lithofacies of cliff top storm deposits examples from the high energy coasts of scotland and ireland abstract cliff top storm deposits ctsds occur on cliffs at elevations of up to 50 m above sea level at exposed sites on the deep water coasts of the british isles this study examines the distribution geomorphology and lithofacies of ctsds at sites from shetland orkney caithness and the outer hebrides in scotland and from the aran islands in galway bay in ireland ctsds are generated largely by the quarrying of blocks from the cliff top and transported by green water bores across cliff top platforms and ramps to be deposited in backing ridges or as debris spreads maximum boulder sizes reach 48 m 3 but it is likely that much larger blocks can be quarried prior to disintegration during transport eye witness accounts and field mapping demonstrate that formation and modification of ctsds has continued during major storms over recent decades recent ctsds bury a range of man made debris but older deposits lack this and instead show weathering effects that indicate a longer residence time in shetland osl dates on intercalated sands suggest that the oldest ctsds date from 800 ad radiocarbon dates on shell buried inside ctsd ridges relate to major storms between 1700 and 1900 ctsds represent an overlooked archive of storm sedimentation that has great potential for the elucidation of local storm chronologies ctsds also provide evidence of wave impacts on any part of the cliff face or top in fundamental contrast to the concentration of wave action at the cliff foot implicit in traditional models of the erosion of rock coasts

long term variability of supratidal coastal boulder activation in brittany france abstract high energy supratidal coastal boulder deposit scbd dynamics were investigated on vierge island and pors carn point north and south of western brittany france respectively morphological changes induced by boulder transport and quarrying were quantified using high resolution topographic survey data taken between 2012 and 2017 additional in situ wave parameters and water levels were also recorded over this period 2014 2017 in order to compute the maximum water levels and assess the relationship between scbd morphological changes and specific hydrodynamic conditions during extreme water levels for maximum water levels exceeding a one in ten year event scbds were broadly reworked up to 40 of the total volume during lower intensity events for which maximum water levels were still very high morphological changes represented 1 to 5 of the total volume these morphological and hydrodynamic observations were then used to calibrate a chronology of scbd activation events based on 70 years of hindcast winter maximum water levels these long term time series showed great interannual variability in scbd activation but no significant long term trend winter frequency scbd activation was better correlated to the wepa index r 0 46 than the nao index r 0 1 therefore the wepa index can be considered to be a more significant climate proxy for assessing storm related geomorphic changes in the temperate latitudes of the n e atlantic basin 36 52 n including the brittany coast the potential of scbds as a morphological storm proxy for macrotidal high energy rocky coasts is addressed

interactions between rock avalanches and glaciers in the mont blanc massif during the late holocene rock avalanches are common in the mont blanc massif which is bordered by valleys with large resident and tourist populations and important highways this paper combines historical data with detailed geomorphological mapping stratigraphic observation and absolute and relative dating to interpret several deposits resulting from rock avalanching onto glaciers nineteen rock falls and rock avalanches are described ranging in volume from 10 000 m3 to 10 106 m3 they occurred between 2500 bp and ad 2007 at six sites the events at three sites miage and drus glaciers and tour des grandes jorasses are characterised by short travel distances those at brenva triolet and frebouge glaciers exhibit excessive travel distances interactions between rock avalanches and glaciers are of four types i rock avalanche triggering where glacial and paraglacial controls include debuttressing of rockwalls due to glacier thinning and retreat oversteepening of rock slopes by glacial erosion and effects of glaciers on permafrost ii rock avalanche mobility in which mobility and travel distance are modified by channelling of rock avalanche debris by moraines and valleys incorporation of ice and snow often 50 for large events and irregularities on the glacier surface iii deposit sedimentology where melting of incorporated ice transforms the final deposit by reducing its thickness typically to 5 m and debris of variable thicknesses is juxtaposed in a hummocky deposit with chaotic piles of angular rock debris and iv glacier dynamics where insulating debris deposited upon a glacier produces a debris covered glacier of different dynamics and high elevated scars can favour the formation of small glaciers

how round is round a new approach to the topic roundness by fourier grain shape analysis numerous methods for roundness measurement have been developed none however has been generally accepted because of conceptual and practical deficiencies modern image processing and fourier grain shape analysis have eliminated the practical shortcomings but the conceptual ones remained single higher harmonics of the fourier series for example fail to serve as reliable equivalents for roundness evaluation the concept outlined in this paper recognizes three criteria for the evaluation of roundness 1 all curvatures convex as well as concave or plane elements must be considered 2 the positions of morphological elements are significant because salient parts of a particle are more easily abraded than protected ones consequently the curvatures have to be weighted by their relative position on the particle 3 positions and curvatures of morphological elements have to be compared with the particle s ultimate abraded shape which is assumed to be an ellipsoid the ellipsoid reflects the aspect of form or sphericity the distinction between sphericity and roundness is retained because there is no evidence that sphericity changes significantly during transport the measurement is based on the outline of a particle s maximum projection plane which is transformed to a fourier series roundness data are derived from the complete amplitude spectrum the aspect of sphericity is eliminated by subtracting the amplitude spectrum of the best approximating ellipse from the spectrum of the empirical shape the residual amplitudes are normalized and summed in a final step the resulting values are rescaled this guarantees reasonable boundaries and a normal distribution of roundness values the procedure is automated and its efficiency permits the calculation of large samples tests on fluvial and coastal gravel populations demonstrate that the method is sensitive to abrasional wear during all stages of roundness

extraordinary boulder transport by storm waves west of ireland winter 2013 2014 and criteria for analysing coastal boulder deposits abstract before and after photos of supratidal coastal boulder deposits cbd in the west of ireland show that storms in the winter of 2013 2014 transported boulders at elevations up to 29 m above high water and at inland distances up to 222 m among the clasts transported are eighteen weighing more than 50 t six of which exceed 100 t the largest boulder moved during those storms weighs a fairly astonishing 620 t the boulders moved in these recent storms provide pinning points for mapping storm wave energies on coasts their topographic positions mark elevations and distances inland reached by wave energies sufficient to dislocate those specific masses taken together the cbd data reveal general relationships that shed light on storm wave hydrodynamics these include a robust correlation inverse exponential between maximum boulder mass transported and emplacement height above high water the greater the elevation the smaller the maximum boulder size with a dependency exponent of about 0 2 times the elevation in metres there is a similar relationship although with a much smaller rate of change exponent 0 02 between boulder mass and distance inland which holds from the shoreline in to about 120 m coastal steepness calculated as the ratio of elevation to inland distance seems to exert the strongest control with an inverse power law relationship between maximum boulder mass and slope ratio the more gentle the topography the larger the moved boulders quantifying cbd dynamics helps us understand the transmission of wave energies inshore during high energy storm events the transported boulders documented here are larger than many of those interpreted to have been moved by tsunami in other locations which means that boulder size alone cannot be used as a criterion for distinguishing between tsunami and storm emplacement of cbd the biggest blocks up to 620 t are new maxima for boulder mass transported by storm waves we predict however that this record will not last long the 2013 2014 storms were strong but not extreme and there are larger boulders in these deposits that didn t move on this occasion bigger storms will surely move larger clasts and clasts at greater distances from the shoreline these measurements and relationships emphasise the extreme power of storm waves impacting exposed coastlines and require us to rethink the upper limits of storm wave energy at coasts

rock avalanches on a glacier and morainic complex in haut val ferret mont blanc massif italy abstract deposits in upper val ferret mont blanc massif italy have been attributed to glacier advances and to a rock avalanche of 12 september ad 1717 we review evidence for the timing and mode of emplacement of the deposit and present a new geomorphic interpretation and relative and absolute dating to show that the ad 1717 deposit is less extensive than previously thought the landslide was deflected along one side of the valley floor preserving older slope and morainic sediments along the other side an earlier rock avalanche onto the triolet glacier occurred before ad 1000 the deposits of these landslides partly cover older moraine several kilometres downstream from the present glacier front and have affected the glacier regimen and construction of its moraines this study highlights the geomorphic impact of rock avalanches in glacierized high mountains

boulder accumulations related to storms on the south coast of the reykjanes peninsula iceland coastal boulder accumulations are often mentioned in the literature even though their interpretation remains difficult especially along rock coasts affected both by storms and tsunamis studies on the geomorphic impact of such high energy events are actually of great interest since their intensity and frequency are key issues for the future evolution of coasts in the framework of the global change the southwest coast of iceland faces the powerful storms of the north atlantic ocean with wave heights of more than 15 m the probability for past and present tsunamis to hit this coast is very low in this paper we describe boulder accumulations along the volcanic rock coast of reykjanes southwest iceland they consist of cliff top boulders clusters and ridges beaches and boulder fields large boulders up to 70 t in weight have been transported and deposited up to 65 m inland 6 masl the maximum limit of boulder deposition and driftwood was found respectively 210 m and 550 m inland storms appear to be a predominant factor in the geomorphic evolution of reykjanes coasts our observations also give new insight for the interpretation of coastal boulder accumulations processes of erosion and deposition by tsunamis are a rising topic in the literature and the effects of recurrent and powerful storms are neglected

geomorphology and clast assemblages of intertidal beachrock implications for submerged shoreline preservation abstract beachrock may be considered a reliable indicator of sea level in addition to a reliable and recognizable source for onshore movement of beachrock clasts by overwash processes associated with extreme events key to this is its geomorphology and preservation potential both of which are poorly understood here we examine the processes and deposits associated with beachrock breakdown from camurupim ne brazil and compare its preservation to beachrocks found on continental shelves in south africa we study a prominent and continuous 50 60 m wide beachrock complex that crops out along a 10 km stretch of coastline and which mostly comprises 1 5 to 2 m thick trough crossbedded sandstones these have generated large joint bounded blocks that have been transported landwards under extreme energy conditions based on numerical modelling and comparisons to the contemporary wave climate tabular clasts have accumulated as isolated very coarse boulders on the seaward margin small clasts in various topographic traps boulder ridges with large landward and seaward dipping clasts on the uppermost part of the outcrop and subaqueous and subaerial washover fans isolated fine meso boulders emplaced during extreme waves hs ca 12 m exhibit fitted textures and pressure solution contacts pointing to subsequent rocking and shaking smaller clasts in boulder ridges and overwash settings are initially liberated and transported by waves within the annual decadal frequency spectrum deposited on the high points of the outcrop subsequent movement during less extreme wave action progressively transports the clasts across the surface where they are often trapped in the fitted fabric on top of the platform our breakdown model and overall beachrock preservation scheme is consistent with reported seismic signatures of submerged holocene beachrock shorelines beachrock preservation during transgression is strongly influenced by the original sedimentary facies thick trough crossbedded joint bound clasts preserve the former shoreline clasts from the planar units accumulate as washover fans to landwards of the ridge

rocky coasts their role as depositional environments abstract the role of rocky coasts as depositional environments has been generally neglected by rock and depositional coast workers although rock coasts can be hostile sedimentary environments they frequently host a variety of deposits consisting of mixes of boulders and megaclasts to sand and cobbles these deposits include pockets of sand and pebble trapped in topographic depressions or at the foot of scarps and cliffs isolated boulders pocket beaches trapped between headlands and sand to boulder beaches in shallow bays exposed to strong wave action the tectonic setting which is reflected in the degree of geological heterogeneity alongshore together with the wave regime and other elements of the morphogenic environment help to determine the amount and mobility of the sediment and consequently whether it plays an essentially abrasional or protectional role many beaches have a resistant rock foundation which will modulate their response to rising sea level and possibly increased storminess during this century wave refraction and temporal and spatial changes in sediment abrasional and protectional efficacy influence the development of crenulated planforms on coasts with a high degree of geological heterogeneity and possibly on more geologically homogeneous coasts with longshore variations in cliff height or in the amount of sediment theory suggests that these coasts may develop equilibrium planforms with uniform rates of erosion in bays and on headlands or they may undergo a series of cyclical transformations involving alternating increases and decreases in the depth of the bays relative to the headlands