reinterpreting rotherslade gower peninsula implications for last glacial ice limits and quaternary stratigraphy of the british isles rotherslade on the gowerpeninsula in southwales has beenviewed asa keysite for the reconstruction of quaternary depositional environments in the british isles since the early 20th century and certainly since the 1980s the accepted view has been that rotherslade is the most westerly location on the south gower coast where there is in situ basal till exposed and that logically this location marks the position of the lgm ice limit however reinvestigation of the sediments and their architecture and analysis of clast fabrics and thin sections of critical sedimentary units show that none of the exposed sediments has properties diagnostic of subglacial deposition or deformation we postulate here that lgm ice terminated at the western side of swansea bay a few kilometres to the north east of rotherslade and propose that the sedimentary sequence comprises early to middle devensian periglacial sediments overlain by a complex of late devensian ice proximal outwash fan deposits an assemblage of paraglacial debris and finally periglacial mass movement deposits the proposed repositioning of the late devensian ice limit and the associated new subaerial interpretation of the sediments suggest that a reassessment of sedimentary sequences hunts bay western slade and landforms paviland moraine farther west on gower which have attained similar stratigraphical status is now warranted copyright 2008 john wiley sons ltd

hydrologic connections of a stream aquifer vegetation zone in south central platte river valley nebraska field investigation and numerical modeling approaches were used to examine the hydrologic relations between the platte river and the adjacent alluvial aquifer and riparian zone in south central nebraska field methods include direct push techniques for coring and electric logging in the river channel permeameter tests for estimating the hydraulic conductivity of the streambed and monitoring of groundwater levels responding to changes in stream stages and to groundwater evapotranspiration the channel sediments consist mostly of coarse sand and gravels at the study site with large values of horizontal and vertical hydraulic conductivity groundwater in the riparian zone responded nearly simultaneously to the changes in stream stages and diurnal fluctuations of the water table are correlated with fluctuations of stream stage in summer all these indicate a well connected river aquifer vegetation hydrologic system numerical models based on the galerkin finite element method were developed to construct detailed flow nets for examining the changes in the patterns of groundwater flow dynamics resulting from the use of groundwater and stream water by riparian vegetation simulation results suggest that a number of hydrologic factors such as the thickness of the aquifer and vertical anisotropy of aquifer hydraulic conductivity also affect the flow patterns vertical flow is a major component more significant than the horizontal flow below the river and the vegetation zone in the growing season groundwater evapotranspiration can bring deeper groundwater to the water table by hydraulic lift this function of riparian vegetation could cause a complicated situation in an investigation of groundwater quality in riparian zones

the interrelation of glaciotectonic and glaciodepositional processes within the glacial environment abstract in recent years it has been recognised that ice sediment coupling occurred beneath the quaternary ice sheets that advanced over the soft sediments of lowland areas this paper looks in detail at the effects of this coupling on the sediments which results in glaciotectonic deformation and also discusses the interaction of deformation and deposition within the subglacial environment two types of glaciotectonic deformation are discussed that are produced by the active movement of ice 1 proglacial tectonics at the margin which include compressive fold styles such as listric thrusts and faults and open folding 2 subglacial tectonics formed beneath the glacier which include fold styles resulting from simple shear and represent a soft rock purely dynamic shear zone styles of deformation associated with stagnant ice are also investigated we argue that glaciotectonic deformation is a common phenomenon and an integral part of geological record from continental ice sheets it is suggested that zones of deformation within the sediment are related to similar zones of strain in the ice sheet and complex deformation sequences are produced by the superimposition of these differing styles upon one another as the ice sheet advances and retreats it is also argued that subglacial deposition and deformation are related and that on soft beds underformed till is rare whilst deformed till is very common

heterogeneous characteristics of streambed saturated hydraulic conductivity of the touchet river south eastern washington usa traditionally a streambed is treated as a layer of uniform thickness and low saturated hydraulic conductivity k in surface and ground water studies recent findings have shown a high level of spatial heterogeneity within a streambed and such heterogeneity directly affects surface and ground water exchange and can have ecological implications for biogeochemical transformations nutrient cycling organic matter decomposition and reproduction of gravel spawning fish in this study a detailed field investigation of k was conducted in two selected sites in touchet river a typical salmon spawning stream in arid south eastern washington usa in stream slug tests were conducted to determine k following the bouwer and rice method for the upper and lower sites each 50 m long and 9 m wide and roughly 20 m apart a sampling grid of 5 m longitudinally and 3 m transversely was used the slug tests were performed for each horizontal coordinate at 0 3 0 45 0 6 0 75 0 9 1 05 and 1 2 1 35 m depth intervals unless a shallower impenetrable obstruction was encountered additionally water levels were measured to obtain vertical hydraulic gradient vhg between each two adjacent depth intervals results indicated that k ranged over three orders of magnitude at both the upper and lower sites and differed between the two sites at the upper site k did not differ significantly among different depth intervals based on nonparametric statistical tests for mean median and empirical cumulative distribution but the spatial pattern of k varied among different depth intervals at the lower site k for the 0 3 0 45 m depth interval differed statistically from those at other depth intervals and no similar spatial pattern was found among different depth intervals zones of upward and downward water flow based on vhg also varied among different depth intervals reflecting the complexities of the water flow regime detailed characterization of the streambed as attempted in this study should be helpful in providing information on spatial variations of streambed hydraulic properties as well as surface and ground water interaction copyright 2009 john wiley sons ltd

the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

the glacial sequence at killiney se ireland terrestrial deglaciation and polyphase glacitectonic deformation depositional conditions of a complexly deformed glacigenic sequence at killiney bay on the west central margin of the irish sea are reconstructed deformation geometries provide conclusive evidence for polyphase glacitectonic deformation generated by terrestrial ice sheets they are dominated by pure shear simple shear and compressional deformation styles with abundant evidence for glacitectonic induced fracturing and hydrofracturing there is no evidence of subaqueous sediment flow induced deformation and impact deformation iceberg scouring rained out clasts glacigenic diamicton facies associations fa s are interpreted as glacitectonically stacked diachroneous units younging laterally away from palaeo ice margins simultaneous deposition of proximal overconsolidated subglacial tills and distal low viscosity flowtills occurred with the latter being deformed during re advances structural chronology of deformation styles demonstrates polyphase deformation of tills where glacial overriding produced overconsolidated and polyphase deformed subglacial tills from sediments initially deposited as low viscosity flowtills it is proposed that relatively late during deglaciation after retreat of a grounded irish sea ice sheet midland ice invaded the area and deformed and reworked recessional irish sea ice sequences deformation of these recessional sequences led to a heterogeneous stack of polyphase deformed glacigenic sediments with abundant hydrofracturing the killiney bay sequence and other sequences in the southern irish sea basin demonstrate that mis 2 deglaciation took place under terrestrial conditions with lower relative sea levels than present

tsunami recurrence revealed by porites coral boulders in the southern ryukyu islands japan information about past tsunami hazards such as their recurrence interval and magnitude is needed for future disaster prediction and mitigation we examined radiocarbon ages of the surfaces of massive coral boulders cast ashore by past tsunamis in the southern ryukyu islands japan where few historical and geological records of past tsunamis are available we selected only non eroded porites coral boulders along the shoreline because their characteristics make it possible to determine the probable timing of their deposition by tsunamis and we applied a dating method that uses the cumulative probability distributions of large numbers of radiocarbon measurements of those boulders to determine the timing of past tsunamis the results demonstrate that the southern ryukyu islands have repeatedly experienced tsunami events since at least 2400 yr ago with a recurrence interval of 150 400 yr the largest porites tsunami boulder that we studied long axis 9 m which is probably the largest single colony tsunami boulder in the world was displaced by the a d 1771 meiwa tsunami although the 1771 meiwa tsunami was likely the largest event in at least the past 700 yr calculations of current velocity show that all identified tsunamis occurring before 1771 were probably large enough to cause considerable damage to human built structures and loss of life this study demonstrates that by reliably dating large numbers of selected coastal boulders it is possible to ascertain the timing recurrence interval and magnitude of past tsunamis in a location where few adequate survey sites of sandy tsunami deposits exist

vertical dimensions and age of the wicklow mountains ice dome eastern ireland and implications for the extent of the last irish ice sheet abstract patterns of erratic distribution show that the wicklow mountains formerly supported an independent ice cap or ice dome geomorphological mapping of the upper limits of evidence for glaciation ice scoured and moulded bedrock perched boulders and the distribution of features indicative of prolonged periglacial conditions tors frost shattered rock blockfields indicates that along the main axis of high ground erosive warm based ice buried all but the highest 725 m summits and over ran adjacent lower peaks and cols the presence of gibbsite in soil samples from above the inferred upper limit of glacial erosion and its absence in all samples from below this limit is consistent with the geomorphological evidence and implies removal of gibbsitic soils below 725 m by glacial erosion during the last glacial stage cosmogenic 10 be exposure ages for rock outcrops above the inferred upper limit of glacial erosion yield pre last glacial maximum lgm ages of 46 9 3 0 ka to 95 9 6 1 ka whereas rock outcrops on summits over ridden by warm based ice give post lgm ages of 18 2 1 2 to 19 1 1 2 ka all geomorphological and dating evidence thus indicates an lgm age for the ice dome the thickness of the ice dome and limited lateral dispersal of erratics indicate that at the lgm the wicklow ice was encircled by and confluent with thick powerful ice streams moving se from the irish midlands and southwards down the irish sea basin this conclusion is irreconcilable with the traditional view that the last irish ice sheet terminated at the south ireland end moraine but consistent with recent proposals that the last ice sheet was much more extensive than previously believed and over ran the south coast of ireland

differential subsidence of the forearc wedge of the ryukyu nansei shoto arc caused by subduction of ridges on the philippine sea plate abstract the philippine sea plate psp carrying several ridges has been sudbucting under the ryukyu nansei shoto arc since middle miocene because no extensive accretionary prism has been growing along the ryukyu trench the arc provides an opportunity to examine effects of ridge subduction on structure of the forearc wedge and a clue to reconstruct ancient plate motion of the psp that is inferred to have changed between nw and nnw to examine this perspective we clarified structure of the ryukyu forearc wedge based on seismic profiles and bathymetric data and related them to ridge subduction an erosional unconformity between pre neogen and neogene rocks is widely recognized through the ryukyu arc and we divided the forearc wedges into zones i to iv from southwest to northeast by difference of depth of the erosional unconformity we correlated these four zones to the locations of ridge subduction that have been shifting ne or sw along the ryukyu trench zone i is underlain by the largely subsided unconformity and we attributed the structure to tearing of the eurasia plate due to subduction of the western margin of the psp including the luzon arc zone ii consists of a wide terrace on the shallow erosional unconformity and no ridge that was subducting in this zone is known zone iii is characterized by the seaward descending unconformity covered with a thick sequence of neogene sediments and is related to subduction of the nw se trending daito ridge and the e w trending amami plateau zone iv has the deeper unconformity and slope geometry and corresponds to subduction of the nnw sse trending kyushu palau ridge the structure of the ryukyu forearc is consistently related to subduction of ridges on the psp suggesting that the change of the plate motion of the psp can be precisely reconstructed by further detailed survey

glaciomarine deposition around the irish sea basin some problems and solutions reconstructing the depositional processes and setting marine or terrestrial depositional environment of late devensian age glacigenic sediments around the irish sea basin isb is critical for developing an all embracing and consistent glacial model that can account for all observed field evidence identifying episodes of marine and terrestrial glacial deposition from field data is considered the first step in achieving this goal criteria for distinguishing marine and terrestrial glacial environments in the isb include the geomorphology sedimentology and faunal content biofacies of the associated deposits exposures of glacigenic sediments around the isb are very diverse in terms of their morphosedimentary characteristics and associated biofacies and thus inferred depositional processes and setting possible reasons for the diverse geological record include the differing geometry of eastern and western isb coasts time transgressive ice retreat and differential land rebound effects as a result of forebulge collapse and neotectonics poor geochronometric control on ice sheet events has not helped the correlation of isb events with glacial and climatic events elsewhere future investigations of glacial sites around the isb should use an integrated methodological approach involving a range of geomorphological sedimentary and biofacies data and dating control where possible this will help in developing a more precise and holistic late devensian glacial model that is constrained rigorously by field geological evidence copyright 2001 john wiley sons ltd

seafloor morphology and sediment magnetic fabric in a putative 1771 meiwa tsunami source region in the southern ryukyu islands southwest japan

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

sedimentary evidence for deforming bed conditions associated with a grounded irish sea glacier southern ireland along the south coast of ireland a shelly diamict facies the irish sea till has been variously ascribed to subglacial deposition by a grounded irish sea glacier or to glacimarine sedimentation by suspension settling and iceberg rafting observations are presented here from five sites along the south coast to directly address this question at these sites sedimentary evidence is preserved for the onshore advance of a grounded irish sea glacier which glacitectonically disturbed and eroded pre existing sediments and redeposited them as deformation till recession of this irish sea glacier resulted in the damming of ice marginal lakes in embayments along the south coast into which glacilacustrine sedimentation then took place these lake sediments were subsequently glacitectonised and reworked by overriding glacier ice of inland origin which deposited deformation till on top of the succession there is no evidence for deposition of the irish sea diamicts by glacimarine sedimentation at these sites the widespread development of subglacial deforming bed conditions reflected the abundance of fine grained marine and lacustrine sediments available for subglacial erosion and reworking stratigraphical and chronological data suggest that the advance of a grounded irish sea glacier along the south coast occurred during the last glaciation and this is regionally consistent with marine geological data from the celtic sea these observations demonstrate extension of glacier ice far beyond its traditional limits in the celtic sea and on land in southern ireland during the last glaciation and remove the stratigraphical basis for chronological differentiation of surficial glacial drifts and thus the munsterian glaciation in southern ireland copyright 2001 john wiley sons ltd

progressive soft sediment deformation within a subglacial shear zone a hybrid mosaic pervasive deformation model for middle pleistocene glaciotectonised sediments from eastern england this paper presents a hybrid pervasive and mosaic model for the progressive deformation of a stratified diamicton complex in eastern england within an active subglacial shear zone sedimentary evidence from undeformed low strain zones towards the base of the sediment pile indicates that the tectonised sediments were originally deposited as a series of subaqueous flows in a glaciolacustrine basin these sediments have subsequently been deformed during a progressive subglacial shearing event this event is divided into three stages ductile folding and sediment remobilisation d1 brittle faulting in the form of reidel shears d2 and hydrofracturing and sediment remobilisation d3 the dominant control on the pattern and style of deformation appears to relate to the rate of thrust induced till accretion and the aquifer properties and pore water content and or pressure of the deforming sediments

global changes in intensity of the earth s magnetic field during the past 800kyr recent advances in palaeomagnetic and dating techniques have led to increasingly precise records of the relative intensity of the earth s past magnetic field at numerous field sites the compilation and analysis of these records can provide important constraints on changes in global magnetic field intensity and therefore on the earth s geodynamo itself a previous compilation for the past 200 kyr integrated 17 marine records into a composite curve1 with the geomagnetic origin of the signal supported by an independent analysis of 10be production made on different cores2 the persistence of long term features in the earth s magnetic intensity or the existence of long term periodic changes cannot however be resolved in this relatively short time span here we present the integration of 33 records of relative palaeointensity3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 into a composite curve spanning the past 800 kyr we find that the intensity of the earth s dipole field has experienced large amplitude variations over this time period with pronounced intensity minima coinciding with known excursions in field direction reflecting the emergence of non dipole components no stable periodicity was found in our composite record and therefore our data set does not support the hypothesis that the earth s orbital parameters have a direct and strong influence on the geodynamo

subglacial bedform geomorphology of the irish ice sheet reveals major configuration changes during growth and decay the belated realisation that ribbed rogen moraines form such an integral part of irish geomorphology and the piecemeal approach to previous drumlin mapping is probably responsible for the highly contrasting views of palaeoflow patterns of the irish ice sheet using a high resolution 25 m digital elevation model we present morphological maps of a large part 100 100 km of the so called drumlin belt of north central ireland the landforms comprise mostly ribbed moraine much larger than found elsewhere up to 16 km in length which in places are superimposed on each other contrary to most prior assessments we find the bedform record to contain numerous and overlapping episodes of bed formation ribbed moraine drumlins and crag and tails that provide a palimpsest record of changing flow geometries these demonstrate an ice sheet with a centre of mass and flow geometry that changed during growth and decay using distinctive flow patterns and relative age relationships between them we reconstruct ice sheet evolution into four phases during a single glacial cycle in phase 1 early in the glacial cycle scottish and local ice coalesced to form a northeast centred irish ice sheet as it grew its centre of mass migrated southwards culminating in a major n s divide positioned down the east of ireland phase 2 ca last glacial maximum during retreat the centre of mass migrated at least 120 km northwards and became established in northwest ireland and at this point a dramatic bedforming event produced one of the world s largest and most contiguous ribbed moraine fields phase 3 final deglaciation is thought to be by fragmentation into many topographically controlled minor ice caps phase 4 rather than any dramatic or unexpected behaviour the reconstructed phases indicate a relatively predictable pattern of ice sheet growth and decay with changes in centres of mass and does not require major readvances or ice stream events copyright 2001 john wiley sons ltd

glacial deposits in great britain and ireland with the increasing awareness of environmental problems there is a growing desire for a de tailed understanding of superficial deposits in general and glacial deposits in particular this is because these sediments have a profound influence on groundwater protection waste management and nature conservation they are also of vital importance to civil engineering because they provide the foundation for as well as the materials extracted to build our roads and buildings the greater part of the british isles was glaciated at least once during the quater nary era in the regions subjected to glaciation glacial deposits underlie much of the present land surface although there have been many recent publica tions on various quaternary geological topics the present volume is the first dedicated to a detailed assessment of the glacial deposits of britain and ireland after introductory chapters presenting the glacial history the sedimentary sequences in 24 critical regions are discussed these regions include all of ireland the gla ciated area of great britain and the adjoining offshore region of the north sea the controver sial evolution of the irish sea basin during the last glaciation is discussed from various view points a collection of critical topics presented in the later part of the book range from the classification of glacigenic landforms and de posits to the results of geophysical geotechnical and geochemical analyses the book includes 368 figures 40 tables and 51 colour photographs a detailed index and a list of over 1000 references with 45 contributions by 48 scientists this volume represents a truly contemporary view of this field of research to gether with its companion volume the glacial deposits in north west europe this book pro vides an excellent textbook for the advanced student or the amateur as well as an indispen sible source and guidebook for the professional scientist

localized tsunamigenic earthquakes inferred from preferential distribution of coastal boulders on the ryukyu islands japan the occurrence of large earthquakes and tsunamis along the ryukyu trench is a subject of continuing interest the key to which is the long term geological record here we describe the clast size and spatial distributions of 2900 boulders on the reefs of the ryukyu islands japan as markers of paleotsunamis and causative tsunamigenic earthquakes boulders of tsunami origin were observed only at a specific island group at the southern end suggesting the local occurrence of tsunamigenic earthquakes there in contrast in the central to northern ryukyu islands no evidence exists of tsunamis larger than those at the southern end of the ryukyu islands during the past 2000 3000 yr these islands have numerous boulders deposited by storm waves during the past 2300 yr or earlier their spatial distribution has not been disturbed by large tsunamis this suggests that large tsunamis did not strike this area during that period nevertheless these regions are seismically active our study shows that coastal boulder deposits present great potential to not only ascertain the histories and effects of paleotsunamis but also to constrain fault models of the causative earthquakes

blueprint for a coupled model of sedimentology hydrology and hydrogeology in streambeds the streambed constitutes the physical interface between the surface and the subsurface of a stream across all spatial scales surface water groundwater interactions are controlled by the physical properties of the streambed streambed properties such as topography or hydraulic conductivity are continuously altered through erosion and sedimentation processes recent studies from the fields of ecology hydrogeology and sedimentology provide field evidence that sedimentological processes themselves can be heavily influenced by surface water groundwater interactions giving rise to complex feedback mechanisms between sedimentology hydrology and hydrogeology more explicitly surface water groundwater exchanges play a significant role in the deposition of fine sediments which in turn modify the hydraulic properties of the streambed we explore these feedback mechanisms and critically review the extent of current interaction between the different disciplines we identify opportunities to improve current modeling practices for example hydrogeological models treat the streambed as a static rather than a dynamic entity while sedimentological models do not account for critical catchment processes such as surface water groundwater exchange a blueprint for a new modeling framework is proposed that bridges the conceptual gaps between sedimentology hydrogeology and hydrology specifically this blueprint 1 fully integrates surface subsurface flows with erosion transport and deposition of sediments and 2 accounts for the dynamic changes in surface elevation and hydraulic conductivity of the streambed the opportunities for new research within the coupled framework are discussed

spatial and depth variability of streambed vertical hydraulic conductivity under the regional flow regimes this study investigated the influence of the regional flow on the streambed vertical hydraulic conductivity k v within the hyporheic zone in three stream reaches of the weihe river in july 2016 the streambed k v with two connected depths was investigated at each test reach based on the sediment characteristics the three test reaches could be divided into three categories a sandy streambed without continuous silt and clay layer a sandy streambed with continuous silt and clay layer and a silt clay streambed the results demonstrate that the streambed k v mainly decreases with the depth at the sandy streambed without continuous silt and clay layer and increases with the depth at the other two test reaches at the sandy streambed with continuous silt and clay layer where streambed k v mainly decreases with the depth the regional upward flux can suspend fine particles and enhance the pore spacing resulting in the elevated k v in the upper sediment layers at another sandy streambed the continuous silt and clay layer is the main factor that influences the vertical distribution of fine particles and streambed k v an increase in streambed k v with the depth at the silt clay streambed is attributed to the regional downward movement of water within the sediments that may lead to more fine particles deposited in the pores in the upper sediment layers the streambed k v is very close to the bank in the sandy streambed without continuous silt and clay layer and the channel centre in the other two test reaches differences in grain size distribution of the sediments at each test reach exercise a strong controlling influence on the streambed k v this study promotes the understanding of dynamics influencing the interactions between groundwater and surface water and provides guidelines to scientific water resources management for rivers

the last climatic cycles in western europe a comparison between long continuous lacustrine sequences from france and other terrestrial records abstract during the last two decades numerous studies applied to various continental deposits have highly improved the knowledge of environmental changes in western europe during the last climatic cycles here we review a set of available data and try to correlate and compare the three long lacustrine sequences from france la grande pile les echets and le velay with other west european discontinuous limnic deposits fluvial systems and l ss accumulations limnic sequences provide the best records of the last interglacial and early glacial ca 125 75 kyr allowing a clear picture of environmental changes during this interval nevertheless there are divergent interpretations on the timing and climate regime of the last interglacial during the last glacial in the north atlantic deep sea cores and greenland ice cores short term abrupt climatic fluctuations bond events dansgaard oeschger events which are poorly or partly reflected on the continent have been recognised the classical subdivision in a lower ca 75 55 kyr very cold middle ca 55 29 kyr cold and upper pleniglacial ca 29 15 kyr very cold is confirmed both by limnic and terrestrial sequences in the rhine valley north eastern france belgium and the netherlands subcontinuous l ss accumulation river systems and associated periglacial features provide quantitative climate reconstructions that are compared with those obtained from limnic sequences interstadial events may be correlated with the major warm oscillations of the grip core during the upper pleniglacial no clear vegetation changes are apparent from lacustrine pollen sequences whereas thick l ss accumulations have registered a succession of climatic changes the timing of the lateglacial warming is now well documented from rare annually laminated lake sediments

push moraines and glacier contact fans in marine and terrestrial environments the local climatic regime and the mass balance state are important determinants of the dynamics of terrestrial and marine glacier fronts which in turn determine the sediments and landforms produced at the glacier front many modern glaciers undergoing overall retreat in areas of maritime climate produce winter push moraines during a late winter readvance followed by a summer retreat whilst in more continental regions no significant winter readvance occurs and annual push moraines are absent the frontal dynamics which lead to these changes are analysed and the form structure sequence and field relations of both terrestrial and marine push moraines are described from iceland spitsbergen and baffin island long term changes in mass balance leading to major glacier advances or readvances also generate large push moraines in terrestrial environments push moraine formation is accompanied by uplift rejuvenation and down cutting of outwash systems whose sediments become closely associated with glaciotectonic structures which permit pre syn and post tectonic sequences to be identified the development of ice marginal fan moraine complexes is modelled as a function of the relative magnitude of two parameters the velocity of ice movement and the calving rate a high ice velocity just exceeded by the calving rate gives closely spaced push moraines and confluent ice marginal fans a high velocity far exceeded by the calving rate produces closely spaced moraines but separate ice marginal fans a low ice velocity in combination with a high calving rate results in well separated and feebly developed push moraines while a low ice velocity and a low calving rate produces feeble push moraines and coalescent fans

glaciomarine sediments of the isle of man as a key to late pleistocene stratigraphic investigations in the irish sea basin the northern part of the isle of man in the central irish sea basin is identified as a raised marine foreland containing the largest subaerial exposure of last glaciation marine and glaciomarine sediments yet recognized on the british continental shelf a large push ridge that crosses the foreland identifies a major ice limit the ridge divides the foreland stratigraphy into a coarsening upward marine sequence of pelagic muds with dropstones sand and gravel to the south from offlapping stratified and massive sandy diamict assemblages overlying glaciotectonized marine sediments to the north coarse grained diamicts are argued to form part of a push ridge subaqueous outwash depositional system deposited when processes of suspension deposition density underflow ice rafting highly variable traction current activity and sediment gravity flow were operative adjacent to a grounded marine ice margin the identification of large offshore submarine banks aligned parallel to the bride moraine suggests that construction of the push ridge subaqueous outwash depositional system may have been repeated during ice recession this and published descriptions of other irish sea tills indicate that analogous structures and sediments are present offshore and around the irish sea basin

subglacial water escape structures and till structures slettjokull iceland beyond slettjokull the north part of the ice cap m rdalsjokull south iceland an undulating till plain is dissected by meltwater streams throughout a transect from the ice margin to the 1900 ice marginal moraine a distance of about 1 2 km finely laminated wedge shaped water escape structures wes are present originating in the till and disappearing down ice into the underlying sands and fine gravels a second set of much smaller and deformed black wes occurring within the till has been produced by upward injection into the till as a response to stiffening of the till after dewatering by the downward developing wes at present the toe of the glacier is frozen to its bed and the frozen bed material is more than 2 m thick during the relatively cold period around the turn of the century and until the late 1920s a similar submarginal body of permafrost must have existed the sequence reveals that subglacial meltwater attributed to drainage following the 1918 katla eruption was blocked by a frozen glacier toe causing the formation of water escape structures subsequently glacier flow deformed the substratum and produced the threefold division of the till bed the study has important implications for theories envisaging subglacial floods because it demonstrates that it is very difficult for temperate glaciers with a temporary frozen bed in the toe region to retain subglacial meltwater copyright 1999 john wiley sons ltd

heat tracing of heterogeneous hyporheic exchange adjacent to in stream geomorphic features there are many field techniques used to quantify rates of hyporheic exchange which can vary in magnitude and direction spatially over distances of only a few metres both within and between morphological features we used in stream mini piezometers and heat transport modelling of stream and streambed temperatures to quantify the rates and directions of water flux across the streambed interface upstream and downstream of three types of in stream geomorphic features a permanent dam a beaver dam remnant and a stream meander we derived hyporheic flux estimates at three different depths at six different sites for a month and then paired those flux rates with measurements of gradient to derive hydraulic conductivity k of the streambed sediments heat transport modelling provided consistent daily flux estimates that were in agreement directionally with hydraulic gradient measurements and also identified vertical heterogeneities in hydraulic conductivity that led to variable hyporheic exchange streambed k varied over an order of magnitude 1 9 10 6 to 5 7 10 5 m s average rates of hyporheic flux ranged from static q 0 02 m day to 0 42 m day heat transport modelling results suggest three kinds of flow around the dams and the meander copyright 2010 john wiley sons ltd

vertical movement of water in a high plains aquifer induced by a pumping well field observation and numerical simulations were carried out to evaluate the hydraulic relationship between the shallow and deep aquifer of a high plains aquifer system in which shallow and deep aquifers are separated by an aquitard pumping from the lower aquifer resulted in a small drawdown in the upper aquifer and a larger drawdown in the aquitard pumping from the shallow aquifer caused a small drawdown in the aquitard and the deep aquifer analysis of pumping test data gives the values of the hydraulic conductivity of the aquitard and the deep aquifer long term observation of groundwater levels in the shallow and deep aquifers showed that a strong downward hydraulic gradient was maintained during an irrigation season numerical simulations were used to calculate the induced leakage of water from the shallow to the deep aquifer water budget analyses suggested that after pumping continues for a couple of days the leakage from the overlying layers begins to supply the majority of the withdrawal from the deep aquifer however the induced leakage from the upper shallow aquifer can travel only a few meters into the aquitard and it can not reach the lower aquifer during a 90 day pumping period the major portion of the induced leakage occurred during the pumping period but a small leakage can continue as a residual effect after the pumping period the vertical hydraulic conductivity of the aquitard plays a major role in partitioning the ratio of the induced leakage for the pumping and after pumping periods

iceberg drop dump and grounding structures from pleistocene glacio lacustrine sediments scotland abstract dropstone dump and grounding structures resulting from the melt out of debris contained in floating and grounded icebergs are described from a pleistocene ice marginal glacio lacustrine sequence in scotland dropstones display bending penetration rucking and complete rupture of stratum occurring beneath them and onlap above them with the degree of deformation varying as a function of the size shape and axial disposition of the clast and of the sediment type into which they fell dump structures are conical mounds of gravel or diamict formed by the break up and overturning of dirt laden icebergs and the consequent release of large quantities of debris to the lake floor grounding structures are caused by the grounding of icebergs the down warping of underlying lake floor se iment and the subsequent in situ melt out of contained debris to form isolated troughs of diamict

electrical and hydraulic vertical variability in channel sediments and its effects on streamflow depletion due to groundwater extraction summary the stratification of channel sediments and their vertical hydraulic conductivity kv are important hydrologic information in the analysis of stream aquifer interactions this paper describes the use of direct push technology to generate electrical conductivity ec logs and collect continuous sediment cores beneath river channels the techniques were applied to nine study sites along a 130 km reach of the platte river in southeast nebraska ec logs for the channel surface down to as much as 24 m below the channel surface indicate that the channel sediments in the western part of the reach consist predominantly of sand and gravel low kv silt clay layers occur in the rest of the reach these silt clay layers are either interbedded with sand and gravel or occur as a major unit within the channel sediments as a result the values of kv determined from the sediment cores can vary by four to five orders of magnitude in the same vertical profile of channel sediments at a number of sites the river channel is not lined by a low kv layer at the surface instead the kv values for the top part of channel sediments were consistently greater than kv values for sediments in deeper parts they show a decreasing tendency with the depth this paper also analyzes the effect of low kv layers within channel sediments on streamflow depletion induced by groundwater pumping simulation results suggest that the effectiveness of low kv layers on the calculation of streamflow depletion depends on their depth thickness vertical permeability the length along the channel and the width within the channel as well as the extension into the aquifer on both sides of the river a low kv layer present at the channel surface seems to be the most effective hydrologic feature in reducing the hydrologic connection of stream aquifer a 2008 elsevier b v all rights reserved

the interpretation and classification of subglacially deformed materials abstract a general classification of subglacially deformed materials is proposed based on sediment properties and their relationship to styles of subglacial strain deformation till is defined as homogenized usually diamictic material formed by glacially induced shear of subsole materials three types are recognized type a formed by pervasive ductile deformation type b formed by brittle shear and comminution till produced by the reduction of void space by in situ crushing and abrasion the term glacitectonite is adopted for materials that have undergone subglacial shear but retain some of the structural characteristics of the parent material original structures may be truncated by glacitectonic fabric elements type a or distorted but not truncated type b the principles of strain and material response particle orientation mechanisms fabric development and drainage conditions are reviewed examples of deformation tills and glacitectonites from breidamerkurjokull iceland slettmarkbreen norway loch lomond scotland and east yorkshire england are used to illustrate the nature of subglacially deformed materials and their relationship to former subglacial strain and drainage conditions the geologic evidence suggests a continuum of bed strengths can be recognized in deforming substrata ranging from high strength low strain type b deformation till and comminution till to low strength high strain type a deformation till

nitrate concentration changes at the groundwater surface water interface of a small cumbrian river for an experimental field site at the river leith united kingdom the spatial and temporal distribution of nitrate was observed along the upwelling flow path from groundwater to surface water the study was carried out during baseflow conditions for two successive years for two contrasting stream reaches the physical and chemical characteristics of streambed sediment cores were analysed together with observations of hydraulic head dissolved oxygen redox and nitrogen speciation using an array of nested streambed piezometers pressure head gradients in the streambed piezometers showed that upwelling flows dominated the exchange between groundwater and surface water throughout the observation period infiltration of surface water into the streambed was not evident at depths below 10 cm pore water collected from sediment cores and streambed piezometers showed spatially variable redox conditions and nitrogen speciation within up to 100 cm depth in the streambed in particular nitrate concentrations along upwelling flow paths appeared to follow two opposite trends with both decreasing and increasing nitrate concentrations being observed at different points in the experimental reach the observed changes of nitrate concentrations in the upwelling groundwater are restricted to the loose superficial sediments that overlay the sandstone bedrock and do not appear to coincide with surface water groundwater mixing in the streambed the magnitude of variation in nitrate concentration along the upwelling flow path to the streambed appears to be governed by the sediment structure and characteristics in the two contrasting field sites the results suggest that changes in redox status and pore water nitrate concentrations in the hyporheic may occur at depths greater than surface water infiltration into the streambed and may call for new conceptual understanding of hyporheic nutrient transformations

constraints on backstop geometry of the southwest ryukyu subduction based on reflection seismic data abstract based on the analysis of 45 seismic reflection profiles the top of the ryukyu arc basement is mapped in the forearc region east of taiwan the ryukyu arc slope dips 10 trenchward while beneath the forearc basins the arc basement shows a series of morphologic along arc highs and lows one of the basement highs the nanao basement rise has been described as an area uplifted by the subduction of the gagua ridge the other one the hoping basement rise is suggested in this study to be an uplifted feature caused by the subduction or the underplating of some local asperity the nature of this asperity could either be a detached block of the luzon arc an isolated seamount or some material removed from the frontal part southernmost extremity of the ryukyu margin from seismic reflection profiles we infer that the right lateral transcurrent fault system located at the rear of the accretionary wedge defines the surface projection of the southern termination of the ryukyu arc basement two crustal sections across the ryukyu subduction system demonstrate that the backstop terminates in the form of a near vertical wall with its height over 5 km such an unusual geometry could be produced by crustal truncation at the toe of the backstop

spatial variability in streambed hydraulic conductivity of contrasting stream morphologies channel bend and straight channel streambed hydraulic conductivity is one of the main factors controlling variability in surface water groundwater interactions but only few studies aim at quantifying its spatial and temporal variability in different stream morphologies streambed horizontal hydraulic conductivities kh were therefore determined from in stream slug tests vertical hydraulic conductivities kv were calculated with in stream permeameter tests and hydraulic heads were measured to obtain vertical head gradients at eight transects each comprising five test locations in a groundwater dominated stream seasonal small scale measurements were taken in december 2011 and august 2012 both in a straight stream channel with homogeneous elevation and downstream of a channel meander with heterogeneous elevation all streambed attributes showed large spatial variability kh values were the highest at the depositional inner bend of the stream whereas high kv values were observed at the erosional outer bend and near the middle of the channel calculated kv values were related to the thickness of the organic streambed sediment layer and also showed higher temporal variability than kh because of sedimentation and scouring processes affecting the upper layers of the streambed test locations at the channel bend showed a more heterogeneous distribution of streambed properties than test locations in the straight channel whereas within the channel bend higher spatial variability in streambed attributes was observed across the stream than along the stream channel copyright 2014 john wiley sons ltd

the spatial variability of streambed vertical hydraulic conductivity in an intermittent river northwestern china streambed vertical hydraulic conductivity k plays an important role in river water and groundwater interaction the k at the ten transects ts1 ts10 at the donghe river an intermittent river in the ejina basin northwestern china was measured to investigate its spatial variation based on the sediment characteristics and vertical hydraulic conductivity of the riverbed the entire riverbed of the donghe river could be divided arbitrarily into two parts an upper part starting at ts1 and ending at ts9 without an obvious and continuous clogging layer and a lower part the remaining riverbed with an obvious and continuous clogging layer in the upper part although the k varied with depth within the 0 30 cm layer the variability with depth could be ignored in practice the arithmetic mean k of the upper part ranged from 12 to 27 6 m day three orders of magnitude larger than that of the lower part 0 06 m day the change of k along the river cross section was significant and larger values of k often occurred in the parts of the channels with greater water depth however there were no consistent patterns of the variability of k at transects across the river which was influenced by the variation in streambed characteristics the results could be useful for the estimation of groundwater recharge from river and groundwater resources evaluation in the ejina basin

under pressure clastic dykes in glacial settings abstract clastic dykes are widespread in glacial settings and we provide examples from switzerland patagonia iceland and the antarctic ranging in age from tertiary to recent on the basis of these examples we establish the general characteristics of clastic dykes and proceed to establish the direction of propagation on sedimentological grounds micromorphological analysis reveals that sedimentation in the dykes is ruled by pressure gradients and that ordinary sedimentological rules do not apply clastic dykes act like safety valves in the subglacial hydraulic system their development depends on specific subglacial conditions like water volume and pressure the nature of the bed sediments or bedrock and the hydraulic properties of the bed a number of scenarios for clastic dyke development are presented as there is not just one set of conditions under which they form development of clastic dykes affects glaciodynamics like velocity and surging and landform formation like till thickness and bedrock disruption

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

consolidation of sediments by glaciers relations between sediment geotechnics soft bed glacier dynamics and subglacial ground water flow a theory of subglacial consolidation is developed which shows how the meltwater flux beneath a glacier leaves a consolidation signature from which many important glacier dynamic properties can be inferred conditions under which water is discharged through channels or in a thin film at the ice bed interface or by ground water flow are discussed and it is concluded that glaciers flowing over aquifers of high transmissibility can induce deep circulation patterns quite different from non glacial circulation

variation in reach scale hydraulic conductivity of streambeds abstract streambed hydraulic conductivity is an important control on flow within the hyporheic zone affecting hydrological ecological and biogeochemical processes essential to river ecosystem function despite many published field measurements few empirical studies examine the drivers of spatial and temporal variations in streambed hydraulic conductivity reach averaged hydraulic conductivity estimated for 119 surveys in 83 stream reaches across continental france even of coarse bed streams are shown to be characteristic of sand and finer sediments this supports a model where processes leading to the accumulation of finer sediments within streambeds largely control hydraulic conductivity rather than the size of the coarse bed sediment fraction after describing a conceptual model of relevant processes we fit an empirical model relating hydraulic conductivity to candidate geomorphic and hydraulic drivers the fitted model explains 72 of the deviance in hydraulic conductivity and 30 using an external cross validation reach hydraulic conductivity increases with the amplitude of bedforms within the reach the bankfull channel width depth ratio stream power and upstream catchment erodibility but reduces with time since the last streambed disturbance the correlation between hydraulic conductivity and time since a streambed mobilisation event is likely a consequence of clogging processes streams with a predominantly suspended load and less frequent streambed disturbances are expected to have a lower streambed hydraulic conductivity and reduced hyporheic fluxes this study suggests a close link between streambed sediment transport dynamics and connectivity between surface water and the hyporheic zone

effects of hyporheic processes on streambed vertical hydraulic conductivity in three rivers of nebraska 1 streambed hydraulic conductivity is of great importance in the analysis of stream aquifer interactions and stream ecosystems we investigated streambed vertical hydraulic conductivity kv with two connected depths in three rivers of nebraska our results demonstrated that streambed kv in the upper sediment layer was much higher than that in the sediment of the lower layer we speculate that hyporheic processes can result in larger streambed kv in the upper layer specifically water exchange through upwelling and downwelling zones can lead to bigger pore spaces and a more unconsolidated structure of sediments in the upper layer the upward movement of gas produced by redox processes can loosen the sediments and further enlarge pore spaces in the upper layers also permeability can increase as a result of expanded pore spaces caused by invertebrate activities in the upper part of streambed the higher kv will likely enhance exchange processes between stream and sediments

theory of glacial erosion transport and deposition as a consequence of subglacial sediment deformation a theory of erosion transport and deposition of unlithified sediments by glaciers is presented it predicts the large scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle together with the resultant intensity of large scale lincations drumlins which will be incised in the landscape the theory also predicts the dispersal patterns of subglacial lithologies together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till it predicts major erosional discontinuities within tills and the formation of boulder pavements it suggests that the dominant proportion of the lowland tills produced by pleistocene mid latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine grained the theory is based on an analysis of glacier dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition

statistical and geostatistical features of streambed hydraulic conductivities in the platte river nebraska this paper presents streambed hydraulic conductivities of the platte river from south central to eastern nebraska the hydraulic conductivities were determined from river channels using permeameter tests the vertical hydraulic conductivities k v from seven test sites along this river in south central nebraska belong to one statistical population its mean value is 40 2 m d however the vertical hydraulic conductivities along four transects of the ashland test site in eastern nebraska have lower mean values are statistically different from the k v values in south central nebraska and belong to two different populations with mean values of 20 7 and 9 1 m d respectively finer sediments carried from the loup river and elkhorn river watersheds to the eastern reach of the platte river lowers the vertical hydraulic conductivity of the streambed correlation coefficients between water depth and k v values along a test transect indicates a positive correlation a larger k v usually occurs in the part of channel with deeper water experimental variograms derived from the vertical hydraulic conductivities for several transects across the channels of the platte river show periodicity of spatial correlation which likely result from periodic variation of water depth across the channels the sandy to gravelly streambed contains very local silt and clay layers spatially continuous low permeability streambed was not observed in the river channels the horizontal hydraulic conductivities were larger than the vertical hydraulic conductivities for the same test locations

an investigation of subglacial shear zone processes from weybourne norfolk uk abstract the glacial sediments of north norfolk are a type site for subglacial deforming bed sediments this investigation focussed on subglacial shear zone process at the field and thin section scale in order to understand subglacial processes as well as considering the implications for regional stratigraphies the sandy and chalky tills from three sites within 1 km at weybourne norfolk showed evidence for subglacial deformation associated with simple shear producing extension compression and rotation it was demonstrated how these processes interacted to cause chalk fragmentation and predictable fabric strengths dependant on sorting and grain size it is suggested that the marly drift is a diachronous unit and the resultant stratigraphy at weybourne reflects one deformation till resulting from a series of ice advances but with a lithology derived from the local chalk bed rock with some far travelled erratics which have undergone different degrees of chalk fragmentation reflecting the nature and duration of the subglacial deformation

sedimentary facies and depositional architecture of ice contact glaciomarine systems abstract the characteristics of ice contact glaciomarine systems are reviewed based on a range of weichselian and holocene examples from the fjordal basins in norway and svalbard these depositional systems occur as large morphological ridges end moraines including push moraines which are coarse grained and show large scale foreset bedding the paper addresses some of the major problems with regard to the recognition classification and stratigraphic analysis of these systems the ice proximal glaciomarine systems are classified here into three categories 1 ice contact submarine fans 2 ice contact deltas and 3 glaciofluvial deltas this classification integrates morphological and sedimentological criteria and renders these glaciomarine systems not only easier to recognize in the stratigraphic record but also possible to compare with common non glacial deltaic systems the emphasis is on the criteria for the recognition of the ice contact glaciomarine systems i e ice contact fans and ice contact deltas and their discrimination from common gilbert type deltas and fan deltas the review further focuses on ice contact glaciomarine systems as highly sensitive recorders of glacier dynamics and climatic fluctuations it is shown that both the periods of ice front stability and changes in the ice front position as well as the magnitude and rate of those changes are all recorded in the ice contact depositional system the sedimentary record further reflects glacio isostatic sea level changes and local palaeogeography a new conceptual model is suggested which places these ice contact glaciomarine systems in a dynamic stratigraphic context the model integrates sedimentary facies and their depositional architecture in an allostratigraphic framework and is meant to be a guide for the analysis of the sedimentary record of ice contact systems

new data for the last glacial maximum in great britain and ireland abstract understanding the history of the british and irish ice sheet biis at the last glacial maximum lgm has been advanced by new approaches in particular by cosmogenic nuclide surface exposure dating aminostratigraphy of shelly glacial deposits ams radiocarbon dating and the evidence from continental margin marine cores all of which supersede the previously weak geochronologic control it was formerly believed that great britain and ireland was largely ice free between the last interglacial oxygen isotope sub stage 5e and the late devensian when the lgm occurred as such the biis was effectively out of phase with laurentide and scandinavian ice sheets as well as inferences of ice volume from oxygen isotope stratigraphy the biis during the late devensian maximum was also perceived as having been relatively stationary new evidence shows that the lgm was an important event during the evolution of an earlier biis when the extent of ice was greater repeated iceberg rafting events over the past 50 ka are shown by marine cores while the derivative inference of numerous corresponding glacial advances is supported by several clusters of 36 cl ages on glaciated surfaces and glacial boulders that are indicative of deglacial events between 40 and 12 ka these appear to be associated with heinrich events the earliest being inferred as heinrich 4 at about 40 ka during this advance the biis and scandinavian ice sheet sis were in contact and all of ireland was glaciated the ice sheet appears to have fluctuated several times between 40 and 25 ka although evidence for this is poorly preserved but the 36 cl and 14 c evidence is clear that the biis reached its lgm maximum size about 22 ka soon after heinrich event 2 when the biis and sis were not in contact one cluster of 36 cl and 14 c ages at 21 4 1 3 ka records an initial pulse of deglaciation that was followed by extensive deglaciation about 17 4 0 4 ka just before heinrich event 1 when the ice sheet readvanced contrary to previous views the biis probably existed throughout much of devensian time as a mobile and sensitive ice sheet during which the lgm advance was but one important event in places glacial deposits of the earlier devensian glaciation have previously been incorrectly identified as products of the later lgm glaciation

magnetic paleointensity stratigraphy and high resolution quaternary geochronology successes and future challenges abstract magnetic paleointensity stratigraphy is used to detect variations in the strength of earth s ancient magnetic field paleointensity studies have demonstrated that a dominantly dipolar geomagnetic signal can be recorded in a globally coherent manner in different types of sediments and in non sedimentary archives including ice core records and marine magnetic anomaly profiles the dominantly dipolar nature of geomagnetic paleointensity variations provides a global geophysical signal that has come to be widely used to date quaternary sediments despite the many successful applications of paleointensity assisted chronology the mechanisms by which sediments become magnetized remain poorly understood and there is no satisfactory theoretical foundation for paleointensity estimation in this paper we outline past successes of sedimentary paleointensity analysis as well as remaining challenges that need to be addressed to place such work on a more secure theoretical and empirical foundation we illustrate how common concepts for explaining sedimentary remanence acquisition can give rise to centennial to millennial offsets between paleomagnetic and other signals which is a key limitation for using paleointensity signals for geochronology our approach is intended to help non specialists to better understand the legitimate uses and limitations of paleointensity stratigraphy while pointing to outstanding problems that require concerted specialist efforts to resolve

ams c 14 dating of deglacial events in the irish sea basin and other sectors of the british irish ice sheet sedimentary sequences deposited by the decaying marine margin of the british irish ice sheet biis record isostatic depression and successive ice sheet retreat towards centres of ice dispersion radiocarbon dating by accelerator mass spectrometry ams of in situ marine microfaunas that are commonly associated with these sequences constrain the timing of glacial and sea level fluctuations during the last deglaciation enabling us to evaluate the dynamics of the bus and its response to north atlantic climate change here we use our radiocarbon dated stratigraphy to define six major glacial and sea level events since the last glacial maximum 1 initial deglaciation may have occurred 18 3 kyr c 14 bp along the northwestern irish coast in agreement with a deglacial age of similar to 22 cl 36 kyr bp for southwestern ireland ice retreated to inland centres and areas of transverse moraine began to form across the north irish lowlands 2 channels cut into glaciomarine deglacial sediments along the western irish sea coast are graded to below present sea level identifying a fall of relative sea level rsl in response to isostatic emergence of the coast 3 marine mud that rapidly infilled these channels records an abrupt rise in global sea level of 10 15 m similar to 16 7 c 14 kyr bp that flooded the irish sea coast and may have triggered deglaciation of a marine based margin in donegal bay 4 intertidal boulder pavements in dundalk bay indicate that rsl similar to 15 0 c 14 kyr bp was similar to present 5 a major readvance of all sectors of the biis occurred between 14 and 15 kyr 14 c bp which overprinted subglacial transverse moraines and delivered a substantial sediment flux to tidewater ice sheet margins this event the killard point stadial indicates that the bus participated in heinrich event 1 6 subsequent deposition of marine muds on drumlins 12 7 c 14 kyr bp indicates isostatic depression and attendant high rsl resulting from the killard point readvance these events identify a dynamic biis during the last deglaciation as well as significant changes in rsl that reflect a combination of isostatic loading and eustatic changes in global sea level c 2005 elsevier ltd all rights reserved

source fault model of the 1771 yaeyama tsunami southern ryukyu islands japan inferred from numerical simulation the 1771 yaeyama tsunami is successfully reproduced using a simple faulting model without submarine landslide the yaeyama tsunami m 7 4 which struck the southern ryukyu islands of japan produced unusually high tsunami amplitudes on the southeastern coast of ishigaki island and caused significant damage including 12 000 casualties previous tsunami source models for this event have included both seismological faults and submarine landslides however no evidence of landslides in the source has been obtained despite marine surveying of the area the seismological fault model proposed in this study describing a fault to the east of ishigaki island successfully reproduces the distribution of tsunami runup on the southern coast of the ryukyu islands the unusual runup heights are found through the numerical simulation attributable to a concentration of tsunami energy toward the southeastern coast of ishigaki island by the effect of the shelf to the east thus the unusual runup heights observed on the southeastern coast of ishigaki island can be adequately explained by a seismological fault model with wave ray bending on the adjacent shelf

fault model of the 1771 yaeyama earthquake along the ryukyu trench estimated from the devastating tsunami 1 the 24 april 1771 yaeyama earthquake generated a large tsunami with a maximum runup of 30 m causing significant damage in south ryukyu japan despite the weak ground shaking previously proposed mechanisms of the tsunami include intraplate faulting or submarine landslide in the forearc slope in this study i estimate the fault parameters of the 1771 earthquake by numerically computing the tsunami heights and comparing them with the recorded heights the result indicates that the source fault of the tsunami is very close to the ryukyu trench the results are consistent with a thrust faulting earthquake that had a fault width of less than 50 km the 1771 yaeyama tsunami was caused by a tsunami earthquake mw 8 0 that occurred in the subducted sediments beneath the accretionary wedge

a mega splay fault system and tsunami hazard in the southern ryukyu subduction zone abstract in april 1771 a subduction earthquake generated a great tsunami that struck the south ryukyu islands and killed 12 000 people whereas its mechanism is still enigmatic nakata and kawana 1995 nakamura 2006 matsumoto et al 2009 in this paper we show its probable source on a mega splay fault system existing along the southern ryukyu forearc analyses of deep multi channel seismic reflection profiles indicate that the mega splay fault system is rising from the summit of a 1 km high ridge situated at a 5 landward dipping plate interface an outer ridge marks the seafloor outcrop of the splay fault system and separates the landward inner wedge and the oceanward outer wedge the inner wedge is uplifting and exhibits widespread normal faulting while the outer wedge shows folded structures the mega splay fault system is parallel to the ryukyu trench east of 125 5 e and is estimated to be 450 km long the origin of this south ryukyu mega splay fault system is ascribed to a resistant subduction of the elevated transverse ridges associated with the subducting portion of the trench parallel luzon okinawa fracture zone in contrast no similar splay fault is found west of 125 5 e where the oblique subduction has produced large shear zones along the south ryukyu forearc we infer that a thrust earthquake linked to the mega splay fault system is responsible for the south ryukyu tsunami however another possible scenario of generating a large tsunami affecting the south ryukyu islands is that the subducted ridge in the western end of the mega splay fault system nucleated a large earthquake and simultaneously triggered the 100 km long e w trending strike slip fault west of 125 5 e and induced a southward dipping tsunami genic subsidence in any case after a quiescence of 241 yr a large earthquake and tsunami is anticipated in the south ryukyu forearc in the near future

deformation styles as a key for interpreting glacial depositional environments lithostratigraphical and lithofacies approaches used to interpret glacial sediments often ignore deformation structures that can provide the key to environment of formation we propose a classification of deformation styles based on the geometry of structures rather than inferred environment of formation five styles are recognised pure shear p simple shear s compressional c vertical v and undeformed u these dictate the first letter of the codes the remaining letters conveying the evidence this information can be used to reconstruct palaeostress fields and to infer physical properties of sediments when they deformed individual structures are not diagnostic of particular environments but the suite of structures their relative scale stratigraphical relationships and orientation relative to palaeoslopes and to palaeoice flow directions can be used to infer the environment in which they formed this scheme is applied at five sites in west wales the typical succession is interpreted as subglacial sediments overlain by meltout tills flow tills and sediment flows paraglacial redistribution of glacial sediments is widespread large scale compressional deformation is restricted to sites where glaciers readvanced large scale vertical deformation occurs where water was locally ponded near the ice margin there is no evidence for glaciomarine conditions copyright 2003 john wiley sons ltd

depth dependent hydraulic conductivity distribution patterns of a streambed characterization of streambed hydraulic conductivity from the channel surface to a great depth below the channel surface can provide needed information for the determination of stream aquifer hydrologic connectedness and it is also important to river restoration however knowledge on the streambed hydraulic conductivity for sediments 1 m below the channel surface is scarce this study describes a method that was used to determine the distribution patterns of streambed hydraulic conductivity for sediments from channel surface to a depth of 15 m below the method includes geoprobe s direct push techniques and permeameter tests direct push techniques were used to generate the electrical conductivity ec logs and to collect sequences of continuous sediment cores from river channels as well as from the alluvial aquifer connected to the river permeameter tests on these sediment cores give the profiles of vertical hydraulic conductivity k v of the channel sediments and the aquifer materials this method was applied to produce k v profiles for a streambed and an alluvial aquifer in the platte river valley of nebraska usa comparison and statistical analysis of the k v profiles from the river channel and from the proximate alluvial aquifer indicates a special pattern of k v in the channel sediments this depth dependent pattern of k v distribution for the channel sediments is considered to be produced by hyporheic processes this k v distribution pattern implied that the effect of hyporheic processes on streambed hydraulic conductivity can reach the sediments about 9 m below the channel surface copyright c 2010 john wiley sons ltd

subglacial till formation sedimentary characteristics and classification we review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members processes of deformation flow sliding lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton the dominance of any one subglacial process varies both spatially and temporally giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation deposition at the ice bed interface we recommend that while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes genetic fingerprinting of subglacial tills should be less process specific and till classification must reflect the range of products encompassed by the subglacial till production continuum glacial geologists can presently unequivocally identify a glacitectonite rock or sediment that has been deformed by subglacial shearing deformation but retains some of the structural characteristics of the parent material b subglacial traction till sediment deposited by a glacier sole either sliding over and or deforming its bed the sediment having been released directly from the ice by pressure melting and or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing and support the theoretical case for c melt out till sediment released by the melting of stagnant or slowly moving debris rich glacier ice and directly deposited without subsequent transport or deformation because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions the patterns of which change temporally and spatially it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone

comparison of vertical hydraulic conductivity in a streambed point bar system of a gaining stream summary vertical hydraulic conductivities k v of both streambed and point bars can influence water and solute exchange between streams and surrounding groundwater systems the sediments in point bars are relatively young compared to the older sediments in the adjacent aquifers but slightly older compared to submerged streambeds thus the permeability in point bar sediments can be different not only from regional aquifer but also from modern streambed however there is a lack of detailed studies that document spatial variability of vertical hydraulic conductivity in point bars of meandering streams in this study the authors proposed an in situ permeameter test method to measure vertical hydraulic conductivity of the two point bars in clear creek nebraska usa we compared the k v values in streambed and adjacent point bars through 45 test locations in the two point bars and 51 test locations in the streambed the k v values in the point bars were lower than those in the streambed kruskal wallis test confirmed that the k v values from the point bars and from the channel came from two statistically different populations within a point bar the k v values were higher along the point bar edges than those from inner point bars grain size analysis indicated that slightly more silt and clay particles existed in sediments from inner point bars compared to that from streambed and from locations near the point bar edges while point bars are the deposits of the adjacent channel the comparison of two groups of k v values suggests that post depositional processes had an effect on the evolution of k v from channel to point bars in fluvial deposits we believed that the transport of fine particles and the gas ebullition in this gaining stream had significant effects on the distribution of k v values in a streambed point bar system with the ageing of deposition in a floodplain the permeability of point bar sediments can likely decrease due to reduced effects of the upward flow and gas ebullition

fault slip distribution of the 2016 fukushima earthquake estimated from tsunami waveforms the 2016 fukushima normal faulting earthquake mjma 7 4 occurred 40 km off the coast of fukushima within the upper crust the earthquake generated a moderate tsunami which was recorded by coastal tide gauges and offshore pressure gauges first the sensitivity of tsunami waveforms to fault dimensions and depths was examined and the best size and depth were determined tsunami waveforms computed based on four available focal mechanisms showed that a simple fault striking northeast southwest and dipping southeast strike 45 dip 41 rake 95 yielded the best fit to the observed waveforms this fault geometry was then used in a tsunami waveform inversion to estimate the fault slip distribution a large slip of 3 5 m was located near the surface and the major slip region covered an area of 20 km 20 km the seismic moment calculated assuming a rigidity of 2 7 1010 n m2 was 3 70 1019 nm equivalent to mw 7 0 this is slightly larger than the moments from the moment tensor solutions mw 6 9 large secondary tsunami peaks arrived approximately an hour after clear initial peaks were recorded by the offshore pressure gauges and the sendai and ofunato tide gauges our tsunami propagation model suggests that the large secondary tsunami signals were from tsunami waves reflected off the fukushima coast a rather large tsunami amplitude of 75 cm at kuji about 300 km north of the source was comparable to those recorded at stations located much closer to the epicenter such as soma and onahama tsunami simulations and ray tracing for both real and artificial bathymetry indicate that a significant portion of the tsunami wave was refracted to the coast located around kuji and miyako due to bathymetry effects

criteria to distinguish between subglacial glaciotectonic and glaciomarine sedimentation i deformation styles and sedimentology abstract this paper compares and contrasts the sedimentology and structural geology of a quaternary glaciomarine site melabakkar asbakkar iceland and a quaternary subglacial glaciotectonic site west runton uk research suggests that the glaciomarine environment is dominated by sedimentary processes related to sediment supply water content and distance from the glacier margin glaciotectonic deformation however is dominated by deformational processes related to effective pressure shear strain nature of the subglacial material and distance from the glacier margin from this study a series of criteria are suggested to distinguish both quaternary and contemporary glaciotectonic and glaciomarine environments in addition the paper also discusses the subsequent effects of glaciotectonic deformation on a primary glaciomarine site due to a glacial readvance

trench parallel stretching and folding of forearc basins and lateral migration of the accretionary wedge in the southern ryukyus a case of strain partition caused by oblique convergence detailed seafloor mapping in the area east of taiwan revealed trench parallel stretching and folding of the ryukyu forearc and lateral motion of the accretionary wedge under oblique convergence east of 122 40 e a steep accretionary wedge is elongated in an e w direction a major transcurrent right lateral strike slip fault accommodates the strain partitioning caused by an oblique convergence of 40 a spectacular out of sequence thrust may be related to the subduction of a structural high lying in the axis of the n s trending gagua ridge this asperity is likely responsible for the uplift of the accretionary wedge and forearc basement and may have augmented strain partitioning by increasing the coupling between the two plates west of 122 40 e the low taper accretionary wedge is sheared in a direction subparallel to the convergence vector with respect to the ryukyu arc the bayonet shape of the southern ryukyu arc slope partly results from the recent re opening of the southern okinawa trough at a rate of about 2 to 4 cm yr right lateral shearing of the sedimentary forearc with respect to the nonlinear ryukyu backstop generates trench parallel extension in the forearc sediment sequence at dilational jogs and trench parallel folding at compressive jogs the hoping basin lies above a diffuse trench trench fault ttf or tff unstable triple junction moving toward the south along a n s transform zone which accommodates the southward drift of the ryukyu arc with respect to eurasia

glaciomarine facies within subglacial tunnel valleys the sedimentary record of glacioisostatic downwarping in the irish sea basin coastal exposures of late pleistocene sediments deposited after 19 000 yr bp near dublin ireland provide a window into the infill of a subglacially cut tunnel valley exposures close to the steeply dipping bedrock wall of the valley show boulder gravels within multi storey u shaped channels cut and filled by subglacial meltwaters driven by a high hydrostatic head gravels are truncated by poorly sorted ice proximal glaciomarine sediments that record the pumping of large volumes of subglacial debris along the tunnel valley to a tidewater ice sheet margin the sedimentary succession is dominated by sediment gravity flow facies comprising interbedded diamict and massive poorly sorted gravel facies interpreted as subaqueous debris flow deposits gravel beds show local inverse and normal coarse tail graded facies recording the restricted development of turbulent flow sediment gravity flow deposits fill broad 2 km shallow 10 m and overlapping channels penetrative deformation structures e g dykes are common at the base of channels the same subglacially eroded topography and glaciomarine infill stratigraphy can be identified on high resolution seismic profiles across nearly 600 km2 of the western irish sea tunnel valleys are argued to have been exposed to glaciomarine processes by the rapid retreat of a calving tidewater ice sheet margin in response to marine flooding caused by glacio isostatic downwarping below the last british ice sheet the facies associations described in this paper comprise an event stratigraphy that may be found on other glaciated continental shelves

source to mainstream hydrochemical water changes in a channel head in the young glacial area pomeranian lakeland poland abstract a channel head is a zone where hydrological changes occur that shape the chemical features of water during the final stage of underground flow and the beginning of the surface water cycle the study aims were as follows i to characterise spatial water chemistry patterns ii to establish the role played by the hyporheic zone in the chemical transformations associated with the groundwater that supplies the first order stream and iii to identify the factors that control the chemical composition transformations that occur in headwater alcoves the analysis was performed on three sets of samples taken at the arnowo channel head situated in the young glacial landscape of the parseta drainage basin nw poland the performed hydrochemical measurements showed that the waters found in the alcoves displayed a mosaic pattern with spatial variability in the levels of trace metals and nutrients in turn geogenic ions featured in the mineralogical petrographic compositions of deposits found in headwater catchments such as ca2 hco3 mg2 and na showed low temporal variability and small differences among the various sampled headwater alcoves these results indicated that the majority of spatial variance associated with the chemical composition of water is driven by the transformation of groundwater discharges in the hyporheic zone the locations of hydrochemical transformation hotspots can be explained by the influences of critical physical variables such as the intensity of seepage erosion sediment texture bottom microtopography groundwater discharge characteristics water temperatures and the diversity of groundwater fed vegetation hydrochemical studies performed in the ground and surface water contact zones within a channel head can identify the underlying causes of changes to water chemistry which in turn can facilitate the protection of water resources against unfavourable changes that may affect the water quality at the headwater catchment