instantaneous end moraine and sediment wedge formation during the 1890 glacier surge of bruarjokull iceland abstract contemporary understanding of the behaviour of surging glaciers and ice streams is hampered by the lack of data on landsystem evolution and sedimentary environments this study concerns the ice marginal environment of the surge type bruarjokull in iceland the sediment distribution in the glacier forefield as well as the morphology sedimentology and tectonic architecture of the 1890 end moraine is investigated for highlighting the interaction between very dynamic ice and sediment landform associations as a result of substrate bedrock decoupling during the 1890 surge subglacial sediment was dislocated across the bedrock surface and deformed compressively leading to gradual substrate thickening and the formation of a sediment wedge in the marginal zone a drop in subglacial porewater pressure at the very end of the surge led to substrate bedrock coupling and a stress transfer up into the sediment sequence causing brittle deformation of the substrate simultaneously the glacier toe ploughed into the topmost part of the marginal sediment wedge initiating the moraine ridge construction fine grained and incompetent sediment deformed in ductile manner resulting in a narrow moraine dominated by rooted folds while coarse grained and competent sediment deformed in brittle fashion resulting in a wider moraine dominated by thrust blocks a new sequential model of subglacial and ice marginal processes operating during a glacier surge is proposed illustrating the stepwise formation of a marginal sediment wedge and an end moraine a twofold inseparable marginal end product that formed during the last days of the 1890 surge

on the time dependent behaviour of glacial sediments a geotechnical approach abstract soft sediments can deform under both changes in stress and changes in strain rate as well as during sustained loading e g creep in glacial conditions soft subglacial sediments can contribute to glacier movements and when the ice sediment system is coupled the rate sensitivity of the sub layer can affect the velocity of the glacier these issues have been the object of studies by several geologists in parallel the effects of time and strain rate on the behaviour of soils have been studied for many years by geotechnical engineers to estimate the long term performance of ground structures this paper applies the knowledge acquired in soil mechanics to a geological problem results on two glacial sediments of different origins obtained from advanced geotechnical laboratory tests are presented and analysed in the light of recent advances in soil mechanics independently of time effects the test data show that the pre failure behaviour is not elastic but that the sediments develop plastic strains before reaching their peak strength with the stiffness gradually degrading results from tests performed with variable strain rates suggest that the time dependent viscous behaviour of the sediments may be governed by their mineralogy in particular the presence of plastic fines the viscous behaviour observed in the plastic tills seems to affect the pre failure behaviour only for example the yield surface stiffness strength but the criteria of failure e g critical or residual angle of failure are found to be constant and independent of strain rate the test data also suggest that the viscous behaviour may be related to stress level being more prevalent at low stresses these results obtained under laboratory controlled conditions over a large range of strains pre and post peak strength are a necessary step towards developing constitutive models for subglacial sediments rigorously it is only after this has been achieved that such models should be implemented in finite element code to analyse ice sediment systems with the aim to understand glacier movements better

alkali mapping of the japanese quaternary volcanic rocks abstract of ca 200 quaternary volcanic centers in the japanese islands ca 120 are characterized by k 2 o and na 2 o concentrations of their ejecta normalized to sio 2 60 k 2 o values give a geographically well defined trend of regularly increasing away from the volcanic front na 2 o values show no geographical trend relationships between the sio 2 normalized k 2 o and the depth of the deep seismic zone k h relation are different for different arcs the southwest japan arc shows distinctly higher k 2 o and less regular geographic trend than the others probably due to crustal contamination in the normal segments of the northeastern japan belt k 2 o increases ca 2 5 to 3 0 per 100 km depth of the seismic zone groups of volcanic centers near the junction between the northeast honshu and izu mariana arcs give characteristically lower k 2 o while rishiri volcano far behind the arc junction between the kurile and honshu arcs also gives a low k 2 o value

glaciotectonically induced water throughflow structures in a late pleistocene drumlin kanrawer county galway western ireland abstract during drumlinisation brecciated bedrock was sheared over the proximal end of a late pleistocene drumlin at kanrawer western ireland high effective water pressures generated by shearing at the ice substrate interface during this event created a marked proximal to distal hydrostatic gradient affecting about 60 of the diamict which forms most of the drumlin sediment pile this resulted in large scale sediment reorganisation by darcian through flow and closed conduit flow of expelled pore waters and subglacial meltwater proximally this is reflected in the development of integrated honeycomb gravel structures formed by glaciotectonic shunting and tortuous throughflow in the diamicts distally the honeycomb structures give way to dish and pillar structures which are connected to gravelly and laminated sandy channel fill facies which cut obliquely across the long axis of the drumlin this facies transition reflects throughflow of pore water rising through the sediment pile and expelled along nye type channels excavated on the distal drumlin surface these proximal to distal sediment transformations suggest that current theoretical models of drumlin formation do not adequately represent the continuum of subglacial processes which accompany drumlinisation

characteristics of wall deflections and ground surface settlements in shanghai the characteristics of wall deflections and surface ground settlements at six deep multi strutted excavations in shanghai soft soils were studied and compared with those of similar case histories reported worldwide particularly in taipei and singapore the measured wall deflections at the six metro stations of the pearl ii circle line show a typical bulging profile or deep seated shape at the end of the excavation the ratio between the measured maximum wall deflection and the depth of the excavation hm h in shanghai was 0 007 which was similar to the ratio measured in taipei but it was substantially smaller than the peck bounding limit of 0 01 at each station the measured maximum displacement was 0 45 of the final excavation depth because of the large aspect ratios of the underground excavations no significant three dimensional effects or corner effects were observed the measured maximum settlements of the six metro excavations fell within zone i of the peck classical normalized settleme

size and shape characteristics of drumlins derived from a large sample and associated scaling laws abstract ice sheets flowing across a sedimentary bed usually produce a landscape of blister like landforms streamlined in the direction of the ice flow and with each bump of the order of 102 to 103 m in length and 101 m in relief such landforms known as drumlins have mystified investigators for over a hundred years a satisfactory explanation for their formation and thus an appreciation of their glaciological significance has remained elusive a recent advance has been in numerical modelling of the land forming process in anticipation of future modelling endeavours this paper is motivated by the requirement for robust data on drumlin size and shape for model testing from a systematic programme of drumlin mapping from digital elevation models and satellite images of britain and ireland we used a geographic information system to compile a range of statistics on length l width w and elongation ratio e where e l w for a large sample mean l is found to be 629 m n 58 983 mean w is 209 m and mean e is 2 9 n 37 043 most drumlins are between 250 and 1000 metres in length between 120 and 300 metres in width and between 1 7 and 4 1 times as long as they are wide analysis of such data and plots of drumlin width against length reveals some new insights all frequency distributions are unimodal from which we infer that the geomorphological label of drumlin is fair in that this is a true single population of landforms rather than an amalgam of different landform types drumlin size shows a clear minimum bound of around 100 m horizontal maybe drumlins are generated at many scales and this is the minimum or this value may be an indication of the fundamental scale of bump generation proto drumlins prior to them growing and elongating a relationship between drumlin width and length is found with r2 0 48 and that is approximately w 7 l 1 2 when measured in metres a surprising and sharply defined line bounds the data cloud plotted in e w l space and records a scale dependent maximum elongation limit approximated by emax l1 3 when l measured in metres for a given length for some reason as yet unknown drumlins do not exceed the elongation ratio defined by this scaling law we also report and compare our statistics to an amalgamated sample 25 907 drumlins of measures derived from around 50 published investigations any theory must be able to explain the drumlin statistics and fundamental scaling properties reported herein and they thus provide powerful tests for drumlin modelling

bedform topography and basal conditions beneath a fast flowing west antarctic ice stream a grid of seismic reflection lines has been used to image basal topography and infer basal conditions and flow processes beneath similar to 140 km 2 of rutford ice stream west antarctica the subglacial topography in this region consists of two troughs flanking a central high and the bed is composed of water saturated sediments the two troughs are filled with deforming sediment whereas the bed in the central region appears to undergo a transition from largely deforming conditions upstream to basal sliding downstream the deforming bed is very flat along flow but undulates across flow sliding areas show rougher bed topography cross stream bed topography is characterised by streamlined mounds of deforming sediment aligned in the ice flow direction these bedforms occur superimposed on the bed in regions of both basal sliding and sediment deformation in places they form finger like mounds of material which extend into the sliding region further downstream mean bedform height is 22 m mean width is 267 m and many of them extend for at least 1 2 km along flow we interpret most of these bedforms as drumlins and one as a mega scale glacial lineation the juxtaposition of different basal conditions is consistent with models proposed from terrestrial studies in which the glacier bed is a mosaic of stable and deforming bed areas variable both spatially and temporally any theory of subglacial sediment rheology must also be able to account for our conclusion that at any given time pervasive deformation extends at least a few metres into the bed and can persist over a considerable area many km 2 bedform geometry and basal conditions concur with interpretations of former ice streams with evidence for increasing elongation ratio with distance downstream however those studies also identified bedrock cropping out at the ice bed interface for which there is no evidence on rutford ice stream c 2008 elsevier ltd all rights reserved

nd and sr isotopic variations in acidic rocks from japan significance of upper mantle heterogeneity initial nd and sr isotopic ratios have been measured for cretaceous acidic and related intermediate rocks 24 volcanic and two plutonic rocks from the inner zone of southwest japan izswj to investigate the genesis of acidic magmas the initial nd and sr isotopic ratios for these rocks show three interesting features 1 end values for acidic rocks 2 to 9 are negatively correlated with esr values 10 to 90 together with those for intermediate rocks end 3 to 8 esr 0 to 65 2 the end values for silica rich rocks 60 sio2 correlate with the longitude of the sample locality decreasing from west to east in a stepwise fashion four areas characterized by uniform end values are discriminated 3 low silica rocks 60 sio2 in a certain area have distinctly different end values from those of the high silica rocks in the same area

textural and compositional evidence for magma mixing and its mechanism abu volcano group southwestern japan quaternary basalts andesites and dacites from the abu monogenetic volcano group sw japan composed of more than 40 monogenetic volcanoes show two distinct chemical trends especially on the feo mgo vs sio2 diagram one trend is characterized by feo mgo enrichment with a slight increase in sio2 content fe type trend whereas the other shows a marked sio2 enrichment with relatively constant feo mgo ratios si type trend the fe type trend is explained by fractional crystallization with subtraction of olivine and augite from a primitive alkali basalt magma rocks of the si type trend are characterized by partially melted or resorbed quartz and sodic plagioclase phenocrysts and or fine grained basaltic inclusions they are most likely products of mixing of a primitive alkali basalt magma containing olivine phenocrysts with a dacite magma containing quartz sodic plagioclase and hornblende phenocrysts petrographic variation as well as chemical variation from basalt to dacite of the si type trend is accounted for by various mixing ratios of basalt and dacite magmas pargasitic hornblende and clinopyroxene phenocrysts in andesite and dacite may have crystallized from basaltic magma during magma mixing olivine and spinel and quartz sodic plagioclase and common hornblende had crystallized in basaltic and dacitic magmas respectively before the mixing within a lava flow the abundance of basaltic inclusions decreases from the area near the eruptive vent towards the perimeter of the flow and the number of resorbed phenocrysts varies inversely suggesting zonation in the magma chamber

nd and sr isotope systematics of miocene to holocene volcanic rocks from southwest japan volcanism since the opening of the japan sea isotope nd and sr and geochemical data for twelve volcanic rocks from the shimane oki san in region of southwest japan give some insight into the miocene recent volcanic history of southern japan since rifting from the asian mainland the oldest rocks examined dolerites and ushikiri formation were erupted during the opening of the japan sea at about 15 ma and comprise arc tholeiites derived from a depleted source end 0 esr 0 interpreted in terms of a depleted mantle source modified by a slab derived fluid volcanics of oki dozen island in the japan sea are alkalic derived from an enriched mantle plume isotopically distinct from nearly oki dogo island eruption of the calc alkaline wakurayama andesite early pliocene and both arc and within plate type basalts 1 ma show that magmas were tapped from a variety of sources taking into account plate tectonics and seismic data the subduction influence until the quaternary was the pacific plate with philippines sea plate subduction affecting quaternary and younger volcanics

the sedimentology of a late pleistocene drumlin near kingscourt ireland abstract an exposure in a late pleistocene drumlin near kingscourt ireland provides a good insight into some of the processes that give rise to such subglacial bedforms the drumlin is located on a ridge cored by red sandstone of carboniferous namurian age which rises to 150 m above m s l the drumlin itself is about 380 m long by 170 m wide and is 20 m in height it is orientated vvnw ese ice flow direction in the area as inferred from general drumlin orientation striae and erratic dispersal was nw se the drumlin is composed of diamicton with four constituent facies containing large scale up to 20 m long and 1 5 m high slabs of the sandstone bedrock which have been displaced tens of metres by ice dragging the thin diamicton matrix is sand rich with few clasts greater than pebble size it contains green sandstone erratics from west and northwest of the study site along with clasts of weathered namurian sandstone which have been sheared from local bedrock the diamicton attains a maximum thickness of 5 4 m the slabs are confined to the basal 2 5 m of the diamicton thus the drumlin is essentially rock cored parts of the matrix are interpreted as injection sediments that have been squeezed into fractures and voids in the bedrock and between rock slabs under high porewater pressures when the ice began to displace fractured substrate deformation structures at a variety of scales are seen in the matrix deformation erosion and deposition were all important in the formation of the drumlin much of the upper part of the diamicton has been sheared subsequent to initial deposition by ice action the sheared units are uppermost in the stratigraphic sequence the shearing is the last glacial process apparent in the drumlin sediment and may have been contemporaneous with drumlinisation both the squeezing process which deposited the injections within the matrix and the deflection in flow of ice were influenced by the obstructing bedrock ridge which in this case is also responsible for the anomalous orientation of the feature

the effect of grain texture on the occurrence of microstructural properties in subglacial till in this paper we examine whether till grain size affects the range and occurrence of micromorphological features associated with subglacial shear our till samples were collected from two glaciers in iceland and varied in texture from a coarse sandy clast rich till fjallsjokull to a fine grained silty sandy till vestari hagafellsjokull we found a wide range of deformational microstructures that included skelsepic plasmic fabric intraclasts of pre existing eroded bedrock basalt and weathered clay and mini shear zones between clasts we classified our micromorphological data into three classes rotational intermediate and linear in addition to these observations we performed extensive microfabric analysis at different scales on all of our samples we found that the coarse grained till contained a greater number and variety of microstructures than the fine grained till in addition the fine grained till showed a distinct lack of rotational structures that we attribute to the lack of significantly sized clasts in the matrix we argue that the varied texture of the coarse grained till provides a greater degree of perturbation within the shearing layer and so more distinct microstructures form in a more fine grained till shearing is more homogeneous since there are less perturbations in the matrix and this leads to a more singular kind of microstructure our observations suggest that subglacial shear occurs within a multi layered patchwork of different grain sizes competence and pore water pressures it is these factors that are so crucial in determining the occurrence and type of microstructural evidence we see in subglacial tills

clastic dykes in over consolidated tills evidence for subglacial hydrofracturing at killiney bay eastern ireland abstract a swarm of vertical gravel filled dykes up to 6 m high and several decimetres wide cut through an over consolidated till at killiney bay the dykes are rooted in a gravel layer and many display plumes of clastic debris ejected into the overlying sediments burst out structures such features have not previously been described these clastic dykes are interpreted as the infillings of hydrofractures which formed when water pressures in the basal gravel layer exceeded the overburden pressure and tensile shear strength of the capping till the burst out structures extend up to 7 m from the tops of the dykes and provide strong evidence for forceful upward flow evidence suggests that the hydrofractures formed subglacially probably during a minor re advance their presence in late devensian 26 13 ka bp tills with an irish sea provenance irish sea till may have important implications for the subglacial hydrology of the last irish sea ice sheet these hydrofractures cannot form in unconsolidated glacimarine sediment and their presence precludes a glacimarine origin for these deposits they greatly affect the geotechnical properties of irish sea tills in particular providing very permeable routes through otherwise impermeable layers with important consequences in situations elsewhere in the irish sea basin where they have been used as aquicludes in landfill and low level nuclear waste disposal sites

the origin of a giant downward directed clastic dyke in a kame belchatow mine central poland a kame near czubata gora in the pleistocene overburden of the belchatow open cast browncoal mine in central poland shows several types of deformations a number of diapirs occur but also a structure that shows all characteristics of a diapir but consists of sediments that apparently intruded the underlying rather than the overlying sediments analysis of this structure shows that it consists of material that was originally deposited as a fine grained mainly silty glacilacustrine sediment seismic activity triggered the material to fluidise resulting in a structureless mass part of the fluidised material flowed down into a fissure that had formed in the underlying sediments probably due to tectonics in the active graben thus forming a clastic dyke more of the overlying silty material was later pressed down into a dyke with the shape of a downward directed diapir

glacial striae glacigenous sediments and weichselian ice movements in southernmost sweden abstract the southernmost part of sweden is a classical area to study ice movement patterns during the course of time different hypotheses about glacial events and ice dynamics have been proposed and there is still no consensus of opinion the author has tried to integrate studies of glacial erosional features registered on bedrock with glacigenic sediments on top of the eroded rock surfaces this paper concentrates on ice directions according to glacial striae and clast fabrics from the hardeberga quarry in skane the results from hardeberga are discussed in a regional context the youngest ice movement registered comes from the sw striae fabrics overturned sandwedges and displaced shattered bedrock most probably this flow direction is due to quite different ice flow conditions in the flat and low lying areas south of the fennoscandian border zone environment with deforming bed conditions in contrast to the ice dynamics in the higher crystalline shield areas and the horst ridges of hard palaeozoic and crystalline rocks crossing skane from nw to se

geographical distribution of 3 he 4 he ratios in the chugoku district southwestern japan we have collected 34 hot spring and mineral spring gases and waters in the chugoku and kansai districts southwestern japan and measured the 3he 4he and 4he 20ne ratios by using a noble gas mass spectrometer observed 3he 4he and 4he 20ne ratios range from 0 054 ratm to 5 04 ratm where ratm is the atmospheric 3he 4he ratio of 1 39 10 6 and from 0 25 to 36 8 respectively they are well explained by a mixing of three components mantle derived radiogenic and atmospheric helium dissolved in water the 3he 4he ratios corrected for air contamination are low in the frontal arc and high in the volcanic arc regions which are consistent with data of subduction zones in the literature the geographical contrast may provide a constraint on the position of the volcanic front in the chugoku district where it was not well defined by previous works taking into account the magma aging effect we cannot explain the high 3he 4he ratios of the volcanic arc region by the slab melting of the subducting philippine sea plate the other source with pristine mantle material may be required more precisely the highest and average 3he 4he ratios of 5 88 ratm and 3 8 1 6 ratm respectively in the narrow regions near the volcanic front of the chugoku district are lower than those in kyushu and kinki spot in southwestern japan but close to those in ne japan this suggests that the magma source of the former may be related to the subduction of the pacific plate in addition to a slight component of melting of the philippine sea slab

strontium isotopic relations of bimodal volcanic rocks at kikai volcano in the ryūkyū arc japan bimodal associations of mafic and silicic rocks are observed at kikai volcano in the ry ky arc japan we determined 87sr 86sr ratios of 16 representative volcanic rocks of this volcano the ratios scatter in the narrow range between 0 70477 and 0 70508 despite the varying sio2 content of the rocks except for one sample with a ratio of 0 70539 this suggests that both basaltic and rhyolitic rocks at kikai volcano are generated from the same source material in contrast to the separate origin required for the bimodal volcanism typically observed in the western united states the origin of the bimodal volcanism in the island arc setting is distinctly different from that in the continental setting in view of source materials of basaltic and rhyolitic magmas

geochemical features of collision related volcanic rocks in central and eastern anatolia turkey in central and eastern anatolia volcanism related to continental collision occurred in neogene to quaternary times major and trace element compositions 87sr86 sr and k ar ages were determined for volcanic rocks from selected volcanoes in this region 87sr86 sr for basalts from erciyes volcano in the eastern part of central anatolia as well as ararat nemrut and karacadag volcanoes in eastern anatolia are in the range 0 7035 0 7040 these ratios are higher than those of n type morb but overlap arc volcanic rock values this suggests that the mantle source which was possibly contaminated by fluids and melts with higher87sr86 sr during the pre collisional events has similar sr isotopic compositions in wide areas of the eastern part of central anatolia and eastern anatolia even across the collision plate boundary in addition chemical compositions of the mantle source are not homogeneous with respect to hfs element contents indicating that the slab derived components resulting from past subductions are not homogeneously distributed the mantle source beneath the western part of central anatolia which corresponds to the transitional region from collision tectonics in the east to subduction tectonics in the west has different chemical and sr isotopic signatures from other parts of anatolia in the western part of central anatolia the87sr86 sr of basaltic rocks from three regions characterized by monogenetic volcanoes are in the range 0 70427 to 0 70581 and differ from region to region in spite of indistinguishable chemical compositions this indicates either source heterogeneity on a small scale or different contributions of local crustal contaminants calc alkaline lavas from ararat and kars in eastern anatolia have chemical compositions with subduction signatures inherited from pre collision subduction events in contrast the chemical and sr isotopic features of volcanic rocks from erciyes volcano in central anatolia indicate that the combined process of fractional crystallization of basaltic magma and crustal assimilation without injection of slab derived components is the dominant process generating calc alkaline andesite under the collision tectonics regime operating in this region

dynamic cycles ice streams and their impact on the extent chronology and deglaciation of the british irish ice sheet we present results from a suite of forward transient numerical modelling experiments of the british and irish ice sheet biis consisting of scottish welsh and irish accumulation centres spanning the last glacial period from 38 to 10 ka bp the 3d thermomechanical model employed uses higher order physics to solve longitudinal membrane stresses and to reproduce grounding line dynamics surface mass balance is derived using a distributed degree day calculation based on a reference climatology from mean 1961 1990 precipitation and temperature patterns the model is perturbed from this reference state by a scaled ngrip oxygen isotope curve and the specmap sea level reconstruction isostatic response to ice loading is computed using an elastic lithosphere relaxed asthenosphere scheme a suite of 350 simulations were designed to explore the parameter space of model uncertainties and sensitivities to yield a subset of experiments that showed close correspondence to offshore and onshore ice directional indicators broad biis chronology and the relative sea level record three of these simulations are described in further detail and indicate that the separate ice centres of the modelled biis complex are dynamically interdependent during the build up to maximum conditions but remain largely independent throughout much of the simulation the modelled biis is extremely dynamic drained mainly by a number of transient but recurrent ice streams which dynamically switch and fluctuate in extent and intensity on a centennial time scale a series of binge purge advance retreat cycles are identified which correspond to alternating periods of relatively cold based ice associated with a high aspect ratio and net growth and wet based ice with a lower aspect ratio characterised by streaming the timing and dynamics of these events are determined through a combination of basal thermomechanical switching spatially propagated and amplified through longitudinal coupling but are modulated and phase lagged to the oscillations within the ngrip record of climate forcing phases of predominant streaming activity coincide with periods of maximum ice extent and are triggered by abrupt transitions from a cold to relatively warm climate resulting in major iceberg melt discharge events into the north sea and atlantic ocean the broad chronology of the modelled biis indicates a maximum extent at 20 ka with fast flowing ice across its western and northern sectors that extended to the continental shelf edge fast flowing streams also dominate the irish sea and north sea basin sectors and impinge onto sw england and east anglia from 19 ka bp deglaciation is achieved in less than 2000 years discharging the freshwater equivalent of 2 m global sea level rise a much reduced ice sheet centred on scotland undergoes subsequent retrenchment and a series of advance retreat cycles into the north sea basin from 17 ka onwards culminating in a sustained younger dryas event from 13 to 11 5 ka bp modelled ice cover is persistent across the western and central highlands until the last remnant glaciers disappear around 10 5 ka bp

sr isotopic and trace element variations in oligocene to recent igneous rocks from the philippine island arc evidence for recent enrichment in the sub philippine mantle oligocene miocene plutonic rocks from the philippine island arc are characterized by uniform87sr 86sr isotopic ratios of 0 7035 0 7039 in contrast volcanics erupted in the past 5 ma in central luzon marinduque and mindoro have higher radiogenic sr 0 7042 0 7054 and show regional variations in their sr isotopic compositions volcanics of the pliocene recent bicol volcanic chain of southern luzon have87sr 86sr in the same range 0 7034 0 7040 as the mid tertiary plutonics increases in radiogenic sr are coupled with increases in rb sr ba and th abundances in the central luzon mindoro marinduque volcanic belt while no such correlation exists for the mid tertiary plutonics we consider the low values observed for mid tertiary plutonics and bicol volcanics to be controlled by fluids released from the subducting philippine sea plate basalt that have87sr 86sr of the same range sr isotopic compositions of the volcanics in the northern part of the central luzon volcanic belt may be controlled by fluids generated from the subducted south china sea crust the highest values of radiogenic sr 0 7051 0 7054 and highest lil abundances which are observed in the southern part of the central luzon volcanic arc appear to be the result of source contamination by slivers of the continental crust of the north palawan mindoro terrane that collided with the philippine arc in the miocene

wall and ground movements associated with deep excavations supported by cast in situ wall in mixed ground conditions field monitoring data on lateral wall deflection and ground settlement from 14 deep excavation case histories in hong kong involving cast in situ concrete wall were collected and analyzed mixed ground conditions consisted of successive layers of fill marine deposit and or alluvium and decomposed geomaterials the measured data were differentiated into two groups based on the standard penetration test n values of the ground n 30 group a and n 30 group b at half of the excavation depth the mean values of the maximum wall deflection hm and ground settlement vm in the excavations in group a are 0 23 and 0 12 of the excavation depth h respectively for the excavations in group b the mean value of hm is 0 13 h which is similar to other excavations in predominantly other stiff soils hm h 0 10 0 16 but vm is only 0 02 h which is small when compared to other similar database hm h 0 1 0 2 the settlement influence zone of the excavations in both groups reaches a distance of

the influence of crustal structure on compositions of subduction related magmas abstract a survey of sr isotopic ratios and other compositional features of subduction related magma suites reveals significant correlations between these averaged parameters and characteristics of the underlying crust i e thickness composition and age these observations lead to the conclusion that crust and or mantle rocks in the hanging walls of subduction zones are involved in modification of primary mafic magmas typically basalt or basaltic andesite it is proposed that mafic magmas will stagnate within the crust or uppermost mantle where they may differentiate and react with wall rocks the extent to which such processes manifest themselves will depend upon details of the local crustal structure in particular the composition and age of the crust will strongly influence such parameters as sr nd and pb isotopic compositions such data strongly indicate the involvement of crustal rocks in locales underlain by old sialic crust e g central andes depending upon the level of magma stagnation and evolution within the crust different trends in isotopic composition may result these isotopic trends may be enhanced by partial melting of the wall rocks to produce relatively silicic anatectic magmas and locally they may reflect subduction of continental sediments interpretation of the isotopic data may be more ambiguous in locales underlain by younger and more mafic continental crust cascades e eleutians and those underlain by oceanic crust owing to the similarity in isotopic composition of primary magmas and the latter crustal materials yet some degree of crustal involvement in magmatic evolution seems highly probable even in these more primitive terranes consequently most island arc magmas and especially those more evolved than basalt are probably not primary in the sense that they do not represent direct melts of the upper mantle studies of arc volcanic rocks may yield misleading conclusions concerning processes of magma generation related to subduction unless evolutionary processes are defined and their effects considered it appears that modern volcanic arcs provide a poor analog for models of early crustal development because the modern mantle derived magmatic components are more mafic in composition than average continental crust

diamict fans in subglacial water filled cavities a new glacial environment abstract the occurrence of glaciolacustrine diamict fans on the south side of volcanic tuyas in the laugarvatn area iceland is reported these fans are composed of sheets of diamict gravel and sand and contain little or no primary volcanic material they post date the volcanic pile within the tuyas and appear to have been deposited in subglacial water filled cavities confined to the down ice side of the tuyas it is suggested that these subglacial water bodies formed as result of an enhanced geothermal heat flux associated with the tuyas the volume of glacial sediment within the fans implies that either basal sediment loads were high in this sector of the former ice sheet or that ice flow converged towards the tuyas during their formation concentrating basal sediment into the lee side cavity and fan the glaciolacustrine diamict fans add to our knowledge of the landforms and sediments associated with tuyas and may also provide evidence of ice flow convergence at thermal anomalies

fissure fill and tunnel fill sediments expressions of permafrost and increased hydrostatic pressure a spectacular network of fissure fillings and pipes tunnels cuts quaternary gravelly delta deposits northeast of myvatn precisely on the spreading axis of the north icelandic rift zone the delta was formed in an ice contact lake during deglaciation towards the end of the last glaciation subsequently the lake was drained and permafrost conditions developed in these poorly sorted gravel deposits hydrostatic pressure was transmitted from the adjacent glacier to the non frozen core of the delta beneath the discontinuous permafrost crust and the seasonally frozen active layer owing to increased hydrostatic pressure a network of subhorizontal to vertical fissures was opened along the taliks in these fissures free ground water flow and sediment transport were established tunnel erosion and probably also seepage erosion were associated with these fissures subsequently the fissures and tunnels were filled by laminated fine sediments interbedded with poorly sorted material resulting in the formation of fissure fill sediments and tunnel fill sediments

formation of fluidization pipes during liquefaction examples from the uratanna formation lower cambrian south australia usually well preserved fluidization pillars and sand filled fluidization pipes occur within submarine channel sands of the basal uratanna formation lower cambrian in the adelaide geosyncline of south australia the morphology of these structures reflects complex lateral and vertical movement of fluids during liquefaction and dewatering fluidization pipes acted as conduits for highly concentrated upward directed fluid flow the formation and maintenance of these pipes was dependent upon the development of a pipe wall composed of clay plugged fine sand formed during initial fluidization this lining acted as a permeability barrier confining and concentrating fluidized flow within the pipe each of the pipes is surrounded by a cylindrical fluidization halo in which leakage through the pipe lining produced partial fluidization of the surrounding sediment fine scale structures within these haloes indicate that fluids flowed radially and upward out of the fluidization pipes at an acute angle these fluids merged with and influenced the orientation and size of adjacent fluidization pillars the fluidization pipes of the uratanna formation may represent unusual preservation of the unstable fluid flow conditions that occur during incipient fluidization of sand beds

deep excavation of the gate of the orient in suzhou stiff clay composite earth retaining systems and dewatering plans abstractfrom 2005 to 2010 a large excavation approximately 26 000 m2 in plane was conducted in stiff clay deposits for the gate of the orient building in suzhou china to reduce project cost a

howe lake a hydrodynamic blowout structure howe lake formerly called goudie lake is an unusual feature of southeast saskatchewan almost perfectly circular diameter 295 m it is much deeper 26 m than almost any other prairie lake i

the post yield behaviour of four eocene to jurassic uk stiff clays a detailed study is described of the post yield behaviour of four medium plasticity heavily overconsolidated uk stiff clays sub layers of the stiff to hard gault kimmeridge and oxford clays were identified sampled and tested these along with facies investigated in an earlier london clay study had broadly similar depositional histories the intention in considering a spread of similar sediments from the jurassic to the eocene was to allow any strong effects of geological age or burial depth to be identified a strongly fissured meso structure was present in three of the four clays which had a controlling influence on their effective shear strengths considering that the representative element volume is of paramount importance in measuring the strengths of such soils all four soils were brittle in shear and when sheared to sufficient displacements developed low residual shear strengths the stiff clays were investigated further through comparisons between natural and reconstituted behaviour usi

arctic ice export events and their potential impact on global climate during the late pleistocene 1 ice sheets in the north american arctic and to a lesser extent those in northern eurasia calved large quantities of icebergs that drifted through fram strait into the greenland sea several times during the late pleistocene these icebergs deposited fe oxide grains 45 250 m and coarse lithic clasts 250 m matched to specific circum arctic sources four massive arctic iceberg export events are identified from the laurentide and the innuitian ice sheets between 14 and 34 ka calendar years in a sediment core from fram strait these relatively short duration 1 4 kyr events contain 3 5 times the background levels of fe oxide grains they began suddenly as indicated by a steep rise in the number of grains matched to an ice sheet source suggesting rapid purges of ice through fram strait due perhaps to collapse of ice sheets the larger events from the northwestern laurentide ice sheet are preceded by events from the innuitian ice sheet despite the chronological uncertainties the arctic export events appear to occur prior to heinrich events

formation and deformation of subglacial intrusive clastic sheets in the dwyka formation of northern natal south africa abstract an arenaceous diamictite rests on fissile silty mudstone and argillaceous diamictite and is overlain by a laminated muddy siltstone east of helpmekaar in the dundee district of northern natal the argillaceous deposits originated either in the subglacial or proglacial zone of a partly grounded marine ice sheet where sediment was supplied by debris laden floating ice meltwater plumes and turbidity currents the arenaceous diamictite is the product of melt out debris released close to the grounding line of the ice sheet where it was subjected to overriding by the ice and slumping and redeposition by sediment gravity flow the laminated siltstone represents sediment that was deposited in a low energy setting by turbidity currents and suspension settling downslope from a retreating g ounding line dispersed ice rafted clasts occur in these fine grained deposits the upper surface of the arenaceous diamictite displays regularly spaced linear undulations that are parallel to the former iceflow direction as are corrugations in discrete subhorizontal slip planes in its upper part dike like bodies of this diamictite are found in the underlying mudstone and argillaceous diamictite these dikes or wedge shaped sheets of sandy diamictite are nearly vertical in their upper parts but at depth curl to the southeast to form sill like bodies these intrusive diamictites record a novel and previously undescribed form of subglacial bed shear by repeated hydraulic injections which shuffled the upper layers of the substrate to the south southeast bed compaction and shear beneath the grounded ice is recorded by folds in steepened portions of the clastic intrusive sheets and by pinch and swell and folded pinch and swell of the clastic sills displacement of steep folded sheet elements along subhorizontal slicken sided slip planes indicate that bed shear continued along spaced planes of slip during the process of compaction the corrugated and planar slip surfaces and the formation of the listric or spoon shaped intrusions are all shown to be different expressions of bed shear induced by traction from the overriding ice flowing to the southeast when it was temporarily grounded the base of an ice sheet flowing from land into the sea undergoes flow acceleration and forms a ramp where it decouples from the high friction substrate the arenaceous diamictite mound most likely to have developed beneath this ramp is inferred to have a structural core of sediments that have been squeezed and sheared and have slipped from beneath the ice in the tidal grounding zone

subglacial clast behaviour and its implication for till fabric development new results derived from wireless subglacial probe experiments this study has investigated the three dimensional movement of clasts within deformation till using embedded wireless probes these probes were part of an environmental sensor network which measured subglacial properties temperature water pressure resistivity case strain and tilt six times a day and relayed that data via radio to the glacier surface where they were forwarded and broadcast on line the systemwas installed at briksdalsbreen norway and operated from august 2004 until august 2006 approximately 2000 probe days worth of data were collected with an increase in performance 41 more readings during the second year the probes showed similar patterns of water pressure rises throughout the two years but with slightly different magnitudes and timings these changes in water pressure could be related to clast behaviour the probes decreased their dip over the year and the rate of change was related to an increase in glacier velocity after initial changes in dip the probes experienced changes in orientation followed by rotation about the a axis this continuous rotation was similar to the motion suggested by jeffery 1922 the motion of ellipsoidal particles immersed in a viscous fluid proceedings of the royal society of london series a 102 161 179 for the behaviour of clasts within a viscous material in addition some probes also showed short frequent dip oscillations in spring and autumn which were interpreted to reflect stick slip events similar to lodging and demonstrated how local conditions can interrupt the predicted rotation pattern overall it is demonstrated that when water pressures were high decoupling occurred associated with basal sliding and dip oscillations and when water pressures fell the ice and sediment were coupled and till deformation occurred these events happened during summer and autumn it is this combination of lodgement and deformation that builds up both a complex but predictable fabric and a resultant composite till sedimentology

ground movements caused by braced excavations the causes and patterns of ground movement associated with braced excavations are examined field measurements of displacements for braced cuts in sand and soft to medium clay show a relationship between the deflection of the excavation wall and the ratio of horizontal to vertical movement adjoining the cut a review of various case histories indicates that soil displacement depends strongly on the construction process practices are recommended for promoting a stiff bracing system excavating beneath the lowest braces and using berms to restrain ground movement

submarine hydrothermal mineralization in the okinawa trough sw of japan an overview abstract the okinawa trough is a heavily sedimented rifted back arc basin formed in an intracontinental rift zone submarine hydrothermal activity is located within the six back arc rifts located in the middle and southern okinawa trough and its distribution is controlled principally by tectonic factors subduction of the daito and gagua ridges beneath the ryukyu arc has resulted in fracturing of the brittle lithosphere beneath the okinawa trough hydrothermal activity is strongest in the volcanic arc rift migration phenomenon vamp area plus the jade site and southernmost part of the okinawa trough spot area which form the prolongation of these two ridges these areas are characterized by extremely high heat flow locally submarine hydrothermal fluids from the okinawa trough tend to be strongly influenced by interaction of the hydrothermal fluids with organic matter in the sediment resulting in high alkalinity and nh 4 concentrations of the fluids the fluids also contain high concentrations of co 2 of magmatic origin submarine hydrothermal mineralization in the trough is diverse the clam site consists principally of carbonate chimneys interaction of the hydrothermal fluid with organic matter in the sediment is particularly strong at this site this is most probably a sediment hosted deposit in which sulphide minerals have deposited within the sediment column leaving spent ore fluids to emerge at the seafloor the jade site consists of active and inactive sulphide sulphate chimneys and mounds the zn pb rich sulphides at this site contain the highest concentrations of pb ag and au so far recorded in submarine hydrothermal sulphide deposits at minami ensei knoll and hatoma knoll active and inactive chimneys consist principally of anhydrite and barite as a result of phase separation of the hydrothermal fluids beneath the seafloor an intense black smoker has recently been discovered at yonaguni knoll in the spot area if it is confirmed that sulphide mineralization is dominant at this site this could be a highly prospective area the most prospective areas for economic grade minerals in the okinawa trough appear to be the jade site and the spot area

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

an investigation of subglacial processes at the microscale from briksdalsbreen norway the subglacial processes at briksdalsbreen norway are examined by a combination of sedimentology thin section and scanning electron microscope sem analysis of till samples from an exposed subglacial surface and from beneath the glacier studies of a fluted surface indicate that subglacial deformation is occurring on a field scale with flutes forming behind most clasts 0 6 m high at the thin section scale 0 014 2 0 mm it is seen that deformation is by rotation and attenuation and is dependent on till texture at the sem scale 0 1 0 4 mm it is seen that erosion is controlled by abrasion and percussion which produces distinct grain styles as part of an erosional continuum overall it is shown that rotation and attenuation is a dominant process at all scales and that the clast interactions associated with different scale perturbations within the shear zone control erosion and deposition as well as landform and fabric production

liquefaction and fluidization of lacustrine deposits from lahaul spiti and ladakh himalaya geological evidences of paleoseismicity along active fault zone abstract soft sediment deformational structures are important diagnostic features of paleoseismic studies these seismites result from local vigorous fluidization and hydroplastic deformation formed during liquefaction as a direct consequence of permanent deformation of ground surface due to earthquakes of large magnitude the region of eastern ladakh spiti basin and the upper sutlej river basin record a concentration of earthquakes in a well defined ne trending seismic zone sub parallel to the strike of leo pargil horst and the kaurik chango fault zone soft sediment deformational studies of the fluvial and fluvio lacustrine sequences near sumdo village along sangla valley of himachal pradesh and near saspol village of ladakh indicate that the kaurik chango fault zone is a seismogenic fault causing liquefaction and fluidization as the consequence of earthquake activity in the past thermal luminescence tl date of the deformational structures near the sumdo village constrains the paleoseismic activities of large magnitude between 90 000 years third activity to 26 000 years last geological evidence with a recurrence interval of approximately 10 000 years during the quaternary period

a wireless multi sensor subglacial probe design and preliminary results this paper introduces a new way to investigate in situ processes the wireless multi sensor probe as part of an environmental sensor network instruments are housed within a probe which can move freely and so behave like a clast these were deployed in the ice and till at briksdalsbreen norway the sensors measure temperature resistivity case stress tilt angle and water pressure and send their data to a base station on the glacier surface via radio links these data are then forwarded by radio to a reference station with mains power 2 5 km away from where they are sent to a web server in the uk the system deployed during 2004 05 was very successful and a total of 859 probe days worth of data from the ice and till were collected along with gps weather and diagnostic data about the system

the palaeoglaciology of the central sector of the british and irish ice sheet reconciling glacial geomorphology and preliminary ice sheet modelling digital elevation models of the area around the solway lowlands reveal complex subglacial bedform imprints relating the central sector of the lgm british and irish ice sheet drumlin and lineation mapping in four case studies show that glacier flow directions switched significantly through time these are summarised in four major flow phases in the region phase i flow was from a dominant scottish dispersal centre which transported criffel granite erratics to the eden valley and forced lake district ice eastwards over the pennines at stainmore phase ii involved easterly flow of lake district and scottish ice through the tyne gap and stainmore gap with an ice divide located over the solway firth phase iii was a dominant westerly flow from upland dispersal centres into the solway lowlands and along the solway firth due to draw down of ice into the irish sea basin phase iv was characterised by unconstrained advance of scottish ice across the solway firth forcing of a numerical model of ice sheet inception and decay by the greenland ice core record facilitates an assessment of the potential for rapid ice flow directional switching during one glacial cycle the model indicates that after fluctuations of smaller radially flowing ice caps prior to 30 ka bp the ice sheet grows to produce an elongate triangular shaped dome over nw england and sw scotland at the lgm at 19 5 ka bp recession after 18 5 ka bp displays a complex pattern of significant ice flow directional switches over relatively short timescales complementing the geomorphologically based assessments of palaeo ice dynamics the palaeoglaciological implications of this combined geomorphic and modelling approach are that a the central sector of the biis was as a major dispersal centre for only ca 2 5 ka after the lgm b the ice sheet had no real steady state and comprised constantly migrating dispersal centres and ice divides c subglacial streamlining of flow sets was completed over short phases of fast flow activity with some flow reversals taking place in less than 300 years

water escape structures in coarse grained volcaniclastic fluvial deposits of the ellensburg formation south central washington abstract the miocene ellensburg formation of south central washington consists largely of volcaniclastic fluvial sediments deposited on a gentle eastward sloping surface off the cascade volcanic belt the ellensburg fluvial systems were periodically choked with texturally immature volcanic detritus and were probably characterized by rapid deposition and aggradation pillar structures and pocket structures of water escape origin are generally uncommon in coarse grained sediments but are common in conglomeratic deposits of the ellensburg development of water escape structures in the ellensburg and in other coarse grained units is probably dependent on a combination of variables that includes depositional slope rates of sediment deposition and aggradation textural maturity sediment density and regional seismicity

rifting of kyushu japan based on the fault controlled concurrent eruption of oceanic island basalt type and island arc type lavas the tectonic environment of kyushu japan is affected both by the subduction of the philippine sea plate and by the extensional tectonics related to rifting of okinawa trough at the eastern margin of the eurasia plate we found that the sendai fault zone acts as a channel for concurrent eruption of oceanic island basalt oib type and island arc ia type basaltic rocks propagating west to east in the sendai region of southern kyushu the location of the sendai fault zone is likely to correspond to the left lateral shear zone in southern kyushu as inferred by gps earth observation network a similar magmatic association is present in the beppu shimabara bs graben system in central kyushu the associate magmas of oib type rocks in kyushu can be classified into typical em ii like and their intermediate oib type magmas in addition to morb like oib type magma in 87sr 86sr nb y systematics typical oib type and intermediate oib type magmas are erupted within the sendai fault zone and bs graben system respectively the former is characterized by highest nb y but low 87sr 86sr similar to morb like oib type magma erupted in northern kyushu and the latter has intermediate nb y and 87sr 86sr between typical and em ii like oib type magmas almost all the ia type rocks within the sendai fault zone are generated from parental ia type magma in kyushu and characterized by weak crustal assimilation having the lowest 87sr 86sr similar to typical oib type magma but the highest 143nd 144nd of arc magmas in kyushu the ages of both types of basaltic rocks within the sendai fault zone range from 1 6 to 0 01 ma clearly younger than those of andesitic rocks on northern and southern outsides of the fault zone and become younger from west to east initial formation of the fault zone has been induced by the counterclockwise rotation of southern kyushu during the last 2 ma as well as the bs graben system kyushu has continued to be split into three parts by the sendai fault zone and bs graben during the quaternary northern central and southern zones their initial formation ages are likely to be linked to the initial rifting age of the middle okinawa trough back arc basin

observed performance of multipropped excavation in stiff clay a 10 m deep multipropped excavation in the overconsolidated and fissured gault clay has been monitored unusual features of the field monitoring were to measure strut loads and earth pressures as well as wall deflections and rebar stresses at one of the diaphragm wall panels and to monitor both vertical subsurface movements and pore pressures in the center of the site in addition overall ground response to construction activities was recorded the results of the field monitoring have shown a significant reduction in lateral stresses associated with small ground movements after wall installation as a result of low horizontal stresses in the ground after wall installation the observed strut forces wall deflections and earth pressures were substantially lower than conventional design predictions in the center of the site unusual pore pressures and soil swelling behavior were observed following each stage of excavation a rapid rise of pore pressures existed accompanied by general swelling of the clay throughout the stratum the pore pressures in the fissure system appeared to be very different from those in the soil lumps and the observed vertical subsurface strain distribution with depth does not seem to fit with classical swelling theory a new displacement ratio is defined as the ratio of total horizontal to vertical surface ground movement for the top down construction in gault clay this ratio was 1 during the wall installation and piling but it gradually reduced to 0 6 at the end of excavation

micromorphological aspects of glaciolacustrine sediments in northern patagonia argentina in this study the sedimentology micromorphology and structure of four deformation sites in end moraines or near end moraine settings are presented micromorphology has proven to be a powerful tool in the interpretation of the sediments the four sites are related to three of the four major glaciations known from this part of patagonia nahuel huapi anfiteatro and pichileufu all four sites are characterised by glaciolacustrine environments in which sedimentation occurred at least partly on and or against dead ice with the exception of one section in the san martin de los andes area where deformation occured by active ice push all major disturbances faults and folds are the result of dead ice collapse comparison with micromorphological observations on basal tills shows that the sediments all lack a clear subglacial imprint

what causes till thickness to change over distance answers from mýrdalsjokull iceland abstract many explanations have been provided for variations of the spatial distribution and thickness of till sheets this paper gives new insight into the architecture of a stratigraphically distinct till sheet as a function of the type of substratum and preadvance topography at a scale of 10 km this emphasises the sensitivity of the subglacial system to changes in the basal drainage conditions the study area is the forefield of slettjokull at the northern margin of the m rdalsjokull ice cap central south iceland here detailed lithostratigraphical and sedimentological investigations including mapping of the thickness for two till units sediment logging clast fabric and geotechnical measurements provide a basis for interpretations the results show that the thickness of a stratigraphically distinct till sheet is directly correlated to the type of substratum where the substratum consists of sorted sediments the till is thin conversely the till is thick where the substratum consists of till overlying sorted sediments a sedimentological model is presented in which till thickness is tied to the variable hydraulic conditions experienced in a deforming subglacial bed

three dimensional seismic structure beneath southwest japan the subducting philippine sea plate abstract a three dimensional seismic structure beneath southwest japan has been investigated in detail by applying an inversion method this analysis clearly reveals the present and possibly the past subduction of the philippine sea plate beneath southwest japan beneath the izu peninsula the philippine sea plate does not appear to subduct but collides against the continental asian plate here and its thickness appears thinnest at most about 30 km from the tokai to the shikoku regions the high velocity zone corresponds well to the zone of subcrustal earthquakes down to a depth of about 60 70 km indicating that the subduction of the present philippine sea plate does not reach below this depth here however a small high velocity portion appears at depths between 100 km and 150 km beneath a part of the kinki region and probably extends to the chugoku region where no corresponding seismic activities exist these high velocities might be an indication of the remnants of the past subduction of the philippine sea plate in the kyushu region the high velocity zone continues down to a depth of about 150 km or even to 200 km in the southern part corresponding to a steeply inclined seismic zone the philippine sea plate in this region appears to be thicker than in regions east of the kyushu palau ridge it was also found that there exist narrow low velocity zones intervening within the philippine sea plate where two aseismic ridges the kyushu palau and shichito iwojima ridges extend northwards and the nankai trough shows warping these low velocity zones give support to the buoyant subduction hypothesis it also appears that lateral heterogeneities existing within and around the subducting plate are closely related to the mode of rupture of large earthquakes occurring around there

quantitative assessment of the hydraulic role of subglaciofluvial interbeds in promoting deposition of deformation till northern till ontario the northern till is a thick 65 m deformation till underlying some 7500 km2 of southern ontario canada including the peterborough drumlin field it was deposited below the lake ontario ice stream of the laurentide ice sheet the till rests on glaciotectonized aquifer sediments and consists of multiple beds of till up to 6 m thick these are separated by boulder lags sometimes in the form of striated pavements with thin 30 cm interbeds of poorly sorted waterlaid sand the composite till stratigraphy indicates punctuated aggradation where the subglacial bed was built up incrementally by the repeated immobilization of deforming overpressured till layers boulders and sands indicate pauses in subglacial aggradation marked by sluggish sheet flows of water that reworked the top of the underlying till interbeds are laterally extensive and correlated using downhole electrical conductivity core recovery and natural gamma data a 3 d finite element model feflow using data from 200 cored and geophysically logged boreholes and a large digital water well dataset of 3400 individual records shows that the till functions as a leaky aquitard as a consequence of water flow through interbeds it is proposed that interbeds played a similar role in the subglacial hydraulic system below the laurentide ice sheet by allowing drainage of excess porewater pressures in deforming sediment and promoting deposition of till this is in agreement with theoretical studies of deforming bed dynamics and observations at modern glaciers where porewater in the deforming layer is discharged into underlying aquifers in this way the presence of interbeds may be fundamental in retarding downglacier transport of deforming bed material thereby promoting the build up of thick subglacial till successions

subglacial decoupling at the sediment bedrock interface a new mechanism for rapid flowing ice abstract in undetermined on millennial or even centennial time scales the activity of rapid flowing ice can affect climate variability and global sea level through release of meltwater into the ocean and positive feedback loops to the climate system at the surge type glacier bruarjokull an outlet of the vatnajokull ice cap eastern iceland extremely rapid ice flow was sustained by overpressurized water causing decoupling beneath a thick sediment sequence that was coupled to the glacier this newly discovered mechanism has far reaching consequences for our understanding of fast flowing ice and its integration with sediment discharge and meltwater release c 2006 elsevier ltd all rights reserved

ice fracturing during jokulhlaups implications for englacial floodwater routing and outlet development theoretical studies of glacial outburst floods jokulhlaups assume that i intraglacial floodwater is transported efficiently in isolated conduits ii intraglacial conduit enlargement operates proportionally to increasing discharge iii floodwater exits glaciers through pre existing ice marginal outlets and iv the morphology and positioning of outlets remains fixed during flooding direct field observations together with historical jokulhlaup accounts confirm that these theoretical assumptions are not always correct this paper presents new evidence for spatial and temporal changes in intraglacial floodwater routing during jokulhlaups secondly it identifies and explains the mechanisms controlling the position and morphology of supraglacial jokulhlaup outlets and finally it presents a conceptual model of the controls on supraglacial outbursts field observations are presented from two icelandic glaciers skei ararjokull and solheimajokull video footage and aerial photographs taken before during and after the skei ararjokull jokulhlaup and immediately after the solheimajokull jokulhlaup reveal changes in floodwater routing and the positioning and morphology of outlets field observations confirm that glaciers cannot transmit floodwater as efficiently as previously assumed rapid increases in jokulhlaup discharge generate basal hydraulic pressures in excess of ice overburden under these circumstances floodwater can be forced through the surface of glaciers leading to the development of a range of supraglacial outlets the rate of increase in hydraulic pressure strongly influences the type of supraglacial outlet that can develop steady increases in basal hydraulic pressure can retro feed pre existing englacial drainage whereas transient increases in pressure can generate hydraulic fracturing the position and morphology of supraglacial outlets provide important controls on the spatial and temporal impact of flooding the development of supraglacial jokulhlaup outlets provides a new mechanism for rapid englacial debris entrainment

nd and sr isotopic study of volcanic rocks from japan two older granitic rocks and some selected quaternary volcanic rocks from the japanese islands were analyzed in a reconnaissance study for the purpose of examining the relationships between nd and sr isotopic abundances and the megatectonic structure around the japanese islands model ages of 0 9 ae were determined by the nd and sr methods on a paleozoic gneiss which confirms that a relatively ancient acidic basement exists in the japanese islands the nd and sr isotopic data show that the cretaceous granodiorite is the result of partial melting of older crust the nd of tholeiitic rocks from the izu arc gives e nd ranging from 8 3 to 9 3 and with the corresponding e sr from 14 5 to 18 5 these results are identical to those found for the mariana arc these values are distinctly lower than typical morb by around 1 2 eu this difference in e nd between arcs and morb is attributed to the contribution of oceanic sediments to the partial melts produced during subduction of oceanic crust the hakone volcano is clearly confirmed as belonging to an oceanic source by nd isotopic results e sr e nd values of the volcanics from a section along the fossa magna show a clear indication that they are a blend of oceanic mantle material and continental crustal material the crustal component clearly increases in going from south to north volcanics across the northeast japan arc also show a distinct correlation of e sr e nd related to the position relative to the active subduction zone but with the opposite trend these relationships of the present isotopic pattern and the zonal arrangement relative to the subduction zone suggest the former existence of a local spreading center in the japan sea in general there appear to be regular isotopic relationships between the izu mariana oceanic island arc and the continental island arc of japan which indicates that partially melted or assimilated older continental basement is admixed with young rising oceanic arc magmas

a complex subglacial clastic dyke swarm solheimajokull southern iceland abstract a complex network of clastic dykes dissects loosely consolidated holocene sediments along the east flank of the proglacial braid plain of solheimajokull southern iceland the dykes comprise downward bifurcating intrusions up to 0 5 m thick and several metres in length and are intruded into glaciogenic deposits sandy gravel gravelly sand interlaminated silt and sand and diamicton the dykes were sourced from a clast poor sandy diamicton interpreted as a subglacial till and were intruded downwards beneath solheimajokull glacier during a previous phase of advance as the glacier advanced southwards it loaded the sediment column resulting in the intrusion of dykes with a consistent south southwest dip with rare northward dipping examples the dyke fills are characterised by laminated sediment with laminae oriented parallel to the dyke margins and comprise interlaminated clay silty clay silt sand sandy gravel and diamicton in some dykes high concentrations of pebble to boulder sized clasts occur in association with rotated pods of the laminated sediment the laminae are thought to have evolved by a slow long lived intrusion process that involved the repeated fracture and expansion of the host sediments followed by viscous smearing on of subglacial material onto the dyke walls rather than rapid injection of fluidised sediment

strontium isotopic composition of hot spring and mineral spring waters japan abstract in japan hot springs and mineral springs are distributed in quaternary and neogene volcanic regions as well as in granitic sedimentary and metamorphic regions lacking in recent volcanic activity the87sr 86sr ratio was determined in hot spring and mineral spring waters obtained from 47 sites the ratios of waters from quaternary and neogene volcanic regions were in the range 0 703 0 712 which is lower than that from granitic sedimentary and metamorphic regions 0 706 0 712 the geographical distribution of the ratios coincides with the bedrock geology and particularly the ratios of the waters in quaternary volcanic regions correlate with those of surrounding volcanic rocks these features suggest that subsurface materials control the87sr 86sr ratios of soluble components in the hot spring and mineral spring waters

geochemistry of the quaternary volcanic rocks of the northeast japan arc major and trace element data are presented for a series of lavas from 17 volcanic centres in the ne japan arc these represent a transect of the quaternary arc from its volcanic front type a volcanoes in the east across its central zone type b to its western margin type c rocks range from basalt to dacite in composition and the variation is attributed to fractionation of plagioclase mafic silicates and titanomagnetite for comparative purposes trace element data for each volcano are presented on a 55 wt sio2 normalised basis the volcanoes display the characteristic features of arc volcanism viz enrichment in large ion lithophile elements rb sr ba k and depletion in high field strength elements zr nb hf ta using these data and derived primary magma compositions tatsumi et al 1983 mixing calculations give the percentages of fractionating mineral phases necessary to derive the 55 wt sio2 liquids these data together with published distribution coefficients allow the calculation of trace element abundances in the primary magmas reciprocal trace element plots indicate that irrespective of position with respect to the volcanic front the elements la ba k sr nb y and zr of the primary magmas all lie on a common line strongly suggesting that the melts are the products of varying degrees of melting of a common homogeneous source however those melts close to the volcanic front type a show anomalous rb th and pb values suggesting that their mantle source was enriched in these elements further calculations suggest that the hfs depletion is not due to retention by residual mineral phases but is a feature of the source thus the data suggest a that the source of the arc volcanism was homogeneous and b that the characteristic chemical features were an inherent feature of the source since zr nb ratios in the source melts are close to those found in n type morb it is suggested that a major component of arc volcanic source rocks was a depleted mantle of the type which has given melts of n type morb composition lil elements added to such a depleted source are derived by the loss of silica rich aqueous fluids from the descending subducting slab such losses occur within the first 100 km and are fixed in the overlying mantle wedge this contaminated material is transported down by drag induced convection producing a homogeneous but metasomatised mantle within the melting zone diapiric uprise produced by small scale melting produces further melting with the major control of melt chemistry being the degree of partial melting superimposed on this chemistry is a localised addition of pb rb and th in the source of those volcanoes nearest the volcanic front

two overlapping plates subducting beneath central japan as revealed by strontium isotope data abstract in central japan the pacific plate subducts westward beneath the eurasian plate and the philippine sea plate subducts northwestward into the mantle wedge between the eurasian plate and the subducted pacific slab there the northeast japan arc is joined to the izu ogasawara arc we determined 87 sr 86 sr ratios and rb and sr contents for 47 volcanic rock samples from 15 quaternary volcanoes in central japan and summarized the geographical distribution of the ratios the general trend of slowly increasing 87 sr 86 sr ratio from the back arc side toward the volcanic front in the northeast japan arc is broken by a marked high ratio above 0 7060 centered around akagi volcano located at the southernmost region of the arc elsewhere the ratio along the volcanic front in this arc varies within the range 0 7038 to 0 7045 the marked high 87 sr 86 sr ratio is considered to be due to the addition of slab derived components transported by the philippine sea plate to the magma generating region in the mantle wedge beneath central japan therefore the geographical distribution of the high ratio may correspond to that of the philippine sea slab derived components in the mantle wedge and we may draw the underground outline of the philippine sea plate this outline implies that an aseismic portion of the philippine sea plate continues a few tens km ahead of the seismic one a belt of low 87 sr 86 sr ratios from the izu peninsula northwestward along the northern end of the izu ogasawara arc coincides with the zone where the subducting philippine sea plate is not observed seismologically while it is detected seismologically on both sides of the belt

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

drainage beneath ice sheets groundwater channel coupling and the origin of esker systems from former ice sheets abstract the nature of the drainage system beneath ice sheets is crucial to their dynamic behaviour but remains problematic an experimentally based theory of coupling between groundwater and major channel systems is applied to the esker systems in the area occupied the last ice sheet in europe which we regard as a fossil imprint of major longitudinal drainage channels we conclude that the large scale distribution and spacing of major eskers is consistent with the theory of groundwater control in which esker spacing is partly controlled by the transmissivity of the bed it is concluded that esker patterns reflect the large scale organisation of the subglacial drainage pattern in which channel development is coupled to groundwater flow and to the ice sheet s dynamic regime the theory is then used to deduce basal meltwater recharge rates and their spatial variability from esker spacing in an area in which the ice sheet was actively streaming during its final retreat patterns of palaeo groundwater flow and head distribution and the seasonally varying magnitude of discharge from stream tunnels at the retreating ice sheet margin major channel esker systems appear to have been stable at least over several hundred of years during the retreat of the ice sheet although major dynamic events are demonstrably associated with major shifts in the hydraulic regime modelling suggests that glaciation can stimulate deep groundwater circulation cells that are spatially linked to channel locations with groundwater flow predominantly transverse to ice flow that the circulation pattern has the potential to create large scale anomalies in groundwater chemistry and that the spacing of channels will change through the glacial cycle influencing water pressures in stream tunnels subglacial hydraulic gradients and effective pressure if the latter is reduced sufficiently it could trigger enhanced bed deformation thus coupling drainage to ice sheet movement it suggests the possibility of distinctive phases of sediment deformation and drumlin mobilisation during a glacial cycle

glaciotectonics of the ltterbeck uelsen push moraines germany the two saalian push moraines of ltterbeck uelsen formed during the older saalian glaciation consist of tertiary and quaternary deposits locally glaciofluvial deposits are prominent as a result of reworking of older deposits by meltwater the push moraines are built up from a number of imbricated and folded structural units which have moved laterally and in part frontally from two glacial basins dominant structures are large shallow and flat lying glaciotectonic nappes that have been displaced over distances of at lest 1 km in the direction of tectonic transport overprinting relations of two deformation phases give a relative age difference between the two push morianes

strontium isotopic characteristics of arc volcanic rocks at the initial stage of subduction in western japan abstract in western japan the philippine sea plate subducts northwestward from the ryukyu trench and the nankai trough to form two volcanic arcs the ryukyu and southwest japan arcs respectively these arcs are thought to be in the initial stage of subduction because microearthquake data show that the subducting slab extends only a short distance from the trenches in the southwest japan arc volcanoes are aligned parallel to the nankai trough although the leading edge of the subducted slab does not reach under the volcanic arc to the south the subducted slab reaches just under the ryukyu volcanic arc we determined 87sr 86sr ratios and rb and sr contents for 39 volcanic rock samples from 14 quaternary volcanoes of both arcs and summarized the spatial distribution of the ratios the ranges of 87sr 86sr ratios of volcanic rocks from the ryukyu and southwest japan arcs are 0 7040 0 7069 and 0 7035 0 7066 respectively in the ryukyu arc the regional variation in 87sr 86sr ratios of volcanic rocks is hidden under the wide scatter of ratios of different volcanic rocks from each one volcano in the southwest japan arc the ratios of volcanic rocks from volcanoes on the volcanic front vary in the along arc direction 0 7040 0 7048 for the western part 0 7035 0 7039 for the central part and 0 7048 0 7066 for the eastern part the across arc variations in the ratios are different from place to place these isotopic features suggest the absence of slab derived components in the source mantle and reflect the heterogeneous nature of 87sr 86sr ratios in the upper mantle modified by crustal processes this coincides with the seismological observation that the subducting philippine sea slab does not reach under the volcanic arc at all

late wisconsinan sub glacial clastic intrusive sheets along lake erie bluffs at bradtville ontario canada abstract numerous clastic intrusive sheets a few decimetres to more than 16 m long 1 120 cm thick and extending one to more than 25 m laterally occur along a 350 m long section of the late wisconsinan catfish creek drift in the lake erie bluffs at bradtville southwestern ontario most of them are downglacier dipping dikes the largest one terminating in the underlying middle wisconsinan tyrconnell formation most dikes strike nne ssw at right angles to the local direction of glacier movement during the deposition of catfish creek drift the tops of some of them are truncated or displaced downglacier by shearing the main concentration of clastic intrusive sheets is on the upglacier side of a glaciotectonically folded anticline of tyrconnell formation clays and silts underlying the catfish creek drift the host sediments are catfish creek till gravel sand and silt and tyrconnell formation silt and clay most intrusive sheets particularly the small to medium ones consist of massive to crudely laminated sand and silt intruded from below by a dewatering process the largest dike reflects in its composition mainly the adjoining or higher lying host sediment materials and its main part was formed by downward infilling or by gravity flows into an open fracture the large dike is flanked by small laminated silty sand sheets and several small apophyses some of them injected downward and sideways others upward by dewatering the clastic intrusive sheets were formed under a moving glacier the erie lobe probably both at the beginning and towards the end of the deposition of catfish creek till their location and position was predetermined by glaciotectonically induced listric planar structures and zones of weakness mainly tension fractures that strike transverse to glacier movement and dip downglacier and also by confinement of pore water in a permeable sediment wedge between the less pervious tyrconnell formation and massive catfish creek basal till

controls on englacial sediment deposition during the november 1996 jokulhlaup skeiđararjokull iceland this paper presents sedimentary evidence for rapid englacial debris entrainment during jokulhlaups previous studies of jokulhlaup sedimentology have focused predominantly on proglacial impact rather than depositional processes within glaciers however observations of supraglacial floodwater outbursts suggest that englacial sediment emplacement is possible during jokulhlaups the november 1996 jokulhlaup from skei ararjokull iceland presented one of the first opportunities to examine englacial flood deposits in relation to former supraglacial outlets using observations from skei ararjokull this paper identifies and explains controls on the deposition of englacial flood sediments and presents a qualitative model for englacial jokulhlaup deposition englacial jokulhlaup deposits were contained within complex networks of upglacier dipping fractures simultaneous englacial deposition of fines and boulder sized sediment demonstrates that englacial fracture discharge had a high transport capacity fracture geometry was an important control on the architecture of englacial jokulhlaup deposits the occurrence of pervasively frozen flood deposits within skei ararjokull is attributed to freeze on by glaciohydraulic supercooling floodwater flowing subglacially or through upglacier dipping fractures would have supercooled as it was raised to the surface faster than its pressure melting point could increase as glaciostatic pressure decreased evidence for floodwater contact with the glacier bed is supported by the ubiquitous occurrence of sheared diamict rip ups and intra clasts of basal ice within jokulhlaup fractures deposited englacially some 200 350 m above the bed of skei ararjokull evidence for fluidal supercooled sediment accretion is apparent within stratified sands deposited englacially at exceptionally high angles of rest in the absence of post depositional disturbance such primary sediment structures cannot be explained unless sediment is progressively accreted to opposing fracture walls ice retreat from areas of former supraglacial outbursts revealed distinct ridges characterized by localized upwellings of sediment rich floodwater these deposits are an important addition to current models of englacial sedimentation and demonstrate the potential for post jokulhlaup landform development copyright 2001 john wiley sons ltd keywords jokulhlaup englacial debris entrainment glaciofluvial sediment hydrofracturing iceland

subglacial drainage by groundwater channel coupling and the origin of esker systems part ii theory and simulation of a modern system abstract the observations from breidamerkurjokull reported in part i are used as a basis for a theory of coupled channel groundwater flow that suggests that the large scale geometry of the hydraulic system self organises as a consequence of coupling between groundwater and channel flow the pattern of channel esker distribution is largely determined by winter conditions and the sedimentary characteristics of eskers are largely determined by summer conditions when large discharges of surface meltwater penetrate to the bed in the terminal zone a simulation model is developed to explore evolution of the channel groundwater system during a period of glacier growth it suggests that as the glacier grows channel esker frequencies will increase as will the proportion of the melt flux discharged by channel flow that groundwater impacts can extend to depth that low water pressure bulbs will extend downwards beneath channels that groundwater upwelling towards channels are strong enough to create widespread conditions for liquefaction and that pressure shocks can occur as the channel system reorganises itself

contemporaneous ascent of within plate type and island arc type magmas in the beppu shimabara graben system kyushu island japan abstract within plate wp type and island arc ia type magmas have erupted in north kyushu and south kyushu respectively during quaternary time the former is related to the eastern end of the east asian extensional province and the latter to the subduction zone of the philippine sea plate the beppu shimabara graben system in the central part of kyushu island is located in the area of overlap between them quaternary volcanic rock samples from the graben system can be chemically classified as wp and ia types by their multi element patterns and positions on a zr nb y discrimination diagram rocks of both type and of similar ages occur throughout the graben system furthermore the rocks of wp type give systematically higher 87sr 86sr ratios 0 7048 0 7049 than those of the associated ia type around 0 7040 the relations between 87sr 86sr and nb y ratios of the former are clearly distinguished from those of the latter these results demonstrate that this graben system is characterized by the contemporaneous ascents of wp and ia type magmas to the same quaternary volcanic areas such rivalrous ascents of wp and ia type magmas seem to be a common feature of magmatism associated with graben in extensional provinces related to subduction zones of island arcs and their boundary areas

strontium isotope composition in volcanic rocks from the northeast japan arc abstract in the northeast japan arc a number of quaternary volcanoes form a long narrow belt parallel to the japan trench 87 sr 86 sr ratios were determined in 52 specimens of volcanic rocks from 27 volcanoes in the northeast japan arc area the results reveal that the ratios change systematically in space decreasing 87 sr 86 sr ratios across the arc were confirmed over a wide area of northeast japan in the same direction increases in both rb and sr contents were also found the regular trends are considered to be a strong constraint for elucidation of subduction originated magma genesis at the eurasia plate vs pacific plate boundary in the northern region of the northeast japan arc 87 sr 86 sr ratios in volcanic rocks along the volcanic front were almost constant 0 7038 0 7045 and slightly higher than those from the izu ogasawara arc 0 7032 0 7038 this suggests that interactions between the eurasia plate and the pacific plate and those between the philippine sea plate and the pacific plate are slightly different the southern region of the northeast japan arc where the direction of the volcanic front bends from southward to westward showed anomalously high 87 sr 86 sr ratios reaching to 0 7077 this region coincides with the triple junction of the eurasia pacific and philippine sea plates suggesting anomalous interaction at the triple junction

evidence for multiphase water escape during rafting of shelly marine sediments at clava inverness shire ne scotland abstract the pleistocene shelly glaciomarine sediments exposed at clava near inverness northeast scotland occur in a series of thrust bound rafts accreted at on the up ice side of a bedrock high 150 m above od on the se side of the valley of the river nairn these sediments originally formed part of a coarsening upwards deltaic or subaqueous fan sequence deposited in the marine fjord of the loch ness basin located some 50 km to the sw the geometry of these allochthonous rafts coupled with the associated thrusting and large scale folding of these bodies are typical of many glacially transported rafts described in literature however at clava macro and microscopic evidence indicates that these ice rafted sediments were not frozen with liquefaction hydrofracturing and water escape occurring repeatedly during their transport and accretion the presence of large scale detachments within the sequence has led to the development of a purely glacitectonic model for rafting at clava the detachments acted as a focus for fluid flow which lubricated these decollement surfaces aiding in the subglacial transport of the rafts

modeling dependence of moraine deposition on climate history the effect of seasonality abstract a simple shallow ice flowline glacier model coupled to a model of sediment transport and deposition is used to simulate formation and preservation of moraines the number positions and volume of moraines formed all are sensitive to the climate history assumed we drive the model with the gisp2 central greenland temperature record and with reduced millennial amplitude versions of that record to test the hypothesis that the younger dryas and other millennial oscillations were primarily wintertime events and thus had less influence on glacier behavior than did the last glacial maximum with its strong summertime as well as wintertime signal we find that forcing the model by gisp2 with dampened strength of the millennial scale signal provides modeled moraine configurations that reflect observed moraine records in the northern hemisphere

glaciovolcanic landsystems and large scale glaciotectonic deformation along the brekknafjoll jarlhettur iceland abstract this paper documents the glaciovolcanic landsystem of the brekknafjoll jarlhettur ridge in central iceland glaciolacustrine diamict is found beneath and in association with a complex assemblage of pillow lava lava breccias and hyaloclastites three depositional environments are identified glaciolacustrine fan pillow lava dome and hyaloclastite fan these subaqueous environments occurred both simultaneously and at different times along the volcanic fissures which underlie the ridge and have given rise to a complex facies architecture this facies architecture provides evidence that the ridge evolved in a time transgressive fashion during several episodes of volcanism some of which may have been punctuated by periods of ice erosion associated with the ridge are large diapiric folds in diamict and gravel which form by the loading and lateral displacement of saturated diamict beneath the developing volcanic pile a depositional model is presented which emphasises the glaciolacustrine component and the time transgressive nature of the glaciovolcanic landsystem much of the eruption occurred in subglacial to englacial lakes or vaults which were probably linked by water and sediment exchange the initial subglacial vaults appear to have extended beyond the fissure limits and were infilled by glaciolacustrine diamicts subaqueous outwash and the eruption of pillow lava this was followed by the eruption of hyaloclastite sand and breccia forming an elongated fan

major changes in ice stream dynamics during deglaciation of the north western margin of the laurentide ice sheet abstract victoria island lies at the north western limit of the former north american laurentide ice sheet in the canadian arctic archipelago and displays numerous cross cutting glacial lineations previous work suggests that several ice streams operated in this region during the last wisconsinan glaciation and played a major role in ice sheet dynamics and the delivery of icebergs into the arctic ocean this paper produces the first detailed synthesis of their behaviour from the last glacial maximum through to deglaciation 21 9 5 cal ka bp based on new mapping and a previously published radiocarbon constrained ice sheet margin chronology over 70 discrete ice flow events flow sets are fitted to the ice margin configuration to allow identification of several ice streams ranging in size from large and long lived thousands of years to much smaller and short lived hundreds of years the reconstruction depicts major ice streams in m clure strait and amundsen gulf which underwent relatively rapid retreat from the continental shelf edge at some time between 15 2 and 14 1 cal ka bp a period which encompasses climatic warming and rapid sea level rise meltwater pulse 1a following this overall retreat was slower and the ice streams exhibited asynchronous behaviour the amundsen gulf ice stream continued to operate during ice margin retreat whereas the m clure strait ice stream ceased operating and was replaced by an ice divide within 1000 years this ice divide was subsequently obliterated by another short lived phase of ice streaming in m clintock channel 13 cal ka bp the timing of this large ice discharge event coincides with the onset of the younger dryas subsequently a minor ice divide developed once again in m clintock channel before final deglaciation of the island shortly after 9 5 cal ka bp it is concluded that large ice streams at the nw margin of the laurentide ice sheet equivalent in size to the hudson strait ice stream underwent major changes during deglaciation resulting in punctuated delivery of icebergs into the arctic ocean published radiocarbon dates constrain this punctuated delivery as far as is possible within the limits imposed by their precision and we note their coincidence with pulses of meltwater delivery inferred from numerical modelling and ocean sediment cores

isotopic characteristics of neogene quaternary tephra from iodp site u1438 a record of explosive volcanic activity in the kyushu ryukyu arc a m acknowledges support from the swiss national science foundation grant 200020 135511 to othmar muntener and grant p2lap2 171819 to a m and swiss iodp this work was also supported by grants to g m y and m b from nsf oce 1537135 and iodp

ice flow modulated by tides at up to annual periods at rutford ice stream west antarctica 1 for over 2 years we have collected gps data 40 km upstream of the grounding line on rutford ice stream west antarctica here we examine deviations from mean downstream flow although the record is incomplete during winter there is clear modulation of flow at semi diurnal diurnal two weekly semi annual and annual ocean tidal frequencies this is the first observation of ice stream flow variations over such a long time period and such a wide range of frequencies the ice stream flows fastest at equinoxes when there are two semi diurnal tides of equal magnitude and slowest at solstices when one of the semi diurnal tides has lower amplitude the sensitivity of the downstream flow is greatest to the long period forcing which suggests that ice stream velocity may be affected by future changes in sea level if so this effect would provide a feedback whereby rising sea levels could increase ice stream velocity and hence discharge

dike filled extensional structures in cenozoic deposits of the kleszczow graben central poland abstract the origin and development of the cenozoic kleszczow graben were strongly influenced by a pre existing fault pattern within the permian mesozoic bedrock dike filled fractures penetrating neogene quaternary deposits analysed in the opencast belchatow browncoal mine follow extensional structural patterns parallel to the axes of the local anticlinal forms established or rejuvenated in the quaternary these structures are particularly well developed along the fold crests the spacing and structural features of the fractures and normal faults are explained in terms of the tensile stress operating in beds subjected to folding the main localities of the quaternary folds precisely align with segments of two deep seated reverse faults the kleszczow kodr b fault and the gomunice piaski fault both are nw se orientated dislocations along a hinge zone of the laramide ekinsko anticline subcropping the cenozoic graben infill in the open mine the origin of the quaternary folds as fault overlying folds is attributed to a young block uplift on the ekinsko anticline area which is well recorded by a strong reduction in thickness of the cenozoic sediments the quaternary succession is reduced in thickness twice as much as the neogene the successive stages of quaternary reactivation of the ekinsko anticline during the cromerian through the late saalian with diminishing intensity are believed to be correlatable with the sequence of glacial rebound events coupled with mobility of the deep rooted fault zone

oxygen and strontium isotopic characteristics of calc alkalic volcanic rocks from the central and western japan arcs evaluation of contribution of crustal components to the magmas abstract 18o 16o and 87sr 86sr ratios were determined for quaternary calc alkalic volcanic rocks from six volcanic rock suites in the central and western japan arcs the 18o values relative to smow and 87sr 86sr ratios range from 6 3 to 9 90 00 and 0 70357 to 0 70684 respectively both the o and sr isotopic compositions are higher than those for island arc primitive magmas and their differentiates the isotopic compositions of the calc alkalic rocks cannot be derived by a simple fractional crystallization of the primitive magmas on the other hand the 18o and 87sr enrichment is confined to the rock suites located in well developed island arcs having thick continental type crust with low or negative bouguer anomalies involvement of 18o and 87sr rich crustal material in the magma formation is suggested the isotopic compositions vary remarkably within individual rock suites as well as from volcano to volcano the data points in 18o vs 87sr 86sr plot accord with a mixing model between primitive magmas and crustal material of dioritic composition on an average assuming their comparative sr contents the primitive magmas involved could not be low sr tholeiites but magmas more or less enriched in incompatible elements including sr which correspond to high alkali tholeiites or alkali basalts and their evolved magmas the nature of the primitive magmas seems to change from tholeiitic to more alkalic with progressing island arc evolution mixing of crust derived melts is more plausible than assimilation of solid rocks for involving 20 to 30 crustal material in the magmas along simple mixing curves isotopic variations between the rock suites are ascribed to variable sr concentration radio of the end members variable isotopic compositions of crustal material or variable mixing ratio of the end members extremely high 18o rocks with moderate increase in 87sr 86sr ratio suggest another mixing process in shallower magma chambers between andesite magmas and metasedimentary rocks having high 18o and 87sr 86sr values but low sr content subsequent fractional crystallization of once derived magmas would be the prominent process for the rock suites showing gradual increase in 18o up to 10 00 with uniform 87sr 86sr ratios

subglacial drainage by groundwater channel coupling and the origin of esker systems part 1 glaciological observations this work is presented in two parts part i presents observations on the coupling between subglacial channel flow and groundwater flow in determining subglacial hydraulic regime and creating eskers from an icelandic glacier that is suggested as an analogue for many parts of pleistocene ice sheets part ii develops a theory of perennial subglacial stream flow and the origin of esker systems and models the evolution of the subglacial stream system and associated groundwater flow in a glacier of the type described in part i it is suggested that groundwater flow may be the predominant mechanism whereby meltwater at the glacier bed finds its way to the major subglacial streams that discharge water to glacier margins

the role of seasonality in abrupt climate change abstract a case is made that seasonality switches dominated by wintertime were instrumental in abrupt climate changes in the north atlantic region during the last glaciation and into the holocene the primary evidence comes from mismatches between mean annual temperatures from greenland ice cores in comparison with snowline changes in east greenland northern europe and north america the most likely explanation is a shutdown or reduction in strength of the conveyor this allows the spread of winter sea ice across the north atlantic thus causing the northern region to experience much colder winters because they mimic the greenland temperature rather than the snowline signal changes in the atlantic intertropical convergence zone and the asian monsoon may also share a winter linkage with greenland thus the paleoclimate record is consistent with the notion that a huge continental sector of the northern hemisphere stretching from greenland to asia was close to an extreme winter threshold during much of the last glaciation winter climate crossed this threshold repeatedly with marked changes in seasonality that may well have amplified and propagated a signal of abrupt change throughout the hemisphere and into the tropics

strong impact of ion filtration on the isotopic composition of chlorine in young clay rich oceanic sediment pore fluids abstract a collection of 34 pore fluids from young clay rich sedimentary piles of the shikoku basin on the philippine oceanic plate at the front of the nankai subduction zone southeast of japan were analyzed for their chloride content and chlorine stable isotope composition 35cl and 37cl reported as 37cl these pore fluids are samples from iodp sites c0011 and c0012 which penetrate deeper than 500 meters below the seafloor at both sites the 37cl values display a regular decrease with depth from about 0 seawater value at the seafloor to 8 5 and 6 5 respectively in hydrogeologically isolated low permeability sediment levels at some depths local deviations of up to 6 in 37cl interrupt the overall decreasing trends they may be interpreted as the injection of external fluids into the sedimentary piles as a result of sedimentary levels with higher permeability at the bottom of the sedimentary piles the injected fluids probably originating from the altered oceanic crust systematically have 37cl values closer to seawater literature data indicate the display of downward trends of decreasing 37cl values of the pore fluids in many other young clay rich sedimentary piles nankai trough and the japan trench accretionary prisms black ridge and juan de fuca ridge flank here we use conservation equations to demonstrate that these 37cl depth profiles can be modeled using the effect of the compaction of growing clay rich sedimentary piles on the water and chlorides including 35cl and 37cl isotopes this modeling shows that a small isotope fractionation of chlorine isotopes 37cl 35clexpulsed fluid residual fluid in the range of 1 006 to 1 001 may explain the observed negative 37cl chlorides at the bottom of the sedimentary piles the complementary positive 37cl chlorides must accumulate at the top but are very likely erased by dilution with seawater chlorides across the seafloor interface this range of chlorine isotope fractionation values is in agreement with the theory of ion filtration of phillips and bentley 1987 in which the mobility of chlorides through semi permeable clay membrane is determined by ion repulsion based on this study we show that young pore fluids in clay rich sediments of the oceanic crust are 37cl depleted chloride reservoirs they might be the source of 37cl depleted chloride fluids advected at mud volcanoes on the seafloor but do not seem to contribute largely to subduction zone magmatic tectonic metamorphic products where no such 37cl depleted chlorine is documented this in turn is a strong argument to propose that most of the clay rich sediment s pore waters are released back into the ocean rather than subducted

the origin and glaciodynamic significance of sandstone ridge networks from the hirnantian glaciation of the djado basin niger the djado basin niger was located beneath the inner part of the late ordovician ice sheet the felar felar formation consists mainly of glaciomarine deposits associated with the major ice sheet recession within the glaciation and is bounded by two glacial unconformities structures corresponding to sandstone ridges are found within the felar felar formation sandstone ridges are several metres high about 10 m wide and hundreds of metres long these structures are organized in extensive anastomosed to subpolygonal networks the association of sandstone ridge networks with the later glacial unconformity and with other glacial evidence suggests sub glacial conditions for their origin sandstone ridge sedimentological characteristics indicate that sandstone ridges result from the scouring of the felar felar formation by sub glacial turbulent and pressurized meltwater then subglacial cavities were infilled with sand derived from glacial abrasion sandstone ridge networks are comparable with tunnel channels and document unusual drainage structures of the inner part of the palaeo ice sheet

paleogeographic reconstruction and origin of the philippine sea abstract our reconstruction of the philippine sea suggests that it formed by two distinct episodes of back arc spreading each of which resulted from seaward retreat of the trench in the first episode the protoizu bonin trench retreated northward and the west philippine basin formed behind the northern half of the palau kyushu ridge in the second episode the izu mariana trench retreated eastward and the shikoku and parece vela basins formed behind it during the last 17 ma the philippine sea basin has been moving northwestward with respect to eurasia shifting the ttt triple junction off central japan westward by about 50 km the motion of the philippine sea with respect to eurasia at the triple junction changed from north northwestward to west northwestward 10 5 ma ago for the period before 17 ma ago we construct two models retreating trench model and anchored slab model the izu bonin trench migrated from south to northeast rotating in a clock wise sense since 48 ma ago in the retreating trench model in the anchored slab model the trench has been fixed with respect to eurasian margin since 43 ma ago we prefer the retreating trench model because the deformation of the plate boundary along the eastern margin of eurasia during 30 17 ma ago is much simpler for this model than for the anchored slab model furthermore rotations of the bonin mariana islands are consistent with those predicted from the retreating trench model the 48 ma ages of the northern part of the palau kyushu ridge and of chichi jima of the bonin islands indicate that there was subduction beneath the northern half of the ridge beginning at least 48 ma ago from this and the subparallelism in trend between the northern part of the palau kyushu ridge and the central basin ridge we propose that the major part of the west philippine basin formed by back arc spreading in a n s direction behind the northern part of the palau kyushu ridge the pacific plate was moving northward with respect to hot spots from 48 to 43 ma ago which implies that the pacific plate is not likely to have been subducting beneath the west philippine basin during this time we speculate that another plate existed south of the pacific plate and thai it was subducting beneath both tile west philippine basin and australia the annihilation of this plate might he a cause for the sudden change of the pacific plate motion at 43 ma ago

geomorphological mapping of glacial landforms from remotely sensed data an evaluation of the principal data sources and an assessment of their quality abstract this paper presents the results of an experiment to compare glacial geomorphology mapped from remotely sensed imagery with 1 10 000 scale field mapping the field mapping was validated against high resolution lidar imagery of an area glacierized during the younger dryas and found to provide an essentially reliable if not complete representation of the glacial geomorphology the experiment consists of comparing the field mapping with digital elevation models shuttle radar topography mission c band landmap os panorama os profile nextmap and satellite imagery landsat thematic mapper of a 100 km2 region of central scotland north of glasgow that was last glaciated during the last glacial maximum and during the younger dryas respectively c 14 5 and 11 5 cal ka bp for the purposes of this exercise we concentrated on glacial lineaments flutes drumlins and crag and tail but attention was also given to moraine ridges and eskers qualitative and quantitative comparisons are performed and the results show that of the remotely sensed data sets only nextmap great britain provided results that showed any approximation to the field mapping os panorama and os profile provided very poor approximations and the other methods fail to provide any information of value attention is given to the issues of scale and the differences between a small scale detailed study such as this experiment in which a high resolution glacial geomorphological reconstruction is required and the small scale studies where the remote sensing techniques used here provide important evidence of regional significance when glaciers formed the largest elements of the landscape the paper concludes with a consideration of protocols for future geomorphological mapping exercises and outlines some of the requirements that must be adopted as these protocols are developed