upb dating of fe rich phases using a sequential leaching method a sequential leaching method was developed for upb dating of fe rich phases which uses a series of successively stronger acids the method was applied to date fe rich phases of magmatic origin in the kinsman quartz monzonite new hampshire usa and of sedimentary origin in the dales gorge member of the brockman iron formation hamersley basin australia using the composition of major element released by the acid leaching and combining it with x ray and sem analyses of the residues we were able to identify the relatively pure phases released and use these samples for dating magnetite separates from the kinsman quartz monzonite yielded upb age of 372 34 ma which is consistent with smnd and a rbsr isochron ages determined in previous studies leached whole rock samples of the brockman iron formation yielded a 207pb206pb age of 2213 250 ma which agrees with previously determined pbpb smnd and rbsr isochron ages this age is interpreted as the time of redistribution of u and pb associated with the fe rich phases during regional metamorphism while the potential of the sequential leaching method is demonstrated more work is needed in order to improve the precision of the data this requires further investigation of the nature of the pure phases

seismic velocity structure of the slab and continental plate in the region of the 1960 valdivia chile slip maximum insights into fluid release and plate coupling the south central chilean subduction zone has witnessed some of the largest earthquakes in history making this region particularly important for understanding plate coupling here we present the results of a local earthquake tomography study from a temporary local seismic network in the villarrica region between 39 and 40 s where the largest coseismic displacement of the 1960 valdivia earthquake occurred a lowvelocity anomaly and high vp vs values occur under the coastal region indicating mantle serpentinisation and or underthrusting of forearc material further east a high velocity anomaly is observed interpreted as normal high velocity mantle under the active volcanic arc a low velocity anomaly together with high vp vs ratios 1 8 and higher likely images fluid ascent beneath the volcanoes close to the subducting valdivia fracture zone the coastal low velocity anomaly extends further inland where it interrupts and shifts the high velocity anomalies associated with normal fast mantle velocities this may indicate enhanced fluid presence along this part of the margin probably caused by a stronger hydration of the incoming plate along the valdivia fracture zone this is consistent with geochemical fluid proxies u th pb ce ba nb in young volcanic rocks displaying peak values along the volcanic front at llaima and villarrica volcanoes and with recent gps measurements which suggested a local reduction in plate coupling in this region the shift in the high velocity anomaly underlying the central part may be caused by a north to south decrease in plate age and hydration across the valdivia fracture zone and may explain why a central valley is absent in this segment of the margin the low la yb ratios in the volcanic rocks from villarrica and llaima suggest that the high slab derived fluid flux causes elevated degrees of melting beneath these volcanoes providing an explanation as to why these are amongst the most active volcanoes in south america

the subglacial thermal organisation sto of ice sheets abstract this paper examines ice sheet wide variations in subglacial thermal regime and ice dynamics using the landform record exposed on the beds of former mid latitude ice sheets the laurentide cordilleran fennoscandian and british irish ice sheets we compare the landform patterns beneath these former ice sheets to the flow organisation beneath parts of the contemporary antarctic ice sheet inferred from radarsat 1 antarctic mapping project ramp data the evidence preserved in the landform record and observed on contemporary ice masses can be grouped into four major ice dynamical components that collectively define the subglacial thermal organisation sto of ice sheets these ice dynamical components are frozen bed patches ice streams ice stream tributaries and lateral shear zones frozen bed patches appear at a wide range of spatial scales spanning four orders of magnitude in some areas frozen bed zones comprise large proportions of the bed e g near the ice divide in continental areas whilst in other areas they constitute isolated islands in areas dominated by thawed bed conditions ice streams narrow zones of fast flow in ice sheets that are otherwise dominated by slow sheet flow are also common features of quaternary ice sheets tributaries to ice streams flow at velocities intermediate between full ice stream and sheet flow and may divert ice drainage from one primary ice stream corridor to an adjacent one sharp lateral boundaries between landforms indicate sliding and non sliding conditions respectively these lateral boundaries represent important discontinuities in the glacial landscape and mark the location of shear zones between thawed bed ice streams and intervening frozen bed areas we use the landform evidence in the area around great bear lake canada to trace the evolution of an ice stream web through time demonstrating that frozen bed patches are integral components of this complex system we conclude that frozen bed patches are important for the stability of ice sheets because they laterally constrain and isolate peripheral drainage basins and their ice streams

the isotopic evolution of atmospheric pb in central ontario since ad 1800 and its impacts on the soils waters and sediments of a forested watershed kawagama lake abstract a peat core from an ombrotrophic bog documents the isotopic evolution of atmospheric pb in central ontario since ad 1804 53 210pb dating despite the introduction of unleaded gasoline in the mid 1970 s the ratio 206pb 207pb in atmospheric deposition has not increased as expected but rather continues to decline in fact snowpack sampling 2005 and 2009 and rainwater samples 2008 show that the isotopic composition of atmospheric pb today is often far less radiogenic than the gasoline lead that had been used in canada in the past the peat snow and rainwater data presented here are consistent with the pb isotope data for aerosols collected in dorset in 1984 and 1986 which were traced by sturges and barrie 1989 to emissions from the noranda smelter in northern quebec canada s largest single source of atmospheric pb understanding atmospheric pb deposition in central ontario therefore requires not only consideration of natural sources and past contributions from leaded gasoline but also emissions from metal smelting and refining lead in the streams which enter kawagama lake today 206pb 207pb 1 16 1 19 represents a mixture between the natural values 1 191 1 201 estimated using pre industrial lake sediments and the values found in the humus layer of the surrounding forest soils 206pb 207pb 1 15 1 19 in the lake itself however pb is much less radiogenic 206pb 207pb as low as 1 09 than in the streams with the dissolved fraction less radiogenic than particulate material the evolution of pb isotope ratios within the watershed apparently reflects preferential removal by sedimentation of comparatively dense radiogenic terrestrial particles derived from the mineral fraction of soils from the humus particles with lower ratios of 206pb 207pb because of atmospheric pb contamination despite the contemporary enrichments of pb in rain and snow concentrations of dissolved pb in the lake are extremely low sometimes below 10 ng l with pb concentrations and pb sc ratios approaching natural values because of efficient binding to particles and their subsequent removal in the watershed

the morphological characteristics of ribbed moraine abstract ribbed rogen moraines are large subglacially formed transverse ridges that cover extensive areas of the former laurentide scandinavian and irish ice sheets given their ubiquitous and conspicuous nature it is surprising that their characteristics are poorly understood to date most ribbed moraine studies have been spatially restricted and rely on small sample sizes thus published accounts of their characteristics are most likely unrepresentative of ribbed moraines generally this study addresses this deficit by producing the first representative data set on ribbed moraine size shape pattern and distribution and we describe their spatial characteristics various remote sensing and gis techniques were used to map ribbed moraines over a combined area of 81 000 km 2 in canada ireland and sweden producing a database of just over 33 000 individual landforms in all 25 082 ridges were mapped in two areas in central and northern quebec the lac naococane and river kaniapiskau regions 5637 in the lake rogen area of central sweden and 2500 in north central ireland in comparison against the published accounts of ribbed moraine we demonstrate that some widely held assertions are inaccurate or untrue and we show that ribbed moraine morphological characteristics are more complex than has been hitherto reported our data reveals they exist over a larger scale range than was previously stated this study concludes by presenting a list of ribbed moraine characteristics and argues that formational hypotheses must account for these if they are to remain valid explanations of ribbed moraine genesis

bed ribbing instability explanation testing a numerical model of ribbed moraine formation arising from coupled flow of ice and subglacial sediment 1 ribbed moraines are large up to 16 km long ridges of sediment produced transverse to ice flow direction that formed widely beneath palaeo ice sheets since ice sheet stability is sensitive to conditions operating at the bed an understanding of ribbed moraine genesis will provide critical information on ice sheet dynamics currently there is no consensus on ribbed moraine formation and various competing hypotheses have been presented to account for their genesis only one of these theories has been developed into a physically based numerical model that quantitatively describes ribbed moraine formation this theory known as the bed ribbing instability explanation brie argues that ribbed moraines are produced by a naturally arising instability in the coupled flow of ice and till brie demonstrates that transverse subglacial ridges i e ribbed moraine spontaneously grow under certain parameter combinations and it predicts their wavelength spacing between ridges the model represents a significant advance because it is the first time a theory of subglacial bedform generation has been developed to make quantitative predictions which can be formally tested this paper discusses the types of tests that are currently possible and reports the results from the first testing of brie this analysis centers on the ability of brie to predict the primary characteristics of ribbed moraine which are patterning and wavelength results show that brie successfully predicts the correct ribbed moraine pattern and appropriate wavelengths the tests fail to falsify the model and it is concluded that brie remains a viable explanation of ribbed moraine formation

reconstructing the last irish ice sheet 2 a geomorphologically driven model of ice sheet growth retreat and dynamics the ice sheet that once covered ireland has a long history of investigation much prior work focussed on localised evidence based reconstructions and ice marginal dynamics and chronologies with le

advection and removal of 210pb and stable pb isotopes in the oceans a general circulation model study abstract natural pb isotope variability in the oceans encodes information about the sources of continental material to the oceans about ocean circulation and about pb removal in order to use this information we must understand the natural cycle of pb in the oceans which is overprinted by large anthropogenic input in this study we use 210 pb which has not been significantly anthropogenically perturbed to investigate oceanic pb geosecs 226 ra and model derived atmospheric fluxes of 210 pb are used to input 210 pb into an ocean general circulation model irreversible scavenging of this 210 pb onto settling biogenic particles and at the seafloor are tuned so that the model replicates the observed pattern of 210 pb in the oceans the best fit model run provides a map of the variability of residence time for pb the global average residence time of pb in this model is 48 yr but there is over an order of magnitude variation between areas of high and low productivity this is expected to enhance provinciality of pb isotope ratios in the oceans because stable pb isotopes are expected to behave in seawater in a similar fashion to 210 pb the pattern of removal of 210 pb derived by the model can be used to investigate the behavior of stable pb isotopes we use a simplified input of pb consisting of five point sources representing major rivers and a disseminated dust input although this simplified input scheme does not allow precise reconstruction of pb concentration and isotopes in the oceans it allows us to answer some first order questions about the behavior of pb as an ocean tracer with a total pb input of 6 3 10 7 mol yr chow t j and patterson c c the occurrence and significance of pb isotopes in pelagic sediments geochim cosmochim acta 26 263 308 1962 the model predicts natural seawater pb concentrations averaging 2 2 pmol kg even in the absence of anthropogenic input the model ocean exhibits a near surface maximum in pb concentration and the model suggests natural pb concentrations in the northern hemisphere an order of magnitude higher than in the southern hemisphere a point source of pb is suggested to dominate the seawater pb inventory close to the source but is reduced to typically less than 10 of the inventory by the time that pb is advected out of the originating ocean this length scale of advection for pb isotope signals confirms their potential as tracers of ocean circulation assuming an 8 dissolution of dust their input to the open ocean are seen to be a significant portion of pb inventory throughout the oceans and make up 50 of the pb inventory in the model s southern ocean finally a preliminary investigation of the response of pb isotope distributions to changes in boundary conditions between glacial and interglacial times illustrates that significant variation in the pb isotopes are expected in some regions even for reasonably small changes in climate conditions

elemental partitioning into mn and fe oxides derived from dolomitic shale hosted pbzn deposits northwest queensland australia abstract exploration for dolomitic shale hosted base metal mineralization in northwest queensland is largely dependent upon geochemical evaluation of ironstones fe oxides because of their abundance in the weathered zone often quantitatively account for most of the base metal content of an ironstone mn oxides are less well developed but provide particularly good hosts for ba zn and pb and hence assume importance where present the mn fe coatings found in stream coatings vigorously scavenge and concentrate solution transported base metals and hence have to be very carefully evaluated when used during exploration however the present survey of base metal contents in gossans and ironstones in northwest queensland has shown that the ba cu p pb ni s and zn contents of the mn and fe oxides can be used to accurately indicate their parent material only ce and co are possibly preferentially incorporated into mn oxides but neither element is a pathfinder for pb zn mineralization development of the mn oxides chalcophanite todorokite lithiophorite and the cryptomelane group incorporating k ca mg ba co zn and pb reflects acid conditions during sulfide oxidation when an ironstone consistently contains mn oxides with greater than 1 pb or 10 zn it can be regarded as derived from pb or zn rich mineralization as ba is often associated with sulfides and facilitates the incorporation of pb into cryptomelane ba without accompanying base metals in a mn oxide implies derivation from base metal barren pyrite and or pyrrhotite cu pb zn al phosphate sulfate and arsenate are all incorporated into fe oxides however only pb which is more strongly partitioned into hematite and al and phosphate which are preferentially incorporated into goethite show clear partitioning between the fe oxide phases the preferential incorporation of phosphate rather than sulfate into an fe oxide makes areas showing higher sulfate contents particularly good targets knowledge of the nature of the distributions of pathfinder elements helps understanding of the associations seen in whole rock analyses and leads to rational application of geochemical data during exploration

saturated and subcooled hydrothermal boiling in groundwater flow channels as a source of harmonic tremor the potential of hydrothermal boiling in groundwater flow channels for generating harmonic tremor a relatively monochromatic ground vibration associated with volcanic activity is examined we use simple organ pipe theory of normal mode fluid vibration and fundamental energy considerations to develop a first order analytical model of a hydrothermal boiling source of harmonic tremor we use this model to estimate order of magnitude groundwater flow channel lengths and boiling heat transfer rates required to produce harmonic tremor with dominant frequencies in the range 0 5 5 hz and surface wave reduced displacements of up to 100 cm2 depending on groundwater sound speed flow channel lengths of the order of 1 1000 m are required to produce fluid vibration eigenfrequencies in the range 0 5 5 hz the boiling heat transfer rate required to produce tremor with a given surface wave reduced displacement depends on the tremor frequency and on whether saturated boiling or subcooled boiling is the cause of the tremor saturated boiling produces groundwater vibration via steam bubble growth whereas subcooled boiling produces groundwater vibration via steam bubble collapse we find that subcooled hydrothermal boiling is from 102 to 104 times more efficient than saturated boiling in converting boiling thermal power to seismic power for example the boiling heat transfer rates required to produce 1 hz tremor with reduced displacements of up to 100 cm2 via subcooled boiling are generally less than a few thousand megawatts for saturated boiling the required boiling heat transfer rates are several orders of magnitude larger than this the highest values of heat flow reported in the literature for volcanic crater lakes and terrestrial and ocean floor geothermal areas are of the order of 1000 mw taking this value as a first order estimate of an upper limit on possible boiling heat transfer rates in volcanic hydrothermal systems our results suggest that saturated hydrothermal boiling is capable of generating only low amplitude harmonic tremor with surface wave reduced displacements no higher than a few square centimeters however subcooled hydrothermal boiling could potentially generate high amplitude harmonic tremor with reduced displacements as large as several hundred square centimeters as a specific application of our model we evaluate the potential of hydrothermal boiling for generating harmonic tremor at recently active mount st helens and nevado del ruiz volcanoes we conclude that subcooled boiling likely could have produced the tremor episodes considered at both volcanoes saturated boiling also could explain the nevado del ruiz tremor but probably not the more powerful mount st helens tremor

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

relative motion of the nazca farallon and south american plates since late cretaceous time by combining reconstructions of the south american and african plates the african and antarctic plates the antarctic and pacific plates and the pacific and nazca plates we calculated the relative positions and history of convergence of the nazca and south american plates despite variations in convergence rates along the andes periods of rapid convergence averaging more than 100 mm a between the times of anomalies 21 49 5 ma and 18 42 ma and since anomaly 7 26 ma coincide with two phases of relatively intense tectonic activity in the peruvian andes known as the late eocene incaic and mio pliocene quechua phases the periods of relatively slow convergence 50 to 55 30 mm a at the latitude of peru and less farther south between the times of anomalies 30 31 68 5 ma and 21 and between those of anomalies 13 36 ma and 7 correlate with periods during which tectonic activity was relatively quiescent thus these reconstructions provide quantitative evidence for a correlation of the intensity of tectonic activity in the overriding plate at subduction zones with variations in the convergence rate

landscape imprints of changing glacial regimes during ice sheet build up and decay a conceptual model from svalbard the behaviour of ice sheets and their geologic imprints in fjord regions are often multifaceted fjords which were temporarily occupied by fast flowing ice streams during major glaciations and inter fjord areas which were covered by less active ice show different signatures of past glaciations the land and marine records of glaciations over the western svalbard fjord region have been extensively studied during the last few decades we have re examined ice flow records from stratigraphic and geomorphic settings and propose a succession of ice flow events that occurred repeatedly over glacial cycles the maximum the transitional and the local flow style the differently topographically constrained segments of the ice sheet switched behaviour as glacial dynamics developed through each glacial cycle these segments as well as the different flow styles are reflected differently in the offshore stratigraphic record we propose that the glacial geomorphological signatures in the inter ice stream areas mostly developed under warm based conditions during a late phase of the glaciations and that the overall glacial imprints in the landscape are strongly biased towards the youngest events

distribution of natural and anthropogenic lead in mediterranean soils abstract the concentrations and isotopic composition of pb have been combined with a selective sequential dissolution procedure to track the distribution of anthropogenic and natural pb in the soil of semiarid climate and the penetration pathway of petrol pb within the soil profile soil samples were collected from soil profiles adjacent to a major highway 8 23 m and from soil profiles 500 m away from the same highway the selective sequential dissolution procedure was used to determine the distribution of pb between the different soil components soil carbonate organic matter fe oxides and hydrous oxides and aluminosilicates natural pb is associated mainly with aluminosilicates 60 and fe oxides 30 and only a small fraction with the soil carbonate and organic matter 10 in contrast to the distribution of natural pb the distribution of anthropogenic pb which accumulates mainly in the upper part of the soil profile is 40 with the soil carbonate 10 with organic matter 35 with fe oxides and only 15 with aluminosilicates on the basis of concentration and isotopic composition of total pb the deeper horizon of the roadside soil 10 30 cm and the soil sampled 500 m from the highway seem uncontaminated however the isotopic composition of the labile components in the soil pbcarb pborg and pbfe ox indicates that these soils are actually contaminated this contamination implies that over the period of vehicle pollution 40 yr petrol pb has penetrated through the entire roadside soil profile 25 30 cm furthermore pb isotopes in aluminosilicates of the upper part of the roadside soil indicate that this pb too is anthropogenic measurements of pb concentration and isotopic composition in roadside soil profiles sampled in 1997 and archived samples collected at the same location in 1982 provided a unique opportunity to trace petrol pb penetration into the soil

the composition and internal structure of drumlins complexity commonality and implications for a unifying theory of their formation investigation of drumlins is significant to both glaciology and palaeoglaciology but the sheer diversity of their composition and internal structure is often cited as a major obstacle towards a satisfactory unifying explanation of their formation this paper presents the first systematic survey of the vast literature on this subject with the aim of concisely summarising observations and identifying any emergent patterns or commonality that theories of drumlin formation should be able to explain results confirm that investigations are often limited by availability of suitable sediment exposures 40 of studies report data from 5 drumlins and 44 do not specify sample size although borehole data and geophysical techniques can alleviate this problem however it is clear that the constituents of drumlins are incredibly diverse in terms of their composition e g a range of lithologies clast shapes sizes and fabrics structure e g sediments that are sorted homogeneous surface conformable unconformable and evidence of deformation e g ranging from pervasive to non pervasive limited to absent despite this diversity our review leads us to suggest that drumlin composition can be simplified to five basic types i mainly bedrock ii part bedrock part till iii mainly till iv part till part sorted sediments and v mainly sorted sediments this is a potentially significant step in that it reduces the oft cited complexity of drumlin composition and provides a more realistic goal for theories or numerical models of drumlin formation to target the various types can occur within the same drumlin field which leaves us with two possible implications for drumlin formation 1 different types of drumlin are formed seeded by different processes despite being morphologically similar equifinality investigation of drumlin composition may therefore reveal diagnostic processes explanations for these different types of drumlin and we argue that bedrock drumlins are an example 2 a single process occurs across large parts of the ice bed interface to create drumlinised terrain in a variety of sediments investigation of drumlin composition may in this case simply reflect pre existing sediments but importantly the way in which the drumlin forming mechanism modifies is modified by them we argue that the latter simpler explanation applies to all other types of drumlin excluding purely bedrock forms and conclude that the diversity in drumlin composition is no obstacle to a single unifying theory

palaeo ice streams abstract the location and behaviour of ice streams is one of the most important controls on ice sheet configuration and stability in order to reconstruct former ice sheets we need to know ice stream location and timing once identified the beds of palaeo ice streams provide an unprecedented opportunity to glean information about their basal environment something that remains very difficult under contemporary ice streams this paper represents the first synthesis and discussion of palaeo ice stream research from a variety of former ice sheets and includes new insights relating their configuration and activity to the evidence they leave behind the ambiguous use of the term ice stream is addressed and four possible configurations for ice streams are presented diagnostic landforms and landform assemblages that we would expect an ice stream to produce are discussed and the temporal context of bedform generation is described as either a rubber stamped or smudged bedform imprint resulting from isochronous or time transgressive landform generation in particular we focus on the configuration of terrestrially terminating ice streams for which there are no modern analogues technological advances in marine geophysics are helping to generate a convergence of interest between antarctic glaciology and palaeo glaciology it is suggested that investigations around the fringes of contemporary ice sheets i e west antarctica can provide evidence that directly links the geomorphological record of palaeo ice streams with their contemporary counterparts in addition computational advances and modelling adaptations have permitted the incorporation of ice streams within ice sheet models we argue that data from palaeo ice stream beds are invaluable to ice sheet stream modelling experiments and will help us understand ice stream operation and the linkages between climate perturbations and both palaeo and contemporary ice sheets

the link between volcanism and tectonics in the southern volcanic zone of the chilean andes a review abstract the nature of the interplay between tectonics and volcanism is a major question in continental margin tectonics the southern andes volcanic zone svz located at the obliquely convergent nazca south america plate margin between 33 s and 46 s offers a unique opportunity to address this question because of along strike changes in crustal thickness tectonic style and well constrained long term and short term kinematic history the complex interaction between tectonic and magmatic processes is evidenced by both the architecture and geochemical signature of volcanic systems main first order factors accounting for the along strike variations in the nature and composition of volcanism are crustal thickness and the existence of a major intra arc fault system the liquine ofqui fault zone lofz second order factors include the local nature of the volcanic arc basement two main categories of volcano tectonic associations have been identified according to the spatial distribution and internal organization of individual volcanoes and clusters of volcanoes with respect to both the overall strike of the volcanic arc and the first and second order active inactive basement faults kinematically coupled associations those that are directly related to the current dextral transpressional tectonic regime include ne trending volcanic alignments of stratovolcanoes and or monogenetic cones kinematically uncoupled associations in which coupling with the current regime is not required include stratovolcanoes built on top of ancient reverse and strike slip faults of the volcanic arc basement and monogenetic cones lying along master faults of the lofz whereas mostly primitive magmas are found in the first category more evolved terms can occur genetically associated with the second category we propose a simplified three dimensional model for the magma plumbing system along and across the svz that integrates kinematically coupled and kinematically uncoupled volcano tectonic associations within the framework of first and second order geological and structural constraints

tracing the transport of anthropogenic lead in the atmosphere and in soils using isotopic ratios the isotopic composition of lead in aerosols and soils in israel is used to characterize the sources of anthropogenic lead in the region to ascertain the isotopic composition of natural rock derived lead in specific areas and to determine rates of anthropogenic lead migration in soils the isotopic composition of lead currently emitted from cars in israel 206pb207pb 1 115 2 is controlled by alkyl lead produced in france and germany in addition to petrol lead two more sources of anthropogenic lead can be detected in sampled aerosols the first one has low concentrations of lead 4 ng m3 and 206pb207pb 1 157 and is most likely lead emitted in turkey that traveled across the eastern mediterranean basin the second type of aerosols contains a mixture of lead emitted in several countries including turkey greece and ukraine 206pb207pb value of 1 155 1 160 pb 20 30 ng m3 anthropogenic lead is more accessible for acid leaching than natural lead therefore it is more labile in the soil the isotopic composition of lead in the acid leached fraction of near road soil profiles record the histor of alkyl lead emission in the country based on changes in the isotopic composition of lead with soil depth it is estimated that anthropogenic lead migrates into the soil at approximately 0 5 cm y a soil profile from a relatively remote area is less contaminated by anthropogenic lead and displays a different distribution of lead isotopic values with depth the isotopic composition of lead suggests that natural lead in soils developed on carbonate bedrock is derived from clays either from the rock esidue the clay fraction in the carbonate bedrock or from airborne clay but not from lead released from the carbonate fraction in the rock

comparison of seismic activity for llaima and villarrica volcanoes prior to and after the maule 2010 earthquake llaima and villarrica are two of the most active volcanoes in the chilean southern volcanic zone and presently show contrasting types of activity llaima is a closed vent edifice with fumarolic activity while villarrica has an open vent with a lava lake continuous degassing and tremor activity this study is focused on characterizing the relationships between volcanic and seismic activity in the months before and after the 2010 m8 8 maule earthquake which was located in nnw direction from the volcanoes time series for tremors long period and volcano tectonic events were obtained from the catalogue of the volcanic observatory of the southern andes ovdas and from the sfb 574 temporary volcanic network an increase in the amount of tremor activity long period events and degassing rates was observed at villarrica weeks before the mainshock and continued at a high level also after it this increase in activity is interpreted to be caused by enhanced magma influx at depth and may be unrelated to the maule event in llaima an increase in the volcano tectonic activity was observed directly after the earthquake the simultaneous post earthquake activity at both volcanoes is consistent with a structural adjustment response since this enhanced activity lasted for more than a year we suggest that it is related to a medium term change in the static stress thus the maule earthquake may have affected both volcanoes but did not trigger eruptions from which we assume that none of the volcanoes were in a critical state

quaternary glaciations of northern europe this paper presents the outcome of a workshop held in berlin in february 2009 concerned with current research on the glacial history of northern europe including the british isles the methodologies presently used to resolve this topic are outlined particular attention is given to new analytical methods deriving from high resolution remote imaging of glacial terrain both on land and on the sea bed key new stratigraphic sections higher resolution results from conventional geochronological methods like radiocarbon and more recently developed technologies such as luminescence and cosmogenic radionuclide dating the relationships between the results derived from these two methods are discussed in further detail along with possible explanations for these differences an outline of a most likely glacial history of the scandinavian and british and irish ice sheets is presented along with possible links to global climate change as represented by the marine isotope mis record tentative evidence for glaciation is identified in mis 22 16 12 10 8 6 4 and 2 and correlations of phases within the last glaciation are also explored for both the scandinavian and british and irish ice sheets the results show that the character and extent of glaciation in different parts of the region are not synchronous and much more geochronological work is required before regional correlations can be established with confidence

reconstructing the flow pattern evolution in inner region of the fennoscandian ice sheet by glacial landforms from gausdal vestfjell area south central norway abstract more than 17 000 landforms from detailed lidar data sets have been mapped in the gausdal vestfjell area south central norway the spatial distribution and relationships between the identified subglacial bedforms mainly streamlined landforms and ribbed moraine ridges have provided new insight on the glacial dynamics and the sequence of glacial events during the last glaciation this established evolution of the late weichselian ice flow pattern at this inner region of the fennoscandian ice sheet is stepwise where a topography independent ice flow phase i are followed by a regional phase ii before a strongly channelized topography driven ice flow phase iii the latter phase is divided into several substages where the flow sets are becoming increasingly confined into the valleys likely separated by colder less active ice before down melting of ice took place a migrating ice divide and lowering of the ice surface seems to be the main reasons for these changes in ice flow pattern formation of ribbed moraine can occur both when the ice flow slows down and speeds up forming respectively broad fields and elongated belts of ribbed moraines

size shape and spatial arrangement of mega scale glacial lineations from a large and diverse dataset mega scale glacial lineations msgls are a characteristic landform on ice stream beds solving the puzzle of their formation is key to understanding how ice interacts with its bed and how this in turn influences the dynamics of ice streams however a comprehensive and detailed characterization of this landform s size shape and spatial arrangement which might serve to test and refine formational theories is largely lacking this paper presents a detailed morphometric analysis and comparison of 4043 msgls from eight palaeo ice stream settings three offshore norway and antarctica four onshore canada and one from under a modern ice stream in west antarctica the length of msgls is lower than previously suggested mode 1000 2000 m median 2892 m and they initiate and terminate at various locations on an ice stream bed their spatial arrangement reveals a pattern that is characterized by an exceptional parallel conformity 80 of all mapped msgls have an azimuth within 5 from the mean values and a fairly constant lateral spacing mode 200 300 m median 330 m which we interpret as an indication that msgls are a spatially self organized phenomenon results show that size shape and spatial arrangement of msgls are consistent both within and also generally between different ice stream beds we suggest this results from a common mechanism of formation which is largely insensitive to local factors although the elongation of msgls mode 6 8 median 12 2 is typically higher than features described as drumlins these values and those of their width mode 100 200 m median 268 m overlap which suggests the two landforms are part of a morphological continuum and may share a similar origin we compare their morphometry with explicit predictions made by the groove ploughing and rilling instability theories of msgl formation although the latter was most compatible neither is fully supported by observations 2014 the authors earth surface processes and landforms published by john wiley sons ltd

ribbed moraines in northern manitoba canada characteristics and preservation as part of a subglacial bed mosaic near the core regions of ice sheets abstract ribbed moraines are enigmatic glacial landforms for which different models with contrasting paleoglaciologic implications have been proposed to explain their formation despite the great deal of attention this type of landform has received over the last several decades ribbed moraine fields in northern manitoba canada are among the largest in the world but have been seldom studied ribbed moraines in this part of the world overlie the low relief canadian shield are not constrained by topography and are part of a spatial subglacial landform assemblage associated with drumlinoid ridges within palimpsest and relict type glacial terrain zones field observations herein provide new insights into the characteristics of these transverse to ice flow ridges at landscape mapping and spatial analysis and landform internal structure using high resolution shear wave s wave seismic reflection surveys sedimentological characteristics clast fabric analyses scales two main types of ribbed moraine are recognized pristine high amplitude straight crested ridges and secondarily modified subdued drumlinized ridges ribbed moraine in northeast manitoba consist of massive matrix supported till at surface which is similar in matrix texture and composition to the regional till sheet though pristine moraines show a higher concentration of boulders a seismic profile reveals subparallel to surface layered stratigraphy with only minor folding and no major unconformities stacking or faulting the demonstrated fragmentary nature of ribbed moraine fields the inherited signature of the till within these fields the secondary patchy drumlinization of the ridges and the more abundant granitoid outcrops in areas of intense modification all suggest that subglacial ribbed moraine formed from pre existing sediments and were later preserved and or partially reworked through a regional mosaic of shifting subglacial bed conditions we therefore make the case that pristine unmodified moraines were preserved beneath stable sticky spots we support a link between ribbed moraine and widespread cold based and or dewatered subglacial conditions in inner core regions of ice sheets but for reasons of preservation and not necessarily formation

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

inflation and deflation at the steep sided llaima stratovolcano chile detected by using insar 1 llaima volcano chile is a typical basaltic to andesitic stratovolcano in the southcentral andes llaima had at least four explosive eruptions in the decade 2000 2010 however little is known about the physical processes and magma storage at this volcano in this study we present an insar deformation field at llaima from 2003 2008 covering both the post eruptive and syn eruptive periods the satellite insar data are significantly affected by environmental decorrelation due to steep topography snow and vegetation because of this we applied a model assisted phase unwrapping approach the analysis of these data suggests two main deformation episodes subsidence associated with the post eruptive period and uplift associated with the syn eruptive period maximum summit subsidence and uplift are 10 cm and 8 cm respectively through inverse modeling of both periods a deflating and inflating magma body can be inferred located at a depth of 4 12 km subject to a volume decrease of 10 46 106 m3 during the subsidence period followed by a volume increase of 6 20 106 m3 during the uplift period therefore this study presents the first evidence of magma driven deformation at llaima volcano and suggests that eruption periods are associated with the inflation and deflation of a deep magma body that can be monitored by using space geodesy

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

triggering of volcanic eruptions although earthquakes and volcanic eruptions are each manifestations of large scale tectonic plate and mantle motions it is usually thought that the occurrences of these events are not directly related there have been some studies however in which triggering of volcanic eruptions by earthquakes remote from the volcano has been proposed1 2 the 1992 landers southern california earthquake caused triggered seismicity at very large distances3 including the magmatically active4 long valley caldera region which also experienced a significant coincident deformation transient5 motivated by this demonstration of the ability of a distant earthquake to disturb a volcanic system and the earlier studies of specific cases of eruption triggering we examine here the historical record of eruptions and earthquakes to see if there are indeed significantly more eruptions immediately following large earthquakes we find that within a day or two of large earthquakes there are many more eruptions within a range of 750 km than would otherwise be expected additionally it is well known6 that volcanoes separated by hundreds of kilometres frequently erupt in unison the characteristics of such eruption pairs are also consistent with the hypothesis that the second eruption is triggered by earthquakes associated with the first

middle and late weichselian devensian glaciation history of south western norway north sea and eastern uk data from eastern england scotland the northern north sea and western norway have been compiled in order to outline our current knowledge of the middle and late weichselian glacial history of this region radiometric dates and their geological context from key sites in the region are presented and discussed based on the available information the following conclusions can be made i prior to 39 cal ka and most likely after ca 50 cal ka scotland and southern norway were extensively glaciated most likely the central north sea was not glaciated at this time and grounded ice did not reach the shelf edge ii during the time interval between 29 and 39 ka periods with ameliorated climate including the alesund sandnes and tolsta interstadials alternated with periods of restricted glaciation in scotland and western norway iii between 29 and 25 ka maximum weichselian glaciation of the region occurred with the fennoscandian and british ice sheets coalescing in the central north sea iv decoupling of the ice sheets had occurred at 25 ka with development of a marine embayment in the northern north sea v between 22 and 19 ka glacial ice expanded westwards from scandinavia onto the north sea plateau in the tampen readvance vi the last major expansion of glacial ice in the offshore areas was between 17 5 and 15 5 ka at this time ice expanded in the north western part of the region onto the maloy plateau from norway and across caithness and orkney and to east of shetland from the moray firth the norwegian channel ice stream ncis which drained major parts of the south western fennoscandian ice sheet was active at several occasions between 29 and 18 ka

the liquine ofqui fault zone a long lived intra arc fault system in southern chile abstract plate reconstructions for the cenozoic document relatively steady right oblique subduction of the farallon nazca plate beneath the chilean continental margin the kinematic signature recorded along the intra arc liquine ofqui fault zone lofz a major feature of the southern andes may help to understand the way in which the nazca south america slip vector has been partitioned into strain and displacement along and across the continental margin the lofz consists of two nne trending right stepping straight lineaments a strike slip duplex at the right step and curved features which splay off the straight lineaments toward the northwest the lofz runs mostly through heterogeneously deformed cenozoic plutonic rock of the north patagonian batholith and patchy metamorphic wall rock early cenozoic volcano sedimentary rocks and dyke swarms found in close spatial association with the strike slip duplex are believed to have developed in strike slip related basins quaternary volcanoes are aligned parallel to the lofz both ductile and brittle kinematic indicators within centimeter to meter wide high strain zones document late cenozoic dextral shear deformation contrasting left lateral deformation recorded on older and wider mylonitic zones suggests that the lofz may be a long lived shear zone that accommodated continental scale deformation arising from the farallon nazca south america plate convergence a block rotation pattern as indicated by paleomagnetic data is consistent with the geometry and cenozoic kinematics of the lofz

space geodetic estimation of the nazca south america euler vector abstract gps data from four sites in the nazca plate easter island galapagos robinson crusoe and san felix islands and from five sites in the stable core of the south american plate enabled us to estimate the euler vector of the nazca plate with respect to south america the observed velocities of easter island 6 6 cm yr at 102 3 galapagos 5 1 cm yr at 90 0 robinson crusoe 6 6 cm yr at 80 1 and san felix 6 0 cm yr at 82 1 are significantly slower than the global plate model nuvel 1a velocites for those four sites our estimated euler pole is located at 48 8 n 91 7 w with a rate of 0 59 m y the nuvel 1a and earlier space geodetic studies give rotation rates that are 20 faster

teleseismic inversion for rupture process of the 27 february 2010 chile mw 8 8 earthquake the 27 february 2010 chile m w 8 8 earthquake is the fifth largest earthquake to strike during the age of seismological instrumentation the faulting geometry slip distribution seismic moment and moment rate function are estimated from broadband teleseismic p sh and rayleigh wave signals we explore some of the trade offs in the rupture process estimation due to model parameterizations limited teleseismic sampling of seismic phase velocities and uncertainty in fault geometry the average slip over the 81 500 km 2 rupture area is about 5 m with slip concentrations down dip up dip and southwest and up dip and north of the hypocenter relatively little slip occurred up dip offshore of the hypocenter the average rupture velocity is 2 0 2 5 km s

rogen moraine an example of glacial reshaping of pre existing landforms abstract rogen moraine is widely distributed in the core areas of the former scandinavian and laurentide ice sheets it is generally agreed upon that these gently arched ice flow transverse ridges can be used in reconstructions of paleo ice flow patterns and that they indicate a melted bed or poly thermal basal ice regime however the processes of ridge generation have been contentious this study proposes a two stage formation of rogen moraine based on detailed sedimentological and structural investigations in excavated trenches in a rogen moraine landscape in the province of dalarna central sweden field data suggest that rogen moraine ridges are the reshaped remains of pre existing transverse moraine ridges originally deposited from ice cored moraines in an ice marginal zone due to back and down wasting of ice cores inter ridge troughs were filled with debris flow and fluvial deposits which after landscape inversion were transformed to areas of transverse and hummocky moraines it is proposed that this primary landscape formation occurred during an early weichselian deglaciation this relict landscape was later preserved beneath cold based mid to late weichselian ice sheet s which turned wet based during the preboreal deglaciation phase and re moulded the precursor landforms into rogen moraine

impact of megathrust geometry on inversion of coseismic slip from geodetic data application to the 1960 chile earthquake 1 we analyze the role of megathrust geometry on slip estimation using the 1960 chile earthquake mw 9 5 as an example a variable slip distribution for this earthquake has been derived by barrientos and ward 1990 applying an elastic dislocation model with a planar fault geometry their model shows slip patches at 80 110 km depth isolated from the seismogenic zone interpreted as aseismic slip we invert the same geodetic data set using a finite element model fem with precise geometry derived from geophysical data isoparametric fem is implemented to constrain the slip distribution of curve shaped elements slip resolved by our precise geometry model is limited to the shallow region of the plate interface suggesting that the deep patches of moment were most likely an artifact of the planar geometry our study emphasizes the importance of fault geometry on slip estimation of large earthquakes

geomorphological criteria for identifying pleistocene ice streams ice streams are critical regulatory mechanisms in contemporary ice sheets it has been inferred that they also had a significant effect on the dynamics of former ice sheets subsequently many people have invoked their widespread occurrence from a variety of formerly glaciated areas hypothesised locations however have often outweighed meaningful evidence this paper addresses the problem using the characteristics of contemporary ice streams as a basis for their identification from former ice sheet beds a convergence of knowledge gained from contemporary ice stream research coupled with theories of glacial geomorphology allows several geomorphological criteria to be identified as suggestive signatures of ice stream activity it is envisaged that the geomorphological criteria developed here will introduce a more objective approach to the study of former ice streams the criteria are used to construct conceptual land system models of the beds of former ice streams and it is hoped such models can provide an observational template upon which hypotheses of former ice streams can be better based

glaciology of the british isles ice sheet during the last glacial cycle form flow streams and lobes abstract the last ice sheet over the british isles together with other mid latitude pleistocene ice sheets and in contrast to the modern ice sheets of greenland and antarctica had a relatively low profile low summit elevation and extensive elongated lobes at its margin a thermo mechanically coupled numerical ice sheet model driven by a proxy climate has been used to explore the properties that would have permitted these characteristics to develop the approach the key to quantitative palaeoglaciology is to determine the boundary conditions that permit the simulated ice sheet to mimic the evolution of the real ice sheet through the last glacial cycle simulations show how a british ice sheet may have been confluent with a scandinavian ice sheet during some parts of its history and how unforced periodic and asynchronous oscillations could occur in different parts of its margins marginal lobes are a reflection of streaming within the ice sheet such streams can be ephemeral dynamic streams located because of ice sheet properties or fixed streams whose location is determined by bed properties the simulations that best satisfy constraints of extent elevation and relative sea levels are those with major fixed streams that strongly draw down the ice sheet surface in these the core upland areas of the ice sheet were cold based at the last glacial maximum basal streaming velocities were between 500 and 1000 ma 1 compared with surface velocities of 10 50 ma 1 in inter stream zones shear stresses were as low as 15 25 kpa in streams compared with 70 110 kpa in upland areas and 60 84 of the ice flux was delivered to the margin via streams

the relationships between rock derived lead and iron in natural waters abstract the relationships between fe and pb released to the hydrocycle via rock weathering is examined in terms of field observations and laboratory experiments rock soil and unpolluted water samples from granodiorite basalt and carbonate terrains were analyzed for their pb fe and other element ca mg na k si al mn concentrations samples of granodiorite soil developed on the granodiorite basalt and dolomite rocks as well as biotite and feldspar minerals were also used for laboratory leaching experiments fe pb ratios found in granodiorite basalt and insoluble residue of carbonate bedrocks are preserved within an order of magnitude in surface and shallow groundwater reservoirs draining these rocks with the exception of carbonate rocks leachates of these rocks have fe pb ratios similar to that of the bedrock laboratory experiments suggest that pb is adsorbed and coprecipitates with fe rich particles even in the presence of higher concentrations of competing ions e g mg2 complexation of pb by ethylenediaminetetraacetate edta however substantially decreases the amount of pb bound to surface sites ligand competition based on our results we suggest that in early phases of the weathering cycle pb both coprecipitates and is adsorbed on surfaces of fe rich particles because of complementary transport mechanisms and comparable rates of release from common source rock and soil minerals the molar ratio of fe to natural rock derived pb in the particulate load of rivers in many cases it includes particles which pass through 0 45 m pore size filters is similar to that of the upper continental crustal rock approximately 6500 this ratio can vary in watersheds which drain rocks with different fe pb ratios than the average upper continental crust in rivers loaded with dissolved natural organic matter or in rivers polluted with pb or with anthropogenic chelators secondary pollution effect

ribbed moraine stratigraphy and formation in southern finnish lapland characteristics of ribbed moraines the dominating moraine type in southern finnish lapland have been studied in detail the ridges are composed of several till units of which the bottommost units consist of mature basal tills and the surficial parts are enriched with local short transport rock fragments and boulders in till and at the surface of ridges as a result of this re examination a two step model of the formation process of ribbed moraines is presented in the first stage while cold based conditions prevailed both the bottommost part of the ice sheet and the frozen substrate fractured under compressive ice flow following glacial transport of fractured blocks and formation of the transverse ridge morphology erosion between the ridges continued owing to freeze thaw process under variable pressure conditions in the areas with a low pre existing till sheet the process caused quarrying of the bedrock surface and subsequent deposition of rock fragments and boulders under high pressure on the next ridge the most suitable conditions for ribbed moraine formation existed during late weichselian deglaciation after the younger dryas when the climate warmed very quickly leading to an imbalance between a warm glacier surface and a cold base copyright 2006 john wiley sons ltd

temporal variability of lead in the western north atlantic consumption of alkyl leaded gasoline has decreased considerably in the united states over the last 15 years in order to evaluate the chemical response of the ocean to decreased atmospheric deposition of anthropogenic lead new 210pb and stable pb data have been obtained near bermuda june 1983 to december 1984 concentrations of these tracers in the mixed layer are highly variable during the period of observations 25 from june through september soluble eolian deposits accumulate in the shallow mixed layer because mixing and productivity are inhibited by the seasonal thermocline in the fall these enriched surface waters mix with upper thermocline waters and surface pb concentrations decrease in the winter storms from the east coast of north america cause local episodes of high pb and 210pb input into the ocean surface the resulting areally limited high pb concentrations are dispersed within less than 2 weeks by vertical and horizontal mixing pb 210pb ratios in surface waters are almost invariant over this period averaging 669 pmol dpm ranging from 564 to 718 pmol dpm surface pb 210pb appears to have declined by a factor of 2 since 1979 similar to the 2 6 fold decrease in u s leaded gasoline consumption during this period a substantial fraction on the order of 10 of gasoline pb is transported into the ocean pb concentrations in the upper thermocline may have declined by about 15 from 1979 to 1984 the helium tritium thermocline ventilation model of jenkins 1980 coupled with boundary conditions appropriate for pb and 210pb shows that the supply of pb and 210pb to the thermocline is dominated by lateral isopycnal ventilation the shape of the vertical profile is dominated by this physical ventilation near surface biological removal processes in situ scavenging and for stable lead time dependent input vertical transport by particles is responsible for minimal transport of dissolved lead into the upper ocean similar processes are likely to account for the plutonium maximum in the thermocline of the north pacific observations of pb and other reactive species in winter surface outcrops of thermocline isopycnals would provide valuable constraints on chemical processes within the thermocline

glacial geomorphological mapping a review of approaches and frameworks for best practice geomorphological mapping is a well established method for examining earth surface processes and landscape evolution in a range of environmental contexts in glacial research it provides crucial data for a wide range of process oriented studies and palaeoglaciological reconstructions in the latter case providing an essential geomorphological framework for establishing glacial chronologies in recent decades there have been significant developments in remote sensing and geographical information systems gis with a plethora of high quality remotely sensed datasets now often freely available most recently the emergence of unmanned aerial vehicle uav technology has allowed sub decimetre scale aerial images and digital elevation models dems to be obtained traditional field mapping methods still have an important role in glacial geomorphology particularly in cirque glacier valley glacier and icefield ice cap outlet settings field mapping is also used in ice sheet settings but often takes the form of necessarily highly selective ground truthing of remote mapping given the increasing abundance of datasets and methods available for mapping effective approaches are necessary to enable assimilation of data and ensure robustness this paper provides a review and assessment of the various glacial geomorphological methods and datasets currently available with a focus on their applicability in particular glacial settings we distinguish two overarching work streams that recognise the different approaches typically used in mapping landforms produced by ice masses of different sizes i mapping of ice sheet geomorphological imprints using a combined remote sensing approach with some field checking where feasible and ii mapping of alpine and plateau style ice mass cirque glacier valley glacier icefield and ice cap geomorphological imprints using remote sensing and considerable field mapping key challenges to accurate and robust geomorphological mapping are highlighted often necessitating compromises and pragmatic solutions the importance of combining multiple datasets and or mapping approaches is emphasised akin to multi proxy approaches used in many earth science disciplines based on our review we provide idealised frameworks and general recommendations to ensure best practice in future studies and aid in accuracy assessment comparison and integration of geomorphological data these will be of particular value where geomorphological data are incorporated in large compilations and subsequently used for palaeoglaciological reconstructions finally we stress that robust interpretations of glacial landforms and landscapes invariably requires additional chronological and or sedimentological evidence and that such data should ideally be collected as part of a holistic assessment of the overall glacier system

superimposition of ribbed moraines on a palaeo ice stream bed implications for ice stream dynamics and shutdown the sediments and landforms preserved on palaeo ice stream beds can provide important information about their subglacial conditions and flow mechanisms and the processes accompanying their shutdown in this paper detailed observations of an intriguing subglacial landform assemblage of ribbed moraines superimposed on glacial lineations on the dubawnt lake ice stream bed north west canadian shield are presented including their morphometry internal structure from ground penetrating radar gpr surveys and from glaciogeological analysis and sedimentological characteristics from sediment architecture and lithofacies analysis the observations suggest an abrupt change in ice dynamics that correlates with two phases of glacial landform development this hypothesis is based on evidence from a deformed lodgement till which subsequently underwent brittle deformation and developed prominent thrust shear structures and tension fractures tension fractures are observed in a sediment exposure and thrust structures are observed in gpr surveys where they occur most prominently in the ribbed moraine ridge crests the presence of the fractures and their association with a population of clasts in the till that are orientated with their a axes transverse to the inferred ice flow direction suggests a compressional flow regime it is therefore inferred that the glacial lineations were formed under an extensional flow regime during ice stream activity but that at some point patches of till under the ice stream stiffened through dewatering the subsequent increase in basal shear stress resulted in compressional flow and the development of subglacial thrusting and the building of ribbed moraines we therefore suggest that ribbed moraines may form in areas of compressional flow under ice streams i e sticky spots and or at the transition between slow and fast ice flow along parts of an ice stream the general absence of ribbed moraines on most other palaeo ice stream beds suggests that either these ice streams continued operating during deglaciation or processes other than the development of localized compressional flow sticky spots led to their shutdown e g ice depletion

formalising an inversion methodology for reconstructing ice sheet retreat patterns from meltwater channels application to the british ice sheet glacial meltwater channels yield important information regarding patterns of palaeo ice sheet retreat however it is important to distinguish between channels formed at different positions in relation to the ice mass e g lateral subglacial in britain whilst meltwater channels have been widely reported in the literature such categorisation is often lacking here we develop an inversion methodology for extracting ice margin retreat patterns from meltwater channels diagnostic geomorphological criteria are presented derived from published descriptions of meltwater channel form by which a channel of unknown origin may be assigned to its appropriate category these criteria are applied to channels recorded in the britice gis database of glacial landforms and we find most channels to be of lateral or subglacial origin the categorisation of channels enables palaeo margin positions and the direction of retreat stage ice flow to be approximated and a preliminary reconstruction is made of fragments of the ice sheet retreat pattern further mapping and integration of melt traces with other geomorphic data will permit a more complete palaeo glaciological reconstruction of the last british ice sheet copyright 2007 john wiley sons ltd

a pb isotope tracer of ocean ice sheet interaction the record from the ne atlantic during the last glacial interglacial cycle abstract ice sheet ocean interactions are both a response to climate forcing and a source of climate feedback releasing freshwater to the surface ocean and influencing climate and atmospheric co2 through changes in ocean circulation documenting the outcomes of these interactions for recent glacial cycles is important given current and future scenarios of polar ice retreat however this is currently hampered by lack of accurate constraints on ice sheet development and demise marine sedimentary pb isotope records have potential to investigate these aspects of ice sheet feedbacks at high temporal resolution because of the sensitivity of the pb isotope composition to continental weathering intensity and solute flux here we present a pb isotope record sourced from the femn oxyhydroxide fraction in marine sediments from odp site 980 on feni drift 2168 mbsl rockall trough ne atlantic spanning the last 43 ka the location of site 980 at the northern edge of the british irish ice sheet biis makes it well placed to monitor changes in biis development as it responded to migration of the polar front during the last glacial interglacial cycle the data reveal millennial scale cyclicity in pb isotope composition reminiscent of dansgaard oeschger cycles from the start of the record until heinrich event 2 43 24 ka characterised by extreme shifts to radiogenic compositions i e variation in 206pb 204pb from 18 9 to 20 5 the period 24 17 5 ka is also characterised by exceptionally radiogenic and highly variable pb isotope compositions associated with the rapid and repeated expansion and collapse of the biis the presence of such radiogenic pb isotope compositions during periods of maximum ice sheet activity support interpretation of the subglacial environment as an active weathering environment contributing to biogeochemical cycles through the transport vectors of meltwater release and debris laden ice calving

early break up of the norwegian channel ice stream during the last glacial maximum 10be dating last glacial maximum abstract we present 18 new cosmogenic 10 be exposure ages that constrain the breakup time of the norwegian channel ice stream ncis and the initial retreat of the scandinavian ice sheet from the southwest coast of norway following the last glacial maximum lgm seven samples from glacially transported erratics on the island utsira located in the path of the ncis about 400 km up flow from the lgm ice front position yielded an average 10 be age of 22 0 2 0 ka the distribution of the ages is skewed with the 4 youngest all within the range 20 2e20 8 ka we place most confidence on this cluster of ages to constrain the timing of ice sheet retreat as we suspect the 3 oldest ages have some inheritance from a previous ice free period three additional ages from the adjacent island karmoy provided an average age of 20 9 0 7 ka further supporting the new timing of retreat for the ncis the 10 be ages from utsira and karmoy suggest that the ice stream broke up about 2000 years earlier than the age assignment based on 14 c ages on foraminifera and molluscs from marine sediment cores we postulate that the scandinavian ice sheet flowed across the norwegian channel to denmark and onto the north sea plateau during early phases of the lgm when the ncis started to operate this ice supply to the north sea was cut off and the fast flow of the ncis also led to a lowering of the ice surface along the norwegian channel and thereby drawdown of the entire ice sheet this facilitated rapid calving of the ice front in the north sea and we reconstruct a large open bay across the entire northern north sea by 20 ka based on our 10 be ages in the

morphological characteristics formation and glaciological significance of rogen moraine in northern scotland rogen moraine are enigmatic landforms whose exact origin is still debated we use nextmap digital surface models and aerial photographs to map the distribution of previously unreported fields of rogen moraine in the vicinity of loch shin northern scotland existing models of formation are tested against detailed morphological rogen moraine characteristics obtained from the remote sensing data and field observations detailed morphometric analyses combined with their geographical setting lead us to postulate a likely mechanism of formation rogen moraine appear to have formed in areas where there were strong basal ice flow velocity gradients thrusting by compression or fracturing by extension of preexisting partially frozen sediment probably occurred in these areas resulting in rogen moraine formation a general down ice increase in ridge crest spacing suggests that the latter process may have been dominant and is consistent with the location of rogen moraine in the lee of topographic obstructions in areas that experienced overall extensional ice flow we also suggest that at least one field of rogen moraine formed where lateral basal ice flow velocity gradients were strongest possibly in a subglacial shear margin setting given their location the landforms may be consistent with formation during headward scavenging of the moray firth palaeo ice stream into a shrinking core of cold based ice

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

reconstructing the last irish ice sheet 1 changing flow geometries and ice flow dynamics deciphered from the glacial landform record the glacial geomorphological record provides an effective means to reconstruct former ice sheets at ice sheet scale in this paper we document our approach and methods for synthesising and interpre

ribbed moraine formation ribbed rogen moraines are conspicuous landforms found in interior parts of formerly glaciated areas two major theories for ribbed moraine formation have been suggested in recent years i the shear and stack theory which explains ribbed moraine formation by shearing and stacking of till slabs or englacially entrained material during compressive flow followed by basal melt out of transverse moraine ridges and ii the fracturing theory according to which ribbed moraines form by fracturing of frozen pre existing till sheets at the transition from cold to warm based conditions under deglaciating ice sheets in this paper we present new data on the distribution of ribbed moraines and their close association with areas of frozen bed conditions under ice sheets in addition we show examples of ribbed moraine ridges that fit together like a jig saw puzzle these observations indicate that fracturing and extension of a pre existing till sheet may be a predominant process in ribbed moraine formation in summary we conclude that all described characteristics of ribbed moraines are compatible with the fracturing theory while the shear and stack theory is hampered by an inability to explain many conspicuous features in the distribution pattern and detailed morphology of ribbed moraines one implication of the fracturing theory is that the distribution of ribbed moraines can be used to reconstruct the extent of areas that underwent a change from frozen bed to thawed bed conditions under former ice sheets

do subglacial bedforms comprise a size and shape continuum understanding the evolution of the ice bed interface is fundamentally important for gaining insight into the dynamics of ice masses and how subglacial landforms are created however the formation of the suite of landforms generated at this boundary subglacial bedforms is a contentious issue that is yet to be fully resolved bedforms formed in aeolian fluvial and marine environments either belong to separate morphological populations or are thought to represent a continuum of forms generated by the same governing processes for subglacial bedforms a size and shape continuum has been hypothesised yet it has not been fully tested here we analyse the largest data set of subglacial bedform size and shape measurements ever collated 96 900 bedforms our results show that flutes form a distinct population of narrow bedforms however no clear distinction was found between drumlins and megascale glacial lineations msgls which form a continuum of subglacial lineations a continuum of subglacial ribs also exists with no clear size or shape distinctions indicating separate populations furthermore an underreported class of bedform with no clear orientation to ice flow quasi circular bedforms overlaps with the ribbed and lineation continua and typically occurs in spatial transition zones between the two potentially merging these three bedform types into a larger continuum

geochemical cycles of elements and human perturbation abstract the pollution inputs of various elements are omnipresent in aerosols snows rivers and the ocean of the northern hemisphere the mid ocean ridges are not important sinks or sources for most of the elements the settling of fecal pellets is the predominant transport mechanism of most elements except mn co and ni from the surface to deep oceans dissolved mn co and ni are directly incorporated into pelagic clays at the sediment water interface

basin scale patterns of subglacial sediment mobility implications for glaciological inversion modelling abstract patterns of glacial bedforms and their internal sediments are described from the omagh basin north central ireland here drumlins and ribbed moraines were variously formed preserved and remoulded during several late devensian ice flow stages and their patterns can be used as input into glaciological inversion models more detailed examination of the morphology and internal sediments of these bedforms shows a complex pattern of reworking driven by local scale basal thermal and hydrological regime sediment lithofacies associations and patterns of erratic carriage can be used to better evaluate ice bed conditions and basal processes than bedforms alone the sedimentary evidence suggests that bedforms were unlikely to have been formed during a single glacial episode as is implicit in glaciological inversion models and more likely formed during several episodes that cannot be resolved by crosscutting or superimposed bedform relationships alone

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

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

beryllium 10 exposure ages of erratic boulders in southern norway and implications for the history of the fennoscandian ice sheet the margins of the fennoscandian ice sheet fis during the last glacial maximum lgm are fairly well constrained yet the thickness of the fis and its temporal evolution are poorly known here we use beryllium 10 be 10 exposure ages of glacially transported boulders along three vertical transects in southern norway to determine past ice sheet elevations the ice surface elevation during the lgm at our westernmost site skala was likely at approximately 1440 in coinciding with a previously mapped trimline at our central site blaho the ice surface elevation at the lgm was at least at similar to 1620m likely closer to 1800m at elgahogna our easternmost site lgm ice was above the summit elevation of 1460m rapid deglaciation began at skala and blaho at approximately 13 5 14 5 10 beka and at approximately 12 be 10 ka at elgdhogna by approximately 9 be 10 ka the fis had thinned to below our lowest sample at each location periods of rapid thinning correlate with an exposure dated ice margin history as well as the glaciation curve for western scandinavia our data when combined with previous bedrock and blockfield highly weathered bedrock on summits exposure ages resolve a long standing debate over the age and geomorphic interpretation of blockfields and weathering zones in southern norway frozen bed low erosive ice clearly covered the summit blockfields at blaho and especially at elgdhogna where we find a large and progressive divergence between boulder and bedrock exposure ages with elevation we conclude that the lower limit of blockfields in these areas should be interpreted as an englacial thermal boundary rather than the upper limit of the lgm fis and that blockfields have survived multiple glacial cycles we also compare our deglaciation record with several models of the fis models that predict how the fis changed during deglaciation either through inversion of crustal rebound or through climate dependent forward modeling generally match our exposure ages reasonably well during deglaciation but predict larger lgm surface elevations than our data indicate on the other hand the climap maximum model which provides lgm elevations only agrees with our results fairly well c 2007 elsevier ltd all rights reserved

2010 maule earthquake slip correlates with pre seismic locking of andean subduction zone analysis of seismic data and global positioning system gps observations from the region around the site of the recent magnitude 8 8 maule earthquake in chile have been combined with modelling of the andean subduction zone to build up a detailed image of the event the earthquake occurred at a seismic gap part of the fault that has not experienced a major earthquake since 1835 and it seems to have released most of the stress accumulated since that time the observations suggest that coseismic slip heterogeneity at the scale of single asperities and therefore the seismic potential of future great earthquakes might be anticipated by geodetic observations these authors show evidence for a high coherence between the slip distribution inferred from the 2010 maule earthquake chile and the patchwork of interseismic locking distribution derived from global positioning system observations during the previous decade their work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future earthquakes which thus might be anticipated by geodetic observations the magnitude 8 8 maule chile earthquake of 27 february 2010 ruptured a segment of the andean subduction zone megathrust that has been suspected to be of high seismic potential1 2 3 4 5 6 it is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space geodetic network before the event this provides an image of the pre seismically locked state of the plate interface of unprecedentedly high resolution allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip pre seismic locking might be used to anticipate future ruptures in many seismic gaps6 7 8 9 10 11 12 given the fundamental assumption that locking and slip are similar this hypothesis however could not be tested without the occurrence of the first gap filling earthquake here we show evidence that the 2010 maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system gps observations during the previous decade the earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835 two regions of high seismic slip asperities appeared to be nearly fully locked before the earthquake between these asperities the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip the rupture stopped in areas that were highly locked before the earthquake but where pre stress had been significantly reduced by overlapping twentieth century earthquakes our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes which thus might be anticipated by geodetic observations

flow pattern evolution of the last british ice sheet we present a 10 stage reconstruction of the evolution in ice flow patterns of the last british ice sheet from build up to demise derived from geomorphological evidence 100 flowsets identified in the subglacial bedform record drumlins mega scale glacial lineations and ribbed moraine are combined with ancillary evidence erratic transport paths absolute dates and a semi independently reconstructed retreat pattern to define flow patterns ice divides and ice sheet margins during build up maximum glaciation and retreat overprinting and cross cutting of landform assemblages are used to define the relative chronology of flow patterns and a tentative absolute chronology is presented based on a collation of available dates for ice advance and retreat the ice flow configuration of the last british ice sheet was not static some ice divides were remarkably stable persisting through multiple stages of the ice sheet evolution whereas others were transient features existing for a short time and or shifting in position 10s km the 10 reconstructed stages of ice sheet geometry capture two main modes of operation first as an integrated ice sheet with a broadly n s orientated ice divide and second as a multi domed ice sheet orientated parallel with the shelf edge a thick integrated ice sheet developed as ice expanded out of source areas in scotland to envelop southerly ice caps in northern england and wales and connect with the irish ice sheet to the west and the scandinavian ice sheet across the north sea following break up of ice over the north sea ice streaming probably drove mass loss and ice sheet thinning to create a more complex divide structure where ice flow patterns were largely controlled by the form of the underlying topography ice surface lowering occurred before separation of and retreat to multiple ice centres centred over high ground we consider this 10 stage reconstruction of the evolution in ice sheet configuration to be the simplest palaeo glaciological interpretation of the flowsets identified from the geomorphological record and their relative timing this empirically based reconstruction of flow pattern geometry provides a framework for more detailed local and regional studies and numerical modelling to provide robust explanations of the observed changes in ice sheet structure in terms of climate and glacial dynamics as a minimum numerical model outputs should be able to reproduce the identified flowset patterns in space and satisfy their chronological order

ribbed moraines in sweden distribution pattern and palaeoglaciological implications abstract a detailed map of ribbed moraines in central and northern sweden is presented they are frequent features over much of the mapped area and the distribution has well defined limits the most abundant ribbed moraines are situated in close connection to areas that are inferred to have been cold based during the retreat of the late weichselian ice sheet while outer fully warm based areas lack ribbed moraine observations have also been made on a more local scale where cold based patches grade into ribbed moraines via a zone of a broken up till cover a model of origin is presented which includes contracting of a frozen core area of a retreating ice sheet at the transition from non sliding to sliding conditions there will be high stresses resulting in local extensional flow at the base of the ice sheet a rising phase change surface frozen thawed material would cause detachment and boudinage like breaking up of a pre existing till cover thawed at the bedrock contact but still frozen to the ice sole the orientation of ice flow during the formation of the ribbed moraines closely matches the ice flow directions of the deglaciating late weichselian ice sheet thus ribbed moraines are considered to be deglaciation landforms typical of shrinking cold based zones of a retreating ice sheet

applications of lead and strontium isotopic relationships to the petrogenesis of granitoid rocks central sierra nevada batholith california pb isotope data are given on 80 whole rock and or feldspar samples from 51 dated samples covering a traverse across the central sierra nevada batholith largely between latitudes 36 and 37 n in addition sr isotope data were measured on 30 whole rock samples no correlation is observed between age and isotope ratios in agreement with previously published data 87 sr 86 sr ratios are low 0 704 along the western margin and increase to high values 0 707 at the eastern margin 206 pb 204 pb ratios increase from 18 6 at the western margin to 19 5 in the middle of the batholith then decrease regularly to 18 5 toward the eastern margin 2o8 pb 204 pb ratios mirror the 206 pb 204 pb data but do not exhibit the decrease in values toward the eastern margin pb and sr isotopic data from the western margin plutons plot within or close to the field of primitive island arc magmas indicating predominantly mantle sources the high 206 pb 204 pb ratios in the central batholith suggest assimilation of sediments derived from precambrian basement rocks the decrease in 206 pb 204 pb ratios in the eastern segment of the batholith without corresponding reduction in 208 pb 204 pb ratios is attributed to assimilation of lower crustal granulitic amphibolitic rocks by mafic magmas initial pb ratios for samples with 87 sr 86 sr 0 706 from the central and eastern segments of the batholith indicate components from recycled crustal rocks with a mean 207 pb 206 pb age of ca 1 8 ga nd and o isotopic data from the literature are consistent with the pb sr model obtained in this study very similar isotope patterns to the present model are reported across the salinian block

slip distribution of the february 27 2010 mw 8 8 maule earthquake central chile from static and high rate gps insar and broadband teleseismic data 1 the shallow depth underthrust earthquake of february 27 2010 mw 8 8 ruptured the subduction plate interface in central chile between 34 s and 38 s we retrieve the spatial and temporal distribution of slip during this mega earthquake through a joint inversion of teleseismic records insar and high rate gps hrgps data additionally our model is shown to agree with broadband surface waves rupture initiated at about 32 km depth and propagated bilaterally resulting in two main slip zones located ssw and nne of the hypocenter nucleation did not take place within or at the edge of one of these main asperities but in between during the first 30s slip propagated predominantly southwards later on the rupture evolved more slowly and more symmetrically eventually the northern asperity became predominant with maximum slip reaching about 20 m most of the seismic moment was released within 110s a relatively short time explained by the bilateral propagation the overall average rupture velocity is 2 6 km s but propagation occurred initially faster towards the south 3 2 km s large slip did not reach the trench a result consistent with the moderate size of the tsunami down dip rupture stopped at about 50 km depth in agreement with the lower limit of the locked zone inferred by ruegg et al 2009 from pre seismic gps data

estimates of stress drop and crustal tectonic stress from the 27 february 2010 maule chile earthquake implications for fault strength 1 the great 27 february 2010 mw 8 8 earthquake off the coast of southern chile ruptured a 600 km length of subduction zone in this paper we make two independent estimates of shear stress in the crust in the region of the chile earthquake first we use a coseismic slip model constrained by geodetic observations from interferometric synthetic aperture radar insar and gps to derive a spatially variable estimate of the change in static shear stress along the ruptured fault second we use a static force balance model to constrain the crustal shear stress required to simultaneously support observed fore arc topography and the stress orientation indicated by the earthquake focal mechanism this includes the derivation of a semianalytic solution for the stress field exerted by surface and moho topography loading the crust we find that the deviatoric stress exerted by topography is minimized in the limit when the crust is considered an incompressible elastic solid with a poisson ratio of 0 5 and is independent of young s modulus this places a strict lower bound on the critical stress state maintained by the crust supporting plastically deformed accretionary wedge topography we estimate the coseismic shear stress change from the maule event ranged from 6 mpa stress increase to 17 mpa stress drop with a maximum depth averaged crustal shear stress drop of 4 mpa we separately estimate that the plate driving forces acting in the region regardless of their exact mechanism must contribute at least 27 mpa trench perpendicular compression and 15 mpa trench parallel compression this corresponds to a depth averaged shear stress of at least 7 mpa the comparable magnitude of these two independent shear stress estimates is consistent with the interpretation that the section of the megathrust fault ruptured in the maule earthquake is weak with the seismic cycle relieving much of the total sustained shear stress in the crust

limited overlap between the seismic gap and coseismic slip of the great 2010 chile earthquake the mw 8 8 chile earthquake on 27 february 2010 occurred in a broad region where tectonic loading has been accumulating since the great 1835 earthquake a joint inversion of tsunami and geodetic data suggests that the 2010 earthquake rupture only partly overlapped with the zone of preseismic locking

lead in corals reconstruction of historical industrial fluxes to the surface ocean twentieth century environmental lead chronologies for the western north atlantic pacific and indian oceans have been reconstructed from annually banded scleractinian corals measurements of lattice bound pb in sequential coral bands reveal temporal changes in surface water pb concentrations and pb isotopic distributions perturbations are observable in all specimens studied attesting to global augmentation of environmental pb by industrialization in the western north atlantic pb perturbations have occurred in direct response to the american industrial revolution and the subsequent introduction and phasing out of alkyl pb additives in gasoline surface ocean conditions near bermuda may be reliably reconstructed from the coral data via a lead distribution coefficient of 2 3 for the species diploria strigosa based on210pb measurements a similar distribution coefficient may be characteristic of corals in general surface pb concentrations in the pre industrial sargasso sea were about 15 20 pm concentrations rose to near 90 pm by 1923 as a result of metals manufacture and fossil fuel combustion beginning in the late 1940 s increased utilization of leaded gasoline eventually led to a peak concentration of 240 pm in 1971 representing an approximate 15 fold increase over background surface ocean concentrations are presently declining rapidly 128 pm in 1984 as a result of curtailed alkyl pb usage lead isotopic shifts parallel the concentration record indicating that characteristic industrial and alkyl pb source signatures have not changed appreciably in time industrial releases recorded in the florida keys reflect a weaker source and evidence of recirculated pb 5 6 years old from the north atlantic subtropical gyre an inferred background concentration of 38 pm suggests influence of shelf and or resuspended inputs of pb to these coastal waters in remote areas of the south pacific and indian oceans industrial signals are fainter and the corals studied much younger than their atlantic counterparts contemporary pb concentrations implied by coral measurements assumingkd 2 3 are 40 50 pm for surface waters near tutuila and galapagos in the south pacific and 25 29 pm near mauritius in the indian ocean a single coral band from fiji 1920 5yr implies a pre industrial surface water concentration of 16 19 pm pb for the south pacific in view of reported surface water measurements and the north atlantic coral data the pacific coral extrapolations may be slightly high this could be a result of small variations inkd among different coral genera or incorporation of diagenetic pb by corals sampled in coastal environments

fennoscandian palaeoglaciology reconstructed using a glacial geological inversion model the evolution of ice sheet configuration and flow pattern in fennoscandia through the last glacial cycle was reconstructed using a glacial geological inversion model i e a theoretical model that formalises the procedure of using the landform record to reconstruct ice sheets the model uses mapped flow traces and deglacial melt water landforms as well as relative chronologies derived from cross cutting striae and till lineations as input data flow trace systems were classified into four types i time transgressive wet bed deglacial fans ii time transgressive frozen bed deglacial fans iii surge fans and iv synchronous non deglacial event fans using relative chronologies and aggregation of fans into glaciologically plausible patterns a series of ice sheet configurations at different time slices was erected a chronology was constructed through correlation with dated stratigraphical records and proxy data reflecting global ice volume geological evidence exists for several discrete ice sheet configurations centred over the scandinavian mountain range during the early weichselian the build up of the main weichselian fennoscandian ice sheet started at approximately 70 ka and our results indicate that it was characterised by an ice sheet with a centre of mass located over southern norway this configuration had a flow pattern which is poorly reproduced by current numerical models of the fennoscandian ice sheet at the last glacial maximum the main ice divide was located overthe gulf of bothnia a major bend in the ice divide was caused by outflow of ice to the northwest over the lowest part of the scandinavian mountain chain widespread areas of preserved pre late weichselian landscapes indicate that the ice sheet had a frozen bed core area which was only partly diminished in size by inward transgressive wet bed zones during the decay phase

submarine landforms and the reconstruction of fast flowing ice streams within a large quaternary ice sheet the 2500 km long norwegian svalbard margin 57 80 n morphological interpretation of regional and detailed bathymetric data sets on the 2500 km long norwegian shelf from the north sea 57 n to svalbard 80 n has revealed a dynamic ice flow pattern along the western marginof the scandinavian and barents svalbard ice sheets about 20 cross shelf troughs with megascale glacial lineations msgl elongate ridges and grooves oriented parallel to trough long axes are interpreted as former pathways for fast flowing ice streams studies of large scale margin morphology and seismic profiles have identified large submarine fans at the mouths of several major cross shelf troughs less dynamic ice probably existed on shallower banks the two largest paleo ice streams were the norwegian channel ice stream and bear island trough ice stream each 150 200 km wide at the mouth the lengths of individual msgl vary from hundreds of meters to several tens of kilometers and the distance between ridges varies from 0 1 to 3 km msgl amplitudes reach 15 m but are commonly 10 m the onset of msgl and hence fast ice flow is generally close to the outer coast at the border zone between crystalline rocks and softer sedimentary rocks transverse submarine ridges on various scales commonly parallel to the shelf edge reflect either the maximum ice sheet position or the recessional pattern of the ice sheet lateral ice stream moraines several tens of kilometers long have also been mapped along the sides of several cross shelf troughs identifying the border zone between fast ice flow and stagnant or slow flowing ice on intervening banks

fabric pattern in a basal till succession and its significance for reconstructing subglacial processes abstract fabric data from a 2 5 m thick basal till succession in kurzetnik poland consisting of three structurally distinct till units including a deformation till were examined to test whether different processes of deposition and deformation as indicated by till structure are reflected in the till fabric pattern surprisingly throughout the succession the till fabric is unidirectional and very highly clustered mean s1 0 876 and standard fabric interpretation methods including binary and triangular diagrams failed to differentiate between the three units and constrain the origin of the till facies it is shown that the a axis length as well as the ratio between a b and a c axes has no effect on the fabric strength and there is no correlation between the fabric strength and clast size within the 0 7 5 6 cm grain size range the bootstrapping method applied to test the statistical significance of variance shows that 1 some variations in the fabric strength within the same till facies are due to the sampling effect while other variations can be interpreted as true effects of strain and 2 fabric strength may vary significantly over very short distances within the same till facies very high fabric strength in the deformation till is inconsistent with a model of weak to moderate fabric strength resulting from penetrative deformation supporting the theory that subglacial deforming tills behave as coulomb plastic rather than viscous materials

pattern recognition of lidar data and sediment anisotropy advocate a polygenetic subglacial mass flow origin for the kemijarvi hummocky moraine field in northern finland abstract object based image analysis and supervised machine learning on a digital elevation model derived from airborne laser scanning data were conducted to assess the aggregate raw material potential over the kemijarvi hummocky moraine field in finnish lapland geomorphometric analysis revealed surface stoniness to be diagnostic of moraine hummocks it was utilized to detect true moraine hummocks from among the potential hummocks delineated using object based image analysis with logistic regression of curvature features derived from the digital elevation model area under the receiver operating characteristics curve auc 0 77 based on the electrical sedimentary anisotropy data the kemijarvi moraine is polygenetic such that the ridges are diagonally and erosionally fluted from sector 280 290 on their surfaces while the ridge cores are deposited from the nw from sector 310 340 the cores are composed of infill gravels and crudely stratified diamict sequences we consider the core of the kemijarvi hummocky moraine field to represent pre existing early weichselian subglacial ridges rather than being generated through monogenetic late weichselian compressional shearing and stacking frozen bed extension or bed ribbing instability mechanisms as presented for ribbed moraines that are transverse to ice flow recently evidence has been presented of multiple slip events earthquakes with moment magnitudes mw 6 7 7 0 up ice from kemijarvi we therefore propose that the genesis of the hummocks may be associated with past early weichselian fault instability within glacio isostatic adjustment s which was able to generate subglacial water bodies possibly lakes and saturated materials that were forced towards the se based on this new geomorphological evidence from mapping using a digital elevation model derived from airborne laser scanning data and azimuthal conductivity surveys combined with the reinterpretation of previously presented geophysics and sedimentological observations we suggest the kemijarvi hummocky moraine field to be reconsidered as the kemijarvi subglacial mass flow field which holds significant potential for construction aggregate materials

pattern and timing of retreat of the last british irish ice sheet during the last glacial the ice sheet that subsumed most of britain ireland and the north sea attained its maximum extent by 27 ka bp and with an ice volume sufficient to raise global sea level by ca 2 5 m when it melted we reconstruct the demise of this british irish ice sheet biis and present palaeo glaciological maps of retreat stages between 27 and 15 ka bp the whole land area was investigated using remote sensing data and we present maps of moraines meltwater channels eskers and drumlins and a methodology of how to interpret and bring them together for the continental shelf numerous large moraines were discovered recording an extensive pattern of retreat stretching from sw ireland to the shetland isles from an integration of this new mapping of glacial geomorphology 26 000 landforms with previously published evidence compiled in the britice database we derive a pattern of retreat for the whole biis we review and compile relevant dates 881 examples that constrain the timing of retreat all data are held within a geographic information system gis and are deciphered to produce a best estimate of the combined pattern and timing of retreat pattern information reveals an ice sheet mainly comprised of a shelf parallel configuration from sw ireland to ne scotland but it spread far enough to the south to incorporate outlying ice domes over wales the lake district and kerry final disintegration was into a number of separate ice caps rather than reduction as a single mass and paradoxically retreat was not always back to high ground by 23 ka bp ice withdrew along its northern boundaries at the same time as the southern margins were expanding including transient ice streaming down the irish sea and advances of lobes in the cheshire basin vale of york and east coast of england ice divides migrated south by 19 ka the ice sheet was in crisis with widespread marine based ice losses particularly in the northern north sea and the irish sea considerable dynamic thinning occurred during this phase final collapse of all marine sectors occurred by 17 ka bp and with most margins beginning to back step onshore disintegration of the north sea ice bridge between britain and norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted the north channel and irish sea ice streams had finally cleaved the ice sheet into separate irish and scottish ice sheets by 16 ka bp rates of ice loss were found to vary widely over space and time e g 65 260 km3 per year the role of ice streams and calving losses of marine based sectors are examined retreat rates of up to ca 150 ma 1 were found for some ice stream margins that large parts 2 3 of the biis were marine based drained by ice streams and possibly with fringing ice shelves in places makes it a useful analogue for the west antarctic ice sheet wais this is especially so because the biis deglaciated in response to rising temperatures and a rising sea level driven by melting of other ice masses which are the current forcings that might cause collapse of the wais our reconstruction when viewed from the opposite perspective documents when fresh land became exposed for exploitation by plants animals and man and records for how long such land has been available for soil and geochemical development and ecological succession

formation of mega scale glacial lineations on the dubawnt lake ice stream bed 1 size shape and spacing from a large remote sensing dataset abstract mega scale glacial lineations msgls are the largest flow parallel bedforms produced by ice sheets and are formed beneath rapidly flowing ice streams knowledge of their characteristics and genesis is likely to result in an improved understanding of the rate at which ice and sediment are discharged by ice sheets but there is little consensus as to how they are formed and there are few quantitative datasets of their characteristics with which to formulate or test hypotheses this paper presents the results of a remote sensing survey of 46 000 bedforms on the dubawnt lake palaeo ice stream bed focussing on a central transect of 17 038 that includes highly elongate bedforms previously described as msgls within this transect lineations exceed 10 km in length max 20 km and 23 have elongation ratios 10 1 max 149 1 highly elongate features are interspersed with much shorter drumlin like features but longer bedforms are typically narrower suggesting that their length develops more quickly than or at the expense of their width bedforms are broadly symmetrical in plan form and have a preferred lateral spacing of 50 250 m which implies a regular rather than random pattern of corrugations comparison with drumlins reveals that the more attenuated msgls simply extend the tail of the distribution of data rather than plotting as a separate population taken together this supports the idea of a subglacial bedform continuum primarily controlled by ice velocity but existing hypotheses of msgl formation are either not supported or are insufficiently developed to explain our observations rather we conclude that under conditions of rapid ice flow msgls attain their great length relatively quickly decades through a probable combination of subglacial deformation which attenuates ridges and erosional processes that removes material from between them

seismicity near the slip maximum of the 1960 mw 9 5 valdivia earthquake chile plate interface lock and reactivation of the subducted valdivia fracture zone understanding the processes behind subduction related hazards is an important responsibility and major challenge for the earth sciences few areas demonstrate this as clearly as south central chile where some of the largest earthquakes in human history have occurred we present the first observation of local seismicity in the villarrica region 39 40 s based on a temporary local network of 55 stations installed from the chilean coast into the argentinian back arc for one year while consistent with the chilean national catalog ssn our results allow us to observe smaller magnitudes with a completeness of about 2 0 and image the geometry of the wadati benioff zone from the chile trench down to 200 km offshore a gap in interplate seismicity is observed in the region of the 1960 valdivia earthquake slip above the interface two offshore seismicity clusters possibly indicate ongoing stress relaxation in the subducting nazca plate we find a prominent seismicity cluster along the extrapolated trace of the oceanic valdivia fracture zone vfz the seismicity cluster is observed between 70 and 130 km depth and comprises mainly strike slip events it indicates weakening and reactivation of the major vfz by dehydration of oceanic crust and mantle interpreting the subducted vfz section as a localized reservoir of potential fluid release offers an explanation for the villarrica volcanic complex that is located above the reactivated vfz and shows the highest volcanic activity in south america crustal seismicity is observed near puyehue volcano which recently started to erupt june 2011 key points we observe local seismicity near the 1960 valdivia maximum slip region the subducted valdivia fracture zone is reactivated by fluid release the seismogenic zone is free of seismicity events occur at faults and volcanoes

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

land level changes produced by the mw 8 8 2010 chilean earthquake we observed vertically displaced coastal and river markers after the 27 february 2010 chilean earthquake moment magnitude mw 8 8 land level changes range between 2 5 and 1 meters evident along an approximately 500 kilometers long segment identified here as the maximum length of coseismic rupture a hinge line located 120 kilometers from the trench separates uplifted areas to the west from subsided regions a simple elastic dislocation model fits these observations well model parameters give a similar seismic moment to seismological estimates and suggest that most of the plate convergence since the 1835 great earthquake was elastically stored and then released during this event

mega scale glacial lineations and cross cutting ice flow landforms landsat images reveal a previously unsuspected large scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow such a glacial grain can be regarded as a landform assemblage comprised of a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain the ice moulded landform assemblage is described and illustrated with reference to examples from canada possible modes of genesis of such landforms are discussed and their glaciological implications outlined the discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment and demands a radical re interpretation of ice sheet dynamics

weathering fluxes and sediment provenance on the sw scottish shelf during the last deglaciation the reconstruction of past ice sheet dynamics can shed a light on long term ice stream activity and in turn provide constraints on the response of modern ice sheets to climate change the hebrides ice stream his flowed across part of the western scottish shelf to the shelf break during the last glacial cycle and drained a large portion of the northern sector of the british irish ice sheet to investigate the deglacial dynamics of the his following the last glacial maximum lead pb isotope records were extracted from the femn oxyhydroxide and detrital fractions of recovered laminated glacimarine mud sequences to monitor the changing activity of his during its retreat these provide timing and some source information of glacially weathered inputs to the marine environment the femn oxyhydroxide fraction in the samples is dominated by allochthonous particles pre formed and shows a marked decrease from radiogenic 20 05 206pb 204pb at 21 cal ka bp to less radiogenic pb isotope compositions 19 48 towards the windermere interstadial 15 4 13 ka this decrease represents a reduction in the flux of subglacially derived radiogenic pb to the continental shelf is interpreted as being associated with the break up of the ice stream in western scotland around that time the pb sr and nd isotopic signatures of the detrital fraction indicate a preponderance of moine sourced fine sediments originated from the nw highlands in the core locations from 21 to 15 cal ka bp dimlington stadial windermere interstadial most likely dictated by the orientation of ice flow tidal and oceanic current directions and sediment delivery in contrast ice rafted debris in a 21 cal ka bp old basal diamicton contains volcanic derived material suggesting different provenance for different grain sizes the femn oxyhydroxide 208pb 204pb ratio shows an unusual inversion relative to the other pb isotope ratios and is attributed to the introduction of secondary weathering phases from a source with contrasting 208pb 204pb but similar 206pb 204pb and 207pb 204pb in the detrital fraction the inversions are constrained to periodic spikes which may indicate an increased contribution from a high th u source potentially the neighbouring archaean amphibolitic lewisian basement in the outer hebrides this study demonstrates how geochemical investigation on continental shelves can be used to constrain the timing activity and flow sources of palaeo ice streams