interpentadal variability of temperature and salinity at intermediate depths of the north atlantic ocean 1970 1974 versus 1955 1959 we have composited historical hydrographic observations for the world ocean for two pentads 1955 1959 and 1970 1974 and have objectively analyzed these data for the purpose of studying the temporal variability of temperature and salinity in the north atlantic ocean the subtropical gyre 500 1300 m of the north atlantic was colder and fresher during 1970 1974 compared to 1955 1959 the relatively large changes in temperature and salinity on constant depth surfaces in the subtropical gyre were due to upward displacements of isopycnal surfaces at intermediate depths the eastern portion of the subarctic gyre was also colder and fresher during the 1970 1974 pentad in contrast the western portion of the subarctic gyre exhibited higher temperatures and salinities during 1970 1974 compared to 1955 1959 characteristic differences in temperature and salinity for both gyres were 0 5 c and 0 025 respectively analysis of changes in potential vorticity indicates that in the subtropical gyre potential vorticity increased in all density layers above the 26 5 surface suggesting that convection in this region may have been shallower in 1970 1974 compared to 1955 1959 below the 26 5 surface potential vorticity decreased through the 27 3 surface indicating that deeper than normal convection may have formed the water masses in these layers at 250 m depth relatively large changes in temperature and salinity occurred along the line of maximum climatological mixed layer depth that extends northeast to southwest across the north atlantic ocean

chemical influence on α recoil damage annealing in apatite implications for u th he dating article apatite u th he ahe ages reflect the influence of several parameters such as grain size thermal history and diffusion kinetics previous work has suggested that recoil damage produced by the u th decay chains can have a significant effect on he diffusion kinetics models taking into account damage production and annealing via a parameterization similar to that for apatite fission tracks aft have been proposed comple mentary to these models in this work we demonstrate that grain chemistry influences the annealing rate of diffusivity altering damage in the same manner as for aft and thus is not constant across all apatites the key parameter of the annealing law rmr0 is examined and its theoretical impact on ahe age is tested in cer tain situations the ahe age can be significantly affected by changes in the damage annealing rate for sam ples having undergone a long stay in the ahe partial retention zone 50 80 c ahe ages can diverge by more than 15 over a reasonable range of annealing rates in addition this hypothesis is tested on a geolog ical case well samples of triassic sandstones at 67 5 1 5 c at depth in the paris basin france aft data and ahe ages have been measured on detrital apatite in addition to chemical analysis of the grains dated for aft ages for both thermochronometers present similar histogram distributions with younger ages for ahe aft 14 208 ma n 117 ahe 4 76 ma and one grain at 120 ma n 36 the apatite grains are character ized by dpar values from 1 2 m to 2 9 m and cl content ranging from 0 05 to 0 9 wt using a thermal his tory reconstruction based on aft data and geological evidence it is shown that the non correlation observed between ahe age and eu content can be simply explained by changing the rmr0 value we conclude that to fully access the ahe age meaning in terms of temperature sensitivity the parameters of the annealing law stemming from the grain chemistry need to be considered

early cenozoic denudation of central west britain in response to transient and permanent uplift above a mantle plume upwelling mantle plumes beneath continental crust are predicted to produce difficult to quantify modest uplift and denudation the contribution of permanent and transient components to the uplift is also difficult to distinguish a pulse of denudation in britain in the early paleogene has been linked although with some controversy with the arrival of the proto iceland mantle plume in this contribution we show that combining apatite and zircon u th sm he and apatite fission track analyses from central west britain with numerical modeling clearly identifies a pulse of early cenozoic denudation the data indicate that rock uplift and denudation were centered on the northern east irish sea basin and 1 0 2 4 km of rocks were removed during the latest cretaceous early paleogene uplift and erosion appears to have started a few million years before the earliest magmatism in the region the regional denudation pattern mirrors the distribution of low density magmatic rocks that has been imaged in the deep crust however the injection of the underplating melt is not enough to account for the total denudation an additional regional uplift of at least 300 m is required which is consistent with a transient thermal effect from the hot mantle plume the rapid exhumation event ceased by 40 ma and the data do not require significant neogene exhumation

early tertiary paleo thermal effects in northern england reconciling results from apatite fission track analysis with geological evidence abstract the paleozoic lake district block in northwest england has traditionally been thought of as tectonically stable since the late paleozoic receiving only small thicknesses of late paleozoic to mesozoic cover although some workers have put forward different views apatite fission track analysis afta data from outcrop samples across the region reveal early tertiary paleotemperatures around 100 c requiring kilometre scale late paleozoic and mesozoic cover removed during tertiary uplift and erosion with no evidence for elevated basal heat flow in nw england during the early tertiary and no a priori justification for invoking it earlier studies favoured an explanation involving burial by up to 3 km of overburden removed during tertiary uplift and erosion this conclusion was met with scepticism by many workers and provoked a range of comments and criticisms with a variety of alternative interpretations put forward although these are also open to criticism results from the west newton 1 hydrocarbon exploration well on the northern flank of the lake district gave the first indication of a possibly more realistic interpretation involving a combination of elevated heat flow and more restricted burial but some aspects of the interpretation of these data were equivocal more detailed sampling was therefore undertaken in order to shed more light on the origin of the elevated early tertiary paleotemperatures observed across nw england new afta data in outcrop samples from different elevations around sca fell characterised by the highest elevations in the lake district with the summit of scafell pike at 978 m asl define an early tertiary paleogeothermal gradient of 61 c km and require around 700 m of section removed from the summit during tertiary uplift and erosion these results together with those from the west newton 1 well provide strong support for an interpretation involving early tertiary paleogeothermal gradients between 50 and 100 higher than present day values providing clear evidence of elevated basal heat flow during the early tertiary contrary to earlier assumptions combined with amounts of section removed during tertiary exhumation varying between 0 7 km from mountain peaks and 1 5 2 km from coastal plains and glacial valleys near sea level over the region this interpretation finally provides a geologically plausible mechanism for the origin of the observed early tertiary paleo thermal effects in nw england

mesozoic cover over northern england interpretation of apatite fission track data whether a significant thickness of mesozoic cover rocks once rested upon the palaeozoic rocks which form the structural highs of the english lake district and the northern pennines is a subject of long debate which has been revived recently by apatite fission track analysis afta studies evidence from adjacent basins suggests that 1200 1750 m of mesozoic cover was probably formerly present on the highs prior to cenozoic erosion higher estimates c 3000 m of cover thickness based on such fission track derived palaeotemperatures result from underestimation of early cenozoic surface temperatures and from not allowing for the relatively low thermal conductivity of the eroded cover rocks for similar reasons apatite fission track estimates of eroded cover rocks elsewhere in britain may also prove to be overestimates

u and th zonation in fish canyon tuff zircons implications for a zircon u th he standard the inability to accurately determine the distribution of u and th in zircon crystals analysed using u th he is a major source of error and limits the confidence in subsequent data interpretation the fish canyon tuff fct zircon standard shows u th he age reproducibility in excess of 10 we have tested the extent to which this is due to u and th zonation using a combination of cathodoluminescence and ion probe analysis of a population of fct zircons primarily we find that fct zircons exhibit extreme u and th zonation and the population has large inter crystalline variability furthermore the net cathodoluminescence intensity from the fct zircons is negatively correlated with u and th concentration allowing cathodoluminescence emission to be used as a proxy for u and th zonation this correlation was exploited to constrain the u and th zonation within the crystal population and to show that the poor age reproducibility of the fct zircons is consistent with the observed zonation

flow of variably fluidized granular masses across three dimensional terrain 2 numerical predictions and experimental tests numerical solutions of the equations describing flow of variably fluidized coulomb mixtures predict key features of dry granular avalanches and water saturated debris flows measured in physical experiments these features include time dependent speeds depths and widths of flows as well as the geometry of resulting deposits three dimensional 3 d boundary surfaces strongly influence flow dynamics because transverse shearing and cross stream momentum transport occur where topography obstructs or redirects motion consequent energy dissipation can cause local deceleration and deposition even on steep slopes velocities of surge fronts and other discontinuities that develop as flows cross 3 d terrain are predicted accurately by using a riemann solution algorithm the algorithm employs a gravity wave speed that accounts for different intensities of lateral stress transfer in regions of extending and compressing flow and in regions with different degrees of fluidization field observations and experiments indicate that flows in which fluid plays a significant role typically have high friction margins with weaker interiors partly fluidized by pore pressure interaction of the strong perimeter and weak interior produces relatively steep sided flat topped deposits to simulate these effects we compute pore pressure distributions using an advection diffusion model with enhanced diffusivity near flow margins although challenges remain in evaluating pore pressure distributions in diverse geophysical flows riemann solutions of the depth averaged 3 d coulomb mixture equations provide a powerful tool for interpreting and predicting flow behavior they provide a means of modeling debris flows rock avalanches pyroclastic flows and related phenomena without invoking and calibrating rheological parameters that have questionable physical significance

the many surface expressions of mantle dynamics plate tectonic theory suggests that present day topography can be explained by the repeated interactions between the tectonic plates moving along earth s surface however mounting evidence indicates that a significant proportion of earth s topography results from the viscous stresses created by flow within the underlying mantle rather than by the moving plates this dynamic topography is transient varying as mantle flow changes and is characterized by small amplitudes and long wavelengths it is therefore often hidden by or confused with the more obvious topographic anomalies resulting from horizontal tectonic movements however dynamic topography can influence surface processes and thus enter the geological record it has for example played a role in the establishment of amazon drainage patterns in turn surface processes such as the erosion of topographical anomalies could affect mantle flow this emerging view of dynamic topography suggests that the concept of plate tectonics as the driver of surface deformation needs to be extended to include the vertical coupling between the mantle and the surface unravelling this coupling back in time with the help of models and the geological record can potentially provide unprecedented insights into past mantle dynamics

velocity of debris flow determined by grain composition abstractvelocity is one of the most important parameters of debris flows and it is usually calculated using manning formula in hydraulics mostly ignoring the granular effects due to flow material

dynamic analysis of the 2012 johnsons landing landslide at kootenay lake british columbia the importance of undrained flow potential the johnsons landing landslide occurred on 12 july 2012 on the shores of kootenay lake british columbia the landslide consisted of poorly sorted low plasticity debris that initially descended a

linking paleogene denudation and magmatic underplating beneath the british isles a simple flexural model is used to explore the relationship between magmatic underplating and denudation first we show how denudation can be calculated as a function of underplating the distribution and density of underplate are obviously important parameters in determining the wavelength and amplitude of denudation however the denudational pattern can be considerably modulated by the flexural rigidity of the lithosphere several other parameters also play a significant role for example we show how variations in pre existing bathymetry and in present day topography affect denudational calculations we have applied our simple algorithm to the problem of paleogene underplating beneath the british isles forward and inverse modelling of travel time data from a wide angle seismic experiment which traversed the british isles suggests that a large pod of high velocity material occurs at moho depths beneath the irish sea the shape and inferred density of this pod are used to calculate the amplitude and wavelength of denudation for different flexural rigidities we compare our predictions with the observed pattern of paleogene denudation and conclude that the bulk of the observed denudation can be accounted for by magmatic underplating associated in a general way with the iceland plume notwithstanding this agreement there is compelling evidence for additional mild uplift events especially during the neogene these mild events may reflect fluctuating dynamic topography associated with the iceland plume

the angle of reach as a mobility index for small and large landslides the relations between the angle of reach fahrboschung and other indexes expressing the mobility of landslides and vertical drop horizontal reach and volume of landslide mass have been analyzed by means of simplified plots and regression equations results for 204 landslides of all sizes show that whatever the mechanism of motion all kinds of landslides experience a continuous reduction of the angle of reach with volume increase this reduction starts from the smallest sizes scattering in this relation is mostly due to mechanisms of motion and to both obstacles and topographic constraints on the path this synthesis indicates that small landslides less than 0 5 106 m3 in relative terms display excesses of travel distance similar to large landslides since most small landslides are not expected to develop any change in the mechanism of progression while moving the decrease in the reach angle with volume suggests that scale effects should be taken into account the angle of reach is found to be

transient convective uplift of an ancient buried landscape sedimentary basins in the north atlantic ocean preserve a record of intermittent uplift during cenozoic times1 these variations in elevation are thought to result from temperature changes within the underlying icelandic mantle plume2 when parts of the european continental shelf were episodically lifted above sea level new landscapes were carved by erosion but these landscapes then subsided and were buried beneath marine sediments3 here we use three dimensional seismic data to reconstruct one of these ancient landscapes that formed off the northwest coast of europe during the palaeocene eocene thermal maximum we identify a drainage network within the landscape and by modelling the profiles of individual rivers within this network we reconstruct the history of surface uplift we show that the landscape was lifted above sea level in a series of three discrete steps of 200 400 m each after about 1 million years of subaerial exposure this landscape was reburied we use the magnitude and duration of uplift to constrain the temperature and velocity of a mantle plume anomaly that drove landscape formation we conclude that pulses of hot chemically depleted mantle material spread out radially beneath the lithospheric plate at velocities of 35 cm yr 1

the geochemistry and petrogenesis of the lower paleozoic granitoids of the lleyn peninsula north wales abstract the lleyn peninsula of north wales is penetrated by at least twenty stocks varying from microtonalite through to microgranite and these are closely associated with caradocian volcanic rocks which include andesitic lavas major and trace element analyses show that the sample population may be separated into a peralkaline group and a sub alkaline group this latter group may be sub divided into three compositional series which range from andesite to granite the andesites are represented by the caradocian lavas of the moel y penmaen district and these plot at one end of major and trace element variation diagrams their coherent relationships to the granitoids demonstrate the latter to be ordovician and therefore ends a longstanding controversy concerning their age the distinctive geochemistry of the andesites indicates the strong probability that they have evolved from transitional tholeiitic magma by low pressure crystal fractionation apatite fractionation has strongly controlled the rare earth element abundances in the granitoids and for most compositions from andesite through granite their bulk distribution coefficient is greater than unity the association of peralkaline granites transitional tholeiites and other geological and geophysical evidence suggests that the area was a region of ensialic crustal tension during the mid ordovician

steric sea level variations during 1957 1994 importance of salinity 1 spatially averaged 50 s 65 n temperature and salinity changes in the 0 3000 m layer during the 1957 1994 period resulted in a sea level rise at a mean rate of about 0 55 mm per year about 10 of this rate is due to a decrease of the volume mean salinity the magnitude of total steric sea level tssl changes and the ratio of thermosteric and halosteric anomalies to tssl anomaly are nonuniform geographically salinity effects are critically important to the tssl changes in some regions of the ocean for example the thermosteric anomaly is nearly compensated by the halosteric anomaly in the subpolar north atlantic this fact will cause erroneous heat content estimates based on altimetric observations from space if a climatological salinity is assumed based on the present historical archive of salinity data a decrease in global mean salinity has occurred this increase of fresh water would cause sea level rise at a rate of 1 3 0 5 mm yr if the added water comes from sources other than floating sea ice

north atlantic sea level and circulation summary monthly sea levels from an extensive array of north atlantic tide gauges 26 50 n are examined the spatial scale of the sea level variations and the reasons for them are discussed one application of such a study is clearly in the design of a tide gauge network for monitoring eustatic changes of sea level the spatial scale of the sea level changes is large there is a coherent sealevel signal which can be traced along the eastern boundary of the north atlantic from newlyn 50 n to tenerife 28 n there are also two distinct groupings of tide gauges along the western boundary separated by cape hatteras the contribution of local air pressure and wind stress is quantified at each gauge through multiple regression techniques and the gains are then interpreted in terms of recent theoretical and numerical modelling studies for example the gains suggest that the wind forced boundary current along the nova scotian shelf is trapped to within about 16 km of the coast the influence of local meteorology cannot account for the large scale modes of variability the coherent signal along the eastern boundary is correlated with changes in the sverdrup transport of the north atlantic and hence the large scale wind field the two modes on the western boundary appear to be related to baroclinic boundary current variations the newlyn sea level record is finally corrected for some of the above effects to illustrate the utility of such a residual series in the identification of eustatic changes and vertical crustal movement

control of regional sea level by surface uplift and subsidence caused by magmatic underplating of earth s crust magmatic underplating of the crust is a common feature of major basalt provinces the emplacement of magma within the lithosphere leads to surface uplift with a magnitude of the order of 10 of the thickness of the underplated material the composition of associated igneous rock samples suggests that much of the underplated material is made of gabbro this gabbro is denser than the magma from which it crystallizes so uplift of earth s surface caused by the emplacement of magma at the crust mantle boundary must be followed by subsidence as the magma solidifies this subsidence is equal to approximately half the original uplift and takes place within 0 1 m y of injection of the magma the association of magmatic underplating with surface uplift followed by subsidence provides a mechanism for changes of sea level including previously unexplained episodic highstands of sea level

granular flow experiments on the interaction with stationary runout path materials and comparison to rock avalanche events the central focus of this work is to study the processes acting well below the surface of a moving rock or debris avalanche during travel over stationary substrate material small scale physical models at a linear scale of 1 104 used coal as avalanche analogue material and different granular material simulating sedimentary substrates varying in frictional resistance thickness and relative basal boundary roughness as well as inerodible non deformable runout path conditions substrate materials with the least frictional resistance showed the greatest response to granular flow overriding becoming entirely mobilized beneath and ahead of the moving mass and producing the longest runout observed with a unique deposit profile shape with a smooth substrate basal contact failure occurred along this plane and avalanche and substrate became coupled during runout with a rough base however temporary force chains of grain contacts in the substrate prevailed longer imparted their resistance to motion shear into the granular flow and the flow rear section consequently halted earlier than when moving over substrates with a weak base reducing substrate thickness diminished the effect of basal contact roughness on granular flow runout and deposit length inerodible non deformable substrate conditions caused changes in granular flow behaviour from essentially en masse sliding on low friction surfaces to increasing granular agitation over rougher paths copyright 2012 john wiley sons ltd

a latest cretaceous hotspot and the southeasterly tilt of britain the southeasterly regional dip of england and wales is usually ascribed to miocene movements loss of up to 2 km of cover from northern england shown by apatite fission track analysis has been related to uplift and erosion induced by a mantle hotspot but its effects were far more widespread than considered hitherto outcrop patterns throughout much of england wales and eastern ireland can be related to a hotspot beneath the irish sea uplift occurred within the late maastrichtian and erosion continued into the late palaeogene after post oligocene down faulting of the irish sea the modern drainage was initiated on the eroded surface unconformities provide the best means of dating orogenic movements in some localities the time interval between the youngest rocks preserved beneath the unconformity and the oldest preserved above may be small enough to enable the dating of fold movements to be determined with some precision thus in southeastern britain the major e w structures of the hampshire basin the weald and the london basin can be dated as miocene as rocks of oligocene age are involved in the folding in the hampshire basin and pliocene sands rest in erosional pockets of the chalk of se england because fold movements tend to affect large areas of the crust at discrete intervals of time the southeasterly tilt of britain evident from the fact that a nw se transect from anglesey to london crosses outcrops of rocks getting progressively younger from the precambrian of anglesey to the tertiary of the london basin has

can long term variability in the gulf stream transport be inferred from sea level recent studies by sturges and collaborators suggest a simple but powerful technique to estimate climatic changes in the transport of the gulf stream from the difference between the oceanic sea level calculated with a simple wind driven rossby wave model and the observed coastal sea level the hypothesis behind this technique is tested using 40 years of data 1950 to 1989 obtained from a three dimensional atlantic ocean model forced by observed surface data the analysis shows that variations in sea level difference between the ocean and the coast are indeed coherent with variations of the gulf stream transport for periods shorter than 1 year or longer than 4 5 years the results obtained from the three dimensional model confirm the findings of the simple rossby wave model that decadal climatic changes in the gulf stream transport vary considerably with latitude

backstacking apatite fission track stratigraphy a method for resolving the erosional and isostatic rebound components of tectonic uplift histories measuring tectonic uplift of the mean surface of earth using thermochronological data to document uplift histories is often plagued by confusion arising from the independent nature of the thermal and sea level frames of reference the technique of backstacking apatite fission track stratigraphy differentiates between vertical movement of rocks toward earth9s surface due to erosional or tectonic denudation and tectonic uplift of earth9s surface apatite fission track analysis can also be used to identify episodes of erosion where no other evidence for the erosional event exists in addition to providing information about the timing magnitude and geographic distribution of erosion

crustal trace of a hot convective sheet the iceland plume has played an influential role in the evolution of the north atlantic ocean and margins over the past 60 m y it is believed that this plume formed at the conjunction of a tetrad of hot subvertical convective sheets the impingement of these hot sheets at the base of the lithospheric lid caused decompressional melting generating substantial quantities of high temperature magma that were injected into the cold overlying lid over the next 10 m y these sheets partly coalesced to form a crudely axisymmetric plume head here we analyze the lithospheric fingerprint of one of these hot convective sheets by forward and inverse modeling of densely sampled wide angle seismic data in conjunction with gravity observations we determined the three dimensional shape of magmatic underplating trapped within the lithosphere the injection of this melt into the lithosphere generated substantial permanent and minor transient uplift of earth s surface predicted and measured amounts of consequent denudation and sedimentation agree within error temporal variations in the patterns of deposition and oceanic circulation adjacent to the convective sheet show its evolution through time and space our results suggest that this linear sheet has probably been directly and indirectly responsible for cyclical events over 60 m y these events have 0 5 1 and 4 6 m y periodicities the existence of which may help to elucidate the dynamic behavior of convective sheets during and after impingement thus in particular circumstances surficial geological processes yield an indirect record of mantle convection and melt generation processes

topographic relief driven by variations in surface rock density earth s surface topography is generated by tectonically induced variations in crustal thickness combined with erosion and to a lesser degree by vertical stresses caused by convection in the underlying mantle rock hardness and resistance to erosion are also commonly thought to influence topography because hard rocks such as granites and basalts usually form topographic highs in the landscape here we use analytical and numerical models to simulate the erosion induced isostatic rebound of rocks we find that the isostatic rebound that accompanies erosion causes denser rocks to occupy higher elevations in the landscape thereby creating topographic relief that is proportional to surface rock density differences rather than rock hardness we quantify this effect taking into account the flexural strength of the continental lithosphere we show that in a steady state erosional setting density dependent isostatic rebound can cause the densest rocks to be exhumed at double the rate of surrounding less dense rocks and has a stronger effect than typical rock hardness variations the results imply that denser rock formations should erode faster and therefore be characterized by younger thermochronological ages thermochronological data sets from the kinabalu granite in borneo and the shakhdara alichur gneiss domes in pamir confirm this counter intuitive result our findings imply that lateral variations in surface rock density have significant control on the shaping of the large scale features of earth s surface the high elevation in earth s topography of hard rocks such as granites and basalts was thought to be caused by their inherent resistance to erosion numerical modelling now demonstrates counterintuitively that erosion induced isostatic rebound of rocks which is density dependent causes granites and basalts to occupy high elevations because they are more dense than surrounding rocks

interdecadal climate variability in the subpolar north atlantic the statistical relationships between various components of the subpolar north atlantic air sea ice climate system are reexamined in order to investigate potential processes involved in interdecadal climate variability it is found that sea surface temperature anomalies concentrated in the labrador sea region have a strong impact upon atmospheric sea level pressure anomalies over greenland which in turn influence the transport of freshwater and ice anomalies out of the arctic ocean via fram strait these freshwater and ice anomalies are advected around the subpolar gyre into the labrador sea affecting convection and the formation of labrador sea water this has an impact upon the transport of north atlantic current water into the subpolar gyre and thus also upon sea surface temperatures in the region an interdecadal negative feedback loop is therefore proposed as an internal source of climate variability within the subpolar north atlantic through the lags associated with the correlations between different climatic components observed horizontal advection time scales and the use of boolean delay equation models the time scale for one cycle of this feedback loop is determined to have a period of about 21 years

development of a remotely controlled debris flow monitoring system in the dolomites acquabona italy direct measurements of the hydrological conditions for the occurrence of debris flows and of flow behaviour are of the outmost importance for developing effective flow prevention techniques an automated and remotely controlled monitoring system was installed in acquabona creek in the dolomites italian eastern alps where debris flows occur every year its present configuration consists of three on site stations located in the debris flow initiation area in the lower channel and in the retention basin the monitoring system is equipped with sensors for measuring rainfall pore water pressure in the mobile channel bottom ground vibrations debris flow depth total normal stress and fluid pore pressure at the base of the flow three video cameras take motion pictures of the events at the initiation zone in the lower channel and in the deposition area data from the on site stations are radio transmitted to an off site station and stored in a host pc from where they are telemetrically downloaded and used by the padova university for the study of debris flows the efficiency of the sensors and of the whole monitoring system has been verified by the analysis of data collected so far examples of these data are presented and briefly discussed if implemented at the numerous debris flow sites in the dolomitic region the technology used derived from the development of this system will provide civil defence and warn residents of impending debris flows copyright 2003 john wiley sons ltd

the thermal history of the western irish onshore we present here a low temperature thermochronological study that combines the apatite fission track and u th he dating methods with a pseudo vertical sampling approach to generate continuous and well constrained temperature time histories from the onshore irish atlantic margin the apatite fission track and u th he ages range from the late jurassic to early cretaceous and the mean track lengths are relatively short thermal histories derived from inverse modelling show that following post orogenic exhumation the sample profiles cooled to c 75 c a rapid cooling event to surface temperatures occurred during the late jurassic to early cretaceous and was diachronous from north to south it was most probably caused by c 2 5 km of rift shoulder related exhumation and can be temporally linked to the main stage of mesozoic rifting in the offshore basins a slow phase of reheating during the late cretaceous and early cenozoic is attributed to the deposition of a thick sedimentary sequence that resulted in c 1 5 km of burial our data imply a final pulse of exhumation in neogene times probably related to compression of the margin however it is possible that an early cenozoic cooling event compatible with our data but not seen in our inverse models accounts for part of the cenozoic exhumation supplementary material details on the apatite fission track and u th he methods are available at www geolsoc org uk sup18765

the inference of north atlantic circulation patterns from climatological hydrographic data we present a review of spiral techniques which have recently been developed for the determination of absolute velocity profiles from hydrographic observations a specific technique is then designed and applied to the north atlantic part of levitus 1982 climatological hydrographic atlas with the aim of estimating reference velocities and diffusivities for heat salt and potential vorticity these quantities are determined on a 1 grid from the local gradients of temperature and salinity under the constraints of the thermal wind relations and the conservation of the respective tracers including diapycnic and isopycnic mixing terms the estimation procedure includes the statistical framework of inverse modeling in the weighting of the constraints by the data noise variances and the determination of the covariances of the model parameters the resulting circulation pattern bears strong resemblance to the classical view of the north atlantic circulation as put foreward by wust 1935 and defant 1941 the upper layers are dominated by the gulf stream north atlantic current system with a broad subtropical gyre recirculation in the lower layer a western boundary current is fed from norwegian sea overflow penetrating the gibbs fracture zone and partly circulating around the labrador sea as a consequence of the climatological averaging the currents appear in broad shape with much reduced velocities in particular in the upper layer the vertical structure reveals an almost horizontal level of no motion pattern much along the concepts of defant 1941 diffusion coefficients were determined for an upper layer depth of mixed layer to 800 m depth and a lower layer 800 m to 2000 m the spatial pattern of these coefficients correlates with maps of eddy activity showing higher values in the strong current regimes and low values within the subtropical and subpolar gyre average values in the lower layer of the quiet regions are 10 5 m s and 10 m s for the diapycnal and isopycnal diffusivity respectively and 10 1 m s for the vertical diffusivity of vorticity which yields 10 m s for the lateral diffusivity of potential vorticity toward the regions of strong currents and in the upper layer these values roughly increase by an order of magnitude

positive feedback and momentum growth during debris flow entrainment of wet bed sediment debris flows typically occur when intense rainfall or snowmelt triggers landslides or extensive erosion on steep debris mantled slopes the flows can then grow dramatically in size and speed as they entrain material from their beds and banks but the mechanism of this growth is unclear indeed momentum conservation implies that entrainment of static material should retard the motion of the flows if friction remains unchanged here we use data from large scale experiments to assess the entrainment of bed material by debris flows we find that entrainment is accompanied by increased flow momentum and speed only if large positive pore pressures develop in wet bed sediments as the sediments are overridden by debris flows the increased pore pressure facilitates progressive scour of the bed reduces basal friction and instigates positive feedback that causes flow speed mass and momentum to increase if dryer bed sediment is entrained however the feedback becomes negative and flow momentum declines we infer that analogous feedbacks could operate in other types of gravity driven mass flow that interact with erodible beds the mechanisms by which debris flows acquire mass and momentum as they entrain material are unclear large scale experiments suggest that the pore pressure of wet bed sediment increases as the flow moves over the bed leading to reduced friction and progressive scouring of the base

variability of the simulated meridional heat transport in the north atlantic for the period 1951 1993 a 43 year ocean model simulation for the period 1951 1993 is analyzed with a focus on the meridional heat transport mht as a proxy for the strength of meridional overturning cell moc at 25 n the surface heat flux forcing associated with the north atlantic oscillation nao pattern is related to the variability in mht both on interannual and longer timescales the manifestation of the interannual and decadal oceanic response to nao is nonlocal as evidenced by the concentrated heat content and sea level variability at the gulf stream and north atlantic current regions and shown by the comparison of the model sea level variability to the altimeter data between low mht years in mid 1980s and high mht years in early 1990s the same area is singled out by empirical orthogonal function analysis in the leading mode of the sea level mht and time series of the leading sea level mode are highly correlated which reflects the importance of the moc in determining the variability of the heat content of the whole basin also the model suggests that the mht moc has entered a very strong phase since the mid 1980s and this trend has continued up to the end of 1993 this behavior follows the general trend in the nao index

field and laboratory analysis of the runout characteristics of hillslope debris flows in switzerland abstract hillslope debris flows are unconfined flows that originate by shallow failures in unconsolidated material at steep slopes in spite of their significant hazard for persons and infrastructure in mountainous regions research on hillslope debris flows is rather scarce in comparison to other landslide types this study focusses on the runout characteristics of hillslope debris flows applying two different approaches first detailed landslide inventories which include field measurements of 548 slope failures that occurred during the last two decades in seven parts of switzerland were analysed second laboratory tests were carried out to study the effect of the soil water content grain size distribution and mobilized volume on the runout behaviour of hillslope debris flows most of the failures in the field started as shallow translational slides at terrain slopes between 25 and 45 and involved volumes of some tens to a few hundred cubic meters an analysis of the runout distance of 117 hillslope debris flows showed that they normally travelled some tens of meters but sometimes the runout exceeded 300 m a positive relation between volume and runout distance and between volume and affected area was observed although there is considerable scatter in the data the affected area of 63 hillslope debris flows ranged from 100 to 1500 m2 based on the field data a 7 5 m long laboratory hillslope was designed with a geometrical scale factor of 20 a total of 75 runs with volumes from 4 to 20 dm3 water contents from 18 to 38 and four grain size distributions were carried out the laboratory tests revealed that water content is the dominant control but also the clay content strongly influences the runout distance and the affected area even a small increase in water or clay content produces a considerably larger or smaller runout distance respectively in contrast the influence of the volume on the runout was smaller and a positive relation was observed between these two parameters the field and laboratory results are in general agreement and consistent with the results of other studies the results of this work improve the understanding of hillslope debris flows and may aid in the hazard assessments of these processes

laboratory analysis of mudflow properties a rotational viscometer has been designed for laboratory measurements of the rheological properties of natural mudflow deposits in colorado the mudflow matrices comprised of silt and clay particles are sheared under temperature controlled conditions at volumetric sediment concentrations ranging from 0 10 0 45 this study stresses the importance of conducting rheological measurements at low rates of shear because 1 those are the conditions found in natural channels and 2 they avoid the slippage problems observed at large sediment concentrations at low rates of shear the bingham model is fitted to the measured rheograms and both the viscosity and yield stress increase exponentially with the sediment concentration of the fluid matrix both the yield stress and the viscosity increase by three orders of magnitude as the volumetric concentration of sediments in the fluid matrix changes from 10 to 40 the addition of sand particles does not significantly alter the rheological properties of the matrix unless the volumetric concentration of sands exceeds 0 20

effect of alpha damage annealing on apatite u th he thermochronology recent data on he diffusion challenge the temperature sensitivity of apatite u th he thermochronology the damage induced by recoil of u and th decay series during emission of particles recoil damage has been proposed to modify he diffusion properties through time however we propose that annealing of these irradiation defects may be an important phenomenon and may be significant in case of slowly cooled or reheated basement rocks to test this hypothesis we developed a quantitative model including an explicit treatment of recoil damage annealing and their effect on he diffusion kinetics and calibrate it against literature data our model is based on two hypotheses 1 helium is in equilibrium between an apatite crystal and its defects and 2 alpha recoil damage annealing can be described analogously to fission track annealing this model has been embedded into a monte carlo simulation of helium production ejection diffusion and applied to data from the french massif central a complex slowly cooled terrain with burial reheating where the thermal history has been constrained by previous fission track ft data including ft length distributions u th he ages are close to the ft ages from the same samples and are generally reproducible among replicates but some samples present he age dispersion that is not correlated with crystal size our model reproduces the massif central data very well except for three samples where he ages are older than corresponding ft ages we show that annealing of irradiation damage has an important impact on retentivity of helium and that the he content he is only a rough approximation of the damage level in particular our results show that independence of he ages on crystal sizes in case of reheated samples is a clear indication of the higher he retentivity induced by recoil defects and that an explicit treatment of defect annealing is required for a correct interpretation of u th he ages in such a case more generally a correlation with the crystal size can bring information on the thermal path only if the age of defects well represented by the fission track age is available due to the dependence of the partial retention zone on damages conversely in case of rapid cooling or for samples having low u and th contents damage effects can be ignored without significant effects on he ages

accounting for long alpha particle stopping distances in u th sm he geochronology 3d modeling of diffusion zoning implantation and abrasion in apatite u th he thermochronology the helium distribution in a crystal is a function of the simultaneous processes of radiogenic production thermally activated volume diffusion and the ejection of he caused by long alpha stopping distances these processes are further complicated by zonation of u th and sm within the grain and implantation of 4he from neighboring u th sm bearing minerals we use a refined version of the 3d monte carlo diffusion code of gautheron and tassan got 2010 to simulate the interplay between ejection and diffusion with or without zonation ejection and abrasion for a suite of thermal histories we examine the phenomenon of over correction produced by the alpha ejection correction parameter ft or fzac for homogeneous or heterogeneous eu repartition by comparing the raw measured and ft or fzac corrected ages for a number of scenarios to the ejection free age aef which we define as the age that would be obtained if alpha ejection had not occurred or equivalently if the stopping distance was zero we show that the use of ft or fzac corrected ages generally reproduces the ejection free age to within typical u th he uncertainties 8 even for zoned apatites we then quantify the effect of alpha implantation on u th he ages showing that implantation from a single external source with modest relative u or th enrichment can generate as much as 50 excess he for more extreme cases where an apatite is surrounded by multiple external sources the measured age can be 300 of that determined from an isolated crystal while abrasion of the outer 20 25 m can significantly reduce the age dispersion for rapidly cooled samples slowly cooled samples can still retain 10 30 excess he the removal of the rim of the crystal reduces the thermal information from very low temperatures 40 c and introduces additional technical complications and biases and should therefore be used with caution overall we demonstrate that although zonation and implantation may not be routinely determined we now have the 3d modeling capability to fully investigate and constrain the causes of age dispersion within a sample leading to significant improvement in our ability to interpret u th he data

decadal variabilities of the upper layers of the subtropical north atlantic an ocean model study numerical simulations of the atlantic ocean during the period 1950 to 1989 using a sigma coordinate free surface numerical model show long term variabilities in the upper ocean subtropical gyre similar to those obtained from observations the simulations show how westward propagating planetary waves originated in the eastern north atlantic affect interdecadal variabilities of ocean properties such as the bermuda sea level the gulf stream position and strength and subsurface temperature anomalies in the western north atlantic special attention is given to the dramatic sea level drop at bermuda in the early 1970s which is accompanied by cooling of subsurface layers in the western north atlantic and a northward shift and weakening of the gulf stream following these events between 1970 and 1980 the cold temperature anomalies in the upper layers of the western north atlantic slowly propagated eastward and downward the strongest propagating signal in the model is found at 200 m depth suggesting that advection of anomalies downstream by the gulf stream current and changes in winter mixing are involved significant correlations were found between the sea level anomalies at bermuda and sea level anomalies in the eastern north atlantic up to eight years earlier sensitivity experiments with different atmospheric forcing fields are used to study the ocean response to observed sea surface temperature and wind stress anomalies it is shown that on decadal timescales the ocean model responds in a linear fashion to the combined effect of sst and wind stress anomalies a fact that might be exploited in future climate prediction studies

multidecadal variability of north atlantic temperature and salinity during the twentieth century abstract substantial changes occurred in the north atlantic during the twentieth century here the authors demonstrate through the analysis of a vast collection of observational data that multidecadal fluctuations on time scales of 50 80 yr are prevalent in the upper 3000 m of the north atlantic ocean spatially averaged temperature and salinity from the 0 300 and 1000 3000 m layers vary in opposition prolonged periods of cooling and freshening warming and salinification in one layer are generally associated with opposite tendencies in the other layer consistent with the notion of thermohaline overturning circulation in the 1990s widespread cooling and freshening was a dominant feature in the 1000 3000 m layer whereas warming and salinification generally dominated in the upper 300 m except for the subpolar north atlantic where complex exchanges with the arctic ocean occur the single signed basin scale pattern of multidecadal variability is evident from decadal 1000 3000 m temperature and salin

apatite u th he age constraints on the development of the great escarpment on the southeastern australian passive margin the southeast australian margin like other high elevation passive margins is characterised by a steep escarpment that separates a dissected coastal plain from a low relief inland plateau quantitative constraints on the generation of escarpments can be provided by apatite u th he ages here we use a coast perpendicular traverse across the coastal lowlands escarpment and plateau to test the three prevailing models of se australian escarpment formation namely retreat into a downwarped rift shoulder escarpment retreat and down wearing on high elevation rift shoulder with flexural rebound apatites from the coastal plain have he ages of between 87 and 112 ma suggesting that the coastal lowlands developed very rapidly after rifting and continental break up at 85 100 ma the he age data are inconsistent with the erosion of a downwarped rift margin and cannot be explained by a constant post break up rate of lateral escarpment retreat across the coastal plain or by constant down wearing the data require either rapid escarpment retreat or rapid in place excavation of the escarpment soon after break up in response to rifting and the lowering of base levels on the margin of the new continent at break up followed by a period of landscape stability and low erosion combined with the existing apatite fission track record the he data are consistent with erosion of 3 4 km within a maximum of 28 myr of break up at a minimum vertical erosion rate of 130 m myr 1 along the coast the rapid denudation period across the coastal plain in this region took less than 48 myr from the coast to the escarpment base which corresponds to an average vertical erosion rate of 45 m myr 1 this is equivalent to a mean escarpment retreat rate of 5 10 km myr 1 apatite he ages from the plateau 183 247 ma indicate that the highlands remained stable throughout continental break up experiencing average erosion rates of less than 10 m myr 1 since the late palaeozoic early mesozoic

interpentadal variability of steric sea level and geopotential thickness of the north atlantic ocean 1970 1974 versus 1955 1959 we have composited and objectively analyzed historical hydrographic observations for the north atlantic ocean for two periods 1955 1959 and 1970 1974 difference fields of steric sea level and geopotential thickness for the north atlantic ocean in the 0 to 1500 m depth range between the 1955 1959 and 1970 1974 pentads were computed we find that in the central portion of the subtropical gyre steric sea level decreased by up to 17 5 dyn cm whereas in the western subarctic gyre north of the gulf stream steric sea level increased by an amount up to 7 5 dyn cm from the earlier to the later pentad a decrease in steric sea level 5 dyn cm occurred along the eastern boundary of the north atlantic

geothermal resources of the united kingdom geothermal prospects in the uk are represented by low enthalpy resources in deep sedimentary basins and 9hot dry rock9 hdr resources in radiothermal granites and possibly in deep basement rocks where they are overlain by thick low conductivity sediments the low enthalpy resources are in permo triassic sandstones at temperatures of more than 40 c four deep exploration wells have been drilled to investigate the potential of these sedimentary aquifers the main hdr resource potential is associated with major granite batholiths in southwest and northern england where temperatures are predicted to be 200 c at about 5 4 and 6 km respectively the hdr potential is being investigated by the camborne school of mines at their test site in cornwall where three boreholes have been drilled to depths of between 2 and 2 5 km the hot dry rock accessible resource base at temperatures of more than 100 c and depths of less than 7 km is 36 x 10 21 joules equivalent to 130 10 4 million tons of coal the low enthalpy geothermal resource of the permo triassic sandstones at temperatures of more than 40 c is 200 10 l8 joules equivalent to about 8000 million tons of coal if only a small fraction of these resources could be developed it would be significant in terms of the uk s energy balance

cenozoic post rift sedimentation off northwest britain recording the detritus of episodic uplift on a passive continental margin the cenozoic sedimentary basins on the atlantic margin of nw britain contain a remarkable record of tectonically influenced post breakup sedimentation we have mapped the distribution and quantified the solid grain volume of four unconformity bound successions in the region the eocene 6 8 104 km3 oligocene 2 104 km3 miocene lower pliocene 4 5 104 km3 and lower pliocene holocene 4 5 104 km3 complementing previous work on the paleocene succession approximately 80 of the total cenozoic sediment volume on the atlantic margin of nw britain was deposited in eocene and later times the relative volumes of the cenozoic succession do not support previous claims that the paleocene was the main period of cenozoic uplift and erosion of sediment source areas rather the cenozoic sedimentary basins on the atlantic margin of nw britain record the detritus of four major episodes of cenozoic uplift of the british isles paleocene eocene oligocene miocene and pliocene pleistocene

interplay of rheology and entrainment in debris avalanches a numerical study flow type landslides are a major global hazard they occur worldwide and are responsible for a large number of casualties significant structural damage to property and infrastructure and economic losses the features of debris avalanches are particularly important as they involve open slopes and affect triangular source areas when initial slides turn into avalanches through further failures or eventual soil entrainment in this paper the propagation stage of debris avalanches is numerically modelled to provide information such as the propagation pattern of the mobilized material and its velocity thickness and run out distance the use of a depth integrated model has the following advantages i it adequately accommodates the irregular topography of real slopes which greatly affects the evolution of the propagation stage and ii it is less time consuming than full three dimensional approaches the model is named geoflow sph and has previously been applied to theoretical experimental and re

natural age dispersion arising from the analysis of broken crystals part i theoretical basis and implications for the apatite u th he thermochronometer abstract over the last decade major progress has been made in developing both the theoretical and practical aspects of apatite u th he thermochronometry and it is now standard practice and generally seen as best practice to analyse single grain aliquots these individual prismatic crystals are often broken and are fragments of larger crystals that have broken during mineral separation along the weak basal cleavage in apatite this is clearly indicated by the common occurrence of only 1 or no clear crystal terminations present on separated apatite grains and evidence of freshly broken ends when grains are viewed using a scanning electron microscope this matters because if the 4 he distribution within the whole grain is not homogeneous because of partial loss due to thermal diffusion for example then the fragments will all yield ages different from each other and from the whole grain age here we use a numerical model with a finite cylinder geometry to approximate 4 he ingrowth and thermal diffusion within hexagonal prismatic apatite crystals this is used to quantify the amount and patterns of inherent natural age dispersion that arises from analysing broken crystals a series of systematic numerical experiments were conducted to explore and quantify the pattern and behaviour of this source of dispersion using a set of 5 simple thermal histories that represent a range of plausible geological scenarios in addition some more complex numerical experiments were run to investigate the pattern and behaviour of grain dispersion seen in several real data sets the results indicate that natural dispersion of a set of single fragment ages defined as the range divided by the mean arising from fragmentation alone varies from c 7 even for rapid c 10 c ma monotonic cooling to over 50 for protracted complex histories that cause significant diffusional loss of 4 he the magnitude of dispersion arising from fragmentation scales with the grain cylindrical radius and is of a similar magnitude to dispersion expected from differences in absolute grain size alone spherical equivalent radii of 40 150 m this source of dispersion is significant compared with typical analytical uncertainties on individual grain analyses c 6 and standard deviations on multiple grain analyses from a single sample c 10 20 where there is a significant difference in the u and th concentration of individual grains eu the effect of radiation damage accumulation on 4 he diffusivity assessed using the rdaam model of flowers et al 2009 is the primary cause of dispersion for samples that have experienced a protracted thermal history and can cause dispersion in excess of 100 for realistic ranges of eu concentration i e 5 100 ppm expected natural dispersion arising from the combined effects of reasonable variations in grain size radii 40 125 m eu concentration 5 150 ppm and fragmentation would typically exceed 100 for complex thermal histories in addition to adding a significant component of natural dispersion to analyses the effect of fragmentation also acts to decouple and corrupt expected correlations between grain ages and absolute grain size and to a lesser extent between grain age and effective uranium concentration eu considering fragmentation explicitly as a source of dispersion and analysing how the different sources of natural dispersion all interact with each other provides a quantitative framework for understanding patterns of dispersion that otherwise appear chaotic an important outcome of these numerical experiments is that they demonstrate that the pattern of age dispersion arising from fragmentation mimics the pattern of 4 he distribution within the whole grains thus providing an important source of information about the thermal history of the sample we suggest that if the primary focus of a study is to extract the thermal history information from u th he analyses then sampling and analytical strategies should aim to maximise the natural dispersion of grain ages not minimise it and should aim to analyse circa 20 30 grains from each sample the key observations and conclusions drawn here are directly applicable to other thermochronometers such as the apatite rutile and titanite u pb systems where the diffusion domain is approximated by the physical grain size

direct measurement of channel erosion by debris flows illgraben switzerland 1 the timing and magnitude of channel bed erosion by three debris flows was measured in 2008 at the illgraben catchment switzerland using a scour sensor which consisted of a vertical array of erodible sensor elements during the largest debris flow sediment was entrained progressively and stepwise at the flow head within 20 s after front arrival and onset of erosion started before maximum values for flow height and normal and shear stress measured nearby were reached erosion in one of the two smaller debris flows also occurred at the head of the flow but the magnitude of erosion was at the detection limit for the sensor for the other small debris flow we were not able to determine the timing of erosion due to the presence of a sediment layer covering the sensors measurements of pressure fluctuations along the channel sidewall which are produced by interparticle collisions within the flow indicate that the entrainment of sediment is coincident with the largest mean and fluctuating pressures suggesting that interparticle collisions may drive the erosion process at the front of debris flows after erosion at the head of the debris flows sediment was deposited on top of the erosion sensor columns indicating that the bed was reworked to a larger depth than directly visible at the surface after the event observations from elsewhere along the channel support our measurements of the magnitude of net debris flow erosion and indicate that significant erosion can be expected on debris fans when the flow is confined to a channel debris flow entrainment and subsequent bulking of the flow influence the flow dynamics and therefore should be considered in debris flow models and hazard assessment

a model for the runout analysis of rapid flow slides debris flows and avalanches runout analyses are used for risk assessment and design of remedial measures against rapid landslides such as debris flows debris avalanches rockslide avalanches large scale liquefaction failure

effects of debris flow composition on runout depositional mechanisms and deposit morphology in laboratory experiments predicting debris flow runout is of major importance for hazard mitigation apart from topography and volume runout distance and area depends on debris flow composition and rheology but how is poorly understood we experimentally investigated effects of composition on debris flow runout depositional mechanisms and deposit geometry the small scale experimental debris flows were largely similar to natural debris flows in terms of flow behavior deposit morphology grain size sorting channel width depth ratio and runout deposit geometry lobe thickness and width in our experimental debris flows is largely determined by composition while the effects of initial conditions of topography i e outflow plain slope and channel slope and width and volume are negligible we find a clear optimum in the relations of runout with coarse material fraction and clay fraction increasing coarse material concentration leads to larger runout however excess coarse material results in a large accumulation of coarse debris at the flow front and enhances diffusivity increasing frontal friction and decreasing runout increasing clay content initially enhances runout but too much clay leads to very viscous flows reducing runout runout increases with channel slope and width outflow plain slope debris flow volume and water fraction these results imply that debris flow runout depends at least as much on composition as on topography this study improves understanding of the effects of debris flow composition on runout and may aid future debris flow hazard assessments

the perfect debris flow aggregated results from 28 large scale experiments 1 aggregation of data collected in 28 controlled experiments reveals reproducible debris flow behavior that provides a clear target for model tests in each experiment 10 m3 of unsorted water saturated sediment composed mostly of sand and gravel discharged from behind a gate descended a steep 95 m flume and formed a deposit on a nearly horizontal runout surface experiment subsets were distinguished by differing basal boundary conditions 1 versus 16 mm roughness heights and sediment mud contents 1 versus 7 percent dry weight sensor measurements of evolving flow thicknesses basal normal stresses and basal pore fluid pressures demonstrate that debris flows in all subsets developed dilated coarse grained high friction snouts followed by bodies of nearly liquefied finer grained debris mud enhanced flow mobility by maintaining high pore pressures in flow bodies and bed roughness reduced flow speeds but not distances of flow runout roughness had these effects because it promoted debris agitation and grain size segregation and thereby aided growth of lateral levees that channelized flow grain size segregation also contributed to development of ubiquitous roll waves which had diverse amplitudes exhibiting fractal number size distributions despite the influence of these waves and other sources of dispersion the aggregated data have well defined patterns that help constrain individual terms in a depth averaged debris flow model the patterns imply that local flow resistance evolved together with global flow dynamics contradicting the hypothesis that any consistent rheology applied we infer that new evolution equations not new rheologies are needed to explain how characteristic debris flow behavior emerges from the interactions of debris constituents

inverse modelling of extension and denudation in the east irish sea and surrounding areas abstract epeirogenic uplift and denudation are difficult to quantify because unlike basin subsidence they do not leave an unambiguous record in recent years much research has been focussed on calculating regional denudation from sonic velocity measurements from vitrinite reflectance profiles and from fission track analyses here we show that inverse modelling of the remnant stratigraphy within extensional sedimentary basins yields estimates of denudation within a corridor which crosses the british isles for a variety of reasons these estimates are minima but they do broadly agree with those determined by inversion of vitrinite reflectance profiles our results also demonstrate that denudation estimates from fission track analyses are meaningful a combined stratigraphic and thermal indicator approach should now be used to map denudation across different continents

the elastic thickness of the british isles free air gravity and topography data from the british isles have been analysed in the frequency domain to determine the mechanisms of topographic support first we calculate how the admittance between measured free air gravity and topography varies as a function of wavelength a simple model which consists of a crust with two layers of different densities overlying a higher density mantle was then used to calculate admittance functions the misfit between observed and calculated admittance was minimized by varying elastic thickness and the proportion of the total load due to internal loading at short wavelengths c 0 2 the general behaviour of the observed admittance suggests that topography is primarily supported by elastic stresses in the crust a small departure between observed and calculated admittance at the longest wavelengths 400

the triggering of debris flow due to channel bed failure in some alpine headwater basins of the dolomites analyses of critical runoff the debris deposits at the bottom of very steep natural channels and streams in high mountain areas can be mobilized by runoff triggering a water sediment mixture flow known as debris flow the routing of debris flow through human settlements can cause damage to civil structures and loss of human lives the prediction of such an event or the runoff discharge that triggers it assumes an interest in risk analyses and the planning of defence measures the object of this study is to find a method to determine the critical runoff value that triggers debris flow as a result of channel bed failure historical and rainfall data on 30 debris flows that occurred in six watersheds of the dolomites north eastern italian alps were collected from different sources field investigations at the six sites together with the hydrologic response to the rainfalls that triggered the events were performed to obtain a realistic scenario of the formation of the debris flow there occurred field observations include a survey along the channel of the triggering reach of debris flow with measurements of the channel slope and cross section and sampling of debris deposits for grain size distribution simulated runoff discharge values based on the rainfall recorded by pluviometers were then compared with values obtained through experimental criteria on the initiation and formation of debris flow by bed failure the results are discussed to provide a plausible physical based method for the prediction of the triggering of debris flow by channel bed failure copyright 2007 john wiley sons ltd

decadal wind forcing of the north atlantic subtropical gyre abstract in the central north atlantic ocean there are large decadal scale fluctuations of sea level and of the depth of the thermocline this variability can be explained by low frequency rossby waves forced by wind the authors have used a simple model of ocean fluctuations driven by the coads wind stress curl and find that their model results and hydrographic data to the limited extent they can be compared meaningfully agree rather well the variation in wind curl over the ocean leads to surprisingly large north south variability in the computed oceanic response over the subtropical gyre the peak to peak sea level differences are as great as 20 cm and persist for many years these large variations could induce major errors in calculations of the mean ocean flow when hydrographic sections from many years are combined it appears possible however to correct for these wind induced effects to allow the lower frequency signals to be determined the westernmost edge of our oceanic calculations is at the

evolution of a natural debris flow in situ measurements of flow dynamics video imagery and terrestrial laser scanning many theoretical and laboratory studies have been undertaken to understand debris flow processes and their associated hazards however complete and quantitative data sets from natural debris flows needed for confirmation of these results are limited we used a novel combination of in situ measurements of debris flow dynamics video imagery and pre and postflow 2 cm resolution digital terrain models to study a natural debris flow event our field data constrain the initial and final reach morphology and key flow dynamics the observed event consisted of multiple surges each with clear variation of flow properties along the length of the surge steep highly resistant surge fronts of coarse grained material without measurable pore fluid pressure were pushed along by relatively fine grained and water rich tails that had a wide range of pore fluid pressures some two times greater than hydrostatic surges with larger nonequilibrium pore fluid pressures had longer travel distances a wide range of travel distances from different surges of similar size indicates that dynamic flow properties are of equal or greater importance than channel properties in determining where a particular surge will stop progressive vertical accretion of multiple surges generated the total thickness of mapped debris flow deposits nevertheless deposits had massive vertically unstratified sedimentological textures

cenozoic exhumation of the southern british isles rocks that crop out across southern britain were exhumed from depths of as much as 2 5 km during cenozoic time this has been widely attributed to paleocene regional uplift resulting from igneous underplating related to the iceland mantle plume our compilation of paleothermal and compaction data reveals spatial and temporal patterns of exhumation showing little correspondence with the postulated influence of underplating instead being dominated by kilometer scale variations across cenozoic compressional structures which in several basins are demonstrably of neogene age we propose that crustal compression due to plate boundary forces transmitted into the plate interior was the major cause of cenozoic uplift in southern britain witnessing a high strength crust in western europe

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

interannual and interdecadal oscillation patterns in sea level relative sea level height rslh data at 213 tide gauge stations have been analyzed on a monthly and an annual basis to study interannual and interdecadal oscillations respectively the main tools of the study are singular spectrum analysis ssa and multi channel ssa m ssa very low frequency variability of rslh was filtered by ssa to estimate the linear trend at each station global sea level rise after postglacial rebound corrections has been found to equal 1 62 0 38 mm y by averaging over 175 stations which have a trend consistent with the neighboring ones we have identified two dominant time scales of el nino southern oscillation enso variability quasi biennial and low frequency in the rslh data at almost all stations however the amplitudes of both enso signals are higher in the equatorial pacific and along the west coast of north america rslh data were interpolated along ocean coasts by latitudinal intervals of 5 or 10 degrees depending on station density interannual variability was then examined by m ssa in five regions eastern pacific 25 s 55 n at 10 resolution western pacific 35 s 45 n at 10 equatorial pacific 123 e 169 w 6 stations eastern atlantic 30 s 0 and 30 n 70 n at 5 and western atlantic 50 s 50 n at 10 throughout the pacific we have found three dominant spatio temporal oscillatory patterns associated with time scales of enso variability their periods are 2 2 5 3 and 4 6 y in the eastern pacific the biennial mode and the 6 y low frequency mode propagate poleward there is a southward propagation of low frequency modes in the western pacific rslh between 35 n and 5 s but no clear propagation in the latitudes further south however equatorward propagation of the biennial signal is very clear in the southern hemisphere in the equatorial pacific both the quasi quadrennial and quasi biennial modes at 10 n propagate westward strong and weak el nino years are evident in the sea level time series reconstructed from the quasi biennial and low frequency modes interannual variability with periods of 3 and 4 8 y is detected in the atlantic rslh data in the eastern atlantic region we have found slow propagation of both modes northward and southward away from 40 45 n interdecadal oscillations were studied using 81 stations with sufficiently long and continuous records most of these have variability at 9 13 and some at 18 y two significant eigenmode pairs corresponding to periods of 11 6 and 12 8 y are found in the eastern and western atlantic ocean at latitudes 40 n 70 n and 10 n 50 n respectively

field and laboratory investigations of runout distances of debris flows in the dolomites eastern italian alps abstract the estimation of runout distances on fans has a major role in assessing debris flow hazards different methods have been devised for this purpose volume balance limiting topographic methods empirical equations and physical approaches data collected from field observations are the basis for developing testing and improving predictive methods while laboratory tests on small scale models are another suitable approach for studying debris flow runout under controlled conditions and for developing predictive equations this paper analyses the problem of assessing runout distance focusing on six debris flows that were triggered on july 5th 2006 by intense rainfall near cortina d ampezzo dolomites north eastern italy detailed field surveys were carried out immediately after the event in the triggering zone along the channels and in the deposition areas a fine scale digital terrain model of the study area was established by aerial lidar measurements total travel and runout distances on fans measured in the field were compared with the results of formulae from the literature empirical statistical and physically oriented and samples of sediment collected from deposition lobes were used for laboratory tests the experimental device employed in the tests consists of a tilting flume with an inclination from 0 to 38 on which a steel tank with a removable gate was installed at variable distances from the outlet a final horizontal plane works as the deposition area samples of different volumes and variable sediment concentrations were tested multiple regression analysis was used to assess the length of the deposits as a function of both the potential energy of the mass and the sediment concentration of the flow our comparison of the results of laboratory tests with field data suggests that an energy based runout formula might predict the runout distances of debris flows in the dolomites

new views of granular mass flows concentrated grain fluid mixtures in rock avalanches debris flows and pyroclastic flows do not behave as simple materials with fixed rheologies instead rheology evolves as mixture agitation grain concentration and fluid pressure change during flow initiation transit and deposition throughout a flow however normal forces on planes parallel to the free upper surface approximately balance the weight of the superincumbent mixture and the coulomb friction rule describes bulk intergranular shear stresses on such planes pore fluid pressure can temporarily or locally enhance mixture mobility by reducing coulomb friction and transferring shear stress to the fluid phase initial conditions boundary conditions and grain comminution and sorting can influence pore fluid pressures and cause variations in flow dynamics and deposits

sph run out modelling of channelised landslides of the flow type abstract rainfall induced channelised landslides of the flow type may reach high velocities and travel large run out distances the proper modelling of the propagation stage is fundamental to risk analysis and management the correct selection of mass rheology is fundamental to this procedure and the variation of pore water pressures and bed entrainment along the landslide path must also be properly taken into account all of these processes can be consistently simulated through a quasi 3d depth integrated coupled sph model in this study such a model is applied to a relevant case history from southern italy for which an advanced dataset is available the numerical results provide a satisfactory back analysis of the case history and clearly indicate that the bed entrainment rate and the extent of the erodible areas affect the propagation paths the velocities and the deposition heights on the basis of the results general insights into this type of landslide are discussed with reference to different hypotheses for propagation modelling

north atlantic oscillation induced changes of the upper layer circulation in the northern north atlantic ocean 1 hydrographic data of the 1990s along world ocean circulation experiment sections a1e greenland ireland and a2 newfoundland france indicate a redistribution of cold low saline subarctic waters and warm saline subtropical waters in the upper layer of the northern north atlantic within about 2 years after the north atlantic oscillation had turned from a period with strong westerlies until 1995 to a period with weak westerlies in 1996 and 1997 in the latter period subarctic waters spread preferably southward along the continental slope east of newfoundland rather than eastward with the north atlantic current nac into the irminger iceland and west european basins as a consequence the subarctic front and the associated nac shifted eastward in the newfoundland basin where subarctic waters accumulate and westward in the iceland basin where a large warm and saline anomaly was found in 1996 and 1997 indicating a contraction of the subpolar gyre in the irminger basin the anomaly occurred in 1998 and 1999 whereas the cyclonic circulation in the irminger and iceland basins weakened it intensified in the newfoundland basin where a strengthened labrador current retroflection joined the nac this and the increased anticyclonic recirculation of subtropical waters in the newfoundland and west european basins caused a considerable reduction of the northward heat transport across 47 n in the upper layer in 1997 the anticyclonic circulation occurring in the west european basin suggested a northward expansion of the subtropical gyre

field investigations of the interaction between debris flows and forest vegetation in two alpine fans abstract a key objective in debris flow hazard mitigation is the reduction of the potential depositional area in the fan from this point of view forested areas are able to provide a protective function hindering the flow motion and promoting the surge deposition despite extensive research on alpine forests and their protective functions relatively few studies in the literature have quantitatively focused on the relationship between debris flow depositional features and vegetation in light of the above our research investigates how vegetation characteristics in the fan area interact with debris flow deposition field investigations were carried out in two alpine fans where debris flow events occurred in the summer of 2012 by recording the characteristics of 1567 involved trees and the associated deposit thicknesses this paper provides a data set that contributes to the improvement of the knowledge of these interaction processes the integration of literature findings and the analysis of the collected dataset adds insights into the relationships between tree characteristics and the dynamics of debris flow during the runout path the main results prove the capacity of the forest of uniformly promoting flow energy dissipation presence of high species diversity in debris flow deposits when comparing disturbed and undisturbed forest stands tree mortality largely affecting small diameters

experimental study of the grain flow fluid mud transition in debris flows abstract we have performed a series of laboratory experiments that clarify the nature of the transition between fluid mud and grain flow behavior the surface velocity structure and the speed of the nose of debris flows in channels with semicircular cross sections were measured with several cameras and visual tracers while the mass flow rate was recorded using a load cell at the exit chamber other rheological tests were used to calculate independently the yield strength and matrix viscosity of the debris flow mixture shear rates were varied by nearly an order of magnitude for each mixture by changing the channel radius and slope shear rates were significantly higher than expected 6 55 s 1 given the modest slopes examined 10 7 15 2 the large values were primarily a result of the concentration of shear into narrow bands between a central nondeforming plug and the sidewall as a result the shear rate of interest was calculated by using the width of the shear band and the plug velocity as oppose

ocean gyre circulation changes associated with the north atlantic oscillation abstract observational evidence is presented for interannual to interdecadal variability in the intensity of the north atlantic gyre circulation related to the atmospheric north atlantic oscillation nao patterns a two point baroclinic pressure difference between the subtropical and subpolar gyre centers an oceanic analogue to the much used sea level pressure slp based atmospheric nao indices is constructed from time series of potential energy anomaly pea derived from hydrographic measurements in the labrador basin and at station s near bermuda representing the upper 2000 db eastward baroclinic mass transport between the two centers the transport index indicates a gulf stream and north atlantic current that gradually weakened during the low nao period of the 1960s and then intensified in the subsequent 25 years of persistently high nao to a record peak in the 1990s the peak to peak amplitude difference was 15 20 megatons per second mt s 1 with a 43 yr mean of about 60 mt s 1 a change of 25 33

a precise 40ar 39ar reference age for the durango apatite u th he and fission track dating standard the distinctive durango apatite is widely distributed as a reference material for mineralogy geochemistry and thermochronology the apatite occurs within the cerro de mercado open pit iron mine located in the northern portion of durango city mexico it is largely confined to vugs and open fractures within the lower portion of the ore deposit apatite and iron ore formed in situ and concurrently along with emplacement of small felsic intrusions along the southern margin of the chupaderos caldera complex this activity occurred between eruptions of two major ignimbrites from the caldera complex four single crystal sanidine anorthoclase 40 ar 39 ar ages from these ignimbrites and from a conformable older unit have been used to compute a reference age of 31 44 0 18 ma 2 for the apatite itself four additional multi crystal measurements are in general agreement with this age also in agreement are a set of 24 u th sm he ages recently determined directly on the apatite which have a mean of 31 02 1 01 ma 1 with a standard error s e of 0 22 ma

basal shear stress of debris flow in the runout phase abstract a laboratory device is proposed to assess the basal shear stresses generated by debris flow mixtures during their runout phase the device consists of an inclinable box with a gate facing a deposition plane the box is filled with a selected debris flow mixture and after sudden opening of the gate the features of the dam break deposit can be measured based on some simplified assumptions of the energy balance a methodology is proposed to assess basal shear stresses the device has been tested using sediment samples from debris flow deposits generated by two catchments of the dolomites cortina d ampezzo belluno italy by carrying out runout tests for different sediment concentrations by volume the results show how the static coulomb friction law is valid in the runout phase with friction angles on the order of the angle of repose of the same material in dry conditions the data elaboration also yields an innovative constitutive equation for shear stresses this relation merges the coulomb mixture approach with the concept of a one phase flow with a certain rheology this integration offers a useful insight into the weaknesses of the rheological approach if it is not properly scaled up to the ambient pressure of interest

crustal structure south of the iapetus suture beneath northern england the crustal structure just south of the iapetus suture1 along a line extending from the mid north sea high across northern england to the solway basin has been investigated as part of the caledonian suture seismic experiment of 1982 this unique sea to land wide angle explosion seismology project has produced data of unprecedented quantity and quality the main innovation was the use of both closely spaced shots mainly at sea and closely spaced stations mainly on land yielding a data set which can eventually be arranged in a variety of new ways for phase correlation and modelling such as constant offset and common mid point the line was extended by irish and german groups across ireland to the shannon estuary having a total length of over 600 km but here we present only preliminary results for northern england and adjacent marine regions the results for this region differ radically from those of the earlier lispb experiment2 in that we have recognized a well defined 6 15 km s 1 basement interpreted as pre caledonian metamorphic basement beneath most of the line at relatively shallow depth and there is a well defined mid crustal refractor starting at approximately 16 km depth beneath the north sea and northern england which is not recognized beneath the irish sea

effects of u th rich grain boundary phases on apatite helium ages abstract single grain apatite u th sm he ages he ages from non detrital samples sometimes show larger dispersions than can be explained by known sources of age dispersion such as grain size radiation damage parent zonation fracturing or intracrystalline inclusions we present observations and model age bias effects of an additional source of apatite he age dispersion observed in some cases u th rich grain boundary phases gbps precipitated on apatite crystal surfaces apatite grains from several samples with dispersed apatite he ages are coated or partially coated by reddish orange gbps rich in fe u and th these gbps are heterogeneous in thickness grain coverage and composition and have effective u concentrations eu up to 1000 ppm these phases may have large effects on the bulk eu and 4he compositions of apatite grains and can produce significant he age biases the direction and magnitude of this age bias is primarily a function of four factors 1 the host grain s size 2 the gbps thickness and eu relative to the host grain 3 the timing of gbp formation relative to the cooling age of the host grain and 4 whether the gbps are preserved and analyzed with the grain during he dating some of the most severe effects occur when gbps formed before or near the time of the apatite cooling age but were lost just prior to analysis for example during mineral separation in this case gbps of commonly observed thicknesses 1 10 m with eu 2 10 times that of the host apatite grain implant enough 4he into typical sized apatite grains to produce hundreds of percent positive age biases in contrast when u th rich gbps are preserved and analyzed with apatite grains the resulting he ages can be negatively biased though the heterogeneity variable preservation and ambiguous formation ages of gbps preclude a general quantitative and practical solution to this problem our model demonstrates that observed age dispersions in some samples are consistent with the effects of u th rich grain boundary phases and illustrates the conditions under which and by how much they will bias he ages

natural age dispersion arising from the analysis of broken crystals part ii practical application to apatite u th he thermochronometry abstract we describe a new numerical inversion approach to deriving thermal history information from a range of naturally dispersed single grain apatite u th he ages the approach explicitly exploits the information about the shape of the 4he diffusion profile within individual grains that is inherent in the pattern of dispersion that arises from the common and routine practice of analysing broken crystals additional dispersion arising from differences in grain size and in u and th concentration of grains and the resultant changes to helium diffusivity caused by differential accumulation and annealing of radiation damage is explicitly included in this approach we calculate the ingrowth and loss due to both thermal diffusion and the effects of ejection of helium over time using a finite cylinder geometry broken grains are treated explicitly as fragments of an initially larger crystal the initial grain lengths l0 can be treated as unknown parameters to be estimated although this is computationally demanding a practical solution to the problem of solving for the unknown initial grain lengths is to simply apply a constant and sufficiently long l0 value to each fragment we found that a good value for l0 was given by the maximum fragment length plus two times the maximum radius of a given set of fragments currently whole crystals and fragments with one termination are taken into account a set of numerical experiments using synthetic fragment ages generated for increasingly complex thermal histories and including realistic amounts of random noise 5 15 are presented and show that useful thermal history information can be extracted from datasets showing very large dispersion these include experiments where dispersion arises only from fragmentation of a single grain length 400 m and radius 75 m c 6 50 dispersion including the effects of grain size variation for spherical equivalent grain radii between 74 and 122 m c 10 70 dispersion and the combined effects of fragmentation grain size and radiation damage for eu between 5 and 150 ppm c 10 107 dispersion additionally we show that if the spherical equivalent radius of a broken grain is used as a measure of the effective diffusion domain for thermal history inversions then this will likely lead to erroneous thermal histories being obtained in many cases the viability of the new technique is demonstrated for a real data set of 25 single grain u th he apatite ages obtained for a gabbro sample from the bk 1 bierkraal borehole drilled through the bushveld complex in south africa the inversion produces a well constrained thermal history consistent with both the u th he data and available fission track analysis data the advantage of the new approach is that it can explicitly accommodate all the details of conventional schemes such as the effects of temporally variable diffusivity zonation of u and th and arbitrary grain size variations and it works equally effectively for whole or broken crystals and for the most common situation where a mixture of both are analysed for the routine application of the apatite u th he thermochronometry technique with samples where whole apatite grains are rare our experiments indicate that 15 20 single grain analyses are typically required to characterise the age dispersion pattern of a sample the experiments also suggest that picking very short crystal fragments as well as long fragments or even deliberately breaking long crystals to maximise the age dispersion in some cases would ensure the best constraints on the thermal history models the inversion strategy described in this paper is likely also directly applicable to other thermochronometers such as the apatite rutile and titanite u pb systems where the diffusion domain is approximated by the physical grain size