10be and 26al evidence for exceptionally low rates of australian bedrock erosion and the likely existence of pre pleistocene landscapes analysis of in situ produced 10be and 26al demonstrate that some australian inselbergs granitic domes are among the most stable geomorphic surfaces in the world eroding at rates as low as 0 6 m myr twenty isotopic analyses of ten samples suggest that the bare bedrock tops of these isolated granitic domes have been exposed to cosmic radiation for at least 0 5 myr and are eroding at a mean model rate less than 0 7 0 1 m myr n 6 isotopic analyses of samples collected from the top of mt wudinna little wudinna and yarwondutta rock are most consistent with continuous exposure during erosion on the other hand samples collected from the flanks of some domes and the tops of other domes have isotopic abundances suggestive of complex exposure histories including burial and reexposure these unique isotopic data provide the first quantitative information for evaluating longstanding but previously untested hypotheses regarding the antiquity and development of these enigmatic landforms and indicate that some eyre peninsula inselbergs are probably relict features of pre pleistocene landscapes

evidence for muon induced production of 10be in near surface rocks from the congo distributions of 10be in vein quartz from a lateritic weathering profile from the congo provide evidence for significant in situ production of 10be by reactions other than neutron induced spallation after consideration of geomorphological and nuclear processes which might contribute to the observed depth variability we conclude that cosmic ray muon induced reactions are the most likely mechanism and that such reactions lead to 1 to 3 of 10be production at the surface this small muon induced component has only minor implications for the use of 10be for quantification of exposure histories of surficial rocks nevertheless the muogenic component has the potential to expand the utility of cosmogenic nuclides in examination of surficial processes overcoming some of the limitations associated with the use of the neutron produced component

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

pace of landscape evolution in the sierra nevada california revealed by cosmogenic dating of cave sediments we report 26 al 10 be based ages of sierra nevada caves that constrain detailed late pliocene and quaternary river incision his tories for five river canyons rapid incision of 0 2 mm yr from 2 7 to ca 1 5 ma slowed markedly to 0 03 mm yr thereafter likely reflecting the combined effects of a transient erosional re sponse to pliocene rock uplift and periodic mantling of riverbeds with glacially derived sediment in the late quaternary while 400 m of incision has occurred in the past 2 7 m y outpacing interfluve erosion and thereby increasing the local relief canyons as deep as 1 6 km existed prior to that time these new erosion rates strength en the case for tectonically driven late cenozoic uplift

pleistocene drainage reorganization driven by the isostatic response to deep incision into the northeastern tibetan plateau pleistocene drainage basin integration led to progressive excavation of tertiary quaternary sedimentary basins along the yellow river in the northeastern tibetan plateau cosmogenic burial dating of ancestral river deposits and basin fi ll from two key watershed divides confi rms a fl uvial connection between basins at 0 5 1 2 ma prior to excavation by the yellow river pres ervation of the relict depositional surface that represents the maximum height of basin fi ll allows reconstruction of the volume of eroded material across a broad region we quantify the iso static response to this erosional unloading using a two dimensional fl exural model calculated maximum vertical displacements for different effective elastic thicknesses vary from 160 m to 260 m near the pleistocene spillway from the qinghai paleo lake we suggest that the isostatic response to fl excavation along the yellow river defeated local tributaries isolated lake qinghai and led to the development of an internally drained basin in the past 0 5 1 2 m y

dating plio pleistocene glacial sediments using the cosmic ray produced radionuclides 10be and 26al we use the cosmic ray produced radionuclides 26al and 10be to date plio pleistocene glacial sediment sequences these two nuclides are produced in quartz at a fixed ratio but have different decay constants if a sample is exposed at the surface for a time and then buried by overburden and thus removed from the cosmic ray flux the 26al 10be ratio is related to the duration of burial we first attempted to date pre wisconsinan tills by measuring 26al and 10be in fluvial sediments beneath them and applying the method of burial dating which previous authors have used to date river sediment carried into caves this method however requires simplifying assumptions about the 26al and 10be concentrations in the sediment at the time of burial we show that these assumptions are not valid for river sediment in glaciated regions 26al and 10be analyses of such sediment do not provide accurate ages for these tills although they do yield limiting ages in some cases we overcome this difficulty by instead measuring 26al and 10be in quartz from paleosols that are buried by tills we use a more general mathematical approach to determine the initial nuclide concentrations in the paleosol at the time it was buried as well as the duration of burial this technique provides a widely applicable improvement on other means of dating plio pleistocene terrestrial glacial sediments as well as a framework for applying cosmogenic nuclide dating techniques in complicated stratigraphic settings we apply it to pre wisconsinan glacial sediment sequences in southwest minnesota and eastern south dakota pre wisconsinan tills underlying the minnesota river valley were deposited 0 5 to 1 5 ma and tills beneath the prairie coteau in eastern south dakota and adjacent minnesota were deposited 1 to 2 ma

the erosion response to quaternary climate change quantified using uranium isotopes and in situ produced cosmogenic nuclides abstract studying how catchment erosion has responded to past climate change can help us better understand not only how landscape evolution operates but also predict the consequences of future climate change on soil resource availability recent years have seen the development of tools that allow a quantitative assessment of past changes in catchment erosion this work reviews the principles of the application of in situ produced cosmogenic nuclides and uranium isotopes to quantifying past erosion rates results highlight the role of periglacial processes and mass wasting in dictating how catchment erosion responds to climatic variability at the 10 kyr scale at the million year scale it is more difficult to untangle the role of climate and tectonics a strong coupling exists at the 10 kyr to 100 kyr scales between climatic cycles and the transfer time of regolith from source to sink this coupling reflects changes in sediment source that are either set by changes in vegetation cover at the catchment scale or by the storage of sediments on continental shelves at a larger scale although further analytical developments are required for these tools to reach their full potential existing works suggest that in the near future they will provide unprecedented quantitative insights on how soil and fluvial systems adapt to external perturbations climatic tectonic and or anthropic

management of topsoil for geo environmental reclamation of coal mining areas topsoil is an essential component for land reclamation in mining areas it is seriously damaged if it is not mined out separately without being contaminated eroded and protected systematic handling and storage practices can protect topsoil while in storage and after it has been redistributed onto the regraded area impact of coal mining on topsoil quality in indian context has been described systematic removal of topsoil its storage practice geometry of topsoil heap are discussed in this study removed topsoil should be reclaimed technically and its shelf life period should be ascertained to assess the shelf life period an investigation was conducted in a large opencast coal project soil dumps of different age classes in the area were identified and analyzed critically to evaluate the deterioration of soil quality with respect to time and compared with those of unmined areas changes in soil quality showed a continuous decrease every year and ultimately became biologically sterile biological reclamation is essential if the soil is to be stored beyond the shelf life period preservation of stockpiled topsoil its redistribution on the regraded areas nutrients and amendments to be added are discussed briefly in this study

new magnetostratigraphic and numerical age of the fuente nueva 3 site guadix baza basin spain abstract sediments of the plio pleistocene guadix baza basin have provided a wealth of information on the first hominin populations in western europe to better constrain the age of the fuente nueva 3 archaeological site within the basin and to complement previous magnetostratigraphic studies two vertical boreholes were taken that provide a continuous record of the lower part of the sequence results indicate that the sequence is dominated by negative inclinations but some additional intervals with positive inclination are also identified in the lower part of the sequence a new cosmogenic nuclide burial age of 1 50 0 31 ma helps constrain the magnetostratigraphic record the abundance of normal polarity directions at the bottom of a borehole may indicate proximity to the olduvai subchron however further analyses are required to confirm this hypothesis

large deformation finite element modelling of progressive failure leading to spread in sensitive clay slopes the occurrence of large landslides in sensitive clays such as spreads can be modelled by progressive development of large inelastic shear deformation zones shear bands the main objective of the present study is to perform large deformation finite element modelling of sensitive clay slopes to simulate progressive failure and dislocation of failed soil mass using the coupled eulerian lagrangian cel approach available in abaqus finite element software the degradation of undrained shear strength with plastic shear strain strain softening is implemented in abaqus cel which is then used to simulate the initiation and propagation of shear bands due to river bank erosion the formation of horsts and grabens and dislocation of soil masses that lead to large scale landslides are simulated this finite element model explains the displacements of different blocks in the failed soil mass and also the remoulding of soil around the shear bands the main advantages of the present finite element model over othe

incision and differential bedrock uplift along the indus river near nanga parbat pakistan himalaya from 10be and 26al exposure age dating of bedrock straths abstract well preserved river cut bedrock surfaces straths abandoned by the progressive incision of the indus river in northern pakistan were dated using in situ cosmogenic 10 be and 26 al exposure age dating measurements on young and modern straths show no significant ingrowth of 10 be and 26 al implying that strath exposure ages closely approximate their abandonment age strath exposure ages range up to 65 ka and increase with height above the river the straths can be divided into two groups low straths dated at about 7 ka which yield very rapid bedrock incision rates 9 12 m ka and high straths 7 ka in age which yield somewhat slower incision rates 1 6 m ka incision rates for both groups increase by 1 3 m ka downstream toward an active reverse fault the raikot fault that forms the western border of the nanga parbat haramosh massif nphm the downstream increases in incision rates for the low straths mimic downstream increases in the modern gradient suggesting that bedrock incision rates have been proportional to stream power over the last 7 ka gradient increases are probably the result of the creation of knickpoints by bedrock uplift along the raikot fault the longitudinal profile and steep gorge of the indus river in the study area indicate that bedrock incision appears to keep pace with differential vertical motions between the nphm and surrounding regions thus the 1 3 m ka difference in incision rates likely reflects the differential bedrock uplift rate between the nphm and the skardu basin the differential incision rate is consistent with differential exhumation rates obtained from apatite fission track ages assuming geotherms of 80 90 c km in the nphm and 35 c km in the skardu basin this relation suggests that rapid bedrock incision of at least 1 3 m ka has persisted within the nphm for the last 0 5 ma the acceleration of incision rates throughout the study area since 15 ka is likely to be a climatic signal that records an increase in the discharge and or sediment load of the indus river in the study area related to deglaciation of the surrounding terrane

development of progressive failure in sensitive clay slopes the development of progressive failure in sensitive clay slopes is analysed using principles from fracture mechan ics where failure stress depends on a material property toughness and length of an existing weakness unlike traditional soil mechanics where failure stress is generally assumed to be only a function of material strength an existing weakness or partially developed failure surface can propagate due to sudden loads as might be induced by seasonal erosion cycles small local landslides at a river bank or earthquake shaking the paper examines the growth of the failure surface over time due to such loads the analysis shows that a large landslide in sensitive clay can occur after a number of seasonal erosion cycles with no obvious trigger it also shows that a larger load due to either a small landslide or earthquake can cause a de veloping failure surface to propagate freely toward general collapse large landslides in sensitive clay are often preceded by a smaller landslide at the river bank but can be triggered by large earthquakes or may occur for no obvious reason the agreement between predictions and real behaviour suggests that the model for progressive failure of large landslides in sen sitive clay deserves further consideration

role of in situ cosmogenic nuclides 10be and 26al in the study of diverse geomorphic processes the central premises of applications of the in situ cosmogenic dating method for studying specific problems in geomorphology are outlined for simple and complex exposure settings in the light of these general models we discuss the information that can be derived about geomorphic processes utilizing concentrations of in situ produced cosmogenic radionuclides 10be half life 1 5 ma and 26a1 half life 0 7 ma in a variety of geomorphic contexts glacial polish and tills meteorite impact craters alluvial fans paleo beach ridges marine terraces sand dunes and bedrock slopes we also compare 10be 26al data with results obtained by other dating methods we conclude that the technique of measuring in situ cosmic ray produced nuclides holds promise for quantitative studies of processes and time scales in a wide range of geomorphological problems

10be and 26al production rates deduced from an instantaneous event within the dendro calibration curve the landslide of kofels otz valley austria surface exposure dating requires the knowledge of cosmogenic nuclide production rates when determining time integrated production rates the exposure ages of the calibration samples need to be accurately known the landslide of kofels austria is very well suited for this purpose it is the largest landslide in the crystalline alps of austria dating back to 7800 100 years bc ams 14c dating of buried wood which is well within the 14c dendro calibration curve exposed quartz veins were sampled from the tops of large boulders from the toe of the landslide for analysis of 10be and 26al to calculate sea level high geomagnetic latitude 60 open sky radionuclide production rates corrections were applied for altitude and latitude for shielding by surrounding mountains for sample geometry vegetation and snow cover and for sample thickness the production rates for an exposure age of 10 000 years are 5 75 0 24 10be atoms yr g sio2 and 37 4 1 9 26al atoms yr g sio2 a 26al 10be ratio of 6 52 0 43 can be calculated the influence of the geomagnetic field on these production rates has been estimated using two different geomagnetic field records our production rates should be a good approximation for the use of surface exposure dating between about 5000 and 13 000 years bp

effective attenuation lengths of cosmic rays producing 10be and 26al in quartz implications for exposure age dating we have measured cosmic ray produced 10be t 1 5 my and 26al t 0 72 my as functions of depth in a core of quartz sandstone bedrock collected in south victoria land antarctica these data were used to place limits on the exposure age and erosion rate of the exposed surface and to calculate the effective attenuation lengths of cosmic rays producing these nuclides these latter results indicate that the production attenuation length for 26al is comparable to that for 10be this suggests that the production ratio 26al 10be does not vary substantially with depth in a rock and that its value at the surface of exposed rock is not strongly affected by erosional losses allowing wider use of the ratio in determining exposure ages

quaternary downcutting rate of the new river virginia measured from differential decay of cosmogenic 26al and 10be in cave deposited alluvium the concentrations of the cosmogenic radionuclides sup 26 al and sup 10 be in quartz can be used to date sediment burial here we use sup 26 al and sup 10 be in cave deposited river sediment to infer the time of sediment emplacement sediment burial dates from a vertical sequence of caves along the new river constrain its quaternary downcutting rate to 27 3 4 5 m m y and may provide evidence of regional tectonic tilt 32 refs 3 figs 1 tab

fragility of a dark gray shale in northeastern jamaica effects and implications of landslip exposure rapid weathering of strong hitherto un weathered shale rocks was fast enough to have been measurable weekly 4 mm depth per week regular early morning rain showers followed by hot dry afternoons caused frequent wet dry cycles which facilitated rapid slaking of the shale other landslips occurred concurrently on the south bank of the wild cane river where the rock beds dip towards lower ground resistance to impacts in the rock fabric was equally low after decades or weeks of exposure it was concluded that the combination of high frequency wet dry cycles on steeply dipping shale beds and rock attitude caused very rapid weathering rapid slaking of the illitic shales could cause high turbidity levels in contiguous aquatic environments building foundations and roads could be rapidly de stabilized even on such freshly exposed apparently consolidated sites

controlling factors for post failure evolution of subaqueous landslides subaqueous slope failures can evolve in various patterns whereas some slides run out and further evolve into highly mobile turbidity currents others maintain a continuum like structure and remain

soil production on a retreating escarpment in southeastern australia the functional dependence of bedrock conversion to soil on the overlying soil depth the soil production function has been widely recognized as essential to understanding landscape evolution but was quantified only recently here we report soil production rates for the first time at the base of a retreating escarpment on the soil mantled hilly slopes in the upper bega valley southeastern australia concentrations of 10 be and 26 al in bedrock from the base of the soil column show that soil production rates decline exponentially with increasing soil depth these data define a soil production function with a maximum soil production rate of 53 m m y under no soil mantle and a minimum of 7 m m y under 100 cm of soil thus constraining landscape evolution rates subsequent to escarpment retreat the form of this function is supported by an inverse linear relationship between topographic curvature and soil depth that also suggests that simple creep does not adequately characterize the hillslope processes spatial variation of soil production shows a landscape out of dynamic equilibrium possibly in response to the propagation of the escarpment through the field area within the past few million years in addition we present a method that tests the assumption of locally constant soil depth and lowering rates using concentrations of 10 be and 26 al on the surfaces of emergent tors

catastrophic failure of submerged slopes in normally consolidated sediments the application of fracture mechanics methods to shear band growth in granular materials requires careful consideration of the elasto plastic nature of the material behaviour in this paper the palmer and rice fracture mechanics approach is applied to the problem of catastrophic shear band propagation in a submerged slope built of normally consolidated sediments this allows for catastrophic unstable and progressive stable types of soil failure to be properly distinguished many submerged landslides are triggered by earthquakes via the shear strength degradation due to the excess pore water pressure accumulation the conventional analysis assumes that the excess water pressure zone develops simultaneously along the entire landslide length often reaching several kilometres when a mechanism of the catastrophic shear band propagation is considered a much shorter excess water pressure zone e g several hundred metres can still cause a full scale landslide often generating a tsunami wave of consid

using in situ produced cosmogenic isotopes to estimate rates of landscape evolution a review from the geomorphic perspective the application of in situ produced cosmogenic isotopes to problems in geomorphology has increased rapidly over the past decade at least 57 papers and numerous abstracts have been published since the mid 1980s when the first mass spectrometric measurements of terrestrially produced cosmogenic isotopes were made taken at face value these studies provide quantitative information about rates of landscape evolution and landform age however the significance of calculated erosion rates and exposure ages depends strongly on the models used to interpret isotopic data the validity of assumptions inherent to these models and the geologic surroundings in which the samples were collected this paper attempts to place cosmogenic isotope studies in a geomorphic context by reviewing fundamentals of the method and evaluating the validity of assumptions under which these data have been interpreted at present the establishment of high precision cosmogenically based glacial and alluvial chronologies is stymied by the evolution of geomorphic surfaces the erosion of rock from sampled boulders the potential for isotope inheritance from previous exposure and the uncertainty of isotopic measurements uncertainties in isotope production rates and the observed variability of exposure ages on individual geomorphic surfaces limit the confidence with which cosmogenic ages can be correlated reliably with those obtained by other techniques estimation of erosion rates at single points on the landscape gives useful small scale information extrapolation of these rates over longer time and larger spatial scales is less sure and most likely biased toward lower erosion rates by die inadvertent selection of resistant sample sites however because erosion rates are so poorly constrained at present even estimates to within a factor of 2 may be of significant value to geomorphologists and tectonicists

quenching of phosphorus fixation with organic wastes in a bauxite mine overburden capabilities of two phosphate rich organic wastes to quench phosphorus p fixation in a stored high phosphorus fixing tropical bauxite overburden were examined in a field experiment prior grinding and ensiling of shrimp shell waste facilitated increased solubility and hence phosphorus fixation quenching in the soil normal plant available p concentrations were exhibited by the overburden for up to 4 months after application despite the cultivation and harvesting of plants in the treated beds ten year old stored overburden treated with ensiled shrimp shell silage or chicken manure exhibited p levels of 1 0 and 1 1 respectively 4 months after treatment application this represents a small excess over normal concentrations of free p in the overburdens these p levels dropped to 0 055 and 0 060 respectively after 8 months the capacity of the soil to fix phosphorus was thus rapidly filled with an excess of p in the overburden however increased p fixation in the second 4 month period was attributed to the inherently high levels of ca2 in the ground therefore amelioration based on quarterly applications promises a long term corrective for p fixing in stored bauxite overburdens

climate driven unsteady denudation and sediment flux in a high relief unglaciated catchment fan using 26al and 10be panamint valley california abstract environmental changes within erosional catchments of sediment routing systems are predicted to modulate sediment transfer dynamics however empirical and numerical models that predict such phenomena are difficult to test in natural systems over multi millennial timescales tectonic boundary conditions and climate history in the panamint range california are relatively well constrained by existing low temperature thermochronology and regional multi proxy paleoclimate studies respectively catchment fan systems present there minimize sediment storage and recycling offering an excellent natural laboratory to test models of climate sedimentary dynamics we used stratigraphic characterization and cosmogenic radionuclides crns 26al and 10be in the pleasant canyon complex pcc a linked catchment fan system to examine the effects of pleistocene high magnitude high frequency climate change on crn derived denudation rates and sediment flux in a high relief unglaciated catchment fan system calculated 26al 10be burial ages from 13 samples collected in an 180 m thick outcropping stratigraphic succession range from ca 1 55 0 22 ma in basal strata to ca 0 36 0 18 0 52 0 20 ma within the uppermost part of the succession the mean long term crn derived paleodenudation rate 36 8 mm kyr 1 is higher than the modern rate of 24 0 6 mm kyr from pleasant canyon and paleodenudation rates during the middle pleistocene display some high frequency variability in the high end up to 54 10 mm kyr the highest crn derived denudation rates are associated with stratigraphic evidence for increased precipitation during glacial pluvial events after the middle pleistocene transition post ca 0 75 ma suggesting 100 kyr milankovitch periodicity could drive the observed variability we investigated the potential for non equilibrium sedimentary processes i e increased landslides or sediment storage recycling to influence apparent paleodenudation rates end member mixing models suggest that a mixture of 50 low crn concentration sediment from landslides is required to produce the largest observed increase in paleodenudation rate the overall pattern of crn derived burial ages paleodenudation rates and stratigraphic facies suggests milankovitch timescale climate transitions drive variability in catchment denudation rates and sediment flux or alternatively that climate transitions affect sedimentary process regimes that result in measurable variability of crn concentrations in unglaciated catchment fan systems

beryllium 10 dating of the duration and retreat of the last pinedale glacial sequence accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes cosmogenic beryllium 10 measurements in the wind river range indicate that the last glacial maximum marine oxygen isotope stage 2 was achieved there by 21 700 700 beryllium 10 years and lasted 5900 years ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12 100 500 beryllium 10 years

a first attempt to date the original deckenschotter of penck and bruckner with cosmogenic nuclides abstract in the classical area of alpine quaternary stratigraphy bavaria germany a succession of four gravel spreads that are separated from each other by valley incision was recognized by penck and bruckner 1909 die alpen im eiszeitalter tauchnitz leipzig 1199p the two older gravel terraces attributed to glaciations named gunzian and mindelian have so far not been dated recent advances in the use of cosmogenic nuclides allow the burial age determination of sediments the method uses the different decay of the two nuclides 26al and 10be to date the time since a deposit was shielded from further radiation a depth profile makes it possible to model ages for surface sediments that are not shielded completely this paper discusses the various constraints that must be addressed in order to date surface sediments and it presents the ages obtained 2 35 ma for gunzian 0 68 ma for mindelian these dates are in good agreement with measurements of tectonic displacement and development of catchments the results confirm that the burial age determination method is basically feasible for such terraces

quantifying passive margin denudation and landscape development using a combined fission track thermochronology and cosmogenic isotope analysis approach abstract a new approach to empirically constraining numerical models of denudation and landscape development across passive continental margins is presented involving a combination of apatite fission track thermochronology and cosmogenic isotope analysis this integrated strategy is applied to the namibian sector of the south west african margin where the conventional landscape evolution model of inland retreat of an escarpment initiated at the coast at break up implies a mean rate of retreat of 1 km ma 1 the thermochronological and cosmogenic isotope data are incompatible with a simple escarpment retreat model since they show that denudation rates oceanward of the present escarpment position have been low 1 since the end of the eocene and the estimated rate of escarpment retreat has been only 10 m ma 1 this low rate of retreat is however consistent with numerical landscape evolution models where the escarpment is pinned at an inland drainage divide

mid pleistocene cosmogenic minimum age limits for pre wisconsinan glacial surfaces in southwestern minnesota and southern baffin island a multiple nuclide approach abstract paired 10 be and 26 al analyses n 14 indicate that pre wisconsinan glaciated bedrock surfaces near the northern baffin island and southern minnesota paleo margins of the laurentide ice sheet have long and complex histories of cosmic ray exposure including significant periods of partial or complete shielding from cosmic rays using the ratio 26 al 10 be we calculate that striated outcrops of sioux quartzite in southwestern minnesota southern margin were last overrun by ice at least 500 000 years ago weathered bedrock tors on the once glaciated uplands of baffin island northern margin are eroding no faster than 1 1 m myr 1 the equivalent of at least 450 000 years of surface and near surface exposure our data demonstrate that exposure ages and erosion rates calculated from single nuclides can underestimate surface stability dramatically because any intermittent burial and the resultant lowering of nuclide production rates and nuclide abundances will remain undetected

a new model for large landslides in sensitive clay using a fracture mechanics approach a new model is proposed for the development of large landslides in sensitive clay and supported by concepts from fracture mechanics a key assumption in this new model is that the complete failure surface develops before the onset of significant movement thus predetermining the final extent of failure the appearance of retrogression is actually the rear ward advancing disruption of a monolithic slide mass over a growing zone of liquefied clay it is seen that the likelihood of propagation of failure and the resulting occurrence of a large landslide depend primarily on the brittleness of the sensitive clay the potential length of shear band propagation is limited by slope geometry and increases for higher riverbanks and for flatter slopes above the riverbank the model explains why large landslides in sensitive clay often terminate just adjacent to a reverse break in slope such as an older landslide crater or a stream gully the model also indicates that large landslides in sensitive clay could be expected to occur suddenly after a large single perturbation such as an earthquake or after a seemingly innocuous small trigger following the accumulation of a large number of annual load cycles as observed fre quently in nature

dating sediment burial with in situ produced cosmogenic nuclides theory techniques and limitations abstract dating sediment burial over million year time scales is crucial in many areas of the earth sciences and archeology but is often difficult using traditional techniques sediment burial can be dated by the radioactive decay of cosmogenic nuclides provided that the sediment was exposed to cosmic rays prior to burial dating calculations are straightforward if sediment is buried deeply and rapidly enough to prevent cosmogenic nuclide production after burial however the analysis can be complicated by postburial production if sediment is insufficiently shielded from secondary cosmic ray nucleons and muons this paper discusses how buried sediments can be dated over timescales up to 5 myr using 26 al and 10 be in quartz

effects of shear band propagation on early waves generated by initial breakoff of tsunamigenic landslides the landslide mechanism based on the phenomenon of the dynamic shear band propagation suggests that landslide run out begins with a non zero initial velocity the initial uplift of the passive failure block during the landslide breakoff is similar to the reverse fault and therefore can generate an early tsunami wave that will be one of the first waves to start propagating and could be potentially detected by the deep ocean warning systems this paper attempts to quantify this phenomenon using the coupled eulerian lagrangian cel approach within abaqus and modeling both soil and water as eulerian materials this approach allows for capturing the entire process of failure initiation propagation and breakoff taking into account large landslide deformations soil plasticity and interaction of the sliding layer with the seawater the study shows that the highest breakoff velocities are achieved for the shortest lengths of the initial weak zones initiating the shear band propagation it also shows that both interaction of the sliding layer with water and appearance of the large plastic failure zones during the shear band propagation cause slower uplift velocities and accelerations for the computed example of a typical mid size landslide in normally consolidated clays with the initial weak zone length of several hundred meters and the final landslide length of about 1 km the breakoff velocities can reach up to 4 m s within 15 s leading to an early wave of 0 5 1 5 m height caused purely by this breakoff such waves can be easily detected by existing deep ocean assessment and reporting of tsunamis dart systems potentially allowing for some early tsunami warning

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

retrogressive shear band propagation and spreading failure criteria for submarine landslides the paper proposes a mechanism of submarine spreading failures which combines retrogressive shear band propagation sbp with a series of active block failures in the stable zone of the slope where the gravitational shear stress is smaller than the residual shear strength gradual downhill removal of the failed material causes a decrease in the supporting earth pressure leading to the progressive uphill propagation of the shear band termed here retrogressive sbp and uniquely determining its length which can be linked to the dimensions of the spreading failure block mechanisms two conjugate energy balance based criteria have been formulated for the spreading failure in terms of either the critical depth of the sliding surface or the critical drop of the failed seabed level both criteria have been validated against the observed phenomena presence and absence of the evidence of spreading failure for different landslide depths and a step in the sliding surface in palaeo landslide examples from

simple criteria for ploughing and runout in post failure evolution of submarine landslides this paper extends shear band propagation analysis of slope failures to the investigation of ploughing and runout phenomena in submarine landslides the ability to predict the two different modes of post failure landslide evolution is critical for determining the tsunami hazard and type of landslide impact on offshore structures the proposed analysis is based on the analogy between ploughing and spreading failures it uses the energy balance approach to develop the criterion for progressive shear band propagation driven by accumulation of sliding material on top of the stable slope this criterion is then combined with the kinematic passive block mechanism to produce analytical ploughing failure criteria formulated in terms of the critical rise in the seabed level if the minimum rise of the seabed level at which ploughing can take place is larger than the maximum possible free standing step in the seabed surface the first passive failure block will start crumbling over top the stable zone causing the l

scaling factors for production rates of in situ produced cosmogenic nuclides a critical reevaluation abstract new scaling factors are presented describing the altitude and latitudinal dependence of production rates for in situ produced cosmogenic nuclides the new factors incorporate the influence of the non dipole contributions to the geomagnetic field on the cosmic ray flux the currently used scaling factors of lal earth planet sci lett 104 1991 424 439 are based on the assumption of a dipole field the overall strategy used in deriving the new scaling factors is however very similar to that of lal and relies on the same and or similar nuclear data in this reevaluation data are only used if the effective geomagnetic parameters inclination horizontal field strength can be reconstructed for the time of measurement the absorption free pathlengths for cosmic rays selected for this study are based on observational data at altitudes relevant for exposure age dating sea level to 7000 m at sea level and latitudes between 20 and 40 the new factors are up to 18 lower and at high altitudes more than 30 higher than those of lal in addition to accounting for the influence of the effective geomagnetic field and providing more applicable estimates of the new factors also allow for correction for the significant deviations from the standard pressure altitude relationship that exist in the atmosphere 10

exposure ages from mountain dipsticks in mac robertson land east antarctica indicate little change in ice sheet thickness since the last glacial maximum past changes in east antarctic ice sheet eais volume are poorly known and diffi cult to measure yet are critical for predicting the response of the ice sheet to modern climate change in particular it is important to identify the sources of sea level rise since the last glacial maximum lgm and ascertain the present day stability of the world s largest ice sheet we present altitudinal transects of 10 be and 26 al exposure ages across the framnes mountains in mac robertson land that allow the magnitude and timing of eais retreat to be quantifi ed our data show that the coastal eais thinned by at most 350 m in this region during the past 13 k y this reduction in ice sheet volume occurred over a 5 k y period and the present icesheet profi le was attained ca 7 ka in contrast to the west antarctic ice sheet which continues to retreat today combined with regional offshore and terrestrial geologic evidence our data suggest that the reduction in eais volume since the lgm was smaller than that indicated by contemporary ice sheet models and added little meltwater to the global oceans stability of the ice margin since the middle holocene provides support for the hypothesis that eais volume changes are controlled by growth and decay of northern hemisphere ice sheets and associated global sea level changes

progressive failures in eastern canadian and scandinavian sensitive clays observations from past events are used to show that the concept of progressive failure may explain translational progressive landslides and spreads large landslides occurring in sensitive clays during progressive failure the strain softening behaviour of the soil causes unstable forces to propagate a failure surface further in the slope translational progressive landslides generally take place in long gently inclined slopes instability in a steeper upslope area is followed by redistribution of stress which increases earth pressure further downslope passive failure may therefore occur in less inclined ground heaving the soil spreads are usually trigged by erosion of a deposit having a higher angle near the toe instability starts near the toe of the slope and propagates into the deposit reducing earth pressure this may lead to the formation of an active failure with dislocation of the deposit into horsts and grabens the failure mechanism of both types of landslides is controlled by the stress

numerical ages for plio pleistocene glacial sediment sequences by 26al 10be dating of quartz in buried paleosols abstract we describe a method for dating plio pleistocene sediments by analysing 26 al and 10 be in quartz from buried paleosols the method amounts to a generalization of the technique of burial dating which has previously been used to date river sands deposited in caves as well as fluvial terraces we a measure nuclide concentrations at multiple depths in the paleosol b use the geologic context of the sample to construct an exposure burial history an exposure model that can be used to predict the nuclide concentrations in the samples as a function of whatever unknown parameters are of geological interest e g the ages of geologic units and then c find the parameters in the exposure model that result in the best fit between predicted and observed nuclide concentrations we apply the method to a paleosol developed on the uppermost till in eastern nebraska which is buried by several middle to late pleistocene loess units the ages of some of which are known independently the lowest loess unit whose age was not previously known was deposited 0 58 0 12 ma and the till was emplaced 0 65 0 14 ma which agrees with existing age constraints from paleomagnetic measurements and the position of the lava creek ash in the regional stratigraphy the most important source of uncertainty in these age determinations is the analytical uncertainty in 26 al and 10 be measurements uncertainties in either the nuclide production rates or the geologic model are comparatively unimportant

post mining deterioration of bauxite overburdens in jamaica storage methods or subsoil dilution rapid degradation of disturbed soil from a karst bauxite mine in jamaica was recorded substantial macronutrient losses were incurred during a short 1 month or a long 12 months storage of the replaced topsoils during frequent wet dry changes the results suggested very high rates 70 in the first year of soil degradation from storage alongside moderate rates 30 within the same storage dump however higher levels of soil organic matter som were indicated just below the surface compared with the surface horizons it was unlikely that under a high leaching humid tropical rainfall regime natural degradation processes could have re emplaced such material firmly intact in the 15 30 cm zone it was therefore concluded that these som anomalies were due to mechanical dilution of surface soil with subsoil material during overburden removal and emplacement rather than from long storage increasing the soil organic content during storage could be one corrective approach however it is far less costly to exercise greater care to apply more precise overburden removal and emplacement techniques initially than it is to correct the results of topsoil contamination with subsoil although this study was limited to one mine in the context of imminent large scale mining expansion and current practices further investigations are needed to accurately ascertain the proportion of similar subsoil contamination in other bauxite mined sites

pliocene pleistocene incision of the green river kentucky determined from radioactive decay of cosmogenic 26al and 10be in mammoth cave sediments cosmogenic 26al and 10be in sediments washed into mammoth cave kentucky record the history of 3 5 m y of water table position governed by incision and aggradation of the green river a tributary of the ohio river upper levels of the cave formed during a period of slow river incision and were later filled with sediment due to river aggradation at 2 3 2 4 ma a brief surge of river incision ca 2 ma was followed by river stability and cave passage formation at a lower level rapid incision through 15 m of bedrock ca 1 5 ma was prompted by repositioning of the ohio river to its present course along an ice sheet margin renewed incision ca 1 2 ma and aggradation at 0 7 0 8 ma correlate with major ice advances in the ohio river basin measurements of 26al and 10be also indicate that sandstone capped uplands have maintained slow erosion rates of 2 7 m m y for the past 3 5 m y despite accelerated pleistocene river incision rates of 30 m m y

geochemical methods to infer landscape response to quaternary climate change and land use in depositional archives a review abstract understanding and quantifying the processes and geochemical cycles associated with catchment erosion the development of soils and weathering horizons and terrestrial habitat change beyond the scales of modern observations remain challenging such research however has become increasingly important to help predict future landscape change in light of increasing land use and rapid global warming we herein review organic and inorganic geochemical tools applied to depositional archives to better understand various aspects of landscape evolution on geological time scales we highlight the potentials and limitations of inorganic geochemical analytical methods such as major element geochemistry metal and radiogenic isotopes and in situ cosmogenic nuclides as qualitative semi quantitative and quantitative proxies for the transformation of bedrock material via regolith and soils to sediments we also show how stable isotope geochemistry applied to lacustrine endogenic carbonates can be used to infer rock water interactions vegetation change and soil development in limestone rich catchments proxies focusing on the silicilastic element of sediment formation transport and deposition are ideally combined with organic geochemical proxies for vegetation change and soil organic matter evolution in a catchment to gain a comprehensive picture of the critical zone s evolution over time multi proxy and multidisciplinary research combining organic and inorganic geochemical techniques from several sedimentary archives in the same catchment have high potential to provide comprehensive information on quaternary landscape evolution and thus improve the robustness of associated forecasting models

greenland was nearly ice free for extended periods during the pleistocene measurements of cosmic ray produced 10be and 26al in a bedrock core from beneath the summit of the greenland ice sheet show that greenland was nearly ice free for extended periods under pleistocene climate forcing the greenland ice sheet is a main contributor to modern sea level rise but its stability during past warm periods is uncertain thus compromising our ability to robustly predict future rates and magnitudes of ice loss joerg schaefer and colleagues present cosmogenic isotope evidence from bedrock samples from beneath an ice core near the summit of the ice sheet to show that the greenland ice sheet was largely ice free at some point during the pleistocene the data cannot constrain the time or duration of ice free conditions and seem incompatible with our current understanding of ice sheet behaviour nevertheless alternative explanations for the cosmogenic data are lacking suggesting that our understanding of the response of the greenland ice sheet to past warmth remains incomplete the greenland ice sheet gis contains the equivalent of 7 4 metres of global sea level rise1 its stability in our warming climate is therefore a pressing concern however the sparse proxy evidence of the palaeo stability of the gis means that its history is controversial compare refs 2 and 3 to ref 4 here we show that greenland was deglaciated for extended periods during the pleistocene epoch from 2 6 million years ago to 11 700 years ago based on new measurements of cosmic ray produced beryllium and aluminium isotopes 10be and 26al in a bedrock core from beneath an ice core near the gis summit models indicate that when this bedrock site is ice free any remaining ice is concentrated in the eastern greenland highlands and the gis is reduced to less than ten per cent of its current volume our results narrow the spectrum of possible gis histories the longest period of stability of the present ice sheet that is consistent with the measurements is 1 1 million years assuming that this was preceded by more than 280 000 years of ice free conditions other scenarios in which greenland was ice free during any or all pleistocene interglacials may be more realistic our observations are incompatible with most existing model simulations that present a continuously existing pleistocene gis future simulations of the gis should take into account that greenland was nearly ice free for extended periods under pleistocene climate forcing