temperatures at the base of the laurentide ice sheet inferred from borehole temperature data 1 we use temperature profiles from 4 deep 1600 m boreholes across canada to determine ground surface temperature histories gsth s through and after the last glacial maximum lgm inversion yields the temperature history at the base of the glacier and the surface temperature evolution after the glacial retreat the results indicate geographic differences in basal temperature history across the ice sheet during the last glacial maximum temperatures at the base of the ice sheet were lower in eastern canada at the southeastern edge of the glacier than in central canada southwest of the glacier center at all sites basal temperatures were above the melting point of ice during and after the lgm which may explain the highly unstable character of the ice sheet the gsth s are consistent with information on the history of the laurentide ice sheet and provide quantitative constraints on glacier flow dynamics

groundwater controls on biogeomorphic succession and river channel morphodynamics biogeomorphic succession describes feedbacks between vegetation succession and fluvial processes that at the decadal timescale lead to a transition from bare river deposited sediment to fully developed riparian forest where the rate of stabilization by biogeomorphic succession is greater than the rate of ecological disturbance by fluvial processes a river is likely to evolve into less dynamic states while river research has frequently considered the physical dimensions of morphodynamics less is known about physical controls on succession rates and how these impact stream morphodynamics here we test the hypothesis that groundwater dynamics influence morphodynamics via the rate of biogeomorphic succession we applied historic imagery analysis in combination with dendroecological methods for willows growing on young gravelly fluvial landforms along a steep groundwater depth gradient we determined the following floodplain morphodynamics and plant encroachment at the decadal scale pioneer willow growth rates and their relationships to hydrological variables willow growth rates were correlated with moisture availability groundwater discharge and precipitation variability in the downwelling reach while little correlation was found in the upwelling reach after a reduction in ecological disturbance frequency data suggest that where groundwater is upwelling biogeomorphic succession is fast the engineering effect of vegetation is quickly established and hence channel stability increased and active channel width reduces where groundwater is downwelling deeper and more variable biogeomorphic succession is slower the engineering effect is reduced and a wider active width is maintained thus groundwater is an important control on biogeomorphic feedbacks intensity and through the stabilizing effect of vegetation may drive long term river channel morphodynamics

simulated effect of soil depth and bedrock topography on near surface hydrologic response and slope stability this paper explores the effect of hillslope hydrological behavior on slope stability in the context of transient subsurface saturation development and landslide triggering we perform a series of virtual experiments to address how subsurface topography affects the location and spatial pattern of slip surface development and pore pressure dynamics we use a 3d darcy richards equation solver hydrus 3 d combined with a cellular automata slope stability model to simulate the spatial propagation of the destabilized area our results showed that the soil bedrock interface and in particular bedrock depressions played a key role in pore pressure dynamics acting as an impedance for the downslope drainage of perched water filling and spilling of depressions in the bedrock surface microtopography induced localized zones of increased pressure head such that the development of pore pressure fields not predictable by surface topography lead to rapid landslide propagation our work suggests that landslide models should consider the subsurface topography in order to include a connectivity component in the mathematical description of hydrological processes operating at the hillslope scale copyright 2012 john wiley sons ltd

age models and the younger dryas impact hypothesis israde alcantara et al 1 drew on interpretations of a core from lake cuitzeo mexico to support the younger dryas yd impact hypothesis a key aspect of their study was identifying and dating the yd interval in the sediments the authors stated that they recovered impact indicators from a 10 cm thick zone dating to 12 9 kcal bp but provided no direct numerical age control or chronological uncertainties for this interval depending on the carbon sources 14c ages of bulk lake sediment can be offset by several centuries 2 however even though the study used bulk 14c dates no offset was quantified dating of the section was accomplished by interpolating through 1 m of undated sediment because the six dates in that interval were rejected even so the rejected dates were in stratigraphic order and there seems no a priori basis to exclude them their age model was anchored by a tephra layer identified as the cieneguillas rhyolitic tephra dated elsewhere as 31 kcal bp 3 but no geochemical evidence was provided to support this tephra identification

supply and removal of sediment in a landslide dominated mountain belt central range taiwan abstract a strong coupling between hillslope and valley systems is often inferred for mountain landscapes dominated by bedrock landsliding we reveal the nature of this link using data sets on landsliding and sediment transport from two montane catchments draining the eastern central range of taiwan here the magnitude frequency distribution of landslides can be modeled by a robust power law but this scale invariance is not mirrored in the sediment discharge at the mountain front instead downstream sediment loads reflect a complex response to both sediment supply and ambient hydraulic conditions the rivers do not transport significant amounts of sediment unless it is provided by hillslope mass wasting in the catchment removal of landslide debris is a function of the transport capacity of the stream at the site of entry thus there is a dual supply and transport control on sediment loads in bedrock floored streams over a monitoring period of 25 yr the bulk of the sediment leaving the mountain bel

geomorphometric assessment of spatial sediment connectivity in small alpine catchments abstract complex and rugged topography induces large variations in erosion and sediment delivery in the headwaters of alpine catchments an effective connection of hillslopes with the channel network results in highly efficient sediment transfer processes such as debris flows in contrast morphological conditions producing decoupling of hillslopes from channels e g glacial cirques may exclude large areas of the catchment from sediment delivery to its lower parts moreover an efficient connection between hillslopes and channel network does not always ensure an effective downstream transfer of sediment low slope channel reaches e g in hanging valleys cause sediment deposition which often results in changes of the sediment transport processes typically from debris flow to streamflow with low bedload and suspended load rates the availability of high resolution digital terrain models such as those derived from aerial lidar improves our capability to quantify the topographic controls on sediment connectivity a geomorphometric index based on the approach by borselli et al 2008 was developed and applied to assess spatial sediment connectivity in two small catchments of the italian alps featuring contrasting morphological characteristics the results of the geomorphometric analysis were checked against field evidences showing good performance and thus potential usefulness of the index

observations and experiments on the origin and formation of inertinite group macerals the inertinite group macerals include fusinite semifusinite inertodetrinite macrinite micrinite and funginite and secretinite which together replace sclerotinite the macrolithotype fusain comprises fusinite and semifusinite and is now widely accepted as charcoal formed by wildfire activity however alternative origins for fusinite and semifusinite are still claimed this paper considers the use of the terms pyrofusinite degradofusinite rank fusinite and primary fusinite misleading while the definitions of the terms funginite and secretinite are also considered problematic observations made on modern wildfire derived and volcanogenic charcoal assemblages using reflectance and scanning electron microscopy together with experimental charcoalification studies demonstrate that most if not all inertinite macerals have acquired their optical and physical characteristics through the action of elevated temperatures the criteria for the identification of charcoals produced by wildfire and volcanic activity are outlined and the role of the petrographic nomenclature system is discussed

early paleogene wildfires in peat forming environments at schoningen germany wildfire activity in early paleogene greenhouse conditions can be used as an analogue to gauge the effect of future warming trends on wildfire in the current climate system inertinite fossil charcoal in coal from 11 autochthonous early paleogene lignite seams from the schoningen mine germany was quantified using macerations in situ pillars and industry standard crushed samples a new three transect method was developed to quantify in situ charcoal the combination of in situ pillars and crushed samples accounts for temporal and spatial variation in charcoal through a stratigraphically oriented pillar whilst maintaining comparability with industry standards and previous work charcoal occurs as a range of randomly distributed particle sizes indicating that fires were burning locally in the schoningen peat forming environment and in the surrounding areas but according to petrological data not in an episodic or periodic pattern although charcoal abundance is low relative to previous high fire worlds such as the cretaceous three quantitative and semi quantitative methods show increased wildfire activity relative to the modern world in the warmest parts of the early paleogene as atmospheric oxygen levels stabilised to modern values and precipitation and humidity became the main control on wildfire increased rainfall followed by drier intervals would have created an environment rich in dry fuel in which wildfires could easily propagate if humidity was low enough in the later part of the early eocene ypresian charcoal abundance fell to levels similar to those found in modern peats this indicates that the transition to the modern low fire world occurred within the early eocene earlier than previous records suggest

limits on the validity of infinite length assumptions for modelling shallow landslides the infinite slope method is widely used as the geotechnical component of geomorphic and landscape evolution models its assumption that shallow landslides are infinitely long in a downslope direction is usually considered valid for natural landslides on the basis that they are generally long relative to their depth however this is rarely justified because the critical length depth l h ratio below which edge effects become important is unknown we establish this critical l h ratio by benchmarking infinite slope stability predictions against finite element predictions for a set of synthetic two dimensional slopes assuming that the difference between the predictions is due to error in the infinite slope method we test the infinite slope method for six different l h ratios to find the critical ratio at which its predictions fall within 5 of those from the finite element method we repeat these tests for 5000 synthetic slopes with a range of failure plane depths pore water pressures friction angles soil cohesions soil unit weights and slope angles characteristic of natural slopes we find that 1 infinite slope stability predictions are consistently too conservative for small l h ratios 2 the predictions always converge to within 5 of the finite element benchmarks by a l h ratio of 25 i e the infinite slope assumption is reasonable for landslides 25 times longer than they are deep but 3 they can converge at much lower ratios depending on slope properties particularly for low cohesion soils the implication for catchment scale stability models is that the infinite length assumption is reasonable if their grid resolution is coarse e g 25 m however it may also be valid even at much finer grid resolutions e g 1 m because spatial organization in the predicted pore water pressure field reduces the probability of short landslides and minimizes the risk that predicted landslides will have l h ratios less than 25

the spatial and temporal patterns of aggradation in a temperate upland gravel bed river intensive field monitoring of a reach of upland gravel bed river illustrates the temporal and spatial variability of in channel sedimentation over the six year monitoring period the mean bed level in the channel has risen by 0 17 m with a maximum bed level rise of 0 5 m noted at one location over a five month winter period these rapid levels of aggradation have a profound impact on the number and duration of overbank flows with flood frequency increasing on average 2 6 times and overbank flow time increasing by 12 8 hours this work raises the profile of coarse sediment transfer in the design and operation of river management specifically engineering schemes it emphasizes the need for the implementation of strategic monitoring programmes before engineering work occurs to identify zones where aggradation is likely to be problematic exploration of the sediment supply and transfer system can explain patterns of channel sedimentation the complex spatial seasonal and annual variability in sediment supply and transfer raise uncertainties into the system s response to potential changes in climate and land use thus there is a demand for schemes that monitor coarse sediment transfer and channel response copyright 2009 john wiley sons ltd

a process based model for colluvial soil depth and shallow landsliding using digital elevation data a model is proposed for predicting the spatial variation in colluvial soil depth the results of which are used in a separate model to examine the effects of root strength and vertically varying saturated conductivity on slope stability the soil depth model solves for the mass balance between soil production from underlying bedrock and the divergence of diffusive soil transport this model is applied using high resolution digital elevation data of a well studied site in northern california and the evolving soil depth is solved using a finite difference model under varying initial conditions the field data support an exponential decline of soil production with increasing soil depth and a diffusivity of about 50 cm 2 yr the predicted pattern of thick and thin colluvium corresponds well with field observations soil thickness on ridges rapidly obtain an equilibrium depth which suggests that detailed field observations relating soil depth to local topographic curvature could further test this model bedrock emerges where the curvature causes divergent transport to exceed the soil production rate hence the spatial pattern of bedrock outcrops places constraints on the production law the infinite slope stability model uses the predicted soil depth to estimate the effects of root cohesion and vertically varying saturated conductivity low cohesion soils overlying low conductivity bedrock are shown to be least stable the model may be most useful in analyses of slope instability associated with vegetation changes from either land use or climate change although practical applications may be limited by the need to assign values to several spatially varying parameters although both the soil depth and slope stability models offer local mechanistic predictions that can be applied to large areas representation of the finest scale valleys in the digital terrain model significantly influences local model predictions this argues for preserving fine scale topographic detail and using relatively fine grid sizes even in analyses of large catchments

terrestrial carbon and nitrogen isotopic ratios from cretaceous tertiary boundary nanodiamonds one hypothesis for the origin of the nanometer size diamonds found at the cretaceous tertiary k t boundary is that they are relict interstellar diamond grains carried by a postulated asteroid the 13 c 12 c and 15 n 14 n ratios of the diamonds from two sites in north america however show that the diamonds are two component mixtures differing in carbon and nitrogen isotopic composition and nitrogen abundance samples from a site from italy show no evidence for either diamond component all the isotopic signatures obtained from the k t boundary are material well distinguished from known meteoritic diamonds particularly the fine grain interstellar diamonds that are abundant in primitive chondrites the k t diamonds were most likely produced during the impact of the asteroid with earth or in a plasma resulting from the associated fireball

regional test of a model for shallow landsliding landslides mapped in 14 watershed analyses in oregon and washington provide a regional test of a model for shallow landsliding a total of 3224 landslides were mapped in watersheds covering 2993 km2 and underlain by a variety of lithologies including tertiary sedimentary rocks of the coast ranges volcanic rocks of the cascade range and quaternary glacial sediments in the puget lowlands gis geographical information system techniques were used to register each mapped landslide to critical rainfall values predicted from a theoretical model for the topographic control on shallow landsliding using 30 m dems digital elevation models a single set of parameter values appropriate for simulating slide hazards after forest clearing was used for all watersheds to assess the regional influence of topographic controls on shallow landsliding model performance varied widely between watersheds with the best performance generally in steep watersheds underlain by shallow bedrock and the worst performance in generally low gradient watersheds underlain by thick glacial deposits landslide frequency slides km2 varied between physiographic provinces but yielded consistent patterns of higher slide frequency in areas with lower critical rainfall values simulations with variable effective cohesion predicted that high root strength effectively limits shallow landsliding to topographic hollows with deep soils and locations that experience excess pore pressures but that low root strength leads to higher probabilities of failure across a greater proportion of the landscape 1998 john wiley sons ltd language en

geothermal evidence of very low glacial temperatures on a rim of the fennoscandian ice sheet 1 the mean ground temperature as low as 10 c and the existence of more than 500 m thick permafrost during the last glacial are apparent from the analysis of deep borehole temperature profiles in north eastern poland the largest thickness of the permafrost and its survival deep into the holocene was restricted to a region known for its low terrestrial heat flow where the negative temperature gradient is observed in the uppermost 400 m we have shown that the profiles are consistent with warming from the glacial mean of 10 c to the holocene mean of 7 c 14 ka ago and to 8 c in the last 150 years

radiocarbon simulation fails to support the temporal synchroneity requirement of the younger dryas impact hypothesis fine scale temporal processes such as the synchronous deposition of organic materials can be challenging to identify using 14 c datasets while some events such as volcanic eruptions leave clear evidence for synchronous deposition synchroneity is more difficult to establish for other types of events this has been a source of controversy regarding 14 c dates associated with a hypothesized extraterrestrial impact at the younger dryas boundary ydb to address this controversy we first aggregate 14 c measurements from northern hemisphere ydb sites we also aggregate 14 c measurements associated with a known synchronous event the laacher see volcanic eruption we then use a monte carlo simulation to evaluate the magnitude of variability expected in a 14 c dataset associated with a synchronous event the simulation accounts for measurement error calibration uncertainty old wood effects and laboratory measurement biases the laacher see 14 c dataset is consistent with expectations of synchroneity generated by the simulation however the ydb 14 c dataset is inconsistent with the simulated expectations for synchroneity these results suggest that a central requirement of the younger dryas impact hypothesis synchronous global deposition of a ydb layer is extremely unlikely calling into question the younger dryas impact hypothesis more generally

paleoecological changes at lake cuitzeo were not consistent with an extraterrestrial impact israde alcantara et al 1 reported evidence for the younger dryas yd impact hypothesis ydih which proposes that an extraterrestrial impact triggered the yd 2 although most ydih research has focused on the impact event itself ydih proponents as in this article have argued that the ecological consequences included widespread biomass burning and contributed to the extinction of late pleistocene megafauna and to major declines in human populations to fully test the ydih the authors must evaluate evidence and mechanisms for the ecological consequences of an impact we believe there are flaws in both the interpretation of the paleoecological evidence reviewed by israde alcantara et al and in its application in testing the ydih

geomorphic coupling and sediment connectivity in an alpine catchment exploring sediment cascades using graph theory through their relevance for sediment budgets and the sensitivity of geomorphic systems geomorphic coupling and sediment connectivity represent important topics in geomorphology since the introduction of the systems perspective to physical geography by chorley and kennedy 1971 a catchment has been perceived as consisting of landscape elements e g landforms subcatchments that are coupled by geomorphic processes through sediment transport in this study we present a novel application of mathematical graph theory to explore the network structure of coarse sediment pathways in a central alpine catchment numerical simulation models for rockfall debris flows and hillslope and channel fluvial processes are used to establish a spatially explicit graph model of sediment sources pathways and sinks the raster cells of a digital elevation model form the nodes of this graph and simulated sediment trajectories represent the corresponding edges model results are validated by visual comparison with the field situation and aerial photos the interaction of sediment pathways i e where the deposits of a geomorphic process form the sources of another process forms sediment cascades represented by paths a succession of edges in the graph model we show how this graph can be used to explore upslope contributing area and downslope source to sink functional connectivity by analysing its nodes edges and paths the analysis of the spatial distribution composition and frequency of sediment cascades yields information on the relative importance of geomorphic processes and their interaction however regardless of their transport capacity in the study area the analysis stresses the importance of mass movements and their interaction e g the linkage of large rockfall source areas to debris flows that potentially enter the channel network moreover it is shown that only a small percentage of the study area is coupled to the channel network which itself is longitudinally disconnected by natural and anthropogenic barriers besides the case study we discuss the methodological framework and alternatives for node and edge representations of graph models in geomorphology we conclude that graph theory provides an excellent methodological framework for the analysis of geomorphic systems especially for the exploration of quantitative approaches towards sediment connectivity

charcoal recognition taphonomy and uses in palaeoenvironmental analysis abstract charcoal predominantly the product of wildfires is abundant in many sedimentary rocks deposited in a wide range of environments from terrestrial to marine it also occurs in some volcanic rocks this paper outlines aspects of charcoal formation both natural and experimental and briefly considers the taphonomic processes leading to a final assemblage this is done using examples from recent fires and through experimentation the ways in which charcoal assemblages are recognized in the field and extraction in the laboratory are also considered methods of charcoal identification are presented the range of charcoalified plant organs that can be found is discussed and a wide range of study methods outlined including light microscopy dark field light microscopy reflectance microscopy scanning electron microscopy and synchrotron radiation x ray tomographic microscopy emphasis in this paper is on the study of macro and meso charcoal above180 m finally there is a consideration of the broad use of charcoal from plant evolution studies fire history studies vegetation studies anatomical studies climate and atmospheric studies and the wider importance of charcoal for the earth and biological sciences charcoal is information rich but yet is an under utilized resource

a physically based model for the topographic control on shallow landsliding a model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near surface through flow and slope stability models the hydrologic model topog o loughlin 1986 predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries the slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity the steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding the spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high resolution digital elevation data are available tennessee valley in marin county california mettman ridge in the oregon coast range and split creek on the olympic peninsula washington model predictions in each of these areas are consistent with spatial patterns of observed landslide scars although hydrologic complexities not accounted for in the model e g spatial variability of soil properties and bedrock flow control specific sites and timing of debris flow initiation within areas of similar topographic control

a probabilistic sediment cascade model of sediment transfer in the illgraben we present a probabilistic sediment cascade model to simulate sediment transfer in a mountain basin illgraben switzerland where sediment is produced by hillslope landslides and rockfalls and exported out of the basin by debris flows and floods the model conceptualizes the fluvial system as a spatially lumped cascade of connected reservoirs representing hillslope and channel storages where sediment goes through cycles of storage and remobilization by surface runoff the model includes all relevant hydrological processes that lead to runoff formation in an alpine basin such as precipitation snow accumulation snowmelt evapotranspiration and soil water storage although the processes of sediment transfer and debris flow generation are described in a simplified manner the model produces complex sediment discharge behavior which is driven by the availability of sediment and antecedent wetness conditions system memory as well as the triggering potential climatic forcing the observed probability distribution of debris flow volumes and their seasonality in 2000 2009 are reproduced the stochasticity of hillslope sediment input is important for reproducing realistic sediment storage variability although many details of the hillslope landslide triggering procedures are filtered out by the sediment transfer system the model allows us to explicitly quantify the division into transport and supply limited sediment discharge events we show that debris flows may be generated for a wide range of rainfall intensities because of variable antecedent basin wetness and snowmelt contribution to runoff which helps to understand the limitations of methods based on a single rainfall threshold for debris flow initiation in alpine basins

tocuila mammoths basin of mexico late pleistocene early holocene stratigraphy and the geological context of the bone accumulation abstract we report new stratigraphic tephrochronology and dating results from the tocuila mammoth site in the basin of mexico at the site there is evidence for a thin meteorite airburst layer dated between 10 878 and 10 707 cal bc at the onset of the younger dryas yd cool period the upper toluca pumice utp tephra marker caused by a plinian eruption of the nevado de toluca volcano dated from 10 666 to 10 612 cal bc is above that layer the eruption must have caused widespread environmental disruption in the region with evidence of extensive reworking and channelling by the lake texcoco shoreline and contributed to the widespread death and or extinction of megafaunal populations as suggested by earlier authors but the new work reinforces the view that both catastrophic events must have caused large environmental disruption in a short time period of around two hundred years there is no evidence for megafauna mammoths sabre toothed cats camels bison glyptodonts after the utp volcanic event and subsequent lahars in the basin of mexico at tocuila although there are some in situ tephra markers in nearshore lake sediments such as the great basaltic ash gba and the utp ash there is evidence of much reworking of several tephra populations in various combinations the mammoth bone accumulation is reworked in a lahar sequence volcanic mudflow derived from several source sediments but associated with the major utp plinian eruption paleoindian populations were also present in the basin of mexico during the yd period where several paleoindian skeletons were found associated with the utp ash deposits e g metro man chimalhuacan man and tlapacoya man

nanodiamonds in the younger dryas boundary sediment layer we report abundant nanodiamonds in sediments dating to 12 9 0 1 thousand calendar years before the present at multiple locations across north america selected area electron diffraction patterns reveal two diamond allotropes in this boundary layer but not above or below that interval cubic diamonds form under high temperature pressure regimes and n diamonds also require extraordinary conditions well outside the range of earth9s typical surficial processes but common to cosmic impacts n diamond concentrations range from 10 to 3700 parts per billion by weight comparable to amounts found in known impact layers these diamonds provide strong evidence for earth9s collision with a rare swarm of carbonaceous chondrites or comets at the onset of the younger dryas cool interval producing multiple airbursts and possible surface impacts with severe repercussions for plants animals and humans in north america

nanodiamond rich layer across three continents consistent with major cosmic impact at 12 800 cal bp abstracta major cosmic impact event has been proposed at the onset of the younger dryas yd cooling episode at 12 800 150 years before present forming the yd boundary ydb layer distributed over 50 million km2 on four continents in 24 dated stratigraphic sections in 10 countries of the northern hemisphere the ydb layer contains a clearly defined abundance peak in nanodiamonds nds a major cosmic impact proxy observed nd polytypes include cubic diamonds lonsdaleite like crystals and diamond like carbon nanoparticles called n diamond and i carbon the nd abundances in bulk ydb sediments ranged up to 500 ppb mean 200 ppb and that in carbon spherules up to 3700 ppb mean 750 ppb 138 of 205 sediment samples 67 contained no detectable nds isotopic evidence indicates that ydb nds were produced from terrestrial carbon as with other impact diamonds and were not derived from the impactor itself the ydb layer is also marked by abundance peaks in other impact related proxies including

origin and provenance of spherules and magnetic grains at the younger dryas boundary abstract one or more bolide impacts are hypothesized to have triggered the younger dryas cooling at 12 9 ka in support of this hypothesis varying peak abundances of magnetic grains with iridium and magnetic microspherules have been reported at the younger dryas boundary ydb we show that bulk sediment and or magnetic grains microspherules collected from the ydb sites in arizona michigan new mexico new jersey and ohio have 187os 188os ratios 1 0 similar to average upper continental crust 1 3 indicating a terrestrial origin of osmium os in these samples in contrast bulk sediments from ydb sites in belgium and pennsylvania exhibit 187os 188os ratios 1 0 and at face value suggest mixing with extraterrestrial os with 187os 188os of 0 13 however the os concentration in bulk sample and magnetic grains from belgium is 2 8 pg g and 15 pg g respectively much lower than that in average upper continental crust 31 pg g indicating no meteoritic contribution the ydb site in pennsylvania is remarkable in yielding 2 to 5 mm diameter spherules containing minerals such as suessite fe ni silicide that form at temperatures in excess of 2000 c gross texture mineralogy and age of the spherules appear consistent with their formation as ejecta from an impact 12 9 ka ago the 187os 188os ratios of the spherules and their leachates are often low but os in these objects is likely terrestrially derived the rare earth element patterns and sr and nd isotopes of the spherules indicate that their source lies in 1 5 ga quebecia terrain in the grenville province of northeastern north america

long lived magmatic phases at los azufres volcanic center mexico abstract the los azufres volcanic complex has had a long eruptive history of 1 5 myr or more less than 3 myr subsequent to the building of a large miocene and pliocene andesitic complex since about 1 5 ma its development consists of two main periods of volcanic activity the first period from 1 5 to 0 8 ma has two magmatic cycles about 200 000 years in duration characterized by acidic followed basaltic volcanism such a magmatic evolution suggests successive emptyings of a shallow reservoir in which differentiation previously occurred about 0 6 ma major deep magma supplies were probably responsible for the resurgent doming which led to uplift of the southern part of the caldera from 0 6 ma to present the second period exposes volcanic products grading from basalts to rhyolites considering the recent age of the last ignimbrites 26 000 to 29 000 years one can assume that the volcanic activity related to a voluminous differentiated magma body at shallow depth has not yet ended especially in the southern area in and around the resurgent zone occupied by the geothermal field

quantifying the distribution of nanodiamonds in pre younger dryas to recent age deposits along bull creek oklahoma panhandle usa high levels of nanodiamonds nds have been used to support the transformative hypothesis that an extraterrestrial et event comet explosion triggered younger dryas changes in temperature flora and fauna assemblages and human adaptations firestone rb et al 2007 proc natl acad sci usa 104 41 16016 16021 we evaluate this hypothesis by establishing the distribution of nds within the bull creek drainage of the beaver river basin in the oklahoma panhandle the earlier report of an abundance spike of nds in the bull creek i younger dryas boundary soil is confirmed although no pure cubic diamonds were identified the lack of hexagonal nds suggests bull creek i is not near any impact site potential hexagonal nds at bull creek were found to be more consistent with graphene graphane an additional nd spike is found in deposits of late holocene through the modern age indicating nds are not unique to the younger dryas boundary nd distributions do not correlate with depositional environment pedogenesis climate perturbations periods of surface stability or cultural activity

time and the persistence of alluvium river engineering fluvial geomorphology and mining sediment in california abstract river managers need to understand fluvial systems as they change through time many river systems are presently in a state of flux as a result of substantial anthropogenic changes to water and sediment regimes and channel hydraulics yet historical approaches to understanding river systems rarely receive adequate attention because historical methodologies are not conducive to the application of quantitative analysis while there is limited precision in most historical reconstructions the information derived from these studies constrains other interpretations and is essential to a full understanding of the behavior of fluvial systems geomorphology provides a perspective on river systems in which time at various scales is interwoven into practical and theoretical aspects of scientific inquiry thus geomorphology is important to our understanding of not only physical systems but also fundamental concepts of time this study examines channel morphological changes in the bear and american basins brought about by two episodes of sedimentation from hydraulic gold mining the primary event was the production of more than 1 billion m3 of sediment throughout the northern sierra nevada from 1853 to 1884 which caused aggradation in many channels across the sierra foothills and sacramento valley assumptions by both engineers and geomorphologists that morphologic responses to this event were ephemeral that sediment loads have returned to previous levels and that deposits have stabilized are not borne out by field and historical data in the sacramento valley a secondary sedimentation event not previously studied was the production of at least 24 million m3 of sediment during a period of licensed mining from 1893 to 1953 this episode of sedimentation has been largely overlooked as a geomorphic hydrologic or water quality event yet channel morphologic responses in phase with mining during this period are demonstrated systematic changes in stage discharge relationships reflect channel morphological changes that are relevant to flood risk assessments stability of engineering structures on floodplains and geomorphic interpretations

the timing and magnitude of coarse sediment transport events within an upland temperate gravel bed river this paper describes the application of a new instrument to continuously measure bedload transport an impact sensor to a 72 km2 test catchment in the yorkshire dales northern england data from a network of impact sensors are linked to repeat surveys of channel morphological response to get a better understanding of the conditions that lead to sediment generation and transfer results suggest certain areas of the catchment act as key sediment sources at the annual time scale with material being quickly delivered to the lower parts of the catchment along the steep bedrock channel sediment transfer within the tributaries occurs in significantly smaller magnitudes than within the main channel but it moves more frequently and at different times of the year with transfer rates being strongly conditioned by larger scale valley geomorphology the lower 5 6 km reach sees a significant reduction in gradient and a widening of the valley this permits significant accumulation within the channel which has persisted for many years this lower reach is very sensitive to changes in sediment supply and there is good agreement between changes in bedload transport data and the surveyed channel response these observations have major implications for how river management projects should be developed in upland environments especially those where large scale geomorphological controls have a major impact upon the sediment transfer process evidence suggests that where river management restricts lateral movement of the channel and transfer of sediment into floodplain storage changes in sediment supply can lead to areas of severe accumulation acceleration of bank erosion and exacerbated flood risk

the micromorphology of younger dryas aged black mats from nevada arizona texas and new mexico abstract black mats are organic rich sediments and soils that form in wet environments associated with spring discharge micromorphological and geochemical analyses of 25 black mats dating to the younger dryas chronozone 12 9 11 7 ka and early holocene were conducted to determine their composition and depositional environment samples were collected from arizona new mexico texas and nevada micromorphological analyses were conducted on thin sections using polarized and blue fluorescent light these analyses determined that black mats contain humic acids fine 5 20 m plant fragments diatoms phytoliths and gastropods the dominant type of organic matter in black mats is derived from herbaceous plants contradicting previous studies that supported algal or charcoal sources differences in the micromorphological characteristics of the samples revealed that black mats formed as three different types organic horizons moist soils and ponded sediments depending on their topographic position in relation to the water table the microscopic evidence found in black mats supports the presence of widespread wet environments in nevada and arizona during the younger dryas chronozone clearly indicating a sustained period of greater effective moisture optimal for spring discharge and black mat formation

reconceptualising coarse sediment delivery problems in rivers as catchment scale and diffuse this paper assesses river channel management activities in the context of the interaction between coarse sediment delivery climate change river channel response and flood risk it uses two main sources of evidence 1 an intensive instrumentation of an upland river catchment using both traditional hydrometric and novel sediment sensing methods and 2 a sediment delivery model that combines a treatment of sediment generation from mass failure with a treatment of the connectivity of this failed material to the drainage network the field instrumentation suggests that the precipitation events that deliver sediment from hillslopes to the drainage network are different to those that transfer sediment within the network itself extreme events that could occur at any time in the year i e they are not dependent on wet antecedent conditions were crucial for sediment delivery however sustained high river flows were responsible for the majority of transfer within the river itself application of three downscaling methods to climate model predictions for the 2050s and 2080s suggested a significant increase in the number and potential volume of delivery events by the 2050s regardless of the climate downscaling scenario used first approximations suggested that this would translate into annual bed level aggradation rates of between 0 10 and 0 20 m per year in the downstream main channel reaches second the importance of this delivery for flood risk studies was confirmed by simulating the effects of 16 months of measured in channel simulation with river flows scaled for climate change to the 2050s and 2080s short term sedimentation could result in similar magnitude increases in inundated area for 1 in 0 5 and 1 in 2 year floods to those predicted for the 2050s in relation to increases in flow magnitude finally we were able to develop an alternative approach to river management in relation to coarse sediment delivery based upon reducing the rates of coarse sediment delivery through highly localised woodland planting under the assumption that reducing delivery rates should reduce the rate of channel migration and hence the magnitude of the bank erosion problem thus the paper demonstrates the need to conceptualise local river management problems in upland river environments as point scale manifestations of a diffuse sediment delivery process with a much more explicit focus on the catchment scale if our river systems are to become more insulated from the impacts of future climate changes

the murray springs clovis site pleistocene extinction and the question of extraterrestrial impact some of the evidence for the recent hypothesis of an extraterrestrial impact that caused late pleistocene megafaunal extinctions firestone et al 2007 proc natl acad sci usa 104 16016 16021 was based upon samples collected at murray springs a clovis archaeological site in southeastern arizona here we describe sampling and analyses of magnetic separates from within above and below the lower younger dryas boundary lydb black mat at murray springs as well as radiation measurements from the lydb at murray springs and two other well stratified clovis sites the main magnetic fraction at murray springs is maghemite magnetic microspherules have terrestrial origins but also occur as cosmic dust particles we failed to find iridium or radiation anomalies the evidence for massive biomass burning at murray springs is addressed and found to be lacking we could not substantiate some of the claims by firestone and others but our findings do not preclude a terminal pleistocene cosmic event

hydrologic processes in a low gradient source area discharge piezometric and other field observations from a 3 year monitoring program indicate that runoff from a low gradient source area in marin county california is controlled by the interaction of throughflow macropore flow and saturation overland flow throughflow response integrates multiple storm events and exhibits both seasonal trends and rapid response to midwinter storms upon saturation of highly conductive near surface soils after saturation of the deeper colluvium along the hollow axis macropore flow responds rapidly to individual storm events and locally provides a ceiling to piezometric response saturation overland flow occurs along the axis of the unchanneled valley only during large storms when both soil matrix and macropore transmissivity are exceeded during large runoff producing storms saturation overland flow extends continuously over most of the unchanneled valley axis during smaller runoff producing events however ground surface saturation may be discontinuous reflecting either variations in the conductivity of the underlying soil bedrock or a variable soil thickness along the hollow axis results of this study document a sequence of flow path activation in which the temporal distribution of rainfall events within a season determines both the mechanism and magnitude of runoff generation

wildfire and abrupt ecosystem disruption on california s northern channel islands at the allerod younger dryas boundary 13 0 12 9 ka abstract sedimentary records from california s northern channel islands and the adjacent santa barbara basin sbb indicate intense regional biomass burning wildfire at the allerod younger dryas boundary 13 0 12 9 ka all age ranges in this paper are expressed in thousands of calendar years before present ka radiocarbon ages will be identified and clearly marked 14c years multiproxy records in sbb ocean drilling project odp site 893 indicate that these wildfires coincided with the onset of regional cooling and an abrupt vegetational shift from closed montane forest to more open habitats abrupt ecosystem disruption is evident on the northern channel islands at the allerod younger dryas boundary with the onset of biomass burning and resulting mass sediment wasting of the landscape these wildfires coincide with the extinction of mammuthus exilis pygmy mammoth the earliest evidence for human presence on these islands at 13 1 12 9 ka 11 000 10 900 14c years is followed by an apparent 600 800 year gap in the archaeological record which is followed by indications of a larger scale colonization after 12 2 ka although a number of processes could have contributed to a post 18 ka decline in m exilis populations e g reduction of habitat due to sea level rise and human exploitation of limited insular populations we argue that the ultimate demise of m exilis was more likely a result of continental scale ecosystem disruption that registered across north america at the onset of the younger dryas cooling episode contemporaneous with the extinction of other megafaunal taxa evidence for ecosystem disruption at 13 12 9 ka on these offshore islands is consistent with the younger dryas boundary cosmic impact hypothesis firestone r b west a kennett j p becker l bunch t e revay z s schultz p h belgya t kennett d j erlandson j m dickenson o j goodyear a a harris r s howard g a kloosterman j b lechler p mayewski p a montgomery j poreda r darrah t que hee s s smith a r stich a topping w wittke j h wolbach w s 2007 evidence for an extraterrestrial impact 12 900 years ago that contributed to the megafaunal extinctions and younger dryas cooling proceedings of the national academy of sciences 104 16016 16021

a distributed slope stability model for steep forested basins a distributed physically based slope stability model dslam based on an infinite slope model a kinematic wave groundwater model and a continuous change vegetation root strength model is presented it is integrated with a contour line based topographic analysis and a geographic information system gis for spatial data extraction and display the model can be run with either individual rainfall events or long term sequences of storms these inputs can be either actual storm records or synthesized random events based on monte carlo simulation the model is designed to analyze rapid shallow landslides and the spatial distribution of safety factor fs in steep forested areas it can investigate the slope stability problem in both temporal and spatial dimensions for example the impact of timber harvesting on slope stability either at a given time or through an extended management period the probability of landslide occurrence for a given year and the delivery of landslide sediments to headwater streams the dslam model was applied in a steep forested drainage of cedar creek in the oregon coast ranges using actual spatial patterns of timber harvesting and measured rainfall during a major storm which triggered widespread landslides in that area in 1975 simulated volume and number of failures were 733 m3 and 4 respectively these values agreed closely with field measurements following the 1975 storm however the effect of parameter uncertainty may complicate this comparison for example when soil cohesion values of 2 0 and 3 0 kpa were used the failure volume changed by factors of 2 04 and 0 41 respectively compared with the average condition of 2 5 kpa used in the simulation for soil depths 30 higher and lower than the standard condition the failure volume changed by factors of 2 0 and 0 27 respectively when maximum root cohesion changed from 12 5 kpa average condition to 10 kpa the failure volume increased 1 73 fold for the case of 15 kpa the failure volume changed by a factor of 0 55 the simulated failures caused by the storm were mostly in hollows the simulations show that the spatial distribution of fs is controlled mainly by topography and timber harvesting patterns and is greatly affected by groundwater flow patterns during major rainstorms most areas with fs 3 0 corresponded with the distribution of blocks clear cut in 1968 and all elements with fs 2 0 were in areas clear cut in 1968 areas with low fs 1 0 1 6 expanded dramatically during the rainstorm and decreased at a slow rate after the storm factors of safety in hollows declined sharply during the storm

late pleistocene to early holocene natural and human influenced sediment dynamics and soil formation in a 0 order catchment in sw germany palatinate forest this paper presents the dynamics of sedimentation processes and soil development of a steeply sloping 0 order catchment in the sandy lower bunter of the south western mid range mountains in the palatinate forest germany during the transition period from the late glacial to the early holocene field investigations chemical physical micromorphological and anthracological analyses revealed a complex palaeosol sediment sequence along the thalweg of a dry valley where a significant amount of the sediment from the adjacent slopes had been captured the deposition of aeolian sands in the lowermost sediment layer took place in the early late glacial the subsequent sediments were deposited by slope wash and aeolian processes it contains a higher amount of silt and dates from the allerod the occurrence of laacher see tephra lst indicates that this sediment has been near the surface around 12 900 cal bp it also shows characteristics of palaeosols similar to the usselo finow soils in north eastern germany in the overlying material the amount of root remnants other organic matter and rounded bone fragments possibly indicates the presence of people in this area on top alternating reddish brown coarse to fine sand and small partly rounded stones with some small intercalated aggregations of humic material rich in charcoal dating to between 11 000 and 12 000 cal bp were deposited the layers are overlain by clearly visible and evenly distributed wavy clay illuviation bands typical for a luvisol in the upper metre a cambisol has developed the sediment structure shows typical features of a flash flood event in the preboreal the stratigraphy suggests that phases of sedimentation caused by water and aeolian erosion took place in the allerod younger dryas and preboreal discussion considers climate driven natural processes as well as the possibility that the manipulation of forest vegetation by fire through sedentary mesolithic hunter gatherer groups created open areas and enabled intensive soil erosion at a local scale

does hydrological connectivity improve modelling of coarse sediment delivery in upland environments modelling the delivery of landslide generated sediment to channel networks is challenging due to uncertainty in the magnitude frequency distribution of failures connected to the channel network here we investigate a simplified treatment of hydrological connectivity as a means for improving identification of coarse sediment delivery to upland rivers sediment generation from hillslopes and channel banks and its delivery to the channel network are modelled based on a modified form of shalstab coupled to a network index version of topmodel the network index treatment has two important hydrological effects a it only allows saturated areas to connect to the hydrological network when there is full saturation along the associated flow path and 2 overland flow associated with unconnected but saturated zones is assumed to remain within the catchment and to contribute to a reduction in the catchment averaged saturation deficit we use this hydrological treatment to restrict sediment delivery to situations where there is surface hydrological connection i e saturation along the complete flow path that connects failure areas to the drainage network this represents an extreme restriction on the possibility of connected failure as it does not allow for failed material to connect if failures are associated with partial saturation or where delivery involves runout across areas where hydrological connection is not maintained the impact of this restriction is assessed by comparing model predictions with field mapping of connected failures and data from continuously recording coarse sediment sensors for two storm events the hydrological connection requirement restricted connected failures to zones closer to the drainage network and resulted in a better level of agreement with the field mapped failures simulations suggested that in the study catchment the majority of sediment inputs occur from hydrologically connected areas close to the channel network during moderate sized rainstorms that occur relatively frequently 2007 elsevier b v all rights reserved

a network based framework for identifying potential synchronizations and amplifications of sediment delivery in river basins long term prediction of environmental response to natural and anthropogenic disturbances in a basin becomes highly uncertain using physically based distributed models particularly when transport time scales range from tens to thousands of years such as for sediment yet such predictions are needed as changes in one part of a basin now might adversely affect other parts of the basin in years to come in this paper we propose a simplified network based predictive framework of sedimentological response in a basin which incorporates network topology channel characteristics and transport process dynamics to perform a nonlinear process based scaling of the river network width function to a time response function we develop the process scaling formulation for transport of mud sand and gravel using simplifying assumptions including neglecting long term storage and apply the methodology to the minnesota river basin we identify a robust bimodal distribution of the sedimentological response for sand of the basin which we attribute to specific source areas and identify a resonant frequency of sediment supply where the disturbance of one area followed by the disturbance of another area after a certain period of time may result in amplification of the effects of sediment inputs which would be otherwise difficult to predict we perform a sensitivity analysis to test the robustness of the proposed formulation to model parameter uncertainty and use observations of suspended sediment at several stations in the basin to diagnose the model the proposed framework has identified an important vulnerability of the minnesota river basin to spatial and temporal structuring of sediment delivery

saturation regions in catchments and their relations to soil and topographic properties abstract criteria are derived for the existence of saturated areas on draining hillslopes in natural catchments these are given in terms of soil transmissivity the hillslope gradient and its wetness state characterised by the baseflow discharge from the catchment analyses are made for idealised hillslopes with uniform soils to obtain expression for the width of the saturated zone the size of saturated zones on undulating hillslopes with gradiational soils is shown to depend strongly on topographic convergence or divergence the effects of soil transmissivity hillslope geometry and drainage flux density are lumped into a dimensionless parameter whose value determines the location of seepage boundaries on slopes of specified geometry scaling relations for seepage area in catchments of different size are shown to be generally nonlinear and depend primarily on local hillslope gradients relative predictions of seepage zone size are confirmed by observed hydrographs from three catchments with different physical characteristics

chronological evidence fails to support claim of an isochronous widespread layer of cosmic impact indicators dated to 12 800 years ago according to the younger dryas impact hypothesis ydih 12 800 calendar years before present north america experienced an extraterrestrial impact that triggered the younger dryas and devastated human populations and biotic communities on this continent and elsewhere this supposed event is reportedly marked by multiple impact indicators but critics have challenged this evidence and considerable controversy now surrounds the ydih proponents of the ydih state that a key test of the hypothesis is whether those indicators are isochronous and securely dated to the younger dryas onset they are not we have examined the age basis of the supposed younger dryas boundary layer at the 29 sites and regions in north and south america europe and the middle east in which proponents report its occurrence several of the sites lack any age control others have radiometric ages that are chronologically irrelevant nearly a dozen have ages inferred by statistically and chronologically flawed age depth interpolations and in several the ages directly on the supposed impact layer are older or younger than 12 800 calendar years ago only 3 of the 29 sites fall within the temporal window of the yd onset as defined by ydih proponents the ydih fails the critical chronological test of an isochronous event at the yd onset which coupled with the many published concerns about the extraterrestrial origin of the purported impact markers renders the ydih unsupported there is no reason or compelling evidence to accept the claim that a cosmic impact occurred 12 800 y ago and caused the younger dryas

suspect cubic diamond impact proxy and a suspect lonsdaleite identification the presence of nanometer sized diamonds in purported younger dryas yd boundary dated sediments carbon spherules and greenland ice was cited as evidence of a yd impact event 1 although cubic and hexagonal lonsdaleite diamond have been found in shocked metamorphosed meteorites and are associated with terrestrial impact structures cubic diamonds are well known to occur in terrestrial deposits that have no associations with impact processes for example submicron and smaller cubic diamond crystals have been found recently in carbonaceous spherules isolated in upper soils from various german and belgian sites 2 lacking links to impact structures these diamonds are evidently not products of impact

comprehensive analysis of nanodiamond evidence relating to the younger dryas impact hypothesis during the end of the last glacial period in the northern hemisphere near 12 9k cal a bp deglacial warming of the bolling allerod interstadial ceased abruptly and the climate returned to glacial conditions for an interval of about 1300 years known as the younger dryas stadial the younger dryas impact hypothesis proposes that the onset of the younger dryas climate reversal pleistocene megafaunal extinctions and disappearance of the clovis paleoindian lithic technology were coeval and caused by continent wide catastrophic effects of impact bolide events in north america while there are no known impact structures dated to the younger dryas onset physical evidence of the impact bolide events is argued to be present in sediments spanning several continents at stratigraphic levels inferred to date to the bolling allerod younger dryas boundary ydb reports of nanometer to submicron sized diamonds in ydb sediments in particular the rare 2h hexagonal polytype of diamond lonsdaleite have been presented as strong evidence for shock processing of crustal materials we review the available data on diamonds in sediments and provide new data we find no evidence for lonsdaleite in ydb sediments and find no evidence of a spike in nanodiamond concentration at the ydb layer to support the impact hypothesis

accumulation of impact markers in desert wetlands and implications for the younger dryas impact hypothesis the younger dryas impact hypothesis contends that an extraterrestrial object exploded over north america at 12 9 ka initiating the younger dryas cold event the extinction of many north american megafauna and the demise of the clovis archeological culture although the exact nature and location of the proposed impact or explosion remain unclear alleged evidence for the fallout comes from multiple sites across north america and a site in belgium at 6 of the 10 original sites excluding the carolina bays elevated concentrations of various impact markers were found in association with black mats that date to the onset of the younger dryas black mats are common features in paleowetland deposits and typically represent shallow marsh environments in this study we investigated black mats ranging in age from approximately 6 to more than 40 ka in the southwestern united states and the atacama desert of northern chile at 10 of 13 sites we found elevated concentrations of iridium in bulk and magnetic sediments magnetic spherules and or titanomagnetite grains within or at the base of black mats regardless of their age or location suggesting that elevated concentrations of these markers arise from processes common to wetland systems and not a catastrophic extraterrestrial impact event

fungus not comet or catastrophe accounts for carbonaceous spherules in the younger dryas impact layer 1 a claim attributes the onset of the younger dryas climate interval and a range of other effects 12 900 years ago to a comet airburst and or impact event one key aspect of this claim centers on the origin of carbonaceous spherules that purportedly formed during intense impact ignited wildfires samples from pleistocene holocene sedimentary sequences in the california channel islands and other sites show that carbon spherules and elongate forms are common in samples dating to before during and well after the 12 900 year time horizon including from modern samples microscopic studies show that carbon spherules have morphologies and internal structures identical to fungal sclerotia such as sclerotium and cenococcum experimental charring of fungal sclerotia shows that their reflectance increases with temperature reflectance measurements of modern and late pleistocene spherules show that the latter indicate at most low intensity burning these data cast further doubt upon the evidence suggesting a catastrophic younger dryas impact event

towards establishing climatic thresholds for slope instability use of a physically based combined soil hydrology slope stability model shallow landslides are often linked to high magnitude rainstorms research has attempted to establish threshold rainfall totals that trigger shallow landslides based mainly on field evidence complications arise because not all regolith has the same hydrological behaviour and research frequently fails to take this into account this paper uses a combination of field and modelling approaches to explore the triggering rainfall thresholds for shallow failures in deforested hill country of new zealand it emphasises the role of variations in regolith hydrology focussing on unsaturated and saturated zone responses by using a modelling approach detailed variations in pore pressure positive and negative responses are investigated developing ideas initially derived from field evidence this paper defines and develops earlier research that establishes values for maximum and minimum probability thresholds for shallow landslides and provides a more generalised model that can be applied more widely hydrological mechanisms for shallow landslides are investigated in greater detail than previously possible using a combined hydrology and stability model chasm

sediment flux from a mountain belt derived by landslide mapping in humid uplands landsliding is the dominant mass wasting process in the western southern alps of new zealand landslides are scale invariant and have a power law magnitude frequency distribution independent studies from other regions suggest that this is a general property of landsliding this observation is of critical importance to the evaluation of the impact of events of different length scales over different time intervals on landscape evolution it is particularly useful when estimating regional geomorphic rates because it constrains the frequency and overall significance of extreme events which cannot otherwise be evaluated by integrating the complete response of the system we estimate the regional denudation rate due to landsliding to be 9 4 mm yr 1 sediment discharge from the western southern alps is dominated by landslide derived material

evidence for deposition of 10 million tonnes of impact spherules across four continents 12 800 y ago airbursts impacts by a fragmented comet or asteroid have been proposed at the younger dryas onset 12 80 0 15 ka based on identification of an assemblage of impact related proxies including microspherules nanodiamonds and iridium distributed across four continents at the younger dryas boundary ydb spherule peaks have been independently confirmed in eight studies but unconfirmed in two others resulting in continued dispute about their occurrence distribution and origin to further address this dispute and better identify ydb spherules we present results from one of the largest spherule investigations ever undertaken regarding spherule geochemistry morphologies origins and processes of formation we investigated 18 sites across north america europe and the middle east performing nearly 700 analyses on spherules using energy dispersive x ray spectroscopy for geochemical analyses and scanning electron microscopy for surface microstructural characterization twelve locations rank among the world s premier end pleistocene archaeological sites where the ydb marks a hiatus in human occupation or major changes in site use our results are consistent with melting of sediments to temperatures 2 200 c by the thermal radiation and air shocks produced by passage of an extraterrestrial object through the atmosphere they are inconsistent with volcanic cosmic anthropogenic lightning or authigenic sources we also produced spherules from wood in the laboratory at 1 730 c indicating that impact related incineration of biomass may have contributed to spherule production at 12 8 ka an estimated 10 million tonnes of spherules were distributed across 50 million square kilometers similar to well known impact strewnfields and consistent with a major cosmic impact event

evidence from central mexico supporting the younger dryas extraterrestrial impact hypothesis we report the discovery in lake cuitzeo in central mexico of a black carbon rich lacustrine layer containing nanodiamonds microspherules and other unusual materials that date to the early younger dryas and are interpreted to result from an extraterrestrial impact these proxies were found in a 27 m long core as part of an interdisciplinary effort to extract a paleoclimate record back through the previous interglacial our attention focused early on an anomalous 10 cm thick carbon rich layer at a depth of 2 8 m that dates to 12 9 ka and coincides with a suite of anomalous coeval environmental and biotic changes independently recognized in other regional lake sequences collectively these changes have produced the most distinctive boundary layer in the late quaternary record this layer contains a diverse abundant assemblage of impact related markers including nanodiamonds carbon spherules and magnetic spherules with rapid melting quenching textures all reaching synchronous peaks immediately beneath a layer containing the largest peak of charcoal in the core analyses by multiple methods demonstrate the presence of three allotropes of nanodiamond n diamond i carbon and hexagonal nanodiamond lonsdaleite in order of estimated relative abundance this nanodiamond rich layer is consistent with the younger dryas boundary layer found at numerous sites across north america greenland and western europe we have examined multiple hypotheses to account for these observations and find the evidence cannot be explained by any known terrestrial mechanism it is however consistent with the younger dryas boundary impact hypothesis postulating a major extraterrestrial impact involving multiple airburst s and and or ground impact s at 12 9 ka

coupling between hillslopes and channels in upland fluvial systems implications for landscape sensitivity illustrated from the howgill fells northwest england abstract the sensitivity of upland fluvial systems depends on the magnitude and frequency of sediment and flood producing events modified by the internal coupling characteristics of the system this paper assesses the role of hillslope channel coupling for the sensitivity of upland geomorphic systems using evidence from a 30 year monitoring programme of geomorphic change in the carlingill valley howgill fells northwest england in the hillslope zone there is little sediment supply to the stream system locally slope failures occur in response to extreme events six such events in 30 years within the ca 6 km 2 carlingill valley in the footslope coupling zone basally induced gullies are major sediment sources to the stream sediment production events occur ca 30 times per year feeding sediment to basal debris cones stream floods which can entrain these sediments occur once every ca 2 5 years stream channel morphology is adjusted to this regime downstream of gullies channels are wide and braided elsewhere they are narrow and single thread as the gullies develop however this coupling weakens and the eroding slopes eventually stabilise by revegetation over the 30 year monitoring period there has been a progressive trend towards gully stabilisation and an associated reduction in channel instability massive destabilisation may occur in response to rare extreme flood events such an event return period 100 years occurred in neighbouring langdale and bowderdale valleys in june 1982 that event destabilised the system causing slope failures fan deposition and in some places a switch in channel style to wide braided channels since 1982 there has been a progressive recovery by slope stabilisation and single thread sinuous channels have become reestablished a different style of extreme event occurred in carlingill in october 1998 in response to the wettest week in the 30 year period a slope failure fed debris flows 400 m downslope almost coupling with the channel system future climatic change could render the system prone to destabilisation through either extreme flood events or through major slope failures

channel floodplain connectivity during an extreme flood event implications for sediment erosion deposition and delivery the term connectivity has emerged as a powerful concept in hydrology and geomorphology and is emerging as an innovative component of catchment erosion modeling studies however considerable confusion remains regarding its definition and quantification especially as it relates to fluvial systems this confusion is exacerbated by a lack of detailed case studies and by the tendency to treat water and sediment separately extreme flood events provide a useful framework to assess variability in connectivity particularly the connection between channels and floodplains the catastrophic flood of january 2011 in the lockyer valley southeast queensland australia provides an opportunity to examine this dimension in some detail and to determine how these dynamics operate under high flow regimes high resolution aerial photographs and multi temporal lidar digital elevation models dems coupled with hydrological modeling are used to assess both the nature of hydrologic and sedimentological connectivity and their dominant controls longitudinal variations in flood inundation extent led to the identification of nine reaches which displayed varying channel floodplain connectivity the major control on connectivity was significant non linear changes in channel capacity due to the presence of notable macrochannels which contained a 3000 average recurrence interval ari event at mid catchment locations the spatial pattern of hydrological connectivity was not straight forward in spite of bankfull discharges for selected reaches exceeding 5600m 3 s 1 data indicate that the main channel boundary was the dominant source of sediment while the floodplains where inundated were the dominant sinks spatial variability in channel floodplain hydrological connectivity leads to dis connectivity in the downstream transfer of sediments between reaches and affected sediment storage on adjacent floodplains consideration of such variability for even the most extreme flood events highlights the need to carefully consider non linear changes in key variables such as channel capacity and flood conveyance in the development of a quantitative connectivity index copyright c 2013 john wiley sons ltd

inconsistent impact hypotheses for the younger dryas israde alcantara et al 1 presented evidence from lake cuitzeo sediments and argued that it supports the younger dryas yd impact hypothesis of firestone et al 2 for a major extraterrestrial impact event involving multiple airburst s and or ground impact s at 12 9 ka firestone et al 2 did not specify the details of the impact but proposed that it had continent wide effects and was most likely a comet the yd hypothesis requires an energy of 107 megatons equivalent to a 4 km wide comet because no late pleistocene craters have been identified firestone et al 2 argue for prior fragmentation of a large impactor and suggest that multiple 2 km objects struck the laurentide ice sheet at oblique angles

absence of geochemical evidence for an impact event at the bolling allerod younger dryas transition high concentrations of iridium have been reported in terrestrial sediments dated at 12 9 ka and are interpreted to support an extraterrestrial impact event as the cause of the observed extinction in the rancholabrean fauna changes in the paleoindian cultures and the onset of the younger dryas cooling firestone rb et al 2007 proc natl acad sci usa 104 16016 16021 here we report platinum group element pge os ir ru rh pt pd gold au concentrations and 187os 188os ratios in time equivalent terrestrial lacustrine and marine sections to seek robust evidence of an extraterrestrial contribution first our results do not reproduce the previously reported elevated ir concentrations second 187os 188os isotopic ratios in the sediment layers investigated are similar to average crustal values indicating the absence of a significant meteoritic os contribution to these sediments third no pge anomalies distinct from crustal signatures are present in the marine record in either the gulf of california dsdp 480 guaymas basin or the cariaco basin odp 1002c our data show no evidence of an extraterrestrial et pge enrichment anomaly in any of the investigated depositional settings investigated across north america and in one section in belgium the lack of a clear et pge signature in this sample suite is inconsistent with the impact of a large chondritic projectile at the bolling allerod younger dryas transition

topographic fingerprints of bedrock landslides bedrock landslides in mountainous regions may be triggered by either storms or earthquakes the dominant mechanism in a region affects both landscape evolution and landslide hazard we describe a simple observational test to distinguish between storm and earthquake triggers based on a probabilistic measure of hillslope morphology in areas that are dominated by storm triggered landslides steep topographic slopes are concentrated on the lowermost parts of the hillslopes storm triggers act primarily on the hillslope toes and landslides preferentially remove material from those locations giving rise to inner gorges areas where most landslides are earthquake triggered have more uniform spatial distributions of steep topographic slopes because coseismic shaking causes failures at both ridge crests and hillslope toes earthquake triggered landslides lead to planar hillslopes and rare or absent inner gorges

a multi proxy study of changing environmental conditions in a younger dryas sequence in southwestern manitoba canada and evidence for an extraterrestrial event multi proxy analyses of a sequence spanning the younger dryas yd in the glacial lake hind basin of manitoba provides insight into regional paleohydrology and paleovegetation of meltwater rivers and lakes spanning 4000 yr the sequence is controlled by 25 new accelerator mass spectrometry ages this lake dammed by the laurentide ice sheet overflowed into lake agassiz the pre yd interval records rapid sedimentation from meltwaters that headed in proglacial lakes in the canadian prairies that are known to have been catastrophically released when ice or sediment barriers were breached pollen in this phase is dominated by pre quaternary forms eroded from paleocene bedrock at the onset of the yd at 12 8 cal ka the sudden appearance of concentrations of nanodiamonds high temperature magnetic spherules platinum and iridium provide evidence of an extraterrestrial et event that others have identified at more than 40 sites in north america major changes in oceans and climate and the catastrophic outflow of nearby lake agassiz at the onset of the yd may be related lower water levels and a reduction of souris river inflow to lake hind followed which are reflected by more clayey and organic rich sediments and a decrease in pre quaternary palynomorphs this may have resulted from the deepening of river valleys caused by the release of meltwater triggered by the et event wetlands then began to develop leading to peat deposition from 12 3 to 11 cal ka this was followed by a fluvial episode depositing sand and then by increased holocene aridity that resulted in accumulation of a thick sequence of dune sands a dry woodland environment with a mix of conifers especially picea and larix and deciduous trees especially populus and quercus covered the uplands from 13 to 10 cal ka

nanodiamonds and wildfire evidence in the usselo horizon postdate the allerod younger dryas boundary the controversial younger dryas impact hypothesis suggests that at the onset of the younger dryas an extraterrestrial impact over north america caused a global catastrophe the main evidence for this impact after the other markers proved to be neither reproducible nor consistent with an impact is the alleged occurrence of several nanodiamond polymorphs including the proposed presence of lonsdaleite a shock polymorph of diamond we examined the usselo soil horizon at geldrop aalsterhut the netherlands which formed during the allerod early younger dryas and would have captured such impact material our accelerator mass spectrometry radiocarbon dates of 14 individual charcoal particles are internally consistent and show that wildfires occurred well after the proposed impact in addition we present evidence for the occurrence of cubic diamond in glass like carbon no lonsdaleite was found the relation of the cubic nanodiamonds to glass like carbon which is produced during wildfires suggests that these nanodiamonds might have formed after rather than at the onset of the younger dryas our analysis thus provides no support for the younger dryas impact hypothesis

the younger dryas impact hypothesis a requiem abstract the younger dryas yd impact hypothesis is a recent theory that suggests that a cometary or meteoritic body or bodies hit and or exploded over north america 12 900 years ago causing the yd climate episode extinction of pleistocene megafauna demise of the clovis archeological culture and a range of other effects since gaining widespread attention in 2007 substantial research has focused on testing the 12 main signatures presented as evidence of a catastrophic extraterrestrial event 12 900 years ago here we present a review of the impact hypothesis including its evolution and current variants and of efforts to test and corroborate the hypothesis the physical evidence interpreted as signatures of an impact event can be separated into two groups the first group consists of evidence that has been largely rejected by the scientific community and is no longer in widespread discussion including particle tracks in archeological chert magnetic nodules in pleistocene bones impact origin of the carolina bays and elevated concentrations of radioactivity iridium and fullerenes enriched in 3 he the second group consists of evidence that has been active in recent research and discussions carbon spheres and elongates magnetic grains and magnetic spherules byproducts of catastrophic wildfire and nanodiamonds over time however these signatures have also seen contrary evidence rather than support recent studies have shown that carbon spheres and elongates do not represent extraterrestrial carbon nor impact induced megafires but are indistinguishable from fungal sclerotia and arthropod fecal material that are a small but common component of many terrestrial deposits magnetic grains and spherules are heterogeneously distributed in sediments but reported measurements of unique peaks in concentrations at the yd onset have yet to be reproduced the magnetic grains are certainly just iron rich detrital grains whereas reported yd magnetic spherules are consistent with the diffuse non catastrophic input of micrometeorite ablation fallout probably augmented by anthropogenic and other terrestrial spherular grains results here also show considerable subjectivity in the reported sampling methods that may explain the purported yd spherule concentration peaks fire is a pervasive earth surface process and reanalyses of the original yd sites and of coeval records show episodic fire on the landscape through the latest pleistocene with no unique fire event at the onset of the yd lastly with yd impact proponents increasingly retreating to nanodiamonds cubic hexagonal lonsdaleite and the proposed n diamond as evidence of impact those data have been called into question the presence of lonsdaleite was reported as proof of impact related shock processes but the evidence presented was inconsistent with lonsdaleite and consistent instead with polycrystalline aggregates of graphene and graphane mixtures that are ubiquitous in carbon forms isolated from sediments ranging from modern to pre yd age important questions remain regarding the origins and distribution of other diamond forms e g cubic nanodiamonds in summary none of the original yd impact signatures have been subsequently corroborated by independent tests of the 12 original lines of evidence seven have so far proven to be non reproducible the remaining signatures instead seem to represent either 1 non catastrophic mechanisms and or 2 terrestrial rather than extraterrestrial or impact related sources in all of these cases sparse but ubiquitous materials seem to have been misreported and misinterpreted as singular peaks at the onset of the yd throughout the arc of this hypothesis recognized and expected impact markers were not found leading to proposed yd impactors and impact processes that were novel self contradictory rapidly changing and sometimes defying the laws of physics the yd impact hypothesis provides a cautionary tale for researchers the scientific community the press and the broader public

shock synthesized hexagonal diamonds in younger dryas boundary sediments the long standing controversy regarding the late pleistocene megafaunal extinctions in north america has been invigorated by a hypothesis implicating a cosmic impact at the llerod younger dryas boundary or ydb 12 900 100 cal bp or 10 900 100 14c years abrupt ecosystem disruption caused by this event may have triggered the megafaunal extinctions along with reductions in other animal populations including humans the hypothesis remains controversial due to absence of shocked minerals tektites and impact craters here we report the presence of shock synthesized hexagonal nanodiamonds lonsdaleite in ydb sediments dating to 12 950 50 cal bp at arlington canyon santa rosa island california lonsdaleite is known on earth only in meteorites and impact craters and its presence strongly supports a cosmic impact event further strengthened by its co occurrence with other nanometer sized diamond polymorphs n diamonds and cubics these shock synthesized diamonds are also associated with proxies indicating major biomass burning charcoal carbon spherules and soot this biomass burning at the younger dryas yd onset is regional in extent based on evidence from adjacent santa barbara basin and coeval with broader continent wide biomass burning biomass burning also coincides with abrupt sediment mass wasting and ecological disruption and the last known occurrence of pygmy mammoths mammuthus exilis on the channel islands correlating with broader animal extinctions throughout north america the only previously known co occurrence of nanodiamonds soot and extinction is the cretaceous tertiary k t impact layer these data are consistent with abrupt ecosystem change and megafaunal extinction possibly triggered by a cosmic impact over north america at 12 900 100 cal bp

physically based modelling of shallow landslide sediment yield at a catchment scale a shallow landslide erosion and sediment yield component applicable at the basin scale has been incorporated into the physically based spatially distributed hydrological and sediment transport modelling system shetran the component determines when and where landslides occur in a basin in response to time varying rainfall and snowmelt the volume of material eroded and released for onward transport and the impact on basin sediment yield derived relationships are used to link the shetran grid resolution up to 1 km at which the basin hydrology and final sediment yield is modelled to a subgrid resolution typically around 10 100 m at which landslide occurrence and erosion is modelled the subgrid discretization landslide susceptibility and potential landslide impact are determined in advance using a geographic information system gis with shetran then providing information on temporal variation in the factors controlling landsliding the ability to simulate landslide sediment yield is demonstrated by a hypothetical application based on a catchment in scotland

urban fluvial flood modelling using a two dimensional diffusion wave treatment part 1 mesh resolution effects high resolution data obtained from airborne remote sensing is increasing opportunities for representation of small scale structural elements e g walls buildings in complex floodplain systems using two dimensional 2d models of flood inundation at the same time 2d inundation models have been devel oped and shown to provide good predictions of flood inundation extent with respect to both full solution of the depth averaged navier stokes equations and simplified diffusion wave models however these models have yet to be applied extensively to urban areas this paper applies a 2d raster based diffusion wave model to determine patterns of fluvial flood inundation in urban areas using high resolution topog raphic data the aim of this paper is to explore the effects of spatial resolution upon estimated inundation extent and flow routing process this is important as the complexity of urban surfaces is such that chang ing data resolution may have a major effect upon surface representation and hence flow routing similarly few applications to date have explicitly considered the timing of the inundation process the model assumes that the prime source of the flood is fluvial pluvial floods and floods associated with urban drainage systems are not addressed the topographic data are based upon airborne laser altimetry li dar obtained for the city of york u k a series of image processing steps are used to pre prepare the topographic data a one dimensional hydraulic model of the ouse from skelton upstream of the city through to naburn weir downstream of the city is used to provide estimates of flux from the river to the floodplain for a major flood inundation event estimated to have a return period of greater than 100 years in november 2000 validation data were available in the form of inundation patterns obtained using aerial photography at a point on the falling limb of the flood event model response shows that even relatively small changes in model resolution have considerable effects on the predicted inundation extent and the timing of flood inundation timing sensitivity would be expected given the relatively poor representation of inertial processes in a diffusion wave model compared with previous work sensitivity to inundation extent is more surprising and is associated with three connected effects 1 the smoothing effect of mesh coarsening upon input topographical data 2 poorer representation of both cell blockage and surface routing processes as the mesh is coarsened where the flow routing is especially complex and 3 the ef fects of 1 and 2 upon water levels and velocities which in turn determine which parts of the floodplain the flow can actually travel to the combined effects of wetting and roughness parameters can compen sate in part for a coarser mesh resolution however the coarser the resolution the poorer the ability to control the inundation process as these parameters not only affect the speed but also the direction of wet ting thus high resolution data will need to be coupled to more sophisticated representation of the inun dation process in order to obtain effective predictions of flood inundation extent this is explored in a companion paper

impact of borehole depths on reconstructed estimates of ground surface temperature histories and energy storage estimates of ground surface temperature changes and continental energy storage from geothermal data have become well accepted indicators of climatic changes these estimates are independent contributions to the ensemble of paleoclimatic reconstructions and have been used for the validation of general circulation models and as a component of the energy budget accounting of the global climate system recent global and hemispheric analyses of geothermal data were based on data available in the borehole paleoclimatology database which contains subsurface temperature profiles from a minimum depth of 200 m to about 600 m because of the nature of heat conduction different depth ranges contain the record of past and persistent changes in the energy balance between the lower atmosphere and the ground for different time periods here we examine the dependency of estimated ground surface temperature histories and the magnitude of the subsurface heat content on the depth of borehole temperature profiles our results show that uncertainties in the estimates of the long term surface temperature are in the range of 0 5k we conclude that previous estimates of ground surface temperature change remain valid for the period since industrialization but longer term estimates are subject to considerable uncertainties the subsurface heat content shows a larger range of variability arising from differences in depth of the borehole temperature profiles as well as from differences in the time of data acquisition spanning four decades these results indicate that estimates of subsurface heat should be carried out with caution to decrease cumulative errors in any spatial analysis

a cellular model of braided rivers a broad sheet of water flowing over non cohesive sediment typically breaks up into a network of interconnected channels called a braided stream fig 1 the dynamics of such networks are complex channels migrate laterally split rejoin and develop bars with the flow shifting unpredictably from one part of the network to another many processes are known to operate in a braided river1 3 but it is unclear which of these are essential to explain the observed dynamics we describe here a simple deterministic numerical model of water flow over a cohesionless bed that captures the main spatial and temporal features of real braided rivers the patterns arise from local scour and deposition caused by a nonlinear dependence of bedload sediment flux on water discharge although the morphology of the resulting network depends in detail on the sediment transport rule used in the model our results suggest that the only factors essential for braiding are bedload sediment transport and laterally unconstrained free surface flow

continental scale temperature variability during the past two millennia past global climate changes had strong regional expression to elucidate their spatio temporal pattern we reconstructed past temperatures for seven continental scale regions during the past one to two millennia the most coherent feature in nearly all of the regional temperature reconstructions is a long term cooling trend which ended late in the nineteenth century at multi decadal to centennial scales temperature variability shows distinctly different regional patterns with more similarity within each hemisphere than between them there were no globally synchronous multi decadal warm or cold intervals that define a worldwide medieval warm period or little ice age but all reconstructions show generally cold conditions between ad 1580 and 1880 punctuated in some regions by warm decades during the eighteenth century the transition to these colder conditions occurred earlier in the arctic europe and asia than in north america or the southern hemisphere regions recent warming reversed the long term cooling during the period ad 1971 2000 the area weighted average reconstructed temperature was higher than any other time in nearly 1 400 years

effective timescales of coupling within fluvial systems this paper presents a review of the coupling concept in fluvial geomorphology based mainly on previously published work coupling mechanisms link the components of the fluvial system controlling sediment transport down the system and the propagation of the effects of base level change up the system they can be viewed at several scales at the local scale involving within hillslope coupling hillslope to channel coupling and within channels tributary junction and reach to reach coupling at larger scales coupling can be considered as zonal coupling between major zones of the system or as regional coupling relating to complete drainage basins these trends are illustrated particularly by the examples of hillslope to channel coupling in the howgill fells northwest england badland systems in southeast spain alluvial fans in spain usa and uae and base level induced dissection of neogene sedimentary basins in southeast spain as the spatial scales increase so do the timescales involved effective temporal scales relate to magnitude and frequency characteristics recovery time and propagation time the relative importance changing with the spatial scale for downsystem coupling at the local scale the first two are important with propagation time increasing in importance in larger systems especially in those involving upsystem coupling related to base level change the effective timescales range from the individual event with a return period of decades through decadal to century timescales for downsystem coupling to tens to hundreds of thousands of years for the basinwide response to base level change the effective timescales influence the relative importance of factors controlling landform development

impacts of the last glacial cycle on ground surface temperature reconstructions over the last millennium borehole temperature profiles provide robust estimates of past ground surface temperature changes in agreement with meteorological data nevertheless past climatic changes such as the last glacial cycle lgc generated thermal effects in the subsurface that affect estimates of recent climatic change from geothermal data we use an ensemble of ice sheet simulations spanning the last 120ka to assess the impact of the laurentide ice sheet on recent ground surface temperature histories reconstructed from borehole temperature profiles over north america when the thermal remnants of the lgc are removed we find larger amounts of subsurface heat storage 2 8 times and an increased warming of the ground surface over north america by 0 75k both relative to uncorrected borehole estimates

a network index based version of topmodel for use with high resolution digital topographic data this paper describes the preliminary development of a network index approach to modify and to extend the classic topmodel application of the basic beven and kirkby 1979 form of topmodel to high resolution 2 0 m laser altimetric data based upon the u k environment agency s light detection and ranging lidar system to a 13 8 km 2 catchment in an upland environment identified large areas of saturated areas that remained unconnected from the drainage network even during an extreme flood event this is shown to be a particular problem with using high resolution topographic data especially over large spatial scales to deal with the hydrological consequences of disconnected areas we present a simple network index modification in which saturated areas only connect when the topographic index is sufficient for there to be zero or negative saturation deficits along a complete flow path this is combined with an enhanced method for dealing with the problem of pits and hollows which is shown to become more acute with higher resolution topographic data the paper concludes by noting the implications of the research as presented for both methodological and substantive research that is currently under way

stratigraphy of the younger dryas chronozone and paleoenvironmental implications central and southern great plains abstract the great plains of the united states was the setting for some of the earliest research in north america into patterns and changes in the character of late pleistocene environments and their effects on contemporary human populations many localities in the region have well stratified records of terminal pleistocene and early holocene human paleoindian activity and past environments these have proven important in debates over the character of the younger dryas chronozone ydc 11 000 10 000 14c bp 12 900 11 700 cal bp in the continental interior this paper reviews the lithostratigraphic record of the ydc on the central and southern great plains and summarizes paleobiological records largely isotopic the goal is to determine if there is any uniformity in the timing character direction and or magnitude of changes in depositional environments or broader geomorphic systems before during or after the ydc in order to address the question of the character of environments through this time the stratigraphic records of the late pleistocene to early holocene transition and in particular the stratigraphic records of the ydc vary through time and space the data clearly show that a host of geomorphic processes produced the terminal pleistocene and early holocene stratigraphic records of the great plains moreover the ydc is not necessarily manifest as a distinct lithostratigraphic or biostratigraphic entity in these different types of deposits and soils the various geomorphic systems of the great plains did not behave synchronously in response to any common climate driver these stratigraphic records reflect local environmental conditions and probably a complex response to the reorganization of mid latitude climates in the terminal pleistocene and early holocene

bedload transport of fine gravel observed by motion picture photography motion pictures taken at duck creek a clear stream 6 5 m wide and 35 cm deep near pinedale wyoming provide detailed quantitative information on both the modes of motion of individual bedload particles and the collective motions of large numbers of them bed shear stress was approximately 6 pa 60 dynes cm 2 which was about twice the threshold for movement of the 4 mm median diameter fine gravel bed material and transport was almost entirely as bedload the displacements of individual particles occurred mainly by rolling of the majority of the particles and saltation of the smallest ones and rarely by brief sliding of large angular ones entrainment was principally by rollover of the larger particles and liftoff of the smaller ones and infrequently by ejection caused by impacts whereas distrainment was primarily by diminution of fluid forces in the case of rolling particles and by collisions with larger bed particles in the case of saltating ones the displacement times averaged about 0 2 0 4 s and generally were much shorter than the intervening repose times the collective motions of the particles were characterized by frequent brief localized random sweep transport events of very high rates of entrainment and transport which in the aggregate transported approximately 70 of the total load moved these events occurred 9 of the time at any particular point of the bed lasted 1 2 s affected areas typically 20 50 cm long by 10 20 cm wide and involved bedload concentrations approximately 10 times greater than background the distances travelled during displacements averaged about 15 times the particle diameter despite the differences in their dominant modes of movement the 8 16 mm particles typically travelled only about 30 slower during displacement than the 2 4 mm ones whose speeds averaged 21 cm s 1 particles starting from the same point not only moved intermittently downstream but also dispersed both longitudinally and transversely with diffusivities of 4 6 and 0 26 cm 2 s 1 respectively the bedload transport rates measured from the films were consistent with those determined conventionally with a bedload sampler the 2 4 mm particles were entrained 6 times faster on finer areas of the bed where 8 16 mm particles covered 6 of the surface area than on coarser ones where they covered 12 even though 2 4 and 4 8 mm particles covered practically the same percentage areas in both cases the 4 8 and 8 16 mm particles in contrast were entrained at the same rates in both cases to within the statistical uncertainty the rates of distrainment balanced the rates of entrainment for all three sizes and were approximately proportional to the corresponding concentrations of bedload

lateglacial and early holocene palaeoenvironmental events in sluggan bog northern ireland comparisons with the greenland ngrip gicc05 event stratigraphy a multi proxy lateglacial environmental record is described from sluggan bog in county antrim northern ireland pollen plant macrofossil charcoal sediment chemistry stable isotope and sedimentological data provide a multi faceted picture of local and regional environmental changes during the transition from the last cold stage to the beginning of the present interglacial and enable a series of distinctive palaeoenvironmental events to be identified a combination of radiometric and ams radiocarbon dates on both humic and humin sediment fractions and on charcoal fragments and plant macrofossils provides one of the most closely constrained radiocarbon timescales for any lateglacial site in the british isles the evidence suggests that an initial period of warm conditions beginning in the sluggan record around 14 2 ka b2k before ad 2000 and when open salix betula woodland was locally present was succeeded first by a heathland phase then by a re establishment of wood and scrub before this was replaced during the later part of the lateglacial woodgrange interstadial by species rich grassland in terms of timing this sequence corresponds very closely to the gi 1e gi 1d gi 1c series of events in the greenland ngrip ice core a short lived betula phase towards the end of the interstadial in the sluggan sequence may reflect the short lived climatic warming of gi 1a although the radiocarbon age model suggests that it occurred prior to that event there is a similar age discrepancy between the two sequences at the end of the interstadial with the onset of the nahanagan younger dryas stadial in sluggan appearing to predate that in ngrip by up to 200 yrs by contrast there is a very close correspondence between the date on the onset of the holocene inferred from the pollen record in sluggan 11 69 ka b2k and the age of the pleistocene holocene boundary 11 7 ka b2k in ngrip while uncertainties remain over the climatic signals in the later interstadial the evidence suggests that during the early and mid interstadial and at the onset of the holocene northern ireland and greenland appear to have been broadly phase locked in their response to hemispherical climate change

reply to blaauw et al boslough daulton gill et al and hardiman et al younger dryas impact proxies in lake cuitzeo mexico blaauw et al 1 take issue with our age depth model for the cuitzeo core they state that no offset for our accelerator mass spectrometry ams 14c dates was quantified that our identification of the cieneguillas tephra is doubtful that we used an outdated calibration model and they object to our rejection of six ams dates in the anomalous zone

sediment connectivity a framework for understanding sediment transfer at multiple scales a major challenge for geomorphologists is to scale up small magnitude processes to produce landscape form yet existing approaches have been found to be severely limited new ways to scale erosion and transfer of sediment are thus needed this paper evaluates the concept of sediment connectivity as a framework for understanding processes involved in sediment transfer across multiple scales we propose that the concept of sediment connectivity can be used to explain the connected transfer of sediment from a source to a sink in a catchment and movement of sediment between different zones within a catchment over hillslopes between hillslopes and channels and within channels using fluvial systems as an example we explore four scenarios of sediment connectivity which represent end members of behaviour from fully linked to fully unlinked hydrological and sediment connectivity sediment travel distance when combined with an entrainment parameter reflecting the frequency magnitude response of the system maps onto these end members providing a coherent conceptual model for the upscaling of erosion predictions this conceptual model could be readily expanded to other process domains to provide a more comprehensive underpinning of landscape evolution models thus further research on the controls and dynamics of travel distances under different modes of transport is fundamental copyright 2014 john wiley sons ltd

discovery of a nanodiamond rich layer in the greenland ice sheet we report the discovery in the greenland ice sheet of a discrete layer of free nanodiamonds nds in very high abundances implying most likely either an unprecedented influx of extraterrestrial et material or a cosmic impact event that occurred after the last glacial episode from that layer we extracted n diamonds and hexagonal diamonds lonsdaleite an accepted et impact indicator at abundances of up to about 5 10 6 times background levels in adjacent younger and older ice the nds in the concentrated layer are rounded suggesting they most likely formed during a cosmic impact through some process similar to carbon vapor deposition or high explosive detonation this morphology has not been reported previously in cosmic material but has been observed in terrestrial impact material this is the first highly enriched discrete layer of nds observed in glacial ice anywhere and its presence indicates that ice caps are important archives of et events of varying magnitudes using a preliminary ice chronology based on oxygen isotopes and dust stratigraphy the nd rich layer appears to be coeval with nd abundance peaks reported at numerous north american sites in a sedimentary layer the younger dryas boundary layer ydb dating to 12 9 0 1 ka however more investigation is needed to confirm this association

effect of postglacial warming seen in high precision temperature log deep into the granites in ne alberta the method how to reconstruct surface temperature history from inversions of precise temperature logs done in wells was pioneered earlier by cermak 1971 and by lachenbruch and marshall 1986 see bodri and cermak 2007 for review and list of references on the subject the method is based on the inversion of stabilized high precision deep borehole temperature logs which are in thermal equilibrium with surrounding rock deep down to some 2 km depth perturbation of the heat flow could be caused by warming since recent glaciations ending some 12 13 kyr ago in canada ritchie 1983 surface temperatures peaked in the holocene optimum 6 7 kyr ago known to be some 1 2 c warmer than recent centuries temperature level kerwin et al 1999 perturbations observed down to 0 1 0 3 km are mainly related to the climate changes of the last 1 2 centuries pollack et al 1998 bodri and cermak 2007 rath et al 2012 on large regional and continental scale all these surface temperature changes influence the subsurface heat flow the method has been applied to reconstruct timing and amplitude of surface temperature change from latest glacial to postglacial climatic history through many areas in eurasia and north america hotchkiss and ingersoll 1934 cermak 1971 kukkonen 1993 kukkonen and safanda 1996 kukkonen et al 1998 mareschal et al 1999 rolandon et al 2003 kukkonen and joeleht 2003 demezhko et al 2007 demezhko and golovanova 2007 majorowicz

conceptual assessment of dis connectivity and its application to the ganga river dispersal system abstract connectivity in river dispersal systems is an important evolving concept and helps in understanding their dynamics in this study the types of connectivity have been defined on the basis of two components namely physical contact and transfer of material based on this four types of connectivity are recognized these are a active connected system b inactive connected system c partially active connected system and d disconnected system connectivity indices have been proposed based on the process understanding of different types of connectivity this conceptual understanding of connectivity has been applied to the ganga dispersal system a large river system results of the connectivity analysis on the ganga dispersal system reveal that different sets of data such as sediment budgets geochemical isotopic data and radiogenic 238 u 234 u 230 th data are noncoherent therefore developing rigorous and well constrained quantitative multidisciplinary data sets is needed to have a better understanding of connectivity at multiple spatio temporal scales in large river dispersal systems this would ultimately help model the dynamics of such systems