a transferable method for the automated grain sizing of river gravels 1 the spatial and temporal resolution of surface grain size characterization is constrained by the limitations of traditional measurement techniques in this paper we present an extremely rapid image processing based procedure for the measurement of exposed fluvial gravels and other coarse grained sediments defining the steps required to minimize the errors in the derived grain size distribution this procedure differs significantly from those used previously it is based around a robust object detection algorithm that produces excellent results on images exhibiting a wide range of sedimentary conditions crucially without any user intervention or site specific parameterization the procedure is tested using a data set comprising 39 images from three rivers with contrasting grain lithology shape roundness and packing configuration and representing a very wide range of textures it is shown to perform more consistently than the best existing automated method achieving a precision equivalent to that obtainable by wolman sampling but taking between one sixth and one twentieth of the time the error in area by number grain size distribution percentiles is typically less than 0 05

influence of late quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont eastern mojave desert california radiocarbon dating of late quaternary deposits and shorelines of lake mojave and cation ratio numerical age dating of stone pavements dorn 1984 on the adjacent soda mountains piedmont provide age constraints for alluvial and eolian deposits these deposits are associated with climatically controlled stands of lake mojave during the past 15 000 yr six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces as well as on soil geomorphic data all but one of these stratigraphic units were deposited in response to time transgressive climatic changes beginning approximately 10 000 yr ago increased eolian flux rates occurred in response to the lowering of lake mojave and a consequent increase in fine sediment availability increased rates of deposition of eolian fines and associated salts influenced pedogenesis stone pavement development and runoff infiltration relations by 1 enhancing mechanical weathering of fan surfaces and hillslopes and 2 forming clay and silt rich surface horizons which decrease infiltration changes in alluvial fan source areas from hillslopes to piedmonts during the holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less permeable soils inferred increased in early to middle holocene monsoonal activity resulted in high magnitude paleo sheetflood events on older fan pavements this runoff triggered piedmont dissection which in turn caused increased sediment availability along channel walls thus runoff infiltration changes during the late quaternary have occurred in response to eolian deposition of fines pedogenesis increased sheetflood activity in the holocene and vegetational changes which are related to many complicated linkages among climatic change lake fluctuations and eolian hillslope and alluvial fan processes

sampling surficial fluvial gravels the precision of size distribution percentile sediments abstract grid by number wolman sampling is commonly used to characterize the texture of surficial fluvial sediments assessments of sampling precision have concentrated on the median grain size but adequate representation of other grain size percentiles is paramount in a number of sedimentological contexts the field effort required to construct percentile sampling distributions by replication is prohibitive and the absence of any general size distribution for fluvial sediments precludes theoretical calculation of percentile standard errors bootstrapping is used in this paper to determine percentile standard errors for large samples from two gravel bar surfaces the improvement of percentile precision with sample size follows the theoretical expectation hence improvement in percentile recision is achieved only at the expense of much greater sampling effort once sample sizes reach about 400 stones however absolute percentile standard errors differ significantly from theoretically derived values of particular interest is the stability of coarser percentile estimates in coarse skewed distributions d95 estimates may be as precise as d50 estimates for a given sample size the sensitivity of the precision of estimated percentiles to distribution shape is examined using synthetic skewed and bimodal grain size distributions the absolute precision of percentile estimates is shown to vary with the grain size distribution of a particular sediment our field results provide a reference for further work

natural responses to quaternary climatic change in the greater nevada test site region u s a abstract many natural processes particularly those that occur at or near the earth s surface e g erosion infiltration soil formation and plant growth are influenced or altered by climatic change migration of hazardous and radioactive contaminants into and through the environment depends on these natural processes climatic fluctuations can affect the nature magnitude and rate of these processes in any long term environmental evaluation of natural processes responses to climatic change must be considered four generalized categories of natural responses to quaternary climatic change are recognized for the greater nevada test site nts region of southern nevada and adjacent california 1 biologic 2 geomorphic 3 hydrologic including surface and subsurface and 4 pedologic diagenetic specific examples that correspond to the four categories illustrate the broad range of complex natural processes that are affected by climatic change these responses dictate the potential effect of climatic change on waste isolation and contaminant transport this effect is being examined by existing and planned environmental restoration and waste management programs within the region regulatory requirements for many of these programs include long term 10 000 year waste isolation because of radiologic components an overview is presented of the slowly growing data base of the complex relationships between climate and natural processes that must be considered in performance and risk assessments for environmental programs in this region limitations in and inconsistencies between various data sets are noted as appropriate in particular better quantified estimates or ranges of estimates of magnitudes and rates are commonly needed for these processes and responses these estimates allow climatic change and related responses to be incorporated explicitly into conceptual and numerical models and into performance and risk assessments of the various environmental restoration and waste management programs within the greater nts region

texture based image segmentation applied to the quanti cation of superficial sand in salmonid river gravels the presence of fine sediment in river gravels is widely recognized as being detrimental to salmonid habitat quality in order to facilitate quantification of sand presence at larger scales this paper presents an application of image processing allowing for rapid and accurate assessments of superficial sand presence in dry exposed fluvial gravels images for the process are acquired with a 35 mm slr film camera and then scanned with a desktop scanner texture based segmentation is then applied to differentiate between sand and clast areas results show that the method is accurate and therefore it offers an alternative to bulk sampling in cases where rapid assessments of sand presence are required copyright 2005 john wiley sons ltd

palynological evidence for early holocene aridity in the southern sierra nevada california sediments of balsam meadow have produced a 11 000 yr pollen record from the southern sierra nevada of california the balsam meadow diagram is divided into three zones 1 the artemisia zone 11 000 7000 yr b p is characterized by percentages of sagebrush artemisia and other nonarboreal pollen higher than can be found in the modern local vegetation vegetation during this interval was probably similar to the modern vegetation on the east slope of the sierra nevada and the climate was drier than that of today 2 pinus pollen exceeded 80 from 7000 to 3000 yr b p in the pinus zone the climate was moister than during the artemisia zone 3 fir abies cupressaceae and oak quercus percentages increased after 3000 yr b p in the abies zone as the modern vegetation at the site developed and the present cool moist climatic regime was established decreased fire frequency after 1200 yr b p is reflected in decreased abundance of macroscopic charcoal and increased concentration of abies magnifica and pinus murrayana needles

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

mass spectrometric 230th 234u 238u dating of the devils hole calcite vein the devils hole calcite vein contains a long term climatic record but requires accurate chronologic control for its interpretation mass spectrometric u series ages for samples from core dh 11 yielded 230 th ages with precisions ranging from less than 1 000 years 2 for samples younger than 140 ka thousands of years ago to less than 50 000 years for the oldest samples 566 ka the 234 u 238 u ages could be determined to a precision of 20 000 years for all ages calcite accumulated continuously from 566 ka until 60 ka at an average rate of 0 7 millimeter per 10 3 years the precise agreement between replicte analyses and the concordance of the 230 th 238 u 234 u 238 u ages for the oldest samples indicate that the dh 11 samples were closed systems and validate the dating technique in general

short duration holocene lakes in the mojave river drainage basin southern california stratigraphic sedimentologic and pedologic studies of beach ridge and lacustrine deposits indicate that up to five times during the holocene shallow lakes covered silver lake playa in southeastern california for periods of years to decades the two youngest lacustrine events at about 390 90 yr b p and 3620 70 yr b p coincide with the early and late neoglacial episodes of north america increasing evidence in recent years from other nonglaciated areas leads us to conclude that the effects of these climatic episodes were much more widespread than previously thought the climate during these episodes was characterized by an increased frequency of winter storms in the southwestern united states causing wetter conditions that affected diverse hyperarid environments in the mojave desert and adjacent regions we propose that this wide areal coverage was caused by large scale winter atmospheric circulation patterns which are probably related to changes in sea surface temperatures and oceanic circulation in the eastern north pacific ocean

the camera and the geomorphologist abstract the methods we use to produce geomorphic data are deeply interwoven with the geomorphic questions we choose to ask and with the geomorphic theories we construct authors have described major changes in the history of geomorphology in terms of theoretical shifts and or social cultural changes but it seems clear that shifts in methodological practices also can produce deep changes in geomorphology as a whole the camera has had a long illustrious and complex history as a geomorphic tool and as such is useful for assessing larger geomorphological concerns and themes the camera is also a symbol of the ongoing revolution in geomorphology from a data poor to a data rich subject this revolution is built upon many methodological changes and it has had many side effects the interrelated history of cameras and fluvial geomorphology provides an illuminating case study in past and present changes in the geomorphic sciences some past geomorphic practices such as using photos as descriptive evidence for verifying geomorphic theory remain as important approaches today other camera based practices have dwindled to some degree such as the production of large area topographic maps through traditional aerial photogrammetry which have been overtaken by alternative methods such as lidar and interferometric radar and newer camera based techniques such as structure from motion photogrammetry are at the heart of the recent democratization of geomorphic data as the modern data revolution progresses it is important to ask questions such as who has been part of the data revolution and what have been their motivations and have winners and losers been produced as part of the data revolution not all effects of the data revolution have been completely positive many geomorphologists feel overwhelmed by big data expectations and methodological concerns from a philosophy of science perspective the moves toward population like geomorphic data have strained normal inductive inference procedures and recent research has brought to light inferential alternatives such as advanced data mining and the hypothetico deductive approach even so most current analytical techniques appear to be lagging behind the newly introduced big data producing new wine in old bottles new data for old analyses beyond pure geomorphic research the camera and its derivatives are also part of profound shifts in educational and outreach expectations and practices clearly the data revolution in geomorphology is still in its infancy and much of that revolution has been wrought by the humble camera

information on grain sizes in gravel bed rivers by automated image analysis abstract the time required in the field to characterize textural variation over gravel surfaces can be reduced by taking vertical photographs for subsequent image analysis we present modified edge detection algorithms which combine edge seeding with an image porosity concept and partial watershed segmentation the methods allow quick reliable and operator independent size analysis from a wide range of vertical bed surface images they are tested using 24 naturally lit images of an exposed river bed with mixed lithologies and partial burial of gravel by sand grain size percentiles derived by automated image analysis correlate closely with those from manual image analysis with only small and consistent degrees of bias they also correlate well with percentiles from field measurements with substantial bias which however is consistent so that it can be corrected for leaving a residual scatter of 0 25 where log2 mm over a wide range of bed conditions the bias depends somewhat on sand cover and the biggest residual discrepancies are for tail percentiles

atmospheric circulation during holocene lake stands in the mojave desert evidence of regional climate change it is commonly thought that the climate conditions that supported lakes over a period of years in the mojave desert in southern california only existed before 8 000 yr bp and that the environment has been arid since1 2 here we look at a drill core in the silver lake playa at the terminus of the mojave river and find holocene lake deposits which indicate that shallow lakes existed for at least a few decades these deposits were radiocarbon dated at 3620 70 and 390 90 yr bp corresponding to the early neo glacial and the little ice age respectively3 to identify the conditions necessary to produce these holocene lake events we have examined the modern climate and hydrological patterns that produce ephemeral lakes in this usually arid watershed available data indicate that there is a link between anomalous winter atmospheric conditions over the north pacific and mojave river floods that produced ephemeral lakes in the silver lake playa and that the mojave river filters out small to medium floods and allows only the extreme floods to reach the terminal playa and leave a record of the anomalous conditions we suggest that the late holocene lakes may have resulted from persistent similar atmospheric circulation patterns and winter floods

sedinet a configurable deep learning model for mixed qualitative and quantitative optical granulometry i describe a configurable machine learning framework to estimate a suite of continuous and categorical sedimentological properties from photographic imagery of sediment and to exemplify how machine learning can be a powerful and flexible tool for automated quantitative and qualitative measurements from remotely sensed imagery the model is tested on a large dataset consisting of 400 images and associated detailed label data the data are from a much wider sedimentological spectrum than previous optical granulometry studies consisting of both well and poorly sorted sediment terrigenous carbonate and volcaniclastic sands and gravels and their mixtures and grain sizes spanning over two orders of magnitude i demonstrate the model framework by configuring it in several ways to estimate two categories describing grain shape and population respectively and nine numeric grain size percentiles in pixels from a single input image grain size is then recovered using the physical size of a pixel finally i demonstrate that the model can be configured and trained to estimate equivalent sieve diameters directly from image features without the need for area to mass conversion formulas and without even knowing the scale of one pixel thus it is the only optical granulometry method proposed to date that does not necessarily require image scaling the flexibility of the model framework should facilitate numerous application in the spatio temporal monitoring of the grain size distribution shape mineralogy and other quantities of interest of sedimentary deposits as they evolve as well as other texture based proxies extracted from remotely sensed imagery

cause and implications of rock varnish microchemical laminations rock varnish is a dark coating composed mostly of clays and manganese and iron oxides1 that accretes on rock surfaces in all terrestrial environments2 perry and adams3 first observed micron scale manganese rich and manganese poor relatively iron rich layers in varnish and proposed that these may be related to unspecified environmental changes electron microprobe analyses reported here suggest that mn fe ratios vary systematically with depth in varnishes on k ar dated volcanic rocks from the coso and cima volcanic fields eastern california and on talus flatirons in the negev desert israel these microchemical laminations probably reflect past fluctuations in the level of aeolian alkalinity and possibly climatic change this new indicator of terrestrial environmental change may be of importance to research on geomorphology archaeology palaeoclimatology and quaternary studies in arid environments

sedimentological characterization of antarctic moraines using uavs and structure from motion photogrammetry in glacial environments particle size analysis of moraines provides insights into clast origin transport history depositional mechanism and processes of reworking traditional methods for grain size classification are labour intensive physically intrusive and are limited to patch scale 1m2 observation we develop emerging high resolution ground and unmanned aerial vehicle based structure from motion uav sfm photogrammetry to recover grain size information across an moraine surface in the heritage range antarctica sfm data products were benchmarked against equivalent datasets acquired using terrestrial laser scanning and were found to be accurate to within 1 7 and 50mm for patch and site scale modelling respectively grain size distributions were obtained through digital grain classification or photo sieving of patch scale sfm orthoimagery photo sieved distributions were accurate to 2mm compared to control distributions derived from dry sieving a relationship between patch scale median grain size and the standard deviation of local surface elevations was applied to a site scale uav sfm model to facilitate upscaling and the production of a spatially continuous map of the median grain size across a 0 3 km2 area of moraine this highly automated workflow for site scale sedimentological characterization eliminates much of the subjectivity associated with traditional methods and forms a sound basis for subsequent glaciological process interpretation and analysis

quantification of fluvial wood using uavs and structure from motion abstract fluvial wood is recognized as one of the key elements of riverine environments its importance role and potential related risks are widely considered and analysed still to characterize and measure wood elements in the field a large investment in terms of time and cost is normally required these activities are often carried out in complex and potentially dangerous environments in this context the use of unmanned aerial vehicles uavs provides a powerful alternative technology to traditional approaches in this work we propose a novel approach combining uav surveys with structure from motion sfm photogrammetry to quantify fluvial wood the proposed methodology was tested in the blanco river southern chile which was severely affected by the chaiten volcanic eruption in 2008 that delivered large quantities of wood to the channel an area of about 1 2 ha was surveyed using uav and field measurements a comparative analysis between the traditional field based and uav surveys was carried out to quantify the accuracy of the latter and to better understand the strengths and potential limitations of the proposed methodology results showed that differences between the two methodologies were about 13 for both single large wood elements and wood jam volumes moreover a sensitivity analysis applied to 12 different scenarios allowed us to define the measurement precision achieved using the orthomosaics and dems our results showed that the proposed approach is effective in terms of field and laboratory activities saving around half the time this study demonstrates that the combination of uav and sfm can yield accurate results covering large areas in less time and providing a powerful tool for performing repeated surveys and thus acquiring relevant information for wood budgets and wood dynamics in rivers

catchment scale mapping of surface grain size in gravel bed rivers using airborne digital imagery 1 this study develops and assesses two methods for estimating median surface grain sizes using digital image processing from centimeter resolution airborne imagery digital images with ground resolutions of 3 cm and 10 cm were combined with field calibration measurements to establish predictive relationships for grain size as a function of both local image texture and local image semivariance independently acquired grain size data were then used to assess the algorithm performance results showed that for the 3 cm imagery both local image semivariance and texture are highly sensitive to median grain size with semivariance being a better predictor than image texture however in the case of 10 cm imagery sensitivity of image semivariance and texture to grain size was poor and this scale of imagery was found to be unsuitable for grain size estimation this study therefore demonstrates that local image properties in very high resolution digital imagery allow for automated grain size measurement using image processing and remote sensing methods

a 250 000 year climatic record from great basin vein calcite implications for milankovitch theory a continuous record of oxygen 18 18o variations in the continental hydrosphere during the middle to late pleistocene has been obtained from a uranium series dated calcitic vein in the southern great basin the vein was deposited from ground water that moved through devils hole an open fault zone at ash meadows nevada between 50 and 310 ka thousand years ago the configuration of the 18o versus time curve closely resembles the marine and antarctic ice core vostok 18o curves however the u th dates indicate that the last interglacial stage marine oxygen isotope stage 5 began before 147 3 ka at least 17 000 years earlier than indicated by the marine 18o record and 7 000 years earlier than indicated by the less well dated antarctic 18o record this discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine 18o chronology may need revision and that orbital forcing may not be the principal cause of the pleistocene ice ages

geomorphological effectiveness of floods to rework gravel bars insight from hyperscale topography and hydraulic modelling bars are key morphological units in river systems fashioning the sediment regime and bedload transport processes within a reach reworking of these features underpins channel adjustment at larger scales thereby acting as a key determinant of channel stability despite their importance to channel evolution few investigations have acquired spatially continuous data on bar morphology and sediment size to investigate bar reworking to this end four bars along a 10 km reach of a wandering gravel bed river were surveyed with terrestrial laser scanning tls capturing downstream changes in slope bed material size and channel planform detrended standard deviations z were extracted from tls point clouds and correlated to underlying physically measured median grain size d50 across a greater range of z values than have hitherto been reported the resulting linear regression model was used to create a 1 m resolution median grain size map a fusion of airborne lidar and optical empirical bathymetric mapping was used to develop reach scale digital elevation models dems for rapid two dimensional hydraulic modelling using jflow software the ratio of dimensionless shear stress over critical shear stress was calculated for each raster cell to calculate the effectiveness of a range of flood events 2 33 100 year recurrence intervals to entrain sediment and rework bar units results show that multiple bar forming discharges exist whereby frequent flood flows rework tail and back channel areas whilst much larger less frequent floods are required to mobilise the coarser sediment fraction on bar heads valley confinement is shown to exert a primary influence on patterns of bar reworking historical aerial photography hyperscale dems and hydraulic modelling are used to explain channel adjustment at the reach scale the proportion of the bar comprised of more frequently entrained units tail back channel supra platform relative to more static units bar head exerts a direct influence upon geomorphic sensitivity

terrestrial structure from motion spatial error analysis of roughness and morphology structure from motion sfm photogrammetry is rapidly becoming a key tool for morphological characterisation and change detection of the earth surface this paper demonstrates the use of terrestrial structure from motion tsfm photogrammetry to acquire morphology and roughness data at the reach scale in an upland gravel bed river we quantify 1 spatially distributed error in tsfm derived digital elevation models dems and 2 identify differences in roughness populations acquired from tsfm photogrammetry versus tls we identify an association between local topographic variation and error in the tsfm dem on flatter surfaces e g bar and terrace surfaces the difference between the tsfm and tls dems are generally less than 0 1 m however in areas of high topographic variability 0 4 m such as berm or terrace edges differences between the tsfm and tls dems can be up to 1 m our results suggest that grain roughness estimates from the tsfm point cloud generate values twice those derived from the tls point cloud on coarse berm areas and up to four fold those derived from the tls point cloud over finer gravel bar surfaces this finding has implications when using sfm data to derive roughness metrics for hydrodynamic modelling despite the use of standard filtering procedures noise pertains in the sfm dem and the time required for its reduction might partially outweigh the survey efficiency using sfm therefore caution is needed when sfm surveys are employed for the assessment of surface roughness at a reach scale

packrat midden evidence of late quaternary vegetation change in the white mountains california nevada packrat neotoma spp middens from the white mountains indicate climatic and plant community conditions for the last 19 000 yr during full glacial times ca 19 000 yr b p and at the pleistocene holocene boundary juniper woodlands were 600 m lower in elevation than at present midden assemblages and stable isotope data suggest lower temperatures and increased precipitation relative to the present into the early holocene two early holocene middens ca 8000 yr b p from lower elevations of the white mountains contain fragments of pinyon pine and indicate that both pinyon and juniper grew at a site that today supports only a pinyon woodland two middle holocene middens ca 5000 yr b p indicate that there was an upward migration of pinyon juniper woodlands along a high elevation ecotone but little change in the middle of the pinyon juniper woodland middens from the late holocene indicate that present day plant communities were in place by ca 2000 yr b p or before

modeling river bed morphology roughness and surface sedimentology using high resolution terrestrial laser scanning 1 recent advances in technology have revolutionized the acquisition of topographic data offering new perspectives on the structure and morphology of the earth s surface these developments have had a profound impact on the practice of river science creating a step change in the dimensionality resolution and precision of fluvial terrain models the emergence of hyperscale survey methods including structure from motion photogrammetry and terrestrial laser scanning tls now presents the opportunity to acquire 3 d point cloud data that capture grain scale detail over reach scale extents translating these data into geomorphologically relevant products is however not straightforward unlike traditional survey methods tls acquires observations rapidly and automatically but unselectively this results in considerable noise associated with backscatter from vegetation and other artifacts moreover the large data volumes are difficult to visualize require very high capacity storage and are not incorporated readily into gis and simulation models in this paper we analyze the geomorphological integrity of multiscale terrain models rendered from a tls survey of the braided river feshie scotland these raster terrain models are generated using a new computationally efficient geospatial toolkit the topographic point cloud analysis toolkit topcat this performs an intelligent decimation of point cloud data into a set of 2 5 d terrain models that retain information on the high frequency subgrid topography as the moments of the locally detrended elevation distribution the results quantify the degree of terrain generalization inherent in conventional fluvial dems and illustrate how subgrid topographic statistics can be used to map the spatial pattern of particle size grain roughness and sedimentary facies at the reach scale

estimation of grain size distributions and associated parameters from digital images of sediment abstract a new technique to estimate the grain size distribution gsd from a digital image of sediment is proposed advancing the applicability of a suite of sedimentary look up catalogue approaches originated by rubin rubin d m 2004 a simple autocorrelation algorithm for determining grain size from digital images of sediment journal of sedimentary research 74 1 160 165 the outputs of an automated procedure to estimate the gsd from digital images of sediment are examined with reference to the distributions obtained from both manually sieving the corresponding sediment samples and axial measurements made on the grains in the images measures of grain size obtained from the imaging procedure correlate very well with grain size measures derived from both the number frequency and mass frequency curve as expected the gsd obtained from the new automated approach based on kernel density compared better with point counts because of a shared two rather than three dimensionality the gsd shape is not always mimicked exactly however the percentiles obtained from the cumulative gsd compare well with those from sieved distributions which allow for the first time computation of graphical sorting and skewness from digital images of sediment which are accurate reflections of those measures obtained for point count and sieved samples the new approach allows for realistic gsds from which the residual can be computed thus a numerical criterion upon which the grain size distribution from an image can be accepted or rejected finally a method is presented whereby two dimensional autocorrelogram fields are derived from image power spectra ellipsoids are fitted to isolines of autocorrelation coefficients and from this the dominant axial lengths and orientation of these isolines which could facilitate computation of major and minor axis lengths of grains in sample images as well as their dominant orientation in turn this could allow for parameterisation of axial ratios for parameterisation of 2d shape such analysis is completely automated rapid and non intrusive

the alkali element and boron geochemistry of the escanaba trough sediment hosted hydrothermal system a suite of conjugate pore fluid and sediment samples were collected during leg 169 of the odp from within the clastic sedimentary sequences which host massive sulphides at central hill escanaba trough odp site 1038 we report the alkali element and boron and li and b isotope data for these samples relative to a reference site site 1037 located outside the zone of high heat flow pore fluids from site 1038 show a wide variation in cl 300 800 mm and have far higher concentrations of li up to 6 2 mm b up to 9 7 mm cs up to 5 0 m and rb up to 97 m we show that the pore fluids are derived from hydrothermal circulation that has extended into the basement oceanic crust with input of the alkali elements and b as the rising hydrothermal fluids interact geochemically with the overlying clastic sediments there is however no marked depletion of these elements in the conjugate sediments suggesting that there has been advective transport of fluids away from the primary hydrothermal reaction site this is supported by modelling of the li and b isotope systematics of the pore fluids which shows that they record extensive formation of secondary minerals during cooling of the fluids from 350 to 20 c precipitation of metal rich sulphides would have occurred prior to the formation of these minerals thus the pore fluid li and b isotope data can place important constraints on the locus of sulphide deposition beneath the seafloor at escanaba

scanning electron microscope method for rock varnish dating rock varnish coatings on cobbles from geomorphic surfaces and exposed deposits in arid environments are an effective medium for dating over a time range of several thousand to a few million years a new analytical method for dating of rock varnish is presented wherein the varnish cation ratio vcr is determined by a scanning electron microscope sem equipped with an energy dispersive x ray analyzer edax the experimental sem method is a nondestructive technique that has several potential advantages over the original method of analysis described by r i dorn that uses particle induced x ray emission pixe of varnish scraped from rock surfaces the sem method can potentially eliminate analytical errors due to contamination from rock substrate because variations in varnish thickness and irregularities on the substrate surface are examined before cation ratios are determined because varnish surfaces remain intact varnish sites that yield anomalous results may be reanalyzed or verified in addition the general accessibility of scanning electron microscopes will make rock varnish dating more widely available for use in quaternary studies cation ratios were calculated for rock varnish from espanola basin new mexico and the yucca mountain region nevada and were used to construct rock varnish dating curves for these areas

discharge of hydrothermal fluids through sediment at the escanaba trough gorda ridge odp leg 169 assessing the effects on the rock magnetic signal an integrated rock magnetic and multivariate statistical analysis of a suite of sediment samples recovered from odp sites 1037 and 1038 leg 169 escanaba trough gorda ridge spreading center ne pacific ocean has been carried out to assess the use of the sediment magnetic signal as a tracer of post depositional alteration related to the discharge of hydrothermal fluids through these sediments the uppermost above 40 mbsf section of three separate holes holes 1037 b 1038 i and 1038 g was sampled previous sedimentological and geochemical studies indicated that these holes represent a transect from unaltered to strongly hydrothermally influenced sediments analysis of nrm arm anisotropy of magnetic susceptibility ams hysteresis parameters and low temperature magnetic properties suggest increasing alteration of the magnetic minerals with increasing circulation of hydrothermal circulation of fluids fuzzy c means clustering combined with non linear mapping yields a more elaborate picture because similar alteration groupings at different holes can be compared at hole 1037 b a sedimentary reference site drilled away from the area of high heat flow the rock magnetic signal is a sensitive record of changes in detrital inputs magnetite and some monoclinic pyrrhotite are detected the detrital magnetic signal is still apparent at intermediate hole 1038 i but cluster analysis detects an increasing hydrothermal influence on the magnetomineralogy in the lower part of the hole strong hydrothermal alteration at hole 1038 g results in a complete loss of the detrital diagenetic magnetic signal which is replaced by a much weaker hydrothermal signal composed of monoclinic pyrrhotite and pyrite the alteration of the magnetic signal is not restricted to the uppermost few meters of the sediment column and the magnetic properties of the sediment can be used to trace even minor alterations of marine sediments related to the lateral and vertical advection of hydrothermal fluids which may easily be overlooked by more traditional methods fl 2000 elsevier science b v all rights reserved

evaluating short term morphological changes in a gravel bed braided river using terrestrial laser scanner abstract braided rivers are dynamic and complex environments shaped by the balance of the flow and sediment regimes and by the influence of the riparian vegetation and disturbances such as floods in particular the balance between sediment supply and transport capacity can determine the morphological evolution of a river for instance aggrading and widening trends are distinctive of reaches where sediment supply is higher than transport capacity in contrast incising and narrowing tendencies are dominant the aim of the present study is to analyze the short term morphological dynamics and the processes of erosion and sediment deposition along a small reach of a relatively unimpacted gravel bed braided river tagliamento river northeast italy using a terrestrial laser scanner tls the study area is around 23 ha and has been surveyed before after two periods with relevant flood events two of which were higher than the bankfull level and occurred between september 2010 and september 2011 the very high point clouds density allowed us to derive three high resolution digital elevation models dems with 0 125 0 125 m pixel size scan data cloud merging was achieved with an overall high degree of accuracy and resolution subcentimeter topographic data were more accurate for exposed surfaces than those collected in wet areas a detailed net of dgps control points allowed us to verify the high quality of the dems derived from the surveys rmse of about 5 cm two dems of difference dod were computed revealing different and consistent episodes of erosion and deposition within the analyzed area and changes in morphology of channel and bars could also be detected such as bar edge accretion and bank erosion demonstrating a strong dynamicity of the tagliamento river moreover a very detailed estimation of the surface roughness in the study area has been carried out permitting a large scale analysis of the roughness values distribution the results of the analysis on the tls collected data show that along a river with a high natural character i e tagliamento river the dynamic processes are also common during low magnitude events

deep sea sedimentary record of the late wisconsin cataclysmic floods from the columbia river new results from ocean drilling program site 1037 and u s geological survey high resolution seismic reflection profiles confirm the great thickness fast deposition rate distant source and convolute path of turbidites that fill the escanaba trough the rift valley of the southernmost segment of the gorda ridge accelerator mass spectrometry 14 c measurements provide the first direct dating of the escanaba trough turbidites demonstrating an average deposition rate faster than 10 m k y between 32 and 11 ka and as fast as 15 m k y during the oxygen isotope stage 2 lowstand in the upper 60 m of sediment the petrology of turbidite sand beds which are as much as 12 m thick show that the dominant source for the turbidites is from the columbia river which is more than 800 km to the north rather than from the much closer rivers of northern california new high resolution seismic reflection profiles show that except for areas of very recent volcanism the entire escanaba trough below 3200 m water depth is floored by the turbidite sequence that was cored in the upper 60 m at site 1037b the ages of the upper 120 m of turbidites correspond with the ages of channeled scabland deposits associated with latest quaternary jokulhlaups from glacial lake missoula the age and source characteristics suggest that these megaturbidite beds in escanaba trough are most likely deposits formed by hyperpycnally generated turbidity currents as the largest of the lake missoula floods entered the sea

late quaternary environments in ruby valley nevada abstract palynological data from sediment cores from the ruby marshes provide a record of environmental and climatic changes over the last 40 000 yr the modern marsh waters are fresh but no deeper than 3 m a shallow saline lake occupied this basin during the middle wisconsin followed by fresh and perhaps deep waters by 18 000 to 15 000 yr b p no sediments were recovered for the period between 15 000 and 11 000 yr b p possibly due to lake desiccation by 10 800 yr b p a fresh water lake was again present and deeper than modern conditions lasted until 6800 yr b p the middle holocene was characterized by very shallow water and perhaps complete desiccation the marsh system deepened after 4700 yr b p and fresh water conditions persisted until modern times vegetation changes in ruby valley were more gradual than those seen in the paleolimno logical record sagebrush steppe was more widespread than at present through the late pleistocene and early holocene giving way somewhat to expanded shadscale vegetation between 8500 and 6800 yr b p shadscale steppe contracted by 4000 yr b p but had greater than modern coverage until 1000 to 500 yr ago pinyon juniper woodland was established in the southern ruby mountains by 4700 yr b p

a simple autocorrelation algorithm for determining grain size from digital images of sediment abstract autocorrelation between pixels in digital images of sediment can be used to measure average grain size of sediment on the bed grain size distribution of bed sediment and vertical profiles in grain size in a cross sectional image through a bed the technique is less sensitive than traditional laboratory analyses to tails of a grain size distribution but it offers substantial other advantages it is 100 times as fast it is ideal for sampling surficial sediment the part that interacts with a flow it can determine vertical profiles in grain size on a scale finer than can be sampled physically and it can be used in the field to provide almost real time grain size analysis the technique can be applied to digital images obtained using any source with sufficient resolution including digital cameras digital video or underwater digital microscopes for real time grain size mapping of the bed

making riverscapes real abstract the structure and function of rivers have long been characterized either by 1 qualitative models such as the river continuum concept or serial discontinuity concept which paint broad descriptive portraits of how river habitats and communities vary or 2 quantitative models such as downstream hydraulic geometry which rely on a limited number of measurements spread widely throughout a river basin in contrast authors such as fausch et al 2002 and wiens 2002 proposed applying existing quantitative spatially comprehensive ecology and landscape ecology methods to rivers this new framework for river sciences which preserves variability and spatial relationships is called a riverine landscape or a riverscape application of this riverscape concept requires information on the spatial distribution of organism scale habitats throughout entire river systems this article examines the ways in which recent technical and methodological developments can allow us to quantitatively implement and realize the riverscape concept using 3 cm true color aerial photos and 5 m resolution elevation data from the river tromie scotland we apply the newly developed fluvial information system which integrates a suite of cutting edge high resolution remote sensing methods in a spatially explicit framework this new integrated approach allows for the extraction of primary fluvial variables such as width depth particle size and elevation from these first order variables we derive second order geomorphic and hydraulic variables including velocity stream power froude number and shear stress channel slope can be approximated from available topographic data based on these first and second order variables we produce riverscape metrics that begin to explore how geomorphic structures may influence river habitats including connectivity patchiness of habitat and habitat distributions the results show a complex interplay of geomorphic variable and habitat patchiness that is not predicted by existing fluvial theory riverscapes thus challenge the existing understanding of how rivers structure themselves and will force development of new paradigms

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

magnetic transition at 30 34 kelvin in pyrrhotite insight into a widespread occurrence of this mineral in rocks abstract a characteristic magnetic transition at 30 34 k is shown to provide a powerful tool for the identification of pyrrhotite with concentration down to 10 ppm through the same low temperature techniques as applied to magnetite and hematite extended down to liquid helium temperature a review of rock magnetic and petrological data on pyrrhotite suggests that this mineral should be considered as a major carrier of paleomatnetic signals unblocking temperature up to 350 c and extreme resistance against af may be encountered in fine grained pyrrhotite

influences of eolian and pedogenic processes on the origin and evolution of desert pavements well developed desert pavements are present above eolian deposits that mantle flows of the cima volcanic field located in the mojave desert california soil stratigraphic data and geochemical data demonstrate that eolian and pedogenic processes play major roles in the evolution of these pavements eolian dust 1 accelerates mechanical fragmentation of flow rock providing the source material for pavements and 2 accumulates slowly below basaltic colluvium in flow depressions eventually promoting development of cumulate soils below the evolving stone pavement an increase in dust flux during the holocene has raised ancient pleistocene pavements as much as 20 cm above the former land surface the results of our studies demonstrate for the first time that most desert pavements do not form by deflation by overland flow or by upward migration of stones through a slowly formed clayey argillic horizon desert pavements are born and maintained at the surface

transferable wavelet method for grain size distribution from images of sediment surfaces and thin sections and other natural granular patterns in images of sedimentary or granular material or simulations of binary two phase granular media in which the individual grains are resolved the complete size distribution of apparent grain axes is well approximated by the global power spectral density function derived using a morlet wavelet this approach overcomes many limitations of previous automated methods for estimating the grain size distribution from images all of which rely on either identification and segmentation of individual grains calibration and or relatively large sample sizes the new method presented here is tested using i various types of simulations of two phase media with a size distribution with and without preferred orientation ii 300 sample images drawn from 46 populations of sands and gravels from around the world displaying a wide variability in origin biogenic and mineralogical size surface texture and shape iii petrographic thin section samples from nine populations of sedimentary rock iv high resolution scans of marine sediment cores and v non sedimentary natural granular patterns including sea ice and patterned ground the grain size distribution obtained is equivalent to the distribution of apparent intermediate grain diameters grid by number style for images containing sufficient well resolved grains root mean square errors are within tens of percent for percentiles across the entire grain size distribution as such this method is the first of its type which is completely transferable unmodified without calibration for both consolidated and unconsolidated sediment isotropic and anisotropic two phase media and even non sedimentary granular patterns the success of the wavelet approach is due in part to it quantifying both spectral and spatial information from the sediment image simultaneously something which no previously developed technique is able to do

a revised chronology for the last pleistocene lake cycle in the central lahontan basin radiocarbon dates of plant materials from packrat middens in caves below the elevation of the last high stand of pleistocene lake lahontan in conjunction with radiocarbon dates of ancient archaeological materials provide evidence that the last high stand terminated before 12 070 yr b p this new information suggests that the last major fluctuation in the level of lake lahontan was approximately synchronous with those of lakes bonneville and russell and that these three lakes probably responded contemporaneously to the same regional paleoclimatic changes

chronology of expansion and contraction of four great basin lake systems during the past 35 000 years abstract during the past 35 000 years lake bonneville lake russell and lake searles underwent a major period of lake level change the lakes were at moderate levels or dry at the beginning of the period and seem to have achieved highstands between about 15 000 and 13 500 yr b p the rise of lake lahontan was gradual but not continuous in part because of topographic constraints intrabasin spill lake lahontan also had an oscillation in lake level at 15 500 yr b p radiocarbon age estimations for materials that were deposited in the lake basins indicate that lake bonneville rose more or less gradually from 32 000 yr b p and had major oscillations in level between 23 000 and 21 000 yr b p and between 15 250 and 14 500 yr b p lake russell and lake searles had several major oscillations in lake level between 35 000 and 14 000 yr b p the timing and exact magnitude of the oscillations are difficult to decipher but both lakes may have achieved multiple highstand states all four lakes may have had nearly synchronous recessions between about 14 000 and 13 500 yr b p after the recessions the lakes seem to have temporarily stabilized or experienced a minor increase in size between about 11 500 and 10 000 yr b p these data provide circumstantial evidence that the younger dryas event affected climate on at least a hemispheric scale during the holocene the four lakes remained at low levels and small oscillations in lake level occurred an important aspect of the lake level data is the accompanying expansion of lake surface area at the time of the last highstand lake bonneville and lake lahontan had surface areas about 10 times larger than their mean historical reconstructed areas whereas lake russell and lake searles had surface areas about 5 times larger than their mean historical reconstructed areas differences in the records of effective wetness may have been due to the locations of the basins relative to the position of the jetstream or they may have resulted from lake atmosphere feedback processes

debris flow dominance of alluvial fans masked by runoff reworking and weathering arid alluvial fan aggradation is highly episodic and fans often comprise active and inactive sectors hence the morphology and texture of fan surfaces are partly determined by secondary processes of weathering and erosion in addition to primary processes of aggradation this introduces considerable uncertainty in the identification of formative processes of terrestrial and martian fans from aerial and satellite imagery the objectives of this study are i to develop a model to describe the sedimentological and morphological evolution of inactive fan surfaces in arid settings and ii to assess the relative importance of primary processes of aggradation and secondary processes of weathering and reworking for surface morphology and sedimentology and for the stratigraphic record we studied an alluvial fan characterized by a recently active sector and a long abandoned inactive sector along the coast of the hyperarid atacama desert here rates of primary geomorphic activity are exceptionally low because of extreme aridity while weathering rates are relatively high because of the effects of coastal fogs long term processes of fan aggradation and reworking were determined through sedimentological facies analysis of stratigraphic sections ground surveys for textural and morphological patterns at the fan surface were integrated with remote sensing by an unmanned airborne vehicle uav discharges and sediment transport capacities were calculated to estimate the efficiency of secondary runoff in reshaping the inactive fan sector stratigraphic sections reveal that the fan was dominantly aggraded by debris flows whereas surface morphology is dominated by debris flow signatures in the active sector and by weathering and runoff on the inactive sector on the latter rapid particle breakdown prevents the formation of a coarse desert pavement furthermore relatively frequent local runoff events erode proximal debris flow channels on the inactive sector to form local lag deposits and accumulate fine sediment in low gradient distal channels forming a well developed drainage pattern that would suggest a runoff origin from aerial images nevertheless reworking is very superficial and barely preserved in the stratigraphic record this implies that fans on earth and mars that formed dominantly by sporadic mass flows may be masked by a surface morphology related to other processes

high resolution grain size characterisation of gravel bars using imagery analysis and geo statistics abstract the scarcity of grain size data from gravel bed rivers has traditionally hindered hydraulic sediment transport and river habitat studies a new remote sensing methodology to estimate grain size distribution is presented it combines textural digital images of the riverbed at 1 1000 and 1 40 scales with grain size sampling it was applied to a 12 km reach of the isabena river central pyrenees ne spain first textural patterns for each grain size range were obtained selecting the most closely related texture variables including the use of semivariograms second multiple linear regression equations were derived from the textural variables to estimate each value of the grain size distribution the highest correlation values r 2 were obtained from the central part of the distribution d 50 with a rms error of 12 7 finally new multiple linear regression equations to estimate the d 50 and d 84 were obtained from 1 1000 images and four textural variables these were used to derive d 50 and d 84 maps of the riverbed re sampled at a resolution of 1 5 m pixels with rms estimation errors of 26 and 32 respectively downstream change in grain size is also well reproduced by the method the mean d 50 of 72 and 32 mm were estimated in the upper and the lower reaches of the river respectively the methodology shows great potential for application the relation between the spatial resolution of the images and the mean grain size of the riverbed sediment being the main issue for future development

subaerial gravel size measurement using topographic data derived from a uav sfm approach fluvial grain size plays a fundamental role in determining the condition and availability of aquatic habitats remote sensing provides rapid and objective methods of quantifying fluvial grain size and typically provide coarse grain size outputs c 1m at the catchment scale up to 80km channel lengths or fine resolution outputs c 1mm at the patch scale c 1m2 recently drone based approaches have started to fill the gap between these scales providing hyperspatial resolution data 10cm over reaches up to a few hundred metres in length this mesoscale is of importance to habitat assessments and is aligned with the ideals of the riverscape concept most drone based grain size measurement approaches use textural variables computed from drone orthoimagery to date however no published works provide quantitative evidence of the success of this approach despite significant differences in platform stability and the image quality obtained by manned aircraft versus drones with interest in drone surveys growing rapidly such error quantification is essential for making reliable evidence based recommendations about the suitability of drones for routine management of fluvial environments here we provide an initial assessment of the accuracy and precision of grain size estimates produced using two different drone based methods 1 the image textural variable negative entropy and 2 the roughness of point clouds derived from drone imagery processed using structure from motion photogrammetry data is collected from a small gravel bed river in cumbria uk results from jack knife analyses show that the point cloud roughness method gives more accurate and precise measures of grain size at this site as indicated by the mean 0 0002m and standard deviation 0 0184m of residual errors however both methods struggle to provide grain size measures with sub centimetre precision we suggest that blur within the drone imagery prevents better precision resulting from an inadequate camera gimbal

in situ characterization of grain scale fluvial morphology using terrestrial laser scanning the grain scale morphology of fluvial sediments is an important control on the character and dynamics of river systems however current understanding of its role is limited by the difficulties of robustly quantifying field surface morphology terrestrial laser scanning tls offers a new methodology for the rapid acquisition of high resolution and high precision surface elevation data from in situ sediments to date most environmental and fluvial applications of tls have focused on large scale systems capturing macroscale morphologies application of this new technology at scales necessary to characterize the complexity of grain scale fluvial sediments therefore requires a robust assessment of the quality and sources of errors in close range tls data this paper describes both laboratory and field experiments designed to evaluate close range tls for sedimentological applications and to develop protocols for data acquisition in the former controlled experiments comprising high resolution scans of white grey and black planes and a sphere were used to quantify the magnitude and source of three dimensional 3d point errors resulting from a combination of surface geometry reflectivity effects and inherent instrument precision subsequently a methodology for the collection and processing of grain scale tls data is described through an application to a coarse grained gravel system the river feshie d50 32 to 63 mm this stepwise strategy incorporates averaging repeat scans and filtering scan artefact and non surface points using local 3d search algorithms the sensitivity of the results to the filter parameter values are assessed by careful internal validation of digital terrain models dtms created from the resulting point cloud data the transferability of this methodology is assessed through application to a second river bury green brook dominated by finer gravel d50 18 to 33 mm the factor limiting the resolution of dtms created from this second dataset was found to be the relative sizes of the laser footprint and smallest grains copyright 2009 john wiley sons ltd

grain size information from the statistical properties of digital images of sediment abstract the autocorrelation technique for estimating grain size from digital images ofsand beds has been extended and validated for use on coarse sand 0ae7 mm and gravel up to 20 mm a number of aspects of the technique have beenexplored and some potential improvements suggested autocorrelation is justone suitable statistical method sensitive to the grain size of sediment in digitalimages four additional techniques are presented and their relative meritsdiscussed a collective suite of techniques applicable to the general problem ofgrain size estimation from digital images of sediment might broaden theapplicability to more sedimentary environments as well as improve itsaccuracy these techniques are compared using a large data set from a gravelbarrier beach in southern england based on over 180 samples mean grain sizeof sieved and imaged sediments correspond to within between 8 and 16 some theoretical aspects of the spatial arrangement of image intensity indigital images of natural sediments are addressed including the fractal natureof sediments in images which has potential implications for derivation ofgrain size distributions from images of sand sized material throughsegmentation and thresholding the methods outlined in this contributionmay also nd application in further uncovering the geometric structure ofsediment beds as well as in the simulation of sedimentation processes keywordsgrain size analysis digital images statistical models gravel beach introductiongrain size information from natural environ ments traditionally is obtained using methodssuch as sieving laser diffraction and settling which do not help measure equivalent propertiesof the sample in addition the slow and labour intensive nature of these methodologies has lim ited the spatial and temporal resolution at whichgrain size data are obtained where grain size isan important parameter such as in determiningsediment transport studies can be limited funda mentally by the dif culty in sampling for sedi ment at the required frequency a furtherdisadvantage is that sediment must be removedfrom the natural environment potentially alteringsubsequent system development in contrast photographic methods can be used to measuresediment size at a resolution comparable withmeasurements of hydraulic hydrodynamic andmorphological topographical conditions withoutdisrupting the sediment body by direct sampling the problem of deriving sediment size infor mation from digital images of sediment has beenapproached using two different families of tech niques the rst is based on edge detection andimage segmentation principles e g butler et al 2001 sime ferguson 2003 graham et al 2005 such techniques rely on marked image intensity contrasts between grains and gapsbetween grains interstices such that thresholdscan be speci ed to discriminate individual grainsfrom the background intensity levels e g sime ferguson 2003 thus far these methods aresedimentology 2009 56 421 438

the influence of continental ice sheets on the climate of an ice age the climate influence of the land ice that existed 18 000 years before present 18k b p is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean simulated climates are obtained from two versions of the model one with the land ice distribution of the present and the other with that of 18k b p in the northern hemisphere the tropospheric flow field is strongly influenced by the laurentide ice sheet and features a split flow straddling the ice sheet with a strong jet stream forming the southern branch the northern branch of the flow brings very cold air over the north atlantic ocean where thick sea ice is maintained the distribution of sea surface temperature sst difference between the two experiments in the northern hemisphere resembles the difference between the sst at 18k b p and at present as estimated by the climap project 1981 the 18k b p ice sheets have very little influence upon atmospheric temperature and sst in the southern hemisphere this is because the interhemispheric heat transport hardly changes as the loss of heat energy due to the reflection of solar radiation by continental ice sheets in the northern hemisphere is almost completely counterbalanced by the in situ reduction of upward terrestrial radiation hydrologic changes in the model climate are also found with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in north america and eurasia these findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum

can high resolution 3d topographic surveys provide reliable grain size estimates in gravel bed rivers high resolution topographic surveys such as those provided by structure from motion sfm contain a wealth of information that is not always exploited in the generation of digital elevation models dems in particular several authors have related sub metre scale topographic variability or surface roughness to sediment grain size by deriving empirical relationships between the two in fluvial applications such relationships permit rapid analysis of the spatial distribution of grain size over entire river reaches providing improved data to drive three dimensional hydraulic models allowing rapid geomorphic monitoring of sub reach river restoration projects and enabling more robust characterisation of riverbed habitats however comparison of previously published roughness grain size relationships shows substantial variability between field sites using a combination of over 300 laboratory and field based sfm surveys we demonstrate the influence of inherent survey error irregularity of natural gravels particle shape grain packing structure sorting and form roughness on roughness grain size relationships roughness analysis from sfm datasets can accurately predict the diameter of smooth hemispheres though natural irregular gravels result in a higher roughness value for a given diameter and different grain shapes yield different relationships a suite of empirical relationships is presented as a decision tree which improves predictions of grain size by accounting for differences in patch facies large improvements in d50 prediction are possible sfm is capable of providing accurate grain size estimates although further refinement is needed for poorly sorted gravel patches for which c axis percentiles are better predicted than b axis percentiles

nivation landforms in the western great basin and their paleoclimatic significance abstract more than 10 000 nivation landforms occur in the higher mountain ranges of the western great basin they range from small subtle hollows with head scarps a few meters high and a few tens of meters long to broad clearly defined terraces as much as 220 m wide bounded by bold steeply sloping head scarps as much as 30 m high and 1600 m long distribution of these nivation hollows is strongly influenced by elevation slope orientation local relief and substrate lithology about 95 occur between 2200 and 3000 m elevation and nearly 80 are situated on north northwest to east northeast facing slopes they occur mainly in areas of moderately sloping terrain and moderate local relief and they are preferentially developed on relatively incompetent substrates including terrigenous sedimentary deposits volcanic and metavolcanic rocks of intermediate composition and deeply weathered granitoid rocks nearly all of these nivation hollows are relict they are most abundant near areas of late pleistocene glaciation but rarely occur within such areas most are veneered with colluvium and are well vegetated and many hollows in the mono basin area are veneered with volcanic ash at least 700 yr old distribution of nivation hollows suggests that 1 the full glacial nivation threshold altitude nta rose from north to south at 190 m per degree of latitude subparallel to and approximately 740 m lower than the full glacial equilibrium line altitude ela and about 1370 m lower than the estimated modern ela 2 the difference between the full glacial and modern elas indicates an approximate 7 c full glacial mean annual temperature depression throughout the great basin and 3 the full glacial mean annual temperature at the nta is estimated to have been approximately 0 to 1 c assuming little change in accumulation season precipitation

combining geomorphometry feature extraction techniques and earth surface processes research the way forward abstract in recent years the wealth of technological development revolutionised our ability to collect data in geosciences due to the unprecedented level of detail of these datasets geomorphologists are facing new challenges giving more in depth answers to a broad er range of fundamental questions across the full spectrum of the earth s and planetary processes this contribution builds on the existing literature of geomorphometry the science of quantitative land surface analysis and feature extraction translate land surface parameters into extents of geomorphological elements it provides evidence of critical themes as well as emerging fields of future research in the digital realm supporting the likely effectiveness of geomorphometry and feature extractions as they are advancing the theoretical empirical and applied dimension of geomorphology the review further discusses the role of geomorphometric legacies and scientific reproducibility and how they can be implemented in the hope that this will facilitate action towards improving the transparency and efficiency of scientific research and accelerate discoveries in geomorphology in the current landscape substantial changes in landforms ecosystems land use hydrological routing and direct anthropogenic modifications impact systems across the full spectrum of geomorphological processes although uncertainties in the precise nature and likelihood of changes exist geomorphometry and feature extraction can aid exploring process regimes and landscape responses taken together they can revolutionise geomorphology by opening the doors to improved investigations crossing space and time scales blurring the boundaries between traditional approaches and computer modelling and facilitating cross disciplinary research ultimately the exploitation of the available wealth of digital information can help to translate our understanding of geomorphic processes which is often based on observations of past or current conditions into the rapidly changing future

magnetic mineral diagenesis in suboxic sediments at bettis site w n ne pacific ocean the effects of iron diagenesis on paleomagnetism and rock magnetism were examined in suboxic sediments from bettis site w n in the ne pacific ocean as part of the oxidative decomposition of organic matter ultrafine grained authigenic magnetites are produced immediately above the iron reduction zone this zone is commonly observed in deep sea sediments as a prominent color change from brown to greenish grey the magnetite authigenesis is evidenced by systematic increases in natural magnetic intensities and stabilities and by comparable shifts in other rock magnetic properties the magnetites are composed of relatively pure fe3o4 and fall within a restricted size range of 0 06 0 12 m which is nominally single domain some of these finest grained magnetites are rapidly destroyed during burial upon entering the zone of iron reduction leaving a relatively coarser population magnetite dissolution appears to continue with depth according to a first order surface area reaction process when at steady state iron reduction is independent of sulfide formation in these sediments because solid sulfur profiles show no increase at depth and most of the sulfur occurs as barite despite a well constrained carbonate stratigraphy comparisons of paleomagnetic directions between nearby cores show little agreement suggesting that the directions are composed of a complex mixture of remanences acquired at different depths subsurface magnetic peaks may represent paleoredox markers preserved by non steady state redox conditions caused by climatically induced variations in organic matter flux and sedimentation rates

stuck at the bar larger than average grain lag deposits and the spectrum of particle mobility larger than average grain deposits in gravel bed rivers potentially exert a distinctive influence upon fluvial morphodynamics and flow resistance they are products of historical contingency sourced from rare events that supply atypically coarse material larger than average grain lag deposits are emblematic attributes of the tongariro river new zealand they are deposited on bar edges and heads derived from lahar valley floor deposits that subsequently became terraces these materials are less likely to be reworked across a range of flows compared to other bar material conceptual models that consider channel configuration and incorporate distributions of particle mobility and flood flows are necessary to assess the role of larger than average grain deposits on river morphodynamics

magnetic properties of sedimentary greigite fe3s4 new data are presented here that document the previously poorly known magnetic characteristics of sedimentary greigite fe3s4 several diagnostic magnetic properties can be used in conjunction to rapidly screen sediments to detect the presence of greigite such discriminants are necessary because greigite displays a similar or higher range of coercivities compared to most ferrimagnetic minerals and the commonly used method of alternating field demagnetization cannot be used to distinguish between palaeomagnetic remanence components due to greigite and other ferrimagnetic minerals sedimentary greigite has high ratios of the saturation isothermal remanent magnetization to magnetic susceptibility mrs which are accompanied by hysteresis ratios of mrsms 0 5 and bcr bc 1 5 ms is the saturation magnetization bc is the coercive force and bcr is the coercivity of remanence greigite has no low temperature phase transition whereas the ferrimagnetic iron sulphide pyrrhotite undergoes a major phase transition at about 34 k and unoxidized magnetite displays the verwey transition at 118 k low temperature measurements may therefore prove valuable in distinguishing between magnetite pyrrhotite and greigite although the absence of a low temperature transition cannot be taken as definitive evidence for the presence of greigite greigite also displays characteristic high temperature behaviour with a major drop in magnetization between 270 and 350 c determination of the mrs ratio is an excellent means of rapidly screening sediments to identify stratigraphic intervals that may contain greigite subsequent low and high temperature analyses can then provide unambiguous identification of greigite and enable the evaluation of the presence of other magnetic minerals

photo sieving a method for grain size analysis of coarse grained unconsolidated bedding surfaces the photo sieving method enables the grain size analysis of particles 10 mm from unconsolidated openwork bedding surfaces the accuracy is equal to the machine sieving method the sediment surface is photographed in the field using a camera stand the enlarged print is digitized for computer processing by tracing the outlines of the pebbles from the size and shape of the projection area of the individual pebble images the computer determines the ellipsoids of revolution classifies these ellipsoids and establishes their grain size distribution in percentage by weight thus photo sieving differs distinctly from point counting techniques with the aid of photo sieving the surface grain size distributions of larger sedimentary systems may be regularly mapped alluvial fans braided rivers both onshore and offshore coasts or areas of relict sediments and manganese nodules are suitable for this method

modeling the topography of shallow braided rivers using structure from motion photogrammetry abstract recent advances in computer vision and image analysis have led to the development of a novel fully automated photogrammetric method to generate dense 3d point cloud data this approach termed structure from motion or sfm requires only limited ground control and is ideally suited to imagery obtained from low cost non metric cameras acquired either at close range or using aerial platforms terrain models generated using sfm have begun to emerge recently and with a growing spectrum of software now available there is an urgent need to provide a robust quality assessment of the data products generated using standard field and computational workflows to address this demand we present a detailed error analysis of sub meter resolution terrain models of two contiguous reaches 1 6 and 1 7 km long of the braided ahuriri river new zealand generated using sfm a six stage methodology is described involving i hand held image acquisition from an aerial platform ii 3d point cloud extraction modeling using agisoft photoscan iii georeferencing on a redundant network of gps surveyed ground control points iv point cloud filtering to reduce computational demand as well as reduce vegetation noise v optical bathymetric modeling of inundated areas and vi data fusion and surface modeling to generate sub meter raster terrain models bootstrapped geo registration as well as extensive distributed gps and sonar based bathymetric check data were used to quantify the quality of the models generated after each processing step the results obtained provide the first quantified analysis of sfm applied to model the complex terrain of a braided river results indicate that geo registration errors of 0 04 m planar and 0 10 m elevation and vertical surface errors of 0 10 m in non vegetation areas can be achieved from a dataset of photographs taken at 600 m and 800 m above the ground level these encouraging results suggest that this low cost logistically simple method can deliver high quality terrain datasets competitive with those obtained with significantly more expensive laser scanning and suitable for geomorphic change detection and hydrodynamic modeling