digital elevation model resolution effects on terrain attribute calculation and quantitative soil landscape modeling the accuracy of digital elevation models dem and dem derived products depends on several factors including the horizontal resolution and vertical precision at which the elevation data are represented and the source of the elevation data this accuracy becomes increasingly important as we extend the use of dem data for spatial prediction of soil attributes our objective was to compare terrain attributes and quantitative soil landscape models derived from grid based dem represented at different horizontal resolutions 10 and 30 m represented at different vertical precisions 0 1 and 1 m and acquired from different sources decreasing the horizontal resolution of the field survey dem produced lower slope gradients on steeper slopes steeper slope gradients on flatter slopes narrower ranges in curvatures larger specific catchment areas in upper landscape positions and lower specific catchment areas values in lower landscape positions overall certain landscape features were less discernible on the 30 m dem than on the 10 m dem decreased vertical precision produced a large proportion of points with zero slope gradient and zero slope curvature and a large number of steeply sloping and more highly curved areas differences among dem from different sources were more significant with less accurate representation of depressions and drainage pathways with the usgs dem as compared to the field survey dem empirical models developed from different dem included similar predictive terrain attributes and were equally successful in predicting a horizon depth ahd in the validation data set

modeling the precision of structure from motion multi view stereo digital elevation models from repeated close range aerial surveys the accuracy of digital elevation models dems derived from structure from motion sfm multi view stereo mvs 3d reconstruction is commonly computed for a single realization of model elevations this approach may be adequate to estimate an overall measure of systematic error however it cannot provide a good estimation of measurement precision knowing measurement precision is crucial for measuring elevation surface changes observed by dem comparisons in this paper we illustrate an approach to characterize spatial variation in the precision for sfm mvs derived dems we use a snow covered surface of an active rock glacier located in the southern french alps as the case study a spatially varying precision estimate is calculated from repeated close range aerial surveys for a single acquisition period by calculating the standard deviation per grid cell between the dems created for each flight repetition regression analysis using a generalized additive model gam is performed to model the estimated precision and provide insights regarding how sensor survey design and field site conditions may spatially influence the measurement precision additionally we define how dem error can be described differently depending on the available validation data in our study image height above ground level and distance to ground control points had the greatest explanatory power for spatial variation in dem precision image overlap mean reprojection error and saturation were also useful for explaining spatially varying measurement precision of the dems field site characteristics such as slope angle and shading had the least importance in our model of precision from a practical point of view regression modeled relationships between precision and image and site characteristics can be utilized to design future surveys with similar sensing platforms and site conditions for improved dem precision

an efficient and comprehensive method for drainage network extraction from dem with billions of pixels using a size balanced binary search tree abstract with the increasing resolution of digital elevation models dems computational efficiency problems have been encountered when extracting the drainage network of a large river basin at billion pixel scales the efficiency of the most time consuming depression filling pretreatment has been improved by using the o n log n complexity least cost path search method but the complete extraction steps following this method have not been proposed and tested in this paper an improved o n log n algorithm was proposed by introducing a size balanced binary search tree bst to improve the efficiency of the depression filling pretreatment further the following extraction steps including the flow direction determination and the upslope area accumulation were also redesigned to benefit from this improvement therefore an efficient and comprehensive method was developed the method was tested to extract drainage networks of 31 river basins with areas greater than 500 000 km 2 from the 30 m resolution aster gdem and two sub basins with areas of approximately 1000 km 2 from the 1 m resolution airborne lidar dem complete drainage networks with both vector features and topographic parameters were obtained with time consumptions in o n log n complexity the results indicate that the developed method can be used to extract entire drainage networks from dems with billions of pixels with high efficiency

scientific visualization of landscapes and landforms scientific visualization of geospatial data provides highly effective tools for analysis and communication of information about the land surface and its features properties and temporal evolution whereas single surface visualization of landscapes is now routinely used in presentation of earth surface data interactive 3d visualization based upon multiple elevation surfaces and cutting planes is gaining recognition as a powerful tool for analyzing landscape structure based on multiple return light detection and ranging lidar data this approach also provides valuable insights into land surface changes captured by multi temporal elevation models thus animations using 2d images and 3d views are becoming essential for communicating results of landscape monitoring and computer simulations of earth processes multiple surfaces and 3d animations are also used to introduce novel concepts for visual analysis of terrain models derived from time series of lidar data using multi year core and envelope surfaces analysis of terrain evolution using voxel models and visualization of contour evolution using isosurfaces has potential for unique insights into geometric properties of rapidly evolving coastal landscapes in addition to visualization on desktop computers the coupling of gis with new types of graphics hardware systems provides opportunities for cutting edge applications of visualization for geomorphological research these systems include tangible environments that facilitate intuitive 3d perception interaction and collaboration application of the presented visualization techniques as supporting tools for analyses of landform evolution using airborne lidar data and open source geospatial software is illustrated by two case studies from north carolina usa

a new fossil vent biota in the ballynoe barite deposit silvermines ireland evidence for intracratonic sea floor hydrothermal activity about 352 ma considerable controversy exists as to the timing of the important mississippian carbonate hosted irish type zn pb ba ag deposits the silvermines deposits have been defined as an end member of this style in that they have been interpreted to display textures indicative of sea floor deposition one of the strongest arguments in favor of this interpretation was the report of a hydrothermal vent field including pyritic chimneys in the ballynoe open pit barite deposit this paper adds to that body of evidence by describing a hydrothermal vent fauna from the same vent field consisting of a delicately pyritized worm tube hosted by massive pyrite and hematized filaments of apparent microbial origin the worm tube is remarkably similar to fossil worm tubes from modern and ancient volcanic hosted massive sulfide deposits and the filamentous microfossils have similarities to modern fe oxidizing bacteria we have found no correlation between the worm tube and normal mississippian fossils such as crinoids whose replacement by pyrite in the immediately underlying ballynoe footwall destroys original morphology the sulfur isotope composition of the worm tube and host pyrite is essentially identical to that of the vent field pyrite and the main sulfide ore stage of silvermines sulfides all having a mean value about 20 per mil indicating an open system bacteriogenic sulfide source these discoveries provide additional evidence for the exhalative nature of parts of the silvermines orebodies and imply that mineralization had begun in the irish ore field by the late tournaisian 352 ma

an evaluation of methods to determine slope using digital elevation data variation in the computation of slope from digital elevation data can result in significantly different slope values and can in turn lead to widely varying estimates of environmental phenomena such as soil erosion that are highly dependent on slope ten methods of computing slope from distributed elevation data utilizing capabilities inherent in five different geographic information systems gis were compared with field measurements of slope the methods were compared based on 1 overall estimation performance 2 estimation accuracy 3 estimation precision and 4 independence of estimation errors and the magnitude of field measured slopes a method utilizing a very high resolution digital elevation model dem 1 m produced slightly better estimates of slope than approaches utilizing somewhat lower resolution dems 2 5 2 m and significantly better estimates than a method utilizing a 12 5 m dem the more accurate method was significantly biased however frequently underestimating actual slope methods that averaged or smoothed high resolution dems over larger areas also produced good estimates of slope but these were somewhat less accurate in areas of shallow slopes methods utilizing differential geometry to compute percent slope from dems outperformed methods utilizing trigonometric functions errors in slope computation are exaggerated in soil erosion prediction models because erosion typically increases as a power function of slope d 2004 elsevier b v all rights reserved

global open access dem performances in earth s most rugged region high mountain asia a multi level assessment abstract over the past decades climate change has exerted pronounced influences on the cryo hydrologic environments in high mountain asia hma digital elevation models dems are one of the critical datasets required in many hydrology and cryosphere related studies in hma which include estimations of glacier mass balances and lake water storage changes and hydrological runoff modelling several global or near global coverage dems e g srtm and aster missions have been widely utilized for such studies however a comprehensive assessment of the quality of these dems particularly over the high relief hma area is still lacking this study investigated the performances of seven public freely accessed dem datasets aster gdem v2 srtm 3 v4 1 dem srtm 1 dem aw3d30 dem vfp dem merit dem seamless srtm 1 dem over the hma region by referring to high accuracy elevation data from icesat altimetry we also provided an additional detailed assessment for typical lake basins and extremely rugged areas in the himalayas by using available global positioning system gps measurements and gridded setsm dem raster data results show that aw3d30 exhibits the highest accuracy in hma land areas among these datasets the accuracy of all studied dems demonstrates high spatial variation which shows the strongest relationship with slope among several topographical factors such as elevation and aspect over these rugged terrains with a large slope such as the hengduan mountains and himalayas the vertical accuracy is relatively low in all investigated dems we established empirical models for fitting the relationship between dem vertical error and mean slope which can be used to estimate the average elevation errors for any given local or basin scale dem grids in addition this study identified regions with anomalous elevation data in each dataset caused by the imperfect void filling processing scheme in sum the 3 arc second merit dem is judged to be relatively dependable for hma which not only achieves good performances in statistical error values but also retains few void filling anomalies the 1 arc second aw3d30 could be the most promising product over hma with its high spatial resolution and accuracy although some void filling anomalies need to be noted in some regions

visualization and comparison of dem derived parameters application to volcanic areas abstract digital elevation models dems are fruitfully used in volcanology as the topographic base for mapping and quantifying volcanic landforms the increasing availability of free topographic data on the web decreasing production costs for high accuracy data and advances in computer technology has triggered rapid growth of the number of dem users in the volcanological community dems are often visualized only as hill shaded maps and while this is among the major advantages in using them the possibility of deriving a very large number of parameters from a single grid of elevation data makes dems a powerful tool for morphometric analysis however many of these parameters have almost the same informative content and before starting to elaborate topographic data it is recommended to know a priori what parameters best visualize the investigated landform and therefore what is necessary and what is redundant in this work we review a number of analytical procedures used to parameterize and represent dems a lidar derived dem matrix acquired over the valle del bove valley on mt etna is used as test case elevation data for deriving the parameters we first review well known parameters such as hill shading slope and aspect curvature and roughness before extending the review to some less common parameters such as sky view factor svf openness and red relief image maps rrim for each parameter a description is given emphasizing how it can be used for identifying and delimiting specific volcanic elements the analyzed surface parameters are then cross compared in order to infer which of them is most uncorrelated and the results are represented in the form of a correlation matrix finally the reviewed dem derived parameters and the correlation matrix are used for analyzing the volcanic landforms of two case studies michoacan guanajuato volcanic field and a phonolitic lava flow at the island of tenerife

landform classification and soil distribution in hummocky terrain saskatchewan canada this study presents a classification of distinct three dimensional landform elements and examines the relationship between these landform elements and selected soil morphological properties of udic boroll soils in southern saskatchewan canada the classification is based on defined ranges of three criteria derived from topographic data gradient profile downslope curvature and plan across slope curvature seven landform elements are recognized convergent shoulders divergent shoulders convergent backslopes divergent backslopes convergent footslopes divergent footslopes and level elements all of the elements are easily identified in the field the thicknesses of a horizons and depths to calcium carbonate of the soils were consistently greater in convergent versus divergent elements in the same profile group e g shoulders and showed an overall increase in the sequence shoulders backslopes level footslope elements distinct groups of elements emerge from a statistical analysis of the differences between individual and bivariate means of soil morphological properties associated with each landform element the differences in soil properties among the elements can be largely explained by differences in water movement and distribution in hillslope systems the results of the study highlight the need to consider land surface morphology during the development of research designs for soil related studies

world s largest known precambrian fossil black smoker chimneys and associated microbial vent communities north china implications for early life abstract black smoker chimneys and biological vent communities have been identified at many sites on the deep seafloor particularly along oceanic spreading centers we report the largest and oldest known microbe rich sub meter sized black smoker chimneys and mounds from a 1 43 billion year old sulfide deposit in a continental graben in northern china these chimneys are especially well preserved with characteristic morphology internal textures and internal cylindrical mineralogical zonation four main types of chimneys are distinguished on textural and mineralogical criteria exhibiting either zn fe sulfide or pb zn fe sulfide internal cylindrical mineralogical zones the chimneys mark vent sites in submarine grabens indicating focused flow venting processes the fossil chimneys have mineralogical and geological evolutionary features similar to their counterparts on the modern seafloor and other submarine hydrothermal vents black smoker vent fluids and seafloor tectonism played important roles for formation of the massive sulfide deposits in the mesoproterozoic we also report the first known remarkably diverse assemblage of fossil microbialites from around and inside precambrian vent chimneys demonstrating that proterozoic life flourished around submarine hot vents and deep within the chimney vent passages filamentous spherical rod and coccus shaped fossil microbes are preserved preferentially on sulfide precipitates based on the depth and setting of the fossil biota the organisms that produced the microbialites were likely sulfate reducing chemosynthetic and thermophyllic microbes textural and mineralogical evidence shows that biomineralization processes enhanced chimney growth and sulfide precipitation close association of microorganisms with sulfide chimneys in modern deep sea hydrothermal vents and younger ophiolites has sparked speculation about whether life may have originated at similar vents however little is known about fossil equivalents of vent microfossils and black smoker chimneys from earth s early evolution the fossilized microorganisms from the gaobanhe black smoker chimney sulfide deposits include thread like filaments with branching and twisted forms and preserved organic carbon representing fossilized remnants of microbial mats metabolized at high temperatures characteristic of venting fluids the preservation of fossil microorganisms provides evidence that microbial populations were closely associated with black smoker chimneys in earth s early history the microbial population clearly constitutes the site for mediating mineral formation these ancient microbial fossils lead to a much better understanding of early life on the deep seafloor the discovery of the mesoproterozoic microfossils within black smoker hydrothermal chimneys indicates that hydrothermal activity around sea floor vents supported dense microbial communities and supports speculation that vent sites may have hosted the origin of life

metallic ion binding by bacillus subtilis implications for the fossilization of microorganisms the silicification of bacterial cells has been followed in a laboratory simulation by electron microscopy and energy dispersive x ray spectroscopy structural degradation of the bacteria was not influenced by silica availability but the remains of degraded cells did promote the precipitation of silica in contrast cells reacted with ferric iron before aging remained intact and structures conforming to the original morphology of the bacteria were preserved by silicification the binding of metallic ions by microbial cells in particular the retention of iron is therefore considered to be an important contributing factor to the fossilization of microorganisms

geomorphological response of fluvial and coastal terraces to quaternary tectonics and climate as revealed by geostatistical topographic analysis geostatistical topographic analysis is widely recognized as a useful tool for the statistical reconstruction of planar geomorphic markers from relict surfaces this work is aimed at improving the geostatistical approach used in previous works and developing a method for evaluating the incision rates of rivers in their lower catchments during the late quaternary we chose the major valleys of the adriatic foothills central italy affected since late miocene by a differential tectonic uplift which is still active in particular i we applied the geostatistical analysis to reconstruct the original top surfaces of fluvial to coastal terrace bodies at the metauro river and cesano river mouths ii we performed correlations between the height distribution of the alluvial terrace sequences and the quaternary climatic curve to estimate the average long term fluvial incision rates in the lowermost reaches of the metauro cesano misa and esino rivers the obtained averaged incision rates have been interpreted also in the light of the stream length gradient index sl index steepness index ks and concavity index as proxies of the stream power per unit length results confirm that geostatistical and terrain analysis of topographic and geometric arrangements of fluvial and coastal terraces is an effective tool in detecting geomorphic and tectonic factors inducing perturbations on planar geomorphic markers in particular we better delineated the surface geometry and boundaries of well developed coastal fans at the mouths of the metauro and cesano rivers already recognized in previous works through sedimentological morphostratigraphic and chronological data moreover we found evidence for cut and fill phases that took place during and immediately after the river aggradation of the late quaternary glacial periods despite the slope area analysis evidenced a widespread influence of the regional differential uplift on single river basin configuration we observed some space and time variability of averaged incision rates for adjacent valleys mainly explained by physiographic configuration and dynamics of drainage network copyright 2011 john wiley sons ltd

biogeological mineralization in deep sea hydrothermal deposits oriented drill cores retrieved from active massive sulfide edifices at the endeavour segment of the juan de fuca ridge contain an abundance of fossilized tube structures associated with vestimentiferan and annelid worms the petrological evolution of these biogeological structures and their presence deep inside the edifice walls demonstrate that an initial worm mediated texture directly affects the subsequent steps of inorganic precipitation wall infilling and outward growth of these black smoker deposits the presence of fossilized structures in hydrothermal discharge sites that are 2 kilometers apart and their similarity to structures observed in other modern and ancient deposits suggest that these biogeological processes are general phenomena

spatial analysis of stream length gradient sl index for detecting hillslope processes a case of the gallego river headwaters central pyrenees spain abstract a morphometric analysis of drainage networks and relief using geomorphic indices and geostatistical analyses of topographical data are useful tools for discussing the morphoevolution of a given area among the geomorphic indices the stream length gradient sl index represents a practical tool to highlight anomalous changes in river gradients perturbations of sl are usually indicative of 1 differences in the resistance of outcropping lithological units to erosion 2 sub surface processes such as active faulting and 3 slope failures that directly reach the stream channels particularly in small catchments in this work the sl index was calculated for the upstream sector of the gallego river basin in the central spanish pyrenees to test its accuracy and sensitivity for detecting the imprints of different surface processes a geostatistical procedure is proposed to obtain sl index maps through the interpolation and filtering of the values estimated along the drainage network this method allows computing of sl validation and assessing of its spatial distribution with robust statistical accuracy and objectively defining the anomalies in sl the anomalies in the sl map of the study area which coincide with knickpoints and knickzones were analyzed in detail the results indicate 1 perturbation in the drainage network caused by differences in the resistance to erosion of outcropping lithological units and 2 hillslopes affected by large landslides earth flows and rock falls directly reaching the stream bed this study indicates that the sl index has strong potential to solve geomorphological problems in different geological settings especially in detecting the role of active large scale features that influence landscape evolution

evidence of bacterial activity from micrometer scale layer analyses of black smoker sulfide structures pito seamount site easter microplate abstract we report the observation of an external layer less than 20 m thick attached to hydrothermal chimney fragments of black smokers collected from the pito seamount site on the easter microplate scanning electron microscope observations revealed bacterial imprints located on and within the layer which was associated with underlying layers of thin jarosite deposits and iron sulfides displaying corrosion features x ray electron microprobe drift and hplc measurements were used to determine the precise chemical composition and nature of compounds in the layer the external layer was composed mainly of a combination of hydrated ferric sulfate ferrous sulfate iron oxi hydroxide and elemental sulfur species a jarosite like mineral was found deeper in the layer we suggest that this layer may not be the result of an abiotic thermochemical precipitation but instead was formed chemically by bacterial processes these processes were 1 elemental sulfur oxidation which represents major energetic exchanges within the external layer and 2 bioleaching processes inducing iron oxidation originally elemental sulfur probably resulted from thermochemical precipitation the results of this study give new insight on the possible role and impact of related acidophilic microorganisms living in hot vent environments of the deep sea

removal of artifact depressions from digital elevation models towards a minimum impact approach artifact depressions in digital elevation models dems interrupt flow paths and alter drainage directions techniques for removing depressions should enforce continuous flow paths in a way that requires the least modification of the dem impacts on the spatial and statistical distributions of elevation and its derivatives were assessed for four methods of removing depressions 1 filling 2 breaching 3 a combination of filling and breaching with breaching constrained to a maximum of two grid cells 4 a combination of filling and breaching based on an impact reduction approach ira the ira removes each depression using either filling or breaching depending on which method has the least impact in terms of the number of modified cells and the mean absolute difference in the dem analysis of a lidar dem of a landscape on the canadian shield showed significant differences in the impacts among the four depression removal methods depression filling a removal method that is widely implemented in geographical information system software was found to impact terrain attributes most severely constrained breaching which relies heavily on filling for larger depressions also performed poorly both depression breaching and the ira impacted spatial and statistical distributions of terrain attributes less than depression filling and constrained breaching the most sensitive landscapes to depression removal were those that contained large i e 10 flat areas because of the occurrence of relatively large depressions in these areas copyright 2005 john wiley sons ltd

mineralization of soft bodied invertebrates in a jurassic metalliferous deposit the jurassic marine biota of la voulte sur rhone france is characterized by three dimensional preservation of soft bodied animals and their internal organs in contrast to other soft bodied fossils those from la voulte are preserved in an unusual suite of minerals dominated by apatite calcite gypsum barite and pyrite with accessory cu pb and zn sulfides these are thought to be sedimentary in origin fossilization occurred rapidly enough to be influenced by tissue composition and involved a diagenetic sequence apatite calcite gypsum pyrite chalcopyrite galena the la voulte fossils reveal the role of apatite as a template for calcification and pyritization in soft tissue preservation

digital terrain modelling a review of hydrological geomorphological and biological applications the topography of a catchment has a major impact on the hydrological geomorphological and biological processes active in the landscape the spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems furthermore topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology digital elevation models are the primary data used in the analysis of catchment topography we describe elevation data sources digital elevation model structures and the analysis of digital elevation data for hydrological geomorphological and biological applications some hydrologic models that make use of digital representations of topography are also considered

pyritization of soft bodied fossils beecher s trilobite bed upper ordovician new york state although pyrite is ubiquitous in fine grained organic carbon bearing marine sediments it is only rarely involved in the preservation of soft bodied organisms beecher9s trilobite bed in upper ordovician strata of new york state is an exception it is a classic locality for trilobites having appendages and other soft tissues preserved in pyrite the relative timing and duration of the formation of pyrite associated with the fossils and their host sediments were determined by use of sulfur isotope ratios the exoskeleton and appendages of the trilobites show relatively light sulfur isotope values in contrast to the enclosing sediment which is characterized by a substantial excursion to heavy isotope values preservation of soft parts requires rapid burial of carcasses in sediments otherwise low in metabolizable organic matter in these circumstances pyrite formation within the sediments is suppressed thus concentrations of sulfate and reactive iron are initially high enough to promote early rapid and extensive pyritization of nonmineralized tissue

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

early jurassic hydrothermal vent community from the franciscan complex san rafael mountains california the figueroa massive sulfide deposit located in franciscan complex rocks in the san rafael mountains of california preserves the only known jurassic hydrothermal vent fossils the figueroa fossil assemblage is specimen rich but of low diversity and comprises in order of decreasing abundance vestimentiferan worm tubes the rhynchonellid brachiopod anarhynchia cf gabbi and a species of nododelphinulid gastropod the figueroa fossil organisms lived at a deep water high temperature vent site located on a mid ocean ridge or seamount at an equatorial latitude the fossil vent site was then translated northwestward by the motion of the farallon plate and was subsequently accreted to its present location an iron silica exhalite bed the probable lateral equivalent of the figueroa deposit contains abundant filamentous microfossils with two distinct morphologies and probably represents a lower temperature diffuse flow environment the figueroa fossil community was subject to the same environmental conditions as modern vent communities but it is unique among modern and other fossil vent communities in having rhynchonellid brachiopods

neotethyan late cretaceous volcanic arc hydrothermal vent fauna the barite polymetallic ore zone of the late cretaceous madneuli volcanogenic massive sulfide vms deposit in the republic of georgia contains large tube worm fossils that represent the first ancient hydrothermal vent fauna to be identified from a volcanic arc setting and very likely the shallowest ancient example yet found the fossil tube walls are formed of an unusual quartz barite pyrite and galena mineral assemblage rather than only pyrite as in other vent fossils this probably reflects the low temperature high salinity vent chemistry at the time of preservation as deduced from fluid inclusion analyses the madneuli vent fauna is one of three examples that occurred over a time span of 6 m y in an area of the neotethyan ocean that was as tectonically complex as the present day west pacific the ancient and modern vent faunas appear to occur in a similar range of tectonic settings and bathymetry

comparison of the performance of flow routing algorithms used in gis based hydrologic analysis flow direction and specific catchment area were calculated for different flow routing algorithms using tapes g and taudem a fuzzy classification was used along with eight topo climatic attributes to delineate six landscape classes from a 10 m usgs dem a series of maps and tabular outputs were produced to compare flow routing predictions in different parts of the study area in the santa monica mountains of southern california the matched pair t test was used to compare the performance of pairs of specific catchment area grids across six user defined fuzzy landscape classes the results show that 1 the source cells predicted with the d demon and fd8 algorithms were confined to hilltops 2 two single flow routing algorithms rho8 d8 produced poor results and 3 the choice of flow routing algorithm has potentially important consequences for the calculation of upslope contributing areas sediment transport capacity topographic wetness and several other topographic indices copyright 2007 john wiley sons ltd

channel initiation and the problem of landscape scale since the 1940s it has been proposed that landscape dissection into distinct valleys is limited by a threshold of channelization that sets a finite scale to the landscape this threshold is equal to the hillslope length that is just shorter than that necessary to support a channel head a field study supports this hypothesis by showing that an empirically defined topographic threshold associated with channel head locations also defines the border between essentially smooth undissected hillslopes and the valley bottoms to which they drain this finding contradicts assertions that landscapes are scale independent and suggests that landscape response to changes in climate or land use depends on the corresponding changes in the threshold of channelization

mapping outlet points used for watershed delineation onto dem derived stream networks outlet point positions taken from hydrometric stations commonly do not coincide with stream locations extracted from digital elevation models dems this is a serious problem for accurate watershed delineation of data sets containing numerous outlets which is critical in regional scale studies that relate catchment characteristics to basin responses the advanced outlet repositioning approach aora presented here replicates the processes involved in manual outlet placement while reducing inefficiency and potential for blunders the technique uses water body names to identify locations for outlet repositioning that are consistent with nearby outlets the aora performance was compared against two existing automated techniques using 993 stations in seven basins in northwest england the aora had the fewest repositioning errors in each basin and nearly halved the overall number of errors in the data set compared with the second best method this work highlights the potential errors that may be present in studies that have employed existing automated watershed mapping methods

assessing significant geomorphic changes and effectiveness of dynamic restoration in a coastal dune ecosystem article i nfo a shift from restoring coastal dunes as stabilized landscapes toward more morphodynamic ecosystems is un derway this paper uses results from a recent case study where invasive vegetation was removed from a coastal dune complex in western canada as a first step in a dynamic ecosystem restoration project spatial statistical methods used in the natural sciences to quantify patterns of significant spatial temporal changes are reviewed and the local moran s ii spatial autocorrelation statistic is explored for detecting and assessing significant changes cluster maps of positive depositional and negative erosional changes were used to derive statistically significant volumetric changes within discrete geomorphic units beach foredune trans gressive dune over one year following vegetation removal all units experienced net increases in sediment budgets compared to a pre restoration surface the beach experienced the highest episodic erosion and vol umetric change and greatest net annual sediment budget compared to the beach the annual sediment budget of the foredune was 19 whereas the transgressive dune was 33 the foredune recovered rapidly to initial erosion during restoration and subsequent natural events with consistently positive sediment volumes and attained a form similar to that pre restoration aeolian deflation and sand bypassing through the foredune was greatest in the two months following vegetation removal and peak accretion in the transgressive dune resulted from depositional lobes extending from the foredune smaller dunes migrating within the complex and growth of a precipitation ridge along the eastern margin several methodological and logistical considerations for detecting significant change in dynamic dune land scapes are discussed including sampling strategy design data normalization and control measures and incorpo rating uncertainty and inherent spatial relations within acquired datasets to ensure accuracy and comparability ofresults generally underutilizedincoastalgeomorphology spatialautocorrelation methods e g localmoran s ii are recommended over spatially uniform threshold approaches for the ability to detect local change processes and explore hypotheses on spatial temporal dynamics finally several key geomorphic indicators that are believed to aid in re establishing ecological conditions and processes that favor more resilient and natural dune ecosystems are identified for assessing the effective ness of dynamic restoration projects including increased aeolian activity enlarged active sand surface area positive sediment budgets increased dune morphodynamics improved geomorphic diversity and enhanced geomorphic resilience although limited in temporal scope the case study results show that the initial phase of the restoration treatment was effective in enhancing all indicators except for increasing sand surface area given decadal scale observations of climatic changes and longer term eco geomorphic trajectory toward stabi lization in the region however it is unlikely that the geomorphic effectiveness of this restoration effort will con tinue without continued frequent treatment interventions

a multiresolution index of valley bottom flatness for mapping depositional areas 1 valley bottoms function as hydrological buffers that significantly affect runoff behavior distinguishing valley bottoms from hillslopes is an important first step in identifying and characterizing sediment deposits for hydrologic and geomorphic purposes valley bottoms occur at a range of scales from a few meters to hundreds of kilometers in extent this paper describes an algorithm for using digital elevation models to identify valley bottoms based on their topographic signature as flat low lying areas the algorithm operates at a range of scales and combines the results at different scales into a single multiresolution index this index classifies degrees of valley bottom flatness which may be related to depth of deposit the index can also be used to identify groundwater constrictions and to delineate hydrologic and geomorphic units

surface texture analysis of a high resolution dtm interpreting an alpine basin abstract this study focuses on a geomorphometric analysis of a small headwater basin of the dolomites eastern italian alps the analysis of the fine scale surface morphology was performed on a high resolution digital elevation model cell size 2 m derived from an airborne lidar survey the topography was synthesized by a set of spatial statistical indexes representing a signature of the local surface morphology and the relationships between the geomorphometric indexes and morphological features were evaluated the studied basin was then segmented by means of a fuzzy k means classification algorithm into different spatial subdomains characterized by specific local geomorphic signatures this method allows us to objectively choose the optimal combination of the number of classes and degree of fuzziness characterizing the studied basin accordingly the analysis can be adopted to the characteristics of the studied area improving the interpretation of surface morphology and offering a valuable tool for comparative analysis between different geomorphological contexts the results of the classification were compared with the actual surface morphology based on high resolution orthophotos aerial photos and field surveys

a simple three dimensional model of diffusion with precipitation applied to localised pyrite formation in framboids fossils and detrital iron minerals a three dimensional diffusion with precipitation model is constructed to estimate radial variations in the amounts of pyrite which precipitate where a spherical mass of organic matter producing h2s by sulphate reduction is enveloped in a dissolved iron bearing porewater the model indicates that higher rates of sulphate reduction more readily metabolisable organic matter and larger organic masses require increasingly high dissolved iron concentrations in order to confine pyrite or iron sulphide precipitation to the decay site the maximum size sphere of exceedingly metabolisable organic matter equivalent to fresh planktonic material which can be pyritised is about 50 m radius where decay occurs in porewaters with typical dissolved iron levels this radius is close to the maximum radius of framboidal pyrite the formation of which could involve model type processes fossil carcases although mainly composed of less readily metabolisable organic matter may be orders of magnitude larger and the model demonstrates that their pyritisation requires unusually high porewater dissolved iron concentrations these inferred chemical conditions are consistent with sedimentological observations of pyritisation in beecher s trilobite bed new york state at greater depths within the sediment pyritisation is controlled by the kinetics of iron mineral reactivity towards h2s sediments vary widely in their exposure times to h2s which can range at least from 50 to 106 years at low exposure times only iron oxides are pyritised whereas at high exposure times even the most refractory iron silicates can become pyritised

influence of a tube building polychaete on hydrothermal chimney mineralization high temperature chimneys on the juan de fuca ridge are the preferred habitat of the sulfide worm paralvinella n sp an investigation of interactions between the biology of the sulfide worm and chimney mineralization has led to a hypothesis linking formation of marcasite pyrite crusts on chimney surfaces to colonization and tube building by the worms marcasite precipitation beneath worm tubes and worm migration to newly formed areas of chimney together create a moving front of biomineralization that keeps pace with chimney growth sulfide oxidation by this organism can potentially produce enough s to form the fes sub 2 crusts the marcasite pyrite crusts act as a sealing layer within the outer chimney wall reducing inflow of cold seawater or outflow of hydrothermal fluid this may enhance temperature increases within the chimney conduit and hasten replacement of the early anhydrite matrix in the chimney wall by higher temperature sulfides

a new procedure for gridding elevation and stream line data with automatic removal of spurious pits abstract a morphological approach to the interpolation of regular grid digital elevation models dems from surface specific elevation data points and selected stream lines is described the approach has given rise to a computationally efficient interpolation procedure which couples the minimization of a terrain specific roughness penalty with an automatic drainage enforcement algorithm the drainage enforcement algorithm removes spurious sinks or pits yielding dems which may be used to advantage in hydrological process studies the drainage enforcement algorithm has also been found to significantly increase the accuracy of dems interpolated from sparse but well chosen surface specific elevation data moreover it facilitates the detection of errors in elevation data that would not be detected by more conventional statistical means and forms a sound physical basis for cartographic generalization

near global validation of the srtm dem using satellite radar altimetry abstract this paper reports the results of a near global validation of the srtm dem dataset using a unique database of completely independent height measurements derived from satellite altimeter echoes primarily gathered by ers 1 these heights are obtained using a rule based expert system which identifies each echo as 1 of 11 different characteristic shapes and selects the optimal retracking algorithm to obtain best range to surface the results of this comparison which includes over 54 million altimeter derived heights show generally very good agreement with the srtm data with global statistics for mean difference of 3 m and a standard deviation of 16 m quantitative validation results are given for each continent and are summarised here mean difference m standard deviation of differences m africa 1 86 15 62 australia 1 09 11 49 eurasia 2 54 16 09 north america 3 15 15 18 south america 12 22 18 51 global 3 60 16 16 a range of examples are included to illustrate key findings of this work and to indicate synergistic applications of these two datasets currently being studied including the potential for forest canopy measurement

the influence of elevation error on the morphometrics of channel networks extracted from dems and the implications for hydrological modelling stream network morphometrics have been used frequently in environmental applications and are embedded in several hydrological models this is because channel network geometry partly controls the runoff response of a basin network indices are often measured from channels that are mapped from digital elevation models dems using automated procedures simulations were used in this paper to study the influence of elevation error on the reliability of estimates of several common morphometrics including stream order the bifurcation length area and slope ratios stream magnitude network diameter the flood magnitude and timing parameters of the geomorphological instantaneous unit hydrograph giuh and the network width function dems of three uk basins ranging from high to low relief were used for the analyses the findings showed that moderate elevation error rmse of 1 8 m can result in significant uncertainty in dem mapped network morphometrics and that this uncertainty can be expressed in complex ways for example estimates of the bifurcation length and area ratios and the flood magnitude and timing parameters of the giuh each displayed multimodal frequency distributions i e two or more estimated values were highly likely furthermore these preferential estimates were wide ranging relative to the ranges typically observed for these indices the wide ranging estimates of the two giuh parameters represented significant uncertainty in the shape of the unit hydrograph stream magnitude network diameter and the network width function were found to be highly sensitive to elevation error because of the difficulty in mapping low magnitude links uncertainties in the width function were found to increase with distance from outlet implying that hydrological models that use network width contain greater uncertainty in the shape of the falling limb of the hydrograph in light of these findings care should be exercised when interpreting the results of analyses based on dem mapped stream networks copyright 2007 john wiley sons ltd

faunal composition and organic surface encrustations at hydrothermal vents on the southern juan de fuca ridge examination of a small collection of macroinvertebrates from three vents of the southern juan de fuca vent field reveals differences between the vents with respect to species composition species habits and microbial and metallic deposits on their surfaces two apparently new vestimentiferan species were found and for the first time the juan de fuca palm worm was observed to dwell on smokers high acidity values recorded in this system may interfere with the process of shell calcification in an archaeogastropod snail the surfaces of vestimentifer an tubes at two vents are heavily encrusted with microbial and metallic accumulations scanning electron microscope transmission electron microscope and energy dispersive x ray microanalysis observations show that iron based crusts on orange tubes are built from accumulations of an fe rich particle of distinctive size and shape morphological evidence is presented for the microbial origin of fe rich particles zn rich particles found on black tubes are not of microbial origin we suggest that iron deposition on surfaces in the vent environment is initially biocatalytic but subsequent deposits may build by simple inorganic reactions

methodology for estimating the topographic factor ls of rusle3d and usped using gis abstract in the rusle3d revised universal soil loss equation 3d and usped unit stream power based erosion deposition models the effects of topography on soil loss are represented by the combined factor ls where l is the slope length factor and s the slope gradient factor the problems with measuring slope gradient and length over large areas are i they are not always estimated correctly and ii different ways are used for their calculation gis geographical information systems software has several algorithms for estimating topographic parameters included in the equations of ls the objective of this research was developing a methodology for ls calculation using gis in order to define the most accurate algorithm for each parameter for the estimation of s and upslope contribution area l the zevenbergen and thorne algorithm and the deterministic infinity algorithm respectively were selected

karst landforms revealed at various scales using lidar and uav in semi arid brazil consideration on karstification processes and methodological constraints abstract this paper analyzes different types of karst landforms and their relationships with fracture systems sedimentary bedding and fluvial processes we mapped karst features in the cretaceous carbonates of the jandaira formation in the potiguar basin brazil we used high resolution digital elevation models acquired using lidar and aerial orthophotographs acquired using an unmanned aerial vehicle uav we grouped and described karst evolution according to scale and degree of karstification these degrees of karst evolution are coeval fractures are opened by dissolution forming vertical fluid conduits whereas coeval dissolution occurs along horizontal layers this conduit system acts as pathways for water flow the enlargement of conduits contributes to the collapse of blocks in sinkholes and expansion of caves during an intermediate degree of karstification propagation of dissolution can cause the coalescence of sinkholes and the capture of small streams fluvial processes dominate karst dissolution at an advanced degree of karstification comparisons with previously published ground penetrating radar gpr borehole and seismic surveys in sedimentary basins indicate that these structures can be partially preserved during burial

a multi resolution method to map and identify locations of future gully and channel incision abstract while channel erosion is recognised as a major often dominant source of river sediment channel geometry and its change remain impractical to measure for anything but small experimental watersheds designing remediation strategies in landscapes affected by channel erosion requires information on the extent and location of current incised channel features as well as a method to determine locations where incision may occur in the future we present a multi resolution algorithm that uses topographic information to concurrently map both existing incised landform elements and areas at risk of future incision the former uses elevation slope and profile curvature to identify topographic signatures of incised landform elements and the latter uses landscape position topographic wetness index and stream power index to isolate areas likely susceptible to future incision we aimed to develop a computationally efficient method capable of operating across a broad range of landscapes the algorithm was tested in three contrasting environments in eastern australia with promising results sensitivity analysis indicates the method performs reasonably consistently across landscapes but that outputs become more sensitive as the average slope of the landscape increases a comparison between cleared and uncleared hillsides suggested that areas indicated at risk of future incision are plausible and that cleared areas were more susceptible to channel incision the only required input is a digital elevation model and outputs can provide a rapid visual assessment of landscapes affected by incisional erosion this technique enables the identification of gully erosion and the planning of remediation works across landscapes of thousands of square kilometres it may assist in prioritisation of works and further insights into the processes associated with channel incision

use of terrain variables for mapping gully erosion susceptibility in lebanon this paper predicts the geographic distribution and size of gullies across central lebanon using a geographic information system gis and terrain analysis eleven primary elevation upslope contributing area aspect slope plan profile and tangential curvature flow direction flow width flow path length rate of change of specific catchment area along the direction of flow and three secondary steady state quasi dynamic topographic wetness sediment transport capacity topographic variables were generated and used along with digital data collected from other sources soil geology to statistically explain gully erosion field measurements three tree based regression models were developed using 1 all variables 2 primary topographic variables only and 3 different pairs of variables the best regression tree model combined the steady state topographic wetness and sediment transport capacity indices and explained 80 of the variability in field gully measurements this model proved to be simple quick realistic and practical and it can be applied to other areas of the mediterranean region with similar environmental conditions thereby providing a tool to help with the implementation of plans for soil conservation and sustainable management copyright 2007 john wiley sons ltd

carving and adaptive drainage enforcement of grid digital elevation models 1 an effective and widely used method for removing spurious pits in digital elevation models consists of filling them until they overflow however this method sometimes creates large flat regions which in turn pose a problem for the determination of accurate flow directions in this study we propose to suppress each pit by creating a descending path from it to the nearest point having a lower elevation value this is achieved by carving i e lowering the terrain elevations along the detected path carving paths are identified through a flooding simulation starting from the river outlets the proposed approach allows for adaptive drainage enforcement whereby river networks coming from other data sources are imposed to the digital elevation model only in places where the automatic river network extraction deviates substantially from the known networks an improvement to methods for routing flow over flat regions is also introduced detailed results are presented over test areas of the danube basin

automatically derived catchment boundaries and channel networks and their hydrological applications abstract a method of generating drainage networks and catchment boundaries from gridded ground elevation data a digital terrain model is presented the method includes an algorithm for coping with localised low points in the data the paper suggests two objective ways of comparing the conventionally mapped with the automatically generated drainage network emphasis is placed on the way that this approach is capable of benefiting a variety of hydrological applications in particular the automatic estimation of flow statistics from catchment characteristics

probabilistic landslide hazard assessment at the basin scale abstract we propose a probabilistic model to determine landslide hazard at the basin scale the model predicts where landslides will occur how frequently they will occur and how large they will be we test the model in the staffora river basin in the northern apennines italy for the study area we prepare a multi temporal inventory map through the interpretation of multiple sets of aerial photographs taken between 1955 and 1999 we partition the basin into 2243 geo morpho hydrological units and obtain the probability of spatial occurrence of landslides by discriminant analysis of thematic variables including morphological lithological structural and land use for each mapping unit we obtain the landslide recurrence by dividing the total number of landslide events inventoried in the unit by the time span of the investigated period assuming that landslide recurrence will remain the same in the future and adopting a poisson probability model we determine the exceedance probability of having one or more landslides in each mapping unit for different periods we obtain the probability of landslide size by analysing the frequency area statistics of landslides obtained from the multi temporal inventory map assuming independence we obtain a quantitative estimate of landslide hazard for each mapping unit as the joint probability of landslide size of landslide temporal occurrence and of landslide spatial occurrence

trace and minor element variations and sulfur isotopes in crystalline and colloform zns incorporation mechanisms and implications for their genesis abstract various models have been proposed to explain the formation mechanism of colloform sphalerite but the origin is still under debate in order to decipher influences on trace element incorporation and sulfur isotope composition crystalline and colloform sphalerite from the carbonate hosted mississippi valley type mvt deposit near wiesloch sw germany were investigated and compared to sphalerite samples from 52 hydrothermal vein type deposits in the schwarzwald ore district sw germany to study the influence of different host rocks formation mechanisms and fluid origin on trace element incorporation trace and minor element incorporation in sphalerite shows some correlation to their host rock and or origin of fluid gangue paragenetic minerals and precipitation mechanisms e g diagenetic processes fluid cooling or fluid mixing furthermore crystalline sphalerite is generally enriched in elements like cd cu sb and ag compared to colloform sphalerite that mainly incorporates elements like as pb and tl in addition sulfur isotopes are characterized by positive values for crystalline and strongly negative values for colloform sphalerite the combination of trace element contents typical minerals associated with colloform sphalerite from wiesloch sulfur isotopes and thermodynamic considerations helped to evaluate the involvement of sulfate reducing bacteria in water filled karst cavities sulfate reducing bacteria cause a sulfide rich environment that leads in case of a metal rich fluid supply to a sudden oversaturation of the fluid with respect to galena sphalerite and pyrite this however exactly coincides with the observed crystallization sequence of samples involving colloform sphalerite from the wiesloch mvt deposit

metal fixation by bacterial cell walls all biomass contains a significant quantity of metallic constituents and mineralization in living and dead biodebris may contribute to element transport from the hydrosphere into sediments the anionic cell walls of bacteria are remarkable in their ability to fix metals and provide sites for nucleation and growth of minerals results presented show the types of cell wall polymers that are responsible for metal binding in walls of gram positive and gram negative bacteria

comparison of single and multiple flow direction algorithms for computing topographic parameters in topmodel single flow direction sfd and multiple flow direction mfd algorithms were used to compute the spatial and statistical distributions of the topographic index used in the watershed model topmodel an sfd algorithm assumes that subsurface flow occurs only in the steepest downslope direction from any given point an mfd algorithm assumes that subsurface flow occurs in all downslope directions from any given point the topographic index in topmodel is in a tan 3 where in is the napierian logarithm a is the upslope area per unit contour length and tan 3 is the slope gradient the in a tan 3 distributions were computed from digital elevation model dem data for locations with diverse topography in arizona colorado louisiana nebraska north carolina oregon pennsylvania tennessee vermont and virginia the means of the in a tan 3 distributions were higher when the mfd algorithm was used for computation compared to when the sfd algorithm was used the variances and skews of the distributions were lower for the mfd algorithm compared to the sfd algorithm the differences between the mfd and sfd algorithms in the mean variance and skew of the in a tan 3 distribution were almost identical for the various dems and were not affected by dem resolution or watershed size topmodel model efficiency and simulated flow paths were affected only slightly when the in a tan 3 distribution was computed with the sfd algorithm instead of the mfd algorithm any difference in the model efficiency and simulated flow paths between the sfd and mfd algorithms essentially disappeared when the model was calibrated by adjusting subsurface hydraulic parameters

protracted construction of gabbroic crust at a slow spreading ridge constraints from 206pb 238u zircon ages from atlantis massif and iodp hole u1309d 30 n mar sensitive high resolution ion microprobe shrimp u pb zircon ages of 24 samples from oceanic crust recovered in integrated ocean drilling program iodp hole u1309d and from the surface of atlantis massif mid atlantic ridge mar 30 n document a protracted history of accretion in the footwall to an oceanic detachment fault ages for 18 samples of evolved fe ti oxide gabbro and felsic dikes collected 40 1415 m below seafloor in u1309d yield a weighted mean of 1 20 0 03 ma mean square of weighted deviates 7 1 however the ages range from 1 08 0 07 ma and 1 28 0 05 ma indicating crustal construction occurred over a minimum of 100 200 ka the zircon ages along with petrologic observations indicate at least 2 major periods of intrusive activity with age peaks separated by 70 ka the oldest ages are observed below 600 mbsf an observation inconsistent with models requiring constant depth melt intrusion beneath a detachment fault the data are most consistent with a multiple sill model whereby sills intrude at random depths below the ridge axis over a length scale greater than 1 4 km zircon ages from broadly spaced samples collected along the southern ridge of atlantis massif yield a detachment fault slip rate of 28 7 6 7 mm a and imply significant asymmetric plate spreading up to 100 on the north american plate for at least 200 ka during core complex formation

three dimensional landscape process modelling the effect of dem resolution many landscape models have been developed over the past decades however relatively little is known about handling the effects of changing spatial and temporal resolutions therefore resolution effects remain a factor of uncertainty in many hydrological and geomorphological modelling approaches in this paper we present an experimental multi scale study of landscape process modelling emphasis was laid on quantifying the effect of changing the spatial resolution upon modelling the processes of erosion and sedimentation a simple single process model was constructed and equal boundary conditions were created using artificial digital elevation models dems eliminated effects of landscape representation the only variable factors were dem resolution and the method of flow routing both steepest descent and multiple flow directions our experiments revealed an important dependency of modelled erosion and sedimentation rates on these main variables the general trend is an increase of erosion predictions with coarser resolutions an artificial mathematical overestimation of erosion and a realistic natural modelling effect of underestimating resedimentation cause this increasing the spatial extent eliminates the artificial effect while at the same time the realistic effect is enhanced both effects can be quantified and are expected to increase within natural landscapes the modelling of landscape processes will benefit from integrating these types of results at different resolutions

digital terrain modeling abstract this article examines how the methods and data sources used to generate dems and calculate land surface parameters have changed over the past 25 years the primary goal is to describe the state of the art for a typical digital terrain modeling workflow that starts with data capture continues with data preprocessing and dem generation and concludes with the calculation of one or more primary and secondary land surface parameters the article first describes some of ways in which lidar and radar remote sensing technologies have transformed the sources and methods for capturing elevation data it next discusses the need for and various methods that are currently used to preprocess dems along with some of the challenges that confront those who tackle these tasks the bulk of the article describes some of the subtleties involved in calculating the primary land surface parameters that are derived directly from dems without additional inputs and the two sets of secondary land surface parameters that are commonly used to model solar radiation and the accompanying interactions between the land surface and the atmosphere on the one hand and water flow and related surface processes on the other it concludes with a discussion of the various kinds of errors that are embedded in dems how these may be propagated and carried forward in calculating various land surface parameters and the consequences of this state of affairs for the modern terrain analyst

application of integrated gnss hydroacoustic measurements and gis geodatabase models for bottom analysis of lake hancza the deepest inland reservoir in poland since almost 40 of the world s largest lakes have not yet been studied their volumes are therefore approximated shiklomanov and rodda 2003 the most challenging situation is with smaller reservoirs and inland lakes due to high costs and time required for acquiring bathymetric data some inland reservoirs have not been investigated there are some probes to estimate certain morphometric parameters using existing publicly available datasets hollister and milstead 2010 h ollister et al 2011

error in a usgs 30 meter digital elevation model and its impact on terrain modeling calculations based on us geological survey usgs digital elevation models dems inherit any errors associated with that particular representation of topography we investigated the potential impact of error in a usgs 30 m dem on terrain analysis over 27 km 2 the difference in elevation between 2652 differential global positioning systems measurements and usgs 30 m dem derived elevations provided the comparative error dataset analysis of this comparative error data suggested that although the global average error is small local error values can be large and also spatially correlated stochastic conditional simulation was used to generate multiple realizations of the dem error surface that reproduce the error measurements at their original locations and sample statistics such as the histogram and semivariogram model the differences between these alternative error surfaces provide a model of uncertainty for the unknown dem error spatial distribution these dem errors had a significant impact on terrain attributes which compound elevation values of many grid cells e g slope wetness index etc a case study using terrain modeling demonstrates that the result of error propagation is most dramatic in valley bottoms and along streamlines q 2000 elsevier science b v all rights reserved

drainage networks from grid digital elevation models current algorithms that deduce the drainage network from a digital elevation model dem represented by a regular array of surface elevations share a fault unless the terrain is rugged the derived water channels tend to flow in parallel lines along preferred directions engendered by the sampling grid orientation we present a simple solution to the problem a second difficulty is the presence of noise that creates artificial pits we briefly describe a method which deals with pits in what we believe to be a more efficient manner for virtual memory environments than previous efforts our system has treated dems of nearly 9 000 000 pixels we show how depth first search of the resulting drainage network permits segmentation of the dem into basins by various criteria analysis of stream sediment anomaly dilution profiles improved hydrological models and other applications

verification of the vertical error in c band srtm dem using icesat and landsat 7 otter tail county mn the shuttle radar topography mission srtm provided scientists with digital elevation data on a nearly global scale and with highly consistent accuracy this paper compares elevation values of the c band srtm 30 m digital elevation model dem with pointwise elevations from the ice cloud and land elevation satellite icesat laser altimetry for otter tail county minnesota the accuracy of srtm dem is measured as a function of land covers and geomorphologic characteristics the typical mean vertical difference between the srtm dem and icesat elevations in this paper was determined in each classified land use type and is approximately 1 5 m over bare ground with the srtm measuring lower elevations significant changes in the srtm dem uncertainties have been identified over different surface types classified from landsat 7 imagery e g bare ground urban and forested areas based on this result the difference of the srtm 30 m dem and icesat elevations has been removed from the dem and made available for improved hydrological applications

sulphide mineralisation in the deep sea hydrothermal vent polychaete alvinella pompejana implications for fossil preservation abstract hydrothermal vent fauna particularly vestimentiferan and polychaete worm tubes are occasionally preserved in the geological record the early stages of mineralisation are particularly important in defining whether or not preservation will occur and they are poorly understood tube samples of the polychaete worm alvinella pompejana collected from 13 n on the east pacific rise have been studied to identify the processes occurring during early pyrite marcasite mineralisation iron sulphide mineralisation is present within the walls of the organic dwelling tube and is induced by microbial fauna preserved within the tube micro layers various microorganisms were observed coating the inner tube surfaces together with 10 100 m sized fe and zn sulphide particles precipitated from vent fluids the microbes and particulate sulphides become entombed within the tube wall as further layers of organic material are secreted by the worm during tube building episodes this results in a laminated tube structure being formed composed of alternating layers of tube material and microbial sulphide rich interlayers the microbial sulphide layers provide a template for further mineralisation and replacement of the microbes with pyrite while degradation of the organic components occurs the iron monosulphides mackinawite and greigite have been identified as intermediatory phases that occur as precursor minerals during the formation of pyrite later marcasite mineralisation is observed to form over some of the pyritised organic layers once mineralisation has replaced most of the organic tube material the structure will then be preserved along with the host sulphide body these observations enhance our understanding of the mechanisms of fossil pyritisation in fine scaled organic structures throughout the geological record

digital elevation model networks demon a model of flow over hillslopes for computation of contributing and dispersal areas current algorithms for computing contributing areas from a rectangular grid digital elevation model dem use the flow routing model of o callaghan and mark 1984 which has two major restrictions 1 flow which originates over a two dimensional pixel is treated as a point source nondimensional and is projected downslope by a line one dimensional moore and grayson 1991 and 2 the flow direction in each pixel is restricted to eight possibilities we show that large errors in the computed contributing areas result for any terrain topography divergent convergent or planar we present a new model called digital elevation model networks demon which avoids the above problems by representing flow in two dimensions and directed by aspect demon allows computation of both contributing and dispersal areas demon offers the main advantage of contour based models e g moore et al 1988 the representation of varying flow width over nonplanar topography while having the convenience of using rectangular grid dems

the assignment of drainage direction over flat surfaces in raster digital elevation models abstract drainage direction assignment over flat surfaces in raster digital elevation models dem has been a stubborn problem for dem processing methods a new approach that improves upon current methods of flat surface treatment is presented the approach is based on the recognition that in natural landscapes drainage is generally away from higher and towards lower terrain to produce such a drainage dem elevations of a flat surface are modified to impose two gradients one away from higher terrain and one towards lower terrain subsequent processing of the dem produces a drainage pattern over the flat surface that is topographically consistent and exhibits flow convergence properties the proposed approach is not restricted by the shape of the flat surface the number of outlets on its edge or the complexity of the surrounding topography a comparison with the drainage pattern of an established method that displays the parallel flow problem shows significant improvements in producing realistic drainage patterns the proposed approach extends automated dem processing to digital landscapes for which existing methods cannot provide adequate flow directions over flat surfaces to conduct a drainage analysis the necessary algorithmic details for implementation of the approach are provided 1997 elsevier science b v

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

a geochemical framework for the application of stable sulphur isotopes to fossil pyritization pyrite formation is associated with fossils where the organic material decays by sulphate reduction or where the carbonate skeleton acts either as a nucleation substrate or induces iron sulphide precipitation by dissolution these requirements define specific combinations of porewater chemistry and saturation state with respect to carbonates and iron sulphides a review of modern marine sediments suggests that near surface porewaters are always over saturated or close to saturation with iron sulphides but are alternately rich in either dissolved iron or dissolved sulphide however significant variations in carbonate saturation state may occur with porewaters being undersaturated in the early stages of sulphate reduction but subsequently becoming oversaturated until the later stages of methanogenesis here undersaturation may return if there is a substantial input of carbon dioxide and if little alkalinity has arisen from iron reduction organic matter pyritization requires that soft tissue material decays by sulphate reduction to release dissolved sulphide with dissolved iron supplied by the surrounding porewaters the modern sediment studies therefore suggest that organic matter pyritization can occur only during the earliest stages of sulphate reduction where there are iron rich porewaters which are saturated with iron sulphides pyrite replacement of carbonate shell material requires porewater undersaturation with respect to carbonates and analogy with modern sediments suggests that these conditions occur either during the earliest stages of sulphate reduction or when methanogenesis produces undersaturation between these periods porewaters are saturated with respect to carbonates and pyrite of different morphologies can precipitate on carbonate shells sulphur isotope data provide support for these associations of porewater chemistry and style of fossil pyritization the best described examples are for soft tissue pyritization in beecher9s trilobite bed ordovician and the hunsruck slate devonian where the isotopic data are consistent with rapid early pyritization in iron rich porewaters more data are needed on shell pyritization with the range of isotopic compositions indicating formation through all stages of diagenesis

the prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models the accuracy of the predictions of distributed hydrological models must depend in part on the proper specification of flow pathways this paper examines some of the problems of deriving flow pathways from raster digital terrain data in the context of hydrological predictions using topmodel distributed moisture status is predicted in topmodel on the basis of spatial indices that depend on flow path definition the sensitivity of this index to flow path algorithm and grid size is examined for the case where the surface topography is a good indicator of local hydraulic gradients a strategy for the case where downslope subsurface flow pathways may deviate from those indicated by the surface topography is described with an example application

automatic watershed delineation in the tibetan endorheic basin a lake oriented approach based on digital elevation models abstract watershed delineation from digital elevation models dems is an essential prerequisite for land surface hydrology studies although existing automatic methods perform well in exorheic basins finding a suitable watershed delineation approach in endorheic basins is still challenging this study develops a lake oriented approach given that lakes are important hydrological components in the tibetan endorheic basin the designed workflow of the proposed approach contains four steps flow direction calculation hydrological structure features extractions classification of lake types and watershed labeling the experiments are conducted on a sub region of the inner tibetan plateau with an area of 119 055 km2 extraction results prove that the proposed strategies i e elevation profile judgment and overflow point control correction can support the accurate delineation of watershed boundaries in addition the proposed approach can achieve two level watershed boundaries in which the independences of all the endorheic basins can be maintained meanwhile further delineation within extracted exorheic basins satisfies various application requirements at different spatial scales unlike manual processing and existing datasets e g hydrosheds the proposed approach can fully explore the advantages of high quality dems and can be expanded to much larger regions to handle scientific and engineering issues

quantitative analysis of land surface topography land surface topography significantly affects the processes of runoff and erosion a system which determines slope aspect and curvature in both the down slope and across slope directions is developed for an altitude matrix also the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix a fortran 66 program performs the analysis

mineral microbe interactions in deep sea hydrothermal systems a challenge for raman spectroscopy in deep sea hydrothermal environments steep chemical and thermal gradients rapid and turbulent mixing and biologic processes produce a multitude of diverse mineral phases and foster the growth of a variety of chemosynthetic micro organisms many of these microbial species are associated with specific mineral phases and the interaction of mineral and microbial processes are of only recently recognized importance in several areas of hydrothermal research many submarine hydrothermal mineral phases form during kinetically limited reactions and are either metastable or are only thermodynamically stable under in situ conditions laser raman spectroscopy is well suited to mineral speciation measurements in the deep sea in many ways and sea going raman systems have been built and used to make a variety of in situ measurements however the full potential of this technique for hydrothermal science has yet to be realized in this focused review we summarize both the need for in situ mineral speciation measurements in hydrothermal research and the development of sea going raman systems to date we describe the rationale for further development of a small low cost sea going raman system optimized for mineral identification that incorporates a fluorescence minimizing design and we present three experimental applications that such a tool would enable