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

surface and bed topography of trapridge glacier yukon territory canada digital elevation models and derived hydraulic geometry measurements of ice thickness and surface elevation are prerequisite to many glaci ological investigations a variety of techniques has been develo ped for inter pret ation of these data including means of constructing regularly gridded digital eleva tion models dem s for use in numcrical studies here we present a simple yet stati sti cally sound method for processing ice pe netr ating radar data and descr ibe a tech nique for interpol ating these data onto a regular grid dems generatcd fort rapridge glacier yukon territory canada are used to derive geometric quantities lhal give pre liminary insights into the underlying basin scale hydrol ogical syste m this simple geo metric analysis suggests that at low water press ures a dendrilic drainage netw ork exists that evolves into a uniaxial morphology as water pressure approaches notation these pre dictions are compared to hydraulic connection probabilities based on bore hole drilling

influence of dem resolution on drainage network extraction a multifractal analysis article i nfo drainage network geometry dem resolution d8 algorithm multifractal analysis flow accumulation threshold terrain attributes different hydrological algorithms have been developed to automatically extract drainage networks from digital elevation models dems d8 is the most widely used algorithm to delineate drainage networks and catchments from a dem this algorithm has certain advantages such as simplicity the provision of a reasonable representa tion for convergent flow conditions and consistency among flow patterns calculated contributing areas and the spatial representation of subcatchments however it has limitations in selecting suitable flow accumulation threshold values to determine the pixels that belong to drainage networks although the effects of dem resolu tiononsometerrainattributes streamcharacterisationandwatersheddelineationhavebeenstudied analysesof the influence of dem resolution on flow accumulation threshold values have been limited recently multifractal analyses have been successfully used to find appropriate flow accumulation threshold values the application of thistype of analysisto evaluate therelationship betweendem resolution and flow accumulation threshold value needs to be explored therefore this study tested three dem resolutions for four drainage basins with different levels of drainage network distribution by comparing the renyi spectra of the drainage networks that were ob tained with the d8algorithmagainstthose determined byphotogrammetric restitution according totheresults dem resolution influences the selected flow accumulation threshold value and the simulated network morphol ogy thesuitable flowaccumulationthresholdvalue increasesasthedemresolutionincreasesandshowsgreater variability for basins with lower drainage densities the links between dem resolution and terrain attributes were also examined

compositions of large metal nodules in mesosiderites links to iron meteorite group iiiab and the origin of mesosiderite subgroups large mesosiderite metal nodules were studied petrographically and by neutron activation their large sizes minimized the effects of silicate contamination and dilution by fe reduced from feo the remarkable mixture of subequal amounts of metal and basaltic and pyroxenitic silicates in mesosiderites can be explained by the accretion of a core like metal mass from one asteroid onto the surface of another asteroid our data show that the accreted mass had a composition roughly similar to that of the iiiab iron meteorite core consistent with other evidence of close genetic links between these and other related groups the siderophile compositional pattern the very limited compositional range the inferred large projectile target ratio and the electrical interconnectedness of mesosiderite metal indicate that the bulk of the metal was molten when accreted mesosiderites have been divided into plagioclase and tridymiterich subgroup a and orthopyroxene rich subgroup b on the basis of modal silicate mineralogy roughly the same subgroups are defined by metal compositions au as ni and cu are generally higher and w lower in subgroup a than in subgroup b in our sample set a widmanstatten pattern is only observed in nodules from subgroup a a plausible model is that subgroup a best preserves the compositions of the target regolithic silicates and accreted core subgroup b is comprised of these materials together with a minor amount of coremantle materials consisting of olivine and refractory ni poor metal the independent covariation of ga re and ir may in part reflect fractionations during impact heating events the anomalous mesosiderite reckling peak a79015 is strongly depleted in refractory siderophiles and slightly enriched in volatile siderophiles such evolved metal requires a formation distinct from common mesosiderite metal

oxygen isotope studies of achondrites abstract oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites among the differentiated achondrites three isotopic groups are recognized l snc mars 2 earth and moon and 3 hed howardites eucrites diogenites the hed group also contains the mesosiderites main group pallasites and silicates from iiiab irons the angrites may be marginally resolvable from the hed group within each of these groups internal geologic processes give rise to isotopic variations along a slope 1 2 fractionation line as is well known for terrestrial materials variations of 17o from one planet to another are inherited from the inhomogeneities in the solar nebula as illustrated by the isotopic compositions of chondrites and their constituents among the undifferentiated achondrites five isotopic groups are found 1 aubrites 2 winonaites and iab iiicd irons 3 brachinites 4 acapulcoites and lodranites and 5 ureilites the isotopic compositions of aubrites coincide with the earth and moon and also with the enstatite chondrites these bodies apparently were derived from a common reservoir the isotopic composition of which was established at the chondrule scale by nebular processes isotopic similarities between chondrites and achondrites are seen only for the following instances 1 enstatite chondrites and aubrites 2 h chondrites and he irons and 3 l or ll chondrites and iva irons the isotopic data also support the following genetic associations 1 winonaites and iab iiicd irons 2 acapulcoites and lodranites and 3 ureilites and dark inclusions of c3 chondrites an attempt to reconcile the whole planet isotopic compositions of earth mars and the eucrite parent body with mixing models of their chemical compositions failed it is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive solar system components

evaluation of morphometric parameters of drainage networks derived from topographic maps and dem in point of floods an evaluation of morphometric parameters of two drainage networks derived from different sources was done to determine the influence of sub basins to flooding on the main channel in the havran river basin balikesir turkey drainage networks for the sub basins were derived from both topographic maps scaled 1 25 000 and a 10 m resolution digital elevation model dem using geographic information systems gis blue lines representing fluvial channels on the topographic maps were accepted as a drainage network which does not depict all exterior links in the basin the second drainage network was extracted from the dem using minimum accumulation area threshold to include all exterior links morphometric parameters were applied to the two types of drainage networks at sub basin levels these parameters were used to assess the influence of the sub basins on the main channel with respect to flooding the results show that the drainage network of sub basin 4 where a dam was constructed on its outlet to mitigate potential floods has a lower influence morphometrically to produce probable floods on the main channel than that of sub basins 1 3 and 5 the construction of the dam will help reduce flooding on the main channel from sub basin 4 but it will not prevent potential flooding from sub basin 1 3 and 5 which join the main channel downstream of sub basin 4 therefore flood mitigation efforts should be considered in order to protect the settlement and agricultural lands on the floodplain downstream of the dam in order to increase our understanding of flood hazards and to determine appropriate mitigation solutions drainage morphometry research should be included as an essential component to hydrologic studies

multifractal analysis applied to the study of the accuracy of dem based stream derivation abstract a correct description of river network morphology is very important when it is used to study different features of a river s morphology as well as phenomena related to it such as erosion nitrogen retention or sediment pollution in recent years different algorithms have been developed to extract drainage networks directly from digital elevation models in this paper the suitability of archydro extension developed for arcgis desktop and based on the d8 algorithm to generate river networks has been studied by using multifractal analysis the river networks generated by archydro tools were compared to those provided by photogrammetric restitution for different flow accumulation threshold values one limitation of the d8 algorithm in order to generate the most appropriate river networks is the correct choice of the flow accumulation threshold value multifractal analysis has shown itself to be an efficient approach to determine the most suitable flow accumulation threshold values moreover this approach has allowed characterizing the morphology of river networks and testing the quality of archydro results according to the multifractal spectra the main difference between the networks considered here is the lesser stream density with a low channel order detected for archydro results compared to photogrammetric restitution in addition the relationship between ruggedness number for the largest contributing area and fractal dimensions in each study area has been explored the use of multifractal analysis has been extended to drainage network simulation going beyond the descriptive aim of previous works

landform oriented flow routing algorithm for the dual structure loess terrain based on digital elevation models the loess landform in the loess plateau of china is with typical dual structure namely the upper smooth positive terrain and the lower cliffy negative terrain p n terrain for short obvious differences in their morphological feature geomorphological mechanism and hydrological process could be found in the both areas based on the differences a flow routing algorithm that separately addresses the dual structure terrain would be necessary to encompass this spatial variation in their hydrological behaviour this paper proposes a mixed flow routing algorithm to address aforementioned problems first the loess landform surface is divided into p n terrains based on digital elevation models then specific catchment area is calculated with the new algorithm to simulate the water flows in both positive and negative terrain areas the mixed algorithm consists of the multiple flow routing algorithm multiple flow direction for positive areas and the d8 algorithm for negative areas respectively the approach is validated in two typical geomorphologic areas with low hills and dense gullies in the northern shaanxi loess plateau four indices are used to examine the results which show that the new algorithm is more suitable for loess terrain in simulating the spatial distribution of water accumulation as well as in modeling the flow characteristics of the true surface by considering the morphological structures of the terrain copyright 2013 john wiley sons ltd

lidar based quantification of lava flow susceptibility in the city of auckland new zealand abstract lava flows represent one of the most significant volcanic hazards from basaltic monogenetic volcanoes such as spatter cones scoria cones maars and tuff rings they are common features emanating from parasitic vents on the flanks of polygenetic volcanoes and in dominantly flat lying intraplate volcanic fields the auckland volcanic field avf is a volcanic field that has been active for the last ca 250 ka hosting at least 50 monogenetic volcanoes morphometric parameters of lava flows such as volume length thickness and area were used to quantify the potential lava flow inundation susceptibility to new zealand s most densely populated area the city of auckland based on an airborne light detection and ranging lidar digital surface model dsm the morphometric parameters of fifteen studied flows included average length of 2 5 km range 0 7 6 5 km overall average thickness of 14 8 m range 3 4 43 8 m average of maximum thicknesses of 48 2 m range 18 3 180 5 m average area occupied of 5 1 km 2 range 0 4 25 1 km 2 and average volume of 0 12 km 3 range 0 005 1 km 3 based on these parameters and a lidar derived dsm the present topography was classified into sea topographic depressions low lying areas prone to inundation by an average lava flow buffer zones prone to inundation only by extremely thick lava flows and peaks or ridges which are unlikely to be overtopped in monogenetic fields each new vent occurs in a new location creating uncertainty around the spatial location of the volcanic hazard thus this research provides a general vent location independent approach to describe the lava flow susceptibility for a potentially active monogenetic volcanic field what this analysis reveals is that the city of auckland can be divided into two distinct areas with strongly different susceptibility to lava flow inundation the southern part of the city is predominantly flat without hindrance to lava flow whereas the hilly northern and central part has many ridges that can limit or channelise lavas these contrasting properties must be accounted for in scenario based or probabilistic hazard and risk models developed for the avf

magnetic hysteresis properties and 57fe mossbauer spectroscopy of iron and stony iron meteorites implications for mineralogy and thermal history abstract since the solid matter in our solar system began to assemble 4 57 billion years ago meteorites have recorded a large range of processes including metamorphism melting irradiation and hypervelocity impacts these processes as well as solar system magnetic fields can be accessed through the investigation of magnetic properties of meteorites in this work we present magnetic hysteresis properties isothermal remanent magnetization acquisition curves and 57fe mossbauer spectra for nineteen iron and eleven stony iron meteorites these data will be the background for a discussion about the thermal and shock history of these meteorites although mossbauer spectroscopy and hysteresis measurements are not able to provide cooling rates like the conventional metallographic method does we show that the combination of the ordering degree of taenite phase measured by mossbauer spectroscopy and hysteresis properties are useful for constraining the thermal and shock history of meteorites in particular strong shock and the associated thermal event that result in disordering of tetrataenite can be easily identified

compositional trends among iid irons their possible formation from the p rich lower magma in a two layer core group iid is the fifth largest group of iron meteorites and the fourth largest magmatic group i e that formed by fractional crystallization we report neutron activation data for 19 of 21 known iid irons these confirm earlier studies showing that the group has a relatively limited range in ir concentrations a factor of 5 this limited range is not mainly due to incomplete sampling instead it seems to indicate low solid liquid distribution coefficients reflecting very low s contents of the parental magma the same explanation responsible for the limited range in group iva despite this similarity these two groups have very different volatile patterns group iva has very low abundances of the volatile elements ga sb and ge whereas in group iid ga and sb abundances are the highest known in a magmatic group of iron meteorites and ge abundances are the second highest after group iiab group iid appears to be the only large magmatic group having high volatile abundances but low s in the volatile depleted groups iva and ivb it is plausible that s was lost as a volatile from a chondritic precursor material because group iid seems to have experienced minimal loss of volatiles we suggest that s was lost as an early melt having a composition near that of the fe fes eutectic 315 mg g s when temperatures had risen 400 500 k higher p rich melts formed became gravitationally unstable and drained through the first melt to form an inner core that was parental to the iid irons as discussed by kracher a wasson j t 1982 the role of s in the evolution of the parental cores of the iron meteorites geochim cosmochim acta46 2419 2426 it is plausible that a metal rich inner core and a s rich outer core could coexist metastably because stratification near the interface permitted only diffusional mixing the initial liquidus temperature of the inner p rich core is estimated to have been 1740 k after 60 crystallization the increase in p and the decrease in temperature may have permitted immiscibility with the s rich outer core we have not recognized samples of the outer core

determination of the drainage structure of a watershed using a digital elevation model and a digital river and lake network abstract distributed hydrological models require a detailed definition of a watershed s internal drainage structure the conventional approach to obtain this drainage structure is to use an eight flow direction matrix d8 which is derived from a raster digital elevation model dem however this approach leads to a rather coarse drainage structure when monitoring or gauging stations need to be accurately located within a watershed this is largely due to limitations of the d8 approach and the lack of information over flat areas and pits the d8 approach alone is also unable to differentiate lakes from plain areas to avoid these problems a new approach using a digital river and lake network drln as input in addition to the dem has been developed this new approach allows for an accurate fit between the drln and the modelled drainage structure which is represented by a flow direction matrix and a modelled watercourse network more importantly the identification of lakes within the modelled network is now possible the proposed approach which is largely rooted in the d8 approach uses the drln to correct modelled flow directions and network calculations for dem cells overlapped by the drln flow directions are determined using drln connections only the flow directions of the other dem cells are evaluated with the d8 approach which uses a dem that has been modified as a function of distance to the drln the proposed approach has been tested on the chaudiere river watershed in southern quebec canada the modelled watershed drainage structure showed a high level of coherence with the drln a comparison between the results obtained with the d8 approach and those obtained by the proposed approach clearly demonstrated an improvement over the conventionally modelled drainage structure the proposed approach will benefit hydrological models which require data such as a flow direction matrix a river and lake network and sub watersheds for drainage structure information

basin form characteristics causes and implications of the ten kongduis in the upper reaches of the yellow river the ten kongduis the transliteration of ephemeral flood gullies in mongolian are one of the main sediment sources of the upper reaches of the sediment laden yellow river in china the basin form characteristics and their causal factors and environmental effects of the kongduis are important knowledge for understanding the geomorphic processes and for managing the kongduis in this study we extracted the drainage networks and watersheds of the kongduis from the dem calculated the geometric and structural indices of the watersheds and networks investigated relations of the gully density with surface material composition vegetation coverage and topography and the relations of the sediment yield with gully density and other geometric indices of watersheds and associated the gully density with the evolution stage of landforms of the basins the results reveal that the ten kongduis are 5th 6th order streams and their watersheds are long and narrow with a circularity ratio of 0 16 0 26 an elongation ratio of 0 29 0 43 and a power of drainage area of 0 89 4 52 in the power function between mainstream length and drainage area yet the available data do not support the impacts of the geometric indices of watersheds on the sediment yield in the ten kongduis and the insignificant relation between the specific sediment yield and drainage area denies the existence of scale effect in sediment yield in the kongduis in contrast the gully density is found to be closely and positively related with the sediment yield the hypsometric integrals of the upstream reaches of the ten kongduis and the relation between gully density and hypsometric integral suggest that the kongduis are in the mature stage of landform evolution and the west five kongduis are in the early mature stage with a potential increase trend of gully density and a concomitant escalation of sediment yield in future

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

a phenomenon based approach to upslope contributing area and depressions in dems description of the terrain surface through digital elevation models dems strongly depends on data collection methods and dem data structures for efficiency and availability reasons regular point distributions are most common which yield artefacts such as depressions and preferential flow directions these facts need to be considered when natural phenomena are modelled as is shown for handling depressions and for estimation of flow paths and upslope contributing areas analysis of the main reasons for the occurrence of depressions shows that they usually better reflect the terrain than their surroundings thus the most common remedial method of raising depressions is rejected algorithms that cut a flow path from the depression through its bounding barrier are favoured instead several flow routing algorithms are evaluated for their behaviour in regular grids it is shown that the multiple flow direction mfd algorithm that distributes water from a grid cell to the lower of its eight neighbours proportionally to their elevation differences slope exhibits correct flow directions and the best rotation invariance it is suggested that the estimation of upslope contributing areas tcas is undertaken in two steps first a high quality flow direction data set is derived by a well behaved mfd algorithm or by subgrid modelling of flow paths secondly the upslope contributing areas are obtained by counting the upslope elements

characterization of fluvial activity in parana valles using different age dating techniques martian valley networks provide the best evidence that the climate on mars was different in the past although these features are located primarily in heavily cratered terrain of noachian age 3 7 ga the ages of the features and the time when they were active is not well understood from superposed craters several recent global studies determined that most valley networks formed during the late noachian to early hesperian however there were some disparities between the techniques in this study our principal objective was to test the reliability of the different age dating techniques to better understand their accuracy and limitations we applied these techniques to parana valles using a variety of high resolution images taken from different instruments that allow us to identify smaller craters d 125 m while providing sufficient coverage to support a statistically reliable sampling of crater populations which is necessary to reduce the uncertainties in age determination our results indicate that parana valles formed during the early hesperian period but that the crater density d 353 m is heterogeneous inside the parana valles basin the crater population decreases from the headwaters downstream recording a resurfacing event that is most likely related to the erosion of downstream sub basins the terrain near the source area is late noachian to early hesperian in age while terrains closer to the outlet are early to late hesperian in age crater densities d 125 m inside the valley are also heterogeneous and record several resurfacing events on the valley floor where the width of the valley network narrows to 2 km we found evidence of an amazonian age eolian deposit that is a relatively thin layer of only few meters that was probably deposited as a result of topographic influences our results validate the reliability of several proposed age dating techniques but we also determined the accuracy and applicability of these techniques our results also demonstrate that crater populations can be used to not only determine the relative ages of valley networks but also to map the distribution of sedimentary materials and the extent of resurfacing events that occurred after valley network formation

an integrated algorithm to evaluate flow direction and flow accumulation in flat regions of hydrologically corrected dems in order to conduct an accurate hydrological analysis of a watershed certain conditions need to be understood flow direction and flow accumulation are important watershed characteristics that need to be determined before an analysis can be made other important characteristics which can be gleaned from analysing the digital elevation model dem of a watershed include channel networks stream lengths and watershed boundaries determining flow direction and flow accumulation is usually carried out in separate steps flat regions are types of terrain in raster dems without local elevation gradients evaluating flow direction and flow accumulation in flat regions using dems is a well known problem in watershed analysis because of the occurrence of problematic parallel flow lines calculations also tend to be time consuming we have developed an efficient and comprehensive integrated approach to assign flow directions and flow accumulation in flat regions this approach uses values for non flat flow accumulation and a maze algorithm with a weight value mw method to determine several things a main flow line through the flat area to the local outlet an octree tree and first in first out queue structures to calculate flow accumulation the mw method can be applied to hydrologically corrected dems and a single flow path can be provided to resolve all flat areas to investigate the influence on the topological properties of the channel networks we used this integrated algorithm to extract three sets of flow accumulation areas from existing dems using this new integrated method was faster than using the two existing methods and produced continuous channel networks without the occurrence of problematic parallel flow lines

sensitivity of watershed attributes to spatial resolution and interpolation method of lidar dems in three distinct landscapes this study investigates scaling relationships of watershed area and stream networks delineated from lidar dems the delineations are tested against spatial resolution including 1 5 10 25 and 50 m and interpolation method including inverse distance weighting idw moving average ma universal kriging uk natural neighbor nn and triangular irregular networks tin study sites include mosquito creek scotty creek and thomas brook representing landscapes with high low and moderate change in elevation respectively results show scale dependent irregularities in watershed area due to spatial resolution at thomas brook and mosquito creek the highest sensitivity of watershed area to spatial resolution occurred at scotty creek due to high incidence of lidar sensor measurement error and subtle changes in elevation length of drainage networks did not show a scaling relationship with spatial resolution due to algorithmic complications of the stream initiation threshold stream lengths of main channels at thomas brook and mosquito creek displayed systematic increases in length with increasing spatial resolution described through an average fractal dimension of 1 059 the scaling relationship between stream length and dem resolution allows estimation of stream lengths from low resolution dems in the absence of high resolution dems single stream validation at thomas brook showed the 1 m dem produced the lowest length error and highest spatial accuracy at 3 7 and 71 3 respectively single stream validation at mosquito creek showed the 25 m dem produced the lowest length error and the 1 m dem the highest spatial accuracy at 0 6 and 61 0 respectively

the treatment of flat areas and depressions in automated drainage analysis of raster digital elevation models methods developed to process raster digital elevation models dem automatically in order to delineate and measure the properties of drainage networks and drainage basins are being recognized as potentially valuable tools for the topographic parameterization of hydrological models all of these methods ultimately rely on some form of overland flow simulation to define drainage courses and catchment areas and therefore have difficulty dealing with closed depressions and flat areas on digital land surface models some fundamental assumptions about the nature of these problem topographic features in dem are implicit in the various techniques developed to deal with them in automated drainage analysis the principal assumptions are 1 that closed depressions and flat areas are spurious features that arise from data errors and limitations of dem resolution 2 that flow directions across flat areas are determined solely by adjacent cells of lower elevation and 3 that closed depressions are caused exclusively by the underestimation of dem elevations it is argued that while the first of these assumptions is reasonable given the quality of dems generally available for hydrological analysis the others are not rather it seems more likely that depressions are caused by both under and overestimation errors and that flow directions across flat areas are determined by the distribution of both higher and lower elevations surrounding flat areas two new algorithms are introduced that are based on more reasonable assumptions about the nature of flat areas and depressions and produce more realistic results in application these algorithms allow breaching of depression outlets and consider the distribution of both higher and lower elevations in assigning flow directions on flat areas the results of applying these algorithms to some real and hypothetical landscapes are presented 1998 john wiley sons ltd

antarctic ice sheet balance velocities from merged point and vector data we estimate antarctic ice flow balance velocities which are the average speeds that ice must flow downslope through a volume assuming that there are equal amounts of ice entering and leaving the ice volume we use the osu ohio state university digital elevation model of antarctica recent ice accumulation rate data and the bedmap ice thickness data compilations for antarctica to characterize the physical properties of the ice sheet that are included in the balance velocity calculation we adapt a flux algorithm from the hydrology literature that enables us to calculate the flux distribution from any cell in any order flux from one cell to its neighbors is partitioned as a simple function of surface slope direction digitized flow stripe directions from satellite images minimize errors in flow direction where surface slopes are low or complex we estimate errors in balance velocity arising from errors in the data and show semi quantitatively how properties of the algorithm bias the balance velocity result we find a favorable comparison between our model and observed velocity data as well as the balance velocity patterns reported by other researchers

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

relationship between iron meteorite composition and size compositional distribution of irons from north africa abstract during the past three decades many iron meteorites have been collected from the deserts of north africa almost all are now characterized and the distribution among classes is found to be very different from those that were in museums prior to the collection of meteorites from hot and cold antarctica deserts similar to the iron meteorites from antarctica the irons from northwest africa include a high fraction of ungrouped irons and of minor subgroups of group iab the different distribution is attributed to the small median size of the desert meteorites 1 3 kg in north african irons 30 kg in non desert irons it appears that a sizable fraction of these small several centimeter masses constitute melt pockets produced by impacts in chondritic regoliths they were never part of a large meter to kilometer magma bodies as a result a meter size fragment ejected from the regolith of the asteroid may contain several of these small metallic masses it may be that such stochastic sampling effects enhanced the fraction of iab shl irons among the irons from northwest africa the variety observed in small meteoroids is also enhanced because relative to large small fragments are more efficiently ejected from asteroids and because the orbital parameters of small meteoroids are more strongly affected by collisions and drag effects they evolve to have earth crossing perihelia more rapidly than large meteoroids as a result the set of small meteoroids tends to sample a larger number of parent asteroids than does the set of larger meteoroids

how long is a hillslope hillslope length is a fundamental attribute of landscapes intrinsically linked to drainage density landslide hazard biogeochemical cycling and hillslope sediment transport existing methods to estimate catchment average hillslope lengths include inversion of drainage density or identification of a break in slope area scaling where the hillslope domain transitions into the fluvial domain here we implement a technique which models flow from point sources on hilltops across pixels in a digital elevation model dem based on flow directions calculated using pixel aspect until reaching the channel network defined using recently developed channel extraction algorithms through comparisons between these measurement techniques we show that estimating hillslope length from plots of topographic slope versus drainage area or by inverting measures of drainage density systematically underestimates hillslope length in addition hillslope lengths estimated by slope area scaling breaks show large variations between catchments of similar morphology and area we then use hillslope length relief structure of landscapes to explore nature of sediment flux operating on a landscape distinct topographic forms are predicted for end member sediment flux laws which constrain sediment transport on hillslopes as being linearly or nonlinearly dependent on hillslope gradient because our method extracts hillslope profiles originating from every ridgetop pixel in a dem we show that the resulting population of hillslope length relief measurements can be used to differentiate between linear and nonlinear sediment transport laws in soil mantled landscapes we find that across a broad range of sites across the continental united states topography is consistent with a sediment flux law in which transport is nonlinearly proportional to topographic gradient

a new triangular multiple flow direction algorithm for computing upslope areas from gridded digital elevation models 1 gridded digital elevation data often referred to as dems are one of the most widely available forms of environmental data topographic analysis of dems can take many forms but in hydrologic and geomorphologic applications it is typically used as a surrogate for the spatial variation of hydrological conditions topographic indices and flow routing here we report on a new flow routing algorithm and compare it to three common classes of algorithms currently in widespread use the advantage of the new algorithm is that unrealistic dispersion on planar or concave hillslopes is avoided whereas multiple flow directions are allowed on convex hillslopes we suggest that this new triangular multiple flow direction algorithm md1 is more appropriate for a range of flow routing and topographic index applications

a contour based topographic model for hydrological and ecological applications a digital model for discretizing three dimensional terrain into small irregularly shaped polygons or elements based on contour lines and their orthogonals is described from this subdivision the model estimates a number of topographic attributes for each element including the total upslope contributing area element area slope and aspect this form of discretization of a catchment produces natural units for problems involving water flow as either a surface or subsurface flow phenomenon the model therefore has wide potential application for representing the three dimensionality of natural terrain and water flow processes in the fields of hydrology sedimentology and geomorphology three example applications are presented and discussed they are the prediction of zones of surface saturation the prediction of the distribution of potential daily solar radiation and the prediction of zones of erosion and deposition in a catchment

spatial organization of soil depths using a landform evolution model 1 the evolution of soil depths is investigated by modeling the interaction between soil production and surface erosion within a landform evolution model an enhanced version of the landform evolution model siberia that incorporates a soil evolution module is used to simulate evolving landforms and soils depths over geologic timescales the spatial and temporal evolution of soil depths are examined at the hillslope scale though it is widely accepted among the geomorphology community that soil water enhances chemical physical and biological weathering processes its effect has not been explicitly included in published models of soil production the main scientific questions that we address are 1 what are the implications of incorporating soil moisture dependency in the soil production function and 2 what type of soil production dynamics is needed to generate a bedrock topography that has a different spatial pattern from that of the ground surface a range of physics for the soil production model is explored the effect of soil moisture is included using the wetness index obtained from drainage analysis of either surface elevations or the bedrock topography the results show that the various soil production functions that incorporate either a wetness index or subsurface flow depth based on the bedrock topography give rise to soils that self organize with well defined spatial patterns and bedrock elevations with spatial organization significantly different from that of the surface the model that incorporates the influence of subsurface water on soil production is able to naturally generate a soil production rate with a maximum value for a nonzero soil depth and overcomes an inconsistency of previously published humped soil production models

channel network extraction from high resolution topography using wavelets 1 the availability of high resolution topography from lidar offers new opportunities for objectively extracting the channels directly from a dem using local topographic information instead of inferring them indirectly based on global criteria such as area or area slope threshold relationships here we introduce the use of wavelet filtering to delineate threshold curvatures for defining valleys and threshold slope direction change for defining probable channeled portions of the valleys this approach exploits the topographic signatures uniquely found in high resolution topography and reveals the fuzzy topographic transition in which local weakly convergent areas lie at the transition between hillslopes and valleys

compositional range in the canyon diablo meteoroid abstract the ir distribution in the iab canyon diablo meteorites associated with the formation of meteor crater arizona ranges from 2 1 to 2 5 g g with peaks at 2 17 and 2 34 g g only ir ni and cu show appreciably more variance in the large set of specimens than observed within a single specimen the ir peaks may reflect random sampling of the large 40 100 m fractionated meteoroid or the presence of two distinct metallic regions differing in composition none of the other elements we determined show strong correlations with ir the au range is strikingly small 1 5 1 6 g g the presence of chondritic silicates and high contents of planetary type noble gases in iab indicates that these solidified rapidly following melting as expected if they originated as pools of impact generated melt on a chondritic body the absence of fractional crystallization trends is consistent with such a model that 14 of 15 ir contents fall into two peaks suggests the possibility that the meteoroid included two pools the alternative that the distribution is continuous can be tested by the study of additional specimens those from the crater rim are particularly important since these are largely shrapnel spalled from the trailing hemisphere of the meteoroid our studies show that the irons named helt township idaho las vegas mamaroneck moab and pulaski county are probably mislabelled canyon diablo specimens jenny s creek and jenkins are also compositionally indistinguishable alexander county allan hills a77283 ashfork fairfield and rifle are compositionally distinct independent falls

an automated method for producing synoptic regional maps of river gradient variation procedure accuracy tests and comparison with other knickpoint mapping methods abstract the study of abrupt changes in longitudinal river profiles or knickpoints is currently approached through an empirical power law the slope area relationship results based on digital elevation model dem analyses and stream extractions are generally intended to determine crustal uplift rates and identify transient landscape conditions in this article we present an alternative geomorphometric method for locating knickpoints and knickzones based on local slope gradient and curvature attributes intended as a rapid regional scale automated knickpoint detection technique the accuracy of this slope curvature method is tested on two digital elevation grids nasa s srtm ground resolution of 90 m resampled here to 75 m and the aster dem 15 m in the sierra nacimiento new mexico usa a basement cored mountain range recently exhumed by waves of headward drainage integration in response to remote tectonic deformation in the adjacent rio grande rift out of every 10 gradient anomalies detected by the srtm derived numeric routine up to 8 are certifiable knickpoints recognized among a population of georeferenced occurrences surveyed in the field an independent comparison with the slope area method provided a further accuracy test which was particularly useful at sites that could not be validated in the field for practical reasons given the low tectonic activity of the study area the majority of knickpoints was also found to coincide with lithologic boundaries making it difficult without further geomorphological data to single out dynamic knickpoints directly caused by the upstream propagation of channel instabilities relating to base level change

on the application of sar interferometry to geomorphological studies estimation of landform attributes and mass movements this paper presents two examples of application of synthetic aperture radar sar interferometry insar to typical geomorphological problems the principles of insar are introduced taking care to clarify the limits and the potential of this technique for geomorphological studies the application of insar to the quantification of landform attributes such as the slope and to the estimation of landform variations is investigated two case studies are presented a first case study focuses on the problem of measuring landform attributes by interferometric sar data the interferometric result is compared with the corresponding one obtained by a digital elevation model dem in the second case study the use of insar for the estimation of landform variations caused by a landslide is detailed

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

siderophile element systematics of iab complex iron meteorites new insights into the formation of an enigmatic group siderophile trace element abundances and the 187re 187os isotopic systematics of the metal phases of 58 iab complex iron meteorites were determined in order to investigate formation processes and how meteorites within chemical subgroups may be related close adherence of 187re 187os isotopic data of most iab iron meteorites to a primordial isochron indicates that the siderophile elements of most members of the complex remained closed to elemental disturbance soon after formation minor presumably late stage open system behavior however is observed in some members of the slm slh shl and shh subgroups the new siderophile element abundance data are consistent with the findings of prior studies suggesting that the iab subgroups cannot be related to one another by any known crystallization process equilibrium crystallization coupled with crystal segregation solid liquid mixing and subsequent fractional crystallization can account for the siderophile element variations among meteorites within the iab main group mg the data for the slm subgroup are consistent with equilibrium crystallization combined with crystal segregation and mixing by contrast the limited fractionation of siderophile elements within the sll subgroup is consistent with metal extraction from a chondritic source with little subsequent processing the limited data for the other subgroups were insufficient to draw robust conclusions about crystallization processes involved in their formation collectively multiple formational processes are represented in the iab complex and modeling results suggest that fractional crystallization within the mg may have been a more significant process than has been previously recognized

evaluation of approaches to calculate debris flow parameters for hazard assessment abstract many different runout prediction methods can be applied to estimate the mobility of future debris flows during hazard assessment the present article reviews the empirical analytical simple flow routing and numerical techniques all these techniques were applied to back calculate a debris flow which occurred in 1982 at la guingueta catchment in the eastern pyrenees a sensitivity analysis of input parameters was carried out while special attention was paid to the influence of rheological parameters we used the voellmy fluid rheology for our analytical and numerical modelling since this flow resistance law coincided best with field observations the simulation results indicated that the basal friction coefficients rather affect the runout distance while the turbulence terms mainly influence flow velocity a comparison of the velocity computed on the fan showed that the analytical model calculated values similar to the numerical ones the values of our rheological parameters calibrated at la guingueta agree with data back calculated for other debris flows empirical relationships represent another method to estimate total runout distance the results confirmed that they contain an important uncertainty and they are strictly valid only for the conditions which were the basis for their development with regards to the simple flow routing algorithm this methods could satisfactorily simulate the total area affected by the 1982 debris flow but it was not able to directly calculate total runout distance and velocity finally a suggestion on how different runout prediction methods can be applied to generate debris flow hazard maps is presented taking into account the definition of hazard and intensity the best choice would be to divide the resulting hazard maps into two types final hazard maps and preliminary hazard maps only the use of numerical models provided final hazard maps because they could incorporate different event magnitudes and they supplied output values for intensity calculation in contrast empirical relationships and flow routing algorithms or a combination of both could be applied to create preliminary hazard maps the present study only focussed on runout prediction methods other necessary tasks to complete the hazard assessment can be looked up in the guidelines for landslide susceptibility hazard and risk zoning included in this special issue

composition and formation of metal nodules and veins in ordinary chondrites abstract five large metal nodules a composite sample of five small metal nodules one troilite nodule and two metal veins from five ordinary chondrites were analyzed by electron microprobe and neutron activation analysis metal nodules and veins in h chondrites generally consist of large single crystals of kamacite whereas l nodules contain significant taenite most nodules and veins are depleted by large factors ranging up to 240 in refractory siderophiles re os ir pt tungsten normally a refractory siderophile and au as and ga volatile siderophiles have abundance ratios similar to those of the common siderophiles fe co and ni we propose that the metal with extremely low refractory element contents was produced by shock induced vaporization of chondritic material the refractory elements condensed near the point of vaporization and were not transported with the vapor because the shock generated gas was mildly oxidizing w formed volatile oxides the low ni fe ratio and the resulting high kamacite contents may reflect dilution by fe from dissociated fes subsequent condensation of the refractory depleted vapor into fractures and voids formed the metal veins and nodules

chemical classification of iron meteorites xi multi element studies of 38 new irons and the high abundance of ungrouped irons from antarctica abstract we report concentrations of 14 elements in the metal of 38 iron meteorites and a pallasite the meteorites are classified based on these data and on structural observations three samples are paired with previously classified irons thus these additional 35 irons raise the number of well classified independent iron meteorites to 598 one yamato iron contains 342 mg g ni the second highest ni content in an iab iron after oktibbeha county two small irons from western australia appear to be metal nodules from mesosiderites several of the new irons are from antarctica of 24 independent irons from antarctica 8 are ungrouped the fraction 0 333 is much higher than the fraction 0 161 among all 598 classified irons statistical tests show that it is highly improbable 2 9 probability that the antarctic population is a random sample of the larger population the difference is probably related to the fact that the median mass of antarctic irons is about two orders of magnitude smaller than that of non antarctic irons it is doubtful that the difference results from fragmentation patterns yielding different size distributions favoring smaller masses among ungrouped irons more likely is the possibility that smaller meteoroids tend to sample a larger number of asteroidal source regions perhaps because small meteoroids tend to have higher ejection velocities or because small meteoroids have random walked a greater increment of orbital semimajor axis away from that of the parent body

effects of catchment discretization on topographic index distributions summary digital elevation models dems are widely used in topographically based hydrology models most researchers dealing with dems have worked exclusively with either grid or contour based techniques intercomparisons of these techniques are empirical in nature few in number and limited to a small number of catchments we examine the relative effects of these techniques on the distribution of the topographic index ti for nine idealised hillslope types and eight natural catchments 4 4 83 km 2 in southeast australia in particular we investigate the underlying causes for the frequently observed increase in the ti with grid size a simple analytical model for a parallel planar hillslope indicates that median ti is asymptotic with respect to the number of grid cells and a linear function of grid size we demonstrate that the latter result holds for hillslopes with more complex geometry using a multiple flow direction algorithm we find that hillslope geometry and flow partitioning affect the spatial pattern of the ti and the rate of change m of median ti with grid size this makes it impractical to recommend general guidelines for the value of the directional parameter in flow partitioning algorithms for the natural catchments we show that median ti is also a linear function of grid size and that there is some evidence for a linear relationship between m and the inverse of the median topographic slope throughout the investigation we find that contour dems are less sensitive to changes in resolution than grid dems

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

vesta and extensively melted asteroids why hed meteorites are probably not from vesta abstract most researchers hold that the hed clan of differentiated meteorites originated on vesta largely based on the assumption that nearly all v type asteroids with basaltic reflection spectra are fragments spalled off vesta although it is a reasonable working hypothesis that most of the v type asteroids in the vesta family originated on vesta the spectra are not unique enough to confirm this a sizable fraction may have been produced during the destruction of a differentiated asteroid in the same large region of dynamic space observations of asteroids in the inner asteroid belt show that more than half of the v type asteroids do not belong to the vesta dynamic family iron meteorite evidence shows that at least 26 asteroids experienced extensive melting and would have generated basalts and other differentiated stony meteorites most iron meteorites show high degrees of elemental fractionations that lead to the conclusion that they experienced fractional crystallization it is probable that all these bodies generated basalts there are 9 of these magmatic iron meteorite groups and test criteria mainly based on extreme fractionations indicate that an additional 17 disrupted asteroids hosted fractionally crystallized cores and thus that 26 asteroids experienced extensive melting this estimate is much lower than previous estimates that included nonmagmatic irons within expected planetary heterogeneities the o isotopic composition of heds is the same as that in oxides from iiiab irons the largest magmatic group of iron meteorites e cr 54 values are also very similar in iiiabs and heds the o and cr isotopic ties are much stronger than the spectral tie thus the working hypothesis should be that heds are from the iiiab parent asteroid remote elemental analysis could confirm that heds are not from vesta if future remote analysis measures k contents 0 6 mg g this will indicate that heds did not originate on vesta

estimation of shear velocity profiles using shear source data in marine environment this paper estimates seabed shear velocity profiles and their uncertainties using interface wave dispersion curves extracted from data generated by a shear source the data were collected by 4c ocean bottom cable in a testing experiment of a shear source in the north sea the shear source generated a seismic signature over a frequency range between 2 and 60 hz and was polarized in both in line and cross line orientation low frequency scholte and love wave were recorded dispersion curves of the scholte and love wave for the fundamental mode and higher order modes are extracted by different time frequency analysis method both vertical sv and horizontal sh polarized shear velocity profiles are estimated by scholte and love wave dispersion curves respectively bayesian approach is used for the inversion differential evolution de global search algorithm is applied to estimate the most probable shear velocity models marginal posterior probability profiles are computed by metropolis hastings sampling the estimated sv and sh velocity profiles are compared and the results provide possibility of studying seabed anisotropy we thank statoil asa for permission to publish the data the work is partly supported by nfr under grant no 186923 i30

a comparison of simplified methods for routing topographically driven subsurface flow a series of numerical experiments are used to evaluate the accuracy of two approaches for modeling topographically driven subsurface flow suitable for inclusion in spatially distributed hydrologic models the first is an explicit grid cell by grid cell approach and the second is a statistical dynamic method widely used in topmodel both approaches were compared with analytical solutions to the kinematic wave equation for flow down an inclined plane of constant slope using a power law transmissivity function the hillslope discharge and water table profiles simulated by the explicit method were in good agreement with the analytic solution in all test cases the statistical dynamic method converged on the correct steady state solution but failed to reproduce accurately transient conditions the two algorithms were then compared using a 30 m dem representation of the mahantango pa basin and hourly precipitation measured at the site the agreement in discharge between the two methods improved with increasing soil thickness surface conductivity and power law exponent however the percent root mean squared difference rmsd in hourly discharge was above 20 percent in all cases the statistical dynamic model was then calibrated to discharge simulated by the explicit method calibration was most effective for soils with low power law exponents generally producing discharge hydrographs in closemore agreement for soils with linear transmissivity profiles however even under these conditions there are large discrepancies between local water table depths simulated by the two models the level of agreement is best during dry conditions and decreases during wetter conditions as the number of cells with surface soil saturation increases less

shear wave velocity structure of the shallow sediments in the bohai sea from an ocean bottom seismometer survey abstractto investigate the seismic velocity structure of the shallow sediments in the bohai sea of china we conducted a shear wave velocity inversion of the surface wave dispersion data from a survey of 12 ocean bottom seismometers obss and 377 shots of a 9000 in3 air gun with obs station spacing of approximately 5 km and air gun shot spacing of approximately 190 m high quality scholte wave data were recorded by the obss within 0 4 5 km offset we retrieved the scholte wave phase velocity dispersion for the fundamental mode and first overtone in the frequency band of 0 9 3 0 hz with the phase shift method and inverted for the shear wave velocity structure of the shallow sediments with a damped iterative least squares algorithm pseudo 2d shear wave velocity profiles with a depth of approximately 400 m revealed coherent features of relatively weak lateral velocity variation we also estimated the uncertainty in shear wave velocity structure based on the pseudo 2d profiles from six trial inversions wi

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

terrain controls on depressional soil distribution in a hummocky morainal landscape in hummocky morainal landscapes soil distribution in well drained landscape positions tends to follow a consistent pattern soils in depressions however are more difficult to predict reliably this study had two objectives 1 to determine the parent material and landscape properties controlling the formation of the different depressional soils and 2 to use these controls to identify quantitative terrain based predictors of soil type in depressions only two terrain attributes specific dispersal area sda and elevation relative to open water bodies were required to distinguish three main soil groups gley recharge non gley recharge and discharge soils specific dispersal area is the downslope area draining flow from a given grid cell gley recharge soils occur primarily at points with sda of less than 2 m2 m 1 regardless of elevation within a given site because most of the runoff flowing to a point with very low sda values will pond or infiltrate vertically rather than flow downslope non gley recharge soils and discharge soils both occur at points with sda of greater than 2 m2 m 1 the majority of the non gley recharge soils occur above 5 m elevation relative to an open water body and the majority of the discharge soils occur below 5 m elevation relative to an open water body reflecting the importance of solute cycling in the development of discharge conditions buried and depositional soils could not be predicted from current terrain attributes because their profile characteristics were derived from the paleosurface

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

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

the information content theory for the estimation of the topographic index distribution used in topmodel this paper analyses the significance of the entropy concept in the topography parameterization within the model topmodel proposed by beven and kirkby 1979 by means of the hydrological behaviour of an experimental basin in southern italy for a significant number of flood events recorded at the basin outlet the performance of topmodel for different spatial distributions of the topographic index ln a tan has been observed performance is related to the information content estimated as an entropy measure corresponding to each of the spatial distributions of the topographic index with the aim of identifying the procedures most suitable to represent the hydrological process of rainfall runoff the results obtained have shown that for flood events corresponding to brief heavy precipitation some procedures provide better performances than others moreover these improvements are justified by greater information content in the corresponding spatial distributions of the topographic index finally topmodel performances for some procedures have been analysed varying the resolution scale of the topographic index for analogous hydrological performances scale change produced variations in some of the subsurface hydraulic parameters these variations were proportional to a spatial variability measure of the topographic index distribution derived from the corresponding information content 1997 john wiley sons ltd

the iab iron meteorite complex a group five subgroups numerous grouplets closely related mainly formed by crystal segregation in rapidly cooling melts abstract we present new data for iron meteorites that are members of group iab or are closely related to this large group and we have also reevaluated some of our earlier data for these irons in the past it was not possible to distinguish iab and iiicd irons on the basis of their positions on element ni diagrams but we now show that plotting the new and revised data yields six sets of compact fields on element au diagrams each set corresponding to a compositional group the largest set includes the majority 70 of irons previously designated ia we christened this set the iab main group the remaining five sets we designate subgroups within the iab complex three of these subgroups have au contents similar to the main group and form parallel trends on most element ni diagrams the groups originally designated iiic and iiid are two of these subgroups they are now well resolved from each other and from the main group the other low au subgroup has ni contents just above the main group two other iab subgroups have appreciably higher au contents than the main group and show weaker compositional links to it we have named these five subgroups on the basis of their au and ni contents the three subgroups having au contents similar to the main group are the low au l subgroups the two others the high au h subgroups the ni contents are designated high h medium m or low l thus the old group iiid is now the slh subgroup the old group iiic is the slm subgroup in addition eight irons assigned to two grouplets plot between sll and slm on most element au diagrams a large number 27 of related irons plot outside these compact fields but nonetheless appear to be sufficiently related to also be included in the iab complex many of these irons contain coarse silicates having similar properties most are roughly chondritic in composition the mafic silicates show evidence of reduction during metamorphism in each case the silicate o isotopic composition is within the carbonaceous chondrite range 17o 0 3 in all but four cases these are within the so called iab range 0 30 17o 0 68 fine silicates appear to be ubiquitous in the main group and low au subgroups this requires that viscosities in the parental melt reached high values before buoyancy could separate these the well defined main group trends on element au diagrams provide constraints for evaluating possible models we find the evidence to be most consistent with a crystal segregation model in which solid and melt are essentially at equilibrium the main arguments against the main group having formed by fractional crystallization are a the small range in ir and b the evidence for rapid crystallization and a high cooling rate through the iron stability field the evidence for the latter are the small sizes of the iron crystals parental to the widmanstatten pattern and the limited thermal effects recorded in the silicates including retention of albitic plagioclase and abundant primordial rare gases in contrast crystal segregation in a cooling metallic melt and related processes such as incomplete melting and melt migration can produce the observed trends in the main group we infer that this melt was formed by impact heating on a porous chondritic body and that the melt was initially hotter than the combined mix of silicates and metal in the local region the melt cooled rapidly by heat conduction into the cooler surroundings mainly silicates we suggest that the close compositional relationships between the main group and the low au subgroups are the result of similar processes instigated by independent impact events that occurred either at separate locations on the same asteroid or on separate but compositionally similar asteroids