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

hazard assessment of rainfall induced landsliding in mexico abstract rainfall induced landsliding represents a major hazard in mexico about 200 municipalities in the states of puebla veracruz and hidalgo were affected by flooding and mass movement processes that resulted from a tropical depression from the atlantic ocean in october 1999 hundreds of slope failures were triggered by intense precipitation which in some localities reached 420 mm during a 24 h period according to official information 263 people died and 1 475 654 inhabitants were affected by flooding and landsliding rainfall event and cycle coefficient defined and the ratios between event and antecedent rainfalls respectively and the mean annual rainfall are summed to give a total coefficient for landslide triggering rainfalls in the sierra norte values for the total coefficient of 0 8 and 0 4 for beginning and end of the wet season respectively appear to be important in addition a hazard assessment was carried out through the development of a landslide susceptibility indicator this was elaborated by using aerial photographs integrating field observations and the coupling of slope instability analysis within a digital elevation model framework field validation indicated that this approach provides a good representation of shallow translational failures 81 of the observed landslides were satisfactorily predicted as potential unstable zones results suggested that this type of dem based hazard assessment can be extremely valuable not only after but also before any landslide related event so that disaster preparedness and planning could be adequately structured

enclaves provide new insights on the dynamics of magma mingling a case study from salina island southern tyrrhenian sea italy abstract three lava flows hereafter flows a b and c from salina island italy consist of basaltic andesitic enclaves dispersed in a dacitic matrix enclaves represent 8 12 vol of the erupted magma the number of enclaves and the surface covered by the enclaves at each outcrop do not vary significantly with the distance from the vent in the flows a and b these feature reflect the dynamics of magma mingling within the reservoir and not the kinematics of the lava flow in the flow c these parameters vary irregularly the statistical entropy s t of the enclaves which is a measure of their spatial distribution dispersion is estimated in outcrops located at different distance from the vent the kolmogorov sinai entropy rate k which describes the variations of s t with time is also determined in the lava flow a s t increases linearly with time t for 0 0 5 s t attains its maximum value and maintains constant with increasing t in the lava flow b s t linearly increases with t and k is 0 01 in the lava flow c there is not correlation between s t and t the comparison between the results from the analysis of the porri enclaves and those from numerical experiments on the variation of s t in chaotic advective mixing systems and from previous experimental models on magma mixing allow us to draw some conclusions on dynamics of the basaltic andesite dacite mingling in the magma chamber fully chaotic magma mingling systems show three evolution stages an initial stage which is unknown because of the disruption of the initial configuration of the interacting magmas a second stage characterized by a linear increase of the statistical entropy with time and a third stage in which the uniformity of the system is reached and the entropy does not vary with increasing time a system in which the uniformity is never attained is characterized by irregular variations of s t with time in the flows a and b the relations between s t and t are consistent with those of a fully chaotic dynamics possibly associated to convection the basaltic andesite was uniformly distributed in the dacitic host due to the occurrence of convective movements driven by the injection of the basaltic andesite within the dacitic chamber the mingling system recorded by the lava flow a evolved with a higher rate with respect to that of the flow b this suggests that chaotic advection stirring and folding is more efficient in the magmatic system a than in b on the contrary the mingling system c is characterized by a non uniform distribution of the basaltic andesite within dacite this reflects the occurrence of a dynamics in which stirring and folding processes do not operate efficiently and are unable to uniformly distribute the dispersed phase within the continuous one the decrease of k from a to b and the lack of a measurable k in c along with the observation that a and b were emitted before c indicate that the efficiency of advective movements within the porri magma chamber declined with decreasing time mingled magmas characterized by a homogeneous spatial distribution of enclaves or an initially inhomogeneous distribution evolving towards a homogeneous one are indicative of efficient advection processes that may favor magma mixing mingled magmas characterized by an inhomogeneous distribution of enclaves suggest low dynamical interaction between the two end members magma mixing is not allowed

gis techniques and statistical models in evaluating landslide hazard geographical information systems gis and numerical cartography may greatly facilitate the development and use of statistical models for the assessment of regional landslide hazard from a small drainage basin located in central italy relevant geological and geomorphological factors were collected and processed by applying gis technology in particular modules were used which both generate high fidelity digital terrain models and automatically partition the terrain into main slope units the resulting information was then analysed by discriminant analysis which enabled landslide hazard and risk to be evaluated in each slope unit although not lacking drawbacks the method proved to be a feasible and cost effective approach to landslide susceptibility assessment and mapping

mapping of risk and susceptibility of shallow landslide in the city of sao paulo brazil abstract in the city of sao paulo where about 11 million people live landslides and flooding occur frequently especially during the summer these landslides cause the destruction of houses and urban equipment economic damage and the loss of lives the number of areas threatened by landslides has been increasing each year the objective of this article is to analyze the probability of risk and susceptibility to shallow landslides in the limoeiro river basin which is located at the head of the aricanduva river basin one of the main hydrographic basins in the city of sao paulo to map areas of risk we created a cadastral survey form to evaluate landslide risk in the field risk was categorized into four levels based on natural and anthropogenic factors r1 low risk r2 average risk r3 high risk and r4 very high risk to analyze susceptibility to shallow landslides we used the shalstab shallow landsliding stability mathematical model and calculated the distribution frequency df of the susceptibility classes for the entire basin finally we performed a joint analysis of the average risk concentration rc and risk potential rp we mapped 14 risk sectors containing approximately 685 at risk homes more than half of which presented a high r3 or very high r4 probability of risk to the population in the susceptibility map 41 of the area was classified as stable and 20 as unconditionally unstable although the latter category accounted a smaller proportion of the total area it contained a concentration rc of 41 of the mapped risk areas with a risk potential rp of 12 we found that the locations of areas predicted to be unstable by the model coincided with the risk areas mapped in the field this combination of methods can be applied to evaluate the risk of shallow landslides in densely populated areas and can assist public managers in defining areas that are unstable and inappropriate for occupation

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

strug landslide in w slovenia a complex multi process phenomenon abstract large rock slides frequently cause secondary unstable phenomena many such instability processes happened after december 2001 when the strug rockslide estimated at 95 000 m3 was triggered above the kosec village near kobarid in the julian alps w slovenia it was initiated at the contact between high permeable calcareous rocks cretaceous scaglia thrusted over nearly impermeable clastic rocks cretaceous flysch soon after the rockslide initiation a rock fall with a volume of 45 000 m3 was initiated within the rockslide the kinetic push of the rock fall caused the movement of a translational soil landslide with a volume of 180 000 m3 that partially slipped into the torrential ravine of the brusnik stream after a sudden drop of 15 m in december 2001 the rockslide average velocity exponentially slowed down to less than 10 m year till the end of 2002 and came to a practical stillstand in 2003 after the rainfall in spring 2002 small debris flows made of clayey gravels with a volume of up to 1000 m3 started to flow from the zone of accumulation of the rock fall over the soil landslide to and along the channel of the brusnik stream in 2002 more than 20 debris flow events were registered the statistical analysis of the measured local rainfall intensities showed that debris flows were initiated at daily rainfall reaching from 20 to 30 mm depending on the antecedent precipitation this value may be taken as a specific hydrologic threshold for this site because in 2003 no more debris flows were registered a conclusion was drawn that debris flow events were rainfall induced but governed on the same time by the availability of rock fall debris in its zone of accumulation

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

rainfall induced landslide hazard assessment using artificial neural networks in japan landslides triggered by heavy rainfall tend to occur during the annual rainy season from early june until the middle of july these landslides constitute a major hazard causing significant property damage and loss of life this paper proposes the use of back propagation neural networks bpnn to predict the probability of landslide occurrence for a scenario of heavy rainfall in the minamata area of southern kyushu island japan all of the landslides were detected from aerial photographs taken in 1999 2001 and 2003 and a geospatial database of lithology topography soil characteristics land use and precipitation was constructed using geographical information systems gis the training sample consists of 602 cells that include landslide activity and 1600 cells in stable areas using the trained bpnn with 49 input nodes three hidden layers and one output node 239 589 cells were processed to produce a map of landslide probability for a maximum daily precipitation of 329 mm and a maximum cumulative precipitation of 581 mm for an incessant intense rainfall event in the future the resultant hazard map was classified into four hazard levels it can be referenced for land use planning and decision making for community development copyright 2005 john wiley sons ltd

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 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

effects of digital elevation model map scale and data resolution on a topography based watershed model the effects of digital elevation model dem map scale and data resolution on watershed model predictions of hydrologic characteristics were determined for topmodel a topography based watershed model the effects of topography on watershed hydrology are represented in topmodel as the distribution of ln a tan b where ln is the napierian logarithm a is the upslope area per unit contour length and tan b is the gravitational gradient the minimum maximum mean variance and skew values of the ln a tan b distribution were computed from 1 24 000 scale 24k dems at 30 and 90 m resolutions and from 1 250 000 scale 250k dems at 90 m resolution for 71 areas in pennsylvania new york and new jersey an analysis of topmodel showed that model predictions of the depth to the water table the ratio of overland flow to total flow peak flow and variance and skew of predicted streamflow were affected by both the dem map scale and data resolution further topmodel analyses showed that the effects of dem map scale and data resolution on model predictions were due to the sensitivity of the predictions to the mean of the ln a tan b distribution which was affected by both dem map scale and data resolution dem map scale affected the mean of the ln a tan b distribution through its influence on the mean of the ln a distribution which characterizes land surface shape and the mean of ln 1 tan b distribution which characterizes land surface slope dem resolution in contrast affected the mean of the ln a tan b distribution primarily by its influence on the mean of the ln a distribution

the 1998 debris avalanche at casita volcano nicaragua investigation of structural deformation as the cause of slope instability using remote sensing abstract during hurricane mitch in 1998 a debris avalanche occurred at casita volcano nicaragua resulting in a lahar that killed approximately 2500 people the failure that initiated the avalanche developed at a pre existing cliff part of the headwall of a gravitational slide of approximately 1 8 km 2 in plan view that cuts the southern flank of the volcano structural analysis primarily based on a high resolution dem has shown that this slide is caused by edifice deformation casita s eastern side is spreading radially outwards forming a convex concave profile and steepening original slopes this deformation is possibly facilitated by millennia of persistent hydrothermal alteration of the volcano s core the gravity slide has some typical features of smaller slumps such as steep headwalls an inner flatter area and a pronounced basal bulge fronted by thrusts the headwall is the source of the 1998 avalanche as well as several previous mass movements edifice deformation has led to extensive fracturing of the hydrothermally altered andesitic source rock increasing instability further field evidence indicates that the gravity slide is still actively deforming and with steep headscarps remaining the hazard of future avalanches is increasing the analysis presented here shows how small but highly damaging landslides can occur during the deformation of a volcanic edifice we show that identification of instability is possible with remote sensing data and minimal reconnaissance work implying the possibility of similar efficient and cost effective analysis at other volcanoes known to host extensive hydrothermal systems we demonstrate this with a simple structural analysis of two similar stratovolcanoes orosi costa rica and maderas nicaragua

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

predicting landslides from rainfall in a humid sub tropical region abstract topography geology and a humid sub tropical climate make the durban region on the east coast of south africa particularly prone to sliding mass movements records of individual landslides and landslide events between 1970 and 1990 were compared with 22 rainfall variables calculated for the same period correlation coefficients demonstrated statistically significant relationships between annual and wet season landslide frequencies and maximum 3 day and maximum monthly wet season rainfall whereas precipitation for shorter and longer periods was unrelated envelopes of critical values for cycle and total coefficients based on the percent of mean annual rainfall were identified for both the timing and magnitude of landslide events they suggest a two stage equilibrium condition for the rainfall mass movement relationship controlled by average wet season rainfall moreover once the pattern of rainfall for any particular wet season is established the envelopes allow the prediction of rainfall conditions necessary for landslides to occur the likelihood of an inaccurate prediction is approximately 10

an approach towards deterministic landslide hazard analysis in gis a case study from manizales colombia a one dimensional deterministic slope stability model infinite slope model was used to calculate average safety factors and failure probabilities for the city of manizales in central colombia an engineering geological data base has been created on the basis of a series of parameter maps geology geomorphology digital terrain models and slope classes using logic reasoning in geographic information systems gis a two dimensional hydrological model was applied to estimate groundwater levels in relation to rainfall events a simple method for the calculation of horizontal seismic acceleration was used for different earthquake events to calculate average safety factors a number of scenarios were developed by combining the effects of groundwater and seismic acceleration with different return periods a simple method for error propagation was used to calculate the variance of the safety factor and the probability that it will be less than 1 for each pixel within a time period of 20 years the highest probability value of the various scenarios was selected for each pixel and a final hazard map for translational landslides was constructed the results presented here are a first approach towards a deterministic landslide hazard analysis using gis it has a number of drawbacks which should be solved in future work

derivation of the chalk superficial deposits of the north downs england an application of discriminant analysis abstract stepwise discriminant analysis was used on particle size and heavy mineral data from 276 sediment samples including 39 from published sources to distinguish between palaeocene and plio pleistocene deposits found above the cretaceous chalk in southeast england and to determine parent materials of the soils and superficial deposits of the central north downs of 71 known cases in situ deposits 85 9 were correctly classified using textural data sig 99 9 and 89 7 of 29 known cases sig 99 9 using heavy mineral data the best textural discriminating variables were sand graphic mean clay and graphic skewness and the best heavy mineral discriminants were kyanite plus staurolite andalusite and garnet discriminant analysis has achieved good differentiation between marine plio pleistocene sands clay with flints loess and palaeocene groups and allowed objective classification of sediments of unknown origin the distribution of parent materials revealed strongly upholds the earlier interpretation z geomorphol 39 1995 433 that in the central north downs except where palaeocene residuals survive the superficial cover above the chalk consists of in situ clay with flints sensu stricto beneath plateau drift and loess clay with flints is seen as residual and plateau drift as a pleistocene soliflucted deposit textural affinities of reading beds clay and clay with flints elicited by a third discriminant analysis using additional published data from 22 samples suggest their common derivation from chalk residua

erosion thresholds and land surface morphology we propose a graphical technique to analyze the entirety of landforms in a catchment to define quantitatively the spatial variation in the dominance of different erosion processes high resolution digital elevation data of a 1 2 km2 hilly area where the channel network had been mapped in the field were used in the digital terrain model topog to test threshold theories for erosion the land surface was divided into 20 m2 elements whose shapes were then classified as convergent planar or divergent the entire landscape plotted on a graph of area per unit contour length against surface gradient shows each planform plotting as a separate field a simple steady state hydrologic model was used to predict zones of saturation and areas of high pore pressure to mimic the extreme hydrologic events responsible for erosive instability of the land surface the field observation that saturation overland flow is rare outside convergent zones provided a significant constraint on the hydrologic parameter in the model this model was used in threshold theories to predict areas of slope instability and areas subject to erosion by saturation overland flow both of which can contribute to channel initiation the proportion of convergent elements predicted to exceed the threshold varies greatly with relatively small changes in surface resistance demonstrating a high sensitivity to land use such as cattle grazing overall the landscape can be divided using erosion threshold lines into areas prone to channel instability due to runoff and stable areas where diffusive transport predominates

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

landslide characteristics and slope instability modeling using gis lantau island hong kong steep terrain and high a frequency of tropical rainstorms make landslide occurrence on natural terrain a common phenomenon in hong kong this paper reports on the use of a geographical information systems gis database compiled primarily from existing digital maps and aerial photographs to describe the physical characteristics of landslides and the statistical relations of landslide frequency with the physical parameters contributing to the initiation of landslides on lantau island in hong kong the horizontal travel length and the angle of reach defined as the angle of the line connecting the head of the landslide source to the distal margin of the displaced mass are used to describe runout behavior of landslide mass for all landslides studied the horizontal travel length of landslide mass ranges from 5 to 785 m with a mean value of 43 m and the average angle of reach is 27 7 this gis database is then used to obtain a logistic multiple regression model for predicting slope instability it is indicated that slope gradient lithology elevation slope aspect and land use are statistically significant in predicting slope instability while slope morphology and proximity to drainage lines are not important and thus excluded from the model this model is then imported back into the gis to produce a map of predicted slope instability the results of this study demonstrate that slope instability can be effectively modeled by using gis technology and logistic multiple regression analysis