evaluation of different machine learning models for predicting and mapping the susceptibility of gully erosion abstract gully erosion constitutes a serious problem for land degradation in a wide range of environments the main objective of this research was to compare the performance of seven state of the art machine learning models svm with four kernel types bp ann rf and brt to model the occurrence of gully erosion in the kashkan poldokhtar watershed iran in the first step a gully inventory map consisting of 65 gully polygons was prepared through field surveys three different sample data sets s1 s2 and s3 including both positive and negative cells 70 for training and 30 for validation were randomly prepared to evaluate the robustness of the models to model the gully erosion susceptibility 12 geo environmental factors were selected as predictors finally the goodness of fit and prediction skill of the models were evaluated by different criteria including efficiency percent kappa coefficient and the area under the roc curves auc in terms of accuracy the rf rbf svm brt and p svm models performed excellently both in the degree of fitting and in predictive performance auc values well above 0 9 which resulted in accurate predictions therefore these models can be used in other gully erosion studies as they are capable of rapidly producing accurate and robust gully erosion susceptibility maps gesms for decision making and soil and water management practices furthermore it was found that performance of rf and rbf svm for modelling gully erosion occurrence is quite stable when the learning and validation samples are changed

distribution of local landforms at head and end points of gullies on different grid spacing abstract local landforms described by signs of curvatures can be considered as potential indicators of gully formation however the role of these landforms is not generally investigated in literature hence the goals of the present research are i identification of the relationships of land surface attributes at the head and end points of gullies with the size of these gullies at different grid spacings of a digital elevation model dem ii explanation of the frequency of occurrence fo of local landforms investigations were conducted on the example of 439 gullies of the hronska pahorkatina hill land in slovakia the sizes of the gullies were described by their area and perimeter altitude slope steepness maximal catchment area mca and curvatures were calculated at the head and end points of these gullies 12 types of main local landforms mllfs were identified by the signs of six curvatures for calculation of land surface attributes a set of dems with grid spacings at every 10 m interval from 10 m to 100 m was prepared at the head points of gullies significant spearman s rank correlation coefficients rs show that mca and curvatures related with gully size at dem grid spacings from 10 m to 30 m at the end points such relationships are observed at all grid spacings a negative rs between gully size and slope steepness is obtained at the head points it is demonstrated that the large gullies reached more flat locations in comparison with small gullies at the end points negative rs indicates that large gullies are characterized by flatter outlets in comparison with small gullies the fo of mllfs at the head and end points of gullies relative to their frequency for the whole dem indicate that only four types of mllf are systematically related to gully occurrence

a gis based approach for gully erosion susceptibility modelling a test in sicily italy the aim of this study is to analyze the susceptibility conditions to gully erosion phenomena in the magazzolo river basin and to test a method that allows for driving the factors selection the study area is one of the largest 225 km2 watershed of southern sicily and it is mostly characterized by gentle slopes carved into clayey and evaporitic sediments except for the northern sector where carbonatic rocks give rise to steep slopes in order to obtain a quantitative evaluation of gully erosion susceptibility statistical relationships between the spatial distributions of gullies affecting the area and a set of twelve environmental variables were analyzed stereoscopic analysis of aerial photographs dated 2000 and field surveys carried out in 2006 allowed us to map about a thousand landforms produced by linear water erosion processes classifiable as ephemeral and permanent gullies the linear density of the gullies computed on each of the factors classes was assumed as the function expressing the susceptibility level of the latter a 40 m digital elevation model dem prepared from 1 10 000 scale topographic maps was used to compute the values of nine topographic attributes primary slope aspect plan curvature profile curvature general curvature tangential curvature secondary stream power index topographic wetness index ls usle factor from available thematic maps and field checks three other physical attributes lithology soil texture land use were derived for each of these variables a 40 m grid layer was generated reclassifying the topographic variables according to their standard deviation values in order to evaluate the controlling role of the selected predictive variables one variable susceptibility models based on the spatial relationships between each single factor and gullies were produced and submitted to a validation procedure the latter was carried out by evaluating the predictive performance of models trained on one half of the landform archive and tested on the other large differences of accuracy were verified by computing geometric indexes of the validation curves prediction and success rate curves roc curves drawn for each one variable model in particular soil texture general curvature and aspect demonstrated a weak or a null influence on the spatial distribution of gullies within the studied area while on the contrary tangential curvature stream power index and plan curvature showed high predictive skills hence predictive models were produced on a multi variable basis by variously combining the one variable models the validation of the multi variables models which generally indicated quite satisfactory results were used as a sensitivity analysis tool to evaluate differences in the prediction results produced by changing the set of combined physical attributes the sensitivity analysis pointed out that by increasing the number of combined environmental variables an improvement of the susceptibility assessment is produced this is true with the exception of adding to the multi variables models a variable as slope aspect not correlated to the target variable the addition of this attribute produces effects on the validation curves that are not distinguishable from noise and as a consequence the slope aspect was excluded from the final multi variables model used to draw the gully erosion susceptibility map of the magazzolo river basin in conclusion the research showed that the validation of one variable models can be used as a tool for selecting factors to be combined to prepare the best performing multi variables gully erosion susceptibility model

is ambient noise tomography across ocean basins possible 1 based on year long cross correlations of broad band seismic records obtained at sixty six stations within or adjacent to the pacific basin we show that broad band ambient noise is observed to propagate coherently between island stations and between island and continent stations for many station pairs high signal to noise ratio snr fundamental mode rayleigh wave green functions are observed which establishes the physical basis for ambient noise tomography across the pacific similar trends for continental and oceanic stations are observed in the relationship between the ambient noise level at a station and the noise coherence distance the longest distance at which a high snr cross correlation signal is observed for a station because locally generated noise obscures long distance coherent noise situating stations at quiet locations on islands is necessary for the success of ambient noise tomography local noise poses a particular challenge at atoll sites and on the basis of analysis of data from station h2o at ocean bottom sites at periods above 25 sec citation lin f c m h ritzwoller and n m shapiro 2006 is ambient noise tomography across ocean basins possible geophys res lett 33 l14304 doi 10 1029 2006gl026610

predicting gully occurrence at watershed scale comparing topographic indices and multivariate statistical models abstract in this study the ability of five topographic indices to predict the gully trajectories observed in two adjacent watersheds located in sicily italy was evaluated two of these indices named mspi and mtwi as far as we know have never been employed to this aim they were obtained by multiplying the stream power index spi and the topographic wetness index twi respectively by the convergence index ci the predictive ability of the topographic indices was measured by using both cut off independent auc area under the receiver operating characteristic curve and dependent statistics cohen s kappa index sensitivity specificity these statistics were calculated also for 100 mars multivariate adaptive regression splines and 100 lr logistic regression model runs which used as predictors the topographic variables i e contributing area slope steepness plan curvature and convergence index combined into the five indices performance statistics of both topographic indices and statistical models were calculated using 100 random samples of 2 m grid cells which were extracted only from flow concentration lines this was done in order to focus the validation process on where gully erosion is more likely to occur mspi achieved the best predictive skill auc 0 93 0 71 among the topographic indices and exhibited similar and better accuracy than local i e trained and validated in the same watershed and transferred i e trained in one watershed and tested in the other one lr models respectively on the other hand mspi performed similarly to transferred mars runs auc 0 92 0 71 but slightly worse than local mars runs auc 0 95 0 77 based on the results of this experiment it can be inferred that i including ci helps in detecting hollow areas where gullies are more likely to occur and ii mpsi can be a valid alternative to a data driven approach for mapping gully erosion susceptibility in areas where a gully inventory is not available which is necessary to calibrate statistical models

threshold conditions for initiation of valley side gullies in the middle veld of swaziland abstract gullied and ungullied catchments in four areas of deeply weathered saprolite in the middle veld of swaziland can be successfully separated p

gully formation and the role of valley floor vegetation southeastern australia attempts to understand the causes of gully erosion have been hampered by a poor understanding of quantitative changes to the force of flows and the resistance to scour we used flume experiments on an unincised valley floor to determine flow resistance and the critical shear stress for scour under natural and degraded vegetation covers applying the results to sites of gully formation in southeastern australia demonstrates the crucial role that reduced vegetation cover plays in increasing the susceptibility of valleys to channel incision widespread and rapid gully formation in the 19th century required degradation of valley floor vegetation and was not solely the result of land use or climatically induced increases in discharge

an objective method to rank the importance of the factors predisposing to landslides with the gis methodology application to an area of the apennines valnerina perugia italy the present work aims at contributing to further our knowledge on the predisposing factors to landslides as well as proposing a method that allows us to weigh up as objectively as possible the influence that the various factors have on landslides in order to construct a realistic map of potential landslide hazards in order to assess the differential incidence of very predisposing factor to landslides maps of the various factors considered were drawn up with the aid of idrisi software 1997 the factors were as follows the distance from faults parallelism between the fractures and the landslide scarps land use lithology distance from the streams orientation and steepness of slopes orientation of layers compared to the slope the global analysis of the different incidence of the factors analyzed on the landslides present in the study area was carried out by comparing the respective maps with that of the scarps in this way the number of pixels forming the scarps which fell into the various classes of the maps was calculated the result thus obtained can form the basis of an objective assignation of the different ratings to be attributed to the various factors under consideration in fact the analysis carried out in this study has shown that the factors act differently and for every factor only some of the classes considered have marked importance

on the coherent components of low frequency ambient noise in the indian ocean this letter demonstrates that the dominant coherent component of low frequency 1 hz f 20 hz ambient noise propagating between hydrophone pairs of the same hydroacoustic station deployed in the deep sound channel of the indian ocean is directional and mainly originates from antarctica however the amplitude of the peak coherent noise arrivals obtained using a 4 month long averaging interval was relatively low given the small hydrophones spacing hydrophones 2 km hence extracting similar coherent arrivals between two distinct hydroacoustic stations separated instead by thousands of kilometers for noise based acoustic thermometry purposes seems unlikely even using a year long averaging

a gis based approach for gully erosion susceptibility modelling using bivariate statistics methods in the ourika watershed morocco gully erosion is an important environmental issue with severe impacts this study aimed to characterize gully erosion susceptibility and assess the capability of information value infval and frequency ratio fr models for its spatial prediction in ourika watershed of the high atlas region of morocco these two bivariate statistical methods have been used for gully erosion susceptibility mapping by comparing each data layer of causative factor to the existing gully distribution weights to the gully causative factors are assigned based on gully density gullies have been mapped through field surveys and google earth high resolution images lithofacies land use slope gradient length slope aspect stream power index topographical wetness index and plan curvature were considered predisposing factors to gullying the digitized gullies were randomly split into two parts sixty five percent 65 of the mapped gullies were randomly selected as training set to build gully susceptibility models while the remaining 35 cases were used as validation set for the models validation the results showed that barren and sparse vegetation lands and slope gradient above 50 were very susceptible to gully erosion the roc curve was used for testing the accuracy of the mentioned models the analysis confirms that the fr model auc 80 61 shows a better accuracy than infval model auc 52 07 the performance of the gully erosion susceptibility map constructed by fr model is greater than that of the map produced by infval model the findings proved that gis based bivariate statistical methods such as frequency ratio model could be successfully applied in gully susceptibility mapping in morocco mountainous regions and in other similar environments the produced susceptibility map represents a useful tool for sustainable planning conservation and protection of land from gully processes

water erosion susceptibility mapping by applying stochastic gradient treeboost to the imera meridionale river basin sicily italy abstract soil erosion by water constitutes a serious problem affecting various countries in the last few years a number of studies have adopted statistical approaches for erosion susceptibility zonation in this study the stochastic gradient treeboost sgt was tested as a multivariate statistical tool for exploring analyzing and predicting the spatial occurrence of rill interrill erosion and gully erosion this technique implements the stochastic gradient boosting algorithm with a tree based method the study area is a 9 5 km 2 river catchment located in central northern sicily italy where water erosion processes are prevalent and affect the agricultural productivity of local communities in order to model soil erosion by water the spatial distribution of landforms due to rill interrill and gully erosion was mapped and 12 environmental variables were selected as predictors four calibration and four validation subsets were obtained by randomly extracting sets of negative cases both for rill interrill erosion and gully erosion models the results of validation based on receiving operating characteristic roc curves showed excellent to outstanding accuracies of the models and thus a high prediction skill moreover sgt allowed us to explore the relationships between erosion landforms and predictors a different suite of predictor variables was found to be important for the two models elevation aspect landform classification and land use are the main controlling factors for rill interrill erosion whilst the stream power index plan curvature and the topographic wetness index were the most important independent variables for gullies finally an roc plot analysis made it possible to define a threshold value to classify cells according to the presence absence of the two erosion processes hence by heuristically combining the resulting rill interrill erosion and gully erosion susceptibility maps an integrated water erosion susceptibility map was created the adopted method offers the advantages of an objective and repeatable procedure whose result is useful for local administrators to identify the areas that are most susceptible to water erosion and best allocate resources for soil conservation strategies

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

geologic evidence for earthquakes during the past 2000 years along the copalis river southern coastal washington evidence for several prehistoric earthquakes is present in deposits less than 2000 years old that crop out at the copalis river estuary 47 07 2 n 124 09 7 w the deposits show that land subsided decimeters into the intertidal zone on as many as three occasions and that sand vented while the land underwent little or no subsidence on another occasion the evidence for earthquake induced subsidence consists of buried marsh and forest soils that evince sudden estuarine submergence attended on at least one occasion by a landward directed surge of sandy water this combination of submergence and surge implies subsidence and tsunami exposed evidence for subsidence and tsunami along the copalis river is strong for a time within a few decades of 300 years ago moderate for a time 1400 1900 years ago and weak subsidence or lacking tsunami for an intermediate time also about 1400 1900 years ago the history of sudden submergence and tsunami in the past 2000 years at the copalis river estuary resembles that shown by buried soils farther south in coastal washington at grays harbor and willapa bay the history can be explained most simply by great mw of 8 or 9 thrust earthquakes at the boundary between the juan de fuca and north america plates with one or two earthquakes occurring 1400 1900 years ago and another close to 300 years ago the evidence for earthquake induced venting along the copalis river consists of sand intrusions and vented sand volcanoes the sand rose through muddy estuarine deposits at least 3 m thick entraining these deposits in fragments as much as 0 3 m long intrusion occurred at one or more times in the past 2000 years and at least some of the venting occurred 900 1300 years ago the sand bodies do not imply artesian flow of flood pressured groundwater because the sand vented forcefully and infrequently through a lowland that probably lacked natural levees the earthquake implied by the venting of sand 900 1300 years ago could have come from a source below above or at the boundary between the juan de fuca and north america plates if from the subducted juan de fuca plate the implied earthquake was farther west or larger than the largest earthquakes within that plate during the past 100 years evidence permitting a source within the north america plate includes a fault scarp an uplifted tideflat and landslides near puget sound dating from the interval 700 1700 years ago a plate boundary source would explain buried soils whose estuarine submergence and burial imply coseismic subsidence for parts of coastal washington in the interval 600 1300 years ago however stratigraphy shows that little or no coseismic subsidence occurred along the copalis river during the venting 900 1300 years ago if a plate boundary earthquake struck coastal washington 900 1300 years ago the earthquake produced a different distribution of land level change than did the plate boundary earthquakes inferred for 1400 1900 and 300 years ago

extracting coherent wave fronts from acoustic ambient noise in the ocean a method to obtain coherent acoustic wave fronts by measuring the space time correlation function of ocean noise between two hydrophones is experimentally demonstrated though the sources of ocean noise are uncorrelated the time averaged noise correlation function exhibits deterministic waveguide arrival structure embedded in the time domain green s function a theoretical approach is derived for both volume and surface noise sources shipping noise is also investigated and simulated results are presented in deep or shallow water configurations the data of opportunity used to demonstrate the extraction of wave fronts from ocean noise were taken from the synchronized vertical receive arrays used in the frame of the north pacific laboratory npal during time intervals when no source was transmitting

assessment of susceptibility to earth flow landslide using logistic regression and multivariate adaptive regression splines a case of the belice river basin western sicily italy abstract in this paper terrain susceptibility to earth flow occurrence was evaluated by using geographic information systems gis and two statistical methods logistic regression lr and multivariate adaptive regression splines mars lr has been already demonstrated to provide reliable predictions of earth flow occurrence whereas mars as far as we know has never been used to generate earth flow susceptibility models the experiment was carried out in a basin of western sicily italy which extends for 51 km 2 and is severely affected by earth flows in total we mapped 1376 earth flows covering an area of 4 59 km 2 to explore the effect of pre failure topography on earth flow spatial distribution we performed a reconstruction of topography before the landslide occurrence this was achieved by preparing a digital terrain model dtm where altitude of areas hosting landslides was interpolated from the adjacent undisturbed land surface by using the algorithm topo to raster this dtm was exploited to extract 15 morphological and hydrological variables that in addition to outcropping lithology were employed as explanatory variables of earth flow spatial distribution the predictive skill of the earth flow susceptibility models and the robustness of the procedure were tested by preparing five datasets each including a different subset of landslides and stable areas the accuracy of the predictive models was evaluated by drawing receiver operating characteristic roc curves and by calculating the area under the roc curve auc the results demonstrate that the overall accuracy of lr and mars earth flow susceptibility models is from excellent to outstanding however auc values of the validation datasets attest to a higher predictive power of mars models auc between 0 881 and 0 912 with respect to lr models auc between 0 823 and 0 870 the adopted procedure proved to be resistant to overfitting and stable when changes of the learning and validation samples are performed in conclusion the highly acceptable predictive skill of the statistical models confirms the reliability of the procedure adopted to reconstruct the pre failure topographic conditions such a method solves the conceptual problem arising when post failure elevation data are the only source of topographic information available to model landslide susceptibility furthermore with respect to other solutions proposed in the past which identify as unstable the conditions of landslide surroundings our approach allows for more accurate measurement of those variables e g curvature convergence index topographic position index that depend on the relative position of a cell with respect to its nearby pixels

t phase observations in northern california acoustic to seismic coupling at a weakly elastic boundary plans for a hydroacoustic network intended to monitor compliance with the ctbt call for the inclusion of five t phase stations situated at optimal locations for the detection of seismic phases converted from ocean borne t phases we examine factors affecting the sensitivity of land based stations to the seismic t phase the acoustic to seismic coupling phenomenon is described by upslope propagation of an acoustic ray impinging at a sloping elastic wedge we examine acoustic to seismic coupling characteristics for two cases the first in which the shear velocity of the bottom is greater than the compressional velocity of the fluid i e vp vs vw the second is a weakly elastic solid in which vs vw vw we show that acoustic energy couples primarily to shear wave energy except at very high slope angles we show that the weakly elastic solid i e vs vw behaves nearly like a fluid bottom with acoustic energy coupling to both p and s waves even at low slope angles

accuracy of topographic index models at identifying ephemeral gully trajectories on agricultural fields abstract topographic index ti models have been widely used to predict trajectories and initiation points of ephemeral gullies egs in agricultural landscapes prediction of egs strongly relies on the selected value of critical ti threshold and the accuracy depends on topographic features agricultural management and datasets of observed egs this study statistically evaluated the predictions by ti models in two paired watersheds in central kansas that had different levels of structural disturbances due to implemented conservation practices four ti models with sole dependency on topographic factors of slope contributing area and planform curvature were used in this study the observed egs were obtained by field reconnaissance and through the process of hydrological reconditioning of digital elevation models dems the kernel density estimation analysis was used to evaluate ti distribution within a 10 m buffer of the observed eg trajectories the eg occurrence within catchments was analyzed using kappa statistics of the error matrix approach while the lengths of predicted egs were compared with the observed dataset using the nash sutcliffe efficiency nse statistics the ti frequency analysis produced bi modal distribution of topographic indexes with the pixels within the eg trajectory having a higher peak the graphs of kappa and nse versus critical ti threshold showed similar profile for all four ti models and both watersheds with the maximum value representing the best comparison with the observed data the compound topographic index cti model presented the overall best accuracy with nse of 0 55 and kappa of 0 32 the statistics for the disturbed watershed showed higher best critical ti threshold values than for the undisturbed watershed structural conservation practices implemented in the disturbed watershed reduced ephemeral channels in headwater catchments thus producing less variability in catchments with egs the variation in critical thresholds for all ti models suggested that ti models tend to predict eg occurrence and length over a range of thresholds rather than find a single best value

predicting the susceptibility to gully initiation in data poor regions permanent gullies are common features in many landscapes and quite often they represent the dominant soil erosion process once a gully has initiated field evidence shows that gully channel formation and headcut migration rapidly occur in order to prevent the undesired effects of gullying there is a need to predict the places where new gullies might initiate from detailed field measurements studies have demonstrated strong inverse relationships between slope gradient of the soil surface s and drainage area a at the point of channel initiation across catchments in different climatic and morphological environments such slope area thresholds s a can be used to predict locations in the landscape where gullies might initiate however acquiring s a requires detailed field investigations and accurate high resolution digital elevation data which are usually difficult to acquire to circumvent this issue we propose a two step method that uses published s a thresholds and a logistic regression analysis lr s a thresholds from the literature are used as proxies of field measurement the method is calibrated and validated on a watershed close to the town of algiers northern algeria where gully erosion affects most of the slopes the gullies extend up to several kilometres in length and cover 16 of the study area first we reconstruct the initiation areas of the existing gullies by applying s a thresholds for similar environments then using the initiation area map as the dependent variable with combinations of topographic and lithological predictor variables we calibrate several lr models it provides relevant results in terms of statistical reliability prediction performance and geomorphological significance this method using s a thresholds with data driven assessment methods like lr proves to be efficient when applied to common spatial data and establishes a methodology that will allow similar studies to be undertaken elsewhere

modelling the occurrence of gullies in rangelands of southwest spain gully erosion has been recognized as an important soil degradation process in rangelands of southwest spain in this paper a relatively new data mining technique called multivariate adaptive regression splines mars was applied to construct a model capable of predicting the location of gullies a large database was used to support the model composed of a target variable presence or absence of gullies and 36 independent variables related to topography lithology soils rainfall land use and vegetation cover the performance of the model was evaluated using the receiver operating characteristic roc curve for five external datasets the model had high predictive power with values for the area under the roc curve of the external validation datasets varying from 0 75 to 0 98 1 0 being perfect prediction the most important variables explaining the spatial distribution of gullies were lithology and soil type finally the model was compiled and implemented into a geographical information system to obtain maps of susceptible areas for gully erosion these maps show that approximately 7 of the study area presents favourable conditions for the development of gullies the results demonstrate that mars constitutes a valuable model in geomorphic research and could also be a useful tool for assessing the impacts of changing climate and land use on gully erosion copyright 2009 john wiley sons ltd

logistic analysis of channel pattern thresholds meandering braiding and incising a large and geographically diverse data set consisting of meandering braiding incising and post incision equilibrium streams was used in conjunction with logistic regression analysis to develop a probabilistic approach to predicting thresholds of channel pattern and instability an energy based index was developed for estimating the risk of channel instability associated with specific stream power relative to sedimentary characteristics the strong significance of the 74 statistical models examined suggests that logistic regression analysis is an appropriate and effective technique for associating basic hydraulic data with various channel forms the probabilistic diagrams resulting from these analyses depict a more realistic assessment of the uncertainty associated with previously identified thresholds of channel form and instability and provide a means of gauging channel sensitivity to changes in controlling variables

assessment of sidewall erosion in large gullies using multi temporal dems and logistic regression analysis although in the last decades gully erosion has been a thriving research field few studies have specifically addressed the contribution and location of sidewall erosion processes in gullies in this paper sidewall erosion in some large gullies in a mediterranean area anoia penedes ne spain is mapped and assessed for two time intervals 1975 1995 and 1995 2002 using detailed digital elevation models derived from aerial photographs at a scale of 1 5000 to 1 7000 logistic regression analysis is applied to compute the probability of occurrence of gully sidewall erosion from terrain variables the results confirm the complex nature of sidewall processes whose intensity is most probably related to rainfall characteristics prolonged wet soil conditions in the period 1995 2002 together with the large and high intensity rainfall of an extreme event occurred on 10th june 2000 help to explain the different sediment production rates 16 0 4 mg ha 1 year 1 in 1975 1995 and 83 6 3 mg ha 1 year 1 in 1995 2002 the logistic regression analysis revealed that gully wall slope angle was the main factor controlling gully sidewall failure in gully walls with high slope angles tension crack development is the main process promoting wall collapse the application of the logistic regression model showed a high overall accuracy 87 but over 50 of commission and omission errors for the class of interest sidewall erosion in agreement with the variance explained by the model

exploring the effect of absence selection on landslide susceptibility models a case study in sicily italy abstract a statistical approach was employed to model the spatial distribution of rainfall triggered landslides in two areas in sicily italy that occurred during the winter of 2004 2005 the investigated areas are located within the belice river basin and extend for 38 5 and 10 3 km 2 respectively a landslide inventory was established for both areas using two google earth images taken on october 25th 2004 and on march 18th 2005 to map slope failures activated or reactivated during this interval geographic information systems gis were used to prepare 5 m grids of the dependent variables absence presence of landslide and independent variables lithology and 13 dem derivatives multivariate adaptive regression splines mars were applied to model landslide susceptibility whereas receiver operating characteristic roc curves and the area under the roc curve auc were used to evaluate model performance to evaluate the robustness of the whole procedure we prepared 10 different samples of positive landslide presence and negative landslide absence cases for each area absences were selected through two different methods i extraction from randomly distributed circles with a diameter corresponding to the mean width of the landslide source areas and ii selection as randomly distributed individual grid cells a comparison was also made between the predictive performances of models including and not including the lithology parameter the models trained and tested on the same area demonstrated excellent to outstanding fit auc 0 8 on the other hand predictive skill decreases when measured outside the calibration area although most of the landslides occur where susceptibility is high and the overall model performance is acceptable auc 0 7 the results also showed that the accuracy of the landslide susceptibility models is higher when lithology is included in the statistical analysis models whose absences were selected using random circles showed a significantly better performance when learning and validation samples were extracted from the same area whereas conversely no significant difference was observed when testing the models outside the training area

gully erosion susceptibility assessment by means of gis based logistic regression a case of sicily italy article i nfo article history this research aims at characterizing susceptibility conditions to gully erosion by means of gis and multivariate statistical analysis the study area is a 9 5 km 2 river catchment in central northern sicily where agriculture ac tivities are limited by intense erosion by means of field surveys and interpretation of aerial images we prepared a digitalmap of thespatial distribution of 260 gulliesinthestudy area inaddition fromavailable thematicmaps a 5 m cell size digital elevation model and field checks we derived 27 environmental attributes that describe the variability of lithology land use topography and road position these attributes were selected for their potential influence on erosion processes while the dependent variable was given by presence or absence of gullies within two different types of mapping units 5 m grid cells and slope units average size 2 66 ha the functional re lationships between gully occurrence and the controlling factors were obtained from forward stepwise logistic regression to calculate the probability to host a gully for each mapping unit in order to train and test the predictive models three calibration and three validation subsets of both grid cells and slope units were randomly selected results of validation based on roc receiving operating characteristic curves attest for acceptable to excellent accuracies of the models showing better predictive skill and more stable performance of the susceptibility model based on grid cells

sound channel observations of ice generated tremor in the indian ocean 1 mid to low southern latitude hydrophone stations within the indian ocean have recorded two distinct types of low frequency 100 hz tremor that can be correlated with drifting icebergs and glacial features along the wilkes land coast of eastern antarctica the most common of these signals is a variable harmonic tremor vht with spectral peaks that exhibit frequency fluctuations through time these signals typically display a 4 to 10 hz fundamental frequency and may have as many as ten harmonic bands individual vht signal packets have durations of up to 30 min and occur throughout the year in clusters that continue for hours to days a second less commonly observed signal is characterized by shorter duration 25 to 90 s pulses with a convex upward spectrogram appearance these cusped pulse tremors cpt often exhibit a near uniform pulse spacing with episodes continuing for minutes to hours tremor received levels at hydrophones near 32 s 114 e and 7 s 72 e reach as high as 142 and 133 db re 1 pa peak to peak respectively propagation likely occurs as a sea surface reflected phase at high latitudes and a sound channel phase north of the convergence zone with low frequency transmission loss estimates suggesting maximum acoustic source levels of 245 db re 1 pa at 1 m source locations for a subset of the loudest vht signals correlate with the satellite derived locations of a large iceberg b 15d that migrated westward along the wilkes land shelf region during 2002 and early 2003 most vht sources however cannot be correlated with known iceberg locations suggesting that these signals also may be sourced from smaller unnamed icebergs and or associated with outlet glaciers distributed along the wilkes land coast cpt signals have a more limited spatial distribution originating from five specific regions where ice streams are observed the harmonic nature of both signal types is consistent with the resonance of an ice layer or fluid filled cavity within an ice mass

recent gully erosion in the el cautivo badlands tabernas se spain abstract detailed geomorphic observations in el cautivo badland area in the semiarid se of spain show a recent renewal of linear channel erosion following a period of aggradation prior to this renewal the landscape was characterized by smooth colluvial pediments on the north east facing aspects and relatively steep crusted microhillslopes on south west facing aspects first order valleys within the badland landscape were smooth floored and filled with silty deposits connected with pediment colluvial deposits the conditions under which valley bottom deposition was replaced by channel incision were analyzed by a study of flow hydraulics magnitude frequency of eroding events vs resistance of valley floor to water flow and the pollen sequence in the recently cut deposits changes in the vegetation carpeting the valley bottom seem to be responsible for the deposition erosion alternation rather than changes in the magnitude frequency of major runoff events given the high sensitivity of flow hydraulics to changes in roughness present rainfall rates would not on their own be able to erode a well vegetated valley bottom yet the pollen sequence in the valley fills demonstrates a progressive deterioration in climatic conditions with the eventual disappearance of groups that require a constant level of soil moisture alnus corylus cyperaceae an increase in yearly rainfall or a change in temporal patterns would increase infiltration leading to permanent denser vegetation on footslopes and valley floors helped by the natural water harvesting system this vegetation cover would reduce the flow velocity and induce the deposition of the colluvium and valley fills whereas erosion on headslopes would have been active enough to supply the sediments that were deposited downslope or on the valley bottoms the reactivation of linear erosion would seem therefore to be a consequence of the decay of this permanent vegetation induced by an increase in the duration or severity of drought periods which meant that the water storage capacity of the valley fillings was insufficient to support it

superficial and subterranean soil erosion in tabasco tropical mexico development of a decision tree modeling approach tropical countries suffer from a lack of financial resources to monitor and model sources and outcomes of soil degradation and therefore a scarcity of data in this study it was tried to model superficial and subterranean water erosion based on basic environmental variables such as geological formation soil type or vegetation cover data which are potentially available even in developing countries different forms of water erosion and karst or pseudokarst formations in tabasco southeastern mexico were estimated the study region 3500 km 2 consists of plain and hilly areas with an annual precipitation ranging from 2000 to 4000 mm main land use form is rangeland the area is geologically composed of sedimentary rocks limestone sandstone and conglomerates collecting data by field observations over the entire study area a cartography of different soil loss forms such as rill and gully erosion mass movement sinkholes and tunnels was created including field data from available maps of geological formation soil type precipitation and former land use 20 years ago additionally data collected in the field such as actual land use vegetation cover and inclination were added in the entire study area 1039 sites were affected by soil erosion with 2435 single manifestations of soil erosion 482 sites were found with one gully each 57 sites with erosion rills with a total of 416 392 sites with one mass movement each 85 sites with sinkholes with a total of 1122 and 23 sites with one tunnel each rendzic leptosols over oligocene limestone are strongly affected by sinkholes and tunnels in regions with inclinations of less than 5 this phenomenon is explained by karstic and pseudokarstic formation superficial erosion forms are mainly found on rendzic leptosols over shale sandstone and on eutric or peli eutric vertisols on andesit in areas with inclinations between 5 and 30 the application of classification trees allowed to successfully predict the occurrence of sinkholes and tunnels degree of agreement between prediction and observation very good to excellent even in areas with scarce data bases this could allow for easy identification of high risk areas predictive success of the occurrence of the different forms of superficial soil losses however is low superficial erosion seems to be mainly caused by more specific pedological factors nevertheless automated induction of classification trees can be a valuable tool for preliminary data analysis and hypothesis generation in areas with lack of local expertise and can guide erosion risk mapping and soil conservation planning 2007 elsevier b v all rights reserved

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

probabilistic assessment of volcanic hazard to radioactive waste repositories in japan intersection by a dike from a nearby composite volcano geologic hazards such as volcanism must be assessed when evaluating potential sites for the geologic disposal of high level radioactive waste the japanese islands comprise one of the more volcanically active regions on earth and the risk of volcanism to a geologic repository is being evaluated as part of the japanese high level radioactive waste disposal program one hazard that is being evaluated as part of volcanic risk assessment is the possible intersection of a repository by a dike if a composite volcano were to form near a repository during the long 100 k y performance period of the repository in this paper we use the characteristics of a well exposed radial dike system at the summer coon volcano in colorado to define monte carlo simulations that estimate the probability of a dike intersection of a repository as a function of volcano distance dike length and density and repository area the models indicate that the probability of intersection declines rapidly as a function of distance from a volcano as dike density decreases due to the radial dike geometry the probability of intersection for a mafic dike set with shorter average length declines more rapidly than that of a silicic dike set with longer average length however mafic dikes have a higher probability of intersecting a repository close to a volcano 5 6 km because they are more numerous than longer silicic dikes the probability of a silicic dike intersecting a repository is 10 2 at distances greater than 15 km from the volcano decreasing to 10 4 at distances greater than 30 km