probabilistic rainfall thresholds for landslide occurrence using a bayesian approach 1 various methods have been proposed in the literature to predict the rainfall conditions that are likely to trigger landslides in a given area most of these methods however only consider the rainfall events that resulted in landslides and provide deterministic thresholds with a single possible output landslide or no landslide for a given input rainfall conditions such a deterministic view is not always suited to landslides slope stability in fact is not ruled by rainfall alone and failure conditions are commonly achieved with a combination of numerous relevant factors when different outputs landslide or no landslide can be obtained for the same input a probabilistic approach is preferable in this work we propose a new method for evaluating rainfall thresholds based on bayesian probability the method is simple statistically rigorous and returns a value of landslide probability from 0 to 1 for each combination of the selected rainfall variables the proposed approach was applied to the emilia romagna region of italy taking advantage of the historical landslide archive which includes more than 4000 events for which the date of occurrence is known with daily accuracy the results show that landsliding in the study area is strongly related to rainfall event parameters duration intensity total rainfall while antecedent rainfall seems to be less important the distribution of landslide probability in the rainfall duration intensity shows an abrupt increase at certain duration intensity values which indicates a radical change of state of the system and suggests the existence of a real physical threshold

airborne biogeophysical mapping of hidden mineral deposits three mapping surveys of cotter basin montana and spirit lake washington the tree cover with widespreading and deeply penetrating root systems is turned to an advantage in the airborne biogeophysical technique by detecting metal induced changes in the chlorophyll reflectance spectrum modified journal abstract

anomalies on geologic maps from multispectral and textural classification the bleida mining district morocco the variogram analysis of different reference image facies on a spot xs scene enables the definition of a discriminant texture index the values of this index are extracted locally in a given neighborhood this textural information is matched with the multispectral information in order to realize a combined classification the result is subsequently compared to a digitized geological map in order to extract zones of anomaly regarded as the differences between the combined classification and the geological map a majority of the anomalies require further interpretation while certain others are interesting to mineral prospecting

rainfall control of debris flow triggering in the real torrent southern french prealps abstract this paper investigates the occurrence of debris flow due to rainfall forcing in the real torrent a very active debris flow prone catchment in the southern french prealps the study is supported by a 4 year record of flow responses and rainfall events from three high frequency monitoring stations equipped with geophones flow stage sensors digital cameras and rain gauges measuring rainfall at 5 min intervals the classic method of rainfall intensity duration id threshold was used and a specific emphasis was placed on the objective identification of rainfall events as well as on the discrimination of flow responses observed above the id threshold the results show that parameters used to identify rainfall events significantly affect the id threshold and are likely to explain part of the threshold variability reported in the literature this is especially the case regarding the minimum duration of rain interruption mdri between two distinct rainfall events in the real torrent a 3 h mdri appears to be representative of the local rainfall regime a systematic increase in the id threshold with drainage area was also observed from the comparison of the three stations as well as from the compilation of data from experimental debris flow catchments a logistic regression used to separate flow responses above the id threshold revealed that the best predictors are the 5 min maximum rainfall intensity the 48 h antecedent rainfall the rainfall amount and the number of days elapsed since the end of winter used as a proxy of sediment supply this emphasizes the critical role played by short intense rainfall sequences that are only detectable using high time resolution rainfall records it also highlights the significant influence of antecedent conditions and the seasonal fluctuations of sediment supply

the transformation of nesquehonite to hydromagnesite in the system cao mgo h20 co2 an experimental spectroscopic study abstract this study reports the nature of the nesquehonite to hydromagnesite transition at 52 c in an aqueous medium hosting magnesian calcite and nesquehonite the latter mineral occurs with abundant calcite at the floor of the experimental chamber substrate and as a film of needles at the interface between the mother liquor and the atmosphere surface film the experimental vessel was held at 52 c for 336 h and at 60 c for a further 192 h precipitates were analyzed by fourier transform ft raman augmented by ft infrared and x ray diffraction at 52 c hydromagnesite and dypingite occur with abundant quantities of a hitherto unreported transitory magnesium hydrate carbonate tmhc together with huntite magnesian calcite and traces of nesquehonite and monohydrocalcite the ft raman spectra of the first formed hydromagnesite crystals contain the raman forbidden v2 mode interpreted to indicate a relaxation in selection rules caused by rapid precipitation hydromagnesite growth at the expense of t

shuttle imaging radar experiment the shuttle imaging radar sir a acquired images of a variety of the earth s geologic areas covering about 10 million square kilometers structural and geomorphic features such as faults folds outcrops and dunes are clearly visible in both tropical and arid regions the combination of sir a and seasat images provides additional information about the surface physical properties topography and roughness ocean features were also observed including large internal waves in the andaman sea

reconstructing recent landslide activity in relation to rainfall in the llobregat river basin eastern pyrenees spain abstract a chronology of recent landslides in the upper basin of the llobregat river eastern pyrenees has been reconstructed from technical reports field reconnaissance and dendrogeomorphological analysis the precipitation conditions responsible for triggering and reactivating landslides have been deduced by analysis of rainfall records from two rain gauges located in the area two different rainfall patterns relate to landslide occurrence i without antecedent rainfall high intensity and short duration rains trigger mostly debris flows and shallow slides developed in colluvium and weathered rocks a rainfall threshold of around 190 mm in 24 h initiates failures whereas more than 300 mm in 24 48 h are needed to cause widespread shallow landsliding ii with antecedent rain moderate intensity precipitation of at least 40 mm in 24 h reactivates mudslides and both rotational and translational slides affecting clayey and silty clayey formations in this case several weeks and 200 mm of precipitation are needed to cause landslide reactivation dendrochronological analysis shows that landslide activity in the eastern pyrenees was relatively low between 1926 and 1959 but has since increased significantly with reactivation now occurring about every 3 years

dolomitization a critical view of some current views the principal models in vogue today for dolomitization are the mixing zone and the sabkha models despite the wide acceptance of these models there has been little critical assessment of their validity such an assessment is the objective of the present paper a close look at the dorag mixing zone model badiozamani 1973 reveals several serious weaknesses 1 the range of freshwater seawater mixtures that meet the dorag requirement for dolomitization shrinks to a small window if the geologically more realistic disordered dolomite is used in the calculations instead of the ordered dolomite on which the model is based 2 in none of the known modern coastal mixing zones in limestone or lime sediments has replacement by dolomite been observed 3 in a number of dolomites interpreted to be of mixing zone origin dolomite has precipitated without dissolution of the calcite substrate evidence that negates the fundamental premise of the dorag model in addition to these weaknesses isotope and trace element data used to identify mixed water dolomite are inadmissible because 1 isotopic fractionation factors for dolomites remain unresolved 2 isotope values uncorrected for temperature for a host of dolomites interpreted to be of different origins overlap 3 nonisomorphous trace elements such as na in dolomite cannot on theoretical grounds be relied on to identify dolomitizing fluids similar overall objections can be brought against folk and land9s 1975 schizohaline version of mixing zone dolomitization in summary mixing zone models have such weak underpinnings that they should be questioned as viable explanations for massive dolomitization contemporaneous dolomite formation in modern sabkhas is well documented but the important question of whether the mechanism of dolomite formation is replacement or direct precipitation remains to be resolved in the well studied sabkha at abu dhabi brine chemistry changes have been used as evidence of a replacement origin for the dolomite but it is shown here that this evidence is far from unequivocal an alternative origin of direct precipitation of dolomite is offered an origin in keeping with dolomite precipitation known from other modern sabkhas and saline lakes and in line with our laboratory experience with dolomite synthesis moreover it is suggested here that in general contemporaneous dolomite will form at low temperatures only by direct precipitation a mechanism that requires special conditions of highly super saturated waters of high mg ca ratio and elevated co 3 hco 3 concentrations this may explain why modern dolomite is mainly restricted to evaporitic environments a bias not shared by ancient dolomites in contrast replacement dolomite appears to require at low temperatures long reaction times or 10 4 yr a requirement that is mainly to be met in large regional groundwater flow systems both marine and nonmarine a third dolomitization model considered here is that of baker and kastner 1981 based on the experimental finding that sulfate ions inhibit or retard dolomitization a number of modern sedimentary dolomites are not in accord with this model in that they are forming from brines with large sulfate concentrations 2 to 70 times that of seawater thus the baker kastner model should be held in abeyance until these serious contradictions are resolved the current emphasis on mixing zone and sabkha dolomitization has diverted attention from other promising avenues of approach to the dolomite problem four of these avenues each of which deemphasizes the special water approach are briefly addressed and are as follows 1 influence of temperature and time 2 mass transfer processes 3 burial diagenesis of epigenetic dolomites 4 fluid inclusion studies at elevated temperatures the dolomite problem essentially disappears ordered dolomite can be made in the laboratory in days at 100 degrees c what is more at temperatures above 60 degrees c ca rich waters become dolomitizing fluids which makes most natural subsurface waters capable of dolomitization at low temperatures time may be the key element so that seawater will become a major dolomitizing fluid only where stable circulation systems such as kohout convention can drive seawater through carbonate platforms for many thousands to millions of years this paper has tried to show that currently favored models of dolomitization carry serious uncertainties enough to warn us to look more critically at the validity of these models and also it is hoped enough to spur new efforts to find new solutions to the problems of dolomitization

estimation of debris flow triggering rainfall influence of rain gauge density and interpolation methods abstract the forecast of debris flow occurrence relies mainly on empirical rainfall intensity duration thresholds which are based on rain gauge observations this work focuses on the effect of rainfall estimation uncertainty on the estimation of debris flow triggering rainfall events and on the identification of rainfall thresholds for debris flow occurrence specifically the influence of rain gauge network density and the interpolation method on the estimation of debris flow triggering rainfall is investigated these questions are examined using high resolution carefully corrected radar data to represent space time patterns of true precipitation at the debris flow initiation points and in the surrounding area radar rainfall fields are sampled by simulated rain gauge networks stochastically generated with varying rain gauge densities based on these networks rainfall is estimated by using three rainfall interpolation methods nearest neighbor nn inverse distance weighting idw and ordinary kriging ok results show that nn provides the estimates with bias smaller than idw and ok but larger estimation variance overall decrease in gauge density leads to increased underestimation and increased estimation variance of debris flow triggering rainfall rainfall estimation error leads to large underestimation of the intensity duration thresholds however comparison of results shows that no particular benefit in intensity duration threshold estimation is obtained by using approaches that are more complex than the nn method

prediction of debris flow inundation areas using empirical mobility relationships abstract a method proposed for delineating lahar hazard zones in volcanic valleys is adapted to debris flows the original method is based on two predictive equations that relate the lahar volume to the cross sectional inundated area and to the planimetric inundated area these predictive equations were derived by combining a scaling analysis of lahar kinematics with the statistical analysis of data for 27 historical lahars this paper tests the applicability of this approach to debris flow fans forty debris flow basins in the italian alps were surveyed and data on 27 historical debris flow events were collected in the field or by means of aerial photo analysis collected data reveal that the flow area a and the planimetric area b of a debris flow are linearly correlated to the debris flow volume v on a logarithmic scale with high statistical significance moreover the computed regression equations are very similar to those obtained from other published datasets on debris flows leading to the global fitting equations a 0 08 v 2 3 and b 17 v 2 3 these predictive equations are then implemented in an automated code dflowz that delineates the inundated area on a debris flow fan on the basis of a user specified debris flow volume taking the statistical uncertainty in the prediction into account dflowz is simple reproducible and it can handle both confined and unconfined flow the model is tested against 10 historical debris flow events providing a satisfactory agreement between observed and computed inundated areas in spite of the limitations due to dem accuracy and statistical uncertainty of the regression parameters test results show that the method can be useful for practical applications

the continuous re equilibration of carbon isotope compositions of hydrous mg carbonates in the presence of cyanobacteria abstract the hydrous magnesium carbonate minerals dypingite mg5 co3 4 oh 2 5h2o and nesquehonite mgco3 3h2o were precipitated in the presence and absence of gloeocapsa sp and synechococcus sp cyanobacteria in batch reactors the 13cmineral dic is similar in both biotic and abiotic systems stable carbon isotope analyses of the precipitated minerals and co existing fluids indicated that the 13c values of the precipitated carbonates co vary over time with the 13cdic of the fluid phase even after the precipitation of the carbonate is complete this observation indicates the continuous isotopic exchange between the carbonates and the fluid a process that efficiently resets the original 13c values of the solids therefore although cyanobacterial induced mg carbonates are 10 5 enriched in 13c compared to inorganic carbonates the 13c values of natural hydrous mg carbonates may reflect post precipitation processes and may not be reliable for paleo environmental reconstructions

automated mapping of land components from digital elevation data an algorithm for automating the mapping of land components from digital elevation data is described land components are areas of relatively uniform slope and aspect and often correspond with ridge crests shoulders head slopes back slopes or foot slopes aspect regions which generally span from stream to ridge are first identified by generalizing an aspect map derived from digital elevation data the aspect regions are then split successively into land components by grouping pixels above or below an automatically determined contour of elevation or distance from stream the contour approximates a slope break the land components mapped in this way give a complete polygonization of a hilly landscape and are a reasonable approximation of manually mapped land components

debris flows rainfall thresholds in the apennines of emilia romagna italy derived by the analysis of recent severe rainstorms events and regional meteorological data abstract recent severe rainstorms events in october 2014 and september 2015 triggered more than a hundred debris flows in the western part of the apennines of emilia romagna italy in this work we tested a novel method to define debris flows rainfall thresholds for the 2014 and 2015 rainstorms which have been used as reference events and to extend these results across the apennines of emilia romagna making use of long term rainfall data of the regional raingauges network results are compared for validation to rainfall rates recoded during other past rainstorm debris flows events which have been used as validation events at first the method involves a spatial discriminant analysis between the spatial distribution of debris flows and the high frequency weather radar rainfall data for the 2014 and 2015 reference events the analysis defines rainfall cutoff values over rainfall durations from 30 to 6 h related to verification indices in the roc curves which are used as debris flows rainfall thresholds exceedance ratios are calculated between the computed rainfall thresholds and the rainfall rates at 10 years return periods at corresponding rainfall durations computed for raingauges located in the areas affected by the 2014 and 2015 events the ratios are then used as multipliers of the rainfall rates at 10 years return periods over rainfall durations from 30 to 6 h calculated for all other raingauges in the regional study area to spatialize thresholds calculation to the regional scale the computed thresholds are interpolated across the apennines of emilia romagna the research resulted in the assessment of two levels debris flows rainfall thresholds curves which seem to be adequate to discriminate rainfall rates recorded during past debris flows events used for validation discussion evidences advantages and limits of our approach compares results to existing debris flows thresholds and highlights their possible use in a multi stage warning procedure at regional scale

multipolarization radar images for geologic mapping and vegetation discrimination the nasa jpl airborne synthetic aperture radar system produces radar image data simultaneously in four linear polarizations hh vv vh hv at 24 6 cm wavelength l band with 10 m resolution across a swath width of approximately 10 km the signal data are recorded optically and digitally and annotated in each of the channels to facilitate a completely automated digital correlation both standard amplitude and also phase difference images are produced in the correlation process individual polarization and range dependent gain functions improve the effective dynamic range but as yet do not permit absolute quantitative measurements of the scattering coefficients however comparison of the relative intensities of the different polarizations in individual black and white and color composite images provides discriminatory mapping information in the death valley california area rough surfaces of young alluvial deposits produce strong responses at all polarizations smoother surfaces of older alluvial deposits show significantly lower responses evaporite deposits of different types and moisture contents have distinct polarization signatures in the wind river basin wyoming sedimentary rock units show polarization responses that relate to differences in weathering local intensity variations in like polarization images result from topographic effects strong cross polarization responses denote the effects of vegetation cover and in some cases possible scattering from the subsurface in the savannah river plant south carolina forest cover characteristics are discriminated by polarization responses that reflect the density and structure of the canopy and the presence or absence of standing water beneath the canopy

the use of variograms in remote sensing i scene models and simulated images abstract extraction of information from remotely sensed images would greatly benefit from increased use of spatial data however the utility of spatial data has been undermined by a lack of understanding of the nature and causes of observed spatial variation in images one approach to this problem is to model the spatial variation in images as a function of ground scene and sensor parameters variograms are the tool used to link models of ground scenes to spatial variation in images explicit variograms are calculated for simple models of ground scenes consisting of randomly located discs on a continuous background by incorporating the effect of the ifov of the sensor through a process called regularization explicit variograms for images of these scene models are derived verification of the explicit variograms is accomplished by simulating images that match the assumed scene model and sensor parameters and calculating empirical variograms for these images for a simple scene model of randomly located discs on a continuous background explicit and empirical variograms match verifying the convergence of these two dissimilar approaches the sensitivity of variograms is studied through varying parameters of scene models both in calculating explicit variograms and in simulating images results indicate direct ties between several scene parameters and the behavior of variograms the height of the sill of the variogram is related to the density of objects the range of influence is related to the size of objects increased variance in the size distribution of objects results in a more rounded shape in the variogram near the sill primary effects of increasing the units of regularization or larger pixel size are a decrease in the height of the sill and an increase in the range of influence

incorporation of polarimetric radar images into multisensor data sets a technique is presented for registering polarimetric synthetic aperture radar sar data to other aircraft and spaceborne data sets resampling is done on the full stokes matrix allowing full polarization synthesis on the coregistered data set analysis of data acquired over pisgah crater in the mojave desert ca as part of the mojave field experiment shows that the resampling does not seriously affect the pedestal heights of polarization signatures or estimates of rms heights for smooth to moderately rough surfaces

estimation of debris flow magnitude in the eastern italian alps the estimation of debris ow magnitude is an essential step in the assessment of debris ow hazard although different methods have been developed for the assessment of debris ow magnitude this is still a dif cult task because of the complexity of ow processes and the lack of data to test estimation procedures in many mountainous regions data on debris ow magnitude from 127 basins in the eastern italian alps have been collected from scienti c and technical journals technical reports historical documents gathered from local archives and eld surveys these data were used to develop and test different predictive approaches encompassing regression equations geomorphological surveys and probabilistic analysis of time series regression techniques were used to correlate debris ow magnitude to morphometric parameters and geological characteristics of the basins values of the channel debris yield rate contribution per unit length of channel proposed in the literature were compared with data from the study area for identifying reference values for channel stretches of different morphological characteristics although limited to the few basins in which suf cient data were available the probabilistic analysis of time series of debris ow magnitude provides indications about the relations between magnitude and frequency of debris ows some observations about the capability and drawbacks of considered methods are presented and the combined use of different approaches for the estimation of debris ow magnitude is suggested copyright 2004 john wiley sons ltd

mineralogic information from a new airborne thermal infrared multispectral scanner a new six channel aircraft multispectral scanner has been developed to exploit mineral signature information at wavelengths between 8 and 12 micrometers preliminary results show that igneous rock units can be identified from their free silica content and that carbonate as well as clay bearing units are readily separable on the digitally processed images

multisensor classification of sedimentary rocks abstract this paper compares linear discriminant analysis and supervised classification results based on signatures from the landsat thematic mapper tm the thermal infrared multispectral scanner tims and airborne synthetic aperture radar sar alone and combined into extended spectral signatures for seven sedimentary rock units exposed on the margin of the wind river basin wyoming results from a linear discriminant analysis showed that training area classification accuracies based on the multisensor data were improved an average of 15 over tm alone 24 over tims alone and 46 over sar alone with similar improvement resulting when supervised multisensor classification maps were compared to supervised individual sensor classification maps when training area signatures were used to map spectrally similar materials in an adjacent area the average classification accuracy improved 19 using the multisensor data over tm alone 2 over tims alone and 11 over sar alone the conclusion of this study is that certain sedimentary lithologies may be accurately mapped using a single sensor but classification of a variety of rock types can be improved using multisensor data sets that are sensitive to different characteristics such as mineralogy and surface roughness

analysis of coregistered landsat seasat and sir a images of varied terrain types multisensor image data sir a seasat sar and landsat mss over areas in nothern algeria and eastern utah have been coregistered in order to assess the complementary effects of the orbital sensors for geologic mapping in two very different terrains this first attempt at registering such a data set shows that the radar backscatter information provided by the sir a image increases the classification accuracy of several geologic units over the landsat image alone and over combined landsat and seasat images

lateglacial to early holocene recursive aridity events in the se mediterranean iberian peninsula the salines playa lake case study abstract twelve pollen inferred aridity major and minor events s1 to s12 have been identified at salines playa lake se iberian peninsula 475 m asl 38 30 02 n 00 53 18 w from the lateglacial to the early holocene boreal these dry events consist of an increase in the aridity quotient calculated as a function of selected pollen taxa at 13 4 13 12 55 12 2 11 9 11 45 11 10 6 10 3 10 9 5 and 8 3 ka cal bp these dry events correspond to the previous identified cold spells such as the younger dryas as well as the 8 7 6 and 5 bond events and 11 4 and 9 3 events this climate record highlights the complex glacial interglacial transition in extra tropical latitudes with centennial scale abrupt climate fluctuations a signature scarcely recorded in other palaeoecological records of the se iberian peninsula this work has major implications for the study of human socio ecological systems and resilience in se iberia during the epipaleolithic and mesolithic periods

a new technique for recognition of geological and geomorphological patterns in digital terrain models abstract we have developed a technique that recognizes monoclinal sedimentary strata showing strike ridge geomorphology and fluvial deposits from digital terrain models dtms this technique is efficient and reliable and may be expanded to analysis of other landforms techniques for rapid geomorphic analysis of dtms are becoming increasingly useful since digital stereoscopic spot data will soon be available worldwide our technique recognizes geomorphic elements in two steps first elementary objects including crests thalwegs and various slope types are classified from slope changes along n s e w nw se and ne sw profiles through pixels in the dtm image second grammatical pattern recognition is used to identify and map geomorphic forms from the succession of elementary objects

ten years of debris flow monitoring in the moscardo torrent italian alps abstract field data on debris flows are of utmost importance for improving knowledge of these hazardous phenomena and for the development of attenuation measures in alpine basins debris flows generally occur with a frequency high enough to create serious risk to human settlements and transportation routes but too low to justify monitoring activity capable of providing enough data in a sufficiently short time the moscardo torrent a small stream in the eastern italian alps is an exception to this general situation since it displays a high frequency of debris flows commonly at least one event per year in 1989 this torrent was instrumented and the results of the following 10 years 1989 1998 of debris flow monitoring are presented with an analysis of collected data the equipment installed allowed measurement of rainfall flow stage and ground vibrations caused by debris flows other important debris flow variables that is mean front velocity peak discharge and flowing volume were estimated from instrumental records video pictures have proved to be useful for the visual interpretation of debris flow waves and have made it possible to estimate the surface velocity of debris flows recorded data are compared with other experimental data sets collected and documented worldwide advantages and shortcomings of different types of sensors are discussed with relevance both for research monitoring purposes and for possible use in debris flow warning systems

problems in automated recognition of valley features from digital elevation models and a new method toward their resolution valley recognition methods given in the literature fail to produce valley networks suitable for locating valley heads for one of two main reasons a they are based on the concept of higher than or b they are based on contributing area thresholds in this paper a new method for recognizing valley bottoms is presented this is based on two improvements of carroll s 1983 method and produces a network that reflects the topography well the network is used to locate valley heads once located the valley heads are delineated using criteria suggested by geomorphologists and hydrologists the resultant valley heads are generally well recognized although two problems are evident a there are a number of commission errors and b the valley heads recognized by the method are too small

rainfall induced debris flows in pyroclastic deposits campania southern italy abstract a combination of empirical and physically based hydrological models has been used to analyze historical data on rainfall and debris flow occurrence in western campania to examine the correlation between rainfall and debris flow events rainfall data from major storms recorded in recent decades in western campania were compiled including daily series from several rain gauges located inside landslide areas supplemented by hourly rainfall data from some of the principal storms a two phase approach is proposed during phase 1 soil moisture levels have been modelled as the hydrological balance between precipitation and evapotranspiration on a daily scale using the method of thornthwaite geograph rev 38 1948 55 phase 2 is related to the accumulation of surplus moisture from intense rainfall leading to the development of positive pore pressures these interactions take place on an hourly time scale by the leaky barrel lb model described by wilson and wiezoreck env eng geoscience 1 1995 11 in combination with hourly rainfall records the lb model has been used to compare hydrological effects of different storms the critical level of retained rain water has been fixed by the timing of debris flow activity related to recorded storm events new rainfall intensity duration thresholds for debris flow initiation in western campania are proposed these thresholds are related to individual rain gauge and assume a previously satisfied field capacity condition the new thresholds are somewhat higher than those plotted by previous authors but are thought to be more accurate and thus need less conservatism

lithologic mapping in arid regions with landsat thematic mapper data meatiq dome egypt digital landsat thematic mapper tm data were evaluated for lithologic mapping capabilities over the meatiq dome area in the hyper arid eastern desert of egypt bi directional spectral reflectance data 0 4 2 5 m for powders of the major rock types exposed in the dome and published spectral reflectance data were used as guides in selecting tm band reflectance ratios that maximize discrimination of individual rock types on the basis of their respective mineralogies comparison of tm data with field and petrographic observations shows 1 increasing amounts of magnetite and other opaque minerals with low flat spectral reflectances decrease the ratio of tm band 5 1 55 to 1 75 to band 1 0 45 to 0 52 m 2 increasing amounts of hydroxyl bearing minerals with hydroxyl ion vibrational absorptions in tm band 7 wavelength region 2 08 to 2 35 m increase the ratio of tm band 5 to band 7 3 increasing amounts of fe bearing aluminosilicates that absorb in the band 4 wavelength region 0 76 to 0 9 m increase the product of the following two tm ratios band 5 to band 4 and band 3 0 63 to 0 69 m to band 4 and 4 thin 5 m desert varnish that covers many outcrops modulates but does not obscure the spectral reflectance signatures of the meatiq rocks the varnish consists of amorphous to poorly crystalline dioctahedral smectite iron oxides and or oxyhydroxides serpentinite mafic mylonite massive amphibolite quartzofeldspathic mylonite biotite schist and quartz phyllonite were mapped on the basis of their unique values in one or more of the three ratio images whereas coarse and fine grained granites granite gneiss and tonalite with similar mineralogies and tm band ratios were mapped as a group finer subdivisions were made where field traverses provided local verification results demonstrate that appropriate processing and presentation of landsat tm data can significantly augment field observations for lithologic mapping of large areas in arid regions

automated segmentation of hillslope profiles across ridges and valleys using a digital elevation model abstract we developed a three step algorithm to automate the recognition and segmentation of hillslopes across ridges and valleys using a gridded digital elevation model dem the first step involves the delineation of a side slope profile by locating the lower and upper boundaries in the second step the cross profile pattern of a ridge or a valley floor which is defined and bounded by a pair of side slopes is examined in order to distinguish upland flats from ridges and lowlands from valley floors the width and gradient of these landform units are also measured in the third step a side slope profile is segmented into lower mid and upper slopes with a line simplification algorithm to identify changes and breaks in the slope in this step the footslope and crestslope can also be distinguished within the lower and upper slopes respectively using a 15 m dem this method was applied to five sites in low to high relief fluvial landscapes in japan the results showed good agreement 86 9 2 7 with manual slope segmentation indicating the effectiveness of our algorithm

scale dependent analysis of satellite imagery for characterization of glacier surfaces in the karakoram himalaya abstract information regarding process structure relationships and change in the karakoram himalaya is of great importance in studying glacier hydrollogy mass balance and dynamic environmental change such information is not readily available detailed spatio temporal assessment requires field investigation coupled with quantitative remote sensing studies we conducted an investigation of the large batura glacier in pakistan to determine if spectral variability can be quantified and used to characterize glacier surfaces specifically spot panchromatic satellite data were evaluated for differentiating features of glacier structure resulting from ice movement ablation and supraglacial fluvial action image semivariogram analysis was conducted for assessing spectral variability patterns and fractal analysis was used to examine scale dependent variation in the data results indicate that spectral variability from fields of ice seracs can exhibit fractal characteristics although most surface features on the glacier exhibit a change in the fractal dimension over different ranges in scale the fractal dimension was found to be useful for differentiating between glacier surfaces such as white ice and debris covered ice characteristics of the debris load and the scale dependent nature of calculating the fractal dimension ultimately determined the potential of class separability

authigenic calcium carbonate flux in groundwater controlled lakes implications for lacustrine paleoclimate records groundwater dominated lakes are an important feature of many landscapes their sediments are a particularly valuable source of paleoenvironmental information in semiarid regions where perennial lakes may otherwise be scarce where groundwater and lake composition are favorable carbonate mineral precipitation evaporative concentration of lake water and microbial processes can combine to strongly deplete dissolved ca relative to influent groundwaters the authigenic carbonate flux acf can then become limited by water column cation availability and thereby be coupled to groundwater inflow rates and aquifer recharge here we analyze sedimentary records from two marl producing groundwater controlled lakes and demonstrate a link between one dimensional acf and the palmer drought severity index pdsi a measure of land surface wetness in a restricted outflow lake with high carbonate alkalinity acf is enhanced during historically wet climatic periods in response to increased aquifer recharge rates acf in this lake declines during droughts a neighboring dilute lake with a high rate of groundwater outflow shows comparatively weak coupling between acf and pdsi history ionic chemistry carbonate mineral equilibria and 13 c patterns of dissolved inorganic carbon show that the sensitivity of the acf signal depends on the degree of evaporative evolution of lake water and the mineral saturation state of the water column under conditions of stratification and ice cover copyright 2005 elsevier ltd

impact of uncertainty in rainfall estimation on the identification of rainfall thresholds for debris flow occurrence abstract estimation of rainfall intensity duration thresholds used for the identification of debris flow landslide triggering rainfall events has been traditionally based on raingauge observations the main drawback of using information from gauges is that the measurement stations are usually located far away from the debris flow initiation areas in complex terrain where debris flows take place the spatial variability of rainfall can be very high and this translates in large uncertainty of raingauge based estimates of debris flow triggering rainfall this work focuses on the assessment of the impact of rainfall estimation uncertainty on identification and use of rainfall thresholds for debris flow occurrence the upper adige river basin northern italy is the area of study a detailed database of more than 400 identified debris flow initiation points during the period 2000 2010 and a raingauge network of 100 stations comprise the database used for this work the methodology examines the intensity duration thresholds derived from a set of raingauges that are assumed to be located at debris flow initiation points dfrs and an equivalent set of raingauges assumed to have the role of the closest to debris flow available measurement mrs a set of reference rainfall thresholds is used to identify the rainfall events at dfrs that triggered debris flows i e exceed the threshold for these same events the corresponding rainfall thresholds are derived from mr observations comparison between the rainfall thresholds derived from dfrs and mrs revealed that uncertainty in rainfall estimation has a major impact on estimated intensity duration thresholds specifically the results showed that thresholds estimated from mr observations are consistently underestimated evaluation of the estimated thresholds for warning procedures showed that while detection is high the main issue is the high false alarm ratio which limits the overall accuracy of the procedure overall performance on debris flow prediction was shown to be good for low rainfall thresholds and poor for high rainfall thresholds examined lastly it was found that filtering out rainfall events with duration

modern dolomite deposition in continental saline lakes western victoria australia microcrystalline dolomite forms a major constituent of holocene sediments of numerous continental saline playa lakes in southeastern australia the lake waters are highly supersaturated with respect to dolomite as well as other mg carbonates but undersaturated or near saturation with respect to calcite and aragonite the dolomite shows no replacement textures and most likely formed by direct precipitation conditions in these lakes that appear conducive to the precipitation of dolomite are 1 high salinity 2 high mg ca ratios and 3 high alkalinity the moderate sulfate levels of the brines do not seem to be inhibiting carbonate precipitation

computer aided recognition of relief patterns on radar images using a syntax analysis abstract we present computerized recognition of relief patterns on an airborne sar image band x 3 2 cm using a syntax analysis the test site is the montagne sainte victoire provence france the pixel size is 2m 2m severe filtering to eliminate the speckle has reduced ground resolution but geologic and geomorphologic objects to extract thalwegs structural escarpments lithologic boundaries and landslides have large dimensions tens of meters far range correction was necessary to compensate weakening of radar signal with aircraft distance significant retrodiffusion values are for horizontal surfaces projected shadows surfaces whose normal is subperpendicular to radar beam steep radiometric gradients elements of the topographic profiles have been correlated with the elementary signals of radar image permitting a codification for syntactic analysis the radar image has been transformed into an image of elementary topographic symbols from which crests and thalwegs can be directly extracted recognition of structural escarpments and landslides involves search for typical sequences of symbols in different profile orientations and determination of a specific grammar syntax assessment of the results was made by comparison with similar syntactic methods of pattern recognition applied to a digital elevation model of the same area and field knowledge the radar image classifications have produced results close to reality imperfections are mainly due to the filtering process radar distance correction and difficulty in measuring significant retrodiffusion values for example retrodiffusion of horizontal surfaces artifacts inherent to radar acquisition also introduced confusions

calibration and validation of rainfall thresholds for shallow landslide forecasting in sicily southern italy abstract empirical rainfall thresholds are tools to forecast the possible occurrence of rainfall induced shallow landslides accurate prediction of landslide occurrence requires reliable thresholds which need to be properly validated before their use in operational warning systems we exploited a catalogue of 200 rainfall conditions that have resulted in at least 223 shallow landslides in sicily southern italy in the 11 year period 2002 2011 to determine regional event duration cumulated event rainfall ed thresholds for shallow landslide occurrence we computed ed thresholds for different exceedance probability levels and determined the uncertainty associated to the thresholds using a consolidated bootstrap nonparametric technique we further determined subregional thresholds and we studied the role of lithology and seasonal periods in the initiation of shallow landslides in sicily next we validated the regional rainfall thresholds using 29 rainfall conditions that have resulted in 42 shallow landslides in sicily in 2012 we based the validation on contingency tables skill scores and a receiver operating characteristic roc analysis for thresholds at different exceedance probability levels from 1 to 50 validation of rainfall thresholds is hampered by lack of information on landslide occurrence therefore we considered the effects of variations in the contingencies and the skill scores caused by lack of information based on the results obtained we propose a general methodology for the objective identification of a threshold that provides an optimal balance between maximization of correct predictions and minimization of incorrect predictions including missed and false alarms we expect that the methodology will increase the reliability of rainfall thresholds fostering the operational use of validated rainfall thresholds in operational early warning system for regional shallow landslide forecasting

high resolution saline lake sediments as enhanced tools for relating proxy paleolake records to recent climatic data series abstract lake level in an endorheic saline lake in southern europe has been inferred for the last 105 years 1889 1994 at an annual level of resolution using two independent methods first ordination analyses factor analysis fa correspondence analysis ca and detrended correspondence analysis dca have been used to point out the mineral successions of the sedimentary record these successions are evidenced by the arch disposition of both samples and mineral phases in the plane defined by the first two eigenvectors calculated by these analyses these temporal evolutions are the same as those obtained during the drying and refilling phases of saline lakes relay indices ri were obtained from distances to the first two eigenvectors which accurately reconstructed the lake level evolution during this period second an inferred lake level series was obtained using a multivariate time series model from the average maximum temperatures and total rainfall six main drought periods were found which coincided with known droughts in the area a high level of agreement was found between the two reconstructions which offered the possibility of directly extending the instrumental record back into the past therefore climatic changes could be reconstructed from saline lakes provided that an accurate chronological control of sedimentary processes is available

geologic interpretation of space shuttle radar images of indonesia the national aeronautics and space administration nasa space shuttle mission in november 1981 acquired images of parts of the earth with a synthetic aperture radar system at a wavelength of 23 5 cm 9 3 in and spatial resolution of 38 m 125 ft this report describes the geologic interpretation of 1 250 000 scale images of irian jaya and eastern kalimantan indonesia where the all weather capability of radar penetrates the persistent cloud cover the inclined look direction of radar enhances subtle topographic features that may be the expression of geologic structures on the indonesian images the following terrain categories are recognizable for geologic mapping carbonate clastic volcanic alluvial and coastal melange and metamorphic as well as undifferentia ed bedrock regional and local geologic structures are well expressed on the images in the vogelkop region of irian jaya the major tectonic elements tamrau mountains sorong fault kemum block bintuni basin and lengguru foldbelt are readily mapped on the image of the sorong fault geomorphic features offset drainage shutterridges aligned notches provide clear evidence for left lateral strike slip displacement several lineaments on the image correlate with previously mapped faults other lineaments may be the expression of previously unrecognized faults on the image of the mainland of irian jaya a belt of metamorphic and melange terrain marks the zone of collision between the pacific plate and the australian plate the high central range of irian jaya is located south of the metamorphic and melange belt the generally homoclinal structure of the central range is interrupted in the paniai lake region by a series of southward directed thrust plates indicated by belts of carbonate terrain new guinea limestone group that alternate with belts of clastic terrain kembelangan formation in the image of eastern kalimantan several major foldbelts are clearly expressed these limited examples of space shuttle radar images demonstrate their value for geologic interpretation of indonesia it is recommended that future shuttle missions acquire complete radar coverage of the main islands of indonesia for use in geologic mapping and energy exploration shuttle radar images would also be valuable for other cloud covered forested regions

a hydrous ca bearing magnesium carbonate from playa lake sediments salines lake spain sediments of playa lake salines se spain contain a carbonate mineral characterized by x ray diffraction peaks very similar to but systematically shifted from those of pure magnesite analyses sem ir and raman spectroscopy dta tga and icp indicate the mineral is a hydrous ca bearing magnesium carbonate with the chemical formula mg sub 0 92 ca sub 0 08 co 3 3h 2 o thermal characteristics of the mineral are similar to those of other known hydrated magnesium carbonates x ray and electron diffraction data suggests a monoclinic system p21 n space group with unit cell parameters of a 6 063 6 b 10 668 5 and c 6 014 4 aa and beta 107 28 degrees

modern and holocene carbonate sedimentology of two saline volcanic maar lakes southern australia the basin lakes are two adjacent maar lakes located in the centre of the western volcanic plains district of victoria australia both lakes are saline and alkaline west basin lake is meromictic whereas east basin is a warm monomictic lake the carbonate mineral suite of the modern offshore bottom sediments of these basins consists mainly of dolomite and calcite with smaller amounts of hydromagnesite and magnesite in west basin and monohydrocalcite in east basin the dolomite hydromagnesite magnesite and monohydrocalcite are endogenic in origin being derived by primary inorganic precipitation within the water columns of the lakes or at the sediment water interface the calcite is biologically precipitated as ostracod valves in addition to the carbonates in the modern offshore deep water sediments the lakes also contain a girdle of nearshore carbonate hardgrounds both beachrock and microbialites algal boundstones are present these modern lithified carbonate units exhibit a wide range of depositional and diagenetic fabrics morphologies and compositions in west basin the hardgrounds are composed mainly of dolomite hydromagnesite and magnesite whereas dolomite and monohydrocalcite dominate the east basin sediments aragonite high mg calcite kutnahorite siderite and protohydromagnesite also occur in these lithified carbonate units stratigraphic variations in the carbonate mineralogy of the holocene sediment record in the lakes were used to help decipher the palaeochemistry and palaeohydrology of the basins these changes in conjunction with fluctuations in organic remains and fossil content indicate a pattern of lake level histories similar to that deciphered from other maar lakes in western victoria

estimates of surface roughness derived from synthetic aperture radar sar data radar remote sensing data provide a unique perspective on the earth s crust and the processes that have influenced its evolution physically based models are required however to relate the geophysical quantities being measured by the radar sensor to useful geologic information synthetic aperture radar sar data over the cima volcanic field in the mojave desert of california are quantitatively connected with microtopography through inversion of a radar backscatter model changes in surface roughness inferred from the derived microtopography are modeled and found to be consistent with aeolian mantling as surfaces age estimated rates of aeolian deposition for the cima area are compared to the lunar crater volcanic field in nevada rates of deposition appear to be higher at cima volcanic field most likely because of its proximity to soda lake the main source of the aeolian material

a warning system for rainfall induced shallow failures abstract it is widely recognised that soil slips and debris flows are triggered by short intense storms owing its geologic geomorphologic and climatic settings the piedmont region nw italy is highly prone to the occurrence of this kind of landslides in the last two centuries in fact a total of 105 severe meteoric events which triggered shallow failures occurred and of these 18 events took place from 1990 to 2002 a fair number of rainfall thresholds have been proposed in the literature defined both on empirical or on physical bases empirical thresholds are defined collecting rainfall data for landslide meteoric events and for events without landslides while physical thresholds are based on numerical models that consider the relation between rainfall pore pressure and slope stability the main objective of this paper is the identification of the empirical triggering thresholds for the piedmont region four meteoric events were selected and analysed november 4 5 1994 july 7 8 1996 april 27 30 2000 october 13 16 2000 because they supply a wide range of variation for both rainfall parameters duration intensity cumulative rainfalls and the number of induced landslides in the intensity duration plot the critical limit is described by the equation i 19d 0 50 where i rainfall intensity expressed in mm h and d rainfall duration expressed in hours such a limit is traced to envelop 90 of the points on the graph in the ni d diagram the triggering thresholds are given by the equations ni 0 76d 0 33 and ni 4 62d 0 79 where ni normalised intensity with respect to the annual precipitation map expressed in mm h pma 100 in the article the different meaning of these thresholds is discussed finally the diagram ni ncr is proposed the triggering threshold is given by the expression ni 0 09ln ncr 0 54 where ncr is the normalised cumulative critical rainfall mm pma 100 the application of the triggering thresholds as a fundamental element in a warning system dedicated to the safeguarding of population in landslide prone areas is discussed in detail an operating procedure which is presently being verified and tested in the studied area is described

stable isotope characterisation of co existing carbonates from the holocene gallocanta lake ne spain palaeolimnological implications the sedimentary succession of gallocanta lake a closed saline lake located in the iberian range ne spain documents two successive lacustrine stages 1 brackish lake stage and 2 shallow saline lake stage the saline stage corresponds to the present day situation in which the lake water properties are mainly controlled by a strongly negative annual water balance the carbonates of the brackish lake stage have relatively constant 18o values however they are rather high 18odo 2 4 and 18occ 4 5 mean values suggesting a hydrologically closed lake with a long residence time of the waters 18o values of carbonates from the saline stage vary greatly and are lighter than in the previous stage 18odo 0 5 18occ 0 7 18omgs 2 3 mean values these carbonates also precipitated in a hydrologically closed lake but in equilibrium with a lake water of more variable isotopic composition the 13c values for carbonates of both stages reflect a mixing of different pools of carbon but during saline stage 13c values have been more controlled by the equilibrium of the lake waters with atmospheric co2 during the current stage calcite and dolomite precipitate in gallocanta lake mainly during spring and summer although dolomite precipitation is more favoured towards the summer magnesite precipitates at the beginning of autumn when the first rainfall re dissolves the saline surface crust producing saline waters with a high mg2 content the isotopic composition of lake waters sampled in 2005 are far higher than those calculated from the carbonates it is considered that this could be due to two factors either because there have not been many extremely dry years like the year 2005 during the development of the lake or because the physical and chemical characteristics of the lake waters in such conditions are not appropriate for the development of these minerals

rainfall thresholds for possible landslide occurrence in italy abstract the large physiographic variability and the abundance of landslide and rainfall data make italy an ideal site to investigate variations in the rainfall conditions that can result in rainfall induced landslides we used landslide information obtained from multiple sources and rainfall data captured by 2228 rain gauges to build a catalogue of 2309 rainfall events with mostly shallow landslides in italy between january 1996 and february 2014 for each rainfall event with landslides we reconstructed the rainfall history that presumably caused the slope failure and we determined the corresponding rainfall duration d in hours and cumulated event rainfall e in mm adopting a power law threshold model we determined cumulated event rainfall rainfall duration ed thresholds at 5 exceedance probability and their uncertainty we defined a new national threshold for italy and 26 regional thresholds for environmental subdivisions based on topography lithology land use land cover climate and meteorology and we used the thresholds to study the variations of the rainfall conditions that can result in landslides in different environments in italy we found that the national and the environmental thresholds cover a small part of the possible de domain the finding supports the use of empirical rainfall thresholds for landslide forecasting in italy but poses an empirical limitation to the possibility of defining thresholds for small geographical areas we observed differences between some of the thresholds with increasing mean annual precipitation map the thresholds become higher and steeper indicating that more rainfall is needed to trigger landslides where the map is high than where it is low this suggests that the landscape adjusts to the regional meteorological conditions we also observed that the thresholds are higher for stronger rocks and that forested areas require more rainfall than agricultural areas to initiate landslides finally we observed that a 20 exceedance probability national threshold was capable of predicting all the rainfall induced landslides with casualties between 1996 and 2014 and we suggest that this threshold can be used to forecast fatal rainfall induced landslides in italy we expect the method proposed in this work to define and compare the thresholds to have an impact on the definition of new rainfall thresholds for possible landslide occurrence in italy and elsewhere

mass movement in the himalaya new insights and research directions abstract ongoing studies that relate tectonics to the processes at the surface of earth show that many more sources of information about agents of shallow denudation such as mass movement are required to comprehend the long term erosion that leads to deep denudation over geologic time mass movement in the himalaya is scale dependent from the massive extension of whole mountain ranges gravity tectonics through the sackung failure of single peaks to the smallest slope failures generally denudation of the himalayan orogen begins with slope failure onto glaciers and into river valleys and continues by glacial and fluvial transport the maximum size of stable slopes and mean angles of slope that are produced by these failures are complex and controlled by a variety of factors including mass strength of the rocks stress fields angles of internal friction controlled by rock type cohesion that includes the control of rock temperature bulk unit weight of rock and discontinuities the processes of mass movement in the himalaya have been described many times for the past two centuries recently developments in a variety of fields have been introduced to assess the character of mass movement geomorphometry remote sensing digital elevation models and geographic information system technology are revolutionizing the study of mass movement in the himalaya

geomorphological signatures classification of aggregated slope unit objects from digital elevation and remote sensing data the concept of a geomorphological signature is developed for classifying and mapping slope units with an automated procedure for analysing digital elevation and remote sensing data slope units are extracted from a digital elevation model dem using a break of slope rule on downslope profiles each slope unit is an aggregated object of contiguous pixels and is summarized with five suites of variables shape topography topographic variability spectral characteristics and variability in spectral characteristics the variables are derived from the dem and a corresponding spot satellite image a ten class scheme is used to classify slope units for a study area in southwest yukon canada discriminant analysis results show the power of various combinations of variables to distinguish the classes with a maximum classification accuracy of 90 per cent training signatures are employed for classifying the entire study area to produce a map with 88 5 per cent accuracy the study shows that generating extensive geomorphological signatures for aggregated slope unit objects is a valuable exercise for discrimination and mapping 1998 john wiley sons ltd

an automated approach to the classification of the slope units using digital data abstract digital elevation and remote sensing data sets contain different yet complementary information related to geomorphological features digital elevation models dems represent the topography or land form whereas remote sensing data record the reflectance emittance or spectral characteristics of surfaces computer analysis of integrated digital data sets can be exploited for geomorphological classification using automated methods developed in the remote sensing community in the present study geomorphological classification in a moderate to high relief area dominated by slope processes in southwest yukon territory canada is performed with a combined set of geomorphometric and spectral variables in a linear discriminant analysis an automated method was developed to find the boundaries of geomorphological objects and to extract the objects as groups of aggregated pixels the geomorphological objects selected are slope units with the boundaries being breaks of slope on two dimensional downslope profiles each slope unit is described by variables summarizing the shape topographic and spectral characteristics of the aggregated group of pixels overall discrimination accuracy of 90 is achieved for the aggregated slope units in ten classes

integrated analysis of high resolution field and airborne spectroradiometer data for alteration mapping oatman epithermal gold deposit in northwest arizona pervasive argillic and wall rock phyllic and propylitic alteration discrimination of these zones rests on identification of the dominant alteration minerals alunite illite mica and chlorite modified journal abstract

characterization of volcanic geomorphology and geology by slope and topographic openness abstract we used a digital elevation model dem of iwate volcano japan to calculate slope and topographic openness for every geological unit in that area further we conducted principal component analysis pca and stepwise discriminant analysis sda to evaluate statistical differences in the morphometric parameters of the geological units we categorized the geological units according to their ages and their formation processes the categorization based on formation processes was as follows lava flow lava central cone stratocone air fall deposit pyroclastic flow deposit volcanic fan deposit and debris avalanche deposit pca allowed us to select geological units suitable for analysis while sda was used to select some morphometric parameters which could explain the differences in the formation processes and ages of the geological units we found that the formation processes correspond well to mean slope and that the geological ages that control the degree of surface dissection correspond well to the standard deviations of slope and negative topographic openness

regionalization of rainfall thresholds an aid to landslide hazard evaluation rainfall soil properties and morphology are major factors controlling shallow landsliding a series of meteorological events that triggered soil slips in northern italy were studied to define rainfall thresholds and to evaluate a possible regionalization soil properties triggering rainfall and local lithological and morphometrical settings of different sites were used as input to an infiltration model the approach allows the recognition of several triggering conditions in the piedmont pre alpine and alpine regions this suggests the need for different rainfall thresholds with respect to those derived with other methods intensity versus rainfall duration relationships become particularly important when related to soil permeability and thickness and demonstrate the role of antecedent precipitation events with exceptional water discharge from obstructed road culverts reveal the role played by anthropic structures in triggering such phenomena different approaches to slope stability analysis are shown taking into account bedrock lithology topography seepage and local saturation conditions

spatial estimation of debris flows triggering rainfall and its dependence on rainfall return period abstract forecasting the occurrence of debris flows is fundamental for issuing hazard warnings and often focuses on rainfall as a triggering agent and on the use of empirical rainfall thresholds based on rain gauge observations a recognized component of the uncertainty associated with the use of rainfall thresholds is related to the sampling of strongly varying rainfall variability with sparse rain gauge networks in this work we examine the spatial distribution of rainfall depth in areas up to 10 km from the debris flow initiation points as a function of return period and we exploit this information to analyze the errors expected in the estimation of debris flow triggering rainfall when rain gauge data are used in particular we investigate the impact of rain gauge density and of the use of different interpolation methods high resolution adjusted radar rainfall estimates representing the best available spatially distributed rainfall estimates at the debris flows initiation point and in the surrounding area are sampled by stochastically generated rain gauge networks characterized by varying densities debris flow triggering rainfall is estimated by means of three rainfall interpolation methods nearest neighbor inverse distance weighting and ordinary kriging on average triggering rainfall shows a local peak corresponding to the debris flow initiation point with a decay of rainfall with distance which increases with the return period of the triggering rainfall interpolation of the stochastically generated rain gauge measurements leads to an underestimation of the triggering rainfall that irrespective of the interpolation methods increases with the return period and decreases with the rain gauge density for small return period events and high rain gauge density the differences among the methods are minor with increasing the return period and decreasing the rain gauge density the nearest neighbor method is less biased because it makes use only of the closest rain gauge to the debris flow initiation point on the contrary inverse distance weighting and ordinary kriging which are using rain gauges located farther from the debris flows in addition to the closest one exhibit negative biases that increase with return period the standard deviation of the interpolated values is larger when the nearest neighbor is used with respect to inverse distance weighting and ordinary kriging for large return period and low rain gauge density the differences among the methods are minor