the early paleozoic evolution of the argentine recordillera as a laurentian rifted drifted and collided terrane a geodynamic model discussion and reply

frequency and initiation of debris flows in grand canyon arizona 1 debris flows from 740 tributaries transport sediment into the colorado river in grand canyon arizona creating rapids that control its longitudinal profile debris flows mostly occur when runoff triggers failures in colluvium by a process termed the fire hose effect debris flows originate from a limited number of geologic strata almost exclusively shales or other clay rich fine grained formations observations from 1984 through 2003 provide a 20 year record of all debris flows that reached the colorado river in grand canyon and repeat photography provides a 100 year record of debris flows from 147 tributaries observed frequencies are 5 1 events year from 1984 to 2003 and historic frequencies are 5 0 events year from 1890 to 1983 logistic regression is used to model historic frequencies based on drainage basin parameters observed to control debris flow initiation and transport from 5 to 7 of the 16 parameters evaluated are statistically significant including drainage area basin relief and the height of and gradient below debris flow source areas variables which reflect transport distance and potential energy the aspect of the river channel which at least partially reflects storm movement within the canyon is also significant model results are used to calculate the probability of debris flow occurrence at the river over a century for all 740 tributaries owing to the variability of underlying geomorphic controls the distribution of this probability is not uniform among tributaries of the colorado river in grand canyon

the formation and failure of natural dams of the numerous kinds of dams that form by natural processes dams formed from landslides glacial ice and late neoglacial moraines present the greatest threat to people and property landslide dams form in a wide range of physiographic settings the most common types of mass movements that form landslide dams are rock and debris avalanches rock and soil slumps and slides and mud debris and earth flows the most common initiation mechanisms for dam forming landslides are excessive rainfall and snowmelt and earthquakes landslide dams can be classified into six categories based on their relation with the valley floor type i dams 11 of 184 landslide dams from around the world that we were able to classify do not reach from one valley side to the other type ii dams 44 span the entire valley floor in some cases depositing material high on opposite valley sides type iii dams 41 move considerable distances both upstream and downstream from the landslide failure type iv dams 1 are rare and involve the contemporaneous failure of material from both sides of a valley type v dams 1 also are rare and are created when a single landslide sends multiple tongues of debris into a valley and forms two or more landslide dams in the same reach of river type vi dams 3 involve one or more failure surfaces that extend under the stream or valley and emerge on the opposite valley side many landslide dams fail shortly after formation in our sample of 73 documented landslide dam failures 27 of the landslide dams failed less than 1 day after formation and about 50 failed within 10 days over topping is by far the most common cause of failure the timing of failure and the magnitude of the resulting floods are controlled by dam size and geometry material characteristics of the blockage rate of inflow to the impoundment size and depth of the impoundment bedrock control of flow and engineering controls such as artificial spill ways diversions tunnels and planned breaching by blasting or conventional excavation glacial ice dams can produce at least nine kinds of ice dammed lakes the most dangerous are lakes formed in main valleys dammed by tributary glaciers failure can occur by erosion of a drainage tunnel under or through the ice dam or by a channel over the ice dam cold polar ice dams generally drain supraglacially or marginally by downmelting of an outlet channel warmer temperate ice dams tend to fail by sudden englacial or subglacial breaching and drainage late neoglacial moraine dammed lakes are located in steep mountain areas affected by the advances and retreats of valley glaciers in the last several centuries these late neoglacial dams pose hazards because 1 they are sufficiently young that vegetation has not stabilized their slopes 2 many dam faces are steeper than the angle of repose 3 these dams and lakes are immediately downslope from steep crevassed glaciers and near vertical rock slopes and 4 downstream from these dams are steep canyons with easily erodible materials that can be incorporated in the flow and increase flood peaks the most common reported failure mechanism is overtopping and breaching by a wave or series of waves in the lake generated by icefalls rockfalls or snow or rock avalanches melting of ice cores or frozen ground and piping and seepage are other possible failure mechanisms natural dams may cause upstream flooding as the lake rises and downstream flooding as a result of failure of the dam although data are few for the same potential energy at the dam site ownstream flood peaks from the failure of glacier ice dams are smaller than those from landslide moraine and structed earth fill and rock fill dam failures moraine dam failures appear to produce some of the largest downstream flood peaks for potential energy at the dam site greater than 1011 1012 joules differences in flood peaks natural dam failures appear to be controlled by dam characteristics and failure mechanisms

impact of chi chi earthquake on the occurrence of landslides and debris flows example from the chenyulan river watershed nantou taiwan abstract the chenyulan river watershed in central taiwan was chosen for evaluating the impact of the chi chi earthquake on the occurrence of landslides and for exploring the initial conditions triggering debris flows interpretations of aerial photographs and spot images as well as field investigations were used to identify landslide and debris flow occurrences precipitation data were then utilized to investigate critical conditions leading to the debris flow comparison of five spot images taken between june 1996 before the july 1996 typhoon herb and september 1999 before the chi chi earthquake shows that the landslide area increased from 7 1 106 to 7 5 106 m2 during that time however by january 2000 after the chi chi earthquake the landslide area almost tripled to 20 8 106 m2 measurement of images taken in march and august 2001 reveals that the landslide area had further expanded to 24 2 106 and 27 5 106 m2 respectively significant differences before and after the earthquake are also noticed in 1 the intensity and amount of precipitation required for triggering debris flow 2 the size of contributing drainage basin in which debris flows occurred and 3 the frequency of debris flows after the chi chi earthquake maximum hourly rainfall intensity and critical accumulated precipitation necessary to initiate debris flow reduced to as low as 1 3 of the pre earthquake figures prior to the chi chi earthquake most debris flows occurred in gullies with slopes greater than 10 and in drainage basins larger than 0 1 km2 conversely after the earthquake debris flows were observed even in gullies with effective drainage area smaller than 0 03 km2 furthermore before the earthquake the debris flow recurrence time in the study area was greater than 5 years whereas six debris flow events have been observed in the 2 years since the earthquake

zircon and whole rock nd pb isotopic provenance of middle and upper ordovician siliciclastic rocks argentine precordillera graptolite bearing middle and upper ordovician siliciclastic facies of the argentine precordillera fold thrust belt record the disintegration of a longlived cambro mid ordovician carbonate platform into a series of tectonically partitioned basins a combination of stratigraphic petrographic u pb detrital zircon and nd pb whole rock isotopic data provide evidence for a variety of clastic sediment sources four upper ordovician quartzo lithic sandstones collected in the eastern and central precordillera yield complex u pb zircon age spectra dominated by 1ae05 1ae10 ga zircons secondary populations of 1ae22 1ae30 and 1ae46 ga rare 2ae2 and 1ae8 ga zircons and a minor population 2 of concordant zircons in the 600 700 ma range archaean age grains comprise 1 of all zircons analysed from these rocks in contrast a feldspathic arenite from the middle ordovician estancia san isidro formation of the central precordillera has two well defined peaks at 1ae41 and 1ae43 ga with no grains in the 600 1200 ma range and none older than 1ae70 ga the zircon age spectrum in this unit is similar to that of a middle cambrian quartz arenite from the la laja formation suggesting that local basement rocks were a regional source of ca 1ae4 ga detrital zircons in the precordillera terrane from the cambrian onwards the lack of grains younger than 600 ma in upper ordovician units reinforces petrographic data indicating that ordovician volcanic arc sources did not supply significant material directly to these sedimentary basins nd isotopic data n 32 for middle and upper ordovician graptolitic shales from six localities define a poorly mixed signal end 450 ma 9ae 6t o 4ae5 that becomes more regionally homogenized in upper ordovician rocks 6ae 2 1 ae0 tdm 1ae51 0ae15 ga n 17 a trend reinforced by the u pb detrital zircon data it is concluded that proximal recycled orogenic sources dominated the siliciclastic sediment supply for these basins consistent with rapid unroofing of the precordillera terrane platform succession and basement starting in mid ordovician time common pb data for middle and upper ordovician shales from the western and eastern precordillera n 15 provide evidence for a minor 30 component that was likely derived from a high l u pb terrane

experimental study on initiation of gully type debris flow based on artificial rainfall and channel runoff debris flows usually occur abruptly and rapidly in mountainous areas and it is difficult to observe their occurrence progress therefore an experiment has become an important method to study debris flow initiation mechanism in recent years in this paper taking xiongjia gully in sw china as an example and on the basis of artificial rainfall experiment the author has studied the initiation of gully type debris flow experiment results indicate some relation between rainfall intensity and gully erosion failure mode of soil mass initiation mechanism and characteristics of debris flow based on several groups of experiments conclusions were drawn as follows 1 under strong precipitation the infiltration rate and soil water content in different depths are inversely proportional to the rainfall intensity intense rainfall favors the overland flow gully runoff and erosion but is not conducive to water infiltration 2 slope failure modes and initiation mechanism of debris flow vary with different rainfall and runoff conditions under the condition with the rainfall intensity of 55 mm h the slope failure mode presents a soil liquefaction and landslide accordingly the debris flow initiation mechanism belongs to landslide transformation however under the condition of intense rainfall and runoff gully beds are easy to be eroded and slopes are prone to collapse then debris flows occurred with initiation mechanism of entrainment 3 in terms of debris flow characteristics the debris flow occurrence process consists of several intermittent flows in addition the debris flow magnitude and flow viscosity are not consistent with rainfall intensity on the contrary under condition of intense rainfall of 65 and 75 mm h debris flows tend to be watery however under the rainfall condition of 55 mm h the flow viscosity is higher the experiment results are consistent well with the natural debris flow occurrence from xioangjia gully

transformation of dilative and contractive landslide debris into debris flows an example from marin county california abstract the severe rainstorm of january 3 4 and 5 1982 in the san francisco bay area california produced numerous landslides many of which transformed into damaging debris flows the process of transformation was studied in detail at one site where only part of a landslide mobilized into several episodes of debris flow the focus of our investigation was to learn whether the landslide debris dilated or contracted during the transformation from slide to flow the landslide debris consisted of sandy colluvium that was separable into three soil horizons that occupied the axis of a small topographic swale failure involved the entire thickness of colluvium however over parts of the landslide the soil a horizon failed separately from the remainder of the colluvium undisturbed samples were taken for density measurements from outside the landslide from the failure zone and overlying material from the part of the landslide that did not mobilize into debris flows and from the debris flow deposits the soil a horizon was contractive and mobilized to flows in a process analogous to liquefaction of loose granular soils during earthquakes the soil b and c horizons were dilative and underwent 2 to 5 volumetric expansion during landslide movement that permitted mobilization of debris flow episodes several criteria can be used in the field to differentiate between contractive and dilative behavior including lag time between landsliding and mobilization of flow episodic mobilization of flows and partial or complete transformation of the landslide

spatial distribution and susceptibility zoning of geohazards along the silk road xian lanzhou the region between xi an and lanzhou is the first and most important part of the so called silk road in china however this section is highly susceptible to geohazards including landslides debris flows etc as a result of complex geological formations steep landforms seasonal heavy rainfall and intensive anthropogenic activity that characterize this region these geohazards have resulted in significant damage to the local infrastructure and economy and are becoming increasingly frequent with time to identify the distribution of characteristics of geohazards and susceptibility zoning in this region a frequency analysis and logistic analysis were used to study the spatial distribution of geohazards the key factors of surface topography and geology associated with geohazards were considered including slope gradient height differential profile curvature slope aspect and rock hardness first the distribution and frequency of geohazards were discussed in relation to the five factors second each factor s influence was evaluated by logistic regression and the relative importance of each of the variables was discussed finally geohazard susceptibility zoning was mapped using logistic regression and geography information system tools the results of the susceptibility zoning model were validated using the locations that had recorded geohazards in recent decades the accuracy of the model was greater than 86 8 the model validation proved that there was good agreement between the susceptibility mapping and historically recorded geohazards the logistic regression model produced acceptable results using a receiver operating characteristics curve in which the total area under the receiver operating characteristics curve was 0 879 the results of this study can assist in preliminary planning for land use particularly with reference to construction projects in high risk areas

analysis of rainstorm induced slide debris flows on natural terrain of lantau island hong kong abstract lantau island the largest outlying island of the territory of hong kong experienced a severe rainstorm on 4 5 november 1993 which induced 800 slope failures on natural terrain there detailed field investigations were carried out to study the failure modes in relation with various influencing factors it was found that the occurrence of slide debris flows has a close relationship with bedrock geology slope gradient vegetation cover and micro landform the failure modes of slide debris flows may be classified into translational slides and rotational slides and the former are predominant analysis of the hydrological response of colluvial slopes during the rainstorm indicated that the majority of the failures were caused by the development of a perched water table in the thin surface layer of colluvium of volcanic origin due to infiltration during the heavy rain undisturbed soil samples from south lantau have been subjected to anisotropically consolidated undrained compression tests at comparatively low stress levels constant deviatoric stress path tests cqd simulating the stress path in the field at in situ stress levels have been performed to investigate soil behavior the cqd test results indicate that the material of slopes at undisturbed state is brought to dilation because of the increase in pore water pressure caused by infiltration of rain water for a translational slide the displacement resulting from dilation may destroy cohesion along the failure surface and locally within the interior of the slide the surplus water during the intense rainstorm was able to equilibrate the reduction in pore pressure caused by dilation and the dilation and displacement may be further increased the strain softening after significant strains triggered debris flow mobilization however for a rotational slide the increase in pore water pressure caused by surplus water infiltration during the intense rainstorm could not equilibrate the reduction in pore pressure caused by dilation much or even all of the sliding block could not mobilize into a debris flow

field observations of a debris flow event in the dolomites a debris flow event occurred in june 1997 in the dolomites eastern alps italy the phenomenon was directly observed in the field and recorded by a video camera near its initiation area the debris flow originated shortly after an intense rainstorm 25 mm in 30 min whose runoff mobilised the loose coarse debris that filled the bottom of the channel in its upper part the analysis of the steep headwater basin indicates a very short concentration time 9 14 min that fits the quick hydrological response observed in the field the debris flow mobilisation was not contemporaneous with the arrival of the peak water discharge in the initiation area probably due to the time required for the saturation of the highly conductive channel bed material channel cross section measurements taken along the flow channel indicate debris flow peak velocity and discharge ranging from 3 1 to 9 0 m s and from 23 to 71 m3 s respectively samples collected immediately after deposition were used to determine the water content and bulk density of the material channel scouring fines enrichment and transported volume increase testify erosion and entrainment of material along the flow channel field estimates of the rheological properties based on open channel flow of bingham fluid indicate a yield strength of 5000 400 pa and relatively low viscosity 60 326 pa s probably due to a high percentage of fines approx 30

flume tests to study the initiation of huge debris flows after the wenchuan earthquake in s w china abstract in the wenchuan area in the southwest of china a huge amount of loose co seismic landslide material was deposited on slopes during the wenchuan earthquake of may 2008 these loose deposits formed the source material for rainfall induced debris flows or shallow landslides in the years after the earthquake on august 13 2010 about 20 large debris flows were triggered by heavy rainfall in the area around the epicenter of the wenchuan earthquake field reconnaissance revealed that the initiation of these post earthquake debris flows was closely related to severe erosion of the loose deposits flume tests were carried out to study the initiation mechanism of these post earthquake debris flows and the related influencing factors the flume was instrumented with ten combination sets of suction and pore pressure sensors these sensors were accompanied by tdr probes to measure the soil water content the flume has a length of 2 5 m and a width of 1 5 m a series of 26 tests was conducted to study the influence of slope gradient and discharge on the initiation mechanism and scale of the debris flows the amount of debris flow discharge was obtained by collecting the washed out deposits every 20 s the experimental results showed that the initiation mechanism of debris flows for gentle slopes and steep slopes was different on steeper slope incision by run off water was very rapid initiating directly the start of a debris flow the debris flow volume increased rapidly by a chain of subsequent cascading processes starting with collapses of the side walls damming and breaching leading to a rapid widening of the erosion channel at gentler slopes less intensive run off incision caused an accumulation of material down slope which after saturation failed as shallow slides transform in a second stage into debris flows it was demonstrated that the slope was the dominant factor in controlling the scale of the debris flows while the effect of discharge on erosion and the size of the debris flows was less clear

potential for a ganhaizi landslide generated surge in xiluodu reservoir jinsha river china xiluodu hydropower station is located on the jinsha river the upper course of the yangtze river and is the third largest hydropower station in the world in may 2013 impoundment of the xiluodu reservoir started and preliminarily operation began and the reservoir area was subject to frequent landslides and collapses on 23rd july 2013 huangping landslide with a volume of 20 104 m3 slid into the xiluodu reservoir and generated an impulse water wave that killed 12 people on the opposite bank the reservoir water level will fluctuate by 60 m each year between the elevations of 540 and 600 m so any impulse wave generated by a landslide in the reservoir is a major concern in the preliminary impoundment phase ganhaizi landslide is the biggest landslide in xiluodu reservoir with a volume of about 7 800 104 m3 this landslide is only 14 km upstream from the xiluodu dam in particular the landslide deformation has obviously intensified after impounding this paper analyzes the terrain and deformation features of ganhaizi landslide and we propose that sliding on the ganhaizi slope may occur at the front part of the landslide the front part of landslide has a volume of around 300 104 m3 the elevation of the barycenter of this part is 510 m the sliding mass is thus largely underwater and can pose a threat mainly in the form of surges based on the underwater landslide terrain in the mountain reservoir area the authors have modified the seabed landslide generated surge source model of grilli and watts 2005 to form an initial source model for an underwater landslide generated surge using this model the authors predicted possible surge disasters that can be caused by a ganhaizi landslide at both the dead water level of 540 m and the normal water level of 600 m in xiluodu reservoir the surge disaster might mainly strike the area within 5 km along the river channel both upstream and downstream of the landslide area but generally poses no threat to xiluodu dam this paper aims to provide technical support for the safety of xiluodu dam and the reservoir area the newly established underwater landslide generated surge initial source model for mountain reservoir areas may serve as reference for calculation of underwater landslide in other reservoir areas around the world

geostatistical interpolators for the estimation of the geometry of anthropogenic deposits in rome italy and related physical mechanical characterization with implications on geohazard assessment the role played by the anthropogenic deposits with poor geotechnical characteristics to induce seismic amplification and its influence on hydrogeological conditions due to its permeability characteristics has been demonstrated by numerous studies conducted in urban environments the historical center of rome italy is characterized by the presence of high thickness of anthropogenic deposits a stratigraphic unit that accumulated during the centuries of urban development the modeled reconstruction of this unit could provide a tool for the elaboration of preliminary maps used for urban planning by public institutions in this work the reconstruction of the basal surface of the anthropogenic deposits was carried out using lithostratigraphical and geotechnical data recorded in 1355 boreholes drilled within the historical center of rome deterministic and geostatistical estimators have been then used to predict the values at non sampled locations to construct different maps of the basal surface grid statistics allowed the comparison of the obtained maps to select the best spatial predictor mono and multivariate geostatistical intepolators ordinary kriging kriging with external drift ked and cokriging have been selected and discussed and ked was the best interpolator for the used dataset the obtained surface was then used to calculate a thickness map by subtracting it to the digital terrain model furthermore results of some mechanical characteristics of the anthropogenic deposits are presented and discussed in the light of the reconstructed geometry the knowledge of both geometry i e basal surface and thickness and mechanical characteristics of these deposits could provide useful information for the evaluation of geological hazards in urban areas

a rational method for estimating maximum discharge of a landslide induced debris flow a case study from southwestern china this paper presents a rational method for estimating the maximum discharge of a landslide induced debris flow the method has five basic principles or steps a to identify and measure representative bends and straight zones along a channel through which a debris flow went down b to evaluate peak debris flow velocity in the bends c to assess peak debris flow velocity in the straight channel zones d to use the peak velocities to estimate the distribution of peak discharge along the entire channel and e to find the maximum velocity and discharge of the debris flow the method is illustrated with a case study of a landslide induced debris flow at a mountainous region near chengdu southwestern china the results show that the peak debris velocity was between 2 4 and 4 7 m s 1 and the peak debris discharge was between 6 7 and 35 7 m 3 s 1 the peak discharge initially increased at the upper portion of the channel then decreased at the lower portion indicating that the upper channel experienced erosion but the lower channel experienced deposition the location with the maximum debris flow discharge corresponds to the point where the volume of the debris flow started to decrease the method presented in this paper can help to prevent or mitigate debris flow hazards c 2006 elsevier b v all rights reserved

application and design of an efficient siphon dewatering system for debris flow mitigation a case study of a small catchment in zhejiang province china abstract excessive water in a channel is an important factor that triggers channelized debris flows in this study we propose a new system for the separation of water and sediment and drainage in order to drain water away from channels and reduce the potential for debris flows the main component of the system contains a siphon drainage pool covered with an inclined perforated plate and siphon drainage pipes the inclined perforated plate can separate sediment from the water and the siphon drainage pipe can drain flood water quickly to test the effectiveness of the new structure a field experiment was developed and tested in a small catchment in which debris flow was an issue the experimental results showed that the drainage pool effectively decreased the maximum depth of the flow in the triggering area thereby avoiding the occurrence of debris flow to set the optimize design parameters of the pool three main design parameters were evaluated i e peak discharge during storms separation ability of drainage pool and the maximum depth of surface flow in the triggering areas the peak discharge was obtained by using the nam model and a rational formula and the nam model provided more accurate results the results of the calculation of the separated ratio showed large runoff volumes and a lower separated ratio the results of the nam model were used to simulate the maximum depth of flow using the flo 2d model

the triggering of debris flow due to channel bed failure in some alpine headwater basins of the dolomites analyses of critical runoff the debris deposits at the bottom of very steep natural channels and streams in high mountain areas can be mobilized by runoff triggering a water sediment mixture flow known as debris flow the routing of debris flow through human settlements can cause damage to civil structures and loss of human lives the prediction of such an event or the runoff discharge that triggers it assumes an interest in risk analyses and the planning of defence measures the object of this study is to find a method to determine the critical runoff value that triggers debris flow as a result of channel bed failure historical and rainfall data on 30 debris flows that occurred in six watersheds of the dolomites north eastern italian alps were collected from different sources field investigations at the six sites together with the hydrologic response to the rainfalls that triggered the events were performed to obtain a realistic scenario of the formation of the debris flow there occurred field observations include a survey along the channel of the triggering reach of debris flow with measurements of the channel slope and cross section and sampling of debris deposits for grain size distribution simulated runoff discharge values based on the rainfall recorded by pluviometers were then compared with values obtained through experimental criteria on the initiation and formation of debris flow by bed failure the results are discussed to provide a plausible physical based method for the prediction of the triggering of debris flow by channel bed failure copyright 2007 john wiley sons ltd

post earthquake changes and prediction of debris flow scales in subao river valley beichuan county sichuan province china subao river lies along the beichuan yingxiu fault in beichuan county which has been heavily impacted by the wenchuan earthquake on 12 may 2008 and has become sources of many geo hazards on 24 september 2008 a rainstorm triggered a large debris flow in the catchment causing several deaths and significant damages a case study on changes of the debris flow was conducted in the river the peak discharges were calculated in the guanmenzi huangnidi and daanshan gullies results indicated that the peak discharges corresponded to various return periods in different gullies 200 years in daanshan 100 years in huangnidi and 50 years in guanmenzi however the triggering precipitation in these three gullies was only of a 20 year return period the debris flows had undergone significant changes analysis indicated that the changes should be ascribed to the flow characteristics initiation conditions and the channel blockage impacted by the rapid accumulation of loose material channel blockage was the principal factor increasing the scale of the debris flow the values on the blocking coefficient were presented based on density height and other characteristics of dams finally all of the peak debris flow discharges of the subao river valley for a 20 year return period were calculated using the recommended blocking coefficient values

initiation process of debris flows on different slopes due to surface flow and trigger specific strategies for mitigating post earthquake in old beichuan county china the 12 may 2008 wenchuan earthquake ms 8 0 in china produced an estimated volume of 28 108 m3 loosened material which led to debris flows after the earthquake debris flows are the dominant mountain hazards and serious threat to lives properties buildings traffic and post earthquake reconstruction in the earthquake hit areas it is very important to understand the debris flow initiation processes and characteristics for designing debris flow mitigation the main objective of this article is to examine the different debris flow initiation processes in order to identify suitable mitigation strategies three types of debris flow initiation processes were identified designated as types a b and c by field survey and experiments in a type initiation the debris flow forms as a result of dam failure in the process of rill erosion slope failure landslide dam or dam failure this type of debris flow occurs at the slope of 10 2 with a high bulk density and several surges following dam failure b type initiation is the result of a gradual increase in headward down cutting bank and lateral erosion and then large amount of loose material interfusion into water flow which increases the bulk density and forms the debris flow this type of debris flow occurs mainly on slopes of 15 3 without surges c type debris flow results from slope failures by surface flow infiltration loose material crack slope failure and fluidization this type of debris flow occurs mainly on slopes of 21 4 and has several surges of debris flow following slope failure and a high bulk density to minimize the hazards from debris flows in areas affected by the wenchuan earthquake the erosion control measures such as the construction of grid dams slope failure control measures the construction of storage sediment dams and the drainage measures such as construction of drainage ditches are proposed based on our results it is recommend that the control measures should be chosen based on the debris flow initiation type which affects the peak discharge bulk density and the discharge process the mitigation strategies discussed in this paper are based on experimental simulations of the debris flows in the weijia huashiban and xijia gullies of old beichuan city the results are useful for post disaster reconstruction and recovery as well as for preventing similar geohazards in the future

debris flow formation conditions and optimal characteristics of drainage canal following wenchuan earthquake the debris flow formation conditions changed after the wenchuan earthquake for studying the optimal characteristics of the drainage canal under the changed formation conditions the zhangjia gully in beichuan county a typical debris flow gully was selected as the study area two debris flow events occurred on september 24 2008 and july 17 2009 respectively which threatened the safety of the inhabitants and destroyed the properties and transportation routes on the alluvial fan huge amounts of solid loose materials triggered by the earthquake and the effective antecedent precipitation were responsible for the debris flow occurrence for eliminating the damage caused by debris flows the construction of a drainage canal on the alluvial fan became necessary a design method for the optimal cross section characteristics of a debris flow drainage canal is discussed in this paper using the standard measurements for the depth h and the width b the cross section size parameter f and the cross section configuration parameter m under optimal hydraulic conditions are defined and deduced subsequently formulas for calculating the cross section measurements are deduced under optimal hydraulic conditions when peak discharge q grain composition d50 and d10 and longitudinal slope i are known finally this method is applied for the cross section design of the debris flow drainage canal in zhangjia gully

identification of mechanisms for landslide type initiation of debris flows the modelling of debris flow initiation in slopes is addressed in this paper first possible factors governing debris flow initiation are established then a coupled hydro mechanical model for deformable porous media with two pore fluids that is used to assess the problem of the debris flow initiation in slopes is briefly outlined various ways to identify failure and to approach the transition of the failed mass into a debris flow are discussed in the framework of small strain theory and elasto plastic behaviour a parametric study was carried out to evaluate the relative importance of the most commonly cited parameters that are assumed to influence debris flow initiation it was found that the slope angle is of minor importance in the development of slope instability under loading due to internal water supply transient behaviour was found to be decisive and some critical combinations of water supply over time yielded situations that were likely to encourage the onset of debris flow the significant role of permeability as a function of the degree of saturation in relation to the water supply is demonstrated the proposed three phase model is shown to be an adequate and promising way to address debris flow initiation

the mechanisms behind shallow failures in slopes comprised of landslide deposits in areas hit by the 2008 wenchuan earthquake that occurred in sichuan province china debris flows are often generated from landslide deposits during heavy rainstorms the broadly graded and unconsolidated landslide deposits respond to rainfall in very complex mechanical and hydraulic manners an artificial rainfall test was conducted to simulate the rainfall infiltration and surface runoff processes occurring on the landslide deposit slope at the wenjiagou gully china with heavy rainfall rates 140 mm h incorporated an innovative flume was designed to collect the slope interflow and surface runoff separately sensors to monitor the pore water content pwp and volumetric water content vwc were deployed the results indicated that there were four stages in the hydrological response of landslide deposits during the artificial rain event infiltration a slow increase in interflow surface runoff begins a rapid increase in interflow surface runoff slowly increases and a steady state bed gradient increase will lead to pwp rapidly ascending and regressive failure happening concomitant with the observed increases in pwp and vwc the shear strength of the landslide deposits decreased and led to the occurrence of small scale shallow failures surface runoff interflow and fine particle migration effects are presented to interpret the process of shallow failure and although shallow slope failure is the result of interaction with the above three factors induced by rainfall the key underlying factor is the characteristically loose structure of landslide deposits c 2014 elsevier b v all rights reserved

effects of strong ground motion on the susceptibility of gully type debris flows abstract typhoon herb in 1996 caused widespread debris flows in central taiwan the 7 3 chi chi earthquake on september 21 1999 which also took place in central taiwan induced many landslides in the region these landslides turned into debris flows when typhoon toraji struck taiwan in 2001 this research selects three regions which suffered a ground motion class of 5 6 and 7 on the richter scale during the chi chi earthquake as study areas air photos from 1997 and 2001 of these regions are used to map the gully type debris flows that took place after typhoons herb and toraji respectively the gullies adjacent to the debris flow but without a trace of debris flows are also mapped as the non debris flow data the topography hydrogeology and rainfall factors where debris flow occurred and in which there was no occurrence of debris flows in these gullies were retrieved from dtm geological maps and iso countour maps and of rainfall through gis processing these characteristic are introduced into a probabilistic neural network to build a predicting model for the probability of the occurrence of debris flows three series of cross analyses are conducted to compare the probability of the occurrence of debris flows of the same dataset predicted by different prediction models the results reveal that the susceptibility of debris flows was elevated after the chi chi earthquake struck the upsurge of susceptibility was more obvious for the regions that received a higher class of ground motion

effective mitigation of debris flows at lemon dam la plata county colorado abstract to reduce the hazards from debris flows in drainage basins burned by wildfire erosion control measures such as construction of check dams installation of log erosion barriers lebs and spreading of straw mulch and seed are common practice after the 2002 missionary ridge fire in southwest colorado these measures were implemented at knight canyon above lemon dam to protect the intake structures of the dam from being filled with sediment hillslope erosion protection measures included lebs at concentrations of 220 620 ha 200 600 of typical densities straw mulch was hand spread at concentrations up to 5 6 metric tons hectare 125 of typical densities and seeds were hand spread at 67 84 kg ha 150 of typical values the mulch was carefully crimped into the soil to keep it in place in addition 13 check dams and 3 debris racks were installed in the main drainage channel of the basin the technical literature shows that each mitigation method working alone or improperly constructed or applied was inconsistent in its ability to reduce erosion and sedimentation at lemon dam however these methods were effective in virtually eliminating sedimentation into the reservoir which can be attributed to a number of factors the density of application of each mitigation method the enhancement of methods working in concert the quality of installation and rehabilitation of mitigation features to extend their useful life the check dams effectively trapped the sediment mobilized during rainstorms and only a few cubic meters of debris traveled downchannel where it was intercepted by debris racks using a debris volume prediction model developed for use in burned basins in the western u s recorded rainfall events following the missionary ridge fire should have produced a debris flow of approximately 10 000 m3 at knight canyon the mitigation measures therefore reduced the debris volume by several orders of magnitude for comparison rainstorm induced debris flows occurred in two adjacent canyons at volumes within the range predicted by the model

debris flow initiation and sediment recharge in gullies landslides that enter gullied low order drainages can either initiate debris flow or stop depositing sediment in the channel this process is one of the most common ways that debris flows initiate but little attention to date has been paid to evaluating the factors that affect whether or not the initial landslide will become a debris flow or deposit sediment in the channel statistically significant parameters that determine whether slope failures become debris flows or act to recharge in channel sediment are channel gradient angle of entry of failure into the channel initial failure volume and the amount of in channel stored sediment steeper channels low angles of entry lower volumes of in channel sediment and larger initial failures were more likely to result in debris flows this study found that as the volume of in channel stored sediment increased the volume of initial failure required to initiate a debris flow also increased this result calls into question the simple supply limited model of cyclical debris recharge and debris flow in low order gullied drainages and suggests a negative feedback mechanism between debris accumulation and debris flow susceptibility

the hydrogeological attributes and mechanisms of a receding sedimentary terrain in the anambra basin southern nigeria this research investigated the hydrogeological aspects associated with severe gulling and landsliding on a vulnerable sedimentary terrain in the context of the newly identified deformation patterns and large numbers of recently discovered scars clustering slopes on identical coordinates results of field survey remote sensing vertical electrical sounding and experimental analyses were presented to explain the causes and mechanisms of the mass movements ravaging the terrain a digital elevation model accurately captured the diverse geomorphologic elements including landslide scars hills ridges valleys plains and rivers that matched field observations the model aided the identification of previously unknown steep incised channels active headcuts unstable side walls and a seasonal river flowing near the slopes having large number of landslide scars it was observed that areas that lay on higher elevations where the clusters occur were dominated by fresh scars while the moderate to low elevations were dominated by older ones majority of the slope failures initiated within the sandstone as shallow slides 1 m to the sliding surface covering 104 m2 with short runout distances bigger landslides although few occurred as isolated individual events initiated at the sandstone shale boundary on distinct slopes the steepness of the slopes seemed controlled by slope morphology concavity which probably influenced the number and distribution of landslide events the steeper slopes were more concave and had the highest concentration of scars shallow water table 4 11 m and increased instability brittleness index under increasing over consolidation ratio are the critical failure factors

pore pressure response during failure in soils three experiments were performed on natural slopes to investigate variations of soil pore water pressure during induced slope failure two sites in the wasatch range utah and one site in the san dimas experimental forest of southern california were forced to fail by artificial subsurface irrigation the sites were instrumented with electronic piezometers and displacement meters to record induced pore pressures and movements of the slopes during failure piezometer records show a consistent trend of increasing pressure during the early stages of infiltration and abrupt decreases in pressure from 5 to 50 minutes before failure displacement meters failed to register the amount of movement due to location and ineffectual coupling of meter pins to soil observations during the experiments indicate that fractures and macropores controlled the flow of water through the slope and that both water flow paths and permeability within the slopes were not constant in space or time but changed continually during the course of the experiments

wildfire related debris flow initiation processes storm king mountain colorado a torrential rainstorm on september 1 1994 at the recently burned hillslopes of storm king mountain co resulted in the generation of debris flows from every burned drainage basin maps 1 5000 scale of bedrock and surficial materials and of the debris flow paths coupled with a 10 m digital elevation model dem of topography are used to evaluate the processes that generated fire related debris flows in this setting these evaluations form the basis for a descriptive model for fire related debris flow initiation the prominent paths left by the debris flows originated in 0 and 1st order hollows or channels discrete soil slip scars do not occur at the heads of these paths although 58 soil slip scars were mapped on hillslopes in the burned basins material derived from these soil slips accounted for only about 7 of the total volume of material deposited at canyon mouths this fact combined with observations of significant erosion of hillslope materials suggests that a runoff dominated process of progressive sediment entrainment by surface runoff rather than infiltration triggered failure of discrete soil slips was the primary mechanism of debris flow initiation a paucity of channel incision along with observations of extensive hillslope erosion indicates that a significant proportion of material in the debris flows was derived from the hillslopes with a smaller contribution from the channels because of the importance of runoff dominated rather than infiltration dominated processes in the generation of these fire related debris flows the runoff contributing area that extends upslope from the point of debris flow initiation to the drainage divide and its gradient becomes a critical constraint in debris flow initiation slope area thresholds for fire related debris flow initiation from storm king mountain are defined by functions of the form acr tan 3 s where acr is the critical area extending upslope from the initiation location to the drainage divide and tan is its gradient the thresholds vary with different materials

paleomagnetic confirmation of the laurentian origin of the argentine precordillera abstract several recent tectonic models have portrayed the argentine precordillera has been recently portrayed as an early paleozoic laurentian derived exotic terrane now found in southwestern south america these models have primarily been based on strong biogeographic and stratigraphic evidence however no paleomagnetic data have previously been available to independently test them a paleomagnetic study was therefore carried out on the early cambrian cerro totora formation exposed in the northern reaches of the argentine precordillera after stepwise thermal demagnetization a pre folding remanence was identified in ten sites of this formation yielding a paleomagnetic pole ct at 37 0 n 314 1 e a95 5 8 this pole is not consistent with the latest proterozoic early paleozoic apparent polar wander path for gondwana but it agrees with the early cambrian section of the laurentian path if the argentine precordillera is positioned as the conjugate margin of the ouachita embayment in southeast laurentia this result confirms that the precordillera is an allochthonous terrane derived from laurentia in cambrian times that was later accreted to gondwana probably in middle ordovician times

identification of soil redistribution using 137cs for characterizing landslide prone areas a case study in sarno quindici italy debris flows are among the most hazardous and unpredictable processes whose hazard evaluation requires an understanding of the processes that govern sediment supply sediment bulking flow volume and deposition in line with this challenge we estimate the net soil redistribution rates in an area characterized by recurrent instability phenomena using 137cs as a tracer for monitoring soil dynamics an extension of this method by applying it to the case of major landslides is addressed specifically surveys of soil 137cs content at sites in the pizzo d alvano massif italy where a set of particularly damaging landslides occurred on 5 6 may 1998 are reported being this region prone to debris flows two zero order basins are examined one of which experienced a landslide event in that basin deposition is observed whereas the other shows a net loss of soil these results appear to be relevant particularly because the rate of hollow filling could be correlated with the magnitude and or frequency of debris flow occurrence or with some measure of the hazard presented by individual gullies