reservoir heterogeneity and quality of khuff carbonates in outcrops of central saudi arabia abstract the khuff carbonates host several main gas reservoirs in the middle east these reservoirs are known for their heterogeneity both of sub seismic scale and beyond the interwell spacing to get a better insight in these reservoirs the heterogeneity of the upper khartam member placed in a high frequency sequence stratigraphic framework was studied with a lateral resolution between logged sections of 5 m the sedimentology and sequence stratigraphy of four outcrop localities were studied and approximately 600 samples were collected for petrographic porosity and permeability analyses seventeen lithofacies types were recognised and six major diagenetic processes could be differentiated in the studied outcrops dissolution is likely the result of intensive circulation of meteoric water undersaturated with respect to calcite significantly cementation has blocked most of the original intergranular porosity pore lining detrital clay severely impacted reservoir permeability and complicated the pore geometry dolomitization is associated with the upper khuff sudair boundary and is likely the result of influx of water highly saturated with mg 2 that developed during the deposition of the sudair evaporites finally stylolites are to a major extend controlled by lithofacies and geobody configuration ten porosity types could be namely intergranular intragranular shelter dissolution enlarged moldic vuggy micro porosity and porosity in relation to dolomite dedolomite dolomite leaching and fracture development overall intertidal creeks are characterized by a complex and heterogeneous pore geometry if compared to the intertidal channels and this can be attributed to the geobody architecture with intertidal creeks being composed of dense and small tidal bodies 1 m in length and 20 cm in thickness while intertidal channels are composed of thick amalgamations of intertidal channels 5 m by 50 cm most critically the horizontal reservoir quality was influenced differentially by diagenesis which resulted in a lateral segmentation of single bodies into different hydraulic units the differential mold filling calcite cements have significantly reduced porosity and permeability generally mineral content has little impact on the reservoir quality although clay minerals played a central role in lining the pore space and affecting permeability finally horizontal reservoir heterogeneity seems to have been controlled by fractures and stylolites which respectively acted as conduits to and barriers for vertical fluid flow and hence controlled the differential cementation and dissolution processes

landsliding and the evolution of normal fault bounded mountains much of the tectonic and climatic history in high relief regions such as the mountains of the western u s basin and range province is contained in the morphology of hillslopes drainage networks and other landforms that range in scale from 10 1 to 101km to understand how these landforms evolve we have developed a numerical landscape evolution model that combines a detailed tectonic displacement field with a set of physically based geomorphic rules bedrock landsliding long recognized as a significant geomorphic process in mountainous topography is for the first time explicitly included in the rule set in a series of numerical experiments we generate synthetic landscapes that closely resemble mountainous topography observed in the basin and range the production of realistic landscapes depends critically on the presence of bedrock landslides and landsliding yields rates of long term erosion that are comparable in magnitude to those of fluvial erosion the erosive efficiency of bedrock landsliding implies that hillslopes may respond very quickly to changes in local base level and that fluvial erosion is the rate limiting process in steady state experimental landscapes our experiments generate power law distributions of landslide sizes somewhat similar to both field and laboratory observations thus even a simple model of bedrock landsliding is capable of quantitatively reproducing mountainous topography and landslide distributions and represents a significant step forward in our understanding of the evolution of normal fault bounded ranges

scale invariance of soil moisture variability and its implications for the frequency size distribution of landslides abstract power spectral analyses of soil moisture variability are carried out from scales of 100 m to 10 km on the microwave remotely sensed data from the washita experimental watershed during 1992 the power spectrum s k has an approximate power law dependence on wave number k with the exponent 1 8 this behavior is consistent with the behavior of a stochastic differential equation for soil moisture at a point and it has important consequences for the frequency size distribution of landslides we present the cumulative frequency size distributions of landslides induced by precipitation in japan and bolivia as well as landslides triggered by the 1994 northridge california earthquake large landslides in these regions despite being triggered by different mechanisms have a cumulative frequency size distribution with a power law dependence on area with an exponent ranging from 1 5 to 2 we use a soil moisture field with the above statistics in conjunction with a slope stability analysis to model the frequency size distribution of landslides in our model landslides occur when a threshold shear stress dependent on cohesion pore pressure internal friction and slope angle is exceeded this implies a threshold dependence on soil moisture and slope angle since cohesion pore pressure and internal friction are primarily dependent on soil moisture the cumulative frequency size distribution of domains of shear stress greater than a threshold value with soil moisture modeled as above and topography modeled as a brownian walk is a power law function of area with an exponent of 1 8 for large landslide areas this distribution is similar to that observed for landslides the effect of strong ground motion from earthquakes lowers the shear stress necessary for failure but does not change the frequency size distribution of failed areas this is consistent with observations this work suggests that remote sensing of soil moisture can be of great importance in monitoring landslide hazards and proposes a specific quantitative model for landslide hazard assessment

a theoretical model coupling chemical weathering and physical erosion in landslide dominated landscapes a current theory that links the uplift of the himalayas to the drawdown of atmospheric co2 assumes that rates of chemical weathering are enhanced by accelerated physical erosion due to the increased exposure of fresh minerals although several studies have concluded that weathering rates do increase with erosion rates there is disagreement over the form of that relationship some find a linear relationship between weathering rate and erosion rate others however find that weathering is only approximately proportional to the square root of physical erosion such that changes in erosion rate are not matched by equivalent changes in weathering rate defining the nature of the relationship is critical because it determines the sensitivity of changes in weathering rate to changes in erosion rate in this study a theoretical model that couples erosion by landslides with chemical weathering processes was derived to explore the nature of this relationship in rapidly eroding landscapes results from the model suggest that where landsliding is the dominant erosional process the rate of chemical weathering is only proportional to the erosion rate raised to the 0 6 power therefore even if weathering rate is wholly dependent on erosion rate increases in erosion will not be matched by equivalent increases in chemical weathering 2007 elsevier b v all rights reserved

erosion rates for taiwan mountain basins new determinations from suspended sediment records and a stochastic model of their temporal variation abstract we estimate erosion rates from suspended sediment records for 11 basins in the eastern central range ecr of taiwan using methods based on mean measured sediment discharge a rating curve of sediment and water discharge and a rating curve corrected for periods of limited sediment due to the lack of landslide supplied sediment the preferred method for any basin depends on record length and sampling frequency with higher quality records being analyzed by the latter method erosion rate estimates range from 2 2 to 8 3 mm yr for records with varying sampling frequencies and durations between 8 and 27 yr this variation in erosion rates does not seem to reflect lithology tectonic environment or climate we interpret the variation in terms of natural stochastic variation in water discharge and sediment supply to assess the quality of the erosion rate estimates and to better understand the dependence of uncertainty on the duration and frequency of sampling we construct a stochastic model of sedi

erosional power in the swiss alps characterization of slope failure in the illgraben landslides and rockfalls are key geomorphic processes in mountain basins their quantification and characterization are critical for understanding the processes of slope failure and their contributions to erosion and landscape evolution we used digital photogrammetry to produce a multi temporal record of erosion 1963 2005 of a rock slope at the head of the illgraben a very active catchment prone to debris flows in switzerland slope failures affect 70 of the study slope and erode the slope at an average rate of 0 39 0 03 m yr the analysis of individual slope failures yielded an inventory of 2500 failures ranging over 6 orders of magnitude in volume despite the small slope area and short study period the slope failures form a characteristic magnitude frequency distribution with a rollover and a power law tail between 200 m and 1 6 106 m with an exponent of 1 65 slope failure volume scales with area as a power law with an exponent of 1 1 both values are low for studies of bedrock landslides and rockfall and result from the highly fractured and weathered state of the quartzitic bedrock our data suggest that the magnitude frequency distribution is the result of two separate slope failure processes type 1 failures are frequent small slides and slumps within the weathered layer of highly fractured rock and loose sediment and make up the rollover type 2 failures are less frequent and larger rockslides and rockfalls within the internal bedded and fractured slope along pre determined potential failure surfaces and make up the power law tail rockslides and rockfalls of high magnitude and relatively low frequency make up 99 of the total failure volume and are thus responsible for the high erosion rate they are also significant in the context of landscape evolution as they occur on slopes above 45 and limit the relief of the slope copyright 2012 john wiley sons ltd

supply and removal of sediment in a landslide dominated mountain belt central range taiwan abstract a strong coupling between hillslope and valley systems is often inferred for mountain landscapes dominated by bedrock landsliding we reveal the nature of this link using data sets on landsliding and sediment transport from two montane catchments draining the eastern central range of taiwan here the magnitude frequency distribution of landslides can be modeled by a robust power law but this scale invariance is not mirrored in the sediment discharge at the mountain front instead downstream sediment loads reflect a complex response to both sediment supply and ambient hydraulic conditions the rivers do not transport significant amounts of sediment unless it is provided by hillslope mass wasting in the catchment removal of landslide debris is a function of the transport capacity of the stream at the site of entry thus there is a dual supply and transport control on sediment loads in bedrock floored streams over a monitoring period of 25 yr the bulk of the sediment leaving the mountain bel

erosional processes in the hard rock coastal cliffs at staithes north yorkshire the processes of change on near vertical coastal cliffs have been quantified using terrestrial photogrammetry and laser scanning the approach allows discrete rockfall geometry to be measured and source located in three dimensions this paper presents the analysis of an inventory of over 100000 discrete rockfalls recorded from the liassic coast at staithes north yorkshire uk where a rock face area of over 16000 m 2 has been monitored over a 20 month period the data obtained on three dimensional scar geometry and source position give an insight into rockfall characteristics from a range of rock types cliff heights and geometries multiple failure mechanisms such as overhang collapse constant spalling fragmentation and large scale coherent rockfalls have been observed and related to rock type controlled processes on the rock face the spatially referenced rockfall scar data are used to assess the influence of environmental controls on variable rock mass properties such as rock type structure and cliff geometry analysis of rockfall magnitude frequency reveals notable similarities between coastal rockfalls and inventories from non coastal environments the resolution of the monitoring data allows quantification of rockfalls down to volumes of 1 25 x 10 4 m 3 to be consistently sampled and measured this complete magnitude frequency relationship suggests that rather than evolving exclusively through isolated sporadic losses coastal cliff geomorphology reflects interconnected processes in which each rockfall is part of a continuum of change to the rock face further detailed assessment of the rock face reveals the control of the pre failure morphology on subsequent failure patterns for example the quantity of rock protrusion from the cliff is positively correlated with subsequent failure volume the continuum of activity and the controls on failure identified within these data suggest that the episodic behaviour of coastal cliffs previously assumed may have been overstated by coarser resolution monitoring data the findings improve our understanding of the evolution of coastal cliffs and highlight areas for further research into both cliff processes and the character of rock slope failures in general

the relative efficacy of fluvial and glacial erosion over modern to orogenic timescales it has been debated whether rivers or glaciers are more effective agents of erosion a global compilation of erosion rates reveals that both are capable of generating rates of erosion that match or exceed the highest rates of rock uplift since the late nineteenth century it has been debated whether rivers or glaciers are more effective agents of erosion1 the dramatic landscapes associated with glaciated terrain have often led to the argument that glaciers are more erosive than rivers and recent studies have documented the topographic signature of an ice controlled limit of mountain height known as the glacial buzz saw 2 3 here we present a new global compilation of erosion rates which questions the conventional view of glaciers and erosion in regions of rapid tectonic uplift erosion rates from rivers and glaciers both range from 1 to over 10 mm yr 1 indicating that both are capable of generating erosion rates matching or exceeding the highest rates of rock uplift moreover a comparison of erosion rates over timescales ranging from 101 to 107 years indicates that glacial erosion tends to decrease by one to two orders of magnitude over glacial cycles whereas fluvial erosion rates show no apparent dependence on time we conclude that tectonics controls rates of both fluvial and glacial erosion over millennial and longer timescales and that the highest rates of erosion 10 mm yr 1 generally result from a transient response to disturbance by volcanic eruptions climate change and modern agriculture

the potential impact of climate change on typhoon triggered landslides in taiwan 2010 2099 abstract in the western north pacific including taiwan typhoons tropical cyclones and rainfall rates are predicted to intensify as a result of climate change because typhoons are the major triggers of shallow landslides in taiwan landslide activity is expected to increase as global warming continues to assess the worst scenario of landslide occurrence in a mountainous watershed till the end of the century this study developed a method to select a global climate model gcm from 21 available gcms and correct its monthly precipitation data before downscaling annual maximum 24 h rainfall from the corrected gcm data as input to the factor of safety model for landslide prediction average annual maximum rainfall is expected to increase from 322 mm in 1960 2008 to 371 mm in 2010 2099 average total unstable area is expected to increase from 1135 ha in 1960 2008 to 1280 ha in 2010 2099 a 12 increase as a first attempt to assess landslide activity due to global warming this study is useful as a reference for watershed management in taiwan the results must be evaluated in light of uncertainties caused by the correction and downscaling of gcm data and the input parameters to the slope stability model

monitoring and modelling morphological change in a braided gravel bed river using high resolution gps based survey recent research in fluvial geomorphology has emphasized the direct monitoring of channel topography as a useful tool to better understand the interrelationship between river form and process and in particular to estimate bedload transport rates and reach scale sediment budgets until recently however this morphometric approach has been limited to comparison of repeatedly surveyed cross sections with the associated problems of low frequency sampling and an emphasis on cross stream as opposed to downstream morphological dynamics recent advances in analytical photogrammetry have however permitted the acquisition of data at sufficient resolutions to represent macroform 101 m and microform 10 m channel geometry in fully three dimensions while inherently spatially distributed the photogrammetric approach to land surveying is however restricted to observable areas of the channel and is thus of limited use in the subaqueous zone especially if flows are turbid or highly coloured this paper presents an alternative approach to the study of three dimensional morphological dynamics of a divided reach of the gravelly river feshie scotland in which topographic survey of both exposed and submerged areas of the reach was undertaken using the global positioning system gps survey results from two field programmes in 1998 and 1999 are presented in which a geotronics geotracer 2000 real time kinematic gps receiving unit was used to survey a 200 80 m reach rapid radial survey methods were employed permitting the collection of 2000 survey points per day giving a mean density over the 13 ha reach of 1 1 points per square metre a detailed assessment of survey errors and dem quality is presented and a limit of detection of c 10 cm proposed as an upper threshold for the identification of significant change between dems preliminary interpretation of channel dynamics in 1998 99 reveals relatively little change to the overall macroscale reach structure dem differencing techniques however highlight important local changes including the progradation of submerged bar fronts bar head aggradation and scour along major channel thalwegs and the erosion of fines from sloughs copyright 2000 john wiley sons ltd

influence of rock mass strength on the erosion rate of alpine cliffs collapse of cliff faces by rockfall is a primary mode of bedrock erosion in alpine environments and exerts a first order control on the morphologic development of these landscapes in this work we investigate the influence of rock mass strength on the retreat rate of alpine cliffs to quantify rockwall competence we employed the slope mass rating smr geomechanical strength index a metric that combines numerous factors contributing to the strength of a rock mass the magnitude of cliff retreat was calculated by estimating the volume of talus at the toe of each rockwall and projecting that material back on to the cliff face while accounting for the loss of production area as talus buries the base of the wall selecting sites within basins swept clean by advancing last glacial maximum lgm glaciers allowed us to estimate the time period over which talus accumulation occurred i e the production time dividing the magnitude of normal cliff retreat by the production time we calculated recession rates for each site our study area included a portion of the sierra nevada between yosemite national park and lake tahoe rockwall recession rates determined for 40 alpine cliffs in this region range from 0 02 to 1 22 mm year with an average value of 0 28 mm year we found good correlation between rockwall recession rate and smr which is best characterized by an exponential decrease in erosion rate with increasing rock mass strength analysis of the individual components of the smr reveals that joint orientation with respect to the cliff face is the most important parameter affecting the rockwall erosion rate the complete smr score however best synthesizes the lithologic variables that contribute to the strength and erodibility of these rock slopes our data reveal no strong independent correlations between rockwall retreat rate and topographic attributes such as elevation aspect or slope angle copyright 2009 john wiley sons ltd

landsliding and sediment flux in the central swiss alps a photogrammetric study of the schimbrig landslide entlebuch abstract this study explores the effects of hillslope mass failure on the sediment flux in the waldemme drainage basin central swiss alps over decadal time scales this area is characterized by abundant landslides affecting principally flysch units and is therefore an important sediment source the analysis concentrates on the schimbrig landslide that potentially contributes up to 15 to the sediment budget of the waldemme drainage basin volumetric changes are quantified using high resolution elevation models that were extracted using digital photogrammetric techniques sediment discharge data were used to constrain the significance of the landslide for sediment flux in the channel network the temporal extent of the photogrammetric analysis ranges from 1962 to 1998 including an earth slide event in 1994 the analyses reveal that during periods of low slip rates of the landslide nearly all of the displaced sediments were eroded and supplied to the channel network in contrast during active periods only a fraction of the displaced landslide mass was exported to the trunk stream interestingly the 1994 earth slide event did not disturb the long term sediment discharge pattern of the channel network nor did it influence the sediment flux at a weekly scale however suspended sediment pulses correlate with higher than average precipitation events this was especially the case in august 2005 when a storm event 100 years return period triggered several debris flows and earth flows in the whole drainage basin and in the schimbrig area this storm did not result in a significant increase in the slip rates of the entire landslide s main body it is therefore proposed that debris flows and earth flows perform the connectivity between hillslope processes e g landsliding and the trunk stream during and between phases of landslide activity in this particular setting

characteristics of the size distribution of recent and historical landslides in a populated hilly region despitetheavailabilityofstudiesonthefrequencydensityoflandslideareasinmountainousregions frequency areadistributions of historical landslide inventories in populated hilly regions are absent this study revealed that the frequency area distribution derived from a detailed landslide inventory of the flemish ardennes belgium is significantly different from distributions usually obtainedinmountainousareaswherelandslidesaretriggeredbylarge scalenaturalcausalfactorssuchasrainfall earthquakesorrapid snowmelt instead the landslide inventory consists of the superposition of two populations i e i small b1 2 10 2 km 2 shallow complexearthslides that areat most30yrold and ii large n1 2 10 2 km 2 deep seatedlandslides that areolder than100yr both subpopulations are best represented by a negative power law relation with exponents of 0 58 and 2 31 respectively this study focused on the negative power law relation obtained for recent small landslides and contributes to the understanding of frequency distributions of landslide areas by presenting a conceptual model explaining this negative power law relation for small landslides in populatedhilly regions according to the model hilly regions canberelatively stable under the present dayenvironmental conditions andlandslidesaremainlytriggeredbyhumanactivitiesthathaveonlyalocalimpactonslopestability therefore landslidescausedby anthropogenic triggers are limited in size and the number of landslides decreases with landslide area the frequency density of landslide areas for old landslides is similar to those obtained for historical inventories compiled in mountainous areas as apart from the negative power law relation with exponent 2 31 for large landslides a positive power law relation followed by a rollover is observed for smaller landslides however when analysing the old landslides together with the more recent ones the present day higher temporal frequency of small landslides compared to large landslides obscures the positive power law relation and rollover 2007 elsevier b v all rights reserved

without power landslide inventories in the face of climate change projected scenarios of climate change involve general predictions about the likely changes to the magnitude and frequency of landslides particularly as a consequence of altered precipitation and temperature regimes whether such landslide response to contemporary or past climate change may be captured in differing scaling statistics of landslide size distributions and the erosion rates derived thereof remains debated we test this notion with simple monte carlo and bootstrap simulations of statistical models commonly used to characterize empirical landslide size distributions our results show that significant changes to total volumes contained in such inventories may be masked by statistically indistinguishable scaling parameters critically depending on among others the size of the largest of landslides recorded conversely comparable model parameter values may obscure significant i e more than twofold changes to landslide occurrence and thus inferred rates of hillslope denudation and sediment delivery to drainage networks a time series of some of earth s largest mass movements reveals clustering near and partly before the last glacial interglacial transition and a distinct step over from white noise to temporal clustering around this period however elucidating whether this is a distinct signal of first order climate change impact on slope stability or simply coincides with a transition from short term statistical noise to long term steady state conditions remains an important research challenge copyright 2011 john wiley sons ltd

statistical analysis of rockfall volume distributions implications for rockfall dynamics we analyze the volume distribution of natural rockfalls on different geological settings i e calcareous cliffs in the french alps grenoble area and granite yosemite cliffs california sierra and different volume ranges i e regional and worldwide catalogs contrary to previous studies that included several types of landslides we restrict our analysis to rockfall sources which originated on subvertical cliffs for the three data sets we find that the rockfall volumes follow a power law distribution with a similar exponent value within error bars this power law distribution was also proposed for rockfall volumes that occurred along road cuts all these results argue for a recurrent power law distribution of rockfall volumes on subvertical cliffs for a large range of rockfall sizes 102 1010 m3 regardless of the geological settings and of the preexisting geometry of fracture patterns that are drastically different on the three studied areas the power law distribution for rockfall volumes could emerge from two types of processes first the observed power law distribution of rockfall volumes is similar to the one reported for both fragmentation experiments and fragmentation models this argues for the geometry of rock mass fragment sizes to possibly control the rockfall volumes this way neither cascade nor avalanche processes would influence the rockfall volume distribution second without any requirement of scale invariant quenched heterogeneity patterns the rock mass dynamics can arise from avalanche processes driven by fluctuations of the rock mass properties e g cohesion or friction angle this model may also explain the power law distribution reported for landslides involving unconsolidated materials we find that the exponent values of rockfall volume on subvertical cliffs 0 5 0 2 is significantly smaller than the 1 2 0 3 value reported for mixed landslide types this change of exponents can be driven by the material strength which controls the in situ topographic slope values as simulated in numerical models of landslides densmore et al 1998 champel et al 2002 index terms 5104 physical properties of rocks fracture and flow 1815 hydrology erosion and sedimentation 8122 tectonophysics dynamics gravity and tectonics

stochastic forcing of sediment supply to channel networks from landsliding and debris flow sediment influx to channel networks is stochastically driven by rainstorms and other perturbations which are discrete in time and space and which occur on a landscape with its own spatial variability in topography colluvium properties and state of recovery from previous disturbances the resulting stochastic field of sediment supply interacts with the topology of the channel network and with transport processes to generate spatial and temporal patterns of flux and storage that characterize the sedimentation regime of a drainage basin the regime varies systematically with basin area we describe how the stochastic sediment supply is generated by climatic topographic geotechnical and biotic controls that vary between regions the general principle is illustrated through application to a landscape where sediment is supplied by mass wasting and the forcing variables are deterministic thickening of colluvium random sequences of root destroying wildfires and random sequences of rainstorms that trigger failure in a population of landslide source areas with spatial variance in topography and colluvium strength landslides stop in channels or convert to scouring debris flows depending on the nature of the low order channel network sediment accumulates within these channels for centuries before being transferred downstream by debris flows time series of sediment supply transport and storage vary with basin scale for any combination of climatic topographic and geotechnical controls in a companion paper benda and dunne this issue we use simulations of timing volumes and locations of mass wasting to study the interaction between a stochastically forced sediment supply and systematic changes of storage and flux through channel networks

the power law relationship between landslide occurrence and rainfall level article i nfo article history zhejiang province is highly prone to the occurrence of landslides during the annual rainy season from may to september we studied the relationship between landslide frequency and rainfall level based on 1414 shallow landslides that have detailed records on the location the date of occurrence and the corresponding daily rainfall data from 1257 rain gauges during the 1990 2003 period in the region cumulative rainfall levels were examined for the periods from the failure day to the prior 10 days the results show that the cumulative frequency of the landslide occurrence correlates well with the landslide triggering rainfall and that their relationship can be described using two power law relations with different scaling exponents for two different ranges of the rainfall level the rainfall level corresponding to the intersection point of two fitted correlation lines can be defined as the upper bound for shallow landslide triggering cumulative rainfall threshold thcr a large number of shallow landslides may be induced when the amount of cumulative rainfall reaches the thcr value the 814 landslides that occurred from 2004 to 2007 in the region are used to examine the method which shows that about 80 of these landslides are induced when the cumulative 1 day rainfall is 200 mm we suggest that the power law relationship between rainfall level and landslide occurrence can be used to estimate the probability of various levels of landslide activity during a rainfall event as a guide for making decisions related to emergency preparedness

limits of sediment transfer in an alpine debris flow catchment illgraben switzerland abstract the 9 5 km 2 illgraben catchment located in the rhone valley in the central alps of switzerland is one of the most active debris flow torrents in the alps in this paper we present sediment yield data collected in 2006 for segments where hillslopes and channels form a fully connected network and contrast these with sediment yields measured for disconnected hillslopes the data reveal that sediment yields are 1 2 orders of magnitude larger in segments where hillslopes are connected with the channel network than on disconnected hillslopes support for this conclusion is provided by observations made on 1959 1999 and 2004 aerial photographs that the vegetation cover in the disconnected segments is still intact whereas denudation rates of several centimeters per year in the connected segments have inhibited the establishment of a stable vegetation cover furthermore sediment supplied from hillslopes during the past 40 years has temporarily accumulated along the illgraben channel indicating that the channel aggraded over this period and has not yet recovered an implication of this observation is that initiation of debris flows in the illgraben catchment is limited more by the availability of intense rainfall than sediment in contrast on disconnected hillslopes sediment flux does not appear to be driven by precipitation the petrographic composition of the illgraben fan deposits indicates two distinct sediment sources one related to rockfall and the other to landslides and debris flows the presence of clasts from both sources implies multiple processes of erosion deposition mixing and re entrainment in the catchment before the material is exported to the illgraben fan and to the rhone river in addition delivery of large amounts of coarse grained sediment to the rhone causes a modification of the flow pattern from meandering or anastomosing upstream to braided downstream hence the direct connectivity between hillslope and channelized processes in the illgraben catchment causes not only rapid topographic modifications in the catchment but also morphologic adjustment in the rhone valley downstream

magnitude frequency relationships of debris flows and debris avalanches in relation to slope relief abstract probability of occurrence hazard intensity and encounter probability are key parameters in the quantitative risk analysis qra of landslides all are strongly dependent on magnitude of the landslides as a result magnitude frequency analysis should be a part of qra deriving representative magnitude frequency relationships for debris avalanches and debris flows however is difficult one key problem is illustrated with the example of a unique database from the coastal region of british columbia canada which was compiled entirely from detailed ground investigations the magnitude of debris avalanches and debris flows is not an independent statistical quantity but a function of the scale of a given slope as characterized by the slope length thus attempting to derive probability and magnitude for a given location or sub region from a regionally derived magnitude frequency curve may lead to incorrect predictions the same problem is pertinent to the application of the same approach to any type of landslide in which the largest combined dimension of the source volume including entrainment is of the same order as the length of the slope it is recommended that greater emphasis be placed on site specific geological observations at the expense of generalized statistics

sediment flux from a mountain belt derived by landslide mapping in humid uplands landsliding is the dominant mass wasting process in the western southern alps of new zealand landslides are scale invariant and have a power law magnitude frequency distribution independent studies from other regions suggest that this is a general property of landsliding this observation is of critical importance to the evaluation of the impact of events of different length scales over different time intervals on landscape evolution it is particularly useful when estimating regional geomorphic rates because it constrains the frequency and overall significance of extreme events which cannot otherwise be evaluated by integrating the complete response of the system we estimate the regional denudation rate due to landsliding to be 9 4 mm yr 1 sediment discharge from the western southern alps is dominated by landslide derived material

landslide rupture and the probability distribution of mobilized debris volumes 1 landslide driven erosion is controlled by the scale and frequency of slope failures and by the consequent fluxes of debris off the hillslopes in this paper we tackle the magnitude frequency part of the process and develop a theory of initial slope failure and debris mobilization that reproduces the heavy tailed distributions probability density function or pdfs observed for landslide source areas and volumes landslide rupture propagation is treated as a quasi static noninertial process of simplified elastoplastic deformation with strain weakening debris runout is not considered the model tracks the stochastically evolving imbalance of frictional cohesive and body forces across a failing slope and uses safety factor concepts to convert the evolving imbalance into a series of incremental rupture growth or arrest probabilities a single rupture is simulated with a sequence of weighted coin tosses with weights set by the growth probabilities slope failure treated in this stochastic way is a survival process that generates asymptotically power law tail pdfs of area and volume for rock and debris slides predicted scaling exponents are consistent with analyses of landslide inventories the primary control on the shape of the model pdfs is the relative importance of cohesion over friction in setting slope stability the scaling of smaller shallower failures and the size of the most common landslide volumes are the result of the low cohesion of soil and regolith whereas the negative power law tail scaling for larger failures is tied to the greater cohesion of bedrock

landslide volumes and landslide mobilization rates in umbria central italy abstract a catalogue of 677 landslides of the slide type was selected from a global database of geometrical measurements of individual landslides including landslide area al and volume vl the measurements were used to establish an empirical relationship to link al in m2 to vl in m3 the relationship takes the form of a power law with a scaling exponent 1 450 covers eight orders of magnitude of al and twelve orders of magnitude of vl and is in general agreement with existing relationships published in the literature the reduced scatter of the experiential data around the dependency line and the fact that the considered landslides occurred in multiple physiographic and climatic environments and were caused by different triggers indicate that the relationship between vl and al is largely independent of the physiographical setting the new relationship was used to determine the volume of individual landslides of the slide type in the collazzone area central italy a 78 9 km2 area for which a multi temporal landslide inventory covering the 69 year period from 1937 to 2005 is available in the observation period the total volume of landslide material was vlt 4 78 107 m3 corresponding to an average rate of landslide mobilization l 8 8 mm yr 1 exploiting the temporal information in the landslide inventory the volume of material produced during different periods by new and reactivated landslides was singled out the wet period from 1937 to 1941 was recognized as an episode of accelerated landslide production during this 5 year period approximately 45 of the total landslide material inventoried in the collazzone area was produced corresponding to an average rate of landslide mobilization l 54 mm yr 1 six times higher than the long term rate the volume of landslide material in an event or period was used as a proxy for the magnitude of the event or period defined as the logarithm base 10 of the total landslide volume produced during the event or period with this respect the new relationship to link al and vl is a starting point for the adoption of a quantitative process based landslide magnitude scale for landslide events

denudation processes and rates in the transverse ranges southern california erosional response of a transitional landscape to external and anthropogenic forcing 1 quantification of denudation in the transverse ranges of california permits reconstruction of spatial and temporal variations in erosion that represent both the response and evolution of interacting hillslopes and channels on the southern front of the san gabriel mountains observational records of the infilling of debris basins and dams define twentieth century landscape erosion rates averaging 1 6 and 0 9 mm yr 1 respectively although all major sediment transport occurs during intense winter storms debris production on hillslopes is greatly enhanced by recurrent fires consequently in this populated region anthropogenic fires have augmented the natural erosion rates we perform a global inversion to estimate the role of precipitation intensity burned areas and local slope on catchment denudation rates after subtracting the effects of anthropogenic fires we estimate landscape denudation rates given natural fire ignition rates increased fire during the past century has augmented sediment production in debris basins by an average of 60 and individual basins show increases up to 400 to identify the dominant hillslope erosion processes the volumetric contribution of landslides was estimated using repeat aerial photographs for the same time interval over which the debris basins have been operative between 1928 and 1973 landsliding produced only 10 of the sediment in debris basins even in the long term when infrequent but volumetrically important landslides occur bedrock landslides appear to contribute a maximum of 50 to the long term landscape denudation previous mapping of soil slippage in the san dimas experimental forest within the san gabriel mountains rice et al 1969 rice and foggin 1971 indicates that shallow landsliding is likely to be the dominant modern hillslope erosion process when compared to incision rates derived from a fluvial shear stress model and to exhumation rates based on low temperature thermochronological data blythe et al 2000 modern natural erosion rates are comparable to denudation rates since the pliocene comparisons of modern erosion rates suggest that debris production on hillslopes and first order channels is directly dependent on vegetation cover and precipitation intensity for higher order channels drainage areas 2 km2 only major storms convey the sediments down valley during the past century some temporal decorrelation occurs between small scale and large scale catchments because hillslope produced sediment is stored in second order and higher channels until major storms mobilize it thus the larger fluvial network damps the episodic fire induced hillslope sediment pulses that occur within small watersheds at a longer temporal scale however uplift and denudation may have been sustained sufficiently long in much of the san gabriel mountains for the topography to reach a macroscale steady state in contrast to rapidly eroding 2 mm yr 1 ranges for which quantification of bedrock landsliding will approximate the sediment flux the san gabriel mountains occupy a niche of intermediate rates 0 1 1 0 mm yr 1 in which a broad suite of hillslope processes including shallow seated and deep seated landslides debris flows and wet and dry ravel contribute to the sediment flux

power law correlations of landslide areas in central italy abstract we have studied the frequency area statistics of landslides in central italy we consider two data sets data set a contains 16 809 landslide areas in the umbria marche area of central italy they represent a reconnaissance inventory of very old old and recent modern landslides the noncumulative frequency area distribution of these landslides correlates well with a power law relation exponent 2 5 over the range 0 03 km 2 a l 2 data set b contains 4233 landslides that were triggered by a sudden change in temperature on 1 january 1997 resulting in extensive melting of snow cover an inventory of these snow melt triggered landslides was obtained from aerial photographs taken 3 months after the event these landslides also correlate well with a power law relation with exponent 2 5 over the range 0 001 km 2 a l 2 we show that the correlation of data set b is essentially identical to the correlation of 11 000 landslides triggered by the 17 january 1994 northridge california earthquake we attribute a rollover for small landslides in data set a to incompleteness of the record due to erosion and other processes and to limitations in the reconnaissance mapping technique used to complete the inventory on the other hand we conclude that rollovers for small landslides in data set b and the california earthquake data are real and are associated with the surface morphology we conclude that the power law distribution is valid over a wide range of landslide areas and discuss possible reasons we also discuss the contribution of the snow melt and earthquake triggered landslide events to the total landslide inventory

sediment transfer patterns at the illgraben catchment switzerland implications for the time scales of debris flow activities debris flows strongly control sediment transfer patterns in mountainous catchments we quantify sediment transfer at the illgraben switzerland where debris flows are frequent and geomorphic change is rapid four sequential aerial image series from fall 2007 to fall 2009 were used to measure landscape change in relation to debris flows the debris often originating from bedrock landslides was transported in patterns of erosion storage and remobilization the landslides typically stopped on the downslope hillslope or in the channel and they did not transform directly into debris flows the magnitude and nature of sediment transfer patterns show large spatial and temporal variability and the storage time of the deposits was shorter than one year landslide volumes were an order of magnitude smaller than the debris flows at the catchment outlet while the mechanism of debris flow initiation could not be determined unambiguously clearly debris flows must entrain substantial amounts of sediment along the flow path to attain the volumes estimated at the distal end of the fan

evidence of a changing size frequency distribution of landslides in the kyrgyz tien shan central asia there is a strong possibility that environmental change whether climate or land use will be manifest as changes in the size frequency distribution of landslides here evidence is presented for this from western kyrgyzstan central asia remote sensing and spatial analysis have been applied to map mass movements in the central part of the maily say valley and to detect recent landslide activations the evolution of landslide activity over the past 50 years has been analysed on the basis of pre existing landslide maps and new analyses of aerial photographs as well as quickbird images five inventories were produced for the years 1962 based on the existing map of 1962 and aerial photographs of 1962 1984 based on the existing map of 1977 and aerial photographs of 1984 1996 based on aerial photographs of 1996 2002 based on the existing map of 2003 and quickbird imagery of 2002 and 2007 based on quickbird imagery of 2007 the geomorphologic features contained in the catalogues represent the landslide bodies observed from remote imagery of the corresponding year mapped landslides are generally considered as the result of a series of slope failure events size frequency analyses applied to the five landslide inventories show that both the number and size of unstable slopes increased from 1962 162 objects to 2007 208 objects and the power law exponent decreased over time this changing power law exponent may indicate that landslide related hazards are increasing this tendency is documented in more detail for two active landslide zones one in the main valley and one located to the west of it landslide detection methods were used to assist the evolution of slope instabilities choosing appropriate thresholds the image subtraction method based on normalized difference vegetation index ndvi allowed accurate detection of new sliding activation in these two zones this confirmed the results of the more extensive survey that there is a systematic shift in power law exponents and size frequency distributions for central asian landslides copyright 2011 john wiley sons ltd

representing the landslide magnitude frequency relation capilano river basin british columbia we use magnitude frequency analysis as a statistical tool to quantify the erosion caused by landslides and debris ows using air photo and ground derived data we show that the departure from power law distribution customarily observed for small magnitude is an artefact of sampling de ciencies nonetheless the total distribution is not sensitive to the frequency of small slides and total erosion remains adequately represented in the air photo derived data our data also demonstrate a real departure from simple scaling at much larger magnitudes the cause of which is not de nitively established copyright 2004 john wiley sons ltd

the role of landslides in mountain range evolution abstract we review the role of landslides in current concepts of the topographic development of mountain ranges we find that many studies in this field address basin or orogen scale competition between rock uplift and fluvial bedrock erosion hillslopes in general and bedrock landslides in particular are often assumed to respond rapidly to incision and development of the fluvial drainage network this leads to a one sided view of the geomorphic coupling between hillslopes and rivers that emphasizes the fluvial control of hillslopes but ignores the alternative view that landslides can affect the fluvial network there is growing evidence that landslides are a dominant source of sediment in mountain belts and that they exert a direct geomorphic control on fluvial processes landslides can influence the river network in a variety of ways from determining basin area and drainage divide positions to setting streamwise variations in sediment load and calibre the geomorphic legacy of large landslides on hillslope and channel morphologies may persist for up to 104 yr adding considerable variability to fluvial erosion and sedimentation patterns over these timescales we identify a number of questions for future research and conclude that a better understanding and quantification of the geomorphic feedbacks between landslides and river channels builds an important link between short term 105 yr landscape evolution models

the role of the mantle during crustal extension constraints from geochemistry of volcanic rocks in the lake mead area nevada and arizona one of the fundamental questions in areas of large magnitude extension and magmatism is the role of the mantle in the extension process the lake mead area is ideally suited for developing models that link crustal and mantle processes because it contains both mantle and crustal boundaries and it was the site of large magnitude crustal extension and magmatism during miocene time in the lake mead area the boundary between the amagmatic zone and the northern colorado river extensional corridor parallels the lake mead fault system and is situated just to the north of lake mead this boundary formed between 11 and 6 ma during and just following the peak of extension and corresponds to a contact between two mantle domains during thinning and replacement of the lithospheric mantle in the northern colorado river extensional corridor the lithospheric mantle in the amagmatic zone remained intact contrasting behavior to the north and south of this boundary may have produced the mantle domain boundary the domain to the north of the boundary is characterized by mafic lavas with a lithospheric mantle isotopic and geochemical signature nd 3 to 9 87 sr 86 sr 0 706 0 707 to the south of the boundary in the northern colorado river extensional corridor lavas have an ocean island basalt oib mantle signature and appear to have only a minor lithospheric mantle component in their source nd 0 to 4 87 sr 86 sr 0 703 0 705 mafic lavas of the northern colorado river extensional corridor represent the melting of a complex and variable mixture of asthenospheric mantle lithospheric mantle and crust pliocene alkali basalt magmas of the fortification hill field represent the melting of a source composed of a mixture of asthenospheric mantle high u pb himu like mantle and lithospheric mantle depth of melting of alkali basalt magmas remained relatively constant from 12 to 6 ma during and just after the peak of extension but probably increased between 6 and 4 3 ma following extension miocene and pliocene low nd and high 87 sr 86 sr magmas and tholeiites at malpais flattop were derived from a lithospheric mantle source and were contaminated as they passed through the crust the shift in isotopic values due to crustal interaction is no more than 4 units in nd and 0 002 in 87 sr 86 sr and does not mask the character of the mantle source the change in source of basalts from lithospheric mantle to asthenospheric mantle with time the oib character of the mafic lavas and the himu like mantle component in the source are compatible with the presence of rising asthenosphere as an upwelling convective cell or plume beneath the northern colorado river extensional corridor during extension the lake mead fault system a major crustal shear zone parallels the mantle domain boundary the lake mead fault system may locally represent the crustal manifestation of differential thinning of the lithospheric mantle