ice moraine and landslide dams in mountainous terrain we review recent work on ice moraine and landslide dams in mountainous terrain thus complementing several comprehensive summaries on glacier dams in intracontinental and arctic areas of low relief we discuss the roles of tectonic and climatic forcing on ice moraine and landslide dam formation and sudden drainage and focus on similarities and differences between their geomorphic impacts on confined valleys drained by steep bedrock and gravel bed rivers despite numerous reported failures of natural dams in mountain belts throughout the world their relevance to long term dynamics of mountain rivers remains poorly quantified all types of dams exert local base level controls thus trapping incoming sediment and inhibiting fluvial bedrock incision pervasive geomorphic and sedimentary evidence of outburst events is preserved even in areas of high erosion rates suggesting that sudden dam failures are characterized by processes of catastrophic valley floor aggradation active channel widening and downstream dispersion of sediment during which little bedrock erosion seems to be achieved we find that in the absence of direct evidence of former dams a number of similarities among the geomorphic and sedimentologic characteristics of catastrophic outburst flows may give rise to ambiguous inferences on the dam forming process this is especially the case for tectonically active mountain belts where there is ample and comparable potential for the formation and failure of ice moraine landslide and polygenetic dams concomitant with climatic oscillations or earthquake disturbance hence the palaeoclimatic implications of erroneously inferring the cause of dam formation may be significant we recommend that future research on natural dams in mountainous terrain addresses a climate and earthquake controlled systematics in the pattern of formation and failure b quantification of response of mountain rivers to catastrophic outburst events and their concomitant process sequences c elaboration of a comprehensive classification of natural dams in mountainous terrain with special attention to polygenetic dams d physical based modelling of dam formation failure and routing of water and sediment outbursts and e quantitative controls on the contribution of natural dams to sediment budgets in mountainous terrain

influence of a large debris flow fan on the late holocene evolution of squamish river southwest british columbia canada cheekye fan is a large paraglacial debris flow fan in southwest british columbia it owes its origin to the collapse of mount garibaldi a volcano that erupted in contact with glacier ice near the end of the pleistocene epoch the fan extended across howe sound isolating a freshwater lake upstream of the fan from a fjord downstream of it squamish river built a delta into this lake during the holocene we use 28 radiocarbon ages to describe the final infilling of the lake and the subsequent evolution of the squamish river floodplain over the past 3300 years these events are recorded in fine grained lacustrine wetland river channel and overbank sediments exposed in the banks of squamish river over a distance of more than 10 km upstream of the fan we link these deposits to construction persistence and eventual degradation of the dam formed by cheekye fan and a smaller inset fan formed by cheakamus river into which cheekye river flows the coupled cheekye fan squamish river floodplain system is si

characterisation and engineering properties of tectonically undisturbed but lithologically varied sedimentary rock masses tectonically undisturbed sedimentary rocks deposited in a quiescent shallow marine environment often include a sequence of strata that may present significant lithological variety at the scale of an engineering structure such rock masses exhibit engineering properties that are significantly different from tectonically disturbed rock masses of similar composition for example molasse consists of a series of tectonically undisturbed sediments of sandstones conglomerates siltstones and marls produced by the erosion of mountain ranges after the final phase of an orogeny they behave quite differently from flysch which has the same composition but which was tectonically disturbed during the orogeny the molasses behave as continuous rock masses when they are confined at depth and the bedding planes do not appear as clearly defined discontinuity surfaces close to the surface the layering of the formations is discernible and only then similarities may exist with the structure of some types of flysch therefore extreme care is necessary in the use of geotechnical classification systems for the selection of design parameters in order to avoid penalizing the rock mass unnecessarily a discussion on the use of the geological strength index gsi for the characterisation of such rock masses is presented two gsi charts are proposed for estimating the mechanical properties of these masses one mainly for tunnels and the second for surface excavations an example is given to illustrate the process of tunnel design in molassic rocks

particle dynamics the continuum of bedrock to alluvial river segments abstract particle dynamics refers to production erosion transport and storage of particulate material including mineral sediment and organic matter particle dynamics differ significantly between the end members of bedrock and alluvial river segments and between alluvial river segments with different grain size distributions bedrock segments are supply limited and resistant to change with relatively slow linear adjustments and predominantly erosion and transport particle dynamics in alluvial segments in contrast are transport limited and dominated by storage of mineral sediment and production of organic matter alluvial segments are resilient to change with relatively rapid multidirectional adjustments and stronger internal influences because of feedbacks between particles and biota bedrock segments are the governors of erosion within a river network whereas alluvial segments are the biogeochemical reactors fundamental research questions for both types of river segments center on particle dynamics which limit network scale incision in response to base level fall bedrock segments and habitat biogeochemical reactions and biomass production alluvial segments these characterizations illuminate how the spatial arrangement of bedrock and alluvial segments within a river network influence network scale resistance and resilience to external changes in relative base level climate and human activities

anabranching rivers their cause character and classification anabranching rivers consist of multiple channels separated by vegetated semi permanent alluvial islands excised from existing floodplain or formed by within channel or deltaic accretion these rivers occupy a wide range of environments from low to high energy however their existence has never been adequately explained they occur concurrently with other types of channel pattern although specific requirements include a flood dominated flow regime and banks that are resistant to erosion with some systems characterized by mechanisms to block or constrict channels thereby triggering avulsion the fundamental advantage of an anabranching river is that by constructing a semi permanent system of multiple channels it can concentrate stream flow and maximize bed sediment transport work per unit area of the bed under conditions where there is little or no opportunity to increase gradient on the basis of stream energy sediment size and morphological characteristics six types of anabranching river are recognized types 1 3 are lower energy and types 4 6 are higher energy systems type 1 are cohesive sediment rivers commonly termed anastomosing with low w d ratio channels that exhibit little or no lateral migration they are divisible into three subtypes based on vegetative and sedimentary environment type 2 are sand dominated island forming rivers and type 3 are mixed load laterally active meandering rivers type 4 are sand dominated ridge forming rivers characterized by long parallel channel dividing ridges type 5 are gravel dominated laterally active systems that interface between meandering and braiding in mountainous regions type 6 are gravel dominated stable systems that occur as non migrating channels in small relatively steep basins anabranching rivers represent a relatively uncommon but widespread and distinctive group that because of particular sedimentary energy gradient and other hydraulic conditions operate most effectively as a system of multiple channels separated by vegetated floodplain islands or alluvial ridges

maintaining geological reality in application of gsi for design of engineering structures in rock abstract in rock engineering design significant advances have occurred in recent years in numerical modelling capability with increasing trends to ever greater use of synthetic rock mass models and discrete fracture network dfn modelling but all too often with little comparative improvement in geologic base data as a consequence there is even more need that reliable estimates be available of strength and deformation characteristics of the rock masses on which or within which engineering structures are to be created be it a tunnel a foundation or a slope geological strength index gsi characterization linked with hoek brown strength determination as a basis for modelling has been widely adopted by engineers and geologists involved in design and construction of engineering structures the need for geological definition of rock mass properties required as inputs into numerical analysis constitutes one of the greatest reasons for application of the gsi chart allowing characterization of even difficult to describe rock masses including tackling even the most problematic of weak and complex rock masses back analyses of tunnels slopes and foundation behaviour using gsi and its reliable application in rock engineering designs attest to its reliability with continuing use worldwide the gsi system has continued to evolve but greater understanding is needed in the definition of input constants for establishing both gsi and intact rock properties this need for improved evaluation particularly from a geological perspective is addressed in this paper geological processes of tectonism weathering and alteration all affect gsi evaluation of these factors which are each critical to proper gsi definition are analyzed based on real rock mass cases suggested ranges in variability of intact rock parameters uniaxial compressive strength ci and material constant mi for common rock masses are presented in the context of a composite new gsi chart this chart allows selection of appropriate gsi ranges for any specific rock suite specific key engineering geological characteristics that differentiate igneous metamorphic and sedimentary one from each other are highlighted through discussion of various example rock units including gneisses granites ophiolites limestones schists siltstones mudstones shales and molassic and flysch formations illustrations are given of how geological differentiation dictates variability in geotechnical properties of most common rock masses

structurally controlled instability damage and slope failure in a porphyry rock mass abstract rock slopes fail through structurally controlled mechanisms global circular failures or complex mechanisms depending on structural patterns and rock mass damage here structural geology rock mass characterisation terrestrial laser scanning tls ground based radar interferometry gb insar and finite element modelling are integrated to explore relationships between structure damage and global slope failure at mt gorsa trentino italy there a porphyry quarry has been excavated in complex strongly anisotropic rhyolitic ignimbrite rock masses the slope was affected by a major rockslide in 2003 and undergoes continuing instability site investigations and gb insar monitoring revealed that the 2003 failure was a roto translational rockslide involving about 400 000 m3 of disrupted rock structural analysis of tls and field data shows that the slope is affected by widespread structurally controlled mechanisms sliding toppling strain localization in kink bands the non obvious relationships between structurally controlled and global roto translational slope failure mechanisms are investigated by characterising rock mass damage in different slope sectors a new approach to quantify rock mass damage by mapping the geological strength index and interpreting its topographic signatures in tls point clouds is presented a persistent geological marker is systematically mapped in tls point clouds and correlations between attitude variability statistics and rock mass damage are established providing an efficient assessment tool rock mass damage increases in kinematic domains affected by structurally controlled instability gsi 35 40 and is maximum in areas of ongoing global instability gsi 15 20 the 2003 rockslide occurred inside a damaged rock mass zone with gsi

prehistoric debris avalanches from mount cayley volcano british columbia reply an investigation of diamicton units exposed in an extensive accumulation of volcanic debris in the squamish valley west of mount cayley volcano has yielded evidence for at least three major debris avalanches initiated by the collapse of the western flank of mount cayley in the mid holocene radiocarbon ages obtained from tree fragments contained in the deposits indicate that the events took place at 4800 1100 and 500 bp all three debris avalanches dammed the squamish river and formed temporary lakes upstream of the debris failure of the cone took place after considerable dissection of the original edifice had exposed weak pyroclastic materials at the base of the steep upper slope of the volcano no evidence of older debris avalanches from mount cayley has been discovered smaller scale debris avalanches probably have been common and at least two have occurred in historic time 1963 and 1984 debris avalanches from mount cayley and the effects of a possible damming of the squamish river are major

a cross anisotropic elastoplastic model applied to sedimentary rocks abstract strength and deformability properties of sedimentary rocks are difficult to characterize as these geomaterials show anisotropic mechanical behavior which cannot be adequately evaluated by an isotropic constitutive model this essay proposes a cross anisotropic elastoplastic model to evaluate stress strain relationships of sedimentary rocks the approach couples the twelve parameter lade kim isotropic model with a non uniform scaling of the stress tensor and includes two scaling parameters that link the orientation of the bedding planes with the loading direction the anisotropic model parameters can be conveniently determined using bayesian analysis we illustrate our method using triaxial tests on a variety of confining stresses and bedding plane orientations for a travertine and a tournemire shale our results demonstrate that the predicted maximum deviatoric stresses and the simulated stress strain curves are shown to be in good agreement with the measured data

stability assessment of jinlong village landslide sichuan the jinlong village landslide is located in zitong county sichuan and approximately 150 km east of wenchuan the landslide has exhibited creep deformation for nearly 30 years field investigations indicated that the slope deformation was caused by the combined effects of unfavorable topographic and geological conditions and earthquakes the sliding surface is along a contact between silty clay and mudstone the wenchuan earthquake accelerated the creep causing bulging of the ground surface shear test results of the silty clay near the sliding surface indicated that the residual strength is consistent with the stability state of the landslide the factors of safety were calculated using the limit equilibrium method lem and the method of fast lagrangian analysis of continua in two dimensions the results using the lem indicate that the stability is clearly affected by seismic shaking and when the peak ground acceleration is 0 08g the slope reaches the limit state the shear failure surface given by numerical simulation develops on the contact between the clay and silty mudstone which confirmed the assumed sliding surfaces location using the lem

fluvial sediment transport and deposition following the 1991 eruption of mount pinatubo the 1991 eruption of mount pinatubo generated extreme sediment yields from watersheds heavily impacted by pyroclastic flows bedload sampling in the pasig potrero river one of the most heavily impacted rivers revealed negligible critical shear stress and very high transport rates that reflected an essentially unlimited sediment supply and the enhanced mobility of particles moving over a smooth fine grained bed dimensionless bedload transport rates in the pasig potrero river differed substantially from those previously reported for rivers in temperate regions for the same dimensionless shear stress but were similar to rates identified in rivers on other volcanoes and ephemeral streams in arid environments the similarity between volcanically disturbed and arid rivers appears to arise from the lack of an armored bed surface due to very high relative sediment supply in arid rivers this is attributed to a flashy hydrograph whereas volcanically disturbed rivers lack armoring due to sustained high rates of sediment delivery this work suggests that the increases in sediment supply accompanying massive disturbance induce morphologic and hydrologic changes that temporarily enhance transport efficiency until the watershed recovers and sediment supply is reduced d 2002 elsevier science b v all rights reserved

geomorphology of conglomerate terrains global overview abstract conglomerates are widespread clastic rock often occurring in thick successions and supporting complex geomorphological landscapes yet by contrast to some other rock types little systematic work has been done on geomorphology of conglomeratic terrains major geographical gaps exist and no review has been offered up to now this paper partially fills this gap and provides an overview of characteristic landforms landscape types and geologic controls present in areas built of conglomerates distinctive landforms developed in conglomerates include bedrock cliffs and overhangs domed hills and hilltops crags slots and clefts tafoni caves and various karst features they combine into specific landform assemblages of dome clusters dissected plateaus and cuestas stepped hillslopes and conglomeratic badlands if lithification of sediment is poor some dissected plateaus and dome clusters represent spectacular morphology awarded the status of unesco world heritage china danxia meteora kata tjuta a variety of geological controls is identified and presented including composition of conglomerate packages their thickness jointing patterns presence of sandy and clayey intercalations as well as the style and magnitude of regional uplift clast by clast breakdown is identified as a principal mechanism of rock disintegration analogous to grain by grain disintegration pattern of many sandstones this explains striking similarities between some sandstone and conglomeratic sceneries and the common presence of rounded shapes in the closing part of the paper research avenues for the future are suggested both regional studies aimed at the complete inventory of conglomeratic landforms as well as detailed insights into the nature of bedrock control at the variety of scales are recommended

erosion of calcimagnesic soils as aggregates in jurassian pedological systems summary calcimagnesic soils either humiferous or brown which occupy the convex zones of jurassian plateaux are associated in ranges with colluvial soils of depressions to which they provide materials the hyppothesis is put forward that this erosion acts on entire aggregates and not on particles in order to demonstrate this calcimagnesic soil aggregates on the one hand as well as sediments brought in by violent rains in furrowed pathways on the other hand are collected their composition and resistance with respect to destructive treatments of increasing intensity are compared it is shown that the high structural stability allows the displacement and transport of entire aggregates and thus becomes paradoxically a factor of soil erosion and vulnerability

observations on the dispersion and aggregation of clays by humic substances ii short term effects of humus rich peat water on clay aggregation abstract the phenomenon of aggregation was studied by percolating a peat extract through columns containing mixtures of sand and one of the following types of clay kaolinite illite vermiculite and montmorillonite optical and scanning electron microscopy of the various mixtures after a 10 month period demonstrated that the presence of humic substances within the clay sand deposits had resulted in the formation of well defined structures which were a function of the type of clay present

the july 29 1998 debris flow and landslide dam at capricorn creek mount meager volcanic complex southern coast mountains british columbia a very large debris flow was triggered during a period of record breaking high temperatures in upper capricorn creek within the mount meager volcanic complex a part of the garibaldi volcanic belt of the southern coast mountains the debris flow deposit impounded meager creek creating an 800 m long landslide dammed lake the total event volume was 1 2 106 m3 the debris flow was followed by three days of almost continuous hyperconcentrated flow surges which caused significant fluvial aggradation in the meager creek flood plain below the capricorn creek confluence within a few days of the formation of the landslide dam a spillway notch had been cut through the deposit thereby preventing the occurrence of a catastrophic dam break the landslide which triggered the debris flow originated in deep volcanic colluvium having a previous history of progressive slope deformation a consequence of glacial downwasting since the neoglacial maximum this paper highlights an important landslide response to rec

geomorphology and engineering geology of a landslide in ultramafic rocks dawson city yukon abstract the dawson city landslide is located at the northern edge of dawson city yukon and took place prior to 1740 years b p the landslide occurred at the contact between the metasedimentary rocks of the yukon tanana terrane and the overlying altered ultramafic rocks of the slide mountain terrane the main part of the failure comprises altered ultramafic rocks which have a lower geological strength index rock mass quality than the underlying metasedimentary sequence division of the study area into smaller structural domains identified discontinuity sets associated with faulting along the contact of the two lithological units a kinematic analysis of the identified discontinuity sets suggests that a toppling failure mechanism may be feasible due to the highly fractured nature of the ultramafic rock mass a circular failure controlled by the low strength of the rock mass is considered a potential mechanism for the dawson city landslide limit equilibrium and finite difference numerical modelling codes support a circular failure mechanism hypothesis however a combination of high pore water pressure ru 0 3 and seismic loading are required to produce a factor of safety the dominant trends of linear geomorphic features tension cracks trenches anti slope scarps ridges correspond to a discontinuity set recognised in the headscarp of the failure tension cracks exposing roots and split trees indicate recent movement of a small section of the headscarp that is potentially unstable the downslope risk represented by this unstable block is difficult to assess due to the uncertainties related to entrainment of talus material and potential travel distance over the rough and irregular surface of the middle coarse debris material the movement rate of this block should be monitored and the surrounding area routinely investigated for the development of other potentially unstable sections of the landslide sheared trenches stretched roots and split trees suggest that the middle to lower section of the debris is currently moving

floodplain dynamics of a wandering river dendrochronology of the morice river british columbia canada dendrochronological techniques are used to develop a history of flood occurrence and relative stage for the middle section of the morice river based on flood scars bank undercutting dates and tree establishment dates on fluvial features the morice river is the major tributary of the bulkley river skeena river system northwest british columbia canada reach 2 of the morice river drainage area 3499 km2 is forested and little disturbed by human activity it is presently a wandering multiple channel river and shows evidence of frequent channel changes which have reworked most of the floodplain several times in the last 180 years airphoto analysis and dendrochronology demonstrate that many channels show evidence of two or more periods of activity reoccupation and re excavation of pre existing channel segments is more frequent than development of new channels thirty one significant floods over the past 105 years were detected through dendrochronology of flood scarred trees on the morice river flood scars are predominantly caused by flood transported logs abundant log transport results in damage to channel margin trees during events only slightly above bankfull discharge the record of flood scars on channel margin trees and establishment dates of forest stands on abandoned channels and surfaces show that the morice river has maintained its present regimen for the past 115 years during the neoglacial the morice river was more active than in recent times and its channels occupied twice the present area tree establishment dates show that neoglacial surfaces and channels of the morice river were abandoned during the 1820 s the modern floodplain configuration was assumed by 1870

why joints are more abundant than faults a conceptual model to estimate their ratio in layered carbonate rocks it is a commonplace field observation that extension fractures are more abundant than shear fractures the questions of how much more abundant and why are posed in this paper and qualitative estimates of their ratio within a rock volume are made on the basis of field observations and mechanical considerations a conceptual model is also proposed to explain the common range of ratios between extension and shear fractures here called the j f ratio the model considers three major genetic stress components originated from overburden pore fluid pressure and tectonics and assumes that some of the remote genetic stress components vary with time i e stress rates are included other important assumptions of the numerical model are that i the strength of the sub volumes is randomly attributed following a weibull probabilistic distribution ii all fractures heal after a given time thus simulating the cementation process and therefore iii both extensional jointing and shear fracturing could be recurrent events within the same sub volume as a direct consequence of these assumptions the stress tensor at any point varies continuously in time and these variations are caused by both remote stresses and local stress drops associated with in situ and neighbouring fracturing events the conceptual model is implemented in a computer program to simulate layered carbonate rock bodies undergoing brittle deformation the numerical results are obtained by varying the principal parameters like depth viz confining pressure tensile strength pore fluid pressure and shape of the weibull distribution function in a wide range of values therefore simulating a broad spectrum of possible mechanical and lithological conditions the quantitative estimates of the j f ratio confirm the general predominance of extensional failure events during brittle deformation in shallow crustal rocks and provide useful insights for better understanding the role played by the different parameters for example as a general trend it is observed that the j f ratio is inversely proportional to depth viz confining pressure and directly proportional to pore fluid pressure while the stronger is the rock the wider is the range of depths showing a finite value of the j f ratio and in general the deeper are the conditions where extension fractures can form moreover the wider is the strength variability of rocks i e the lower is the m parameter of the weibull probabilistic distribution function the wider is the depth range where both fractures can form providing a finite value of the j f ratio natural case studies from different geological and tectonic settings are also used to test the conceptual model and the numerical results showing a good agreement between measured and predicted j f ratios

channel response to sediment wave propagation and movement redwood creek california usa redwood creek north coastal californa usa has experienced dramatic changes in channel confguation since the 1950s a series of large floods in 1955 1964 1972 and 1975 combined with the advent of widespread commercial timber harvest and road building resulted in extensive erosion in the basin and contributed high sediment loads to redwood creek since 1975 no peak flows have exceeded a 5 year recurrence interval twenty years of cross sectional survey data document the downstream movement of a sediment wave in the lower 26 km of this gravel bedded river at a rate of 800 to 1600 m a i durng this period of moderately low flows higher transit rates are associated with reaches of higher unit stream power the wave was initially deposited at a site with an abrupt decrease in channel gradient and increase in channel width the amplitude of the wave has attenuated more than i m as it moved downstream and the duration of the wave increased from eight years upstream to more than 20 years downstream channel aggradation and subsequent degradation have been accommodated across the entire channel bed channel width has not decreased significantly after initial channel widening from large 25 year recurrence interval floods three sets of longitudinal surveys of the streambed showed the highest increase in pool depths and frequency in a degrading reach but even the aggrading reach exhbited some pool development through time the aggraded channel bed switched from functioning as a sediment sink to a significant sediment source as the channel adjusted to high sediment loads from 1980 to 1990 sediment eroded from temporary channel storage represented about 25 per cent ofthe total sediment load and 95 per cent of the bedload exported from the basin

geomorphic control of persistent mine impacts in a yellowstone park stream and implications for the recovery of fluvial systems a half century after mine closure metal contamination from sulfide ore mining in the headwaters continues to impair riparian vegetation and aquatic macroinvertebrates along soda butte creek yellowstone national park a tailings dam failure in 1950 emplaced metal rich sediment at high flood plain levels above 50 yr to 100 yr flood stages in 1996 and 1997 these large natural floods removed only a small part of the contaminated sediment through bank erosion they also failed to lower in channel cu concentrations because increased erosion of mine waste during high flows balances increased inputs of uncontaminated sediments generating no net change in concentrations geomorphic processes controlling movement of contaminated sediments indicate that mine impacts will persist for centuries in soda butte creek and imply long lasting impacts in similarly affected streams worldwide

hydrological controls of surficial mass movements in peat peat deposits occur in areas where water logging is common large areas of blanket mire occur throughout the temperate and cold regions of the northern and southern hemispheres and are particularly extensive in the uk uplands mass movements of peat reported usually as peat slides and bog bursts have been well documented for over 150 years however the fundamental controls of this form of shallow instability are still poorly understood the aim of this paper is to review critically the available evidence linking peat hydrology and slope instability then using data from the north pennine uplands in northern england we examine the importance of rainfall macroscale drainage conditions and peat hydrological processes in initiating slope instability shear failure by loading buoyancy effects basal liquefaction and surface or marginal rupturing have all been proposed as potential failure mechanisms data from northern england demonstrate that hydrological processes are fundamental in determining the spatial and temporal occurrence of peat slides most instabilities are associated with convective summer thunderstorms although instances of rapid snowmelt and intense winter rainfall have also triggered these events all instabilities occur in association with distinct drainage features slides are initiated along natural drainage lines or in association with artificial drainage often brought about by mining activity or agricultural practices at the scale of the soil profile the special hydrological properties of peat in particular shallow water tables and low soil hydraulic conductivity offer important clues to failure mechanisms pore water pressures are generally low and vary little in the peat profile and throughout the year it is clear from observations of subsurface flow that significant volumes of runoff reach considerable depths in the soil macropores flow occurring in pores greater than 1 mm in diameter are important in delivering surface runoff to deeper parts of the profile and in some instances high pipe water pressures may develop these findings define several important hydrological controls for surficial mass movements in peat but the prospect of predicting the location and timing of such events is still a long way off

the gigantic seymareh saidmarreh rock avalanche zagros fold thrust belt iran the seymareh rock avalanche first described by j v harrison and n l falcon in the 1930s is the largest known subaerial non volcanic landslide on earth the volume of its debris 44 gm 3 is approximately equal to that of the largest known subaerial landslide of any kind the 100 ka collapse of mount shasta volcano 45 gm 3 and approaches those of gigantic landslides on mars using satellite imagery srtm 3 data and detailed field investigations we gain a new understanding of the gigantic rock avalanche the initial failure 38 gm 3 involving a dip slope consisting of a relatively weak interbedded limestone mudrock sequence capped by resistant asmari limestone had an average thickness of 410 m along a 15 5 km width of the kabir kuh anticline the rockslide transformed into a rock avalanche that travelled 19 0 km with a fahrboschung the angle between the highest point of the pre landslide source area topography and the distal limit of the debris of only 3 6 initial failure involved complex planar sliding dictated by four structural elements 1 bedding parallel shears and 2 across bedding break throughs combined to produce a low angle 11 overall sliding surface that 3 broke out through the asmari carapace at the toe of the failed slope while 4 tectonically weakened bedding normal joints provided lateral release surfaces nine discrete bedding parallel basal sliding surfaces divided the detached mass into nine stacked plates the upper plate 23 gm 3 included 20 7 gm 3 of asmari limestone analysis of accelerator mass spectrometry radiocarbon dates from this study and by others indicates that the rock avalanche occurred between c 8710 and 9800 14 c years bp supplementary material a summary of the tectonics stratigraphy and physiography of the zagros fold thrust belt together with a description of surficial gravity collapse structures in the region harrison falcon 1934 1936 is available at www geolsoc org uk sup18612

determination of mechanical properties of flysch using laboratory methods abstract the paper deals with the determination of the mechanical properties of heterogeneous rocks in the laboratory and proposes a methodology for predicting the rock mass strength of flysch formations consisting of siltstone sandstone alternations in different proportions in order to simulate such formations composite specimens comprising superimposed disks of intact sandstone and siltstone material with different thickness ratios were prepared wave velocity p and s uniaxial and triaxial compressive strength and young s modulus of the composite samples were determined in the laboratory according to the laboratory results the uniaxial compressive strength and young s modulus decrease with the increase of the siltstone percentage in the specimens and yield the strength of siltstone when the siltstone percentage in the rock is equal to 37 additionally the triaxial compression tests on composite samples revealed a significant decrease of the m i parameter for a siltstone percentage of only 17 a comparison is made between the results of the present study with similar laboratory and empirical references from literature finally it was possible to suggest how the relation between uniaxial compressive strength ci and siltstone percentage sl may differ according to the ratio of the compressive strength of the two main rocks weak and strong which comprise the heterogeneous rock

river adjustment to changes in sediment load the effects of tin mining on the ringarooma river tasmania 1875 1984 the mining of alluvial tin in the ringarooma basin began in 1875 reached a peak in 1900 20 and had virtually ceased by 1982 during that time 40 million m3 of mining waste were supplied to the main river quickly replacing the natural bed material and requiring major adjustments to the channel based on estimates of sediment supply from more than 50 widely scattered mines and the frequency of flows capable of transporting the introduced load the river s transport history is reconstructed using a mass conservation model because of the lengthy time period 110 years and river distance 75 km involved the model cannot predict detailed change but it does reproduce the main pattern of sediment movement in which successive phases of aggradation and degradation progress downstream peak storage is predicted in that part of the river where braiding and anastomosis are best developed aggradation was most rapid in the upper reaches close to major supply points becoming slower and later with distance downstream channel width increased by up to 300 per cent where the valley floor was broad and braiding became relatively common bridges had frequently to be replaced while bed levels were still rising in lower reaches degradation began in upper ones notably after 1950 and by 1984 had progressed downriver over 30 km rates of incision reached 0 5 m yr 1 especially in the early 1970s when record high flows occurred as a result of degradation the bed material became gravelly through either reexposure of the original bed or lag concentration of coarser fractions also a narrower unbraided channel has developed the river is beginning to heal itself and upper reaches now have reasonably stable beds but at least another 50 years will be required for the river to cleanse its channel of mining debris

slope instability mechanisms in dipping conglomerates over weathered marls bol landslide croatia in february 2005 a landslide of significant dimensions occurred at bol on the island of brac in croatia the location of the landslide was in a geological structure of weakly bounded conglomerates lying above a flysch in an area where numerous slides have been previously reported in the paper the results of a geological engineering investigation of the bol landslide are presented the investigation results show that the landslide was triggered by a combination of improperly started earthworks an increase in air temperature in days preceding landslide that caused snow melt and abundant rainfall but the primary cause of the landslide was weathering of the flysch in other words despite the fact that contact between the flysch and the conglomerates slopes is in approximate correspondence with the slope of the hillside the landslide surface was not in contact between the conglomerates and marl but deeper in the flysch provoked by the penetration of the weathering front into the flysch numerical modelling results were able to reproduce this mechanism by incorporating strength degradation into the weathered zone determined by field investigation the results of the research can be used to predict potential slides not only in the area under study

the failure mechanism and construction practice of large underground caverns in steeply dipping layered rock masses abstract the stability of large underground caverns in steeply dipping layered rock masses is not only affected by the engineering geological characteristics of surrounding rock masses but also by the excavation sequences and reinforcement measures certain places around the periphery of underground openings such as the high sidewalls would exhibit significant displacement increases and various failure patterns if the excavation and support were not properly designed these issues can according to the basic principles of structurally controlled concept be largely attributed to the mechanical properties of bedding planes and other discontinuities in order to clarify the possible mechanisms behind these failures and to realize the dynamic adjustment of construction a thorough investigation was conducted to the underground caverns of the wudongde hydropower station throughout the excavation process the geological conditions and mechanical properties of the rock masses in the study area were first introduced in detail four examples were then presented following the overall logic from geological background to failure mechanism and finally to reinforcement practice the first example focused on the local wedge type instability analyses including the collection of necessary information the identification of potential blocks as well as the determination strategies for the factors of safety the second example illustrated typical tensile failure mode of steeply inclined strata induced by large scale excavation the sudden normal unloading of bedding planes led to observable fractures along these weaknesses and considerable increases in sidewall displacements large quantities of extra reinforcements had to be installed to control further development of fractured range of the upstream sidewall the third example highlighted the long range influence of excavations on the stability of downstream roof where multistage displacement increase and shotcrete cracking took place as a result of stress concentration and strata buckling possibly also of the local unfavorable discontinuities the last example was related to the failure mode of combined discontinuities on the surfaces of piers between two pits lessons learned from these examples mainly involve what the mechanical behaviors of the steeply dipping layered rock masses in different places after excavation will be like and to what extent these behaviors could be predicted or anticipated which then put emphasis on the importance of geological investigations and how the optimization of excavation sequence and bench height as well as the timely installation of regular supports could effectively reduce the risks of instability

the lillooet terraces of fraser river a palaeoenvironmental enquiry the history of holocene fluvial terraces was investigated by stratigraphic morphological and palaeohydrologic methods the terraces were formed in glaciofluvial and glaciolacustrine sediments by the fraser river degradation alternated with episodes of stability and aggradation the uppermost terraces four nonpaired surfaces were occupied by a braided river vertical stability was controlled either by the water and sediment discharge of the river or by backwater effects from downstream landslides the lower terraces two paired surfaces and associated fluvial sediments provide evidence for at least two cycles of aggradation and downcutting these can be attributed to the effects of landslides that occurred a short distance downstream climatic variations may also have influenced terrace formation but direct evidence is lacking palaeohydraulic investigations based on gravel texture terrace gradients and geometry of palaeochannels provide results that although approximate conform with conclusions

effective timescales of coupling within fluvial systems this paper presents a review of the coupling concept in fluvial geomorphology based mainly on previously published work coupling mechanisms link the components of the fluvial system controlling sediment transport down the system and the propagation of the effects of base level change up the system they can be viewed at several scales at the local scale involving within hillslope coupling hillslope to channel coupling and within channels tributary junction and reach to reach coupling at larger scales coupling can be considered as zonal coupling between major zones of the system or as regional coupling relating to complete drainage basins these trends are illustrated particularly by the examples of hillslope to channel coupling in the howgill fells northwest england badland systems in southeast spain alluvial fans in spain usa and uae and base level induced dissection of neogene sedimentary basins in southeast spain as the spatial scales increase so do the timescales involved effective temporal scales relate to magnitude and frequency characteristics recovery time and propagation time the relative importance changing with the spatial scale for downsystem coupling at the local scale the first two are important with propagation time increasing in importance in larger systems especially in those involving upsystem coupling related to base level change the effective timescales range from the individual event with a return period of decades through decadal to century timescales for downsystem coupling to tens to hundreds of thousands of years for the basinwide response to base level change the effective timescales influence the relative importance of factors controlling landform development

mechanical anisotropy of columnar jointed basalts an example from the baihetan hydropower station china abstract columnar jointed basalts are characterized by a self organized joint network of discontinuities and pose a difficult challenge for geotechnical engineering design due to their inherent anisotropic nature we explore here the anisotropic characteristics of the columnar basalt formation in the chinese baihetan hydropower station including aspects of the geometrical rock structure deformation and strength anisotropy site investigations reveal that a typical cross section of the columnar basalt blocks is mainly quadrangular and pentagonal with an average edge length of 0 152 m three types of joints with different macro and micro characteristics form the columnar jointed rock mass and are identified by scanning electron microscopy in situ ultrasonic tests further confirm that the columnar basalt prisms exhibit transverse isotropy with the plane of isotropy perpendicular to the column axis as can also be observed in the field strength anisotropy is confirmed by point load and uniaxial compression tests the mechanical and anisotropic characteristics of baihetan s jointed basalt mass can be explained by its multi scale joints pattern by means of goodman s stiffness equation we find that the anisotropic coefficients obtained for its deformability and strength are similar for all testing methods employed including in situ p wave velocity point load tests and uniaxial compression tests this result confirms the strong anisotropic effect in these rock masses and facilitates an issue that must be considered when assigning input parameters for various classification and numerical analyses schemes

catastrophic landslides and their effects on the upper indus streams karakoram himalaya northern pakistan abstract the paper examines the nature and geomorphic influences of deposits from rock avalanches that obstruct rivers most of the 115 rockslide rock avalanche events identified in the karakoram himalaya straddled one or more stream valleys at least 73 of these landslides formerly dammed the indus or its tributaries upstream of the barriers remnants exist of once very extensive lacustrine deposits the stability and long term survival of dams from large rock avalanches is addressed and the reasons for the gradual or phased rather than catastrophic and sudden breaching case histories emphasise the erosional and depositional forms associated with the barriers they are reconstructed in terms of the emplacement and properties of the deposits from rock avalanches and the response of the river to interruption by them these barriers have exerted a substantial control over stream response and development for most of the holocene at least today they are associated with distinctive features of channel form and thalweg river terrace systems intermontane sediment sinks and sources and local erosional forms in bedrock more broadly the landslide barriers have created a naturally fragmented river system deposition and erosion in the lower few tens or hundreds of meters of the upper indus stream valleys have been dominated by epicycles of aggradation trenching and downcutting that mainly reflect the scale timing and history of each barrier the landforms involved are only indirectly related to the late glacial and paraglacial conditions that have hitherto been regarded as the main explanation

an x ray computed tomography based index to characterize the quality of cataclastic carbonate rock samples x ray computed tomography xrct can reconstruct in a nondestructive way and in three dimension the distribution of densities within opaque materials consequently it provides an effective possibility to characterize the inner content of rock core samples and in particular their alteration products sensu lato which generally appear less dense than the intact rock matrix in this paper a new index based on xrct data is tested for evaluating the degree of alteration of highly tectonized carbonate rock samples and is compared with visual based classification systems this xrct based analysis leads to a diagnosis of alteration which appears objective precise and in agreement with the visual observations besides this method takes into account the entire volume of the sample is rapid to carry out and allows an intact rock core to be used for further laboratory testing

landslide induced river channel avulsions in mountain catchments of southwest new zealand pulsed or chronic supply of landslide debris to valley floors has historically caused substantial aggradation and channel instability in several alpine catchments of sw new zealand in this regional investigation of landslide impacts on river morphology three types of landslide induced channel avulsion are discerned i upstream backwater avulsions ii contact avulsions and iii downstream loading avulsions the basis for this qualitative geomorphic process response framework is the principal direction of fluvial response with respect to its position relative to the causative landslide emplacement site downstream avulsions have the highest damage potential to land use and infrastructure on unconfined mountain fringe alluvial fans in the wake of such events catastrophic aggradation may obliterate up to several km2 of mature floodplain forests by burial under several metres within a few decades estimates of mean aggradation rates are high 220 mm year 1 and exceed long term 103 year trends of fluvial degradation by an order of magnitude future potential avulsion routeways may be detected by geomorphic mapping of abandoned channels which are preferentially reactivated in the wake of landslide induced sediment waves

numerical modelling of shallow abandoned mine working subsidence affecting transport infrastructure abstract this work presents details of a shallow mining subsidence event that occurred in the summer of 2001 causing the formation of crown holes at the surface which affected the east coast main railway line in the uk this subsidence event caused significant disruption and the remediation effort required the construction of a 1 8 km long diversion built on a piled reinforced concrete raft details of the ground investigation are summarised along with a large parametric numerical modelling study undertaken in flac 3d into the potential causes of the instability including the role of variations of the level of the groundwater table the influence of the structure of the rock mass and also the potential geometry of the abandoned workings ultimately the modelling allowed constraints to be placed on the likely excavation width of the workings at the site along with bedding spacing and strength of the overlying rock mass the modelling also suggests that the increase in the ground water table may also have been a factor in the occurrence of instability on the site

record of recent river channel instability cheakamus valley british columbia rivers flowing from glacier clad quaternary volcanoes in southwestern british columbia have high sediment loads and anabranching and braided planforms their floodplains aggrade in response to recurrent large landslides on the volcanoes and to advance of glaciers during periods of climate cooling in this paper we document channel instability and aggradation during the last 200 years in lower cheakamus river valley cheakamus river derives much of its flow and nearly all of its sediment from the mount garibaldi massif which includes a number of volcanic centres dominated by mount garibaldi volcano stratigraphic analysis and radiocarbon and dendrochronological dating of recent floodplain sediments at north vancouver outdoor school in cheakamus valley show that cheakamus river aggraded its floodplain about 1 2 m and buried a valley floor forest in the early or mid 1800s the aggradation was probably caused by a large ca 15 2510 6 m 3 landslide from the flank of mount garibaldi 15 km north of our study site in 1855 or 1856 examination of historical aerial photographs dating back to 1947 indicates that channel instability triggered by this event persisted until the river was dyked in the late 1950s our observations are consistent with data from many other mountain areas that suggest rivers with large but highly variable sediment loads may rapidly aggrade their floodplains following a large spike in sediment supply channel instability may persist for decades to centuries after the triggering event crown copyright d 2002 published by elsevier science b v all rights reserved

channel response to increased and decreased bedload supply from land use change contrasts between two catchments abstract the catchments of pine creek idaho usa 200 km 2 and the drome river in the drome department france 1640 km 2 illustrate contrasting changes in land use bedload sediment production and channel response hard rock mining began in the catchment of pine creek near the end of the 19th century and together with road construction timber harvest and historically heavy grazing of uplands resulted in increased tributary bedload yield increased bedload migrating to the channel combined with removal of large cedar trees on the floodplain resulted in channel instability which propagated downstream over a period of decades on many reaches of pine creek active channel width has increased by over 50 since 1933 over roughly the same time period the drome river catchment was extensively reforested after at least one century of denudation and heavy grazing and numerous check dams were constructed on torrents to reduce erosion as a result the drome river has experienced a reduction in bedload sediment supply since the late 19th century in addition gravel has been extracted from some reaches consequently the channel has degraded and gravel bars have been colonized with woody riparian vegetation channel widths in wide braided reaches decreased from 1947 to 1970 by 60 on pine creek channel instability has resulted in bank erosion exposing contaminated mine tailings and increased flood hazard on the drome river degradation has undermined bridges and embankments and lowered the water table in areas dependent on groundwater for irrigation resulting in loss of 6 million m 3 of groundwater storage since 1960 though they differ in drainage area by nearly an order of magnitude pine creek and the drome river provide an excellent contrast in that they represent two sides of an epicycle of alluvial sedimentation set off in each case by land disturbance in both cases the most recent channel changes though in opposite directions were viewed as negative by river managers on pine creek managers have removed or protected from erosion mine tailings and have attempted to train the stream into a more stable channel and most rock waste piles the principal sediment sources have recently been controlled on the drome river managers have prohibited gravel mining and adopted new policies to permit coarse sediment to migrate through the river system

the quaternary stratigraphic record of british columbia evidence for episodic sedimentation and erosion controlled by glaciation the terrestrial quaternary stratigraphic record of british columbia is largely a product of brief depositional events separated by long periods of nondeposition and erosion thick stratified quaternary sediments are present mainly in valleys and coastal lowlands and accumulated during periods of growth and decay of the cordilleran ice sheet at glacial maxima till was deposited over large areas of low and moderate relief however at the same time much of the landscape was eroded by glaciers sedimentation has been more restricted and has occurred at lower rates during nonglacial periods than during glaciations on land the only important sediment accumulation sites during nonglacials have been lakes floodplains and fans however large amounts of sediment have accumulated offshore especially in fjords and basins such as the strait of georgia because of the restricted aspect of sedimentation during nonglacials the stratigraphic record of these periods is meagre in most places true nonglacial uni