decoding downstream trends in stratigraphic grain size as a function of tectonic subsidence and sediment supply downstream grain size fining in stratigraphy is driven primarily by selective deposition of sediment and the long term efficiency of this process is determined by 1 the magnitude and characteristics of the input sediment supply 2 the spatial distribution of subsidence rate which creates accommodation for sediment preservation and 3 the dynamics of sediment transport and deposition a key challenge is to determine how these first two factors control the caliber and spatial distribution of deposits over time scales of 10 4 10 6 yr without incorporating sediment transport details that are largely unknowable for time averaged stratigraphy in the geological past we address this using grain size data collected from fluvial conglomerates in the eocene pobla basin spanish pyrenees a synorogenic basin where the timing of sediment deposition is well constrained the sediment budget is closed and good exposure enables time lines within stratigraphy to be picked out unambiguously for successive stratigraphic horizons downstream trends in grain size and composition are derived for basin filling sediment routing systems with length scales of 6 and 40 km respectively our data show that the rate of grain size fining varies over time and with system length and can be linked to changes in source area these results are contrasted with grain size data from the antist group a 60 km long oligocene system that mantles the southern pyrenees where very slow rates of grain size fining on the wedge top of this fold and thrust belt are observed we apply a self similarity based selective deposition model to quantify the competing controls of tectonic subsidence and sediment supply on derived grain size trends and model results are compared with independent constraints on the eocene oligocene evolution of the pyrenees our results suggest that it is now possible to invert time averaged grain size trends in stratigraphy to gain quantitative information on the geological boundary conditions governing the evolution of sedimentary basins

deep weathering of a group of thick argillaceous limestone rocks near three gorges reservoir central china rock mass characterization is one of the most basic and important tasks in rock mechanics and engineering literature review indicates that although there are many publications available on weathered rocks there are few reports in english on weathered argillaceous limestone rocks and their chemical and mechanical properties this paper presents a case study of characterizing a group of highly weathered thick argillaceous limestone rocks most importantly they can be easily and quickly decomposed into soils after they are exposed due to excavation consequently they would substantially lose their mechanical strengths geohazards such as landslides and sinkholes could occur in uncovered highly weathered argillaceous limestone rocks the problematic weathered rocks were found during the development of a new town in upper mountains above the three gorges reservoir on yangtze river in central china in the past 20 years the factual data are presented on the changes of chemical compositions and mechanical properties of the weathered argillaceous limestone rocks due to chemical weathering some empirical correlations are given to quantify the changes in their uniaxial compressive strength and deformation moduli in terms of their contents of calcium carbonate the data and findings presented in the paper can be useful to future urban development in geologically poor mountainous environments occupied by highly weathered argillaceous limestone rocks in the world

weathering mechanisms and their effects on the landsliding of ignimbrite subject to vapor phase crystallization in the shirakawa pyroclastic flow northern japan abstract ignimbrite which is consolidated by vapor phase crystallization is weathered in humid regions to form a special type of weathering profile that consists of a hydrated zone an exfoliated zone and a disintegrated zone from the depth to the ground surface with each zone having a basal front the ignimbrite is hydrated first and loses a significant amount of phosphorous at the hydration front where rock forming tridymite is dissolved and cristobalite is precipitated the ignimbrite further loses its alkali and alkali earth components at the top of the hydrated zone by reacting with reactive water from the exfoliated zone then the leached layers are exfoliated and become part of the exfoliated zone and then they soften significantly at the top of the exfoliated zone rock is disintegrated so completely that rock texture disappears water from rainstorms infiltrates down to the exfoliation front but penetrates only slightly further downward thus saturating the weathered rock in the exfoliated and disintegrated zones and leading to a landslide with a slip surface within the exfoliated zone

preservation of inner gorges through repeated alpine glaciations the origins of alpine valleys are controversial topographic data from the swiss alps suggest that the valleys have been incised progressively during consecutive glacial interglacial cycles

a new numerical approach to weathering and alteration in rock using a pilot area in the tuzla geothermal area turkey abstract weathering and subsequent alteration processes affect rocks by changing their physical chemical mineralogical petrographical and mechanical properties although these changes are important inputs for project designs especially in engineering geology and civil engineering their complex nature in rocks makes evaluation difficult for non specialists in this paper we propose a new simplified method for quantifying the degree of weathering and subsequent alteration in rock materials based on pycnometer measurements of specific gravity and a combination of relevant formulas using porosity void ratio and dry unit weight the relationship between these properties and rock material change is defined using a point rock change value rcvp at pi xi yi coordinates and a point rock change ratio rcrp another numerical value the overall rock change value rcvo is introduced to characterize specific geological formations in the study area rcvo uses dry unit weight d saturated unit weight sat porosity n void ratio e degree of saturation s and specific gravity s and optical properties of rock material these optical properties are quantified from thin sections of the rocks with a numerical image value niv rcvp and rcvo range from 0 to 1 where 1 indicates no change by weathering or alteration and 0 indicates completely weathered or altered rocks application of this method in the tuzla geothermal field of northwest turkey reveals strong similarity in the distribution maps for the physical parameters and the calculated values for rcvp and rcvo the new method correctly identified greater alteration near hot water sources and along fault planes

distribution of erosion across bedrock channels lateral erosion in bedrock rivers is an important control on the shape of channel crosssections and the coupling of channels and hillslopes recent observations link lateral erosionto the variability of flow we propose two mechanisms to explain this one is based on changing shear stress distributions within the channel with varying flood level the other on the competition between cover and tool effects in fluvial bedrock erosion we assess these processes for the liwu river taiwan and conclude that cover and tool effects dominate the partitioning of lateral and vertical erosion in this case

rapid formation of river terraces in non welded ignimbrite along the hishida river kyushu japan abstract river terraces are well preserved in the middle to lower reaches of the hishida river that flows through the extensive ignimbrite field produced by the large scale ito eruption about 24 500 years ago from aira caldera in southern kyushu japan the terraces are erosional and formed during dissection of the initial topography of the ito ignimbrite these occur within the upper non welded zone of the ito ignimbrite about 20 60 m below the depositional surface and usually more than 20 m above the welded zone streams associated with terrace formation were ephemeral because perennial streams are considered highly unlikely within the porous non welded ignimbrite all tephra layers on the original ignimbrite depositional surface also cover the terraces this indicates that the formation of terraces preceded the accumulation of the oldest tephra the age of which is about 23 000 years old high erodibility of the non welded ito ignimbrite and absence of vegetation on the initial surface would have permitted a rapid dissection of the initial topography and the formation of the river terraces thus it is interpreted that the river terraces were formed very rapidly in a period of far less than 1500 years immediately after the deposition of the ito ignimbrite and before cover of new vegetation on the depositional surface

hydromechanical triggering of landslides from progressive local failures to mass release 1 water infiltrating during intense rainfall on steep slopes gradually weakens the wet soil mass inducing localized failures that may initiate a cascade of load redistributions and successive failures propagating across a hillslope the challenge of linking the progressive nature of local events culminating in an abrupt landslide is addressed by a new hydromechanical triggering model that links key hydrologic processes with threshold based mechanical interactions a hillslope is represented as assembly of soil columns interconnected by frictional and tensile mechanical bonds represented as virtual bundles of fibers increasing water load exerted on mechanical bonds causes gradual failure of fibers until restraining forces are exceeded following failure at the soil bedrock interface the load on a column is redistributed to its neighbors via intact mechanical primarily tensile bonds which in turn may also fail and transmit the load downslope as compressive stresses when soil internal compressive strength is exceeded a load bearing column may liquefy and initiate a landslide release that could propagate downslope or retrogressively upslope the model reproduces observed power law frequency magnitude relationships of landslides with exponents ranging between 1 0 and 2 2 in agreement with landslide inventory data we applied a criticality measure defined by ramos 2011 to evaluate the specific influences of slope angle soil texture and root reinforcement on attainment of hillslope criticality in which a small local failure may trigger release of a large soil mass the model provides new insights on the conditions giving rise to an abrupt transition from a seemingly stable hillslope to a catastrophic landslide

a quantification of the glacial imprint on relief development in the french western alps abstract the morphology of the western alps has been strongly influenced by quaternary glaciations on the basis of observations of glacial morphology in the belledonne grandes rousses taillefer and pelvoux ecrins massifs south eastern france we reconstitute the glacial trimline and equilibrium line altitude ela during the most extensive glaciation meg our best estimate of the meg ela is 1800 100m using digital elevation models we compare our glacial reconstruction with the relief structure of nine major catchments draining the massifs modal elevations of the largest catchments occur at 2000 2500m and coincide with minima in plots of mean slope angles as a function of elevation modal elevations and slope minima occur between the modern and meg elas confirming a strong glacial imprint on relief in order to quantify glacial valley carving in the massifs we isolated high elevation low relief surfaces that form rock shoulders adjacent to the glacial valleys from a digital elevation model and constructed an interpolated surface passing through these subtracting the present day topography from this surface allows us to quantify the maximum glacial valley depths maximum valley depths determined in this manner are typically 1000m with spatial maxima occurring around the location of the meg ela in most valleys these numbers do not take into account glacial valley widening and local glacial overdeepenings the also neglect however potential pre glacial fluvial valley incision which could account for 20 50 of the measured valley depths in spite of these problems inferred valley depths are reasonably well correlated with the mean reconstructed ice thickness and constitute about half of the sub ridgeline relief of the studied catchments these results lead us to propose a significant quaternary increase in the relief of the french western alps controlled by climate and associated with the initiation of alpine glaciations for reasonable values of the effective elastic thickness of the lithosphere the isostatic response to glacial valley carving reaches values of 300m across the massifs this number is insufficient to substantially offset topographic lowering due to regional denudation and we conclude that the isostatic response to glacial valley carving has not increased peak elevations significantly

the diversion capacity of capillary barriers an arrangement of unsaturated fine grained soil overlying unsaturated coarse grained soil along a sloping contact can under appropriate circumstances divert infiltrating water away from the coarser material such an arrangement is called a capillary barrier the water diverted by a capillary barrier flows downdip above the contact the volume of water moving laterally increases in the downdip direction as additional infiltration is diverted by the barrier sufficiently far downdip the laterally moving water wets the contact to the point that an amount of water equal to the infiltration flows downward through the coarse soil the lateral flow at such a point represents the diversion capacity of the capillary barrier because this flow will not increase farther downdip if the width measured in the direction of dip of the system is large enough that total infiltration exceeds the diversion capacity the downdip portion of the barrier will not be effective the diversion capacity can be calculated exactly in the quasi linear approximation where the relationship between relative permeability krel and pressure potential takes the form krel e this calculation shows that an upper bound on the width of capillary barriers is ks tan o q where ks is the saturated hydraulic conductivity of the fine soil o is the dip angle of the contact and q is the infiltration rate

bedrock channel incision along piccaninny creek australia piccaninny creek in northwestern australia drains approximately 60 km 2 of high relief sandstone and conglomerate terrain the drainage basin lies within the seasonal tropics and is characterized by ephemeral high magnitude flows flood flows of 50 to 100 m 3 s 1 are probably primarily responsible for the spectacular erosional features along the bedrock channel segments of the creek these erosional features occur in two basic forms as parallel longitudinal grooves and as a downstream sequence that begins with shallow linear depressions parallel to flow and ends in a deep narrow inner channel the longitudinal grooves are assumed to result from longitudinal vortices while the erosional sequences which closely resemble von karman vortex streets are interpreted to result from turbulent vortices shed off irregularities of the channel bed the longitudinal grooves and the inner channel sequence alternate with each other and with gravel floored depositional reaches downstream along the channe

lightning as a geomorphic agent on mountain summits evidence from southern africa abstract the presence of angular bedrock derived debris on mountain summits worldwide has usually been associated with present or past periglacial frost shattering thermal fracturing and other climatically mediated weathering processes climatic inferences are commonly made based on such geomorphological evidence even if frost shattering and other processes are unlikely under present climatic conditions this paper questions this assumed genetic link between present past climate and production of angular bedrock derived debris by describing the geomorphological impacts of lightning strikes on exposed mountain summits using examples from the high drakensberg of eastern lesotho southern africa the impacts of lightning strikes are described which include the generation of angular fractured bedrock derived debris these impacts are identified in the field based on clear and unambiguous criteria that can be used to distinguish between lightning induced weathering processes and those processes associated with more typical alpine weathering this paper argues that lightning strikes are an important geomorphic agent of in particular low latitude mountain summits and that to make uncritical climatic inferences based on the presence of frost shattered debris on mountain summits is wholly erroneous

relief rejuvenation and topographic length scales in a fluvial drainage basin napf area central switzerland this paper explores how and to what extent a phase of relief rejuvenation modifies the mode of surface erosion in an approximately 63 km2 drainage basin located at the northern border of the swiss alps luzern area in the study area the retreat of the alpine glaciers at the end of the last glacial maximum lgm caused base level to lower by approximately 80 m the fluvial system adapted to the lowered base level by headward erosion this is indicated by knickzones in the longitudinal stream profiles and by the continuous upstream narrowing of the width of the valley floor towards these knickzones in the headwaters above these knickzones processes are still to a significant extent controlled by the higher base level of the lgm there frequent exposure of bedrock in channels and especially on hillslopes implies that sediment flux is to a large extent limited by weathering rates in the knickzones however exposure of bedrock in channels implies that sediment flux is supply limited and that erosion rates are controlled by stream power the morphometric analysis reveals the existence of length scales in the topography that result from distinct geomorphic processes along the tributaries where the upstream sizes of the drainage basins exceed 100 000 200 000 m2 the mode of sediment transport and erosion changes from predominantly hillslope processes i e landsliding creep of regolith rock avalanches and to some extent debris flows to processes in channels fluvial processes and debris flows this length scale reflects the minimum size of the contributing area for channelized processes to take over in the geomorphic development i e threshold size of drainage basin this threshold size depends on the ratio between production rates of sediment on hillslopes and export rates of sediment by processes in channels consequently in the headwaters erosion rates and sediment flux and hence landscape evolution rates are to a large extent limited by weathering processes in contrast in the lower portion of the drainage basin that adjusts to the lowered base level rates of channelized erosion and relief formation are controlled mainly by stream power hence this paper shows that base level lowering headward erosion and establishment of knickzones separate drainage basins in two segments with different controls on rates of surface erosion sediment flux and relief formation

weathering profile of non welded ignimbrite and the water infiltration behavior within it in relation to the generation of shallow landslides the mechanism underlying rain induced shallow landslides of non welded ignimbrite is found to be a special type of weathering profile and the behavior of water infiltrating through that profile according to our study of ito ignimbrite in southern kyushu japan rhyolitic volcanic glass the primary component of ignimbrite is first hydrated and dissolved forming halloysite halloysite near ground surface is then transported through the ignimbrite by infiltrating water and becomes clogged in interstices to form clay bands suction monitoring across a weathering profile indicated that downward infiltration of water is disrupted once by a zone of less permeable clay bands and again at the weathering front this disruption at the front is caused by a capillary barrier effect caused by the structure where finer weathered material overlies coarser fresh material this results in a well defined weathering front particularly beneath a slope where water flux is parallel to the front whereas the front is transitional beneath a ridge top where the front is nearly horizontal and the water flux is normal to the front infiltrating water from rain increases the weight of weathered material and decreases the suction within the material which is the final trigger of a shallow landslide of non welded ignimbrite long term weathering which proceeds on the order of years provides slide material

lateral sediment sources and knickzones as controls on spatio temporal variations of sediment transport in an alpine river modern mixed alluvial bedrock channels in mountainous areas provide natural laboratories for understanding the time scales at which coarse grained material has been entrained and transported from their sources to the adjacent sedimentary sink where these deposits are preserved as conglomerates this article assesses the shear stress conditions needed for the entrainment of the coarse bed particles in the glogn river that drains the 400 km2 val lumnezia basin eastern swiss alps in addition quantitative data are presented on sediment transport patterns in this stream the longitudinal stream profile of this river is characterized by three ca 500 m long knickzones where channel gradients range from 0 02 to 0 2 m m 1 and where the valley bottom confined into a 10 m wide gorge downstream of these knickzones the stream is flat with gradients 0 01 m m 1 and widths 30 m measurements of the grain size distribution along the trunk stream yield a mean d84 value of ca 270 mm whereas the mean d50 is ca 100 mm the consequences of the channel morphology and the grain size distribution for the time scales of sediment transport were explored by using a one dimensional step backwater hydraulic model hydrologic engineering centre river analysis system the results reveal that along the entire trunk stream a two to 10 year return period flood event is capable of mobilizing both the d50 and d84 fractions where the shields stress exceeds the critical shields stress for the initiation of particle motion these return periods however varied substantially depending on the channel geometry and the pebble boulder size distribution of the supplied material accordingly the stream exhibits a highly dynamic boulder cover behaviour it is likely that these time scales might also have been at work when coarse grained conglomerates were constructed in the geological past

mechanism and effect of chemical weathering of sedimentary rocks the mineralogy geochemistry and physical and mechanical properties of rocks from four weathering profiles of miocene to pleistocene mudstones and sandstones in japan showed that chemical weathering of sedimentary rocks is characterized by sequential reaction between percolating groundwater and rock forming minerals pyrite a common mineral contained in sedimentary rocks is especially important in these sequential reactions pyrite is oxidized by oxygen coming from the ground surface and sulfuric acid is generated at the base of the oxidized zone the sulfuric acid in turn dissolves rock forming materials to make a dissolved zone if the fluxes of oxygen and water are in the same direction sulfuric acid generated at the oxidation front migrates farther and forms a dissolved zone if these fluxes are in opposite directions the oxidized and dissolved zones are not differentiated rocks in the dissolved zone are caused to deteriorate by the acid leaching and are acidic if buffering minerals such as calcite and zeolite are absent in the oxidized zone sandstone is strengthened because of cementation by iron oxide or hydroxide while mudstone is weakened because it has greater clay fractions and larger specific surface areas than sandstone

weathering indices for rhyolitic tuff and granite in hong kong a series of chemical analyses and dry density tests of rhyolitic tuff and granitic samples have been carried out the test results have been interpreted using a newly developed theoretical weathering model for calculating a mobility index of major elements in rock and soil it is found that this index is useful for describing changes of rock and soil during weathering and classifying the degrees of weathering based on the theoretical model a new parameter called the volume index which combines chemical and physical data is suggested this index appears to be a good indicator for classifying the degree of weathering in hong kong a quantitative classification scheme is suggested

meteorological controls on glacier mass balance empirical relations suggested by measurements on glacier de sarennes france glacial mass balance reconstruction for a long term time scale requires knowledge of the relation between climate change and mass balance fluctuations a large number of mass balance reconstructions since the beginning of the century are based on statistical relations between monthly meteorological data and mass balance the question examined in this paper is are these relationships reliable enough for long term time scale extrapolation from the glacier de sarennes long mass balance observations series we were surprised to discover large discrepancies between relations resulting from different time periods the importance of the albedo in relation to ablation and mass balance is highlighted and it is shown that it is impossible to ignore glacier surface conditions in establishing the empirical relation between mass balance fluctuations and climatic variation to omit this parameter leads to incorrect results for mass balance reconstruction in the past based on meteorological data

fluvial incision into bedrock insights from morphometric analysis and numerical modeling of gorges incising glacial hanging valleys western alps france bedrock gorges incising glacial hanging valleys potentially allow measurements of fluvial bedrock incision in mountainous relief using digital elevation models topographic maps and field reconnaissance we identified and characterized 30 tributary hanging valleys incised by gorges near their confluence with trunk streams in the romanche watershed french western alps longitudinal profiles of these tributaries are all convex and have abrupt knickpoints at the upper limit of oversteepened gorge reaches we reconstructed initial glacial profiles from glacially polished bedrock knobs surrounding the gorges in order to quantify the amount of fluvial incision and knickpoint retreat from morphometric analyses we find that mean channel gradients and widths as well as knickpoint retreat rates display a drainage area dependence modulated by bedrock lithology however there appears to be no relation between horizontal retreat and vertical downwearing of knickpoints assuming a postglacial origin of these gorges our results imply high postglacial fluvial incision 0 5 15 mm yr 1 and knickpoint retreat 1 200 mm yr 1 rates that are however consistent with previous estimates numerical modeling was used to test the capacity of different fluvial incision models to predict the inferred evolution of the gorges results from simple end member models suggest transport limited behavior of the bedrock gorges a more sophisticated model including dynamic width adjustment and sediment dependent incision rates predicts present day channel geometry only if a significant supply of sediment from the gorge sidewalls 10 mm yr 1 is triggered by gorge deepening combined with pronounced inhibition of bedrock incision by sediment transport and deposition

morphologically based model of bed load transport capacity in a headwater stream 1 field measurements of channel and bed material properties are used to develop a network based model of bed load transport capacity in halfmoon creek a high gradient stream in the rocky mountains of colorado the formerly glaciated watershed contains self formed reaches that are generally disconnected from hillslopes and major sediment perturbations strung together by a sequence of bedrock and cascade channels measurements of channel geometry slope and bed sediment texture surface and substrate were taken in 27 reaches with gradients ranging from 0 6 to 6 to examine interactions among key variables affecting bed load transport the analysis shows that the grain size distribution of the substrate is relatively uniform throughout the basin however the distinction between surface and substrate texture varies systematically with channel gradient and shear stress reaches with high shear stress are characterized by coarse surface layers with a high threshold for transport limiting the mobility of the sediment supplied in reaches with lower gradient and shear stress the difference between surface and substrate texture is less increasing both the frequency of transport and the mobility of the bed load while it might appear that the steeper reaches of halfmoon creek have a high capacity for carrying fine medium gravel the relative mobility of these sizes is affected by the presence of very coarse sediment on the bed surface as a result modeled estimates of bed load transport rate indicate that average annual bed load sediment yields increase downstream nearly linearly with discharge suggesting a simple scaling of bed load transport capacity with discharge and drainage area

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

water percolating behavior indicated by the water chemistry within a decomposed granite slope central japan abstract monitoring rainfall discharge amount and the chemistry of water from just beneath the groundwater table yielded a conceptual model of water percolation behavior within a decomposed granite slope in central japan providing a clue to evaluate a landslide hazard potential by rainstorms when rainfall is strong enough more than about 50 mm a day in this case air pressure in the vadose zone probably increases temporarily because of the downward movement of a wetting front pushing down the water of the capillary fringe the capillary water has sio2 concentrations controlled by the precipitation of cristobalite the water is rich in ca which is supplied from plagioclase with sio2 after the pushing down of the capillary water rainwater with soil water in the unsaturated zone reaches the groundwater surface the cation concentrations in the unsaturated soil water and the capillary water are affected by ion exchange

high altitude varve records of abrupt environmental changes and mining activity over the last 4000 years in the western french alps lake bramant grandes rousses massif abstract two twin short gravity cores and a long piston core recovered from the deepest part of proglacial lake bramant grandes rousses massif french alps under and overlying a large slump identified by high resolution seismic profile allow the investigation of holocene natural hazards and interactions between human activity and climatic changes at high altitude annual sedimentation throughout the cores glacial varves is identified on photographs itrax high resolution continuous microfluorescence x and cat scan computerized axial tomography analyses and is supported by 1 the number of dark and light laminations between dates obtained by radionuclide measurements 137cs 241am 2 the correlation of a slump triggered by the nearby ad 1881 allemond earthquake msk intensity vii and of a turbidite triggered by the ad 1822 chautagne regional earthquake msk intensity viii 3 the number of laminations between two accelerator mass spectrometry ams 14c dates and 4 archaeological data in lake bramant dark layers are coarser contain less detrital elements but more neoformed elements and organic matter content these darker laminations result from calm background sedimentation whereas the lighter layers are finer and rich in detrital elements and reflect the summer snowmelt traces of mining activity during the roman civilization apogee ad 115 330 and during the early bronze age 3770 3870 cal bp are recorded by lead and copper content in the sediments and probably result from regional and local mining activity in the nw alps warmer climate during the bronze age in this part of the alps is suggested by 1 two organic deposits 4160 3600 cal bp and 3300 2850 cal bp likely reflecting a lower lake level and smaller glaciers and 2 evidence of a different vegetation cover around 2500 m a s l the onset of clastic proglacial sedimentation between 3600 3300 cal bp and since 2850 cal bp is synchronous with periods of glacier advances documented in the alps and high lake levels in west central europe this major change in proglacial sedimentation highlights the development of a larger st sorlin glacier in the catchment area of lake bramant

water flow in unsaturated soil in layered slopes abstract the water flow in unsaturated soil in layered slopes sandwiching coarse materials was measured using inclined soil containers placed under a rain simulator the refraction law of water flow in saturated soils was extended to the flow in unsaturated soils the extended refraction law of water flow in saturated and unsaturated soils was applied to the flow at the interface between the masa sandy loam and either the plant or gravel layer using a jump condition and particular assumptions of hydraulic conductivity of materials the data obtained on infiltration steady percolation and drainage in the soil containers could be well explained by the proposed new concept of saturated and unsaturated refraction flow so far as we know the work reported here is the first specifically designed to elucidate the effects of abrupt change of hydraulic conductivity on the flow of water in unsaturated soil slopes

a framework for unsaturated soil behaviour a framework is put forward which explains the shear behaviour of an unsaturated soil in terms of the total stresses and suctions acting within the soil it is based on the critical state model for

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

lithological controls on hydrological processes that trigger shallow landslides observations from granite and hornfels hillslopes in hiroshima japan abstract a comprehensive understanding of landslide processes is critical in explaining the spatial distribution of shallow landslides and rainfall thresholds for triggering landslides under different bedrock conditions here we discuss the observed shallow landslide mechanisms on adjacent granite and hornfels hillslopes in northern hiroshima city western japan the thickness structure and geotechnical properties of the shallow subsurface materials were characterized via field based surveys and laboratory experiments the observed pore water pressure responses in the soil layer due to rainfall infiltration were monitored using tensiometers in the granite hillslopes the rapid percolation of rainwater from the near surface high permeability sandy soil to the low permeability saprolite at depth and the limited water storage capacity of the saprolite led to the development of a saturated zone that extended upward from the base of the soil layer the cohesionless soils in the granite hillslopes can slip along the boundary between the weak upper layer and stiff lower layer once this boundary experiences weak positive pore fluid pressure as the perched water table rises from the underlying saprolite boundary conversely the hornfels hillslopes are covered by cohesive soils in which permeability decreases with depth which contributes to the formation of a perched groundwater body above the lower soil layer when a large positive pressure acts on the potential sliding surface the upper soil layer can slip along the hydraulic and mechanical discontinuity between two soil layers in the hornfels hillslopes these results indicate that the underlying bedrock lithology controls the subsurface structures that shape the hydraulic and mechanical properties of the hillslope materials as well as their subsurface hydrological processes which in turn influence the potential for shallow landslides

paleohydraulic reconstruction of a 40 ka old terrace sequence implies that water discharge was larger than today the evolution of landscapes crucially depends on the climate history this is particularly evident in south america where landscape responses to orbital climate shifts have been well documented however while most studies have focused on inferring temperature variations from paleoclimate proxy data estimates of water budget changes have been complicated because of a lack of adequate physical information here we present a methodology and related results which allowed us to extract water discharge values from the sedimentary record of the 40 ka old fluvial terrace deposits in the pisco valley western peru in particular this valley hosts a quaternary cut and fill succession that we used in combination with beryllium 10 10be based sediment flux gauging records channel geometries and grain size measurements to quantitatively assess sediment and water discharge values c 40 ka ago in relation to present day conditions we compare these discharge estimates to the discharge regime of the modern pisco river and find that the water discharge of the paleo pisco river during the minchin pluvial period c 40 ka ago was c 7 8 times greater than the modern pisco river if considering the mean and the maximum water discharge in addition the calculations show that inferred water discharge estimates are mainly dependent on channel gradients and grain size values and to a lesser extent on channel width measures finally we found that the c 40 ka old minchin terrace material was poorer sorted than the modern deposits which might reflect that sediment transport during the past period was characterized by a larger divergence from equal mobility compared to the modern situation in summary the differences in grain size distribution and inferred water discharge estimates between the modern and the paleo pisco river suggests that the 40 ka old minchin period was characterized by a wetter climate and more powerful flood events

alluvial cover dynamics in response to floods of various magnitudes the effect of the release of glaciogenic material in a swiss alpine catchment abstract fluvial incision into formerly glaciated landscapes is commonly affected by the release of glaciogenic sediments from the hillslopes via landsliding hillslope failure and debris flow activity these deposits typically comprise abundant block size clasts here we determine the ability of the fluvial processes to evacuate glacially derived sediments in an alpine hanging valley blanketed by 100 m thick glacial till we assess along stream profiles of basal shear stress during annual decadal and centennial floods by means of the hydrological model hec ras we use bed surface grain size data to i evaluate the shields stress profiles for these floods ii determine at which timescale the bed undergoes significant changes and to iii predict transport capacity patterns for each flood in addition we present digital photogrammetry based estimates of bed elevation changes over two selected time intervals that experienced low and high magnitude floods respectively the results indicate that floods with return periods of 10 years are capable of mobilizing the coarse fraction of the bed material thereby substantially altering the channel geometry the predicted near critical shields stress values for these floods in the area where the glacial deposits are thickest suggest a strong hillslope channel coupling which may have resulted in the formation of the knickzone observed in this sector however decadal to centennial floods are required to transport the material over long distances and scour the bed in the upper part of the inner gorge in addition the observed downstream trend from bed scouring to deposition in the inner gorge for these floods and the opposite trend for low magnitude floods suggest that these patterns are not directly controlled by downstream variations of transport capacity we propose that the supply of sediment through hillslope failure and bank collapse significantly contributes to the sediment flux for high magnitude floods we conclude that the morphology and the timescale of sediment transport in this glacially conditioned landscape have been substantially controlled by the hillslope derived supply of coarse grained material

bedrock benches and boulder bars floods in the burdekin gorge of australia the burdekin gorge of northeastern australia lies within the seasonal tropics and is characterized by high discharge variability slackwater sediments and paleostage indicators in the gorge record seven large floods that have occurred during the past 1 200 yrs these floods range in magnitude from 11 000 to 30 000 m 3 s 1 and are characterized by large downstream variations in hydraulics the floods generate high values of velocity boundary shear stress and stream power per unit area downstream fluctuations in these variables help to explain the location of boulder bars high flood levees small scale erosional features in the bedrock and the formation of inner channels boulder bars and flood levees form where shear stress and stream power decrease due to channel widening small scale erosional features such as potholes and troughs are best developed at sites of channel constriction and associated increases in shear stress and stream power the development of the inner channel appears to be controlled by complex interactions between bedrock lithology and structure and by flow hydraulics all of the channel features are related to the hydraulics of large floods which therefore are the dominant controls on many aspects of channel morphology in this bedrock gorge

flood magnitude frequency and lithologic control on bedrock river incision in post orogenic terrain abstract mixed bedrock alluvial rivers bedrock channels lined with a discontinuous alluvial cover are key agents in the shaping of mountain belt topography by bedrock fluvial incision whereas much research focuses upon the erosional dynamics of such rivers in the context of rapidly uplifting orogenic landscapes the present study investigates river incision processes in a post orogenic cratonic landscape undergoing extremely low rates of incision the mobility of coarse bed materials up to 2 m diameter during late holocene palaeofloods of known magnitude and age is evaluated using step backwater flow modelling in conjunction with two selective entrainment equations a new approach for quantifying the formative flood magnitude in mixed bedrock alluvial rivers is described here based on the mobility of a key coarse fraction of the bed materials in this case the d84 size fraction a 350 m3 s formative flood fully mobilises the coarse alluvial cover with b 200 300 n m2 across the upper and lower gorge riffles peaking over 500 n m2 in the knickzone such floods have an annual exceedance probability much less than 10 2 and possibly as low as 10 3 the role of coarse alluvial cover in the gorge is discussed at two scales 1 modulation of bedrock exposure at the reach scale coupled with adjustment to channel width and gradient accommodates uniform incision across rocks of different erodibility in steady state fashion and 2 at the sub reach scale where coarse boulder deposits corresponding to b minima cap topographic convexities in the rock floor thereby restricting bedrock incision to rare large floods while recent studies postulate that decreasing uplift rates during post orogenic topographic decay might drive a shift to transport limited conditions in river networks observations here and elsewhere in post orogenic settings suggest to the contrary that extremely low erosion rates are maintained with substantial bedrock channel exposure although bed material mobility is known to be rate limiting for bedrock river incision under low sediment flux conditions exactly how a partial alluvial cover might be spatially distributed to either optimise or impede the rate of bedrock incision is open to speculation observations here suggest that the small volume of very stable bed materials lining sandy creek gorge is distributed so as to minimise the rate of bedrock fluvial incision over time

weathering distribution in a steep slope of soft pyroclastic rocks as an indicator of slope instability abstract weathering of rocks on steep slopes influences slope instability and sometimes leads to slope failure during heavy rainfall to determine the weathering intensity of hillslope rocks and its inward change from the slope surface measurements of the penetrative hardness of rocks which correlates with their strength were made in some slopes composed of soft pyroclastic rocks on kyushu island japan a gradual reduction in hardness from the interior to the slope surface was recognized within slopes the hardness change was almost concordant with changes in other weathering indices such as rock color clay minerals and apparent grain size the weathered zone indicated by the reduction in hardness was 1 2 m thick at the foot of steep slopes which are frequently subjected to gullying and surface failures whereas the zone was 7 8 m thick at slope summits which are gentle and stable for a long period although the inward change in hardness was gradual on all parts of a slope the change was marked on the foot slope where the strength contrast between weathered and non weathered rock was greater the thickness of the weathered zone on the foot slope therefore controls the volume of failed materials when a failure occurs the difference in weathered thickness between the foot and the summit of a slope much affects the style of failure in general and consequently shapes the characteristic configuration of slopes in this region the estimated weathering rate on a slope surface based on hardness distribution was on the order of 10 2 to 100 cm year 1 assuming a constant rate this rate is far greater than that of other rocks therefore the frequent occurrence of slope failures in this region was attributed to this rapid weathering

chemical weathering mechanisms and their effects on engineering properties of soft sandstone and conglomerate cemented by zeolite in a mountainous area abstract sandstone and conglomerate cemented by zeolite crystals in a humid mountainous area in japan are weathered and also weakened or strengthened by chemical interaction with percolating water that was originally in equilibrium with the atmosphere near the ground surface carbonic acid generated by the dissolution of carbon dioxide from the atmosphere and biological activity in the soil dissolves zeolite and thereby weakens the rocks at the oxidation front the base of the oxidized zone oxygen from the atmosphere reacts with pyrite in the rock to form sulfuric acid and iron oxide and or hydroxide the iron oxide and or hydroxide precipitates on zeolite surfaces and strengthens the rocks by cementing the grains to each other beneath the oxidation front and extending to the dissolution front sulfuric acid migrates downward dissolves zeolite and thus weakens the rocks this weathering mechanism and the resulting changes in mechanical properties of rocks generally are to be expected in marine sandstone and conglomerate with small amounts of clay in the matrix because the most common cementing mineral is carbonate which is also easily dissolved by acid and further because pyrite is a common rock forming mineral in marine sedimentary rocks the effects of chemical weathering on the mechanical properties of sandstone and conglomerate are different from those of mudstone because the latter contains much larger amounts of clay minerals the cementation of constituent grains by iron oxide and or hydroxide is inhibited by clay minerals because clay minerals have high specific surface areas and also because large amounts of iron can be incorporated in the minerals

are icelandic rock slope failures paraglacial age evaluation of seventeen rock slope failures in the skagafjorður area based on geomorphological stacking radiocarbon dating and tephrochronology in iceland there are numerous rock slope failures especially in the tertiary basaltic formations of the northern eastern and northwestern regions the temporal pattern of rock slope failures is fundamental for understanding post glacial events in the skagafjor ur district central northern iceland 17 rock slope failures were investigated to determine the age of their occurrence a geomorphic survey was carried out to identify and characterize landform units both on the rock slope failures and in their immediate vicinity in this coastal area we used geomorphological stacking which included the relationship between rock slope failures and raised beaches caused by glacial isostatic rebounds the chronology of which was established in previous studies we searched for depressions on the rock slope failures to then excavate a series of pits and map the stratigraphy the resulting stratigraphic framework was then validated using i radiocarbon dating of wood remains and ii tephrochronology both of which were complemented by age depth model calibration the results confirm that all the rock slope failures potentially occurred before the boreal 8 ka while 94 occurred before the preboreal 10 ka they all potentially occurred after the glacial retreat following the maximal ice extent and the preboreal more precisely 11 of them potentially occurred between the preboreal and the first half of the holocene this study demonstrates the relationship between the deglaciation and destabilization of slopes during the paraglacial phase debuttressing decompression glacial isostatic rebound seismic activity etc which are also controlling factors favouring landsliding but are difficult to identify for each individual rock slope failure

testing for reach scale adjustments of hydraulic variables to soluble and insoluble strata buckeye creek and greenbrier river west virginia abstract an open question exists as to whether channel geometries and hydraulics are adjusted in bedrock streams with stable concave profiles in a manner analogous to alluvial rivers as a test of this problem a comparison was undertaken of channel geometries and hydraulics among reaches with substrates that are of high mechanical resistance but of variable chemical resistance reaches were selected from buckeye creek and greenbrier river west virginia usa because these streams flow over sandstones limestones and shales the limestones have selby rock resistance scores similar to those of the sandstones a total of 13 reaches consisting of between 6 and 26 cross sections were surveyed in the streams hec ras was used to estimate unit stream power and shear stress for each reach the reaches were selected to evaluate the null hypothesis that that and are equal atop soluble versus insoluble bedrock hypothesis tests consisted of paired t tests and simultaneous multiple comparisons geomorphic setting was included for greenbrier river because previous studies have suggested that bedrock streams are intimately coupled with hillslopes holding geomorphic setting constant three separate comparisons of and reveal that these variables are lowest atop soluble substrates in greenbrier river significance 0 05 and that changes in and are mediated by changes in channel geometry similarly headwater reaches of buckeye creek developed atop shale and sandstone boulders are statistically distinguishable from downstream reaches wherein corrosion of limestone is the primary means of incision however comparisons in each stream reveal that channel geometries and are not strictly controlled by bed solubility for constant substrate solubility along the greenbrier river and are consistently higher where a bedrock cutbank is present or coarse insoluble sediment enters the channel the latter is also associated with locally high values of and in buckeye creek assuming that incision by corrosion requires lower values of and because the channel need not be adjusted for block detachment and tool acceleration we posit that the statistically lower values of and are tentative evidence in favor of differential geometric and hydraulic adjustments to substrate resistance we observe that these adjustments are not made independent of geomorphic setting

indication of active overthrust faulting along the holocene wisconsin transition in the marginal zone of jakobshavn isbrae 1 a zone of highly irregular ice motion has been detected within the ice sheet adjacent to jakobshavn isbrae a fast moving ice stream in west greenland two tilt sensors in different boreholes and frozen into the ice show angle variations of up to 0 1 and 0 3 within a 1200 s interval the amplitude of these flutter oscillations increases toward the transition from holocene to wisconsin ice at 682 m depth 150 m above bedrock all other tilt sensors above and below show low background noise a numerical model confirms that the stress configuration is exceptional in the neighborhood of the ice stream stress transfer from the ice stream to the margins causes an extra forcing of the basal ice at the drill site several possible explanations for the observed flutter oscillations are given the most likely being dynamic rupture events or stick slip motion along the holocene wisconsin transition if true this would correspond to an active overthrust fault with very high loading rates

a systematic analysis of eight decades of incipient motion studies with special reference to gravel bedded rivers data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size t c 50 calculated t c 50 values were stratified by initial motion definition median grain size type surface subsurface or laboratory mixture relative roughness and flow regime a traditional shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition t c 50 values determined from reference bed load transport rates and from visual observation of grain motion define subparallel shields curves with the latter generally underlying the former values derived from competence functions define a separate but poorly developed field while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous rather than time averaged critical shear stresses the available data indicate that for high critical boundary reynolds numbers and low relative roughnesses typical of gravel bedded rivers reference based and visually based studies have t c50 ranges of 0 052 0 086 and 0 030 0 073 respectively the apparent lack of a universal t 50 for gravel bedded rivers warrants great care in choosing defendable t c50 values for particular applications

modeling fluvial incision and transient landscape evolution influence of dynamic channel adjustment 1 channel geometry exerts a fundamental control on fluvial processes recent work has shown that bedrock channel width depends on a number of parameters including channel slope and is not solely a function of drainage area as is commonly assumed the present work represents the first attempt to investigate the consequences of dynamic gradient sensitive channel adjustment for drainage basin evolution we use the channel hillslope integrated landscape development child model to analyze the response of a catchment to a given tectonic perturbation using as a template the topography of a well documented catchment in the footwall of an active normal fault in the apennines italy that is known to be undergoing a transient response to tectonic forcing we show that the observed transient response can be reproduced to first order with a simple detachment limited fluvial incision law transient landscape is characterized by gentler gradients and a shorter response time when dynamic channel adjustment is allowed the differences in predicted channel geometry between the static case width dependent solely on upstream area and dynamic case width dependent on both drainage area and channel slope lead to contrasting landscape morphologies when integrated at the scale of a whole catchment particularly in presence of strong tilting and or pronounced slip rate acceleration our results emphasize the importance of channel width in controlling fluvial processes and landscape evolution they stress the need for using a dynamic hydraulic scaling law when modeling landscape evolution particularly when the relative uplift field is nonuniform

stable channels with mobile gravel beds regime type equations for mobile gravel bed rivers are presented based on data obtained from 62 stable gravel bed river reaches in the united kingdom multiple regression techniques are applied to derive equations relating reach average and riffle values of width mean and maximum depth slope velocity sinuosity and riffle spacing to bankfull discharge bed and bank material characteristics valley slope bank vegetation type and an independent estimate of bankfull bed load transport rates although discharge has a dominant control on channel geometry these equations indicate that bed load discharge also has a significant influence particularly with regard to channel slope bank vegetation has a major control on width and velocity while depth velocity and slope are storngly affected by bed material size reasons for these results are considered in terms of the physical processes controlling channel adjustment the application of these regime equations is discussed and particular consideration is given to the design of sinuous channels with a pool riffle bed topograph

weathering and mineralogical variation in gneissic rocks and their effect in sangrumba landslide east nepal sangrumba landslide is one of the largest and the most active landslides in nepal himalaya geologically the landslide belongs to the higher himalaya and consists of pre cambrian biotite garnet and sillimanite gneiss with some quartzite the present paper aims at describing various degrees of rock weathering and their effect in sangrumba landslide field study followed by mineralogical geochemical and geotechnical analyses of the collected rock and soil samples from the landslide zone were used in characterizing weathering degree the gneisses are intensely weathered while quartzite is unweathered petrographical and x ray diffraction analyses showed that the rocks in the landslide zone had undergone weathering process with the formation of different types of clay minerals as kaolinite vermiculite smectite and chlorite this was further confirmed by the scan electron microscope and energy dispersive x ray analyses these clay minerals drastically reduced the rock strength facilitating the extensive failure of the sangrumba landslide the major and trace element composition of the rock and soil samples was calculated from the xrf analyses the geochemical analyses and weathering indexes of rocks showed that they are significantly weathered and had a major influence in the formation of the sangrumba landslide in addition mechanical strength measurement of rock soil showed that the strength drastically decreases as the weathering intensity increases rainfall followed by the rock type are the most dominant parameters influencing the weathering process which leads to the formation of large landslide as the present one these findings can be used in other areas with similar geological and topographical conditions

coupling between hillslopes and channels in upland fluvial systems implications for landscape sensitivity illustrated from the howgill fells northwest england abstract the sensitivity of upland fluvial systems depends on the magnitude and frequency of sediment and flood producing events modified by the internal coupling characteristics of the system this paper assesses the role of hillslope channel coupling for the sensitivity of upland geomorphic systems using evidence from a 30 year monitoring programme of geomorphic change in the carlingill valley howgill fells northwest england in the hillslope zone there is little sediment supply to the stream system locally slope failures occur in response to extreme events six such events in 30 years within the ca 6 km 2 carlingill valley in the footslope coupling zone basally induced gullies are major sediment sources to the stream sediment production events occur ca 30 times per year feeding sediment to basal debris cones stream floods which can entrain these sediments occur once every ca 2 5 years stream channel morphology is adjusted to this regime downstream of gullies channels are wide and braided elsewhere they are narrow and single thread as the gullies develop however this coupling weakens and the eroding slopes eventually stabilise by revegetation over the 30 year monitoring period there has been a progressive trend towards gully stabilisation and an associated reduction in channel instability massive destabilisation may occur in response to rare extreme flood events such an event return period 100 years occurred in neighbouring langdale and bowderdale valleys in june 1982 that event destabilised the system causing slope failures fan deposition and in some places a switch in channel style to wide braided channels since 1982 there has been a progressive recovery by slope stabilisation and single thread sinuous channels have become reestablished a different style of extreme event occurred in carlingill in october 1998 in response to the wettest week in the 30 year period a slope failure fed debris flows 400 m downslope almost coupling with the channel system future climatic change could render the system prone to destabilisation through either extreme flood events or through major slope failures

pleistocene holocene climate change re establishment of fluvial drainage network and increase in relief in the swiss alps abstract data are presented about modern sediment discharge of the swiss rivers and related to the size of catchments the information reveals that the central alps have experienced denudation rates of 0 15 mm yr 1 in the foreland and 0 5 mm yr 1 in the alpine core mapping however indicates that modern erosion only affects 30 50 of the alpine surface and that fluvial and associated hillslope processes have focused erosion in 50 200 m deep valleys these valleys are incised into the glacial surface if this limited spatial extent of erosion is considered then effective erosion rates are significantly higher than average denudation rates these effective rates equal or locally exceed modern rates of rock uplift this implies that the modification of erosional processes related to the pleistocene holocene climate change has resulted in an increase in the relief at a local scale at a drainage basin scale however the relief appears not to change at present

slope instability in relation to glacial debuttressing in alpine areas upper durance catchment southeastern france evidence from field data and 10be cosmic ray exposure ages the upper durance catchment is an area prone to rock slope failures such failures reflect the combination of high relief litho structural controls and paraglacial stress release the aim of this study is to determine the role of deglacial unloading and resulting paraglacial stress release in conditioning or triggering slope failure former dimensions of the durance glacier are reconstructed then combined with digital elevation model data in a raster geographic information system to quantify the spatial pattern of stresses associated with glacial loading at the last glacial maximum preliminary calculations suggest that major rock falls and rock avalanches are associated with areas subject to the highest decompression stresses focus on two case studies allows the consequences of paraglacial stress release on slope instability to be evaluated description of slope failure runout deposits allows reconstruction of the nature of slope failure surface exposure dates based on concentration of cosmogenic 10be allows the timing of both deglaciation and that of post glacial rock slope failures to be established it is shown that rock slope failures are concentrated on lower valley side slopes within the area occupied by ice at the last glacial maximum and that their locations coincide with zones of inferred high glacial loading stress consistent with interpretation of both bedrock disruption and large scale rock slope failures as paraglacial phenomena induced by stress release following deglaciation timing of initial rock avalanche runout deposition at one site is consistent with this conclusion though later instability episodes at the same site may have occurred independent of the influence of paraglacial stress release

rates of weathering and temporal changes in strength of bedrock of marine terraces in boso peninsula japan the weathering rates of bedrock of the dated erosional marine terraces were examined for two definitions 1 the rates at which the thicknesses of weathered zones with different strengths increase with weathering time and 2 the rates at which the strength of weathered materials at an arbitrary depth decrease with time the bedrock of terraces in the study area consists mainly of tertiary sandstone and mudstone the weathering profiles were observed from drill cores on three levels of terrace surfaces i e 2850 290 and 70 years b p in the emergence age of terraces which is regarded as the weathering time of bedrock the degree of weathering grade was described by the residual strength ratio which is defined as the ratio of the needle penetration hardness of weathered part to that of fresh part of bedrock the weathering rates of the first definition do not decrease monotonically but decelerate logarithmically with time zones with lower weathering grades have faster weathering rates than those with higher weathering grades with respect to the weathering rates of the second definition mudstone starts to weather earlier than sandstone but is exceeded by the latter after a certain time has elapsed because mudstone has a higher slaking susceptibility

bedrock landsliding river incision and transience of geomorphic hillslope channel coupling evidence from inner gorges in the swiss alps 1 the formation of inner gorges cut into bedrock has been explained as relief rejuvenation by fluvial incision in response to rapid base level drop repeated glaciations frequent pore pressure driven landsliding focused at hillslope toes or catastrophic outburst flows from natural dam failures prominent inner gorges occur in soft mesozoic bundner schist and lower tertiary flysch units of the formerly glaciated alpenrhein catchment eastern swiss alps their channel and hillslope morphologies differ from basins characterized by strong glacial or landslide imprints while formally resembling the theoretically predicted transient response of detachment limited bedrock rivers to rapid base level fall by headward knickpoint migration assuming a postglacial onset of fluvial bedrock incision into a last glacial maximum surface in response to base level drop induced by downwasting of trunk valley glaciers requires downcutting rates e 20 mm yr 1 and requires hillslopes to adjust by frequent landsliding toward development of a threshold state we test this scenario using data on surface uplift geomorphometry geomorphic hillslope coupling and probabilistic slope stability models we find that adjustment of inner gorge walls through landsliding is mainly strength limited and structurally controlled and threshold conditions are restricted to the lower 25 of local hillslope relief mass movement processes on upper hillslopes remain largely decoupled from channel incision despite inferred postglacial specific sediment yields of 104 m3 km 2 yr 1 from the studied basins conversely several constraints imposed by fluvial bedrock detachment postglacial sediment yields and bedrock landsliding argue for a pre holocene origin for at least some of the inner gorges in the area this implies partial protection of fluvial gorge topography by subglacial sediment fill during the last wurm extensive glaciation and implies that glaciers were insufficient to fully eradicate fluvially sculpted bedrock topography this leads us to conclude that lithology and major climate oscillations should be considered as further alternative controls on inner gorge formation

geologic factors contributing to landslide generation in a pyroclastic area august 1998 nishigo village japan vertical contrasts in permeability particularly where permeable surface materials overlie impermeable materials that prohibit the downward infiltration of groundwater concentrate the groundwater and become an important focus of landslides that are triggered by intense rainfall just such a hydrogeological structure is present within the pyroclastics in nishigo village in fukushima prefecture japan where intense rainfall of 1200 mm in 6 days generated more than 1000 landslides in august 1998 three types of landslides occurred the first type occurred along the edges of small plateaus where horizontal beds of permeable ash scoria and pumice overlie impermeable mudflow deposits consisting of tuffaceous fines and andesite blocks and massive weakly consolidated ignimbrites the rainfall on the plateaus infiltrated downward first then laterally within the permeable beds finally gushing out at the plateau edges and triggering landslides the second type of landslide occurred where weathered tuff of the same ignimbrite was present with a slip surface at the base of the heavily weathered zone within this heavily weathered zone the tuff exfoliated into thin weak plates running parallel to the slope surface the third type of landslide involved failure of colluvium or ash that filled hollows this type occurred as a result of subsurface erosion caused by the groundwater infiltrating the superficial beds above the impermeable tuff

bar resistance in gravel bed streams at bankfull stage total flow resistance in gravel bed streams with high width depth ratios and low sinuosities is primarily a result of grain and bar roughnesses the relative importance of these two roughness elements has not been established the relative importance of grain and bar resistance is examined for 12 straight and divided gravel bed reaches at bankfull stage by using the keulegan equation to determine a resistance division of energy slope the remaining slope is assumed to represent the relative importance of bar resistance bar resistance accounts for 50 to 75 of the total resistance in these reaches calculated values of reach averaged bar slope correlate closely with field measurements of bar magnitude

extension of glacier de saint sorlin french alps and equilibrium line altitude during the little ice age glacier de saint sorlin french alps left terminal moraines at 1 3 2 9 and 3 7 km ahead of the present terminus according to proxy data and to historical maps these were formed in the 19th 18th and 17th centuries respectively a plateau at 2700 2625 m was then surrounded by ice but never became an accumulation area this fact shows that the equilibrium line altitude ela on the glacier never dropped below 2300 m the following simple models apply sufficiently to yield reliable estimations of past ela 1 a uniform and constant vertical gradient of the mass balance down to the terminus and 2 a plane bed with a slope of 8 5 and a uniform width then in a steady situation the accumulation area ratio is 1 2 compared to the mean for 1956 72 at the onset of the little ice age the balances were higher by 3 75 m ice a 1 and the ela was 400 m lower correlations between 1956 72 balances and meteorological data suggest that during the melting season the 0 c isotherm was about 800 m lower while the winter precipitation at low altitudes did not change these correlations may have been different in the past but an equal lowering of the ela and of the 0 c isotherm as assumed by several authors seems excluded

dynamic earth system and ecological controls of rainfall initiated landslides abstract rainfall initiated landslides continue to inflict damages and loss of life throughout the world processes and mechanisms revealed from hydrological geomorphic geotechnical pedological geological hydrochemical and biological investigations have advanced our understanding of these effects on slope stability however the interactions amongst these processes and attributes as they affect the initiation and propagation of landslides are not as well understood too often landslide studies are conducted from only one or at most two of these perspectives moreover while precipitation and hydrology are recognized as dynamic influences the earth system and ecological effects are often assumed to be static we assess the interplay of these processes related to landslides triggered by positive pore water accretion and loss of soil suction each of these conditions arguably requires a different view on the processes that cause slope failure and predictive approaches this review starts from the perspective of dynamic adapting earth and ecological systems and discusses how these attributes relate to landslide initiation mode location and timing specifically the role that large and small scale preferential flow plays in both contributing to and mitigating instability is elucidated including effects of bedrock exfiltration we also examine how and under what conditions these pathways manifest in different soils lithology and landforms the multiple effects of rhizosphere processes on slope stability are discussed including root reinforcement evaporation from canopies and litter layers transpiration and the role of root structure affecting preferential flow paths rainfall initiated landslides involve highly dynamic hydrologic earth surface and ecological processes that persist over a range of spatial and temporal scales however guidance for overcoming these challenges has been elusive a conceptual framework is presented to shed light on these dynamic and interactive processes that should lend insights into why and when certain slopes fail during storms while other seemingly similar slopes do not fail such advances will benefit landslide hazard assessments and disaster responsiveness protocols

weathering profiles in granitoid rocks of the sila massif uplands calabria southern italy new insights into their formation processes and rates abstract in this paper we characterized several weathering profiles developed on granitoid rocks in the sila massif upland calabria southern italy integrating detailed macro and micromorphological observations with physico mechanical field tests and petrographic mineralogical and geochemical analyses we focused our attention on the main weathering and pedogenetic processes trying to understand apparent discrepancies between weathering grade classes based on field description and geomechanical properties and two common weathering indices such as the micropetrographic index ip and the chemical index of alteration cia our results showed that sericite on plagioclase and biotite chloritization that represent inherited features formed during late stage hydrothermal alteration of granitoid rocks may cause an overestimation of the real degree of weathering of primary mineral grains under meteoric conditions especially in lower weathering grade classes moreover the frequent identification of fe mn oxides and clay coatings of illuvial origin rather than or in addition to those formed in situ both at the macro and microscale may also explain an overestimation of the weathering degree with respect to field based classifications finally some apparent inconsistencies between field geomechanical responses and chemical weathering were interpreted as related to physical weathering processes cryoclastism and thermoclastism that lead to rock breakdown even when chemical weathering is not well developed hence our study showed that particular caution is needed for evaluating weathering grades because traditional field and geochemical petrographic tools may be biased by inherited hydrothermal alteration physical weathering and illuvial processes on the basis of chronological constraints to soil formation obtained from a 42 ka old volcanic input mixed to granite parent materials detected in the soil cover of the sila massif upland a first attempt to estimate soil formation rates was achieved for different depths of corresponding weathering profile zones soil formation rates ranged from 0 01 0 07 mm a 1 for a and bw horizons weathering class vi to 0 04 0 36 mm a 1 for the underlying saprolite c and cr layers class v by comparing these results with the corresponding erosion rates available in the literature for the study area that range from

structural composition and sediment transfer in a composite cirque glacier glacier de st sorlin france robserson s 2008 structural composition and sediment transfer in a composite cirque glacier glacier de st sorlin france earth surface processes and landforms 33 13 1931 1947

cosmogenic nuclide based investigation of spatial erosion and hillslope channel coupling in the transient foreland of the swiss alps abstract transient landscape disequilibrium is a common response to climatic fluctuations between glacial and interglacial conditions such landscapes are best suited to the investigation of catchment wide response to changes in incision the geomorphology of the trub and grosse fontanne adjacent stream systems in the napf region of the swiss molasse was analyzed using a 2 m lidar dem the two catchments were impacted by the last glacial maximum lgm even though the glaciers never overrode this region they did however cause base levels to drop by as much as 80 m despite their similar tectonic lithologic and climatic settings these two basins show very different responses to the changing boundary conditions stream profiles in the trub tend to be smooth while in the fontanne numerous knickzones are visible similarly cut and fill terraces are abundant in the trub watershed but absent in the fontanne where deep valleys have been incised the trub appears to be a coupled hillslope channel system because the morphometrics throughout the basin are uniform the morphology of hillslopes upstream of the knickzones in the fontanne is identical to that of the trub basin but different downstream of the knickzones suggesting that the lower reaches of the fontanne have been decoupled from the hillslopes however the rapid incision of the fontanne is having little effect on the adjacent upper hillslopes we tested this interpretation using cosmogenic 10 be derived basin averaged denudation rates and terrace dating the coupled nature of the trub basin is supported by the similarity of denudation rates 350 50 mm ky 1 at a variety of spatial scales upstream of the knickzones rates in the fontanne 380 50 mm ky 1 match those of the trub downstream of the knickzones denudation rates increase to 540 100 mm ky 1 the elevated rates in the downstream areas of the fontanne are due to rapid incision causing a decoupling of the hillslope from the channel basin response time and the magnitude of base level drop exert the principal control over the difference in geomorphic response between the two basins the timing of the filling of the trub valley 17 2 ka and the initial incision of the fontanne 16 3 ka were calculated verifying that these are responses to late glacial perturbations unique lithologic controls allow for one of the fastest regolith production rates yet to be reported 380 mm ky 1

low gradient permeability measurements in a triaxial system permeability measurements were conducted with the flow pump method on sand sandy silt and silty clay specimens in a conventional triaxial system by introducing and withdrawing water at known constant flow rates into the base of a specimen with a flow pump and by monitoring the head difference induced across the length of the specimen with a sensitive differential pressure transducer the results show that the previously reported advantages of the flow pump method compared with conventional constant head and falling head methods were realized for permeability measurements in conventional triaxial equipment these advantages are that direct flow rate measurements are avoided together with the associated errors that arise from the effects of contaminants on capillary menisci and the long periods of time involved in flow rate measurements permeability measurements can be obtained much more rapidly and at substantially smaller gradients errors from the small intercept in the otherwise linear flow rate ve

glacial conditioning as an erosional driving force in the central alps unparalleled data availability in the european alps has led to an ongoing debate about the driving mechanism behind the concurrent patterns of surface denudation and modern rock uplift analysis of stream channels reveals that oversteepened stream segments are primarily located in landscapes with strong glacial inheritance this leads to a transient signal in the landscape with the result that erosion is spatially focused by a combination of glacial conditioning and lithologic controls we postulate that the effect of glacial forcing is a positive feedback cycle between erosion and rock uplift driving rapid rates of both in the alpine landscape this mechanism may explain the observed increases in sediment flux since the late pliocene

10be derived assessment of accelerated erosion in a glacially conditioned inner gorge entlebuch central alps of switzerland inner gorges often result from the propagation of erosional waves related to glacial interglacial climate shifts however only few studies have quantified the modern erosional response to this glacial conditioning here we report in situ 10be data from the 64 km2 entlen catchment swiss alps this basin hosts a 7 km long central inner gorge with two tributaries that are 100 m deeply incised into thick glacial till and bedrock the 10be concentrations measured at the downstream end of the gorge yield a catchment wide erosion rate of 0 42 0 04 mm yr 1 while erosion rates are consistently lower upstream of the inner gorge ranging from 0 14 0 01 mm yr 1 to 0 23 0 02 mm yr 1 however 10be based sediment budget calculations yield rates of similar to 1 3 mm yr 1 for the inner gorge of the trunk stream likewise in the two incised tributary reaches erosion rates are similar to 2 0 mm yr 1 and similar to 1 9 mm yr 1 moreover at the erosional front of the gorge we measured bedrock incision rates ranging from similar to 2 5 mm yr 1 to similar to 3 8 mm yr 1 these rates however are too low to infer a post glacial age 1520 ka for the gorge initiation this would require erosion rates that are between 2 and 6 times higher than present day estimates however the downcutting into unconsolidated glacial till favored high erosion rates through knickzone propagation immediately after the retreat of the lgm glaciers and subsequent hillslope relaxation led to a progressive decrease in erosion rates this hypothesis of a two to sixfold decrease in erosion rates does not conflict with the 10be based erosion rate budgets because the modern erosional time scale recorded by 10be cover the past 23 ka only these results point to the acceleration of holocene erosion in response to the glacial overprint of the landscape

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

a mechanism of chemical weathering of mudstone in a mountainous area abstract the chemical weathering of marine mudstone in humid mountainous areas of japan is dominated by the oxidation of pyrite a common mineral in marine sedimentary rocks this process occurs at the oxidation front that is the base of the oxidized zone and sulfuric acid is formed chlorite is transformed into smectite due to the oxidizing and acidic conditions as sulfuric acid migrates downward from the oxidation front minerals are dissolved and components are leached out from the underlying dissolved zone whose lower boundary is the dissolution front the oxidation and dissolution fronts migrate downward as weathering progresses in mountainous areas

velocities strain rates stresses crevassing and faulting on glacier de saint sorlin french alps 1957 76 stake surveys on glacier de saint sorlin french alps during the period 1957 76 show that annual surface velocities fit a linear vectorial model with a term depending on the site another on the year and an important random component strain rates viscosities and stresses at shallow depth are computed using strain triangles ofhectometric 10 2 m size between 1961 62 and 1972 73 the isotropic point where streamlines cease to converge moved downstream about 200 m this trend may explain increasing velocities crevasses appear where annual strain is 1 2 faults limit the effective shear stress at the surface to about 0 38 bar ten modes of flow are distinguished instead of only two for the two dimensional model compressive and extensive the gradients of shallow stresses which ensure extra driving forces are computed with another mosaic of triangles of similar size stress triangles there are also important extra driving forces at the bottom which force the flow to deviate from the direction of the steepest surface slope two criteria allow elimination of stress triangles where these unknown basal extra driving forces are important even so no sliding law in terms of mean annual values can be obtained this study shows that the classical perturbation theory which explains advances and retreats by the arrival of kinematic waves is unsuitable for glaciers of kilometric size

landslide susceptibility mapping for ayvalik western turkey and its vicinity by multicriteria decision analysis this paper presents the results of geographical information system gis based landslide susceptibility mapping in ayvalik western turkey using multi criteria decision analysis the methodology followed in the study includes data production standardization and analysis stages a landslide inventory of the study area was compiled from aerial photographs satellite image interpretations and detailed field surveys in total 45 landslides were recorded and mapped the areal extent of the landslides is 1 75 km2 the identified landslides are mostly shallow seated and generally exhibit progressive character they are mainly classified as rotational planar and toppling failures in all 51 45 and 4 of the landslides mapped are rotational planar and toppling types respectively morphological geological and land use data were produced using existing topographical and relevant thematic maps in a gis framework the considered landslide conditioning parameters were slope gradient slope aspect lithology weathering state of the rocks stream power index topographical wetness index distance from drainage lineament density and land cover and vegetation density these landslide parameters were standardized in a common data scale by fuzzy membership functions then the degree to which each parameter contributed to landslides was determined using the analytical hierarchy process method and the weight values of these parameters were calculated the weight values obtained were assigned to the corresponding parameters and then the weighted parameters were combined to produce a landslide susceptibility map the results obtained from the susceptibility map were evaluated with the landslide location data to assess the reliability of the map based on the findings obtained in this study it was found that 5 19 of the total area was prone to landsliding due to the existence of highly and completely weathered lithologic units and due to the adverse effects of topography and improper land use

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

when does bedload transport begin in steep boulder bed streams the paper presents the results of field measurements of critical conditions for bedload motion conducted in the rio cordon a steep boulder bed stream in the italian alps under conditions of high reynolds numbers and low relative submergence poorly explored before two methods have been used to determine threshold of motion the displacement of marked clasts and the flow competence approach which uses the largest grain size diameter transported by each flood event the high values of confirm the great relevance of non bedload effective shear stresses in step pool streams given by the additional form drag associated with this morphology relative submergence effects on the dimensionless critical shear stress have been quantified by considering the relative submergence ratio rh d84 and the major effect of relative size on the mobility of each particle in steep widely graded bed mixtures has been evaluated finally the dimensionless critical unit discharge has also been adopted in the regression equations as the critical hydraulic parameter because it may represent an easier parameter to use than the critical shear stress for steep rough mountain rivers copyright 2006 john wiley sons ltd

dating bedrock gorge incision in the french western alps ecrins pelvoux massif using cosmogenic 10be terra nova 22 18 25 2010 abstract we report in situ produced 10be data from the gorge du diable french western alps to date and quantify bedrock gorge incision into a glacial hanging valley we sampled gorge sidewalls and the active channel bed to derive both long term and present day incision rates 10be ages of sidewall profiles reveal rapid incision through the late holocene ca 5 ka at rates ranging from 6 5 to 13 mm yr 1 present day incision rates are significantly lower and vary from 0 5 to 3 mm yr 1 within the gorge our data imply either delayed initiation of gorge incision after final ice retreat from internal alpine valleys at ca 12 ka or post glacial surface reburial of the gorge our results suggest that fluvial incision rates 1 cm yr 1 into crystalline bedrock may be encountered in transient landscape features induced by glacial interglacial transitions

failure of a rock slope 16 5 years after excavation in repeated strata of sandstone and mudstone the present study focuses on failure of a rock slope excavated in the autumn of 1997 and located in the repeated strata of sandstone and mudstone in chongqing of china the rock slope failed suddenly on april 28 2014 the elapsed time from excavation to failure is about 16 5 years the failure was sudden and unexpected seemingly but it was mainly resulted from the initial excavation and the subsequent weathering in the long term the initial excavation in 1997 as a reason why the rock cut slope failed was undoubted because the excavation broke original ground stress balance resulted in inducement or expansion of cracks and induced deformation and looseness of local rock masses the weathering process especially physical weathering process in the long term 16 5 years after excavation is the most important reason of the failure because it resulted in disintegration of material on slope surface and induced reduction of strength in the interior of the slope water as a key factor speeding up the weathering process weakened mechanical properties of rocks and discontinuities and urged formation of argillation intermediate layer based on the analyses of failure modes and corresponding factors of safety an integrated stabilization system on the rock slope was put in place

time scale for adjustment of glaciers to changes in mass balance the length of time tm over which a glacier responds to a prior change in climate is investigated with reference to the linearized theory of kinematic waves and to results from numerical models we show the following tm may in general be estimated by a volume time scale describing the time required for a step change in mass balance to supply the volume difference between the initial and final steady states the factor f in the classical estimate of m l u where i is glacier length and u is terminus velocity has a simple geometrical interpretation ft is the ratio of thickness change averaged over the full length i to the change at the terminus although both u and f relate to dynamic processes local to the terminus zone the ratio f u and therefore tm are insensitive to details of the terminus dynamics in contrast to conclusions derived from some simplified kinematic wave models a more robust estimate of tm independent of terminus dynamics is given by tm h b where h is a thickness scale for the glacier and b is the mass balance rate negative at the terminus we suggest that tm for mountain glaciers can be substantially less than the 1o2 103 years commonly considered to be theoretically expected

micro sheeting of granite and its relationship with landsliding specifically after the heavy rainstorm in june 1999 hiroshima prefecture japan certain types of granite in mountainous areas are microscopically sheeted to a depth of 50 m due to unloading under the stress field that reflects slope morphology micro sheets generally strike parallel to major slope surfaces and gently dip downslope forming cataclinal overdip slopes the cataclinal overdip slope accelerates creep movement of micro sheeted granite which in turn loosens and disintegrates granite via the widening or neoformation of cracks probably in combination with stress release temperature change and changes in water content near the ground surface the surface portion of micro sheeted granite is thus loosened with a well defined basal front which finally slides in response to heavy rain innumerable landslides of this type occurred in hiroshima prefecture western japan following the heavy rainstorm of 29 june 1999 following such landslides the weathering of micro sheeted granite exposed on the landslide scar recommences setting the stage for future landslide

relationship between the initiation of a shallow landslide and rainfall intensity duration thresholds in japan abstract the empirical rainfall intensity and duration i d threshold for the initiation of shallow landslide is newly defined for japan where heavy rainfalls frequently occur during the east asian summer monsoon season the rainfall causes sediment related disasters annually this paper presents an examination of 1174 rainfall induced shallow landslides that occurred during 2006 2008 their i d conditions were analyzed objectively from rainfall data radar raingauge analyzed precipitation to derive the i d threshold using the quantile regression method i 2 18 d 0 26 where i is measured in millimeters per hour and d in hours as measured from the beginning of rainfall to the landslide occurrence rainfall events are separated by the absence of rainfall for 24 h we then established a rescaled i d threshold by dividing the rainfall intensity by the mean annual precipitation map as imap 0 0007 d 0 21 where imap is the rescaled average per hour rainfall intensity these thresholds were defined by the second percentile regression line for d of 3 537 h the new thresholds are considerably lower than those previously reported for the world humid subtropical regions the asian monsoon region and japan the result suggests that japan is highly prone to rainfall induced shallow landslides because of its high relief topography geologic conditions human interference and rainfall characteristics during the east asian summer monsoon season

weathering rate of mudstone and tuff on old unlined tunnel walls abstract the mechanisms and rate of weathering of soft sedimentary rocks exposed along unlined tunnel walls were investigated using mineralogical chemical and physical methods tunneling occurred several decades ago within the kakinokidai formation middle pleistocene and the kiwada formation lower pleistocene of the kazusa group of chiba prefecture as well as within the fukuda formation miocene of saitama prefecture in japan since then the walls of the tunnels have been desiccated by ventilation sulfuric acid has been generated by pyrite oxidation calcite and glass have been dissolved by sulfuric acid and gypsum has crystallized on the surface of the tunnel walls the oxidized zone was formed on the surface of the walls by the weathering the formation of this zone and weathering rates determined as rates of movement of the oxidation fronts in the vadose zone are explained by the diffusion of oxygen from the surface of the tunnel walls the relationship between the depth of the oxidation front lcm and the number of years since excavation tyear was expressed by l r oxi t the roxi values from the tunnels ranged among 5 for the middle pleistocene sandy mudstone 2 4 for the middle pleistocene mudstone 0 3 for the lower pleistocene mudstone and 1 3 for the miocene tuff roxi depends on the diffusion coefficients of oxygen and the chemical composition of rocks the diffusion coefficients of oxygen de calculated using the roxi and chemical compositions of the four kinds of rock above were 10 5 cm2 s 10 7 10 5 cm2 s 5 10 8 cm2 s and 4 10 7 3 10 6 cm2 s respectively depending on the air permeabilities of the rocks that correlate closely with the coefficient of water permeabilities k the relationship for the mudstone was log de cm2 s 0 91 log k cm s 0 71 the values of de for the tuff were smaller than for the mudstone due to the smaller air porosities of 0 01 0 04

entrainment of gravel from naturally sorted riverbed material the critical dimensionless shear stress ci required to entrain a given size particle di was computed from extensive bedload transport measurements in three self formed rivers that have naturally sorted gravel and cobble bed material the value of ci was determined to be significantly affected by the size distribution of the riverbed material for bed particles between 0 3 to 4 2 times the median diameter of the subsurface bed material d50 the average critical dimensionless shear stress ci is equal to ci 0 0834 di d50 0 872 with a coefficient of determination of 0 980 for bed particles larger than 4 2 times d50 ci appears to approach a constant value of approximately 0 020 in a noneroding channel thus ci varies from 0 25 to 0 020 for a given particle depending on the ratio of di to d50 previous investigations of the hydraulic conditions required to entrain coarse riverbed material have reported critical shear stress values ranging from 0 25 to 0 020 for a given particle size this analysis indicates that virtually all of the variation is due to differences in the subsurface bed material size distribution this analysis shows that ci varies almost inversely proportional to the particle diameter for a nonuniform bed material therefore bed particles between 0 3 to 4 2 times d50 are entrained at nearly the same discharge an investigation of the hydraulic characteristics and bed material mobility of 24 self formed gravel bed rivers in colorado determined that particles as large as the median diameter of the bed surface were entrained by discharges equal to the bankfull stage or less particles as large as the 90th percentile fraction were entrained by the bankfull discharge in nine of the rivers studied consequently in these rivers a significant fraction of the riverbed was entrained rather frequently over a period of years although the transport rate was very small

patterns of bedrock channel erosion on the boso peninsula japan three channels on the boso peninsula japan were examined to assess how cross sectional to reach scale channel morphology relates to substrate variables and how cross sectional to reach scale erosional patterns relate to basin scale longitudinal profile two of the channels shichiri gawa and torii zawa are deeply incised into interbedded sandstone and mudstone whereas the third channel futama gawa is incised into mudstone reach scale channel morphologies include knickpoints chutes and pools plane beds and both transverse and longitudinal bed erosional features step backwater modeling of a september 1996 typhoon related flood flow along each channel indicated that unit stream power is highly variable downstream stream power minima are associated with bends and with coarse clast deposition magnitude of erosional bed features correlates with hydraulics and flow energy expenditure along futama gawa and with variability in substrate resistance along shichiri gawa and torii zawa thickness and ori