shallow landsliding root reinforcement and the spatial distribution of trees in the oregon coast range the influence of root reinforcement on shallow landsliding has been well established through mechanistic and empirical studies yet few studies have examined how local vegetative patterns influence slope stability because root networks spread outward from trees the species size and spacing of trees should influence the spatial distribution of root strength we documented the distribution and characteristics of trees adjacent to 32 shallow landslides that oc curred during 1996 in the oregon coast range although broadly classified as a conifer dominated forest we observed sparse coniferous and abundant hardwood trees near landslide scars in an industrial forest mapleton that experienced widespread burning in the 19th century in industrial forests that were burned selectively harvested and not replanted elliott state forest swordfern was ubiquitous near landslides and we observed similar numbers of live conifer and hardwood trees proximal to landslide scarps we demonstrate that root strength quantified in landslide scarps and soil pits correlates with a geometry based index of root network contribution derived from mapping the size species condi tion and spacing of local trees indicating that root strength can be predicted by mapping the distribution and charac teristics of trees on potentially unstable slopes in our study sites landslides tend to occur in areas of reduced root strength suggesting that to make site specific predictions of landslide occurrence slope stability analyses must account for the diversity and distribution of vegetation in potentially unstable terrain

lithologic and glacially conditioned controls on regional debris flow sediment dynamics debris flow is an efficient process of sediment transfer from slope base to piedmont depositional fans in mountain drainage basins to advance understanding of debris flow sediment dynamics at the regional scale we analyze a historical 1998 2009 database of debris flows from 77 basins of alto adige province northeastern italy by combining information on event volumetric deposition high resolution digital topography and quaternary sediment mapping we are able to link debris flow sediment flux to morphometry lithologic variability and sediment availability we show that basin wide specific sediment yield ssy scales as an inverse power function of basin area this function is strongly controlled by the way rock type and abundance of quaternary deposits affect the rate of downstream sediment recruitment when sediment flux associated with each debris flow event is subsumed across discrete spatial increments of the entire region a complex sedimentary signature in the area ssy space is apparent that is ssy increases downstream up to areas as large as 1 km2 and starts to decline beyond this scale regardless of sediment availability we propose that this area ssy relation is characteristic of debris flow dominated settings

a probabilistic model of debris flow delivery to stream channels demonstrated for the coast range of oregon usa debris flows are important geomorphic agents in mountainous terrains that shape channel environments and add a dynamic element to sediment supply and channel disturbance identification of channels susceptible to debris flow inputs of sediment and organic debris and quantification of the likelihood and magnitude of those inputs are key tasks for characterizing spatial and temporal patterns found in channel conditions and associated habitats in a river network widely available digital elevation and land cover data 10 m dems and 25 m satellite imagery offer the potential to assess debris flow runout paths over regional extents this paper presents a model for using these data to calculate empirical probabilities for debris flow runout over dem determined flow paths and shows how these probabilities can be combined over all sources to estimate the potential for debris flow delivery to stream reaches throughout entire channel networks the model is calibrated and model predictions are compared to field mapped debris flow travel paths from study sites in the coast range of oregon usa this model predicts debris flow probability over channel reach scales that can be aggregated to basin scale measures of debris flow potential it offers unprecedented ability to characterize debris flow effects over channel networks providing a tool for risk assessment and for generating hypotheses that relate topographic and forest cover controls on debris flow runout to the types and abundance of channel habitats in a river basin

transient landscapes at fault tips 1 fault growth produces patterns of displacement and slip rate that are highly variable in both space and time this transience is most pronounced near fault tips where along strike displacement gradients vary in time as the fault array lengthens we use a set of statistical and field observations to quantify the response of catchments and their associated fans in three large normal fault arrays to transient patterns of displacement and slip rate catchments near the fault tips show distinct scaling of channel slope with drainage area compared with catchments near the strike center this scaling becomes uniform beyond about 10 km from the fault tips and is therefore like footwall relief largely decoupled from the fault displacement profile the estimated catchment response times to a change in slip rate also vary between fault tips and strike center the response times for tip catchments are much longer than the inferred time since fault activity began indicating that they are unlikely to be in equilibrium with the current fault displacement field this disequilibrium combined with the decoupling of slope area scaling from displacement indicates that landscapes are most sensitive to fault activity near fault tips active faults characterized by along strike variation in slip rate thus provide excellent opportunities to explore the transient response of landscapes to tectonic forcing

controls on sediment evacuation from glacially modified and unmodified catchments in the eastern sierra nevada california the degree of glacial modification in small catchments along the eastern sierra nevada california controls the timing and pattern of sediment flux to the adjacent fans there is a close relationship between the depth of fan head incision and the pattern and degree of late pleistocene catchment erosion by valley glaciers catchments with significant glacial activity are associated with deeply incised fan heads whereas fans emerging from glacially unmodified catchments are unincised we suggest that the depth of fan head incision is controlled by the potential for sediment storage during relatively dry ice free periods which in turn is related to the downstream length of the glacially modified valley and creation of accommodation through valley floor slope lowering and glacial valley overdeepening and widening significant storage in glacially modified basins during ice free periods leads to sediment supply limited conditions at the fan head and causes deep incision in contrast a lack of sediment trapping allows quasi continuous sediment supply to the fan and prevents incision of the fan head sediment evacuation rates should thus show large variations in glacially modified basins with major peaks during glacial and lows during interglacial or ice free periods respectively in contrast sediment removal from glacially unmodified catchments in this type of setting should be free of this effect and will be dominated instead by short term variations modulated for example by changes in vegetation cover or storm frequency this distinction may help improve our understanding of long term sediment yields as a measure of erosional efficiency

correction of deposit ages for inherited ages of charcoal implications for sediment dynamics inferred from random sampling of deposits on headwater valley floors abstract inherited age is defined herein as the difference between times of carbon fixation in a material and deposition of that material within sediments from which it is eventually sampled in order to estimate deposit age via radiocarbon dating inheritance generally leads to over estimation of the age by an unknown amount and therefore represents unquantified bias and uncertainty that could potentially lead to erroneous inferences inherited ages in charcoal are likely to be larger and therefore detectable relative to analytic error where forests are dominated by longer lived trees material is stored for longer periods upslope and downstream post fire delivery of that material is dominated by mass movements such as in the near coastal mountains of northwestern north america inherited age distribution functions were estimated from radiocarbon dating of 126 charcoal pieces from 14 stream bank exposures of debris flow deposits fluvial fines and fluvial gravels along a headwater stream in the southern oregon coast range usa in the region these 3 facies are representative of the nearly continuous coalescing fan fill complexes blanketing valley floors of headwater streams where the dominant transport mechanism shifts from debris flow to fluvial within each depositional unit and for each charcoal piece within that unit convolution of the calibrated age distribution with that of the youngest piece yielded an inherited age distribution for the unit fits to the normalized sums of inherited age distributions for units of like facies provided estimates of facies specific inherited age distribution functions finally convolution of these distribution functions with calibrated deposit age distributions yielded corrections to published valley floor deposit ages and residence time distributions from nearby similar sites residence time distributions were inferred from the normalized sums of distributions of 30 deposit ages at each of 4 sites 2 adjacent valley reaches 103 m long and within 102 m of 2 tributary confluences mean inherited ages from the observed distributions are 666 688 and 1506 yr for debris flow deposits fluvial fines and fluvial gravels respectively on average correction reduced estimates of individual deposit age means by a factor of 0 71 0 56 0 94 and increased standard deviations by a factor of 6 1 0 97 43 across sites mean residence times decreased by 24 0 and standard deviations by 12 5 on average corrected residence time distributions have thicker tails as indicated by gamma distribution fits with smaller shape factors and these changes are significant relative to the bootstrapped 95 confidence limits representing potential error in the sampling for inherited ages the ratio of the means of sediment age and residence time ranged from 1 03 to 1 80 across sites before correction and 1 21 to 2 18 after correction where a value of one implies that probability of evacuation from the reservoir comprising valley floor deposits is independent of time since deposition corrected values of this ratio therefore indicate that evacuation favors younger deposits at all sites whereas uncorrected results implied age independent evacuation from the more downstream valley reach

drillability prediction geological influences in hard rock drill and blast tunnelling usually the main subject in preliminary site investigations prior to tunnelling projects is the prediction of tunnel stability during the past years in conventional drill and blast tunnelling problems have occurred also connected to the accurate prediction of drillability in hard rock the drillability is not only decisive for the wear of tools and equipment but is along with the drilling velocity a standard factor for the progress of excavation works the estimation of drillability in predicted rock conditions might bear an extensive risk of costs therefore an improved prediction of drilling velocity and bit wear would be desireable the drillability of a rock mass is determined by various geological and mechanical parameters in this report some major correlations of specific rock properties and especially geological factors with measured bit wear and drilling velocity are shown drilling velocity is dependent on a lot of geological parameters those principal parameters include jointing of rock mass orientation of schistosity rock anisotropy degree of interlocking of microstructures porosity and quality of cementation of clastic rock degree of hydrothermal decomposition and weathering of a rock mass drilling bit wear increases with the equivalent quartz content the equivalent quartz content builds the main property for the content of wear relevant minerals for various groups of rock types different connections with the equivalent quartz content could be detected in sandstone bit wear is also dependent on porosity or the quality of the cementation finally an investigation program is submitted which helps to improve the estimation of rock drillability in planning future tunnel projects

numerical study on the entrainment of bed material into rapid landslides the entrainment of channel path material plays an important role during runout of many rapid landslides such a mechanism is able to change the mobility of a flow significantly through rapid chang

southern hemisphere circulation features associated with el nino southern oscillation events abstract composite seasonal mean and anomaly fields prepared from operational numerical analyses have been used to describe the southern hemisphere sh circulation features associated with el nino southern oscillation enso events the period of analyses available 1972 83 has limited the composites to include only three enso events the reliability and stability of the composites has been tested using multiple permutation methods and by comparison with the results obtained using a longer period 1950 79 of sh rawinsonde station data in the sh winter a weak equivalent barotropic wavetrain pattern of anomalies extends over australia and the south pacific ocean to south america this wavetrain pattern is quite variable in amplitude and location between enso events although it is more stable over the subtropical pacific in the sh summer the circulation anomalies are more zonally symmetric with increased height at low and high latitudes and decreased height in middle latitudes the circulation anoma

influence of bed patchiness slope grain hiding and form drag on gravel mobilization in very steep streams steep streams are a major portion of channel networks and provide a link to transport sediment from hillslopes to lower gradient rivers despite their importance key unknowns remain perhaps foremost of which is evaluating in steep streams empirical laws for fluvial sediment transport developed for low gradient rivers to address this knowledge gap we painted sediment in situ over 3 years to monitor incipient sediment motion and sediment patch development in five small drainage areas of 0 04 2 km 2 and steep slopes of 5 37 tributaries of elder creek california united states we found that channel beds organized into size sorted sediment patches which displayed active fluvial transport of gravel annually consistent year to year patch median grain sizes partial transport of bed material and significantly higher values of critical shields stress for incipient sediment motion compared to that observed for lower gradient rivers the high critical shields stresses up to 0 5 for the median grain size agree within a factor of 3 to theoretical predictions which account for slope dependent hydraulics grain hiding and sediment patches for grains of approximately the same size as the roughness length scale slope dependent hydraulics and bed patchiness are the dominant controls on critical shields stress values while grain hiding is important for grains larger or smaller than the roughness length scale form drag exists in our monitored tributaries but has a smaller influence than the above effects our field observations show fluvial processes contribute to sediment mobilization in steep channels which are often considered to be dominated by debris flows

controls on zero order basin morphology zero order basins are common features of soil mantled landscapes defined as unchanneled basins at the head of a drainage network their geometry and volume control how quickly sediment may re accumulate after landslide evacuation and how water and subsequently pore pressure is delivered to hollow axes they also deliver water and sediment to the uppermost portions of the fluvial network despite this role as the moderator between hillslope and fluvial processes little analysis on their morphology has been conducted at the landscape scale we present a method to identify zero order basins in landscapes and subsequently quantify their geometric properties using elliptical fourier analysis we deploy this method across the coweeta hydrologic laboratory usa properties such as length relief width and concavity follow distinct probability distributions which may serve as a basis for testing predictions of future landscape evolution models surprisingly in a landscape with an orographic precipitation gradient and large hillslope to channel relief we observe no correlation between elevation or spatial location and basin geometry however we find that two physiographic units in coweeta have distinct zero order basin morphologies these are the steep thin soiled high elevation nantahala escarpment and the lower gradient lower elevation thick soiled remainder of the basin our results indicate that basin slope and area negatively covary producing the distinct forms observed between the two physiographic units which we suggest arise through competition between spatially variable soil creep and stochastic landsliding

using hilltop curvature to derive the spatial distribution of erosion rates 1 erosion rates dictate the morphology of landscapes and therefore quantifying them is a critical part of many geomorphic studies methods to directly measure erosion rates are expensive and time consuming whereas topographic analysis facilitates prediction of erosion rates rapidly and over large spatial extents if hillslope sediment flux is nonlinearly dependent on slope then the curvature of hilltops will be linearly proportional to erosion rates in this contribution we develop new techniques to extract hilltop networks and sample their adjacent hillslopes in order to test the utility of hilltop curvature for estimating erosion rates using high resolution 1 m digital elevation data published and new cosmogenic radionuclide analyses in the feather river basin california suggest that erosion rates vary by over an order of magnitude 10 to 250 mm kyr 1 hilltop curvature increases with erosion rates allowing calibration of the hillslope sediment transport coefficient which controls the relationship between gradient and sediment flux having constraints on sediment transport efficiency allows estimation of erosion rates throughout the landscape by mapping the spatial distribution of hilltop curvature additionally we show that hilltop curvature continues to increase with rising erosion rates after gradient limited hillslopes have emerged hence hilltop curvature can potentially reflect higher erosion rates than can be predicted by hillslope gradient providing soil production on hilltops can keep pace with erosion finally hilltop curvature can be used to estimate erosion rates in landscapes undergoing a transient adjustment to changing boundary conditions if the response timescale of hillslopes is short relative to channels

erosion of steepland valleys by debris flows episodic debris flows scour the rock beds of many steepland valleys along recent debris flow runout paths in the western united states we have observed evidence for bedrock lowering primarily by the impact of large particles entrained in debris flows this evidence may persist to the point at which debris flow deposition occurs commonly at slopes of less than 0 03 0 10 we find that debris flow scoured valleys have a topographic signature that is fundamentally different from that predicted by bedrock river incision models much of this difference results from the fact that local valley slope shows a tendency to decrease abruptly downstream of tributaries that contribute throughgoing debris flows the degree of weathering of valley floor bedrock may also decrease abruptly downstream of such junctions on the basis of these observations we hypothesize that valley slope is adjusted to the long term frequency of debris flows and that valleys scoured by debris flows should not be modeled using conventional bedrock river incision laws we use field observations to justify one possible debris flow incision model whose lowering rate is proportional to the integral of solid inertial normal stresses from particle impacts along the flow and the number of upvalley debris flow sources the model predicts that increases in incision rate caused by increases in flow event frequency and length as flows gain material downvalley are balanced by rate reductions from reduced inertial normal stress at lower slopes and stronger less weathered bedrock these adjustments lead to a spatially uniform lowering rate although the proposed expression leads to equilibrium long profiles with the correct topographic signature the crudeness with which the debris flow dynamics are parameterized reveals that we are far from a validated debris flow incision law however the vast extent of steepland valley networks above slopes of 0 03 0 10 illustrates the need to understand debris flow incision if we hope to understand the evolution of steep topography around the world

a zonal wave 3 index for the southern hemisphere 1 in this study 500 hpa geopotential heights from the ncar ncep reanalysis are used to calculate an index describing the spatial and temporal characteristics of zonal wave three zw3 in the high latitude southern hemisphere atmosphere the index spans the period 1958 2001 wavelet analysis of the index shows the strong interannual variation which is characteristic of zw3 and also reveals significant high amplitude decadal scale variation this interannual variation takes the form of marked fluctuation in sign and magnitude of the index it appears to occur when there are rapid changes from strongly meridional to strongly zonal flow or vice versa initial indications are that some of this variability may be associated with enso events

factors controlling the near surface wind field in antarctica abstract using data from the regional atmospheric climate model racmo ant1 the momentum budget of the antarctic atmospheric surface layer sl taken as the lowest model layer located at 6 7 m above the surface is presented in july winter the katabatic pressure gradient force pgf dominates the sl momentum budget over the steep coastal slopes which results in strong 10 15 m s 1 and directionally constant katabatic winds farther inland where surface slopes are more gentle the large scale pgf may become equally important with the circumpolar pressure trough north of the antarctic coastline the large scale pgf acts along with the katabatic pgf in the downslope direction in wilkes land dronning maud land and on the western ross ice shelf the large scale pgf causes equivalent geostrophic winds in excess of 10 m s 1 thermal wind effects that oppose the downslope acceleration are especially strong in areas where large scale forcing is weak which allows cold air to pile up over the flat ice she

impact of iceberg c 19 on ross sea primary production 1 for the second time in 26 months a large iceberg c 19 calved off the face of the ross ice shelf rather than breaking up as did its predecessor b 15 the iceberg c 19 remained largely intact eventually stopping temporarily near pennell bank before moving out of the southwestern ross sea the presence of c 19 restricted advection of sea ice out of the region resulting in unusually high sea ice cover during the spring and summer consequently phytoplankton blooms in the region were diminished dramatically and primary production was reduced by over 90 relative to normal years calving events over the last two decades indicate that reduced primary productivity may be a typical consequence of large icebergs that drift through the southwestern ross sea during spring and summer

wintertime antarctic coastal polynya area 1992 2008 1 an iterative classification technique based on special sensor microwave imager data is used to estimate the total daily circum antarctic coastal polynya area for 1992 2008 the average wintertime june to september area is estimated at 245 000 10 000 km2 and varies between 210 000 km2 1997 and 281 000 km2 2007 the polynyas along east antarctica 60 to 160 e contribute about 40 to this area the most persistent polynyas are located along east antarctica lars christensen coast lcc prydz bay western davis sea mertz glacier and in the ross sea ross ice shelf and terra nova bay the polynya at the lcc is observed on 110 5 days during winter for 1992 2008 it is the most persistent of the observed polynyas covering an average area of 2400 km2 on more than 90 days trends in the average wintertime area of the major coastal polynyas during 1992 2008 are small and not significant

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

flow of variably fluidized granular masses across three dimensional terrain 1 coulomb mixture theory rock avalanches debris flows and related phenomena consist of grain fluid mixtures that move across three dimensional terrain in all these phenomena the same basic forces govern motion but differing mixture compositions initial conditions and boundary conditions yield varied dynamics and deposits to predict motion of diverse grain fluid masses from initiation to deposition we develop a depth averaged three dimensional mathematical model that accounts explicitly for solid and fluid phase forces and interactions model input consists of initial conditions path topography basal and internal friction angles of solid grains viscosity of pore fluid mixture density and a mixture diffusivity that controls pore pressure dissipation because these properties are constrained by independent measurements the model requires little or no calibration and yields readily testable predictions in the limit of vanishing coulomb friction due to persistent high fluid pressure the model equations describe motion of viscous floods and in the limit of vanishing fluid stress they describe one phase granular avalanches analysis of intermediate phenomena such as debris flows and pyroclastic flows requires use of the full mixture equations which can simulate interaction of high friction surge fronts with more fluid debris that follows special numerical methods described in the companion paper are necessary to solve the full equations but exact analytical solutions of simplified equations provide critical insight an analytical solution for translational motion of a coulomb mixture accelerating from rest and descending a uniform slope demonstrates that steady flow can occur only asymptotically a solution for the asymptotic limit of steady flow in a rectangular channel explains why shear may be concentrated in narrow marginal bands that border a plug of translating debris solutions for static equilibrium of source areas describe conditions of incipient slope instability and other static solutions show that nonuniform distributions of pore fluid pressure produce bluntly tapered vertical profiles at the margins of deposits simplified equations and solutions may apply in additional situations identified by a scaling analysis assessment of dimensionless scaling parameters also reveals that miniature laboratory experiments poorly simulate the dynamics of full scale flows in which fluid effects are significant therefore large geophysical flows can exhibit dynamics not evident at laboratory scales

implications of the shear stress river incision model for the timescale of postorogenic decay of topography 1 the reason for the survival of mountainous topography in ancient orogenic belts is a long standing problem in geomorphology and geodynamics we explore the geomorphologic controls on the timescale for the postorogenic decay of topography to address the question of whether there is a viable geomorphologic explanation for the persistence of topography in ancient orogenic belts or whether alternative geodynamic explanations must be sought using both approximate analytical solutions and numerical simulations we show that the standard detachment limited stream power river incision model predicts for reasonable initial topographies relatively short postorogenic decay times of 1 10 myr additional layers of complexity are introduced to this simplest model including isostasy and flexural strength a transition to transport limited conditions during decline and the incorporation of the combined effects of a critical threshold for erosion and the stochastic variability of flood magnitudes each of these additional factors acts to lengthen the decay timescale pure airy isostatic rebound of a thick crustal root results in decay times that are at most a factor of 6 longer than the detachment limited result the transition to transport limited conditions involves partial protection of the bed by a thin layer of alluvium which inhibits erosion and therefore increases decay times by a factor of 2 3 in our analysis finally including critical shear stress results increases decay time by approximately a factor of 20 for the parameter values in our example calculation more importantly however a significant portion of topography remains after predicted lowering rates have dropped to values less than measured rates of denudation in weathering limited low relief environments thus a model combining isostasy a transition to transport limited conditions and a critical shear stress for erosion could account for the presence of residual topography for hundreds of million years all three of these factors can be expected to play a role in natural settings

landscape response to tectonic forcing digital elevation model analysis of stream profiles in the mendocino triple junction region northern california the topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock channel incision quantitative field assessments of process based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate we evaluate and calibrate the shear stress or similar unit stream power bedrock incision model by studying stream profiles in a tectonically active mountain range previous work on emergent marine terraces in the mendocino triple junction region of northern california provides spatial and temporal control on rock uplift rates digital elevation models and field data are used to quantify differences in landscape morphology associated with along strike northwest to southeast changes in tectonic and climatic conditions analysis of longitudinal profiles supports the hypothesis that the study area channels are in equilibrium with current uplift and climatic conditions consistent with theoretical calculations of system response time based on the shear stress model within uncertainty the profile concavity of the trunk streams is constant throughout the study area 0 43 as predicted by the model channel steepness correlates with uplift rate these data help constrain the two key unknown model parameters the coefficient of erosion k and the exponent associated with channel gradient n this analysis shows that k cannot be treated as a constant throughout the study area despite generally homogeneous substrate properties for a reasonable range of slope exponent values n best fit values of k are positively correlated with uplift rate this correlation has important implications for landscape evolution models and likely reflects dynamic adjustment of k to tectonic changes due to variations in orographic precipitation and perhaps channel width sediment load and frequency of debris flows the apparent variation in k makes a unique value of n impossible to constrain with present data

a morphometric analysis of gullies scoured by post fire progressively bulked debris flows in southwest montana usa in the fall of 2001 an intense thunderstorm in southwest montana triggered many debris flows in the burned area of sleeping child creek in most instances the debris flows cut deep gullies into previously unchannelized colluvial hollows and deposited large volumes of sediment onto the valley floor the presence of rill networks above the gullies as well as the absence of landslide features indicate that the gullies were scoured by progressively bulked debris flows a process in which dilute surface runoff becomes increasingly more laden with sediment until it transforms into a debris flow in this contribution we present a morphometric analysis of six of the gullies to better understand this relatively understudied process we find that the locations of the rill heads and gully heads conform to slope area thresholds that are characteristic of erosion by overland flow our data also suggest that the volumes of the debris flows increase exponentially with normalized drainage area thus lending support to an assumption used in a recently proposed debris flow incision law finally the debris flow fans have been relatively unaltered since deposition suggesting that the valley may be currently aggrading while the hillslopes are being denuded

fire storms and erosional events in the idaho batholith in late december 1996 the south fork payette river basin in west central idaho experienced a prolonged storm that culminated on january 1 1997 with intense rain on melting snow that triggered slide failures producing debris flows and sediment charged floods failures occurred in saturated cohesionless grussy colluvium derived from weathered idaho batholith granitic rocks many failures along the south fork payette river originated in ponderosa pine forests burned in the 1989 stand replacing lowman fire an example is the 0 49 km 2 jughead creek basin where a single large colluvial failure produced almost 40 of the total volume eroded from the basin and generated a massive and rapid debris flow failures also occurred in steep unburned and unforested drainages such as hopkins creek in this south facing 0 58 km 2 basin 15 colluvial hollows failed but no single failure produced more than 10 of the total eroded volume sediment transport in hopkins creek occurred by prolonged sediment charged sheetflooding despite vegetation differences sediment yields from the geomorphically similar hopkins creek 42 000 mg km 2 and jughead creek 44 000 mg km 2 basins were quite similar these 1997 erosion events are equivalent to several thousand years of sediment yield at low rates 2 7 30 mg km 2 year 1 measured by short term sediment trapping and gauging in idaho batholith watersheds if similar large events were solely responsible for sediment export recurrence intervals ris of several hundred years would account for higher sediment yields averaged over 10 4 year from idaho batholith watersheds dating of small fire induced sheetflooding events in an early holocene tributary junction fan of jughead creek indicates that frequent small sedimentation events ri 33 80 year occurred between 7400 and 6600 cal year bp with an average yield not greatly exceeding 16 mg km 2 year 1 compared with the holocene average erosion rates during that 800 year period were unusually low suggesting that sediment yields have not been constant over time and that climatic variations and related fire regime changes may exert a strong influence on the probability of major erosional events copyright 2001 john wiley sons ltd

time and the rivers flowing fluvial geomorphology since 1960 fluvial geomorphology has been the largest single subdiscipline within geomorphology for many decades fluvial geomorphic expertise is integral to understanding and managing rivers and to developing strategies for sustainable development this paper provides an overview of some of the significant advances in fluvial geomorphology between 1960 and 2010 with respect to conceptual models fluvial features and environments being studied tools used by fluvial geomorphologists geomorphic specialty groups within professional societies journals in which fluvial geomorphic research is published and textbooks of fluvial geomorphology during this half century fluvial geomorphology broadened considerably in scope from a focus primarily on physical principles underlying process and form in lower gradient channels with limited grain size range to a more integrative view of rivers as ecosystems with nonlinear behavior and great diversity of gradient substrate composition and grain size the array of tools for making basic observations analyzing data and disseminating research results also expanded considerably during this period as did the diversity of the fluvial geomorphic community

climate patterns and phytoplankton dynamics in antarctic latent heat polynyas 1 seasonal coherence between satellite derived phytoplankton parameters chlorophyllaconcentration chl and phytoplankton bloom initiation time bit environmental variables sea ice concentration surface solar radiation and wind speed and climate patterns el nino 3 4 the southern annular mode the pacific south america pattern the semiannual oscillation and the wave 3 stationary pattern was investigated in four latent heat polynyas amundsen sea western ross sea dumont d urville and prydz bay using data corresponding to 1998 2006 phytoplankton growing seasons in general polynyas in the western sector i e amundsen sea and western ross sea had a greater sea ice cover lower solar radiation levels higher and more variable chl and more variable and delayed i e high bit phytoplankton blooms differences in chl and bit were mainly attributed to differences in water stratification and interannual variability of sea ice concentration caused by ice shelf calving events in the ross sea changes in solar radiation reaching the sea surface played an important role in determining phytoplankton blooms in the western ross sea and prydz bay stronger winds tend to benefit development of phytoplankton blooms in polynyas having more stratified waters sensitivity of phytoplankton to climate variability in polynyas under investigation was highly influenced by the polynya size during summer e g chl in dumont d urville and bit in the western ross sea also the response of chl to the same climate pattern changed with the polynya s location e g correlation between chl and el nino 3 4 in amundsen sea positive and dumont d urville negative

erosion and mobility in granular collapse over sloping beds 1 we describe laboratory experiments of granular material flowing over an inclined plane covered by an erodible bed designed to mimic erosion processes of natural flows travelling over deposits built up by earlier events two controlling parameters are the inclination of the plane and the thickness of the erodible layer we show that erosion processes can increase the flow mobility i e runout over slopes with inclination close to the repose angle of the grains r by up to 40 even for very thin erodible beds erosion efficiency is shown to strongly depend on the slope of the topography entrainment begins to affect the flow at inclination angles exceeding a critical angle c r 2 runout distance increases almost linearly as a function of the thickness of the erodible bed suggesting that erosion is mainly supply dependent two regimes are observed during granular collapse a first spreading phase with high velocity followed by a slow thin flow provided either the slope or the thickness of the erodible bed is high enough surprisingly erosion affects the flow mostly during the deceleration phase and the slow regime the avalanche excavates the erodible layer immediately at the flow front waves are observed behind the front that help to remove grains from the erodible bed steep frontal surges are seen at high inclination angles over both rigid or erodible bed finally simple scaling laws are proposed making it possible to obtain a first estimate of the deposit and emplacement time of a granular collapse over a rigid or erodible inclined bed

glacial interglacial climate changes recorded by debris flow fan deposits owens valley california abstract it is hotly debated whether and how climate changes are recorded by terrestrial stratigraphy basin sediments produced by catchment alluvial fan systems may record past climate over a variety of timescales and could offer unique information about how climate controls sedimentation unfortunately there are fundamental uncertainties about how climatic variables such as rainfall and temperature translate into sedimentological signals here we examine 35 debris flow fan surfaces in owens valley california that record deposition throughout the past 125 000 years during which climate has varied significantly we show that the last full glacial interglacial cycle is recorded with high fidelity by the grain size distributions of the debris flow deposits these flows transported finer sediment during the cooler glacial climate and became systematically coarser grained as the climate warmed and dried we explore the physical mechanisms that might explain this signal and rule out changes in sediment supply through time instead we propose that grain size records past changes in storm intensity which is responsible for debris flow initiation in this area and is decoupled from average rainfall rates this is supported by an exponential clausius clapeyron style scaling between grain size and temperature and also reconciles with climate dynamics and the initiation of debris flows the fact that these alluvial fans exhibit a strong sustained sensitivity to orbital climate changes sheds new light on how eroding landscapes and their sedimentary products respond to climatic forcing finally our findings highlight the importance of threshold controlled events such as storms and debris flows in driving erosion and sedimentation at the earth s surface in response to climate change

baroclinicity meridional temperature gradients and the southern semiannual oscillation abstract it has long been known that a strong half yearly oscillation exists in surface pressure at high southern latitudes there are two minima during the year the one occurring in october being more intense than that in march the semiannual oscillation sao has been related to the different surface types and inertia at 50 and 65 s these conspire to produce a semiannual wave in the meridional temperature gradient between those two latitudes the timing of the maxima for these is as above but the stronger is in march however if the arguments of van loon are applied literally then the seasonal evolution of temperature gradient should follow a comparable seasonal evolution of baroclinicity and surface pressure a full calculation of baroclinicity shows that the seasonal evolution of static stability combined with the twice annual maxima of meridional temperature gradient produces a larger peak of baroclinicity in october consistent with the sao in surface pressure

how well can hillslope evolution models explain topography simulating soil transport and production with high resolution topographic data the morphology of hillslopes is a direct refl ection of tectonic forcing and climatic and biologic processes that drive soil production mobilization and transport soil transport on hillslopes affects river incision by providing tools for channel abrasion and controls the distribution of sediment that infl uences aquatic habitat although numerous hillslope transport relationships have been proposed over the past 60 years a comprehensive analysis of model predictions for a real landscape has not been performed here we use high resolution topographic data obtained via airborne laser swath mapping alsm to simulate the long term evolution of oregon coast range hillslopes and test three published transport models and a new model that accounts for nonlinear depth and slopedependent transport analysis of one dimensional steady state solutions for these four models suggests that plots of gradient curvature may be diagnostic for distinguishing model predictions to evaluate two dimensional model predictions for our fi eld site we assumed local steady state erosion for a 72 000 m 2 sequence of hillslopes and valleys after calibrating each of the four models we imposed constant base level lowering for cells within the valley network simulated 500 000 yr of soil production and transport and determined which transport model best preserved morphologic patterns that describe the current landscape form models for which fl ux varies proportionally with hillslope gradient generated broadly convex hilltops inconsistent with the sharp crested steep sided slopes of our study site whereas the two nonlinear slope dependent models produced convex planar slopes consistent with current hillslope form our proposed nonlinear slope and depth dependent model accounts for how soil thickness controls the magnitude of biogenic disturbances that drive transport this model best preserved the current landscape form particularly the narrow sharply convex hilltops characteristic of the oregon coast range according to our formulation which provides an explicit linkage for relating the distribution of biota to hillslope processes the degree of hilltop convexity varies nonlinearly with the ratio of erosion rate to maximum soil production rate highlighting the profound infl uence of soil depth on hillslope evolution

the influence of atmospheric zonal wave three on antarctic sea ice variability 1 the study examines the relationship between atmospheric zonal wave three and antarctic sea ice variability using an index of zonal wave three and sea ice concentration the net sensible heat flux and the surface air temperature are used to explain the apparent atmosphere sea ice interaction the results show that zonal wave three forces an alternating pattern of equatorward colder and poleward warmer flow which influences the temperature difference between the atmosphere and the ocean the net sensible heat flux is positive ocean heat loss is greater and sea ice growth and expansion is greater in regions of colder air the reverse is true in regions of warmer air this influence of zonal wave three on sea ice concentration appears greatest in the southern fall and early winter it is most clearly seen in the ross and weddell seas outflows and off the amery iceshelf

field measurements of incision rates following bedrock exposure implications for process controls on the long profiles of valleys cut by rivers and debris flows until recently published rates of incision of bedrock valleys came from indirect dating of incised surfaces a small but growing literature based on direct measurement reports short term bedrock lowering at geologically unsustainable rates we report observations of bedrock lowering from erosion pins monitored over 1 7 yr in 10 valleys that cut indurated volcanic and sedimentary rocks in washington oregon california and taiwan most of these channels have historically been stripped of sediment their bedrock is exposed to bed load abrasion plucking and seasonal wetting and drying that comminutes hard intact rock into plates or equant fragments that are removed by higher fl ows consequent incision rates are proportional to the square of rock tensile strength in agreement with experimental results of others measured rates up to centimeters per year far exceed regional long term erosionrate estimates even for apparently minor sediment transport rates cultural artifacts on adjoining strath terraces in washington and taiwan indicate at least several decades of lowering at these extreme rates lacking sediment cover lithologies at these sites lower at rates that far exceed long term rock uplift rates this rate disparity makes it unlikely that the long profi les of these rivers are directly adjusted to either bedrock hardness or rock uplift rate in the manner predicted by the stream power law despite the observation that their profi les are well fi t by power law plots of drainage area vs slope we hypothesize that the threshold of motion of a thin sediment mantle rather than bedrock hardness or rock uplift rate controls channel slope in weak bedrock lithologies with tensile strengths below 3 5 mpa to illustrate this hypothesis and to provide an alternative interpretation for power law plots of area vs slope we combine shields threshold transport concept with measured hydraulic relationships and downstream fi ning rates in contrast to fl uvial reaches none of the hundreds of erosion pins we installed in steep valleys recently scoured to bedrock by debris fl ows indicate any postevent fl uvial lowering these results are consistent with episodic debris fl ows as the primary agent of bedrock lowering in the steepest parts of the channel network above 0 03 0 10 slope

constraints on the long term colluvial erosion law by analyzing slope area relationships at various tectonic uplift rates in the siwaliks hills nepal 1 the large database of topographic form and uplift rates that exists for the siwaliks hills central nepal makes possible a thorough analysis of the long term erosion model the study especially focuses on drainage areas larger than 5 10 3 km2 fixed by the database resolution and smaller than 1 km2 above which a fluvial signature is recorded this area range corresponds to colluvial valleys in which the dominant erosion process is likely debris flow we evaluate a phenomenological model wherein erosion is considered to depend on drainage area and slope we test this model by assuming that the uplift rate is in approximate equilibrium with erosion the stream power law model formulated by analogy to river incision and transport problems is found to be consistent with data since an inverse power law relationship between slope and drainage area is systematically observed between 7 10 3 and 1 km2 with little variability on the exponent 0 24 thanks to the range of uplift rates we obtain constraints on the slope dependency of erosion law which appears linear and which predicts a significant erosion threshold the linear dependence on slope in the debris flow zone is consistent with findings by kirby and whipple 2001 in the fluvial downstream zone and with the linear relationship between local relief and uplift rate documented by hurtrez et al 1999 the transition between this colluvial channel regime and the fluvial regime appears quite sharp in contrast with recent studies but the latter regime is not sufficiently documented to derive definite conclusions

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

the southern oscillation part iii associations with the trades and with the trough in the westerlies of the south pacific ocean abstract differences of sea level pressure between pairs of stations in the south pacific ocean are used to examine the trades and the trough in the westerlies during the development of the phase of the southern oscillation when pressures fall over the tropical pacific equatorial waters warm and rainfall increases in many otherwise dry places it is demonstrated that this phase is characterized by an appreciable enhancement of the annual cycle of the trades and the trough compared to the year before the warm event of 1982 followed this pattern closely

role of debris flows in long term landscape denudation in the central appalachians of virginia four major storms that triggered debris flows in the virginia west virginia appalachians provide new insights into the role of high magnitude low frequency floods in longterm denudation and landscape evolution in mountainous terrain storm denudation in the blue ridge mountain drainage basins is approximately an order of magnitude greater compared to basins located in the mountains of the valley and ridge province this difference is probably the result of higher storm rainfall from the blue ridge storms radiocarbon dating of debris flow deposits in the blue ridge indicates a debris flow return interval of not more than 2 4 k y in mountainous river basins this finding combined with measurements of basin denudation suggests that approximately half of the long term denudation from mechanical load occurs episodically by debris flow processes although floods of moderate magnitude are largely responsible for mobilizing sediment in lowgradient streams our data suggest that high magnitude low frequency events are the most significant component in delivering coarse grained regolith from mountainous hollows and channels to the lowland floodplains

sediment yield spatial characteristics and the long term evolution of active earthflows determined from airborne lidar and historical aerial photographs eel river california in mountainous landscapes with weak fine grained rocks earthflows can dominate erosion and landscape evolution by supplying sediment to channels and controlling hillslope morphology to estimate the contribution of earthflows to regional sediment budgets and identify patterns of landslide activity earthflow movement needs to be quantified over significant spatial and temporal scales presently there is a paucity of data that can be used to predict earthflow behavior beyond the seasonal scale or over spatially extensive study areas across 226 km 2 of rapidly eroding franciscan complex rocks of the eel river catchment northern california we used a combination of lidar light detection and ranging and orthorectified historical aerial photographs to objectively map earthflow movement between 1944 and 2006 by tracking the displacement of trees growing on earthflow surfaces we find that 7 3 of the study area experienced movement over this 62 yr interval preferentially in sheared argillaceous lithology this movement is distributed across 122 earthflow features that have intricate elongate planform shapes a preferred south southwesterly aspect and a mean longitudinal slope of 31 the distribution of mapped earthflow areas is well approximated by a lognormal distribution with a median size of 36 500 m 2 approximately 6 of the study area is composed of earthflows that connect to major channels these flows generated an average sediment yield of 19 000 t km 2 yr 1 rock erosion rate of 7 6 mm yr over the 62 yr study period equating to a regional yield of 1100 t km 2 yr 1 0 45 mm yr if distributed across the study area as such a small fraction of the landscape can account for half of the regional denudation rate estimated from suspended sediment records 2200 t km 2 yr 1 or 0 9 mm yr we propose a conceptual model for long term earthflow evolution wherein earthflows experience intermittent activity and long periods of dormancy when limited by the availability of readily mobilized sediment on upper slopes ultimately high order river channels and ephemeral gully networks may serve to destabilize hillslopes controlling the evolution of earthflow prone terrain

post fire geomorphic response in steep forested landscapes oregon coast range usa abstract the role of fire in shaping steep forested landscapes depends on a suite of hydrologic biologic and geological characteristics including the propensity for hydrophobic soil layers to promote runoff erosion during subsequent rainfall events in the oregon coast range several studies postulate that fire primarily modulates sediment production via root reinforcement and shallow landslide susceptibility although few studies have documented post fire geomorphic response here we describe field observations and topographic analyses for three sites in the central oregon coast range that burned in 1999 2002 and 2003 the fires generated strongly hydrophobic soil layers that did not promote runoff erosion because the continuity of the layers was interrupted by pervasive discontinuities that facilitated rapid infiltration at each of our sites fire generated significant colluvial transport via dry ravel consistent with other field based studies in the western united states fire driven dry ravel accumulation in low order valleys of our sulphur creek site equated to a slope averaged landscape lowering of 2 5 mm given holocene estimates of fire frequency these results suggest that fire may contribute 10 20 of total denudation across steep dissected portions of the oregon coast range in addition we documented more rapid decline of root strength at our sites than has been observed after timber harvest suggesting that root strength was compromised prior to fire or that intense heat damaged roots in the shallow subsurface given that fire frequencies in the pacific northwest are predicted to increase with continued climate change our findings highlight the importance of fire induced dry ravel and post fire debris flow activity in controlling sediment delivery to channels

particle friction angles in steep mountain channels sediment transport rates in steep mountain channels are typically an order of magnitude lower than predicted by models developed for lowland rivers one hypothesis for this observation is that particles are more stable in mountain channels due to particle particle interlocking or bridging across the channel width this hypothesis has yet to be tested however because we lack direct measurements of particle friction angles in steep mountain channels here we address this data gap by directly measuring the minimum force required to dislodge sediment pebbles to boulders and the sediment weight in mountain channels using a handheld force gauge at eight sites in california with reach averaged bed angles ranging from 0 5 to 23 and channel widths ranging from 2 m to 16 m we show that friction angles in natural streams average 68 and are 16 larger than those typically measured in laboratory experiments which is likely due to particle interlocking and burial results also show that larger grains are disproportionately more stable than predicted by existing models and that grains organized into steps are twice as stable as grains outside of steps however the mean particle friction angle does not vary systematically with bed slope these results do not support systematic increases in friction angle in steeper and narrower channels to explain the observed low sediment transport rates in mountain channels instead the spatial pattern and grain size dependence of particle friction angles may indirectly lower transport rates in steep narrow channels by stabilizing large clasts and channel spanning steps which act as momentum sinks due to form drag

the role of three dimensional boundary stresses in limiting the occurrence and size of experimental landslides the occurrence of seepage induced shallow landslides on hillslopes and steep channel beds is important for landscape evolution and natural hazards infinite slope stability models have been applied for seven decades but sediment beds generally require higher water saturation levels than predicted for failure and controlled experiments are needed to test models we initiated 90 landslides in a 5 m long laboratory flume with a range in sediment sizes d 0 7 2 5 and 15 mm and hillslope angles 20 to 43 resulting in subsurface flow that spanned the darcian and turbulent regimes and failures that occurred with subsaturated and supersaturated sediment beds near complete saturation was required for failure in most experiments with water levels far greater than predicted by infinite slope stability models although 3 d force balance models predict that larger landslides are less stable observed downslope landslide lengths were typically only several decimeters not the entire flume length boundary stresses associated with short landslides can explain the increased water levels required for failure and we suggest that short failures are tied to heterogeneities in granular properties boundary stresses also limited landslide thicknesses and landslides progressively thinned on lower gradient hillslopes until they were one grain diameter thick corresponding to a change from near saturated to supersaturated sediment beds thus landslides are expected to be thick on steep hillslopes with large frictional stresses acting on the boundaries whereas landslides should be thin on low gradient hillslopes or in channel beds with a critical saturation level that is determined by sediment size

evidence for debris flow gully formation initiated by shallow subsurface water on mars abstract the morphologies of some martian gullies appear similar to terrestrial features associated with debris flow initiation erosion and deposition on earth debris flows are often triggered by shallow subsurface throughflow of liquid water in slope mantling colluvium this flow causes increased levels of pore pressure and thus decreased shear strength which can lead to slide failure of slope materials and subsequent debris flow the threshold for pore pressure induced failure creates a distinct relationship between the contributing area supplying the subsurface flow and the slope gradient to provide initial tests of a similar debris flow initiation hypothesis for martian gullies measurements of the contributing areas and slope gradients were made at the channel heads of martian gullies seen in three hirise stereo pairs these gullies exhibit morphologies suggestive of debris flows such as leveed channels and lobate debris fans and have well defined channel heads and limited evidence for multiple flows our results show an area slope relationship for these martian gullies that is consistent with that observed for terrestrial gullies formed by debris flow supporting the hypothesis that these gullies formed as the result of saturation of near surface regolith by a liquid this model favors a source of liquid that is broadly distributed within the source area and shallow we suggest that such liquid could be generated by melting of broadly distributed icy materials such as snow or permafrost this interpretation is strengthened by observations of polygonal and mantled terrain in the study areas which are both suggestive of near surface ice

cosmogenic 3he ages and frequency of late holocene debris flows from prospect canyon grand canyon usa abstract lava falls rapid which was created and is maintained by debris flows from prospect canyon is the most formidable reach of whitewater on the colorado river in grand canyon and is one of the most famous rapids in the world debris flows enter the colorado river at tributary junctures creating rapids the frequency of debris flows is an important consideration when management of regulated rivers involves maintenance of channel morphology we used cosmogenic 3 he 14 c and historical photographs to date 12 late holocene and historic debris flows from prospect canyon the highest and oldest deposits from debris flows on the debris fan yielded a 3 he date of about 3 ka which indicates predominately late holocene aggradation of one of the largest debris fans in grand canyon the deposit which has a 25 m escarpment caused by river reworking crossed the colorado river and raised its base level by 30 m for an indeterminate although likely short period we mapped depositional surfaces of 11 debris flows that occurred after 3 ka two deposits inset against the highest deposit yielded 3 he ages of about 2 2 ka and at least two others followed shortly afterwards at least one of these debris flows also dammed the colorado river the most recent prehistoric debris flow occurred no more than 0 5 ka the largest historic debris flow which constricted the river by 80 occurred in 1939 five other debris flows occurred after 1939 these debris flows constricted the colorado river by 35 80 assuming the depositional volumes of late holocene debris flows can be modeled using a lognormal distribution we calculated recurrence intervals of 15 to more than 2000 years for debris flows from prospect canyon

direct measurement of channel erosion by debris flows illgraben switzerland 1 the timing and magnitude of channel bed erosion by three debris flows was measured in 2008 at the illgraben catchment switzerland using a scour sensor which consisted of a vertical array of erodible sensor elements during the largest debris flow sediment was entrained progressively and stepwise at the flow head within 20 s after front arrival and onset of erosion started before maximum values for flow height and normal and shear stress measured nearby were reached erosion in one of the two smaller debris flows also occurred at the head of the flow but the magnitude of erosion was at the detection limit for the sensor for the other small debris flow we were not able to determine the timing of erosion due to the presence of a sediment layer covering the sensors measurements of pressure fluctuations along the channel sidewall which are produced by interparticle collisions within the flow indicate that the entrainment of sediment is coincident with the largest mean and fluctuating pressures suggesting that interparticle collisions may drive the erosion process at the front of debris flows after erosion at the head of the debris flows sediment was deposited on top of the erosion sensor columns indicating that the bed was reworked to a larger depth than directly visible at the surface after the event observations from elsewhere along the channel support our measurements of the magnitude of net debris flow erosion and indicate that significant erosion can be expected on debris fans when the flow is confined to a channel debris flow entrainment and subsequent bulking of the flow influence the flow dynamics and therefore should be considered in debris flow models and hazard assessment

diagenetic variation in the oregon coast range implications for rock strength soil production hillslope form and landscape evolution the mechanisms by which lithology modulates geomorphic processes are poorly known in the oregon coast range ocr rhythmically bedded sandstones of the eocene tyee formation underlie steep soil mantled hillslopes with relatively uniform ridge valley spacing these characteristic landforms are perturbed where diagenetic variations manifest as resistant cliffs here we use petrology rock mechanics and lidar to characterize grain scale variations in rock properties and their influence on rock strength hillslope processes and landscape morphology in two adjacent watersheds petrographic analyses suggest that a suite of diagenetic products in the resistant bedrock account for a 2 5 times increase in tensile strength relative to typical tyee bedrock our reference catchment exhibits negligible resistant outcrops and consistent hillslope gradients and longitudinal valley profiles by contrast the adjacent catchment teems with resistant 1 to 10 m thick noncontiguous sandstone beds that form hanging valleys with gentle upstream hillslopes and anomalously narrow valleys mechanical and topographic analyses suggest that the low fracture density characteristic of these resistant beds may render them relatively impervious to comminution by tree root activity the dominant ocr soil production mechanism based on both hillslope gradient and hilltop curvature erosion models we estimate that hillslopes perched above resistant beds erode at approximately half the pace of hillslopes unencumbered by downstream knickpoints the diagenetic variations likely influence relief at the watershed scale depositional position and diagenetic processes appear to control the occurrence of resistant beds providing a framework to quantify how seemingly subtle variations in rock properties can impose first order controls on landscape form and evolution

debris flows on the great kobuk sand dunes alaska implications for analogous processes on mars abstract we observed niveo aeolian deposits denivation features and small meltwater induced debris flows that had formed at the great kobuk sand dunes northwestern interior alaska in late march 2010 this high latitude cold climate dune field is being studied as a planetary analog to improve our understanding of factors that may trigger debris flows on the lee slopes of martian aeolian dunes debris flows consisted of a sand and liquid water mixture that cascaded down the lee slopes of two barchanoid dunes on days when measured ground surface temperatures were below freezing we hypothesize that relatively dark sand on snow caused local hot spots where solar radiation could be absorbed by the sand and conducted into the underlying snow enabling meltwater to form and sand to be mobilized this investigation provides insights into the interactions between niveo aeolian deposition slope aspect and insolation thawing and initiation of alluvial processes these debris flows are morphologically similar to those associated with seasonal gullies or erosion tracks visible on the slopes of mid to high latitude dune fields in both martian hemispheres localized heating and thawing at scales too small for orbital sensors to identify may yield martian debris flows at current climate conditions

predicting deposition of debris flows in mountain channels an empirical model for predicting deposition of coarse textured debris flows in confined mountain channels is developed based on field measurements of 14 debris flows in the pacific northwest u s a the model uses two criteria for deposition channel slope less than 3 5 and tributary junction angle greater than 70 the model is tested by predicting travel distances of 15 debris flows in the oregon coast range and six debris flows in the washington cascades u s a the model is further tested on 44 debris flows in two lithological types in the oregon coast range using aerial photos and topographic maps on these flows only the approximate travel distance is known the model can be used by resource professionals to identify the potential for impacts from debris flows key words debris flow deposition travel erosion

drainage area bedrock fracture spacing and weathering controls on landscape scale patterns in surface sediment grain size sediment grain size affects river function at the reach and landscape scale yet models of grain size delivery to river networks remain unconstrained due to a scarcity of field data we analyze ho

calculating bed load transport in steep boulder bed channels 1 steep rough channels occupy a large fraction of the total channel length in mountainous regions most sediment mobilized on hillslopes must pass through these streams before reaching lower gradient channels steep channels have wide grain size distributions that are composed of finer more mobile sediment and large rarely mobile grains the large grains can bear a significant portion of the total shear stress and thereby reduce the stress available to move the finer sediment conventional bed load transport equations often overpredict the sediment flux in steep channels by several orders of magnitude we hypothesize that sediment transport equations overpredict the sediment flux because they do not 1 account for the stress borne by rarely mobile grains 2 differentiate between highly and rarely mobile sediment and 3 account for the limited availability of mobile sediment here we modify a conventional bed load transport equation to include these three effects we use measurements of the flow bed properties and sediment flux in a small steep flume to test this equation we supply gravel at a constant rate through fields of regularly spaced immobile spheres and measure the bed coverage by gravel and sphere protrusion the percent of the sphere that protrudes above the gravel deposit for a given sphere spacing the proportion of the bed covered by gravel increases and the sphere protrusion decreases with greater sediment supply thus bed coverage and immobile grain protrusion may serve as proxies for sediment availability in steep rough streams unlike most transport equations that we tested our modified bed load equation predicts sediment fluxes to within an order of magnitude of the measured values our results demonstrate that accurately predicting bed load transport in steep rough streams may require accounting for the effects of local sediment availability coverage by mobile sediment and drag due to rarely mobile particles

numerical simulation of the impact of sediment supply and streamflow variations on channel grain sizes and chinook salmon habitat in mountain drainage networks climatically driven changes in streamflow and hillslope sediment supply could potentially alter stream surface grain size distribution patterns and thereby impact habitat for a number of threatened and endangered in stream fish species relatively little is known about hydrograph shape peak flow influence or the relative importance of chronic and episodic hillslope inputs on channel conditions to better understand these external drivers we calculated sediment routing through a gravel bedded river network using a one dimensional 1d bedload transport model we calculated changes in grain sizes and estimated chinook salmon habitat suitability caused by a dry year and an extreme flood hydrograph and chronic diffusive overland flow or pulse landslide debris flow hillslope sediment supplies to obtain accurate channel conditions a relatively high reference shields stress representative of steep mountain streams was needed an extreme event flood without any hillslope sediment inputs caused widespread bed coarsening and a decrease in aquatic habitat chronic sediment input combined with this hydrograph eliminated any changes in grain size and habitat although when combined with a dry year flow caused systematic bed fining the influence of a given hydrograph therefore highly depends on the hillslope sediment supply regardless of the flow hydrograph or sediment pulse timing grain size distribution or location pulse sediment inputs did not cause widespread grain size changes despite being 100 times the total chronic input volume widespread and continuous hillslope sediment inputs may influence channel grain sizes and aquatic habitat more than a single discrete sediment pulse depending on the magnitudes of flow hydrograph and sediment supply alterations climate change may induce no differences in grain sizes or very dramatic changes with significant consequences for long term sustainability copyright 2013 john wiley sons ltd

definition of antarctic oscillation index following walker s work about his thmous three oscillations published during the 1920 30s many papers were written about atmospheric oscillations a iburth atmospheric oscillation in the middle and high southern latitudes was lbund and nanted the grotarctic oscillation ao a refiers to a large scale alternation of atmospheric mass between the mid latitudes and high latitudes surthce pressure in order to understand the spatial structure of sea level pressure variation in detail empirical orthogonal fitnction analysis is applied an objective index of the antarctic oscillation index aoi is defined as the diffierence of zonal mean sea level pressure between 40os and 65os the aoi has the potential tbr clarifying climate regimes in the southern hemisphere similar to how the na and the npo has been used in the northern hemisphere were there other oscillation s besides nao npo and s especially in the southern hemisphere it had been supposed that there might be other atmospheric oscillation s in the high southern latitudes although as early as in the first quarter of this century walker 1928 had stated that just as in the north atlantic there is a pressure opposition between the azores and iceland there is an opposition between the high pressure belt across chile and the argentine on the one hand and the low pressure area of weddell sea and the bellingshausen sea on the other the scarcity of data in the southern hemisphere hindered the search tbr new oscillation s during the last two decades more comprehensive data over the southern hemisphere became available and more analyses were carried out see kidson 1975 rogers and van loon 1982 mo and l 7 ite 1985 2 4o 1986 connolley 1997 gong and wang 1998 a tburth atmospheric oscillation in the middle and high southern latitudes was tbund and nanted as the antarctic oscillation a wang 1992 gong and wang 1998 the term ao relrs to a large scale alternation of atmospheric mass between the mid latitude sur hce pressure

effect of air sea ice interaction on winter 1996 southern ocean subpolar storm distribution air sea ice interaction processes in the southern ocean are investigated utilizing space observed surface winds sea ice concentration and sea surface temperature sst from september through december 1996 the sea ice edge sie shows three ice extent maxima around the antarctic during september and october when sea ice coverage is maximum they are located in the central indian ocean east of the ross sea and in the eastern weddell gyre during september and october most of the strong and long lasting storms initiate northeast of the three sea ice maxima such spatial distributions of storms and sea ice reflect coupling processes of the air sea ice interaction a relatively stable wave number 3 atmospheric circulation pattern that is believed to be fixed by the land ocean distribution prevails during the ice maximum season the ice extent maxima coincide with strong southerlies and divergent wind fields associated with this pattern which suggests that the mean atmospheric circulation determines the ice distribution the ice extent maxima can enhance the regional meridional surface pressure gradient and therefore strengthen the westerly winds north of the ice edge the decreasing ice extent east of the ice maxima creates a local zonal thermal gradient which enhances local southerlies this positive feedback between the wave pattern in the mean atmospheric circulation and ice distribution partially causes the eastward propagation of the ice maxima and also provides a favorable condition for cyclogenesis northeast of the ice extent maxima the mechanism of the cyclogenesis is the baroclinic instability caused by the cold air blown from the ice pack to the warm open ocean waters where the sst is warmest off the sie and the southerlies are the strongest the potential for cyclogenesis is most likely this is consistent with the observations

quantification of the transient response to base level fall in a small mountain catchment sierra nevada southern spain 1 we integrated optically stimulated luminescence dating and 10be cosmogenic nuclide measurements to quantify short to medium term 102 104 years catchment dynamics and response to active tectonics in the 27 km2 rio torrente catchment sierra nevada southern spain rapid base level fall has triggered knickpoint migration up both trunk and tributary channels resulting in two distinct geomorphic zones 1 a steep lower catchment with concordant rates of hillslope erosion and channel incision over both short 100 years 5 8 mm yr 1 and medium 12 ka 5 1 mm yr 1 timescales and 2 a low relief soil mantled upland topography with uniformly low bedrock and hillslope erosion rates 0 05 0 02 mm yr 1 the uniformity of erosion in this upland surface indicates that catchment topography was previously in steady state rapid river incision below the channel knickpoints has resulted in the development of steep landslide dominated hillslopes that are essentially tracking the incising channel the magnitude of base level fall required to generate these steep hillslopes is 100 m at least 50 m of this base level fall occurred during the past 21 ka these steep hillslopes are eroding back into the low angled upland surface at a much slower rate than the channel knickpoint consequently the trunk channel knickpoint has already reached the catchment headwaters while hillslopes continue to adjust to the new base level indicating that the channel profile will regain equilibrium form long before hillslopes thus hillslopes are the limiting factor for the duration of landscape transience in this small mountain catchment

new views of granular mass flows concentrated grain fluid mixtures in rock avalanches debris flows and pyroclastic flows do not behave as simple materials with fixed rheologies instead rheology evolves as mixture agitation grain concentration and fluid pressure change during flow initiation transit and deposition throughout a flow however normal forces on planes parallel to the free upper surface approximately balance the weight of the superincumbent mixture and the coulomb friction rule describes bulk intergranular shear stresses on such planes pore fluid pressure can temporarily or locally enhance mixture mobility by reducing coulomb friction and transferring shear stress to the fluid phase initial conditions boundary conditions and grain comminution and sorting can influence pore fluid pressures and cause variations in flow dynamics and deposits

characterizing the primary material sources and dominant erosional processes for post fire debris flow initiation in a headwater basin using multi temporal terrestrial laser scanning data abstract wildfire dramatically alters the hydrologic response of a watershed such that even modest rainstorms can produce hazardous debris flows relative to shallow landslides the primary sources of material and dominant erosional processes that contribute to post fire debris flow initiation are poorly constrained improving our understanding of how and where material is eroded from a watershed during a post fire debris flow requires 1 precise measurements of topographic change to calculate volumetric measurements of erosion and deposition and 2 the identification of relevant morphometrically defined process domains to spatially constrain these measurements of erosion and deposition in this study we combine the morphometric analysis of a steep small 0 01 km 2 headwater drainage basin with measurements of topographic change using high resolution 2 5 cm multi temporal terrestrial laser scanning data made before and after a post fire debris flow the results of the morphometric analysis are used to define four process domains hillslope divergent hillslope convergent transitional and channelized incision we determine that hillslope divergent and hillslope convergent process domains represent the primary sources of material over the period of analysis in the study basin from these results we conclude that raindrop impact induced erosion ravel surface wash and rilling are the primary erosional processes contributing to post fire debris flow initiation in the small steep headwater basin further work is needed to determine 1 how these results vary with increasing drainage basin size 2 how these data might scale upward for use with coarser resolution measurements of topography and 3 how these results change with evolving sediment supply conditions and vegetation recovery

an integrated method for rapid estimation of the valley incision by debris flows abstract valley incision by debris flow is an important process in creating and maintaining the topography of a valley in addition to explaining the significant growth of the magnitudes of debris flow hazards in this paper we introduce a semi empirical method to quantitatively estimate the valley incision process by debris flows over complex bed surface we first reproduce natural bed surface across the valley by a polyline and use a hydrograph of discharge versus time to represent the temporal variation of debris flow process the presented method subsequently predicts the debris flow behavior over an irregular bed surface a dynamic erosion law considers the solved debris flow behavior and estimates an instantaneous erosion rate finally the accumulative incision depth of bed sediment is calculated reshaping the initial bed surface across the valley the presented method is simple and therefore notably beneficial for practical work the performance of the proposed method has been tested using two case study applications results demonstrate that the presented method estimates comparable incision depth as revealed in the in situ survey and the numerical simulation

survey of precursors to p p fine structure of mantle discontinuities 1 the jumps in seismic velocity and density near 410 and 660 km depths have been postulated to mark phase changes in a locally chemically homogeneous mantle seismic estimates of upper mantle discontinuity thickness and lateral variability have varied posing difficulties for assessing models with chemical and phase transition layering observations of underside high frequency 1 hz p wave reflections from the 410 and 660 km discontinuity that precede the p p phase provide unique constraints on the physical properties of these dynamically critical features we have collected high quality recordings of p p and its precursors from three sources the california seismic network the large aperture seismic array in montana and the global seismic network the array and regional network data have great sensitivity to weak p p precursors whereas the global network recordings have good geographical distribution of bounce points the only consistently observed reflections originate from depths near 410 km and 660 km the reflector observed near 520 km depth with longer period waves which has been interpreted as the olivine phase transition is too small in impedance contrast or too thick to reflect 1 hz p waves data from all three networks indicate that the 1 hz p waves from the 660 are bigger than those from the 410 although large variability in p p and its precursors amplitudes prevents strong conclusions we show that the p p precursor amplitudes travel time dispersion and frequency content are consistent with a sharp 2 km 660 and a more diffuse 410 consistent with mineral physics predictions

the variability of root cohesion as an influence on shallow landslide susceptibility in the oregon coast range decades of quantitative measurement indicate that roots can mechanically reinforce shallow soils in forested landscapes forests however have variations in vegetation species and age which can dominate the local stability of landslide initiation sites to assess the influence of this variability on root cohesion we examined scarps of landslides triggered during large storms in february and november of 1996 in the oregon coast range and hand dug soil pits on stable ground at 41 sites we estimated the cohesive reinforcement to soil due to roots by determining the tensile strength species depth orientation relative health and the density of roots 1 mm in diameter within a measured soil area we found that median lateral root cohesion ranges from 6 8 23 2 kpa in industrial forests with significant understory and deciduous vegetation to 25 6 94 3 kpa in natural forests dominated by coniferous vegetation lateral root cohesion in clearcuts is uniformly 10 kpa some 100 year old industrial forests have s

climatic control of denudation in the deglaciated landscape of the washington cascades erosion in the washington cascades mountains was dominated by glacier activity until the end of the last glacial maximum when fluvial incision and mass wasting became the dominant drivers an analysis of millennial scale rates of denudation in the range suggest erosion is sensitive both to spatial variations in precipitation and inherited topography

flexural models of continental lithosphere based on the long term erosional decay of topography summary the most easily observed geophysical characteristic of continents is their surface topography topographic power in the spectral range 1000 100 km has been computed for north american geological provinces and is found to decrease systematically as the tectonic age of the underlying crust increases these data have been quantitatively modelled in terms of topographic erosion and stress relaxation within the continental lithosphere through geological time spans the lithosphere is treated as a thin maxwell viscoelastic plate which deforms flexurally in response to the vertical surface loads of topography and its erosion effective rheological model parameters are flexural rigidity d a measure of the lithosphere s elastic strength and viscous relaxation time constant a measure of its viscosity erosion is assumed to occur at a rate linearly proportional to the height of topography at any given time the proportionality being determined by the erosion time constant the models are constructed in space and time frequency domains using simple linear systems theory two loading schemes are considered model 1 assumes that a flexurally competent lithosphere is suddenly loaded by topography which subsequently erodes whereas model 2 ignores the emplacement and erosion of topography during orogenesis when the lithosphere is thermally activated and considers only the load effected by erosion beginning some time later when the lithosphere has cooled and strengthened both models predict that the remnant topography of very old regions such as the canadian shield can be maintained in fact is favoured by a viscoelastic lithosphere with as small as 1 10ma the continued existence of such topography does not necessarily imply significant long term lithospheric strength model 1 results indicate low values of the flexural rigidity d 1021 1022nm which are interpreted to characterize not so much presentday d but that which was effective when topography was formed model 2 more successfully reproduces the data and constrains the product d to values 1024 1025nm ma which compare very favourably to those found from studies of individual loads on continental lithosphere the model results show that the erosion time constant is probably wavenumber dependent and falls in the range 200 400ma for the topographic wavelengths under consideration

geologic constraints on bedrock river incision using the stream power law denudation rate in unextended terranes is limited by the rate of bedrock channel incision often modeled as work rate on the channel bed by water and sediment or stream power the latter can be generalized as ka m s n where k represents the channel bed s resistance to lowenng whose variation with lithology is unknown a is drainage area a surrogate for discharge s is local slope and m and n are exponents whose values are debated we address these uncertainties by simulating the lowering of ancient river profiles using the finite difference method we vary m n and k to match the evolved profile as closely as possible to the corresponding modern river profile over a time period constrained by the age of the mapped paleoprofiles we find at least two end member incision laws ka 0 3 0 5 s for australian rivers with stable base levels and k f a 0 1 0 2 s n for rivers in kauai subject to abrupt base level change the long term lowering rate on the latter expression is a function of the frequency and magnitude of knickpoint erosion characterized by k f incision patterns from japan and california could follow either expression if they follow the first expression with m 0 4 k varies from 10 7 10 6 m 0 2 yr for granite and metamorphic rocks to 10 5 10 4 m 0 2 yr for volcaniclastic rocks and 10 4 10 2 m 0 2 yr for mudstones this potentially large variation in k with lithology could drive strong variability in the rate of long term landscape change including denudation rate and sediment yield

sediment and rock strength controls on river incision into bedrock recent theoretical investigations suggest that the rate of river incision into bedrock depends nonlinearly on sediment supply challenging the common assumption that incision rate is simply proportional to stream power our measurements from laboratory abrasion mills support the hypothesis that sediment promotes erosion at low supply rates by providing tools for abrasion but inhibits erosion at high supply rates by burying underlying bedrock beneath transient deposits maximum erosion rates occur at a critical level of coarse grained sediment supply where the bedrock is only partially exposed fine grained sediments provide poor abrasive tools for lowering bedrock river beds because they tend to travel in suspension experiments also reveal that rock resistance to fluvial erosion scales with the square of rock tensile strength our results suggest that spatial and temporal variations in the extent of bedrock exposure provide incising rivers with a previously unrecognized degree of freedom in adjusting to changes in rock uplift rate and climate furthermore we conclude that the grain size distribution of sediment supplied by hillslopes to the channel network is a fundamental control on bedrock channel gradients and topographic relief

dendrochronological analysis of debris flow disturbance on rishiri island abies sachalinensis dominates the alluvial fan head of the ochiushinai gully on rishiri island japan this species is able to adapt to frequent disturbances by debris flows even aged stands composed of a sachalinensis or alnus maximowiczii were found along the channel and standing dead trees buried by debris flows were discovered at the alluvial fan head we used dendrochronological data in order to analyse the geomorphic history of the fan head we determined the master ring width chronology by synchronizing ring width variations in living trees this master chronology was used to cross date the establishment and death of the buried trees results indicated that most of the buried trees were established in the 1870s and died in the early 1950s further debris flow was estimated to have occurred in the 1890s and the late 1960s based upon the distribution of even aged stands seen in aerial photos the ring width variations of the trees adjacent to the channel indicate a low correlation for synchronization while those located on the hillslope have a high correlation a low correlation in the riparian trees can be attributed to the instability of geomorphic surfaces caused by debris flow disturbances

correlation between dredgeability and mechanical properties of rock abstract due to high investments involved in rock dredging a good prediction of the dredgeability is essential the aim of this study is to investigate the correlation between rock mechanical properties and parameters describing the dredgeability the site studied is an area of 3 5 km2 at ra s laffan port in qatar the rock mass dredged consists of dolomitic limestone calcarenite and caprock rock mechanical properties used in the study are the point load index is50 the unconfined compressive strength ucs the rock quality designation rqd and the fissure index fi is50 varies between 0 5 and 6 5 mpa ucs between 5 and 70 mpa rqd between 0 and 70 and the average fi per borehole between 5 and 13 m the two production parameters investigated in this study are the volume excavation rate and the wear rate the volume excavation rate or productivity is expressed as volume of rock material dredged per hour the wear rate is expressed as the volume of rock material dredged per pick point used a correlation is noted between the individual rock mechanical properties and the wear rate however a correlation between these individual properties and the volume excavation rate is not observed the main reason for this is without doubt that a process as complex as dredging is not influenced by one property only but by a combination of several properties therefore a rock mass rating system has been developed to incorporate three properties into one system the three properties considered are the strength of the intact rock material cf ucs the frequency of discontinuities cf fi and the thickness of the various layers firstly the strength of the intact rock is reduced as a function of the fissure index secondly the newly determined strength is divided in three classes 20 mpa a rating value is given to each package of successive layer s belonging to one class the arbitrarily chosen rating values are a function of the strength and of the thickness of the package the latter parameter is compared to the diameter of the cutterhead and of the suction pipe for a complete borehole the values for each layer or package of layers are added resulting in the total rating by making such a combination of the three rock mechanical properties a correlation is observed with wear rate as well as with the volume excavation rate

objective extraction of channel heads from high resolution topographic data fluvial landscapes are dissected by channels and at their upstream termini are channel heads accurate reconstruction of the fluvial domain is fundamental to understanding runoff generation storm hydrology sediment transport biogeochemical cycling and landscape evolution many methods have been proposed for predicting channel head locations using topographic data yet none have been tested against a robust field data set of mapped channel heads across multiple landscapes in this study four methods of channel head prediction were tested against field data from four sites with high resolution dems slope area scaling relationships two techniques based on landscape tangential curvature and a new method presented here which identifies the change from channel to hillslope topography along a profile using a transformed longitudinal coordinate system our method requires only two user defined parameters determined via independent statistical analysis slope area plots are traditionally used to identify the fluvial hillslope transition but we observe no clear relationship between this transition and field mapped channel heads of the four methods assessed one of the tangential curvature methods and our new method most accurately reproduce the measured channel heads in all four field sites feather river ca mid bailey run oh indian creek oh piedmont va with mean errors of 11 7 5 and 24 m and 34 3 12 and 58 m respectively negative values indicate channel heads located upslope of those mapped in the field importantly these two independent methods produce mutually consistent estimates providing two tests of channel head locations based on independent topographic signatures

patterns and controls of sediment production transfer and yield in the illgraben quantification of the volumes of sediment removed by rock slope failure and debris flows and identification of their coupling and controls are pertinent to understanding mountain basin sediment yield and landscape evolution this study captures a multi decadal period of hillslope erosion and channel change following an extreme rock avalanche in 1961 in the illgraben a catchment prone to debris flows in the swiss alps we analyzed photogrammetrically derived datasets of hillslope and channel erosion and deposition along with climatic and seismic variables for a 43 year period from 1963 to 2005 based on these analyses we identify and discuss 1 patterns of hillslope production channel transfer and catchment sediment yield 2 their dominant interactions with climatic and seismic variables and 3 the nature of hillslope channel coupling and implications for sediment yield and landscape evolution in this mountain basin our results show an increase in the mean hillslope erosion rate in the 1980s from 0 24 0 01 m yr 1 to 0 42 0 03 m yr 1 that coincided with a significant increase in air temperature and decrease in snow cover depth and duration which we presume led to an increase in the exposure of the slopes to thermal weathering processes the combination of highly fractured slopes close to the threshold angle for failure and multiple potential triggering mechanisms means that it is difficult to identify an individual control on slope failure on the other hand the rate of channel change was strongly related to variables influencing runoff a period of particularly high channel erosion rate of 0 74 0 02 m yr 1 1992 1998 coincided with an increase in the frequency and magnitude of intense rainfall events hillslope erosion exceeded channel erosion on average indicative of a downslope directed coupling relationship between hillslope and channel and demonstrating the first order control of rock slope failure on catchment sediment yield and landscape evolution

the influence of debris flows on channels and valley floors in the oregon coast range u s a debris flows are one of the most important processes which influence the morphology of channels and valley floors in the oregon coast range debris flows that initiate in bedrock hollows at heads of first order basins erode the long accumulated sediment and organic debris from the floors of headwater first and second order channels this material is deposited on valley floors in the form of fans levees and terraces in channels deposits of debris flows control the distribution of boulders the stochastic nature of sediment supply to alluvial channels by debris flows promotes cycling between channel aggradation which results in a gravel bed morphology and channel degradation which results in a mixed bedrock and boulder bed morphology temporal and spatial variability of channel bed morphology is expected in other landscapes where debris flows are an important process

the surface windfield over the antarctic ice sheets the intense radiative cooling of air over the ice slopes of antarctica generates a surface wind regime that is strongly controlled by topography and plays a key role in determining the behaviour of the atmosphere and ocean in high southern latitudes1 7 resultant surface winds are intimately linked to the orientation of the ice terrain fig 1 and display the highest degree of persistence found on earth the close coupling between wind and topography allows estimation of the former if the latter is known with some precision here we report on time averaged near surface airflow over the antarctic continent during winter diagnosed from a recent accurate synthesis of terrain slopes and from estimates of the lower atmospheric temperature structure the simulated drainage pat tern exhibits strong spatial variability with the airflow concentrated into several zones near the coastal margin these confluence regions are responsible for strong persistent katabatic winds over downstream coastal stretches and are indicative of zones of greatest katabatic potential

late quaternary stream incision and uplift in the forearc of the cascadia subduction zone western oregon documentation of a latest pleistocene earliest holocene episode of strath formation and fluvial aggradation in the oregon coast range provides a datum from which long term bedrock stream incision rates are determined variations in long term incision rates probably reflect cumulative differential uplift in the forearc of the cascadia subduction zone although factors such as bedrock and climatic controls and isostatic adjustments to erosion obscure the precise relationship between surface uplift and stream incision patterns of differential incision are most striking near the latitude of newport where a steep gradient divides a region of higher rates 0 6 0 9 mm yr in the northern coast range from a region of lower rates 0 1 0 3 mm yr in the central coast range the steep incision gradient is nearly coincident with abrupt changes in marine terrace 80 125 kyr uplift rates the locations of quaternary faults and the southern flank of a saddle of low historic 40 70 years uplift the exact causes of these variable patterns of incision uplift are unknown analogies with uplift patterns in other subduction zones and comparisons with other neotectonic data in the region indicate that patterns of differential incision probably are caused by variations in permanent strain accumulation along the cascadia subduction zone such variations may be related to differences in seismic moment release during individual earthquakes to changes in plate geometry or rates of wedge accretion to segmentation of earthquake ruptures and or to deformation on active structures in the north american plate and accretionary wedge

dynamics of penguin population size and food availability at prydz bay east antarctica during the last millennium a solar control abstract the paleoecology of the adelie penguin pygoscelis adeliae is controlled by multiple factors in this study we analyzed two millennial scale ornithogenic sediment cores rnl and rl from the vestfold hills east antarctica using the al normalized phosphorus content of the bulk sediment and carbon nitrogen fractions in penguin remains we reconstructed relative changes in the penguin population size of each sub colony and relative krill abundance in the summer prydz bay polynya both records are correlated to solar irradiance at the centennial scale the penguin population recorded in core rnl decreased from 1120 860 yr bp reached a peak from 860 630 yr bp remained at a low level from 630 320 yr bp and then increased with large fluctuations during the past 400 years these changes are all in phase with the trend of solar irradiance at the decadal scale penguin population minima correspond to solar minima from 490 400 yr bp sporer minimum 290 220 yr bp maunder minimum and from 160 120 yr bp dalton minimum whereas population maxima correspond to solar maxima from 1030 980 yr bp 350 290 yr bp 210 160 yr bp 120 70 yr bp the population recorded in core rl exhibited the same changes as in rnl during the last 480 years the reconstructed krill abundance also corresponds to these trends when data are available this correspondence demonstrates a food chain mechanism that is related to solar activity and light availability at the ocean surface which influence the intensity of photosynthesis and phytoplankton productivity and thus the abundance of krill and apex predators such as penguins our findings highlight the fact that despite the various climatic impacts on penguin populations their effects on the base of the food chain are usually the direct drive

geomorphic response of coastal streams to low intermediate and high rates of uplift medocino triple junction region northern california analysis of three dimensional morphological properties of 24 coastal drainage basins that have evolved in areas of low 3 m 1 000 yr rates of uplift near the mendocino triple junction mtj coastal northern california identified channel gradients as the best indicator of tectonism in the landscape lower order tributaries best reflect tectonically controlled differences the largest streams examined of third order are able to adjust to most base level change and maintain their profile form whereas lower order streams farther upstream tend to accumulate the effects of net base level fall and have steepest profiles in the areas of highest uplift rates variations in steepness of first order channel gradients indicate that 1 high uplift rates in the wake of the mtj have existed for at least 73 000 yr and 2 differential tilt of the region to the north and south of the current locus of highest uplift rate is occurring in association with regional uplift although first order streams are excellent indicators of areas of both high uplift rates and regional differential tilting they are less useful in distinguishing between areas of low and intermediate uplift rate analysis of the longitudinal profile of the main trunk stream of ten of the 24 drainage basins using the stream gradient index was more useful to categorize broadly the uplift rates and to distinguish between streams in low and intermediate uplift rate areas although the hypotheses tested herein do not identify the exact mechanism off uplift in the mtj region they do indicate that the nature of deformation is most likely regional tilt rather than crustal shortening with localized compressional folding and thrust faulting they also indicate that geomorphic responses trail in the wake of the uplift rate response caused by development of a slab window beneath the north american plate 1 maximum uplift rates occur 9 km south of the northern boundary of the slab window 2 maximum mean first order channel gradient occurs 16 km south of the northern edge of the slab window and 3 maximum drainage basin relief occurs 20 km south of the northern edge of the slab window associated lag times between passage of the southern edge of the subducted gorda plate slab and geomorphic responses are 160 000 yr for maximum uplift rates 290 000 yr for maximum channel gradients and 370 000 yr for maximum relief