a spatially distributed model for the dynamic prediction of sediment erosion and transport in mountainous forested watersheds 1 erosion and sediment transport in a temperate forested watershed are predicted with a new sediment model that represents the main sources of sediment generation in forested environments mass wasting hillslope erosion and road surface erosion within the distributed hydrology soil vegetation model dhsvm environment the model produces slope failures on the basis of a factor of safety analysis with the infinite slope model through use of stochastically generated soil and vegetation parameters failed material is routed downslope with a rule based scheme that determines sediment delivery to streams sediment from hillslopes and road surfaces is also transported to the channel network a simple channel routing scheme is implemented to predict basin sediment yield we demonstrate through an initial application of this model to the rainy creek catchment a tributary of the wenatchee river which drains the east slopes of the cascade mountains that the model produces plausible sediment yield and ratios of landsliding and surface erosion when compared to published rates for similar catchments in the pacific northwest a road removal scenario and a basin wide fire scenario are both evaluated with the model

large scale dam removal on the elwha river washington usa river channel and floodplain geomorphic change abstract a substantial increase in fluvial sediment supply relative to transport capacity causes complex large magnitude changes in river and floodplain morphology downstream although sedimentary and geomorphic responses to sediment pulses are a fundamental part of landscape evolution few opportunities exist to quantify those processes over field scales we investigated the downstream effects of sediment released during the largest dam removal in history on the elwha river washington usa by measuring changes in riverbed elevation and topography bed sediment grain size and channel planform as two dams were removed in stages over two years as 10 5 million t 7 1 million m3 of sediment was released from two former reservoirs downstream dispersion of a sediment wave caused widespread bed aggradation of 1 m greater where pools filled changed the river from pool riffle to braided morphology and decreased the slope of the lowermost river the newly deposited sediment which was finer than most of the pre dam removal bed formed new bars largely pebble granule and sand material prompting aggradational channel avulsion that increased the channel braiding index by almost 50 as a result of mainstem bed aggradation floodplain channels received flow and accumulated new sediment even during low to moderate flow conditions the river system showed a two to tenfold greater geomorphic response to dam removal in terms of bed elevation change magnitude than it had to a 40 year flood event four years before dam removal two years after dam removal began as the river had started to incise through deposits of the initial sediment wave 1 2 million t of new sediment 10 of the amount released from the two reservoirs was stored along 18 river km of the mainstem channel and 25 km of floodplain channels the elwha river thus was able to transport most of the released sediment to the river mouth the geomorphic alterations and changing bed sediment grain size along the elwha river have important ecological implications affecting aquatic habitat structure benthic fauna salmonid fish spawning and rearing potential and riparian vegetation the response of the river to dam removal represents a unique opportunity to observe and quantify fundamental geomorphic processes associated with a massive sediment influx and also provides important lessons for future river restoration endeavors

shredding of environmental signals by sediment transport 1 landscapes respond to climate tectonic motions and sea level but this response is mediated by sediment transport understanding transmission of environmental signals is crucial for predicting landscape response to climate change and interpreting paleo climate and tectonics from stratigraphy here we propose that sediment transport can act as a nonlinear filter that completely destroys shreds environmental signals this results from ubiquitous thresholds in sediment transport systems e g landsliding bed load transport and river avulsion this morphodynamic turbulence is analogous to turbulence in fluid flows where energy injected at one frequency is smeared across a range of scales we show with a numerical model that external signals are shredded when their time and amplitude scales fall within the ranges of morphodynamic turbulence as signal frequency increases signal preservation becomes the exception rather than the rule suggesting a critical re examination of purported sedimentary signals of external forcing citation jerolmack d j and c paola 2010 shredding of environmental signals by sediment transport geophys res lett 37 l19401 doi 10 1029 2010gl044638

channel and floodplain response to recent abrupt climate change the tyne basin northern england this paper examines the timing nature and magnitude of river response in upland piedmont and lowland reaches of the tyne basin northern england to high frequency 20 30 year changes in climate and flood regime since 1700 ad over this period fluvial activity has been characterized by alternating phases of river bed incision and stability coinciding with non random decadal scale fluctuations in flood frequency and hydroclimate that appear to be linked to changes in large scale upper atmospheric circulation patterns episodes of widespread channel bed incision 1760 1799 1875 1894 1955 1969 result from a higher frequency of large floods 20 year return period and cool wet climate under meridional circulation regimes phases of more moderate floods 5 20 year return period corresponding to zonal circulation types 1820 1874 1920 1954 are characterized by enhanced lateral reworking and sediment transfer in upper reaches of the catchment and channel narrowing and infilling downstream rates of fluvial activity are reduced in intermediate periods 1800 1819 1895 1919 with no dominant circulation regime associated with lower flood frequency and magnitude the results of this study provide a valuable guide for forecasting probable drainage basin and channel response to future climate change

jokulhlaups a reassessment of floodwater flow through glaciers 1 in glaciated catchments glacier generated floods jokulhlaups put human activity at risk with large sporadic jokulhlaups accounting for most flood related fatalities and damage to infrastructure in studies of jokulhlaup hydrodynamics the view predominates that floodwater travels within a distinct conduit eroded into the underside of a glacier however some jokulhlaups produce subglacial responses wholly inconsistent with the conventional theory of drainage by focusing on icelandic jokulhlaups this article reassesses how floodwater flows through glaciers it is argued that two physically separable classes of jokulhlaup exist and that not all jokulhlaups are an upward extrapolation of processes inherent in events of lesser magnitude and smaller scale the hydraulic coupling of multiple nonlinear components to the flood circuit of a glacier can induce extreme responses including pressure impulses in subglacial drainage representing such complexity in mathematical form should be the basis for upcoming research as future modeling results may help to determine the glaciological processes behind heinrich events moreover such an approach would lead to more accurate predictive models of jokulhlaup timing and intensity

the fate of sediment wood and organic carbon eroded during an extreme flood colorado front range usa identifying and quantifying the dominant processes of erosion and tracking the fate of sediment wood and carbon eroded during floods is important for understanding channel response to floods downstream sediment and carbon loading and the influence of extreme events on landscapes and the terrestrial carbon cycle we quantify sediment wood and organic carbon oc from source to local sink following an extreme flood in the tectonically quiescent semi arid colorado usa front range erosion of 500 000 m3 or as much as 115 yr of weathering products occurred through landsliding and channel erosion during september 2013 flooding more than half of the eroded sediment was deposited at the inlet and delta of a water supply reservoir resulting in the equivalent of 100 yr of reservoir sedimentation and 2 loss in water storage capacity the flood discharged 28 mg c km2 producing an event oc flux equivalent to humid tectonically active areas post flood remobilization resulted in a further 100 yr of reservoir sedimentation plus export of an additional 1 3 mg c km2 of wood demonstrating the ongoing impact of the flood on reservoir capacity and carbon cycling pronounced channel widening during the flood created accommodation space for 40 of flood sediment and storage of wood and eroded carbon we conclude that confined channels normally dismissed as transport reaches can store and export substantial amounts of flood constituents

olenelloid trilobites from cambrian series 2 of devon island nunavut arctic canada four species of olenelloid trilobites characterized by advanced or robust genal spines are described from the lower cambrian rabbit point formation cambrian series 2 stage 4 of eastern devon island representing the most diverse assemblage of olenelloids yet described from arctic canada new taxa bristolia kurtzi n sp paranephrolenellus cowiei n sp siciliolenellus fritzi n gen and n sp

gravel bed river evolution in earthquake prone regions subject to cycled hydrographs and repeated sediment pulses sediment often enters rivers in the form of sediment pulses associated with landslides and debris flows this is particularly so in gravel bed rivers in earthquake prone mountain regions such as southwest china under such circumstances sediment pulses can rapidly change river topography and leave the river in repeated states of gradual recovery in this paper we implement a one dimensional morphodynamic model of river response to pulsed sediment supply the model is validated using data from flume experiments so demonstrating that it can successfully reproduce the overall morphodynamics of experimental pulses the model is then used to explore the evolution of a gravel bed river subject to cycled hydrographs and repeated sediment pulses these pulses are fed into the channel in a fixed region centered at a point halfway down the calculational domain the pulsed sediment supply is in addition to a constant sediment supply at the upstream end results indicate that the river can reach a mobile bed equilibrium in which two regions exist within which bed elevation and surface grain size distribution vary periodically in time one of these is at the upstream end where a periodic discharge hydrograph and constant sediment supply are imposed and the other is in a region about halfway down the channel where periodic sediment pulses are introduced outside these two regions bed elevation and surface grain size distribution reach a mobile bed equilibrium that is invariant in time the zone of fluctuation free mobile bed equilibrium upstream of the pulse region is not affected by repeated sediment pulses under the scenarios tested but downstream of the pulse region the channel reaches different fluctuation free mobile bed equilibriums under different sediment pulse scenarios the vertical bed structure predicted by the simulations indicates that the cyclic variation associated with the hydrograph and sediment pulses can affect the substrate stratigraphy to some depth copyright 2017 john wiley sons ltd

effects of bedrock landslides on cosmogenically determined erosion rates abstract the successful quantification of long term erosion rates underpins our understanding of landscape formation the topographic evolution of mountain ranges and the mass balance within active orogens the measurement of in situ produced cosmogenic radionuclides crns in fluvial and alluvial sediments is perhaps the method with the greatest ability to provide such long term erosion rates although deep seated bedrock landsliding is an important erosional process in active orogens its effect on crn derived erosion rates is largely unquantified we present a numerical simulation of cosmogenic nuclide production and distribution in landslide dominated catchments to address the effect of bedrock landsliding on erosion rates results of the simulation indicate that the temporal stability of erosion rates determined from crn concentrations in sediment decreases with increased ratios of landsliding to bedrock weathering rates within a given catchment area and that as the frequency of landsliding increases larger catchment areas must be sampled in order to accurately evaluate long term erosion rates in addition results of this simulation suggest that sediment sampling for crns is the appropriate method for determining long term erosion rates in regions dominated by mass wasting processes whereas bedrock surface sampling for crns may generally underestimate long term erosion rates response times of crn concentrations to changes in erosion rate indicate that climatically driven cycles of erosion may be detected but that complete equilibration of crn concentrations to new erosional conditions may take tens of thousands of years comparison of simulated crn derived erosion rates with a new data set of such rates from the nepalese himalaya underscore the conclusions drawn from the model results

beyond threshold hillslopes channel adjustment to base level fall in tectonically active mountain ranges numerous empirical and model based studies argue that in general hillslopes and river channels increase their gradients to accommodate high rates of base level fall to date however few data sets show the dynamic range of both these relationships needed to test theoretical models of hillslope evolution and river incision here we utilize concentrations of 10 be in quartz extracted from river sand on the eastern margin of the tibetan plateau to explore relationships among short term 10 2 10 5 a erosion rate hillslope gradient and channel steepness our data illustrate nonlinear behavior and a threshold in the relationship between erosion rate and mean hillslope gradient confi rming the generalization that hillslopes around the world are limited by slope stability and cease to provide a metric for erosion at high rates 0 2 mm a the relationship between channel steepness index and erosion rate is also nonlinear but channels continue to steepen beyond the point where threshold hillslopes emerge up to at least 0 6 mm a demonstrating that channel steepness is a more reliable topographic metric than mean hillslope gradient for erosion rate and that channels ultimately drive landscape adjustment to increasing rates of base level fall in tectonically active settings

landscape form and millennial erosion rates in the san gabriel mountains ca abstract it has been long hypothesized that topography as well as climate and rock strength exert first order controls on erosion rates here we use detrital cosmogenic 10 be from 50 basins ranging in size from 1 to 150 km 2 to measure millennial erosion rates across the san gabriel mountains in southern california where a strong e w gradient in relief compared to weak variation in precipitation and lithology allow us to isolate the relationship between topographic form and erosion rate our erosion rates range from 35 to 1100 m ma and generally agree with both decadal sediment fluxes and long term exhumation rates inferred from low temperature thermochronometry catchment mean hillslope angle increases with erosion rate until 300 m ma at which point slopes become invariant with erosion rate although this sort of relation has been offered as support for non linear models of soil transport we use 1 d analytical hillslope profiles derived from existing soil transport laws to show that a model with soil flux linear in slope but including a slope stability threshold is indistinguishable from a non linear law within the scatter of our data catchment mean normalized channel steepness index increases monotonically though non linearly with erosion rate throughout the san gabriel mountains even where catchment mean hillslope angles have reached a threshold this non linearity can be mostly accounted for by a stochastic threshold incision model though additional factors likely contribute to the observed relationship between channel steepness and erosion rate these findings substantiate the claim that the normalized channel steepness index is an important topographic metric in active ranges

response of glacial landscapes to spatial variations in rock uplift rate 1 the response of glaciated landscapes to rapid rock uplift driven by tectonic convergence is an important often neglected aspect of proposed interactions between plate tectonic processes and climate change rivers typically respond to more rapid rock uplift in part through increasing channel gradients in contrast the glacial buzzsaw hypothesis suggests that glaciers can erode as quickly as the fastest rock uplift rates 6 10 mm yr without any increase in mean elevations however it has not been established how this is achieved we examined moving window maps swath and longitudinal profiles hillslope relief and hypsometry for glacierized and formerly glacierized basins in areas of spatially variable rock uplift rate in the southern alps new zealand and around nanga parbat pakistan to determine whether glaciers have a specific response to rapid rock uplift the response of these glaciated landscapes to rapid rock uplift 6 10 mm yr comprises 1 modest steepening of the longitudinal profiles in smaller glaciated basins 2 maintenance of shallow downvalley slopes in larger glaciated basins 30 km2 southern alps 100 km2 nanga parbat 3 development of tall headwalls and 4 steepening of the basin as a whole dominated by hillslope lengthening around nanga parbat headwalls several kilometers high constitute 50 of the basin relief at rapid rock uplift rates although glaciers can incise the valley floor swiftly they cannot prevent headwalls from reaching exceptional heights the associated increase in mean distance between cirque heads i e a decrease in drainage density causes regional mean elevation to rise with increasing rock uplift rate however this is much less than the changes in elevation expected in unglaciated ranges

the north pacific climatology of winter mixed layer and mode waters abstract a climatology of the winter mixed layer in the north pacific ocean was constructed using hydrographic data from historical archives and recent observational programs including the world ocean circulation experiment the main aim was to provide better knowledge about source areas of upper water masses the authors have endeavored to preserve water properties near the frontal regions by keeping the smoothing scale as small as possible the resulting climatology shows considerable differences in the mixed layer depth and its water properties from those derived from the world ocean atlas woa maps of the potential vorticity field of the north pacific pycnocline are presented using the isopycnally averaged climatology hydrobase three distinct lateral minima of potential vorticity are identified as subtropical mode water stmw central mode water cmw and eastern subtropical mode water estmw in the western central and eastern parts of the subtropical gyre respectively the hydrobase isopy

discharges of turbid water during mini surges of variegated glacier alaska u s a discharges of water sediment and dissolved impurities from variegated glacier ala ska were monitored in the early summers of 1980 and 1981 during the occurrence of mini surg es sea sonal trends weat her related eve nts and diurnal variat ions similar to behavior of other temperat e gl acier streams were found the prin cipal effect in the stream associated with mini surge occurrence was a brief discharge of extremely turbi d water the turbidity is assumed to be introduced into the basal hydraulic system by initiation of the fast motion of a mini surge at a time and locat ion on the upper glacier known from oth er meas ure ments the mean water velocity in the hydraulic system over the int erven ing distance is thereby determined 0 3 m s i the mean water velocity together with the water discharge 16 m3 s 1 at the terminus places con straints on the distribution of water velocity u and total cros s sectional area at of the flow paths along the gl acier base this leads to the con clusion that within the zone of mini surge occurrence in its unpe rturbed state u is about 0 1 m s 1 or possibly less at is about 10 2 m2 or possibly more and it must be divided into a very large number of small passag eways be blocked by constrict ions or both the total water cro ss se ction corresponds to a layer 0 1 2 m thick when spr ead unifo rmly over the glacier width the water velocity is clos e to or less than the propa gation velo city of the mini s urges bet ween the zone affected by mini surges and the stream a dyna mically less active lower section of the glacier is proba bly underlain by a small number of conduits in which the water velocity may be very high 2 m s i water di scharge follo wing the mini surges puts an upper limit on water storage changes ass ociated with the anomalous ice motion

rapid glacial erosion at 1 8 ma revealed by 4he 3he thermochronometry alpine glaciation and river incision control the topography of mountain ranges but their relative contributions have been debated for years apatite 4 he 3 he thermochronometry tightly constrains the timing and rate of glacial erosion within one of the largest valleys in the southern coast mountains of british columbia canada five proximate samples require accelerated denudation of the klinaklini valley initiating 1 8 0 2 million years ago ma at least 2 kilometers of overlying rock were removed from the valley at 5 millimeters per year indicating that glacial valley deepening proceeded 6 times as fast as erosion rates before 1 8 ma this intense erosion may be related to a global transition to enhanced climate instability 1 9 ma

channel response to an extreme flood and sediment pulse in a mixed bedrock and gravel bed river we exploit a natural experiment caused by an extreme flood 500 year recurrence interval and sediment pulse derived from more than 2500 concurrent landslides to explore the influence of valley scale geomorphic controls on sediment slug evolution and the impact of sediment pulse passage and slug deposition and dispersion on channel stability and channel form sediment slug movement is a crucial process that shapes gravel bed rivers and alluvial valleys and is an important mechanism of downstream bed material transport further increased bed material transport rates during slug deposition can trigger channel responses including increases in lateral mobility channel width and alluvial bar dominance pre and post flood lidar and aerial photographs bracketing the 2007 flood on the chehalis river in south western washington state usa document the channel response with high spatial and temporal definition the sediment slug behaved as a gilbert wave with both channel aggradation and sequestration of large volumes of material in floodplains of headwaters reaches and reaches where confined valleys enter into broad alluvial valleys differences between the valley form of two separate sub basins impacted by the pulse highlight the important role channel and channel floodplain connectivity play in governing downstream movement of sediment slug material finally channel response to the extreme flood and sediment pulse illustrate the connection between bed material transport and channel form specifically the channel widened lateral channel mobility increased and the proportion of the active channel covered by bars increased in all reaches in the study area the response scaled tightly with the relative amount of bed material sediment transport through individual reaches indicating that the amount of morphological change caused by the flood was conditioned by the simultaneous introduction of a sediment pulse to the channel network copyright 2015 john wiley sons ltd

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

thin film channelized drainage or sheetfloods beneath a portion of the laurentide ice sheet an examination of glacial erosion forms northern new york state usa abstract morphologic analyses of characteristic bedrock erosion forms found in northern new york state usa were used to reconstruct the subglacial conditions under which they may have been produced observations from sites on wellesley island n y at point salubrious n y and at an open pit mine near balmat n y were combined with regional mapping of a diverse suite of glacial erosion forms in order to establish the areal extent and significance of subglacial drainage in northern new york results of these site specific and regional studies are the basis for discussion of the probable role of subglacial meltwater in the region bedrock erosion forms preserved at various locations in northern new york are interpreted as products of flow separation of localized subglacial meltwater during ice bed decoupling the regional distribution of these forms indicates that they are largely restricted to pre existing subglacially modified bedrock valleys that served as subglacial tunnel channels regionally extensive deep subglacial meltwater flow characterized as sheetfloods is not required to account for the erosional features described from specific sites in northern new york state

oxygen isotope evidence for the late cenozoic development of an orographic rain shadow in eastern washington usa topographic development of the southern washington cascade range and its influence on regional climate on the leeward side of the range for the past 15 6 m y are evaluated using oxygen isotope ratios d 18 o of ancient meteoric water recorded in authigenic smec tites the d 18 o values of authigenic smectites from paleosols and altered tuffs on the east side of the range exhibit a temporal and continuous decrease of 3 4 from 15 6 ma to the present taking into account a regional temperature change in eastern washington since the middle miocene the calculated d 18 o values of regional meteoric water show a negative shift of 3 5 4 5 over the same interval such a decrease is similar to the change in the d 18 o values of modern precipitation from the coastal side to a region down wind of the washington cascades this negative shift of the calculated d 18 o values on the east side of the range is best explained by the development of a rain shadow due to the tectonic rock uplift of the cascades during the late cenozoic based on the empirically calculated relationship between change in elevation and change in the d 18 o value of pre cipitation paleorelief of the southern washington cascades since 15 6 ma is estimated to be 1 2 1 7 km

interannual to interdecadal changes in the bering sea and concurrent 1998 99 changes over the north pacific abstract sea surface temperatures ssts upper water heat storage hs sea level displacements slds sea ice concentration sics in the bering seas and associated atmospheric circulations are analyzed to identify dominant interannual to interdecadal variations as a representative time series of the sst variations principal component pc of the first mode of a seasonally combined empirical orthogonal function eof is employed the corresponding eof spatial pattern exhibits the smallest amplitudes in winter and largest in summer pc1 is characterized by a warming trend throughout the record 1921 2001 with the warmest year in 1997 which is followed by rapid cooling until 1999 the warming from 1995 1997 and cooling from 1997 1999 are commonly found in hs along the southern rim of the bering sea and also accompanied by sld rise and fall respectively the sic variability corresponding to sst pc1 is prominent in the eastern bering sea in spring with correlations as high as 0 7 but good correlations were mainly observed prior to 1990 the correlations between the sst pc1 and sea level pressures slps also suggest that the spring atmospheric circulation anomalies play an important role in the variations of the sst and sea ice in the bering sea the cooling and sld fall in the late 1990s in the bering sea might be related with a possible major regime shift in 1998 1999 which was discussed by minobe 2000 hare and mantua 2000 and schwing and moore 2000 in the 1998 99 change over the north pacific ssts and hs increased abruptly both in the kuroshio oyashio extension region and the central north pacific accompanied by cooling in the eastern north pacific at the same time slds rose from japan to 160 w roughly along kuroshio extension path with a tongue like structure the tongue like sld rise is likely forced by wintertime atmospheric anomalies associated with slp increase in the eastern north pacific

a physically based model for the topographic control on shallow landsliding a model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near surface through flow and slope stability models the hydrologic model topog o loughlin 1986 predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries the slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity the steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding the spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high resolution digital elevation data are available tennessee valley in marin county california mettman ridge in the oregon coast range and split creek on the olympic peninsula washington model predictions in each of these areas are consistent with spatial patterns of observed landslide scars although hydrologic complexities not accounted for in the model e g spatial variability of soil properties and bedrock flow control specific sites and timing of debris flow initiation within areas of similar topographic control

on steady states in mountain belts the dynamic system of tectonics and erosion contains important feedback mechanisms such that orogenic systems tend toward a steady state this concept is often invoked but the nature of the steady state is commonly not specified we identify four types of steady state that characterize the orogenic system and illustrate these cases by using numerical model results and natural examples these types are 1 flux steady state 2 topographic steady state 3 thermal steady state and 4 exhumational steady state they refer to the erosional flux the topography the subsurface temperature field and the spatial pattern of cooling ages respectively models suggest that the topography will reach a steady mean form at the scale of an orogenic belt but perfect topographic steady state is unlikely to be achieved at shorter length scales thermal steady state is a precondition for exhumational steady state and in the case of temperature dependent deformation topographic steady state exhumational steady state is characterized by reset age zones spatially nested according to closure temperature as illustrated in natural systems from new zealand the cascadia accretionary margin and taiwan

erosion rates driven by channel network incision in the bolivian andes the bolivian andes flank one of earth s major topographic features and dominate sediment input into the amazon basin millennial scale erosion rates and dominant controls on erosion patterns in this range are poorly known to define these patterns we present 48 erosion rate estimates derived from analysis of in situ 10 be in quartz bearing alluvium collected from the upper beni river basin erosion rates corrected for the non uniform distribution of quartz in the sample basins range from 0 04 mm a 1 to 1 35 mm a 1 and thus integrate over 10 2 10 4 years mean and modal values are 0 42 standard deviation 0 29 and 0 2 0 4 mm a 1 respectively within the range of long term average erosion rates in this area derived from apatite fission track thermochronology 0 1 0 6 mm a 1 hence our data do not record any significant variation in erosion rate over the last several million years mean and modal short term erosion rates for the andes are an order of magnitude lower than rates in the ganges river headwaters in the high himalaya and an order of magnitude greater than rates typical of the european alps in the upper beni river region of the bolivian andes short term basin averaged erosion rates correlate with normalized channel steepness index a metric of relative channel gradient corrected for drainage area neither normalized channel steepness index nor basin averaged erosion rate shows strong correlation with mean basin hillslope gradient or mean basin local relief because many hillslopes in the upper beni river region are at threshold values of slope and local relief patterns of normalized channel steepness index appear primarily to reflect tectonic patterns and transient adjustment to those patterns by channel networks climate and lithology do not appear to exert first order controls on patterns of basin averaged erosion rates in the bolivian andes copyright 2005 john wiley sons ltd

temperature inversions in the subarctic north pacific abstract hydrographic data from the world ocean database 2001 and argo profiling floats were analyzed to study temperature inversions in the subarctic north pacific ocean the frequency distribution of temperature inversions f t inv at a resolution of 1 latitude 3 longitude was calculated temperature inversions seldom occurred around 50 n in the eastern subarctic north pacific but were more common in the northern gulf of alaska and the southeastern subarctic north pacific 42 48 n 140 170 w large temperature inversions occurred throughout the year in the western and central subarctic north pacific north of 42 n and west of 180 except near the aleutian and kuril islands near those islands f t inv was characterized by pronounced seasonal variations forced by surface heating cooling and strong tidal mixing

imprint of climate and climate change in alluvial riverbeds continental united states 1950 2011 alluvial riverbed elevation responds to the balance between sediment supply and transport capacity which is largely dependent on climate and its translation into fl uvial discharge we examine these relations using u s geological survey streamfl ow and channel measurements in conjunction with basin characteristics for 915 reference least disturbed measurement stations across the conterminous united states for the period a d 1950 2011 we fi that 1 68 of stations have bed elevation change bec trends p 0 05 with median values of 0 5 cm yr for aggradation and 0 6 cm yr for degradation with no obvious relation to drainage basin structure physiography or lithology 2 bec correlates with drainage basin area 3 high fl ow variability q 90 q 50 where q is discharge and 90 and 50 are annual fl ow percentiles translates directly into the magnitude though not the direction of bec after accounting for the scale dependence 4 q 90 q 50 declines systematically from dry to wet climates producing disproportionately high rates of bec in drier regions and 5 marked increases in precipitation and streamfl ow occurred disproportionately at dry sites while streamfl ow declined disproportionately at wet sites climatic shifts in streamfl ow have the potential to increase decrease sediment fl ux and thus affect riverbed elevation by altering fl ood frequency these unforeseen responses of bed elevation to climate and climate change have important implications for sediment budgets longitudinal profi les ecology and river management

the dominance of dispersion in the evolution of bed material waves in gravel bed rivers bed material waves are temporary zones of sediment accumulation created by large sediment inputs recent theoretical experimental and field studies examine factors influencing dispersion and translation of bed material waves in quasi uniform gravel bed channels exchanges of sediment between a channel and its floodplain are neglected within these constraints two factors influence relative rates of dispersion and translation 1 interactions between wave topography flow and bed load transport and 2 particle size differences between wave material and original bed material our results indicate that dispersion dominates the evolution of bed material waves in gravel bed channels significant translation requires a low froude number which is uncharacteristic of gravel bed channels and low wave amplitude which for a large wave can be achieved only after substantial dispersion wave material of small particle size can promote translation but it primarily increases bed load transport rate and thereby accelerates wave evolution copyright 2001 john wiley sons ltd

erosional equilibrium and disequilibrium in the sierra nevada inferred from cosmogenic 26al and 10be in alluvial sediment we used cosmogenic 26 al and 10 be in stream sediment to measure landscape scale erosion rates for topographically diverse catchments at seven sierra nevada sites at three sites erosion rates and hillslope gradients are strongly correlated increasing with proximity to fault scarps and river canyons which appear to have accelerated local base level lowering rates and thus increased catchment erosion rates by up to 15 fold at four other sites far from fault scarps and river canyons erosion rates are much more uniform and less sensitive to average hillslope gradient our measurements show that contrasts in landscape erosion rates cannot be inferred from hillslope gradients alone because landscapes can evolve toward a state of erosional equilibrium in which steep and gentle slopes erode at similar rates

river response to variations of periglacial climate in mid latitude europe abstract the last glaciation was characterised by considerable changes in climate many european river basins reacted to these changes by initial incision and subsequent pattern change earlier research explained this by the time lag of vegetation development after a climatic change which considerably affected the sediment load however since some river basins react differently or do not react at all this model needs to be refined this paper deals with the fluvial evolution of several rivers in northern and central europe during the last glaciation and two of them the weise elster river in the leipzig area and the spree river in the niederlausitz germany are discussed in more detail the vegetation cover on the floodplain in combination with the presence of frozen ground which affects the discharge characteristics largely determines the river type nevertheless when the sequences are compared not only synchronous changes in fluvial development may be observed but also distinct differences in fluvial development by analysing the different rivers in their varying geomorphological settings it appears that grain size basin configuration and catchment size are important parameters also which can determine whether a threshold is exceeded or not

hydraulics of subglacial cavities modele theorique du comportement a l etat stationnaire des cavites remplies d eau et interconnectees sur le lit du glacier

reconstructing a sediment pulse modeling the effect of placer mining on fraser river canada gold mining along 525 km of the fraser river between 1858 and 1909 added an estimated 1 1 108 t of tailings half gravel and the rest finer to the river s natural sediment load we simulate the response using a 1 d multigrain size morphodynamic model since premining conditions are unknown and modern data are insufficient for tuning the process representation we devised a novel modeling strategy which may be useful in other data poor applications we start the model from a smoothed version of the modern longitudinal profile with bed grain size distributions optimized to match alternative assumptions about natural sediment supply and compare runs that include mining with control runs that can be used to quantify the effects of deficiencies in process representation and initialization simulations with an appropriate choice of natural supply rate closely match the best available test data which consist of a detailed 1952 1999 gravel budget for the distal part of the model domain the simulations suggest that the main response to mining was rapid bed fining which allowed a major increase in bed load transport rate with only slight 0 1 m mean aggradation within the mining region and most of the excess sediment exported well beyond the mountain front within the mining period or soon afterward we compare this pattern of response by a large powerful river with previous case studies of river adjustment to sediment supply change

disequilibrium of holocene sediment yield in glaciated british columbia it is generally supposed that specific sediment yield the quantity of sediment passing a monitored river cross section per unit area drained upstream of that section declines as the area drained increases1 3 part of the sediment mobilized from the land surface is supposed to go back into storage at field edges and on footslopes and floodplains in contrast we show here that data from british columbian rivers reveal a pattern of increasing specific sediment yield at all spatial scales up to 3 104 km2 this results from the dominance of secondary remobilization of quaternary sediments along river valleys over primary denudation of the land surface the result controverts the conventional model which has been derived from studies of small highly disturbed agricultural catch ments the rivers are still responding to the last glaciation giving a landscape relaxation time greater than 10 kyr this holds pro found implications for geomorphological theory and for studies of erosion

changes in glacial lakes and glaciers of post 1986 in the poiqu river basin nyalam xizang tibet glacial lakes and glaciers are sensitive indicators of recent climate change in the poiqu river basin of southern tibet 60 100 km nw of mt everest landsat imagery defines post 1986 changes in the size and distribution of both glacial lakes and glaciers total area of glaciers in the 229 km2 drainage area has decreased by 20 the number of glacial lakes with areas in excess of 0 020 km2 has increased by 11 and the total area of glacial lakes has increased by 47 the areas of typical large glacial lakes of the area galongco gangxico and cirenmaco have increased by 104 118 and 156 respectively and these increases are confirmed by field investigations comparing the 1986 data the area of glaciers in the basin headwaters has decreased by 46 18 km2 to a present total area of 183 12 km2 an annual rate of change of 3 30 km2 year trends indicate that the total area of glaciers will continue to decrease and that both the numbers and areas of glacial lakes will continue to increase accompanying these trends will be an increased risk of debris flows formed by entrainment of sediment in glacial outburst floods and in surges from both failure and avalanche and landslide induced overtopping of moraine dams based on both the local and world wide history of catastrophes from flows of these origins disaster mitigation must be planned and appropriate engineering countermeasures put in place as soon as possible

a synoptic survey of young mesoscale eddies in the eastern gulf of alaska eddies in the gulf of alaska are important sources of coastal water and associated nutrients iron and biota to the high nutrient low chlorophyll central gulf of alaska three primary eddy formation regions along the eastern boundary of the gulf have been identified from south to north haida sitka and yakutat in the spring of 2005 three eddies one of each type were sampled soon after their formation the subsurface eddy core water in all three eddies was defined by high iron concentrations and low dissolved oxygen compared with surrounding basin water the sitka and yakutat core waters also exhibited a subsurface temperature maximum mesothermal water coincident in depth with the iron maximum suggesting that eddies may play a role in the formation of temperature inversions observed throughout the gulf of alaska the data suggest different formation regions with the yakutat eddy forming in shallow shelf water with riverine input while the sitka and haida eddies appear to form in deeper water

glacier outburst floods at mount rainier washington state u s a during the twentieth century glacial outburst floods have been the most destructive natural events on mount rainier a stratovolcano in the cascade range in washington state u s a in the period between 1930 and 1980 numerous floods were reported from five glaciers on the mountain most of which flowed from nisqually kautz or south tahoma glaciers on its southern flank such floods threaten lives and property because they occur without warning and quickly mobilize the loose volcanic debris into debris flows a monitoring program was begun in 1987 which was designed to measure the dimensions and timing of outburst floods but this has been unsuccessful because no floods have yet occurred on the monitored streams four floods did burst from south tahoma glacier that was unmonitored but in spite of this they have been useful in providing evidence of flood storage and release mechanisms all flood volumes were found to be of approximately similar orders of magnitude of 1 10 5 m 3 of water indicating that all floods probably had similar mechanisms for storage and release of water hydraulic pressure considerations indicate that such a large volume of flood water would be stored at the bed of the glacier rather than in isolated englacial cavities the stepped bedrock terrain provides an ideal setting for the formation of subglacial cavities capable of storing the volumes of flood water noted

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

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

landslides control the spatial and temporal variation of channel width in southern taiwan implications for landscape evolution and cascading hazards in steep tectonically active landscapes

detection of a subglacial lake in glacier de tete rousse mont blanc area france the processes that form intraglacial lakes are poorly understood because of the difficulty in detecting and assessing such hidden lakes extensive geophysical surveys were performed between 2007 and 2010 in order to reassess the risk of an outburst flood from glacier de tete rousse where outburst flooding from an intraglacial lake caused 175 fatalities in 1892 our geophysical survey combined ground penetrating radar measurements and nuclear magnetic resonance imaging we found a subglacial water filled reservoir with a volume of 55 000 m 3 artesian outpourings occurred when the subglacial cavity was reached by two borehole drillings indicating that the hydrostatic water pressure exceeded the ice pressure at the bottom of the cavity on the basis of these geophysical and glaciological findings we warned the public authorities in july 2010 of the risk facing the 3000 inhabitants downstream of the glacier the subglacial reservoir was drained artificially this example demonstrates how geophysical surveys can be used to detect this type of hazard when it is suspected in particular when no hydraulic outlet from the snout exists numerous ice temperature measurements have shown that the tongue of this glacier is cold based this thermal regime could explain the accumulation of water in this glacier

numerical model of sediment pulses and sediment supply disturbances in mountain rivers sediment pulses in rivers can result from many mechanisms including landslides entering from side slopes and debris flows entering from tributaries artificial sediment pulses can be caused by the removal of a dam this paper presents a numerical model for the simulation of gravel bedload transport and sediment pulse evolution in mountain rivers a combination of the backwater and quasi normal flow formulations is used to calculate flow parameters gravel bedload transport is calculated with the surface based bedload equation of parker in 1990 the exner equation of sediment continuity is used to express the mass balance at different grain size groups and lithologies as well as the abrasion of gravel the river is assumed to have no geological controls such as bedrock outcrops and immobile boulder pavements the results of nine numerical experiments designed to study various key parameters relevant to the evolution of sediment pulses are reported here results of the numerical runs indicate that the evol

geologic and physiographic controls on bed material yield transport and channel morphology for alluvial and bedrock rivers western oregon the rivers of western oregon have diverse forms and characteristics with channel substrates ranging from continuous alluvial gravel to bare bedrock analysis of several measurable morphologic attributes of 24 valley reaches on 17 rivers provides a basis for comparing nonalluvial and alluvial channels key differences are that alluvial reaches have greater bar area greater migration rates and show systematic correlation among variables relating grain size to bed material transport capacity we relate these differences between channel types to bed material transport rates as derived from a coupled regional analysis of empirical sediment yield measurements and physical experiments of clast attrition during transport this sediment supply analysis shows that overall bed material transport rates for western oregon are chiefly controlled by 1 lithology and basin slope which are the key factors for bed material supply into the stream network and 2 lithologic control of bed material attrition from in transport abrasion and disintegration this bed material comminution strongly affects bed material transport in the study area reducing transport rates by 50 90 along the length of the larger rivers in the study area a comparison of the bed material transport estimates with the morphologic analyses shows that alluvial gravel bed channels have systematic and bounding relations between bed material transport rate and attributes such as bar area and local transport capacity by contrast few such relations are evident for nonalluvial rivers with bedrock or mixed bed substrates which are apparently more influenced by local controls on channel geometry and sediment supply at the scale of western oregon the physiographic and lithologic controls on the balance between bed material supply and transport capacity exert far reaching influence on the distribution of alluvial and nonalluvial channels and their consequently distinctive morphologies and behaviors differences germane for understanding river response to tectonics and environmental perturbations as well as for implementing effective restoration and monitoring strategies

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

minimal climatic control on erosion rates in the sierra nevada california climate is widely thought to regulate erosion rates but the relationships among precipitation temperature and erosion rate have remained speculative because long term erosion rates have been difficult to measure we used cosmogenic nuclides to measure long term erosion rates at climatically diverse sites in the sierra nevada california spanning 20 180 cm yr in annual precipitation and 4 15 8c in mean annual temperature average erosion rates vary by only 2 5 fold across these sites and are not correlated with climate indicating that climate only weakly regulates nonglacial erosion rates in mountainous granitic terrain

differentiating the effects of logging river engineering and hydropower dams on flooding in the skokomish river washington usa abstract a decades long progressive loss of channel capacity in the skokomish river a 622 km2 basin draining the southeast olympic mountains of washington state has caused increasing flooding with severe consequences to endangered salmon runs infrastructure and private property to differentiate among multiple potential drivers of the capacity loss we analyze the geomorphic evidence for the potential effects of flow regulation by two dams constituting the cushman hydroelectric project which began regulating flow in the river s north fork in 1925 and diverting water out of the basin in 1930 sediment production from mid twentieth century logging in the river s south fork basin and twentieth century river engineering in the mainstem bankfull channel capacity in the mainstem has steadily declined since about 1940 from 370 m3 s 1 to

polypleuraspis arthropoda trilobita from the middle cambrian miaolingian series around kane basin nunavut and greenland polypleuraspis poulsen 1927 originally established on the basis of a single trilobite pygidium from the cape wood formation of inglefield land northwestern greenland is redescribed on the basis

relation between rock uplift and denudation from cosmogenic nuclides in river sediment in the central alps of switzerland 1 a north south traverse through the swiss central alps reveals that denudation rates correlate with recent rock uplift rates in both magnitude and spatial distribution this result emerges from a study of in situ produced cosmogenic 10be in riverborne quartz in central alpine catchments as a prerequisite we took care to investigate the potential influence of shielding from cosmic rays due to snow glaciers and topographic obstructions to calculate a possible memory from last glacial maximum lgm glaciation and to identify a watershed size that is appropriate for systematic sampling mean denudation rates are 0 27 0 14 mm a for the alpine foreland and 0 9 0 3 mm a for the crystalline central alps the measured cosmogenic nuclide derived denudation rates are in good agreement with post lgm lake infill rates and are about twice as high as denudation rates from apatite fission track ages that record denudation from 9 to 5 ma in general denudation rates are high in areas of high topography and high crustal thickness the similarity in the spatial distribution and magnitude of denudation rates and those of rock uplift rates can be interpreted in several ways 1 postglacial rebound or climate change has introduced a transient change in which both uplift and denudation follow each other with a short lag time 2 the amplitude of glacial to interglacial changes in both is small and is contained in the scatter of the data 3 both are driven by ongoing convergence where their similarity might hint at some form of long term quasi steady state or 4 enhanced continuous quaternary erosion and isostatic compensation of the mass removed accounts for the distribution of present day rock uplift

channel responses to varying sediment input a flume experiment modeled after redwood creek california article i nfo storage flume aggradation degradation at the reach scale a channel adjusts to sediment supply and flow through mutual interactions among channel form bed particle size and flow dynamics that govern river bed mobility sediment can impair the beneficial uses of a river but the timescales for studying recovery following high sediment loading in the field setting make flume experiments appealing we use a flume experiment coupled with field measurements in a gravel bed river to explore sediment transport storage and mobility relations under various sediment supply conditions our flume experiment modeled adjustments of channel morphology slope and armoring in a gravel bed channel under moderate sediment increases channel bed elevation increased and sediment output increased but channel planform remained similar to pre feed conditions during the following degradational cycle most of the excess sediment was evacuated from the flume and the bed became armored under high sediment feed channel bed elevation increased the bed became smoother mid channel bars and bedload sheets formed and water surface slope increased concurrently output increased and became more poorly sorted during the last degradational cycle the channel became armored and channel incision ceased before all excess sediment was removed selective transport of finer material was evident throughout the aggradational cycles and became more pronounced during degradational cycles as the bed became armored our flume results of changes in bed elevation sediment storage channel morphology and bed texture parallel those from field surveys of redwood creek northern california which has exhibited channel bed degradation for 30 years following a large aggradation event in the 1970s the flume experiment suggested that channel recovery in terms of reestablishing a specific morphology may not occur but the channel may return to a state of balancing sediment supply and transport capacity published by elsevier b v

formation and variation of temperature inversions in the eastern subarctic north pacific 1 hydrographic data from profiling float observations for 2001 2005 and from expendable bathythermograph observations for 1993 2005 were analyzed to study the formation and variation of temperature inversions t inversions in the eastern subarctic north pacific snp the formation and variation of t inversions differed significantly between the northern and southern regions of the eastern snp in the northern region the temperature minimum t min at the top of t inversions outcropped to the sea surface and was cooled in the mixed layer nearly every winter this process caused a seasonal cycle in the magnitude of t inversions t with a maximum in winter in the southern region the winter t min outcropped relatively infrequently and the t did not exhibit a significant maximum in winter during most years the t min in the southern region was likely to outcrop upstream near the date line roughly one year earlier and was then advected to the southern region

cosmogenic nuclide derived rates of diffusive and episodic erosion in the glacially sculpted upper rhone valley swiss alps denudation rates of small tributary valleys in the upper rhone valley of the swiss central alps vary by more than an order of magnitude within a very small distance tens of kilometers morphometric data indicate two distinct erosion processes operate in these steep mountain valleys we determined the rates of these processes using cosmogenic beryllium 10 10be in pooled soil and stream sediment samples denudation in deep glacially scoured valleys is characterized by rapid non uniform processes such as debris flows and rock falls in these steep valleys denudation rates are 760 2100 mm kyr 1 in those basins which show minimal previous glacial modification denudation rates are low with 60 560 mm kyr 1 the denudation rate in each basin represents a binary mixture between the rapid non uniform processes and soil creep the soil production rate measured with cosmogenic 10be in soil samples averages at 60 mm kyr 1 mixing calculations suggest that the debris flows and rock falls are occurring at rates up to 3000 7000 mm kyr 1 these very high rates occur in the absence of baselevel lowering since the tributaries drain into the rhone trunk stream up stream of a knickzone the flux weighted spatial average of denudation rates for the upper rhone valley is 1400 mm kyr 1 which is similar to rock uplift rates determined in this area from leveling the pace and location of erosion processes are determined by the oscillation between a glacial and a non glacial state preventing the landscape from reaching equilibrium copyright 2010 john wiley sons ltd

influence of a glacial buzzsaw on the height and morphology of the cascade range in central washington state usa abstract analysis of climatic and topographic evidence from the cascade range of washington state indicates that glacial erosion limits the height and controls the morphology of this range glacial erosion linked to long term spatial gradients in the ela created a tilted planar zone of 373 cirques across the central part of the range peaks and ridges now rise 600 m above this zone hypsometric analysis of the region shows that the proportion of land area above the cirques drops sharply and mean slopes 30 indicate that the areas above the cirques may be at or near threshold steepness the mean plus 1 relief of individual cirque basins 570 m corresponds to the 600 m envelope above which peaks rarely rise the summit altitudes are set by a combination of higher rates of glacial and paraglacial erosion above the ela and enhanced hillslope processes due to the creation of steep topography on the high precipitation western flank of the cascades the dominance of glacial and hillslope erosion at altitudes at and above the ela may explain the lack of a correspondence between stream power erosion models and measured exhumation rates from apatite u th he thermochronometry

interannual variability in northeast pacific circulation 1 interannual variability of the circulation in the northeast pacific ocean is explored through a joint analysis of expendable bathythermograph xbt and expendable conductivity temperature depth xctd data satellite altimetry and output from a model that was constrained by ocean data xbt temperature profiles with high spatial resolution are available in the eastern north pacific along two repeated transects these ship tracks along with the coast of north america define a closed box which is used to study the time mean circulation and its variability on interannual timescales geostrophic velocities from xbt data are compared with geostrophic velocities from model output as well as the full model velocity fields correlations in variability on interannual timescales between transport in the subpolar gyre and in the subtropical gyre are present in both model output and data the nature of the variability and its relation to the changes of the strength of the north pacific current npc which supplies the water for both gyres are explored interannual variability in gyre transport is found to be related to both the bifurcation of the npc resulting in an anticorrelation in transport between the two gyres and to variations in npc strength resulting in simultaneous changes in the two gyres the dominant signal is found to be a long term increase in the npc which results in a strengthening of the subtropical gyre possible connections with local scale wind stress changes and with the el nino southern oscillation phenomenon are also explored

incision and morphologic evolution of an alluvial channel recovering from hydraulic mining sediment hydraulic gold mining in the sierra nevada california produced such a large volume of sediment from 1853 to 1884 that channels could not carry a substantial proportion of the delivered sediment the lower bear river aggraded as much as 5 m and underwent a major avulsion during the 1870s channel morphology continues to respond to these changes more than 100 years after the cessation of most hydraulic mining textures of mine tailings and older alluvium are contrasted and channel incision and channel shape changes from 1930 to 1985 are documented unlike the yuba and sacramento rivers the lower bear river had not returned to pre mining base levels by 1950 as sediment loads decreased nor were incision rates or morphological change governed by reduced sediment loads below dams built in 1928 and in the mid 1960s channel stability was due to resistance of a cohesive stratum on the channel bed an episode of channel down cutting was instigated by a moderately large flood in december 1955 that pierced the cohesive layer and was sustained through the 1970s by moderate magnitude floods the 1955 flood did not directly erode large volumes of sediment but it destabilized the channel allowing smaller floods to erode the channel at an accelerated rate episodic channel bed incision is contrasted to progressive morphologic changes cross section shape narrowed and deepened steadily from 1930 through the mid 1970s as the channel was superimposed onto cohesive older alluvium progressive deepening set up a positive feedback that ensured the ultimate penetration of the paved bed channel morphologic readjustment from the avulsion thus was both progressive and episodic

geomorphic response of lillooet river british columbia to meander cutoffs and base level lowering abstract a detailed record of channel profiles slopes and stream discharge on lillooet river provides an opportunity to study the effects of natural and artificial channel changes that have occurred over the past century we analyze the long term effects of channel alterations that may affect flood hazard in the mid 1940s several meanders were artificially severed side channels blocked off and the level of downstream lillooet lake was lowered these measures were thought to increase hydrologic efficiency and decrease flood risk in the largely agricultural valley between 1947 and 1994 average channel width in the upper reaches decreased by 50 most of which occurred by the late 1950s between 1945 and 1969 lillooet river degraded its bed elevation by 3 4 m 12 5 to 16 7 cm a 1 in the upper reaches and up to 2 m 8 3 cm a 1 in the lower reaches this sudden and profound degradation compares to average bed elevation increases of 2 4 cm a 1 prior to the engineering works between 1969 and 1985 the cross section area increased by 22 in the upper reaches and 13 in the lower reaches and decreased to 12 and 8 respectively for the time period 1985 to 2000 the increased sediment supply that was caused by channel straightening accelerated delta advance in lillooet lake from 7 m a 1 1858 to 1948 to 30 m a 1 for the five year period following the 1948 channel works these rates have decreased over time but with a current advance rate of 10 5 m a 1 1986 2009 are still above the long term average prior to the channel changes this study demonstrates the time scale direction and magnitude of channel changes following significant artificial river alterations while the initial goal of decreasing flood risk had been achieved in the short term the lower river apparently is slowly returning to an overall aggradational phase ongoing delta advance will ultimately increase channel elevations in the lower reaches and lead to significant flood hazards for populated areas

mechanisms of subglacial cavity filling in glacier de tete rousse french alps the deadliest outburst flood from an englacial cavity occurred on glacier de tete rousse in the mont blanc area french alps in 1892 a subglacial reservoir was discovered in the same glacier in 2010 and drained artificially in 2010 2011 and 2012 to protect the 3000 inhabitants downstream the mechanism leading to the spontaneous refilling of the cavity following these pumping operations has been analyzed for this purpose the subglacial water volume changes between 2010 and 2013 were reconstructed the size of the cavity following the pumping was found to have decreased from 53 500 m 3 in 2010 to 12 750 m 3 in 2013 creep and the partial collapse of the cavity roof explain a large part of the volume loss analysis of cavity filling showed a strong relationship between measured surface melting and the filling rate with a time delay of 4 6 hours a permanent input of 15 m 3 d 1 not depending on surface melt was also found the meltwater and rain from the surface is conveyed to bedrock through crevasses and probably through a permeable layer of rock debris at the glacier bed the drainage pathway permeability was estimated at 0 054 m s 1 from water discharge measurements and dye tracing experiments

cosmogenic 10be as a tracer for hillslope and channel sediment dynamics in the clearwater river western washington state we use the 10be concentration in alluvial sand and gravel to document hillslope exposure history and trace the reduction in grain size of river alluvium in the clearwater river basin western washington state clearwater tributary basins wilson creek wc 6 km2 and east fork miller creek efmc 12 km2 were each sampled in headwater and downstream sites for 10be in alluvial sand 0 25 0 50 mm and gravel 22 6 90 mm grain size distributions were determined at each sampling site as well as at several locations along the main stem of the clearwater river channel and watershed geomorphology were quantified using long profile modeling and related morphometric analyses we found that the 10be concentrations differ significantly between the two grain size fractions at all four sampling locations at both headwater sites the gravel exhibits 25 lower 10be concentrations compared to the sand similarly the downstream site of lower wc exhibits 55 lower 10be concentration in the gravel compared to the sand in contrast the gravel from the downstream site on lower efmc exhibited 22 higher 10be concentration in the gravel compared to the sand the disparity in 10be concentration at the wc sites is best explained by shielding of the coarser grain size fraction and its delivery to the channel by deep seated landslide processes more intense landsliding in the downstream wc site is consistent with the increased disparity of 10be between the sand and gravel fractions at that site the inverse relationship between the sand and gravel 10be concentrations at the headwater efmc site is best explained by a sediment provenance mechanism where the hillslope weathering rate exceeds the down slope transport rate for this particular basin the inverse grain size dependency gravel sand observed in the downstream efmc site requires a more complex interplay between hillslope and channel processes including cobble weathering and grain size reduction during fluvial transport resulting in a dilution of the 10be signal in the sand fraction downstream these results underscore the importance of geomorphic consideration and the grain size sampled in the correct interpretation of basin average erosion rates

water and sediment outbursts from advanced franz josef glacier new zealand the franz josef glacier westland new zealand has a history of catastrophic sediment laden outburst oods associated with extreme rainfall events when the glacier toe is advanced over its own sediments consideration of these events and inspection of recent sediment deposits suggest that there are three distinct modes of outburst the rst is associated with fans fed by over ow along the glacier margin as the glacier has advanced across its own fore eld gravels it is inferred that the primary drainage conduit has developed a reach of negative slope in high ows massive boulders can block the conduit trapping lesser clasts the resulting backup of water causes over ows through marginal moulins producing the fan type of deposit the second type of outburst deposits massive imbricated boulders at a greater or lesser distance from the glacier portal in this case pressure buildup drives the blockage out of the portal where the boulders deposit smaller materials are generally carried away the third type consists of very shallow ows and produces massive gravel deposits of uncertain provenance in this condition the excess pressure in the conduit results in slight uplift of the glacier and widespread discharge of water and sediment below the glacier snout gravels and smaller sediments are laid down in a massive deposit across the fore eld the massive boulder veneered deposit from the december 1995 outburst is interpreted in the light of the above mechanisms as a hyperconcentrated ow deposit from hydraulic jacking overlain by boulders emplaced by a subsequent conduit outburst a possible association of outbursts with the present advanced position of the glacier is suggested copyright 2003 john wiley sons ltd

evolution of a landslide induced sediment wave in the navarro river california a streamside landslide delivered 60 000 m3 of mixed size sediment to the navarro river a sinuous gravel bed channel drainage area 535 km2 at the end of the annual high runoff period in spring 1995 the deposit formed a 9 m high dam that partially breached within several hours but recessional flows entrained little material until the following high runoff season the landslide afforded the opportunity to measure the evolution of a sediment wave from its inception to near obliteration and particularly to test relative tendencies for translation and dispersion of a sediment wave in a natural gravel bed channel this study represents a simple case the wave originated from a single input the preexisting channel was relatively uniform and resistant banks prevented adjustments in width we surveyed channel topography over a 1 5 4 5 km reach centered on the landslide dam each year from 1995 to 1999 and we sampled bed material downstream of the dam in 1995 and 1997 landslide material was coarser than ambient bed material but all sizes were mobilized by subsequent peak flows abrasion of weathered and fractured graywacke sandstone landslide material was roughly an order of magnitude greater than the ambient river gravel the sediment wave dispersed and mostly disappeared within a few years with no measurable translation sediment filled the reservoir created by the eroding landslide dam until throughput of bed load was restored in 1998 the stationary wave crest eroded until in 1999 it was 1 m higher e mail dsutherl fs fed us than the preslide elevation as the wave profile flattened its detectable leading edge extended downstream from 620 m in 1995 to 1600 m in 1997 downstream advance of the wave was associated with coarsening of bed material the sediment wave created a longitudinal disturbance in sediment transport by using the dam as a reference datum of zero bed load transport we computed longitudinal variations in annual bed load and suspended sediment transport rates in 100 m increments downstream of the dam these longitudinal variations were controlled by scour and fill of the bed and by abrasion of bed load particles bed load transport rates in the first and second years after the landslide increased in the landslide vicinity and then decreased downstream as sediment deposited behind the advancing leading edge of the wave the location of peak bed load transport rate advanced from the first year 400 m to the second 800 m we used a physically based one dimensional model cui et al 2002b to hindcast annual changes in transversely averaged bed elevation over the study reach agreement between measured and predicted bed elevations was very good this result supports our conclusion that once emplaced sediment waves in gravel bed rivers tend to disperse with little or no translation

sediment pulse evolution and the role of network structure abstract sediment pulses are triggered through a variety of mechanisms from landslides to land use change how do these pulses move through the fluvial system and how do they evolve in a system with perfect sediment connectivity the erosional response to a perturbation and the resulting signal at the river mouth would match however this rarely occurs many studies have addressed reach scale dynamics of sediment pulses and how they translate or disperse downstream at the watershed scale network structure and storage become more important in modulating the sediment signal here we review the current literature on sediment pulse behavior and then address the role of network structure on maintaining dispersing or transforming sediment pulses in a fluvial system we use a reduced complexity network routing model that simulates the movement of bed material through a river basin this model is run in the greater blue earth river gber basin in minnesota usa first with spatially uniform inputs and then with inputs constrained by a detailed sediment budget once the system reaches equilibrium a sediment pulse is introduced first at a single location and then throughout the system and tracked as it evolves downstream results indicate that pulses able to translate downstream disperse in place upon arriving at over capacity reaches as sediment goes into storage in the gber basin these zones occur just upstream of a knickpoint that is propagating upstream through all mainstem channels as the pulses get caught in these sediment bottlenecks there is a decoupling of the original pulse of sediment and the resulting bed material wave these results show that the network structure both in terms of network geometry and the spatial pattern of transport capacity can play a dominant role in sediment connectivity and should be considered when predicting sediment pulse behavior at the watershed scale

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

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

water flow through temperate glaciers understanding water movement through a glacier is fundamental to several critical issues in glaci ology including glacier dynamics glacier induced floods and the prediction of runoff from glacierized drainage basins to this end we have synthesized a conceptual model of water movement through a temper ate glacier from the surface to the outlet stream pro cesses that regulate the rate and distribution of water input at the glacier surface and that regulate water movement from the surface to the bed play important but commonly neglected roles in glacier hydrology where a glacier is covered by a layer of porous perme able firn the accumulation zone the flux of water to the glacier interior varies slowly because the firn tempo rarily stores water and thereby smooths out variations in the supply rate in the firn free ablation zone in con trast the flux of water into the glacier depends directly on the rate of surface melt or rainfall and therefore varies greatly in time water moves from the surface to the bed through an upward branching arborescent net work consisting of both steeply inclined conduits formed by the enlargement of intergranular veins and gently inclined conduits spawned by water flow along the bottoms of near surface fractures crevasses engla cial drainage conduits deliver water to the glacier bed at a limited number of points probably a long distance downglacier of where water enters the glacier englacial conduits supplied from the accumulation zone are quasi steady state features that convey the slowly varying water flux delivered via the firn their size adjusts so that they are usually full of water and flow is pressurized in contrast water flow in englacial conduits supplied from the ablation area is pressurized only near times of peak daily flow or during rainstorms flow is otherwise in an open channel configuration the subglacial drainage system typically consists of several elements that are distinct both morphologically and hydrologically an up glacier branching arborescent network of channels in cised into the basal ice conveys water rapidly much of the water flux to the bed probably enters directly into the arborescent channel network which covers only a small fraction of the glacier bed more extensive spatially is a nonarborescent network which commonly includes cav ities gaps between the glacier sole and bed channels incised into the bed and a layer of permeable sediment the nonarborescent network conveys water slowly and is usually poorly connected to the arborescent system the arborescent channel network largely collapses during winter but reforms in the spring as the first flush of meltwater to the bed destabilizes the cavities within the nonarborescent network the volume of water stored by a glacier varies diurnally and seasonally small temper ate alpine glaciers seem to attain a maximum seasonal water storage of 200 mm of water averaged over the area of the glacier bed with daily fluctuations of as much as 20 30 mm the likely storage capacity of subglacial cavities is insufficient to account for estimated stored water volumes so most water storage may actually occur englacially stored water may also be released abruptly and catastrophically in the form of outburst floods

anticyclonic eddies in the alaskan stream abstract anticyclonic eddies propagating southwestward in the alaskan stream as were investigated through analysis of altimetry data from satellite observations during 1992 2006 and hydrographic data from profiling float observations during 2001 06 fifteen long lived eddies were identified and categorized based on their area of first appearance three eddies were present at the beginning of the satellite observations another three formed in the eastern gulf of alaska off sitka alaska and four were first detected at the head of the gulf of alaska near yakutat alaska the other five eddies formed along the as between 157 and 169 w and were named as eddies while the eddies that formed in the gulf of alaska mainly decayed before exiting the gulf of alaska the as eddies mostly crossed the 180 meridian and reached the western subarctic gyre four of five as eddies formed under negative or weakly positive wind stress curls which possibly caused as separation from the coast comparison of eddy propag

frequent outburst floods from south tahoma glacier mount rainier u s a relation to debris flows meteorological origin and implications for subglacial hydrology destructive debris flows occur frequently at glacierized mount rainier volcano washington u s a twenty three such lows have occurred in the tahoma creek valley since 1967 hydrologic and geomorphic evidence indicate that all or nearly all of these lows began as outburst loods from south tahoma glacier flood waters are stored subglacially the volume of stored water discharged during a typical outburst flood would form a layer several centimeters thick over the bed of the entire glacier although it is more likely that large linked cavities account for most of the storage statistical analysis shows that outburst floods usually occur during periods of atypically hot or rainy weather in summer or early autumn and that the probability of an outburst increases with temperature a proxy measure of ablation rate or rainfall rate we suggest that outburst floods are triggered by rapid water input to the glacier bed causing water pressure transients that destabilize the linked cavity system the correlation between outburst floods and meteorological factors casts doubt on an earlier hypothesis that melting around geothermal vents triggers outburst floods from south tahoma glacier

a fluvial record of long term steady state uplift and erosion across the cascadia forearc high western washington state six late quaternary river terraces preserved along the clearwater river in northwestern washington state provide a 140 ka record of long term incision and uplift across the western side of the cascadia forearc high terrace ages are constrained by weathering rind and radiocarbon dating and by correlation to dated coastal glacio fluvial deposits and the global eustatic curve the terraces overlie flat bedrock surfaces called straths which represent uplifted segments of the river channel bedrock incision is measured by the height of a strath relative to the adjacent modern river channel the straths along the clearwater show an upstream increase in bedrock incision ranging from 0 at the coast to a maximum of 110 m in the headwaters the incision at any point along the profile increases systematically with strath age the calculated incision rates range from 10 ky the clearwater river valley has maintained a steady state profile defined by a long term balance in the rates of incision and rock uplift upstream divergence of terraces is best explained by an increase in the rate of rock uplift from the coast toward the central part of the range these results are consistent with other evidence indicating a long term steady state balance between the accretionary influx and the erosional outflux for this part of the cascadia subduction wedge since 14 ma these results help show how terrace deposits form in tectonically active landscapes the dominantly fluvial clearwater drainage was forming straths while alpine glaciers were advancing in adjacent drainages in turn the straths were buried during the transition to interglacial times because of increased sediment supply due to local deglaciation and because of eustatic highstands that forced aggradation in the lower reach of the drainage and across the continental shelf as well the fluvial system shows strong forcing by the glacial climate cycle even so the river appears to have returned to the same valley profile during each cycle of strath cutting thus bedrock incision is clearly unsteady at time scales shorter than the glacial climate cycle 100 ky but appears to be relatively steady when averaged over longer time scales a simple kinematic model is used to examine how uplift of the cl our analysis indicates that the accretionary flux into the wedge occurs mainly by frontal accretion and not by underplating if accretion occurred entirely at the front of the wedge the present west coast should be moving to the northeast at 3 m ky relative to a fixed puget sound this prediction is in good agreement with offset of a 122 ka sea cliff preserved at the southwest side of the clearwater valley profile in this case the long term margin perpendicular shortening would account for 20 to 35 percent of the geodetically measured northeast southwest shortening across the olympic mountains

annual down glacier drainage of lakes and water filled crevasses at helheim glacier southeast greenland supraglacial lake drainage events are common on the greenland ice sheet observations on the west coast typically show an up glacier progression of drainage as the annual melt extent spreads inland we use a suite of remote sensing and modelling techniques in order to study a series of lakes and water filled crevasses within 20km of the terminus of helheim glacier south east greenland automatic classification of surface water areas shows a down glacier progression of drainage which occurs in the majority of years between 2007 and 2014 we demonstrate that a linear elastic fracture mechanics model can reliably predict the drainage of the uppermost supraglacial lake in the system but cannot explain the pattern of filling and draining observed in areas of surface water downstream we propose that the water levels in crevasses downstream of the supraglacial lake can be explained by a transient high pressure wave passing through the subglacial system following the lake drainage we support this hypothesis with analysis of the subglacial hydrological conditions which can explain both the position and interannual variation in filling order of these crevasses similar behaviour has been observed in association with jokulhaups surging glaciers and antarctic subglacial lakes but has not previously been observed on major outlets of the greenland ice sheet our results suggest that the behaviour of near terminus surface water may differ considerably from that of inland supraglacial lakes with the potential for basal water pressures to influence the presence of surface water in crevasses close to the terminus of tidewater glaciers

debris flow initiation in proglacial gullies on mount rainier washington article i nfo effects of climate change retreating glaciers and changing storm patterns on debris flow hazards concern managers in the cascade range usa and mountainous areas worldwide during an intense rainstorm in november 2006 seven debris flows initiated from proglacial gullies of separate basins on the flanks of mount rainier gully heads at glacier termini and widespread failure of gully walls imply that overland flow was trans formed into debris flow along gullies we characterized gully change and morphology and assessed spatial distributions of debris flows to infer the processes and conditions for debris flow initiation slopes at gully heads were greater than 0 35 m m 1 19 and exhibited a significant negative relationship with drainage area a break in slope drainage area trends among debris flow gullies also occurs at 0 35 m m 1 representing a possible transition to fluvial sediment transport and erosion an interpreted hybrid model of debris flow initi ation involves bed failure near gully heads followed by sediment recruitment from gully walls along gully lengths estimates of sediment volume loss from gully walls demonstrate the importance of sediment inputs along gullies for increasing debris flow volumes basin comparisons revealed significantly steeper drainage networks and higher elevations in debris flow producing than non debris flow producing proglacial areas the high slopes and elevations of debris flow producing proglacial areas reflect positive slope elevation trends for the mount rainier volcano glacier extent therefore controls the slope distribution in proglacial areas and thus potential for debris flow generation as a result debris flow activity may increase as glacier termini retreat onto slopes inclined at angles above debris flow initiation thresholds

evidence for nonlinear diffusive sediment transport on hillslopes and implications for landscape morphology steep soil mantled hillslopes evolve through the downslope movement of soil driven largely by slope dependent transport processes most landscape evolution models represent hillslope transport by linear diffusion in which rates of sediment transport are proportional to slope such that equilibrium hillslopes should have constant curvature between divides and channels on many soil mantled hillslopes however curvature appears to vary systematically such that slopes are typically convex near the divide and become increasingly planar downslope this suggests that linear diffusion is not an adequate model to describe the entire morphology of soil mantled hillslopes here we show that the interaction between local disturbances such as rainsplash and biogenic activity and frictional and gravitational forces results in a diffusive transport law that depends nonlinearly on hillslope gradient our proposed transport law 1 approximates linear diffusion at low gradients and 2 indicates that sediment flux increases rapidly as gradient approaches a critical value we calibrated and tested this transport law using high resolution topographic data from the oregon coast range these data obtained by airborne laser altimetry allow us to characterize hillslope morphology at 2 m scale at five small basins in our study area hillslope curvature approaches zero with increasing gradient consistent with our proposed nonlinear diffusive transport law hillslope gradients tend to cluster near values for which sediment flux increases rapidly with slope such that large changes in erosion rate will correspond to small changes in gradient therefore average hillslope gradient is unlikely to be a reliable indicator of rates of tectonic forcing or baselevel lowering where hillslope erosion is dominated by nonlinear diffusion rates of tectonic forcing will be more reliably reflected in hillslope curvature near the divide rather than average hillslope gradient