surface based transport model for mixed size sediment we present a transport model for mixed sand gravel sediments fractional transport rates are referenced to the size distribution of the bed surface rather than subsurface making the model completely explicit and capable of predicting transient conditions the model is developed using a new data set of 48 coupled observations of flow transport and bed surface grain size using five different sediments the model incorporates a hiding function that resolves discrepancies observed among earlier hiding functions the model uses the full size distribution of the bed surface including sand and incorporates a nonlinear effect of sand content on gravel transport rate not included in previous models the model shares some common elements with two previous surface based transport models but differs in using the full surface size distribution and in that it is directly developed from a relatively comprehensive data set with unambiguous measurement of surface grain size over a range of flow transport rate and sediments

how do geomorphic effects of rainfall vary with storm type and spatial scale in a post fire landscape abstract in post fire landscapes increased runoff and soil erosion can cause rapid geomorphic change we examined how different types of rainfall events in 2013 affected hillslope scale erosion and watershed scale channel change in two 14 16 km 2 watersheds within the 2012 high park fire burn area in northern colorado usa the first set of rainfall events was a sequence of 12 short spatially variable summer convective rain storms and the second was a 200 mm week long storm in september we compared rainfall characteristics hillslope sediment yields stream stage and channel geometry changes from the summer storms to those from the september storm the summer storms had a wide range of rainfall intensities and each storm produced erosion primarily in one study watershed the september storm rainfall had less spatial variability covered both watersheds and its total rainfall depth was 1 5 to 2 5 times greater than the total summer rainfall because rainfall intensities were highest during some summer storms average hillslope sediment yields were higher for summer storms 6 mg ha 1 than for the september storm 3 mg ha 1 maximum storm rainfall intensities were good predictors of hillslope sediment yield but sediment yield correlated most strongly with total depths of rainfall exceeding 10 30 mm h 1 intensity thresholds the combined summer storms produced relatively small changes in mean channel bed elevation and cross section area with no clear pattern of incision or aggradation in contrast the sustained rain across the entire study area during the september storm led to extensive upstream incision and downstream aggradation because of different spatial coverage of storms summer storms produced more total hillslope erosion whereas the september storm produced the greatest total channel changes at both scales high intensity rainfall above a threshold was responsible for inducing most of the geomorphic change

sediment delivery after a wildfire we use a record of sedimentation in a small reservoir within the cerro grande burn area new mexico to document postfire delivery of ash other fine grained sediment carried in suspension within floods and coarse grained sediment transported as bedload over a five year period ash content of sediment layers is estimated using fallout 137 cs as a tracer and ash concentrations are shown to rapidly decrease through a series of moderate intensity convective storms in the first rainy season after the fire over 90 of the ash was delivered to the reservoir in the first year and ash concentrations in suspended sediment were negligible after the second year delivery of the remainder of the fine sediment also declined rapidly after the first year despite the occurrence of higher intensity storms in the second year fine sediment loads after five years remained significantly above prefire averages deposition of coarse grained sediment was irregular in time and was associated with transport by snowmelt runoff of sediment stored along the upstream channel during short duration summer floods coarse sediment delivery in the first four years was strongly correlated with snowmelt volume suggesting a transport limited system with abundant available sediment transport rates of coarse sediment declined in the fifth year consistent with a transition to a more stable channel as the accessible sediment supply was depleted and the channel bed coarsened maximum impacts from ash and other fine grained sediment therefore occurred soon after the fire whereas the downstream impacts from coarse grained sediment were attenuated by the more gradual process of bedload sediment transport

erosion and channel changes due to extreme flooding in the fourmile creek catchment colorado abstract infrequent large magnitude geomorphic events generate quantifiable change on geologically short timescales and are crucial to understanding landscape evolution airborne lidar surveys and field measurements were used to investigate floodplain erosion and deposition along a 19 5 km reach of fourmile creek colorado that was devastated by severe flooding in 2013 that followed a 2010 wildfire 350 mm of rain fell on the fourmile catchment from september 9 15 2013 generating discharge that exceeded bankfull for 120 h at the orodell gage with local unit stream power 300 w m 2 throughout the study reach debris flows occurred on steep hillslopes and tributary channels in the most intensely burned areas lidar difference measurements and field studies highlight zones of local deposition along the study reach but demonstrate overall net erosion of 0 25 m for the 19 5 km reach of fourmile floodplain mainly by channel widening tributary junctions where debris flow sediment entered the floodplain and local decreases in unit stream power controlled some zones of deposition overall mass balance calculations show that a total sediment loss of 91 000 161 000 m3 from the fourmile creek floodplain and hillslopes which is broadly consistent with channel sediment flux estimates of 71 000 111 000 m3 measurements from the fourmile catchment demonstrate that floodplain erosion was a major source of sediment in the 2013 flood and demonstrate that infrequent events marked by long duration flooding and high total energy expenditure can account for a large fraction of total sediment transport in mountain streams

evaluating channel response to an extreme sedimentation event in the context of historical range of variability upper colorado river usa in may 2003 a breach in a large irrigation ditch within rocky mountain national park rmnp initiated a debris flow that entered lulu creek and the colorado river where 36 000 m3 of sediment substantially altered channel forms and processes we present a proof of concept to understand whether the 2003 disturbance is within the historical range of variability hrv and whether the recovery potential of the system is sufficient to adapt to the disturbance flow and sediment regimes and channel morphology and stability were monitored on lulu creek and the colorado river from 2004 to 2011 dominant channel response following the debris flow within lulu creek included step development bed armoring and channel widening step height to length ratios h l for three reaches on lulu creek are outside the hrv of reference channels with one reach approaching reference conditions erosion of approximately 23 of the debris fan volume occurred as a result of the long duration 2011 peak flow sediment within the lulu creek fan will persist for 30 190 years assuming current maximum and mean removal rates planform changes on the colorado river since the debris flow include an increase in single thread geometries with braided reaches where bar deposition occurred bedload transport and grain size analysis of bedload indicate translational spreading of a sand wave front with a dispersive component in steeper reaches lulu creek is returning to a condition of natural variability but the colorado river is outside the hrv expected for steep gradient pool riffle channels applying hrv to a situation where management questions require a longer term perspective and pre disturbance baseline data are limited is a useful approach the hrv analysis facilitates a better understanding of site variability and delineates the range of possibilities of channel form and process to achieve management goals copyright 2012 john wiley sons ltd

landslides associated with the may 12 2008 wenchuan earthquake implications for the erosion and tectonic evolution of the longmen shan abstract satellite images and aerial photography following the wenchuan earthquake show that a broad area experienced severe landsliding in association with the main earthquake and aftershocks a zone of high density landsliding 10 landslide surface area affected stretches for 240 km along the earthquake region in proximity to the yingxiu beichuan and pennguan faults which ruptured during the earthquake the width of this severe landsliding zone varies along the strike from 25 30 km wide in the southwestern section of the earthquake region to 3 5 in the northeastern section these variations coincide with differences in hillslope gradients bedrock lithologies co seismic slip and ground shaking observed in these sections of the earthquake region in general there is good correlation between the magnitude and distribution of ground shaking experienced during the earthquake and mapped landslide density though limited data and varying fault models prevent any in depth comparison with high resolution maps of ground shaking experienced landslides associated with wenchuan earthquake highlight interesting aspects of erosion and tectonic evolution of the longmen shan short term erosion rates in the longmen shan region measured from cosmogenic nuclides prior to the earthquake were 0 2 0 3 mm yr reflecting the last 2000 3000 years a time period shorter than the estimated recurrence interval of large earthquakes along the fault that ruptured while long term erosion rates measured by low temperature thermochronology were higher 0 5 0 7 mm yr for the last 8 10 ma integrating the total amount of erosion associated the earthquake into the short term erosion rate estimates pushes the rate much higher this suggests that the earthquake and associated landslide erosion was necessary for the landscape to catch up and balance the long term tectonic growth of the longmen shan particularly in the southwestern section of the earthquake region taken together the earthquake and associated landslide erosion can be seen as the most recent expression of the rapid deformation uplift and erosion that previous geomorphic evidence and geodynamic models had argued for along longmen shan front

basins and bedrock spatial variation in 10be erosion rates and increasing relief in the southern rocky mountains usa we used measurements of cosmogenic 10 be in alluvium to estimate erosion rates on a 10 3 10 4 yr time scale for small 0 01 47 km 2 unglaciated basins in northern colorado southern wyoming and adjacent western nebraska western united states basins formed in proterozoic cores of laramide ranges are eroding more slowly 23 7 mm k y 1 n 19 than adjacent basins draining weakly lithified cenozoic sedimentary rocks 75 36 mm k y 1 n 20 erosion rates show a relationship to rock resistance and for granitic rocks to basin slope but not to mean annual precipitation we estimated longer term 10 5 yr time scale erosion rates for the granitic core of the front range by measuring the concentration of 10 be and 26 al produced mainly by muon interactions at depths 1 7 10 m below the surface concentrations imply erosion rates of 9 31 mm k y 1 similar to shorter term erosion rates inferred from alluvial sediment the spatial distribution of erosion rates and stratigraphic evidence imply that relief in the southern rocky mountains increased in the late cenozoic modern relief probably dates from post middle miocene time

detection of surface change in complex topography using terrestrial laser scanning application to the illgraben debris flow channel detection of surface change is a fundamental task in geomorphology terrestrial laser scanners are increasingly used for monitoring surface change resulting from a variety of geomorphic processes as they allow the rapid generation of high resolution digital elevation models irrespective of instrument specifics survey design or data processing such data are subject to a finite level of ambiguity in position measurement a consideration of which must be taken into account when deriving change the propagation of errors is crucial in change detection because even very small uncertainties in elevation can produce large uncertainties in volume when extrapolated over an area of interest in this study we propose a methodology to detect surface change and to quantify the resultant volumetric errors in areas of complex topography such as channels where data from multiple scan stations must be combined we find that a commonly proposed source of error laser point elongation at low incidence angles has a negligible effect on the quality of the final registered point cloud instead ambiguities in elevation inherent to registered datasets have a strong effect on our ability to detect and measure surface change similarly we find that changes in surface roughness between surveys also reduce our ability to detect change explicit consideration of these ambiguities when propagated through to volume calculations allows us to detect volume change of 87 5m3 over an area of 4900m2 due to passage of a debris flow down a 300m reach of the illgraben channel in switzerland

multitemporal alsm change detection sediment delivery and process mapping at an active earthflow remote mapping and measurement of surface processes at high spatial resolution is among the frontiers in earth surface process research remote measurements that allow meter scale mapping of landforms and quantification of landscape change can revolutionize the study of landscape evolution on human timescales at mill gulch in northern california usa an active earthflow was surveyed in 2003 and 2007 by airborne laser swath mapping alsm enabling meter scale quantification of landscape change we calculate four year volumetric flux from the earthflow and compare it to long term catchment average erosion rates from cosmogenic radionuclide inventories from adjacent watersheds we also present detailed maps of changing features on the earthflow from which we can derive velocity estimates and infer dominant process these measurements rely on proper digital elevation model dem generation and a simple surface matching technique to align the multitemporal data in a manner that eliminates systematic error in either dataset the mean surface elevation of the earthflow and an opposite slope that was directly influenced by the earthflow decreased 14 1 mm yr from 2003 to 2007 by making the conservative assumption that these features were the dominant contributor of sediment flux from the entire mill gulch drainage basin during this time interval we calculate a minimum catchment averaged erosion rate of 0 30 0 02 mm yr analysis of beryllium 10 10be concentrations in fluvial sand from nearby russian gulch and the south fork gualala river provide catchment averaged erosion rates of 0 21 0 04 and 0 23 0 03 mm yr respectively from translated landscape features we can infer surface velocities ranging from 0 5 m yr in the wide upper source portion of the flow to 5 m yr in the narrow middle transport portion of the flow this study re affirms the importance of mass wasting processes in the sediment budgets of uplifting weak lithologies copyright 2011 john wiley sons ltd

illuminating wildfire erosion and deposition patterns with repeat terrestrial lidar erosion following a wildfire is much greater than background erosion in forests because of wildfire induced changes to soil erodibility and water infiltration while many previous studies have documented post wildfire erosion with point and small plot scale measurements the spatial distribution of post fire erosion patterns at the watershed scale remains largely unexplored in this study lidar surveys were collected periodically in a small first order drainage basin over a period of 2 years following a wildfire the study site was relatively steep with slopes ranging from 17 to 30 during the study period several different types of rain storms occurred on the site including low intensity frontal storms 2 4 mm h 1 and high intensity convective thunderstorms 79 mm h 1 these storms were the dominant drivers of erosion erosion resulting from dry ravel and debris flows was notably absent at the site successive lidar surveys were subtracted from one another to obtain digital maps of topographic change between surveys the results show an evolution in geomorphic response such that the erosional response after rain storms was strongly influenced by the previous erosional events and pre fire site morphology hillslope and channel roughness increased over time and the watershed armored as coarse cobbles and boulders were exposed the erosional response was spatially nonuniform shallow erosion from hillslopes 87 of the study area contributed 3 times more sediment volume than erosion from convergent areas 13 of the study area however the total normalized erosion depth volume area was highest in convergent areas from a detailed understanding of the spatial locations of erosion we made inferences regarding the processes driving erosion it appears that hillslope erosion is controlled by rain splash for detachment and overland flow for transport and quasi channelized erosion with the sites of highest erosion corresponding to locations with the lowest roughness by contrast in convergent areas we found erosion caused by overland flow soil erosion was locally interrupted by immobile objects such as boulders bedrock or tree trunks resulting in a patchy erosion network with increasing roughness over time

geochemical controls on hydrothermal fluids from the kairei and edmond vent fields 23 25 s central indian ridge prior to 2000 no mid ocean ridge hydrothermal systems were identified and sampled in the indian ocean the kairei field central indian ridge was discovered and sampled in 2000 gamo et al 2001 hashimoto et al 2001 this paper reports the chemical composition of hydrothermal fluids collected in 2001 from both the kairei and newly discovered edmond hydrothermal systems data are used to infer subsurface processes and conditions at the two sites as well as to place them within the global context of known hydrothermal sites on the mid ocean ridge system while both sites are located on the intermediate spreading central indian ridge their hydrologic systems have affinities with those observed on slow spreading ridges although the compositions of fluids from the four individual vents sampled at edmond and the three individual vents sampled at kairei vary respectively our interpretation is that a single source fluid at each site is subsequently modified by processes including phase separation subsurface mixing with seawater and deposition and or remobilization of metal sulfide deposits to generate the observed range of compositions both fields are located 6 km from the neovolcanic zone on steps on the east wall of the axial valley with the edmond field 160 km north of kairei and almost 1000 m deeper 3300 versus 2450 m the edmond fluids are extremely hot with maximum measured temperatures of 382 c compared to 365 c for kairei all of the fluids sampled have chlorinities greater than local ambient seawater due to phase separation of seawater at supercritical conditions visual observations suggest both sites have been active for a substantial period of time again similar to observations of slow spreading ridges our chemical data suggest that the substrate underlying kairei is highly altered while that at edmond is not significant albitization appears to be occurring below the edmond field but not at kairei the edmond fluids are by far the hottest brines yet observed venting from a mid ocean ridge hydrothermal site resulting in unusually high concentrations of several transition metals

gradients in stream power influence lateral and downstream sediment flux in floods locations of landslides bank failures and floodplain deposition during recent intense flooding in vermont and colorado usa were spatially nonuniform indicating that some reaches are more prone to these types of geologic hazards these three key flood effects signal redistribution of sediment across landscapes reflecting hillslope channel coupling and the sources and or sinks of material we show that spatial gradients in total stream power provide critical additional information beyond at a point magnitudes for predicting which reaches are likely to be susceptible to these hazards during floods field tests in four rivers watershed areas 0 8 180 km 2 indicate that downstream increases in coincide with erosion and mass wasting into channels and downstream decreases in are associated with floodplain deposition our analytical approach supported by field evidence predicts geologic hazards and more broadly sources and sinks of material along rivers these are critical concerns from a practical and theoretical standpoint

episodes of vertical accretion and catastrophic stripping a model of disequilibrium flood plain development this paper describes flood plains formed episodically by vertical accretion along high energy laterally stable channels in southeastern australia overbank deposition gradually builds a flood plain of fine textured alluvium over a period of hundreds or thousands of years following which catastrophic erosion by a single large flood or a series of more moderate floods strips the flood plain to a basal lag deposit from which it slowly reforms this periodic destruction appears due to the progressive development of large levee banks and flood plain surfaces of highly variable relief as the levees and flood plain grow overbank flow is gradually displaced from the broad flood plain into the main channel and flood plain backchannels with a resulting concentration of erosional energy eventually high flows greatly exceed erosional thresholds and wholesale scour of the channel boundary and flood plain occurs vertical accretion flood plains at different stages of development result in a wide range of bankfull recurrence intervals even along the same river some of these flood plains are so infrequently flooded that they can be mistaken for terraces formed under a prior flow regime the almost random but catastrophic nature of this flood plain erosion means that sediment supply and transport are highly variable and probably impossible to predict this model of flood plain formation is seen as only part of a continuum of alluvial environments ranging from vestigial coarsegrained traction load flood plains along high energy rivers in narrow gorges to extensive low gradient flood plains in which alluvial stratigraphy is dominated by fine grained overbank deposition

low frequency 0 045 hz swell from the southern ocean unusual low frequency one dimensional energy spectra of surface gravity waves from measurements with a buoy in deep water 167 m near cape town south africa are discussed here classical treatment of the time series of spectra showed that the wave source was 2 800 nautical miles distant and probably in the southern ocean examination of south african weather bureau surface pressure analyses of the south atlantic depict an intense slow moving cyclone with geostrophic wind velocities 50 knots at the same time and place as the origin of the waves the wave spectra are highly unusual in that they reveal quasi regular swell at very low frequencies with spectral energy densities an order of magnitude larger than those normally present at these frequencies the wave event and its associated meteorological conditions are also discussed

geomorphic complexity and sensitivity in channels to fire and floods in mountain catchments abstract fires and floods are important drivers of geomorphic change while the hydrologic and geomorphic effects of fires have been studied at the hillslope scale we have much more limited data on post fire runoff channel changes and inferred or measured sediment storage and delivery at larger scales in this study we intensively documented channel changes over four years in two very similar 15 km2 catchments in the northern colorado front range skin gulch and hill gulch that were burned primarily at high and moderate severity in june 2012 ten and 11 cross sections and longitudinal profiles along the lower channel network were repeatedly surveyed in skin gulch and hill gulch respectively summer thunderstorms generally caused deposition in the valley bottoms while incision resulted from the intervening baseflows and spring snowmelt but a very high intensity summer thunderstorm in skin gulch just one week after burning caused much more deposition than in hill gulch fifteen months after burning both watersheds experienced an exceptional long duration flood resulting from a multi day rainstorm with a several hundred year recurrence interval this removed nearly all of the deposited post fire sediment along with some of the older valley bottom deposits the expansion and coarsening of the channel has greatly decreased the geomorphic sensitivity of both watersheds to future floods and eliminated the more typical and persistent post fire depositional signature the channel changes in skin gulch after the fire and long duration flood were much greater than in hill gulch and this can be attributed to the much greater sediment deposition in skin gulch shortly after the fire reduced geomorphic sensitivity in hill gulch resulting from a large erosional flood in 1976 and the spatial distribution of burn severity and storm rainfalls leading to lower peak flows in hill gulch these results suggest that fires in the rocky mountains can trigger significant and dynamic hillslope and channel changes over sub decadal timescales but unusually long or intense rainstorms can cause larger and more persistent changes regardless of whether a catchment has recently burned

preface to anthropogenic fluvial sedimentation centennial celebration of g k gilbert s hydraulic mining debris in the sierra nevada

thresholds and the spatial variability of flood power during extreme floods abstract analysis of the effects of extreme events on overall landscape form has shifted geomorphic attention away from a focus on the magnitude and frequency relationship of discharge to a focus on flood power this paper analyzes the variation in flood power both at a station and downstream in a basin of differing lithologies and discusses the geologic and geomorphic controls on flood power design floods ranging from the 2 year discharge tothe 500 year discharge are routed trough a drainage basin and channel boundary shear stress and unit stream power are calculated using hec 2 along 21 cross valley transects because of the strong lithologic control on valley width and channel slope an irregular downstream pattern of flood power emerges which reflects primarily the pattern in valley width narrow valleys correspond to a greater percent of channel conveyance during large magnitude floods and increasing rates of depth increases thus maximizing flood power in these zones the opposite occurs in anomalously wide valleys where flood power is minimized a downstream spatial pattern emerges reflecting both local and general controls for a given probability event flood power varies at least threefold within the basin with a maximum occuring in a specific downstream section holding flood power constant produces an extremely wide range in flow probabilities in order to establish a link between critical flood power magnitude and flow frequency minimum flood powers are developed from an analysis of previous work on catastrophic flooding for humid alluvial channels these minimum thresholds tentatively correspond to 100 n m2 or 300 w m2 for shear stress and unit stream power respectively discharges required to attain these critical flood powers vary from events roughly twice the 100 year flood to a maximum of roughly 18 times the discharge of the 100 year flood

recent large magnitude floods and their impact on valley floor environments of northeastern yellowstone abstract the lamar river watershed of northeastern yellowstone contains some of the most diverse and important habitat in the national park broad glacial valley floors feature grassland winter range for ungulates riparian vegetation that provides food and cover for a variety of species and alluvial channels that are requisite habitat for native fish rapid neogene uplift and quaternary climatic change have created a dynamic modern environment in which catastrophic processes exert a major influence on riverine riparian ecosystems uplift and glacial erosion have generated high local relief and extensive cliffs of friable volcaniclastic bedrock as a result steep tributary basins produce voluminous runoff and sediment during intense precipitation and rapid snowmelt recent major floods on trunk streams deposited extensive overbank gravels that replaced loamy soils on flood plains and allowed conifers to colonize valley floor meadows tree ring dating identifies major floods in 1918 ca 1873 and possibly ca 1790 in 1996 and 1997 discharge during snowmelt runoff on soda butte creek approached the 100 year flood estimated by regional techniques with substantial local bank erosion and channel widening indirect estimates show that peak discharges in 1918 were approximately three times greater than in 1996 with similar duration and much greater flood plain impact nonetheless 1918 peak discharge reconstructions fall well within the range of maximum recorded discharges in relation to basin area in the upper yellowstone region the 1873 and 1918 floods produced lasting impacts on the channel form and flood plain of soda butte creek channels may still be locally enlarged from flood erosion and net downcutting has occurred in some reaches leaving the pre 1790 flood plain abandoned as a terrace gravelly overbank deposits raise flood plain surfaces above levels of frequent inundation and are well drained therefore flood plain soils are drier noncohesive gravels also reduce bank stability and may have persistent effects on channel form overall floods are part of a suite of catastrophic geomorphic processes that exert a very strong influence on landscape patterns and valley floor ecosystems in northeastern yellowstone

sediment variability in a small catchment of the polish western carpathians during transition from centrally planned to free market economics abstract the purpose of this study was to analyse suspended sediment ss transport in a small catchment 13 km2 located in the polish carpathians affected by various forms of human activity in the period 1970 2017 this period covers two stages of socioeconomic development with contrasting forms of human activity the centrally planned economy related to the communist system up to 1989 and the period of a free market economy following analysis indicates increases in grassland and forest areas of the analysed catchment of 90 and 10 respectively and a decrease in cultivated land of 82 changes in land use and land cover lulc have reduced soil erosion by 74 as calculated using the revised universal soil loss equation at the same time population number of buildings and construction works along the stream increased and number of cart roads decreased hydrometeorological data as well as suspended sediment load ssl have not shown a statistically significant trend despite changes in forms of human activity in 1970 2017 in the first three decades of the analysed period 1970 1979 1980 1989 and 1990 1999 ssl gradually decreased in 2010 2017 suspended sediment load was the highest in the whole investigated period principal component analysis pca confirmed that it was a result of the appearance of new sediment sources associated with intensification of landslides and new forms of human activity such as construction works the imposition on these factors resulted in an increase in ssl and masked the effects of rainfall lulc change in the catchment analysis shows that proper recognition of changes in sediment sources in the catchment is fundamental for correct interpretation of long term sediment transport in the streams

unsteady late pleistocene incision of streams bounding the colorado front range from measurements of meteoric and in situ 10be 1 dating of gravel capped strath terraces in basins adjacent to western u s laramide ranges is one approach to document the history of late cenozoic fluvial exhumation we use in situ 10be measurements to date the broad surfaces adjacent to the eastern edge of the rocky mountains in colorado and compare these calculated ages with results from meteoric 10be measurements we analyze three sites near boulder colorado gunbarrel hill table mountain and pioneer that have been mapped as the oldest terrace surfaces with suggested ages ranging from 640 ka to the plio pleistocene transition our in situ 10be results reveal abandonment ages of 95 129 ka at table mountain 175 27 ka at pioneer and ages of 251 10 ka and 307 15 ka at gunbarrel hill all are far younger than previously thought inventories of meteoric 10be support this interpretation yielding ages that are comparable to table mountain and 20 lower than pioneer in situ ages we argue that lateral beveling by rivers dominated during protracted times of even moderate glacial climate and that vertical incision rates of several mm yr likely occurred during times of very low sediment supply during the few interglacials that were characterized by particularly warm climate conditions in contrast to the traditional age chronology in the area our ages suggest that the deep exhumation of the western edge the high plains occurred relatively recently and at an unsteady pace

floodplain sedimentation in the upper mississippi valley natural versus human accelerated abstract understanding the time scales and pathways for response and recovery of rivers and floodplains to episodic changes in erosion and sedimentation has been a long standing issue in fluvial geomorphology floodplains are an important component of watershed systems because they affect downstream storage and delivery of overbank flood waters and they also serve as sources and temporary sinks for sediments and toxic substances delivered by river systems here 14c and 137cs isotopic dating methods are used along with ages of culturally related phenomena associated with mining and agriculture to determine rates of sedimentation and morphologic change for a reach of the upper mississippi river and adjacent tributaries in southwestern wisconsin and northwestern illinois the most important environmental change that influenced fluvial activity in this region during last 10 000 years involved the conversion of a late holocene mosaic of prairie and forest to a landscape dominated by cropland and pastureland associated with euro american settlement results presented herein for the upper mississippi valley umv show that the shift from pre agriculture natural land cover to landscape dominance by agricultural land use of the last 175 200 years typically increased rates and magnitudes of floodplain sedimentation by at least an order of magnitude accelerated overbank flooding led to increased bank heights on tributary streams and in turn contributed to more frequent deep flows of high energy these high energy flows subsequently promoted bank erosion and lateral channel migration and the formation of a historical meander belt whose alluvial surface constitutes a new historical floodplain inset against the earlier historical floodplain the new historical floodplain serves as a flume like channel that provides efficient downstream transport of water and sediment associated with moderate and large magnitude floods floodplains on lower tributaries however continue to experience rates of overbank sedimentation that are of anomalously high magnitude given improved land cover and land conservation since about 1950 this lower valley anomaly is explained by minimal development of historical agriculture period meander belts because of relatively low stream power in these channel and floodplain reaches of relatively low gradient in general long term pre agriculture rates of vertical accretion between about 10 000 and 200 years ago averaged about 0 2 mm yr 1 in tributary watersheds smaller than about 700 km2 and about 0 9 mm yr 1 on the floodplain of the upper mississippi river where the contributing watershed area increases to about 170 000 km2 on the other hand rates of historical vertical accretion during the period of agricultural dominance of the last 200 years average between 2 and 20 mm yr 1 with short episodes of even higher rates during times of particularly poor land conservation practices significant hydrologic effects of mining and agricultural started by the 1820s and became widespread in the study region by the mid 19th century the hydrologic and geomorphic influences of mining were relatively minor compared to those related to agriculture high resolution dating of floodplain vertical accretion deposits shows that large floods have frequently provided major increments of sedimentation on floodplains of tributaries and the main valley upper mississippi river the relative importance of large floods as contributors to floodplain vertical accretion is noteworthy because global atmospheric circulation models indicate that the main channel upper mississippi river should experience increased frequencies of extreme hydrologic events including large floods with anticipated continued global warming instrumental and stratigraphic records show that coincident with global warming a shift to more frequent large floods occurred since 1950 on the upper mississippi river and these floods generally contributed high magnitudes of floodplain sedimentation

predicting the type location and magnitude of geomorphic responses to dam removal role of hydrologic and geomorphic constraints abstract using a dam removal on the ashuelot river in southern new hampshire we test how a sudden spatially non uniform increase in river slope alters sediment transport dynamics and riparian sediment connectivity site conditions were characterized by detailed pre and post removal field surveys and high resolution aerial lidar data and locations of erosion and deposition were predicted through one dimensional hydrodynamic modeling the homestead dam was a 200 year old 4 m high 50 m wide crib dam that created a 9 5 km long relatively narrow reservoir following removal an exhumed resistant bed feature of glaciofluvial boulders located 400 m upstream and 2 5 m lower than the crest of the dam imposed a new boundary condition in the drained reservoir acting as a grade control that maintained a backwater effect upstream during the 15 months following removal non uniform erosion in the former reservoir totaled 60 000 m3 equivalent to 9 3 cm when averaged across the reservoir net deposition of 10 700 m3 was measured downstream of the dam indicating most sediment from the reservoir was carried more than 8 km downstream beyond the study area the most pronounced bed erosion occurred where modeled sediment transport increased in the downstream direction and deposition occurred both within and downstream of the former reservoir where modeled sediment transport decreased in the downstream direction we thus demonstrate that spatial gradients in sediment transport can be used to predict locations of erosion and deposition on the stream bed we further observed that bed incision was not a necessary condition for bank erosion in the former reservoir in this characteristically narrow and shallow reservoir lacking abundant dam induced sedimentation the variable resistance of the bed and banks acted as geomorphic constraints overall the response deviated from the common conceptual model of knickpoint erosion and channel widening due to dam removal with thousands of dams likely to be considered for removal or repair in the coming decades this study helps to advance predictions of the geomorphic response to dam removal and contributes to a broader understanding of the variability in both style and timing of fluvial responses to disturbances

pleistocene incision rates in the western united states calibrated using lava creek b tephra the lava creek b ash bed erupted from the yellowstone caldera ca 0 64 ma provides a datum for measuring long term fluvial incision west of the mississippi river the ash is widely preserved due to its substantial volume broad initial dispersal and the aggrading environment into which the ash fell drainages incised soon after lava creek b deposition isolating the ash from fluvial erosion and preserving it in fill terraces calculated rates of incision since ca 0 60 ma range from 2 to 30 cm k y 1 rates are high in most areas near the rocky mountains and downstream along rivers draining mountainous terrain and are lowest east of the high plains and along the snake river incision rates along many rivers decrease downstream rates of downcutting increased in the late pleistocene along several major rivers indicating that climate change altered sediment budgets regional and temporal data suggest that fluvial incision records increased middle and late pleistocene runoff from the southern rocky mountains rather than epeirogenic uplift but regional rock uplift cannot be excluded as a significant factor

geomorphic inferences from regolith thickness chemical denudation and crn erosion rates near the glacial limit boulder creek catchment and vicinity colorado granitic regolith developed in the boulder creek catchment and adjacent areas records a history of deep weathering some of which may predate quaternary time field and well log measurements of weathering chemical denudation and rates of erosion derived from 10be cosmogenic radionuclide crn data help to quantify rates of landscape change in the post orogenic rocky mountains the density of oxidized fractured bedrock ranges from 2 7 to about 2 2 g cm 3 saprolite and grus have densities between 2 0 and 1 8 g cm 3 and 30 soil samples averaged 1 6 0 2 g cm 3 highly weathered regolith in 540 wells averages 3 3 m thick mean depth to bedrock in 1661 wells is 7 m and the weathered thickness exceeds 10 m in relatively large local areas east of the late pleistocene glacial limit thickness of regolith shows no simple relationship to rock type or structure local slope or distance from channels catchments in the vicinity of the boulder creek have an average crn erosion rate of 2 2 0 7 cm kyr 1 for the past 10 000 to 40 000 yr annual losses of cations and sio2 vary from about 2 to 5 g m 2 over a runoff range of 10 to nearly 160 cm using measured rates in simple box models shows that if a substantial fraction of void space is created by volume expansion in the weathering rock materials 7 m of weathered rock materials could form in as little as 230 kyr if density loss results mainly from chemical denudation and some volume expansion however the same weathering profile would take 1340 kyr to form rates of erosion measured by crn could be balanced by the rate of soil formation from saprolite if the annual solute loss from soil is 2 0 g m 2 and 70 of the density decrease from saprolite to grus and soil results from strain saprolite however forms from oxidized bedrock at a far slower rate and rates of saprolite formation cannot balance soil and grus losses to erosion the zone of thick weathered regolith is likely an eroding relict landscape the undulating surface marked by relatively low relief and tors is not literally a topographic surface of eocene oligocene or miocene age unless it was covered with deposits that were removed in pliocene or quaternary time

exhumation by debris flows in the 2013 colorado front range storm the relative importance of extreme events in the long term exhumation of landscapes is difficult to determine the degree to which modern records capture long term mean process rates is therefore commonly unknown in september 2013 a massive precipitation event in the front range of colorado usa triggered over 1100 landslides and debris flows in a historically sedate landscape here we employ topographic differencing utilizing repeat aerial lidar to quantify net sediment transport volumes in 120 of these mass movements within an area of 102 km 2 west of boulder colorado comparing our results against published long term erosion rates we find that these mass movements evacuated the equivalent of hundreds to thousands of years of hillslope weathering products we conclude that 1 rare debris flows perform the majority of sediment transport and channel erosion within steep channels along the eastern edge of the front range potentially explaining discrepancies between modern sediment yields and long term erosion rates in such settings and 2 the high spatial density of debris flows along the corridors bounding steep canyons suggests that the landscape switches to debris flow dominance as knickpoints pass headward along the canyons

directional recording of swell from distant storms almost fifteen years ago in the pages of this journal one of us presented power spectra of ocean waves and swell off pendeen and perranporth in north cornwall barber ursell 1948 the outstanding feature of these spectra is the successive shift of peaks toward higher frequencies this is the expected behaviour of dispersive wave trains from rather well defined sources storms generate a broad spectrum of frequencies the low frequencies are associated with the largest group velocity and accordingly are the first to arrive at distant stations the time rate of increase in the frequency of peaks determines the distance and time of origin in this way barber ursell were able to identify the dispersive arrivals with a low pressure area in the north atlantic a tropical storm off florida and a storm off cape horn at distances of 1200 2800 and 6000 miles respectively from the cornish stations the measurements were consistent with the simple classical result that each frequency is propagated with its appropriate group velocity v g 47 the present study is in a sense a refinement to the work of barber ursell the frequency resolution and sensitivity have each been increased by an order of m agnitude and this makes it possible to detect and resolve meteorological sources that have previously been out of reach the antipodal swell from the indian ocean is a case in point

elastic response of floating glacier ice to impact of long period ocean waves 1 disintegration of ice shelves along the antarctic peninsula over the past two decades has clearly demonstrated their high sensitivity to recent changes in the local thermal regime of the atmosphere and ocean and has given rise to the question of whether mechanical coupling with waves in the ocean may provide the triggering mechanism that starts collapse events motivated by these events this study considers a more general question how ocean waves affect the stress regime of floating ice and in particular how ocean waves can influence the creation of fractures and its fatiguing that may lead to breakup and collapse a new treatment of ice shelf ocean wave interaction in which the typical thin plate approximation is relaxed is presented here and exact analytic solutions describing ice shelf stresses induced by long 60 s period ocean waves in various idealized ice ocean geometries are derived the numerical calculations demonstrate that the amplitudes of the wave induced stresses are sufficiently large to initiate top to bottom crevasse penetration through the depth of the ice shelf the cyclic nature of the wave induced stresses contributes to ice fatigue and damage that is also a precursor to ice shelf disintegration although primarily theoretical the results of the present analysis suggest that ocean waves could be a potential trigger of ice shelf collapse as well as less dramatic but equally important episodic calving

the use of multi temporal lidar to assess basin scale erosion and deposition following the catastrophic january 2011 lockyer flood se queensland australia advances in remote sensing and digital terrain processing now allow for a sophisticated analysis of spatial and temporal changes in erosion and deposition digital elevation models dems can now be constructed and differenced to produce dems of difference dod which are used to assess net landscape change for morphological budgeting to date this has been most effectively achieved in gravel bed rivers over relatively small spatial scales if the full potential of the technology is to be realised additional studies are required at larger scales and across a wider range of geomorphic features this study presents an assessment of the basin scale spatial patterns of erosion deposition and net morphological change that resulted from a catastrophic flood event in the lockyer creek catchment of se queensland seq in january 2011 multitemporal light detection and ranging lidar dems were used to construct a dod that was then combined with a one dimensional flow hydraulic model hec ras to delineate five major geomorphic landforms including inner channel area within channel benches macrochannel banks and floodplain the lidar uncertainties were quantified and applied together with a probabilistic representation of uncertainty thresholded at a conservative 95 confidence interval the elevation change distribution ecd for the 100 km2 study area indicates a magnitude of elevation change spanning almost 10 m but the mean elevation change of 0 04 m confirms that a large part of the landscape was characterised by relatively low magnitude changes over a large spatial area mean elevation changes varied by geomorphic feature and only two the within channel benches and macrochannel banks were net erosional with an estimated combined loss of 1 815 149 m3 of sediment the floodplain was the zone of major net deposition but mean elevation changes approached the defined critical limit of uncertainty areal and volumetric ecds for this extreme event provide a representative expression of the balance between erosion and deposition and importantly sediment redistribution which is extremely difficult to quantify using more traditional channel planform or cross sectional surveys the ability of lidar to make a rapid and accurate assessment of key geomorphic processes over large spatial scales contributes to our understanding of key processes and as demonstrated here to the assessment of major geomorphological hazards such as extreme flood events

does climate change create distinctive patterns of landscape incision 1 incised fluvial systems are typically interpreted as recording geologically recent changes in either climate or tectonics however few diagnostic tools exist to evaluate whether particular incised landscapes primarily reflect climatic or tectonic perturbation here we summarize the results of a simple fluvial sediment transport model that allows us to contrast patterns of fluvial incision driven by changes in hydrology and sediment flux climate with those driven by changes in rock uplift patterns relative to sea level tectonics our modeling suggests that there may be diagnostic differences between the spatial and temporal patterns of incision caused by these different processes in particular incision driven by climate change is most commonly accompanied by downstream migrating waves of incision and decreases in channel gradient while under most circumstances incision driven by tectonics will be accompanied by upstream migrating incision and increases in channel gradient we apply our modeling to a case study of the north american high plains where regionally elevated surfaces east of the rockies have been incised up to 500 m by the fluvial systems draining the core of the range although this incision has been interpreted as reflecting a tectonic rejuvenation of the high plains our analysis suggests that climate change is at least as plausible an explanation to explain the incision of this landscape diagnostic differences between the climate and tectonic end member scenarios might be obtained via detailed study of the spatial and temporal patterns of terrace abandonment providing a potentially fruitful target for field investigation

the efficacy of stream power and flow duration on geomorphic responses to catastrophic flooding abstract geomorphologists have long studied the impacts of extreme floods yet the association between the magnitude of flow parameters discharge velocity shear stress or stream power and resulting geomorphic effectiveness remains vague and non deterministic attempts have been made to include flow duration and total expenditure of stream power in combination with peak unit stream power as important variables but there has been minimal exploration of this hydraulic combination taking advantage of tropical storm irene s rapid track through eastern vermont usa in late summer 2011 this paper presents the array of geomorphic responses to a short duration time to peak of

26al and10be dating of late pleistocene and holocene fill terraces a record of fluvial deposition and incision colorado front range cosmogenic 26al 10be and 14c dating of fluvial fill terraces in steep canyons of the colorado front range provides a temporal framework for analysing episodic aggradation and incision results from boulder canyon show that terrace heights above the modern channel grade can be divided into 1 bull lake 100 ka 20 15 m above grade 2 pinedale 32 10 ka 15 4 m above grade and 3 holocene age 15 m above grade record bull lake deposition well preserved terraces of pinedale age suggest that the range of terrace height above grade reflects short term fluctuations in the river profile during periods of rapidly changing stream load and power net river incision apparently occurred during transitions to interglacial periods soil development and stratigraphic position along with limited cosmogenic and 14c dating suggest that 130 ka terraces in boulder canyon correlate with the louviers alluvium and that 32 to 10 ka fills in the canyon correlate with the broadway alluvium on the adjacent high plains late pleistocene incision rates 0 15 m ka 1 along boulder canyon exceed pre late pleistocene incision rates and are higher than middle to late pleistocene incision rates 0 04 m ka 1 on the high plains this study provides an example of how modern geochronologic techniques allow us to understand better rivers that drain glaciated catchments copyright 2002 john wiley sons ltd