cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

enhanced sediment delivery in a changing climate in semi arid mountain basins implications for water resource management and aquatic habitat in the northern rocky mountains the delivery and transport of sediment through mountain rivers affects aquatic habitat and water resource infrastructure while climate change is widely expected to produce significant changes in hydrology and stream temperature the effects of climate change on sediment yield have received less attention in the northern rocky mountains we expect climate change to increase sediment yield primarily through changes in temperature and hydrology that promote vegetation disturbances i e wildfire insect pathogen outbreak drought related die off here we synthesize existing data from central idaho to explore 1 how sediment yields are likely to respond to climate change in semi arid basins influenced by wildfire 2 the potential consequences for aquatic habitat and water resource infrastructure and 3 prospects for mitigating sediment yields in forest basins recent climate driven increases in the severity and extent of wildfire suggest that basin scale sediment yields within the next few years to decades could be greater than the long term average rate of 146 t km 2 year 1 observed for central idaho these elevated sediment yields will likely impact downstream reservoirs which were designed under conditions of historically lower sediment yield episodic erosional events massive debris flows that dominate post fire sediment yields are impractical to mitigate leaving road restoration as the most viable management opportunity for offsetting climate related increases in sediment yield however short term sediment yields from experimental basins with roads are three orders of magnitude smaller than those from individual fire related events on the order of 101 t km 2 year 1 compared to 104 t km 2 year 1 respectively for similar contributing areas suggesting that road restoration would provide a relatively minor reduction in sediment loads at the basin scale nevertheless the ecologically damaging effects of fine sediment material

latest jurassic early cretaceous events and the late cimmerian unconformity in north sea area each of several regional or local unconformities may have been identified locally as the late cimmerian unconformity a supposed major break at the base of the valhall formation or roedby formation over most of the north sea the base of the valhall formation is isochronous and conformable with underlying sediments it is detected on seismic reflection profiles because it represents a widespread facies change marking the late ryazanian transgression most of the unconformities are of eustatic origin and the effects of eustatic sea level changes were never completely masked by local tectonics thus in the modeling of individual oil fields the possibility of sedimentary breaks occurring can be predicted in part by reference to regional or eustatic events modified journal abstract

how do sediment yields from post wildfire debris laden flows depend on terrain slope soil burn severity class and drainage basin area insights from airborne lidar change detection we derived a high resolution spatially continuous map of erosion and deposition associated with the debris laden flows triggered by the 2011 las conchas wildfire and subsequent rainstorms over a 197 km2 area in new mexico usa this map was produced using airborne lidar derived bare earth digital elevation models dems acquired approximately one year before and one year after the wildfire differencing of the pre wildfire and post wildfire and rainstorm bare earth dems yielded a dem of difference dod map that quantifies the magnitude of ground surface elevation changes due to erosion deposition within each 1 m2 pixel we applied a 0 3 m threshold filter to our dod to remove changes that could have been due to artifacts and or imperfect georeferencing the 0 3 m value for the threshold filter was chosen based on the stated accuracy of the lidar as well as a comparison of areas of significant topographic change mapped in aerial photographs with those predicted using a range of candidate threshold values for the dod filter we developed an automated procedure that accepts the dod map as input and computes for every pixel in the dem the net sediment volume exported through each pixel by colluvial and or fluvial processes using a digital routing algorithm an analysis of the resulting sediment volume map for the las conchas fire demonstrates that sediment volume is proportional to upstream contributing area after normalized by contributing area the average sediment yield defined as the sediment volume divided by the contributing area increases as a power law functions of the average terrain slope and soil burn severity class sbsc with exponents equal to approximately 1 5 our analysis quantifies the relationships among sediment yield average terrain slope and average soil burn severity class at the watershed scale and should prove useful for predicting the geomorphic response of wildfire affected drainage basins copyright 2014 john wiley sons ltd

holocene fire occurrence and alluvial responses at the leading edge of pinyon juniper migration in the northern great basin usa abstract fire and vegetation records at the city of rocks national reserve ciro south central idaho display the interaction of changing climate fire and vegetation along the migrating front of single leaf pinyon pinus monophylla and utah juniper juniperus osteosperma radiocarbon dating of alluvial charcoal reconstructed local fire occurrence and geomorphic response and fossil woodrat neotoma middens revealed pinyon and juniper arrivals fire peaks occurred 10 700 9500 7200 6700 2400 2000 850 700 and 550 400 cal yr bp whereas 9500 7200 6700 4700 and 1500 1000 cal yr bp are fire free wetter climates and denser vegetation fueled episodic fires and debris flows during the early and late holocene whereas drier climates and reduced vegetation caused frequent sheetflooding during the mid holocene increased fires during the wetter and more variable late holocene suggest variable climate and adequate fuels augment fires at ciro utah juniper and single leaf pinyon colonized ciro by 3800 and 2800 cal yr bp respectively though pinyon did not expand broadly until 700 cal yr bp increased fire related deposition coincided with regional droughts and pinyon infilling 850 700 and 550 400 cal yr bp early and late holocene vegetation change probably played a major role in accelerated fire activity which may be sustained into the future due to pinyon juniper densification and cheatgrass invasion

15 k y paleoclimatic and glacial record from northern new mexico the southern sangre de cristo mountains new mexico contain evidence of glacial activity from the late pleistocene to late holocene sediment cores recovered from an alpine bog 3100 m trapped behind a pinedale age moraine 2 km downvalley from a high elevation cirque reached glacial age debris and recovered 6 m of lake clays overlain by gyttja accelerator mass spectrometry dating sedimentology variations in magnetic properties and organic carbon data reveal six distinct periods of glacial and or periglacial activity these include a late pleistocene pinedale glacial termination just before 12120 1 4 c yr b p a younger dryas chron cirque glaciation an early neoglacial periglacial event ca 4900 1 4 c yr b p a late holocene cirque glaciation 3700 1 4 c yr b p as well as late holocene periglacial events at 2800 1 4 c yr b p and the little ice age ca 120 1 4 c yr b p cold events in the middle to late holocene correlate with subtle ice rafting events in the north atlantic and records of cold events in north america and europe and were probably hemispheric in extent

the predominance of post wildfire erosion in the long term denudation of the valles caldera new mexico nsf ear 0724958 ear 1331408 valles caldera national preserve gsa graduate student research grant

modeling of the interactions between forest vegetation disturbances and sediment yields in the idaho batholith are investigated through numerical modeling the model simulates soil development based on continuous bedrock weathering and the divergence of diffusive sediment transport on hillslopes soil removal is due to episodic gully erosion shallow landsliding and debris flow generation in the model forest vegetation provides root cohesion and surface resistance to channel initiation forest fires and harvests reduce the vegetation vegetation loss leaves the land susceptible to erosion and landsliding until the vegetation cover reestablishes in time simulation results compare well with field observations of event sediment yields and long term averages over 10 000 years when vegetation is not disturbed by wildfires over thousands of years sediment delivery is modeled to be less frequent but with larger event magnitudes increased values of root cohesion representing denser forests lead to higher event magnitudes wildfires appear to control the timing of sediment delivery compared to undisturbed forests erosion is concentrated during the periods with low erosion thresholds often called accelerated erosion periods following wildfires our modeling suggests that drainage density is inversely proportional to root cohesion and that reduced forest cover due to wildfires increases the drainage density we compare the sediment yields under anthropogenic harvest and natural wildfire disturbances disturbances due to forest harvesting appear to increase the frequency of sediment delivery however the sediment delivery following wildfires seems to be more severe these modeling based findings have implications for engineering design and environmental management where sediment inputs to streams and the fluctuations and episodicity of these inputs are of concern index terms 1625 global change geomorphology and weathering 1824 1886 1815 hydrology erosion and sedimentation 1824 hydrology geomorphology 1625 keywords sediment yield wildfires forest management hydrology

vegetative and climatic controls on holocene wildfire and erosion recorded in alluvial fans of the middle fork salmon river idaho the middle fork salmon river watershed spans high elevation mixed conifer forests to lower elevation shrub steppe in recent decades runoff from severely burned hillslopes has generated large debris flows in steep tributary drainages these flows incised alluvial fans along the mainstem river where charcoal rich debris flow and sheetflood deposits preserve a record of latest pleistocene to holocene fires and geomorphic response through deposit sedimentology and 14c dating of charcoal we evaluate the processes and timing of fire related sedimentation and the role of climate and vegetation change fire related deposits compose 66 of the total measured fan deposit thickness in more densely forested upper basins versus 33 in shrub steppe dominated lower basins fires during the middle holocene 8000 5000 cal yr bp mostly resulted in sheetflood deposition similar to modern events in lower basins decreased vegetation density during this generally warmer and drier period likely resulted in lower sev

a sediment transport model for incision of gullies on steep topography 1 we have conducted surveys of gullies that developed in a small steep watershed in the idaho batholith after a severe wildfire followed by intense precipitation we measured gully length and cross sections to estimate the volumes of sediment loss due to gully formation these volume estimates are assumed to provide an estimate of sediment transport capacity at each survey cross section from the single gully forming thunderstorm sediment transport models commonly relate transport capacity to overland flow shear stress which is related to runoff rate slope and drainage area we have estimated the runoff rate and duration associated with the gully forming event and used the sediment volume measurements to calibrate a general physically based sediment transport equation in this steep high shear stress environment we find that a shear stress exponent of 3 corresponding to drainage area and slope exponents of m 2 1 and n 2 25 match our data this shear stress exponent of 3 is approximately 2 times higher than those for bed load transport in alluvial rivers but is in the range of shear stress exponents derived from flume experiments on steep slopes and with total load equations the concavity index of the gully profiles obtained theoretically from the area and slope exponents of the sediment transport equation c m 1 n agrees well with the observed profile concavity of the gullies our results although preliminary because of the uncertainty associated with the sediment volume estimates suggest that for steep hillslopes such as those in our study area a greater nonlinearity in the sediment transport function exists than that assumed in some existing hillslope erosion models which calculate sediment transport capacity using the bed load equations developed for rivers

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

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

sensitivity analysis of a one dimensional model of a volcanic plume with particle fallout and collapse behavior abstract we run a volcanic plume model with uncertain boundary conditions and entrainment related model parameters output variables tested for their sensitivity to the inputs are total rise height and mass flux of particles into the umbrella cloud or downwind plume boundary or source conditions are vent radius initial velocity grain size mean and grain size standard deviation model parameters are entrainment rate wind entrainment rate and wind speed five sensitivity metrics were considered three of these are calculated for each given point in the input parameter space by perturbing the input variable around fixed points two global sensitivity measures quantify the impact on the output of the input over its entire uncertain domain we find that vent radius and initial speed have a much more profound effect on both outputs than does total grain size distribution plume rise height and particle mass flux are sensitive to the entrainment parameters and but these parameters are not of greater importance than the wind speed this suggests that while efforts to better characterize entrainment parameters through laboratory experiments is important similar efforts should be made to collect appropriate meteorological data for the region near the site of the eruption

quantifying the time scale of elevated geomorphic response following wildfires using multi temporal lidar data an example from the las conchas fire jemez mountains new mexico abstract sediment yields commonly increase following wildfires in mountainous landscapes quantifying the magnitude and duration of elevated sediment yields following wildfires is important for quantifying the relative importance of wildfire affected versus non wildfire affected erosion in the long term evolution of landscapes and for understanding the processes of post wildfire erosion in this study we use bi annual terrestrial laser scanning tls surveys conducted over a 2 yr period together with repeat airborne laser scanning als surveys conducted over a 1 yr period to estimate the dependence of sediment yield on time following the high severity las conchas fire of 2011 within two small approximately 1 3 km 2 watersheds the dependence of sediment yield on time since the wildfire was quantified using dems of difference dods of the upland watersheds to measure erosion and of the adjacent piedmonts to measure the deposition of eroded sediment over the 2 yr study period sediment volume decreased linearly with time and sediment yield decreased exponentially with time in one watershed while the other watershed showed a more complex relationship with time influenced by the specific sequence of rainstorms that impacted that watershed both watersheds had a recovery time of approximately 1 yr suggesting that vegetation regrowth and the stabilization of incised valley bottoms were primarily responsible for the decline in sediment yield versus time following the wildfire multi temporal dods of the piedmonts show how they responded to the delivery of elevated sediment yields from the upland watersheds i e by 1 incision of the proximal portion of the piedmont triggering distal deposition 2 infilling of the incised channel and avulsion and 3 incision of the distal portion creating an incised channel connecting the proximal and distal ends of the piedmont the dynamic nature of incision aggradation and channel shifting on piedmonts following wildfires has important implications for post wildfire flood hazard assessments

the 40ar 39ar age constraints on the duration of resurgence at the valles caldera new mexico 1 the 40ar 39ar ages for rocks from the valles caldera new mexico imply that resurgent uplift of the caldera floor occurred within 27 27 ka of caldera collapse the structural resurgent dome of the valles caldera was uplifted approximately 1000 m above the surrounding caldera floor during resurgence the upper bandelier tuff which yields an age of 1 256 0 010 ma 2 ages relative to fish canyon tuff sanidine at 28 02 ma is the lower constraint on the timing of resurgence the oldest postcollapse ring fracture dome cerro del medio is the upper time constraint and yields an age of 1 229 0 017 ma for one of its oldest flow lobes therefore resurgent uplift probably occurred within 54 ka at a minimum rate of 1 9 cm yr sanidine phenocrysts from rhyolites of the postcollapse intracaldera deer canyon and redondo creek members yield 40ar 39ar single crystal laser fusion ages ranging from 1 229 0 013 ma to 1 283 0 017 ma deer canyon member n 8 and 1 208 0 017 ma to 1 239 0 017 ma redondo creek member n 4 with one exception from each unit these ages are statistically indistinguishable from the upper bandelier tuff indicating that eruption of these postcollapse rhyolites probably commenced shortly after caldera formation melt inclusion hosted excess argon was not found to have a measurable effect on the age of sanidine from the upper bandelier tuff or the deer canyon member

post fire bedload sediment delivery across spatial scales in the interior western united states post fire sediment yields can be up to three orders of magnitude greater than sediment yields in unburned forests much of the research on post fire erosion rates has been at small scales 100 m2 or less and post fire sediment delivery rates across spatial scales have not been quantified in detail we developed relationships for post fire bedload sediment delivery rates for spatial scales up to 117 ha using sediment yield data from six published studies and two recently established study sites sediment yields and sediment delivery ratios sdrs sediment delivered at the catchment scale divided by the sediment delivered from a plot nested within the catchment were related to site factors including rainfall characteristics area length and ground cover unit area sediment yields significantly decreased with increasing area in five of the six sites the annual sdrs ranged from 0 0089 to 1 15 and these were more closely related to the ratio of the plot lengths than the ratio of plot areas the developed statistical relationships will help quantify post fire sediment delivery rates across spatial scales in the interior western united states and develop process based scaling relationships published in 2013 this article is a u s government work and is in the public domain in the usa

mountain erosion over 10 yr 10 k y and 10 m y time scales we used cosmogenic 10 be to measure erosion rates over 10 k y time scales at 32 idaho mountain catchments ranging from small experimental watersheds 0 2 km 2 t o large river basins 35 000 km 2 these long term sediment yields are on average 17 times higher than stream sediment fluxes measured over 10 84 yr but are consistent with 10 m y erosion rates measured by apatite fission tracks our results imply that conventional sediment yield measurements even those made over decades can greatly underestimate long term average rates of sediment delivery and thus overestimate the life spans of engineered reservoirs our observations also suggest that sediment delivery from mountainous terrain is extremely episodic sporadically subjecting mountain stream ecosystems to extensive disturbance

development of the mixed conifer forest in northern new mexico and its relationship to holocene environmental change chihuahuenos bog 2925 m in the jemez mountains of northern new mexico contains one of the few records of late glacial and postglacial development of the mixed conifer forest in southwestern north america the chihuahuenos bog record extends to over 15 000 cal yr bp an artemisia steppe then an open picea woodland grew around a small pond until ca 11 700 cal yr bp when pinus ponderosa became established c n ratios 13c and 15n values indicate both terrestrial and aquatic organic matter was incorporated into the sediment higher percentages of aquatic algae and elevated c n ratios indicate higher lake levels at the opening of the holocene but a wetland developed subsequently as climate warmed from ca 8500 to 6400 cal yr bp the pond desiccated in what must have been the driest period of the holocene there c n ratios declined to their lowest holocene levels indicating intense decomposition in the sediment wetter conditions returned after 6400 cal yr bp with conversion of the site to a sedge bog as groundwater levels rose higher charcoal influx rates after 6400 cal yr bp probably result from greater biomass production rates only minor shifts in the overstory species occurred during the holocene suggesting that mixed conifer forest dominated throughout the record

spatially averaged long term erosion rates measured from in situ produced cosmogenic nuclides in alluvial sediment spatially averaged erosion rates of small catchments can be accurately inferred from the concentrations of cosmogenic nuclides in stream sediment here we test this technique at two catchments by comparing erosion rates inferred from cosmogenic nuclides with rates of alluvial fan deposition over the past 16 000 years these two independent estimates agree within one standard error demonstrating that cosmogenic nuclide signatures of stream sediment can be used to measure spatially averaged long term erosion rates using this technique we show that long term erosion rates are an exponential function of average hillslope gradient at these sites