dating alluvial fan surfaces in owens valley california using weathering fractures in boulders a wide range of sedimentological and geomorphological field research depends on the availability of accurate and detailed depositional age models although exposure dating techniques such as cosmogenic nuclide and luminescence dating are now widely available they remain expensive and time consuming and this frequently limits the density of age constraints and the resolutions of age models for many study areas we present a simple and effective field based approach for extending and correlating existing age models to un dated surfaces in owens valley california we make use of detailed beryllium 10 10be chronologies reported for four different alluvial fan systems to precisely calibrate the rate at which weathering fractures are enlarged in granitic surface boulders we show that these fractures have widened at a time integrated rate of 1 05 0 03 mm ka 1 for at least 140 ka at this location and this relationship can be represented by a linear regression that makes them ideal chronometers for surface dating our analysis offers a new approach to refining the uncertainties of both surface erosion rate and cosmogenic age estimates at this location ultimately we integrate our observations to devise a robust age calibration for clast fracture widths in owens valley and we demonstrate its application by estimating the ages of 27 additional local fan surfaces we present an updated and extended stratigraphy for eight sierra nevada fan systems in total with exceptional age control this novel approach to dating sedimentary surfaces is inexpensive and easily applied in the field and has the potential to significantly increase the temporal and spatial density of age constraints available for a particular study area copyright 2014 john wiley sons ltd

10be and 26al evidence for exceptionally low rates of australian bedrock erosion and the likely existence of pre pleistocene landscapes analysis of in situ produced 10be and 26al demonstrate that some australian inselbergs granitic domes are among the most stable geomorphic surfaces in the world eroding at rates as low as 0 6 m myr twenty isotopic analyses of ten samples suggest that the bare bedrock tops of these isolated granitic domes have been exposed to cosmic radiation for at least 0 5 myr and are eroding at a mean model rate less than 0 7 0 1 m myr n 6 isotopic analyses of samples collected from the top of mt wudinna little wudinna and yarwondutta rock are most consistent with continuous exposure during erosion on the other hand samples collected from the flanks of some domes and the tops of other domes have isotopic abundances suggestive of complex exposure histories including burial and reexposure these unique isotopic data provide the first quantitative information for evaluating longstanding but previously untested hypotheses regarding the antiquity and development of these enigmatic landforms and indicate that some eyre peninsula inselbergs are probably relict features of pre pleistocene landscapes

transient sediment supply in a high altitude alpine environment evidenced through a 10be budget of the etages catchment french western alps although beryllium 10 10be concentrations in stream sediments provide useful synoptic views of catchment wide erosion rates little is known on the relative contributions of different sediment supply mechanisms to the acquisition of their initial signature in the headwaters here we address this issue by conducting a 10be budget of detrital materials that characterize the morphogenetic domains representative of high altitude environments of the european alps we focus on the etages catchment located in the ecrins pelvoux massif southeast france and illustrate how in situ 10be concentrations can be used for tracing the origin of the sand fraction from the bedload in the trunk stream the landscape of the etages catchment is characterized by a geomorphic transient state high topographic gradients and a large variety of modern geomorphic domains ranging from glacial environments to scarcely vegetated alluvial plains beryllium 10 concentrations measured in the etages catchment vary from similar to 1 x 104 to 4 5 x 105 atoms per gram quartz while displaying consistent 10be signatures within each representative morphogenetic unit we show that the basic requirements for inferring catchment wide denudation from 10be concentration measurements are not satisfied in this small dynamic catchment however the distinct 10be signature observed for the geomorphic domains can be used as a tracer we suggest that a terrestrial cosmogenic nuclide tcn budget approach provides a valuable tool for the tracing of material origin in basins where the let nature do the averaging principles may be violated

estimation of episodic exfoliation rates of rock sheets on a granite dome in korea from cosmogenic nuclide analysis we have measured concentrations of cosmogenic 10be and 26al produced in situ at bare bedrock surfaces of successive sheets developing on a granite dome in korea and calculated the exfoliation rate of sheeting joints the exfoliation rate was obtained using a simple model in which the sheeting joints experience intermittent denudation i e peeling off along the bedrock face we find that the average exfoliation erosion rate of the episodic peeling off process is 5 6 cm ka 1 the analysis is useful for understanding the evolution of granite sheeting structures on this dome in korea copyright 2006 john wiley sons ltd

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

modeling the tor dotted crests bedrock edges and parabolic profiles of high alpine surfaces of the wind river range wyoming abstract broad low curvature surfaces common to many alpine landscapes and particularly well expressed in the laramide ranges of the western usa appear to be roughly in steady state with respect to the current surface processes uniform thin order 1 m regolith covers the crystalline bedrock with the exception of occasional tors at ridgecrests the surfaces are commonly edged by bedrock lips at the tops of cliffs that bound the intervening glacial troughs regolith production is low order 10 m year on bare bedrock and reaches a maximum under tens of centimeters of regolith all of these characteristics may be accounted for with a numerical model that is faithful to the periglacial surface processes presently operating on these surfaces hillslope transport is modeled assuming the dominant process is frost creep transport efficiency depends linearly upon local slope and appropriately vanishes in the absence of regolith frost frequency scales the rate of motion while the ratio of frost penetration depth to regolith thickness dictates the degree to which the process is curtailed by available regolith initial conditions include initial mean slope and bedrock roughness and a uniform regolith cover boundary conditions are imposed by dictating that the edges of the calculation space be lowered at a rate appropriate for glacial incision broad convex surfaces emerge over time scales of order 1 million years all surfaces rapidly decouple from the bounding glacial troughs as the high negative curvature at the edges disallows accumulation of regolith these bedrock edges lower at a few microns per year while the troughs lower at many times this rate as the bedrock edges therefore serve as the effective boundary condition for the remaining surface the surfaces operate independently of both lowering and widening of the glacial troughs for a reasonable set of transport and weathering rates the final steady state landscape is sensitive to the initial condition in particular the steeper the initial landscape the more likely tors are to develop as the high curvature disallows accumulation of regolith these tors in turn limit the lowering rate of the crest and the landscape retains significant local relief low relief initial conditions more likely lead to parabolic surfaces that lack tors that tors are more likely on the crests reflects the high initial curvature at the crest tors on the side slopes are eliminated the present high surfaces in the laramide ranges of the western usa imply operation of periglacial surface processes over millions of years the occasional tors imply a steeper rather than flatter initial landscape the strong decoupling of surfaces from glacial troughs justifies their use as local geomorphic markers that allow calculation of relief production since glacial incision was initiated on the other hand their present low curvature does not require a landscape history in which these surfaces were once joined as an initially widespread erosion surface

denudation rates and a topography driven rainfall threshold in northern chile multiple cosmogenic nuclide data and sediment yield budgets abstract the quantification of geomorphic process rates on the outcrop and the orogen scale is important to describe accurately the interaction between the relative effects of erosion tectonics and climate on landscape evolution we report single and paired cosmogenic nuclide 10 be 26 al and 21 ne derived erosion rates and exposure ages on hillslope interfluves from the tectonically active western central andes that show a distinct spatial variation a positive correlation of erosion rates with elevation and present day rainfall rates is observed erosion rates at lower altitudes the hyperarid coastal cordillera and the western escarpment with the northern part of the atacama desert are extremely low and of the order of 10 100 cm my nominal exposure ages 1 6 my in contrast erosion rates at higher altitudes the semiarid western cordillera range up to 4600 cm my nominal exposure ages 0 02 0 1 my this latter average long term bedrock erosion rate record suggested to be coupled to an orographically controlled pattern of rainfall is also reflected in the pattern of denudation rates derived from a short term decadal record of limited sediment yield data specifically denudation rates calculated from sediment flux data are of a similar order of magnitude as erosion rates deduced from long lived cosmogenic nuclides from bedrock hillslope interfluves of the western cordillera nevertheless the production and the supply of sediment from the western andean slope are very limited analysis of multiple cosmogenic nuclides allows simultaneous determination of erosion rates and exposure ages but also reveals complex exposure histories of non bedrock samples such as boulders or amalgamated clast samples notably this study shows that saturation of nuclides usually assumed in studies where only a single nuclide is analyzed is rather the exception than the rule as revealed by erosion island plots constant erosion that started much later than the formation age of the rocks or episodic erosion by spalling can partially explain non steady state concentrations and more complicated exposure scenarios furthermore the use of multiple nuclides with different half lives allowed us to infer that no significant variations in long term erosion rates have occurred and that at the western escarpment erosion rates have been low and constant for most of the late neogene nevertheless the time intervals necessary to reach steady state concentrations for cosmogenic nuclides can be quite different from those needed for landscapes to reach steady state

relict non glacial surfaces in formerly glaciated landscapes abstract relict non glacial surfaces occur within many formerly glaciated landscapes and contain important information on past surface processes and long term landscape evolution relict non glacial surfaces are distinguishable from glacial surfaces by large scale morphologies including rounded summits fluvial valleys and cryoplanation terraces and pediments and the presence of tors blockfields and or saprolites preservation during glaciation occurs either through coverage by non erosive cold based ice or as nunataks although surface morphologies and denudation rates indicate a continuous non glacial surface history since preglacial times relict non glacial surfaces are dynamic features that have evolved during the quaternary depending on spatial variables such as lithology slope regolith depth and the abundance of fine matrix and water some surfaces are denuding very slowly while others display more rapid denudation high spatial variability in denudation rates results in changing surface morphologies over time denudation rates also display high temporal variability with much surface evolution having perhaps occurred soon after the initial onset of glaciation or during paraglacial phases while some parts of non glacial landscapes are currently active others may be largely inactive relicts of past higher energy regimes although non glacial surfaces are dynamic much remains to be determined regarding surface denudation rates and the magnitude of morphological changes over time

controls of tor formation cairngorm mountains scotland tors occur in many granitic landscapes and provide opportunities to better understand differential weathering we assess tor formation in the cairngorm mountains scotland by examining correlation

pace of landscape evolution in the sierra nevada california revealed by cosmogenic dating of cave sediments we report 26 al 10 be based ages of sierra nevada caves that constrain detailed late pliocene and quaternary river incision his tories for five river canyons rapid incision of 0 2 mm yr from 2 7 to ca 1 5 ma slowed markedly to 0 03 mm yr thereafter likely reflecting the combined effects of a transient erosional re sponse to pliocene rock uplift and periodic mantling of riverbeds with glacially derived sediment in the late quaternary while 400 m of incision has occurred in the past 2 7 m y outpacing interfluve erosion and thereby increasing the local relief canyons as deep as 1 6 km existed prior to that time these new erosion rates strength en the case for tectonically driven late cenozoic uplift

geomorphically driven late cenozoic rock uplift in the sierra nevada california geologists have long accepted that the sierra nevada california experienced significant late cenozoic tectonically induced uplift a flexural isostatic model presented here shows however that a large fraction of the primary evidence for uplift could be generated by the lithospheric response to coupled erosion of the sierra nevada and deposition in the adjacent central valley and therefore requires less tectonic forcing than previously believed the sum of range wide erosion and the resultant isostatic rock uplift would have lowered sierra mean elevation by 200 to 1000 meters since 10 million years ago and could also have increased summit elevations during the current period of relief production

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

erosion rates in and around shenandoah national park virginia determined using analysis of cosmogenic 10be we use cosmogenic 10be analysis of fluvial sediments and bedrock to estimate erosion rates 104 105 year timescale and to infer the distribution of post orogenic geomorphic processes in the blue ridge province in and around shenandoah national park virginia our sampling plan was designed to investigate relationships between erosion rate and lithology mean basin slope basin area and sediment grain size fifty nine samples were collected from a variety of basin sizes inferred erosion rates for the medium sand fraction of all fluvial samples from all lithologies range from 3 0 to 21 m my the area weighted mean erosion rate for single lithology basins in the park is 12 2 m my single lithology erosion rate ranges for fluvial samples are granite 7 0 to 20 m my metabasalt 3 8 to 21 m my quartzite 3 8 to 15 m my and siliciclastic rocks 5 2 to 15 m my multilithology basins erode at rates between 3 0 16 m my the shenandoah river basin 3305 km2 is eroding at 6 6 m my bedrock erosion rates range from 1 8 to 11 m my across all lithologies with a mean of 6 5 4 3 m my grain size specific 10be analysis of four samples showed no consistent trend of concentration with grain size cosmogenic analysis of bedrock and sediment from the shenandoah national park area allows us to speculate about why some parts of the appalachian mountains erode more slowly and some more rapidly overall it appears that steep drainage basins erode more rapidly than gently sloped basins climate and lithology may also influence basin scale rates of erosion as suggested by the difference in average erosion rates east and west of the divide and the difference between the erosion rates of quartzite and granite dominated basins data are conflicting in regards to the evolution of relief over time analyses made of exposed bedrock along ridgelines suggest that such rock is eroding either more slowly than adjacent drainage basins susquehanna river shenandoah national park region or at similar rates great smoky mountains providing a mechanism for growing relief at the scale of individual ridgelines however considering relief on a landscape or physiographic province scale by comparing erosion rates of the highlands versus the lowlands suggests that relief of the range as a whole is either steady or very slowly decreasing over multi millennial timescales the presence of significant erosion rate slope relationships negates a broad hackian view of the landscape because there is not uniform erosion across this landscape the aspect erosion rate and slope erosion rate relationships present in the shenandoah area suggest that the landscape is not fully adjusted to rock strength

diurnal freeze thaw depth in rockwalls field measurements and theoretical considerations rock temperatures were monitored for a year at two alpine rockwalls in the akaishi range japan where permafrost is absent diurnal frost and thaw penetration depths were evaluated from subsurface isotherms drawn on the basis of the temperature records at 0 10 and 40 cm depths the surface of the rockwalls experienced more than 100 diurnal freeze thaw cycles most of which accompanied a frost or thaw penetration shallower than 50 cm and several long duration cycles with deeper frost or thaw penetration theoretical frost and thaw depths were also calculated by incorporating the surface freezing indices into the modified berggren equation the results from which were then compared with the actual values the modified berggren equation provided values that showed a strong correlation with observed depths despite somewhat underestimating the actual values using the modified berggren equation the seasonal frost depth in the observed winter was estimated to be about 4 5 m the frost and thaw depths are considered to give the maximum estimation of the depth to which frost induced cracking can propagate in the bedrock

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

geochemistry and water dynamics of a medium sized watershed the herault southern france abstract the aim of this study of the herault watershed is to constrain the river groundwater relations with a global geochemical investigation major and trace elements radiogenic isotopes sr pb and stable isotopes oxygen deuterium among the six sampling campaigns in high and low flows this paper focuses on the first one march 1995 sampled during a low flow period for major and trace elements and sr isotopes on both dissolved and particulate loads a companion paper will focus on the river karst relations in a dynamical scheme over a complete hydrological cycle the objective of this paper is to constrain the spatial organisation of the different water reservoirs to show the relations between surficial and groundwaters and to assess the mechanical and chemical weathering in this low flow period the herault main stream successively drains a palaeozoic basement a karstified mesozoic cover and a tertiary and quaternary alluvial plain the different tributaries also drain these lithologies this watershed is also impacted by ancient mining and agricultural activities especially in the southern part major element concentrations generally reflect the drained lithologies the chemistry of the herault main stream is mainly controlled by silicate and carbonate endmembers whereas the karstic springs show clearly a mixture of limestones and dolomitic limestones major elements point out some specific characteristics of some karstic springs and sr isotopes are used to check previous underground circulation hypotheses and sometimes reveal strong connections with overlying surface waters mixing phenomena between the herault river and its tributaries can be quantified in the 87 sr 86 sr vs 87 rb 86 sr diagram based on a simple two component scheme and agree within 10 with the real discharge measurements as in large basins the suspended matter presents more variable and more radiogenic 87 sr 86 sr than the dissolved load due to the more important contribution of silicate particles which are less soluble than carbonate dissolved ca fluxes were estimated to be 36 51 and 38 kg km 2 day 1 in the palaeozoic basement the mesozoic cover and the alluvial plain respectively this implies a chemical erosion estimated to be 20 m year in the palaeozoic basement and 58 m year in the mesozoic cover similar to values calculated for large basins

tectonic denudation and topographic development in the spanish sierra nevada 1 the denudation history of the rapidly uplifting western part of the spanish sierra nevada was assessed using apatite fission track aft ages and 10be analyses of bedrock and fluvial sediments major contrasts in the denudation history are recorded within the 27 km2 rio torrente catchment upland areas are characterized by low relief low slope angles and locally the preservation of shallow marine sediments which have experienced 2 km of denudation since circa 4 ma the minimum denudation rates of 0 4 mm yr 1 derived from aft also contrast with the slow medium term 104 years erosion rates 0 044 0 015 mm yr 1 estimated from 10be measurements at high elevations the local medium long term contrasts in denudation rates within the high sierra nevada indicate that much of the unroofing occurs by tectonic denudation on flat lying detachments in lower elevation parts of the catchment rapid river incision coupled to rock uplift has produced 1 6 km of relief implying that the rivers and adjacent hillslopes close to the edge of the orogen are sensitive to normal fault driven changes in base level however these changes are not transmitted into the low relief slowly eroding upland areas thus the core of the mountain range continues to increase in elevation until the limits of crustal strength are reached and denudation is initiated along planes of structural weakness we propose that this form of tectonic denudation provides an effective limit to relief in young orogens

the spatial variation of weathering and soil depth across a triassic sandstone outcrop in this study we used an archive of borehole logs from the british geological survey to collect information on the spatial structure of weathering that extends from the surface to competent bedrock across the triassic sherwood sandstone group outcrop 750 km2 in the east midlands uk the borehole logs were used to estimate the thickness of the soil n 280 and soil and saprolite ss the overburden of ice may have increased sub glacial pore water pressure with the fractures and faults acting as a drainage system for the removal of dissolved weathering products

the freeze thaw weathering regime at a section of the niagara escarpment on the bruce peninsula southern ontario canada the bedrock freeze thaw and moisture regimes at an actively eroding site on the niagara escarpment bruce peninsula southern ontario were monitored between december 1983 and april 1984 and the results compared with amounts of debris collected in an adjacent rock trap frost wedging in pre existing rock fissures is the primary mechanism responsible for the observed rockfall events hydration effects are negligible debris production was more closely related to the duration of the freezing leg of the freeze thaw cycle than to intensity or to cycle frequency release also coincided with periods of high pore saturation 60 per cent and the seepage of water from cracks and fissures fewer freeze thaw cycles were recorded in the air than at 1 and 3 5 cm in the bedrock the number of cycles that could be declared geomorphologically effective according to established temperature criteria was normally less than half the total number of freeze thaw cycles recorded in both air and bedrock under the current temperature regime at the field site few effective cycles are capable of penetrating more than 5 cm into the free face

improving in situ cosmogenic chronometers new radiocarbon ages for sierra nevada deglaciation the first 10 be measurements from the laurentide terminal moraine and calculations based on paleomagnetic field strength have the potential to substantially improve the accuracy of cosmogenic age estimates specifically three new constraints apply to the interpretation of measured abundances of in situ produced cosmogenic 10be and 26al 1 a suite of minimum limiting radiocarbon dates indicates that the sierra nevada was deglaciated at least several thousand years earlier than assumed when nishiizumi et al 1989 first calibrated 10be and 26 al production rates based on polished bedrock surfaces in the range with retreat beginning by 18 000 cal yr b p and completed by 13 000 cal yr b p 2 concentrations of 10be in moraine boulders and glacier polished bedrock in new jersey show little variance 10 1 and can be used to calculate a preliminary 10be production rate integrated over the past 21 000 22 000 cal yr b p at 41 200 300 m altitude that is about 20 lower than currently accepted 3 calculations of the effect of past geomagnetic field strength variations on production rates suggest that the use of temporally averaged production rates may generate age errors of 20 however cosmogenic exposure ages can be corrected for this effect although the corrections currently are imprecise many previously reported late pleistocene 10be and 26al exposure ages are probably too young and are less accurate and less precise than implied by reported uncertainties the discrepancy between accepted production rates and those calculated from laurentide exposures when considered together with the sierran deglacial chronology and the model results suggest that correlations between cosmogenic and other numerical ages especially for brief events like the younger dryas and heinrich events will not be robust until temporal variations and the altitude latitude scaling of production rates are fully understood and quantified at levels comparable to current analytic uncertainties 3

development of the truckee river terraces on the northeastern flank of the sierra nevada abstract the distribution and elevation of the abandoned strath terraces along the truckee river in the carson range on the eastern flank of the sierra nevada are mapped and quantified with measurements from lidar accompanied by field survey each mapped strath terrace is formed by incision into the hunter creek sandstone and deposition of fluvial gravel by the truckee river the gravel contains granitic boulders sourced from the glaciated headwaters of the truckee 20 km upstream from the terraces and display boulders ranging from 4 to 12 m in dimension in comparison to the

evidence from the rio bayo valley on the extent of the north patagonian icefield during the late pleistocene holocene transition abstract this paper presents data on the extent of the north patagonian icefield during the late pleistocene holocene transition using cosmogenic nuclide exposure age and optically stimulated luminescence dating we describe geomorphological and geochronological evidence for glacier extent in one of the major valleys surrounding the north patagonian icefield the rio bayo valley geomorphological mapping provides evidence for the existence of two types of former ice masses in this area i a large outlet glacier of the north patagonian icefield which occupied the main rio bayo valley and ii a number of small glaciers that developed in cirques on the slopes of the mountains surrounding the valley cosmogenic nuclide exposure age dating of two erratic boulders on the floor of the rio bayo valley indicate that the outlet glacier of the icefield withdrew from the rio bayo valley after 10 900 1000 yr the mean of two boulders dated to 11 400 900 yr and 10 500 800 yr single grain optically stimulated luminescence osl dating of an ice contact landform constructed against this glacier indicates that this ice mass remained in the valley until at least 9700 700 yr the agreement between the two independent dating techniques osl and cosmogenic nuclide exposure age dating increases our confidence in these age estimates a date obtained from a boulder on a cirque moraine above the main valley indicates that glaciers advanced in cirques surrounding the icefield some time around 12 500 900 yr this evidence for an expanded north patagonian icefield between 10 900 1000 yr and 9700 700 yr implies cold climatic conditions dominated at this time

role of in situ cosmogenic nuclides 10be and 26al in the study of diverse geomorphic processes the central premises of applications of the in situ cosmogenic dating method for studying specific problems in geomorphology are outlined for simple and complex exposure settings in the light of these general models we discuss the information that can be derived about geomorphic processes utilizing concentrations of in situ produced cosmogenic radionuclides 10be half life 1 5 ma and 26a1 half life 0 7 ma in a variety of geomorphic contexts glacial polish and tills meteorite impact craters alluvial fans paleo beach ridges marine terraces sand dunes and bedrock slopes we also compare 10be 26al data with results obtained by other dating methods we conclude that the technique of measuring in situ cosmic ray produced nuclides holds promise for quantitative studies of processes and time scales in a wide range of geomorphological problems

onset timing and slip history of the teton fault wyoming a multidisciplinary reevaluation the dramatic relief of the teton range in northwestern wyoming results from motion along the teton normal fault new apatite u th he ahe and fission track aft ages of samples collected in the footwall yield fundamental constraints on contrasting models of teton fault activity and consequent relative footwall uplift low elevation samples in the immediate footwall of the fault range from 12 5 to 6 5 ma ahe ages of samples from subvertical transects range from 57 8 to 6 5 ma rendezvous 54 0 to 6 8 ma grand and 20 5 to 7 1 ma moran with all three transects yielding an expected trend of decreasing age with decreasing elevation aft ages obtained from the three transects range from 55 4 to 45 7 ma rendezvous 43 2 to 13 3 ma grand and 38 0 to 11 7 ma moran inverse thermal history modeling indicates that the onset of relatively rapid cooling as a proxy for relative footwall uplift initiated first in the northern part of the range 15 13 ma and then migrated south as fault displacement continued 7 ma to present at rendezvous thus this work suggests that although the teton fault likely initiated due to basin and range extension this structure remains active normal fault displacement models also suggest a minimum of 6 km displacement for footwall uplift of 2 km if evaluated in the context of established normal fault length displacement relationships this yields a length of 180 km substantially longer than current estimates of teton fault length and putting the northern end of the fault well into and potentially beyond the bounds of yellowstone national park

cosmic ray produced 10be and 26al in antarctic rocks exposure and erosion history we have measured cosmic ray produced t1 2 1 5 million years 10be and t1 2 0 705 million years 26al in purified quartz fractions of selected rock samples from antarctic mountains from these data we calculate 1 mean erosion rates for the limiting case of steady state surface exposure to cosmic rays and 2 minimum exposure ages for the limiting case of no erosion calculated mean erosion rates are very low on the order of a few times 10 5 cm yr we believe the sampling to be sufficient to generalize this result to exposed bedrock in antarctica in favorable cases it is possible to distinguish between the limiting cases steady state erosion seems a better description in such cases most samples including some taken a few meters above the present ice level seem to have been exposed for millions of years without major episodes of burial or abrasion by ice

erosion history of the tibetan plateau since the last interglacial constraints from the first studies of cosmogenic 10be from tibetan bedrock abstract the cosmogenic 10be exposure histories of in situ bedrock surfaces from the tibetan plateau indicate low erosion rates of

numerical and analytical models of cosmogenic radionuclide dynamics in landslide dominated drainage basins 1 in many tectonically active regions on earth landslides dominate sediment delivery to channels while cosmogenic radionuclides crn represent a valuable tool to document basin averaged erosion rates a better understanding of crn dynamics in these systems is required before erosion rates can be reliably inferred from crn concentrations the stochastic nature of landslides results in variability of crn concentrations in both alluvial and hillslope samples that is both difficult to document and poorly understood to guide sampling strategies we developed a 2 d plan view model to simulate the influence of landslides on crn dynamics we employ a sediment mixing model in which concentrations of crns from material eroded by both landslides and steady processes are combined to evaluate how best to infer erosion rates from crn concentrations this model is further used to test a new analytical solution for the distribution of crn concentrations on hillslopes in a landslide prone system results suggest that for landscapes dominated by deep 5 m landslides only large drainage basins 100 km2 provide consistently reliable estimates of erosion rates from crn concentrations for landscapes dominated by shallow landslides 0 7 2 m smaller basins can produce reliable estimates results further suggest that the distribution of concentrations from hillslope samples could be used to deduce the relative contribution of material derived from landslide and steady processes these findings underscore the need to consider carefully the sources of natural variability in sampling and analyzing crns if properly done the variability can reveal useful information about geomorphic processes in landslide prone areas

the evolution of the sciara del fuoco subaerial slope during the 2007 stromboli eruption relation between deformation processes and effusive activity abstract focusing on the island of stromboli this research investigates whether airborne remote sensing systems such as those based on digital photogrammetry and laser scanner sensors can be adopted to monitor slope deformation and lava emplacement processes in active volcanic areas thanks to the capability of extracting accurate topographic data and working on flexible time schedules these methods can be used to constrain the regular and more frequent measurements derived from satellite observations this work is dedicated to the monitoring of stromboli s volcanic edifice which is beneficial when obtaining quantitative data on the geometry of deformation features and the displaced failures and landslides and emplaced lava flows volumes in particular we focus on the capability of extracting average effusion rates from volume measurements that can be used to validate or integrate satellite derived estimates since 2001 a number of airborne remote sensing surveys namely digital photogrammetry dp and airborne laser scanning als have been carried out on stromboli s volcano to obtain high resolution digital elevation models dem and orthophotos with sub meter spatial resolution and a time schedule suitable for monitoring the morphological evolution of the surface during the quiescent phases during the last two effusive eruptions 2002 2003 and 2007 the surface modifications created on the sciara del fuoco slope and on the crater area as a consequence of effusive activity were quantified and monitored using the same methodologies this work which is based on the results obtained from the multi temporal quantitative analysis of the data collected from 2001 to 2007 mainly focuses on the 2007 eruption but also accounts for analogies and differences regarding the 2002 2003 event the 2007 eruption on the sciara del fuoco slope from 27 february until 2 april produced a compound lava field including a lava delta on the shoreline discharging most of the lava into the sea the comparison of the 2007 dems with a pre eruption surface 2006 lidar survey allowed for the evaluation of the total lava volume that accumulated on the subaerial slope while two syn eruption dems were used to calculate the average effusion rates during the eruption since the evolution of a lava field produced during an eruption can be seen as a proxy for the magma intrusion mechanism hypotheses are formulated on the connection between the lava discharge and the instabilities suffered by the slope

effective attenuation lengths of cosmic rays producing 10be and 26al in quartz implications for exposure age dating we have measured cosmic ray produced 10be t 1 5 my and 26al t 0 72 my as functions of depth in a core of quartz sandstone bedrock collected in south victoria land antarctica these data were used to place limits on the exposure age and erosion rate of the exposed surface and to calculate the effective attenuation lengths of cosmic rays producing these nuclides these latter results indicate that the production attenuation length for 26al is comparable to that for 10be this suggests that the production ratio 26al 10be does not vary substantially with depth in a rock and that its value at the surface of exposed rock is not strongly affected by erosional losses allowing wider use of the ratio in determining exposure ages

timing and extent of late quaternary glaciation in the western himalaya constrained by 10be moraine dating in garhwal india glacial chronologies from the himalayan region indicate various degrees of asynchronous glacial behavior part of this has been related to different sensitivities of glaciers situated in contrasting climatic compartments of the orogen but so far field data in support for this hypothesis is lacking here we present a new 10 be derived glacial chronology for the upper tons valley in western garhwal india and initial results for the pin and thangi valleys in eastern himachal pradesh these areas cover a steep gradient in orographic precipitation and allow testing for different climatic sensitivities our data provide a record of five glacial episodes at w16 ka w11 12 ka w8 9 ka w5 ka and 1 ka in the thangi valley our results indicate a glacial episode at w19 ka but no data are available for younger glacial deposits in this valley at their largest mapped extent w16 ka the two main glaciers in the upper tons valley joined and descended down to w2500 m asl which represents a drop of w1400 m compared to the present day glacial extent during the holocene the two largest glaciers produced distinct glacial landforms that allowed us to reconstruct changes in the equilibrium line altitude ela over w20 km north south distance that is presently associated with a steep gradient in rainfall we observe that ela changes have been consistently w2 times higher for the glacier located in a presently wetter climate pointing at different climate sensitivities related to the amount of precipitation that they receive at regional scale our data is in reasonable agreement with other published glacial chronologies from the western himalaya and suggest that glacial advances during the holocene have been largely synchronous in this region comparison of glacial chronologies from the western himalaya with other palaeoclimatic proxy data suggests that long term changes in glacial extents are controlled by glacial interglacial temperature oscillations related to the waxing and waning of the large northern hemisphere ice sheets while the timing of millennial scale advance and retreat cycles are more directly related to monsoon strength

quaternary erosion and cosmic ray exposure history derived from 10be and 26al produced in situ an example from pajarito plateau valles caldera region 10 be and 26 al concentrations measured by accelerator mass spectrometry in 20 samples of quartz separated from rhyolitic volcanic ash flow tuffs collected on the pajarito plateau of the valles caldera new mexico were used to model time integrated erosion rates and cosmic ray exposure histories the model erosion rates determined for different stratigraphic units within the tshirege member upper bandelier tuff vary from 0 1 cm ka for the resistant unit to 1 1 cm ka for the softer unit intermediate erosion rates are thought to indicate earlier age cover by post tuff lithologies of different hardness the geographic distribution of these intermediate rates allows an approximate determination of the extent of material now gone stratigraphic ghosts periods of burial can be determined from 26 al 10 be ratios for the pajarito plateau burial most likely resulted from cover by soil and sediment held in place by vegetation our data allow us to model the duration and extent of thick forest cover which today exists only at higher altitudes

cosmogenic nuclide chronology of pre last glacial maximum moraines at lago buenos aires 46 s argentina at lago buenos aires argentina 10 be 26 al and 40 ar 39 ar ages range from 190 000 to 109 000 yr for two moraines deposited prior to the last glaciation 23 000 16 000 yr ago two approaches maximum boulder ages assuming no erosion and the average age of all boulders and an erosion rate of 1 4 mm 10 3 yr both yield a common estimate age of 150 000 140 000 yr for the two moraines the erosion rate estimate derives from 10 be and 26 al concentrations in old erratics deposited on moraines that are n760 000 yr old on the basis of interbedded 40 ar 39 ar dated lavas the new cosmogenic ages indicate that a major glaciation during marine oxygen isotope stage 6 occurred in the mid latitude andes the next five youngest moraines correspond to stage 2 there is no preserved record of a glacial advance during stage 4 the distribution of dated boulders and their ages suggest that at least one major glaciation occurred between 760 000 and n200 000 yr ago the mid latitude patagonian glacial record which is well preserved because of low erosion rates indicates that during the last two glacial cycles major glaciations in the southern andes have been in phase with growth and decay of northern hemisphere ice sheets especially at the 100 000 yr periodicity thus glacial maxima are global in nature and are ultimately paced by small changes in northern hemisphere insolation d 2005 university of washington all rights reserved

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

chronology of late cenozoic volcanic eruptions onto relict surfaces in the south central sierra nevada california early twentieth century geologists ob served extensive areas of subdued topography in the otherwise strongly dissected landscape of the southern sierra nevada that they ascribed to periods of stability following episodes of orogenic uplift from this evidence they developed an uplift history for the sierra nevada this conceptual model for landscape evolution of the sierra has largely been rejected or ignored since the middle of the twentieth century based in considerable part on observations indicating that these surfaces can be explained as dynamic landforms actively developing in response to conditions of the relatively recent geological past and that long term erosion rates are much too high to permit pre quaternary surfaces to be preserved we investigated the chronology of basaltic flows and ejecta on several such apparent relict surfaces located west of bishop california most of the basalt cones and flows that were sampled are nearly concordant with the present topography generally showing no more than 50 m of landscape inversion the 40 ar 39 ar ages of the basalts fall into two groups 11 76 0 05 ma and 3 40 0 06 ma these ages demonstrate that paleosurfaces dating back to at least the miocene can be preserved close to the summits of the sierra nevada with minimal erosion the elevations and relative sequences of these surfaces do indeed appear to preserve a topographic history of the sierra nevada encouraging continued investigation of their significance within the tectonic history of the sierra nevada

surface ages and rates of erosion at the calico archaeological site in the mojave desert southern california abstract erosion rates and surface exposure ages were determined at the calico archaeological site in the calico hills of the mojave desert california using 10be terrestrial cosmogenic nuclides tcn methods the calico hills are composed of miocene lacustrine deposits of the barstow formation and fanglomerates debris flows of the pleistocene yermo deposits these deposits are highly denuded and dissected by arroyos that have surfaces armored with chert surface erosion rates based on cosmogenic 10be concentrations in stream sediments range from 19 to 39 m ma with an average of 30 5 6 2 m ma surface boulders have 10be tcn ages that range from 27 ka to 198 ka reflecting significant erosion of the calico hills the oldest boulder age 197 20 ka places a minimum limit on the age of yermo deposits depth profile ages at four locations within the study area have minimum ages that range from 31 to 84 ka and erosion rate corrected surface exposure ages ranging from 43 to 139 ka these surface exposure ages support the view that the surfaces in yermo deposits formed during the late pleistocene to latest middle pleistocene this chronology has important implications for interpreting the context of possible artifacts geofacts at the site that might provide evidence for early human occupation of north america and for reconstructing paleoenvironment change and landscape evolution in the region

landscape disequilibrium on 1000 10 000 year scales marsyandi river nepal central himalaya in an actively deforming orogen maintenance of a topographic steady state requires that hillslope erosion river incision and rock uplift rates are balanced over timescales of 10 5 10 7 years over shorter times 10 5 years hillslope erosion and bedrock river incision rates fluctuate with changes in climate on 10 4 year timescales the marsyandi river in the central nepal himalaya has oscillated between bedrock incision and valley alluviation in response to changes in monsoon intensity and sediment flux stratigraphy and 14 c ages of fill terrace deposits reveal a major alluviation coincident with a monsoonal maximum ca 50 35 ky bp cosmogenic 10 be and 26 al exposure ages define an alluviation and reincision event ca 9 6 ky bp also at a time of strong south asian monsoons the terrace deposits that line the lesser himalayan channel are largely composed of debris flows which originate in the greater himalayan rocks up to 40 km away the terrace sequences contain many cubic kilometers of sediment but probably represent only 2 8 of the sediments which flushed through the marsyandi during the accumulation period at f10 4 year timescales maximum bedrock incision rates are f7 mm year in the greater himalaya and f1 5 mm year in the lesser himalayan mahabarat range we propose a model in which river channel erosion is temporally out of phase with hillslope erosion increased monsoonal precipitation causes an increase in hillslope derived sediment that overwhelms the transport capacity of the river the resulting aggradation protects the bedrock channel from erosion allowing the river gradient to steepen as rock uplift continues when the alluvium is later removed and the bedrock channel re exposed bedrock incision rates probably accelerate beyond the long term mean as the river gradient adjusts downward toward a more equilibrium profile efforts to document dynamic equilibrium in active orogens require quantification of rates over time intervals significantly exceeding the scale of these millennial fluctuations in rate d 2003 elsevier b v all rights reserved

a theoretical model of the fracture of rock during freezing we present a mathematical model for the breakdown of porous rock by the growth of ice within cracks the model is founded upon well established principles of fracture mechanics and recent advances in soil physics ijong with the assumption that progressive crack growth results from water migrating to ice bodies in cracks much as water migrates to ice lenses in freezing soil our model predicts crack growth rates compatible with empirical data calculations for a granite and a marble indicate that sustained freezing is most effective in producing crack growth when temperatures range from 4 c to 15 c at higher temperatures thermodynamic limitations prevent ice pressure from building up sufficiently to produce significant crack growth at lower temperatures the migration of water necessary for sustaining crack growth is strongly inhibited in hydraulically open systems in which pore water pressure remains near atmospheric pressure during the freezing process crackgrowth rates during continuous cooling will generally be greatest at low rates of cooling less than 0 1 0 5 c h at higher rates of cooling the influx of water to growing cracks is significantly inhibited the model delineates clearly the role of material parameters elastic moduli fracture mechanical properties grain size and shape and crack size environmental conditions temperature temperature gradient water pressure and time in frost damage to rocks our calculations along with recent experimental work on water migration in freezing rocks fukuda 1983 lead us to question the widely accepted importance of two phenomena freezing of water in sealed cracks and freeze thaw cycling in the fracture of rock exposed to natural freezing conditions

using in situ produced cosmogenic isotopes to estimate rates of landscape evolution a review from the geomorphic perspective the application of in situ produced cosmogenic isotopes to problems in geomorphology has increased rapidly over the past decade at least 57 papers and numerous abstracts have been published since the mid 1980s when the first mass spectrometric measurements of terrestrially produced cosmogenic isotopes were made taken at face value these studies provide quantitative information about rates of landscape evolution and landform age however the significance of calculated erosion rates and exposure ages depends strongly on the models used to interpret isotopic data the validity of assumptions inherent to these models and the geologic surroundings in which the samples were collected this paper attempts to place cosmogenic isotope studies in a geomorphic context by reviewing fundamentals of the method and evaluating the validity of assumptions under which these data have been interpreted at present the establishment of high precision cosmogenically based glacial and alluvial chronologies is stymied by the evolution of geomorphic surfaces the erosion of rock from sampled boulders the potential for isotope inheritance from previous exposure and the uncertainty of isotopic measurements uncertainties in isotope production rates and the observed variability of exposure ages on individual geomorphic surfaces limit the confidence with which cosmogenic ages can be correlated reliably with those obtained by other techniques estimation of erosion rates at single points on the landscape gives useful small scale information extrapolation of these rates over longer time and larger spatial scales is less sure and most likely biased toward lower erosion rates by die inadvertent selection of resistant sample sites however because erosion rates are so poorly constrained at present even estimates to within a factor of 2 may be of significant value to geomorphologists and tectonicists

rock to sediment slope to sea with 10be rates of landscape change abstract measurements of cosmogenic nuclides predominately 10be allow new insights into the ways in which and the rates at which sediment is generated transported and deposited over timescales ranging from 103 to 106 years samples from rock exposures are used to estimate erosion rates at points on the landscape whereas samples of fluvial sediment provide estimates of basin scale rates of denudation integrated over 104 km2 nuclide data show that hilltop bare rock outcrops erode more slowly than basins as a whole suggesting the potential for relief to increase over time as well drained outcrops grow higher more elaborate experiments and interpretive models provide insight into the distribution of hillslope processes including the bedrock to soil conversion rate which appears to increase under shallow soil cover and then decrease under deeper soils changes in average nuclide activity down slopes can be used to estimate grain speed over millennia suggesting for example that sediment o

control of geomorphic processes on 10be concentrations in individual clasts complexity of the exposure history in gobi altay range mongolia the dating of alluvial landforms by cosmogenic nuclides requires distinguishing the pre deposition inheritance from the post deposition history of the clasts in the studied marker moreover estimating catchment scale erosion rates from the concentrations of cosmogenic nuclides in active alluvia requires a good knowledge of the local regional relationships between rock exhumation and transport through space and time this is still poorly known for timescales of tens of thousand years in order to document the evolution of clast exhumation and transport rates through time we analyze in situ 10be concentrations in boulders and cobbles from hillslopes to outlet of an arid mountainous catchment located in gobi altay mongolia strongly affected by global climatic changes during the pleistocene holocene period samples were collected on bedrock abandoned alluvial deposits active colluvia and alluvia our results show a large 10be scattering in the active river bed consistent with a low and discontinuous catchment erosion rate dominated by mass wasting and fluvial incision on the contrary pre exposure signal within abandoned terraces is much more homogeneous consistent with climatic pulses responsible of strong erosional events on hillslopes and rapid fluvial transport these results show that exhumation transport processes at the catchment scale vary in style and intensity through time as a consequence of climatic oscillations the occurrence of abrupt climatic changes during short periods of time recorded by 10be concentrations in abandoned alluvia raise questions about the temporal applicability of catchment erosion rates derived from cosmogenic nuclide concentrations measured in sediments of active rivers on the other hand strong and short erosion events limit and homogenize the pre exposure 10be signal in associated deposits like debris flows making them particularly suitable markers for dating in active tectonic and paleoclimatic studies

beryllium 10 terrestrial cosmogenic nuclide surface exposure dating of quaternary landforms in death valley quaternary alluvial fans and shorelines spits and beach bars were dated using 10 be terrestrial cosmogenic nuclide tcn surface exposure dating in death valley the 10 be tcn ages show considerable variance on individual surfaces samples collected in the active channels date from 6 ka to 93 ka showing that there is significant inheritance of 10 be tcn within cobbles and boulders that were dated which suggests that slopes erode and sediment is transferred very slowly in most regions within death valley comparisons of 10 be tcn ages on alluvial fan surfaces with chronostratigraphies based on soil development and optically stimulated luminescence dating show that minimum 10 be tcn ages within sample sets on individual surfaces most closely approximate to the age of landforms that are younger than 70 ka alluvial fan surfaces older than 70 ka have begun to undergo significant erosion so that the majority of 10 be tcn ages for data sets on individual surfaces underestimate the true age of the surface due to erosion and exhumation of fresh cobbles and boulders the spread of 10 be tcn ages for beach bars near beatty junction and shorelines 8 km south of furnace creek is large ranging from 119 ka to 385 ka and 109 ka to 465 ka respectively however new and previously published luminescence ages soil development and geomorphic context suggest that these landforms formed during high lake level stands in marine isotope stage 2 22 18 ka but these younger ages my reflect soil development and material elluviated into the bar deposit long after deposition this suggests that the cobbles and boulders dated with 10 be methods have inherited 10 be tcns which have been derived from older shorelines or associated landforms these results highlight the problems associated with using surface cobbles and boulders to date quaternary surfaces in death valley and other similar dryland settings moreover this study emphasizes the need to combine multiple different dating methods to accurately date landforms in death valley and similar settings

do fluid inclusions preserve δ18o values of hydrothermal fluids in epithermal systems over geological time evidence from paleo and modern geothermal systems milos island aegean sea stable isotope compositions of quartz d 18 oquartz and fluid inclusion waters d 18 ofi and ddfi were analysed from profitis ilias a low sulphidation epithermal gold mineralisation deposit on milos island greece to establish if d 18 ofi preserve a record of paleogeothermal processes previous studies show that mineralisation at profitis ilias resulted from extreme boiling and vaporisation with a zone located at approximately 430 m above sea level asl representing the transition between liquid and vapor dominated systems miner depos 36 2001 32 the deposit is also closely associated with an active geothermal system whose waters have a well characterised stable isotope geochemistry pflumio c boulegue j liakopoulos a briqueu l 1991 source transport and deposition of metals balkema rotterdam the samples were collected over an elevation interval of 440 m 210 650 m asl to give information on the liquid and vapor dominated sections of the paleosystem the data show systematic variations with sample elevation samples from the highest elevations ca 650 m asl have the lightest d 18 ofi 7 3x and ddfi 68 0x whilst the deepest ca 210 m asl are isotopically heavier d 18 ofi 0 3x ddfi 19 0x relative changes in d 18 ofi closely parallel those in ddfi d 18 oquartz shows an opposite trend from the lightest values 13 9x at the lowest elevations to the heaviest 15 1x at the highest elevations d 18 ofi shows correlations with other parameters for example variable fluid inclusion homogenisation temperatures in the vapor dominated part of the system correlate with a rapid shift in ddfi 33 3xto 50 5x and d 18 ofi 4 1xto 6 2x gold contents also increase in the same zone up to 50 ppm au comparable correlations in d 18 oquartz or d 18 ocalculated estimated geothermal fluid from fluid inclusion homogenisation data are absent d 18 ocalculated are always 5 10xheavier than d 18 ofi comparison with the present day geothermal field shows that ddfi and d 18 ofi are similar isotope data for the modern system and fluid inclusion waters fall on linear trends subparalleling the meteoric water line and project towards seawater values numerical modelling favours kinetically controlled fractionation to explain differences in d 18 ocalculated and d 18 ofluid rather than diffusive posttrapping reequilibration the evidence suggests that in low temperature epithermal systems d 18 ofi may represent

range fires a significant factor in exposure age determination and geomorphic surface evolution physical weathering of rock spalling removal of adhered rock varnish and diffusive loss of noble gases are accelerated by heating in range fires a dramatic and widespread geomorphic process that must be considered when samples are collected for determining surface exposure ages or for measuring in situ production rates of cosmogenic isotopes exposure ages and production rates will be minima if the effects of spalling and or the effects of accelerated diffusive loss of gaseous isotopes such as he and ne are not considered to minimize the effect of fire induced diffusive loss samples for noble gas analysis should be collected 5 10 cm below the rock surface or form outcrops that are unlikely to have been heated by fire in addition by determining the concentration of in situ produced cosmogenic isotopes of different half lives the magnitude of spalling loss site specific erosion rate can be constrained for each sample

late quaternary slip rates along the sierra nevada frontal fault zone california slip partitioning across the western margin of the eastern california shear zone basin and range province new geologic mapping tectonic geomorphologic and cosmogenic radionuclide geochronologic data provide the fi rst numerical constraints on late quaternary vertical slip and horizontal extension rates across the southern sierra nevada frontal fault zone california this fault zone exposes numerous nnw striking east facing normal fault scarps that offset seven distinct quaternary alluvial surfaces and a rockslide deposit beryllium 10 cosmogenic radionuclide surface exposure dating of these surfaces provides surface abandonment model ages of 123 7 16 6 ka 60 9 6 6 ka 25 8 7 5 ka 4 4 1 1 ka and 4 1 1 0 ka on alluvial fan surfaces and 18 7 3 9 ka on the rockslide deposit these age constraints combined with measurements of vertical surface offset across fault scarps yield preferred late pleistocene to holocene vertical and horizontal extensional slip rates of 0 2 0 3 mm yr and 0 1 0 2 mm yr vertical slip rate estimates in this study are comparable to late pleistocene vertical slip rate estimates across other prominent range front normal faults within the basin and range province these geologic and geochronologic results indicate that the eastern escarpment of the southern sierra nevada has remained tectonically active throughout the late quaternary combining our data with slip data from the owens valley and lone pine faults implies that slip along the eastern escarpment of the sierra nevada block is partitioned into three components dominantly dextral slip along the owens valley fault intermediate oblique slip along the lone pine fault and subordinate normal slip along the sierra nevada frontal fault zone these observations are consistent with global positioning system gps data which indicate that dextral shear strain accumulation dominates today along the western boundary of the eastern california shear zone and basin and range province

geomorphic and cosmogenic nuclide constraints on escarpment evolution in an intraplate setting darling escarpment western australia the 900 km long darling scarp in western australia is one of the most prominent linear topographic features on earth despite the presence of over steepened reaches in all westerly flowing streams crossing the scarp and significant seismic activity within 100 km of the scarp there is no historical seismicity and no reported evidence for quaternary tectonic displacements on the underlying darling fault consequently it is unclear whether the scarp is a rapidly evolving landform responding to recent tectonic and or climatic forcing or a more slowly evolving landform in order to quantify late quaternary rates of erosion and scarp relief processes we obtained measurements of the cosmic ray produced nuclide beryllium 10 10be from outcropping bedrock surfaces along the scarp summit and face in valley floors and at stream knickpoints erosion rates of bedrock outcrops along the scarp summit surface range from 0 5 to 4 0 m myr 1 these are in the same range as erosion rates of 2 1 to 3 6 m myr 1 on the scarp face and similar to river incision rates of 2 6 to 11 0 m myr 1 from valley floor bedrock straths indicating that the darling scarp is a slowly eroding steady state landform without any significant contemporary relief production over the last several 100 kyr and possibly several million years knickpoint retreat rates determined from 10be concentrations at the bases of two knickpoints on small streams incised into the scarp are 36 and 46 m myr 1 if these erosion rates were sustained over longer timescales then associated knickpoints may have initiated in the mid tertiary to early neogene consistent with early mid tertiary marginal uplift ongoing maintenance of stream disequilibrium longitudinal profiles is consistent with slow regional base level lowering associated with recently proposed continental scale tilting as opposed to differential uplift along discrete faults cosmogenic 10be analysis provides a useful tool for interpreting the palaeoseismic history of intraplate near fault landforms over 105 to 106 years copyright 2010 john wiley sons ltd

rates of basin wide rockwall retreat in the k2 region of the central karakoram defined by terrestrial cosmogenic nuclide 10be abstract basin wide rockwall retreat rates are estimated using cosmogenic 10 be concentrations in supraglacial debris from the baltoro glacier basin in k2 region of the central karakoram pakistan total cosmogenic 10 be concentrations of the supraglacial debris were measured using accelerator mass spectrometry to determine 10 be concentrations inherited from the rockwalls within the glaciated basin given that rockfall induced by periglacial weathering and snow and ice avalanches is the most important source of supraglacial debris production in the high mountain glaciated basin the erosion rate of the bare bedrock can be considered to be the rate of rockwall retreat the rate of the rockwall erosion converted from the calculated inheritance of 10 be concentrations using the maximum velocity of the active glacier places an upper limit ranging from 0 65 mm year to 2 48 mm year this rate of rockwall retreat is in the same order of magnitude reported in other high himalayan mountains the rate however is an order of magnitude higher than erosion rates inferred from sediment budget studies and half that of the fluvial incision rate and exhumation rate for the same region the difference between rates of basin wide rockwall retreat and fluvial incision rates over the late quaternary suggests that in this glaciated basin fluvial incision is likely enhanced by localized differential tectonism and or isostatic uplift

arrested development erosional equilibrium in the southern sierra nevada california maintained by feedbacks between channel incision and hillslope sediment production tributary creeks of the southern sierra nevada have pronounced knickpoints that separate the landscape into an alternating sequence of gently sloped treads and steeply sloped risers these knickpoints and the surrounding stepped topography suggest that the landscape is still responding to pleistocene changes in base level on main stem rivers we tested this hypothesis using cosmogenic nuclides and uranium isotopes measured in stream sediment from widely distributed locations catchment scale erosion rates from the cosmogenic nuclides suggest that the treads are relict surfaces that have adjusted to a previous base level nevertheless erosion rates of relict interfluves are similar to canyon incision rates implying that relief is unchanging in the lower kings and san joaquin rivers in addition our results suggest that much of the southern sierra nevada is in a state of arrested development the landscape is not fully adjusted to and moreover is not responding to changes in base level lowering in the canyons we propose that this can be explained by a paucity of coarse sediment supply which fails to provide sufficient tools for bedrock channel incision at knickpoints we hypothesize that the lack of coarse sediment in channels is driven by intense weathering of the local granitic bedrock which reduces the size of sediment supplied from hillslopes to the channels our analysis highlights a feedback in which sediment size reduction due to weathering on hillslopes and transport in channels is both a key response to and control of bedrock channel incision and landscape adjustment to base level change

rapid slip along the central altyn tagh fault morphochronologic evidence from cherchen he and sulamu tagh consistent with the d 18 o record from the guliya ice cap in the west kunlun the features of interest were all formed by glacial and fluvial processes subsequent to marine isotope stage 5e with the youngest features having formed during the early holocene optimum this near field morphochronological slip rate is averaged over many earthquake cycles and is hence little affected by interseismic strain it is kinematically consistent with other somewhat lower geomorphic slip rate measurements to the east the average rate and lower bounds obtained from alternate interpretational models 18 4 mm yr cannot be reconciled with the most rece geodetic measurements 7 mm yr suggesting that interseismic strain and interactions with adjacent faults may lead to disparate geologic and geodetic rate estimates this late pleistocene holocene morphochronologic rate would imply that at this longitude the altyn tagh fault on the north edge of tibet might absorb almost as much of india s convergence relative to siberia as the himalayan main frontal thrust does on the southern edge of the plateau index terms 1035 geochemistry geochronology 1208 geodesy and gravity crustal movements intraplate 8110 8102 tectonophysics continental contractional orogenic belts 8107 tectonophysics continental neotectonics keywords slip rates cosmogenic dating indo asian collision

measurement of tectonic surface uplift rate in a young collisional mountain belt measurement of the rate of tectonically driven surface uplift is crucial to a complete understanding of mountain building dynamics the lack of a suitable rock record typically prevents determination of this quantity but the unusual geology of papua new guinea s finisterre mountains makes measurement of this rate possible the tectonic surface uplift rate at the finisterre range is 0 8 2 1 mmyr 1 approximately that expected to arise from crustal thickening

denudation rates determined from the accumulation of in situ produced 10be in the luquillo experimental forest puerto rico we present a simple method for estimation of long term mean denudation rates using in situ produced cosmogenic 10be in fluvial sediments procedures are discussed to account for the effects of soil bioturbation mass wasting and attenuation of cosmic rays by biomass and by local topography our analyses of 10be in quartz from bedrock outcrops soils mass wasting sites and riverine sediment from the icacos river basin in the luquillo experimental forest puerto rico are used to characterize denudation for major landform elements in that basin the 10be concentration of a discharge weighted average of size classes of river sediment corresponds to a long term average denudation of 43 m ma 1 consistent with mass balance results

erosion rates on subalpine paleosurfaces in the western mediterranean by in situ 10be concentrations in granites implications for surface processes and long term landscape evolution in corsica france a study of erosion rates by in situ 10be concentrations in granites of miocene high elevation paleosurfaces in corsica indicates maximum erosion rates between 8 and 24 mm kyear the regional distribution of measured erosion rates indicates that the local climatic conditions namely precipitation the petrographic composition of granites and the degree of brittle deformation govern erosion rates chemical erosion dominates even at elevations around 2 000 m in presently subalpine climate conditions field evidence indicates that erosion operates by continuous dissolution and or disintegration to grains grusification the erosion rates are relatively high with respect to the preservation of inferred early miocene landscapes we infer temporal burial in the middle miocene and significantly lower erosion rates in the neogene until 3 ma to explain the preservation of paleosurfaces in line with fission track data valley incision rates that are a magnitude higher than erosion rates on summit surfaces result in relief enhancement and long term isostatic surface uplift on the other hand widening and deepening of valleys by cyclic glaciation progressively destroys the summit surface relics

long term slip rate of the southern san andreas fault from 10be 26al surface exposure dating of an offset alluvial fan we determine the long term slip rate of the southern san andreas fault in the southeastern indio hills using 10 be and 26 al isotopes to date an offset alluvial fan surface field mapping complemented with topographic data air photos and satellite images allows precise determination of piercing points across the fault zone that are used to measure an offset of 565 80 m a total of 26 quartz rich cobbles from three different fan surfaces were collected and dated the tight cluster of nuclide concentrations from 19 samples out of 20 from the offset fan surface implies a simple exposure history negligible prior exposure and erosion and yields an age of 35 5 2 5 ka the long term slip rate of the san andreas fault south of biskra palms is thus 15 9 3 4 mm yr this rate is about 10 mm yr slower than geological 0 14 ka and short term geodetic estimates for this part of the san andreas fault implying changes in slip rate or in faulting behavior this result puts new constraints on the slip rate of the san jacinto and on the eastern california shear zone for the last 35 kyr our study shows that more sites along the major faults of southern california need to be targeted to better constrain the slip rates over different timescales

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

erosion of a high altitude low relief area on the korean peninsula implications for its development processes and evolution the processes involved in the development of high altitude low relief areas hlas are still poorly understood although cosmogenic nuclides have provided insights into the evolution of hlas interpreted as paleo surfaces most studies focus on estimating how slowly they erode and thereby their relative stability to understand actual development processes of hlas we applied several techniques of cosmogenic nuclides in the daegwanryeong plateau a well known hla in the korean peninsula our denudation data from strath terraces riverine sediments soils and tors provide the following conclusions 1 bedrock incision rate in the plateau 127 m myr 1 is controlled by the incision rate of the western part of the korean peninsula and is similar to the catchment wide denudation rate of the plateau 93 m myr 1 2 the soil production function we observed shows weak depth dependency that may result from highly weathered bedrock coupled with frequent frost action driven by alpine climate 3 a discrepancy between the soil production and catchment wide denudation rates implies morphological disequilibrium in the plateau 4 the tors once regarded as fossil landforms of the tertiary do not reflect tertiary processes and 5 when compared with those of global paleo surfaces 20 m myr 1 our rapid denudation rates suggest that the plateau cannot have maintained its probable initial paleo landscape and thus is not a paleo surface our data contribute to understanding the surface processes of actively eroding upland landscapes as well as call into question conventional interpretations of supposed paleo surfaces around the world copyright 2015 john wiley sons ltd

stochastic processes of soil production and transport erosion rates topographic variation and cosmogenic nuclides in the oregon coast range landscapes in areas of active uplift and erosion can only remain soil mantled if the local production of soil equals or exceeds the local erosion rate the soil production rate varies with soil depth hence local variation in soil depth may provide clues about spatial variation in erosion rates if uplift and the consequent erosion rates are sufficiently uniform in space and time then there will be tendency toward equilibrium landforms shaped by the erosional processes soil mantle thickness would adjust such that soil production matched the erosion previous work in the oregon coast range suggested that there may be a tendency locally toward equilibrium between hillslope erosion and sediment yield here results from a new methodology based on cosmogenic radionuclide accumulation in bedrock minerals at the base of the soil column are reported we quantify how soil production varies with soil thickness in the southern oregon coast range and explore further the issue of landscape equilibrium apparent soil production is determined to be an inverse exponential function of soil depth with a maximum inferred production rate of 268 m ma 1 occurring under zero soil depth this rate depends however on the degree of weathering of the underlying bedrock the stochastic and large scale nature of soil production by biogenic processes leads to large temporal and spatial variations in soil depth the spatial variation of soil depth neither supports nor rejects equilibrium morphology our observed catchment averaged erosion rate of 117 m ma 1 is however similar to that estimated for the region by others and to soil production rates under thin and intermediate soils typical for the steep ridges we suggest that portions of the oregon coast range may be eroding at roughly the same rate but that local competition between drainage networks and episodic erosional events leads to landforms that are out of equilibrium locally and have a spatially varying soil mantle copyright 2001 john wiley sons ltd

glacial and periglacial buzzsaws fitting mechanisms to metaphors the buzzsaw hypothesis refers to the potential for glacial and periglacial processes to rapidly denude mountains at and above glacier equilibrium line altitudes elas irrespective of uplift rates rock type or pre existing topography here the appropriateness of the buzzsaw metaphor is examined alongside questions of the links between glacial erosion and elas and whether the glacial system can produce low relief surfaces or limit summit heights plateau fragments in mountains on both active orogens and passive margins that have been cited as products of glacial and periglacial buzzsaw erosion instead generally represent dissected remnants of largely inherited pre glacial relief summit heights may correlate with elas but no causal link need be implied as summit erosion rates are low cirque headwalls may not directly abut summits and on passive margins cirques are cut into pre existing mountain topography any simple links between elas and glacial erosion break down on passive margins due to topographic forcing of ice sheet growth and to the km scale vertical swaths through which elas have shifted through the quaternary glaciers destroy rather than create low relief rock surfaces through the innate tendency for ice flow to be faster thicker and warmer along valleys the glacial buzzsaw cuts down

quantification of subaerial and episodic subglacial erosion rates on high latitude upland plateaus cumberland peninsula baffin island arctic canada abstract long term rates of subaerial and episodic subglacial erosion by predominately cold based ice cover are determined for tors on weathered plateaus on cumberland peninsula by measuring terrestrial cosmogenic nuclide concentrations in differentially weathered surfaces on a given tor we reconstruct the complex exposure and erosion history involving recurring cold based ice cover the style and rate of subaerial and subglacial erosion at multiple tor sites on cumberland peninsula are assessed with a monte carlo approach that computes plausible exposure histories based on a proxy record of global ice volume constant subaerial erosion rates by weathering are low

erosion rates of alpine bedrock summit surfaces deduced from in situ 10be and 26al we have measured the concentration of in situ produced cosmogenic 10be and 26al from bare bedrock surfaces on summit flats in four western u s mountain ranges the maximum mean bare bedrock erosion rate from these alpine environments is 7 6 3 9 m my 1 individual measurements vary between 2 and 19 m my 1 these erosion rates are similar to previous cosmogenic radionuclide crn erosion rates measured in other environments except for those from extremely arid regions this indicates that bare bedrock is not weathered into transportable material more rapidly in alpine environments than in other environments even though frost weathering should be intense in these areas our crn deduced point measurements of bedrock erosion are slower than typical basin averaged denudation rates 50 m my 1 if our measured crn erosion rates are accurate indicators of the rate at which summit flats are lowered by erosion then relief in the mountain ranges examined here is probably increasing we develop a model of outcrop erosion to investigate the magnitude of errors associated with applying the steady state erosion model to episodically eroding outcrops our simulations show that interpreting measurements with the steady state erosion model can yield erosion rates which are either greater or less than the actual long term mean erosion rate while errors resulting from episodic erosion are potentially greater than both measurement and production rate errors for single samples the mean value of many steady state erosion rate measurements provides a much better estimate of the long term erosion rate

explicit treatment of inheritance in dating depositional surfaces using in situ 10be and 26al we describe a new strategy for dating depositional landscape surfaces using in situ produced cosmogenic radionuclides crns that removes the complication of nuclide inheritance by clasts prior to depositon two amalgamated samples each consisting of 30 clasts one from the surface and one from a fixed depth in the subsurface constrain this crn inheritance and date the surface the inheritance may be used to estimate minimum exhumation rates and maximum transport times within the geomorphic system we test the technique using sup 10 be and sup 26 al to date the third fr3 of five terraces along the fremont river utah and the third wr3 of 15 along the wind river wyoming whereas effective ages based solely upon the surface samples yield 118 138 ka fr3 and 93 ka wr3 the subsurface samples reveal that inheritance accounts for 22 wr3 to 43 fr3 of the total crn concentration taking this into account yeilds terrace ages of nearly 61 81 ka for fr3 and nearly 67 76 ka for wr3 we explore the dependence of age estimates on the accumulation history of the terrace silt caps 22 refs 3 figs 1 tab

pleistocene relief production in laramide mountain ranges western united states gently sloped summits and ridges collectively referred to as summit flats are abundant in many laramide ranges in the western united states the erosion rate of summit flats is 10 m m y on the basis of the concentrations of cosmogenic radionuclides because erosion rates in valleys between summit flats are an order of magnitude faster relief within these ranges is currently increasing by about 100 m m y if summit flat erosion is slower than rock uplift driven by the isostatic response to valley erosion then this relief production could result in increased summit elevations the mean depth of material eroded from a smooth surface fit to existing summit flats varies from 280 to 340 m in four laramide ranges based on geographic information system gis analyses of digital elevation models this erosion would result in a maximum of 250 300 m of rock uplift assuming airy isostasy however because the laramide ranges examined here are narrow relative to the flexural wavelength of the lithosphere erosionally driven rock uplift is limited to 50 100 m over the past several million years summit erosion would approximately offset this rock uplift therefore we conclude that summit elevations have remained essentially constant even though several hundred meters of relief has been produced on the basis of valley and summit erosion rates and the average depth of erosion we estimate that relief production in laramide ranges began at ca 3 ma we hypothesize that this relief production was climatically driven and was associated with the onset or enhancement of alpine glaciation in these ranges

rates of surface processes on slopes slope retreat and denudation results taken from 270 publications on rates are summarized and collated with those from 149 publications reviewed previously young 1969 1974 the data are classified by major climatic zone normal or steep relief and consolidated or unconsolidated rocks representative rates and their ranges are given for soil creep solifluction surface wash solution chemical denudation rock weathering slope retreat cliff free face retreat marine cliff retreat and denudation the last being compared with representative rates of uplift solifluction is of the order of 10 times faster than soil creep but both cause only very slow ground loss solution is an important cause of ground loss for siliceous rocks on which it may be half as rapid as on limestones total denudation brought about mainly by surface wash reaches a maximum in the semi arid and probably also the tropical savanna zones acceleration of natural erosion rates by human activities ranges from 2 3 times with moderately intense land use to about 10 times with intensive land use and considerably higher still where there is recognized accelerated soil erosion where there is active uplift typical rates are of the order of 10 times faster than denudation although in some high steep mountain ranges these may approach equality

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

very slow erosion rates and landscape preservation across the southwestern slope of the ladakh range india erosion rates are key to quantifying the timescales over which different topographic and geomorphic domains develop in mountain landscapes geomorphic and terrestrial cosmogenic nuclide tcn methods were used to determine erosion rates of the arid tectonically quiescent ladakh range northern india five different geomorphic domains are identified and erosion rates are determined for three of the domains using tcn 10be concentrations along the range divide between 5600 and 5700 m above sea level asl bedrock tors in the periglacial domain are eroding at 5 0 0 5 to 13 1 1 2 meters per million years m m y principally by frost shattering at lower elevation in the unglaciated domain erosion rates for tributary catchments vary between 0 8 0 1 and 2 0 0 3 m m y bedrock along interfluvial ridge crests between 3900 and 5100 m asl that separate these tributary catchments yield erosion rates 850 ky respectively these results highlight the persistence of very slow erosion in different geomorphic domains across the southwestern slope of the ladakh range which on the scale of the orogen records spatial changes in the locus of deformation and the development of an orogenic rain shadow north of the greater himalaya copyright 2014 john wiley sons ltd

integrating soils and geomorphology in mountains an example from the front range of colorado soil distribution in high mountains reflects the impact of several soil forming factors soil geomorphologists use key pedological properties to estimate ages of quaternary deposits of various depositional environments estimate long term stability and instability of landscapes and make inferences on past climatic change once the influence of the soil forming factors is known soils can be used to help interpret some aspects of landscape evolution that otherwise might go undetected the front range of colorado rises from the plains of the colorado piedmont at about 1700 m past a widespread dissected tertiary erosion surface between 2300 and 2800 m up to an alpine continental divide at 3600 to over 4000 m pleistocene valley glaciers reached the western edge of the erosion surface parent rocks are broadly uniform granitic and gneissic climate varies from 46 cm mean annual precipitation map and 11 jc mean annual temperature mat in the plains to 102 cm and 4 jc respectively near the range crest vegetation follows climate with grassland in the plains forest in the mountains and tundra above 3450 m soils reflect the bioclimatic transect from plains to divide a bw or bt bk or k grassland to a e bw or bt c forest to a bw c tundra corresponding soil ph values decrease from 8 to less than 5 with increasing elevation the pedogenic clay minerals dominant in each major vegetation zone are smectite grassland vermiculite forest and 1 0 1 8 nm mixed layer clays tundra within the lower forested zone the topographic factor aspect results in more leached colder soils with relatively thin o horizons well expressed e horizons and bt horizons alfisols on n facing slopes whereas soils with thicker a horizons less developed or no e horizons and bw or bt horizons mollisols are more common on s facing slopes the topographic factor in the tundra results in soil patterns as a consequence of wind redistributed snow and the amount of time it lingers on the landscape an important parent material factor is airborne dust which results in fine grained surface horizons and if infiltrated contributes to clay accumulation in some bt horizons the time factor is evaluated by soil chronosequence studies of quaternary deposits in tundra upper forest and plains grassland few soils in the study area are 10 000 years old in the tundra 100 000 years old in the forest and 2 million years old in the grassland stages of granite weathering vary with distance from the continental divide and the best developed is grus near the sedimentary granitic rock contact just west of the mountain front grus takes a minimum of 100 000 years to form

timing of multiple late quaternary glaciations in the hunza valley karakoram mountains northern pakistan defined by cosmogenic radionuclide dating of moraines moraines and associated landforms in the upper hunza valley karakoram mountains northern pakistan provide an excellent record of multiple glaciations during the late quaternary glaciers advanced at least eight times by using 10 be and 26 al surface exposure dating on moraine boulders and scoured bedrock we determined the timing of glaciation for four of these glacial advances ca 54 7 43 2 ka borit jheel glacial stage ca 25 7 21 8 ka ghulkin i glacial stage ca 18 4 15 3 ka ghulkin ii glacial stage and ca 10 8 9 0 ka batura glacial stage for two of the older advances the yunz and shanoz glacial stages our data set a limit of 60 ka although at present the uncertainties in dating make it impossible to describe unequivocally the climate processes controlling glaciations in the hunza valley the results suggest that precipitation changes related to oscillations in the southwest asian monsoonal system combine with cooling that is broadly associated with heinrich events to cause glacial advances in this region

surface dating of dynamic landforms young boulders on aging moraines the dating of landforms is crucial to understanding the evolution history and stability of landscapes cosmogenic isotope analysis has recently been used to determine quantitative exposure ages for previously undatable landform surfaces a pioneering application of this technique to date moraines illustrated its considerable potential but suggested a chronology partially inconsistent with existing geological data consideration of the dynamic nature of landforms and of the ever present processes of erosion deposition and weathering leads to a resolution of this inconsistency and more generally offers guidance for realistic interpretation of exposure ages

middle pleistocene glaciation in patagonia dated by cosmogenic nuclide measurements on outwash gravels the well preserved glacial record in argentine patagonia offers a 1 ma archive of terrestrial climate extremes in southern south america these glacial deposits remain largely undated beyond the range of radiocarbon dating at ca 40 ka dating old glacial deposits several 105 a by cosmogenic surface exposure methods is problematic because of the uncertainty in moraine degradation and boulder erosion rates here we show that cobbles on outwash terraces can reliably date old glacial deposits in the lago pueyrredon valley 47 5 s argentina favorable environmental conditions e g aridity and strong winds have enabled continuous surface exposure of cobbles and preservation of outwash terraces the data demonstrate that nuclide inheritance is negligible and we therefore use the oldest surface cobbles to date the deposit 10be concentrations in outwash cobbles reveal a major glacial advance at ca 260 ka concurrent with marine isotope stage 8 mis 8 and dust peaks in antarctic ice cores a 10be concentration depth profile in the outwash terrace supports the age and suggests a low terrace erosion rate of ca 0 5 mm ka 1 we compare these data to exposure ages obtained from associated moraines and find that surface boulders underestimate the age of the glaciation by 100 ka thus the oldest boulders in this area do not date closely moraine deposition the 10be concentration in moraine cobbles help to constrain moraine degradation rates these data together with constraints from measured 26al 10be ratios suggest that all moraine boulders were likely exhumed after original deposition we determine the local last glacial maximum lgm occurred at 27 25 ka consistent with the maximum lgm in other parts of patagonia

geochemical methods to infer landscape response to quaternary climate change and land use in depositional archives a review abstract understanding and quantifying the processes and geochemical cycles associated with catchment erosion the development of soils and weathering horizons and terrestrial habitat change beyond the scales of modern observations remain challenging such research however has become increasingly important to help predict future landscape change in light of increasing land use and rapid global warming we herein review organic and inorganic geochemical tools applied to depositional archives to better understand various aspects of landscape evolution on geological time scales we highlight the potentials and limitations of inorganic geochemical analytical methods such as major element geochemistry metal and radiogenic isotopes and in situ cosmogenic nuclides as qualitative semi quantitative and quantitative proxies for the transformation of bedrock material via regolith and soils to sediments we also show how stable isotope geochemistry applied to lacustrine endogenic carbonates can be used to infer rock water interactions vegetation change and soil development in limestone rich catchments proxies focusing on the silicilastic element of sediment formation transport and deposition are ideally combined with organic geochemical proxies for vegetation change and soil organic matter evolution in a catchment to gain a comprehensive picture of the critical zone s evolution over time multi proxy and multidisciplinary research combining organic and inorganic geochemical techniques from several sedimentary archives in the same catchment have high potential to provide comprehensive information on quaternary landscape evolution and thus improve the robustness of associated forecasting models

mean bedrock to saprolite conversion and erosion rates during mountain growth and decline abstract weathering and associated atmospheric co2 consumption are thought to increase during the erosion of uplifting mountain ranges but the effect of enhanced erosion on weathering is still the subject of active debate we explore the possibility that erosion heterogeneity in uplifting landscapes significantly impacts the temporal relationships among mean uplift erosion and weathering using a 3d landscape evolution model applied to a synthetic surface with different uplift and climate scenarios although we do not strictly simulate the weathering outflux of the mountain we analyze the weathering response through the evolution of the mountain mean saprolite production rate and compare it to the mountain mean erosion rate through time the parametrical analysis shows that the temporal relationship between the mean erosion and saprolite production rates depends mainly on the ratio of the maximum saprolite production rate and the uplift rate wm u we explore two end members 1 when wm u 1 which corresponds to mountain ranges under a hot and humid climate the mean erosion and saprolite production rates vary at the same rate during the uplift and after once the uplift is stopped when the uplift is stopped the mean saprolite production increases and then decreases locally at different times this heterogeneity induces an overall decrease in the mean saprolite production rate 2 when wm u

the rate of bedrock weathering by frost action field measurements and a predictive model shattering rate surface temperature moisture content and the physical and strength properties of bedrock were measured in four rockwall sites of the japanese alps five year observations revealed that the bedrock shattering rate was usually much higher in the freeze thaw period from october to next may than in the frost free period from june to september this indicates that frost action is the most important shattering process although unusual heavy rainstorms in summer are also responsible for the shattering a combination of some empirical relationships derived from recent laboratory experiments leads to a predictive model of the frost shattering rate this model shows that the annual shattering rate is dependent on the annual freeze thaw frequency on the rock surface and the degree of saturation and tensile strength of the rock masses the coefficients involved in the model were determined using the field data

what factors control mechanical erosion rates mechanical erosion rates are important factors in understanding how continents evolve mechanical erosion is much faster than chemical erosion especially for highly elevated regions of the earth s surface it is a principal way in which mountain ranges are removed exposing deep metamorphic roots which comprise much of the older portions of the continental masses in addition there has to be a long term balance between erosion and mountain building a new data set allows us to explore in greater detail some of the many factors which control mechanical erosion rates the most important factors are some expression of the average slope of a drainage basin some measurement of the amount of water available for erosion some environmental measurements and also a measurement of basin length for which we have no good explanation the estimate of global mechanical erosion rate obtained here is considerably lower than those obtained by some other workers some of whom have concentrated on the fact that smaller river basins tend to get eroded faster than larger basins and it is mainly smaller basins which have not been measured and which are therefore not allowed for by simple arithmetic averaging of observed erosion rates it is shown here that although smaller basins are eroded faster this is mainly because they are steeper than larger basins we also show that extrapolation of current data to smaller basins does not work because the observed continental area which is draining to the ocean cannot be attained by the simplest extrapolation scheme

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