quaternary tectonic response to intensified glacial erosion in an orogenic wedge active orogens are thought to behave as internally deforming critical taper wedges that are in rough long term equilibrium with tectonic influx and erosional outflux spatial and temporal variations in climate are therefore hypothesized to have a significant influence on denudation topography and deformation of orogens thereby affecting wedge taper however the impact of the most severe transition in northern hemisphere climate during the cenozoic era the onset of glaciation has hitherto not been empirically documented here we analyse the spatial patterns of denudation and deformation and their temporal variations in the heavily glaciated st elias orogen in southern alaska low temperature thermochronometry thermokinematic modelling and offshore seismic reflection and borehole data suggest that the global scale intensification of glaciation in the middle pleistocene epoch enhanced glacier growth and caused ice streams to advance to the edge of the continental shelf this led to focused denudation across the subaerial reaches of the orogen and burial of the actively deforming wedge toe by the eroded sediment we propose that this climatically driven mass redistribution forced a structural reorganization of the orogen to maintain critical taper our empirical results thus support decades of numerical model predictions of orogenesis and provide compelling field evidence for the significant impact of climate change on tectonics intense glaciation during the middle pleistocene epoch led to focused denudation and mass redistribution within the st elias orogen in southern alaska and resulted in structural reorganization of the orogen the tectonic response of this orogen to climate change is consistent with predictions of numerical models

quantifying periglacial erosion in the nepal high himalaya abstract quantifying erosion rates in high mountain environments is challenging because the erosional processes are often stochastic and catastrophic distinguishing between periglacial and glacial rates is especially challenging in this study we focus on determining erosion rates from a glaciated alpine landscape where the bedrock sidewalls are eroding predominantly by blockfall we utilize a topographically well constrained debris covered glacier on the north slope of the annapurna range central nepal himalaya to quantify an average headwall retreat rate by measuring supraglacial debris depths from 0 1 to 2 4 m and average short term down valley transport rates of 17 m yr we calculate a yearly sediment flux of 5820 1990 m3 yr the supraglacial debris originates from the steep rocky headwall of the valley and we use the calculated flux with an estimated headwall contributing area to determine a slope perpendicular headwall retreat rate of 1 3 0 5 mm yr which corresponds to a vertical lowering rate of 0 42 0 16 mm yr and a horizontal retreat rate of 1 2 0 5 mm yr this rate is significantly greater than the steady state erosion rates that we determine for the valley ridge crests and sidewalls 0 08 0 03 mm yr and 0 20 0 05 mm yr respectively using concentrations of the in situ produced cosmogenic radionuclide 10be additionally 10be exposure ages of the lateral moraine crests and supraglacial debris suggest a glacial advance about 470 yr ago and a long term supraglacial transport rate of about 10 m yr using this long term transport rate reduces our inferred headwall retreat and suggests that the up glacial bedrock slopes are eroding at roughly the same rate while our results do not quantify the rate of glacial erosion the absence of a glacial gorge suggests that there may be a rough balance between glacial downcutting and the erosion of the valley sidewalls rates quantified here are almost an order of magnitude lower than fluvial incision rates of the upper marsyandi river that drains the study area suggesting that even glaciated catchments are not keeping pace with the rapidly down cutting rivers of the himalaya

topography relief and trmm derived rainfall variations along the himalaya 1 along the southern himalayan topographic front the indian summer monsoon modulates erosive processes and rates to investigate the influence of topography and relief on rainfall generation and resultant erosion we processed satellite rainfall amounts for the last 8 years 1998 2005 from the tropical rainfall measurement mission trmm based upon a spatial resolution of 5 5 km for the himalaya we identify 1 the spatial distribution of rainfall and 2 the large scale relationships between topography relief and rainfall locations our results show two distinct rainfall maxima along strike in the himalaya the first outer rainfall peak occurs along the southern margin of the lesser himalaya within a narrow band of mean elevation 0 9 0 4 km and mean relief 1 2 0 2 km the second discontinuous inner band typically occurs along the southern flank of the greater himalaya elevation and relief both 2 1 0 3 km

evaluation of precipitation data sets along the himalayan front precipitation is one of the main factors which controls surface processes and landscape morphology large orogenic belts such as the himalayas control precipitation distribution as a result of orographic effects due to their prominent relief however precipitation is difficult to monitor because mountain regions are largely inaccessible and therefore not sufficiently covered by ground based gauge stations the complexity of orographic effects resulting from the interaction between elevation and climatic processes and the lack of precise meteorological data thus limit our understanding of climatic influence on landscape formation therefore high quality precipitation observations with good spatiotemporal coverage are needed here we evaluate five gridded precipitation data sets derived from remote sensing and interpolation of rain gauge data with ground based precipitation measurements first we evaluate the bulk error of each data set then we evaluate the temporal quality of data within five watersheds and last we compare the spatial performance along seven swath profiles across strike to the himalayan range in nepal our evaluation shows that the data sets vary significantly along the orographic front and get more consistent toward the adjacent low relief domains while bulk errors are largest during monsoon season in particular where topographic gradients are important the resolution of gridded data sets cannot incorporate small scale spatial changes of precipitation we show that the data set derived from interpolation of gauge data performs best in the himalayas this study gives an overview on the applicability of precipitation data sets within the himalayan orographic domains where relief has a pronounced impact on precipitation

abnormal monsoon years and their control on erosion and sediment flux in the high arid northwest himalaya abstract the interplay between topography and indian summer monsoon circulation profoundly controls precipitation distribution sediment transport and river discharge along the southern himalayan mountain front shf the higher himalayas form a major orographic barrier that separates humid sectors to the south and arid regions to the north during the indian summer monsoon vortices transport moisture from the bay of bengal swirl along the shf to the northwest and cause heavy rainfall when colliding with the mountain front in the eastern and central parts of the himalaya precipitation measurements derived from passive microwave analysis ssm i show a strong gradient with high values at medium elevations and extensive penetration of moisture along major river valleys into the orogen the end of the monsoonal conveyer belt is near the sutlej valley in the nw himalaya where precipitation is lower and rainfall maxima move to lower elevations this region thus comprises a climatic transition zone that is very sensitive to changes in indian summer monsoon strength to constrain magnitude temporal and spatial distribution of precipitation we analyzed high resolution passive microwave data from the last decade and identified an abnormal monsoon year amy in 2002 during the 2002 amy violent rainstorms conquered orographic barriers and penetrated far into otherwise arid regions in the northwest himalaya at elevations in excess of 3 km asl while precipitation in these regions was significantly increased and triggered extensive erosional processes i e debris flows on sparsely vegetated steep hillslopes mean rainfall along the low to medium elevations was not significantly greater in magnitude this shift may thus play an important role in the overall sediment flux toward the himalayan foreland using extended precipitation and sediment flux records for the last century we show that these events have a decadal recurrence interval during the present day monsoon circulation hence episodically occurring amys control geomorphic processes primarily in the high elevation arid sectors of the orogen while annual recurring monsoonal rainfall distribution dominates erosion in the low to medium elevation parts along the shf

climate control on erosion distribution over the himalaya during the past 100 ka sediment samples from a 50 m long core representing 100 ka of deposition taken from the ganga plain on the campus of the indian institute of technology kanpur were analyzed for sr and nd isotope compositions both 87 sr 86 sr and nd vary significantly with depth in the core 0 72701 0 76708 and 14 4 to 16 6 respectively within the range for silicate rocks of the higher and the lesser himalaya the variations in the isotope compositions reflect variations in the mixing proportion of sediments from the higher and lesser himalaya the two major sediment sources to the ganga the opposite trends in 87 sr 86 sr and nd depth profiles further confirm this hypothesis the isotope profiles exhibit two major excursions ca 20 ka and ca 70 ka ago coinciding with periods of precipitation minima and larger glacial cover these excursions are the result of a decrease in the proportion of sediment from the higher himalaya due to a decrease in monsoon precipitation and an increase in glacial cover that are in turn caused by lower solar insolation this study highlights the significant influence of climate on erosion in the himalaya

wind erodibility of soils at fort irwin california mojave desert usa before and after trampling disturbance implications for land management recently disturbed and control i e less recently disturbed soils in the mojave desert were compared for their vulnerability to wind erosion using a wind tunnel before and after being experimentally trampled before trampling control sites had greater cyanobacterial biomass soil surface stability threshold friction velocities tfv i e the wind speed required to move soil particles and sediment yield than sites that had been more recently disturbed by military manoeuvres after trampling all sites showed a large drop in tfvs and a concomitant increase in sediment yield simple correlation analyses showed that the decline in tfvs and the rise in sediment yield were significantly related to cyanobacterial biomass as indicated by soil chlorophyll a however chlorophyll a amounts were very low compared to chlorophyll a amounts found at cooler desert sites where chlorophyll a is often the most important factor in determining tfv and sediment yield multiple regression analyses showed that other factors at fort irwin were more important than cyanobacterial biomass in determining the overall site susceptibility to wind erosion these factors included soil texture especially the fine medium and coarse sand fractions rock cover and the inherent stability of the soil as indicated by subsurface soil stability tests thus our results indicate that there is a threshold of biomass below which cyanobacterial crusts are not the dominant factor in soil vulnerability to wind erosion most undisturbed soil surfaces in the mojave desert region produce very little sediment but even moderate disturbance increases soil loss from these sites because current weathering rates and dust inputs are very low soil formation rates are low as well therefore soil loss in this region is likely to have long term effects published in 2006 by john wiley sons ltd

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

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

erratum to the control mechanisms of erosion and weathering at basin scale from cosmogenic nuclides in river sediment earth planet sci lett 237 2005 462 479

large scale erosion rates from in situ produced cosmogenic nuclides in european river sediments abstract we have calculated long term erosion rates of 20 100 mm kyr from quartz contained 10be in the bedload of middle european rivers for catchments ranging from 102 to 105 km2 these rates average over 10 40 kyr and agree broadly with rock uplift incision and exhumation rates historic soil erosion rates and erosion rates calculated from the measured sediment loads of the same rivers moreover our new erosion rate estimates correlate well with lithology and relief however in the regen neckar loire and meuse catchments cosmogenic nuclide derived erosion rates are consistently 1 5 4 times greater than the equivalent rates derived from measured river loads this may be due to the systematic under representation of high magnitude low frequency transport events in the gauging records which cover less than a century alternatively the discrepancy may derive from spatially non uniform erosion and preferential tapping of deeper sections of the irradiation profile a third explanation relates the high cosmogenic nuclide derived erosion rates to inheritance of an elevated pleistocene erosion signal uncertainties associated with the cosmogenic nuclide derived erosion rate estimates are not greater than the potential errors in conventional estimates therefore the cosmogenic nuclide approach is an effective tool for rapid catchment wide assessment of time integrated rates of bedrock weathering and erosion and we anticipate its fruitful application to the quaternary sedimentary record

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

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

assessing the relative efficiency of fluvial and glacial erosion through simulation of fluvial landscapes the relative rates of erosion by rivers and glaciers and the topographic effects of these two different styles of erosion remain outstanding problems in geomorphology we use a quantitative description of local fluvial landscapes to estimate how glaciated landscapes might look now had glaciers not developed this indicates the landscape modification attributable to glacial erosion we present examples from the sierra nevada california and the sangre de cristo range colorado in smaller drainage basins glacial modification is focussed above the mean quaternary equilibrium line altitude ela where both ridgelines and valley floors have been lowered as a consequence of glaciation at lower elevations small glaciers have apparently widened valleys without incising the valley floor beyond what a river would have this may reflect the short residence time of the glaciers at their full extent or differences in the subglacial drainage network between the glacier margins and the thalweg in larger drainage basins the pattern of glacial erosion is dramatically different here the glaciers have modified longitudinal profiles as well as valley cross sections far below the mean quaternary ela possible causes of this difference in the larger basins include the larger accumulation area greater shading of the valley floor longer residence times for ice at its full extent and the influence of the shallower valley slope prior to glaciation on the subsequent glacier and subglacial drainage conditions

predesign failure and displacement mechanisms of large rockslides in the annapurna himalayas nepal abstract the paper analyses and compares four major mass movements rockslides and rock avalanches with volumes of 1 to 5 km3 around the annapurna himalayan region from engineering geological quaternary geological and geomorphological viewpoints it shows how paleotectonic and neotectonic predesign as well as morphological overprint caused by glacial activities are the main preparatory causal factors for the sliding events that is why giant failures of mountain crests have mainly occurred in areas of tectonic activity the mechanism of failure and displacement of the resulting large mass movements also strongly depends on this litho tectonic predesign and continues in giant translational rockslides in which the primary rock structure or fabric is preserved but shattered by mechanical stress during the sliding event

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

the use of ablation dominated medial moraines as samplers for 10be derived erosion rates of glacier valley walls kichatna mountains ak we use cosmogenic 10be concentrations in amalgamated rock samples from active ice cored medial moraines to constrain glacial valley sidewall backwearing rates in the kichatna mountains alaska range alaska this dramatic landscape is carved into a small 65 ma granitic pluton about 100 km west of denali where kilometer tall rock walls and cathedral spires tower over a radial array of over a dozen valley glaciers these supraglacial landforms erode primarily by rockfall but erosion rates are difficult to determine we use cosmogenic 10be to measure rockwall backwearing rates on timescales of 103 104 years with a straightforward sampling strategy that exploits ablation dominated medial moraines a medial moraine and its associated englacial debris serve as a conveyor system bringing supraglacial rockfall debris from accumulation zone valley walls to the moraine crest in the ablation zone we discuss quantitatively several factors that complicate interpretation of cosmogenic concentrations in this material including the complex scaling of production rates in very steep terrain the stochastic nature of the rockfall erosion process the unmixed nature of the moraine sediment and additional cosmogenic accumulation during transport of the sediment we sampled medial moraines on each of three glaciers of different sizes and topographic aspects all three moraines are sourced in areas with identical rock and similar sidewall relief of 1 km each sample was amalgamated from 25 to 35 clasts collected over a 1 km longitudinal transect of each moraine two of the glaciers yield similar 10be concentrations 1 6 2 2 104 at g and minimum sidewall slope normal erosion rates 0 5 0 7 mm yr the lowest 10be concentrations 8 103 at g and the highest erosion rates 1 3 mm yr come from the largest glacier in the range with the lowest late summer snowline these rates are reasonable in an alpine glacial setting and are much faster than long term exhumation rates of the western alaska range as determined by thermochronometric studies copyright 2010 john wiley sons ltd

short term dynamics of wind erosion of three newly cultivated grassland soils in northern china this study examined the dynamic nature of short term wind erosion processes of three grassland soils under simulated cultivation in a laboratory wind tunnel soil loss on a sandy loam a loamy sand and a sand soil was measured in six successive 10 3 and 1 min exposures at the speeds of 10 18 and 26 m s 1 respectively erodible soil particle sizes of each interval were determined through direct dry sieving it was observed that increasing blowing duration generally led to rapid decrease of soil loss decrease of the erodible soil particle size from a definitely restricted area by any definite speed of wind and the non erodible particles remaining on the soil surface increased from the first to the last blowing interval soil loss decreased by 86 4 94 8 at 10 m s 1 in 60 min 90 0 95 4 at 18 m s 1 in 18 min and 71 5 97 8 at 26 m s 1 in 6 min the results indicate that wind erosion on the newly cultivated soils is most intense during the initial blowing the decrease of soil loss with time is presumed due to modification of soil surface by blowing wind i e the concentration of non erodible aggregates with the deflation of the erodible particles on the soil surfaces

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

glaciation as a destructive and constructive control on mountain building glacial erosion is thought to have an important role in controlling mountain height a common perception is that glaciers are powerful erosive agents inhibiting the ability of active mountains to rise significantly above the elevation of permanent glaciation through a process known as the glacial buzzsaw but now a study of erosion patterns and climate data from the late cenozoic in the glaciated patagonian andes suggests that glaciation can also have the reverse effect in effect making mountains higher at these polar latitudes glaciation acts as a protective layer preserving the uplifting mountains from erosion and allowing them to reach heights well above those predicted had a glacial buzzsaw been active it has been suggested that glacial erosion has an important role in controlling mountain height here spatial and temporal patterns of erosion in the glaciated patagonian andes have been assessed with the help of a low temperature thermochronologic data set the results show that between 38 s and 49 s accelerated erosion at the onset of widespread glaciation limits mountain height but at higher latitudes glaciation protects the landscape from erosion and leads to growth in mountain height and width theoretical analysis predicts that enhanced erosion related to late cenozoic global cooling can act as a first order influence on the internal dynamics of mountain building leading to a reduction in orogen width and height1 2 3 the strongest response is predicted in orogens dominated by highly efficient alpine glacial erosion producing a characteristic pattern of enhanced erosion on the windward flank of the orogen and maximum elevation controlled by glacier equilibrium line altitude3 4 where long term glacier mass gain equals mass loss however acquiring definitive field evidence of an active tectonic response to global climate cooling has been elusive5 here we present an extensive new low temperature thermochronologic data set from the patagonian andes a high latitude active orogen with a well documented late cenozoic tectonic climatic and glacial history data from 38 s to 49 s record a marked acceleration in erosion 7 to 5 myr ago coeval with the onset of major patagonian glaciation6 and retreat of deformation from the easternmost thrust front7 the highest rates and magnitudes of erosion are restricted to the glacial equilibrium line altitude on the windward western flank of the orogen as predicted in models of glaciated critical taper orogens where erosion rate is a function of ice sliding velocity3 8 in contrast towards higher latitudes 49 s to 56 s a transition to older bedrock cooling ages signifies much reduced late cenozoic erosion despite dominantly glacial conditions here since the latest miocene6 the increased height of the orogenic divide at these latitudes well above the equilibrium line altitude leads us to conclude that the southernmost patagonian andes represent the first recognized example of regional glacial protection of an active orogen from erosion leading to constructive growth in orogen height and width

tensile test of natural microbiotic crust abstract the mechanical properties of microbiotic crust are important to stabilize sandy surfaces in arid and semi arid regions we developed a new experimental approach to perform the tensile test of natural microbiotic crust the modulus of elasticity ultimate stress and one dimensional stress strain relation was obtained the microbiotic crust we measured exhibits linear elastic behavior firstly and then breaks this mechanical character was applied to the study of the rupture of microbiotic crust under the impact of one saltating grain a very simple dimensionless variable was suggested to quantitatively assess surface stability

hillslope glacier coupling the interplay of topography and glacial dynamics in high asia 1 high asian glacial landscapes have large variations in topographic relief and the size and steepness of snow accumulation areas associated differences in glacial cover and dynamics allow a first order determination of the dominant processes shaping these landscapes here we provide a regional synthesis of the topography and flow characteristics of 287 glaciers across high asia using digital elevation analysis and remotely sensed glacier surface velocities glaciers situated in low relief areas on the tibetan plateau are mainly nourished by direct snowfall have little or no debris cover and have a relatively symmetrical distribution of velocities along their length in contrast avalanche fed glaciers with steep accumulation areas which occur at the deeply incised edges of the tibetan plateau are heavily covered with supraglacial debris and flow velocities are highest along short segments near their headwalls but greatly reduced along their debris mantled lower parts the downstream distribution of flow velocities suggests that the glacial erosion potential is progressively shifted upstream as accumulation areas get steeper and hillslope debris fluxes increase our data suggest that the coupling of hillslopes and glacial dynamics increases with topographic steepness and debris cover the melt lowering effect of thick debris cover allows the existence of glaciers even when they are located entirely below the snow line however slow velocities limit the erosion potential of such glaciers and their main landscape shaping contribution may simply be the evacuation of debris from the base of glacial headwalls which inhibits the formation of scree slopes and thereby allows ongoing headwall retreat by periglacial hillslope processes we propose a conceptual model in which glacially influenced plateau margins evolve from low relief to high relief landscapes with distinctive contributions of hillslope processes and glaciers to relief production and decay

small valley glaciers and the effectiveness of the glacial buzzsaw in the northern basin and range usa the glacial buzzsaw hypothesis suggests that efficient erosion limits topographic elevations in extensively glaciated orogens studies to date have largely focussed on regions where large glaciers tens of kilometres long have been active in light of recent studies emphasising the importance of lateral glacial erosion in lowering peaks and ridgelines we examine the effectiveness of small glaciers in limiting topography under both relatively slow and rapid rock uplift conditions four ranges in the northern basin and range idaho montana and wyoming usa were chosen for this analysis estimates of maximum pleistocene slip rates along normal faults bounding the beaverhead bitterroot mountains similar to 0 14 mm y 1 lemhi range similar to 0 3 mm y 1 and lost river range similar to 0 3 mm y 1 are an order of magnitude lower than those on the teton fault similar to 2 mm y 1 we compare the distribution of glacial erosion estimated from cirque floor elevations and last glacial maximum lgm equilibrium line altitude ela reconstructions and fault slip rate with three metrics of topography in each range the along strike maximum elevation swath profile hypsometry and slope elevation profiles in the slowly uplifting beaverhead bitterroot mountains and lemhi and lost river ranges trends in maximum elevation parallel elas independent of variations in fault slip rate maximum elevations are offset similar to 500 m from lgm elas in the lost river range lemhi range and northern beaverhead bitterroot mountains and by similar to 350 m in the southern beaverhead bitterroot mountains where glacial extents were less the offset between maximum topography and mean quaternary elas inferred from cirque floor elevations is similar to 350 m in the lost river and lemhi ranges and 200 250 m in the beaverhead bitterroot mountains additionally slope elevation profiles are flattened and hypsometry profiles show a peak in surface areas close to the ela in the lemhi range and beaverhead bitterroot mountains suggesting that small glaciers efficiently limit topography the situation in the lost river range is less clear as a glacial signature is not apparent in either slope elevation profiles or the hypsometry in the rapidly uplifting teton range the distribution of elas appears superficially to correspond to maximum topography hypsometry and slope elevations profiles with regression lines on maximum elevations offset by similar to 700 and similar to 350 m from the lgm and mean quaternary ela respectively however grand teton and mt moran represent high elevation teflon peaks that appear impervious to glacial erosion formed in the hard crystalline bedrock at the core of the range glacier size and drainage density rock uplift rate and bedrock lithology are all important considerations when assessing the ability of glaciers to limit mountain range topography in the northern basin and range it is only under exceptional circumstances in the teton range that small glaciers appear to be incapable of imposing a fully efficient glacial buzzsaw emphasising that high peaks represent an important caveat to the glacial buzzsaw hypothesis c 2008 elsevier b v all rights reserved

numerical modeling of glacial erosion and headwall processes in alpine valleys abstract how rock relief is developed by glacial erosion in alpine landscapes is a key question in understanding the controls on mountain range topography any generation of relief by glaciers at the highest elevations in mountain ranges can affect the distribution of precipitation in alpine landscapes creating feedbacks between glacier mass balance and glacial erosion relief production at high elevation mountain crests is addressed using a numerical model that incorporates glacier dynamics and subglacial erosion as well as relevant hillslope processes blowing snow from a valley bounding plateau and avalanching onto the accumulation zone of the glacier is included in the model furthermore temperature dependent frost cracking is used as a proxy for headwall backwearing the parameterization of subglacial erosion produces about 500 m of erosion over the 400 ka of each numerical simulation in steady and varying climate scenarios valley floors flatten as headwalls increase in height and retreat headward over time headwall slopes increase in simulations in which quarrying is explicitly incorporated rates of quarrying are high near the base of the headwall increasing headwall length and slope as a result of valley floor lowering high rates of subglacial erosion and production of headwall relief also result when elastic flexural uplift occurs in response to mass unloading small overdeepenings form at the base of the headwall in steady climate simulations when the glacier is small at the end of the model run while the final profiles are relatively insensitive to the erosion rule used quarrying is most effective near the head of the glacier whereas rates of abrasion reflect the instantaneous pattern of integrated ice discharge or ice flux in simulations in which cirques are formed the equilibrium line altitude is hundreds of meters above the cirque floor however the time averaged horizontal position of the equilibrium line corresponds well with the downvalley position of the cirques

glacial effects limiting mountain height the height of mountain ranges reflects the balance between tectonic rock uplift crustal strength and surface denudation tectonic deformation and surface denudation are interdependent however and feedback mechanisms in particular the potential link to climate are subjects of intense debate spatial variations in fluvial denudation rate caused by precipitation gradients are known to provide first order controls on mountain range width crustal deformation rates and rock uplift moreover limits to crustal strength are thought to constrain the maximum elevation of large continental plateaus such as those in tibet and the central andes there are indications that the general height of mountain ranges is also directly influenced by the extent of glaciation through an efficient denudation mechanism known as the glacial buzzsaw here we use a global analysis of topography and show that variations in maximum mountain height correlate closely with climate controlled gradients in snowline altitude for many high mountain ranges across orogenic ages and tectonic styles with the aid of a numerical model we further demonstrate how a combination of erosional destruction of topography above the snowline by glacier sliding and commensurate isostatic landscape uplift caused by erosional unloading can explain observations of maximum mountain height by driving elevations towards an altitude window just below the snowline the model thereby self consistently produces the hypsometric signature of the glacial buzzsaw and suggests that differences in the height of mountain ranges mainly reflect variations in local climate rather than tectonic forces

climate and tectonic controls on glaciated critical taper orogens abstract in this work we present the results of a new analytical model that examines the coupling between glacial erosion and orogen development surface processes are assumed to be glacially dominated and tectonic activity is controlled by critical wedge mechanics in these circumstances we find that orogen width is strongly dependent on both the rate of accretion and on the rate of precipitation the orogen size is linked to tectonic and climate changes via proportionality constants the orogen width scales with the rate of accretion to between the 2 3rd and 2nd powers and with the rate of precipitation to the 1 3rd and 5 4th powers the value of the proportionality constants varies with the taper angle and the relative rates of ice deformation and sliding in all cases the sensitivities are higher than those calculated for fluvially eroding critical wedge orogens analytical solutions are supported by the results of a numerical flow line model the flow line model further predicts that uplift rates will be highest at and just below the equilibrium line altitude if glacial ablation is largely a calving process rock uplift in the wedge will be strongly focused towards the toe the predicted response time of glaciated orogens to changes in climate and tectonic forcing is dependent upon the constants of erosion the rheology and the rate of precipitation these analyses predict that actual orogens have variable e folding response times for example approximately 1 5 myr for the southern alps of new zealand and the olympic mountains of washington state and approximately 5 5 myr for the european alps

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

southward extrusion of tibetan crust and its effect on himalayan tectonics the tibetan plateau is a storehouse of excess gravitational potential energy accumulated through crustal thickening during india asia collision and the contrast in potential energy between the plateau and its surroundings strongly influences the modern tectonics of south asia the distribution of potential energy anomalies across the region derived from geopotential models indicates that the himalayan front is the optimal location for focused dissipation of excess energy stored in the plateau the modern pattern of deformation and erosion in the himalaya provides an efficient mechanism for such dissipation and a review of the neogene geological evolution of southern tibet and the himalaya shows that this mechanism has been operational for at least the past 20 million years this persistence of deformational and erosional style suggests to us that orogens like other complex systems can evolve toward steady state configurations maintained by the continuous flow of energy the capacity of erogenic systems to self organize into temporally persistent structural and erosional patterns suggests that the tectonic history of a mountain range may depend on local energetics as much as it does on far field plate interactions

a comparative study of detrital mineral and bedrock age elevation methods for estimating erosion rates traditional age elevation method using detrital and bedrock 40 ar 39 ar muscovite data sets from a single river catchment in the annapurna range nepal himalaya a nominal erosion rate estimate of 0 6 km myr for the 5 0 2 5 ma period was calculated from the bedrock data presented here for the first time this result agrees with the 0 7 km myr maximum estimate from the detrital data set which was derived from the dmt variant that emphasizes the range of single grain ages for a detrital sample in this case 11 2 5 ma however the other dmt variant which emphasizes the mean of the sample age distribution yields an erosion rate estimate of 2 3 km myr the simplest explanation for this discrepancy is that erosion rate increased significantly after 2 5 ma a scenario that is supported by apatite fission track data from the catchment

the effects of plantation development on biological soil crust and topsoil properties in a desert in northern china abstract afforestation was one of most successful measures to rehabilitate desertified lands and to improve regional eco environments in the horqin sand land a field experiment was conducted during 2005 and 2006 in the horqin sand land to investigate the effects of populus simonii plantation growth on soil crust formation and topsoil properties the results showed that plantation establishment promoted the development of biological soil crust and improved properties of topsoil 0 5 cm under the crust in sand dunes as the plantation aged soil crust developed gradually from a physical crust to a lichen crust and then to a moss crust and crust coverage thickness hardness very fine sand content clay silt organic carbon and nutrients increased significantly clay silt organic carbon and nutrients in topsoil 0 2 5 cm and 2 5 5 0 cm under the soil crust increased with plantation age and crust development but the magnitude of changes decreased with increasing soil depth changes in soil physical and chemical properties in the crust had a significant positive correlation with plantation age and changes in physical and chemical properties in the 0 5 0 cm layer of topsoil had a significant positive correlation with soil crust development and plantation age soil crust development and changes in topsoil properties under the soil crust can be attributed primarily to the reestablishment of vegetation and the duration that the vegetation is in place

cosmogenically enabled sediment budgeting we used 10 be and 26 al to constrain the millennial scale sedi ment and nuclide budget for a common long studied but poorly understood landform in arid regions the desert piedmont we sampled the chemehuevi mountain piedmont a complex multi surfaced landform in the mojave desert western united states the nuclide data indicate that sediment is produced more rapidly 1 1 3 10 5 kg yr 21 km 22 in steep mountain source basins than on the low gradient pediment 4 0 3 10 4 kg yr 21 km 22 or the intra piedmont mountain range 2 5 3 10 4 kg yr 21 km 22 however the bulk of the sediment in transport is derived from erosion of the large abandoned alluvial surface 3 9 3 10 4 kg yr 21 km 22 the combination of mass and nuclide budgeting suggests that sediment transport speeds decrease downslope from tens of meters per year in confined channels on the proximal pediment to decimeters per year in unconfined distributaries on distal wash surfaces the sed iment and nuclide budgeting approach we use is particularly valu able in arid regions where geomorphically significant events are infrequent and dating control is poor thus confounding traditional sediment budgeting techniques

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

frost cracking control on catchment denudation rates insights from in situ produced 10be concentrations in stream sediments ecrins pelvoux massif french western alps the potential tectonic and climatic controls on erosion rates in the european alps and other mountain belts remain strongly debated we have quantified denudation rates at catchment scales using in situ produced cosmogenic nuclides 10be in stream sediments sampled at the outlets of twelve variously sized 27 1072 km2 catchments of the ecrins pelvoux massif french western alps with average elevations ranging from 1700 to 2800 m spatially averaged denudation rates corrected for potential shielding by little ice age glaciers vary from 0 27 0 05 to 1 07 0 20 mm yr on millennial timescales our results exhibit a correlation 2 0 56 between denudation rate and mean catchment elevation in the absence of significant correlation with any other morphometric parameters relief slope catchment size hypsometry etc although such variations in erosion rates have been previously linked to variations in tectonic uplift rate the relatively small size and tectonic homogeneity of our study area exclude a strongly variable tectonic control we interpret the increase in erosion rate with elevation as the effect of frost controlled processes which are strongly temperature dependent we use a one dimensional heat flow model driven by high resolution instrumental temperature records from the study area to correlate the variability in denudation rates with the integral of the absolute temperature gradient within the frost cracking window 3 to 8 c a proxy of the frost cracking intensity for each catchment the results imply that the efficiency of frost cracking constitutes a major control on catchment wide denudation rates in the study area explaining more than half the measured variability in these rates our study shows that present day denudation of the ecrins pelvoux massif is controlled by a climatically driven factor and suggests that frost cracking processes impose an important control on the post glacial topographic evolution of mid latitude mountain belts

erosion and exhumation in the himalaya from cosmogenic isotope inventories of river sediments the outward erosional flux is a key factor in the tectonic evolution of mountain belts and there is much debate about the feedbacks between tectonics erosion and climate here we use cosmogenic nuclides 10be and 26al analysed in quartz from river sediments from the upper ganges catchment to make the first direct measurements of large scale erosion rates in a rapidly uplifting mountain belt the erosion rates are highest in the high himalaya at 2 7 0 3 mm yr 1 errors fall to 1 2 0 1 mm yr on the southern edge of the tibetan plateau and are 0 8 0 3 to 0 6 mm yr in the foothills to the south of the high mountains these relative estimates are corroborated by the nd isotopic mass balance of the river sediment analysis of sediment from an abandoned terrace suggests that similar erosion rates have been maintained for at least the last few thousand years the data presented here along with data recently published for european river catchments demonstrate that a log linear relationship between relief and erosion rate holds over three orders of magnitude variation in erosion rate and between very different climatic and tectonic regimes the erosion rate estimates from cosmogenic nuclides correlate well with exhumation rates calculated from previously published apatite fission track ages in the indian himalaya this confirms that much of the exhumation in the himalayan mountain chain is now balanced by erosion however exhumation rates calculated from high blocking temperature systems such as 40ar 39ar in muscovite imply lower exhumation rates rocks presently at the surface must have undergone a three to six fold increase in exhumation rate within the last few million years we show how this could be explained either by climatic forcing of erosion rate changes or by tectonics published evidence for equally rapid changes of exhumation rate in the past and the probable diachroneity in the time at which the present exhumation rates accelerated imply that tectonics has moderated at least some of the change in exhumation rates

spatial distribution of denudation in eastern tibet and regressive erosion of plateau margins article i nfo the longmen shan range is one of the major topographic and structural features of the eastern margin of the tibetan plateau with an impressive topographic gradient and low convergence rates across the range this region has raised important questions concerning the dynamics of plateau margin settings such as the long term mechanisms of topographic evolution the investigation of the distribution in space and time of denudation can provide critical insight into such dynamics and shed light on still unresolved controversies for that purpose we present a new dataset that documents the intensity and distribution of denudation processes across this plateau margin through field survey of fluvial incision markers quantitative geomorphology and cosmogenic nuclide derived basin wide erosion rates erosion is b0 5 mm year in the frontal region of the longmen shan and between 0 5 and 1 mm year further west with a gradual decrease when reaching the northern headwaters of the min jiang watershed adjacent to the beginning of the tibetan plateau the spatial distribution of denudation inferred from the various methods we use suggests that most of the differential uplift in the central longmen shan is accommodated by the beichuan fault and frontal structures located in the foothills the denudation pattern seems also to reflect the large scale propagation of erosion from the sichuan basin toward the plateau this suggests that the longmen shan range is submitted to the combined influences of slow thrusting activity on the frontal structures and progressive westward regressive erosion as a probable response to a pulse of uplift of the tibetan plateau eastern margin that

modern erosion rates in the high himalayas of nepal abstract current theories regarding the connections and feedbacks between surface and tectonic processes are predicated on the assumption that higher rainfall causes more rapid erosion to test this assumption in a tectonically active landscape a network of 10 river monitoring stations was established in the high himalayas of central nepal across a steep rainfall gradient suspended sediment flux was calculated from sampled suspended sediment concentrations and discharge rating curves accounting for solute and bedload contributions the suspended sediment fluxes were used to calculate watershed scale erosion rates that were then compared to monsoon precipitation and specific discharge we find that in individual watersheds annual erosion rates increase with runoff in addition our data suggest average erosion rate increases with discharge and precipitation across the entire field site such that the wetter southern watersheds are eroding faster than the drier northern watersheds the spatially non uniform contemporary erosion rates documented here are at odds with other studies that have found spatially uniform long term rates 10 5 10 6 yr across the pronounced rainfall gradient observed in the region the discrepancy between the modern rates measured here and the long term rates may be reconciled by considering the high erosional efficiency of glaciers the northern catchments were much more extensively glacierized during the pleistocene and therefore they likely experienced erosion rates that were significantly higher than the modern rates we propose that in the northern watersheds the high rates of erosion during periods of glaciation compensate for the low rates during interglacials to produce a time averaged rate comparable to the landslide dominated southern catchments

glacial topographic interactions in the teton range wyoming 1 understanding interactions among tectonics topography climate and erosion is fundamental to studies of mountainous landscapes here we combine topographic analyses with modeled distributions of precipitation insolation and flexural isostasy to present a conceptual model of topographic evolution in the teton range wyoming and test whether efficient glacial relief production has contributed to summit elevations the conceptual model reveals a high degree of complexity inherent in even a relatively small glaciated mountain range back tilting has caused topographic asymmetry with the greatest relief characterizing eastern catchments in the center of the range two high summits grand teton and mount moran rise hundreds of meters above the surrounding landscape their elevations set by the threshold hillslope angle and the spacing between valleys hosting large erosionally efficient glaciers only basins 20 km2 held glaciers capable of eroding sufficiently rapidly to incise deeply and maintain shallow downvalley gradients on the eastern range flank glacial erosion here was promoted by 1 prevailing westerly winds transporting snow to high relief eastern basins leading to cross range precipitation asymmetry 2 the wind blown redistribution of snow from open western headwaters into sheltered eastern cirques with the associated erosion driven migration of the drainage divide increasing eastern accumulation areas and 3 tall steep hillslopes providing shading snow influx from avalanching and insulating debris cover from rockfalls to valley floor glaciers in comparison the topographic enhancement of glacial erosion was less pronounced in western and smaller eastern basins despite dramatic relief production insufficient rock mass is removed from the teton range to isostatically raise summit elevations

role of transient water pressure in quarrying a subglacial experiment using acoustic emissions 1 probably the most important mechanism of glacial erosion is quarrying the growth and coalescence of cracks in subglacial bedrock and dislodgement of resultant rock fragments although evidence indicates that erosion rates depend on sliding speed rates of crack growth in bedrock may be enhanced by changing stresses on the bed caused by fluctuating basal water pressure in zones of ice bed separation to study quarrying in real time a granite step 12 cm high with a crack in its stoss surface was installed at the bed of engabreen norway acoustic emission sensors monitored crack growth events in the step as ice slid over it vertical stresses water pressure and cavity height in the lee of the step were also measured water was pumped to the lee of the step several times over 8 days pumping initially caused opening of a leeward cavity which then closed after pumping was stopped and water pressure decreased during cavity closure acoustic emissions emanating mostly from the vicinity of the base of the crack in the step increased dramatically with repeated pump tests this crack grew with time until the step s lee surface was quarried our experiments indicate that fluctuating water pressure caused stress thresholds required for crack growth to be exceeded natural basal water pressure fluctuations should also concentrate stresses on rock steps increasing rates of crack growth stress changes on the bed due to water pressure fluctuations will increase in magnitude and duration with cavity size which may help explain the effect of sliding speed on erosion rates

production of cosmogenic radionuclides at great depth a multi element approach abstract for the last two decades in situ produced cosmogenic nuclides are increasingly applied in earth sciences to quantify surface processes in parallel significant reduction of the analytical uncertainties linked to advances in accelerator mass spectrometry ams allows more precise measurements however among all the published works on cosmogenic nuclides only few studies are dedicated to a better understanding of their production systematic or to a better constrain of the physical parameters involved in their production thus an approach to investigate in situ produced cosmogenic nuclides 10 be 26 al and 36 cl along a single 11 meter long core drilled from the surface and composed of carbonates and quartzose conglomerates has been launched these measurements have been used to quantify muon induced productions based on natural samples for each studied nuclide contrary to the current most oftenly used calculation of muon induced production parameters which are based on irradiation experiments at discrete energies productions based on natural samples are considering the entire energy range of particles reaching the ground surface the evolution of 36 cl concentrations with depth needs to agree with those parameters deduced from 10 be and 26 al data this is optimized when considering a fast muon induced 36 cl production contribution and a spallation production rate at sea level high latitude slhl of 42 0 2 0 atoms 36 cl g ca 1 a 1 1 sigma uncertainty

observations in a cavity beneath grinnell glacier abstract during a 3 year period several aspects of the glacier rock interface were studied in a cavity beneath 5 8 m of ice near the terminus of grinnell glacier montana u s a continuous week long records of the summer sliding rate revealed a very uniform speed of about 12 m a during the summer a value about 20 per cent higher than the average annual sliding rate several decimetre sized rock fragments were broken from the glacier bed near the lee sides of bedrock ledges and transported down glacier in the course of a two week long experiment the glacier abraded its bed significantly and non uniformly it is of interest that significant quarrying and abrasion occurred under thin ice with relatively little entrained debris key words glacier sliding subglacial erosion introduction subglacial cavities provide easy access to the bases of glaciers where information can be gathered on a variety of processes and features at the ice rock interface a more complete understanding of these processes is essential for continued advances in studies of the dynamics of temperate glaciers and of erosion and deposition by glaciers a number of topical questions can be addressed through studies conducted in subglacial cavities for example is the sliding motion of the ice steady or is it jerky as might be expected if sliding is influenced significantly by rock to rock friction what is the debris content of the ice what can be observed regarding the poorly understood phenomena of glacial quarrying and abrasion is there any indication that at the base of a temperate glacier ice might locally freeze to its bed site description

quantifying periglacial erosion insights on a glacial sediment budget matanuska glacier alaska glacial erosion rates are estimated to be among the highest in the world few studies have attempted however to quantify the flux of sediment from the periglacial landscape to a glacier here erosion rates from the nonglacial landscape above the matanuska glacier alaska are presented and compare with an 8 yr record of proglacial suspended sediment yield non glacial lowering rates range from 1 8 0 5 mm yr 1 to 8 5 3 4 mm yr 1 from estimates of rock fall and debris flow fan volumes an average erosion rate of 0 08 0 04 mm yr 1 from eight convex up ridge crests was determined using in situ produced cosmogenic 10be extrapolating these rates based on landscape morphometry to the matanuska basin 58 ice cover it was found that nonglacial processes account for an annual sediment flux of 2 3 1 0 106 t suspended sediment data for 8 years and an assumed bedload to estimate the annual sediment yield at the matanuska terminus to be 2 9 1 0 106 t corresponding to an erosion rate of 1 8 0 6 mm yr 1 nonglacial sources therefore account for 80 45 of the proglacial yield a similar set of analyses were used for a small tributary sub basin 32 ice cover to determine an erosion rate of 12 1 6 9 mm yr 1 based on proglacial sediment yield with the nonglacial sediment flux equal to 10 7 of the proglacial yield it is suggested that erosion rates by nonglacial processes are similar to inferred subglacial rates such that the ice free regions of a glaciated landscape contribute significantly to the glacial sediment budget the similar magnitude of nonglacial and glacial rates implies that partially glaciated landscapes will respond rapidly to changes in climate and base level through a rapid nonglacial response to glacially driven incision copyright 2009 john wiley sons ltd

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

a model for the origin of himalayan anatexis and inverted metamorphism the origin of the paired granite belts and inverted metamorphic sequences of the himalaya has generally been ascribed to development of the main central thrust mct although a variety of models have been proposed that link early miocene anatexis with inverted metamorphism recent dating studies indicate that recrystallization of elements of the mct footwall occurred in the central himalaya as recently as 6 ma the recognition that hanging wall magmatism and footwall metamorphism are not spatially and temporally related renders unnecessary the need for exceptional physical conditions to explain generation of the high himalayan leucogranites and north himalayan granites which differ in age petrogenesis and emplacement style we suggest that their origin is linked to shear heating on a continuously active thrust that cuts through indian supracrustal rocks that had previously experienced low degrees of partial melting numerical simulations assuming a shear stress of 30 mpa indicate that continuous slip on the himalayan decollement beginning at 25 ma could trigger partial melting reactions leading to formation of the high himalayan granite chain between 25 and 20 ma and the north himalayan belt between 17 and 8 ma the ramp flat geometry we apply to model the himalayan thrust system requires that the presently exposed rocks of the hanging wall resided at middle crustal levels above the decollement throughout the early and middle miocene late miocene out of sequence thrusting within the broad shear zone beneath the mct provides a mechanism to bring these rocks to the surface in their present location i e well to the north of the present tectonic front and has the additional benefit of explaining how the inverted metamorphic sequences formed beneath the mct we envision that formation of the mct zone involved successive accretion of tectonic slivers of the lesser himalayan formations to the hanging wall and incorporate these effects into the model the model predicts continued anatexis up to 400 km north of the himalayan range consistent with the timing and geochemistry of leucogranites exhumed on the flank of a south tibetan rift

biological soil crust development and its topsoil properties in the process of dune stabilization inner mongolia china this study was undertaken at horqin sand land inner mongolia northern china field samples of biological soil crusts bscs and underlying topsoil 0 5 cm under bsc were taken in areas of different dune stabilization stages and their physicochemical properties were analyzed including particle size distribution bulk density organic matter nitrogen phosphorus electrical conductivity ec ph and caco3 content the results revealed that semi mobile dunes semi fixed dunes and fixed dunes had developed a physical crust algae crust and moss crust respectively the thickness hardness water content fine fraction and nutrient contents of bscs were gradually increasing along the dune stabilization gradient meanwhile bsc establishment and development enhanced the bulk density silt and clay content and nutrients of the topsoil under it in an increasing tend from semi mobile dune to fixed dune organic matter concentrations and other nutrients in the 0 5 cm topsoil layer under bscs were significantly higher compared to unconsolidated soil control moreover there were strong significant positive correlations between topsoil and bscs organic matter total nitrogen available nitrogen available phosphorus caco3 and 0 05 mm particle content suggesting that bscs have an influence on some of the properties of the underlying topsoil

scaling factors for the rates of production of cosmogenic nuclides for geometric shielding and attenuation at depth on sloped surfaces abstract the decrease in rates of production of cosmogenic nuclides occurs because of shielding of cosmic rays by mountains sloped surfaces and local rock formations that block them when a large part of the sky is blocked this correction is large and requires detailed model calculations this paper considers three geometries a rectangular obstruction a triangular obstruction and a sloped surface other geometries can be considered as a combination of these the results are presented in terms of formulas and graphs so that the reader can easily apply them to common field situations any use of cosmogenic nuclides in the study of geomorphic processes or forms must consider factors that introduce variations in the production of nuclides

erosion rates and mechanisms of knickzone retreat inferred from 10be measured across strong climate gradients on the northern and central andes western escarpment escarpment edge deep gorges and distinct knickzones in river profiles characterize the landscape on the western escarpment of the andes between 5 s and 18 s northern peru to northern chile th

numerical modelling of erosion processes in the himalayas of nepal effects of spatial variations of rock strength and precipitation the interplay between tectonics and erosion has a predominant control on the evolution of the morphology of mountain belts here we investigate the modalities of deformation in central nepal on a c 100 ka time scale in response to tectonic and external forcings through the use of a finite element thermomechanical model coupled with an integrative denudation formulation that accounts for fluvial incision and hillslope landsliding we study the complex coupling existing between tectonics and erosion with special emphasis on the influences of rock strength and rainfall distributions our results underline the key role played by lithologic variations in the elevation of both rivers and mean topography we show that the location of the main frontal thrust is mainly controlled by the low erodability of the unconsolidated sandstone in the siwaliks hills as previously suspected burbank et al 2003 our simulations demonstrate that the pattern of uplift in nepal is mainly dependent on both erodability and fault geometry rather than on rainfall distribution

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

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

deglaciation and landscape history around annapurna nepal based on 10be surface exposure dating abstract the high himalaya is a key area for tectonic geomorphological and climate studies because of its extreme relief and location at the transition zone between areas with abundant monsoonal precipitation and the arid semiarid tibetan plateau we present 10be surface exposure ages on 22 boulders from the annapurna area in nepal the ages improve understanding of the late quaternary landscape history and the geomorphological processes operating in this part of the himalaya although our study is reconnaissance in nature it highlights the importance of catastrophic events such as landslides and debris flows for denudation of high mountains holocene exposure ages for the dhampu chooya landslide 4 1 0 6 ka and for 600 m of alluviation in kali gandaki valley 2 1 0 6 ka for example indicate the frequent occurrence and extent of catastrophic events and their implications for natural hazards we also offer an explanation for the differences in late quaternary glacial chronologies at closely spaced study sites in the nepal himalaya topographically controlled and spatially variable precipitation in the himalaya determines the sensitivity of glaciers to changes in temperature and precipitation accordingly some glaciers advanced in phase with northern hemisphere ice sheets whereas others reached their maximum extent at times of increased monsoonal precipitation during marine isotope stage 3 and the early holocene

fluvial response to horizontal shortening and glaciations a study in the southern alps of new zealand 1 it has been postulated that a steady state between erosional and tectonic processes may develop in continental collision however it is not clear whether steady state conditions can be reached for all components of the landscape here we show using landscape evolution models and field evidence that a true geomorphic steady state may never be reached in the southern alps of new zealand the strong asymmetries in tectonic uplift and tectonic advection and the onset of glaciations constantly interact to prevent the landscape from reaching a topographic steady state evidence suggests that the first order geomorphology on the western side of the southern alps is controlled by orographic precipitation combined with extreme rates of tectonic uplift whereas the development of deep glacial valleys on the eastern side is initiated by differential uplift along large faults we also develop a first order equation governing the dynamics of the main divide to show that both tectonic advection and fluvial erosion efficiency control the position and the height of the main drainage divide using a two dimensional landscape evolution model we demonstrate that the transition from glacial to fluvial conditions at the end of the last glaciation led to substantial modifications of the landscape while the main trunk channels get slowly uplifted ridges are leveled down causing the relief to decrease hillslopes appear to be affected by fluvial processes which seem to be driven by incision of river tributaries this reduction of relief will probably never reach a steady state since warmer interglacial periods are substantially shorter than glacial periods

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

use of cosmogenic radionuclides as a sediment tracer in the santa cruz littoral cell california united states we demonstrate that cosmogenic radionuclides can be employed to trace sediment when the sources have sufficiently distinct concentrations and develop a theoretical mixing model for a rocky coastline littoral system we combine the resulting mixing model with existing cosmogenic radionuclide methods that quantify river inputs and terrace ages to determine the major components of the long term littoral sediment budget of the santa cruz california coastline sediment derived from coastal basins eroding at 0 2 mm yr has a much lower concentration than sediment derived from 60 84 ka terrace sands atop backwearing seacliffs the complex pattern of cosmogenic radionuclide concentrations in littoral sands along 100 km of coastline can be explained by mixing sediment derived from seacliffs backwearing at 10 cm yr with that delivered by rivers having widely different amounts of sediment discharge

erosion rates during rapid deglaciation in icy bay alaska 1 contemporary glacial erosion rates based on sediment yields in southeast alaska merit considerable attention because they are unsurpassed worldwide and they significantly exceed long term exhumation rates in the region two issues are likely to contribute to these high rates contemporary sediment yields in fjords 1 have generally been overestimated by failing to account for the considerable input of subaerially derived material and 2 are exceptionally high because tidewater glaciers in southeast alaska have been anomalously dynamic and erosive during the past century of rapid retreat to investigate these influences and to quantify the rate at which tyndall glacier erodes its basin we present seismic data defining the volume of sediments in taan fjord icy bay we subtract the contribution of subaerially derived sediments from the fjord sediment package to determine the sediment yield directly from tyndall glacier during the most recent period of retreat 1962 1999 using a numerical model of proglacial glacimarine sedimentation we then calculate the annual sediment yield from and the corresponding erosion rate of tyndall glacier during this period which averages 28 5 mma 1 a strong correlation emerges between glacial retreat rates and glacial sediment yields implying that most contemporary sediment yield data from retreating tidewater glaciers may correspond to contemporary erosion rates that are a factor of 3 5 1 5 higher than in the long term hence we estimate the long term erosion rate for tyndall glacier to be 9 2 mma 1

theory of glacial erosion transport and deposition as a consequence of subglacial sediment deformation a theory of erosion transport and deposition of unlithified sediments by glaciers is presented it predicts the large scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle together with the resultant intensity of large scale lincations drumlins which will be incised in the landscape the theory also predicts the dispersal patterns of subglacial lithologies together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till it predicts major erosional discontinuities within tills and the formation of boulder pavements it suggests that the dominant proportion of the lowland tills produced by pleistocene mid latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine grained the theory is based on an analysis of glacier dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition

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

the response of infiltration depth evaporation and soil water replenishment to rainfall in mobile dunes in the horqin sandy land northern china to understand the relationships among rainfall infiltration evaporation replenishment in mobile dunes in the semi arid areas of china we used the container of water distribution 100 100 120 cm3 to examine rainfall infiltration soil water redistribution and soil surface evaporation under natural and simulated rainfall conditions the results showed that infiltration depth was linearly related to rainfall amount and intensity rainfall amounts larger than 13 4 mm could replenish soil water at 60 cm depth after redistribution while with rainfalls larger than 39 8 mm infiltration depth could exceed 120 cm rainfall amounts larger than 50 mm produced saturated soil water at 120 cm depth and replenishment amount accounted for 40 4 of the total amount of rainfall soil surface evaporation exhibited a relatively minor change with increases in rainfall when rainfall was larger than 11 8 mm the amount of evaporation and soil water content were significantly correlated at 0 60 cm soil depth but not below these results suggest that the maximum effective depth of evaporation is 60 cm below the ground surface and that rainfall of 13 4 mm is a threshold distinguishing effective from ineffective rainfall in the mobile dunes of the horqin sandy land

impact of glacial erosion on 10 be concentrations in fluvial sediments of the marsyandi catchment central nepal several processes contribute to denudation in high mountain environments of these glacial erosion is particularly difficult to constrain despite its critical importance in the evolution of many mountain ranges in this study we present a new data set of 10be concentrations in fluvial sediments sampled along the marsyandi river and its main tributaries in central nepal we interpret the 10be concentrations as being significantly impacted by glacially derived sediments along the marsyandi river such additions complicate conventional interpretations of 10be derived catchment scale denudation rates using a simple linear mass conservation formulation we invert our data set in order to separate the different denudational contributions to the observed signal as well as to constrain their magnitude and spatial distribution our results suggest significant variations in glacial erosion both in space and magnitude within the marsyandi catchment

features of glacial valley profiles simply explained 1 glacial occupation of alpine valleys results in a distinct signature in the long valley profile including steepening of the profile in the headwaters flattening at lower elevations and a step in the profile at the convergence of headwater tributaries we present analytic results for glacial erosion patterns by making the following assumptions 1 the initial profile is linear 2 the width of the valley is uniform 3 the annual mass balance varies linearly with elevation 4 the glacier at any time is quasi steady 5 the erosion rate is proportional to ice discharge per unit valley width and 6 glacial erosion rates far exceed fluvial erosion rates a steady glacier under these conditions would erode a parabolic divot in the longitudinal valley profile with its maximum depth coinciding with the down valley position of the equilibrium line altitude ela the calculated flattening of the valley floor down valley of the ela and the steepening of it up valley captures the essence of the glacial signature when a reasonable probability distribution of elas is allowed the predicted erosion peaks at 30 40 of the down valley distance to the glacial limit and the pattern merges smoothly with the steeper fluvial profile downstream of the glacial limit profiles of mass balance that are capped at a maximum value produce shorter glaciers and a slight asymmetry in the expected erosion pattern only when we mimic the tributaries of glacial headwaters by specifying a valley width distribution do we obtain the upper step observed in many valley profiles

spatiotemporal trends in erosion rates across a pronounced rainfall gradient examples from the southern central andes abstract the tectonic and climatic boundary conditions of the broken foreland and the orogen interior of the southern central andes of northwestern argentina cause strong contrasts in elevation rainfall and surface process regimes the climatic gradient in this region ranges from the wet windward eastern flanks 2 m yr rainfall to progressively drier western basins and ranges 0 1 m yr bordering the arid altiplano puna plateau in this study we analyze the impact of spatiotemporal climatic gradients on surface erosion first we present 41 new catchment mean erosion rates derived from cosmogenic nuclide inventories to document spatial erosion patterns second we re evaluate paleoclimatic records from the calchaquies basin 66 w 26 s a large intermontane basin bordered by high 4 5 km mountain ranges to demonstrate temporal variations in erosion rates associated with changing climatic boundary conditions during the late pleistocene and holocene three key observations in this region emphasize the importance of climatic parameters on the efficiency of surface processes in space and time 1 first order spatial patterns of erosion rates can be explained by a simple specific stream power ssp approach we explicitly account for discharge by routing high resolution satellite derived rainfall this is important as the steep climatic gradient results in a highly nonlinear relation between drainage area and discharge this relation indicates that erosion rates er scale with er ssp1 4 on cosmogenic nuclide time scales 2 we identify an intrinsic channel slope behavior in different climatic compartments channel slopes in dry areas 0 75 m yr with equal drainage areas thus compensating lower amounts of discharge with steeper slopes 3 erosion rates can vary by an order of magnitude between presently dry 0 05 mm yr and well defined late pleistocene humid 0 5 mm yr conditions within an intermontane basin overall we document a strong climatic impact on erosion rates and channel slopes we suggest that rainfall reaching areas with steeper channel slopes in the orogen interior during wetter climate periods results in intensified sediment mass transport which is primarily responsible for maintaining the balance between surface uplift erosion sediment routing and transient storage in the orogen

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 as a driving mechanism of intracontinental mountain growth in nature mountains can grow and remain as localized tectonic features over long periods of time 10 m y by contrast according to current knowledge of lithospheric rheology and neglecting surface processes any intracontinental range with a width that exceeds that which can be supported by the strength of the lithosphere should collapse within a few tens of millions of years for example assuming a quartz dominated crustal rheology the relief of a range initially 3 km high and 300 400 km wide is reduced by half in about 15 m y as a result of lateral spreading of its crustal root we suggest that surface processes might actually prevent such a subsurface collapse removal of material from topographic heights and deposition in the foreland oppose spreading of the crustal root and could eventually drive a net influx of material toward the orogeny we performed a set of numerical experiments in order to validate this hypothesis a section of a lithosphere with a brittle elasto ductile rheology initially loaded by a mountain range is submitted to horizontal shortening and to surface processes if erosion is intense material is removed more rapidly than it can be supplied by crustal thickening below the range and the topography is rapidly smoothed for example a feature 3 km high and 300 400 km wide is halved in height in about 15 m y for an erosion coefficient k 10 3 m 2 yr the erosion rate is of the order of a few 0 1 mm yr this regime might be called erosional collapse if erosion is not active enough the crustal root spreads out laterally and subsurface collapse occurs in the third intermediate regime removal of the material by erosion is dynamically compensated by isostatic rebound and inward flow in the lower crust so that the range can grow in this mountain growth regime the range evolves toward a characteristic graded shape that primarily depends on the erosion law the erosion rate may be high e g 0 5 0 9 mm yr close to the rate of tectonic uplift e g 0 7 1 1 mm yr and few times higher than the rate of topographic uplift 0 15 0 2 mm yr these experiments show that surface processes can favor localized crustal shortening and participate in the development of an intracontinental mountain surface processes must therefore be taken into account in the interpretation and modeling of long term deformation of continental lithosphere conversely the mechanical response of the lithosphere must be accounted for when large scale topographic features are interpreted and modeled in terms of geomorphologic processes

comparison of late pleistocene and modern glacier extents in central nepal based on digital elevation data and satellite imagery abstract late pleistocene and modern ice extents in central nepal are compared to estimate equilibrium line altitude ela depressions new techniques are used for determining the former extent of glaciers based on quantitative objective geomorphic analyses of a 90 m resolution digital elevation model dem for every link of the drainage network valley form is classified as glacial or fluvial based on cross valley shape and slope statistics down valley transitions from glacial to fluvial form indicate the former limits of glaciation in each valley landsat multispectral scanner imagery for the same region is used to map current glacier extents for both full glacial and modern cases elas are computed from the glacier limits using the dem and a toe to headwall altitude ratio of 0 5 computed ela depressions range from 100 900 m with a modal value of 650 m and a mean of 500 m values consistent with previously published estimates for the central himalaya but markedly smaller than estimates for many other regions we suggest that this reflects reduced precipitation rather than a small temperature depression consistent with other evidence for a weaker monsoon under full glacial conditions

mechanical analysis of controls on strain partitioning in the himalayas of central nepal we present a mechanical analysis of the problem of slip partitioning between the major thrust systems in a collisional range we focus on two structures in the himalayas of central nepal the main himalayan thrust mht and the main central thrust mct we use finite element modeling to test the influence of various parameters such as friction coefficients and surface processes and we investigate how they affect the distribution of deformation between these two faults we observe that reproduction of the late quaternary kinematic pattern across the range with our model requires strict conditions on the friction coefficients such that the mht is very weak whereas the mct is significantly stronger the most important parameter that controls slip partitioning appears to be the dip angle of the mct with a gentler or steeper mct promoting or inhibiting slip respectively we also show that transient loading and unloading through focused glacial erosion in the higher part of the range can unclamp the mct and allow a significant increase in slip rates the results of this mechanical sensitivity investigation have important implications for the dynamics of the himalayan wedge and point toward along strike structural variations as a first order control on slip partitioning

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

in situ produced 10be measurements at great depths implications for production rates by fast muons in situ cosmogenic 10be values have been used to investigate a brazilian quartz vein from the surface to a depth of 15 m at depths greater than 1000 g cm2 deep enough for neutron induced reactions to be insignificant there is only a slight decrease in 10be concentration with increasing depth our results are consistent with deep production of 10be by a mechanism presumably induced by fast muons with an attenuation length of 5300 950 g cm2 and a contribution of 0 65 0 25 to the total surface production results are compared with values from the literature and implications of this re evaluation are discussed

estimating rates of denudation using cosmogenic isotope abundances in sediment we propose as a testable hypothesis a basin scale approach for interpreting the abundance of in situ produced cosmogenic isotopes an approach which considers explicitly both the isotope and sediment flux through a drainage basin unlike most existing models which are appropriate for evaluating in situ produced cosmogenic isotope abundance at discrete points on earth s surface our model is designed for interpreting isotope abundance in sediment because sediment is a mixture of materials in favourable cases derived from throughout a drainage basin we suggest that measured isotope abundances may reflect spatially averaged rates of erosion we investigate the assumptions and behaviour of our model and conclude that it could provide geomorphologists with a relatively simple means by which to constrain the rate of landscape evolution if a basin is in isotopic steady state and if sampled sediments are well mixed

simulation of the transition of earthquake rupture from quasi static growth to dynamic propagation we have simulated a rupture transition from quasi static growth to dynamic propagation using the boundary integral equation method in order to make a physically reasonable model of earthquake cycle we have to evaluate the dynamic rupture propagation in the context of quasi static simulation we used a snapshot of the stress distribution just before the earthquake in the quasi static simulation the resultant stress will be fed back to the quasi static simulation since the quasi static simulation used the slip and time dependent constitutive relation the friction law itself evolves with time thus we used the slip weakening constitutive relation for dynamic rupture propagation consistent with that used for the quasi static simulation we modeled a san andreas type strike slip fault in which two different size asperities existed

rates of deposition on lateral moraine embankments glacier de tsidjiore nouve valais switzerland une tentative de reconstitution des taux moyens d accumulation de debris sur les terrasses morainiques pendant la periode neoglaciaire a ete faite ces taux sont compares avec ceux de la periode 1978 82 calcules a partir des changements detailles des profils de la moraine topographie par photogrammetrie terrestre et aerienne ainsi que de l ablation mesuree sur les bords du glacier actuellement l apport total de sediments au glacier de tsidjiore nouve a la fois par remblaiement lateral et transport par l eau de fonte est de l ordre de 6400 9500 m 3 a 1 ceci suggere la possibilite d une vitesse d erosion moyenne elevee dans le bassin versant de 1 55 2 99 mm a 1

rates of sediment delivery from the fennoscandian ice sheet through an ice age sediment delivery rates through an entire ice age are investigated using seismic records of glacial erosion products from the fennoscandian ice sheet deposited offshore of mid norway in the 2 7 m y old naust formation volume 100 000 km 3 the mean sedimentation rate over the ice age is 0 24 m k y 1 with bedrock lowering of 520 m in the ice sheet catchment the mean sediment delivery is 2 3 times higher for the most recent 600 k y than for earlier naust sequences the hypothesis that glacial erosion is most rapid early in an ice age when there was presumably much weathered bedrock and preglacial sediment available is not accepted for our study area more important are changing ice sheet dimensions and dynamics varying intensity of individual glacial cycles and complex ice sheet dynamics in single deglaciations the mean rate of sediment delivery from ice sheets is an order of magnitude higher than from fluvial activity in the huge amazon and mississippi systems implying that ice is a very effective agent of long term denudation during cold periods of earth history

modelling landscape evolution under ice sheets we use an ice sheet model glimmer with an erosion component to examine the evolution of landscapes under ice sheets over long time scales in hypothetical situations glimmer is a fully coupled thermomechanical 3 dimensional ice sheet model with a sliding component the model thus has the ability to predict ice thickness the distribution of areas at pressure melting point and basal velocities the erosion rate is assumed to be a simple linear function of the basal velocity and therefore erosion only occurs where the bed is not frozen and basal sliding is possible in addition sliding velocities are assumed to be related to basal water production thus giving a mechanism for smooth temporal and spatial transitions between eroding and non eroding portions of the bed the eroding glacial landscape system is modelled for long term persistent glaciation assuming a variety of initial landscapes results indicate that without the inclusion of basal water production in the calculation of sliding velocities any thermal feedbacks are exaggerated because of steep horizontal basal temperature gradients additionally bed morphology exerts a greater influence under low basal slip conditions because ice cannot respond readily to thermal instabilities we suggest that erosion and valley overdeepening may aid stabilisation of the thermal regime of an ice sheet and that it is possible to generate glacial signals in previously fluvial systems after only 100 kyr of glaciation at conservative erosion rates

subglacial observations from oksfjordjokelen north norway stepped bedrock topography at the snout of a small outlet glacier from oksfjordjokelen north norway produces an extensive subglacial cavity system which stretches some 70m across and 100m up glacier giving access beneath ice 50 m thick inside the cavity regelation ice clean glacier ice and deforming basal ice have been observed samples were taken and basal debris concentrations at the glacier sole were found to vary between 0 005 and 15 38 per cent by volume the basal ice velocity has been determined using a linear variable differential transformer attached to an analogue recorder and also by means of measured displacements of ice crews and clasts embedded in the basal ice velocities were found to differ both spatially and temporally from a maximum of 2 55 mm h1 to a minimum of 0 3 mm h 1 the measurements and observations which have been related to present theory show how spatially averaged values for a number of variables could lead to inaccuracies in predicted erosion values certainly at a local scale on the exposed foreland jointcontrolled lee side faces provide evidence for extensive subglacial plucking here taken to mean the removal of preloosened bed material and or material resulting from bed failure indeed in the cavity the early stages of removal of joint controlled blocks by ice deformation along joints have been observed the importance of debris rich basal ice is shown in the formation of large striations up to 500cm 16cm 2cm present on the foreland

distribution of active rock uplift along the eastern margin of the tibetan plateau inferences from bedrock channel longitudinal profiles 1 current models of long term river incision into bedrock suggest that the local rate of differential rock uplift should exert a primary control on the gradient of channel longitudinal profiles however discrimination of this effect from the influence of variations in substrate erodibility sediment flux precipitation and transient changes in profile shape has proved difficult in practice here we investigate the controls on the spatial distribution of bedrock channel gradients adjacent to the sichuan basin in an effort to assess the degree and nature of active deformation along this margin of the tibetan plateau analysis of river longitudinal profiles utilizing a channel steepness index a measure of profile gradient normalized for drainage area reveals a zone of anomalously steep channels adjacent to the topographic front of the plateau margin channel profiles are systematically less steep in their headwater reaches on the plateau and in their lower reaches east of the plateau margin comparison of steepness indices to mapped lithologic variations reveals that lithology has only a limited influence on channel gradient in this field area we observe no systematic relationship between steepness indices and upstream drainage area channels of all size are steeper near the plateau margin we argue that these systematic changes are not readily explained as a consequence of increased sediment flux or of orographic precipitation we are led to conclude that steep channel profiles along the topographic front of the plateau reflect active differential rock uplift between this region and the foreland

aeolian dust in colorado plateau soils nutrient inputs and recent change in source aeolian dust windblown silt and clay is an important component in arid land ecosystems because it may contribute to soil formation and furnish essential nutrients few geologic surfaces however have been characterized with respect to dust accumulation history and resultant nutrient enrichment we have developed a combination of methods to identify the presence of aeolian dust in arid regions and to evaluate the roles of this dust in ecosystem processes unconsolidated sandy sediment on isolated surfaces in the canyonlands region of the colorado plateau differs greatly in mineralogical and chemical composition from associated bedrock mainly aeolian sandstone detrital magnetite in the surficial deposits produces moderately high values of magnetic susceptibility but magnetite is absent in nearby bedrock a component of the surficial deposits must be aeolian to account for the abundance of magnetite which formed originally in far distant igneous rocks particle size analysis suggests that the aeolian dust component is typically as much as 20 30 dust inputs have enriched the sediments in many elements including p mg na k and mo as well as ca at sites where bedrock lacks calcite cement soil surface biologic crusts are effective dust traps that apparently record a change in dust sources over the past several decades some of the recently fallen dust may result from human disturbance of land surfaces that are far from the canyonlands such as the mojave desert some land use practices in the study area have the potential to deplete soil fertility by means of wind erosion removal of aeolian silt