reverse and normal drag along a fault an analysis of the theoretical displacement field around a single dip slip fault at depth reveals that normal and reverse fault drag develop by perturbation flow induced by fault slip we analytically model the heterogeneous part of the instantaneous displacement field of an isolated two dimensional mode ii fault in an infinite homogeneous elastic body in response to fault slip material on both sides of the fault is displaced and opposing circulation cells arise on opposite sides of the fault with displacement magnitudes increasing towards the center of the fault both normal and reverse drag can develop at the fault center depending on the angle between the markers and the fault normal drag develops there for low angles 30 408 and reverse drag for higher angles a comparison of the theoretical results with published models and natural examples reveals that the characteristics of normal and reverse fault drag are largely insensitive to the scale and rheology of the faulted rocks and that drag forces generated by frictional resistance need not be the primary cause of fault drag fault drag has some interesting geometric implications for normal and reverse fault terminology emphasizing the importance for discrimination of vertical separation and throw furthermore our results lead us to propose an alternative model for the formation of rollover anticlines above normal faults

tectonic control on 10 be derived erosion rates in the garhwal himalaya india erosion in the himalaya is responsible for one of the greatest mass redistributions on earth and has fueled models of feedback loops between climate and tectonics although the general trends of erosion across the himalaya are reasonably well known the relative importance of factors controlling erosion is less well constrained here we present 25 10 be derived catchment averaged erosion rates from the yamuna catchment in the garhwal himalaya northern india tributary erosion rates range between 0 1 and 0 5 mm yr 1 in the lesser himalaya and 1 and 2 mm yr 1 in the high himalaya despite uniform hillslope angles the erosion rate data correlate with catchment averaged values of 5 km radius relief channel steepness indices and specific stream power but to varying degrees of nonlinearity similar nonlinear relationships and coefficients of determination suggest that topographic steepness is the major control on the spatial variability of erosion and that twofold to threefold differences in annual runoff are of minor importance in this area instead the spatial distribution of erosion in the study area is consistent with a tectonic model in which the rock uplift pattern is largely controlled by the shortening rate and the geometry of the main himalayan thrust fault mht our data support a shallow dip of the mht underneath the lesser himalaya followed by a midcrustal ramp underneath the high himalaya as indicated by geophysical data finally analysis of sample results from larger main stem rivers indicates significant variability of 10 be derived erosion rates possibly related to nonproportional sediment supply from different tributaries and incomplete mixing in main stem channels

temporally and spatially uniform rates of erosion in the southern appalachian great smoky mountains we measured 1 0 be in fluvial sediment samples n 27 from eight great smoky mountain drainages 1 330 km 2 results suggest spatially homogeneous sediment generation on the 10 4 10 5 yr time scale and 100 km 2 spatial scale at 73 11 t km 2 yr 1 equivalent to 27 4 m m y of bedrock erosion this rate is consistent with rates derived from fission track long term sediment budget and sediment yield data all of which indicate that the great smoky mountains and the southern appalachians eroded during the mesozoic and cenozoic at 30 m m y in contrast unroofing rates during the paleozoic orogenic events that formed the appalachian mountains were higher 10 2 m m y erosion rates decreased after termination of tectonically driven uplift enabling the survival of this ancient mountain belt with its deep crustal root as an isostatically maintained feature in the contemporary landscape

high resolution fault displacement mapping from three dimensional seismic data evidence for dip linkage during fault growth abstract detailed mapping using high resolution three dimensional seismic data has revealed a number of sub horizontal anomalies in the distribution of vertical displacement throw on the planes of growth faults in the gulf of mexico recognition of these anomalies is highly sensitive to the interval at which the fault displacements are sampled because they represent local decreases in throw which are confined to small discrete parts of the fault planes the distribution of the anomalies is inconsistent with model displacement fields of quasi elliptical concentric contours and is therefore incompatible with models of fault growth by uniform slip distribution and radial tip line propagation an alternative model is proposed whereby the evolution of a fault plane is established by the propagation and linkage of precursor fault segments in the dip direction dip linkage overlap and linkage of fault tips in the dip direction results in relay structures that are sub parallel to fault strike and therefore displacement minima that are sub horizontal on normal and thrust faults however since they are orthogonal to the main slip direction on the fault these structures have a low preservation potential and are therefore unlikely to be well resolved on cross sectional seismic profiles

hydrological modelling of a pleistocene landslide dammed lake in the santa maria basin nw argentina abstract around 30 000 14 c yr bp multiple landslides in the quebrada de cafayate 26 s 66 w dammed the rio de las conchas and caused a lake in the santa maria basin nw argentina since climate could have played a major role in landslide generation we used a lake balance model to compare the present day climate with the conditions during landsliding this model reveals that a hypothetical present day lake would stabilize around 70 m below the reconstructed paleolake level the volume of the water body would be one third of the corresponding paleolake volume however a minimum 10 15 increase in mean annual precipitation accompanied by at least a 3 4 c drop in temperature would result in a stable lake level at the reconstructed elevation this result implies wetter and cooler conditions at 30 000 14 c yr bp as compared to the present wetter climate in turn could help to explain enhanced landsliding in the quebrada de cafayate during this time

landscape response to pleistocene holocene precipitation change in the western cordillera peru 10be concentrations in modern sediments and terrace fills 1 the landscape response to climate change is frequently investigated with models because natural experiments on geologic timescales are rare in quebrada veladera in the western andes mountains the formation of alluvial terraces during periods of high precipitation presents opportunities for such an experiment we compare drainage average erosion rates during pleistocene terrace deposition with holocene rates using cosmogenic 10be samples for seven pairs of quartz sand taken from the trunk and tributaries of quebrada veladera and adjacent terraces each pair consists of sediment collected from the modern channel and excavated from an adjacent fill terrace the terrace fill was deposited at 16 ka and preserved an isotopic record of paleoerosion rates in the late pleistocene modern sands yield 10be concentrations between 1 68 105 and 2 28 105 atoms g corresponding to holocene erosion rates between 43 3 and 58 4 mm kyr the 10be concentrations in terrace sands range from 9 46 104 to 3 73 105 atoms g corresponding to paleoerosion rates from 27 2 to 103 8 mm kyr smaller upstream tributaries show a substantial decline in erosion rate following the transition from a wet to dry climate but larger drainage areas show no change we interpret this trend to indicate that the wetter climate drove landscape dissection which ceased with the return to dry conditions as channel heads propagated upslope erosion accelerated in low order drainages before higher order ones this contrast disappeared when the drainage network ceased to expand at that point erosion rates became spatially uniform consistent with the uniformity of modern hillslope gradients

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

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 change and mass movements in the nw argentine andes abstract the chronology of multiple landslide deposits and related lake sediments in the eastern argentine cordillera suggests that major mass movements cluster in two time periods during the quaternary between 35 000 and 25 000 14 c yr bp and after 5000 14 c yr bp the older cluster may correspond to the minchin wet period 40 000 and 25 000 14 c yr bp identified in tropical and subtropical south america suggesting a causal relation between enhanced landslide activity and climate change the younger cluster predates the titicaca wet period that began at about 3900 14 c yr bp which also affected other regions in the andes and the amazon basin no landslide and associated lake sediments are documented during the tauca wet period between 16 000 and 8000 14 c yr bp however the two clusters correspond to periods where it assumed that the el nino southern oscillation enso and tropical atlantic sea surface temperature dipole tad were active the analysis of the present day precipitation patterns in nw argentina indicates significant spatial and temporal differences between the intra andean part of the study area and the andean foreland whereas the tad seems to consistently increase rainfall the intensity of precipitation during the el nino phase of the enso is reduced to only 25 of the mean annual average in the intra andean basins whereas the regions east of the andes receive more than 125 similar results but with an opposite sign characterize la nina events the comparison of this pattern with paleo precipitation data as inferred from varved lake sediments suggests that increased interannual climate variability and therefore increased fluctuations in rainfall and river discharge in narrow valleys may reduce landsliding thresholds

pliocene orographic barrier uplift in the southern central andes sedimentary basin fills along the windward flanks of orogenic plateaus are valuable archives of paleoenvironmental change with the potential to resolve the history of surface uplift and orographic barrier formation the intermontane basins of the southern central andes contain thick successions of sedimentary material that are commonly interbedded with datable volcanic ashes we relate variations in the hydrogen isotopic composition of hydrated volcanic glass delta d g of neogene to quaternary fills in the semiarid intermontane humahuaca basin eastern cordillera northwest argentina to spatiotemporal changes in topography and associated orographic effects delta d values from volcanic glass in the basin strata 117 parts per thousand to 98 parts per thousand show two main trends that accompany observed tectonosedimentary events in the study area between 6 0 and 3 5 ma delta d g values decrease by similar to 17 parts per thousand this is associated with surface uplift in the catchment area after 3 5 ma delta d g values show abrupt deuterium enrichment which we associate with 1 the attainment of threshold elevations for blocking moisture transport in the basin bounding ranges to the east and 2 the onset of semiarid conditions in the basin such orographic barriers throughout the eastern flanks of the central andes have impeded moisture transport into the orogen interior this has likely helped maintain aridity and internal drainage conditions on the adjacent andean plateau

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

distinguishing allogenic from autogenic causes of bed elevation change in late quaternary alluvial stratigraphic records abstract allogenic and autogenic mechanisms both cause changes in the bed elevation of rivers and thereby influence the characteristics of alluvial stratigraphic records asrs allogenic forcing mechanisms can be grouped into five categories whose relative influence varies with timescale climate tectonism base level land use land cover and direct human modification of channels late quaternary asrs are influenced by the greatest range of allogenic forcing variables with climate among the most important autogenic mechanisms of bed elevation change are ubiquitous throughout fluvial systems and are always time transgressive autogenic bed elevation change propagates through drainage networks at predictable rates and results in a time space envelope within which its effects are capable of operating asrs that can be correlated over geographical areas large enough and time intervals small enough to exist outside this envelope most likely result from allogenic forcing this formulation represents a quantitative and geographic set of threshold criteria for distinguishing between autogenic and allogenic mechanisms over late quaternary timescales 10 2 to 10 5 years in tectonically stable regions climate change is the dominant allogenic mechanism and therefore the first order control on the morphology sedimentology pedologic characteristics and chronology of alluvial stratigraphic records that meet or exceed the threshold criteria for demonstrating allogenic causality

a geologically constrained monte carlo approach to modeling exposure ages from profiles of cosmogenic nuclides an example from lees ferry arizona we present a user friendly and versatile monte carlo simulator for modeling profiles of in situ terrestrial cosmogenic nuclides tcns our program available online at http geochronology earthsciences dal ca downloads models html permits the incorporation of site specific geologic knowledge to calculate most probable values for exposure age erosion rate and inherited nuclide concentration while providing a rigorous treatment of their uncertainties the simulator is demonstrated with 10be data from a fluvial terrace at lees ferry arizona interpreted constraints on erosion based on local soil properties and terrace morphology yield a most probable exposure age and inheritance of 83 9 14 1 19 1 ka and 9 49 2 52 1 21 104 atoms g 1 respectively 2 without the ability to apply some constraint to either erosion rate or age shallow depth profiles of any cosmogenic nuclide except for nuclides produced via thermal and epithermal neutron capture e g 36cl cannot be optimized to resolve either parameter contrasting simulations of 10be data from both sand and pebble sized clasts within the same deposit indicate grain size can significantly affect the ability to model ages with tcn depth profiles and when possible sand not pebbles should be used for depth profile exposure dating

load strengthening versus load weakening faulting increases in shear stress along a fault during loading to failure cannot generally occur without changes in the normal stress across the fault n the fault loading parameter n n pf distinguishes situations of load strengthening n 0 where the frictional shear strength of faults increases as tectonic shear stress rises from load weakening environments n t6 0 where it decreases compressional faulting in tectonic regimes with v 3 is always load strengthening unless fluid pressure is rapidly increasing extensional faulting in regimes where v 1 is load weakening unless fluid pressure is dropping rapidly strike slip faulting in terrains where v 2 can be either load weakening or load strengthening the particular case where n 0 so that frictional shear strength stays constant during fault loading is a very special situation corresponding to direct shear load strengthening strike slip faulting appears to correlate with tectonic transpression and load weakening with transtension differing loading characteristics of faults in different tectonic regimes must induce varying patterns of cyclic fluid redistribution accompanying the seismic cycle with implications for earthquake recurrence and precursory groundwater phenomena

displacement geometry in the volume containing a single normal fault fault displacements measured in coal mines and from seismic data are used to develop a model describing the near field displacements associated with an ideal single normal fault displacement on a fault surface ranges from a maximum at the center of the fault to zero at the edge or tip line the tip line is elliptical with the shorter axis of the ellipse parallel to the displacement direction contours of equal displacement form concentric ellipses centered on the point of maximum displacement displacement gradients vary with fault size and with mechanical properties of host rock fault radius to maximum displacement ratios range from 5 to 500 plotting of displacement contour diagrams and knowledge of displacement gradients are useful in interpreting seismic reflectio data both for quality control of interpretations and for quantitative extrapolation of limited data displacements associated with faulting decrease systematically with increasing distance along the normal to the fault surface this decrease is seen as reverse drag in both hanging wall and footwall hanging wall rollover and tilting of the reflectors cannot be used to distinguish listric from planar normal faults even where fault block rotation can be demonstrated neither listric fault geometry nor a flat detachment surface is geometrically necessary because faulting is accommodated by ductile deformation rigid fault bounded blocks cannot exist except in some special circumstances related to a free surface the displacements within the rock volume affected by a single fault are not simply related to regional extension apparent horizontal extension by faulting varies from one layer to another and a significant proportion of the extension in a basin may be due to ductile deformation

local erosion rates versus active tectonics cosmic ray exposure modelling in provence south east france over the past decade in situ produced cosmogenic nuclides have revolutionised the study of landscape evolution in particular numerous studies have demonstrated that in active tectonic settings cosmic ray exposure dating of deformed or displaced geomorphic features makes it possible to quantify long term deformation rates in western european countries erosion due to climatically driven processes and human activities is probably the factor that most limits the accuracy of exposure ages and landscape modification rates in this study we present the results of a depth profiling technique applied to alluvial terraces located along the rhone and the moyenne durance rivers the expected decrease with depth of the measured 10be concentrations has been modelled using a 2 inversion method in order to constrain the exposure history of the alluvial sediments the results suggest that 1 over the quaternary the local surface erosion rates including both regional uplift and climatically driven processes acting on landforms are on the order of 30 m myr in southeastern france and 2 providing a fairly good bracketing of the exposure age the modelled abandonment age of alluvial terraces affected by the moyenne durance fault allows estimating incision rates comparing the alluvial terrace elevations with topographic river profiles and a minimum vertical slip rate value of roughly 0 02 mm yr for the southern segment of the moyenne durance fault

single grain cosmogenic 21ne concentrations in fluvial sediments reveal spatially variable erosion rates we evaluated the hypothesis that the spatial variation in erosion in a catchment is reflected in the distribution of the cosmogenic nuclide concentrations in sediments leaving the catchment using published data and four new 10be measurements in fluvial sediment collected from the outlets of small river catchments we constrained the spatial variability of erosion rates in the gaub river catchment in namibia we combined these catchment averaged erosion rates and the mean slope values with which they are associated in a digital elevation model dem based analysis to predict distributions of cosmogenic 21ne concentrations in the sediment leaving the gaub catchment we compared these synthetic distributions with the distribution of concentrations of cosmogenic 21ne 21nec in 32 quartz fluvial pebbles 16 21 mm collected from the catchment outlet the 21nec concentrations span nearly two orders of magnitude 2 6 160 106 atoms g and are highly skewed toward low values the dem based analysis confirms this skew the measured 21nec distribution plots within the envelope of distributions predicted for the catchment this match between measured and synthetic 21ne distributions implies that the measured distribution is a signature of the spatial variation in erosion rates

planar high angle faulting in the basin and range geodetic analysis of the 1983 borah peak idaho earthquake geodetic elevation changes record the broad scale deformation associated with the m 7 0 october 28 1983 borah peak idaho earthquake on the lost river fault the crest of the lost river range rose 0 2 m and adjacent thousand springs valley subsided 1 0 m in relation to reference points 45 km from the main shock epicenter the deformation was modeled by dislocations in an elastic half space a planar fault with uniform dip slip of 2 05 0 10 m dipping 47 o 2osw and extending to a vertical depth of 13 3 1 2 km fits the geodetic data best and is also consistent with the main shock hypocenter and fault plane solution the geodetic moment is 2 6 0 5 x 1019 n m 2 6 0 5 x 1026 dyn cm and the estimated static stress drop is 2 9 0 4 mpa 29 4 bars tests for coseismic slip on listric faults which flatten with depth and on detachments horizontal faults or shear zones showed fits to the geodetic data that are inferior to those for planar high angle faults no detectable coseismic slip occurred on the mesozoic white knob thrust fault although the low angle thrust sheet intersects the south end of lost river fault near the 1983 mainshock epicenter if the high angle lost river fault abuts a flat lying detachment fault or shear zone such a structure must lie at depths of 12 km near the brittle ductile transition where stick slip behavior gives way to creep the depth and geometry of faulting at borah peak is similar to that inferred from seismic and geodetic evidence for the 1954 m 7 2 fairview peak nevada and the 1959 m 7 3 hebgen lake montana events suggesting that if detachments are active at these localities they are deep and most likely slip by creep

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

the puncoviscana trough a large basin of late precambrian to early cambrian age on the pacific edge of the brazilian shield during the late precambrian to early cambrian a large basin with a homogeneous psammitic pelitic sediment fill existed in the area of the nw argentine andes it is now exposed in different tectonic levels this basin of meridional elongation was situated on a stable continental margin at the western edge of the brazilian shield it was underlain by segmented older continental crust according to the modal and chemical composition of the greywackes and subgreywackes a predominant metasedimentary source may be supposed four clastic facies types indicate a transport by gravity currents within a submarine fan system while massive red pelites represent cut off periods and rare carbonates deposition on rises the gravity currents derived from easterly directions the sedimentation age is proved by a rich ichnofauna and some medusoid impressions

the growth of geological structures by repeated earthquakes 2 field examples of continental dip slip faults a strong test of our understanding of the earthquake cycle is the ability to reproduce extant fault bounded geological structures such as basins and ranges which are built by repeated cycles of deformation along strike slip faults the coseismic and interseismic deformation can be nearly equal in magnitude and opposite in sign resulting in little permanent deformation except for the fault offset for dip slip faults portions of the crust are lifted and dropped and so buoyancy forces are exerted the seismic and interseismic deformations do not balance and structures grow and become subject to erosion and deposition we consider three examples for which the structure and fault geometry are well known the white wolf reverse fault in california site of the 1952 kern county m 7 3 earthquake the lost river normal fault in idaho site of the 1983 borah peak m 7 0 earthquake and the cricket mountain normal fault in utah site of quaternary slip events basin stratigraphy and seismic reflection records are used to profile the structure and coseismic deformation measured by leveling surveys is used to estimate the fault geometry to reproduce these structures we add the deformation associated with the earthquake cycle the coseismic slip and postseismic relaxation to the flexure caused by the observed sediment load treating the crust as a thin elastic plate overlying a fluid substrate the cumulative deformation is principally dependent on the elastic plate thickness modestly sensitive to the sediment substrate density difference and insensitive to the fluid viscosity for the 4 to 8 ma structures we deduce a longterm flexural rigidity of 2 15 1019 nm this is equivalent to an elastic plate thickness of 2 4 km for a young s modulus of 2 5 1010 nm 2 this value is found where independent estimates of the elastic thickness from the coherence between surface topography and gravity yield values of about 4 km but where coseismic fault slip extends to a depth of 10 15 km thus much of the seismogenic crust must weaken substantially during the life of active faults causing the fault bounded basins to narrow over time

chaco low level jet events characterization during the austral summer season 1 previous studies showed a relationship between convection maxima and the convergence of vapor flux over southeastern south america nicolini and saulo 2000 explored the hypothesis of an intensification of this mutual dependency during the chaco jet events they defined these events as extreme cases of low level jets east of the andes that penetrate southernmost to 25 s using eta operative products during the 1997 1998 austral warm season the interest of the present paper centers on the climatic characterization of the chaco jet events cjes and the possibility of researching this hypothesis using the european centre for medium range weather forecasts reanalyses era which cover a 15 year period 1979 1993 the cjes represent a subensemble of low level jet events east of the andes that are infrequent in the era data set their duration varies from 1 to 10 days more frequently extending from 1 to 5 days the outstanding features of the circulation and the thermodynamic field that represent this ensemble are a maximum contrast of air masses in a latitude close to 39 s the presence of a trough centered on 70 w within a baroclinic wave train penetrating from the pacific ocean and a maximum of heat and moisture over northen argentina and paraguay during the cjes there is an important flux of moisture and convergence at low and mid levels that is about 10 times more intense than the summer mean the intensity found in the water vapor flux anomaly reinforces the importance of studying these episodes for the purpose of determining the water balance over southeastern south america the statement that the cjes represent an important characteristic of the southeastern south american climate is founded on the fact that although the cjes only represent 17 of the austral summer days they account for a significant fraction of the precipitation a maximun of 55 over northeastern argentina however it is indispensable to contrast these results with future field experiments to test the hypothesis addressed in this paper

climatic controls on debris flow activity and sediment aggradation the del medio fan nw argentina in the central andes several studies on alluvial terraces and valley fills have linked sediment aggradation to periods of enhanced sediment supply however debate continues over whether tectonic or climatic factors are most important in triggering the enhanced supply the del medio catchment in the humahuaca basin eastern cordillera nw argentina is located within a transition zone between sub humid and arid climates and hosts the only active debris flow fan within this intermontane valley by combining 10be analyses of boulder and sediment samples within the del medio catchment with regional morphometric measurements of nearby catchments we identify the surface processes responsible for aggradation in the del medio fan and their likely triggers we find that the fan surface has been shaped by debris flows and channel avulsions during the last 400 years among potential tectonic climatic and autogenic factors that might influence deposition our analyses point to a combination of several favorable factors that drive aggradation these are in particular the impact of occasional abundant rainfall on steep slopes in rock types prone to failure located in a region characterized by relatively low rainfall amounts and limited transport capacity these characteristics are primarily associated with the climatic transition zone between the humid foreland and the arid orogen interior which creates an imbalance between sediment supply and sediment transfer the conditions and processes that drive aggradation in the del medio catchment today may provide a modern analog for the conditions and processes that drove aggradation in other nearby tributaries in the past

too young or too old evaluating cosmogenic exposure dating based on an analysis of compiled boulder exposure ages cosmogenic exposure dating has greatly enhanced our ability to define glacial chronologies spanning several global cold periods and glacial boulder exposure ages are now routinely used to constrai

listric versus planar normal fault geometry an example from the eisenstadt sopron basin e austria in a gravel pit at the eastern margin of the eisenstadt sopron basin a satellite of vienna basin austria neogene sediments are exposed in the hanging wall of a major normal fault the anticlinal structure and associated conjugated secondary normal faults were previously interpreted as a rollover anticline above a listric normal fault the spatial orientation and distribution of sedimentary horizons and crosscutting faults were mapped in detail on a laser scan of the outcrop wall subsequently in order to assess the 3d distribution and geometry of this fault system a series of parallel ground penetrating radar gpr profiles were recorded behind the outcrop wall both outcrop and gpr data were compiled in a 3d structural model providing the basis for a kinematic reconstruction of the fault plane using balanced cross section techniques however the kinematic reconstruction results in a geologically meaningless normal fault cutting down and up section additionally no evidence for a weak layer serving as ductile detachment horizon i e salt or clay horizon can be identified in stratigraphic profiles instead the observed deflection of stratigraphic horizons may be caused by a displacement gradient along a planar master fault with a maximum displacement in the fault centre decreasing towards the fault tips accordingly the observed deflection of markers in the hanging wall and in a nearby location in the footwall of the normal fault is interpreted as large scale fault drag along a planar fault that records a displacement gradient instead of a rollover anticline related to a listric fault

modelling of bed contours and cross sections adjacent to planar normal faults the geometry of beds in the volume surrounding a single blind planar fault depends on i the axial ratio of the fault surface ellipse ii the ratio between the maximum displacement and the maximum dimension of the fault surface iii the displacement distribution on the fault surface from the point of maximum displacement to zero displacement at the tip line loop fault surface displacement profile and iv the rate at which the displacement decreases to zero along a normal to the fault surface reverse drag displacement profile these relationships which are either known or can be estimated are incorporated in a computer model which generates structural contours on horizons intersected by a planar fault structural contour patterns also vary with the pre faulting dip and strike of beds the dip and strike of the fault and the level at which a bed intersects the fault surface when the boundary conditions are relaxed to include synsedimentary faults the ratio of hangingwall to footwall displacement varies systematically with fault dip a synthetic structural contour map is matched with that of an actual fault model isopachs based on simple depositional models are generated for synsedimentary units cross sections are generated for synsedimentary faults by sequential fault growth and sedimentary deposition and show features similar to actual cross sections the soft domino model is applicable primarily to dip slip tectonic faults with maximum displacements of up to about 5 km listric faults are not considered

average pleistocene climatic patterns in the southern central andes controls on mountain glaciation and paleoclimate implications abstract despite elevations of 5000 6800 m modern glaciers occur along the southern puna plateau and the northern sierras pampeanas in the southern central andes the modern snowline rises from 5100 m in sierra aconquija to 5800 m in the puna as a result of a westward decrease in precipitation from 450 to less than 100 mm yr during the pleistocene these arid highlands experienced multiple cirque and valley glaciation that likely postdate the last interglacial period although lack of age control prevents an absolute chronology glaciation in the puna and along the eastern puna edge produced a 300 m pleistocene snowline psl depression while in the sierras pampeanas the psl depression was at least 900 m the greater psl depression in the sierras pampeanas is best explained by a combination of cooling and increase of easterly moisture whereas the psl depression in the puna appears more sensitive to moisture increases than temperature previously glaciations in this region have been explained by increa

large rockslides in the southern central andes of chile 32 34 5 s tectonic control and significance for quaternary landscape evolution abstract the distribution and age of large 0 1 km2 pliocene to recent rockslides in the chilean cordillera principal 32 34 5 s the southern central andes has been analyzed to determine the rockslide triggering mechanisms and impact on regional landscape evolution most of the rockslides appear in the western cordillera principal and cluster along major geological structures variographic analyses show spatial correlation between rockslides geological structures and shallow seismicity a relative chronosequence was calibrated with existing 14c and 40ar 39ar dates and new cosmogenic nuclide exposure ages for selected rockslides rockslide induced sediment yield was estimated with empirical relations for rockslide area distributions throughout the quaternary rockslides have delivered sediment to streams at rates equivalent to denudation rates of 0 10 0 06 mm a 1 while estimates using short term 20 a seismicity records are 0 3 0 2 0 6 mm a 1 the estimates of sediment transfer and the spatial distribution of rockslides reflect a landscape in which tectonic and geological controls on denudation are more significant than climate

the geometrical evolution of normal fault systems abstract the purpose of this paper is to examine the kinematic behaviour of normal fault systems and see what general conditions govern their geometrical evolution we pay particular attention to seismological and surface data from regions of present day active normal faulting as the instantaneous three dimensional geometry at the time of fault movement is better known in active regions than in areas where the faults are now static most normal faults are concave upward or listric this shape can be produced by geometric constraints either because the faults reactivate curved thrusts or because they must be curved to accommodate rotations another effect which will produce curved faults is the variation of rheology with depth brittle failure at shallow depths produces less fault rotation than does distributed creep in the lower part of the crust an important geometric feature of normal faulting is the uplift of the footwall the amount of such uplift is related not only to the elastic properties of the lithosphere but also to the throw and dip of the fault a striking feature of active normal faults is that they occur in groups in which all the faults dip in the same direction this behaviour arises because the faults cannot intersect if they do one must cease to be active the rotation which such fault systems produce reduces the dip of the faults until a new steeply dipping fault is formed once a new fault cuts pre existing faults the earlier faults become locked and a new set of faults must propagate rapidly across the whole region involved many of these geometric constraints also apply to thrust faulting

stable isotope constraints on the transport of water to the andes between 22 and 26 s during the last glacial cycle abstract the modern climate over much of the andes between 22 and 26 s is very dry dated sediment cores from desiccated lake beds contain saline deposits salars that have halite fabrics that indicate during previous less arid climates saline lakes existed at salar de hombre muerto northwest argentina andean plateau and salar de atacama northern chile west flank of andes paleoclimate conditions are reconstructed from the stable isotope composition of paleo saline lake waters trapped in fluid inclusions in lacustrine halite models of isotopic steady state are applied to estimate the isotopic composition of inflow meteoric water to the paleo lake and paleo atmospheric water vapor the two salars climate records differ the timing of atacama saline lakes is similar to lake level highstands on the altiplano to the northeast with the deepest lake occurring between 24 and 19 8 ka the modern meteoric water source for atacama and the central andes is currently the tropical atlantic via the amazon basin and stable isotopic evidence indicates the same source of water for the paleo lakes in the atacama in contrast to the southeast at hombre muerto the lakes that intermittently occupied the salar became progressively smaller since 45 ka water isotope composition today reflects atmospheric recycling by evaporation condensation as it did between 24 and 20 ka whereas water transported to the earlier lakes does not indicate significant isotopic recycling using knowledge of modern day atmosphere oceanic circulation and forcing mechanisms we hypothesize that the shifts in moisture transport to these andean sites are directly tied to equatorial and south atlantic atmospheric and oceanic surface circulation

field examples and numerical modelling of oversteps and bends along normal faults in cross section abstract oversteps and bends along cross sections through small scale numerical modelling distinct element analysis has been carried out to simulate the patterns of deformation at oversteps and bends area increase pull apart development and localised stress concentration occur at extensional oversteps and bends stress concentration and a tendency for compaction are typical of contractional oversteps and bends such results are compatible with the structures observed in the field a sensitivity analysis of the modelling has been carried out to investigate the effects of variations in mechanical parameters on deformation although models with weaker properties are more deformable the overall geometry of deformation varies little with variations in mechanical parameters

the growth of geological structures by repeated earthquakes 1 conceptual framework in many places earthquakes with similar characteristics have been shown to recur if this is common then relatively small deformations associated with individual earthquake cycles should accumulate over time to create geological structures following this paradigm we show that existing models developed to describe leveling line changes associated with the seismic cycle can be adapted to explain geological features associated with a fault in these models an elastic layer containing the fault overlies a viscous half space with a different density fault motion associated with an earthquake results in immediate deformation followed by a long period of readjustment as stresses relax in the viscous layer and isostatic equilibrium is restored deformation is also caused as a result of the loading and unloading due to sediment deposition and erosion in this paper the parameters that control the growth of dip slip structures are identified we find that the flexural rigidity of the crust or the apparent elastic thickness provides the main control of the width of a structure the loading due to erosion and deposition of sediment determines the ratio of uplift to subsidence between the two sides of the fault the flexure due to sediment load is much more important in this respect than whether the fault is normal or reverse in character we find that in general real structures are associated with apparent elastic thicknesses of 4 km or less and thus with very low flexural rigidities

lacustrine chronology links late pleistocene climate change and mass movements in northern new mexico well dated lacustrine deposits in northern white rock canyon new mexico record damming of the rio grande by at least four separate failures of a slump complex between about 17 5 and 12 4 ka sup 14 c linking mass movements to a period of rapid climate change in the western united states failure of metastable slumps probably resulted from removal of lateral support during down cutting and erosion by the rio grande and from a decrease in resisting forces due to increased pore pressures our chronology suggests that the lake that formed between 17 5 and 15 0 ka may record effects of both glacial melt and pluvial activity mainly enhanced rainfall the youngest lake neary 12 4 ka may record pluvial runoff and the intermediate lakes 13 7 to 13 1 ka may record pluvial and minor melt water activity we have not found lacustrine deposits younger than about 12 4 ka the record of geomorphic response along the rio grande suggests that late pleistocene climatic changes may have triggered similar mass movements elsewhere in the southwest 27 refs 4 figs

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

a cellular model of holocene upland river basin and alluvial fan evolution coulthard t j macklin m g kirkby m j 2002 a cellular model of holocene upland river basin and alluvial fan evolution earth surface processes and landforms 27 3 269 288

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

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

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

millennial scale record of landslides in the andes consistent with earthquake trigger landslide deposits are often interpreted as the consequence of precipitation a millennial scale record of landslides inferred from river cobbles in the arid andes is instead consistent with earthquake triggering

denudation processes and rates in the transverse ranges southern california erosional response of a transitional landscape to external and anthropogenic forcing 1 quantification of denudation in the transverse ranges of california permits reconstruction of spatial and temporal variations in erosion that represent both the response and evolution of interacting hillslopes and channels on the southern front of the san gabriel mountains observational records of the infilling of debris basins and dams define twentieth century landscape erosion rates averaging 1 6 and 0 9 mm yr 1 respectively although all major sediment transport occurs during intense winter storms debris production on hillslopes is greatly enhanced by recurrent fires consequently in this populated region anthropogenic fires have augmented the natural erosion rates we perform a global inversion to estimate the role of precipitation intensity burned areas and local slope on catchment denudation rates after subtracting the effects of anthropogenic fires we estimate landscape denudation rates given natural fire ignition rates increased fire during the past century has augmented sediment production in debris basins by an average of 60 and individual basins show increases up to 400 to identify the dominant hillslope erosion processes the volumetric contribution of landslides was estimated using repeat aerial photographs for the same time interval over which the debris basins have been operative between 1928 and 1973 landsliding produced only 10 of the sediment in debris basins even in the long term when infrequent but volumetrically important landslides occur bedrock landslides appear to contribute a maximum of 50 to the long term landscape denudation previous mapping of soil slippage in the san dimas experimental forest within the san gabriel mountains rice et al 1969 rice and foggin 1971 indicates that shallow landsliding is likely to be the dominant modern hillslope erosion process when compared to incision rates derived from a fluvial shear stress model and to exhumation rates based on low temperature thermochronological data blythe et al 2000 modern natural erosion rates are comparable to denudation rates since the pliocene comparisons of modern erosion rates suggest that debris production on hillslopes and first order channels is directly dependent on vegetation cover and precipitation intensity for higher order channels drainage areas 2 km2 only major storms convey the sediments down valley during the past century some temporal decorrelation occurs between small scale and large scale catchments because hillslope produced sediment is stored in second order and higher channels until major storms mobilize it thus the larger fluvial network damps the episodic fire induced hillslope sediment pulses that occur within small watersheds at a longer temporal scale however uplift and denudation may have been sustained sufficiently long in much of the san gabriel mountains for the topography to reach a macroscale steady state in contrast to rapidly eroding 2 mm yr 1 ranges for which quantification of bedrock landsliding will approximate the sediment flux the san gabriel mountains occupy a niche of intermediate rates 0 1 1 0 mm yr 1 in which a broad suite of hillslope processes including shallow seated and deep seated landslides debris flows and wet and dry ravel contribute to the sediment flux

drainage basin response to climate change in the pisco valley peru the quaternary development of the pisco valley in central peru has been characterized by multiple phases of sediment accumulation and erosion that formed distinct levels of cut and fill terraces and alluvial fans luminescence dating shows that they formed in response to at least two different stages of sediment accumulation and erosion during the past 60 ka the main phase of sediment aggradation occurring between ca 54 and 38 ka ago the ages show that sediment accumulation was contemporaneous with the time intervals of the minchin 47 8 36 ka ago with enhanced precipitation beginning ca 54 8 ka ago and tauca 26 14 9 ka ago paleolakes on the altiplano where the headwaters of the pisco river are located we conclude that sediment accumulation was triggered by shifts toward a more humid climate whereas erosion is the response of the fluvial system to the depletion of the hillslope sediment reservoirs

effects of layering and anisotropy on fault geometry the geometry and orientation of faults are examined using several field examples of small scale 1 with dihedral angles usually of about 50 as predicted by the coulomb theory of failure in layered rocks the geometry of faults varies with the orientation of layering with respect to the stress field where 1 is approximately normal to layering or anisotropy conjugate faults also develop symmetrically about 1 where rocks have interbedded layers with different mechanical behaviours however faults tend to initiate orthogonal to the more brittle layers i e originate as extension fractures sub parallel to 1 but oblique to the less brittle layers as the fault steps through the layering pull aparts are developed which may reduce the dihedral angle where 1 is oblique c 25 75 to anisotropy one set of faults is developed at a high angle to layering with another at a low angle usually showing a ramp flat geometry large dihedral angles up to 90 may result and 1 does not bisect this angle where 1 is approximately parallel to layering two cases can be recognized where 3 is approximately normal to layering faults with layer parallel flats and contractional ramps develop where 2 is approximately normal to layering conjugate faults develop which are symmetrical about 1 the geometry resembling that in isotropic rocks these observations are in agreement with rock deformation experiments which show the strong effect of anisotropy on fault orientation but the observations incorporate the effects of layering of materials with different deformation characteristics

paleo erosion rates and climate shifts recorded by quaternary cut and fill sequences in the pisco valley central peru fluvial cut and fill sequences have frequently been reported from various sites on earth nevertheless the information about the past erosional regime and hydrological conditions have not yet been adequately deciphered from these archives the quaternary terrace sequences in the pisco valley located at ca 13 s offer a manifestation of an orbitally driven cyclicity in terrace construction where phases of sediment accumulation have been related to the minchin 48 36 ka and tauca 26 15 ka lake level highstands on the altiplano here we present a 10be based sediment budget for the cut and fill terrace sequences in this valley to quantify the orbitally forced changes in precipitation and erosion we find that the minchin period was characterized by an erosional pulse along the pacific coast where denudation rates reached values as high as 600 80 mm ka600 80 mm ka for a relatively short time span lasting a few thousands of years this contrasts to the younger pluvial periods and the modern situation when 10be based sediment budgets register nearly zero erosion at the pacific coast we relate these contrasts to different erosional conditions between the modern and the minchin time first the sediment budget infers a precipitation pattern that matches with the modern climate ca 1000 km farther north where highly erratic and extreme el nino related precipitation results in fast erosion and flooding along the coast second the formation of a thick terrace sequence requires sufficient material on catchment hillslopes to be stripped off by erosion this was most likely the case immediately before the start of the minchin period because this erosional epoch was preceded by a 50 ka long time span with poorly erosive climate conditions allowing for sufficient regolith to build up on the hillslopes finally this study suggests a strong control of orbitally and ice sheet forced latitudinal shifts of the itcz on the erosional gradients and sediment production on the western escarpment of the peruvian andes at 13 during the minchin period

orographic barriers high resolution trmm rainfall and relief variations along the eastern andes 1 quantifying the degree to which tectonic and erosive processes shape landscapes is key to understanding the evolution of tectonically active mountain belts here we explore the interplay of these two processes along the humid eastern flank of the south american andes we use high resolution tropical rainfall measurement mission trmm and srtm data to characterize elevation relief and hillslope angle of peak rainfall at orographic barriers over a distance of more than 3500 km along the eastern flanks we find that peak rainfall 3 5 m yr occurs at a mean elevation of 1 3 0 17 km a mean relief of 0 95 0 08 km and at moderate mean hillslope angles of 18 3 1 7 we suggest that topographic relief is the best first order rainfall predictor and we demonstrate how relief changes along strike south of the andean orocline alter rainfall distribution changes in climatic sedimentary and tectonic processes prevent the formation of high relief amounts at the mountain front and these areas are not characterized by pronounced rainfall peak

a model for turbulent hydraulic fracture and application to crack propagation at glacier beds glaciological observations of under flooding suggest that fluid induced hydraulic fracture of an ice sheet from its bed sometimes occurs quickly possibly driven by turbulently flowing water in a broad sheet flow taking the approximation of a fully turbulent flow into an elastic ice medium with small fracture toughness we derive an approximate expression for the crack tip speed opening displacement and pressure profile we accomplish this by first showing that a manning strickler channel model for resistance to turbulent flow leads to a mathematical structure somewhat similar to that for resistance to laminar flow of a power law viscous fluid we then adapt the plane strain asymptotic crack solution of desroches et al 1994 and the power law self similar solution of adachi and detournay 2002 for that case to calculate the desired quantities the speed of crack growth is shown to scale as the overpressure in excess of ice overburden to the power 7 6 inversely as ice elastic modulus to the power 2 3 and as the ratio of crack length to wall roughness scale to the power 1 6 we tentatively apply our model by choosing parameter values thought appropriate for a basal crack driven by the rapid drainage of a surface meltwater lake near the margin of the greenland ice sheet making various approximations perhaps relevant to this setting we estimate fluid inflow rate to the basal fracture and vertical and horizontal surface displacements and find order of magnitude agreement with observations by das et al 2008 associated with lake drainage finally we discuss how these preliminary estimates could be improved

late pleistocene fans and terraces in the majes valley southern peru and their relation to climatic variations this study investigates the connection between sediment aggradation erosion and climate in a desert environment of the majes valley southern peru luminescence dating of terraces and fans shows that sediment aggradation correlates with wet time intervals on the altiplano suggesting a climatic influence on the aggradation degradation cycles major periods of aggradation occurred between 110 100 60 50 and 12 8 ka more precipitation in the majes catchment resulted in increased erosion and transportation of sediment from the hillslopes into the trunk river as a result the sediment loads exceeded the transport capacity of the majes river and aggradation started in the lower reaches where the river gradient is less depletion of the hillslope sediment reservoirs caused a relative increase in the capacity of the trunk river to entrain and transport sediment resulting in erosion of the previously deposited sediment consequently although climate change may initiate a phase of sediment accumulation degradation can be triggered by an autocyclic negative feedback and does not have to be driven by climatic change

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

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

identifying fault segments from 3d fault drag analysis vienna basin austria abstract the segmented growth of the markgrafneusiedl normal fault in the late miocene clastic sediments of the central vienna basin austria was investigated by construction of a detailed three dimensional 3d structural model using high resolution 3d seismic data the fault surface and marker horizons in the hanging wall and the footwall of the markgrafneusiedl fault were mapped and orientation displacement and morphology of the fault surface were quantified individual fault segments were identified by direct mapping of the deflection of the marker horizons close to the fault surface correlating the size of the identified segments with the magnitude of fault drag and displacement distribution showed that fault evolution progressed in several stages the proposed method allows the detection of segments that are not recorded by the magnitude of displacement or fault morphology most importantly detailed mapping of marker deflections in the hanging wall could help to constrain equivalent structures in the footwall which may represent potential hydrocarbon traps

bedrock fracture control of glacial erosion processes and rates the importance of rock type and tectonic history on rates of glacial erosion and the relative roles of glacial quarrying and abrasion are poorly understood we use concentrations of cosmogenic 10be in glacial polish and measurements of bedrock fracture spacing to explore the relationship between erosion rates and rock fracturing at 23 sites along tuolumne river valley and five sites in tenaya canyon in yosemite national park california usa most sites yield 10be concentrations that can be best explained as reflecting solely postglacial nuclide accumulation six sites however display anomalously high concentrations implying incomplete removal of the pre glacial nuclide inventory during the last glaciation these require that erosion in the last glacial cycle was 2 3 m these low erosion sites occur preferentially in massive units of the cathedral peak granodiorite and the el capitan granite fractures in high erosion sites are more closely spaced than in low erosion sites with spacings that average 1 1 0 03 m and 3 3 0 1 m respectively our data suggest that the distance between fractures in the rock dictated in part by the original spacing in a particular pluton and in part by the specific tectonic history of the sierra nevada governs the pace of glacial erosion in yosemite

response of intracontinental deformation in the central andes to late cenozoic reorganization of south american plate motions new stratigraphic chronologic and fault kinematic data from the quebrada del toro in northwestern argentina provide a detailed view of late cenozoic kinematic reorganization in the southern central andes the quebrada del toro is a thrust bounded basin filled with 2 km of synorogenic clastic deposits ranging in age from early miocene to holocene as observed elsewhere in northwestern argentina faults in the quebrada del toro record an early phase of horizontal nw se contraction beginning between early and late miocene and ending after 0 98 ma and a later phase of horizontal ne sw contraction beginning between late miocene and 4 17 ma and still active these results require both kinematic regimes to have been active between 4 17 and 0 98 ma compatible with timing and kinematic data from the adjacent central andes and best explained by a temporal pattern of serial recurrence of the kinematic regimes a hypothesis that intraplate deformation in the central andes is driven by the absolute motion of the south american plate with respect to the hotspot reference frame is tested by comparing quebrada del toro kinematics to plate reconstructions and space based geodetic results nazca south america relative motion and absolute nazca plate motion show consistent azimuths throughout the past 20 5 myr in contrast absolute south american plate motion azimuths mimic the changing contraction directions determined from intraplate andean faults although the timing of the south american plate motion change is poorly resolved by current data it is compatible with the quebrada del toro data absolute upper plate motion might control intraplate kinematics along many of the earth s convergent margins

global imaging of polar cap patches with dual airglow imagers during a 2 h interval from 2240 to 2440 ut on 12 november 2012 regions of increased 630 0 nm airglow emissions were simultaneously detected by dual all sky imagers in the polar cap one at longyearbyen norway 78 1 n 15 5 e and the other at resolute bay canada 74 7 n 265 1 e the resolute bay incoherent scatter radar observed clear enhancements of the f region electron density up to 1012 m 3 within these airglow structures which indicates that these are optical manifestations of polar cap patches propagating across the polar cap during this interval of simultaneous airglow imaging the nightside dawnside dayside duskside half of the patches was captured by the imager at longyearbyen resolute bay this unique situation enabled us to estimate the dawn dusk extent of the patches to be around 1500 km which was at least 60 70 of the width of the antisunward plasma stream seen in the super dual auroral radar network convection maps in contrast to the large extent in the dawn dusk direction the noon midnight thickness of each patch was less than 500 km these observations demonstrate that there exists a class of patches showing cigar shaped structures such patches could be produced in a wide range of local time on the dayside nearly simultaneously and spread across many hours of local time soon after their generation