orogen response to changes in climatic and tectonic forcing despite much progress many questions remain regarding the potential dynamic coupling between atmospheric and lithospheric processes in the long term evolution of mountain belts as a complement to recent efforts to discover the interrelationships among climate topography erosion and rock deformation under conditions of mass flux steady state we explore orogen response to changes in climate and tectonic influx we derive an analytical model that predicts a powerful climatic control on orogen evolution and distinct potentially diagnostic responses to climatic and tectonic perturbations due to isostatic compensation the near surface rock uplift rate during transients is tightly coupled to climate modulated erosional efficiency system response is approximately exponential with a characteristic response timescale that is inversely proportional to the climate and lithology modulated erosional efficiency and is largely insensitive to initial conditions tectonic influx and both the sign and magnitude of perturbations

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

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

post tectonic landscape evolution of a coupled basin and range pinaleno mountains and safford basin southeastern arizona the pinaleno mountains and adjacent safford basin are a landscape defined by the extensional tectonics of the basin and range physiographic province however over the last 4 m y this coupled basin and range have been actively degrading in the absence of widespread regional extension while rates of relief generation and upland erosion during active subsidence ca 12 5 ma are reflected in the geometry of the basin s structure and the stratigraphy it contains rates of post tectonic landscape evolution from the pliocene to the present have been heretofore unknown we combined topographic analyses of the pinaleno mountains with cosmogenic nuclide derived catchment averaged erosion rates and burial dates of axial and piedmont deposits to quantify rates of post tectonic landscape evolution and define a chronology for the last stages of deposition and subsequent incision in safford basin in addition to constraining the timing of a deposit s formation cosmogenic nuclide burial dates provide paleo upland erosion rates at the time of deposition erosion rates in the pinaleno mountains have been generally moderate over the past 4 m y ranging between 30 and 60 m m y with no strong relationship to the drainage basins modern topography a potential acceleration of erosion rates to 100 250 m m y between 3 5 and 2 ma correlates with an inferred period of enhanced precipitation as well as the arrival from upstream of the gila river in safford basin sometime shortly before 2 8 ma widespread incision of safford basin was under way by ca 2 ma as recorded by the dissection of piedmont basin highstand deposits frye mesa and two intermediate gila river terraces on the northeast margin of safford basin dated to 1 8 ma and 0 64 ma gila river incision rates have ranged from 30 to 60 m m y over the past 3 m y paleo upland erosion rates and modern millennial scale upland erosion rates fall within the same range as incision rates of the gila river in safford basin suggesting that upland erosion rates are predominantly a function of base level fall driven by axial incision however based on similarities between catchment averaged erosion rates and topography from basins draining into the integrated safford basin and the still internally drained sulphur springs basin to the south it appears that upland erosion rates during the quaternary are not being driven exclusively by regional incision rates

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

landscape form and millennial erosion rates in the san gabriel mountains ca abstract it has been long hypothesized that topography as well as climate and rock strength exert first order controls on erosion rates here we use detrital cosmogenic 10 be from 50 basins ranging in size from 1 to 150 km 2 to measure millennial erosion rates across the san gabriel mountains in southern california where a strong e w gradient in relief compared to weak variation in precipitation and lithology allow us to isolate the relationship between topographic form and erosion rate our erosion rates range from 35 to 1100 m ma and generally agree with both decadal sediment fluxes and long term exhumation rates inferred from low temperature thermochronometry catchment mean hillslope angle increases with erosion rate until 300 m ma at which point slopes become invariant with erosion rate although this sort of relation has been offered as support for non linear models of soil transport we use 1 d analytical hillslope profiles derived from existing soil transport laws to show that a model with soil flux linear in slope but including a slope stability threshold is indistinguishable from a non linear law within the scatter of our data catchment mean normalized channel steepness index increases monotonically though non linearly with erosion rate throughout the san gabriel mountains even where catchment mean hillslope angles have reached a threshold this non linearity can be mostly accounted for by a stochastic threshold incision model though additional factors likely contribute to the observed relationship between channel steepness and erosion rate these findings substantiate the claim that the normalized channel steepness index is an important topographic metric in active ranges

evidence for basaltic volcanism on the moon within the past 100 million years the majority of basaltic volcanism on the moon occurred more than 3 billion years ago small mounded formations on the lunar nearside may be products of basaltic eruptions less than 100 million years ago suggesting a long decline of magmatic activity

resolving time space histories of late cenozoic bedrock incision along the upper colorado river usa abstract the upper colorado river basin drains the western slope of the rocky mountains province of north america and hosts a rich record of fluvial terraces and volcanic deposits that provide an archive of bedrock river incision since the late miocene here we present new geochronology from fluvial deposits and associated volcanic units using multiple methods luminescence cosmogenic burial 40ar 39ar basalt and detrital sanidine and u pb detrital zircon to reconstruct a detailed record of bedrock incision in the upper colorado river over timescales ranging from miocene to late pleistocene late miocene ca 11 8 ma basalt flows perched 800 1700 m above the colorado river and the oldest known ancestral colorado river deposits preserved beneath basalt flows on grand mesa provide the basis for average long term 107 yr incision rates rates range from 110 160 m ma between grand junction downstream and glenwood canyon upstream with rates decreasing upvalley intermediate scale 105 106 yr incision rates are 200 320 m m y over the past 1 3 ma and these rates are faster than the average over the past 8 11 ma short term

gld100 the near global lunar 100 m raster dtm from lroc wac stereo image data 1 we derived near global lunar topography from stereo image data acquired by the wide angle camera wac of the lunar reconnaissance orbiter camera lroc system from polar orbit tracks the lroc wac provides image data with a mean ground resolution at nadir of 75 m pixel with substantial cross track stereo overlap wac stereo images from the one year nominal mission and the first months of the science mission phase are combined to produce a near global digital terrain model dtm with a pixel spacing of 100 m the global lunar dtm 100 m or gld100 it covers 79 s to 79 n latitudes 98 2 of the entire lunar surface we compare the gld100 with results from previous stereo and altimetry based products particularly with the lunar orbiter laser altimeter lola altimetry which is the current topographic reference for the moon we describe typical characteristics of the gld100 and based upon the comparison to the lola data set assess its vertical and lateral resolution and accuracy we conclude that the introduced first version of the stereo based gld100 is a valuable topographic representation of the lunar surface complementary to the lola altimetry data set further improvements can be expected from continuative investigations

rock uplift rates in south africa from isochron burial dating of fluvial and marine terraces the high plateau of southern africa is considered to be either uplifting due to mantle driven dynamic topography or to have been stable since mesozoic rifting to address this debate we determined rock uplift in south africa from the long term incision rate of the sundays river near port elizabeth and from an uplifted marine terrace near durban we dated the terraces with cosmogenic 26 al and 10 be using both isochron and simple burial dating methods we find that the sundays river has incised at 16 1 1 3 m m y for the past 4 m y and the marine terrace yields a rock uplift rate of 9 4 2 2 m m y these results are inconsistent with rapid neogene uplift

biostratigraphy and magnetostratigraphy late pliocene rocks 111 ranch arizona fossiliferous strata exposed along the northwestern flank of dry mountain on the 111 ranch 27 km southeast of safford graham county arizona were dated by means of isotopic methods and the magnetic reversal time scale a 100 m fossiliferous interval contains the later part of the gauss chron and the early part pre olduvai of the matuyama chron zircon fission track ages on an ash bed just below the gauss matuyama boundary support this identification owing to these age constraints the fossil mammals at the 111 ranch locality are all constrained within the later part of the blancan mammal age rather than the latest blancan and early irvingtonian as previously stated in the literature they are therefore synchronous with certain localities wolf ranch and california inst technology in the saint david formation of the san pedro valley 130 km to the southwest of dry mountain the horse nannippus persisted in the 111 ranch locality at least until the end of the gauss chron in confirmation of data from the san pedro valley a diverse group of equine and asinine equids is evident in the 111 ranch fauna which argues for an early divergence of these major branches of horse phylogeny the 111 ranch fauna records the first appearance of three neotropical immigrants in the southwest including the sloth glossotherium the glyptodont glyptotherium and the capybara neochoerus a palearctic immigrant the vole synaptomys is also present

lunar impact basins stratigraphy sequence and ages from superposed impact crater populations measured from lunar orbiter laser altimeter lola data 1 impact basin formation is a fundamental process in the evolution of the moon and records the history of impactors in the early solar system in order to assess the stratigraphy sequence and ages of impact basins and the impactor population as a function of time we have used topography from the lunar orbiter laser altimeter lola on the lunar reconnaissance orbiter lro to measure the superposed impact crater size frequency distributions for 30 lunar basins d 300 km these data generally support the widely used wilhelms sequence of lunar basins although we find significantly higher densities of superposed craters on many lunar basins than derived by wilhelms 50 higher densities our data also provide new insight into the timing of the transition between distinct crater populations characteristic of ancient and young lunar terrains the transition from a lunar impact flux dominated by population 1 to population 2 occurred before the mid nectarian this is before the end of the period of rapid cratering and potentially before the end of the hypothesized late heavy bombardment lola derived crater densities also suggest that many pre nectarian basins such as south pole aitken have been cratered to saturation equilibrium finally both crater counts and stratigraphic observations based on lola data are applicable to specific basin stratigraphic problems of interest for example using these data we suggest that serenitatis is older than nectaris and humboldtianum is younger than crisium sample return missions to specific basins can anchor these measurements to a pre imbrian absolute chronology

late quaternary lacustrine history and paleoclimatic significance of pluvial lake cochise southeastern arizona abstract during the latest quaternary freshwater pluvial lakes intermittently formed in the topographically closed willcox basin arizona a lacustrine sequence of six separate high stands of lake cochise is documented by stratigraphic studies 19 radiocarbon ages and supplementary evidence two stands of pluvial lake cochise older than 14 000 yr b p reached elevations above 1290 m the prominent 1274 m shoreline of lake cochise which circumscribes the basin was largely created during a high stand between 13 750 and 13 400 yr b p during the holocene water filled the willcox basin three times to an elevation slightly below the crest of the 1274 m shoreline this occurred once during the early holocene around or before 8900 yr b p and twice during the later part of the middle holocene since the middle holocene only shallow ephemeral lakes have occupied the deflated central portion of ancient lake cochise a depression known as the willcox playa the lacustrine sequence of lake cochise provides an independent evaluation of late quaternary paleoclimatic reconstructions for southern arizona and the american southwest

the steepest slopes on the moon from lunar orbiter laser altimeter lola data spatial distribution and correlation with geologic features abstract we calculated topographic gradients over the surface of the moon at a 25 m baseline using data obtained by the lunar orbiter laser altimeter lola instrument onboard the lunar reconnaissance orbiter lro spacecraft the relative spatial distribution of steep slopes can be reliably obtained although some technical characteristics of the lola dataset preclude statistical studies of slope orientation the derived slope frequency distribution revealed a steep rollover for slopes close to the angle of repose slopes significantly steeper than the angle of repose are almost absent on the moon due to 1 the general absence of cohesion strength of the fractured and fragmented megaregolith of the lunar highlands and 2 the absence of geological processes producing steep slopes in the recent geological past the majority of slopes steeper than 32 35 are associated with relatively young large impact craters we demonstrate that these impact craters progressively lose their steepest slopes we also found that features of early imbrian and older ages have almost no slopes steeper than 35 we interpret this to be due to removal of all steep slopes by the latest basin forming impact orientale probably by global seismic shaking the global spatial distribution of the steepest slopes correlates moderately well with the predicted spatial distribution of impact rate however a significant paucity of steep slopes in the southern farside remains unexplained

quaternary downcutting rate of the new river virginia measured from differential decay of cosmogenic 26al and 10be in cave deposited alluvium the concentrations of the cosmogenic radionuclides sup 26 al and sup 10 be in quartz can be used to date sediment burial here we use sup 26 al and sup 10 be in cave deposited river sediment to infer the time of sediment emplacement sediment burial dates from a vertical sequence of caves along the new river constrain its quaternary downcutting rate to 27 3 4 5 m m y and may provide evidence of regional tectonic tilt 32 refs 3 figs 1 tab

provenance in drainage integration research case studies from the phoenix metropolitan area south central arizona abstract studies of the evolution of drainage systems in extensional settings like the basin and range province of western north america benefit from well drilling as a means of acquiring valuable insight cuttings from two wells drilled into sediments of the phoenix metropolitan region arizona usa offer new insights into the drainage history of the salt and verde river drainage basins analyses of detrital zircons with u pb dating reveal a different signature for ancestral salt river deposits asrd as compared to the underlying basin fill trace element 87sr 86sr ratios and electron microprobe analyses of basalt fragments in the basal deposits of the asrd in two different wells from mesa arizona show matches for outcrop sources near bartlett dam in the verde drainage and near stewart mountain dam in the salt drainage this indicates that the salt and verde rivers were transporting these basalts when the salt river first flowed into the metropolitan phoenix area we employed tephrochronology to determine that the 3 3 ma nomlaki tuff accumulated in closed basin playa deposits located near the present day junction of the salt and verde rivers providing a maximum limiting age for the integration of both rivers because the age of mountains crossed by the salt and verde rivers pre date 12 cm yr across multiple bedrock uplands and iv mescal limestone clasts on the highest salt river strath terrace cannot be explained by headward erosion however all analyzed evidence are consistent with the process of lake overflow based on our findings and the use of geomorphic criteria douglass et al 2009 we conclude that lake overflow is the most likely cause of drainage integration of both the salt river and the verde river

using 10be and 26al to determine sediment generation rates and identify sediment source areas in an arid region drainage basin we measured 10 be and 26 al in 64 sediment and bedrock samples collected throughout the arid 187 km 2 yuma wash drainage basin southwestern arizona from the measurements we determine long term time integrated rates of upland sediment generation 81f 5gm 2 year 1 and bedrock equivalent lowering 30f 2mm a 1 consistent with other estimates for regions of similar climate lithology and topography in a small f 8k m 2 upland sub basin differences in nuclide concentrations between bedrock outcrops and hillslope colluvium suggest weathering of bedrock beneath a colluvial cover is a more significant source of sediment 4010 4 kg year 1 than weathering of exposed bedrock surfaces 1010 4 kg year 1 mixing models constructed from nuclide concentrations of sediment reservoirs identify important sediment source areas hillslope colluvium is the dominant sediment source to the upper reaches of the sub basin channel channel cutting of alluvial terraces is the dominant source in the lower reaches similarities in nuclide concentrations of various sediment reservoirs indicate short sediment storage times 10 3 years nuclide concentrations measured in channel sediment from tributaries of yuma wash and in samples collected along the length of the wash were used to construct mixing models and determine sediment sources to the main stem channel we find an exponential decrease in the channel nuclide concentrations with distance downstream suggesting that as much as 40 of sediment discharged from yuma wash has been recycled from storage within basin fill alluvium sediment generation and denudation rates determined from the main stem are greater 25 than rates determined from upland sub basins suggesting that currently sediment may be exported from the basin more quickly than it is being generated in the uplands independence of nuclide concentration and sediment grain size indicates that channels transport sediment in discrete pulses before rapidly depositing poorly sorted material suggesting that differences in transport times for different size materials are minimal d 2002 elsevier science b v all rights reserved

climatic influences on continental deposition during late stage filling of an extensional basin southeastern arizona climatic rather than tectonic influences on continental deposition are recorded in the late stage fill of a neogene extensional basin in south eastern arizona regional geomorphic relations low sedimentation rates and stratigraphic overlap of the principal basin bounding structures identified in a gravity anomaly profile indicate that the plio pleistocene st david formation accumulated in the san pedro valley during a period of tectonic quiescence stable isotopic composition of paleosol calcite is placed within a magnetostratigraphic framework that provides an interpretive record of variable arid to semiarid climate in the valley before 3 4 ma the valley was hydrologically closed and experienced an arid climate with seasonal precipitation drainage integration at ca 3 4 ma corresponds with a transition to wetter conditions less seasonally variable precipitation and a rising water table indicated by hydromorphic paleosols and pond deposits gradually increasing seasonality of precipitation after 2 8 ma and further decrease in winter rainfall after 2 2 ma led to establishment of a dry monsoonal climate between 1 6 and 0 6 ma the change in climate at ca 1 6 ma coincides with abrupt appearance of sheet flood dominated fan gravels above earlier vertically aggraded fluvial channel and interfluve flood plain deposits this change in facies is interpreted as the result of climatic change rather than an example of subsidence driven gravel progradation sedimentation rates were greatest when climate was relatively wet with dominant winter rainfall and about equally low for relatively dry with dominant summer rain and relatively wet but nonseasonal conditions contrary to past model simulations channel flood plain facies ratios and sedimentation rate varied directly ribbon as opposed to sheet channel bodies were favored by relatively wet climatic conditions and were less commonly formed during dry strongly seasonal times precise process response interpretation of this correlation of sedimentological variability to changing climate is limited by the restricted interpretation of paleosolisotope paleoclimate data and the poor understanding of sedimentological response to climate change during 10 5 to 10 6 yr time intervals the results of this study suggest however that caution be applied to a priori interpretations of stratigraphic variations within thick syntectonic basin fills as responses to varying subsidence rates only

late pleistocene paleohydrology near the boundary of the sonoran and chihuahuan deserts southeastern arizona usa abstract ground water discharge gwd deposits form in arid environments as water tables rise and approach or breach the ground surface during periods of enhanced effective precipitation where preserved these deposits contain information on the timing and elevation of past ground water fluctuations here we report on the investigation of a series of gwd deposits that are exposed in discontinuous outcrops along a 150 km stretch of the san pedro valley in southeastern arizona near the boundary of the sonoran and chihuahuan deserts chronologic isotopic geochemical faunal assemblage ostracodes and gastropods and sedimentological evidence collectively suggest that the elevation of the regional water table in the valley rose in response to a change in climate 50 ka ago and remained relatively high for the next 35 ka before falling during the bolling allerod warm period rebounding briefly during the younger dryas cold event and falling again at the onset of the holocene the timing of these hydrologic changes coincides closely with variations in 18o values of calcite from a nearby speleothem to the west and changes in lake levels at pluvial lake cochise to the east thus in southeastern arizona the assumption that changes in climate are reflected in all aspects of the hydrologic cycle of a region simultaneously is validated the timing of these changes also broadly coincides with variations in the gisp2 18o record which supports the hypothesis that atmospheric teleconnections existed between the north atlantic and the deserts of the american southwest during the late pleistocene

post wildfire landscape change and erosional processes from repeat terrestrial lidar in a steep headwater catchment chiricahua mountains arizona usa abstract flooding and erosion after wildfires present increasing hazard as climate warms semi arid lands become drier population increases and the urban interface encroaches farther into wildlands we quantify post wildfire erosion in a steep initially unchannelized 7 5 ha headwater catchment following the 2011 horseshoe 2 fire in the chiricahua mountains of southeastern arizona using time lapse cameras rain gauges and repeat surveys by terrestrial laser scanner we quantify the response of a burned landscape to subsequent precipitation events repeat surveys provide detailed pre and post rainfall measurements of landscape form associated with a range of weather events the first post fire precipitation led to sediment delivery equivalent to 0 017 m of erosion from hillslopes and 0 12 m of erosion from colluvial hollows volumetrically 69 of sediment yield was generated from hillslope erosion and 31 was generated from gully channel establishment in colluvial hollows processes on hillslopes included erosion by extensive shallow overland flow formation of rills and gullies and generation of sediment laden flows and possibly debris flows subsequent smaller rain events caused ongoing hillslope erosion and local deposition and erosion in gullies winter freeze thaw led to soil expansion likely related to frost heaving causing a net centimeter scale elevation increase across soil mantled slopes by characterizing landscape form the properties of near surface materials and measuring both precipitation and landscape change we can improve our empirical understanding of landscape response to environmental forcing this detailed approach to studying landscape response to wildfires may be useful in the improvement of predictive models of flood debris flow and sedimentation hazards used in post wildfire response assessments and land management and may help improve process based models of landscape evolution

an isochron method for cosmogenic nuclide dating of buried soils and sediments we describe an improved method for dating buried paleosols using measurements of the cosmic ray produced radionuclides 10be and 26al in quartz grains and apply it to a sequence of intercalated tills and paleosols in central missouri usa that record plio pleistocene advances of the laurentide ice sheet a buried paleosol implies a period of surface exposure and nuclide accumulation followed by burial and a halt to nuclide production if the paleosol is formed in a sedimentary unit such as till this unit may also have been emplaced with unknown 26al and 10be concentrations inherited from past surface exposure if the inherited nuclide concentrations are the same at all depths in the soil as is true for well mixed sediments such as till then the 26al and 10be concentrations at different depths in the paleosol will show a linear relationship the slope of this line depends on the duration of burial of the paleosol but not on the inherited nuclide concentrations or on the sample depths thus one can date strata overlying buried paleosols by measuring 26al and 10be at multiple depths in the paleosol and calculating the burial age of the paleosol from the resulting isochron we focus on applying this approach to till paleosol sequences but the basic idea of forming an 26al 10be burial isochron with a set of samples that share the same burial age but differ in other aspects of their exposure history applies to other stratigraphic settings as well the method yields ages for four tills in missouri that are stratigraphically consistent agree with paleomagnetic age constraints and show that ice advanced into missouri near 1 25 ma near 0 8 ma and twice between ca 0 4 and 0 2 ma

initial observations from the lunar orbiter laser altimeter lola as of june 19 2010 the lunar orbiter laser altimeter an instrument on the lunar reconnaissance orbiter has collected over 2 0 10 9 measurements of elevation that collectively represent the highest resolution global model of lunar topography yet produced these altimetric observations have been used to improve the lunar geodetic grid to 10 m radial and 100 m spatial accuracy with respect to the moon s center of mass lola has also provided the highest resolution global maps yet produced of slopes roughness and the 1064 nm reflectance of the lunar surface regional topography of the lunar polar regions allows precise characterization of present and past illumination conditions lola s initial global data sets as well as the first high resolution digital elevation models dems of polar topography are described herein

responses of ground water in the black mesa basin northeastern arizona to paleoclimatic changes during the late pleistocene and holocene paleorecharge and paleo ground water flow patterns are reconstructed for the past 31 k y for the n aquifer in the black mesa basin northeastern arizona by 14 c dating of groundwater and numerical simulation of ground water flow and 14 c transport paleorecharge rates varied significantly and correlate with 18 o and d records of paleotemperatures in the n aquifer waters as well as other proxy records of regional paleoclimate and an atmospheric general circulation model recharge rates were two to three times higher than today during the late wisconsin when inferred temperatures were 5 6 c cooler but about 50 lower during early to mid holocene when inferred summer temperatures were 2 4 c warmer the pulse of the highest estimated recharge between 14 and 17 ka may be related to the northward migration of the southern branch of the split jet stream model simulations suggest that thousands of years are required for water levels to fully respond to the changes in recharge and that water levels fluctuated from 60 m higher to 6 m lower than today

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

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

eros shape topography and slope processes stereogrammetric measurement of the shape of eros using images obtained by near s multispectral imager provides a survey of the major topographic features and slope processes on this asteroid this curved asteroid has radii ranging from 3 1 to 17 7 km and a volume of 2535 20 km3 the center of figure is within 52 m of the center of mass provided by the navigation team this minimal difference suggests that there are only modest variations in density or porosity within the asteroid three large depressions 10 8 and 5 3 km across represent different stages of degradation of large impact craters slopes on horizontal scales of 300 m are nearly all less than 35 although locally scarps are much steeper the area distribution of slopes is similar to those on ida phobos and deimos regions that have slopes greater than 25 have distinct brighter markings and have fewer large ejecta blocks than do flatter areas the albedo patterns that suggest downslope transport of regolith have sharper boundaries than those on phobos deimos and gaspra the morphology of the albedo patterns their lack of discrete sources and their concentration on steeper slopes suggest transport mechanisms different from those on the previously well observed small bodies perhaps due to a reduced relative effectiveness of impact gardening on eros regolith is also transported in talus cones and in connected sinuous paths extending as much as 2 km with some evident as relatively darker material talus material in at least one area is a discrete superposed unit a feature not resolved on other small bodies flat floored craters that apparently contain ponded material also suggest discrete units that are not well mixed by impacts

response of a landslide to reservoir impoundment in model tests abstract landslides are often induced or activated by reservoir impoundment within the reservoir area in this paper a physical model test was conducted and compared with another published test to investigate the deformation characteristics and failure behavior of a colluvial landslide for conditions with and without reservoir impoundment the laboratory landslide model represented the lower part of a landslide in the three gorges reservoir area a thrust load was applied to represent the upper part of the landslide the thrust load surface deformation pore water pressure and soil pressure were recorded during the experiments the results show that the effect of the reservoir impoundment reduces the time to failure of the landslide and the load causing the failure as expected when water submerged the lower part of the landslide the shearing resistance was reduced the slip surfaces and failure behavior of the landslide under the two conditions are different the entire landslide mass slid along the contact between the colluvium and the bedrock under reservoir impoundment however without a reservoir the landslide slides partially along this contact and multiple slip surfaces through the colluvium

comparison of a paleosol carbonate isotope record to other records of pliocene early pleistocene climate in the western united states paleoecological and paleoenvironmental interpretations of stable isotope composition of pedogenic carbonate collected from the pliocene early pleistocene st david formation in southeastern arizona united states correlate with other proxy records of paleoclimate in the western united states wetter and perhaps cooler conditions between 3 2 and 2 8 ma are associated with lacustrine highstands at tulelake and searles lake in california a general trend toward drier conditions in the late pliocene is also apparent in all records a protracted arid monsoonal climate in the early pleistocene implied by the soil isotope data from arizona is not as readily correlated to other climate records and is perhaps related to uplift in the southern cordillera soil carbonate isotope data provide relatively continuous paleoclimatic records from fluvial sequences that supplement lacustrine records together they provide a framework for interpreting pliocene climate

recent extensional tectonics on the moon revealed by the lunar reconnaissance orbiter camera on the moon extensional tectonic features have only been observed close to the influence of the mare basalt filled basins and floor fractured craters analysis of lunar reconnaissance orbiter camera images reveals several potentially very young extensional tectonic features in the farside highlands implying that extensional stresses may locally exceed compressional ones

moisture variability in the southwestern united states linked to abrupt glacial climate change the atmospheric response to millennial scale circulation changes in the north atlantic ocean during the last glacial period has been difficult to constrain cave deposits from southwestern north america reveal that atmospheric moisture in this region increased in response to slowdowns of the atlantic meridional overturning circulation

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

impact of drainage integration on basin geomorphology and landform evolution a case study along the salt and verde rivers sonoran desert usa abstract the salt and verde rivers sonoran desert usa integrated multiple endorheic extensional basins near the start of the quaternary integration began via spillover on both rivers spillover resulted in headward erosion in upstream basins leading to basin wide incision and excavation of large volumes of sediment transported into downstream basins as a result the verde river aggraded to what is now the highest terrace in the lower verde river valley lvrv the lousley hills terrace evidence suggests deposition of the lousley hills terrace fill led to aggradation and backfilling of adjacent pediments ancestral salt river deposits asrd of the combined salt and verde rivers deposited an extensive alluvial fan in the higley basin raising local base level for over 2 million years eventually this led to aggradational piracy of the salt river 0 46 ma that integrated the higley and luke basins consequently this shortened and steepened the salt river resulting in 30 m of aggradation downstream and headward incision upstream headward incision abandoned the asrd and created the sawik stream terrace piedmont pediment and alluvial fan systems that were formerly adjusted to the asrd incised in response since abandonment the asrd floodplain has accumulated a sheet of silt and fine sand from aeolian and local fluvial processes sedimentary metamorphic and granitic pediments that developed in slowly aggrading endorheic basins display evidence of response to base level adjustments resulting from drainage integration processes classic ballena landforms eroding alluvial fans began to form in the lvrv only after drainage integration providing the first known maximum age for the ballena form drainage integration of the salt and verde rivers clearly demonstrates the impact of base level fluctuations on basin scale geomorphology however integration led to very different geomorphic responses in different extensional basins revealing the difficulty of a one size fits all conceptual model of geomorphic response drainage integration

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

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

wetter or colder during the last glacial maximum revisiting the pluvial lake question in southwestern north america abstract well preserved shorelines in estancia basin and a relatively simple hydrologic setting have prompted several inquiries into the basin s hydrologic balance for the purpose of estimating regional precipitation during the late pleistocene estimates have ranged from 86 to 150 of modern the disparity largely the result of assumptions about past temperatures in this study we use an array of models for surface water runoff groundwater flow and lake energy balance to examine previously proposed scenarios for late pleistocene climate constraints imposed by geologic evidence of past lake levels indicate that precipitation for the last glacial maximum lgm may have doubled relative to modern values during brief episodes of colder and wetter climate and that annual runoff was as much as 15 of annual precipitation during these episodes

dating sediment burial with in situ produced cosmogenic nuclides theory techniques and limitations abstract dating sediment burial over million year time scales is crucial in many areas of the earth sciences and archeology but is often difficult using traditional techniques sediment burial can be dated by the radioactive decay of cosmogenic nuclides provided that the sediment was exposed to cosmic rays prior to burial dating calculations are straightforward if sediment is buried deeply and rapidly enough to prevent cosmogenic nuclide production after burial however the analysis can be complicated by postburial production if sediment is insufficiently shielded from secondary cosmic ray nucleons and muons this paper discusses how buried sediments can be dated over timescales up to 5 myr using 26 al and 10 be in quartz

a 36 000 yr vegetation history from the peloncillo mountains southeastern arizona usa a 36 200 cal yr b p vegetation history was developed from macrofossils and pollen from 55 packrat middens from 1287 to 1442 m elevation in the peloncillo mountains of southeasternmost arizona usa today these elevations are dominated by semidesert grassland with a mixture of chihuahuan and sonoran desert shrubs including an eastern disjunct population of jojoba simmondsia chinensis from 36 200 to 15 410 cal yr b p rocky areas just above large pluvial lakes that occupied what are now dry playas supported pinus edulis juniperus osteosperma juniperus cf coahuilensis quercus cf turbinella and a rich understory of summer flowering c4 annuals and grasses indicating abundant summer rains and mild winters after 15 410 cal yr b p p edulis declined in abundance and disappeared briefly at 13 925 cal yr b p coincident with expansion of more xeric species and paleohydrological evidence for regional aridity during the bolling allerod warm interval p edulis rebounded briefly during the younger dryas at 12 405 cal yr b p before disappearing along with other mesic woodland species sometime after 12 100 cal yr b p the few middens dating from the early to middle holocene 10 000 4000 yr b p indicate wetter conditions than today at 7790 cal yr b p followed by a general drying trend the 35 middens from the late holocene detail the sequential arrival of desertscrub species as vegetation became more modern in character