quantitative morphologic analysis of boulder shape and surface texture to infer environmental history a case study of rock breakdown at the ephrata fan channeled scabland washington boulder morphology reflects both lithology and climate and is dictated by the combined effects of erosion transport and weathering at present morphologic information at the boulder scale is underutilized as a recorder of environmental processes partly because of the lack of a systematic quantitative parameter set for reporting and comparing data sets we develop such a parameter set incorporating a range of measures of boulder form and surface texture we use standard shape metrics measured in the field and fractal and morphometric classification methods borrowed from landscape analysis and applied to laser scanned molds the parameter set was pilot tested on three populations of basalt boulders with distinct breakdown histories in the channeled scabland washington 1 basalt outcrop talus 2 flood transported boulders recently excavated from a quarry and 3 flood transported boulders extensively weathered in situ on the ephrata fan surface size and shape data were found to distinguish between flood transported and untransported boulders size and edge angles 120 of flood transported boulders suggest removal by preferential fracturing along preexisting columnar joints and curvature data indicate rounding relative to outcrop boulders surface textural data show that boulders which have been exposed at the surface are significantly rougher than those buried by fan sediments past signatures diagnostic of flood transport still persist on surface boulders despite ongoing overprinting by processes in the present breakdown environment through roughening and fracturing in situ further use of this quantitative boulder parameter set at other terrestrial and planetary sites will aid in cataloging and understanding morphologic signatures of environmental processes

constraints on the geologic history of home plate materials provided by clast morphology and texture 1 we quantified and classified the size shape roundness and texture of 333 loose surface particles clasts along the spirit rover traverse from martian solar days 750 to 1889 these data provided clues to origin transport mechanisms association with geologic units and other alteration processes clasts average 15 mm in size and 0 73 sphericity and display a low degree of roundness textures include vesicular smooth and rough flat faceted and granular platy clasts characteristics are comparable to those for clasts outside the home plate region mapped geologic units around home plate are characterized by distinctive clast morphologic parameters and only minor adjustments were made to unit boundaries and definitions mapped by others no new units are suggested by the data consistent roundness values seen from unit to unit coupled with the correlation between unit boundaries and clast characteristics in and outside home plate indicate that no appreciable transport has occurred subsequent to fragmentation from outcrop and emplacement rather clasts have been emplaced through volcanic activity and or impact and have been subjected to weathering processes since that time we interpret vesicular and flat faceted clasts texture types 1 3 to be derived from mitcheltree ridge basalts and the presence of these clasts to provide a general outline of the original extent of this unit platy granular textured clasts texture type 5 are derived from the upper home plate unit

rates of weathering rind formation on costa rican basalt weathering rind thicknesses were measured on 200 basaltic clasts collected from three regionally extensive alluvial fill terraces qt 1 qt 2 and qt 3 preserved along the pacific coast of costa rica mass balance calculations suggest that conversion of unweathered basaltic core minerals plagioclase and augite to authigenic minerals in the porous rind kaolinite allophane gibbsite fe oxyhydroxides is iso volumetric and ti and zr are relatively immobile the hierarchy of cation mobility ca na k mg si al fe p is similar to other tropical weathering profiles and is indicative of differential rates of mineral weathering anorthite albite hypersthene orthoclase apatite alteration profiles across the cm thick rinds document dissolution of plagioclase and augite and the growth of kaolinite with subsequent dissolution of kaolinite and precipitation of gibbsite as weathering rinds age the rate of weathering rind advance is evaluated using a diffusion limited model which predicts a parabolic rate law for weathering rind thickness rr as a function of time t rr t and an interface limited model which predicts a linear rate law for weathering rind thickness as a function of time rr kappt in these rate laws is a diffusion parameter and kapp is an apparent rate constant the rate of advance is best fit by the interface model terrace exposures are confined to the lower reaches of streams draining the pacific slope near the coast where the stream gradient is less than 3 m km and terrace deposition is influenced by eustatic sea level fluctuations geomorphological evidence is consistent with terrace deposition coincident with sea level maxima when the stream gradient would be lowest assigning the most weathered regionally extensive terrace qt 1 mean rind thickness 6 9 0 6cm to oxygen isotope stage ois 7 ca 240 ka and assuming that at time 0 rind thickness 0 it is inferred that terrace qt 2 rr 2 9 0 1 cm is coincident with stage 5e ca 125 ka and that qt 3 rr 0 9 0 1 cm is consistent with ois 3 ca 37 ka these assignments yield a value of kapp of 8 6 10 13 cm s 1 r 2 0 99 only this value satisfies both the existing age controls and yields ages coincident with sea level maxima using this value elemental weathering release fluxes across a weathering rind from qt 2 range from 6 0 10 9 mol si m 2 s 1 to 2 5 10 11 mol km 2 s 1 the rate of rind advance for the costa rican terraces is 2 8 10 7 my r 1 basalt rind formation rates in lower temperature settings described in the literature are also consistent with interface controlled weathering with an apparent activation energy of about 50 kj mol 1 rates of rind formation in costa rica are an order of magnitude slower than reported for global averages of soil formation rates copyright 2004 elsevier ltd

a cellular model of river meandering river meandering has been successfully modelled using vector based methods but these can not simulate multiple or braided channels conversely cellular braided river models fail to replicate meandering this paper describes a new method to simulate river meandering within a cellular model caesar a novel technique for determining bend radius of curvature on a cell by cell basis is described that importantly allows regional information on bend curvature to be transferred to local points this local curvature is then used to drive meandering and lateral erosion through two methods key difficulties are identified including the deposition of material on point bars and cut off development but the method illustrates how meandering can be integrated within a cellular framework this demonstrates the potential to produce a single model that can incorporate both meandering and braiding copyright 2006 john wiley sons ltd

quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

calibration of the calcite water oxygen isotope geothermometer at devils hole nevada a natural laboratory abstract the 18 o of ground water 13 54 0 05 and inorganically precipitated holocene vein calcite 14 56 0 03 from devils hole cave 2 in southcentral nevada yield an oxygen isotopic fractionation factor between calcite and water at 33 7 c of 1 02849 0 00013 1000 ln calcite water 28 09 0 13 using the commonly accepted value of calcite water t of 0 00020 k 1 this corresponds to a 1000 ln calcite water value at 25 c of 29 80 which differs substantially from the current accepted value of 28 3 use of previously published oxygen isotopic fractionation factors would yield a calcite precipitation temperature in devils hole that is 8 c lower than the measured ground water temperature alternatively previously published fractionation factors would yield a 18 o of water from which the calcite precipitated that is too negative by 1 5 using a temperature of 33 7 c several lines of evidence indicate that the geochemical environment of devils hole has been remarkably constant for at least 10 ka accordingly a re evaluation of calcite water oxygen isotopic fractionation factor may be in order assuming the devils hole oxygen isotopic value of calcite water represents thermodynamic equilibrium many marine carbonates are precipitated with a 18 o value that is too low apparently due to a kinetic isotopic fractionation that preferentially enriches 16 o in the solid carbonate over 18 o feigning oxygen isotopic equilibrium

the eruption environment of multi tiered columnar basalt lava flows field studies on the eruption environment and prevailing cooling conditions of multi tiered lava flows of the type exemplified by the giant s causeway were carried out at localities on the columbia river plateau southern iceland on the islands of mull and staffa and around the giant s causeway ne ireland common features can be recognized in the volcanology of such flows in all the localities examined these include palaeotopographic evidence of river valleys giving conditions conducive to the ponding of flows and the damming of existing drainage evidence of high rainfall regimes or abundant surface water association of interlava lacustrine and fluviatile sediments association of hyaloclastite flow foot breccias within multi tiered basalt lava successions and evidence of large volume lava flows and high eruption rates examination of the petrography of the upper curvi columnar parts of the lava the entablature shows textural signs of quenching compared with the lower more regular columnar zone the colonnade these common field and petrographic features confirm the model of multi tiered flow formation by modification of the cooling regime in the upper part of the flow following inundation of the hot lava surface by displaced river drainage

terrestrial analogs to wind related features at the viking and pathfinder landing sites on mars 1 features in the mojave desert and iceland provide insight into the characteristics and origin of martian wind related landforms seen by the viking and pathfinder landers the terrestrial sites were chosen because they exhibit diverse wind features that are generally well understood these features have morphologies comparable to those on mars and include origins by deposition and erosion with erosional processes modifying both soils and rocks duneforms and drifts are the most common depositional features seen at the martian landing sites and indicate supplies of sand sized particles blown by generally unidirectional winds erosional features include lag deposits moat like depressions around some rocks and exhumed soil horizons they indicate that wind can deflate at least some sediments and that this process is particularly effective where the wind interacts with rocks the formation of ripples and wind tails involves a combination of depositional and erosional processes rock erosional features or ventifacts are recognized by their overall shapes erosional flutes and characteristic surface textures resulting from abrasion by windblown particles the physics of saltation requires that particles in ripples and duneforms are predominantly sand sized 60 2000 m the orientations of duneforms wind tails moats and ventifacts are correlated with surface winds above particle threshold such winds are influenced by local topography and are correlated with winds at higher altitudes predicted by atmospheric models

scale issues in weathering studies a review of the major scale issues in weathering studies reveals concerns over the fundamental spatio temporal distributions of weathering phenomena as well as issues of upscaling microscope based observations and linking different scales of observations in explanations of landform development various strategies are proposed which can be used to tackle these issues many rooted in non linear dynamical systems ideas as an initial step spatio temporal scale distributions are estimated here for weathering processes landforms and controls based on a range of empirical data two case studies of phytokarst in grand cayman and blistering and scaling of building stones are presented to illustrate the types of data that might be used to establish more convincing scale linkages in weathering investigations

progressive incision of the channeled scablands by outburst floods the surfaces of earth and mars contain large bedrock canyons that were carved by catastrophic outburst floods reconstructing the magnitude of these canyon forming floods is essential for understanding the ways in which floods modify planetary surfaces the hydrology of early mars and abrupt changes in climate flood discharges are often estimated by assuming that the floods filled the canyons to their brims with water however an alternative hypothesis is that canyon morphology adjusts during incision such that bed shear stresses exceed the threshold for erosion by a small amount here we show that accounting for erosion thresholds during canyon incision results in near constant discharges that are five to ten fold smaller than full to the brim estimates for moses coulee a canyon in the channeled scablands which was carved during the pleistocene by the catastrophic missoula floods in eastern washington usa the predicted discharges are consistent with flow depth indicators from gravel bars within the canyon in contrast under the assumption that floods filled canyons to their brims a large and monotonic increase in flood discharge is predicted as the canyon was progressively incised which is at odds with the discharges expected for floods originating from glacial lake outbursts these findings suggest that flood carved landscapes in fractured rock might evolve to a threshold state for bedrock erosion thus implying much lower flood discharges than previously thought

evoluton of polygonal fracture patterns in lava flows cooling induced fractures also known as columnar joints divide basaltic lava flows into prismatic columns with polygonal cross sections the regularity and symmetry of the fracture patterns have long fascinated naturalists in view of the recent selection of two candidate nuclear waste sites in areas where polygonally fractured volcanic rocks are located a better understanding of the fracture patterns is required field data indicate that the tetragonal networks at flow surfaces evolve systematically to hexagonal networks as the joints grow inward during solidification of lava this evolution occurs by the gradual change of most orthogonal intersections to nonorthogonal intersections of about 120 degrees the surface features and intersection geometries of columnar joints show that joint segments at any given level form sequentially yet harmoniously

the nature and rate of weathering by lichens on lava flows on lanzarote abstract samples of lichen covered and bare lava surfaces from lanzarote dating from the 1730 1736 eruption have been analysed using scanning electron microscopy sem energy dispersive spectroscopy eds and x ray diffraction xrd to investigate the relative roles of biological and inorganic weathering processes lichens here grow preferentially on n and ne facing surfaces and create a range of nanomorphological features as a consequence of their weathering activities the fruticose lichen stereocaulon vesuvianum and a mixture of crustose lichen species are found to be particularly effective agents of weathering comparison of the thickness of the weathering rind on bare and lichen covered samples mean thickness 15 7 and 253 9 m respectively shows a significant difference at the 99 confidence level following previous studies in hawaii by jackson and keller am j sci 269 1970 466 these results are used to suggest that lichens on lanzarote lava flows cause a 16 times increase in weathering rates over those found on bare surfaces comparison of these results with those from similar lava flows in hawaii indicates that under the wetter climate of hawaii both biological and inorganic rates are over double those found in lanzarote

deciphering boulder mobility and erosion from cosmogenic nuclide exposure dating large boulders are prominent features in many geomorphic systems and are frequently targeted for cosmogenic exposure dating presently there are little data or theory predicting exposure age erosion rate and mobilization frequency of boulders in environments such as channels talus slopes or moraines here we explore the potential for cosmogenic isotope analysis to constrain the transport and erosion history of boulders through a series of numerical experiments we model the statistical evolution of nuclide concentrations around the surface of boulders stable boulders have distinctive radial distributions of surface concentration in comparison to those that are periodically mobile and this can be used to establish boulder stability mean nuclide accumulation rates around the surface of an eroding boulder increase when the radius is smaller than approximately 1 5 e folding lengths 1 2 m of neutron flux intensity whereupon nuclide accumulation on the underside of the boulder becomes non negligible 10 model results for cases of no cosmogenic inheritance and uniform erosion indicate the normalized standard deviation of nuclide surface concentration systematically decreases with increasing number of boulder mobilization events this may be used to constrain the minimum number of times a boulder has moved for up to approximately four events or distinguish between rarely and frequently mobilized boulders using non dimensional scaling relations between surface concentration statistics boulder size and time we propose methods to estimate the minimum age frequency of movement and erosion rate of mobile boulders with application to a range of geomorphic problems

spectral evidence for weathered basalt as an alternative to andesite in the northern lowlands of mars mineral abundances derived from the analysis of remotely sensed thermal emission data from mars have been interpreted to indicate that the surface is composed of basalt surface type 1 and andesite surface type 2 1 the global distribution of these rock types is divided roughly along the planetary dichotomy which separates ancient heavily cratered crust in the southern hemisphere basalt from younger lowland plains in the north andesite 1 but the existence of such a large volume of andesite is difficult to reconcile with our present understanding of the geological evolution of mars here we reinterpret martian surface rock lithologies using mineral abundances from previous work1 and new mineralogies derived from a spectral end member set representing minerals common in unaltered and low temperature aqueously altered basalts our results continue to indicate the dominance of unaltered basalt in the southern highlands but reveal that the northern lowlands can be interpreted as weathered basalt as an alternative to andesite the coincidence between locations of such altered basalt and a suggested northern ocean basin implies that lowland plains material may be composed of basalts weathered under submarine conditions or weathered basaltic sediments transported into this depocentre

low stable isotope ratios of tropical cyclone rains tropical cyclone rains have distinctly lower stable isotope ratios than rains in other tropical and summer precipitation systems with a mean value slightly above that of water vapor near the sea surface the isotope ratios also decrease radially inward to the eye wall but appear to be anomalously low even near the periphery of the rain shield these findings indicate that tropical cyclones are highly efficient precipitation systems and suggest the use of stable isotope ratios as dynamic tracers of a tropical cyclone s water and energy budgets

in situ weathering rind erosion abstract the use of cosmogenic nuclide dating methods place in doubt the long term future of weathering rinds wrs as a chronometric tool why estimate ages when radiometric control is possible this paper presents evidence that wrs can provide invaluable clues about what particular sample would provide the most accurate cosmogenic age by avoiding inheritance of cosmogenic nuclides and by avoiding boulders undergoing spalling the key to this new use requires testing the occurrence and nature of wr erosion back scattered electron microscopy reveals that ignimbrite andesite basalt and granitic clasts experience wr erosion in all subsurface and surface contexts thus far studied in arizona california hawaii oregon and washington to understand the magnitude of wr erosion we measured wr thicknesses all while controlling the cosmogenic and surface stability ages of clasts by chlorine 36 and rock varnish microlamination dating methods our data reveal that traditional methodologies of sampling cobbles remove two thirds of the true thickness of weathering rinds calling into question many beliefs including the notion that clay minerals are not produced during weathering rind formation comparisons of optical and electron microscope measurements support concerns that measurement of wrs by color changes while useful as a pedagogical tool creates serious biases in underestimating the true dynamics of wrs in the end we found that concordance of wr and rock coating age trends indicates the ideal boulder for cosmogenic nuclide dating offsets reveal either ongoing boulder erosion invalidating zero erosion model ages or a potential problem with inheritance of cosmogenic nuclides

oxygen isotope variations in rainfall drip water and speleothem calcite from a well ventilated cave in texas usa assessing a new speleothem temperature proxy abstract measurements of the oxygen isotopic composition 18o value of rainfall drip water and associated calcite grown on artificial substrates and in a natural speleothem at multiple drip sites in a well ventilated cave in central texas were conducted to investigate the potential use of speleothem 18o for quantitative temperature reconstructions from 2009 to 2011 rainfall 18o varied by 11 5 10 5 to 1 0 v smow whereas drip waters had a much narrower range of 0 3 4 7 to 4 4 v smow this contrast indicates that mixing processes along flow paths in the vadose zone above the cave produce a well homogenized water reservoir that supplies drip water to the cave the 18o values for calcite grown on substrates over the same time period show seasonal variations summer 6 winter 3 that are strongly correlated with surface air temperatures ta at all three monitored sites r2 0 88 0 96 p

geomorphic expression of abrupt climate change in southwestern north america at the glacial termination eolian and subaqueous landforms composed of gypsum sand provide geomorphic evidence for a wet episode at the termination of glacial climate in southwestern north america drying of pluvial lake estancia central new mexico occurred after ca 12 000 14c yr b p thereafter eolian landforms on the old lake floor constructed of gypsum sand were overridden by rising lake water modified by subaqueous processes and organized into beach ridges along the lake s eastern shore preservation of preexisting eolian landforms in the shallow lake suggests abupt changes in lake level and climate available radiocarbon ages suggest that the final highstand recorded by beach ridges may have developed during the younger dryas yd stade the beach ridges provide information about lake surface area which was 45 of the lake area reached during the maximum highstands of the late pleistocene a similar proportional response has been reported for yd climate changes outside the north atlantic region

catastrophic flood sediments in chryse basin mars and quincy basin washington application of sandar facies model viking visible and thermal infrared observations and terrestrial catastrophic flood deposits provide clues to identify the outflow channel sediments that went into chryse basin on mars on earth sandar outwash plains formed by coalescence of many jokulhlaup floods are described in terms of three laterally adjacent facies proximal midfan and distal the missoula flood sediments deposited in quincy basin washington comprise a miniature analog of chryse basin the terminology and general characteristics of the sandar facies model are applied to quincy basin although the depositional environment and clast sizes are somewhat different higher energy flood larger clasts subaqueous rather than subaerial deposition for example the ephrata fan a deposit of boulders cobbles and pebbles forms the midfan facies analog a downfan sandy deposit reworked into a dune field comprises the distal facies analog in chryse basin the midfan is defined by a heterogeneous rocky 0 25 intermediate albedo 0 21 0 26 intermediate thermal inertia 260 460 j m 2 s 0 5 k 1 surface while the distal facies has a low albedo 0 14 0 16 and higher thermal inertia 340 700 j m 2 s 0 5 k 1 the chryse midfan unit has rocks and windblown dust exposed at the surface the sand of the distal facies in chryse acidalia is reworked by the wind as in quincy basin the viking 1 and mars pathfinder landing sites are located on the midfan unit observations that can be made at the mars pathfinder site might help in reevaluating whether or not viking 1 landed on outflow channel sediments

d h variations of meteoric waters in albuquerque new mexico u s a abstract meteoric waters in the vicinity of albuquerque new mexico u s a exhibit a wide range of d values local precipitation sampled on a monthly basis over a 2 yr period had d values ranging between 158 and 6 with the most negative values in the winter months and the most positive in the summer waters of the rio grande at albuquerque ranged in d from 103 to 79 over the same 2 yr period however for about half the sample period rio grande d values were within 2 of a baseline value of 92 the most negative rio grande d values were produced by the contribution of spring meltwater while runoff from summer rain produced positive shifts in the river water d values the principal components of local groundwater recharge have significantly different d values 1 average rio grande water with d of 92 and 2 recharge from the sandia and manzano mountains with d values of 83 to 70 groundwater d values in the local aquifer the upper tertiary santa fe formation vary from 104 to 77 over a horizontal distance of 20 km the d data suggest that there are distinct domains of groundwater within the santa fe formation which retain their isotopic identities over relatively long time scales isotopic differences between these domains seem to reflect the differences in their respective local sources of recharge the most negative d values appear to characterize deeper groundwater in the domain of rio grande recharge and may reflect climatic conditions different from those at present

physical weathering in arid landscapes due to diurnal variation in the direction of solar heating despite the prominent role of physical weathering in arid and semi arid landscapes there has been little study of the specifi c processes responsible for the rapid breakdown of subaerially exposed rocks for example many boulders and cobbles in deserts exhibit fi ne near vertical cracks although workers have hypothesized that these and other cracks are initiated by diurnal heating and cooling no convincing specifi c mechanism for their formation has been proposed we have characterized these cracks at eight sites on surfaces of different ages in the mojave sonoran and chihuahuan deserts and the high desert of central new mexico our data reveal four basic types of cracks longitudinal surfaceparallel fabric related and meridional the orientations of the fi rst three types are associated with clast shape and rock fabric the azimuths of meridional cracks however are preferentially aligned north south typically with a nonrandom multimodal distribution we propose that these cracks are caused by tensile stresses that arise in the interior of clasts due to strong radial gradients in temperature that evolve and rotate in alignment with the sun s rays we suggest that the multimodal nature of crack orientations may be in part attributable to the seasonally varying latitude dependent solar elevation angle over millennial time scales we suggest that this thermal cracking is an effi cient weathering process that together with cumulic soil epipedon development creates the key attributes of most desert pavements in addition to individual clasts exposed on desert surfaces this mechanism of cracking is potentially signifi cant in other climates and on other planets as well as for rock outcrops and for man made structures

technology and geomorphology are improvements in data collection techniques transforming geomorphic science in recent years technological developments have revolutionized our ability to collect data in geomorphology enhanced data collection not only enables us to provide deeper answers to a wider range of fundamental questions about the earth s surface but also encourages us to pose new questions this paper considers in more detail the relationships between science technology and the development of geomorphological tools and techniques reviews the spectrum of tools and techniques now available to geomorphologists and critically assesses what impact new technologies are having on geomorphology it focuses on the role of technology in biogeomorphology and weathering research and how it is advancing theoretical empirical and applied dimensions of these growing sub fields of geomorphology five areas of important technological development are reviewed remote sensing dating geophysical techniques field and laboratory based analysis and sensing of physical and chemical characteristics and field and laboratory based analysis of biological properties there is good evidence that taken together technological developments are revolutionizing geomorphology through opening the doors to better cross scalar investigations blurring the boundaries between laboratory field and computer model and facilitating cross disciplinary and democratized research

cavernous weathering dynamical instability and self organization cavernous weathering may be conceptualized as a self reinforcing process characterized by positive feedback within the weathering system a morphometric study of caverns in the valley of fire state park nevada usa demonstrates the applicability of a dynamically unstable or conditionally unstable model of cavernous weathering systems outcrop surfaces displaying caverns tend to show increasing fragmentation of the surface in the early stages of cavernous weathering succeeded by convergent evolution of the surface in which caverns tend to grow and coalesce a paradoxical relationship exists between the weathering system output at the scale of individual forms and the outcrop scale caverns tend toward minimum interior surface area by developing a spheroidal form yet the outcrop surface tends toward maximum exposed surface area by increasing the degree of fragmentation of the surface copyright 2004 john wiley sons ltd

changing amounts and sources of moisture in the u s southwest since the last glacial maximum in response to global climate change abstract the u s southwest has a limited water supply and is predicted to become drier in the 21st century an improved understanding of factors controlling moisture sources and availability is aided by reconstruction of past responses to global climate change new stable isotope and growth rate records for a central texas speleothem indicate a strong influence of gulf of mexico gom moisture and increased precipitation from 15 5 to 13 5 ka which includes the majority of the bolling allerod warming ba 14 7 12 9 ka coeval speleothem records from 900 and 1200 km to the west allow reconstruction of regional moisture sources and atmospheric circulation the combined isotope and growth rate time series indicates 1 increased gom moisture input during the majority of the ba producing greater precipitation in texas and new mexico and 2 a retreat of gom moisture during younger dryas cooling 12 9 11 5 ka reducing precipitation these results portray how late pleistocene atmospheric circulation and moisture distribution in this region responded to global changes providing information to improve models of future climate

the roughness of natural terrain a planetary and remote sensing perspective we examine the various methods and parameters in common use for quantifying and reporting surface topographic roughness it is shown that scale dependent roughness parameters are almost always required though not widely used we suggest a method of standardizing the parameters that are computed and reported so that topographic data gathered by different workers using different field techniques can be directly and easily intercompared we illustrate the proposed method by analyzing topographic data from 60 different surfaces gathered by five different groups and examine the information for common features we briefly discuss the implications of our analysis for studies of planetary surface roughness lander safety and radar remote sensing modeling and analysis

weathering history of an exposed bedrock fault surface interpreted from its topography abstract morphologic features of bedrock fault scarps are underutilized in studying faulting and weathering history partly because of a lack of accurate quantitative parameters for topography the study employs ground based lidar to measure five patches at different levels on the same fault surface and then calculates roughness in the form of power spectral density in directions parallel and perpendicular to the slip the power spectral density and spatial frequency typically follow a power law for each fault patch showing approximately linear relationships in a log log plot however due to additional power introduced by weathering all spectral curves especially those parallel to the slip can be divided into two segments lower frequency wavelengths of several centimeters several meters and higher frequency wavelengths of several centimeters and below domains this shows that the topographic features at different spatial scales are dominated by different mechanical processes faulting abrasion in the lower frequency domain and the weathering process in the higher frequency domain moreover we develop two parameters to quantify the degree of weathering of a fault outcrop which is significant to describe the evolution of the fault scarp and infer the date of faulting under calibration

impact fragmentation of lonar crater india implications for impact cratering processes in basalt impact fragmentation is an energetic process that has affected all planetary bodies to understand its effects in basalt we studied lonar crater which is a rare terrestrial simple impact crater in basalt and analogues to kilometer scale simple craters on mars the lonar ejecta consists of basaltic fragments with sizes ranging from silt to boulder the cumulative size and mass frequency distributions of these fragments show variation of power index for different size ranges suggesting simple and complex fragmentation the general shape of the fragments is compact platy bladed and elongated with an average edge angle of 100 the size distribution of cobble to boulder sized fragments is similar to the fracture spacing distribution in the upper crater wall indicating the provenance of those large fragments its consistency with a theoretical spallation model suggests that the large fragments were ejected from near surface of the target whereas the small fragments from deeper level the petrophysical properties of the ejecta fragments reflect the geophysical heterogeneity in the target basalt that significantly reduced the original size of spall fragments the presence of fe mg phyllosilicates smectites both in the ejecta and wall indicates the role of impact in excavating the phyllosilicates from the interior of basaltic target affected by aqueous alteration the seismic images reveal a thickness variation in the ejecta blanket segregation of boulders fractures and faults in the bedrock beneath the crater rim the fracturing fragmentation and fluvial degradation of lonar crater have important implications for mars

overview of the spirit mars exploration rover mission to gusev crater landing site to backstay rock in the columbia hills spirit landed on the floor of gusev crater and conducted initial operations on soil covered rock strewn cratered plains underlain by olivine bearing basalts plains surface rocks are covered by wind blown dust and show evidence for surface enrichment of soluble species as vein and void filling materials and coatings the surface enrichment is the result of a minor amount of transport and deposition by aqueous processes layered granular deposits were discovered in the columbia hills with outcrops that tend to dip conformably with the topography the granular rocks are interpreted to be volcanic ash and or impact ejecta deposits that have been modified by aqueous fluids during and or after emplacement soils consist of basaltic deposits that are weakly cohesive relatively poorly sorted and covered by a veneer of wind blown dust the soils have been homogenized by wind transport over at least the several kilometer length scale traversed by the rover mobilization of soluble species has occurred within at least two soil deposits examined the presence of monolayers of coarse sand on wind blown bedforms together with even spacing of granule sized surface clasts suggests that some of the soil surfaces encountered by spirit have not been modified by wind for some time on the other hand dust deposits on the surface and rover deck have changed during the course of the mission detection of dust devils monitoring of the dust opacity and lower boundary layer and coordinated experiments with orbiters provided new insights into atmosphere surface dynamics

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

ice age terminations 230th dated oxygen isotope records of stalagmites from sanbao cave china characterize asian monsoon am precipitation through the ends of the third and fourthmost recent ice ages as a result am records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments establishing the timing and sequence of major events in all four cases observations are consistent with a classic northern hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets meltwater and icebergs entering the north atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon causing increases in atmospheric co2 and antarctic temperatures that drive the termination in the southern hemisphere increasing co2 and summer insolation drive recession of northern ice sheets with probable positive feedbacks between sea level and co2

the schmidt hammer weathering and rock surface roughness measures of the differential relief of adjacent feldspar and pyroxene grains provide the first clear negative correlation of schmidt hammer rebound r values and degree of weathering however weathering and roughness are intimately related so the latter cannot be seen simply as a source of error limiting the utility of the schmidt hammer only where surfaces had similar textures prior to weathering can r values be compared directly even where surface texture is well controlled differences in r values should be viewed critically rather than assigned indiscriminately to differences in degree of weathering

resistance to pull out of chilean riverine species evidence from laboratory experiments abstract vegetation growing in river bars and banks determines the morphological processes in river channels the presence and dynamics of riverine vegetation depend on the magnitude and frequency of floods able to change morphology and uproot plants and on the plant s resistance to pull out a series of pull out experiments were carried out with the objective to determine the resistance of riverine vegetation to be uprooted and its effects on river bed dynamics nine riverine species were used for the experiment seven of them are native from chile and the other two are exotic and invasive in chilean environments a total of 200 specimens were transplanted in a substrate simulating a bar of a gravel bed river and after 7 months they were individually pulled out and the force and time needed to uproot the plant quantified data were analysed by means of generalised linear models glm and linear regressions and force time curves were interpreted and related to the root morphology of the species glm results showed that resistance values were dependent on root and plant physical characteristics and by the factor species among the species studied the three species showing higher resistance values were native while the less resistant was an exotic invasive species the time needed to uproot the individuals did not seem to be influenced by plant parameters nor by the factor species root architecture seemed to have an effect on plant pull out resistance and uprooting rapidity being heart shaped roots the ones that registered higher resistance values despite this when incorporating flow strength on the findings the exotic invasive ones seemed to be some of the more resistant to uprooting the findings of this paper contribute to the better understanding of river vegetational and sedimentary dynamics and are useful for parameterising the modelling of fluvial landscapes evolution and for the design of river restoration projects

transient simulation of last deglaciation with a new mechanism for bolling allerod warming we conducted the first synchronously coupled atmosphere ocean general circulation model simulation from the last glacial maximum to the bolling allerod ba warming our model reproduces several major features of the deglacial climate evolution suggesting a good agreement in climate sensitivity between the model and observations in particular our model simulates the abrupt ba warming as a transient response of the atlantic meridional overturning circulation amoc to a sudden termination of freshwater discharge to the north atlantic before the ba in contrast to previous mechanisms that invoke amoc multiple equilibrium and southern hemisphere climate forcing we propose that the ba transition is caused by the superposition of climatic responses to the transient co 2 forcing the amoc recovery from heinrich event 1 and an amoc overshoot

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

morphologies of rocks within and near the rock garden at the mars pathfinder landing site this paper considers the morphology of several rocks and rock fragments within and near the rock garden at the mars pathfinder landing site we have analyzed stereo images taken both by the lander imp camera and by the rover forward cameras the rocks were found to differ in their roundness angularity and in their densities of millimeter to centimter sized pits and flute like features on the rock facets no correlation between rock roundness and the degree of rock pitting was found indicating that rounding and pitting formed by different processes pits are either gas bubbles implying the rocks are volcanic or resulted from eolian abrasion deflation putting no constraints on the nature of the rocks or both if pits are of eolian origin variations in the density of pits on different rocks imply that either the rock surfaces have been exposed for different times or the susceptibility of different rocks to pitting varies significantly from rock to rock implying differences in composition and or lithology the densities of pits and flutes on the rocks show anti correlation this may be connected to their formation but probably is mostly related to issues of observation and definition of what is a pit and what is a flute flute like features may be a result of eolian abrasion but in this case the spatial closeness of fluted rocks and those having delicately pitted textures requires explanation other mechanisms producing flute like features such as collisions in the deposit forming flows and the breaking of rock in impact cratering should not be ignored our observations agree with the conclusion of golombek et al this issue that deflational exhumation in this area was minor the observed relatively large rocks typically do not show a concentration of small rock fragments at their feet this implies diurnal thermal cycles are very ineffective at destructing rocks the rock half dome may be a conglomerate as suggested by smith et al 1997a for this and several other rocks but this hypothesis remains to be proven impact craters of a few meters to a few tens meters in diameter may have played a role in the local geology

methods for measuring rock surface weathering and erosion a critical review studies of rates processes and modes of rock surface and near surface deterioration and also hardening are central to rock weathering and building stone research conservation and management there is a need to measure and monitor weathering at the rock atmosphere interface to facilitate understanding of climatic environmental and lithological controls on the evolution and development of surface weathering features this paper reviews long established and recently developed field and laboratory methods used by geomorphologists to monitor and measure the impact of weathering and erosion on physical and mechanical properties of exposed rock surfaces and their immediate subsurface key advances are highlighted their application to multi scalar understanding and modelling of rock surface weathering in different contexts is discussed and potential future advances to provide new insights into rock weathering durability and materials conservation are identified in highlighting key advantages and disadvantages of a wide range of methods to the broader earth science community the paper aims to contribute to further innovative thinking across disciplines to develop new methods for measuring and monitoring rock weathering

a continuous high resolution record of late pleistocene climate variability from the estancia basin new mexico lake sediments that accumulated in the estancia basin central new mexico provide a detailed record of submillennial latest pleistocene climatic oscillations sedimentologic biologic and geochemical proxies for changes in salinity and lake level were used to identify episodes of wet and dry climate that occurred between 24 and 12 k y b p as dated by 14c by means of accelerator mass spectrometry from shoreline and basin center deposits these dates determine the timing and duration of the episodes of wet and dry climate the lake expanded and contracted repeatedly during the last glacial maximum and fluctuated near its highest elevation several times during the interval ca 20 to 15 k y b p a pronounced lowstand lasting 1 k y occurred between ca 15 and 14 k y b p followed by two more highstands of the lake between ca 14 and 12 5 k y b p desiccation of the perennial lake after 12 k y b p was followed by a final poorly dated highstand at ca 10 k y b p the record of lake level fluctuations from the estancia basin provides a high resolution record of changes in water budget in a basin the comparatively simple physiography and hydrogeology of which ensured a direct response to the strong climatic fluctuations that occurred during the last glacial maximum and termination

in situ fragmentation of lunar blocks and implications for impacts and solar induced thermal stresses abstract this study deals with an aspect of blocks observed on many rocky planetary surfaces in situ fragmentation using lroc nac images we characterized the morphology morphometry and abundance of in situ fractured blocks observed on the rim of six large impact craters of known emplacement age on the moon the relative number of disrupted blocks increases with crater retention age of surfaces on which blocks are hosted consistent with fragmentation post emplacement due to impacts of small meteoroids the type of break up morphologies we observe appears to be independent of surface exposure age of the blocks the inferred flux and size frequency distribution of projectiles responsible for disrupting blocks is consistent with expected lunar impact fluxes block fragmentation due to insolation driven thermal stresses is subordinate to impacts the possible effects of thermal stresses are evident as meridional cracks which have preferred orientations in a young block population 4 ma and as loose material fillet developing on top of surviving blocks in old populations 800 ma

tracing sea level changes during the mid holocene in the southern mediterranean coast an example from the gulf of gabes abstract mid holocene sea level emergence was recorded along a mid latitude coastal site in the gulf of gabes tunisia in beach rock deposits however the post emergence sea level curve and associated hydro sedimentary processes have rarely been documented this study presents new records of sea level changes along the tunisian coast since the mid holocene each phase of the sea level curve was evidenced and supported by lithostratigraphic morphological and archaeologic markers post emergence sea level fall due to postglacial isostatic rebound was recognized in regressive sequences which vary depending on available accommodation space from a small pocket beach to a well developed dune system sea level stabilization following isostatic rebound has promoted the end phase deposits of the regressive sequences however this stability was interrupted during the late holocene by a high energy storm event that accumulated a transgressive boulder unit at 2 m above present shape and disposition of the boulder ridge behind a prograding modern shoreline suggests that sea level has not changed during the late holocene the existence of a roman fish pond on the upper foreshore confirms stability of sea level during the last two millennia the combination of lithostratigraphic morphological and archaeologic markers represents a tool for improving the accuracy of dating of erosional and depositional periods in mid coastal sections

oxygen isotopic fractionation between drip water and speleothem calcite a 10 year monitoring study central texas usa abstract speleothem 18o values can serve as a paleoclimate proxy yielding information about past temperature and rainfall an accurate determination of the equilibrium calcite water oxygen isotopic fractionation factor and an assessment of kinetic isotopic fractionation are required for interpretation of speleothem 18o data in this study 18o values were measured for calcite deposited on artificial substrates at four sites in two central texas caves monitored for over 10 years the results are used to evaluate the equilibrium isotopic fractionation factor and the impact of climatic and hydrologic conditions on kinetic isotopic fractionation the 18o values of calcite from the four sites ranged from 24 8 to 26 7 v smow and associated drip water values ranged from 4 6 to 3 9 a comparison of predicted equilibrium calcite 18o values calculated using a commonly used isotopic fractionation factor with measured values indicates that 94 of the calcite samples are not in oxygen isotopic equilibrium with respect to their associated drip water the departure from oxygen isotopic equilibrium expressed as 18occ e ranges from 0 7 to 1 4 three of the four drip sites yield similar linear relationships between 18occ e and water temperature tw and can be collectively expressed as 18occ e 0 3tw 4 7 r2 0 56 n 93 therefore calcite deposited during time periods of lower tw lower cave air co2 concentration and faster calcite deposition rates have 18o values closer to equilibrium this contradicts conceptual models which predict that a faster calcite deposition rate leads to a larger departure of calcite 18o from equilibrium if slower calcite deposition indeed facilitates equilibrium fractionation i e 18occ e 0 then the results of this study support a larger than commonly accepted value for the equilibrium calcite water oxygen isotopic fractionation factor adopting a larger published value for the fractionation factor yields negative 18occ e values of up to 2 4 these negative values cannot be explained by existing kinetic fractionation models alternatively they may reflect the trapping of a calcite surface layer with a lower 18o value than that of calcite in isotopic equilibrium with ambient water the relationship between deposition rates and 18occ e for this study is consistent with the same relationship using data for synthetic calcite from the literature this relationship indicates a 0 8 shift of calcite 18o for every ten fold increase in deposition rate at 5 to 25 c and a ph of 8 3 the significant kinetic fractionation observed in this study warrant consideration in applying measured speleothem calcite 18o values to interpret past climate conditions

pleistocene water intrusions from the mediterranean and caspian seas into the black sea the hydrological balance of the black sea is governed by riverine input and by the exchange with the mediterranean sea a speleothem record from a cave in northern turkey that tracks the isotopic signature of black sea surface water suggests an open connection to the mediterranean sea in at least twelve periods in the past 670 000 years

the importance of wind as a driver of earthen heritage deterioration in dryland environments abstract dryland regions are exposed to extreme environmental conditions that create hotspots of weathering and erosion many earthen heritage sites are located in these dryland regions and experience extensive deterioration driven by interactions with environmental processes however previous research has focused largely on the role of rain as a driver of deterioration this study combines approaches from geomorphology with understandings of earthen materials from heritage science to investigate the relative importance of wind and rain in driving earthen heritage deterioration in drylands we use geomorphological signatures to infer the environmental histories of earthen walls with a range of known ages at suoyang ancient city china using semi quantitative deterioration assessments we find rain driven deterioration features to be associated with the loss of larger volumes of material and to have higher persistence than wind driven deterioration features however we argue that the high frequency nature of wind events means that wind is an important initiator of deterioration across the site in addition walls exposed to the prevailing wind are dominated by wind driven deterioration features outcomes from this study present an opportunity for earthen heritage conservation to investigate potential strategies to minimise wind speed at earthen heritage sites in drylands

simulating weathering of basalt on mars and earth by thermal cycling physical weathering induced by heating and cooling may cause rock breakdown on mars and earth we report results from parallel weathering simulations on basalt blocks exposed to diurnal cycles representing mars like two simulation runs from 55 to 20 oc and 75 to 10 oc 1 100 relative humidity 4 8 mbar pressure co 2 atmosphere and hot arid earth 23 72o c 30 100 relative humidity conditions under earth conditions thermally pre stressed blocks showed measurable strength declines whilst salt pre treated blocks showed strength gains under mars like conditions pre stressed blocks recorded greater or similar strength declines and salt pre treated blocks showed more muted strength declines than under earth conditions the results imply that on earth and mars diurnal cycling of temperature alone can cause deterioration of basalt with a pre existing stress history the type of stress history is important with salt pre treatment affecting the response of thermally pre stressed blocks under both earth and mars conditions

innovative applications of laser scanning and rapid prototype printing to rock breakdown experiments we present the novel application of two technologies for use in rock breakdown experiments i e close range ground based 3d triangulation scanning and rapid prototype printing these techniques aid analyses of form process interactions across the range of scales relevant to breakdown m m this is achieved through a the creation of dems which permit quantitative description and aanalysis of rock surface morphology and morphological change and b the production of more realistically shaped experimental blocks we illustrate the use of these techniques alongside appropriate data analysis routines in experiments designed to investigate the persistence of fluvially derived features in the face of subsequent wind abrasion and weathering these techniques have a range of potential applications in experimental field and lab based geomorphic studies beyond those specifically outlined here copyright 2008 john wiley sons ltd

sedimentology of rocky shorelines 2 shoreline megaclasts on the north shore of oahu hawaii origins and history abstract limestone megaclasts up to 96 t in weight rest on a coastal rock platform near sunset beach on the north shore of oahu hawaii they occur in seaward dipping imbricate clusters and as solitary clasts the rock platform is subject to large swell waves and very large waves associated with winter storms and tsunami a series of photographs covering the period from ca 1905 to 1996 show episodic rearrangement of megaclasts on the platform and the appearance of new megaclasts near the platform edge the largest solitary megaclast ca 96 t was emplaced on the platform between 1940 and 1950 possibly by the 1946 aleutian tsunami and has moved twice since then in ca 30 m jumps along two different trajectories larger clasts have been broken from the platform edge and emplaced on the platform only by very large wave events whereas formation and movement of smaller tabular clasts ca 30 40 t appear to be a continuously ongoing process on the surface of the rock platform partial detachment of clasts by marine erosion processes along joints and cracks in the limestone bedrock facilitates their complete detachment from both the platform edge and platform surface the larger numbers of megaclasts emplaced on the north and northwest sectors of the platform relative to other sectors are attributed to exertion of maximum wave power on these sectors due to a combination of steep slope and ramp like submarine topography

phasing of deglacial warming and laurentide ice sheet meltwater in the gulf of mexico evidence is emerging that the tropical climate system played a major role in global climate change during the last deglaciation however existing studies show that deglacial warming was asyn chronous across the tropical band complicating the identification of causal mechanisms the orca basin in the northern gulf of mexico is ideally located to record subtropical atlantic sea surface temperature sst warming in relation to meltwater input from the laurentide ice sheet paired d 18 o and mg ca data on the planktonic foraminifer globigerinoides ruber from core en32 pc6 are used to separate deglacial changes in sst and d 18 o of sea water sst as calculated from mg ca data increased by 3 8c from ca 17 2 to 15 5 ka in association with heinrich event 1 and was not in phase with greenland air temperature subtracting tem perature effects from d 18 o values in g ruber reveals two excur sions representing laurentide meltwater input to the gulf of mex ico one of 1 5 from ca 16 1 to 15 6 ka and a second major spike of 2 5 from ca 15 2 to 13 0 ka that encompassed melt water pulse 1a and peaked ca 13 8 ka during the bolling allerod conversion to salinity through the use of a laurentide meltwater end member of 225 indicates that near surface salinity de creased by 2 4 during these spikes these results suggest that gulf of mexico sst warming preceded peak laurentide ice sheet decay and the bolling allerod interval by 2 k y and that heat was retained in the subtropical atlantic during heinrich event 1 consistent with modulation of deglacial climate by thermohaline circulation

morphology and texture of particles along the spirit rover traverse from sol 450 to sol 745 1 we quantified and classified the shape roundness size and texture of 935 loose surface particles along the spirit rover traverse from sols 450 745 to assess origin transport and other alteration mechanisms that altered particles during and after formation variation in particle morphologic parameters along traverse is consistent with crossing mapped geologic unit boundaries texture is divided into four types vesicular smooth and flat faceted rough and flat faceted and very rough sphericity and roundness are intermediate and low respectively comparable to particles moved by high energy transport or to crushed particles this indicates intermittent high energy emplacement or modification of a single lithology rather than systematic continuous low energy abrasion or wear over time comparison with particle morphology at other mars landing sites is consistent with the hypothesis that no secondary systematic transport or wide scale chemical alteration was active at a significant enough level to alter macromorphology in particular particle morphology at the mars pathfinder site shows stronger evidence of abrasion than along the spirit traverse suggesting mars pathfinder particles have undergone abrasion processes that particles in this study area have not additionally morphology indices have correlation coefficients near zero indicating that a fluvial transport mechanism is likely not responsible for morphology morphology and texture are instead related to origin and composition rather than subsequent modification morphology and texture support a volcanic origin possibly without modification but most likely altered primarily by ballistic impact implying that the spirit landing site and traverse may be utilized in the future as a standard site for characterization of impact derived morphology

isotopic paleoecology of clovis mammoths from arizona the causes of megafaunal extinctions in north america have been widely debated but remain poorly understood mammoths mammuthus spp in the american southwest were hunted by clovis people during a period of rapid climate change just before the regional onset of younger dryas cooling and mammoth extirpation thus these mammoths may provide key insights into late pleistocene extinction processes here we reconstruct the seasonal diet and climatic conditions experienced by mammoths in the san pedro valley of arizona using the carbon 13c 12c and oxygen 18o 16o isotope compositions of tooth enamel these records suggest that clovis mammoths experienced a warm dry climate with sufficient summer rainfall to support seasonal c4 plant growth monsoon intensity may have been reduced relative to the preceding time period but there is no isotopic evidence for severe drought however it is possible that the clovis drought inferred from stratigraphic evidence occurred suddenly at the end of the animals lives and thus was not recorded in the enamel isotopic compositions unlike mammoths that lived before the last glacial maximum clovis mammoths regularly increased c4 grass consumption during summer probably seeking seasonally green grasslands farther from the river valley this predictable seasonal behavior may have made mammoths easier to locate by clovis hunters furthermore clovis mammoths probably had no previous experience of such sudden climatic change as is believed to have occurred at the time of their extinction

interacting loop current variability and mississippi river discharge over the past 400 kyr the loop current mediating the oceanic heat and salt flux from the caribbean sea into the atlantic ocean and its interference with the mississippi river discharge are critical for both the regional climate in the gulf of mexico area and the water vapor transport towards high northern latitudes we present a 400 kyr record of sea surface temperature and local surface salinity from the northeastern gulf of mexico images core md02 2575 approximated from combined planktonic foraminiferal 18o and mg ca which reflects the temporal dynamics of the loop current and its relationship to both varying mississippi discharge and evolution of the western hemisphere warm pool the reconstructed sea surface temperature and salinity reveal glacial interglacial amplitudes that are significantly larger than in the western hemisphere warm pool sea surface freshening is observed during the extreme cool periods of marine isotope stages 2 8 and 10 caused by the strengthened mississippi discharge which spread widely across the gulf favored by the less established loop current interglacial and interstadial sea surface conditions instead point to a strengthened northward flowing loop current in line with the northward position of the intertropical convergence zone allowing northeastern gulf of mexico surface hydrographic conditions to approach those of the caribbean at these times the mississippi discharge was low and deflected westward promoted by the extended loop current previously described deglacial megadischarge events further to the west did not affect the northeastern gulf of mexico hydrography implying that meltwater routing from the laurentide ice sheet via the mississippi river is unlikely to have affected atlantic meridional overturning circulation

carbon mass balance modelling and carbon isotope exchange processes in dynamic caves abstract diverse interpretations have been made of carbon isotope time series in speleothems reflecting multiple potential controls here we study the dynamics of 13 c and 12 c cycling in a particularly well constrained site to improve our understanding of processes affecting speleothem 13 c values the small tubular grotta di ernesto cave ne italy hosts annually laminated speleothem archives of climatic and environmental changes temperature air pressure pco 2 dissolved inorganic carbon dic and their c isotopic compositions were monitored for up to five years in soil water and gas cave dripwater and cave air mass balance models were constructed for co 2 concentrations and tested against the carbon isotope data air advection forces winter pco 2 to drop in the cave air to ca 500 ppm from a summer peak of ca 1500 ppm with a rate of air exchange between cave and free atmosphere of approximately 0 4 days the process of cave ventilation forces degassing of co 2 from the dripwater prior to any calcite precipitation onto the stalagmites this phase of degassing causes kinetic isotope fractionation i e 13 c enrichment of dripwater whose 13 c dic values are already higher by about 1 than those of soil water due to dissolution of the carbonate rock a subsequent systematic shift to even higher 13 c values from 11 5 in the cave drips to about 8 calculated for the solution film on top of stalagmites is related to degassing on the stalagmite top and equilibration with the cave air mass balance modelling of c fluxes reveals that a very small percentage of isotopically depleted cave air co 2 evolves from the first phase of dripwater degassing and shifts the winter cave air composition toward slightly more depleted values than those calculated for equilibrium the systematic 13 c enrichment from the soil to the stalagmites at grotta di ernesto is independent of drip rate and forced by the difference in pco 2 between cave water and cave air this implies that speleothem 13 c values may not be simply interpreted either in terms of hydrology or soil processes

the oxygen isotopic composition of seawater during the last glacial maximum high resolution oxygen and hydrogen isotope measurements were made on pore fluids from deep sea sediments from sites in the north and south atlantic the data provide direct measurements of changes in the isotopic composition of bottom waters during the last glacial maximum lgm results from ocean drilling program odp site 981 in the north atlantic currently bathed in north atlantic deep water nadw reproduces previous results from the ceara and bermuda rises constraining the glacial interglacial change in 18 o of the deep atlantic to be 0 7 0 8 results from site 984 which is located north of site 981 and at a shallower water depth yield a similar value 0 8 providing insight into the properties of glacial north atlantic intermediate water gnaiw sites from odp leg 177 in the south atlantic span the modern boundary between northern and southern sources of deep water data from the northern site 1088 yield a similar result to sites in the tropical and north atlantic 0 7 at the southern site 1093 located south of the polar front the change is substantially larger 1 1 representing the change in 18 o of southern source waters since the lgm these results confirm previous estimates that the global average change in 18 o of seawater is 1 0 0 1 hydrogen isotopes measured on pore fluids from three sites are consistent with the oxygen isotopes from these locations giving further support to these results at all sites studied the temperature of the deep ocean during the lgm calculated by combining the pore fluid results with oxygen isotope data from benthic foraminifera was within 1 c of the freezing point of seawater

structures textures and cooling histories of columbia river basalt flows flood basalt flows of the columbia river basalt group commonly exhibit well developed colonnade and entablature structures formed during cooling of individual flows the colonnade refers to the well defined columnar structure of many flows which appears in the lowermost 10 to 30 and in places the uppermost 10 to 20 entablature refers to those parts of a flow that have smaller column diameters and more irregular pattern fractures than those of colonnade entablature commonly occupies the central 60 to 70 of a flow in some cases however the entablature is interrupted by colonnade in such cases the entablature and colonnade may be repeated once or twice within a single flow in other cases flows may lack an entablature entirely petrographic examination reveals a pronounced correlation between structural and textural features thin sections of colonnade basalt have relatively coarse cruciform or octahedral fe ti oxide crystals and 20 glassy mesostasis the central entablature basalt in contrast has much more mesostasis as much as 60 and has textural features such as feathery fe ti oxide crystals indicative of more rapid cooling these features are the reverse of what might be expected for normal conductive cooling because cooling rates at the flow margins should be greater than those in the flow interior we reconciled the observed basalt textures with thermal models by taking into account rainfall and deranged drainage during crystallization of the flow downward migration of water through cracks would cause convective cooling of underlying unsolidified lava this effect and its consequences have been modeled numerically in order to clarify the physical constraints on the mechanism by which the central part of the lava can be quenched we have found that a water infiltration front can explain the presence of a thick quenched flow interior provided that the infiltration front moves downward just behind the lava solidification front despite heavy rainfall on hawaii for example 250 cm yr at kilauea iki exposed prehistoric lava flows on that island exhibit only colonnades we deduce from this that heavy rainfall alone is inadequate to quench flow interiors extensive flooding by deranged drainage or perhaps extremely heavy rainfall 250 cm yr is apparently required to produce entablatures the model also can be used to explain the occurrence of repeated entablature and colonnade by considering the effects of intermittent inundation the imposition of boundary conditions that mimic the removal and reoccurrence of flooding yields cooling histories that are consistent with the development of multiple colonnades and entablatures

quantitative morphology of rocks at the mars pathfinder landing site 1 we adapt and test a standard terrestrial technique of assessing morphology quantitatively for use with sites on mars based on two dimensional equations and particle outlines whereby images of particles obtained remotely may yield dimensionless numerical shape and roundness values consistent with previous knowledge of the lithology and sedimentary transport history our test site was the particle rich rock garden at the mars pathfinder landing site a location where the primary geologic processes and lithology have been determined by other means a total of 575 particles were assessed in terms of size sphericity elongation and roundness qualitative roundness was determined for 460 particles particles are mostly pebble to cobble sized and have an average sphericity of 0 75 elongation of 0 63 and relative roundness of 0 083 69 of particles are subangular or subrounded particle sphericity is unimodal with a size sphericity profile matching trends for terrestrial populations of similar lithology and elongations nearly identical to those for particles at vikings 1 and 2 this matches the predictions for a site with the single overall lithology implied from other analyses roundness data indicate one or possibly two particle populations representing the primary processes that likely affected particle roundness most strongly impact and catastrophic flooding finally we tested a hypothesis suggesting that darker smaller more angular particles comprise a population transported through impact cratering while larger less dark more rounded particles are associated with catastrophic flood transport the opposite result is seen larger particles throughout the rock garden are more angular than smaller ones

geomorphometric analysis for characterizing landforms in morelos state mexico landforms can be described and quantified into simple relief elements by parametrization of digital elevation model dem in this research we investigate the use of morphometric parameters and a new classification scheme to characterize selected elemental forms associated with landforms we apply and test this methodology on a geomorphologically diverse region located in central mexico these simple elements are known as morphometric classes and include ridge plane channel pit peak and pass these classes correspond to real entities and are of practical significance the morphometric classes were grouped according to their areal parameters ridge plane and channel and pointed parameters pit peak and pass which can be used to form the basis of a system of characterization and classification of landforms landform elements display statistically significant compositional differences with respect to their proportions of morphometric classes this in turn can be plotted onto a diagram of characterization and classification known as a double ternary diagram dtd which comprises both areal and pointed parameters and any combination thereof the dtd is useful for studying geomorphological processes wherein areal and point values and properties have expressions which are topographically quantifiable

rounded cobbles that have not travelled far incorporation of corestones from saprolites in the south mountain area of southern nova scotia canada saprolitic palaeosurfaces occur at several localities on the granitoid rocks of the south mountain batholith of nova scotia there are three ages of saprolites within the study area pre pleistocene pre triassic and pre carboniferous within these in place weathered horizons there are remnant ellipsoidal blocks of unweathered granitoid referred to as corestones these corestones are isolated rounded pods of relatively unweathered material surrounded by rotted granitoid saprolitic material the weathered material which surrounds these corestones is poorly consolidated and easily eroded the erosion of these horizons produces a lag deposit that contains many rounded corestones which can be incorporated into subsequent sedimentary units the rounded boulders cobbles and pebbles of granite within many of the pleistocene glacial deposits in southern nova scotia are probably related to the incorporation of these saprolite related structures given the locally derived within 400 m of the source nature of the tills the presence of saprolites at unconformities of various ages on the south mountain granitoid rocks suggests that incorporation of saprolitic material probably occurred along a number of palaeosurfaces in the past the recognition of this process has implications for the interpretation of rounded granite clast conglomerates and quartz rich sandstones of various ages within the stratigraphic record of eastern canada similar palaeosurfaces elsewhere in the world also have related saprolite derived sedimentary rocks associated with them in summary well rounded spherical pebbles cobbles and boulders of granitoid material incorporated in sedimentary strata need not have travelled far from source nor are they necessarily recycled from older conglomerates

the effect of rock moisture on schmidt hammer rebound tests on rock samples from marion island and south africa in an assessment of the influence of internal rock moisture content on schmidt hammer readings rebound r values are found to decrease with increasing moisture content for samples of basalt sandstone and dolerite the maximum decrease in r values is found between oven dry values and saturated rock rebound values the magnitude of which varies from 2 to 10 points on the r scale a quartzite block has the greatest decline of 6 points at 60 per cent saturation for certain rock types under differing site to site field moisture conditions the moisture effect can be a significant factor in the interpretation of the relative state of weathering from rebound values copyright 2002 john wiley sons ltd

rock surface roughness as an indicator of degree of rock surface weathering rock surface weathering often leads to increased rock surface roughness but roughness has proved difficult to quantify several instruments are available for micro mapping and recording rock surface profiles but the most appropriate for most purposes is the simple profile gauge short profiles can be recorded quickly and accurately a range of roughness indices has been proposed in other areas of geomorphology and their efficacy as measures of roughness at scales of interest in studies of weathering is assessed some are too complex or labour intensive and others are too sensitive to the scale of roughness to provide reliable measures of magnitude the most appropriate indicator of both the scale and magnitude of roughness is the standard deviation of the differences between height values at a range of set horizontal intervals along a profile the deviogram varying the measurement interval records roughness at different scales a regression approach root mean square roughness provides a reliable measure of the magnitude of roughness at the maximum scale present three case studies confirm the efficacy of these approaches to studies of weathering of different rocks in different environments software is supplied which automates the calculation of roughness indices from gauge profiles

a casting procedure for reproducing coarse grained sedimentary surfaces in the field the measurement of near bed hydraulics remains problematic greater precision is possible in the laboratory but in the case of gravels it is difficult to create a water worked channel bed that is realistic enough to replicate faithfully the conditions found in nature in this paper a technique to reproduce coarse grained sedimentary fabrics of large areal extent is described it involves moulding natural river bed surfaces from which facsimiles are cast remarkably realistic casts with dimensions of 1 m by 2 m have been produced and their quality assessed using spatial data derived using automated digital photogrammetry the casts reproduce the prototype surfaces with errors at millimetre scale 0 5 per cent of the microrelief the technique has facilitated the introduction of sedimentary surfaces that incorporate natural complex structures of grains up to cobble size into experimental channels where detailed studies of near bed hydraulics can be carried out copyright 2003 john wiley sons ltd

chemical discrimination of columbia river basalt flows 1 the homogeneity and distinctive chemical composition of individual columbia river basalt flows are illustrated in a series of chemical plots and the procedure for flow identification is outlined the unique characterization of many individual eruptions permits units to be mapped from feeder dike to flow margins across the columbia plateau for hundreds of kilometers and so provides critical constraints on the physical and chemical evolution of this continental flood basalt province

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

controls on dissolved inorganic carbon and δ13c in cave waters from desoto caverns implications for speleothem δ13c assessments abstract unraveling the factors controlling the carbon chemistry and transport of carbon within extant karst systems has important implications concerning the assessment of time series 13c records of speleothems here we report the results of a 3 year study of total dissolved inorganic carbon dic and 13cdic from cave waters at desoto caverns southeastern usa that offer valuable insight on carbon transport and the accompanied isotope fractionations from end member sources to speleothems dic and 13cdic values of cave waters range from 0 2 to 6 0 mm and 2 7 to 12 9 vpdb respectively dic and 13cdic of seasonal drips show seasonal albeit noisy variability and are inversely related 13cdic 2 49 dic 0 64 r2 0 84 a shallow pool fed by multiple drips shows a bimodal 13cdic distribution with an isotopically heavier mode during winter 4 to 5 vpdb relative to summer months 9 to 10 vpdb a multi year trend of decreasing water availability during the study period is not reflected in a response of cave water carbon chemistry suggesting that rainfall amount may not be a significant controlling factor of the carbon chemistry coupled cave air winter ventilation summer stagnation and varying co2 fluxes through the soil horizon and epikarst exert the strongest influence on seasonal dic and 13cdic variability measured values of high dic and low 13cdic from cave waters collected during the summer early fall closely approximate isotopic equilibrium conditions conversely low dic and high 13cdic values during winter early months indicate kinetically enhanced isotopic fractionations within the cave waters the kinetically enhanced isotopic fractionation of hco 3 partitioned between degassed co2 and precipitated caco3 1000 ln co 2 hco 3 caco 3 ar hco 3 2 is greater by about a factor of two 6 7 0 3 relative to the same isotopic fractionation under equilibrium conditions 3 1 on the basis of 14c mass balance and paired 14c u th measurements we estimate that on average about 23 of c delivered annually by the drips to the aragonite stalagmites is derived from 14c dead dolomite cap while the remainder of 77 is derived from 14c live biomass 13c measurements of aragonite n 12 sampled from the tips of active speleothems during the summer months are consistent with theoretical aragonite 13c values calculated using the shallow pool summer early fall data thus confirming the 13c seasonality in both drips and coeval aragonite 13c values of an active stalagmite section spanning the last 200 years show a normal distribution with a mean of 7 1 1 2 n 81 and a mode of 7 to 8 that are statistically indistinguishable from the annual mean and mode of all dripwaters thus secular time series 13c records of stalagmites at desoto caverns with resolving power 10 1 year will likely carry the imprints of drip annual means that record climate driven 13c seasonal biases

dynamic single thread channels maintained by the interaction of flow and vegetation most rivers on earth today flow as a single channel in some cases with occasional islands and follow a more or less sinuous course however single thread channels have proven difficult to reproduce and study experimentally experimental self formed channels tend to widen and subdivide leading to a braided pattern cohesive sediment has been the main mechanism studied for stabilizing banks and producing a single thread channel we show how laboratory experiments using vegetation to stabilize banks can organize the flow and convert the planform morphology from braided to single thread our experimental strategy a repeated cycle of short periods of high water discharge alternating with longer periods of low discharge accompanied by plant seeding and growth leads to the evolution of a dynamic self maintaining single thread channel with well defined banks and floodplain by eliminating weak flow paths the vegetation corrals the water into a single dominant channel until the reduction in total wetted width leads to a new self organized state in which the flow removes vegetated area as fast as it is produced the new channel is deeper and has a broader distribution of depths than the braided one with channel size adjusted to carry almost all the flood flow the resulting system maintains a dynamic steady state via similar mechanisms to those that operate in meandering channels in the field specifically erosion at the outside of bends bend growth and bar development our methodology provides a basis for experimental development of self sustaining high amplitude meanders and has applications for river management and basic research purposes

weathering of igneous rocks during shallow burial in an upland peat environment observations from the bronze age copney stone circle complex northern ireland abstract the stone circle complex at copney county tyrone is a key bronze age site that forms part of the mid ulster stone circle complex this site was excavated in 1995 and since then deterioration of the archaeological stonework has been a serious problem deterioration is visible as splitting fracturing of stones the development of a bleached outer margin surface scaling and granular disintegration and in some cases complete disintegration of individual stones to sandy regolithic material environmental conditions at this site exacerbate the deleterious action of weathering processes with periodic waterlogging and sub zero temperatures during winter months the copney stones comprise two igneous lithologies quartz porphyry and porphyritic andesite both lower ordovician 470 ma in age both rock types show extensive alteration by hydrothermal processes resulting in weakened stone fabrics exploited by weathering processes during burial and subsequent exposure mineralogy of buried and exposed material indicates that approximately 2500 years of burial in a peat bog has produced secondary porosity comprising extensive microfracture networks and dissolution voids which permitted further ingress of moisture and acidic waters thus promoting chemical alteration of mineral constituents the occurrence of completely grussified stones and arenisation of boulder surfaces at copney indicates that the processes of grussification are not solely restricted to deep weathering environment but can be achieved by burial in a shallow aggressive environment over periods measured in thousands of years

fluvial islands first stage of development from nonmigrating forced bars and woody vegetation interactions abstract fluvial islands can develop from the channel bed by interactions between pioneer trees and bars although vegetation recruitment and survival is possible on all bar types it is easier for trees to survive on nonmigrating bars developed from a change in channel geometry or to the presence of a steady perturbation this field study details the first stages of development of a vegetated mid channel nonmigrating or forced bar and its evolution toward an island form over six years analysis of bed topographical changes vegetation density and roughness scour and fill depths sediment grain size and architecture and excess bed shear stress highlighted a specific signature of trees on topography and grain size segregation two depositional processes combining the formation of obstacle marks and upstream shifting deposition of sediments led to the vertical accretion of the vegetated bar during the first stage of the bar accretion bedload sediment supply coming from surrounding channels during floods was identified as a key process modulated by the presence of woody vegetation and a deflection effect induced by the preexisting topography grain size segregation between vegetated and bare areas was also highlighted and interpreted as an important process affecting the development of surrounding channels and the degree of disconnection and hence the speed of development of a growing island the heterogeneity of bedload supply can explain why sediment deposition and density of trees are not strictly related a general conceptual model detailing the first stages of evolution from a bar to an established island is proposed for relatively large lowland rivers

impact of floods on the statistical distribution of riverbed vegetation investigating the colonization of river bars by pioneer vegetation we discuss how the balance between uprooting by flooding events and reinforcement of plant roots determines the ability for vegetation to colonize the riverbed in order to access the competition between growth and uprooting we work in a regime where the arrival time of flooding events is comparable with the timescales associated with vegetation i e plant germination and development rates we present new results for a flume experiment using converging channel walls and draw contrasts with previously published results for a simple channel with parallel sides this comparison highlights the role of varying local stream power in these processes we collected the statistics of vegetation root length number of roots and stem height for both riverbed and uprooted vegetation and show using a stochastic approach how the statistics for vegetation surviving in the riverbed alter a flood result from both the distribution of riverbed biomass before the flood and the distribution of biomass that is uprooted by the flood finally we compare our laboratory results with data obtained in a field experiment to show the similarities in the uprooting processes at both scales c 2012 elsevier b v all rights reserved

flow and deposition in and around a finite patch of vegetation this laboratory study describes the flow and deposition observed in and around a finite patch of vegetation located at the wall of a channel two patch densities are considered with 2 and 10 solid volume fraction the velocity field measured in and around the patch by acoustic doppler velocimetry revealed three distinct zones first there is a diverging flow region at the leading edge of the patch where the flow in line with the patch decelerates and the bulk of the flow is diverted toward the open channel second there is a fully developed region within the vegetation where the velocity is uniform across the patch width and along the length of the patch third a shear layer forms at the interface between the patch and adjacent open channel the pattern of deposition in and around the vegetation was characterized by releasing 12 micron spherical glass particles and recording net deposition on a set of glass slides in the diverging region net deposition increases in the stream wise direction as the local velocity decreases in the fully developed region of the patch deposition decreases with longitudinal position as the concentration in the water column is depleted the deposition pattern is nearly uniform across the patch width consistent with the velocity field and suggesting that turbulent diffusive flux across the lateral edge of the patch is not a significant source of particles to the patch under the conditions studied here

geochronology of late pleistocene to holocene speleothemsfrom central texas implications for regional paleoclimate a detailed chronology for four stalagmites from three central texas caves separated by as much as 130 km provides a 71 000 yr record of temporal changes in hydrology and climate mass spectrometric 238 u230 th and 235 u231 pa analyses have yielded 53 ages the accuracy of the ages and the closedsystem behavior of the speleothems are indicated by interlaboratory comparisons concordance of 230 th and 231 pa ages and the result that all ages are in correct stratigraphic order over the past 71 000 yr the stalagmites have similar growth histories with alternating periods of relatively rapid and slow growth the growth rates vary over more than two orders of magnitude and there were three periods of rapid growth 71 60 ka 39 33 ka and 24 12 ka these growth rate shifts correspond in part with global glacial interglacial climatic shifts paleontological evidence indicates that around the last glacial maximum 20 ka climate in central texas was cooler and wetter than at present this wetter interval corresponds with the most recent period of increased growth rates in the speleothems which is consistent with conditions necessary for speleothem growth the temporal shift in wetness has been proposed to result

the effect of surface texture on the determination of the surface hardness of rock using the schmidt hammer the schmidt hammer is employed by geomorphologists as a convenient field instrument for measuring the hardness of rock surfaces field trials indicate that the readings obtained are a function of not only the hardness of the surfaces but also their texture smooth planar surfaces give much higher readings than rough or irregular surfaces this makes interpretation of the results particularly difficult when the hammer is used to measure the hardness of natural rock surfaces that have been roughened by weathering

characteristics of terrestrial basaltic rock populations implications for mars lander and rover science and safety abstract we analyzed the morphometry of basaltic rock populations that have been emplaced or affected by a variety of geologic processes including explosive volcanic eruptions as a proxy for impact cratering catastrophic flooding frost shattering salt weathering alluvial deposition and chemical weathering morphometric indices for these rock populations were compared to an unmodified population of rocks that had broken off a solidified lava flow to understand how different geologic processes change rock shape we found that a majority of rocks have an sphericity described as either a disc or sphere in the zingg classification system and posit that this is a function of cooling fractures in the basalt zingg 1935 schweiz miner petrogr mitt 15 39 140 angularity roundness is the most diagnostic morphometric index but the corey shape factor csf oblate prolate index opi and deviation from compactness d also sometimes distinguished weathering processes comparison of our results to prior analyses of rock populations found at the mars pathfinder spirit and curiosity landing sites support previous conclusions the observation that the size frequency distribution of terrestrial rock populations follow exponential functions similar to lander and orbital measurements of rocks on mars which is expected from fracture and fragmentation theory indicates that these distributions are being dominantly controlled by the initial fracture and fragmentation of the basalt

experimental characterization of vegetation uprooting by flow we investigate vegetation uprooting by flow for avena sativa seedlings with stem to sediment size ratio close to unity and vanishing obstacle induced scouring by inducing parallel riverbed erosion within an experimental flume we measure the time to uprooting in relation to root anchoring and flow drag forces we link the erosion rate to the uprooting timescales for seedlings with varying mean root length we show that the process of continuous erosion leading to uprooting resembles that of mechanical fatigue where system collapsing occurs after a given exposure time by this analogy we also highlight the nonlinear role of the residual root anchoring versus the flow drag acting on the canopy when uprooting occurs as a generalization we propose a framework to extend our results to time dependent erosion rates which typically occur for real river hydrographs finally we discuss how the characteristic timescale of plant uprooting by flow erosion suggests that vegetation survival is conditioned by multiple erosion events and their interarrival time

hydrothermal alteration and earth surface rock weathering a basalt example geomorphologists have not devoted sufficient attention to the formation of clay minerals by hydrothermal activity this paper describes the breakdown of freshly quarried basalt by cyclic wetting and drying breakdown is attributed to the swelling of hydrothermally derived smectite and it is argued that the effects of endogenic processes can exert a significant control upon weathering behaviour under earth surface conditions

paleomagnetic and tephra evidence for tens of missoula floods in southern washington paleomagnetic secular variation and a hiatus defined by two tephra layers confirm that tens of floods from glacial lake missoula montana entered washington s yakima and walla walla valleys during the last glaciation in these valleys the field evidence for hiatuses between floods is commonly subtle however paleomagnetic remanence directions from waterlaid silt beds in three sections of rhythmically bedded flood deposits at zillah touchet and burlingame canyon display consistent secular variation that correlates serially both within and between sections the secular variation may further correlate with paleomagnetic data from fish lake oregon and mono lake california for the interval 12 000 17 000 14 c yr b p deposits of two successive floods are separated by two tephras derived from mount st helens washington the tephras differ in age by decades indicating that a period at least this long separated two successive floods the beds produced by these two floods are similar to all of the 40 beds in the slack water sediment sequence suggesting that the sequence is a product of tens of floods spanning a period of perhaps a few thousand years

moraine preservation and boulder erosion in the tropical andes interpreting old surface exposure ages in glaciated valleys cosmogenic dating provides a long awaited means of directly dating glacial deposits that pre date the last glacial cycle although the potential benefits of longer chronologies are obvious the greater uncertainty associated with older cosmogenic ages may be less readily apparent we illus trate the challenges of developing and interpreting a long chronology using our data from the peruvian andes we used surface exposure dating with cosmogenic radionuclides crns 10 be and 26 al to date 140 boulders on moraines in valleys bordering the junin plain 11 s 76 w in central peru our chronology spans multiple glacial cycles and includes exposure ages greater than 1 million years which indicate that long term rates of boulder erosion have been very low interpreting the chronology of moraines for glaciations that predate the last glacial cycle is complicated by the need to consider boulder erosion and exhumation surface uplift and inheritance of crns from pre vious exposure intervals as an example we recalculate exposure ages using our boulder erosion rates 0 3 0 5 metres per million years and estimated surface uplift rates to emphasise both the chal lenges involved in interpreting old surface exposure ages and the value of chronological data even with large uncertainties when reconstructing the palaeoclimate of a region copyright 2005 john wiley sons ltd

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

size frequency distributions of rocks on mars and earth analog sites implications for future landed missions the size frequency distribution of rocks at the viking landing sites and a variety of rocky locations on the earth that formed from a number of geologic processes all have the general shape of simple exponential curves which have been combined with remote sensing data and models on rock abundance to predict the frequency of boulders potentially hazardous to future mars landers and rovers rock data from the near field of the viking landers where dimensions can be measured accurately in stereo images and estimates from the far field of viking 1 have convex up curved shapes on log log graphs of cumulative frequency per square meter or cumulative fractional area versus diameter the rock data show a sharp drop off at large diameters and a progressive approach to a plateau with decreasing diameter approaching the total rock coverage which can be fit well with simple exponential functions similar shaped size frequency distributions of rocks are found at a wide variety of rocky surfaces on the earth and can be fit well with simple exponential functions this distribution is compatible with fracture and fragmentation theory which provides a physical basis for its wide application a combined fit to rock area data at both viking sites was made with a general exponential function in which the pre exponential is the total area covered by rocks simple linear height versus diameter relationships were also derived from height diameter ratios at the viking sites which suggest that rockier areas on mars have higher standing rocks than less rocky areas height was then substituted into the general exponential function derived for diameter yielding the cumulative fractional area of rocks versus height for any given total rock coverage on mars results indicate that most of mars is rather benign with regard to hazards from landing on large rocks for total rock coverage of 8 equivalent to modal rock coverage on mars and the viking 1 site without the outcrops about 1 of the surface is covered by 20 cm or higher rocks a lander designed to accommodate landing on 0 5 m high boulders such as the mars pathfinder airbag system could land on a surface covered by about 20 rocks similar to the viking 2 site which is rockier than 95 of the planet with 1 of the surface covered by rocks of 0 5 m or higher

review of close range three dimensional laser scanning of geological hand samples abstract the morphological study of geological hand samples has a wide variety of applications in the geosciences which is conventionally accomplished by measuring the distance between features of interest on the sample s surface close range three dimensional 3d laser scanners provide an opportunity to study the form and shape of geological samples in a digital environment and have been increasingly utilized in fields such as paleontology rock mechanics and sedimentology with some uptake in planetary sciences and structural geology for paleontological studies primary applications are in quantitative analysis of fossil morphology and integration into 3d animated models for understanding species movements in the field of rock mechanics typical uses of 3d digital geological hand sample models include quantifying joint roughness coefficient jrc determining the surface roughness of rock samples and assessing morphological changes over time due to processes such as weathering in the field of sedimentology such models are incorporated to characterize the shape of sediment particles and to calculate key parameters such as bulk density this paper aims to provide a comprehensive review of established literature that includes substantial use of digital geological hand samples acquired from 3d close range