long term atmospheric deposition as the source of nitrate and other salts in the atacama desert chile new evidence from mass independent oxygen isotopic compositions abstract isotopic analysis of nitrate and sulfate minerals from the nitrate ore fields of the atacama desert in northern chile has shown anomalous 17 o enrichments in both minerals 17 o values of 14 21 in nitrate and 0 4 to 4 in sulfate are the most positive found in terrestrial minerals to date modeling of atmospheric processes indicates that the 17 o signatures are the result of photochemical reactions in the troposphere and stratosphere we conclude that the bulk of the nitrate sulfate and other soluble salts in some parts of the atacama desert must be the result of atmospheric deposition of particles produced by gas to particle conversion with minor but varying amounts from sea spray and local terrestrial sources flux calculations indicate that the major salt deposits could have accumulated from atmospheric deposition in a period of 200 000 to 2 0 m years during hyper arid conditions similar to those currently found in the atacama desert correlations between 17 o and 18 o in nitrate salts from the atacama desert and mojave desert california indicate varying fractions of microbial and photochemical end member sources the photochemical nitrate isotope signature is well preserved in the driest surficial environments that are almost lifeless whereas the microbial nitrate isotope signature becomes dominant rapidly with increasing moisture biologic activity and nitrogen cycling these isotopic signatures have important implications for paleoclimate astrobiology and n cycling studies

mapping surface mineralogy using imaging spectrometry abstract imaging spectrometry simultaneous measurement of spectra and images in up to hundreds of spectral channels or bands is a proven technology for identifying and mapping minerals based on their reflectance or emissivity signatures also known as hyperspectral imaging or hsi extraction of key spectral signatures from these data allows direct identification of iron minerals such as hematite goethite and jarosite in the visible near infrared vnir clays carbonates micas sulfates and other minerals in the short wave infrared swir and silicates and carbonates in the long wave infrared lwir the unique capability of imaging spectrometry to produce detailed maps of the spatial distribution of specific minerals mineral assemblages and mineral variability on the surface of earth makes it an ideal tool for enhanced geomorphic mapping case histories illustrate the use of hsi for characterizing and mapping active and relict geothermal hydrothermal systems and determining relations between mineralogy and derived landforms imaging spectrometry used in conjunction with complimentary datasets such as insar interferometric synthetic aperture radar light detection and ranging lidar or stereo photogrammetric derived digital elevation models dems provides a unique means of visualizing the spatial distribution and association of mineralogy with topography thus contributing to the understanding of the relations between geology and landscape and to improved interpretation of surface geologic processes

salt weathering in dual porosity building dolostones abstract the influence of rock fabric on physical weathering due to the salt crystallization of selected brecciated dolostones is discussed these dual porosity dolostones are representative of heterogeneous and anisotropic building rocks and present highly complex and heterogeneous rock fabric features the pore structure of the matrix and clasts is described in terms of porosity and pore size distribution whereas the relative strength for each textural component is assessed using the knoop hardness test the whole characterisation process was carried out using the same samples as those used in the standard salt durability test en 12370 including connected porosity the water saturation coefficient fissure density compressional wave velocity and waveform energy results show the most important rock fabric elements to be considered are the matrix and clast properties and the nature of fissures firstly a relatively weak matrix was the focus of major granular disintegration as it presents high porosity low pore radius and reduced strength secondly narrow micro fissures appear to be important in the decay process due to the effectiveness of crystallization pressure generated by salt growth on the contrary macro fissures do not contribute greatly to rock decay since they act as sinks to consume the high supersaturations caused by growth of large crystals additionally an analysis of stress generated by crystallization was carried out based on the general situation of a lenticular crystal geometry finally the relationships between whole petrophysical properties and durability were established using a principal component analysis this analysis has clearly established that the durability of rocks affected by salt crystallization mechanisms diminishes in weaker and anisotropic rocks with high porosity and fissure density

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

nitrate perchlorate and iodate co occur in coastal and inland deserts on earth abstract deserts accumulate soluble salts from atmospheric deposition that impact human health are a source of nutrients for organisms and provide insight into how landscapes evolved on earth and mars we quantified perchlorate nitrate and iodate abundances and co occurrence in terrestrial deserts to identify fundamental controls on soluble salt deposition and post depositional cycling soils and nitrate deposits were examined in death valley usa atacama desert chile kumtag desert china and along an environmental gradient in the transantarctic mountains antarctica concentrations of soluble salts were highest in the transantarctic mountains and atacama desert where stable hyper arid landscapes accumulate atmospheric salts over million year time scales average nitrate concentrations of 61 3 g kg 1 in the transantarctic mountains and 53 0 g kg 1 in the atacama desert were significantly greater than respective averages of 8 60 g kg 1 and 5 14 g kg 1 in kumtag desert and death valley perchlorate and iodate concentrations in the atacama desert averaged 206 mg kg 1 and 344 mg kg 1 respectively which were two to three orders of magnitude greater than in antarctica and other sites our findings suggest that local processes in the atacama desert result either in higher rates of perchlorate and iodate deposition or a greater preservation of these salts relative to nitrate when compared to antarctic landscapes lower salt concentrations in the death valley and kumtag desert deposits likely result from relatively wet present day and paleoclimatic conditions a more active geologic history and a greater likelihood that biocycling disrupted long term salt accumulation associations of perchlorate and nitrate were significantly higher than iodate nitrate and iodate perchlorate correlations in the four deserts perchlorate nitrate relationships ranged from insignificant to highly significant with stronger correlations in the atacama desert and kumtag desert compared to the transantarctic mountains and death valley weaker geochemical associations with iodate were attributed to differences in local deposition rates or post depositional cycling interestingly relationships among perchlorate nitrate and iodate were generally stronger when examined by site within each desert compared to analyzing the soils for each desert as a whole suggesting more localized controls on soluble salt preservation we conclude that soluble salts vary in concentration and type across earth s deserts as a result of present day environment paleoclimate conditions biocycling and geologic age

geotechnical properties of rock masses their control on slope form and mechanisms of change along the napier range western australia abstract slope form and the mechanisms of change which slope profiles exhibit are frequently subject to scrutiny by geomorphologists however the majority of studies do not consider fundamental material properties and rock mass geotechnical characteristics the results presented here highlight the importance of synthesisistandard geomorphological site investigation techniques with quantifiable rock geotechnical parameters in order to understand slope form and development field research has been undertaken along the napier range of the kimberly region western australia the napiers are an extensive upraised devonian limestone reef along which a number of characteristic slope profiles can be identified laboratory studies of yield strength stress strain characteristics elastic properties and discontinuity parameters have been conducted on material sampled at sites representative of each slope profile type the results suggest that highly concave slopes have formed in limestone which exhibits little deformation before yield has a high modulus of elasticity and few irregular fractures convexo concave slopes on the other hand are characteristic of material which displays a greater ability to strain below yield a relatively low modulus of elasticity and a pronounced discontinuity pattern it is the combination of field investigation and laboratory study which most successfully explains variations in slope form

lithologic and tectonic controls on bedrock channel form at the northwest himalayan front 1 recognition that channel form reflects a river s ability to erode rock and transport material has spawned stream power models that estimate incision patterns by approximating energy dissipation within a channel these models frequently assume that channel width scales as a power law with drainage area partly because drainage area is easily extracted from digital elevation models dems however this assumption is often confounded by local variations in rock strength and rock uplift rate that can cause channel constriction downstream here we investigate the morphological response to spatial changes in rock strength and rock uplift rate of 10 bedrock channels traversing the mohand range along the northwest himalayan front we present a new method to continuously measure and compare channel width slope and other hydraulic parameters that integrate satellite imagery and dem analysis our method corrects for an 13 overestimation of average channel gradient from a 90 m resolution dem that arises from short circuits of fine scale meanders we find that channels 1 narrow 1 km upstream from knickpoints formed by an increase in rock strength 2 adjust laterally more than vertically in response to downstream decreases rock erodibility and uplift rate and 3 meander where shear stresses are high and channel widths are low we attribute these results to a high ratio of sediment supply to transport capacity which enhances lateral erosion relative to vertical incision our results suggest that substrate strength and sediment supply substantially influence channel form and that channel width should be explicitly measured when interpreting tectonic signals from bedrock channel morphology

a lacustrine record from lop nur xinjiang china implications for paleoclimate change during late pleistocene abstract climate variability during the late pleistocene is studied from the proxies in core ck 2 drilled from the luobei depression 91 03 e 40 47 n lop nur in the eastern tarim basin xinjiang china geophysical and geochemical properties including magnetic susceptibility granularity chroma carbonate content loss on ignition and trace elements have been determined to reconstruct the environmental evolution of the area during 32 9 ka bp the chronology is established by uranium thorium disequilibrium dating techniques our data suggest four paleoclimate stages indicating glacial variations between cold humid and warm arid environments a period of extreme humidity occurred during 31 900 19 200 yr bp is attributed the last glacial maximum lgm the period was followed by a warm arid episode during 19 200 13 500 yr bp then a cold humid interval during 13 500 12 700 yr bp may correspond to another cooling phases at high latitudes of the northern hemisphere the last stage from 12 700 to 9000 yr bp has a trend that the climate turned warm and arid the lop nur region is characterized by particularly humid stadials and arid interstadials the climate variability in lop nur was constrained by global climate change because it is correlated with dansgaard oeschger and heinrich events which were observed at the northern high latitudes the synchroneity of the palaeoclimatic events suggested that cold air activity at the northern high latitudes was the most important factor that influenced the climate evolution in the lop nur region a probable mechanism that involves the migration of westerly winds is proposed to interpret this synchroneity

scale dependence of lithological control on topography bedrock channel geometry and catchment morphometry in western scotland abstract we propose that a scale dependent topographic signature of erodibility arises due to fluvial and glacial erosion acting on different parts of the landscape at different times for 14 catchments in western scotland we define three levels of substrate erodibility in order of decreasing resistance quartzite rocks nonquartzite rocks and zones of fault related fracture then using digital topographic and planimetric data coupled with field measurements we identify regression based scaling relationships between substrate erodibility and morphometric parameters at two spatial scales catchment scale morphometry shows a weak to variable relationship with substrate metrics overall erodibility can be inferred from catchment steepness indices i e channel steepness index and relief ratio but the existence of multiple exceptions could confound a more general application of this approach nonetheless major valley troughs trace fault zones and nonquartzite rocks leaving much of the higher and stee

shore platform downwearing in eastern canada the mega tidal bay of fundy abstract laboratory and field work was conducted to determine rates of surface downwearing on shore platforms at two sites in the bay of fundy canada these data are needed to assess and model the effect of downwearing mechanisms on platform evolution sandstone and basalt samples 900 were exposed to semidiurnal tidal cycles over 3 years using de ionized water or artificial sea water they were immersed for 1 6 or 11 h over each 12 h tidal cycle representing the lowest high lht mid and highest low hlt tidal levels respectively a further 600 samples were immersed in de ionized water or artificial sea water for 90 min every 1 2 or 3 weeks representing increasingly higher elevations above the lht level or exposed for 90 min every 1 2 or 3 weeks representing increasingly lower elevations below the hlt level these experiments ran for 12 months in the field surface downwearing was measured at 108 transverse micro erosion meter tmem stations over 2 to 6 year periods in the laboratory mean downwearing rates between the lht and hlt levels were 0 61 1 80 mm yr 1 in sandstones and 0 01 0 18 mm yr 1 in basalts rates were highest at the lht level rates decreased with elevation above the lht level and were uniformly low below the hlt level salt weathering was dominant above the lht level salt weathering and wetting and drying were important in sandstones between the lht and hlt levels but salts inhibited rock breakdown in basalts in the field the mean downwearing rate was 1 254 mm yr 1 in sandstones which was similar to the experimental data and 0 722 mm yr 1 in basalts which was much higher than in the experiments with artificial sea water but similar to the experiments with de ionized water there was no relationship in the field between downwearing rate and rock hardness or tmem station elevation

weakening of gneiss surfaces colonized by endolithic lichens in the temperate climate area of northwest italy a role of lithobionts in geomorphological processes is increasingly argued but the spatio temporal scale of their impact is largely unexplored in many ecosystems this study first characterizes in the temperate zone northwest italy the relationships between lithobiontic communities including endolithic lichens and the hardness of their siliceous rock substrate villarfocchiardo gneiss the communities are characterized on humid and xeric quarry surfaces exposed for decades and natural outcrops exposed for centuries in terms of lichen and microbial constituents using a combined morphological and molecular approach and with regard to their development on and within the gneiss a lichen species belonging to acarosporaceae polysporina sarcogyne acarospora group needing taxonomic revision chasmoendolithically colonizes both the humid and xeric quarry surfaces on which epilithic cyanobacterial biofilms and epilithic pioneer lichens respectively occur light and electron microscopic observations show the development of the endolithic thalli within rock microcracks and the hyphal penetration along crystal boundaries down to depths of 1 to 3 mm more pronounced within the humid surfaces such colonization patterns are likely related to biogeophysical deterioration while no chemical alteration characterizes minerals contacted by the endolithic lichen by contrast on natural outcrops where the endolithic colonization is negligible a reddish rind below epilithic lichens indicates chemical weathering processes schmidt hammer measurements highlight that the endolithic lichens deeply affect the hardness of the gneiss down to 60 with respect to fresh controls and surfaces only colonized by cyanobacteria exerting a significantly higher weakening effect with respect to the associated epilithic lithobionts the phenomenon is more remarkable on humid than on xeric quarry surfaces and natural outcrops where epilithic lichens are likely involved in long term hardening processes supporting surface stabilization endolithic lichens are thus active biogeomorphological agents at the upper millimetric layer of siliceous rocks in temperate areas exerting their weakening action during the early decade scaled stages of surface exposure copyright 2015 john wiley sons ltd

massive atmospheric nitrate accumulation in a continental interior desert northwestern china large scale nitrate deposits are rare on earth s surface due to the high solubility of nitrate minerals exceptions are found in extremely old to 14 m y and hyperarid deserts such as the atacama desert in northern chile or the mcmurdo dry valleys in antarctica the nitrate in both of these regions has been determined to originate from atmospheric oxidation of nox here we report a new type of massive atmospheric nitrate deposit with resources equivalent to the atacama deposits in the turpan hami area northwestern china this deposit is characterized by 1 a location in the center of a large continent 2 young age pleistocene 3 general enrichment near the surface rather than at depth and 4 high spatial variability in the nitrogen and triple oxygen isotope composition within this arid region the 15n ranging from 0 7 to 27 6 18o from 30 2 to 46 7 and 17o from 5 9 to 20 7 the turpan hami nitrate deposit nitrogen and triple oxygen isotope composition is closely between those of the mojave desert southwestern united states and the atacama desert suggesting that 1 earth s low middle latitudes i e non polar sites have been receiving atmospheric nitrate deposition of similar nitrogen and triple oxygen isotope composition and 2 local or regional isotope differences in nitrate deposits can be attributed to postdepositional processes namely the difference in aridity and associated microbial activities

geoelectric investigations into sandstone moisture regimes implications for rock weathering and the deterioration of san rock art in the golden gate reserve south africa the clarens sandstone in the golden gate reserve south africa is the canvas for a collection of san bushmen rock art dating from neolithic times until as recently as 150 years ago this rock art is under threat from human interference but also to a greater degree from weathering processes on the rock surface the dominant weathering processes occurring in the rock shelters which host the rock art are flaking and honeycombing two rock shelter sites in the reserve have been investigated using electric resistivity tomography ert and supportive methods for measuring surface moisture protimeter and surface hardness equotip these non destructive techniques can be used in situ to assess the extent of weathering within a rock outcrop and are especially suited for investigations in sensitive areas such as rock art sites moisture movement has been mapped and related to the weathering processes observed on the surface the aim of the study is to aid rock art conservation in the golden gate reserve through a better understanding of the driving processes of surface weathering the evidence shows that the extensive flaking and honeycombing found in the rock shelters is most likely caused by water pockets in the near surface zone which are replenished through internal moisture transport driving the superficial weathering processes these weathering processes pose a significant problem rock art in the golden gate reserve shows severe deterioration due to flaking conservation strategies should therefore take internal processes into account as much as their superficial expression

a new quantitative weathering classification for igneous rocks the description and classification of the rocks provide important information for geotechnical modeling in order to predict their engineering behaviors one of the most imperative parameters influencing the engineering behaviors of the rocks is the degree of weathering therefore it is evident that a realistic weathering classification is necessary mostly for establishing the geotechnical models in the engineering geology studies for this reason development of a qualitative weathering classification is the main purpose of the present study the weathering state parameter has been first created by describing the chemical and physical changes separately owing to weathering by employing the ultrasonic wave velocity in the rock material then a quantitative weathering index was introduced by combining the weathering condition and the slake durability known as the indicator of the rock soil ratio in the rock material finally this index obtained was applied on the prediction of the engineering properties of the harsit granitic rocks giresun ne turkey as a consequence of this study it has been determined that the engineering properties of the samples and the numerical index proposed could be predicted in addition the use and the limitations of the index introduced herein were discussed

rock strength along a fluvial transect of the colorado plateau quantifying a fundamental control on geomorphology a b s t r a c t bedrock strength is a key parameter that influences slope stability landscape erosion and fluvial incision yet it is often ignored or indirectly constrained in studies of landscape evolution as with the k erodibility parameter in stream power models empirical datasets of rock strength suited to address geomorphic questions are rare in part because of the difficulty in measuring those rocks at earth s surface that are heterolithic weak or poorly exposed here we present a large dataset of measured bedrock strength organized by rock units exposed along the length of the trunk green colorado river through the iconic colorado plateau of the western u s measurements include field compressive tests fracture spacing and selby rock mass strength at 168 localities as well as 672 individual tensile strength tests in the laboratory tensile strength results are compared to geomorphic metrics of unit stream power river gradient and channel and valley bottom width through the arid colorado plateau where the influence of bedrock is intuitive but unquantified our dataset reveals logical trends between tensile and compressive strength as well as between strength rock type and age in bedrock reaches of the fluvial transect there is a positive rank correlation and a strong power law correlation between reach averaged rock strength and unit stream power as well as a linear relation between tensile strength and river gradient expected relations between fracture spacing and topography are masked partly by the massive yet weak sandstones in the dataset to constrain values for weak rock types such as shale we utilize the inverse power law scaling between tensile strength and valley bottom width to estimate their effective tensile strength results suggest that tensile strength varies to at least an order of magnitude smaller values than evident with directly testable rocks in this landscape and values for erodibility k in numerical simulations may be informed by this dataset in terms of landscape evolution these results support the finding that equilibrium adjustment to bedrock strength not differential uplift or transient incision is the first order control on large scale fluvial geomorphology in the colorado plateau this has broad implications for the interpretation of topography in terms of tectonic drivers

remnants of a fossil alluvial fan landscape of miocene age in the atacama desert of northern chile using cosmogenic nuclide exposure age dating we have used cosmogenic nuclides to estimate limits on the surface exposure durations and erosion rates of alluvial fans and bedrock surfaces in the atacama desert in chile the oldest landforms we studied are extensive alluvial fans referred to as atacama gravels with the exception of samples collected in antarctica the cobbles collected on these alluvial surfaces have the lowest erosion rates of any samples as determined by cosmogenic nuclides analyzed to date the oldest cobble has a model surface exposure age of 9 myr based on combined measurements of cosmogenic 10be 26al and 21ne concentrations cobbles from the alluvial fans are eroding slower than the surrounding steep mountainous bedrock surfaces maximum erosion rates for cobbles on alluvial surfaces are uniformly 0 1 m myr the survival of these gravels specifically and more generally the stability of landform features in this geographic area is made possible by the attainment of hyperarid conditions in the atacama desert resulting from global climatic cooling about 15 myr ago combined with the rain shadow effect caused by uplift of the central andes the landform features observed presently in the atacama desert are remarkably stable and despite the inevitable erosion that is detectable using cosmogenic nuclides undoubtedly bear considerable resemblance to conditions as they existed in the miocene over geologic time the atacama landscape is evolving in such a manner as to erode the higher bedrock ridges relative to the more stable but stratigraphically lower depositional surfaces through which clastic detritus now travels occasionally along the floors of incised drainage systems leaving the older permeable alluvial fan surfaces largely intact as widespread remnants of a miocene fossil landscape

an investigation on the effect of accelerated weathering on strength and durability of tertiary sandstones qazvin province iran damages to stones induced by the action of freeze thaw and salt crystallization are considered to be of great importance in engineering construction these processes can influence the strength and durability of porous materials and consequently deteriorate them in this study the effects of freeze thaw f t and salt crystallization s c phenomena on strength and durability of upper red formation sandstones were investigated nine specimens of sandstones were collected from different parts of qazvin area iran and then their physical and mechanical characteristics were determined to assess the effect of f t and s c on physical and mechanical characteristics of sandstones 60 cycles of f t test and 20 cycles of s c test were performed physical and mechanical characteristics of these sandstones including wave velocity vp changes weight loss point load index and brazilian tensile strength were determined after different cycles for assessing the effect of freeze thaw and salt crystallization phenomena on slake durability index sdi of sandstones slake durability test was performed on specimens subjected to f t and s c then changes occurred in the sdi after 15 cycles were investigated finally the long term durability of sandstones against freeze thaw and salt crystallization action was evaluated using a decay function model this model postulates a first order process and provides some meaningful parameters such as decay constant and half life for the evaluation of long term durability of stones based on results obtained from current study it can be concluded that in comparison to freeze thaw salt crystallization can considerably reduce the strength and durability of sandstones also parameters obtained from decay function model showed that the rate of integrity loss is different for different weathering processes and stone durability can be predicted by this method with good accuracy

integrated provenance analysis of a complex orogenic terrane mesozoic uplift of the bogda shan and inception of the turpan hami basin nw china we employ petrographic and advanced geochemical tech niques to better document the evolution of the turpan hami basin based on the unique geologic histories of the arc terranes that served as potential sources of turpan hami deposits first a provenance study of permian through cretaceous sandstone of the turpan hami basin reveals temporal and spatial changes in dominant source ter ranes that provided detritus to the basin volcanic lithic rich upper permian sandstone mean qm 19f18lt63 q p 7lvm89lsm4 q m 48p39k13 followed by more quartzose compositions in triassic sandstone mean qm 41f19lt40 q p 20lvm75lsm5 q m 68p21k11 indicate progressive un roofing of the extinct northern and central tian shan arc terranes to the south of turpan hami a sharp change to sedimentary lithic rich lower jurassic sandstone mean qm 47f16lt37 q p 16lvm42lsm42 qm 75p12k13 overlain by a return to volcanic lithic rich middle ju rassic sandstone mean qm 39f21lt40 q p 14lvm51lsm35 q m 65p21k14 points to the initial uplift and unroofing of the largely andesitic bogda shan to the north which first shed its sedimentary cover as it emerged to become the partition between the turpan hami and southern jung gar basins second geochronological trace element and sm nd isotopic varia tions among granitoids in the late paleozoic tian shan orogenic belt provide a further test of mesozoic uplift of the bogda shan on the basis of previous models of crustal compositions throughout the south central and north tian shan bogda shan and east and west jung gar terranes we infer that isotopically enriched granitic cobbles av erage endi 5 20 50 n 5 6 contained in lower triassic deposits in the north central turpan hami basin were derived from the continen tal crustal central tian shan terrane south of turpan hami and not from the more oceanic north tian shan bogda shan and east and west junggar terranes north of the turpan hami basin we therefore infer that the ancestral bogda shan had not been uplifted by the early triassic and that prior to this time a unified junggar turpan hami basin existed during late permian deposition of extensive lacustrine deposits

variability of rock erodibility in bedrock floored stream channels based on abrasion mill experiments we quantify variations in rock erodibility kr within channel cross sections using laboratory abrasion mill experiments on bedrock surfaces extracted from streams with sandstone bedrock in utah and basaltic bedrock in the hawaiian islands samples were taken from the thalweg and channel margins the latter at a height that is inundated annually for each sample a sequence of abrasion mill experiments was completed to quantify variations in erosion rate with erosion depth erosion rate data from these experiments shows two things first the erosion rate from channel margin samples is greater than for thalweg samples with the greatest difference observed for the rock surface that was exposed in the stream channel second erosion rate decreases with depth beneath the original rock surface by an order of magnitude in most cases the erosion rate becomes steady at depths of 1 3 mm for channel margin samples and 0 1 0 4 mm for thalweg samples because only rock properties and microtopography vary throughout the sequence of mill experiments these results suggest that kr of the bedrock surface exposed in stream channels is higher at the margins than near the channel center and that kr decreases over depths of 1 mm the simplest explanation for these patterns is that kr is enhanced at the bedrock surface and along the channel margins due to the effects of weathering on rock strength and surface roughness we hypothesize that a balance exists between weathering enhanced erodibility and episodic incision to allow channel margins to lower at rates similar to the thalweg

influence of rock mass strength on the erosion rate of alpine cliffs collapse of cliff faces by rockfall is a primary mode of bedrock erosion in alpine environments and exerts a first order control on the morphologic development of these landscapes in this work we investigate the influence of rock mass strength on the retreat rate of alpine cliffs to quantify rockwall competence we employed the slope mass rating smr geomechanical strength index a metric that combines numerous factors contributing to the strength of a rock mass the magnitude of cliff retreat was calculated by estimating the volume of talus at the toe of each rockwall and projecting that material back on to the cliff face while accounting for the loss of production area as talus buries the base of the wall selecting sites within basins swept clean by advancing last glacial maximum lgm glaciers allowed us to estimate the time period over which talus accumulation occurred i e the production time dividing the magnitude of normal cliff retreat by the production time we calculated recession rates for each site our study area included a portion of the sierra nevada between yosemite national park and lake tahoe rockwall recession rates determined for 40 alpine cliffs in this region range from 0 02 to 1 22 mm year with an average value of 0 28 mm year we found good correlation between rockwall recession rate and smr which is best characterized by an exponential decrease in erosion rate with increasing rock mass strength analysis of the individual components of the smr reveals that joint orientation with respect to the cliff face is the most important parameter affecting the rockwall erosion rate the complete smr score however best synthesizes the lithologic variables that contribute to the strength and erodibility of these rock slopes our data reveal no strong independent correlations between rockwall retreat rate and topographic attributes such as elevation aspect or slope angle copyright 2009 john wiley sons ltd

geomorphology emergent sculpture sandstone arches and other striking landforms are the showpieces of national parks around the globe experiments and numerical analyses show that they result from a self organization process that involves vertical load wind erosion and grain locking

characterising the spatial distribution frequency and geomorphic controls on landslide occurrence molise italy abstract an 815 km2 area in molise central italy was used as a natural laboratory to characterise the lithological topographic and fluvial controls on the spatial distribution and frequency of active landslides in temperate climates the study area is part of the central apennines fold and thrust belt and is characterised by the presence of a tectonic melange of scaly clays known as argille varicolori as well as more competent limestone and sandstone units the area has been subjected to a cumulative stream incision of up to 400 m since the mid pleistocene the landslide inventory was developed by combining satellite image interpretation and existing data sets ground truthed in the field statistical analysis of the inventory data demonstrates that the coupling between landslide occurrence in the area and lithology is strong with landslides occurring 3 10 times more frequently where the mechanically weak argille varicolori scaly clays outcrops compared to other lithologies analysis of the relationship between landslide occurrence and hillslope gradients shows that 50 of all landslides occur on slopes between 10 and 15 despite this interval representing only 30 of hillslope gradients in the study area these results demonstrate the major control that the properties of the regionally significant argille varicolori have on landslide occurrence in the area directly and through their control on hillslope gradients additionally our results show that more than 50 of the landslides occur at a distance of

rock weathering by the lichenlecidea auriculata in an arctic alpine environment scanning electron microscopy reveals that lecidea auriculata penetrates rock surfaces detaching incorporating and expelling flakes of rock measurements on an age sequence of moraine ridges illustrate changes in the extent and intensity of weathering over time a minimum rate of surface lowering 0 0012 mm a 1 is 25 to 50 times faster than weathering due to other processes in the same area the spatial pattern of weathering is influenced by the narrow ecological range of the species surface rocks on dry exposed sites are probably weathering much more rapidly than those in adjacent damp hollows and beneath snowpatches

a non destructive tool for detecting changes in the hardness of engineering materials application of the equotip durometer in the coastal zone non destructive tools capable of measuring the condition and geomechanical properties of construction materials through time are of considerable value in engineering here the ability of the equotip durometer proceq type d to detect changes in the hardness of concrete and rock exposed to marine conditions was tested results indicated a progressive loss of hardness for limestone while concrete hardness increased granite showed no significant change our results relate to alteration of the materials primarily via chemical and biological weathering the equotip is sensitive enough to detect subtle changes in the condition of construction materials over relatively short periods of time

the role of rock surface hardness and internal moisture in tafoni development in sandstone the development of cavernous weathering features such as tafoni remains poorly understood in particular the roles played by internal moisture and case hardening remain unclear in this study electric resistivity tomography ert has been used to map moisture distribution within inner walls of tafoni developed in sandstone and an equotip device used to measure rock surface hardness as a proxy measure of the degree of weathering and case hardening seven large tafoni in the golden gate highlands national park south africa varying in size and degree of development have been monitored a dynamic relationship between surface hardness degree of weathering and internal moisture regimes has been found we propose a new conceptual model which illustrates the complex interaction between case hardening and internal moisture and suggests a new direction for cavernous weathering research copyright 2011 john wiley sons ltd

biofilms and case hardening on sandstones from al quwayra jordan on cambrian and ordovician sandstone inselbergs at al quwayra in southern jordan many near vertical rock walls exhibit marked case hardening detailed examination of the case hardened layer from four sites on both red and white sandstones has been carried out using schmidt hammer simple chemical analyses scanning electron microscopy energy dispersive spectroscopy and inductively coupled plasma mass spectrometry these analyses reveal a range of types of case hardening often in association with cryptoendolithic bio lms containing cyanobacteria and fungi iron manganese and calcium are all found to be common constituents of cements within the case hardened layer micro organic bio lms may assist in the formation of case hardening through aiding cementation but are by no means a necessary component of all the hardened layers in the wadi rum area copyright 2004 john wiley sons ltd

developments in a non destructive method of determining rock strength material strength is an important variable for any study of the relationships between rock mass geomechanical characteristics and landform development standard field and laboratory tests for measuring strength present a variety of problems to the geomorphologist recent studies allison 1988 have described a laboratory based non destructive method for indirectly determining material strength by measuring dynamic young s modulus data presented here suggest that the same apparatus can be used as a field technique tests have been conducted on the devonian limestone of the napier range western australia laboratory results obtained using the non destructive ultrasonic apparatus have a high correlation with triaxial hoek cell tests results from on site tests have much greater accuracy than data collected using the schmidt hammer which is currently the most widely used geomorphological field technique for determining rock strength

stable isotope evidence for an atmospheric origin of desert nitrate deposits in northern chile and southern california u s a natural surficial accumulations of nitrate rich salts in the atacama desert northern chile and in the death valley region of the mojave desert southern california are well known but despite many geologic and geochemical studies the origins of the nitrates have remained controversial n and o isotopes in nitrate and s isotopes in coexisting soluble sulfate were measured to determine if some proposed n sources could be supported or rejected and to determine if the isotopic signature of these natural deposits could be used to distinguish them from various types of anthropogenic nitrate contamination that might be found in desert groundwaters high grade calich a type nitrate deposits from both localities have 15n values that range from 5 to 5 but are mostly near 0 values of 15n near 0 are consistent with either bulk atmospheric n deposition or microbial n fixation as major sources of the n in the deposits 18o values of those desert nitrates with 15n near 0 range from about 31 to 50 v smow significantly higher than that of atmospheric o2 23 5 such high values of 18o are considered unlikely to result entirely from nitrification of reduced n but rather resemble those of modern atmospheric nitrate in precipitation from some other localities assuming that limited modern atmospheric isotope data are applicable to the deposits and allowing for nitrification of co deposited ammonium it is estimated that the fraction of the nitrate in the deposits that could be accounted for isotopically by atmospheric n deposition may be at least 20 and possibly as much as 100 34s values are less diagnostic but could also be consistent with atmospheric components in some of the soluble sulfates associated with the deposits the stable isotope data support the hypothesis that some high grade caliche type nitrate rich salt deposits in some of the earth s hyperarid deserts represent long term accumulations of atmospheric deposition possibly in the order of 104 yr for the death valley region 107 yr for the atacama desert in the relative absence of soil leaching or biologic cycling the combined n and o isotope signature of the nitrate in these deposits is significantly different from those of many other natural and anthropogenic sources of nitrate

measurement and calibration of weathering using the schmidt hammer on wave washed moraines on the upper norrland coast sweden the schmidt hammer has for some years been used to measure the hardness of different rock surfaces and to date relatively boulders in moraine deposits in this paper applications on isostatically raised boulder beaches and rocky shores are described the research area is the northern swedish bothnian coast where present isostatic uplift is between 0 8 1 0 cm year 1 elevations above sea level can be converted to a timescale rebound values r of the schmidt hammer are correlated with the altitude and the degree of rock weathering can be estimated for each site eight sites with boulder beaches and nine sites with rocky shores have been analysed for boulder beaches correlation coefficients of 0 82 0 97 for weathering values r and the elevations above sea level were obtained for the rocky shores these values were calculated to 0 75 0 97 this method has applications in both geomorphology and archaeology for example a deep layer of weathered dolerite in the nordingra region which previously has been regarded as a post weichselian formation can be shown to be of pre weichselian origin several archaeological applications are also mentioned in the paper

glacial valley cross profile development the influence of in situ rock stress and rock mass strength with examples from the southern alps new zealand abstract the evolution of the glacial valley cross profile form is commonly attributed primarily to the glaciological variables that control the erosion of the channel however studies in the new zealand southern alps suggest that the rock mass strength rms of the eroded rock mass is a major control on slope stability and hence on the final form of the trough rms of the slope rock will alter with time and erosional excavation and oversteepening of the valley slopes the in situ rock stress field induced by 1 the extreme topography in the axial ranges of the new zealand southern alps and 2 tectonically by collision of the australian and pacific crustal plates may play a role in valley slope development by controlling the location of rock failure and reducing rms this provides weakened rock that may provide sites for selective glacial erosion of the rock mass hence valley form evolution models should also take into account the rms and the in situ stress field acting in the eroded rock mass this study has implications for the development and modification of alpine glacial troughs in similar tectonic settings elsewhere

rock resistance and the development of horizontal grooves on danxia slopes experimental analyses of uniaxial mechanical compressive strength resistance against sulfuric acid and freezing and thawing properties were performed on 137 sandstone cores collected from the danxiashan mountain guangdong province langshan mountain hunan province taining fujian province and longhushan mountain jiangxi province in addition 42 rock slices were collected for analysis under a polarizing microscope the results show that the sandstone samples from the longhu mountain are the weakest in terms of the uniaxial mechanical strength and in the resistance against sulfuric acid freezing and thawing followed by danxiashan langshan and taining as the conglomerates they are the weakest in taining in the uniaxial mechanical strength and in the resistance against sulfuric acid freezing and thawing followed by danxiashan longhushan and langshan as proved by the experiment in the same area of the danxia landscape the uniaxial mechanical strength of the conglomerates over the flat grooves is universally higher than the sandstones in the flat grooves in addition the uniaxial mechanical strength without saturated water of both the sandstone and conglomerate are generally higher than those stones with saturated water implying that in rainy and water saturated season danxia rocks tend to crack and collapse more easily also discovered in this research the developments of flat grooves in the strata of sandstones have certain reasons the uniaxial mechanical strength and the resistance against sulfuric acid freezing and thawing of the sandstones in the four sites of the danxia landscape are universally lower than that of the conglomerates over the grooves in terms of the physical composition and structure of the rocks sandstone universally has a higher content of calcium fragments more tensile cracks and can be more easily penetrated into calcite veins and the crystal fragments can be easily carbonated and are mostly cemented in the style of pores and contacts in contrast the conglomerates contain more high temperature recrystallized fragments of volcanic tuff lavas glass lavas containing quartz crystallized fragments and fragments of metamorphic rocks in addition the carbonated cementations can be found between crystallized fragments so that the uniaxial mechanical compressive strengths and the resistance against sulfuric acid freezing and thawing of conglomerates are universally higher than that of sandstones as also indicated by the experiments the sandstones and conglomerates in the four research sites are highly sensitive to the action of acid erosion various rocks will become immediately and completely loose after having been immersed in a 10 sulfuric acid solution for 72 h and some rocks will even become immediately and completely loose after having been immersed in a 2 sulfuric acid solution for 1 h results show that the environment with acid rains tended to come into being more easily in the late cretaceous period because of the frequent eruptions of volcanoes and the environment of the frequent alternations of intensive freezing and thawing in the quaternary glacial stage and the interglacial stage should have highly promoted the development of many flat grooves in the danxia landscape

the use of the schmidt hammer and equotip for rock hardness assessment in geomorphology and heritage science a comparative analysis rapid field based measurements of rock hardness are of use in investigating many geomorphological and heritage science problems several different methods are now available for taking such measurements but little work has been done to assess their comparability and strengths and weaknesses we review here the capabilities of two types of schmidt hammer classic n type and silver schmidt bl type alongside two types of equotip standard type d and piccolo for investigating rock hardness in relation to rock weathering on various types of sandstone and limestone as well as basalt and dolerite whilst the two schmidt hammers and the two equotips show comparable results when tested at 15 individual sites interesting differences are found between the equotip and schmidt hammer values which may reveal information about the nature of weathering on different surfaces operator variance is shown to be an issue in particular for the equotip devices which also exhibit higher variability in measurements and necessitate larger sample sizes carborundum pre treatment also has varying effects on the data collected depending on the nature of the surface studied the equotip devices are shown to be particularly useful on smaller blocks and in situations where edge effects may affect schmidt hammer readings we conclude that whilst each device contributes to geomorphological research they do not necessarily produce comparable information indeed using schmidt hammer and equotip in combination and looking at any differences in results may provide invaluable insights into the structure of the near surface zones and the nature of weathering processes copyright 2010 john wiley sons ltd

climate change and tectonic uplift triggered the formation of the atacama desert s giant nitrate deposits the giant nitrate deposits of the hyperarid atacama desert chile are one of the most extraordinary yet enigmatic mineral occurrences on earth these deposits are complex assemblages of highly soluble nitrates chlorides sulfates perchlorates iodates and chromates and their preservation is the result of prevalent hyperarid climate conditions in the atacama desert since the late miocene with average rainfall rates of 10 mm yr in the past 3 m y although several hypotheses have been proposed since the mid 1800s the formation of these extensive deposits still remains highly controversial despite the fact that recent studies have argued toward an atmospheric source for the nitrate sulfate and perchlorate components in this report we focus on the often overlooked and poorly studied iodine and chromium components of atacama s nitrates we present the fi rst cosmogenic iodine 129 i and stable chromium 53 52 cr isotope data of nitrates showing that groundwater has played an unforeseen role in the formation of these massive deposits the isotopic signature of i in the nitrates 129 i i 150 600 10 15 share similarities with deep sedimentary marine pore waters and shales deviating signifi cantly from atmospheric iodine 129 i i 1500 10 15 while the positive and highly fractionated 53 52 cr srm979 values 0 7 to 3 are indicative of intense cr redox cycling due to groundwater transport our evidence points toward a multi source genetic model for the atacama desert nitrate deposits where these extensive accumulations were the result of long lived near surface mineral precipitation driven by groundwater i e chromates iodates coupled with dry atmospheric deposition i e nitrates perchlorates and sea spray inputs i e sulfates chlorides triggered by increasing aridity and tectonic uplift

slaking durability and its effect on the doline formation in the gypsum texture and grain size is of great importance in understanding the mechanical properties of rocks the aim of this study was to investigate textural and slaking durability characteristics and correlate them with the gypsum types where the dolines occurred with particular reference to the texture and crystal size the investigation comprised two stages field work and laboratory testing initially rock samples were obtained from various representative karstified and non karstified locations thereafter mineralogical physical and slaking durability characteristics of the gypsum samples were determined by means of laboratory testing after the field and laboratory works the geological mineralogical and slaking durability characteristics of the study area gypsum were reviewed and discussed from the point of view of doline formation results showed that fine grain sized alabastrine gypsum tends to be karstified and leads to doline formation this is closely related to the crystal size texture and attributable to the slaking durability of the gypsum consequently the results demonstrate that the texture especially crystal size and effective porosity are important parameters controlling the slake durability of the gypsum and doline formation

aspect related microclimatic influences on slope forms and processes northeastern arizona 1 climate is a major control on geomorphology yet the effects of aspect related differences in microclimate have been little studied we examined several 60 100 m deep canyons in semiarid northeastern arizona where rock type and structure are essentially constant but where field data and a high resolution digital elevation model reveal consistent morphologic and microclimatic differences between asymmetric north and south facing sideslopes cliffs account for 29 of the vertical relief of south facing slopes but only 2 5 of north facing slopes excluding cliffs south facing slopes are 1 3 steeper than north facing slopes and have significantly less weathered bedrock we monitored air surface and subsurface temperatures and soil moisture at 0 5 h intervals at four locations over 1 year south facing slopes were 1 4 5 6 c warmer and soil moisture tension at 10 cm depth averages at least 78 kpa lower drier than on north facing slopes the dominant rock type in the study area morrison formation sandstone weathers primarily by clay hydration these sandstones form disaggregated mantles where weathering exceeds erosion but also maintain steep slopes and cliffs where little weathered south facing slopes were too dry during most of the instrumented year for significant clay expansion whereas the north facing bedrock slope was moist all year cliff growth thus occurs preferentially on warmer and drier slopes where weathering is reduced small north facing cliffs typically 3 m could have formed during the holocene but cliffs up to 70 m high on southerly aspects require more time to form and likely persisted or expanded under cooler and wetter late pleistocene climates

laboratory and field characterization of visible to near infrared spectral reflectance of nitrate minerals from the atacama desert chile and implications for mars

bedrock fracturing threshold hillslopes and limits to the magnitude of bedrock landslides abstract bedrock fracturing and rock strength are widely believed to influence landscape morphology and erosional resistance yet understanding of the quantitative relationship between rock mass strength and landscape evolution remains limited here we present a new application of seismic refraction surveys that uses variations in seismic velocity to interpret differences in bedrock fracture density with depth we use a comparative study of fiordland and the western southern alps of new zealand to examine how differences in rock type and bedrock fracturing influence landscape morphology and landslide response to rock uplift in both regions slopes appear invariant with differential rock uplift rates and slope distributions reveal modal hillslope angles of 32 the majority of landslides initiate on slopes steeper than the modal hillslope angle however landslide magnitude frequency distributions reveal order of magnitude differences between the regions with fiordland experiencing considerably smaller and less frequent landsliding events landslide driven denudation rates of 9 mm yr in the western southern alps and between 0 1 and 0 3 mm yr in fiordland approximate estimates of long term rock uplift rates for each region the invariance of hillslope angles near normal slope distributions predominance of landslide initiation on slopes steeper than modal values and the apparent balance between rates of uplift and landslide driven erosion suggest that hillslopes in both regions are at threshold angles their similar modal slopes further suggest that both ranges are characterized by equivalent rock mass strength despite striking differences in lithology additionally our seismic analysis reveals nearly identical surface p wave velocities the unexpected equivalence of both modal slopes and surface velocities between these lithologically distinct ranges is attributed to contrasting degrees of surface fracturing that have differentially affected the intact rock properties such that they now yield equivalent surface velocities and hillslope scale strengths given that surface fractures help regulate threshold angles by modulating hillslope strength we propose that shallow seismic velocities may provide a quantitative proxy for rock mass strength we define two contrasting fracture and landsliding environments in fiordland dense geomorphic fracturing that is focused within the shallow subsurface appears to limit the depth and magnitude of most bedrock landslides conversely in the western southern alps tectonic forces produce pervasive fracturing with depth that results in larger and deeper landslides our data suggest that bedrock fracturing at the earth s surface modulates threshold hillslope angles whereas the depth of bedrock fracturing influences the magnitude and frequency of landslide response to tectonic rock uplift

the role of some site geochemical processes in the development and stabilisation of three badland sites in almeria southern spain samples of both surface and subsurface soils were collected on various surfaces in three badland areas of differing ages tabernas vera and mocatan in almeria province southern spain data were explored with the aim of identifying any diagnostic geochemical relationships between site ec ph sediment size and sar which might constitute typical signatures for site materials with some success data for the three sites are further used to explore the hypothesis that changes in site geochemistry through time are involved in badland stabilisation it was found that 1 the physico chemical properties of the three sites can be differentiated by the functional relationship between ec and sar and this may represent a useful tool in characterising sites where piping predominates 2 there is some equivocal evidence that sediment size distribution may play an additional role in site diagnosis and evolution and 3 surfaces appear to lose sodium over time the suggestion being that sodium is either progressively buffered by calcium during leaching or exchanges with hydrogen on the cation exchange sites under a vegetation cover since other research suggests that smectite can also relocate down the profile on some marl sites reducing hydraulic conductivity and suppressing pipes we argue that the surface at tabernas may be capable of long term autostabilisation in which piping intensity progressively reduces however this possibility really applies only to fine grained densely structured materials and evidence from the silty triassic rich unit in the mocatan basin suggests that without a high clay content piping may be expected to increase through time from this standpoint contemporary badland morphology at mocatan does not represent an early stage of the forms seen in vera and tabernas

diagenetic variation in the oregon coast range implications for rock strength soil production hillslope form and landscape evolution the mechanisms by which lithology modulates geomorphic processes are poorly known in the oregon coast range ocr rhythmically bedded sandstones of the eocene tyee formation underlie steep soil mantled hillslopes with relatively uniform ridge valley spacing these characteristic landforms are perturbed where diagenetic variations manifest as resistant cliffs here we use petrology rock mechanics and lidar to characterize grain scale variations in rock properties and their influence on rock strength hillslope processes and landscape morphology in two adjacent watersheds petrographic analyses suggest that a suite of diagenetic products in the resistant bedrock account for a 2 5 times increase in tensile strength relative to typical tyee bedrock our reference catchment exhibits negligible resistant outcrops and consistent hillslope gradients and longitudinal valley profiles by contrast the adjacent catchment teems with resistant 1 to 10 m thick noncontiguous sandstone beds that form hanging valleys with gentle upstream hillslopes and anomalously narrow valleys mechanical and topographic analyses suggest that the low fracture density characteristic of these resistant beds may render them relatively impervious to comminution by tree root activity the dominant ocr soil production mechanism based on both hillslope gradient and hilltop curvature erosion models we estimate that hillslopes perched above resistant beds erode at approximately half the pace of hillslopes unencumbered by downstream knickpoints the diagenetic variations likely influence relief at the watershed scale depositional position and diagenetic processes appear to control the occurrence of resistant beds providing a framework to quantify how seemingly subtle variations in rock properties can impose first order controls on landscape form and evolution

sandstone landforms shaped by negative feedback between stress and erosion the formation and preservation of sandstone landforms such as pillars and arches is enigmatic experiments and numerical modelling show that load bearing material weathers more slowly and thus the internal stress field can shape and stabilize sandstone landforms

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

effect of groundwater and sea weathering cycles on the strength of chalk rock from unstable coastal cliffs of nw france abstract the aim of this paper is to evaluate the role of groundwater and sea weathering on the strength of the chalk rocks exposed on the coastline of the english channel in normandy nw france we present a study of the rock strength variations of three representative chalk units lewes chalk seaford chalk and newhaven chalk exposed at various locations on the coastal chalk cliffs the combination of ucs tests and sem observations have been used 1 on dry natural chalk samples 2 on chalk samples at various moisture contents 3 on dry chalk samples submitted to a 10 day cycle of alternating wetting and drying by distilled water and by sea water dry chalk samples show low ucs strength 3 46 4 mpa indicative of very weak rocks when chalk samples are submitted to progressive water wetting they present a decrease of ucs strength and young s modulus of 40 to 50 this behaviour begins at low values of water content within the chalk i e for a degree of water saturation ranging between 10 and 17 when chalk samples are submitted to an artificial weathering cycle with distilled water a decrease in strength is observed whereas the young s modulus increases sem observations indicate the occurrence of microcracks and particle aggregates in the sample when chalk samples are submitted to an artificial weathering with sea water the decrease of ucs strength and young s modulus achieves a minimum sem observations indicate salt crystals within the chalk on the coastal cliffs of nw france weathering processes depend both on chalk lithology which show a range of sensitivity to weathering and on the location of the chalk in the coastal area processes allied to the degree of weathering e g salt crystallisation or fresh water disaggregation differ in the chalk massif on the cliff face and on the shore platform

clay mineralogy as a crucial factor in badland hillslope processes abstract comprehensive and important work has been done in understanding badland processes on both the big scale and more recently on smaller scale in order to understand the subtle differences between sites however most studies lack important information regarding clay mineralogy and their importance for weathering processes type and rate of weathering depend on material physico chemical properties climatic regimes and slope characteristics as weathering progresses the surface conditions change influencing erosion processes usually badland lithologies are reported as sodium rich highly dispersive materials but that is not invariably true the primary objective of this study is to show that clay minerals have an important role in defining surface and subsurface processes on badland hillslopes field studies conducted in dinosaur park badlands alberta canada chinguacousy badlands ontario canada and sestino badlands tuscany italy have shown that there are two dominant clay rich lithologies smectite rich and smectite poor mudrocks different surface crust and weathering profiles were observed on smectite rich mudrocks during two field years with distinct precipitation inputs after a dry fall winter season the popcorn surface was very well developed 2 3 cm the subsurface layer 10 15 cm thick overlaid the layer of smaller shards followed by the unweathered material after a very wet fall winter season the surface layer was denser and thinner 0 5 cm with wider cracks and a thin subsurface layer attached to the crust weathering profiles on smectite poor lithologies did not show any differences with variable climatic conditions a thin surface layer was composed of soft thin and small 0 5 0 3 0 1 cm shards a layer of larger shards overlying unweathered material was beneath it in order to better understand the described occurrences badland materials were monitored in controlled laboratory conditions during an incremental weathering experiment six samples of each material were subjected to 10 cycles of simulated rainfall which duration ranged 10 60 min very short rainfalls 10 20 min can cause swelling of clay minerals in smectite rich materials and formation of popcorn surface during drying periods during subsequent wetting drying periods the crust becomes flatter and denser and desiccation cracks become wider and deeper samples subjected to 50 and 60 min of rainfall showed maximum swelling after only one cycle of rainfall after this swift swelling samples became unstable and dispersive during subsequent wetting dispersion became dominant resulting in flatter surfaces thinner crust and narrower desiccation cracks smectite poor mudrocks appeared to be resistant to variable wetting and drying large shards broke down into smaller due to differential swelling of illite and chlorite once they were reduced to tiny flaky shards the surface became compacted the surface cracks served as the initial pathways for sediment and water movement knowing if the material is smectite rich or smectite poor can help in prediction of processes and the erosion rates the amount intensity and duration of precipitation will determine not only the rate of weathering but also the type of the weathered surface on smectite rich surfaces smectite poor materials appear to be more resistant to change in precipitation

weathering grade of rock masses as a predisposing factor to slope instabilities reconnaissance and control procedures weathering of rock masses often assumes importance as a predisposing factor to slope instability and it is possible to map it at various scales depending on the different purposes the effects of weathering processes are particularly intense on crystalline rocks plutonic and metamorphic these rocks are present in large areas of the globe and widespread in calabria the relationships between rock mass weathering grades and slope instabilities are analysed with reference to sectors 1 50 000 scale and areas 1 10 000 scale where crystalline rocks are strongly affected by weathering to this aim a reconnaissance procedure has been proposed to delimitate the zones with different weathering condition three macro classes at average scale 1 50 000 and six classes at detail scale 1 10 000 in this procedure first analysis of aerial photos and then field observations of representative situations have been used the reconnaissance procedure has been verified in a selected study area acri whose geological features are provided by the comparison with weathering maps obtained by means of a control procedure this last procedure consists of observations and index tests carried out in check points located in representative check sites discolouration sound when struck by geological hammer effect of the point of geological pick breaking with the hands rebound of schmidt hammer grain size analysis the results obtained confirm through quantitative data that the weathering of a rock mass can be assumed as a predisposing factor to slope instability at average scale 1 50 000 the reconnaissance procedure is able to give weathering maps representative for this type of evaluation the ratio between the landslides area in each weathering macro class and the whole landslide area goes from 67 to 14 for the macro class a and from 24 to 9 for the macro class b at detail scale 1 10 000 it is necessary to use a control procedure to obtain weathering maps indicative of predisposition to slope instabilities

rock hardness and landform development in the gunong mulu national park sarawak e malaysia rock hardness measured by the schmidt test hammer is an important factor in explaining some of the sharp contrasts in relief and wide variety of landforms in the gunong mulu national park it is also useful in consideration of contemporary geomorphological processes such as landsliding

correlating river terrace remnants using an equotip hardness tester an example from the mino river northwestern iberian peninsula abstract this paper describes a new method to distinguish river terrace levels based on clast hardness and degree of weathering measured with an equotip hardness tester the technique was applied to a series of terraces on the mino river in the northwestern iberian peninsula where the lack of suitable material high degree of weathering and intense iron cementation precluded routine dating detailed mapping demonstrated that terrace sediments occupy a range of altitudes that make assignment to a specific terrace and or correlation between levels difficult statistical analysis of the equotip hardness data from quartzite clasts using k means clustering allowed four probable terrace levels to be identified a series of t tests generally supported these groupings a fifth lowermost terrace level was not included in the analysis because of limited exposure above a reservoir clast hardness and degree of terrace weathering were generally consistent with progressive river downcutting the occurrence of faulted sediments however suggested that terrace elevations were modified locally by post depositional tectonic movements which may explain why probable younger terraces in some sectors of the mino river are at higher elevations than older terraces in adjacent sectors the equotip tester helped to resolve stratigraphic uncertainties and to assign deposits to specific terrace levels and was found to be a useful tool to distinguish and correlate river terraces

spatial characterization of salt accumulation in early stage limestone weathering using probe permeametry this research characterizes the weathering of natural building stone using an unsteady state portable probe permeameter variations between the permeability properties of fresh rock and the same rocks after the early stages of a salt weathering simulation are used to examine the effects of salt accumulation on spatial variations in surface rock permeability properties in two limestones from spain the fraga and tudela limestones are from the ebro basin and are of miocene age both stone types figure largely in the architectural heritage of spain and in common with many other building limestones they are prone to physical damage from salt crystallization in pore spaces to examine feedbacks associated with salt accumulation during the early stages of this weathering process samples of the two stone types were subjected to simulated salt weathering under laboratory conditions using magnesium sulphate and sodium chloride at concentrations of 5 and 15 permeability mapping and statistical analysis aspatial statistics and spatial prediction before and after salt accumulation are used to assess changes in the spatial variability of permeability and to correlate these changes with salt movement porosity change potential rock deterioration and textural characteristics statistical analyses of small scale permeability measurements are used to evaluate the drivers for decay and hence aid the prediction of the weathering behaviour of the two limestones copyright 2010 john wiley sons ltd

rapid salt weathering in the coastal namib desert implications for landscape development data on the rate and style of breakdown on naturally occurring rock types are important to improving geomorphological understanding of landscape development in arid environments two years exposure of rock blocks cut from an english limestone bath stone as well as locally relevant namibian rocks karibib marble and damara granite within four distinctive microenvironments in and around a coastal salt pan environment reveals high rates of breakdown in the bath stone blocks observable breakdown in the marble blocks and weight gains and strength increases in the granite blocks breakdown is associated with high conductivities and large amounts of halite and gypsum within the surface sediments frequency of wetting and drying appears to be a major control on the resultant breakdown rates these findings can be compared with recent data from further inland in the namib desert which suggest very slow rates of breakdown of similar blocks of damara granite and karibib marble even where salts are readily available high rates of rock breakdown within coastal salt pans appear to contribute to dust production and the effective flattening of relief along the coastal strip

rock mass strength and the form of some inselbergs in the central namib desert a rock mass strength classification involving eight parameters has been applied to selected inselbergs in the namib desert the inselbergs are formed of schists gneiss granite and marble their slope inclinations are in a strength equilibrium with their rocks the study suggests that the strength classification is consistent and has a general validity and that rock slopes undergoing uniform weathering retreat to form slopes which are adjusted to their rock mass strength this is a more general statement than the common hypothesis of parallel retreat the favoured hypothesis of slope evolution in the namib is one of retreat rather than downwearing

identification of strength equilibrium rock slopes further statistical considerations strength equilibrium slopes are rock slopes whose gradient and rock mass strength rms are in adjustment the identification of such slopes depends on the accurate specification of the strength equilibrium envelope previous attempts to delimit the envelope are reviewed and modifications are proposed that permit its more rigorous statistical definition because can be measured much more reliably than rms the structural relation between these variables is estimated by regressing rms on and the strength equilibrium envelope is defined by the 95 per cent confidence limits the analysis is performed on a data set of 268 rock slopes representing all the data on rms and hitherto employed in published studies of strength equilibrium slopes

the influence of rock mass strength on glacial valley cross profile morphometry a case study from the southern alps new zealand the erosional morphology in the vicinity of the main divide of the southern alps and fiordland new zealand appears to be a product of the interaction between alpine fault induced tectonic processes rock mass strength of the uplifted and eroded bedrock and the processes acting to denude the developing mountain landscape the magnitude of the effects of glacial erosion on the landscape is directly controlled by the size and physical properties of the glaciers whilst the form of the trough is a direct consequence of the rock mass strength rms properties of the slope rock realistic models of development of the cross profile shape of glacial valleys must take into consideration the rms properties of the eroded substrate

investigations into the relationship between changes in internal moisture regimes and rock surface deterioration in cavernous sandstone features cavernous features commonly develop in sandstone but their development over time remains enigmatic it has been suggested that moisture movements within the rock mass play a key role in the location development and dynamics of cavernous features in this research the role of internal moisture movement is tested through monitoring moisture and surface deterioration dynamics in april 2008 and april 2009 within two large cavernous features mega tafoni in the golden gate highlands national park south africa gghnp data are presented from surveys of internal moisture using electrical resistivity tomography ert surface moisture using a protimeter and deterioration using surface hardness as recorded with an equotip as a proxy for surface deterioration across five 2 45 m long transects in addition a high resolution temperature record is presented to assess the influence of micro climates within the caverns the results indicate consistency in the gross spatial pattern of moisture flow within the rock mass over a one year period but significant changes in mean moisture contents and in the fine detail of moisture patterning some noticeably weakened areas had developed within the central parts of the cavernous features often linked to wetter subsurface conditions supporting the theory that core softening is a main driver of cavernous feature formation however in some areas surface hardening is also found to be associated with wetter subsurface conditions supporting the theory that case hardening is a main driver of cavernous feature formation in addition the presence of well established biofilms suggests an even more complex interaction between moisture surface development and biological activity a model is presented therefore which integrates this paradox by proposing a non linear relationship between moisture dynamics facilitation of biofilm formation and deterioration within cavernous features

downwearing rates on shore platforms of different calcareous lithotypes article i nfo vertical lowering downwearing of shore platform surfaces is a very important mechanism in their morphological evolution albeit much remains incompletely understood the efficacy of mechanical and chemical weathering acting on a given substrate together with erosional processes influences downwearing rates in order to determine the relationship between lithotypes and downwearing rates data collected from a transverse micro erosion meter were obtained for shore platforms of three different calcareous lithotypes biocalcarenite calcarenite and carbonated siltstone along the central algarve coast southern portugal downwearing rates ranged between 0 096 mm year 1 and 1 676 mm year

landslide susceptibility assessment using logistic regression and its comparison with a rock mass classification system along a road section in the northern himalayas india landslide studies are commonly guided by ground knowledge and field measurements of rock strength and slope failure criteria with increasing sophistication of gis based statistical methods however landslide susceptibility studies benefit from the integration of data collected from various sources and methods at different scales this study presents a logistic regression method for landslide susceptibility mapping and verifies the result by comparing it with the geotechnical based slope stability probability classification sspc methodology the study was carried out in a landslide prone national highway road section in the northern himalayas india logistic regression model performance was assessed by the receiver operator characteristics roc curve showing an area under the curve equal to 0 83 field validation of the sspc results showed a correspondence of 72 between the high and very high susceptibility classes with present landslide occurrences a spatial comparison of the two susceptibility maps revealed the significance of the geotechnical based sspc method as 90 of the area classified as high and very high susceptible zones by the logistic regression method corresponds to the high and very high class in the sspc method on the other hand only 34 of the area classified as high and very high by the sspc method falls in the high and very high classes of the logistic regression method the underestimation by the logistic regression method can be attributed to the generalisation made by the statistical methods so that a number of slopes existing in critical equilibrium condition might not be classified as high or very high susceptible zones

how mudrock and soil physical properties influence badland formation at vallcebre pre pyrenees ne spain abstract soils regoliths and their parent materials were investigated in relation to the development of badlands in the pre pyrenees in ne spain on late cretaceous mudrocks under a mountain mediterranean climate whilst all the soils in the area which are developed on mudrocks show a good structure and support a dense plant cover the bare parent materials slake very rapidly giving rise to badlands characterized by high erosion rates several physical chemical mineralogical and micromorphological properties of soils regoliths and related parent materials were analyzed in order to explain their different susceptibility to erosion and to determine which of all these properties are better related to such erosive behaviour only micromorphological and porosity properties were able to explain the erosion susceptibility whilst mineralogical chemical and physico chemical specific surface area properties were not among the aggregate stability tests performed to estimate the relationships of soil components with the susceptibility to erosion the emerson test for macroaggregate evaluation was particularly well suited although no good correlation was found between the emerson test classes and organic matter content we observed that the degree of slaking in organic rich horizons was always lower than in subsurface horizons and regoliths consequently as far as organic rich aggregates are present in the soil surface the influence of water in producing slaking swelling and then erosion will be minimum however when regoliths and rocks are uncovered the influence of water in these particular materials through freeze drying and swell shrinking will give rise to mudrock desintegration leading to accelerated erosion

shore platform development around lord howe island southwest pacific this paper describes the morphology of near horizontal basalt and calcarenite shore platforms around lord howe island as well as the lithological and process environment in which they occur the morphology of platforms around the island is highly varied for instance they occur at a wide range of elevations between low tide level and several metres above the highest tides and their width ranges between just a few metres to over 100 m however common to most platforms is that they have near horizontal surfaces that terminate abruptly in a steep scarp at their seaward edge correlations indicate that the variability in platform elevation and width is attributable to variability in key parameters of erosion such as rock resistance and shoreline water depth whereas wider platforms occur in rocks of lesser resistance platform elevation is shown to increase both as rock resistance and the depth of water at the shoreline increases wave exposure has a significant control on platform width in some instances but an over arching relationship was not detected most platforms around the island appear to have developed over the holocene and a conceptual model is proposed to account for the varied morphology of platforms that have developed over this period resistant plunging cliffs occur along about 18 of the rocky coastline of lord howe island and represent the starting point for the model where cliffs have yielded to wave erosion platforms have been initiated at an elevation controlled predominantly by rock resistance and shoreline water depth at lord howe island narrow platforms up to about 20 m wide in exposed locations generally occur about 4 to 6 m above high tide level and have apparently been subject to very infrequent erosion shore platforms about 20 to 40 m wide have generally formed in less resistant rocks are somewhat lower at about 2 to 3 m above high tide level and have been subject to more frequent erosion over the holocene most basalt platforms around the island fall within these first two categories but there are some instances of platforms about 50 m wide these platforms have formed in rocks of comparatively low resistance and are relatively low in elevation occurring close to the level of high tide an interesting feature of some of these wide platforms is that unlike the morphology of narrower platforms raised ramparts sometimes occur on their outer edge

refinement of a technique for determining rock mass strength for geomorphological purposes use of a field technique recently devised by selby for the measurement of rock mass strength has resulted in the understanding of the relationship between rock mass strength and slope form it is suggested that the accuracy of rock mass strength assessments may be enhanced by further subdividing the rating scales for intact rock strength and the spacing of partings the relationship between rock mass strength and gradient is reformulated using southern african data and statistically based confidence limits for identifying strength equilibrium slopes are proposed

schmidt hammer studies in the maritime antarctic application to dating holocene deglaciation and estimating the effects of macrolichens on rock weathering in order to contribute to the reconstruction of the deglaciation history of the marguerite bay area 68 s maritime antarctic and to estimate the rock weathering rate in this antarctic sector 28 sites 7 on rothera point and 21 on anchorage island were characterised using schmidt hammer values the weathering effect of two of the most widespread species of macrolichens in this area usnea sphacelata and umbilicaria decussata was tested at 5 different sites on rothera point schmidt hammer data in conjunction with recent 14c age suggest a deglaciation age for the marguerite bay area of around 12 ka and an average uplift rate of 5 4 mm year 1 on anchorage island for the period between 3 3 and 5 2 ka the weathering rates are extremely slow e g three times slower than reported in norway our data confirm that lichens exert a strong impact on weathering decreasing the schmidt hammer r values on lichenised surfaces by a factor of 3 4 compared to bare rock surfaces the effect of lichens on weathering is mainly due to edaphic conditions and the type of the lichen involved rather the period of exposure

the distribution of inselbergs and their relationship to geomorphological structural and lithological controls in southern zimbabwe abstract the gneissic granitic basement of southern zimbabwe is characterized by a wide variety of inselbergs preferentially developed on the granitoid rocks however there are significant differences in the frequency of inselbergs and most inselbergs occur in the younger granitoid rocks particularly in rocks with microcline as the dominant k feldspar but their distribution is not uniform completely isolated inselbergs are rare and most inselbergs are arranged in clusters or are associated with plateaus or they occur as the detached ends of spurs and ridges chemical and mineralogical investigations indicate significant differences in the composition of the older and younger granitoid rocks the latter are characterized by a higher content of alkali feldspars and a lower content of plagioclase and mafic minerals the influences of texture fabric and fracture characteristics on the resistance of the rocks vary in the southern part of the study area the majority of rock domes is associated with porphyritic granites and fine grained granites whilst inselbergs of the large batholith complexes in the northern part of the study area show virtually no relationships to the grain size of the rocks thin sections analysis indicate that the rocks of the terrains with a higher density of inselbergs are characterized by an intense intergrowth of minerals and a higher number of contacts between quartz and alkali feldspars particularly in the case of the porphyritic granites the influence of texture on the frequency of rock domes is linked with two factors these are a high content of microcline minerals that have filled the interstices of the surrounding mineral framework and enclosed the surrounding minerals overgrowths and replacement micro structures indicate a long lasting crystallization which appears to be responsible for a lower density of cooling fractures enclosure of the more vulnerable minerals in the more resistant microcline megacrysts retards the loosening of the rock constituents the marked differences in the lithological and structural characteristics of the various granitoid rocks influence the weathering behaviour of the rocks and illustrate that the divergent weathering characteristics of the rocks are strongly dependent on lithological and structural factors

structural and lithological guidance on speleogenesis in quartz sandstone evidence of the arenisation process a detailed petrographic structural and morphometric investigation of different types of caves carved in the quartz sandstones of the tepui table mountains in venezuela has allowed identification of the main speleogenetic factors guiding cave pattern development and the formation of particular features commonly found in these caves such as funnel shaped pillars pendants and floor bumps samples of fresh and weathered quartz sandstone of the mataui formation roraima supergroup were characterised through wds dispersive x ray chemical analyses picnometer measurements edax analyses sem and thin section microscopy in all the caves two compositionally different strata were identified almost pure quartz sandstones with content of silica over 95 and high primary porosity around 4 and phyllosilicate rich quartz sandstone with contents of aluminium over 10 and low primary porosity lower than 0 5 phyllosilicates are mainly pyrophyllite and kaolinite sem images on weathered samples showed clear evidence of dissolution on quartz grains to different degrees of development depending on the alteration state of the samples grain boundary dissolution increases the rock porosity and gradually releases the quartz grains suggesting that arenisation is a widespread and effective weathering process in these caves the primary porosity and the degree of fracturing of the quartz sandstone beds are the main factors controlling the intensity and distribution of the arenisation process weathering along iron hydroxide or silt layers which represent inception horizons or a strata bounded fracture network predisposes the formation of horizontal caves in specific stratigraphic positions the loose sands produced by arenisation are removed by piping processes gradually creating anastomosing open fracture systems and forming braided mazes geometric networks or main conduit patterns depending on the local lithological and structural guidance on the weathering process this study demonstrates that all the typical morphologies documented in these quartz sandstone caves can be explained as a result of arenisation which is guided by layers with particular petrographic characteristics primary porosity content of phyllosilicates and iron hydroxides and different degrees of fracturing strata bounded fractures or continuous dilational joints

mineralogical and textural controls on the weathering of granitoid rocks summary the results obtained in several recent studies provide convincing evidence that potassium rich granitoid rocks are relatively more resistant to weathering than their less potassic counterparts this reflects the fact that microcline and orthoclase are more stable in most weathering environments than calcic plagioclase and biotite relatively slight differences in bulk rock chemical composition can lead to differential rates of weathering in areas of inhomogeneous granitoid terrain thereby leading to the development of topographic features such as inselbergs a second major control on the rate of weathering is rock permeability this is largely a function of degree of microfracturing and jointing in most circumstances grain size and other textural differences probably exert a minor influence on rates of chemical weathering although laboratory tests have shown they may profoundly affect physical strength parameters

geomorphological chemical and physical study of calanchi landforms in nw sicily southern italy abstract this work deals with an integrated geomorphological and chemical physical study of calanchi landforms in two sites ottosalme and catalfimo of nw sicily southern italy developed on dominant silty clay deposits the calanchi fronts are characterized by different morphological features and dominant geomorphic processes sharp knife edged ridges and concentrated water runoff dominate at ottosalme and smoother landforms affected by mass movements mud flows and translational slides prevail at catalfimo we focused on some geochemical and physical parameters such as ph total dissolved salts sodium adsorption ratio sar porosity plastic and liquid limits as possible causes of the above differences with special emphasis on their role in discriminating the behavior of peculiar microforms such as a weathered outer crust and the corresponding inner massive portion unweathered substrate our results show that the main chemical physical features of calanchi morphologies and microforms often display no clear correlations with respect to those reported in the existing literature pointing to a higher complexity of patterns and behaviors in particular all samples consist of dispersive material sar values 10 but a more plastic and liquid behavior at catalfimo can explain a higher occurrence of landslides and smoother morphology than at ottosalme higher sar values at ottosalme well explain the dominance of concentrated water erosion the chemical behavior of the studied microforms is better described by ph being alkaline with higher values in the inner substrate than the outer crust and appears to minimize the effects of all other parameters and their responses to other external controlling factors lower sar values in the crust suggest that clay dispersivity is not the prominent factor controlling its surface detachment and mobility downslope which is more likely promoted by its higher porosity and consequent water absorption than the inner portion with changes in the saturation state shear strength and water pressure

quantification of rock control in geomorphology abstract rock control the influence of rock properties on landform development has for long been a relatively under researched topic but numerous techniques have been developed especially by geotechnical engineers and stone conservationists that are now being applied to geomorphological issues by geomorphologists these techniques range in scale from the quantification of major discontinuities through to analysis of micro pores rock control studies that have taken place over the last few decades have contributed important insights into our understanding of such diverse phenomena as 1 river terraces bedrock channel forms and gradients pot hole development drainage density and gully badland development 2 slope forms and failures especially with respect to rock mass strength 3 the form of glacial troughs and of subglacial erosional landforms 4 weathering controls on rock durability and the association of weathering with porosity 5 classic karst features including various types of karren 6 sandstone landforms 7 inselbergs and tors and 8 cliffs and shore platforms

the relative influence of lithology and weathering in shaping shore platforms along the coastline of the gulf of la spezia nw italy as revealed by rock strength abstract along the rock coasts of the gulf of la spezia which are characterised by a mediterranean microtidal environment a limited number of small rock platforms are scattered constrained in elevation within 5 m above present day sea level this work deals with a number of these rock platforms formed in different rock types one in limestone and two in dolomite that show differences in their morphology this paper aims to provide a quantitative examination of why there are morphological differences between platforms in this region to achieve this purpose factors controlling platform morphology and the processes acting on them are investigated through a comparative analysis of rock strength rebound values obtained testing rock surfaces with the schmidt hammer were compared between different platforms and between different sectors of the same platform each platform was subdivided into two parts based on visual difference in rock surface colour characterised by differences in occurrence of weathering microforms and bioerosive agents rebound values in the lower part of the platforms proved to be lower than in the upper part providing quantitative assessment of the occurrence of weathering acting to different extents in the upper and lower part of the shore platforms weathering degraded rock strength in the lower part by about 15 it was demonstrated that on the upper part of platforms displaying moderate evidence of physical and biological weathering lithology significantly influences the rock strength on the portion of platforms closer to sea level instead differential exposure histories of the same rock type in the same environmental setting can yield statistically significant variations in rock strength values thus it is clear that in the lower part of the investigated platforms the degree of weathering has strong bearing on rock strength and that variations in rock strength are not solely due to lithology according to the results of this work experimental values of rock strength of platforms in the study area depend both on the rock type and on physical weathering due to frequently repeated wetting and drying and bioerosion lithology is then an important factor controlling platform shape and weathering is an important process operating on them

a multi method investigation of temperature moisture and salt dynamics in tafoni tafraoute morocco despite numerous investigations and theoretical models tafoni weathering is still not fully understood largely because of limited data available on temperature moisture and salt regimes we investigated tafoni developed in granite in the tafraoute region morocco through an exploratory two week multi method field campaign temperatures were measured with ibuttons and by means of infrared thermography moisture distribution and progress were captured with handheld moisture sensors and with drilled in ibuttons salts were analysed in drill dust samples from different positions and rock depths the results derived from very different techniques mutually support one another salts and moisture are concentrated near the base of the investigated tafoni probably due to a saturated pore water body around the base of rock tors salts are accumulated close to the rock surface in tafoni but not on the surrounding rock surfaces a clear correlation was found between moisture and salt contents within a tafone areas of higher humidity also display increased salt concentration near the surface the temperature humidity records allied with ionic analyses suggest that sodium sulfate dominates and is likely to undergo frequent phase changes from thenardite to mirabilite and vice versa two pathways of salt transport in and around tafoni are assumed based on the data infiltration with rainfall on the top and around tors and boulders and capillary rise from saturated pore water bodies to the surface copyright 2015 john wiley sons ltd

on the role of discontinuities in mediating shore platform erosion in this paper we quantitatively demonstrate that dominant erosion processes on different shore platforms can be explained in part by geological properties we selected sites with a considerable history of rock coast geomorphology study to evaluate whether geological data can improve our understanding of spatial variations in erosion between sites schmidt hammer tests and discontinuity data were collected on blue lias limestone shore platforms in wales uk and sandstone platforms in victoria australia significant differences in joint spacing persistence of discontinuities and block size were found between the australian and welsh study sites these data were related to evidence of meso scale erosion to examine how geological contingency influences the nature and scale of erosion processes and thresholds this study quantitatively demonstrates that discontinuities play a fundamental role in altering rock resistance the findings of this research have important implications for the design of rock coast erosion studies concerned with measuring rates of change and determining the relative contributions of different processes to platform development

a non destructive method of determining rock strength rock material strength is an important component of many geomorphological studies current methods for determining this parameter result in sample destruction preventing further analysis a new non destructive technique is described for indirectly determining material strength by measuring dynamic young s modulus tests have been conducted on jurassic portland limestone and upper cretaceous chalk to assess the apparatus young s modulus is becoming an increasingly important rock material property

oligocene miocene age of aridity in the atacama desert revealed by exposure dating of erosion sensitive landforms the age of onset of hyperaridity in the atacama desert chile which is needed to validate geological and climatological concepts has been heretofore uncertain measurement of cosmogenic 21 ne in clasts from erosion sensitive sediment surfaces in northern chile shows that these surfaces have been barely affected by erosion since 25 ma surface exposure ages of sediment clasts give replicate values at 25 20 and 14 ma and individual values at 37 and 9 ma predominantly hyperarid conditions are required to preserve these oldest continuously exposed surfaces on earth our findings are compatible with the hypothesis that the onset of aridity in the atacama desert could be the reason for rather than the consequence of uplift of the high andes

oxygen 17 anomaly in soil nitrate a new precipitation proxy for desert landscapes abstract the nitrogen cycle in desert soil ecosystems is particularly sensitive to changes in precipitation even of relatively small magnitude and short duration because it is already under water stress this suggests that desert soils may have preserved past evidence of small variations in continental precipitation we have measured nitrate no 3 concentrations in soils from the atacama chile kumtag china mojave us and thar india deserts and stable nitrogen and oxygen isotope 15 n 17 o and 18 o abundances of the soil no 3 17 o anomalies 17 o the deviations from the mass independent isotopic fractionation were detected in soil no 3 from almost all sites of these four deserts there was a strong negative correlation between the mean annual precipitation map and soil no 3 17 o values o no 3 soil 17 this map o no 3 soil 17 correlation advocated o no 3 soil 17 as a new precipitation proxy and was then used to assess precipitation changes in southwestern us at the pliocene pleistocene boundary in south america during the miocene and the sahara desert in the past 10 kyr using no 3 17 o in paleosols or ancient aquifers global and the us maps of surface o no 3 soil 17 were also projected with available map datasets based on the map o no 3 soil 17 model

sandstone alterations triggered by fire related temperatures the aim of the study was to identify and describe changes in two different sandstone types when undergoing different environmental and extreme temperature regimes to assess the possibility of finding insolation weathering and how these sandstones would behave during and after a fire the first step was the simulation in the laboratory of temperature regimes up to 60 c which would correspond to extreme events that could be found in insolation cycles even in central europe and the second one was the temperature above 200 c simulating in laboratory conditions the thermal regime of a potential fire situation at temperatures up to 200 400 600 and 800 c heating the samples above 400 c led to gradual changes in mineral composition colour surface roughness and physical properties reaching eventually total rock breakdown through spalling and granular disaggregation the different behaviour of sandstones exposed to high temperatures is mainly caused by their different mineral composition with various ratios of minerals that are more or less chemically stable at high temperatures as well as by the differences in the porosity

residual strength of clays in landslides folded strata and the laboratory the post peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages first at relatively small displacements the strength decreases to the fully softened or critical state value owing to an increase in water content dilatancy second after much larger displacements the strength falls to the residual value owing to reorientation of platy clay minerals parallel to the direction of shearing if the clay fraction is less than about 25 the second stage scarcely comes into operation the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20 degrees conversely when the clay fraction is about 50 residual strength is controlled almost entirely by sliding friction of the clay minerals and further increase in clay fraction has little effect the angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15 degrees for kaolinite 10 degrees for illite or clay mica and 5 degrees for montmorillonite when the clay fraction lies between 25 and 50 there is a transitional type of behaviour residual strength being dependent on the percentage of clay particles as well as on their nature the post peak drop in strength of a normally consolidated clay is due only to particle reorientation measurements of strength on natural shear surfaces agree within practical limits of variation with values derived from back analysis of reactivated landslides this field residual strength can be recovered by multiple reversal shear box tests on cut plane samples but in high clay fraction materials it is typically somewhat higher than the strength measured in ring shear tests residual strength is little affected by variation in the slow rates of displacement encountered in reactivated landslides and in the usual laboratory tests but at rates faster than about 100 mm min qualitative changes take place in the pattern of behaviour a substantial gain in strength is followed with increasing displacement by a fall to a minimum value in clays and low clay fraction silts this minimum is not less than the slow or static residual but in clayey silts with clay fractions around 15 25 according to tests currently in progress the minimum can be as low as one half of the static value author trrl

lias clay slope sections and their implications for the prediction of limiting or threshold slope angles a series of previously published engineering studies of lias clay slopes in the east midlands is summarized along with the description of some further slope sections all the slopes studied show evidence of landsliding though some of it may be of periglacial origin the very disparate nature of the different landslides suggest that various different erosion regimes were responsible for the original slope formation it is believed that the smaller landslides are more typical of the area piezometric observations show that at the present day maximum pore pressures are proportionately less in the larger landslides the average value of the pore pressure parameter ru varying between 0 48 for shallow landslides to 0 32 in the largest stability analyses show that the residual strength is strongly stress dependent r c r 0 varying from 16 in shallow landslides to 10 in the case of the largest these and other factors have important implications for the often used practice of combining laboratory measurements of residual strength with the infinite slope method of stability analysis to predict threshold slope inclinations for landsliding