a minimum sample size required from schmidt hammer measurements the schmidt hammer is a useful tool applied by geomorphologists to measure rock strength in field conditions the essence of field application is to obtain a sufficiently large dataset of individual rebound values which yields a meaningful numerical value of mean strength although there is general agreement that a certain minimum sample size is required to proceed with the statistics the choice of size i e number of individual impacts was usually intuitive and arbitrary in this paper we show a simple statistical method based on the two sample student s t test to objectively estimate the minimum number of rebound measurements we present the results as 1 the mean and median solutions each providing a single estimate value and 2 the empirical probability distribution of such estimates based on many field samples schmidt hammer data for 14 lithologies 13 81 samples for each with each sample consisting of 40 individual readings have been evaluated assuming different significance levels the principal recommendations are 1 the recommended minimum sample size for weak and moderately strong rock is 25 2 a sample size of 15 is sufficient for sandstones and shales 3 strong and coarse rocks require 30 readings at a site 4 the minimum sample size may be reduced by one third if the context of research allows for higher significance level for test statistics interpretations based on less than 10 readings from a site should definitely be avoided copyright 2009 john wiley sons ltd

extensive carbonate algal bioherms in upper pleistocene saline lakes of the central altiplano of bolivia during the upper pleistocene the central altiplano of bolivia was repeatedly flooded by deep and extensive saline lakes in response to climatic fluctuations development of carbonate algal bioherms took place during at least three major periods of lacustrine highstands discontinuously covering the 300 km long and 100 km wide lacustrine slopes and terraces up to an elevation of 100 m above the surface of the modern halite crust of uyuni distribution size and shape of the bioherms are diverse due to various factors e g the nature and morphology of the substrate and the hydrodynamic conditions that prevailed during growth on larger palaeoterraces the build ups coalesced to form platform like carbonate accumulations although the morphologies closely resemble those induced by cyanobacteria they were predominantly constructed by other plant communities probably dominated by filamentous green algae cyanobacterial communities flourished in association with these plants but they did not contribute significantly to the architecture of the bioherms they participated to encrust the plant stems and algal bushes or to form thin laminated layers covering the build ups a prominent feature of some bioherms is their composite structure due to repeated algal growth during successive lacustrine episodes that were separated by subaerial exposures with moderate erosional effects the build ups located between 3660 and 3680 m elevation display up to three major parts 1 a massive inner core formed during an early minchin highstand before 40 ka 2 a large peripheral envelope deposited at about 40 ka late minchin and 3 a thinner outermost crust formed during a late glacial event lake level dropped during interlacustrine stages sometimes leading to desiccation and deposition of salt layers in the deepest parts of the system i e the present day salar of uyuni

large scale geomorphological mapping of tors proposal of a key and landform interpretation abstract isolated bedrock outcrops amidst regolith covered slopes often named as tors have been the object of interest in many geomorphological studies usually as a part of long term landscape evolution inquiries however detailed presentation of tor morphology on maps in publications is very uncommon in this paper we propose a new comprehensive method of detailed large scale geomorphic mapping of tors it is tested on selected tor groups located in the sudetes in southwestern poland they are diversified in terms of lithology granite greenstone and sandstone bedrock and morphological features solitary tor rock city cluster of tors rock cliffs etc the method consists of three stages preparation of digital spatial data field mapping and final legend and map design the legend consists of 40 symbols which allows to show tor morphology in considerable detail assisting thereby in the interpretation of controls behind tor formation and evolutionary pathways of different types of tors using detailed maps one can extract information about major vertical joint sets and the patterns of tor decay weathering of rock surfaces in subaerial conditions structure of slope covers and internal morphological differentiation within large clusters of tors the latter being a possible manifestation of certain stages in the development of these landforms

underground erosion and sand removal from a sandstone tableland stolowe mountains sw poland abstract models of geomorphic evolution of tablelands vary as far as the patterns of cliff line degradation and hence scarp retreat are concerned among surface processes rock slope failures from caprock cliffs often induced by preferential seepage from rock faces are emphasized in this paper evidence is provided that mechanical removal of sand from inside the caprock through underground erosion may also play an important role in the long term evolution of cliffed escarpments in sandstone tablelands more than 140 sandy cones and nearly 80 sand sheets emerging from fissures in the sandstone cap were mapped and measured along six cliff sections of variable length in the stolowe mountains tableland in sw poland the density of sandy accumulation forms varies along the cliff length with cones preferentially associated with intact cliffs and sand sheets being more common along degraded cliff sections further redistribution of sand downslope results in widespread sandy covers below cliff lines which extend for a few hundred metres and are 1 3 m thick as demonstrated by electrical resistivity tomography sand removal from caprock accounts for progressive non catastrophic degradation of tableland margins through gradual subsidence of blocky compartments and the development of ruiniform relief behind the cliff lines thus it may be an important component of long term evolution of stepped relief in sedimentary terrains

late evolutionary stages of residual hills in tablelands elbsandsteingebirge germany abstract it is commonly assumed that geomorphic evolution of tablelands where durable caprock overlies weaker formations proceeds via escarpment retreat which leaves residual tabular hills mesas in front of the receding scarps these in turn are reduced in extent towards buttes and then pinnacles in the final stage in this paper we use empirical evidence from elbsandsteingebirge sandstone tableland in east germany to show that different pathways of mesa decay exist and that various scenarios are possible depending on mesa morphology and the degree of its dissection penultimate stages may include classic buttes series of small isolated crags or rock labyrinths rock cities subject to slow lateral outward displacement these may evolve into pinnacles or boulder scatters no longer rooted in bedrock the latter are the last remnants of no longer existing tabular hills these different trajectories are mainly controlled by lithology and structure including the thickness of caprock the proportion of caprock versus subcaprock slope the pattern of jointing and the presence of weaker intercalations within stronger lithological units literature review shows that some of these pathways were hypothesized long ago but little empirical evidence was offered and multiple trajectories were apparently not considered

the role of landslides in downslope transport of caprock derived boulders in sedimentary tablelands stolowe mts sw poland abstract escarpment slopes in sedimentary tablelands are often mantled by extensive boulder blankets while lithology shows beyond doubt that caprock is the source of boulders the processes involved in boulder movement and their distribution patterns are rarely examined in this paper we investigate the role of landslides initiated within middle and lower escarpment slopes in redistributing boulder covers on the example of the stolowe mountains in sw poland quartz sandstones form caprock and give rise to precipitous albeit rather low 30 m high at most typically 10 15 m uppermost slope sections and are the source of boulders which occur at distances even 1 km away from the caprock on the nearly flat footslope sedimentary series beneath caprock include fine grained rocks such as mudstones claystone and calcareous sandstones geomorphological mapping and geomorphometric analysis of a high resolution dem allowed us to identify landform patterns interpreted as resulting from landslides both rotational and translational the latter produced distinctive tread and riser topography with risers up to 10 m high results of geophysical prospecting using electrical resistivity tomography ert confirm the presence of allochthonous sandstone derived upper layer that wedges out downslope and indicate resistivity contrasts at depth of 5 15 m interpreted as basal boundaries of landslide material sandstone boulders rafted on top of slid masses and reached very distant footslope settings the primary role of landsliding consists of transporting allochthonous boulders further than would be possible otherwise and accumulating boulders in clusters and linear belts across the slope notably on risers

pathways of geomorphic evolution of sandstone escarpments in the gory stolowe tableland sw poland insights from lidar based high resolution dem abstract the tableland of the stolowe mountains sw poland with its prominent mesas and sandstone capped escarpments belongs to the most spectacular geomorphic landscapes of central europe while the gross morphological features of the area have long been recognized the evolutionary pathways of densely forested and poorly accessible escarpment slopes remained poorly understood in this paper we use lidar data to shed a new light on landform inventories within the escarpments their spatial patterns and using process from form reasoning on the longer term evolution of the escarpments four sites two on each major escarpment have been subject to detailed analysis which involved examination of shaded relief slope plan and profile curvature and topographic wetness index in each case the 1 1 m model was used while for the most complex site at mt szczeliniec wielki the results were compared with the 5 5 m model to check the impact of model resolution on geomorphic interpretation despite some loss of information involved in model re interpolation to the coarser scale the main features of escarpment morphology could still be recognized on the other hand automatic landform classification based on the calculation of topographic position index from the 10 10 m model and performed for the entire tableland failed to reveal differences between various sections of the escarpments detectable on finer models the analysis of spatial patterns of minor landforms within the escarpments identified on lidar derived models shows that no single pathway of escarpment evolution exists both the upper slopes in sandstone caprock and the mid slopes in weaker rocks show signs of instability and these are not necessarily coupled large scale caprock failures do occur but seem rare and localized sandstone free faces are rather subject to continuous slow retreat by detachment of individual joint bound blocks another zone of instability occurs well below the caprock and the dominant processes are shallow landslips initiated within weak deformable rocks

a history of basin inversion scarp retreat and shallow denudation the araripe basin as a keystone for understanding long term landscape evolution in ne brazil at the border between the states of ceara and pernambuco northeast brazil the chapada do araripe is a high plateau 800 1000 m a s l formed by a slab of cenomanian fluvial sandstone this caprock is underlain by lacustrine or marine albian layers and older rift deposits during the cretaceous the araripe basin lay at a palaeoelevation close to sea level through a presentation and discussion of original field and cartographic data we analyse the mechanisms of topographic inversion in this sedimentary basin in relation to local or regional crustal upwarp the contrast between the plateau a weakly dissected structural surface and the surrounding lowlands is explained through a study of the erosional scarps cuesta like landforms and their outliers that fringe the chapada no evidence of local tectonic inversion is found river incision spring sapping landslides and other forms of mass movement are listed as efficient processes of topographic inversion and scarp retreat the rates and patterns of which appear to be controlled by lithological contrasts and conditions of exhumation of the basement geometric relationships with regional stepped surfaces e g the low elevation sertaneja surface exhumed palaeosurfaces and regional drainage systems are analysed our estimation of the amplitude of denudation and topographic inversion 0 6 0 7 km differs significantly from apatite fission track derived estimates reported in recent literature which would imply burial by considerable thicknesses of younger sediments followed by 1 5 km or more of post rift denudation not just in the study area but also in the tucano jatoba basin to the south the exhumation and reworking of surrounding basement surfaces probably began during the early cenozoic as shown to the northwest of the chapada by the presence of widespread laterites of probable palaeogene age a second stage of topographic inversion occurred during the oligocene or later this would correspond to the major stages of river incision partial planation and basin inversion

block controlled hillslope form and persistence of topography in rocky landscapes rocky hillslopes dotted with boulder sized blocks and covered by a thin nonuniform soil are common in both steep landscapes and arid environments on earth as well as on other planets while the evolution of soil mantled convex upward hillslopes in uniform lithology is reasonably well understood the influence of heterogeneous lithology and geologic structure on hillslope form and evolution has yet to be properly addressed landscapes developed in layered sedimentary rocks feature sharp edged landforms such as mesas and hogbacks that exhibit steep linear to concave upward ramps with scattered blocks calved from resistant rock layers overlying softer strata here we show that blocks can control the persistence of topography and the form and evolution of hillslopes in these landscapes we present a numerical model demonstrating that incorporation of feedbacks between block release interruption of soil creep by blocks and sporadic downslope movement of blocks are necessary and sufficient to capture the morphology and evolution of these landscapes numerical results are reproduced by a simple analytical solution that predicts steady state concave hillslope form and average slope angle from block size and spacing our results illuminate previously unrecognized hillslope feedbacks advancing our understanding of the geomorphology of rocky hillslopes on a landscape scale our findings establish a quantitative method to address the migration of sharp edges and the persistence of topography in layered landscapes

can grain size sensitive flow lubricate faults during the initial stages of earthquake propagation recent friction experiments carried out under upper crustal p t conditions have shown that microstructures typical of high temperature creep develop in the slip zone of experimental faults these mechanisms are more commonly thought to control aseismic viscous flow and shear zone strength in the lower crust upper mantle in this study displacement controlled experiments have been performed on carbonate gouges at seismic slip rates 1 m s 1 to investigate whether they may also control the frictional strength of seismic faults at the higher strain rates attained in the brittle crust at relatively low displacements 900 c grain boundary sliding gbs deformation mechanisms the observed micro textures are strikingly similar to those predicted by theoretical studies and those observed during experiments on metals and fine grained carbonates where superplastic behaviour has been inferred to a first approximation the measured drop in strength is in agreement with our flow stress calculations suggesting that strain could be accommodated more efficiently by these mechanisms within the weaker bulk slip zone rather than by frictional sliding along the main slip surfaces in the slip zone frictionally induced grainsize sensitive gbs deformation mechanisms can thus account for the self lubrication and dynamic weakening of carbonate faults during earthquake propagation in nature

escarpment retreat in sedimentary tablelands and cuesta landscapes landforms mechanisms and patterns abstract although the general concept that escarpments in layered rocks retreat through time was offered more than 150 years ago recognizing the exact mechanisms patterns and rates of retreat remains a challenge in this paper we provide the state of the art of the theme of escarpment retreat reviewing both the classic contributions often forgotten but important case studies and the latest research in separate parts of the paper we discuss 1 terminology applied to the geomorphology of escarpments 2 the main assumptions and pathways of long term evolution of escarpments including conceptual models presented so far 3 processes involved in cliff retreat mainly weathering mass movements and erosion 4 the role of spring erosion and fluvial processes leading to fluvial dissection and development of canyons present in many tablelands 5 the possible role of climate change in escarpment evolution 6 rates of escarpment retreat in conclusions we summarize the major advances in our understanding of escarpment evolution of the last two three decades such as the recognition of the key role of emerging groundwater in non uniform escarpment retreat of an important role of silica dissolution and underground removal of dissolved solids increasing appreciation of rock properties in governing the patterns of escarpment retreat the proposal that cliffs do not necessarily retreat via catastrophic rock slope failures but may disintegrate in situ and the first attempts to date escarpment retreat using cosmogenic isotopes finally the remaining gaps and possible research priorities for the future are identified

the assessment of rockfall hazard at the base of talus slopes fragmental rockfall is characterized by the independent movement of individual rock fragments after detachment from a rock face the continued operation of the process leads to the accumulation of talus slopes on talus slopes the rockfall shadow extends beyond the base of the talus and consists of scattered boulders that have run out beyond the base of the slope the landing probability of boulders in the shadow is examined return periods of the order of 1000 years relative to a house site are typical rockfall behaviour particularly with respect to run out into the shadow can be assessed using geological evidence empirical methods physical modelling and computer based analytical models an empirical minimum shadow angle of 27 5 i e the angle between the distal limit of the shadow and the top of the talus slope is suggested and would be useful in rockfall vulnerability studies at the base of talus slopes as a first approximation to shadow limits it is preferable to the use of the rockfall fahrb

sediment dynamics below retreating cliffs the retreat of cliffs may constitute the dominant erosional response to base level fall in arid settings underlain by horizontally bedded sedimentary rock these vertical cliffs typically loom above a relatively straight bedrock slope plinth that is mantled with a thin layer of sediment and perched near the angle of repose in detail a plinth consists of a system of quasi parallel ridges and channels we ask how the sediment supplied from a retreating cliff influences the erosion of the plinth hillslopes and channels and how this affects the rate of cliff retreat motivated by field observations and high resolution topographic data from two sites in western colorado we develop a two dimensional 2d rules based numerical model to simulate the erosion of channels draining a plinth and diffusive erosion of the intervening interfluves in this model retreat of a cliffband occurs when the height of the vertical cliff exceeds a threshold due to incision by channels on the plinth below debris derived from cliff retreat is distributed over the model plinth according to the local topography and distance from the source this debris then weathers in place and importantly can act to reduce local bedrock erosion rates protecting both the plinth and ultimately the cliff from erosion in this paper we focus on two sets of numerical model experiments in one suite we regulate the rate of rockfall to limit the cliff retreat rate in most cases this results in complete loss of the plinth by erosion in a second suite we do not impose a limit on the cliff retreat rate but instead vary the weathering rate of the rockfall debris these runs result in temporally steady cliff plinth forms and retreat rates both depend on the weathering rate of the debris copyright 2011 john wiley sons ltd

relict slope rings and talus flatirons in the colorado piedmont origin chronology and paleoenvironmental implications abstract in the colorado piedmont talus flatiron chronosequences are associated with buttes that consist of erodible arkosic sandstone and resistant caprock following the removal of the caprock some buttes evolve into crater like relict slope rings resulting from the differential erosion of the soft bedrock in the core of the hills these unique landforms are only documented in the colorado piedmont their development is attributed to the unusually high erodibility contrast between the low cohesion sandy bedrock and the bouldery colluvial armor the talus flatiron sequences and relict slope rings mapped in the three studied areas record alternating periods of accumulation and incision in the slopes that are likely controlled by changes in moisture availability and vegetation cover density the obtained osl dates place slope accumulation phases at 124 ka and ca 73 ka 50 40 ka 15 ka and 10 6 ka a comparison of these geochronological data with paleoclimatic records from the region suggests that colluvium deposition occurred during periods of denser vegetation cover which are controlled by climate changes further investigations including additional and more accurate geochrological data from the relict slopes will help to better understand the paleoclimatic significance of these largely unknown morphostratigraphic features

the schmidt hammer as a relative age dating tool and its potential for calibrated age dating in holocene glaciated environments the schmidt hammer is a relatively cheap portable sturdy instrument with proven value over the last two decades or so in rapidly dating coarse inorganic deposits of diverse origins early views were that its dating role was limited to distinguishing recently exposed from much older typically either a few sites of possibly different ages or occasional older surfaces amongst many young sites were studied more recently calibration curves based on individual r value means from small numbers 2 4 of sites of known ages have been used to estimate the ages of undated sites we present schmidt hammer rebound r values from 28 little ice age and younger 23 preboreal and 7 younger dryas glaciated surfaces in southern norway in order first to test rigorously the robustness of the instrument as a relative age dating tool despite being obtained from different surfaces moraines glaciofluvial deposits and bedrock and varied metamorphic lithologies the r value overall means and 95 confidence intervals for the little ice age preboreal and younger dryas age categories respectively 60 0 1 6 41 6 1 4 and 34 2 2 0 are statistically significantly different only two outlying sites in the two younger age categories have overlapping confidence intervals demonstrating remarkable robustness in differentiating early and late holocene surfaces the distinction between preboreal and younger dryas sites with terminal dates 2000 years apart is less clear but still statistically significant though possibly partly because of enhanced weathering conditions at the predominantly well vegetated younger dryas sites second we examine the feasibility and desirability of controlling non age related factors including some previously considered critical instrument wear operator bias initial rock surface texture which emerge either as less important than previously argued or as relatively unimportant together with others previously unreported e g long term changes in lichen soil snow and vegetation covers third we investigate the potential for calibrated age dating by applying exploratory linear rates of r value decline to selected combinations of sites the results suggest that error limits of ca 700 to 1600 years should be achievable over the holocene timescale this improved dating capability however will require adequate numbers of site means not only for each age category used to define these curves but also for each set of test surfaces of the same ages recommendations are made for a suitable sampling protocol for developing further the schmidt hammer as a calibrated age dating tool

surface processes and interactions with forest vegetation on a steep mudstone slope stolowe mountains sw poland abstract in this study we recognize complex physical biotic abiotic interactions on a steep forested slope in the moderately elevated mountain terrain of the sudetes central europe using geomorphological pedological and dendrochronological methods on the forested hillslopes of mt rogowa kopa the evidence of disturbance in natural systems is widespread in the geomorphic subsystem its most obvious manifestation is the origin and disappearance of pit and mound microtopography resulting from tree uprooting 82 pit and mound associations have been mapped on a test slope providing quantitative data for calculating sediment flux the flux is around 2 10 4 m 3 m 1 year 1 hence less than suggested in the literature but within the same order of magnitude nevertheless in the long term such a transport rate is comparable with the one typical for creep while it affects a greater thickness of hillslope regolith tree bending and abrupt changes in tree ring width are indicators of disturbed tree growth causally linked to soil creep of mudstone derived regolith eccentric growth is best recorded in wet years and in younger trees which have to adapt to the pre existing pit and mound surface topography we offer a conceptual model that links biotic and abiotic factors and discuss implications of the widespread tree uprooting we suggest that veneers of angular clasts and occasional larger boulders are not necessarily residuals of washed pleistocene solifluction mantles but may result from root plate degradation after uprooting recent catastrophic wind events may through tree uprooting lead to structural changes in cover deposits so that they lose their inherited periglacial signatures

landslide geomorphology an argument for recognition with examples from new zealand the role and significance that have been ascribed to landsliding within geomorphology were examined with respect to some of the influential historical concepts of landform evolution landsliding was almost completely ignored as a geomorphic process in the earliest models of landform evolution while there has been a growing acknowledgement of landsliding as a hillslope process capable of performing significant erosion and transportation it has received only sparse recognition as a formative process in its own right notable exceptions are the rarely referenced model of relief development of skempton a w 1953 soil mechanics in relation to geology proceedings of the yorkshire geological society 29 3 33 62 pt 1 and the reply of selby m j 1974 dominant geomorphic events in landform evolution bulletin international association of engineering geology 9 85 89 to the frequency magnitude findings of wolman m g miller j p 1960 magnitude and frequency of forces in geomorphic processes journal of geology 68 1 54 74 together these two contributions provide a sound basis of geomechanical theory and ample empirical evidence to indicate that landslides have the potential to control landform evolution it is proposed that landslide geomorphology systems exist within which landslides dominate form and process by governing the mechanisms rhythm and pace of geomorphic change in time and space a review of new zealand terrain suggests that these criteria are met in six distinctive landslide geomorphology systems each of these can be characterised not only by the landslide regime but also by the fundamental pre conditions of tectonic setting and geology it is argued that the existence of such systems and the complex interrelations involved require the recognition of a landslide geomorphology in its own right

fault mirrors along carbonate faults formation and destruction during shear experiments glossy light reflective surfaces are commonly exposed in carbonate fault zones it was suggested that such surfaces recently termed fault mirrors fms form during seismic slip ultramicroscopic analyses indicate that fms are highly smooth and composed of a cohesive thin layer of nano size grains we explore here mechanisms of formation and destruction of fms by shear experiments that were conducted on three types of limestone which were sheared at wide range of slip velocities of v 0 001 0 63 m sv 0 001 0 63 m s and normal stress up to 1 57 mpa the experiments showed that fms started to develop as local patches when the slip velocity exceeded a critical value of 0 07 m s the area coverage by fm patches increases systematically with increasing velocity reaching in a few cases 100 coverage the measured quasi steady state friction coefficient ss was inversely correlated with the fm coverage ss 0 8 ss 0 8 for no fm at v 0 07 m sv 0 07 m s and ss 0 4 ss 0 4 for 50 fm coverage at v 0 6 m sv 0 6 m s further in a series of slip velocity alternation between low and high values the fms which formed at a high velocity stage were destroyed during a subsequent low velocity stage our analyses of the experimental thermal conditions and ultramicroscopy imaging of the fms suggest that the fms form by sintering of gouge nanograins during shear we propose that formation destruction of fms in high low slip velocity reflects a competition between brittle and ductile processes fms form in a ductile mode and are destroyed by brittle wear shear heating during high velocity leads to ductile deformation and sintering so that fm construction rate exceeds brittle fm destruction rate based on our results we suggest that at least for shallow faults the presence of extensive fm coverage along natural carbonate faults indicates that the fault segment slipped at seismic velocities and experienced dynamic weakening

scarp retreat and slope development near picton new south wales australia summary slope profiles measured on a ridge extending out from a plateau capped with gently dipping sandstone fall into an evolutionary sequence controls on slope form in the area are the sandstone caprock the processes operating on the slopes themselves and the activity of the channel at the base of the slope as the slopes become older mean slope angles decline from about 18 degrees to about 8 degrees and maximum slope angles decline from 43 to 21 degrees modal slope angles of 6 8 10 12 22 24 and 28 30 degrees appear to be related both to the processes occurring on the slopes and to the strength of the regolith materials a five stage sequence of slope evolution is postulated in which the younger slopes undergo parallel retreat whilst slopes of increasing age first undergo slope replacement and later slope decline soil profile characteristics and a radiocarbon date show that the regolith on the older hillslopes is much older than the adjacent valley fill materials hillslope development is affected much more by incision at the base than by removal or accumulation of debris

phase transformation and nanometric flow cause extreme weakening during fault slip faults weaken during earthquakes laboratory simulations of earthquake rupture show that the nanometric scale fault gouge created during slip is inherently weak and flows by grain boundary sliding providing a mechanism to weaken faults

boulder aprons indicate long term gradual and non catastrophic evolution of cliffed escarpments stolowe mts poland abstract caprock crowned escarpments are characteristic geomorphic features of the sandstone tableland of the stolowe mountains sw poland their mid and lower slopes truncate weaker sedimentary formations but are littered with sandstone boulders of various size often more than 5 m long which form nearly continuous aprons a model of escarpment retreat by rock fall has been widely accepted in literature but in the stolowe mountains it has never been tested against field evidence in addition no rock fall events except one minor fall in 1921 have been recorded in historical times in this paper we erected five hypotheses of how escarpments may have evolved through time to result in widespread boulder presence on the slopes mapping boulder extent and slope morphology run out distance simulations using conefall software and rock strength determinations using the schmidt hammer carried out on boulders along eight representative slope profiles provide data about characteristics of the boulder covers systematic decrease in intact rock strength with an increasing distance from the sandstone cliffs suggests that the boulder aprons are diachronic and record long term retreat of escarpments there exists no conclusive evidence of widespread boulder downslope movement although in a few localities shallow landslides have rafted boulders far away from the cliff lines modelling exercise shows that the actual extent of boulders is 2 3 times bigger than suggested by conefall predictions these findings coupled with observations along the cliff lines themselves lead us to propose a model of free face in situ disintegration as the most likely hypothesis to explain block detachment and release from rock faces as cliff lines recede and the slope surface below is lowered remnant boulders occupy a position increasingly further away from escarpment rims but experience little actual movement this model complements the existing models of tableland evolution which tend to emphasize catastrophic mass movement processes on cliffed escarpments

p t t paths and post metamorphic exhumation of the day nui con voi shear zone in vietnam abstract the day nui con voi belt in vietnam is the southeasternmost part of the red river shear zone in asia it is a narrow high grade metamorphic core complex consisting of garnet sillimanite biotite gneisses mylonite bands amphibolite layers and migmatites geothermobarometric study of the complex revealed that the peak metamorphism took place under amphibolite facies conditions of 690 60 30 c and 0 65 0 15 gpa and the subsequent mylonitization occurred under greenschist facies conditions of 480 c and under 0 3 gpa fifteen synkinematic hornblende and biotite separates from gneisses amphibolites and mylonites were dated with the k ar method hornblende separates from the day nui con voi give k ar ages of 26 4 28 5 ma and the biotite separates do give 24 5 24 7 ma combination of thermobarometric and geochronological data yields the cooling history of 500 c at 28 ma and 300 c at 24 ma with a cooling rate of 70 110 c ma 1 and 23 km post metamorphic exhumation of the core complex the first 16 km exhumation from the peak of metamorphism at probably 31 ma to 28 ma was triggered by the left lateral strike slip displacement of the red river shear zone

schmidt hammer exposure age dating shd of rock glaciers in the schoderkogel eisenhut area schladminger tauern range austria schmidt hammer rebound values r values enable relative age dating of landforms with r values relating to degree of weathering and therefore length of exposure this method recently termed as schmidt hammer exposure age dating shd was applied to date five rock glaciers size range 0 01 0 12 km2 and one recent rockfall deposit at the study area schoderkogel eisenhut in the schladminger tauern range 14 03 e 47 15 n austria the rock glaciers consist of gneiss or high metamorphic series of mica schist that are comparable in their r values four of them are relict permafrost absent and one is intact containing patches of permafrost on each of the five rock glaciers shd was carried out at 4 6 sites 50 measurements per site along a longitudinal transect from the frontal ridge to the root zone results at all five rock glaciers are generally consistent with each other sharing statistically significant r values along transects the range between the highest and the lowest mean r value at ea

schmidt hammer exposure age dating shd of late quaternary fluvial terraces in new zealand schmidt hammer sh r values are reported for surface clasts from numerically dated holocene and pleistocene fluvial terraces in the south island of new zealand the r values are combined with previously obtained weathering rind radiocarbon terrestrial cosmogenic nuclide and luminescence terrace ages to derive sh r value chronofunctions for greywacke clasts from four distinct locations our results show that different weathering rates affect the form of the sh r value versus age curve however a fundamental dependency between the two remains constant over timescales ranging from 102 to 105 years power law scaling constants suggest changes in clast weathering rates are primarily affected by climatic precipitation and temperature and sedimentologic variables source terrane petrology age uncertainties of 22 of the surface age suggest that schmidt hammer exposure age dating shd is a reliable calibrated age dating technique for fluvial terraces copyright 2013 john wiley sons ltd

landscape development in an hyperarid sandstone environment along the margins of the dead sea fault implications from dated rock falls in this study we explored the spatial and temporal relations between boulders and their original in situ locations on sandstone bedrock cliffs thiswas accomplished bycombining field observations withdating methods using cosmogenicisotopes 10 be and 14 c and optically stimulated luminescence osl our conclusions bear both on the landscape evolution and cliff retreat process in the hyperarid region of timna and on the methodology of estimating exposure ages using cosmogenic isotopes we recognize three discrete rock fall events at 31 ka 15 ka and 4 ka in this hyperarid region the most plausible triggering mechanism for rock fall events is strong ground acceleration caused by earthquakes generated by the nearby dead sea fault dsf our record however under represents the regional earthquake record implying that ongoing development of detachment cracks prior to the triggering event might be slower than the earthquake cycle cliff retreat rates calculated using the timing of rock fall events and estimated thickness of rock removed in each event range between 0 14 m ky 1 and 2 m ky 1 when only full cycles are considered we derive a more realistic range of 0 4 m ky 1 to 0 7 mk y 1 these rates are an order of magnitude faster than the calculated rate of surface lowering in the area we conclude that sandstone cliffs at timna retreat through episodic rock fall events that preserve the sharp imposing landscape characteristic to this region and that ongoing weathering of the cliff faces is minor a 10 20 difference in the 10 be concentrations in samples from matching boulder and cliff faces that have identical exposure histories and are located only a few meters apart indicates that cosmogenic nuclide production rates are sensitive to