schmidt hammer exposure age dating shd performed on periglacial and related landforms in opplendskedalen geirangerfjellet norway implications for mid and late holocene climate variability schmidt hammer exposure age dating shd was applied to a variety of boulder dominated periglacial landforms in an attempt to establish a local mid late holocene chronology for the geirangerfjelle

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

rock weathering rates as functions of time the scarcity of documented numerical relations between rock weathering and time has led to a common assumption that rates of weathering are linear this assumption has been strengthened by studies that have calculated long term average rates however little theoretical or empirical evidence exists to support linear rates for most chemical weathering processes with the exception of congruent dissolution processes the few previous studies of rock weathering rates that contain quantitative documentation of the relation between chemical weathering and time suggest that the rates of most weathering processes decrease with time recent studies of weathering rinds on basaltic and andesitic stones in glacial deposits in the western united states also clearly demonstrate that rock weathering processes slow with time some weathering processes appear to conform to exponential functions of time such as the square root time function for hydration of volcanic glass which conforms to the theoretical predictions of diffusion kinetics however weathering of mineralogically heterogeneous rocks involves complex physical and chemical processes that generally can be expressed only empirically commonly by way of logarithmic time functions incongruent dissolution and other weathering processes produce residues which are commonly used as measures of weathering these residues appear to slow movement of water to unaltered material and impede chemical transport away from it if weathering residues impede weathering processes then rates of weathering and rates of residue production are inversely proportional to some function of the residue thickness this results in simple mathematical analogs for weathering that imply nonlinear time functions the rate of weathering becomes constant only when an equilibrium thickness of the residue is reached because weathering residues are relatively stable chemically and because physical removal of residues below the ground surface is slight many weathering features require considerable time to reach constant rates of change for weathering rinds on volcanic stones in the western united states this time is at least 0 5 my

erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

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

longitudinal changes in the size and shape of stream bed material evidence of variable transport conditions summary the pattern of downstream changes in particle size and shape is used to identify dominant transport conditions in a basin with two main lithologies having distinct spatial distributions grain size decreases exponentially and roundness increases geometrically in the sandstone group but shale particles show no such changes largely because shale is supplied discontinuously below headwater reaches where abrasion is no longer at its most effective particle flatness varies more consistently between the lithological groups an initial increase being followed by a geometric decrease discs and blades are the dominant zingg shapes reflecting the influence of bedrock structure and preferential transport three process regimes are identified in which different processes are dominant abrasion and size sorting in the headwater area shape and size sorting in the middle reaches sorting and breakage towards the downstream end of the stream underlying the general tendencies are discontinuities related to tributary inflow the main effects being to increase grain size and flatness below junctions

long term bedload mobility in gravel bed rivers using iron slag as a tracer abstract bedload dispersion is evaluated in gravel bed rivers using slag elements from ironworks established along rivers in the ardenne region between the fourteenth and the nineteenth centuries large quantities of slag were dumped close to these rivers or even directly into the channels for centuries slag elements were dispersed in the bedload and transported by floods of varying importance consequently slag may be considered as a reliable tracer to analyze bedload dispersion over several centuries the size of slag elements was studied along 16 ardenne rivers the longitudinal size trend of the largest slag particles allows the effective competence of these rivers to be determined between 19 and 129 mm for rivers where specific stream power for the bankfull discharge ranges between 20 and 134 w m a direct relationship doesn t exist between these two parameters as the size of slag elements must be considered with regard to the d 50 of the bed selective transport was analyzed directly downstream of the input sites the sorting distance varies from river to river and depends on the velocity of the coarse elements introduced into the river since the inception of the iron industry downstream of two metallurgic sites the slag propagation fronts were located as the periods of activity at these sites are known from historical studies the virtual velocity of bedload movement in these rivers was estimated to be 2 4 km century

the three dimensional geometry of simulated porphyroblast inclusion trails inert marker viscous flow models a fluid dynamic model for a rigid spherical porphyroblast growing in a viscous fluid matrix undergoing simple shear deformation predicts an arrangement of captured inert inclusions that is remarkably similar to the spiral pattern observed in synkinematic rolled garnets the model assumes only creeping stokes flow of the matrix and a kinetic model for the growth of the porphyroblast of the form rm km where r is the crystal radius is the amount of shear induced rotation and m and k are kinetic parameters for rotation less than 18d j b thompson and j l rosenfeld s simple ring model provides a surprisingly accurate description of the three dimensional geometry of the central inclusion surface in the simulated porphyroblasts although marker planes originally parallel to the shear plane are deflected around the porphyroblast their intersections with its surface remain approximately circular for much larger amounts of rotation than anticipated by rosenfeld the polar coordinate equation t r of the double spiral formed by the trace of the central inclusion surface in a section through the centre of simulated porphyroblasts is also surprisingly simple as follows rm 6 5k m this relationship was observed over the complete range of rotation angles investigated 0 720d and could form a reasonable basis for estimating the growth rotation history of rolled garnets from the shape of their spiral inclusion trails two dimensional sections through the simulated porphyroblasts parallel to the rotation axis yield clamshell rosenfeld s term inclusion geometries similar to the controversial millipede patterns observed in many natural porphyroblasts

southern laurentide ice sheet retreat synchronous with rising boreal summer insolation establishing the precise timing for the onset of ice sheet retreat at the end of the last glacial maximum lgm is critical for delineating mechanisms that drive deglaciations uncertainties in the timing of ice margin retreat and global ice volume change allow a variety of plausible deglaciation triggers using boulder 10 be surface exposure ages we date initial southern laurentide ice sheet lis retreat from lgm moraines in wisconsin usa to 23 0 0 6 ka coincident with retreat elsewhere along the southern lis and synchronous with the initial rise in boreal summer insolation 24 23 ka we show with climate surface mass balance simulations that this small increase in boreal summer insolation alone is potentially sufficient to drive enhanced southern lis surface ablation we also date increased southern lis retreat after ca 20 5 ka likely driven by an acceleration in rising isolation this near instantaneous southern lis response to boreal summer insolation before any rise in atmospheric co 2 supports the milankovic hypothesis of orbital forcing of deglaciations

surface and sub surface schmidt hammer rebound value variation for a granite outcrop this study presents rock strength variations at granite outcrops and in subsurface vertical profiles in the jizerske hory mountains czech republic schmidt hammer rebound values in subsurface profiles change gradually from the bedrock surface downward an exponential relation has been observed between the r values and depth in rock outcrops to a depth of around 4 5 m the exponential nature of the curve indicates that rock hardness increases more rapidly with depth in the uppermost 1 m section of the rock profile a detailed study of rebound values obtained from both intact and polished rock exposures reveal effects of surface grinding on results of the schmidt hammer method the range of data collected increases after grinding allowing more precise discrimination of rock surfaces in respect of age and weathering the schmidt hammer method may be used effectively as a relative age dating tool for rock surfaces that originated during the late pleistocene it is concluded that this time limitation can be significantly mitigated by surface grinding before measurement copyright 2010 john wiley sons ltd

cirques have growth spurts during deglacial and interglacial periods evidence from 10be and 26al nuclide inventories in the central and eastern pyrenees cirques are emblematic landforms of alpine landscapes the statistical distribution of cirque floor elevations is used to infer glacial equilibrium line altitude and the age of their frontal moraines for reconstructing glacial chronologies very few studies however have sought to measure cirque floor and supraglacial ridgetop bedrock downwearing rates in order to confront these denudation estimates with theoretical models of quaternary mountain landscape evolution here we use 10 be nuclide samples n 36 from moraines bedrock steps and supraglacial ridgetops among a population of cirques in the east central pyrenees in order to quantify denudation in the landscape and detect whether the mountain topography bears any relevance to the glacial buzzsaw hypothesis minimum exposure ages meas obtained for a succession of moraines spanning the oldest dryas to the holocene produced a deglaciation chronology for three different pyrenean ranges maladeta bassies and carlit based on a series of corrections calibrations and chronostratigraphic tuning procedures meas on ice polished bedrock exposures were further used to model denudation depths at nested timescales during the wurm the younger dryas and the holocene results show that subglacial cirque floor denudation was lower during glacial periods wurm 10 mm ka than during deglacial and interglacial periods tens to hundreds of mm ka the relative inefficiency of glacial denudation in the cirque zone during the wurm would have resulted from i cold based and or ii low gradient glaciers situated in the upper reaches of the icefield and or from iii glacier load starvation because of arrested clast supply from supraglacial rockslopes situated in the permafrost zone denudation peaked during the younger dryas and holocene glacial advances a time when cirque glaciers became steeper warmer based and when frost cracking weakened supraglacial ridgetops thus enhancing sub glacial erosion by providing debris to the sliding glacier base cirques therefore grow faster during more temperate periods of cirque glaciation than under full glacial conditions another key finding was the very low rates of ridgetop lowering averaged over the wurm and holocene 10 25 mm ka a comparison of the denudation rates obtained from the cirque zone with regional estimates of crustal uplift indicates that the alpine topography is not in a steady state the low intensity of glacial denudation failed to bring the topography to a buzzsaw equilibrium state

age determination of glacially transported boulders in ireland and scotland using schmidt hammer exposure age dating shd and terrestrial cosmogenic nuclide tcn exposure age dating schmidt hammer exposure age dating shd was applied at 15 sites with glacially transported granite boulders in parts of northern and western ireland and southwest scotland that had been exposed by retreat of the last british irish ice sheet biis or younger dryas yd ice masses seven of these surfaces had previously been dated using terrestrial cosmogenic nuclide tcn exposure age dating application of the granite calibration equation of tomkins et al 2018c indicated a close correspondence between the shd ages and the tcn ages within 1 or 2 uncertainties these findings demonstrate that shd ages can be of comparable accuracy precision and reliability to tcn ages and are a strong argument for the more extensive use of shd in some quaternary dating projects however surface ages obtained by both shd and tcn dating should not be accepted uncritically they must be assessed in relation to the wider geological geomorphological and geochronological evidence evaluation of eight shd ages for which corresponding tcn ages are not available indicate that most are consistent with current theory and field evidence but some anomalous age estimates occur

interpretation age and significance of a relict paraglacial and periglacial boulder dominated landform assemblage in alnesdalen romsdalsalpane southern norway abstract a boulder dominated landform assemblage in an alpine setting in norway is described interpreted and dated using a combination of schmidt hammer exposure age dating shd and cosmogenic 10be surface exposure dating the origin and formation of these features is determined from their morphology topographic setting and age three main components of the assemblage are recognized first a 300 m long and 160 m wide tongue shaped rock slope failure with a shd age of 11 49 0 82 12 96 0 86 ka is identified on the basis of its planform thickness runout distance and association with a fractured backing scarp this is interpreted as a relict paraglacial landform triggered by deglaciation second a 400 m long unequivocal pronival protalus rampart with an shd age of 6 95 0 97 8 35 1 21 ka is identified on the basis of its narrow ridge form aligned close to the foot of an extensive talus slope although formation of the rampart probably commenced with deglaciation the younger shd ages indicate formation at a diminishing rate through the holocene third a 550 m by 150 m lobate component with transverse ridges longitudinal and transverse depressions and enclosed pits previously identified as a rock glacier is dated to 11 33 0 83 13 33 0 90 ka with the schmidt hammer and between 13 3 2 0 14 7 2 0 ka with 10be this third component may also be a product of rock slope failure but attribution to rock glacier creep associated with either interstitial ice permafrost or buried glacier ice during the allerod interstadial younger dryas stadial and to which one or more rock slope failures contributed debris cannot be rejected the advantages and limitations of compiling such evidence for identifying differentiating and classifying apparently similar boulder dominated colluvial landforms are exemplified

bedload entrainment travel lengths step lengths rest periods studied with passive iron magnetic and active radio tracer techniques this paper reports results from bedload transport investigations with active radio and passive iron magnetic tracers in the lainbach a step pool mountain river in bavaria southern germany the spatial distributions of the iron tracers after flood events can be best described by exponential or gamma distributions there is some indication of a tendency of size selective transport of the iron tracers but there is also a considerable amount of scatter in the correlations between weight size and travel length owing to the masking influence of other variables such as the shape of the particles and different positions in the river bed the experiments with artificial magnetic tracers showed that elongated pebbles rods had the longest mean transport distance platy ones discs remained relatively close to the starting points the particles from the pool showed the greatest transport lengths and a 100 per cent chance of being eroded the pebble transmitter system petsy consists of transmitters implanted into individual pebbles a computerized receiver a stationary antenna system with an antenna switchboard and a data logging system the particles do not move continuously but in a series of transport steps and non movement intervals a single value for a given size class is not adequate to describe the critical conditions of entrainment under natural circumstances a probability approach is much more suitable the critical unit discharges total discharge divided by active channel width along the measuring reach are dependent on river bed morphology in the steps bedload needs higher unit discharges to be entrained once entrained the transport of bedload is stochastic in nature and the single particle transport is controlled by the step lengths and the duration of rest periods the distributions of both parameters can be approximated by exponential functions applying the stochastic concept proposed by einstein the mean values of the random variables step length and duration of rest period measured with the petsy technique were used for the simulation of spatial distributions of bedload particles from point sources more field and laboratory data are needed to include varying flow and roughness conditions with tracers representing different particle characteristics

timing and climatic drivers for glaciation across semi arid western himalayan tibetan orogen abstract mapping and forty seven new 10 be ages help define the timing of glaciation in the ladakh and pangong ranges in northwest india five new local glacial stages are defined for the ladakh range from oldest to youngest these include the ladakh 4 glacial stage at 81 20 ka the ladakh 3 glacial stage not dated the ladakh 2 glacial stage at 22 3 ka the ladakh 1 glacial stage not dated and the ladakh cirque glacial stage at 1 8 0 4 ka three local glacial stages are defined for the pangong range which include the pangong 2 glacial stage at 85 15 ka the pangong 1 glacial stage at 40 3 ka and the pangong cirque glacial stage at 0 4 0 3 ka the new 10 be ages are combined with 645 recalculated 10 be ages from previous studies to develop the first regional framework of glaciation across the dryland regions of the greater himalaya transhimalaya pamir and tian shan at the western end of the himalayan tibetan orogen nineteen regional glacial stages are recognized that are termed semi arid western himalayan tibetan stages swhts these include swhts 9 at 311 32 ka swhts 7 at 234 44 ka tentative swhts 6 at 146 18 ka swhts 5e at 121 11 ka swhts 5a at 80 5 ka swhts 5a at 72 8 ka swhts 4 at 61 5 ka swhts 3 at 46 4 ka swhts 2f at 30 3 ka swhts 2e at 20 2 ka swhts 2d at 16 9 0 7 ka swhts 2c at 14 9 0 8 ka swhts 2b at 13 9 0 5 ka swhts 2a at 12 2 0 8 ka swhts 1e at 8 8 0 3 ka tentative swhts 1d at 6 9 0 2 ka tentative swhts 1c at 3 8 0 6 ka swhts 1b at 1 7 0 2 ka and swhts 1a at 0 4 0 1 ka regional glacial stages older than 21 ka are broadly correlated with strong monsoons swhts that are 21 ka or younger have smaller uncertainties and broadly correlate with global ice volume given by marine oxygen isotope stages and northern hemisphere climatic events oldest dryas older dryas younger dryas roman humid period and little ice age

bankfull discharge recurrence interval in gravel bed rivers bankfull discharge was identified in some 30 gravel bed rivers representing in total c 40 gauging stations the catchment sizes vary from 4 km 2 to nearly 2700 km 2 bankfull discharge value increases with basin size in the case of gravel bed rivers developed on an impermeable substratum the following equation emerges q b 0 087 a 1 044 bankfull discharge recurrence interval was determined by fitting maximum annual floods t a into gumbel s distribution and then using the partial duration series t p in this same distribution recurrence interval is below 0 7 years t p for small pebble bed rivers developed on an impermeable substratum it reaches 1 1 to 1 5 years when the catchment size of these rivers exceeds 250 km 2 rivers incised in the soft schists of the famenne show larger channel capacity at bankfull stage a small width depth ratio and thus higher recurrence intervals 1 4 5 3 years with t a and 1 4 4 years with t p baseflow dominated gravel bed streams and sandy or silty rivers experience less frequent bankfull discharges with a recurrence interval higher than 2 or even 3 years t p 1997 by john wiley sons ltd

a note on cluster bedform behaviour in a gravel bed river abstract the behaviour of cluster bedforms was investigated in the farma r central italy a study reach was surveyed and the three components of the pebble clusters occuring on the surface of a gravel bar were painted using different colours before and after each flood all the clusters were photographed and a comparison was made this simple methodology allowed the evolution of the painted clusters to be followed and also allowed a survey of the dislodgment of the clusters particles and the addition of new ones the experiment shows that the mobility of the wake grains is higher than that of the stoss particles a pebble cluster generally loses the wake grain first followed by the stoss pebbles the obstacel clast is commonly the last to be entrained and acts as a single particle after the wake and stoss particles have been dislodged different explanations of this unexpected behaviour are postulated and the interaction of pebble with bed armouring and bedload size distribution is discussed

deglaciation in the central pyrenees during the pleistocene holocene transition timing and geomorphological significance abstract in this study we document deglaciation in a sector of the southern central pyrenees the panticosa massif and the upper gallego and ossau valleys using cosmic ray exposure cre dating methods which were applied to samples from high altitude polished rock steps and rock glacier boulders the obtained cre dates show a coherent spatial distribution and confirm results previously obtained in this study area thus demonstrating the reliability and robustness of the method the results of analyses based on two distinct isotopes 10 be and 36 cl are consistent although the error is higher for results based on the 36 cl isotope the study provides evidence for ice extent in the high gallego valley during the oldest dryas with glacial advance until the bottom of the valleys although the main glacier tongues remained disconnected from each other during this period the extent of glacier advance was directly related to the elevation of the associated summits the younger dryas glaciers were constrained to cirques or very short ice tongues and dating of the polished rock steps indicates that the ice masses were present until the first millennium of the holocene the brazato rock glacier developed at the beginning of the holocene and remained active until the holocene thermal optimum because of the protective effect of large masses of blocks and boulders

accuracy of cosmogenic ages for moraines analyses of all published cosmogenic exposure ages for moraine boulders show an average age range of 38 between the oldest and youngest boulders from each moraine this range conflicts with the common assumption that ages of surface boulders are the same as the age of the landform the wide spread in boulder ages is caused by erosion of the moraine surface and consequent exhumation of fresh boulders a diffusion model of surface degradation explains the age range and shows that a randomly sampled small set of boulders n 3 7 will always yield a lower age limit for the moraine the model indicates that for identical dating accuracy six to seven boulders are needed from old and tall moraines 40 000 100 000 yr 50 100 m initial height but only one to four boulders from small moraines 20 000 100 000 yr 10 20 m by following these guidelines the oldest obtained boulder age will be 90 of the moraine age 95 probability this result is only weakly sensitive to a broad range of soil erosion rates our analysis of published boulder ages indicates that 3 of all moraine boulders have prior exposure and 85 of these boulders predate the dated moraine

exposure age chronology of the last glaciation in the eastern pyrenees abstract we present a chronology of ice recession in the eastern pyrenees based on in situ produced 10be data obtained from the tet paleoglacier complex the sampling strategy is based on the relative chronology provided by a detailed geomorphological map of glacial landforms results indicate that the last maximum ice advance occurred late i e during marine isotope stage 2 compared to the chronology currently established for the rest of the pyrenees despite debatable evidence for a glacial readvance during the oldest dryas stade ice cap melt out was rapid residual cirque glaciers having disappeared by the allerod interstade this is consistent both with north atlantic excursions established by the greenland ice cores and paleoenvironmental data for the region the rapid response of the east pyrenean ice cap to temperature variations is primarily linked to its small size compared to larger pyrenean ice fields to the dry mediterranean climate and to topography related nonlinearities in which a small vertical rise in equilibrium line altitude generates a large change in ice mass possible sources of age uncertainty are discussed in the context of sampling design for single nuclide 10be dating of landform sequences in formerly glaciated landscapes

critical specific stream power in gravel bed rivers experiments with marked pebbles were carried out on different sized rivers of the belgian ardenne catchment areas varying from less than 1 km2 to 2700 km2 specific stream power required to cause bedload movement was evaluated and critical values were obtained three types of relationship between critical specific stream power 0 and grain size d were established the values for 0 in the largest river the ourthe were the lowest and were close to the values obtained for mountainous rivers carrying large boulders in medium sized rivers catchment area between 40 and 500 km2 the critical unit stream power was higher it is likely that it is due to the bedform s greater resistance this resistance would use up some of the energy that can cause movement and transport of bedload the amount of resistance of the bedform can be expressed as bedform shear stress determined by the relationship between grain shear stress that determines movement and transport of the bedload and the total shear stress this ratio varies between 0 4 and 0 5 in the medium sized rivers compared to 0 7 in the ourthe in headwater streams less than 20 km2 there is greater loss of energy due to bedform resistance 0 3 critical specific stream power is higher in this third type of river than in the other two

scour fill and burial depth of coarse material in gravel bed streams scour fill and burial depths of coarse particles were examined in two ephemeral streams using magnetically tagged particles and scour chains the burial depth varied within a bedform and from one bedform to another the maximum burial depth was recorded in bars but differences in the mean burial depth in the pools bar and thalweg were insignificant mean burial depth was three to six times the median size of material on bar surfaces and ten to thirty times that in the pools and thalweg more than eighty per cent of the tagged particles which were located on or close to the bed surface moved in each event although previously buried particles were moved by flood events others which were initially exposed remained stationary on the surface or were buried in situ the data indicate that the mean burial depth was intermediate between the mean depths of scour and fill deeply buried particles probably reflect the development of scour holes during flood flows aggradation and degradation changed the recorded burial depth relative to the local bed surface of stationary tracer particles these observations indicate that scour and fill processes during a flow event are sporadic and change with water discharge

palaeoenvironments of the late miocene pruedo basin implications for the uplift of the central pyrenees the nature structure and extent of a palaeo basin sedimentary infill exposed in the aran valley central pyrenees was studied by combining stratigraphical and biostratigraphical analyses and an audio magnetotelluric survey the basin developed on top of a pre existing peneplain and was formed by the north maladeta fault activity the fluvio palustrine sequence filling the basin was at least 100 m thick specimens of the taxon hippuris cf parvicarpa nikitin were identified for the first time in a european palaeoflora the palynological and carpological analyses allowed us to 1 constrain the age of the basin infill as vallesian 11 1 8 7 ma 2 characterize the vegetation of the belt surrounding the basin as a mainly temperate to warm temperate assemblage and 3 estimate the palaeoaltitude of the site at between 700 and 1000 m which leads to an altitude change of 900 1200 m for the north maladeta fault downthrown block and 1640 1640 m for the upthrown block these data allowed us to estimate the regional uplift of the area at between 0 08 and 0 19 mm a 1 the different exhumation values obtained by other researchers for sites located at both sides of the north maladeta fault are in agreement with its activity as a normal fault since the late miocene supplementary materials details of the data acquisition processing and modelling for the porera profile are available at www geolsoc org uk sup18551

grain sorting in gravel bed streams and the choice of particle sizes for flow competence evaluations flow competence assessments of floods have been based on the largest particle sizes transported and yield either the mean flow stress mean velocity or discharge per unit flow width the use of extreme particle sizes has potential problems in that they may have been transported by debris flows rather than by the flood it may be difficult to locate the largest particles within the flood deposits and there are questions concerning how representative one or a few large particles might be of the transported sediments and therefore of the flood hydraulics such problems would be eliminated for the most part if competence evaluations are based on median grain sizes of transported sediments or perhaps on some coarse percentile that is established by a reasonable number of grains in order to examine such issues the gravel transport data of milhous from oak creek oregon and of carling from great eggleshope beck england have been analysed in terms of changing grain size percentiles with varying flow stresses a comparison between these two data sets is of added interest because the bed material in oak creek is segregated into well developed pavement and subpavement layers while such a layering of bed materials is largely absent in great eggleshope beck the analyses show that the trend of increasing sizes of the largest particles in the bedload samples diameter dm with increasing flow stresses is consistent with similar dependencies based on sieve percentiles ranging from the medians d50 to the 95th percentiles d95 this indicates that the largest particles are an integral part of the overall distributions of bedload grain sizes and respond to changing flow hydraulics along with the rest of the size distribution in oak creek the median grain size shows the largest change with increasing flow stresses followed by d60 and so on to d95 which shows the smallest change the variations in dm continue this trend and are similar to those for d95 this systematic variation of grain size percentiles in oak creek is consistent with changes in the overall distributions which tend to be symmetrical and gaussian for low discharges but become skewed rosin distributions for high discharges in contrast in great eggleshope beck the several percentiles and dm show the same rate of shift to coarser sizes as flow stresses increase this results in part from differences in sampling techniques wherein the bedload samples from great eggleshope beck represent a complete flood event while shorterterm samples at a specific flow stage were obtained in oak creek as a result of the integrated sampling in great eggleshope beck the bedload grain size distributions are more complex commonly with a bimodal pattern however after accounting for differences in sampling schemes in the two streams contrasting patterns in changing grain size distributions remain and these are concluded to reflect grain sorting differences as the bedload grain size distributions approach the distributions of the bed materials it is surprising that if criteria commonly employed to demonstrate the equal mobility of different grain sizes are used in the comparison then great eggleshope beck is far closer to this condition in spite of its minimal development of a pavement it is concluded that the respective shapes of the bed material grain size distributions in particular their degrees of skewness are more important to the observed sorting patterns than are the effects of a pavement layer regulating grain entrapment to produce an equal mobility of different grain sizes therefore the comparison has established that flow competence relationships will differ from one stream to another depending on the pattern of grain sorting which is a function of the bedmaterial grain size distribution

palaeogeography and 10be exposure age chronology of middle and late pleistocene glacier systems in the northern pyrenees implications for reconstructing regional palaeoclimates abstract we present constraints on the chronology palaeogeography and palaeoclimatic implications for western europe of middle and late pleistocene glaciation in the ariege catchment north eastern pyrenees based on 37 cosmogenic 10 be exposure ages obtained from moraines and glacially scoured bedrock exposures we have dated six regional glacial stades the chronology emphasises several conclusions that are new to the region i in the pyrenees the global lgm occurred several thousands of years after the maximum ice extent of the wurmian glaciation ii almost full glacier extent occurred again during the global lgm but only in the eastern pyrenees iii valley glaciers such as in the ariege trunk valley attained lengths of 25 km during the oldest dryas stadial the cosmogenic exposure ages additionally provide the first direct evidence of 10 km scale fluctuations of ice front positions during the late pleistocene glacial cycle probably at the time of marine isotope stage 3 as well as rare insights into middle pleistocene ice margin positions compared with existing evidence of glacial palaeogeography in other catchments of the pyrenan range the data also reveal a sharp contrast in relative ice extent between the glacierized catchments of the eastern pyrenees ariege carol malniu tet where wurmian mie and lgm ice fronts reached similar positions and the rest of the range where ice fronts at the time of the mis 2 and global lgm palaeotemperature minima lagged far behind the wurmian mie terminal moraines we ascribe this non uniform behaviour among catchments to non uniform palaeoclimatic conditions along the strike of the pyrenees a range of palaeoenvironmental proxies reviewed in the literature highlight a sharp difference in sea surface temperatures between the warmer western mediterranean and the cooler bay of biscay the consequences of such an e w temperature gradient on weather patterns during the global lgm are compatible with a strengthening of mediterranean low pressure systems particularly the semi permanent balearic low generating greater precipitation over the eastern pyrenees compared to atlantic weather systems further west

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

younger dryas glaciers and climate in the mourne mountains northern ireland here we present evidence to suggest that the mourne mountains northern ireland were last occupied by glaciers during the younger dryas stadial the margins of these glaciers are marked by moraines chronologically constrained to the younger dryas by schmidt hammer exposure dating reconstructions indicate that these glaciers had equilibrium line altitudes elas ranging from 356 33 m a s l to 570 9 m a s l with a mean of 475 36 m a s l elas rise from west to east probably reflecting the contribution of windblown snow and ice to the accumulation of younger dryas glaciers in the western mournes taking this into consideration a mean climatic ela of 529 4 m a s l is calculated for the mountains as a whole assuming a mean annual sea level air temperature of 8 c and an annual temperature range of 34 c degree day modelling suggests that during the younger dryas accumulation at the climatic ela of glaciers in the mournes was 846 990 mm a 1 this suggests increased aridity relative to present and is consistent with other parts of nw europe where reduced precipitation alongside notable cooling is thought to reflect increased north atlantic sea ice extent during the younger dryas

glacial to interglacial vegetation changes in the northern and southern pyrenees deglaciation vegetation cover and chronology abstract new palynological investigations have been carried out in the southern northern and mediterranean part of the pyrenean chain pollen percentage and concentration diagrams are compared for a period including the end of the glacial period the late glacial and postglacial periods from the new results and from comparisons with previous published data the steppe and semi desert vegetation of the end of the last glacial period are described as well as the plant communities of the period 15 13 ka a dry climate was responsible for the early glacial retreat before 30 ka deglaciation was continuous up to about 15 14 ka without any readvance around 20 18 ka different aspects of the late glacial vegetation are studied and the first stages of the postglacial are described the younger dryas event is found everywhere but particularly clearly in the mediterranean area the most important 14 c dates are discussed and a plateau of 14 c ages is clearly visible around 10 000 bp

a northern lead in the orbital band north south phasing of ice age events abstract re analysis of existing data sets shows that they are fully consistent with northern insolation control of ice age cycles and do not provide strong support for alternate models invoking tropical or southern controls the coldest time of the last 100 ka in central greenland was nearly synchronous with the minimum in summer insolation about 24 ka bp thousand years before 1950 approximately one third of the total termination i warming since then was achieved over the almost 10 ka before the abrupt warming into the bolling which some workers have interpreted as the start of the warming southern warming as recorded in the byrd station antarctica ice isotopic record lagged northern warming co2 rise was roughly synchronous with southern warming methane rise may have been delayed a little as was sea level rise and the change in the isotopic composition of atmospheric oxygen was delayed significantly the data for the extrema just before termination ii are consistent with occurrence of the same phasing as for termination i but with somewhat different progression of the two terminations once initiated perhaps because of differences in the forcing

the relationship between shear stress and the shaping of the bed of a pebble loaded river la rulles ardenne summary geomorphological modifications in the bed of a small pebble loaded river were related to different parameters such as flow velocity and shear stress experiments carried out with marked pebbles of known diameter demonstrated that shear stress calculated from the energy grade line slope and the hydraulic radius is a reliable criterion in explaining erosion and transport of the pebble load increase in shear stress with discharge entrainment varies according to site at times of low flow shear stress is weak in the pools allowing transitory accumulation of fine deposits and pebbles these originate mainly from erosion downstream of riffles where shear stress is already considerable at times of discharge near bankfull stage shear stress becomes considerable in the pools so that pebbles deposited at lower discharge rates are then displaced however the coarser elements are halted on the counter slope of the pools and upstream of riffles since shear stress there is then weaker than in the pools riffles thus appears as stopping places with only small elements 1 5 cm diameter able to cross them at times of high discharge the size of these elements thus provides an estimate of the true competence of the river

regional synthesis of mediterranean atmospheric circulation during the last glacial maximum atmospheric circulation leaves few direct traces in the geological record making reconstructions of this crucial element of the climate system inherently difficult we produced a regional mediterranean synthesis of paleo proxy data from the sea surface to alpine altitudes this provides a detailed observational context for change in the three dimensional structure of atmospheric circulation between the last glacial maximum lgm 23 000 to 19 000 years ago and the present the synthesis reveals evidence for frequent cold polar air incursions topographically channeled into the northwestern mediterranean anomalously steep vertical temperature gradients in the central mediterranean imply local convective precipitation we find the lgm patterns to be analogous though amplified to previously reconstructed phases of enhanced meridional winter circulation during the maunder minimum the little ice age

schmidt hammer exposure age dating shd of sorted stripes on juvflye jotunheimen central south norway morphodynamic and palaeoclimatic implications abstract measurements with an electronic schmidt hammer rockschmidt were conducted on 23 sites of sorted stripes periglacial patterned ground on juvflye jotunheimen central south norway all were located above the current lower limit of alpine permafrost performing schmidt hammer exposure age dating shd based on application of a new local age calibration equation for rrock values yielded shd ages between 7975 370 and 6660 355 years ago which are closely comparable to results obtained previously from sorted circles at the same location the age estimates are interpreted as composite ages indicative of upfreezing of boulders lateral sorting and subsequent stabilisation formation of patterned ground essentially ceased with the onset of the regional holocene thermal maximum htm neither sorted stripe sites at higher altitude continuously underlain by permafrost during the entire holocene nor those at lower altitudes affected by re aggradation of permafrost in the late holocene show signs of significant recent morphodynamic activity likely explanations for early to mid holocene stabilisation include 1 substantial changes of soil moisture conditions and related thermodynamics within the active layer affecting frost action 2 loss of fine grained substrate matrix from the coarse stripes and hence reduced frost susceptibility and 3 exhaustion of supply of boulders from the fines dominated areas whereas the sorted stripe data set as a whole did not reproduce the altitudinal gradient characteristic of sorted circles on juvflye the strength of the relationship between sorted stripe mean rrock values and altitude increased with declining slope gradient although interpretation of shd ages for patterned ground remains challenging this successful application of the electronic schmidt hammer with its increased efficiency and technical improvements over the mechanical schmidt hammer offers considerable potential for future shd studies in both morphodynamic and palaeoclimatic contexts

climate sensitivity and geomorphological response of cirque glaciers from the late glacial to the holocene sierra nevada spain abstract through a detailed geomorphological study including thourough mapping of the geomorphic features as well as 10be cosmic ray exposure cre dating the geomorphological evolution of the mulhacen cirque since the maximum ice extent of the last glacial cycle until nowadays was determined this glacial cirque is shaped on the northern face of the mulhacen peak 3479 m a s l 37 03 12 n 3 18 41 w sierra nevada southern spain it includes several depositional and erosional glacial landforms that allowed reconstructing its environmental evolution since the last glacial cycle furthermore the sequence of glacial oscillations from this site was compared to that of other cirques of the massif evidencing that i new glaciers formed in these cirques during the younger dryas yd and ii disappeared at 11 7 1 0 ka depending on the altitude orientation and height of the cirque walls the final deglaciation of the cirques generated a diversity of landscapes including a wide range of glacial and periglacial landforms such as polished surfaces sequences of moraines proto rock glaciers or large rock glacier systems no glaciers existed in the sierra nevada during the middle holocene only the cirques whose summits exceed 3300 m are north exposed and whose walls exceed 300 m high i e mulhacen and veleta hosted glaciers during neoglacial phases including the little ice age lia approx 1300 1850 ce during these periods climate oscillations favoured the formation of small glaciers in these cirques which generated large moraine systems with either one polygenic ridge or a sequence of spaced frontal arcs the existence of glaciers impeded the formation of permafrost related landforms such as rock glaciers and protalus lobes until the end of the lia when they started to form these results are compared with the deglacial evolution in 55 cirques from iberian mountains as well as from glacial cirques from other mid latitude mountains and subpolar regions the chronology of their deglaciation as well as the landforms generated during glacial retreat followed similar patterns with no significant differences at regional scale for each mountain range the geomorphological diversity existing in each cirque depends on the local topographic characteristics although they formed during the same climatic phases

a stratigraphical basis for the last glacial maximum lgm abstract the last glacial maximum lgm is widely used to refer to the episode when global ice volume last reached its maximum and associated sea levels were at their lowest however the boundaries of the interval are ill defined and the term and acronym have no formal stratigraphical basis this is despite a previous proposal to define it as a chronozone in the marine records on the basis of oxygen isotopes and sea levels spanning the interval 23 19 or 24 18 ka and centred on 21 ka in terrestrial records the lgm is poorly represented since many sequences show a diachronous response to global climate changes during the last glacial cycle for example glaciers and ice sheets reached their maximum extents at widely differing times in different places in fact most terrestrial records display spatial variation in response to global climate fluctuations and changes recorded on land are often diachronous asynchronous or both leading to difficulties in global correlation however variations in the global hydrological system during glacial cycles are recorded by atmospheric dust flux and this provides a signal of terrestrial changes whilst regional dust accumulation is recorded in loess deposits global dust flux is best recorded in high resolution polar ice core records providing an opportunity to define the lgm on land and establish a clear stratigraphical basis for its definition on this basis one option is to define the global lgm as an event between the top end of greenland interstadial 3 and the base onset of greenland interstadial 2 spanning the interval 27 540 23 340 ka greenland stadial 3 this corresponds closely to the peak dust concentration in both the greenland and antarctic ice cores and to records of the global sea level minima this suggests that this definition includes not just the coldest and driest part of the last glacial cycle but also the peak in global ice volume the later part of the lgm event is marked by heinrich event 2 which reflects the onset of the collapse of the laurentide at c 24 ka together with other ice sheets in the north atlantic region a longer and later span for the lgm may be desirable although defining this in chronostratigraphical terms is problematic whichever formal definition is chosen this requires the contribution of the wider quaternary community

timing of glacial retreat in the wicklow mountains ireland conditioned by glacier size and topography this paper presents 170 schmidt hammer exposure ages from moraine boulders and glacially sculpted bedrock to reveal the post last glacial maximum lgm history of the wicklow mountains ireland these data suggest that large ice masses survived for 4 7 ka after retreat of the irish sea ice stream and were sustained by summit ice fields until 16 6 ka post lgm retreat was dynamic with re advance moraines deposited in response to heinrich stadial 1 however these events reflect short term ice front oscillations 1 ka during the long term retreat phase retreat from re advance positions was synchronous across the range and paced by climate with time progressive deglaciation from low to high elevation in contrast marked asynchroneity in the timing of younger dryas deglaciation is closely linked to snow redistribution and indicates that for small cirque glaciers 1 km2 topography can exert the primary control on glacier survival this result has important implications for palaeoclimate econstructions as cirque glacier dynamics may be unrelated to climate this is further complicated by post depositional processes which can result in moraine ages e g 10be which post date retreat future palaeoclimate studies should prioritise cirque glaciers where snow contributing areas are small and where postdepositional disturbance is limited matrix poor boulder rich moraines

application of schmidt hammer relative age dating to late pleistocene moraines and rock glaciers in the western tatra mountains slovakia abstract in order to evaluate the potential of the schmidt hammer for relative age dating of late pleistocene moraines and rock glaciers rebound r values were collected at 38 sites in two formerly glaciated valleys in the western tatras in northern slovakia a large statistical population of measurements obtained from moraine and rock glacier surfaces was used to analyze the variability of mean r values in the same lithology and overall southern valley exposition four separate sets of glacial periglacial morphosystems are present at different positions in the western tatras starting from valley outlets to the highest cirques which represent successive phases of deglaciation r value means and 95 confidence intervals for selected last glacial maximum lgm and late glacial lg 1 lg 2 and lg 3 stages respectively 40 1 1 1 46 0 5 53 5 1 0 and 60 5 0 3 are significantly statistically different and values for each age category are comparable for the two analyzed valleys the results of weathering indexes used in conjunction with geomorphological relationships were taken together to reconstruct the pattern of deglaciation on southern tatra slopes it is stated that the schmidt hammer technique may be successfully used as a relative age dating tool for late pleistocene glacial and periglacial deposits and with this method it is possible to differentiate between late glacial moraines and rock glacier systems of different age

latest pleistocene glacier advances and post younger dryas rock glacier stabilization in the mt krivaň group high tatra mountains slovakia abstract the timing of glacier disappearance and rock glacier stabilization in the highest massifs of the carpathians is still poorly documented in this paper we establish the extent and chronology of the final stages of glaciation and timing of stabilization of the uppermost rock glaciers in the tatra mountains which are the highest 2654 m a s l northernmost n 49 12 and coldest range in the carpathians on the base of morphostratigraphic principles schmidt hammer tests and glacier equilibrium line altitude ela estimation we assigned moraines and rock glaciers in the mt kriva massif sw part of high tatras to a threefold stratigraphic sequence with glacial stages advances from older to younger popradske pleso pp sucha va ecka i sv i and sucha va ecka ii sv ii landforms attributed to two younger advances sv i and sv ii were sampled for the purpose of cosmogenic 10be surface exposure dating our data show that pp and sv i glacial advances occurred during the oldest dryas climatic downturn the younger advance sv i occurred just before the bolling allerod b a warming at 14 9 0 4 ka at this time small glaciers occupied lower glacial cirques in the study area the youngest sv ii advance was characterized by rock glaciers and small debris covered glaciers confined to the highest cirques the mean exposure age of four relict rock glaciers of this stage is 11 1 0 9 ka but individual rock glacier mean ages spanned between 11 8 and 10 4 ka our research results show that the youngest moraines and rock glaciers in the tatra mountains were formed during the younger dryas yd but the final permafrost melting and rock glacier stabilization period was delayed until the early holocene but no later than 10 4 ka in high elevation cirque bottoms up to 2120 m a s l the yd glaciers and rock glaciers readvanced across land which was ice free as early as 14 8 14 2 ka thus it is likely that during the b a interphase glaciers completely disappeared in the tatra mountains the yd was the last period of glacial periglacial activity in the massif as we investigated one of the highest situated rock glaciers in the tatras up to 2220 m a s l we conclude that all rock glaciers in this massif are relict landforms which developed in response to severe lateglacial climate conditions the lateglacial climate of the tatra mountains is discussed herein on the basis of glacier equilibrium line altitude ela estimation and the vertical distribution of rock glacier belts we argue that paleoclimate significance of the presented geomorphological record may match paleobotanical proxy reconstructions and the results of climate simulations but only if the impact of enhanced temperature seasonality on glacier mass balance and rock glacier activity is taken into account

mobility of river tracer pebbles over different timescales 1 tracer pebbles are widely used to learn about gravel transport along rivers movement over short times and distances is dominated by factors controlling entrainment relative particle size and shear stress movement at longer scales also involves depositional factors burial and reexposure and exchange between channels bars and other depositional environments we mapped mixed size tracers in six reaches of a small scottish river after 2 and 8 years to investigate differences in relative and absolute mobility and infer the importance of burial and exchange patterns of relative mobility according to size and shear stress both within and between reaches did not change significantly some local bunching of tracers was apparent in both surveys with redistribution from pools into riffles and bars the main change was that virtual velocities were 50 lower and estimated gravel fluxes were also lower in the longer term this slowdown is attributed to vertical mixing giving decreased mobility as surface seeded tracers become buried long term storage in bars and other less active parts of the system and in this channel advection of tracers downstream onto a finer bed giving higher relative size

late quaternary glacial phases in the iberian peninsula abstract the only glaciers existing today in the iberian peninsula are small features located in the pyrenees though their number and extension has undergone significant changes over the late quaternary the wide range of glacial landforms and deposits distributed across different iberian ranges suggests the occurrence of several past periods with larger glacial systems the objective of this research is to summarize the current knowledge on the spatial and temporal patterns of glacial activity in the iberian mountains during the late quaternary to this purpose the chronological framework was divided in six periods glaciations prior to the last glacial cycle middle pleistocene last glacial cycle late pleistocene termination 1 holocene little ice age lia and present day the data were geographically divided considering the mountain systems where glacial evidence exists pyrenees cantabrian range nw ranges central range iberian range and sierra nevada during quaternary cold stages ice accumulated in the head valleys of these mountain ranges and glaciers flowed down valleys in all cases glaciers remained confined within the mountain systems and did not reach the surrounding lowlands depending on the combination of temperatures and moisture conditions more or less ice was stored in some ranges there is evidence of middle pleistocene glaciations one potentially correlating with marine isotope stage mis 12 and another correlating with mis 6 with glaciation dated to ca 130 170 ka however most of the glacial records correspond to the last glacial cycle and subsequent termination the maximum glacial expansion of this last pleistocene glaciation stage occurred well before the global last glacial maximum lgm between 30 and 60 ka in the cantabrian mountains and pyrenees at ca 30 ka in sierra nevada and nw ranges and almost synchronously to the lgm in the central range and iberian range a massive glacial retreat occurred in all ranges at 19 20 ka but the long term deglaciation process was interrupted by cold intervals such as the oldest and younger dryas which favoured glacial expansion in the highest mountains temperature increase recorded during the holocene conditioned the melting of glaciers which only reappeared in the highest massifs during the coldest periods such as the lia however post lia warming led to glacier disappearance in the cantabrian mountains sierra nevada and most massifs of the pyrenees together with an accelerated shrinkage of the small glaciers still existing in this range at elevations near 3000 m

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

development of a holocene glacier fed composite alluvial fan based on surface exposure age dating techniques the illae fan jotunheimen norway abstract holocene development of a composite alpine alluvial fan is reconstructed and dated based on its geomorphology and schmidt hammer exposure age dating shd supplemented by terrestrial cosmogenic nuclide dating tcnd lichenometry radiocarbon dating soil development and palaeohydrological analysis shd ages of 7080 450 to 8220 440 years and a tcnd age of 6075 1220 years from the fan surface indicate that fan aggradation occurred in the early holocene through episodic debris floods phase 1 in response to paraglacial processes following deglaciation of the catchment 9 7 ka stabilisation during the holocene thermal maximum phase 2 was followed by re activation of the fan involving entrenchment and terrace formation phase 3 which occurred in response to neoglaciation after 5 5 ka and culminated in the little ice age the main control on fan development was the effect of the changing extent of glaciers in the catchment on sediment supply initially evinced in high magnitude debris floods hyperconcentrated flows and later in water floods typical fluvial processes aggradation switched to stabilisation as paraglacial activity waned while later entrenchment was associated with relatively low bedload results provide the basis of a conceptual model of alluvial fan evolution for glacierized catchments related to holocene environmental change

the nature and controls on downstream fining within sedimentary links abstract at scales of 100 to 102 km grain size change in gravelly alluvial systems is characterized by punctuated downstream fining significant lateral sediment inputs define a sequence of sedimentary links within which fluvial processes produce fining trends using a new set of surface grain size data eighteen such links along two canadian gravel bed rivers are examined negative exponential functions are found to be most appropriate for describing within link grain size changes development of a pragmatic means of predicting grain size is then pursued by searching for a means to relate model diminution coefficients to link attributes consideration of lithologically differentiated fining trends indicates that lithology plays an insignificant role in controlling fining rate examination of within link longitudinal profiles indicates a reasonable relation between fining rate and the rate of change of channel slope the predictive value of this relation is limited by the regional nature of the data upon which it is based and the relative difficulty of obtaining accurate gradient information however as previously noted for alluvial fans although for different reasons channel gradient is correlated with link length and a reasonable predictive tool is apparent in a relation between link length and diminution rate the validity of the derived relation cannot be tested for want of a suitable data set several lines of evidence indicate that abrasion is unimportant as a fining mechanism on these rivers and it is argued that this may be typical of sedimentary links fining rate must then be a function of the efficiency with which sorting processes operate and it is suggested that this efficiency is dependent on aggradation rates associated with the lateral sediment influxes at the head and terminus of individual links

small isolated glacial catchments as priority targets for cosmogenic surface exposure dating of pleistocene climate fluctuations southeastern pyrenees a new 10 be data set from a small glacial catchment in the pyrenees confirms almost full glacier extent during marine isotope stage mis 2 extends the oldest cosmogenic exposure ages of moraines in this mountain range to mis 5 and constrains paleoclimate reconstructions in the mediterranean region it also illustrates the advantageous conditions for the long term preservation of terminal moraines provided by small low gradient glacier catchments that did not merge with compound ice masses even during glacial maxima these small gently sloping and isolated glacier catchments are proposed as priority targets for terrestrial cosmogenic nuclide dating of peak pleistocene glacier advances providing scope for greater accuracy in interregional paleoclimatic correlations

transport of tracer gravels on a coastal california river abstract tracer gravels can provide information about the transport of coarse gravels not sampled by standard sampling methods white dolomite fragments emplaced as riprap on the carmel river monterey county california were entrained by progressively higher flows in 1981 1982 and 1983 and were transported progressively further following the 1981 flow tracer gravel concentration decreased exponentially downstream after the 1982 flows and again after the 1983 flows the distribution of gravels reflected channel morphology not an exponential downstream decrease peak concentrations corresponded to locations of major gravel bars while tracer concentration decreased overall in the downstream direction its distribution suggested movement by discrete jumps from bar to bar rather than continuous movement calculation of bedload transport rates for rocks 45 mm by spatial integration of tracer data yields bedload transport rates of about 3 5 of the total bedload flux measured by helley smith sampler 5 5 km downstream the spatial integration method is not strictly applicable here because injection of tracer was not instantaneous and channel form is quite irregular nonetheless it is notable that results by this method are compatible with sampled transport rates downstream the results of this study show the dominant influence of channel morphology on tracer gravel distribution reflecting the importance of in channel storage sites in coarse sediment movement this effect and the low recovery rate reported for tracer gravels in the literature are reason for caution in using short term tracer gravel studies to compute rates of coarse bedload flux however tracer studies can be profitably used to provide data on the movement of coarse particles unmeasured by helley smith samplers

a stratigraphic framework for abrupt climatic changes during the last glacial period based on three synchronized greenland ice core records refining and extending the intimate event stratigraphy due to their outstanding resolution and well constrained chronologies greenland ice core records provide a master record of past climatic changes throughout the last interglacial glacial cycle in the north atlantic region as part of the intimate integration of ice core marine and terrestrial records project protocols have been proposed to ensure consistent and robust correlation between different records of past climate a key element of these protocols has been the formal definition and ordinal numbering of the sequence of greenland stadials gs and greenland interstadials gi within the most recent glacial period the gs and gi periods are the greenland expressions of the characteristic dansgaard oeschger events that represent cold and warm phases of the north atlantic region respectively we present here a more detailed and extended gs gi template for the whole of the last glacial period it is based on a synchronization of the ngrip grip and gisp2 ice core records that allows the parallel analysis of all three records on a common time scale the boundaries of the gs and gi periods are defined based on a combination of stable oxygen isotope ratios of the ice 18o reflecting mainly local temperature and calcium ion concentrations reflecting mainly atmospheric dust loading measured in the ice the data not only resolve the well known sequence of dansgaard oeschger events that were first defined and numbered in the ice core records more than two decades ago but also better resolve a number of short lived climatic oscillations some defined here for the first time using this revised scheme we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the last glacial period that are represented in the greenland ice records the final product constitutes an extended and better resolved greenland stratotype sequence against which other proxy records can be compared and correlated it also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations

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

late pleistocene and holocene glaciation in the pyrenees a critical review and new evidence from 10be exposure ages south central pyrenees a compilation and a critical assessment of the 14c data set available show that the chronology of glacial events in the pyrenees is not well constrained after reviewing the literature on glacial reconstruction we suggest a simplified subdivision of the pyrenean last glacial cycle record into last pleniglacial deglaciation and neoglacial to improve the numerical glacial chronology we provide 10be surface exposure ages for 5 glacial erosion surfaces 9 moraines and 2 erratics in the upper noguera ribagorcana valley south central pyrenees published corrected 14c data and new 10be exposure ages indicate that the major phase of moraine building recorded in this valley during the last pleniglacial probably occurred after 25 ka bp this age calls in question the generally accepted hypothesis of a very early deglaciation of the pyrenees ca 70 40 ka bp and strongly suggests that the pyrenees could have been in pleniglacial conditions during the last glacial maximum lgm however we do not exclude the possibility that the maximum glacier extent during the last glacial cycle had taken place much earlier than the lgm as indicated by some published u th ams 14c and osl data we suggest that pleniglacial conditions could have taken place during a longer 30 20 ka period than generally assumed and that the last pleniglacial could include several glacier fluctuations recorded irregularly in different valleys with a last major glacier readvance taking place around the lgm in addition the deglaciation is represented by a series of moraines deposited between ca 13 7 0 9 and 10 1 0 6 ka this moraine series indicates a highly variable climatic pattern that is partly correlated with greenland stadial 1 the younger dryas and suggests that the deglaciation could have continued into the early holocene

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

surface dating of dynamic landforms young boulders on aging moraines the dating of landforms is crucial to understanding the evolution history and stability of landscapes cosmogenic isotope analysis has recently been used to determine quantitative exposure ages for previously undatable landform surfaces a pioneering application of this technique to date moraines illustrated its considerable potential but suggested a chronology partially inconsistent with existing geological data consideration of the dynamic nature of landforms and of the ever present processes of erosion deposition and weathering leads to a resolution of this inconsistency and more generally offers guidance for realistic interpretation of exposure ages

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

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

low long term erosion rates in high energy mountain belts insights from thermo and biochronology in the eastern pyrenees abstract we relate the high elevation of flat topography in the eastern pyrenees to the resurrection of a mountain belt which prior to 12 ma was a low relief landscape or peneplain bevelling eroded stumps of the pyrenean compressional orogen new apatite fission track and u th he data together demonstrate the consistently young age

rapid age assessment of glacial landforms in the pyrenees using schmidt hammer exposure dating shed schmidt hammer sh sampling of 54 10 be dated granite surfaces from the pyrenees reveals a clear relationship between exposure and weathering through time n 52 r 2 0 96 p 0 01 and permits the use of the sh as a numerical dating tool to test this10 be sh calibration curve 100 surfaces were sampled from five ice front positions in the tet catchment eastern pyrenees with results verified against independent 10 be and 14 c ages gaussian modelling differentiates holocene 9 4 0 6ka younger dryas 12 6 0 9ka oldest dryas 16 1 0 5ka last glacial maximum lgm 24 8 0 9ka and wurmian maximum ice extent stages mie 40 9 1 1ka these data confirm comparable glacier lengths during the lgm and mie 300m difference in contrast to evidence from the western pyrenees 15km reflecting the relative influence of atlantic and mediterranean climates moreover pyrenean glaciers advanced significantly during the lgm with a local maximum at 25ka driven by growth of the laurentide ice sheet southward advection of the polar front and a solar radiation minimum in the northern hemisphere this calibration curve is available online http shed earth to enable wider application of this method throughout the pyrenees

timescales climate and river development abstract in the long term glacial interglacial sequences river development follows general climatic evolution however at the scale of one cold warm cycle it appears that the geomorphological effect of river activity is best expressed at times of climatic change such periods of pronounced fluvial action last only a short time in more detail the internal evolution in a drainage basin after a climatic event results in a delayed response of the morphology and sedimentation pattern finally on the shortest timescale local thresholds may play a decisive role in the reactions of river systems it is concluded that the relation between fluvial development and climate is not a simple one but is fundamentally dependant on the timescale

entrainment of gravel from naturally sorted riverbed material the critical dimensionless shear stress ci required to entrain a given size particle di was computed from extensive bedload transport measurements in three self formed rivers that have naturally sorted gravel and cobble bed material the value of ci was determined to be significantly affected by the size distribution of the riverbed material for bed particles between 0 3 to 4 2 times the median diameter of the subsurface bed material d50 the average critical dimensionless shear stress ci is equal to ci 0 0834 di d50 0 872 with a coefficient of determination of 0 980 for bed particles larger than 4 2 times d50 ci appears to approach a constant value of approximately 0 020 in a noneroding channel thus ci varies from 0 25 to 0 020 for a given particle depending on the ratio of di to d50 previous investigations of the hydraulic conditions required to entrain coarse riverbed material have reported critical shear stress values ranging from 0 25 to 0 020 for a given particle size this analysis indicates that virtually all of the variation is due to differences in the subsurface bed material size distribution this analysis shows that ci varies almost inversely proportional to the particle diameter for a nonuniform bed material therefore bed particles between 0 3 to 4 2 times d50 are entrained at nearly the same discharge an investigation of the hydraulic characteristics and bed material mobility of 24 self formed gravel bed rivers in colorado determined that particles as large as the median diameter of the bed surface were entrained by discharges equal to the bankfull stage or less particles as large as the 90th percentile fraction were entrained by the bankfull discharge in nine of the rivers studied consequently in these rivers a significant fraction of the riverbed was entrained rather frequently over a period of years although the transport rate was very small

timing and climatic drivers for glaciation across monsoon influenced regions of the himalayan tibetan orogen abstract mapping and thirty eight 10 be terrestrial cosmogenic nuclide tcn ages help define the timing of glaciation in the monsoon influenced greater himalaya in central garwhal india glacial landforms in central garwhal are present only within a few kilometers of the present glaciers and all date to less than 12 5 ka this suggests that the lateglacial and or holocene glacial advances were more extensive than their predecessors and hence destroyed or buried evidence for earlier glaciation or that other processes such as intensive fluvial erosion and or hillslope mass movements have destroyed evidence of earlier glaciation prominent laterofrontal moraines date to the lateglacial the early holocene and the neoglaciation moraines next to the active ice and boulders on contemporary glaciers date to 10 1 10 2 years before present this suggests only a minor glacial advance during the little ice age occurred in central garhwal these young ages indicate that inheritance of tcns in areas that were recently glaciated is very small and likely has little effect when considering tcn ages on moraines older than the global last glacial maximum the new 10 be ages are combined with 1081 recalculated 10 be ages from previous studies to develop a regional framework of glaciation across the monsoon influenced and adjacent regions of the himalayan tibetan orogen we separate what appears to be continuous glaciation into 27 regional glacial stages plus 2 tentative glacial stages that are termed monsoonal himalayan tibetan stages mohits the regional glacial stages cover a wide chronologic range that includes five regional glacial stages older than the last glacial cycle mohits 13 at 483 38 ka to mohits 5e at 122 15 ka thirteen regional glacial stages within the last glacial cycle mohits 5b at 91 15 ka to mohits 2a at 12 9 0 9 ka and eleven regional glacial stages during the holocene mohits 1k at 11 4 0 7 ka to mohits 1a at 0 4 0 1 ka there are strong correlations both with periods of strong monsoons and northern hemisphere events throughout the entire chronologic range with 16 stages linked to the monsoon 11 stages linked to the mid latitude westerlies and two unassigned because of large age uncertainties overall we see a complex pattern of glaciation influenced by two climatic systems throughout the mid late quaternary