improved schmidt hammer exposure ages for active and relict pronival ramparts in southern norway and their palaeoenvironmental implications abstract eight pronival protalus ramparts from alpine southern norway were dated using schmidt hammer exposure age dating shd based on local high precision linear calibration equations shd ages were 1355 1240 to 815 1000 years for three active ramparts and 8730 1050 to 14 635 1060 years for five relict ramparts different parts of the same rampart yielded ages that were in generally good agreement r value frequency distributions enabled the identification single age and mixed age boulder populations and the differentiation of active and relict rampart surfaces the relict ramparts are located outside younger dryas glacier limits and probably formed over a period of 6000 years between deglaciation following the last glacial maximum of the late weichselian 18 000 years ago and the end of the younger dryas 11 700 years ago at that time glacial debuttressing and permafrost degradation apparently enhanced the release of rock debris from rock faces to the ramparts the active ramparts which are located in areas deglaciated after the younger dryas are relatively uncommon in the study area due to diminished paraglacial effects and limited debris supply associated with seasonally frozen ground during the holocene thus the legacy of glaciers glacier permafrost interaction and the specific type of periglacial environment must all be considered when assessing the palaeoenvironmental and palaeoclimatic significance of pronival ramparts

sensitivity persistence and resolution of the geomorphological record of valley floor floods in an alpine glacier fed catchment leirdalen jotunheimen southern norway coarse grained flood deposits including 52 discrete berms bars terraces splays and sheets were investigated along a 6 6 km stretch of the leira river in a catchment containing several alpine glaciers these landforms were mapped characterized in terms of clast size and reconstructed hydrological parameters and dated using several techniques with differing temporal range and resolution high resolution lichenometric dating indicated that 60 65 of the deposits date from the 20th century whereas 5 7 are 300 600 years old in contrast low resolution schmidt hammer exposure age dating shd indicated that 85 of deposits have an age 500 years whereas 13 5 are older deposits with age estimates of 1000 6000 years simple indicators of soil development and vegetation succession demonstrated extensive recent disturbance of most surfaces by floods optically stimulated luminescence osl and radiocarbon dating of fine grained flood layers and buried palaeosols confirmed the existence of flood deposits

schmidt hammer exposure age dating shd of snow avalanche impact ramparts in southern norway approaches results and implications for landform age dynamics and development schmidt hammer exposure age dating shd was applied to the problem of dating the diachronous surfaces of five distal river bank boulder ramparts deposited by snow avalanches plunging into the jostedola and sprongdola rivers in the jostedalsbreen region of southern norway approaches to local high precision linear age calibration which controlled in different ways for boulder roundness were developed the mean age shdmean and the maximum age shdmax of surface boulders were estimated for whole ramparts crests and distal fringes interpretation was further assisted by reference to r value distributions shdmean ages with 95 confidence intervals ranged from 520 270 years to 5375 965 years whereas shdmax ages expected to be exceeded by 5 of surface boulders ranged from 675 to 9065 years shd ages from the jostedola ramparts tended to be older than those associated with the sprongdola rampart crests were younger than the respective distal fringes and use of relatively rounded boulders yielded more consistent shd ages than angular boulders the shdmean ages indicate differences in recent levels of snow avalanche activity between ramparts and provide insights into rampart dynamics as boulders are deposited on rampart crests and in smaller numbers on the distal fringes shdmax ages provide minimum age estimates of rampart age i e the time elapsed since the ramparts began to form and suggest that at least some of the ramparts have been developing since the early holocene copyright 2015 john wiley sons ltd

marine geophysical evidence for late pleistocene ice sheet extent and recession off northwest ireland abstract multibeam swath bathymetry data collected through the irish national seabed survey provides direct evidence for extensive glaciation of the continental shelf off northwest ireland streamlined subglacial bedforms on the inner shelf record former offshore directed ice flow the major glacial features however consist of well developed nested arcuate moraines which mark the position of former ice sheet margins on the shelf distal to these moraines on the outermost shelf prominent zones of iceberg ploughmarks give way into a well developed system of gullies and canyons which incise the continental slope the large scale nested arcuate moraines record the episodic retreat probably punctuated by minor readvances or oscillations of a lobate grounded ice sheet across this sector of the continental shelf during deglaciation initial retreat from the outer shelf was associated with an episode of ice sheet break up and calving as recorded by extensive zones of iceberg ploughmarks distal to the outermost moraine it is conceivable that this initial phase of retreat could have been driven by rising sea level the data indicate a major reorganisation of the irish ice sheet on the northwest shelf during deglaciation an initial elongate ice sheet configuration extending along the shelf edge changed to a pronounced lobate form during retreat consideration of dated marine stratigraphic records from the wider northwest margin suggests that ice sheet advance to the shelf edge likely occurred at about 29 27 cal ka bp but that retreat from this shelf edge position did not take place until after 24 cal ka bp large scale contrasts in continental margin morphology west of ireland from trough mouth fans in the north to gully canyon systems further to south reflects a combination of factors including spatial variations in sediment flux related to palaeo glaciology

rates of holocene chemical weathering little ice age glacial erosion and implications for schmidt hammer dating at a glacier foreland boundary fabergstolsbreen southern norway average rates of holocene chemical weathering and little ice age glacial erosion of bedrock are estimated across the glacier foreland boundary of an outlet glacier of the jostedalsbreen ice cap southern norway estimates are derived from two types of evidence 1 the heights of quartz veins above adjacent surfaces of granitic or granodioritic gneiss and 2 schmidt hammer r values of rock hardness average and maximum rates of surface lowering of gneiss surfaces by chemical weathering are 1 63 and 3 61 mm ka respectively whereas many quartz veins exhibit negligible weathering after c 9700 years little ice age glacial erosion rates are at least two orders of magnitude greater than the chemical weathering rates except in a narrow marginal zone inside but close to the little ice age limit where patches of weathered surface survive bedrock surfaces outside and well inside the little ice age glacier foreland boundary are shown to have potential for improved calibrated age dating using r val

rock control on microweathering of bedrock surfaces in a periglacial environment abstract microweathering of ice smoothed bedrock surfaces was investigated in the roldal area of hardanger plateau 60 southern norway postglacial rates of weathering were determined from surface lowering using quartz veins as reference surfaces weathering processes are inferred from assessment of weathering rind formation surface hardness and the preservation of small scale glacial erosional features surface lowering rates for a range of metamorphic rocks vary from 0 05 to 2 20 mm ka 1 and are broadly comparable with those obtained from crystalline rocks in other periglacial environments the mean rate of surface lowering at 0 55 mm ka 1 is low and demonstrates the relatively small impact of microweathering on postglacial landscape evolution variations in bedrock microweathering can be explained by lithological variation amphibolite and mica rich bedrock surfaces experience greater denudation and weakening least weathering rind formation and abundant preservation of glacial striae despite greater surface lowering conversely quartz rich bedrock surfaces are most resistant to denudation and weakening but have greater weathering rind formation and fewer preserved striae postglacial microweathering is achieved primarily through granular disintegration involving detachment and removal of mineral grains and weakening from increased porosity granular decomposition is manifest in the formation of weathering rinds analysis of interactions between weathering indices indicates that rind accumulation is limited by microerosion a conceptual model is proposed that illustrates the temporal interrelationships between in situ and erosional facets of microweathering in two contrasting mineral assemblages the model proposes that cyclic processes of in situ disintegration decomposition and erosion are at work the relative balance between these processes varies with lithology so that in more resistant quartz rich rocks the net effect is minimal surface lowering and accumulation of weathering rind in weaker amphibolitic and micaceous rocks the net effect is greater surface lowering and minimal accumulation of weathering rind the results of the research demonstrate the important influence of rock properties notably mineral composition in postglacial microweathering of crystalline bedrock in a periglacial environment

the donegal ice dome northwest ireland dimensions and chronology geomorphological evidence indicates that donegal was formerly occupied by an ice dome that extended offshore to the west northwest and north and was confluent with adjacent ice masses to the east and south erosive warm based ice over rode almost all the highest mountains implying an ice divide altitude greater than 700 m only six peripheral summits escaped glacial modification implying either that they remained above the ice surface as nunataks or supported a thin cover of protective cold based ice gibbsite a pre last glacial weathering product is preferentially represented on summits that escaped glacial modification cosmogenic 10be exposure ages of 18 6 1 4 to 15 9 1 0 k yr for coastal sites confirm that donegal ice extended offshore at the last glacial maximum reconstruction of the form of the donegal ice dome suggests a former minimum ice thickness of 500 m close to the present coastline in the west and northwest and 400 m near the coast of the inishowen peninsula in the north with the ice extending at least 20 km across the adjacent shelf to the west and northwest copyright 2007 john wiley sons ltd

lateglacial rock slope failures in north west ireland age causes and implications nine postglacial quartzite rock slope failures rsfs in north west ireland were dated using cosmogenic 10be weighted mean rsf ages range from 17 7 0 9 to 12 5 0 7 ka or 16 6 0 7 to 11 7 0 5 ka depending on assumed 10be production rate all dated rsfs occurred within 5000 years following ice sheet deglaciation at 17 4ka 16 3 ka and all but two occurred within 2000 years after deglaciation the timing of rsfs rules out glacial debuttressing permafrost degradation and enhanced deglacial cleft water pressures as triggers of failure in most cases we infer that paraglacial stress release and associated fracture propagation were critical in reducing rock masses to critical stability although earthquakes caused by lateglacial glacio isostatic rebound and or release of stored tectonic stresses may have triggered failure in some or all cases in conjunction with data from related studies our results imply that most undated rsfs outside the limit of younger dryas glaciation in the british isles are of lateglacial age and that numerous lateglacial rsfs occurred inside these limits with subsequent removal of debris by glaciers they support the view that paraglacial rsf activity in tectonically stable intraplate terrains was concentrated within a few millennia following deglaciation

age assessment and implications of late quaternary periglacial and paraglacial landforms on muckish mountain northwest ireland based on schmidt hammer exposure age dating shd abstract schmidt hammer exposure age dating shd was applied to a variety of late quaternary periglacial and paraglacial landforms composed of coarse rock debris on muckish mountain northwest ireland landform ages were determined using a linear high precision age calibration curve derived from young and old control surfaces of known age on the same rock type the shd ages represent maximum estimates of the time elapsed since the boulders stabilised and the landforms became inactive most ages are also minimum estimates for the start of landform development because older boulders are buried beneath the sampled surface boulders ages and 95 confidence intervals obtained for blockfield boulder lobes and talus indicate these features were likely active during several of the early holocene cold events evidenced in greenland ice cores and north atlantic sediment records activity ceased at different times 9 7 ka bp these landforms are the first indication of a geomorphological response to early holocene cooling in the oceanic mountains of ireland late holocene ages obtained for rock slope failure run out debris and debris cone boulders overlap with shifts to cooler and or wetter conditions including the little ice age geomorphological impacts associated with these changes in climate have not previously been recorded in the irish uplands the shd results indicate that previously implied timings for the stabilisation of some accumulations of coarse rock debris on mountain slopes are in need of revision

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

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

lake isotope records of the 8200 year cooling event in western ireland comparison with model simulations the early holocene cooling which occurred around 8200 calendar years before present was a prominent abrupt event around the north atlantic region here we investigate the timing duration magnitude and regional coherence of the event as expressed in carbonate oxygen isotope records from three lakes on northwest europe s atlantic margin in western ireland namely loch avolla loch gealain and lough corrib an abrupt negative oxygen isotope excursion lasted about 200 years comparison of records from three sites suggests that the excursion was primarily the result of a reduction of the oxygen isotope values of precipitation which was likely caused by lowered air temperatures possibly coupled with a change in atmospheric circulation comparison of records from two of the lakes loch avolla and loch gealain which have differing bathymetries further suggests a reduction in evaporative loss of lake water during the cooling episode comparison of climate model experiments with lake sediment isotope data indicates that effective moisture may have increased along this part of the northeast atlantic seaboard during the 8200 year climatic event as lower evaporation compensated for reduced precipitation

glacial survival of blockfields on the varanger peninsula northern norway for more than hundred years it has been debated whether blockfields in mountain summit areas can be used to delimit the vertical extent of pleistocene ice sheets in this study the relationship between blockfields developed in quartzites and sandstones on the varanger peninsula northern norway and glacially derived features have been evaluated erratics and circular ablation moraines are superimposed on the blockfields and lateral meltwater channels are eroded into them glacial striations and other signs of glacial sculpturing are restricted to low lying areas with channelled ice flow relative ages of the blockfields and the features in them are inferred and the first measurements of in situ produced cosmogenic nuclides from the varanger peninsula are reported we conclude that the blockfields have survived underneath at least one thick cold based ice sheet thus these blockfields cannot be used as indicators of ice free conditions as previously suggested for southern norway our results have implications for the potential for land surface preservation beneath ice sheets and for glacial reconstructions in northern fennoscandia

a regional 8200 cal yr bp cooling event in northwest europe induced by final stages of the laurentide ice sheet deglaciation the most notable change in 18o in greenland ice cores during the holocene occurs at 8200 cal yr bp here we present a new high resolution marine record from the northern north sea along with tree ring data from germany which contain evidence of a pronounced temperature drop 2 c contemporaneous with that of the greenland ice core records the synchronous timing of the cooling event in the greenland ice cores marine record and tree ring data from northwest europe reflects a regional influence on the north atlantic ocean atmospheric system suggesting a prominent role of the north atlantic thermohaline circulation the operation of the north atlantic ocean circulation is sensitive to variation in the freshwater budget implying that any change in freshwater flux is capable of altering the north atlantic circulation system we hypothesise minor but long term freshwater fluxes in the final stages of the deglaciation of the laurentide ice sheet as a forcing mechanism 1998 john wiley sons ltd

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

determining the sun s influence on lateglacial and holocene climates a focus on climate response to centennial scale solar forcing at 2800 cal bp abstract the influence of solar variability on the climate of the lateglacial and holocene periods has been the subject of increasing discussion during the last decade in the mid holocene several studies have identified cold wet events that occur at ca 2800 cal bp and a link with a reduction in solar activity inferred from the 14c record has been postulated we present results from a multi proxy study of peat humification plant macrofossils and testate amoebae from a raised bog at glen west northwest ireland that indicate that dry bog surface conditions were experienced in the north of ireland at the time of the solar anomaly starting at 2800 cal bp with the aid of 14c wiggle matching and tephrochronology an abrupt shift to wetter conditions is dated to ca 2700 cal bp coinciding with a 14c maximum but clearly post dating the 2800 cal bp event identified elsewhere in europe we explore the significance of this apparent lag in the irish record considering the possible role of the ocean in generating spatial and temporal complexities in the climate patterns of the north atlantic region we conclude that these complexities are likely to give rise to time transgressive climate responses around the north atlantic that will only be recognised by more critical chronological approaches

assessing the age weathering correspondence of cosmogenic 21ne dated pleistocene surfaces by the schmidt hammer the schmidt hammer sh method is used to quantify the rock weathering degree and has been proposed as a relative dating tool terrestrial cosmogenic nuclide tcn methods provide absolute exposure ages for erosive surfaces few works combine both methods for surfaces older than the holocene we compare data obtained by both methods for c 150 ka bp glacial and fluvial erosive granite surfaces from northwest spain rebound values r have been firstly compared with the rock density to assess the correlation with the rock strength independently from influence of factors such as wetness and roughness in the r values for erosive glacial surfaces older than 100 ka r values are confined in a narrow range with no differences within errors stepped fluvial surfaces of 700 m to 70 m above present sea level show an inverse correspondence between tcn ages and r values although no age predictions can be done on the basis of the r values thus age inferences exclusively based on r values may not be realistic but sh studies could be a useful tool for selecting surfaces for tcn dating copyright 2009 john wiley sons ltd

relative surface age dating of rock glacier systems near holar in hjaltadalur northern iceland schmidt hammer rebound values and photogrammetric measurements of surface displacement were used to date two active polymorphic high altitude and two relict monomorphic low altitude rock glaciers near holar in hjaltadalur trollaskagi peninsula northern iceland 65 40 n 19 00 w both low altitude rock glaciers are of late weichselian or preboreal origin ca 10 3 9 2 k yr bp with minor later reshaping until the early neoglacial period vatnsdalur i ca 5 2 k yr bp both high altitude rock glaciers consist of an upper lobe overriding a lower lobe corresponding to initiation during different cool phases the initiation of the lower lobes can possibly be attributed to the gh 8 2 event 8 6 8 0 k cal yr bp they reached their terminal position at the end of the vatnsdalur i stage the upper lobes of the high altitude rock glaciers were initiated sometimes between the vatnsdalur i but substantially before the vatnsdalur ii ca 3 0 3 2 k yr bp stages and underwent modification during each following holocene glacier expansion episode culminating the last time in the little ice age thus it is suggested that similar looking rock glaciers occurring elsewhere in the trollaskagi peninsula may have a similar complex history therefore they may not be seen as rather simple landforms developed during the little ice age copyright 2007 john wiley sons ltd

clast size variations on talus some observations from northwest ireland clast size variations are reported for a relict talus slope in northwest ireland alternating longitudinal zones of coarse debris below buttresses and less coarse debris below gullies give the talus pronounced lateral variations in clast size that are related to joint spacing variations in the talus source area longitudinal variations in clast size are also present the talus accumulated predominantly by the process of rockfall other processes frequently associated with lateral size variations were not significantly effective during talus development talus sliding may have modified some patterns of rockfall size grading

trimlines blockfields mountain top erratics and the vertical dimensions of the last british irish ice sheet in nw scotland periglacial trimlines separating glacially eroded lower slopes from blockfield covered plateaus on british and irish mountains have been interpreted either 1 in terms of representing the maximum altitude of the last ice sheet during the last glacial maximum lgm or 2 as a thermal boundary separating wet based ice at pressure melting point from cold based ice on summit plateaus we test these competing hypotheses through 10be exposure dating of high level erratic boulders above trimlines on five mountains in nw scotland nine out of 14 erratics yielded post lgm exposure ages ranging from 14 0 0 7 ka to 16 5 0 9 ka or from 14 9 0 9 ka to 17 6 1 1 ka depending on the 10be production rate employed in exposure age calculation these ages refute hypothesis 1 as they imply that the last ice sheet overtopped the mountains preservation of apparently intact blockfields on the summits implies cold based ice cover supporting hypothesis 2 as altitudinally consistent high level trimlines extend from our sampled sites across much of nw scotland and the hebrides our conclusions apply to all trimlines in this broader area and probably to all high level trimlines elsewhere in the british isles preservation of blockfields under cold based ice is consistent with blockfield evolution on plateaus throughout much or all of the quaternary averaged exposure ages of 15 16 ka for plateau top erratics implies nunatak emergence from the downwasting ice sheet prior to a regional readvance of the ice margin the wester ross readvance and before rapid warming at 14 7 ka at the onset of the lateglacial interstade but after the timing of ice sheet thinning as retrodicted by recent proxy climate driven thermo mechanical coupled models our findings provide an additional constraint on the future development of such models by implying that high level trimlines represent the altitude of a former transition zone between ice at pressure melting point and ice below pressure melting point

determination of the internal structure of alpine talus deposits using different geophysical methods lechtaler alps austria abstract the total thickness and structure of alpine talus accumulations were investigated in a study area in the northern alps using ground penetrating radar gpr completed by 2d geoelectric ert and seismic refraction soundings the loose steep talus cones of the parzinn cirque are situated at an elevation of 2100 2300 m a s l and end downslope at late glacial protalus ramparts the surrounding rockwalls consist of hauptdolomit a brittle dolostone in most of the gpr profiles the bedrock surface was clearly recognizable from the radargrams total talus thicknesses of up to 45 m were estimated the uppermost talus layer is characterized by surface parallel radar reflection patterns intermediate resistivities 4 10 k m and low seismic velocities 400 500 m s these deposits are interpreted as stratified debris built up during the holocene by rockfall deposits occasionally resorted by debris flows below this unit a zone of more irregular radar reflection patterns and enhanced electrical resistivities follows the combined results lead to the assumption of very coarse grained paraglacial rockfall deposits or to a core of basal moraine beneath the talus some zones of especially high resistivity 25 k m may be related to sporadic permafrost occurrence in the depressions between the talus and the moraine ridges striped radar structures are also recognizable in the moraine bodies the stratified sediments give evidence for glaciofluvial transport or debris flows as an agent of protalus rampart formation however these features probably result from a combination of different processes including periglacial creep gpr turned out to be a powerful tool for the determination of debris volumes and internal structures however supporting geoelectric and seismic investigations are advisable to validate the results and to facilitate and improve the interpretation the results point to an average holocene rockwall retreat of 500 to 800 mm ka which is roughly three times higher than recent backweathering rates

garnet bearing ultramafic rocks from the erzgebirge and their relation to other settings in the bohemian massif garnet bearing ultramafic rocks gbu enclosed in high grade gneisses are known from several parts of the bohemian massif one of these is the high pressure hp unit 1 in the erzgebirge crystalline complex which is the subject of the present study hitherto two different models have been put forward to explain the stabilisation of garnet in mantle derived ultramafic rocks from the bohemian massif and their emplacement into the crust 1 garnetiferous assemblages were formed in the ultramafics before they came in contact with their crustal host rocks 2 garnet was formed in the ultramafics at the expense of spinel due to cooling caused by their tectonic emplacement in the crust the pt evolution revealed by the investigated gbu from the erzgebirge crystalline complex however requires a third model the reconstruction of the pt paths for the erzgebirge gbu is based on both conventional thermobarometry and phase relations thermodynamic calculations allowed the construction of a pt phase diagram for the system na2o cao mgo al2o3 sio2 h2o which is the first quantitative petrogenetic grid in this model system relevant to ultramafic hp rocks the grid shows the uni di and tri variant assemblages stable in peridotitic rocks at different pt conditions providing a tool to constrain pt paths from the succession of mineral assemblages observed in a rock the pt path obtained for the erzgebirge gbu suggests that the garnet bearing assemblages formed by hp metamorphism of spinel peridotite which was emplaced into the crust prior to or during the hp compressional stage this model is supported by peak pt conditions around 900 c and 30 35 kbar recorded by the ultramafic rocks which are very similar to those attained in the eclogites sensu stricto which occur in the same tectonic unit hp unit 1 and for which an in situ metamorphism has been inferred schmadicke et al 1992 on the other hand the other two high pressure units in the erzgebirge hp units 2 and 3 which also contain eclogites sensu stricto but lack peridotites record lower peak pt conditions of 650 750 c 24 26 kbar and 600 650 c 20 24 kbar respectively postulating an in situ hp metamorphism for the garnet peridotites as result of continental collision during the variscan orogeny a crustal thickness of 90 110 km would be required a comparison of the distribution of eclogites sensu stricto and mantle derived rocks from the bohemian massif together with their reported pt conditions reveals a correlation between peak pt conditions in eclogites sensu stricto and the prevailing assemblages in the ultramafic rocks in the same unit furthermore the erzgebirge crystalline complex and the snieznik complex on one hand as well as the granulitgebirge and the sowie gory on the other hand are thought to be genetically linked the garnet peridotites from the granulitgebirge the sowie gory and the gfohl unit seem to have experienced peak pt conditions not recorded by their country rocks with non eclogitic basic interlayers inferring a formation of hp assemblages in the ultramafics prior to their emplacement into the crust

boulder dynamics on an atlantic facing rock coastline northwest ireland abstract the rock coast of northwest ireland comprises steep cliffed headlands and more open coastal sections where bedrock shore platforms are developed many shore platforms are overlain by boulders the locations on the platform from which boulders are derived are marked by holes of fresh and unweathered rock surfaces that are not or are poorly covered by lichen these areas of boulder detachment are termed sockets this paper examines the mapped distributions and physical properties of boulders sockets and shore platform context of an atlantic facing granite shore in county donegal northwest ireland results from schmidt hammer rebound tests show statistically significant differences in rebound values between areas inside and outside of sockets and between sockets and boulders based on their distributions and physical properties relationships between sockets and boulders are explored we calculate that sockets are formed rapidly by winter storms but are also rapidly weathered over c 5 years becoming indistinguishable from the surrounding bedrock platform we argue that in contrast to some studies boulders here were formed during recent winter storms episodically during the last 150 200 years rather than by more ancient waves or by tsunamis however a significant proportion of boulders c 20 are morphometrically dissimilar to sockets we argue that these were formed by infrequent and unusually powerful waves that stripped whole bedrock sheets off the platform surface and which detached boulders from the lower shoreface

a 3400 year lacustrine paleoseismic record from the north anatolian fault turkey implications for bimodal recurrence behavior high resolution physical geochemical and geochronological analyses on the sedimentary sequence of yenicaga lake located in a fault bounded basin along the north anatolian fault reveal fingerprints of paleoearthquakes a robust sediment chronology spanning the last 3400 years is constructed by radiocarbon dating and time stratigraphical correlation with the precisely dated sofular cave speleothem record yenicaga sedimentary sequence contains 11 seismically induced event deposits characterized by siliciclastic enriched intervals some of the event deposits are also associated with implications of sudden lake deepening which may be related to coseismic subsidence the paleoearthquake series having an average recurrence interval of ca 260 years are interrupted by two possible seismic gaps of ca 420 and 540 years

multiproxy evidence for terrestrial and aquatic ecosystem responses during the 8 2 ka cold event as recorded at hojby so denmark abstract a sediment succession from hojby so a lake in eastern denmark covering the time period 9400 7400 cal yr bp was studied using high resolution geochemistry magnetic susceptibility pollen macrofossil diatom and algal pigment analysis to investigate responses of the terrestrial and aquatic ecosystems to the 8 2 ka cold event a reduced pollen production by thermophilous deciduous tree taxa in the period c 8250 8000 cal yr bp reveal that the forest ecosystem was affected by low temperatures during the summer and winter early spring seasons this finding is consistent with the timing of the 8 2 ka cold event as registered in the greenland ice cores at hojby so the climate anomaly appears to have started 200 250 yr earlier than the 8 2 ka cold event as the lake proxy data provide strong evidence for a precipitation induced distinct increase in catchment soil erosion beginning around 8500 cal yr bp alteration of the terrestrial environment then resulted in a major aquatic ecosystem change with nutrient enrichment of the lake and enhanced productivity which lasted until c 7900 cal yr bp

a comparison of the lichenometric and schmidt hammer dating techniques based on data from the proglacial areas of some icelandic glaciers abstract measurements of rhizocarpon section and schmidt hammer r values are reported from the proglacial geomorphic features on the forelands of the icelandic glaciers of kviarjokull holarjokull and heinabergsjokull oraefi and south vatnajokull sandfellsjokull and oldufellsjokull east m rdalsjokull and bruarjokull eyjabakkajokull and west snaefell north vatnajokull these data are used in reconstructions of patterns of glacier recession since the little ice age maximum and the geomorphic signals of climatic versus non climatic events are discussed age control was obtained from various dated substrates by utilizing historical accounts aerial photographs and grave stones three lichen growth rates are calculated a 0 51 mm a 1 corrected to 0 50 mm a 1 with a colonization lag time of

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

comparison of electronic and mechanical schmidt hammers in the context of exposure age dating are q and r values interconvertible application of schmidt hammer exposure age dating shd to landforms has substantially increased in recent years the original mechanical schmidt hammer records r rebound values although the newly introduced electronic schmidt hammer silverschmidt facilitates greatly improved data processing it measures surface hardness differently recording q velocity values that are not a priori interconvertible with r values this study is the first to compare the performance of both instruments in the context of field based exposure age dating with a particular focus on the interconvertibility of r values and q values the study was conducted on glacially polished pyroxene granulite gneiss jotunheimen southern norway results indicate that mean q values are consistently 8 10 units higher than mean r values over the range of values normally encountered in the application of shd to glacial and periglacial landforms a convenient conversion factor of 10 units may therefore be appropriate for all but the softest rock types close to the technical resolution of the instruments the electronic schmidt hammer should therefore be regarded as a useful complement and potential replacement for the mechanical schmidt hammer conversion of published r values data to q values requires however careful control and documentation of instrument calibration copyright 2014 john wiley sons ltd

large rock slope failures in the highlands of scotland characterisation causes and spatial distribution abstract a comprehensive database of larger rock slope failures rsfs has been compiled and characterised for a whole mountain range possibly for the first time apart from iceland most rsfs in the scottish highlands occurred soon after deglaciation a threshold size of 0 25 km 2 focuses on rsfs which contribute significantly to gross erosion in the glacial paraglacial cycle and on the spatial concentration of this poorly recognised process database verification indicates that at least 90 of the total extant population in the highlands is covered standard mass movement typologies are broadly applicable but require some refinement to characterise rsfs in a passive margin glaciated mountain range comprised mainly of ancient metasediments most larger rsfs here are complex and difficult to categorise a continuum from cataclasmic failures including rock avalanches through arrested translational slides to almost in situ slope deformations is identified the prevailing modes of large rsf are arrested short travel translational sliding and gravitational sagging cataclasmic failure is rare and sub cataclasmic outcomes are more evident a significant class of deformations exhibits compressional rather than extensional features and may be responding to localised glacio isostatic rebound stresses the large rsf population is widely but very unevenly distributed across the main mountain areas 65 are in seven main clusters with the rest non randomly scattered previous glaciological lithological and seismotectonic explanations are insufficient to explain this spatial pattern and overlook the basic engineering geology prerequisites for failure massifs of similar relief and lithology can display intense or sparse rsf incidence geomorphological appraisal suggests an association with recently active glacial breaches of main and secondary watersheds with rsf being scarce or absent in valleys inherited from tertiary uplift and in mountain groups away from the main watersheds valleys which adapted early to ice discharge are seen as stress hardened with their slopes unlikely to reach critical thresholds for failure after subsequent reoccupations by ice concentrated erosion in the last glaciations is most likely to be found close to where breaches are actively forming or enlarging such erosion in the slope foot and valley floor may have daylighted failure planes or generated rebound stresses augmenting those from other endemic sources sufficiently to provoke widespread paraglacial rsf slope stress models for deglaciated valleys and comparative studies in other glaciated mountain ranges are required to test this concept and may assist in geohazard assessments