paraglacial rock slope stability glaciation and deglaciation along with their associated climatic and non climatic processes modify slope stresses and influence slope stability paraglacial slope failures are those that are a part of or influenced by the transition from glacial conditions to non glacial conditions gravitational failure of rock slopes is a primary and dominant process of slope evolution in mountainous terrain and is the subject of this paper which 1 reviews the approaches taken for researching paraglacial rock slope failure patterns and processes 2 summarises the spatial and temporal patterns of post glacial failures 3 assesses the factors influencing slope stability during glaciation and deglaciation 4 explores some of the applications of paraglacial research and 5 highlights some of the outstanding issues to be resolved and provides recommendations for terminology relating to paraglacial slope processes

a theoretical model coupling chemical weathering and physical erosion in landslide dominated landscapes a current theory that links the uplift of the himalayas to the drawdown of atmospheric co2 assumes that rates of chemical weathering are enhanced by accelerated physical erosion due to the increased exposure of fresh minerals although several studies have concluded that weathering rates do increase with erosion rates there is disagreement over the form of that relationship some find a linear relationship between weathering rate and erosion rate others however find that weathering is only approximately proportional to the square root of physical erosion such that changes in erosion rate are not matched by equivalent changes in weathering rate defining the nature of the relationship is critical because it determines the sensitivity of changes in weathering rate to changes in erosion rate in this study a theoretical model that couples erosion by landslides with chemical weathering processes was derived to explore the nature of this relationship in rapidly eroding landscapes results from the model suggest that where landsliding is the dominant erosional process the rate of chemical weathering is only proportional to the erosion rate raised to the 0 6 power therefore even if weathering rate is wholly dependent on erosion rate increases in erosion will not be matched by equivalent increases in chemical weathering 2007 elsevier b v all rights reserved

weathering rates of sandstone in a semi arid environment hunter valley australia the rate of sandstone weathering in the semi arid climate of the hunter valley new south wales australia has been estimated from observations of gravestone weathering in the area the gravestone data points to two distinct stages in the weathering process the first stage covering the first century of exposure is characterised by a relatively low recession rate of 0 5 mm 100 years this is followed by a second stage in which the rate of weathering increases sharply to ca 2 5 mm 100 years the non linear nature of the weathering trends over time suggests that during the first century of exposure structural changes took place within the sandstone material which lay the foundation for accelerated weathering after further exposure laboratory trials were also conducted to identify the effectiveness of different weathering processes in the decay of sandstone in this region of the four processes examined only the freeze thaw cycle produced a significant degree of mass loss and is therefore most likely a strong contributor to the weathering of sandstone in this region

marine and subaerial controls of coastal chalk cliff erosion in normandy france based on a 7 year laser scanner monitoring abstract between october 2010 and november 2017 surveys using terrestrial laser scanning tls were carried out every 4 5 months to monitor erosion on three chalk cliff faces with close structural characteristics in normandy the two dieppe sites are abandoned cliffs while the varengeville sur mer site is an active one the uniqueness of this paper is the comparison between these cliff sections and the significance of marine and or subaerial controls in erosion beyond the quantification of annual retreat rates which on the active cliff are currently 36 times greater than on the abandoned cliffs this paper highlights the fundamental efficacy of marine controls in the current cliff erosion and the removal of falls analyses of modalities of retreat and profile evolution according to a naturalistic approach subaerial processes appear to have a less erosive action than marine ones because the studied abandoned cliffs show low erosion dynamics and have maintained a subvertical profile despite continentalization for between 30 to more than 120 years

comparison of darcian flux calculations and seepage meter measurements in a sandy streambed in north carolina united states 1 we compared two methods for estimating groundwater flux into a stream reach seepage meters and darcian flux calculations both methods were applied at the same 53 points on the streambed of a 62 5 m long reach of west bear creek in the coastal plain of north carolina at each point a seepage meter was used to measure groundwater flux vmeter and several minutes later the streambed hydraulic conductivity k and hydraulic head gradient j were measured we compared the 53 paired point values of groundwater flux from each method vmeter and vdarcy kj the integrated volumetric groundwater flux to the stream reach from each method qdarcy and qmeter and the spatial distributions of vdarcy and vmeter on the streambed values of qmeter 268 m3 d and mean vmeter 0 66 m d were each about 0 70 the corresponding darcian flux quantities qdarcy 375 m3 d and mean vdarcy 0 92 m d despite their differences the two methods gave the same direction of groundwater flow into the stream at all 53 points a result not found in all previous comparison studies and thus not to be taken for granted also vdarcy and vmeter had similar spatial distributions on the streambed the ratio vmeter vdarcy 0 70 is within the range of 0 3 7 from previous studies and is closer to 1 than in previous studies the differences between the two methods are probably in part due to random measurement error and to the spatial scales for the darcy and seepage meter measurements being of a slightly different size and offset several centimeters from each other on the heterogeneous streambed but these effects are unlikely to produce the observed consistent bias the mean bias between the methods ratio of 0 70 may be related to gas bubbles in the streambed pore spaces e g collection of gas bubbles in the seepage meters lowering vmeter and loss of gas from the streambed upon seepage meter removal or permeameter insertion increasing the subsequent vdarcy measurement

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

on the record reduction in 1998 western arctic sea ice cover during summer 1998 record reductions in ice cover occurred in the beaufort and chukchi seas open water formed earlier than in prior years and september ice extent in this region was 25 percent less than the previous minimum for 1953 1997 seven percent of the arctic basin that had been perennially ice covered was ice free in 1998 this reduction in western arctic ice extent can be attributed in part to preconditioning by light ice cover in autumn 1997 and to atmospheric circulation patterns during the following winter through autumn that favored southerly and easterly winds such decreases in northerly winds and the associated weakening or displacement of the beaufort gyre is found to be typical of winters that precede years with below normal ice extent in the western arctic

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

varieties of shallow temperature maximum waters in the western canadian basin of the arctic ocean the properties and spreading pathways of shallow temperature maximum waters stms in the western canadian basin are investigated using ctd and mooring data obtained in 1997 98 as part of the sheba surface heat budget of the arctic ocean drift experiment and available historical data three distinct varieties of stm are recognized on the basis of salinity range 1 surface mixed layer water smlw with s 32 psu these stms carry sufficient heat within the upper layers of the ocean to significantly affect the rates of ice cover and decay for example during the winter of 1997 98 anomalously warm stm 0 c originating from ecsw was observed to spread northwards along the northwind ridge and chukchi plateau where the maximum reduction of the ice covers was subsequently observed in late summer 1998 maslanik et al 1999 regional climate variability and ice cover in the western canadian basin are thus affected not only by anomalous atmospheric circulation patterns but also by the circulation of upper ocean water masses

direct observation of frost wedging in alpine bedrock width and temperature of rock joints were automatically monitored in the japanese alps three years of monitoring on a sandstone rock face shows two seasonal peaks of joint widening in autumn and spring the autumn events are associated with short term freeze thaw cycles and the magnitude of widening reflects the freezing intensity and water availability the short term freezing can produce wedging to a depth of at least 20 cm the spring events follow a rise in the rock surface temperature to 0 c beneath the seasonal snowcover and likely originate from refreezing of meltwater entering the joint some of these events contribute to permanent enlargement of the joint two other joints on nearby rock faces experience only sporadic widening accompanying freeze thaw cycles and insignificant permanent enlargement observations indicate that no single thermal criterion can explain frost weathering the temperature range at which wedging occurs varies with the bedrock conditions water availability and duration of freezing copyright 2001 john wiley sons ltd

impact of the arctic ocean atlantic water layer on siberian shelf hydrography this paper examines the role of the arctic ocean atlantic water aw in modifying the laptev sea shelf bottom hydrography on the basis of historical records from 1932 to 2008 field observations carried out in april may 2008 and 2002 2009 cross slope measurements a climatology of bottom hydrography demonstrates warming that extends offshore from the 30 50 m depth contour bottom layer temperature time series constructed from historical records links the laptev sea outer shelf to the aw boundary current transporting warm and saline water from the north atlantic the aw warming of the mid 1990s and the mid 2000s is consistent with outer shelf bottom temperature variability for april may 2008 we observed on shelf near bottom warm and saline water intrusions up to the 20 m isobath these intrusions are typically about 0 2 c warmer and 1 1 5 practical salinity units saltier than ambient water the 2002 2009 cross slope observations are suggestive for the continental slope upward heat flux from the aw to the overlying low halocline water lhw the lateral on shelf wind driven transport of the lhw then results in the bottom layer thermohaline anomalies recorded over the laptev sea shelf we also found that polynya induced vertical mixing may act as a drainage of the bottom layer permitting a relatively small portion of the aw heat to be directly released to the atmosphere finally we see no significant warming up until now over the laptev sea shelf deeper than 10 15 m in the historical record future climate change however may bring more intrusions of atlantic modified waters with potentially warmer temperature onto the shelf which could have a critical impact on the stability of offshore submarine permafrost

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

thermal fatigue and thermal shock in bedrock an attempt to unravel the geomorphic processes and products widespread acceptance in science at large notwithstanding the ability of thermal stresses to produce thermal fatigue tf and or thermal shock ts in bedrock and coarse debris in the field is often doubted commonly called insolation weathering in geomorphology the results of questionable laboratory experiments have led many geomorphologists to consider terrestrial temperatures to be inadequate to generate thermally induced stresses leading to rock failure the exceptions are the action of fire or lightning we comprehensively survey the general scientific literature on tf and ts while rigorously scrutinizing that relating to geomorphology findings indicate theoretical and experimental information is adequate to establish the feasibility of tf and ts in rock stemming from rock temperatures monitored in the field while ts may exhibit fracture patterns that are uniquely diagnostic those of tf lack any such attributes it would appear unlikely that tf can prepare or weaken rock to increase the likelihood of ts the question of whether widespread polygonal versus rectilinear cracking is diagnostic of ts is presently an open one as possible explanations invoke process es and or host material s and consequently to assign palaeoenvironmental significance to such fracture patterns is premature at this time further geomorphological laboratory research into tf and ts is merited as sufficient theoretical underpinning already exists however laboratory experimentation needs to be much more rigorously defined and executed and is faced with significant hurdles if it is to be effectively linked to field observations

controls on the geotechnical response of sedimentary rocks to weathering weathering reduces the strength of rocks and so is a key control on the stability of rock slopes recent research suggests that the geotechnical response of rocks to weathering varies with ambient stress conditions resulting from overburden loading and or stress concentrations driven by near surface topography in addition the stress history experienced by the rock can influence the degree to which current weathering processes cause rock breakdown to address the combined effect of these potential controls we conducted a set of weathering experiments on two sedimentary lithologies in laboratory and field conditions we firstly defined the baseline geotechnical behaviour of each lithology characterising surface hardness and stress strain behaviour in unconfined compression weathering significantly reduced intact rock strength but this was not evident in measurements of surface hardness the ambient compressive stress applied to samples throughout the experiments did not cause any observable differences in the geotechnical behaviour of the samples we created a stress history effect in sub sets of samples by generating a population of microcracks that could be exploited by weathering processes we also geometrically modified groups of samples to cause near surface stress concentrations that may allow greater weathering efficacy however even these pronounced sample modifications resulted in insignificant changes in geotechnical behaviour when compared to unmodified samples the observed reduction in rock strength changed the nature of failure of the samples which developed post peak strength and underwent multiple stages of brittle failure although weakened these samples could sustain greater stress and strain following exceedance of peak strength on this basis the multi stage failure style exhibited by weaker weathered rock may permit smaller magnitude higher frequency events to trigger fracture through intact rock bridges as well as influencing the characteristics of pre failure deformation these findings are consistent with patterns of behaviour observed in field monitoring results

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

rockfall activity from an alpine cliff during thawing periods abstract rockfall activity during thawing periods was investigated by collecting rockfall debris fallen on the snow covered talus slope in a cirque in the japanese alps near surface rock temperature was also monitored on the cirque wall maximum rockfall activity occurs on average about 10 days after the meltout of the cirque wall the intensive activity is rarely associated with precipitation events or diurnal frost cycles on the rockface a thermal conduction model suggests that rockfalls at this site occur most frequently when the seasonal thawing front penetrates to a depth of about 1 m in the bedrock while the freeze thaw penetration controls the maximum dimensions of detachable rock mass joint spacing on the rockface affects the size distribution of rockfall debris boulder falls resulting from seasonal frost weathering are considered to be the most important process responsible for the contemporary modification of the cirque wall the rockfall volume during a thawing period is usually 1 3 m3 which is equivalent to the rate of cirque wall retreat of the order of 0 01 mm year 1 however big boulder falls that occur once per decade can increase the retreat rate significantly

a semi analytical generalized hvorslev formula for estimating riverbed hydraulic conductivity with an open ended standpipe permeameter the well known hvorslev 1951 formula was developed to estimate soil permeability using single well slug tests and has been widely applied to determine riverbed hydraulic conductivity using in situ standpipe permeameter tests here we further develop a general solution of the hvorslev 1951 formula that accounts for flow in a bounded medium and assumes that the bottom of the river is a prescribed head boundary the superposition of real and imaginary disk sources is used to obtain a semi analytical expression of the total hydraulic resistance of the flow in and out of the pipe as a result we obtained a simple semi analytical expression for the resistance which represents a generalization of the hvorslev 1951 the obtained expression is benchmarked against a finite element numerical model of 2 d flow in r z coordinates in an anisotropic medium the results exhibit good agreement between the simulated and estimated riverbed hydraulic conductivity values furthermore a set of simulations for layered stochastically heterogeneous riverbed sediments was conducted and processed using the proposed expression to demonstrate the potential associated with measuring vertical heterogeneity in bottom sediments using a series of standpipe permeameter tests with different lengths of pipe inserted into the riverbed sediments

comparison of vertical hydraulic conductivity in a streambed point bar system of a gaining stream summary vertical hydraulic conductivities k v of both streambed and point bars can influence water and solute exchange between streams and surrounding groundwater systems the sediments in point bars are relatively young compared to the older sediments in the adjacent aquifers but slightly older compared to submerged streambeds thus the permeability in point bar sediments can be different not only from regional aquifer but also from modern streambed however there is a lack of detailed studies that document spatial variability of vertical hydraulic conductivity in point bars of meandering streams in this study the authors proposed an in situ permeameter test method to measure vertical hydraulic conductivity of the two point bars in clear creek nebraska usa we compared the k v values in streambed and adjacent point bars through 45 test locations in the two point bars and 51 test locations in the streambed the k v values in the point bars were lower than those in the streambed kruskal wallis test confirmed that the k v values from the point bars and from the channel came from two statistically different populations within a point bar the k v values were higher along the point bar edges than those from inner point bars grain size analysis indicated that slightly more silt and clay particles existed in sediments from inner point bars compared to that from streambed and from locations near the point bar edges while point bars are the deposits of the adjacent channel the comparison of two groups of k v values suggests that post depositional processes had an effect on the evolution of k v from channel to point bars in fluvial deposits we believed that the transport of fine particles and the gas ebullition in this gaining stream had significant effects on the distribution of k v values in a streambed point bar system with the ageing of deposition in a floodplain the permeability of point bar sediments can likely decrease due to reduced effects of the upward flow and gas ebullition

rockfall rebound comparison of detailed field experiments and alternative modelling approaches the accuracy of rockfall trajectory simulations mainly rests on the calculation of the rebound of fragments following their impact on the slope this paper is dedicated to the comparative analysis of two rebound modelling approaches currently used in rockfall simulation using field experiments of single rebounds the two approaches consist in either modelling the rock as a single material point lumped mass approach or in explicitly accounting for the fragment shape rigid body approach a lumped mass model accounting for the coupling between translational and rotational velocities and introducing a slope perturbation angle was used a rigid body approach modelling the rocks as rigid locally deformable in the vicinity of the contact surface assemblies of spheres was chosen the comparative analysis of the rebound models shows that both of them are efficient with only a few parameters the main limitation of each approach are the calibration of the value of the slope perturbation roughness angle for the lumped mass approach and the estimation of the rock length and height from field geological and historical analyses for the rigid body approach finally both rebound models require being improved in a pragmatic manner to better predict the rotational velocities distribution copyright 2012 john wiley sons ltd

morphometric comparison of weathering features on side by side carbonate rock surfaces with different exposure ages a case from the croatian coast this study presents the comparison of morphometry of karren features developed on two rock surfaces located side by side having different exposure times cosmogenic 36cl analyses were used to determine the age of a rock surface exposed after a rockslide that occurred 2400 years ago whereas the rock surface not affected by the slide was exposed to weathering for a longer time period clint and grikes trittkarren rillenkarren solution pits and kamenitzas were measured comparatively less density of grikes on the surface affected by the slide made it having a fresh appearance most of the grikes were inherited from previous weathering stage and exposure time since the rockslide event has not been sufficient to homogenize these features between both rock surfaces tritkarren and rillenkarren were preferentially found on the rockslide surface indicating that their genesis is likely to occur at decadal to centennial timescale solution pits and kamenitzas were found on both surfaces and some of their size parameters were indistinguishable between the populations of both rock surfaces area and depth parameters of both forms were clearly correlated and we define a morphometric index a d ratio as the slope between these two parameters within each population after an initial stage preferential weathering occurs along the vertical axis in solution pits and laterally in kamenitzas thus we suggest that the a d ratio is related to the evolution relative age of the karren features thus under rock surfaces affected by the same weathering conditions lower a d ratios of solution pits and higher a d ratios of kamenitzas indicate longer time exposed to weathering thus although solution pits and kamenitzas are likely to be developed in decadal to centennial timescales their morphology changes through time at millennial timescale and it can be tracked by morphometric analysis

flow variability at the continental shelf break of the mackenzie shelf in the beaufort sea observations from four yearlong current meter deployments made in 1987 1988 near the shelf break in the canadian beaufort sea are analyzed by statistical and spectral methods to characterize the structure and variability vertical and horizontal of the velocity field and to compare measurements obtained during summer ice free and winter ice covered conditions three main frequency bands are defined low frequencies 0 01 0 07 cpd intermediate or synoptic scale frequencies 0 07 0 7 cpd and high frequencies 0 7 cpd including tides and inertial currents within this division about 65 of the kinetic energy is in the low frequency band 15 in the intermediate band and 20 is in the high frequency band the latter is dominated by tidal motions low frequency variability is well correlated both vertically and horizontally along the shelf for separation distances exceeding 200 km variability in this band appears to be related to wind forcing and topographic wave propagation over large horizontal scales low frequency variability is highest during october and november in association with the occurrence of intense autumn storms and lowest during periods of ice cover due to wind shielding and increased frictional damping by ice cover intermediate scale motions have significant correlation in the vertical but poor correlation in the horizontal motions in this frequency band appear to be associated with mesoscale eddies advected by the mean flow there is also evidence of local generation of intermediate frequency current fluctuations by storms in late autumn and again an apparent damping during winter periods of ice cover finally high frequency motions show significant peaks in diurnal and semidiurnal tidal bands which are well correlated horizontally and vertically however other high frequency motions in this band show no significant correlation in either the vertical or horizontal direction there is no clear evidence in the current meter records of coupling between high frequency motions and direct atmospheric forcing

upwelling in the alaskan beaufort sea atmospheric forcing and local versus non local response abstract the spin up and relaxation of an autumn upwelling event on the beaufort slope is investigated using a combination of oceanic and atmospheric data and numerical models the event occurred in november 2002 and was driven by an aleutian low storm the wind field was strongly influenced by the pack ice distribution resulting in enhanced winds over the open water of the chukchi sea flow distortion due to the brooks mountain range was also evident mooring observations east of barrow canyon show that the beaufort shelfbreak jet reversed to the west under strong easterly winds followed by upwelling of atlantic water onto the shelf after the winds subsided a deep eastward jet of atlantic water developed centered at 250 m depth an idealized numerical model reproduces these results and suggests that the oceanic response to the local winds is modulated by a propagating signal from the western edge of the storm the disparity in wave speeds between the sea surface height signal traveling at the fast barotropic shelf wave speed versus the interior density signal traveling at the slow baroclinic wave speed leads to the deep eastward jet the broad scale response to the storm over the chukchi sea is investigated using a regional numerical model the strong gradient in windspeed at the ice edge results in convergence of the offshore ekman transport leading to the establishment of an anti cyclonic gyre in the northern chukchi sea accordingly the chukchi shelfbreak jet accelerates to the east into the wind during the storm and no upwelling occurs west of barrow canyon hence the storm response is fundamentally different on the beaufort slope upwelling versus the chukchi slope no upwelling the regional numerical model results are supported by additional mooring data in the chukchi sea

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

coastline retreat via progressive failure of rocky coastal cliffs despite much research on the myriad processes that erode rocky coastal cliffs accurately predicting the nature location and timing of coastline retreat remains challenging and is confounded by the apparently episodic nature of cliff failure the dominant drivers of coastal erosion marine and subaerial forcing are anticipated to increase in the future so understanding their present and combined efficacy is fundamental to improving predictions of coastline retreat we captured change using repeat laser scanning across 2 7 104 m2 of near vertical rock cliffs on the uk north sea coast over 7 yr to determine the controls on the rates patterns and mechanisms of erosion for the first time we document that progressive upward propagation of failure dictates the mode and defines the rate at which marine erosion of the toe can accrue retreat of coastline above this is a failure mechanism not conventionally considered in cliff stability models propagation of instability and failure operates at these sites at 10 yr time scales and is moderated by local rock mass strength and the time dependence of rock fracture we suggest that once initiated failure propagation can operate ostensibly independently to external environmental forcing and so may not be tightly coupled to prevailing subaerial and oceanographic conditions our observations apply to coasts of both uniform and complex lithology where failure geometry is defined by rock mass strength and structure and not intact rock strength alone and where retreat occurs via any mode other than full cliff collapse

rock slope instability and erosion toward improved process understanding rock slopes in a range of environments are among the landscape elements most sensitive to climate change the latter affecting rock mass properties altering slope boundary conditions and changing geosystem configurations major climate dependent influences promoting destabilization include stress redistribution with changing glacial ice extents degradation of mountain permafrost altered slope hydrology and weathering environments loading and unloading due to deposition and erosion and changes in the spectrum of magnitude and frequency of driving forces in steep bedrock terrain erosional processes control slope morphology by modulating rates of i weathering in response to climate and pre disposition ii rock slope retreat in response to magnitude and frequency of detachment and iii channel incision or valley infilling in response to variable sediment supply modelling landscape evolution and anticipating natural hazards in these environments thus requires deeper insights into the processes driving rock slope instability and erosion this special issue emphasizes new understanding of rock slope processes through a collection of manuscripts at the forefront of research in the field copyright 2014 john wiley sons ltd

weathering instability and landscape evolution abstract the argument in this paper is that the fundamental control on landscape evolution in erosional landscapes is weathering the possibility of and evidence for instability in weathering at four scales is examined the four scales are concerned with weathering processes allocation of weathered products the interrelations of weathering and denudation and the topographic and isostatic responses to weathering limited denudation the regolith hillslope landscape unit and landscape scales respectively the stability conditions for each model and the circumstances under which the models themselves are relevant are used to identify scale related domains of stability and instability at the regolith scale the interactions among weathering rates resistance and moisture are unstable but there are circumstances over long timescales and where weathering is well advanced under which the instability is irrelevant at the hillslope scale the system is stable when denudation is transport rather than weathering limited and where no renewal of exposure via regolith stripping occurs at the level of landscape units the stability model is based entirely on the mutual reinforcements of weathering and erosion while this should generally lead to instability the model would be stable where other external controls of both weathering and erosion rates are stronger than the weathering erosion feedbacks at the broadest landscape scale the inclusion of isostatic responses destabilizes erosion topography uplift relationships thus if the spatial or temporal scale is such that isostatic responses are not relevant the system may be stable essentially instability is prevalent at local spatial scales at all but the longest timescales stability at intermediate spatial scales is contingent on whether weathering erosion feedbacks are strong or weak with stability being more likely at shorter and less likely at longer timescales at the broadest spatial scales instability is likely although stability may be present at intermediate temporal scales if weathering erosion feedbacks are weak the distinction is important because stability is associated with convergent evolution whereby the effects of initial variations or disturbances are reduced over time as the landscape converges toward a stable equilibrium state instability by contrast indicates divergent evolution increasing differentiation over time and the persistence and growth of disturbance effects and initial variations

a record minimum arctic sea ice extent and area in 2002 1 arctic sea ice extent and area in september 2002 reached their lowest levels recorded since 1978 these conditions likely resulted from 1 anomalous warm southerly winds in spring advecting ice poleward from the siberian coast 2 persistent low pressure and high temperatures over the arctic ocean in summer promoting ice divergence and rapid melt

wind driven shelf basin exchange on an arctic shelf the joint roles of ice cover extent and shelf break bathymetry 1 the efficiency of shelf basin exchange sbe in polar regions during summer is strongly moderated by the location of the ice edge relative to underlying topography numerical model calculations suggest that upwelling favorable winds generate very little sbe so long as the ice edge remains shoreward of the shelf break but an abrupt onset of shelf break upwelling takes place when the ice edge retreats beyond the shelf break a climatology 1968 2000 of ice conditions from the canadian shelf of the beaufort sea shows large interannual variability in ice edge extent and duration of ice free conditions in summer similarly available hydrographic data reflect a corresponding variability in water mass properties under scenarios of climate warming associated with greenhouse gas build up both the extent and duration of summer melt back are predicted to increase and this may have dramatic impacts on sbe and biological productivity

rock fall dynamics and deposition an integrated analysis of the 2009 ahwiyah point rock fall yosemite national park usa we analyzed a combination of airborne and terrestrial lidar high resolution photography seismic and acoustic data in order to gain insights into the initiation dynamics and talus deposition of a complex rock fall a large 46 700 m3 rock fall originated from near ahwiyah point in eastern yosemite valley and fell a total of 730 m to the valley floor on 28 march 2009 analyses of remote sensing seismic and acoustic data were integrated to reconstruct the rock fall which consisted of 1 the triggering of a 25 400 m3 rock block in an area of intersecting and sometimes highly weathered joint planes 2 the sliding and subsequent ballistic trajectory of the block from a steeply dipping ledge 3 dislodging of additional rock from the cliff surface from beneath the rock fall source area 4 a mid cliff ledge impact that detached a volume of rock nearly equivalent in volume to the initial block 5 sliding of the deteriorating rock mass down the remainder of the cliff and 6 final impact at the base of the cliff that remobilized the existing talus downward and outward and produced an airblast that knocked down hundreds of trees the depositional geomorphology indicates that the porosity of the fresh talus is significantly lower than that expected for typical blocky talus slopes likely because the rock debris from this event was pulverized into smaller more poorly sorted fragments and densified via dynamic compaction when compared to less energetic fragmental type rock falls these results suggest that accumulation of individual rock fall boulders tends to steepen talus slopes whereas large energetic rock falls tend to flatten them detachment and impact signals were recorded by seismic and acoustic instruments and highlight the potential use of this type of instrumentation for generalized rock fall monitoring while lidar and photography data were able to quantify the cliff geometry rock fall volume source and impact locations and geomorphological changes to the cliff and talus published in 2012 this article is a us government work and is in the public domain in the usa

interannual variability of arctic landfast ice between 1976 and 2007 abstractanalysis of weekly sea ice charts produced by the u s national ice center from 1976 to 2007 indicates large interannual variations in the averaged winter landfast ice extent around the arctic basin during the 32 yr period of the record landfast ice cover was relatively extensive from the early to mid 1980s but since then has declined in many coastal regions of the arctic particularly after the early 1990s while the barents baltic and bering seas show increases in landfast ice area the overall change for the northern hemisphere is negative about 12 27 2 8 103 km2 yr 1 or 7 1 5 decade 1 relative to the long term mean except in a few coastal regions the seasonal duration of landfast ice is shorter overall particularly in the laptev east siberian and chukchi seas the decreased winter landfast ice extent is associated with some notable changes in ice growth and melt patterns in particular the slowed landfast ice expansion during fall and early winter since 1990 the observed

spatial variability in streambed hydraulic conductivity of contrasting stream morphologies channel bend and straight channel streambed hydraulic conductivity is one of the main factors controlling variability in surface water groundwater interactions but only few studies aim at quantifying its spatial and temporal variability in different stream morphologies streambed horizontal hydraulic conductivities kh were therefore determined from in stream slug tests vertical hydraulic conductivities kv were calculated with in stream permeameter tests and hydraulic heads were measured to obtain vertical head gradients at eight transects each comprising five test locations in a groundwater dominated stream seasonal small scale measurements were taken in december 2011 and august 2012 both in a straight stream channel with homogeneous elevation and downstream of a channel meander with heterogeneous elevation all streambed attributes showed large spatial variability kh values were the highest at the depositional inner bend of the stream whereas high kv values were observed at the erosional outer bend and near the middle of the channel calculated kv values were related to the thickness of the organic streambed sediment layer and also showed higher temporal variability than kh because of sedimentation and scouring processes affecting the upper layers of the streambed test locations at the channel bend showed a more heterogeneous distribution of streambed properties than test locations in the straight channel whereas within the channel bend higher spatial variability in streambed attributes was observed across the stream than along the stream channel copyright 2014 john wiley sons ltd

progressive failure of sheeted rock slopes the 2009 2010 rhombus wall rock falls in yosemite valley california usa progressive rock fall failures in natural rock slopes are common in many environments but often elude detailed quantitative documentation and analysis here we present high resolution photography video and laser scanning data that document spatial and temporal patterns of a 15 month long sequence of at least 14 rock falls from the rhombus wall a sheeted granitic cliff in yosemite valley california the rock fall sequence began on 26 august 2009 with a small failure at the tip of an overhanging rock slab several hours later a series of five rock falls totaling 736 m3 progressed upward along a sheeting joint behind the overhanging slab over the next 3 weeks audible cracking occurred on the rhombus wall suggesting crack propagation while visual monitoring revealed opening of a sheeting joint adjacent to the previous failure surface on 14 september 2009 a 110 m3 slab detached along this sheeting joint additional rock falls between 30 august and 20 november 2010 totaling 187 m3 radiated outward from the initial failure area along cliff sub parallel sheeting joints we suggest that these progressive failures might have been related to stress redistributions accompanying propagation of sheeting joints behind the cliff face mechanical analyses indicate that tensile stresses should occur perpendicular to the cliff face and open sheeting joints and that sheeting joints should propagate parallel to a cliff face from areas of stress concentrations the analyses also account for how sheeting joints can propagate to lengths many times greater than their depths behind cliff faces we posit that as a region of failure spreads across a cliff face stress concentrations along its margin will spread with it promoting further crack propagation and rock falls published in 2012 this article is a us government work and is in the public domain in the usa

on the persistence of weathering abstract the term weathering has been in use for a very long time but it has come to mean different things to different people and hence as scientific short hand it no longer functions here we question the tenets underpinning the most common usage of the term and note that the climate process linkage implicit to the term is often missing and amounts to misdirection rather than climate as the primary driver behind specific weathering processes it is argued that rock properties constitute the dominant control further a case is made for reconsideration of our present bipartite mechanical chemical division of weathering processes and of the weathering processes currently deemed to be those that occur as process studies become evermore reductionist in nature so the functionality of the term comes more and more into question the linkage between process and landform the scaling up attribute is seen as a current weakness and one that will become more confusing as reductionist approaches continue as a way forward it is suggested that weathering stripped of specific preconceived notions of specific processes be envisaged as a function of energy transfer and be investigated in that light identification of new processes as well as restructuring of known processes particularly when considering weathering on other planets is a potential outcome of such an approach with a process foundation rooted in energy transfer rock decay provides a better umbrella term and liberates researchers from the inescapable conceptual baggage implicit to the term weathering

effects of hyporheic processes on streambed vertical hydraulic conductivity in three rivers of nebraska 1 streambed hydraulic conductivity is of great importance in the analysis of stream aquifer interactions and stream ecosystems we investigated streambed vertical hydraulic conductivity kv with two connected depths in three rivers of nebraska our results demonstrated that streambed kv in the upper sediment layer was much higher than that in the sediment of the lower layer we speculate that hyporheic processes can result in larger streambed kv in the upper layer specifically water exchange through upwelling and downwelling zones can lead to bigger pore spaces and a more unconsolidated structure of sediments in the upper layer the upward movement of gas produced by redox processes can loosen the sediments and further enlarge pore spaces in the upper layers also permeability can increase as a result of expanded pore spaces caused by invertebrate activities in the upper part of streambed the higher kv will likely enhance exchange processes between stream and sediments

the interior shelves of the arctic ocean physical oceanographic setting climatology and effects of sea ice retreat on cross shelf exchange abstract the interior shelves of the arctic mediterranean are the shelves of the kara sea laptev sea east siberian sea and beaufort sea they comprise approximately 40 of the total arctic shelf area 2 5 10 6 km 2 and are distinguished from inflow and outflow shelves by their principal forcing dynamics along their southern continental boundary the interior shelves are dominated by the major arctic rivers receiving over 80 of the total freshwater input to the arctic ocean in the mid shelf region wind and ice motion surface stresses dominate mixing and circulation resulting in high variability along their northern seaward boundary they are forced by upwelling and downwelling favourable surface stresses which drive shelf basin exchanges with atlantic and pacific origin cyclonic boundary currents over the upper slope shelf basin exchange is further modified by shelf break morphometry e g canyons valleys headlands and bottom slope here we review the physical oceanographic settings and forcing of the interior shelves and then focus on shelfbreak exchange and supply of nutrients for new primary production due to upwelling across the shelfbreak as a proxy for this nutrient supply we show seasonal and annual time series of along shelfbreak surface stress due to wind and ice motion from 1979 to 2011 we apply this analysis to the shallow shelves from the kara sea to the beaufort sea and comment on recent increases due to atmospheric changes and sea ice retreat

is climate change responsible for changing landslide activity in high mountains climate change manifested by an increase in mean minimum and maximum temperatures and by more intense rainstorms is becoming more evident in many regions an important consequence of these changes may be an increase in landslides in high mountains more research however is necessary to detect changes in landslide magnitude and frequency related to contemporary climate particularly in alpine regions hosting glaciers permafrost and snow these regions not only are sensitive to changes in both temperature and precipitation but are also areas in which landslides are ubiquitous even under a stable climate we analyze a series of catastrophic slope failures that occurred in the mountains of europe the americas and the caucasus since the end of the 1990s we distinguish between rock and ice avalanches debris flows from de glaciated areas and landslides that involve dynamic interactions with glacial and river processes analysis of these events indicates several important controls on slope stability in high mountains including the non linear response of firn and ice to warming three dimensional warming of subsurface bedrock and its relation to site geology de glaciation accompanied by exposure of new sediment and combined short term effects of precipitation and temperature based on several case studies we propose that the following mechanisms can significantly alter landslide magnitude and frequency and thus hazard under warming conditions 1 positive feedbacks acting on mass movement processes that after an initial climatic stimulus may evolve independently of climate change 2 threshold behavior and tipping points in geomorphic systems 3 storage of sediment and ice involving important lag time effects

depth dependent hydraulic conductivity distribution patterns of a streambed characterization of streambed hydraulic conductivity from the channel surface to a great depth below the channel surface can provide needed information for the determination of stream aquifer hydrologic connectedness and it is also important to river restoration however knowledge on the streambed hydraulic conductivity for sediments 1 m below the channel surface is scarce this study describes a method that was used to determine the distribution patterns of streambed hydraulic conductivity for sediments from channel surface to a depth of 15 m below the method includes geoprobe s direct push techniques and permeameter tests direct push techniques were used to generate the electrical conductivity ec logs and to collect sequences of continuous sediment cores from river channels as well as from the alluvial aquifer connected to the river permeameter tests on these sediment cores give the profiles of vertical hydraulic conductivity k v of the channel sediments and the aquifer materials this method was applied to produce k v profiles for a streambed and an alluvial aquifer in the platte river valley of nebraska usa comparison and statistical analysis of the k v profiles from the river channel and from the proximate alluvial aquifer indicates a special pattern of k v in the channel sediments this depth dependent pattern of k v distribution for the channel sediments is considered to be produced by hyporheic processes this k v distribution pattern implied that the effect of hyporheic processes on streambed hydraulic conductivity can reach the sediments about 9 m below the channel surface copyright c 2010 john wiley sons ltd

forensic analysis of rockfall scars abstract we characterise and analyse the detachment scar surfaces of rockfalls to understand the mechanisms that underpin their failure rockfall scars are variously weathered and comprised of both discontinuity release surfaces and surfaces indicative of fracturing through zones of previously intact rock known as rock bridges the presence of rock bridges and pre existing discontinuities is challenging to quantify due to the difficulty in determining discontinuity persistence below the surface of a rock slope rock bridges form an important control in holding blocks onto rockslopes with their frequency extent and location commonly modelled from the surface exposure of daylighting discontinuities we explore an alternative approach to assessing their role by characterising failure scars we analyse a database of multiple rockfall scar surfaces detailing the areal extent shape and location of broken rock bridges and weathered surfaces terrestrial laser scanning and gigapixel imagery were combined to record the detailed texture and surface morphology from this scar surfaces were mapped via automated classification based on rgb pixel values our analysis of the resulting data from scars on the north yorkshire coast uk indicates a wide variation in both weathering and rock bridge properties controlled by lithology and associated rock mass structure importantly the proportion of rock bridges in a rockfall failure surface does not increase with failure size rather larger failures display fracturing through multiple rock bridges and in contrast smaller failures fracture occurs only through a single critical rock bridge this holds implications for how failure mechanisms change with rockfall size and shape additionally the location of rock bridges with respect to the geometry of an incipient rockfall is shown to determine failure mode weathering can occur both along discontinuity surfaces and previously broken rock bridges indicating the sequential stages of progressively detaching rockfall our findings have wider implications for hazard assessment where rock slope stability is dependent on the nature of rock bridges how this is accounted for in slope stability modelling and the implications of rock bridges on long term rock slope evolution

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 mechanism of rockfall disaster a case study from badouzih keelung in northern taiwan abstract on august 31st 2013 high intensity rainfall caused a severe rockfall disaster in badouzih keelung this study combines the results of detailed field investigation and process based as well as empirical based method to point out unsafe road sections the mechanisms and the characteristics of motions of rockfall are analyzed in the field two intersecting joints and the bedding plane divided bedrock into blocks weathering and the infiltration of rainfall accelerated the erosion process and precipitated ruptures when the rainfall reached its highest intensity which is 94 5 mm h in this event a great deal of water on the slope surface eroded the matrix causing instability and leading to the failure of the rock blocks the process of rockfall took 23 s and can be divisible into 4 stages including roll fall bounce and roll process based simulations are adopted in this case and several critical road sections to understand the characteristic of movements with the empirical based energy line angle analysis potential road sections which may affect by rockfall are showed and their energy are also estimated for the purpose of mitigating rockfall impact reducing similar disasters in this area

bedrock fracture by ice segregation in cold regions the volumetric expansion of freezing pore water is widely assumed to be a major cause of rock fracture in cold humid regions data from experiments simulating natural freezing regimes indicate that bedrock fracture results instead from ice segregation fracture depth and timing are also numerically simulated by coupling heat and mass transfer with a fracture model the depth and geometry of fractures match those in arctic permafrost and ice age weathering profiles this agreement supports a conceptual model in which ice segregation in near surface permafrost leads progressively to rock fracture and heave whereas permafrost degradation leads episodically to melt of segregated ice and rock settlement

on the spatiotemporal behavior of sea ice concentration anomalies in the northern hemisphere 1 reduction in the aerial extent and thickness of sea ice in the northern hemisphere is an important element in understanding how the arctic responds to global scale climate variability and change previous studies have demonstrated a significant reduction in minimum sea ice extent serreze et al 2003 with record reduction in 2005 observational studies attribute this phenomenon to variations in sea level pressure and large scale atmospheric teleconnection patterns such as the northern annular mode nam deser et al 2000 serreze et al 2003 in this study we examine variations in sea ice in the context of spatiotemporal variability of sea ice concentration sic anomalies in the northern hemisphere during the onset of ice formation examined in particular are timescales associated with coherent regions of persistence in an e folding time spatial distribution efsd annual variations of weekly sic anomalies are studied and spatial relations between positive and negative sic anomalies are explored on a hemispheric scale the results from this investigation demonstrate coherent sic persistence patterns throughout the northern hemisphere with timescales ranging from 3 to 7 weeks spatial correspondence between negative trends in sic anomalies and the efsd suggests that the same mechanism may be responsible for both increased ice reduction and persistence in this region examination of spatial coherence in sic anomalies indicates that maximum sic anomalies prevail near the kara sea beaufort sea and chukchi sea regions during late summer early fall from 1979 to 2004 a latitudinal assessment at 80 70 and 60 n indicates a poleward shift and retreat in sic anomalies while also underlining the decadal shift in variability often attributed to the nam

regional scale controls on the spatial activity of rockfalls turtmann valley swiss alps a multivariate modeling approach abstract in mountain geosystems rockfalls are among the most effective sediment transfer processes reflected in the regional scale distribution of talus slopes however the understanding of the key controlling factors seems to decrease with increasing spatial scale due to emergent and complex system behavior and not least to recent methodological shortcomings in rockfall modeling research in this study we aim i to develop a new approach to identify major regional scale rockfall controls and ii to quantify the relative importance of these controls using a talus slope inventory in the turtmann valley swiss alps we applied for the first time the decision tree based random forest algorithm rf in combination with a principal component logistic regression pclr to evaluate the spatial distribution of rockfall activity this study presents new insights into the discussion on whether periglacial rockfall events are controlled more by topo climatic cryospheric paraglacial or and rock mechanical properties i both models explain the spatial rockfall pattern very well given the high areas under the receiver operating characteristic roc curves of 0 83 highest accuracy was obtained by the rf correctly predicting 88 of the rockfall source areas the rf appears to have a great potential in geomorphic research involving multicollinear data ii the regional permafrost distribution coupled to the bedrock curvature and valley topography was detected to be the primary rockfall control rockfall source areas cluster within a low radiation elevation belt 2900 3300 m a s l consistent with a permafrost probability of 90 the second most important factor is the time since deglaciation reflected by the high abundance of rockfalls along recently deglaciated the study demonstrates the benefit of combined statistical approaches for predicting rockfall activity in deglaciated permafrost affected mountain valleys and highlights the complex interplay between rock mechanical paraglacial and topo climatic controls at the regional scale

effects of sediment transport and seepage direction on hydraulic properties at the sediment water interface of hyporheic settings summary relations between seepage flux and hydraulic properties are difficult to quantify in fluvial settings because of the difficulty in measuring these variables in situ tests conducted in a 1 5 m diameter by 1 5 m tall sediment filled tank indicate that hydraulic gradient increased and hydraulic conductivity k decreased following the onset of downward seepage but both parameters were little changed following the onset of upward seepage reductions in k during downward seepage were more pronounced when surface water current was sufficient to mobilize sediment on the bed averaged ratios of k determined during upward seepage to k determined during downward seepage k up k down through a sand and gravel bed increased from 1 4 to 1 7 with increasing surface water velocity and decreased to slightly greater than 1 when the sediment bed became fully mobile k up k down for tests conducted with a silt veneer on the bed surface was greater than 2 for all but the fastest surface water velocities substantial reductions in k also were associated with a silt floc that formed on the bed surface during and following test runs although the silt floc was typically less than 0 5 mm in thickness most of the hydraulic gradient was distributed across this thin layer k of the thin silt floc was reduced by two to three orders of magnitude relative to the underlying sediment directional bias in k and relation between k and surface water velocity require the presence or absence of a layer of lower k sediment at or near the bed surface without which no reduction in k and corresponding increase in hydraulic gradient can occur at the bed surface the lack of prior observation of the consistent bias in k associated with seepage direction is somewhat surprising given the numerous studies where k has been measured in fluvial settings but may be explained by the small value of the bias relative to the typical uncertainty associated with field determinations of k if shown to exist in field settings this bias and its relation to fluvial processes will be relevant to many studies conducted in hyporheic settings that require determination of fluxes across the sediment water interface

modeling ice dynamics of coastal seas a coupled sea ice barotropic ocean model with a 1 km resolution and a seaward domain of 200 km quantifies three coastal processes coupling of ice motion to wind driven coastal currents ice thickness redistribution under compaction at the coast and formation of coastal shear zones the model consists of an ice momentum balance mass concentration and two parameter ice thickness distribution and equations for horizontal water motion and continuity using vertical structure functions an appropriate constitutive law appears to be a hardening plastic based on qualitative observations from alaskan continental shelves for first year sea ice strength is taken to be proportional to the square of ice thickness a north wind example of 10 m s with the coastline to the west shows the depth dependence of rotational shear in the sea ice ocean boundary layer and sea surface tilt which contributes an alongshore slope current there is slight convergence of sea ice over the shelf a coastal shear zone of 4 km and an alongshore ice speed seaward of the shear zone of 6 of the wind speed caused by the combination of an under ice shear layer and an alongshore slope current for an onshore wind ice is near free drift at 3 of the wind seaward of a ridging front which propagates seaward a square dependence of ice strength on thickness is required for the rubble field to approach a limiting thickness consistent with observations the hardening plastic interpretation of the rubble field has the stress state at the yield limit in contrast with a rigid plastic of high constant strength that yields only at the coast we conclude that 1 ice thickness motion feedback is important on scales less than 10 km 2 the observational base to discriminate between mesoscale constitutive laws is not yet available and 3 the relation of ice velocity to wind stress is variable because the ocean slope current responds only to the alongshore component of the wind

holocene rockwall retreat in svalbard a triple rate evolution volumetric calculations of slope deposits direct measurements of rockwall retreat and chronological control based on lichenometry provide a wide range of rockwall retreat rates in svalbard 0 1580 mm ka 1 that appears consistent with previous evaluations from other arctic areas in northwest and central spitsbergen 79 n a triple rate rockwall retreat is suggested for the last two millennia very slow biogenic flaking 2 mm ka 1 moderate retreat due to frost shattering 100 ka 1 and rapid retreat associated with post glacial stress relaxation c 1000 mm ka 1 examination of the distribution of various processes indicates that the holocene retreat of most rockwalls has not exceeded one or two metres bedrock conditions appear to be the main control on retreat rates the massiveness of igneous and metamorphic outcrops widespread in arctic shield areas largely accounts for the slowness of rockwall retreat which on these lithologies is primarily due to chemical and biological processes more rapid rates are usually associated with stress relaxation following glacial surges or with local frost susceptibility of bedrock often where faulting has induced high joint density at such sites rockwall retreat rates are of the same order of magnitude as those reported from alpine areas 1000 3000 mm ka 1 where both bedrock weakening due to tectonic stresses and the greater height of steep rockwalls account for the more rapid rockwall retreat rate 1997 by john wiley sons ltd

dense water formation in the laptev sea flaw lead 1 two primitive equation based models are used to estimate the formation of total volumes either of arctic cold halocline water chw intermediate water imw or deep water dw through freeze related salt rejection in the siberian laptev sea flaw lead system model a assumes that the rejected salt remixes with surface mixed water smw beyond the leads until salinities allow for contribution to the midlayers of either the chw the imw or the dw model b simulates direct salt rejection to the upper layer of the cold halocline and after remixing here further contribution to the midlayers of chw imw or dw averaging both model estimates laptev leads contribute either 0 161 sv of chw 0 075 sv of imw or 0 065 sv of dw which represents as much as 23 16 or 30 of arctic wide lead derived dense water contribution to the appropriate layer respectively northwestern laptev leads produce the greatest amount of dense water these lead sections show very short buoyancy equilibrium timescales 6 to 13 days and local dense water production may potentially be amplified by lateral brine injection into the cold halocline through bottom eddies central southern and southeastern leads generally produce little salt due to low surface water salinities as definite separation mechanisms and proportion distributions of rejected lead brines into chw iwm and dw are still unidentified in nature a combination of lead salt rejection and remixing model a and direct downward expulsion of brine packages model b is assumed to steer laptev lead dense water production

nutrient supply and biological response to wind induced mixing inertial motion internal waves and currents in the northern chukchi sea a fixed point observation station was set up in the northern chukchi sea during autumn 2013 and for about 2 weeks conductivity temperature depth ctd water samplings 6 h and microstructure turbulence measurements 2 to 3 times a day were performed this enabled us to estimate vertical nutrient fluxes and the impact of different types of turbulent mixing on biological activity there have been no such fixed point observations in this region where incoming low salinity water from the pacific ocean river water and sea ice meltwater promote a strong pycnocline halocline that stabilizes the water column previous studies have suggested that because of the strong pycnocline wind induced ocean mixing could not change the stratification to impact biological activity however the present study indicates that a combined effect of an uplifted pycnocline accompanied by wind induced inertial motion and turbulent mixing caused by intense gale force winds 10 m s 1 did result in increases in upward nutrient fluxes primary productivity and phytoplankton biomass particularly large phytoplankton such as diatoms convective mixing associated with internal waves around the pycnocline also increased the upward nutrient fluxes and might have an impact on biological activity there for diatom production at the fixed point observation station it was essential that silicate was supplied from a subsurface silicate maximum a new feature that we identified during autumn in the northern chukchi sea water mass distributions obtained from wide area observations suggest that the subsurface silicate maximum water was possibly derived from the ventilated halocline in the canada basin

thermo cryogenic controls of fracture kinematics in permafrost rockwalls thermo cryogenic processes prepare and trigger rockfalls and rockslides in alpine environments temporal occurrence controls and applied stresses of thermo cryogenic processes on rock masses are poorly understood this paper reports annual crackmeter measurements with 3 h resolution across perennially ice filled fractures in an unstable rock permafrost crestline thermo cryogenic processes are controlled by snow cover onset and duration thermal changes in snow free periods control expansion and contraction coincident temperature gradients on a daily to seasonal scale we can show how snow cover promotes sustained temperatures from 9 to 1 c and boosts ice segregation related fracture opening up to 1 cm in 8 months during snowmelt meltwater induces ice erosion and ice relaxation which occur in the freeze thaw window close to the thawing point we hypothesize that thermo cryogenic processes and their cyclic repetition can lead to thermo cryogenic fatigue preparing rock slope failure and can control type and location of rockfalls in a changing climate

wind forced upwelling and internal kelvin wave generation in mackenzie canyon beaufort sea low frequency current temperature and salinity variations over the shelf break in the southeastern beaufort sea mackenzie shelf are examined to determine the response of seasonally ice free waters to wind forcing and the role of submarine canyons in upwelling events and shelf circulation upwelling events were found to be statistically correlated to northeasterly winds which transport surface waters offshore and draw up water from deeper layers the response to alongshore wind stress is significantly amplified in mackenzie canyon where isopycnal displacements of over 400 m are observed such displacements are then observed to propagate eastward at a phase velocity near 0 6 m s 1 the canyon is thus a site of intense upwelling while the collapse of displaced isopycnals subsequent to cessation of wind forcing creates a disturbance propagating northeast along shelf as a free internal kelvin wave

water mass structure and boundaries in the mackenzie shelf estuary the mackenzie shelf is a broad estuarine region bordering the southeastern beaufort sea in the arctic ocean its fields of temperature and salinity result from the modification of offshore water masses by river inflow ice melting and freezing solar insolation and air sea exchange we here relate water masses resident on the mackenzie shelf to the large scale oceanography of the arctic mediterranean the summertime exchange between the shelf and open ocean is largely confined to waters lying above the main halocline s 34 2 psu cross shelf property distributions show that individual water masses maintain their structural identity i e core properties and buoyancy frequency as they move across the shelf and participate in the estuarine circulation shelf waters are strongly influenced by river inflow however the concept of a single plume issuing from the incoming river and forming a strictly two layered structure over uniform shelf water is misleading since a variety of temperature salinity and turbidity fronts co exist on the shelf at any given time

the spatial variability of streambed vertical hydraulic conductivity in an intermittent river northwestern china streambed vertical hydraulic conductivity k plays an important role in river water and groundwater interaction the k at the ten transects ts1 ts10 at the donghe river an intermittent river in the ejina basin northwestern china was measured to investigate its spatial variation based on the sediment characteristics and vertical hydraulic conductivity of the riverbed the entire riverbed of the donghe river could be divided arbitrarily into two parts an upper part starting at ts1 and ending at ts9 without an obvious and continuous clogging layer and a lower part the remaining riverbed with an obvious and continuous clogging layer in the upper part although the k varied with depth within the 0 30 cm layer the variability with depth could be ignored in practice the arithmetic mean k of the upper part ranged from 12 to 27 6 m day three orders of magnitude larger than that of the lower part 0 06 m day the change of k along the river cross section was significant and larger values of k often occurred in the parts of the channels with greater water depth however there were no consistent patterns of the variability of k at transects across the river which was influenced by the variation in streambed characteristics the results could be useful for the estimation of groundwater recharge from river and groundwater resources evaluation in the ejina basin

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

effects of along shore wind on dsw formation beneath coastal polynyas application to the sea of okhotsk 1 it is known that salinity anomaly under a polynya reaches and remains an equilibrium value s after termination of its initial increase associated with brine rejection at the surface in this paper we investigate effect of along shore downwelling favorable wind on the equilibrium salinity anomaly by idealized numerical calculations and scale based estimates numerical calculations showed that high saline water beneath polynya is advected downstream by wind driven circulations over the shelf besides baroclinically developed eddies which consequently induces a decrease in s beneath polynya the downwelling favorable wind generates an offshore overturning flow through lower layers referred to as ekman compensation flow ecf which causes a great offshore salinity flux as well as an along shore current we also constructed an equation for estimation of s from the viewpoint of salinity budget over the polynya region in which lateral salinity fluxes caused by ecf along shore wind driven current and baroclinic eddies are scaled the solution s was also verified by a series of numerical calculations furthermore we investigated the effects of along shore wind on dense water generation beneath the okhotsk coastal polynyas we conducted simplified numerical experiments assuming the okhotsk situation in which fs and offshore width b of polynya are predicted by a thermodynamic polynya model with ecmwf meteorological variables the simulated salinity shows a good agreement with the direct measurements the theoretical estimates for s was also applied to two okhotsk polynyas northwestern polynya nwp and northern polynya np in conclusion we found that the along shore wind causes greater salinity decrease in np than in nwp whose variations substantially depend on the aleutian low activity

case hardening of sandstone the case hardened crust developed on the aztec sandstone in the valley of fire nevada has been characterized by a variety of techniques including electron microscopy and infrared spectroscopy the case hardened crust consists mainly of host rock with a fine grained cement and wind deposited kaolinite the cement is usually calcite but in some cases the hydrated calcium borate colemanite was found to be the case hardening cement

climatic controls on frost cracking and implications for the evolution of bedrock landscapes 1 in mountainous landscapes the role of periglacial processes in producing sediment is poorly defined despite evidence of abundant talus slopes ice growth in rock has long been recognized as an efficient erosion mechanism but the effects have not been readily applied to landscape evolution in response to tectonic and climatic forcing here we quantify how and where ice driven mechanical erosion occurs in cold bedrock dominated landscapes using a simple one dimensional numerical heat flow model in our model ice grows by water migration to colder regions in shallow rock by the reduction in chemical potential associated with intermolecular forces between ice and mineral surfaces a process called segregation ice growth the depth and intensity of frost cracking is primarily dependent on mean annual temperature mat with positive mat sites characterized by intense cracking in the top meter of the rock mass and a maximum frost penetration of 4 m in contrast negative mat areas have less intense cracking that primarily occurs at depths between 50 and 800 cm we compare the depth and intensity of frost cracking predicted by our model with measures of the intensity of frost processes determined in three studies the first measured the timing of rockfall in the canadian rockies niagara escarpment and japanese alps the second analyzed scree deposits in the southern alps new zealand and the third documented rockfall frequency in utah these natural examples show that rockfalls tend to nucleate at elevations that coincide with zones of intense frost cracking predicted by our model as such climatic variations associated with interglacial glacial cycles may impart a significant influence on the denudation of mountainous landscapes

the historical legacy of spatial scales in freeze thaw weathering misrepresentation and resulting misdirection discussion of weathering in cold regions has historically been dominated by widespread acceptance of the significance of the freeze thaw concept among periglacial geomorphologists and an essentially universal acceptance by those geomorphologists not directly involved in researching the topic debris produced by freeze thaw is frequently deemed to be angular in form and the observation of such debris has been used to identify the former or present operation of this weathering mechanism large debris blocks and small debris grains or flakes have been recognised as the outcome of the two scales of freeze thaw weathering macrogelivation and microgelivation respectively however the fusion of climatic geomorphology and process geomorphology in the ongoing development of the freeze thaw concept has resulted in the confusion of product with process whereby microgelivation producing small products and macrogelivation producing large products are seen due to the product dichotomy as distinctly different processes despite the recent highly sophisticated laboratory experimentation on freeze thaw weathering this historical process scale dichotomy still pervades thinking and experimental evaluation here we consider the historical development of microgelivation macrogelivation and outline what are thought to be fundamental flaws with the concepts and their underpinnings built within the two notions are elements of rock properties hard and soft and scale issues regarding rock attributes solid rock and existing weaknesses in rock that serve only to confuse the process and scale issues even more the whole notion of frost weathered debris having a specific form is also highly spurious there being no shape attribute that is uniquely diagnostic of frost action and this in turn leads to the further problem of process synergy or other processes entirely being the cause of rock failure in cold regions ultimately we argue that while there may be a range of product sizes and shapes resulting from frost weathering per se the widely invoked scale concepts are fraught with problems and are best dropped as too are any process shape connotations

on sea ice concentration anomaly coherence in the southern beaufort sea 1 the circumpolar flaw lead polynya system is a region of enhanced biological productivity and for significant portions of the annual cycle dominates the exchange of energy and mass across the ocean sea ice atmosphere osa interface we investigate the nature of sea ice concentration sic anomalies for spatial and temporal statistical persistence within a portion of this flaw lead system we find such a structure in the shelf break zone between amundsen gulf and the canada basin ncep ncar reanalysis data is used to determine the potential roles of oceanic and atmospheric forcing in creating and maintaining this observed coherence in the sic anomalies results suggest that the coherence pattern is consistent over the instrumental record 1979 to 2000 although it changes in shape and extent between years the forcing mechanisms creating this coherence in sic anomalies appear to be tied to surface wind driven upwelling in the shelf break areas of the southern beaufort sea sbs

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

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

erosional processes in the hard rock coastal cliffs at staithes north yorkshire the processes of change on near vertical coastal cliffs have been quantified using terrestrial photogrammetry and laser scanning the approach allows discrete rockfall geometry to be measured and source located in three dimensions this paper presents the analysis of an inventory of over 100000 discrete rockfalls recorded from the liassic coast at staithes north yorkshire uk where a rock face area of over 16000 m 2 has been monitored over a 20 month period the data obtained on three dimensional scar geometry and source position give an insight into rockfall characteristics from a range of rock types cliff heights and geometries multiple failure mechanisms such as overhang collapse constant spalling fragmentation and large scale coherent rockfalls have been observed and related to rock type controlled processes on the rock face the spatially referenced rockfall scar data are used to assess the influence of environmental controls on variable rock mass properties such as rock type structure and cliff geometry analysis of rockfall magnitude frequency reveals notable similarities between coastal rockfalls and inventories from non coastal environments the resolution of the monitoring data allows quantification of rockfalls down to volumes of 1 25 x 10 4 m 3 to be consistently sampled and measured this complete magnitude frequency relationship suggests that rather than evolving exclusively through isolated sporadic losses coastal cliff geomorphology reflects interconnected processes in which each rockfall is part of a continuum of change to the rock face further detailed assessment of the rock face reveals the control of the pre failure morphology on subsequent failure patterns for example the quantity of rock protrusion from the cliff is positively correlated with subsequent failure volume the continuum of activity and the controls on failure identified within these data suggest that the episodic behaviour of coastal cliffs previously assumed may have been overstated by coarser resolution monitoring data the findings improve our understanding of the evolution of coastal cliffs and highlight areas for further research into both cliff processes and the character of rock slope failures in general

spatial and depth variability of streambed vertical hydraulic conductivity under the regional flow regimes this study investigated the influence of the regional flow on the streambed vertical hydraulic conductivity k v within the hyporheic zone in three stream reaches of the weihe river in july 2016 the streambed k v with two connected depths was investigated at each test reach based on the sediment characteristics the three test reaches could be divided into three categories a sandy streambed without continuous silt and clay layer a sandy streambed with continuous silt and clay layer and a silt clay streambed the results demonstrate that the streambed k v mainly decreases with the depth at the sandy streambed without continuous silt and clay layer and increases with the depth at the other two test reaches at the sandy streambed with continuous silt and clay layer where streambed k v mainly decreases with the depth the regional upward flux can suspend fine particles and enhance the pore spacing resulting in the elevated k v in the upper sediment layers at another sandy streambed the continuous silt and clay layer is the main factor that influences the vertical distribution of fine particles and streambed k v an increase in streambed k v with the depth at the silt clay streambed is attributed to the regional downward movement of water within the sediments that may lead to more fine particles deposited in the pores in the upper sediment layers the streambed k v is very close to the bank in the sandy streambed without continuous silt and clay layer and the channel centre in the other two test reaches differences in grain size distribution of the sediments at each test reach exercise a strong controlling influence on the streambed k v this study promotes the understanding of dynamics influencing the interactions between groundwater and surface water and provides guidelines to scientific water resources management for rivers

weathering of sandstone by the combined action of frost and salt preliminary results from a continuing series of laboratory experiments designed to examine the combined effects of salt and frost weathering indicate that some salts greatly enhance the breakdown of rocks by frost samples of ardingly sandstone from southeast england were soaked in saturated solutions of sodium chloride or sodium sulphate and subjected to alternating cycles of freezing and thawing rapid disintegration of the sandstone occurred within twenty cycles in each of the salt solutions in contrast samples subjected to freezing and thawing in deionized water suffered very little damage unless they were saturated under vacuum when samples were subjected to twenty cycles of wetting and drying at temperatures above 0 c those soaked in deionised water or sodium chloride suffered no appreciable damage but those soaked in sodium sulphate rapidly disintegrated tentative explanations of these results are offered the enhancement of frost weathering by salt appears to have been overlooked by many writers yet it is likely to be an important geomorphological process in those areas of mid and high latitudes where rocks are saturated with sodium salts

seasonal ice loss in the beaufort sea toward synchrony and prediction the seasonal evolution of sea ice loss in the beaufort sea during 1979 2012 is examined focusing on differences between eastern and western sectors two stages in ice loss are identified the day of opening doo is defined as the spring decrease in ice concentration from its winter maximum below a value of 0 8 areal concentration the day of retreat dor is the summer decrease below 0 15 concentration we consider three aspects of the subject i e i the long term mean ii long term linear trends and iii interannual variability we find that in the mean doo occurs earliest in the eastern beaufort sea ebs owing to easterly winds which act to thin the ice there relative to the western beaufort sea wbs where ice has been generally thicker there is no significant long term trend in ebs doo although wbs doo is in fact trending toward earlier dates this means that spatial differences in doo across the beaufort sea have been shrinking over the past 33 years i e these dates are becoming more synchronous a situation which may impact human and marine mammal activity in the area retreat dates are also becoming more synchronous although with no statistical significance over the studied time period finally we find that in any given year an increase in monthly mean easterly winds of 1 m s during spring is associated with earlier summer dor of 6 15 days offering predictive capability with 2 4 months lead time

changes in the thickness distribution of arctic sea ice between 1958 1970 and 1993 1997 1 submarine sonar data collected in the central arctic basin during middle and late summer were used to examine differences in the sea ice thickness distribution function g h between the periods 1958 1970 and 1993 1997 cruises during the former period were made in july and august whereas the 1993 1997 cruises were made in september and october seasonal correction was applied to adjust for the differences in thickness while ice drafts were from only seven submarine cruises and somewhat spatially limited results indicate that the fractional area covered by open water and first year ice increased from 0 19 to 0 30 during the time interval this was balanced by an 11 reduction of level multiyear and ridged ice substantial losses occurred in ice thicker than 2 m with an increase in the amount of 1 2 m ice the volume of ice less than 4 m thick remained nearly the same and the total volume decreased about 32 losses in the volume of thicker ice increased with increasing thickness part of the change in g h is likely caused by increased ice area export through fram strait in the late 1980s and early 1990s because decadal variations in the north atlantic oscillation and arctic oscillation indices correlate with ice export anomalies export induced changes in g h probably tend to be cyclical in nature however a substantial shift in the peak of g h suggests that changes in thermal forcing were also a major factor in the observed thinning

quantitative study of a rapidly weathering overhang developed in an artificially wetted sandstone cliff those factors controlling the weathering and erosion of sandstone on the field scale are still not well understood in this study a specific sandstone overhang and its surroundings with artificially induced and extremely high erosion rates was subjected to a complex investigation contrast between the erosion rate of the wet and dry portions of the same cliff enabled isolation of the factors responsible for rapid sandstone retreat erosion rates moisture and salt content as well as suction were monitored in the field mineral phases and water chemistry were analyzed the measurement of tensile strength laboratory frost weathering tests and numerical modeling of stress were performed the acquired data show that an increase of moisture content in pores in the area of the studied overhang decreased tensile strength of the sandstone to 14 of its dry value and increases the sandstone weathering and erosion rate by nearly 4 orders of magnitude compared to the same sandstone under natural moisture condition outside on the cliff area consequently frost weathering in combination with wetting weakening was found to play a major role in weathering erosion of the sandstone cliff and overhang frost weathering rate in both the laboratory and field increases up to 15 times with decreasing gravity induced stress the results also indicate that sandstone landforms in temperate climates may potentially develop very rapidly if the pore space is nearly saturated with water and will later remain relatively stable when the moisture content decreases as a general implication it is suggested that overhangs in central europe and elsewhere might be the result of rapid frost weathering of nearly saturated sandstone during the last glacial this article is protected by copyright all rights reserved

air circulation in deep fractures and the temperature field of an alpine rock slope the subsurface temperature field of a rock slope is a key variable influencing both bedrock fracturing and slope stability however significant unknowns remain relating to the effect of air and water fracture flow which can rapidly transmit temperature changes to appreciable depths in this work we analyze a unique set of temperature measurements from an alpine rock slope at 2400 m a s l in southern switzerland the monitored area encompasses part of an active slope instability above the village of randa vs and is traversed by a network of open cracks some of which have been traced to 80 m depth we first describe distributed temperature measurements and borehole profiles highlighting deep steady temperatures and different transient effects and then use these data to approximate the conductive temperature field at the site in a second step we analyze the impact of air and water circulation in deep open fractures on the subsurface thermal field on multiple visits to the study site in winter we consistently noted the presence of warm air vents in the snowpack following the trace of deep tension cracks measurements showed that venting air changed temperature gradually from 3 to 2 c between december and may which is similar to the rock temperature at around 50 m depth comparison with ambient air temperature suggests that winter conditions favor buoyancy driven convective air flow in these fractures which acts to cool the deep subsurface as the rock gives up heat to incoming air the potential impact of this process on the local thermal field is revealed by a disturbed temperature profile in one borehole and transient signals observed at depths well below the thermal active layer seasonal water infiltration during snowmelt appears to have little impact on the temperature field in the monitored area copyright 2011 john wiley sons ltd

the distribution of nutrients in the southeastern beaufort sea implications for water circulation and primary production hydrographic data collected above the shelf and slope in the southeastern beaufort sea show marked contrast in surface properties of nutrients temperature salinity and oxygen between august 1974 a year when ice remained close to shore and august 1975 a year with much open water the near surface properties are dominated by river inputs biological activity and the ice regime below the winter mixed zone 40 50 m properties are similar to those observed elsewhere in the arctic ocean bering sea water is detected at 50 60 m as a very weak signal in temperature nutrients and oxygen upwelling in both years was observed at the eastern side of mackenzie canyon this upwelling likely results from the interaction of coastal circulation with topography estimates of new productivity based on nutrient budgets are low 20 g c m 2 yr 1 compared to temperate coastal waters but fall in the range expected for the arctic in 1974 the heavy ice year turbid water and ice cover appear to have reduced new production by about 30 calculations show that this production over the shelf could potentially supply a significant portion of the nutrients found in the upper halocline over a wide region of the arctic ocean by regeneration at the shelf bottom and transport off the shelf in brine drainage

linking weathering and rock slope instability non linear perspectives weathering is linked complexly to the erosion and evolution of rock slopes weathering influences both the strength of rock slopes and the stresses that act upon them while weathering has often been portrayed in an over simplified way by those studying rock slope instability in reality it consists of multiple processes acting over different spatial and temporal scales with many complex inter linkages through a demonstration of the sources of non linearities in rock slope weathering systems and their implications for rock slope instability this paper proposes five key linkages worthy of further study copyright 2012 john wiley sons ltd

weathering and deterioration of geotechnical properties in time of groundmasses in a tropical climate abstract weathering and degradation of slope materials govern erosion and stability of slopes over time weathering is often ignored or over simplified in engineering due to absence of time series of material properties and uncertainty on future environment the research in this paper investigates the rate of deterioration of geotechnical properties due to weathering over time after excavation of cut slopes in completely weathered material and residual soil in a tropical environment three cut slopes are studied with different excavation dates but with similar geological geotechnical and groundwater conditions identical slope aspect and land cover index and strength properties are determined by field and laboratory tests the results show that the hydro mechanical properties of completely weathered material in cut slopes evolve very rapidly to those of residual soil within time spans of 30 to 90 years in a tropical humid environment the properties reduce so much that instability of cut slopes is inevitable if this reduction is not taken into account during design and excavation of the slopes change of strength properties is around 1 1 to 1 3 pt per year from the original completely weathered material strength at the time of excavation this is based on simplified linear and logarithmic relationships the deterioration of geotechnical properties is likely the main reason for many slope failures in cut slopes after many years of stability in the research area of yen bai city in vietnam

seasonal variability of sea surface height in the coastal waters and deep basins of the nordic seas sea surface height measured by the envisat radar altimeter over open ocean and from leads in sea ice are combined to generate a complete view of variability in the nordic seas geographically and seasonally the observed seasonal variability is decomposed using empirical orthogonal functions and is consistent with seasonal variations in steric and dynamic forcing wintertime increase in sea surface height on the east greenland shelf is hypothesised to be caused by wind forced downwelling which provides direct evidence for the regional play of coastal dynamics high levels of eddy kinetic energy around the sea ice edge in fram strait and off east greenland and svalbard are consistent with the interaction of the wind with the ice edge

meteorological forcing of sea ice concentrations in the southern beaufort sea over the period 1979 to 2000 1 northern hemisphere sea ice areal extent and perhaps thickness have shown a detectable reduction over the past several decades this situation is particularly apparent in the southern beaufort sea the region encompassing the mackenzie shelf the cape bathurst polynya and the canada basin mobile pack ice all occur in a region referred to here as the canadian arctic shelf exchange study area cases in this paper we present results from an analysis of atmosphere sea ice and ocean coupling over the period 1979 to 2000 as a means of setting a physical science context for the cases research network operating over the period 2001 2005 results show that the cape bathurst polynya complex can be considered as a recurrent polynya particularly the flaw leads associated with the early opening of the polynya the polynya appears to be a consequence of the beaufort sea gyre acting like an ice bridge and a series of flaw leads creating conditions conducive to oceanic upwelling the sea ice average areal extent has been decreasing in this region over the period 1979 to 2000 large regional reductions are found i north of the yukon and alaska coasts in the region between the canada basin pack ice and the landfast sea ice and 2 at the eastern limit of the cape bathurst polynya in amundsen gulf the meteorological forcing of sea ice anomalies occurs through a full range of timescales and space scales at hemispheric scales a statistical cross correlation analysis between weekly sea ice concentration anomalies and the arctic oscillation accounts for a maximum of about 25 percent of the explained variance and show a surprising spatial coherence in correlation magnitudes both within the study area and northward along the canadian archipelago coast at local scales positive and negative concentration anomaly periods can be explained through local scale advective processes associated with regional scale sea level pressure 500 hpa geopotential heights and surface temperature anomalies

response of sea ice drift to wind forcing on the northeastern newfoundland shelf observations of sea ice drift obtained with satellite tracked ice beacons in march april of 1988 and 1989 have been used to examine the response of sea ice drift to wind forcing over the northern newfoundland continental shelf the short term 5 20 days response of sea ice drift ranges from 2 6 to 5 4 of the local wind over much of the inner continental shelf which is comparable to that in the bering sea and the antarctic but larger than that in arctic sea ice drifts to the right of the local wind at angles ranging from 10 to 63 the response to wind forcing is largest near the ice edge both over the middle portions of the shelf and along the southern margins of the seasonal ice zone and during strong and steady wind of several days duration the large wind driven response of ice drift observed in this study in comparison with the arctic may result from 1 reduced levels of internal ice stress associated with the generally thin ice cover and lower areal concentration of sea ice 2 large atmospheric drag coefficients associated with the small ice floes in areas of comparatively higher ice concentration and 3 smooth ice bottom caused by melting in nearshore areas the ice to wind coupling is reduced owing to larger internal ice stresses experienced locally due to ice pileup

rapid formation of a sea ice barrier east of svalbard 1 daily seawinds scatterometer images acquired by the quikscat satellite show an elongated sea ice feature that formed very rapidly 1 2 days in november 2001 east of svalbard over the barents sea this sea ice structure called the svalbard sea ice barrier spanning approximately 10 in longitude and 2 in latitude restricts the sea route and poses a significant navigation hazard the secret of its formation appears to lie in the bottom of the sea a comparison between bathymetry from the international bathymetric chart of the arctic ocean data and the pattern of sea ice formation from scatterometer data reveals that the sea ice barrier conforms well with and stretches above a deep elongated channel connecting the franz josef victoria trough to the hinlopen basin between svalbard and franz josef land historic hydrographic data from this area indicate that this sea channel contains cold arctic water less than 50 m below the surface strong and persistent cold northerly winds force strong heat loss from this shallow surface layer leading to the rapid formation of the sea ice barrier heat transfer rates estimated from european centre for medium range weather forecasts temperature and wind data over this region suggest that the surface water along the deep channel can be rapidly cooled to the freezing point scatterometer results in 1999 2003 show that sea ice forms in this area between october and december understanding the ice formation mechanisms helps to select appropriate locations for deployment of buoys measuring wind and air sea temperature profile and to facilitate ice monitoring modeling and forecasting

between a beam and catenary influence of geometry on gravitational stresses and stability of natural rock arches abstract the self weight of freestanding natural arches imparts stresses on the lintel and abutments setting the conditions for rock fracture and erosion rock is weak in tension therefore an ideal arch form is one that minimizes tensile stresses and supports the weight of the lintel in compression e g an inverted catenary however rock mass structure including bedding cross bedding and other discontinuities often imparts strong control on the geometry of arches leading to forms that are less favorable from a stress perspective here we analyze a suite of nineteen arch models created from ground and drone based photogrammetry to assess the three dimensional static stress field under gravitational loading the models represent a range of arch lengths from 4 to 88 m as well as a variety of forms and use material properties previously calibrated from dynamic analysis of ambient vibrations our results demonstrate that arches shaped like beams have relatively high tensile stresses and a nearly symmetrical statistical distribution of principal stresses while those with convex forms have comparably lower tensile stresses and statistical distributions favoring compressive stresses in situ observations of tensile cracks frequently correspond to the location of predicted tensile stresses in our models we calculated the ratio of mean principal stresses for each arch which is theoretically 1 for a flat prismatic beam and approaches infinity for an ideal inverted catenary we found several arches with mean principal stress ratio around 1 and that values increased with lintel convexity these results indicate that while self sculpture might attempt to create ideal stress based forms discontinuities can control lintel geometry and natural arches evolve with forms that may be less favorable for long term stability the mean principal stress ratio is a simple metric to classify and compare arches which may be useful for assessment of arch stability supporting conservation and hazard analyses

current denudation rates in dolostone karst from central spain implications for the formation of unroofed caves abstract rock tablets of known weight were buried in the soil of a karst region in central spain to evaluate the carbonate weathering during a period of a year the experiment was conducted at two different soil depths 5 10 and 50 55 cm from the surface the parental rock used in the experiment is composed of dolomite and magnesite with variable proportion of accessory minerals and minor elements soil mineral and chemical composition as well as its texture was also characterized meteorological conditions at the site together with temperature and co2 in both soil levels were monitored sets of tablets were retrieved after 6 and 12 months of the start of the experiment to account for seasonal weathering different lithologies do not exhibit significant differences in weathering although a large inter sample variability is attributed to variable size and distribution of the porosity results show an enhanced weathering during the wet and cold season that accounts for 78 1 of the total annual weathering rock tablets examined under scanning electron microscopy prior and after exposure to natural environment show that most of the material lost occurred along cracks edges or large pores although dissolution is a common process most of the weathering is due to crystal detachment rock tablets at the depth of 5 10 cm were weathered 68 1 more than those set at 50 55 cm from the surface higher soil moisture and concentration of co2 were found deeper in the soil which likely enhanced the dissolution of carbonate however physical weathering dominated weight loss of rock tablets at both soil depths especially at the 5 10 cm level where soil thermal and moisture cycles were more frequent and greater denudation rate calculated from the 12 months set provides values of 2 48 1 07 m yr and 1 75 0 66 m yr at the depths of 5 10 and 50 55 cm respectively since the conditions at the average contact between soil and bedrock are similar to those at the 50 55 cm depth we consider that this is a more reliable denudation rate for the studied location during the studied period the calculated weathering rate suggests that denudation has a limited contribution to the thinning of bedrock over caves at this site therefore we consider that the formation of unroofed caves in this region most likely results from the thinning of bedrock cover over caves due to collapse of blocks from their ceilings

unraveling driving factors for large rock ice avalanche mobility large rock ice avalanches have attracted attention from scientists for decades and some of these events have caused high numbers of fatalities a relation between rock slope instabilities in cold high mountain areas and climate change is currently becoming more evident and questions about possible consequences and hazard scenarios in densely populated high mountain regions leading beyond historical precedence are rising to improve hazard assessment of potential rock ice avalanches their mobility is a critical factor this contribution is an attempt to unravel driving factors for the mobility of large rock ice avalanches by synthesizing results from physical laboratory experiments and empirical data from 64 rock ice avalanches with volumes 1x106 m3 from glacierized high mountain regions around the world the influence of avalanche volume water and ice content low friction surfaces and topography on the apparent coefficient of friction as a measure of mobility is assessed in laboratory experiments granular ice in the moving mass was found to reduce bulk friction up to 20 while water led to a reduction around 50 for completely saturated material compared with dry flows evidence for the effects of water as a key driving factor to enhance mobility was also found in the empirical data while the influence of the ice content could not be confirmed to be of much relevance in nature besides liquefaction it was confirmed that mobility increases with volumes and that frictional surface characteristics such as flow paths over glaciers are also dominant variables determining mass movement mobility effects of the topography along the flow path as well as channeling are assumed to be other critical factors the results provide an empirical basis to roughly account for different path and flow characteristics of large rock ice avalanches and to find appropriate ranges for friction parameters for scenario modeling and hazard assessments copyright 2011 john wiley sons ltd