atmospheric methane flux from bubbling seeps spatially extrapolated quantification from a black sea shelf area bubble transport of methane from shallow seep sites in the black sea west of the crimea peninsula between 70 and 112 m water depth has been studied by extrapolation of results gained through different hydroacoustic methods and direct sampling ship based hydroacoustic echo sounders can locate bubble releasing seep sites very precisely and facilitate their correlation with geological or other features at the seafloor here the backscatter strength of a multibeam system was integrated with single beam data to estimate the amount of seeps m2 for different backscatter intensities resulting in 2709 vents in total direct flux measurements by submersible revealed methane fluxes from individual vents of 0 32 0 85 l min or 14 5 37 8 mmol min at ambient pressure and temperature conditions a conservative estimate of 30 mmol min per site was used to estimate the flux into the water to be 1219 1355 mmol s the flux to the atmosphere was calculated by applying a bubble dissolution model taking release depth temperature gas composition and bubble size spectra into account the flux into the atmosphere 3930 4533 mol d or into the mixed layer 6186 6899 mol d from the 21 8 km2 large study area is three times higher than independently measured fluxes of dissolved methane for the same area using geochemical methods 1030 2495 mol d the amount of methane dissolving in the mixed layer is 2256 2366 mol d this close match shows that the hydroacoustic approach for extrapolating the number of seeps m2 and the applied bubble dissolution model are suitable to extrapolate methane fluxes over larger areas

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

u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

slope development reconstruction at two sites in the bohemian forest mountains although the bohemian forest is generally considered to be geomorphologically a rather stable region there are localities which bear proof of a surprisingly high intensity of recent and even present day processes a multidisciplinary methodology based on the analysis of slope systems was used for researching the present and past dynamics of two hillslopes using the results of direct dilatometric monitoring the slow creep of rock blocks reached a maximum of 1 mm year 1 gps field mapping sedimentology geodetic measurements and dem analyses several common rules have been observed for the behaviour of two model localities and a likely polycyclic development established with recurrence of mass wasting cycles related to material supply thresholds radiometric dating of debris flow activity showed that the cycles span approximately 4000 years in this area of rather stable bedrock conditions at least two factors that decrease slope stability need to act together to activate slope processes i e a favourable structural predisposition dip of major joint or bedding planes and an increase in relief through either glaciation or river incision copyright 2010 john wiley sons ltd

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

variations in permafrost thickness in response to changes in paleoclimate solutions to the stefan problem for the motion of the base of ice bearing permafrost in response to changes in paleoclimate were obtained using perturbation finite difference and finite element methods paleotemperature models were used to investigate the thickness response to compare solution methods to determine the current state of the permafrost and to determine constraints on the models the perturbation and finite difference methods used the approximation of linear temperature profiles while the finite element method did not there was a transient thickness response of about 41 kyr implying that paleotemperature records of greater length are needed for models and that the permafrost loses its memory of past conditions for much longer times faster thawing rates slower freezing rates and greater variations in thickness were found for the perturbation and finite difference solutions compared to the finite element solution these results appear to be caused by the simplifying assumptions in the former solutions a lag about 20 kyr exists between changes in surface temperature and thickness response and a small thermal offset is apparent in the finite element solution small asymmetries exist in the freezing and thawing rates and the thickness response paleotemperature models based on ice cores predict current permafrost thicknesses that are too large models with the long term mean surface temperature of permafrost within a few degrees of the current value of 11 c and with the last glacial period temperatures no more than 6 8 c lower are compatible with current prudhoe bay conditions these include models developed for east siberia from isotopic profiles in deep sea sediments and for barrow alaska modified for prudhoe bay these models predict that the permafrost thickness at prudhoe bay varied by about 10 or less 60 m over the last glacial cycle freezing and thawing rates were less than 6 mm yr 1 at present this permafrost should be near its long term equilibrium thickness and thawing at 1 mm yr 1

quantifying sediment supply at the end of the last glaciation dynamic reconstruction of an alpine debris flow fan in this paper we quantify the sediment dynamics in the formerly glaciated zielbach catchment in the italian alps from the end of the last glacial maximum lgm until today as a basis for our quantification we use the stratigraphic record offered by a 3 5 km2 large fan that we explore with a seismic survey stratigraphic analyses of drillhole material and 14c ages measured on organic matter encountered in these drillings in addition we calculate past denudation rate variability in the fan deposits using concentrations of cosmogenic 10be we merge this information into a scenario of how the sediment flux has changed through time and how this variability can be related to climatic variations framed within well known paraglacial models the results document a highly complex natural system from the lgm to the very early holocene ice melted discharge and climate variability promoted a high sediment flux sedimentation rate up to 40 mm yr this flux then dramatically decreased toward interglacial values 0 8 mm yr at 5 4 calibrated kyr b p however in contrast to the trend of classic paraglacial models the flux recorded at zielbach shows secondary peaks at 6 5 ka and 2 5 ka with values of 13 mm yr and 1 5 mm yr respectively paleo denudation rates also decrease from 33 mm yr at the beginning of the holocene to 0 42 mm yr at 5 ka with peaks of 6 mm yr and 1 1 mm yr at 6 5 ka and 2 5 ka high amplitude climate change is the most likely cause of the secondary peaks but anthropogenic activities may have contributed as well the good correlation between paleo sedimentation and paleo denudation rates suggests that the majority of the deglaciated material destocked from the zielbach catchment is stored in the alluvial fan

evidence for gas hydrate occurrences in the canadian arctic beaufort sea within permafrost associated shelf and deep water marine environments the presence of a wedge of offshore permafrost on the shelf of the canadian beaufort sea has been previously recognized and the consequence of a prolonged occurrence of such permafrost is the possibility of an underlying gas hydrate regime we present the first evidence for wide spread occurrences of gas hydrates across the shelf in water depths of 60 100 m using 3d and 2d multichannel seismic mcs data a reflection with a polarity opposite to the seafloor was identified 1000 m below the seafloor that mimics some of the bottom simulating reflections bsrs in marine gas hydrate regimes however the reflection is not truly bottom simulating as its depth is controlled by offshore permafrost the depth of the reflection decreases with increasing water depth as predicted from thermal modeling of the late wisconsin transgression the reflection crosscuts strata and defines a zone of enhanced reflectivity beneath it which originates from free gas accumulated at the phase boundary over time as permafrost and associated gas hydrate stability zones thin in response to the transgression the wide spread gas hydrate occurrence beneath permafrost has implications on the region including drilling hazards associated with the presence of free gas possible overpressure lateral migration of fluids and expulsion at the seafloor in contrast to the permafrost associated gas hydrates a deep water marine bsr was also identified on mcs profiles the mcs data show a polarity reversed seismic reflection associated with a low velocity zone beneath it the seismic data coverage in the southern beaufort sea shows that the deep water marine bsr is not uniformly present across the entire region the regional discrepancy of the bsr occurrence between the us alaska portion and the mackenzie delta region may be a result of high sedimentation rates expected for the central mackenzie delta and high abundance of mass transport deposits that prohibit gas to accumulate within and beneath the gas hydrate stability zone

numerical model of the geothermal regime on the beaufort shelf arctic canada since the last interglacial 1 a finite element geothermal model is developed for the outer mackenzie delta beaufort sea shelf to predict permafrost evolution since the last interglacial 130 116 kabp cal the purpose is to reconcile sparse observations of the depth and extent of ice bonded permafrost with sediment properties and the paleoenvironment sea level curves determine as a function of time areas of the shelf that were subaerially exposed promoting permafrost aggradation and areas that were submerged promoting permafrost degradation assuming as a model starting point that a paleoclimate similar to today persisted through the last interglacial permafrost subsequently aggrades in depth and advances seaward from the present shoreline to the shelf slope bathymetric break by the last glacial maximum lgm 26 kabp cal modeled permafrost exhibits reduced growth in depth and seaward progression that correlate with early and middle wisconsin stillstands in sea level following the lgm and rise in sea level offshore permafrost degrades and permafrost base rises 100 m to its present depth of 600 m the offshore limit of modeled ice bonded permafrost lies at the 95 m isobath within 1 km of the bathymetric shelf slope break the model replicates features of offshore permafrost body observed seismically and demonstrates that warm outflow from the mackenzie river depresses the upper surface of offshore permafrost by tens of meters to the 20 m isobath although pleistocene permafrost predated the wisconsinan the model demonstrates that the paleoenvironment of the last 125 000 years is sufficient to develop the depth seaward extent and principal features of the permafrost body

the angle of reach as a mobility index for small and large landslides the relations between the angle of reach fahrboschung and other indexes expressing the mobility of landslides and vertical drop horizontal reach and volume of landslide mass have been analyzed by means of simplified plots and regression equations results for 204 landslides of all sizes show that whatever the mechanism of motion all kinds of landslides experience a continuous reduction of the angle of reach with volume increase this reduction starts from the smallest sizes scattering in this relation is mostly due to mechanisms of motion and to both obstacles and topographic constraints on the path this synthesis indicates that small landslides less than 0 5 106 m3 in relative terms display excesses of travel distance similar to large landslides since most small landslides are not expected to develop any change in the mechanism of progression while moving the decrease in the reach angle with volume suggests that scale effects should be taken into account the angle of reach is found to be

catastrophic rock avalanche 3600 years bp from el capitan yosemite valley california large rock slope failures from near vertical cliffs are an important geomorphic process driving the evolution of mountainous landscapes particularly glacially steepened cliffs the morphology and age of a 2 19 106 m3 rock avalanche deposit beneath el capitan in yosemite valley indicates a massive prehistoric failure of a large expanse of the southeast face geologic mapping of the deposit and the cliff face constrains the rock avalanche source to an area near the summit of 8 5 104 m2 the rock mass free fell 650 m reaching a maximum velocity of 100 m s 1 impacted the talus slope and spread across the valley floor extending 670 m from the base of the cliff cosmogenic beryllium 10 exposure ages from boulders in the deposit yield a mean age of 3 6 0 2 ka the 13 kyr time lag between deglaciation and failure suggests that the rock avalanche did not occur as a direct result of glacial debuttressing the 3 6 ka age for the rock avalanche does coincide with estimated late holocene rupture of the owens valley fault and or white mountain fault between 3 3 and 3 8 ka the coincidence of ages combined with the fact that the most recent ad 1872 owens valley fault rupture triggered numerous large rock falls in yosemite valley suggest that a large magnitude earthquake m7 0 centered in the south eastern sierra nevada may have triggered the rock avalanche if correct the extreme hazard posed by rock avalanches in yosemite valley remains present and depends on local earthquake recurrence intervals published in 2010 by john wiley sons ltd

exhaustion and steady state models for predicting landslide hazards in the canadian rocky mountains abstract the temporal distribution of landslides can be evaluated by steady state and exhaustion models the probability of landsliding remains constant through time in the steady state model but the probability decreases in the exhaustion model as more slopes fail rock sliding down bedding surfaces on overdip slopes exhausts hazardous sites to leave stable dipslope landforms in kananaskis country in the canadian rocky mountains the distribution of rock slides in this area can be better explained by the exhaustion model than by the steady state model

characteristics of the active layer and shallow subsea permafrost a seasonal active layer associated with subsea permafrost was found in the sediments near the seabed of the beaufort sea near prudhoe bay alaska the active layer existed where sea ice was frozen to the seabed and also in shallow water where the under ice seawater salinities exceeded open water values initial freezing of the active layer was about coincident with the formation of new sea ice within 400 m of shore it appeared to freeze to an underlying ice bonded permafrost table ibpt farther offshore where this table is deeper the active layer thickness decreased with distance offshore and the layer was underlain by a talik relative ice contents in the active layer generally decreased with distance offshore were a few hundred parts per thousand ppt in the fall and ranged to more than 800 ppt in the spring seasonal changes in the bulk soil solution salinity showed that the partially frozen active layer redistributed salts during freezing was infiltrated by concentrated brines derived from the growth of sea ice and affected the timing of brine drainage to lower depths in the sediments these brines provide the salts required for thawing the underlying subsea permafrost in the presence of negative sediment temperatures the region near shore had a partially frozen transition layer just above the ibpt where the ice content increased and the brine content decreased with depth temperature at the ibpt is nearly constant beyond about 412 m to at least 3 5 km offshore at about 2 41 c implying relatively constant soil solution salinities there

a sea level curve for the canadian beaufort shelf radiocarbon dated peat and peaty clay samples from geotechnical boreholes in the canadian beaufort continental shelf have been used to reconstruct a late quaternary relative sea level rsl curve the samples were carefully selected and evaluated using palynological techniques to ensure that reasonable age error limits could be given to each sample the dated samples were then related to the local geological setting using seismic profiles to determine the environment of deposition the resulting data show a rise of 140 m in rsl since 27 000 years bp a minor lowering of rsl at some time between 20 000 and 10 000 years bp is inferred from acoustic data contributions from basin subsidence sediment loading and consolidation account for 35 m of the total rsl rise the rsl curve is interpreted in the light of recent models of the isostatic and eustatic responses of the earth s crust at the laurentide ice sheet margin ice may have been more extensive during the middle wisconsinan than previously thought a

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

rockfall talus slopes and associated talus foot features in the glaciated uplands of great britain and ireland periglacial paraglacial or composite landforms

a chronology of post glacial landslides suggests that slight increases in precipitation could trigger a disproportionate geomorphic response large deep seated landslides are common throughout the southeastern san juan mountains of colorado and new mexico but their timing and initiation are not well understood determining when the landslides occurred would aid in clarifying the mechanisms for initiating landslides in the region and would help us to understand post glacial landscape evolution we studied seven prehistoric landslides located within the tertiary volcanic rocks of the san juan volcanic field the landslides range in area from 0 8 km2 to 11 3 km2 and most are located in areas that were previously mapped as having been ice covered during the last glaciation landslide deposits were dated using a variety of methods including surface exposure dating 36cl radiocarbon dating of basal bog sediments and organic material buried in soils and relative soil development the resulting limiting ages range from approximately 14 ka to 2 ka and show that deep seated landsliding has occurred throughout the post glacial period this broad range in ages is inconsistent with our initial hypothesis which proposed that landslides were likely the result of debuttressing of glacial walls during glacial retreat furthermore the timing of landslides does not seem to correlate with documented post glacial climatic shifts therefore we conclude that landsliding in the region was the result of wetter than normal periods lasting months to years acting on weak bedrock pre conditioned to failure and prepared by glacial debuttressing our findings suggest that the study area is likely still susceptible to deep seated landsliding and may become even more prone to large scale slope failure if future climate change increases precipitation in the san juan mountains

differential glacio isostatic uplift of crustal blocks at glen roy scotland abstract detailed measurements of the altitudes of the shorelines of former ice dammed lakes in glen roy and vicinity in the scottish highlands prove erroneous the conventional view that former shorelines in areas affected by glacio isostatic uplift are uniformly tilted and or gently warped the measurements demonstrate differential uplift of blocks of the earth s crust the surfaces of some blocks have no detectable tilt whereas others have gradients up to at least 4 6 m km and are tilted in different directions in three areas 0 7 2 0 km long shorelines are distorted by crustal movements all these areas have landslides attributed to earthquakes that accompanied the release of stress in the area of greatest local distortion three shorelines rose about 3 m above their average altitudes for the immediately surrounding area and a fault scarp was produced possibly these local distortions accompanied catastrophic lake drainage by jokulhlaup analogous to crustal movements associated with man made lakes a relationship between crustal movement and the limit of a glacial advance is demonstrated these findings have implications for other parts of the world affected by glacioisostatic uplift

the last ice sheet in north west scotland reconstruction and implications recent models of the last scottish ice sheet suggest that nunataks remained above the ice surface in areas peripheral to the main centres of accumulation this proposition has been investigated on 140 mountains over an area of 10 000 km2 in nw scotland outside the limits of the later loch lomond readvance in this area there is evidence for a single high level weathering limit that separates glacially eroded terrain from higher areas of in situ frost debris this limit occurs at altitudes ranging from 425 to 450 m in the outer hebrides to 950 m on the mainland and is best developed on lithologies that resisted breakdown after ice sheet downwastage interpretation of this weathering limit as a periglacial trimline cut by the last ice sheet at its maximum thickness is supported by 1 joint depth and schmidt hammer measurements that indicate significantly more advanced rock breakdown above the weathering limit 2 a much greater representation of gibbsite a pre late devensian weathering product in the clay fraction of soils above the limit 3 cosmogenic isotope dating of the exposure ages of rock outcrops above and below the limit 4 the sharpness of the limit at some sites and its regular decline along former ice flowlines and 5 shear stress calculations based on the inferred altitude and gradient of the former ice surface reconstruction of the ice surface based on trimline evidence indicates that the mainland ice shed lay near or slightly east of the present watershed and descended northwards from 900 m to ca 550 m at the north coast independent dispersion centres fed broad ice streams that occupied major troughs on skye an ice dome 800 m deflected the northwestwards movement of mainland ice but the mountains of rum were over ridden by mainland ice up to an altitude of ca 700 m the outer hebrides supported an independent ice cap that was confluent with mainland ice in the minches extrapolation of the trimline evidence indicates that most reconstructions of ice extent are too conservative and suggests that low gradient ice streams extended across the hebridean shelf offshore wider implications of this research are 1 that blockfields and other periglacial weathering covers are not all of the same age or significance depending on the resistance of different lithologies to frost weathering 2 that the contrasting degree of glacial modification in the western and eastern highlands of scotland may reflect a former cover of predominantly warm based ice in the former and predominantly cold based ice in the latter and 3 that the approach and techniques developed in this study have potential application for constraining ice sheet models not only in areas peripheral to the main centres of ice accumulation in britain and ireland but also in other mountain areas where nunataks protruded through warm based late pleistocene ice masses

relict rock glaciers and protalus lobes in the british isles implications for late pleistocene mountain geomorphology and palaeoclimate many relict rock glaciers and protalus lobes have been described in mountainous areas of the british isles this paper reviews their distribution chronology supposed origin and development and places the research within current investigations and knowledge rock glaciers and protalus lobes are located in a number of different topographic locations and settings they developed at the base of steep cliffs following the catastrophic failure of rock faces at the base of scree slopes following the gradual accumulation of rock debris and in association with glaciers protalus lobes probably developed in response to the permafrost creep of talus material while rock glaciers formed through the deformation and sliding of large bodies of buried ice rock glaciers probably developed or were last active during the younger dryas although the possibility exists that some of these landforms are dimlington stadial in age the development of protalus lobes during the younger dryas suggests that precipitation levels were low and permafrost was widespread during this time the lack of rock glaciers sensu stricto in the british isles compared with other mountain areas is believed to be a consequence of the rock type and relative scarcity of weathered debris for their formation rather than a lack of suitable sites or appropriate environmental conditions copyright 2007 john wiley sons ltd

the effect of the extent of freezing on seismic velocities in unconsolidated permafrost we develop a model to relate velocities of seismic waves in unconsolidated permafrost is idealized as an assemblage of spherical quartz grains imbedded in a matrix composed of spherical water inclusions in ice the theory of kuster and toksoz based on wave scattering considerations is used to determine the effective elastic moduli and hence the wave speeds the hasin shtrikman theoretical bounds on the elastic moduli of heterogeneous materials and considerations establish the plausibility of the model the model predicts vp and vs to be decreasing functions of both the porosity and the water to ice ratio and the ratio vp vs to be an increasing function of these two parameters the theory is then applied to laboratory measurements of shear and compressional wave velocities in 23 permafrost samples from different sites in the beaufort sea mackenzie river valley and canadian arctic islands although no direct measurements were made of the extents of freezing in these samples the data are consistent w

long term dynamics of rockslides and damage propagation inferred from mechanical modeling 1 long term observations of large active rockslides show accelerating deformation over many thousands of years since the last deglaciation the effect of deglaciation on slope stability is however poorly understood due to 1 limited long term observations and 2 a complex interaction between glacier retreat and hydrogeological mechanical and morphological processes to assess the sensitivity of rockslide dynamics to these different processes a model of progressive damage through intact rock mass is developed in this study based on the finite element method this model uses time to failure laws based on rock laboratory creep experiments it is able to reproduce progressive damage localization along shear bands associated with strain rate acceleration as observed during tertiary creep the model reproduces the different phases of deformation associated with morphologies typical of large rockslides this model is thus suitable for simulating the dynamics of large rockslides and the transition from initiation to rapid sliding the sensitivity of rockslide kinematics and morphology to different mechanical properties is analyzed this analysis shows that the time evolution of the rockslide can be inferred with the knowledge of only one time parameter independent of the knowledge of the mechanical properties of the rock mass this parameter is here chosen as the time when the summit slope displacement has reached 10 m a parameter that can be estimated with cosmogenic dating the model is then used to study the effects of deglaciation on the valley flank stability and the formation of large rockslides this study shows that the deglaciation velocity can affect the morphology of the rockslide with the shear band of the rockslide emerging at higher elevation as the velocity decreases we also show that the response to the deglaciation can last several thousands of years after the glacier retreat

the hofðaholar rock avalanche sturzstrom chronological constraint of paraglacial landsliding on an icelandic hillslope the hof aholar rock avalanche in the skagafjor ur area of northern iceland was investigated on the basis of a geomorphological analysis of its landforms and close surrounding environment thanks

quaternary sedimentation of the alaskan beaufort shelf influence of regional tectonics fluctuating sea levels and glacial sediment sources abstract the offshore stratigraphy of the quaternary gubik formation of arctic alaska has been studied on high resolution seismic profiles with a maximum sub seafloor penetration of about 100 m in general marine transgressive subunits of the gubik formation are wedge shaped on the shelf thickening slightly seaward to the shelf break beyond which they are offset by landslides and slumps beneath the eastern third of the alaskan beaufort shelf active folding has created two persistent structural depressions the eastern and western wedge terranes in which the wedge morphology is especially well developed the youngest transgressive marine wedge which was deposited in such a way as to fill these depressions leaving a generally flat present day shelf surface is inferred to be late wisconsin or younger in age because it overlies a prominent disconformity interpreted to have been formed during the late wisconsin glacial sea level minimum the thickness of this youngest wedge unit a locally exceeds 40 m on the outer shelf yet apparently relict gravel deposits collected from its seabed surface indicate that the depositional rate is presently quite low on the middle and outer shelf lithologies of the gravels are exotic to alaska but similar to suites exposed in the canadian arctic islands these observations suggest a depositional scenario in which the retreating laurentide ice sheet shed sediment laden icebergs from the canadian arctic islands into the arctic ocean following the late wisconsin glacial maximum these bergs were then rafted westward by the beaufort gyre and grounded on the alaskan shelf by northeasterly prevailing winds especially large numbers of bergs accumulated in the wedge terrane embayments created as sea level rose and melted there filling the embayments with their sedimentary cargo as glacial retreat slowed depositional rates on the shelf dwindled this mode of deposition in the alaskan beaufort wedge terranes may be typical of early post glacial transgressive phases throughout quaternary time it has resulted in the preservation of disconformities that apparently formed during glacioeustatic lowstands and whose seaward termination depths appropriately corrected may yield estimates of lowstand magnitudes knowledge of global sea level fluctuations back through the sangamon interglacial oxygen isotope stage 5e and possible correlations with dated onshore deposits have facilitated a tentative correlation of major disconformities in the beaufort sea record with major 18 o enrichment maxima in the oxygen isotope curve back through stage 8 in this tentative scheme close similarities between the two data sets occur both in magnitudes and in numbers of fluctuations intervening between major correlation points further testing of the quaternary depositional model suggested here and of the resulting sea level curve awaits the collection and dating of core samples from the beaufort wedge terranes

evidence for active retreat of a coastal cliff between 3 5 and 12 ka in cassis south east france this study on the cap canaille cliff n 43 19 e 5 55 cassis se france combines cosmic ray exposure cre dating using two cosmogenic nuclides in situ produced 10be and 36cl and morphological analyses to gain a better understanding of a major coastal cliff collapse event morphological analysis reveals evidence cliff morphology presence of big collapsed blocks of a possible major collapse of cap canaille in the past aerial pictures and gis software allow estimation of a potential collapsed volume of at least 7 106 m3 of which roughly 6 106 m3 fell into the mediterranean sea in situ produced 10be and 36cl concentrations were measured in samples collected on collapsed block surfaces and in situ produced 10be was measured along the cliff face to date the last major collapse event statistical analysis of the cre ages calculated from cliff samples shows that these ages cluster around 3 5 and 6 7 ka suggesting the existence of a two step past major collapse the older ages obtained at 9 and 12 ka coincides with the approach of present day sea level implying a control of sea level on the cliff retreat the cre ages calculated from collapsed block samples are more scattered toward younger ages due to several geomorphological factors the estimated collapsed volume associated with the last major collapse around 3 5 ka seems sufficient to have triggered a local tsunami in the cassis bay if it fell at once into the sea

minimum distribution of subsea ice bearing permafrost on the u s beaufort sea continental shelf 1 starting in late pleistocene time 19 ka sea level rise inundated coastal zones worldwide on some parts of the present day circum arctic continental shelf this led to flooding and thawing of formerly subaerial permafrost and probable dissociation of associated gas hydrates relict permafrost has never been systematically mapped along the 700 km long u s beaufort sea continental shelf and is often assumed to extend to 120 m water depth the approximate amount of sea level rise since the late pleistocene here 5 000 km of multichannel seismic mcs data acquired between 1977 and 1992 were examined for high velocity 2 3 km s 1 refractions consistent with ice bearing coarse grained sediments permafrost refractions were identified along 5 of the tracklines at depths of 5 to 470 m below the seafloor the resulting map reveals the minimum extent of subsea ice bearing permafrost which does not extend seaward of 30 km offshore or beyond the 20 m isobath

offshore permafrost decay and massive seabed methane escape in water depths 20 m at the south kara sea shelf 1 since the last glacial maximum 19 ka coastal inundation from sea level rise has been thawing thick subsea permafrost across the arctic although subsea permafrost has been mapped on several arctic continental shelves permafrost distribution in the south kara sea and the extent to which it is acting as an impermeable seal to seabed methane escape remains poorly understood here we use 1300 km of high resolution seismic data to map hydroacoustic anomalies interpreted to record seabed gas release on the west yamal shelf gas flares are widespread over an area of at least 7500 km2 in water depths 20 m we propose that continuous subsea permafrost extends to water depths of 20 m offshore and creates a seal through which gas cannot migrate this arctic shelf region where seafloor gas release is widespread suggests that permafrost has degraded more significantly than previously thought

modeling the evolution of climate sensitive arctic subsea permafrost in regions of extensive gas expulsion at the west yamal shelf thawing subsea permafrost controls methane release from the russian arctic shelf having a considerable impact on the climate sensitive arctic environment expulsions of methane from shallow russian arctic shelf areas may continue to rise in response to intense degradation of relict subsea permafrost here we show modeling of the permafrost evolution from the late pleistocene to present time at the west yamal shelf modeling results suggest a highly dynamic permafrost system that directly responds to even minor variations of lower and upper boundary conditions e g geothermal heat flux from below and or bottom water temperature changes from above permafrost scenarios of permafrost evolution show a potentially nearest landward modern extent of the permafrost at the west yamal shelf limited by 17 m isobaths whereas its farthest seaward extent coincides with 100 m isobaths the model also predicts seaward tapering of relict permafrost with a maximal thickness of 275 390 m near the shoreline previous field observations detected extensive emissions of free gas into the water column at the transition zone between today s shallow water permafrost 20 m the model adapts well to corresponding heat flux and ocean temperature data providing crucial information about the modern permafrost conditions it shows current locations of upper and lower permafrost boundaries and evidences for possible release of methane from the seabed to the hydrosphere in a warming arctic

subsea ice bearing permafrost on the u s beaufort margin 2 borehole constraints borehole logging data from legacy wells directly constrain the contemporary distribution of subsea permafrost in the sedimentary section at discrete locations on the u s beaufort margin and complement recent regional analyses of exploration seismic data to delineate the permafrost s offshore extent most usable borehole data were acquired on a 500 km stretch of the margin and within 30 km of the contemporary coastline from north of lake teshekpuk to nearly the u s canada border relying primarily on deep resistivity logs that should be largely unaffected by drilling fluids and hole conditions the analysis reveals the persistence of several hundred vertical meters of ice bonded permafrost in nearshore wells near prudhoe bay and foggy island bay with less permafrost detected to the east and west permafrost is inferred beneath many barrier islands and in some nearshore and lagoonal back barrier wells the analysis of borehole logs confirms the offshore pattern of ice bearing subsea permafrost distribution determined based on regional seismic analyses and reveals that ice content generally diminishes with distance from the coastline lacking better well distribution it is not possible to determine the absolute seaward extent of ice bearing permafrost nor the distribution of permafrost beneath the present day continental shelf at the end of the pleistocene however the recovery of gas hydrate from an outer shelf well belcher and previous delineation of a log signature possibly indicating gas hydrate in an inner shelf well hammerhead 2 imply that permafrost may once have extended across much of the shelf offshore camden bay

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

large rockslides in the southern central andes of chile 32 34 5 s tectonic control and significance for quaternary landscape evolution abstract the distribution and age of large 0 1 km2 pliocene to recent rockslides in the chilean cordillera principal 32 34 5 s the southern central andes has been analyzed to determine the rockslide triggering mechanisms and impact on regional landscape evolution most of the rockslides appear in the western cordillera principal and cluster along major geological structures variographic analyses show spatial correlation between rockslides geological structures and shallow seismicity a relative chronosequence was calibrated with existing 14c and 40ar 39ar dates and new cosmogenic nuclide exposure ages for selected rockslides rockslide induced sediment yield was estimated with empirical relations for rockslide area distributions throughout the quaternary rockslides have delivered sediment to streams at rates equivalent to denudation rates of 0 10 0 06 mm a 1 while estimates using short term 20 a seismicity records are 0 3 0 2 0 6 mm a 1 the estimates of sediment transfer and the spatial distribution of rockslides reflect a landscape in which tectonic and geological controls on denudation are more significant than climate

modeling sub sea permafrost in the east siberian arctic shelf the laptev sea region 1 models of sub sea permafrost evolution vary significantly in employed physical assumptions regarding the paleo geographic scenario geological structure thermal properties initial temperature distribution and geothermal heat flux this work aims to review the underlying assumptions of these models as well as to incorporate recent findings and hence develop an up to date model of the sub sea permafrost dynamics at the laptev sea shelf in particular the sub sea permafrost model developed here incorporates thermokarst and land ocean interaction theory and shows that the sediment salinity and a temperature based parametrization of the unfrozen water content are critical factors influencing sub sea permafrost dynamics from the numerical calculations we suggest development of open taliks may occur beneath submerged thaw lakes within a large area of the shelf

permafrost associated natural gas hydrate occurrences on the alaska north slope abstract in the 1960s russian scientists made what was then a bold assertion that gas hydrates should occur in abundance in nature since this early start the scientific foundation has been built for the realization that gas hydrates are a global phenomenon occurring in permafrost regions of the arctic and in deep water portions of most continental margins worldwide in 1995 the u s geological survey made the first systematic assessment of the in place natural gas hydrate resources of the united states that study suggested that the amount of gas in the gas hydrate accumulations of northern alaska probably exceeds the volume of known conventional gas resources on the north slope researchers have long speculated that gas hydrates could eventually become a producible energy resource yet technical and economic hurdles have historically made gas hydrate development a distant goal this view began to change in recent years with the realization that this unconventional resource could be developed with existing conventional oil and gas production technology one of the most significant developments was the completion of the bpxa doe usgs mount elbert gas hydrate stratigraphic test well on the alaska north slope which along with the mallik project in canada have for the first time allowed the rational assessment of gas hydrate production technology and concepts almost 40 years of gas hydrate research in northern alaska has confirmed the occurrence of at least two large gas hydrate accumulations on the north slope we have also seen in alaska the first ever assessment of how much gas could be technically recovered from gas hydrates however significant technical concerns need to be further resolved in order to assess the ultimate impact of gas hydrate energy resource development in northern alaska

rock slope failure following late pleistocene deglaciation on tectonically stable mountainous terrain the ages of 31 postglacial rock slope failures rsfs in scotland and nw ireland derived from 89 cosmogenic isotope exposure ages are employed to analyse the temporal pattern of failure and its relationship to the timing of deglaciation rates of glacio isostatic crustal uplift and periods of rapid climate change rsf ages span almost the whole period since ice sheet retreat from 18 2 1 2 ka to 1 7 0 2 ka or from 17 1 1 0 ka to 1 5 0 1 ka depending on the production rate used in 10 be age calculation but catastrophic failure of rock slopes was w4 6 times more frequent prior to w11 7 ka than during the holocene 95 of dated rsfs at sites deglaciated during retreat of the last ice sheet occurred within w5400 years after deglaciation with peak rsf activity 1600e1700 years after deglaciation this time lag is inferred to represent 1 stress release initiated by deglacial unloading leading to 2 time dependent rock mass strength degradation through progressive failure plane development and ultimately 3 to either spontaneous kinematic release or failure triggered by some extrinsic mechanism by contrast 11 dated rsfs at sites reoccupied by glacier ice during the younger dryas stade yds of w12 9e11 7 ka exhibit no clear temporal pattern suggesting that glacial reoccupance during the yds was ineffective in preconditioning a renewed cycle of enhanced rsf activity comparison of timing of individual rsfs with that of deglaciation and rapid warming events at w14 7 ka and w11 7 ka suggests that glacial debuttressing enhanced joint waterpressuresduringdeglaciationandthawofpermafrosticeinrockjointscouldhavetriggeredfailurein only a small number of cases conversely the timing of maximum rsf activity following ice sheet deglaciation corresponds broadly with maximum rates of glacio isostatic crustal uplift suggesting that the two are linked by enhanced seismic activity a seismic failure trigger is consistent with full slope failure at all sites where failure planes are clearly defined our results indicate that numerous rsfs must have occurred in areas that were reoccupied by glacier ice during the yds but have not been identified because runout debris was removed by yds glaciers more generally they provide the first reliably dated body of evidence to support the view that retreat of the last ice sheets in tectonically stable mountainous terrain initiated a period of enhanced rock slope failure due to deglacial unloading and probably lateglacial seismic activity implying that most undated rsfs in such areas are probably of lateglacial or veryearly holocene age they also demonstrate however that a low frequency of rsf activity extended throughout the holocene

cosmogenic cl 36 dating of postglacial landsliding at the storr isle of skye scotland major postglacial rock slope failures are a common feature of the scottish highlands and other mountainous areas that were deglaciated at the end of the pleistocene but evaluation of the causes and triggers of failure has been hindered by a lack of reliable dating evidence we report the result of a pilot study designed to establish the absolute age of a large postglacial rotational rockslide at the storr on the isle of skye scotland using 36cl surface exposure dating exposure ages of 6 3 0 7 cal ka bp and 6 6 0 8 cal ka bp were obtained for rock samples from two separate landslide blocks giving an overall age estimate of 6 5 0 5 cal ka bp for rock slope failure at this site this date is consistent with ams radiocarbon dating of windblown sand derived from the failure scarp and with previous inferences based on relative dating evidence concerning an early holocene age for most rock slope failures in the scottish highlands the long time lag 7 ka between deglaciation and failure sugge

impacts of post glacial rebound on landslide spatial distribution at a regional scale in northern iceland skagafjorður in de glaciated areas para glaciation i e the conditioning of landscapes by prior glaciation has often been considered a major predisposing factor in landslide occurrence its consequences have been particularly well identified at a fine scale especially on bedrock jointing hitherto the relative impacts of para glaciation on hillslope dynamics at a regional scale had nevertheless not been quantified statistically we examine skagafjor ur area northern iceland where landslides are widespread at least 108 were mapped in an area of c 3000km2 we compare the role of para glaciation debuttressing influence of post glacial rebound with that of classic factors topography lithology etc in landslide occurrence and location using a spatial analysis based on a chi square test on the one hand the results highlight that landslides are over represented in areas where post glacial rebound was at its maximum with a stronger concentration of landslides in the northern part of the fjord on the other hand the distribution of landslides did not show any clear relationship with the pattern of glacial debuttressing tschuprow coefficient highlights that the influence of post glacial rebound on landslide location is higher than the combined influence of slope gradient curvature or geological structure this result is supported by our initial evidence for the timing of landslides in the area most landslides occurred during the first half of the holocene and a period of hillslope instability was initiated when the post glacial uplift was at its maximum finally the mechanisms that link post glacial rebound and landsliding as well as the geomorphic impacts of landslides are discussed

recent fault movement and palaeoseismicity in western scotland abstract field study at two locations in western scotland is described and gives evidence for fault movement and seismic activity during the late and post glacial epochs the evidence comprises levelling survey of raised marine shorelines remote sensing study of lineaments radiocarbon dating of quaternary sediment and detailed field examination of faults and fault gouge material vertical fault displacements of up to 3 m are observed on a c 10 500 year old raised marine shoreline on the isle of mull and repeated predominantly lateral movement is observed on a prominent 14 km long fault lineament active since ice retreat and as recently as c 2000 yrs b p the fault movements are located close to the edge of the area formerly covered by the loch lomond readvance ice cap 11 000 10 000 yrs b p they are considered to have been caused by rapid rates of isostatic rebound soon after deglaciation

sequence stratigraphy of cenozoic continental rocks southwestern montana because the presently used bozeman group lithostratigraphy is difficult to apply to cenozoic basin fill rocks in the jefferson beaverhead melrose and divide valleys southwestern montana we advocate the use of sequence stratigraphy surface sequence boundaries are in many cases marked by calcic paleosol zones these zones can be projected into the subsurface and tied to seismic reflection data density velocity contrasts between calcic paleosol zones and overlying nonpedogenic rocks generate bright reflectors that define sequence boundaries sequence boundary delineation is further enhanced by reflection termination patterns similar to those found in marine strata sequence age calibration is based upon vertebrate fossil and radiometric age data five sequences separated by basin wide unconformities are recognized most sequence bounding unconformities are marked by paleosols an occurrence not previously reported for cenozoic strata of southwestern montana the sequences and their age ranges are 1 bridgerian uintan approximately 50 to 44 ma calc alkaline volcanic flows and interstratified sedimentary rocks 2 duchesnian to whitneyan approximately 42 to 30 ma terrestrial sedimentary and volcanic rocks 3 arikareean approximately 27 to 21 ma terrestrial sedimentary and volcanic rocks 4 barstovian to blancan approximately 16 to 4 ma terrestrial sedimentary and volcanic rocks and 5 early quaternary approximately 1 8 ma to holocene terrestrial sedimentary and volcanic rocks

recent climatic change and catastrophic geomorphic processes in mountain environments climatic warming during the last 100 150 years has resulted in a significant glacier ice loss from mountainous areas of the world certain natural processes which pose hazards to people and development in these areas have accelerated as a result of this recent deglaciation these include glacier avalanches landslides and slope instability caused by glacier debuttressing and outburst floods from moraine and glacier dammed lakes in addition changes in sediment and water supply induced by climatic warming and glacier retreat have altered channel and floodplain patterns of rivers draining high mountain ranges the perturbation of natural processes operating in mountain environments caused by recent climatic warming ranges from tens of decades for moraine dam failures to hundreds of years or more for landslides the recognition that climatic change as modest as that of the last century can perturb natural alpine processes has important implications for hazard assessment and future development in mountains even so these effects are probably at least an order of magnitude smaller than those associated with late pleistocene deglaciation ca 15 000 to 10 000 years ago

are there any relict rock glaciers in the british mountains the existence of a small population of relict rock glaciers scattered across the main british mountain areas has previously been inferred from published cases of individual sites or local clusters discrete debris accumulations ddas of widely differing character have been identified as ice debris landforms whether rock glaciers or protalus lobes partly from morphological sedimentological and topo locational evidence but principally by analogy with both active and relict examples in present day arctic alpine environments with consequent palaeoclimate inferences however re interpretation of several supposed rock glaciers as rock slope failures has cast doubt on both the palaeoclimatic reconstructions and the origin of the remaining features issues of polygenesis and mimicry equifinality have contributed to some previous misidentifications we re evaluate the 28 candidate cases based on new field and image analysis evidence and place them on a continuum from no ice presence through passive ice presence and glacial shaping to emplacement onto glacier ice with consequent melt out topography a null hypothesis approach that there are no relict rock glaciers in the british mountains is pursued and the evidence indicates that none of the 28 cases clearly warrants classification as a relict rock glacier their characteristics can be explained without recourse to any significant forward debris movement controlled or facilitated by incorporated or underlying ice as it deforms and melts out however only one third of the candidate ddas are attributed in whole or part to rock slope failure sensu stricto with other debris sources including incremental rockfall bedrock knolls with coarse debris veneer protalus rampart and moraine a few cases deserve more detailed investigation of their structure morphology and sediments within a broader local glaciological topographical context with multitemporal polygenetic evolution in mind but it is for future researchers to demonstrate that deforming ice played an incontestable part in shaping these often enigmatic ddas given that other causes are simpler and commoner copyright 2013 john wiley sons ltd

a chronostratigraphy of mid and late holocene slope evolution creagan a chaorainn northern highlands scotland unusual exposure of the drift stratigraphy of a typical vegetated hillslope in the northern highlands of scotland has allowed reconstruction of its holocene history graphic logging of palaeogully fill sediment analysis radiocarbon dating and microscopic investigation of horizon boundaries link periodic slope instability to changes in hydrology and vegetation cover the oldest preserved organic matter dates from about 7 5 cal ka bp several millennia of subsequent stability were followed at about 4 3 cal ka bp by destabilization whose magnitude and frequency markedly increased after about 2 7 cal ka bp precipitation driven weathering and erosion offer the best explanation for late holocene slope rejuvenation at this site with change effected through long lasting shifts in system equilibria as well as high magnitude inputs anthropogenic impacts on slope stability are apparently restricted to the last few hundred years the timing and episodicity of slope evolution suggests climate forcing resu

the beinn alligin rock avalanche nw scotland cosmogenic 10be dating interpretation and significance a tongue of very coarse rockslide debris that extends 1 25km downvalley below beinn alligin in nw scotland has been variously interpreted as a glacier cored rock glacier landslide debris redistributed by glacier ice or an excess runout landslide exposure dating with cosmogenic 10be demonstrates that the the debris mass was emplaced at 3950 320 yr bp and therefore was not associated with glacier ice calculations based on frictional considerations imply that the feature is an excess runout rock avalanche sturzstrom deposit the morphological characteristics of the deposit appear consistent with movement by grainflow or fragmental flow failure is inferred to reflect time dependent paraglacial stress release and consequent propagation of an internal joint network but may have been triggered by seismic activity the late holocene age of failure implies persistence of the e ects of paraglacial stress release over a time scale of several millennia

age evaluation and causation of rock slope failures along the western margin of the antrim lava group alg northern ireland based on cosmogenic isotope 36cl surface exposure dating the temporal pattern of postglacial rock slope failure in a glaciated upland area of ireland the western margin of the antrim lava group was evaluated using both 36cl exposure dating of surface boulders on run out debris and 14c dating of basal organic soils from depressions on the debris the majority of the 36cl ages 21 15 ka indicate that major failures occurred during or immediately following local deglaciation 18 17 ka other ages 14 9 ka suggest some later smaller scale failures during the lateglacial and or early holocene the 14c ages 2 36 0 15 cal ka bp indicate the very late onset of organic accumulation and do not provide close limiting age constraints rock slope failure during or immediately following local deglaciation was probably in response to some combination of glacial debuttressing slope steepening and paraglacial stress release later failures may have been triggered by seismic activity associated with glacio isostatic crustal uplift and or permafrost degradation consequent upon climate change the 36cl ages support the findings of previous studies that show the deglacial lateglacial period in northwest ireland and scotland to have been one of enhanced rock slope failure

origin of pingo like features on the beaufort sea shelf and their possible relationship to decomposing methane gas hydrates 1 the arctic shelf is currently undergoing dramatic thermal changes caused by the continued warming associated with holocene sea level rise during this transgression comparatively warm waters have flooded over cold permafrost areas of the arctic shelf a thermal pulse of more than 10 c is still propagating down into the submerged sediment and may be decomposing gas hydrate as well as permafrost a search for gas venting on the arctic seafloor focused on pingo like features plfs on the beaufort sea shelf because they may be a direct consequence of gas hydrate decomposition at depth vibracores collected from eight plfs had systematically elevated methane concentrations rov observations revealed streams of methane rich gas bubbles coming from the crests of plfs we offer a scenario of how plfs may be growing offshore as a result of gas pressure associated with gas hydrate decomposition

slope instability in relation to glacial debuttressing in alpine areas upper durance catchment southeastern france evidence from field data and 10be cosmic ray exposure ages the upper durance catchment is an area prone to rock slope failures such failures reflect the combination of high relief litho structural controls and paraglacial stress release the aim of this study is to determine the role of deglacial unloading and resulting paraglacial stress release in conditioning or triggering slope failure former dimensions of the durance glacier are reconstructed then combined with digital elevation model data in a raster geographic information system to quantify the spatial pattern of stresses associated with glacial loading at the last glacial maximum preliminary calculations suggest that major rock falls and rock avalanches are associated with areas subject to the highest decompression stresses focus on two case studies allows the consequences of paraglacial stress release on slope instability to be evaluated description of slope failure runout deposits allows reconstruction of the nature of slope failure surface exposure dates based on concentration of cosmogenic 10be allows the timing of both deglaciation and that of post glacial rock slope failures to be established it is shown that rock slope failures are concentrated on lower valley side slopes within the area occupied by ice at the last glacial maximum and that their locations coincide with zones of inferred high glacial loading stress consistent with interpretation of both bedrock disruption and large scale rock slope failures as paraglacial phenomena induced by stress release following deglaciation timing of initial rock avalanche runout deposition at one site is consistent with this conclusion though later instability episodes at the same site may have occurred independent of the influence of paraglacial stress release

large scale landslide simulations global deformation velocities and basal friction the cause of the apparent small friction exhibited by long runout landslides has long been speculated upon in an attempt to provide some insight into the matter this paper describes results obtained from a discrete particle computer simulation of landslides composed of up to 1 000 000 two dimensional discs while simplified the results show many of the characteristics of field data the volumetric effect on runout preserved strata etc and with allowances made for the two dimensional nature of the simulation the runouts compare well with those of actual landslides the results challenge the current view that landslides travel as a nearly solid block riding atop a low friction basal layer instead they show that the mass is completely shearing and indicate that the apparent friction coefficient is an increasing function of shear rate the volumetric effect can then be understood with all other conditions being equal different size slides appear to travel with nearly the same average velocity however as the larger landslides are thicker they experience smaller shear rates and correspondingly smaller fractional resistance

subsea ice bearing permafrost on the u s beaufort margin 1 minimum seaward extent defined from multichannel seismic reflection data subsea ice bearing permafrost ibpf and associated gas hydrate in the arctic have been subject to a warming climate and saline intrusion since the last transgression at the end of the pleistocene the consequent degradation of ibpf is potentially associated with significant degassing of dissociating gas hydrate deposits previous studies interpreted the distribution of subsea permafrost on the us beaufort continental shelf based on geographically sparse datasets and modeling of expected thermal history the most cited work projects subsea permafrost to the shelf edge 100 m isobath this study uses a compilation of stacking velocity analyses from 100 000 line km of industry collected multichannel seismic reflection data acquired over 57 000 km2 of the us beaufort shelf to delineate continuous subsea ibpf gridded average velocities of the uppermost 750 ms two way travel time range from 1475 to 3110 m s 1 the monotonic cross shore pattern in velocity distribution suggests that the seaward extent of continuous ibpf is within 37 km of the modern shoreline at water depths 25 m these interpretations corroborate recent beaufort seismic refraction studies and provide the best margin scale evidence that continuous subsea ibpf does not currently extend to the northern limits of the continental shelf this article is protected by copyright all rights reserved

methane release from pingo like features across the south kara sea shelf an area of thawing offshore permafrost the holocene marine transgression starting at 19 ka flooded the arctic shelves driving extensive thawing of terrestrial permafrost it thereby promoted methanogenesis within sediments the dissociation of gas hydrates and the release of formerly trapped gas with the accumulation in pressure of released methane eventually triggering blowouts through weakened zones in the overlying and thinned permafrost here we present a range of geophysical and chemical scenarios for the formation of pingo like formations plfs leading to potential blowouts specifically we report on methane anomalies from the south kara sea shelf focusing on two plfs imaged from high resolution seismic records a variety of geochemical methods are applied to study concentrations and types of gas its character and genesis plf 1 demonstrates ubiquitously low methane concentrations 14 2 55 3 ppm that are likely due to partly unfrozen sediments with an ice saturated internal core reaching close to the seafloor in contrast plf 2 reveals anomalously high methane concentrations of 120 000 ppm where frozen sediments are completely absent the methane in all recovered samples is of microbial and not of thermogenic origin from deep hydrocarbon sources however the relatively low organic matter content 0 52 1 69 of seafloor sediments restricts extensive in situ methane production as a consequence we hypothesize that the high methane concentrations at plf 2 are due to microbial methane production and migration from a deeper source

runout lengths of sturzstroms the control of initial conditions and of fragment dynamics sturzstroms are giant landslides that travel kilometers within minutes data from terrestrial examples of 0 001 10 km3 suggest that their runout lengths increase in proportion to the square root of their volume this trend is investigated assuming that runout is controlled by fragmental flow the results indicate that runout lengths depend on the potential energy available for motion after initial collapse itself a function of the dimensions of the collapse zone on the degree of rock fragmentation and on the rate of momentum loss by fragment collisions in a basal boundary layer assumed to thicken with time by diffusion a dependence on initial conditions during collapse would explain claims that a minimum volume is required for sturzstroms to form beneath a critical volume insufficient energy is available to initiate fragmental flow and so the unstable mass slumps downslope the drop height h is often similar to the vertical extent of the collapse zone and so is linked by geometry to sturzstrom volume the ratio of h to l the horizontal distance of effective transport normally interpreted as a measure of frictional resistance is thus reinterpreted as an inverse measure of the energy available for runout after collapse by providing a physical basis for observed trends the analysis justifies use of empirical limits for forecasting the runout lengths of major landslides

timing and features of a late mis 2 rock avalanche in the eastern himalayas constrained by 10be exposure dating abstract we investigate a previously unrecorded rock avalanche deposit yadong rock avalanche that resulted from a major mountain slope failure on the northwest slopes of mt chomo lhari in the eastern himalayas we provide detailed mapping of the yadong rock avalanche and date the rock avalanche using 10be surface exposure dating the 10be exposure ages of six samples suggest that the yadong rock avalanche occurred between 14 2 1 3 13 1 1 3 ka during the bolling allerod ba period the climate was semi arid during the ba period as it is today which suggests that precipitation was unlikely the trigger for this rock avalanche the relatively small paleo glaciers make glacial debuttressing trigger unlikely since the rock scar is situated above the lower permafrost limit degradation of permafrost associated with deglaciation was also unlikely to be the trigger given the rock avalanche is located near the yadong fault which is part of the active yadong gulu rift and the yadong gulu rift has experienced great earthquakes on centennial to millennial timescales we suggest that the most probable trigger for this rock avalanche was a seismic event associated with the yadong fault the result provides evidence for identifying a paleo seismic event occurred during 14 2 1 3 13 1 1 3 ka these findings have important implications for understanding the mechanisms for driving rock avalanches and associated landscape evolution across the himalayas as well as for extending the limited scientifically documented records of major mass movements in the eastern himalayan region

effects of submarine groundwater discharge on the present day extent of relict submarine permafrost and gas hydrate stability on the beaufort sea continental shelf we investigate the role of submarine groundwater discharge on the offshore temperature and salinity field and its effect on the present day extent of submarine permafrost and gas hydrate stability on the north american beaufort shelf with a two dimensional numerical model based on the finite volume method this study finds that submarine groundwater discharge can play a large role in submarine permafrost evolution and gas hydrate stability suggesting that local hydrology may control the evolution of submarine permafrost as strongly as does sea level or paleoclimatic conditions submarine permafrost evolution shows transient behavior over potentially long time scales e g several glacial cycles before a balance of density and pressure driven flows is established with the permeability variations imposed by the overlying permafrost layer the detectable offshore permafrost extent is related to the quasi stationary location of the saltwater freshwater transition larger values of submarine groundwater discharge allow permafrost to extend farther offshore because fresh pore water preserves relict ice therefore differences in the permafrost extent at locations that share similar paleoclimatic history may be explained in part by differences in the local hydrology gas hydrate stability on the north american beaufort shelf may be more widespread than currently thought because low ice saturation highly degraded submarine permafrost likely exists beyond the boundary detectable by common geophysical methods

holocene sea level history of the canadian beaufort shelf new radiocarbon ages pertaining to the holocene sea level history of the canadian beaufort shelf are presented the ages were obtained on samples of freshwater and tidal marsh peat beds from offsho

late holocene catastrophic slope collapse affected by deep seated gravitational deformation in flysch ropice mountain czech republic the region of the flysch western carpathians is characterized by abundant deep seated gravitational slope deformations dsgsds this study deals with a detailed analysis of late holocene catastrophic collapse of a fault created slope of mountain ropice in the moravskoslezske beskydy mountains eastern czech republic the catastrophic collapse was initialized by huge compound rotational slide toppling deformation which occurs on the upper part of the studied slope and affects tectonically weakened subhorizontally inclined sandstone beds detailed geomorphological mapping accompanied by morphotectonic analysis and geophysical sounding revealed at least two historic flowslides the older event f1 affected 0 5 0 8 mm3 of bedrock and created a 1000 m long and up to 150 m wide accumulation with abundant transverse steps and a carapace like surface the landslide toe blocked an adjacent valley which led to the development of a small impoundment with 4 m thick deposits containing lacustrine peat bog floodplain and alluvial fan facies radiocarbon dating and pollen analysis indicate the valley blockage at 1 5 ka bp the other flowslide f2 of much smaller dimensions 10 000 12 000 m3 overlaid the main landslide body and according to the dating of minerogenic horizon in the impoundment may have taken place 0 3 ka bp the organisation of landforms character of slope failures and dynamic back modelling point to a likely rock avalanche or combined rock slide debris avalanche mechanism of movement this case study shows that rapid rock avalanches can operate also in mountainous terrain with moderate relief if toppling together with deep seated gravitational deformation of slopes modifies the original stable position of bedding planes