predicting incipient motion including the effect of turbulent pressure fluctuations in the bed 1 incipient motion of particles on a river bed can in principle be understood and predicted from a balance of the forces acting on the particles on a natural river bed the exposure of particles to the flow is variable the effect of exposure on the initiation of motion including the case of deep embedding is studied in this paper so far the turbulence induced lifting force has been derived exclusively from examinations of the surface flow the understanding of destabilization processes of the riverbed is improved when turbulence induced vertical pressure gradients in the upper sediment layer are included this is particularly important for particles that lie in the lee of larger ones an analytical solution for the critical shields parameter of spherical particles is found including the effects of pressure fluctuations in the bed macroscale flow structures average bed slope and shallow flow existing laboratory data designed to test the effect of exposure and roughness conditions are in excellent agreement with the new model

mobility of bed material in harris creek 1 the mobility of bed material is investigated in a small gravel bed river in which the bed is weakly bimodal in texture and relatively stable the bed surface remained intact throughout the freshet and scour was limited to small areas of the bed observations of bedload caught in pit traps and displacement of magnetically tagged particles during two spring freshets permit analysis of the mobility of each size fraction fractional transport rates plot up to three orders of magnitude below the reference transport rate suggested in the literature at low flows no size fraction was fully mobile at intermediate flows shear stress 27 pa sand was fully mobile while larger material remained partially mobile at high flows 43 pa the division between the full and partial mobility regimes occurred around 16 mm which remains finer than the median size of the subsurface material the largest material scarcely moves at mean annual flood magnetic tracers confirmed results obtained from the pit traps three distinct zones of mobility can be defined in fractional transport plots partial mobility full mobility and overpassing suspended critical shear stress for incipient motion varied over an order of magnitude a qualitatively similar result for bimodal sediment was reported by wilcock and mcardell 1993 incipient motion analysis based on the largest grain observed to move yielded an upper envelope implying transport similarity for sizes found on the bed surface and a lower envelope that corresponds with our nonsimilar entrainment criterion

a mixing layer theory for flow resistance in shallow streams 1 a variety of surface roughness characterizations have emerged from nineteenth and twentieth century studies of channel hydraulics when the water depth h is much larger than the characteristic roughness height ks roughness formulations such as manning s n and the friction factor f can be explicitly related to the momentum roughness height zo in the log law formulation for turbulent boundary layers thereby unifying roughness definitions for a given surface however when h is comparable to or even smaller than ks the log law need not be valid using a newly proposed mixing layer analogy for the inflectional velocity profile within and just above the roughness layer a model for the flow resistance in shallow flows is developed the key model parameter is the characteristic length scale describing the depth of the kelvin helmholtz wave instability it is shown that the new theory originally developed for canopy turbulence recovers much of the earlier roughness results for flume experiments and shallow gravel streams this study is the first to provide such a unifying framework between canopy atmospheric turbulence and shallow gravel stream roughness characterization the broader implication of this study is to support the merger of a wealth of surface roughness characterizations independently developed in nineteenth and twentieth century hydraulics and atmospheric sciences and to establish a connection between roughness formulations across traditionally distinct boundary layer types

glacial cirques as palaeoenvironmental indicators their potential and limitations abstract glacial cirques are armchair shaped erosional hollows typified by steep headwalls and often overdeepened floors they reflect former regions of glacier initiation and their distribution is therefore linked to palaeoclimate because of this association cirques can be analysed for the information they provide about past environments an approach that has a strong heritage and has seen resurgence over recent years this paper provides a critical assessment of what cirques can tell us about past environments and considers their reliability as palaeoenvironmental proxies specific focus is placed on information that can be obtained from consideration of cirque distribution aspect altitude and morphometry the paper highlights the fact that cirques potentially provide information about the style duration and intensity of former glaciation as well as information about past temperatures precipitation gradients cloud cover and wind directions in all cirques are considered a valuable source of palaeoenvironmental information if used judiciously particularly as they are ubiquitous within formerly glaciated mountain ranges globally thus making regional or even global scale studies possible furthermore cirques often occupy remote and inaccessible regions where other palaeoenvironmental proxies may be limited or lacking

sediments in palaeo notches potential proxy records for palaeoclimatic changes in antarctica abstract many climatic proxy materials such as ice cores coastal and lacustrine sediments and abandoned penguin rookeries have been used to study palaeoclimatic changes and the palaeoenvironmental evolution of antarctica in this paper we report another geological record well preserved sedimentary sequences in the palaeo notches in marine terraces of fildes peninsula king george island based upon grain size distribution and microtexture geochemical element compositions and radiocarbon dating we identified the sediments in one palaeo notch as lacustrine sediments most likely deposited in a small palaeo lake from these data we inferred that between 4000 and 3000 yr b p a moderate chemical weathering occurred and the climate was warmer and more humid than present in good agreement with the findings from other climatic proxy materials we believe that the sediments in palaeo notches provide another reliable proxy material for studying the palaeoclimate and the palaeoenvironment in antarctica

quaternary glaciations recorded by glacial and fluvial landforms in the shaluli mountains southeastern tibetan plateau abstract the shaluli mountains a tectonically controlled mountain range between the jinsha and yalong river rifts are located in southeastern tibetan plateau in the central shaluli mountains an ice cap of 3600 km 2 once developed on the haizi shan abundant glacial landforms are present on the haizi shan and in the surrounding river valleys together with the outwash terraces in the yazheku river the northeastern part of the haizi shan provides an ideal site to examine the quaternary glacial history of the region sedimentological and morphostratigraphical analysis field mapping and dating by electron spin resonance esr define at least seven major glacier advances in the haizi shan area six major glacier advances likely occurred during marine oxygen isotope stage mis 16 mis 14 12 mis 6 mis 3 early mis 2 and the global last glacial maximum these can be defined on the basis of esr dating and stratigraphical analysis of the glacial landforms in front of the kuzhaori glacial trough on the southern slope of the haizi shan the outwash terraces in the yazheku river also record four major glacier advances which occurred during mis 16 mis 12 mis 6 and mis 2 in addition the moraines preserved on the southwestern part of the haizi shan suggest that a glacial advance likely occurring during the lateglacial the extent of glaciation on the haizi shan decreased with time

quaternary glacial chronology of the kanas river valley altai mountains china the kanas river originates on the southern slope of youyi peak the largest center of modern glaciation in the altai mountains in central asia glaciers advanced and retreated repeatedly during quaternary glacialeinterglacial cycles in the kanas river valley and four moraine complexes and associated glaciofluvial deposits are preserved in the valley optically stimulated luminescence osl dating has been used to determine ages of glaciofluvial deposits sand lenses sandwiched between tills in moraines using a single aliquot regenerative dose sar protocol based on dating results from this and previous studies including 14 c electron spin resonance esr and osl dates and geomorphic relationships the innermost moraine complex was concluded to deposit during the little ice age lia the second akekule moraine complex was deposited during the neoglacial the third kanas moraine complex was deposited during the last glacial cycle marine oxygen isotope stage mis 2e4 and the outermost set of moraines is mis 6 in ages penultimate glaciation the kanas moraine complex could be divided into three subsets iii1 iii2 and iii3 with inferred ages of mis 2 mid mis 3 and mis 4 respectively which is consistent with moraine records from other areas in central asia and climate reconstructions from the guliya ice core the glaciers in the kanas valley at their maximum extents during the lia neoglacial last glaciation and penultimate glaciation were 13 8 km 32 km w100 km and w120 km long respectively

frost weathering versus glacial grinding in the micromorphology of quartz sand grains processes and geological implications abstract micromorphology of quartz sand grains is used to reconstruct processes occurring in the glacial environment and to distinguish the latter from other environments two processes dominate in the glacial environment i e crushing and abrasion or a combination thereof their effect is a wide range of microstructures on the surface of quartz grains e g chattermarks conchoidal fractures and multiple grooves however the periglacial environment also effectively modifies the surface of quartz grains the active layer of permafrost is considered to have a significantly higher contribution to the formation of crushed grains and the number of microstructures resulting from mechanical destruction e g breakage blocks or conchoidal fractures as compared to deposits which are not affected by freeze thaw cycles however only a few microstructures are found in both environments at the same time there are several processes in subglacial environments related to freeze thaw cycles e g regelation congelation basal adfreezing and glaciohydraulic supercooling most likely therefore the role of the glacial environment in the destruction of quartz grains has been misinterpreted and consequently the conclusions regarding environmental processes drawn on the basis of the number of crushed grains and edge to edge contacts are erroneous

incipient sediment motion at high slopes in uniform flow condition 1 this paper reviews the problem of the incipient motion of cohesionless particles in a high sloping water stream a theoretical analysis of the equilibrium of a gravel particle is developed by a deterministic approach with the introduction of the relative degree of exposure of the particle itself to the stream flow the parameter relative degree of exposure relates the positioning of a particle with the upstream one the problem of velocity distribution and the definition of drag coefficient is also revised to better account for low submergence the results of the theory are compared with a series of ad hoc experiments performed by c gregoretti

hydrogeomorphic processes in a steep debris flow initiation zone 1 many debris flows initiate in steep channels 20 degrees yet studies have focused on lower gradient streams where failure is controlled by water height above channel deposits multiple debris flows in a steep channel in ohya landslide central japan were linked to infilling processes i e freeze thaw and dry ravel and partial saturation of accumulated sediment because of very active geomorphic processes in this catchment 39 debris flows were observed in the past 6 yr pre and post event imagery indicates selective transport of finer materials during most debris flows that comprise saturated and unsaturated flows however fluvial sediment processes important in relation to debris flow initiation in gentler channels were minimal critical conditions for the movement of such unsaturated materials are derived by equating shear stress with solid friction of the channel bed

review of the timing and extent of glaciers during the last glacial cycle in the bordering mountains of tibet and in east asia new accelerator mass spectrometry 14c ams14c electron spin resonance esr and thermoluminescence tl dates for glacial successions in tibetan bordering mountains and in east asia show that glacier extent during the early middle mis3 4 parts of the last glacial cycle was larger than that of the late stage mis2 in last glacial cycle glaciation was not synchronous with the north hemisphere ice sheet maxima and changes in oceanic circulation that predominately control global climate there exist three seasonal precipitation patterns that control the accumulation and ablation on glaciers in the study areas areas dominated by westerlies including the east asia coastal islands experience glacier advance mainly because of increased winter precipitation these glaciers expand during glacial stages in contrast in areas dominated by summer precipitation in the interior of mainland except in the monsoonal high precipitation zone in southeast tibet and the hengduan mountain range tend not to develop large glaciers during major glacial stages

unequal mobility of gravel and sand in weakly bimodal river sediments bed load was trapped during flood events over a 20 month period at the lower end of the allt dubhaig a small river in scotland with rapid downstream fining of gravel bed material on a slowly aggrading concave long profile the channel bed near the trap is predominantly gravel with a secondary sand mode total transport in each event depended mainly on peak shear stress rather than duration over a threshold bed load was mainly sand in smaller events bimodal in intermediate events and mainly gravel in the biggest floods mean and maximum grain diameter both increased with peak shear stress but in different ways analysis of fractional transport rates and maximum grain size in relation to peak shear stress suggests that gravel transport is slightly size selective but sand transport is close to equal mobility the slight selectivity in gravel transport is consistent with previous field studies of near equilibrium unimodal beds and supports assumptions made in the numerical model of hoey and ferguson 1994 which successfully simulates the observed amount of downstream fining over the 2 5 km upstream of the bed load trap

esr dating of glacial tills and glaciations in the urumqi river headwaters tianshan mountains china abstract electron spin resonance esr dating of the shangwangfeng the xiawangfeng and the gaowangfeng tills in the headwaters of the urumqi river was carried out using ge centers in quartz grains the shangwangfeng till is dated at 35 3 5 ka bp three dates from the lower portion of the xiawangfeng till are 171 1 17 176 18 and 184 7 18 ka bp respectively and the age of the gaowangfeng till is 459 7 46 ka bp considering the available ages i e 14 c tl and esr and the principles of geomorphology and stratigraphy the shangwangfeng till is determined to be deposited in marine isotopic stage 2 3 mis2 3 the upper part of the xiawangfeng till was formed in mis4 and the lower part was deposited in mis6 the gaowangfang till is the oldest at the head of the urumqi river corresponding to mis12 the age of the gaowangfang till also demonstrates that the tianshan mountains lay at a suitable altitude for a glacial climate at that time when the glaciers on this segment of the mountain began to develop

incipient motion of sand particles on side slopes several criteria have been theoretically proposed for the critical shear stress of noncohesive sediment on side slopes however no laboratory work has ever been done on this problem a theoretical study of the incipient motion of sediment particles on side slopes is presented including the effects of viscous sublayer turbulence and lift force as a special case of level beds the theory describes the experimental values reported by several workers a specially designed rotary wind tunnel permits the evaluation of the critical shear stress on side slopes and the experiment supports the theory these works reveal that the lift force can be neglected in estimating the critical shear stress using the proposed theory if the averaged experimental values are concerned but inclusion of the lift force in the theory is recommended for safety and for describing the lower limit of the possibility of incipient motion

aeolian microtextures in silica spheres induced in a wind tunnel experiment comparison with aeolian quartz abstract microtextures in quartz attributed to aeolian transport principally bulbous edges and abrasion fatigue have seldom been tested in the laboratory under controlled conditions a wind tunnel experiment was conducted using glass spheres 70 sio 2 as a proxy for quartz with the objective of determining the extent of mechanical damage to silica glass transported in a mixture with quartz beach sand the microspheres were microscopically imaged prior to transport in a wind tunnel subjected at velocities ranging from 4 to 13 m s in sequential runs of 10 min the range in velocity is capable of lifting grains into the air column or saltating quartz grains and silica glass spheres to produce mechanical impact i e abrasion commonly experienced in aeolian transport with increasing velocity silica glass spheres which displayed minor imperfections prior to transport began to show significant grain damage exhibiting increasing depth into the silica glass fabric a result of mechanical contact as well as increasing frequency of craters dislodged plates and abrasion fatigue while pits appear earlier in the experiment 8 m s dislodged plates and abrasion fatigue need a threshold velocity of near 10 m s to become more frequent bulbous edges on the grain surface often considered the hallmark of aeolian transport are not seen in the grain population analyzed possibly because of the initial near perfect sphericity of the silica glass spheres the experiment proved that aeolian transport throughout short distances and during a relatively short period of time is enough to imprint significant abrasion marks in microspheres in fact the microtextures produced were fresh surfaces fractures and abrasion that imprinted areas of different sizes a comparison of microtextural imprints on silica glass spheres relative to coastal dune sands was made to better understand energy thresholds required to achieve grain damage

quaternary glacial chronology of the ateaoyinake river valley tianshan mountains china abstract the ateaoyinake river originates on the southern slope of the tumur peak the largest center of modern glaciation in the central tianshan mountains in china six sets of moraines and associated glacial sediments are well preserved in the ateaoyinake river drainage recording a complex history of quaternary glacial cycles and landscape evolution dating the landforms allow the temporal and spatial shifts of past cryosphere and climate to be determined dating of the tills and outwashes was undertaken with electron spin resonance esr and optically stimulated luminescence osl two osl ages date outwash and till to 7 3 0 8 ka and 12 3 1 2 ka respectively the esr ages date six sets of moraines to 3 4 ka 14 27 ka 40 54 ka 55 62 ka 134 4 12 6 ka and 219 7 20 5 ka 440 6 41 7 ka if these are correct ages of deposition they suggest that glaciers advanced during the neoglacial and during marine oxygen isotope stages mis 2 3b 4 6 and 12 the mis 3b moraine was created by a glacier nearly as large as or possibly larger than those of the global last glacial maximum of mis 2 the oldest till belongs to the qingshantou glacial stage its single age is consistent with two published esr ages 459 7 46 and 471 1 ka from the gaowangfeng till near the headwaters of the urumqi river in the eastern tianshan mountains these dates suggest that the central and the eastern segments of the tianshan mountains were high enough to be glaciated by mis 12 the geochronology of the glacial landforms in this valley is the first step towards understanding glacial and landscape evolution in this region furthermore this geochronology and previously published geochronology near the headwaters of the urumqi river provide a temporal framework for examining the rates of landscape evolution in the glaciated regions of the tianshan mountains

reach averaged sediment routing model of a canyon river 1 spatial complexity in channel geometry indicates that accurate prediction of sediment transport requires modeling in at least two dimensions however a one dimensional model may be the only practical or possible alternative especially for longer river reaches of practical concern in river management or landscape modeling we have developed a one dimensional model of the colorado river through upper grand canyon that addresses this problem by reach averaging the channel properties and predicting changes in sand storage using separate source and sink functions coupled to the sand routing model the model incorporates results from the application of a two dimensional model of flow sand transport and bed evolution and a new algorithm for setting the near bed sand boundary condition for sand transported over an exposed bouldery bed model predictions were compared to measurements of sand discharge during intermittent tributary inputs and varying discharges controlled by dam releases the model predictions generally agree well with the timing and magnitude of measured sand discharges but tend to overpredict sand discharge during the early stages of a high release designed to redistribute sand to higher elevation deposits

is the critical shields stress for incipient sediment motion dependent on channel bed slope data from laboratory flumes and natural streams show that the critical shields stress for initial sediment motion increases with channel slope which indicates that particles of the same size are more stable on steeper slopes this observation is contrary to standard models that predict reduced stability with increasing slope due to the added downstream gravitational force processes that might explain this discrepancy are explored using a simple force balance model including increased drag from channel walls and bed morphology variable friction angles grain emergence flow aeration and changes to the local flow velocity and turbulent fluctuations surprisingly increased drag due to changes in bed morphology does not appear to be the cause of the slope dependency because both the magnitude and trend of the critical shields stress are similar for flume experiments and natural streams and significant variations in bed morphology in flumes is unlikely instead grain emergence and changes in local flow velocity and turbulent fluctuations seem to be responsible for the slope dependency due to the coincident increase in the ratio of bed roughness scale to flow depth i e relative roughness a model for the local velocity within the grain roughness layer is proposed based on a 1 d eddy viscosity with wake mixing in addition the magnitude of near bed turbulent fluctuations is shown to depend on the depth averaged flow velocity and the relative roughness extension of the model to mixed grain sizes indicates that the coarser fraction becomes increasingly difficult to transport on steeper slopes

microtextures on quartz grains in tills from antarctica quartz grains of the sand 63 2000 m fractions from tills of oligocene to quaternary age in antarctica were analyzed by scanning electron microscope sem to test the hypothesis that relative ice thickness and distance of transport influence the type and range of microtextures observed on individual grains in this study replicated subsamples were analyzed from tills emplaced by thick glaciers with both short and long transport distances till samples with grains transported over long distances up to several hundred km under thick ice 1000 m were compared with quartz grains from relatively thinner e g 500 m thick outlet glaciers with shorter transport distances 100 km a range of microtextures including subparallel linear fractures conchoidal fractures arc shaped steps grain relief edge sharpness grain angularity and roundness straight and curved grooves crescentic gouges dissolution features precipitation features and presence of adhering particles was used to determine the environmental history of these grains microtextures on sand size clasts including microfractures abrasion etching and coatings can provide important information on paleoenvironmental history including glacier activity and severity of weathering inferred from etching and dissolution features

channel morphology gradient profiles and bed stresses during flood in a step pool channel abstract the stability of a step pool channel is investigated on the basis of measurements during a median annual flood the study reaches range in gradient from 5 to 10 and the flow was 3 m3 s 1 in an 8 m wide channel the estimated shear stress based on the channel gradient was 102 pa which implies that the channel ought to move half meter class boulders calculations of the shear stress using flow resistance equations yield values of about 30 pa these figures imply that the largest boulders in the channel could be moved in fact the channel is stable the effective stress remains well below the threshold to move the large structure forming boulders the steps are stable structures that result from interlocking of the larger stones they are semi randomly located depending on the location of keystones that are deposited in the channel by debris flows or fall out of the banks the high variation in step pool wavelength step height residual pool depth and pool length is indicative of the random nature of step location and structure along a reach there is no convincing evidence that special conditions govern their formation

esr dating of the sediments of the last glaciation at the source area of the urumqi river tian shan mountains china abstract electron spin resonance esr dates were obtained from glacial quartz sands formed during the last glaciation at the source area of the urumqi river tian shan mountains northwestern china esr dating of a basal till interpreted as a subglacial melt out till deposited in an end moraine which was produced in the late stage of the last glaciation is consistent with ages determined through the ams 14c method however dating of the overlying sediment interpreted as supraglacial melt out till associated with the same moraine produced a result that differs from that determined using the ams 14c method subglacial comminution could reset the esr signal thus making esr dating of basal till possible the lower wangfeng group formerly of controversial age was formed ca 50 70 ka during the early stage of the last glaciation it was deposited throughout the main valley as low as 2300 m a s l over a length in excess of 19 km fluvial sandy gravel was deposited in the interstadial between the early and late stages of the last glaciation

calculating bed load transport in steep boulder bed channels 1 steep rough channels occupy a large fraction of the total channel length in mountainous regions most sediment mobilized on hillslopes must pass through these streams before reaching lower gradient channels steep channels have wide grain size distributions that are composed of finer more mobile sediment and large rarely mobile grains the large grains can bear a significant portion of the total shear stress and thereby reduce the stress available to move the finer sediment conventional bed load transport equations often overpredict the sediment flux in steep channels by several orders of magnitude we hypothesize that sediment transport equations overpredict the sediment flux because they do not 1 account for the stress borne by rarely mobile grains 2 differentiate between highly and rarely mobile sediment and 3 account for the limited availability of mobile sediment here we modify a conventional bed load transport equation to include these three effects we use measurements of the flow bed properties and sediment flux in a small steep flume to test this equation we supply gravel at a constant rate through fields of regularly spaced immobile spheres and measure the bed coverage by gravel and sphere protrusion the percent of the sphere that protrudes above the gravel deposit for a given sphere spacing the proportion of the bed covered by gravel increases and the sphere protrusion decreases with greater sediment supply thus bed coverage and immobile grain protrusion may serve as proxies for sediment availability in steep rough streams unlike most transport equations that we tested our modified bed load equation predicts sediment fluxes to within an order of magnitude of the measured values our results demonstrate that accurately predicting bed load transport in steep rough streams may require accounting for the effects of local sediment availability coverage by mobile sediment and drag due to rarely mobile particles

the development of small scale bedforms in tidal environments an empirical model for unsteady flow and its applications dimensions and plan morphology of current ripples are generally considered to vary with flow velocity and grain size recently however it has been shown that for sand of d50 0 095 and 0 238 mm the equilibrium dimensions are identical at all velocities within the stability field of ripples and that the plan form of equilibrium ripples is linguoid on this basis an empirical unsteady flow model has been developed and tested with flume experiments in order to predict ripple development in natural depositional environments the model includes the development of washed out ripples and upper stage plane bed the unsteady flow model explains the development and preservation of small scale bedforms in various tidal environments more accurately than previous models such bedforms can serve therefore as indicators of prevailing hydrodynamic conditions

a critical examination of evidence for a quaternary glaciation in mt laoshan eastern china abstract accurately determining how far south quaternary glaciers existed in eastern china has important implications for understanding global quaternary climate in this study we provide evidence for a colder paleoclimate in the late pleistocene of the laoshan range on the eastern shandong peninsula at 36 05 36 19 n latitude through documentation of erosional and depositional landforms that were possibly formed by glaciation we integrate field observations documenting and mapping the existence of typical glacial cirques glacial horns moraines aretes tarn lakes and other paleoglacial features in mt laoshan with a detailed digital elevation model dem created in an arcgis environment merged with landsat etm imagery to document the spatial relations of these features other features that may or may not be glacial in origin include large boulder fields that could be moraines or debris avalanches and potholes that could have formed beneath glaciers or in river systems additionally some features previously interpreted as glacial features are here re interpreted as weathering related phenomena although some of these features alone provide only weak to moderate evidence for glaciation together the suite of indicators provides strong evidence for sea level glaciation at 36 n in the late pleistocene of eastern china we further integrate the evidence of glaciation with the late pleistocene paleogeography and climate and suggest that the glaciers formed as a result of orographic effects from moist monsoonal breezes crossing a paleolake developed in north china then rising over mt laoshan and dropping their moisture there with a wide desert formed on the leeward side of the mountains

downstream coarsening in headwater channels 1 field data from four mountain drainage basins in western washington document systematic downstream coarsening of median bed surface grain size d50 and a subsequent shift to downstream fining at a drainage area of about 10 km2 analyses of network wide patterns of unit stream power derived from both channel surveys and digital elevation models reveal maximum unit stream power that in all four study areas roughly corresponds with both the grain size maxima and an inflection in the drainage area slope relation thought to represent the transition from debris flow dominated channels to fluvially dominated channels our results support the hypothesis that basin wide trends in d50 are hydraulically controlled by systematic variations in unit stream power in addition to lag deposits forced by mass wasting processes the similar relations found in our four study areas suggest that the tendency for downstream coarsening may be ubiquitous in headwater reaches of mountain drainage basins where debris flow processes set the channel gradient

scanning electron microscopy of pleistocene sands from yamal and taz peninsulas ob river estuary northwestern siberia coastal sediments in the ob river estuary of northwestern siberia are considered to have either glacial and or estuarine alluvial origins one school of thought argues for interconnected ice domes on the continental shelf that linked the fenno scandinavian and siberian ice grosswald thesis another school of thought argues for an estuarine alluvial origin danilov vtyermin thesis the key to solving the problem of the origin of these sediments lies in detailed stratigraphic oxygen 18 and scanning electron microscopic sem analysis of sediments both the stratigraphy and sem results support the hypothesis of very limited pleistocene glacial activity on yamal gydan and taz peninsulas the sem analysis points to a vast majority of rounded quartz grains with v shaped percussion microfractures and a great range of preweathered microtextures the sem microtextures support a fluvial origin for the sediments far removed from any glacial source a companion paper in this volume by fred michel discusses the 18o analysis of ground ice in the area

dynamics of the barents kara ice sheet as revealed by quartz sand grain microtextures of the late pleistocene arctic ocean sediments abstract during the entire quaternary ice sheets advanced and retreated across the circum arctic margins in a series of climate related glacial interglacial cycles it is critical to obtain evaluation of the nature of initiated glaciers at the arctic margins after the pronounced interglacial periods in this study this will be done by inferring from glacially generated quartz sand grain surface microtextures and related sedimentology extracted from the central arctic ocean sediments these microtextures can be correlated with the generation and fluctuations in the extent of the late pleistocene eurasian ice sheet i e barents kara ice sheet the central arctic ocean sediments in the lomonosov ridge having been deposited after the late pleistocene interglaciations and having had no internal hiatuses provide an excellent time window for usage of quartz sand grain surface textures for evaluating possible evolving glaciers and continental ice sheets this is based on the fact that iceberg and sea ice transported quartz sand grains and their mechanically formed surface textures created under high cryostatic stress are diagnostic for glacier thickness and dynamics having been existed in sediment source areas sand sized quartz grains in deep marine sediments favour iceberg or sea ice transportation with characteristic content of microtextures formed prior this transportation the sand grain surface microtextures and their frequencies of the selected submarine lomonosov ridge sediments during marine isotope stage mis 5 to mis 3 are analysed using a scanning electron microscope sem coring during the arctic ocean 96 expedition core 96 12 1pc provided alternating clay to silty clay sediments which are characterised by prominent silt to sand size containing intervals the specific glacial crushing and high cryostatic stress generated features such as high angularity conchoidal fractures steps and sub parallel linear fractures were observed from quartz sand grain surfaces continental ice generation and extent are evident soon after the eemian interglaciation and the following mis 4 stage shows the highest frequencies of glacigenic microtextures the microtexture generation under high cryostatic pressure underneath ice more than 1 km thick can be taken as concurrent signal of the temporal expansion of the northernmost continental ice sheets which could easily have reached the shelf break of the barents kara and western laptev seas during that time

macroscopic and microscopic evidence of quaternary glacial features and esr dating in the daweishan mountain area hunan eastern china whether quaternary glaciers existed in the daweishan mountain area is of great significance to the reconstruction of the quaternary environments in the yangtze valley this study investigated the macroscopic and microscopic features of quaternary glacial features in the daweishan mountain area and applied electron spin resonance esr dating to the clay and gravel sediments to determine their age aster gdem with a resolution of 30 m combined with field investigation recognized the glacial landforms in the daweishan mountain area cirques and firn basins were distinguished using a flat index of f l 2d and a length width ratio of g l w scanning electron microscopy sem identified glacial traces on quartz sand grains of the clay and gravel sediments esr dating of 6 sections showed that the sediments were formed in 2 stages 205 262 ka and 377 425 ka equivalent to the late stage and middle stage of the middle pleistocene respectively there were at least 2 glaciations in the daweishan mountain area in the late stage and middle stage of the middle pleistocene the yangtze valley was influenced by a cold trough and promoted glaciations developed in the daweishan mountain area

quaternary glaciation of the bailang river valley qilian shan abstract the qilian shan on the northeast margin of the qinghai tibetan plateau is weakly influenced by the asian monsoon until recently the quaternary glacial geology of this region has been poorly understood this paper describes a sequence of quaternary glacial deposits in the upper reaches of the bailang river using electron spin resonance esr thermoluminescence tl and radiocarbon dating tills loess buried soils and landforms were dated the oldest till was dated 463 ka bp by esr a younger till and its outwash terrace were dated to 135 and 130 ka bp the loess on this outwash terrace was dated to 141 7 11 4 ka bp at its base and 43 7 3 5 ka bp in its central part by tl dating a buried soil on a younger till was dated at 6920 78 ka bp using 14c the glacial landforms and these dating results show that glacial advances occurred during the little ice age the neoglacial mis 2 4 mis 6 and mis 12 glaciation during mis 12 implies that the qilian mountains were rising coevally with the qinghai tibetan plateau and were probably at a sufficient elevation for glaciation since at least 463 ka bp

the 2011 japanese 9 0 magnitude earthquake test of a kinetic energy wave model using coastal configuration and offshore gradient of earth and beyond abstract based on geological investigations of coastal geometry and stratigraphy offshore gradient variation wave velocity energy and quartz grain microtexture analysis of key sites inundated by tsunamis during the holocene we have developed a postulated model that could be used to assess modern and ancient onshore environmental conditions during tsunami emplacement given that tsunami waves can travel up to 900 km h the kinetic energy of the wave is determined by frictional release on the offshore slope to seabed nearshore sand and sediment supply and coastal geomorphology specifically coast linearity or embayments that constrict wave energy with gentle offshore gradients and relatively linear coastlines the kinetic energy of the tsunami is decreased by friction with the seabed and radiated outward along the coast thus producing reduced flooding of the affected coast and fewer collisions of entrained grains in contrast steep offshore gradients reduce friction to mere milliseconds of wave impact and embayments specifically narrow coastal constrictions increase wave energy both of which increase on land run up heights and importantly to our proposed model grain collision effects damage to quartz grains deposited by tsunamis along coastal extents ranges from slight on linear coasts with gentle offshore gradients to highly resurfaced mineral surfaces on coasts with steep offshore gradients and narrow embayments our model can be further tested through collection analyses and comparison of quartz grains in relatively low and high energy environments of the recently tsunami impacted northeastern coast of japan for example the location of the fukushima nuclear plant along a linear coastline with a less steep offshore gradient may have attenuated the energy of the incoming wave and thus yielding less resurfaced grains when compared to the coastline located to the north of sendai city where coastal embayments of variable size coupled with steep offshore gradients would produce higher energy waves of greater magnitude as attested by greater penetration inland with considerable loss of life and property damage and resulting highly deformed grain surfaces the model could be applicable for assessing modern and ancient coastal environmental conditions on earth and postulated ancient marine conditions on the red planet

variation in the reference shields stress for bed load transport in gravel bed streams and rivers 1 the present study examines variations in the reference shear stress for bed load transport r using coupled measurements of flow and bed load transport in 45 gravel bed streams and rivers the study streams encompass a wide range in bank full discharge 1 2600 m3 s average channel gradient 0 0003 0 05 and median surface grain size 0 027 0 21 m a bed load transport relation was formed for each site by plotting individual values of the dimensionless transport rate w versus the reach average dimensionless shear stress the reference dimensionless shear stress r was then estimated by selecting the value of corresponding to a reference transport rate of w 0 002 the results indicate that the discharge corresponding to r averages 67 of the bank full discharge with the variation independent of reach scale morphologic and sediment properties however values of r increase systematically with average channel gradient ranging from 0 025 0 035 at sites with slopes of 0 001 0 006 to values greater than 0 10 at sites with slopes greater than 0 02 a corresponding relation for the bank full dimensionless shear stress bf formulated with data from 159 sites in north america and england mirrors the relation between r and channel gradient suggesting that the bank full channel geometry of gravel and cobble bedded streams is adjusted to a relatively constant excess shear stress bf r across a wide range of slopes

the extent and chronology of cenozoic global glaciation abstract the quaternary is synonymous with extensive glaciation of earth s mid and high latitudes although there were local precursors significant glaciation began in the latest eocene ca 35 ma in eastern antarctica it was followed by glaciation in mountain areas through the miocene in alaska greenland iceland and patagonia later in the pliocene e g in the bolivian andes and possibly in tasmania and in the earliest pleistocene e g in the alps new zealand iceland and greenland today evidence from both the land and the ocean floors demonstrates that the major continental glaciations outside the polar regions rather than occurring throughout the 2 6 ma of the quaternary were markedly restricted to the last 1 ma 800 ka or less marine isotope stage mis 22 ca 870 880 ka included the first of the major worldwide events with substantial ice volumes that typify the later pleistocene glaciations i e mis 16 12 10 6 4 2

surface textural analysis of quartz grains by scanning electron microscopy sem from sample preparation to environmental interpretation abstract surface microtextures on quartz grains provide an insight into the sedimentary history of clastic sediments not only information on the depositional environment is provided but also in some cases successive sedimentary cycles can be recognised sample preparation and sem imaging are the initial and therefore crucial steps in the study of microtextures a sample preparation procedure using 15 hydrochloric acid and 50 g l tetrasodium pyrophosphate solutions removes most of the grain coatings and adhering particles the study of microtextures on 1300 quartz grains from a wide variety of environments was complemented with the reference works and atlases krinsley and doornkamp 1973 le ribault 1977 higgs 1979 mahaney 2002 to construct an interpretation scheme allowing to differentiate between fluvial marine eolian glacial and diagenetic alteration environments based on microtextures in a case study the known littoral setting of two samples was confirmed by using the interpretation scheme for quartz microtextures furthermore successive reworking of the grains in eolian and intertidal environments was recognised by presenting the research of microtextures from starting point to interpretation new researchers may find this review a useful and practical introduction into the technique

characteristics of turbulent unidirectional flow over rough beds double averaging perspective with particular focus on sand dunes and gravel beds 1 we address some unsolved methodological issues in modeling of natural rough bed flows by critically examining existing approaches that parameterize rough bed flows these often utilize loosely defined variables here we suggest that double averaging in time and in a volume occupying a thin slab in a plane parallel to the mean bed provides a rigorous straightforward alternative that can aid in the parameterization process we further present two examples two dimensional bed form and gravel bed flows we argue that the double averaging approach based on momentum equations should serve as a better methodological basis for modeling phenomenological developments and parameterizations these equations explicitly include drag terms and form induced momentum fluxes due to spatial heterogeneity of the time averaged flow in the near bed region they also provide a solid basis for better definitions of basic flow variables including the shear stress partitioning into turbulent and form induced momentum fluxes skin friction and pressure form drag we show that for a range of rough bed flows the vertical distribution of the double averaged velocity consists of two distinct regions 1 a linear region below roughness tops and 2 a logarithmic region above them