methane fluxes and carbonate deposits at a cold seep area of the central nile deep sea fan eastern mediterranean sea abstract high acoustic seafloor backscatter signals characterize hundreds of patches of methane derived authigenic carbonates and chemosynthetic communities associated with hydrocarbon seepage on the nile deep sea fan ndsf in the eastern mediterranean sea during a high resolution ship based multibeam survey covering a 225 km2 large seafloor area in the central province of the ndsf we identified 163 high backscatter patches at water depths between 1500 and 1800 m and investigated the source composition turnover flux and fate of emitted hydrocarbons systematic parasound single beam echosounder surveys of the water column showed hydroacoustic anomalies flares indicative of gas bubble streams above 8 of the high backscatter patches in echosounder records flares disappeared in the water column close to the upper limit of the gas hydrate stability zone located at about 1350 m water depth due to decomposition of gas hydrate skins and subsequent gas dissolution visual inspection of three high backscatter patches demonstrated that sediment cementation has led to the formation of continuous flat pavements of authigenic carbonates typically 100 to 300 m in diameter volume estimates considering results from high resolution autonomous underwater vehicle auv based multibeam mapping were used to calculate the amount of carbonate bound carbon stored in these slabs additionally the flux of methane bubbles emitted at one high backscatter patch was estimated 0 23 to 2 3 106 mol a 1 by combined auv flare mapping with visual observations by remotely operated vehicle rov another high backscatter patch characterized by single carbonate pieces which were widely distributed and interspaced with sediments inhabited by thiotrophic chemosynthetic organisms was investigated using in situ measurements with a benthic chamber and ex situ sediment core incubation and allowed for estimates of the methane consumption 0 1 to 1 106 mol a 1 and dissolved methane flux 2 to 48 106 mol a 1 our comparison of dissolved and gaseous methane fluxes as well as methane derived carbonate reservoirs demonstrates the need for quantitative assessment of these different methane escape routes and their interaction with the geo bio and hydrosphere at cold seeps

a similarity solution for a dual moving boundary problem associated with a coastal plain depositional system assuming that the sediment flux in the exner equation can be linearly related to the local bed slope we establish a one dimensional model for the bed load transport of sediment in a coastal plain depositional system such as a delta and a continental margin the domain of this model is defined by two moving boundaries the shoreline and the alluvial bedrock transition these boundaries represent fundamental transitions in surface morphology and sediment transport regime and their trajectories in time and space define the evolution of the shape of the sedimentary prism under the assumptions of fixed bedrock slope and sea level the model admits a closed form similarity solution for the movements of these boundaries a mapping of the solution space relevant to field scales shows two domains controlled by the relative slopes of the bedrock and fluvial surface one in which changes in environmental parameters are mainly recorded in the upstream boundary and another in which these changes are mainly recorded in the shoreline we also find good agreement between the analytical solution and laboratory flume experiments for the movements of the alluvial bedrock transition and the shoreline

ebullition and storm induced methane release from the east siberian arctic shelf vast quantities of carbon are stored in shallow arctic reservoirs such as submarine and terrestrial permafrost submarine permafrost on the east siberian arctic shelf started warming in the early holocene several thousand years ago however the present state of the permafrost in this region is uncertain here we present data on the temperature of submarine permafrost on the east siberian arctic shelf using measurements collected from a sediment core together with sonar derived observations of bubble flux and measurements of seawater methane levels taken from the same region the temperature of the sediment core ranged from 1 8 to 0 degrees c although the surface layer exhibited the lowest temperatures it was entirely unfrozen owing to significant concentrations of salt on the basis of the sonar data we estimate that bubbles escaping the partially thawed permafrost inject 100 630 mg methane m 2 d 1 into the overlying water column we further show that water column methane levels had dropped significantly following the passage of two storms we suggest that significant quantities of methane are escaping the east siberian shelf as a result of the degradation of submarine permafrost over thousands of years we suggest that bubbles and storms facilitate the flux of this methane to the overlying ocean and atmosphere respectively

effects of tectonic deformation and sea level on river path selection theory and application to the ganges brahmaputra meghna river delta the set of active rivers of the ganges brahmaputra meghna gbm delta in bangladesh overlies an active plate boundary that continually modifies the landscape of the delta by deformation the response of rivers to spatially variable subsidence from tectonic tilting or other causes has been thought to include preferred occupation of regions of higher subsidence in this paper we develop further the theoretical framework for analysis of the interplay of tectonics and river dynamics and apply this model to conditions in the gbm delta first we examine the overall competition between variable subsidence and channel dynamics and find that tilting in bangladesh should be strong enough to influence river path selection we then present new theory for the effect of subsidence that is spatially not temporally variable we find a constant residence timescale on different parts of the delta and differing frequencies of avulsion to these locations and describe the effects of incision or floodplain deposition on these quantities we present estimates of the channel residence timescale of the jamuna brahmaputra river reconstructed from the lithology provenance and dating of sediment cores we apply our framework to a map of regional subsidence to predict the effects on avulsion for the jamuna river comparison between our predicted 2150 years and our stratigraphically based estimates of avulsion timescale 1800 years shows encouraging consistency

shoreline autoretreat substantiated in flume experiments abstract under conditions of constant sediment supply s to the basin and a steady rate of rise a in relative sea level the autoretreat theory predicts that shorelines can retreat landwards at a relatively early stage of delta growth and attain an autobreak state after which the existing subaqueous slope begins to be starved of sediment and thereby lose its clear delta front configuration a numerical model based on this theory further suggests that shoreline migration depends on the inclination of basin s basement slope and subaqueous depositional slope and to a lesser degree on the inclination of subaerial depositional slope two dimensional flume experiments in which a miniature delta is subject to steady forcing a const 0 s const 0 were conducted to test the expectations of the autoretreat theory the experiments consisted of two different series of runs one was of modulation associated with a narrow range of the ratio of water discharge to sediment discharge q s the other was of q s modulation with kept nearly constant the q s ratio was mostly responsible for changes in but also affected to some extent all experimental runs substantiated the landward turnaround feature of shoreline accretion i e autoretreat and the geometrical break of the delta front shape during its retreat phase i e autobreak the obtained shoreline trajectories hold their geometrical patterns even after they were nondimensionalized in terms of the s a ratio a key hypothesis confirmed in the experiments is that a and s can never balance each other both of the experimental series brought some systematic change of shoreline trajectories but the variations of shoreline trajectory due to modulation were much more striking than those related to q s even these contrasting results are consistent with the numerical predictions the present experimental results support the applicability of the autoretreat concept to natural environments and help clarify the processes governing the regression and transgression of a shoreline on a constructional margin

the relative efficacy of fluvial and glacial erosion over modern to orogenic timescales it has been debated whether rivers or glaciers are more effective agents of erosion a global compilation of erosion rates reveals that both are capable of generating rates of erosion that match or exceed the highest rates of rock uplift since the late nineteenth century it has been debated whether rivers or glaciers are more effective agents of erosion1 the dramatic landscapes associated with glaciated terrain have often led to the argument that glaciers are more erosive than rivers and recent studies have documented the topographic signature of an ice controlled limit of mountain height known as the glacial buzz saw 2 3 here we present a new global compilation of erosion rates which questions the conventional view of glaciers and erosion in regions of rapid tectonic uplift erosion rates from rivers and glaciers both range from 1 to over 10 mm yr 1 indicating that both are capable of generating erosion rates matching or exceeding the highest rates of rock uplift moreover a comparison of erosion rates over timescales ranging from 101 to 107 years indicates that glacial erosion tends to decrease by one to two orders of magnitude over glacial cycles whereas fluvial erosion rates show no apparent dependence on time we conclude that tectonics controls rates of both fluvial and glacial erosion over millennial and longer timescales and that the highest rates of erosion 10 mm yr 1 generally result from a transient response to disturbance by volcanic eruptions climate change and modern agriculture

a sand gravel gilbert delta subject to base level change laboratory experiments were conducted on a sand gravel gilbert delta to gain insight on its dynamics under varying base level base level rise results in intensified aggradation over the topset as well as a decrease in topset slope and topset surface coarsening the signals of which migrate in an upstream direction preferential deposition of coarse sediment in the topset results in a finer load at the topset foreset break which creates a fine signature in the foreset deposit base level fall has the opposite effects entrainment of the topset mobile armor causes a coarsening of the load at the topset foreset break and so a coarse signature in the foreset deposit the entrainment of the topset substrate and fine top part of the foreset may follow which causes a fining of the load and a fine signature in the foreset deposit the fact that the upstream sediment supply requires a certain slope and bed surface texture to be transported downstream under quasi equilibrium conditions counteracts the effects of base level change this information travels in the downstream direction in nature base level change is likely so slow that the upstream sediment load maintains the topset slope and bed surface texture and so keeps the topset in a quasi equilibrium state base level change is therefore not expected to leave a clear signal in a mixed sediment gilbert delta other than a change in elevation of the topset foreset interface

submarine canyons in the bathtub abstract submarine megafans and their associated canyons have long attracted the attention of a large community in the earth sciences because they record the history of past erosional processes as such their morphology and sedimentary infill may be of use to unravel past climatic and tectonic evolution yet despite an important corpus of research on their structural characteristics we lack a well accepted quantitative description for the dynamics of the formation and growth of these sedimentary systems one of the main reasons for this lies in our inability to successfully understand reproduce and predict the dynamics of the channel systems tens to hundreds of meters deep several kilometers in width and hundreds of kilometers in length that build submarine fans here we report on a series of small scale laboratory experiments on the formation of subaqueous channels and lobes our experiments show that steady flow of a dense current on a bed of light particles can induce both spontaneous formation of channels longer than a few channel widths and spontaneous meandering

spatial patterns and variation of suspended sediment yield in the upper indus river basin northern pakistan summary much of the flow of the indus originates in the mountainous regions of the karakoram and himalayas resulting in a high sediment yield that creates a number of operational and maintenance problems for downstream water use in pakistan analysis of the available hydro climatological data indicates that the upper indus basin can be subdivided into three characteristic regions based on whether runoff production is controlled by temperature region 1 upper glacierized sub basins precipitation caused by the monsoon and western disturbances region 3 lower sub basins or a combination of the two region 2 middle reach sub basins the runoff and sediment transport regimes for the shyok gilgit hunza and indus rivers in region 1 show the role of snow and ice melt in generating high runoff and 80 85 of the annual sediment load is transported in july and august the astore river at doyian in region 2 shows an early rise of the sediment yield starting in may due to the interaction of rainfall and snowmelt at lower elevations and a comparatively lower sediment yield in august indicating a lesser influence of glacier melt region 3 experiences two types of rainfall summer monsoons and the western disturbances in late winter and early spring consequently the gorband river at karora in region 3 exhibits two separate sediment yield peaks of equal height in april and july the runoff and sediment transport regime along the main stem of the indus river is dominated by the melt of snow and ice in its headwaters and consequently is similar to the regimes of the region 1 sub basins contrary to the conventional model the specific sediment yield increases markedly with drainage area along the indus river from 355 t km 2 yr 1 at kharmong to 1197 t km 2 yr 1 at besham qila likely because of the large number of small and relatively steep catchments discharging straight into the indus river analysis of the magnitude frequency characteristics of sediment transport for the tributaries shows that the effective discharge in the basin ranges from 1 5 2 0 to 5 5 6 0 times the average discharge and decreases downstream the main indus river however shows a consistent effective discharge of 2 5 3 0 times the average discharge

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

incision and differential bedrock uplift along the indus river near nanga parbat pakistan himalaya from 10be and 26al exposure age dating of bedrock straths abstract well preserved river cut bedrock surfaces straths abandoned by the progressive incision of the indus river in northern pakistan were dated using in situ cosmogenic 10 be and 26 al exposure age dating measurements on young and modern straths show no significant ingrowth of 10 be and 26 al implying that strath exposure ages closely approximate their abandonment age strath exposure ages range up to 65 ka and increase with height above the river the straths can be divided into two groups low straths dated at about 7 ka which yield very rapid bedrock incision rates 9 12 m ka and high straths 7 ka in age which yield somewhat slower incision rates 1 6 m ka incision rates for both groups increase by 1 3 m ka downstream toward an active reverse fault the raikot fault that forms the western border of the nanga parbat haramosh massif nphm the downstream increases in incision rates for the low straths mimic downstream increases in the modern gradient suggesting that bedrock incision rates have been proportional to stream power over the last 7 ka gradient increases are probably the result of the creation of knickpoints by bedrock uplift along the raikot fault the longitudinal profile and steep gorge of the indus river in the study area indicate that bedrock incision appears to keep pace with differential vertical motions between the nphm and surrounding regions thus the 1 3 m ka difference in incision rates likely reflects the differential bedrock uplift rate between the nphm and the skardu basin the differential incision rate is consistent with differential exhumation rates obtained from apatite fission track ages assuming geotherms of 80 90 c km in the nphm and 35 c km in the skardu basin this relation suggests that rapid bedrock incision of at least 1 3 m ka has persisted within the nphm for the last 0 5 ma the acceleration of incision rates throughout the study area since 15 ka is likely to be a climatic signal that records an increase in the discharge and or sediment load of the indus river in the study area related to deglaciation of the surrounding terrane

reservoir infill by hyperpycnal deltas over bedrock 1 we propose a simple morphodynamic theory of reservoir deltas prograding over bedrock under the influence of turbid underflows the theory models the geomorphic actions of fluvial and hyperpycnal flows as diffusion processes and treats bedrock alluvial and river lake transitions as moving internal boundaries it yields self similar analytical solutions for the co evolving river and lake bed profiles under different slope and influx conditions these include a special case in which delta deposits are swept underwater to prograde into a subaqueous turbid pool the theoretical predictions are in good agreement with microscale experiments and should help interpret and anticipate longitudinal sedimentation patterns in mountain reservoirs

stream power controls the braiding intensity of submarine channels similarly to rivers we use physical experiments to investigate the response of submarine braided channels driven by saline density currents to increasing inflow discharge and bed slope we find that similarly to braided rivers only a fraction of submarine braided networks have active sediment transport we then find similar response to imposed change between submarine and fluvial braided systems 1 both the active and total braiding intensities increase with increasing discharge and slope 2 the ratio of active braiding intensity to total braiding intensity is 0 5 in submarine braided systems regardless of discharge and slope and 3 the active braiding intensity scales linearly with dimensionless stream power thus braided submarine channels and braided rivers are similar in some important aspects of their behavior and responses to changes in stream power and bed slope in light of the scale independence of braided channel planform organization these results are likely to apply beyond experimental scales

two diffusion description of hyperpycnal deltas 1 alluvial deltas formed upstream of lakes and reservoirs often exhibit concave foresets with maximum inclinations smaller than the angle of repose in the present work we test whether this morphology could be attributed to bed load sediment transport by turbid underflows acting along the foreset beds before their fine sediment load settles out of suspension under hyperpycnal conditions both the topset and foreset of the delta would thus be subject to the geomorphic influence of the dense river inflow to describe this joint geomorphic action by subaerial and subaqueous currents we derive a two diffusion theory and modify it to account for inclination thresholds different diffusion strengths apply to the topset and foreset on either side of the moving shoreline for a channel of uniform initial slope and a constant water level in the body of standing water we show that the resulting moving boundary problem admits exact similarity solutions to test the theory the analytical solutions are compared with small scale laboratory experiments in which turbid underflows are replaced by brine currents the curved profiles predicted by the theory and measured in the experiments resemble those of surveyed deltaic deposits in lakes known to be prone to turbidity currents

dynamics of sediment laden underflows passing over a subaqueous sill glacier fed peyto lake alberta canada the dynamic behaviour of sediment laden underflows was examined in peyto lake alberta canada which contains a midlake sill 7 m high sediment laden underflows are driven by the downslope component of negative buoyant gravity multiplied by the current s thickness our measurements of wind lake currents and water properties indicate that underflows pass over the sill due to the active storage of turbid suspension near the bottom in the deepest proximal region sill overflows occurred only when a hydrological threshold of the inflowing river was exceeded causing quasicontinuous underflow and associated sedimentation in the distal region of the lake basin

quantification of gas bubble emissions from submarine hydrocarbon seeps at the makran continental margin offshore pakistan 1 evidence for twelve sites with gas bubble emissions causing hydroacoustic anomalies in 18 khz echosounder records flares was obtained at the convergent makran continental margin the hydroacoustic anomalies originating from hydrocarbon seeps at water depths between 575 and 2870 m disappeared after rising up to 2000 m in the water column dives with the remotely operated vehicle quest 4000 m revealed that several individual bubble vents contributed to one hydroacoustic anomaly analyzed gas samples suggest that bubbles were mainly composed of methane of microbial origin bubble size distributions and rise velocities were determined and the volume flux was estimated by counting the emitted bubbles and using their average volume we found that a low volume flux flare 1 at 575 mbsl 90 ml min caused a weak hydroacoustic signal in echograms whereas high volume fluxes flare 2 at 1027 mbsl 1590 ml min flare 5 c at 2870 mbsl 760 ml min caused strong anomalies the total methane bubble flux in the study area was estimated by multiplying the average methane flux causing a strong hydroacoustic anomaly in the echosounder record with the total number of equivalent anomalies an order of magnitude estimate further considers the temporal variability of some of the flares assuming a constant flux over time and allows a large range of uncertainty inherent to the method our results on the fate of bubbles and the order of magnitude estimate suggest that all of the 40 32 106 mol methane emitted per year within the gas hydrate stability zone remain in the deep ocean

on homogeneous ice formation in liquid clouds primary ice formation by homogeneous freezing of supercooled cloud droplets in moist adiabatic air parcels is investigated theoretically and by means of numerical simulations dependencies of nucleated ice crystal number and size and associated freezing temperatures are systematically studied as functions of updraught speed and cloud droplet number and size droplet freezing temperatures range between 235 and 239 k depending on dynamical forcing and liquid water content vertical resolutions on the order of 10 m are required in numerical cloud models to resolve the thin layers in which homogeneous ice formation processes unfold only a fraction of droplets freeze in weakly forced clouds small scale variability in updraught speeds encountered by air parcels containing supercooled cloud droplets results in broad ice crystal number distributions when sampled across a parcel ensemble the strong dynamical control of ice initiation in tropospheric clouds initiates homogeneous freezing in the presence of heterogeneous ice nuclei even at moderate mean updraught speeds suggesting that such particles play a limited role in affecting droplet freezing in cold convective cloud outflow regions these findings have important implications for microphysical and optical properties of condensed phase convective detrainment setting the stage for the evolution of anvil cirrus

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

supply limited sediment transport in a high discharge event of the tropical burdekin river north queensland australia interactions between catchment variables and sediment transport processes in rivers are complex and sediment transport behaviour during high flow events is not well documented this paper presents an investigation into sediment transport processes in a short duration high discharge event in the burdekin river a large sand and gravel bed river in the monsoon and cyclone influenced semi arid tropics of north queensland the burdekin s discharge is highly variable and strongly seasonal with a recorded maximum of 40 400 m s sediment was sampled systematically across an 800 m wide 12 m deep and straight reach using helley smith bedload and us p 61 suspended sediment samplers over 16 days of a 29 day discharge event in february and march 2000 peak 11 155 m s about 3 7 10 tonnes of suspended sediment and 3 10 tonnes of bedload are estimated to have been transported past the sample site during the flow event the sediment load was predominantly supply limited wash load included clay silt and very fine sand the concentration of suspended bed material including very coarse sand varied with bedload transport rate discharge and height above the bed bedload transport rate and changes in channel shape were greatest several days after peak discharge comparison between these data and sparse published data from other events on this river shows that the control on sediment load varies between supply limited and hydraulically limited transport and that antecedent weather is an important control on suspended sediment concentration neither the empirical relationships widely used to estimate suspended sediment concentrations and bedload e g ackers white 1973 nor observations of sediment transport characteristics in ephemeral streams e g reid frostick 1987 are directly applicable to this river

hydroacoustic methodology for detection localization and quantification of gas bubbles rising from the seafloor at gas seeps from the eastern black sea 1 detailed acoustic investigation of bubble streams rising from the seafloor were conducted during r v meteor cruise m72 3a at a deep submarine hydrocarbon seep environment the area is located offshore georgia eastern part of the black sea at a water depth between 840 m and 870 m the sediment echosounder parasound ds 3 p70 was used for detecting bubbles in the water column that causes strong backscatter in the echographs flares employing the swath echsounder kongsberg em710 flares in the water column were mapped along the entire swath width of approximately 1000 m at high spatial resolution the exact location of the flares could be extracted manually subsequently the horizontally looking sonar kongsberg digital telemetry ms1000 mounted on a remotely operated vehicle rov was utilized to quantify the flux of bubbles a model was developed that is based on the principle of finding the acoustic mass in order to quantify the bubble flux at various seeps the acoustic approach from the backscatter data of the rov sonar resulted in bubble fluxes in the range of 0 01 to 5 5 l min corresponding to 0 037 to 20 5 mol ch4 min at in situ conditions 850 m water depth 9 c independent flux estimations using a funnel shaped device showed that the acoustic model consistently produced lower values but the offset is less than 12 furthermore the deviation decreased with increasing flux rates a field of bubble streams was scanned three times from different directions in order to reveal the reproducibility of the method flux estimations yielded consistent fluxes of about 2 l min 7 4 mol ch4 min with variations of less than 10 although gas emissions have been found at many sites at the seafloor in a range of geological settings the amount of escaping gas is still largely unknown with this study presenting a novel method of quantifying bubble fluxes employing a horizontally looking sonar system it is intended to contribute to the global effort of better constraining bubble fluxes at deep sea settings

self similar evolution of semi infinite alluvial channels with moving boundaries mathematical solutions are obtained for several sedimentary problems featuring semi infinite alluvial channels evolving under diffusional sediment transport moving boundaries are considered at one end of the channels and represent transitions between alluvial reaches and either bedrock floored channels or bodies of standing water three elementary cases are considered bedrock alluvial transitions lake breaches and prograding deltas it is shown that idealized formulations of all three problems share the same mathematical structure and admit exact similarity solutions elementary solutions can further be assembled to describe composite profiles this is illustrated by the case of a natural lake undergoing simultaneous breaching and backfill for both elementary and composite cases the explicit solutions clarify the link between alluvial profile evolution and the migration of channel boundaries for the case of lake breaching for instance the outlet channel profile is controlled simultaneously by downwards incision and upstream migration of the channel head the pace of the resulting water level drawdown in turn affects the form of the backfill deposits upstream of the lake

glacier and landslide feedbacks to topographic relief in the himalayan syntaxes despite longstanding research on the age and formation of the tibetan plateau the controls on the erosional decay of its margins remain controversial pronounced aridity and highly localized rock uplift have traditionally been viewed as limits to the dissection of the plateau by bedrock rivers recently however glacier dynamics and landsliding have been argued to retard headward fluvial erosion into the plateau interior by forming dams and protective alluvial fill here we report a conspicuous clustering of hundreds of natural dams along the indus and the tsangpo rivers where these cross the himalayan syntaxes the indus is riddled by hundreds of dams composed of debris from catastrophic rock avalanches forming the largest concentration of giant landslide dams known worldwide whereas the tsangpo seems devoid of comparable landslide dams in contrast glacial dams such as river blocking moraines in the headwaters of both rivers are limited to where isolated mountain ranges intersect the regional snowline we find that to first order high local topographic relief along both rivers corresponds to conspicuously different knickzones and differences in the type and potential longevity of these dams in both syntaxes glacier and landslide dams act as a negative feedback in response to fluvial dissection of the plateau margins natural damming protects bedrock from river incision and delays headward knickpoint migration thereby helping stabilize the southwestern and southeastern margins of the tibetan plateau in concert with the effects of upstream aridity and localized rock uplift

factors controlling specific sediment yield in the upper indus river basin northern pakistan estimates of sediment yield are essential in water resources analysis modelling and engineering in investigations of continental denudation rates and in studies of drainage basin response to changes in climate and land use the availability of high resolution global environmental datasets offers an opportunity to examine the relationships between specific sediment yield sysp and drainage basin attributes in a geographical information system gis environment this study examines sysp at 14 long term gauging stations within the upper indus river basin twenty nine environmental variables were derived from global datasets the majority with a 1 1 km resolution the sysp ranges from 194 to 1302 t km 2 yr 1 for sub basins ranging from 567 to 212 447 km2 the high degree of scatter in sysp is greatly reduced when the stations are divided into three groups upper glacierized sub basins lower monsoon sub basins and the main indus river percentage snow ice cover lcs emerges as the single major land cover control for sysp in the high mountainous upper indus river basin a regression model with percentage snow ice cover lcs as the single independent variable explains 73 4 of the variance in sysp for the whole indus basin a combination of percentage snow ice cover lcs relief and climate variables explains 98 5 of the variance for the upper glacierized sub basins for the lower monsoon region a regression model with only mean annual precipitation p explains 99 4 of the variance along the main indus river a regression model including just basin relief r explains 92 4 of the variance in sysp based on the r2adj and p value statistics the variables used are capable of explaining the majority of variance in the upper indus river basin copyright 2007 john wiley sons ltd

fluvial fan deltas linking channel processes with large scale morphodynamics 1 alluvial fan deltas are built by aggrading and avulsing river channels a numerical model of flow and sediment transport in channels is combined with a condition for channel avulsion to describe evolution of the fan surface the model combines elements of two recent approaches 1 diffusional models of depositional basin filling which describe the evolution of overall morphology and 2 cellular models of channel evolution which provide simplified descriptions of channel dynamics here the cellular formulation is used simply as a template for discretizing a standard set of equations describing flow and sediment transport within channels the basic formulation is thus grid invariant and the results are in actual rather than arbitrary time and length scales the model captures the interaction between microscale channel morphodynamics including converging and diverging flow and avulsion and morphodynamics at the macroscale fan it provides a starting point for the study of a wide range of topics including the three dimensional stratigraphy of fan delta deposits and the response of fan deltas to engineering activities

vertical velocities and turbulence in midlatitude anvil cirrus a comparison between in situ aircraft measurements and ground based doppler cloud radar retrievals this study introduces a statistical comparison of vertical velocity observations within cirrus from aircraft and ground based doppler cloud radar two cases of midlatitude anvil cirrus forming under very similar environmental conditions are examined the case studies benefit from simultaneous observations of vertical velocities in cirrus collected at and around the atmospheric radiation measurement southern great plains site during the u s department of energy small particles in cirrus field campaign observations from both platforms suggest that the majority of vertical velocities in the examined midlatitude anvil cirrus cases are roughly within 1 m s 1 although higher vertical velocities are occasionally observed the quality of the vertical velocity comparison between in situ aircraft measurements and ground based doppler radar retrievals depends on the case for the first case on 23 april 2010 the comparison suggests that the radar retrieval may underestimate vertical velocities in the range between roughly 50 cm s 1 and 1 m s 1 for the second case on 14 june 2010 the agreement between radar and aircraft is excellent and the differences are largely within the observed variability of vertical velocities within cirrus differences in the spatial scales of vertical velocities and turbulence sampled by the aircraft and doppler radar which arise due to differences in the temporal resolution of the observational platforms are not found to explain the observed discrepancies estimates for the dissipation rate of turbulent kinetic energy agree to within 1 order of magnitude between the two observational platforms

expression of active tectonics in erosional landscapes understanding the manner and degree to which topography in active mountain ranges reflects deformation of the earth s surface remains a first order goal of tectonic geomorphology a substantial body of research in the past decade demonstrates that incising channel systems play a central role in setting relationships among topographic relief differential rock uplift rate and climatically modulated erosional efficiency this review provides an introduction to the analysis and interpretation of channel profiles in erosional mountain ranges we show that existing data support theoretical expectations of positive monotonic relationships between channel steepness index a measure of channel gradient normalized for downstream increases in drainage area and erosion rate at equilibrium and that the transient response to perturbations away from equilibrium engenders specific spatial patterns in channel profiles that can be used to infer aspects of the forcing these aspects of channel behavior lay the foundation for a series of case studies that we use to illustrate how focused quantitative analysis of channel morphology can provide insight into the spatial and temporal dynamics of active deformation although the complexities of river response to climate lithology and uplift patterns mean that multiple interpretations of topographic data alone will always possible we show that application of stream profile analysis can be a powerful reconnaissance tool with which to interrogate the rates and patterns of deformation in active mountain belts

k ar and ar ar geochronology of the himalayan collision in nw pakistan constraints on the timing of suturing deformation metamorphism and uplift mica and hornblende k ar and ar ar data are presented from each of the three crustal components of the himalayan collision zone in north pakistan the asian plate the kohistan island arc and the indian plate together with u pb and rb sr data published elsewhere these new data 1 date the age of suturing along the northern suture which separates kohistan from asia at 102 85 ma 2 establish that the basic magmatism in kohistan which postdates collision along the northern suture predates 60 ma and that the later granite magmatism spanned a range of 60 25 ma 3 show that uplift amounts within kohistan are greater toward the nanga parbat syntaxis than away from it and that rate of uplift near the syntaxis increased over the last 20 ma to a current figure of about 5 5 mm a year 4 show that much of southern kohistan had cooled to below 500 c by 80 ma and that the major deformation which imbricated kohistan probably predated 80 ma and certainly predated 60 ma and was related to the kohistan asia collision rather than the kohistan india one 5 imply that uplift along the hunza shear in the asian plate together with imbrication of the metamorphics in its hanging wall took place at about 10 ma and was associated with breakback thrusting in the hanging wall of the main mantle thrust 6 suggest that the indian plate has a lengthy pre himalayan history with an early metamorphism at about 1900 ma major magmatism at 500 550 ma and early jurassic lithospheric extension or inversion and 7 show that the indian plate rocks were metamorphosed shortly after the collision within kohistan which occurred at circa 50 ma and subsequently cooled back through 500 c at circa 38 ma and 300 c at 30 35 ma with ages of cooling through 200 and 100 c as determined by fission track data locally controlled by nanga parbat related uplift tectonics

effects of episodic sediment supply on bedload transport rate in mountain rivers detecting debris flow activity using continuous monitoring abstract monitoring of sediment transport from hillslopes to channel networks as a consequence of floods with suspended and bedload transport hyperconcentrated flows debris and mud flows is essential not only for scientific issues but also for prevention and mitigation of natural disasters i e for hazard assessment land use planning and design of torrent control interventions in steep potentially unstable terrains ground based continuous monitoring of hillslope and hydrological processes is still highly localized and expensive especially in terms of manpower in recent years new seismic and acoustic methods have been developed for continuous bedload monitoring in mountain rivers since downstream bedload transport rate is controlled by upstream sediment supply from tributary channels and bed external sources continuous bedload monitoring might be an effective tool for detecting the sediments mobilized by debris flow processes in the upper catchment and thus represent an indirect method to monitor slope instability processes at the catchment scale however there is poor information about the effects of episodic sediment supply from upstream bed external sources on downstream bedload transport rate at a single flood time scale we have examined the effects of sediment supply due to upstream debris flow events on downstream bedload transport rate along the yotagiri river central japan to do this we have conducted continuous bedload observations using a hydrophone japanese pipe microphone located 6 4 km downstream the lower end of a tributary affected by debris flows two debris flows occurred during the two years long observation period as expected bedload transport rate for a given flow depth showed to be larger after storms triggering debris flows that is although the magnitude of sediment supply from debris flows is not large their effect on bedload is propagating 6 km downstream at a single flood time scale this indicates that continuous bedload observations could be effective for detecting sediment supply as a consequence of debris flow events

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

evidence that ice forms primarily in supercooled liquid clouds at temperatures 27 c using 4 years of radar and lidar observations of layer clouds from the chilbolton observatory in the uk we show that almost all 95 ice particles formed at temperatures 20 c appear to originate from supercooled liquid clouds at colder temperatures there is a monotonic decline in the fraction of liquid topped ice clouds 50 at 27 c falling to zero at 37 c where homogeneous freezing of water droplets occurs this strongly suggests that deposition nucleation plays a relatively minor role in the initiation of ice in mid level clouds it also means that the initial growth of the ice particles occurs predominantly within a liquid cloud a situation which promotes rapid production of precipitation via the bergeron findeison mechanism