laboratory experiments simulating the geomorphic response to tectonic uplift 1 we present the results of an experimental study of topography dynamics under conditions of constant precipitation and uplift rate the experiment is designed to develop a complete drainage network by the growth and propagation of erosion instabilities in response to tectonic perturbations the quantitative analysis of topographic evolution is made possible by using telemetric lasers that perform elevation measurements at an excellent level of precision we focus our study on the effect of initial surface organization and of uplift rate on both the transient dynamics and the steady state forms of topography we show that the transient phase is strongly dependent on the initial internally drained area which is found to decrease exponentially with time the topography always reaches a steady state whose mean elevation depends linearly on uplift rate with a strictly positive value when uplift is zero steady state surfaces are characterized by a well defined slope area power law with a constant exponent of 0 12 and an amplitude that depends linearly on uplift rate with a strictly positive value when uplift is zero these results are consistent with a stream power law erosion model that includes a nonnegligible threshold for particle detachment uncertainty regarding the sediment transport length is resolved by calibrating the transient dynamics with a surface process model reappraising published results on the linear dependency between mean elevation or relief and denudation rate we suggest that an erosion threshold is worth considering for large scale systems

sand volcano generated by a violent degassing from methane saturated aquifers the case study of medolla modena italy abstract sand volcano is an unusual and remarkable geological feature which forms when water saturated sand deposits are set in motion by liquefaction and are ejected onto the surface commonly it is generated during earthquakes as a result of liquefaction of waterlogged bodies at shallow depth often causing wide damages the generation of a sand volcano however can also occur unrelated to a seismic event on the 10th of october 2014 near medolla italy during a cone penetration test a large amount of natural gas co2 and ch4 together with a mixture of water and sand were erupted creating a sand volcano the study of this event gives the possibility of understanding the dynamics of sand volcano generation may enable to prevent other anomalies during future cpt tests and more importantly underlines the role that natural gas stored in a sand aquifer may play in triggering a liquefaction phenomenon our results suggest that episodes of gas eruptions require the onset of very peculiar conditions within the reservoir that feeds the emission the simulations suggest that a geyser discharging a mixture of gas and water capable of building a sand volcano requires the presence of a shallow pressurized reservoir 1 2 mpa where water coexists with a small amount of exsolved gas a volume fraction of 0 05 the violent degassing occurred in medolla confirms the role that a free gas phase may have in favoring the mobilization of liquid water and loose deposits even in the absence of a seismic event

composition and exhalation flux of gases from mud volcanoes in taiwan many mud volcanoes are distributed along the tectonic sutures in southern taiwan and can be divided into five zones based on their relative positions in different tectonic domains most active mud volcanoes are exhaling methane dominated gases nevertheless some gases show unusual carbon dioxide dominated and or nitrogen excess compositions this implies that there are multiple sources for the gas compositions of mud volcanoes in taiwan

preferential mode of gas invasion in sediments grain scale mechanistic model of coupled multiphase fluid flow and sediment mechanics 1 we present a discrete element model for simulating at the grain scale gas migration in brine saturated deformable media we rigorously account for the presence of two fluids in the pore space by incorporating forces on grains due to pore fluid pressures and surface tension between fluids this model which couples multiphase fluid flow with sediment mechanics permits investigation of the upward migration of gas through a brine filled sediment column we elucidate the ways in which gas migration may take place 1 by capillary invasion in a rigid like medium and 2 by initiation and propagation of a fracture we find that grain size is the main factor controlling the mode of gas transport in the sediment and we show that coarse grain sediments favor capillary invasion whereas fracturing dominates in fine grain media the results have important implications for understanding vent sites and pockmarks in the ocean floor deep subseabed storage of carbon dioxide and gas hydrate accumulations in ocean sediments and permafrost regions our results predict that in fine sediments hydrate will likely form in veins following a fracture network pattern and the hydrate concentration will likely be quite low in coarse sediments the buoyant methane gas is likely to invade the pore space more uniformly in a process akin to invasion percolation and the overall pore occupancy is likely to be much higher than for a fracture dominated regime these implications are consistent with laboratory experiments and field observations of methane hydrates in natural systems

effects of sediment load on hydraulics of overland flow on steep slopes eroded sediment may have significant effects on the hydraulics of overland flow but few studies have been performed to quantify these effects on steep slopes this study investigated the potential effects of sediment load on reynolds number froude number flow depth mean velocity darcy weisbach friction coefficient shear stress stream power and unit stream power of overland flow in a sand glued hydraulic flume under a wide range of hydraulic conditions and sediment loads slope gradients were varied from 8 7 to 34 2 unit flow rates from 0 66 to 5 26 10 3 m2 s 1 and sediment loads from 0 to 6 95 kg m 1 s 1 both reynolds number re and froude number fr decreased as sediment load increased implying a decrease in flow turbulence this inverse relationship should be considered in modeling soil erosion processes flow depth increased as sediment load increased with a mean value of 1 227 mm caused by an increase in volume of sediment laden flow contribution 62 4 and a decrease in mean flow velocity contribution 37 6 the mean flow velocity decreased by up to 0 071 m s 1 as sediment load increased the darcy weisbach friction coefficient f increased with sediment load showing that the total energy consumption increased with sediment load the effects of sediment load on f depended on flow discharge as flow discharge increased the influence of sediment load on f decreased due to increased flow depth and reduced relative roughness flow shear stress and stream power increased with sediment load on average by 80 5 and 60 2 respectively however unit stream power decreased by an average of 11 1 as sediment load increased further studies are needed to extend and apply the insights obtained under these controlled conditions to real world overland flow conditions copyright 2010 john wiley sons ltd

misrepresentation of hydro erosional processes in rainfall simulations using disturbed soil samples abstract interrill erosion is a primary soil erosion process which consists of soil detachment by raindrop impact and particle transport by shallow flow interill erosion affects other soil erosion sub processes e g water infiltration sealing crusting and rill initiation interrill erosion has been widely studied in laboratories and the use of a sieved soil i e disturbed soil has become a standard method in laboratory experiments the aims of our study are to evaluate the hydro erosional response of undisturbed and disturbed soils in a laboratory experiment and to quantify the extent to which hydraulic variables change during a rainstorm we used a splash pan of 0 3 m width 0 45 m length and 0 1 m depth a rainfall simulation of 58 mm h 1 lasting for 30 min was conducted on seven replicates of undisturbed and disturbed soils during the experiment several hydro physical parameters were measured including splashed sediment mean particle size runoff water infiltration and soil moisture we conclude that use of disturbed soil samples results in overestimation of interrill processes of the nine assessed parameters four displayed greater responses in the undisturbed soil infiltration topsoil shear strength mean particle size of eroded particles and soil moisture in the disturbed soil five assessed parameters displayed greater responses wash sediment final runoff coefficient runoff splash and sediment yield therefore contextual soil properties are most suitable for understanding soil erosion as well as for defining soil erodibility

bubble growth and rise in soft sediments the mechanics of uncemented soft sediments during bubble growth are not widely understood and no rheological model has found wide acceptance we offer definitive evidence on the mode of bubble formation in the form of x ray computed tomographic images and comparison with theory natural and injected bubbles in muddy cohesive sediments are shown to be highly eccentric oblate spheroids disks that grow either by fracturing the sediment or by reopening preexisting fractures in contrast bubbles in soft sandy sediment tend to be spherical suggesting that sand acts fluidly or plastically in response to growth stresses we also present bubble rise results from gelatin a mechanically similar but transparent medium that suggest that initial rise is also accomplished by fracture given that muddy sediments are elastic and yield by fracture it becomes much easier to explain physically related phenomena such as seafloor pockmark formation animal burrowing and gas buildup during methane hydrate melting

correlation of shape and size of methane bubbles in fine grained muddy aquatic sediments with sediment fracture toughness abstract gassy sediments contribute to destabilization of aquatic infrastructure air pollution and global warming in the current study a precise shape and size of the buoyant mature methane bubble in fine grained muddy aquatic sediment is defined by numerical and analytical modeling their results are in a good agreement a closed form analytical solution defining the bubble parameters is developed it is found that the buoyant mature bubble is elliptical in its front view and resembles an inverted tear drop in its cross section the size and shape of the mature bubble strongly correlate with sediment fracture toughness bubbles formed in the weaker sediments are smaller and characterized by a larger surface to volume ratio that induces their faster growth and may lead to their faster dissolution below the sediment water interface this may prevent their release to the water column and to the atmosphere shapes of the bubbles in the weaker sediments deviate further from the spherical configuration than those in the stronger sediments modeled bubble characteristics important for the acoustic applications are in a good agreement with field observations and lab experiments

channel width flow discharge relationships for rills and gullies abstract research conducted during the first half of the last century has shown that a strong power relationship exists between channel width and total flow discharge in streams recent studies have shown that this power relationship can be theoretically derived for bankfull discharge in channels the relationship has been extended empirically to rills and gullies revealing that the discharge exponent for rills and gullies is significantly smaller than that for rivers however water flow in rills and gullies is only rarely bankfull indicating that the theoretical explanation for the power relationship found for rivers does not apply to rills and gullies in order to investigate the width discharge relationships for rills and gullies a new method is proposed based on field measurements of widths of concentrated flow erosion channels both upstream and downstream of channel junctions although the method only allows the determination of the exponent of the power relationship it is easy and inexpensive to apply a total of 322 rill and gully channel junctions with various soils and land use types were investigated in belgium italy and spain the obtained data confirmed the existence of the power relationship for rills and gullies with the exponent varying from 0 43 for small rills about 3 cm in width to 0 5 for gullies about 50 to 100 cm in width the data did not allow deciding whether the exponent varies consistently with channel width or in a step wise fashion the exponent values obtained in this study are larger than those reported in previous studies but this may result from differences in the definition of the discharge that eroded the channel to its current width

flow resistance equation for rills in this paper a new flow resistance equation for rill flow was deduced applying dimensional analysis and self similarity theory at first the incomplete self similarity hypothesis was used for establishing the flow velocity distribution whose integration gives the theoretical expression of the darcy weisbach friction factor then the deduced theoretical resistance equation was tested by some measurements of flow velocity water depth cross section area wetted perimeter and bed slope carried out in 106 reaches of some rills modelled on an experimental plot a relationship between the velocity profile the channel slope and the flow froude number was also established the analysis showed that the darcy weisbach friction factor can be accurately estimated by the proposed theoretical approach based on a power velocity profile

comparison of hydrodynamic parameters for predicting soil and water loss on simulation landslide deposit slope in wenchuan earthquake area china hydrodynamic parameters should be identified firstly for predicting soil and water loss with specific issues and objectives the laboratory simulation scouring experiments were conducted with different gravel contents flow discharges and slopes based on the field investigation which achieved the most suitable parameter for predicting soil and water loss on simulation landslide deposit slope in wenchuan earthquake area china the results showed that the gravel content of 25 always was the threshold that controlled the flow shear stress and stream power increased or decreased under different flow discharges the unit stream power up and unit flow energy e both decreased when gravel contents increased the ratio of manning coefficient to flow depth n h was higher in fine sediments with gravels than that without gravels the flow discharge had the consistent effects on hydrodynamics which was ordered as 4 8 12 l min 1 the was the most suitable parameter for predicting soil and water loss by considering the degree of reliability even though the also had significant positive power function with soil and water loss the n h could describe the hydrodynamics and soil and water loss and be the alternative parameter for predicting soil and water loss the results provide useful information for soil and water loss prediction in landslide deposits

transporting capacity of overland flow on plane and on irregular beds in this paper the transporting capacity of thin flows in the laminar and transitional flow regime is studied experiments were carried out on irregular as well as on plane beds using two totally different set ups the results of these two types of experiment were convergent in both cases sediment concentration was clearly related to grain shear velocity and unit stream power expressed as the product of mean velocity and slope yang 1973 the data agreed with those of kramer and meyer 1969 for a sandy bed the unit stream power relationship was able to predict reasonably well the sediment concentrations measured on a mulched surface for laminar and transitional flows both the unit stream power and the shear velocity are related in the same way to slope and unit discharge the unit stream power is a parameter which in particular can be very easily measured and might therefore become useful in obtaining a quick estimate of the transporting capacity of a thin flow however before a sediment transport equation for thin flows can be developed more information is needed about the influence of the flow regime and grain size and density

elasticity of marine sediments rock physics modeling we offer an effective medium model for the elastic moduli of high porosity ocean bottom sediments the elastic constants of the dry sediment frame depend on porosity elastic moduli of the solid phase and effective pressure the model connects two end points in the elastic modulus porosity plane the hertz mindlin modulus of a dense elastic sphere pack at critical porosity and zero at 100 porosity the elastic moduli of saturated sediment are calculated from those of the dry frame using gassmann s equation unlike the suspension model our model assigns non zero elastic constants to the dry sediment frame and can predict the shear wave velocity unlike various modifications of the travel time average equation it is first principle based and contains only physical parameters we justify this model by matching sonic data in shallow marine sediments and in an odp well

a long flume study of the dynamic factors affecting the resistance of a loamy soil to concentrated flow erosion experiments were carried out in a 20 m long flume to assess the variation of the runoff erosion resistance of a loamy soil as a function of initial moisture content and compaction the results of seven experimental runs show that the runoff erosion resistance of a loamy material is extremely sensitive to variations in initial moisture content and to a somewhat lesser extent in bulk density the very low resistance to runoff erosion of initially dry material is explained by structural changes which take place at the time of wetting slaking and microfissuration cause a considerable decrease of the soil s shear strength and therefore of its resistance to runoff erosion a first analysis shows that during a given rainfall event initially dry soils may well show significantly more erosion than initially wet soils despite the increase of infiltration with decreasing initial moisture content

interaction between bed roughness and flow hydraulics in eroding rills govers 1992 showed that the flow velocity in rills eroding loose nonlayered materials could be predicted from knowledge of discharge only without significant slope or soil effect the objective of this paper is to investigate to what extent the observed slope independence of flow velocity in eroding rills can be explained by the interaction between rill bed roughness and flow hydraulics in a laboratory study two situations were compared 1 rills which can freely erode a uniform soil layer and 2 rills with a fixed bed geometry during the experiments rill discharge and flow velocity were recorded after each experiment a detailed topographic survey of the rill bed was carried out using a laser scanner from these data the main hydraulic variables mean values of flow depth wetted perimeter and hydraulic radius were estimated the experiments confirmed the slope independence of rill flow velocities on mobile beds when the bed is fixed the flow velocity in rills is clearly slope dependent the slope independence of flow velocity on mobile beds is due to a feedback between rill bed morphology and flow conditions the roughness amplitude which was assessed from the standard deviation of corrected height values and the frequency of macroroughness elements which was assessed by counting the number of peaks per unit length in a previously simplified longitudinal profiles both increase and tend to counteract the effect of the increase in slope gradient on rill flow velocity the final rill flow velocity appears to be characterized by a constant average froude number

the abad composite se spain a messinian reference section for the mediterranean and the apts a high resolution integrated stratigraphy is presented for the abad marls of the sorbas and nijar basins in se spain preevaporitic messinian of the western mediterranean detailed cyclostratigraphic and biostratigraphic analyses of partially overlapping subsections were needed to overcome stratigraphic problems in particular encountered at the complex transition from the lower to the upper abad the resulting abad composite section contains a continuous stratigraphic record from the tortonian messinian boundary up to the transition to the messinian evaporites of the yesares member all together 18 calcareous plankton events were recognized which were shown to be synchronous throughout the mediterranean by means of detailed bed to bed cyclostratigraphic correlations the magnetostratigraphy allowed the identification of the four magnetic reversals of chron c3an in the upper abad details in the sedimentary cycle patterns allowed the abad composite to be astronomically calibrated this calibration to the 658n summer insolation curve of solution la90 1 1 yielded astronomical ages for all sedimentary cycles calcareous plankton bioevents ash layers and paleomagnetic reversals up to now the abad composite is the only astronomically well calibrated section that provided a reliable cyclostratigraphy magnetostratigraphy and calcareous plankton biostratigraphy as such it will serve as a reference section both for the pre evaporite messinian in the mediterranean as well as for the messinian interval in the astronomical polarity time scale q 2001 elsevier science b v all rights reserved

comparison of rill flow velocity regimes between developing and stationary rills abstract flow velocity is fundamental in calculating related parameters of physical soil erosion models it has been well known that rill flow velocity varies with developing rill form which complicates and impedes the development of soil erosion models in filed rainfall erosion frequently occurs with pre existing rills not damaged by tillage practices however the rill flow velocity in this case has received little attention in this study we investigated rill flow velocity regimes for both developing and stationary rills using 5 m length plots in the laboratory the experiments included two consecutive rainfalls which had similar runoff rate the first rainfall had an intensity of 90 mm h 1 which generated well developed rills the second had an intensity of 60 mm h 1 and did not damage the rills formed by the first rainfall the results show that for a developing rill rill flow velocity is higher in the lower slope than that in the upper slope and rill flow velocity in the lower slope fluctuates much more over time as a result of the variation of rill morphology following rill development with rill development the rill flow velocity of the lower slope decreased responding to the stabilizing rill channel and exhibited a similar trend to that in upper slope for a stationary rill the rill flow velocities at both sections varied little over time demonstrating that rill flow velocity is primarily influenced by rill morphology hence the results suggested that the strength of fluctuation in rill flow velocity could be used to characterize the instantaneous intensity of soil erosion and active level of rill development the channel of the stationary rill simply acted as transport pathways of sediment supplied by inter rill erosion the physical models of soil erosion should take into account the micro topography on land surface related to the antecedently formed rills

new technique for measuring water depth in rill channels abstract water erosion is one of the most important soil degradation processes and rill erosion contribution to total soil loss is usually dominant as compared to interrill erosion rill erosion modelling requires that rill flow has to be adequately modelled flow depths in rills are typically of the order of millimeters to several centimeters and bed topography characterized by steep slope values significantly affects flow hydraulics in this paper a new technique for measuring the water depth inside a rill channel is proposed and the effects on flow resistance estimate are examined this technique couples an accurate ground survey of the rill channel obtained by close range photogrammetry with the survey of the water tracks inside the channel the comparison between the water depth measurements carried out by a micro hydrometer local technique and those obtained by the water tracks volumetric technique demonstrated that the data pairs are characterized by a wide scattering respect to the line of perfect agreement furthermore the hydraulic radius values obtained by the proposed volumetric technique are always greater than those corresponding to the local technique the developed analysis showed that the volumetric technique is affected by the adopted cross section spacing even if reliable results can be also obtained using a distance interval which is equal to ten times the best investigated reference condition which corresponds to the minimum tested distance interval having the same order of magnitude of the mean 3d dtm resolution using of the volumetric measurement technique for the water depth improved the agreement between the measured darcy weisbach friction factor values and those calculated by the theoretical flow resistance law based on a power velocity profile finally a constant scale factor equal to 0 8257 was proposed to convert the function of the power velocity profile obtained by local measurements into that corresponding to the volumetric technique

mud volcanism by repeated roof collapse 3d architecture and evolution of a mud volcano cluster offshore nigeria abstract using 3d seismic data we document the subsurface architecture of a cluster of 3 mud volcanoes located on the upper continental slope offshore nigeria in a background of gently dipping stratified sediments the subsurface of the cluster contains 8 seismic sequences made of one subcircular syncline 1 3 km in diameter and adjoining unstratified units synclines flatten out upward through intercalation of unstratified concave up lenses between stratified units and are eventually filled by a convex up unstratified lens onlapped by background sediments the lower boundary of each sequence is a 0 5 1 5 km deep bowl shaped unconformity across which high dip strata rest above truncated low dip series we interpret each seismic sequence as a mud volcano system mvs sourced from a connected region and evolving through episodes of roof collapse three are associated with the surface mud volcanoes and another 4 to fossil ones mud volcano systems are dynamic features that record the evolution of 1 the material extruded from one single connected source region depletion zone as it grows downwards and stepwise becomes depleted 2 the basal unconformity which joins strata originally separated by material evacuated in the remobilization process by analogy with salt tectonics we propose to call it a mud weld 3 the conduits and 4 the successive collapsed roofs of the depletion zone the evolution of each mud volcano system in this interpretation records progressive growth of the depletion zone by downbuilding punctuated by episodes of roof collapse and extrusion the geometry and evolution of this type of mvs can be interpreted in the light of analogue models of magmatic caldera development in early stages the thin roof experiences downsagging while remobilized material is extruded through an axial pipe like conduit in later stages the thickened roof undergoes piston like subsidence and mud extrusion occurs along the peripheral fault

the undrained shear strength of soils containing large gas bubbles measurements of undrained shear strength are reported from a series of triaxial tests on reconstituted soil samples containing large bubbles of methane gas the experimental results indicate that the undrained strength can be either increased or reduced by the presence of large gas bubbles depending upon the values of the consolidation pressure and the initial pore water pressure a conceptual model for soils containing large gas bubbles developed in the companion paper is analysed to provide theoretical predictions for the undrained shear strength the analysis leads to theoretical upper and lower bounds for the undrained strength which show good agreement with the experimental data the experimental and theoretical developments have led to a better understanding of the strength of soils containing large gas bubbles this could be of considerable benefit to the offshore construction industry if platforms pipelines and other structures are to be built in areas of gas bearing sediments l article pre

the undrained equilibrium behaviour of gassy sediments gassy soils are defined as those soils which contain a relatively large amount of gas dissolved in the pore fluid examples include the alberta oil sands marine sediments from deep ocean locations

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

field measurement of the velocity of overland flow using dye tracing a new method of computing the mean velocity of overland flow using dye tracing is proposed in which a specified cross section is divided into zones of relatively uniform flow characteristics termed partial sections the mean surface velocity for each partial section is determined by timing the passage of injected dye and this figure is multiplied by 0 67 0 70 or 0 80 depending on whether the flow is laminar transitional or turbulent to give mean velocity the mean velocity for the entire cross section is calculated by multiplying the mean velocity of each partial section by its cross sectional area summing the products for all the partial sections and dividing by the total area of the cross section a field test shows that mean velocity derived in this manner differs from mean velocity derived by the discharge method i e by dividing discharge measured volumetrically by cross sectional area by an average of only 7 07 per cent thus the partial section technique appears to provide a reliable method of estimating mean velocity of overland flow

triggering of the lusi mud eruption earthquake versus drilling initiation abstractthe lusi mud volcano in east java has erupted unabated for almost 2 yr ooding an area of 7 km 2 and displacing more than 25 000 people despite its disastrous impact the mechanism for triggering the lusi eruption remains highly controversial two distinct mechanisms have been proposed one hypothesis suggests that the eruption was triggered by the m w 6 3 earth quake that struck yogyakarta 250 km from lusi two days before the eruption however an examination of static and dynamic stress changes and stress transfer mechanisms indicates that the yogyakarta earthquake was at least an order of magnitude too small to reactivate faults and open uid ow pathways under lusi an alternate theory suggests that lusi was triggered by a blowout following drilling problems in the nearby banjar panji 1 well blowouts result from an inability to control pore uid intakes into the borehole and typically occur when the drilling win dow fracture pressure minus pore pressure is approximately zero and when there is insuf cient protective casing of the well bore pore and fracture pressure data from banjar panji 1 indicate that the well had a narrow drilling window of only 0 2 3 mpa furthermore two planned casing points were skipped during drilling resulting in 1742 m of unprotected borehole the combina tion of hazardously narrow drilling window and long uncased borehole would have made drill ing problems in banjar panji 1 dif cult to control placing the well at high risk of blowing out furthermore well bore pressures following drilling problems in banjar panji 1 reached magni tudes in excess of the fracture pressure and thus were suf cient to create uid ow pathways in the subsurface therefore we suggest that no viable method is known by which the yogyakarta earthquake could have triggered the mud ow and that a blowout in the banjar panji 1 well was the most likely mechanism for triggering the lusi eruption keywords

similarity between morphological characteristics of rills and ephemeral gullies in sicily italy this paper reports the results of a field investigation aimed to establish morphological similarity between rills and ephemeral gullies rill measurements were made on 14 plots having a surface area of 22 352 m2 located on a 14 9 slope and on a plot 6 0 m wide and 22 0 m long having a uniform 22 0 slope the plots are located on the experimental station for soil erosion measurements sparacia of the agricultural faculty of palermo university in sicily italy all plots are subjected to natural rainfall the measurements were made immediately following five events between november 2004 and december 2005 the ephemeral gully measurements were made on a cultivated area of about 120 ha located in central sicily which is representative of many soil crop conditions in the mediterranean basin the morphological similarity between rill and ephemeral gully was first tested then a power relationship between rill or gully volume and length theoretically deduced by dimensional analysis and self similarity theory was applied this power relationship needs a different scale factor for rill and gully measurements finally using two dimensionless groups representative of the channel morphology variables the analysis showed that a single relationship can be applied to rill and gully measurements copyright 2009 john wiley sons ltd

morphometric and hydraulic geometry assessment of a gully in sw spain abstract gully erosion represents one of the most significant types of land degradation in the mediterranean areas giving place to important on and off site effects in this paper a second order gully located in sw spain is analyzed along the gully 28 cross sections were established and measured with a leica tcrm1102 laser total station approximately every 6 months from 2001 to 2007 the sections were located at variable distance placing them in areas where active erosion was evident in total 13 field measurements were carried out and the geometric characteristics of 28 cross sections were obtained morphometric analyses were carried out in both the main gully and a tributary reach by applying an empirical relationship between channel length and eroded volume morphometric variables of the gully sections were combined into two dimensionless groups and a morphological similarity between different linear erosion landforms rills ephemeral and permanent gullies was obtained then the coefficient of variation of the calculated volumes was used to compare the instability between the main gully and the tributary reach finally the hydraulic geometry of the gully was assessed by calibrating three empirical power equations which relate bankfull discharge with mean flow velocity cross sectional depth and width the hydraulic characterization of the main gully and the tributary reach was investigated for each field survey and a different behavior was detected the hydraulic analysis also demonstrated that higher values of discharge provide better predictions of flow velocity the size of the main and tributary gullies affects the discharge width relationship and that gully depth is the variable which can be predicted with the highest accuracy

hydrodynamic description for advective sediment transport processes and rill initiation a physically based model for advective sediment transport during rill initiation is developed based on 1 a short wavelength rescaling of the momentum balance equations for the surface water flux 2 a deforming coordinate system which characterizes local morphological changes of the surface during erosion and 3 a generalized transport function for the surface sediment flux which distinguishes the contributions of diffusive and advective transport a linear stability analysis of the coupled system indicates that an intrinsic minimum transverse length scale for rill initiation is forced by the cross slope pressure gradient in the surface water the wavelength of this initial rill spacing is dependent upon the relative significance of the advective component of sediment transport and the hydraulic efficiency of the surface water flux and is independent of the total length of the hillslope the hydrodynamic model presented can also be used to evaluate the nonlinear development of rills and rill networks subsequent to initiation

dye tracer technique for rill flows by velocity profile measurements abstract water flow on hillslope soil surface supplies energy which is required to detach soil particles to transport and deposit sediments therefore flow velocity is a key variable related to hillslope hydrodinamics of soil erosion processes among the different methods available for measuring velocity of shallow interrill and rill flow the trace technique is widely used trace technique is applied by adding a material salt magnetic material water isotope floating object and then measuring the speed of the material to travel a known distance from the injection point when flow velocity is measured using a dye tracing method the mean velocity is calculated by multiplying the measured surface velocity of the leading edge of the tracer plume by a correction factor which was generally empirically deduced the main uncertainty of the dye tracing technique stands in the estimate of this correction factor which is the ratio between the mean flow velocity and the surface velocity the main goal of this paper is establishing a theoretical relationship for calculating the correction factor by using a power velocity profile at first the developed analysis demonstrated that the correction factor only depends on the exponent of the power velocity distribution eq 5 then this theoretical expression of the correction factor was applied using the velocity profiles measured by baiamonte and ferro for the condition of sediment free flow in motion on a rough bed and by coleman for a sediment laden flow moving on a smooth flume using the correction factor values calculated by the velocity measurements carried out for the sediment free flow in motion on a rough bed the relationship between the correction factor and roughness height was established in agreement with a previous study by ali et al for a sediment free flow the correction factor increases with roughness height finally the velocity profile measurements carried out for a sediment laden flow in motion on a smooth bed were used to state the effect of sediment load on the correction factor this last analysis allowed to conclude in agreement with li and abrahams and zhang et al that the correction factor decreases when the sediment load increases

structure and emplacement of mud volcano systems in the south caspian basin the term mud volcano system is coined to describe the set of structures associated with a constructional edifice mud volcano and feeder complex that connects the volcano to its source stratigraphic unit three dimensional 3 d seismic data from the south caspian basin are used to investigate the structural elements and evolution of these systems mud volcano systems initiate via early kilometer scale biconic edifices termed pioneer cones these are fed by fluidization pipes tens of meters in width subsequent kilometer scale mud volcanoes grew via persistent extrusion fed by numerous additional fluidization pipes injected in the country rock this subvolcanic intrusion complex creates a densely intruded cylindrical zone similar in cross section to gryphon swarms observed at an outcrop onshore wall rock erosion and compaction of the intruded zone leads to the collapse of a downward tapering cone enveloping the cylindrical zone capped by ring faults that define a kilometer scale caldera that downthrows the overlying mud volcano mud volcanoes get buried during basin subsidence and can look like intrusive laccoliths at first glance on seismic data reactivation of mud flow through a conduit system generates a stack of superimposed mud volcanoes through time large volcanoes continue to dewater during burial and may locally remobilize this model of mud volcano evolution has similarities with igneous and salt tectonic systems to reduce drilling and geologic uncertainty mud volcano system extent and impacts on a reservoir can be assessed on 3 d seismic data simon stewart received his ph d from the imperial college london in 1992 in 1992 2000 he was seismic interpreter at amerada hess in support of exploration and appraisal drilling in the north sea in 2000 he moved to bp and has since worked on structural geology and well planning in the americas middle east and the former soviet union his special interest is in the integration of structural geology and seismic interpretation richard davies received his ph d from the university of edinburgh in 1995 in 1995 2003 he was with mobil and exxonmobil working on field development and exploration the north sea the west of shetlands and the west niger delta deep water slope in 2003 2005 he was a senior lecturer in earth sciences at cardiff university united kingdom currently he is professor and director of cerees center for research into earth energy systems durham university united kingdom his special interest is in seismic scale expression of fluid migration and diagenesis

soil erosion by surface water flow on a stony semiarid hillslope soil erosion on hillslopes occurs by processes of soil splash from raindrop impacts and sediment entrainment by surface water flows this study investigates the process of soil erosion by surface water flow on a stony soil in a semiarid environment a field experimental method was developed whereby erosion by concentrated flow could be measured in predefined flow areas without disturbing the soil surface the method allowed for measurements in this study of flow erosion at a much wider range of slopes 2 6 to 30 1 per cent and unit discharge rates 0 0007 to 0 007 m2 s 1 than have been previously feasible flow velocities were correlated to discharge and hydraulic radius but not to slope the lack of correlation between velocity and slope might have been due to the greater rock cover on the steeper slopes which caused the surface to be hydraulically rougher and thus counteract the expected effect of slope on flow velocity the detachment data illustrated limitations in applying a linear hydraulic shear stress model over the entire range of the data collected flow detachment rates were better correlated to a power function of either shear stress r2 0 51 or stream power r2 0 59 published in 1999 by john wiley sons ltd

comment on rill erosion processes on steep colluvial deposit slope under heavy rainfall in flume experiments with artificial rain by f jiang et al abstract since rill flows are characterized by small water depths and steeply sloping channels the corresponding hydraulic conditions are very different to those which are typically found in channels of streams and rivers furthermore limited information is currently available on the effect of rainfall on flow resistance the objective of this comment was to investigate the applicability of a recently theoretically deduced rill flow resistance equation based on a power velocity profile using measurements carried out by jiang et al for both different slope steepness conditions and rainfall intensity the relationship between the velocity profile parameter the channel slope and the flow froude number was calibrated using the data by jiang et al the theoretical approach and the measurements carried out in the investigated conditions allowed to state that a the darcy weisbach friction factor can be accurately estimated using the proposed theoretical approach b the data were supportive of the slope independence hypothesis of rill velocity stated by govers and c the darcy weisbach friction factor varies with rainfall intensity

sediment damage caused by gas exsolution a key mechanism for mud volcano formation abstract gassy sediments are common in marine environments and are characterized by a specific mechanical behavior significantly different from that of water saturated sediments it is shown that gas causes damage and initiates fractures in sediments to define the controlling parameters dominating the damage process during gas exsolution and its consequences in terms of hydro mechanical behavior we developed a specific consolidation apparatus to test sediments collected from the active absheron mud volcano indeed mud volcano formation is initiated by gas exsolution and subsequent mud generation at depth from stratified sediments gas was generated in the samples by circulating carbonated water through the fine grained sediments then decreasing the total pressure particular attention was given to the impact of gas saturation and associated damage and fractures on p wave velocity sediment compressibility permeability and preconsolidation pressure results show that fracture geometry is mainly controlled by the degree of gas saturation and preconsolidation pressure the damage level increases with the degree of gas saturation while the elastic modulus of sediments is degraded experimental data show that sediments do not entirely recover their original mechanical behavior when gas dissipates finally the experimental data confirm that gas exsolution and expansion is a key mechanism for mud generation

mud volcanism an updated review abstract mud volcanism or sedimentary volcanism represents one of the most intriguing phenomena of the earth s crust with important implications in energy resource exploration seismicity geo hazard and atmospheric budget of greenhouse gases since the first review papers were issued at the beginning of 2000s a large amount of new geological geophysical and geochemical data has been acquired which clarified ambiguous concepts and significantly improved our knowledge of mud volcanism here we offer an updated review of the knowledge and implications of mud volcanoes with emphasis on the terminology used to describe different processes and structures the physical chemical and morphological characteristics of the several fluid emission structures the chemical properties of the released fluids in particular the molecular and isotopic composition of the gas the mud volcano formation dynamics and the several implications for petroleum exploration geo hazards and global atmospheric methane budget this review integrates new fluids data collected in azerbaijan and is complemented with field observations from various mud volcano provinces worldwide although the total number of mud volcanoes on earth is still uncertain 600 main onshore structures with a large variety in shapes and sizes are documented in recent global data sets and several thousand are assumed to exist in the oceans it is clear that a mud volcanoes are broadly distributed throughout the globe in active margins compressional zones of accretionary complexes thrust and overthrust belts passive margins deep sedimentary basins related to active plate boundaries as well as delta regions b they are specifically located in hydrocarbon bearing basins along anticline axes strike slips and normal faults and fault related folds in petroleum systems c they represent a specific category of natural gas oil seepage manifestation often related to deep and pressurised reservoirs d the main engine driving mud volcanism is given by a combination of gravitative instability of shales and fluid overpressure build up followed by hydrofracturing e hydrocarbons are generally of thermogenic origin while microbial gas is released in only a few cases mud volcanism on other planets e g mars and titan and microbial activity associated with gas seepage represent emerging issues and opportunities for future research

hydrodynamic characteristics of rill flow on steep slopes rill erosion is a dominant sediment source on sloping lands however the amount of soil loss from rills on steep slopes is vastly more than that on gentle slopes because of differences in rill shape and hydraulic patterns the aims of this paper are to determine the hydrodynamic characteristics of rills and the friction coefficients in steep slope conditions and to propose modifications of some hydraulic parameters used in soil loss prediction models a series of inflow experiments was conducted on loess slopes the results show that the geometric and hydraulic properties of rill on the steep loess slopes which are characterized by the mean width of cross sections mean velocity and mean depth of flow are related to discharge and slope gradient in power functions however the related exponents to discharge are 0 26 0 48 and 0 26 respectively which are different from the exponents derived in previous studies which were conducted on gentle slopes the manning roughness coefficient ranged from 0 035 to 0 071 with an average of 0 0536 and the darcy weisbach friction coefficients varied from 0 4 to 1 9 the roughness coefficients are closely related to the reynolds numbers and flow volumes however the correlations vary with slope gradient the roughness coefficients are directly proportional to the reynolds number and the flow volume on steep slopes in contrast with the roughness coefficients found on gentle slopes which decrease as the reynolds number and flow volume increase this difference is caused by the interactions among the hydraulics of the flow the shape of the rills and the sediment concentrations on steep slopes the results indicate that parameters used in models to predict rill erosion have to be modified according to slope gradient copyright 2015 john wiley sons ltd

a new hydrothermal scenario for the 2006 lusi eruption indonesia insights from gas geochemistry abstract the 29th of may 2006 gas and mud eruptions suddenly appeared along the watukosek fault in the north east of java indonesia within a few weeks several villages were submerged by boiling mud the most prominent eruption site was named lusi to date november 2011 lusi is still active and a 7 km2 area is covered by the burst mud breccia the mechanisms responsible for this devastating eruption remain elusive while there is consensus about the origin of the erupted mud the source of water is uncertain the origin of the gas is unknown and the trigger of the eruption is still debated in order to shed light on these unknowns we acquired a wide set of data of molecular and isotopic composition of gas sampled in several lusi vents in the surrounding mud volcanoes in the closest natural gas field wunut and in the hydrothermal vents at the neighbouring volcanic complex in the period 2006 2011 the boiling fluids erupted in the crater zone are apparently co2 dominated while colder ch4 dominated and c2 c3 bearing fluids are identified at several sites around the crater zone gas genetic diagrams maturity plots and gas generation modelling suggest that the hydrocarbons are thermogenic 13c1 up to 35 13c2 up to 20 deriving from marine kerogen with maturity of at least 1 5 ro for instance in the 4400 m deep ngimbang source rocks co2 released from the crater and surrounding seeps is also thermogenic 13c from 15 to 24 related to kerogen decarboxylation or thermal ch4 oxidation in deep rocks although three vents just outside the crater showed an apparent inorganic signature 7 5 4000 m magmatic intrusions and hydrothermal fluids responsible for the enhanced heat that altered source rocks and or gas reservoirs the neighbouring magmatic arjuno complex and its fluid pressure system combined with high seismic activity could have played a key role in the lusi genesis and evolution within this new model framework lusi is better understood as a sediment hosted hydrothermal system rather than a mud volcano

dissipative analogies of step pool features from rills to mountain streams abstract in this paper the dissipative similarity of step pool units at different spatial scales ranging from rills to streams is analyzed this investigation benefits from the latest theoretical advances in open channel flow resistance high resolution topography from close range photogrammetry applied to rill erosion and the availability of published data from literature on step pool streams at first the integration of a power velocity distribution allowed to obtain a theoretically based expression of darcy weisbach friction factor in which function and exponent of the velocity profile are included then this theoretically deduced flow resistance relationship is calibrated and tested by flow measurements carried out in rill reaches where the step pool units occurred in particular the proposed function is calibrated using the measurements corresponding to 88 rill reaches shaped on a plot having a slope equal to 14 22 and 24 and the calibrated equation is also positively tested with measurements carried out in 48 rill reaches shaped on a 26 sloping plot for the rill flow the developed analysis stated that the friction factor is characterized by estimate errors which are less than or equal to 15 for 86 of cases and less than or equal to 10 for 70 of cases using measurements of flow velocity water depth width and bed slope measurements carried out in 109 reaches of step pool streams this investigation demonstrates that the theoretical flow resistance equation can be applicable to step pool streams carrying out a specific calibration of the function the comparison between the darcy weisbach friction factor values measured in streams and step pool rills demonstrates that in the stream features the friction factor values are on average higher than those related to rills with step pool sequences in conclusion the comparison between rills and streams with step pool units highlights that the same theoretical flow resistance equation can be applied even if a scale effect between the two features is detected

measurement and modelling of high resolution flow velocity data under simulated rainfall on a low slope sandy soil the study presented here is focussed on the question of the hydraulic nature of the threshold that allows a rill to start a rainfall simulation experiment was carried out to produce high resolution flow velocity data the experiment employed a 10 m 4 m experimental plot with a 1 slope which had been previously eroded and had a small rill formed in the middle the experiment consisted of a 2 h 15 long rainfall at a constant intensity of 69 mm h 1 surface elevation was measured before rainfall at a horizontal resolution of 2 5 cm across and 5 cm along the slope direction during rainfall flow velocities were measured at 68 locations on the plot with the salt velocity gauge technology an automated miniaturized device based on the inverse modelling of the propagation of a salt plume the experiment led to the collection of flow velocity measurements which are novel in three ways i the small size of the measured section which was only 10 cm long and 1 cm wide ii the wide range of measured flow velocities which ranged from 0 006 m s 1 to 0 27 m s 1 and iii the large number of measured locations the flow velocity field was simulated with three models psem 2d solves the saint venant equations in 2d mahleran uses a 1d kinematic wave in the slope direction coupled with a 2d flow routing algorithm and rillgrow2 which involves an empirical runoff algorithm that is close in principle to the diffusion wave equation in 2d the darcy weisbach friction factor ff and the infiltration parameters were calibrated in all cases to investigate the capabilities of the different models to reproduce flow hydraulics compatible with the onset of rilling in a first set of numerical experiments ff was set uniform and calibration used only the hydrograph the comparison of simulated and observed flow velocity field showed that psem 2d was the most satisfying model at the cost of longer computational time mahleran gave surprisingly good results with regards to the simplicity of the model and its low computational needs however all models largely underestimated the highest velocity values located in the rill furthermore none of the models was able to simulate the reynolds re and froude fr numbers the next numerical experiment was done with psem 2d non uniform ff values were calibrated by fitting the simulated flow velocity field to the observed one the latter simulation produced realistic simulations of re and fr the hydraulic conditions at the transition from interrill flow to rill flow are discussed the results support the theory that supercritical flows are a necessary condition for a rill to emerge from a smooth surface

first order description of the mechanical fracture behavior of fine grained surficial marine sediments during gas bubble growth 1 bubbles in sediments imaged via computed tomography ct scanning and in surrogate transparent material gelatin are well described geometrically as eccentric oblate spheroids while sediments are undoubtedly visco elasto plastic solids only part of that complex behavior appears to influence significantly the formation and shape of gas bubbles specifically the shape of these bubbles can be explained if the mechanical response of fine grained sediment is approximated by linear elastic fracture mechanics lefm to determine the adequacy of the lefm approximation for gas bubble growth in fine grained sediments a number of gas bubbles were injected and grown in natural sediments while monitoring the size and shape using an industrial ct scanner a comparison of measured inverse aspect ratios iars of the injected bubbles with calculated iars from pressure records provides support for the lefm theory deviations from lefm are observable in the data but as bubbles grow larger they trend more closely toward the theory the use of lefm has been shown to describe gas bubble growth in shallow coastal sediments to first order

experimental observations of mechanical dilation at the onset of gas flow in callovo oxfordian claystone understanding the mechanisms controlling the advective movement of gas and its potential impact on a geological disposal facility gdf for radioactive waste is important to performance assessment in a clay based gdf four primary phenomenological models can be defined to describe gas flow i diffusion and or solution within interstitial water ii visco capillary or two phase flow in the original porosity of the fabric iii flow along localized dilatant pathways micro fissuring and iv gas fracturing of the rock to investigate which mechanism s control the movement of gas two independent experimental studies on callovo oxfordian claystone cox have been undertaken at the british geological survey bgs and laego ensg nancy laego the study conducted at bgs used a triaxial apparatus specifically designed to resolve very small volumetric axial and radial strains potentially associated with the onset of gas flow the laego study utilized a triaxial setup with axial and radial strains measured by strain gauges glued to the sample both studies were conducted on cox at in situ stresses representative of the bure underground research laboratory url with flux and pressure of gas and water carefully monitored throughout long duration experiments a four stage model has been postulated to explain the experimental results stage 1 gas enters at the gas entry pressure gas propagation is along dilatant pathways that exploit the pore network of the material around each pathway the fabric compresses which may lead to localized movement of water away from the pathways stage 2 the dendriticflow path network has reached the mid plane of the sample resulting in acceleration of the observed radial strain during this stage outflow from the sample also develops stage 3 gas has reached the backpressure end of the sample with end to end movement of gas dilation continues indicating that gas pathway numbers have increased stage 4 gas fracturing occurs with a significant tensile fracture forming resulting in failure of the sample both studies clearly showed that as gas started to move through the cox the sample underwent mechanical dilation i e an increase in sample volume under in situ conditions the onset of dilation micro fissuring is a necessary precursor for the advective movement of gas

rill erosion in natural and disturbed forests 1 measurements 1 rill erosion can be a large portion of the total erosion in disturbed forests but measurements of the runoff and erosion at the rill scale are uncommon simulated rill erosion experiments were conducted in two forested areas in the northwestern united states on slopes ranging from 18 to 79 we compared runoff rates runoff velocities and sediment flux rates from natural undisturbed forests and in forests either burned at low soil burn severity 10 months or 2 weeks post fire high soil burn severity or subject to skidding of felled logs the runoff rates and velocities in the natural sites 2 7 l min 1 and 0 016 m s 1 respectively were lower than those in all the disturbed sites 12 to 21 l min 1 and 0 19 to 0 31 m s 1 respectively except for the 10 month old low soil burn severity site where the velocity 0 073 m s 1 was indistinguishable from the natural sites the mean sediment flux rate in the natural sites also was very small 1 3 10 5 kg s 1 as compared to the rates in the disturbed areas 2 5 10 4 to 0 011 kg s 1 the hillslope gradient did not affect the runoff or sediment responses the sediment flux rates generally were greater in the initial stage of each inflow period than in the steady state condition but there was no corresponding transient effect in runoff rates rill erosion modeling implications based on these data are presented in part 2 of this study

mechanical behaviour of gas charged marine plastic sediments understanding how free gas modifies the mechanical behaviour of marine plastic sediments remains a challenging issue special triaxial tests were carried out on natural sediments recovered from the gulf of guinea special attention was devoted to the laboratory preparation procedure involving saturation of natural marine sediment samples with carbonated water and generation of free gas following undrained unloading experimental data show that soil destructuration and damage generated by gas expansion and exsolution are at the origin of a the increase in the isotropic compressibility and decrease in the preconsolidation pressure and b the decrease in the peak undrained strength and abrupt increase of the pore pressure during undrained shearing the experimental data also show that flooding of gas bubbles and dissolution of free gas do not imply a complete strength recovery of natural sediments

terrestrial laser scanning soil surfaces a field methodology to examine soil surface roughness and overland flow hydraulics smith m w cox n j bracken l j 2011 terrestrial laser scanning soil surfaces a field methodology to examine soil surface roughness and overland flow hydraulics hydrological processes 25 6 842 860

relationship between discharge velocity and flow area for rills eroding loose non layered materials a relationship between discharge flow velocity and flow area in rills is established using data from four field and laboratory studies the proposed relationship is shown to predict successfully flow velocities measured in six other studies although slopes range from 0 035 to 0 45 and soil materials range from stony sands over silt loams to vertisols mean flow velocity can be well predicted from discharge alone thus there is no important influence of slope and or soil material characteristics on flow velocities in rills the proposed relationship may be used to improve performance of deterministic flow routing models when applied to rilled catchments furthermore it allows the calculation of unit stream power which has been shown to be related to the transporting capacity of overland flow in terms of slope and discharge

sediment transport capacity of sheet and rill flow application of unit stream power theory theoretical equations for calculating the unit stream power of both sheet and rill flow were developed and used to predict the sediment transport capacity of such flows independent data sets from three sources representing both finely aggregated clay soils and coarse textured nonaggregated soils sheet rill and composite sheet rill flow systems and a range of slopes were used to test the utility of the method the results were very good and demonstrated the simplicity and robustness of the method for shallow overland flow the best results were obtained when the critical unit stream power at incipient sediment motion was treated as a constant value that was independent of slope the results also suggest that a unique value of critical unit stream power for rill initiation exists that is independent of soil type for noncohesive loams or fine sands and finely aggregated clay soils the sediment transport capacity can be accurately predicted from a knowledge of the physical characteristics of the soil or bed material alone for aggregated clay soils this requires information on the aggregate size distribution and the effects of soil particle size differentiation as flow rates and unit stream powers increase with the transition from sheet to rill flow

rill erosion and morphological evolution a simulation model a mathematical model is advanced to simulate dynamically and spatially varied shallow water flow and soil detachment transport and deposition in rills the model mimics the dynamic process of rill evolution including variable rates of sediment redistribution along the bed and changes in local bed morphology the sediment source term in the model uses a point scale probabilistic relationship based on turbulent flow mechanics and a recently developed sediment transport relationship for rills based on stream power the interdependent feedback loops between channel bed morphology local flow hydraulics and local scour and deposition within the framework of the full hydrodynamic equations with inertial terms constitute a mathematical model with the capacity to represent spatial variability and temporal evolution of the rill finite elements were applied to numerically solve the hydrodynamic and sediment continuity equations a series of laboratory flume experiments were performed to evaluate the model initial bed slopes were 3 5 and 7 with step increases of water inflow rates of 7 6 11 4 and 15 2 l min 1 the soil material used in the flume was a kaolinitic sandy clay loam the rill model equations were solved for increasingly complex cases of spatial and temporal variabilities the model followed measured patterns of morphological changes as the rill evolved which suggests that the feedback loops in the model between erosion bed morphological changes and hydraulics were adequate to capture the essence of rill evolution

rill hydraulics on a semiarid hillslope southern arizona seventy field experiments were conducted in seven rills located on a semiarid rangeland hillslope underlain by gravelly soils at walnut gulch arizona the rills which are characterized by wide shallow cross sections and gravel covered beds have mean at a station hydraulic geometry exponents of b 0 33 f 0 34 and m 0 33 although the differences between these values and typical values of b 0 30 f 0 40 and m 0 30 for cropland rills are not statistically significant they are thought to be real as cropland rills often have more rectangular cross sections and steeper sides than the rangeland rills under study for rills formed in silty loamy soils govers developed an empirical relation between mean flow velocity and discharge emphasizing the generality of this relation he suggested that it may be used as a simple means of routing runoff through rills he also noted that this relation appeared to be unaffected by either slope or soil materials the present data represent rills underlain by coarser and somewhat more varied gravel rich soils these data do not conform to govers relation and a multiple regression analysis reveals that slope and soil materials either directly or indirectly through bed roughness exert almost as much influence on flow velocity as does discharge three alternative methods are developed for predicting flow velocity in the rills under study all three methods give good results with the largest root mean square deviation being 3 115 cm s 1

the physics of bubbles in surficial soft cohesive sediments abstract this paper reviews current understanding of the physics of bubbles in soft unlithified cohesive sediments certainly in the top 100 m from the sediment water interface but likely much deeper experimental evidence primarily ct scans and internal pressure records indicate that near surface bubbles grow by elastically compressing and fracturing these sediments which results in thin irregular disks of gas these data do not suggest either plastic or fluid behavior on the part of the bulk sediment in addition there is no hint of capillary invasion of gas into the pores of fine grained sediments the growth rate of an elastic fracturing disk shaped bubble can vastly exceed that of a spherical bubble depending on the eccentricity of the bubble this effect results from the far more favorable surface to volume ratio of flattened bubbles the initial rate of rise of bubbles in cohesive sediments also appears to be governed by a fracture process which is driven by pseudo buoyancy the rate of bubble rise could be controlled by various possible mechanisms but only the predictions from a visco elastic fracture propagation model seem to produce rise velocities that are not ballistic experimental evidence demonstrates that a rising bubble can deviate from its path to the surface if it encounters a zone of sediment with lower lateral fracture toughness such a bubble will begin to move in a lateral direction but stall because pseudo buoyancy is no longer operative subsequent bubbles will do the same and accumulate in the low fracture toughness zone this explains the occurrence of shallow sub seafloor domes of gas and modeling of this process predicts only modest over pressures in such structures

cyclic liquefaction of loose gassy sand gas can be found in many soils but none more common than in seabed soils gas charged sediments are known to be widely distributed throughout the world s oceans numerous research programs have studied saturated soil response to cyclic loading however little is known about the behavior of gassy soils subjected to cyclic loading the response of loose gassy specimens subjected to cyclic loading was studied in a laboratory program triaxial tests were performed on specimens of reconstituted ottawa sand prepared to various gas contents and densities the specimens were consolidated and then sheared under undrained cyclic loading gas content was measured at the beginning and end of each test using time domain reflectometry the response of the gassy specimens has been shown to be influenced by the soil state and grain characteristics and the intensity duration and frequency of the cyclic loading the propensity of a soil to liquefy is represented by a cyclic resistance ratio defined as the cyclic stres

effects of intensification of the indian summer monsoon on northern andaman sea sediments during the past 700 years recent studies have revealed an intensification of the indian summer monsoon ism over the past 700 years but its influence on the sediments in the northern andaman sea is unclear to examine this influence we used radiocarbon dated sediment core stmy6 acquired 100 km offshore in the northern andaman sea from the ayeyarwady river mouth and obtained a 700 year long record of the grain size distribution and geochemistry of the sedimentary sequence the ism influences precipitation surrounding the ayeyarwady river and thus the river water and sediment discharges to the northern andaman sea near the river mouth in the ayeyarwady river and the weathering intensity in the river catchment based on the system we propose that higher sedimentation rates and larger modal grain size the most abundant size in the grain size distribution of sediments and lower carbonate concentrations after about ad 1600 can be attributed to higher ism intensity profiles of total organic carbon toc content and carbon nitrogen c n ratios however did not show any trends after about ad 1600 which suggests that the ism has had little influence on these proxies at this site

elastic wave velocity in marine sediments with gas hydrates effective medium modeling we offer a first principle based effective medium model for elastic wave velocity in unconsolidated high porosity ocean bottom sediments containing gas hydrate the dry sediment frame elastic constants depend on porosity elastic moduli of the solid phase and effective pressure elastic moduli of saturated sediment are calculated from those of the dry frame using gassmann s equation to model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions a hydrate modifies the pore fluid elastic properties without affecting the frame b hydrate becomes a component of the solid phase modifying the elasticity of the frame the goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data we apply the model to sonic and vsp data from odp hole 995 and obtain hydrate concentration estimates from assumption b consistent with estimates obtained from resistivity chlorinity and evolved gas data

experimental studies on the effects of fracture on the p and s wave velocity propagation in sedimentary rock calcarenite del salento abstract experimental studies were carried out in laboratory in order to investigate the effects of fracture on compressional p wave and shear s wave velocity propagation and therefore the relations between seismic properties and rock mass parameters the discontinuity index i d fracture density parameter c linear fracture parameter and the rock quality designation rqd were used to describe the rock mass parameters these parameters are analyzed and then related to the seismic properties four vertical aligned fractures were created on an intact calcarenite block 0 6 m long 0 4 m thick and 0 4 m width by sawing the measures were carried out in four different blocks of cacarenite having the same physical properties and in four different phases in first block the fractures were filled with air in the second block the fractures were filled with terra rossa in third block the fractures were filled with wet terra rossa and in the fourth block the fractures were filled with clay the test results were statistically analysed using the method of least squares regression and polynomial relationships with high correlation coefficient were found between the fractured rock parameters and p wave s wave velocities and v p v s ratio the investigations suggest that the p wave and s wave velocities decrease with increasing the fracture parameters while the v p v s ratio increases with decreasing the fracture parameters furthermore the results of the experimental studies were applied on the seismic refraction tomography data acquired in a great measurements campaign undertaken in the adriatic salentina coast south italy in order to monitor the coastal erosion the geophysical results using the polynomial relationships between the fractured rock parameters and p wave velocity are in good agreement with the geomorphological and geological results

occurrence of monsoon depressions in the southwest indian ocean synoptic descriptions and stratosphere to troposphere exchange investigations this study focuses on monsoon depressions md in the southwest indian ocean swio basin a md is a subcategory of tropical depressions some aspects of md dynamical characteristics differ from those of the classical tropical depressions a md displays a broader horizontal extension 1000 km and its structure is marked by deep convection clusters that are generally poorly organized these convective clusters often develop as a wide convection belt in the eastern semicircle of the system the mdnucleus is characterized by an area of weak winds about 200 km wide and by a hazy central cloud system surrounded by a larger belt of strong winds in the swio basin between 2000 and 2008 5 systems out of the 100 tropical cyclones that were followed by rsmc la reunion comply with these criteria and then have been identified as md using potential vorticity from european centre for medium range weather forecasts analyses as stratospheric tracer stratospheric signatures have been identified in the troposphere for the five events involving different dynamical mechanisms tropopause fold between an anticyclone and md tropopause fold between md and a jet front system and cut off low the dynamical structure of md especially the external belt of strong winds seems to favor tropopause disturbances and leads to stratosphere troposphere exchange

sediment connectivity a framework for understanding sediment transfer at multiple scales a major challenge for geomorphologists is to scale up small magnitude processes to produce landscape form yet existing approaches have been found to be severely limited new ways to scale erosion and transfer of sediment are thus needed this paper evaluates the concept of sediment connectivity as a framework for understanding processes involved in sediment transfer across multiple scales we propose that the concept of sediment connectivity can be used to explain the connected transfer of sediment from a source to a sink in a catchment and movement of sediment between different zones within a catchment over hillslopes between hillslopes and channels and within channels using fluvial systems as an example we explore four scenarios of sediment connectivity which represent end members of behaviour from fully linked to fully unlinked hydrological and sediment connectivity sediment travel distance when combined with an entrainment parameter reflecting the frequency magnitude response of the system maps onto these end members providing a coherent conceptual model for the upscaling of erosion predictions this conceptual model could be readily expanded to other process domains to provide a more comprehensive underpinning of landscape evolution models thus further research on the controls and dynamics of travel distances under different modes of transport is fundamental copyright 2014 john wiley sons ltd

flume experimental evaluation of the effect of rill flow path tortuosity on rill roughness based on the manning strickler equation abstract numerous soil erosion models compute concentrated flow hydraulics based on the manning strickler equation v kst r2 3 i1 2 even though the range of the application on rill flow is unclear unconfined rill morphologies generate local friction effects and consequently spatially variable rill roughness which is in conflict with the assumptions of sectional uniform channel flow and constant channel roughness of the manning strickler equation the objective of this study is to evaluate the effect of rill morphology on roughness and hence to assess the manning strickler roughness coefficient kst by rill morphological data a laboratory experiment was set up to analyse rill hydraulics and roughness of i free developed rill fdr flows and ii straight constrained rill scr flows in the flume the flume experiment generated manning strickler roughness coefficients kst between 22 m1 3 s 1 and 44 m1 3 s 1 reflecting a potential area of the roughness parameter uncertainty it was found that fdr experiments generated significantly lower kst values compared to scr experiments because skin and local friction effects in the fdr experiments were more efficient reducing flow velocity probably due to higher energy dissipation rill flow path tortuosity tort was used to describe the rill morphology of the experiments and correlation statistics between tort and kst identified considerable explanatory capacity of rill flow path tortuosity on rill roughness the flume study demonstrated that a regression model between tort and kst can be used to assess local friction effects of unconfined rill morphologies and hence to reduce the area of uncertainty of the manning strickler roughness parameter

effect of initial pore pressure on undrained shear behaviour of fine grained gassy soil many of the world reserves of fossil fuels are located at various water depths in fine grained sediment under the seabed the fine grained sediment contains relatively large biogas bubbles which has been posing challenges to the stability of offshore foundations supporting oil and gas platforms although fine grained gassy soil was found to exhibit different undrained shear strengths cu by altering the initial pore pressure ui relevant to water depth systematic studies concerning the effect of ui on undrained shear behaviours of the soil are still lacking this study reports a series of undrained triaxial tests aiming to compare and investigate the responses of reconstituted fine grained gassy soil with the same consolidation pressure p c but at a wide range of varying ui 0 1000 kpa the shearing induced excess pore pressure u in the gassy specimens highly depends on ui it can be either smaller than that of the saturated specimen with the same p c due to partial dissipation of u int

effects of freshly incorporated straw residue on rill erosion and hydraulics abstract rill hydraulics and hence flow detachment are modified by the presence of incorporated vegetation residue typically water flow in the rill is retarded due to the extra shear stress generated by the residue the main objective of this study was to develop an approach to predict soil detachment by rill flow in the presence of freshly incorporated vegetation residue that is compatible with our current understanding of rill hydraulics and requires no additional information on rill geometry laboratory experiments were carried out to collect a dataset on rill flow detachment on surfaces with incorporated straw that was compatible with existing dataset on bare soils gimenez and govers 2001 interaction between bed roughness and flow hydraulics in eroding rills water resources research vol 37 no 3 791 799 we found that effective unit length shear force e is well related to soil detachment when incorporated residue is present the determination of e is based on the recalculation of the wetted cross section area for a given flow velocity and slope a hypothetical wetted cross section area is estimated using empirical relationships defined for rills formed in bare soils this procedure was also successfully applied to data from former field experiments the procedure allows estimating erosion rates when flow characteristics velocity and hydraulic radius are known however the prediction of these flow characteristics remains uncertain

distribution of depth of overland flow on desert hillslopes and its implications for modeling soil erosion abstract data collected during field experiments on hillslopes in southern arizona reveal that the depth of overland flow in interrill areas can be approximated by a negative exponential distribution soil erosion over the greater part of most hillslopes is equal to detachment capacity flow detachment in interrill areas is generally modeled using a du boys type equation in which shear stress is calculated using the mean depth of flow it is shown that using the mean depth rather than the distribution of depth can result in the severe underestimation of flow detachment insofar as the exponential density is characterized by a single parameter that is the reciprocal of the mean a knowledge of the mean depth is all that is needed to specify the distribution thus utilization of the depth distribution rather than the mean depth does not require any additional information yet it yields much more accurate estimates of flow detachment and hence soil erosion in interrill areas