decadal scale change of infiltration characteristics of a tephra mantled hillslope at mount st helens washington the cataclysmic 1980 eruption of mount st helens radically reduced the infiltration characteristics of 60 000 ha of rugged terrain and dramatically altered landscape hydrology two decades of erosional biogenic cryogenic and anthropogenic activity have modified the infiltration characteristics of much of that devastated landscape and modulated the hydrological impact of the eruption we assessed infiltration and runoff characteristics of a segment of hillslope thickly mantled with tephra but now revegetated primarily with grasses and other plants to evaluate hydrological modifications due to erosion and natural turbation eruptive disturbance reduced infiltration capacity of the hillslope by as much as 50 fold between 1980 and 2000 apparent infiltration capacities of plots on the hillslope increased as much as ten fold but remain approximately three to five times less than the probable pre eruption capacities common regional rainfall intensities and snowmelt rates presently produce little surface runoff however high magnitude low frequency storms and unusually rapid snowmelt can still induce broad infiltration excess overland flow after 20 years erosion and natural mechanical turbation have modulated but not effaced the hydrological perturbation caused by the cataclysmic eruption copyright 2005 john wiley sons ltd

ultrasonic velocity and anisotropy of hydrocarbon source rocks an experimental study of the physical properties of black kerogen rich shales also including maturation analysis scanning electron microscope sem observations and physical modeling revealed fairly peculiar petrophysical parameters specifically these rocks have very low porosity and density but most importantly both p and s ultrasonic velocities normal to bedding are extremely low whereas they are much higher parallel to bedding giving rise to a strong anisotropy even at high confining pressures we found that these parameters primarily reflect kerogen content microstructure and maturation level of these rocks we found also that microcracks inferred from ultrasonic velocity measurements occur only in mature shales these microcracks are parallel to the bedding plane and further enhance strong intrinsic anisotropy notably at low effective pressure our results show that on a small scale kerogen rich shales are transversely isotropic rocks and can be effectively modeled using the thin laye

erosion of tephra from the 1980 eruption of mount st helens erosion of tephra on hillslopes north of mount st helens was measured at intervals of several months between 1980 and 1983 using large arrays of stakes rill erosion was initially greater than sheetwash but its importance decreased comparatively quickly both rill erosion and sheetwash decreased by one to two orders of magnitude over the three year period because a stable rill network developed and more permeable and less erodible substrates were created or exposed the decrease occurred prior to recovery of plants the causes for the rapid decline in erosion at mount st helens explain patterns of erosion following several other recent tephra eruptions basin wide annual rates of erosion were computed by mapping the surface cover the hillslope gradient and the texture and thickness of tephra and by using statistical relations developed between them and erosion rates annual erosion decreased from 26 mm between may 1980 and may 1981 to 1 8 mm between may 1982 and may 1983 projecting this rate of decline into the future indicated that only about one sixth of the tephra on hillslopes will be removed by water erosion before soil creep and other forms of mass wasting again dominate hillslope evolution

effects of contact line movement on the dissipation of waves in partially saturated rocks a model is presented to describe the attenuation of seismic waves in a partially saturated rock in particular we include the dissipation due to contact line movement in some cases this can dominate the dissipation mechanisms the model includes both dissipation due to viscosity and contact line movement this additional dissipation can increase the specific dissipation function by an order of magnitude this could account for some of the observed difference between theory and experiment an exact calculation of the dissipation due to contact line movement in an in viscid fluid is also presented

post disturbance sediment recovery implications for watershed resilience abstract sediment recovery following disturbances is a measure of the time required to attain pre disturbance sediment fluxes insight into the controls on recovery processes and pathways builds understanding of geomorphic resilience we assess post disturbance sediment recovery in three small 1 5 100 km2 largely unaltered watersheds within the northern colorado rocky mountains affected by wildfires floods and debris flows disturbance regimes span 102 floods debris flows to 103 years wildfires for all case studies event sediment recovery followed a nonlinear pattern initial high sediment flux during single precipitation events or high annual snowmelt runoff followed by decreasing sediment fluxes over time disturbance interactions were evaluated after a high severity fire within the south fork cache la poudre basin was followed by an extreme flood one year post fire this compound disturbance hastened suspended sediment recovery to pre fire concentrations 3 years after the fire wildfires over the last 1900 ybp in the south fork basin indicate fire recurrence intervals of 600 years debris flows within the upper colorado river basin over the last two centuries have shifted the baseline of sediment recovery caused by anthropogenic activities that increased debris flow frequency an extreme flood on north st vrain creek with an impounding reservoir resulted in extreme sedimentation that led to a physical state change we introduce an index of resilience as sediment recovery disturbance recurrence interval providing a relative comparison between sites sediment recovery and channel form resilience may be inversely related because of high or low physical complexity in streams we propose management guidelines to enhance geomorphic resilience by promoting natural processes that maintain physical complexity finally sediment connectivity within watersheds is an additional factor to consider when establishing restoration treatment priorities

spatial structures of stream and hillslope drainage networks following gully erosion after wildfire the drainage networks of catchment areas burned by wildfire were analysed at several scales the smallest scale 1 1000 m2 representative of hillslopes and the small scale 1000 m2 to 1 km2 representative of small catchments were characterized by the analysis of field measurements the large scale 1 1000 km2 representative of perennial stream networks was derived from a 30 m digital elevation model and analysed by computer analysis scaling laws used to describe large scale drainage networks could be extrapolated to the small scale but could not describe the smallest scale of drainage structures observed in the hillslope region the hillslope drainage network appears to have a second order effect that reduces the number of order 1 and order 2 streams predicted by the large scale channel structure this network comprises two spatial patterns of rills with width to depth ratios typically less than 10 one pattern is parallel rills draining nearly planar hillslope surfaces and the other pattern is three to six converging rills draining the critical source area uphill from an order 1 channel head the magnitude of this critical area depends on infiltration hillslope roughness and critical shear stress for erosion of sediment all of which can be substantially altered by wildfire order 1 and 2 streams were found to constitute the interface region which is altered by a disturbance like wildfire from subtle unchannelized drainages in unburned catchments to incised drainages these drainages are characterized by gullies also with width to depth ratios typically less than 10 in burned catchments the regions hillslope interface and channel had different drainage network structures to collect and transfer water and sediment copyright 2005 john wiley sons ltd

rate of sediment yield following small scale volcanic eruptions a quantitative assessment at the merapi and semeru stratovolcanoes java indonesia sediment yields were calculated on the anks of merapi and semeru volcanoes in java indonesia using two different methods during the rst year following the 22 november 1994 eruption of merapi a sediment yield in excess of 1 5 105 m3 km 2 yr 1 was calculated in the boyong river drainage basin based on the volumes of sediment that were trapped by ve check dams at semeru sediment discharges were assessed in the curah lengkong river from direct measurements on the lahars in motion and on the most signi cant stream ows the calculated rate of sediment yield during one year of data in 2000 was 2 7 105 m3 km 2 yr 1 sediment yields are dominated by rain triggered lahars which occur every rainy season in several drainage basins of merapi and semeru volcanoes mostly during the rainy season extending from october to april the return period of lahars carrying sediment in excess of 5 105 m3 is about one year in the curah lengkong river at semeru at merapi the volume of sediments transported by a lahar did not exceed 2 8 105 m3 in the boyong river during the rainy season 1994 95 on both volcanoes the sediments are derived from similar sources pyroclastic ow surges deposits rockfalls from the lava domes and old material from the riverbed and banks however daily explosions of vulcanian type at semeru provide a more continuous sediment supply than at merapi therefore sediment yields are larger at semeru copyright 2004 john wiley sons ltd

multiphase flow numerical modeling of the 18 may 1980 lateral blast at mount st helens usa volcanic lateral blasts are among the most spectacular and devastating of natural phenomena but their dynamics are still poorly understood here we investigate the best documented and most controversial blast at mount st helens washington state united states on 18 may 1980 by means of three dimensional multiphase numerical simulations we demonstrate that the blast front propagation final runout and damage can be explained by the emplacement of an unsteady stratified pyroclastic density current controlled by gravity and terrain morphology such an interpretation is quantitatively supported by large scale observations at mount st helens and will influence the definition and predictive mapping of hazards on blast dangerous volcanoes worldwide

fluvial sediment transport and deposition following the 1991 eruption of mount pinatubo the 1991 eruption of mount pinatubo generated extreme sediment yields from watersheds heavily impacted by pyroclastic flows bedload sampling in the pasig potrero river one of the most heavily impacted rivers revealed negligible critical shear stress and very high transport rates that reflected an essentially unlimited sediment supply and the enhanced mobility of particles moving over a smooth fine grained bed dimensionless bedload transport rates in the pasig potrero river differed substantially from those previously reported for rivers in temperate regions for the same dimensionless shear stress but were similar to rates identified in rivers on other volcanoes and ephemeral streams in arid environments the similarity between volcanically disturbed and arid rivers appears to arise from the lack of an armored bed surface due to very high relative sediment supply in arid rivers this is attributed to a flashy hydrograph whereas volcanically disturbed rivers lack armoring due to sustained high rates of sediment delivery this work suggests that the increases in sediment supply accompanying massive disturbance induce morphologic and hydrologic changes that temporarily enhance transport efficiency until the watershed recovers and sediment supply is reduced d 2002 elsevier science b v all rights reserved

swift snowmelt and floods lahars caused by great pyroclastic surge at mount st helens volcano washington 18 may 1980 the initial explosions at mount st helens washington on the moring of 18 may 1980 developed into a huge pyroclastic surge that generated catastrophic floods off the east and west flanks of the volcano near source surge deposits on the east and west were lithic sorted lacking in accretionary lapilli and vesiculated ash not plastered against upright obstacles and hot enough to char wood all attributes of dry pyroclastic surge material deposited at the surge base on steep slopes near the volcano transformed into high concentration lithic pyroclastic flows whose deposits contain charred wood and other features indicating that these flows were hot and dry stratigraphy shows that even the tail of the surge had passed the east and west volcano flanks before the geomorphically distinct floods lahars arrived this field evidence undermines hypotheses that the turbulent surge was itself wet and that its heavy components segregated out to transform directly into lahars nor is there evidence that meters thick snow slab avalanches intimately mixed with the surge to form the floods the floods must have instead originated by swift snowmelt at the base of a hot and relatively dry turbulent surge impacting hot pyroclasts probably transferred downslope momentum to the snow surface and churned snow grains into the surge base melting snow and accumulating hot surge debris may have moved initially as thousands of small thin slushflows as these flows removed the surface snow and pyroclasts newly uncovered snow was partly melted by the turbulent surge base this and accumulating hot surge debris in turn began flowing a self sustaining process feeding the initial flows the flows thus grew swiftly over tens of seconds and united downslope into great slushy ejecta laden sheetfloods gravity accelerated the floods to more than 100 km h as they swept down and off the volcano flanks while the snow component melted to form great debris rich floods lahars channeled into valleys

seismic anisotropy in sedimentary rocks part 2 laboratory data part one of this paper presents a method for measuring seismic velocities and transverse isotropy in rocks using a single core plug this method saves at least two thirds of the time for preparing core samples and measuring velocities in transversely isotropic ti rocks using this method we have measured velocity and anisotropy of many shale and reservoir rocks from oil and gas fields around the world we present some of the data in this paper which include seismic velocity and anisotropy in 17 brine saturated shale samples 1 gas and brine saturated coal sample 8 brine saturated sands 12 gas saturated sands 32 gas saturated carbonate samples and 25 brine saturated carbonate samples the results show that clays and fine layering in sedimentary rocks are the main causes of seismic anisotropy very little intrinsic anisotropy exists in unfractured reservoir rocks such as sands sandstones and carbonates under reservoir conditions in contrast all shales were found seismically anisotropic anisotr

effects of coarse woody debris and its removal on a channel affected by the 1980 eruption of mount st helens washington during the may 18 1980 eruption of mount st helens washington a pyroclastic surge introduced large volumes of coarse woody debris cwd and fine grained sediment to clearwater creek approximately 15 km northeast of the summit effects of controlled cwd removal on sediment storage substrate and pool frequency and volume were measured in four reaches each with three 200 m segments from 1982 to 1990 in each reach the upstream segment served as a control with no debris removal and cwd was totally and selectively removed from the other two segments unique among similar experiments are the large size and volume of cwd and the large inputs of fine grained sediment except for segments of two reaches that received debris torrents the clearwater channel thalweg scoured until 1985 in three reaches total debris removal caused additional scour and coarsening of the bed surface compared to segments with no or partial debris removal pools contracted from 1982 to 1985 and expanded afterward especially in control segments total debris removal apparently caused pools to become shallower and in segments of low sinuosity decreased the frequency of major pools habitat complexity decreased after total debris removal as indicated by a decrease in the standard deviation of residual depth and an increase in the size of substrate patches

seismic attenuation due to wave induced flow analytical expressions for three p wave attenuation mechanisms in sedimentary rocks are given a unified theoretical framework two of the models concern wave induced flow due to heterogeneity in the elastic moduli at mesoscopic scales scales greater than grain sizes but smaller than wavelengths in the first model the heterogeneity is due to lithological variations e g mixtures of sands and clays with a single fluid saturating all the pores in the second model a single uniform lithology is saturated in mesoscopic patches by two immiscible fluids e g air and water in the third model the heterogeneity is at microscopic grain scales broken grain contacts and or micro cracks in the grains and the associated fluid response corresponds to squirt flow the model of squirt flow derived here reduces to proper limits as any of the fluid bulk modulus crack porosity and or frequency is reduced to zero it is shown that squirt flow is incapable of explaining the measured level of loss 10 sup 2 q sup 1 10 sup 1 within the seismic band of frequencies 1 to 10 sup 4 hz however either of the two mesoscopic scale models easily produce enough attenuation to explain the field data

sediment yield following severe volcanic disturbance a two decade perspective from mount st helens explosive volcanic eruptions perturb water and sediment fluxes in watersheds consequently posteruption sediment yields can exceed preeruption yields by several orders of magnitude annual suspended sediment yields following the catastrophic 1980 mount st helens eruption were as much as 500 times greater than typical background level and they generally declined nonlinearly for more than a decade although sediment yields responded primarily to type and degree of disturbance streamflow fluctuations significantly affected sediment yield trends consecutive years 1995 1999 of above average discharge reversed the nonlinear decline and rejuvenated yields to average values measured within a few years of the eruption after 20 yr the average annual suspended sediment yield from the 1980 debris avalanche deposit remains 100 times 10 4 mg megagrams km 2 above typical background level 10 2 mg km 2 within five years of the eruption annual yields from valleys coated by lahar deposits roughly plateaued and average yields remain about 10 times 10 3 mg km 2 above background level yield from a basin devastated solely by a blast pyroclastic current diminished to background level within five years these data demonstrate longterm instability of eruption generated detritus and show that effective mitigation measures must remain functional for decades

a robust experimental determination of thomsen s δ parameter abstracta novel inversion method for the laboratory determination of thomsen s anisotropy parameter on cylindrical rock specimens from ultrasonic data has been recently reported in the literature we further assessed this method through a direct comparison of the results of the traditional method involving a single off axis p wave velocity measurement at 45 and the new method involving 65 p wave velocity measurements at several angles to the symmetry axis we prepared and characterized two vertical shale specimens from the same preserved vertical core to assess their similarity in terms of structure mineralogy porosity and density the shale was assumed to be transversely isotropic in view of the observed horizontal bedding we subjected both specimens to the same brine saturation and effective stress state using the two methods we obtained similar results for thomsen s vertical p wave and e p wave anisotropy parameters however a significant discrepancy was observed for thomsen s p

the effects of bioturbation on soil processes and sediment transport abstract plants and animals exploit the soil for food and shelter and in the process affect it in many different ways for example uprooted trees may break up bedrock transport soil downslope increase the heterogeneity of soil respiration rates and inhibit soil horizonation in this contribution we review previously published papers that provide insights into the process of bioturbation we focus particularly on studies that allow us to place bioturbation within a quantitative framework that links the form of hillslopes with the processes of sediment transport and soil production using geometrical relationships and data from others work we derive simple sediment flux equations for tree throw and root growth and decay

effects of forest land management on erosion and revegetation after the eruption of mount st helens the 1980 eruption of mount st helens covered soils with a tephra blanket and killed the forest tree cover in a 550 km2 area after the eruption rates of sheetwash and rill erosion and plant cover were measured on tephra covered hillslopes which had been subject to three land management practices grass seeding scarification and salvage logging on rapidly eroding hillslopes subject to grass seeding limited plant covers were established only after erosion had declined sharply logging of trees downed by the eruption and scarification of previously logged surfaces slowed erosion although the effect was small because erosion rates had already slowed substantially by the time these two practices were implemented the factors controlling erosion revegetation and their relative timing at mount st helens are similar to those following explosive volcanic eruptions elsewhere suggesting that grass seeding is not likely to be effective at slowing erosion following most tephra eruptions and that early mechanical disturbance could be an effective erosion control measure the results also indicate that even without deliberate conservation measures processes which mechanically disturb a surface layer of low hydraulic conductivity such as frost action or trampling can radically reduce runoff and erosion before revegetation has an important effect

ultrasonic velocities in cretaceous shales from the williston basin compressional and shear wave velocities were measured in the laboratory from 1 bar to 4 kbar confining pressure for wet undrained samples of cretaceous shales from depths of 3200 and 5000 ft in the williston basin north dakota these shales behave as transversely isotropic elastic media the plane of circular symmetry coinciding with the bedding plane for compressional waves the velocity is higher for propagation in the bedding plane than at right angles to it and the anisotropy is greater for the 5000 ft shale for shear waves the sh wave perpendicular to bedding and the sv wave parallel to bedding propagate with the same speed which is about 25 percent lower than that for the sh wave parallel to bedding in general compressional and shear velocities are higher for the indurated 5000 ft shale than for the friable 3200 ft shale all velocities increase with in increasing confining pressure to 4 kbar the 3200 ft shale exhibits velocity hysteresis as a function of pressure whereas this effect is a

channel bed mobility response to extreme sediment loading at mount pinatubo since the 1991 eruption of mount pinatubo the specific sediment yields from watersheds draining its slopes have been the highest ever recorded in spite of this overwhelming sediment load rivers inundated by pyroclastic flow deposits delivered almost half of the initial deposits to downslope alluvial and or debris fans by 1996 although most of this transport occurred by hyperconcentrated flows and debris flows lahars very high sediment transport rates also characterize low flow measured flow velocities and depths channel properties and the size of both mobile and stable clasts in the sacobia and pasig potrero rivers indicate median bed surface grain sizes of 2 to 8 mm grain size independent dimensionless critical shear stresses c of 0 016 to 0 041 and manning s n values of 0 017 to 0 024 values well below those previously reported for steep mountain channels the dramatic bed surface fining bed mobility and selective transport in these extremely sediment rich channels indicate that changes in grain size c values and bed roughness can increase transport capacity in response to high sediment supply our observations also suggest viewing the apparently contradictory concepts of an equal threshold of bed mobility and grain size dependent selective transport as end member concepts that apply to channels with low or intermittent and high or continuous sediment supply respectively

morphological evolution of the north fork toutle river following the eruption of mount st helens washington abstract the north fork toutle river nftr has undergone extensive morphological changes following the catastrophic eruption of mount st helens washington in 1980 especially the upper reaches affected by a 2 5 km3 debris avalanche deposit caused by the eruption this paper reports analysis and interpretation of vertical adjustments to the thalweg long profile at some 33 km river reaches redeveloped on the debris avalanche deposit during the 30 year period since the eruption the results confirm that adjustments in the upper part of the study reaches have generally been led by degradation while that in the lower reaches have been led by aggradation with the middle reaches acting as a hinge zone trends of change in the thalweg long profile and bedslope reveal that channel gradients have decreased nonlinearly through time and with distance downstream from the volcano values of stream power have decreased with time commensurately owing to reductions in slope and channel widening while the bed has coarsened so that rates of erosion of the debris avalanche deposit in the upper nftr have slowed to the point that the long profile now perched and slightly steeper is relaxing toward a new equilibrium or graded condition thirty year relaxation paths for thalweg elevation were simulated at seven key cross sections using newly developed comprehensive rate law models based on nonlinear decay in rates of morphological response to perturbation the results indicate that both single and multistep rate law models can simulate the observed records consequently the rate law approach provides an effective method for studying and simulating morphological response of the fluvial system to a major instantaneous disturbance such as a volcanic eruption

environmental impact of the 1 8 ka taupo eruption new zealand landscape responses to a large scale explosive rhyolite eruption abstract large scale ignimbrite eruptions from rhyolitic caldera volcanoes can trigger geologically instantaneous changes in sedimentary systems over huge areas by either burying existing environments or overloading them with vast quantities of unconsolidated particulate material the post eruption readjustment of the landscape to such perturbations is one of the most dramatic processes in physical sedimentology exemplified here by the 1 8 ka taupo eruption in the central north island of new zealand this eruption generated voluminous fall deposits then climaxed with emplacement of a c 30 km 3 non welded ignimbrite over a near circular area of c 20 000 km 2 approximately 90 of the area but the headwaters of many of the north island s largest rivers were impacted by both the primary pyroclastic fall and flow material large scale post eruption remobilisation of this material coupled with the re establishment of fluvial systems occurred in a distinct sequence as recorded by the evolution of sedimentary facies in different sub environments following an initial period dominated by mass flows re establishment of fluvial systems began with the headward erosion of box canyons through the ponded ignimbrite deposits a process often associated with the break out of temporary lakes aggradational streams developed in these channels rapidly evolved from shallow ephemeral sediment laden outbursts associated with flash flood events to deeper permanent braided rivers before declining sediment yields led to retrenchment of single thread rivers and a return to pre eruption gradients and bedloads years to decades later typically the modern profile of many streams and rivers follow closely their pre eruption profiles and incision and erosion is overwhelmingly confined to the deposits of the eruption itself although the general remobilisation pattern is similar for all impacted river systems detailed studies of the waikato rangitaiki mohaka ngaruroro and whanganui catchments show that the relative timing and scale of each eruption response phase differs between each catchment these reflect differences in catchment physiography and hydrology and the volume and type of pyroclastic material deposited in each ultimately the landscape response reflects the relative spatial distributions of and the volumetric ratios between the volumes of pyroclastic debris water and accommodation space in the basin cf kataoka and manville this volume

seismic wave attenuation and dispersion resulting from wave induced flow in porous rocks a review one major cause of elastic wave attenuation in heterogeneous porous media is wave induced flow of the pore fluid between heterogeneities of various scales it is believed that for frequencies below 1 khz the most important cause is the wave induced flow between mesoscopic inhomogeneities which are large compared with the typical individual pore size but small compared to the wavelength various laboratory experiments in some natural porous materials provide evidence for the presence of centimeter scale mesoscopic heterogeneities laboratory and field measurements of seismic attenuation in fluid saturated rocks provide indications of the role of the wave induced flow signatures of wave induced flow include the frequency and saturation dependence of p wave attenuation and its associated velocity dispersion frequency dependent shear wave splitting and attenuation anisotropy during the last four decades numerous models for attenuation and velocity dispersion from wave induced flow have been developed with varying degrees of rigor and complexity these models can be categorized roughly into three groups according to their underlying theoretical framework the first group of models is based on biot s theory of poroelasticity the second group is based on elastodynamic theory where local fluid flow is incorporated through an additional hydrodynamic equation another group of models is derived using the theory of viscoelasticity though all models predict attenuation and velocity dispersion typical for a relaxation process there exist differences that can be related to the type of disorder periodic random space dimension and to the way the local flow is incorporated the differences manifest themselves in different asymptotic scaling laws for attenuation and in different expressions for characteristic frequencies in recent years some theoretical models of wave induced fluid flow have been validated numerically using finite difference finite element and reflectivity algorithms applied to biot s equations of poroelasticity application of theoretical models to real seismic data requires further studies using broadband laboratory and field measurements of attenuation and dispersion for different rocks as well as development of more robust methods for estimating dissipation attributes from field data

long term elevated post eruption sedimentation at mount pinatubo philippines post eruption sedimentation rates from two basins draining mount pinatubo philippines are compiled and extended through a d 2009 to compare short term predictions with long term yields the pasig potrero and sacobia rivers were covered by 1 km 3 of thick pyroclastic flow deposits during the 1991 eruption of mount pinatubo blanketing 30 of each basin with highly erodible sediments erosion of these deposits led to some of the highest sediment yields ever recorded yields peaked in 1991 and declined exponentially for the first decade following the eruption deposition on the aggrading alluvial fan shows that sedimentation rates from 2001 to 2009 were almost twice as high as an exponential decay model would predict with rates that have leveled off and are no longer declining exponentially patterns of long term sedimentation are similar to those of the north fork toutle river washington state united states at mount st helens with two phases of erosion and sediment export in the first erosion of hillslope tephra and carving of the initial valley network lead to high sediment yields that decline exponentially over 5 10 yr in the second phase continued valley widening and fluvial instability maintain high sediment yields for at least two decades a comparison of post eruption deposition with pre eruption yields indicates that century to millennial scale sedimentation is dominated by sediment associated with discrete eruptive events

seismic anisotropy of shales the seismic properties and preferred clay mineral orientation of a suite of shales are investigated using laboratory velocity measurements as a function of confining pressure x ray diffraction techniques and electron microprobe backscatter bse imaging the velocity measurements indicate that these shales are transversely isotropic with the main symmetry axis perpendicular to bedding anisotropy at elevated pressures caused mainly by preferred orientation of clays illite parallel to bedding ranges from 20 vp and 19 vs for a sample of new albany shale to 30 vp and 35 vs for a sample of chattanooga shale the degree of clay mineral alignment in the shales is constrained by orientation indices produced using simple x ray diffraction techniques a strong positive correlation is found between the degree of preferred orientation as expressed in the orientation indices and seismic anisotropy bse images of the shale fabrics confirm in a qualitative manner the results of the x ray study to investigate wave propagation in the shales elastic constants of each sample are calculated and used to produce phase and group wave velocity surfaces which describe variation in velocity as a function of angle to the bedding normal the calculated velocity surfaces constrained by independent velocity measurements display a lack of shear wave splitting at near normal incidence in even the most anisotropic shales for the highly anisotropic chattanooga shales group velocity surfaces differ significantly from corresponding phase velocity surfaces

the impact of saturation on seismic dispersion in shales laboratory measurements previous studies found a significant increase of acoustic velocities between seismic and ultrasonic frequencies seismic dispersion for shales which would have to be taken into account when comparing seismic or sonic field data with ultrasonic measurements in the laboratory we report on a series of experiments performed with partially saturated mancos shale and pierre shale i in which the influence of water saturation on acoustic velocities and seismic dispersion was investigated the experiments were carried out in a triaxial set up allowing for combined measurements of quasi static rock deformation ultrasonic velocities and dynamic elastic stiffness at seismic frequencies under deviatoric stresses prior to testing the rock samples were preconditioned in desiccators at different relative humidities for both shale types we present and discuss experimental results that demonstrate strong saturation and frequency dependence of dynamic young s moduli poisson s ratios and thomsen s anisotropy parame

sediment routing in a small drainage basin in the blast zone at mount st helens washington u s a abstract a quantitative description of the routing of 400 10 3 t km 2 of sediment delivered to a 2 4 km 2 basin by the may 18 1980 eruption of mount st helens has been developed for the period may 1980 june 1981 on hillslopes this sediment resided in primary and secondary remobilized primary storage sites hillslope erosion processes redistributed sediment on hillslopes and delivered sediment to the channel system these processes included shallow sliding from slopes steeper than 0 70 sheet erosion and rill erosion the most important discrete sites of storage on hillslopes were colluvial wedges and sites upslope of logs or other organic debris most tephra delivered to the basin by the eruptions is likely to be preserved in the stratigraphic record twelve percent of the sediment delivered to the study area was transported to the channel system directly by the eruption and by hillslope erosion processes of this approximately half remained in storage in the channel system and the remainder was exported from the drainage basin important sites of alluvial sediment storage included alluvial fans sites related to logs channel beds and alluvial terraces

physical properties of shale at temperature and pressure deformational properties p wave and s wave velocities and electrical resistivity were measured for three north sea malm shales in the laboratory under pressures to 800 bars and temperatures to 100 c these data were used to evaluate how factors such as mineralogy microstructure compaction and pore fluid conductivity affect a shale s seismic and electrical responses deformation in the shales is dominated by inelastic processes which cause time dependent changes in velocity resistivity and pore pressure overall shales are less sensitive to pressure changes as compared to sandstones of similar porosity however changes in temperature result in large changes in physical properties as compared to sandstones or shaly sands p wave and s wave velocities may decrease by as much as 10 percent over the temperature range studied and calculated activation energies for surface conduction are nearly twice those observed in shaly sands these comparisons emphasize fundamental differences in fabric among the

spatial and temporal patterns in fluvial recovery following volcanic eruptions channel response to basin wide sediment loading at mount pinatubo philippines the june 1991 eruption of mount pinatubo philippines was one of the largest volcanic eruptions of the twentieth century emplacing 5 6 km 3 of pyroclastic fl ow material on the fl anks of the volcano the combination of abundant relatively fi ne grained easily erodible material and intense tropical rainfall led to numerous lahars immediately following the eruption even after major lahars ended sediment yields in some basins remained orders of magnitude above pre eruption levels using data collected from 1996 through 2003 we investigated fi ve basins that experienced varying amounts of sediment loading in the 1991 eruption from 1 to 33 of the basin area covered by valley fi lling pyroclasticfl ow deposits from measurements of fl ow and bed characteristics made through time we developed a general conceptual model for channel recovery following basin wide sediment loading initially fi ner grained sediment and pumice are mobilized preferentially through selective transport once the bed is coarse enough for gravel size clasts to interact with one another clast structures develop increasing form roughness and critical shear stress and inhibiting initial clast mobility as sediment inputs continue to decline the channel incises into valley bottom sediments progressively armoring through winnowing at pinatubo incision and armoring occur fi rst as dry season phenomena due to reduced sediment inputs eventually moving to year round low fl ow bed stability observed timing of the onset of in channel biological recovery suggests that reestablishment of channel stability helps catalyze aquatic ecosystem recovery

theoretical derivation of a brie like fluid mixing law prediction of the velocity of acoustic waves in partially saturated rocks is very important in geophysical applications the need to accurately predict acoustic velocities has resulted in a widespread popularity of brie s effective fluid mixing law this empirical model together with gassmann s formula are used routinely in fluid substitution problems in petroleum geophysics and seismic monitoring of carbon capture and storage most attempts to justify brie s model have been focused on interpretation in terms of patchy saturation models and attaching meaning to the brie parameter in terms of the patch size in this paper using a microstructural description of the rock and a parameter relating to capillary pressure we calculate an effective fluid modulus that is very similar to brie s law the fluid mixing law we propose is independent of frequency and has a solid theoretical foundation this proposed law produces analytically harmonic and arithmetic averaging at the endpoints our results indicate that brie like behaviour may not necessarily be related to frequency and patch size dependent phenomena

the geomorphological evolution of the paricutin cone and lava flows mexico 1943 1990 abstract erosion and sedimentation processes in the paricutin cone and adjacent lava fields have been evaluated 47 years after the eruption through field study of the morphological characteristics of the area previous studies indicate an initial stage of accelerated erosion decreasing quickly after the stripping of the ash layers and cessation of the volcanic activities in the cone and crater area revegetation is the main process after the first stage of stripping of fine ash the lava fields are the least affected areas by erosional processes with vegetation development in minor depressions crevices and along the edges of the lava flows the llanos or lava dammed plains are the most active physiographic units with continuous deposition of sediments they are completely covered by vegetation or under agricultural use incision of channels along the lava field edge promotes the integration of the drainage system but still most of the affected area drains into the lave field present erosion rates are higher than normal rates and a complete rehabilitation of the pyroclastic area may extend over decades filling of sediments and revegetation of the lava fields will develop in a longer period of several millennia

initiation and flow behavior of the 1980 pine creek and muddy river lahars mount st helens washington two large high velocity lahars volcanic debris flows were triggered by a pyroclastic surge during the first few minutes of the may 18 1980 eruption of mount st helens the initial surge cloud evolved progressively by gravity segregation from a gas mobilized highly inflated density flow to a dense water mobilized basal debris flow lahar and accompanying ash cloud as it flowed down the east flank of the volcano the main source of the water for the lahars was probably from eroded snow and ice incorporated into the flow by turbulent mixing but ground water expelled together with the rock debris by the initiating volcanic explosions also may have contributed peak lahar discharge from the pine muddy fan upper smith creek and ape canyon probably exceeded 250 000 m 3 s initially but decreased exponentially in the downstream direction total volume of the lahars was in excess of 1 4 10 7 m 3 initial peak flow velocities in excess of 30 m s also decreased markedly downstream where flow was not impeded velocity was strongly related to the depth slope term r 2 3 s 1 2 from the manning uniform flow equation as a power law function during much of the route traveled lahar flow appears to have been supercritical deposits left in channels were generally thin relative to flow depth 0 to 2 5 m particles up to small boulder size were randomly distributed in the poorly sorted nonstratified matrix indicating complete suspension in a fully developed debris flow slurry however much larger clasts were transported as bed load computed sediment concentrations of matrix slurry samples ranged from 84 to 91 solids by weight and were similar for the two lahars two indirect methods for computing peak flow velocity previously only tentatively applied to debris flows were tested for accuracy by comparing computed lahar arrival times with recorded arrival times at swift reservoir the computed velocities appear to be 15 slower than the recorded velocities which is consistent with the restriction that the velocity formulas produce only minimum values

a new laboratory apparatus for the measurement of seismic dispersion under deviatoric stress conditions abstract a better understanding of seismic dispersion and attenuation of acoustic waves in rocks is important for quantitative interpretation of seismic data as well as for relating seismic data sonic log data and ultrasonic laboratory data in the present work a new laboratory setup is described allowing for combined measurements of quasistatic deformations of rocks under triaxial stress ultrasonic velocities and dynamic elastic stiffness young s modulus and poisson s ratio at seismic frequencies the setup has been used mainly for the study of shales for such rocks it is crucial that the saturation of the samples is preserved which requires fast sample mounting the design of our setup together with a technique that was developed for rapid mounting of strain gauges onto the sample and subsequent sealing of the sample allows for sample preservation which is of particular importance for shales the performance of the new experimental setup and sample mounting procedure is demonstrated with test materials aluminium and polyetheretherketone and two different shale types mancos shale and pierre shale furthermore experimental results are presented that demonstrate the capability of measuring the impact of saturation stress and stress path on seismic dispersion for the tests with mancos shale and pierre shale large dispersion up to 50 in young s modulus normal to bedding was observed increased water saturation of mancos shale results in strong softening of the rock at seismic frequencies whereas hardening is observed at ultrasonic frequencies due to an increase in dispersion counteracting the rock softening the poisson s ratio of mancos shale strongly increases with the level of saturation but appears to be nearly frequency independent we have found that the different types of shale exhibit different stress sensitivities during hydrostatic loading and that the stress sensitivity is different at seismic and ultrasonic frequencies

frequency dependent seismic attenuation in shales experimental results and theoretical analysis claudio delle piane 1 joel sarout 1 claudio madonna 2 erik h saenger 2 david n dewhurst1 and mark raven3 1csiro earth science and resource engineering australian resources research centre 26 dick perry avenue kensington wa 6151 australia e mail claudio dellepiane csiro au 2geological department eth sonneggstrasse 5 ch 8092 zurich switzerland 3csiro land and water waite rd urrbrae sa 5064 australia

dynamic poroelasticity a unified model with the squirt and the biot mechanisms the velocities and attenuation of seismic and acoustic waves in rocks with fluids are affected by the two most important modes of fluid solid interaction 1 the biot mechanism where the fluid is forced to participate in the solid s motion by viscous friction and inertial coupling and 2 the squirt flow mechanism where the fluid is squeezed out of thin pores deformed by a passing wave traditionally both modes have been modeled separately with the biot mechanism treated in a macroscopic framework and the squirt flow examined at the individual pore level we offer a model which treats both mechanisms as coupled processes and relates p velocity and attenuation to macroscopic parameters the biot poroelastic constants porosity permeability fluid com pressibility and viscosity and a newly introduced microscale parameter a characteristic squirt flow length the latter is referred to as a fundamental rock property that can be determined experimentally we show that the squirt flow mechanism dominates the biot mechanism and is responsible for measured large velocity dispersion and attenuation values the model directly relates p velocity and attenuation to measurable rock and fluid properties therefore it allows one to realistically interpret velocity dispersion and or attenuation in terms of fluid properties changes e g viscosity during thermal enhanced oil recovery eor or to link seismic measurements to reservoir properties as an example of the latter transformation we relate permeability to attenuation and achieve good qualitative correlation with experimental data

posteruption suspended sediment transport at mount st helens decadal scale relationships with landscape adjustments and river discharges received 11 december 2002 revised 30 september 2003 accepted 18 november 2003 published 17 january 2004 1 widespread landscape disturbance by the cataclysmic 1980 eruption of mount st helens abruptly increased sediment supply in surrounding watersheds the magnitude and duration of the redistribution of sediment deposited by the eruption as well as decades to centuries old sediment remobilized from storage have varied chiefly with the style of disturbance posteruption suspended sediment transport has been greater and more persistent from zones of channel disturbance than from zones of hillslope disturbance despite the severe landscape disturbances caused by the eruption relationships between discharge magnitudes and frequencies and suspended sediment transport have been remarkably consistent discharges smaller than mean annual flows generally have transported 5 but locally 15 of the annual suspended sediment loads and infrequent p 0 01 large floods have transported as much as 50 of the annual suspended sediment loads in a single day however moderate magnitude discharges those greater than mean annual flows but less than 2 year floods have transported the greatest amounts of sediment from all disturbance zones such discharges have transported on average 60 to 95 of the annual suspended sediment loads usually within cumulative periods of 1 3 weeks each year although small magnitude and largemagnitude discharges have locally and episodically transported considerable amounts of suspended sediment there has not been any notable change in the overall nature of the effective discharges moderate magnitude flows have been the predominant discharges responsible for transporting the majority of suspended sediment during 20 years of posteruption landscape adjustment index terms 1824 hydrology geomorphology 1625 1815 hydrology erosion and sedimentation 1860 hydrology runoff and streamflow keywords sediment yield suspended sediment transport mount st helens erosion volcano geomorphology

post eruption erosion processes and plant recovery in the summit atrio of mt usu japan abstract the 1977 1978 eruptions of mt usu in japan provided a unique opportunity to examine recovery processes of erosional and vegetational patterns in the thickly tephra covered summit atrio surficial slope erosion in relation to revegetation was studied on the basis of field examination and aerial photo interpretation during the period 1980 1984 although heavy rilling and gullying brought about high sediment yield and impeded plant establishment they also had a positive effect on revegetation by allowing the survival and invasion of herbaceous plants such erosion processes thinned the tephra mantle and transported organic debris and seeds from upper somma walls to lower slopes and alluvial fans

fluid mobility and frequency dependent seismic velocity direct measurements the influence of fluid mobility on seismic velocity dispersion is directly observed in laboratory measurements from seismic to ultrasonic frequencies a forceddeformation system is used in conjunction with pulse transmission to obtain elastic properties at seismic strain amplitude 10 7 from 5 hz to 800 khz varying fluid types and saturations document the influence of pore fluids the ratio of rock permeability to fluid viscosity defines mobility which largely controls pore fluid motion and pore pressure in a porous medium high fluid mobility permits pore pressure equilibrium either between pores or between heterogeneous regions resulting in a low frequency domain where gassmann s equations are valid in contrast low fluid mobility can produce strong dispersion even within the seismic band here the low frequency assumption fails since most rocks in the general sedimentary section have very low permeability and fluid mobility shales siltstones tight limestones etc most rocks are not in the lowfrequency domain even at seismic frequencies only those rocks with high permeability porous sands and carbonates will remain in the low frequency domain in the seismic or sonic band

experimental laboratory determination of the dynamic elastic properties of wet drained shales the ultrasonic anisotropic elastic properties of drained saturated shales were measured as a function of confining pressure two shales were characterized in this study a jurassic outcrop shale retrieved under the sea in a saturated state and a kimmeridge clay shale cut from a north sea borehole both shales were highly anisotropic both texturally as revealed by scanning electron microscopy analysis and elastically as measured ultrasonically in the laboratory the strongest anisotropy was seen in the kimmeridge clay shale where up to 38 compressional wave anisotropy thomsen s parameter e and up to 58 shear wave anisotropy thomsen s parameter were observed in addition for both shales e and were found to decrease as a function of increasing confining pressure with the pore pressure drained to atmosphere while the anellipticity deviation of the slowness surfaces from ellipses was found to be positive and decreased as a function of increasing confining pressure accompanying these changes in elastic properties was a decrease in porosity with increasing confining pressure from 10 5 to 8 5 for the jurassic shale the decrease in overall anisotropy of the shales with increasing confining pressure was found to be consistent with theoretical modeling of shale properties where the shale anisotropy and anellipticity were predicted to decrease as a function of decreasing fluid filled porosity

the illusion of diffusion field evidence for depth dependent sediment transport soil covered upland landscapes are common in much of the habitable world and our understanding of their evolution as a function of different climatic tectonic and geologic regimes is important across a wide range of disciplines erosion laws direct quantitative study of the processes shaping earth s surface and form the basis of landscape evolution modeling but are based on limited field data here we use in situ produced cosmogenic 1 0 be and 2 6 al concentrations from granitic saprolite to quantify an exponential decline in soil production with increasing soil thickness for a new field site in point reyes california results are similar to soil production functions from two different previously studied field sites and are used with extensive measurements of soil thickness to quantify depth integrated sediment transport flux plots of calculated sediment fluxes against the product of soil depth and hillslope gradient provide the first field based evidence that soil transport is a nonlinear depth dependent function data from all sites suggest that the widely used linear diffusion equation is only appropriate for shallow gradient convex up regions while the depth dependent transport law is more broadly applicable quantifying both the mobile soil thickness and landscape morphology is therefore critical to understanding how landscapes evolve

how does water near clay mineral surfaces influence the rock physics of shales clays and clay bearing rocks like shale are extremely water sensitive this is partly due to the interaction between water and mineral surfaces strengthened by the presence of nanometer size pores and related large specific surface areas molecular scale numerical simulations using a discrete element model show that shear rigidity can be associated with structurally ordered bound or adsorbed water near charged surfaces building on these and other molecular dynamics simulations plus nanoscale experiments from the literature the water monolayer adjacent to hydrophilic solid surfaces appears to be characterised by shear stiffness and or enhanced viscosity in both cases elastic wave propagation will be affected by the bound or adsorbed water using a simple rock physics model bound water properties were adjusted to match laboratory measured p and s wave velocities on pure water saturated kaolinite and smectite to fit the measured stress sensitivity particularly for kaolinite the contribution from solid grain contact stiffness needs to be added the model predicts particularly for s waves that viscoelastic bound water could be a source of dispersion in clay and clay rich rocks the bound water based rock physics model is found to represent a lower bound to laboratory measured velocities obtained with shales of different mineralogy and porosity levels