statistical properties of armored gravel bed surfaces 1 roughness of successively developed armor layers in a large laboratory flume is analyzed considering gravel surfaces as two dimensional random fields of bed elevations statistically derived roughness parameters are evaluated from precise digital elevation models dems of bed surfaces and are discussed with respect to successive development of stable armor layers the key results relate to evolution of the probability distribution of bed elevations and its moments and structure functions of various orders with respect to armoring discharge our results suggest that statistical analysis of bed elevations is a helpful tool for defining roughness parameters quantifying armoring effects and identifying particle orientation flow direction and surface forming processes

modelling the effect of time dependent river dune evolution on bed roughness and stage this paper presents an approach to incorporate time dependent dune evolution in the determination of bed roughness coefficients applied in hydraulic models dune roughness is calculated by using the process based dune evolution model of paarlberg et al 2009 and the empirical dune roughness predictor of van rijn 1984 the approach is illustrated by applying it to a river of simple geometry in the 1 d hydraulic model sobek for two different flood wave shapes calculated dune heights clearly show a dependency on rate of change in discharge with time dunes grow to larger heights for a flood wave with a smaller rate of change bed roughness coefficients computed using the new approach can be up to 10 higher than roughness coefficients based on calibration with the largest differences at low flows as a result of this larger bed roughness computed water depths can be up to 15 larger at low flow the new approach helps to reduce uncertainties in bed roughness coefficients of flow models especially for river systems with strong variations in discharge with time

bed topography and sand transport responses to a step change in discharge and water depth abstractat base flow conditions ephemeral streams with mobile beds may inherit bed topography caused by previous higher flow events resulting in bed topography that is not in equilibrium with flow conditions major flow events can generate large bedforms that result in hydrodynamics and sediment transport that are not in equilibrium with subsequent lower flow conditions to simulate a large storm runoff driven stream flow followed by lower base flow conditions changes in sand bed topography and sand transport caused by a simultaneous reduction in discharge and flow depth in a laboratory flume with an equilibrium sand bed and steady approximately uniform flow were investigated bed topography was evaluated using second order structure functions semivariograms and statistical analyses sediment transport responded rapidly to a near instantaneous negative step in mean flow depth and discharge the relative contributions of reduced bedform height and celerity to the decreased transport rate are quantif

seismic quantification of the explosions that destroyed the dome of volcan de colima mexico in july august 2003 in july august 2003 the andesitic lava dome at volcan de colima mexico was destroyed by a sequence of explosions that replaced the 2 106 m3 dome with a crater 200 m across and 30 m deep the two strongest explosions occurred on july 17 and august 28 the initial low frequency impulses that they produced which were recorded on broadband seismic records allowed an estimation of the counter forces of the initiating process as being equal to 0 3 1011 n and 1 1011 n for the july and august events respectively the seismic characteristics follow the nishimura hamaguchi scaling law for volcanic explosions reflecting self similarity in the processes initiating explosive events the results also show that counter forces can discriminate between the sizes of explosive eruptions that are assigned the same magnitude by conventional methods of classification such as the volcanic explosivity index the increasing use of broadband seismometers may therefore provide the basis for using counter forces to determine the magnitude of explosive eruptions

rootless shield and perched lava pond collapses at kīlauea volcano hawai i effusion rate is a primary measurement used to judge the expected advance rate length and hazard potential of lava flows at basaltic volcanoes the rapid draining of lava stored in rootless shields and perched ponds can produce lava flows with much higher local effusion rates and advance velocities than would be expected based on the effusion rate at the vent for several months in 2007 2008 lava stored in a series of perched ponds and rootless shields on k lauea volcano hawai i was released episodically to produce fast moving a lava flows several of these lava flows approached royal gardens subdivision and threatened the safety of remaining residents using time lapse image measurements we show that the initial time averaged discharge rate for one collapse triggered lava flow was approximately eight times greater than the effusion rate at the vent though short lived the collapse triggered a lava flows had average advance rates approximately 45 times greater than that of the p hoehoe flow field from which they were sourced the high advance rates of the collapse triggered lava flows demonstrates that recognition of lava accumulating in ponds and shields which may be stored in a cryptic manner is vital for accurately assessing short term hazards at basaltic volcanoes

alongshore momentum balances in the nearshore the one dimensional time averaged over many wave periods along shore momentum balance between forcing by wind and breaking waves and the bottom stress is examined with field observations spanning a wide range of con ditions on a barred beach near bottom horizontal currents were measured for 2 months at 15 locations along a cross shore transect extending 750 m from the shoreline to 8 m water depth the hourly averaged bottom stress was estimated from observed currents using a quadratic drag law the wave radiation stress was estimated in 8 m depth from an array of pressure sensors and the wind stress was estimated from an anemometer at the seaward end of a nearby pier the combined wind and wave forcing integrated over the entire cross shore transect is balanced by the integrated bottom stress the wind stress contributes about one third of the forcing over the transect analysis of the momentum balances in different cross shore regions shows that in the surf zone wave forcing is much larger than wind forcing and that the bottom drag coefficient is larger in the surf zone than farther seaward consistent with earlier studies

decomposition location and persistence of seismic signals recovered from continuous tremor at erta ale ethiopia abstract subband decomposition and reconstruction sdr provides a quantitative semi automated rapid means of analyzing volcanic tremor which can recover signals that dominate different parts of the frequency spectrum while preserving polarization and phase here applied to data from a two week experiment at erta ale in nov dec 2003 we demonstrate that the sdr method can identify signals corresponding to source processes active in several different physical regions of the erta ale caldera different recovered signals suggest that the continuous tremor at erta ale is a composite of several seismic sources including conduit resonance bubble bursting phenomena and degassing at fumaroles these signals are seen throughout the 2003 experiment suggesting that several competing source models of volcanic tremor can produce signals at the same volcanic conduit system simultaneously

near bed hydrodynamics and turbulence below a large scale plunging breaking wave over a mobile barred bed profile detailed measurements are presented of velocities and turbulence under a large scale regular plunging breaking wave in a wave flume measurements were obtained at 12 cross shore locations around a mobile medium sand breaker bar they focused particularly on the dynamics of the wave bottom boundary layer wbl and near bed turbulent kinetic energy tke measured with an acoustic concentration and velocity profiler acvp the breaking process and outer flow hydrodynamics are in agreement with previous laboratory and field observations of plunging waves including a strong undertow in the bar trough region the wbl thickness matches with previous studies at locations offshore from the bar crest but it increases near the breaking wave plunge point this relates possibly to breaking induced tke or to the diverging flow at the shoreward slope of the bar outer flow tke is dominated by wave breaking and exhibits strong spatial variation with largest tke above the breaker bar crest below the plunge point breaking induced turbulence invades the wbl during both crest and trough half cycle this results in an increase in the time averaged tke in the wbl with a factor 3 and an increase in peak onshore and offshore near bed reynolds stresses with a factor 2 from shoaling to breaking region a fraction of locally produced tke is advected offshore over a distance of a few meters to shoaling locations during the wave trough phase and travels back onshore during the crest half cycle the results imply that breaking induced turbulence for large scale conditions may significantly affect near bed sediment transport processes

surf zone wave overtopping a trapezoidal structure 1 d modelling and piv comparison experiments have been undertaken on surf zone waves with a surf similarity parameter of about 0 3 overtopping a trapezoidal obstacle with 1 2 side slopes on a beach of 1 20 slope particle image velocimetry piv investigation has shown complex vortical structures resulting from shoreward propagating bores interacting colliding with bores partially reflected from the obstacle before overtopping the obstacle a 1 d depth averaged shallow water model captures qualitatively much of the wave dynamics however the marked turbulent air entrainment in the collision zone appears significant in raising mean water level relative to the model and causing a phase lag in the model relative to the experiment peak overtopping levels are overpredicted by about 100 with this phase lag

on the dense bubble clouds and near bottom turbulence in the surf zone 1 measurements of high frequency 100 khz acoustical backscatter in the surf zone have identified the presence of a wall formed by dense assemblages of bubbles generated by breaking gravity waves and persisting for periods up to 30 min these bubbles are advected by alongshore and cross shore rip currents and are controlled by the local wave field turbulence dissolution and buoyancy during the summer of 2000 the location of the bubble wall south of scripps pier california was tracked for a 6 week period distinct categories of bubble wall defined by the backscatter intensity data are observed distinguished by the presence or absence of rip current activity the results suggest that presence or absence of long period waves 10 20 s may play a role in controlling the bubble wall type during periods without rip currents the location of the bubble wall is controlled by the incoming wave field simultaneous turbulence dissipation measurements 0 4 m above the seafloor show clear dependence on the local water depth beneath incoming waves the acoustical backscatter data are interpreted using in situ bubble and turbulence measurements in conjunction with a simple model based on bubble sorting by buoyancy dissolution and turbulence

modeling of coastal profile evolution on the abandoned delta of the huanghe river abstract this paper presents a quantitative dynamic model for simulating and predicting the evolution of the nearshore muddy profile on the abandoned huanghe delta which has been undergoing severe erosion since the shift of the huanghe river in 1855 the model computes the wave induced bed shear stresses on the muddy profile and therefore calculates the erosion rate the sea level fluctuation caused by the oceanic tide plays an important role in redistributing the wave force and hence the sediment transport this factor is introduced into the model the steady state nearshore muddy profile is simulated as a response to the average erosion rate of the local wave climate however at long time scales the averaged erosion rate is significantly influenced by the surface sand armouring and the vertical increase with depth of cohesive sediment consolidation during coastal erosion leading to an irreversible evolution of the muddy profile the effective scouring wave derived from local wave climate is proposed to quantitatively incorporate these time variant geological influences the evolution of the muddy profile is determined by the change in the effective scouring wave climate the eroding muddy coast exhibits a monotonic concave upward profile whose curvature increases as the coastal erosion continues the maximum curvature of the profile lies below the mean low tidal level as the erosion continues the maximum curvature moves down and shoreward the position of the maximum curvature of the nearshore muddy profile can be used to estimate the evolutionary stages of the muddy coast on the northern abandoned huanghe delta the muddy profile approaches an equilibrium configuration when the maximum curvature reaches down to a water depth of about 6 m below the mean sea level the model reveals a dynamic geomorphic system as a response to the abandonment on the huanghe delta similar patterns and evolutionary processes may be generalized to erosional muddy coasts in other settings

laboratory observation of boundary layer flow under spilling breakers in surf zone using particle image velocimetry abstract a boundary layer flow under spilling breakers in a laboratory surf zone with a smooth bottom is investigated using a high resolution particle image velocimetry piv technique by cross correlating the images oscillatory velocity profiles within a viscous boundary layer of o 1 mm in thickness are resolved over ten points using piv measurements taken for an earlier study and the present study flow properties in the wave bottom boundary layer wbbl over the laboratory surf zone are obtained including the mean velocities turbulence intensity reynolds stresses and intermittency of coherent events the data are then used to estimate the boundary layer thickness phase variation and bottom shear stress it is found that while the time averaged mass transport inside the wbbl is onshore in the outer surf zone it changes to offshore in the inner surf zone the zero eulerian mass transport occurs at h hb 0 92 in the outer surf zone the maximum overshoot of the streamwise velocity and boundary layer thickness are not constant across the surf zone the bottom shear stress is mainly contributed by the viscous stress through mean velocity gradient while the reynolds stress is small and negligible the turbulence level is higher in the inner surf zone than that in the outer surf zone although only a slight increase of turbulent intensity is observed inside the wbbl from the outer surf zone to the inner surf zone the variation of phase inside and outside the wbbl was examined through the spatial velocity distribution it is found the phase lead is not constant and its value is significantly smaller than previous thought by analyzing instantaneous velocity and vorticity fields a remarkable number of intermittent turbulent eddies are observed to penetrate into the wbbl in the inner surf zone the size of the observed large eddies is about 0 11 to 0 16 times the local water depth its energy spectra follow the 5 3 slope in the inertial subrange and decay exponentially in the dissipation subrange

the entrainment of bubbles by drop impacts various processes are described by which a drop of water impacting on a water surface may entrain a bubble there are i irregular entrainment in which the complex details of a splash entrain bubbles ii regular entrainment in which the crater formed by the drop impact develops in a predictable way to form a single bubble iii entrainment of large bubbles in which most of the volume of the crater is trapped as a bubble and iv mesler entrainment in which many very small bubbles are trapped in the very early stages of the impact process possibly between wave crests of capillary waves which develop on the drop and on the water surface this last process is different from the preceding three in that it produces very little sound all of the processes except the third one have been described individually in the literature here we present them together for comparison the regular entrainment process is discussed in the greatest detail and some new experimental results are presented which concern the size and nature of the entrained bubbles the significance of the regular and irregular entrainment processes to the generation of underwater sound by rain is discussed

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

the optical volume scattering function in a surf zone inverted to derive sediment and bubble particle subpopulations 1 the effects of particle fields including bubbles on the optical volume scattering function vsf were investigated in the surf zone off scripps pier as part of an ongoing effort to better understand the underlying dynamics in the vsf in the subsurface ocean vsfs were measured at 20 hz at angles spanning 10 170 in 10 increments with a device called the multiangle scattering optical tool mascot modification of the phase function was observed in passing suspended sediment plumes wave injected bubble plumes and combinations of these particle populations relative to the background phase function enhancement in the 60 80 range was observed in association with bubble plumes consistent with theoretical predictions vsfs were inverted to infer size distributions and composition using a least squares minimization fitting procedure applied to a library of phase functions each representing a lognormally distributed subpopulation with refractive index and coating where applicable phase functions representative of nonspherical mineral particle subpopulations were computed using discrete dipole approximation dda and improved geometric optics method igom techniques for randomly oriented asymmetric hexahedra phase functions for coated bubbles were computed with the lorenz mie theory inversion results exhibited stable solutions that qualitatively agreed with concurrent acoustical measurements of bubbles aggregate particle size distribution expectations and anecdotal videography evidence from the field although a comparable inversion with a library that assumed spherical shaped particles alone provided less stable results with some incorrectly assigned subpopulations several dominant subpopulation trends were consistent with the results obtained using nonspherical representations of mineral particles

soil temperature and co 2 degassing so 2 fluxes and field observations before and after the february 29 2016 new vent inside nyiragongo crater nyiragongo volcano threatens 1 5 million inhabitants of goma dr congo and gisenyi rwanda cities and people living in the surrounding villages in 2002 the volcano produced lava flows which invaded goma and destroyed the economic district of the city forced a mass exodus of the population and caused the loss of several lives nyiragongo volcanic activity is therefore closely followed by the inhabitants and any news related to increased activity agitates people in the area especially those in goma here we report a short time series of soil temperature and carbon dioxide degassing for four locations and plume sulphur dioxide fluxes preceding and following the opening of a new vent inside the main nyiragongo crater on february 29 2016 the observed sudden and unexpected changes in nyiragongo activity raised the fear of a new volcanic eruption and led to panic in goma and the surroundings inducing some people to leaving the city we use the dataset and field observations before and after the opening of the new vent in conjunction with published information about nyiragongo s eruptive mechanism and of the volcano s plumbing system geometry mainly the crater to show that the new vent was fed by magma intruded from the lava lake or the upper conduit

ghost tilt signal during transient ground surface deformation events insights from the september 3 2010 mw7 1 darfield earthquake new zealand 1 this work assesses whether tiltmeters can reliably measure ground tilt in the 2 20 s band similar to that of very long period volcanic earthquakes seismic waves recorded with co located high rate gps borehole seismometer and bubble tiltmeter during the 2010 mw7 1 darfield earthquake in new zealand are used to determine the response of the tiltmeter the joint analysis of this dataset shows that at least for periods within the aforementioned band the observed tilt signal was in fact not related to ground tilt but instead to translational ground acceleration caused by passing s and surface waves if no independent control on translational motion is provided for recorded very long period volcanic earthquakes within the 2 20 s band the signal recorded on bubble tiltmeters may therefore be misinterpreted the use of co located high rate gps data provides such control and is essential to discriminate translational motion from ground tilt on the recorded seismic and tiltmeter signals

landslide seismic magnitude abstract landslides have become one of the most deadly natural disasters on earth not only due to a significant increase in extreme climate change caused by global warming but also rapid economic development in topographic relief areas how to detect landslides using a real time system has become an important question for reducing possible landslide impacts on human society however traditional detection of landslides either through direct surveys in the field or remote sensing images obtained via aircraft or satellites is highly time consuming here we analyze very long period seismic signals 20 50 s generated by large landslides such as typhoon morakot which passed though taiwan in august 2009 in addition to successfully locating 109 large landslides we define landslide seismic magnitude based on an empirical formula lm log a 0 55 log 2 44 where a is the maximum displacement m recorded at one seismic station and is its distance km from the landslide we conclude that both the location and seismic magnitude of large landslides can be rapidly estimated from broadband seismic networks for both academic and applied purposes similar to earthquake monitoring we suggest a real time algorithm be set up for routine monitoring of landslides in places where they pose a frequent threat

bottom shear stress in the surf zone to investigate the bottom shear stress in the surf zone detailed laboratory measurements were made of the free surface elevations and velocities for the case of regular waves spilling on a rough impermeable 1 35 slope the velocity profiles were measured at several vertical lines in the cross shore direction to include the shoaling region seaward of breaking the break point the transition region and the inner surf zone each vertical line included measuring points at a fraction of the grain height above the rough fixed bottom a logarithmic layer was found to exist in the bottom boundary layer for most of the phases over a wave period seaward of the break point and in the surf zone a regression analysis was used at each phase to estimate the shear velocity and bottom roughness from the phase averaged horizontal velocities in the lower portion of the bottom boundary layer the bottom friction factor was estimated from a quadratic friction equation based on the measured horizontal velocity above the bottom boundary layer together with the estimated shear velocity the quadratic friction equation with the fitted friction factor was shown to predict the temporal variation of the bottom shear stress within a factor of 2 the bottom roughness estimated from the grain size assuming rough turbulent flow was shown to agree qualitatively with the measured values the cross shore variation of the friction factor estimated from an empirical formula developed for nonbreaking waves was shown to agree within a factor of 2 of the measured values

modeling the evolution of incised streams i model formulation and validation of flow and streambed evolution components a robust computational model for simulating the long term evolution of incised and restored or rehabilitated stream corridors is presented the physically based model simulates the three main processes that shape incised streams hydraulics sediment transport and streambed and bank adjustments a generalized implicit preissmann scheme is used for the spatial and temporal discretization of the flow governing equations to accommodate large time steps and cross sections spaced at irregular intervals the solution method introduces several enhancements that increase its robustness specifically to simulate flashy flows transport of cohesive or cohesionless graded bed material is based on a total load concept and suspended and bed load transport modes are accounted for through nonequilibrium effects the model simulates channel width adjustment by hydraulic erosion and gravitational mass failure of heterogeneous bank material the present paper focuses mainly on the treatment of streamflow hydraulics and evolution of graded streambeds and reports simulations of published experiments on degrading and aggrading channels with graded bed material description and validation of the model s stream bank erosion component and the application of the model to incised stream systems are presented elsewhere

the effect of entrained air in violent water wave impacts the effects of entrained air in cushioning water impact on a wall are estimated by using a flow which has many similarities to the severe flip through impacts that have been identified for water waves hitting a vertical wall this is a filling flow which rapidly fills a confined region such as a crack between blocks or the space beneath a deck projecting from the coast peregrine kalliadasis 1996 the main properties of the filling flow are easily calculated including the high pressure peak which corresponds to the pressure peak of a flip through this work extends the study of filling flows to the case where the filling liquid is an air water mixture thus giving explicit results for the reduction of peak pressure due to the compressibility of entrained air the behaviour of a bubbly liquid subject to substantial pressure changes is considered expressions are derived for an air water mixture treated as a compressible fluid the reduction in pressure from the incompressible case is found to be large even for relatively small air content and depends more on the reduction in fluid volume than any other feature of the pressure density relation results are presented in such a way that they may be used to estimate compressibility corrections to both the maximum and background pressures in a flip through wave impact if corresponding incompressible pressure values are available

geometry and kinematics of dunes during steady and unsteady flows in the calamus river nebraska usa the geometry and kinematics of river dunes were studied in a reach of the calamus river nebraska during day long surveys dune height length steepness migration rate creation and destruction were measured concurrently with bedload transport rate flow depth flow velocity and bed shear stress within a survey individual dune heights lengths and migration rates were highly variable associated with their three dimensional geometry and changes in their shape through time notwithstanding this variability there were discernible changes in mean dune height length and migration rate in response to changing discharge over several days changes in mean dune height and length lagged only slightly behind changes in discharge therefore during periods of both steady and unsteady flow mean dune lengths were quite close to equilibrium values predicted by theoretical models mean dune steepnesses were also similar to predicted equilibrium values except during high falling flows when the steepness was above that predicted variations in mean dune height and length with discharge are similar to those predicted by theory under conditions of low mean dune excursion and discharge variation with a short high water period and long low water period however the calculated rates of change of height of individual dunes vary considerably from those measured rates of dune creation and destruction were unrelated to discharge variations contrary to previous results instead creations and destructions were apparently the result of local variations in bed shear stress and sediment transport rate observed changes in dune height during unsteady flows agree with theory fairly well at low bed shear stresses but not at higher bed shear stresses when suspended sediment transport is significant

the morphodynamics of fluvial sand dunes in the river rhine near mainz germany i sedimentology and morphology the dynamics of large isolated sand dunes moving across a gravel lag layer were studied in a supply limited reach of the river rhine germany bed sediments dune geometry bedform migration rates and the internal structure of dunes are considered in this paper hydrodynamic and sediment transport data are considered in a companion paper the pebbles and cobbles d50 of 10 mm of the flat lag layer are rarely entrained dunes consist of well sorted medium to coarse sand d50 of 0 9 mm small pebbles move over the dunes by overpassing but there is a degree of size and shape selectivity populations of ripples in sand d50 0 6 mm and small and large dunes are separated by distinct breaks in the bedform length data in the regions of 0 7 1 m and 5 10 m ripples and small dunes may have sinuous crestlines but primarily exhibit two dimensional planforms in contrast large dunes are primarily three dimensional barchanoid forms ripples on the backs of small dunes rarely develop to maximum steepness small dunes may achieve an equilibrium geometry either on the gravel bed or as secondary dunes within the boundary layer on the stoss side of large dunes secondary dunes frequently develop a humpback profile as they migrate across the upper stoss slope of large dunes diminishing in height but increasing in length as they traverse the crestal region however secondary dunes more than 5 m in length are rare the dearth of equilibrium ripples and long secondary dunes is probably related to the limited excursion length available for bedform development on the parent bedforms large dunes with lengths between 20 m and 100 m do not approach an equilibrium geometry a depth limitation rather than a sediment supply limitation is the primary control on dune height dunes rarely exceed 1 m high in water depths of 4 m dune celerity increases as a function of the mean flow velocity squared but this general relationship obscures more subtle morphodynamics during rising river stage dunes tend to grow in height owing to crestal accumulation which slows downstream progression and steepens the dune form during steady or falling stage an extended crestal platform develops in association with a rapid downstream migration of the lee side and a reduction in dune height these diminishing dunes actually increase in unit volume by a process of increased leeside accumulation fed by secondary dunes moving past a stalled stoss toe a six stage model of dune growth and diminution is proposed to explain variations in observed morphology the model demonstrates how the development of an internal boundary layer and the interaction of the water surface with the crests of these bedload dominated dunes can result in dunes characterized by gentle lee sides with weak flow separation this finding is significant as other studies of dunes in large rivers have attributed this morphological response to a predominance of suspended load transport

centroid single force inversion of seismic waves generated by landslides the centroid moment tensor cmt waveform inversion method of dziewonski et al 1981 is modified to analyze long period seismic waves generated by single force events such as the gigantic landslides associated with the 1980 eruption of mount st helens we refer to the method as centroid single force csf inversion as the result of the inversion we obtain the spatio temporal centroid and three components of a vector we call the csf vector which is the seismic point source representation of a landslide and whose direction is the opposite of the direction of sliding the sealer magnitude of the csf vector measures the overall size of the landslide and is given by mcsf md where m is the mass of the sliding object and d is the sliding distance we apply csf inversion to the long period surface waves generated by the 1980 mount st helens event the 1975 kalapana earthquake and the 1974 mantaro landslide using seismograms from the gdsn ida and hglp networks the csf solution for the st helens event is remarkably consistent with the actual geological observations and proves the efficacy of csf inversion the csf solution for the kalapana event does not fit the overall waveforms better than the cmt solution does however because the cmt solution does not explain the observed love wave radiation pattern it may be necessary to invoke a combination of both types of mechanism for this event although the geometry of the csf solution the direction of the force for the mantaro event is consistent with the actual landslide mcsf is about 5 times smaller than that expected from the mass and travel distance of the landslide estimated by geological observations this discrepancy may suggest either the relatively aseismic nature of this landslide or that the total volume of the slide was overestimated by analogy to single station cmt inversion single station csf inversion also appears to be stable and useful

longshore current forcing by irregular waves 1 the terms in the wave averaged depth integrated alongshore momentum balance are populated with detailed measurements from a laboratory basin experiment obliquely incident irregular waves were generated in a large wave basin equipped with instruments to collect free surface elevation and velocity measurements over a sand beach pumps matched the wave generated currents and experimental evidence indicates that the equations can justifiably be simplified by assuming alongshore uniformity while the use of data measured below the trough level is straightforward the velocity field in the region near the surface is extrapolated from the measured positions and constrained by conservation of cross shore mass flux the role of the dispersive mixing mechanism due to depth dependent currents is shown to be small but acts to shift the peak of the longshore velocity shoreward slightly radiation stresses are the primary forcing mechanism and computed stresses based on measured wave induced hydrodynamics are considerably smaller than the widely used linear representation indicating that the small amplitude assumption of linear theory is not appropriate in the surf zone the time averaged bottom shear stress remains as the primary balance to the gradient in alongshore momentum and the inferred shear stress compares favorably with the values computed using the quadratic drag law and a spatially constant friction coefficient

analysis of long period seismic waves excited by the may 18 1980 eruption of mount st helens a terrestrial monopole long period 100 to 260 s love and rayleigh waves excited by the eruption of mount st helens on may 18 1980 and recorded by ida sro and asro stations were analyzed to determine the mechanism of the eruption the amplitude radiation patterns of both rayleigh and love waves are two lobed with a nodal direction in e5 s for rayleigh waves and in n5 e for love waves these radiation patterns preclude any double couple mechanism the radiation pattern the initial phase the relatively large amplitude ratio of love to rayleigh waves and the existence of clear nodes in the radiation patterns of fundamental mode and higher mode rayleigh waves suggest that the source is represented by an almost horizontal less than 15 from the horizontal single force pointed toward s5 w the surface wave spectra fall off very rapidly at periods shorter than 75 s suggesting a very slow source process although the details of the source time history could not be determined a smooth bell shaped time function f o s t 1 2 f o l cos t for 0 t 2 and f o s t 0 for t 2 with 75 s is considered appropriate on the basis of comparison between synthetic and observed seismograms and of the shape of the source spectrum the peak value of the force f 0 is about 10 18 dynes the tailing end of the source time function could not be resolved and some overshoot may be added the magnitude and the time history of the force can be explained by a northward landslide followed by a lateral blast observed at the time of the eruption two distinct events about 110 s apart can be identified on body wave and short period surface wave records the first event may correspond to the earthquake which triggered the landslide and the lateral blast the second event appears to correspond to a second large earthquake and explosion which took place about 2 minutes after the first earthquake

bubble transport in rip currents a number of remote and in situ acoustical sensors were mounted in the surf zone off scripps pier la jolla california during march 1997 and used to characterize rip currents and their ability to transport bubbles offshore from the surf zone the bubble size distributions and air fractions at the injection point were measured using an acoustical resonator and a conductivity sensor right in the surf zone the offshore moving bubble plume was tracked with a multibeam 100 khz doppler sidescan sonar giving the spatial extent and offshore variability in the rip events as well as information about the surface wave field furthermore three acoustical resonators were mounted at 2 5 m depth 55 60 m farther offshore to probe the bubble field 300 400 s after injection these results are interpreted using models that include bubble buoyancy and dissolution rip current advection and the turbulent boundary layer which is represented by the christoffersen and jonsson 1985 formulation

the swash of solitary waves on a plane beach flow evolution bed shear stress and run up the swash of solitary waves on a plane beach is studied using large scale experiments ten wave cases are examined which range from non breaking waves to plunging breakers the focus of this study is on the influence of breaker type on flow evolution spatiotemporal variations of bed shear stresses and run up measurements are made of the local water depths flow velocities and bed shear stresses using a shear plate sensor at various locations in the swash zone the bed shear stress is significant near the tip of the swash during uprush and in the shallow flow during the later stages of downrush in between the flow evolution is dominated by gravity and follows an explicit solution to the nonlinear shallow water equations i e the flow due to a dam break on a slope the controlling scale of the flow evolution is the initial velocity of the shoreline immediately following waveform collapse which can be predicted by measurements of wave height prior to breaking but also shows an additional dependence on breaker type the maximum onshore directed bed shear stress increases significantly onshore of the stillwater shoreline for non breaking waves and onshore of the waveform collapse point for breaking waves a new normalization for the bed shear stress which uses the initial shoreline velocity is presented under this normalization the variation of the maximum magnitudes of the bed shear stress with distance along the beach which is normalized using the run up follows the same trend for different breaker types for the uprush the maximum dimensionless bed shear stress is approximately 0 01 whereas for the downrush it is approximately 0 002

seismic signals associated with landslides and with a tsunami at stromboli volcano italy in this article we analyze the seismic signals produced by two landslides that occurred at the stromboli volcano on 30 december 2002 recorded by both broadband and short period seismic stations located in the 2 5 22 km distance range from the source for both landslides the characteristics of the low frequency seismograms indicate a complex time history in the release of seismic energy the first landslide occurred over the submerged part of the northwest sector of the volcano and had associated a large amplitude low frequency pulse representative of the abrupt detachment of a large mass lower amplitude phases in the following 3 minutes possibly indicate minor detachment events the highest amplitude low frequency signals are well described by a single force source model the second mass failure episode is also characterized by a complex source and can be interpreted as a multiple event with a less abrupt onset and at least four detachments occurring during 4 5 minutes and producing low frequency signals synthetic seismograms generated by a shallow single force located in the submerged area of sciara del fuoco and directed upslope fit well the first low frequency seismic pulse recorded at stromboli and panarea by three component stations from this simulation we estimated the force exerted by the first mass failure the estimate of the volume through two different procedures gives values in the range of 1 0 1 5 million m3 and about 14 million m3 respectively the landslides which involved both the submarine and the subaerial northwest flank of the volcano produced a tsunami that struck the coast of stromboli island and in a few minutes reached the other islands of the aeolian archipelago three broadband seismic stations installed on land about 100 m from the coastline at panarea island located 20 km southwest of stromboli recorded very long period seismic signals produced by the tsunami waves analysis of these signals gives invaluable information on the spectral content and propagation properties of tsunami waves and on their interaction with the ground at a short distance from the coast synthetic tsunami waves obtained by a landslide source model and taking into account the bathymetry of the sea surrounding stromboli and panarea islands fit the observed phenomena and the experimental data very well manuscript received 19 november 2003

process of the 1977 nyiragongo eruption inferred from the analysis of long period earthquakes and volcanic tremors abstract the lava lake present in the summit crater of nyiragongo from 1928 to 1977 completely disappeared after the short lived eruption of january 10th 1977 the sequence of events during this eruption was elucidated by analysis of seven long period earthquakes lp events and volcanic tremors recorded at stations lwi nai and bul the seven lp events observed were composed mainly of rayleigh waves with large amplitudes and were classified into two groups one containing three and the other containing four events based on waveform similarities it was determined that the former events were excited by the vertical downward single forces and the latter events by the vertical upward ones the short period seismograms recorded at lwi and nai showed that continuous volcanic tremors began roughly 6 min before the occurrence of the first lp event after the appearance of seven burst type tremor activities tremor amplitudes suddenly increased and then gradually decreased taking the analytical results of seismic events and observed surface activities into consideration we inferred the process of the 1977 nyiragongo eruption to be as follows 1 1 quick draining of the liquid lava through the fissures and disappearance of the long lived lava lake less than 6 min 2 2 large terraces collapsing onto the bottom of crater causing the first three lp events during the next 8 min 3 3 intermittent vesiculation of lava at the top of magma chamber exciting the last four lp events during the next 8 min 4 4 magma flowing in deeper parts of the conduit generating the intense tremors measurable at nai and lasting for roughly 30 min

origin of hysteresis in bed form response to unsteady flows 1 field and laboratory studies indicate that changes in riverbed morphology often lag changes in water discharge this lagged response produces hysteresis in the relationship between water discharge and bed form geometry to understand these phenomena we performed flume experiments to observe the response of a sand bed to step increases and decreases in water discharge for an abrupt rise in discharge we observed that bed forms grew rapidly by collision and merger of bed forms migrating with different celerities growth rate slowed as bed forms approached equilibrium with the higher discharge regime after an abrupt discharge drop bed form decay occurred through formation of smaller secondary bed forms in equilibrium with the lower discharge which cannibalized the original relict features we present a simple model framework to quantitatively predict time scales of bed form adjustment to flow changes based on equilibrium bed form heights lengths and celerities at low and high flows for rising discharge the model assumes that all bed form collisions result in irreversible merger due to a dispersion of initial celerities for falling discharge we derive a diffusion model for the decay of relict high stage features our models predict the form and time scale of experimental bed form adjustments additional experiments applying slow and fast triangular flood waves show that bed form hysteresis occurs only when the time scale of flow change is faster than the modeled and measured bed form adjustment time we show that our predicted adjustment time scales can also be used to predict the occurrence of bed form hysteresis in natural floods

detection of landslides and submarine slumps using broadband seismic networks 1 we detected 52 seismic events associated with landslides and submarine slumps on 8 august 2009 when typhoon morakot hit taiwan these events were neither felt nor reported because their seismic energy was primarily in the long period band 20 50 s most of these events were located in mountain areas where the accumulated rainfall was extremely high though some were found offshore southern taiwan among all events the fatal landslide earthquake was located at hsiaolin village where 474 people were buried inversion modelling of the seismic waveforms generated by the hsiaolin landslide shows that the seismic source was represented by single force consistent with downhill sliding some offshore seismic events indicate that submarine slumps probably occurred along submarine canyons and steep slopes our study shows that broadband seismic monitoring can be used to issue early warnings for mitigating disasters generated by inland and offshore landslides

was the 18 may 1980 lateral blast at mt st helens the product of two explosions the 18 may 1980 lateral blast at mt st helens has been interpreted as the product of a single explosion by some stratigraphers and as two closely spaced explosions by others the stratigraphic evidence that bears on this question is inconclusive strata change dramatically over short distances and this complexity provides wide latitude for interpretation some independent non stratigraphic evidence however suggests that the blast was the product of two explosions or clusters of explosions the independent evidence comes from eyewitness accounts and photographs from satellite sensors and from seismic records this paper reviews the pertinent evidence offers a new interpretation and concludes that the blast was indeed the product of two explosions or clusters of explosions

eruption source processes derived from seismic and acoustic observations of the 25 september 2007 ruapehu eruption north island new zealand abstract mt ruapehu erupted on 25 september 2007 at 20 26 pm nzdt 8 26 ut generating a steam column to about 15 000 ft 4600 m a directed ballistic and surge deposit of coarse blocks and ash to the north of the crater lake and initiated lahars in the whangaehu catchment and whakapapa ski field the eruption was recorded on three broadband seismometers and two acoustic pressure sensors which indicated broadly coherent waveform characteristics across the network the eruption had a duration of less than 1 min as indicated by strong seismic and acoustic pulses the acoustic wave coincided with observed very long period vlp seismic signal 2 25 s period the acoustic pulse had a positive pressure indicating an explosion and travelled at a velocity of 320 m s the syn eruptive vlp was composed of surface waves having strong radial and transverse components the immediate aftermath of the eruption produced about 4 min of continued high amplitude spasmodic tremor signals that probably resulted from post explosion phase associated vent backfill stabilisation the eruption was preceded by minor volcano tectonic earthquakes and tremor bursts which began 10 min before the main eruption two smaller vlp signals were associated with these tremor pulses at 20 17 and 20 25 these pre eruptive vlp signals had particle motions indicating body and surface waves from a sub surface source region modelling of the vlp sources using a 3d finite difference method shows that that the pre eruption vlp signals are consistent with a volume fluctuation at 3 7 km depth from a radially symmetric source the main eruption vlp was consistent with a south and downward directed single force in response to a northward directed jet and northward directed ballistic deposits

seismic characteristics of variable convection at erta ʻale lava lake ethiopia abstract the active summit lava lake of erta ale volcano ethiopia offers a unique opportunity to study magma convection in february 2002 we collected a multiparametric set of seismic thermal and video data these data indicate that the lake cycled between periods characterized by low 0 01 0 08 m s 1 and high 0 1 0 4 m s 1 convection rates typically lasting tens to hundreds of minutes three seismometers placed around the active crater recorded continuous tremor with a dominant frequency of 2 hz and energy at frequencies from 0 8 to 12 hz here we characterize the seismic signature of each regime by its spectral content wavefield polarization and tremor source location for both regimes the wavefield is mostly rectilinear azimuths and incidence angles are consistent with p waves originating in one of two locations the north edge of the active lava lake or a region 100 150 m ene of the lava lake because both regimes are dominated by a low frequency rectilinearly polarized wavefield we investigate the source location using a method that solves for location and isotropic source power by a weighted least squares amplitude based inversion of seismic data we find that tremor source regions are unique to each convective regime although some location overlap exists when tremor is located in short time windows wavefield composition suggests that the convective phases may share a common source process but their differing locations indicate that either the source region is non stationary or a second source skews the location during the high convective phase tremor polarization and location suggests that the low frequency tremor is caused by bubble coalescence and bursting in a conduit whose surface is the lava lake the higher frequency signal associated with the high convective regime is associated with a scattered more complex wavefield superimposed on the low frequency background tremor caused by bubble bursting and cracking of cooled crust at the lava lake surface

an integral swash zone model with friction an experimental and numerical investigation abstract experimental and numerical analyses have been used to assess the validity and potentialities of the integral swash zone model by brocchini and peregrine proc coastal dynamics 95 asce 1 1996 221 which is extended to include seabed friction effects previously neglected applications of the model to experimental data show it represents a simple and useful tool for modelling swash zone flows the model allows for computation of integral swash zone properties and shoreline motion from local variables defined at the seaward limit of the swash for most properties correlation between local and integral properties is very good correlation coefficient about 0 80 a suitable parametric form of frictional forces in the swash zone is defined on the basis of both experimental data and analytical investigation numerical tests showed that the proposed parameterization models well integral frictional forces within the swash zone the parametric friction force improves capabilities of the integral swash zone model of representing real swash motions this is particularly evident when considering the momentum equation the correlation coefficient between the rate of change of the onshore momentum in the swash zone and its forcings increases from about 0 85 to about 0 95 due to the inclusion of the seabed friction

interactions between bed forms topography turbulence and transport 1 results are presented examining the interaction between two sandy bed forms under low sediment transport conditions in a small laboratory flume the initial artificially made bed forms were out of equilibrium with the flow field temporal evolution of bed forms was monitored using time lapse photography in order to characterize bed form adjustment to the imposed flow velocity measurements were collected using an acoustic doppler velocimeter to characterize both mean flow and turbulence associated with different bed form geometries sandy bed forms all had identical initial geometries however the initial distance between bed form crests was varied between experiments overall deformation of the bed varied as a function of initial bed form spacing however bed forms evolved unpredictably as periods of relatively slow change were punctuated by periods of rapidly changing geometry subtle changes in bed form trough geometry were found to have a strong influence on turbulence and therefore sediment transport comparison with field studies suggests that the mechanisms described herein are active in natural systems

a flume study on the development and equilibrium morphology of current ripples in very fine sand an empirical model is constructed for the development and equilibrium dimensions of small scale unidirectional bedforms in sand with a median grain size of 0 095 mm based on a series of steady flow experiments in a flume current ripples always attain a linguoid plan morphology with constant average height 13 1 mm and wavelength 115 7 mm provided that sufficient time is allowed for their formation the development pattern of these ripples on a flat bed is independent of flow velocity and involves four stages 1 incipient ripples 2 straight and sinuous ripples 3 non equilibrium linguoid ripples and 4 equilibrium linguoid ripples straight and sinuous ripples are non equilibrium bedforms at all flow velocities the time needed to reach equilibrium dimensions is related to the inverse power of flow velocity and ranges from several minutes to more than hundreds of hours at flow velocities where washed ripples are stable the equilibrium wavelength is similar to that of equilibrium linguoid ripples but the equilibrium height rapidly decreases from 13 1 mm to zero towards upper stage plane bed conditions the results of the flume experiments correspond reasonably well with those of previous studies provided that various complicating factors such as different experimental methods different sediment characteristics shallow flow depths and non equilibrium runs are accounted for

comment on a single force model for the 1975 kalapana hawaii earthquake by holly k eissler and hiroo kanamori

seismic and acoustic signatures of surficial mass movements at volcanoes abstract surficial mass movements such as debris avalanches rock falls lahars pyroclastic flows and outburst floods are a dominant hazard at many volcanoes worldwide understanding these processes cataloging their spatio temporal occurrence and detecting tracking and characterizing these events would advance the science of volcano monitoring and help mitigate hazards seismic and acoustic methods show promise for achieving these objectives many surficial mass movements generate observable seismic and acoustic signals and many volcanoes are already monitored significant progress has been made toward understanding modeling and extracting quantitative information from seismic and infrasonic signals generated by surficial mass movements however much work remains in this paper we review the state of the art of the topic covering a range of scales and event types from individual rock falls to sector collapses we consider a full variety of volcanic settings from submarine to subaerial shield volcano to stratovolcano finally we discuss future directions toward operational seismo acoustic monitoring of surficial mass movements at volcanoes

long time base observations of surf noise a year of surf noise observations in the very near shore region of la jolla shores beach are presented ambient sound levels and surface wave height were recorded for 9 min every hour from july 1997 through june 1998 at a monitoring station located 360 m seaward of the beach in 8 m deep water sound segments that were dominated by the noise from breaking surf formed the basis of a correlation analysis between surf noise level and wave height wave period wind speed and mean water depth the analysis shows that surf noise is primarily determined by wave height and scales approximately with the wave height squared the surface wave energy flux onto the beach also scales with wave height squared leading to the conclusion that the conversion of the mechanical energy of the surface wave field into noise energy is approximately constant in fact the ratio of noise energy to surface wave energy flux varies by up to a factor of 3 over the range of energy fluxes considered 100 3000 w per m

identification of intense intermittent coherent motions under shoaling and breaking waves laboratory measurements of the instantaneous horizontal and vertical turbulent velocities u and w induced by regular waves spilling on a rough impermeable slope were analyzed to elucidate the nature of turbulence generated in the bottom boundary layer and by wave breaking the analyses focused on the instantaneous turbulent events such as the absolute shear stress u w and turbulent kinetic energy k u 2 w 2 2 below trough level inside the surf zone the horizontal and vertical velocity records showed intense intermittent turbulent events that did not occur with the passing of each wave and the instantaneous quantities of and k could not be explained in terms of the phase averaged quantities the intermittent turbulent events extended into the bottom boundary layer inside the surf zone and in this region the infrequent but intense turbulence generated by wave breaking was an order of magnitude larger than the turbulence generated locally at the boundary two techniques were used to analyze the turbulent motions a quadrant analysis technique showed that although the large turbulent motions did not occur with each wave they were phase dependent near trough level and less so near the bottom a conditional sampling technique quantified the intensity and duration of the turbulent motions indicating that coherent events intense events occurred for 10 2 of the record and accounted for approximately 50 20 of the turbulent motion it is likely that the exactitude of these statistics will differ depending on breaker type nevertheless these statistics indicated that large turbulent motions are infrequent but contribute significantly to the turbulence intensity and possibly the suspension of bottom sediments

fluvial dunes initiation characterization flow structure research into fluvial dunes spans disciplines studies at grain to reach scales and methodological approaches that include theoretical experimental numerical and field investigations despite significant research efforts to date it remains difficult to provide definitive answers to some fundamental questions regarding dunes this paper reviews three notable challenges that remain regarding fluvial dunes namely scale consistent linking of bed morphologies with turbulent flow fields the intriguing question of what causes trains of highly ordered sediment waves to form in beds of river sediments and how to define the important characteristics of a dune covered bed including lengths shapes and their statistical nature in each case the particular challenge is discussed and then recent research and ways forward are presented copyright 2010 john wiley sons ltd

seismic wavefields in the deep seafloor area from a submarine landslide source we use the finite difference method to simulate seismic wavefields at broadband land and seafloor stations for a given terrestrial landslide source where the seafloor stations are located at water depths of 1 900 4 300 m our simulation results for the landslide source explain observations well at the seafloor stations for a frequency range of 0 05 0 1 hz assuming the epicenter to be located in the vicinity of a large submarine slump we also model wavefields at the stations for a submarine landslide source we detect propagation of the airy phase with an apparent velocity of 0 7 km s in association with the seawater layer and an accretionary prism for the vertical component of waveforms at the seafloor stations this later phase is not detected when the structural model does not consider seawater for the model incorporating the seawater the amplitude of the vertical component at seafloor stations can be up to four times that for the model that excludes seawater we attribute this to the effects of the seawater layer on the wavefields we also find that the amplification of the waveform depends not only on the presence of the seawater layer but also on the thickness of the accretionary prism indicating low amplitudes at the land stations and at seafloor stations located near the trough but high amplitudes at other stations particularly those located above the thick prism off the trough ignoring these characteristic structures in the oceanic area and simply calculating the wavefields using the same structural model used for land areas would result in erroneous estimates of the size of the submarine landslide and the mechanisms underlying its generation our results highlight the importance of adopting a structural model that incorporates the 3d accretionary prism and seawater layer into the simulation in order to precisely evaluate seismic wavefields in seafloor areas

blast dynamics at mount st helens on 18 may 1980 at 8 32 a m on 18 may 1980 failure of the upper part of the north slope of mount st helens triggered a lateral eruption the blast that devastated the conifer forests in a sector covering 500 km2 north of the volcano i present here a steady flow model for the blast dynamics and propose that through much of the devastated area the blast was a supersonic flow of a complex multiphase solid liquid vapour mixture the shape of the blast zone pressure temperature velocity mach number and density distributions within the flow positions of weak and strong internal shocks and mass flux energy flux and total energy are calculated the shape of blast zone was determined by the initial areal expansion from the reservoir by internal expansion and compression waves including shocks and by the density of the expanding mixture the pressure within the flow dropped rapidly away from the source of the blast until at a distance of 11 km the flow became underpressured relative to the surrounding atmosphere weak shocks within the flow subparallel to the east and west margins coalesced at about this distance into a strong mach disk shock across which the flow velocities would have dropped from supersonic to subsonic as the pressure rose back towards ambient the positions of the shocks may be reflected in differences in the patterns of felled trees at the limits of the devastated area the temperature had dropped only 20 from the reservoir temperature because the entrained solids thermally buffered the flow the dynamic and thermodynamic effects of the admixture of the surrounding atmosphere and the uprooted forest and soils into the flow are not considered the density of the flow decreased with distance until at the limits of the blast zone 20 25 km from the volcano the density became comparable with that of the surrounding dirty atmosphere and the flow became buoyant and ramped up into the atmosphere according to the model the mass flux per unit area at the source was 0 6 104 g s 1 cm 2 and the energy flux per unit area was 2 5 mw cm 2 from the measured total ejected mass 0 25 1015 g the total energy released during the eruption was 1024 erg or 24 megatons the model triggering of the eruption and the transition from unsteady to steady flow and applications to eyewitness observations and atmospheric effects are discussed in ref 1

a quasi 3d phase resolving hydrodynamic and sediment transport model a two dimensional phase resolving wave transformation module is combined with an intra wave sediment transport module to calculate the two dimensional sediment transport rates the wave module is based on the boussinesq equations extended into the surf zone two hydrodynamic modules are developed for the calculation of the vertical variation of the eddy viscosity and the currents the intra wave sediment concentrations and sediment transport rates are also calculated the model was verified against several test cases and a sensitivity analysis was performed both hydrodynamic modules produced close results for the mean currents the two models also produced close results for the sediment transport rates with larger differences observed at the locations with a stronger undertow the model results showed that for irregular breaking waves the mean sediment concentration cannot be calculated directly from the mean eddy viscosity

laboratory observations of flow and sediment transport induced by plunging regular waves 1 two parallel experiments involving the evolution and runup induced by plunging regular waves near the shoreline of a sloping bed are considered 1 a rigid bed experiment allowing direct hot film measurements of bed shear stresses and 2 a sediment bed experiment allowing for the measurement of pore water pressures as well as observation of sediment suspension and bed morphological changes both experiments utilize the same initial bed profile and wave forcing the experiments show that the mean bed shear stresses experienced onshore of incipient breaking are amplified by nearly a factor of 2 relative to prebreaking conditions whereas their corresponding turbulent fluctuations are amplified even more strongly by a factor of 5 6 the plunging processes lead to a series of vortices whose formation may be explained as the result of shear layer instability measurements show that these vortices can significantly enhance peaks in the offshore directed bed shear stresses moreover near bed pore pressure measurements indicate that these vortices cause large upward directed pressure gradients which in turn produce a corresponding series of suspended sediment plumes shoreward of the initial breaking event these findings are related to the induced morphological changes over both short and long time scales the present results are also compared and contrasted with previous experiments utilizing a similar methodology but involving plunging solitary waves

air entrainment processes and bubble size distributions in the surf zone abstract a new optical instrument was deployed in the surf zone in a trial experiment to measure bubble size distributions and visualize air entrainment and bubble formation mechanisms within breaking surf images of bubbles and the evolving air water mixture inside and beneath breaking wave crests are presented the images resolve features of the air water mixture to length scales of hundreds of microns across a 3 7 cm field of view two qualitatively different large scale air entrainment processes are observed first intrusions of air and water thought to be created by jets penetrating the water s surface fragment into plumes of bubbles second an air cavity trapped by the overturning wave crest is observed to disintegrate into bubbles the timescale for the evolution from a compacted air water mass to individual bubbles was on the order of 90 ms or less for both of these processes in addition small scale air filaments hundreds of microns wide and millimeters long have been discovered beneath wave

seismic hazard of volcanic activity abstract seismic activity is a common feature of volcanic eruptions the majority of volcanic earthquakes are small their magnitudes do not exceed 2 or 3 at the same time significant moderate size and large volcanic earthquakes may also occur the study of 28 significant m w 4 5 earthquakes associated with volcanic eruptions of 20th century allowed us to formulate the following results about seismic hazard of volcanic activity 1 during the 20th century only three large m w 7 0 earthquakes directly associated with volcanic eruptions in the world were recorded 2 the maximum magnitude m w was estimated to be 5 4 for earthquakes related to central eruptions 7 0 for caldera collapse 5 9 for central eruptions accompanied by flank and or fissure eruptions 7 1 for flank and or fissure eruptions without central eruptions and 5 9 for submarine eruptions for seismicity just before the eruption the maximum magnitude of earthquakes was estimated to be m w 7 1 for seismicity at the initial stage of eruption m w 7 0 for paroxysmal stage of eruption m w 5 6 and for final stage of eruption m w 6 1 3 it was shown that the recurrence time of eruptions of the same type of volcano associated with significant m w 4 5 earthquakes was more than 100 years for 86 of events studied

reconstruction of the 2018 tsunamigenic flank collapse and eruptive activity at anak krakatau based on eyewitness reports seismo acoustic and satellite observations abstract after several months of eruptive activity the subaerial cone of anak krakatau collapsed on december 22 2018 the landslide event generated a tsunami that had deadly consequences within the sunda strait in indonesia such significant collapse events are common in the geologic record but are a rare phenomenon in the instrumented record however these events can have a potentially large impact on society we have reconstructed the collapse along with the activity preceding and following it by combining information from official reports remote geophysical observations and local eyewitness accounts it appears that the collapse of anak krakatau s subaerial cone led to a drastic change in the eruptive style from continuous strombolian explosions to sustained surtseyan those changes are detectable in the seismo acoustic measurements which when combined with eyewitnesses allows us to reconstruct the timing and phenomenology of the sequence our analysis reveals that intense eruptive activity generated sustained infrasound unusual but not unique at anak krakatau starting approximately eight hours before the collapse within this timeframe two seismic signals consistent with minor mass movements as well as a momentary quiescence were identified prior to the main collapse the data presented here indicate that anak krakatau failed in one collapse event producing a tsunami with multiple waves around the volcano the last one being the largest following the collapse three volcanic plumes could be clearly identified in the satellite data and by eyewitnesses as well as spectral lines in the seismic data these lines observed up to 371 km suggest a repeating energetic explosive source lasting for seven days the collapse produced multiple infrasound arrivals observed at regional infrasound stations but was not recorded on the regional hydroacoustic network our analysis of the eruptive sequence demonstrates that a detailed eruption chronology can be reconstructed using remote methods even in the event of failure or destruction of local monitoring infrastructure this event also highlights that tsunamigenic flank collapses can occur with little to no warning and be difficult to interpret in real time as a significant amount of non operational analysis was required after the event to complete the chronology

a review of controls on lava lake level insights from halema uma u crater kīlauea volcano the height of the lava column is a fundamental measure of open vent volcanic activity but little continuous long term data exist to understand this parameter the recent 2008 2018 lava lake activity at the summit of k lauea volcano provides an opportunity to track and understand the processes that control lava level over timescales ranging from minutes to years we review recently published data as well as analyze the long term record of lava level at k lauea s summit during 2009 2017 longer timescale fluctuations over days to months have a strong positive linear correlation with ground deformation suggesting they reflect pressure changes in the summit magma reservoir shorter timescale fluctuations over minutes to hours have an inverse relationship with spattering i e outgassing intensity at the lake surface increased outgassing lowers the lake level and vice versa our analysis of the long term lava level data thus confirms that lava level at halema uma u is controlled by these two types of processes 1 those related to magma reservoir pressure changes such as magma supply rate and 2 shallow outgassing fluctuations such as gas pistoning frequency filtering can isolate pressure and outgassing driven components of lava level change time series analysis indicates that there was no large persistent periodicity in the lava level a minor fortnightly oscillation might be related to earth tides but was not continuously present the correlation between lava level and deformation of the summit indicates that the lava lake acts as a reliable piezometer tracking lava level over time may thus provide an indication of flank eruptive potential we show that long term interdisciplinary monitoring is necessary to discriminate the processes that control lava level

preservation of cross strata due to the migration of subaqueous dunes an experimental investigation this experimental investigation examined the controls on the geometry of cross sets formed by subaqueous dunes a range of steady unidirectional flow conditions spanning the field of dune existence was investigated andaggradation rate ranged from 0 mm s 1 to 0 014 mm s 1 data from an ultrasonic depth profiler consist of high resolution temporal and spatial series of bed profiles from which dune height and length migration rate and the depth of trough scour were measured cross set thickness and length were measured from sediment peels the size and shape of dunes from an equilibrium assemblage change continuously individual dunes commonly increase in height by trough scouring and occasionally by being caught up by the upstream dune both types of behaviour occur suddenly and irregularly in time and hence do not appear to depend on dunes further upstream however dune climbing or flattening is a typical response of dunes that disappear under the influence of the upstream dune all types of behaviour occur at any flow velocity or aggradation rate successive dune trough trajectories defined by dunes showing various behaviours affect the geometry of the preserved cross sets mean cross set thickness mean dune height averages 0 33 0 7 and mean cross set length mean dune length averages 0 49 0 08 and both show no systematic variation with aggradation rate or flow velocity mean cross set thickness mean cross set length tends to decrease with increasing flow velocity and froude number therefore allowing a qualitative estimation of flow conditions quantitative analysis of the temporal changes in the geometry and migration rate of individual dunes allows the development of a two dimensional stochastic model of dune migration and formation of cross sets computer realizations produced stacks of cross sets of comparable shape and thickness to laboratory flume observations indicating a good empirical understanding of the variability of dune trough trajectories however interactions among dunes and aggradation rates of the order of 10 2 mm s 1 should be considered in future improved models

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

broadband parametric imaging of breaking ocean waves an acoustic array was deployed in the near surface layer of a fetch limited coastal inlet to image breaking waves using only the sound radiated in the band 400 hz to 2000 hz from the breaking region the breakers were assumed to possess predominantly spiller characteristics for this frequency band the wavelength of sound in bubble free water is much larger than the surface wave height and the depth of the breaker bubble plume so both were considered insignificant the 15 element array was configured as a sparse horizontal cross with an 8 m aperture bottom moored and positioned nominally 3 m beneath the surface propagation from the source to the array elements assumed dipole sources an acoustically flat surface and an acoustically thin bubble plume the radiating region was parameterized by a broadband two dimensional gaussian profile information from up to six independent frequencies was combined to yield a maximum likelihood image analysis shows that the images align closely with the wind and can be observed moving downwind with a speed roughly equal to 70 of the phase speed of the dominant wind waves a model of acoustic source strength which is linear in log frequency is found fit the data reasonably well and model parameters are provided for a single wind speed unlike other imaging experiments this technique provides measurements of the size and shape of the bubble creation region at or near the peak of the radiated autospectrum

capabilities and limits for advp measurements of breaking waves and bores this paper presents experience from the use of an acoustic doppler velocity profiler in the surf zone over a large scale experimental barred beach in the first part of the paper attention is focused on the description of a proper advp set up and on the determination of relationships for the horizontal and vertical velocity components valid for the oscillatory flow case in the second part horizontal velocity component data from the advp are compared to the pre processed measurements from two other velocity measuring devices for breaking waves as well as near the end of the surf zone as expected in the outer region of the surf zone velocity measurements appear influenced by air entrainment in the bore like region where the effects of wave breaking are less intense and where the wave is reforming the horizontal velocity is in reasonable agreement with the rest of the measurements although the advp appears much noisier than other instruments the role of bubbles in outer zone is prevalent in its measuring error and gives a large underestimation furthermore for the adopted experimental conditions the analysis shows that the use in the bore like region of relationships for the horizontal velocity component that are valid for a uniform flow generates a negligible error

void fraction measurements beneath plunging and spilling breaking waves 1 the temporal and spatial variations of the void fraction fields beneath deepwater breaking waves were investigated in the laboratory there were a total of 13 measurement positions along the plunging wave the peak void fractions measured varied from 0 024 to 0 96 and the time averaged void fractions varied from 0 012 to 0 37 for the spilling wave there were four measurement positions and the mean void fractions varied from 0 17 to 0 29 it was found that an energetic spilling breaker may entrain approximately the same volume of air as a steeper larger amplitude plunging breaker the speed of advance of the air cavity entrained beneath the plunging wave was estimated to be 70 of the phase speed of the breaking wave the speed of the third bubble cloud entrained by the splash up was found to be approximately 90 of the phase speed beneath the spilling breaker the speed of advance of the bubble cloud was estimated to be 100 of the phase speed these measurements have lead to the identification of four significant events during the breaking of a plunging wave the plunging water jet impacting the forward face of the wave the air cavity collapse the splash up impact on the forward wave face and the location and timing of the peak void fraction in the splashing zone numerical models of plunging breakers should be able to accurately predict the timing and nature of these events

observations of swash zone velocities a note on friction coefficients 1 vertical flow structure and turbulent dissipation in the swash zone are estimated using cross shore fluid velocities observed on a low sloped fine grained sandy beach raubenheimer 2002 with two stacks of three current meters located about 2 5 and 8 cm above the bed the observations are consistent with an approximately logarithmic vertical decay of wave orbital velocities within 5 cm of the bed the associated friction coefficients are similar in both the uprush and downrush as in previous laboratory results turbulent dissipation rates estimated from velocity spectra increase with decreasing water depth from o 400 cm2 s3 in the inner surf zone to o 1000 cm2 s3 in the swash zone friction coefficients in the swash interior estimated with the logarithmic model and independently estimated by assuming that turbulent dissipation is balanced by production from vertical shear of the local mean flow and from wave breaking are between 0 02 and 0 06 these values are similar to the range of friction coefficients 0 02 0 05 recently estimated on impermeable rough nonerodible laboratory beaches and to the range of friction coefficients 0 01 0 03 previously estimated from field observations of the motion of the shoreward edge of the swash run up

model space exploration for determining landslide source history from long period seismic data the seismic signals generated by two large volcanic debris avalanches montserrat lesser antilles 1997 and mount st helens usa 1980 and a large rock ice avalanche mount steller usa 2005 have been analyzed for the two debris avalanches given the times and locations of such landslides their signals were recorded by only a few seismic stations moreover these signals cover only a very narrow frequency band and include considerable noise the mount steller on the contrary was precisely recorded for each event the source mechanism i e point force has been determined by waveform inversion using at most two broadband seismic stations the resulting force is very difficult to interpret in terms of landslide characteristics a monte carlo inversion was therefore performed by imposing a simple force model associated with the landslide based on the schematic view of an accelerating decelerating mass traveling down the slope the best parameter set of the force model was then found by minimizing misfits and maximizing correlations between data and synthetic signals this model appears to contain the minimum degree of complexity required to well reproduce the seismic data we detail here the method for the montserrat debris avalanche and then present it s validation on the well studied mount st helens debris avalanche and the well recorded mount steller rock ice avalanche the horizontal and vertical components of the resulting force have different source time functions the best force model compares well with the force obtained by waveform inversion finally this simple force model was interpreted using analytical and empirical relations derived from the sliding block model granular flow model and landslide studies this made it possible to estimate the order of magnitude of the mass flow duration and direction initial topography slope mean velocity and travel distance of the avalanches for these three avalanches the calculated characteristics are consistent with former studies

a single force model for the 1975 kalapana hawaii earthquake a single force mechanism is investigated as the source of long period seismic radiation from the 1975 kalapana hawaii earthquake m s 7 1 the observed love wave radiation pattern determined from the spectra of world wide standard seismograph network and high gain long period records at 100 s is two lobed with azimuth consistent with a near horizontal single force acting opposite strike 330 to the observed displacement direction of the earthquake this pattern is inconsistent with the expected double couple pattern assuming a form of the force time history of a one cycle sinusoid the total duration of the event estimated from rayleigh waves at two international deployment of accelerometers stations is approximately 180 s the peak amplitude f o of the time function is 1 10 15 n from amplitudes of love and rayleigh waves the interpretation is that the bulk of the seismic radiation was produced by large scale slumping of a large area of the south flank of kilauea volcano the single force is a crude representation of the effect on the earth of the motion of a partially decoupled large slide mass using the mass estimated from the tsunami generation area 10 15 10 16 kg the peak acceleration of the slide block 0 1 1 m s 2 inferred from the seismic force is comparable with the acceleration due to gravity on a gently inclined plane the slump model for the kalapana earthquake is also more qualitatively consistent with the large horizontal deformation 8 m on land and tsunami associated with the earthquake which are difficult to explain with the conventional double couple source model the single force source has been used previously to model the long period seismic waves from the landslide accompanying the eruption of mount st helens volcano and may explain other anomalous seismic events as being due to massive slumping of sediments or unconsolidated material and not to elastic dislocation

analysis of broadband seismic recordings of landslide using empirical green s function the 2010 mount meager landslide generated strong seismic waves we used seismic signals generated by a smaller landslide that occurred within 2 min of the end of the main landslide as the empirical green s function egf with which to obtain landslide dynamics from high frequency signals we then obtained the apparent force time function of the landslide based on the egf by inverting the higher frequency seismic signals the apparent force time function shows that the source material of the main landslide came from four collapses and that the second collapse involved multiple small collapses we also used the egf to simulate the vertical seismogram recorded at one station and found that the synthesized seismogram fits the response of the bulk mobilization of the sliding materials remarkably well our study demonstrates that the use of the egf can significantly broaden quantitative insights into landslide dynamics plain language summary seismic records reflect the effects of landslide dynamics and the path of seismic waves through the earth because the calculation of the high frequency component of the effect of a wave s path through the earth requires a detailed characterization of the velocity and attenuation structure the effects of landslide dynamics can only be estimated by inverting the long period seismic signals to study the high frequency seismic signals generated from the mount meager landslide we considered the seismic signals generated by a smaller landslide as the effects of the path of seismic waves we used the seismic signals generated by the smaller landslide to simulate the signal generated by the main landslide to overcome the effects of a potential overlap in the frequency domain between signals from the bulk and those from smaller particles our results show that the seismic signals generated by a small landslide can be used to improve our understanding of those generated by the main landslide

the effect of air bubbles on optical backscatter sensors the sensitivity of an optical backscatter sensor obs to bubbles is tested using a variety of bubble generating mechanisms that span the range of bubble sizes typically observed in surf zone studies over 1200 one minute runs were performed in a stirred test tank by altering the bubbler type water type air flow rate and sand or mud concentration the laboratory data shows a strong dependence of obs response to bubble size and concentration for sand or mud sediments the optical backscatter sensor voltage is increased by the presence of bubbles and smaller bubbles had a larger effect the effect was more pronounced in salt water than fresh water we conservatively report that obs output voltage is increased due to the presence of bubbles by 25 for the trials undertaken here in the cases performed in vigorously stirred salt and synthetic salt water bubbles were smaller than those measured under quiescent water conditions due to bubble shattering at the bubbler orifices and by the pumps used for stirring it was found in those cases that the bubble effect on obs was larger than the 25 reported here but the extension of this finding to a natural setting such as in the direct vicinity of the breakpoint or a bore is not known

volcanic plume height measured by seismic waves based on a mechanical model journal of geophysical research vol 116 b01306 doi 10 1029 2010jb007620 2011 volcanic plume height measured by seismic waves based on a mechanical model stephanie g prejean 1 and emily e brodsky 2 received 4 april 2010 revised 3 november 2010 accepted 23 november 2010 published 26 january 2011 1 in august 2008 an unmonitored largely unstudied aleutian volcano kasatochi erupted catastrophically here we use seismic data to infer the height of large eruptive columns such as those of kasatochi based on a combination of existing fluid and solid mechanical models in so doing we propose a connection between a common observable short period seismic wave amplitude to the physics of an eruptive column to construct a combined model we estimate the mass ejection rate of material from the vent on the basis of the plume height assuming that the height is controlled by thermal buoyancy for a continuous plume using the estimated mass ejection rate we then derive the equivalent vertical force on the earth through a momentum balance finally we calculate the far field surface waves resulting from the vertical force the model performs well for recent eruptions of kasatochi and augustine volcanoes if v the velocity of material exiting the vent is 120 230 m s 1 the consistency between the seismically inferred and measured plume heights indicates that in these cases the far field 1 s seismic energy radiated by fluctuating flow in the volcanic jet during the eruption is a useful indicator of overall mass ejection rates thus use of the model holds promise for characterizing eruptions and evaluating ash hazards to aircraft in real time on the basis of far field short period seismic data this study emphasizes the need for better measurements of eruptive plume heights and a more detailed understanding of the full spectrum of seismic energy radiated coeruptively citation prejean s g and e e brodsky 2011 volcanic plume height measured by seismic waves based on a mechanical model j geophys res 116 b01306 doi 10 1029 2010jb007620 1 introduction and motivation 2 empirical studies have suggested that the amplitude of high frequency or broadband seismic waves radiated during large volcanic eruptions generally scales with the height of an eruption column mcnutt 1994a however a direct calculation of the expected seismic wave amplitude based on physical models has not yet been successful connecting commonly observable data such as seismic wave amplitudes to a model of the flow in the eruptive jet would provide a new tool to test and improve our understanding of eruptive physics for instance small scale turbulence is thought to play a major role in the entrainment of hot particles and gases and hence the buoyancy of eruptive columns yet there are few measurements of the strength or distribution of small scale features in real eruptive columns andrews and gardner 2009 using seismic data to provide observational constraints on eruption column flow processes is particularly attractive as seismic data are often available even in remote u s geological survey alaska volcano observatory anchorage alaska usa department of earth and planetary sciences university of california santa cruz california usa copyright 2011 by the american geophysical union 0148 0227 11 2010jb007620 settings thus use of the seismic database would greatly increase the number and type of eruptions amenable to study 3 pragmatically a physical model connecting plume height and seismic data would allow the use of seismology as a remote sensing technology to infer volcanic plume height it would be a particularly useful tool for exploring eruption dynamics in remote environments where direct observation is not possible such as the volcanoes of the northern pacific ocean although many volcano observa tories worldwide are gradually replacing short period seismometers with broadband seismometers we still largely rely on short period instruments for forecasting monitoring and analyzing eruptions these realities motivate the development of the model described below 4 in this study we build on previous work to develop a physical model for the expected amplitude of seismic waves from an eruption that generates a plume of a given height as a cautionary note we explore the potential errors in this formulation and describe situations where the model is not applicable such as small eruptions or eruptions where most mass ejected is not entrained in the plume after reviewing previous work on coeruptive seismology and the char acteristics of the 2008 kasatochi and 2006 augustine eruptions we use the connection between plume height and b01306 1 of 13

seismicity and outgassing dynamics of nyiragongo volcano abstract active lava lakes at volcanoes can be regarded as open windows to their magmatic systems the dynamics of such lakes may therefore provide decisive insights into deeper magmatic processes potentially leading to fundamental theoretical implications and volcano monitoring improvements among the rare volcanoes on earth hosting a persistent lava lake nyiragongo in d r congo directly threatens a massive population of roughly 1 million inhabitants here we analyze close range i e summit and distant around 17 km seismic measurements acquired at this african volcano between 2011 and 2018 in order to better understand the seismic signature of the lava lake activity and how it relates to the deeper volcanic processes both summit and distant seismic records contain a similar continuous tremor pattern attributable to the lava lake activity combining this information with time lapse camera images and lava lake level measurements confirms the mechanism of gas pistoning at nyiragongo which is characterized by short duration a few minutes long and meter scale level variations during the period of observation we also characterize the dominant periodicity of this shallow tremor signature of about a few tens of minutes because this marked periodic pattern varies during a significant one month fluctuation of so2 emissions estimated from space we suggest that this particular seismic periodicity corresponds to the convective lake movement driven by the persistent degassing typical of active open vent volcanoes finally new seismic evidence reveals the effect of deep magmatic intrusion and consequent major pressure changes in the plumbing system resulting in sudden and large drops of the lava lake level associated with strong degassing such transient episodes have similar characteristics to total lava lake drainage associated with flank eruptions already observed at this volcano in 1977 and 2002 or at k lauea volcano in 2018

particulate kinematic simulations of debris avalanches interpretation of deposits and landslide seismic signals of mount saint helens 1980 may 18 summary we construct a new class of granular landslide models in which avalanches are simulated with large numbers of independent particles moving under the influence of topographically derived gravitational and centripetal acceleration concurrently the particles suffer deceleration due to basal and dynamic friction the novel aspect of the calculation is that complex particle toparticle interactions fluctuating basal contacts and unresolved topographic roughness within and below the deforming flow are mimicked by random perturbations in along track and cross slope acceleration we apply the method to the 1980 may 18 mount saint helens debris avalanche by constraining the initial geometry and structure of the slide mass from geological data and the initial failure sequence from eyewitness accounts after tuning coefficients of mechanical friction and random accelerations the landslide simulation generates a final deposit whose extent thickness morphological structure and lithological variation closely replicate those observed moreover the model avalanche is consistent kinematically with mapped patterns of bedrock scouring deposit superelevation and net force history implied from seismic records to be successful the slide mass must be divided into upper high friction and lower low friction members this division corresponds to fresh water unsaturated and hydrothermally altered water saturated rock units and points to a mechanical explanation of the kinematics of the debris avalanche success in reproducing many features of the mount saint helens avalanche indicates that debris deposit data may be used to determine the kinematic histories of less well observed landslides

ground coupled acoustic airwaves from mount st helens provide constraints on the may 18 1980 eruption abstract the may 18 1980 mount st helens eruption perturbed the atmosphere and generated atmosphere to ground coupled airwaves which were recorded on at least 35 seismometers operated by the pacific northwest seismograph network pnsn from 102 distinct travel time picks we identify coherent airwaves crossing washington state primarily to the north and east of the volcano the travel time curves provide evidence for both stratospheric refractions at 200 to 300 km from the volcano as well as probable thermospheric refractions at 100 to 350 km the very few first hand reports of audible volcano sounds within about 80 km of the volcano coincide with a general absence of ground coupled acoustic arrivals registered within about 100 km and are attributed to upward refraction of sound waves from the coherent refracted airwave arrivals we identify at least four distinct sources which we infer to originate 10 s 114 s 180 s and 319 s after the onset of an 8 32 11 pdt landslide the first of these sources is attributed to resultant depressurization and explosion of the cryptodome most of the subsequent arrivals also appear to be coincident with a source located at or near the presumed volcanic conduit but at least one of the later arrivals suggests an epicenter displaced about 9 km to the northwest of the vent this dislocation is compatible with the direction of the sector collapse and lateral blast we speculate that this concussion corresponds to a northern explosion event associated with hot cryptodome entering the toutle river valley

linking bed morphology changes of two sediment mixtures to sediment transport predictions in unsteady flows flume experiments were conducted to measure bed morphology adjustments in sand gravel and sand silt sediment mixtures during repeated hydrographs and to link these changes to sediment transport patterns over multiple time scales sediment composition and hydrograph flow magnitude greatly influenced channel morphology which impacted sediment yield hysteresis and transport predictions bed load yields were larger and more variable for the sand silt mixture as gravel in the sand gravel sediment inhibited grain entrainment limited bed form growth and acted to stabilize the bed hysteresis patterns varied due to bed form and surface structure adjustments as well as the stabilizing effect of antecedent low flows using half the data set a dimensionless fractional transport equation was derived based on excess shear stress dimensionless reference shear stresses were estimated in two ways as bulk values from all transport measurements and by applying a separate limb approach in which values were estimated for each limb of each hydrograph for the other half of the data set transport predictions with the separate limb approach were more accurate than those from six existing transport equations and the fractional relationship applied with bulk reference shear stresses thus hydrograph limb dependent dimensionless reference shear stress links changing bed morphology and sediment transport providing a parameter to improve transport predictions during individual flood events and in unsteady flow regimes this approach represents a framework with which to develop site specific transport relationships for varying flow regimes particularly in cases where detailed bed morphology measurements are not feasible and heterogeneous sediment complicates bed structure over time

bioluminescence imaging of wave induced turbulence 1 the ability to measure turbulent processes on small spatial and temporal scales is a long standing problem in physical oceanography here we explore a novel means of measuring fluid shear stress using the cell flashing behavior of bioluminescent dinoflagellates to illustrate this technique we present estimates of the heterogeneous time varying shear stress inside a breaking wave crest these results have implications for a better understanding of upper ocean wave physics air sea gas transfer and the biology of planktonic near surface organisms as well as providing a new quantitative fluid visualization tool

analysis of seismic body waves excited by the mount st helens eruption of may 18 1980 seismic body waves which were excited by the may 18 1980 eruption of mount st helens and recorded by the global digital seismographic network stations are analyzed to determine the nature and the time sequence of the events associated with the eruption the polarity of teleseismic p waves period 20s is identical at six stations which are distributed over a wide azimuthal range this observation together with a very small s to p amplitude ratio at 20 s suggests that the source is a nearly vertical single force a simple model shows that for seismic radiation a volcanic eruption can be represented by a single force applied in the direction opposite to the blast direction the time history of the vertical force suggests two distinct groups of events about 2 min apart each consisting of several subevents with a duration of about 25 s the magnitude of the force is approximately 2 6 10 12 n this vertical force is in contrast with the long period 150 s southward horizontal single force which has been determined by a previous study and interpreted to be due to the massive landslide an m s 5 2 earthquake initiated the eruption sequence the direction of the p wave first motion of this event observed at two nearby stations is consistent with the radiation pattern expected for the landslide and suggests that it represents the onset of the landslide the ground motions observed at station lon 67 km are dominated by rayleigh waves i e lamb pulse and provide tight constraints on the time sequence of the events

wave transformation and swash oscillation on gentle and steep slopes the numerical model developed previously for coastal structures is slightly modified and applied to predict the wave transformation in the surf and swash zones on gentle slopes as well as the wave reflection and swash oscillation on relatively steep beaches the numerical model is one dimensional in the cross shore direction and is based on the finite amplitude shallow water equations including the effect of bottom friction which are solved in the time domain for the incident wave train specified as input at the seaward boundary of the computation located outside the breakpoint the slight modification is related to the effect of the time averaged current on the seaward boundary condition and improves the agreement between the computed and measured mean water levels on gentle slopes the modified numerical model is compared with available small scale test data for monochromatic waves spilling on gentle slopes as well as for monochromatic waves plunging and surging on a relatively steep slope additional comparisons are made with small scale tests conducted using transient monochromatic and grouped waves on a 1 8 smooth slope with and without an idealized nearshore bar at the toe of the 1 8 slope as a whole the numerical model is shown to be capable of predicting both time varying and time averaged hydrodynamic quantities in the surf and swash zones on gentle as well as steep slopes

field observations of the wave bottom boundary layer this paper presents a comprehensive set of velocity and suspended sediment observations in the nearshore wave bottom boundary layer collected during the duck94 field experiment on the outer banks of the north carolina coast cross shore velocity measurements in the wave bottom boundary layer were made using five hot film anemometers nominally spaced from 1 to 5 cm above the bed in 2 m of water depth the time varying location of the seabed was estimated to roughly 1 cm with a stacked set of bed penetrating fiber optic backscatter sensors the instrument array was intermittently located in the surf zone on the crest of a bar the location of the bottom varied several centimeters over a 34 min data run even over 4 min segments of quasi steady statistics occasional large waves caused short erosion and redeposition events complicating the definition of bottom location and causing the root mean square velocity statistics to be nonzero below the mean bed location this leads to obvious difficulties in comparisons with two one dimensional time dependent eddy viscosity wave bottom boundary layer models for example bed shears based on rms amplitude decay were lower than predicted the observations show some evidence for a velocity overshoot region within the wave bottom boundary layer the observations were compared with two linear eddy viscosity models larger estimates of a constant eddy viscosity and smaller than predicted phase leads are indicative of more rapid mixing of momentum than predicted by the models the phase and amplitude frequency response estimated with frequency domain empirical orthogonal functions shows a nonlinear response of the wave bottom boundary layer over the incident band these observations are among the first coherent looks at the wave bottom boundary layer under conditions of significant sediment response they highlight the added complexity of the dynamics in natural environments

spatial variability of the wave bottom boundary layer over movable rippled beds observations of the spatially dependent velocity field over movable bed forms subjected to slightly skewed and asymmetric regular wave forcing were collected the dynamics between the ripple elements is dominated by coherent vortices characterized by the swirling strength and evidenced in the temporal and spectral characterization within the boundary layer spectral energy in the second harmonic 3f0 is amplified at the ripple slopes and is consistent with the location of the expected strongest pressure gradients first moment and second moment velocity statistics were used to address the spatial variability of the intra ripple hydrodynamics estimates of displacement and momentum thicknesses and mom are smaller than suggested by the higher harmonics but consistently highlight areas of adverse and favorable pressure gradients shear stress and roughness estimates were inferred by fitting a logarithmic model to first moment and second moment statistics of the velocity field the maximum shields parameter was observed to peak at the stoss slope of asymmetric ripples during the strongest and shorter half wave period onshore first moment roughness estimates are similar in magnitude to bed load parameterizations provided by li et al 1997 and about a factor of 3 larger than second moment estimates assessment of the vertical transfer of horizontal momentum derived using a reynolds decomposition suggests that stresses inferred from the logarithmic law using first moment velocity statistics appropriately reproduce the mean momentum transfer for the longer and weaker offshore half wave period

sound generation and air entrainment by breaking waves in the surf zone this paper presents the results of acoustic and optical measurements of individual breaking waves in the surf zone two hydrophones horizontally separated and deployed in 2 m of water off la jolla shores beach california were used to measure the source spectrum of breaking surf and characterize propagation through the surf zone over length scales of order 10 m the acoustic data show an acoustically active region within a wave which propagates shoreward the production of sound within the active region is associated with the formation of bubble plumes above 500 hz the sound is consistent with the radiation from individual bubble oscillations pictures were taken of the bubble plumes formed beneath the breaking surf providing estimates of the plume size and bubble size distribution and void fraction within a plume the density of bubbles scales as a 2 5 for a 1 mm where a is bubble radius and total void fractions of 0 3 0 4 were measured theoretical calculations show that ra