the mechanism of surtseyan volcanism during eruption the vent of a surtseyan volcano is occupied by a highly mobile slurry of tephra hyaloclastite and water as magma ascends rapidly through the slurry mixing occurs due to velocity shear acceleration of the fluid fluid contacts and mass incorporation consequent expansion of the admixed water causes the jetting and continuous up rush activity that characterizes surtseyan volcanism there is no evidence of the widely accepted fuel coolant interaction mechanism

water magma interaction some theory and experiments on peperite formation experiments using molten thermite as a magma analog produce peperite when the melt interacts with wet sand these experiments also show explosive behavior developing strombolian and surtseyan like bursts the results demonstrate that the application of fuel coolant interaction fci theory is appropriate for interpretation of peperites the theory described includes discussion of the importance of mass interaction ratios of wet sediment and magma rs which determine thermal equilibrium temperature limits and contact interface dynamics the dynamics of the interface between magma and wet sediments involves heat transfer over a wide range of rates from passive quenching to explosive fragmentation a vapor film layer develops at the interface and acts both as an insulating barrier promoting passive quenching as well as a potential energy reservoir that can cause magma fragmentation mingling of the magma with wet sediments and explosive quenching when the vapor film becomes unstable an important parameter in determining the behavior of the vapor film is the value of rs which controls whether heat can be convectively removed from the layer as more is being added from its contact with magma if rs 1 for fully saturated sediments there is enough water in the sediments to make convective heat flow effective in quenching the magma but below that value there is the potential that the vapor film will be unstable producing highly dynamic phenomena including explosive fragmentation at values of rs 0 1 there is insufficient water to allow the escalation of explosive fragmentation

endogenous growth of dacite dome at unzen volcano japan 1993 1994 a dacite dome at unzen volcano grew mainly exogenously when it was small and the effusion rate was high but endogenously when the dome became large and the effusion rate declined the endogenous dome that has grown since late 1993 shows a shape classified as pelean whereas the earlier stage had a low lava dome shape the carapace of the endogenous dome moved like the crust of a basaltic lava pillow although the dome is several hundred times larger than such pillows the surface carapace was carried from the inside of the dome where it had been produced and it thickened as it cooled the crater floor was strongly deformed by the advancing endogenous dome the movement and crater floor deformation can be compared to that of a tractor tread moving on unconsolidated ground

instruments for particle size and settling velocity observations in sediment transport in this paper we describe two sensors for measurement of particle size distribution and settling velocity distribution these measurements are critical to the correct estimation of the true sediment concentration in the field as well as to evaluating models for transport rates of sediments a multi angle measurement of laser scattering is made and inverted to obtain the particle size distribution since small angle scattering is relatively insensitive to particle composition the size distribution measurements are robust and do not require particle refractive index it is shown that with a knowledge of the size distribution true particulate volume concentration can be obtained unaffected in calibration by changes in particle size distribution the data from bottom boundary layer experiments using the instrument show the presence of temporal variability in size distribution associated with the strength of forcing of the boundary layer the importance of these observations lies in the implication that historical data acquired with single parameter optical or other sensors needs to be revisited in the second instrument analyzing the observation of size distributions during settling in a settling column produces settling velocity estimates in this case the history of concentration of each size class is examined to determine the settling velocity without invoking any assumptions of settling regime settling velocity data from a field experiment off the new jersey coast fit the model wf na 0 45 10 23 a 1 2 n

migration direction of sand wave structures in pyroclastic surge deposits implications for depositional processes sand wave structures of both progressive downstream migrating and regressive upstream migrating types occur within the same pyroclastic surge deposit at both roccamonfina volcano southern italy and sugarloaf mountain arizona united states both wet and dry surge deposits are described that contain examples of regressive and progressive sandwave structures at sugarloaf mountain progressive and regressive sand waves occur within metres of each other within the same bedset indicating that penecontemporaneous deposition of the two different sand wave structures occurred in close proximity on the basis of this evidence it is suggested that the migration direction of sand waves in these pyroclastic surge deposits is controlled by the flow regime of the surge cloud rather than the temperature and or moisture content

evolving infrasound detections from bogoslof volcano alaska insights from atmospheric propagation modeling bogoslof volcano a back arc volcano in alaska s aleutian arc began an eruptive sequence in mid december 2016 that ended in late august 2017 with 70 individual eruptive episodes because there were no local seismic or infrasound stations on the island the alaska volcano observatory avo relied on distant geophysical networks and remote sensing techniques to assess activity during the eruption avo maintains six infrasound arrays to monitor activity along the aleutian arc adak the island of four mountains okmok akutan sand point and dillingham eruption detection at infrasound arrays is subject to local as well as mesoscale meteorological conditions that vary greatly over both short and long timescales infrasound detections from the array nearest to bogoslof okmok with a latency of about 3 min played a crucial role in monitoring activity during the eruption despite the relative proximity of the okmok array to bogoslof 60 km infrasound detections were not uniformly observed with only about two thirds of the events successfully detected the farthest array at dillingham 816 km detected approximately half of the explosive events with all other arrays detecting less than half of the events we compare observations with infrasound propagation model predictions using both normal mode and parabolic equation forward models to interpret the variation in detections of the 70 explosive events across the avo infrasound network the forward models utilize the newly created publicly available avo g2s atmospheric reconstruction using numerical weather predictions data for the lower atmosphere coupled with upper atmosphere empirical models of wind speeds and temperature we find that long range detections 100 km of bogoslof events are largely aligned with seasonal variability in favorable propagation conditions while regional detections 100 km are less consistent with propagation modeling understanding the output of numerical models in comparison to past observations will facilitate their use in future operational settings for avo and other observatories

mechanisms for ballistic block ejection during the 2016 2017 shallow submarine eruption of bogoslof volcano alaska ejection of ballistic blocks was a characteristic feature of the 2016 2017 bogoslof eruption high resolution satellite images acquired throughout the duration of the 9 month long eruptive period permitted the recognition and mapping of ballistic blocks on the surface of bogoslof island many of the satellite images recorded the accumulation of ballistic material over several individual eruptive events but a few images recorded the effects of a single event the nonuniform spatial distribution of blocks suggests that some of the eruption columns were inclined ballistic trajectories were estimated using the eject model and indicate that accumulation of blocks on bogoslof island required launch angles of 45 80 and initial velocities of 50 100 ms 1 to reproduce observed travel distances the amount of ballistic fallout observed in satellite data indicates that there must have been a shallow submarine source of rock within the conduit upper edifice system dense accidental cryptodome trachyandesite and juvenile basalt to trachybasalt scoria make up the bulk of the surface ejecta abundant accidental fragments and inclined eruption columns point to periodic vent wall collapse and jetting around edges of temporarily blocked vents as the likely cause of ballistic ejection

in situ study of the spatiotemporal variability of sediment erodibility in a microtidal estuary abstract seabed erosion is a vital process for sediment transport in estuaries and coasts in this study we investigated the seabed erosion process and its spatiotemporal variability in the pearl river estuary china via in situ observations and laboratory experiments it is found that the seabed was more erodible in the channel than at the shoal in most cases due to the difference in sediment size in a neap spring neap tidal cycle a laminated seabed with different sediment ages was inferred to form due to deposition on flood tides and erosion on ebb tides the seabed was more erodible during spring tides than neap tides because of the difference in sediment availability at the unconsolidated fresh layer furthermore the erosion curve showed evident flood ebb asymmetry which was found to be related to the variations of sediment availability and bottom stress besides erosion experiments with different sediment consolidations revealed that sediment erodibility decreased with the growth of consolidation this study promotes our understanding on the spatiotemporal variability of sediment erodibility and has significant implications for simulation and prediction of estuarine sediment transport and morphological evolution

geology and eruptive history of bogoslof volcano bogoslof volcano is a shallow submarine subaerial volcano in the southern bering sea about 100 km west of the community of dutch harbor alaska the subaerial parts of the volcano consist of two small islands bogoslof island and fire island that together have a total area of about 1 6 km2 bogoslof was first depicted on a russian map in 1772 and since then has been observed and visited occasionally the volcano has had at least nine periods of eruptive activity since 1796 and all of its historical eruptions have been similar in style historical bogoslof eruptions involved the effusion of basalt trachybasalt basaltic trachyandesite and trachyandesite lava domes with above sea level relief of 100 200 m many of the eruptions are accompanied by the formation of tuff rings and ejection of ballistic particles historical observations suggest that eruption clouds are relatively ash poor minor ash fallout has typically occurred within about 100 km of the volcano many of the historical eruptions began at vents that were below sea level and thus seawater has played an important role in the style of eruptive activity exhibited by the volcano at times eruptive activity has been characterized by surtseyan style eruptions and magma interaction with wet vent fill deposits at other times the eruptive style has been more magmatically driven and has resulted in the formation of pyroclastic flows and small ash clouds preliminary studies of the deposits produced during the 2016 2017 eruption indicate vertical sequences of coarse grained horizontally bedded pyroclastic flow and fall deposits with numerous blocks bombs and lapilli of dense juvenile and accidental lithic material these deposits were emplaced by near vent pyroclastic flows surges and explosions some of which originated from shallow highly crystalline cryptodomes

depositional mechanics and sequences of base surges songaksan tuff ring cheju island korea the songaksan mount in the southwestern part of cheju island korea is a taalian tuff ring produced by phreatomagmatic explosions at an aquifer a detailed analysis of proximal to distal facies changes reveals that the tuff ring sequence can be represented by 21 sedimentary facies one lateral facies sequence lfs and three vertical facies sequences vfs the vfs 1 and 2 are representative of facies relationships in horizontal near vent deposits the vfs 1 comprises scour fill bedded tuff inversely graded tuff massive tuff and laminated tuff from base to top the vfs 2 is a variant of the vfs 1 replaced by an inversely graded lapilli tuff unit at the base the sequences suggest traction carpet suspension and minor traction sedimentation from a high concentration near vent base surge the lfs 1 and the vfs 3 are distilled from outward dipping flank deposits both sequences begin with disorganized lapilli tuff followed successively by stratified lapilli tuff dune bedded lapilli tuff very thinbedded tuff and accretionary lapilli they are suggestive of waning base surge which decreases in particle concentration suspended load fall out rate and flow regimes with an increase in traction and sorting these facies sequences suggest that a base surge experiences flow transformation with its flow characters changing with time and space a near vent base surge is turbulent uniformly mixed and highly concentrated and produces scour fill bedded tuff as capacity decreases the surge transforms into a dense and laminar underflow and a dilute and turbulent upper part gravity transformation depositing inversely graded massive and normally graded lapilli tuff ensuing loss of sediment load and mixing of ambient air result in flow dilution surface transformation stratified and dune bedded units are produced by tractional processes of turbulent and low concentration surge further dilution causes deceleration and cooling and results in precipitation of moistened ash and accretionary lapilli from suspension

overview chronology and impacts of the 2016 2017 eruption of bogoslof volcano alaska the 2016 2017 eruption of bogoslof volcano a back arc shallow submarine volcano in alaska s aleutian arc began in december 2016 and included 70 explosive events and at least two episodes of subaerial dome building because the volcano had no local monitoring stations during the eruption a combination of distant seismic stations regional infrasound sensors lightning detection a variety of satellite data and observer reports and a field visit in 2018 were used to recreate the events that occurred during the nine month eruption following precursory seismicity that started in september 2016 the eruption began in december 2016 with a series of explosive events that persisted through mid march 2017 after a 6 week hiatus activity resumed on may 17 and lasted through the end of august 2017 and consisted of additional explosions and two short lived subaerial lava domes that formed in june and august for most of the eruption bogoslof s vent was submerged in shallow seawater though during several of the longer events a subaerial edifice grew and the vent migrated above sea level resulting in more ash rich volcanic clouds eruptive products geophysical signals and eruptive style are all broadly consistent with vulcanian activity where slow magma ascent led to repetitive dome or plug formation overpressurization in the upper conduit and sudden release during short lived explosions infiltration of seawater may have prohibited large domes from forming especially in the first half of the eruption when explosions were closely spaced in time the largest four explosions in the sequence occurred after inter event times of 10 days or more three events produced ashfall on nearby communities and mariners east and south of bogoslof and the eruption resulted in dozens of flight cancelations and flight diversions around the volcano and its ash clouds

factors controlling the field settling velocity of cohesive sediment in estuaries abstract it has long been recognized that the suspended sediment concentration ssc is one of the major determinants for the flocculation of cohesive particles into sediment flocs in estuaries it is furthermore well known that the turbulent shear of the water significantly influences the flocculation process and the equilibrium settling velocity of flocculated sediment in a turbulent flow a vast number of authors have reported algorithms relating the median settling velocity w 50 to suspended sediment concentration however only a few studies have dealt with the impact of the turbulent shear in this paper expressed as the root mean square rms velocity gradient g in the water on the w 50 in situ there is a strong need to establish algorithms based on in situ measurements describing the dual impact of both ssc and g on the flocculation process and hence w 50 the present paper addresses this topic field settling velocities of suspended cohesive sediment have been measured in micro meso and macro tidal estuaries regression analyses between the w 50 ssc and g are presented it is shown that by including both g and ssc in the regression analyses a significant increase in the correlation of the description of w 50 and the controlling parameters from each area can be obtained a generic algorithm describing the data from all the investigated areas is suggested it works well within specific tidal areas but fails to give a generic description of the field settling velocity

evidence for the relative depths and energies of phreatomagmatic explosions recorded in tephra rings experimental work and field observations have inspired the revision of conceptual models of how maar diatreme eruptions progress and the effects of variable energy depth and lateral position of explosions during an eruption sequence this study reevaluates natural tephra ring deposits to test these new models against the depositional record two incised tephra rings in the hopi buttes volcanic field are revisited and published tephra ring stratigraphic studies are compared to identify trends within tephra rings five major facies were recognized and interpreted as the result of different transportation and depositional processes and found to be common at these volcanoes tephra rings often contain evidence of repeated discrete phreatomagmatic explosions in the form of couplets of two facies 1 massive lapilli tuffs and tuff breccias and 2 overlying thinly stratified to cross stratified tuffs and lapilli tuffs the occurrence of repeating layers of either facies and the occurrence of couplets are used to interpret major trends in the relative depth of phreatomagmatic explosions that contribute to these eruptions for deposits related to near optimal scaled depth explosions estimates of the mass of ejected material and initial ejection velocity can be used to approximate the explosion energy the 19 stratigraphic sections compared indicate that near optimal scaled depth explosions are common and that the explosion locations can migrate both upward and downward during an eruption suggesting a complex interplay between water availability and magma flux reverse to normal coarse tail graded tuff breccias inferred to be the product of closely timed phreatomagmatic explosions and deposits of magmatic gas driven explosions were observed interspersed with discrete explosion deposits this study not only provides a framework for more detailed interpretations of eruption sequences from tephra rings but also highlights the gap in our understanding of syn eruptive hydrology and variations in magma flux that enables phreatomagmatic explosions

hydrovolcanic explosions the systematics of water pyroclast equilibration the initial contact of external water with erupting magma and the mass ratio of water to magma govern the development of hydrovolcanic phenomena the phase relations of water within the runout system and the separation of vapor or liquid from the pyroclasts explain gradational transitions between some pyroclastic flows base surges mud hurricanes mudflows and sheetfloods

the spreading of lower circumpolar deep water in the atlantic ocean abstract a stommel arons model of the circulation of lower circumpolar deep water lcdw in the atlantic ocean is presented and compared with observations the lcdw is defined as a layer of uniform thickness over a flat bottom the lateral boundaries are given by the 4000 m isobath the drake passage and the throughflow between africa and antarctica are closed the model is forced by a concentrated source in the weddell sea representing the net atlantic gain of lcdw due to production in the weddell sea and inflow through drake passage this net gain is termed the lcdw formation rate it is compensated by upwelling over the rest of the atlantic best agreement with observed net transport rates in the western atlantic was found using a lcdw formation rate of about 8 sv sv 106 m3 s 1 in reality however a higher rate is required in order to establish the outflow to the indian ocean the interior transport the transport through topographic gaps and the transport rates of western boundary currants on t

model based interpretation of sediment concentration and vertical flux measurements in a shallow estuarine environment a one dimensional numerical model describing tidally varying vertical mixing and settling was used to interpret sediment concentrations and vertical fluxes observed in the shoals of south san francisco bay by two acoustic doppler velocimeters advs at elevations of 0 36 m and 0 72 m above bed measured sediment concentrations changed by up to 100 g m 3 over the semidiurnal tidal cycle these dynamics were dominated by local resuspension and settling multiple particle class models suggested the existence of a class with fast settling velocities ws of 9 0 10 4 m s 1 in spring and 5 8 10 4 m s 1 in fall and a slowly settling particle fraction ws of 1 10 7 m s 1 in spring and 1 4 10 5 m s 1 in fall modeled concentrations of slowly settling particles at 0 36 m were as high as 20 g m 3 during fall and varied with the spring neap cycle while fine sediment concentrations in spring were constant around 5 g m 3 analysis of in situ water column floc size distributions suggested that floc properties in the lower part of the water column were most likely governed by particle size distribution on the bed and not by coagulation validating our multiple particle size approach a comparison of different sediment bed models with respect to model performance sensitivity and identifiability suggested that the use of a sediment erosion model linear in bottom shear stress b e m b c was the most appropriate choice to describe the field observations when the critical shear stress c and the proportionality factor m were kept constant

depositional processes of the suwolbong tuff ring cheju island korea the suwolbong pyroclastic sequence in the western part of cheju island korea comprises partly preserved rim beds of a quaternary basaltic tuff ring whose vent lies about 1 km seaward of the present shoreline the sequence consists of breccia lapillistone lapilli tuff and tuff eighteen sedimentary facies are established and organized into six lateral facies sequences lfs and seven vertical facies sequences vfs the lfs 1 4 and 5 begin with massive lapilli tuff which transforms downcurrent into either planar bedded lfs 1 undulatory bedded lfs 4 or climbing dune bedded lfs 5 lapilli tuff units they are representative of relatively dry base surge whose particle concentration decreases downcurrent with a progressive increase in both tractional processes and sorting the lfs 2 begins with disorganized and massive lapilli tuff and transforms into crudely stratified units downcurrent it results from relatively wet base surge in which sorting is poor due to the cohesion of damp ash the lfs 3 comprises well sorted lapilli tuff and stratified tuff further downcurrent suggestive of deposition from combined fall and surge of relatively dry hydroclastic eruption all seven vertical facies sequences generally comprise two facies units of coarse grained fines depleted lapilli tuff and an overlying fine grained tuff these sequences are suggestive of deposition from base surge that consists of a turbulent head and a low concentration tail depositional processes in the suwolbong tuff ring were dominated by a relatively dry base surge the base surge comprises turbulent and high concentration suspension near the vent whose deposits are generally unstratified due to the lack of tractional transport as the base surge becomes diluted downcurrent through fallout of clasts and mixing of ambient air it develops large scale turbulent eddies and is segregated into coarse grained bedload and overlying fine grained suspension forming thinly stratified units further downcurrent the base surge may be either cooled and deflated or pushed up into the air depending on its temperature the suwolbong tuff ring comprises an overall wet to dry cycle with several dry to wet cycles in it suggestive of overall decrease in abundance of external water and fluctuation in the rate of magma rise

did ice charging generate volcanic lightning during the 2016 2017 eruption of bogoslof volcano alaska the 2016 2017 shallow submarine eruption of bogoslof volcano in alaska injected plumes of ash and seawater to maximum heights of 12 km more than 4550 volcanic lightning strokes were detected by the world wide lightning location network wwlln and vaisala s global lightning dataset gld360 over 9 months lightning assisted monitoring efforts by confirming ash producing explosions in near real time but only 32 out of the 70 explosive events produced detectable lightning what led to electrical activity within some of the volcanic plumes but not others and why did the lightning intensity wax and wane over the lifetime of individual explosions we address these questions using multiparametric observations from ground based lightning sensors satellite imagery photographs acoustic signals and 1d plume modeling detailed time series of monitoring data show that the plumes did not produce detectable lightning until they rose higher than the atmospheric freezing level approximated by 20 c temperatures for example on 28 may 2017 event 40 the delayed onset of lightning coincides with modeled ice formation in upper levels of the plume model results suggest that microphysical conditions inside the plume rivaled those of severe thunderstorms with liquid water contents 5 g m 3 and vigorous updrafts 40 m s 1 in the mixed phase region where liquid water and ice coexist based on these findings we infer that thunderstorm style collisional ice charging catalyzed the volcanic lightning however charge mechanisms likely operated on a continuum with silicate collisions dominating electrification in the near vent region and ice charging taking over in the upper level plumes a key implication of this study is that lightning during the bogoslof eruption provided a reliable indicator of sustained ash rich plumes and associated hazards above the atmospheric freezing level

seismic character and progression of explosive activity during the 2016 2017 eruption of bogoslof volcano alaska bogoslof volcano in the central aleutian arc experienced a major eruption between december 2016 and august 2017 that was characterized by explosive activity volcanic explosivity index 2 to 3 and the extrusion of lava domes the alaska volcano observatory tracked the activity in real time using seismicity observed on distant stations as well as infrasound lightning satellite data and occasional visual observations in this study we measure the duration of seismic signals associated with individual explosive events to track their progression during the two explosive phases of the eruption seismic recordings of bogoslof explosions show complex waveforms that suggest both individual explosive events and sequences of several explosions separated by lower amplitude tremor the lack of local seismic monitoring stations at distances of 1 km to 15 km distance unfortunately limits our ability to closely observe seismicity and to interpret changing conditions at the vent such as position the presence of a lava dome or plug and the role of seawater associated with the eruption we use the rate of explosive activity seismic waveform character and repose time between explosions to infer the conditions within the conduit

petrology of the 2016 2017 eruption of bogoslof island alaska the 2016 2017 eruption of bogoslof primarily produced crystal rich amphibole basalts the dominant juvenile tephra were highly microlitic with diktytaxitic vesicles and amphiboles had large reaction rims both observations support a magma history of slow ascent and or shallow stalling prior to eruption plagioclase amphibole clinopyroxene mineralogy are also suggestive of shallow magma crystallization lavas were emplaced as shallow submarine lava domes and cryptodomes that produced 70 relatively short lived and water rich explosions over the course of the 9 month long eruption the explosions ejected older trachyandesite lavas that were likely uplifted by cryptodome emplacement that began in december 2016 and continued for many months trachyte pumice similar in composition to a 1796 lava dome was entrained in basalts by the end of the eruption the pumice appears to be a largely crystalline magma that was rejuvenated entrained in the basalt and heated to 1000 c the composition of trachytes require differentiation through stronger amphibole control than the apparent shallow crustal evolution implied for the basalt this suggests that they are magmas derived from a mid crustal zone of amphibole crystallization nearby arc front volcanoes that notably lack amphibole have strikingly similar compositional trends trace element signatures of the bogoslof basalts however suggest derivation from a mantle source with residual garnet and lower degree melting than basalts from nearby arc front volcanoes the diversity of magmas erupted at bogoslof thus provides an opportunity not only to probe rare backarc compositions from the aleutian arc but also to examine the apparent role of amphibole in generating evolved compositions more broadly in arc environments

evolution of the submarine subaerial edifice of bogoslof volcano alaska during its 2016 2017 eruption based on analysis of satellite imagery the 2016 2017 eruption of bogoslof volcano involved at least 70 detected eruptive events between mid december 2016 and august 30 2017 acquisition of high resolution satellite imagery throughout the duration of the eruptive period allowed us to document and map the various morphologic changes that occurred on the subaerial part of bogoslof island the emplacement of pyroclastic flow and surge deposits caused the island to increase in area by about 1 5 km2 the dominant volcanic landforms of the eruption were a series of tuff rings emplaced around various submarine vents many of the tuff rings were mantled with surface dunes and impressive amounts of ballistic ejecta likely derived from erupting magma bodies or previously emplaced submarine lava domes debris flow deposits and surface channels extending over tuff ring surfaces apparent in multiple satellite images are evidence for explosive ejection of seawater in most cases erupting vents were initially submarine or began at subaerial lava domes and were largely flooded by seawater suggesting that water magma ratios were likely high under such conditions where water is abundant eruptive products typically reflect a high degree of water involvement and are dominated by the formation of wet tephra jets and flows and associated deposits typically consist of fine ash and lapilli contain accretionary lapilli and ash aggregates and usually form tuff cones and mounds we observed none of these features in our analysis of satellite data or during our examination of eruptive deposits on bogoslof island in 2018 on the contrary the dominant landform associated with the bogoslof eruption was tuff rings the development of tuff rings and surface dunes are commonly associated with the formation of pyroclastic base surges that are by comparison emplaced relatively dry dry base surge deposits can be generated from phreatomagmatic explosions involving superheated steam it is possible that shallow submarine magma wet sediment interactions were a characteristic and possibly a dominant eruptive process of the 2016 2017 bogoslof eruption

interactions between waves sediment and turbulence on a shallow estuarine mudflat measurements were collected on a shallow estuarine mudflat in northern san francisco bay to examine the physical processes controlling waves turbulence sediment resuspension and their interactions tides alone forced weak to moderate currents of 10 30 cm s 1 in depths of 0 3 m and maintained a background suspension of 30 50 mg l 1 of fine sediment in the presence of wind waves bottom orbital velocities spanned 20 30 cm s 1 suspended sediment concentrations ssc at 15 and 30 cm above the bed cmab increased by 1 2 orders of magnitude and vertical gradients in ssc were strong enough to produce turbulence limiting stratification with gradient richardson numbers exceeding 0 25 simultaneously turbulent stresses decomposed from wave motions increased by an order of magnitude the apparent contradiction of energetic turbulence in the presence of strong stratification was reconciled by considering the turbulent kinetic energy tke budget in general dissipation and buoyancy flux were balanced by local shear production and each of these terms increased during wave events the classic wave current boundary layer model represented the observations qualitatively but not quantitatively since the velocity profile could not be approximated as logarithmic rather the mean shear was elevated by the stokes drift return flow and wind generated surface stress which diffused sediment upward and limited stratification our findings highlight a pathway for waves to supply energy to both the production and destruction of turbulence and demonstrate that in such shallow depths tke and ssc can be elevated over more of the water column than predicted by traditional models

a stochastic formulation for erosion of cohesive sediments the linear formulation for erosion e m b c often applied in engineering applications has two properties which do not always comply with field and laboratory observations they are as follows 1 the erosion rate is zero below the critical bed shear stress c and increases linearly with bed shear stress b when exceeding the critical bed shear stress incipient motion b simeq c is poorly represented 2 the erosion rate is constant in time for constant values of m and c whereas observations often suggest time dependency in this paper we analyze the process of incipient motion and time dependency by using a stochastic forcing bed shear stress and a stochastic bed strength critical bed shear stress it is well known that the bed shear stress is not constant but varies due to turbulence this stochastic nature of the turbulent motion is accounted for by a probability density distribution for the bed shear stress which is based on the formulation of hofland and battjes 2006 this distribution is implemented in the linear erosion formulation an analytical solution for the erosion rate is obtained which only depends on the mean bed shear stress a parametrization is made for efficient application in numerical models the sediment in the bed is considered to be nonuniform therefore it is subdivided into several classes distinguished by the critical bed shear stress and not necessarily by the grain size the variability of the critical bed shear stress is treated in a discritized way sediment balance equations are solved for each class considering different classes the total erosion rate becomes time dependent as the erosion depends on the availability of sediment the model is applied to two annular flume data sets jacobs 2009 and amos et al 1992a the results show that with a proper choice of the required parameters the time dependence of the erosion rate and the concentration can be reproduced we conclude that the occurrence of incipient motion can be explained from a stochastic forcing time varying erosion rates can be explained from a stochastic bed strength distribution or from a vertical gradient in bed strength the latter is however not likely and not measurable in the top layers of dense consolidated cohesive sediment beds

giant mounded drifts in the argentine continental margin origins and global implications for the history of thermohaline circulation abstract partially buried giant drifts are located in the southern most sector of the argentine continental margin generating a bathymetric jump at the base of the slope they are characterised as giant asymmetrical elongated mounded contourite drifts and are described in detail here for the first time this description is mainly based on the bathymetric and multichannel seismic reflection profiles data their origin and evolution in the argentine basin are decoded and their implications in an area crucial for geologic and palaeoceanographic reconstruction between the atlantic and antarctica are discussed the buried giant drifts are divided into two zones by a large seamount the major giant drift 50 km wide 300 km long and having a sedimentary thickness of nearly 1 km is located to the south of this seamount and oriented to the north where its summit outcrops at present seafloor here its asymmetric external shape is characterised by a steep western side and a gently dipping smooth eastern side with internal reflections prograding eastward based on its position morphology and internal characteristics it has been deduced that this giant drift was generated in the argentine basin by the southward branch of a confined large loop of the antarctic bottom deep water from the eocene oligocene boundary coevally with the drake passage opening until the middle miocene however after a major palaeoceanographic change in the mid to late miocene a new oceanographic scenario was established that fossilised these giant drifts these changes produced a new depositional style in the margin resulting in initiation of the present contourite depositional system and morphologic features over the slope extension of north atlantic deep water circulation into the southern hemisphere and deepening of antarctic bottom water circulation in the argentine basin are herein postulated as the factors that controlled said changes these giant drifts show strong seismic evidence of hydrates and free gas that are ripe for energy resources exploration thus demonstrating the economic potential of contourite deposits in deep marine environments

comparison of short term seismic precursors and explosion parameters during the 2016 2017 bogoslof eruption in december 2016 the unmonitored bogoslof volcano unexpectedly began erupting producing at least 70 explosions over the next 8 5 months roughly half of the explosions were preceded by observable short term precursory activity defined here as seismic activity ending within 30 min of the explosion onset or an earthquake swarm ending within a few hours before the explosion onset five different types of precursors were noted during the bogoslof eruption non swarm earthquakes earthquake swarms rapid rate events tremor and chromatic tremor most of the precursors that were detectable by the nearby seismic networks 45 km away occurred during the first 3 months of the eruption with nearly all precursory earthquake swarms occurring during this period a hydrophone deployed 7 km northeast of the summit for the last 3 months of the eruption detected weaker activity that was not recorded by the more distant seismic networks we describe the observed precursors and discuss their inter relations overall the precursors seem indicative of processes occurring throughout the volcanic system and suggest possible changes in the system during the eruption we then compare the short term precursors with explosion parameters such as plume height duration and occurrence of lightning to look for relations that may provide more insight into the eruption dynamics and subsurface processes and help to further improve forecasting we find no obvious relations between any of the precursor or explosion parameters suggesting that their use in forecasting eruption characteristics at bogoslof is limited

nutrient mineralization rates and ratios in the eastern south atlantic the physical and biogeochemical components of nutrients and inorganic carbon distributions along woce line a14 are objectively separated by means of a constrained least squares regression analysis of the mixing of eastern south atlantic water masses contrary to previous approaches essentially devoted to the intricate south atlantic circulation this work is focused on the effects of circulation on nutrients and carbon biogeochemistry with special emphasis on the stoichiometry and the rate of mineralization processes combination of nutrient and apparent cfc age anomalies derived from the mixing analysis indicate faster mineralization rates in the equatorial 12 10 2 mol p kg 1 yr 1 and subequatorial 5 3 10 2 mol p kg 1 yr 1 than in the subtropical 4 3 10 2 mol p kg 1 yr 1 regime at the south atlantic central water sacw depth range lower rates are obtained in the antarctic intermediate water aaiw domain 3 0 10 2 mol p kg 1 yr 1 significant variation with depth of o2 c n p anomalies indicates preferential mineralization of proteins in thermocline waters as compared with the reference redfield composition

evaluation of two conflicting paradigms for cohesive sediment deposition abstract laboratory experiments using steady flows and simulated tidal flows were conducted to evaluate two conflicting paradigms for cohesive sediment transport mutually exclusive vs simultaneous erosion and deposition due to the secondary flow and skewed distribution of bed shear stress b the deposition space is mostly confined to the inner wall of an annular flume the area of deposition or the length of deposition because of the axially symmetrical flow provides an indicator to determine when deposition at the sediment water interface starts the direct observation of deposition stemming from the inner corner suggests that a critical shear stress for deposition cd 0 03 0 06 pa does exist changes in deposit length and depth averaged suspended sediment concentration ssc under simulated tidal cycles demonstrate that deposition can happen only in tidal decelerating phases when local b is less than cd the exclusive paradigm incorporated with the correct erosion threshold ce profile and erosion behavior could explain changes in laboratory and field observed depth averaged ssc under all tidal regimes

co eruptive tremor from bogoslof volcano seismic wavefield composition at regional distances we analyze seismic tremor recorded during eruptive activity over the course of the 2016 2017 eruption of bogoslof volcano alaska only regional recordings of the tremor wavefield exist for bogoslof making it a challenge to place the recordings in context with other eruptions that are normally captured by local seismic data we apply a technique of time frequency polarization analysis to three component seismic data to reveal the wavefield composition of bogoslof eruption tremor we find that at regional distances the tremor is dominated by p waves in the band from 1 5 to 10 hz using this information along with an enriched bogoslof earthquake catalog we obtain estimates of average reduced displacement dr for eruption tremor during 25 of the 70 bogoslof events dr reaches as high as approximately 40 cm2 for two of the major events similar to other vei 3 eruptions in alaska overall average reduced displacement displays a weak correlation to plume height during the first half of the 9 month long eruption sequence with a few notable exceptions the two events with the highest dr values also generated measurable eruption tremor at very long periods vlp between 0 05 and 0 15 hz

satellite observations of a surtseyan eruption hunga ha apai tonga abstract on march 17 2009 a surtseyan eruption occurred around hunga ha apai island tonga a series of observations from the high spatial resolution advanced spaceborne thermal emission and reflection radiometer aster and the high temporal resolution moderate resolution imaging spectroradiometer modis was used to estimate the magnitude location start time and duration of the eruption and measure the evolving characteristics of the new hunga ha apai island the eruption start time was estimated to be between 01 50 and 11 10 local time on march 17 2009 i e between 12 50 and 22 10 utc march 16 the initial explosive phase lasted 3 5 days and consisted of multiple steam and tephra explosions from two distinct vent sources one on the northwest side and another about 100 m off the south shore of the pre existing island the eruption plume reached 4 0 to 7 6 km altitude above sea level and tephra added new land around each of the vents initially tripling the area of the pre existing island the next phase of steaming from newly formed crater lakes around the vents lasted a few days three warm crater lakes formed initially but disappeared with time as the shoreline eroded after 2 months vegetation that was initially buried by tephra was recovering after 10 months the size of the island had eroded down to twice that of the pre existing island and the one remaining crater lake had a temperature of 68 17 c the volume of erupted material was estimated to be 0 0176 km3 and the volcanic explosivity index vei was estimated to be vei 2

infrasound generated by the 2016 2017 shallow submarine eruption of bogoslof volcano alaska the 2016 2017 shallow submarine eruption of bogoslof volcano produced numerous infrasound signals over 9 months that were recorded on six alaska volcano observatory avo arrays at ranges of 59 to over 800 km from the volcano the lack of geophysical monitoring near bogoslof and the repeated production of volcanic clouds to flight levels made monitoring by remote infrasound critical during the eruption for the first time avo relied extensively on automated infrasound detections from regional arrays to dispatch timely notifications of the ongoing activity most of the 70 eruptive events were detected on at least one array but no array detected all of the events mainly because atmospheric conditions were highly variable during the eruption acoustic propagation modeling helps explain some of the variation in array detections but also highlights limitations in regional propagation models to our knowledge this is the first example of well recorded infrasound from an explosive eruption occurring in shallow seawater providing extensive insights into eruption dynamics in this unique environment the dominance of low frequency infrasound 0 1 1 hz is attributed to eruptions occurring beneath tens of meters of seawater higher frequency infrasound signals were mostly limited to eruptions where the vent was isolated from major interaction with seawater or in several cases where a lava dome grew above sea level

seismo acoustic evidence for vent drying during shallow submarine eruptions at bogoslof volcano alaska characterizing the state of the volcanic vent is key for interpreting observational datasets and accurately assessing volcanic hazards this is particularly true for remote complex eruptions such as the 2016 2017 bogoslof volcano alaska eruption sequence bogoslof s eruptions in this period were either shallow submarine or subaerial or some combination of both our results demonstrate how low frequency sound waves infrasound integrated with seismic and satellite data can provide unique insight into shallow vent processes otherwise not available we use simple metrics such as the infrasound frequency index fi event duration and acoustic seismic amplitude ratio to look at changes in the elastic energy radiation and infer changes in seawater access to the vent satellite imagery before and after selected eruptions is used to ground truth inferences on vent conditions high fi and gradual increases in infrasound frequency content at bogoslof correspond with transitions from submarine to subaerial vent conditions and a diminished or absent role of water likely resulting in a drying out of the vent region event durations generally correlate with high fi and the range of fi values for each event suggesting long duration events were more effective at drying out the vent region a trend from low to high acoustic seismic amplitude ratios for some long duration events also suggests an increase in acoustic efficiency as the vent dried out we demonstrate that infrasound can serve as a robust indicator of seawater involvement for bogoslof and other shallow submarine eruptions that may not be inferable from other datasets particularly in near real time

satellite observations of the 2016 2017 eruption of bogoslof volcano aviation and ash fallout hazard implications from a water rich eruption satellite data goes viirs modis avhrr were used in near real time during the 2016 2017 eruption of bogoslof volcano alaska to detect explosive eruptive activity and to characterize the resulting volcanic clouds this study examines satellite data to estimate volcanic cloud heights and mass eruption rates for 47 of the 70 explosive events eighteen of the volcanic clouds reached an altitude in excess of 8 5 km asl where they posed a potential hazard to aviation we estimate eruption rates were in the range of 104 107 kg s eruption durations were available for 28 events and the total mass of these events was 5 7 1010 kg most of the explosions occurred from submarine vents producing volcanic clouds with water rich characteristics in satellite data we infer that these water rich phreatomagmatic events contained ice coated ash particles which changed their visible and multispectral characteristics only two of the explosions produced clouds with satellite characteristics that would be considered ash rich we conclude that these events were relatively dry eruptions with limited access to ocean water although some of the explosive events transitioned from submarine to subaerial vents we observed no change in the character of the volcanic clouds during these transitions we speculate that enhanced removal of fine grained volcanic ash likely occurred due to aggregation with implications for modeling ash transport and fallout we conclude that the majority of bogoslof s water rich volcanic clouds did contain volcanic ash despite the lack of conventional ash signature in satellite data this has implications for satellite monitoring of future water rich shallow submarine eruptions

fractionally modified flow in a deep ocean channel application to the vema channel the modification of the exchange flow in a deep southern hemisphere passage resembling the vema channel by frictionally induced secondary circulation is investigated numerically the hydrostatic primitive equation model is a two dimensional version of the sigma coordinate princeton ocean model the time dependent response of a stratified along channel flow forced by barotropic or baroclinic pressure gradients is examined near the bottom where the along channel flow is retarded there is cross channel ekman flux that is associated with downwelling on the eastern side and upwelling on the western side of the channel in the presence of stratification the cross channel flow rearranges the density structure which in turn acts on the along channel velocity via the thermal wind relation eventually the cross isobath ekman flux is shut down in the case of baroclinically driven flow of antarctic bottom water through the vema channel the model reproduces the observed shape of the deep temperature profiles and their cross channel asymmetry the model offers an explanation that is alternative or supplementary to inviscid multilayer hydraulic theory that was proposed in earlier studies it explains the extremely thick bottom boundary layers in the center and on the western slope of the channel the deep thermocline is spread out in the west and sharpened in the east and the coldest water is found on the eastern side of the deep trough the modified density field reduces the along channel flow near the bottom and focuses it into a narrow jet on the eastern side of the channel

characteristics of suspended particles at an 11 hour anchor station in san francisco bay california hourly measurements of suspended sediment in situ floc size distributions constituent grain size distributions total concentrations and average particle densities are presented for five depths from an 11 hour anchor station in san francisco bay the flocs formed well sorted distributions with modal sizes between 100 and 500 m whereas the disaggregated sediment was poorly sorted with about the same volume of material in all size classes and relatively little material coarser than 100 m for both types of size spectra concentrations at the coarse end of the size distribution fall off rapidly at a size range which varied with bottom shear stress the settling rates corresponding to the modal floc diameters were generally related to the maximum disaggregated diameters by a square relationship but turbulence appeared to limit floc size in the coarsest samples both the floc and disaggregated grain size vary with total concentration suggesting that flocs are relatively stable entities which do not change during alternating settling and resuspension

estimates of bottom roughness length and bottom shear stress in south san francisco bay california a field investigation of the hydrodynamics and the resuspension and transport of particulate matter in a bottom boundary layer was carried out in south san francisco bay south bay california during march april 1995 using broadband acoustic doppler current profilers detailed measurements of turbulent mean velocity distribution within 1 5 m above bed have been obtained a global method of data analysis was used for estimating bottom roughness length zo and bottom shear stress or friction velocities u field data have been examined by dividing the time series of velocity profiles into 24 hour periods and independently analyzing the velocity profile time series by flooding and ebbing periods the global method of solution gives consistent properties of bottom roughness length zo and bottom shear stress values or friction velocities u in south bay estimated mean values of zo and u for flooding and ebbing cycles are different the differences in mean zo and u are shown to be caused by tidal current flood ebb inequality rather than the flooding or ebbing of tidal currents the bed shear stress correlates well with a reference velocity the slope of the correlation defines a drag coefficient forty three days of field data in south bay show two regimes of zo and drag coefficient as a function of a reference velocity when the mean velocity is 25 30 cm s 1 the ln zo and thus the drag coefficient is inversely proportional to the reference velocity the cause for the reduction of roughness length is hypothesized as sediment erosion due to intensifying tidal currents thereby reducing bed roughness when the mean velocity is 25 30 cm s 1 the correlation between zo and the reference velocity is less clear a plausible explanation of scattered values of zo under this condition may be sediment deposition measured sediment data were inadequate to support this hypothesis but the proposed hypothesis warrants further field investigation

seismic and hydroacoustic observations of the 2016 17 bogoslof eruption in mid december 2016 bogoslof volcano alaska began an 8 5 month long eruption that produced at least 70 explosions and three lava domes bogoslof is an emergent submarine volcano with only the very top forming a small island so the eruptive activity mostly occurred from a vent submerged beneath a bay or lagoon the bogoslof eruption was recorded on regional seismic and infrasound arrays as well as by a hydrophone that was deployed locally during the second half of the eruption since few emergent volcanic eruptions have seismo acoustic recordings these observations taken in context with satellite and other observations provide an opportunity to greatly improve our understanding of the seismo acoustic signals produced by these eruptions the instruments detected a range of activity including earthquakes tremor and mass flow events earthquakes occurred before during after and unassociated with explosions and also often occurred in swarms the 47 seismically detected swarms and 27 additional hydroacoustically detected swarms can be further broken into four types precursory post eruptive general and tremor dominated most seismic swarms were less than 10 h long had fewer than 50 earthquakes and had average earthquake rates below 20 h for the explosions we calculate a tremor magnitude frequency index and average frequency the tremor magnitudes determined from the hydrophone data show a roughly linear relation to explosion plume height though this relation was not clear in the more limited seismic data lastly we categorize the activity into five eruption phases based on seismo acoustic character precursory opening explosive i pause and explosive ii

magma water interactions in subaqueous and emergent basaltic in the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of 1 explosive release of magmatic volatiles 2 explosive expansion and collapse of steam formed at magma water contact surfaces 3 explosive expansion of steam following enclosure of water in magma or entrapment of water close to magma and 4 cooling contraction these processes named respectivelymagmatic explosivity contact surface steam explosivity bulk interaction steam explosivity andcooling contraction granulation can be enhanced by mutual interaction and feedback the first three explosive processes are limited at certain water depths hydrostatic pressures and become increasingly vigorous at shallower levels the depth of onset of magmatic explosivity depends largely on juvenile volatile content it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas at the depth where formation of clastic deposits becomes predominant over effusion of lavas magmatic explosivity is subordinate to steam explosivity as a clast forming process the upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it contact surface explosivity commonly requires initiation by a vigorous impact between magma and water and although no certain depth limit is known likelihood of such explosivity decreases rapidly with depth clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water which in sea water is at about 3 km cooling contraction granulation can occur in any depth of water but at shallow levels may be replaced by contact surface explosivity during continuous eruption under water tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur emergent volcanoes are characterized by distinctive steam explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material water and steam the water gets into the vent by flooding across or through the top of the tephra pile and violent explosions cease when this access is sealed the eruptions during emergence of surtsey and capelinhos typify the distinctive explosive activity the style and controls of which are different from those of maar volcanoes

wind enhanced resuspension in the shallow waters of south san francisco bay mechanisms and potential implications for cohesive sediment transport 1 we investigated the driving forces of sediment dynamics at the shoals in south san francisco bay two stations were deployed along a line perpendicular to a 14 m deep channel 1000 and 2000 m from the middle of the channel station depths were 2 59 and 2 19 m below mean lower low water respectively we used acoustic doppler velocimeters for the simultaneous determination of current velocities turbulence sediment concentration and fluxes maximum current shear velocities were 0 015 m s 1 at the station further from the channel closer to the shore and 0 02 m s 1 at the station closer to the channel peak wave induced shear velocities exceeded 0 015 m s 1 at both stations maximum sediment concentrations were around 30 g m 3 during calm periods root mean square wave height 0 10 g m 2 s 1 at the station further from the channel 0 36 m above the bed closer to the channel sediment concentrations and vertical fluxes due to wind wave resuspension were persistently lower maximum concentrations around 50 g m 3 and maximum fluxes around 0 04 g m 2 s 1 most resuspension events occurred during flood tides that followed wave events during low water although wave motions are able to resuspend sediment into the wave boundary layer at low tide the observed large increases in sediment fluxes are due to the nonlinear interaction of wind waves and the tidal currents

modeling stratified wave and current bottom boundary layers on the continental shelf the glenn and grant 1987 continental shelf bottom boundary layer model for the flow and suspended sediment concentration profiles in the constant stress layer above a noncohesive movable sediment bed has been updated the reynolds fluxes for sediment mass and fluid momentum are closed using a continuous time invariant linear eddy viscosity modified by a continuous stability parameter to represent the influence of suspended sediment induced stratification throughout the constant stress region glenn and grant 1987 use a less realistic discontinuous eddy viscosity and neglect the stratification correction in the wave boundary layer for typical model parameters the two models produce currents above the wave boundary layer that are in better agreement than the suspended sediment concentrations within the wave boundary layer the differences are much greater for both the current and the sediment concentration this leads to significant differences in the sediment transport throughout the constant stress layer sensitivities of the updated model were examined on the basis of observed wave and current data acquired during storms on the inner continental shelf comparisons between the stratified and neutral versions of the updated model indicate that the stratified version produces a total depth integrated sediment transport that can be 2 orders of magnitude less than and time averaged shear velocities that can be nearly half of that predicted by the neutral version sensitivities to grain size distributions indicate that even a small amount of finer sediment can stratify the storm driven flows sensitivities to closure constants within the range of reported values also produce up to an order of magnitude variation in sediment transport illustrating the need for dedicated field experiments to refine further estimates of these parameters

shallow seated explosions in the construction of the motukorea tuff ring auckland new zealand evidence from lithic and sedimentary characteristics at least 52 eruption centres are scattered within the 360 km2 auckland volcanic field avf motukorea now an island in the waitemata harbour is one of 39 avf volcanoes that experienced a phreatomagmatic explosive phase before a magmatic phase the volcano erupted through a 200 300 m thick consolidated mudstone sandstone sequence of the miocene waitemata group which overlies the waipapa terrane greywacke basement detailed field descriptions of the sedimentary characteristics of the early phreatomagmatic deposits were carried out along with examination of lithics the ejecta ring deposit comprises 55 to 60 vol lithics of which waitemata group fragments constitute approximately 90 vol whereas 10 vol are waipapa fragments suggesting a dominance of shallow fragmentation the sedimentary characteristics of the stratigraphic sequence at motukorea suggest a dominance of wet surges at the beginning of the eruption with progression into drier sequences upwards this is reflected in increasing inter bedded juvenile pyroclast dominated fall deposits up sequence these characteristics are attributed to the changing hydrogeological conditions within the diatreme and the host rocks these findings shed light on the eruption dynamics of phreatomagmatic eruptions through consolidated rocks in the avf and enable the depiction of a scenario of future eruptions within the field in similar substrates

erosion of soft cohesive sediment deposits erosion behavior of soft cohesive sediment deposits has been investigated in laboratory experiments such deposits are representative of the top active layer of estuarial beds an experimental procedure involving layer by layer erosion under a range of bed shear stresses b of successively increasing magnitude was utilized interpretation of the resulting concentrationtime data together with bed density profiles yielded a description of the variation of the bed shear strength s with depth as well as an expression for the rate of surface erosion in general s increased with depth and was also influenced by the type of sediment bed consolidation period and salinity the rate of erosion was found to vary exponentially with b s 1 2 in modeling estuarial bed erosion it is essential to take these characteristics of s and the rate of erosion into account

mineralization of biogenic materials in the water masses of the south atlantic ocean i assessment and results of an optimum multiparameter analysis abstract this is the first of two manuscripts dealing with the circulation mixing ventilation and organic matter mineralization of the south atlantic ocean sao the present work quantifies the complex mixing of water masses in the sao using a constrained least squares regression optimum multiparameter omp analysis the omp based on temperature salinity silicate and the conservative parameter no was applied on two world ocean circulation woce lines a17 and a14 in the western and eastern sao respectively the constrained omp sensitivity to sources of error in the end member characteristics measured parameters equation weights and oxygen to nitrogen mineralization ratio rn was carefully assessed using perturbation tests perturbation of rn was the only test that changed significantly the mixing proportions although by less than 5 the constrained omp method allowed defining the realm and identifying the core of flow of each water mass to study its circulation the evolution of its chemical composition and eventually to separate the contribution of physical and biogeochemical processes relevant specific outputs of this first manuscript are 1 north of the south equatorial current the silicate maximum is primarily composed of antarctic intermediate water aaiw rather than circumpolar deep water cdw 2 the two degree discontinuity tdd experiences a dramatic meridional change of water masses composition being dominated by north atlantic deep water nadw north of the vema channel and by cdw southwards 3 the 50 proportion horizon of weddell sea deep water wdsw with a of 0 3 c at the entry of the sao defines the upper limit of the wsdw realm more properly than the classical isopycnals of 46 04 or 46 06 4 where the proportion of wsdw is around 75

mass settling flux of fine sediments in northern european estuaries measurements and predictions abstract this study describes a new flocculation model which was based entirely on observations of settling floc spectra and turbulent shear stresses acquired primarily from a series of in situ experiments conducted in several european estuaries the synthesis identified that the key components which best quantitatively describe a floc population are the changes in the macrofloc 160 m and microfloc settling velocities ws macroem and ws microem together with how the suspended matter is distributed across each floc sub population spm ratioem the ws macroem algorithm displayed an increase in settling velocity at low shear stresses due to flocculation enhanced by shear and floc disruption at higher stresses for the same concentration the transition being a turbulent shear stress of about 0 36 n m 2 the combination of the three algorithms into a single equation to predict mass settling flux msf em estimated the total flux of the 157 measured floc samples with a cumulative error 1 and 5 mm s 1 were both in error by an average of 86 and 41 respectively a concentration settling parameterisation and the van leussen techniques under predicted the total cumulative flux by 35 and 38 respectively furthermore the analysis indicated that the various existing methods all incurred high predictive errors at times under estimating by over 70 as concentration levels rose in close proximity to the bed the findings of this study demonstrate the new manning floc settling velocity mfsv empirical model has flexibility in adapting to a wide range of both turbulent shear stress and suspended sediment concentration estuarine conditions

suspended sediment transport in an estuarine tidal channel within san francisco bay california abstract a recently developed instrumentation system has been used to monitor simultaneously flow conditions and suspended sediment distribution in the bottom boundary layer of a tidal channel within san francisco bay california measurements were made every 15 min over six successive flood and ebb tidal cycles they included mean velocity profiles from four electromagnetic current meters within 1 m of the seabed mean suspended sediment concentration profiles from seven miniature nephelometers placed within 1 m of the seabed near bottom pressure fluctuations vertical temperature gradient and bottom photographs additionally suspended sediment was sampled from four levels within 1 m of the seabed three times during the tidal cycle the instrument system was retrieved during each slack water period to exchange suspended sediment sample bags while the instrument was deployed std nephelometer measurements were made thoughout the water column and water samples were collected each 1 h and bottom sediment was sampled at the deployment site size distributions of the suspended sediment samples estimates of particle settling velocity s friction velocity u and reference concentration c a at z 20 cm were used in the suspended sediment distribution equations to evaluate their ability to predict the observed suspended sediment profiles three suspended sediment particle conditions were evaluated 1 individual particle sizes in the 4 11 62 5 0 5 m size range with the reference concentration c a at z 20 cm c 2 individual particle sizes in the 4 6 size range flocs representing the 7 11 size range with the reference concentration c a at z 20 cm c f and 3 individual particle sizes in the 4 6 size range flocs representing the 7 11 size range with the reference concentration predicted as a function of the bed sediment size distribution and the square of the excess shear stress an analysis was also carried out on the sensitivity of the suspended sediment distribution equation to deviations in the primary variables s u and c a in addition computations of mass flux were made in order to show vertical variations in mass flux for varying flow conditions

the effects of suspended sediment on turbulence within an estuarine turbidity maximum predictions of cohesive sediment transport are hampered by poor understanding of the effects of sediment suspensions upon the nature of near bed turbulence in this study current velocities associated turbulence and flow characteristics were measured within an estuarine turbidity maximum during two spring ebb tides measurements at two heights both within and above a near bed high concentration layer show the importance of intermittent internal waves the ratio of vertical to horizontal turbulence intensities exceeded 1 0 when waves were present the waves were more significant above the layer than within it comparison between the turbulent kinetic energy and the reynolds stresses showed inactive turbulence occurring at stresses less than about 0 2 n m 2 during these periods negative suspended sediment fluxes occurred indicating that the turbulence could enhance settling of the sediment the effect of the intermittent internal waves on the turbulent bursting structure and their interaction with the concentration profile appears to increase the variability of the reynolds fluxes of suspended sediment and cause downwards reynolds fluxes especially beneath the lutocline

deterministic coastal morphological and sediment transport modeling a review and discussion 1 modern coastal ocean modeling systems are now capable of numerically simulating a variety of coastal and estuarine problems and can thus provide useful information for managing coastal zones here we review state of the art eulerian implementations of bottom up sediment transport and morphological change in coastal ocean hydrodynamic models in order to investigate the fate of suspended sediment in coastal and estuarine waters as well as the evolution of sea or river beds sediment dynamics need to be represented at a scale relevant to the numerical discretized solution and significant effort is devoted to parameterize sediment processes we discuss boundary layer hydrodynamics and the computation of the bed shear stress we also focus on approaches used to represent near bed processes such as bed load transport and sediment erosion and deposition sediment diffusivities settling velocities and cohesive processes such as flocculation all have an impact on suspended sediment throughout the water column we then describe the implementation of process parameterizations in coastal hydrodynamic models explicitly reviewing five widely used systems the approaches implemented in these coastal models may present distinct strengths and shortcomings with regard to some important issues for coastal zones both numerical and physical while these detailed limitations need to be considered as part of model assessment more general issues also hinder present state of the art models in particular sediment transport is inherently highly empirical which is further compounded by issues arising from turbulence closure schemes we conclude by suggesting some possible directions toward improving sediment dynamics understanding and coastal scale predictive ability

the effect of particle settling velocity on computed suspended sediment concentration profiles abstract a field study was performed at a site in san pablo bay california to evaluate how well suspended sediment distribution equations reproduce observed concentrations near bed measurements of current velocity suspended sediment concentrations and fluid and particle characteristics were made an in situ settling cylinder was used to determine settling velocity values of aggregated suspended sediments and photographs from a plankton camera provided size estimates in situ weighted average settling velocities were generally an order of magnitude greater than a weighted average for stokes calculations of settling velocity for the grain size distribution of the reference suspended sediment sample and two orders of magnitude greater than a stokes settling velocity for the median grain size of suspended sediment flocs were commonly 100 m in diameter and as large as 450 m with settling velocities as high as 0 2 cm s 1 calculated suspended sediment concentration profiles using in situ estimates of settling velocity yielded closer agreement with observed concentration profiles within 25 than using settling velocities calculated from the grain size distribution of suspended sediment samples within 40 50

characteristics of dune bedded pyroclastic surge bedsets abstract the grainsize characteristics of dune bedded pyroclastic surge bedsets are surveyed the variance between coarsest and finest beds ranges from 1 to 6 phi in different surge bedsets and it increases as the grainsize of the coarsest bed increases reflecting an increasing velocity of emplacement deposits of wet surges identified as those which contain accretionary and ash coated lapilli tend to be finer and show less variance this partly because wet ash is cohesive but mainly because wet surges tend to be weaker dry surge bedsets are strongly fines depleted wet ones less so the lack of erosion of underlying ash layers shows that the environment is a strongly depositional one individual bedsets are demarcated by thin intervening fine ash fall layers which are the complementary ash cloud deposits settled or flushed out after the passage and decay of each turbulent surge surge deposits are generally less coarse than the coarsest associated airfall deposits which shows that they are formed by generally weaker events this study helps interpret the dune bedded parts of the landscape mantling may 18th 1980 blast deposit of mount st helens the blast was a very violent event but the variance and the grainsize of the coarsest bed are those of a relatively weak surge this suggests that the dune bedding was produced by a weak effect such as minor turbulence in a thin pyroclastic flow coming to rest in a mountainous terrain roughened by tree stumps and fallen logs

experimental interaction of magma and dirty coolants the presence of water at volcanic vents can have dramatic effects on fragmentation and eruption dynamics but little is known about how the presence of particulate matter in external water will further alter eruptions volcanic edifices are inherently dirty places where particulate matter of multiple origins and grainsizes typically abounds we present the results of experiments designed to simulate non explosive interactions between molten basalt and various coolants ranging from homogeneous suspensions of 0 to 30 mass bentonite clay in pure water to heterogeneous and or stratified suspensions including bentonite sand synthetic glass beads and or naturally sorted pumice four types of data are used to characterise the interactions 1 visual video observations 2 grainsize and morphology of resulting particles 3 heat transfer data from a network of eight thermocouples and 4 acoustic data from three force sensors in homogeneous coolants with 20 sediment heat transfer is by forced convection and conduction and thermal granulation is less efficient resulting in fewer blocky particles larger grainsizes and weaker acoustic signals many particles are droplet shaped or and vesicular containing bubbles filled with coolant both of these particle types indicate significant hydrodynamic magma coolant mingling and many of them are rewelded into compound particles the addition of coarse material to heterogeneous suspensions further slows heat transfer thus reducing thermal granulation and variable interlocking of large particles prevents efficient hydrodynamic mingling this results primarily in rewelded melt piles and inefficient distribution of melt and heat throughout the coolant volume our results indicate that even modest concentrations of sediment in water will significantly limit heat transfer during non explosive magma water interactions at high concentrations the dramatic reduction in cooling efficiency and increase in mingling help to explain globular peperite and provide information relevant to analyses of premixing associated with highly explosive molten fuel coolant interactions in debris filled volcanic vents

structure and eruptive mechanisms at surtsey volcano iceland glassy basalt tuff was the primary material cored in 1979 from a 181 m deep drill hole on the east tuff ring of surtsey volcano despite the fact that the hole extends 122 m below sea level all the core is similar to the exposed tephra composing the two tuff rings of the island the tuff includes abundant accretionary lapilli and tuff vesicles indicating that it was all deposited subaerially during the growth of the tuff rings repeated hydromagmatic explosion cycles began with a series of intermittent tephra finger explosions leading up to continuous uprush explosions which lasted for several minutes to several hours this nozzle like continuous activity produced eruption columns 100 250 m in diameter and 500 2000 m in height which probably quarried several hundred metres below the ground surface the continuous uprush explosion type provides a reasonable mechanism to excavate a diatreme from the top down during construction of the tuff rings concentric faults repeatedly downdropped a funnel like structure 400 800 m in diameter several hundred metres thus accounting for the presence of subaerially deposited tephra in the drill core far beneath sea level ring dykes later intruded upward along these faults and fed small lava flows heat in the surface tephra probably originated primarily from these shallow intrusions