turbulent viscosity in natural surf zones 1 waves breaking in the shallow surf zone near the shoreline inject turbulence into the water column that may reach the bed to suspend sediment breaking wave turbulence in the surf zone is however poorly understood which is one of the reasons why many process based coastal evolution models predict coastal change during severe storms inadequately here we use data collected in two natural surf zones to derive a new parameterization for the stability functionc that determines the magnitude of the eddy viscosity tin two equation turbulent viscosity models t c k2 e where k is turbulent kinetic energy and e is the turbulence dissipation rate in both data sets the ratio of turbulence production to dissipation is small 0 15 while vertical turbulence diffusion is significant this differs from assumptions underlying existing c parameterizations which we show to severely overpredict observed c for most conditions additionally we rewrite our new c parameterization into a formulation that accurately reproduces our reynolds stress based estimates of turbulence production this formulation is linear with strain consistent with earlier theoritical work for large strain rates also it does not depend oneand can therefore also be applied in one equation turbulent viscosity models we anticipate our work to improve turbulence modeling in natural surf zones and to eventually lead to more reliable predictions of coastal evolution in response to severe storms

contrasting styles of welding observed in the proximal askja 1875 eruption deposits i regional welding abstract as an alternative to classical welding models of fall deposits due to the progressive accumulation of hot tephra which then weld we describe here welded deposits on the northern 1875 caldera rim of askja volcano that have welded due to the influence of hot discrete spatter bombs impacting into and supplying heat to a halo of surrounding tephra this style of welding we term local welding in contrast to regional welding which is described elsewhere carey r j houghton b f thordarson t 2008 contrasting styles of welding observed in the proximal askja 1875 eruption deposits i regional welding j volcanol geotherm res 171 1 19 doi 10 1016 j jvolgeores 2007 11 020 locally welded deposits are associated with the rhyolitic plinian phase of the 1875 eruption of askja volcano two distinct welding units w1 and w2 are interbedded with plinian fall on the northern caldera rim and grade outwards to weakly dispersed non welded fall spatter bombs are found in both welding units but vary in their characteristic sizes and internal features in the w1 unit simple bombs with homogeneous internal characteristics up to 60 cm in diameter are found in the w2 unit large discrete spatter bombs with complex internal features range up to 9 m in diameter we describe here two case studies showing the effects of a single small spatter bombs b multiple small spatter bombs and c large discrete spatter bombs varying in size vertical and lateral profiles through welding zones reveal that the primary controls on local welding are the availability of supplied or added heat and the loading capacity of the spatter bomb local welding grades are much higher than that of regional welding as the combined effects of heat compaction and insulation can provide suitable conditions which lead to dense welding and proximal to the spatter bomb rheomorphic flowage if heating and loading exceed the critical requirement for welding porosity loss via matrix welding and vesicle collapse occurs to a point where further strain must be accommodated as shearing and ductile flowage the spatter bombs are found only within the weakly dispersed welding units and are the final erupted products of each fountaining phase their low viscosities are evident by their deformation on impact and fluidal forms and hold some important clues to eruption dynamics in the shallow conduit and vent regions

suspended sediment transport in the surf zone response to cross shore infragravity motion a field experiment to investigate the magnitude and temporal and spatial scales of suspended sediment transport in the inner surf zone was conducted at san marine oregon on october 7 13 1984 instrumentation consisted of five electromagnetic current meters three strain gauge type pressure transducers and 25 optical backscatter sensors to measure the concentrations of suspended sediment the instruments were deployed approximately 70 m x seaward of the mean high water line mean depth h 1 1 1 3 m in a closely spaced cross shaped pattern data were collected for 68 min periods spanning high tide during the 7 day experiment during the experiment waves varied in angle of approach from shore normal to southwesterly offshore significant swell heights were 3 5 m with periods of 12 14 s local sea conditions with wind waves of approximately 8 s also occurred a visual estimation of the width of the surf zone indicated it to be approximately 500 m and the breaker pattern suggested that there were two longshore bars at approximately 200 and 500 m offshore the data resulting from the experiment encompass a broad range of wave and current conditions which included periods of extreme infragravity motion 30 t 300 s and weak longshore currents and periods of low infragravity motion and strong longshore currents periods of incident wave dominance also occurred the field study section of this paper qualitatively describes the sediment response to strong 240 cm s 1 low frequency 0 01 hz cross shore fluid motions which dominated the inner surf zone during two of the data runs the infragravity band accounted for 85 of the cross shore velocity variance the peak 0 01 hz of which was associated with shore normal standing waves concentration gradients of suspended sediment appear to be associated with diffusive processes and develop and decay on time scales of the infragravity motions rather than those of incident waves suspension events during times of infragravity dominance often persisted for periods of 30 45 s and reached peak concentrations of 20 40 g l 1 at elevations in excess of 26 cm mean suspended load was 3 4 times larger than that associated with incident wave motions the modeling section of the paper attempts to quantitatively describe the observed time dependent vertical suspended sediment distribution with a one dimensional turbulent diffusion model formulations of eddy diffusion and erosion rate coefficients associated with peak cross shore flows are found to agree with or fall within the range of values from previous laboratory and field studies and are used in the model the model is evaluated by its ability to reproduce the time dependent vertical distribution of suspended sediment and to estimate the observed mean suspended load and the correct direction and magnitude of the mean longshore and cross shore flux level above the bed z 31 cm of suspended sediment

a unified spectral parameterization for wave breaking from the deep ocean to the surf zone 1 a new wave breaking dissipation parameterization designed for phase averaged spectral wave models is presented it combines wave breaking basic physical quantities namely the breaking probability and the dissipation rate per unit area the energy lost by waves is first explicitly calculated in physical space before being distributed over the relevant spectral components the transition from deep to shallow water is made possible by using a dissipation rate per unit area of breaking waves that varies with the wave height wavelength and water depth this parameterization is implemented in the wavewatch iii modeling framework which is applied to a wide range of conditions and scales from the global ocean to the beach scale wave height peak and mean periods and spectral data are validated using in situ and remote sensing data model errors are comparable to those of other specialized deep or shallow water parameterizations this work shows that it is possible to have a seamless parameterization from the deep ocean to the surf zone

the influence of whitecapping waves on the vertical structure of turbulence in a shallow estuarine embayment abstract the vertical distribution of the turbulent kinetic energy dissipation rate was measured using an array of four acoustic doppler velocimeters in the shallow embayment of grizzly bay san francisco bay california owing to the combination of wind and tide forcing in this shallow system the surface and bottom boundary layers overlapped whitecapping waves were generated for a significant spectral peak steepness greater than 0 05 or above a wind speed of 3 m s 1 under conditions of whitecapping waves the turbulent kinetic energy dissipation rate in the upper portion of the water column was greatly enhanced relative to the predictions of wind stress wall layer theory instead the dissipation followed a modified deep water breaking wave scaling near the bed bottom 10 of the water column the dissipation measurements were either equal to or less than that predicted by wall layer theory stratification due to concentration gradients in suspended sediment was identified as the likely cause for t

wave induced sediment transport and sandbar migration onshore sediment transport and sandbar migration are important to the morphological evolution of beaches but are not well understood here a model that accounts for fluid accelerations in waves predicts the onshore sandbar migration observed on an ocean beach in both the observations and the model the location of the maximum acceleration induced transport moves shoreward with the sandbar resulting in feedback between waves and morphology that drives the bar shoreward until conditions change a model that combines the effects of transport by waves and mean currents simulated both onshore and offshore bar migration observed over a 45 day period

the architecture and shallow conduits of laki type pyroclastic cones insights into a basaltic fissure eruption pyroclastic cones built along basaltic fissures provide important volcanological information but it is often difficult to examine the early erupted products due to burial by later products furthermore it is rare to see the link between the feeder dyke and overlying cone fully exposed in this study we detail the architecture of a hybrid spatter cone scoria half cone and feeder dyke that has been dissected to below the pre eruption surface by glacial floods the cones were constructed during the 6 8 ka rau uborgir kvenso ul fissure eruption in north iceland during hawaiian and strombolian style activities widening of their feeder dyke in the shallow sub surface to produce an upward flaring morphology was accommodated by country rock removal and elastic host rock deformation ballistic calculations and stratigraphic relationships indicate that the scoria half cone was constructed early in the eruption from the deposits of a lava fountain 100 m high a decline in fountain height and the generation of abundant welded deposits resulted in the formation of a nested spatter cone within the scoria half cone the cones are similar in structure and size to the hybrid scoria and spatter cones produced during the 15 km3 1783 laki eruption and serve as a valuable window into the construction of pyroclastic edifices during basaltic fissure eruptions

spatter and welded air fall deposits generated by fire fountaining eruptions cooling of pyroclasts during transport and deposition abstract according to the physico mathematical model presented here juvenile ballistic fragments can travel through the atmosphere during fire fountaining eruptions preserving enough heat to agglutinate or to weld on impact with the ground s surface even a few kilometres from the source area the range is mostly related to exit velocity and ejection angle as well as to such typical properties of the transported particles as size density and shape the selective nature of the transport system can give rise to inverse lateral size density grading the most important interdependent factors that control the degree of final agglutination or welding are accumulation rate grain size and duration of deposition in the investigated grain size range an accumulation rate of 0 2 m h appears as a minimum value to promote welding this value cannot be considered as an absolute threshold because it can be significantly lowered by increasing the grain size duration of deposition appears as another critical factor because it controls the maximum temperature of the whole deposit and its final thickness and therefore the cooling rate of its main portion after the end of deposition in the case of high accumulation rates of coarse particles but during a short period of time primary agglutination may be the dominant factor in controlling the final sintering of particles conversely high accumulation rates of coarse particles during a long period of time give rise to both primary agglutination and welding

complexities of plinian fall deposition at vent an example from the 1912 novarupta eruption alaska abstract an extremely proximal ejecta ring with exposures to within 100 m of vent was deposited during later stage plinian fall activity during the 1912 novarupta eruption in alaska one bed in the ejecta ring bed s contains predominantly andesitic clasts which serve to delineate the striking contrast in thinning rates along dispersal axis of the ejecta ring pyle bt values of 70 m bed s alone or 190 m whole ejecta ring and the coeval dacitic plinian fall deposits pyle bt values of 4 km proximal and 37 km medial distal the locally deposited andesitic and dacitic clasts of the ejecta ring are interpreted as products of an irregular collar of low fountaining ejecta partially sheathing the core of higher velocity dacitic ejecta that fed the stable converting 23 km high column the presence of such an extremely proximal accumulation of ejecta appears to be a feature common to several other historic eruptions that generated widespread fall deposits this feature in part accounts for conflicts between measured and calculated values for thickness maxima in plinian fall deposits and suggests that modifications may be required of existing models for plinian eruption columns

effects of waves on coastal water dispersion in a small estuarine bay 1 a three dimensional wave current model is used to investigate wave induced circulations in a small estuarine bay and its impact on freshwater exchanges with the inner shelf related to stratified river plume dispersion modeled salinity fields exhibit a lower salinity surface layer due to river outflows with typical depth of 1 m inside the bay the asymmetric wave forcing on the bay circulation related to the local bathymetry significantly impacts the river plumes it is found that the transport initiated in the surf zone by the longshore current can oppose and thus reduce the primary outflow of freshwater through the bay inlets using the model to examine a high river runoff event occurring during a high energy wave episode waves are found to induce a 24 h delay in freshwater evacuation at the end of the runoff event waves have reduced the freshwater flux to the ocean by a factor 5 and the total freshwater volume inside the bay is increased by 40 according to the model and for this event the effect of the surf zone current on the bay flushing is larger than that of the wind the freshwater balance is sensitive to incident wave conditions maximum freshwater retention is found for intermediate offshore wave heights 1 m hs 2 m for higher energy waves the increase in the longshore current reduces the retention which is two times lower for hs 4 m than for hs 2 m

deformation of the wineglass welded tuff and the timing of caldera collapse at crater lake oregon abstract four types of deformation occur in the wineglass welded tuff on the northeast caldera rim of crater lake a vertical tension fractures b ooze outs of fiamme c squeeze outs of fiamme and d horizontal pull apart structures the three types of plastic deformation b d developed in the lower part of the wineglass welded tuff where degree of welding and density are maximum deformation originated from concentric normal faulting and landsliding as the caldera collapsed the degree of deformation of the wineglass welded tuff increases toward the northeast part of the caldera where plastic deformation occurred more easily because of a higher emplacement temperature probably due to proximity to the vent the probable glass transition temperature of the wineglass welded tuff suggests that its emplacement temperature was 750 c where the tuff is densely welded calculation of the conductive cooling history of the wineglass welded tuff and the preclimactic cleetwood lava flow under assumptions of a initially isothermal sheet and uniform properties suggests that a caldera collapse occurred a maximum of 9 days after emplacement of the wineglass welded tuff and that b the period between effusion of the cleetwood lava flow and onset of the climactic eruption was

the effect of wave breaking on surf zone turbulence and alongshore currents a modeling study the effect of breaking wave generated turbulence on the mean circulation turbulence and bottom stress in the surf zone is poorly understood a one dimensional vertical coupled turbulence k and mean flow model is developed that incorporates the effect of wave breaking with a time dependent surface turbulence flux and uses existing published model closures no model parameters are tuned to optimize model data agreement the model qualitatively reproduces the mean dissipation and production during the most energetic breaking wave conditions in 4 5 m water depth off of a sandy beach and slightly underpredicts the mean alongshore current by modeling a cross shore transect case example from the duck94 field experiment the observed surf zone dissipation depth scaling and the observed mean alongshore current although slightly underpredicted are generally reproduced wave breaking significantly reduces the modeled vertical shear suggesting that surf zone bottom stress cannot be estimated by fitting a logarithmic current profile to alongshore current observations model inferred drag coefficients follow parameterizations manning strickler that depend on the bed roughness and inversely on the water depth although the inverse depth dependence is likely a proxy for some other effect such as wave breaking variations in the bed roughness and the percentage of breaking wave energy entering the water column have a comparable effect on the mean alongshore current and drag coefficient however covarying the wave height forcing and dissipation and bed roughness separately results in an alongshore current drag coefficient only weakly strongly dependent on the bed roughness because of the competing effects of increased turbulence wave forcing and orbital wave velocities

abrupt shifts between wet and dry phases of the 1875 eruption of askja volcano microscopic evidence for macroscopic dynamics abstract the eruption of askja in 1875 was a powerful eruption with intervals of sustained activity yet also with abrupt shifts in eruption style shifts from dry to wet fall from buoyant to collapsing column conditions and sharp fluctuations of eruption intensity occurred throughout the duration of the eruption deep ascent processes including decompression bubble nucleation and early growth of bubbles were similar among the four main phases regardless of style or column conditions uniformly high vesicle number densities 8 0 108 to 2 109 cm 3 suggest that magma degassing throughout the eruption was a disequilibrium process with very high nucleation rates power law distributions of the subpopulations of small bubbles on cumulative number density plots suggest continuous nucleation of bubbles shallow processes of bubble growth and magma ascent were at times decoupled from deep ascent processes at the onset of each phase the erupted magma appears to have a mature vesicle signature suggesting extended residence times in the shallow conduit irrespective of decompression or magma ascent rate during each phase the textural and density data suggest more uniform conditions of ascent and shallow degassing two pauses in the eruption were accompanied by shifts in vent position and we suggest that magma during this eruption was intruded in an elongated dike like geometry and vent migrations between phases led to the eruption of magma that had slightly greater residence time and hence more mature textures the major yet reversible shifts between dry or magmatic and wet or phreatomagmatic eruption styles were driven by changing external conditions accompanying the shifts in vent position the migration of the vent into and out of water sources rather than by changes of mass flux the shift between buoyant phreatoplinian wet plume conditions to the production of wet density currents is inferred to be a function of vent widening during the high intensity phreatoplinian phase thereby decreasing the exit velocity of the wet mixture in terms of the role of external water in the phreatoplinian phase our qualitative textural observations and quantitative data suggest that the magma was a foam prior to fragmentation however presently we cannot resolve the exact role and timing of the interaction with the external water

formation of oskjuvatn caldera at askja north iceland mechanism of caldera collapse and implications for the lateral flow hypothesis the oskjuvatn caldera at askja volcano north iceland was formed as a result of an explosive eruption at askja on 28th 29th march 1875 oskjuvatn is one of the youngest collapse calderas on earth and its initiation and growth were observed and documented by explorers and geologists working in the askja region between 1875 and 1932 it is an example of caldera formation where the volume of the caldera collapse far exceeds the volume of associated erupted products the discrepancy between the collapse volume and associated erupted products has been used by previous workers as a justification for the hypothesis that the injection of lateral dykes from askja fed the february to october 1875 n jahraun fissure eruptions at the sveinagja graben some 60 km north of askja however historical accounts documenting the caldera formation in sufficient detail show clearly that oskjuvatn formed by piecemeal collapse taking over 40 years to reach its current form we use these accounts to undertake a detailed examination of the stages of caldera collapse and to compare them with the known magmatic output of askja in the years following the 1875 eruption arcgis software was used to calculate the volume of oskjuvatn during the various stages of collapse and the volume of material erupted after 1875 while a dyke extending between askja and sveinagja may be implied to account for the missing volume our results demonstrate that the volume of oskjuvatn in july 1875 closely corresponds to the volume of rhyolitic material erupted on 28th 29th march 1875 in addition geochemical evidence indicates that the n jahraun magmas were sourced from a deeper reservoir rather than by lateral injection from askja s shallow crustal magma chamber we therefore suggest that the injection of sills and dykes in a coherent intrusion complex beneath askja central volcano combined with background deflation of the magma storage zone beneath oskjuvatn caldera over 30 to 40 years following 1875 satisfactorily accommodates the volume required to form oskjuvatn caldera

proximal record of the 273 ka poris caldera forming eruption las canadas tenerife lithofacies architecture analysis is applied to the most proximal exposures of the 273 ka poris formation in the diego hernandez caldera wall of las canadas here the succession records an opening plinian phase followed by generation of a pyroclastic density current pdc that was partly blocked by near vent topography the upper part of the current surmounted the barrier and deposited an ignimbrite veneer during a hiatus in energetic flow ash and various ash aggregates were deposited from a hybrid cloud comprising parts of both the plinian and the co ignimbrite plumes phreatomagmatic explosions then generated currents rich in fine grained lithics current waxing with local erosion was followed by pulsing unsteady waning recorded in repeated sets of graded tuff reversion to magmatic activity was marked by hybrid deposition as coarse pumice fallout and juvenile ballistics entered pyroclastic currents to form stratified pumice block tuff increasingly energetic flow is recorded in 9 m of mainly massive lapilli tuff that includes evidence of widespread scour and bypass lithic rich layers record incremental onset of edifice disruption due to magma withdrawal laterally variable stratification and load structures show that the pdc was unsteady and highly non uniform at times with locally rapid aggradation of gas rich ignimbrite climactic edifice disruption is marked by a lithic block layer in erosional contact with the underlying ignimbrite recording intense pyroclastic current activity and widespread bypass of material to distal volcano slopes pumice block breccia 10 m thick and with blocks up to 1 2 m in diameter forms the top of the succession and registers modification of the magmatic plumbing the timing of collapse to form a major summit depression is uncertain however the abrupt termination of the proximal aggradation of coarse breccia with no record there of any waning stage pyroclastic currents suggests subsidence at that time conceivably with formation of a caldera that contained late erupted material

variations in welding characteristics within the plinian air fall deposit of the middle pumice eruption santorini greece abstract the welded plinian air fall deposit of the middle pumice a mp a eruption santorini greece 144 6 ka was analysed in order to document welding characteristics and determine the factors that control welding due to the sintering of hot ash to block sized pyroclasts there are vertical and lateral variations in welding intensity with welding increasing upwards within deposit sections and decreasing laterally away from the source four welding grades are distinguished a densely welded b slightly welded c tack welded and d non welded lateral welding zones are defined by the highest welding grade observed zone a densely welded 3 7 km pumice density increases and porosity decreases with welding with the most densely welded part having a density of 2290 kg m 3 and a porosity of 5 distal non welded pumices have a density of 370 kg m 3 and porosities of 75 clast oblateness varies from 0 79 in the densely welded proximal deposit sections to 0 54 in the distal non welded deposits in southern thera strain determined using the rf method indicates that the deposit is moderately flattened but relatively undeformed the mp a deposit is dacitic to andesitic in composition becoming more mafic with stratigraphic height where the degree of welding is highest welding is controlled by geochemical variations compactional load and local variations in accumulation rate and clast sizes

an asymptotic theory for the interaction of waves and currents in coastal waters a multi scale asymptotic theory is derived for the evolution and interaction of currents and surface gravity waves in water of finite depth under conditions typical of coastal shelf waters outside the surf zone the theory provides a practical and useful model with which wave current coupling may be explored without the necessity of resolving features of the flow on space and time scales of the primary gravity wave oscillations the essential nature of the dynamical interaction is currents modulating the slowly evolving phase of the wave field and waves providing both phase averaged forcing of long infra gravity waves and wave averaged vortex and bernoulli head forces and hydrostatic static set up for the low frequency current and sea level evolution equations analogous relations are derived for wave averaged material tracers and density stratification that include advection by horizontal stokes drift and by a vertical stokes pseudo velocity that is the incompressible companion to the horizontal stokes velocity illustrative solutions are analysed for the special case of depth independent currents and tracers associated with an incident surface wave field and a vortex with o 1 rossby number above continental shelf topography

cooling degassing and compaction of rhyolitic ash flow tuffs a computational model previous models of degassing cooling and compaction of rhyolitic ash flow deposits are combined in a single computational model that runs on a personal computer the model applies to a broader range of initial and boundary conditions than riehle s earlier model which did not integrate heat and mass flux with compaction and which for compound units was limited to two deposits model temperatures and gas pressures compare well with simple measured examples the results indicate that degassing of volatiles present at deposition occurs within days to a few weeks compaction occurs for weeks to two to three years unless halted by devitrification near emplacement temperatures can persist for tens of years in the interiors of thick deposits even modest rainfall significantly chills the upper parts of ash deposits but compaction in simple cooling units ends before chilling by rainwater influences cooling of the interior of the sheet rainfall does however affect compaction at the boundaries of deposits in compound cooling units because the influx of heat from the overlying unit is inadequate to overcome heat previously lost to vaporization of water three density profiles from the matahina ignimbrite a compound cooling unit are fairly well reproduced by the model despite complexities arising from numerous cooling breaks uncertainties in attempts to correlate in detail among the profiles may be the result of the non uniform distribution of individual deposits regardless it is inferred that model compaction is approximately valid thus the model should be of use in reconstructing the emplacement history of compound ash deposits for inferring the depositional environments of ancient deposits and for assessing how long deposits of modern ash flows are capable of generating phreatic eruptions or secondary ash flows

laboratory measurements of the vertical structure of rip currents 1 this paper describes the three dimensional variation of rip currents through the use of experimental measurements of rip currents in a directional wave basin the rip currents are unstable appearing sporadically at any given location the vertical profile of the rip current is found to vary from depth uniform inside the channel to depth varying further offshore offshore from the channel the rip current has much stronger velocities at the surface than near the bottom the instantaneous profiles twist rapidly over depth farther offshore and are fairly uniform in the channel the depth variations are shown to be sensitive to the total volume flux in the rip

vertical structure of dissipation in the nearshore abstract the vertical structure of the dissipation of turbulence kinetic energy was observed in the nearshore region 3 2 m mean water depth with a tripod of three acoustic doppler current meters off a sandy ocean beach surface and bottom boundary layer dissipation scaling concepts overlap in this region no depth limited wave breaking occurred at the tripod but wind induced whitecapping wave breaking did occur dissipation is maximum near the surface and minimum at middepth with a secondary maximum near the bed the observed dissipation does not follow a surfzone scaling nor does it follow a log layer surface or bottom boundary layer scaling at the upper two current meters dissipation follows a modified deep water breaking wave scaling vertical shear in the mean currents is negligible and shear production magnitude is much less than dissipation implying that the vertical diffusion of turbulence is important the increased near bed secondary dissipation maximum results from a decrease in the tu

observations of sand bar evolution on a natural beach waves currents and the location of the seafloor were measured on a barred beach for about 2 months at nine locations along a cross shore transect extending 255 m from 1 to 4 m water depth the seafloor location was measured nearly continuously even in the surf zone during storms with sonar altimeters mounted on fixed frames the crest of a sand bar initially located about 60 m from the shoreline moved 130 m offshore primarily when the offshore significant wave height exceeded about 2 m with 1 5 m of erosion near the initial location and 1 m of accretion at the final location an energetics type sediment transport model driven by locally measured near bottom currents predicts the observed offshore bar migration but not the slow onshore migration observed during low energy wave conditions the predicted offshore bar migration is driven primarily by cross shore gradients in predicted suspended sediment transport associated with quasi steady near bottom offshore flows these strong 50 cm s currents intensified near the bar crest by wave breaking are predicted to cause erosion on the shoreward slope of the bar and deposition on the seaward side the feedback amoung morphology waves circulation and sediment transport thus forces offshore bar migration during storms

tephra fountaining rheomorphism and spatter flow during emplacement of the pitigliano tuffs latera caldera italy abstract toward the end of the main ash flow phase ca 156 ka of the latera caldera central italy explosive eruptions near the nw caldera rim produced coarse grained tephra exposed in 35 m high faces of the toscapomice casa collina quarry the pyroclastic sequence fills a narrow sw ne paleovalley and records the near continuous eruption of a compositionally zoned magma batch white phonolitic pumice clasts abruptly grade upward to and partly intrude black spatter like pumice fragments also of phonolite composition this sequence in turn is overlain by densely welded tuff that grades upward to tephriphonolitic scoriae and ash the upper welded part of this sequence referred to as the vulcanite complessa di pitigliano has long been among the more enigmatic deposits in the latera area this sequence displays evidence for both fall and flow emplacement and is here interpreted as an ash fountain fed deposit that locally welded as spatter yet became sufficiently fluidized in distal parts to behave as a spatter rich pyroclastic flow this mechanism requires that the eruption underwent abrupt transition from a vigorously convecting column to a weakly convecting ash fountain and that this period of explosive activity culminated with unusually high accumulation rates the rapidly emplaced tephra retained sufficient heat to weld by compaction and undergo rheomorphism close to the vent yet contained high enough proportions of fluidized dust to have flowed outward along the northern caldera rim and eventually to have welded by vapor phase sintering

physical volcanology and eruption dynamics of peralkaline agglutinates from pantelleria peralkaline rhyolitic lava like lobes showing direct evidence for a spatter fed origin are associated with eruptive centres that document a transition from explosive to effusive fountain fed activity owing to the preservation of spatter clasts clast dimensions can be used to model the eruptive dynamics of these deposits we conducted an integrated field experimental and theoretical study of the cala di tramontana centre pantelleria italy with the aim to better understand its eruptive behaviour this centre is composed of four units and a close association of fall lapilli tack welded agglutinate and spatter fed lava like lobes these units were fed initially from a fissure vent and later from a circular vent for the last erupted lobe field evidence indicates that fall out accumulated rapidly coalescing into a 10 m thick deposit that flowed downslope and became lava like high eruption rates and high heat flows are interpreted to promote welding of spatter proximal to the vent overburden pressures and thermal insulation from the accumulating spatter caused complete homogenisation of spatter within the interior of the flow laboratory vesiculation experiments show that peralkaline obsidian can vesiculate at temperatures as low as 620 c over a 4 hour period and indicate that airborne agglutinate can deform and weld rapidly within minutes of landing we measured viscosity on a natural pantellerian sample using the parallel plate method over a temperature range of 560 600 c viscosities of 1010 1011 pa s and an activation energy of 311 kj mol were obtained based on undeformed clast sizes and densities eruption dynamics modelling indicates that gas eruption velocities ranged from 90 to 130 m s 1 erupted mass fluxes were 200 kg s 1 m 1 and 2 104 kg s 1 from the fissure and localised circular vents respectively magmatic viscosities of between 105 and 107 pa s for t 750 850 c precluded intermittent strombolian activity due to gas bubble coalescence in addition the amount of magmatic water available to drive the eruption fountains ranged from 0 4 to 0 6 wt significantly less than the estimated 1 5 wt of exsolved volatiles implying that significant passive degassing occurred

proximal tephra hazards recent eruption studies applied to volcanic risk in the auckland volcanic field new zealand abstract auckland new zealand is unique in being a metropolitan area built on an active volcanic field despite the small size and intensity of auckland eruptions the risk from tephra fall is high because of the high density of buildings and lifelines the nature of this threat can be evaluated by comparisons with historical strombolian and hawaiian eruptions which have occurred in non populated areas cone building phases of such eruptions are typically protracted i e weeks to months in duration prolonging the period during which emergency managers will have to fine tune mitigation for numerous parameters such as fluctuations in intensity and wind shifts rapid cone growth during future eruptions will define a region of some 30 to 100 ha where complete destruction will occur on a time scale of hours the cost of this destruction is likely to range between nz 200m and nz 1 4b ca us 130m to us 900m beyond this we have modeled the cumulative long term effect of the build up of a downwind blanket of lapilli and ash by estimating accumulation rates for three phases of the 1959 k lauea iki eruption in hawai i the effect of changing wind direction was evaluated using low level wind data from auckland these results show that intervals between 4 and 100 h will lapse before onset of significant damage to buildings

cooling and welding history of the bishop tuff in adobe valley and chidago canyon california abstract a numerical model for cooling and welding of ash flow tuffs was developed to obtain a quantitative understanding of the welding compaction that occurs during the cooling of ash flow sheets and to evaluate the relative effects of emplacement temperature thickness and emplacement histories on compaction zonation density profiles of large ash flow sheets this model includes a set of two phase compressible navier stokes equations for the transport of mass momentum and energy for a variable density volatile outfluxing through a porous media ash flow tuff with this model we calculated theoretical compaction profiles density vs elevation to match actual data measured in sections of bishop tuff compaction profiles from the adobe basin indicate that there were 3 periods of non deposition 5 10 and 40 days separating 4 distinct rapidly emplaced packets rep of pyroclastic flow deposition in contrast the 3 periods of quiescence 400 20 and 800 days between the 4 reps in chidago canyon were considerably longer these data constrain models of eruption for the bishop tuff by implying an eruption cycle that lasted longer than 3 years the average calculated deposition temperatures for all 4 reps in the adobe basin are fairly uniform at 667 33 c in chidago canyon two of the reps had a higher deposition temperature 660 c than the other two 534 c

oceanic turbulence dissipation measurements in swade abstract recent experiments measuring turbulence dissipation rates in the upper ocean can be divided into two types those supporting an analogy between the upper ocean and lower atmosphere with dissipation rates following wall layer behavior and those finding oceanic dissipation rates to be much higher than wall layer predictions in an attempt to reconcile these two diverse acts of observations terray et al proposed a wave dependent scaling of the dissipation rate based on the significant wave height and the rate of energy input from the wind to the waves their parameterization was derived from observations of strongly forced fetch limited waves although they conjectured that it would apply in typical oceanic conditions as well this paper reports new measurements of turbulent kinetic energy dissipation made in the north atlantic ocean from a swath ship during the recent surface waves dynamics experiments swade these data support the scaling of terray et al verifying its validity when applied

spectral wave modeling in fringing reef environments abstract this study examines the implementation and validity of phase averaged spectral models in describing wave transformation over fringing reefs the wave breaking mechanism over the abrupt reef crest dissipation due to bottom friction and nonlinear energy transfer over the reef flat set the problem apart from general applications in non tropical settings the simulating wave nearshore swan model which is widely used in coastal engineering applications has embedded parameterizations of these surf zone processes for examination in addition we extend the model to include a recently implemented bottom friction source term for tropical reefs comparisons of model predictions with laboratory and field observations over fringing reefs identify promising wave breaking and bottom friction parameterizations for calibration the calibrated parameterizations enable swan to reproduce the observed wave height and setup and extend the applicability of spectral models to fringing reef environments swan however lacks the parameterization to describe the nonlinear energy transfer toward the infra gravity band that was observed in the laboratory and field studies

large scale laboratory observations of wave breaking turbulence over an evolving beach 1 wave breaking turbulence over an evolving beach was observed in a large scale laboratory flume as part of the cross shore sediment transport experiment crosstex the data set included comprehensive measurements of water surface elevation fluid velocity and morphology for irregular waves under erosive and accretive wave conditions for the both conditions the beach reached a quasi equilibrium state defined as when the bar shape was stable wave breaking characteristics such as wave heights average rate of energy dissipation by bores and surf similarity parameter were investigated in response to morphodynamics of the bar turbulent kinetic energy tke was estimated using the method by shaw and trowbridge 2001 as the beach evolved a less amount of tke was observed at the trough for the erosive case while more tke was observed at the trough for the accretive case it was also found that the temporal variation of the time averaged tke were closely associated with the average rate of energy dissipation by bores comparing with the bar trough the vertical distribution of nondimensionalized time averaged tke and turbulence dissipation rate at the bar crest showed a large increase near the bottom probably due to a strong cross shore rms velocity finally in the quasi equilibrium state time averaged tke and turbulence dissipation rate at the bar trough were smaller than those inside the surf zone inside the surf zone significant turbulence intensities were observed due to a second breaking on a shallow water depth

spectral wave dissipation over a barrier reef 1 a 2 week field experiment was conducted to measure surface wave dissipation on a barrier reef at kaneohe bay oahu hawaii wave heights and velocities were measured at several locations on the fore reef and the reef flat which were used to estimate rates of dissipation by wave breaking and bottom friction dissipation on the reef flat was found to be dominated by friction at rates that are significantly larger than those typically observed at sandy beach sites this is attributed to the rough surface generated by the reef organisms which makes the reef highly efficient at dissipating energy by bottom friction results were compared to a spectral wave friction model which showed that the variation in frictional dissipation among the different frequency components could be described using a single hydraulic roughness length scale surveys of the bottom roughness conducted on the reef flat showed that this hydraulic roughness length was comparable to the physical roughness measured at this site on the fore reef dissipation was due to the combined effect of frictional dissipation and wave breaking however in this region the magnitude of dissipation by bottom friction was comparable to wave breaking despite the existence of a well defined surf zone there under typical wave conditions the bulk of the total wave energy incident on kaneohe bay is dissipated by bottom friction not wave breaking as is often assumed for sandy beach sites and other coral reefs

observing surf zone dispersion with drifters abstract surf zone dispersion is studied using drifter observations collected within about 200 m of the shoreline at depths of less than about 5 m on a beach with approximately alongshore uniform bathymetry and waves there were about 70 individual drifter releases each 10 20 min in duration on two consecutive days on the first day the sea swell significant wave height hs was equal to 0 5 m and mean alongshore currents were moderate 0 1 m s 1 on the second day the obliquely incident waves were larger with hs equal to 1 4 m and at some surf zone locations was greater than 0 5 m s 1 the one particle diffusivity was larger with larger waves and stronger currents on both days the one particle diffusivity tensor is nonisotropic and time dependent the major axis is initially parallel to the cross shore direction but after a few wave periods it is aligned with the alongshore direction in both the along and cross shore directions the asymptotic diffusivity is reached sooner within r

surf zone surface retention on a rip channeled beach the retention of floating matter within the surf zone on a rip channeled beach is examined with a combination of detailed field observations obtained during the rip current experiment and a three dimensional 3 d wave and flow model the acoustic doppler current profiler observed hourly vertical cross shore velocity structure variability over a period of 3 days with normally incident swell is well reproduced by the computations although the strong vertical attenuation of the subsurface rip current velocities at the most offshore location outside the surf zone in 4 m water depth is not well predicted corresponding mean alongshore velocities are less well predicted with errors on the order of 10 cm s for the most offshore sensors model calculations of very low frequency motions vlfs with o 10 min timescales typically explain over 60 of the observed variability both inside and outside of the surf zone the model calculations also match the mean rip current surface flow field inferred from gps equipped drifter trajectories seeding the surf zone with a large number of equally spaced virtual drifters the computed instantaneous surface velocity fields are used to calculate the hourly drifter trajectories collecting the hourly drifter exits good agreement with the observed surf zone retention is obtained provided that both stokes drift and vlf motions are accounted for in the modeling of the computed drifter trajectories without stokes drift the estimated number of virtual drifter exits is o 80 almost an order of magnitude larger than the o 20 of observed exits during the drifter deployments conversely when excluding the vlf motions instead the number of calculated drifter exits is less than 5 thus significantly underestimating the number of observed exits

sequence and eruptive style of the 1783 eruption of asama volcano central japan a case study of an andesitic explosive eruption generating fountain fed lava flow pumice fall scoria flow and forming a cone the 3 month long eruption of asama volcano in 1783 produced andesitic pumice falls pyroclastic flows lava flows and constructed a cone it is divided into six episodes on the basis of waxing and waning inferred from records made during the eruption episodes 1 to 4 were intermittent vulcanian or plinian eruptions which generated several pumice fall deposits the frequency and intensity of the eruption increased dramatically in episode 5 which started on 2 august and culminated in a final phase that began on the night of 4 august lasting for 15 h this climactic phase is further divided into two subphases the first subphase is characterized by generation of a pumice fall whereas the second one is characterized by abundant pyroclastic flows stratigraphic relationships suggest that rapid growth of a cone and the generation of lava flows occurred simultaneously with the generation of both pumice falls and pyroclastic flows the volumes of the ejecta during the first and second subphases are 0 21 km3 dre and 0 27 km3 dre respectively the proportions of the different eruptive products are lava cone pumice fall 84 11 5 in the first subphase and lava cone pyroclastic flow 42 2 56 in the second subphase the lava flows in this eruption consist of three flow units l1 l2 and l3 and they characteristically possess abundant broken phenocrysts and show extensive welding texture these features as well as ghost pyroclastic textures on the surface indicate that the lava was a fountain fed clastogenic lava a high discharge rate for the lava flow up to 106 kg s may also suggest that the lava was initially explosively ejected from the conduit the petrology of the juvenile materials indicates binary mixing of an andesitic magma and a crystal rich dacitic magma the mixing ratio changed with time the dacitic component is dominant in the pyroclasts of the first subphase of the climactic phase while the proportion of the andesitic component increases in the pyroclasts of the second subphase the compositions of the lava flows vary from one flow unit to another l1 and l3 have almost identical compositions to those of pyroclasts of the first and second subphases respectively while l2 has an intermediate composition suggesting that the pyroclasts of the first and second subphases were the source of the lava flows and were partly homogenized during flow the complex features of this eruption can be explained by rapid deposition of coarse pyroclasts near the vent and the subsequent flowage of clastogenic lavas which were accompanied by a high eruption plume generating pumice falls and or pyroclastic flows

undertow over a barred beach the spatial distribution of the mean cross shore flow undertow over a barred beach is examined with field data obtained on three energetic wave days during the duck94 experiment the vertical structure of the undertow is modeled using a turbulent eddy viscosity closure and includes the important effects of wave breaking described using the roller concept and convective acceleration of the current other than a more realistic description of observed turbulence variations a depth dependent eddy viscosity compared with a constant does not improve the agreement between predicted and observed undertow profiles the effect of using different boundary conditions is investigated by extending the formulations of stive and wind 1986 and svendsen et al 1987 to include random waves by ensemble averaging over the wave height distribution the contribution of breaking wave rollers to the surface mass flux can be of the same order or greater than the contribution associated with the organized wave motion the largest discrepancies between model predictions and observations occur over the sandbar where the mass transport of the breaking waves appears to be underestimated

ranking welding intensity in pyroclastic deposits welding of pyroclastic deposits involves flattening of glassy pyroclasts under a compactional load at temperatures above the glass transition temperature progressive welding is recorded by changes in the petrographic e g fabric and physical e g density properties of the deposits mapping the intensity of welding can be integral to studies of pyroclastic deposits but making systematic comparisons between deposits can be problematical here we develop a scheme for ranking welding intensity in pyroclastic deposits on the basis of petrographic textural observations e g oblateness of pumice lapilli and micro fabric orientation and measurements of physical properties including density porosity point load strength and uniaxial compressive strength our dataset comprises measurements on 100 samples collected from a single cooling unit of the bandelier tuff and parallel measurements on 8 samples of more densely welded deposits the proposed classification comprises six ranks of welding intensity ranging from unconsolidated rank i to obsidian like vitrophyre rank vi and should allow for reproducible mapping of subtle variations in welding intensity between different deposits the application of the ranking scheme is demonstrated by using published physical property data on welded pyroclastic deposits to map the total accumulated strain and to reconstruct their pre welding thicknesses

rheology of welding inversion of field constraints at present the mechanisms and rheological behaviour of pyroclastic deposits during welding and compaction are poorly understood here we explore the extent to which the rheological properties of pyroclastic deposits are constrained by physical property distributions in welded ignimbrite physical properties of samples from a 20 m section of the bandelier tuff new mexico are used as proxies for strain the observed strain et is ascribed to a combination of a time dependent viscous compaction ev and a time independent mechanical compaction em described by

flow and turbulence structure in a hypertidal estuary with the world s biggest tidal bore turbulent and flow structure associated with breaking tidal bores are deliberately investigated on the basis of field measurements high resolution velocity and hydrographic data are collected in the middle qiantang estuary by a vertical array of acoustic doppler velocimeters and optical backscatter sensors collaborated with a bottom mounted acoustic doppler current profiler besides obvious variations in diurnal and spring neap tidal cycles the estuarine dynamics is featured by extreme asymmetry in flood and ebb tides the flood tide is abnormally accelerated to generate tidal bores at the first 10 min or more with breaking or undular configurations at the front the occurrence of peak flow velocity turbulent kinetic energy tke and tke dissipation rate e is definitely associated with breaking bores with their values several times to 2 orders of magnitude larger than the corresponding secondary peak values during the maximum ebb flows flow and turbulence dynamics are significantly affected by the tidal bore froude number a sandwich e structure is clear exhibited with the maximum value at the surface secondary maximum near the bed and the minimum at the intermediate dual tke sources are indicated by an approximate local balance between shear production and dissipation near the bottom and a top down tke dissipation using the modified froude scaling in the vertical water column the highly elevated dissipation by breaking bores is comparable to that by intense breaking waves in the surf zone and the former potentially penetrates the entire water column to produce extreme sediment resuspension events in combination with intense bottom shear stress

cross shore deformation of a surfzone released dye plume by an internal tide on the inner shelf abstractan inner shelf is dye plume that formed following a 3 84 h early morning surfzone sz dye release off of imperial beach california is analyzed with in situ and aerial remotely sensed o

formation of the green tuff pantelleria the strongly peralkaline green tuff pantelleria is an example of a thin densely welded air fall tuff which mantles an area of at least 85 km2 offshore the tuff is correlated with the y 6 ash layer in the central mediterranean sea and the total volume of the eruption is estimated at 7 km3 d r e new petrological data suggests that the tuff was erupted from a zoned magma chamber containing a cooler more fractionated upper zone relative to be bulk of the magma analysis of the distribution of accessory lithic fragments in terms of existing models of eruption dynamics indicates emplacement by a plinian type eruption it is shown that due to the low viscosity of pantelleritic ejecta dense welding can occur at moderate tephra accumulation rates and a rate of the order of 1 cm minute is suggested for the green tuff this yields an estimate for the eruption duration of rather less than one day it is predicted that welded tuff should be formed during large plinian eruptions of pantelleritic magma and therefore that welded airfall tuffs should be common in areas of peralkaline volcanism

observations and a model of undertow over the inner continental shelf abstract onshore volume transport stokes drift due to surface gravity waves propagating toward the beach can result in a compensating eulerian offshore flow in the surf zone referred to as undertow observed offshore flows indicate that wave driven undertow extends well offshore of the surf zone over the inner shelves of martha s vineyard massachusetts and north carolina theoretical estimates of the wave driven offshore transport from linear wave theory and observed wave characteristics account for 50 or more of the observed offshore transport variance in water depths between 5 and 12 m and reproduce the observed dependence on wave height and water depth during weak winds wave driven cross shelf velocity profiles over the inner shelf have maximum offshore flow 1 6 cm s 1 and vertical shear near the surface and weak flow and shear in the lower half of the water column the observed offshore flow profiles do not resemble the parabolic profiles with maximum flow at middepth observed within the su

wave transformation across the inner surf zone sea and swell wave heights observed on transects crossing the mid and inner surf zone on three beaches a steep concave up beach a gently sloped approximately planar beach and a beach with an approximately flat terrace adjacent to a steep foreshore were depth limited i e approximately independent of the offshore wave height consistent with previous observations the wave evolution is well predicted by a numerical model based on the one dimensional nonlinear shallow water equations with bore dissipation the model is initialized with the time series of sea surface elevation and cross shore current observed at the most offshore sensors located about 50 to 120 m from the mean shoreline in mean water depths 0 80 to 2 10 m the model accurately predicts the cross shore variation of energy at both infragravity nominally 0 004 f 0 05 hz and sea swell here 0 05 f 0 18 hz frequencies in models of surf zone hydrodynamics wave energy dissipation is frequently parameterized in terms of s the ratio of the sea swell significant wave height to the local mean water depth the observed and predicted values of s increase with increasing beach slope and decreasing normalized by a characteristic wavenumber k water depth kh and are well correlated with kh a measure of the fractional change in water depth over a wavelength errors in the predicted individual values of s are typically less than 20 it has been suggested that infragravity motions affect waves in the sea swell band and hence s but this speculation is difficult to test with field observations numerical simulations suggest that for the range of conditions considered here s is insensitive to infragravity energy levels

a rare occurrence of a crater filling clastogenic extrusive coherent kimberlite victor northwest ontario canada kimberlite pipes can contain significant proportions of dark and dense kimberlite that have mostly been interpreted as intrusive coherent hypabyssal in origin this study reports a well documented occurrence of a fresh intra crater clastogenic extrusive coherent kimberlite that is concluded to have formed as a result of lava fountaining this paper focuses on a dark dense competent generally crystal rich massive kimberlite unit within the victor northwest kimberlite pipe ontario canada using a comprehensive volcanological and petrographic analysis of all available drill cores it is shown that this unit has a fresh well crystallised coherent groundmass and is extrusive and pyroclastic in origin the proposed clastogenic coherent extrusive origin is based on deposit morphology gradational contacts to enveloping pyroclastic units as well as the presence of remnant pyroclast outlines and angular broken olivines this paper and an increasing number of other studies suggest that fragmental extrusive coherent kimberlite in intra crater settings may be more common than previously thought the emplacement history and volcanology of these pipes need to be reconsidered based on the emerging importance of this particular kimberlite facies

observations and modeling of a tidal inlet dye tracer plume a 9 km long tracer plume was created by continuously releasing rhodamine wt dye for 2 2 h during ebb tide within the southern edge of the main tidal channel at new river inlet nc on 7 may 2012 with highly obliquely incident waves and alongshore winds over 6 h from release coawst coupled roms and swan including wave wind and tidal forcing modeled dye compares well with aerial hyperspectral and in situ observed dye concentration dye first was transported rapidly seaward along the main channel and partially advected across the ebb tidal shoal until reaching the offshore edge of the shoal dye did not eject offshore in an ebb tidal jet because the obliquely incident breaking waves retarded the inlet mouth ebb tidal flow and forced currents along the ebb shoal the dye plume largely was confined to 4 m depth dye was then transported downcoast in the narrow few 100 m wide surfzone of the beach bordering the inlet at 0 3 m s 1 driven by wave breaking over 6 h the dye plume is not significantly affected by buoyancy observed dye mass balances close indicating all released dye is accounted for modeled and observed dye behaviors are qualitatively similar the model simulates well the evolution of the dye center of mass lateral spreading surface area and maximum concentration as well as regional inlet and ocean dye mass balances this indicates that the model represents well the dynamics of the ebb tidal dye plume details of the dye transport pathways across the ebb shoal are modeled poorly perhaps owing to low resolution and smoothed model bathymetry wave forcing effects have a large impact on the dye transport

the 5 660 ybp boqueron explosive eruption teide pico viejo complex tenerife quantitative hazard assessments of active volcanoes require an accurate knowledge of the past eruptive activity in terms of eruption dynamics and the stratified products of eruption teide pico viejo tpv is one of the largest volcanic complexes in europe but the associated eruptive history has only been constrained based on very general stratigraphic and geochronological data in particular recent studies have shown that explosive activity has been significantly more frequently common than previously thought our study contributes to characterization of explosive activity of tpv by describing for the first time the subplinian eruption of el boqueron 5 660 ybp a satellite dome located on the northern slope of the pico viejo stratovolcano stratigraphic data suggest complex shifting from effusive phases with lava flows to highly explosive phase that generated a relatively thick and widespread pumice fallout deposit this explosive phase is classified as a subplinian eruption of vei 3 that lasted for about 9 15 h and produced a plume with a height of up to 9 km above sea level i e 7 km above the vent mer of 6 9 8 2 105 kg s the tephra deposit minimum bulk volume of 4 6 107 m3 was dispersed to the ne by up to 10 m s winds a similar eruption today would significantly impact the economy of tenerife e g tourism and aviation with major consequences mainly for the communities around the icod valley and to a minor extent the orotava valley this vulnerability shows that a better knowledge of the past explosive history of tpv and an accurate estimate of future potentials to generate violent eruptions is required in order to quantify and mitigate the associated volcanic risk

emplacement history of a low viscosity fountain fed pantelleritic lava flow abstract the strongly peralkaline 8 ka flow mayor island new zealand was emplaced as a low viscosity fountain fed lava flow the flow stratigraphy comprises from top to base a finely vesicular pumiceous carapace an upper obsidian layer central crystalline rhyolite a lower obsidian layer incorporating a crumble breccia above a fall lapilli unit rare relict clasts welded within the lowermost 0 5 m of the lower obsidian layer support a fountain fed origin for the 8 ka flow five physical parameters density porosity microlite size void and autoclast aspect ratios and water content were measured throughout the thickness of the lava flow and show that prolonged vesiculation occurred in the upper 33 of the flow thickness and that autoclast and pyroclast shapes and microlite lengths were influenced by the thermal conditions of the lava after eruption crystallisation of the flow interior commenced before the flow stopped moving compared with calc alkaline rhyolites the high flow temperature 950 c and peralkaline chemistry contributed to a less polymerised low viscosity melt log 6 4 pa s these data and structural observations of the 8 ka flow suggest that near complete homogenisation and remobilisation of spatter from a lava fountain occurred on the caldera rim producing a distally tapering lava sheet that also spilled back down the caldera wall towards the vent

observations of turbulence within the surf and swash zone of a field scale sandy laboratory beach abstract current coastal evolution models generally lack the ability to accurately predict bed level change in shallow

estimating wave energy dissipation in the surf zone using thermal infrared imagery thermal infrared ir imagery is used to quantify the high spatial and temporal variability of dissipation due to wave breaking in the surf zone the foam produced in an actively breaking crest or wave roller has a distinct signature in ir imagery a retrieval algorithm is developed to detect breaking waves and extract wave roller length using measurements taken during the surf zone optics 2010 experiment at duck nc the remotely derived roller length and an in situ estimate of wave slope are used to estimate dissipation due to wave breaking by means of the wave resolving model by duncan 1981 the wave energy dissipation rate estimates show a pattern of increased breaking during low tide over a sand bar consistent with in situ turbulent kinetic energy dissipation rate estimates from fixed and drifting instruments over the bar when integrated over the surf zone width these dissipation rate estimates account for 40 69 of the incoming wave energy flux the duncan 1981 estimates agree with those from a dissipation parameterization by janssen and battjes 2007 a wave energy dissipation model commonly applied within nearshore circulation models

modeling wave effects on storm surge and coastal inundation abstract we present a parametric study of surface wave effects on storm surge and coastal inundation hurricane wind forcing terms atmosphere pressure gradient terms and radiation open boundary conditions are implemented into an existing quasi 3d nearshore model nearcom tvd which uses a shock capturing tvd scheme and can better simulate the wetting drying process during inundation than a conventional finite difference model systematic numerical experiments are carried out in an idealized continental shelf beach land system to identify the role of waves in modeling storm surge and inundation under different storm characteristics four storm parameters including storm intensity storm size translation speed and incident angle are investigated modeling results reveal that the presence of waves can increase the maximum storm surge heights significantly through wave setup and the contribution of waves varies considerably depending on the storm characteristics in addition to direct wave forcing the wave enhanced bottom stress in the surfzone also promotes higher wave setup and hence higher surge heights waves also have a major influence on the maximum inland inundation distance however we find that waves do not always favor more inundation as expected for storms traveling at very slow translation speeds or nearly parallel to the coast waves surprisingly exert a negative effect on the maximum inundation distance we argue that wave enhanced bottom stress combined with longer forcing duration in such storms counteract the positive effect of wave setup and thus less inundation is predicted in wave current coupled simulations our results highlight the necessity of fully incorporating wave effects in storm surge and inundation modeling

complex proximal deposition during the plinian eruptions of 1912 at novarupta alaska proximal 3 km deposits from episodes ii and iii of the 60 h long novarupta 1912 eruption exhibit a very complex stratigraphy the result of at least four transport regimes and diverse depositional mechanisms they contrast with the relatively simple stratigraphy and inferred emplacement mechanisms for the previously documented better known medial distal fall deposits and the valley of ten thousand smokes ignimbrite the proximal products include alternations and mixtures of both locally and regionally dispersed fall ejecta and numerous thin complex deposits of pyroclastic density currents pdcs with no regional analogs the locally dispersed component of the fall deposits forms sector confined wedges of material whose thicknesses halve radially from and concentrically about the vent over distances of 100 300 m cf several kilometers for the medial distal fall deposits this locally dispersed fall material and many of the associated pdc deposits is rich in andesitic and banded pumices and richer in shallow derived wall rock lithics in comparison with the coeval medial fall units of almost entirely dacitic composition there are no marked contrasts in grain size in the near vent deposits however between locally and widely dispersed beds and all samples of the proximal fall deposits plot as a simple continuation of grain size trends for medial distal samples associated pdc deposits form a spectrum of facies from fines poor avalanched beds through thin bedded landscape mantling beds to channelized lobes of pumice block rich ignimbrite the origins of the novarupta near vent deposits are considered within a spectrum of four transport regimes 1 sustained buoyant plume 2 fountaining with co current flow 3 fountaining with counter current flow and 4 direct lateral ejection the novarupta deposits suggest a model where buoyant stable regime 1 plumes characterized most of episodes ii and iii but were accompanied by transient and variable partitioning of clasts into the other three regimes only one short period of vent blockage and cessation of the plinian plume occurred separating episodes ii and iii which was followed by a single pdc interpreted as an overpressured blast involving direct lateral ejection in contrast regimes 2 and 3 were reflected by spasmodic sedimentation from the margins of the jet and perhaps lower plume which were being strongly affected by short lived instabilities these instabilities in turn are inferred to be associated with heterogeneities in the mixture of gas and pyroclasts emerging from the vent of the parameters that control explosive eruptive behavior only such sudden and asymmetrical changes in the particle concentration could operate on time scales sufficiently short to explain the rapid changes in the proximal 1912 products

breaking wave induced cross shore tracer dispersion in the surf zone model results and scalings 1 the dispersion of surf zone tracers including pollutants and bacteria is determined by many processes acting over a range of timescales and space scales breaking waves bores are clearly important to cross shore tracer dispersion in the surf zone but little is known about the dispersal effects of bores here a simple model for bore induced cross shore dispersion are developed based upon the diffusion equation with an eddy diffusivity that propagates with the bores depth uniform tracer and bore induced mixing along with alongshore uniformity are assumed the bores are assumed well developed and the dispersion results are for a self similar constant wave height to water depth ratio surf zone four nondimensional parameters are identified and solution space is explored the tracer center of mass is approximately constant and tracer width grows with the square root of time tracer distribution becomes initially skewed after the passage of the first bore but becomes symmetric after multiple bores have passed the nondimensional tracer patch growth and dilution rates depend strongly upon the nondimensional phase speed and wave period the simple model results are consistent with the a boussinesq wave model where the breaking wave eddy viscosity is used for the bore eddy diffusivity the scaling of the dimensional parameters regarding the bore eddy diffusivity and the ranges of the nondimensional parameters are examined covariation of the nondimensional phase speed and wave period suggest that nondimensional tracer dispersion is largely cross shore independent

miocene rhyolitic welded tuff infilling a funnel shaped eruption conduit shiotani southeast of matsue sw japan at shiotani sw japan rhyolitic welded tuff forms a steep sided funnel shaped body confined by paleogene granitic rocks to an elliptical area 1 1 5 km across the shiotani welded tuff is pervasively welded and foliated concordantly with the contact that dips inward at angles of 70 90 in contrast nearby contemporary volcaniclastic deposits are non welded and gently inclined near the contact with the granite the tuff is plastically deformed and shows lineations that plunge inward at angles of 40 65 lithic and crystal clasts in the rheomorphic outer part are rotated in a plane normal to the foliations and parallel to the lineations indicating downward flow of the welded tuff the geometry and internal structures suggest that the shiotani welded tuff was emplaced and welded in a funnel shaped eruption conduit upon collapse of a plinian or phreatoplinian eruption column the majority of the conduit filling pyroclasts probably fell back en masse into the conduit heat and steam from underlying magma and diffusion of interstitial volatiles into the glass perhaps reduced the viscosity of juvenile pyroclasts and facilitated welding in the conduit especially at deep levels the hot welded pyroclasts then flowed down the conduit wall during welding compaction and retreat of the magma these processes resulted in increased welding toward the contacts and welding foliations concordant with the steep wall emplacement of nearby correlative volcaniclastic mass flow deposits in a shelf to upper bathyal environment suggests a possibility that when active the shiotani conduit was under the sea welding compaction would occur even under the sea provided that the steam generated in the upper part of the conduit fill prevented water access

observations of turbulence within a natural surf zone abstract here the reynolds stresses u w and w where u and w are the cross shore alongshore and vertical turbulence velocities respectively and the angle brackets represent time averaging are used to diagnose turbulence dynamics beneath natural breaking surf zone waves the data were collected at truc vert beach france during a 12 day period in 1 3 m water depth with strong cross shore and alongshore currents under high energy wave conditions offshore significant wave heights ranged between 2 and 8 m the u w term is predominantly negative increases with the ratio of wave height hs to water depth h degree of wave breaking and decreases in magnitude toward the bed this supports the view that the cross shore shear stress is due to breaking induced vortices that transport high speed cross shore flow downward and disintegrate close to the bed the occasional positive sign of u w within the lower 15 20 of the water column indicates that sometimes surface generated turbule

complex proximal sedimentation from plinian plumes the example of tarawera 1886 the 1886 eruption of tarawera new zealand was unusual for a plinian eruption because it involved entirely basaltic magma originated in a 17 km long fissure and produced extremely overthickened proximal deposits with a complex geometry this study focuses on an 8 km long segment cutting across mount tarawera where over 50 point source vents were active during the 5 5 h eruption a detailed characterization of the proximal deposits is developed and used to interpret the range of styles and intensities of the vents including changes with time we identify the four vents that contributed most heavily to the plinian fall and evaluate the extent to which current volcanic plume models are compatible with the depositional patterns at tarawera three proximal units are mapped that have phreatomagmatic magmatic and phreatomagmatic characteristics respectively within the magmatic proximal unit beds of like character are grouped into packages and delineated on scaled cross sections package dispersal is quantified by measuring the linear thickness half distance t1 2 in the planes of the fissure walls most packages have localized dispersals low t1 2 indicating that strombolian style activity dominated most vents the more widely dispersed packages high t1 2 reflect contributions from additional transport regimes that were more vigorous but still contributed considerable material to the proximal region we conclude that the geometry of the observed proximal deposits requires three modes of fall transport 1 fallout from the upper portions of the plinian plumes produced principally by vents in four craters 2 sedimentation from the margins of the lower portions of the plinian plumes including the jets and possibly the lower convective regions and 3 ejection by weak strombolian style explosions from vents that did not contribute significant volumes of particles to the high plume we suggest that the curvature of the velocity profile across the jet region of each plume 1 4 km height was important and that the lower velocity at the margins allowed proximal deposition of a large volume of material with a wide grain size range

experimental validation of a 2d overland flow model using high resolution water depth and velocity data summary this paper presents a validation of a two dimensional overland flow model using empirical laboratory data unlike previous publications in which model performance is evaluated as the ability to predict an outlet hydrograph we use high resolution 2d water depth and velocity data to analyze to what degree the model is able to reproduce the spatial distribution of these variables several overland flow conditions over two impervious surfaces of the order of one square meter with different micro and macro roughness characteristics are studied the first surface is a simplified representation of a sinusoidal terrain with three crests and furrows while the second one is a mould of a real agricultural seedbed terrain we analyze four different bed friction parameterizations and we show that the performance of formulations which consider the transition between laminar smooth turbulent and rough turbulent flow do not improve the results obtained with manning or keulegan formulas for rough turbulent flow the simulations performed show that using keulegan formula with a physically based definition of the bed roughness coefficient a two dimensional shallow water model is able to reproduce satisfactorily the flow hydrodynamics it is shown that even if the resolution of the topography data and numerical mesh are high enough to include all the small scale features of the bed surface the roughness coefficient must account for the macro roughness characteristics of the terrain in order to correctly reproduce the flow hydrodynamics

seismic body wave constraint on mechanisms of intermediate depth earthquakes 1 source parameters of six large earthquakes 7 1 mw 7 7 in the depth range between 112 and 277 km from five different subduction zones are derived from teleseismic body waves recorded by global seismic networks except for the 21 october 1995 mexican event which is consistent with the model of simple rupture on a planar surface the investigated earthquakes show complex rupture processes that can be explained by irregularities in the focal region as is the case of shallow events the inferred velocity of the moment release varies between 2 5 and 4 km s corresponding to 40 90 of the shear velocity at the focus four of the six earthquakes show stress drops in the range observed for shallow events 1 10 mpa ruptures extend mainly parallel to the strike of subducting slabs with dimensions reaching up to 50 km the extent of rupture perpendicular to slab dip of generally less than 15 km is comparatively small this suggests that the rupture during large intermediate depth earthquakes propagates predominantly parallel to the strike of the subducting plate and that the seismogenic zone perpendicular to the dip direction is limited to a narrow width the relatively small rupture size perpendicular to slab dip suggests that the rupture process does not extend into regions of significantly different temperatures the spatial extent of the investigated earthquakes is consistent with the orientation of trench parallel faults that are generally observed in near trench outer rise regions suggesting that these events may result from reactivation of such preexisting faults at intermediate depths through dehydration of hydrous minerals concentrated in these zones of weakness depths of most of the earthquakes are consistent with the dehydration embrittlement of serpentine the bolivian earthquake of 23 january 1997 seems to be too deep 277 km for such an explanation

textural studies of vesicles in volcanic rocks an integrated methodology abstract vesicles in volcanic rocks are frozen records of degassing processes in magmas for this reason their sizes spatial arrangements numbers and shapes can be linked to physical processes that drive magma ascent and eruption although numerous techniques have been derived to describe vesicle textures there is no standard approach for collecting analyzing and interpreting vesicular samples here we describe a methodology for techniques that encompass the entire data acquisition process from sample collection to quantitative analysis of vesicle size and number carefully chosen samples from the lower mean and higher density vesicularity endmembers are characterized using image nesting strategies we show that the texture of even microvesicular samples can be fully described using less than 20 images acquired at several magnifications to cover efficiently the range of existing vesicle sizes a new program foams was designed to perform the quantification stage from vesicle measurement to distribution plots altogether this approach allows substantial reduction of image acquisition and processing time while preserving enough user control to ensure the validity of obtained results we present three cameo investigations on basaltic lava flows scoria deposits and pumice layers to show that this methodology can be used to quantify a wide range of vesicle textures which preserve information on a wide range of eruptive conditions

mafic plinian volcanism and ignimbrite emplacement at tofua volcano tonga tofua island is the largest emergent mafic volcano within the tofua arc tonga southwest pacific the volcano is dominated by a distinctive caldera averaging 4 km in diameter containing a freshwater lake in the south and east the latest paroxysmal vei 5 6 explosive volcanism includes two phases of activity each emplacing a high grade ignimbrite the products are basaltic andesites with between 52 wt and 57 wt sio2 the first and largest eruption caused the inward collapse of a stratovolcano and produced the tofua ignimbrite and a sub circular caldera located slightly northwest of the island s centre this ignimbrite was deposited in a radial fashion over the entire island with associated plinian fall deposits up to 0 5 m thick on islands 40 km away common sub rounded and frequently cauliform scoria bombs throughout the ignimbrite attest to a small degree of marginal magma water interaction the common intense welding of the coarse grained eruptive products however suggests that the majority of the erupted magma was hot water undersaturated and supplied at high rates with moderately low fragmentation efficiency and low levels of interaction with external water we propose that the development of a water saturated dacite body at shallow 6 km depth resulted in failure of the chamber roof to cause sudden evacuation of material producing a plinian eruption column following a brief period of quiescence large scale faulting in the southeast of the island produced a second explosive phase believed to result from recharge of a chemically distinct magma depleted in incompatible elements this similar but smaller eruption emplaced the hokula ignimbrite sheet in the northeast of the island a maximum total volume of 8 km3 of juvenile material was erupted by these events the main eruption column is estimated to have reached a height of 12 km and to have produced a major atmospheric injection of gas and tephra recorded in the widespread series of fall deposits found on coral islands 40 80 km to the east in the direction of regional upper tropospheric winds radiocarbon dating of charcoal below the tofua ignimbrite and organic material below the related fall units imply this eruption sequence occurred post 1 000 years bp we estimate an eruption magnitude of 2 24 1013 kg sulphur release of 12 tg and tentatively assign this eruption to the ad 1030 volcanic sulphate spike recorded in antarctic ice sheet records

a new offshore transport mechanism for shoreline released tracer induced by transient rip currents and stratification offshore transport from the shoreline across the inner shelf of early stage larvae and pathogens is poorly understood yet is critical for understanding larval fate and dilution of polluted shoreline water with a novel coupling of a transient rip current trc generating surf zone model and an ocean circulation model we show that transient rip currents ejected onto a stratified inner shelf induce a new previously unconsidered offshore transport pathway for incident waves and stratification typical for southern california in the fall this mechanism subducts surf zone origin tracers and transports them at least 800 m offshore at 1 2 km d analogous to subduction at ocean fronts this mechanism requires both trcs and stratification as trcs are ubiquitous and the inner shelf is often stratified this mechanism may have an important role in exporting early stage larvae pathogens or other tracers onto the shelf

surf zone longshore currents and random waves field data and models abstract analytic and numerical models for longshore currents generated by obliquely incident random waves am compared with field observations five days of observations were selected during which the waves were narrow banded in both frequency and direction in keeping with model assumptions the extensive measurements included radiation stress and wave directional spectra in 9 m depth and a closely spaced array of current and pressure sensors on a line perpendicular to shore the longshore current models are based on balancing the gradient of the radiation stress with the alongshore bed shear and reynold s stresses assuming stationary wave conditions and straight and parallel bottom contours the spatial variation of wave height required to determine the gradient of the radiation stress is modeled using linear random wave theory given hrms in 9 m depth the model predicts hrms at shoreward locations with an average error of less than 9 using a nonlinear bottom shear stress formulation and the meas

scaling surf zone turbulence 1 turbulence in the surf zone the shallow region adjacent to the shoreline has a key role in beach erosion fertilization dispersal and larval settlement of marine invertebrates and microbial contamination dilution in beach waters breaking wave generated the dominant source surf zone turbulence is understood poorly a new surf zone turbulent dissipation rate scaling is derived that collapses new field surf zone observations with relatively high skill compared to other scalings the vertically uniform length scale is 1 6 the water depth and 15 of the wave energy flux gradient is dissipated below the mean surface field and laboratory surf zone turbulence observations are shown to be consistent using the scaling the non dimensional surf zone diffusivity and suspended sediment profile can be applied to sediment transport and a range of biological processes including microbial pathogen contamination of beach waters

formation of clastogenic lava flows during fissure eruption and scoria cone collapse the 1986 eruption of izu oshima volcano eastern japan the 1986 eruption of b fissure at izu oshima volcano japan produced among other products one andesite and two basaltic andesite lava flows locally the three flows resemble vent effused holocrystalline blocky or aa lava however remnant clast outlines can be identified at most localities indicating that the flows were spatter fed or clastogenic the basaltic andesite flows are interpreted to have formed by two main processes a reconstitution of fountain generated spatter around vent areas by syn depositional agglutination and coalescence followed by extensional non particulate flow and b syn eruptive collapse of a rapidly built spatter and scoria cone by rotational slip and extensional sliding these processes produced two morphologically distinct lobes in both flows by a earlier non particulate flow of agglutinate and coalesced spatter which formed a thin lobe of rubbly aa lava ca 5 m thick with characteristic open extension cracks revealing a homogeneous holocrystalline interior and b later scoria cone collapse which created a larger lobe of irregular thickness 20 m made of large detached blocks of scoria cone interpreted to have been rafted along on a flow of coalesced spatter the source regions of these lava flows are characterized by horseshoe shaped scarps 30 m high with meso blocks ca 30 m in diameter of bedded scoria at the base one lava flow has a secondary lateral collapse zone with lower ca 7 m scarps backward tilted meso blocks are interpreted to be the product of rotational slip and forward tilted blocks the result of simple toppling squeeze ups of coalesced spatter along the leading edge of the meso blocks indicate that coalescence occurred in the basal part of the scoria cone this low viscosity coalesced spatter acted as a lubricating layer along which basal failure of the scoria cone occurred rotational sliding gave way to extensional translational sliding as the slide mass spread out onto the present caldera floor squeeze ups concentrated at the distal margin indicate that the extensional regime changed to one of compression probably as a result of cooling of the flow front sliding material piled up behind the slowing flow front and coalesced spatter was squeezed up from the interior of the flow through fractures and between rafted blocks the andesite flow although morphologically similar to the other two flows has a slightly different chemical composition which corresponds to the earliest stage of the eruption it is a much smaller lava flow emitted from the base of the scoria cone 2 days after the eruption had ceased this lava is interpreted to have been formed by post depositional coalescence of spatter under the influence of the in situ cooling rate and load pressure of the deposit extrusion occurred through the lower part of the scoria cone and subsequent non particulate flow of coalesced material produced a blocky and aa lava flow the mechanisms of formation of the lava flows described may be more common during explosive eruptions of mafic magma than previously envisaged

modeling the influence of wave enhanced turbulence in a shallow tide and wind driven water column 1 the ability of one dimensional hydrodynamic models to reproduce dissipation of turbulent kinetic energy and velocity profiles for conditions of whitecapping waves in a shallow water tide and wind forced environment was assessed the models were forced with the conditions experienced during a month long field experiment in a shallow estuarine embayment and the results were compared with the observed dissipation and mean velocity profiles three turbulence models were assessed the k model and two k l models with different prescribed bilinear relationships for the turbulent length scale l the k turbulence model was found to best replicate the measured decay of dissipation with depth with a surface roughness length z0s 1 3hs and wave energy parameter 60 the k l model achieved equally as good reproduction of the observations as the k model when the proportionality constant in the prescribed linear length scale relationship for the upper half of the water column was modified from the traditionally employed von karman s constant 0 4 to 0 25 the model results show that the whitecapping waves often supplied the dominant source of turbulent kinetic energy over the majority of the water column in the shallow tide and wind forced system

structure from motion photogrammetry a low cost effective tool for geoscience applications abstract high resolution topographic surveying is traditionally associated with high capital and logistical costs so that data acquisition is often passed on to specialist third party organisations the high costs of data collection are for many applications in the earth sciences exacerbated by the remoteness and inaccessibility of many field sites rendering cheaper more portable surveying platforms i e terrestrial laser scanning or gps impractical this paper outlines a revolutionary low cost user friendly photogrammetric technique for obtaining high resolution datasets at a range of scales termed structure from motion sfm traditional softcopy photogrammetric methods require the 3 d location and pose of the camera s or the 3 d location of ground control points to be known to facilitate scene triangulation and reconstruction in contrast the sfm method solves the camera pose and scene geometry simultaneously and automatically using a highly redundant bundle adjustment based on matching features in multiple overlapping offset images a comprehensive introduction to the technique is presented followed by an outline of the methods used to create high resolution digital elevation models dems from extensive photosets obtained using a consumer grade digital camera as an initial appraisal of the technique an sfm derived dem is compared directly with a similar model obtained using terrestrial laser scanning this intercomparison reveals that decimetre scale vertical accuracy can be achieved using sfm even for sites with complex topography and a range of land covers example applications of sfm are presented for three contrasting landforms across a range of scales including an exposed rocky coastal cliff a breached moraine dam complex and a glacially sculpted bedrock ridge the sfm technique represents a major advancement in the field of photogrammetry for geoscience applications our results and experiences indicate sfm is an inexpensive effective and flexible approach to capturing complex topography

constraints on cooling and degassing of pumice during plinian volcanic eruptions based on model calculations during explosive volcanic eruptions pumice clasts are transported into the atmosphere and their thermal and degassing histories determine how much volatiles are lost syneruptively this process is studied by combining a steady state eruption column model with a model for the cooling and degassing of pumice in the model we investigate the impact of various parameters e g mass eruption rate biot number eruption temperature and geometry on the cooling and degassing of pumice and find that the biot number and the eruption temperature are the most influential during typical risetimes of pumices inside eruption columns 200 300 s those smaller than 0 5 cm in diameter are found to lose little of their volatiles syneruptively and remain in thermal equilibrium with the plume in the case of larger pumices the ratio of the cooling timescale r p 2 where rp is the pumice radius and is the thermal diffusivity to the degassing timescale w 2 d 0 where w is the vesicle wall thickness and d 0 is the species diffusivity controls degassing if this ratio is larger than 50 degassing of the pumice will be nearly complete with a few percent of the original volatiles left in the outer rind of the pumice for a ratio of less than 0 1 no volatiles escape the pumice typical values for thermal and species diffusivity as well as vesicle wall thickness indicate that in the case of degassing cl and h 2 o the transition from 0 1 to 50 will be in the pumice size range of 1 10 cm here volatile concentration is a strong function of position inside the pumice suggesting that values for volatile contents measured on picked matrix glass from crushed samples may not be the best way to estimate the volatile content of matrix glass a number which is frequently used to estimate the total volatile input of volcanic eruptions this effect is even more pronounced when looking at hydrogen isotopic fractionation with larger pumices tending toward d 80

cross shore surfzone tracer dispersion in an alongshore current 1 cross shore surfzone tracer dispersion in a wave driven alongshore current is examined over a range of wave and current conditions with 6 continuous dye releases each roughly 1 2 hours in duration at huntington beach california fluorescent dye tracer released near the shoreline formed shore parallel plumes that were sampled on repeated cross shore transects with a jet ski mounted fluorometer ensemble averaged cross shore tracer concentration profiles are generally shoreline attached maximum at or near the shoreline with increasing cross shore widths and decreasing peak values with downstream distance more than a few 100 m from the source tracer is often well mixed across the surfzone i e saturated with decreasing tracer concentrations farther seaward for each release cross shore surfzone absolute diffusivities are estimated using a simple fickian diffusion solution with a no flux boundary at the shoreline and range from 0 5 2 5 m2 s 1 surfzone diffusivity scalings based on cross shore bore dispersion surfzone eddy mixing length and undertow driven shear dispersion are examined the mixing length scaling has correlation r2 0 59 and the expected best fit slope 1 indicating that horizontal rotational motions are important for cross shore tracer dispersion in the surfzone

formation of composite pyroclasts by welding inside a lithic rich mafic eruption column los marteles caldera canary islands abstract the tuff ring of the los marteles phreatomagmatic maar gran canaria canary islands includes a particular unit that comprises abundant composite spheroidal clasts however these clasts differ from cored clasts elsewhere that consist of erupted lithic pyroclasts with an adhering rim of coherent chilled magma the composite clasts here studied range from lapilli to bombs and are cored or concentrically banded among the welded components several types of primary clasts are discerned that include i juvenile clasts resultant of the magma inertial fragmentation and ii cognate or accessory lithic clasts juvenile clasts include glass spheres nano and microachneliths and crystals lithic clasts include lava fragments scoriae and olivine xenocrysts primary clasts are interpreted to have been produced by the explosion of a partially crystallized mafic sio 2 50 55 magma that erupted into a maar filled up with scoriae plus lava fragments the explosion would have originated as a dense and turbulent gas thrust into which the repeated collisions of melt droplets with solid clasts generated droplet coated crystals lithic clasts and single glass spheres we interpret the cored and concentrically banded pyroclasts to be made of coalesced and or agglutinated particles coated with a melt rim to the rest of the components these composite clasts developed spheroidal shapes during transport within a violent strombolian eruption column due to spin effect and finally landed in solid state

interaction between central volcanoes and regional tectonics along divergent plate boundaries askja iceland activity within magmatic divergent plate boundaries mdpb focuses along both regional fissure swarms and central volcanoes an ideal place to investigate their mutual relationship is the askja central volcano in iceland askja consists of three nested calderas namely kollur askja and oskjuvatn located within a hyaloclastite massif along the nne ssw trending icelandic mdpb we performed an extensive field based structural analysis supported by a remote sensing study of tectonic and volcanic features of askja s calderas and of the eastern flank of the hyaloclastite massif in the massif volcano tectonic structures trend n 10 e to n 40 e but they vary around the askja caldera being both parallel to the caldera rim and cross cutting on the western side structural trends around the oskjuvatn caldera are typically rim parallel volcanic vents and dikes are preferentially distributed along the caldera ring faults however they follow the nne ssw regional structures when located outside the calderas our results highlight that the askja volcano displays a balanced amount of regional fissure swarm related and local shallow magma chamber related tectonic structures along with a mutual interaction among these this is different from krafla volcano to the north of askja dominated by regional structures and grimsvotn to the south dominated by local structures therefore askja represents an intermediate tectono magmatic setting for volcanoes located in a slow divergent plate boundary this is also likely in accordance with a northward increase in the spreading rate along the icelandic mdpb

the effect of stokes drift and transient rip currents on the inner shelf part i no stratification abstractthis is part ii of a two part study focused on stokes drift and transient rip current trc effects on the unstratified part i and stratified this paper inner shelf part i focuses on funwavec coupled ocean atmosphere wave sediment transport coawst coupling and trc effects on mixing and exchange on an unstratified inner shelf here two simulations r3 and r4 are performed on a stratified inner shelf and surfzone with typical bathymetry stratification and wave conditions r3 is a coawst only simulation no trcs while r4 has funwavec coawst coupling with trcs in r4 trcs lead to patchy near surface cooling vertical isotherm displacement and increased water column mixing for both r3 and r4 the mean lagrangian circulation has two nearly isolated surfzones and inner shelf overturning circulation cells with a stronger r4 inner shelf circulation cell the r4 inner shelf vertical velocity variability is 2 3 times stronger than a simulation with trcs and no stratification relative

the welded air fall tuff layer at krafla northern iceland a composite eruption triggered by injection of basaltic magma abstract a composite welded tuff layer surrounding the krafla volcanic center in northern iceland was erupted when the caldera was formed during the last interglacial period in iceland 70 to 100 thousand years ago the stratigraphic units of the up to 50 m thick layer are silicic ash basaltic scoria intermediate vitrophyre intermediate welded and agglutinated spatter and intermediate densely welded tuff stratigraphic and petrochemical study of the layer suggests that it was formed by an initial explosive eruption of silicic magma triggered and immediately followed by basaltic magma both erupting in plinian activity the eruption continued with strombolian activity producing incompletely mixed silicic basaltic pyroclastics most of the layer is made up of this apparently intermediate heterogeneous welded tuff welding within the layer is the result of the different solidus temperatures of basalt and dacite after deposition the silicic component is being kept above its softening point by the hotter but solid basaltic component isopleth and isopach maps of the layer indicate a source area in the southeastern part of the caldera estimated dre volume of the layer is 2 4 km 3 which accounts for a 50 55 m subsidence of the 45 km 2 caldera floor drill hole data from within the southern margin of the caldera reveals the layer at a depth of 290 m which indicates accumulation of about 13 5 km 3 of volcanic rocks since its formation

lithofacies characteristics of diatreme deposits examples from a basaltic volcanic field of sw sardinia italy abstract a deeply eroded diatreme field consisting in several decametric sized vertical mainly clastic volcanic bodies of basaltic composition is described for the first time in the variscan basement of sw sardinia the recognition and description of four different lithofacies in these diatremes allowed discussion of the role of the different processes which control magma eruption and conduit infilling and making general inferences about diatremes the studied diatremes have a cross sectional shape from elliptical to sub triangular and are slightly elongated nearly parallel to the main foliation of the intruded meta sedimentary rocks foliation of host rocks is locally reoriented or folded close to the contact with the diatremes suggesting that magma possibly rose to the surface through fissures oriented nearly parallel to host rock foliation textural features of the volcanic bodies show many analogies with kimberlitic diatremes despite the difference in petrography and composition juvenile lapilli are mainly made by ghosts of mafic phenocrysts olivine and clinopyroxene set in a groundmass formed by plagioclase microlites immersed in a cryptocrystalline chlorite rich matrix the four lithofacies were described mainly based on the shape and physical features of the clasts and textural anisotropy a globular juvenile rich lapilli tuff facies gjlt an angular juvenile rich lapilli tuff facies ajlt a lithic rich lapilli tuff facies lirlt and a coherent lava like facies coh all the clastic lithofacies are generally well sorted and typically lack a fine grained matrix juvenile fragments are lapilli sized and from equant to oblate in axial ratio and from rounded globular to very angular in shape conversely lithic clasts are largely variable in shape and size and are mainly represented by basement derived clasts the absence of bedding the scarcity of the coherent facies and the dominance of clast supported structureless volcaniclastic facies suggest that the outcropping portion of these volcanic bodies represents the lower diatreme zone the presence of diffuse welding and the globular shapes of some juvenile fragments together with their vesicularity suggest that magma fragmentation was mainly driven by magmatic gas exsolution occurring at a deeper level respect to classical basaltic explosive activity textural features facies association and facies architecture of the studied deposits are suggestive of an important affinity with kimberlitic and other ultramafic diatremes

using a 2d shallow water model to assess large scale particle image velocimetry lspiv and structure from motion sfm techniques in a street scale urban drainage physical model abstract physically based numerical modelling of surface processes in urban drainage such as pollutant wash off or the assessment of flood risks requires appropriate calibration and terrain elevation data to properly simulate the overland flows and thus to achieve useful results accordingly this study aims to obtain an accurate representation of the runoff generated by three different rain intensities 30 50 and 80 mm h in a full scale urban drainage physical model of 36 m2 the study focuses firstly on applying the structure from motion sfm photogrammetric technique to carry out a high resolution and accurate topographic survey this topography was implemented in a 2d shallow water model and the results were compared with those obtained using traditional data point measured topography negligible differences were found when comparing the two models with measured discharges at the physical model gully pots however significant differences were obtained in the velocity distributions especially in the shallowest flow areas where drainage channels of a few millimeters depth appeared in the high resolution topographic survey results from the numerical model were compared with overland flow velocities determined by applying a modified large scale particle image velocimetry lspiv methodology using fluorescent particles with the sfm topography the 2d model was able to obtain a better representation of the experimental data since small scale irregularities of the pavement surface could be represented in the model domain at the same time lspiv was presented as a very suitable tool for the accurate measurement of runoff velocities in urban drainage models avoiding the interference of raindrop features in the recorded images and with overland water depths in the order of few millimeters

the role of morphology and wave current interaction at tidal inlets an idealized modeling analysis the outflowing currents from tidal inlets are influenced both by the morphology of the ebb tide shoal and interaction with incident surface gravity waves likewise the propagation and breaking of incident waves are affected by the morphology and the strength and structure of the outflowing current the 3 d coupled ocean atmosphere wave sediment transport coawst modeling system is applied to numerically analyze the interaction between currents waves and bathymetry in idealized inlet configurations the bathymetry is found to be a dominant controlling variable in the absence of an ebb shoal and with weak wave forcing a narrow outflow jet extends seaward with little lateral spreading the presence of an ebb tide shoal produces significant pressure gradients in the region of the outflow resulting in enhanced lateral spreading of the jet incident waves cause lateral spreading and limit the seaward extent of the jet due both to conversion of wave momentum flux and enhanced bottom friction the interaction between the vorticity of the outflow jet and the wave stokes drift is also an important driving force for the lateral spreading of the plume for weak outflows the outflow jet is actually enhanced by strong waves when there is a channel across the bar due to the return current effect for both strong and weak outflows waves increase the alongshore transport in both directions from the inlet due to the wave induced setup over the ebb shoal wave breaking is more influenced by the topography of the ebb shoal than by wave current interaction although strong outflows show intensified breaking at the head of the main channel

on the characteristics of velocities fields in the vicinity of manhole inlet grates during flood events the accurate characterisation of flow from urban surfaces to sewer stormwater systems is important for urban drainage design and flood modelling risk identification however the geometrical complexity and large variety of drainage structures linking elements available makes model calibration and verification difficult in this study an extensive comparison between experimentally measured and numerically modelled flow characteristics in the vicinity of ten different designs of manhole grate was performed under drainage flow in sub critical conditions using a 2d surface piv spiv system the work presents the first detailed characterisation of velocity fields around these linking elements in addition it provides the first detailed verification of the ability of a 2d numerical model to describe both velocity fields and drainage flows the overall comparison shows a close relationship between numerical and the experimental results with some higher inflows in the experimental results as a consequence of a localised transition from weir to orifice condition near the void areas of the grates it was also noted that velocity differences decreased further from the manhole due mainly to the more directional flow overall the work demonstrates the potential for further use of 2d numerical models to describe flow conditions at linking elements either directly within modelling simulations or indirectly via the characterisation of energy loss coefficients