discharge controls on the sediment and dissolved nutrient transport flux of the lowermost mississippi river implications for export to the ocean and for delta restoration abstract lagrangian longitudinal surveys and fixed station data are utilized from the lowermost mississippi river reach in louisiana at high and low discharge in 2012 2013 to examine the changing stream power sediment transport capacity and nitrate conveyance in this backwater reach of the river nitrate appears to remain conservative through the backwater reach at higher discharges 15 000 m 3 s thus nitrate levels supplied from the catchment are those exported to the gulf of mexico fueling coastal hypoxia at lower discharges interaction with fine sediments and organic matter stored on the bed due to estuarine and tidal processes likely elevates nitrate levels prior to entering the gulf a further 1 2 week long spike in nitrate concentrations is associated with the remobilization of this sediments during the rising discharge phase of the mississippi backwater characteristics are clearly observed in the study reach starting at river kilometer 703 vicksburg in both longitudinal study periods stream power at the lowermost station is only 16 of that at vicksburg in the high discharge survey and 0 6 at low flow the high to low discharge study differential in unit stream power at a station increases between vicksburg and the lowermost station from a factor of 3 to 47 50 times at high discharge 30 of this energy loss can be ascribed to the removal of water to the atchafalaya at old river control suspended sediment flux decreases downstream in the studied reach in both studies the lowermost station has 75 of the flux at vicksburg in the high discharge study and 0 9 in the low discharge study the high discharge values given that this study was conducted during the highest rising hydrograph of the water year are augmented by sediment resuspended from the bed that was deposited in the previous low discharge phase examination of this first detailed field observation studies of the backwater phenomenon in a major river shows that observed suspended particle sizes and calculated shear velocities compare favorably with suspension coefficients derived by previous investigators using flume experiments and modeling

variations in natural levee morphology in anastomosed channel flood plain complexes abstract natural levees are common features of alluvial river systems yet their origin and evolution are poorly understood in this paper we present morphologic and sedimentologic data from two anastomosed rivers and offer a hypothesis of natural levee growth in these systems based on mechanisms of sediment transport in settings where floodbasins fill at the same rate as the channel levees form by turbulent diffusion of suspended sediment away from a high velocity thread into a floodbasin of relatively stagnant water the theory of diffusive transport suggests that these levees should be narrow steep and display abrupt decreases in grain size due to rapid decreases in carrying capacity with distance into the floodbasin in environments where an appreciable water surface slope is maintained between the main channel and the floodbasin levees form by advection of sediment out of the channel and into the floodbasin advective transport theory indicates that these levees should be broad and gently sloped with grain sizes gradually decreasing away from the main channel natural levees occurring in the anastomosed reach of the upper columbia river in se british columbia display significantly different morphology from levees in the cumberland marshes region of the lower saskatchewan river in east central saskatchewan at the upper columbia site the rise in stage of the floodbasin water nearly keeps up with that of the channel water because of good communication between channel and floodbasins through crevasses this inhibits the establishment of a water surface slope and the bulk of the escaping sediment is deposited close to the channel in contrast the cumberland marshes region is characterized by wide and volumetrically large floodbasins these conditions keep floodbasin water surface elevations relatively low and maintain an appreciable elevation head between the channel and its floodbasin fostering levee growth by advective transport

congruent bifurcation angles in river delta and tributary channel networks we show that distributary channels on river deltas exhibit a mean bifurcation angle that can be understood using theory developed in tributary channel networks in certain cases tributary network bifurcation geometries have been demonstrated to be controlled by diffusive groundwater flow feeding incipient bifurcations producing a characteristic angle of 72 we measured 25 unique distributary bifurcations in an experimental delta and 197 bifurcations in 10 natural deltas yielding a mean angle of 70 4 2 6 95 confidence interval for field scale deltas and a mean angle of 68 3 8 7 for the experimental delta consistent with this theoretical prediction the bifurcation angle holds for small scales relative to channel width length scales furthermore the experimental data show that the mean angle is 72 immediately after bifurcation initiation and remains relatively constant over significant time scales although distributary networks do not mirror tributary networks perfectly the similar control and expression of bifurcation angles suggests that additional morphodynamic insight may be gained from further comparative study

basaltic calderas collapse dynamics edifice deformation and variations of magma withdrawal 1 the incremental caldera collapses of fernandina 1968 miyakejima 2000 and piton de la fournaise 2007 are analyzed in order to understand the collapse dynamics in basaltic setting and the associated edifice deformation for each caldera the collapse dynamics is assessed through the evolution of the 1 time interval t between two successive collapse increments 2 amount of vertical displacement during each collapse increment and 3 magma outflow rate during the whole collapse caldera process we show from the evolution of t that piton de la fournaise and fernandina were characterized by a similar collapse dynamics despite large differences in the caldera geometry and the duration of the whole collapse caldera process this evolution significantly differs from that of miyakejima where t strongly fluctuated throughout the whole collapse process quantification of the piston vertical displacements enables us to determine the magma outflow rates between each collapse increment displacement data tiltmeter and or gps for piton de la fournaise and miyakejima are used to constrain the edifice overall deformation and the edifice deformation rates these data reveal that both volcanoes experienced edifice inflation once the piston collapsed into the magma chamber such a deformation which lasts during the first collapse increments only is interpreted as the result of larger volume of piston intruded in the magma chamber than magma withdrawn before each collapse increment once the effect of the collapsing rock column vanishes edifice deflates we also determine for each caldera the critical amount of magma evacuated before collapse initiation and compare it to analog models the significant differences between models and nature are explained by the occurrence of preexisting weak zones in nature i e the ring faults that are not taken into account in analog models finally we show that t at piton de la fournaise and fernandina was equally controlled by the frictional resistance along the ring faults and the magma outflow rate in addition to these two parameters the collapse dynamics of miyakejima was also influenced by variations of the magma bulk modulus which changed after the influx of deep gas rich magma into the collapse related magma chamber altogether our results show that the dynamics of caldera collapse in basaltic volcanoes proceeds in two phases phase 1 starting with the first collapse is characterized by the largest collapse amplitude an incremental edifice inflation and a step by step increase of the rate of magma outflow phase 2 shows a rapid decrease of the magma discharge rate to a low level concomitant with the continuous edifice deflation if deep magma is injected into the magma chamber as at miyakejima an additional phase occurs phase 3

shoreline response to autogenic processes of sediment storage and release in the fluvial system 1 experimentally determined shoreline migration rates show high frequency autogenic variability superimposed on low frequency allogenic shoreline responses induced by eustatic base level change this variability persists even when the shoreline migration is averaged laterally indicating time variation in total sediment discharge reaching the shoreline the magnitude of autogenic variability in shoreline migration rate changes by roughly a factor of 3 depending on the shoreline migration direction it is strongest during transgression when the shoreline is on average migrating against the mean sediment flow and weakest during regression when the shoreline is migrating with the mean sediment flow we propose that this time variation is due to overall sediment storage and release in the fluvial system we use a one dimensional geometric model to model the autogenic signals observed in the experiment the model uses small periodic changes in the fluvial slope to represent the effects of storage and release of supplied sediment due to intrinsic variation in the transport efficiency of the fluvial system the periodic pulses of sediment discharge to the shoreline required in the model to explain the variations in shoreline migration can exceed by an order of magnitude the mean allogenic sediment discharge the slope variability required in the model to explain the autogenic shoreline signals is 1 4 of the mean slope this is well within the range of observed variability in depositional fluvial slopes we propose that at least part of this observed variability is real that is the long profile slope of a depositional river system may have an intrinsic elasticity of a few percent of its mean value even under steady forcing autogenic slope variation of this magnitude could readily produce parasequence scale deposits in the stratigraphic record

identifying environmental controls on the shoreline of a natural river delta river deltas form where sediment laden water debouches into a basin the spatial delineation of a delta is nontrivial and yet is fundamental to systematically evaluating fluxes across its surface here we study shoreline dynamics of the wax lake delta wld a naturally developing delta downstream of the atchafalaya river usa we demonstrate the ability to extract hydrodynamic and morphodynamic shorelines from time series of satellite imagery and topography data respectively the hydrodynamic shoreline corresponds to the traditional dry wet interface whereas we introduce the concept of a morphodynamic shoreline demarcating the topset foreset transition of a delta to quantitatively express the degree of inundation of a delta plain these shorelines enable us to assess environmental controls on inundation of the wld delta plain noting the abundance of satellite imagery whereas time series of bathymetric data from delta plains are scarce from the analysis of noaa and u s geological survey environmental data we identify the effects of river discharge tides wind and vegetation on shoreline position in particular using delft3d simulations and a simplified momentum balance we highlight the nonuniform and nonlinear effect of wind on delta plain inundation our analyses reveal that wind riverine discharge and tides significantly contribute to inundation of the wld and hence incorporating their interaction is essential to the accurate modeling of hydrodynamics and ecodynamics of the wld delta plain as well as to the dynamic shape of delta plains in general

pumice fall deposits of the western vulsini volcanoes central italy abstract widely dispersed pyroclastic fall deposits are prominent among the volcanic products of the western part of the vulsini volcanic district central italy in this paper we describe major pumice fall deposits in the area that correlate to the early activity of the latera volcanic complex 0 3 0 2 ma they represent excellent stratigraphie markers for a wide area mostly extending west and south of the present latera caldera pumice fall deposits lower b and upper b are closely associated with major pyroclastic flow units of the canino eruptive unit pumice fall c caps the canino products without relevant time hyatus pyroclastic falls d and e the latter part of the minor stenzano explosive eruption belong to the stratigraphic interval between canino and farnese eruptive units pumice fall f is part of the initial products of the farnese eruptive sequence we present detailed stratigraphy depositional features vertical and lateral variations of grain size componentry and chemical composition in individual fallout beds source areas as inferred from thickness and maximum pumice and lithic clast size distributions are located in the area of the present day latera caldera tentative estimates of volume column height and magma discharge rate indicate moderate large to large plinian eruptive events

sediment transport and topographic evolution of a coupled river and river plume system an experimental and numerical study sediment transfer from rivers to the ocean is the fundamental driver of continental sedimentation with implications for carbon burial land use dynamics and unraveling global climate change and earth history from sedimentary strata coastal rivers are dynamically coupled to their offshore plumes at the river mouth creating regions of nonuniform flow that can dictate patterns of erosion and deposition both onshore and offshore however there are limited experimental and modeling studies on sediment transport and morphodynamics of coupled river and river plume systems and their response to multiple flood events to address this knowledge gap we developed a quasi 2 d morphodynamic numerical model and conducted exploratory flume experiments in a 7 5 m long flume where a 10 cm wide river channel was connected to a 76 cm wide ocean basin both the numerical model and the flume results demonstrate that 1 during low discharge flows backwater hydrodynamics cause spatial flow deceleration and deposition in the river channel and the offshore plume area and 2 during high flows the water surface is drawn down to sea level resulting in spatial flow acceleration and bed scour during high discharge flows we also found that the offshore river plume self channelized owing to both levee formation and bed scour our study suggests that coastal rivers may be in a perpetual state of morphodynamic adjustment and highlights the need to link rivers and river plumes under a suite of flow discharges to accurately predict fluvio deltaic morphodynamics and connectivity between fluvial sediment sources and marine sinks

how summit calderas collapse on basaltic volcanoes new insights from the april 2007 caldera collapse of piton de la fournaise volcano in april 2007 piton de la fournaise volcano experienced a caldera collapse during its largest historical eruption we present here a structural analysis both of the caldera and the surrounding area and precise gps data recorded with a dense gps network specifically dedicated to the analysis of deformation related to the summit collapse structures despite a collapse of more than 300 m in the central zone the geometry of the new caldera is similar in map view to that of the pre existing collapsed structure which was formed from the coalescence of several pit craters the caldera shows an asymmetric inner geometry with sub vertical walls in the nw quadrant and steep scarps composed of inward tilted blocks in the southern half the presence of preserved polished surfaces on the lower part of the sub vertical scarp indicates that it corresponds to the caldera north western ring fault the april 2007 caldera collapse led to the development and the reactivation of concentric fractures on the caldera rim mostly along the southern limit of the caldera gps data show that fractures result from radial extensional stresses that are restricted within the first tens of meters of the caldera edge gps data also reveal that the caldera collapse was coeval with a centripetal deflation whose magnitude is largest along the southern half of the caldera the displacements recorded by gps result from both a general deflation due to magma withdrawal from piton de la fournaise s summit magma chamber and additional local effects related to the caldera collapse comparison of the caldera collapses at piton de la fournaise miyakejima and fernandina reveals striking similarities with cyclic seismic signals accompanying small scale deflation inflation cycles this strongly suggests a common mode of collapse hence we propose a unifying model of caldera collapse in basaltic setting in which the inward deflation due to magma withdrawal from the magma chamber prevents the collapse of the caldera roof until the gravitational stress acting on the rock column above the magma chamber exceeds the shear strength along pre existing ring faults the downward displacement stops when the pressure increase into the magma chamber is able to again sustain the rock column the succession of 1 inward deflation that prevents the collapse 2 collapse due to gravitational stress and 3 stopping of the downward motion is repeated many times the frequency of the cycles is influenced by the rate of magma withdrawal and by the amount of intrusion of magma along the ring faults

effect of stress fields on magma chamber stability and the formation of collapse calderas 1 the summits of many of the earth s and other planets larger volcanoes are occupied by calderas that formed by collapse into an evacuating underlying magma chamber these collapse calderas are typically several tens of square kilometers in area and are commonly elliptical in shape we show that the long axes of late quaternary collapse calderas in the kenya rift valley the western basin and range province the snake river yellowstone plateau and the iceland rift zone are parallel to the upper crustal minimum horizontal stress direction sh as determined by independent criteria we suggest that circular magma chambers beneath these volcanoes became elliptical by stress induced spalling of their chamber walls by a mechanism that is analogous to the formation of breakouts in boreholes and tunnels in breakouts the hole becomes elongate parallel to the far field minimum stress in the kenya rift late pleistocene caldera collapse was accompanied by a 45 rotation of sh and an increase in the magnitude of the maximum horizontal stress sh the breakout model predicts increasingly unstable caldera walls under these conditions a possible explanation for the sudden appearance of so many collapse events in a volcanic setting that had never experienced them before this mechanism of stress change induced collapse may have played a role in other caldera settings

asymmetric growth of collapsed caldera by oblique subsidence during the 2000 eruption of miyakejima japan abstract oblique development of the ring faults reflecting the structural heterogeneities inside the volcano formed many asymmetric structures of miyakejima 2000 ad caldera the asymmetry includes a offset location of the ring faults with respect to the associated shallow magma chamber b unequal outward migration of the caldera wall 600 m at the southeastern rim but only 200 m at the northwestern rim c development of tilted terrace only at the southeastern caldera margin d eruption sites and fumaroles being confined to the southern part of the caldera geophysical data including ground deformation and seismic activity indicates the offset of the location of the magma chamber about 2 km south of the caldera center on the surface the ring faults propagated from the deflating magma chamber obliquely about 30 degrees toward the summit the oblique subsidence of the cylindrical block formed a wider instable zone particularly in the southeastern side of the ring fault that enhanced the larger outward migration of the caldera rim and also caused the formation of the outer half ring fault bordering the tilting slope at the southern part ascending pass of the buoyant magma along the tilted ring faults was concentrated in the southern half of the caldera and consequently the distributions of the eruption sites and fumaroles are localized in the southern half part of the caldera the structure of the miyakejima 2000 caldera with complete development of the ring faults its high roof aspect ratio and oblique subsidence is clearly distinguishable from trapdoor type caldera the oblique development of the ring faults can be controlled by the mechanical contrast between the solidified conduits and surrounding fragile volcanic edifice asymmetric development of the miyakejima caldera shows that the collapsed calderas are potential indicators of the heterogeneous structures inside of the volcano particularly in the case of small size caldera

geochronology and stratigraphy of the ignimbrites from the 21 30 s to 23 30 s portion of the central andes of northern chile the central volcanic zone cvz of the andes which extends from 14 to 28 s is one of the largest provinces of late tertiary to recent ignimbrite volcanism in the world in the 21 30 s to 23 30 s portion of the cvz in northern chile ignimbrite volcanism was initiated at the beginning of the late miocene 10 4 ma ago and continued until the recent the stratigraphy is dominated by the products of five major dacitic ignimbrite eruptions 100 km3 the artola ignimbrite member 9 4 ma the sifon ignimbrite member 8 3 ma the pelon ignimbrite member 5 5 ma the puripicar ignimbrite member 4 2 ma and the atana ignimbrite member 4 1 ma at least three of these represent only portions of larger ignimbrite sheets erupted from centres of sw bolivia two of the ignimbrites the sifon and atana ignimbrites must represent erupted volumes in excess of 1000 km3 each the major units which represent 90 of the total volume of ignimbrite in this area are intercalated with smaller 50 km3 less extensive volcanic units some of which were erupted from source structures within the study area the upper tertiary to recent volcanic stratigraphy has been revised using the large ignimbrites as the major stratigraphic horizons the ignimbrite formations can be divided into two groups on a geographic basis those in the northern and central portions of the study area are known as the san bartolo group while those in the southern portion belong to the silapeti group these two groups appear to be contemporaneous although the silapeti group may represent a period of ignimbrite volcanism which was initiated later about 6 ma ago the ignimbrite formation of sw bolivia and the punense arancaniano formation of nw argentina are equivalent to the san bartolo and silapeti groups based on correlation of the stratigraphy into adjacent areas in sw bolivia and nw argentina the beginning of the late miocene 10 4 ma marks the onset of the most intense phase ignimbrite volcanism in the cvz this phase of volcanism is suggested to be the result of crustal melting in response to crustal thickening during the quechua phase of deformation and subduction approximately 10 000 km3 of ignimbrite erupted over a period of 9 ma in the 21 30 23 30 s portion and led to the development of a major ignimbrite province

relationship between tectonism and volcanism along the great sumatran fault zone deduced by spot image analyses abstract satellite images provide evidence for numerous stepovers pull apart grabens and volcanic structures along the nw trending right lateral great sumatran fault zone high resolution spot images permit us to analyze the relationship between volcanic and tectonic structures this analysis reveals that releasing stepovers and pull aparts are ephemeral structures along the great sumatran fault zone and that the geometry of the strike slip fault evolves permanently through time the interpretative structural maps obtained from spot image analysis reveal that the formation of huge peculiarly shaped volcanic calderas has occurred in large releasing stepover fault zones and that the bounding faults of rectangular pull apart basins are analogous to the circular ring faults of calderas in particular detailed study of the segments at the southernmost 150 km long termination of the great sumatran fault zone from northwest of ranau lake to semangka bay allows us to describe the development of the ranau collapse caldera this caldera is located within a pull apart basin bounded by a stepover its peculiar rectangular shape and its relatively large size about 200 km 2 are controlled by the evolution of the extinct ranau releasing stepover similarly the toba elliptical caldera one of the largest volcanic caldera in the world is elongated parallel to the present trace of the great sumatran fault and appears to be related to a releasing stepover associated with a wide pull apart basin that is not active at present

understanding caldera structure and development an overview of analogue models compared to natural calderas abstract understanding the structure and development of calderas is crucial for predicting their behaviour during periods of unrest and to plan geothermal and ore exploitation geological data including that from analysis of deeply eroded examples allow the overall surface setting of calderas to be defined whereas deep drillings and geophysical investigations provide insights on their subsurface structure collation of this information from calderas worldwide has resulted in the recent literature in five main caldera types downsag piston funnel piecemeal trapdoor being viewed as end members despite its importance such a classification does not adequately examine a the structure of calderas particularly the nature of the caldera s bounding faults and b how this is achieved including the genetic relationships among the five caldera types various sets of analogue models specifically devoted to study caldera architecture and development have been recently performed under different conditions apparatus materials scaling parameters stress conditions the first part of this study reviews these experiments which induce collapse as a result of underpressure or overpressure within the chamber analogue the experiments simulating overpressure display consistent results but the experimental depressions require an exceptional amount of doming seldom observed in nature to form therefore these experiments are not appropriate to understand the structure and formation of most natural calderas the experiments simulating underpressure reveal a consistent scenario for caldera structure and development regardless of their different boundary conditions these show that complete collapse proceeds through four main stages proportional to the amount of subsidence progressively characterized by 1 downsag 2 reverse ring fault 3 peripheral downsag 4 peripheral normal ring fault the second part of this study verifies the possibility that these latter calderas constitute a suitable analogue to nature and consists of a comprehensive comparison of the underpressure experiments to natural calderas this shows that all the experimental structures as well as their progressive development are commonly observed at natural calderas highlighting a consistency between models and nature as the shallow structure of experimental calderas corresponds to a precise architecture at depth it provides a unique key to infer the deeper structure of natural calderas recognizing diagnostic surface features within a caldera will thus allow it to be categorized within a precise structural and evolutionary context the general relationship between the evolutionary stage of a caldera and its d s diameter subsidence ratio allows such a quantification with stage 1 calderas characterized by d s 40 stage 2 by 18 the four stages adequately explain the architecture and development of the established caldera end members along a continuum where one or more end members downsag piston funnel piecemeal trapdoor may correspond to a specific stage while such a continuum is controlled by progressive subsidence specific collapse geometries will result from secondary contributory factors roof aspect ratio collapse symmetry pre existing faults these considerations allow proposing an original classification of calderas incorporating their structural and genetic features

lithic breccia and ignimbrite erupted during the collapse of crater lake caldera oregon abstract the climactic eruption of mount mazama 6845 y b p vented a total of 50 km3 of compositionally zoned rhyodacitic to basaltic magma from a a single vent as a plinian pumice fall deposit and the overlying wineglass welded tuff and b ring vents as ignimbrite and coignimbrite lithic breccia accompanying the collapse of crater lake caldera new field and grain size data for the ring vent products are presented in this report the coarse grained poorly bedded clast supported lithic breccia extends as far as 18 km from the caldera center like the associated ignimbrite the breccia is compositionally zoned both radially and vertically and silicic mixed and mafic types can be recognized based on the proportion of rhyodacitic pumice matrix fractions in silicic breccias are depleted of fines and are lithic and crystal enriched relative to silicic ignimbrite due to vigorous gas sorting during emplacement ignimbrite occurs as a proximal veneer deposit overlying the breccia a medial 8 to 25 km from the caldera center compositionally zoned valley fill as much as 110 m thick and an unzoned distal 20 km facies which extends as far as 55 km from the caldera breccia within 9 km of the caldera center is interpreted as a coignimbrite lag breccia formed within the deflation zone of the collapsing ring vent eruption columns expanded pyroclastic flows of the deflation zone were probably vertically graded in both size and concentration of blocks as recently postulated for some turbidity currents an inflection in the rate of falloff of lithic clast size within the lithic breccia at 9 km may mark the outer edge of the deflation zone or may be an artifact of incomplete exposure the onset of ring vent activity at mt mazama was accompanied by a marked increase in eruptive discharge pyroclastic flows were emplaced as a semicontinuous stream as few ignimbrite flow unit boundaries are evident as eruption from the ring vents progressed flow runout distance and the extent of breccia deposition decreased due to a greater internal flow friction and b decreasing eruption column heights effect b probably resulted from a progressive decrease in magmatic gas content and discharge rate waning discharge may have been promoted by the tapping of more viscous crystal rich magma collapse of conduit walls and declining caldera collapse rate

experimental evidence for different strain regimes of crack populations in a clay model we report results from clay extension experiments used as a model for the evolution of fault populations due to stress interactions at yielding cracks begin to appear and the brittle strain due to them quickly reaches a rate matching the applied stretching rate the crack density number of cracks per unit area initially increases apace then reaches a maximum at a critical strain decreasing thereafter at low strains where the crack population is dilute a power law length distribution is observed which at high strain gradually transitions to an exponential this agrees with fault populations data observed in low and high strain settings these results indicate that fault populations ranging from power law to exponential size frequency distributions reflect the population evolution with increased strain

the pit craters and pit crater filling lavas of masaya volcano lava flowing into a pit crater will become entrapped to form an inactive lava lake at masaya volcano nicaragua pit filling lavas are exposed in the walls of nindiri santiago and san pedro pits mapping of these lavas shows that fill can involve emplacement of both a a and pahoehoe with single fill units ranging in thickness from 2 to 22 m thick units with columnar joints were emplaced as simple inactive lava lakes during high effusion rate episodes sequences of thinner units which can form pit floor shields or compound lakes were emplaced at lower effusion rates lava withdrawal caused unsupported sections of three 20 m thick units to subside resulting in unit flexure and faulting and viscous peeling features reveal that subsidence occurred while at least one unit was still partially molten where withdrawal has not occurred fill sequences are flat lying and symmetrically distributed around the feeder structures cinder cones and dykes the filled nindiri pit holds 5 107 m3 of lava in a 215 m thick sequence partial fill of santiago pit with 1 107 m3 of lava has filled the pit with a 110 m thick lava sequence of which 50 has been consumed by formation of a secondary pit altogether 6 4 107 m3 of lava was erupted into nindiri and santiago during 1525 1965 with 94 of this volume remaining pit contained the remainder forms a north flank lava flow field pit development and filling is a dynamic and ephemeral process having short lived effects on volcano morphology where pits develop and fill over hours to centuries however pits play an important role in shaping an edifice representing lava sinks and controlling whether lavas are trapped or able to spread onto the flanks

discharge estimation from h adcp measurements in a tidal river subject to sidewall effects and a mobile bed horizontal acoustic doppler current profilers h adcps can be employed to estimate river discharge based on water level measurements and flow velocity array data across a river transect a new method is presented that accounts for the dip in velocity near the water surface which is caused by sidewall effects that decrease with the width to depth ratio of a channel a boundary layer model is introduced to convert single depth velocity data from the h adcp to specific discharge the parameters of the model include the local roughness length and a dip correction factor which accounts for the sidewall effects a regression model is employed to translate specific discharge to total discharge the method was tested in the river mahakam representing a large river of complex bathymetry where part of the flow is intrinsically three dimensional and discharge rates exceed 8000 m3 s 1 results from five moving boat adcp campaigns covering separate semidiurnal tidal cycles are presented three of which are used for calibration purposes whereas the remaining two served for validation of the method the dip correction factor showed a significant correlation with distance to the wall and bears a strong relation to secondary currents the sidewall effects appeared to remain relatively constant throughout the tidal cycles under study bed roughness length is estimated at periods of maximum velocity showing more variation at subtidal than at intratidal time scales intratidal variations were particularly obvious during bidirectional flow conditions which occurred only during conditions of low river discharge the new method was shown to outperform the widely used index velocity method by systematically reducing the relative error in the discharge estimates

sediment eddy diffusivity in meandering turbulent jets implications for levee formation at river mouths 1 depositional patterns characteristic of river mouths are controlled by the sediment laden turbulent jet exiting from rivers here we show that jet instability developing at river mouths with small width to depth ratio can affect these patterns numerical simulations indicate that sediment eddy diffusivity which is a measure of the spreading of sediments out of the jet core depends on the interplay between sediment settling and large coherent flow structures which are associated with unstable jets our results suggest that optimal conditions for eddy diffusivity are met when the time scale of sediment settling is equal to the characteristic eddy time scale in this condition sediments are deposited at the farthest distance from the jet centerline thus promoting the formation of lateral deposits settling time scales much greater or much smaller than the eddy time scale is associated with low eddy diffusivity which promotes the formation of a central deposit such eddy mediated sediment transport is more evident in the zone of established flow than in the zone of flow establishment since the former is characterized by fully developed vortices a simplified model is proposed to estimate the settling and eddy time scales and to predict the optimal condition for levee formation

la peligrosa caldera 47 15 s 71 40 w a key event during the jurassic ignimbrite flare up in southern patagonia argentina pyroclastic and lava vent facies from the late jurassic el quemado complex are described at the southern lake ghio in the cordillera patagonica austral based on the comprehensive study of lithology and structures the reconstruction of the volcanic architecture has been carried out four ignimbrites and one rhyolitic lava unit affected by oblique slip normal faults have been recognized the evolution of la peligrosa caldera has been modeled in three different stages 1 initial collapse consisting of a precursory downsag subsidence related to a dilatational zone which controlled the location of the caldera 2 main collapse with the emplacement of large volume crystal rich ignimbrites and megabreccias under a progressive subsidence controlled by a pull apart structure related to a transtensional regime and 3 post collapse in which lava flows and associated domes were emplaced under an oblique extensional regime the caldera records a remarkable change from transtension to oblique extension which may represent an important variation in regional deformation conditions during jurassic times la peligrosa caldera may be considered a key event to understand the eruptive mechanisms of the flare up volcanism in the chon aike silicic province 2013 elsevier b v

hydrological connectivity in river deltas the first order importance of channel island exchange deltaic systems are composed of distributary channels and interdistributary islands while previous work has focused either on the channels or on the islands here we study the hydrological exchange between channels and islands and point at its important role in delta morphology and ecology we focus our analysis on wax lake delta in coastal louisiana usa and characterize the surface water component of hydrological connectivity through measurements of water discharge and hydraulic tracer propagation we find that deltaic islands are zones of significant water flux as 23 54 of the incoming distributary channel flux enters the islands a calculation of the travel times through a channel island complex shows travel times through the islands to be at least 3 times their channel counterparts a dye release experiment also indicates that travel times in islands are much longer that those within channels as dye remained in the island for the 3 8 day duration of the experiment additionally islands are more sensitive than channels to environmental forces such as tides which cause flow reversal and thus can increase travel times through the islands our work defines the hydrological network of a river delta to include not only the distributary channel network but also the interdistributary islands quantifies the implications of channel island hydrological connectivity to travel times through the system and discusses the relevance of our findings to channel mouth dynamics at the delta front and the potential for denitrification in coastal systems

formation and development of normal fault calderas and the initiation of large explosive eruptions the ring fractures that form most collapse calderas are steeply inward dipping shear fractures i e normal faults at the surface of the volcano within which the caldera fault forms the tensile and shear stresses that generate the normal fault caldera must peak at a certain radial distance from the surface point above the center of the source magma chamber of the volcano numerical results indicate that normal fault calderas may initiate as a result of doming of an area containing a shallow sill like magma chamber provided that the area of doming is much larger than the cross sectional area of the chamber and that the internal excess pressure in the chamber is smaller than that responsible for doming this model is supported by the observation that many caldera collapses are preceded by a long period of doming over an area much larger than that of the subsequently formed caldera when the caldera fault does not slip eruptions from calderas are normally small nearly all large explosive eruptions however are associated with slip on caldera faults during dip slip on and doming of a normal fault caldera the vertical stress on part of the underlying chamber suddenly decreases this may lead to explosive bubble growth in this part of the magma chamber provided its magma is gas rich this bubble growth can generate an excess fluid pressure that is sufficiently high to drive a large fraction of the magma out of the chamber during an explosive eruption

regional and local tectonics at erta ale caldera afar ethiopia erta ale volcano lies along the on shore red sea rift northern afar ethiopia separating the nubia and danakil plates erta ale has a nnwesse elongated caldera with a subvertical rim scarp hosting a lava lake structural field work was aimed at defining the deformation pattern around the caldera the caldera consists of along rim and across rim structures resulting from local and regional maximum extension wneesw stress fields respectively these structures cross cut each other at high angles suggesting that the two stress fields remain distinct each prevailing during rifting or caldera collapse the local along rim extensional fractures are gravity driven structures that formed due to the retreat of the caldera wall after collapse and are confined to the region of caldera subsidence the across rim structures are mainly located to the n and s of the caldera where they form rift zones each accommodating a similar amount of extension w6 3 m but displaying different trends and extension directions analogue models of interacting fractures are consistent with the southern rift being representative of the regional fault kinematics while the northern rift is a local perturbation resulting from the interaction between two right stepping rift segments along the erta ale range 2006 elsevier ltd all rights reserved

flow patterns and morphology of a prograding river delta the transition of flow between laterally confined channels and the unchannelized delta front controls the morphodynamic evolution of river deltas but has rarely been measured at the field scale we quantify flow patterns and bathymetry that define the evolution of the subaqueous delta front on the wax lake delta a rapidly prograding delta in coastal louisiana a significant portion of flow 59 departs the channel network over lateral channel margins as opposed to the downstream channel tips bathymetric surveys and remotely sensed estimates of flow direction allow spatial changes in flow velocity to be quantified and patterns of erosion and deposition to be estimated shallowing along channel margins produces spatial acceleration and erosion lateral spreading deceleration and deposition occur within three to eight channel widths outside of the channel margins in interdistributary bays the shape of each flow path is constrained by nourishment boundaries that separate the outflows from neighboring channels deposit elevation decreases with a basinward slope of 2 4 10 4 with distance from a channel margin along any flow path regardless of the channel or location that flow departed the network bathymetric depressions called interdistributary troughs form along nourishment boundaries where flow paths are the longest and deposit elevation is correspondingly low we conclude that the deposit morphology exerts a strong control on bathymetric evolution and that interaction between neighboring channels and even neighboring deltas can influence delta front morphology

coarse tail vertical and lateral grading in pyroclastic flow deposits of the latera volcanic complex vulsini central italy origin and implications for flow dynamics abstract coarse tail vertical and lateral grading are common features of pyroclastic flow deposits of the latera volcanic complex vulsini volcanoes central italy and are described for four representative flow units lithic clasts show normal vertical and lateral grading in all four units pumice clasts show reverse vertical and lateral grading within three flow units normal vertical and lateral grading of scoria clasts has been observed in one flow unit the origin of vertical and lateral grading of lithic and pumice clasts is related to mechanisms operating during the transport process within the high particle concentration basal avalanche of pyroclastic flows vertical grading results from the balance between gravitational and dispersive forces and is transferred to a lateral grading by vertical velocity gradients within a nonturbulent flow zone of pyroclastic flows the pyroclastic flows are modeled as bingham type fluids a framework that explains some of the basic deposit features even though it is a highly simplified treatment of the flows plug flow zones in the flows were a relatively minor part of their thicknesses evidence for the flows having had high densities probably within a factor of two of the final deposit density is presented finally their origin by single pulse or progressive formation is discussed

conceptual and numerical models of ring fault formation abstract most ring faults of collapse calderas are primarily shear fractures the initiation and development of which depends on the state of stress in the host rock the state of stress in a volcano is controlled by the loading conditions such as magma chamber geometry and pressure but also by the mechanical properties of its rock units and structures such as existing contacts faults and joints ring fault formation is thus essentially a problem in rock physics field observations show that some ring faults are dip slip whereas others are partly faults shear fractures and partly ring dykes extension fractures although slip on existing ring faults is much more common in basaltic edifices shield volcanoes than in true composite volcanoes in both types of volcanoes most caldera unrest periods do not result in ring fault slip here i present new conceptual and numerical models of caldera formation in volcanoes with shallow spherical circular or oblate ellipsoidal sill like magma chambers in the layered models the host rock above the chamber is composed of 30 comparatively thin layers with stiffnesses young s moduli alternating between 1 gpa and 100 gpa the chamber itself is located in a single thick layer the crustal segment hosting the chamber is either 20 km or 40 km wide but has a constant thickness of 20 km the loading conditions considered are 1 a crustal segment subject to 5 mpa tension 2 crustal segment subject to excess magmatic pressure of 10 mpa at the bottom doming of the volcanic field containing the chamber 3 a combination of tension and doming and 4 chamber subject to underpressure negative excess pressure of 5 mpa the main results are as follows 1 excess pressure and underpressure in a chamber normally favour dyke injection rather than ring fault formation 2 for doming or tension a spherical magma chamber favours dyke injection except when the layer hosting the chamber is very soft 10 gpa or one with recent dyke injections in which case the surface stress field favours ring fault formation 3 for a sill like chamber in a 20 km wide crustal segment a ring fault can be generated by either tension or tension and doming for a 40 km wide segment doming alone is sufficient to generate a ring fault 4 since individual layers in a volcano may develop different local stresses stress field homogenisation through all the layers between the chamber and the surface is a necessary condition for ring fault formation 5 because the mechanical properties of the layers that constitute basaltic edifices are more uniform than those that constitute true composite volcanoes it follows that stress field homogenisation and thus ring fault formation or slip is more commonly reached in basaltic edifices than in composite volcanoes 6 both for basaltic edifices and composite volcanoes the stress fields most likely to initiate ring faults are those generated around sill like chambers subject to tension doming or both

the evolution of latera caldera central italy in the light of subsurface data subsurface geothermal exploration has considerably added to our knowledge of the latera volcanic complex a syenitic body is located about 2 km below the present day surface k ar data point a 0 9 ma age the primary magma was a silica saturated trachyte undersaturated hauyne bearing products are found near the carbonatic wall rocks and have been interpreted as reaction products subsurface data from deep drilling and geophysical surveys suggest that the latera caldera resulted from three main successive collapse phases i formation of an old caldera now buried related to the eruption of ignimbrites from the syenitic magma chamber ii sinking of the eastern sector as a consequence of the formation of the nearby bolsena caldera 0 3 ma iii multistage formation of the present latera caldera 0 16 ma

on the anatomy of magma chamber and caldera collapse the example of trachy phonolitic explosive eruptions of the roman province central italy abstract textural and compositional features of pyroclastic products erupted during caldera forming events often reveal the tapping of different portions of variably zoned magma chambers due to changing geometries of the conduit vent systems here we report on ultrapotassic trachytic phonolitic explosive eruptions of the roman province central italy which show remarkable changes of textural features and glass compositions in the juvenile material even if the bulk chemical composition is essentially constant in each example the lower eruption sequence contains whitish crystal poor leucite free highly vesicular pumice emplaced by early plinian fallout and or pyroclastic currents upsection the eruption sequence contains black low porphyritic sanidine leucite bearing moderately vesicular scoria or spatter emplaced by major pyroclastic flows red tuff with black scoria and associated co ignimbrite coarse lithic rich breccias this suggests a shift from a central feeder conduit tapping the central part of the magma chamber to a ring fracture vent system tapping the peripheral portions of the magma chamber during caldera collapse key features of these evacuating magma chambers are the thermal and volatile concentration xvol gradients that produce the observed textural and compositional spectrum of trachy phonolitic rock types in particular the degrees of freedom during the crystallization of these ultrapotassic magmas are increased by the variation of the leucite stability field at different ph2o conditions both leucite free and leucite bearing differentiated ultrapotassic rock types can be produced in the course of individual eruptions as a result of pre eruptive conditions in the feeder magma with no need to invoke different differentiation suites related to mantle source heterogeneities of parental magmas

calderas and caldera structures a review abstract calderas are important features in all volcanic environments and are commonly the sites of geothermal activity and mineralisation yet it is only in the last 25 years that a thorough three dimensional study of calderas has been carried out utilising studies of eroded calderas geophysical analysis of their structures and analogue modelling of caldera formation as more data has become available on calderas their individuality has become apparent a distinction between caldera caldera complex cauldron and ring structure is necessary and new definitions are given in this paper descriptions of calderas based on dominant composition of eruptives basaltic peralkaline andesitic dacitic rhyolitic can be used and characteristics of each broad group are given styles of eruption may be effusive or explosive with the former dominant in basaltic calderas and the latter dominant in andesitic dacitic rhyolitic and peralkaline calderas four end member collapse styles occur plate or piston piecemeal trapdoor and downsag but many calderas have multiple styles features of so called funnel and chaotic calderas proposed in the literature can be explained by other collapse styles and the terms are considered unnecessary ground deformation comprises subsidence or collapse essential characteristics of a caldera and uplifting doming and fracturing due to tumescence and or resurgence frequent but not essential collapse may occur on pre existing structures such as regional faults or on faults created during the caldera formation and the shape of the collapse area will be influenced by depth size and shape of the magma chamber the final morphology of a caldera will depend on how the caldera floor breaks up whether collapse takes place in one event or multiple events whether vertical movement is spasmodic or continuous throughout the eruptive sequence and whether blocks subside uniformly or chaotically at one or more collapse centres a meaningful description of any caldera should therefore include number of collapse events presence or absence of resurgence caldera floor coherency caldera floor collapse geometry and dominant composition of eruptives

subaqueous calderas in the archean abitibi greenstone belt an overview and new ideas abstract the 300 700 km abitibi greenstone belt in canada contains numerous world class archean volcanogenic massive sulfide vms deposits yet documentation of archean subaqueous calderas hosting such deposits is lacking the modern sunrise deposit in the myojin knoll caldera of the izu bonin arc shows that submarine calderas are first order sites for vms the hunter mine and normetal calderas as well as the blake river megacaldera complex are reviewed with respect to geometry regional geology physical volcanology dyke emplacement and hydrothermal carbonate alteration these subaqueous calderas are placed into the geodynamic context of the abitibi greenstone belt the abitibi belt displays a complex history of oceanic arc formation evolution collision and fragmentation with numerous types of volcanic edifices and sedimentary basins controlled by oblique subduction and mantle plumes analogue models yielding new insights into the sequence of caldera forming events and their synvolcanic fault patterns are applied to explain archean examples underpressure experiments develop a consistent sequence of fault patterns that compare favourably with natural caldera events during subsidence two sets of faults propagate from the magma chamber margin 1 early reverse outward dipping faults and 2 normal inward dipping faults the largest massive sulfide deposits form preferentially at the caldera margin based on experimental studies and detailed facies mapping the hunter mine caldera is of the segmented piecemeal variety and the normetal caldera is akin to a piston structure the blake river megacaldera contains 1 the e w trending misema 2 the nw trending new senator and 3 the ne trending noranda calderas with the latter two being nested graben type calderas consistent with oblique archean subduction the poorly documented hydrothermal carbonate alteration is discussed and a new exploration model for calderas is presented the alteration study was evaluated at three levels microprobe analysis geochemical staining of drill core and whole rock analyses there were two principal stages of alteration related to vms formation an early silicification phase developed either at depth and or at the seawater interface whereby silicification was bedding parallel in fine grained volcaniclastic deposits near the water surface a pervasive and extensive semi conformable carbonate alteration zone with a discordant focused root zone along faults evolved subsequently three distinct carbonate pairings were observed 1 proximal siderite sideroplesite fe ankerite next to the vms deposit 2 an intermediate ankerite fe dolomite zone and 3 a distal calcite dolomite zone the carbonate phase is associated with the mineralizing event transitions between carbonate species are subtle and changes are indicated by mineral assemblage overlap the silica carbonate hydrothermal alteration pattern is a replacement product and is far more widespread than has been documented this alteration can be easily confused with primary carbonates and chemical precipitation deposits e g banded iron formation if detailed volcano sedimentary facies mapping with alteration has not been conducted and if outcrop is insufficient

upper crustal tomographic images of the amiata vulsini geothermal region central italy we computed the three dimensional p wave velocity structure of the upper crust beneath the adjacent amiata and vulsini quaternary volcanoes central italy inverting local earthquake arrival times we used 676 selected earthquakes out of more than 3000 in the m range 1 5 4 0 located between 1977 and 1992 by two contiguous microseismic networks operated by ente nazionale energia elettrica to monitor three geothermal areas namely latera torre alfina and mount amiata the resolving capability of the data set has been verified both with a priori synthetic tests and an a posteriori analysis of the resolution matrix we find a 40 25 7 h km3 crustal volume where we can resolve details as small as 2 to 4 km our analysis is favored by numerous geological and geophysical data collected for geothermal exploration these independent data give us specific constraints for both choosing a starting model and interpreting tomographic results we find high velocity anomalies in the upper 3 km of the crust beneath latera torre alfina and mount amiata geothermal fields related to uplifted limestone units the lateral extension of limestone units is defined by the three dimensional velocity pattern a negative anomaly clearly identifies the radicofani graben a plio quaternary depression filled with low velocity clayey sediments between 1 and 3 km depth a sharp gradient between high velocities 6 9 km s in the northern region and lower velocities in the southern one is recovered at 7 km depth this feature may indicate the transition between the tuscan province uplifted metamorphic crust and thickened carbonate series of the latium province

observational and numerical particle tracking to examine sediment dynamics in a mississippi river delta diversion abstract river diversions may serve as useful restoration tools along coastal deltas experiencing land loss due to high rates of relative sea level rise and the disruption of natural sediment supply diversions mitigate land loss by serving as new sediment sources for land building areas in basins proximal to river channels however because of the paucity of active diversions little is known about how diversion receiving basins evacuate or retain the sediment required to build new land this study uses observational and numerical particle tracking to investigate the behavior of riverine sand and silt as it enters and passes through the west bay diversion receiving basin located on the lowermost mississippi river delta usa fluorescent sediment tracer was deployed and tracked within the bed sediment over a five month period to identify locations of sediment deposition in the receiving basin and nearby river channel a computational fluid dynamics model with a lagrangian sediment transport module was employed to predict selective pathways for riverine flow and sand and silt particles through the receiving basin observations of the fluorescent tracer provides snapshots of the integrated sediment response to the full range of drivers in the natural system the numerical model results offer a continuous map of sediment advection vectors through the receiving basin in response to river generated currents together these methods provide insight into local and basin wide values of sediment retention as influenced by grain size transport time and basin morphology results show that after two weeks of low mississippi river discharge basin silt retention was approximately 60 but was reduced to 4 at the conclusion of the study riverine sand retention was approximately near 100 at two weeks and 40 over the study period modeled sediment storage was predicted to be greatest at the margins of the primary basin transport pathway this matched the observed dynamics of the silt tracer but did not match the behavior of the sand tracer the degree to which the observational measurements deviate from the model predictions may indicate the relative influence of physical processes other than the mean riverine generated currents such as tides wind generated currents and waves

textural equilibria of iron sulfide liquids in partly molten silicate aggregates and their relevance to core formation scenarios the influence of the coexistence of silicate and iron sulfide melts on the wetting of mantle olivine by iron sulfide melt is investigated the dihedral angle between iron alloy and olivine is unaffected by the presence of silicate melt at 1 5 gpa and 1370 1410 c and is much greater than the maximum allowable dihedral angle for melt connectivity at low melt fractions in experimental charges where silicate and sulfide melt occupy the same melt pocket the sulfide melt adheres to olivine grain faces rather than forming discrete droplets the relative interfacial energy between iron sulfide and basaltic silicate melt is lower than that of iron sulfide with olivine but the contrast is not sufficient for basaltic silicate melt to wet fes olivine grain boundaries this result implies that very large silicate melt fractions are necessary to mobilize iron sulfide melts in partially molten silicate phase assemblages therefore segregation of fe rich metallic melts by porous flow at low melt fraction is not a likely process for metal separation the experiments also investigated the influence of the presence of a thermal gradient on sulfide melt migration although the sulfide melt can not migrate through the olivine network by porous flow evidence in the experiments indicates mobility of sulfide through the interconnected silicate melt network the sulfide melt pools in contact with silicate melt at the hot top part of the experimental charges grow over time at the expense of the silicate melt pools in the cooler part of the charge this points to a diffusive transport mechanism for local sulfide redistribution we review literature data on metal olivine wetting angles and find that the metal composition has a dominant influence on the wetting behavior of a metallic liquid on an olivine matrix iron rich metallic liquid compositions are characterized by large dihedral angles 90 the metal olivine dihedral angle decreases with increasing amounts of dissolved light element s c o for light element contents in excess of 59 at the dihedral angle approaches 60 and the wetting behavior of a metallic liquid is similar to that of a silicate liquid

activating and reactivating pairs of nested collapses during caldera forming eruptions campi flegrei italy 1 a structural model for campi flegrei caldera cfc italy one of earth s most hazardous calderas is provided data from the north outer rim show that this formed by downsag soon after the neapolitan yellow tuff emplacement 15 ka campanian ignimbrite s cfc s other major eruption 39 ka displacement at depth also suggests the activity of a buried caldera fault therefore during the campanian ignimbrite eruption the north rim was activated as caldera bounding fault and during the neapolitan yellow tuff eruption as downsag previously published data reveal an inner collapsed structure to the south formed during the campanian ignimbrite eruption and reactivated during the neapolitan yellow tuff eruption so cfc consists of 2 nested depressions both active during the campanian ignimbrite and neapolitan yellow tuff eruptions but with different amounts of collapse cfc is a major example of how 2 nested calderas may 1 form during the same collapse episode 2 be reactivated together during caldera forming eruptions

mapping capable faulting hazard in a moderate seismicity high heat flow environment the tuscia province southern tuscany northern latium italy abstract this study is focused on potential evidence of capable faulting affecting southern tuscany northern latium a region of high heat flow and moderate to low seismicity here we refer to this region as tuscia the latin name for the land of the etruscans the review of the evidence for active tectonics in this area has allowed us to identify several potentially active capable faults mapped using a combination of analysis of digital terrain models with remote sensing and local geological information derived from bibliographic data and different scale maps active and capable faulting is certainly more evident in the eastern sector of tuscia chianti cetona ridge pienza amiata and bolsena caldera however even in the western tuscia e g colline metallifere and tyrrhenian coast capable faulting may be hypothesized along numerous structural elements the characterization of active faulting potential in terms of geometry slip types and rates in such a high heat flow environment beyond its usefulness in improving the assessment of fault displacement and earthquake hazard also helps to improve knowledge of the stress field and structural setting of the many geothermal fields in the area this allows new useful insights into geothermal exploitation and hazard e g induced triggered seismicity moreover this new knowledge of active tectonics and capable faults of the hinterland sector of the northern apennines may also provide useful insights into the siting processes of highly hazardous and strategic structures and more generally in land use planning and management of infrastructures especially during emergencies

quantitative metrics that describe river deltas and their channel networks 1 densely populated river deltas are losing land at an alarming rate and to successfully restore these environments we must understand the details of their morphology toward this end we present a set of five metrics that describe delta morphology 1 the fractal dimension 2 the distribution of island sizes 3 the nearest edge distance 4 a synthetic distribution of sediment fluxes at the shoreline and 5 the nourishment area the nearest edge distance is the shortest distance to channelized or unchannelized water from a given location on the delta and is analogous to the inverse of drainage density in tributary networks the nourishment area is the downstream delta area supplied by the sediment coming through a given channel cross section and is analogous to catchment area in tributary networks as a first step we apply these metrics to four relatively simple fluvially dominated delta networks for all these deltas the average nearest edge distances are remarkably constant moving down delta suggesting that the network organizes itself to maintain a consistent distance to the nearest channel nourishment area distributions can be predicted from a river mouth bar model of delta growth and also scale with the width of the channel and with the length of the longest channel analogous to hack s law for drainage basins the four delta channel networks are fractal but power laws and scale invariance appear to be less pervasive than in tributary networks thus deltas may occupy an advantageous middle ground between complete similarity and complete dissimilarity where morphologic differences indicate different behavior

delta channel networks 1 a graph theoretic approach for studying connectivity and steady state transport on deltaic surfaces river deltas are intricate landscapes with complex channel networks that self organize to deliver water sediment and nutrients from the apex to the delta top and eventually to the coastal zone the natural balance of material and energy fluxes which maintains a stable hydrologic geomorphologic and ecological state of a river delta is often disrupted by external perturbations causing topological and dynamical changes in the delta structure and function a formal quantitative framework for studying delta channel network connectivity and transport dynamics and their response to change is lacking here we present such a framework based on spectral graph theory and demonstrate its value in computing delta s steady state fluxes and identifying upstream contributing and downstream nourishment areas and fluxes from any point in the network we use this framework to construct vulnerability maps that quantify the relative change of sediment and water delivery to the shoreline outlets in response to possible perturbations in hundreds of upstream links the framework is applied to the wax lake delta in the louisiana coast of the u s and the niger delta in west africa in a companion paper we present a comprehensive suite of metrics that quantify topologic and dynamic complexity of delta channel networks and via application to seven deltas in diverse environments demonstrate their potential to reveal delta morphodynamics and relate to notions of vulnerability and robustness

the delta connectome a network based framework for studying connectivity in river deltas abstract many deltas including the mississippi river delta have been losing land at fast rates compromising the safety and sustainability of their ecosystems knowledge of delta vulnerability has raised global concern and stimulated active interdisciplinary research as deltas are densely populated landscapes rich in agriculture fisheries oil and gas and important means for navigation there are many ways of looking at this problem which all contribute to a deeper understanding of the functioning of coastal systems one aspect that has been overlooked thus far yet fundamental for advancing delta science is connectivity both physical how different portions of the system interact with each other as well as conceptual pathways of process coupling in this paper i propose a framework called delta connectome for studying connectivity in river deltas based on different representations of a delta as a network after analyzing the classic network representation as a set of nodes e g bifurcations and junctions or regions with distinct physical or statistical behavior and links e g channels i show that from connectivity considerations the delta emerges as a leaky network that continuously exchanges fluxes of matter energy and information with its surroundings and evolves over time i explore each network representation and show through several examples how quantifying connectivity can bring to light aspects of deltaic systems so far unexplored and yet fundamental to understanding system functioning and informing coastal management and restoration this paper serves both as an introduction to the delta connectome framework as well as a review of recent applications of the concepts of network and connectivity to deltaic systems within the connectome framework

stratigraphy and paleohydrology of delta channel deposits jezero crater mars abstract the jezero crater open basin lake contains two well exposed fluvial sedimentary deposits formed early in martian history here we examine the geometry and architecture of the jezero western delta fluvial stratigraphy using high resolution orbital images and digital elevation models dems the goal of this analysis is to reconstruct the evolution of the delta and associated shoreline position the delta outcrop contains three distinct classes of fluvial stratigraphy that we interpret from oldest to youngest as 1 point bar strata deposited by repeated flood events in meandering channels 2 inverted channel filling deposits formed by avulsive distributary channels and 3 a valley that incises the deposit we use dems to quantify the geometry of the channel deposits and estimate flow depths of 7 m for the meandering channels and 2 m for the avulsive distributary channels using these estimates we employ a novel approach for assessing paleohydrology of the formative channels in relative terms this analysis indicates that the shift from meandering to avulsive distributary channels was associated with an approximately four fold decrease in the water to sediment discharge ratio we use observations of the fluvial stratigraphy and channel paleohydrology to propose a model for the evolution of the jezero western delta the delta stratigraphy records lake level rise and shoreline transgression associated with approximately continuous filling of the basin followed by outlet breaching and eventual erosion of the delta our results imply a martian surface environment during the period of delta formation that supplied sufficient surface runoff to fill the jezero basin without major drops in lake level but also with discrete flooding events at non orbital e g annual to decadal timescales

40 ar 39 ar ages and stratigraphy of the latera caldera italy the latera caldera is a well exposed volcano where more than 8 km3 of mafic silica undersaturated potassic lavas scoria and felsic ignimbrites were emplaced between 380 and 150 ka isotopic ages obtained by 40ar 39ar analysis of single sanidine crystals indicate at least four periods of explosive eruptions from the caldera the initial period of caldera eruptions began at 232 ka with emplacement of trachytic pumice fallout and ignimbrite they were closely followed by eruption of evolved phonolitic magma after roughly 25 ky several phonolitic ignimbrites were deposited and they were followed by phreatomagmatic eruptions that produced trachytic ignimbrites and several smaller ash flow units at 191 ka compositionally zoned magma then erupted from the northern caldera rim to produce widespread phonolitic tuffs tephriphonolitic spatter and scoria bearing ignimbrites after 40 ky of mafic surge deposit and scoria cone development around the caldera rim a compositionally zoned pumice sequence was emplaced around a vent immediately northwest of the latera caldera this activity marks the end of large scale explosive eruptions from the latera volcano at 156 ka

the las canadas caldera tenerife canary islands an overlapping collapse caldera generated by magma chamber migration abstract the las canadas caldera is one of the most important geological structures of tenerife stratigraphic structural volcanological petrological geochronological and geophysical data suggest that the las canadas caldera resulted from multiple vertical collapse episodes that occurred during the construction of the las canadas edifice upper group three long term 200 ka cycles of phonolitic explosive activity each culminating with a caldera collapse have been identified in the upper group during the construction of the upper group the focus of felsic volcanism migrated from west to east using the results of field observations experimental analogue models and numerical studies we propose that the formation of the overlapping las canadas collapse caldera is related to the migration of the associated magma chamber our model implies that each collapse of this overlapping caldera partly or completely destroyed the feeding magma chamber this destruction led to changes in the local stress field that favoured the formation of a new chamber at one side of the previous one resulting in magma chamber migration the proposed model accounts for the formation of the las canadas caldera in particular it explains the geometrical relationships stratigraphy and chronology of the caldera wall deposits comparison with other overlapping collapse calderas suggests that our model may apply to other overlapping calderas

splitting rivers at their seams bifurcations and avulsion river bifurcations are critical but poorly understood elements of many geomorphological systems they are integralelements of alluvial fans braided rivers fluvial lowland plains and deltas and control the partitioning of water and sediment throughthese systems bifurcations are commonly unstable but their lifespan varies greatly in braided rivers bars and channels migrate splitand merge at annual or shorter timescales thereby creating and abandoning bifurcations this behaviour has been studied mainly bygeomorphologists and fluid dynamicists bifurcations also exist during avulsion the process of a river changing course on afloodplain or in a delta which may take 102 103years and has been studied mainly by sedimentologists this review synthesizesour current understanding of bifurcations and brings together insights from different research communities and different environmen tal settings we consider the causes and initiation of bifurcations and avulsion the physical mechanisms controlling bifurcation andavulsion evolution mathematical and numerical modelling of these processes and the possibility of stable bifurcations we end thereview with some open questions copyright 2012 john wiley sons ltd

inferring surface currents within submerged vegetated deltaic islands and wetlands from multi pass airborne sar abstract water flow patterns across coastal and deltaic wetlands affect biogeochemical cycling denitrification organic carbon burial and coastal landscape evolution our understanding of such patterns across these important landscapes is incomplete however because of the inherent difficulty of conducting spatially and temporally dense ground or boat based surveys in shallow vegetated terrain we conducted an airborne l band synthetic aperture radar sar acquisition campaign on wax lake delta louisiana usa in may 2015 to investigate whether water velocities and flow patterns over kilometer scales can be determined from remote sensing thirteen sar flight lines over the delta region were acquired in 3 h with six different flight directions concurrently with a small boat campaign we show that sar azimuth displacement due to doppler shift can be used to estimate the surface water flow relative to the static and submerged vegetation interspersed on delta islands using a simple bragg wave scattering model and accounting for the bragg wave s free velocity and wind drift at wax lake delta we find that 0 40 m s water velocities within the main deltaic channels slow to 0 1 0 2 m s as flow spreads laterally across and converges within the vegetated islands coinciding with shallow

caldera structure amount of collapse and erupted volumes the case of bolsena caldera italy calderas are common on volcanoes but their structure is seldom visible the 19 km wide bolsena caldera italy formed between 0 6 and 0 2 ma the largely preserved structural rim and subsurface data make bolsena ideal to investigate caldera structure in relation to the subsidence and erupted volume in this paper we use remote sensing field analysis and available subsurface data at the surface the caldera passes from a downsag south rim to a narrow and densely faulted area north rim with outer normal and inner reverse faults the caldera structure on the widely faulted east rim appears to be scale dependent with a staircase like fault zone larger scale horst and graben like structures intermediate scale and domino like structures smaller scale subsurface data indicate asymmetric collapse with a northward increase in subsidence ranging from diffuse to the south to focused to the north deformation at the surface the collapse rate constant between ca 490 and 175 ka was more than magma output between ca 330 and 130 ka highlighting significant 200 m and prolonged 200 ka posteruptive subsidence as the nearby latera caldera west rim of bolsena was mostly active between ca 265 and 160 ka much of the subsidence at bolsena may be related to this activity suggesting a common magmatic reservoir the subsidence related structural variations along the caldera rim and the significant posteruptive subsidence found at bolsena have not been found in other calderas

punctuated sand transport in the lowermost mississippi river 1 measurements of sand flux and water flow in the mississippi river are presented for a portion of the system 35 50 km upstream from the head of its subaerial delta these data are used to provide insight into how nonuniform flow conditions present in the lower reaches of large alluvial rivers affect the timing and magnitude of sand transport near the river outlet field surveys during both low and high water discharge include 1 sequential digital bathymetric maps defining mobile river bottom topography which were used to estimate bed material flux 2 multiple water velocity profiles and 3 multiple suspended sediment profiles collected using a point integrated sampler these data show that total sand transport increases by two orders of magnitude over the measured range in water discharge 11 300 to 38 400 m3 s 1 during low water discharge no sand is measured in suspension and sand discharge via bed form migration is minimal during high water discharge 54 of the sand discharge is measured in suspension while 46 of the sand discharge is part of bed form migration the component of boundary shear stress associated with moving this sediment is estimated using a set of established sediment transport algorithms and values for the total boundary shear stress are predicted by fitting logarithmic velocity functions to the measured profiles the estimates of boundary shear stress using measurements of suspended sand transport bed form transport and downstream oriented velocity profiles are internally consistent moreover the analyses show that boundary shear stress increases by nearly 10 fold over the measured water discharge range we show how this increase in shear stress is consistent with backwater flow arising where the river approaches its outlet the hydrodynamic properties of backwater flow affect the timing and magnitude of sand flux and produce punctuated sand transport through the lowermost mississippi river our field data are used to evaluate the influence of this sand transport style on development of the mixed bedrock alluvial channel for the lowermost mississippi river

tectonically controlled piecemeal caldera collapse a case study of glencoe volcano scotland caldera collapse at glencoe scotland was incremental and involved complex movements of numerous fault blocks before formation of the ring fault for which the volcano is renowned intracaldera depocenters had the form of grabens or half grabens locally with downsag and bounding monoclinal flexures and these changed form and location for each of the five major ignimbrite eruptions that represent the early volcanic history this piecemeal caldera collapse is in contrast to previous interpretations in which all subsidence was thought to have involved a coherent crustal block moving on the ring fault collapse and magmatic plumbing were profoundly influenced by preexisting tectonic faults trending northwest and northeast a dominant northwest trending graben controlled the general location and form of major caldera depocenters and repeatedly channeled a major river through glencoe the main graben was transected orthogonally by two cross grabens each of the first three caldera eruption cycles involved initial phreatomagmatic explosivity which built tuff cones followed by magmatic fountaining that produced lava like silicic ignimbrites the three lava like ignimbrites total more than 300 m thick two later eruptions produced eutaxitic silicic ignimbrites together more than 300 m thick and contemporaneous progressive downsag was associated with the formation of extensional fractures crevasses hundreds of meters deep sills up to 100 m thick of mingled andesite and rhyolite between the intracaldera ignimbrites were accommodated by increments of subsidence unconformities and sedimentary layers within the stratigraphic succession record fluvial erosion and abrupt switches to alluvial and or lacustrine deposition between each ignimbrite eruption the changes in drainage and sedimentation and the development of coarse debris avalanche breccias reflect tectonic faulting during the periods between major eruptions the duration of the period including the five caldera forming eruptions was probably 0 5 m y and the magnitude of the tectonic faulting that occurred prior to and during the caldera developments 0 5 km m y normal displacement is similar to that of the most actively subsiding sedimentary basins glencoe shows that the piecemeal nature of calderas may be plainly evident only in deeply dissected systems which with knowledge that caldera volcanoes commonly overlie faults suggests that piecemeal calderas may be more common than previously recognized the research also shows that the emplacement of granites s l was episodic rather than synchronous throughout the magmatic province and it suggests that numerous plutons in the province e g in donegal ireland may have formed at sites of central volcanoes that are no longer preserved

topset dominated deltas a new model for river delta stratigraphy in the late 1800s g k gilbert provided the first stratigraphic description of river delta deposits but later work revealed that the gilbert type model long thought to be universal did not apply to all deltas here we propose that in addition to gilbert type deltas herein called foreset dominated there is a class of deltas with a basic first order stratigraphy that is topset dominated we develop a geometric model that predicts the occurrence of each delta type by calculating the topset and foreset thicknesses under different fluvial and basinal conditions our model predicts that topset dominated deltas have a novel characteristic their distributary channels commonly incise into pre delta sediment this type of delta should be common on shelves where the slope is less than 0 05 and the river feeding the delta has a discharge greater than 200 m 3 s field data from gulf of mexico deltas confirm the prediction that distributary channels often incise into pre delta sediment finally we propose a new stratigraphic model for topset dominated deltas and suggest that future stratigraphic interpretation must distinguish between delta types because the cause of channel incision for each is different and may be unrelated to allogenic changes

dynamic reorganization of river basins river networks evolve as migrating drainage divides reshape river basins and change network topology by capture of river channels we demonstrate that a characteristic metric of river network geometry gauges the horizontal motion of drainage divides assessing this metric throughout a landscape maps the dynamic states of entire river networks revealing diverse conditions drainage divides in the loess plateau of china appear stationary the young topography of taiwan has migrating divides driving adjustment of major basins and rivers draining the ancient landscape of the southeastern united states are reorganizing in response to escarpment retreat and coastal advance the ability to measure the dynamic reorganization of river basins presents opportunities to examine landscape scale interactions among tectonics erosion and ecology

asymmetric multiple block collapse at rotorua caldera taupo volcanic zone new zealand calderas worldwide have been classified according to their dominant collapse styles although there is a good deal of speculation about the processes involved recent laboratory experiments have tried to constrain these processes by modelling magma withdrawal and observing the effects on overlying materials however many other factors also contribute to final caldera morphology rotorua caldera formed during the eruption of the mamaku ignimbrite collapse structure and evolution of rotorua caldera is interpreted based its geophysical response geology and geomorphology and the stratigraphy of the mamaku ignimbrite rotorua caldera is situated at the edge of the extensional taupo volcanic zone in which major faults strike ne sw a second less dominant fault set strikes nw se these two fault sets have a strong influence on the morphology of rotorua caldera no one style of collapse can be applied to rotorua caldera it was formed during a single eruption but subsided as many blocks and shows features of trapdoor piecemeal and downsag types of collapse here rotorua caldera is described according to its composition activity and geometry as a rhyolitic single event asymmetric multiple block single locus collapse structure the mamaku ignimbrite is the only ignimbrite to have erupted from rotorua caldera extracaldera thickness of the mamaku ignimbrite is up to 145 m whereas inside the caldera it may be greater than 1 km thick the mamaku ignimbrite can be separated into a basal tephra sequence and main ignimbrite sequence the main ignimbrite sequence contains no observable flow unit boundaries but can be split into lower middle and upper parts lmi mmi umi respectively based on crystal content welding jointing devitrification and vapour phase alteration juvenile clasts within the ignimbrite comprise three consanguineous silicic pumice types and andesitic fragments only the most evolved pumice type occurs in the basal tephra sequence all three pumice types occur together throughout the main ignimbrite sequence whereas the andesitic fragments are only present in umi lithic lag breccias in umi indicate a late stage of caldera collapse concentration of lithic fragments increases towards the middle of the ignimbrite and may also reflect increased subsidence rate during an earlier stage collapse of rotorua caldera is thought to have occurred throughout the eruption of the main ignimbrite sequence of the mamaku ignimbrite allowing simultaneous eruption of all the different pumice types and causing the abrupt transition from deposition of the basal tephra sequence to the main ignimbrite sequence

modeling river delta formation a model to simulate the time evolution of river delta formation process is presented it is based on the continuity equation for water and sediment flow and a phenomenological sedimentation erosion law different delta types are reproduced by using different parameters and erosion rules the structures of the calculated patterns are analyzed in space and time and compared with real data patterns furthermore our model is capable of simulating the rich dynamics related to the switching of the mouth of the river delta the simulation results are then compared with geological records for the mississippi river

scaling relationships and evolution of distributary networks on wave influenced deltas 1 no genetic model can explain the variability in distributary network pattern on modern deltas here we derive scaling relationships for two processes known to create distributary channels and with these laws construct a simple model for distributary network evolution the first process is mouth bar deposition at the shoreline and subsequent channel bifurcation the second is avulsion the wholesale abandonment of a channel in favor of a new path the former creates relatively small networks with power law distributions of channel length the latter generates relatively few backwater scale distributaries frequency magnitude plots of channel length on natural deltas agree with theoretical predictions and show a clear separation in scale that reflects these processes mouth bar distributary lengths scale with the width of the parent channel and avulsive distributary lengths scale with the backwater length intermediate channel lengths are relatively rare wave energy controls network topology by suppressing mouth bar development thereby preferentially eliminating smaller scale distributaries

turbulent characteristics of a shallow wall bounded plane jet experimental implications for river mouth hydrodynamics jets arising from rivers streams and tidal flows entering still waters differ from most experimental studies of jets both in aspect ratio and in the presence of a solid bottom boundary and an upper free surface despite these differences the applicability of experimental jet studies to these systems remains largely untested by either field or realistically scaled experimental studies here we present experimental results for a wall bounded plane jet scaled to jets created by flow discharging into floodplain lakes a characteristic feature of both our prototype and experimental jets is the presence of large scale meandering turbulent structures that span the width of the jets in our experimental jets we observe self similarity in the distribution of mean streamwise velocities by a distance of six channel widths downstream of the jet outlet after a distance of nine channel widths the velocity decay and the spreading rates largely agree with prior experimental results for plane jets the magnitudes and distributions of the cross stream velocity and lateral shear stresses approach self preserving conditions in the upper half of the flow but decrease in magnitude and deviate from self preserving distributions with proximity to the bed the presence of the meandering structure has little influence on the mean structure of the jet but dominates the jet turbulence a comparison of turbulence analysed at time scales both greater than and less than the period of the meandering structure indicates that these structures increase turbulence intensities by 3 5 times and produce lateral shear stresses and momentum diffusivities that are one and two orders of magnitude greater respectively than turbulence generated by bed friction alone

three types of pyroclastic currents and their deposits examples from the vulsini volcanoes italy abstract this paper deals with ground hugging gas pyroclast currents from explosive volcanic eruptions and their deposits key field observations and laboratory determinations are proposed to relate specific deposit types with flow regimes and particle concentration in the transport and depositional systems three relevant flow scenarios and corresponding deposit types have been recognized from a survey of pyroclastic successions of the vulsini volcanic district central italy 1 dilute turbulent pyroclastic currents producing normally or multiply graded beds by direct suspension sedimentation 2 concentrated bedload regions beneath suspension currents depositing inversely graded beds by traction carpet sedimentation 3 self sustained high particle concentration laminar mass flows developing massive poorly sorted bodies with opposite grading of coarse lithic and pumice clasts overlying fine grained inversely graded basal layers main distinguishing criteria include the occurrence and pattern of clast grading clast thickness relationships grain size ash matrix componentry and pyroclast size density relationships downcurrent and temporal transitions among identified flow scenarios are likely to occur for changing energy conditions and gas pyroclast ratio both on regional and local scales the nature and efficiency of magma fragmentation volatile content conduit geometry which determine the characteristics of the erupted mixture and possible lateral blast component at the vent and the angle of incidence of the column collapse are suggested as the main factors controlling the generation of one type over the other at flow inception dilute fine grained overpressured eruption clouds are thought to favor the formation of low particle concentration turbulent currents column collapse over slightly inclined volcano slopes causing a high degree of compression of the collapsing mixture and of gas expulsion would favor the generation of high particle concentration pyroclastic currents

the restless resurgent campi flegrei nested caldera italy constraints on its evolution and configuration abstract we have collected new stratigraphic data in the campi flegrei caldera through surface geological mapping and study of cores drilled to various depths we integrate these data with geological geochronological and geophysical constraints available in the literature to reconstruct the volcanic and deformational history of the caldera the caldera is a resurgent nested structure resulting from two main collapses related to the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the younger nested caldera structure although most of the caldera floor consists of multiple structural blocks due to long term deformations magmas were able to erupt only in one sector of the resurgent part the caldera has shown signs of unrest during the past 25 years with short term deformations that have generated a net uplift of 3 5 m the short term deformations are related to the neapolitan yellow tuff caldera resurgence and interpreted as the net result of brittle and ductile components the long term deformations likely represent the sum of the permanent brittle component of each short term deformational event

satellite observations of small coastal ocean eddies in the southern california bight this study describes the characteristics of extensive small scale coastal ocean eddies in the southern california bight these surface features were primarily detected by using ers 1 and ers 2 synthetic aperture radar sar satellite imagery from 1992 to 1998 the eddies predominantly cyclonic in their rotation appeared to result from several forcing mechanisms they were mainly observed within the santa barbara channel and the santa monica san pedro basin regions and appeared to be seasonal in their distribution observed eddy diameters were all less than 50 km with over 70 less than 10 km the sar data were complemented by sea surface temperature measurements derived from advanced very high resolution radiometer satellite imagery as well as in situ data from moorings and drifters that provided substantial verification of the small scale eddies these findings are significant in that the eddies were in general smaller in size and more abundant than previously reported additionally these results provide further evidence of the complex near surface circulation within the southern california bight with important implications for nutrient flux productivity plankton patchiness larval transport and recruitment and dispersal of pollutants

mechanics of river mouth bar formation implications for the morphodynamics of delta distributary networks 1 in this paper we use observational data and numerical modeling to present a new explanation for the formation of river dominated delta networks observational data from deltas throughout the world show that distributary channel widths depths and lengths decrease nonlinearly with successive bifurcations trends in width and depth are an outcome of hydraulic geometry scaling the trend in channel length is a consequence of delta growth analyses of serial maps show that the positions of bifurcations are the fossilized locations of river mouth bars also called middle ground and distributary mouth bar in front of old delta channel mouths therefore the trend in channel length can be explained through the mechanics of river mouth bar formation and evolution we use delft3d a coupled hydrodynamic and morphodynamic model to simulate the process of river mouth bar formation within an expanding turbulent jet in front of distributary channel mouths our results describe in detail the formation and evolution of a river mouth bar system and demonstrate that the distance to the river mouth bar is proportional to jet momentum flux and inversely proportional to grain size therefore channel length decreases down delta because with each successive bifurcation the jet momentum flux decreases these results can be used to predict the future evolution of river dominated deltas and can be used to aid in hydrocarbon exploration of these depositional environments

what controls the transition from confined to unconfined flow analysis of hydraulics in a river delta abstractrecent field work at the wax lake delta wld in coastal louisiana indicates lateral outflow from channels to islands upstream of the receiving basin in this region of the delta the flow t

the basal ash deposit of the sovana eruption vulsini volcanoes central italy the product of a dilute pyroclastic density current a low aspect ratio decimeter thick ash deposit axisymmetrically distributed around the latera caldera western vulsini volcanoes central italy has been studied by means of field and laboratory investigations field studies comprise facies analysis at centimeter scale and maximum clast size and deposit thickness measurements grain size and component distribution chemical composition and particle morphoscopic features have been determined on selected samples we discuss the co ignimbrite ash fall vs pyroclastic surge origin of the deposit and the hydrovolcanic vs magmatic eruption nature complex facies association textural features and grain size data rule out an ash fall origin for the whole deposit the hydrovolcanic nature of the eruption has been discarded on the grounds of componentry and morphoscopic features of vitric fragments we propose that the main body of the ash deposit formed from a radially expanding dilute turbulent pyroclastic density current originated by a continuous collapse of a low altitude a few kilometers eruptive column with a possible radial jet component

a unifying framework for shoreline migration 1 multiscale shoreline evolution on sedimentary coasts 1 a unifying framework for shoreline migration is presented which synthesizes problems from coastal engineering geomorphology and stratigraphy into a common quantitative basis consideration of characteristic problems from these fields reveals that multiscale shoreline evolution problems naturally break into three classes on the basis of the morphologic unit of evolution shoreface bed versus shoreline planform versus stratigraphic shoreline trajectory shoreline evolution models correspondingly break into morphodynamic morphokinematic and hybrid approaches a generalized shoreline continuity equation is derived the shoreline exner equation which subsumes equilibrium profile models commonly used in geomorphology and engineering and provides a natural framework for interpreting shoreline trajectories preserved in the sedimentary record the shoreline exner equation provides a rigorous basis for geometric and moving boundary models which have significant untapped potential for shoreline migration problems recent advances in computational methods for evolving interface problems make hybrid models particularly attractive for problems of large scale planform shoreline dynamics such as delta evolution

controls on the spacing of first order valleys 1 many landscapes are composed of ridges and valleys that are uniformly spaced even where valley locations are not controlled by bedrock structure models of long term landscape evolution have reproduced this phenomenon yet the process by which uniformly spaced valleys develop is not well understood and there is no quantitative framework for predicting valley spacing here we use a numerical landscape evolution model to investigate the development of uniform valley spacing we find that evenly spaced valleys arise from a competition between adjacent drainage basins for drainage area a proxy for water flux and that the spacing becomes more uniform as the landscape approaches a topographic equilibrium valley spacing is most sensitive to the relative rates of advective erosion processes such as stream incision and diffusion like mass transport such as soil creep and less sensitive to the magnitude of a threshold that limits the spatial extent of stream incision analysis of a large number of numerical solutions reveals that valley spacing scales with a ratio of characteristic diffusion and advection timescales that is analogous to a peclet number we use this result to derive expressions for equilibrium valley spacing and drainage basin relief as a function of the rates of advective and diffusive processes and the spatial extent of the landscape the observed scaling relationships also provide insight into the cause of transitions from rill like drainage networks to branching networks the spatial scale of first order drainage basins the contributing area at which hillslopes transition into valleys and the narrow range of width to length ratios of first order basins

a review of sediment diversion in the mississippi river deltaic plain abstract one of the proposed methods for restoring the disappearing mississippi delta is sediment diversion which uses channels and structures to divert water and sediment from the mississippi and atchafalaya rivers into adjacent basins this study presents a comprehensive review of geological and physical aspects of sediment dynamics in the mississippi river deltaic plain mrdp with special reference to diversion studies over the past two decades we synthesize these studies present the current understanding of sediment diversions in the context of sediment dynamics identify multiple key knowledge gaps and make recommendations for future studies to maximize net land building in the mrdp management strategies should be focused on a enhancing river sediment delivery both mud and sand b increasing sediment retention in receiving basins and c minimizing erosion in bays and estuaries compared with extensive studies of land building there have been relatively fewer studies of erosional processes a heterogeneous coastal geological framework cohesive sediment erodibility and subsidence together play complicated yet critical roles in future sediment dynamics in bays and estuaries of the mrdp sediment retention rates are highly sensitive to spatial and temporal scales types of sediments and delivery season sediment diversions to seaward receiving basins provide more surge protection but tend to have lower sediment retention due to active coastal processes structures and devices that improve sediment retention trap sediments dissipate waves and build living shorelines should be explored and cost to benefit analysis is needed long term planning should consider more landward diversions strategic community relocation and nonlinear response of the complex sedimentary system of the mrdp

evidence for sub lacustrine volcanic activity in lake bolsena central italy revealed by high resolution seismic data sets abstract the bolsena caldera that formed between 0 6 and 0 2 ma has a well preserved structural rim which makes it an ideal site to study the tectonic and volcanic evolution of calderas however the main area is covered by a 150 m deep lake which makes it rather difficult to investigate the subsurface structure directly to overcome this problem new high resolution hydro acoustic surveys using a multichannel reflection seismic system and a sediment echo sounder system were conducted in september 2012 as space was limited we used a rowing boat towed by a rubber boat to handle a 36 m long and 24 channel streamer to receive seismic reflections produced using a mini gi gun 0 25 l the subsurface structure of lake bolsena was imaged up to a sediment depth of 190 m which is estimated to have filled over a period of 333 kyrs however massive pyroclastic flow deposits found in the deeper parts of the basin indicate an initial infill of volcanic deposits from two adjacent younger calderas the latera w and montefiascone se calderas our data suggest that the caldera has a long history of active volcanism because the lacustrine sediments show post sedimentary influences of geothermal fluids we mapped several mound structures at various stratigraphic depths two volcanic structures outcrop at the modern lake surface implying recent activity one of these structures is hardly covered by sediments and has a crater like feature in its summit the other structure shows a pockmark like depression on top another observable feature is a partially sediment filled crater located in the western part of the lake which further implies the existence of a magma chamber located beneath the bolsena caldera since the late pleistocene and holocene the sedimentation was mainly hemipelagic evidenced by a sediment drape of up to 10 m thick sediment drape on the uppermost sediments beneath the drape we found evidence for a distal tephra layer likely related to an explosive eruption from the campanian volcanic province occurring as the neapolitan yellow tuff our new geophysical data set is a valuable record with a potential to constrain the sedimentary and volcanic evolution of the vulsini volcanic district in areas that have not been assessed previously due to logistical challenges of conducting surveys in water filled settings

caldera collapse during the 2000 eruption of miyakejima volcano japan a collapsed caldera 1 6 km in diameter and 450 m in depth was formed at the summit of miyakejima volcano during the 2000 eruption the collapsed caldera appeared on 8 july with a minor phreatic eruption 12 days after seismic activity and magma intrusion occurred northwest of the volcano growth of the caldera took from 8 july to the middle of august with seismic swarms associated with the continuous intrusion of magma northwest of the volcano the growth rate of the caldera was about 1 4 107 m3 day and the final volume of the collapsed caldera was about 6 108 m3 major phreatomagmatic eruptions produced a total of about 1 6 1010 kg 1 1 107 m3 of volcanic ash after caldera growth the caldera structure and the nature of the eruptive materials of the first collapse on 8 july suggest that the surface subsidence was caused by the upward migration of a steam filled cavity with stoping of the roof rock above the magma reservoir the diameter of the stoping column was estimated to be 600 700 m from circumferential faults that developed in the caldera floor and the collapse of the caldera wall enlarged the diameter of the caldera to 1 6 km the total volume of the caldera and the horizontal diameter of the stoping column gave a subsidence of the caldera floor of 1 6 2 1 km

quantifying the stratigraphic completeness of delta shoreline trajectories understanding the incomplete nature of the stratigraphic record is fundamental for interpreting stratigraphic sequences methods for quantifying stratigraphic completeness for one dimensional stratigraphic columns defined as the proportion of time intervals of some length that contain stratigraphy are commonplace however quantitative assessments of completeness in higher dimensions are lacking here we present a metric for defining stratigraphic completeness of two dimensional shoreline trajectories using topset foreset rollover positions in dip parallel sections and describe the preservation potential of a shoreline trajectory derived from the geometry of the delta surface profile and the kinematics of the geomorphic shoreline trajectory two end member forward models are required to fully constrain the preservation potential of the shoreline dependent on whether or not a topset is eroded during base level fall a laboratory fan delta was constructed under nonsteady boundary conditions and one dimensional stratigraphic column and two dimensional shoreline completeness curves were calculated results are consistent with the hypothesis derived from conservation of sediment mass that completeness over all timescales should increase given increasing dimensions of analysis stratigraphic trajectories and completeness curves determined from forward models using experimental geomorphic trajectories compare well to values from transects when subsampled to the equivalent stratigraphic resolution as observed in the actual preserved sequence the concept of stratigraphic completeness applied to two dimensional trajectory analysis and the end member forward models presented here provide novel tools for a conceptual understanding of the nature of stratigraphic preservation at basin scales

evidence of incremental growth in the vulsinian calderas central italy abstract a comparative work on the vulsini calderas has been carried out fundamentally from volcanological field study drilling and gravity anomalies data on the basis of a detailed stratigraphy four volcanic complexes have been recognized in the vulsini volcanic district from the oldest to the youngest paleo bolsena bolsena montefiascone and latera the latter two complexes having a contemporaneous evolution in their activity each complex gave rise to several little calderas caused by piecemeal collapses due to moderate size explosive eruptions or coherent subsidence of a superficial piston like block nevertheless the extensional volcano tectonic regime affecting this area could have accounted for as much of the total subsidence as the caldera forming eruptions bolsena and latera calderas respectively 16 km and 8 km in average diameter represent the main depressions of the vulsini district and their topographic features are still well preserved several collapses forming the main poligenetic calderas of bolsena and latera are masked at present by the bolsena lake the younger volcanic covering the lacustrine deposits and erosion in a minor amount only the little montefiascone and vepe calderas which represent the youngest collapses of the vulsini area have not been masked bolsena caldera could be considered a depression caused mostly by a subsidence hinged to the southwest by down sagging and by collapses which occurred after the most important explosive eruptions of the paleo bolsena bolsena and montefiascone volcanic complexes meanwhile latera caldera is mostly due to a piecemeal collapse linked to several moderate size ignimbrite units which were emplaced throughout the explosive activity of the latera complex therefore the vulsinian calderas did not form by catastrophic eruptions because several and frequent moderate size eruptions downsagging and tectonic hinged subsidence concur indicating an incremental growth

a potential vorticity theory for the formation of elongate channels in river deltas and lakes 1 rivers empty into oceans and lakes as turbulent sediment laden jets which can be characterized by a gaussian horizontal velocity profile that spreads and decays downstream because of shearing and lateral mixing at the jet margins recent experiments demonstrate that this velocity field controls river mouth sedimentation patterns in nature diffuse jets are associated with mouth bar deposition forming bifurcating distributary networks while focused jets are associated with levee deposition and the growth of elongate channels that do not bifurcate river outflows from elongate channels are similar in structure to cold filaments observed in ocean currents where high potential vorticity helps to preserve coherent structure over large distances motivated by these observations we propose a hydrodynamic theory that seeks to predict the conditions under which elongate channels form our approach models jet velocity patterns using the flow vorticity both shearing and lateral spreading are directly related to the vertical component of vorticity we introduce a new kind of potential vorticity that incorporates sediment concentration and thus allows study of jet sedimentation patterns the potential vorticity equation reduces the number of fluid momentum equations to one without losing generality this results in a compact analytical solution capable of describing the streamwise evolution of the potential vorticity of a sediment laden jet from initial conditions at the river mouth our theory predicts that high potential vorticity is a necessary condition for focused levee deposition and the creation of elongate channels comparison to numerical laboratory and field studies indicates that potential vorticity is a primary control on channel morphology our results may be useful for designing river delta restoration schemes such as the proposed mississippi delta diversion

importance of frictional effects and jet instability on the morphodynamics of river mouth bars and levees 1 in this work extensive numerical simulations have been performed to assess the hydrodynamic and morphodynamic behavior of a river jet debouching in a large quiescent water body a refined three dimensional grid has been used to capture the transition zone between a stable jet and an unstable meandering jet the model results show that the stability number s which is a function of friction and river mouth aspect ratio and the mouth reynolds number are the two parameters that describe the stable unstable character of the jet from a morphodynamic point of view a stable jet always tends to form a mouth bar however a decrease of the stability number together with jet instability increase the delivery of sediments to the jet margins favoring the formation of subaerial levees and elongated channels frictional effects play a major role to set the distance at which the mouth bar becomes stagnant the importance of the stability number in setting depositional patterns at the river mouth is larger than other variables i e momentum of the jet and potential vorticity and therefore should be considered in the design of restoration schemes for deltaic land

airborne radar imaging of subaqueous channel evolution in wax lake delta louisiana usa shallow coastal regions are among the fastest evolving landscapes but are notoriously difficult to measure with high spatiotemporal resolution using uninhabited aerial vehicle synthetic aperture radar uavsar data we demonstrate that high signal to noise l band synthetic aperture radar sar can reveal subaqueous channel networks at the distal ends of river deltas using 27 uavsar images collected between 2009 and 2015 from the wax lake delta in coastal louisiana usa we show that under normal tidal conditions planform geometry of the distributary channel network is frequently resolved in the uavsar images including 700 m of seaward network extension over 5 years for one channel uavsar also reveals regions of subaerial and subaqueous vegetation streaklines of biogenic surfactants and what appear to be small distributary channels aliased by the survey grid all illustrating the value of fine resolution low noise l band sar for mapping the nearshore subaqueous delta channel network

the effect of wind waves on the development of river mouth bars 1 river deltas are among the most important environments on earth housing productive ecosystems and a large fraction of the human population the key process for delta development is the deposition of mouth bars in front of delta distributaries predicting mouth bar formation on marine coastlines is complex because of the interactions between waves tides water and sediment discharge here we study the effects of waves on mouth bar growth with the coupled sediment transport and wave model delft3d swan our results show that wave characteristics height period and direction play an important role in the formation of mouth bars in our numerical experiments waves affect bar development in three ways by modifying the direction of the river jet by increasing bottom shear stresses at the river mouth and by changing bottom friction and hence increasing jet spreading we further show that high waves with long period prevent the formation of mouth bars in particular wave angles between 45 and 60 are the least favorable to bar formation likely producing a deflected river mouth

plinian fall deposits from vulsini volcanic district central italy stratigraphic investigations of the vulsini volcanic district indicate the existence of five prominent plinian fall deposits deposited over a period of about 0 34 ma the oldest deposit basal pumices crops out mainly in the peripheral areas and is one of the largest plinian events in the vulsini district with a volume of about 9 km3 and a calculated column height exceeding 30 km subcircular patterns of isopachs and isopleths around the bolsena lake indicate emplacement in wind free conditions and suggest a source vent location in the northernmost sector of the present bolsena lake where it is possible that an older central volcanic structure existed the four younger plinian fall deposits are related to bolsena activity the oldest of these named the ponticello and orvieto bagnoregio pumices are mainly distributed on the north eastern sector of the vulsini district their volumes are an order of magnitude lower than that of the basal unit and the estimated column heights do not exceed 20 km the younger ospedaletto pumice deposit has a ne sw dispersal axis whereas the youngest casetta pumice deposit is found only in the north eastern sector of the district their estimated volumes are respectively 1 2 and 0 1 km3 whereas the inferred vent areas appear to be located slightly to the east of the ponticello and orvieto bagnoregio pumice deposit source areas the chronology of the ospedaletto and casetta pumices indicates that the final plinian activity from the bolsena complex is contemporaneous with the latera activity the decreasing volumes from the oldest to the youngest units together with the progressive shifting northeastwards of the source vents may be related to the volcano tectonic subsidence of the bolsena area the source vents for the post basal pumices events are mainly clustered just north of bolsena village where the greatest displacement during subsidence occurred accordingly source vent shifting appears to be related to the progressive opening of normal faults from the inner to the outer margin of the bolsena depression

coastal ocean fronts and eddies imaged with ers 1 synthetic aperture radar ers 1 c band synthetic aperture radar sar data were collected during the norwegian continental shelf experiment norcsex both in november 1991 during the ers 1 commissioning phase and at different seasons in 1992 and 1993 characteristic sar image expressions are observed in relation to perturbation of the surface current short wave interaction across the norwegian coastal current front for winds less than 10 12 rn s 1 in situ measurements document the existence of alternating zones of convergence and divergence coexisting with a strong near surface current shear of nearly 4f where f is the coriolis parameter across a distance of a few kilometers under calm to moderate winds i e 4 7 rn s 1 characteristic expressions of upper ocean circulation features also include the manifestation of eddies through the presence of surface film which damps the bragg waves comparison of a near coincident national oceanic and atmospheric administration advanced very high resolution radiometer image and an ers 1 sar image supports the interpretation that surface current fronts are imaged by sar in combination with an sar image simulation model the relative quantitative importance of shear convergence and divergence along the front is examined although the model formulation is simple and the absolute magnitude of the perturbations is uncertain the study shows that the sar images can sometimes be used to interpret frontal dynamics including growth and decay of meanders

morphological and geochemical evidence of neotectonics in the volcanic area of monti vulsini latium italy interdisciplinary research has been carried out to contribute to the definition of the neotectonic arrangement of the eastern area of monti vulsini affected by upper pleistocene volcanic activity particularly geochemical and geomorphological inquiries have been performed to identify tectonic elements whose recent activity could be related to the volcanic history of this area the morphological field evidence of tectonics as well as the analysis of azimuthal distribution of stream channels and the statistical analysis of the amplitude of relief ar revealed the eastern monti vulsini volcanic area to be controlled by different tectonic alignments at the same time the geochemical contribution focused on geostatistical elaboration of soil gas data has attempted to process unbiased criteria to define soil gas anomalies and to infer correlation with their fault related linear geometry in particular rose diagrams of anomalous gas concentration alignments and azimuthal distribution of stream channels performed for each hierarchical order were compared to obtain information about the location and orientation of tectonic elements as well as about the possible reconstruction of their activity in recent times by means of relative chronology

volcanological and petrological evolution of the eastern vulsini district central italy on the basis of recent field mapping data stratigraphic reconstruction and k ar datings a volcanological and petrological study of the bolsena and montefiascone volcanic zones eastern vulsini district has been carried out ten main eruptive phases with both effusive and explosive activity have been recognized these are characterized by a large range of magma compositions belonging to the leucitite basanite and shoshonite magmatic series within each series near primary magmas and slightly to strongly differentiated products are present although in different proportions the great majority of differentiated products mostly trachytic outcrops in the northern sectors of the eastern vulsini district bolsena volcanic zone where lavas or pyroclastics were erupted during moderate to large volume plinian type and ignimbrite forming explosive activity by contrast abundant rather undifferentiated magmas are more frequently found in the southern sectors of the eastern vulsini district montefiascone volcanic zone the structural setting of the sedimentary substratum as well as its lithological characteristics may have played an important role in producing this magma distribution the very shallow position a few hundred meters below the topographic surface of the top of the fracturated carbonate basement would have facilitated the uprising of abundant less evolved magmas in the montefiascone volcanic zone whereas relatively large magma bodies a few kilometer deep can only be inferred in the bolsena volcanic zone bolsena caldera where a front of overthrust sheets of the tuscan and umbrian sedimentology sequences is most probably present in this area source vents of explosive activity show a tendency to shift northeastward with time feeding systems were also differently oriented e w and wnw ese in the southern sectors and nw se and nnw sse in the northern sectors while a ns system was related to a late stage activity of the whole eastern vulsini district