calibration of rock fall modeling parameters abstract rock falls can be a hazard for many facilities in mountainous terrain particularly in areas with high rainfall and freezing temperatures and where seismic events occur design of protection measures against rock falls such as fences barriers and sheds requires information on impact energy to determine the strength of the structure and on trajectories to determine its location and size this paper presents documentation on rock falls at five locations in north america and japan involving impacts on rock talus colluvium asphalt and concrete for which values of the normal and tangential coefficients of restitution have been calculated the field results show that the normal coefficient of restitution is related to the impact angle with coefficients of about 0 2 for normal impacts and values as great as 2 5 for shallow impacts these values for the normal coefficient of restitution are essentially independent of the slope material the tangential coefficient of restitution ranges between 0 3 and 0 8 and is related to the friction coefficient at the impact point and is independent of the velocity and normal force it is also shown that the calculated field values for the coefficients of restitution are consistent with the principles of impact mechanics

mobility of mo u as and sb within modern turbidites modern turbidites uranium molybdenum arsenic antimony we present and discuss porewaters and sediment data of mn fe mo u as and sb within four recent turbidites from the capbreton canyon sw france the deposition of turbidites on continental margins exerts strong influence on the fate of trace metals causing trace metal migration and or immobilization the down core distribution of the elements here depends entirely of ongoing diagenetic processes rather than the diffusion of o2 the persistence of fe mn oxides under anoxic conditions led to anoxic reoxidation of numerous species as nh4 reduced s compounds and trace metals metal oxides thus control the immobilization of mo and as in the solid phase and the remobilization of u and sb to the porewaters although the low sulphide production prevents anoxic authigenesis of mo and as reducing conditions below each horizon rich in mn fe oxides resulted in u and sb accumulation the exact mechanisms of sb immobilization are not known but it is most certainly different from that of as the profile shapes of mn and u were used to estimate the age of the turbidite deposits which cannot be determined by conventional radionuclide methods our interpretations however depend on calculations of diffusion coefficient particularly for u a simple diffusive model applied to mn suggested that the age of the latest deposit noted t1 was 22 months this date is close to the time elapsed between the core sampling and the last known turbiditic event in the capbreton canyon i e martin storm 18 months using the u data set and depending on diffusion coefficients used the estimated ages of the deeper layers were 4 7 yr for t2 and 7 5 14 yr for t3 the reliability and precision of this new approach to date sediments at short timescales is limited by the ignorance of a precise value for u diffusion coefficient reducing uncertainty on u diffusion coefficient will greatly support application of the proposed approach

habitat characterization of deep water coral reefs in la gaviera canyon aviles canyon system cantabrian sea abstract surveys conducted at the complex aviles canyon system southern bay of biscay in order to identify vulnerable habitats and biological communities revealed the presence of noteworthy deep water coral reefs in one of the tributaries of the system la gaviera canyon the aim of the present study is to determine why this deep sea canyon provides suitable environmental conditions for corals to grow this hanging canyon is characterized by an irregular u shaped floor with two narrow differentiated flanks sand ripples and rocky outcrops structured in diverse w e directed steps are observed on the canyon floor suggesting intense hydrodynamic activity accordingly high frequency near bottom current and thermal structure profiles showed that there occur strong shifts in currents hydrography behaving as front like features at each tidal cycle these involve the sudden increase of along axis velocities to over 50 cm s and vertical velocities of over 5 cm s in each tidal cycle associated with the passage of sharp thermal fronts and thermal inversions suggesting overturning a year long near bottom current record showed events with near bottom velocities well over 1 m s lasting for several days three cold water coral settings were distinguished a dense coral reef located on stepped rocky bottoms of the eastern and western flanks carbonate mounds 20 30 m high located on the canyon floor and a cluster of shallower water dead coral framework at the head sector of the canyon video and still images from a towed sled and rov verified the presence of dropstones and rippled sand sheets surrounding the mounds and revealed changes in the coral population alive or dead total or patchy coverage in coral reef and carbonate mound areas the dominant species of the reef are lophelia pertusa and madrepora oculata which considerably increase the habitat s complexity and biodiversity in relation to other facies described in the canyon the presence of living cold water reefs is directly related to a high energy environment at depths between 700 and 1200 m in the levels between the lower bound of eastern north atlantic central water enacw and the core of mediterranean water mw such level matches the water density range 27 35 27 65 kg m 3 which has been identified as limits for cold water coral distribution in the north atlantic

observations of the internal tide in monterey canyon abstract data from two shipboard experiments in 1994 designed to observe the semidiurnal internal tide in monterey canyon reveal semidiurnal currents of about 20 cm s 1 which is an order of magnitude larger than the estimated barotropic tidal currents the kinetic and potential energy evidenced by isopycnal displacements of about 50 m was greatest along paths following the characteristics calculated from linear theory these energy ray paths are oriented nearly parallel to the canyon floor and may originate from large bathymetric features beyond the mouth of monterey bay energy propagated shoreward during the april experiment itex1 whereas a standing wave that is an internal seiche was observed in october itex2 the difference is attributed to changes in stratification between the two experiments higher energy levels were present during itex1 which took place near the spring phase of the fortnightly 14 8 days cycle in sea level while itex2 occurred close to the neap phase further evide

theory and calibration of the pierre 2 stochastic rock fall dynamics simulation program the use of computer models to determine rock fall hazards is increasingly common with increasingly complex models being developed in most practical applications slopes potentially affected by ro

submarine canyons and channels in the lower st lawrence estuary eastern canada morphology classification and recent sediment dynamics abstract series of submarine canyons and channels observed in the lower st lawrence estuary lsle provide an opportunity to analyze in great detail the morphology spatial distribution and modern activity of such systems in a relatively shallow 300 m semi enclosed basin based on their geomorphology and physical settings the canyons and channels were classified into four categories according to their feeding sources ancient or recent glacially fed river fed longshore drift fed and sediment starved systems their activity was interpreted based on geomorphological characteristics such as the presence of bedforms related to gravity flows backscatter intensity axial incision and the presence of rapidly deposited layers in surficial sediments river fed deltas were interpreted as inactive mainly because suspended sediment concentrations at river mouths are low preventing the generation of hyperpycnal currents or delta lip failures related to high sediment supply longshore drift fed canyons present where the coastal shelf narrows were found to be episodically active probably due to earthquakes or extreme storm events unlike other longshore drift fed canyons observed elsewhere in the world they are active infrequently because of the modern low rates of sediment supply to their heads the most active canyons are the sediment starved type and were observed near pointe des monts their activity is probably due to slope failures and to the presence of strong hydrodynamic processes therefore sediment supply is not the main mechanism responsible for modern canyon and channel activity in the lsle however sediment supply has been an important factor during the formation of the submarine channels and canyons their quasi exclusive occurrence on the quebec north shore is attributed to its larger watershed and important sedimentary delivery during deglaciation the quebec north shore watershed is 20 times greater than the quebec south shore watershed which favored the transport of greater volumes of sediment during the early holocene moreover the slope proximity to the shore led to the formation of longshore drift fed systems on the north shore when sediment supplied to rivers were transferred on a narrow shelf

dispersal and deposition of suspended sediment on the shelf off the tagus and sado estuaries s w portugal abstract the portuguese margin in front of the tagus and sado rivers is characterized by a narrow shelf incised by numerous canyons and by a large mud deposit the two estuaries that feed this continental margin have distinct impact the suspended particulate matter concentration values in the mouth of the tagus are four times higher than in the sado during the summer the surface nepheloid layer is always larger than during the winter when it is restricted near the mouth of the estuary this nepheloid layer may reach 30 km in length extending westward the bottom nepheloid layer usually shows higher nephelometer values and has a typical distribution it is usually diverted southward in the direction of the lisbon submarine canyon we estimate the amount of suspended matter being discharged annually from the tagus estuary to be between 0 4 and 1 10 6 t the area covered by fine deposits is about 560 km 2 hence the thickness of sediments deposited annually should be between 0 07 and 0 18 cm the sedimentation rates calculated from the 210 pb excess vary between 0 16 and 2 13 cm y 1 which correspond to the maximum rate for a layer of 1 cm thick 81 000 t of particulate organic carbon poc should be trapped that would represent with a minimum sedimentation rate between 0 07 and 0 18 cm y 1 an entrapment of 6000 15 000 t poc y 1 the trace metals content of box core samples clearly shows the anthropogenic impact in the uppermost level 5 cm thick in the tagus estuary and in all the sedimentary deposits 15 cm thick on the shelf muddy area despite the narrowness of the shelf a significant part of continental fluxes fails to reach the deep ocean

the dangeard and explorer canyons south western approaches uk geology sedimentology and newly discovered cold water coral mini mounds the celtic margin is a complex area in terms of sedimentary dynamics and evolution with a number of submarine canyons dissecting the continental slope and outer continental shelf the complex terrain and diverse range of sea bed sediments play a part in submarine canyons being described as areas of high habitat heterogeneity this study has concentrated on the heads of two canyons dangeard also known as dangaard and explorer first named here located in uk territorial waters in water depths between 138 and 1165 m multibeam echosounder 2d reflection seismic and photographic ground truthing data have been combined to map the sea bed geomorphology sedimentary features and canyon megafauna of these canyons in addition two previously unknown provinces of cold water coral cwc mini mounds were discovered on the interfluves of the dangeard and explorer canyons the study area comprises a dendritic network of gullies feeding into the canyon thalwegs amphitheatre rims where slope angles are commonly in excess of 20 occur along the margins and heads of both canyons and are interpreted as drainage basins indicative of retrogressive mass wasting in a shelfward direction the cwc mini mounds occur in water depths between 250 m and 410 m with more than 400 mounds identified they are up to 3 m in height and 50 150 m in diameter with no sub surface expression suggesting these mounds are in geological terms relatively young and possibly holocene in age biological analyses revealed that the mounds form a habitat for ophiuroids and munida associated with lophelia pertusa coral rubble suggesting these mini mounds are not present day living features

from source to sink a new perspective on the past dynamics of the murray canyon group from benthic foraminiferal communities abstract we present fossil benthic foraminiferal assemblage data from marine sediment core ss02 06 gc2 located in the abyssal plain of the murray canyon group offshore south australia the sedimentological characteristics indicate the presence of turbidite deposits showing classical bouma like sequences dated between 40 and 12 cal ka bp these results confirm the previous interpretation of the observed large deep water holes in the abyssal area where the core was sampled as being gouged by surges of high energy turbidity currents the presence of good indicator taxa and unique assemblages occupying specific bathymetric depths allows the determination of the source origin of the sediments making the turbidites three distinct faunal groups are found 1 mostly shelf species 2 mostly bathyal species and 3 mostly abyssal species in the sediment core these groups present a quasi systematic succession with nearly all bouma like sequences starting with the dominance of bathyal species in the coarse grained base followed by the dominance of shallow species in the silty part and finally with abyssal species in the clays to explain such phenomena turbidites triggered by mixed hyperpycnal hypopycnal flow processes and turbidity currents during periods of river floods are considered for the first time within the murray canyon group they are mostly related to periods of increased fluvial discharges during wet phases in the murray darling basin

observed and numerically simulated structure of a mature supercell thunderstorm abstract through the interactive use of doppler radar analyses and a three dimensional numerical storm simulation the detailed structure of a supercell tornadic storm is analyzed this storm named the del city storm occurred in central oklahoma on 20 may 1977 the storm exhibits certain important features which are essential to maintaining its longevity and which promote the storm s transition to its tornadic phase these features are strongly influenced by the rotational character of the storm separates the precipitation from the updraft and which orients the resulting downdrafts to which reinforce low level convergence along the gust front and sustain the storm analyses of air parcel and rain trajectories within the storm provide a detailed visualization of this internal structure these trajectories reveal that air parcels rising through the cyclonically rotating updraft actually turn anticyclonically with height owing to the influence of the storm relative environmental wind field downdraft traj

a severe frontal rainband part ii tornado parent vortex circulation abstract by means of multiple doppler radar analysis part i established the stormwide hydrodynamic structure as an intense gravity current which advances on a prefrontal low level jet part ii examines the initiation and evolution of a tornado parent vortex circulation in the context of stormwide vorticity production tilting of the prefrontal inflow below the low level jet axis accounts for production of observed vorticity 10 2 s 1 at the surface front the two dimensional flow pattern is modified by the development of an inflectional instability with a wavelength of 13 km breaking or roll up of this instability occurs on a time scale of roughly 500 s and results in small scale vortices along the surface front one such vortex is examined in detail this vortex is the parent circulation of a small tornado the parent vortex structure is determined to be quite similar to those observed in summertime deep convection this suggests a generality to the findings concerning parent vortex initiation and

semiannual patterns of erosion and deposition in upper monterey canyon from serial multibeam bathymetry recently acquired 3 m resolution 244 khz multibeam seafloor bathymetry 0 5 m depth precision reveals geomorphology at sufficient detail to interpret small scale features and short term processes in the upper 4 km of monterey canyon california the study area includes the continental shelf and canyon features from 10 m to 250 m depth the canyon floor contains an axial channel laterally bounded by elevated complex terrace surfaces sand waves with 2 m height and 35 m average wavelength dominate the active part of the canyon floor the sand waves are strongly asymmetrical indicating net down canyon sediment transport in this reach terraces including a broad 25 m tall terrace complex near the head of the canyon bear evidence of recent degradation of the canyon floor slump scars and gullies having a variety of sizes and relative ages shape the canyon walls serial georeferenced digital elevation models were analyzed to detect net changes in bathymetry or morphology occurring during both a six month period september 2002 to march 2003 and a 24 h period 24 march to 25 march significant changes over the six month period include 1 complete reorganization of the sand waves on the channel floor 2 local channel degradation creating new 2 m tall erosional terraces on the channel margins 3 local channel widening that laterally eroded older channel margin terraces and 4 60 m extension of one minor gully head on a steep canyon wall there were no discernable changes in morphology during the 24 h study period raster subtraction of serial bathymetric grids provides estimates of sediment erosion and deposition that occurred between the canyon head and a point 2 km down canyon during the six month study erosion of 320 000 m 3 80 000 m 3 of sediment occurred mainly in the tributaries along the margins of the axial channel and in the lowest 700 m of the analyzed reach this eroded volume was approximately balanced by 260 000 m 3 70 000 m 3 of sediment deposition that was concentrated in the nearshore region along the rim of the canyon head there was no measurable sediment gain or loss during the 24 h study period

hyperpycnal plume formation from riverine outflows with small sediment concentrations a series of laboratory experiments has been conducted in order to elucidate the sediment induced mixing processes accompanying riverine outflows specifically the discharge of a warm fresh particle laden fluid over a relatively dense cool brine in a parameter regime analogous to recently acquired field measurements hypopycnal surface plumes were subject to a convective instability driven by some combination of heat diffusing out of the warm fresh sediment laden plume and particle settling within it convection was robust in the presence or absence of intense turbulence at sediment concentrations as low as 1 kg m 3 and took the form of millimetre scale sediment laden fingers descending from the base of the surface plume a consequence of the convective instability of the original hypopycnal plume is the generation of a hyperpycnal bottom riding flow the experiments presented here indicate that natural river outflows may thus generate hyperpycnal plumes when sediment concentrations are 40 times less than those required to render the outflow heavy relative to the oceanic ambient the resulting hyperpycnal plumes may play an important role in transporting substantial quantities of sediment to the continental slope and beyond

sediment transport processes at the head of halibut canyon eastern canada margin an interplay between internal tides and dense shelf water cascading abstract to investigate the processes by which sediment is transported through a submarine canyon incised in a glaciated margin the bottom boundary layer quadrapod ralph was deployed at 276 m depth in the west halibut canyon off newfoundland during winter 2008 2009 two main sediment transport processes were identified throughout the deployment firstly periodic increases of near bottom suspended sediment concentrations ssc were recorded associated with the up canyon propagation of the semidiurnal internal tidal bore along the canyon axis carrying fine sediment particles resuspended from deeper canyon regions the recorded ssc peaks lasting less than 1 h were observed sporadically and were linked to bottom intensified up canyon flows 40 cm s 1 concomitant with sharp drops in temperature secondly sediment transport was also observed during events of intensified down canyon current velocities that occurred during periods of sustained heat loss from surface waters but were not associated with large storm waves high resolution velocity profiles throughout the water column during these events revealed that the highest current speeds 1 m s 1 were centered several meters above the sea floor and corresponded to the region of maximum velocities of a gravity flow such flows had associated low ssc and cold water temperatures and are interpreted as dense shelf water cascading events channelized along the canyon axis sediment transport during these events was largely restricted to bedload and saltation producing winnowing of sands and fine sediments around larger gravel particles analysis of historical hydrographic data suggests that such gravity flows are not related to the formation of coastal dense waters advected towards the outer shelf that reached the canyon head rather the dense shelf waters appear to be generated around the outer shelf where convection during winter is able to reach the sea floor and generate a pool of near bottom dense water that cascades into the canyon during one or two tidal cycles a similar transport mechanism is likely to occur in other submarine canyons along the eastern canadian margin as well in other canyoned margins where winter convection can reach the shelf edge

high resolution morphobathymetric analysis and evolution of capbreton submarine canyon head southeast bay of biscay french atlantic coast over the last decade using descriptive and numerical modeling abstract in this study the capbreton canyon head just off the coast is investigated using high resolution multibeam bathymetry datasets sediment samples and numerical modeling the hr bathymetry analysis reveals a morphological connection between the longshore trough and the head of the canyon the analysis of recent sediment samples shows a clear correlation between the sediment of the canyon head and that of the nearshore hydrodynamic modeling a coupled wave flow model shows that for high energy waves the rotational nature of surf zone circulation reverses and wave induced currents have the potential to transport large quantities of nearshore sands toward the canyon head all these arguments support the assumption that the canyon head captures a part of the sand transported by longshore drift over the 15 years of observation 1998 2013 time lapse bathymetry shows that the floor of the canyon head and one lateral gully network experienced significant morphological reworking in terms of hazards despite this strong activity the position of the canyon head and the profile of its longitudinal slope remained stable and appear as a comforting factor however the activity of unusual lateral erosions needs to be monitored

multiscale aspects of thunderstorm gust fronts and their effects on subsequent storm development abstract an investigation of severe storms that occurred on 23 may 1974 in central oklahoma reveals interesting information on the multifaceted role of thunderstorm produced gust fronts the data reveal that the interaction of outflow boundaries with a cold front initiate the storms studied in this report then the gust fronts produced by these storms have important effects on their own structure and life histories detailed doppler analysis show that these storms propagate discretely along their outflow boundaries despite their supercell structure additionally one storm is affected by its interaction with the boundary produced by a previous storm this interaction appears responsible for tornadogenesis

the structure and classification of numerically simulated convective storms in directionally varying wind shears abstract using a three dimensional numerical cloud model we investigate the effects of directionally varying wind shear on convective storm structure and evolution over a wide range of shear magnitudes as with a previous series of experiments using unidirectional wind shear profiles weisman and klemp the current results evince a spectrum of storm types ranging from short lived single cells at low shears multicells at intermediate shears to supercells at high shears with a clockwise curved hodograph the supercellular growth is confined to the right flank of the storm system while multicellular growth is favored on the left flank an analysis of the dynamic structure of the various cells reveals that the quasi steady supercell updrafts are strongly enhanced by dynamically induced pressure gradients on the right flank of the storm system we use this feature along with other related storm characteristics such as updraft rotation to propose a dynamically based storm classification scheme following

environmental signal propagation in sedimentary systems across timescales abstract earth surface processes operate across erosionally dominated landscapes and deliver sediment to depositional systems that can be preserved over a range of timescales the geomorphic and stratigraphic products of this source to sink sediment transfer record signals of external environmental forcings as well as internal or autogenic dynamics of the sedimentary system here we evaluate environmental signal propagation across sediment routing systems with emphasis on sediment supply qs as the carrier of up system forcings we review experimental numerical and natural examples of source to sink sediment routing and signal propagation during three timescales 1 historic which includes measurement and monitoring of events and processes of landscape change and deposition during decades to centuries 2 centuries to several millions of years referred to as intermediate timescale and 3 deep time we discuss issues related to autogenic dynamics of sediment transport transient storage and release that can introduce noise lags and or completely mask signals of external environmental forcings we provide a set of conceptual and practical tools for evaluating sediment supply within a source to sink context which can inform interpretations of signals from the sedimentary record these tools include stratigraphic and sediment routing system characterization sediment budgets geochronology detrital mineral analysis e g thermochronology comparative analog approaches and modeling techniques to measure calculate or estimate the magnitude and frequency of external forcings compared to the characteristic response time of the sediment routing systems

a study of the tornadic region within a supercell thunderstorm abstract the transition of a supercell thunderstorm into its tornadic phase is investigated through high resolution numerical cloud model simulations initiated within the interior portion of a previously simulated mature supercell storm with the enhanced grid resolution the low level cyclonic vorticity increases dramatically and the gust front rapidly occludes as small scale downdrafts develop in the vicinity of the low level center of circulation as the occlusion progresses a ring of high vorticity air surrounds the circulation center and could be conducive to multiple vortex tornado formation numerous features of the simulated transition bear resemblance to those observed in tornadic storms in the model simulation the large low level vorticity is generated through the tilting and intense stretching of air from the inflow side of the storm this vertical vorticity is derived from the horizontal vorticity of the environmental shear and also from horizontal vorticity generated solenoidally as low l

wintertime supercell thunderstorms in a subtropical environment a diagnostic study abstract the present study documents the environment initiation and evolution of three isolated supercell storms on 19 december 2002 as the first case near taiwan reported in the literature mainly using radar data and manual and gridded analyses in a subtropical environment the supercells occurred behind a winter cold front that provided a large west southwesterly vertical wind shear of 6 4 10 3 s 1 at 0 3 km this combined with weak to moderate instability cape 887 j kg 1 above the shallow surface cold air to yield a favorable environment for supercells an approaching upper level jet ulj at 200 hpa also provided strong shear through deep layers farther aloft prior to storm initiation significant daytime solar heating occurred over the mountain slopes along the coast of southeastern china leading to development of local circulation and onshore upslope winds resulting in convergence and uplifting three storms were initiated about 80 km inland around 1400 lst near the peaks of local terr

bidirectional bedform fields at the head of a submarine canyon ne atlantic abstract submarine canyons are known to force ocean mesoscale circulation and local hydrodynamics alternate up and down canyon near bottom flows have been widely documented along the upper reaches connecting the canyon heads with the contiguous outer shelves and vice versa nonetheless we still miss clear evidence of bedform fields expressing these complex patterns in this study through a multi scale analysis in both space and time we document rare asymmetric bedforms up to 880 m long and 10 m high developing within a depth range of 168 220 m at the head of the whittard canyon ne atlantic one field of well developed sandwaves has an atypical up slope asymmetry with the steeper slope facing the shallower regions of the shelf and contrasting with surrounding down slope sandwaves facing the canyon the bedforms are interpreted to represent both up slope and down slope bottom currents connecting the upper reaches of the canyon to the outer shelf on the southern celtic margin in the bay of biscay the sandwaves were surveyed with shipboard multibeam bathymetry 5 m grid cell resolution auv sidescan sonar 0 15 m grid cell resolution and rov footage and sampled with three rov mounted vibro cores and two box cores sidescan sonar mosaics groundtruthed by sediment samples and rov footage show with unprecedented detail spectacular trains of fresh overprinting megaripples previously undocumented sand peaks and bowl shaped depressions on the crests of the tallest sandwaves differences in sedimentary settings and benthic habitats indicate that these features are currently active in particularly dynamic areas allowing for very slow migration of sandwaves numerical modelling together with concurrent hydrographic observations suggest large amplitude semi diurnal internal tides possibly transitioning to asymmetric internal bores as the main mechanism maintaining the mapped up slope sandwaves this work highlights the importance of uncommon sediment dynamics in canyon head environments and adds insight to the traditional notions of gravity driven processes being dominant in these environments envisaging implications for improving geo hazard assessment of mobile substrates and quantification of offshore sediment and carbon fluxes

observations related to the rotational dynamics of the 20 may 1977 tornadic storms abstract observations of the 20 may 1977 tornadic storms are used to evaluate recent theories on the initiation of rotation at mid and low levels and to verify recent thermodynamic retrieval results using the lengthy data record from a variety of sensors available for this day it appears that the mechanism that initiates low level rotation is different from that at midlevels attempts to identify the source of the low level rotation as vertical tilting baroclinically generated horizontal vorticity were inconclusive the recent thermodynamic retrieval results of hane and ray and of brandes for these storms are in good agreement with independent measurements where available however verification is hindered by the sparseness of these measurements noticeable differences in the region of the rear flank downdraft suggest that there is room for improvement in the retrieval methods investigation of the cyclic generation of rotation along gust fronts indicates that the source of low level rotation is not der

holocene sedimentary activity in a non terrestrially coupled submarine canyon cook strait canyon system new zealand abstract the cook strait canyon system located between the north and south islands of new zealand is a large 1800 km 2 multi branching shelf indenting canyon on an active subduction margin the canyon comes within 1 km of the coast but does not intercept fluvial or littoral sediment systems and is therefore defined as a non terrestrially coupled system sediment transport associated with a strong tidal stream and seafloor disturbance related to numerous high activity faults is known from previous studies little is known however about the rates of sedimentary activity in the canyon and the processes driving it a substantial dataset of em300 multibeam bathymetry gravity cores 3 5 khz seismic reflection profiles camera and video transects and current meter data have been collected across the region between 2002 and 2011 the canyon system therefore provides an excellent study area for understanding sediment transport in a non coupled submarine canyon system analysis of the data reveals a two staged sediment transport system where 1 oceanographic tidal processes mobilise sediment from the continental shelf and transport it to depocentres in the upper central canyons and 2 tectonic earthquake processes remobilise sediment that is transported through the lower canyon to the deep ocean tidal boundary layer currents within the canyon reach velocities up to 0 53 m s and are capable of mobilising fine sand in the central reach of the upper canyons the velocity is higher at the canyon rim and capable of mobilising coarse sand sediment depocentres resulting from this tidally forced sediment transport have a well formed geomorphology within the mid upper canyon arms of cook strait and nicholson canyons pseudo static stability modelling supported by sediment core analysis indicates that sediment accumulated in the upper canyons fails during seismic events approximately every 100 years the 100 year return period ground shaking level peak ground acceleration ignoring the effect of the water column above the seabed at this site is estimated to be 0 23 g fresh rock outcrops and bed scour in the lower canyon floor indicate that remobilised material is transported to the deep ocean the processes identified here are likely to be analogous to those occurring in many non coupled shelf indenting canyons on active margins globally and provide a framework within which the biological response to geomorphic processes in submarine canyons can be assessed

timing of massive fleuve manche discharges over the last 350 kyr insights into the european ice sheet oscillations and the european drainage network from mis 10 to 2 continuous high resolution mass accumulation rates mar and x ray fluorescence xrf measurements from marine sediment records in the bay of biscay ne atlantic have allowed the determination of the timing and the amplitude of the fleuve manche channel river discharges during glacial stages mis 10 mis 8 mis 6 and mis 4 2 these results have yielded detailed insight into the middle and late pleistocene glaciations in europe and the drainage network of the western and central european rivers over the last 350 kyr this study provides clear evidence that the fleuve manche connected the southern north sea basin with the bay of biscay during each glacial period and reveals that fleuve manche activity during the glaciations mis 10 and mis 8 was significantly less than during mis 6 and mis 2 we correlate the significant fleuve manche activity detected during mis 6 and mis 2 with the extensive saalian drenthe substage and the weichselian glaciations respectively confirming that the major elsterian glaciation precedes the glacial mis 10 in detail massive fleuve manche discharges occurred at ca 155 ka mid mis 6 and during termination i while no significant discharges are found during termination ii it is assumed that a substantial retreat of the european ice sheet at ca 155 kyr followed by the formation of ice free conditions between the british isles and scandinavia until termination ii allowed meltwater to flow northwards through the north sea basin during the second part of the mis 6 we assume that this glacial pattern corresponds to the warthe substage glacial maximum therefore indicating that the data presented here equates to the drenthe and the warthe glacial advances at ca 175 160 ka and ca 150 140 ka respectively finally the correlation of our records with odp site 980 reveals that massive fleuve manche discharges related to partial or complete melting of the european ice masses were synchronous with strong decreases in both the rate of deep water formation and the strength of the atlantic thermohaline circulation fleuve manche discharges over the last 350 kyr probably participated with other meltwater sources in the collapse of the thermohaline circulation by freshening the northern atlantic surface water

simulation and analysis of tornado development and decay within a three dimensional supercell thunderstorm abstract a three dimensional numerical simulation using a two way interactive nested grid is to study tornado genesis within a supercell during a 40 minute period two tornadoes grow and decay within the storm s mesocyclone the tornadoes have life spans of approximately 10 minutes maximum ground relative surface wind speeds exceed 60 m s 1 during both tornadoes and horizontal pressure gradients reach 18 hpa km 1 during the second tornado comparison of the simulated storm evolution with doppler and field observations of supercells and tornadoes shows many similar features vertical vorticity in the mesocyclone and the tornado vortex at low levels is initially created by the tilting of the environmental vorticity and baroclinically generated vorticity along the forward gland gust front of the storm tornadogenesis is initiated when mesocyclone rotation increase above cloud base the increased rotation generates lower pressure in the mesocyclone increasing the upward pressure gradient forces the upwar

a numerical simulation of cyclic mesocyclogenesis abstract a three dimensional nonhydrostatic numerical model the advanced regional prediction system is used to study the process of cyclic mesocyclogenesis in a classic supercell thunderstorm during the 4 h simulation the storm s mesocyclone undergoes two distinct occlusions with the beginning of a third indicated at the end of the simulation the occlusion process exhibits a period of approximately 60 min and is qualitatively similar in each case initial midlevel 3 7 km mesocyclogenesis proceeds according to the classic picture that is via tilting of streamwise environmental vorticity the development of an evaporatively driven rear flank downdraft rfd signals the beginning of the occlusion process the developing rfd wraps cyclonically around the mesocyclone causing the gust front to surge outward simultaneously the occluding mesocyclone rapidly intensifies near the surface trajectory analyses demonstrate that this intensification follows from the tilting and stretching of near ground

palaeoceanographic and palaeoclimatic changes during the last 37 000 years detected in the se bay of biscay based on benthic foraminifera abstract benthic foraminifera assemblages from a sedimentary core pp10 12 701 mwd from the se bay of biscay allow us to trace palaeoceanographic and palaeoclimatic changes occurred in this region during mid mis 3 marine isotope stage 3 and mis 1 interval 37 2 4 ka bp results are based on 176 benthic foraminifera species considering their ecology the difference between autochthonous allochthonous preservation and oxygen rates thus evidencing climatic and oceanographic events mis 3 is characterised by waters with a dominance of cassidulina laevigata and uvigerina peregrina by the end of this interval waters became colder and less oxygenated indicated by the occurrence of melonis affinis these conditions persisted at the beginning of mis 2 the heinrich event 1 h1 is well registered in this core with three intervals h1a h1s s h1b where hyalinea balthica dominates during h1s s the coldest waters are registered and the environment was unstable these conditions continued during h1b when the occurrence of globobulimina affinis evidences some intervals with anoxia during bolling allerod b a waters were warmer and low ventilated indicated by bulimina gibba cassidulina laevigata dominates the younger dryas yd and the beginning of lower holocene evidencing the occurrence of cool waters with low oxygen and high organic matter content the lower to middle holocene transition is registered as a cold interval holocene cooling event hce 5 from the middle holocene onward water temperature were milder based on the dominance of uvigerina peregrina

deep marine tidal bottom currents and their reworked sands in modern and ancient submarine canyons abstract submarine canyons provide a unique setting for tidal processes to operate from shallow marine to deep marine environments in modern canyons current meter measurements at varying water depths 46 4200 m show a close correlation between the timing of up and down canyon currents and the timing of semi diurnal tides these tidal bottom currents in submarine canyons commonly attain maximum velocities of 25 50 cm s based on core and outcrop studies of modern and ancient deep marine deposits it is proposed here that sand mud rhythmites double mud layers climbing ripples mud draped ripples alternation of parallel and cross laminae sigmoidal cross bedding with mud drapes internal erosional surfaces lenticular bedding and flaser bedding can be used to interpret deposits of deep marine tidal currents this approach is an alternative to the conventional approach in which most deep water traction structures e g climbing ripples and cross bedding would be attributed to deposition from turbidity currents underwater photographs show active mass flows i e slides slumps grain flows and debris flows in modern canyons box cores taken from modern submarine canyons e g la jolla california and conventional cores and outcrops of ancient canyon fill facies oua iboe pliocene nigeria and the annot sandstone eocene oligocene se france contain deposits of both tidal processes and mass flows this facies association in the rock record can be used as a criterion for recognizing submarine canyon settings in a channel mouth environment deep marine tidal deposits are likely to develop elongate bars that are aligned parallel to the channel axis within the channel whereas turbidites are more likely to develop depositional lobes that are aligned perpendicular to channel axis turbidite depositional lobes are much larger than the channel width whereas tidal sand bars are much smaller than the channel width therefore the wrong use of a turbidite lobe model with sheet geometry in lieu of a tidal bar model with bar geometry will result in an unrealistic overestimation of sandstone reservoirs in deep water exploration

observations on the origins of rotation the newcastle tornado during vortex 94 abstract observations of a strong f3 tornado near newcastle texas on 29 may 1994 during the verification of the origins of rotation in tornadoes experiment vortex are presented the visual characteristics and intensity of the tornado were revealed by a photogrammmetric analysis of pictures taken by chase teams and by a detailed damage survey the tornado developed from a low level shear feature along the flanking line of a supercell vortex stretching of this feature to tornadic intensity occurred under the influence of an intense updraft from a rapidly growing storm along the flanking line no apparent midlevel mesocyclone accompanied this tornado in contrast the supercell was characterized by a well defined mid and low level mesocyclone however no tornado was observed by ground chase teams the implications of these findings on the current understanding of tornadogenesis are discussed

defining biological assemblages biotopes of conservation interest in the submarine canyons of the south west approaches offshore united kingdom for use in marine habitat mapping in 2007 the upper part of a submarine canyon system located in water depths between 138 and 1165 m in the south west sw approaches north east atlantic ocean was surveyed over a 2 week period high resolution multibeam echosounder data covering 1106 km2 and 44 ground truthing video and image transects were acquired to characterise the biological assemblages of the canyons the sw approaches is an area of complex terrain and intensive ground truthing revealed the canyons to be dominated by soft sediment assemblages a combination of multivariate analysis of seabed photographs 184 1059 m and visual assessment of video ground truthing identified 12 megabenthic assemblages biotopes at an appropriate scale to act as mapping units of these biotopes 5 adhered to current definitions of habitats of conservation concern 4 of which were classed as vulnerable marine ecosystems some of the biotopes correspond to descriptions of communities from other megahabitat features for example the continental shelf and seamounts although it appears that the canyons host modified versions possibly due to the inferred high rates of sedimentation in the canyons other biotopes described appear to be unique to canyon features particularly the sea pen biotope consisting of kophobelemnon stelliferum and cerianthids

the whittard canyon a case study of submarine canyon processes submarine canyons are large geomorphological features that incise continental shelves and slopes around the world they are often suggested to be biodiversity and biomass hotspots although there is no consensus about this in the literature nevertheless many canyons do host diverse faunal communities but owing to our lack of understanding of the processes shaping and driving this diversity appropriate management strategies have yet to be developed here we integrate all the current knowledge of one single system the whittard canyon celtic margin ne atlantic including the latest research on its geology sedimentology geomorphology oceanography ecology and biodiversity in order to address this issue the whittard canyon is an active system in terms of sediment transport the net suspended sediment transport is mainly up canyon causing sedimentary overflow in some upper canyon areas occasionally sediment gravity flow events do occur some possibly the result of anthropogenic activity however the role of these intermittent gravity flows in transferring labile organic matter to the deeper regions of the canyon appears to be limited more likely any labile organic matter flushed downslope in this way becomes strongly diluted with bulk material and is therefore of little food value for benthic fauna instead the fresh organic matter found in the whittard channel mainly arrives through vertical deposition and lateral transport of phytoplankton blooms that occur in the area during spring and summer the response of the whittard canyon fauna to these processes is different in different groups foraminiferal abundances are higher in the upper parts of the canyon and on the slope than in the lower canyon meiofaunal abundances in the upper and middle part of the canyon are higher than on adjacent slopes but lower in the deepest part mega and macrofauna abundances are higher in the canyon compared with the adjacent slope and are higher in the eastern than the western branch these faunal patterns reflect the fact that the whittard canyon encompasses considerable environmental heterogeneity related to a combination of organic matter trapping current regimes due to focused internal tides and different substrates we conclude that coordinated observations of processes driving faunal patterns are needed at a fine scale in order to understand the functioning of communities in this and other submarine canyons

slope transport of suspended particulate matter on the aquitanian margin of the bay of biscay abstract spatial and temporal characteristics of the water masses and the dispersion of the suspended particulate matter were investigated using current meter hydrographic and nephelometric observations gathered during the ecofer experiment 1989 1991 in the cap ferret canyon on the aquitanian margin of the bay of biscay while characteristics of the deep water masses were stable from one year to another large hydrographic change in the upper 500 m related to winter renewal induced by poleward advection of warm and saline water along the continental slope the slope circulation and seasonal eddy activity appear as important dynamical mechanisms that control the entrainment and the dispersion of the suspended particulate matter from the neritic domain to the deep ocean a predominantly northward along slope current with occasional reversal characterizes this circulation the nephelometric structures also showed seasonal changes in the overall suspended particulate matter content but recurrent features such as the presence of intermediate nepheloid layers at the shelf break depth and various depths along the slope 500 1000 and 2000 m were observed these nepheloid layers extended off the slope to about 10 30 km but especially laterally along the slope their presence indicated that suspended particulate matter exchanges between the shelf and the slope occurred mainly in the head of the canyon and along the southern open slope the intermediate nepheloid layers around 500 m depth detached from the slope particularly in regions where the bottom slope is close to critical for the m2 internal tide

wintertime supercell thunderstorms in a subtropical environment numerical simulation abstract following an earlier diagnostic study the present paper performs numerical simulations of the rare wintertime supercell storms during 19 20 december 2002 in a subtropical environment near taiwan using japan meteorology agency jma 20 km analyses and horizontal grid spacing of 1 5 and 0 5 km the cloud resolving storm simulator cress of nagoya university successfully reproduced the three major storms at the correct time and location but the southern storm decayed too early over the taiwan strait the two experiments produce similar overall results suggesting that the 1 5 km grid spacing is sufficient even for storm dynamics model results are further used to examine the storm structure kinematics splitting process and the variation in the mesoscale environment over the taiwan strait the strong surface northeasterly flow enhanced low level vertical shear and helped the storms evolve into isolated supercells consistent with previous studies the vorticity budget analysis indicates that

a reconnaissance survey of the whittard sea fan southwestern approaches british isles abstract the whittard fan is a deep sea fan 148 km long by 111 km wide located in water depths between 3600 and 4400 m at the mouth of the whittard canyon southwest of the british isles a reconnaissance survey examined fan morphology sediments and bottom currents well developed diurnal tidal cycles occur with u 100 max reaching 16 cm s sufficient to erode and transport sediment at some locations at present major fan processes are apparently inactive and sedimentation is predominantly hemipelagic but other material is supplied by slope failure off the continental slope anomalous bottom topography may be interpreted as sediment waves indicating the existence of a slope parallel bottom current which may modifiy the fan surface

case study of a hailstorm in colorado part iii airflow from triple doppler measurements abstract triple doppler measurements are presented for a hailstorm of moderate intensity that occurred over the high plains of northeastern colorado and an airflow model is synthesized the storm had a number of persistent features similar to previous descriptions of supercells however its evolution is shown to be intermediate in a certain sense between classical multicell and supercell models a new model based on the doppler observations termed weak evolution emphasizes gradual changes in the structure of a long lived updraft the new airflow model explains the periodic echo intensifications noted for this storm and seems to apply well to other storms discussed in the literature

external controls on turbidite sedimentation on the glacially influenced armorican margin bay of biscay western european margin abstract sequence stratigraphic models predict increased sediment delivery to deep water areas during sea level lowstand the armorican margin bay of biscay western european margin is an interesting area to test this hypothesis because the margin has a wide continental shelf still partly flooded during sea level lowstand and the armorican turbidite system has experienced fluctuating sediment fluxes since the last glacial period the stratigraphic response of the armorican turbidite system to sea level oscillations and climate changes was assessed for the last 35 000 years through the study of the guilcher crozon and audierne levees millennial timescale resolution chronostratigraphy allowed us to reconstruct the sediment accumulation and turbidite frequency thickness and grain size over this period of time we found that the armorican turbidite system was sediment starved during highstand conditions ca 8 0 ka and that glacial conditions favoured sediment delivery to the deep bay of biscay however contrary to what would be expected from sequence stratigraphic models the turbidite flux did not reach a maximum during the lgm lowstand ca 26 20 ka but at the onset of termination i between ca 20 and 17 ka this makes the armorican turbidite system a transgression dominated one this sediment pulse can be interpreted as a huge increase in the meltwater discharge of the fleuve manche palaeoriver in response to the decay of the british and fennoscandian ice sheets at that time despite the rising sea level a large deltaic system had to have developed on the outer shelf leading to the delivery of the fleuve manche sediment load into the canyon heads on the other hand our dataset suggest that the delivery of sediment into canyons was mainly forced by the winnowing and reworking of the sediment stored on the wide drowned shelf during the last glacial period between ca 35 and 20 ka and between 17 and 8 ka these findings illustrate the competing influences of accommodation and sediment supply on the armorican margin over the last 35 000 years with a shelf acting as a buffer for the sediment supply signal for most of the period except during the last deglaciation at that time the western european sediment routing system was reactive the climatic signal rapidly propagated from the southern limb of the european ice sheet to the armorican turbidite system finally our study demonstrates that precise reconstruction of turbidite flux in deep water areas added to knowledge about the morphology of the margin and the palaeoenvironmental changes fluvial system shoreline position etc are crucial for determining the response of turbidite systems to external forcing

numerical simulation of tornadogenesis in a high precipitation supercell part i storm evolution and transition into a bow echo abstract a nested grid primitive equation model rams version 3b was used to simulate a high precipitation hp supercell which produced two weak tornadoes six telescoping nested grids allowed atmospheric flows ranging from the synoptic scale down to the tornadic scale to be represented in the simulation all convection in the simulation was initiated with resolved vertical motion and subsequent condensation latent heating from the model microphysics no warm bubbles or cumulus parameterizations were used part i of this study focuses on the simulated storm evolution and its transition into a bow echo the simulation initially produced a classic supercell that developed at the intersection between a stationary front and an outflow boundary as the simulation progressed additional storms developed and interacted with the main storm to produce a single supercell this storm had many characteristics of an hp supercell and eventually evolved into a bow echo with a rotating comma head structure an analysi

morphodynamics in sediment starved inner shelf submarine canyons lower st lawrence estuary eastern canada abstract the contemporaneous activity and sedimentary processes in a series of inner shelf submarine canyons located in the lower st lawrence estuary were examined using high resolution multibeam bathymetry and backscatter data the presence of crescent shaped bedforms csbs displaced upslope at the bottom of the canyons between 2007 and 2012 indicates that they are currently active through the remobilization of sediment by gravity flows however the shelf and shores of the region are characterized by the absence of sediment our results indicate that gravity flows currently eroding the canyon floors do not transport new material downslope coming from the shelf but rather remobilize in situ deglacial sediments within the canyon thalweg we suggest that slope failures and internal tides waves are responsible for sediment remobilization in these canyons although their role in the upslope migrating csbs is unclear this paper provides evidence that sediment supply is not a prerequisite for the modern activity of inner shelf submarine canyons when processes such as slope failures and internal tides waves are frequent enough to remobilize in situ sediments

anatomy of turbidites and linked debrites based on long distance 120 x 30 km bed correlation marnoso arenacea formation northern apennines italy much of our understanding of submarine sediment laden density flows that transport very large volumes ca 1 to 100 km3 of sediment into the deep ocean comes from careful analysis of their deposits direct monitoring of these destructive and relatively inaccessible and infrequent flows is problematic in order to understand how submarine sediment laden density flows evolve in space and time lateral changes within individual flow deposits need to be documented the geometry of beds and lithofacies intervals can be used to test existing depositional models and to assess the validity of experimental and numerical modelling of submarine flow events this study of the miocene marnoso arenacea formation italy provides the most extensive correlation of individual turbidity current and submarine debris flow deposits yet achieved in any ancient sequence one hundred and nine sections were logged through a ca 30 m thick interval of time equivalent strata between the contessa mega bed and an overlying columbine marker bed correlations extend for 120 km along the axis of the foreland basin in a direction parallel to flow and for 30 km across the foredeep outcrop as a result of post depositional thrust faulting and shortening this represents an across flow distance of over 60 km at the time of deposition the correlation of beds containing thick 40 cm sandstone intervals are documented almost all thick beds extend across the entire outcrop area most becoming thinly bedded 40 cm in distal sections palaeocurrent directions for flow deposits are sub parallel and indicate confinement by the lateral margins of the elongate foredeep flows were able to traverse the basin in opposing directions suggesting a basin plain with a very low gradient small fractional changes in stratal thickness define several depocentres on either side of the verghereto high area the extensive bed continuity and limited evidence for flow defection suggest that intrabasinal bathymetric relief was subtle substantially less than the thickness of flows thick beds contain two distinct types of sandstone ungraded mud rich sandstone intervals record evidence of en masse debrite deposition graded mud poor sandstone intervals are inferred to result from progressive grain by grain turbidite deposition clast rich muddy sandstone intervals pinch out abruptly in downflow and crossflow directions in a fashion consistent with en masse debrite deposition the tapered shape of mud poor sandstone intervals is consistent with an origin through progressive grain by grain turbidite deposition most correlated beds comprise both turbidite and debrite sandstone intervals intrabed transitions from exclusive turbidite sandstone to turbidite sandstone overlain by debrite sandstone are common in the downflow and crossflow directions this spatial arrangement suggests either i bypass of an initial debris flow past proximal sections ii localized input of debris flows away from available sections or iii generation of debris flows by transformation of turbidity currents on the basin plain because of seafloor erosion and or abrupt flow deceleration a single submarine flow event can comprise multiple flow phases and deposit a bed with complex lateral changes between mud rich and mud poor sandstone

high frequency environmental changes and deposition processes in a 2 kyr long sedimentological record from the cap breton canyon bay of biscay the core md03 2693 43 39 258 n 01 39 805 w 431 m water depth was collected on an abandoned meander of the capbreton canyon se bay of biscay filled over the last millennia by very high sedimentation rates mean sedimentation rate of 1 2 cm yr linked to its specific environmental location and fine grained clayed sediment decantation from the proximal canyon axis this archive thus permits to undertake the study of late holocene regional climatic patterns at a decadal temporal resolution in the present work we use data derived from planktonic foraminifera assemblages coupled to a multiproxy approach that associates grain size measurements x ray fluorescence xrf elemental analysis and stable oxygen isotope on globigerina bulloides shells to infer sea surface temperature sst and sea surface salinity sss changes over the last two millennia signals reconstructed in the bay of biscay show significant oscillations that are consistent with well known temperature anomalies such as the little ice a

the behaviour of arsenic in muddy sediments of the bay of biscay france abstract we have studied particulate and dissolved arsenic species in sediment and porewaters at sites in the bay of biscay france ranging in depths from 150 to 2 800 m at all stations major redox species oxygen nitrate ammonia total and reactive iron and manganese sulphate and sulphur reflect early diagenetic depth sequences of redox reactions comparable to other marine environments vertical distributions of dissolved and particulate as species and major redox species are related to changes in redox conditions and their major carrier phases such as fe and mn oxides arsenic diagenesis appears strongly dependent on fe cycling a subsurface maximum of dissolved as and surface enrichment of particulate as correspond to dissolution and precipitation of fe iii phases except for the shallowest and most bioturbated site flux calculations show three different vertical diffusive as fluxes two upwards and one downwards phase changes of recycled as result in local accumulations of reactive as at different redox fronts mass balance calculations indicate that the upward as flux toward the oxidized layer can explain the enrichment of hcl extractable particulate as in this layer a portion of the upward diffusing as can escape the sediment and may be fixed onto settling fe oxides by adsorption or co precipitation and contribute to reactive particulate as input i e as is recycled across the water sediment interface

spatial and temporal variability of meiobenthic density in the blanes submarine canyon nw mediterranean abstract meiofaunal density distribution was studied from 400 m to 1500 m depth inside blanes submarine canyon nw mediterranean and on the eastern open slope in autumn 2003 and spring 2004 our multidisciplinary approach allowed to study the hydrodynamics and sedimentary processes in the blanes canyon that characterize it as highly heterogeneous environment inside the canyon area particle fluxes were higher than on the slope area increased from autumn to spring and mostly consisted of lithogenic material moreover the canyon s locations experienced more intense bottoms currents and sediment disturbance being reflected in a greater variability of meiobenthic densities both between stations and sampling times than on the open slope no clear trends e g declining densities associated with increasing depths were observed contrary in the open slope current velocities were relatively lower compared with the canyon area and showed lower temporal variability at the same time the nutritional quality of the particle fluxes at deeper grounds were higher probably allowing the meiofaunal densities not to change over time in conclusion the meiobenthos in our system apparently showed a higher temporal variability inside the canyon area strongly affected by particle fluxes or erosive and sediment mixing processes linked to current modifications induced by the canyon topography

swept away by a turbidity current in mendocino submarine canyon california we present unique observations and measurements of a dilute turbidity current made with a remotely operated vehicle in 400 m water depth near the head of mendocino canyon california the flow had a two layer structure with a thin 0 5 to 30 m relatively dense 0 04 vol and fast up to 1 7 m s wedge shaped lower layer overlain by a thicker up to 89 m more dilute and slower current the fast moving lower layer lagged the slow moving dilute flow front by 14 min which we infer resulted from the interaction of two initial pulses the two layers were strongly coupled and the sharp interface between the layers was characterized by a wave like instability this is the first field scale data from a turbidity current to show i the complex dynamics of the head of a turbidity current and ii the presence of multiple layers within the same event

breaching in fine sands and the generation of sustained turbidity currents in submarine canyons natural moderately loosely packed sands can only erode from the surface of the bed after an increase in pore volume because of this shear dilatancy negative pore pressures are generated in the bed in cases of low permeability these negative pressures are released relatively slowly which retards the maximum rate of erosion this effect is incorporated in a new analytically derived pick up function that can explain the observation of gradual retrogressive failure of very steep subaqueous slopes sometimes more than 5 m high in fine non cohesive sands this process termed breaching in the field of sediment dredging may produce large failures in sand bars or river banks the analytical function that describes the breaching process in fine sand is incorporated in a one dimensional steady state numerical model of turbidity currents describing the spatial development of flow this model is applied to simulate a large flushing event in scripps submarine canyon pacific coast of california breach retrogradation and the successive evolution in time of the resulting turbidity current in the canyon are predicted in a sequence of discrete steps predicted velocities are compared with values measured during a flushing event implications for the interpretation of deep water massive sands are discussed

upstream migrating knickpoints and related sedimentary processes in a submarine canyon from a rare 20 year morphobathymetric time lapse capbreton submarine canyon bay of biscay france abstract the capbreton submarine canyon is a striking feature of the south east of the bay of biscay this canyon forms a deep incision through the continental shelf and slope and displays remarkable structures linked to its present day hydrosedimentary activity its head has been disconnected from the adour river since 1310 ce but remains close enough to the coast to be supplied with sediment by longshore drift gravity processes in the canyon body are abundantly described and documented but activity in the head and the fan of the canyon is poorly constrained furthermore many questions remain regarding the details of processes affecting the head the body and the fan of the capbreton canyon in this work we address the paucity of documentation concerning 1 the temporal evolution of sediment transfer between the head and the deep reaches of the canyon and 2 the interaction between gravity processes and the morphology of the canyon floor including both shaping and feedback mechanisms this study is based on the analysis and comparison of eight multibeam bathymetric surveys acquired in the upper part of the capbreton canyon between 1998 and 2018 in depths ranging 10 320 m below sea level this rare time series exposes the morphological evolution of this outstanding dynamic area over the last 20 years our work shows that much of the changes are located in the canyon floor and head following a period characterized by a unique flat floor thalweg the canyon was affected by an incision with low lateral terraces which resulted in a narrow axial thalweg the deepening of the narrow thalweg was induced by retrogressive erosion according to the presence of upstream migrating knickpoints while low elevation residual terraces formed as the canyon reached a local equilibrium profile the flat thalweg observed in 1998 is likely a result of a partial filling of the canyon thalweg by a substantial emptying of the canyon head and significant mass transfer to the proximal part of the canyon a flat floor thalweg was not observed again in the remaining of our time series since 2010 suggesting a possible quieter working mode of the canyon we also propose the first accurate volume quantification of sediment displacement on the canyon floor our findings underline the alternation of filling and erosive periods in the canyon axis and an unexpected continuous sediment deposition in the canyon head during the last 20 years

long term morphological changes in simulated supercells following mergers with nascent supercells in directionally varying shear abstractmergers involving supercells remain a challenge for severe thunderstorm forecasting in this study mergers between supercells and ordinary cells e g cells forming in a similar environment but too young to be fully developed supercells are investigated a series of numerical experiments are performed using an idealized homogenous environment supportive of cyclonically rotating right moving supercells warm bubbles are introduced at different times resulting in two storms of different maturity their placement is used to control the location of the merger and the relative maturity of the second storm simplified conceptual models for the long term outcomes of mergers are developed in the simplest mode of merger outflow from the new cell cuts off inflow to the original if the new cell s cold pool is not sufficiently strong to cut off the inflow to the original cell the minimum separation of the updraft maxima during the merger becomes a key controlling factor in the outcome if it is less

a synoptic and photographic climatology of low precipitation severe thunderstorms in the southern plains abstract the occurrence of an unusual type of severe thunderstorm difficult to identify by radar has been documented in the southern plains all of the three storms previously studied occurred near the dryline although tornadoes and large hail were produced little rain was observed at the ground and there was no evidence of a strong surface downdraft two were described as bell shaped ten more cases of this rare type of storm have been recently documented visually and on radar a photographic and synoptic climatology of this class of storm the low precipitation severe storm is suggested on the basis of an analysis of the comparison among 11 of these cases it is found that these storms form in a supercell like environment which is drier in the moist layer and more weakly sheared than that of well documented supercells in oklahoma implications of our findings and additional storm characteristics are discussed in light of the larger sample size

near bottom particulate matter dynamics in the nazare submarine canyon under calm and stormy conditions two mooring lines equipped with near bottom sediment traps were deployed in the axis of the nazare submarine canyon at similar to 1600 and similar to 3300 m depth respectively we studied time series of particle flux composition biogenic silica carbonates organic matter and lithogenic fractions granulometry mineralogy and pb 210 concentration of particulate matter over five sediment trap deployments between october 2002 and december 2004 current meters equipped with turbidimeters were also deployed at trap depths to monitor the water flow temperature salinity and suspended particle concentration the composition of the collected particles was fairly constant year round dominated by the lithogenic fraction and with oc n ratios in the range 11 21 suggesting an important terrigenous influence inside the canyon the results show contrasting dynamic environments in the upper 1600 m depth and middle 3300 m depth canyon high current speeds spring tides up to 80 cm s 1 and high apparent mass fluxes of particulate matter mean 65 g m 2 d 1 maximum 265 g m 2 d 1 are permanent at the shallowest station at the deepest site fluxes were below 10 g m 2 d 1 most of the time and the annual flux was governed by events of sharp flux increase storms affecting the continental shelf during autumn and winter are a major driver of down canyon dispersal of sediments to the middle canyon and beyond important nepheloid activity developed inside the canyon in response to storms with significant wave heights between 4 and 6 m as testified by turbidimeters deployed in midwater and near the seabed at 1600 m water depth on three occasions during the study period significant wave heights of incident storms surpassed 7 m leading to notable episodes of down canyon transport that were clearly observed in the middle canyon during one of these stormy periods january 2003 a sediment gravity flow transporting unusual quantities of sand and coastal plant debris was observed at 3200 m however a storm with significant wave heights as low as 5 m was apparently able to trigger a sediment gravity flow reaching beyond the middle canyon the role of storms in the offshore dispersal of sediments is clearly relevant but seems to be modulated by synergic factors such as river flooding

a case study of nonmesocyclone tornado development in northeast colorado similarities to waterspout formation abstract the evolution of the 26 july 1985 erie colorado tornado is described using data from ncar s cp 2 doppler radar this tornado develops within 20 km of the radar site under weakly forced synoptic conditions and weak tropospheric flow and is not accompanied by a mesocyclone the initial circulation forms near the surface at the intersection of two mesoscale boundaries and develops vertically intensifying into an fl tornado when it becomes collocated with the intense updrafts of a rapidly developing cumulonimbus this tornado appears to be the land equivalent of a waterspout and comparisons between the two vortices are made it is speculated that florida and portions of the western high plains may be prone to nonmesocyclone tornado development and that vortex intensification processes associated with nonmesoscyclone tornadoes may be important in mesocyclone tornadogenesis suggestions on how to better forecast these tornadoes are also presented

in situ measurements of velocity structure within turbidity currents 1 turbidity currents are thought to be the main mechanism to move 500 000 m3 of sediments annually from the head of the monterey submarine canyon to the deep sea fan indirect evidence has shown frequent occurrences of such turbidity currents in the canyon but the dynamic properties of the turbidity currents such as maximum speed duration and dimensions are still unknown here we present the first ever in situ measurements of velocity profiles of four turbidity currents whose maximum along canyon velocity reached 190 cm s two turbidity currents coincided with storms that produced the highest swells and the biggest stream flows during the year long deployment

a decadal record of underflows from a coastal river into the deep sea four periods of extreme turbidity were measured in monterey submarine canyon over the past 12 yr these turbid events occurred simultaneously with the four largest flood events of the nearby salinas river they filled the canyon with fresher warmer and apparently buoyant water that extended to depths below 1 km the low salinity signature must reflect underflow of the salinas river plume that was driven to depth by negative buoyancy contributed from the suspended sediment a flux estimate for the 1995 event suggests that one half or more of the river s suspended sediment load was carried down the canyon in the underflow underflows may contribute significantly to the carbon budget of the continental slope

in situ rockfall testing in new south wales australia abstract despite the significance of rockfall hazards in australia this phenomenon is still poorly characterised in many regional environments in particular the relationship between slope rock properties and rockfall motion parameters needs better definition in the context of rockfall prediction it is important to quantify the normal and tangential restitution coefficients referred to as k n and k t and the equivalent rolling coefficient which are site specific several series of rockfall tests have been conducted in three different geological environments in new south wales the results of the tests show a large variability of the motion parameters which is due to the natural variability of the blocks and to the randomness of the impact positions also values of k n consistently and systematically higher than the benchmark values from the literature have been inferred despite there being no clear correlation between the restitution coefficients and the rotational energy rotational phenomena are believed to be at the origin of such results

the role of midtropospheric winds in the evolution and maintenance of low level mesocyclones abstract using a three dimensional numerical model supercell simulations initialized in environments characterized by hodographs with large curvature in the lowest 3 km and a range of linear midlevel shears are investigated for low values of the midlevel shear 0 005 s 1 the storm develops a mesocyclone at the lowest model level within the first hour of the simulation the gust front starts to move ahead of the main updraft and cuts off the inflow to the storm by approximately 2 h resulting in decay of the initial storm and growth of a new rotating storm on the outflow as the midlevel shear increases to approximately 0 010 s 1 the initial development of the low level mesocyclone is delayed but the mesocyclone that develops is more persistent lasting for over 2 h further increases of the shear to 0 015 s 1 result in the suppression of any low level mesocyclone despite the presence of intense rotation at midlevels of the storm we hypothesize that differences in the distribution of precipitation

benthic foraminifera from capbreton canyon revisited faunal evolution after repetitive sediment disturbance abstract at a 650 m deep site in the axis of capbreton canyon an 18 cm thick turbidite was deposited in december 1999 during subsequent campaigns an almost monospecific fauna of the benthic foraminifer technitella melo considered as a pioneer species was found in may 2000 in 2001 this fauna had disappeared and was replaced by an exceptionally rich fauna strongly dominated by the opportunistic species bolivina subaenariensis we present sedimentological radionuclide and foraminiferal data of new cores sampled in 2005 and 2011 taken with the aim to study the further evolution of the benthic ecosystem cores sampled in 2005 show that in the canyon axis a new ca 5 cm thick turbidite has been deposited the live benthic foraminiferal faunas were much poorer than in 2001 but still had a high dominance and low diversity although less extreme than in 2001 we conclude that in the canyon axis benthic foraminiferal faunas remain in an early stage of ecosystem colonization it appears that the very thick 1999 turbidite marks an exceptional event the uncommonly rich faunas observed in 2001 could be a response to the concentration of organic rich material in the fine grained top of this deposit in 2011 cores were sampled at a slightly different site on the lower canyon flank the sedimentary sequence here is marked by the absence of coarse turbidite layers although some levels show slightly increased grain size and lower 210 pb xs activities indicative of an admixture with advected older sediments live foraminiferal faunas are much more equilibrated as shown by their higher diversity lower dominance and deeper penetration into the sediment all these characteristics are indicative of a much more stable ecosystem dead faunas are present throughout the core indicating that the levels with slightly elevated grain size are not typical turbidites resulting from hyperpycnal currents which are characterized by levels barren of foraminifera but denote other more long term sedimentary processes leading to the advection of older material such as bottom nepheloid layers or repetitive fine grained turbidite deposits due to small scale slumping the comparison of live and dead fauna shows that at both sites the foraminiferal turnover rates are fairly low at the lower canyon flank site sampled in 2011 the foraminiferal faunas are renewed every 1 5 2 years such a fairly long foraminiferal lifespan corresponds to earlier estimates but is surprisingly high for the opportunistic taxa that dominate the faunal assemblages in these unstable and food enriched submarine canyon settings

observation of internal tidal currents in the kaoping canyon off southwestern taiwan abstract internal tidal currents and associated water mass displacements were investigated during multiple cruises in the kaoping submarine canyon off southwestern taiwan observations from both moored and shipboard acoustic doppler current profilers and hydrographic casts were conducted along the canyon the velocity data showed that in the lower layer the major axis of the tidal currents aligned with the orientation of the canyon and currents moved up canyon during flood and down canyon during ebb the vertical phase shift and amplitude of the currents indicated that the semidiurnal internal tide dominated with intensity increasing with depth toward the canyon head tidal energy was channeled from the shelf landward with a beamlike internal wave guided by bottom topography the estimated phase velocity was 1 4 1 7 m s 1 based on normal mode analysis and the phase lag between sampling stations empirical orthogonal function analysis of hydrographic profiles confirmed that the first mode m 2 internal tide explained 70 of the total variance the strong convergence of internal tidal currents near the canyon head during flood may play an important role in the daily migration of cherry shrimps which burrow along the canyon wall

early miocene sedimentary processes and their hydrocarbon implications in the baiyun sag of pearl river mouth basin northern south china sea abstract the shelf slope zone has received considerable attention for hydrocarbon exploration due to its unique location where the sediments are delivered to deep water environment and deposited as hydrocarbon reservoirs that have been discovered around the world however it is realized that the sedimentary processes are very complex and various depositional bodies develop in the shelf slope zone constrained by 3d seismic core and well log data numerical simulations can be applied to better understand the sedimentary processes and predict the distribution and characteristics of deposits as hydrocarbon reservoirs based on core log seismic integration the early miocene shelf margin delta and channelized submarine fan systems along the northern slope of baiyun sag in the pearl river mouth basin are distinguished and they are mainly composed of debris turbidites and slumps the numerical model is built based on early miocene topography acquired by back stripped well tied seismic profiles and the initial boundary conditions including sediment concentration velocity and grain size and so on behaviors and structures of slope system are set according to the results of marine surveys around the world the computational fluid dynamic software ansys fluent was applied for the modelling as a results the distributions and geometries of the simulated deposits are compared with the depositional bodies interpreted from seismic data the hydrodynamic simulations of the two sedimentary systems indicate that depositional bodies converge to the downstream of the slope and the basin floor and turn tractive current into turbidity current during the sedimentary processes which result in obviously various sedimentary characteristics in different locations the identification of sedimentary processes in the shelf margin delta and channelized submarine fan systems has been beneficial for predicting reservoirs and exploring hydrocarbons in the baiyun sag pearl river mouth basin which is also contributing to the understanding of sedimentary process and reservoir prediction in deep water areas around the world

initiation and evolution of updraft rotation within an incipient supercell thunderstorm abstract one of the distinguishing characteristics of a supercell thunderstorm is the presence of a rotating updraft during the past 30 years various hypotheses have been proposed to explain the initiation and maintenance of rotation however attempts to verify the initiation process have been frustrated by the lack of multiple doppler radar measurements at the time that the first rotating updraft appears discussed in this paper are dual doppler radar measurements that successfully captured the initiation and evolution of rotation in the agawam oklahoma storm of 6 june 1979 which occurred during the storm scale phase of the severe environmental storms and mesoscale experiment sesame the process leading to updraft rotation appears to follow that proposed in 1968 by fujita and grandoso whereby a middle altitude vorticity couplet formed on the downwind flanks of a strong nonrotating updraft with cyclonic vertical vorticity on the right forward flank and anticyclonic vertical vorticity on the left

storm induced sediment gravity flows at the head of the eel submarine canyon northern california margin 1 as part of the strataform program a bottom boundary layer bbl tripod was deployed at 120 m depth in the northern thalweg of the eel canyon during winter 2000 increases of the near bottom suspended sediment concentrations ssc recorded at the canyon head were not directly related to the eel river discharge but were clearly linked to the occurrence of storms bbl measurements revealed that during intensifications of the wave orbital velocity sediment transport at the head of the canyon occurred as sediment gravity flows directed down canyon observational evidence for near bed sediment gravity flow transport included an increase toward the bed of the down canyon component of wave averaged velocity and high estimated ssc at higher sampling frequencies 1 hz the current components during these events fluctuated at the same periodicity as the pressure reflecting a clear influence of the surface wave activity on the generation and maintenance of the sediment gravity flows the origin of such flows is not related to the formation of fluid muds on the shelf or to intense wave current sediment resuspension around the canyon head region rather liquefaction of sediment deposited at the head of the canyon induced by wave load excess pore water pressures during storms combined with elevated slopes around the canyon head appear to be the mechanisms initiating sediment transport the resulting fluidized sediment layer can easily be eroded entrained into the water column and transported down canyon as a sediment gravity flow results from this study reveal that storm induced sediment gravity flows occur periodically in the eel canyon head and suggest that this kind of sediment transport process can occur in other submarine canyons more frequently than previously expected

selective transport of palynomorphs in marine turbiditic deposits an example from the ascension monterey canyon system offshore central california abstract the pollen assemblage of a deep sea core 15g collected at lower bathyal depths 3491 m on a levee of monterey canyon off central california was investigated to gain insights into the delivery processes of terrigenous material to submarine fans and the effect this transport has on the palynological record thirty two samples were obtained down the length of the core 19 from hemipelagic and mixed mud deposits considered to be the background record and 13 others from displaced flow deposits the pollen record obtained from the background samples documents variations in the terrestrial flora as it adapted to changing climatic conditions over the last 19 000 cal yrs bp a q mode cluster analysis defined three pollen zones a glacial pollen zone ca 20 000 17 000 cal yr bp an overlying transitional pollen zone ca 17 000 11 500 cal yr bp and an interglacial pollen zone ca 11 500 cal yr bp to present another q mode cluster analysis of both the background mud and flow deposits also defined these three pollen zones but four of the 13 turbiditic deposits were assigned to pollen zones older than expected by their stratigraphic position this was due to these samples containing statistically significant fewer palynomorphs than the background muds as well as being enriched 10 35 in some cases in hydraulically efficient pinus pollen a selective bias in the pollen assemblage such as demonstrated here may result in incorrect interpretations e g climatic shifts or environmental perturbations based on the floral record indicating turbiditic deposits should be avoided in marine palynological studies particularly in the case of fine grained flow deposits that may not be visually distinct granulometry and grain size frequency distribution curves may not be enough to identify these biased deposits determining the relative abundance and source of displaced shallow water benthic foraminifera entrained in these sediments serves as an excellent additional tool to do so

simulations of shallow supercell storms in landfalling hurricane environments abstract numerical simulations of the convective storms that form in tornado producing landfalling hurricanes show that shallow supercells are possible even though buoyancy is limited because ambient lapse rates are close to moist adiabatic updrafts generally reach peak intensity at low levels often around 2 km above the surface by comparison a simulated midlatitude supercell typical of the great plains of the united states exhibits a pronounced increase in storm size both horizontally and vertically at low levels however the hurricane spawned storms may contain updrafts that rival or exceed in intensity those of great plains supercells at similar levels simulations made using a tornado proximity sounding from the remnants of hurricane danny in 1985 produce a small but intense supercell a finding consistent with the available observational evidence although the amplitude of parcel buoyancy is often small in hurricane environments its concentration in the strongly sheared lower troposphere pro

recent sediment transport and deposition in the nazare canyon portuguese continental margin processes pathways and fluxes of sediment transport and deposition in the nazare submarine canyon portuguese continental margin were investigated by water column profiling of suspended particulate matter recording of near bottom currents and suspended particulate matter fluxes with benthic landers and by analysis of surface sediment cores the results show that fine grained suspended sediment from the adjacent shelf is captured in the upper canyon and actively transported through the canyon to the abyssal plain under influence of tidal currents and intermittent sediment gravity flows tidal currents are actively resuspending and transporting sediment in the upper to middle canyon as reflected by high concentration of suspended particles in bottom waters high horizontal and vertical sediment fluxes in the bottom water layer and high sediment accumulation rate on the seabed diminishing strength of tidal currents leads to focussed sediment deposition in the middle canyon further transport of sediments toward the lower canyon takes place predominantly by sediment gravity flows occurring on yearly or longer timescale turbidity currents strong enough to transport sand sized material to the lower canyon occur only on centennial or longer timescales

the structure and evolution of a numerically simulated high precipitation supercell thunderstorm the structure and evolution of a high precipitation hp supercell thunderstorm is investigated using a threedimensional nonhydrostatic cloud scale numerical model tass the model is initialized with a sounding taken from a mesoscale modeling study of the environment that produced the 28 november 1988 raleigh tornadic thunderstorm tass produces a long lived convective system that compares favorably with the observed raleigh tornadic thunderstorm the simulated storm evolves from a multicell type storm to a multiple updraft supercell storm the storm complex resembles a hybrid multicell supercell thunderstorm and is consistent with the conceptual model of cool season strong dynamic hp supercells that are characterized by shallow mesocyclones the origin of rotation in this type of storm is often in the lowest levels interactions between various cells in the simulated convective system are responsible for the transition to a supercellular structure an intense low level updraft core forms on the southwest flank of the simulated storm and moves over a region that is rich in vertical vorticity the stretching of this preexisting vertical vorticity in the storm s lowest levels is the most important vertical vorticity production mechanism during the initial stages of the main updraft s development interactions with an extensive cold pool created by the storm complex are also important in producing vertical vorticity as the main updraft grows overall the development of vorticity associated with the main updraft appears similar to nonsupercellular tornadic storms however classic supercell signatures are seen early in the simulation associated with other updrafts e g formation of vortex couplet due to tilting of ambient horizontal vorticity storm splitting etc and are deemed important in the storm s supercell stage rotation is sustained in the lowest levels of the storm despite large amounts of precipitation located near and within the main mesocyclone pulsating downdrafts periodically invigorate the storm and the gust front never occludes thus allowing the main updraft to persist for a prolonged period of time the storm s intensity is also maintained by frequent updraft mergers

sedimentary processes and cold water coral mini mounds at the ferrol canyon head nw iberian margin abstract the western iberian margin has a complex morphology controlled by both geological and oceanographic processes compared to the submarine canyons in the southern part of this margin e g nazare and setubal the canyons in the northern part e g ferrol and a coruna have received little attention this study maps the geomorphological features around the ferrol canyon head and combines them with oceanographic observations to infer the sedimentary and oceanographic processes active in this area furthermore the occurrence of a cold water coral cwc mini mound province near the canyon head and the ortegal spur pockmark field is investigated with regard to seepage processes oceanographic conditions and anthropogenic impact the ferrol canyon head and outer ortegal spur are characterized by erosional erosional and abraded surfaces contourite channels and furrows depositional contourite drifts and sediment waves and mixed contourite terrace features indicating a dominant control of bottom currents on the sedimentary processes bottom currents are related to the interaction of the canyon head topography with both the mediterranean outflow water mow slope current and with m2 internal tides associated to the interface pycnocline between eastern north atlantic central water enacw and mow due to this interaction the ferrol canyon head is subject to active sediment resuspension and forms a potential source area for the intermediate nepheloid layers along the nw iberian upper slope the cwc mini mounds 1 9 2 7 m high and 75 141 m in diameter occur between 400 and 560 m depth seismic facies signatures indicative of fluid flow and morphometric analysis implies that larger cwc mini mounds adjacent to the pockmark field initiated by colonization of pre existing pockmarks while smaller more clustered mounds developed independently the observed mini mounds are relict features likely related to their position outside of the contemporary enacw mow interface which favours cwc growth through 1 increased bottom currents enhancing food supply and 2 the presence of a potential density envelope 27 35 27 65 kg m3 proposed to control coral larvae transport along the ne atlantic margin alternatively the lack of contemporary coral growth might be related to habitat destruction by bottom trawling however a preliminary age constraint reveals cwc growth occurred during the early holocene coeval to relict cwc mini mounds near canyon heads on the armorican margin their existence suggests a regional shift in the ne atlantic density profile where the enacw mow interface occurred up to 200 m above its contemporary position

direct sediment transfer from land to deep sea insights into shallow multibeam bathymetry at la reunion island abstract submarine canyon heads are key areas for understanding the triggering factors of gravity currents responsible for the transfer of detrital sediment to the deep basins this contribution offers a detailed picture of canyon heads off la reunion island with high resolution multibeam bathymetry in the water depth range of 4 220 m the present feeding of the cilaos turbidite system one of the largest modern volcaniclastic systems in the world is deduced from morphological and sedimentological interpretations of newly acquired data the study highlights small scale sedimentary features indicating hydrodynamic and sedimentary processes a direct connexion between the saint etienne river mouth and submarine canyons is evidenced by the complete incision of the shelf and the presence of canyon heads connected to the modern deltaic bar this direct connection supplied by river torrential floods cyclonic floods every two or three years suggests the continuity of high density fluvial flows to submarine gravity flows forming hyperpycnal flows in the canyon the initiation of secondary submarine gravity flows by storm waves large austral waves and cyclonic waves is also proposed for submarine canyons with large canyon heads developed in the surf zone from a sandy coastal bar bedforms in active canyon axis are considered as an indicator of the frequent activity of high density turbidity currents moreover a morphological record of last glacial and deglacial sea level variations is preserved and particularly the last glacial maximum sea level with the presence of small vertical cliffs observed in this bathymetric data which likely corresponds to a paleo shoreline or paleo reefs

suspended sediment fluxes and transport processes in the gulf of lions submarine canyons the role of storms and dense water cascading contemporary suspended sediment transport was studied in seven submarine canyons of the gulf of lions gol current meters equipped with turbidity sensors were moored 4 m above bottom at 300 m depth in the canyon axis from november 2003 to may 2004 sediment transport events were monitored and studied in relation to forcing conditions there was a large flood in early december during which discharges from all of the coastal rivers increased by more than one order of magnitude a smaller flood of the rhone river occurred later in mid january followed by a persistent high river discharge that lasted until mid february there were also several e se storm events during the measurement period two of them causing large swell one in early december max hs 8 4 m coinciding with the major river flood andoneinlatefebruary maxhs 7m duringaperiodoflowerriverdischarge mostofthevariabilityindown canyoncurrentspeeds waslinkedtostrongdownwellinginducedbye sestormsandtocascadingofdenseshelfwaterinducedbynandnwwinds theintensity and timing of these processes strongly varied spatially eastern storms generated higher waves and induced stronger downwelling in the western than in the eastern sector of the gol shelf dense water cascading events were enhanced during eastern storms and they were also more intense in the western sector of the gol these events occurred frequently from january to may along the western canyons and from february to april along the eastern canyons from february to april they occurred simultaneously in all the canyons sediment transport was mainly down canyon and mostly concentrated during storm induced downwelling and dense water cascading events during the high river discharge season most of the newly supplied and resuspended sediment remained stored on theshelf however duringthelatefebruarystormandcascadingevent thestoredsedimentwasquicklyresuspendedandtransported mainly through the westernmost submarine canyon cap de creus following a flushing pattern later although minor storms and shelfdensewatercascadinghardlyincreasedsuspendedsedimentconcentrationswithinthecanyons theyinducedstrongnear bottom current velocities increasing down canyon sediment fluxes and generating small but significant sediment transport events most of the shelf canyon transfer took place during the late february storm and cascading event through the cap de creus canyon where the net suspended sediment flux was between one and two orders of magnitude higher than in the other canyons

non supercell tornadoes abstract analyses of tornadoes that are not associated with supercells are presented the database for this study was collected during cinde convention initiation and downburst experiment a field project operated during the summer of 1987 in colorado a total of 27 visual vortices were studied they appeared to form as shear instabilities along radar detected convergence lines the circulations initiated at low levels generally in the absence of precipitation echo subsequently as these vortices propagated along the convergence line they appeared to strengthen to tornadic intensity when they became colocated with the updraft of a rapidly developing storm it is hypothesized that vortex stretching is responsible for intensifying the initial rotation although these tornadoes were weaker than those accompanied by strong midlevel mesocyclones estimates of their strength suggest damage capability as high as f2 the implications for operational radars to detect these types of phenomena were identified the

sedimentary evolution of the le danois contourite drift systems southern bay of biscay ne atlantic a reconstruction of the atlantic mediterranean water circulation since the pliocene abstract the evolution of the le danois contourite depositional systems cds during the pliocene and quaternary was investigated based on high resolution seismic reflection data from old to young six seismic units u1 u6 bounded by major discontinuities h1 h6 were identified regarding variations of the bottom current circulation four evolution stages of the le danois cds were identified including onset 5 3 to 3 5 3 0 ma initial 3 5 3 0 to 2 5 2 1 ma intermediate 2 5 2 1 to 0 9 0 7 ma and drift growth 0 9 0 7 ma to present day stages the cds associated with the atlantic mediterranean water amw along the middle continental slope initiated at 3 5 3 ma and was widely built after the mid pleistocene transition mpt 0 9 07 ma at a shallower water depth a second cds associated with the eastern north atlantic central water enacw started to develop from the late quaternary 0 47 ma onwards in the amw related drift system the le danois drift was generated both under glacial and interglacial climatic oscilations repeated internal structures in unit 5 that consist of acoustically transparent lower parts moderate amplitude upper parts and high amplitude erosional surfaces at the top are compared with interglacial glacial cycles since the middle pleistocene to the present day these cyclic features suggest coarsening upward sequences of the le danois drift and processes related to enhanced amw during glacial stages the estimated sedimentation rate of the le danois cds reached a maximum during the mpt at least 27 cm ky and then decreased until present day 5 cm ky variations of sedimentary stacking patterns and processes of the le danois cds imply full domination of the intermediate water mass along the central atlantic and southwest european continental slopes from the late pliocene 3 5 3 0 ma onwards

the genesis of three nonsupercell tornadoes observed with dual doppler radar abstract dual doppler radar analyses of three tornadoes associated with a multicellular line of storms are presented the f2 f3 intensity tornadoes occurred on 15 june 1988 near denver colorado during the terminal doppler weather radar tdwr project these tornadoes developed from misocyclones of no larger than 2 km in diameter that formed along the collision of two surface outflows the misocyclones were observed to build in height and intensify with time coincident with rapid storm growth overhead all three misocyclones were clearly associated with the maximum storm updrafts downdrafts and associated outflows did not play a role in the formation of one of the tornadoes but may have contributed to the genesis of the other two tornadoes it is clear that a downdraft is not a necessary condition for the formation of a nonsupercell tornado but when present likely plays a role in determining the timing and intensity of the tornado this is achieved by the downdraft and outflow causing an increase in

2000years of frequent turbidite activity in the capbreton canyon bay of biscay abstract capbreton canyon extends from 200 m water depth near the aquitanian coast to 3000 m water depth before abruptly turning northward and merging with the cap ferret systems the capbreton canyon has been disconnected from the adour river input since 1310 ad despite this situation modern sedimentary activity is evident in the first kilometres from the head present sedimentation in the capbreton canyon was studied by combined analysis of acoustic data and cores cores from the topographic highs document moderate hemipelagic sedimentation and record the global climatic signal of the bay of biscay within the canyon at 80 km from the head on terraces bordering the thalweg at 1600 m water depth cores attest to recent turbidite activity massive medium sand is restricted to the thalweg floor where sediment transfer dominates fine grained turbidites are preferentially accumulated on the shallower terraces near the thalweg the accumulation rate is 3 and 1 cm year at 75 m and 125 m above the thalweg respectively on a higher terrace 225 m turbidite sequences are absent or too thin to be preserved from bioturbation the sedimentation rate is lower approximately 0 17 cm year but still 10 times higher than the hemipelagic sedimentation outside the capbreton canyon we demonstrate that frequent turbidity currents 1 year are currently responsible for very high accumulation of dominantly fine grained sediments on the terraces that are the nearest from the thalweg we assume an impact of nepheloid layers on the sedimentation of the highest terraces looking for any impact on sediment supply of the disconnection of the capbreton canyon head from the adour river mouth it appears that the impact on the sedimentation affected the nature of the particles which are less carbonate rich rather than the quantity of sediments this result suggests that the longshore drift at the canyon head and hydrodynamic events are major factors in the sedimentation of capbreton canyon

event driven sediment flux in hueneme and mugu submarine canyons southern california vertical sediment fluxes and their dominant controlling processes in hueneme and mugu submarine canyons off south central california were assessed using data from sediment traps and current meters on two moorings that were deployed for 6 months during the winter of 2007 the maxima of total particulate flux which reached as high as 300 g m 2 day in hueneme canyon were recorded during winter storm events when high waves and river floods often coincided during these winter storms wave induced resuspension of shelf sediment was a major source for the elevated sediment fluxes canyon rim morphology rather than physical proximity to an adjacent river mouth appeared to control the magnitude of sediment fluxes in these two submarine canyon systems episodic turbidity currents and internal bores enhanced sediment fluxes particularly in the lower sediment traps positioned 30 m above the canyon floor lower excess 210 pb activities measured in the sediment samples collected during periods of peak total particulate flux further substantiate that reworked shelf rather than newly introduced river borne sediments supply most of the material entering these canyons during storms published by elsevier b v

periodic resuspension in baltimore canyon by focusing of internal waves high concentrations of particulate matter are frequently reported in submarine canyons this study demonstrates that in baltimore submarine canyon elevated concentrations result from periodic resuspension events the sloping bottom and v shaped topography of submarine canyons could accelerate tidal flows in the canyon axis sufficiently to cause resuspension which occurs predominantly at tidal frequencies however current meter and transmissometer data show that resuspension events are often associated with a borelike intrusion of cold water moving upslope near the canyon head an event that is consistent with the focusing of internal wave energy toward the canyon head at tidal frequencies hydrographic conditions for the focusing of energy are most favorable in late winter and early spring when stratification in the canyon is diminished direct observations reveal that the most pronounced resuspension events occur during those seasons bottom stresses generated in the canyon are sufficient to resuspend sediment along the axis at least between 200 and 800 m with little resuspension occurring deeper along the axis on the canyon walls adjacent slope or shelf during a resuspension event the sediment laden water is forced upcanyon then sloshes back down the canyon until it reaches a layer of higher density water detaches from the canyon floor and moves seaward along a density surface this is a means of transferring sediment and associated pollutants intercepted at the canyon head to deeper water across the shelf slope front over geologic time frequent resuspension and seaward transport may aid in the headward erosion of submarine canyons or at least inhibit their infilling during interglacial times

recent sediment transport and deposition in the lisbon setubal and cascais submarine canyons portuguese continental margin abstract recent sediment transport and deposition in the lisbon setubal and cascais submarine canyons portuguese continental margin were investigated on the basis of water column profiles of suspended particulate matter records of near bottom currents and settling fluxes of particulate matter obtained with benthic landers and analysis of surface sediments the results show that fine grained predominantly lithogenic sediment derived from adjacent shelf areas accumulates in the upper reaches of the canyons sediment deposited further down in the middle and lower reaches of the canyons is essentially similar to the hemipelagic sediment found on the adjacent continental slope indicating that down canyon transport of sediment from the upper to the lower canyon is limited tidal currents measured at various depths in the lisbon setubal canyon appear sufficiently strong to resuspend and transport sediment but net up canyon flow of the bottom water may retain shelf derived lithogenic sediment in the upper canyon sediment gravity flows which in the nearby nazare canyon are an effective mechanism for down canyon sediment transport appear rare in the lisbon setubal canyon and probably also in the cascais canyon turbidity current events recorded in the sedimentary record of the canyons may correspond to seismic events of 1969 and 1755 ad

present deep submarine canyons activity in the bay of biscay ne atlantic present sedimentation in three canyons of the bay of biscay audierne blackmud and capbreton is studied by the combined analysis of cores and current meter data collected over a 7 month period at the current meter mooring locations interface cores were collected to characterize the recent sedimentation processes in the two canyons located in the northern part of the bay of biscay audierne and blackmud there is no evidence of recent sedimentary deposits canyons are by passing or erosive areas in the southern part of the bay of biscay capbreton recent turbidite are deposited in the three canyons current meters recorded energetic currents with velocities showing alternating upslope and downslope motions and a period corresponding to the semi diurnal component m2 these currents are supposed to be related to deep internal tides the high speed of the current 1 m s in audierne and blackmud is consistent with the lack of preservation of recent sediments on the canyon floors in capbreton canyon the magnitude of currents is less and recent turbidites are preserved in addition to periodical current motion small magnitude gravity event corresponding to a low concentration turbulent surge or a high concentration nepheloid layer initiated during a storm was recorded during the mooring period these results suggest that deep sea canyons in the bay of biscay have behaviour at present varying between by passing or erosion areas and sediment trapping these examples suggest that sediments are moved up and down by low energy tide initiated hydrodynamic events during most of the time during higher magnitude short duration gravity events the sediments are transferred down canyon towards the deep sea

observations of long duration episodic bottom currents in the middle america trench evidence for tidally initiated turbidity flows 1 benthic flow in the middle america trench off the pacific coast of costa rica is examined using time series from a single point acoustic current meter moored 21 m above bottom at 4386 m depth at the southern end of the trench from november 2005 to april 2007 in addition to significant 0 1 m s 1 tidal currents the instrument recorded a series of 12 episodic northwestward along trench flow events of roughly monthly duration event velocities often exceeded 0 25 m s 1 and were contemporary with enhanced acoustic backscatter intensity events ended with a rapid 1 day reversal to southeastward flow and reduced backscatter seafloor temperature records from two nearby ocean drilling program odp borehole observatory sites reveal that the flow events were accompanied by a steady rise in bottom water temperature temperatures dropped abruptly to background values at the end of each event the event timing generally tracked the envelope of the tidal current modulation on the basis of the november 2002 to february 2009 borehole observatory temperature records the events had a mean duration of 40 20 days and were separated by a between event interlude of 30 25 days findings indicate that the episodic flows were likely rotationally modified autosuspending turbidity currents initiated by tidal current resuspension of sediments above the shoaling trench floor to the southeast of the mooring site suspended particles in the turbidity currents are estimated to range from 0 0003 to 0 006 of the current by volume results suggest that tidally induced turbidity currents may be common to steep well mixed regions of the deep ocean adjacent to sediment rich continental margins

geomorphology of the aviles canyon system cantabrian sea bay of biscay abstract the aviles canyon system acs is a complex structurally controlled canyon and valley system constituted by three main canyons of different morphostructural character they are from east to west la gaviera canyon el corbiro canyon and aviles canyon in addition to this acs a new canyon has been surveyed navia canyon we present for the first time a high resolution multibeam map showing with great detail the morphological and structural complexity of this segment of the cantabrian margin acs presents a tectonic imprint marked by nw se nne ssw and e w structures the morphology of their reaches as well as their single mouth in addition to some rock dredges in their major valleys demonstrates active down slope flushing the continental shelf shows a flat uniform slope with local and well defined rock outcrops south of aviles canyon head sedimentary zones are limited showing thin unconsolidated sedimentary cover strong continental margin water dynamics avoid thicker sediment deposition being littoral sedimentary dynamics responsible for transport to the canyons heads and conduit to the biscay abyssal plain biscay abyssal plain shows evidence of a strong westward current affecting the surveyed strip of this more than 10 km wide plain presence of two parallel deep sea channels erosive scarps and erosion of gully divides on the lower slope may indicate that this is part of the distal fan at the termination of the large turbiditic system fed by cap ferret capbreton and other large canyons santander torrelavega lastres and llanes to the west of acs