the cleft revealed geologic magnetic and morphologic evidence for construction of upper oceanic crust along the southern juan de fuca ridge 1 the geology and structure of the cleft segment of the southern juan de fuca ridge jdfr have been examined using high resolution mapping systems observations by remotely operated vehicle rov rov mounted magnetometer and the geochemical analysis of recovered lavas bathymetric mapping using multibeam em300 coupled with in situ observations that focused on near axis and flank regions provides a detailed picture of 0 to 400 ka upper crust created at the southern terminus of the jdfr a total of 53 rock cores and 276 precisely located rock or glass samples were collected during three cruises that included sixteen rov dives our observations of the seafloor during these dives suggest that many of the unfaulted and extensive lava flows that comprise and or cap the prominent ridges that flank the axial valley emanate from ridge parallel faults and fissures that formed in the highly tectonized zone that forms the walls of the axial valley the geochemically evolved and heterogeneous nature of these near axis and flank eruptions is consistent with an origin within the cooler distal edges of a crustal magma chamber or mush zone in contrast the most recent axial eruptions are more primitive higher mgo chemically homogeneous lobate sheet and massive flows that generate a distinct magnetic high over the axial valley we suggest that the syntectonic capping volcanics observed off axis were erupted from near axis and flank fissures and created a thickened extrusive layer as suggested by the magnetic and seismic data this model suggests that many of the lavas that comprise the elevated ridges that bound the axial valley of the cleft segment were erupted during the collapse of a magmatic cycle not during the robust phase that established a new magmatic cycle

high resolution late maastrichtian early danian oceanic 87sr 86sr record implications for cretaceous tertiary boundary events a high resolution late maastrichtian early danian seawater 87 sr 86 sr reference curve is constructed from two cretaceous tertiary boundary k t boundary sections bidart france and el kef tunisia the 87 sr 86 sr curve shows maxima at 0 3 0 4 ma before the k t boundary and at the k t boundary the first maximum could mark the onset of a major outflow of the deccan traps the second maximum a rapid 0 000 06 87 sr 86 sr shift extends from 3 4 m below to 1 m above the k t boundary this profile probably results from diagenetic smoothing of an originally sharp k t boundary 87 sr 86 sr anomaly rather than from a gradual process the sharp shift could result from 1 the vaporization of the chicxulub target rocks 2 global wildfires and 3 acid rain leaching of soils and sialic surface rocks of these three possibilities only sr release by soil leaching combined with increased rainfall associated with the k t event appears to be sufficiently large to produce the observed k t 87 sr 86 sr anomaly

the cretaceous tertiary boundary cocktail chicxulub impact triggers margin collapse and extensive sediment gravity flows a distinctive mixture of reworked microfossils impact derived materials and lithic fragments occurs in sediments at the cretaceous tertiary boundary in the basinal gulf of mexico and caribbean we have named this mixture the cretaceous tertiary boundary cocktail lithologic and paleontologic evidence suggests that the cocktail was deposited by giant sediment gravity flows apparently triggered by the collapse of continental margins around the gulf of mexico as a result of the chicxulub impact as most microfossils in the gravity flow units are reworked biostratigraphy provides only maximum ages recognition of the cocktail is a reliable way to identify cretaceous tertiary boundary deposits in the basinal gulf of mexico and caribbean

the collapse of the sella zerbino gravity dam abstract when a severe flood wave completely filled the ortiglieto reservoir on august 13 1935 the 14 m high sella zerbino secondary dam failed catastrophically causing 100 casualties both of the dams sella zerbino zerbino saddle and bric zerbino zerbino peak fig 1 were overtopped but only the sella zerbino failed whereas the main barrage did not suffer any damage the lawsuit that followed this tragic event ended with a full acquittal of the dam s designers since the plaintiff experts succeeded in demonstrating that the collapse was due to an extreme rainfall storm of unpredictable intensity the case was then officially closed and still today the failure of the sella zerbino dam is attributed to the unpredictable hydrological event recently natale and petaccia 2013 re examined the case assessing the capacity of the flood spillways which equipped the bric zerbino dam this paper thoroughly reviews the mechanics of the collapse of the sella zerbino dam focusing on the stability of the structure the water pressure underneath the dam and the poor quality of the foundation rock is believed to have played a major role in the sequence of events that ended in the collapse of the barrage

formation of a jump by the dam break wave over a granular bed a previously unreported shock feature associated with the scouring of a horizontal granular bed by a dam break wave is discussed near the wave centre the present study shows the free surface breaks backward and a hydraulic jump forms this behaviour is described from the standpoint of shallow water theory suitably extended to deal with non equilibrium sediment transport the shock formation involves a particularly strong coupling between flow free surface evolution and bed morphodynamics support for our conclusions is sought through experimental and numerical approaches in order to magnify the observed phenomena measurements were performed for the case of light bed particles moving in sheet and debris flow modes a detailed picture of the transient two phase flow is presented based on whole field acquisition of the grain motions by particle tracking techniques corresponding shallow water solutions are constructed numerically using a shock capturing scheme finally an interpretation of the jump formation is proposed based on the theory of characteristics

experimental and numerical analysis of side weir flows in a converging channel abstractthis paper investigates the lateral outflow over a short crested side weir inserted in a converging rectangular channel with linearly decreasing width in the flow direction this type of ov

87sr 86sr test of the degree of impact induced slope failure in the maastrichtian of the western north atlantic analyses of 8 7 sr 8 6 sr in foraminifera and sedimentological observations suggest that the chicxulub impact was not the trigger for slumps or a hiatus within the maastrichtian section recovered at ocean drilling programsites 1049 1050 and 1052 subtropical western north atlantic the slumps and hiatus occur within a sequence dominated by pelagic chalk the 8 7 sr 8 6 sr measurements show a general increase through the maastrichtian at each site but suggest chronostratigraphic gaps on the order of 10 6 yr across the slumps some of the slumps have burrowed upper surfaces and are composed of material that is older and coarser grained than the bounding chalks pelagic deposition punctuated by gravity flows easily explains the maastrichtian record on blake nose whereas an impact based explanation for slumping is difficult to reconcile with sedimentological and geochemical observations

strontium isotopic evidence for extensive reworking in sediments spanning the cretaceous tertiary boundary at odp site 738 the maastrichtian and danian intervals of ocean drilling program odp hole 738c contain numerous microfossils above the level of their putative extinction suggesting either 1 persistence of local communities long after species turnover occurred across the rest of the globe or 2 large scale reworking these interpretations have very different paleoenvironmental implications but discriminating between them has proved difficult to test the competing hypotheses we measured the 87 sr 86 sr ratios of taxon specific separates from a number of samples and compared these values both to each other and to expected seawater values at the time of deposition our results indicate extensive and pervasive reworking throughout maastrichtian and lower danian strata in odp hole 738c we estimate that up to 30 of the mass of foraminifers in any sample can be contributed by individuals that have been reworked

paleotemperature and paleosalinity inferences and chemostratigraphy across the aptian albian boundary in the subtropical north atlantic 1 geochemical analyses of extraordinarily well preserved late aptian early albian foraminifera from blake nose ocean drilling program site 1049 reveal rapid shifts of 18o 13c and 87sr 88sr in the subtropical north atlantic that may be linked to a major planktic foraminifer extinction event across the aptian albian boundary the abruptness of the observed geochemical shifts and their coincidence with a sharp lithologic contact is explained as an artifact of a previously undetected hiatus of 0 8 1 4 million years at the boundary contact but the values before and after the hiatus indicate that major oceanographic changes occurred at this time 87sr 88sr increase by 0 000 200 13c values decrease by 1 5 to 2 2 and 18o values decrease by 1 0 planktics to 0 5 benthics across the hiatus further both 87sr 88sr ratios and 18o values during the albian are anomalously high the 87sr 88sr values deviate from known patterns to such a degree that an explanation requires either the presence of inter basin differences in seawater 87sr 88sr during the albian or revision of the seawater curve for 18o planktic values in some aptian samples likely reflect a diagenetic overprint but preservation is excellent in the rest of the section in well preserved material benthic foraminiferal values are largely between 0 5 and 0 0 and planktic samples are largely between 0 0 to 1 0 with a brief excursion to 2 0 during oae 1b using standard assumptions for cretaceous isotopic paleotemperature calculations the 18o values suggest bottom water temperatures at 1000 1500 m of 8 10 c and surface temperatures of 10 14 c which are 4 6 c and 10 16 c cooler respectively than present day conditions at the same latitude the cool subtropical sea surface temperature estimates are especially problematic because other paleoclimate proxy data for the mid cretaceous and climate model predictions suggest that subtropical sea surface temperatures should have been the same as or warmer than at present because of their exquisite preservation whole scale alteration of the analyzed foraminifera is an untenable explanation our proposed solution is a high evaporative fractionation factor in the early albian north atlantic that resulted in surface waters with higher 18o values at elevated salinities than commonly cited in cretaceous studies a high fractionation factor is consistent with high rates of vapor export and a vigorous hydrological cycle and like the sr isotopes implies limited connectivity among the individual basins of the early cretaceous proto atlantic ocean

simplified method for the characterization of the hydrograph following a sudden partial dam break this paper presents a simplified approach to the characterization of the hydrograph following the partial collapse of concrete gravity dams the proposed approach uses a simplified representation of the reservoir geometry and is based on the numerical solution of shallow water equations to study the two dimensional evolution of the water surface within the reservoir the numerical results are made dimensionless and reorganized so as to compute the peak discharge the duration and the recession limb of the dam break hydrograph the proposed practical approach provides a quite satisfactory reproduction of the computed hydrograph for a wide set of realistic situations that have been simulated in detail

nonintrusive spatiotemporal smart debris tracking in turbulent flows with application to debris laden tsunami inundation abstractflood disasters such as dam breaks and surges from extreme hurricanes or tsunamis entrain and transport substantial amounts of submerged or floating debris understanding of motion and spatiotemporal distribution of debris entrained by a flood is thus of great importance to hydraulic coastal and structural engineers the displacement of debris to a location where it may eventually impact critical infrastructure requires scientific attention at the laboratory scale first in this context the design and application of a novel smart debris system utilizing off the shelf components is presented and discussed the system tracks the spatial location and orientation of a multitude of debris specimens and it proposes an accurate tool to assess their individual trajectory velocity and momentum in a laboratory environment contrary to the traditional camera based approach of video tracking which often fails once objects are submerged the proposed smart debris system delivers six degree of freedom 6d

dam break flows acquisition of experimental data through an imaging technique and 2d numerical modeling this paper presents experimental and two dimensional 2d numerical results of four tests concerning rapidly varying flows induced by the sudden removal of a sluice gate for the acquisition of the experimental data an imaging technique capable of providing spatially distributed information was adopted a coloring agent was added to the water the opalescent bottom of the facility was backlighted and photographs of the area of interest were taken the gray tones of the acquired images were converted into water depths by means of transfer functions derived from a static calibration the potential sources of error of the proposed procedure are discussed a local comparison with an ultrasonic device showed a 20 maximum deviation in 95 of the observations the tests were simulated through a 2d muscl hancock finite volume numerical model based on the classical shallow water approximations in which the intercell water depths are estimated according to the surface gradient method a global analysis of the relative frequency distributions of the deviation between numerical and experimental results is performed despite some evident differences at a local scale the adopted 2d numerical model is capable of reproducing the main features of the flow fields under investigation

evolution of seismic layer 2b across the juan de fuca ridge from hydrophone streamer 2 d traveltime tomography how oceanic crust evolves has important implications for understanding both subduction earthquake hazards and energy and mass exchange between the earth s interior and the oceans although considerable work has been done characterizing the evolution of seismic layer 2a there has been little analysis of the processes that affect layer 2b after formation here we present high resolution 2 d tomographic models of seismic layer 2b along 300 km long multichannel seismic transects crossing the endeavour northern symmetric and cleft segments of the juan de fuca ridge these models show that seismic layer 2b evolves rapidly following a different course than layer 2a the upper layer 2b velocities increase on average by 0 8 km s and reach a generally constant velocity of 5 2 0 3 km s within the first 0 5 myr after crustal formation this suggests that the strongest impact on layer 2b evolution may be that of mineral precipitation due to active hydrothermal circulation centered about the ridge crest and driven by the heat from the axial magma chamber variations in upper layer 2b velocity with age at time scales 0 5 ma show correlation about the ridge axis indicating that in the long term crustal accretion processes affect both sides of the ridge axis in a similar way below the 0 5 ma threshold differences in 2b velocity are likely imprinted during crustal formation or early crustal evolution layer 2b velocities at propagator wakes 5 0 0 2 km s where enhanced faulting and cracking are expected and at areas that coincide with extensional or transtensional faulting are on average slightly slower than in normal mature upper layer 2b analysis of the layer 2b velocities from areas where the hydrothermal patterns are known shows that the locations of current and paleohydrothermal discharge and recharge zones are marked by reduced and increased upper layer 2b velocities respectively additionally the distance between present up flow and down flow zones is related to the amount of sediment cover because as sediment cover increases and basement outcrops become covered direct pathways from the igneous basement through the seafloor are cut off forcing convective cells to find alternate paths

numerical models of diagenesis sediment properties and pore fluid chemistry on a paleoceanographic transect blake nose ocean drilling program leg 171b a critical issue in many paleoceanographic studies is the potential of diagenetic processes to compromise the fidelity of geochemical proxies e g 18o in deep sea carbonate sediments and microfossils a recently established strategy for dealing with this issue is to drill depth transects in anomalously shallowly buried and therefore presumably well preserved target sediments here we report the results of an experiment designed to test the validity of this approach we apply a simple one dimensional numerical model to complex pore water chemical profiles for ca mg sr 87sr 86sr and 18o observed in a shallowly buried paleoceanographic transect of paleogene and cretaceous age drilled on blake nose during ocean drilling program leg 171b we show that it is possible to reproduce these complex pore water profiles simply by invoking 1 a deep seated zone of chemical reaction well below the recovered sections and 2 minimal chemical alteration within the overlying recovered sediments but significant restriction of advective flow by embedded low porosity layers these results suggest that the sediments recovered during ocean drilling program leg 171b can be considered to be virtually chemically inert at their present burial depth their carbonate recrystallization histories having been largely limited to events during early 10 ma timescale burial these findings support the strategy of selecting unusually shallowly buried sections for paleoceanographic transect drilling ironically however the very attraction of targeting such sections the lack of overlying sediments dictates that it is not possible to use pore water chemistry to constrain the early diagenetic histories of such sections because of the diffusion of the pore water signal through the sediment water interface diffusional loss may also account for the absence of pore water chemical anomalies associated with the ooze chalk transition at blake nose however our work suggests that traditional interpretations of this boundary as the inferred locus of maximum rates of carbonate recrystallization require reevaluation

identification and implications of off axis lava flows around the east pacific rise 1 off axis eruptions at ocean ridges provide critical information with respect to underlying crustal plumbing and mantle melting systems a detailed study of basaltic glass samples around the east pacific rise from 12 00 to 12 30 n provides geological evidence for the existence of off axis eruptions with a distinctive chemical composition this composition has not been found along the axis of the epr from 8 to 14 n except at a ridge transform intersection but has been recovered in numerous locations that were farther than 1 km off axis these off axis normal mid ocean ridge basalts or oa nmorb are distinguished by low na2o sr and al2o3 and are unusually depleted in incompatible elements moderately enriched off axis transitional mid ocean ridge basalts oa tmorb with the same compositional tendencies can also be identified comparison of epr axis lavas and the oa type suggests that they come from the same range of unmelted mantle source compositions but that the source of the oa magmas was depleted in incompatible trace elements by removal of a small degree partial melt this would be consistent with the oa type as an epr pooled melt that is missing the low degree melt fraction from deep in the melting regime which provides a reasonable physical model for their formation in this case off axis magmas do not represent the same range of chemical variation as magmas delivered to the axial magma system the oa nmorb are similar to depleted lavas from near epr seamounts other seamount lavas with depleted trace elements have tmorb like major elements and may be classified as oa tmorb the similarity between seamount lavas and the lavas erupted off axis close to the epr suggests that the two are manifestations of the same phenomenon we suggest that seamount type volcanism effectively starts within 1 2 km of the axis this is within the range where lavas derived from the axial plumbing system may also erupt therefore there is a narrow zone where young lava flows from the axial plumbing system and from the off axis systems may overlap lavas erupted off axis may ultimately cover 20 of the seafloor around the epr which is substantially more than previous estimates that were based primarily on morphological studies

u th ra disequilibria and the extent of off axis volcanism across the east pacific rise at 9 30 n 10 30 n and 11 20 n there is widespread interest in the distance that mid ocean ridge magmatism extends beyond the neovolcanic zone off axis magmas also provide a means to map out variations across the melting zone we present 238u 230th 226ra data for 35 well characterized samples that extend up to 50 km away from the ridge axis across the east pacific rise at 9 30 n 10 30 n and 11 20 n the 230th 238u ratios range from 1 00 to 1 19 and the 226ra 230th ratios range from 1 to 2 78 the samples have a bimodal 230th 238u distribution with approximately half overlying published axial data on the u th diagram and the remainder lying close to the equiline the u series disequilibria in the majority of the samples can be explained by aging subsequent to eruption in a zone 8 km wide about the neovolcanic zone consistent with visual evidence for sample age nevertheless seven of the samples lie above calculated 230th 238u axial decay curves and or have 226ra excesses implying eruption tens of kilometers off axis these are consistent with evidence from seamounts and seismic interpretations that magmatism can extend up to 20 km off axis the implication is that magma is not as efficiently focused beneath the ridge axis as has generally been believed there is a decrease in initial 230th 238u in both these and published samples inferred to have formed off axis but there is no compelling evidence that this reflects source heterogeneity simple modeling suggests that this could be explained by a decrease in fertility and melt column length as the overlying lithosphere thickens with age and the solidus shallows

ejecta layer at the cretaceous tertiary boundary bass river new jersey ocean drilling program leg 174ax a continuously cored borehole drilled at bass river new jersey recovered a cretaceous tertiary k t succession with a 6 cm thick spherule layer immediately above the boundary below the spherule layer the cretaceous glauconitic clay is extensively burrowed and contains the uppermost maastrichtian micula prinsii calcareous nannofossil zone spherical impressions of spherules at the top of the cretaceous indicate nearly instantaneous deposition of ejecta from the chicxulub impact the thickest ejecta layer shows clearly that a single impact occurred precisely at k t boundary time above the spherule layer the glauconitic clay contains the planktonic foraminiferal p0 and p alpha zones indicating 1 a complete k t succession and 2 continuous deposition interrupted only by fallout of the ejecta layer clay clasts within a 6 cm interval above the spherule layer contain cretaceous microfossils and may be rip up clasts from a tsunami or possibly a megastorm event extinction of the cretaceous planktonic foraminifers and burrowing organisms occurs abruptly at the k t boundary thus the bass river k t succession unequivocally links the chicxulub bolide impact to the mass extinctions at the end of the mesozoic

magmatic and tectonic extension at mid ocean ridges 1 controls on fault characteristics we use 2 d numerical models to explore the thermal and mechanical effects of magma intrusion on fault initiation and growth at slow and intermediate spreading ridges magma intrusion is simulated by widening a vertical column of model elements located within the lithosphere at a rate equal to a fraction m of the total spreading rate i e m 1 for fully magmatic spreading heat is added in proportion to the rate of intrusion to simulate the thermal effects of magma crystallization and the injection of hot magma into the crust we examine a range of intrusion rates and axial thermal structures by varying m spreading rate and the efficiency of crustal cooling by conduction and hydrothermal circulation fault development proceeds in a sequential manner with deformation focused on a single active normal fault whose location alternates between the two sides of the ridge axis fault spacing and heave are primarily sensitive to m and secondarily sensitive to axial lithosphere thickness and the rate that the lithosphere thickens with distance from the axis contrary to what is often cited in the literature but consistent with prior results of mechanical modeling we find that thicker axial lithosphere tends to reduce fault spacing and heave in addition fault spacing and heave are predicted to increase with decreasing rates of off axis lithospheric thickening the combination of low m particularly when m approaches 0 5 as well as a reduced rate of off axis lithospheric thickening produces long lived large offset faults similar to oceanic core complexes such long lived faults produce a highly asymmetric axial thermal structure with thinner lithosphere on the side with the active fault this across axis variation in thermal structure may tend to stabilize the active fault for longer periods of time and could concentrate hydrothermal circulation in the footwall of oceanic core complexes

mass failure of the north atlantic margin triggered by the cretaceous paleogene bolide impact the 65 ma chicxulub impact is known to have triggered large submarine slope failures near the crater in the gulf of mexico and caribbean here we show that the impact also precipitated massive submarine failure of the continental margin around the western north atlantic we have identified mass flow deposits containing impact ejecta of cretaceous paleogene boundary age in two deep sea cores more than 700 km from the continental margin the mass flows must have originated from the continental margin because they contain microfossils typical of shallow water environments and sedimentary features indicative of deposition by gravity currents geophysical data suggest that the mass wasting deposits may be present over the entire western north atlantic from puerto rico to the grand banks of canada and that much of the eastern margin of north america catastrophically failed during the cretaceous paleogene impact

experimental investigations of partial breach dam break flows abstractthis paper presents experimental results on partial breach dam break flows three dimensional 3d flood waves resulting from an instantaneous breach of a dam are experimentally investigated by combining different measurement techniques the dam break flow is initiated by quickly lifting a gate separating a reservoir and a downstream dry basin three different initial upstream water depths are considered the study utilizes the digital particle tracking velocimetry dptv technique for measuring the free surface velocity and water depth stereoscopic configuration of two high definition video cameras recording the movement of hollow plastic balls enabled measurement of the 3d velocity field and the water surface elevation in the near field the pressure head is measured by pressure transducers at various locations ultrasonic velocity profilers uvp are used to obtain velocity profiles in the emptying reservoir a simple nondimensional relationship for the variation of water surface elevation in

a seismic swarm and regional hydrothermal and hydrologic perturbations the northern endeavour segment february 2005 the february 2005 swarm at the overlapping spreading center osc on the northern end of the endeavour segment is the first swarm on the juan de fuca ridge recorded on a local seafloor seismic network the swarm included several larger earthquakes and caused triggered seismicity and a hydrothermal response in the endeavour vent fields as well as regional scale hydrologic pressure perturbations the spatial and temporal pattern of over 6000 earthquakes recorded during this seismic sequence is complex small magnitude events dominate and seismicity rates wax and wane indicating a magmatic process the main swarm initiates at the northern end of the endeavour ridge however most of the moment release including six strike slip events occurs in the southwest endeavour valley where the swarm epicenters generally migrate south the main swarm is contemporaneous with a hydrologic pressure response at four sealed seafloor boreholes 25 105 km away we infer that the seismic sequence is driven by a largely aseismic magma intrusion at the northern endeavour axis resulting stress changes trigger slip on tectonic faults and possibly dike propagation at the opposing limb of the endeavour osc in the southwest endeavour valley consistent with the eventual decapitation of the endeavour by the west valley segment furthermore 2 5 days after the start of the main swarm seismicity is triggered beneath the endeavour vent fields and temperature increases at a diffuse vent in the mothra field we infer that this delayed response is due to a hydrologic pressure pulse that diffuses away from the main magma intrusion

interplay between faults and lava flows in construction of the upper oceanic crust the east pacific rise crest 9 25 9 58 n the distribution of faults and fault characteristics along the east pacific rise epr crest between 9 25 n and 9 58 n were studied using high resolution side scan sonar data and near bottom bathymetric profiles the resulting analysis shows important variations in the density of deformational features and tectonic strain estimates at young seafloor relative to older sediment covered seafloor of the same spreading age we estimate that the expression of tectonic deformation and associated strain on old seafloor is 5 times greater than that on young seafloor owing to the frequent fault burial by recent lava flows thus the unseen volcanically overprinted tectonic deformation may contribute from 30 to 100 of the 300 m of subsidence required to fully build up the extrusive pile layer 2a many longer lava flows greater than 1 km dam against inward facing fault scarps this limits their length at distances of 1 2 km which are coincident with where the extrusive layer acquires its full thickness more than 2 of plate separation at the epr is accommodated by brittle deformation which consists mainly of inward facing faults 70 faulting at the epr crest occurs within the narrow 4 km wide upper crust that behaves as a brittle lid overlying the axial magma chamber deformation at greater distances off axis up to 40 km is accommodated by flexure of the lithosphere due to thermal subsidence resulting in 50 inward facing faults accommodating 50 of the strain on the basis of observed burial of faults by lava flows and damming of flows by fault scarps we find that the development of layer 2a is strongly controlled by low relief growth faults that form at the ridge crest and its upper flanks in turn those faults have a profound impact on how lava flows are distributed along and across the ridge crest

1923 gleno dam break case study and numerical modeling on the morning of december 1 1923 the gleno dam located in the central italian alps suddenly collapsed a few days after the first complete reservoir filling nearly 4 5 1 0 6 m 3 of water was released the consequent inundation caused significant destruction along the downstream valley and a death toll of at least 356 lives this failure is the only historical case of dam break caused by structural deficiencies that has occurred in italy as a result it has deeply influenced the evolution of italian regulations regarding dam design and hydraulic risk evaluation however in spite of its relevance this event has never been characterized from a hydraulic standpoint this paper reports the main information obtained from the analysis of a vast amount of historical documents regarding the gleno dam break to set up a case study useful for validating dam break models in mountain settings moreover it presents the main results of one dimensional 1d modeling of the dam break wave propagation accomplished with a first order finite volume numerical scheme recently proposed in the literature for field applications the overall effectiveness and reliability of the model are evaluated for this case characterized by very irregular topography finally the practical relevance of several choices that the numerical reconstruction of this kind of event demands is tested doi 10 1061 asce hy 1943 7900 0000327 2011 american society of civil engineers ce database subject headings dam failures shallow water numerical models hydraulic models case studies italy author keywords dam failure 1d dam break modeling shallow water finite volume numerical model hydraulic hazard case study

tectonic forcings of maastrichtian ocean climate evolution a global compilation of deep sea isotopic records suggests that maastrichtian ocean climate evolution tvas tectonically driven during the early maastrichtian the atlantic intermediate deep ocean was isolated from the pacific indian and southern oceans deep water formed in the high latitude north atlantic and north pacific at the early late maastrichtian boundary a major reorganization of oceanic circulation patterns occurred resulting in the development of a thermohaline circulation system similar to that of the modem oceans a combination of isotopic and plate kinematic data suggests that this event was triggered by the final breaching of tectonic sills in the south atlantic and the initiation of north south flow of intermediate and deep water in the atlantic the onset of laramide tectonism during the mid maastrichtian led to the concurrent draining of major epicontinental seaways together these events caused cooling increased latitudinal temperature gradients increased ventilation of the deep ocean and affected a range of marine biota

termination of a 6 year ridge spreading event observed using a seafloor seismic network on the endeavour segment juan de fuca ridge 1 we present automatically determined epicenters and magnitudes for 36 523 earthquakes recorded along the endeavour segment between august 2003 and october 2006 using a local ocean bottom seismometer obs network the catalog is dominated by two swarm sequences in january and february 2005 in the vicinity of the endeavour overlapping spreading center which included earthquakes in west valley the northern portion of the endeavour segment southwest endeavour valley and the endeavour vent fields these swarms are attributed to volcanism including a dike intrusion on the northern endeavour in february 2005 and smaller diking events on the propagating tip of the west valley segment in both swarms the dike on the northern endeavour propagated to the south which is inconsistent with magma sourced from the axial magma chamber beneath the elevated central portion of the segment following the swarms seismic activity on the endeavour segment decreased on average to 15 of pre swarm values and almost ceased at the segment ends we infer that a 6 year non eruptive event that started with a swarm in 1999 and finished with the 2005 swarms ruptured the entire segment and relieved plate spreading stresses the inferred coupling between the 1999 and 2005 events the observation of extensive precursory activity prior to the 2005 swarms and the interaction between seismically active regions during the swarms is consistent with static triggering with delays influenced by viscoelastic relaxation hydraulic diffusion and magma withdrawal and replenishment

paleobiogeography of campanian maastrichtian foraminifera in the southern high latitudes abstract distributions of planktonic and benthic foraminifera have revealed antarctic land sea distributions oceanic surface gyre configurations and changes in the configurations of the tethyan transitional and austral realms during campanian maastrichtian time poleward changes in the diversity of total and keeled planktonic species of the southern hemisphere are compared for the early and late campanian and early and late maastrichtian latitudinal diversity gradients were weakest during the early campanian and more pronounced during the late campanian and maastrichtian shallow marine seaways within west antarctica are suggested by similarity of late cretaceous nearshore benthic and open ocean planktonic assemblages from southern high latitude land and drill sites and by the occurrence of recycle cretaceous marine microfossils from antarctic interior and continental margin localities development of a major water mass boundary between cool surface waters south of about 50 s paleolatitude and warmer surface waters to the north in the south atlantic and indian ocean may have caused biogeographic isolation of austral realm assemblages during late campanian and early maastrichtian time several planktonic foraminifera show significant diachroneity in their latitudinal distributions magnetobiostratigraphic data suggest that abathomphalus mayaroensis migrated from high to low latitudes whereas pseudotextularia elegans globigerinelloides subcarinatus globotruncanella citae globotruncanella petaloidea globotruncana bulloides and globotruncana subcircumnodifer made time transgressive poleward migrations the distribution of a mayaroensis is in agreement with isotopic evidence for late maastrichtian climatic cooling while that of p elegans correlates with a latest maastrichtian warming event about 66 8 66 6 ma delayed first occurrences of the other taxa cannot be explained by paleoclimatic factors alone variations in global eustatic sea level and orogeny between southern south america and west antarctica may have also influenced the taxonomic composition of southern high latitude foraminiferal assemblages

a possible causal relationship between extinction of dinosaurs and k t iridium enrichment in the nanxiong basin south china evidence from dinosaur eggshells multiple distinct iridium anomalies have been observed in dinosaur eggshells in the k t boundary sections of the nanxiong basin guangdong province south china the eggshells collected at and near the fossil pollen defined k t boundary interval show iridium increases of about 19 and 28 times respectively above the background level the enrichment of other trace elements in the eggshells occurs mostly at and near the interval the distribution of ir bearing levels proves the existence of at least six ir delivering events from the latest cretaceous into the earliest paleocene the enrichment of ir and other trace elements in eggshells may have been caused by the assimilation of these elements into the dinosaur body through food and then into the eggs laid by them two types of pathological development i e variation in eggshell thickness and eggshell microstructure have been observed from the basin it seems that they occur frequently during the k t transition the physiological mechanisms producing pathologic dinosaur eggshells are evaluated in the light of homologous phenomena occurring in living birds on this basis it is concluded that the formation of pathologic dinosaur eggshells was caused by anomalous trace element concentrations the extinction of the dinosaurs in the nanxiong basin did not occur instantaneously but spread out within 250 ka with major extinction beginning at the boundary interval the cause may have been environmental poisoning and adverse changes in climatic conditions as indicated by the geochemical analyses of the dinosaur eggshells a repeating short and long term geochemically induced environmental stress adversely affected the reproductive process and contributed to the extinction of the dinosaurs c 2002 elsevier science b v all rights reserved

treatment of natural geometry in finite volume river flow computations a method is proposed for the treatment of irregular bathymetry in one dimensional finite volume computations of open channel flow the strategy adopted is based on a reformulation of the saint venant equations in contrast with the usual treatment of topography effects as source terms the method accounts for slope and nonprismaticity by modifying the momentum flux this makes it possible to precisely balance the hydrostatic pressure contributions associated with variations in valley geometry the characteristic method is applied to the revised equations yielding topographic corrections to the numerical fluxes of an upwind scheme further adaptations endow the scheme with an ability to capture transcritical sections and wetting fronts in channels of abrupt topography to test the approach the scheme is first applied to idealized benchmark problems the method is then used to route a severe flood through a complex river system the tanshui in northern taiwan computational results compare favorably with gauge records discrepancies in water stage represent no more than a fraction of the magnitude of typical bathymetry variations

seawater sr isotopes at the cretaceous tertiary boundary abstract seawater 87 sr 86 sr values increase abruptly by 28 10 6 across the cretaceous tertiary boundary ktb this small but rapid shift is superimposed on the larger scale structure of the seawater sr isotope curve the time scale of radiogenic sr addition appears to be too rapid to reconcile with sources associated with volcanism and we show that the amount of sr required to produce even this small increase is too large to be derived from 1 a kt bolide of the size constrained by the ir anomaly 2 continental crust ejecta from the impact of such a bolide 3 soot from global wildfires initiated by an impact or 4 any combination of these sources the probable source of the radiogenic sr is enhanced continental weathering but the high rate of increase appears to rule out processes such as sea level regression glaciation or tectonism a plausible mechanism for rapid addition of radiogenic sr to the oceans is enhanced weathering associated with globally distributed acid rain ph 1 which is a proposed by product of a bolide impact 51 epsl vol 83

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

more evidence that the chicxulub impact predates the k t mass extinction yaxcopoil 1 yax 1 drilled within the chicxulub crater was expected to yield the final proof that this impact occurred precisely 65 myr ago and caused the mass extinction at the cretaceous tertiary k t boundary instead contrary evidence was discovered based on five independent proxies sedimentologic biostratigraphic magnetostratigraphic stable isotopic and iridium that revealed that the chicxulub impact predates the k t boundary by about 300 000 years and could not have caused the mass extinction this is demonstrated by the presence of five bioturbated glauconite layers and planktic foraminiferal assemblages of the latest maastrichtian zone cf1 and is corroborated by magnetostratigraphic chron 29r and characteristic late maastrichtian stable isotope signals these results were first presented in keller et al 2004 in this study we present more detailed evidence of the presence of late maastrichtian planktic foraminifera sedimentologic and mineralogic analyses that demonstrate that the chicxulub impact breccia predates the k t boundary and that the sediments between the breccia and the k t boundary were deposited in a normal marine environment during the last 300 000 years of the cretaceous

impact dust not the cause of the cretaceous tertiary mass extinction most of the 3 mm thick globally distributed chicxulub ejecta layer found at the cretaceous tertiary k t boundary was deposited as condensation droplets from the impact vapor plume a small fraction of this layer 14 g was submicrometer size dust the global mass and grain size distribution of the clastic debris indicate that stratospheric winds spread the debris from north america over the pacific ocean to europe and little debris reached high southern latitudes these findings indicate that the original k t impact extinction hypothesis the shutdown of photosynthesis by submicrometer size dust is not valid because it requires more than two orders of magnitude more fine dust than is estimated here furthermore estimates of future impact hazards which rely upon inaccurate impact dust loadings are greatly overstated

sulfide geochronology along the endeavour segment of the juan de fuca ridge 1 forty nine hydrothermal sulfide sulfate rock samples from the endeavour segment of the juan de fuca ridge northeastern pacific ocean were dated by measuring the decay of 226ra half life of 1600 years in hydrothermal barite to provide a history of hydrothermal venting at the site over the past 6000 years this dating method is effective for samples ranging in age from 200 to 20 000 years old and effectively bridges an age gap between shorter and longer lived u series dating techniques for hydrothermal deposits results show that hydrothermal venting at the active high rise sasquatch and main endeavour fields began at least 850 1450 and 2300 years ago respectively barite ages of other inactive deposits on the axial valley floor are between 1200 and 2200 years old indicating past widespread hydrothermal venting outside of the currently active vent fields samples from the half graben on the eastern slope of the axial valley range in age from 1700 to 2925 years and a single sample from outside the axial valley near the westernmost valley fault scarp is 5850 205 years old the spatial relationship between hydrothermal venting and normal faulting suggests a temporal relationship with progressive younging of sulfide deposits from the edges of the axial valley toward the center of the rift these relationships are consistent with the inward migration of normal faulting toward the center of the valley over time and a minimum age of onset of hydrothermal activity in this region of 5850 years

geologic history of the summit of axial seamount juan de fuca ridge 1 multibeam 1 m resolution and side scan data collected from an autonomous underwater vehicle and lava samples radiocarbon dated sediment cores and observations of flow contacts collected by remotely operated vehicle were combined to reconstruct the geologic history and flow emplacement processes on axial seamount s summit and upper rift zones the maps show 52 post 410 ce lava flows and 20 precaldera lava flows as old as 31 2 kyr the inferred age of the caldera clastic deposits 1 2 m thick accumulated on the rims postcaldera between 31 ka and 410 ce there are no known lava flows near the summit the oldest postcaldera lava 410 ce is a pillow cone se of the caldera two flows erupted on the w rim between 800 and 1000 ce from 1220 to 1300 ce generally small eruptions of plagioclase phyric depleted mafic lava occurred in the central caldera and on the east rim larger post 1400 ce eruptions produced inflated lobate flows of aphyric less depleted and less mafic lava on the upper rift zones and in the n and s caldera all caldera floor lava flows and most uppermost rift zone flows postdate 1220 ce activity shifted from the central caldera to the upper s rift outside the caldera to the n rift and caldera floor and then to the s caldera and uppermost s rift where two historical eruptions occurred in 1998 and 2011 the average recurrence interval deduced from the flows erupted over the last 800 years is statistically identical to the 13 year interval between historical eruptions

closure to treatment of natural geometry in finite volume river flow computations by h capart t i eldho s y huang d l young and y zech

eruptive and tectonic history of the endeavour segment juan de fuca ridge based on auv mapping data and lava flow ages high resolution bathymetric surveys from autonomous underwater vehicles abe and d allan b were merged to create a coregistered map of 71 7 km2 of the endeavour segment of the juan de fuca ridge radiocarbon dating of foraminifera in cores from three dives of remotely operated vehicle doc ricketts provide minimum eruption ages for 40 lava flows that are combined with the bathymetric data to outline the eruptive and tectonic history the ages range from modern to 10 700 marine calibrated years before present yr bp during a robust magmatic phase from 10 700 yr bp to 4300 yr bp flows erupted from an axial high and many flowed 5 km down the flanks some partly buried adjacent valleys axial magma chambers amcs may have been wider than today to supply dike intrusions over a 2 km wide axial zone summit seamount formed by 4770 yr bp and was subsequently dismembered during a period of extension with little volcanism starting 4300 yr bp this tectonic phase with only rare volcanic eruptions lasted until 2300 yr bp and may have resulted in near solidification of the amcs the axial graben formed by crustal extension during this period of low magmatic activity infrequent eruptions occurred on the flanks between 2620 1760 yr bp and within the axial graben since 1750 yr bp this most recent phase of limited volcanic and intense hydrothermal activity that began 2300 yr bp defines a hydrothermal phase of ridge development that coincides with the present day 1 km wide amcs and overlying hydrothermal vent fields

north atlantic warming during global cooling at the end of the cretaceous differences in regional responses to climate fluctuations are well documented on short time scales e g el nino southern oscillation but with the exception of latitudinal temperature gradients regional patterns are seldom considered in discussions of ancient greenhouse climates contrary to the expectation of global warming or global cooling implicit in most treatments of climate evolution over millions of years this paper shows that the north atlantic warmed by as much as 6 c 1 5 decrease in 18o values of planktic foraminifera during the maastrichtian global cooling interval we suggest that warming was the result of the importation of heat from the south atlantic decreasing north atlantic 18o values are also associated with increasing gradients in planktic 13c values suggesting increasing surface water stratification and a correlated strengthening of the north atlantic polar front if correct this conclusion predicts arctic cooling during the late maastrichtian beyond implications for the maastrichtian these data demonstrate that climate does not behave as if there is a simple global thermostat even on geologic time scales

impact induced mass wasting at the k t boundary blake nose western north atlantic seismic reflection data combined with results from ocean drilling document regional scale slumping associated with the cretaceous tertiary k t impact event the k t boundary is biostratigraphically complete at three ocean drilling program sites 1049 1050 and 1052 located on blake nose 30 n 75 w off eastern florida in water depths of 1300 2600 m maastrichtian chalk is folded and fractured below the k t boundary at all three sites whereas lowermost paleocene clays and chalks are undeformed deformation is pervasive in maastrichtian at the deepest water site site 1049 whereas at the shallower water sites sites 1050 and 1052 thick intervals of structurally intact maastrichtian chalk are separated by thinner intervals of highly deformed sediments correlation of core to seismic reflection data indicates that the k t boundary immediately overlies seismic facies characteristic of mass wasting that extend across most of the 55 km distance of the depth transect maastrichtian sediments appear to have moved as large slump blocks on the upper part of blake nose but deformed more uniformly in the deeper water parts of the transect we suggest that mass wasting occurred on the blake nose 1600 km from the chicxulub crater in response to the cataclysmic seismicity generated by the impact

the nahal oz reservoir dam break flood geomorphic impact on a small ephemeral loess channel in the semi arid negev desert israel abstract the nahal oz reservoir in the coastal semi arid southwestern israel was designed to enhance local irrigation of crops using reclaimed sewage water during the dry summer months on march 2001 part of the western dike of the reservoir was breached and generated a flow release of 3 5 106 m3 of secondary irrigation water that was channeled down the 1st order ephemeral loess stream nahal yare akh the consequent 12 hour flood surge with an estimated peak discharge of 1000 m3s 1 inflicted severe loess erosion agricultural property and infrastructural damage downstream 6 million post flood mapping documented the geomorphic response to the flood which included channel scour and widening along the initial 2 km downstream of the reservoir where a spillway channel was formed the increase in the cross sectional area was about 60 and had an estimated 170 000 m3 of sediment bed bank and floodplain erosion calculated maximum shear stress and stream power along this section are estimated at 300 nm 2 and 900 wm 2 respectively the peak discharge at the end of this segment was estimated at 800 m3s 1 indicating only minor attenuation along this segment two km downstream of the breach a wide braided fan indicated deposition of the eroded sediments at the end of this segment the floodwater diverged into several watercourses and inundated tilled agricultural fields and neighborhoods downstream 9 km from the reservoir the discharge attenuated to 100 m3s 1 slightly above bankfull further downstream and upon reaching the large shikma stream the flow was already very low this reduction in discharge is attributed to the anthropogenic infrastructure roads neighborhoods and agricultural fields and the large transmission losses typical of sandy ephemeral streams the study shows that channels within erodible materials respond to high peak discharges very locally erosional thresholds that severely incised the channel are only maintained for 2 km below the breached reservoir and as distance from the source area increases available energy is substantially reduced due to high transmission losses gentler valley gradients very wide shallow flow and the ability of the drainage network to accommodate large discharges consequently the geomorphic impact was limited to the first 2 6 km with only minor erosional or depositional evidence downstream the current natural flow regime has only minor impact on the newly formed channel geometry below the breached dam accordingly the channel geometry may be preserved for a relatively long time however channel recovery in this segment was rapid and within a few years all bare loess surfaces exposed during the flood have been covered by dense vegetation the analysis also shows that nahal oz reservoir s dam break flood transmission losses and flood attenuation rates were extreme in comparison to other case studies this artificial flood event in a desert environment offers a rare opportunity to quantify channel and bank erosion evolution processes during an extremely high magnitude flood within highly erodible fine sediment as well as to detect the recovery processes a few years later

reply to comment on gonzalez acebron l mas r arribas j gutierrez mas j m perez garrido c very coarse grained beaches as a response to generalized sea level drops in a complex active tectonic setting pleistocene marine terraces at the cadiz coast sw spain abstract a series of pleistocene marine terraces comprised of conglomerate and coarse grained sandstone aligned nnw sse along the cadiz coast have been recognized and interpreted as formed in very coarse grained beaches in our work gonzalez acebron et al 2016 they unconformable overlie either pliocene units or older pleistocene deposits in these terraces five sedimentary sequences were described and dated by sr isotopic analysis of well preserved oysters this dating provided an early pleistocene age 1 3 ma for the oldest marine terrace which corresponds to sequence 1 aguirre 2018 does not agree with the dating of the first sequence instead in aguirre 1995 and aguirre et al 1995 these deposits are considered as laterally equivalent to lacustrine deposits located more than 50 km far away mesas de asta jerez basin and their age late pliocene lowermost early pleistocene extrapolated to sequence 1 this is an impossible correlation given the fact that the studied deposits sequences 1 to 5 are marine terraces without lateral continuity inland finally aguirre s 2018 sedimentological interpretation of the deposits of sequence 1 as part of a wave and tide dominated delta breaks down when one considers that this delta would be a mixture of non coeval deposits the continental deposits of mesas de asta together with sequence 1 deposits

evidence for a small 0 000 030 but resolvable increase in seawater 87sr 86sr ratios across the cretaceous tertiary boundary previous studies of 87 sr 86 sr patterns across the cretaceous tertiary k t boundary have generated inconsistent results analyses of samples from ocean drilling program hole 1049c provide better taphonomic and diagenetic control than has been previously achieved and indicate 1 that there was a rapid increase of 0 000 030 in seawater 87 sr 86 sr ratios across the k t boundary 2 that post k t cretaceous foraminifera at this site are reworked and 3 that subtle diagenetic overprinting affects the basal 15 cm of the danian ooze these conclusions are consistent with the asteroid impact hypothesis reworking rather than survivorship confirms nearly complete extinction of cretaceous tethyan planktic foraminifera the 87 sr 86 sr excursion can be explained by enhanced continental weathering perhaps related to acid rain in the aftermath of the k t impact