the palaeomagnetic record of the santiago volcanics republic of cape verde multiphase magnetization and age consideration abstract the palaeomagnetism of the older volcanic complex of santiago constitutes a multicomponent structure and magnetomineralogical evidence suggests that the various remanence vectors are carried principally by titanomaghaemites when viewed in the context of the african palaeomagnetic reference frame the predominant magnetization is consistent with an upper tertiary age but two older magnetizations of inferred lower tertiary age are also in evidence the demonstrable secondary nature of all three palaeomagnetic axes each of them represented by both polarities makes it likely that the actual emplacement of the older complex is of pre tertiary age being probably an integral component of the pronounced tectonomagmatic uplift phase that affected the entire northwest african margin in upper cretaceous time the older complex of santiago can probably be correlated with the igneous core of the neighbouring island of maio which apparently formed during turonian time 90 ma ago some younger lavas of upper miocene age the flamengos formation show a much simpler palaeomagnetic history than rocks of the older complex yielding only the upper tertiary palaeomagnetic field axis

influence of cohesion on river bed scour in the wake region of piers abstractstudies on scour in the wake region of piers in cohesive sediments containing gravel were not reported in literature to the best of our knowledge results from the laboratory experiments based study on the process of wake scour are presented here the sediment used for the experiment were of two types 1 fine gravel mixed with clay in proportions varying from 20 to 60 by weight and 2 fine gravel and fine sand in equal proportion by weight mixed with clay in proportions varying from 20 to 60 by weight the experiments revealed that the process of scour as well as depth shape and geometry of scour hole developed in such cohesive sediment were significantly different from that of cohesionless sediments proportion of clay fraction and unconfined compressive strength of cohesive sediment mixture were found to be the most significant variables controlling the depth of scour in the wake of piers on the basis of dimensional considerations relationships have been proposed for the estimation

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

history of the celebes sea basin based on its stratigraphic and sedimentological record abstract the stratigraphic and sedimentary history of the celebes sea basin provides the basis for a tectonic model for its evolution which is consistent with new regional plate reconstructions cores drilled on leg 124 of the ocean drilling program sites 767 and 770 form a stratigraphic record from the basement to the sea floor in just under 800 metres of sedimentary succession the basement itself is basalt with a strong morb affinity radiolaria in pelagic mudstones at the base of the succession indicate a late middle eocene age a very condensed pelagic sequence 90 m in 20 ma suggests a setting which was distal from sources of terrigenous clastics and volcaniclastics and below the ccd these characteristics are similar to the west philippine sea basin drilled on dsdp legs 31 and 59 which also has oceanic basement dated at 44 42 ma and paleogene pelagic strata these data are therefore consistent with any plate reconstruction model which has these two basins forming as part of the same ocean basin during the miocene quartz rich sandy turbidites were deposited in the celebes sea basin this influx of terrigenous clastics occurred for a brief period in middle to late miocene times c 10 ma the nearest large continental landmass which could have acted as the source of this mature siliciclastic detritus was the island of borneo and the onset of this clastic supply may be related to uplift caused by collision events on the island cessation of terrigenous clastic supply to the basin centre occurred as southward subduction of the underlying oceanic crust beneath the northern arm of sulawesi began it is speculated that the development of a trench along the southern margin of the basin acted as a trap for detritus coming from borneo diverting material from the basin centre

intracontinental movements in western gondwanaland a palaeomagnetic test abstract early cretaceous intracontinental movements within africa and or south america to account for misfit problem in the pre drift reconstruction of western gondwana have been tested using palaeomagnetic poles from both continents each continent has been considered as comprising separate subplates according to the boundaries proposed by pindell and dewey 1982 and curie 1983 i e northern africa naf southern africa saf northern south america nsa and southern south america ssa visual and statistical distribution of late permian to jurassic poles from the african subplates indicate two distinct groups before rotating saf relative to naf while after the rotation they become indistinguishable the distribution and sparsity of data from south america limit the study in this continent as the data are statistically indistinguishable before and after rotation of ssa with respect to nsa when the test is extended to the reconstruction of western gondwana the tightest grouping of the poles occurs when an intracontinental movement is assumed within africa this suggests that the misfit between the two continents is probably due to intracontinental deformation within africa and not in south america if confirmed this may have profound implications in the kinematics of the processes related to the opening of the south and central atlantic oceans and also the origin of the west african rift system

the drift history of adria and africa from 280 ma to present jurassic true polar wander and zonal climate control on tethyan sedimentary facies article i nfo the orogenic belts surrounding the undeformed adriatic sea represent the margins of an area known as adria the african promontory we have undertaken a critical appraisal of paleomagnetic data from regions of adria considered parautochthonous relative to africa obtained either from biostratigraphically dated sed imentary rocks corrected for inclination shallowing or from igneous rocks that are regarded as free from any inclination shallowing bias paleomagnetic directions were used to calculate paleomagnetic poles for compar ison with coeval and inclination flattening free paleomagnetic poles from stable africa visual coherence of paleopoles for several time slices from the early permian to the eocene supports the construction of a com posite apparent polar wander path apwp valid for parautochthonous adria and stable africa this compos ite apwp is compared to previous apwps finding good agreement with the global apwp of kent and irving 2010 both apwps show a remarkable and rapid polar shift of 40 in the jurassic that other apwps tend to underestimate we interpret this shift to represent a major episode of true polar wander tpw from 183 ma in the early jurassic to 151 ma in the late jurassic using a simple zonal climate model the drift motion of adria attached to africa appears to be consistent with the distribution of permian cretaceous sed imentary facies on adria

experimental investigation on the longitudinal evolution of landslide dam breaching and outburst floods abstract accurate prediction of the evolution of a landslide dam that is breached due to overtopping failure is necessary to estimate the outflow hydrograph and the resulting inundation in this study physical flume tests on the breaching of landslide dams were conducted a wide grain size distribution with unconsolidated dam material was used dam breaching was initiated by cutting a notch across the crest of the dam adjacent to the side wall of the flume this allowed water to escape from the dam while a steady inflow of water was continuously supplied upstream the effects of upstream inflow on the timescales and magnitudes of the peak discharges and the time to inflection point were also investigated experimental results reveal that the whole hydrodynamic process of dam breaching can be divided into three stages defined by clear inflection points and peak discharge a new longitudinal evolution model is proposed this model captures the initial increase of the soil erosion rate of landslide dam and its subsequent decrease along the longitudinal direction in addition a linear relationship between the soil erosion rate and shear stress of water flow was observed and this is similar to that observed in large scale natural landslide dams furthermore soil erosion resistances of landslide dam against water flow above are observed to increase with the concentration of entrained sediments along the flow direction

tertiary stratigraphy and basin evolution southern sabah malaysian borneo abstract new mapping and dating of strata in the southern part of the central sabah basin in northern borneo has made it possible to revise the lithostratigraphy and chronostratigraphy of the area the recognition in the field of an early miocene regional unconformity which may be equivalent to the deep regional unconformity recognised offshore has allowed the development of a stratigraphic framework of groups and formations which correspond to stages in the sedimentary basin development of the area below the early miocene unconformity lies ophiolitic basement which is overlain by an accretionary complex of eocene age and a late paleogene deep water succession which formed in a fore arc basin the late paleogene deposits underwent syn depositional deformation including the development of extensive melanges all of which can be demonstrated to lie below the unconformity in this area some localised limestone deposition occurred during a period of uplift and erosion in the early miocene following which there was an influx of clastic sediments deposited in delta and pro deltaic environments in the middle miocene these deltaic to shallow marine deposits are now recognised as forming two coarsening upward successions mapped as the tanjong and kapilit formations the total thickness of these two formations in the central sabah basin amounts to 6000 m only half of the previous estimates although the total stratigraphic thickness of cenozoic clastic strata in sabah may be more than 20 000 m

paleomagnetism of jurassic and cretaceous rocks in central patagonia a key to constrain the timing of rotations during the breakup of southwestern gondwana abstract a paleomagnetic study in jurassic and cretaceous rocks from the canadon asfalto basin central patagonia indicates the occurrence of about 25 30 clockwise rotation in upper jurassic lowermost cretaceous rocks whereas the overlying mid cretaceous rocks do not show evidence of rotation this constrains the tectonic rotation to be related to a major regional unconformity in patagonia which in turn seems to be close in time with the early opening of the south atlantic ocean the sense and probably the timing of this rotation are similar to those of other paleomagnetically detected rotations in different areas of southwestern gondwana suggesting a possible relationship between these and major tectonic processes related with fragmentation of the supercontinent on the other hand the mid cretaceous rocks in the region yield a paleopole located at lat 87 south long 159 east a95 3 8 this pole position is consistent with coeval high quality paleopoles of other plates when transferred to south american coordinates implying it is an accurate determination of the aptian circa 116 ma geomagnetic field in south america

a new jurassic recent apparent polar wander path for south america and a review of central andean tectonic models abstract the jurassic to recent palaeomagnetic data from the stable cratonic areas of south america and africa are reviewed and evaluated from the combined data set seven mean reference pole positions are calculated for the early middle and late jurassic early and late cretaceous palaeogene and neogene most of these new palaeopoles are well defined and indicate a complex course of apparent polar wander for the south american plate comparison of the palaeomagnetic data from the andean margin with the reference poles indicates vertical axis rotations defining a broad pattern of anticlockwise rotations north of the arica deflection at approximately 19 s and clockwise rotations to the south further analysis indicates however that the distribution and magnitude of rotations is more complicated than this broad division tectonic models proposed to explain the pattern of rotations and the possible origins of the arica deflection are discussed it is suggested that the rotations probably result from localised in situ rotations controlled by strike slip fault systems or thrust sheets rather than large scale rotation mechanisms the broad rotation pattern may result from the influence of pre existing structures in the margin or variations in the flexural rigidity of the brazilian shield behind the deformation zone

analysis of a detention basin impact on dike failure probabilities and flood risk for a channel dike floodplain system along the river elbe germany highly concentrated asset values are often protected by dikes stretching along the river course during extreme floods dikes may fail due to various breach mechanisms and cause considerable damage therefore detention basins are often additionally installed to reduce the flood risk for downstream communities in such situations however the systemic performance of dikes and spatial redistribution of inundation patterns are often unknown intuitively expected effects such as more probable breaches downstream due to fewer breaches upstream and consequently higher conveyance of upstream reaches lack evidential proof with a coupled probabilistic deterministic 1d channel dike breach 2d inundation flood damage model chain the impact of a detention basin on losses to residential buildings and agricultural crops is investigated we demonstrate the changes in dike performance due to systemic load and relief along the river course on the middle elbe germany considering three breach mechanisms overtopping piping and slope micro instability the reduction of overtopping failures due to the detention basin resulted in the slightly increased breach probabilities due to piping and micro instability farther downstream finally the uncertainty in hazard and damage estimations are analysed using the monte carlo simulation and applying several damage models despite high uncertainties in flood hazard and damage estimations we conclude that the risk reduction to residential buildings downstream of the detention basin exceeds the higher losses to agricultural crops within the filled detention area

laboratory experiments on failure characteristics of non cohesive sediment natural dam in progressive failure mode natural dam failure may cause disastrous floods in the downstream especially for dam outbursts in progressive failure mode until now researches about the characteristics of progressive failure are still completely unclear in this paper a series of flume tests were conducted to investigate the formation mechanism of progressive failure of natural dam the breaching characteristics and the effect of outburst flood on the channel bed according to the results three typical features in the progressive failure process of natural dams were observed seepage on downstream slope slide of the downstream slope and overtopping with phreatic line rising continuously seepage occurred on the downstream slope which caused slide of downstream slope of the dam the breaching discharge hydrographs were asymmetric on both sides of peak discharge which was similar to the breaching discharge of overtopping the relationship between breach width and depth was like a shape of s which followed a logistic function in the breaching process sediment in the channel bed near the dam was first deposited and then scoured where the flow velocity was large with strong turbulence while flow on channel bed far away from the dam showed lower velocity and the flow regime transferred from supercritical flow to subcritical flow sediment deposited at first and then scoured gradually on channel bed but only deposited at a large distance from the dam the outburst flood eroded the channel bed continuously the erosion mechanism was from tractive erosion to backward erosion and returned to tractive erosion finally in addition the further away from the dam the weaker the erosion intensity was the results of this paper enriched the understanding of the failure mechanism of progressively outburst natural dam which is helpful to predict breaching parameters in progressive failure mode and to provide some reference about flood prevention

lateral outflow over side weirs note 66 reference lch article 1987 011 record created on 2007 04 24 modified on 2016 08 08

comment on stability of the earth with respect to the spin axis for the last 130 million years by j a tarduno and a y smirnov earth planet sci lett 184 2001 549 553 in a recent issue of earth and planetary science letters tarduno and smirnov 1 claim that no true polar wander tpw occurred over the last 130 ma this claim is in contradiction with the conclusion of several studies devoted to this topic 2 8 including our recent epsl paper 9 in this paper 9 we showed that some 110 10 ma ago the earth s spin axis shifted by 18 4 at a rate larger than 1 ma or possibly even larger than 5 ma with respect to the main hotspots presently located in the atlantic and indian oceans we interpreted this shift as a displacement of the earth s spin axis with respect to the global solid earth i e tpw tarduno and smirnov 1 contest this conclusion and a rm that tpw is an artifact their argument relies on the fact that a few north american paleomagnetic poles not included in our selection do not t the trends predicted by two simplistic models however we show below that these additional poles very nicely t our tpw model tarduno and smirnov s reasoning 1 is based upon the consideration of seven north american poles labeled a g gure 2 in 1 note that pre vot et al s whole database 9 is now available through anonymous ftp at ftp dstu univmontp2 fr use your email address as the password and type cd pub paleomag epls2000 our own selection criteria discussed in detail in 9 are particularly stringent which led us to reject in a completely objective manner three of the seven poles of tarduno and smirnov especially we rejected poles b d and g on the basis of too large fisher concentration parameter u poles obtained mainly from syenitic intrusions not granites as mentioned in 1 and sierra nevada batholith respectively in particular sierra nevada obviously is not part of the north american craton and this pole cannot be considered a reliable datum for the present purpose we list in table 1 the selected poles of pre vot et al 9 for the period between approximately 80 and 130 ma tarduno and smirnov 1 believe they can check the reality of the tpw shift observed around 110 ma 9 by comparing in the 40 ma long bounding interval between 90 and 130 ma the paleolatitudes computed from these seven paleomagnetic poles with the paleolatitude curves predicted from two distinctly diierent models i model 1 curve 1 in the present fig 1 assumes that the north american plate moved with respect to the hotspot system as described by muller et al 10 while the earth s rotation axis remained in its present posi

overtopping induced failure of noncohesive homogeneous fluvial dikes accurate predictions of breach characteristics are necessary to reliably estimate the outflow hydrograph and the resulting inundation close to fluvial dikes laboratory experiments on the breaching of fluvial sand dikes were performed considering a flow parallel to the dike axis the breach was triggered by overtopping the dike crest a detailed monitoring of the transient evolution of the breach geometry was conducted providing key insights into the gradual and complex processes involved in fluvial dike failure the breach develops in two phases 1 the breach becomes gradually wider and deeper eroding on the downstream side along the main channel and 2 breach widening controlled by side slope failures continuing in the downstream direction only increasing the inflow discharge in the main channel the breach formation time decreases significantly and the erosion occurs preferentially on the downstream side the downstream boundary condition has a strong influence on the breach geometry and the resulting outflow hydrograph

new paleomagnetic data from the antarctic peninsula and their tectonic implications new paleomagnetic data presented here further constrain the relative motion of the antarctic peninsula relative to east antarctica during the mesozoic development of the southern ocean basins the antarctic peninsula ap is one of four crustal blocks that define west antarctica the others being the ellsworth whitmore mountains ewm thurston island eights coast ti and marie byrd land mbl a jurassic pole 155ma 124 e 64 s a95 7 1 n 10 vgps was obtained from the ap block which suggests that the ap block rotated clockwise between 175 and 155 ma due to significant early opening in the weddell sea basin a new early cretaceous paleomagnetic pole 182 e 74s a95 5 9 n 6 site mean vgps indicates that the ap block was in or near to its present day position with respect to east antarctica by 130 ma between 155 and 130 ma counterclockwise rotation of the ap ti blocks together with the southward motion of east gondwanaland probably resulted in subduction of weddell sea ocean floor beneath the southern ap block and initiated the palmer land deformational event a 130 ma pole from the ti block requires clockwise rotation of the ti and possibly the ewm blocks between 130 and 110 ma producing sinsistral strike slip motion between the ewm block and east antarctica and dextral transpressional motion between the ti ewm blocks and the ap block new ap block 110 ma and 85 ma poles from this study 199 e 74 s a95 6 9 n 13 vgps 152 e 86 s a95 7 5 n 6 vgps respectively are similar to equivalent age poles from east antarctica and suggest little or no relative motion between the antarctic peninsula and east antarctica northern and southern antarctic peninsula mid cretaceous poles are very much alike suggesting that the s shape of the antarctic peninsula is not due to oroclinal bending since 110 ma

geologic conditions underlying the 2005 17th street canal levee failure in new orleans a careful program of subsurface sampling and cone penetration test soundings was employed to characterize the geologic conditions beneath the failed portion of the 17th street canal levee in new orleans where a 150 m long section of the levee and floodwall translated up to 16 m when flood waters rose to 1 2 m of the wall s crest on august 29 2005 during hurricane katrina the subsurface conditions are characterized by discrete layers of fill placed upon the historic cypress swamp which is underlain by a deeper prehistoric cypress swamp these swamp deposits were consolidated beneath the levee and in the area of the 2005 failure the swamp materials infilled a natural depression believed to be an old slough which dipped below the sheetpile tips for a distance of about 50 m which corresponds to where the breach appears to have initiated detailed examination of the recovered soils suggest that recent hurricanes periodically inundated the swamps with saline and or brackish water which cause a mass

geostatistical estimations of bathymetric lidar errors on rivers the geometry of river channels is a key descriptive element for hydromorphology hydraulics and hydroecology gravel bed rivers usually have a mean water depth of 0 5 m for such shallow waters the accuracy of bathymetric lidar data has to be precisely assessed alongside this accuracy investigation methodological questions arise how to assess the data quality of elevation lidar when comparing reference topographic points on river beds to laser beam footprints of several square metres at different locations what are the consequences of uncertainties and scaling in accuracy estimations in this study we designed a methodology to assess the quality of lidar topographical data within rivers using a specific geostatistical method that conducts upscaling as well as interpolation of reference data that takes into account uncertainties this method uses an anisotropic block kriging from dgps points on lidar footprint areas within a channel fitted coordinate system this assessment focused on a 1 5 km long reach of the gardon gravel bed river in the south of france dgps points pseudo regularly located along the river were acquired at the same time as the lidar survey with the hawkeyeii system lidar accuracy results for river bottom elevation show a negative bias for high depth added to that bias a random error with 0 32 m standard deviation was found by considering upscaling and uncertainties in reference data and a 0 20 m standard deviation was found if they were not considered consequently if lidar bias can be corrected measuring a water depth less than 32 cm i e for 28 of the river area is unrealistic however this experiment shows that lidar provides an accurate representation of the riverbed forms it also provided a useful continuous topographic surface from the underwater river bed up to riparian areas copyright 2010 john wiley and sons ltd

numerical modeling of breach erosion of river embankments the process of breach erosion of river embankments depends on the interaction among flow sediment transport and the corresponding morphological changes levees often consist of noncohesive material with a wide range of grain sizes the dam material is mainly eroded due to the transport capacity of the overtopping water both bed load and suspended load are of importance for breach formation the lateral erosion due to slope instabilities has a significant impact a depth averaged two dimensional numerical model was developed to account for these processes the sensitivity of the discharge through the breach related to different processes and material parameters was investigated and compared to experimental and field data the results show that the most sensitive parameter of an erosion based dike breach simulation is the breach side slope angle which determines the lateral erosion the application of the described model 2dmb to different embankment failures at the elbe river illustrates its capability in simulating overtopping breaching

a new methodology for flood hazard assessment considering dike breaches 1 this study focuses on development and application of a new modeling approach for a comprehensive flood hazard assessment along protected river reaches considering dike failures the proposed inundation hazard assessment model iham represents a hybrid probabilistic deterministic model it comprises three models that are coupled in a dynamic way 1 1d unsteady hydrodynamic model for river channel and floodplain between dikes 2 probabilistic dike breach model which determines possible dike breach locations breach widths and breach outflow discharges and 3 2d raster based inundation model for the dike protected floodplain areas due to the unsteady nature of the 1d and 2d models and runtime coupling the interdependence between the hydraulic loads on dikes at various locations along the reach is explicitly considered this ensures a more realistic representation of the fluvial system dynamics under extreme conditions compared to the steady approaches the probabilistic dike breach model describes dike failures due to three failure mechanisms overtopping piping and slope instability caused by seepage flow through the dike core micro instability the 2d storage cell model computes various flood intensity indicators such as water depth flow velocity and inundation duration iham is embedded in a monte carlo simulation in order to account for the natural variability of the input hydrograph form and the randomness of dike failures besides binary wet dry inundation patterns iham generates new probabilistic flood hazard maps for each intensity indicator and the associated uncertainty bounds furthermore the novel probabilistic dike hazard maps indicate the failure probability of dikes for each considered breach mechanism

discharge coefficient for sharp crested side weir in subcritical flow to estimate the outflow over a rectangular sharp crested side weir the discharge coefficient in the weir equation needs to be known although this type of structure has been designed and used extensively by hydraulic engineers a universally acceptable discharge coefficient does not exist in this study over 250 laboratory tests were conducted and the results were analyzed to find the influence of the flow hydraulics and the geometric channel and weir shapes on the coefficient the results show that for subcritical flow the de marchi assumption of constant energy is acceptable and the weir discharge can therefore be used furthermore it was discovered that the de marchi coefficient of discharge is a function of the upstream froude number and the ratios of weir height to upstream depth and weir length to channel width whereas the channel slope in subcritical flow can be ignored hence an accurate equation for the coefficient of discharge is introduced

paleomagnetic study of sicily consequences for the deformation of italian and african margins over the last 100 million years abstract paleomagnetic analysis of cenozoic sediments from the iblean platform 12 sites 100 samples has provided four new poles these data are combined with those available from volcanic series to yield a new apparent polar wander path for stable sicily since the upper cretaceous this curve when compared to a revised curve for africa using a selection of available data points demonstrates a 15 rotation of sicily with respect to africa during the plio pleistocene this rotation accounts for the extensional tectonic regime that prevails in the pelagian sea and which is evidenced by en relais rifts malta pantelleria linosa associated with alkaline volcanism of pliocene and quaternary age paleomagnetic directions from various areas of the italian peninsula also indicate anticlockwise rotations with diverse amplitudes the chronology of these rotations is consistent with a deformation of the western italian margin during progressive suturation from north to south of the corsican sardinian block since the end of the oligocene

the applicability of microbially induced calcite precipitation micp for internal erosion control in gravel sand mixtures seepage induced internal erosion in earth filled embankment dams has been attracting the attention of civil engineering researchers and practitioners for decades microbially induced carbonate prec

breaching parameters for earth and rockfill dams dam risk analysis is at the heart of dam failure prevention and mitigation in order to assess dam risk it is essential to conduct a quantitative analysis of the process of a dam breach which can be described by such parameters as breach geometry breaching duration and peak outflow rate the main objective of this paper is to develop robust empirical formulas with physical meaning for predicting dam breaching parameters based on past dam failure data a database of 182 earth and rockfill dam failure cases has been compiled among these cases nearly one half are for large dams higher than 15 m a multiparameter nonlinear regression model is recommended to develop empirical relationships between five breaching parameters breach depth breach top width average breach width peak outflow rate and failure time and five selected dam and reservoir control variables dam height reservoir shape coefficient dam type failure mode and dam erodibility the relative importance of each control variable is evaluated the dam erodibility is found to be the most important factor influencing all five breaching parameters the reservoir shape coefficient and the failure mode also play an important role in the prediction models two case studies are presented to show the application of the empirical models developed in this paper

dike failure mechanisms and breaching parameters abstractdike risk management requires breaching parameters that can be estimated rapidly to support the prediction of inundation zones and decision making the objectives of this paper are to compile a database of dike breaching cases study common dike failure mechanisms and develop a set of empirical equations for estimating breaching length depth and peak discharge a database of over 1 000 dike failure cases was collected with information on pre breach dike geometry materials type of dike failure mechanisms breaching length depth and peak discharge a set of regression models are formulated using five control variables dike height width material type of dike and failure mechanism the standard error is set as a selection criterion and the akaike information criterion is used to optimize the proposed empirical models the new models are validated using independent cases and compared with available empirical equations for dikes and man made dams

on the spatial variation of resistance to flow in upland channel networks 1 detailed field measurements of channel properties and flow characteristics collected in the ashley and cropp catchments new zealand are used to investigate the spatial variation of resistance to flow across upland channel networks the application of the darcy weisbach equation and semilogarithmic flow resistance relationships reveals that mean flow velocities calculated from local measurements of bed material particle size hydraulic depth and channel bed slope may be inaccurate the manning gauckler strickler equation with resistance coefficient independent of bed material particle size is found to be relatively more reliable but not sufficiently general to reproduce the spatial variation of resistance to flow across a complex channel network a new methodology is developed by combining a hydraulic equation of the manning gauckler strickler type a flow discharge upstream drainage area relationship and geomorphological fluvial relationships for mean flow velocity gauckler strickler resistance coefficient hydraulic depth and friction slope this methodology is found to improve the reproduction of the spatial variation of mean flow velocity across the ashley catchment and appears of general applicability for the parameterization of resistance to flow in distributed catchment models

evaluation and prediction of 17th street canal i wall stability using numerical limit analyses numericallimitanalyseshavebeenusedtoevaluatethestabilityofthe17thstreetcanali wallleveeduringhurricanekatrina the potential formation of a water filled gap along the canal side soil wall interface at failure is included in both the lower and upper bound for mulations the analyses replicate published two dimensional 2d cross sections and soil properties developed in forensic investigations car ried out by the interagency performance evaluation task force ipet and by the independent levee investigation team ilit the current results provide anindependent basis forunderstanding andevaluating the proposedfailure mechanisms anddemonstrate that awater filled gap is a necessary condition for the critical i wall failure mechanism further limit analysis calculations produce credible estimates of the surge elevation that caused failure of the 17th street canal i wall as well as predictions of a consistent failure mechanism the numerical limit anal yses show clearly how differences in the stability of the i wall are linked to different interpretations of the stratigraphy and undrained shear strengths by ipet and ilit the analyses also show that effects of a thin layer of weak organic clay as postulated by ilit are not necessary to explain the i wall failure doi 10 1061 asce gt 1943 5606 0000814 2013 american society of civil engineers ce database subject headings drainage walls clays lateral loads levees and dikes louisiana hurricanes structural stability author keywords upper and lower bound limits undrained stability walls clays limit equilibrium lateral loading

a palaeomagnetic study of the upper mesozoic succession in northern tunisia summary the upper mesozoic section from northern tunisia provided an upper jurassic palaeomagnetic pole of 65 2 s 20 3 e ag5 6 1 calculated from the means of normal and reversely magnetized samples from the uppermost callovian oxfordian kimmeridgian and portlandian rocks in general the only cretaceous rocks to yield acceptable results were the few samples collected from fresh outcrops a polarity sequence can be established for the upper jurassic which can be correlated with the oceanic keathley anomaly sequence one consequence of the proposed correlation of the oceanic anomaly with the terrestrial palaeomagnetic sequence is to suggest a slightly different age for the oxfordiankimmeridgian boundary one interpretation of the frequent intermediate directions of magnetization in the cretaceous sequence is that there may be a number of unrecognized short period reversals within the cretaceous and more particularly during the so called cretaceous normal period

modeling river bed morphology roughness and surface sedimentology using high resolution terrestrial laser scanning 1 recent advances in technology have revolutionized the acquisition of topographic data offering new perspectives on the structure and morphology of the earth s surface these developments have had a profound impact on the practice of river science creating a step change in the dimensionality resolution and precision of fluvial terrain models the emergence of hyperscale survey methods including structure from motion photogrammetry and terrestrial laser scanning tls now presents the opportunity to acquire 3 d point cloud data that capture grain scale detail over reach scale extents translating these data into geomorphologically relevant products is however not straightforward unlike traditional survey methods tls acquires observations rapidly and automatically but unselectively this results in considerable noise associated with backscatter from vegetation and other artifacts moreover the large data volumes are difficult to visualize require very high capacity storage and are not incorporated readily into gis and simulation models in this paper we analyze the geomorphological integrity of multiscale terrain models rendered from a tls survey of the braided river feshie scotland these raster terrain models are generated using a new computationally efficient geospatial toolkit the topographic point cloud analysis toolkit topcat this performs an intelligent decimation of point cloud data into a set of 2 5 d terrain models that retain information on the high frequency subgrid topography as the moments of the locally detrended elevation distribution the results quantify the degree of terrain generalization inherent in conventional fluvial dems and illustrate how subgrid topographic statistics can be used to map the spatial pattern of particle size grain roughness and sedimentary facies at the reach scale

laboratory experiments on the failure of coarse homogeneous sediment natural dams on a sloping bed we present the results of a systematic series of 168 laboratory experiments that examine the critical conditions for the failure of landslide dams which obstruct the course of mountain rivers the experiments were carried out by using three different sediment materials with a quasiuniform grain size distribution and with a flume bed slope angles that ranged between 0 and 5 71 0 10 three main typologies of dam failure were observed for increasing values of the dam s downstream face angle 1 overtopping 2 headcutting which led to the formation of an erosion channel on the dam s downstream face that progressively migrated up to the dam crest and 3 initial slide of large part of superficial layer of the dam s downstream face which was followed by headcutting the experiments focused on the second type of failure to provide a safety criterion based on the upstream reservoir level the quantities that govern this phenomenon have been identified and a functional relationship is proposed based on

isopach and borehole data as indicators of rifted margin evolution in southwestern africa abstract isopach and borehole data are used to document post rifting sediment accumulation along the western margin of southern africa the isopach data reveal an increasing rate of sediment accumulation up to the end of the eocene but the borehole data generally show the opposite trend an integrated analysis of both types of data however is consistent with a general model of post rifting drainage development in which the area supplying sediment expanded significantly after breaching of a linear upwarp along the margin allowed a dominant drainage network to develop the borehole data suggest that such a major sediment outlet from the interior of the sub continent the palaeo orange became established in the late cretaceous coniacian in the vicinity of the present orange river mouth after conversion to equivalent rock volumes the isopach data can be combined with the general drainage model to infer the likely spatial and temporal patterns of erosion over southern africa during the accumulation of four offshore sedimentary sequences beginning with the onset of rift related sedimentation and extending up to the present this analysis using three variant forms of the general model to encompass a wide range of drainage development possibilities indicates that the average rate of erosion for catchment areas draining to the western margin has declined from 41 82 m ma 1 during the first sedimentary sequence 152 to 113 ma to about 7 9 m ma 1 during the last sequence 37 to 0 ma maximum depths of post rifting erosion of several kilometres appear to have occurred in a narrow zone bordering the margin primarily during its early development while depths of erosion in some interior areas have probably been an order of magnitude less the average depth of post rifting erosion for the present day catchment as a whole is estimated to be about 1 8 km and the erosion rate over this period has averaged about 12 m ma 1

the significance of the pdaeomagnetism of jurassic cretaceous rocks from south america predrift movements hairpins and magnetostratigraphy summary in this paper we show that 1 the positions of the cretaceous palaeomagnetic poles pp for south america and africa exhibit elongated distributions that are due to rapid movement of these continents from the south pole 2 the positions of the middle late jurassic virtual geomagnetic poles for south america exhibit an elongated distribution along the meridians 20 200 e it is suggested that this is due to a rapid shift of south america in middle late jurassic time 3 the late early early late cretaceous sections of the apparent polar wandering paths for south america and africa are consistent with south atlantic seafloor spreading data on the basis of the comparison of the reliable late palaeozoic late cretaceous pps for south america and africa taking into account the restrictions established by geological palaeontological and seafloor spreading data it is suggested that minor movements could have occurred within western gondwana in middle late jurassic time along a narrow zone which later became the south atlantic divergent boundary four hairpins are defined in the late palaeozoic late cretaceous section of the apparent polar wandering path for south america the two youngest of these can be correlated with the origin of the south atlantic ocean basin and the onset of the andean orogeny respectively the magnetostratigraphy for the serra geral lava flow sequence suggests that some of these flows were poured out rapidly without significant interruption

experimental investigation of the effects of soil properties on levee breach by overtopping abstractlevee failure due to overtopping during floods is a common phenomena an experimental study was conducted in the hydraulics laboratory university of south carolina to develop an understanding of the effects of soil properties on the breaching process of earthen levees a total of eight experiments were conducted a new methodology to measure the subaqueous breach evolution has been developed and validated measurements of breach width evolution and headcut migration are shown to be related to soil properties inclusion of noncohesive silt size crushed silica in the levee material 45 by weight significantly reduced the peak discharge and breach evolution time compared to a levee constructed with sand alone increase in kaolin clay in the levee material led to an increase in unconfined compressive strength which in turn increased resistance to levee failure nondimensional equations relating the breach width evolution and headcut migration to the soil properties have been developed by performi

age of mesozoic igneous rocks in northwesternnamibia and their relationship to continental breakup mesozoic igneous rocks of northwestern namibia comprise continental flood basalts and quartz latites of the parana etendeka province and a suite of central sub volcanic intrusions the damaraland complexes conventional k ar ages published for these rocks range from 377 88 ma with the majority of samples yielding ages of 150 110 ma this large spread of ages is interpreted as being due to disturbance of the k ar system by low temperature alteration which is ubiquitous among the volcanic rocks rb sr and 40 ar 39 ar dating methods which are less susceptible to such disturbance yield a narrower range of ages 132 124 ma with one outlier at 149 ma new rb sr internal isochron ages of 129 8 3 8 ma 126 8 1 3 ma and 126 1 7 3 ma have been determined for an etendeka quartz latite and nepheline syenite intrusions in the messum and okorusu complexes respectively in addition 40 ar 39 ar release spectrum ages of 137 0 0 7 ma 135 0 0 7 ma and 126 9 0 6 ma have been determined for samples from the paresis comendite cape cross nepheline syenite and okorusu nepheline syenite complexes respectively a 13 ma period between 137 and 124 ma is considered to be the best estimate of the timing of mesozoic igneous activity in northwestern namibia the continental flood basalt volcanism was probably limited to the early part of this period and is inferred to have been relatively short lived 1 2 ma magmatic activity among the damaraland complexes was contemporaneous with the onset of flood basalt volcanism but continued for approximately 15 ma and terminated after the onset of sea floor spreading in this area 130 125 ma both the flood basalt volcanism and the magmatic activity of the damaraland complexes are thought to have occurred in response to rifting across the upwelling tristan mantle plume the linear distribution of intrusions in damaraland is interpreted as being due to magmatism focused along a structural discontinuity between the pan african damara terrain to the south and proterozoic cratonic basement to the north

embankment dam breach parameters and their uncertainties potential flood hazards that would be created by breached embankment dams need to be evaluated to select spillway design floods and to prepare emergency action plans the breaches are often modeled simply usually in the shape of a trapezoid that is defined by its final height base width or average width and side slopes along with the time needed for the opening to form completely data collected from 74 embankment dam failures were used to develop mathematical expressions for the expected values of the final width and side slope of a trapezoidal breach along with its formation time information is provided that allows variances of the predicted quantities to be calculated as well the findings of the statistical analysis were then applied in a monte carlo simulation to estimate the degree of uncertainty of predicted peak flows and water levels downstream from breached embankment dams

modeling gradual dam breaches a simulation model of the gradual failure of an earth dam has been formulated developed and tested with real life data a significant feature of the model is its ability to account for the growth of the breach and the eventual draining of the reservoir concepts of water and sediment routing are used in conjunction with a channel geometry descriptor to arrive at a self contained mathematical model of the breach enlargement and the ensuing flood wave unsteady flow elements of the simulation are an implicit numerical solution of the complete saint venant equations coupled with a sequential sediment routing technique this approach provides an increased rational basis for determining outflow hydrographs from postulated earth dam breaches

modeling sea dike breaching induced by breaking wave impact laboratory experiments and computational model abstract sea dikes are of crucial importance for the defense systems of low lying coastal areas in countries such as germany the netherlands denmark etc as sea dike breaching induced by storm surges is regarded as one of the main causes of coastal flood disasters reliable predictions of both the breach initiation formation and breach development is urgently needed although a simple preliminary model for the simulation of sea dike breaching initiated from the seaside was developed stanczak et al 2006 its limitations showed the necessity for further research and for the development of a more detailed model this paper therefore provides a summary of the results of laboratory experiments on the erosion of grass and clay revetment of a sea dike induced by breaking wave impact and describes the new detailed computational model including an uncertainty analysis

new orleans levee system performance during hurricane katrina 17th street canal and orleans canal north centrifuge modeling of the 17th street canal and orleans canal north levees was performed in this study during hurricane katrina the levees on the 17th street canal failed leading to breaches in the outfall canal in the city two mechanisms were observed in the centrifuge modeling that could cause a breach first a water filled crack formed in front of the floodwall as the water in the canal rose above the top of the levee the levees on the 17th street canal which were supported on clay foundations failed when this cracking led to a translational sliding failure in the clay layer commencing at the toe of the floodwall the levees at orleans canal north where failure did not occur were also modeled to demonstrate that the model tests could successfully simulate failure and nonfailure conditions the centrifuge model tests identified the importance of the crack formation in relation to the stability of the floodwall these tests also confirmed that levee geometry floodwall depth of penetration and the underlying soil profile were all critical to the performance of the system under flood loading

paleomagnetism of 122 ma plutons in new england and the mid cretaceous paleomagnetic field in north america true polar wander or large scale differential mantle motion a paleomagnetic study of cretaceous white mountains plutonic complexes in new hampshire and vermont yields high unblocking temperature dual polarity magnetizations in different types of igneous rocks the resulting pole position for three plutons 71 9 n 187 4 e a95 6 9 age 122 5 ma agrees with previously published mid cretaceous poles for north america which together give a mid cretaceous standstill reference pole slightly revised from globerman and irving 1988 at 71 2 n 194 1 e a95 3 7 n 5 studies we argue on the basis of the wide geographic distribution of these studies the variety in tectonic settings and rock types positive reversal tests and an overall reversal pattern consistent with geomagnetic polarity time scales that this mean pole represents the north american mid cretaceous reference field for nominally 36 m y 124 to 88 ma the standstill pole limits to within 4 the motion of the north american plate relative to the earth s spin axis during the same mid cretaceous interval the new england hotspot track 124 ma monteregian hills 122 5 ma cretaceous white mountains and 103 to 84 ma new england seamounts requires 11 4 of north poleward motion of north america in direct conflict with the paleomagnetic standstill a similar 13 discrepancy is independently demonstrated between the spin axis and the tristan da cunha hotspot track on the african plate during the mid cretaceous interval the hotspot spin axis discrepancies ended by 90 ma when it is shown that both atlantic hotspots agree with north american and african dipole paleolatitudes and present day locations nondipole fields are an unlikely explanation of the uniform motion of these two widely separated hotspots with respect to the spin axis leaving as possible interpretations true polar wander and large scale but differential mantle motion the southerly motion of the mid cretaceous louisville hotspot relative to the spin axis is ostensively at odds with what would be predicted under the true polar wander interpretation and points to differential mantle kinematics the motions of the three widely separated mid cretaceous hotspots with respect to the spin axis may be related to the recently proposed increase in global oceanic lithosphere production rates which gave rise to the mid cretaceous superplume

depositional history of the celebes sea from odp sites 767 and 770 leg 124 of the ocean drilling project drilled sites 767 and 770 in the northern celebes sea reaching late middle eocene basaltic basement at both sites major shifts in sediment provenance record the changing tectonic setting of the basin from late middle eocene into early miocene time pelagic sedimentation prevailed with little influence from continental or volcanic arc sources a major continental influence is first documented in middle miocene time as a thick sequence of quartzose mud rich turbidites accumulated on the deeper basin floor possibly in response to middle miocene orogeny in northern borneo terrigenous turbidite deposition waned during the late miocene as active arc volcanism began to contribute significant amounts of hemipelagic sediment and ash layers which have remained the dominant basinal sediment to the present although the celebes sea is now nearly surrounded by volcanic arc terranes the absence of volcaniclastic sediment in the eocene to early miocene section suggests that the basin did not form by back arc spreading

submarine volcaniclastic rocks in this chapter we are concerned with underwater volcaniclastic eruptions and products as well as pyroclastic flows and debris generated on land and transported by mass flowage into the sea submarine fallout deposits derived from land based eruptions are treated in chapter 7 clastic materials redistributed as mass flows or turbidity currents originating from the rapid build up of tephra and epiclastic volcanic debris along coastal parts of volcanoes are also discussed in various places throughout the text e g chap 13

new early cretaceous palaeomagnetic pole from cordoba province argentina revision of previous studies and implications for the south american database summary a continental sequence of red beds and interbedded basaltic layers crops out in the sierra chica of cordoba province argentina 31 5 s 64 4 w this succession was deposited in a half graben basin during the early cretaceous we have carried out a palaeomagnetic survey on outcrops of this basin 147 sites in seven localities from an analysis of irm acquisition curves and detailed demagnetization behaviour three diverent magnetic components are identified in the volcanic rocks components a b and x are carried by single or pseudo single domain titano magnetite haematite and multidomain magnetite respectively component a is interpreted as a primary compo nent of magnetization because it passes conglomerate contact tilt and reversal tests the carrier of the primary magnetization fine grained titano magnetite is present in basalts with a high degree of deuteric oxidation this kind of oxidation is interpreted to have occurred during cooling components b and x are discarded because they are interpreted as recent magnetizations in the sedimentary rocks haematite and magnetite are identified as the carriers of remanence both minerals carry the same component which passes a reversal test the calculated palaeomagnetic pole based on 55 sites is lat 86 0 s long 75 9 e a 95 3 3 k 35 this palaeomagnetic pole supersedes four with anomalous positions reported in previous papers

neogene rock uplift and erosion in northern borneo evidence from the kinabalu granite mount kinabalu thermochronological data from the kinabalu granite emplaced between c 7 2 and 7 8 ma provide a unique record of northern borneo s exhumation during the neogene biotite 40 ar 39 ar ages c 7 32 7 63 ma record rapid cooling of the granite in the late miocene as it equilibrated with ambient crustal temperatures zircon fission track ages c 6 6 5 8 ma and apatite u th sm he ages central age c 5 5 ma indicate rapid cooling during the late miocene early pliocene this cooling reflects exhumation of the granite uplift and erosion bringing it closer to the earth s surface thermochronological age versus elevation relationships suggest exhumation rates of more than 7 mm a 1 during the latest miocene and early pliocene neither the emplacement of the kinabalu granite nor its exhumation is related to the sabah orogeny which terminated in the early miocene instead granite magmatism was caused by extension related to subduction rollback of the sulu arc and mio pliocene exhumation of the kinabalu granite was driven either by lithospheric delamination or break off of a subducted slab beneath sabah plio pleistocene tectonism offshore and onshore northern borneo reflects continuing large scale gravity driven tectonics in the region supplementary material full 40 ar 39 ar fission track and u th sm he analytical data and 40 ar 39 ar age spectra plots can be found at www geolsoc org uk sup18613

uncertainty of predictions of embankment dam breach parameters risk assessment studies considering the failure of embankment dams often require the prediction of basic geometric and temporal parameters of a breach or the estimation of peak breach outflows many of the relations most commonly used to make these predictions were developed from statistical analyses of data collected from historic dam failures the prediction uncertainties of these methods are widely recognized to be very large but have never been specifically quantified this paper presents an analysis of the uncertainty of many of these breach parameter and peak flow prediction methods application of the methods and the uncertainty analysis are illustrated through a case study of a risk assessment recently performed by the bureau of reclamation for a large embankment dam in north dakota

2d process based morphodynamic model for flooding by noncohesive dyke breach abstractinundation models based on the shallow water equations swe have been shown to perform well for a wide variety of situations even at the limit of their theoretical applicability and arguably somewhat beyond one of these situations is the catastrophic event of floods induced by dyke breach and consequent dyke erosion the dyke collapse is often not sudden as assumed by many flood simulations in which the dyke boundary is treated as a dam break the dyke erosion is a gradual and complex process that delays the onset of the flood affecting the hydrograph of the flow to simulate correct temporal passage of a flood it is important to understand the rate at which these dykes collapse in this paper an overtopping flood event combined with dyke erosion is simulated the model is built upon the two dimensional 2d shallow water equations together with sediment flow interactions and incorporates a sediment transport equation the model is solved using a second order godunov type finite volume me

inundation of a dutch river polder sensitivity analysis of a physically based inundation model using historic data 1 the inundation model delft flooding system delft fls was applied to simulating the historical flood of 1805 in the polder land van maas en waal netherlands delft fls is a two dimensional 2 d hydrodynamic model that simulates overland flow sensitivity analyses show a large influence of floodplain topography and hydraulic friction on the propagation of the inundation because of the typical topography of dutch polders a virtually flat floodplain bordered by high dikes the extent of the inundated area alone cannot be used for evaluating the model performance therefore the inundation time and water levels within the inundated area were used to test the model capabilities this study shows that using historic data has a potential advantage over using contemporary data historic data allow evaluation of a model for real flood disasters that have long return periods and fortunately have not occurred in modern times

the sulu sea a back arc basin setting within a neogene collision zone abstract the southeast sulu sea is a small oceanic basin that opened in middle miocene time in a back arc setting along the sundaland margin during subduction of the celebes sea plate beneath the sulu arc this back arc extension post dates compressive tectonism present in this back arc area in early middle miocene time progressive and still incomplete closing of this basin initiated in late miocene time is the result of collision of exotic terranes with the sundaland margin this collision also induced flipping of the sulu subduction zone the neogene geodynamic evolution of the sulu sea provides a modern example of how young oceanic crust can be incorporated within an orogenic belt

palaeomagnetism and k ar ages of the south west african basalts and their bearing on the time of initial rifting of the south atlantic ocean summary palaeomagnetic and isotopic results from the kaoko lavas hoachanas basalts and dolerite sills of south west africa indicate that the upper triassic lower jurassic stormberg flows of south africa may have extended into sw africa and that younger igneous events of lower cretaceous age were simultaneous with the serra geral volcanism in brazil five analyses on three samples of the keetmanshoop sills gave k ar ages between 178 4 and 199 4 ma four analyses of two samples of the hoachanas basalts gave ages between 161 3 and 173 2 ma and eight analyses of five samples of kaoko basalt gave ages between 110 4 and 128 2 ma the components of remanent magnetization rm used to compute palaeomagnetic pole positions for the kaoko lavas 48 n 93 w a95 3 and for the hoachanas basalts 61 n 106 w a95 7 are stable to alternating field af and thermal demagnetization correlation on a pre drift map and on a map reconstructed for 112 ma bp before present between the palaeomagnetic poles from the kaoko and serra geral lavas suggests that the south atlantic had not opened appreciably by 112 ma bp cretaceous pole positions for s america and africa on a map reconstructed for 80 ma bp are also discussed

magnetization properties of intrusive extrusive rocks from east maio republic of cape verde and their geological implications summary the remanent magnetization of intrusive extrusive rocks of the basement complex of east maio constitutes four components that define two different axes of magnetization at around dec 328 inc 12 and dec 007 inc 14 respectively in general two or more components co exist in separate specimens or sites but both axes are present most frequently in the normal sense the nnw striking axis the b axis fits very well with the upper cretaceous polar wander path for africa it is consequently inferred that the major phase of sheet intrusions in maio dates from this time probably from the interval 90 70 myr bp comparisons of the directional dispersions in the folded and unfolded states suggest that this injection phase post dates the uplift of the central igneous complex of the island the second axis of magnetization the a axis agrees very well with late teritary quaternary palaeomagnetic data for africa and the canary islands the a axis is therefore regarded as of secondary origin being the consequence of a thermal chemical overprint during the miocene pliocene volcanism on the island the occurrence of a 50 70 myr long period of volcanic quiescence and erosion between the termination of the early igneous activity upper cretaceous and the rejuvenated magmatism in miocene pliocene time is compatible with similar observations in the canary islands in contrast to the palaeomagnetic conclusions the k ar data only give ages around 10 myr the unusually young isotope dates are regarded as being due to an almost complete age resetting and are seen in conjuction with the overprinted magnetization this explanation is further supported by the fact that k ar results of pillow lavas underlying upper jurassic limestones only give tertiary ages

the basins of sundaland se asia evolution and boundary conditions abstract most of the basins developed in the continental core of se asia sundaland evolved since the late cretaceous in a manner that may be correlated to the conditions of the subduction in the sunda trench by the end of mesozoic times sundaland was an elevated area composed of granite and metamorphic basement on the rims which suffered collapse and incipient extension whereas the central part was stable this promontory was surrounded by a large subduction zone except in the north and was a free boundary in the early cenozoic starting from the palaeogene and following fractures initiated during the india eurasia collision rifting began along large faults mostly n s and nnw sse strike slip which crosscut the whole region the basins remained in a continental fluvio lacustrine or shallow marine environment for a long time and some are marked by extremely stretched crust phu khanh natuna n makassar or even reached the ocean floor spreading stage celebes flores western sundaland was a combination of basin opening and strike slip transpressional deformation the configuration suggests a free boundary particularly to the east trench pull associated with the proto south china sea subduction java sulawesi trench subduction rollback in the early miocene australian blocks reached the sunda subduction zone and imposed local shortening in the south and southeast whereas the western part was free from compression after the indian continent had moved away to the north this suggests an important coupling of the sunda plate with the indo australian plate both to se and nw possibly further west rollback had ceased in the java sumatra subduction zone and compressional stress was being transferred northwards across the plate boundary the internal compression is expressed to the south by shortening which is transmitted as far as the malay basin in the late miocene most of the sunda plate was under compression except the tectonically isolated andaman sea and the damar basins in the pliocene collision north of australia propagated toward the north and west causing subduction reversal and compression in the short lived damar basin docking of the philippine plate confined the eastern side of sundaland and created local compression and uplift such as in nw borneo palawan and taiwan transpressional deformation created extensive folding strike slip faulting and uplift of the central basin and arakan yoma in myanmar minor inversion affected many thailand rift basins all the other basins record subsidence the uplift is responsible for gravity tectonics where thick sediments were accumulated sarawak ne luconia bangladesh wedge

a new kinematic model for iberia further palaeomagnetic and isotopic age evidence abstract palaeomagnetic results and k ar age data from the algarve igneous province have uncovered three ancient relative field components it is inferred that the principal magnetization of the monchique complex with a mean direction of d 42 i 181 95 4 5 was acquired at around the time of the pluton s emplacement some 72 2 ma ago a second magmatic pulse affected the region at 68 2 ma leaving behind a relative field component of d 42 i 341 95 1 7 furthermore an overprinted magnetization characterized by shallow inclination and somewhat smeared northwesterly southeasterly declination most likely originates from the lower tertiary the new palaeomagnetic data are seen in conjunction with previously published upper cretaceous results from the sintra and sines intrusive complexes the resulting database gives entirely new perspectives for evaluating the plate tectonic history of the peninsula in upper cretaceous lower tertiary time a two phase rotation of the iberian micro plate an anticlockwise one of 40 followed by a clockwise one of 70 is clearly in evidence the net clockwise rotation provided a major impetus for the compressive deformation in the pyrenees and the bay of biscay and led to extensive remagnetization of older rock formations in the northern regions of iberia previous palaeomagnetic conclusions in favour of a single anticlockwise rotation of 35 supposed to be directly connected with the formation of the bay of biscay appear to be artefacts which stem from an incorrectly adopted palaeomagnetic reference frame

paleomagnetism of the lesotho basalt southern africa paleomagnetic study of four sections from middle jurassic karoo lava located in lesotho and south africa yielded a new paleomagnetic pole for africa with coordinates 71 6 n 273 5 e a95 3 7 k 33 n 47 paleosecular variation estimated as the angular standard deviation of vgps distribution is 14 1 2 4 1 8 which is considerably lower than expected for this time interval and latitudinal band preliminary paleointensity results indicate a low field intensity during the acquisition of the magnetization this new result tends to support a possible correlation between secular variation and dipole intensity when the lower to middle jurassic paleomagnetic data set for africa is considered a difference of 13 9 8 7 of arc is found to exist between the mean northwest and south african poles furthermore while the northwest african pole is in very good agreement with the lower to middle jurassic north american pole whichever set of rotation parameters is used to close the north atlantic ocean the south african pole falls some 12 15 of arc apart as intraplate deformation models developed to achieve tighter fit of west gondwana prior to the opening of the south atlantic fail to account fully for the difference between northwest and south african poles the pre cretaceous apparent polar wander path for africa has to be considered with caution

discussion of laboratory study on 3d flow structures induced by zero height side weir and implications for 1d modeling by giovanni michelazzo hocine oumeraci and enio paris

new paleomagnetic results from cretaceous sediments near lisboa portugal and implications for the rotation of iberia abstract paleomagnetic study of outer platform sediments of late jurassic early cretaceous age from portugal lisboa area leads to characteristic remanent magnetization directions for the hauterivian barremian d 317 i 58 and the aptian d 344 i 47 the absolute rotation of iberia between 125 and 110 ma is consequently of about 27 in an anticlockwise sense a later rotation of about 14 follows the first one in the same sense from 110 ma the total absolute rotation of iberia from the hauterivian age determined by paleomagnetism is thus about 41 the comparison of declinations measured with paleodeclinations calculated in lisboa from the eurasian and african poles of similar age indicates that the main phase of relative rotation of iberia with respect to eurasia occurs during the first stage of relative motion i e hauterivian to aptian the tectonic history of the bay of biscay is in good agreement with these two stages of rotation the total relative rotation with respect to europe is 34 this value is consistent with results previously established by van der voo 2 3 25 but we have established that the main phase of rotation 30 occurs in the hauterivian aptian interval the movement of iberia is clearly linked to the movement of africa in direction and age but the amount of rotation of iberia during the early cretaceous is much larger and implies that iberia was not a real part of the african plate

paleomagnetism and potassium argon age of the messejana dike portugal and spain angular limitation to the rotation of the iberian peninsula since the middle jurassic abstract a paleomagnetic and potassium argon dating investigation has been carried out on a 530 km long dike system which transects the western iberian peninsula in a northeasterly direction the k ar age determinations were made on mineral separates exclusively they range between 160 and 200 ma and the authors suppose that this reflects the actual time interval of the intrusion in accord with previous results the paleomagnetic pole derived from 12 sites regularly distributed along the dike 71 n 236 e coincides well with other mesozoic paleomagnetic poles from the western africa a contemporaneous pole from stable europe is tentatively deduced from african and north american late triassic early jurassic poles using different reconstruction models around the north atlantic ocean the divergence between this pole and the iberian pole corresponds to the result obtained for permian poles

palaeomagnetism rock magnetism and ams of the cabo magmatic province ne brazil and the opening of south atlantic summary reconstruction of the south atlantic opening has long been a matter of debate and several models have been proposed one problem in tracing properly the atlantic history arises from the existence of a long interval without geomagnetic reversals the cretaceous normal superchron for which ages are difficult to assign palaeomagnetism may help in addressing this issue if high quality palaeomagnetic poles are available for the two drifting continental blocks and if precise absolute ages are available in this work we have investigated the cabo magmatic province northeastern brazil recently dated at 102 1 ma zircon fission tracks ar 39 ar 40 all volcanic and plutonic rocks showed stable thermal and af demagnetization patterns and exhibit primary magnetic signatures ams data also support a primary origin for the magnetic fabric and is interpreted to be contemporaneous of the rock formation the obtained pole is located at 335 9 e 87 9 s n 24 a95 2 5 k 138 and satisfies modern quality criteria resulting in a reference pole for south america at 100 ma this new pole also gives an insight to test and discuss the kinematic models currently proposed for the south atlantic opening during mid cretaceous

contraction and extension in northern borneo driven by subduction rollback abstract during the paleogene the proto south china sea was subducted beneath northern borneo subduction ended with early miocene collision of the dangerous grounds reed bank north palawan block and the sabah cagayan arc much of northern borneo then became emergent forming the top crocker unconformity later in the early miocene subsidence resumed it is proposed that northward subduction of the celebes sea initiated formation of the sulu sea backarc basin followed by subduction rollback to the se this formed a volcanic arc which emerged briefly above sea level and collapsed in the middle miocene as rollback continued the sulu arc was active during middle and late miocene between sabah and the philippines rollback drove extension in northern borneo and palawan accompanied by elevation of mountains crustal melting and deformation offshore there were two important extensional episodes the first at about 16 ma is marked by the deep regional unconformity and the second at about 10 ma produced the shallow regional unconformity both episodes caused exhumation of deep crust probably on low angle detachments and were followed by granite magmatism the nw borneo palawan trough and offshore sabah fold and thrust belt are often interpreted as features resulting from collision regional compression or subduction however there is no seismicity dipping slab or volcanicity indicating subduction nor obvious causes of compression the trough developed after the middle miocene and is not the position of the paleogene trench nor the site of neogene subduction inboard of the trough is a thick sediment wedge composed of an external fold and thrust belt and internal extensional zone with structures broadly parallel to the trough the trough is interpreted as a flexural response to gravity driven deformation of the sediment wedge caused by uplift on land that resulted from extension with a contribution of deep crustal flow

paleomagnetism of mesozoic kimberlites in southern africa and the cretaceous apparent polar wander curve for africa including those previously published good paleomagnetic data have been obtained from 48 of 51 sites in 28 separate kimberlites radiometric dates by one or more methods are available for 17 of these bodies and range from 81 to 145 ma with maxima around 90 and 120 ma these ages correlate with geochemical contrasts distinguishing what have been designated group i younger and ii older kimberlites smith et al 1985b stable magnetization appears to be associated with magnetite developed deuterically after emplacement but in most bodies secular variation has not been completely averaged in the remanence acquired the distribution of vgps calculated is distinctly but not sequentially streaked yet correlates broadly with the older and younger petrochemical types mean north poles calculated on this basis yield kp1 n 14 81 100 ma 64 1 n 226 1 e a95 5 2 and kp2 n 10 113 145 ma 47 6 n 269 9 e a95 9 7 with the exception of one undated pipe meltonwold which was not included in the averages and the melilititic male fissure at swartruggens in group ii average all the kimberlites sampled are normally magnetized including these new data 10 of 17 published african cretaceous poles meet acceptability criteria specified and define an apparent polar wander apw curve from 130 to 75 ma the curve appears to consist of two segments trending latitudinally before 100 ma and meridionally thereafter the latter trend is evident even in the distribution of the individual kp1 poles and may be related to the true polar wander speculated by gordon and livermore 1987 to have occurred in that interval

paleogeographic maps of the continents bordering the indian ocean since the early jurassic paleomagnetic data from the african plate from the early jurassic onward are critically re evaluated and updated resulting in a set of 30 paleopoles from which an apparent polar wander path is derived using 20 ma intervals this path is then used in conjunction with kinematic models of the indian and atlantic oceans to place other continents bordering the indian ocean eurasia india islands and plateaus madagascar seychelles mascarene and blocks involved in the collision of india with eurasia south tibet indochina in an absolute paleogeographic frame fixed with respect to africa paleogeographic maps are presented for the early jurassic pre breakup the jurassic cretaceous boundary anomaly ml5 the early cretaceous m2 the late cretaceous a 34 the cretaceous tertiary boundary a 29 the early eocene a 24 the middle eocene a 21 and the oligocene miocene boundary a 6 observed and predicted paleomagnetic directions for landmasses other than africa i e for western europe china korea india and australia which are not used in deriving the maps are found to be in very satisfactory agreement the quality of reconstructions as measured by rms discrepancies between observed and predicted paleolatitudes is of the order of 5 the main features of the paleogeographic maps are discussed with the aim of relating oceanic and on land geodynamic events the constraints provided by tibetan data on the india asia collision and the 20 ma reorganization of geology and plate boundaries in a band extending from the south china sea through tibet to the red sea system are discussed in more detail we emphasize the episodic nature of the breakup of gondwanaland and formation of the indian ocean and subsequent interaction with eurasia in which six major discrete events are identified separated by 30 ma phases of rather uniform plate motion

testing early cretaceous africa south america fits with new palaeomagnetic data from the etendeka magmatic province namibia abstract we provide an independent test for the proposed pre breakup fits between the south american and african continental margins based on new palaeomagnetic data in the course of modelling the opening of the south atlantic ocean several reconstructions have been proposed which correspond to different estimates of the amount of pre drift extension in the south american and african continental margins and amounts of displacement along intracontinental accommodation zones the parana etendeka large igneous province erupted during a brief time interval between 136 and 131 ma just prior to opening of the south atlantic and has magmatic products on both the african etendeka lavas and south american parana lavas plates here we provide new palaeomagnetic constraints on the etendeka volcanic rocks these yield a declination of d dx 314 4 7 0 and inclination of i ix 42 7 8 3 plat 47 5 plon 88 9 k 26 1 a95 6 3 n 21 when our results are combined with another recently published dataset we obtain an etendeka palaeopole at 49 1 s 87 6 e d dx 315 9 3 8 i ix 43 9 4 4 k 23 4 a95 3 5 n 75 we compare three recent models for south atlantic ocean opening discuss which of the models best fits the palaeomagnetic data and present a revised reconstruction for west gondwana during the early cretaceous

surface subsurface flow modeling with path based runoff routing boundary condition based coupling and assimilation of multisource observation data received 21 october 2008 revised 2 september 2009 accepted 16 september 2009 published 13 february 2010 1 a distributed physically based model incorporating novel approaches for the representation of surface subsurface processes and interactions is presented a path based description of surface flow across the drainage basin is used with several options for identifying flow directions for separating channel cells from hillslope cells and for representing stream channel hydraulic geometry lakes and other topographic depressions are identified and specially treated as part of the preprocessing procedures applied to the digital elevation data for the catchment threshold based boundary condition switching is used to partition potential atmospheric fluxes into actual fluxes across the land surface and changes in surface storage thus resolving the exchange fluxes or coupling between the surface and subsurface modules nested time stepping allows smaller steps to be taken for typically faster and explicitly solved surface runoff routing while a mesh coarsening option allows larger grid elements to be used for typically slower and more compute intensive subsurface flow sequential data assimilation schemes allow the model predictions to be updated with spatiotemporal observation data of surface and subsurface variables these approaches are discussed in detail and the physical and numerical behavior of the model is illustrated over catchment scales ranging from 0 0027 to 356 km 2 addressing different hydrological processes and highlighting the importance of describing coupled surfacesubsurface flow

rapid profiling of an evolving bed form using planar laser sheet illumination traditional methods of measuring the profile of a scour hole or bed form have poor temporal resolution and may require the temporary cessation of the flow in order to be executed these are undesirable characteristics since many hydraulic flows have unsteady water sediment interfaces that can display considerable differences between their dynamic flow on and static flow off states the present technical note discusses the application of planar laser sheet illumination to the erosion of a cohesionless granular bed due to a planar turbulent wall jet the measurements allow for the quantitative study of the evolution of the bed in its earliest stages in some cases an ephemeral bed form is observed to form prior to the development of the main bed form additionally the measurements illustrate the oscillatory nature of the bed form under certain conditions the experiments therefore demonstrate the great potential of this experimental technique for gaining previously inaccessible information on scour processes

detection and characterization of animal burrows within river embankments by means of coupled remote sensing and geophysical techniques lessons from river panaro northern italy abstract the damage and the eventual breach of river embankments may be due to internal erosion and instability processes in the waterside and landside slopes beside the progressive degradation of soil properties different types of macro pores inside the levee body can influence its short and long term performance among macro pores burrows are a widespread form of biologic erosion of earthen structures potentially producing damage or even their collapse in fact animal burrows are erosion tunnels which can lead to piping phenomena thus the emergent risk connected to burrowing animals in earthen levees has to be tackled given also the environmental changes driven by human activity and climate remote sensing and geophysical surveys can complement data from in situ investigation campaigns in the definition of the real embankment model as well as in the imaging of local defects which may influence its local and or global stability several techniques were integrated in the study area of the panaro river where an active animal burrow was detected in spring 2015 two campaigns were carried out survey 1 in june 2015 just after the relocation of the animals and survey 2 in december 2015 after the filling of the burrow with a cement bentonite slurry here we highlight the peculiarity of each method and the choice of an integrated multi technique approach the results allowed the known burrow as well as two other tunnels to be imaged in 3d providing specific guidelines for the best integrated strategy to detect and characterize these macro pores in a fluvial levee the proposed approach can advance our knowledge of embankments in space and time so that effective remedial actions in flood risk and wildlife management can be identified

palaeomagnetic evidence for the origin of madeira abstract the remanent magnetization of basement volcanics from madeira define three different axes of magnetization each having a dual polarity build up the suggested oldest of these components with declination 302 and inclination 4 is assigned to the late lower cretaceous and is thought to reflect the age of the early volcanism of the island subsequent magnetization overprints seem to have occurred in the late cretaceous early tertiary minor and in neogene times respectively the latter magnetization which is strongly developed was most likely impressed during the extensive volcanism that swept the island in post late miocene the palaeomagnetic evidence for a cretaceous origin of madeira is supported by the finding of lower middle cretaceous tuff layers in dsdp site 136 which is located only 160 km north of the island the inferred palaeomagnetic structure of the basement rocks of madeira is similar to that found in the old volcanic complexes of other east central atlantic islands

examination of the seepage face boundary condition in subsurface and coupled surface subsurface hydrological models a seepage face is a nonlinear dynamic boundary that strongly affects pressure head distributions water table fluctuations and flow patterns its handling in hydrological models especially under complex conditions such as heterogeneity and coupled surface subsurface flow has not been extensively studied in this paper we compare the treatment of the seepage face as a static dirichlet versus dynamic boundary condition we assess its resolution under conditions of layered heterogeneity we examine its interaction with a catchment outlet boundary and we investigate the effects of surface subsurface exchanges on seepage faces forming at the land surface the analyses are carried out with an integrated catchment hydrological model numerical simulations are performed for a synthetic rectangular sloping aquifer and for an experimental hillslope from the landscape evolution observatory the results show that the static boundary condition is not always an adequate stand in for a dynamic seepage face boundary condition especially under conditions of high rainfall steep slope or heterogeneity that hillslopes with layered heterogeneity give rise to multiple seepage faces that can be highly dynamic that seepage face and outlet boundaries can coexist in an integrated hydrological model and both play an important role and that seepage faces at the land surface are not always controlled by subsurface flow the paper also presents a generalized algorithm for resolving seepage face outflow that handles heterogeneity in a simple way is applicable to unstructured grids and is shown experimentally to be equivalent to the treatment of atmospheric boundary conditions in subsurface flow models

evidence of an emerging levee failure mechanism causing disastrous floods in italy a levee failure occurred along the secchia river northern italy on 19 january 2014 resulting in flood damage in excess of 500 million in response to this failure immediate surveillance of other levees in the region led to the identification of a second breach developing on the neighboring panaro river where rapid mitigation efforts were successful in averting a full levee failure the paired breach events that occurred along the secchia and panaro rivers provided an excellent window on an emerging levee failure mechanism in the secchia river by combining the information content of photographs taken from helicopters in the early stage of breach development and 10 cm resolution aerial photographs taken in 2010 and 2012 animal burrows were found to exist in the precise levee location where the breach originated in the panaro river internal erosion was observed to occur at a location where a crested porcupine den was known to exist and this erosion led to the collapse of the levee top this paper uses detailed numerical modeling of rainfall river flow and variably saturated flow in the levee to explore the hydraulic and geotechnical mechanisms that were triggered along the secchia and panaro rivers by activities of burrowing animals leading to levee failures as habitats become more fragmented and constrained along river corridors it is possible that this failure mechanism could become more prevalent and therefore will demand greater attention in both the design and maintenance of earthen hydraulic structures as well as in wildlife management

depositional history of the sulu sea from odp sites 768 769 and 771 holes were drilled at three sites in the sulu sea on ocean drilling program leg 124 site 768 lies in the deeper part of the se sub basin and sites 769 and 771 lie on the flanks of the cagayan ridge the results indicate that the sulu basin originated in the late early miocene c 18 8 ma in a backarc setting the cagayan ridge was a site of early to early middle miocene arc volcanism with the deposition of a thick sequence of andesitic to basaltic volcaniclastic deposits in the basin center an early miocene pelagic sequence is interrupted by a thick unit of rhyolitic to dacitic pyroclastic flows middle to late miocene sedimentation is more continental in character with thick quartz rich turbidites in the basin center only the hemipelagic claystone related to these terrigenous turbidites were deposited on the cagayan ridge a decrease in the supply of clastic detritus from arc and continental sources and a change in the level of the carbonate compensation depth in the upper pliocene resulted in pelagic carbonate deposition throughout the late pliocene and pleistocene

formulas for the peak discharge from breached earthfill dams abstractalthough advanced physically based models have been presented in the last years there is still much interest in equations for predicting the peak discharge indeed simple relations are very useful for technical purposes especially when rough calculations are acceptable this paper presents new equations for assessing the peak discharge of the flood hydrograph caused by the gradual erosion of earth dams the equations are obtained by a regression analysis carried out on the peak discharges provided by a physically based numerical model the approach proposed in this paper has the advantage of taking into account some parameters usually neglected by common best fit equations that have strong influence on the peak discharge in particular the equations discussed in this paper take into account the susceptibility to erosion of the dam the shape of the reservoir and the ratio of filling of the reservoir for failures caused by piping the usefulness of the equations is shown through a comparison w

evaluation of the paleo geothermal gradient at site 768 sulu sea paleo temperature gradients for site 768 are determined by modelling organic maturities it is found that the measured maturity of the organic matter cannot be attributed to the present day thermal gradient of 130 c km from a comparison between modelled and measured maturities a high paleogradient of 250 c km is derived