interferometric daylight seismic imaging summary claerbout s daylight imaging concept is generalized to a theory of interferometric seismic imaging ii interferometric seismic imaging is defined to be any algorithm that inverts correlated seismic data for the reflectivity or source distribution as examples we show that ii can image reflectivity distributions by migrating ghost reflections in passive seismic data and generalizes the receiver function imaging method used by seismologists interferometric seismic imaging can also migrate free surface multiples in common depth point cdp data and image source distributions from passive seismic data both synthetic and field data examples are used to illustrate the different possibilities of ii the key advantage of ii is that it can image source locations or reflectivity distributions from passive seismic data where the source position or wavelet is unknown in some cases it can mitigate defocusing errors as a result of statics or an incorrect migration velocity the main drawback with ii is that severe migration artefacts can be created by partial focusing of virtual multiples

wood storage in a wide mountain river case study of the czarny dunajec polish carpathians storage of large woody debris in the wide mountain czarny dunajec river southern poland was investigated following two floods of june and july 2001 with a seven year frequency within a reach to which wood was delivered only by bank erosion and transport from upstream wood quantities were estimated for eighty nine 100 m long channel segments grouped into nine sections of similar morphology results from regression analysis indicated the quantity of stored wood to be directly related to the length of eroded wooded banks and river width and inversely related to unit stream power at the flood peak the largest quantities of wood up to 33 t ha 1 were stored in wide multi thread river sections here the relatively low transporting ability of the river facilitated deposition of transported wood while a considerable length of eroded channel and island banks resulted in a large number of trees delivered from the local riparian forest in these sections a few morphological and ecological situations led to the accumulation of especially large quantities of wood within a small river area very low amounts of wood were stored in narrow single thread sections of regulated or bedrock channel high stream power facilitated transport of wood through these sections while the high strength of the banks and low channel sinuosity prevented bank retreat and delivery of trees to the channel considerable differences in the character of deposited wood existed between wide multi thread channel sections located at different distances below a narrow 7 km long channellized reach of the river wood deposited close to the downstream end of the channellized reach was highly disintegrated and structured into jams whereas further downstream well preserved shrubs and trees prevailed this apparently reflects differences in the distance of wood transport and shows that in a mountain river wider than the height of trees growing on its banks wood can be transported long distances along relatively narrow single thread reaches but is preferentially deposited in wide multi thread reaches copyright 2005 john wiley sons ltd

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

sampling techniques for gravel sized sediments the methods commonly used for sampling the coarser surface layers of gravel bed streams are reviewed it is found that while an areal sample is biased toward the coarser grains compared with a volumetric sample of the same material the conversion formula suggested by a voidless cube model overcompensates for this effect a modified version of the cube model that accounts for porosity is proposed the modified cube model and tests conducted with areal sampling using wax indicate that area by weight analyses can be converted successfully to the equivalent bulk sieve analyses the average depth of the wax samples ranged from d65 d91 increasing with median grain size the equivalence of the grid by number and bulk sieve analyses is reaffirmed

preservation and detectability of shock induced magnetization preservation and detectability of shock induced magnetization abstract an understanding of the effects of hypervelocity impacts on the magnetization of natural samples is required for interpreting paleomagnetic records of meteorites lunar rocks and cratered planetary surfaces rocks containing ferromagnetic minerals have been shown to acquire shock remanent magnetization srm due to the passage of a shock wave in the presence of an ambient magnetic field in this study we conducted pressure remanent magnetization prm acquisition experiments on a variety of natural samples as an analog for srm acquisition at pressures ranging up to 1 8 gpa comparison of the alternating field af and thermal demagnetization behavior of prm confirms that af demagnetization is a more efficient method for removing srm overprints than thermal demagnetization because srm may persist to unblocking temperatures approaching the curie temperatures of magnetic minerals the blocking of srm to high temperatures suggests that srm could persist without being eradicated by viscous relaxation over geologic timescales however srm has been rarely observed in natural samples likely because of two factors 1 other forms of impact related remanence e g thermal remanent magnetization from impact related heating or chemical remanent magnetization from post impact hydrothermal activity are often acquired by target rocks that overprint srm and 2 low srm acquisition efficiencies may prevent srm from being distinguished from the underlying primary remanence or other overprints due to its low magnetization intensity sonia m tikoo 1 2 jerome gattacceca 3 4 nicholas l swanson hysell 1 benjamin p weiss 1 4 clement suavet 4 and cecile cournede 3 department of earth and planetary science university of california berkeley ca 94720 usa berkeley geochronology center 2455 ridge road berkeley ca 94709 usa cnrs aix marseille university cerege um34 aix en provence france department of earth atmospheric and planetary sciences massachusetts institute of technology mit 77 massachusetts avenue cambridge ma 02139 usa final version for publication in journal of geophysical research planets accepted 07 24 2015 doi 10 1002 2015je004840

a paleomagnetic estimate of the age and thermal history of the kentland indiana cryptoexplosion structure the kentland indiana cryptoexplosion structure consists of a centrally uplifted zone of steeply dipping fault blocks surrounded by a ring depression and a low amplitude structural high with a radius of 12 km the age of the deformation is constrained stratigraphically to the interval between mississippian and quaternary paleomagnetic samples were collected from seven carbonate formations and one siltstone unit of these only the middle ordovician quimby s mill limestone contains a stable magnetization with consistent directions stepwise thermal and alternating field demagnetization shows the presence of a northwesterly moderately steep characteristic remanence with a median destructive field of 10 to 30 mt and maximum unblocking temperatures of 300 c the pole position calculated from the mean direction falls near late cretaceous paleomagnetic poles dispersion increases when a bedding correction is applied indicating post deformational magnetization because the magnetization fails the fold test it

multi thread rivers in the polish carpathians occurrence decline and possibilities of restoration multi thread rivers are typified by the presence of interconnected channels separated by mid channel bars or the islands forming as a result of vegetation encroachment on mid channel bars high gradients of channels and valley floors high discharge variability relatively low content of fine cohesive sediments in the alluvial plain coarse bed material and high sediment supply are environmental conditions that favour the development of braided channel pattern under natural conditions of the holocene island braided channel pattern was typical of the rivers in the foreland of the tatra mountains and most likely also those draining the parts of the flysch outer carpathians underlain by thick bedded sandstones complexes these braided channels formed in the rivers flowing through mostly non cohesive floodplains and fed with coarse grained material exceeding competence of the rivers progressive deforestation of mountain catchments with the increasing area of cultivated hillslopes resulted in higher flood peaks and substantially increased sediment supply to river channels coupled with greater humidity of the final stages of the little ice age this led to the transformation of the island braided rivers into bar braided ones throughout the nineteenth century the braided channel morphology expanded downstream to the foreland river reaches in turn over the twentieth century the braided morphology nearly disappeared from polish carpathian rivers mostly as a result of their channelization the effectiveness of these works was however strengthened by a decrease in sediment supply to the rivers caused by land use changes and by the reduced availability of bed material for fluvial transport resulting from in channel gravel mining and partitioning of rivers with dam reservoirs environmental changes which have since occurred in the river catchments and disruption of the continuity of sediment transport by dams limit the feasibility of the restoration of braided channel pattern in polish carpathian rivers to their reaches supporting such morphology under natural conditions of the holocene

imaging with deep water multiples acquisition of on bottom hydrophone data recording of a near surface source provides an opportunity to treat water column multiples as useful signal a ray equation based kirchhoff depth migration is used to image primary reflections and deep water multiples recorded on an ocean bottom hydrophone obh the image of the subbottom sediments is shown to be improved by inclusion of the deep water multiple in the imaging process field data jointly acquired by woods hole oceanographic institute and university of texas institute for geophysics at austin and consisting of an obh 2300 m depth recording a 10 800 cubic inch air gun array are used to illustrate the feasibility of the technique images are obtained from both the primary reflections and from energy that has undergone an additional passage through the water column comparison of these images reveals an excellent correlation of reflectors with the predicted polarity reversal observed in the multiple s image synthetic data are used to examine the d

thermoluminescence measurements on shock metamorphosed sandstone and dolomite from meteor crater arizona 2 thermoluminescence age of meteor crater thermoluminescence tl dating measurements were performed on shock metamorphosed rocks from meteor crater arizona il ages were obtained for eight specimens four coconino sandstone and four kaibab dolomite which experienced sufficient shock heating during the impact to reset their preimpact tl postimpact radiation doses were determined for each shocked fragment from thermoluminescence measurements on quartz mineral separates effective radiation dose rates were calculated from concentrations of uranium thorium potassium and rubidium in the rocks and their burial environment and the distributions of these elements as determined by fission track and microprobe analyses cosmic radiation dose rates were estimated by altitude scaling of sea level data and were corroborated by tl dosimeter measurements at the crater the mean tl ages for the two rock types were reasonably concordant 50 400 2900 and 46 000 3100 years for sandstones and dolomites respectively the overall mean age 49 000 3000 years is significantly older than the 25 000 year age estimate based on the inferred correlation of the oldest pluvial episode at the crater with radiometrically dated 18o maxima

polar wander and paleomagnetic reference pole controversies the purpose of this paper is to review the progress made over the past four years in studies of phanerozoic and precambrian polar wander with an emphasis on the contributions made by u s scientists we perceive a general theme embracing the notion that the accuracy of cratonic reference poles and therefore of apparent polar wander apw paths is not as good as was generally believed four years ago a renewed interest in research concerning cratonic reference poles is largely the result of paleomagnetic studies in orogenic belts namely the western cordillera and appalachians of north america the andes of south america and elsewhere which seek to document the existence or non existence of displacements of suspect terranes i e rotation and or translation with respect to their presently associated cratons some of the results of this research are reviewed in this volume by hillhouse and mcwilliams an important realization of which paleomagnetists have long been aware but which was demonstrated recently by a number of sobering examples for both the paleozoic and mesozoic apw paths for north america is that the reliability of concordance discordance parameters that define terrane displacement is dependent not only on the precision and accuracy of the individual paleomagnetic study but also on the precision and accuracy of the appropriate cratonic reference pole

recursive imaging with multiply scattered waves using partial image regularization a north sea case study as more resources are directed toward reverse time migration an accurate velocity model including strong reflectors is necessary to form a clear image of the subsurface this is of particular importance in the vicinity of salt where singly scattered waves are often not ideal for imaging the salt flanks this has led to interest in processing doubly scattered waves also called duplex or prismatic waves for imaging salt flanks and thus improving the location of salt boundaries in a velocity model we used doubly scattered waves in a two pass one way method to image salt flanks in a north sea data set by working in the one way framework we were able to separately construct images with singly doubly and triply scattered waves we used a multistep imaging process that includes multiply scattered waves by using an imaged reflector to fix one or more of the scattering points allowing for multiply scattered energy from several reflectors potentially with poor continuity to be included without picking each reflector individually with this method we were able to image the flank of a north sea salt body

twentieth century channel change on the dunajec river southern poland patterns causes and controls abstract spatial and temporal patterns of the twentieth century channel changes of the dunajec the second largest river of the polish carpathians are analysed using data from six historical maps hand auger drillings in paleochannels and hydrometric data from 10 gauging stations in its lower course the river was considerably narrowed shortened and embanked between the 1880s and the 1920s here bed degradation commenced in the late 19th century and has so far resulted in 3 1 m of channel incision in the middle river course little change occurred in mountain reaches where the dunajec is confined by valley sides and where bedrock exposures prevent channel incision in the reaches within intramontane basins channelization works carried out in the 1950s 1970s considerably narrowed the river and transformed its multi thread channel into a single thread straight channel rapid bed degradation induced by the works resulted in up to 2 m of channel incision over the second half of the century upstream progression of bed degradation into the adjacent mountain reach was hindered by bedrock exposures at its downstream end in the upper river course reaches with the deeply incised channels up to 3 5 m prevail over a few past decades in response to gravel exploitation river channelization and a reduction in catchment sediment supply more scarce are vertically stable reaches which owe their stability to low unit stream power in wide unmanaged reaches and to fixing of the channel bed by drop structures in channelized reaches this study shows that despite the overall tendency to incision over the 20th century considerable differences in the timing and course of channel changes occurred between particular river reaches due to variable human impact and local geological and geomorphological conditions the main phase of channel incision took place progressively later in the upstream direction however upstream progression of bed degradation from the already incised downstream reaches was precluded by the roznow dam and bedrock controlled reaches where bed material flushed out from an incising upstream reach had been introduced into an artificially narrowed channel of high transport capacity it was easily transferred downstream and could not restore the downstream reach to its pre channelization vertical position

temporal variations of large wood abundance and mobility in the blanco river affected by the chaiten volcanic eruption southern chile abstract the aim of this study is to analyze the temporal variation in abundance and transport of in channel wood along a river affected by a volcanic eruption considering the mobility and retention rates in detail the 2008 eruption of chaiten volcano southern chile severely affected the blanco river basin causing changes in channel morphology and large wood lw dynamics along the fluvial corridor of the river a fourth order stream on the southern slope of the volcano temporal dynamics of lw were investigated from january 2015 until march 2016 in three 80 m long study reaches of the active channel in the lower course of the river every wood element 1 m in length and 0 1 m in diameter within the active channel of each reach was georeferenced measured tagged and characterized wood mobility rate defined as the number of tagged wood pieces repositioned or not found within each study reach to total tagged lw in the same reach and retention rate defined as the number of tagged lw pieces found within each study reach to total tagged wood pieces in the same reach were calculated considering two periods one in summer and one in autumn winter a regional flood frequency analysis estimated flood magnitude defining a recurrence interval of 1 year for summer floods and 10 25 years for autumn winter floods results highlighted how eight years after the eruption the types of lw are still influenced by the impacts of pyroclastic density currents on riparian vegetation the characteristics and abundance of monitored lw are typical of a river system with frequent wood transport the mobility rate ranges between 42 and 94 during the summer and autumn winter period respectively while the wood volume decreases during the summer and increases in autumn winter large wood mobility was also found to vary according to the predominant morphological settings with lower values in narrower channels compared to wider wetted areas in this context the greatest abundance of lw was detected after the higher floods corresponding to an input of lw up to 285 35 m3 ha 1 along the blanco river ordinary floods deliver lw mainly through fluvial transport and bank erosion during higher floods appears as an additional and important wood recruitment process the bank erosion processes with up to 5200 m2 of eroded area confirmed the widening tendency occurring in river systems following volcanic disturbances as there are dead riparian trees along the easily erodible banks it is reasonable to suppose that the blanco river will continue to widen for a long period recruiting and transporting downstream huge volumes of lw in this context these analyses appear of fundamental importance to better manage the river system also for decreasing hazards to the downstream village of chaiten

imaging salt with turning seismic waves turning seismic waves which first travel downward and then upward before and after reflection have been recorded in a 3 d seismic survey conducted over an overhanging salt dome careful processing of these turning waves enables the imaging of the underside of the salt dome and of intrusions of salt into vertical faults radiating from the dome when seismic wave velocity increases with depth waves that initially travel downward are reflected and may turn so as to travel upward before reflection a simple geometrical argument suggests that these turning waves are likely to exhibit abnormal moveout in com mon midpoint cmp gathers in that reflection time decreases with increasing source receiver offset this abnormal moveout and the attenuation of turning waves by most migration methods suggest that conventional seismic processing does not properly image turning waves the most important step in imaging turning waves assuming that they have been recorded is the migration process simple and inexpensive modifications to the conventional phase shift migration method enable turning waves to be imaged for little additional computational cost the examples provided in this paper suggest that these and other such modifications to conventional processing should be used routinely when imaging salt domes

lonar lake palaeomagnetic evidence of shock origin summary palaeomagnetic and rock magnetic investigations were carried out on oriented rock samples collected from the inner walls of lonar lake which is believed to be a meteorite crater these studies show systematic variation in some magnetic parameters q jn k and declination whereas at surrounding localities these parameters show random variation a soft secondary shock component acquired in the present field of d 9 i 47 k 47 6 1 6 4 has been successfully isolated by vector difference analysis whereas the stable primary vector is similar to that of lower tertiary period reverse magnetization nrm and irm of the upper and lower flows respond differently to af demagnetization as a function of their ha it is shown that the nrm carried by the lower flows is similar to that of irm probably reset by the meteorite impact because of their low h carriers it is suggested that such magnetic property variations are characteristic of shock origin and hence we propose an impact origin for lonar lake

contrasting patterns of wood storage in mountain watercourses narrower and wider than the height of riparian trees abstract large wood exerts a beneficial influence on the functioning of riverine and riparian ecosystems but can be also the source of flood risk several studies have recognised a trend of decreasing amounts of large wood on unit channel area with increasing width of mountain streams this study verifies whether this trend can also be generalised for wide mountain rivers longitudinal wood distribution was compared for two watercourses in the polish carpathians second to fourth order kamienica stream 14 m wide on average and the fifth order czarny dunajec river with a mean width of 52 m in the stream both the number and the mean mass of wood deposits were unrelated to channel width and this was reflected in a lack of the relationship between total wood storage the amount of stored wood per channel length and channel width in turn specific wood storage the amount of stored wood per channel area decreased nonlinearly with increasing channel width in the wide czarny dunajec the number and the mean mass of wood deposits increased as the river widened and this was reflected in a marked trend of increasing total wood storage with increasing river width here the width related variation in total wood storage was so high that it overcame the influence of increasing channel area on calculated values of specific wood storage which also increased with increasing river width this study shows that different mechanisms known to govern large wood retention in the channels narrower and wider than the height of riparian trees are reflected in the contrasting patterns of wood storage in mountain watercourses of different relative width different relations between the tendencies of total and specific wood storage in the two types of channels emphasise the need of identifying the spatial density and the total amount of large wood

applications of twin analysis to studying meteorite impact structures abstract this paper describes a technique twin analysis of dolomite and calcite which was used to estimate the level of erosion of an impact crater if the age of impact is known the level of erosion gives the amount of sediments present at that time the estimate of the level of erosion and the presence or absence of tectonic strains in calcite constrains the age of impact this technique might also be useful in identifying deeply eroded impact structures twin analysis gives the greatest shortening direction e 1 tilt corrected e 1 directions converge at or above the present day surface if a shallow gas explosion or meteorite impact explains the structure rather than a deep gas or cryptovolcanic explosion the energy density recorded by twinning distinguishes an impact from a shallow gas explosion for structures 100 m diameter at serpent mound a well established impact structure e 1 directions converge at 1400 390 m 95 confidence interval of the mean above the present day structure and the sample closest to the center of the structure records an energy density of 1 7 10 7 j m 3 these results are consistent with previous studies showing that serpent mound is an impact e g r w carlton c koeberl m t baranoski g a schumacker discovery of microscopic evidence for shock metamorphism at the serpent mound structure south central ohio confirmation of an origin by impact earth and planet sci lett 162 1998 177 185 the level of erosion and other data suggests that serpent mound formed between 290 and 256 ma and was originally 8 5 to 11 km in diameter dolomite twinning is not observed at serpent mound suggesting that this technique may only be useful for studying larger more deeply eroded structures

transport and deposition of large woody debris in streams a flume experiment abstract large woody debris lwd is an integral component of forested streams of the pacific northwest and elsewhere yet little is known about how far wood is transported and where it is deposited in streams in this paper we report the results of flume experiments that examine interactions among hydraulics channel geometry transport distance and deposition of floating wood these experiments were carried out in a 1 22 m wide 9 14 m long gravel bed flume using wooden dowels of various sizes as surrogate logs channel planforms were either self formed or created by hand and ranged from meanders to alternate bars floating pieces tended to orient with long axes parallel to flow in the center of the channel pieces were deposited where channel depth was less than buoyant depth typically at the head of mid channel bars in shallow zones where flow expanded and on the outside of bends we hypothesize that the distance logs travel may be a function of the channel s debris roughness a dimensionless index incorporating ratios of piece length and diameter to channel width depth and sinuosity travel distance decreased as the ratio of piece length to both channel width and radius of curvature increased but the relative importance of these variables changed with channel planform large pieces can move further than our debris roughness models predict if greater than 50 of the active channel area is deeper than the buoyant depth of the piece or if momentum is high enough to carry pieces across shallows our debris roughness model allows first order prediction of the amount of wood transport under various channel geometries

distribution and dynamics of large woody debris and organic matter in a low energy meandering stream this field based study using a combination of bed sediment sampling and large woody debris lwd tracking explores the storage of organic matter and mobility of lwd in poplar creek a low energy meandering river that contains a diverse arrangement of large woody debris lwd this research addresses the following questions 1 does lwd influence the spatial pattern of the storage of benthic organic matter in meander bends 2 how mobile is the lwd in low gradient meandering systems 3 do characteristics of lwd such as length bankfull channel width ratio affect movement based on detailed sampling of sediment and lwd monitoring this study provides a detailed representation of the influence of lwd on the storage of benthic organic matter in meander bends as well as a detailed documentation of the mobility of lwd in the study reach this study has demonstrated that 1 lwd strongly influences patterns of storage of benthic organic matter in low gradient meander bends 2 removal of lwd from meander bends in low gradient systems can substantially reduce the storage of benthic organic matter and 3 the lwd within the study reach at poplar creek is highly mobile the high mobility of lwd observed in this study contrasts with the rates observed in high gradient systems and suggests that lwd influenced patterns of storage of organic matter are temporally variable and that storage of benthic organic matter occurs in pulses interspersed with transport that are keyed to the mobility of lwd although lwd may exert an equally significant control over patterns of storage of organic matter in high and low gradient systems the differences in the mobility rates of lwd suggest a fundamental difference in the dynamics of lwd mediated organic matter between low and high gradient systems

prestack depth migration of primary and surface related multiple reflections part i imaging surface related multiples i e all seismic waves reflected at the free surface at least once often severely contaminate seismic recordings because conventional imaging techniques require input data that consist of primary reflections only significant processing effort is commonly dedicated to attenuating multiples prior to migration on the other hand surface related multiples provide additional illumination of the subsurface and therefore should not be considered as noise we present a prestack depth migration method that allows primary and multiple reflections to be imaged simultaneously depth imaging using primary and multiple reflections dipmr involves decomposing the datainto upgoing and downgoing wave constituents followed by downward extrapolation artifacts generated by interference of upgoing and downgoing events not associated with the same subsurface reflection points crosstalk are attenuated by using a 2d deconvolution imaging condition in contrast to existing methods dipmr doe

log transport and deposition in incised channelized and multithread reaches of a wide mountain river tracking experiment during a 20 year flood abstract distance of large wood transport during floods and conditions for wood deposition in wide mountain rivers are still insufficiently understood tracking of logs tagged with radio transmitters was used to investigate differences in depositional conditions and the length of log displacement during a 20 year flood between channel reaches of different morphology in the czarny dunajec river polish carpathians during the rising limb of the flood logs were placed into the river at three locations at the beginning of an incised reach close to the beginning of a channelized reach and 1 km upstream from the beginning of a wide multithread reach the incised channelized and multithread reaches retained 12 5 33 and 94 of tagged logs introduced to these reaches respectively and of the logs retained in the multithread reach all were deposited in its upstream half significant differences in the length of displacement existed between the logs delivered to the river at the three locations with logs placed into the river at the beginning of the incised reach moving the longest distance and those delivered just upstream from the multithread reach moving the shortest distance before deposition one fourth of the logs were deposited in a low flow channel or on a channel margin one fifth on the floodplain and more than half on gravel bars after the flood river cross sections with deposited logs and a set of cross sections without any wood deposits were surveyed to collect data for one dimensional modelling of hydraulic conditions at the flood peak the cross sections with deposited logs were typified by significantly greater flow width and flow area and by significantly smaller mean flow depth mean velocity froude number mean bed shear stress and unit stream power principal component analysis of the hydraulic parameters in the analysed cross sections grouped the two types of cross sections in distinct clusters indicating that multithread cross sections differed in hydraulic parameters from all the other cross sections the experiment confirmed findings from the previous wood inventory and numerical modelling of wood transport and deposition in the river indicating that in a wide mountain river wood can be transported long distances in a narrow single thread channel it is however preferentially deposited in a wide multithread channel that functions as a natural wood trap preventing or considerably limiting further transfer of large wood to vulnerable sites therefore it is crucial to avoid channelization of multithread reaches that would eliminate their functioning as natural wood traps the hydraulic modelling provided a physical justification for the observed differences in wood behaviour between the distinct channel morphologies

spatial density and characteristics of woody debris in five mountain rivers of the dolomites italian alps abstract this research quantifies amounts and characteristics of woody debris in mountain channels of the alps all pieces of woody debris greater than 5 cm diameter and 0 3 m length have been surveyed along five channels of the dolomites italian alps with channel slopes ranging from 0 04 to 0 26 basin area 2 2 51 km2 during the survey channels were divided into uniform reaches and the mean gradient bankfull width and depth of flow were measured overall 4900 woody debris pieces single and jam forming were measured and classified with respect to several qualitative attributes such as presence absence of rootwads orientation to flow and position in the channel results show that very large variations in the volume of woody debris per unit area of the streambed occur even within single streams and that inputs mainly result from slope instabilities adjacent to the channels amounts of woody debris are low compared to most previous data published from different world regions but match with other mountain rivers of the alps debris transport seems to be of minor importance compared to local inputs from the slopes because reach characteristics are poorly correlated with the volume of woody debris in a reach a strong negative correlation is however observed between basin area and average density of woody debris in the five channels but debris removal in the larger channels likely affects such a trend finally the frequency of log steps is inversely correlated to drainage area and positively related to the density of debris

factors controlling large wood transport in a mountain river as with bedload transport wood transport in rivers is governed by several factors such as flow regime geomorphic configuration of the channel and floodplain or wood size and shape because large wood tends to be transported during floods safety and logistical constraints make field measurements difficult as a result direct observation and measurements of the conditions of wood transport are scarce this lack of direct observations and the complexity of the processes involved in wood transport may result in an incomplete understanding of wood transport processes numerical modelling provides an alternative approach to addressing some of the unknowns in the dynamics of large wood in rivers the aim of this study is to improve the understanding of controls governing wood transport in mountain rivers combining numerical modelling and direct field observations by defining different scenarios we illustrate relationships between the rate of wood transport and discharge wood size and river morphology we test these relationships for a wide multithread reach and a narrower partially channelized single thread reach of the czarny dunajec river in the polish carpathians results indicate that a wide range of quantitative information about wood transport can be obtained from a combination of numerical modelling and field observations and from document contrasting patterns of wood transport in single and multithread river reaches on the one hand log diameter seems to have a greater importance for wood transport in the multithread channel because of shallower flow lower flow velocity and lower stream power hydrodynamic conditions in the single thread channel allow transport of large wood pieces whereas in the multithread reach logs with diameters similar to water depth are not being moved on the other hand log length also exerts strong control on wood transport more so in the single thread than in the multithread reach in any case wood transport strongly decreases with increasing piece volume although this relation is not linear we also document a nonlinear relationship between wood transport and flood magnitude a threshold discharge was identified below which wood transport is negligible this threshold is higher in the multithread reach while in the single thread reach floods of lower magnitude are able to transport wood downstream wood transport ratio increases with discharge until it reaches an upper threshold or tipping point and then decreases or increases much more slowly this threshold is clearly related to bankfull discharge but it is much higher for the multithread reach than for the single thread one although modelling input and field observations were taken from a specific river our findings and conclusions are likely to be applicable to a much larger suite of mountain rivers

islands in a european mountain river linkages with large wood deposition flood flows and plant diversity abstract vegetated islands are characteristic landforms of braided mountain rivers long term observations and recent morphological and botanical surveys conducted in the gravel bed czarny dunajec polish carpathians were used to determine the processes and patterns governing initiation and development of islands and their floristic complexity moreover dendrochronologically estimated years of island inception were compared with the timing and magnitude of flood flows in the period 1970 2011 to infer about controls on the formation and persistence of islands in the river in the high energy braided river islands originate as a result of deposition of large vegetative particles mostly large wood on gravel bars and the associated vegetative regeneration of living wood or the growth of seedlings and saplings in the shelter of wood accumulations tree ring dating of the largest trees growing in particular zones of building and established islands indicated a predominant upstream island growth in the river it results from repeated accumulation of living wood on the head of islands and its subsequent regeneration and contrasts with the progressive downstream growth of islands in the rivers supplied with large stable logs of the tree species without the capability to re sprout the lack of islands from the years 1982 1996 most likely reflects the removal of relatively young islands by two major floods in the 1990s which were however unable to destroy older and larger islands after 1997 the occurrence of low to moderate floods facilitated the formation and persistence of islands the plant inventory demonstrated that species richness increased non linearly with the increasing age area and shoreline length of islands islands supported more plant species than the riparian forest and attained comparable species richness at an early stage of development fast developing dynamic and supporting rich plant communities islands contribute highly to the overall floristic complexity of the river corridor and their re establishment should be viewed as an important factor in the restoration of hydromorphologically degraded mountain rivers

superimposed deformation in seconds breccias from the impact structure at kentland indiana usa abstract breccias from the central uplift at the kentland indiana impact structure have outcrop and microscopic characteristics that give insight into events that may occur in a carbonate dominated sedimentary sequence in the moments following hypervelocity impact three distinct types of brecciated rock bodies fault breccias breccia lenses and breccia dikes suggest multiple mechanisms of fragmentation the fault breccias occur along steeply dipping faults that coincide with compositional discontinuities in the stratigraphic succession the breccia lenses and dikes are less localized in occurrence and show no systematic spatial distribution or orientation the fault breccias and breccia lenses show no consistent cross cutting relationships but both are transected by the breccia dikes textural analysis reveals significant differences in particle size distributions for the different breccias the fault breccias are typically monomict coarsest and least uniform in grain size and yield the highest power law exponent fractal dimension in plots of particle size vs frequency the polymict dike filling is finest and most uniform in grain size has the lowest power law exponent and is locally laminated and size sorted sem images of the dike filling breccia show that fragmentation occurred to the scale of microns material within the breccia lenses has textural characteristics intermediate between the other two types but the irregular morphology of these bodies suggests a mechanism of formation different from that of either of the other breccia categories the breccia lenses and dikes both have sub mm scale spheroidal vugs that may have been formed by carbon dioxide bubbles released during sudden devolatilization of the carbonate country rock collectively these observations shed light on the processes that occur during the excavation and modification phases of crater formation in carbonate strata heterogeneous polyphase multiscale deformation accomplished over a time interval of seconds

the influence of geomorphology on large wood dynamics in a low gradient headwater stream understanding large wood dynamics is critical for a range of disciplines including flood risk management ecology and geomorphology despite the importance of wood in rivers our understanding of the mobility of large wood remains limited in this study individual pieces of large wood were tagged and surveyed over a 32 month period within a third and fourth order lowland forest river individual pieces of wood were found to be highly mobile with 75 of pieces moving during the survey period and a maximum transport distance of 5 6 km multivariate analyses of data from this study and two other published studies identified dimensionless wood length as the important factor in explaining likelihood of movement a length threshold of 2 5 channel widths is identified for near functional immobility with few pieces above this size moving in addition for this study wood type branching complexity location and dimensionless wood diameter were found to be important in determining mobility only for sinuous reaches with readily inundated floodplains where logjams persist over multiple years they were shown to be reworked with component pieces being transported away and replaced by newly trapped pieces the findings of this study have implications for river management and restoration the high mobility observed in this study demonstrates that only very large pieces of wood of length greater than 2 5 channel widths should be considered functionally immobile for pieces of wood of length less than the channel width the possibility of high rates of mobility and long transport distances should be anticipated

geomorphic and stream flow influences on large wood dynamics and displacement lengths in high gradient mountain streams chile understanding large wood lw 1 m long and 10 cm in diameter dynamics in rivers is critical for many disciplines including those assessing flood hazard and risk however our understanding of wood entrainment and deposition is still limited mainly because of the lack of long term monitoring of wood related processes the dataset presented here was obtained from more than 8 years of monitoring of 1264 tagged wood pieces placed in four low order streams of the chilean mountain ranges and is used to further our understanding of key factors controlling lw dynamics we show that lw displacement lengths were longer during periods when peak flow water depths hmax exceeded the bankfull stage hbk than in periods with hmax hbk and that these differences were significantly higher for smaller wood pieces lw length and length relative to channel dimensions were the main factors governing lw entrainment lw displacement lengths were inversely related to the ratio of piece length to h15 i e the level above which the flow remains for 15 of the time and to the ratio of h15 to bankfull width unrooted logs and lw pieces located at the bankfull stage travelled significantly longer distances than logs with attached rootwads and those located in other positions within the bankfull channel a few large logjams were broken during the period of observation and in all occasions lw from these broken logjams did not travel over longer distances than other pieces of lw moved in the same periods and in the same stream segments most importantly our work reveals that lw dynamics tend to be concentrated within a few reaches in each stream and that reaches exhibiting high wood dynamics extensive entrainment deposition or repositioning of lw are significantly wider and less steep than less dynamic reaches

environment friendly reduction of flood risk and infrastructure damage in a mountain river case study of the czarny dunajec abstract migration of a mountain river channel may cause erosional risk to infrastructure or settlements on the valley floor following a flood of 2010 a cutbank in one of the bends of the main channel of the czarny dunajec polish carpathians approached a local road by 50 m to arrest the erosion of the laterally migrating channel water authorities planned construction of a ditch cutting the forested neck of the bend reinforcement of the ditch banks and damming the main channel with a boulder groyne in order to avoid channelization of the highly valued multithread river reach that would deteriorate its ecological status and cause increased flood risk to downstream reaches an alternative approach to prevent bank erosion was proposed the new scheme applied in 2011 included opening of the inlets to inactive side braids located by the neck of the bend of the main channel this solution reestablished the flow in the steeper low flow channels allowing us to expect a cutoff and abandonment of the main channel during subsequent floods gravelly deflectors were constructed directly below the inlets to the reactivated side channels to divert the flow into the channels and prevent the water from entering the main channel hydraulic measurements performed before and after the implementation of the scheme confirmed that it enabled shifting the main water current with the highest average velocity and bed shear stress from the braid closest to the road to the most distant braid similar surveys of fish and benthic macroinvertebrate communities indicated that flow reactivation in the side channels was beneficial for these groups of river biota increasing their abundance and taxonomic richness in the reach not only was the implemented solution significantly less expensive but it also enhanced ecological functions of the multithread channel and the variability of physical habitat conditions and maintained the role of the reach as a wood debris trap however avulsion of the main channel in the river bend immediately upstream during the flood in may 2014 again caused erosional risk to the road although at another location this indicates that with the highly unstable multithread channel pattern of the czarny dunajec the best practice of river maintenance in a relatively unmanaged valley reach would be allowing free channel migration within the floodplain area and reinforcing where necessary the boundary between the erodible river corridor and the managed terrace

tracking log displacement during floods in the tagliamento river using rfid and gps tracker devices large pieces of in channel wood can exert an important role on the ecological and morphological properties of gravel bed rivers on the other side when transported during flood events large wood can become a source of risk for sensitive structures such as bridges however wood displacement and velocity in river systems are still poorly understood especially in large gravel bed rivers this study focuses on log transport in a valley reach of tagliamento river italy log displacement during flood events of different magnitudes recorded from june 2010 to october 2011 has been analysed thanks to the installation of 113 radio frequency identification rfid tags and 42 gps tracker devices in logs of different dimensions recovery rates of logs equipped with rfid and gps trackers were about 43 and 42 respectively the gps devices allowed us to analyse in details the log displacement and transport overtime indicating a higher log entrainment during rising limb of hydrographs the threshold for the entrainment of logs from low bars is around 40 of bankfull water stage no clear relationship was found between the peak of flood and log displacement length and velocity however log displacement length and velocity appear significantly correlated to the ratio between the peak of flow and the water stage exceeding the flow duration curve for 25 of time i e the ratio hmax h25 ratio log deposition was observed to occur at the peak flow and logs transported during ordinary events are preferably deposited on low bars this study reveals the potentials of gps tracker devices to monitor the entrainment and movements of logs in large gravel bed rivers during floods these observations could be useful for better planning of river management practices and strategies involving the use of large wood pieces and could help for calibrating wood budgets at the reach scale

sudden death at the end of the mesozoic abstract a paleoecological analysis of the fossil record before and after the cretaceous tertiary boundary indicates that the widespread extinctions and biological stresses around the boundary are best explained in terms of a sudden significant but short temperature rise l alvarez and co authors having found an enrichment in iridium at the same boundary postulated that it was associated with the impact of an extraterrestrial body if this body struck the ocean the water injected into the atmosphere may have led to a transient increase in the global surface temperature this temperature pulse may have been primarily responsible for the effects observed in the biosphere the pattern of extinction of higher plant species suggests that splash down occurred in the northern pacific bering sea area

changes in the magnitude and transformation of flood waves subsequent to the channelization of the raba river polish carpathians alterations in flood flows of the raba river are examined to determine the influence exerted on flood waves by changing morphological conditions with stable vertical channel position the river increased its sinuosity during the 1920s to 1940s and the change was accompanied by a growing tendency to flood wave attenuation the temporal change in flood wave transformation is typical of a developing low flow system subsequently streambed degradation has been induced due to channnelization works which straightened and narrowed the river flood waves became progressively more flashy as channel incision progressed the increase in magnitude of flood waves passing the deepened reach was greatest for bankfull flows and diminished for lower in bank flows and higher overbank flows the tendency to magnification of peak discharges has been also found in other carpathian rivers which were considerably degraded in the 20th century in response to channelization introducing an empirically found correcting factor into the analysis of the ratio of outflow to inflow peak discharges shows how the conditions of peak flow transformation in a reach have changed since the beginning of the study period a marked coincidence between changes in vertical channel location and variations in the corrected peak discharge ratio proves channel changes to be a very important reason for the growing flood hazard in southern poland gradient oversteepening and channel narrowing caused by channelization lead to formation of a river system having a steep straight narrow and deep channel such a morphology distinguishes the system from natural low flow and high flow systems reduced floodplain water storage and self acceleration of flow concentrated in a channel zone make flood waves progressively more flashy on their way down the channelization formed system

variation in surface bed material along a mountain river modified by gravel extraction and channelization the czarny dunajec polish carpathians abstract longitudinal changes in the grain size of bar sediments of the mountain czarny dunajec southern poland were investigated to determine the impact of human activity in the river on depositional conditions in its channel the grain size of surface bed material was established on 47 gravel bars along an 18 km long river reach without tributaries in which some sections were modified over the past few decades by channelization or gravel extraction and the resultant channel incision a downstream fining trend of bar sediments was determined from samples taken at the sites with close to average river width and a vertically stable channel and used as reference for the other samples in the deeply incised upper part of the reach bar gravels are markedly coarser than the reference grain size in the narrow channelized section in the middle part of the reach bar sediments exhibit better than average sorting and change from coarser gradation to one similar to that of the reference grain size along the section in the wide multithread channel in the lower part of the reach bar gravels are distinctly finer than the reference grain size a similar pattern of downstream variation in the study reach was determined for the river competence on the basis of critical bed shear stress required to entrain d95 particles of the bar gravels the extraction of larger particles from the channel bed in the upper part of the study reach facilitated entrainment of exposed finer grains hence inducing rapid bed degradation at the same time the concentration of flood flows in an increasingly narrow and deep channel must have increased their competence enabling a delivery of the coarse particles previously typical of the upstream reach the middle section has been channelized to prevent sediment delivery to a downstream located dam reservoir however it actually operates as a conveyor belt transferring downstream the bed material flushed out from the upstream incising river section as low unit stream power and high channel form roughness facilitate sediment deposition in the unmanaged lower part of the reach it functions as a sediment sink and may reduce bed material delivery to the dam reservoir

new paleomagnetic age constraints on the decaturville impact structure and weaubleau structure along the 38th parallel in missouri north america 1 eight circular structures along the 38th parallel in the mid continent united states are hypothesized to have formed from multiple impacts only two of these structures have been confirmed as impact features and they are not well dated in this study we use paleomagnetic data to constrain the timing of the poorly dated decaturville impact structure missouri and the weaubleau feature missouri interpreted to be an impact structure to evaluate the possibility of a serial impact event a post depositional mid permian pole derived from impact related breccias at decaturville as well as crosscutting relationships show a pennsylvanian mid permian age for the structure a post tilting late mississippian pole from deformed strata at weaubleau indicates that the deformation event can be no younger than late mississippian our results demonstrate that the decaturville and weaubleau structures are of different ages and could not have been caused by a serial impact event

migration methods for imaging different order multiples multiples contain valuable information about the subsurface and if properly migrated can provide a wider illumination of the subsurface compared to imaging with vsp primary reflections in this paper we review three different methods for migrating multiples the first method is model based and it is more sensitive to velocity errors than primary migration the second method uses a semi natural green s function for migrating multiples where part of the traveltimes are computed from the velocity model and part of the traveltimes i e natural traveltimes are picked from the data to construct the imaging condition for multiples the third method uses cross correlation of traces the last two methods are preferred in the sense that they are significantly less sensitive to velocity errors and statics because they use natural data to construct part of the migration imaging conditions compared with the interferometric i e crosscorrelation imaging method the semi natural green s function method is more computationally efficient and is sometimes less prone to migration artifacts numerical tests with 2 d and 3 d vsp data show that a wider subsurface coverage higher fold and more balanced illumination of the subsurface can be achieved with multiple migration compared with migration of primary reflections only however there can be strong interference from multiples with different orders or primaries when multiples of high order are migrated one possible solution is to filter primaries and different orders of multiples before migration and another possible solution is least squares migration of all events a limitation of multiple migration is encountered for subsalt imaging here the multiples must pass through the salt body more than twice which amplifies the distortion of the image