hydraulic and sedimentary processes causing anastomosing morphology of the upper columbia river british columbia canada abstract the upper columbia river british columbia canada shows typical anastomosing morphology multiple interconnected channels that enclose floodbasins and lateral channel stability we analysed field data on hydraulic and sedimentary processes and show that the anastomosing morphology of the upper columbia river is caused by sediment bedload transport inefficiency in combination with very limited potential for lateral bank erosion because of very low specific stream power 2 3 w m 2 and cohesive silty banks in a diagram of channel type in relation to flow energy and median grain size of the bed material data points for the straight upper columbia river channels cluster separately from the data points for braided and meandering channels measurements and calculations indicate that bedload transport in the anastomosing reach of the upper columbia river decreases downstream because of lateral channel stability no lateral storage capacity for bedload is created therefore the surplus of bedload leads to channel bed aggradation which outpaces levee accretion and causes avulsions because of loss of channel flow capacity this avulsion mechanism applies only to the main channel of the system which transports 87 of the water and 90 of the sediment in the cross valley transect studied because of very low sediment transport capacity the morphological evolution of most secondary channels is slow measurements and calculations indicate that much more bedload is sequestered in the relatively steep upper anastomosing reach of the upper columbia river than in the relatively gentle lower anastomosing reach with anastomosing morphology and related processes e g crevassing being best developed in the upper reach this confirms the notion of upstream rather than downstream control of upper columbia river anastomosis

changes in lowland floodplain sedimentation processes pre disturbance to post rehabilitation cosumnes river ca during the late holocene sediment deposition on the lowland cosumnes river floodplain ca has depended on factors that varied temporally and spatially such as basin subsidence sea level rise flow and sediment supply from both the sacramento river system and from the cosumnes river system itself and anthropogenic changes through field investigations and analyses of historical maps bridge core logs and sediment size distributions we link hydrogeomorphic processes to three stages of floodplain sedimentation on the lowland cosumnes river stage i 1000 200 ybp combined late holocene pre disturbance flood basin overflow and anastomosing river processes deposited spatially variable sediment consisting of gray blue clay 87 clay interlayered with relatively thin coarser sediment pre disturbance holocene deposition rates of up to f3 0 mm year kept pace with sea level rise and tectonic basin subsidence stage ii 200 to f10 ybp anthropogenic disturbances caused a rapid increase in floodplain sedimentation rates up to 25 mm year between 1849 and f1920 and deposited a relatively coarser reddish brown sandy clay f40 clay layer that overlies the basin deposits between f1920 and 1990 ad sedimentation was greatly limited on the lower cosumnes floodplain because levees inhibited connectivity between both the sacramento and cosumnes river systems and the cosumnes floodplain during this stage the density of channel segments in the anastomosing river floodplain decreased by 30 as agricultural activities filled secondary channels and leveled floodplain topography during stage iii f10 ybp to the present post rehabilitation floodplain sand splay complex sediment deposited after 1998 ad resulted from intentionally breaching levees to promote habitat at the cosumnes river preserve the splay complex is dominated by medium to very coarse sand with finer intervening layers the post rehabilitation splay complex overlies the older basin deposits in a generally upward coarsening sequence that reflects depositional processes and land use changes that continue to affect the lowland cosumnes river floodplain d 2003 elsevier science b v all rights reserved

the genesis and recognition of anastomosed fluvial deposits data from the st mary river formation southwestern alberta canada abstract data from modern fluvial systems show that the term anastomosed is best reserved for suspended load systems with multiple channels and very low slope that flow in regions where the hydrograph has a seasonal peak the interchannel areas are topographic lows relative to the channel hanks and are places where crevasse splay marsh and lacustrine sedimentation occurs channel geometry is intrinsically a function of the rate of sediment partitioning the coarsest sediment is deposited in the channels on the levees and in proximal splay complexes whereas the silts and clays are deposited on the rest of the floodplain extrinsic controls on the formation of these systems are geological and climatic they include a source of suspended sediment and a highly seasonal water budget preservat on of anastomosed fluvial deposits requires a mechanism for maintaining very low depositional slopes over geologic time scales data from the st mary river formation in southwestern alberta show that the stratigraphic equivalents of these rivers are ribbon sandstone bodies encased in thin sandstones shales and siltstones the total distribution of facies rather than proof of simultaneous flow in multiple channels can be used to interpret correctly a deposit as anastomosed fluvial although anastomosed fluvial deposits form in a variety of tectonic settings they are apparently most common in foreland basins because these basins provide suitable source rocks and thrusting as a mechanism that can maintain the low depositional slopes over millions of years the mutual interaction among source rock climate and subsidence all of which play critical roles in forming and preserving these distinctive fluvial deposits allows inferences to be drawn regarding paleoclimate and paleoslope that may help constrain models of basin evolution

synoptic scale variability of the polar and subpolar tropopause data analysis and idealized pv inversions the synoptic scale variability of the polar and subpolar tropopause is investigated based on radiosonde and european centre for medium range weather forecasts reanalysis data in combination with idealized potential vorticity pv inversions a regression analysis is performed to examine the relationship between the relative vorticity at tropopause level the tropopause displacement the static stability above the tropopause and the anomalies of tropopause temperature and potential temperature the results are compared with regression coefficients computed from a large number of pv inversions generally a cyclonically influenced tropopause is lower warmer and potentially colder than average and the static stability above the tropopause is reduced the opposite is true under anticyclonic influence typically a cyclonic vorticity of 10 5s 1 is associated with a decrease of the tropopause height by 150 200 m correspondingly the mean vertical temperature gradient in the lowermost 2 km above the tropopause decreases by 0 2 0 3 k km 1 moreover an increase of the tropopause height by 1 km is associated with a temperature decrease by 3 5 k and an increase of the potential temperature by 6 8 k except for the last one these values do not depend significantly on the strength and the sign of the tropopause anomaly distinct annual cycles are observed in parts of the polar regions most of the relations found in the data can be reproduced with the pv inversions except for the observed linearity for large tropopause displacements which is not always reproduced very well the annual cycles can be partly explained with the aid of the pv inversions copyright 2002 royal meteorological society

evaluating competing hypotheses for the origin and dynamics of river anastomosis anastomosing rivers have multiple interconnected channels that enclose flood basins various theories potentially explain this pattern including an increased discharge conveyance and sediment transport capacity of multiple channels deltaic branching avulsion forced by base level rise or a tendency to avulse due to upstream sediment overloading the former two imply a stable anabranching channel pattern whereas the latter two imply disequilibrium and evolution towards a single channel pattern in the absence of avulsion our objective is to test these hypotheses on morphodynamic scenario modelling and data of a well documented case study the upper columbia river proportions of channel and floodplain sediments along the river valley were derived from surface mapping initial and boundary conditions for the modelling were derived from field data a 1d network model was built based on gradually varied flow equations sediment transport prediction mass conservation transverse slope and spiral meander flow effects at the bifurcations the number of channels and crevasse splays decreases in a downstream direction also measured sediment transport is higher at the upstream boundary than downstream these observations concur with bed sediment overloading from upstream which can have caused channel aggradation above the surrounding floodplain and subsequent avulsion the modelling also indicates that avulsion was likely caused by upstream overloading in the model multi channel systems inevitably evolve towards single channel systems within centuries the reasons are that symmetric channel bifurcations are inherently unstable while confluenced channels have relatively less friction than two parallel channels so that more discharge is conveyed through the path with more confluences and less friction furthermore the present longitudinal profile curvature of the valley could only be reproduced in the model by temporary overfeeding

response of fluvial aeolian and lacustrine systems to late pleistocene to holocene climate change lower moravian basin czech republic abstract late pleistocene to holocene morava river valley fill of the eastern czech republic reflects the geomorphic evolution of the valley as forced by climate change valley fill stratigraphy was studied through measured sections optically stimulated luminescence osl and radiocarbon dating ground penetrating radar surveys of relict sand dunes archived drill hole data and a comparison of elevations and ages of stratigraphic units fluvial systems evolved from meandering with floodplains to braided during mis 3 braided fluvio aeolian systems dominated through mis 2 and the last glacial maximum lgm valley aggradation occurred during arid glacial times of a low water to sediment discharge ratio most valley fill was removed at 13 ka with incision by a large bend meandering river with an estimated bankful paleodischarge 3 larger than the modern morava river the holocene morava river has varied from meandering to anabranching with low rates of floodplain aggradation the bzenec sand body up to 36 m thick represents an erosional remnant bypassed during late pleistocene incision and consists of interpreted lacustrine turbidites overlain by braided stream and aeolian dune strata the turbidites consist of laterally continuous thin normally graded beds of rounded and frosted sand grains of aeolian origin dates and elevation data argue that the valley lake formed during the lgm through downstream damming by a braided terminal fan and sand dune complex the turbidites are interpreted to have formed through fluvial undercutting and slumping of dune accumulations as lake level rose this process forced an erosional unroofing of aeolian accumulations reflected in inverted osl dates for the turbidites

anabranching rivers their cause character and classification anabranching rivers consist of multiple channels separated by vegetated semi permanent alluvial islands excised from existing floodplain or formed by within channel or deltaic accretion these rivers occupy a wide range of environments from low to high energy however their existence has never been adequately explained they occur concurrently with other types of channel pattern although specific requirements include a flood dominated flow regime and banks that are resistant to erosion with some systems characterized by mechanisms to block or constrict channels thereby triggering avulsion the fundamental advantage of an anabranching river is that by constructing a semi permanent system of multiple channels it can concentrate stream flow and maximize bed sediment transport work per unit area of the bed under conditions where there is little or no opportunity to increase gradient on the basis of stream energy sediment size and morphological characteristics six types of anabranching river are recognized types 1 3 are lower energy and types 4 6 are higher energy systems type 1 are cohesive sediment rivers commonly termed anastomosing with low w d ratio channels that exhibit little or no lateral migration they are divisible into three subtypes based on vegetative and sedimentary environment type 2 are sand dominated island forming rivers and type 3 are mixed load laterally active meandering rivers type 4 are sand dominated ridge forming rivers characterized by long parallel channel dividing ridges type 5 are gravel dominated laterally active systems that interface between meandering and braiding in mountainous regions type 6 are gravel dominated stable systems that occur as non migrating channels in small relatively steep basins anabranching rivers represent a relatively uncommon but widespread and distinctive group that because of particular sedimentary energy gradient and other hydraulic conditions operate most effectively as a system of multiple channels separated by vegetated floodplain islands or alluvial ridges

sediment provenance and dispersal in a deep marine foreland basin the lower carboniferous culm basin czech republic the lower carboniferous culm basin of the czech republic represents the most easterly and southerly part of the european variscan foreland basin system the nne ssw trending basin is exposed along the eastern flank of the bohemian massif it contains up to 7 5 km of deep marine sediment deposited as an axial turbidite system sourced from south southwest of the basin heavy mineral data and clast types indicate that for much of the visean sediment was sourced from a predominantly low grade metamorphic terrane and visean limestones in the latest visean a progressive change in source material is recorded by an increase in high grade metamorphic detritus studies of variscan nappe pile emplacement along the eastern flank of the bohemian massif allow an assessment of the relationship between basin development and nappe emplacement basin initiation coincided with underthrusting of high grade metamorphic moldanubian nappes at 340 ma sedimentation was synchronous with nappe emplacement throughout the visean which resulted in uplift and erosion of a low grade metamorphic terrane moldanubian nappes were exhumed at approximately 330 ma when high grade metamorphic detritus entered the basin two phases of northward directed sediment progradation are recognized sediment progradation is considered to be related to changes in drainage basin size and or climatic fluctuations within the variscan orogen since sediment is inferred to have been supplied to the basin axially rather than laterally and subsidence curves show no significant change in subsidence rates in contrast to many models of foreland basin sediment distribution filling of the culm basin was largely independent of tectonic activity adjacent to the basin margin and or of subsidence rate changes sedimentation in the culm basin commenced 10 15 ma earlier than the rest of the variscan foreland and records the first impact of the northwardly propagating variscan orogen in northern europe

transport and mixing in the extratropical tropopause region in a high vertical resolution gcm part i potential vorticity and heat budget analysis abstract a high vertical resolution general circulation model gcm output has been analyzed to clarify transport and mixing processes in the extratropical tropopause region the high resolution gcm with a vertical resolution of about 300 m above the extratropical upper troposphere allows simulation of fine atmospheric structures near the tropopause such as the extratropical tropopause transition layer extl and the tropopause inversion layer til the high resolution gcm realistically simulates fine thermal and dynamic structures in the extratropical tropopause region the thickness and maximum stability of the simulated til are consistent with observations the high resolution output was analyzed using a zonal mean potential vorticity pv equation to identify dominant transport processes in the extratropical tropopause region in the northern hemisphere extratropics during winter mean downward advection sharpens the pv gradient between the tropopause and 20 k below it whereas latitudinal variati

investigating fluvial features with electrical resistivity imaging and ground penetrating radar the guadalquivir river terrace jaen southern spain abstract a geophysical survey has been conducted on the lowest terrace levels and the present day floodplain of the current course of the guadalquivir river passing through the province of jaen spain using two techniques electrical resistivity imaging eri and ground penetrating radar gpr three areas have been selected in one of these sectors los barrios there is an old quarry where there are excellent outcrops that allow for the calibration of the survey techniques facies associations on these outcrops are typical of meandering rivers with sequences of channel fills lateral accretion of point bars and floodplain facies the usefulness of the two methods is analysed and compared as a support for stratigraphic and sedimentological studies the geometry and lithofacies of subsurface deposits were characterised using eri and compared with field observations a total of 5 electrical resistivity imaging profiles were obtained the changes in electric resistivity highlight granulometric differences in terrace sediments this technique can thus be used to identify the morphology of these bodies the lithofacies silt sand or gravel and buried channel pattern in addition 16 gpr profiles using 100 and 250 mhz antennas were acquired indicating terrace morphology and the filling of the sedimentary bodies in a more detailed manner than in eri the study thus allows for inferring the existence of channel migration the lateral accretion of point bars and the presence of vertical accretion deposits attributable to the floodplains

net local removal of floodplain sediment by river meander migration abstract erosion from the banks of meandering rivers causes a local influx of sediment to the river channel most of the eroded volume is usually replaced in nearby point bars however the typical geometry of river bends precludes the local replacement of all eroded material because i point bars tend to be built to a lower elevation than cutbanks and ii point bars tend to be shorter than the eroding portion of cutbanks because of channel curvature in a floodplain that is in equilibrium i e neither increasing nor decreasing in volume sediment eroded from cut banks must be replaced elsewhere on the floodplain the local imbalance caused by differences in bank height should be balanced primarily by overbank deposition while the local imbalance caused by curvature should be balanced primarily by deposition in abandoned stream courses or oxbow lakes estimates of these local imbalances based on remotely sensed measurements of bank geometry and channel migration have been made on four systems in the united states a 91 km reach of the pearl river in louisiana and mississippi a 62 km reach of the bogue chitto river in louisiana a 35 km reach of the neuse river in north carolina and a 2 7 km reach of the vermillion river in minnesota for these systems the total local imbalance integrated over many bends ranged from 0 36 to 2 27 m 3 yr m of valley length 0 15 to 1 32 m 3 yr m of channel length or 7 to 45 of gross cutbank erosion with a typical value of about 17 when compared with gauged suspended sediment data the measurements provide estimates of the relative importance of floodplains for storing material transported by a river system the data suggest that even if the studied systems are near long term mass balance equilibrium as opposed to undergoing net deposition or erosion almost all of the sand and in some cases much of the silt and clay in transit through these systems is likely to have spent some time stored in an upstream floodplain

the tropopause in the polar regions abstract the polar and subpolar tropopause in both hemispheres is investigated using the ecmwf reanalysis era data from 1979 to 1993 and radiosonde data from 1989 to 1993 both the thermal and the dynamical criteria are applied to each dataset the tropopauses derived from the radiosonde data are used to validate the era derived tropopauses and to investigate the sharpness of the tropopause the validation reveals that the era data are well suited for the determination of the tropopause a comparison between the thermal and the dynamical tropopause shows a very good agreement except for polar winter and there is clear evidence that the dynamical criterion is more appropriate in winter the results show that the annual cycle of the polar tropopause can be classified into three different patterns a single wave with a tropopause pressure maximum in winter and a minimum in summer is typical for the subpolar parts of eastern siberia and north america a double wave with pressure maxima in spring and autumn

static stability in the extratropical tropopause region abstract idealized axisymmetric anomalies of potential vorticity pv on a midlatitude f plane and their related response in terms of balanced wind and temperature are investigated with special focus on the static stability in the tropopause region the pv anomalies are specified such that they can be interpreted as the result of conservative advection in the tropopause region across the gradients of a prescribed background atmosphere with piecewise constant buoyancy frequency squared n2 related cyclones and anticyclones are treated identically except for the sign of the tropopause potential temperature anomaly composite profiles of n2 are computed for which the thermal tropopause is used as a common reference level and where the number of cyclones in the composite equals the number of anticyclones one obtains a pronounced peak of n2 just above the tropopause and slightly enhanced values below the tropopause in comparison with the background profile within the framework of pv inversion various mechan

climate and related controls on interglacial fluvial sedimentation in lowland britain lewin john gibbard p l 2002 climate and related controls on interglacial fluvial sedimentation in lowland britain sedimentary geology 151 3 4 pp 187 210 rae2008

spatiotemporal evolution of a unique preserved meandering system in central europe the morava river near litovel abstract rivers are naturally dynamic over time and space and respond to the variability of water and sediment inputs and to anthropogenic pressures that cause changes to the river s behaviour and form this study describes the evolution of part of the morava river and the kenick meander in the litovelske pomoravi protected area near the city of olomouc the research describes the historical development of the study area using aerial photos uav images and geodetic measurements long term measurements and imaging using uav technologies have allowed a large amount of information to be collected this information was used to study the kenick meander and the morava river significant lateral channel changes in the banks have occurred in the past and generated the kenick meander a significant event occurred in the spring of 2012 when high water levels were caused a rupture of a meander natural cutoff the water level was monitored in the kenick wood accumulation which formed in the kenick meander before and after the rupture monitoring the movement of wood in the river basin is particularly important because the movement of ice in the winter can cause blockage of the channel and subsequent flooding of water over the banks and into the surrounding communities

rate and processes of river network rearrangement during incipient faulting the case of the cahabon river guatemala deeply incised river networks are generally regarded as robust features that are not easily modified by erosion or tectonics although the reorganization of deeply incised drainage systems has been documented the corresponding importance with regard to the overall landscape evolution of mountain ranges and the factors that permit such reorganizations are poorly understood to address this problem we have explored the rapid drainage reorganization that affected the cahabon river in guatemala during the quaternary sediment provenance analysis field mapping and electrical resistivity tomography ert imaging are used to reconstruct the geometry of the valley before the river was captured dating of the abandoned valley sediments by the be 10 al 26 burial method and geomagnetic polarity analysis allow us to determine the age of the capture events and then to quantify several processes such as the rate of tectonic deformation of the paleovalley the rate of propagation of post capture drainage reversal and the rate at which canyons that formed at the capture sites have propagated along the paleovalley transtensional faulting started 1 to 3 million years ago produced ground tilting and ground faulting along the cahabon river and thus generated differential uplift rate of 0 3 0 1 up to 0 7 0 4 mm y 1 along the river s course the river responded to faulting by incising the areas of relative uplift and depositing a few tens of meters of sediment above the areas of relative subsidence then the river experienced two captures and one avulsion between 700 ky and 100 ky the captures breached high standing ridges that separate the cahabon river from its captors captures occurred at specific points where ridges are made permeable by fault damage zones and or soluble rocks groundwater flow from the cahabon river down to its captors likely increased the erosive power of the captors thus promoting focused erosion of the ridges valley fill formation and capture occurred in close temporal succession suggesting a genetic link between the two we suggest that the aquifers accumulated within the valley fills increased the head along the subterraneous system connecting the cahabon river to its captors and promoted their development upon capture the breached valley experienced widespread drainage reversal toward the capture sites we attribute the generalized reversal to combined effects of groundwater sapping in the valley fill axial drainage obstruction by lateral fans and tectonic tilting drainage reversal increased the size of the captured areas by a factor of 4 to 6 at the capture sites 500 m deep canyons have been incised into the bedrock and are propagating upstream at a rate of 3 to 11 mm y 1 deepening at a rate of 0 7 to 1 5 mm y 1 at this rate 1 to 2 million years will be necessary for headward erosion to completely erase the topographic expression of the paleovalley it is concluded that the rapid reorganization of this drainage system was made possible by the way the river adjusted to the new tectonic strain field which involved transient sedimentation along the river s course if the river had escaped its early reorganization and had been given the time necessary to reach a new dynamic equilibrium then the transient conditions that promoted capture would have vanished and its vulnerability to capture would have been strongly reduced

morava river floodplain development during the last millennium stražnicke pomoravi czech republic floodplain sediments deposited along the lower course of the morava river eastern czech 206 pb 207 pb and pop ddt pcb analysis and 137 cs activity data thecu trienmethodwasusedforstratigraphicallycorrelatingthesedepositsbasedonthevariationofexpand able clay minerals in the sediments the resulting stratigraphic pattern reveals the alluvial history of the cur rently active river channel system since the end of the first millennium ad fine overbank clayey sediments deposited during the mediaeval warm period were eroded from cultivated fields newly formed during mediaeval colonization between 1250 and 1450 these fine deposits are overlain by coarser floodplain sedi mentsofthe littleiceage indicatingachangeinthesedimentsourcesincethesixteenthcentury ad anda substantial increase in the sediment load in the second half of twentieth century the straunicke pomoravi floodplaindepositsrepresentavaluablepalaeoenvironmentalarchiveofthelastmillennium containingrecords offluvialprocessesconsiderablyalteredbyhumanactivities

cyclone anticyclone asymmetry concerning the height of the thermal and the dynamical tropopause abstract the differences between upper tropospheric cyclones and anticyclones are investigated regarding the height of the thermal and the dynamical tropopause the problem is addressed in an idealized framework by analyzing axisymmetric balanced flows which are characterized by a radial scale r and a tropopause potential temperature anomaly where cyclones and anticyclones differ only by the sign of the height of the thermal tropopause significantly differs from the height of the dynamical tropopause unless the anomaly is shallow there is a pronounced asymmetry in that the differences are much larger and more likely to occur in the case of cyclones two factors contribute to this asymmetry first for a given amplitude cyclones and anticyclones have different aspect ratios in geometric space second for a high latitude winter scenario the critical lapse rate of the wmo thermal tropopause is asymmetric with respect to typical tropospheric and stratospheric lapse rates simulated station s

fluvial dynamics of the žitava river sw slovakia during the last 45 ka bp and their influence on early bronze age human occupation as part of a geoarchaeological project exploring the early bronze age settlement of fidvar this geomorphologic study explores the fluvial dynamics of the itava river in southwestern slovakia casting light for the first time on the regional river s holocene and late pleistocene development in order to reconstruct the itava s fluvial evolution floodplain deposits were investigated by electrical resistivity tomography selected percussion drillings and ams radiocarbon dating in combination these methods provided a detailed view into the river s history as a result of the climatic variations engendered by the last glacial cycle the fluvial style repeatedly changed between a braided and anastomosing system however during long time periods of the middle and upper plenivistulian the river retained an anastomosing or even meandering style in contrast to central european rivers therefore in agreement with other investigations our results suggest different climatic conditions in the northern pannonian basin from 40 to 20 ka bp during the early and middle holocene a dense vegetation cover dry mesic oak forests led to stable geomorphological conditions and a meandering channel resulted in lateral erosion of the floodplain fringes accumulation of alluvial loamy sediments did not start until the neolithic and has been related to anthropogenic landscape changes similar to other naturally favoured areas central europe finally two reconstructed river positions indicate a considerable lateral fluvial erosion of the early bronze age settlement at fidvar consequently the original settlement area already thought to be the largest in the region was once significantly larger

evolution of fixed channel alluvial plains in response to carboniferous vegetation the establishment of terrestrial plants during the palaeozoic era was one of the most significant changes to the earth system during the phanerozoic eon the continuing evolution and expansion of land plants irrevocably altered the alluvial landscape the broad unconfined and unconsolidated blankets of coarse sediment found at the start of the cambrian period were replaced by a diverse array of braided and meandering channel styles and stable floodplains by the end of the devonian period here we show that the first appearance of a sedimentary facies suite attributed to low energy organic rich river systems with multiple channels and stable alluvial islands known as anabranching or anastomosing rivers occurred during the carboniferous period our field studies and literature review demonstrate that the appearance of these rivers coincides with the continuing evolution of tree like plants we suggest that increased floodplain stability and new triggers for channel avulsion were provided by the increase in complexity and diversity of root assemblages density of floodplain forests and production of woody debris associated with expansion of arborescence we conclude that the expansion of tree habitats led to the crossing of a threshold in vegetative control of floodplain and river morphology during the carboniferous

using tropopause maps to diagnose midlatitude weather systems the use of potential vorticity pv allows the efficient description of the dynamics of nearly balanced atmospheric flow phenomena but the distribution of pv must be simply represented for ease in interpretation representations of pv on isentropic or isobaric surfaces can be cumbersome as analyses of several surfaces spanning the troposphere must be constructed to fully apprehend the complete pv distribution following a brief review of the relationship between pv and nearly balanced flows it is demonstrated that the tropospheric pv has a simple distribution and as a consequence an analysis of potential temperature along the dynamic tropopause here defined as a surface of constant pv allows for a simple representation of the upper tropospheric and lower stratospheric pv the construction and interpretation of these tropopause maps which may be termed isertelic analyses of potential temperature are described in addition techniques to construct dynamical representations of the lower tropospheric pv and near surface potential temperature which complement these isertelic analyses are also suggested case studies are presented to illustrate the utility of these techniques in diagnosing phenomena such as cyclogenesis tropopause folds the formation of an upper trough and the effects of latent heat release on the upper and lower troposphere

lowland river responses to intraplate tectonism and climate forcing quantified with luminescence and cosmogenic 10be intraplate tectonism has produced large scale folding that steers regional drainage systems such as the 1600 km long cooper ck en route to australia s continental depocentre at lake eyre we appl

patterns and processes of wood debris accumulation in the queets river basin washington field surveys in the 724 km 2 queets river basin on the west slope of the olympic mountains in nw washington reveal basin wide patterns of distinctive wood debris wd accumulations that arise from different mechanisms of wd recruitment hydraulic geometry and physical characteristics of wd individual pieces of wd in an accumulation or jam can be separated into key racked and loose members ten types of wd accumulations are identified based on the mode of recruitment and the orientation of key racked and loose debris relative to the channel axis although some types of wd accumulation have few geomorphic effects others form stable in stream structures that influence alluvial morphology at both subreach and reach length scales ranging from less than 1 to greater than 10 channel widths in the queets river stable accumulations of wd directly influence channel anabranching planform geometry flood plain topography and establishment of long term riparian refugia for old growth forest development the classification of wood debris accumulations in the queets river basin is based on physical observations that offer a template potentially applicable to other forested mountain regions d 2002 elsevier science b v all rights reserved

holocene mississippi river floods and geoarchaeological site formation processes in the sny bottom western illinois usa abstract holocene alluvial deposits are well represented in the sny bottom a reach of the mississippi river in western illinois characterized by the presence of a long anabranch channel the sny prior to its engineered confinement the flood stage mississippi functioned as an anastomosed system comprised of many secondary landscape elements hierarchically arranged to distribute water out across a broad floodplain radiocarbon dated stratigraphic sequences are used to reconstruct the geological history of this river reach as it metamorphosed from a sandy late pleistocene braided floodplain into a system dominated by mud by 7400 cal bp the mississippi migrated to its present position and began to build the natural levee it would use for the remainder of the holocene major subsequent geomorphological adjustments to the system resulted from large floods at ca 6900 4900 3300 and 2000 cal bp valley fill is a complex arrangement of individual sedimentary bodies that accumulated at highly variable rates vertical accretion by sedimentation and soil upbuilding acted together to preserve numerous buried archaeological sites of all ages

anastomosing river system along the subsiding middle yangtze river basin southern china the study focuses on the formation processes of the uprivermost jingjiang reach of three anastomosing river reaches along the middle yangtze river downstream of the three gorges dam site and 1700 km upriver from the seacoast at shanghai in southern china the jingjiang reach consists of large anastomosing channels the songzi hudu anxiang and ouchi rivers which depart from the yangtze trunk channel and flow southward and southeastward up to 200 km into the dongting basin and lake the lake rejoins the yangtze at chenglingji the 7000 km 2 anastomosing reach is characterized by multiple stable low gradient channels 0 00004 m m 4 cm km with low width depth ratios 40 low stream powers 7 w m 2 with very high sedimentation rates 33 5 123 3 mm year in some channels tectonic subsidence caused by the himalayan orogeny is thought to be the primary forcing mechanism in causing the anastomosing channel processes and deposition historical documents have shown that the jingjiang channels were caused by repetitive avulsions southward from the yangtze channel the earliest recorded avulsion occurred in a high flood period before 1644 and subsequent avulsions have continued to modify the topography three major avulsion channels have diverted 14 33 of the discharge and 17 47 of suspended sediment load from the yangtze channel these channels have remained laterally stable a characteristic of anastomosing rivers due to their low gradient silt clay banks densely vegetated natural levees and stable interchannel islands consisting of clayey silt that supports dense riparian vegetation data derived from hydrological gauging stations over the last 45 years demonstrate that total discharge and sediment load of anastomosing channels has decreased by two thirds largely due to sediment aggradation on channel beds reduced sediment load and discharge and human caused channel modification were more pronounced in the eastern channels with the completion of the 3 gorges dam in 2009 the anastomosing channels will cease to carry significant quantities of water and sediment to maintain fluvial vigor in the next 100 years the yangtze main channel may become the only active channel as the anastomosing channels slowly will be infilled c 2004 elsevier b v all rights reserved

fine scale structure of the extratropical tropopause region 1 a vertically high resolved climatology of the thermal and wind structure of the extratropical tropopause region is presented the climatology is based on data from 80 u s radiosonde stations covering the period 1998 2002 time averages for each radiosonde station are computed using the tropopause as a common reference level for all vertical profiles within the mean a strong inversion at the tropopause in the mean vertical temperature gradient is uncovered that is temperature strongly increases with altitude within the lowermost stratosphere this tropopause inversion layer exists on average throughout the investigated extratropics about 30 n to 70 n accordingly the static stability parameter shows considerably enhanced values within the lowermost extratropical stratosphere compared to typical extratropical stratospheric values further aloft conventional averages are not able to capture the tropopause inversion layer mean profiles of the horizontal wind show behavior qualitatively corresponding to thermal wind balance winter and summer exhibit distinctly different climate states in the extratropical tropopause region an approximated potential vorticity is considered and found to be close to well mixed within the troposphere as well as within the tropopause inversion layer this suggests the view of the tropopause inversion layer as representing a dynamically active atmospheric layer some potential implications are discussed

thermal versus dynamical tropopause in upper tropospheric balanced flow anomalies this paper systematically investigates differences between the thermal and the dynamical tropopause for upper tropospheric balanced flow anomalies idealized cyclonic and anticyclonic anomalies are considered which are either axisymmetric or plane symmetric given a distribution of potential vorticity pv the inversion problem is solved numerically to obtain the corresponding balanced flow i e wind and temperature the control parameter is the aspect ratio of the pv anomaly which governs the partitioning into a thermal and a dynamical anomaly for pv anomalies of intermediate and tall aspect ratios the location of the thermal tropopause differs significantly from the location of the dynamical tropopause the thermal tropopause is rather indistinct for intermediate aspect ratios while it is sharp and well defined for both tall and shallow anomalies a barotropic deformation flow field superimposed on a plane symmetric anomaly induces an ageostrophic wind which modifies the static stability throughout the pv anomaly such that the thermal and dynamical tropopauses evolve differently recent observations concerning the correlation between the thermal and ozone tropopauses can be interpreted consistently in terms of the present results

anastomosing river deposits sedimentation rates and basin subsidence magdalena river northwestern colombia south america situated in a tectonically active foreland basin the magdalena river consists of vertically accreting levee confined channels and adjacent extensive wetlands which are interpreted as an anastomosing river sedimentary system equivalent rates of basin filling and subsidence average 3 8 mm yr 1 based on 18 14c dates from five bore holes drilled to depths of 55 m and sediment transport budgets from 35 years of measurement located in a savanna tropical climate anastomosing river deposits of the magdalena are remarkably similar to the anastomosing deposits of the upper columbia river in a temperate cold climate in western canada suggesting that climate is not a controlling factor of anastomosis the geometry of anastomosing channel fills in the magdalena consists of stratigraphically non uniform low sinuous narrow stringers of sand up to 30 m thick by 600 m wide a width depth ratio of 20 thin 1 2 m off channel crevasse splay sand sheets extend laterally up to 10 km distance when buried both sand deposits become encased by lacustrine or marsh mud to form stratigraphic traps while there are few modern anastomosing river systems as compared to braiding and meandering there may be a disproportionately large number of ancient anastomosed fluvial rock sequences due to the rapid rate of vertical accretion such a different depositional style and geometry of sand bodies have considerable significance in the interpretation of some ancient fluvial rock sequences because it provides an alternative to the meandered and braided river deposition models

overbank and channelfill deposits of the modern yellow river delta abstract the huanghe is noted for its high transport rate of silt and clay which may reach depth averaged values of 200 kg m 3 during peak discharge the sediment load transported through the river on entering the delta plain amounts to 1012 kg per year in contrast to most other large deltas only one distributary channel is active at any one time the high sediment load causes the rivermouth to prograde at a yearly rate of 1 4 km into the shallow less than 20 m deep bohai gulf the vertical aggradation of the channel belt and mouth bar complex is also rapid decimetres per year on average so that after a normal average of twelve years increasing channel instability and avulsion create the start of a new delta lobe a series of satellite images covering the last fifteen years has provided insight in the evolution of the river pattern as well as the progradation of the delta front a newly developed distributary passes from a multichannel to a single straight channel system and ends with the formation of meanders the protruding mature delta lobe shows a radiating pattern of crevasse channels overbank crevasse deposits are made of vertically stacked dm scale waning flow sequences structurally characterized by from bottom to top small scour and fills even parallel lamination and climbing ripple crosslamination accumulation rates on crevasse splays can be predicted on the basis of estimated river sediment discharge it can be concluded that each sequence has been deposited within a few hours and that tidal waterlevel fluctuations may have played a role in the generation of a single sequence

fluvial processes in a forested anastomosing river flood partitioning and changing flow patterns in an effort to further our understanding of multiple channel systems this paper presents data on the flood response of channels in one of the last wooded semi natural anastomosing systems in europe the gearagh ireland is characterized by hundreds of small islands separated by interconnected channels of low slope these include channels that cross islands at right angles to the main flow and blind anabranching channels islands are relatively stable and wooded with evidence of division by channel erosion and growth by in channel sedimentation four active zone cross profiles were surveyed each containing between seven and 13 channels velocities were measured in several channels before and during two separate floods from these observations channels have been categorised into three types fast shallow and trapezoidal slow deep and more irregular and flood channels during the floods interchannel flows were caused by variations in water surface elevations due to backing up behind debris dams and it is suggested that this is the origin of the anomalous cross island channels and one cause of island division another potential cause of island division blind anabranching channels is the result of concentrated bank scour between root masses biotic components such as debris dams tree root masses and tree throw pits play a key role in the partitioning of flow and cause variations in channel velocities and the overbank velocity distribution the implications of these observations for channel pattern maintenance are briefly discussed

the evolution of the great hungarian plain fluvial system fluvial processes in a subsiding area from the beginning of the weichselian abstract in the great hungarian plain ghp one of the most complex fluvial systems of europe developed through tectonic and climatic factors and vegetation change the aim of the present study is to summarise these controlling factors and to describe the evolution of the ghp special attention is paid to the latest results on late weichselian and holocene development in the tisza river and their effects on the river s largest tributary the maros river several tectonically active subsiding basins existing in the ghp have determined the direction of river courses and erosional accumulational fluvial processes as a result of uneven subsidence the river s flow routes have shifted frequently for example the danube and the tisza shifted 80 100 km abandoning their alluvial fans where extensive aeolian processes started upstream from the subsiding areas incision propagated headward which resulted in the development of floodplain levels and terraces though climate and vegetation changes also simultaneously influenced the rivers hydro morphology channel pattern changes were found just along the margin of the plain and only meandering paleo channels remained in the center of the ghp during dry and cold periods braided patterns appeared in the alluvial fans most likely the result of abundant sediment supply and due to the inability of sparse riparian vegetation to stabilise the banks effectively based on paleo discharge calculations by the end of the pleistocene the rivers of the ghp produced three to eight times more discharge than they do currently and discharge levels continuously decreased during the holocene however due to the long length of the rivers there is a considerable time lag between the response rates of the different river sections which makes creating paleo hydrological reconstructions even more difficult

synoptic scale disturbances with circular symmetry abstract ate balanced flow structure of various classic synopitc scale disturbances is reviewed using the invertibility principle for isentropic potential vorticity ipv distributions complete solutions are shown for cold and warm core structures of various types the basic model imagines the tropopause to be the interface between the lower potential vorticity of the troposphere and the approximately six fold larger value typical of the lower stratosphere the sensitivity of the structure of the potential temperature variation along the tropopause and at the surface is described results are presented in diagrammatic form to allow easy diagnosis of the vortex structure from synoptic data available at perhaps only a few levels the point is made that upper air ipv and surface potential temperature distributions are often the most crucial in accounting for the balanced flow structure

hydrogeophysical investigations in the western and north central okavango delta botswana based on helicopter and ground based transient electromagnetic data and electrical resistance tomography abstractthe okavango delta is a huge alluvial megafan in northwestern botswana despite numerous geologic geochemical geophysical and hydrologic investigations over the past half century the sedimentary units underlying the delta are largely unknown to address this issue helicopter transient electromagnetic data htem have been collected across the entire delta and coincident ground based electrical resistance tomographic ert and transient electromagnetic tem data have been acquired at two locations one along the delta s western margin and one in its north central region inversions of the htem data have yielded three layer resistivity models in which a relatively homogeneous conductive layer is sandwiched between two resistive layers the three layer htem model is reproduced in models obtained from independently and jointly inverting the ground based data the conductive layer s low resistivities and depths to its upper and lower boundaries are practically equal in the htem and ground based m

the nysa morava zone an active tectonic domain with late cenozoic sedimentary grabens in the western carpathians foreland ne bohemian massif we give an interpretive review of the geological evolution of the nysa morava zone nmz a late cenozoic tectonically active region of the ne bohemian massif located at its contact with the western carpathians orogenic front this crustal domain delimited by generally nw se striking fault system is characterised by oligo miocene and plio pleistocene volcanic activity regionally anomalous weak historical and present day seismicity and increased co2 flux the nmz hosts several elongated mostly nw se trending graben like sedimentary basins upper morava basin system which are filled by more than 300 m thick succession of clastic fluvial lacustrine sediments of pliocene quaternary age based on geometric relations basin architecture coincidence of seismicity with co2 escape and sparse focal mechanism data a model is proposed which explains this active domain as a transfer zone developed between major wnw ese and nw se faults in a right lateral transpressional setting it is suggested that slow horizontal slip at these faults resulted in local permutations of the largest and medium stress directions and formation of transtensional crustal domains in the nmz moreover relation of the nmz to the alpine carpathian system and sedimentary grabens in its foreland is discussed the absence of paleogene and lower miocene deposits suggests that subsidence in the nmz was commenced later than in the european cenozoic rift system ecris which is in agreement with later thrusting in western carpathians at 17 ma the quantitative contrasts to the ecris in terms of faulting and subsidence rates are explained by the absence of lithospheric crustal thinning in the nmz

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

experimental study of avulsion frequency and rate of deposition in existing models of alluvial architecture it is typically assumed that mean avulsion frequency is independent of sedimentation rate however if avulsion is driven by superelevation of a river bed above its surrounding flood plain one might expect avulsion rate to increase with sedimentation rate we have carried out a series of experiments with laboratory scale fluvial fans in which we measured the frequency of apical avulsions as a function of mean sedimentation rate on the fan avulsion frequency increased strongly with increasing sedimentation rate and then stabilized as mass flows began to influence deposition in the regime of increasing avulsion frequency the added volume of sediment needed to trigger an avulsion decreased with increasing sedimentation rate although our experimental results cannot simply be scaled up to natural rivers they suggest the possibility of coupling between avulsion frequency and sedimentation rate that would be strong enough to change qualitatively the results of existing models of alluvial architecture these models should be applied with caution until avulsion mechanics are better understood

brunovistulian terrane bohemian massif central europe from late proterozoic to late paleozoic a review the brunovistulian terrane represents a microcontinent of enigmatic proterozoic provenance that was located at the southern margin of baltica in the early paleozoic during the variscan orogeny it represented the lower plate at the southern margin of laurussia involved in the collision with the armorican terrane assemblage in this respect it resembles the avalonian terrane in the west and the istanbul zone in the east there is a growing evidence about the presence of a devonian back arc at the margin of the brunovistulian terrane the early variscan phase was characterized by the formation of devonian extensional basins with the within plate volcanic activity and formation of narrow segments of oceanic crust the oldest visean flysch of the rheic rhenohercynian remnant basin protivanov andelska hora and horni benesov formations forms the highest allochthonous units and contains together with slices of silurian bohemian facies clastic micas from early paleozoic crystalline rocks that are presumably derived from terranes of armorican affinity although provenance from an active brunovistulian margin cannot be fully excluded either the development of the moravo silesian late paleozoic basin was terminated by coal bearing paralic and limnic sediments the progressive carboniferous stacking of nappes and their impingement on the laurussian foreland led to crustal thickening and shortening and a number of distinct deformational and folding events the postorogenic extension led to the formation of the terminal carboniferous early permian boskovice graben located in the eastern part of the brunovistulian terrane in front of the crystalline nappes the highest allochthonous westernmost flysch units locally with the basal slices of the devonian and silurian rocks thrusted over the silesicum in the nw part of the brunovistulian terrane may share a similar tectonic position with the giessen harz nappes the silesicum represents the outermost margin of the brunovistulian terrane with many features in common with the northern phyllite zone at the avalonia armorica interface in germany

the extratropical tropopause inversion layer global observations with gps data and a radiative forcing mechanism global characteristics of the extratropical tropopause inversion layer identified in radiosonde observations by birner are studied using high vertical resolution temperature profiles from gps radio occultation measurements the gps data are organized according to the height of the thermal tropopause in each profile and a temperature inversion layer above the tropopause with an average magnitude of 3 5 k is found to be a ubiquitous climatological feature the gps data show that the inversion layer is present for all seasons in both hemispheres spanning the subtropics to the pole and there is not strong longitudinal structure dependence of the inversion layer on upper troposphere vorticity is studied while anticyclones exhibit a substantially stronger inversion than cyclones as expected from balanced dynamics the inversion is evident for all circulation types radiative transfer calculations indicate that strong gradients in both ozone and water vapor near the tropopause contribute to the inversion significant absorption of both longwave and shortwave radiation by ozone occurs warming the region above the tropopause water vapor near and immediately above the tropopause contributes to cooling effectively enhancing the inversion

avulsions channel evolution and floodplain sedimentation rates of the anastomosing upper columbia river british columbia canada ages of channels of the anastomosing upper columbia river south eastern british columbia canada were investigated in a cross valley transect by c 14 dating of subsurface floodplain organic material from beneath levees the avulsion history within the transect was deduced from these data and morphological stages in channel development were recognized additionally floodplain sedimentation rates were established the new data demonstrate that the upper columbia river is a long lived dynamic anastomosing system results show that anastomosis at the study location has persisted since at least 2700 cal years bp with avulsions occurring frequently at least nine channels have formed in the studied cross valley transect within the past 3000 years channel lifetimes from formation to abandonment appear to be highly variable ranging from approximately 800 to 3000 years log jams provoking avulsions and or silting up of old channels are proposed as reasons for this variability long term average floodplain sedimentation rates appear to be significantly lower than previously proposed by smith 1983 int assoc sedimentol spec publ 6 155 168 a long term 4550 years average of 1 75 mm per year after compaction was based on c 14 dates whilea short term sedimentation rate of 0 8 mm was determined for a single relatively small seasonal flood in 1994 using sediment traps however short term sedimentation rates vary considerably over the floodplain with levees aggrading up to four times faster than floodbasins channels of the upper columbia river anastomosed reach follow a consistent pattern in their development with each stage being characterized by different morphology and processes channel evolution comprises the following succession 1 avulsion stage in which a crevasse splay channel deepens by scour and levee sedimentation 2 widening and deepening stage in which bank slumping and bed scouring dominates 3 infilling stage in which either channel narrowing bank accretion or channel shallowing bed accretion takes place and 4 abandonment stage in which the residual remnant channel is filled exclusively by silt clay and organic material vertical stacking super imposition of active channels on recent channel fill sand bodies is a notable feature of the upper columbia river which suggests that reoccupation of residual channels is a common process

rapid sea level rise and holocene climate in the chukchi sea three new sediment cores from the chukchi sea preserve a record of local paleoenvironment sedimentation and flooding of the chukchi shelf 50 m by glacial eustatic sea level rise radiocarbon dates on foraminifera provide the first marine evidence that the sea invaded hope valley southern chukchi sea 53 m as early as 12 ka the lack of significant sediment accumulation since ca 7 ka in hope valley southeastern chukchi shelf is consistent with decreased sediment supply and fluvial discharge to the shelf as deglaciation of alaska concluded abundant benthic foraminifera from a site west of barrow canyon indicate that surface waters were more productive 4 6 ka and this productivity varied on centennial time scales an offshore companion to this core contains a 20 m record of the holocene these results show that carefully selected core sites from the western arctic ocean can have a temporal resolution equal to the best cores from other regions and that these sites can be exploited for high resolution studies of the paleoenvironment

geomorphons a pattern recognition approach to classification and mapping of landforms abstract we introduce a novel method for classification and mapping of landform elements from a dem based on the principle of pattern recognition rather than differential geometry at the core of the method is the concept of geomorphon geomorphologic phonotypes a simple ternary pattern that serves as an archetype of a particular terrain morphology a finite number of 498 geomorphons constitute a comprehensive and exhaustive set of all possible morphological terrain types including standard elements of landscape as well as unfamiliar forms rarely found in natural terrestrial surfaces a single scan of a dem assigns an appropriate geomorphon to every cell in the raster using a procedure that self adapts to identify the most suitable spatial scale at each location as a result the method classifies landform elements at a range of different spatial scales with unprecedented computational efficiency a general purpose geomorphometric map an interpreted map of topography is obtained by generalizing allgeomorphons to a small number of the most common landform elements due to the robustness and high computational efficiency of the method high resolution geomorphometric maps having continental and even global extents can be generated from giga cell dems such maps are a valuable new resource for both manual and automated geomorphometric analyses in order to demonstrate a practical application of this new method a 30 m cell 1 geomorphometric map of the entire country of poland is generated and the features and potential usage of this map are briefly discussed the computer implementation of the method is outlined the code is available in the public domain

active tectonics research using trenching technique on the south eastern section of the sudetic marginal fault ne bohemian massif central europe abstract the nw se striking sudetic marginal fault smf is one of the most conspicuous tectonic structures in central europe it controls the pronounced morphotectonic escarpment of the sudetic mountains for a length of 130 km this paper presents the results of trenching on the smf undertaken in order to assess activity of the fault the trenching technique has not hitherto been applied on either this particular fault system or elsewhere in the bohemian massif however it is the most effective tool for near surface fault investigation in areas that are well vegetated and therefore devoid of fault outcrops moreover the study area is situated in an intraplate region with a low displacement rate which is exceeded by an erosion rate and does not favor the preservation of fault scarps the trench sites were selected from prior dem analyses geomorphological fieldwork and geophysical sounding the trenches exposed a range of lithologies of variscan crystalline rocks and caenozoic sediments at least four phases of faulting have been distinguished based on structural data succession and age of the deformed sediments reverse faulting n160 e which displaced the miocene sediments over the crystalline rocks post dates their deposition 15 ma and pre dates late glacial gelifluction horizontal movements that have affected the miocene deposits along a structure striking n35 e have the same wide time constraint younger reverse faulting which caused a co seismic relief step post dates the late glacial gelifluction but preceded the early holocene colluvium deposition 10 940 140 cal yrs bp normal faults striking n145 e which cut the miocene unit might have been reactivated after the early holocene colluvial sedimentation but before the buried soil 430 120 cal yrs bp moreover based on the identified prehistoric earthquake respective minimum moment magnitude m 6 3 and slip rate 0 03 mm year were estimated

balanced asymmetries of waves on the tropopause tropopause disturbances have long been recognized as important features for extratropical weather since they produce organized vertical motion in the troposphere observations of cyclonic tropopause disturbances show localized depressions of the tropopause with stratospheric values of potential vorticity extending to lower altitudes anticyclonic disturbances are associated with comparatively smaller upward deflections of the tropopause analytical solutions for nonlinear interfacial wave motions are derived for an intermediate balanced dynamics based on small rossby number asymptotics beyond quasigeostrophy traveling edge wave solutions reveal realistic asymmetries such that cyclones are associated with greater deflections of the interface as well as larger anomalies in pressure and vertical motion compared to anticyclones

electrical resistivity imaging of anastomosing river subsurface stratigraphy and possible controls of fluvial style change in a graben like basin czech republic abstract subject to frequent channel avulsions due to the increased frequency of floods rise of base level and or sediment overloading anastomosing rivers are sensitive to external climatic or tectonic forcing in sedimentary basins the morava river czech republic shows a well developed holocene anastomosis confined to the pull apart type upper morava basin umb we studied the stratigraphy and aggradation rates of the umb using electrical resistivity tomography ert dipole electromagnetic profiling demp core data and radiocarbon ages with the aim of identifying factors triggering the anastomosis at the pleistocene holocene transition the ert and demp proved to be excellent tools to visualize the shape and thickness of floodplain depositional units abandoned meanders scroll bars etc the major geophysical surfaces identified are the base of the late weichselian braided stream deposits osl age 34 53 3 42 ka interpreted as a palaeo stream gradient of the morava river and their transition to holocene floodplain deposits in the late weichselian the river aggraded at an average rate of 0 2 mm yr the holocene oldest 14c age 7 066 0 072 ka short term aggradation rates reached up to 13 7 mm yr but the average long term rates 0 07 to 0 4 mm yr are comparable to the late weichselian the stratigraphy and sediment ages indicate that the onset of anastomosis was not likely associated with accelerated basin subsidence possible controls of the anastomosis include upstream control by numerous tributaries large wood debris in the floodplain forests and changes in land use the tectonic and geomorphic context of the umb pull apart basin probably favoured the development of the anastomosis