space geodetic observations of nazca south america convergence across the central andes space geodetic data recorded rates and directions of motion across the convergent boundary zone between the oceanic nazca and continental south american plates in peru and bolivia roughly half of the overall convergence about 30 to 40 millimeters per year accumulated on the locked plate interface and can be released in future earthquakes about 10 to 15 millimeters per year of crustal shortening occurred inland at the sub andean foreland fold and thrust belt indicating that the andes are continuing to build little 5 to 10 millimeters per year along trench motion of coastal forearc slivers was observed despite the oblique convergence

controls on overbank deposition in the upper mississippi river abstract floodplains contain valuable stratigraphic records of past floods but these records do not always represent flood magnitudes in a straightforward manner the depositional record generally reflects the magnitude frequency and duration of floods but is also subject to storm scale hysteresis effects flood sequencing effects and decade scale trends in sediment load many of these effects are evident in the recent stratigraphic record of overbank floods along the upper mississippi river umr where the floodplain has been aggrading for several thousand years on low lying floodplain surfaces in iowa and wisconsin 137cs profiles suggest average vertical accretion rates of about 10 mm year since 1954 these rates are slightly less than rates that prevailed earlier in the 20th century when agricultural land disturbance was at a maximum but they are still an order of magnitude greater than long term average rates for the holocene as a result of soil conservation practices accretion rates have decreased in recent decades despite an increase in the frequency of large floods the stratigraphic record of the upper mississippi river floodplain is dominated by spring snowmelt events because they are twice as frequent as rainfall floods last almost twice as long and are sometimes associated with very high sediment concentrations the availability of sediment during floods is also influenced by a strong hysteresis effect peak sediment concentrations generally precede the peak discharges by 1 4 weeks and concentrations are usually low the great flood of 1993 on the mississippi river focused attention on the geomorphic effectiveness and stratigraphic signature of large floods at mcgregor where the peak discharge had a recurrence interval of 14 years the flood was most notable for its long duration 168 days above 1600 m3s 1 high sediment concentrations three episodes 180 mg l and large suspended load 1 71 mt the flood of 2001 despite its greater magnitude recurrence interval 70 years was associated with relatively low sediment concentrations

geomorphic effectiveness a linear concept in a non linear world geomorphic effectiveness has been an influential concept in geomorphology since its introduction by reds wolman and john miller in 1960 it provided a much needed framework to assess the significance of an event by comparing event magnitude to the resultant geomorphic effects initially this concept was applied primarily in river channels under the linear assumption that geomorphic responses to similarly sized flood events will be consistent numerous authors have since attempted to quantify a direct proportional relationship between event magnitude and different forms of geomorphic response in a variety of geomorphic settings in doing so these investigations applied an array of metrics that were difficult to compare across different spatiotemporal scales and physiographic and geomorphic environments critically the emergence of other geomorphic concepts such as sensitivity connectivity thresholds and recovery has shown that relationships between causes events and geomorphic effects responses are often complex and non linear this paper disentangles the complex historical development of the geomorphic effectiveness concept and reviews the utility of various metrics for quantifying effectiveness we propose that total energy joules is the most appropriate metric to use for quantifying the magnitude of disturbance events cause and volumetric sediment flux associated with landform modification is the most appropriate metric for quantifying geomorphic effects while both metrics are difficult to quantify they are the only ones which facilitate comparison across a range of spatiotemporal scales comparability in a variety of geomorphic environments flexibility the geomorphic effectiveness concept can continue to be useful provided that geomorphologists use flexible and comparable metrics today geomorphologists are better prepared to consider the influence of non linear processes on determinations of geomorphic effectiveness allowing investigators to not only determine if a disturbance event was effective but also to explain why or why not copyright

morphological and historical resilience to catastrophic flooding the case of lockyer creek se queensland australia this study aimed to determine the extent of geomorphic change resulting from the catastrophic flood of 2011 in the lockyer valley in southeast queensland and to place these impacts within a history of geomorphic adjustment aerial photographs dated from 1933 to 2011 and parish maps and historical on ground photographs dating from 1865 to 1966 were examined for evidence of geomorphic adjustment since european settlement in the first half of the nineteenth century eleven forms of geomorphic adjustment were identified in three categories erosional depositional and reorganisational only 26 of the lockyer creek channel length has been affected by some form of geomorphic adjustment since european settlement most of this adjustment was localised and dominated by reorganisation of geomorphic unit assemblages within the macrochannel and sediment deposition on floodplains no wholesale river change in the form of lateral migration or avulsion has occurred and the river s morphology has remained relatively characteristic over time i e morphology remains relatively uniform in a reach averaged sense geomorphic responses to extreme flooding have been minor and the geomorphic effectiveness of floods in this system including the 2011 flood has been limited over the last several hundred years the system is likely still adjusting to past flooding events that set the morphology of the current system i e the macrochannel a form of event resilience has resulted in this system such that it is less prone to geomorphic adjustment during events than would normally be considered geomorphically effective as a result antecedent controls on macrochannel presence and capacity are considered to be first order controls on contemporary forms and processes in this system work is required to test whether the resilience of this system will hold in the future with more extreme episodes of flooding predicted to occur in this region under future climate change

determining lateral migration rates of meandering rivers using fallout radionuclides abstract we explore the novel technique of using short lived fallout radionuclides to date fluvial surfaces with the goal of determining lateral migration rates specifically we use the fallout radionuclide 210pb half life t1 2 22 3 years to determine the lateral migration rates of meandering reaches on the winooski river vt the upper connecticut river nh and the genesee river ny we find that particularly near the channel 210pbex inventories are affected by the initial 210pbex inventories of freshly deposited sediment inheritance inheritance differs at each site with lower inheritance occurring at sites with larger upstream drainage areas after accounting for inheritance 210pbex inventories in surface sediments along a transect orthogonal to the channel yield migration rates of 0 7 3 1 and 4 7 m y for the winooski connecticut and genesee rivers respectively these rates agree well with values derived independently from historical aerial photography variations in 210pbex inventories along the transects also provide details of the channel migration histories not evident from the limited available aerial photographs including evidence for both nearly constant linear and episodic channel migrations results suggest the broad applicability and added value of our approach for quantifying decadal scale variations in fluvial surface ages

geomorphic effects flood power and channel competence of a catastrophic flood in confined and unconfined reaches of the upper lockyer valley southeast queensland australia flooding is a persistent natural hazard and even modest changes in future climate are believed to lead to large increases in flood magnitude previous studies of extreme floods have reported a range of geomorphic responses from negligible change to catastrophic channel change this paper provides an assessment of the geomorphic effects of a rare high magnitude event that occurred in the lockyer valley southeast queensland in january 2011 the average return interval of the resulting flood was similar to 2000 years in the upper catchment and decreased to similar to 30 years downstream a multitemporal lidar derived dem of difference dod is used to quantify morphological change in two study reaches with contrasting valley settings confined and unconfined differences in geomorphic response between reaches are examined in the context of changes in flood power channel competence and degree of valley confinement using a combination of one dimensional 1 d and two dimensional 2 d hydraulic modelling flood power peaked at 9800 w m 2 along the confined reach and was 2 3 times lower along the unconfined reach results from the dod confirm that the confined reach was net erosional exporting similar to 287 000 m 3 of sediment whilst the unconfined reach was net depositional gaining similar to 209 000 m 3 of sediment 70 of the amount exported from the upstream confined reach the major sources of eroded sediment in the confined reach were within channel benches and macrochannel banks resulting in a significant increase of channel width in the unconfined reach the benches and floodplains were the major loci for deposition whilst the inner channel exhibited minor width increases the presence of high stream power values and resultant high erosion rates within the confined reach is a function of the higher energy gradient of the steeper channel that is associated with knickpoint development dramatic differences in geomorphic responses were observed between the two adjacent reaches of contrasting valley configuration the confined reach experienced large scale erosion and reorganisation of the channel morphology that resulted in significantly different areal representations of the five geomorphic features classified in this study c 2013 elsevier b v all rights reserved

temporal distribution of suspended sediment transport in a mediterranean basin the lower tordera ne spain abstract suspended sediment dynamics are still imperfectly understood especially in areas of mediterranean climate with strong seasonal contrasts where few studies have been conducted the aim of this study is to analyze the variability in the suspended sediment load at different temporal scales within flood variability monthly seasonal and annual in the tordera river 894 km 2 located in northeastern spain suspended sediment samples were obtained during base flows q 3 5 m 3 s 1 and flood events q 3 5 m 3 s 1 the analysis of the variability in the suspended sediment is structured in two consecutive steps i the construction of statistical relations between suspended sediment concentrations c and discharge q and ii the application of those relations to assess the suspended sediment yield the results show that in a single event the sediment peak generally precedes the peak discharge following a clockwise hysteretic loop furthermore it was observed that the reduction in the suspended sediment concentrations in a sequence of events can be mainly associated with a phenomenon of sediment exhaustion the total amount of suspended sediment transported during a single flood is thus related to its duration and time during the year as well as to its magnitude at a seasonal scale the export of suspended sediment takes place in two phases i sediment preparation and ii sediment transfer and exhaustion during the latter phase the exhaustion of the sediment load is primarily related to the sequence of flood events at the annual scale the results show high inter annual variability according to the number of floods recorded yearly since almost all the suspended load is transported during those events

variations in flood magnitude effect relations and the implications for flood risk assessment and river management abstract in spite of major physical impacts from large floods present river management rarely takes into account the possible dynamics and variation in magnitude impact relations over time in flood risk mapping and assessment nor incorporates feedback effects of changes into modelling using examples from the literature and from field measurements over several decades in two contrasting environments a semi arid region and a humid temperate region temporal variations in channel response to flood events are evaluated the evidence demonstrates how flood physical impacts can vary at a location over time the factors influencing that variation on differing timescales are examined the analysis indicates the importance of morphological changes and trajectory of adjustment in relation to thresholds and that trends in force or resistance can take place over various timescales altering those thresholds sediment supply can also change with altered connectivity upstream and changes in state of hillslope channel coupling it demonstrates that seasonal timing and sequence of events can affect response particularly deposition through sediment supply duration can also have a significant effect and modify the magnitude relation lack of response or deposits in some events can mean that flood frequency using such evidence is underestimated a framework for assessment of both past and possible future changes is provided which emphasises the uncertainty and the inconstancy of the magnitude impact relation and highlights the dynamic factors and nature of variability that should be considered in sustainable management of river channels

reaction and relaxation in a coarse grained fluvial system following catchment wide disturbance abstract the waiapu river catchment drainage area of 1734 km2 is one of the most prolific conveyors of sediment in the world annually delivering roughly 35 mt of fine material to the ocean from eroding gullies hillslopes and reworked sediment on valley floors tectonic and geologic influences in combination with a dynamic climate influenced by tropical cyclones and clearance of vegetation from steep hillslopes predisposes this region to high rates of erosion the bedload sediment regime of the river is strongly influenced by several exceptionally large gullies and gully complexes that produce a coarse grained poorly sorted sediment mixture rapid abrasion and breakdown leads to high rates of suspended sediment yield a wave of bedload material manifesting as elevated bed levels and significant widening of active alluvial fills has been triggered by large inputs of hillslope material from a few key tributary catchments following cyclone bola in 1988 we review the evidence for the relaxation process of the sedimentary system in the subsequent 29 years appraising some of the legacy effects that may endure as associated with reworking of the considerable alluvial stores within the waiapu system we use structure from motion sfm techniques and archival aerial photos to quantify changes in sediment storage at the base of two major gully systems in recent decades a record of over 850 cross section surveys at 62 sites on 10 rivers throughout the catchment 1958 2017 indicates recent transition from a trend of continuous accumulation to downcutting and remobilisation of valley bottom deposits the channel cross sections provide a minimum estimate of sediment flux from source areas to the lower reaches of the river giving a rudimentary but spatially extensive picture of the wave of material cascading through the drainage network the largest impacts occur in the upper steepland rivers closest to the landslide derived sediment supply transport rates here as inferred from cross section change are at a maximum during an aggradational phase following cyclone bola then taper off despite the large sediment accumulations remaining in the system as of 2017 the river is in the process of incising the upper extents of this deposit on a trajectory of recovery toward pre bola conditions the compilation of cross section data provides us with new insights into the sensitivity of particular sites in the landscape as well as the changing relationship between reach sediment storage and transport rates during the response and relaxation phase of a major disturbance in a large catchment

impact of reach geometry on stream channel sensitivity to extreme floods predicting spatial and temporal variations in bank erosion due to extreme floods presents a long standing challenge in geomorphology we develop two methodologies for rapid regional scale assessments of stream reaches susceptible to channel widening the first proposes that channel widening occurs when unit stream power exceeds a critical threshold 300 w m2 the second is motivated by the observation that widening often occurs at channel bends we introduce a new metric the bend stress parameter which is proportional to the centripetal force exerted on a concave bank we propose that high centripetal forces generate locally high bank shear forces and enhance channel bank erosion we test both metrics using the geomorphic signature of tropical storm irene 2011 on the white and the saxtons rivers vermont specifically we test if reaches where significant channel widening occurred during irene required one or both metrics to exceed threshold values we observe two distinct styles of channel widening where unit stream power and bend stress parameter are high widening is usually due to bank retreat elsewhere widening is usually due to the stripping of the upstream end of mid channel islands excluding widening associated with the stripping of the heads of mid channel islands almost all the widening 98 occurred along reaches identified as susceptible to widening the combined metrics identify up to one quarter of the reaches lacking susceptibility to channel widening copyright 2014 john wiley sons ltd

predicting vertical accretion rates at an archaeological site on the mississippi river floodplain effigy mounds national monument iowa abstract the sny magill unit of effigy mounds national monument iowa contains the largest cluster of prehistoric effigy mounds on public land in north america the mounds are situated atop a low terrace of the upper mississippi river where they are slowly being buried by overbank deposition during floods the terrace surface includes forest soils with argillic bt or cambic bw horizons developed in up to 1 m of loamy overbank deposits on top of pleistocene sand and gravel radiocarbon evidence suggests that overbank deposits have accumulated since the end of the mound building period about 700 years bp yielding a vertical accretion rate of about 0 6 mm yr 1 on the basis of 137cs analysis accretion rates over the past 40 50 years average 1 25 2 07 mm yr 1 with some evidence for a decreasing rate since 1964 if these accretion rates are projected forward several of the effigy mounds could be buried by flood deposits within 150 300 years this 137cs derived estimate agrees closely with an estimate of burial times based on flood frequency and observed flood deposit thickness during recent floods however the floodplain and backwater environments of the upper mississippi river are aggrading much more rapidly than the sny magill terrace surface suggesting that burial of the entire terrace could occur within 80 400 years and the entire mound group could be buried within 150 850 years the projected accretion rates and time to burial are subject to large uncertainties because of environmental change in the watershed including recent trends toward increasing flood stages and decreasing suspended sediment loads

an integrated approach for investigating geomorphic response to extreme events methodological framework and application to the october 2011 flood in the magra river catchment italy a high magnitude flash flood which took place on 25 october 2011 in the magra river catchment 1717 km2 central northern italy is used to illustrate some aspects of the geomorphic response to the flood an overall methodological framework is described for using interlinked observations and analyses of the geomorphic impacts of an extreme event the following methods and analyses were carried out i hydrological and hydraulic analysis of the event ii sediment delivery by event landslide mapping iii identification and estimation of wood recruitment deposition and budgeting iv interpretation of morphological processes by analysing fluvial deposits v remote sensing and geographic information system gis analysis of channel width changes in response to the high magnitude hydrological event a large number of landslides occurred consisting of earth flows soil slips and translational slides and a large quantity of wood was recruited in most part deriving from floodplain erosion caused by bank retreat and channel widening the most important impact of the flood event within the valley floor was an impressive widening of the overall channel bed and the reactivation of wide portions of the pre event floodplain along the investigated unconfined or partly confined streams total investigated length of 93 5 km the channel width after the flood was up to about 20 times the channel width before the event the study has shown that a synergic use of different methods and types of evidence provides fundamental information for characterizing and understanding the geomorphic effects of intense flood events the prediction of geomorphic response to a flood event is still challenging and many limitations exist however a robust geomorphological analysis can contribute to the identification of the most critical reaches copyright 2016 john wiley sons ltd

outburst flood evolution at russell glacier western greenland effects of a bedrock channel cascade with intermediary lakes abstract glacial lake outburst floods have produced a distinctive and widespread quaternary record both onshore and offshore via widespread and intense geomorphological impacts yet these impacts remain poorly understood due to a lack of modern analogues this study therefore makes a systematic quantification of the evolution of a bedrock channelled outburst flood channel topography was obtained from digitised aerial photographs a 5 m grid resolution dem and bathymetric surveys flood inundation was measured in the field from dgps measurements flood evolution was analysed with application of a numerical model novel flood metrics including rate of rise to peak and persistence above a value of hydraulics were calculated the key findings were that outburst floods i that enter intermediary lakes are dramatically attenuated in terms of propagation whilst basin filling proceeds to the outlet level dissipated of energy due to considerable flow recirculation during the rising stage of the flood and after overtopping of the outlet are moderated in terms of peak discharge ii can have kinematic waves that are introduced to a flood via hydraulic ponding iii may develop a partitioning of flow regimes for instantaneous peak discharge bed shear stress and froude number due to time transgressive changes in channel cross section specifically between inner channel and overbank regions furthermore normalised change in cross sectional area and normalised change in channel slope can be used to suggest the relative magnitude of instantaneous peak discharge net erosion along a reach can be related to hydraulic persistence above a marker value and net deposition can be related to a time to peak value reconstructions of quaternary outburst floods should consider the importance of including intermediary lakes modern hazard mitigation studies could usefully note the potential use of reservoirs as an outburst flood alleviation resource

event sequence and sediment exhaustion in the lower panuco basin mexico abstract although large tropical river systems transport the majority of the world s runoff and sediment few studies have examined the dynamics of suspended sediment transport in this setting this includes mexico which contains two of the larger river basins draining into the gulf of mexico this study provides a detailed analysis of discharge q and suspended sediment transport dynamics for the lower panuco basin 98 227 km2 of eastern mexico including the lower moctezuma lower tamuin and panuco rivers daily values of discharge and suspended sediment concentration ssc are examined for three stations spanning from the late 1950s to early 1990s although the panuco is a large basin the relationship between discharge and suspended sediment concentration represents a departure from the oft reported study by heidel trans am geophys union 37 1956 56 instead of sediment lagging discharge the sediment wave precedes discharge by an average of 1 7 days displaying pronounced clockwise positive hysteresis this may be due to the sources of runoff and sediment which are derived primarily in the lower reaches of the basin because of precipitation patterns geology and basin morphometry the distinct differences in lithology between the tamuin and moctezuma basins which join in the coastal plain to form the rio panuco allow the influence of geologic setting to be considered q ssc relations display positive hysteresis where the sediment is derived from erodible tertiary shale deposits in the moctezuma basin in contrast q ssc relations in the rio tamuin which transports less suspended sediment because of its karstic setting are more linear due to these relations being dependent on the entrainment of bed material consideration of the sequence of events during the rainy season suggests that much of the hillslope derived sediment is flushed through the system by early events which would occur because of exhaustion of hillslopes sediments q ssc relations are increasingly linear during later events in the rio panuco which is likely due to these events transporting a higher proportion of sediment entrained from the channel this is manifest by a reduction in lead times as the number of days between peak ssc and peak q for early and late events significantly decreases from 2 6 to 0 9 respectively large events 750 m3 s in the latter part of summer and early fall having high suspended sediment concentrations could be due to the replenishment of hillslope sediments or due to the contribution of sediment from source areas that were not previously exhausted the findings from this study are likely common to most drainage systems having seasonal bimodal streamflow regimes whereas the seasonal signature of q ssc relations is likely enhanced in those settings where agriculture is a major component of the landscape

geomorphic impacts of flash flooding in a forested headwater basin abstract geomorphic impacts of a july 2001 flood in the hungry mother basin near marion virginia were examined to shed light on the relationships between channel characteristics and the frequency of channel modifying discharges creeks in the study area have been observed for many years with no significant channel changes since at least 1985 the 2001 flood had a recurrence interval of 200 years and caused the only channel change bank erosion and transport of coarse channel material observed in recent decades the paucity of fines in channels before or after the flood and the absence of sub sand sized material in the flood deposits indicates that normal frequent well below bankfull flows are sufficient to transport the apparently limited supply of fines the large particles transported during the 2001 flood after years of inactivity indicate that relatively rare floods are necessary to mobilize this material this suggests the notion of a bimodal dominant discharge on the one hand frequent flows considerably below bankfull levels are sufficient to maintain the channel and prevent significant accumulation of fine sediments and organic matter on the other hand rare floods are necessary to transport the coarser bed material and erode channel banks in the hungry mother area bed material has no relationship to normal flows or to flows with recurrence intervals on the order of 1 3 years bankfull discharge is apparently not related to either the maintenance or channel changing dominant discharges these results suggest that the use of channel dimensions and or bed material as surrogate indicators of hydrologic regimes can be quite complicated and that in some streams bankfull flow has no particular significance in terms of sediment transport and channel modifications

reconstruction of floodplain sedimentation rates a combination of methods to optimize estimates reconstruction of overbank sedimentation rates over the past decades gives insight into floodplain dynamics and thereby provides a basis for efficient and sustainable floodplain management we compared the results of four independent reconstruction methods optically stimulated luminescence osl dating caesium 137 cs 137 dating heavy metal analysis and flood bed interpretation applied at three embanked floodplain sites along lower rhine river distributaries in the netherlands all methods indicate significant sedimentation rates on the floodplains varying between 2 7 mm a in the distal zones and 3 9 mm a in the proximal zones on a rapidly developing sand bar along a natural levee sedimentation rates of 9 to 25 mm a were found except for some minor inconsistencies in cs 137 dating results all methods show decreasing sedimentation rates with increasing distance from the river channel intercomparison of the results of the different dating methods revealed the potential errors associated with each method particularly where disagreement among the results were found uncertainties may arise due to 1 grain size dependent downward migration of cs 137 2 smoothing of the vertical heavy metal and cs 137 profiles 3 delayed sediment associated input of cs 137 in addition to direct atmospheric fall out 4 overestimation of the burial age in os l dating due to incomplete resetting of the osl signal or 5 non linear relationships between sediment deposition and flood magnitude in the count from the top correlation between sediment lamination and past observed flood records still taking the uncertainties associated with each method into account the results are generally in good agreement using the results we indicate the optimal spatial range of application of each method depending on sediment texture and sedimentation rate the optimal spatial and temporal ranges differ for each method but show significant overlap a combination of the methods will thus provide maximum information for accurate estimation of sedimentation rates on a decadal time scale

integral flow properties of the swash zone and averaging the swash zone is that part of a beach over which the instantaneous shoreline moves back and forth as waves meet the shore this zone is discussed using the nonlinear shallow water equations which are appropriate for gently sloping beaches a weakly three dimensional extension of the two dimensional solution by carrier greenspan 1958 of the shallow water equations for a wave reflecting on an inclined plane beach is developed and used to illustrate the ideas thereafter attention is given to integrated and averaged quantities the mean shoreline might be defined in several ways but for modelling purposes we find the lower boundary of the swash zone to be more useful a set of equations obtained by integrating across the swash zone is investigated as a model for use as an alternative boundary condition for wave resolving studies comparison with sample numerical computations illustrates that they are effective in modelling the dynamics of the swash zone and that a reasonable representation of swash zone flows may be obtained from the integrated variables the longshore flow of water in the swash zone is in many ways similar to the stokes drift of propagating water waves further averaging is made over short waves to obtain results suitable as boundary conditions for longer period motions including the effect of incident short waves in order to clearly present the work a few simplifications are made the main result is that in addition to the kinematic type of boundary condition that occurs on a simple e g rigid boundary two further conditions are found in order that both the changing position of the swash zone boundary and the longshore flow in the swash zone may be determined models of the short waves both outside and inside the swash zone are needed to complete a full wave averaged model only brief indication is given of such modelling

gravity anomaly across the peruvian andes we carried out gravity surveys along four routes across the peruvian andes one in northern peru one in central peru and two in southern peru two of the routes extend from the coast to the flat lands of the amazon basin across the high andes while the other two routes extend only from the coast to the central high plateau or the altiplano one route through nazca contains 250 data points over a length of 800 km and thus offers one of the best gravity profiles across the andes this profile shows quite asymmetric gravity anomalies associated with the western cordillera and the eastern cordillera in marked contrast with the symmetric pattern of topographic profile using these profiles we constructed crustal models varying layer thicknesses rather than layer densities the crustal thickness has a maximum beneath the western cordillera although the maximum thickness varies from 45 km in northern peru to 55 km in central peru and 65 km in southern peru in contrast to the assumed thickness of 35 km beneath the stable brazilian shield possible effects of lateral variations of crustal and mantle densities tend to reduce the above estimates of maximum thickness the very shallow moho beneath the peruvian coast steeply deepens eastward in correspondence to the steep western slope of the andes the crust is thicker in the western cordillera than in the eastern cordillera the moho beneath the eastern cordillera tends to be relatively flat and shallows abruptly eastward across the sub andes the wadati benioff zone lies in general well below the model south american continental crust leaving a mantle wedge in between a notable exception is the nazca profile where the base of the model south american continental crust is in direct contact with the top of the wadati benioff zone this provides a direct evidence for uplifting of the buoyant slab with an aseismic ridge the nazca ridge at its top which tends to attach itself to the bottom of the continental crust we examined whether or not the load due to mountain topography is balanced with the buoyancy load due to excess mass of the crust in the andes the western cordillera is found to be approximately in isostatic equilibrium but the eastern cordillera is not this contrast in mechanical state and the difference in recent geology suggest that the western cordillera and the eastern cordillera have not uplifted through entirely the same tectonic process

a shoreline boundary condition for a highly nonlinear boussinesq model for breaking waves abstract a physically based strategy was used to model swash zone hydrodynamics forced by breaking waves within a boussinesq type of model the position and the velocity of the shoreline were determined continuously in space by solving the physically based equations of the shoreline motion moreover a fixed grid method with a wet dry interface was adopted for integrating the boussinesq model the numerical stability of the model was improved by means of an extrapolation method to validate the proposed methodology the classical analytical solution for the shoreline motion of a monochromatic wave train over a plane beach was considered the comparison between the analytical and numerical horizontal shoreline movements provided a very good agreement several other tests on the run up of non breaking and breaking waves were performed as well these tests showed that the proposed model was always in fairly good agreement with the experimental data even in complex hydrodynamic situations like those forced by breaking solitary waves in particular in comparison with other state of the art shoreline models in all the analyzed cases the proposed model allowed much better predictions of the shoreline velocity to be obtained

source conveyance and fate of suspended sediments following hurricane irene new england usa hurricane irene passed directly over the connecticut river valley in late august 2011 intense precipitation and high antecedent soil moisture resulted in record flooding mass wasting and fluvial erosion allowing for observations of how these rare but significant extreme events affect a landscape still responding to pleistocene glaciation and associated sediment emplacement clays and silts from upland glacial deposits once suspended in the stream network were routed directly to the mouth of the connecticut river resulting in record breaking sediment loads fifteen times greater than predicted from the pre existing rating curve denudation was particularly extensive in mountainous areas we calculate that sediment yield during the event from the deerfield river a steep tributary comprising 5 of the entire connecticut river watershed exceeded at minimum 10 40 years of routine sediment discharge and accounted for approximately 40 of the total event sediment discharge from the connecticut river a seriesof surface sediment corestaken in floodplainponds adjacent to the tidalsec

monitoring channel responses to flood events of low to moderate magnitudes in a bedrock dominated river using morphological budgeting by terrestrial laser scanning abstract changes to channel morphology reflect geomorphic work by flood events of differing magnitude and frequency advances in remote sensing and digital terrain processing now allow for sophisticated analysis of spatial and temporal changes in erosion and deposition although the morphological budgeting approach using digital elevation models of difference has been widely applied to track volume estimation of changes to erosion and deposition over time appraisals of geomorphic effectiveness in high energy confined and partly confined channels are still lacking this study applied terrestrial laser scanning to monitor three reaches of the liwu river a bedrock dominated river in eastern taiwan from 2009 to 2012 to investigate channel responses to flood events of low to moderate magnitude and appraise their geomorphic effectiveness variability in geomorphic effectiveness reflected valley confinement and the composition configuration of geomorphic units on the channel bed annual low magnitude flood events reworked gravel and sand deposits creating local scour and fill

cordillera formation mantle dynamics and the wilson cycle we propose that the andes cordillera formed by a collision between the trenchward moving south american plate and the nazca slab and subslab mantle resistance to trenchward motion in the form of horizontal compressive normal stress deforms south america9s leading edge the advancing continent also perturbs the subslab mantle flow field as mantle is displaced this flow field detected via shear wave splitting includes trench parallel flow away from a central stagnation point and corner flow around the northern and southern ends of the continent the corresponding spatial variation in applied stress accounts for the large scale characteristics of andean deformation buckling at the stagnation point maximum normal stress forming the central andes and bolivian orocline and corner flow associated with the eastward motion of the caribbean and scotia plates the high stresses required to form and maintain the andes imply that south america9s trenchward motion is primarily driven by deep mantle flow coupled to its base no other driving force of sufficient magnitude is available similarities between north and south american plate motion history and large scale cordillera structure indicate that the western north american laramide rockies formed in a similar manner and that the north american plate is also driven westward by deep mantle flow we infer that atlantic spreading itself is similarly driven by contrast slab rollback in a closing ocean basin opens marginal basins at convergent margins as in the western pacific we suggest that there is a causal link between the opening and closing of ocean basins and the formation of cordilleras and marginal basins cordillera formation occurs at the leading continental margin during the spreading phase of the wilson cycle whereas marginal basins form during the closing phase

a thin viscous sheet model for continental deformation summary for the purposes of describing its large scale and long term deformation the continental lithosphere is regarded as a continuum obeying a newtonian or a power law rheology the flow of a thin sheet of power law material overlying an inviscid substrate is studied under the assumption that vertical gradients of the horizontal velocity are negligible a numerical model is used to investigate the deformation of such a sheet under conditions approximating those of continent continent collision the material flows in response to forces applied to its boundaries for example the indenting of one continent by another and to forces in its interior arising from gradients in crustal thickness the horizontal divergence of the flow produces changes in the crustal thickness and hence a time dependent form to the flow itself for a given set of boundary conditions the flow depends on the stress exponent in the power law rheology n and on the argand number which is a measure of the ratio between the stress arising from crustal thickness contrasts and the stress required to deform the material at the ambient strain rates when the effective viscosity of the medium is very high ar o crustal thickness variations do not influence the flow if the material is newtonian n l the deformation associated with an influx of material approximating an indenter is of much greater lateral dimension than the width of the indenter whereas when material has a power law rheology n 3 5 are used the deformation is confined to a region of lateral extent comparable to that of the indenter as ar increases the forces arising from crustal thickness contrasts exert more influence on the flow and the maximum crustal thickness that can be sustained by a given influx of material is related by a simple expression to the effective viscosity of the medium at the ambient strain rates in the limit of a very weak medium ar 10 the lithosphere is unable to sustain appreciable crustal elevation contrasts the results of these numerical experiments show that systems in which the effective viscosities are such that the maximum deviatoric stresses are between 1 kbar

geomorphic complexity and sensitivity in channels to fire and floods in mountain catchments abstract fires and floods are important drivers of geomorphic change while the hydrologic and geomorphic effects of fires have been studied at the hillslope scale we have much more limited data on post fire runoff channel changes and inferred or measured sediment storage and delivery at larger scales in this study we intensively documented channel changes over four years in two very similar 15 km2 catchments in the northern colorado front range skin gulch and hill gulch that were burned primarily at high and moderate severity in june 2012 ten and 11 cross sections and longitudinal profiles along the lower channel network were repeatedly surveyed in skin gulch and hill gulch respectively summer thunderstorms generally caused deposition in the valley bottoms while incision resulted from the intervening baseflows and spring snowmelt but a very high intensity summer thunderstorm in skin gulch just one week after burning caused much more deposition than in hill gulch fifteen months after burning both watersheds experienced an exceptional long duration flood resulting from a multi day rainstorm with a several hundred year recurrence interval this removed nearly all of the deposited post fire sediment along with some of the older valley bottom deposits the expansion and coarsening of the channel has greatly decreased the geomorphic sensitivity of both watersheds to future floods and eliminated the more typical and persistent post fire depositional signature the channel changes in skin gulch after the fire and long duration flood were much greater than in hill gulch and this can be attributed to the much greater sediment deposition in skin gulch shortly after the fire reduced geomorphic sensitivity in hill gulch resulting from a large erosional flood in 1976 and the spatial distribution of burn severity and storm rainfalls leading to lower peak flows in hill gulch these results suggest that fires in the rocky mountains can trigger significant and dynamic hillslope and channel changes over sub decadal timescales but unusually long or intense rainstorms can cause larger and more persistent changes regardless of whether a catchment has recently burned

detection and mapping of the geomorphic effects of flooding using uav photogrammetry in this paper we present a novel technique for the objective detection of the geomorphological effects of flooding in riverbeds and floodplains using imagery acquired by unmanned aerial vehicles uavs also known as drones equipped with an panchromatic camera the proposed method is based on the fusion of the two key data products of uav photogrammetry the digital elevation model dem and the orthoimage as well as derived qualitative information which together serve as the basis for object based segmentation and the supervised classification of fluvial forms the orthoimage is used to calculate textural features enabling detection of the structural properties of the image area and supporting the differentiation of features with similar spectral responses but different surface structures the dem is used to derive a flood depth model and the terrain ruggedness index supporting the detection of bank erosion all the newly derived information layers are merged with the orthoimage to form a multi band data set which is used for object based segmentation and the supervised classification of key fluvial forms resulting from flooding i e fresh and old gravel accumulations sand accumulations and bank erosion the method was tested on the effects of a snowmelt flood that occurred in december 2015 in a montane stream in the sumava mountains czech republic central europe a multi rotor uav was used to collect images of a 1 km long and 200 m wide stretch of meandering stream with fresh traces of fluvial activity the performed segmentation and classification proved that the fusion of 2d and 3d data with the derived qualitative layers significantly enhanced the reliability of the fluvial form detection process the assessment accuracy for all of the detected classes exceeded 90 the proposed technique proved its potential for application in rapid mapping and detection of the geomorphological effects of flooding

the run up of nonbreaking and breaking solitary waves abstract the run up of nonbreaking and breaking solitary waves on plane impermeable beaches is investigated with a lagrangian finite element boussinesq wave model wave breaking is parameterized with an artificial viscosity diffusion term in the momentum equation and bottom friction is modelled with a term quadratic in the horizontal fluid velocity comparisons are presented with laboratory data of maximum run up shoreline motion and spatial profiles of near shore free surface elevation for both steep 20 and gradual 2 88 slopes for the steep slope only waves which do not break on run up are considered and excellent agreement is obtained with the laboratory data for the gradual slope wave shoaling breaking bore formation and subsequent collapse at the shoreline are predicted well by the model although the breaking algorithm does not attempt to model the details of the turbulent flow in the breaking region the backwash bore is also modelled reasonably well although it persists longer in the numerical computations than in the laboratory data it is shown that the inclusion of nonhydrostatic effects reduces the tendency of waves to break and improves the agreement of the numerical results with the laboratory run up data this allows higher amplitude waves to be modelled and larger propagation distances to be treated without the need to limit the wave steepness with artificial dissipation

runup of solitary waves on a circular island this is a study of the interactions of solitary waves climbing up a circular island a series of large scale laboratory experiments with waves of different incident height to depth ratios and different crest lengths is described detailed two dimensional run up height measurements and time histories of surface elevations around the island are presented a numerical model based on the two dimensional shallow water wave equations including runup calculations was developed numerical model predictions agreed very well with the laboratory data and the model was used to study wave trapping and the effect of slope under certain conditions enhanced runup and wave trapping on the lee side of the island were observed suggesting a possible explanation for the devastation reported by field surveys in babi island off flores indonesia and in okushiri island japan

geomorphic diversity in the braided wandering bela river slovak carpathians as a response to flood variability and environmental changes abstract changes in the morphological pattern of the gravel bed bela river slovak carpathians were investigated to infer about the impact of flood events and environmental changes on the evolutionary trend of the river since the mid twentieth century the post flood period serial geomorphic analysis popsega approach coupled with gis analysis was used to identify morphological changes that occurred during particular flood periods the study focused on assessing how six flood periods fp with differing flood characteristics have influenced the evolutionary trend of the river several sets of aerial photos 1949 1961 1973 1986 1992 2003 2009 taken after the periods with the occurrence or lack of major floods provided data about channel landform changes in 227 river segments of 100 m length a decreasing trend of the area of the river s active zone from 2 5 km2 in 1949 to 1 4 km2 in 2009 was identified the first fp 1949 1961 with a very high magnitude flood in 1958 ri50 was characterized by increasing total channel length island number area and the number density of confluence diffluence pairs nodes and by decreasing bar area during this fp the frequency of cores of channel dynamics as well as the shannon s index of landforms diversity reached the highest values the following fp 1962 1973 with four 5 to 10 year floods exhibited the inverse pattern of changes in channel form parameters although the core frequency of channel dynamics and shannon s diversity index were still high the river system seems to have been relatively stable between 1974 and 1986 third fp with some decrease in the area of channel forms and in pattern metrics values during the fourth fp 1987 1992 several 1 5 to 3 year floods occurred and were associated with a decrease in some channel forms and a further decrease of the pattern metrics values an increase in all analysed channel parameters especially bar area and pattern metrics values occurred in the years 1993 2002 fifth fp as a consequence of two floods of moderate magnitude in 1997 ri7 and 2001 ri3 5 the lowest values of bar area and pattern metrics during the whole study period were recorded during the last fp 2002 2008 whereas island area increased at that time the study shows that the occurrence of floods during the last six decades has not returned the bela to its former state because of the overall decrease in flood magnitudes changes in catchment sediment supply induced by the increasing forest cover in the catchment from 22 7 in 1957 to 34 8 in 2008 and changes in channel boundary conditions channelization channel incision small hydropower plant constructions

sedimentological effects and stratigraphic implications of a rare high stage flow in an evolving braided to anabranching stream with riparian woodland abstract low frequency 1 in 25 years high stage flows on the south platte and upper platte rivers in nebraska usa during september october 2013 produced sedimentary effects that are unaccounted for in depositional models of that fluvial system being superimposed on a historically recent trend of channel belt abandonment and encroachment of woody vegetation these outcomes are even more useful for comparison with the wider sedimentary record rooted vegetation particularly riparian trees played a major role in determining where erosion and sedimentation occurred outside of the main perennially flowing channels effects of the 2013 event include 1 small pebble to cobble sized gravel in various bar top and flood channel settings 2 common current or sediment shadows including streamlined sediment shadow bars several meters or more in length which formed downstream from rooted trees and logjams 3 sand lobes that prograded into densely wooded abandoned parts of the historical channel belt at angles of as much as 85 from average downstream flow 4 large scours some approaching 2 m in depth many of which formed behind trees near the diffluences of flood channels and the main channel 5 deposits of sand that were baffled by nonwoody or shrubby vegetation in the abandoned channel belt and 6 local accumulations of large woody debris in front of rooted trees as cross flood channel dams and rarely as walls alongside flood channels in an aggrading system these features should be preserved as a distinctive set of sedimentary structures which may be interpretable as evidence for episodic major flows in a system in which woody vegetation has encroached widely onto the channel belt

parallel thrust and normal faulting in peru and constraints on the state of stress abstract we present evidence for recent normal faulting in the cordillera blanca of peru along planes trending approximately n40 w parallel to the chain this type of faulting suggests that there is an important component of extension perpendicular to the chain and contrasts markedly with the underthrusting of the nazca plate on the west side of peru and with the folding and thrusting observed in the sub andes on the eastern flank of the chain these contrasting styles of deformation and associated stress fields can be explained by buoyancy forces due to the high mountains and crustal roots in so far as this explanation is correct the difference in elevation between zones of normal and thrust faulting can be used to place an upper bound of 500 bars on the average stress difference in the crust

finite strain calculations of continental deformation 2 comparison with the india asia collision zone numerical experiments on a thin viscous sheet model for deformation of continental lithosphere subjected to an indenting boundary condition yield distributions of crustal thickness of stress and strain rate and of latitudinal displacements that may be compared with observations in the india asia collision zone a simple indenting boundary condition applied to initially laterally homogeneous sheets obeying a power law rheology produces results that are in broad agreement with the observations provided that the power law exponent is three or greater and the sheet can support vertically integrated stress differences of 2 1013 5 1012 n m 1 in regions in front of the indenter under these conditions the calculated deformation shows accommodation of convergence primarily by crustal thickening to produce a plateau in front of the indenter palaeomagnetic data from india and tibet and the observed distribution of topography suggest that much of the post eocene convergence of india with asia has been taken up by deformation within asia that involved crustal thickening the principal difference between calculation and observation is the absence from the calculated strain rate fields of east west extension of the plateau in front of the indenting boundary the calculations show that once such a plateau is formed the buoyancy force associated with the crustal thickness contrast inhibits further thickening and the plateau strains at less than half the rate of its immediate surroundings seismically determined regional strain rates exhibit a similar distribution with the tibetan plateau straining at about one quarter the rate of the tien shan and ningxia gansu regions calculated principal compressive stress orientations and regional strain rates agree with the seismically determined quantities in the mongolia baikal tien shan tibet and ningxia gansu regions of asia to within the uncertainty of the latter the vertically integrated stresses that are calculated for the viscous sheet are comparable with those that can be supported by a theologically stratified continental lithosphere obeying laboratory determined flow laws we suggest that the thin viscous sheet model described in this paper and its companion gives a simple and physically plausible description of the observed deformation in central asia in this description the predominant mechanism of accommodation of continental convergence is diffuse crustal thickening with shear on vertical planes playing a subsidiary role once large crustal thickness contrasts have been established

spatio temporal patterns of channel changes in response to a major flood event the case of the magra river central northern italy on october 25th 2011 the magra river central northern italy was affected by a significant flood event with an estimated return interval ranging from 30 to 200 years this study investigates the morphological responses of the magra river to this major flood event with the aims of i documenting the channel changes which occurred in response to the flood ii analysing this response within the context of the historical trend of width changes iii investigating the possible factors controlling the spatial pattern and the intensity of the observed changes significant channel widening was documented along the entire length studied about 34 km ranging from 3 to 90 of the pre flood channel width braided reaches were characterized by the most severe planimetric changes although characterized by high rates of change these variations are however amply included in the historical range of channel width variability over approximately the last 150 years from 1877 to present day and are comparable with though generally lower than the channel width of the 1950s statistical analyses simple and multiple regressions between the observed changes in channel width and a series of selected morphological and hydraulic controlling factors showed no robust correlations to explain the spatial pattern and the variability of channel adjustments instead major adjustments occurred along reaches characterized by the confluence of those streams draining the sub catchments where the storm was concentrated copyright 2014 john wiley sons ltd

effectiveness of monsoon floods on the tapi river india role of channel geometry and hydrologic regime abstract geomorphic effects of floods are a function of several controlling factors such as magnitude frequency rate of sediment movement flood power duration of effective flows sequence of events and the channel geometry in this paper these measures of effectiveness have been evaluated for the monsoon dominated flood controlled and incised tapi river india by defining four flow categories low flows moderate flows floods and large floods ratios between effectiveness parameters of moderate flows on one hand and the floods large floods and maximum floods on the other were computed to understand the relative importance of moderate and large flows in addition to this stream power graphs for large floods were constructed and the changes in channel form were analyzed by using multi date cross sections the results of the study indicate that the morphological characteristics of the bedrock as well as the alluvial channels of the monsoonal and incised tapi river are maintained by large magnitude but low frequency floods that occur at long intervals because the channel is incised the effectiveness of large flows is accentuated the incised channel form enhances the role of large floods by reducing the width depth ratio and by increasing the velocity as well as the energy per unit area the low and moderate flows are superior to high magnitude flows only in terms of suspended sediment transport and frequency of occurrence another conclusion is that the suspended sediment carried by flows may not be the most appropriate criterion for measuring the geomorphic effectiveness of flows particularly for monsoonal rivers

thermal mechanical model for crustal thickening in the central andes driven by ablative subduction the thick up to 65 km crust of the high elevation regions of the andean orogenic belt results from structural thickening of the felsic upper crust of south america the great thickness implies shortening or loss of several hundred kilometers of lithospheric mantle and lower crust through numerical simulation of the thermal and mechanical processes of crustal thickening we test a model of lithospheric mantle removal by ablative subduction the model combines kinematic assumptions regarding mantle motion with dynamic calculations of crustal deformation predictions include the formation of an outwardly growing orogenic plateau analogous to the altiplano that results from high temperature low viscosity flow of the lower crust due to thickening of the high heat production upper crust

moving shoreline boundary condition for nearshore models the paper develops and analyzes two fully nonlinear boundary conditions that incorporate the motion of the shoreline in nonlinear time domain nearshore models a moving shoreline essentially means the computational domain is changing with the solution of the flow the problem is solved in two steps the first is to establish an equation that determines the motion of the shoreline based on the local momentum balance the second is to develop and implement into a shoreline model the capability of accommodating a changing computational domain the two models represent two different ways of addressing this step one is to track the position of the shoreline in a fixed grid by establishing a special shoreline point which generally is not a fixed grid point the second is by a coordinate transformation that maps the changing domain onto a fixed domain and solves the basic equations in the mapped domain the two shoreline conditions are tested against three known solution for nonlinear shoreline motion two are the 1 d solutions to the nonlinear shallow water nsw equations by carrier and greenspan j fluid mech 4 1958 97 one representing the response to a transient change in the offshore water level the other the motion due to a periodic standing wave both on slopes steep enough to allow full reflection the third is the 2 d horizontal 2dh computational solution by zelt coast eng 15 1991 205 for the run up of a solitary wave on a cusped beach in all cases both models are shown to behave well and give high accuracy results for suitably chosen grid and time spacings

sedimentation of overbank floods in the confined complex channel floodplain system of the lower yellow river china the channel boundary conditions along the lower yellow river lyr have been altered significantly since the 1950s with the continual reinforcement and construction of both main and secondary dykes and river training works to evaluate how the confined complex channel floodplain system of the lyr responds to floods this study presents a detailed investigation of the relationship between the tempo spatial distribution of sedimentation erosion and overbank floods occurred in the lyr for large overbank floods we found that when the sediment transport coefficient ratio of sediment concentration of flow to flow discharge is less than 0 034 the bankfull channel is subject to significant erosion while the main and secondary floodplains both accumulate sediment the amount of sediment deposited on the main and secondary floodplains is closely related to the ratio of peak discharge to bankfull discharge volume of water flowing over the floodplains and sediment concentration of overbank flow while the degree of erosion in the bankfull channel is related to the amount of sediment deposited on the main and secondary floodplains water volume and sediment load in flood season the significant increase in erosion in the bankfull channel is due to the construction of the main and secondary dykes and river training works which are largely in a wide and narrow alternated pattern along the lyr such that the water flowing over wider floodplains returns to the channel downstream after it drops sediment for small overbank floods the bankfull channel is subject to erosion when the sediment transport coefficient is less than 0 028 while the amount of sediment deposited on the secondary floodplain is associated closely with the sediment concentration of flow over the entire length of the lyr the situation of erosion in the bankfull channel and sediment deposition on the main and secondary floodplains occurred mainly in the upper reach of the lyr in which a channel wandering in planform has been well developed

flood disturbance recovery and inter flood incision on a large sand bed river abstract the lower 800 km of the missouri river has been incising for decades however the 2011 flood scoured more sediment than the previous 12 yr combined the river rebounded in the following two years re depositing over 70 of the sediment scoured during the 2011 flood historic evidence suggests that past missouri river floods may have followed similar scour rebound patterns this paper analyzes 16 channel surveys from 1987 to 2014 including 50 723 total cross sections to document the morphological history of the lower 800 km of the missouri river over the last thirty years including flood disturbance and long term trends the last thirty years on the missouri river included two basic morphologic regimes steady incision during low to moderate flow periods and rapid scour rebound responses to floods surveys collected during the 2011 flood demonstrate that the river scoured throughout the flood including the falling limb and did not begin a rebound phase until after the flood the analysis also identifies sediment sinks associated with each of these scour regimes flood scour and incision between floods that exceed the total volume eroded from the bed during those periods results suggest that floodplain deposition may induce the supply limitation that drives flood scour on this large sand bed river additionally aggregate mining removes substantially more sediment than the total river incision between floods and the reaches with maximum scour during the 1993 and 2011 floods correspond to the zones of aggregate mining

accelerated overbank accumulation after nineteenth century river regulation works a case study on the maros river hungary abstract in the nineteenth century the meandering rivers of the carpathian basin were extensively regulated and their large up to 100 km wide floodplains were confined by artificial levees on the narrow 0 5 4 km artificial floodplains confined by these levees overbank sedimentation has become the dominant geomorphological process resulting in rising floodplain levels during the last century the maros river is an extreme example of this process as it carries a significant amount of suspended sediment 4 6 10 6 m 3 y and because its lowland reach was drastically shortened by cutoffs resulting in bed scour and an increased sediment load simultaneously a flood embankment system was constructed reducing the floodplain width by 70 80 the resulting accelerated overbank sediment accumulation increases the flood hazard along the river the aim of this study is to determine the spatial and temporal pattern of overbank sediment accumulation on the artificial floodplain of the lower maros river over the last 150 years and to identify its influencing factors the lateral slope of the protected natural floodplain was projected towards the present day channel allowing the volume m 3 and rate cm y of overbank sedimentation to be calculated using digital terrain modelling dtm changes in the rate of sedimentation were determined by pollen analysis the studied reach was divided into five sections based on the rate of aggradation i the distal surface of the alluvial fan where no sedimentation was measured only incision ii the original front of the alluvial fan 1 0 0 4 cm y iii the recently formed secondary alluvial fan 1 4 0 3 cm y iv the low lying floodplain 0 4 0 2 cm y and v the outlet unit 2 0 0 5 cm y the aggradation rate was slower on elevated forms such as the pre regulation natural levee 0 2 cm y and greater on the low lying floodplain 0 6 cm y the greatest accumulation rate 1 3 2 4 cm y was measured in cutoffs the sedimentation rate was high during the regulation period 1 9 2 4 cm y but later decreased to 0 5 0 9 cm y the rate of aggradation was determined by the width height and slope conditions of the floodplain the impoundment of the main river and the land use in the area

the influence of landscape connectivity and landslide dynamics upon channel adjustments and sediment flux in the liwu basin taiwan catchment scale analyzes of spatial and temporal variability in landscape connectivity are critical considerations in appraisals of landscape evolution and disaster mitigation in tectonically active mountain belts such as taiwan this study uses historical aerial photographs flow discharge and seismic data to analyze landslide changes and channel adjustments over a 30 year period in the liwu basin recurrent earthquakes and typhoon events trigger frequent landslide activity channel adjustment and sediment reworking in this system spatial variability in magnitude frequency relations of hillslope valley floor lateral and upstream downstream longitudinal connectivity during the study period are shown to reflect annual reworking in source and accumulation zones while partly confined valleys in the mid catchment area trap sediment behind landslide induced dams that are formed and breached on an approximately decadal basis this promotes partial longitudinal connectivity in these areas landscape responses to disturbance events were especially pronounced following combinations of seismic and typhoon events prior to the 1998 and 2005 images although single high magnitude events and series of moderate events affect patterns of landscape connectivity in the liwu basin residence times for sediment storage are very short in this highly connected river system where confined valley settings extend virtually to the coast copyright 2014 john wiley sons ltd

can we distinguish flood frequency and magnitude in the sedimentological record of rivers consideration of the origin of alluvial deposits and their paleoenvironmental interpretation has traditionally involved two schools of thought that they are either the result of processes that on average have acted uniformly through time or that they are related to exceptional events that occur infrequently despite the long running debate of gradualism versus catastrophism within the earth sciences there are surprisingly few quantitative data to assess the magnitude of events that produce alluvial sedimentary successions this paper reports on a unique natural experiment where surface digital elevation model dem and subsurface ground penetrating radar gpr data were taken immediately prior to and after a large 1 in 40 yr flood event on the sandy braided south saskatchewan river canada results show that although this high magnitude flood reworked the entire braidplain the scale of scour and style of deposition was similar to that associated with lower magnitude annual floods the absence of a distinct imprint of this large flood within the deposits is related to the fact that as river discharge rises and begins to flow overbank channel width increases at a much faster rate than flow depth and thus the rate of increase in channel bed shear stress declines hence rather than being a product of either frequent or rare events alluvial deposits will likely be created by a range of different magnitude floods but discriminating between these different scale events in the rock record may be extremely difficult

channel floodplain connectivity during an extreme flood event implications for sediment erosion deposition and delivery the term connectivity has emerged as a powerful concept in hydrology and geomorphology and is emerging as an innovative component of catchment erosion modeling studies however considerable confusion remains regarding its definition and quantification especially as it relates to fluvial systems this confusion is exacerbated by a lack of detailed case studies and by the tendency to treat water and sediment separately extreme flood events provide a useful framework to assess variability in connectivity particularly the connection between channels and floodplains the catastrophic flood of january 2011 in the lockyer valley southeast queensland australia provides an opportunity to examine this dimension in some detail and to determine how these dynamics operate under high flow regimes high resolution aerial photographs and multi temporal lidar digital elevation models dems coupled with hydrological modeling are used to assess both the nature of hydrologic and sedimentological connectivity and their dominant controls longitudinal variations in flood inundation extent led to the identification of nine reaches which displayed varying channel floodplain connectivity the major control on connectivity was significant non linear changes in channel capacity due to the presence of notable macrochannels which contained a 3000 average recurrence interval ari event at mid catchment locations the spatial pattern of hydrological connectivity was not straight forward in spite of bankfull discharges for selected reaches exceeding 5600m 3 s 1 data indicate that the main channel boundary was the dominant source of sediment while the floodplains where inundated were the dominant sinks spatial variability in channel floodplain hydrological connectivity leads to dis connectivity in the downstream transfer of sediments between reaches and affected sediment storage on adjacent floodplains consideration of such variability for even the most extreme flood events highlights the need to carefully consider non linear changes in key variables such as channel capacity and flood conveyance in the development of a quantitative connectivity index copyright c 2013 john wiley sons ltd

lower bound on the amount of crustal shortening in the central bolivian andes balanced cross sections across the cordillera oriental and subandean zone of the central bolivian andes indicate that crustal shortening probably has played the dominant role in orogeny in this convergent margin setting a minimum amount of shortening 210 km is documented which can account for two thirds of the present day crustal cross sectional area along a transect spanning the entire mountain range substantial crustal shortening may also require loss of the lower lithosphere to the asthenosphere a large minimum amount of crustal shortening in the bolivian andes shows contrary to common assumptions about orogeny that 1 magmatic addition may be volumetrically less important in orogeny in andean type margins and 2 crustal shortening is not uniquely associated with continental or island arc collision

decelerating nazca south america and nazca pacific plate motions space geodetic estimates of the rate of nazca south america convergence and nazca pacific spreading averaging over several years show that present day rates are significantly slower than the 3 million year average nuvel 1a model the implied rates of deceleration are consistent with longer term trends extending back to at least 20 ma about the time of initiation of andes growth and may reflect consequences of ongoing subduction and construction of the andes e g increased friction and viscous drag on the subducted slab as the leading edge of south america thickens

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

experimental validation and characterization of mean swash zone boundary conditions 1 performances of recently developed shoreline boundary conditions for wave averaged nearshore flow solvers are evaluated on the basis of available experimental data applications of the model to experimental data show the chosen equations suitably determine boundary values required for one dimensional mean flow a detailed illustration is also given of the characteristics of flow properties which appear in the model it is finally shown that very simple conditions can be suitably used at the mean shoreline of wave averaged flows for which boundary values of position water depth and velocity are computed on the basis of local quantities known at the seaward boundary of the swash

geomorphic impacts of a 100 year flood kiwitea stream manawatu catchment new zealand abstract the geomorphic impacts of a 100 year flood are assessed in the kiwitea stream 254 km 2 a tributary within the manawatu river catchment new zealand using sequential aerial photographs and reach based morphological sediment budgeting channel expansion and avulsion eroded in excess of one million cubic metres of sediment over 1 km 2 of floodplain along a 30 km long reach of kiwitea stream channel transformation was spatially discontinuous and predominantly associated with large scale bank erosion in response to a flood over 5 times bigger than the mean annual flood annual recurrence interval ari 100 years total energy expenditure of this flood in the kiwitea was 14 900 10 3 j the spatial discontinuity of channel transformation relates to valley floor and channel configurations high stream powers generated in confined channels at bends produced catastrophic channel transformation where flood flows dissipated overbank stream powers and the extent of channel transformation were reduced hydrologic hydraulic and geomorphic variables can be invoked to thus explain the variability of geomorphic impacts encountered during this event

crustal shortening in the andes why do gps rates differ from geological rates gps data indicate 30 40 mm yr 1 present day crustal shortening across the andes whereas geological evidence shows crustal shortening concentrated in the sub andean thrust belt at a much lower rate 15 mm yr 1 we reconcile the discrepancy between the geodetic and the geological crustal shortening using geodynamic modeling that includes timescale dependent crustal deformation the gps velocities reflect the instantaneous deformation in the andes that includes both permanent deformation and elastic deformation that will be recovered during future earthquakes whereas the lower geological rates reflect only the permanent deformation the three dimensional viscoelastic model predicts nearly uniform short term velocity gradients across the andes similar to the gps results and concentrated long term crustal shortening in the sub andean thrust zone consistent with geological observations

a balanced model of the southern central andes to explain the actual crustal thickness of the southern central andes a balanced cross section at 21 s latitude was modeled a forward modeling procedure was used on a crustal scale to explain the gross crustal structure obtained by seismic refraction investigations in the model 320 km of shortening since late cretaceous based on balanced geological cross sections are assumed for the whole andes from the trench to the foreland and the initial crustal thickness varies between 30 and 40 km it results that about 20 of the actual crustal volume must be explained by other sources than crustal shortening structures of high velocity material in the upper crust of the eastern cordillera can be explained by detached and overthrust material from the crustal base thus producing a crustal doubling in the back arc underplating of continental material that was removed by subduction erosion and magmatic addition of derivates of the subducted nazca plate may contribute to the lower crust of the forearc and arc regions crustal thickening of the eastern cordillera and parts of the altiplano was undoubtedly produced by tectonic thickening whereas the sources of thickening in the western cordillera and forearc region are uncertain

the use of multi temporal lidar to assess basin scale erosion and deposition following the catastrophic january 2011 lockyer flood se queensland australia advances in remote sensing and digital terrain processing now allow for a sophisticated analysis of spatial and temporal changes in erosion and deposition digital elevation models dems can now be constructed and differenced to produce dems of difference dod which are used to assess net landscape change for morphological budgeting to date this has been most effectively achieved in gravel bed rivers over relatively small spatial scales if the full potential of the technology is to be realised additional studies are required at larger scales and across a wider range of geomorphic features this study presents an assessment of the basin scale spatial patterns of erosion deposition and net morphological change that resulted from a catastrophic flood event in the lockyer creek catchment of se queensland seq in january 2011 multitemporal light detection and ranging lidar dems were used to construct a dod that was then combined with a one dimensional flow hydraulic model hec ras to delineate five major geomorphic landforms including inner channel area within channel benches macrochannel banks and floodplain the lidar uncertainties were quantified and applied together with a probabilistic representation of uncertainty thresholded at a conservative 95 confidence interval the elevation change distribution ecd for the 100 km2 study area indicates a magnitude of elevation change spanning almost 10 m but the mean elevation change of 0 04 m confirms that a large part of the landscape was characterised by relatively low magnitude changes over a large spatial area mean elevation changes varied by geomorphic feature and only two the within channel benches and macrochannel banks were net erosional with an estimated combined loss of 1 815 149 m3 of sediment the floodplain was the zone of major net deposition but mean elevation changes approached the defined critical limit of uncertainty areal and volumetric ecds for this extreme event provide a representative expression of the balance between erosion and deposition and importantly sediment redistribution which is extremely difficult to quantify using more traditional channel planform or cross sectional surveys the ability of lidar to make a rapid and accurate assessment of key geomorphic processes over large spatial scales contributes to our understanding of key processes and as demonstrated here to the assessment of major geomorphological hazards such as extreme flood events

temporal changes in suspended sediment transport in a gullied loess basin the lower chabagou creek on the loess plateau in china suspended sediment dynamics are still imperfectly understood especially in the loess hilly region on the loess plateau with strong temporal variability where few studies heretofore have been conducted using a dataset up to eight years long in the lower chabagou creek the variability in suspended sediment load at different temporal scales within flood variability monthly seasonal and annual is analyzed in this paper the results show that on the within flood scale most of the sediment peaks lag behind peak discharges implying that slope zones are the main sediment source area independent of the occurring sequences of the peaks of sediment and discharge all the events could present an anti clock wise hysteresis loop resulting from the abundant material and the influence of hyperconcentrated flows on suspended sediment concentration at monthly and seasonal scales there is a store release process i e sediment is prepared in winter spring and late autumn and exported in summer and early autumn at the annual scale the high variability in concentration and sediment yield are highly correlated with water yield resulting from the number and magnitude of floods recorded yearly and almost all the suspended load is transported during these events copyright c 2008 john wiley sons ltd

the geomorphic effectiveness of a large flood on the rio grande in the big bend region insights on geomorphic controls and post flood geomorphic response abstract since the 1940s the rio grande in the big bend region has undergone long periods of channel narrowing which have been occasionally interrupted by rare large floods that widen the channel termed a channel reset the most recent channel reset occurred in 2008 following a 17 year period of extremely low stream flow and rapid channel narrowing flooding was caused by precipitation associated with the remnants of tropical depression lowell in the rio conchos watershed the largest tributary to the rio grande floodwaters approached 1500 m 3 s between a 13 and 15 year recurrence interval and breached levees inundated communities and flooded the alluvial valley of the rio grande the wetted width exceeding 2 5 km in some locations the 2008 flood had the 7th largest magnitude of record however conveyed the largest volume of water than any other flood because of the narrow pre flood channel conditions record flood stages occurred we used pre and post flood aerial photographs channel and floodplain surveys and 1 dimensional hydraulic models to quantify the magnitude of channel change investigate the controls of flood induced geomorphic changes and measure the post flood response of the widened channel these analyses show that geomorphic changes included channel widening meander migration avulsions extensive bar formation and vertical floodplain accretion reach averaged channel widening between 26 and 52 occurred but in some localities exceeded 500 the degree and style of channel response was related but not limited to three factors 1 bed load supply and transport 2 pre flood channel plan form and 3 rapid declines in specific stream power downstream of constrictions and areas of high channel bed slope the post flood channel response has consisted of channel contraction through the aggradation of the channel bed and the formation of fine grained benches inset within the widened channel margins the most significant post flood geomorphic changes have occurred at and downstream from ephemeral tributaries that contribute large volumes of sediment

anomalous crust of the bolivian altiplano central andes constraints from broadband regional seismic waveforms a one year deployment of broadband seismographs in the bolivian altiplano recorded numerous intermediate depth earthquakes at near regional distances we modeled the associated broadband waveforms of two earthquakes to estimate an average crustal structure for the altiplano the resulting model is characterized by an anomalously low mean p velocity of 6 0 km s a low poisson s ratio of 0 25 and a crustal thickness of 65 km the combination of the low mean velocity and low poisson s ratio can be explained only by a predominantly quartz rich felsic bulk composition this constraint precludes significant volumes of magmatic addition from the mantle contributing to the great thickness of the altiplano crust but is consistent with thickening by compressive shortening concentrated in a weak felsic layer

geomorphological and sedimentological analysis of flash flood deposits the case of the 1997 rivillas flood spain on the basis of the description of the 1997 rivillas flood deposits a morphosedimentary feature classification is proposed mapping of the main morphosedimentary deposits in seven reaches along the basin has provided abundant data for each defined typology and for a better adjustment of their stability fields because of their unstable preservation environment immediate post flood field surveys with descriptions of erosive and depositional features were undertaken up to 18 features were classified as either sedimentary or erosive and mapped according to their genetic environments anthropic interference such as land use changes produce modification of sediment supply and in channel and floodplain erosive processes causing flash floods to be more catastrophic erosive features are dominant over sedimentary ones as the sedimentary budget in the river is negative by means of hec ras hydrologic engineering center modelling we were able to obtain mean values of the main variables limiting feature stability velocity depth stream powers and shear stress these provide information regarding maximum stability threshold and peak flood discharge the ephemeral nature of riverine flash flood deposits in this type of setting does not mean that they are not significant and their interpretation after recent floods can significantly improve interpretation of the event dynamics and its flood hydrology and also be useful for flood risk mapping

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

magnitude and frequency in proglacial rivers a geomorphological and sedimentological perspective abstract proglacial fluvial sedimentary systems receive water from a variety of sources and have variable discharges with a range of magnitudes and frequencies little attention has been paid to how these various magnitude and frequency regimes interact to produce a distinctive sedimentary record in modern and ancient proglacial environments this paper reviews the concept of magnitude and frequency in relation to proglacial fluvial systems from a geomorphic and sedimentary perspective rather than a hydrological or statistical perspective the nature of the meltwater inputs can be characterised as low magnitude high frequency primarily controlled by ablation inputs from the source glacier or high magnitude low frequency primarily controlled by exceptional inputs the most important high magnitude low frequency inputs are catastrophic outburst floods often referred to by the term jokulhlaup icelandic for glacier burst glacier surges are an additional form of cyclical variation impacting the proglacial environment which briefly alter the volumes and patterns of meltwater input the sedimentary consequences of low magnitude high frequency discharges are related to frequent variations in stage the greater directional variability that sediment will record and the increased significance of channel confluence sedimentation in contrast the most significant characteristics of high magnitude low frequency flooding include the presence of large flood bars and mid channel jokulhlaup bars hyperconcentrated flows large gravel dunes and the formation of ice block kettle hole structures and rip up clasts glacier surges result in a redistribution of low magnitude high frequency processes and products across the glacier margin and small floods may occur at the surge termination criteria for distinguishing magnitude and frequency regimes in the proglacial environment are identified based on these major characteristics studies of quaternary proglacial fluvial sediments are used to determine how the interaction of the various magnitude and frequency regimes might produce a distinctive sedimentary record consideration of sandur architecture and stratigraphy shows that the main controls on the sedimentary record of proglacial regions are the discharge magnitude and frequency regime sediment supply the pattern of glacier advance or retreat and proglacial topography a model of sandur development is suggested which shows how discharge magnitude and frequency in combination with sandur incision and aggradation controlled by glacier advance and retreat can control sandur stratigraphy

geomorphic and sedimentological controls on the effectiveness of an extreme flood the 1993 flood on the upper mississippi river was a rare large magnitude hydrological event field and aerial survey analyses and landsat 5 thematic mapper data were used to appraise the thickness of overbank deposits on leveed and unleveed reaches results indicate that minimal 5 mm overbank sedimentation occurred except in the immediate vicinity of a levee break unleveed sections also lacked overbank sedimentation little geomorphological or sedimentological evidence of this extreme event is likely to be preserved this raises questions about the completeness of the stratigraphic record in situations where wide floodplains with cohesive soils provide effective resistance and dissipate energy so that erosion is minimized and or sediment supply is limited by event timing or sequencing a large flood may leave little or no substantive evidence of its occurrence

seismicity fault plane solutions depth of faulting and active tectonics of the andes of peru ecuador and southern colombia the intracontinental seismicity of the andes of peru ecuador and southern colombia is concentrated along the easternmost flank of the cordillera beneath the western margin of the sub andes the focal depths and fault plane solutions of the largest events were constrained by comparing the observed long period p waves with synthetic waveforms in general the fault plane solutions show reverse faulting on steeply dipping nodal planes striking northwest southeast and reflect crustal shortening perpendicular to the range probably in response to the subduction of the nazca plate to the west earthquakes in the sub andes occur at depths of between 8 and 38 km indicating that much of the crust deforms in a brittle manner the seismicity seems to reflect antithetic underthrusting of the brazilian shield beneath the eastern margin of the andes however the earthquakes are too deep and their nodal planes are too steep to be associated with the thin skinned decollement of the sedimentary cover instead they appear to reflect the tectonic deformation of the underthrust basement west of the zone of active deformation at the surface in the sub andes hence the earthquakes on the east side of the andes may reflect the style of deformation in the hinterland of fold and thrust belts such as in the canadian rockies while much of the decollement farther east occurs aseismically in contrast normal faulting occurs in the high andes on planes parallel to the strike of the mountain belt thus there is a delicate balance between the compressive stress applied to the andes in the direction of subduction which causes thrust faulting in the sub andes and the gravitational body forces acting on the topographically higher parts and the crustal root of the andes which may cause normal faulting at high elevation

the efficacy of stream power and flow duration on geomorphic responses to catastrophic flooding abstract geomorphologists have long studied the impacts of extreme floods yet the association between the magnitude of flow parameters discharge velocity shear stress or stream power and resulting geomorphic effectiveness remains vague and non deterministic attempts have been made to include flow duration and total expenditure of stream power in combination with peak unit stream power as important variables but there has been minimal exploration of this hydraulic combination taking advantage of tropical storm irene s rapid track through eastern vermont usa in late summer 2011 this paper presents the array of geomorphic responses to a short duration time to peak of

active tectonics of the andes nearly 90 mm a 1 of relative plate convergence is absorbed in the andean plate boundary zone the pattern of active tectonics shows remarkable variations in the way in which the plate slip vector is partitioned into displacement and strain and the ways in which compatibility between different segments is solved along any traverse across the plate boundary zone the sum of relative velocities between points must equal the relative plate motion we have developed a kinematic synthesis of displacement and strain partitioning in the andes from 47 s to 5 n relevant for the last 5 ma based upon 1 relative plate motion deduced from oceanic circuits giving a roughly constant azimuth between 075 and 080 2 moment tensor solutions for over 120 crustal earthquakes since 1960 3 structural studies of deformed plio pleistocene rocks 4 topographic geomorphic studies 5 palaeomagnetic data and 6 geodetic data we recognize four neotectonic zones with subzones and boundary transfer zones that are partitioned in different ways these zones are not coincident with the classic zones defined by the presence or absence of a volcanic chain or differences in finite displacements and strains and tectonic form the long term segmentation and finite evolution of the andes may not occur in constantly defined segments in space and time in segment 1 47 39 s the slip vector is partitioned into roughly orthogonal benioff zone slip with large magnitude large slip surface earthquakes and both distributed dextral shear giving clockwise rotations of up to 50 and dextral slip in the curved liquine ofqui fault system giving 5 10 of anticlockwise fore arc rotation in segment 2 39 20 s the slip vector is partitioned into benioff zone slip roughly parallel with the slip vector andean crustal shortening and a very small component of dextral slip including that on the atacama fault system between 39 and 34 s a cross strike dextral transfer which deflects the chile trench and the volcanic arc absorbs the shortening contrast between segments 1 and 2 in segment 3 20 6 s the slip vector is partitioned into roughly orthogonal benioff zone slip crustal shortening sinistral trench parallel faulting and northeast southwest extension compatibility between segments 2 and 3 is maintained by the sinistral east southeast trending cochabamba shear zone and north trending dextral faults in segment 4 6 s to 5 n the slip vector is partitioned into roughly orthogonal benioff zone slip and dextral strike slip faulting in the fore arc and volcanic chain

seasonal controls on sediment delivery in a small coastal plain watershed north carolina usa field measurements of drainage ditch sedimentation and suspended sediment transport were used to construct a simple sediment budget and relate seasonal variations in vegetation and the hydrological characteristics of storms to sediment dynamics in a small agricultural watershed in north carolina results indicate that seasonal variations in crop coverage and vegetation in drainage ditches influence sediment delivery following the harvesting of crops and mowing of drainage ditches in late autumn conditions are favorable to soil erosion and sediment transport through early spring storms need not be very intense or produce large rainfall totals to transport significant sediment loads the maturation of field crops and ditch vegetation in spring produces conditions less conducive to both soil erosion and sediment transport intense summer thunderstorms however are capable of mobilizing and transporting significant amounts of sediment the computed sediment yield of 0 1 mg ha yr probably represents a low estimate that nevertheless is an order of magnitude less than measured ditch storage and more than two orders of magnitude less than regional estimates of soil loss on coastal plain croplands the results show that headwater ditches may be decoupled from slopes so that much of the eroded soil is stored within small watersheds rather than being transported out of the basin