hydrological controls on the morphogenesis of low energy meanders cher river france summary river restoration is a key issue for european hydrosystems that were modified over centuries by human activities this is particularly true for numerous low energy rivers flowing in the plateaus of western europe because of this limited energy their potential in terms of autogenic restoration a priori appears strongly restricted this study examines the conditions under which the morphogenesis on one of these systems occurs in relation to various hydrologic conditions two complementary approaches are combined on three reaches of the meandering cher river france firstly we examine at a pluri decadal scale the control of duration frequency and intensity of floods on the planimetric erosion bank retreat mainly secondly we estimate the range of effective discharge for bedload transport the results show that the morphogenesis is controlled by low magnitude hydrological events two major controlling factors are suggested low differential of energy between small and large floods peculiar to low energy rivers of mid latitude and low critical discharges for lateral erosion and bedload mobilization for these reasons the ability of the alluvial cher river to self restore its fluvial dynamics seems to be relatively high

gravel bed channel changes upstream of a reservoir the case of the dunajec river upstream of the czorsztyn reservoir southern poland abstract despite a significant increase in the number of dam reservoirs in the world in the last century the effects of these structures on the evolution of river channels above them are poorly understood constructed in 1997 in the polish carpathians the czorsztyn reservoir cr has raised the base level of the single thread gravel bed dunajec river an analysis of five sets of aerial photographs and orthophotos from the period before 1977 1982 1994 and after 2003 2009 the construction of the cr allowed me to investigate the temporal and spatial impact of the raised base level of the river upstream of the reservoir on the evolution of the river channel comparison of channel width changes in the backwater river section with changes observed in the control section unaffected by the presence of the reservoir has shown that in the pre dam period differences in the evolution of the river channel in the backwater section and in the control section were not statistically different in the periods without major floods both channel sections were dominated by channel narrowing or a relative stability of channel width in the post dam period a major flood in 1997 caused more than two times greater channel widening in the backwater section than in the control section the extent of channel widening in the longitudinal channel profile reached farther upstream of the reservoir than the extent of the backwater itself in the later part of the post dam period without major floods channel narrowing were similar in the backwater section and the control section as had been the case in the period before the reservoir construction the comparison of changes in the width of the channel in the backwater and control sections indicates that channel widening in the backwater interpreted as an early stage of backwater channel adjustment was reinforced by the flood of 1997 this study shows that the use of a control section makes it possible to isolate reservoir effects from flood effects in the context of channel dynamics

channel response to extreme floods insights on controlling factors from six mountain rivers in northern apennines italy abstract this work addresses the geomorphic response of mountain rivers to extreme floods exploring the relationships between morphological changes and controlling factors the research was conducted on six tributaries of the magra river northern apennines italy whose catchments were affected by an extreme flood estimated recurrence interval 100 years in most of the basins on 25 october 2011 an integrated approach was deployed to study this flood including i analysis of channel width changes by comparing aerial photographs taken before and after the flood ii estimate of peak discharges in ungauged streams iii detailed mapping of landslides and analysis of their connectivity with the channel network channel widening occurred in 35 reaches out of 39 in reaches with channel slope results indicate that hydraulic variables alone are not sufficient to satisfactorily explain the channel response to extreme floods and inclusion of other factors such as lateral confinement is needed to increase explanatory capability of regression models concerning hydraulic variables this study showed that the degree of channel widening is more strongly related to unit stream power calculated based on pre flood channel width than to cross sectional stream power and to unit stream power calculated with post flood channel width this could suggest that most width changes occurred after the flood peak finally in terms of hazard it is crucial to document the type and magnitude of channel changes to identify controlling factors and most importantly to develop tools enabling us to predict where major geomorphic changes occur during an extreme flood

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

distinguishing allogenic from autogenic causes of bed elevation change in late quaternary alluvial stratigraphic records abstract allogenic and autogenic mechanisms both cause changes in the bed elevation of rivers and thereby influence the characteristics of alluvial stratigraphic records asrs allogenic forcing mechanisms can be grouped into five categories whose relative influence varies with timescale climate tectonism base level land use land cover and direct human modification of channels late quaternary asrs are influenced by the greatest range of allogenic forcing variables with climate among the most important autogenic mechanisms of bed elevation change are ubiquitous throughout fluvial systems and are always time transgressive autogenic bed elevation change propagates through drainage networks at predictable rates and results in a time space envelope within which its effects are capable of operating asrs that can be correlated over geographical areas large enough and time intervals small enough to exist outside this envelope most likely result from allogenic forcing this formulation represents a quantitative and geographic set of threshold criteria for distinguishing between autogenic and allogenic mechanisms over late quaternary timescales 10 2 to 10 5 years in tectonically stable regions climate change is the dominant allogenic mechanism and therefore the first order control on the morphology sedimentology pedologic characteristics and chronology of alluvial stratigraphic records that meet or exceed the threshold criteria for demonstrating allogenic causality

wildfire morphologic change and bed material transport at fishtrap creek british columbia abstract in 2003 a wildfire burned nearly two thirds of the fishtrap creek watershed including the forested floodplain annually repeated surveys of the stream channel combined with bed material tracer studies in 2006 and 2007 indicate that the channel has become unstable and that the bed material transport dynamics have changed since the fire using these data the morphologic changes have been quantified and event scale bed material transport rates have been estimated for four post fire freshets the immediate response of the channel during the 2005 and 2006 freshets was a progressive shift in channel morphology from a relatively featureless plane bed morphology devoid of significant sediment accumulations to a riffle pool morphology in which bars cover a significant proportion of the bed this transformation occurred in association with moderate bed material sediment transport rates and only minor bank erosion within the study reach extensive bank erosion occurred during the 2007 and 2008 freshets producing a dramatic change in channel morphology and increasing the local bed material transport rates by an order of magnitude post fire monitoring of streamflow and suspended sediment concentrations a surrogate for upstream sediment supply indicates that post fire increases are not detectable presented in eaton et al in press and our analysis demonstrates that major morphologic changes can occur following wildfire even when the common external drivers of stream discharge and sediment supply remain unchanged

landslide dammed paleolake perturbs marine sedimentation and drives genetic change in anadromous fish large bedrock landslides have been shown to modulate rates and processes of river activity by forming dams forcing upstream aggradation of water and sediment and generating catastrophic outburst floods less apparent is the effect of large landslide dams on river ecosystems and marine sedimentation combining analyses of 1 m resolution topographic data acquired via airborne laser mapping and field investigation we present evidence for a large landslide dammed paleolake along the eel river ca the landslide mass initiated from a high relief resistant outcrop which failed catastrophically blocking the eel river with an approximately 130 m tall dam support for the resulting 55 km long 1 3 km3 lake includes subtle shorelines cut into bounding terrain deltas and lacustrine sediments radiocarbon dated to 22 5 ka the landslide provides an explanation for the recent genetic divergence of local anadromous ocean run steelhead trout oncorhynchus mykiss by blocking their migration route and causing gene flow between summer run and winter run reproductive ecotypes further the dam arrested the prodigious flux of sediment down the eel river this cessation is recorded in marine sedimentary deposits as a 10 fold reduction in deposition rates of eel derived sediment and constitutes a rare example of a terrestrial event transmitted through the dispersal system and recorded offshore

development of sediment slug upstream from the czorsztyn reservoir southern poland and its interaction with river morphology abstract the effects of base level rising upstream of dam reservoirs on in channel sedimentation and interaction of the stored sediments with the gravel bed channel morphology have received little attention so far previous studies however suggested that the feedback mechanism between in channel sedimentation and bank erosion may affect channel morphology here the pattern of the bar area bank erosion and morphology of the gravel bed dunajec river upstream from the czorsztyn reservoir cr constructed in 1997 in southern poland were analyzed from aerial images 1982 2012 and lidar data 2013 in the part of the post dam period with a large flood the average bar area increased significantly in the backwater section and at some distance upstream and then extended in the upstream direction at an average rate of above 40 m y reaching 2 2 km upstream from the cr in 2012 the bar area variation was 40 and 77 explained by local bank erosion in the periods of large and low to moderate floods respectively the sum of bank erosion from the post dam period explained 80 of the variation in the present width depth ratio significantly increased in the backwater section the results showed that the large floods in 1997 in conjunction with backwater inundation initiated intensive bank erosion and bar growth subsequently in the period with low and moderate floods the localized bar bank interaction connected with the flow divergence around the deposited bar led to localized bank erosion and additional bar growth promoting bend development these processes propagating in the upstream direction were facilitated by the existence of a large amount of easily remobilized sediment stored in the floodplain connected with the sedimentation zone from the end of the nineteenth century bend development was controlled by valley confinement causing downstream bend translation in the narrower valley confined section and its extension in the wider unconfined section of past sediment storage the results obtained from this site specific location imply that the occurrence of similar past sediment storage zones of easily remobilized coarse sediments may favor intensive bank erosion and bar growth during large floods and in the case of low transport competence backwater zones of gravel bed rivers where the remobilized sediments cause localized bar growth it may promote morphologically effective bar bank interaction in the period with low and moderate floods

paleohydrology of southwestern texas current statistical methods may be unable to accurately predict recurrence intervals of rare large magnitude floods especially in semiarid regions having positively skewed annual flood distributions great hydrologic variability and widely spaced gaging stations current approaches rely on historical data but catastrophic floods may have recurrence intervals far greater than the length of historical records in the lower pecos and devils rivers of southwestern texas paleoflood discharge and frequency estimates are extended over 10 000 years by the study of slack water flood sediments slack water deposits are typically fine grained sand and silt that accumulate during floods in areas where current velocity is reduced i e in back flooded tributary mouths channel expansions downstream from bedrock spurs and or slump blocks and in shallow caves along bedrock walls radiocarbon dating of organic detritus in slack water deposits establishes the flood chronology while paleoflood discharges can be estimated by slope area techniques paleoflood information extracted from slack water sediments can greatly extend flood records these floods may be weighted like historical data in log pearson type 3 calculations of flood frequency our morphostratigraphic approach combines recorded data with geomorphic evidence to derive estimates of flood frequency this technique offers an inexpensive and rapid way to assess catastrophic flood risk

response and recovery of a subalpine stream following a catastrophic flood the july 15 1982 lawn lake flood in rocky mountain national park colorado was caused by the failure of a 79 yr old earthen dam peak discharges of the flood far exceeded naturally occurring flows and it caused severe channel disturbance along most of roaring river and some parts of fall river this study documents the geomorphic response of a 5 km reach of fall river in the 5 yr following the flood in 1983 the first year after the lawn lake flood snowmelt flows were well above average these high flows together with very high sediment yields from roaring river resulted in significant geomorphic changes on reaches of fall river downstream during the 1983 snowmelt runoff 15 5 x 106 kg of bed load sediment was eroded from the upper part of the study area these loads were at least 1 000 times higher than before the lawn lake flood most of this sediment was then deposited in a highly sinuous reach of fall river in the lower part of the study area this reach had not been much affected by the lawn lake flood but sedimentation during the period of high flow in 1983 completely filled in the channel resulting in the formation of a continuous 2 3 km long depositional zone in 1984 sediment yield from roaring river declined dramatically and this trend continued for the next 3 yr by 1987 the bed load sediment yield in the upper reaches of fall river was only about 0 4 x 106 kg yr the decline in sediment loads resulted in progressive erosion and recovery of the original channel of fall river in the depositional zone reach recovery in the upstream part of the depositional zone was complete by 1985 recovery in the downstream part of the depositional zone took longer because of the continued supply of sediment and because the sediment was mobile less of the time as of 1987 about 80 of the material initially stored in the sedimentation zone had been eroded bed load sediment yields at a sampling site 1 km downstream of the terminus of the depositional zone ranged from 5 x 106 to 11 x 106 kg yr but showed no significant decline over the 5 yr study period the average rate of bed load transport through this reach was at least 100 times greater than before the lawn lake flood but few discernible channel changes resulted from the higher loads

the role of discharge variability in the formation and preservation of alluvial sediment bodies abstract extant planform based facies models for alluvial deposits are not fully fit for purpose because they over emphasise plan form whereas there is little in the alluvial rock record that is distinctive of any particular planform and because the planform of individual rivers vary in both time and space accordingly existing facies models have limited predictive capability in this paper we explore the role of inter annual peak discharge variability as a possible control on the character of the preserved alluvial record data from a suite of modern rivers for which long term gauging records are available and for which there are published descriptions of subsurface sedimentary architecture are analysed the selected rivers are categorized according to their variance in peak discharge or the coefficient of variation cvqp standard deviation of the annual peak flood discharge over the mean annual peak flood discharge this parameter ranges over the rivers studied between 0 18 and 1 22 allowing classification of rivers as having very low 0 90 annual peak discharge variance deposits of rivers with very low and low peak discharge variability are dominated by cross bedding on various scales and preserve macroform bedding structure allowing the interpretation of bar construction processes rivers with moderate values preserve mostly cross bedding but records of macroform processes are in places muted and considerably modified by reworking rivers with high and very high values of annual peak discharge variability show a wide range of bedding structures commonly including critical and supercritical flow structures abundant in situ trees and transported large woody debris and their deposits contain pedogenically modified mud partings and generally lack macroform structure such a facies assemblage is distinctively different from the conventional fluvial style recorded in published facies models but is widely developed both in modern and ancient alluvial deposits this high peak variance style is also distinctive of rivers that are undergoing contraction in discharge over time because of the gradual annexation of the channel belt by the establishment of woody vegetation we propose that discharge variability both inter annual peak variation and flashiness may be a more reliable basis for classifying the alluvial rock record than planform and we provide some examples of three classes of alluvial sediment bodies representing low intermediate and high very high discharge variability from the rock record that illustrate this point

depth variations of azimuthal anisotropy beneath the tian shan mt range nw china from ambient noise tomography abstract seismic anisotropy beneath the tian shan mt range has been well studied with shear wave splitting the origin of asthenospheric anisotropy is mainly attributed to the north south shortening however the crustal anisotropy and its depth variation are poorly constrained in this study we focus on inversion of rayleigh wave phase velocity azimuthal anisotropy in the 5 35 s period bands beneath the tian shan mt range through analysis of continuous seismic ambient noise we use approximately 7 months of available continuous seismic data recorded by 31 broadband seismic stations deployed in the tian shan mt range the tomographic results reveal substantial variations in the azimuthal anisotropy with an increase in the depth in the upper crustal depths the orogen parallel or orogen subparallel azimuthal anisotropy observed in the tian shan mt range likely originates from the lattice preferred orientation of crustal minerals in response to compression whereas the orogen perpendicular or orogen sub perpendicular azimuthal anisotropy in the southern and northern piedmont of the tian shan mt range is related to the stress alignment of cracks fractures due to ongoing north south shortening the pattern of azimuthal anisotropy in the middle to lower crustal and upper most mantle is different from that at the upper crustal depths an orogen perpendicular or orogen sub perpendicular fast direction associated with prominent lower velocities has been observed north and south of lake issyk kul the spatial correlation between the azimuthal anisotropy and the lower velocity anomalies at the middle to lower crustal and upper most mantle depths may suggest a warm melt rich upper mantle below the tian shan mt range which could be attributed to the upwelling asthenospheric mantle flow in that region

crustal thickness variations across the northern tien shan from teleseismic receiver functions variations in crustal thickness from the kazakh shield to the north central tien shan are determined by receiver function analysis of broadband teleseismic p waveforms recorded on the kyrgyzstan seismic telemetry network knet the receiver functions are calculated using a time domain deconvolution approach and are interpreted in terms of a single crustal layer with thickness determined by a grid search comparison of observed receiver functions with synthetics crustal thicknesses average 42 km in the southern kazakh shield and increase to approximately 60 km in the tien shan together with mass balance calculations these results are consistent with the hypothesis that the compensation of the central tien shan relative to the kazakh shield are accommodated by an airy type crustal root with a modest 300 kg m density contrast across the moho

the role of vegetation and bed level fluctuations in the process of channel narrowing abstract a catastrophic flood ire 1965 on plum creek a perennial sandbed stream in the western great plains removed most of the bottomland vegetation and transformed the single thalweg stream into a wider braided channel following eight years of further widening associated with minor high flows a process of channel narrowing began in 1973 narrowing continues today the history of channel narrowing was reconstructed by counting the annual rings of 129 trees and shrubs along a 5 km reach of plum creek near louviers colorado sixty three of these plants were excavated in order to determine the age and elevation of the germination point the reconstructed record of channel change was verified from historical aerial photographs and then compared to sediment stratigraphy and records of discharge and bed elevation from a streamflow gaging station in the study reach channel narrowing at plum creel occurs in two ways first during periods of high flow sand and fine gravel are delivered to the channel temporarily raising the general bed level subsequently several years of uninterrupted low flows incise a narrower channel second during years of low flow vegetation becomes established on the subaerial part of the present channel bed in both cases surfaces stabilize as a result of vegetation growth and vertical accretion of sediment

late holocene sediment accumulation on the northern california shelf oceanic fluvial and anthropogenic influences the late holocene sedimentary record of the northern california continental shelf archives the combined influences of fluvial and oceanic mechanisms of land to ocean sediment flux and provides perspective on the cumulative impacts of major floods and land use change in the drainage basin during historical time piston cores collected on the shelf 50 150 m water depths off the eel and klamath rivers were analyzed to identify lithologies indicative of depositional processes over the past 5 k y and dated using 137cs and 14c methods to resolve spatial patterns in sediment accumulation rates sediment accumulation rates averaged over the past several millennia display along and across shelf gradients that reflect interactions between the shelf flow field and antecedent tectonically produced topography the highest rates 3 6 mm yr 0 4 0 8 g cm2 yr are associated with structural lows on the middle shelf whereas the lowest rates 0 2 0 6 mm yr 0 03 0 05 g cm2 yr occur at structural highs and at the shelf edge this accumulation pattern is spatially coincident with postglacial sediment thicknesses on the shelf and with depocenters that form on shorter time scales in response to oceanic flood events the sediment column exhibits an upward fining sequence consistent with increased bypass of river silt and clay as delta plains progressively filled during the holocene transgression sedimentary event beds indicative of major river floods including two probable hyperpycnal discharges of the eel river within the past 1 k y are preserved stratigraphic evidence of accelerated sediment delivery to the shelf during historical time in the form of increased burial of fluvial mud relative to fine grained sand is superimposed on this natural record this change is concordant with the regional history of forest clearing and related land use practices in the watershed after the early 1800s and appears to record the combined impacts of timber harvesting and several extreme floods after ca a d 1950

the lithosphere asthenosphere boundary and cratonic lithospheric layering beneath australia from sp wave imaging sp and ps scattered wave receiver functions were calculated for nineteen stations across australia and the island of tasmania in order to image the lithosphere asthenosphere boundary and layering within the lithosphere within phanerozoic eastern australia and the eastern margin of the south australia craton prominent sp phases from a negative velocity contrast were found at depths of 61 11 km to 131 9 km consistent with the lithosphere asthenosphere boundary depth range from surface wave tomography these phases imply significant velocity drops over depth ranges of 30 40 km or less and thus cannot be explained by a lithosphere asthenosphere boundary that is controlled by temperature alone rather they imply that the asthenosphere is hydrated with respect to a drier depleted lithosphere or contains a small amount of partial melt the shallowest sp phases have the largest amplitudes and occur in regions with the most recent voluminous volcanism strengthening the link to partial melt at the base of the lithosphere in contrast no significant negative sp phases were found at the base of the thick cratonic lithosphere at the stations in central and western australia implying that the cratonic lithosphere asthenosphere velocity gradient is distributed over more than 50 70 km in depth this gradient may be purely thermal in origin although gradational changes in composition or melt content cannot be ruled out a negative sp phase was observed at depths of 69 8 km to 85 14 km at stations in central and western australia indicating the presence of a drop in velocity internal to the lithosphere this interface within the lithosphere may be a relic of cratonic mantle formation or the result of alteration by melt and metasomatism

new insight into crustal and lithospheric variability beneath the central tien shan nw china revealed by p wave receiver functions abstract the tien shan has experienced intensive crustal shortening and lithospheric deformation making it an ideal site to study the orogeny processes we applied p wave receiver functions to get new insight into crustal and lithospheric variability beneath the central shan region clear p to s converted phases are observed at many recording stations exhibiting double positive converted phases at 5 9 s the corresponding crustal thickness varies from 35 km to 70 km which appears to be relatively thinner beneath the kazakh shield and tarim basin and thicker beneath the southern and northern flanks of the central tien shan the negative converted phases are observed at depths of 30 45 km beneath the central tien shan corresponding to the extremely low seismic velocities in the middle to lower crust revealed by seismic tomography the receiver function results coupled with a regional shear wave velocity model suggest that the lithosphere of the central tien shan has been significantly modified the thickening and thinning of lithosphere may be related to up warped and down warped of mantle and could be associated with the mantle upwelling triggered by bilateral underthrusting of the tarim basin and the kazakh shield respectively beneath the central tien shan

lithosphere and asthenosphere of the tien shan imaged by s receiver functions 1 the s receiver function technique was applied to the recordings from 36 broad band stations in the tien shan the results reveal a pronounced difference in the properties of the lithosphere asthenosphere of the tien shan and those of the neighboring platforms beneath the tien shan an upper mantle lid with an s velocity of about 4 5 km s is underlain at a depth of about 90 km by a low velocity zone where the s velocity drops to 4 1 4 2 km s trends of p and s travel time residuals are consistent with the presence of melt or other liquids in this zone there is no evidence of any similar layer beneath the platforms the crust is 55 65 km thick beneath most of the tien shan and 45 km below the platforms although it thins to about 45 km near the naryn basin in the central tien shan

long river profiles tectonism and eustasy a guide to interpreting fluvial terraces along three rivers at the mendocino triple junction northern california strath cut and fill terraces have formed in response to tectonic and eustatic processes detailed surveying and radiometric dating at multiple sites indicate that lower reaches of the rivers are dominated by the effects of oscillating sea level primarily aggradation and formation of fill terraces during sea level high stands alternating with deep incision during low stands a eustasy driven deposi tional wedge extends tens of kilometers upstream on all rivers tapering to zero thickness this distance is greater than expected from studies of the effects of check dams on much smaller streams elsewhere due in part to the large size of these rivers however the change in gradient is nearly identical to other base level rise studies the depositional gradient is about half that of the original channel middle to upper reaches of each fiver are dominated by the effects of long term uplift primarily lateral and vertical erosion and formation of steep unpaired strath terraces exposed only upstream of the depositional wedge vertical incision at a rate similar to that of uplift has occurred even during the present sea level high stand along rivers with highest uplift rates strath terraces have steeper gradients than the modem channel bed and do not merge with marine terraces at the river mouth consequently they cannot be used to determine altitudes of sea level high stands strath formation is a continuous process of response to long term uplift and its occurrence varies spatially along a river depending on stream power and hence position upstream strath terraces are found only along certain parts of a coastal stream upstream of the aggradational effects of oscillating sea level and far enough downstream that stream power is in excess of that needed to transport the prevailing sediment load for a given size fiver the greater the uplift rate the greater the rate of vertical incision and consequently the less the like lihood of strath terrace formation and preservation

shear wave splitting at central tien shan evidence for rapid variation of anisotropic patterns at active collisional belts the fast polarization axis of shear wave splitting is generally aligned parallel to the strike of the belt which has been proposed to indicate mantle strain that is coherent with crustal deformation a notable exception is central tien shan where anomalous patterns of splitting have previously been observed we here analyze shear wave splitting of sks phases across north central tien shan using digital data from the kyrgyzstan broadband seismic network knet we find a pattern of short wavelength anisotropic heterogeneity that supports complex mantle flow due to small scale convection the along strike variations in mantle structure contrast with the coherent pattern of crustal shortening and indicate that mantle flow is not directly coupled to crustal deformation in this region

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

role of tree dams in the construction of pseudo terraces and variable geomorphic response to floods in little river valley virginia geomorphic response to a 1985 flood in little river valley northern virginia was different in magnitude and style from the largest historic flood in the same valley in 1949 the primary geomorphic activity during the 1985 flood was severe bank erosion and channel gravel deposition rather than the debris flow and avalanching of the 1949 event an unusual and widespread phenomenon of the recent flood was that large trees eroded and transported by the floodwater were aligned parallel to the river banks and at isolated sites were braced and stacked against trees still standing on the floodplain lateral barriers or dams created from these displaced trees allowed the channel to be locally aggraded above the level of the flood plain in these reaches little if any river gravel was deposited on the floodplain even though the adjacent channel floor was raised well above that surface the river has now shifted around the filled segments leaving flat isolated surfaces underlain by channel gravel standing above the level of the modern floodplain these features may be mistaken for terraces alter they become vegetated and the trees bracing the gravels decay interpreting these surfaces to be terrace remnants would lead to a faulty reconstruction of geomorphic history in the little river valley and other valleys where floodplain morphology is controlled by infrequent flood events

imaging the colliding indian and asian lithospheric plates beneath tibet 1 a high resolution image of the base of the lithosphere from s to p converted seismic waves revealed the collision architecture of the indian and asian continental plates beneath the tibetan plateau the base of the indian lithosphere dips northward from a depth of 160 km beneath the himalayas to a depth of 220 km just south of the bangong suture the base of the asian lithosphere is nearly horizontal at the depth of 160 180 km from central to northern tibet there is a vertical gap of about 50 km between indian and asian lithospheres our observation of a well defined thick lithosphere throughout the entire plateau is not consistent with models of wholesale convective instability of a thickened mantle lithosphere which would predict a very thin asian lithosphere the hypothesized sequential southward subduction of tibetan and asian continental lithospheres leading to the growth of the tibetan plateau if correct cannot be occurring below 180 km depth our results along with available geological and geophysical data strongly support that the plateau is predominantly formed by a relatively coherent north dipping subducted indian continental lithosphere in the south which presently can be traced to the middle of the plateau and a south dipping subducted asian lithosphere in the north at a shallower depth

geology isotopes and geochronology of the caijiaping pb zn deposit in the north wuyi area south china implications for petrogenesis and metallogenesis abstract the caijiaping pb zn deposit is a recently discovered subvolcanic hydrothermal deposit in the north wuyi area its mineralization is generally distributed at the contact of rhyolite porphyry and sandstone and in the interlayer crushed zone of early jurassic sandstone sulfide minerals in this deposit mainly consist of abundant sphalerite galena pyrite and chalcopyrite silicification chloritization and sericitization are widely developed and closely related to the pb zn mineralization the 34s values of early dark brown sphalerite marmatite main stage sphalerite and galena 1 1 2 5 average 0 83 suggest that the sulfur was mainly sourced from a magmatic system lead isotope ratios in the sulfide minerals rhyolite porphyry and sandstone are relatively homogeneous 206pb 204pb 17 786 18 612 207pb 204pb 15 504 15 635 208pb 204pb 38 115 38 798 and are compatible with metamorphic rocks of mesoproterozoic zhoutan group wuyi metamorphosed basement early jurassic sandstone deposited in an active continental margin or continental arc setting exhibits low textural maturity and displays geochemical similarities to the zhoutan group the rhyolite porphyry with features of volcanic arc granite also shows an affinity with the zhoutan group sims zircon u pb dating shows that the rhyolite porphyry was emplaced at 156 0 1 2 ma indicating that caijiaping mineralization formed later than 156 ma hf isotope compositions of the rhyolite porphyry ehf t 14 3 to 8 5 average 10 6 imply that it was mainly derived from reworking of ancient crust potassium feldspar selected from felsic veins within the ore cutting f4 fault yields a 40ar 39ar age of 120 0 4 0 ma indicating that the pb zn mineralization formed before 120 ma therefore the age of mineralization is bracketed between 156 and 120 ma combined with regional geological information we propose that the caijiaping mineralization mainly formed from magmatic hydrothermal processes in a regionally extensional setting and the wuyi metamorphosed basement significantly contributed to diagenetic and metallogenic processes in this deposit

sediment yield spatial characteristics and the long term evolution of active earthflows determined from airborne lidar and historical aerial photographs eel river california in mountainous landscapes with weak fine grained rocks earthflows can dominate erosion and landscape evolution by supplying sediment to channels and controlling hillslope morphology to estimate the contribution of earthflows to regional sediment budgets and identify patterns of landslide activity earthflow movement needs to be quantified over significant spatial and temporal scales presently there is a paucity of data that can be used to predict earthflow behavior beyond the seasonal scale or over spatially extensive study areas across 226 km 2 of rapidly eroding franciscan complex rocks of the eel river catchment northern california we used a combination of lidar light detection and ranging and orthorectified historical aerial photographs to objectively map earthflow movement between 1944 and 2006 by tracking the displacement of trees growing on earthflow surfaces we find that 7 3 of the study area experienced movement over this 62 yr interval preferentially in sheared argillaceous lithology this movement is distributed across 122 earthflow features that have intricate elongate planform shapes a preferred south southwesterly aspect and a mean longitudinal slope of 31 the distribution of mapped earthflow areas is well approximated by a lognormal distribution with a median size of 36 500 m 2 approximately 6 of the study area is composed of earthflows that connect to major channels these flows generated an average sediment yield of 19 000 t km 2 yr 1 rock erosion rate of 7 6 mm yr over the 62 yr study period equating to a regional yield of 1100 t km 2 yr 1 0 45 mm yr if distributed across the study area as such a small fraction of the landscape can account for half of the regional denudation rate estimated from suspended sediment records 2200 t km 2 yr 1 or 0 9 mm yr we propose a conceptual model for long term earthflow evolution wherein earthflows experience intermittent activity and long periods of dormancy when limited by the availability of readily mobilized sediment on upper slopes ultimately high order river channels and ephemeral gully networks may serve to destabilize hillslopes controlling the evolution of earthflow prone terrain

three dimensional elastic wave velocity structure of the western and central tien shan arrival times of compressional p and shear s waves generated by earthquakes at local and teleseismic distances and recorded by seismographs located in the western and central tien shan are used to determine one and three dimensional elastic wave velocity structures of the crust and upper mantle beneath the mountain belt the best fit one dimensional structures suggest that the average depth of the mohorovicic discontinuity in this area is 50 km the three dimensional structure of the upper crust reveals thick sediments within each of the major depressions in the region a 7 km thick wedge of sediment beneath the chu depression is outlined at depth by a south dipping plane of seismic activity suggesting the presence of an active decollemont these low velocities extend continuously to the southeast toward issyk kul suggesting a structural relationship between the two however rather than being consumed it appears that issyk kul is overthrusting the surrounding ranges the low velocity sediments in the fergana basin reach depths of 10 km and are bounded on three sides by amorphous bands of seismicity velocities at midcrustal depths generally are lower beneath the central tien shan than beneath the western tien shan this pattern becomes more evident in the uppermost mantle with p velocity contrasts of as much as 10 across a boundary that corresponds roughly to the geographical position of the talasso fergana fault the low velocities beneath the central tien shan exceed 150 km depth but do not appear to be deeper than 300 km depth there is no evidence for a lithospheric root beneath this part of the range rather the low velocities imply the presence of a positive buoyancy force uplifting the mountains evidence that this low velocity region existed before the collision suggests that the tien shan may not owe its rejuvenation simply to its location at the northern edge of a strong tarim basin but rather to an anomalous upper mantle that was easier to deform than the surrounding lithosphere

channel response to sediment wave propagation and movement redwood creek california usa redwood creek north coastal californa usa has experienced dramatic changes in channel confguation since the 1950s a series of large floods in 1955 1964 1972 and 1975 combined with the advent of widespread commercial timber harvest and road building resulted in extensive erosion in the basin and contributed high sediment loads to redwood creek since 1975 no peak flows have exceeded a 5 year recurrence interval twenty years of cross sectional survey data document the downstream movement of a sediment wave in the lower 26 km of this gravel bedded river at a rate of 800 to 1600 m a i durng this period of moderately low flows higher transit rates are associated with reaches of higher unit stream power the wave was initially deposited at a site with an abrupt decrease in channel gradient and increase in channel width the amplitude of the wave has attenuated more than i m as it moved downstream and the duration of the wave increased from eight years upstream to more than 20 years downstream channel aggradation and subsequent degradation have been accommodated across the entire channel bed channel width has not decreased significantly after initial channel widening from large 25 year recurrence interval floods three sets of longitudinal surveys of the streambed showed the highest increase in pool depths and frequency in a degrading reach but even the aggrading reach exhbited some pool development through time the aggraded channel bed switched from functioning as a sediment sink to a significant sediment source as the channel adjusted to high sediment loads from 1980 to 1990 sediment eroded from temporary channel storage represented about 25 per cent ofthe total sediment load and 95 per cent of the bedload exported from the basin

elevation of the 410 km discontinuity beneath the central tien shan evidence for a detached lithospheric root we analyzed p sv converted phases recorded by the kyrgyzstan broadband network knet to investigate the nature of phase transitions in the upper mantle beneath the central tien shan and the kazakh shield we find that p sv phases from the 410 km discontinuity recorded by several stations located along the range front are about 2 s earlier from beneath the tien shan than they are from beneath the kazach shield because the delay times at stations located on the kazakh shield are normal and seismic velocities in the upper mantle beneath this part of the tien shan apparently are low about 4 less than the kazakh shield to the north the early arrival of the conversion from 410 km implies that this discontinuity is elevated by about 20 km because the 410 km discontinuity can be elevated by the introduction of cold material our results are consistent with a model in which the lithosphere in this area developed a root during collision that later detached and is now residing near 410 km depth

response and recovery of the eel river california and its tributaries to floods in 1955 1964 and 1997 abstract northwestern california is prone to regional high magnitude winter rainstorms which repeatedly produce catastrophic floods in the basins of the northern coast ranges major floods on the eel river in 1955 and 1964 resulted in substantial geomorphic changes to the channel adjacent terraces and tributaries this study evaluated the changes and the effects of a moderate flood in 1997 through field observations and examination of aerial photographs that spanned from 1954 to 1996 the purpose was to document the nature and magnitude of geomorphic responses to these three floods and assess the rates and controls on the recovery of the eel river and its tributaries channel widening from extensive bank erosion was the dominant geomorphic change along the lower eel river during major floods as a result of the 1964 flood the largest amount of widening was 195 m and represented an 80 change in channel width channel narrowing characterized the periods after the 1955 and 1964 floods more than 30 years after the 1964 flood however the river had not returned to pre flood width which suggests that channel recovery required decades to complete a long recovery time is unusual given that the eel river is located in an area with a superhumid climate and has an exceptionally high sediment yield this long recovery time may reflect highly seasonal precipitation and runoff which are concentrated in 3 5 months each winter in contrast to the main stem of the eel river the dominant effects of floods on the tributaries of the eel river were rapid aggradation of channel bed and valley floor followed by immediate downcutting dendrogeomorphic data aerial photographs and field observations indicate that thick wedges of gravel derived largely from hillslope failures in upper reaches of the tributaries are deposited at and immediately upstream of the mouths of tributaries as the stage of the eel river exceeded that of the tributaries during major floods in the waning stages of the flood the tributaries cut through the gravel at a rate equal to the lowering of the eel and generated unpaired terraces and nickpoints the complete process of deposition and incision can occur within a few days of peak discharge although reworking of some sediment on the valley floor may continue for years after large floods channel morphology in the tributaries appears to be a product of infrequent high magnitude events the morphology of the tributary channel also appears to be greatly influenced by the frequency and magnitude of mass wasting in headwater areas of small basins

hydrogeomorphic control on tree growth responses in the elton area of the cheshire saltfield uk increment cores were sampled from oak quercus robur and ash fraxinus excelsior growing at elton an area of the cheshire saltfield that has experienced significant subsidence and damage to the natural and built environments in the latter part of the twentieth century ring width measurements for elton trees permitted the construction of one main site chronology elton and four sub chronologies elton a elton b elton c elton ash ring width difference between these and a control chronology identified periods of sustained growth reduction in oak trees commencing in ad 1859 1861 1886 and 1934 growth reductions after 1934 are related to watertable draw down caused by brine pumping from a concentration of nine boreholes at elton up to 2 km from tree sampling locations growth reductions in 1859 1861 and 1886 are likely to be the result of earlier phases of brine pumping in the wheelock valley up to 5 km to the east of elton and these reductions correlate well with historic records of subsidence and pumping activity cessation of pumping in 1977 led to a lagged growth recovery in oak trees between 1981 and 1986 indicating that an artificial drought had been imposed on the elton area for a period in excess off 100 y this research demonstrates a hydrological separation of surface water and groundwater in an area where salt beds are overlain by till and that ring width records of q robur can be used to reconstruct watertable variability and also the spatial impact of solution mining

transport and storage of bed material in a gravel bed channel during episodes of aggradation and degradation a field and flume study the dynamics of sediment transport capacity in gravel bed rivers is critical to understanding the formation and preservation of fluvial landforms and formulating sediment routing models in drainage systems we examine transport storage relations during cycles of aggradation and degradation by augmenting observations of three events of channel aggradation and degradation in cuneo creek a steep 3 gravel bed channel in northern california with measurements from a series of flume runs modeling those events an armored single thread channel was formed before feed rates were increased in each aggradation run output rates increased as the channel became finer and later widened steepened and braided after feed rates were cut output rates remained high or increased in early stages of degradation as the incising channel remained fine grained and later decreased as armoring intensified if equilibrium was not reached before sediment feed rate was cut then a rapid transition from a braided channel to a single thread channel caused output rates for a given storage volume to be higher during degradation than during aggradation variations in channel morphology and surface bed texture during runs that modeled the three cycles of aggradation and degradation were similar to those observed in cuneo creek and provide confidence in interpretations of the history of change cuneo creek aggraded rapidly as it widened shallowed and braided then degraded rapidly before armoring stabilized the channel such morphology driven changes in transport capacity may explain the formation of flood terraces in proximal channels transport storage relations can be expected to vary between aggradation and degradation and be influenced by channel conditions at the onset of changes in sediment supply published in 2011 this article is a us government work and is in the public domain in the usa

directional variations in travel time residuals of teleseismic p waves in the crust and mantle beneath northern tien shan we study the directional variation in travel time residuals using 13 820 p wave arrivals from 1 998 teleseismic events 15 d 98 4 1 mb 7 3 recorded in 1991 1997 by the kyrgyz digital seismic network knet based on a modified version of the iasp91 model that accounts for the kyrgyz crustal thickness beneath knet we convert p wave travel times to travel time residuals dt the de pendence of dt on backazimuth is modeled as one two and four lobed variations in a horizontal plane backus 1965 a least squares fit of the azimuthal variation of dt indicates that the crust in the northern tien shan is about 11 15 km thicker than it is in the kazakh shield and the chu depression from nine knet stations the one lobe model estimates that the slowest p wave travel time direction is 5 0 4 8 almost directly north and the magnitude of variation is 1 71 0 13 sec this result is consistent with an upwelling lower mantle plume for the two lobe model the slowest p wave travel time directions anisotropy term are 89 7 and 269 7 4 7 i e trending east west we find p wave velocity anisotropy of 2 0 2 9 associated with a layer with a thickness of 440 km at the top of the lower mantle the fast direction of the p wave travel time north south azimuthal anisotropy at the top of the lower mantle is 1 parallel to the absolute motion of the india plate and 2 close to the direction of the upwelling hot mantle flow the last result suggests that the azimuthal aniso tropy of the travel time residuals is due to the shape preferred orientation of middle mantle material that results from plume intrusion shear wave splitting studies mak eyeva et al 1992 wolfe and vernon 1998 estimated the fast polarization direction to be parallel to the strike of the geological structures of the northern tien shan 71 29 thus the fast polarization direction determined from these shear wave splitting studies using knet data contradicts differs by 90 the fast travel time direction 0 3 and 179 7 4 7 we determine here using p wave travel time residuals using knet data this suggests that the azimuthal anisotropy determined from p wave travel time variations and from shear wave splitting in sks and skks have different sources

shelf record of climatic changes in flood magnitude and frequency north coastal california continental shelf deposits off the eel river north coastal california document a recent increase in the magnitude and frequency of major hydrologic floods 10 yr recurrence interval the shelf record reveals a sudden three fold increase in sedimentation rate ca 1954 and a concomitant increase in the frequency of preserved flood beds comparison of sedimentary and river discharge records reveals that major floods after ca 1950 had a more pronounced effect on coastal sediment delivery and accumulation offshore than previous recorded events of similar magnitude and that stratigraphic preservation of flood events is highly dependent on flood frequency and net sedimentation rate we contend that this change in marine sedimentation is a response to documented climatic phenomena that have increased the frequency of major floods throughout the western united states during the past half century together with intrabasinal impacts of extreme floods in 1955 and 1964 anthropogenic increase in watershed sediment production is a probable secondary factor

geomorphologic controls on the age of particulate organic carbon from small mountainous and upland rivers 1 to assess the role that erosion processes play in governing the character of particulate organic carbon poc discharged from small mountainous and upland rivers a suite of watersheds from oregon california and new zealand was investigated the rivers share similar geology tectonic setting and climate but have sediment yields that range over 3 orders of magnitude the 14c age of the poc loads is highly correlated with sediment yield carbon isotope mass balances reveal that the rivers carry bimodal mixtures of modern plant and ancient rock derived oc at lower yields modern plant oc dominates the material delivered to the river by sheetwash and shallow landsliding with increasing yield a progressively larger part of the poc is contributed directly from bedrock erosion via deep gully incision our results support the inference that active margin watersheds are important sources of aged poc to the ocean

evolution of the morphology of the river dragonja sw slovenia due to land use changes the effects of increasing agricultural land use on fluvial morphology have received much attention in fluvial research however in several regions in europe a reversing trend of decreasing agricultural activity and land abandonment followed by reforestation is observed the response of fluvial morphology deserves attention because of its large impacts on landscape and riverine habitats with the help of geomorphological mapping multi date aerial photography and a range of dating techniques we reconstructed the evolution of the morphology of the riverbed and the floodplain of the dragonja river in southwestern slovenia the results of this study show that the fluvial morphology in this mediterranean catchment has changed considerably as a result of shifts in agricultural land use in particular large scale land abandonment in the second half of the 20th century until the first half of the 19th century floodplain aggradation prevailed probably around 1870 a large erosion event occurred from which the floodplain did not fully recover a terrace standing 2 5 m above the present floodplain was formed natural reforestation due to depopulation since world war ii caused a reduction in discharge and sediment supply to the river the decreased intensity and frequency of floods allowed invasion of the riverbed by vegetation causing narrowing and incision of the riverbed this resulted in the formation of a terrace which now stands 1 5 m above the present day river this terrace is about 60 years old however the largest increase in forest area occurred since 1975 which intensified this process of riverbed narrowing and incision creating a local terrace at 0 5 m at 0 5 m above the presently meandering river

teleseismic travel time residuals in north america and anelasticity of the asthenosphere abstract the slope a of the relation t s a t p b for the teleseismic s and p travel time residuals t s and t p is practically the only robust observational value that is equally sensitive to the lateral s and p velocity variations in the upper mantle published estimates of a for north america are about twice higher than those at ultrasonic frequencies in olivine at comparable pressures and temperatures in our study lateral variations of the s residuals in north america are found not from the s wave readings which can be easily biased but from accurately determined delays relative to p of the ps phases converted from 410 km and 660 km discontinuities nevertheless the estimates of a thus derived are close to the values obtained with the standard technique the discrepancy between the ultrasonic and seismic estimates of a can be explained by physical velocity dispersion on the assumption of a single absorption band our value of a is consistent with the published values of q in the seismic frequency band and velocities in the ultrasonic range if the high frequency cutoff of the absorption band in the upper mantle beneath western north america is on the order of several hundred hertz however in the literature there are indications of a cutoff at around 1 hz then our data imply the presence of another absorption band at high frequencies outside the seismic frequency band this band may correspond to the viscous dissipation in the walsh walsh j b 1969 a new analysis of attenuation in partially melted rock j geophys res 74 4333 4337 model of penny shaped inclusions of melt

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

fluvial process and the establishment of bottomland trees the effects of river regulation on bottomland tree communities in western north america have generated substantial concern because of the important habitat and aesthetic values of these communities consideration of such effects in water management decisions has been hampered by the apparent variability of responses of bottomland tree communities to flow alteration when the relation between streamflow and tree establishment is placed in a geomorphic context however much of that variability is explained and prediction of changes in the tree community is improved the relation between streamflow and establishment of bottomland trees is conditioned by the dominant fluvial process or processes acting along a stream for successful establishment cottonwoods poplars and willows require bare moist surfaces protected from disturbance channel narrowing channel meandering and flood deposition promote different spatial and temporal patterns of establishment during channel narrowing the site requirements are met on portions of the bed abandoned by the stream and establishment is associated with a period of low flow lasting one to several years during channel meandering the requirements are met on point bars following moderate or higher peak flows following flood deposition the requirements are met on flood deposits high above the channel bed flood deposition can occur along most streams but where a channel is constrained by a narrow valley this process may be the only mechanism that can produce a bare moist surface high enough to be safe from future disturbance because of differences in local bedrock tributary influence or geologic history two nearby reaches of the same stream may be dominated by different fluvial processes and have different spatial and temporal patterns of trees we illustrate this phenomenon with examples from forests of plains cottonwood populus deltoides ssp monilifera along meandering and constrained reaches of the missouri river in montana

crust and mantle beneath western himalaya ladakh and western tibet from integrated seismic data abstract to understand deep structure of the western himalaya ladakh and western tibet we conduct an integrated analysis of teleseismic body wave recordings from the linear array of 16 portable broadband seismographs along a profile running through the himalaya to the karakoram the database includes p and s receiver functions teleseismic p and s residuals and observations of shear wave splitting in sks the analysis reveals beneath the himalaya a cold region at a depth of several hundred kilometers this anomaly can be caused by remnants of tethys subduction and perhaps is unrelated to the ongoing process the present day process is reflected in velocities beneath the lesser himalaya intermediate between those of the crust and the upper mantle this observation can be explained by scraping off the ductile lower crust of the underthrusting indian plate and accumulation of the high velocity crustal material in the frontal region of the thrust zone a representative value of the crustal thickness at the profile is 65 km and at most stations there is no evidence for a low velocity layer at mid crustal depths which makes crustal channel flow unlikely seismic waves in the upper 200 km of the mantle are faster than in global iasp91 model and the structure includes a low velocity layer sandwiched between two high velocity layers we interpret the lower layer as an image of subducted mantle lithosphere of the indian plate shear wave splitting is different in the south and the north in the south the fast direction of anisotropy is normal to the trend of the himalaya and can be interpreted as an effect of the ne motion of the indian lithosphere in the north the fast direction is oriented e w and can be explained by the fabric left in the presently extinct subduction zones in eastern tibet a similar analysis of the p and s receiver functions reveals upper mantle with the s velocities about 5 lower than in the west the mantle in the vicinity of station lsa lhasa contains a low s velocity layer between 160 km and 230 km depths with a velocity reduction of 0 2 km s underlain by the lehmann discontinuity

effects of aggradation and degradation on riffle pool morphology in natural gravel channels northwestern california after the flood of december 1964 12 gaging sections in northern california widened as much as 100 and aggraded as much as 4 m and then degraded to stable levels during a period of 5 years or more as channels aggraded bed material became finer and low to moderate flow through gaging sections in pools became shallower faster and steeper comparisons of longitudinal profiles also show the diminishment of pools as well as a decrease in bar relief accompanying the excessive sediment load as gaging sections degraded hydraulic geometries recovered to a limited degree full recovery probably depends on channel narrowing and further depletion of sediment supply the hydraulic changes with aggradation indicate an increase in the effectiveness of moderate discharges less than i to 2 year recurrence interval annual flood series to transport bed load and shape the bed bars become smaller pools preferentially fill and rimes armored with relatively small gravel tend to erode headward during falling stages and form a gentler gradient excess sediment can thus be more readily transported out of channels when additional contributions from watersheds are usuall slight

sediment continuity through the upland sediment cascade geomorphic response of an upland river to an extreme flood event hillslope erosion and accelerated lake sedimentation are often reported as the source and main stores of sediment in the upland sediment cascade during extreme flood events while upland valley floodplain systems in the transfer zone have the potential to influence sediment continuity during extreme events their geomorphic response is rarely quantified this paper quantifies the sediment continuity through a regulated upland valley fluvial system st john s beck cumbria uk in response to the extreme storm desmond 4 6 december 2015 flood event a sediment budget framework is used to quantify geomorphic response and evaluate sediment transport during the event field measurements show 6500 710 t of sediment was eroded or scoured from the river floodplains banks and bed during the event with 6300 570 t of sediment deposited in the channel or on the surrounding floodplains 6 of sediment eroded during the flood event was transported out of the 8 km channel floodplain sediment storage was seen to be restricted to areas of overbank flow where the channel was unconfined results indicate that rather than upland floodplain valleys functioning as effective transfer reaches they instead comprise significant storage zones that capture coarse flood sediments and disrupt sediment continuity downstream

relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates the tien shan a high seismically active intracontinental mountain belt 1 000 2 000 km north of the himalaya has grown as a result of india s collision with asia1 the crustal shortening 200 50 km refs 2 3 and thickening that gave rise to the tien shan accommodates only a small fraction of india s total penetration into asia 2 000 3 000km and the temporal relationship of deformation in this belt to the india asia collision remains unclear here we report geodetic measurements of the tien shan using the global positioning system gps that indicate that the current crustal shortening rate is nearly half of india s convergence rate with eurasia in this area4 we infer a total shortening rate for the tien shan of 20 mm yr 1 which is approximately twice that inferred previously from the extrapolation of slip rates in the holocene3 and earthquake induced displacements during this century5 suggesting that the rate of mountain building in this region has accelerated several fold since the onset of collision 50 55 myr ago6 7 if as we argue the current shortening rate can be extrapolated to geological timescales then our results suggest that most of the tien shan has been constructed during the past 10 myr perhaps in response to an increased horizontal force following an abrupt rise of the tibetan plateau8 9

upper mantle stratification by p and s receiver functions summary seismic stratification of the upper mantle is investigated by applying two complementary techniques to the records of the graefenberg array in southern germany the anisotropic p receiver function technique kosarev et al 1984 vinnik montagner 1996 is modified by using summary seismic events instead of individual events and different weighting functions instead of the same function for the harmonic angular analysis of the sv and t components of the pds phases the summary events provide better separation of the second azimuthal harmonic than the individual events the parameters of the second harmonics of sv and t thus evaluated should be similar if they reflect the effects of azimuthal anisotropy this can be used as a criterion to identify the anisotropy to detect the sdp phases and their azimuthal variations caused by azimuthal anisotropy we have developed a stacking technique which can be termed the s receiver function technique it includes axis rotation to separate interfering p and s arrivals determination of the principal m component of the s wave motion deconvolution of the p components of many recordings by their respective m components and stacking of the deconvolved p components with weights depending on the level of noise and the angle between the m direction and the backazimuth of the event both techniques yield consistent results for the graefenberg array as indicated by the p receiver functions the upper layer of the mantle between the moho and 80 km depth is anisotropic with dvs vs around 0 03 and the fast direction close to 20 clockwise from north the fast direction of anisotropy below this layer is around 110 the boundary between the upper and the lower anisotropic layers is manifested by the detectable pds and sdp converted phases shear wave splitting in sks is strongly dominated by azimuthal anisotropy in the lower layer asthenosphere

receiver functions for the tien shan analog broadband network contrasts in the evolution of structures across the talasso fergana fault we determined the structure of the crust beneath the central and western tien shan by analyzing broadband 1 20 s analog seismograms of converted p sv phases generated by earthquakes at teleseismic distances and recorded by 14 seismograph stations the one dimensional structures that best explain the waveforms reveal pronounced differences in crustal velocities east and west of the talasso fergana fault specifically the transition zone between the crust and the mantle east of the fault is about 2 times broader than that west of the fault also velocities at depths between 10 and 35 km are about 10 lower in the east although the depth range of these lower velocities is not well resolved the talasso fergana fault is an important boundary for other observables in addition to the structural discontinuities observed at the surface the areas east of the talasso fergana fault are associated with abnormally low mantle velocities outcrops of basalt low q and short wavelength variations in anisotropy integrating these observations we interpret the broad mantle gradient as being due to vertical intrusions of mantle material into the lower crust likewise the low velocities in the midcrust could be thermally induced or due to the introduction of magmatically derived fluids the gross contrast in structure east and west of the talasso fergana fault could reflect a contrast in the dynamics of mountain building in these two regions we postulate that while crustal shortening is the dominant mechanism controlling topography west of the talasso fergana fault vertical uplift caused by a mass deficiency in the upper mantle may contribute significantly to the generation and maintenance of the high elevations east of the fault