ice sheet sources of sea level rise and freshwater discharge during the last deglaciation we review and synthesize the geologic record that constrains the sources of sea level rise and freshwater discharge to the global oceans associated with retreat of ice sheets during the last deglaciation the last glacial maximum 26 19 ka was terminated by a rapid 5 10 m sea level rise at 19 0 19 5 ka sourced largely from northern hemisphere ice sheet retreat in response to high northern latitude insolation forcing sea level rise of 8 20 m from 19 to 14 5 ka can be attributed to continued retreat of the laurentide and eurasian ice sheets with an additional freshwater forcing of uncertain amount delivered by heinrich event 1 the source of the abrupt acceleration in sea level rise at 14 6 ka meltwater pulse 1a 14 15 m includes contributions of 6 5 10 m from northern hemisphere ice sheets of which 2 7 m represents an excess contribution above that derived from ongoing ice sheet retreat widespread retreat of antarctic ice sheets began at 14 0 15 0 ka which together with geophysical modeling of far field sea level records suggests an antarctic contribution to this meltwater pulse as well the cause of the subsequent younger dryas cold event can be attributed to eastward freshwater runoff from the lake agassiz basin to the st lawrence estuary that agrees with existing lake agassiz outlet radiocarbon dates much of the early holocene sea level rise can be explained by laurentide and scandinavian ice sheet retreat with collapse of laurentide ice over hudson bay and drainage of lake agassiz basin runoff at 8 4 8 2 ka to the labrador sea causing the 8 2 ka event

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

channel hydraulics and geomorphic effects of an extreme flood event on the sabie river south africa the effects of the february 2000 extreme flood 6000 7000 m3 s 1 200 year return period flow on channel morphology are examined over 108 km of the semiarid bedrock influenced sabie river south africa the river is incised into bedrock forming a macrochannel with a planform that is fixed over the timescale of change being investigated within the confines of the macrochannel the river may be zoned into distinct channel types pool rapid bedrock anastomosing etc between 1 and 20 km long each characterised by a distinctive assemblage of smaller morphologic units ranging from large lateral bars filling most of the macrochannel to metre scale lee bars and sand sheets changes in morphologic unit composition and spatial coverage are presented for each channel type along with reconstructed flood hydraulics this appraisal is based on 1 10 000 scale aerial photographs taken 5 months before and 7 months after the event the latter verified by post flood field observations some channel types e g cohesive mixed anastomosing displayed widespread sedimentary stripping while others e g bedrock anastomosing remained essentially unchanged at the morphologic unit scale large cohesive lateral deposits were largely unaffected by the flood whereas smaller active channel unconsolidated and consolidated features associated with perennially flowing sub channels were stripped at the scale of channel type change appears to be controlled by a complex combination of factors including i spatial and temporal flow energy level change affecting sediment transport and ii tributary location susceptibility to erosion at the scale of the morphologic unit appears to be linked to elevation above the low flow active channel with features at lower elevations in the channel being stripped field observations suggest that unconsolidated active channel units are re forming at stripped locations

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

geomorphological impacts of a flood event on ephemeral channels in se spain a flood event occurred on 30 september 1997 in three catchments torrealvilla salada and nogalte in se spain which were being monitored for morphological change peak discharges were high in the torrealvilla catchment moderate in the salada and low in the nogalte detailed topographic surveys were made before and after the flood and from these dems of difference were constructed the two sites with highest flow both underwent significant incision of the channel at other sites both scour and aggradation of the channel took place with scour holes of up to 1 m depth eroded elsewhere within the channels major erosion took place downstream of tracks and structures such as check dams that impeded sediment movement the pattern and amounts of change show little relationship to independent factors other than a scale effect of peak discharge behaviour of channels is closely related to local sediment supply sediment flux calculated from changes in volumes at the site is comparable with the other figures produced for ephemeral channels and much higher than for perennially flowing streams

the radiocarbon reservoir effect in proglacial lakes examples from antarctica abstract we studied the apparently old radiocarbon ages from lakes in the dry valleys of antarctica the radiocarbon reservoir effect in these lakes results from two components the inherited age and the residence age the inherited age is derived from input of old carbon primarily from subsurface melt of adjacent glaciers the residence age comes from in situ aging of lake water in an environment sealed from the atmosphere our results indicate that surface melt of glaciers introduces little ancient carbon to the lake system because of rapid gas equilibration with the atmosphere subsurface melt in lakes with large glacier cross sectional areas at the grounding line however can contribute a significant amount of ancient carbon leading to lake bottom reservoir effects in excess of 2700 yr this value can increase to 20 000 yr immediately at the grounding line in most lakes however surface melt far exceeds that from the subsurface and dilutes the effect of ancient carbon making the inherited age relatively low residence ages generally are on the order of a few thousand years but can be as much as 10 000 yr because a residence age is reset when the lake loses its ice cover and is exposed to wind driven mixing its magnitude can provide important information about lake history

kinematic history of the narragansett basin massachusetts and rhode island constraints on late paleozoic plate reconstructions the formation of the narragansett basin of rhode island and massachusetts and the polyphase deformation geometry of the pennsylvanian age basin sediments can be explained by collision and strike slip interactions between an avalonian microcontinent the european north american plate and the african plate during the late paleozoic sinistral movement between an avalonian microcontinent and the european north american plate resulted in formation of pull apart basins subsequently africa moved toward north america along an east west trending dextral megashear zone and collided with the eastern margin of southern north america the narragansett basin is located on the avalonian microcontinent near the suture with the north american continent and in the transition zone between the megashear and the collision tectonic regimes the basin shape stratigraphy and sedimentary relationships can be explained by the coalescence of two composite grabens which formed at different times the thicker northern graben is only affected by one deformation whereas the southern graben shows evidence of four distinct phases of postrifting deformation the first two coaxial folding deformations of the basin sediments are attributed to the closure of the basin complex during collision of africa and north america the third and fourth deformations are interpreted as sinistral r riedal and dextral shears respectively associated with the east west trending megashear system a prograde barrovian metamorphic front started in the western portion of the southern graben slightly after the first deformation and migrated northward and eastward where it is synchronous with the second deformation

holocene glacial history of antarctica and the sub antarctic islands abstract a history of holocene glaciation in the antarctic and sub antarctic affords insight into questions concerning present and future ice sheet and mountain glacier behavior and global climate and sea level change existing records permit broad correlation of holocene ice fluctuations within the region in several areas ice extent was less than at present in mid holocene time an important exception to this is the west antarctic ice sheet which has undergone continued recession throughout the holocene probably in response to internal dynamics the first neoglacial ice advances occurred at 5 0 ka although some sites e g western ross sea lack firm evidence for glacial expansion at that time glaciers in all areas underwent renewed growth in the past millennium and most have subsequently undergone recession in the past 50 years ranging from near catastrophic in parts of the antarctic peninsula to minor in the western ross sea region and sections of east antarctica this magnitude difference likely reflects the much greater warming that is taking place in the antarctic peninsula region today as compared to east antarctica

holocene depositional environments and surface level changes at lake fryxell antarctica we report on holocene surface level variations of lake fryxell antarctica as determined from multiproxy analyses of 18 sediment cores during this time accumulating sediments were predominantly aeolian sand with algal and carbonate laminae based on stratigraphy mineralogy and diatom assemblages we suggest some carbonate laminae were deposited when lake level dropped leading to concentration and subsequent precipitation of salts although lake level appears to have remained relatively stable throughout the holocene minor 4 5 m below present lowstands occurred at approximately 6400 4700 3800 and 1600 cal yr bp the stability of lake fryxell during the holocene contrasts with large scale variability at other dry valleys lakes eg lake vanda and with suggestions from chemical diffusion models of a near desiccation at 1200 cal yr bp the reason for the comparative stability of lake fryxell is uncertain but may be the result of basin morphology and the number aspect and proximity of meltwater sources

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

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

quantifying different riverbank erosion processes during an extreme flood event riverbank erosion is a major contributor to catchment sediment budgets at large spatial scales data is often restricted to planform channel change with little information on process distributions and their sediment contribution this study demonstrates how multi temporal lidar and high resolution aerial imagery can be used to determine processes and volumes of riverbank erosion at a catchment scale remotely sensed data captured before and after an extreme flood event enabled a digital elevation model of difference dod to be constructed for the channel and floodplain this meant that the spatial area that could be assessed was extensive three dimensional forms of bank failures could be mapped at a resolution that enabled process inference and the volume and rates of different bank erosion processes over time could be assessed a classification of riverbank mass failures integrating form and process identified a total of 437 mass failure polygons throughout the study area these were interpreted as wet flow mass failures based on the presence of a well defined scarp wall and the absence of failed blocks on the failure floor the failures appeared to be the result of bank exfiltration antecedent moisture conditions preceding the event and the historic development of the channel using one dimensional hydraulic modelling to delineate geomorphic features within the main boundary of the macrochannel an estimated 1 466 322m2 of erosion was interpreted as fluvial entrainment occurring across catchment areas from 30 to 1668 km2 only 8 of the whole riverbank planform area was occupied by mass failures whilst fluvial entrainment covered 33 a third of the volume of material eroded came from mass failures even though they occupied 19 of the eroded bank area the availability of repeat lidar surveys combined with high resolution aerial photography was very effective in erosion process determination and quantification at a large spatial scale

geomorphic effectiveness of extraordinary floods on three large rivers of the indian peninsula abstract the efficacy of extreme events is directly linked to the flood power and the total energy expended the geomorphic effectiveness of floods is evaluated in terms of the distribution of stream power per unit boundary area over time for three very large floods of the 20th century in the indian peninsula these floods stand out as outliers when compared with the peak floods per unit drainage area recorded elsewhere in the world we used flood hydrographs and at a station hydraulic geometry equations computed for the same gauging site or a nearby site to construct approximately stream power curves and to estimate the total energy expended by each flood critical unit stream power values necessary to entrain cobbles and boulders were estimated on the basis of empirical relationships for coarse sediment transport developed by williams williams g p 1983 paleohydrological methods and some examples from swedish fluvial environments i cobble and boulder deposits geografiska annaler 65a 227 243 in order to determine the geomorphological effectiveness of the floods the estimates indicate that the minimum power per unit area values for all three floods were sufficiently high and stream energy was above the threshold of boulder movement 90 w m 2 for several tens of hours the peak unit stream power values and the total energy expended during each flood were in the range of 290 325 w m 2 and 65 160 10 6 j respectively the average and peak flood powers were found to be higher or comparable to those estimated for extreme palaeo or modern floods on low gradient alluvial rivers

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

antarctic lakes suggest millennial reorganizations of southern hemisphere atmospheric and oceanic circulation the phasing of millennial scale oscillations in antarctica relative to those elsewhere in the world is important for discriminating among models for abrupt climate change particularly those involving the southern ocean however records of millennial scale variability from antarctica dating to the last glacial maximum are rare and rely heavily on data from widely spaced ice cores some of which show little variability through that time here we present new data from closed basin lakes in the dry valleys region of east antarctica that show high magnitude high frequency oscillations in surface level during the late pleistocene synchronous with climate fluctuations elsewhere in the southern hemisphere these data suggest a coherent southern hemisphere pattern of climate change on millennial time scales at least in the pacific sector and indicate that any hypothesis concerning the origin of these events must account for synchronous changes in both high and temperate latitudes

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

morphological impacts of flow events of varying magnitude on ephemeral channels in a semiarid region abstract flows in ephemeral channels in semiarid areas are only occasional and channel changes are episodic but the flash floods can be devastating and have major geomorphological impacts data on morphological impacts of flows in semiarid areas are needed to increase understanding of the dynamics and variability of geomorphic responses in such channels for this purpose nine reaches of river channel in three catchments in se spain the nogalte torrealvilla and salada have been sites for measurement of flows and their effects over the period 1997 2012 the sites encompass a range of channel size channel morphology substrate vegetation and position within the catchments a major difference is between schist and marl bedrock areas peak flow stage has been recorded and topography surveyed at frequent intervals and after major flow events over the 16 year period an average of 0 5 flow events per year has been recorded at the schist sites and an average of one per year at the marl sites but occurrence has been highly variable from year to year threshold daily rainfall for channel flow is mostly 15 20 mm but higher rainfalls do not always produce flow one to two major floods have occurred in each of the catchments in the period including the extreme flood event of september 2012 in the nogalte catchment measured morphological changes have occurred between 2 and 10 times at the monitored sites the same size flow can have differing effects depending on the state of the system low flow can mobilise sediment without producing much morphological change the long term trajectory of the reaches and the sediment substrate has a major influence on response to events channel change is governed by threshold values of hydraulic conditions the measurements provide an indication of the scale of maximum erosion and deposition that occurs within the channels and on the floodplains over a range of flow magnitudes and the flow impacts that need to be considered in management

radiocarbon reservoir effects in human bone collagen from northern iceland human bone collagen from a series of icelandic human pagan graves was radiocarbon 14c dated to aid understanding of early settlement landnam chronologies in northern iceland these individuals potentially consumed marine protein the 14c age of samples containing marine carbon requires a correction for the marine 14c reservoir effect the proportion of non terrestrial sample carbon was quantified via measurement of carbon stable isotopes 13c using a simple mixing model based on 13c measurements of archaeofaunal samples non terrestrial carbon was also quantified in six pig bones from the archaeofaunal dataset assuming all non terrestrial carbon in human and pig bone collagen was marine derived calibrated age ranges calculated using a mixed intcal09 marine09 calibration curve were consistent with an early settlement date close to landnam but several samples returned pre landnam age ranges measurements of nitrogen stable isotopes 15n strongly suggest that many of the human bone collagen samples contain freshwater diet derived carbon icelandic freshwater systems frequently display large freshwater 14c reservoir effects of the order of 10 000 14c years and we suggest that the presence of freshwater carbon is responsible for the anomalously early ages within our dataset in pig samples the majority of non terrestrial carbon is freshwater in origin but in human samples the proportion of freshwater carbon is within the error of the marine component 10 this presents a major obstacle to assessing temporal patterns in the ages of human remains from sampled graves although the majority of grave ages are within the same broad calibrated range

luminescence dating of paleolake deltas and glacial deposits in garwood valley antarctica implications for climate ross ice sheet dynamics and paleolake duration the formation of perched deltas and other lacustrine deposits in the mcmurdo dry valleys of antarctica is widely considered to be evidence of valley filling lakes dammed by the grounded ross sea ice sheet during the local last glacial maximum with lake drainage interpreted as a record of grounding line retreat we used luminescence dating to determine the age of paleolake deltas and glacial tills in garwood valley a coastal dry valley that opens to the ross sea luminescence ages are stratigraphically consistent with radiocarbon results from algal mats within the same delta deposits but suggest radiocarbon dates from lacustrine carbonates may overestimate deposit ages by thousands of years results suggest that late holocene delta deposition into paleolake howard in garwood valley persisted until ca 3 5 ka this is significantly younger than the date when grounded ice is thought to have retreated from the ross sea our evidence suggests that the local stranded ice cored till topography in garwood valley rather than regional ice sheet dynamics may have controlled lake levels for some mcmurdo dry valleys paleolakes age control from the supraglacial ross sea drift suggests grounding and up valley advance of the ross sea ice sheet into garwood valley during marine oxygen isotope stage mis 4 71 78 ka and the local last glacial maximum 9 10 ka this work demonstrates the power of combining luminescence dating with existing radiocarbon data sets to improve understanding of the relationships among paleolake formation glacial position and stream discharge in response to climate change

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

geomorphological impacts of an extreme flood in se spain abstract long term field studies in semiarid ephemeral streams are rare these geomorphic data are essential for understanding the nature of the processes in order to develop modelling for risk assessments and management an extreme flood event on 28 september 2012 affected the murcia region of se spain including long tem monitoring sites on two fluvial systems in the guadalentin basin the nogalte and torrealvilla detailed morphological data were collected before and immediately after the event and the amount of morphological change erosion and deposition have been related to peak flow conditions at the sites on the nogalte channel peak flow reached 2500 m3 s 1 at the downstream end of the catchment in less than 1 h the event had a recurrence interval of 50 years based on rainfall records and damage to old irrigation structures the major effect in the braided gravel channel of the nogalte was net aggradation with massive deposition in large flat bars the measured changes in bankfull capacity were highly correlated with most hydraulic variables net changes in cut and fill in cross sections on the nogalte were highly related to peak discharge and stream power but much less so to measures of hydraulic force velocity shear stress unit stream power relationships of amount of erosion to hydraulic variables were much weaker than for amount of deposition which was largely scaled to channel size and flow energy changes on the torrealvilla were much less than on the nogalte and net erosion occurred at all sites sites on the nogalte channel in schist exhibited higher deposition than those of the torrealvilla sites on marl for the same hydraulic values overall less morphological change took place in the extreme event on the nogalte than predicted from some published hydraulic relations probably reflecting the high sediment supply and the hydrological characteristics of the event the results demonstrate the high degree of adjustment of these channels to the occasional high magnitude flash flood events and that such events need to be allowed for in management the detailed quantitative evidence produced by these long term monitoring sites provide valuable rare data for modelling morphological response to flood events in ephemeral channels

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

geomorphic response to an extreme flood in two mediterranean rivers northeastern sardinia italy analysis of controlling factors abstract a high magnitude low frequency flash flood affected two ungauged rivers northeastern sardinia italy on 18 november 2013 this study investigates the response of channel reaches in a mediterranean environment featuring different morphological settings i e alluvial semialluvial and bedrock boundaries with the aims of i detecting the morphological effects of this large flood and ii analyzing a range of morphological and hydraulic variables as potential controlling factors of channel response channel widening was the dominant geomorphic response observed and it occurred at different magnitudes among the study subreaches within individual subreaches channel width increased from 1 1 to 6 2 times the pre flood width a significant trend in channel widening is observed especially in alluvial subreaches where the narrowest channels were prone to enlarge more compared to the widest channels considerable erosion of valley sides also occurred in confined and partly confined semialluvial and bedrock subreaches a range of parameters influenced the geomorphic role of the flood and a series of selected morphological and hydraulic controlling factors showed robust correlations with changes in channel width although correlations were stronger in alluvial subreaches analysis and documentation of channel response and its variability through different morphological settings is crucial to provide a basis from which to forecast future river sensitivity to geomorphic adjustment to high magnitude floods and improve flood management strategies

assessment of downstream trends in channel gradient total and specific stream power a gis approach geographic information systems gis analyses of digital elevation models dems coupled with catchment area based discharge estimation techniques provide a relatively simple means of modelling contiguous downstream trends in channel gradient total stream power and in riverscapes conducive to regime analysis also specific stream power for a small high relief coastal catchment in se australia good agreement was obtained between channel gradients derived from a 25 m cell size dem and field survey equivalents over distances of several kilometres indicating that channel gradients derived from dems can have a reasonable degree of absolute as well as relative accuracy over multi kilometre reach scales assessment of downstream rates of change in channel gradient and specific stream power across four river systems suggests that some of the river reaches most responsive to high magnitude floods occur in zones where these variables rapidly decrease downstream modelling of downstream trends in channel gradient total and specific stream power from catchment wide dems has potential to provide a framework with which to investigate conceptual and empirical models between channel gradient stream power and the form and dynamics of river systems

refining measurements of lateral channel movement from image time series by quantifying spatial variations in registration error abstract remotely sensed data provides information on river morphology useful for examining channel change at yearly to decadal time scales although previous studies have emphasized the need to distinguish true geomorphic change from errors associated with image registration standard metrics for assessing and summarizing these errors such as the root mean square error rmse and 90th percentile of the distribution of ground control point gcp error fail to incorporate the spatial structure of this uncertainty in this study we introduce a framework for evaluating whether observations of lateral channel migration along a meandering channel are statistically significant given the spatial distribution of registration error an iterative leave one out cross validation approach was used to produce local error metrics for an image time series from savery creek wyoming usa and to evaluate various transformation equations interpolation methods and gcp placement strategies interpolated error surfaces then were used to create error ellipses representing spatially variable buffers of detectable change our results show that for all five sequential image pairs we examined spatially distributed estimates of registration error enabled detection of a greater number of statistically significant lateral migration vectors than the spatially uniform rmse or 90th percentile of gcp error conversely spatially distributed error metrics prevented changes from being mistaken as real in areas of greater registration error our results also support the findings of previous studies second order polynomial functions on average yield the lowest rmse and errors are reduced by placing gcps on the floodplain rather than on hillslopes this study highlights the importance of characterizing the spatial distribution of image registration errors in the analysis of channel change

garwood valley antarctica a new record of last glacial maximum to holocene glaciofluvial processes in the mcmurdo dry valleys we document the age and extent of late quaternary glaciofluvial processes in garwood valley mcmurdo dry valleys antarctica using mapping stratigraphy geochronology and geochemical analysis of sedimentary and ice deposits geomorphic and stratigraphic evidence indicates damming of the valley at its ross sea outlet by the expanded ross sea ice sheet during the last glacial maximum damming resulted in development of a proglacial lake in garwood valley that persisted from late pleistocene to mid holocene time and in the formation of a multilevel delta complex that overlies intact supraglacial till and buried glacier ice detached from the ross sea ice sheet radiocarbon dating of delta deposits and inferred relationships between paleolake level and ross sea ice sheet grounding line positions indicate that the ross sea ice sheet advanced north of garwood valley at ca 21 5 ka and retreated south of the valley between 7 3 and 5 5 ka buried ice remaining in garwood valley has a similar geochemical fingerprint to grounded ross sea ice sheet material elsewhere in the southern dry valleys the sedimentary sequence in garwood valley preserves evidence of glaciofluvial interactions and climate driven hydrological activity from the end of the pleistocene through the mid holocene making it an unusually complete record of climate activity and paleoenvironmental conditions from the terrestrial antarctic

revisiting growth and decline of late quaternary mega lakes across the south central tibetan plateau abstract lake basins record critical interactions between the hydrosphere cryosphere and atmosphere their sediments and shoreline landforms archive timing duration and intensity of past climatic variability and environmental impacts over a variety of timescales thousands of lake systems spread across the internally drained tibetan plateau today of which many are only the salty remains of much more expansive paleolakes in the past this study presents new shoreline ages integrated with quantitative digital topographic analysis and regional geomorphic evidence to reconstruct the sizes and extents of late quaternary rift lake systems for the south central tibetan plateau this study presents optically stimulated luminescence osl and the first k feldspar post infrared infrared pirir stimulated luminescence ages for zabuye caka and dawa tso and tests if these lakes were once part of a singular pleistocene mega lake established across four n s rift systems our new results show that two large but separate paleolake systems developed in the latest pleistocene earliest holocene and no lake larger than 6460 km2 has existed since at least 41 ka in the lunggar region early holocene paleolakes expanded up to 7 modern 220 335 km3 with two to four fold asymmetric lake expansion in the west compared to the east findings corroborate earlier investigations implying that dramatic runoff increase and or evapotranspiration reduction prompted rapid earliest holocene lake expansion precipitation variability in combination with permafrost degradation temperature and wind strength governed paleolake moisture balance open system lake behavior and evolving drainage configurations across complex topography explain delayed onsets of lake regression and punctuated lake decline this suggests abrupt holocene climate shifts are not necessarily required for punctuated lake decline lastly unique geomorphological and paleoclimatic similarities between tibetan and east african rift lakes highlight the potential for some tibetan paleolakes to function as natural climate amplifiers over both short and geologic timescales

episodes of vertical accretion and catastrophic stripping a model of disequilibrium flood plain development this paper describes flood plains formed episodically by vertical accretion along high energy laterally stable channels in southeastern australia overbank deposition gradually builds a flood plain of fine textured alluvium over a period of hundreds or thousands of years following which catastrophic erosion by a single large flood or a series of more moderate floods strips the flood plain to a basal lag deposit from which it slowly reforms this periodic destruction appears due to the progressive development of large levee banks and flood plain surfaces of highly variable relief as the levees and flood plain grow overbank flow is gradually displaced from the broad flood plain into the main channel and flood plain backchannels with a resulting concentration of erosional energy eventually high flows greatly exceed erosional thresholds and wholesale scour of the channel boundary and flood plain occurs vertical accretion flood plains at different stages of development result in a wide range of bankfull recurrence intervals even along the same river some of these flood plains are so infrequently flooded that they can be mistaken for terraces formed under a prior flow regime the almost random but catastrophic nature of this flood plain erosion means that sediment supply and transport are highly variable and probably impossible to predict this model of flood plain formation is seen as only part of a continuum of alluvial environments ranging from vestigial coarsegrained traction load flood plains along high energy rivers in narrow gorges to extensive low gradient flood plains in which alluvial stratigraphy is dominated by fine grained overbank deposition

a new age model for the sediment cores from academician ridge lake baikal based on high time resolution ams 14c data sets over the last 30 kyr paleoclimatic and environmental implications abstract we constructed a new age model based on high time resolution 14 c data sets from three sediment cores from academician ridge lake baikal for reconstruction of environmental and biological changes in southern siberia during the last ca 30 kyr we used 14 c ages of total organic carbon toc for the model because terrestrial plant residues and biogenic carbonate were not observed in the sediments for accurate dating and age models based on 14 c ages of toc the freshwater 14 c reservoir effect and the effect of dead carbon from land derived organic materials must be estimated in this study we estimated the correction factor for these effects to be 2100 90 yr on the basis of a key layer the 14 c plateau caused by changes in the atmospheric 14 c concentration during the younger dryas yd cooling event the new age scale along with the toc mass accumulation rate mar toc and stable carbon isotope ratio in the sediment cores clearly indicate a rapid decrease in lake productivity and reduced influx of terrestrial organic materials into the lake during the yd 12 8 11 6 cal ka bp productivity was high mar toc up to 19 7 mg cm 2 kyr in and around lake baikal during 9 3 6 4 cal ka bp holocene climate optimum moreover paleoproductivity changes during the last ca 30 kyr in and around the lake baikal were clearly associated with fluctuations in the east asian monsoon intensity as inferred from the 18 o record from sanbao and hulu caves china during the late quaternary wang et al 2008 nature 451 1090 1093

variability of the 14c reservoir effects in lake tangra yumco central tibet china determined from recent sedimentation rates and dating of plant fossils abstract sediments from lakes provide one of the most important archives for past environmental changes on the tibetan plateau the recent sedimentation rate of modern lakes is widely used as an independent method to calibrate 14 c derived chronologies because 14 c values are often affected by a reservoir effect terrestrial plant residues in lake sediments are believed to be the ideal material for 14 c dating because they normally provide the true ages of the sediments in this study we present the spatial and temporal variations in modern sedimentation rates over the past 150 years and evaluate the reservoir effects of 14 c ages determined from bulk sediments and plant residues from lake tangra yumco on the central tibetan plateau the results show that ages determined from plant residues are systematically younger than those of the bulk sediments however the reservoir effects associated with the bulk sediments are much more constant than those of the plant residues highlighting the complicated composition of these macro remains and the fact that they might not be the best dating materials in tangra yumco especially in southern part a similar reservoir effect of 2200 years is observed in the southern and northern parts of tangra yumco based on the dating of modern surface sediments and aquatic plants this study demonstrates the complexity of the reservoir effect in a closed lake on the tibetan plateau and careful consideration must be paid to the use of different approaches to date different materials in order to establish a reliable chronology

large wood recruitment and transport during large floods a review large wood lw elements transported during large floods are long known to have the capacity to induce dangerous obstructions along the channel network mostly at bridges and at hydraulic structures such as weirs however our current knowledge of wood transport dynamics during high magnitude flood events is still very scarce mostly because these are locally rare and thus unlikely to be directly monitored therefore post event surveys are invaluable ways to get insights although indirectly on lw recruitment processes transport distance and factors inducing lw deposition all aspects that are crucial for the proper management of river basins related to flood hazard mitigation this paper presents a review of the quite limited literature available on lw transport during large floods drawing extensively on the authors own experience in mountain and piedmont rivers published and unpublished the overall picture emerging from these studies points to a high catchment specific variability in all the different processes affecting lw dynamics during floods specifically in the lw recruitment phase the relative floodplain bank erosion vs hillslope landslide and debris flows contribution in mountain rivers varies substantially as it relates to the extent of channel widening which depends on many variables itself but also to the hillslope channel connectivity of lw mobilized on the slopes as to the lw transport phase within the channel network it appears to be widely characterized by supply limited conditions whereby lw transport rates and thus volumes are ultimately constrained by the amount of lw that is made available to the flow indeed lw deposition during floods was mostly in terms of volume observed at artificial structures bridges in all the documented events this implies that the estimation of lw recruitment and the assessment of clogging probabilities for each structure for a flood event of given magnitude are the most important aspects for the prediction of lw transport magnitude at any cross section along the river network finally the review discusses the optimal strategies to manage lw related hazard which should consider riparian vegetation and in channel dead wood as key components of river ecosystems and thus should interfere with lw as well as with sediment transport dynamics only for limited spatial and temporal scales

vegetation history climatic changes and indian summer monsoon evolution during the last glaciation 36 400 13 400 cal yr bp documented by sediments from xingyun lake yunnan china abstract we obtained a 9 74 m long sediment core xy08a from xingyun lake in central yunnan province southwest china and used ams radiocarbon dating of terrestrial plant macrofossils to provide a chronology here we present the results of pollen and grain size analyses of the interval 36 400 13 400 cal yr bp and discuss the vegetation history and record of climate change associated with the evolution of the indian summer monsoon ism three stages of regional vegetation change are documented i during the late marine isotope stage 3 36 400 29 200 cal yr bp the study region was occupied by mixed coniferous and evergreen broad leaved forest dominated by pinus and evergreen quercus with tsuga abies picea growing on the surrounding mountains ii during the last glacial maximum lgm 29 200 17 600 cal yr bp cold temperate coniferous forest dominated by species of abies picea expanded and reached a maximum extent and at the same time the extent of evergreen broadleaved forest increased iii from 17 600 to 13 400 cal yr bp the hemlock forest and abies picea forest began to decline until they disappeared completely in the early phase of the last deglaciation while pine forest and evergreen broadleaved forest dominated the surrounding areas the vegetation history indicates a generally drying climate from 36 400 to 13 400 cal yr bp suggesting a gradual weakening of the ism with the weakest ism influence occurring during the early part of the last deglaciation when the climate was the driest the regional temperature first decreased intermittently and then increased gradually being mild and wet during the late mis3 stage followed by the coldest but not the driest climate during the lgm when the temperature was at least 3 c lower than at present

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

accumulation and marine forcing of ice dynamics in the western ross sea during the last deglaciation ice shelf grounding lines off the coast of antarctica have retreated over the past 20 000 years precise dating of moraines suggests the timing of retreat in the ross sea was controlled by the interplay between accumulation and ocean forcing

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

holocene dynamics of the arctic s largest ice shelf ice shelves in the arctic lost more than 90 of their total surface area during the 20th century and are continuing to disintegrate rapidly the significance of these changes however is obscured by the poorly constrained ontogeny of arctic ice shelves here we use the sedimentary record behind the largest remaining ice shelf in the arctic the ward hunt ice shelf ellesmere island canada to establish a long term context in which to evaluate recent ice shelf deterioration multiproxy analysis of sediment cores revealed pronounced biological and geochemical changes in disraeli fiord in response to the formation of the ward hunt ice shelf and its fluctuations through time our results show that the ice shelf was absent during the early holocene and formed 4 000 years ago in response to climate cooling paleoecological data then indicate that the ward hunt ice shelf remained stable for almost three millennia before a major fracturing event that occurred 1 400 years ago after reformation 800 years ago freshwater was a constant feature of disraeli fiord until the catastrophic drainage of its epishelf lake in the early 21st century

thresholds and the spatial variability of flood power during extreme floods abstract analysis of the effects of extreme events on overall landscape form has shifted geomorphic attention away from a focus on the magnitude and frequency relationship of discharge to a focus on flood power this paper analyzes the variation in flood power both at a station and downstream in a basin of differing lithologies and discusses the geologic and geomorphic controls on flood power design floods ranging from the 2 year discharge tothe 500 year discharge are routed trough a drainage basin and channel boundary shear stress and unit stream power are calculated using hec 2 along 21 cross valley transects because of the strong lithologic control on valley width and channel slope an irregular downstream pattern of flood power emerges which reflects primarily the pattern in valley width narrow valleys correspond to a greater percent of channel conveyance during large magnitude floods and increasing rates of depth increases thus maximizing flood power in these zones the opposite occurs in anomalously wide valleys where flood power is minimized a downstream spatial pattern emerges reflecting both local and general controls for a given probability event flood power varies at least threefold within the basin with a maximum occuring in a specific downstream section holding flood power constant produces an extremely wide range in flow probabilities in order to establish a link between critical flood power magnitude and flow frequency minimum flood powers are developed from an analysis of previous work on catastrophic flooding for humid alluvial channels these minimum thresholds tentatively correspond to 100 n m2 or 300 w m2 for shear stress and unit stream power respectively discharges required to attain these critical flood powers vary from events roughly twice the 100 year flood to a maximum of roughly 18 times the discharge of the 100 year flood

developing inorganic carbon based radiocarbon chronologies for holocene lake sediments in arid nw china abstract inorganic carbonates are often used to establish radiocarbon 14c chronologies for lake sediments when terrestrial plant remains tpr are rare or when bulk organic matter is insufficient for dating a problem that is common for many lakes in arid regions however the reservoir effect re as well as old carbon contributed from the lakes catchment make it difficult to establish reliable chronologies here we present a systematic study of inorganic 14c ages of two lake sediment sequences one from a small enclosed saline lake lake gahai in qaidam basin and the other from a large freshwater lake lake bosten in xinjiang modern dissolved inorganic carbon dic of the lakes paleo lake sediments exposed in the catchment and mollusk shells in core sediments from lake gahai were dated to assess the re and the contribution of pre aged carbon to the old ages in the cores we propose a statistical regression to assess more than one re for the 14c carbonate ages within our sedimentary sequences old radiocarbon ages contributed by detrital carbonates were assessed by comparing the ages of mollusk shells with those of carbonates at the same sediment depths we established the re of the authigenic component and assessed detrital old carbon contributions to our two sites and this was used to correct the 14c ages based on this approach we developed age models for both cores and tested them using 210pb ages in both cores and tpr based 14c ages recovered from lake bosten we further tested our age models by comparing carbonate based oxygen isotope 18o records from both lakes to an independently dated regional speleothem 18o record our results suggest if sedimentary sequences are densely dated and the re and the contribution of old carbon from detrital carbonates can be ascertained robust chronological frameworks based on carbonate based 14c determinations can be established

last glacial holocene geochronology of sediment cores from a high altitude tibetan lake based on ams 14c dating of plant fossils implications for paleoenvironmental reconstructions abstract we obtained three sediment cores from a high altitude lake lake pumoyum co altitude 5020 m asl on the southern tibetan plateau for reconstruction of environmental changes during the last glacial holocene transition in this study we established the first reliable chronology for sediment cores from lake pumoyum co ca 18 5 cal ka bp at the bottom by 14c analyses of terrestrial plant residue concentrates prc 125 m and aquatic plant residues the calibrated ages of the prc fraction in the surface sediment were nearly modern 0 1 0 1 cal ka bp and the 13c values 22 to 24 were agreed well with those of modern terrestrial c3 plants in addition we estimated 14c reservoir ages of macrophyte remains from changes in their 13c values the major climate boundary layers in the cores transitions to bolling allerod 14 5 0 5 cal ka bp younger dryas 12 8 0 1 cal ka bp and preboreal 11 6 cal ka bp were confirmed by our new 14c chronology the transition to the bolling allerod warm phase from the last glacial 14 5 0 5 cal ka bp coincided with an obvious lithologic boundary a rapid decrease in the abundance of the macrophyte remains in the lake pumoyum co sediment cores

grain size along two gravel bed rivers statistical variation spatial pattern and sedimentary links a new set of field data facilitates a detailed analysis of variations in bed material grain size within two confluent gravel bed rivers in northeastern british columbia canada a preliminary assessment of grain size variability establishes a basis for examination of the spatial pattern of grain size change standard anova techniques are inappropriate because individual samples have unequal variances and are not normally distributed alternative tests for homoscedasticity and comparison of means are therefore utilized within site between sample variability is not significant the grain size distributions that were obtained at individual sites are therefore representative of the depositional environments that were sampled in both rivers mean grain size does vary significantly between sites and there is therefore a basis for examining the data for spatial patterns such as downstream fining textural variations along the two rivers studied here are complex and show negligible overall fining in over 100 km this is the consequence of a large number of tributary inputs and non alluvial sediment sources which are the legacy of late pleistocene glaciation the identification of lateral sources like these is fundamental for understanding textural changes within rivers the sedimentary link a channel reach between significant lateral sediment inputs provides a means of isolating fluvial maturation processes abrasion and sorting from contingent lateral inputs strong fining trends are apparent in most links and classification of grain size measurements according to their location within particular links greatly improves the statistical explanation of textural variation identification of sedimentary links provides a means of applying models of fluvial fining processes so isolation of link networks will aid the development of basin scale models of textural variation 1998 john wiley sons ltd

high time resolution ams 14c data sets for lake baikal and lake hovsgol sediment cores changes in radiocarbon age and sedimentation rates during the transition from the last glacial to the holocene abstract high time resolution 14 c dating of lake baikal sediment cores indicates negative and positive anomalies of calculated linear sedimentation rate lsr 1 1 and 35 6 cm ka respectively during the period of climate transition from the last glacial to holocene the timing of the lake baikal apparent lsr anomalies is consistent with that of the changes in the atmospheric radiocarbon concentration 14 c during younger dryas rapid cooling event 14 c dating of lipids in the lake baikal surface sediments revealed that the sources of sedimentary lipids were different in each basin in the northern basin of lake baikal the 14 c age of total lipids from the surface sediment 4 0 14 c ka was found to be older than that of toc 1 6 14 c ka by contrast the 14 c age of total lipids in the southern basin was younger than that of the toc by ca 0 7 3 0 ka in the lake hovsgol sediment cores ages of the main lithologic boundaries during the last glacial interglacial transition were estimated based on new 14 c data sets toc concentration in the cores started to rapidly increase at 13 8 0 3 14 c ka at the base of the basinwide finely laminated layer deposited during bolling allerod the base of the layer diatomaceous mud corresponds to the end of younger dryas event 10 6 0 1 14 c ka

changes in vegetation and environment in yamzhog yumco lake on the southern tibetan plateau over past 2000 years abstract high resolution palynological analyses of the sediment of yamzhog yumco lake can potentially provide new insight into vegetation change and climate dynamics of the southern tibetan plateau over the past 2000 years the chronology presented herein is based on 210pb and ams 14c dates from the macro remains of plants reconstruction of vegetation types temperature and moisture indices indicate that the vegetation was alpine meadow under relatively wet and cool conditions from approximately 100 to 780 ce later the vegetation between approximately 780 and 1400 ce was alpine steppe with a warmer and drier climate prevailing during the medieval warm period mwp then the vegetation during the period from approximately 1400 to 1890 ce reverted back to alpine meadow under relatively cold and moist climate conditions which may have corresponded to the little ice age lia since the 20th century an alpine steppe has dominated the landscape developed under a dry climate with a lower effective moisture climate records from yamzhog yumco lake have confirmed a cold moist warm dry climate oscillation on the southern tibetan plateau over the past 2000 years comparison of pollen records with other climatic records suggests that the climate changes in the southern tibetan plateau were generally similar to those in the northern tibetan plateau as well as those in westerly dominated central asia additionally climate patterns were found to be the opposite of those in the east asian monsoon controlled region the temperature variations inferred from the records correlate well with changes in the solar irradiance and northern hemispheric temperature which suggests a possible link between solar forcing and climate variabilities over the last 2000 years on the southern tibetan plateau in addition the enhancement and southward shift of the westerlies is determined to have significantly contributed to the high moisture conditions on the southern tibetan plateau during the lia

use of uranium thorium dating to determine past 14c reservoir effects in lakes examples from antarctica the chronologies of many lacustrine records suffer from radiocarbon reservoir effects due to the presence of dissolved dead carbon or to slow air water exchange here we use the tims uranium thorium disequilibrium method in conjunction with ams radiocarbon dating to determine the age of lacustrine carbonates and to quantify the past radiocarbon reservoir effect in two antarctic lakes with differing characteristics by correcting a single sample u th age for detrital contamination a 14 c offset of v18 000 yr was obtained for carbonates from the former grounding line of the ross sea ice sheet in glacial lake trowbridge this large reservoir effect is believed to result from the direct input of old co2 from glacial meltwater in the second example an isochron approach on coeval samples formed at the bottom of lake vida now exposed due to lower lake level yielded an age of 9550 340 yr b p and a radiocarbon reservoir age of 3600 yr this offset was probably the result of lack of aeration due to perennial ice cover and or strong density stratification this evidence for long term isolation of the lake bottom indicates another level of hardship for life in the dry valley lacustrine environment an environment studied as an analogue for extreme periods of earth history as well as for exobiological implications the success of the u th technique on these two examples indicates that tims u th dating will be of widespread use in dating the important climate information recorded in the dry valleys both within and beyond the 14 c age range fl 2001 elsevier science b v all rights reserved

downstream variation in stream power abstract stream power has a significant influence on many form and process attributes of the fluvial system using a similar approach to that suggested by d m lawler in 1992 and 1995 a model is developed to explore how stream power might vary in the downstream direction based on the assumption that the longitudinal profile of the river has an exponential form no particular discharge is necessarily specified but near bankfull flows are regarded as significant morphologically and one such discharge is the focus here total stream power per unit channel length qs is predicted to peak at an intermediate location the position of which depends on the ratio b where b and are the downstream rates of change of discharge and slope respectively if b is a relatively conservative quantity then the form of the longitudinal profile and in particular its degree of concavity will have the major influence on the position of maximum stream power specific stream power w is even more sensitive to and is expected to peak closer to the headwaters about half way between source and the location of the stream power maximum although this will depend on how channel width w varies with distance from source the model is tested along three connected streams of different size in the catchment of the river trent taking advantage of a relationship between mean annual flood and link magnitude which enables this near bankfull discharge to be estimated at any point within the network the model is verified in so far as stream power does attain a mid basin maximum but the observed and predicted locations of the maxima do not always correspond largely because of the distinctive variation in discharge and especially slope along individual pathways for example maximum power lies far downstream along the trent because of the large increase in mid basin discharge associated with a series of large closely spaced tributaries the importance of slope is borne out by the near headwater locations for specific power maxima which tend to be further upstream than predicted along all three rivers as a result of the steepness of upper reaches the variety of geomorphic settings produces deviations from expectation which has implications for the movement and storage of material in the fluvial system

palaeoshoreline records of glacial isostatic adjustment in the dry valleys region antarctica we present a new record of crustal deformation for the dry valleys and surrounding region of antarctica values of crustal tilt resulting from the differential uplift of lacustrine strandlines are derived and linked with age data to provide a history of solid earth deformation since deglaciation we present tilt directions and gradients for 13 strandlines formed c 18 100 2100 cal yr bp derived gradient magnitudes increase exponentially with age and indicate an ongoing response to deglaciation since the last glacial maximum azimuths of crustal tilting are consistently down to the se towards west antarctica this tilt pattern is opposite to that predicted by models of glacial isostatic adjustment for antarctica tilt magnitudes are significantly larger than tilted strandlines documented elsewhere in the world suggesting an influence from thin crust and weak mantle underlying the region this study presents the first use of lacustrine strandline tilts to document crustal deformation due to glacial unloading in antarctica and provides an important new datum for constraining glacial isostatic adjustment models for more than a century observations of uplifted and tilted marine and lacustrine strandlines have been used to understand glacial isostatic adjustment gia from retreating ice sheets e g spencer 1891 goldthwait 1908 as the earth s crust rebounds in response to ice mass loss ice proximal shorelines are raised and tilted away from ice load centres these geological shoreline records can be used in different ways depending on whether original elevation and or age of the features are known when both the original elevation and age are known uplift through time can be reconstructed the most common application of this case is analysis of marine raised beaches and shorelines where past elevation is determined through comparison to present day sea level radiocarbon dates from organic material extracted from shoreline deposits are correlated with raised beach elevations to produce a relative sea level curve e g hall denton 1999 lambeck et al 2002b baroni hall 2004 when corrected for eustatic sea level change relative sea level curves reflect the influence of solid earth and geoid variations resulting from deglaciation providing essential constraints for models of glacial isostatic adjustment that solve the sea level equation farrell clark 1976 peltier et al 1978 lambeck chappell 2001 mitrovica milne 2003 peltier 2004 for lake palaeoshorelines the original shoreline elevation is unknown but differential uplift since the time of deposition results in shoreline tilt analysis of strandline tilt through time provides a record of solid earth deformation since deglaciation for the case of glacial isostatic adjustment the total amount of uplift is a function of shoreline position relative to former ice mass centres greatest uplift occurs closer to the centre of ice mass loss and decreases away from the load subsidence occurs in the forebulge region e g clark et al 1978 shorelines located between the ice load and forebulge tilt away from the centre of ice loss whereas shorelines outboard of the forebulge tilt towards the load centre in addition to tilt direction both temporal and spatial variances in tilt magnitude manifest ice history and geometry older deglacial shorelines have a greater magnitude of tilt than younger shorelines from the same location and shorelines closer to the centre of ice mass loss have a greater magnitude of tilt than shorelines of the same age located farther away from the load given these relationships analysis of the direction magnitude and rate of tilting provides valuable information regarding ice history intersections of projected strandline tilt directions have been used to interpret the location of past ice mass centres improving reconstructions of former ice geometry barnett peterson 1964 andrews barnett 1972 tilted palaeoshorelines linked with age data provide a relaxation curve for the earth s crust since deglaciation enabling studies of mantle rheology and lithospheric thickness parameters crucial for understanding the geodynamic processes involved in from hambrey m j barker p f barrett p j bowman v davies b smellie j l tranter m eds antarctic palaeoenvironments and earth surface processes geological society london special publications 381 http dx doi org 10 1144 sp381 26 the geological society of london 2013 publishing disclaimer www geolsoc org uk pub ethics by guest on september 16 2013 http sp lyellcollection org downloaded from

glacial lake victoria a high level antarctic lake inferred from lacustrine deposits in victoria valley we present evidence of a large lake glacial lake victoria that existed in victoria valley in the dry valleys region of antarctica between at least 20 000 and 8600 14c yr bp at its highstands glacial lake victoria covered 100 km2 and was ca 200 m deep the chronology for lake level changes comes from 87 ams radiocarbon dates of lacustrine algae preserved in deltas and glaciolacustrine deposits that extend up to 185 m above present day lakes on the valley floor the existence of glacial lake victoria as well as other large lakes in the dry valleys indicates a climate regime significantly different from that of today at the last glacial maximum and in the early holocene copyright 2002 john wiley sons ltd

paleosecular variations refining the chronology of the sediments from the pearl river delta southern china a high resolution paleosecular variations record since 6 kyr including direction and relative intensity was derived from the pearl river delta prd sediments in southern china constrained by the radiocarbon ages in this paper the comparison of both direction and relative intensity with other adjacent records confirmed that the non dipole field has common fluctuations in the centennial to millennial timescales this pattern provides some profound tied points to correlate the sediment sequence in the different deposition environments the significant age offsets of the similar secular variation features between the different records corroborate the radiocarbon errors in dating the sediments this work further showed that the geomagnetic secular variations can serve as an effective tool to determine the sediments age and correlate the stratigraphy for the different deposition environments in a wide region

a holocene palaeomagnetic secular variation record from huguangyan maar lake southern china summary a composite holocene sediment profile 5 m in length constrained by both radiocarbon dating and magnetic susceptibility based correlation was obtained from three livingstone piston cores collected in 10 m water depth in the huguangyan hgy maar lake southern china the homogeneous silty clay indicates stable and continuous deposition the dominant magnetic carrier is magnetite in the pseudo single domain grain size range and thus is suitable for recording palaeomagnetic secular variations psv results show that the hgy psv curves can be correlated faithfully to the counterparts at a regional scale therefore the psv data is a potential tool for stratigraphic correlation and for further refining the chronological framework of lake sediment sequences from southern china further comparison of the hgy psv records with the coeval european and north american counterparts confirms the existence of strong permanent magnetic flux lobes at the core mantle boundary the discrepancy in amplitude and out phase pattern among the different regional records may be ascribed to the evolution of the magnetic flux lobes

holocene ice recession at polygon spur reedy glacier antarctica the holocene history of outlet glaciers affords information on the behavior and mechanisms controlling the extent of the east antarctic ice sheet here we present both new radiocarbon and recalcul

profiling interactions between the westerlies and asian summer monsoons since 45 ka insights from biomarker isotope and numerical modeling studies in the qaidam basin

which tributaries disrupt downstream fining along gravel bed rivers tributaries and other lateral sediment sources can have a significant impact on river bed sediment texture and in turn on channel form sufficiently voluminous or distinct sediment inputs redefine the mainstem grain size distribution punctuating downstream maturation and isolating a sequence of discrete sedimentary links within these links fining processes usually dominate such that models of sorting and abrasion when applied to individual links provide reasonable predictions of grain size change links represent the fundamental natural unit within which fining models can be tested developed and applied identification of significant lateral sources is therefore important yet beyond vague references to relative tributary size sediment load and sediment calibre no criteria exist for the a priori discrimination of such sources in this paper a procedure for identifying significant lateral tributary sources without the benefit of grain size information is outlined a high resolution characterisation of bed material texture along two canadian gravel bed rivers facilitated classification of all their perennial tributaries as either significant or insignificant three absolute tributary basin parameters and their relative counterparts chosen to reflect the likely controls on tributary significance are then used to develop a discriminant function which isolates a large proportion of significant tributaries while minimising incorrect classifications examination of consistently misclassified anomalous tributaries reveals the importance of lateral source spacing and of inconsistencies in the geomorphic history of the contributing basins in turn a general tributary categorisation procedure is suggested which includes a logistic regression model for attaching probability statements to individual classifications the generality of the discriminant and logistic functions cannot be assessed because of the lack of other suitable data sets

glacial and postglacial sedimentation in the fryxell basin taylor valley southern victoria land antarctica abstract a 9 14 m long sediment sequence was recovered from lake fryxell taylor valley southern victoria land antarctica and investigated for its chronology and sedimentological mineralogical and biogeochemical changes the basal part of the sequence is dominated by coarse clastic matter i e mainly sand the sediment composition suggests that a lake existed in fryxell basin during the middle weichselian by ca 48 000 cal year bp after a short period of lake level lowstand ca 43 000 cal year bp lower taylor valley became occupied by the proglacial lake washburn which was at least partly supplied by meltwater and sediments from the ross ice sheet that was advanced to the mouth of taylor valley evaporation of lake washburn to lower levels started during the last glacial maximum at ca 22 000 cal year bp long before the ross ice sheet retreated significantly lake level lowering was discontinuous with a series of high and low stands from ca 4000 cal year bp environmental conditions were similar to those of today and lower fryxell basin was occupied by a small lake this lake evaporated to a saline or hypersaline pond between ca 2500 and 1000 cal year bp and refilled subsequently

flash flood hydrology in karstic terrain flumineddu canyon central east sardinia abstract in the last five winters 2004 2008 several exceptional meteorological events producing flash floods have been registered in central east sardinia the first of these december 2004 was the most severe and caused important geomorphic changes in the riu flumineddu watershed where the influence of human activity is limited the hydrological characterisation of this flood is extremely difficult because of the lack of streamflow gauges and the relative paucity of meteorological stations in the region peak discharge of the fluviokarstic riu flumineddu canyon has been estimated based on a distributed hydrological model topkapi and on empirical methods based on geomorphic and sedimentological observations the comparison between the results derived from these independent methods allows us to obtain the best possible estimate of peak discharge differences between modelled and measured peak flows can be attributed to water losses and or gains along the river channel from interactions with the underground karst drainage network the december 2004 flood with an estimated recurrence interval of at least 65 years generated overbank flow and destroyed several bridges in upstream reaches caused important changes in channel morphology and sediment distribution and was able to move boulders up to 1 m in diameter in downstream reaches

dating quaternary lacustrine sediments in the mcmurdo dry valleys antarctica abstract reports of erroneously old 14c dates for modern antarctic materials have thrown doubt into 14c chronologies the carbon reservoir effect purported to exist in quaternary lacustrine sediments of the mcmurdo dry valleys was investigated by studying 14c distribution and testing alternate dating techniques our results show that the carbon reservoir effect is not pervasive stream and near shore microbial mats and dissolved inorganic carbon dic in the surface waters of lake fryxell are in equilibrium with modern 14co2 the surface waters of lake hoare and lake bonney however have dic 14c ages of 1650 and 2080 yr b p respectively these older age estimates are suggested to be due to the direct input of large amounts of glacial melt with relict dic on the other hand lake fryxell receives only a minor component of its inflow directly from a glacier while a large component must travel long distances in numerous shallow ephemeral streams after leaving local valley glaciers this mode of melt water input allows the water to equilibrate with modern co2 before entering the lake bottom water 14c ages for lake hoare closely match surface sediment ages supporting the widely published period 1200 yr b p after a 1650 yr reservoir correction when most dry valley lakes apparently evaporated to small brine ponds and or disappeared completely lake bonney bottom water is 8000 yr b p carbon dating is shown to be a viable technique for lake edge deposits and possibly lake bottom deposits where a correction to the sediment surface age can be obtained however we conclude that deep water paleolake deposits can not be reliably dated using 14c alone because of an inability to determine the age of the reservoir correction i e accounting for the initial carbon reservoir plus the age of the bottom water a suite of alternative and complimentary dating techniques were tested on modern and late holocene lacustrine deposits these include thermoluminescence tl 210pb 137cs and paleomagnetism of these techniques tl or the more sensitive optically stimulated luminescence holds the most promise for correcting lake sediment 14c ages tl dating of the modern lake hoare sediments showed an 1000 yr relict signal this signal is unaffected by the age of the lake water both 210pb and 137cs occurred in very low levels in the sediments and do not appear to be viable dating techniques for the perennially ice covered lakes of the mcmurdo dry valleys paleomagnetism was not suited to the coarse grained nature of lake hoare bottom sediments but could be a useful alternative given a finer sediment type

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

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

late wisconsin and early holocene glacial history inner ross embayment antarctica abstract lateral drift sheets of outlet glaciers that pass through the transantarctic mountains constrain past changes of the huge ross ice drainage system of the antarctic ice sheet drift stratigraphy suggests correlation of reedy iii reedy glacier beardmore beardmore glacier britannia hatherton darwin glaciers ross sea mcmurdo sound and younger terra nova bay drifts radiocarbon dates place the outer limits of ross sea drift in late wisconsin time at 24 000 13 000 yr b p outlet glacier profiles from these drifts constrain late wisconsin ice sheet surface elevations within these constraints we give two extreme late wisconsin reconstructions of the ross ice drainage system both show little elevation change of the polar plateau coincident with extensive ice shelf grounding along the inner ross embayment however in the central ross embayment one reconstruction shows floating shelf ice whereas the other shows a grounded ice sheet massive late wisconsin holocene recession of grounded ice from the western ross embayment which was underway at 13 040 yr b p and completed by 6600 6020 yr b p was accompanied by little change in plateau ice levels inland of the transantarctic mountains sea level and basal melting probably controlled the extent of grounded ice in the ross embayment the interplay between the precipitation low late wisconsin and high holocene values and the influence of grounding on outlet glaciers late wisconsin thickening and late wisconsin holocene thinning with effects dying out inland probably controlled minor elevation changes of the polar plateau

upper limits of flash flood stream power in europe abstract flash floods are characterized by strong spatial gradients of rainfall inputs that hit different parts of a river basin with different intensity stream power values associated with flash floods therefore show spatial variations that depend on geological controls on channel geometry and sediment characteristics as well as on the variations of flood intensity this stresses the need for a field approach that takes into account the variability of the controlling factors post flood assessment of peak discharge after major floods makes it possible to analyse stream power in fluvial systems affected by flash floods this study analyses the stream power of seven intense return period of rainfall 100 years at least in some sectors of the river basin flash floods that occurred in mountainous basins of central and southern europe from 2007 to 2014 in most of the analysed cross sections high values of unit stream power were observed this is consistent with the high severity of the studied floods the highest values of cross sectional stream power and unit stream power usually occur in mediterranean regions this is mainly ascribed to the larger peak discharges that characterize flash floods in these regions the variability of unit stream power with catchment area is clearly nonlinear and has been represented by log quadratic relations the values of catchment area at which maximum values of unit stream power occur show relevant differences among the studied floods and are linked to the spatial scale of the events values of stream power are generally consistent with observed geomorphic changes in the studied cross sections bedrock channels show the highest values of unit stream power but no visible erosion whereas major erosion has been observed in alluvial channels exceptions to this general pattern which mostly occur in semi alluvial cross sections urge the recognition of local or event specific conditions that increase the resistance of channel bed and banks to erosion or like short flow duration reduce the geomorphic effectiveness of the flood

a methodological framework for hydromorphological assessment analysis and monitoring idraim aimed at promoting integrated river management a methodological framework for hydromorphological assessment analysis and monitoring named idraim has been developed with the specific aim of supporting the management of river processes by integrating the objectives of ecological quality and flood risk mitigation the framework builds on existing and up to date geomorphological concepts and approaches and has been tested on several italian streams the framework includes the following four phases 1 catchment wide characterization of the fluvial system 2 evolutionary trajectory reconstruction and assessment of current river conditions 3 description of future trends of channel evolution and 4 identification of management options the framework provides specific consideration of the temporal context in terms of reconstructing the trajectory of past channel evolution as a basis for interpreting present river conditions and future trends a series of specific tools has been developed for the assessment of river conditions in terms of morphological quality and channel dynamics these include the morphological quality index mqi the morphological dynamics index mdi the event dynamics classification edc and the river morphodynamic corridors mc and emc the monitoring of morphological parameters and indicators alongside the assessment of future scenarios of channel evolution provides knowledge for the identification planning and prioritization of actions for enhancing morphological quality and risk mitigation

a method for the assessment and analysis of the hydromorphological condition of italian streams the morphological quality index mqi article i nfo a new index has been developed for the hydromorphological assessment of italian rivers the method was designed to comply with the eu water framework directive requirements but its use can be extended to other applications in river management the evaluation of stream morphological quality is preceded by a phase of river segmentation consisting ofan initial division of the network intoriver reaches with homogeneous morphological characteristics the evaluation procedure consists of a set of 28 indicators which were defined to assess longitudinal and lateral continuity channel pattern cross section configuration bed structure and substrate and vegetation in the riparian corridor these characteristics are analyzed in terms of geomorpholog ical functionality artificiality and channel adjustments indicators classes and the scoring system were defined based on expert judgement the scoringsystemleads tothe definition of the morphologicalquality index mqi application of the method to 102 river reaches covering a wide range of physical conditions and human pres sures of italian streams enabled the testing of the overall methodology and the refinement of the indicators and scores limitations strengths and the applicability of the method are also discussed in the paper