the geomorphic dynamics and environmental history of an upper deltaic floodplain tract in the sacramento san joaquin delta california usa a multi proxy approach was used to examine the geomorphic dynamics and environmental history of an upper deltaic oodplain tract in the sacramento san joaquin delta california three long cores were collected from the mccormack williamson tract mwt and these cores were analyzed for bulk density loss on ignition ne clay and silt content al concentration magnetic susceptibility pollen and charcoal radiocarbon dates obtained for the cores were converted into calendar years and an age depth model was constructed long term vertical accretion and sedimentation rates were estimated from the age depth model cross core relations show that coarse sediment generally accumulates more rapidly and has greater magnetic susceptibility compared to ne sediment percentage ne and loi data show a strong linear relationship that indicates ooding is the primary mechanism for the deposition of particular organic matter on the oodplain and that landscape wash load has contributed a highly consistent fraction of persistent organic matter averaging 5 5 per cent to the site down core grain size pro les show two hydrological domains in the cores namely millennial ne coarse uctuations superimposed on general up core ning coarse sediment is viewed as channel or near channel overbank deposits whereas ne deposits are considered to be distal overbank ood deposits the coarse ne uctuations are indicative of changing depositional settings as channels migrated laterally across mwt whereas the upward ning trend re ects a combination of self limiting overbank deposition as oodplain elevation increased and decreasing competence as sea level rise reduced ood pulse energy slopes mwt has been cross cut and incised numerous times in the past only to have the channels abandoned and subsequently lled by ne sediment the channels around mwt attained their modern con guration about 4000 years ago mwt likely came under tidal in uence at about 2500 cal bp wetlands have recently developed on mwt but they are inorganic sediment dominated copyright 2004 john wiley sons ltd

evolution of geothermal systems around the red sea the current thermal regime around the red sea was initiated by a mantle plume beneath ethiopia eretria yemen and sw of saudi arabia at about 31 ma before the present the evolution of the geothermal systems around the red sea is coeval to the initial onset of volcanism over the separated land masses eritrea ethiopia djibouti yemen saudi arabia and egypt at 14 ma the entire tectono magmatic activities around the red sea gave rise to several geothermal provinces over the continents surrounding the red sea represented by thermal springs and fumaroles at several locations in eretria djibouti ethiopia yemen and saudi arabia these countries have the potential to develop these resources like ethiopia to mitigate co2 emissions in countries like saudi arabia and to enhance the gdp gross domestic product of the economically backward countries the geothermal resources have the potential to make these countries energy independent in future

preservation potential for late quaternary river alluvium valley sequences of late quaternary alluvial units reflect alluvial preservation as well as alluvial production factors effects of lateral channel migration incision aggradation and channel stability on preservation potential are explored and then considered in the light of 14 available data sets cartographically dated and model data based on lateral channel migration well mapped and dated late quaternary valley unit surveys and composite age frequency plots for dated alluvial units and flood sediments despite much expectable variation between sites and the complex effects of river activity combinations a common characteristic of the data sets examined is the significance of preservation factors lateral migration tends to eliminate older units as it creates new alluvial deposits whereas incision may lead to the preferential preservation of older units beyond the incision slot aggradational environments are likely to preserve more complete records although simultaneous lateral migration may eliminate possibly repeatedly the upper parts of alluvial units the common pattern of inset and incised streams within pleistocene and early holocene fills or bedrock gives finite extent to later units within narrowing valleys so that development of new valley floor units is necessarily at the expense of reprocessing earlier ones floods associated with both slack water deposits and berms are also responsible for the removal of accessible earlier materials thus limiting the preserved record of earlier events in light of these censoring effects of river activities the sequence of preserved late quaternary units within uk sequences is reconsidered it is concluded that preservation potential factors have led to spatial and temporal bias in the alluvial record and that both here and elsewhere preservation potential needs to be considered systematically alongside variable sedimentation resulting from allogenic environmental factors when interpreting the alluvial archive copyright 2003 john wiley sons ltd journal of quaternary science

the chronology and long term dynamics of a low energy river system the kelvin valley central scotland the long term holocene channel and floodplain dynamics of a low gradient low energy fine grained aggradational fluvial system within a formerly glaciated landscape in central scotland the kelvin valley are described from a series of sediment stratigraphic transects and 12 14c assays in a headwater reach between kirkintilloch and kilsyth the 14c assays and dated archaeological sites on the floodplain together suggest that the river kelvin ceased to aggrade more than 2000 years ago probably much more so the 4 6 m of channel and floodplain deposits are almost entirely of early to mid holocene age the kelvin valley is characterized despite its low flow characteristics by a highly variable floodplain architecture in which some transects suggest long term channel stability and strong partitioning of floodplain sedimentation and others indicate high channel mobility this variation makes the application of general models of fluvial evolution difficult copyright 2007 john wiley sons ltd

fluvial development and the sediment regime of the lower calder ribble catchment northwest england in the lower reaches of the calder lancashire tributary of the ribble catchment northwest england five river terraces set into the surrounding glacial terrain have been mapped and their underlying sediments radiocarbon dated the earliest terrace t1 reflects sandur style deposition during deglaciation and it aggraded in a reach cut into glacial diamict and glaciolacustrine muds incision below t1 spanned the start of the holocene driven by a combination of reduced sediment supply under a stabilising landscape and lower base levels t2 had aggraded and was being abandoned by 4000 bc its formation latterly involving a period of comparative stability in terms of channel migration perhaps a function of extensive forest cover and sea levels reaching above present day levels the last 3000 years were marked by substantial changes in the sedimentary regime with increased and varying sediment supply driving cycles of cut and fill and greater lateral channel migration these changes coincided with the first widespread and substantial reductions in forest cover and a progression towards an agricultural landscape between the aggradation of terraces t3 and t4 there was a substantial increase in sediment supply which is broadly in keeping with the erosion history in the surrounding uplands this sediment slug appears to have induced a switch from highly sinuous meandering to lower sinuosity channels characterised by lateral scroll style migration late holocene vegetation changes particularly woodland removal driven by anthropogenic land pressure appear to have rendered the floodplain prone to channel migration and the landscape more susceptible to erosion

geochemistry of some gases in hydrothermal fluids from the southern juan de fuca ridge five samples of hydrothermal fluids from two vent areas on the southern juan de fuca ridge were analyzed for dissolved gases concentrations in the end member hydrothermal fluid of h2 270 527 mol kg ch4 82 118 mol kg and co2 3920 4460 mol kg are well above values in ambient seawater and are similar to concentrations reported for other ridge crest hydrothermal systems the carbon isotopic ratios of the ch4 13c 17 8 to 20 8 and co2 13c 3 6 to 4 7 suggest that at least some of the ch4 and co2 in the fluids is basalt derived the range of 13c values for the basalt derived co2 is 6 8 to 9 7 calculated by assuming conservation of recharge co2 during hydrothermal circulation apparent temperatures of equilibration between the ch4 and the basalt derived co2 range from 640 c to 750 c small amounts of ethane c2h6 ch4 0 9 10 3 2 2 10 3 propane and butane detected in the samples may also have formed in the basalt one sample of almost pure 95 5 hydrothermal fluid contained a significant fraction up to 63 and 74 respectively of the recharge ar and n2 this suggests that the fluid has not undergone extensive vapor liquid phase separation

particle clusters in gravel bed rivers an experimental morphological approach to bed material transport and stability concepts structured gravel river beds clearly exert a major influence on bed stability indexing structural stability by field measurements of bed strength neglects the processes operating to entrain and transport bed material in different parts of each structure this study takes a morphological approach to interpreting the critical processes using particle tracing to determine the movement of individual cluster particles over a range of flood event magnitudes and durations the experiment was carried out on the river south tyne uk it uses flow hydrographs measured nearby and also benefits from previous studies of historical development channel morphology and sediment transport at the same site more than 30 clusters were monitored over a seven month period during which clusters occupied 7 16 per cent of the bed threshold flows delimiting three apparently contrasting bed sediment process regimes for cluster particles are tentatively set at 100 m3 s 1 and 183 m3 s 1 durations of flow at these levels are critical for cluster development rather than flow peak values wake particles are transported most easily flow straightening in the wandering channel planform reduces the stability of clusters since mechanical strength is markedly reduced by this change of direction the overall area covered by clusters between significant transport events varies little implying a dynamic equilibrium condition copyright 2005 john wiley sons ltd

the significance of mid channel bars in an active meandering river mid channel bars are common on many active meandering gravel bed rivers but specific information on timescales of development and on the occurrence of bars is lacking data from the river dane in cheshire nw england are presented here which indicate that a sequence of formation from accumulations of coarse gravel on the centre of riffles through to attachment of bars to floodplains is common and takes a period of 5 15 years the sedimentological and vegetation changes through the sequence are described and the ro1e of flow events is discussed about 10 of bends in this meandering reach contain mid channel bars at any time bars develop in steeper sections of the channel and downstream of sharp corners and rapidly eroding apices many of the bars are caused by excessive erosion of the banks which overwidens the channel in the longer term the bars become incorporated in the developing meanders

spatial distribution and the interdecadal change of leading modes of heat budget of the mixed layer in the tropical pacific and the association with enso using heat budget diagnosis of ocean mixed layer from the global ocean data assimilation system the spatial distribution of the leading modes of the heat budget was examined the analysis was for the tropical pacific in 1979 2013 and was based on combined empirical orthogonal function ceof analysis the interdecadal changes of the leading modes and their associations with el nino southern oscillation enso were also analyzed the first leading ceof mode ceof1 corresponds to the enso mature phase the contribution from the zonal advection was relatively small along the equator except the region near the pacific coast of central america the vertical entrainment and diffusion surface heat flux had pronounced maxima with positive negative values along the equatorial central and eastern pacific the meridional advection displayed a different spatial pattern with large positive values on both sides of the equator and smaller values along the equator the total meridional advection anomaly was mainly determined by advection of anomalous temperature by climatological current responsible for broadening of the enso ssta pattern meridionally the zonal advection varied almost simultaneously with the tendency of ocean temperature anomaly in the mixed layer the second leading ceof mode ceof2 included contribution to ssta tendency during the enso developing phase the distribution pattern and amplitude of the zonal advection in the eastern pacific in ceof2 was similar to but with opposite sign to that in ceof1 the amplitudes of the other dynamical and thermodynamical terms were smaller than that in ceof1 and spatial distributions displayed an opposite variation between the pacific coast of central america and central and eastern tropical pacific in ceof2 a comparison of two periods 1979 1999 and 2000 2013 suggested that coupling in the tropical pacific weakened at enso time scales and shifted to a relatively higher frequency regime from 2 to 4 years averaged in 1979 1999 to 1 5 3 years after 2000

mid holocene sub blanket peat alluvia and sediment sources in the upper liffey valley co wicklow ireland a recently exposed section across a rst order valley buried beneath the regional blanket peat on hillside slopes in the upper liffey valley co wicklow is described the section shows two alluvia within a shallow valley form underlain by an extensive boulder and stone line over regional till and weathered granite 14c dates from wood in the alluvia indicate the older alluvium to have formed between 4324 53 bp and 4126 45 bp and the younger between 3217 53 bp and 2975 53 bp the basal layer of the overlying peat yielded a date of 2208 61 bp the younger alluvium shows the effects of soil paludi cation prior to the peat expansion dated pollen analyses elsewhere in the upper catchment con rm the spread of blanket peat over most areas above 350 m after 4000 3600 bp the buried valley was contributing sediments to the mid holocene oodplains in the upper liffey valley prior to the extension of blanket peat over the catchment after which sediment yields from it and the other catchment slopes declined copyright 2003 john wiley sons ltd

hydrodynamic interpretation of a boulder berm and associated debris torrent deposits abstract the hydrodynamic environment associated with a boulder berm is reconstructed from the geometry and sedimentology of the berm and associated debris torrent deposits berms may result from a variety of hydrodynamic scenarios but in this instance the berm was associated with flow separation downstream of an abrupt change in channel morphology sediment fabric analyses are summarized particularly as eigenvalues and these data compared with the fabric of debris flows and clear water gravel deposits although data are few the eigenvalue results can be interpreted consistently as reflecting a transition between the end members of a sediment fabric continuum the value of detailed studies of berm geometry and sedimentology is discussed with reference to their hydraulic significance this latter aspect is important for palaeo discharge reconstruction of both newtonian and non newtonian flows

geostatistical analysis of ground survey elevation data to elucidate spatial and temporal river channel change a digital elevation model dem of a fluvial environment represented landform surface variability well and provided a medium for monitoring morphological change over time elevation was measured above an arbitrary datum using a ground based three dimensional tacheometric survey in two reaches of the river nent uk in july 1998 october 1998 after flood conditions and june 1999 a detailed geostatistical analysis of the elevation data was used to model the spatial variation of elevation and to produce dems in each reach and for each survey period maps of the difference in elevation were produced and volumetric change was calculated for each reach and each survey period the parameters of variogram models were used to describe the morphological character of each reach and to elucidate the linkages between process and the form of channel change operating at different spatial and temporal scales the analysis of channel change on the river nent shows the potential of geostatistics for investigating the magnitude and frequency of geomorphic work in other rivers a flood modified the channel features but low magnitude and high frequency flows rationalized the morphology in spite of relatively small amounts of net flux the channel features changed as a consequence of the reworking of existing material the blocking of chute entrances and redirection of the channel had a considerable effect on the behaviour of the channel such small changes suggested that the distributary system was sensitive to variation in sediment regime plots of the kriging variances against sampling intervals were used to quantify the temporal variation in sampling redundancy ranging between 11 per cent and 93 per cent these curves illustrated the importance of bespoke sampling designs to reduce sampling effort by incorporating anisotropic variation in space and geomorphic information on flow regime variation in the nugget parameter of the variogram models was interpreted as sampling inaccuracy caused by variability in particle size and is believed to be important for future work on surface roughness copyright 2003 john wiley sons ltd

braiding and meandering parameters modifications to standard definttrons of brarding and meandertng are proposed to indicate the morphology of every rrver channel reach quantrtatrvely whether tt has srngle channel or multiple chinnels srnuosrty p rs defined as p l llr where l ts the length of the midline of the channel rn single channel rivers or the wldest channel inlnulti channel rivers and lp is the overall length of the reach braiding rs a measure of channel multiplicity and a new term brard channel ratlo b has been defined as b l rorll o where l o is the total of the mrd channel lengths of a ll the channels tn a reactt anoiiiir e p ssion for the brard channel ratto which gives the same numerical rcsult is b p rorl p where the total sinuosity p o l o1 lp and p has been defined above scatter pio on braid channel ratlo slnuoslty axes show a negatlve correlatton between these parameters as would be expected from the above relatlonshrps stnglechannel rivers b l have relatrvely hrgher srnuosrtres and the upper hmrt of these rs the point at which cut off becomes hrghly probable for multi channel rivers a i sinuoslty iemains low reflecting the limrtrng effect of braid bars on the development of fully dcveloped spiral seconciary flow data analyses showing that increasesin channel slope and bankfull diiharge are associated with changes from meandering to braided morpiology are diverting attenti on from the importance of the rncreased avarlability of bed load grade sediment as a control a variety of river systems supplying water and sediment to the gangetic al luvial plarns of indta have been investigated these alluvral plains are some of the most extensive in the world so the examination has dcpcndcd hcirvi ly t l thc tr c l topographical maps and satel l l te imagcs i he degree of braiding and meanderrng displayed by these rivers varies greatly from rlver to rtver and along the course of part lcular r lve rs ollc of thc first steps has therefore been to devise methods of measuring the degree of brardrng and meandering which can be applied to al l the rivers using maps and satel l i te tmagcs wrth exist ing schemes a r ivcr channel rcach cun either be expressed ln terms of brardrng or meandering sinuosrty although arguments have been developed against the thresholds between brarding and meandering that were suggested by leopold wolman 1957 there have been very few attempts at devlsing common parameters to quantl tat ively express the morphology of channels that vary from one type to the other the f irst part of this paper discusses definit ions of braiding and nrcanderrng rnd thc modif icat ions of these definrtrons that havc been adopted variat ions of thcsc nume rtcal measurements are then r l lustrated hrghhghting some of thc factors that may bc tnvolvcd tn causlng the variatton the meandering parameter sinuosity two minor modrf icat ions have been adopted to the procedures previously used in defining the slnuosity of channcls e g l copold wolman 1957 first ly the channel length has been measured along a l ine that runs mid way between the channel banks this has al lowed mcasuremcnt readl ly from topographical maps aenal photographs and satel lr te images and also has the advantage that the channel length is unlrkely to change ln a major way with changes of r rver water leve l secondly the r ivers rn india show so many transit ions between srngle channel and brarded morphologies that i t was found necessary to abandon the hard and fast dist inct ion be ween braided and meandering classes of r ivers and employ definit ions of brarding and meandering that can each be applied to every rrver no matter whether i t has single or multrple channels or both therefore the meandering sinuostty parameter has been extended to mult i channel situations where i t is based on the mid channel length o f the channe l tha t rs wtdes t tn each reach of the channel belt the modif ied sinuosttv parameter p rs

a link between reduced barents kara sea ice and cold winter extremes over northern continents the recent overall northern hemisphere warming was accompanied by several severe northern continental winters as for example extremely cold winter 2005 2006 in europe and northern asia here we show that anomalous decrease of wintertime sea ice concentration in the barents kara b k seas could bring about extreme cold events like winter 2005 2006 our simulations with the echam5 general circulation model demonstrate that lower troposphere heating over the b k seas in the eastern arctic caused by the sea ice reduction may result in strong anti cyclonic anomaly over the polar ocean and anomalous easterly advection over northern continents this causes a continental scale winter cooling reaching 1 5 c with more than three times increased probability of cold winter extremes over large areas including europe our results imply that several recent severe winters do not conflict the global warming picture but rather supplement it being in qualitative agreement with the simulated large scale atmospheric circulation realignment furthermore our results suggest that high latitude atmospheric circulation response to the b k sea ice decrease is highly nonlinear and characterized by transition from anomalous cyclonic circulation to anticyclonic one and then again back to cyclonic type of circulation as the b k sea ice concentration gradually reduces from 100 to ice free conditions we present a conceptual model which may explain the nonlinear local atmospheric response in the b k seas region by counter play between convection over the surface heat source and baroclinic effect due to modified temperature gradients in the vicinity of the heating area

gravel extraction and planform change in a wandering gravel bed river the river wear northern england within channel alluvial gravel extraction is one of the most important forms of anthropogenically induced morphological change in river channels in british rivers commercial gravel extraction was widespread between the 1930s and 1960s and limited gravel extraction operations to reduce flood risk or maintain navigation continue to the present day despite this gravel extraction has received little attention in uk river studies this paper examines the significance of within channel gravel extraction during the period 1945 1960 on the planform of the river wear in northern england the study focuses on two 3 km piedmont reaches at wolsingham and harperley park located at the margin of the upland zone examination of detailed archival accounts of the gravel extraction operations supplemented by the analysis of aerial photographs has enabled the impact of gravel extraction on the channel of the river wear to be determined sediment budget calculations suggest large sediment deficits in both study reaches however assessing potential impacts simply in terms of a sediment deficit may be misleading as channel adjustments depend on local factors and a detailed consideration of the reach scale sediment budget differences in the nature of channel adjustments of both reaches were found to be primarily a function of the method of gravel extraction employed overall patterns of channel change along the extraction reaches over the past 150 years were similar to reaches where gravel extraction was not practiced this highlights the difficulty of trying to establish the significance of different processes where both local gravel extraction and catchment scale factors climate and land use are operating

dating of post glacial landforms in the central howgills little is known of holocene landform development in upland britain this paper describes a site at middle langdale in the howgill fells of cumbria where large but now stabilized and inactive gullies cut through periglacial material at the base of the gullies large debris cones have buried earlier alluvial sediments on the valley floor on these sediments and buried by the debris cones is a well developed organic soil from which two 14c dates have been obtained in an attempt to estimate the age range of the soil these dates range from 2580 55 years bp for the fine particulate fraction from the base of the organic horizon to 940 95 years bp for fossil rootlets from the uppermost organic layer immediately below the overlying debris cones the pollen evidence suggests that the valley floor site was initially dominated by alder carr and later by a juncus marsh with birch alder and hazel nearby the pollen from the surrounding upland area suggests woodland on the valley sides dominated by oak and elm that was later replaced by a more open environment rich in heath species and in which disturbed ground species were present the magnetic evidence indicates a stable local environment during soil formation but shows a sudden inwash of unweathered debris at the top of the buried soil the evidence suggests that the valley floor was geomorphologically stable throughout the period of soil formation although there was a local change in valley floor vegetation and a reduction of woodland cover on the valley sides at sometime during the period the evidence then points to major geomorphological changes a wave of soil erosion gully development and debris cone deposition perhaps following the scandinavian introduction of sheep farming in the tenth century a d

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

origin of the δ18o and δ2h composition of meteoric waters in ethiopia abstract understanding the origin of the 18 o and 2 h content of meteoric waters is the initial step in using these isotopes in water resources hydrological and hydro climatic investigations specifically isotopes of water are proven tools in a constraining rate and mechanism of groundwater recharge b tracing movement of groundwaters c reconstructing past climate rainfall amount humidity and temperature at various time scales d quantifying water flux across boundaries e g evaporation rates mixing and e complementing regional and global climate models the 18 o and 2 h values in rainfall waters of ethiopia have long been recognised as a regional anomaly regardless of the station s high altitude 2360 m asl and the region s low mean annual temperature 16 c two conditions that would otherwise lead to relative isotope depletion the rains show the highest 18 o composition with no sign of effect of evaporative enrichment as revealed by d excess this enrichment is also reflected in other local meteoric waters shallow groundwaters lakes ambient vapour and rivers here the 18 o and 2 h of 600 lake water samples 3000 groundwater samples and rainfall isotope data base from iaea wmo stations at addis ababa have been used to show the linkage between rainfall derivation processes and isotope signals the major sources of moisture in ethiopia are recycled moisture from continental sources for western and northern ethiopia and direct moisture from the southern indian ocean for eastern lowlands of ethiopia southern ethiopia is influenced by south indian ocean moisture which is characterised by relatively depleted 18 o and 2 h spatial variation altitude and latitude in 18 o and 2 h is weak with altitude effect accounting for 0 1 100 m depletion in 18 o detailed investigation of the relation between isotope pattern and isotope effects amount seasonality temperature etc shows that these effects are not pronounced the 4 5 18 o shift recorded in deeper groundwaters and other paleo climate achieves from the current wt mean rainfall value of 0 5 can only be explained by a shift in source of moisture such as the northward penetration of the south indian ocean moisture into the ethiopian highlands or changes in evaporation conditions at the source

the leading modes of decadal sst variability in the southern ocean in cmip5 simulations the leading modes of sea surface temperature variability in the southern ocean on decadal and even larger time scales are analysed using coupled model intercomparison project 5 cmip5 model simulations and observations the analysis is based on empirical orthogonal function modes of the cmip5 model super ensemble we compare the modes from the cmip5 super ensemble against several simple null hypotheses such as isotropic diffusion red noise and a slab ocean model to investigate the sources of decadal variability and the physical processes affecting the characteristics of the modes the results show three main modes in the southern ocean the first and most dominant mode on interannual to decadal time scales is an annular mode with largest amplitudes in the pacific which is strongly related to atmospheric forcing by the southern annular mode and el nino southern oscillation the second mode is an almost basin wide monopole pattern which has pronounced multi decadal and longer time scales variability it is firstly inducted by the wave 3 patterns in the atmosphere and further developed via ocean dynamics the third mode is a dipole pattern in the southern pacific that has a pronounced peak in the power spectrum at multi decadal time scales all three leading modes found in the cmip5 super model have distinct patterns and time scale behaviour that can not be explained by simple stochastic null hypothesis thus all three leading modes are ocean atmosphere coupled modes and are likely to be substantially influenced or driven by ocean dynamical processes

river response to rapid holocene environmental change evidence and explanation in british catchments macklin m g jones a f lewin j 2010 river response to rapid holocene environmental change evidence and explanation in british catchments quaternary science reviews 29 13 14 1555 1576 sponsorship welsh assembly government and the higher education funding council for wales for funding this study through its support of the centre for catchment and coastal research at aberystwyth university

late holocene floodplain incision and alluvial fan formation in the central grampian highlands scotland chronology environment and implications a section cut across an alluvial fan and the underlying floodplain terrace in the central grampian highlands provides an unusually complete record of late holocene events at ca 2 7 2 4 cal kyr bp floodplain aggradation was replaced by net floodplain incision pollen evidence and charcoal counts provide no evidence for contemporaneous anthropogenic landscape change and the timing of the transition suggests that it reflects an increase in high magnitude erosive flood events following overall climatic deterioration the overlying fan was deposited by torrential hyperconcentrated flows during three brief storm generated depositional events at ca 2 2 2 1 1 9 1 8 and 0 9 0 7 cal kyr bp separated and succeeded by prolonged periods of stability and peat accumulation during these three events a cumulative total of ca 6750 m3 of sediment was deposited probably in no more than a few hours over a timescale of two millennia these findings imply that proposed links between human activity and the development of alluvial fans or debris cones require reassessment and that different elements of the holocene alluvial landscape have responded in different ways to the same climatic inputs aggregation of dating evidence relating to aggradation or incision of alluvial landforms at different scales therefore may produce misleading results copyright 1999 john wiley sons ltd

survey of damages during the dhamar earthquake of 13 december 1982 in the yemen arab republic the dhamar province of the yemen arab republic was shaken on 13 december 1982 by a moderate earthquake the earthquake caused considerable loss of life and different degrees of damage to the traditional houses in the area the most common forms of construction consisting of stone masonry and adobe suffered very extensive damage the destruction of houses was mainly due to failure of the superstructure and none due to the movement of foundations an above ground reinforced concrete water tank also collapsed ground fissures rupture of stones on a hill side rock falls and slides were also observed an isoseismal map of the earthquake damaged area is also presented

holocene alluvial fan development in the macgillycuddy s reeks southwest ireland holocene alluvial landforms in the macgillycuddy9s reeks southwest ireland were investigated to determine the controls and timing of postglacial geomorphic activity detailed geomorphologic analysis of three alluvial fan and debris cones within high level cirque basins demonstrates evidence of episodic phases of late holocene surface aggradation and incision radiocarbon dates from peat horizons above and below inorganic units show that phases of aggradation cluster into two distinct periods the first after 230 790 calibrated cal yr a d and the second from 1510 cal yr a d to the present an additional phase of fan aggradation at one site is dated after 1040 1280 cal yr a d all three phases coincide with episodes of enhanced late holocene valley floor alluviation and debris flow activity from upland britain alluvial fans and debris cones have developed primarily as a result of the resedimentation of late midlandian wisconsin drift and talus slopes and mobilization of materials involved flooding transitional flow and debris flow processes pollen analysis of peat horizons interbedded with alluvial fan and debris cone sediments indicates that land use changes were an important factor in lowering the threshold for local slope erosion phases of aggradation also coincide with well documented episodes of climate change and hence fan development is probably a function of both anthropogenic and climatic forcing a sequence of events may have involved initial slope destabilization due to overgrazing and removal of vegetation that was followed by debris mobilization and fan aggradation during intense rainstorms associated with climate change

comparing the spatial structure of variability in two datasets against each other on the basis of eof modes in analysis of climate variability or change it is often of interest how the spatial structure in modes of variability in two datasets differ from each other e g between past and future climate or between models and observations often such analysis is based on empirical orthogonal function eof analysis or other simple indices of large scale spatial structures the present analysis lays out a concept on how two datasets of multivariate climate variability can be compared against each other on basis of eof analysis and how the differences in the multivariate spatial structure between the two datasets can be quantified in terms of explained variance in the leading spatial patterns it is also illustrated how the patterns of largest differences between the two datasets can be defined and interpreted we illustrate this method on the basis of several well defined artificial examples and by comparing our approach with examples of climate change studies from the literature these literature examples include analysis of changes in the modes of variability under climate change for the sea level pressure slp of the north atlantic and europe the slp of the southern hemisphere the surface temperature of the northern hemisphere the sea surface temperature of the north pacific and for precipitation in the tropical indo pacific

how do gravel bed rivers braid sedimentary processes and bed forms leading to the onset of braiding were observed in small scale hydraulic models of gravel bed streams the laboratory streams had a variety of combinations of constant discharge and slope but identical bed material particle size distributions from initially straight channels braiding occurred by four different processes deposition and accumulation of a central bar chute cutoff of point bars conversion of single transverse unit bars to mid channel braid bars and dissection of multiple bars in these experiments the chute cutoff mechanism was the most common but the predominant braiding mechanism depends upon sediment mobility excess bed shear stress and the bed form regime at very low excess bed shear stress the central bar process dominates but at higher excess bed shear stress slip face unit bars are more common bed scour at confluences is more pronounced and propogation of alternate convergence scour and divergence deposition is more likely thus chu

the meandering braided river threshold a reappraisal abstract the concept of a threshold discharge slope q s combination that separates braided from meandering streams is critically re examined partly by review of previous data and partly by analysis of new data from south island new zealand it is argue d that discriminant functions that use mean annual discharge provide a poor physical basis for interpretations based on natural processes while bankfull discharge is also deficient because it is not a fully independent variable the common use of channel rather than valley slope adds a further misleading component because channel slope is partly dependent on channel pattern sinuosity most previous studies have inadequately treated the role of bed particle size in pattern discrimination failing to recognize that active gravel streams must plot higher on a q s chart than sand bed channels irrespective of pattern because of the greater power requirements for bed material movement within any one size class of bed material there is no evidence to indicate a clear discrimination between braiding and meandering only a weak statistical association between pattern and slope discharge values while this association may be explicable in terms of the high shear stress and stream power that accompany high qs values promoting braiding the real prerequisite for braiding appears to be high loads of bed calibre material producing wide shallow channels a factor that is only partly controlled by stream power accordingly the search for a pattern threshold based on discharge and slope seems to be a futile exercise an interpretation of existing pattern discriminant functions from the perspective of the threshold shear stress for particle movement is made it is concluded that in effect these functions merely state that gravel bed streams are more likely to be braided than channels in finer sediment statistically this appears to be valid and reasons for that difference are offered based on the balance between imposed bed material load and channel capacity

thermal springs fumaroles and gas vents of continental yemen their relation with active tectonics regional hydrology and the country s geothermal potential abstract most thermal springs of continental yemen about 65 emergences at 48 sampling sites and a couple of fumaroles and boiling water pools have been sampled and analyzed for chemical and isotopic composition in the liquid phase and the associated free gas phase whatever the emergence all the water discharges have an isotopic signature of meteoric origin springs seeping out from high altitudes in the central volcanic plateau show a prevalent na hco3 composition clearly affected by an anomalous flux of deep co2 deriving from active hydrothermal systems located in the jurassic amran group limestone sequence and or the cretaceous tawilah group likely underlying the 2000 3000 m thick volcanic suite at lower elevations co2 also affects the composition of some springs emerging at the borders of the central volcanic plateau although mixing to a limited extent with organic co2 infiltrating together with the meteoric recharge waters cannot be ruled out all the co2 rich gas samples have a 13c co2 signature that falls in the range of mantle co2 3 presently the thermal springs of yemen are prevalently used for spas and or bathing nevertheless liquid and gas geothermometry and geological considerations suggest that there are at least three areas al lisi al makhaya and damt inside the yemen volcanic plateau around dhamar that may be promising prospects for the future development of geothermal energy in yemen alternatively they could be used as a source of energy for small to medium scale agriculture and or industrial purposes moreover most of the thermal water discharges have the chemical characteristics of potable waters and in an arid country like yemen they have to be considered as long term water supply resources if the country should face water shortages

interpreting alluvial archives sedimentological factors in the british holocene fluvial record abstract a holocene alluvial archive of 506 dated units for great britain is analysed in terms of the sedimentation styles involved the database is classified by sedimentation unit channel sediments palaeochannel fills floodplain surface sediments floodbasins and colluvial deposits and alluvial ensemble fans and cones upland gullies and streams braided systems and active inactive meandering and anastomosing systems floodplain palaeochannel and floodbasin sediments dominate the record mostly from meandering anastomosing systems different sediment units show varied potential for recording environmental change some are relatively poorly dated with respect to the volumes of material involved whilst many dates float in periods of depositional activity which lasted for extended time periods much dated activity is autogenic and of relatively little value in interpreting external environmental influence ensembles and units are similar in age patterns in some respects commonly they exhibit sets of short term peaks in sedimentation activity but differ in others floodbasins and to an extent braided systems feature in the earlier holocene whilst dated fan deposition is more evident in the late holocene there is a general bias towards sediment units of late holocene age which probably reflects preservation factors previous british holocene alluviation models are reviewed it is suggested that the majority of earlier models reflect partial views imposed by limited regional coverage and available dating

origin and evolution of intracratonic thermal fluids from central western peninsular india abstract the chemical and isotopic composition of several thermal springs and associated gas phases in a large sector of central western peninsular india has been investigated such springs have meteoric isotopic signature and emerge after very well developed convective circulation at depth along important tectonic structures such as the son narmada tapti rift zone and the west coast fault chemical components in both gas and liquid phases and geothermometric estimations suggest that such springs are not related to the presence of any active hydrothermal systems at shallow depth in any of the studied areas the hottest convective water emerges at tattapani at near boiling point for water at atmospheric pressure 90 c in association with an n2 rich gas phase of clear meteoric signature since such fluids do not carry any corrosive components they could be conveniently exploited for industrial purposes such as drying processes from a tectonic point of view the presence of thermal emergences scattered in a wide area along geologically well defined structures which also generate frequent moderate earthquakes suggests that such structures are active although the isotopic composition of thermal springs points to a meteoric origin their feeding aquifers are not topographically driven as in most active alpine orogenic belts the relative high quantity of total helium in the associated gas phase suggests also that they are really deep old long circulating waters we propose for such waters the term intracratonic thermal waters since the isotopic signature of he in the gas phase does not show any release of primordial 3he in any of the areas of spring emergence based on the quite low 3he 4he ratio in the gas phase we suggest also that in spite of its morphological shape the narmada son tapti rift zone cutting the indian subcontinent in two is more related to paleo suture rather than to a mid continental rift system

flood alluviation and entrenchment holocene valley floor development and transformation in the british uplands the morphology sedimentary properties and sequence of recent coarse grained flood deposits and earlier holocene alluvial fills were investigated in thinhope burn a small 12 km2 catchment in the northern pennine uplands northern england twenty one large flood events are recorded by distinctive cobble boulder bars sheets and splays and boulder berms and lobes lichenometric analysis showed that all but one of these floods dated from the mid eighteenth century the timing of large floods between 1766 and 1960 corresponds with major hydroclimatic trends evident in northern britain and northwest europe over this period discharge estimates suggest that flood magnitudes have decreased since the mid eighteenth century channel and flood plain metamorphosis in late roman times and in the eighteenth century following major valley floor entrenchment locally as much as 8 m would appear to have been caused by increased runoff and flood magnitude this was linked to a shift to a wetter climate with flow augmented by iron age and roman woodland clearance and drainage of the catchment in more recent times results from this study suggest that current models of longer term holocene and pleistocene valley floor development in the british uplands may need to be re evaluated

holocene environmental change in the yorkshire ouse basin and its influence on river dynamics and sediment fluxes to the coastal zone geomorphological geochemical and geochronological investigations of holocene fluvial sedimentary sequences have been undertaken within a range of upland piedmont and lowland valley floor reaches in the yorkshire ouse catchment northern england the aims of these studies have been to a evaluate the effects of prehistoric and historic land use change on catchment erosion and sediment delivery to river channels and floodplains b establish the degree to which episodes of river erosion and sedimentation are controlled by climate related variations in flood regime and c assess the spatial heterogeneity of river response to environmental change and how this is likely to influence short and long term sediment storage as well as sediment transfer to the humber estuary similar discontinuities in the holocene alluvial record are evident at many sites in the yorkshire ouse catchment though local differences in river sensitivity to externally imposed change have resulted in a complicated and often unique relationship between river behaviour and environmental change the large proportion of particulate borne contaminant metals resulting predominantly from historical mining stored in the vale of york strongly indicates that sediment delivery from the ouse catchment to the humber estuary during the holocene may have been relatively low this suggests that the degree of connectivity between river estuarine and coastal transport systems as well as spatial and temporal variations in fluvial sediment storage are the key controls of long term land ocean sediment fluxes

the influence of recent environmental change on flooding and sediment fluxes in the yorkshire ouse basin this study attempts to establish causes of historical variations in flood frequency and magnitude in a 119 year flood stage record at york and assess its likely effects on fluxes of fine sediment and associated base metal contaminants climatic controls of flooding are evaluated through analysis of synoptic flood generation and large scale land use changes are also considered in terms of their influence on food frequency and magnitude and sediment availability the late nineteenth century was characterized by low flood frequency and magnitude but as a consequence of upland metal mining contaminant concentrations and downstream fine sediment delivery would have been high a further decline in flood frequency and magnitude between 1904 and 1943 combined with the cessation of base metal mining resulted in a decline of sediment and contaminant fluxes between 1944 and 1968 increases in upland drainage changes in agricultural practices and high flood frequency and magnitude resulted in significantly enhanced sediment fluxes rates of flux declined between 1969 and 1977 owing to extremely low flood frequencies and magnitudes in the last two decades there have been a series of extreme magnitude floods which through remobilization of mining contaminated alluvium have resulted in high pollutant metal mining loads probably approaching those of the late nineteenth century in an historical context it appears that the lois monitoring programme has been undertaken in a period of extremely high flood frequency and magnitude in the uk and significantly enhanced sediment and contaminant metal flux analysis of synoptic flood generation suggests that any future increase in the frequency and vigour of cyclonic atmospheric circulations may result in a higher frequency of extreme floods and consequently increased sediment fluxes

the age of alluvial fan deposition at a site in the southern uplands of scotland the age of a large alluvial fan debouching onto the valley floor of the river tweed in southern scotland and the sequence of events relating to this are investigated using geomorphological sedimentological palynological archaeological and radiocarbon dating evidence prior to fan deposition the tweed valley floor seems to have been covered by a wooded peat at a time of low fluvial activity the fan commenced deposition in the 11th century ad and appears to have been a local event the tweed showing no response to this accelerated sedimentation later perhaps 200 years later the tweed commenced overbank deposition of the only flandrian terrace preserved local proxy data are examined in order to define the causes of these events but difficulties in temporal correlation despite the good resolution of the radiocarbon chronology mean that the causes of these events remain unknown

river sedimentation and fluvial response to holocene environmental change in the yorkshire ouse basin northern england holocene alluvial sediment sequences and floodplain geomorphological histories from three valley floor sequences in the yorkshire ouse basin have been determined using a variety of field evidence and laboratory methods geomorphological mapping sediment coring and trenching physical and chemical analysis of sedimentary units and 14c dating the application of multiple methods has revealed contrasting phases of river erosion alluviation and depositional styles during the late quaternary at each of the individual study reaches the gravel bedded river swale at catterick has been characterized by progressive valley floor incision during the late holocene with major phases of incision occurring during the cooler and wetter phase of the little ice age within the last c 245 years substantial thicknesses up to 2 m of overbank alluvium contaminated by metalliferous mining have been deposited across thefloodplain in contrast floodplain development in the lower reaches of the river swale at myton and t

alluvial responses to the changing earth system alluvial systems are complex self organizing and hierarchical in structure they represent stored and transitory sediment bodies transported by rivers that have eroded their catchments and created multiscalar landforms and sedimentary architectures over a range of time scales the central question we address in this paper is how environmental signals are autogenically processed and recorded by the fluvial sediment system we compare databases of alluvial units that are well constrained in terms of dating control with direct or proxy records of environmental change river system responses to environmental change are evaluated over three nested time periods spanning the past 200 000 years first focusing on mediterranean european and african catchments river responses to relatively abrupt and short term late pleistocene dansgaard oeschger and heinrich climate events are examined second the effects of rapid and globally significant episodes of holocene climate change on european rivers together with anthropogenic land use impacts are assessed last little ice age flooding and alluvial responses to modern climate warming are reviewed with particular reference to upland britain these studies are shown to have significant implications for modelling local regional and global scale alluvial responses to future environmental change they highlight the necessity for numerical simulation models to be fully informed by field based knowledge and understanding of the memory effects of whole fluvial sediment systems particularly those that have experienced repeated phases of environmental change copyright 2008 john wiley sons ltd

semi diurnal tidal ellipse variability in a region of freshwater influence 1 new insight into a key process instrumental in the onset of stratification in tidally driven systems is presented for the first time using long term field observations from the liverpool bay region of freshwater influence rofi tidal ellipses respond to changes in stratification becoming more circular with greater vertical structure and reveal variability in response to tidal straining an inflection point that occurs before the maximum vertical density difference at the time of maximum positive bed surface cross shore shear is identified as the crucial point where the water column abruptly decouples the surface and bed layers then rotate in clockwise and anti clockwise directions respectively the maximum vertical stratification is observed when the maximum negative bed surface along shore shear is reached decoupling to a two layer system is therefore not the smooth progression predicted using turbulence closure models but rather a very sudden switch highlighting the importance of the role of reynolds stresses

channel change and the significance of floodplain stratigraphy 1990 flood event lower river tay scotland during february 1990 a flood event on the river tay with an estimated recurrence interval of 70 years in its lower reaches caused extensive flooding and geomorphological change the most extensive area of flooding and dramatic geomorphological change the erosion of two new channels across the floodplain was in the vicinity of the village of caputh perthshire the location of the eroded channels relates to the position of former river courses identifiable by depressions in the floodplain surface and floodplain stratigraphy the lower floodplain surface elevation and occurrence of gravel and sand deposits along the line of the former river courses caused the area to be more vulnerable to erosion and controlled the morphology of the eroded channels

sediment transfer and transformation of an alluvial valley floor the river south tyne northumbria u k the amounts of alluvial storage and the mechanisms responsible for the dispersal of sediment associated with historic metal mining are examined for a 115 year timespan on a 22 km reach of the river south tyne northern england analysis of lateral and vertical channel change over this period the extent of actively reworked gravels and identification of metals in alluvial units show five sedimentation zones separated by more stable reaches aggradation in the late nineteenth century was followed by a period of storage and local reworking and then incision some reaches show short term storage of sediment injected from tributaries which may be dispersed by floods there is some evidence of transfer of sediment bodies downvalley within sedimentation zones and of a sediment wave movement between zones in lower parts of the south tyne investigated present day incision the variation in the area of actively reworked gravel spreads and the widespread dispersal of fine grained toxic metal mining wastes all have practical implications the intricate response of the channel system to historic changes in sediment supply is not readily described by either a complex response model or a simple translatory wave

river entrenchment and terrace formation in the uk holocene abstract a meta analysis of a large database of 14c dated fluvial units is used to assess the chronology and controls of episodic holocene river entrenchment and terrace formation in the uk most holocene terraces are of a fill cut type developed in pleistocene sediments in places now reaching down to pre holocene bedrock holocene terraces are widespread in higher relief areas of the uk and peripheral higher energy rivers and include up to 7 levels in some valley floor reaches using 14c constrained data sub sets for incision episodes the onset vertical ranges formation times and rates of entrenchment are examined together with geographical distributions the height range of terrace separation is relatively small 0 5 3 5 m with a long term averaged incision rate over the late and mid holocene of 0 43 0 5 0 67 0 7 and 0 81 m ka in the tweed rheidol severn ouse and ribble catchments and a regional similarity in the scale of incision events the periods 4200 3700 3100 2900 2100 1900 1800 1500 cal bp and most notably the last 1000 years with prominent peaks at 900 800 and 700 600 cal bp were times of accelerated incision it appears likely that extreme flood events triggered the formation of incision slots rather than entrenchment being a direct response to glacio tectonic uplift or the result of incremental valley floor lowering by combined incision and lateral reworking river entrenchment has also been rapid in recent centuries reflecting the coupling of extreme events with anthropogenic effects on catchment hydrology incision results in changes of river channel flood power and overbank flood extent and improved data on the long term and large scale vertical tendency of uk rivers are needed for flood risk management purposes

enso dynamics and diversity resulting from the recharge oscillator interacting with the slab ocean el nino southern oscillation enso is the leading mode of interannual global climate variability which in its essence is often described by the equatorial dynamics of the recharge oscillator with a fixed pattern here we explore the idea that enso can be simulated in a model with a fixed pattern of sea surface temperature variability following the recharge oscillator mechanism which interacts with the thermodynamic red noise of a slab ocean this model is capable of simulating the leading modes of sea surface temperature variability in the tropical pacific in good agreement with the observations and most coupled general circulation models enso dynamics amplitude seasonality the structure of the leading patterns its meridional extension its variations in an eastern and central pacific pattern and associated positive feedbacks are all influenced and simulated well by including the interaction of recharge oscillator and the thermodynamic coupling to the slab ocean model we further point out that much of the enso diversity in the spatial structure is a reflection of this interaction however it also has to be noted that some equatorial dynamics are missing in this model and in coupled general circulation models that are important for the enso diversity

small valley bottom deposits in the sandy districts of the sarthe basin france climatic and or human origin the study of the small valley bottom deposits in a sandy district where several recent erosional events have occurred makes it possible to distinguish deposits which are caused by climatic oscillations from those induced by both climate and human activities the coarse alluvium with flints which reached the main valleys prior to the subboreal was transported by greater flows than those which resulted from later human induced flood discharges where flints were not evacuated from the small valleys radiocarbon dates of peat set those deposits in the iron age in the transition from antiquity to the medieval period at the end of the optimum climatique de l an mil and during the little ice age at the present time human induced flood discharges reach again the main valleys d 2002 elsevier science b v all rights reserved

coupling relationships hillslope fluvial linkages in the hodder catchment nw england abstract variations in the coupling of sediment transfer between different parts of a fluvial catchment e g hillslope to axial stream can hamper understanding but are an integral part of the geomorphological record depositional environments respond to a combination of land use climate storms floods and autogenic conditioning the distribution of sediment in the upland landscapes of nw england is out of equilibrium with contemporary climate and geomorphological processes more a function of peri and paraglacial mobilisation of glacigenic deposits soil and vegetation development after deglaciation have interrupted any progression toward sediment exhaustion with sediment release controlled largely by extrinsic perturbation with late holocene anthropogenic activity climate and extreme hydrological events the likely candidates this paper presents a new radiocarbon dated holocene geomorphological succession for the river hodder nw england alongside evaluating new palaeoecological and geoarchaeological data to discern the impacts of human activity these data show a late holocene expansion in human occupation and use of the landscape since the iron age 700 0 cal b c with more substantial changes in the character and intensity of upland land use in the last 1300 years the geomorphological responses in the uplands were the onset of considerable and widespread hillslope erosion gullying and associated alluvial fan development interpretation of the regional radiocarbon chronology limits gullying to four more extensive and aggressive phases after 500 cal b c the downstream alluvial system has responded with considerable valley floor deposition and lateral channel migration that augmented sediment supply by remobilising the existing floodplain terraces and led to the aggradation of a series of inset alluvial terraces the timing of these changes between states of aggradation and incision in alluvial reaches reflects the increased connectivity between the hillslope and alluvial systems aspects of both the regional climate and land use histories are conducive to increasing discharge and sediment flux but the region wide lowering of erosion thresholds appears a key driver conditioning these sediment rich conditions and producing a landscape that was more susceptible to erosion under lower magnitude flows

a catchment scale assessment of patterns and controls of historic 2d river planform adjustment abstract the supply transfer and deposition of sediment from channel headwaters to lowland sinks is a fundamental process governing upland catchment geomorphology and can begin to be understood by quantifying 2d river planform adjustments over time this paper presents a catchment scale methodology to quantify historic patterns of 2d channel planform adjustment and considers geomorphic controls on 2d river stability the methodology is applied to 18 rivers total length 24 km in the upland headwaters of the previously glaciated wasdale catchment 45 km2 lake district northwest england planform adjustments were mapped from historic maps and air photographs over six contiguous time windows covering the last 150 yr a total of 1048 adjustment and stable reaches were mapped over the full period of analysis 1860 2010 32 8 km of the channels studied were adjusting contrasts were identified between the geomorphic characteristics slope catchment area unit specific stream power channel width and valley bottom width of adjusting and stable reaches the majority of adjustments mapped were observed in third and fourth order channels in the floodplain valley transfer zone where the channels were laterally unconfined mean valley bottom widths of 230 180 m with low sediment continuity in contrast lower order channels were typically confined mean valley bottom widths of 31 43 m and showed relative 2d lateral stability hence valley bottom width was found to be important in determining the available space for rivers to adjust over the full period of analysis 38 of planform adjustments involved combined processes for example as bar and bend adjustments the study demonstrates the importance of stream network hierarchy in determining spatial patterns of historic planform adjustments at the catchment scale the methodology developed provides a quantitative assessment of planform adjustment patterns and geomorphic controls which is needed to support the prioritisation of future river management and restoration

the importance of plant macrofossils in late glacial climatic reconstructions an example from western norway a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract late glacial pollen diagrams from two sites on the outermost coast of western norway are discussed on the islands of utsira paus 1990 and blomoy mangerud 1970 during the allerod chronozone 12 000 11 000 bp their climatic reconstructions depend on the assumed local occurrence of tree betula b pubescens at blomoy and on the presence of pollen of thermophilous taxa at utsira the plant macrofossil analyses at these same sites do not indicate the presence of betula at either during the allerod reconstruction of the local vegetation is of willow shrubs and empetrum dwarf shrub heath at utsira and of salix herbacea dominated vegetation at blomoy these reconstructions accord well with modern analogues above the tree line in the west norwegian mountains the inferred summer temperatures during the allerod are thus 2 6 c lower than had been proposed from pollen evidence alone late glacial plant macrofossil assemblages can generally be easily matched with modern vegetation analogues on the west norwegian coast it would appear that the pollen of betula and thermophilous indicators arrived by long distance dispersal facilitated by the strong winds during the late glacial the frequently found no analogue pollen assemblages of the late glacial period may therefore be due to their previously unsuspected content of extra regional pollen dispersed by strong winds this emphasises that climatic reconstructions should only be made using taxa that were certainly growing locally it demonstrates the importance of using locally derived ecologically sound vegetational reconstructions for the reconstruction of late glacial climates and for this plant macrofossil analysis is invaluable

holocene alluviation and land use change on callaly moor northumberland england archaeological survey and palaeoenvironmental investigations in coe burn callaly moor northumberland have examined the chronology and nature of prehistoric and historic land use change in a small upland river catchment these studies have revealed an intensively used landscape with evidence of late neolithic to bronze age medieval and post medieval land use and settlement two episodes of valley floor alluviation are identified and dated to the middle late bronze age and post medieval periods magnetic mineral and geochemical analyses of fine sediments from the older alluvial fill show it to contain a high proportion of topsoil which is believed to have been produced by soil erosion resulting from bronze age tree clearance and cultivation deposition of the younger alluvial fill post ad 1500 was associated with the inwash of relatively unweathered bedrock generated by coal mining in the catchment it is demonstrated that by integrating archaeological field survey with off site palaeoenvironmental investigations a much fuller picture of human activity and land use change has emerged than otherwise would have been the case studies of this type may be particularly useful in other upland river catchments where archaeological survival is limited or poor

hillslope gullying in the solway firth morecambe bay region great britain responses to human impact and or climatic deterioration abstract in the solway firth morecambe bay region of great britain there is evidence for heightened hillslope instability during the late holocene after 3000 cal bp little or no hillslope geomorphic activity has been identified occurring during the early holocene but there is abundant evidence for late holocene hillslope erosion gullying and associated alluvial fan and valley floor deposition interpretation of the regional radiocarbon chronology available from organic matter buried beneath alluvial fan units suggests much of this geomorphic activity can be attributed to four phases of more extensive gullying identified after 2500 2200 1300 1000 1000 800 and 500 cal bp both climate and human impact models can be evoked to explain the crossing of geomorphic thresholds and palaeoecological data on climatic change bog surface wetness and human impact pollen together with archaeological and documentary evidence of landscape history provide a context for addressing the causes of late holocene geomorphic instability high magnitude storm events are the primary agent responsible for gully incision but neither such events nor cooler wetter climatic episodes appear to have produced gully systems in the region before 3000 cal bp increased gullying after 2500 2200 cal bp coincides with population expansion during iron age and romano british times the widespread and extensive gullying after 1300 1000 cal bp and after 1000 800 cal bp coincides with periods of population expansion and a growing rural economy identified during norse times 9 10th centuries ad and during the medieval period 12 13th centuries ad these periods were separated by a downturn associated with the harrying of the north ad 1069 to 1070 the gullying episode after 500 cal bp also coincides with increased anthropogenic pressure on the uplands with population growth and agricultural expansion after ad 1500 following 150 years of malaise caused by livestock and human the black death plagues poor harvests and conflicts on the scottish english border the increased susceptibility to erosion of gullies is a response to increased anthropogenic pressure on upland hillslopes during the late holocene and the role of this pressure appears crucial in priming hillslopes before subsequent major storm events in particular the cycles of expansion and contraction in both population and agriculture appear to have affected the susceptibility of the upland landscape to erosion and the hillslope gullying record in the region therefore contributes to understanding of the timing and spatial pattern of human exploitation of the upland landscape

dispersion of the afar plume implications from the spatiotemporal distribution of the late miocene to recent volcanics southwestern arabian peninsula abstract forty three new k ar dates from the yemen inland volcanic fields amran sana a dhamar rada and marib sirwah field in the southwestern arabian peninsula reveal a progression that can be divided into four stages stage 1 6 4 5 2 ma stage 2 3 6 2 9 ma stage 3 2 2 1 7 ma and stage 4

the eastward shift of the walker circulation in response to global warming and its relationship to enso variability this study investigates the global warming response of the walker circulation and the other zonal circulation cells represented by the zonal stream function in cmip3 and cmip5 climate models the changes in the mean state are presented as well as the changes in the modes of variability the mean zonal circulation weakens in the multi model ensembles nearly everywhere along the equator under both the rcp4 5 and sres a1b scenarios over the pacific the walker circulation also shows a significant eastward shift these changes in the mean circulation are very similar to the leading mode of interannual variability in the tropical zonal circulation cells which is dominated by el nino southern oscillation variability during an el nino event the circulation weakens and the rising branch over the maritime continent shifts to the east in comparison to neutral conditions vice versa for a la nina event two thirds of the global warming forced trend of the walker circulation can be explained by a long term trend in this interannual variability pattern i e a shift towards more el nino like conditions in the multi model mean under global warming further interannual variability in the zonal circulation exhibits an asymmetry between el nino and la nina events el nino anomalies are located more to the east compared with la nina anomalies consistent with this asymmetry we find a shift to the east of the dominant mode of variability of zonal stream function under global warming all these results vary among the individual models but the multi model ensembles of cmip3 and cmip5 show in nearly all aspects very similar results which underline the robustness of these results the observed data era interim reanalysis from 1979 to 2012 shows a westward shift and strengthening of the walker circulation this is opposite to what the results in the cmip models reveal however 75 of the trend of the walker circulation can again be explained by a shift of the dominant mode of variability but here towards more la nina like conditions thus in both climate change projections and observations the long term trends of the walker circulation seem to follow to a large part the pre existing dominant mode of internal variability

the chronology of late quaternary fluvial activity in part of the milfield basin northeast england the sediment stratigraphy of a 4 m thick intercalated holocene alluvial fill and valley floor peat at a site in the milfield basin northumberland has been dated by a series of eight 14c assays and related to a previously analysed pollen record the sequence extends from the earliest holocene until c 2800 cal bp prior to the onset of peat inception substantial amounts of channel trenching can be demonstrated to have occurred in the milfield basin during the loch lomond stadial there is no measurable early holocene accelerated fluvial activity but a major flooding event occurred at c 7500 cal bp much earlier than recorded elsewhere in the region the explanation for this is not clear however the cessation of mid holocene overbank sedimentation at c 4000 3500 cal bp is tentatively correlated with slope stability associated with woodland regeneration 1998 john wiley sons ltd

analysis of the slab ocean el nino atmospheric feedbacks in observed and simulated enso dynamics in a recent study it was illustrated that the el nino southern oscillation enso mode can exist in the absence of any ocean dynamics this oscillating mode exists just due to the interaction between atmospheric heat fluxes and ocean heat capacity the primary purpose of this study is to further explore these atmospheric slab ocean enso dynamics and therefore the role of positive atmospheric feedbacks in model simulations and observations the positive solar radiation feedback to sea surface temperature sst due to reduced cloud cover for anomalous warm ssts is the main positive feedback in the slab ocean el nino dynamics the strength of this positive cloud feedback is strongly related to the strength of the equatorial cold tongue the combination of positive latent and sensible heat fluxes to the west and negative ones to the east of positive anomalies leads to the westward propagation of the sst anomalies which allows for oscillating behavior with a preferred period of 6 7 years several indications are found that parts of these dynamics are indeed observed and simulated in other atmospheric or coupled general circulation models agcms or cgcms the cmip3 agcm slab ensemble of 13 different agcm simulations shows unstable ocean atmosphere interactions along the equatorial pacific related to stronger cold tongues in observations and in the cmip3 and cmip5 cgcm model ensemble the strength and sign of the cloud feedback is a function of the strength of the cold tongue in summary this indicates that the slab ocean el nino dynamics are indeed a characteristic of the equatorial pacific climate that is only dominant or significantly contributing to the enso dynamics if the sst cold tongue is sufficiently strong in the observations this is only the case during strong la nina conditions the presence of the slab ocean enso atmospheric feedbacks in observations and cgcm model simulations implies that the family of physical enso modes does have another member which is entirely driven by atmospheric processes and does not need to have the same spatial pattern nor the same time scales as the main enso dynamics

morphology and surface sedimentary features of point bars in welsh gravel bed rivers two examples of point bars in single channel gravel bed rivers in wales illustrate some of the morphological and surface sedimentary features observed during a wider examination of 40 sites of recent less than 100 years channel sedimentation the point bars consist of predominantly sandy gravel bar platforms overlain by discontinuous sand bodies cut bank exposures show generally massive sandy gravels abruptly underlying a silt sand unit morphologically the bars are platformlike with primary inner attached or secondary medial chutes this relief together with the effects of seasonal vegetation determines the locations of finer grained non gravel material the frequency with which deposits produced by this type of channel sedimentation may be encountered in quaternary and pre quaternary successions is briefly discussed

multi model representation of the north atlantic oscillation in the 20th and 21st centuries 1 ten coupled ocean atmosphere general circulation models cgcm are used to reproduce nao mean sea level pressure and 2 meter air temperature fields highly correlated to the north atlantic oscillation index naoi during a control period from 1961 1990 three enhanced co2 perturbation scenarios are compared to the control for 2070 2099 using pattern correlations and normalized root mean square errors between perturbation and control periods it is found that models can successfully reproduce observed nao sea level pressure and temperature anomaly fields model control slp anomaly fields however more closely resemble the arctic oscillation than the expected nao slp distribution due to an expansion of the north atlantic low pressure area analysis for the period 2070 2099 under the 3 enhanced co2 scenarios shows intensification of the naoi due to co2 forcing but with a weaker temporal trend relative to the control period

a holocene alluvial sequence in the lower tyne valley northern britain a record of river response to environmental change palaeoenvironmental investigations have been made of late quaternary sediments infilling the lower tyne valley at scotswood newcastle upon tyne 18 km upstream from the mouth of the river attention has focused on the holocene alluvial sedimentary sequence using sedimentological geochemical and palynological analyses holocene valley floor development from c 7500 bp has been largely dominated by a tendency towards river aggradation with some limited lateral and vertical reworking of sediments four alluvial fills have been identified and dated to 1 c 7500 4800 bp 2 from c 2590 bp up to the early first millennium ad and possibly as late as medieval times 3 between the medieval period and the early seventeenth century and 4 between the seventeenth and nineteenth centuries episodes of incision are dated to c 4800 2590 bp and to the period following the early seventeenth century marked variations in the rates and nature of sedimentation and erosion appear to coincide with rising post glacial

holocene coastal change and geoarchaeology at howick northumberland uk the recent discovery of one of the earliest mesolithic occupation sites in northern britain at howick on the northumberland coast in association with multiperiod archaeological evidence nearby highlights the importance of uk coastal settings as focii of human occupation through the holocene environmental evidence from a nearby river valley 8 15 m of sediment ranging in age from about 12 000 cal bp to the present records local and regional environmental change twenty four radiocarbon dates based on plant macrofossils provide a strong chronological framework calcareous microfossil assemblages foraminifera ostracods have been recovered from the fine grained sediments recording a change from marine through to brackish and eventually freshwater conditions between about 8200 and 6500 cal bp a preliminary pollen study of the core has permitted a reconstruction of the regional vegetation as it responded to climatic amelioration and human influence upon the landscape radiocarbon dating and sedimentological evidence indicates a major hiatus between approximately 11 000 and 8000 years bp including the period of mesolithic occupation represented by a 30 cm layer of coarse sands and sandstone pebbles probably the result of a significant high energy event dated to about 8300 cal bp although not a typical tsunami deposit the age and context suggests that this may be associated with the storegga slide event already well documented along the eastern coast of scotland the sedimentary and biological remains at howick record environmental change over much of the holocene and are compared with other environmental change records from the region to provide an environmental framework for the archaeology of this coastline

fluvial chronology and valley floor evolution of the upper bowmont valley borders region scotland two major fluvial terrace surfaces and four less significant surfaces are identified by aerial photographic interpretation field mapping and levelling on one c 2 km long reach of the upper bowmont water an upland stream draining the northern cheviot hills scotland the oldest terrace surface remains undated cartographic radiocarbon and palynological dating suggest that later terraces formed very recently within the last 250 years with the most prominent terrace fill having aggraded in the 18th century incision below this terrace surface is dated to approximately the end of the 18th century correlated with channel trenching at other sites in the region detailed palaeoecological and documentary evidence is used to examine whether climatic or land use changes might have instigated aggradation and a link with increased precipitation and flooding during part of the little ice age is suggested

late holocene channel changes of the middle trent channel response to a thousand year flood record this paper presents recent work on the floodplain sedimentology of the middle trent using data from gravel pits archaeological sites and documentary sources the middle trent has been unusually active during the holocene in comparison with other large lowland rivers in the british isles the holocene floodplain fill is dominated by sands and gravels with abundant structural evidence of changes in channel pattern and channel type a thousand year record of channel change has been reconstructed from palaeochannels and gravel units with radiocarbon dating of brushwood palaeomagnetic dating of fine channel fills dendrochronological dating of timber structures and dating via archaeological typologies the trent also has a reasonably well recorded flood history at least since the 11th century ad a comparison of the flood record and channel change indicates that the same degree of morphological and sedimentary response is not necessarily associated with floods of similar magnitudes i e there is no constant relationship between event magnitude and landform change instead the response seems dependent on the existing state of the channel and medium term trajectory of channel change there is evidence at both the hemington and colwick reaches of a cycle of channel change involving a change in channel typology and dating evidence that this may have migrated downstream the results of this work provide a medium term perspective on channel change which may be more appropriate for large british rivers than short term monitoring for both model validation and planning purposes

the sensitivity of scottish rivers and upland valley floors to recent environmental change abstract rivers in humid zones are delicately adjusted within narrow limits to evacuate the water and sediment supplied from upstream without significant changes in channel type and the morphology of the valley floor prevailing climate and land use are the major controls determining the nature of that adjustment significant environmental change either climate and or land use has the potential to change radically the channel type and destabilise the adjacent valley floor channel metamorphosis in which a river shifts from an aggrading to a degrading regime or from a single thread to multiple thread channel often provides the clearest evidence that environmental change has occurred this paper examines the stability of river channels and their associated valley floors in the uplands of scotland since 1750 changes in global scale atmospheric circulation patterns during this period have resulted in regionally distinct flood rich and flood poor periods with potential geomorphic impacts changes in the planform of nine active rivers in the piedmont zone of upland scotland are examined from series of rectified maps and aerial photographs at scales close to 1 10 000 at none of the sites other than one affected by an artificial increase in base level is there evidence of abrupt changes in river behaviour or channel metamorphosis however rates of lateral channel shift and extents of bare gravels do vary and these are clearly driven by changes in the incidence of floods since the mid 19th century the scale of valley floor reworking is less dramatic than that recently reported for comparable sites in northern england differences in geomorphic history land use and degree of slope channel coupling are identified as the likely causes of marked differences in the behaviour of active rivers in scotland and northern england over the last 250 years

geothermal prospecting by geochemical methods in the quaternary volcanic province of dhamar central yemen abstract this paper deals with geothermal prospecting carried out in the quaternary volcanic field of dhamar which is located almost in the centre of the main oligo miocene basaltic trap plateau of yemen by applying geochemical and thermometric techniques in domestic wells producing water from the shallow unconfined aquifer in the area which is prevalently hosted inside the quaternary volcano clastic material a closed thermal anomaly associated with the quaternary volcanic activity was well delineated although the aquifer s has a ca na hco 3 composition that is typical of shallow groundwater there are several chemical anomalies in the hotter central area compared to typical aquifers i the p h is lower and consequently the calculated partial pressure of co 2 in solution is higher ii the electrical conductivity is higher iii the total salinity is higher and iv the fluoride ion concentration is higher such chemical anomalies in the hotter part of the aquifer do not seem to be generated by the rising and or mixing of deep hydrothermal components rising into the shallow aquifer but rather produced by enhanced water rock interaction processes resulting from the higher temperature of the aquifer and its greater acidity by applying some speculative calculations based on the likely temperature of rainfall in the area and the depth and temperature of individual wells the local thermal gradients in the area have been calculated the thermal gradient varies from less than the average earth gradient at the periphery of the delimitated thermal anomaly to more than 250 c km within an extensive area exceeding 200 km 2 where the gradient is greater than 100 120 c km

an evaluation of the cmip3 and cmip5 simulations in their skill of simulating the spatial structure of sst variability the natural sea surface temperature sst variability in the global oceans is evaluated in simulations of the climate model intercomparison project phase 3 cmip3 and cmip5 models in this evaluation we examine how well the spatial structure of the sst variability matches between the observations and simulations on the basis of their leading empirical orthogonal functions modes here we focus on the high pass filter monthly mean time scales and the longer 5 years running mean time scales we will compare the models and observations against simple null hypotheses such as isotropic diffusion red noise or a slab ocean model to illustrate the models skill in simulating realistic patterns of variability some models show good skill in simulating the observed spatial structure of the sst variability in the tropical domains and less so in the extra tropical domains however most models show substantial deviations from the observations and from each other in most domains and particularly in the north atlantic and southern ocean on the longer 5 years running mean time scale in many cases the simple spatial red noise null hypothesis is closer to the observed structure than most models despite the fact that the observed sst variability shows significant deviations from this simple spatial red noise null hypothesis the cmip models tend to largely overestimate the effective spatial number degrees of freedom and simulate too strongly localized patterns of sst variability at the wrong locations with structures that are different from the observed however the cmip5 ensemble shows some improvement over the cmip3 ensemble mostly in the tropical domains further the spatial structure of the sst modes of the cmip3 and cmip5 super ensemble is more realistic than any single model if the relative explained variances of these modes are scaled by the observed eigenvalues

holocene paleoclimates of southern arabia from lacustrine deposits of the dhamar highlands yemen abstract this paper presents new evidence from the dhamar highlands yemen of paleohydrologic response to fluctuations in holocene climate stratigraphic geochemical and chronological analyses of highland peat and lacustrine deposits contribute to knowledge of the timing of early holocene moisture changes on the arabian peninsula providing a backdrop to understanding early cultural development in the arabian highlands the location of the dhamar highlands characterized by intermontane valleys surrounded by the highest mountains on the arabian peninsula and adjacent to the indian ocean is ideal for examining the influence of the indian ocean monsoon iom on the moisture history of this region fluctuations in the lacustrine and paleosol records of the dhamar highlands reflect both local changes in paleohydrology and regional influences on the holocene paleoclimatic conditions in southwest arabia in addition a peat deposit with a radiocarbon age of 10 253 10 560 cal yr bp documents some of the earliest holocene high moisture conditions on the arabian peninsula

sedimentologic and geomorphic variations in storm generated alluvial fans howgill fells northwest england in june 1982 a storm with a return period greater than 100 yr but lasting less than 2 5 hr destabilized hillslopes and produced a suite of geomorphologically and sedimentologically diverse alluvial fans thirteen major fans were deposited at the tributary junctions between small 2 catchments and two north flowing headwater streams of the river lune northwest england storm generated fans spread over or became inset into older stable fans and produced localized vertical accretion of as much as 3 m and lateral accretion of as much as 100 m sedimentary processes operating during deposition involved debris flow transitional flow and streamflow six facies types are recognized on the basis of depositional topography sedimentary texture and fabric and matrix content viscous debris flow d1 dilute debris flow d2 transitional flow t1 fluvial bars and lobes s1 s2 and fluvial sheet gravels s3 regionally streamflow deposition prevails over debris flow deposition and type s3 facies has the greatest areal extent temporal and spatial variations in facies deposition during the storm however resulted from water sediment ratio variations fan deposition involved an early phase of debris flow to transitional flow due to large inputs of sediment from hillslope failures this was followed by a systematic change to more dilute conditions resulting in streamflow deposition and eventually in channel incision a significant amount of geomorphic work and complex variations in sedimentary processes during the storm resulted in part from extensive overland flow and hillslope destabilization discriminant analyses indicate that catchment size channel gradient and percentage of area eroded during the storm controlled whether debris flow or streamflow facies dominated a fan sequence smaller steeper catchments had a greater percentage of the area yielding sediment and are dominanted by debris flows whereas larger catchments produced more runoff resulting in dilution and streamflow the results indicate that the facies sequences and fan entrenchment in the howgill fells which are typically considered products of longer term climatic change or tectonics in other localities are here primarily affected by thresholds related to catchment geomorphology by the type of sediment available and by the position within the storm cell

late holocene channel and floodplain development in a wandering gravel bed river the river south tyne at lambley northern england geomorphological analyses of the morphology lithostratigraphy and chronology of holocene alluvial fills in a 2 75 km long piedmont reach of the wandering gravel bed river south tyne at lambley in northumberland northern england have identified spatial and temporal patterns of late holocene channel and floodplain development and elucidated the relationship between reach and subreach scale channel transformation and terrace formation five terraced alluvial fills have been dated to periods sometime between c 1400 bc ad 1100 ad 1100 1300 ad 1300 1700 ad 1700 1850 and from ad 1850 to the present palaeochannel morphology and lithofacies architecture of alluvial deposits indicate that the past 3000 years has been characterized by episodic channel and floodplain change associated with development and subsequent recovery of subreach scale zones of instability which have been fixed in neither time nor space cartographic and photographic evidence spanning the past 130 years suggests channel transformation can be accomplished in as little as 50 years the localized and episodic nature of fluvial adjustment at lambley points to the operation of subreach scale controls of coarse sediment transfers these include downstream propagation of sediment waves as well as internal controls imposed by differing valley floor morphology gradient and boundary materials however the preservation of correlated terrace levels indicates that major phases of floodplain construction and entrenchment have been superimposed over locally complex patterns of sediment transfer reach scale lateral and vertical channel adjustments at lambley appear to be closely related to climatically driven changes in flood frequency and magnitude with clusters of extreme floods being particularly important for accomplishing entrenchment and reconfiguring the pattern of localized instability zones confinement of flood flows by valley entrenchment and contamination of catchment river courses by metal rich fine sediments following recent historic mining operations have combined to render the south tyne at lambley increasingly sensitive to changes in flood regimes over the past 1000 years copyright c 2000 john wiley and sons ltd