ice lensing in layered soils the ice lensing phenomenon in layered soils a condition that simulates the process of ice growth in varved soils has been studied experimentally under the limited conditions of layer thicknesses soils used freezing rates and moisture conditions ice lenses formed at the face of the fine textured clay layer when it was encountered by the freezing plane only minor heaving occurred in the coarse textured silt layer when its thickness was increased key words frost action ice lensing frost heaving varved soils layered soils

late quaternary arroyo formation and climate change in the american southwest arroyos entrenched ephemeral streams that form in desert environments first appeared in the arid and semiarid american southwest after 8000 14 c yr b p for at least 7 k y prior to that time climate vegetation and groundwater conditions were not conducive for arroyo formation along the floors of desert valleys after a hiatus in arroyo formation the frequency of arroyo cutting and filling increased dramatically after 4000 14 c yr b p the early holocene arroyos and increased frequency of arroyo incision after 4000 14 c yr b p are related to the establishment and changes in postglacial vegetation climate and groundwater conditions as a result arroyo sequences preserve a record of large scale climate change and small scale climatic perturbations that occurred during the holocene human modification of valley flood plains is an additional factor that contributed to mid nineteenth and early twentieth century arroyo cutting

recent formation of arroyos in the little missouri badlands of southwestern north dakota abstract in the little missouri badlands of southwestern north dakota the channels of ephemeral streams are incised 2 to 10 m or more into mid to late holocene alluvium the objectives of this study were to determine the timing and cause s of the most recent episodes of fluvial incision and to develop a process response model that illustrates the formation and evolution of arroyos in this region the purpose was to distinguish natural from anthropogenic changes to the landscape and to discriminate allogenic from autogenic causes of incision thereby gaining a greater sense of how steep relatively small ephemeral streams evolve dendrochronologic and dendrogeomorphic analyses of riparian cottonwoods provide an inexpensive high resolution dating method to constrain the time of incision thereby permitting determination of the cause s of incision by evaluating environmental conditions prior to and at the onset of fluvial incision an examination of seven small 10 to 100 km2 drainage basins indicated ephemeral streams have undergone a four stage cycle of change within the past 200 years comprising i an initial period of relative geomorphic stability with pedogenesis on the flood plain and low rates of lateral channel migration ii a period of channel incision with subsequent widening of the flood plain through lateral corrasion along middle and upstream reaches iii a concomitant period of aggradation along downstream reaches and finally iv a period of downstream incision dendrochronologic data and dendrogeomorphic relations indicate there have been three distinct periods of fluvial incision in the past 200 years the first period of incision began in the 1860s and 1870s prior to the onset of european settlement and intensive grazing by domesticated cattle in the area this period of incision occurred along the middle reaches of all seven of the streams examined and coincided with a severe protracted drought suggesting an allogenic cause the second period of incision occurred during the end of the 19th century and into the 20th century along the upstream reaches of streams this period of incision was mentioned in some written accounts of early settlers and coincided with the introduction of cattle and historical overgrazing of the region however overgrazing may not have caused the incision of this period but instead exacerbated or accelerated the upstream migration of knickpoints formed earlier along middle reaches a third period of incision has occurred in the past 20 years along the lower reaches of two of the seven streams examined this incision was caused by the process of meander cutoff this autogenic process decreases sinuosity and increases channel slope stream power and the potential to incise along adjacent stream reaches

the nature timing and controls of the quaternary development of the rio bergantes ebro basin northeast spain abstract geomorphological sedimentological and geochronological analyses have been undertaken to decipher the effects of quaternary environmental change on the development of the rio bergantes ebro basin northeast spain field mapping and profiling using aerial photography and airborne lidar data have identified a sequence of six river terraces age control provided by luminescence dating has revealed two major phases of valley floor aggradation that appear to have occurred at 183 130 ka terrace bt1 elevated 25 m above the modern river channel and 111 26 8 ka bt2 18 20 m above the modern river channel punctuated by 20 m of incision in the intervening period following these two phases of large scale aggradation the bergantes river system appears to have adjusted to a relatively sediment limited regime and responded to environmental changes through a series of smaller cut and fill cycles this resulted in four lower elevation terraces bt3 bt6 that are inset within the older bt1 and bt2 valley fills these lower terraces have been temporally constrained to 24 5 14 2 ka bt3 10 6 9 8 ka bt4 8 3 6 2 ka bt5 and 3 ka bt6 field sedimentological and stratigraphic analyses of the alluvial fills indicate the influence of tributary and hill slope derived sediment supply during the aggradation of bt1 and to a lesser extent bt2 this contrasts with the predominantly trunk river derived deposits which make up the fill of bt3 bt6 when the hillslopes and tributaries in the study area appear to have been relatively de coupled from the trunk river data presented in this paper suggest that the bergantes river system has responded to and has preserved a record of environmental changes operating both in synchrony with and at a higher frequency than milankovitch driven glacial interglacial cycles major net aggradation phases those associated with relatively large amounts of fluvial sediment e g bt1 and bt2 appear to coincide with pleistocene glacial conditions in mis 6 and parts of mis 5 and mis 4 when the climate on the iberian peninsula was cool and dry intervening phases of net valley incision appear to coincide with warmer and moister climates in pleistocene interglacials the younger terraces bt3 bt6 are characterised by much smaller amounts of fluvial sediment supply dating control places their development during stadial aggradation and interstadial incision events of the late pleistocene and holocene some phases of aggradation appear to coincide with north atlantic heinrich events and also with other securely dated phases of aggradation elsewhere in the mediterranean basin

shallow and deep failure mechanisms during uplift and lateral dragging of buried pipes in sand this paper presents results of a series of experiments modelling uplift and lateral drag of a rigid pipe buried in dry sand the main aim of these tests is to document the gradual transition from s

holocene climatic changes in the western mediterranean from south east france to south east spain abstract holocene climatic changes along coastal regions from south east france to south east spain were studied using pollen ratios comparing modern pollen rain vegetation and climate along selected transects from the atlantic ocean to the mediterranean we obtained threshold values of two different ratios corresponding to the different climatic conditions along the transects these pollen ratios and threshold values were employed to characterize the holocene climatic changes from nine mediterranean coastal sites the results were compared with data from marine and continental pollen sequences distributed in the western mediterranean basin and with additional regional data independent of human activity lake level fluctuations alpine glacier advance and retreat chronology 14 c anomaly and cooling phases in eastern france and central europe the role of anthropogenic activities and climate on the changes in vegetation is discussed six major changes in vegetation cover were identified they correspond to aridification phases that occurred around 9500 9000 yr bp 10 900 9700 cal bp 7500 7000 yr bp 8400 7600 cal bp 4500 4000 yr bp 5300 4200 cal bp 3700 3300 yr bp 4300 3400 cal bp 2600 1900 yr bp 2850 1730 cal bp and 1300 1000 yr bp 1300 750 cal bp these arid episodes were regional responses to more global climatic changes and determined the changes in the vegetation cover humans undoubtedly enhanced the vegetation changes but none the less had to adapt to these new climatic conditions

high resolution fluvial records of holocene environmental changes in the sahel the yame river at ounjougou mali west africa abstract the yame river in the bandiagara plateau dogon country mali is characterised by extensive alluvial sedimentary records particularly in the 1 km long ounjougou reach where holocene floodplain pockets are inset in the pleistocene formations these alluvial records have been investigated via geomorphologic fieldwork and sedimentologic and micromorphologic analyses and are supported by 79 radiocarbon dates the alluvial deposits of the valley floor correspond to a vertical accretion of 3 10 m the reconstruction of fluvial style changes provides evidence of four main aggradation periods from 11 500 to 8760 cal bp the alluvial architecture and grain size parameters indicate a wandering river this period included phases of pulsed high energy floods and avulsion related to a northward shift of the summer monsoon to around 14 n after 11 500 cal bp from 7800 to 5300 cal bp a swampy floodplain environment with standing water pools within a sudanian savanna woodland mosaic corresponds to the culmination of the holocene humid period from 3800 cal bp onwards rhythmic sedimentation attests to an increase in the duration and or intensity of the dry season giving a precise date for the local termination of the holocene optimum period during the last two millennia and for the first time during the holocene the alluvial formations are progressively restricted whereas the colluvial deposits increase indicating strong soil erosion and redeposition within the watershed related to an increase in human impact four major periods are characterised by incision i1 ante 11 500 i2 8760 7800 i3 6790 6500 cal bp i4 2400 1700 cal bp pointing to dramatic changes in fluvial style they result from high energy flood flows during dry spells and confirm the capacity of the floodplain pocket in the upstream reach of the sahelian belt to record rapid holocene climatic change

estimation of active earth pressure against rigid retaining walls considering arching effects it is known that the distribution of active earth pressure against a translating rigid wall is not triangular but nonlinear owing to arching effects in the backfill in the present paper a new formulation is proposed for calculating the active earth pressure on a rigid retaining wall undergoing horizontal translation it takes into account the arching effects that occur in the backfill or retained soil mass in order to check the accuracy of the proposed formulation the predictions from the equation are compared with both existing full scale test results and values from existing equations the comparisons between calculated and measured values show that the proposed equations satisfactorily predict both the earth pressure distribution and the lateral active earth force on the translating wall in order to facilitate calculation of active earth pressures using the proposed equations a modified active pressure coefficient and an effective height of application of the lateral active force are also prov

western mediterranean environmental changes evidences from fluvial archives abstract when dealing with current and past landscape evolution a key issue addresses responses of geomorphic systems to the large number of influencing variables identifying morphodynamic phases and revealing interrelations with specific driving forces are demanding tasks for quaternary research in this paper we present late pleistocene and holocene fluvial sedimentation patterns of three western mediterranean river catchments namely jarama river guadalete river and guadalquivir river that extent along a climatic transect from semi humid sw spain to semi arid central spain these studies are based on extensive fieldwork conducted on 36 exposures and 13 drillings in floodplain positions field data is supported by geochemical analyses while the chronological framework was obtained from the analyses of 70 radiocarbon samples results show distinct patterns of fluvial sedimentation as well as soil formation linked to floodplain stability for each river catchment on regional or catchment scale pollen stratigraphical correlation and comparison with lacustrine records show that fluvial dynamics have a strong reaction to climatic shifts with phases of high fragility characterized by catchment erosion and floodplain sedimentation in response to climatic aridification events and phases of climate change in general the comparison of the examined river systems reveals that periods of supra regional floodplain sedimentation in several catchments occurred from 8 0 to 7 0 5 0 to 3 8 2 2 to 1 5 and around 1 0 as well as 0 4 ka cal bp while we found periods of supra regional soil formation from 13 3 to 12 7 7 0 to 5 1 with a short interruption around 6 0 to 5 5 ka 2 8 to 2 3 ka 1 4 to 1 2 ka and 0 8 to 0 5 ka cal bp beside these consistencies we found deviating dynamic patterns that are apparently expressed in terms of differing onset and offset differing durations or even the lack of fluvial system response the main reasons for this can be seen in different regional climate condition and impacts of further influencing factors or in different levels of sensitivity of the river catchments that may be controlled by initial hydrological conditions catchment size or the degree of anthropogenic influence a larger scale assessment shows that fluvial dynamic patterns are hardly comparable across entire spain due to strong spatial heterogeneity of physiographic and climatic conditions on the iberian peninsula in particular when areas are influenced by different circulation systems e g regions influenced by the atlantic ocean vs regions influenced by the mediterranean sea however the consideration of north atlantic marine records reveals a certain coupling between north atlantic coolings atmospheric processes leading to arid climate over large parts of spain as well as increased landscape instability including strong fluvial sedimentation activity attendant atmospheric conditions are discussed

palaeoflood and floodplain records from spain evidence for long term climate variability and environmental changes abstract palaeoflood chronologies from seven spanish river basins and floodplain aggradation chronologies from thirteen rivers are analysed these fluvial records were divided in to two sub sets namely atlantic 10 ka record and mediterranean 3 ka record river basins which represent distinct modern hydroclimatic conditions in atlantic basins floods result from intense widespread rainfalls associated with atlantic frontal systems transported by westerly airflow mediterranean river flooding is related to heavy rainfall induced by mesoscale convective systems mcss during autumn months evidence from radiocarbon dates in slackwater flood deposits shows six periods of flood clusters at 10 750 10 240 9550 9130 4820 4440 2865 2350 960 790 and 520 290 cal bp despite the different flood producing weather conditions in atlantic and mediterranean rivers the radiocarbon sample clusters overlap and indicate changes in large scale atmospheric circulation and climatic conditions in the iberian peninsula comparison with proxy records of mean temperature for the northern hemisphere demonstrates a relationship between the period of slackwater flood deposition and cold climatic phases e g the 2650 yr bp climatic event or ad 1590 1650 period of the little ice age radiocarbon dates from aggraded floodplain sediments were clustered at 2710 2320 2000 1830 and 910 500 cal bp the first cluster period is in phase with the timing of slackwater deposition whereas the third 910 500 cal bp occurs in between two periods of increased flood frequency as indicated by the palaeoflood and documentary flood records it is argued that the 910 500 cal bp floodplain aggradation period reflects the first post roman evidence of environmental change related to generalised land use changes at the catchment scale which produced high sediment load transported to overbank areas during high flows

durations of soil formation and soil development indices in a holocene mediterranean floodplain abstract holocene and late pleistocene alluvial sequences of the mid medjerda floodplain northern tunisia reveal three types of soils with gradual transitions fluvisols calcaric cambisols calcaric and calcic luvisols chromic stratigraphic cross correlations palaeomagnetic secular variation and 14 c and irsl dating enable detailed information about ages and durations of soil formation in the floodplain weakly developed fluvisols calcaric commonly reveal late holocene ages with soil formation durations lasting between 100 and 300 years hence holocene soil formation is detectable in the exposures from durations of around 100 years onwards cambisols show predominantly mid holocene ages the durations of soil formation are between 800 and 5000 years calcic luvisols chromic feature late pleistocene ages with durations of soil formation between 10 000 and 40 000 years profile development indices were computed from simple field parameters like soil structure soil colour horizon thickness and leaching features the derived development indices show good correlation r 2 0 804 with the calculated durations of soil formation field parameters are well suited for a quantitative development index of holocene soil formation even if very weak developed soils are predominant the study shows that maturity stages of holocene alluvial soils in a homogeneous mediterranean environment are predominantly driven by soil formation duration

development of a prototype for modelling soil pipe interaction and its application for predicting uplift resistance to buried pipe movements in sand this paper presents a testing rig for measuring the reactions on rigid pipes buried in sand during episodes of relative displacement following a detailed presentation of the 1g prototype the test

the holocene and upper pleistocene pollen record from padul granada spain a new study two borings were made at the site of padul granada pollen analysis of 200 spectra from two successive sequences 14 8 and 8 m deep enables a description of the vegetational and climatic history of this region the most southern one in europe from early wurmian times the chronology is supported by twenty one 14c dates original equivalents are found for the great european prewurm interstadials a markedly arid though thermically not extreme episode exactly equivalent to stage 4 of the marine isotopic stratigraphy closes this relatively temperate period the middle part of the last glacial shows climatic fluctuations that are poorly characterized as is often the case in europe for this period a long section very probably corresponding to the complete last pleniglacial does not show any climatic amelioration towards 15 000 yr b p a change in the diagram is noted that can only be interpreted as reflecting a larger expansion of a regional steppe cover this event also reported on three occasions in southeast france marks the beginning of the oldest dryas the climatic amelioration of ca 13 000 yr b p is far more pronounced here than anywhere else in europe whereas that at 10 000 yr b p is not so clearly marked this unexpected result may be accounted for by the fact that padul is the first continental site so far south and so near pleniglacial refuges to be known on the other hand this result is consistent with what is known from oceanic isotopic stratigraphy a quite new late glacial and holocene vegetational history is revealed characterized by the early appearance and dominance of quercus ilex oak forests of a southern type and the early occurrence of quercus suber and olea it is the first account of a complete history of the postglacial reafforestation in a region with a modern semi arid mediterranean climate from the palaeoclimatic point of view it shows that the hot and humid holocene optimum was attained slightly before 8000 yr b p and that the holocene climatic fluctuations were of but small amplitude

morphological pedological and sedimentary evolution on the fringe of the southwestern european drylands during the late pleistocene and holocene evidence of climate and land use changes abstract late quaternary alluvial sedimentary units in the guadiana menor river valley a tributary of the guadalquivir river in southern spain are described based on geomorphological mapping sedimentological analysis palaeosol development and radiocarbon chronology four infill units in the valleys were differentiated with surfaces at 45 mu1 70 mu2 8 6 mu3 and 10 m mu4 above the riverbed each unit is capped by a palaeosol unit mu1 late pleistocene 43 5 34 cal kyr bp consists of gravel and sand in channels and bars in braided river systems distally evolving to silty clays in the floodplain with vertic and clayic calcisols it is capped by dark clays with gleysol development representing wetland environments in endorheic basins channelized gravels alternating with sandy silts make up unit mu2 34 24 cal kyr bp capped by a gypsisol and interpreted as a semi arid alluvial fan distally evolving to playa lake depositional systems unit mu3 5600 2700 cal yr bp extending along the valley bottom is represented by gravels and sand distally evolving to a red and white laminated rhythmite of silt and clay deposited in the playa unit mu4 600 700 cal yr bp is scattered and represented by centimetre thick gravels and sand sheet layers deposited by sheet flows in semi arid constrained alluvial fans alternating intervals of alluvial aggradation 43 5 24 kyr bp 5700 2700 cal yr bp late middle ages and fluvial incision 24 6 cal kyr bp 2700 cal yr bp to 1200 ad 1500 ad to present are interpreted as valley responses to climate variations and changes in land use two regional geomorphological changes are recorded in the sediments 1 climate induced aridification after 34 cal kyr bp with an arid climax after 24 cal kyr bp before the incision linked to the last glacial period and 2 two human forced aggradation stages 5600 2700 cal yr bp and 1200 1400 ad interrupting the late pleistocene to early holocene incisional trend

bearing capacity mechanisms for pipes buried in sand this paper presents results of scaled physical model tests performed to measure the reaction developing on a rigid pipe buried in dry sand when the pipe is subjected to vertical downwards movement

high resolution fluvial record of late holocene geomorphic change in northern tunisia climatic or human impact abstract in northern tunisia the late holocene alluvial record of medjerda floodplain sediments indicates geomorphic changes due to fluctuations of past climate superimposed by the effects of human activity geomorphic activity occurred several times interrupting stable conditions enhanced fluvial dynamics occurred around 4 7 3 0 1 7 1 0 and 0 7 ka cal bp a peak of activity took place about 0 4 ka cal bp some periods of fluvial activity show event like phenomena in particular when an anthropogenic impact intensifies climatic aridification this has been the case around 1 7 1 0 0 7 and 0 4 ka cal bp with severe floods in the medjerda valley during antiquity as well as around 1 3 0 8 and 0 5 ka cal bp immature alluvial soils have developed the first one being the most distinct late holocene medjerda alluvial history shows that fluvial dynamics in northern tunisia were predominantly climate driven anthropogenic impact only intensified or weakened these processes

processes of arroyo filling in northern new mexico usa we documented arroyo evolution at the tree trench and arroyo scales along the lower rio puerco and chaco wash in northern new mexico usa we excavated 29 buried living woody plants and used burial signatures in their annual rings to date stratigraphy in four trenches across the arroyos then we reconstructed the history of arroyo evolution by combining trench data with arroyo scale information from aerial imagery light detection and ranging lidar longitudinal profiles and repeat surveys of cross sections burial signatures in annual rings of salt cedar and willow dated sedimentary beds greater than 30 cm thick with annual precision along both arroyos incision occurred until the 1930s in association with extreme high flows and subsequent filling involved vegetation development channel narrowing increased sinuosity and finally vertical aggradation a strongly depositional sediment transport regime interacted with floodplain shrubs to produce a characteristic narrow trapezoidal channel the 55 km study reach along the rio puerco demonstrated upstream progression of arroyo widening and filling but not of arroyo incision channel narrowing or floodplain vegetation development we conclude that the occurrence of upstream progression within large basins like the rio puerco makes precise synchrony across basins impossible arroyo wall retreat is now mostly limited to locations where meanders impinge on the arroyo wall forming hairpin bends for which entry to and exit from the wall are stationary average annual sediment storage within the rio puerco study reach between 1955 and 2005 was 4 8 10 5 t yr 16 of the average annual suspended sediment yield and 24 of the long term bedrock denudation rate at this rate the arroyo would fill in 310 yr

succession and stable isotope composition of gastropods in holocene semi arid alluvial sequences bardenas reales ebro basin ne spain palaeoenvironmental implications three alluvial units ranging from the middle to late holocene in age were distinguished in bardenas reales natural park ebro basin ne spain based on morphosedimentary analysis and radiocarbon data in this sensitive mediterranean alluvial system the succession and isotopic composition of gastropods greatly contribute to establishing the prevailing palaeoenvironmental conditions the oldest unit 4763 87 to 2848 55 cal yr bp represents fluvial channels and swamped areas includes the greatest proportion of aquatic gastropods ancylus fluviatilis and lymnaea truncatula and marsh species vallonia pulchella and presents the most negative values of 18o mean 2 21 pdb the intermediate unit 1403 60 to 836 65 cal yr bp shows a high rate of alluvial activity related to irregular torrential rainfall with sedimentary features of aridity and this unit includes only dry open ground gastropods xeroplexa sp chondrinidae indet and granopupa granum and presents the least negative values of 18o

an early holocene short climatic event in the northwest iberian peninsula inferred from pollen and diatoms abstract pollen and diatom analyses have been carried out in a 490 cm long core collected from laguna lucenza 1420 m a s l northwest iberian peninsula spanning the last 10 000 yr pollen analyses show a decrease in deciduous quercus pollen percentages and total pollen concentration after radiocarbon date 8350 80 yr bp the estimated age by linear interpolation for the peak of this event is about 9200 cal yr bp diatom analyses have been carried out using the same samples in order to obtain complementary information about past environmental conditions within the water body pollen and diatom records show a response to changes in the palaeoenvironmental conditions diatom concentrations are relatively low indicating low productivity within the lake fragilaria species are dominant and fragilaria exigua is notably more abundant than during previous periods these changes in the diatom community reflect a decrease in lake ph this would be consistent with longer periods of ice cover and cold conditions in the lake at this time we interpret this episode as a response to climatic change probably due to climatic deterioration this interval coincides at least in part with an episode of abrupt and short widespread climate change lasting from 9000 to 8000 yr bp

a theory for ice till interactions and sediment entrainment beneath glaciers and frozen onto or melted from the glacier base can achieve a steady state that is in balance with the rate that latent heat is transported to or from the basal interface at constant n when a gradual increase in heat flow from the glacier base causes the rate of melting to decrease h increases and continues to do so when the heat flow is great enough to produce freezing as freezing becomes more rapid and h increases further the rate of fluid supply to the glacier base reaches a maximum when the effective permeability is sufficiently reduced by the partial ice saturation in the fringe larger h can be achieved with slower freezing at the glacier base but steady states with larger h are unstable the maximum rate of fluid supply to the glacier base is greater at lower n higher temperature gradients and for sediments with higher permeabilities unsteady behavior can lead to large changes in h when there is a mismatch between the rate that latent heat can be extracted and the rate that fluid is supplied to the glacier base transient behavior driven by abrupt changes in n is characterized by rapid variations in freezing rate followed by slower adjustments to h that are limited by the timescale for the conduction of latent heat the resulting patterns of sediment deformation are expected to commonly be distributed over finite depth ranges even when shear is perfectly localized at any single instant in time

mid and late holocene fluvial chronology of tunisia abstract regarding fluvial response to recent climate change it is important to identify and understand previous changes of fluvial dynamics related to past climatic shifts in this paper periods of increased flood activity in central tunisian river systems are presented changes in holocene flood dynamics are reconstructed through a comprehensive analysis of 195 radiocarbon dates from alluvial archives holocene floodplain deposits in central tunisia normally consists of cohesive overbank fines which exhibit excellent preservation conditions against lateral erosion and therefore permit chronostratigraphic records of the entire holocene at most based on published radiocarbon dates two 14 c cumulative probability density plots are created for central tunisia the former represents activity dates indicating phases of increased fluvial dynamics the latter documents stability dates showing periods of soil formation and enhanced landscape stability within the floodplain and the catchment due to geomorphological considerations activity dates and stability dates should be mutually exclusive there is a good match for the mid holocene with increased periods of flooding from 6 2 to 6 0 4 8 to 4 5 4 1 to 3 7 and 3 3 to 3 0 ka these flood periods coincide with low soil formation signals on the other hand periods of increased alluvial soil formation from 6 8 to 6 6 5 9 to 4 8 4 5 to 4 1 3 7 to 3 3 3 0 to 2 8 and 1 8 to 1 6 ka coincide with periods of low flood plain aggradation the data reveal a coupling with north atlantic cooling short term periods of enhanced fluvial dynamics in central tunisia match well with north atlantic cooling the findings indicate a strong climatic link from 4 7 ka until today compared to the holocene floodplain dynamics in tunisian drylands the temperate mid latitudes show mid holocene switches in fluvial dynamics with opposite signs especially after 5 ka north atlantic driven flooding in the temperate central european river systems contrast sharply to flood dynamics in arid to semiarid mediterranean tunisia while under temperate climate conditions floodplain sedimentation decreases it increases under more arid conditions this may indicate that fluvial archives of dissimilar climatic zones reveal different threshold values and sedimentation patterns and therefore different responses to climatic shifts

environmental response of a fragile semiarid landscape bardenas reales natural park ne spain to early holocene climate variability a paleo and environmental magnetic approach abstract the bardenas reales natural park western ebro basin ne spain constitutes a fragile landscape where the prevailing semiarid climate and erodability of the bedrock have resulted in high sensitivity to erosion sedimentation oscillations during the holocene in this paper we present new chronologic sedimentologic paleomagnetic and environmental magnetic results from the oldest unit qah1 of a system of nested cut and fill alluvial sequences which is 18 m thick and crops out extensively in the central part of the natural park at the bardena blanca depression radiocarbon dating indicates that early holocene unit qah1 is younger than 9 38 8 89 cal kyr bp and gives ages of 8 92 8 42 and 7 59 7 37 cal kyr bp in the middle and uppermost parts of the unit respectively sedimentologic data indicate that distal alluvial sediments of unit qah1 accumulated in sandy mud flats and ephemeral playa lakes under arid conditions the coincidence of enhanced magnetite content with moderate to intense root bioturbation in the lowermost and likely also uppermost sediments of unit qah1 suggests that magnetite formed authigenically in response to relatively wetter conditions at the beginning and end of this dry period these results indicate that onset and cessation of alluvial aggradation mark the passing of a geomorphologic threshold most likely plant cover in the watershed during a progressive drying wetting event the radiocarbon based age model of unit qah1 indicates that alluvial aggradation under arid conditions began at 9 13 cal kyr bp and ended at 7 16 cal kyr bp this period is strikingly centered at around the 8 2 kyr cold event but spans a longer time period supporting the notion of a global climatic deterioration as the underlying cause for this event paleomagnetic directions do not clearly display the characteristic patterns recognized in paleosecular variation curves derived from other european lacustrine sediments and cannot be used to refine the radiocarbon based age model for unit qah1 our results demonstrate a quick and strong response of alluvial systems to early holocene climate variability in fragile mediterranean landscapes such as those at the semiarid bardenas reales natural park

holocene erosion sedimentation and stratigraphy at raven fork southern blue ridge mountains usa holocene colluvial and alluvial stratigraphy and a radiocarbon chronology are presented for the valley of the lower three kilometers of raven fork a mountain stream draining 194 km 2 of high relief 1 3 km terrain of the southern blue ridge mountains in western north carolina usa which is in a region that lacks good chronological data lower hillslopes alluvial colluvial fans alluvial bottomlands first terrace and floodplain and the modern stream channel are landforms described with respect to soils stratigraphy and sedimentary structures standard methods for subsurface investigations core holes excavation units exposures are used in conjunction with extensive archeological excavations and cultural chronologies radiocarbon ages from each landform are used to calculate long term average rates of sedimentation results indicate that the first half of the holocene experienced somewhat more rapid rates of hillslope sedimentation 0 3 to 1 1 mm yr than the last half of the holocene 0 1 0 2 mm yr on footslopes toeslopes and alluvial colluvial fans prior to historic time we suggest that these subtle differences in the rates of sedimentation were driven by changes in global paleoclimate that favored a high frequency of heavy rainfall including tropical storms and or severe thunderstorms and more and possibly larger floods during the first half of the holocene prehistoric rates of vertical accretion on the first terrace t1 ranged from 0 1 to 0 8 mm yr between about 10 000 and 3000 calendar years ago and incision below t1 formed the late holocene floodplain beginning at about 6000 years ago we suggest that this incision is linked to a reduction in the supply of sediment and a reduction in the magnitude of floods historical rates of sedimentation on all parts of the depositional landscape 2 0 2 7 mm yr on hillslopes and fans and 5 8 6 5 mm yr on floodplains were about an order of magnitude greater than prehistoric rates we attribute these rates to human impacts such as timber harvest and land clearing which caused accelerated erosion we attribute the abundance of fine grained sediment in streams of the southern blue ridge province which is atypical in many mountain streams around the world to the regionally widespread mantle of saprolite as a source of sediment to the fluvial system holocene sedimentation on all depositional landforms in the valley led to sedimentary burial of archeological materials which highlights the need to consider site burial on lower hillslopes and terraces for evaluation of the cultural resources in the southern blue ridge mountains these findings show that the entrenched condition of the raven fork channel was inherited from the middle holocene and can be considered a natural state for this mountain stream casting doubt on the negative connotation that is often assigned to entrenched channels

investigation of the pore water pressures of coarse grained sandy soil during open system step freezing and thawing tests abstract an investigation of the pore water pressure in freezing soil has been essential for exploring frost heave mechanisms such as water migration and the initiation of ice lenses in this article the pore water pressures of a coarse grained sandy soil were measured during open system laboratory testing a total of three soil samples were tested and the degrees of saturation were 34 78 61 40 and 100 00 respectively each experienced a first step freezing stage a thawing stage and a second step freezing stage the results showed that changes in the pore water pressure depended on the freeze thaw history degree of saturation and temperature under the same temperature conditions the change pattern of the pore water pressure in the first step freezing stage differed from that in the second step freezing stage the pore water pressures in samples with high water content first decreased and then increased slightly as the temperature had a sudden drop in the step freezing stage the pore water pressures in samples with low water content were less sensitive to the temperature change during thawing the pore water pressures increased as the soil sample temperatures rose in terms of the variations in the pore water pressure we further proposed that the phase change of sandy soil occurred in a temperature range and that there was water migration when sandy soil freezes furthermore the permeability between every two pore water probes was calculated using darcy s law with the pore water pressures and water volumes absorbed into the soil sample

paleoenvironmental and geoarchaeological reconstruction from late holocene slope records lower huerva valley ebro basin ne spain abstract slope deposits in semiarid regions are known to be very sensitive environments especially those that occurred during the minor fluctuations of the late holocene in this paper we analyse holocene colluvium genesis composition and paleoenvironmental meaning through the study of slope deposits in ne spain two cumulative slope stages are described during this period in the study area both slope accumulations are superimposed and this has enabled an excellent preservation of the aggregative sequence and the paleosols corresponding to stabilisation stages 14c and tl dating as well as archaeological remains provide considerable chronological precision for this sequence the origin of the accumulation of the lower unit is placed around 4295 4083 cal yr bp 2346 2134 cal yr bc late chalcolithic and it developed until the iron age in a cooler and wetter climate cold iron age under favourable conditions a soil a horizon was formed on top of this unit a new slope accumulation was formed during the little ice age within the slope two morphogenetic periods ending with a horizons are distinguished and related with two main cold wet climatic events the study of these slopes provides a great amount of data for the paleoenvironmental and geoarchaeological reconstruction of the late holocene in ne spain

bedrock fracture by ice segregation in cold regions the volumetric expansion of freezing pore water is widely assumed to be a major cause of rock fracture in cold humid regions data from experiments simulating natural freezing regimes indicate that bedrock fracture results instead from ice segregation fracture depth and timing are also numerically simulated by coupling heat and mass transfer with a fracture model the depth and geometry of fractures match those in arctic permafrost and ice age weathering profiles this agreement supports a conceptual model in which ice segregation in near surface permafrost leads progressively to rock fracture and heave whereas permafrost degradation leads episodically to melt of segregated ice and rock settlement

infilled valleys in the central ebro basin spain abstract the infilled valleys are one of the most frequent landforms that we have found in the central ebro basin area this study concerns those developed in the ebro basin near the city of zaragoza in a large number of these valleys as many as three levels of fill have been recognized these correspond to different accumulative stages and are separated by other periods with a dominant fluvial incision at present the principal process which acts in this area is gully erosion this fact has allowed us to observe the deposit characteristics these deposits are composed of gravels sands and thick levels of silts they have a large variety of sedimentary structures from these we know they are generated by ephemeral streams but there is also a slope material contribution in several cases there are archaeological fragments within the deposits thus we were able to determine the age of some of the levels the oldest fill has a post roman age the middle could have a post medieval age but we could not confirm that the youngest has been produced in recent times alternating sedimentation incision could be produced by the interaction between climatic and human action

the holocene fluvial chronology of spain evidence from a newly compiled radiocarbon database abstract a critical analysis of 74 radiocarbon dates selected from a total of 102 published and unpublished dates from holocene fluvial environments in spain has identified a number of periods of increased fluvial activity in spain namely 11 170 10 230 9630 8785 7980 6860 5800 4800 3880 3085 2895 1820 1300 0 cal bp the latter period reflecting sustained fluvial response to increased human impact the radiocarbon samples were classified according to type of depositional environment a alluvial overbank b flood basin c alluvial channel gravels d fluvio torrential deposits and e slackwater flood deposits palaeofloods dates from slackwater flood deposits indicated at least five phases of increased frequency of large magnitude floods during the holocene 10 855 10 230 9530 8780 2880 2430 975 790 and 520 265 cal yr bp flood basin type deposition occurred from 7980 to 4830 cal yr bp the main clusters of dates from alluvial floodplain deposits occurred at 2750 2150 and 930 520 cal yr bp the record is discussed in relation to other palaeoenvironmental archives including pollen records of holocene vegetation change and palaeoclimatic proxies such as the north atlantic drift ice record comparison with the latter indicates that major holocene flooding coincided with cold climate phases during 9530 9280 2880 2430 and 520 265 cal yr bp a cooling phase at 10 855 10 230 and warming phases at 9030 8780 and 975 790 cal yr bp

late holocene fluvial chronology of spain the role of climatic variability and human impact abstract a database of published and unpublished radiocarbon dates from late holocene fluvial environments in spain was critically analysed in order to obtain a fluvial chronology for this period the principal types of depositional environment represented in the record were slackwater flood deposits 28 dates alluvial overbank facies 12 dates and alluvial channel facies 7 dates the sedimentary context of each date was classified in order to identify those samples that specifically dated change in the fluvial environment analysis of the different depositional environment data sets using summed probability plots identified phases of alluviation at 2800 2350 and 800 500 cal bp increased frequency of large magnitude floods occurred at 2850 2500 1000 800 and 520 250 cal bp the results indicate that in mediterranean regions slackwater flood deposits are valuable archives of climatic variability even during periods of increased human impact

a quantitative framework for interpretation of basal ice facies formed by ice accretion over subglacial sediment 1 we have constructed a numerical model of basal ice formation for glacier ice in contact with subglacial sediment the model predicts four different ice facies whose formation is controlled by availability of subglacial water to satisfy the basal freeze on rate clean or clotted facies may result from congelation or frazil ice growth occurring when supercooled meltwater separates ice base from substrate or if a groundwater source can supply water to the ice base at a velocity equal to the freezing rate laminated facies develops when the supply of subglacial water is sufficiently constrained for cryostatic suction to raise the subglacial effective stress above a threshold for intrusion of ice into sediment by regelation debris laminas 1 mm are entrained by short periodic regelation events of a few hours separated by longer periods days to months of congelation further meltwater limitation produces a massive dirty ice facies due to stacking of debris laminas the model predicts growth of solid dirty ice facies when the bed is meltwater depleted with fast freezing 5 mm yr 1 causing enhanced erosion 30 mm yr 1 we find that basal ice facies and sediment entrainment are controlled mainly by the ratio of freezing rate to water supply rate the predicted ice facies compare favorably with borehole camera imagery of the basal ice layer in kamb ice stream west antarctica facies variability in this layer suggests complex hydrologic history for the west antarctic ice sheet with significant changes occurring over a period of several thousand years

palaeoflood record of the tagus river central spain during the late pleistocene and holocene abstract palaeoflood hydrology of the tagus river central spain was reconstructed from slackwater deposits and palaeostage indicators in two canyon reaches located at el puente del arzobispo in the central part of the catchment 35 000 km 2 in drainage area and in alcantara at the lower part of the catchment 52 000 km 2 in drainage area near the portuguese border the palaeoflood record with more than 80 flood events shows clusters of floods at specific periods from 9440 to 9210 14 c yr bp 8540 8110 bc 8500 to 8000 14 c yr bp 7500 7000 bc 6750 14 c yr bp 5000 bc 1200 to 950 14 c yr bp ad 785 1205 410 14 c yr bp ad 1450 1500 170 to 80 14 c yr bp ad 1670 1950 the largest flood s occurred during the periods 9440 to 9210 14 c yr bp 6750 14 c yr bp and 1200 to 950 14 c yr bp reaching minimum discharge estimates of between 4000 and 4100 m 3 s 1 in the el puente del arzobispo reach and 13 700 15 000 m 3 s 1 in the alcantara reach these periods with increased flood magnitude and or frequency in the tagus river are strongly related to increased moisture influx and winter precipitation in the iberian peninsula especially in the western zone proxy records sensitive to winter precipitation such as lake levels and vegetation changes indicated by pollen records are in good agreement with the clusters of floods found in the tagus river this flood variability seems to correspond to changes in the prevailing atmospheric circulation pattern affecting the iberian peninsula

geomorphology and late holocene climatic change in northeastern spain abstract during the late holocene accumulation and downcutting stages affected the slopes and infilled valleys in the semiarid areas in ne spain the presence of archaeological remains charcoal and ashes within slope deposits and valley fills makes it possible to carry out accurate datings in the case of infilled valleys the different accumulations may be diachronous at a regional level these diachronisms among different infilled valleys may be caused by both human activity and complex responses of the system on the slopes one can distinguish between two accumulation periods separated by an incision period the older accumulation stage has a widespread distribution and developed from the bronze age to the iberian roman epoch the following accumulation period was formed in the post medieval period and is spatially more restricted because of the widespread synchronism shown by these accumulations a climatic cause is put forward as the possible triggering factor for the accumulation incision stages in the slopes the datings obtained indicate that the first accumulation corresponds to the iron age cold epoch 900 300 years b c and the second to the little ice age between both accumulation periods a downcutting stage took place approximately from 300 b c to 1450 a d this downcutting interval can be related to the warm stages of the subatlantic period during which there was a relatively lower percentage of vegetation cover finally the last incision period which is still taking place has affected previous accumulations

a holocene lacustrine record in the central north atlantic proxies for volcanic activity short term nao mode variability and long term precipitation changes a holocene lacustrine record in the central north atlantic proxies for volcanic activity short term nao mode variability and long term precipitation changes

discontinuous ephemeral streams abstract many ephemeral streams in western north america flowed over smooth valley floors before transformation from shallow discontinuous channels into deep arroyos these inherently unstable streams of semiarid regions are sensitive to short term climatic changes and to human impacts because hillslopes supply abundant sediment to infrequent large streamflow events discontinuous ephemeral streams appear to be constantly changing as they alternate between two primary modes of operation either aggradation or degradation may become dominant attainment of equilibrium conditions is brief disequilibrium is promoted by channel entrenchment that causes the fall of local base level and by deposition of channel fans that causes the rise of local base level these opposing base level processes in adjacent reaches are maintained by self enhancing feedback mechanisms the threshold between erosion and deposition is crossed when aggradational or degradational reaches shift upstream or downstream extension of entrenched reaches into channel fans tends to create continuous arroyos upvalley migration of fan apexes tends to create depositional valley floors with few stream channels less than 100 years is required for arroyo cutting but more than 500 years is required for complete aggradation of entrenched stream channels and valley floors discontinuous ephemeral streams have a repetitive sequence of streamflow characteristics that is as distinctive as sequences of meander bends or braided gravel bars in perennial rivers the sequence changes from degradation to aggradation headcuts concentrate sheetflow a single trunk channel conveys flow to the apex of a channel fan braided distributary channels end in an area of diverging sheetflow and converging sheetflow drains to headcuts the sequence is repeated at intervals ranging from 15 m for small streams to more than 10 km for large streams lithologic controls on the response of discontinuous ephemeral streams include 1 amount and size of sediment yielded from hillslopes 2 infiltration capacity of valley floor alluvium that influences both the unit stream power available for upstream headcut migration and the attenuation of flashy streamflow events by riparian vegetation in sheetflow reaches and 3 cohesiveness of alluvium which affects headcut and streambank morphology and rates of arroyo extension downcutting and widening initiation of arroyo cutting may be too complex to be attributed to a single cause such as change in mean annual precipitation or grazing by livestock but is most likely associated with a decrease in density of protective plant cover on hillsides and along valley floors relatively larger unit stream power makes downstream reaches more susceptible to initial entrenchment during floods than headwaters reaches and favors persistent arroyos entrenchment continues until an equilibrium longitudinal profile is briefly attained then channel widening occurs streambanks are undercut and aggradation begins

testing the reliability of detrital cave sediments as recorders of paleomagnetic secular variations seso cave system central pyrenees spain abstract a paleomagnetic study has been carried out on a waterlaid detrital sedimentary sequence of 240 cm thick within the seso cave system west central pyrenees in these sediments seven charcoal samples were dated using 14c ams ranging from 2080 to 650 cal yr bp 130 bc 1300 ad two levels of human occupation of the cave have been recognized by ceramics associated to the iberian period and to the roman period respectively the detrital sedimentary sequence is made of autochthonous piping detached material from the eocene marls host rock inside of the cavity and allochthonous stream transported sediments from the outside sediments the autochthonous material first 100 cm made of fine grain laminated sediments lutites and marls corresponds to pond facies the allochthonous material 190 240 cm is made of lutites and sands and corresponds to stream facies and both facies are mixed from 100 to 190 cm the increase in sedimentation rate towards the end of the sequence stream facies points to an intensification of the alluvial activity as a possible consequence of a more arid climate during the medieval climate anomaly for the paleomagnetic study 44 discrete cylindrical samples were taken along the detrital sequence the values of the natural remanent magnetization and magnetic susceptibility are significantly lower in the pond sediments than in the stream sediments the declination and inclination of the paleomagnetic characteristic component sister samples analyzed by both alternating field and temperature demagnetizing procedure of each depth point is compared to the spanish archeomagnetic catalog and available geomagnetic models arch3k 1 cals3k 4 cals10k 1b and scha dif 3k in order to determine the accuracy of these sediments recording the earth s magnetic field results suggest that these sediments poorly record the earth s magnetic field however paleomagnetic inclination shows similar results between both demagnetizing methods and the inclination is well recorded especially in the younger stream facies the lack of archeological remains with absolute dates from 925 to 1545 cal yr bp in the iberian paleomagnetic secular variation reference curve has prevented up to now the study of that time period therefore the inclination data from the seso cave deposit is the first record of the iberian paleomagnetic secular variation during most part of the medieval time and they are closer to the inclination values of one geomagnetic model cals10k 1b

environmental evolution and mid late holocene climate events in the valencia lagoon mediterranean coast of spain integration of geomorphological stratigraphic malacological sedimentological and micropalaeontological techniques and 14c dating allows us to characterise the processes and evolution of the coastal barrier lagoon system of valencia spain from the middle holocene to the historical epoch as well as the responses to global climate events four stages are recognised phase 1 around 8240 80 cal yr bp a brackish lagoon of moderate energy and in restricted environment was formed with an energy peak that could correspond to the maximum holocene marine transgression dating 8240 80 cal yr bp carried out in peat corresponds to a cold cycle and low water levels in inland lakes of the western mediterranean phase 2 from 6450 cal yr bp to 3710 130 cal yr bp a lagoon remained in restricted environment and connected with the sea but with a notable energy decrease and recurrent saturation processes similar to those described in other mediterranean continental lakes this phase is contemporaneous

late holocene 1500 yr climatic periodicities and their implications fourier and nonlinear regression analysis of a 4000 yr paleoclimate proxy record in western canada shows strong periodicities of 1500 yr and several weaker century to millenial scale periodicities in conjunction with the 23 708 yr milankovitch periodicity these produce a model of climate fluctuation through the postglacial consistent with recognized paleoclimatic fluctuations of the past 15 000 yr in the northern mid latitudes these results suggest that postglacial climatic anomalies such as the little ice age and the younger dryas were at least in part periodic phenomena rather than the result of unique aperiodic events projecting these periodicities into the future suggests that even in the absence of anthropogenic climate forcing a natural warming trend will continue until ca a d 2400

holocene environmental variability in the central ebro basin ne spain from geoarchaeological and pedological records abstract environmental fluctuations during the holocene caused important landscape changes in the central ebro basin which is a very sensitive region due to its semiarid climate lithology and continuous human presence severe erosion processes hinder palaeoenvironmental and archaeological record preservation infills of ephemeral stream valleys in semiarid environments are some of the best contexts for geoarchaeological studies in this paper we analyse the geomorphological processes pedological features and charcoal and pollen content and composition of the sedimentary sequence of la poza valley catchment area with the support of additional information from la bajada valley 14 c dates for 13 charcoal fragments provide the necessary chronological control we describe 5 sedimentary units and a polycyclic sequence of six soils that covers most of the holocene beginning ca 9 5 ky cal bp buried soils help to identify stability periods in the sedimentary sequence while incision stages are detected through erosive contacts and terraced organisation of the sedimentary units charcoal and pollen content and composition as well as the soil development reveal an open forest of junipers and pines for the early holocene in the lower part of the sequence mainly in unit 1 very different from the current deforested landscape also represented in the sequence unit 4 thus la poza record shows the environment was favourable for hunter gatherers from the late mesolithic and for the first neolithic farmers from then on progressive degradation due to a combination of climate changes and increasing human pressure led to the current deforested landscape

erosion in mediterranean landscapes changes and future challenges abstract intense erosion processes are widespread in the mediterranean region and include sheet wash erosion rilling gullying shallow landsliding and the development of large and active badlands in both subhumid and semi arid areas this review analyses the main environmental and human features related to soil erosion processes and the main factors that explain the extreme variability of factors influencing soil erosion particularly recent land use changes the importance of erosion in the mediterranean is related to the long history of human activity in a region characterized by low levels of annual precipitation the occurrence of intense rainstorms and long lasting droughts high evapotranspiration the presence of steep slopes and the occurrence of recent tectonic activity together with the recurrent use of fire overgrazing and farming these factors have resulted in a complex landscape in which intensification and abandonment wealth and poverty can co exist the changing conditions of national and international markets and the evolution of population pressure are now the main drivers explaining land use changes including farmland abandonment in mountain areas the expansion of some subsidized crops to marginal lands and the development of new terraces affected by landslides and intense soil erosion during extreme rainstorm events the occurrence of human related forest fires affecting thousands of hectares each year is a significant problem in both the northern and southern areas of the mediterranean basin here we highlight the rise of new scientific challenges in controlling the negative consequences of soil erosion in the mediterranean region 1 to reduce the effects and extent of forest fires and restructure the spatial organization of abandoned landscapes 2 to provide guidance for making the eu agricultural policy more adapted to the complexity and fragility of mediterranean environments 3 to develop field methods and models to improve the identification of runoff and sediment contributing areas 4 to contribute to the conservation of landscapes i e bench terraced fields having high cultural and productivity values 5 to improve knowledge of the hydrological and geomorphological functioning of badlands with the aim of reducing sediment yield and accessibility 6 to better understand the effect of climate change on soil erosion in the mediterranean region and 7 to improve quantitative information on long term soil erosion

river braiding caused by rapid floodplain deformation insights from holocene dynamics of the jarama river in central spain abstract in this paper we will use an illustrative example to show the significance of rapid vertical movements inside floodplains as well as varying discharge values for the alteration of channel and sedimentation patterns during the holocene concerning such relationships well documented and well dated references from sedimentary records are rather rare the developments within the lower jarama valley have been significantly supported by an interaction of tectonic activity evaporite dissolution and halokinetics that initiated rapid vertical movements over short distances and caused the formation of knick points and gradient changes along the longitudinal floodplain profile furthermore the specific mediterranean climate caused highly variable discharges including extreme runoff peaks the juxtaposition of different floodplain gradients gave rise to spatial and temporal changes of discharge patterns and channel geometry which is reflected by varying sedimentation as well as erosion patterns we have been able to confirm that alluvial thickening due to intense dissolution and subsidence has been a characteristic and frequently recurring feature during the pleistocene moreover we want to emphasize that also during the holocene gradient adjustments exercised controlling influence on fluvial dynamics in particular with regard to channel response in fact we found consistency between low and moderate gradients and meandering single channel patterns associated with overbank deposition in distal floodplain positions only a section with stronger inclination revealed evidences for multiple channel discharge patterns in form of gravelly braided river deposits in comparison with recent discharge patterns and information from historical sources it appears that braided river deposition took place just within a short time frame between 5 and 3 ka cal bp this matches exactly a period of strong climatic aridity including highly variable precipitation and discharge patterns from that we conclude that in the first instance gradient changes promoted the change of channel and discharge patterns but however specific overlap of the parameters gradient and runoff is considered to have been necessary to generate braided discharge pattern a subsequent formation of braided patterns during the late holocene was presumably prevented by river entrenchment as well as a strong increase of sediment availability during the time of roman colonization on the basis of this study we can establish a number of general relationships between floodplain gradient runoff pattern and channel response during the holocene period that may help us to better understand fluvial behavior in various different areas

response of subglacial sediments to basal freeze on 1 theory and comparison to observations from beneath the west antarctic ice sheet 1 we have constructed a high resolution numerical model of heat water and solute flows in sub ice stream till subjected to basal freeze on the model builds on quantitative treatments of frost heave in permafrost soils the full version of the clapeyron equation is used hence ice water phase transition depends on water pressure osmotic pressure and surface tension the two latter effects can lead to supercooling of the ice base this supercooling in turn induces hydraulic gradients that drive upward flow of pore water which feeds the growth of segregation ice onto the freezing interface this interface may progress into the till and form ice lenses if supercooling is sufficiently strong hence the ice segregation process develops a stratified basal ice layer in our model a high basal temperature gradient 0 054 c m 1 triggers ice stream stoppage and the loss of basal shear heating leads to relatively high basal freeze on rates 3 5 mm a 1 in response the subglacial till experiences comparatively rapid consolidation till porosity can decrease from 40 to 120 kpa approximately within one century basal supercooling arising from redistribution of solutes and ice water interfacial effects amounts to ca 0 35 c below the pressure melting point fine grained till is in our model associated with widely spaced thick ice lenses coarse grained till yields thinner ice lenses that are more closely spaced our model results compare favorably although not in all details with available observational evidence from borehole studies of west antarctic ice streams

do deterministic sediment detachment and transport equations adequately represent the process interactions in eroding rills an experimental field study abstract this paper tackles two main questions by linking observations determination of hydraulic parameters and measurement of sediment transport with the formulae used in soil erosion models first do constant shear stress values in different rills with constant soil parameters result in the same soil detachment values secondly deterministic soil erosion models make the assumption that there is a relationship often further assumed to be linear between shear stress and soil detachment is this suitable for representing real erosion process combinations in natural rills following most process based deterministic soil erosion models derived hydraulic and erosion parameters should be similar however the results from the different experiments showed clear differences in sediment concentration transport rates and other measured as well as calculated values in contrast to our experimental results a model simulation would produce erosion parameters with low variations represented by the relative measurement error and the empirical variation coefficient this reveals the general problems of using process based deterministic models for erosion in shallow rills while soil erosion models simulate the processes resulting from the shear forces of flowing water on the soil surface other processes like side wall failure headcut retreat and plunge pool dynamics are not taken into account our results suggested that these other processes may contribute substantially to rill erosion processes the results of this study strongly suggested that the model concept of most physical based soil erosion models is inadequate for modeling rill erosion processes measured total rill erosion rates were the sum of erosion rates caused by a combination of different soil erosion processes with different spatial and temporal distribution this combination cannot be described by a single equation

climate and anthropogenic factors affecting alluvial fan development during the late holocene in the central ebro valley northeast spain the late holocene in the central ebro depression is characterized by a number of morphodynamic stages that affected hillslopes and channels climate fluctuations and human activities together caused severe erosion and floods resulting in alternating stages of accumulation and incision in the valley floors seven accumulation levels n6 n0 correlated with ebro river fluvial terraces have been identified in the secondary fluvial network of the central ebro depression the main accumulation level n3 corresponds to a long period of increased hillslope erosion and sedimentation in the valleys from the neolithic to the late roman periods the accumulation levels are evident throughout the valleys and extend to the valley mouths where many connect with alluvial fans the study of several sedimentological profiles 14c ams dating and many archaeological remnants have enabled detailed assessment of sedimentation characteristics in the alluvial fans and the relationship thereof to the presence of human sett

uplift mechanisms of pipes buried in sand reliable design against upheaval buckling of offshore pipelines requires the uplift response to be predicted this paper describes a model scale investigation into the mechanisms by which uplift resistance is mobilized in silica sand and illustrates how the observed mechanisms are captured in prediction models a novel image based deformation measurement technique has been used the results show that peak uplift resistance is mobilized through the formation of an inverted trapezoidal block bounded by a pair of distributed shear zones the inclination of the shear zone is dependent on the soil density and therefore dilatancy after peak resistance shear bands form and softening behavior is observed at large pipe displacements either a combination of a vertical sliding block mechanism and a flow around mechanism near the pipe or a localized flow around mechanism without surface heave is observed depending on the soil density and particle size

stone circles form and soil kinematics distinct surface patterns are ubiquitous and diverse in soils of polar and alpine regions where the ground temperature oscillates about 0 c they constitute some of the most striking examples of clearly visible abiotic self organization in nature this paper outlines the interplay of frost related physical processes that produce these patterns spontaneously and presents unique data documenting subsurface soil rotational motion and surface displacement spanning 20 years in well developed circles of soil outlined by gravel ridges these sorted circles are particularly attractive research targets for a number of reasons that provide focus for this paper i their exceptional geometric regularity captures the attention of any observer ii they are currently forming and evolving hence the underlying processes can be monitored readily especially because they are localized near the ground surface on a scale of metres which facilitates comprehensive characterization and iii a recent highly successful numerical model of sorted circle development helps to draw attention to particular field observations that can be used to assess the model its assumptions and parameter choices and to the considerable potential for synergetic field and modelling studies

direct observation of frost wedging in alpine bedrock width and temperature of rock joints were automatically monitored in the japanese alps three years of monitoring on a sandstone rock face shows two seasonal peaks of joint widening in autumn and spring the autumn events are associated with short term freeze thaw cycles and the magnitude of widening reflects the freezing intensity and water availability the short term freezing can produce wedging to a depth of at least 20 cm the spring events follow a rise in the rock surface temperature to 0 c beneath the seasonal snowcover and likely originate from refreezing of meltwater entering the joint some of these events contribute to permanent enlargement of the joint two other joints on nearby rock faces experience only sporadic widening accompanying freeze thaw cycles and insignificant permanent enlargement observations indicate that no single thermal criterion can explain frost weathering the temperature range at which wedging occurs varies with the bedrock conditions water availability and duration of freezing copyright 2001 john wiley sons ltd

anthropogenic and climatic impact on holocene sediment dynamics in se spain a review the climatic and anthropogenic control on holocene sediment dynamics was not well constrained for the western mediterranean basin the paucity of high resolution palaeoenvironmental records long hampered a detailed understanding of the human impact on erosion rates this paper analyses holocene sediment dynamics in the context of regional climatic conditions land cover and human occupation based on an extended compilation of recently published high resolution paleoenvironmental proxy data from both terrestrial and marine environments the palaeoenvironmental reconstruction identified four main aridification episodes a at 5600 4700 a4 4100 3400 a3 2800 2500 a2 and 1900 1300 1200 a1 cal bp most of the severe aridification phases were climatically induced not human driven and well correlated with a large dataset of paleoenvironmental records from the western mediterranean basin and north atlantic ocean the phases of enhanced aridity are generally associated with enhanced sediment dynamics independent of the intensity and type of human occupation in contrast wet climatic conditions are found to be associated with both high and low sediment dynamics dependent on the human impact on the environment the mid late phoenician phoenician ii republican rome civilizations and the christian reconquest are all associated with high human impact on the environment and high erosion rates are reported for the vera basin and ne spain despite the improved hydrological conditions human occupation is not necessarily associated with geomorphic instability as shown by the post argaric omeya and nazarene periods that are characterized by low erosion rates and geomorphic stability

magnetobiochronology of lower miocene ramblian continental sediments from the tudela formation western ebro basin spain abstract the calibration of european lower miocene continental stages is poorly constrained due to the lack of robust magnetostratigraphic data from continental sediments of this age in this paper we present the first magnetostratigraphic results from the mammal fossil bearing continental sediments of the lower middle miocene tudela formation western ebro basin spain the study is based on 331 paleomagnetic sites distributed along a 790 m thick composite section the resulting magnetostratigraphy provides an independent correlation to the geomagnetic polarity time scale and allows accurate dating of previously known and new ramblian upper lower miocene fossil localities of the tudela formation the new age constraints derived for the tudela formation fossil localities provide together with a revaluation of other iberian faunas the first magnetochronology for the ramblian continental stage the lower boundary of the ramblian is placed at the lower part of chron c6r ca 20 4 ma and the boundary between the lower and upper ramblian is located at the middle of chron c6n ca 19 6 ma the upper boundary of the ramblian and hence the base of the aragonian is placed at the upper middle part of chron c5cr 16 8 17 ma our results also provide the first magnetostratigraphically dated mn3 faunas in spain which together with a revaluation of other iberian and european faunas provide a revised calibration of european mammal zone mn3 the lower boundary of zone mn3 is placed at the boundary between chrons c6r and c6n ca 20 1 ma and its upper boundary is located at the upper middle part of chron c5cr 16 8 17 ma

geomorphology and quaternary stratigraphy the roles of morpho litho and allostratigraphy abstract the subdivision and ordering of quaternary sediments and landforms is very often based on geomorphology quaternary landforms such as moraines river terraces palaeoshorelines and indeed any other landform can be arranged and ordered in time based on their relative position in the landscape morphostratigraphy is the subdivision of sedimentary units primarily on the basis of surface form whilst surface form is often used as a criterion for separating sedimentary units morphostratigraphy also usually incorporates lithological criteria to aid stratigraphical subdivision and morpho and lithostratigraphy are often interlinked in quaternary science however another approach allostratigraphy has increasingly been applied to subdivide and order quaternary sediment landforms allostratigraphy uses discontinuities to subdivide sedimentary successions allostratigraphy enables lateral variations in lithology to be included within the same stratigraphical unit furthermore it enables lithologically similar sediments stacked on top of each other to be divided into separate units based on discontinuities this paper examines the applications of morpho litho and allostratigraphy to subdivide sediment landform assemblages and critically reviews their role in quaternary stratigraphy

soil deformation measurement using particle image velocimetry piv and photogrammetry a deformation measurement system based on particle image velocimetry piv and close range photogrammetry has been developed for use in geotechnical testing in this paper the theory underlying this system is described and the performance is validated digital photography is used to capture images of planar soil deformation using piv the movement of a fine mesh of soil patches is measured to a high precision since piv operates on the image texture intrusive target markers need not be installed in the observed soil the resulting displacement vectors are converted from image space to object space using a photogrammetric transformation a series of validation experiments are reported these demonstrate that the precision accuracy and resolution of the system are an order of magnitude higher than previous image based deformation methods and are comparable to local instrumentation used in element testing this performance is achieved concurrent with an order of magnitude increase in the number of meas

a theoretical model of the fracture of rock during freezing we present a mathematical model for the breakdown of porous rock by the growth of ice within cracks the model is founded upon well established principles of fracture mechanics and recent advances in soil physics ijong with the assumption that progressive crack growth results from water migrating to ice bodies in cracks much as water migrates to ice lenses in freezing soil our model predicts crack growth rates compatible with empirical data calculations for a granite and a marble indicate that sustained freezing is most effective in producing crack growth when temperatures range from 4 c to 15 c at higher temperatures thermodynamic limitations prevent ice pressure from building up sufficiently to produce significant crack growth at lower temperatures the migration of water necessary for sustaining crack growth is strongly inhibited in hydraulically open systems in which pore water pressure remains near atmospheric pressure during the freezing process crackgrowth rates during continuous cooling will generally be greatest at low rates of cooling less than 0 1 0 5 c h at higher rates of cooling the influx of water to growing cracks is significantly inhibited the model delineates clearly the role of material parameters elastic moduli fracture mechanical properties grain size and shape and crack size environmental conditions temperature temperature gradient water pressure and time in frost damage to rocks our calculations along with recent experimental work on water migration in freezing rocks fukuda 1983 lead us to question the widely accepted importance of two phenomena freezing of water in sealed cracks and freeze thaw cycling in the fracture of rock exposed to natural freezing conditions

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

late holocene evolution of playa lakes in the central ebro depression based on geophysical surveys and morpho stratigraphic analysis of lacustrine terraces abstract the origin and morpho stratigraphic evolution of the largest playa lake system la playa el pueyo in the bujaraloz sastago endorheic area located in the semiarid central sector of the ebro depression are analysed the enclosed depressions are developed on gypsiferous tertiary bedrock and show a prevalent wnw ese orientation parallel to the direction of the prevalent strong local wind cierzo yardangs have been carved in bedrock and unconsolidated terrace deposits in the leeward sector of the largest lake basins a sequence of three lacustrine terrace levels has been identified by detailed geomorphological mapping the treads of the upper middle and lower terrace levels are situated at 9 m 6 m and 0 5 m above the playa lake floors respectively seismic refraction and electrical resistivity profiles acquired in la playa reveal a thin basin fill 2 m with a planar base these data allow ruling out the genetic hypothesis for the depressions involving the collapse of large bedrock cavities and support a mixed genesis of combined widespread dissolution and subsidence by groundwater discharge and eolian deflation during dry periods the 5 m thick deposit of the middle terrace was investigated in hand dug and backhoe trenches six ams radiocarbon ages from this terrace indicate an aggradation phase between 3 9 ka and ca 2 ka these numerical ages yield a maximum average aggradation rate of 2 6 mm yr and a minimum excavation rate by wind deflation of 3 mm yr subsequent to the accumulation of the middle terrace the latter figure compares well with those calculated in several arid regions of the world using yardangs carved in palaeolake deposits the aggradation phase between 4 and 2 ka is coherent with other iberian and mediterranean records showing relatively more humid conditions after 4 ka including the iron ages and the iberian roman period

glacier permafrost interactions processes products and glaciological implications abstract glaciers and permafrost represent key components of the global cryosphere widely held assumptions that 1 they are largely mutually exclusive and 2 glaciers resting on permafrost are slow moving and geomorphologically ineffectual have meant that glacier permafrost interactions have been given little attention within the research literature recent research however has demonstrated that such interactions are likely to have been more extensive than previously thought particularly during periods of ice sheet growth when glaciers would have advanced over pre existing permafrost work in both modern and ancient environments has revealed that subglacial processes such as basal sliding and subglacial sediment deformation can remain active at temperatures below the pressure melting point due to the persistence of premelted liquid water consequently cold based glaciers resting on permafrost are potentially more dynamic than previously thought and are capable of creating subglacial features typically viewed as only forming beneath warm based ice in addition the active coupling of cold based ice with ice marginal permafrost means such ice masses are capable of deforming sediments and occasionally bedrock to depths of tens or even hundreds of meters and are commonly associated with the development of a range of distinctive ice marginal landforms including push or thrust moraines and hummocky or controlled moraines this reflects the influence of permafrost on the entrainment of debris rich basal ice as well as the hydraulic transmissivity of the groundwater system and the associated porewater pressures within the substrate this review considers the key characteristics of permafrost and its formation likely extent and rheological behaviour within glacial environments traditional conceptions regarding the motion and landscape impact of cold based glaciers resting on permafrost are considered before their re examination in light of recent work demonstrating the operation of basal processes at sub freezing temperatures the implications for our understanding of the dynamics of glaciers and ice sheets as well as landforms and sedimentary sequences indicative of glacier permafrost interactions are explored and exemplified with reference to modern and ancient glacial environments gaps in our existing knowledge are identified and profitable areas for future research suggested

lateglacial and holocene palaeohydrology in the western mediterranean region the lake estanya record ne spain abstract the multi proxy analysis of sediment cores recovered in karstic lake estanya 42 02 n 0 32 e 670 m a s l ne spain located in the transitional area between the humid pyrenees and the semi arid central ebro basin provides the first high resolution continuous sedimentary record in the region extending back the last 21 000 years the integration of sedimentary facies elemental and isotopical geochemistry and biogenic silica together with a robust age model based on 17 ams radiocarbon dates enables precise reconstruction of the main hydrological and environmental changes in the region during the last deglaciation arid conditions represented by shallow lake levels predominantly saline waters and reduced organic productivity occurred throughout the last glacial maximum 21 18 cal kyrs bp and the lateglacial reaching their maximum intensity during the period 18 14 5 cal kyrs bp including heinrich event 1 and the younger dryas 12 9 11 6 cal kyrs bp less saline conditions characterized the 14 5 12 6 cal kyrs bp period suggesting higher effective moisture during the bolling allerod the onset of more humid conditions started at 9 4 cal kyrs indicating a delayed hydrological response to the onset of the holocene which is also documented in several sites of the mediterranean basin higher although fluctuating holocene lake levels were punctuated by a mid holocene arid period between 4 8 and 4 0 cal kyrs bp a major lake level rise occurred at 1 2 cal kyrs bp conducive to the establishment of conditions similar to the present and interrupted by a last major water level drop occurring around 800 cal yrs bp which coincides with the medieval climate anomaly the main hydrological stages in lake estanya are in phase with most western mediterranean and north atlantic continental and marine records but our results also show similarities with other iberian and northern african reconstructions emphasizing peculiarities of palaeohydrological evolution of the iberian peninsula during the last deglaciation

interrelated continental sedimentary environments in the central iberian range spain facies characterization and main palaeoenvironmental changes during the holocene a complex holocene system in the central iberian range ne spain has been reconstructed on the basis of sediments recovered from cores and in situ observations small alluvial fans graded into a wide shallow lacustrine area anavieja lake that connected downstream with a carbonate fluvial system with associated vegetated zones the fluvial system was mainly characterized by the development of tufa barriers especially during the first part of the holocene that separated pools or small lakes oncolites detrital tufas calcarenites and marls were deposited in these pools adjacent vegetated areas were covered by macrophytes and were episodically reached by detrital tufa supplies indicating high flood stages high sedimentary rates existed in both the fluvial including the pools and vegetated areas suggesting that despite the common erosion of tufas a clear aggradating evolution existed by contrast very low sedimentary rates were registered in the anavieja lake all the environments but especially the vegetated areas registered the climate evolution during the holocene although the onset of the holocene was characterized by wide climate variability warm and humid conditions dominated during the first part and drier conditions during the second part a water level recovery seems to have been existed during the last millennium this is a good example of the potential of continental systems other than lakes to be useful for palaeoenvironmental and palaeoclimatic studies

towards a simple and reliable method for calculating the uplift capacity of plate anchors in sand this paper investigates the uplift capacity of horizontal plate anchors in sand through finite element analyses and centrifuge experiments finite element simulations adopt a sophisticated bounding

microscopic and environmental controls on the spacing and thickness of segregated ice lenses the formation of segregated ice is of fundamental importance to a broad range of permafrost and periglacial features and phenomena models have been developed to account for the microscopic interactions that drive water migration and predict key macroscopic characteristics of ice lenses such as their spacings and thicknesses for a given set of sediment properties the temperature difference between the growing and incipient lenses is shown here to depend primarily on the ratio between the effective stress and the temperature deviation from bulk melting at the farthest extent of pore ice this suggests that observed spacing between ice lenses in frozen soils or traces of lenses in soils that once contained segregated ice might be used to constrain the combinations of effective stress and temperature gradient that were present near the time and location at which the lower lens in each pair was initiated the thickness of each lens has the potential to contain even more information since it depends additionally on the rate of temperature change and the permeability of the sediment at the onset of freezing however these complicating factors make it more difficult to interpret thickness data in terms of current or former soil conditions

8 2 ka bp paleoclimatic event and the ebro valley mesolithic groups preliminary data from artusia rock shelter unzue navarra spain abstract this paper presents the results of the first excavation campaign of the artusia rock shelter in unzue navarre spain chronocultural and archaeobiological analyses revealed five different occupation phases artusia i v within the regional mesolithic timeline specifically in the mesolithic of notches and denticulates artusia i and ii and the geometric mesolithic artusia iii iv and v in addition the study of the sedimentological and palaeoenvironmental evolution in the entire record helped to clearly define several climatic events which developed around 6550 cal bc 8500 cal bp and 6250 cal bc 8200 cal bp here we present a description of these events and their pre historical interpretation with the aim of recognizing how they influenced the mesolithic hunter gatherer groups living in the ebro basin of the iberian peninsula

historical morphogenesis of the turia river coastal flood plain in the mediterranean littoral of spain abstract the cross referencing of sedimentological stratigraphic geoarchaeological and radiocarbon data enables us to establish the geomorphologic evolution of the late holocene coastal flood plain of the turia river the holocene marine transgression formed a coastal barrier lagoon environment in the coastal plain during the late holocene increased sediments supplied to the low reach of the river promoted a the progradation of deltaic coastal sandy ridges on the coastline and b the aggradation of the floodplain on top of the sedimentary sequence four phases are clearly recognised in the geoarchaeological record of the flood plain 1 high magnitude flooding events 2800 bp to 3rd century bc 2 slow riverbed aggradation and progressive levee formation low energy flood regime in roman times 2nd century bc to 5th century ad 3 swampy environmental processes 6th to 9th centuries 4 second high magnitude flooding phase 11th century the navigable channel of the roman and early islamic periods became a wide and shallow braided channel in medieval times these phases are correlated with others detected by researchers in many areas of the mediterranean region and with global holocene climate events

impacts of sediment connectivity on holocene alluvial records across a mediterranean basin guadalentin river se spain two contiguous alluvial valleys maria and guadalupe sectors of the upper guadalentin river se spain show distinct holocene alluvial architecture cut and fill nested and stepped fill terraces revealing a strong control of valley morphology and bedrock barriers on sediment delivery storage and preservation the headwater valley maria sector preserves four morphosedimentary alluvial units corresponding to two palaeogeographic stages morphosedimentary unit msu1 the most extensive is a major depositional valley infill dominated by sand and silt texture showing three stratigraphic sets dated 9000 8500 5300 4800 4000 3000 cal bp this vertically stacked alluvial accumulation occurs upstream of a narrow bedrock channel that limited sediment connectivity with the downstream guadalupe sector between 3000 and 2350 cal bp a 15 m deep incision on msu1 occurred and subsequent cut and fill cycles generated three alluvial terraces dated at 2350 1900 cal bp msu2 1800 700 cal bp msu3 and post 400 years msu4 in the downstream valley guadalupe sector six flights of alluvial terraces msug1 to msug6 were formed by episodic aggradation and quasi continuous incision in response to baselevel changes of the lower guadalentin river during the holocene alluvial chronologies in these two contiguous valleys show out of phase sedimentation periods under low connectivity conditions 9 3 ka and in phase cut and fill cycles after valley re connection post 3 0 ka the late holocene alluvial activity periods also coincide with morpho stratigraphic data from the lower guadalentin indicating that fluvial connectivity throughout the catchment was only completed in the late holocene

holocene alluvial morphopedosedimentary record and environmental changes in the bardenas reales natural park ne spain abstract a holocene alluvial morphostratigraphy based on geomorphological mapping sedimentological analysis soil development and radiocarbon chronology is presented for the semiarid blanca basin in the bardenas reales natural park ne spain four morphopedosedimentary alluvial units mu1 mu2 mu3 and mu4 were differentiated which may correspond to two palaeogeographical stages the first one includes the morphopedosedimentary unit mu1 and is the most extensive in the area it is made up of a complex aggradation fill up sequence comprising a braided channel system a sand mud flat 9200 7900 cal bp and a playa lake environment related to a nearly closed depression an intensive fluvial entrenchment period is recognized leading the opening of the blanca basin before the second stage that includes the units mu2 mu3 and mu4 this set of units forms a sequence of cut and fill and nested fill terraces recording the alluvial activity in the blanca basin during the last 6 ka the mu2 unit 5900 3300 cal bp in age represents a period of high geomorphic instability with rapid alluvial sedimentation channel incision oscillating changes on the other hand the mu3 unit has an age of 1050 500 cal bp and appears as a thin extensive alluvial cover overlying previous units finally the mu4 unit comprises superposition of numerous flood depositional sequences centimetric in scale dated from 450 10 cal bp the established soil chronosequence supports the numerical chronology of the four units these accumulation periods mu1 mu2 mu3 mu4 are associated with dry phases and or high hydrological variability floods and droughts at a regional scale changes on the north atlantic atmospheric circulation mode over southern europe may provide the key to explain the nature of alluvial activity during holocene in bardenas reales

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

evaluation of a gully headcut retreat model using multitemporal aerial photographs and digital elevation models 1 a large fraction of soil erosion in temperate climate systems proceeds from gully headcut growth processes nevertheless headcut retreat is not well understood few erosion models include gully headcut growth processes and none of the existing headcut retreat models have been tested against long term retreat rate estimates in this work the headcut retreat resulting from plunge pool erosion in the channel hillslope integrated landscape development child model is calibrated and compared to long term evolution measurements of six gullies at the bardenas reales northeast spain the headcut retreat module of child was calibrated by adjusting the shape factor parameter to fit the observed retreat and volumetric soil loss of one gully during a 36 year period using reported and collected field data to parameterize the rest of the model to test the calibrated model estimates by child were compared to observations of headcut retreat from five other neighboring gullies the differences in volumetric soil loss rates between the simulations and observations were less than 0 05 m3 yr 1 on average with standard deviations smaller than 0 35 m3 yr 1 these results are the first evaluation of the headcut retreat module implemented in child with a field data set these results also show the usefulness of the model as a tool for simulating long term volumetric gully evolution due to plunge pool erosion

an assessment of chamber size effects in the calibration of in situ tests in sand calibration chamber tests are currently used to establish correlations between in situ testing data and the engineering properties of sands and play an important role in the understanding of in situ tests practical and economic considerations require that calibration chambers must be of limited size and so the chosen boundary conditions have an important effect on the results an assessment is made of the effects of chamber size on the measured values of the limit pressure obtained from the pressuremeter test and on the cone resistance values from the cone penetrometer test experimental and numerical data suggest that the effect of the proximity of the chamber boundaries is significant for dense and medium sand and is observed even for loose sand les essais en chambre de calibration sont a present employes pour etablir les correlations entre les donnees des essais in situ et les proprietes des sables pour le calcul des fondations et jouent un role important dans l interpretation de tels essais des

a lower pleistocene to holocene terrestrial record from the eskisehir graben central anatolia paleoclimatic and morphotectonic implications abstract as one of the rare terrestrial archive with continuous sedimentation back to almost 1 ma in anatolia the eskisehir graben was investigated in outcrops and cores by multi proxy analysis regarding chronology and paleoclimatology the present study comprises significant implications for both the impact of climate changes on fluvial systems in the timescales of the milankovitch band and the controversial age and rate of the crustal extension in western anatolia our findings indicate that loi950 and 18ocarb which are indicators for the amount of soil carbonate and paleo temperature respectively are collectively capable of distinguishing between glacial and interglacial periods in the predominantly floodplain deposits of the graben infill secondarily loi550 and 13ccarb values further help this discrimination via primary production and composition of vegetation cover respectively pollen data albeit highly discontinuous due to poor preservation under subaerial conditions point out a steppe like vegetation cover where the forest components expand particularly in the wet interglacial periods in the other hand the chronological frame provided by astronomical calibration of certain proxy records strongly suggest that the eskisehir fault zone initiated as a boundary fault of a half graben some 900 ka the rate of vertical movement on its southern branch since the last 70 ka is unexpectedly high 2 3 mm a a phenomenon that requires urgent risk assessment analysis in the vicinity of the eskisehir city

multi directional force displacement response of underground pipe in sand1 a methodology is presented to evaluate multi directional force displacement relationships for soil pipeline interaction analysis and design large scale tests of soil reaction to pipe lateral and u

environmental changes during the upper pleistocene holocene in mediterranean ne spain as recorded by the mineralogy and geochemistry of alluvial records abstract landscape evolution and environmental conditions from last glacial maximum lgm to late holocene times were reconstructed from the mineralogical and geochemical characteristics of the alluvial morphochronostratigraphy recorded in bardenas reales natural park ebro basin ne spain alluvial architecture includes a lgm holocene gravelly unit 22 9 ka bp a lower holocene silty muddy unit 9 7 ka bp and an upper holocene sandy unit 5 0 1 ka bp increases in illite smectite mixed layers kaolinite chlorite and modified chemical index of alteration cia as well as the decrease in illite fwhm e are indicators of minor increases in the chemical weathering of the alluvial sediments the results suggest that this area although under broad semiarid conditions underwent the following environmental evolution i an increasing trend in moisture availability in the lower holocene and ii a variable pattern in water disposal at the onset of the upper holocene followed by a decrease in humidity during the last millennium this reconstruction proves the usefulness of mineralogical and geochemical proxies as indicators of rapid environmental changes under mediterranean conditions

fragility of western mediterranean landscapes during holocene rapid climate changes abstract in this paper we explore the evidence for holocene rapid climate changes rccs in western mediterranean records examining similarities and differences in the timing and nature of impacts on different components of the natural environment vegetation fluvial and coastal sedimentation fire activity soil formation marine lacustrine and fluvial archives of the western mediterranean iberian peninsula and northwest africa provide evidence for both pervasive millennial scale climatic variability and abrupt decadal to centennial scale transitions we focus in particular on three rccs characterised by high latitude cooling glacier advances and north atlantic ice rafting events the mid holocene rcc interval 6 5 cal ka bp the late holocene rcc interval 3 5 2 5 cal ka bp and the historical rcc interval known as the little ice age lia 1300 1950 ad evidence from multiple records indicates wide ranging impacts of rccs in the western mediterranean region the three rcc intervals were characterised however by contrasting hydrological situations in the western mediterranean with prevailing dry conditions including marked aridification events during the rcc intervals 6 5 and 3 5 2 5 cal ka bp and prevailing or recurrent wet conditions during the lia we examine issues of proxy sensitivity in palaeoecological and geomorphological records and evaluate examples of contrasting geomorphological responses to regional climatic triggers between humid and semi arid sectors of the western mediterranean finally we consider the long term sensitivity of the region to rapid climate change the role of threshold changes and the extent to which this region represents a fragile landscape

holocene climate variability vegetation dynamics and fire regime in the central pyrenees the basa de la mora sequence ne spain abstract high resolution multiproxy data pollen sedimentology geochemistry chironomids and charcoal from the basa de la mora bsm lake sequence 42 32 n 0 19 e 1914 m a s l show marked climate variability in the central southern pyrenees throughout the holocene a robust age model based on 15 ams radiocarbon dates underpins the first precise reconstruction of rapid climate changes during the holocene from this area during the early holocene increased winter snowpack and high snowmelt during summer as a consequence of high seasonality led to higher lake levels a chironomid community dominated by non lacustrine taxa orthocladiinae related to higher inlet streams and a forested landscape with intense run off processes in the watershed from 9 8 to 8 1 cal ka bp climate instability is inferred from rapid and intense forest shifts and high fluctuation in surface run off shifts among conifers and mesophytes reveal at least four short lived dry events at 9 7 9 3 8 8 and 8 3 cal ka bp between 8 1 and 5 7 cal ka bp a stable climate with higher precipitation favoured highest lake levels and forest expansion with spread of mesophytes withdrawal of conifers and intensification of fires coinciding with the holocene climate optimum at 5 7 cal ka bp a major change leading to drier conditions contributed to a regional decline in mesophytes expansion of pines and junipers and a significant lake level drop despite drier conditions fire activity dropped as consequence of biomass reduction two arid intervals occurred between 2 9 and 2 4 cal ka bp and at 1 2 0 7 cal ka bp 800 1300 ad the latter coincides with the medieval climate anomaly and is one of the most arid phases of the holocene in bsm sequence anthropogenic disturbances were small until 700 ad when human pressure over landscape intensified with olea cultivation in the lowlands and significant deforestation in highlands colder and unfavourable weather conditions during the second part of the little ice age caused a temporary cease of high land management the most intense anthropogenic disturbances occurred during the second half of 19th century last decades are characterized by recovery of the vegetation cover as a result of land abandonment and lowered lake levels probably due to higher temperatures

crossing forest thresholds inertia and collapse in a holocene sequence from south central spain a holocene palaeoecological sequence from villaverde south central spain is presented the pollen stratigraphy is used to infer past vegetation changes within a catchment area that represents the boundary between semi arid plateau and mountain vegetation from c 9700 7530 cal yr bp pinus is dominant probably as a result of a combination of a relatively dry climate and natural fire disturbance from c 7530 5900 cal yr bp moderate invasion by quercus appears to be a migrational response following increased moisture and temperature but in part shaped by competitive adjustments from c 5900 5000 cal yr bp the pine forests are replaced by deciduous quercus forests with an important contribution from corylus betula fraxinus and alnus mediterranean type forests spread from c 5000 to 1920 cal yr bp coincident with expansions of artemisia juniperus and other xerophytes from c 1920 1160 cal yr bp pinus becomes dominant after a disturbance mediated invasion of the oak forests human impact u

comment on a quantitative framework for interpretation of basal ice facies formed by ice accretion over subglacial sediment by poul christoffersen et al 1 frost heave is the term given to the deformation at the earth s surface that is caused by the formation and growth of segregated ice lenses in permafrost and seasonally frozen ground efforts to understand and predict the characteristics of solidification in porous media led o neill and miller 1985 to produce the first comprehensive and tractable model for the thicknesses spacings and growth rates of sediment free ice lenses a central feature of the model involved an assessment of the balance of forces within a frozen fringe of partially ice saturated sediments beneath the lowest segregated ice interface when o neill and miller 1985 formulated their rigid ice model it was not yet clear how exactly to calculate the net force transmitted by sediment particles to the ice as a consequence the rigid ice model is only approximately correct in its treatment of the force balance that describes how lenses grow and an ad hoc formulation was needed to prescribe when new lenses would form always somewhere within the frozen fringe accurate predictions could nevertheless be obtained by tuning the model to reproduce the results of available empirical studies we now understand that the forces transmitted by the sediment particles to the ice are a consequence of interfacial premelting which is a basic aspect of phase behavior that ice shares in common with all other classes of solids see e g wettlaufer and worster

the little ice age in iberian mountains abstract the little ice age lia is known as one of the coldest stages of the holocene most records from the northern hemisphere show evidence of significantly colder conditions during the lia which in some cases had substantial socio economic consequences in this study we investigated the magnitude and timing of climate variability during the lia in the mountains of the iberian peninsula based on a wide range of natural records including from glacial periglacial and lacustrine peatland areas fluvial alluvial deposits speleothems and tree rings historical documents and early instrument data the onset of the lia commenced in approximately ce 1300 and cold conditions with alternating moisture regimes persisted until approximately ce 1850 the environmental responses ranged from rapid e g tree rings to delayed e g glaciers the colder climate of the lia was accompanied by severe droughts floods and cold heat waves that showed significant spatio temporal variation across the iberian mountains several phases within the lia have been detected including a 1300 1480 increasing cooling with moderate climate oscillations b 1480 1570 relatively warmer conditions c 1570 1620 gradual cooling d 1620 1715 coldest climate period of the lia particularly during the maunder minimum with temperatures approximately 2 c below those at present e 1715 1760 warmer temperatures and a low frequency of extreme events f 1760 1800 climate deterioration and more climate extremes i e cold and heat waves floods and droughts g 1800 1850 highly variable climate conditions alternating with stability 1800 1815 extreme events 1815 1835 and a slight trend of warming associated with intense hydrometeorological events 1835 1850 h since 1850 a gradual staggered increase in temperature of approximately 1 c post lia warming has led to substantial changes in geo ecological dynamics mainly through shrinking of the spatial domain affected by cold climate processes

flood frequencies reveal holocene rapid climate changes lower moulouya river northeastern morocco current high resolution palaeoenvironmental records reveal short term holocene cool ings one of these major holocene rapid climate changes occurred between 3 2 and 2 7 cal ka bp the sensitivity of river systems vis a vis slight and short term holocene climatic variations is a subject of controversy in the scientific community in this paper we present a 4 0 to 1 4 cal ka bp palaeoflood record from the lower moulouya river northeastern morocco to demonstrate the high sensitivity of semiarid rivers in the southwestern mediterranean towards holocene environmental changes the lower moulouya flood deposits are characterised by thick well stratified predominantly clayey to silty overbank fine sediments these cohesive sediments show evidence of excellent preservation conditions against fluvial erosion and contain a continuous record of mid to late holocene flood sequences the moulouya palaeoflood record can be interpreted in the context of regional and global high resolution proxy data revealing a strong coupling with holocene rapid climate changes the centennial scale moulouya palaeohydrological history will be discussed with palaeoenvironmental data from the same record palaeomagnetics sedimentary charcoal record anthracological analyses snail analyses to generate new ideas about the mid to late holocene hydrological cycle in the southwestern mediterranean the deduced features of pronounced lower moulouya flooding and the decreased fire recurrence during holocene cooling remain somewhat inconsistent with the interpret ation of other palaeohydrological and paleaoecological records from the southwestern mediterranean however enhanced lower moulouya flood frequencies between 3 2 and 2 7 cal ka bp agree with increased floodplain aggradation in other major river systems of mediterranean north africa copyright 2009 john wiley sons ltd

sediment budget quantification of a sub alpine river catchment since the end of the last glaciation changes in sediment budget and quantification of sediment fluxes of a small 5 3 km2 mediterranean sub alpine river catchment charanc catchment southern french alps 44 30 44n 5 51 55e are estimated for the last 20 000 years using a gis based approach and 3d palaeotopographic reconstructions following field surveys a high resolution morphometric map was established ten 14c ages of sub fossil trees and charcoal beds were compiled all datasets were integrated into a geographic information system we computed three palaeosurfaces by masking the digital elevation model of the current topography and calculated the sediment budget of the catchment estimations of specific hillslope erosion sedimentation and export rates highlight the evolution of the catchment and its sensitivity to variations in the ratio of sediment load to stream discharge between 20 000 and 14 500 cal bp sediment that was eroded 37 million m3 within the charanc catchment was entirely exported a change to a sedimentation regime commenced at around 14 500 cal bp between 9000 cal bp and 7000 cal bp footslopes were buried by fan shaped deposits at a rate of 6700 m3 yr since 7000 cal bp the overall morphogenetic regime has been one of vertical incision 73 of the material eroded over the last 14 500 years 14 million m3 was stored in fan shaped deposits at the present time 46 of this volume 6 million m3 is still stored in the catchment 8 million m3 of sediments have thus been exported out of the charanc catchment since 14 500 cal bp annual specific erosion rates on marly slopes are estimated at 1 98 to 111 t ha yr for the period 20 000 14 500 cal bp which is comparable to present rates measured on denudated marls in the southern french alps under a probably climate driven erosion regime and 2 17 to 20 t ha yr since 14 500 cal bp a reduction in erosion rate that may have been favoured by a more extensively wooded landscape

late quaternary fluvial dynamics of the jarama river in central spain the jarama river and its catchment provide a valuable natural archive to study and reconstruct past environmental conditions in central spain this region is highly prone to changes in the hydrological cycle under predicted climate warming in particular with respect to aridity periods rainfall variability and the occurrence of extreme flood events this paper presents 15 exposures covering a time span of the last 44 ka which were documented in the field and of which seven exposures were soil chemical analyzed regarding soil texture organic matter as well as carbonate and iron content ages are based on radiocarbon dating on 32 samples latest holocene sediments were found within the channel belt where permanent remobilization of sediments takes place due to the migration of the meandering river course in more distal floodplain positions sediment sequences show a complex fluvial architecture referring to periods of varying character and intensity of alluviation as well as periods of geomorphic stability indicated by soil formation furthermore sedimentation patterns vary along different river sections aggradations of coarse gravels took place between 40 and 18 ka cal bp over the entire valley floor alluviation of fine material was documented between 17 and 16 at 7 5 between 5 1 and 3 3 at 2 8 between 2 1 and 1 5 at 1 0 and around 0 4 ka cal bp until recent times astonishingly in late holocene times between 4 2 and 3 1 ka cal bp aggradations of coarse gravels even in distal floodplain areas overlap with sedimentation of fine material in adjacent river sections pointing to a complex constellation of parameters involved periods of soil formation were detected around 43 at 31 between 16 and 12 6 after 7 5 until 5 1 between 2 8 and 2 1 and at times after 1 5 ka cal bp phases of geomorphic stagnation were found at 38 ka cal bp and for a duration of 200 years at 3 0 ka cal bp and refer to absent geomorphic or pedogenic processes all these patterns are an expression of the interaction between climatic variations tectonic impulses and human influences a comparison with other terrestrial archives enabled us to reconstruct late pleistocene and holocene palaeoenvironmental conditions on a regional scale and furthermore to link specific stages of floodplain development to prevalent influencing variables thus with emphasis on the fluvial system response a model of a cause and effect relationship is presented that concentrates on rapid climate changes long lasting climatic deteriorations and the role of human interventions