surface and bed topography of trapridge glacier yukon territory canada digital elevation models and derived hydraulic geometry measurements of ice thickness and surface elevation are prerequisite to many glaci ological investigations a variety of techniques has been develo ped for inter pret ation of these data including means of constructing regularly gridded digital eleva tion models dem s for use in numcrical studies here we present a simple yet stati sti cally sound method for processing ice pe netr ating radar data and descr ibe a tech nique for interpol ating these data onto a regular grid dems generatcd fort rapridge glacier yukon territory canada are used to derive geometric quantities lhal give pre liminary insights into the underlying basin scale hydrol ogical syste m this simple geo metric analysis suggests that at low water press ures a dendrilic drainage netw ork exists that evolves into a uniaxial morphology as water pressure approaches notation these pre dictions are compared to hydraulic connection probabilities based on bore hole drilling

sediment resuspension by surface wave action an examination of possible mechanisms abstract detailed spectral and coherence analyses of both nephelometer data and near bottom acoustic concentration profiles support the conclusion of lesht et al 1980 that surfacewave activity is the most important input to the sediment resuspension process the sand sized fraction is suspended primarily by bursts of turbulence which are related to peak values of the envelope of surface waves two mechanisms for the resuspension of fine sediment are considered when the bed is bimodal sand and silt pore water motion induced by wave pressure fluctuations may carry fine particles into the boundary layer where they are suspended motion of the sand matrix as bedload will also expose fine particles to the flow so that they become suspended the combination of these two mechanisms accounts for the observed quasi linear relation between wave orbital velocity and suspended sediment concentration for the long island data the second mechanism is also consistent with observations of near bottom fluid velocity and suspended sediment concentration in norton sound alaska

base level buffers and buttresses a model for upstream versus downstream control on fluvial geometry and architecture within sequences abstract the effects of downstream base level control on fluvial architecture and geometry are well explored in several broadly similar sequence stratigraphic models cretaceous dakota group strata u s western interior have characteristics reflecting combined downstream and upstream base level controls that these models cannot address particularly three layers of amalgamated channel belt sandstone within this group thicken and are continuous for distances 300 km along dip that stretch the reasonable lengths for which these models are intended to apply as well architecture in up dip reaches records repeated valley scale cut and fill cycles this contrasts with equivalent strata down dip which record channel scale lateral migration with no such valley scale cycles apparent we here introduce the concept of buffers and buttresses to address these observations we assume that river longitudinal profiles are each anchored down dip to some physical barrier e g the sea strand etc that we refer to as a buttress buttress shift is considered the primary downstream control on base level profiles extrapolated up dip from the buttress over any modeled duration of buttress shift can range widely because of high frequency variability in upstream base level controls e g discharge etc all these potential profiles however are bounded above by the profile of highest possible aggradation and below by the profile of maximum possible incision these upper and lower profiles are buffers and they envelop the available fluvial preservation space thickness of the buffer zone is determined by variability in upstream controls and should increase up dip to the limit of downstream profile dominance dakota valley scale surfaces record repeated cut and fill cycles driven by up dip controls and are confined between thick stable buffers equivalent strata down dip record lateral reworking within a thinner channel scale buffer zone that was positioned by downstream controls regression exposed slopes similar to the buffer zone thus buffers were stable for long distances and durations this prompted dip extensive lateral reworking of strata into upstream valley scale and downstream channel scale sheets buffers and buttresses provide a broadly applicable model for fluvial preservation that captures upstream vs downstream base level controls on geometry and architecture the model lends general insights into dip oriented variations in fluvial architecture production of sheet vs lens geometry total preservation volumes for fluvial systems and variations in these factors related to contrasting climatic conditions and basin physiography the model can be amended to existing sequence stratigraphic approaches in order to capture dip oriented variations in sequence architecture

on the sea level forcing of the mid atlantic bight the mid atlantic bight circulation is discussed with particular comment directed toward the role of the parabathic pressure gradient a distinction is made between external and local sea level forcing external forcing consists of an oceanic boundary condition on the sea level gradient the shelf response to this is geostrophic the diabathic component drives the parabathic flow and the parabathic component drives diabathic flow the latter together with the bottom stress generated by the former and the physical dimensions of the shelf determine the degree of convergence or divergence within the shelf volume which in turn determines the sea level dependence required to satisfy continuity over the shelf local forcing due to the wind stress the internal field of mass and the total bottom stress in conjunction with local bathymetry determines the extent of local convergence or divergence and as a consequence generates additional sea level distortion conceptually local and external forcing can be considered as independent although they are in fact coupled through bottom stress and internal field of mass adjustment

high resolution magnetostratigraphy of the upper nacimiento formation san juan basin new mexico usa implications for basin evolution and mammalian turnover lower paleocene deposits in the san juan basin document one of the best records of mammalian change and turnover following the cretaceous paleogene mass extinction and is the type area for the puercan pu and torrejonian to north america land mammal age nalma one of the largest mammalian turnover events in the early paleocene occurs between the torrejonian 2 to2 and torrejonian 3 to3 nalma interval zones the nacimiento formation contains the only deposits in north america where the to2 to3 mammalian turnover can be constrained however the precise age and duration of the turnover is poorly understood due to the lack of a precise chronostratigraphic framework we analyzed paleomagnetic samples produced a 40ar 39ar detrital sanidine age and developed a detailed lithostratigraphy for four sections of the upper nacimiento formation in the san juan basin new mexico kutz canyon escavada wash torreon west and east to constrain the age and duration of the deposits and the to2 to3 turnover the polarity stratigraphy for the four sections can be correlated to chrons c27r c26r of the geomagnetic polarity time scale gpts using the local polarity stratigraphy for each section we calculated a mean sediment accumulation rate and developed a precise age model which allows us to determine the age of important late torrejonian mammalian localities using the assigned ages we estimate the to2 to3 turnover was relatively rapid and occurred over 120 kyr 60 50 kyr between 62 59 and 62 47 ma this rapid duration of mammalian turnover suggests that it was driven by external forcing factors such as environmental change driven by the progradation of the distributive fluvial system across the basin and or changes in regional or global climate additionally comparisons of the mean sediment accumulation rates among the sections that span from the basin margin to the basin center indicate that sediment accumulation rates equalized across the basin from the end of c27r through the start of c26r suggesting an accommodation minimum in the basin associated with the progradation of a distributive fluvial system into the basin this accommodation minimum also likely led to the long hiatus of deposition between the paleocene nacimiento formation and the overlying eocene san jose formation

a linkage among pangean tectonism cyclic alluviation climate change and biologic turnover in the late triassic the record from the chinle formation southwestern united states abstract high precision geochronology provides unprecedented insights into the depositional history of the upper triassic chinle formation of the colorado plateau as well as its paleoenvironmental and paleobiological records the chinle succession exposed in the petrified forest national park pefo and vicinity arizona includes two large scale alluvial composite sequences although each composite sequence fines upward the upper composite sequence is more dominated by coarser grained deposits petrographic analysis of sandstone lithic content indicates an upward decrease in the proportion of volcanic rock fragments in each composite sequence paleocurrent indicators in the lower composite sequence suggest a variable paleoflow direction whereas northward paleoflow dominated the upper composite sequence the change in paleoflow appears to coincide with a reorganization of alluvial depositional processes and associated source terranes and precedes a rapid acceleration in basin subsidence climate proxy records from paleosol geochemistry indicate a gradual shift from humid to dry conditions across the transition between the lower and upper composite sequences and the adamanian revueltian biotic turnover composite sequence depositional reorganization climatic shift and biologic turnover in turn appear to coincide with episodes of magmatism recorded in triassic granitoid plutons presently exposed in southern california taken collectively these observations suggest that the late triassic depositional climatic and ecologic history at pefo may be related to emergence of the incipient cordilleran magmatic arc along the convergent western margin of pangea a new u pb date for the lower part of the chinle formation suggests that most or all of the formation was deposited in the norian stage

interpretation of basal ice conditions from radio echo soundings in the eastern heimefrontfjella and the southern vestfjella mountain ranges east antarctica interpretation of basal ice conditions from radio echo soundings in the eastern heimefrontfjella and the southern vestfjella mountain ranges east antarctica

ice bed interface and englacial properties of svalbard ice masses deduced from airborne radio echo sounding data un ensemble de donnees de sondages par echo radio ont ete collectees sur 44 masses de glace au spitsberg et les calottes glaciaires de nordaustlandet svalbard ces donnees ont permis de produire les coefficients de reflexion en puissance pour l interface glace manteau sur une grande etendue de svalbard nord

dynamics of a small surge type glacier using one dimensional geophysical inversion we investigate the dynamics of a small surge type valley glacier as part of a study to characterize glacier response to climate in the donjek range southwest yukon canada pole displacements were measured using kinematic gps techniques during three consecutive summer field seasons measured surface velocities range from 10m a 1 over the lower 1500 m of the 5 km long glacier to a maximum of 25 35 m a 1 over the upper 3500 m basal velocities along an approximate flowline are reconstructed from the measured surface velocities using inverse methods control tests are used to validate the inversion scheme and sensitivity tests are performed to evaluate the influence of the flow law coefficient shape factor and longitudinal averaging length inversion of the real data shows that basal motion accounts for 50 100 of the total surface motion along the flowline based on these results and several other lines of evidence we suggest this glacier may be undergoing a slow surge

melting at the base of the greenland ice sheet explained by iceland hotspot history basal melting is widespread in the north central greenland ice sheet geophysical data and numerical modelling suggest a geothermal anomaly in this region resulting from the earlier passage of greenland over the iceland mantle plume

equation for compaction of paleosols due to burial existing empirically derived compaction curves for marine sediments fail to estimate the compaction of paleosols flood plain sediments and peats as indicated by deformation of clastic dikes dinosaur footprints and sandstone paleochannels yet compaction estimates are vital to reconstructing paleoclimate and geochemical profiles of paleosols to modeling sediment accumulation rates of nonmarine rocks and to tectonic flexural modeling of molasse facies this paper presents a compaction equation and physically derived constants that make geologically realistic estimates of compaction of paleosols and other nonmarine sediments a protocol for the application of the equation is suggested that would allow the following equation to solve for burial compaction c as a fraction of original thickness given depth of burial d in km as c s i f e d k 1 this equation can be applied to nonmarine sedimentary rocks or paleosols given appropriate empirical data on the physical constants in the equation such as initial solidity s i initial porosity f and the corresponding curve fitting constant k data on physical constants useful for this equation are compiled here for a range of paleosol and nonmarine sediment types

eocene hydromorphic paleosols significance for interpreting ancient floodplain processes abstract pervasive mottling iron oxide nodules and slickensides indicate that alluvial paleosols of the lower eocene willwood formation in the elk creek area of the bighorn basin wyoming were hydromorphic two basic groups of hydromorphic paleosols are present cumulative which show evidence for concurrent deposition and pedogenesis and simple noncumulative which show evidence for a single episode of deposition and pedogenesis lithologic packages consisting of vertically stacked simple paleosols and crevasse splay sandstones alternate with cumulative paleosols the simple paleosols are weakly developed indicating rapid deposition with relatively little time for pedogenesis cumulative paleosols show greater pedogenic development indicating significantly longer periods of pedogenic m dification and slower more episodic sediment accumulation differences between the simple and cumulative paleosols reflect differences in the deposition of their parent materials the packages of simple paleosols are similar to avulsion belt deposits described from the saskatchewan river and suggest that avulsion was significant in floodplain construction the upper parts of cumulative paleosols were formed on true overbank deposits which accumulated gradually after avulsion and establishment of a new channel the lower parts of many cumulative paleosols resulted from a prior episode of avulsion deposition and simple soil formation because hydromorphy is associated with texture these different depositional processes influenced lateral variations in hydromorphy of the cumulative paleosols paleosols in the elk creek area provide a simple means of identifying avulsions sediment accumulation rates suggest that avulsions occurred with a regular period of about 20 000 years and may have been induced by climatic cycles

facies analysis of a probable large fluvial fan depositional system the upper triassic chinle formation at petrified forest national park arizona u s a abstract the upper triassic blue mesa member and the overlying sonsela member of the chinle formation consist of paleosol bearing alluvial strata whose characteristics vary markedly strata exposed within a 4 km2 study area at petrified forest national park were evaluated using sedimentologic stratigraphic paleopedologic and petrographic criteria to formulate potential depositional models that may account for varying alluvial deposition the study succession records a progressive up section increase in grain size increase in channel depth and width increase in lateral and vertical connectivity of channel deposits decrease in overbank preservation and crevasse splay and or sheetflood deposition and increase in overbank drainage mean annual precipitation from the calmag paleosol weathering proxy suggests precipitation averages approximately 1300 mm yr 1 3 m yr throughout the succession despite changing paleosol drainage these features are consistent with deposition in a progradational fluvial system such as a large fan or splay complex sediment accumulation rates in the study interval suggest decreased subsidence in the upper blue mesa member reduced rates of accommodation gain may have promoted progradation of the fluvial system an up section decrease in sandstone mineralogical maturity may be related to increasing sediment bypass in proximal fan positions or increased rates of erosion and sedimentation increasingly better drained paleosols are attributed to deposition in more upland positions during fan or avulsion complex progradation rather than changing climate

flow switching and water piracy between rutford ice stream and carlson inlet west antarctica rutford ice stream and carlson inlet are neighbouring glaciers in west antarctica rutford ice stream flows at speeds greater than 350m a 1 whereas carlson inlet which has some similar dimensions and supports a similar driving stress flows 10 50 times slower we discuss a range of observations concerning carlson inlet and conclude that there is good indirect evidence that it is a relict ice stream which ceased streaming more than 240 years bp but sufficiently recently that its surface morphology basal water content and basal morphology still retain characteristics produced by streaming an analysis of expected subglacial drainage pathways indicates that carlson inlet is not streaming because it is currently starved of subglacial water which is currently directed beneath rutford ice stream this current state of water piracy by rutford ice stream is however sensitive to minor thickness changes on the ice streams a similar to 120 m 4 thickening of rutford ice stream would divert almost all the subglacial water in the system towards carlson inlet and could reactivate its flow the result highlights the importance of subglacial drainage in controlling ice stream evolution and the requirement for ice sheet models to couple ice flow with subglacial drainage

climate and landscape reconstruction of the arroyo chijuillita member of the nacimiento formation san juan basin new mexico providing environmental context to early paleocene mammal evolution abstract the sedimentologic stratigraphic and paleopedologic attributes of a laterally continuous outcrop exposure of the basal portion of the lower paleocene arroyo chijuillita member of the nacimiento formation located in the bisti de na zin wilderness area was examined to provide paleoenvironmental context for the puercan north american land mammal age nalma terrestrial ecosystems of the san juan basin new mexico the studied outcrop spans the middle and late puercan pu2 pu3 nalma and thus is an ideal location to assess the potential causes of faunal turnover between pu2 and pu3 the stratal succession consists of fluvial channel and laterally continuous sandstone and associated fine grained floodplain deposits including paleosols that document variability in drainage and maturity quantitative and qualitative reconstructions of paleoclimate from paleosols supplemented by analyses of fossil floras indicate no change in climate through the studied interval further there is no evidence that regional tectonics relate to changes in depositional environments given the lack of evidence for climate change or regional tectonics and the characteristics of the fluvial facies and the paleosols across the study locality we interpret the spatial and temporal variability in paleopedologic and sedimentologic characteristics to be the result of autocyclic channel avulsion and migration additionally the stable climatic conditions and lack of tectonic influence between the pu2 and pu3 biozones suggest that mammalian turnover is unlikely to have been caused by extrinsic environmental changes i e climate or tectonics and is instead probably the result of rapid evolution following the k pg boundary and or competition from the migration of new mammalian species into the basin

basin scale changes in floodplain paleosols implications for interpreting alluvial architecture abstract floodplain paleosols in time equivalent strata of the willwood for mation differ in terms of paleodrainage and degree of pedogenic development ancient soils were more poorly drained and more strongly developed in one area compared to a second area about 45 km away this difference in drainage is attributed to parent material the more poorly drained paleosols formed in an area with less permeable clay rich floodplain deposits in the stratigraphic interval that accumulated more slowly paleosols are more strongly developed less numerous and thicker than in the more rapidly accumulating stratigraphic interval these differences are attributed not only to different sediment accumulation rates which are commonly considered to control the degree of ped ogenic development but also to differences in avulsion frequency a simple model is offered to show how paleosols change with varying basin subsidence rates and the relationship between avulsion frequency and accumulation rate when avulsion frequency increases more rapidly than sediment accumulation rate an increase in subsidence rate causes strongly developed paleosols to be overlain by a stratigraphic interval with paleosols that are less well developed thinner and more densely spaced when avulsion frequency is not related to accumulation rate as early models of alluvial architecture assumed an increase in subsidence rate produces a stratigraphic section in which strongly developed paleosols are overlain by paleosols that are less well developed thicker and more widely spaced study of the thickness and degree of development of floodplain paleosols can be used together with more traditional studies of alluvial architecture to provide a clearer understanding of the factors that influenced the stratigraphic architecture in a particular alluvial basin

the distinction between ground water gley and surface water gley phenomena in tertiary paleosols of the ebro basin ne spain abstract in studies of paleosols the distinction iron segregation due to either surface water or ground water fluctuatins is hardly ever made recognition of subsequent hydromorphic phases is even more rare nevertheless such distinctions can be made and are very useful in determining the paleoenvironment in this study we demonstrate that subsequent stages of hydromorphism and their sequence can be recognized in paleogene paleosols of the ebro basin it appears that in these carbonate rich hydromorphic oils goethite iron segregations are due to ground water influence while hematitic segregations are due to surface water the preservation of original mineralogy in this case is due to absence of late diagenetic transformations the results contradict the thesis that red colours in such paleosols would be the result of the late diagenesis in the studied samples mottledcolour patterns frequently indicate fairly advanced soil formation although weathering of primary minerals is almost absent detailed study of colour patterns gives much additional information on the post depositional environment

regional paleoclimatic and stratigraphic implications of paleosols and fluvial overbank architecture in the morrison formation upper jurassic western interior usa abstract paleosols in the morrison formation upper jurassic from the western interior and colorado plateau regions occur in fluvial overbank and marginal lacustrine depositional facies associated with aggradational settings and at sequence bounding unconformities that mark divisions between major aggradational and degradational successions pedogenic features within these horizons preserve important contextual information about the local and regional paleoclimate and paleoenvironment in which the soils formed floodplain and lake margin paleosols show evidence that most of the morrison basin was characterized by a semi arid to tropical wet dry paleoclimate with fluctuating groundwater conditions a low precipitation to evaporation ratio and weak to moderately seasonal precipitation paleosol ichnofauna show evidence of a diverse and opportunistic flora and fauna that exploited changing conditions and existing nutrient and moisture regimes changes in paleosol type and degree of development over the basin indicate the overall regional paleoclimate was drier in the western and southern portions of the basin vertical trends indicate paleoclimatic conditions over the basin became steadily more humid through time laterally continuous well developed deeply weathered paleosols formed during times of little or no deposition and mark regional unconformities the paleosols at these sequence bounding unconformities serve as useful regional stratigraphic markers to trace genetic packages across the morrison depositional basin and to determine regional accommodation trends

depositional and diagenetic controls on reservoir attributes within a fluvial outcrop analog upper triassic sonsela member of the chinle formation petrified forest national park arizona the upper triassic sonsela member of the chinle formation in the petrified forest national park was evaluated using sedimentologic stratigraphic paleopedologic and petrographic criteria along a continuous 0 5 km 0 3 mi outcrop the study interval consists of interbedded sandstones and mudstones and is composed of a two tiered hierarchy of cyclic alluvial deposits with bounding paleosols the succession is composed of 15 fluvial aggradational cycles facs that comprise two fac sets fac sets the fac sets are composed of architectural elements suggestive of a mixed load fluvial system that is alternately dominated by bed load deposits and suspended load deposits a thinning and fining stacking pattern within fac sets is accompanied by an upward increase in pedogenic modification suggesting that cycles systematically stack in response to a longer period decrease in the rate of accommodation gain sandstones are classified as litharenites feldspathic litharenites and lithic subarkoses and occur within recycled orogen dissected arc and transitional arc provenance fields sandstone compositional maturity increases upward through the fac sets point counts of intergranular volume as a proxy for primary porosity within channel facies and subsequent transform to syndepositional permeability provide a two dimensional depiction of the lateral variability in reservoir quality paleosols are weakly to moderately developed and have little stratigraphic variation these characteristics suggest that climatic fluctuations are not responsible for evolving fluvial depositional style or associated reservoir quality trends in sandstone compositional maturity suggest that fluvial stacking patterns and depositional style are related to pulses of tectonism sandstones are volcanogenic rich and have undergone an almost complete diagenetic loss of porosity caused by the precipitation of authigenic clays paragenetic reconstruction suggests that porosity loss occurred contemporaneous with the silicification of fossil logs in channel deposits log compaction at the time of silicification averaged 9 1 suggesting that log silicification and porosity loss occurred soon after deposition

mapping subglacial surfaces of temperate valley glaciers by two pass migration of a radio echo sounding survey high resolution maps of the glacier bed are developed through a pseudo three dimensional migration of dense array of radio echo sounding profiles resolution of three dimensional maps of subglacial surfaces is determined by the radio echo sounding wavelength data spacing in the field and migration based on synthetic radio echo sounding profile experiments the maximum resolution of the final map cannot exceed one half wavelength a methodology of field and processing techniques is outlined to develop a maximum resolution map of the glacier bed the field and processing techniques are used to develop a map of the glacier bed below part of worthington glacier a temperate valley glacier in south central alaska the field techniques and the processing steps used on the glacier result in a map of 20 m 20 m resolution

lower eocene alluvial paleosols pedogenic development stratigraphic relationships and paleosol landscape associations abstract two kinds of cumulative floodplain paleosols red and grey paleosols formed on overbank deposits of the willwood formation in the sand coulee area of the bighorn basin wyoming although both kinds experienced down profile iron movement due to seasonal saturation of a clay rich a horizon the red paleosols were better drained and their b horizons were rubified various redoximorphic features indicate that the grey paleosols were poorly drained the red paleosols show progressive increases in the degree of profile development away from an associated channel sandstone a paleosol landscape relationship termed pedofacies by bown and kraus 1987 although the grey paleosols show relatively systematic changes in hydromorphy consistent pedofacies changes were not recognized furthermore no lateral relationship between the red and grey paleosols was observed these features suggest that because of the retarding effects of poor drainage on soil weathering poorly drained soils are not amenable to pedofacies modelling and that the landscape associations of well drained and poorly drained soils may be difficult to document without unusually extensive exposures results of this study also show that the pedofacies model is limited by sediment accumulation rates and the kind of fine grained facies on which paleosols developed although readily observable in sand coulee pedofacies are difficult to recognize in the elk creek area where accumulation rates were approximately half as rapid as in sand coulee the attainment of steady state conditions is believed to have obscured pedofacies in the elk creek area finally pedofacies are only developed on true overbank deposits which in the willwood formation and probably many other ancient alluvial sequences make up only a fraction of the fine grained deposits only immature soils formed on the remainder of the fine grained facies because they were deposited very rapidly as a result of channel avulsion

regional and global volumes of glaciers derived from statistical upscaling of glacier inventory data 1 very few global scale ice volume estimates are available for mountain glaciers and ice caps although such estimates are crucial for any attempts to project their contribution to sea level rise in the future we present a statistical method for deriving regional and global ice volumes from regional glacier area distributions and volume area scaling using glacier area data from 123 000 glaciers from a recently extended world glacier inventory we compute glacier volumes and their sea level equivalent sle for 19 glacierized regions containing all mountain glaciers and ice caps on earth on the basis of total glacierized area of 741 103 68 103 km2 we estimate a total ice volume of 241 103 29 103 km3 corresponding to 0 60 0 07 m sle of which 32 is due to glaciers in greenland and antarctica apart from the ice sheets however our estimate is sensitive to assumptions on volume area scaling coefficients and glacier area distributions in the regions that are poorly inventoried i e antarctica north america greenland and patagonia this emphasizes the need for more volume observations especially of large glaciers and a more complete world glacier inventory in order to reduce uncertainties and to arrive at firmer volume estimates for all mountain glaciers and ice caps

changes in geometry and subglacial drainage derived from digital elevation models unteraargletscher switzerland 1927 97 digital elevation models of the bed and surface of unteraargletscher switzerland are used to reconstruct the theoretical pattern of basal water drainage for the years 1927 1947 1961 and 1997 during which period the glacier was thinning and receding the theoretical drainage pattern for 1997 compares well in a broad sense with the locations of active moulins and the hydraulic connection status of boreholes drilled to the glacier bed changes in the basal water flow pattern over the period 1927 97 that are revealed by the theoretical reconstructions of the subglacial drainage system structure are likely to have resulted from changes in glacier geometry concurrent with the retreat and thinning of the glacier the height of medial moraines increased probably due to the insulating effect of the debris cover reducing the melt of the underlying ice this increase of moraine heights has led to the formation of hydraulic barriers at the glacier bed such that water flow has become channelized beneath the ice along drainage axes that parallel the course of the medial moraines on the glacier surface

deformation warming and softening of greenland s ice by refreezing meltwater when basal meltwater refreezes the resulting warm ice can influence the flow dynamics of the ice sheet above an analysis of airborne gravity and radar data identifies extensive basal ice units across the northern greenland ice sheet that coincide with areas of deformed ice and fast ice flow

structure morphology and water flux of a subglacial drainage system midtdalsbreen norway digital elevation models of the surface and bed of midtdalsbreen norway are used to calculate subglacial hydraulic potential and infer drainage system structure for a series of subglacial water pressure assumptions ranging from atmospheric to ice overburden a distributed degree day model is used to calculate the spatial distribution of melt on the glacier surface throughout a typical summer which is accumulated along the various drainage system structures to calculate water fluxes beneath the glacier and exiting the portals for the different water pressure assumptions in addition 78 dye tracing tests were performed from 33 injection sites and numerous measurements of water discharge were made on the main proglacial streams over several summer melt seasons comparison of the calculated drainage system structures and water fluxes with dye tracing results and measured proglacial stream discharges suggests that the temporally and spatially averaged steady state water pressures beneath the glacier are 70 of ice overburden analysis of the dye return curves together with the calculated subglacial water fluxes shows that the main drainage network on the eastern half of the glacier consists of a hydraulically efficient system of broad low channels average width height ratio 75 the smaller drainage network on the west consists of a hydraulically inefficient distributed system dominated by channels that are exceptionally broad and very low average width height ratio 350 the even smaller central drainage network also consists of a hydraulically inefficient distributed system dominated by channels that are very broad and exceptionally low average width height ratio 450 the channels beneath the western and central glacier must be so broad and low that they can essentially be thought of as a linked cavity system

shoreface morphodynamics on wave dominated coasts abstract an open ocean shoreface typical of long wave dominated sandy coasts has been examined through a combination of extensive field measurements of wave and current patterns with computations of marine bedload transport and sedimentation sand transport on the upper shoreface is dominantly controlled by waves with only secondary transport by currents sand on the middle and lower shoreface as well as the inner continental shelf is entrained by storm waves and transported by a complex pattern of bottom boundary layer currents storm events have been studied and modeled for the shoreface off tiana beach long island the dominant effect of coastal frontal storms is to cause significant shore parallel bedload transport with important shore normal secondary components these storms tend to result in net offshore transport of sand removed from the beach and surf zone systems the bedload transport during a storm is convergent on the shoreface leading to accretion most accretion occurs on the upper shoreface with lesser deposits covering the middle and lower shoreface as well as the inner continental shelf longer term equilibrium can be maintained by slow return of sand up the shoreface during non storm conditions annual and geologic time scale budgets of shoreface sand transport and sedimentation yield equilibrium net accretion or net deposition the annual balance results from an integration of the event scale bedload transport patterns and morphologic responses these processes and responses have feedback mechanisms which stabilize the system over longer but not geologic time scales geologic time scale balances are controlled by relative sea level changes and relative availability of sediment supply with the event scale shoreface and transporting processes providing the mechanism to produce the changes in long term morphology and sedimentation patterns in the area of study the long term pattern is one of net shoreface erosion and the permanent loss of sand to the shelf floor

maintenance of the shoreface by wave orbital currents and mean flow observations from the long island coast waves and currents were observed for a total of 36 days in august 1976 and 1977 calculations of wave transport of sediment using a bagnold equation for transport and second order stokes theory show that wave orbital current asymmetry results in landward sediment transport in 10 m or less water depth but does not significantly effect transport at greater depths calculations of sand transport using the madsen grant formulation show that during a 36 day observation period sediment in less than 10 m of water generally moved landward into the breaker and then along coast with the wave driven littoral flow the calculations show that below 10 m the generally upwelling coast parallel mean flow did not move sediment however during two days of a mild summer northeaster storm a downwelling coastal jet developed with 60 cm sec sup 1 maximum current the calculations show that if this flow had been combined with the intense wave regime of the succeeding several days sediment would have been entrained across the lower as well as the upper shoreface movement would have been offshore and alongshore such storm transport is believed to be typical of the more intense winter storms and to be responsible for the erosionalmore shoreface retreat that has caused up to a kilometer of shoreline retreat on the long island coast in the last century less

controls on the basal water pressure in subglacial channels near the margin of the greenland ice sheet assuming a channelized drainage system in steady state we investigate the influence of enhanced surface melting on the water pressure in subglacial channels compared to that of changes in conduit geometry ice rheology and catchment variations the analysis is carried out for a specific part of the western greenland ice sheet margin between 668 n and 66830 0 n using new high resolution digital elevation models of the subglacial topography and the ice sheet surface based on an airborne ice penetrating radar survey in 2003 and satellite repeat track interferometric synthetic aperture radar analysis of european remote sensing satellite 1 and 2 ers 1 2 imagery respectively the water pressure is calculated up glacier along a likely subglacial channel at distances of 1 5 and 9 km from the outlet at the ice margin using a modified version of rothlisberger s equation our results show that for the margin of the western greenland ice sheet the water pressure in subglacial channels is not sensitive to realistic variations in catchment size and mean surface water input compared to small changes in conduit geometry and ice rheology

a chronology for the dome c deep ice core site through radio echo layer correlation with the vostok ice core antarctica ice at the new dome c drill site is correlated directly with the vostok ice core record using internal radio echo layering in the antarctic ice sheet layering observed on 60 mhz radar records at ice depths greater than 1000 m is a result of electro magnetic wave reflections from acidic ice layers formed it is assumed by volcanic eruption derived aerosols these acidic layers represent isochronous surfaces within the ice sheet we are able to trace five prominent layers for over 500 km across the antarctic ice sheet between vostok and the new ice core site at dome c this correlates the stratigraphy and depth age relationship between the two sites the thickness of ice deposited over the last glacial cycle 120 000 years at dome c is 300 m greater than at vostok and at comparable depths the ice at dome c is between about 10 000 and 25 000 years younger than at vostok

paleogeographic and paleotectonic setting of laramide sedimentary basins in the central rocky mountain region in the rocky mountain region between central montana and central new mexico sedimentologically isolated nonmarine basins were produced by basement deformation during the laramide orogeny within the area formerly occupied by a broad late cretaceous foreland basin in which laterally continuous marine facies had accumulated previously laramide structures of varying trend and scale reflect heterogeneity of crustal strain caused by shear between the continental lithosphere and an underlying subhorizontal slab of subducted oceanic lithosphere laramide basins include perimeter basins along the cratonic periphery of the arcuate laramide province axial basins along a north south intramontane trend and ponded basins located farther west closer to the overthrust belt twelve specific stratigraphic and sedimentologic criteria for the onset duration and termination of laramide deformation allow the chronology of basin development to be inferred independently for each basin maastrichtian initiation of laramide deformation was approximately synchronous throughout the laramide province but termination of laramide deformation was systematically diachronous from north to south between early and late eocene time widespread eocene erosion surfaces truncate syntectonic laramide sequences and are overlain by largely volcanic and volcaniclastic post laramide strata of eocene age in the north and oligocene age in the south fluvial depositional systems draining toward the great plains were dominant in perimeter and axial basins but ponded basins were occupied at times by large lakes that served as regional sediment traps paleocene drainages from ponded basins also led eastward toward the continental interior but partly interconnected lakes that developed within several ponded basins by mid eocene time were either closed hydrologically or else they drained westward into the tyee paleoriver of the pacific northwest

an energetics total load sediment transport model for a plane sloping beach bagnold s energetics based total load sediment transport model for streams is used as a basis for the development of a total load model of time varying sediment transport over a plane sloping bed in both the bedload and suspended load the transport rate vectors are found to be composed of a velocity induced component directed parallel to the instantaneous velocity vector and a gravity induced component directed down slope the model is applied to idealized surfzone conditions leading to estimates of the local longshore and onshore offshore sediment transport rates as well as the equilibrium beach slope as a function of the local wave and current conditions the model is combined with a nonlinear longshore current model and spatially integrated to obtain predictions of the total longshore transport rate as a function of the incident wave conditions the results support the general form of the wave power equation except that the wave power coefficient is no longer constant but is instead a complex function of the incident wave and beach characteristics

topographic and hydrological controls on subglacial lake ellsworth west antarctica 1 subglacial lake ellsworth sle was identified using reconnaissance data collected in the 1970s here we present more detailed surveys sle lies beneath 3 2 km of ice in a subglacial valley in west antarctica it has an area of only 18 km2 is dissimilar to the large tectonically controlled lakes beneath east antarctica and is a strong candidate for in situ exploration our analysis indicates that the ice above sle is floating on a fluid whose density is 950 1013 kg m 3 this could indicate freshwater but certainly precludes seawater or high salt acid or clathrate content the water in the lake is unlikely to be produced solely by local melt it is more likely delivered via subglacial drainage our surveys show no identifiable hydrological barrier to outflow meaning sle is effectively full new water entering the lake is likely balanced by outflow which would drain into another lake that we have also identified

eustatic control on alluvial sequence stratigraphy a possible example from the cretaceous tertiary transition of the tornillo basin big bend national park west texas u s a paleosol bearing alluvial strata of latest cretaceous and earliest tertiary age are continuously exposed along dawson creek in big bend national park west texas u s a and exhibit a three tier hierarchy of depositional cyclicity meter scale fluvial aggradational cycles facs occur as fining upward successions that are gradation ally overlain by paleosols or are sharply overlain by the coarser grained base of the succeeding fac without an intervening paleosol facs stack into decameter scale fluvial aggradational cycle sets fac sets that also fine upward and from base to top contain either a grad ual upsection increase in soil maturity and soil drainage or a somewhat symmetrical pattern of increasing and decreasing paleosol maturity longer period trends of fac thickness lithologic proportions paleosol maturity and paleosol drainage indicate that two complete and two partial hectometer scale fluvial sequences occur within the study in terval from base to top each sequence is characterized by an asym metric increase and decrease in fac thickness a decrease in the pro portion of sand prone fluvial facies an increase in paleosol maturity and better paleosol drainage whereas facs and fac sets are interpreted to record cyclic epi sodes of channel avulsion and stability and longer term avulsive chan nel drift within the alluvial valley respectively fluvial sequences may coincide with third order sea level changes within the north american western interior seaway as such the cretaceous tertiary k t transition within the tornillo basin may provide an example of me gascale stratigraphic cyclicity that is controlled by eustatic sea level within a fully fluvial succession thickening and thinning successions of facs record a third order period of accelerating transgressive equivalent and decelerating highstand equivalent base level rise and subsequent base level fall falling stage to lowstand equivalent se quence boundaries are placed at the sharp inflection between thinning and thickening facs sand prone facies and immature more poorly drained paleosols are associated with the transgressive equivalent por tion of each sequence and mudrock dominated overbank facies and their associated mature well drained paleosols are associated with the highstand and falling stage equivalent

identification and control of subglacial water networks under dome a antarctica 1 subglacial water in continental antarctica forms by melting of basal ice due to geothermal or frictional heating subglacial networks transport the water from melting areas and can facilitate sliding by the ice sheet over its bed subglacial water flow is driven mainly by gradients in overburden pressure and bed elevation we identify small median 850 m water bodies within the gamburtsev subglacial mountains in east antarctica organized into long 20 103 km coherent drainage networks using a dense 5 km grid of airborne radar data the individual water bodies are smaller on average than the water bodies contained in existing inventories of antarctic subglacial water and most are smaller than the mean ice thickness of 2 5 km reflecting a focusing of basal water by rugged topography the water system in the gamburtsev subglacial mountains reoccupies a system of alpine overdeepenings created by valley glaciers in the early growth phase of the east antarctic ice sheet the networks follow valley floors either uphill or downhill depending on the gradient of the ice sheet surface in cases where the networks follow valley floors uphill they terminate in or near plumes of freeze on ice indicating source to sink transport within the basal hydrologic system because the ice surface determines drainage direction within the bed constrained network the system is bed routed but surface directed along flow variability in the structure of the freeze on plumes suggests variability in the networks on long 10s of ka timescales possibly indicating changes in the basal thermal state

using pressure pulse seismology to examine basal criticality and the influence of sticky spots on glacial flow 1 here we report results of water pressure pulse studies conducted at storglaciaren sweden and west washmawapta glacier british columbia canada comparison of pressure pulse records with meteorological conditions at storglaciaren indicates that several periods of increased basal slip activity observed during a 10 day interval of summer 2008 were due to precipitation loading of the glacier surface rather than to infiltration of surface water to the glacier bed this indicates that the glacier bed was close to the failure strength for much of this interval pressure pulse magnitudes for the two glaciers were well fit by power law distributions similar to those earlier observed at trapridge glacier and similar in form to the gutenberg richter relationship commonly used in seismology suggesting that the mechanical processes that give rise to these distributions are robust features of soft bedded glaciers in contrast interevent time distributions for both glaciers diverge from those observed at trapridge glacier for short recurrence intervals suggesting that the factors that govern the rate at which these processes occur differ between glaciers an examination of pressure pulse characteristics at west washmawapta glacier indicates that the establishment of a basal drainage system in summer 2008 resulted in increased stability and reduced sensitivity to meltwater input suggesting that common assumptions about the relationship between meltwater production and ice flow are oversimplified these results demonstrate that water pressure pulse observations can provide valuable insight into the dynamics of soft bedded glaciers

does englacial water storage drive temperate glacier surges hydrological studies of surge type and steady flow glaciers combined with recent space borne synthetic aperture radar interferometry measurements of the motion of bagley ice valley alaska u s a during its 1993 95 surge suggest a temperate glacier surge hypothesis that is consistent with observational evidence and appears capable of shedding light on several aspects of surge behavior we propose that the fundamental driver of temperate glacier surges is englacial storage of water combined with gravity driven movement of stored water to the bed during winter whether a given glacier is surge type is a matter not of whether but of the degree to which these processes occur a surge type glacier must have sufficient storage capacity for continued downward movement of englacially stored water during winter to finally overwhelm the constricted basal drainage system thereby forcing pervasive failure of the subglacial till or alternatively widespread and rapid basal sliding thus initiating a surge we further propose that the sufficient storage capacity requirement is most easily met by glaciers with large thickness which are therefore likely to be long and to have on average low surface slopes the average length of the surge cycle in a given region appears to be a function of the mass balances which after each surge determine the time required to restore glaciers to their pre surge geometries we suggest that the stochastic timing of surge onset for a particular glacier however is a result of the uncertainty of the meteorological conditions required to cause englacial storage of a sufficiently large volume of water

acoustic profiling of suspended sediments in the marine bottom boundary layer an acoustic 3 mhz backscattering profilometer has been developed for study of sediment transport in the bottom boundary layer laboratory experiments indicate reasonable correlations between backscattering intensity and mass concentrations for well sorted fine to coarse quartz sands typical of those found in marine sediments departure of the calibration curves from their expected values is thought to be due to the non spherical shape of the quartz grains field experiments on the inner shelf using the profilometer combined with velocity profiles show individual profiles taken at 1 hz during erosion events are characterized by highly variable concentrations surface wave groups rather than individual waves appear to be correlated with groups of profiles with high concentrations extending 25 100 cm above bottom averaging produces smooth profiles which fit well log normal distributions predicted by steady flow suspended load theories

reconstruction of a semi arid late pleistocene paleocatena from the lake victoria region kenya abstract the effect of changing environment on the evolution of homo sapiens is heavily debated but few data are available from equatorial africa prior to the last glacial maximum the karungu deposits on the northeast coast of lake victoria are ideal for paleoenvironmental reconstructions and are best studied at the kisaaka site near karunga in kenya 94 to 33 ka where paleosols fluvial deposits tufa and volcaniclastic deposits tuffs are exposed over a 2 km transect three well exposed and laterally continuous paleosols with intercalated tuffs allow for reconstruction of a succession of paleocatenas the oldest paleosol is a smectitic paleo vertisol with saline and sodic properties higher in the section the paleosols are tuffaceous paleo inceptisols with alfisol like soil characteristics illuviated clay mean annual precipitation map proxies indicate little change through time with an average of 764 108 mm yr 1 for vertisols calmag and 813 182 to 963 182 mm yr 1 for all paleosols cia k field observations and map proxies suggest that karungu was significantly drier than today consistent with the associated faunal assemblage and likely resulted in a significantly smaller lake victoria during the late pleistocene rainfall reduction and associated grassland expansion may have facilitated human and faunal dispersals across equatorial east africa

integration of channel and floodplain suites ii vertical relations of alluvial paleosols abstract extrachannel sediments of the lower eocene willwood formation which were subdivided into different pedofacies or developmental stages exhibit two well developed orders of pedofacies sequences over which a grosser scale cyclicity is superposed simple sequences with thicknesses measured in meters are comprised of one or more soil profiles that are bounded above and below by pedogenically unmodified crevasse splay deposits on a larger scale compound pedofacies sequences are tens of meters thick and consist of several simple sequences sandwiched between channel sandstones between these sandbodies pedogenic maturity of the multistorey paleosols progressively increases and then decreases upwards in response to episodic avulsion formation of both compound and simple pedofacies seq ences was largely controlled by local patterns of deposition and erosion that produced vertical variability in both rate of sediment accumulation and parent material because paleosol maturity also reflects the effects of extrabasinal factors a pedofacies megasequence which is hundreds of meters thick developed in response to changes in tectonic activity through willwood time comparison between willwood deposits in the northern and central parts of the bighorn basin also reveals that areally differing sediment accumulation rates and thereby basin subsidence rates can be interpreted from large scale pedofacies sequences consequently paleosols are useful in determining changes in relative rates of sediment accumulation that are controlled by both intrabasinal and extrabasinal factors

megafloral change in the early and middle paleocene in the williston basin north dakota usa abstract this paper presents a quantitative analysis of megafloral changes in composition and diversity using collections of early and middle paleocene floras 65 51 to 58 ma in the williston basin of north dakota usa based on the floral composition and stratigraphic ranges of taxa the williston basin floral record can be subdivided into three megafloral zones wbi wbii and wbiii each representing 1 myr the floral record of the basin implies that local and regional paleoenvironmental and climatic changes contributed to transitions in the early and middle paleocene plant communities the williston basin floral record documents a decrease in species richness that mirrors a decrease in mean annual temperatures from the latest cretaceous to middle paleocene these results combined with previous work from the hanna and bighorn basins suggest that climate may have played an important role in patterns of floral diversity and plant community composition further these data indicate that it took paleocene plant communities in the northern great plains millions of years to reach diversity levels common in the cretaceous

the thermal regime of sub polar glaciers mapped by multi frequency radio echo sounding radio echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale radar signals of 320 370 mhz penetrate ice at sub freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water radar signals of 5 20 mhz on the other hand see through both the cold and the temperate ice down to the glacier bed radio echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in svalbard kongsvegen uversbreen midre lovenbreen and austre broggerbreen in the ablation area of kongsvegen a cold surface layer 50 160m thick was underlain by a warm basal layer which is advected from the temperate accumulation area the surface ablation of this cold layer may be compensated by freezing at its lower cold temperate interface this requires that the free water content in the ice at the freezing interface is about 1 of the volume the cold surface layer is thicker beneath medial moraines and where cold based hanging glaciers enter the main ice stream on uversbreen the thermal regime was similar to that of kongsvegen a temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between kongsvegen and uversbreen where meltwater accumulates during the summer near the subglacial lake setevatnet 250 m a s l lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer up to 50m thick was fed by temperate ice from two cirques on austre broggerbreen a temperate basal layer was not detected by radio echo soundings but the basal ice was observed to be at the melting point in two boreholes

the sequence stratigraphy of fluvial depositional systems the role of floodplain sediment storage abstract the currently used model for alluvial sequence stratigraphy has been criticised miall 1991 and an alternative model is offered here in this model alluviation mainly takes place during transgressive and not highstand phases when accommodation space allows sediment storage the high capacity for some river systems to store floodplain sediments is a critical consideration the effects of climatic and intrinsic geomorphic changes during fluvial deposition are likely to greatly complicate simple base level controlled sequence models and recognising higher order fourth and fifth order cycles will be particularly difficult

evaluating the use of weathering indices for determining mean annual precipitation in the ancient stratigraphic record abstract different quantitative methods have been developed to determine paleo rainfall using paleosols of particular interest are methods that use bulk geochemistry to calculate a weathering index and from that mean annual precipitation twenty three paleosols that formed during a time of significant climate change the paleocene eocene thermal maximum petm were analyzed to evaluate the relative merits of two geochemical proxies that have been developed for estimating paleoprecipitation one depends on the chemical index of alteration without potash cia k and the other uses the calmag weathering index which depends on cao and mgo the paleosols are located in the paleogene fort union and willwood formations in the bighorn basin wy morphologic differences among the paleosols indicate that they formed under varied soil moisture conditions a morphology index was developed from pedogenic features that are sensitive to soil drainage and thus to rainfall to assess that variability quantitative mean annual precipitation map values were calculated for each paleosol using the cia k index and the calmag index which was developed specifically for vertisols those results were compared to the morphology index for 23 paleosols the results indicate that increases and decreases in map calculated from both methods correlate relatively well to changes in the soil morphology index however the results from the calmag weathering index show a stronger correlation the results suggest that the calmag proxy provides a more robust map estimate for vertisols in addition to comparing map estimates to the soil morphology index we compared the map values to paleorainfall estimates determined from paleofloras at the same stratigraphic levels as three of the paleosols that comparison confirms that the calmag method is reliable for reconstructing map from ancient vertisols the results also show that in the bighorn basin vertisols with a b horizon

velocity and stress fields in grounded glaciers a simple algorithm for including deviatoric stress gradients a new and efficient algorithm for computing the three dimensional stress and velocity fields in grounded glaciers includes the role of deviatoric stress gradients a consistent approximation of first order in the aspect of ratio of the ice mass gives a set of eight field equations for the five stress and three velocity components and the corresponding boundary conditions a coordinate transformation mapping the local ice thickness on to unity and approximating the derivatives in the horizontal direction by centred finite differences yields five ordinary differential and three algebraic equations this allows use of the method of lines starting the integration with prescribed stress and velocity components at the base and a simple iteration procedure converges rapidly the algorithm can lie used for a wide range of stress strain rate relations as long as strain only depends on deviatoric and shear stresses and on temperature sensitivity tests using synthetic and realistic ice geometries show the relevance of normal deviatoric stresses in the solutions for the velocity components even for ice sheets stress and velocity fields may deviate substantially from the widely used shallow ice approximation

a pedotype approach to latest cretaceous and earliest tertiary paleosols in eastern montana a pedotype approach to the study of paleosols emphasizes individual profiles it is an alternative approach to the study of geosols which are laterally extensive suites of paleosols or pedofacies which are pedogenically distinctive sedimentary facies this is the first pedotype study of paleosols across the cretaceous tertiary boundary in eastern montana pedotypes allow assessment of sedimentation and fossilization the sequence of paleosols across the cretaceous tertiary boundary at bug creek is one of high temporal resolution because most available geological time can be accounted for by differing degree of development inferred for each pedotype paleosols at bug creek include pedotypes that preserve plant fossils well but were unfavorable for preservation of fossil vertebrates pedotypes also allow reassessment of ecosystem change despite indications of catastrophe at the cretaceous tertiary boundary the array of paleocene and cretaceous pedotypes are not strikingly different the upper cretaceous hell creek formation includes pedotypes interpreted as gleyed alfisols inceptisols and entisols probably formed under seasonally water logged forest and mean annual rainfall of the order of 900 1200 mm most paleosols of the lower paleocene tullock formation were histosols but some can be interpreted as gleyed inceptisols and entisols probably formed under bald cypress swamps in a humid climate with 1200 mm mean annual rainfall broadly comparable pedotypes were present before and after the cretaceous tertiary boundary although paleocene flood plain forest lived in paleosols chemically a little more oligotrophic than cretaceous paleosols this modest difference supports the idea that change to coaly facies in the earliest paleocene was a local shift in sedimentary environment such local changes do not begin to account for profound disruption in specific composition of plant and animal communities at the cretaceous tertiary boundary in eastern montana

rerouting of subglacial water flow between neighboring glaciers in west greenland investigations of the greenland ice sheet s subglacial hydrological system show that the connectivity of different regions of the system influences how the glacier velocity responds to variations in surface melting here we examine whether subglacial water flow paths can be rerouted beneath three outlet glaciers in the ablation zone of western greenland we use lamont doherty and center for remote sensing of ice sheets of university of kansas cresis ice penetrating radar data to create a new ice thickness map we then use a simple subglacial water flow model to examine whether flow paths can be rerouted and identify the topographic conditions that are sensitive to subglacial rerouting by varying water pressures within an observationally constrained range we show that moderate changes in pressure can cause flow paths to reroute and exchange water from one subglacial catchment to another flow across subglacial overdeepenings is particularly sensitive to rerouting these areas have low hydraulic gradients driving flow so subtle water pressure variations have a strong influence on water flow direction based on correlations between water flow paths and ice velocity changes we infer that water piracy between neighboring catchments can result in a different spatial pattern of hydrologically induced ice velocity speedup depending on the amount and timing of surface melt the potential for subglacial water to reroute across different catchments suggests that multiple hydrographs from neighboring glaciers are likely necessary to accurately ascertain melt budgets from proglacial point measurements the relationship between surface runoff ice dynamics and proglacial discharge can be altered by rerouting of subglacial water flow within and across outlet glaciers

barrier island evolution middle atlantic shelf u s a part i shoreface dynamics abstract in part i of this paper near bottom fluid velocity and sediment concentration measurements from the shoreface of a middle atlantic barrier long island coast are analyzed to provide insight into the dynamics of erosional shoreface retreat in part ii these data are combined with observations of coastal stratigraphy in order to construct a model for the evolution and behavior of middle atlantic barriers wave motions on the long island shoreface tend to drive sediment onshore calculations of the onshore sediment flux driven by asymmetrical shoaling waves show that for the wave states commonly encountered on the middle atlantic shelf values become strongly positive landward of approximately 10 m water depth upper shoreface but drop to very low values shortly seaward of that isobath on the lower shoreface and inner shelf floor fair weather wave current interaction tends to cause a landward creep of sediment even though the wave orbital component of the near bottom velocity field is nearly symmetrical this movement occurs because the wave approach direction generally lies within 90 of the direction up coast or down coast of the alongshore wind driven current therefore fluid shear stress acting on the sediments tends to be reinforced during the shoreward stroke of the wave orbital motion and partially cancelled during the seaward stroke during major storms the rate of sediment transport increases by at least an order of magnitude and the role of wind driven currents becomes important much more sediment is resuspended by the wave orbital current component because storm waves are more powerful than fair weather swells but the wind driven flow component is also much stronger and is now available for transporting the resuspended sediment storm flows over the shoreface occur in distinct dynamic zones surf zone friction dominated zone transition zone geostrophic zone the zones are defined by dynamical considerations and expand or contract with the intensity of the causative wind stress during peak flow events the characteristic length scales of the friction dominated and geostrophic zones tend to correspond with the morphologic zones of the shoreface and inner shelf the storm intensified wind driven alongshore flows of the lower shoreface are frequently jet like in nature and may be upwelling or downwelling wind driven coastal flows with a strong downwelling component occur during most storms on the long island coast and are particularly important to the coastal sand budget during these events sand is entrained by the storm intensified upper shoreface circulation system of wave driven alongshore currents and rip currents and is fed into the main wind driven coastal current because of the offshore component of bottom flow sand is swept down the lower shoreface and onto the adjacent inner shelf fair weather processes may be unable to return storm deposited sand to the beach from such an offshore position the shoreface transport regime of the long island barrier coast thus consists of long periods of time months during which sand moves slowly toward the beach punctuated by short intense periods hours or days during which sand is transferred from the shoreface to the adjacent inner shelf the long term sense of movement of the shoreface whether retreating the long island case or prograding must depend on the loss or gain of sand by shoreface with respect to the inner shelf the data shows that the coastal sand budget is controlled not only by the upper shoreface cycle withdrawl of sand from the beach prism storage in the breakpoint bar and its subsequent return to the beach but by a cycle of larger spatial and temporal scale in which sand is exchanged between the shoreface as a whole and the adjacent inner shelf

fossil crocodilians as indicators of late cretaceous and cenozoic climates implications for using palaeontological data in reconstructing palaeoclimate abstract that the earth s climate has cooled over the last 100 million years has been recognized since the early nineteenth century the transition from the hot house world of the cretaceous a time interval without significant polar icesheets to the ice house world in which we now live today the dynamics process responsible for this change are being examined using computer models especially general circulation models gcm s through such work our understanding of the dynamics of the earth system improves and our ability to predict future trends is enhanced but the success of modelling experiments can only be assessed by comparing results with observations the pattern which for palaeoclimate are drawn exclusively from the geological record palaeoclimate interpreted from geological data is invariably based on analogy with the recent the validity of which depends on corroboration from multiple lines of evidence this requires the compilation and investigation of large global datasets of well constrained geological climate proxies this study uses the palaeodistribution of fossil crocodilians to examine the spatial distribution of palaeoclimate during this transition fossil crocodilians have a relatively good fossil record and are climatically limited in the recent they also provide a manageable global dataset with which to investigate other issues that impinge on the use of geologic data for reconstructing palaeoclimate taphonomy sampling effects time averaging tectonics and for fossils palaeobiogeography and evolution as such this study provides a possible template for examining other climate proxies in order to validate and hone palaeoclimatic interpretations an analysis of modern crocodilians indicates that temperature is the principal influence on their global distribution with the coldest month mean temperature cmm of 5 5 c marking the minimum thermal limit for the group corresponding today to a minimum mean annual temperature mat of 14 2 c the duration of warmth during the year partly indicated by the mean annual range of temperature mart is also important as this affects early juvenile development and survival the presence of standing water provides an essential thermal buffer against temperature extremes by analogy the palaeodistribution of fossil crocodilians suggests the following during the late cretaceous and early palaeogene mat s in excess of 14 2 c cmm s 5 5 c permeated throughout mid latitudes and coastal regions in high latitudes during the oligocene the restriction of fossil crocodilians to low latitudes suggests high latitude cooling as indicated by numerous other lines of evidence coeval restriction of crocodilians to coastal regions in mid latitude north america and much of asia consistent with increased seasonality and aridification in continental interiors may reflect local orographic changes as well as global climate change during the miocene fossil crocodilians return to the great plains of north america but do not reoccupy the continental interior of asia by the pliocene crocodilians are again restricted to low latitudes and coastal regions in mid latitudes coincident with further high latitude cooling and aridification and cooling of mid latitude continental interiors minor distributional changes during the holocene may reflect human effects

dye tracing a jokulhlaup ii testing a jokulhlaup model against flow speeds inferred from measurements observational data allowing the validation of j okulhlaup models are sparse we were able to inject dye tracer directly into the drainage channel of a glacial lake during the onset of its outburst this made it possible to test an established j okulhlaup model not only against discharge measurements but for the first time also against water flow speeds inferred from measurements we drive the j okulhlaup model based on the spring hutter equations with measured subglacial water pressure lake water temperature and lake level the model is fitted to the measured lake discharge and inferred flow speeds using the initial channel size the channel roughness and sinuosity our calculations show that an ingenuous application of the model fitting it to the lake discharge only overestimates water flow speeds for the second day of the outburst this can be remedied by fitting the model to the inferred flow speeds as well requiring that either the heat transfer or the sinuosity of the channel be increased however the low inferred flow speeds on the first day of the outburst cannot be fitted with any parameter combination showing that initially the water does not flow through an r channel hence the early stages of this j okulhlaup cannot be simulated by an r channel model

basal conditions beneath enhanced flow tributaries of slessor glacier east antarctica radio echo sounding data are used to investigate bed roughness beneath the three enhanced flow tributaries of slessor glacier east antarctica slow moving inter tributary areas are found to have rough beds while the bed of the northernmost tributary is relatively smooth a reconstruction of potential subglacial drainage routing indicates that water would be routed down this tributary and investigations of basal topography following isostatic recovery reveal that the bed would have been below sea level in preglacial times so marine sediments may have accumulated here together these factors are further support for the dominance of basal motion in this tributary reported elsewhere conversely although the other two slessor tributaries may have water routed beneath them they would not have been below sea level before the growth of the ice sheet so cannot be underlain by marine sediments they are also found to be rough and within the range of uncertainties it is likely that basal motion does not play a major role in the flow of these tributaries perhaps the most interesting area however is a deep trough where flow rates are currently low but the bed is as smooth as the northern slessor trough it is proposed that although ice deformation currently dominates in this trough basal motion may have occurred in the past when the ice was thicker

new weathering index improves paleorainfall estimates from vertisols vertisols are clayey shrink swell soils that are widely recognized in the rock record thus generating the need to better understand the dynamics of elemental concentrations on the development of weathering indexes for climate interpretations we assessed the weathering performance of the four major base forming oxides cao mgo na 2 o k 2 o along a modern vertisol climosequence spanning a strong precipitation gradient and discovered that the concentration of bulk soil cao and mgo yields the strongest correlation to mean annual precipitation map based on this fi nding we introduce the calmag weathering index defi ned as al 2 o 3 al 2 o 3 cao mgo 100 which improves rainfall estimates for vertisols relative to the wellestablished cia k chemical index of alteration minus potassium weathering index rather than documenting the hydrolysis of weatherable minerals common in many other soil orders in vertisols calmag principally tracks the fl ux of calcium and magnesium sourced from calcium carbonate detrital clay and exchangeable ca 2 and mg 2 application to two mesozoic paleosols reveals that in drier climates cia k yields higher map estimates than calmag but that the reverse is true in wetter climates this work improves paleorainfall estimates from vertisols and suggests that a family of weathering indexes is needed for different paleosol types

a multicomponent coupled model of glacier hydrology 2 application to trapridge glacier yukon canada 1 a new glaciohydraulic model is tailored to trapridge glacier yukon canada where long term measurements of subglacial water pressure provide parameter constraints and a platform for model evaluation using digital elevation models and meteorological data as input we investigate hydrology on diurnal and seasonal timescales quantitative comparisons of simulated and observed pressure records allow us to select a reference model objectively from which we gain first insights into the gross spatial characteristics of the drainage system equilibrium simulations highlight target areas for water storage and potential sticky spots both of which have established relevance to glacier dynamics seasonal simulations capture the key signatures of spring and autumn transitions and corroborate our understanding of the processes involved successfully modeled features of the spring transition include increased hydraulic coupling between the surface and bed with time temporary augmentation of subglacial storage and rapid subglacial transitions from a hydraulically unconnected to connected state autumn transitions are characterized by deterioration of the basal drainage network drawdown of subglacial storage reservoirs and heightened sensitivity to precipitation and surface refreezing finally we draw attention to the important role of groundwater transport in cold glacial environments where permafrost can impede drainage from the ice margin

comparison of a three dimensional model for glacier flow with field data from haut glacier d arolla switzerland a three dimensional finite difference model based on a first order solution of the ice flow equations is applied to haut glacier d arolla switzerland the numerical model successfully converges at horizontal resolutions down to 70 m so a number of detailed comparisons with field data can be made modelled surface velocities with no basal sliding component are compared with surface velocities observed on the glacier over four different time periods the best fit is achieved with over winter surface velocities r 2 0 75 using a rate factor a in glen s flow law of 0 063 a 1 bar 3 surface zones of maximum computed effective stress display a high level of coincidence with observed crevassing the orientation of which is successfully predicted by the direction of the tensile component of the computed principal surface stress comparison of the relative magnitude and direction of computed principal stresses with principal strains measured at the ice surface also correspond closely in an attempt to simulate the observed annual velocity distribution within a cross section of the glacier tongue we incorporate two basal motion patterns into the model by treating net annual ice motion as a time weighted composite of three separate flow situations normal sliding enhanced sliding and no sliding we are able to reproduce the key features of the observed cross sectional ice and basal slip velocity distributions these experiments indicate there may be substantial decoupling taking place along an elongated narrow zone at the bed of haut glacier d arolla and that this decoupling interacts in a complex manner with the englacial stress and strain field

a simple method for estimating barotropic tidal currents on continental margins with specific application to the m2 tide off the atlantic and pacific coasts of the united states abstract theory is developed to describe barotropic tidal currents on smooth continental shelves that is continental shelves with longshore scales much greater than the shelf width two models are considered one in which sea level don not vary significantly across the shelf and the other in which it does both models include longshore gradients and friction parameterized linearly in velocity the models were tested by calculating the m2 tidal currents off the atlantic and pacific coasts of the united states and then comparing the calculated currents to those measured results show that theory and observation are in very good agreement as far offshore as 300 km along the atlantic coast on account of the wide continental shelf current velocities are typically o 0 10 0 15 m s 1 north of cape hatteras and o 0 15 0 28 m s 1 off savannah georgia currents rotate anticyclonically and are highly elliptical ellipticity e 0 4 with the semi major axis oriented normal to the coast friction is sign

slow surge of trapridge glacier yukon territory canada 1 trapridge glacier a polythermal surge type glacier located in the st elias mountains yukon territory canada passed through a complete surge cycle between 1951 and 2005 air photos 1951 1981 and ground based optical surveys 1969 2005 are used to quantify the modifications in flow and geometry that occurred over this period yearly averaged flow records suggest that the active phase began 1980 and lasted until 2000 the average velocity in the central area of the glacier went from 16 m yr 1 in 1974 to 39 m yr 1 in 1980 it peaked at 42 m yr 1 in 1984 and remained above 25 m yr 1 until 2001 over that interval the flow decelerated by steps in 4 year pulses after a particularly vigorous acceleration in 1997 1999 the glacier gradually slowed to presurge velocities in 2005 the flow was less than 9 m yr 1 digital elevation models are generated by stereographic analysis of air photos for 1951 1970 1972 1977 and 1981 these models are updated annually using ground based survey data and a novel implementation of bayesian kriging over the course of the surge the front of active ice advanced 450 m and the glacier area increased by 10 with an associated thinning of the ice the previous surge of trapridge glacier starting before 1939 and ending before 1951 led to a terminus advance of 1 km comparison of the two surges suggests that the 1930s surge started with a slow progression similar to what we observed in the 1980s and 1990s and switched to a faster flow mode after 1941 this second phase was never attained in the recent surge probably owing to a lack of mass

polythermal glacier hydrology a review 1 the manner by which meltwater drains through a glacier is critical to ice dynamics runoff characteristics and water quality however much of the contemporary knowledge relating to glacier hydrology has been based upon and conditioned by understanding gleaned from temperate valley glaciers globally a significant proportion of glaciers and ice sheets exhibit nontemperate thermal regimes the recent growing concern over the future response of polar glaciers and ice sheets to forecasts of a warming climate and lengthening summer melt season necessitates recognition of the hydrological processes in these nontemperate ice masses it is therefore timely to present an accessible review of the scientific progress in glacial hydrology where nontemperate conditions are dominant this review provides an appraisal of the glaciological literature from nontemperate glaciers examining supraglacial englacial and subglacial environments in sequence and their role in hydrological processes within glacierized catchments in particular the variability and complexity in glacier thermal regimes are discussed illustrating how a unified model of drainage architecture is likely to remain elusive due to structural controls on the presence of water cold ice near glacier surfaces may reduce meltwater flux into the glacier interior but observations suggest that the transient thermal layer of near surface ice holds a hydrological role as a depth limited aquifer englacial flowpaths may arise from the deep incision of supraglacial streams or the propagation of hydrofractures forms which are readily able to handle varied meltwater discharge or act as locations for water storage and result in spatially discrete delivery of water to the subglacial environment the influence of such drainage routes on seasonal meltwater release is explored with reference to summer season upwellings and winter icing formation moreover clear analogies emerge between nontemperate valley glacier and ice sheet hydrology the discussion of which indicates how persistent reassessment of our conceptualization of glacier drainage systems is required there is a clear emphasis that continued integrated endeavors focused on process glaciology at nontemperate glaciers are a scientific imperative to augmenting the existing body of research centered on ice mass hydrology

subglacial drainage system structure and morphology of brewster glacier new zealand a global positioning system and ground penetrating radar surveys is used to produce digital elevation models of the surface and bed of brewster glacier these are used to derive maps of subglacial hydraulic potential and drainage system structure using three different assumptions about the subglacial water pressure pw i pw ice overburden ii pw half ice overburden iii pw atmospheric additionally 16 dye tracing experiments at 12 locations were performed through a summer melt season dye return curve shape together with calculations of transit velocity dispersivity and storage are used to infer the likely morphology of the subglacial drainage system taken together the data indicate that the glacier is underlain by a channelised but hydraulically inefficient drainage system in the early summer in which water pressures are close to ice overburden by mid summer water pressures are closer to half ice overburden and the channelised drainage system is more hydraulically efficient surface streams that enter the glacier close to the location of major subglacial drainage pathways are routed quickly to the channels and then to the glacier snout streams that enter the glacier further away from the drainage pathways are routed slowly to the channels and then to the snout because they first flow through a distributed drainage system copyright 2008 john wiley sons ltd

acoustic impedance and basal shear stress beneath four antarctic ice streams the acoustic impedance of the subglacial material beneath 7 2 km profiles on four ice streams in antarctica has been measured using a seismic technique the ice streams span a wide range of dynamic conditions with flow rates of 35 464 in a 1 the acoustic impedance indicates that poorly lithified or dilated sedimentary material is ubiquitous beneath these ice streams mean acoustic impedance across each profile correlates well with basal shear stress and the slipperiness of the bed indicating that acoustic impedance is a good diagnostic not only for the porosity of the subglacial material but also for its dynamic state deforming or non deforming beneath two of the ice streams lodged non deforming and dilated deforming sediment coexist but their distribution is not obviously controlled by basal topography or ice thickness their distribution may be controlled by complex material properties or the deformation history beneath rutford ice stream lodged and dilated sediment coexist and are distributed in broad bands several kilometres wide while on talutis inlet there is considerable variability over much shorter distances this may reflect differences in the mechanism of drainage beneath the ice streams the material beneath the slow moving carlson inlet is probably lodged but unlithified sediment this is consistent with the hypothesis that carlson inlet was once a fast flowing ice stream but is now in a stagnant phase which could possibly be revived by raised basal water content the entire bed beneath fast flowing evans ice stream is dilated sediment

significance of different modes of rhizolith preservation to interpreting paleoenvironmental and paleohydrologic settings examples from paleogene paleosols bighorn basin wyoming u s a abstract different modes of preservation of root traces rhizoliths provide information on soil moisture regimes in alluvial paleosols in the paleogene fort union and willwood formations of the bighorn basin wyoming u s a this paper links different styles of rhizolith preservation to paleosols whose other pedogenic attributes provide information on ancient soil drainage consequently the paleodrainage significance of different rhizolith preservation patterns is established more confidently rhizoliths consisting of elongate gray mottles rhizohaloes with red rims are common in relatively well drained red paleosols the gray zones are depleted of iron fe whereas the color of the rims indicates hematite accumulation these features are typical of surface water gley processes that caused fe and manganese mn to move from the root channel outward to the soil matrix calcareous rhizocretions either calcareous tubular concretions or micro accumulations of carbonate within gray rhizotubules are also common in moderately well drained red paleosols more poorly drained purple paleosols also have rhizoliths consisting of fe depletion zones however the rhizohaloes are surrounded by yellow brown goethite rims rather than red hematitic rims in many paleosols the red and yellow brown accumulation rims were partly removed by continued depletion producing abundant irregular shaped mottles the nature of the rhizohalo and the color of the fe oxide rim provide information about the intensity of gleying that a paleosol underwent the poorly drained paleosols also show rhizoliths preserved as goethite accumulations contained within gray depletion zones indicating movement of reduced fe from the matrix towards the root channel probably as a result of groundwater gley processes the goethite accumulations are intermingled locally with lignite representing preservation of the root organic material some rhizoliths are preserved as tube shaped concentrations of small 0 1 0 2 mm diameter black spheres whose color indicates a mix of mn and fe oxides these are most common in paleosols with low chroma gray matrix colors indicating very poor drainage the very poorly drained paleosols also show rhizoliths preserved in jarosite which is an oxidation product of pyrite careful observational and geochemical analysis of rhizoliths which are common in continental deposits can help produce a clearer and more thorough interpretation of ancient drainage conditions information about degree of ancient soil wetness or moisture is important for understanding past climatic conditions and for reconstructing terrestrial paleolandscapes

continental sequence stratigraphy of the upper triassic norian rhaetian chinle strata northern new mexico u s a allocyclic and autocyclic origins of paleosol bearing alluvial successions abstract two age equivalent upper triassic fluvial successions deposited on the continental interior of the southwestern united states were evaluated using an adapted marine stacking pattern analysis methodology a three tier cyclic hierarchy is present in the strata at both study areas meter scale fining upward fluival aggradation cycles facs comprise fluvial aggradational cycle sets facsets 4 15 m thick avg 8 4 m facsets in turn stack into four fluvial sequences 26 48 m thick avg 41 m within these sequences transgressive systems tract equivalents te are characterized by channel sands and associated minor overbank deposits and relatively immature paleosols i e high rates of deposition whereas highstand to falling stage systems tract equivalents hfe are dominated by overbank muds and relatively well developed paleosols i e lower rates of deposition these two fluvial successions which are 200 km apart contain age equivalent fluvial sequences that record similar histories of deposition and pedogenesis sequence 1 contains only an incomplete hfe sequence 2 includes both the te and hfe sequence 3 is an hfe and sequence 4 contains only a te fluvial sequences likely accumulated in response to pulses of source area uplift and or basin subsidence which resulted in changes in accommodation conversely higher frequency facs and facsets that occur within sequences do not correlate between study areas and are likely the products of autocyclic processes such as channel avulsion floodplain aggradation and channel migration these results suggest that regionally significant tectonic episodes may be discernible in suspended load fluvial deposits that accumulated over a broad area

internal and basal ice changes near the grounding line derived from radio echo sounding evidence of changing basal and internal ice properties near the grounding line was derived from airborne radio echo sounder observations of the ice sheet around the sor rondane mountains antarctica from the trailing figure of the bottom echo signal the roughness of the ice bottom near the grounding line was inferred results show that the specular components of scattering begin to appear on the ice shell side of the grounding line furthermore double trip echoes were observed with at strong scattering in the shelf area and their boundary of occurrence was very close to the grounding line this is evidence of interaction between ice and sea water at the bottom of the ice shelf we also examined the occurrence of internal layered echoes in most of the area around the mountains internal echoes were observed continuously but they were not found at or close to the ice shelf the boundary between the appearance and disappearance of internal layer echoes is distinct and occurs 20 30 km inland from the grounding line these results suggest that some major change may occur in the internal ice on the inland side of the grounding line

mineralogy of magnetic minerals and revised magnetic polarity stratigraphy of continental sediments san juan basin new mexico detailed paleomagnetic and rock magnetic analyses have been performed on samples from multiple sections through the cretaceous tertiary k t boundary and throughout a 750 m thick sequence of late cretaceous through middle paleocene continental deposits in the san juan basin new mexico curie temperatures have been determined for magnetic separates from 52 levels and with only two exceptions they range from 180 to 300 c along with microprobe and x ray analyses these data indicate that the detrital ferrimagnetic mineral is titanohematite with composition 0 45 x 0 60 this magnetic mineralogy indicates derivation of the continental san juan basin sediments from a volcanic probably dacitic or andesitic source these mineralogical data along with other geological data and the pattern of magnetic polarity zonation in multiple sections across the basin argue strongly for deposition of the late cretaceous and paleocene continental deposits in the san juan basin as a clastic wedge derived from a sourc

early paleocene magnetostratigraphy and revised biostratigraphy of the ojo alamo sandstone and lower nacimiento formation san juan basin new mexico usa

water flow through temperate glaciers understanding water movement through a glacier is fundamental to several critical issues in glaci ology including glacier dynamics glacier induced floods and the prediction of runoff from glacierized drainage basins to this end we have synthesized a conceptual model of water movement through a temper ate glacier from the surface to the outlet stream pro cesses that regulate the rate and distribution of water input at the glacier surface and that regulate water movement from the surface to the bed play important but commonly neglected roles in glacier hydrology where a glacier is covered by a layer of porous perme able firn the accumulation zone the flux of water to the glacier interior varies slowly because the firn tempo rarily stores water and thereby smooths out variations in the supply rate in the firn free ablation zone in con trast the flux of water into the glacier depends directly on the rate of surface melt or rainfall and therefore varies greatly in time water moves from the surface to the bed through an upward branching arborescent net work consisting of both steeply inclined conduits formed by the enlargement of intergranular veins and gently inclined conduits spawned by water flow along the bottoms of near surface fractures crevasses engla cial drainage conduits deliver water to the glacier bed at a limited number of points probably a long distance downglacier of where water enters the glacier englacial conduits supplied from the accumulation zone are quasi steady state features that convey the slowly varying water flux delivered via the firn their size adjusts so that they are usually full of water and flow is pressurized in contrast water flow in englacial conduits supplied from the ablation area is pressurized only near times of peak daily flow or during rainstorms flow is otherwise in an open channel configuration the subglacial drainage system typically consists of several elements that are distinct both morphologically and hydrologically an up glacier branching arborescent network of channels in cised into the basal ice conveys water rapidly much of the water flux to the bed probably enters directly into the arborescent channel network which covers only a small fraction of the glacier bed more extensive spatially is a nonarborescent network which commonly includes cav ities gaps between the glacier sole and bed channels incised into the bed and a layer of permeable sediment the nonarborescent network conveys water slowly and is usually poorly connected to the arborescent system the arborescent channel network largely collapses during winter but reforms in the spring as the first flush of meltwater to the bed destabilizes the cavities within the nonarborescent network the volume of water stored by a glacier varies diurnally and seasonally small temper ate alpine glaciers seem to attain a maximum seasonal water storage of 200 mm of water averaged over the area of the glacier bed with daily fluctuations of as much as 20 30 mm the likely storage capacity of subglacial cavities is insufficient to account for estimated stored water volumes so most water storage may actually occur englacially stored water may also be released abruptly and catastrophically in the form of outburst floods

digital elevation model networks demon a model of flow over hillslopes for computation of contributing and dispersal areas current algorithms for computing contributing areas from a rectangular grid digital elevation model dem use the flow routing model of o callaghan and mark 1984 which has two major restrictions 1 flow which originates over a two dimensional pixel is treated as a point source nondimensional and is projected downslope by a line one dimensional moore and grayson 1991 and 2 the flow direction in each pixel is restricted to eight possibilities we show that large errors in the computed contributing areas result for any terrain topography divergent convergent or planar we present a new model called digital elevation model networks demon which avoids the above problems by representing flow in two dimensions and directed by aspect demon allows computation of both contributing and dispersal areas demon offers the main advantage of contour based models e g moore et al 1988 the representation of varying flow width over nonplanar topography while having the convenience of using rectangular grid dems

development of tectonic cyclothems in rift pull apart and foreland basins sedimentary response to episodic tectonism the thickest part of asymmetric rift pull apart and foreland basin fills commonly consists of large scale hundreds to thousands of metres thick tectonically generated cyclothems of fine grained marine lacustrine or longitudinal fluvial deposits and coarse grained transverse braid plain or alluvial fan deposits the appearance of coarse clastics in these basin fills is typically noted as the time of tectonically rejuvenated source area uplift based on the conceptual tie between relief and coarse grain size and on the application of the davis theory of landform development we propose the opposite interpretation that the commencement of fine grained sedimentation above coarse grained deposits in a tectonic cyclothem is the best indicator of renewed tectonic activity this reinterpretation is more consistent with 1 modern examples 2 the consideration of source area and sedimentary basin geomorphology 3 the disparity between the reaction rates of the various environments to subsidence 4 the disparity between the rates of tectonic uplift and erosion and 5 the controls on elastic wedge progradation in our model extensive coarse grained clastic wedge progradation is an indicator of tectonically quiescent phases

paleosols in clastic sedimentary rocks their geologic applications interest in pre quaternary paleosols has increased over the past decade in large part because they have proved to be beneficial in solving diverse geological problems the majority of paleosols are described from continental deposits most commonly from alluvial strata criteria for recognizing these paleosols have been extensively described however classifying them has proved more complicated pre quaternary paleosols are generally classified according to one or more modern soil classification systems although one new classification has been proposed exclusively for paleosols to avoid problems using the modern soil classifications in addition to taxonomic classification paleosols can be categorized according to the interplay among deposition erosion and the rate of pedogenesis when they formed paleosols can be solitary if they formed during a period of landscape stability following the development of an unconformity such paleosols are commonly thick and extremely well developed more commonly paleosols are vertically stacked or multistory because they formed in sedimentary systems undergoing net aggradation if erosion was insignificant and sedimentation was rapid and unsteady compound paleosols generally formed if the rate of pedogenesis exceeded the rate of deposition composite paleosols developed thick cumulative paleosols indicate that erosion was insignificant and that sedimentation was relatively steady both autogenic and allogenic processes can influence depositional and erosion patterns and thus affect the kinds of soils that form consequently paleosols can help to interpret the history of sediment deposition and the autogenic and allogenic processes that influenced a sedimentary basin paleosols are also helpful in stratigraphic studies including sequence stratigraphic analyses they are used for stratigraphic correlations at the local and basinal scale and some workers have calculated sediment accumulation rates based on the degree of paleosol development in addition to their stratigraphic applications paleosols can be used to interpret landscapes of the past by analyzing paleosol landscape associations at different spatial scales ranging from local to basin wide in scope at the local scale lateral changes in paleosol properties are largely the result of variations in grain size and topography at the scale of the sedimentary basin paleosols in different locations differ because of basinal variations in topography grain size climate and subsidence rate paleosols are used to reconstruct ancient climates even to estimate ancient mean annual precipitation map and mean annual temperature mat ancient climatic conditions can be interpreted from modern soil analogs or by identifying particular pedogenic properties that modern studies show to have climatic significance stable carbon and oxygen isotopes are also used to interpret ancient climate and some effort has been made to estimate mat from isotopic composition on the basis of

the prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models the accuracy of the predictions of distributed hydrological models must depend in part on the proper specification of flow pathways this paper examines some of the problems of deriving flow pathways from raster digital terrain data in the context of hydrological predictions using topmodel distributed moisture status is predicted in topmodel on the basis of spatial indices that depend on flow path definition the sensitivity of this index to flow path algorithm and grid size is examined for the case where the surface topography is a good indicator of local hydraulic gradients a strategy for the case where downslope subsurface flow pathways may deviate from those indicated by the surface topography is described with an example application

a new paleothermometer for forest paleosols and its implications for cenozoic climate climate is a primary control on the chemical composition of paleosols making them a potentially extensive archive applicable to problems ranging from paleoclimate reconstruction to paleoaltimetry however the development of an effective widely applicable paleosol temperature proxy has remained elusive this is attributable to the fact that various soil orders behave differently due to their respective physical and chemical properties therefore by focusing on an individual order or a subset of the 12 soil orders whose members exhibit similar process behavior a better constrained paleothermometer can be constructed soil chemistry data were compiled for 158 modern soils in order to derive a new paleosol paleothermometry relationship between mean annual temperature and a paleosol weathering index pwi that is based on the relative loss of major cations na mg k ca from soil b horizons the new paleothermometer can be applied to clay rich paleosols that originally formed under forest vegetation including inceptisols alfisols and ultisols and halves the uncertainty relative to previous approaches a case study using cenozoic paleosols from oregon united states shows that paleotemperatures produced with this new proxy compare favorably with paleobotanical temperature estimates global climatic events are also evident in the oregon paleosol record including a 2 8 c drop across the eocene oligocene transition comparable to marine records and a neogene peak temperature during the mid miocene climatic optimum

quantitative analysis of land surface topography land surface topography significantly affects the processes of runoff and erosion a system which determines slope aspect and curvature in both the down slope and across slope directions is developed for an altitude matrix also the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix a fortran 66 program performs the analysis

changes in geometry and subglacial drainage of midre lovenbreen svalbard determined from digital elevation models digital elevation models dems of the bed and surface of the polythermal midre lovenbreen svalbard are used to identify changes in glacier geometry between 1977 and 1995 the calculated mean annual mass balance 0 61 m water equivalent w e a 1 is more negative than that derived from field measurements 0 35 m w e a 1 although the error associated with this value 0 7 m a 1 suggests that the difference may be accounted for by errors however similar discrepancies between dem based and field based measurements of mass balance have been reported elsewhere in svalbard although errors may be responsible patterns of surface elevation change may also be explained in terms of patterns of ablation accumulation and dynamics the theoretical structure of the subglacial drainage system is modelled using different assumptions about subglacial water pressure in 1977 and 1995 these reconstructions are compared with the observed positions of proglacial outlet streams decreasing subglacial water pressure results in a decrease in the influence of surface morphology and an increase in the role of the bed topography on drainage routing which generally leads to more dispersed drainage long term changes in the position of proglacial outlet streams occur as a result of changes in glacier geometry but short term changes may also occur in response to early season water pressures controlled by meteorological and hydrological conditions copyright 2003 john wiley sons ltd