holocene reef growth in torres strait the platform and fringing reefs of torres strait are morphologically similar to reefs of the northern great barrier reef to the south except that several are elongated in the direction of the strong tidal currents between the coral sea and the gulf of carpentaria surface and subsurface investigations and radiocarbon dating on yam warraber and hammond islands reveal that the initiation and mode of holocene reef growth reflect antecedent topography and sea level history on the granitic yam island fringing reefs have established in some places over a pleistocene limestone at about 6 m depth around 7000 years bp emergent holocene microatolls of porites sp indicate that the reefs have prograded seawards while sea level has fallen gradually from at least 0 8 m above present about 5800 years bp on the warraber island reef platform drilling near the centre indicated a pleistocene limestone foundation at a depth of about 6 m over which reefs established around 6700 years bp reef growth lagged behind that on yam island microatolls on the mature reef flat indicate that the reef reached sea level around 5300 years bp when the sea was around 0 8 1 0 m above present on the reef flat on the western side of hammond island bedrock was encountered at 7 8 m depth overlain by terrigenous mud a progradational reef sequence of only 1 2 m thickness has built seaward over these muds as sea level has fallen over the past 5800 years reef flat progradation on these reefs is interpreted to have occurred by a series of stepwise buildouts marked by lines of microatolls parallel to the reef crest marking individual coalescing coral heads detrital infill has occurred between these this pattern of reef progradation is consistent with the radiocarbon dating results from these reefs and with seismic investigations on the torres reefs

flow resistance in coarse gravel bed rivers flow resistance relations are deduced from data on coarse gravel bed reaches of new zealand rivers measurements of hydraulic variables were made during reasonably uniform subcritical flows at cross sections regular in confirmation channel bed and bank roughness are not distinguished and surface bedmaterial is characterized by the median size when the channel boundary is rigid the darcy weisbach friction factor is only a statistically significant function of the ratio of hydraulic radius to median size of surface bedmaterial a model of this form explained 60 percent of the friction factor variance inherent in the field data set with active bedload transport conditions and changing bed topography the froude number based on median surface bedmaterial size was statistically significant and 40 percent of friction factor variance was explained by this latter model

atoll reef island formation and response to sea level change west island cocos keeling islands abstract reef islands around the margin of coral atolls generally comprise unconsolidated holocene sands and gravels overlying a reef flat or cemented conglomerate platform such islands have accreted within the last 3000 4000 years since sea level has reached a level close to present and the reef flat and conglomerate platform have formed island morphology consists of an oceanward ridge a less distinct lagoonward ridge and low lying central depression several alternative models of how such reef islands might have developed are examined in relation to chronology and sediment provenance particularly in the context of the cocos keeling islands where this issue has been debated since darwin visited the atoll which of these models appears most appropriate for an elongate reef island on the atoll margin is assessed using conventional radiocarbon dating of coral shingle and accelerator mass spectrometry ams radiocarbon dating of individual sand grains from pits across west island the dating results suggest that both coral clasts and individual grains of various components are generally reliable and replicable indicators of the chronology of island accumulation implying rapid transport of skeletal material after death of the contributing organisms across the reef flat zone and relatively little reworking the central part of west island appears to have formed first with oceanward accretion up until about 2000 years bp gradual oceanward accretion with lesser lagoonward extension has continued beyond 2000 years bp at the northern and southern ends of the island and a sequence of lagoonward recurving spits has formed adjacent to the inter island passage at the southern end of the island radiocarbon dating of fossil microatolls indicates a gradual fall of sea level over this period which appears to have had little effect on the pattern of island accretion

wave energy gradients across a maldivian atoll implications for island geomorphology exposure to wave energy has been used to account for a range of ecological geological and geomorphic processes in coral reef systems but few attempts have been made to quantify spatial variations in energy at the atoll scale this study presents results of measurements of wave energy on reef platforms across south maalhosmadulu atoll maldives and their implications for island geomorphology the atoll has a perforated rim 37 effective aperture and experiences predictable shifts in monsoon winds from the west 8 months and northeast 4 months results show that wave energy affecting the atoll is considerably greater during the westerly monsoon atoll structure promotes significant changes in wave energy and wave characteristics across the atoll short period 3 8 s monsoon driven wave energy which is significant on windward reefs is dissipated on the peripheral reef network and the density of lagoonal patch reefs limits development of locally generated wind wave energy across the lagoon however longer period swell 8 20 s propagates through the lagoon to leeward reefs a windward to leeward decay in wave energy is evident in the westerly monsoon but not in the northeast monsoon when long period swell from the southwest remains significant on western reefs net energy calculations that account for seasonal changes in wave energy across the atoll identify a steep west east gradient that has geomorphic significance for island building western reefs are dominated by westerly flowing energy that is 4 5 7 times the total energy input elsewhere in the atoll wave energy on central reefs is balanced whereas net energy on eastern reef platforms is dominated by eastward propagating waves this steep energy gradient provides a physical explanation for the presence and distribution of islands on reef platforms across the atoll and provides quantitative support for the theory of gardiner gardiner j s 1903 the fauna and geography of the maldives and laccadives archipelagoes cambridge university press london to explain the prevalence of islands on the eastern atoll reef rim

transport and dispersal of organic debris peat blocks in upland fluvial systems this paper assesses the mechanisms and pathways by which peat blocks are eroded and transported in upland fluvial systems observations and experiments from the north pennines uk have been carried out on two contrasting river systems mapping of peat block distributions and appraisal of reach based sediment budgets clearly demonstrates that macro size peat is an important stream load component in small streams block sizes can approximate the channel width and much of the peat is transported overbank local peat jams and associated mineral deposition may provide an important component of channel storage in larger systems peat blocks rapidly move down channel and undergo frequent exchanges between bed and bank storage results of peat block tracing using painted blocks indicate that once submerged blocks of all sizes are easily transported and blocks break down rapidly by abrasion vegetation and bars play an important role in trapping mobile peat in smaller streams large block transport is limited by channel jams smaller blocks are transported overbank but exhibit little evidence of downstream fining in larger rivers peat blocks are more actively sorted and show downstream reduction in size from source a simple model relating peat block diameter dp to average flow depth d suggests three limiting transport conditions flotation dp d 2 and deposition dp d 2 experiments demonstrate that peat block transport occurs largely by rolling and floating and the transport mechanism is probably controlled by relative flow depth d dp ratio transport velocity varies with transport mechanism rolling is the slowest mode and transport lengths increase as flow depth increases abrasion rates vary with the transport mechanism rolling produces greater abrasion rates and more rounded blocks abrasion rates vary from 0 to 10 g m 1 for blocks ranging in mass from 10 to 6000 g copyright 2001 john wiley sons ltd

new model of reef island evolution maldives indian ocean a new model of reef island evolution based on detailed morphostratigraphic analysis and radiometric dating of three islands in south maalhosmadulu atoll maldives is presented islands initially formed on a foundation of lagoonal sediments between 5500 and 4500 yr b p when the reef surface was as much as 2 5 m below modern sea level islands accumulated rapidly during the following 1500 yr effectively reaching their current dimensions by 4000 yr b p since then the high circum island peripheral ridge has been subject to seasonal and longer term shoreline changes while the outer reef has grown upward reducing the energy window and confining the islands this new model has far reaching implications for island stability during a period of global warming and raised sea level which will partially reactivate the energy window although it is not expected to inhibit upward reef growth or compromise island stability

mediated equilibrium the influence of riparian vegetation and wood on the long term evolution and behaviour of a near pristine river analysis of the contemporary geomorphology vegetation and in channel wood within the relatively pristine thurra river in southeastern australia provides insight into river behaviour prior to european disturbance this sand bed river has an extremely low channel capacity with a pronounced pool riffle morphology lateral migration rates are low 11 24 mm a 1 as are floodplain aggradation rates average d 0 27 mm a 1 sedimentological evidence is used to place contemporary channel dynamics within a 16 ka evolutionary framework the floodplain has continuously aggraded over this interval despite a number of avulsions and numerous meander cutoffs avulsions occur on a timeframe of once in 5 ka or more while cutoffs occur around once in 1 ka the morphology and evolution of the thurra river are appraised in terms of a mediated equilibrium condition in which channel capacity hydraulics bedload transport rates bank erosion rates and in channel deposition are substantially influenced by vegetation and wood within the channel and on the floodplain copyright 2002 john wiley sons ltd

global color and albedo variations on triton global multispectral mosaics of triton have been produced from voyager approach images six spectral units are defined and mapped the margin of the south polar cap spc is scalloped and ranges in latitude from 10 deg to 30 deg a bright fringe is closely associated with the cap s margin form it diffuse bright rays extend north northeast for hundreds of kilometers thus the rays may consist of fringe materials that were redistributed by northward going coriolis deflected winds from 1977 to 1989 triton s full disk spectrum changed from markedly red and uv dark to nearly neutral white and uv bright this spectral change can be explained by new deposition of nitrogen frost over both the northern hemisphere and parts of a formerly redder spc frost deposition in the southern hemisphere during southern summer is possible over relatively high albedo areas of the cap stansberry et al 1990 which helps to explain the apparent stability of the unexpectedly large spc and the presence of the bright fringe

archaeological and sedimentological data indicate lapita settlement on a newly formed coastal plain tavua island mamanuca group fiji the timing and choice of initial settlement location are examined on the small island of tavua in fiji s mamanuca group the mid to late holocene sea level retreat influenced the island s coastal landforms through the acceleration of coastal progradation and the production of habitable land archaeological sedimentological and chronological data are integrated to better understand the island s settlement and geomorphological history these datasets are then compared with regional and modeled sea level curves for fiji in order to constrain the time period for the onset of coastal regression the results indicate that tavua was initially settled around 3000 years ago within a few centuries of the formation of the coastal plain integrating archaeological sedimentological and sea level datasets helps produce a more precise understanding of the relationship between sea level change and the timing of settlement on small islands in oceania

unifying criterion for the velocity reversal hypothesis in gravel bed rivers it has been hypothesized that velocity reversals provide a mechanism for maintaining pool riffle morphology in gravel bed rivers an important habitat for salmonids which are at risk in many places worldwide and that are the focus of extensive environmental legislation in europe and north america however the occurrence of velocity reversals has been controversial for over 3 decades we present a simple one dimensional criterion that unifies and explains previous disparate findings regarding the occurrence of velocity reversals results show that reversal depends critically on the ratio of riffle to pool width residual pool depth difference between pool and riffle elevations and on the depth of flow over the riffle suggesting that land management activities which alter channel form or divert water from the channel can have negative impacts on the sustainability of pool riffle habitat in gravel bed rivers

a morphodynamic model of reef island development on atolls abstract reef islands on the rims of atolls are deposits of unconsolidated reef sediment that have accumulated as a result of sediment transportation processes reef islands appear especially vulnerable to changing environmental conditions particularly regarding the impact of sea level rise the morphodynamic processes involved in the development of these landforms however are poorly understood and difficult to observe over long time periods several conceptual models of reef island development have been proposed that offer insights into reef island behaviour particularly where these models can be implemented in a computational framework this paper presents an aggregated scale behaviour oriented model that simulates sediment accumulation on an atoll rim a requirement of the behaviour based modeling approach is that the model parameters need to be determined for each application of the model an inversion algorithm is used to estimate values for model parameters including the maximum volume of the island and the sediment production rate the model provides a framework for experimentation with modes of island development links sediment production to the observed morphology of the reef island and quantifies the limits to reef island development

evidence for coral island formation during rising sea level in the central pacific ocean the timing and evolution of jabat island marshall islands was investigated using morphostratigraphic analysis and radiometric dating results show the first evidence of island building in the pacific during latter stages of holocene sea level rise a three phase model of development of jabat is presented initially rapid accumulation of coarse sediments on jabat occurred 4800 4000 years b p across a reef flat higher than present level as sea level continued to rise during the highstand island margins and particularly the western margin accreted vertically to 2 5 3 0 m above contemporary ridge elevations this accumulation phase was dominated by sand size sediments phase three involved deposition of gravel ridges on the northern reef as sea level fell to present position jabat has remained geomorphically stable for the past 2000 years findings suggest reef platforms may accommodate the oldest reef islands in atoll systems which may have profound implications for questions of prehistoric migration through pacific archipelagos

assessment of flow forces on large wood in rivers 1 large wood lw exerts an important influence on the geomorphology and ecology of streams and rivers the magnitudes of flow forces on lw are needed to support stream management activities and are typically computed using time mean lift and drag coefficients determined in laboratory flumes using small smooth cylinders herein we report measurements of forces on lw of varying complexity simple cylinder branching and complex root wad and surface bark roughness made in an outdoor grassed channel under steady and unsteady flows lw orientation relative to the primary flow direction and lw relative submergence were varied drag and lift coefficients for cylindrical unbranched lw followed patterns reported by others for metal cylinders in wind tunnels drag coefficients for cylindrical unbranched lw corrected for blockage effects ranged from 0 05 to 1 29 and lift coefficients ranged from 0 88 to 0 52 varying systematically with lw position relative to the channel bed and incident flow direction measured drag coefficients for the noncylindrical lw corrected for blockage effects ranged from 0 22 to 6 27 while lift coefficients varied from 3 65 to 30 84 systematic relationships between the relative submergence and orientation of branching lw and the drag and lift coefficients were not observed but coefficients were greatest for lw with few branches and converged on smaller values typical of blunt bodies as lw complexity increased for both simple and complex lw maximum lift and drag forces during the rising limb of unsteady flows were about 2 3 times greater than steady flow temporal mean values

a comparison of settling and sieve techniques for the analysis of bioclastic sediments this paper examines differences in the use of sieve and settling techniques for the determination of textural parameters of grain size distributions for 30 bulk bioclastic reefal deposits and examines the interpretive use of the results a comparison of results of the key textural parameters shows that sieve size estimates deviate from settled size determinations of mean grain size and dispersion values by up to 2 and up to 1 5 phi units respectively these differences are explained by the different grain properties measured by the two techniques exacerbated by the heterogeneous character of bioclastic deposits changes in sample components which control grain shape and grain bulk sample density also influence the magnitude of size and dispersion differences observed differences are discussed in relation to interpretation of the depositional environment and hydraulic regime leading to the conclusion that sieve results can grossly distort depositional and energy processes operating within bioclastic environments in contrast settled size estimates an index of deposit hydraulic behaviour show that bioclastic sediment transport systems operate within a much narrower energy regime than sieve sizes suggest hydraulic size estimates are considered to provide a better tool with which to interpret sedimentary processes in bioclastic environments

incremental accretion of a sandy reef island over the past 3000 years indicated by component specific radiocarbon dating 1 low lying reef islands appear particularly threatened by anticipated sea level rise and determining how they formed and whether they are continuing to accumulate sediment is essential for their sustainable management depositional chronology of warraber island a small sand cay in torres strait australia is re examined based on ams radiocarbon dating of specific skeletal components whereas radiometric dating of bulk sand samples indicated one or more discrete phases of mid late holocene deposition component specific ams radiocarbon dating of sand grains indicates sustained incremental growth over the past 3000 years ages on gastropods that lived on the reef flat around the island indicate continuing sediment production and island progradation in contrast to bulk ages and other components produced at greater distances growth of sand cays depends on the rate and pattern of sediment supply which are functions of the local ecology of the surrounding reef and reef flat and hydrodynamic constraints

prediction of effects of woody debris removal on flow resistance a simple technique for predicting the darcy weisbach friction factor for river channels with varying amounts of large woody debris was developed first debris density is determined based on measurement or visual estimation of cross sectional areas of debris formations in the plane perpendicular to flow the darcy weisbach friction factor is then computed using debris density channel geometry mean flow velocity and the debris drag coefficient the debris drag coefficient may be computed fom a power function with experimentally determined coefficients for verification of the proposed procedure debris density and friction factors were measured in river reaches in western tennessee and southeastern new south wales australia friction factors computed using the procedure were within 30 of measured values for straight sand bed reaches and within 38 of measured values for sinuous gravel bed reaches the computational procedure explained 84 of the variance in observed values

flow resistance estimation in mountain rivers examination of the flow resistance of high gradient gravel and boulder bed rivers using data collected in british mountain rivers with slopes of 0 4 4 shows that there are differences in resistance variation between mountain and lowland rivers and that between site variations do not necessarily reflect at a site variations comparison of data with the familiar resistance equation relating the dracy weisbach friction factor to the logarithm of relative submergence shows that the equation tends to overestimate the resistance in uniform flow the equation also tends to underestimate the rate of change of resistance at a site as discharge varies with high gradients the influences of nonuniform channel profile sediment size distribution channel slope and sediment transport are reviewed but the data do not allow any quantification of these effects instead an empirical approach based on the available data is presented allowing the friction factor to be calculated from the relative submergence with an error of up to n25 to n35 a summary of the field data is included

an analytical numerical approach to the hydraulics of floating debris in river channels a new simplified approach is developed for the channel flow dynamics under woody debris transport a continuous carpet of debris is considered covering a uniform stationary current due to the floating debris the shear stresses in the fluid domain are affected as a result the velocity profile is different from the free surface flow the simple model proposed here is able to capture the essential features of flow response to woody debris transport velocity and stress profiles are analytically derived for laminar flow and compared with the zero debris condition more realistic turbulent currents are simulated with the reynolds equations where turbulent stresses are modeled by the simple mixing length concept validation is carried out by comparison with experimental velocity profiles and with direct numerical simulation of the navier stokes equations synthetic diagrams are proposed for the calculation of the flow velocity and the bed shear stresses in terms of the relevant non dimensional parameters

the geomorphology development and temporal dynamics of tepuka island funafuti atoll tuvalu abstract the evolution sedimentary structure and morphodynamics of tepuka island a leeward vegetated sand cay on funafuti atoll tuvalu was examined based on morphostratigraphic analysis and radiometrically dated island sediments tepuka island formed rapidly on the leeward reef platform between 1100 and 500 cal years bp and presents the first evidence of island formation at current sea level postdating the holocene highstand the island is predominantly composed of foraminifera coralline algae and coral sands derived from the surrounding reef flat morphostratigraphic analysis suggests that the island formed as a central core and prograded rapidly through incremental accumulation results indicate that the vegetated core of tepuka has been stable since formation but the island margins have been morphologically dynamic over the past century the island has reduced in net area by approximately 23 substantial planform changes have been documented which have occurred through differential erosion of the shoreline in two phases lagoon shoreline erosion from 1897 to 1984 and ocean shoreline coupled with extension of the terminal ends of islands from 1984 to 2011 collectively these changes have caused a lengthening and clockwise rotation of the island on the reef platform the investigation highlights significant differences in the geomorphology sediment composition timeframe of formation and post formation island dynamics compared with the storm deposited and comparatively stable motu on the exposed eastern atoll rim

a depth averaged two dimensional model for flow sediment transport and bed topography in curved channels with riparian vegetation 1 a depth averaged two dimensional numerical model has been developed to simulate flow sediment transport and bed topography in river channels with emergent and submerged rigid vegetation and large woody debris the effect of helical flow in bends is considered by adopting an algebraic model for the dispersion terms in the depth averaged two dimensional momentum and suspended sediment transport equations and by adjusting the bed load transport angle the governing equations are discretized using the finite volume method on a nonstaggered curvilinear grid model validity has been assessed using experimental data observed in both fixed and movable bed laboratory flumes and a natural channel with submerged and emergent rigid vegetation in general mean flow velocities sediment transport rates and changes in bed topography predicted by the model agree well with the experimental observations for laboratory and field cases root mean square relative errors for velocities were less than about 13 and 44 respectively and about 50 of errors for changes in bed topography were less than 14 5 and 8 of the flow depth respectively

tropical sand cays as natural paleocyclone archives sand cays are valuable paleo archives that can significantly increase our understanding of holocene tropical cyclone variability here we conducted detailed sedimentological and chronological analyses from a 195 cm depth pit excavated on guangjin island northern south china sea a cay influenced by frequent tropical cyclones radiometric dating of multiple deposits revealed that foraminifera soft coral spicules and gastropod shells yielded variable age distributions while u th ages of pristine acropora branches provided a clear record of deposition and cay formation based on this robust chronostratigraphy the proportions of 2 mm grain size fraction within the deposits corresponded with the frequency of paleotyphoons recorded by historical records in recent centuries u th ages ce 1687 12 ce 1735 6 and ce 1813 5 of acropora branches from the deposits matched with three known historical typhoon events our results highlight the potential of cyclone deposited sand cays as new archives for recording paleocyclones

the influence of thermal inertia on temperatures and frost stability on triton abstract seasonal subsurface heat conduction can have a large influence on triton s n2 frost distribution increasing surface thermal inertia reduces the thickness and extent of seasonal n2 frosts if the thermal inertia of the nonvolatile substrate is greater than about 30 of the value for nonporous h2o or co2 or if nonporous h2o or co2 is overlaid by a porous regolith of low thermal inertia but less than a few meters thick the northernmost latitudes visible to voyager should have been frost free at the time of the encounter possibly accounting for their relatively low albedo if the substrate in the northern hemisphere has sufficiently low albedo and or emissivity and also has a thermal inertia comparable to that of nonporous h2o or co2 there may be no seasonal or permanent n2 deposits in the northern hemisphere at all because this model like previous ones predicts a monotonic recession of permanent n2 deposits toward the poles and very limited seasonal n2 frost in the southern hemisphere at voyager time and because of new spectroscopic evidence for nonvolatile co2 on triton s bright southern hemisphere we consider it possible that much of the bright material on triton s southern hemisphere is not n2 bright nonvolatiles in the southern hemisphere may allow seasonal n2 frosts to form there during the southern summer possibly helping to explain triton s spectroscopic changes during the past decade all the models considered here predict 10 fold or greater seasonal variations in atmospheric pressure with pressure currently increasing in high thermal inertia models and decreasing in models with low thermal inertia

surface and airborne evidence for plumes and winds on triton aeolian features on triton that were imaged during the voyager mission have been grouped the term aeolian feature is broadly defined as features produced by or blown by the wind including surface and airborne materials observations of the latitudinal distributions of the features probably associated with current activity known plumes crescent streaks fixed terminator clouds and limb haze with overshoot all occur from latitude 37 to latitude 62 likely indicators of previous activity dark surface streaks occur from latitude 5 to 70 but are most abundant from 15 to 45 generally north of currently active features those indicators which give information on wind direction and speed have been measured wind direction is a function of altitude the predominant direction of the surface wind streaks is found to be between 40 and 80 measured clockwise from north the average orientation of streaks in the northeast quadrant is 59 winds at 1 to 3 kilometer altitude are eastward while those at 8 kilometers blow west

the effect of surface roughness on triton s volatile distribution calculations of radiative equilibrium temperatures on triton9s rough surface suggest that significant condensation of n 2 may be occurring in the northern equatorial regions despite their relatively dark appearance the bright frost is not apparent in the voyager images because it tends to be concentrated in relatively unilluminated facets of the surface this patchwork of bright frost covered regions and darker bare ground may be distributed on scales smaller than that of the voyager resolution as a result the northern equatorial regions may appear relatively dark this hypothesis also accounts for the observed wind direction in the southern hemisphere because it implies that the equatorial regions are warmer than the south polar regions

modeling entrainment of waterlogged large wood in stream channels 1 research has led to an understanding of how floatable wood provides physical complexity and habitat in streams but little is known about large wood that does not float because it is waterlogged mineralized or naturally heavier than water to better understand the dynamics of this largely unrecognized component of streams i derived a theoretical model for predicting entrainment of waterlogged logs then constructed prototype logs to simulate waterlogged wood and used them to measure log friction and critical flow velocities at log entrainment in an alluvial creek i then modeled critical velocities under the same conditions entrainment was observed the model underpredicted critical velocities by an average of 24 with a range of error from 8 to 69 sensitivity analyses indicated that reducing lift and drag coefficients improved the average error but not the error range lack of unique drag coefficients for prototype logs winnowing of bed material from around prototype logs during entrainment tests error estimating friction for logs approaching neutral buoyancy and the variability of flow velocity common in streams were probable causes of error observed critical velocities that entrained prototype logs averaged 0 70 m s 1 critical velocities and log friction increased with branch length bed roughness and log density but only friction increased with log length friction coefficients averaged 0 62 and increased with branch length and bed roughness this model and existing equations for predicting movement of buoyant large wood can be used to compute budgets for logs with a range of attributes in streams

photometry of triton 1992 2004 surface volatile transport and discovery of a remarkable opposition surge abstract triton the large satellite of neptune was imaged by the voyager 2 spacecraft in 1989 with dark plumes originating in its volatile rich south polar region southern summer solstice a time when seasonal volatile transport should be at a maximum occurred in 2001 ground based observations of triton s rotational light curve obtained from table mountain observatory in 2000 2004 reveal volatile transport on its surface when compared with a static frost model constructed from voyager images the light curve shows an increase in total amplitude an earlier light curve obtained in 1992 from mauna kea observatory is consistent with the static frost model this movement of volatiles on the surface agrees with recent imaging results from the hubble space telescope bauer j m buratti b j li j y mosher j a hicks m d schmidt b e goguen j d 2010 astrophys j 723 l49 l52 the changes in the light curve can be explained by the transport of nitrogen frost on the surface or by the uncovering of bedrock of less volatile methane we also find that triton exhibits a large opposition surge at solar phase angles less than 0 1 this surge cannot be entirely explained by the effects of coherent backscatter

global albedos of pluto and charon from lorri new horizons observations abstract the exploration of the pluto charon system by the new horizons spacecraft represents the first opportunity to understand the distribution of albedo and other photometric properties of the surfaces of objects in the solar system s third zone of distant ice rich bodies images of the entire illuminated surface of pluto and charon obtained by the long range reconnaissance imager lorri camera provide a global map of pluto that reveals surface albedo variegations larger than any other solar system world except for saturn s moon iapetus normal reflectances on pluto range from 0 08 1 0 and the low albedo areas of pluto are darker than any region of charon charon exhibits a much blander surface with normal reflectances ranging from 0 20 0 73 pluto s albedo features are well correlated with geologic features although some exogenous low albedo dust may be responsible for features seen to the west of the area informally named tombaugh regio the albedo patterns of both pluto and charon are latitudinally organized with the exception of tombaugh regio with darker regions concentrated at the pluto s equator and charon s northern pole the phase curve of pluto is similar to that of triton the large moon of neptune believed to be a captured kuiper belt object kbo while charon s is similar to that of the moon preliminary bond albedos are 0 25 0 03 for charon and 0 72 0 07 for pluto maps of an approximation to the bond albedo for both pluto and charon are presented for the first time our work shows a connection between very high albedo near unity and planetary activity a result that suggests the kbo eris may be currently active

late holocene sea level change and reef island evolution in new caledonia abstract in new caledonia numerous cays are distributed on platform reefs in the southwest lagoon behind the barrier reef at mba island a vegetated sand cay in this area we examined holocene sea level change and reef development and evolution the late holocene sea level curve for the area was updated using newly found fossil microatolls component specific dating of foraminifera tests in the island sediment provided reliable ages of island formation mba island initially formed around 4500 cal yr b p when sea level was 1 1 m higher than at present the island formed on the leeward side of the platform reef where the base had been constructed of lagoon and reef derived sediment of the platform reef sea level fall since 2800 cal yr b p has likely caused reef flat emergence at low tide and created a suitable habitat for foraminifera such a transition in ecology due to sea level fall has been observed in other pacific reefs suggesting that the interaction between reef flat formation sediment production and sea level fall is one of the critical factors determining island development

paleoshoreline record of relative holocene sea levels on pacific islands abstract understanding the history of relative holocene sea levels on pacific islands is important for constraining fundamental geodynamic theories interpreting the environments of early human occupation sites and forecasting future environmental conditions on the islands an observational paleoshoreline record is provided by emergent paleoshoreline indicators formed at higher relative sea levels hence standing at higher elevations than modern counterparts emergent paleoshoreline notches in limestone seacliffs record paleo high tide levels and emergent paleoreef flats record paleo low tide levels whereas emergent paleobeachrock locally records paleo intertidal levels both paleonotches and paleoreefs occur along the coasts of high standing islands exposing volcanic bedrock and uplifted reef complexes but low lying coralline atolls lack sufficient relief to preserve paleonotches controls on relative holocene sea level include global eustatic and regional hydro isostatic changes in ambient sea level relative to island landmasses and shifts in the elevations of islands relative to sea level caused by thermal subsidence of the oceanic lithosphere or thermally rejuvenated loci of hotspot volcanism by flexure of the lithosphere under the load of growing volcanic edifices hawaii samoa society islands by arching of the lithosphere over trench forebulges loyalty islands niue bellona rennell and by tectonism within forearc belts between active volcanic chains and trenches mariana islands tonga vanuatu the dominant pattern of relative sea level change where not overprinted by local tectonism or lithospheric flexure was a uniform early holocene rise in eustatic sea level followed by a regionally variable late holocene hydro isostatic drawdown in sea level the resultant was a mid holocene highstand in relative sea level that affected the development of shoreline morphology throughout the tropical pacific ocean the earliest human migrations into intra oceanic island groups of both the northwestern and southwestern pacific ocean followed close on the heels of the mid holocene sea level highstand and took advantage of newly attractive coastal environments engendered by sea level drawdown the effects of the mid holocene highstand were modified to varying degrees in different island groups by geodynamic uplift or subsidence

a roughness corrected index of relative bed stability for regional stream surveys abstract quantitative regional assessments of streambed sedimentation and its likely causes are hampered because field investigations typically lack the requisite sample size measurements or precision for sound geomorphic and statistical interpretation we adapted an index of relative bed stability rbs for data calculated from a national stream survey field protocol to enable general evaluation of bed stability and anthropogenic sedimentation in synoptic ecological surveys rbs is the ratio of bed surface geometric mean particle diameter dgm divided by estimated critical diameter dcbf at bankfull flow based on a modified shield s criterion for incipient motion application of rbs to adequately depict bed stability in complex natural streams however has been limited because typical calculations of rbs do not explicitly account for reductions in bed shear stress that result from channel form roughness we modified the index rbs to incorporate the reduction in bed shear stress available for sediment transport that results from the hydraulic resistance of large wood and longitudinal irregularities in channel dimensions form roughness based on dimensional analysis we derived an adjustment to bankfull shear stress by multiplying the bankfull hydraulic radius rbf by the one third power of the ratio of particle derived resistance to total hydraulic resistance cp ct 1 3 where both resistances are empirically based calculations we computed cp using a keulegan equation relating resistance to relative submergence of bed particles we then derived an empirical equation to predict reach scale hydraulic resistance ct from thalweg mean depth thalweg mean residual depth and large wood volume based on field dye transit studies in which total hydraulic resistance ct was measured over a wide range of natural stream channel complexity including manipulation of large wood volumes we tested our estimates of ct and rbs by applying them to data from a summer low flow probability sample of 104 wadeable stream reaches in the coastal ecoregion of oregon and washington usa stream discharges calculated using these ct estimates compared favorably with velocity area measurements of discharge during summer low flow and with the range of 1 to 2 year recurrence floods scaled by drainage area at u s geological survey gauged sites in the same region log rbs ranged from 4 2 to 0 98 in the survey region dgm ranged from silt to boulders while estimated bankfull critical diameter d cbf ranged from very fine gravel to large boulders the median value of d cbf adjusted for form roughness influences averaged 40 inter quartile range 28 to 59 of the unadjusted estimate dcbf log rbs was consistently negatively related to human disturbances likely to produce excess sediment inputs or hydrologic alteration log rbs ranged from 1 9 to 0 5 in the streams within the lower quartile of human disturbance in their basin and riparian areas and was substantially lower 4 2 to 1 1 in streams within the upper quartile of human disturbance the synoptic survey methods and designs we used appear adequate to evaluate regional patterns in bed stability and sedimentation and their general relationship to human disturbances although the rbs concept also shows promise for evaluating sediment and bed stability in individual streams our approach is relatively coarse so site specific assessments using these rapid field methods might prudently be confined to identifying severe cases of sedimentation or channel alteration greater confidence to discern subtle differences in site specific assessments could be gained by calculating rbs using more precise field measurements of channel slope bed particle size and bankfull dimensions and by refining our adjustments for energy loss from channel form roughness

radiocarbon evidence for the timing and rate of island development beach rock formation and phosphatization at lady elliot island queensland australia abstract lady elliot island great barrier reef is a coral cay constructed from near concentric shingle ridges composed of coral tridacna shells and bioclastic sand bound by guano derived phosphatic cement radiocarbon dating of individual tridacna samples is used to investigate the evolution of the island and place constraints on the variations in storminess of the last 3200 years a shallow platform reef existed at lady elliot since at least 6500 yrs b p shortly before 3200 yrs b p island growth by shingle progradation commenced and proceeded to the present at a rather uniform lateral rate 60 m ka 1 to leeward and 90 m ka 1 windward phosphatization may have occurred continuously or episodically at any time throughout the last 3200 years the youngest cemented ridge top is less than 770 years whereas at the base of uncemented ridges phosphatization is a modern 1950 a d process similarly low level beach rock has continued to form within the last 25 years a significant period of instability occurred less than 500 years ago during which marine erosion truncated the southwestern extremity of lady elliot island formed an eastern spit and stranded high level beach rock however the radiocarbon ages of tridacna samples from shingle ridges from lady elliot and curacoa islands are uniformly distributed kolmogorov smirnov test throughout the last 4000 years we interpret this to indicate no significant variation in ridge forming processes or fluctuation in average storminess during this interval

reef island accretion and soil development on makin kiribati central pacific the late holocene accretionary history of reef islands on makin the northernmost table reef of the gilbert atoll chain western kiribati has been reconstructed based on conventional radiocarbon dating of coral shingle and bulk sand samples and ams radiocarbon dating of individual grains makin is geomorphologically and sedimentologically simple comprising one main island with only a minor residual lagoon and composed of sand dominated by the reef flat foraminifera calcarina spengleri amphistegina lobifera and baculogypsina sphaerulata deposition commenced in mid platform around 2500 years ago in situ fossil coral heliopora dated at 2400 80 years bp indicates that sea level was 0 4 0 5 m above present at that time progradation occurred progressively to westward at a relatively constant rate of 200 300 m ka 1 however progradation was interrupted on the eastern side by lagoon encapsulation around 1400 years ago the soil and vegetation characteristics are uniform over most of the reef islands as a result of clearance and the planting and maintenance of coconuts and do not reflect reef island depositional history remnant stands of pisonia forest with an associated phosphatic soil are not related to any particular geomorphological feature or period of deposition the reef islands are continuing to accrete as a result of production of foraminifera on the reef flat

beach development on an uplifted coral atoll niue south west pacific abstract niue is an uplifted coral atoll in the south western pacific characterised by erosional terraces on its coastal margin beaches are found around the island located in pockets at the rear of erosional shore platforms the beaches in niue are

rapid reef island formation and stability over an emerging reef flat bewick cay northern great barrier reef australia a model that resolves reef island formation in relation to both reef platform substrate development and mid holocene sea level change is presented for bewick island northern great barrier reef based on morphostratigraphic analysis and radiometrically dated island sediments and reef corals on bewick island microatolls record reef flat development at higher sea level 1 5 m by 6500 yr b p island building began on a partially emergent reef flat 5000 4000 yr b p when sea level was 0 5 m above present as sea level fell to its present level the reef platform process window closed and the island core stabilized results present the first unequivocal evidence of island building directly over a reef flat comprising microatolls and the first detailed model of island formation from the great barrier reef the model demonstrates that the interplay of sea level and reef surface elevation can vary between sites but their convergence is critical for island initiation future trajectories of island change will vary dependent on the unique relative sea level and substrate depth conditions that govern island formation

radiometric performance of the voyager cameras the voyager imaging experiment provided high quality data of jupiter and the galilean satellites with the two flyby trajectories in march and july of 1979 moderately accurate radio metric measurements have been made using these data this paper evaluates the radiometric results and describes the inflight and ground geometric and radiometric correction factors the radiometric quantities of intensity i and geometric albedo i f are derived and scaling factors for each of the filters are tabulated for correcting the calibrated data from the image processing laboratory at jpl in addition the key characteristics of both voyager 1 and voyager 2 cameras are tabulated

triton s plumes the dust devil hypothesis triton s plumes are narrow columns 10 kilometers in height with tails extending horizontally for distances over 100 kilometers this structure suggests that the plumes are an atmospheric rather than a surface phenomenon the closest terrestrial analogs may be dust devils which are atmospheric vortices originating in the unstable layer close to the ground since triton has such a low surface pressure extremely unstable layers could develop during the day patches of unfrosted ground near the subsolar point could act as sites for dust devil formation because they heat up relative to the surrounding nitrogen frost the resulting convection would warm the atmosphere to temperatures of 48 kelvin or higher as observed by the voyager radio science team assuming that velocity scales as the square root of temperature difference times the height of the mixed layer a velocity of 20 meters per second is derived for the strongest dust devils on triton winds of this speed could raise particles provided they are a factor of 103 to 104 less cohesive than those on earth

sand cay evolution on reef platforms mamanuca islands fiji abstract the sedimentary link between reef islands and their surrounding platforms is critical to understand if the morphological response of these systems to future boundary condition changes such as associated with human induced climate change is to be understood the sand cays of the mamanuca islands in fiji are an ideal system to investigate this link between reef and the islands that have developed on them the mamanuca s are a relatively simple sedimentary system being characterised by oval shaped platform reefs with a relatively uniform and horizontal reef crest and flat nine islands were investigated within the group through gps and auto level surveying with associated surface and subsurface sediment sampling the islands are composed of a typical chlorozoan sediment assemblage which is well mixed across each reef and island this mixing is related to the high transport capacity across the reef platforms with waves able to move sediment for at least 50 of the tidal cycle radiocarbon dating indicates the islands are young with modern ages returned on sand from the reef flat and ages of 500 600 years calbp from the island beaches dating from the centre of the islands at 2 m depth indicate island formation was occurring from at least 2260 2110 years calbp the young age of the sediments combined with the high transport potential suggests each cay is linked to the contemporary reefs that the islands are developed on it is inferred that the islands in the mamanuca group initially started as a subtidal gravel accumulation once wave energy is dissipated enough intertidal sands start to accumulate and eventually the islands reach a critical size where vegetation may colonise the contemporary development of the reef islands in the mamanuca s and their links to sediment production on the reef flat suggests that they may be able to adjust their morphology to future environmental conditions

influence of large woody debris on morphological evolution of incised sand bed channels this paper documents the influence of large woody debris lwd on the morphological evolution of unstable degrading sand bed rivers in the yazoo basin north mississippi usa the study was performed as part of the demonstration erosion control dec project twenty three river reaches were studied with the aim of determining whether the presence of lwd was beneficial or detrimental to the recovery of stability in degrading sand bed river systems and to provide the geomorphic understanding necessary to underpin enhanced lwd management strategies the results demonstrate that locations of lwd inputs volumes of lwd stored in different reaches and number of jams per unit channel length are causally related to the morphological processes occurring during different stages of adjustment in these unstable incised fluvial systems and may be explained using a channel evolution model cem the net impact of lwd jams on reach scale sediment budgets was found in general to be positive that is jams trap more sediment than they mobilise this suggests that lwd probably accelerates rather than retards recovery of a stable longitudinal profile and channel configuration following incision field typing of lwd jams based on their impacts on the flow pattern reveals that jam type is a function of the size of large key elements in the jam in relation to the channel width a debris jam classification scheme is proposed on this basis with the spatial relationship between jam type and drainage basin area expressed using a dimensionless function of the ratio between channel width and average riparian tree height the scheme features four jam types underflow dam deflector and flow parallel bar head each of which has a different morphological impact on local channel geometry these jam types may be used to classify lwd jams as an aid in determining appropriate management strategies according to their location within the drainage basin

constraints on europa s surface properties from primary and secondary crater morphology 1 we investigate the near surface properties of europa s ice shell by examining small crater morphology we use both primary and secondary craters for our analysis for primary craters the simple to complex transition provides an estimate of 0 19 0 36 mpa for the cratering effective strength through the aggregate statistics of over 100 profiles we find that secondary craters on europa tend toward smaller depth to diameter d d ratios than primary craters consistent with observations on other cratered surfaces the moon and mars in addition we find that adjacent secondaries tend to be more shallow than distant secondaries also consistent with trends seen on the moon and mars the presence of numerous and far flung secondaries requires a solid competent surface for spallation that is inconsistent with weak ice although the effective strength evaluated by crater scaling laws does not have a direct quantitative relationship to lab based measurements of shear or tensile strength comparison to other observationally derived effective strengths and geologic materials suggests that the mechanical properties of europa s surface ice should be consistent with terrestrial measurements of cold ice

eco geomorphic processes that maintain a small coral reef island ballast island in the ryukyu islands japan abstract landform changes in ballast island a small coral reef island in the ryukyu islands were investigated by remote sensing analysis and a field survey the area of the island almost doubled after a mass coral bleaching event in 1998 coral branches generated by the mass mortality and broken by waves were delivered and stocked on a reef flat and accumulated to expand the area of the island in 2012 high waves generated by typhoons also changed the island s topography overall the island moved in the downdrift direction of the higher waves waves impacting both sides of the island piled up a large volume of coral gravels above the high tide level eco geomorphic processes including a supply of calcareous materials from the corals on the same reef especially during stormy wave conditions were key factors in maintaining the dynamic topographic features of this small coral reef island