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

responses of stable bay margin and barrier island systems to holocene sea level highstands western gulf of mexico abstract the microtidal wave dominated coast of the western gulf of mexico displays a variety of holocene geomorphic features indicating higher than present water levels that were previously attributed to storm processes while geoidal sea level was at its present position field and aerial photograph examinations of bay margins barrier islands and beach ridge plains following major hurricanes show that the elevated features are inundated periodically by high storm surge despite their inundation these highstand features are not modified by modern storm processes instead storm related erosion and deposition are always seaward of and lower than the highstand features and are always limited to the extant shorezone where elevations typically are less than 1 5 m above present sea level bay margin and lagoonal highstand indicators include raised marshes and subtidal flats wave cut benches abandoned wave cut scarps with fringing marshes and or beach ridges and accretionary islands and recurved spits other emergent marine features include abandoned compound flood tidal delta and washover fan complexes attached to barrier islands and anomalously high beach ridges within both the barrier island complexes and beach ridge plains the highest beach ridges raised marshes and flats and erosional scarps and benches are manifestations of one or more rising phases and highstands in sea level whereas the lower marshes and accretionary topography are mainly products of the falling phases and shoreface adjustment to present sea level different elevations of beach ridge sets discordant truncation of beach ridges and elevated marine and brackish water faunal assemblages preserved in beach ridges raised marshes and flats and natural levees are compelling evidence of sea level fluctuations of 1 to 1 5 m from about 5500 to 1200 cal yr bp independent evidence from studies of geodynamic climatic and glacio eustatic processes can explain the mid holocene highstands and late holocene lowering of sea level that is observed in tectonically stable coastal regions far from former centers of glaciation

effects of sample disturbance on the stress induced microfracturing characteristics of brittle rock the effects of sampling disturbance on the laboratory derived mechanical properties of brittle rock were measured on cored samples of lac du bonnet granite taken from three different in situ stress

late quaternary reef growth and sea level in the maldives indian ocean abstract based on rotary drilling and radiometric and u series dating we present the first comprehensive data on holocene reef anatomy and sea level rise as well as nature and age of underlying pleistocene limestone in the maldives holocene reefs in rasdhoo atoll central maldives are composed of four facies including 1 robust branching coral facies 2 coralline algal facies 3 domal coral facies and 4 detrital sand and rubble facies branching coral and coralline algal facies predominate the marginal reefs and domal corals and detrital facies preferentially occur in a lagoon reef in addition microbialite crusts are found in lower core sections of marginal reefs microbialites formed during the early holocene in reef cavities holocene reef thickness ranges from 14 5 m to 22 m reef growth started as early as 8 5 kyr bp marginal reefs accreted in the keep up mode with rates of 15 m kyr rate of sea level rise significantly slowed down from 7 6 kyr bp and subsequently gradually rose with rates

formation of a jump by the dam break wave over a granular bed a previously unreported shock feature associated with the scouring of a horizontal granular bed by a dam break wave is discussed near the wave centre the present study shows the free surface breaks backward and a hydraulic jump forms this behaviour is described from the standpoint of shallow water theory suitably extended to deal with non equilibrium sediment transport the shock formation involves a particularly strong coupling between flow free surface evolution and bed morphodynamics support for our conclusions is sought through experimental and numerical approaches in order to magnify the observed phenomena measurements were performed for the case of light bed particles moving in sheet and debris flow modes a detailed picture of the transient two phase flow is presented based on whole field acquisition of the grain motions by particle tracking techniques corresponding shallow water solutions are constructed numerically using a shock capturing scheme finally an interpretation of the jump formation is proposed based on the theory of characteristics

three dimensional time lapse velocity tomography of an underground longwall panel three dimensional velocity tomograms were generated to image the stress redistribution around an underground coal longwall panel to produce a better understanding of the mechanisms that lead to ground failure especially rockbursts mining induced microseismic events provided passive sources for the three dimensional velocity tomography surface mounted geophones monitored microseismic activity for 18 days eighteen tomograms were generated and high velocity regions correlated with high abutment stresses predicted by numerical modeling additionally the high velocity regions were observed to redistribute as the longwall face retreated indicating that velocity tomography may be an appropriate technology for monitoring stress redistribution in underground mines

microatolls and recent sea level change on coral atolls microatolls are colonies of corals commonly porties which are dead on top but living around their perimeter and are found in intertidal environments on coral atolls they can grow to several metres in diameter their upward growth is constrained by sea level through prolonged exposure at the lowest spring tides1 2 and their dead upper surfaces have been limited by past sea levels they act as natural recorders of sea level which is of particular significance for coral atolls thought to be susceptible to inundation and erosion if sea level rises in response to global warming x radiographs of vertical slices through microatolls from the maldives and cocos keeling islands indian ocean and kiribati pacific ocean record sea level fluctuations over the past few decades there is a high degree of reproducibility between adjacent corals although on cocos we noted geographical variation in the pattern of change around the atoll the majority of microatolls sampled on these atolls record a slight fall in sea level over the past ten years

the magnitude of a mid holocene sea level highstand in the strait of makassar abstract knowledge on the timing and magnitude of past sea level changes is essential to understand modern and future sea level variability holocene sea level data from literature on the west coast of sulawesi central indonesia suggest that this region experienced two relative sea level highstands over the last 6000 years with magnitudes exceeding two meters however recent datasets from the indo pacific region do not support high magnitude sea level oscillations during the holocene in tectonically stable far field locations here we present a new high precision mid holocene sea level dataset from the spermonde shelf off southwest sulawesi we surveyed 21 fossil microatolls on the reef flats of two coral islands pulau panambungan and pulau barrang lompo and referred their elevations to local mean sea level and to the height of living coral radiometrically calibrated ages from emergent fossil microatolls on pulau panambungan indicate a relative sea level highstand not exceeding 0 5 m above present at ca 5600 cal yr bp the highstand is followed by a relatively rapid sea level fall towards present sea level that was reached at around 4000 cal yr bp fossil microatolls from nearby pulau barrang lompo show the same trend however with a coherent negative vertical offset of about 0 8 m compared to their equivalents on pulau panambungan the largely consistent gradients of both trends 0 14 mm yr 1 the consistent elevation of living microatolls in the spermonde and a number of instructive geomorphic features indicate a localized post formational and probably recent drop of the fossil microatolls on the densely populated island pulau barrang lompo the relative sea level trend inferred from pulau panambungan is well within the range of geophysical predictions based on anice selen ice sheet model which predict a highstand that is significantly lower than those predicted by other gia models for this area although a complete interpretation of the holocene sea level history will require additional high resolution datasets from this and surrounding territories in se asia our results suggest that there was merely a single holocene highstand in central indonesia the magnitude of which was substantially lower than hitherto assumed

the effect of sample disturbance on laboratory properties of lac du bonnet granite laboratory properties of lac du bonnet granite samples collected at depths ranging from near surface to 1000 m were established the laboratory properties indicated that either the in situ properties were changing with depth or the samples were changing with depth comparison of p wave velocities in the samples and in situ confirmed the latter i e sample disturbance was affecting the laboratory properties the strength of the damaged samples indicated that sample disturbance affected the cohesion of the material not the frictional properties and that the cohesion loss cannot be accounted for by applying a confining stress sample disturbance started to affect the laboratory properties of lac du bonnet granite when the maximum far field in situ stress exceeded about 10 of the unconfined compression strength key words sample disturbance core discing cohesion brittle rocks damage microcracks stress dependent young s modulus

maximum level and time to peak of dam break waves on mobile horizontal bed this experimental study focuses the influence of bed material mobility and initial downstream water level on maximum water level and time to peak of dam break waves it covers horizontal bed conditions on fixed bed sand bed and pumice bed results include water surface level time evolution maxima wave levels and time to peak the influence of bed material mobility and downstream water level was identified and characterized stressing the importance of using mathematical models with appropriate sediment transport formulations instead of purely hydrodynamic models to simulate dam break waves on mobile bed channels

influence of stress path on stress memory and stress fracturing in brittle rocks a two dimensional numerical model based on the distinct element method previously calibrated to the laboratory properties of undamaged and damaged lac du bonnet ldb granite was used to investigate the influence of stress path on the development of stress memory and stress fracturing in brittle rocks various cycles of loading and unloading similar to those imposed during kaiser effect tests were first applied to undamaged numerical specimens of ldb granite the results of kaiser effect test simulations were found to be consistent with those of published laboratory and numerical investigations further simulations were conducted to investigate the influence of stress path resulting from the excavation of a tunnel on the depth of stress fracturing around the excavation boundary for this purpose the stress paths at points on and near the tunnel wall obtained from a continuum finite element model were applied to the calibrated numerical specimen it was found that the amount of damage in the numeric

experimental insights on geomorphological processes within dam break outburst floods summary hydraulic behavior and unsteady sediment transport within dam break outburst floods are inherently inter dependent yet poorly constrained this study experimentally determined how the mobility and clast size of channel bed sediments affected the peak flow depth and flow velocities wave propagation and attenuation sediment entrainment and duration of transport flood power energy transfer and geomorphological impact of outburst floods due to our choice of clast size and of a unimodal size distribution the predominant sediment transport mechanism was bedload we found that frontal wave propagation was slower and attenuated faster for flows over a mobile bed versus those over a fixed bed peak flow depth was greater and was attained earlier for flows over a mobile bed and with increased clast size geomorphological power declined logarithmically with time after an initial period where gravitational forces exceeded frictional forces both peak and time to peak geomorphological power varied inversely with clast size peak deposition rates were greatest with coarser bed sediment but time to peak deposition rate was inversely proportional to clast size volume changes down channel were described by an exponential curve which we suggest indicates that sediment transport proceeded in waves via both translation and dispersion mechanisms peak suspended load occurred coincident with peak flow velocity peak bedload occurred coincident with peak flow depth and peak sediment discharge lagged behind peak water discharge these descriptions of kinematic transformation multi phase flow and of geomorphological work due to outburst floods help to provide data for numerical modelling for mitigating outburst flood hazards and for informing on the immediate and longer term geological legacy of outburst floods

potentialities uncertainties and complexities in the response of coral reefs to future sea level rise coral islands formed of largely unconsolidated sands only a few metres above sea level are thought to be particularly vulnerable to sea level rise consequent upon global warming however scenarios which predict catastrophic flooding and loss of island area need reassessment particularly in the light of the continued downwards revision of projected rates of future sea level rise revised questions concern the interactions between reef growth and sea level change biophysical constraints on coral growth and the importance to reef systems of potential changes in the magnitude frequency and location of tropical cyclones and hurricanes it is clear that most reefs have the growth potential to meet even the highest of future sea level rise scenarios but too little is known about physiological and physical constraints to reef growth to adequately evaluate the importance of these two factors in constraining this potential at the present time future sea level rise in the tropical oceans and coral reef responses will take place against a backdrop of inter regional differences in holocene sea levels resulting from the varying interaction of eustatic and hydro isostatic processes these differences have generated varying constraints on the development of modern reefs and varying inherited topographies upon which future sea level changes will be superimposed these controls are particularly important in assessing differences in vulnerability to future sea level rise for reef islands in the pacific ocean and the caribbean sea

experimental study on dam break waves for silted up reservoirs the overall dam break phenomenon is currently well understood for reservoirs filled with water however many dams face serious problems of reservoir sedimentation thus regarding risk management the influence of a large amount of sediment in the reservoir on dam break wave propagation is of great importance experimental investigations were performed to investigate the influence of the silting degree of reservoirs and grain size distribution on wave heights and velocities dam break waves in silted up reservoirs are the result of a two phase flow formed by a layer of water over a layer of saturated sediments in which complex phenomena occur simultaneously sediments flow such as a viscous fluid from the dam breach until complete stoppage and clear water flows over the sediments creating bed load transport the final sediment deposition cone the flow of the positive front and maximum wave heights were studied an empirical formula is proposed to describe the celerity of the positive wave front in the case of silted up reservoirs

last interglacial reef and subsidence of the cocos keeling islands indian ocean abstract poorly consolidated holocene sands and coralline limestones beneath reef islands on the cocos keeling islands are underlain by a well lithified coralline limestone 8 11 m below sea level uranium series ages of 118 000 7000 yrs b p bulk sample and 123 000 7000 yrs b p sample from which secondary cement was removed on a coral from within this lithified unit indicate that it was formed during the last interglaciation oxygen isotope substage 5e the depth at which the reef is encountered supports darwin s hypothesis that this atoll is undergoing gradual subsidence elevation of a reef of this age varies on other islands on the indo australian plate but an average rate of subsidence of 0 1 mm yr 1 is implied for the cocos keeling islands this is significantly faster than the subsidence rate expected from thermal contraction of the lithosphere at this location and suggests that additional factors have to be considered to account for the subsidence

coral reef sedimentation on rodrigues and the western indian ocean and its impact on the carbon cycle coral reefs in the southwest indian ocean cover an area of ca 18530 km2 compared with a global reef area of nearly 300000 km2 these regions are important as fishing grounds tourist attractions and as a significant component of the global carbon cycle the mass of calcium carbonate stored within holocene neritic sediments is a number that we are only now beginning to quantify with any confidence in stark contrast to the mass and sedimentation rates associated with pelagic calcium carbonate which have been relatively well defined for decades we report new data that demonstrate that the reefs at rodrigues like those at reunion and mauritius only reached a mature state reached sea level by 2 3 ka thousands of years later than most of the reefs in the australasian region yet field observations show that the large lagoon at rodrigues is already completely full of carbonate detritus typical lagoon depth less than 1 m at low spring tide the presence of aeolian dunes at rodrigues indicates periodic exposure of past lagoons throughout the pleistocene the absence of elevated pleistocene reef deposits on the island indicates that the island has not been uplifted most holocene reefs are between 15 and 20 m in thickness and those in the southwest indian ocean appear to be consistent with this observation we support the view that the co2 flux associated with coral reef growth acts as a climate change amplifier during deglaciation adding co2 to a warming world southwest indian ocean reefs could have added 7 10 to this global flux during the holocene

response of the ha ha river to the flood of july 1996 in the saguenay region of quebec large scale avulsion in a glaciated valley modifications to valley form due to extreme flooding in the lower 34 km of the ha ha river were analyzed heavy regional precipitation in july 1996 triggered extreme runoff and the catastrophic drainage of ha ha lake producing discharges of 1100 m3 s 8 times the 100 year flood dominant valley modifications revealed by comparing preflood and postflood topographies derived photogrammetrically were related to two large scale avulsions in particular a deep retrogressive incision which bypassed the 30 m high perron falls exporting 6 106 m3 of glacial stratified drift from a 2 km section of valley and producing massive sedimentation in the reach downstream reconstructed maximum flow power values support the existence of a 300 w m2 threshold for major scouring of the alluvial valley bottom the evidence highlights the potential for massive scour and fill and reorganization of the long profile with potentially catastrophic effects on infrastructure during extreme floods in glaciated valley settings

the susceptibility of oklahoma s basement to seismic reactivation recent widespread seismicity in oklahoma is attributed to the reactivation of pre existing critically stressed and seismically unstable faults due to decades of wastewater injection however the structure and properties of the reactivated faults remain concealed by the sedimentary cover here we explore the major ingredients needed to induce earthquakes in oklahoma by characterizing basement faults in the field in seismic surveys and via rock mechanics experiments outcrop and satellite mapping reveal widespread fault and fracture systems with trends that display a marked similarity to the trends of recent earthquake lineaments our three dimensional seismic analyses show steeply dipping basement rooted faults that penetrate the overlying sedimentary sequences representing pathways for wastewater migration experimental stability analysis indicates that oklahoma s basement rocks become seismically unstable at conditions relevant to the dominant hypocentral depths of the recent earthquakes these analyses demonstrate that the geometry structure and mechanical stability of oklahoma s basement make it critically susceptible to seismic reactivation seismicity induced by wastewater injections is widespread in oklahoma probably because its basement is susceptible to the reactivation of basement rooted faults according to three dimensional seismic analyses rock mechanics experiments and field surveys

holocene reef growth in the maldives evidence of a mid holocene sea level highstand in the central indian ocean radiometrically calibrated ages from three reef cores are used to develop a holocene reef growth chronostratigraphy and sea level history in the maldives central indian ocean last interglacial reef u series age 122 7 ka was encountered at 14 1 m below mean sea level an age of ca 8100 calibrated cal yr b p immediately overlying this pleistocene surface records the initiation of holocene reef growth massive in situ corals occur throughout the cores and the consistency of the three age depth plots indicate that the reef grew steadily between 8100 and 6500 cal yr b p and at a decreasing rate for the next 2 k y the position of modern sea level was first achieved ca 4500 cal yr b p and sea level reached at least 0 50 1 m higher from 4000 to 2100 cal yr b p before falling to present level emergent fossil microatolls provide evidence of this higher sea level results are significant to two long standing issues relating to maldivian sealevel history first the ambiguity of a late holocene highstand has been resolved with clear evidence of its existence reported here second the uncertainty of the regional pattern of sea level change in the central indian ocean has been clarified the maldivian results broadly agreeing with island records in the eastern rather than western indian ocean our results provide the first field evidence confirming geophysical model projections of a highstand 4 2 k y ago in the central indian ocean though the observed level 0 50 0 1 m is lower than that projected

holocene sea levels in southeast asia maldives india and sri lanka the seamis database abstract we assembled a database of holocene relative sea level index points n 213 and marine n 211 and terrestrial n 122 limiting points for the broader south and southeast asian region including the maldives india and sri lanka the standardized review of published age elevation information from corals deltaic estuarine and mangrove deposits beachrocks and tidal notches yielded a new suite of relative sea level index and limiting points produced according to a standardized protocol expected spatial variability in holocene relative sea level change due to glacial isostatic adjustment was accounted for by first subdividing the study area into ten geographic sub regions from the central indian ocean to the western tropical pacific and second by comparing sub regional relative sea level data to model predictions of glacial isostatic adjustment results show that some of the regionally constrained relative sea level data are characterized by significant inconsistencies that cannot be explained by glacial isostatic adjustment such inconsistencies of standardized relative sea level data become particularly obvious in areas around the red river delta in vietnam the gulf of thailand the northwest coast of malaysia and the spermonde archipelago in indonesia based on a critical evaluation of the reviewed relative sea level indicators we discuss possible sources of local divergence and identify regions where data are currently insufficient to constrain glacial isostatic adjustment predictions the remaining quality controlled and consistent relative sea level data show that glacial isostatic adjustment and syn post formational influences such as tectonic uplift subsidence and compaction were the dominant local drivers of holocene relative sea level change collectively the results of this review suggest that holocene sea levels in south and southeast asia and surrounding regions have been controlled by a variety of global and local drivers and imply that additional index points from the java sea in indonesia would be valuable to better assess the spatial variability and to calibrate geophysical models of glacial isostatic adjustment

modelling outburst floods from moraine dammed glacial lakes in response to climatic change the size and number of moraine dammed supraglacial and proglacial lake systems have increased dramatically in recent decades given an appropriate trigger the natural moraine dams that impound these proglacial lakes are breached producing catastrophic glacial lake outburst floods glofs these floods are highly complex phenomena with flood characteristics controlled in the first instance by the style of breach formation downstream glofs typically exhibit transient often non newtonian fluid dynamics as a result of high rates of sediment entrainment from the dam structure and channel boundaries combined these characteristics introduce numerous modelling challenges in this review the historical contemporary and emerging approaches available to model the individual stages or components of a glof event are introduced and discussed a number of methods exist to model the stages of a glof event dam breach models can be categorised as being empirical analytical or numerical in nature with each method having significant advantages and shortcomings empirical relationships that produce estimates of peak discharge and time to peak are straightforward to implement but the applicability of these models is often limited by the nature of the case study data from which they are derived furthermore empirical models neglect the inclusion of basic hydraulic principles that describe the mechanics of breach formation analytical or parametric models simulate breach development using simplified versions of the physically based equations that describe breach enlargement whilst complex physically based codes represent the state of the art in numerical dam breach modelling to date few of the latter have been applied to investigate the moraine dam failure problem despite significant advances in the physical complexity and availability of higher order hydrodynamic solvers the majority of published accounts that have attempted to reconstruct or predict glof characteristics have been limited often by necessity to the use of relatively simplistic models this is in part attributable to the unavailability of terrain models of many high mountain catchments at the fine spatial resolutions required for the effective application of numerically sophisticated codes and their proprietary and often cost prohibitive nature however advanced models are experiencing increasing use in the glacial hazards literature in particular the suitability of emerging mesh free particle based methods for simulating dam breach and glof routing may represent a solution to many of the challenges associated with modelling this complex phenomenon sources of uncertainty in the glof modelling chain have been identified by various workers however to date their significance for the robustness of reconstructive and predictive modelling efforts have been largely unexplored and quantified in detail these sources include the geometric and material characterisation of moraine dam complexes including lake bathymetry and the presence and extent of buried ice initial conditions freeboard precise spillway dimensions spatial discretisation of the down valley domain hydrodynamic model dimensionality and the dynamic coupling of successive components in the glof model cascade

late holocene coastal plain stratigraphy and sea level history at hanalei kauai hawaiian islands abstract fluvial marine and mixed fluvial marine deposition on the coastal plain of hanalei bay on the north shore of kauai hawaii records a middle to late holocene fall of relative sea level radiocarbon dating of the regression boundary preserved in the stratigraphy of the coastal plain documents a seaward shift of the shoreline beginning at least 4800 4580 cal yr b p and continuing until at least 2160 1940 cal yr b p marine sands stranded in the backshore and coastal plain environment are buried by fluvial floodplain and channel sands silts and muds in places erosion at the regression contact exposed older marine sands thus increasing the hiatus at the regression disconformity the shoreline regression is best explained as the result of a fall in relative sea level the age and elevation of the cored regression boundary at sites that have not been influenced by erosion are consistent with a middle to late holocene highstand of relative sea level as predicted by geophysical models of whole earth deformation related to deglaciation

sea level and coral atolls late holocene emergence in the indian ocean the cocos keeling islands in the eastern indian ocean were visited by charles darwin who described geomorphological evidence that he considered supported his subsidence theory of coral reef development however several other accounts of the reef islands have questioned darwin9s interpretation and have suggested that a conglomerate platform that underlies most of the reef islands may indicate recent emergence of the atoll radiocarbon ages on corals from this conglomerate platform reported here indicate that it formed in the late holocene fossil in situ microatolls above present upper coral growth limits the elevation of associated beachrock and the morphological similarity of the conglomerate platform to the present reef flat deposits indicate a late holocene sea level above the present relative to the atoll the atoll has undergone at least 0 5 m of emergence since about 3000 yr b p this represents the first radiometrically dated evidence of holocene emergence from islands in the eastern or central indian ocean

stable numerical model for transcritical flow and sediment transport on uneven bathymetry a stable and well balanced finite volume method was proposed to solve the shallow water equations coupled with a sediment transport equation an approximate riemann solver with a monotone upstream centered schemes for conservation laws muscl reconstruction was used for the computation of the flux terms a special but relatively simple treatment of source terms made it possible to ensure numerically and physically balanced computational results on very steep sloped beds various numerical simulations conducted on rigid beds have demonstrated that the proposed numerical scheme could provide stable computational results in the cases of flat and nonflat bottoms from the comparisons of experiments on erodible beds in one and two dimensional channels good agreement was obtained when proper parameters for turbulent flow and sediment transport were provided lastly the effects of the parameters in relation to hydraulic characteristics included in the flow and the sediment transport models were investigated

impacts of eustasy and hydro isostasy on the evolution and landforms of pacific atolls consideration of eustatic and hydro isostatic effects on late quaternary sea levels in the tropical pacific ocean indicates that the configuration of modern atolls with emergent annular reef flats is a transient morphology not developed until post mid holocene time annular atoll reefs perched atop carbonate platforms which cap buried volcanic edifices are underlain by 8 28 m of holocene limestone disconformably overlying a substratum of last interglacial or older limestone comparable thicknesses 9 23 m of holocene sediment are present beneath atoll lagoons that are uniformly 85 m deep during glacio eustatic drawdowns in global sea level by 120 125 m carbonate platforms of modern atoll provinces rose abruptly from the sea as clusters of subaerial limestone plateaus flanked by steep cliffs modern analogues are provided by emergent atolls uplifted on the flexural arches of trench forebulges slow subsidence coupled with karstic erosion of emergent atolls during the last glaciation lowered the surfaces of last interglacial reef edifices by the amounts needed to provide accommodation space for holocene reef growth during the postglacial eustatic rise in sea level modern atoll reef caps began to grow after 9 ka when rising holocene sea level overtopped degraded remnants of interglacial reefs but remained submerged until carbonate buildups approached sea level in mid holocene time 6 4 ka classic atoll morphology with circlets of multiple islets dotting annular reefs formed in combination with late holocene hydro isostatic drawdown in tropical pacific sea level in response to equatorial ocean siphoning a facet of global isostatic adjustment gia to deglaciation early holocene eustatic rise in sea level and late holocene hydro isostatic decline in sea level combined to produce a regionally variable mid holocene highstand in tropical pacific sea level that stood 1 0 2 6 m above modern sea level cemented mid holocene paleoreef flats now stranded well above sea level serve as resistant foundations for non migratory pinned islets that were not present along atoll rims until after the local crossover date when ambient high tide level first fell below mid holocene low tide level existing atoll landforms have a time depth generally 1 2 ka

bed compaction effect on dam break flow over erodible bed experimental and numerical modeling abstract disastrous floods result in severe loss of human lives and intense destruction to the infrastructure and economic activities furthermore it leads to environmental and ecological damages located at the downstream area of the dam the present study aims at investigating experimentally and numerically the sediment transport and morphological evolution of the erodible bed induced by dam break flows experimental runs were conducted in a flume specially designed for dam break flow process equipped with a thin vertical gate at its middle based upon an initial plane bed the effect of three different compaction rates of the bed at both up and downstream of the dam was investigated the experimental data consistently suggested that increasing the bed compaction rate resulted in decreasing the scouring and sedimentation depth as well as the sediment transport rate further increasing the bed compaction rate led to increasing the wave front celerity reducing the scouring rate and the erosion depth both the experimental and numerical outputs highlighted the process of air entrainment at the leading edge of the wave front the numerical results showed that the maximum void fraction was associated with the maximum flow velocity at the zone of wave front comparisons were made between the experimental results and those are provided from a numerical study using standard volume of fluid vof method where three different turbulence closure schemes rng k e and k and three bed load sediment transport approaches van rijn meyer peter muller and nielson were applied accordingly by considering the error values in predicting the free surface height and the bed deformation the k closure model showed the highest accuracy in capturing the turbulence features while the mayer peter muller formula had the highest performance in predicting the bed deformation in non compacted nc bed besides the rng closure model and nielsen bed load formula revealed the highest accuracy in predicting the aforementioned features in a semi compacted sc bed the k closure model and mayer peter muller formula showed the highest accuracy in reproducing the turbulence characteristics and bed profile in a fully compacted fc bed

constraining mid to late holocene relative sea level change in the southern equatorial pacific ocean relative to the society islands french polynesia precisely quantifying the current climate related sea level change requires accurate knowledge of long term geological processes known as glacial isostatic adjustments gia although the major postglacial melting phase is likely to have ended 6 4 ka bp before present gia is still significantly affecting the present day vertical position of the mean sea surface and the sea bottom here we present empirical rsl relative sea level data based on u th dated fossil corals from reef platforms of the society islands french polynesia together with the corresponding gia modeling fossil coral data constrain the timing and amplitude of rsl variations after the holocene sea level maximum hslm upon correction for isostatic island subsidence we find that local rsl was at least 1 5 0 4 m higher than present at 5 4 ka later minor amplitude variations occurred until 2 ka when the rsl started dropping to its present position with a rate of 0 4 mm yr the data match with predicted rsl curves based on global ice sheet chronologies confirming the role of gia induced ocean siphoning effect throughout the mid to late holocene a long lasting late holocene highstand superimposed with second order amplitudinal fluctuations as seen from our data suggest that the theoretical predicted timing of rsl change can still be refined pending future calibration

two hundred thirty years of relative sea level changes due to climate and megathrust tectonics recorded in coral microatolls of martinique french west indies we sampled six coral microatolls that recorded the relative sea level changes over the last 230 years east of martinique on fringing reefs in protected bays the microatolls are cup shaped which is characteristic of corals that have been experiencing submergence x ray analysis of coral slices and reconstructions of the highest level of survival hls curves show that they have submerged at rates of a few millimeters per year their morphology reveals changes in submergence rate around 1829 11 1895 and 1950 tide gauges available in the region indicate a regional sea level rise at a constant mean rate of 1 1 0 8 mm yr which contrasts with our coral record implying additional tectonic subsidence comparing our coral morphology with that of synthetic corals generated with matlab by using the key west tide gauge record florida we show that their growth was controlled by tectonics and that a sudden relative sea level increase drowned them around 1950 simple elastic models show that this sudden submergence probably occurred during the 21 may 1946 earthquake which ruptured the plate interface in front of martinique in the mantle wedge in an area of sustained seismic activity the 1839 m8 earthquake probably occurred in the same area long term subsidence of microatolls indicates that this deep portion of the megathrust is probably locked down to 60 km depth during the interseismic period our oldest coral recorded a long lasting period 50 years of stable relative sea level after the 1839 earthquake indicating that transient interseismic strain rate variations may occur in the lesser antilles

the mechanical behaviour of weak mudstone opalinus clay at low stresses abstract over the last 10 years argillaceous rocks mudrocks such as the jurassic claystone opalinus clay have gained acceptance as a potential host formation for geological disposal of nuclear waste observations from tunnels in opalinus clay at the mont terri rock laboratory switzerland suggest that the excavation induced response is not linear elastic the micro structure of the opalinus clay has been identified as a source for this response it has been demonstrated that diagenetic processes over the last 180 ma have been responsible for the formation of strong diagenetic bonds locking latent strain energy into the micro structure of opalinus clay a conceptual model of the micro structure including the effects of diagenetic processes has been developed as a framework to interpret the mechanical behaviour of the opalinus clay samples recovered at mont terri rock laboratory have been subjected to processes that have resulted in bond breakage and the release of locked in latent strain energy this tends to reduce the strength and deformation properties of samples and induces low stiffness non linearity of the stress strain curve at low stress levels numerical modelling of the sampling stress path at mont terri rock laboratory shows that unloading was the dominant factor resulting in this response as a result samples can shed light on the unloading response of the rockmass to excavation this non linear behaviour has been quantified by means of routine laboratory compressive tests

a half century of coastline change in diego garcia the largest atoll island in the chagos abstract being low and flat atoll islands are often used as case studies against which to gauge the likely impacts of future sea level rise on coastline stability furnished with lengthy temporal datasets pacific atolls form the majority of studies with scant information published for sites in the indian ocean to address this imbalance this study considers diego garcia an atoll island situated in the remote equatorial indian ocean which has undergone pronounced natural and anthropogenic change in the last fifty years to explore the former time separated remote sensing images spanning the years 1963 2013 are assembled to provide insight into the natural dynamics of the shoreline of this island and ocean climate data are compiled to investigate possible controls disregarding the precinct of the atoll on which a military complex has been constructed overall land area of diego garcia decreased by a net value of only 0 92 between 1963 and 2013 while net island area is relatively unchanged 12 of the shoreline that is not in the military precinct displayed discernible accretion and 15 has receded with the lagoon facing coastline having undergone the most pronounced changes and at rates higher than recorded for the island s exterior broad trends in the morphological adjustment of the island exist the north eastern limb of the atoll has generally receded while the south eastern limb has extended the south of the island has also extended the south western region has eroded and the north western part has generally also eroded with the exception of notable shoreline extension at simpson point the most common mechanism by which the lagoon ward coastline has aggraded is through the in filling of cuspate embayments with sediment which is later stabilized by the expansion of terrestrial vegetation this evolution is most active in the complex network of embayments in the south of the atoll lagoon the ocean facing coastline by contrast typically aggrades and erodes through the linear shift of the vegetated coast along the strike of the beach line while the areal extent of diego garcia has been almost static for the last half century the annualized rate of flux of the coastline is considerable at 0 30 m yr 1 a rate comparable to other atoll islands the literature consistently reports two factors as relevant to increasing the rate of shoreline migration human modification of it and sea level rise both are foreseeably set to increase for diego garcia the former due to its strategic importance not least its use as a military base and the latter due to global environmental change the findings of this work serve to remind that the coastline of diego garcia as for all atoll islands is naturally dynamic and will likely become more so in the future

experimental study and numerical verification of silted up dam break abstract in this study multiphase flood waves caused by failure of silted up dams have been scrutinized experimentally and efficacy of the public domain cfd software openfoam numerical models to represent such phenomenon is evaluated experimental observations are sparse on dam break for reservoirs with high sediment depths called silted up reservoirs sediment layer in this case may behave as a viscous fluid and produce a complex multi layer flow of air and water overtopping a sediment layer massive sediment quantities can have a substantial impact on the wave propagation pattern caused by dam break this study contributes to an experiment based understanding of dam break phenomenon with silted up reservoir and elaborates the propagation of multi layer waves herein different hydraulic conditions were experimentally observed including 8 different upstream sediment depths in the range of 0 0 24 m and 4 downstream initial water levels of 0 0 02 0 04 and 0 05 m which collectively created 32 scenarios the resulted waves were filmed by high speed cameras and data were extracted through image processing an open source cfd software namely openfoam was employed to simulate the experiments using two distinct numerical approaches volume of fluid vof and eulerian results of both numerical approaches were in good agreement with the experimental measurements with mae and rmse error values varying from 0 006 m to 0 031 m and 0 008 m to 0 043 m respectively 2 to 10 and 2 6 to 14 with respect to the reservoir height of 0 3 m the eulerian approach showed marginally superior performance to vof especially in cases with high sediment depths which is likely due to accommodating phase mixing a wide collection of high quality data is made available online in the appendix data and could be utilized in future studies

modern vertical deformation above the sumatran subduction zone paleogeodetic insights from coral microatolls coral microatolls from the coast and outer arc islands of western sumatra retain a stratigraphic and morphologic record of relative sea level change which is due in large part to vertical tectonic deformation above the sumatran subduction zone low water levels whose fluctuations produce measurable changes in coral morphology limit the upward growth of the microatolls annual rings derived from seasonal variations in coral density serve as an internal chronometer of coral growth the microatolls act as natural long term tide gauges recording sea level variations on time scales of decades field observations and stratigraphic analysis of seven microatolls five from the outer arc islands and two from the mainland coast indicate that the mentawai islands have been submerging at rates of 4 10 mm yr over the last four or five decades while the mainland has remained relatively stable the presence of fossil microatolls up to several thousand years old in the intertidal zone indicates that little permanent vertical deformation has occurred over that time thus most of the strain accumulated in the past few decades represents interseismic deformation that is recovered during earthquakes elastic dislocation models using these submergence data suggest that elastic strain is being accumulated in the interseismic period and that the subduction zone in this region is fully coupled

bioconstruction bioerosion and disturbance on tropical coasts coral reefs and rocky limestone shores the ecology of tropical carbonate coasts including coral reefs and rocky limestone shores is susceptible to disturbance that may have linked effects on geomorphology biogeomorphology which considers the interrelations between biological and geomorphological processes is particularly well suited toward the understanding of such carbonate systems field observations and experimentation on tropical and temperate coasts by both biologists and geomorphologists and the development of ecological theory have come to stress the importance not of stable successional littoral communities but rather of nonequilibrial multistate systems these ideas now need to be incorporated into improved models of coastal dynamics case studies from the central pacific the caribbean and the western indian ocean illustrate the interactions between external environmental variability and internal biological processes these studies show how changing the balance between bioconstructional and bioerosional processes can interrupt a system s development and in some cases shift carbonate based systems between healthy and degradational states a better understanding of the spatial and temporal complexities present in carbonate coastal and shallow marine environments is an important precursor to effective coastal zone management on these prevalent tropical shorelines

assessing in situ microcrack damage using ultrasonic velocity tomography abstract to characterize the damage induced during excavation of a test tunnel in granite ultrasonic wave velocity and amplitude measurements were made in situ around one quadrant of the tunnel sixteen 1 m deep boreholes were drilled into the tunnel wall these boreholes spanned the region from tensile stress induced damage in the sidewall to compressive stress induced damage in the well developed notch measurements were made by pulsing a source transducer at numerous points within a given borehole and on the tunnel surface and then capturing the transmitted ultrasonic waves at transducers located in the adjacent borehole the travel times of the waves between sources and receivers were used to compute the average velocities and to construct two dimensional 2d tomographic images wave velocities and amplitudes in the tensile stress region are low and show significant anisotropy indicating the presence of oriented microcracks even as deep as 1 m from the tunnel wall velocities and amplitudes are higher in the compressive stress region and show lower anisotropy indicating the rock is relatively undamaged away from the tunnel wall the velocity anisotropy indicates that the dominant orientation of microcrack planes is everywhere tangential to the tunnel wall even though the minimum principal stress is tangential and tensile in the sidewall the distribution of microcracks inferred from these results is consistent with the extensive microseismicity detected during and after excavation and suggests that both the stress history and current stress state have impacted the current state of damage around the tunnel

dam break wave front celerity this work is concerned with the role that friction and inertia effects can play on the magnitude of dam break wave front celerity classic analytical solutions are presented a large collection of experimental data is used covering a wide range of different initial conditions fixed bed or mobile bed five types of bed material dry or wet bed downstream and with or without bed step to overcome the limitations of analytical solutions a numerical model is used the model is based on the shallow water approach with contact load dominated sediment transport and it makes use of developments recently made in the study of sheet flows the analytical and numerical results are compared with experimental data it was found that the celerity is mainly dictated by the friction coefficient by the sediment inertia by the initial downstream water depth and by the initial bed step height for good data fitting the friction coefficient must be influenced by the type of bed fixed or mobile in the latter the coefficient must vary with the bed material characteristics the dissimilarities between the experimental analytical and numerical results are interpreted

microatolls as sea level indicators on a mid ocean atoll microatolls are discoid corals with flat upper surfaces that develop when upward coral growth is constrained by exposure at low tide they have been widely viewed as important and relatively precise indicators of modern and paleo sea level positions because of their sensitivity to the water air interface though this has rarely been directly established by survey to a precise datum this study involved an accurate survey of 282 microatolls growing in a range of intertidal environments open reef flats interisland passages lagoons across the cocos keeling islands a mid ocean atoll in the indian ocean the upper surface elevation of modern microatolls was found to vary through more than 40 cm across the environments in which these corals occur on cocos representing more than 30 of the spring tide range much of the variation reflects subtle ponding at low water levels across extensive low gradient reef surfaces associated with interisland passages microatolls in open reef flat habitats are typically constrained within the narrowest and most consistent elevation range around the atoll the environment in which individual fossil microatolls occurred when they were alive is significant in reconstructing former sea levels

coral reefs and sea level change abstract coral reefs provide significant evidence for former sea level positions because of their geological preservation and suitability for dating interpretation of this evidence presumes an understanding of reef geomorphology modern reef organism distributions and environmental factors influencing them fossil reef terraces formed during the last interglacial marine oxygen isotope mis substage 5e 128 116 ka are prevalent on many tropical shorelines and there has been ongoing debate as to the height reached by sea level during that highstand observations from numerous last interglacial sites suggest that sea level was at least 3 m above present sea level implying less extensive icesheets than at present an elevation of 6 m has commonly been adopted when correcting tectonically active sites for uplift recent compilations suggest elevations up to 8 9 m but incorporate few observations from reefs where the last interglacial is found below sea level oscillation of sea level during mis 5e has been interpreted from several sites with recent studies inferring rapid rise of several metres at the end of the interglacial these interpretations are at the limits to the precision with which corals can currently be dated and their palaeo water depths inferred it is not surprising that constraining last interglacial sea level changes within uncertainties of less than 1 2 m remains controversial considering sea level variations recognised between reef sites in the holocene and observed geographical variation in isostatic or flexural adjustments fossil coral reefs on uplifting margins also provide clear evidence for mis substages 5c and 5a and those on huon peninsula indicate fluctuations related to heinrich events mis 3 interpretations show considerable variability between sites with still greater uncertainties about sea level timing and elevation during previous interglacials future study of extensive sequences of fossil reefs preserved on rapidly subsiding margins could address these uncertainties submerged reefs have already yielded important information about sea level rise during the last deglaciation coring around barbados and tahiti as well as on the huon peninsula has produced a broadly consistent picture of ice melt reflecting eustatic change since the last glacial maximum these studies have shown the sensitivity of reefs to rapid sea level rise associated with meltwater pulses with some reefs drowning while others back stepped integrated ocean drilling program iodp expeditions to tahiti and recently the great barrier reef extended these records but details of timing nature and impact of deglacial meltwater pulses remain elusive studies of holocene reefs have indicated different growth strategies some kept up with sea level while others caught up when sea level decelerated holocene sea level appears to have experienced a gradual rise up to present across the caribbean providing accommodation space for reefs to accrete vertically whereas in the indo pacific sea level has been near its present level since 7 ka with many reef flats emergent following a slight fall of sea level caused by ocean siphoning microatolls on reef flats provide perhaps the clearest evidence of past sea level position but in their absence novel biological or other sea level indicators are required to better constrain palaeo water depths there is an urgent need for further research from additional key reef locations not only to decipher processes driving past sea level change and its geographical variability but also to better understand how coral reefs will respond in the context of future sea level rise

microseismicity monitoring and failure mechanism analysis of rock masses with weak interlayer zone in underground intersecting chambers a case study from the baihetan hydropower station china abstract a weak interlayer zone wiz is a rock mass system with poor mechanical properties large scale random distribution water softening causing an adverse effect on the safety of the construction and project progress to investigate the fracture process and the mechanism of rock masses with wizs in the intersecting chambers during the excavation process in situ microseismic ms monitoring was carried out in the underground powerhouse on the right bank of the baihetan hydropower station china during the monitoring the spatio temporal evolution process of the microseismicity of the rock masses around the intersecting chambers was obtained during the excavation unloading of multiple working faces the spatial evolution of ms events illustrates the dynamic progressive characteristics of ms activities as they propagate and accumulate along the wiz and finally form a cluster zone the fracture mechanism of moment tensor inversion reveals the distribution and evolution of ms events with respect to different fracture types tensile fracture events are distributed near the free surface while non tensile fracture events are far from the free surface finally the study proposes support measures restraining fracture development in surrounding rock masses with wiz the effectiveness of reinforced support measures is verified by ms events and the deformation of surrounding rocks the results of the study are particularly valuable for the stability analysis excavation and support optimization of similar engineering studies