impacts of category 5 tropical cyclone fantala april 2016 on farquhar atoll seychelles islands indian ocean abstract this paper provides new insights on the impacts of a category 5 tropical cyclone on indian ocean atoll reef islands using multi date aerial imagery and field observations the contribution of tropical cyclone fantala to shoreline and island change and to sediment production and transport was assessed on farquhar atoll seychelles islands results show that the two largest islands 3 km 2 only suffered limited land loss 1 19 to 8 35 while small islets lost 13 17 to 28 45 of their initial land area islands and islets exhibited contrasting responses depending on their location topography and vegetation type depending on islands the retreat of the vegetation line occurred either along all shorelines or along ocean shoreline only the structure wooded vs grassy and origin native vs introduced of the vegetation played a major role in island response five days after the cyclone beach width and beach area were multiplied by 1 5 to 10 depending on the setting and were interpreted as resulting from both sediment reworking and the supply of large amounts of fresh sediments by the reef outer slopes to the island system fourth months after the cyclone extended sheets of loose sediments were still present on the reef flat and in inter islet channels and shallow lagoon waters indicating continuing sediment transfer to islands

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

spatiotemporal variability of typhoon impacts and relaxation intervals on jaluit atoll marshall islands storms are important drivers of geomorphic change within atoll settings causing rapid island erosion while also initiating island building through the generation of vast quantities of reef derived sediment due to the combined effects of storms and sea level rise reef islands are thought to be on an erosional trajectory jaluit atoll in the marshall islands was struck by typhoon ophelia in a d 1958 causing significant geomorphic change to reef islands using aerial photographs as well as recent satellite imagery we track the impacts of the typhoon and the multidecadal recovery of islands ophelia caused a significant reduction in total land area of jaluit atoll from 9 95 km 2 to 9 45 km 2 5 1 with islands on the northeast rim collectively reducing in size from 4 72 km 2 to 4 14 km 2 12 2 between 1976 and 2006 73 of 87 islands increased in size with the total landmass exceeding the pre typhoon area 10 25 km 2 however we observe considerable spatiotemporal variability of impacts and relaxation following the typhoon results indicate that despite significant typhoon driven erosion and a relaxation period coincident with local sea level rise islands have persisted and grown

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

contribution of moderate climate events to atoll island building fakarava atoll french polynesia abstract while the geomorphic impacts of extreme climate events including in particular tropical cyclones and distant source swells on atoll islands are widely acknowledged the influence of moderate climate events such as tropical lows that do not reach the cyclone stage and low magnitude distant source swells has to date been overlooked based on multi date image analysis and field observations the geomorphic impacts of a moderate climate event tropical low 13f february 2017 were assessed in the northern part of fakarava atoll northwestern tuamotu archipelago in french polynesia results show that this event which generated strong swells predominantly caused shoreline retreat noted along 54 14 of transects with the minimum net shoreline movement reaching 45 46 m along the highly exposed shoreline section while the rest of the shoreline predominantly exhibited stability the effects of this swell event were mainly constructional as shown by the formation of two small storm ramparts and of extensive sediment sheets and tracts on the conglomerate platform in low lying areas the waves crossed over the islands from ocean to lagoon depositing sediment inland the erosional impacts of the storm waves and overwash induced sediment deposition were lower along shoreline exhibiting high vegetation density one year after the event intertidal sediment deposits had significantly migrated landward this study which reveals an important research gap in atoll geomorphic studies calls for the more systematic assessment of the geomorphic impacts of moderate climate events on atoll islands especially in atoll regions that are located outside the cyclone belt e g tuamotu maldives etc where such events can be hypothesised to be more influential than extreme climate events

relationship between gases and volcanic activity of mount etna in 1986 the long lived 222rn decay products 210pb 210bi and 210po have been monitored in the plumes of several vents at mount etna sicily from may to october 1986 the results show that the four main craters of this volcano emit gases whose compositions are different from each other the 210bi 210pb ratios for the plumes have similar mean values close to 25 which correspond to a degassing time of 1 5 to 2 7 days according to the model of lambert et al 1985 86 in contrast 210po 210pb ratios have very different mean values in each plume 35 at the voragine crater 20 at the bocca nuova crater and 14 at the south east crater these figures enable us to calculate proportions of deep magma of 50 29 and 19 in the degassing cells of these craters respectively moreover the se crater appears to be a secondary degassing vent not directly related to the main magma reservoir the evolution of these ratios has been related to variations in volcanic activity

response of reef island shorelines to seasonal climate oscillations south maalhosmadulu atoll maldives 1 the maldives experience seasonal shifts in monsoon winds from the west northwest to northeast the morphologic response of reef island beaches and shorelines to these predictable shifts in climate was examined on eight islands in south maalhosmadulu atoll based on global positioning system surveys of island shoreline planform in january and june 2002 and february 2003 surveys show that islands exhibit large gross changes 31 120 of beach area in shoreline position between seasons such changes reflect large reversals in sediment flux of 9 23 103 m3 on a biannual basis driven by seasonal reversals in wind and wave conditions annual net change is small 2 15 suggesting islands spatially exhibit a dynamic equilibrium an island oscillation index io is defined that describes the spatial extent of shoreline change around islands island shape ellipticity e is found to be positively correlated with io in the expression io 1 021e 0 275 suggesting island shape is a better indicator of the susceptibility of island shorelines to morphological change than wave energy exposure

nature and stability of atoll island shorelines gilbert island chain kiribati equatorial pacific islands rimming pacific atolls typically form narrow low lying lands that are commonly perceived to be particularly vulnerable to global changes such as sea level rise as these low islands form the only habitable land for many island nations understanding the character of shorelines and the rates and controls that operate to bring about changes is an issue of central importance the purpose of this study is to unravel the characteristics of coastal change on atoll islands of the gilbert island chain of the equatorial pacific nation of kiribati especially as they relate to autogenic shoreline processes and el nino southern oscillation variability integration of field observations differential global positioning system data historical aerial photographs and ultra high resolution remote sensing images demonstrates the nature spatial patterns and rates of change from 17 islands on maiana and aranuka atolls the results illustrate that between 2005 and 2009 ca 50 of the shorelines on these islands displayed a discernable shift in position some shorelines were accretionary at net rates up to ca 8 m year 1 and others were erosional up to ca 18 m year 1 long term net rates of change on maiana between 1969 and 2009 were lower than short term net rates measured between 2005 and 2009 both short term and long term observations illustrate some of the greatest change occur near terminations of the largest north south oriented islands associated with longshore movement of coarse sand and gravel direct hits by tropical depressions and marked seasonality factors interpreted as being essential in island growth and shoreline dynamics elsewhere do not directly impact these equatorial atolls and can be eliminated as fundamental controls on shoreline dynamics similarly observations over four years suggested that shoreline variability probably is not influenced directly by marked sea level change although a recent increase in the rates of shoreline change could reflect instability related to the cumulative effect of a long term increase in the rate of sea level rise within this framework of global change local anthropogenic effects autogenic shoreline processes and el nino southern oscillation influenced wind and wave variability control many aspects of these dynamic shorelines these results provide quantitative insights into the character and variability of rates of shoreline change information essential for evaluating and mitigating the vulnerability of island nations such as kiribati

monsoonally influenced circulation around coral reef islands and seasonal dynamics of reef island shorelines synchronous measurements of reef flat waves and nearshore currents were made around the perimeter of three coral reef islands in the central maldives nearshore current velocities were shown to be tidally modulated in most instances with maximum velocities associated with lower tidal stages peak currents were consistently observed on the windward and lateral flanks of island shorelines 0 3 0 4 ms 1 the relatively low elevation of reef surfaces and medium to low energy incident wave energy hs 0 2 0 3 m accounts for low tidal stage peaks in velocity as this corresponds to the period when wave setup induced current processes are maximised significantly all nearshore currents were unidirectional and alongshore the generation of unidirectional alongshore flow patterns results from island configuration which deflects flow and variations in reef geometry that control spatial variations in wave setup around the reef platform edge and at the island shoreline which can drive alongshore currents the presence of a nearshore moat that channelizes flow in the nearshore and variations in reef geometry where topographic low points act as preferential drainage points results show that changes in monsoon conditions that modulate wind and wave patterns from the west to northeast can force substantial changes in reef platform and nearshore current flows but that the degree of change is dependent on reef platform shape and position in the atoll the circular study island was found to exhibit a near complete reversal in unidirectional flow from northeast flow in the westerly monsoon to southwest flow in the northeast monsoon however the elongate and triangular shaped reef platforms exhibited more localised changes in flow patterns significantly those shorelines that exhibit the greatest changes in shoreline currents correspond to the sections of coast that exhibit the largest morphological adjustments between seasons results provide significant insights for the morphodynamics of reef platform islands in particular the nearshore process regime is dominated by alongshore processes furthermore reef platform shape and the magnitude of change in direction of wave approach to reef platforms provide critical indicators of the morphodynamic behaviour of reef platform islands

radioactive isotopes and trace elements in gaseous emissions from white island new zealand abstract measurements of the radioactivity of gases released by white island volcano show variations in 210 po concentrations with temperature in fumarolic gases and this is interpreted to be due to dilution of magmatic gases with vapours derived from an envelope of acid brines surrounding the vent system the degassing model derived for mount etna emissions is tested on white island magmatic gases the results are a short degassing time 2 days small degassing magma volume 5 10 6 m 3 and the following estimations of emanation coefficients pb 1 bi 2 7 cd 0 05 and cu 0 07 the initial content of s in the magma is estimated to be within the range 300 600 mg kg fluxes of trace metals kg day emitted by the volcano are estimated to be pb 125 bi 6 cu 300 and cd 9

shoreline changes in reef islands of the central pacific takapoto atoll northern tuamotu french polynesia abstract atoll reef islands are considered highly vulnerable to the impacts of climate change while accelerated sea level rise is expected to destabilize reef islands ocean warming and acidification are considered as major threats to coral reef growth which is of primary importance for the persistence of islands and of food supply to islanders using multi date aerial imagery shoreline and island changes between 1969 and 2013 were assessed on takapoto atoll northern tuamotu region in french polynesia results show that over the 44 year study period 41 of islands were stable in area while 33 expanded and 26 contracted island expansion was the dominant mode of change on the leeward side of the atoll tropical cyclone orama category 3 1983 contributed to shoreline and island change on the windward side of the atoll through the reworking of previous storm deposits and the injection of fresh sediments in the island system with up to 62 of an island s land area being covered with fresh sediments human activities contributed significantly to shoreline and island change throughout the atoll through infrastructure construction the removal of the indigenous vegetation from a number of islets and sediment mining

rates of sulfur dioxide and particle emissions from white island volcano new zealand and an estimate of the total flux of major gaseous species airborne correlation spectrometry cospec was used to measure the rate of so2 emission at white island on three dates i e november 1983 1230 300 t d november 1984 320 120 t d and january 1985 350 150 t d t metric tons the lower emission rates are likely to reflect the long term emission rates whereas the november 1983 rate probably reflects conditions prior to the eruption of december 1983 the particle flux in the white island plume as determined with a quartz crystal microbalance cascade in november 1983 was 1 3 t d unusually low for volcanic plumes the observed plume particles as shown from scanning electron microscopy include halite native sulfur and silicates and are broadly similar to other volcanic plumes

multi decadal shoreline changes on taku atoll papua new guinea observational evidence of early reef island recovery after the impact of storm waves hurricanes tropical cyclones and other high magnitude events are important steering mechanisms in the geomorphic development of coral reef islands sandy reef islands located outside the storm belts are strongly sensitive to the impact of occasional high magnitude events and show abrupt commonly erosive geomorphic change in response to such events based on the interpretation of remote sensing data it is well known that the process of landform recovery might take several decades or even longer however despite the increasing amount of scientific attention towards short and long term island dynamics the lack of data and models often prevent a robust analysis of the timing and nature of recovery initiation here we show how natural island recovery starts immediately after the impact of a high magnitude event we analyze multi temporal shoreline changes on taku atoll papua new guinea and combine our findings with a unique set of published field observations smithers and hoeke 2014 trends of shoreline change since 1943 and changes in planform island area indicate a long term accretionary mode for most islands apparent shoreline instability is detected for the last decade of analysis however this can be explained by the impact of storm waves in december 2008 that temporarily masked the long term trend the transition from negative to positive rates of change in the aftermath of this storm event is indicative of inherent negative feedback processes that counteract short term changes in energy input and represent the initiation of island recovery collectively our results support the concept of dynamic rather than static reef islands and clearly demonstrate how short term processes can influence interpretations of medium term change

shoreline changes interpreted from multi temporal aerial photographs and high resolution satellite images wotje atoll marshall islands abstract wotje atoll is located at 9 25 n and 170 04 e within the republic of the marshall islands in the central pacific ocean as on other atolls the islands perched along the rim of wotje are low lying and considered highly vulnerable to the impacts of climate change a widely anticipated impact of continued sea level rise is the chronic erosion of island shorelines using a combination of aerial photographs and satellite imagery shoreline changes are assessed over a 67 year period characterized by rising sea level results indicate that between 1945 and 2010 shoreline accretion is more prevalent than erosion with an average net shoreline movement nsm of 1 74 m indicating accretion shorelines were accretionary along the lagoon ocean and channel facing shorelines as well as on elongate spits and small islands a high frequency assessment of shoreline change on a subset of islands in the east of wotje reveals that islands were stable with a balance between shoreline accretion and erosion shorelines interpreted from high resolution satellite imagery captured between 2004 and 2012 indicate that shorelines within this sample of islands are largely in an erosive state the post 2004 shift toward erosion may be sea level rise induced or part of an unresolved shoreline oscillation this study demonstrates the critical need for improved shoreline change monitoring within atoll settings in order to assess sea level rise impacts along island shorelines

formation and adjustment of typhoon impacted reef islands interpreted from remote imagery nadikdik atoll marshall islands abstract in 1905 a devastating typhoon hit nadikdik atoll 5 54 n and 172 09 e in the southern marshall islands evidence suggests that large sections of reef islands on nadikdik were overwashed and destroyed comparison of aerial photographs taken in 1945 and modern satellite imagery provides a unique record of the geomorphic adjustment of islands after the typhoon between 1945 and 2010 the vegetated area of islands on nadikdik grew from 0 74 to 0 90 km2 observed changes to nadikdik reef islands manifested through a range of styles and were largely accretionary of note the formation of a new island was tracked from an embryonic deposit to a fully vegetated and stable island over a 61 year period similarly a number of previously discrete islands have agglomerated and formed a single larger island these changes were rapid and indicate that reef island formation can occur quickly evidence suggests that despite the typhoon occurring over a century ago the geomorphic adjustment of islands is still on going

physical modelling of reef island topographic response to rising sea levels abstract low lying coral reef islands are considered extremely vulnerable to the impacts of climate change particularly sea level rise and increasing storm magnitude inundation and erosion are expected to destabilise reef islands and render them uninhabitable within decades however such assertions are founded upon the assumption that reef islands are geomorphologically inert landforms whereas recent planform and cross sectional analysis of reef island morphodynamics demonstrates that many islands are highly dynamic landforms changing in size shape and position on the reef platform this paper describes the first physical modelling experiments to model the whole of island morphodynamic response of reef islands to changes in sea level and wave regime a wave basin is utilised to construct a 1 50 scale three dimensional model of fatato island tuvalu and document the whole of island response across a broad range of wave and water level conditions whole of island results corroborate flume studies and provide new insights into the modes and styles of island change spit rotation as well as lagoonward island recession and vertical oceanward crest accretion are identified as the core island responses to increasing water level and wave conditions however results show that the rate and magnitude of physical adjustment is strongly dependent on the rate and magnitude of sea level rise and wave conditions results challenge existing models of future island susceptibility to wave driven flooding demonstrating that washover processes can provide a mechanism to build and potentially maintain island freeboard above sea level these insights highlight an urgent need to incorporate island morphodynamics into flood risk models in order to produce accurate assessments of future wave driven flood risks and better resolve island vulnerability

geological effects of tsunami on mid ocean atoll islands the maldives before and after the sumatran tsunami low lying coral islands are fragile landforms susceptible to long term sea level rise and extreme events such as hurricanes and tsunamis the sumatran earthquake of 26 december 2004 generated waves that reached the maldives 2500 km away observations of the effects of the tsunami are presented here based on pre and post tsunami topographic and planform surveys of 13 uninhabited maldivian islands the surveys showed there was no substantial island erosion and no significant reduction in island area rather the tsunami accentuated predictable seasonal oscillations in shoreline change including localized retreat of exposed island scarps by up to 6 m deposition of cuspate spits to leeward and vertical island building through overwash deposition of sand sheets up to 0 3 m thick covering up to 17 of island area these results have implications for island stability indicating that low lying reef islands are physically robust and the geological signature of tsunamis on atoll island development is minor

high human influence on beach response to tropical cyclones in small islands saint martin island lesser antilles using multi date satellite imagery and field observations this paper assesses the inferred impacts of september 2017 cyclones on the beaches of saint martin island twenty two beaches out of 30 predominantly exhibited shoreline retreat with the highest retreat value 166 45 m recorded on the north eastern coast while erosion predominated on beaches and at the sand dune front inner areas generally exhibited accretion with sand sheets up to 135 m from the pre cyclone vegetation line indicating landward sediment transfer natural back reef beaches exhibited the formation of new beach ridges marked up to 2 m upward growth and alongshore beach extension the high spatial variability of inferred impacts is attributed to the cyclone s track coast exposure beach configuration and importantly human driven environmental change whereas vegetation removal exacerbated marine inundation and inhibited the vertical accretion of beaches shoreline hardening aggravated wave induced sediment loss while also inhibiting sediment deposition four beach response modes are distinguished based on findings we identified three major areas of action for risk reduction and adaptation to climate change depending on beach response and site specificities relocation and the determination of set back lines coastal buffer restoration or engineered structures upgrading should be prioritized

medium temperature fumarolic gas sampling in order to sample medium temperature fumaroles gases are collected by means of iron or glass tubings and conveyed to the condensation system through glass dewar tubes one type of condenser was designed for condensate measurement and gas sampling for radon activity determination the other with naoh absorbing solution for the s cl ratio measurement and the sampling of rare gases with this method it is possible to obtain precise gas vapour measurements as well as air free gas samples

exploring carbonate reef flat hydrodynamics and potential formation and growth mechanisms for motu abstract atolls which develop as reef building coral platforms extend to near sea level typically consist of a shallow reef flat encircling a central lagoon often sub aerial islets known as motu or reef islands consisting of sand gravel and coral detritus can be found perched atop the reef flat here we use hydrodynamic numerical modeling xbeach to better understand the role of waves and wave driven currents on the reef flat and the processes driving motu formation and evolution by differing representative reef flat geometry e g width and water depth we investigate the effects of varying wave climate on hydrodynamics and resultant bed shear stresses across the reef flat model results suggest that as a reef flat shallows bed shear increases then after passing a critical value decreases again using these results we hypothesize that reef flats should attain a critical water depth just at the threshold for sediment mobilization resulting in a constant depth reef flat in both abrasional and depositional settings as reef flats widen prograding into the back reef lagoon shear stress decreases across the flat with a minimum in shear stress arising approximately midway on the reef flat motu formation would be expected to initiate at this mid flat nucleation site either from a storm when coarse sediment is mobilized and deposited or gradually as the reef flat widens a mid flat deposit need not be subaerial to form a motu sediment piled shallower than the critical depth would continue to accumulate once a motu is present reef flat shear stress directions reverse and the motu shoreline should prograde seawards until reaching a relatively narrow critical reef flat width 200 m together these results suggest that reef flats and motu spatially self organize through a series of morphodynamic feedbacks

how lime sand islands in the south china sea have responded to global warming over the last 30 years evidence from satellite remote sensing images abstract as global warming threatens their existence there are widespread concerns regarding the persistence of lime sand islands and the future of mid ocean atoll nations to investigate how climate change has affected lime sand islands changes in vegetation and other characteristics of such islands in the south china sea scs were investigated from 1989 to 2019 using 67 satellite images first boundaries of the lime sand islands and their vegetation were extracted using an active contour extraction procedure called the gradient vector flow snake model afterwards the spatial extents were estimated by enclosing the extracted boundaries and the digital shoreline analysis system was used to calculate beach widths finally area growth rates and speeds were used to evaluate areal changes in the lime sand islands and their respective vegetation based on the estimated area growth rates area growth speeds and beach widths the lime sand islands in scs eroded over the past three decades whereas their vegetation expanded further analysis suggested that direct inundation caused by sea level rise might not be clearly identified from the satellite images however other climate change related factors were most likely responsible for the observed island erosions these factors included higher wave energy stronger typhoon intensity and destructiveness and accelerated coral reef degradation in addition the observed expansion of vegetation on the lime sand islands was likely due to the increase in precipitation in a warming world the results show that 1 the lime sand islands will continue to erode whereas vegetation will continue to expand 2 as vegetation growth is significantly inhibited by salt water when it is adjacent to the ocean vegetation areas on lime sand islands may start to continuously decline overall this study is the first to quantitatively examine changes in scs lime sand islands due to global warming

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

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

geochemical characteristics and the provenance of aeolian material in the hexi corridor desert china abstract the hexi corridor desert is in gansu province northwestern china the material provenance of desert formation and development is the primary factor of aeolian geomorphology and it is still not fully understood in the hexi corridor desert to identify sources of aeolian sand in the formation of dunes in the hexi corridor desert we investigated 12 sites and collected 70 samples from the dune surface this study used ratios between na2o al2o3 versus k2o al2o3 and sio2 al2o3 ba sr versus rb sr and rb sr versus ce sr as well as cao and cl composition to identify sediment provenance cao was enriched relative to the composition of the upper continental crust ucc consistent with a previous study conducted in the taklamakan and badain jaran deserts on adjacent fluvial lacustrine and gravel deserts but it differed from one study conducted in the kumtagh and tengger deserts cl concentrations differed in lacustrine and sand sediments being higher in lacustrine sediments followed by sand sediment sand sample geochemistry was similar throughout indicating that sources of sand formation were also similar which was confirmed by the multidimensional scaling mds and principal component analysis pca methods additionally based on regional topography the hexi corridor acts as a sediment sink not only for sediment from the qilian mountains but also for sediment from the beishan mountains the mds and pca approaches also indicated that sediment provenance was similar in the hexi corridor and the tengger badain jaran and kumtagh deserts therefore it can be concluded that dry fluvial deposits alluvial deposits and lacustrine sediments that combined comprised sand dune provenance were the sources of sand in the hexi corridor desert and these deposits derived from the qilian mountains in the southwest and the beishan mountains in the north through alluvial processes

fractionation of metals in volcanic emissions abstract the enrichment of some metals al mg na k cu zn cd in volcanic gases is measured by an emanation coefficient ex relating the amount of the element x in lavas and in aerosols ex is determined in the volcanic emissions of mount etna sicily with regard to that of210pb the accuracy of the results is limited by the geochemical behavior of common lead compared to that of210pb concerning the most volatile species it appears that practically all the volcanic aerosols are produced by evaporation followed by gas to particle conversion and the spattered fraction appears to be negligible

long lived radon decay products in mount st helens emissions an estimation of the magma reservoir volume abstract the size of the mount st helens magma reservoir is estimated from long lived radon decay products in fumarole emissions samples were collected in september 1981 on filters and by a new sampling technique developed for fumarole condensate the po 210 pb 210 activity ratios were significantly higher in the condensate than on the filters the difference is attributed to po 210 losses from the filters by a variety of processes and to trapping of po 210 in sulfur precipitate that prevents detection of alpha particles model calculations based on po 210 pb 210 and bi 210 activities give volume estimates for the degassing magma of about either 1 10 8 m 3 or 4 10 5 m 3 d according to the model utilized

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

eruption of basalt and andesite lava degasses 222rn and 210po activities of 222rn and 210po were measured in a september 1983 basic andesite lava from arenal and a november 1983 basalt from kilauea starting 3 and 1 days after eruption respectively in both cases in growth patterns show that all rn volatalized during eruption po degassing also was complete at kilauea but only 84 10 at arenal

volcanic emission of radionuclides and magma dynamics 210pb 210bi and210po the last decay products of the238u series are highly enriched in volcanic plumes relative to the magma composition moreover this enrichment varies over time and from volcano to volcano a model is proposed to describe 8 years of measurements of mt etna gaseous emissions the lead and bismuth coefficients of partition between gaseous and condensed phases in the magma are determined by comparing their concentrations in lava flows and condensated volatiles in the case of volatile radionuclides an escaping time is calculated which appears to be related to the volcanic activity finally it is shown that that magma which is degassing can already be partly degassed it should be considered as a mixture of a few to 50 of deep non degassed magma with a well degassed superficial magma cell

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