origins of mineral matter in peat marsh and peat bog deposits spain abstract the mineralogy of three back barrier peat marshes torreblanca benicasim and moncofar marshes from eastern spain and one peat bog orihuela del tremedal bog from central east spain have been investigated using x ray diffraction xrd and scanning electronic microscope sem techniques a combination of xrd methods was used to quantify the mineralogy of dried bulk peat samples the water source in the peat marshes is both continental and marine water is highly mineralised water flow is both low and slow accumulative system the water source in the peat bog is continental draining from the hill the higher concentration of ions in the water of the back barrier peat marshes leads to a higher concentration of authigenic minerals in the peat marshes compared to the peat bog three main mineral origins have been recognized namely detrital syngenetic epigenetic and biogenic the more important contribution comes from the detrital system biogenic and bio influenced minerals are the main non detrital minerals in the peatlands this paper discusses the biogenic origin of halite and other minor halides and sulphates such as sylvite carnalite epsomite glauberite mirabilite and anhydrite from halophytic plants as well as amorphous silica opal a from sponge spicules and phytoliths of several plants pyrite in the peat bog has both syngenetic and epigenetic origins from plant decomposition and sulphur release in the peat marsh the pyrite has a syngenetic origin from sulphate reduction s sulphate s pyritic and an epigenetic origin in the older peat from plant decomposition s organic s pyritic

new zealand s most easterly palaeotsunami deposit confirms evidence for major trans pacific event abstract sedimentary geochemical geomorphological radiocarbon and numerical modelling data were used to examine the nature extent and age of a boulder scatter at okawa point chatham island new zealand boulders up to 98 t were traced around 800 m inland and comprised both a landward and seaward grouping on either side of a mid holocene high stand storm ridge dated to around 4840 4810 cal bp the landward boulder scatter was linked with an enigmatic coarse sand gravel layer that extends up to 1100 m inland and has been dated to around 3500 4500 cal bp numerical modelling indicated that while the seaward boulders that mainly rest upon the chatham island schist shore platform could have been emplaced by either storm or tsunami waves those landward of the mid holocene storm ridge were most probably transported by a tsunami there are several near contemporaneous palaeotsunami deposits reported from mainland new zealand australia sw pacific and the wider pacific region if some or all of these are associated with the same basin wide palaeotsunami then it appears likely to have been one of the largest holocene pacific palaeotsunamis an analysis of historical and numerically modelled data suggests that the most likely candidate is from within the northern chile seismic gap with early evidence suggesting that a large palaeoseismic and palaeotsunami event may have occurred around 4000 yr bp if correct this has important implications for assessing the largest possible magnitude earthquakes in the northern chile seismic gap and the size of the tsunamis they generate

the largest local tsunami in 20th century hawaii abstract the 1975 kalapana tsunami had waves that ran up to 14 6 m high it deposited a discontinuous basalt boulder and carbonate sand veneer on the halape apua point coast of the island of hawaii these deposits fine up to 320 m inland and 10 4 masl the deposit is an unusual sedimentary association in which sand sized material is a minor component both boulders and sand fine inland over the same distance not in a continuum and they terminate at approximately the same point boulders were transported and deposited by only one wave the second whereas the sand deposit was in part reworked by subsequent smaller waves boulder transport by one wave in association with a relative paucity of finer sediment reduced internal clast interference and helped to impart a marked fining inland sequence this fining inland sequence is at odds with work that proposes a chaotic or random nature of boulder emplacement by tsunamis where there is abundant sediment clast interference during entrainment will impede the fining inland of larger material in cases where it is difficult to determine the nature of inundation or the number of tsunamis a chaotic pattern may simply reflect deposition by storm tsunami or a combination of the two

a record of local storms and trans pacific tsunamis eastern banks peninsula new zealand this study of five sand units at lavericks bay new zealand reports on the sedimentary evidence for three trans pacific tsunamis and two local storms the 1868 arica 1877 iquique and 1960 valdivia tsunamis from chile were the largest distantly generated events in new zealand s history but have never before been identified at the same location it is also the first time that the 1877 iquique tsunami deposit has been found in new zealand two further sand units were identified as local storm deposits laid down in 1869 1870 and 1929 the identification and chronology of these events were established through the use of geochemistry palynology diatoms charcoal abundance and historical documents their relative magnitudes were estimated through the use of grain size parameters and lateral extent of the recognisable sand layers the recognisable sandy tsunami deposits extend about 60 of the inundation distance while the storm sediments are finer and less extensive there were two notable geochemical diffe

reply to comments by kelletat 2008 comments to dawson a g and stewart i 2007 tsunami deposits in the geological record sedimentary geology 200 166 183

microstructural preservation and the effects of diagenesis on the carbon and oxygen isotope composition of late cretaceous aragonitic mollusks from the gulf coastal plain and the western interior seaway the carbon and oxygen isotope compositions of calcium carbonate shells are widely accepted and applied proxies for tracking changes in paleoenvironmental conditions such as temperature salinity and productivity in order to accurately interpret isotopic measurements diagenetic alteration must first be assessed the occurrence of aragonitic shells is often taken as a first order sign of unaltered material because aragonite at the earth9s surface is metastable and converts to calcite however even specimens that retain an aragonitic composition and are macroscopically well preserved often exhibit subtle to considerable signs of alteration when shell microstructure is examined using scanning electron microscopy sem to determine the textural and isotopic effects of progressive alteration on differing types of shell microstructure we undertook a comparative study of aragonitic shells from two regions frequently used in paleoenvironmental reconstructions and diagenetic studies the upper cretaceous of the gulf coastal plain gcp and the western interior seaway wis because the gcp is within a passive margin setting and the wis has experienced tectonic processes we also evaluate how diagenetic history affects isotopic composition visually well preserved ammonite bivalve and gastropod shells were collected from one locality in the gcp and examined using sem to evaluate microstructural preservation we used a previously published scale based on wis specimens for nacreous shell material and a complementary scale we developed for crossed lamellar microstructure the stable carbon and oxygen isotope compositions of specimens across the preservational scale from both regions were analyzed isotopic composition does not change systematically with degrading preservation in the gcp specimens a result that contrasts strongly with patterns in wis specimens where isotopic composition systematically decreases with decreasing microstructural preservation dissimilar tectonic regimes that led to unique post depositional conditions for each region are invoked to explain this difference the wis was a foreland basin subjected to significant meteoritic groundwater flow driven by active uplift while the gcp was a passive margin that has remained close to sea level with low hydraulic potential since the time of deposition thus during diagenesis the wis shells were exposed to fluids that differed greatly from the seawater in which the organisms grew whereas diagenetic fluids in gcp settings likely were similar to marine waters as expected shells with the best preserved microstructure provide the most consistently reliable isotopic data for paleoenvironmental reconstructions but our comparisons show that similar degrees of microstructural alteration can express very different diagenetic shifts in isotopic values

comments to dawson a g and stewart i 2007 tsunami deposits in the geological record sedimentary geology 200 166 183

a 7300 year record of environmental changes in a coastal wetland moawhitu new zealand and evidence for catastrophic overwash tsunami abstract three sedimentary sequences from a coastal wetland behind a sand barrier on the west coast of d urville island new zealand were examined using a multi proxy approach including sedimentological geochemical and microfossil diatom analyses with the chronology established using radiocarbon and 210pb dating data show that a brackish lagoon started developing 7300 year ago after formation of the sand barrier in moawhitu this was followed by periods of alternating wetland encroachment and open water displaying spatial variations until a peatland was established about 1300 cal yr bp the wetland was then partially drained in the early 1900s leading to compaction of the peat near the surface a coarse layer containing gravel sand and shells with a sharp lower contact in the northern area of the wetland is attributed to an overwash about 2500 3000 yr bp most probably a tsunami generated by the rupture of a local or regional fault the high resolution continuous record obtained with xrf core scanning revealed a geochemical signature ca and s for the overwash 600 m inland in the middle area of the wetland while it was absent from the southern site 1 1 km from the shore this suggests that except at the northern end of moawhitu the sand dune acted as an effective barrier preventing any sediment from overtopping 2500 3000 yr bp with only a geochemical evidence marking the extent of seawater inundation no sedimentological or geochemical evidence could be found in the wetland for the 15th century tsunami that had destroyed almost an entire community in moawhitu as recounted in m ori oral tradition p r kau although pebbles at the surface of the dune are likely to be linked to this event thus the sand dune appears to have again acted as an effective barrier for the overwash in the 15th century however our study suggests that the area might have been impacted by more than one tsunami in the last 3000 years it also shows that a high resolution continuous xrf record can provide the evidence for short term changes catastrophic or not that did not leave any clear sedimentological signature thus providing a better insight of environmental changes in any depositional environment

geochemical evolution of kohala volcano hawaii kohala volcano the oldest of five shield volcanoes comprising the island of hawaii consists of a basalt shield dominated by tholeiitic basalt pololu volcanics overlain by alkalic lavas hawi volcanics in the upper pololu volcanics the lavas become more enriched in incompatible elements and there is a transition from tholeiitic to alkalic basalt in contrast the hawi volcanics consist of hawaiites mugearites and trachytes 87sr 86sr ratios of 14 pololu basalts and 5 hawi lavas range from 0 70366 to 0 70392 and 0 70350 to 0 70355 respectively this small but distinct difference in sr isotopic composition of different lava types especially the lower 87sr 86sr in the younger lavas with higher rb sr has been found at other hawaiian volcanoes our data do not confirm previous data indicating sr isotopic homogeneity among lavas from kohala volcano also some abundance trends such as mgo p2o5 are not consistent with a simple genetic relationship between pololu and hawi lavas we conclude that all kohala lavas were not produced by equilibrium partial melting of a compositionally homogeneous source

multi proxy evidence for trans pacific tsunamis in the hawai ian islands abstract the origin of two sand layers buried in polol wetland on the northeast coast of the island of hawai i was investigated using a multi proxy approach including radiometric dating sedimentology geochemistry micropalaeontology palynology and historical records based on 210 pb 137 cs and pollen data the lower sand unit extending 250 to 350 m inland is attributed to the 1946 aleutian tsunami while the upper sand unit was laid down by the 1957 aleutian tsunami chronological information does not appear to support any link between these deposits and historical storm events furthermore sedimentological geochemical diatom and pollen results suggest deposition of marine and near beach sediments under high energy conditions typically associated with tsunami inundation this work presents the first conclusive sedimentary evidence for distantly generated tsunamis on the hawai ian islands opening the way for more comprehensive historical and palaeotsunami studies indeed a brief review of archaeological data suggests that the hawai ian coast may have experienced similar large magnitude events in the past from both local and distant sources

historical tsunami and storm deposits during the last five centuries on the sanriku coast japan abstract nine event deposits in a small alluvial valley along the sanriku coast japan were correlated with historical tsunamis and storms that have been recorded in this region since the 15th century we identified nine sandy layers in 15 geo slices collected at distances ranging from 140 to 260 m from the coast in a lowland back marsh protected from the sea by a high sandy ridge based on their sedimentary characteristics grain size distribution and marine microfossil assemblages namely coccoliths these event layers which were well preserved in their order of deposition were probably either tsunami or storm deposits diatom analysis revealed four stages of paleo environmental change from tidal marsh to wetland the uppermost event layer covering the ground surface is probably the deposit from the 2011 tohoku oki tsunami ages for other event deposits were radiometrically dated using 14 c 137 cs and 210 pb with bayesian estimation the second event layers can be correlated with the 1960 chilean or 1968 aomori oki earthquake tsunamis the candidates for the third event layer are the 1947 catherine and 1948 ione typhoons as well as the candidates for the second event layer the fourth and fifth event layers are likely associated with the 1933 and 1896 sanriku oki earthquake tsunamis four lower event layers can be correlated with historical tsunamis and storms that occurred during the 15th to 18th centuries such as the 1611 sanriku oki earthquake tsunami

geological evidence and sediment transport modelling for the 1946 and 1960 tsunamis in shinmachi hilo hawaii abstract the japanese community of shinmachi established on low lying land between downtown hilo and waiakea hawaii was obliterated by the 1946 aleutian tsunami but was rebuilt only to be destroyed again by the 1960 chilean tsunami the aim of this study was to find out if any geological evidence of these well documented events had been preserved in the sedimentary record in wailoa river state park which replaced shinmachi after the 1960 tsunami this was achieved by collecting cores in the park and performing sedimentological chronological and geochemical analyses the latter also processed by principal component analysis sediment transport modelling was carried out for both tsunamis to infer the source of the sediment and areas of deposition on land the field survey revealed two distinct units within peat and soil a thin lower unit composed of weathered basalt fragments within mud unit 1 and an upper unit dominated by fine volcanic sand within fine silt exhibiting subtle upward fining and coarsening unit 2 consisting of unit 2a and unit 2b although these two anomalous units only occur on the western shore of waiakea mill pond analysis with an itrax core scanner shows that unit 1 is characterised by high mn fe rb la and ce counts combined with elevated magnetic susceptibility based on its chemical and sedimentological characteristics unit 1 is attributed to a flood event in wailoa river that occurred around 1520 1660 ce most probably as a result of a tropical storm the sharp lower contact of unit 2 coincides with the appearance of arsenic contemporaneous with an increase in ca sr si ti k zr mn fe la and ce in this study as is used as a chronological and source material marker as it is known to have been released into wailoa river estuary and waiakea mill pond by the canec factory between 1932 and 1963 thus not only the chemical and sedimentological evidence but also sediment transport modelling corroborating the historical record suggest that unit 2a was deposited by the 1946 tsunami and the sediment most likely originated from wailoa river estuary beach and nearshore seafloor the upper part of this unit unit 2b is believed to have been deposited by the 1960 tsunami as suggested by sediment transport modelling although limited accommodation space is likely to have resulted in the thin deposit 3 cm thickness present at that site limited accommodation space on the island of hawaii has led to only rare locations where tsunami deposits are preserved despite the repeated occurrence of tsunamis affecting the island

chemical signatures of palaeotsunamis a forgotten proxy article i nfo article history a range of diagnostic criteria are required to help identify palaeotsunami deposits although chemical signatures have long been used as indicators of palaeosalinity in sedimentary sequences their use in the studies of palaeotsunami deposits is rarely applied and is yet to be widely recognised the chemical composition of interstitial water in coastal ponds and sedimentary sequences in coastal marshes and lagoons has been used successfullyasanindicatoroftsunamiinundation chemicalsignaturescanalsoprovidecluesaboutthelandward limit of runup of a tsunami beyond the area of sediment deposition like most palaeotsunami proxies however the preservation of chemical signatures varies with environmental conditions

the tsunami phenomenon abstract with human activity increasingly concentrating on coasts tsunamis from japanese tsu harbour nami wave are a major natural hazard to today s society stimulated by disastrous tsunami impacts in recent years for instance in south east asia 2004 or in japan 2011 tsunami science has significantly flourished which has brought great advances in hazard assessment and mitigation plans based on tsunami research of the last decades this paper provides a thorough treatise on the tsunami phenomenon from a geoscientific point of view starting with the wave features tsunamis are introduced as long shallow water waves or wave trains crossing entire oceans without major energy loss at the coast tsunamis typically show wave shoaling funnelling and resonance effects as well as a significant run up and backflow tsunami waves are caused by a sudden displacement of the water column due to a number of various trigger mechanisms such are earthquakes as the main trigger submarine and subaerial mass wastings volcanic activity atmospheric disturbances meteotsunamis and cosmic impacts as is demonstrated by giving corresponding examples from the past tsunamis are known to have a significant sedimentary and geomorphological off and onshore response so called tsunamites form allochthonous high energy deposits that are left at the coast during tsunami landfall tsunami deposits show typical sedimentary features as basal erosional unconformities fining upward and landward a high content of marine fossils rip up clasts from underlying units and mud caps all reflecting the hydrodynamic processes during inundation the on and offshore behaviour of tsunamis and related sedimentary processes can be simulated using hydro and morphodynamic numerical models the paper provides an overview of the basic tsunami modelling techniques including discretisation guidelines for appropriate temporal and spatial resolution as well as the nesting method furthermore the boussinesq approximation a simplification of the three dimensional navier stokes equations is presented as a basic theory behind numerical tsunami models which adequately reflects the non linear dispersive wave behaviour of tsunamis the fully non linear boussinesq equations allow the simulation of tsunamis e g in the form of n waves based on the various subtopics presented recommendations for future multidisciplinary tsunami research are made it is especially discussed how the combination of sedimentary and geomorphological tsunami field traces and numerical modelling techniques can contribute to derive locally relevant tsunami sources and to improve the assessment of tsunami hazards considering the individual pre history and physiogeographical setting of a specific region

diatom assemblages in tsunami deposits associated with the 2004 indian ocean tsunami at phra thong island thailand abstract diatom assemblages in sandy deposits of the 2004 tsunami at phra thong island thailand may provide clues to flow conditions during the tsunami the tsunami deposits contain one or more beds that fine upward commonly from medium sand to silty very fine sand diatom assemblages of the lowermost portion of the deposit predominantly comprise unbroken beach and subtidal species that live attached to sand grains the dominant taxa shift to marine plankton species in the middle of the bed and to a mix of freshwater brackish and marine species near the top these trends are consistent with expected changes in current velocities of tsunami through time during high current velocities medium sand is deposited only beach and subtidal benthic diatoms attached to sediment can be incorporated into the tsunami deposit high shear velocity keeps finer material including planktonic diatoms in suspension with decreasing current velocities finer material including marine plankton can be deposited finally during the lull between tsunami waves the entrained freshwater brackish and marine species settle out with mud and plant trash low numbers of broken diatoms in the lower medium sand implies rapid entrainment and deposition whilst selective breakage of marine plankton thalassionema nitzschioides and thalassiosira and coscinodiscus spp in the middle portion of the deposit probably results from abrasion in the turbulent current before deposition

expanding the proxy toolkit to help identify past events lessons from the 2004 indian ocean tsunami and the 2009 south pacific tsunami article i nfo some of the proxies used to identify palaeotsunamis are reviewed in light of new findings following the 2004 indian ocean tsunami and the 2009 south pacific tsunami and a revised toolkit provided the new application of anisotropy of magnetic susceptibility ams to the study of tsunami deposits and its usefulness to determine the hydrodynamic conditions during the emplacement of tsunami sequences together with data from grain size analysis are presented the value of chemical proxies as indicators of saltwater inundation associated marine shell and or coral high energy depositional environment and possible contamination is demonstrated and issues of preservation addressed we also provide new findings from detailed studies of heavy minerals new information gathered during the unesco international oceanographic commission ioc international tsunami survey of fine onshore sediments following the 2009 south pacific tsunami is presented and includes grain size chemical diatom and foraminifera data the tsunami deposit varied ranging from fining upward sand layers to thin sand layers overlain by a thick layer of organic debris and or a mud cap grain size characteristics chemical data and microfossil assemblages provide evidence for marine inundation from near shore and changes in flow dynamics during the tsunami

extreme wave deposits on the pacific coast of mexico tsunamis or storms a multi proxy approach abstract historical and instrumental data show that the pacific coast of mexico has been exposed to destructive tsunamis over at least the past 500 years this coast is also affected by hurricanes generated in the eastern pacific the great 1985 mexico earthquake and its aftershock generated tsunamis that affected the ixtapa zihuatanejo and michoacan coast the purpose of our study was two fold a to determine whether storm and tsunami deposits could be distinguished and b whether tsunami deposits from historical events are preserved in the tropical environments of the ixtapa zihuatanejo coast two anomalous sand units in the ixtapa estuary are interpreted to be the result of high energy marine inundation events that occurred in the last century several lines of evidence using a multi proxy approach historical studies interviews with local witnesses geomorphological and geological surveys coring and trenching laboratory analyses including grain size micropaleontology geochemistry magnetic susceptibility and radiometric dating and numerical modeling indicate the occurrence of two tsunamis that we link to local events the 21st september 1985 mexico and possibly the 14th march 1979 petatlan earthquakes we thereby provide the first onshore geological evidence of historical tsunamis on the pacific coast of mexico

coseismic and pre seismic subsidence associated with great earthquakes in alaska abstract alternating beds of peat and mud in sediment sequences on the south central alaskan coast record coseismic and inter seismic relative land and sea level movements caused by repeated great earthquakes on the alaska aleutian subduction zone during the ad 1964 mw 9 2 earthquake tidal marshes and wetlands around upper cook inlet experienced up to 2 m of subsidence burying peat forming communities with intertidal mud here we use quantitative analyses of fossil diatoms within peat mud couplets to reconstruct land sea level changes for the 1964 and five earlier great earthquakes during the past 3300 years in contrast to geodetic observations that are limited to the present post seismic phase we quantify varying spatial patterns of uplift and subsidence through complete earthquake cycles relative land uplift characterises most of the inter seismic phase of each cycle at our sites whereas each great earthquake was preceded by a short period of pre seismic relative land subsidence

analysis of environmental controls on tsunami deposit texture abstract tsunamis transport large amounts of sediment and can leave recognisable signatures in the landscape the form and composition of onshore tsunami deposits are a function of wave dynamics sediment availability and characteristics of the local environment the latter of which also partially controls preservation of the deposit this research reviews these relationships in a global context and assesses the connection between tsunami deposit particle size and four controlling parameters climate temperature and rainfall density of tsunami sediments degree of coastal protection and distance between tsunami source and sediment deposition an international dataset of tsunami deposit locations and texture was compiled from published literature and existing databases values for environmental variables were calculated for each location from global datasets of temperature rainfall coastline shape and tsunami source locations spearman s rank order correlation principal component analysis pca and hierarchical cluster analysis ca were used to analyse relationships between these variables pca results show an inverse relationship between particle size and sediment density climate variables and distance from source ca results support this suggesting a cluster structure controlled primarily by particle size and secondly by climate and sediment density these relationships can be explained by the influence of the environment on antecedent morphology and the composition of sediments available for tsunami transport

historical tsunamis and storms recorded in a coastal lowland shizuoka prefecture along the pacific coast of japan four sand units deposited by tsunamis and one sand unit deposited by storm surge s were identified in a muddy marsh succession in a narrow coastal lowland along the pacific coast of central japan tsunamis in ad 1498 1605 1707 and 1854 that were related to large subduction zone earthquakes along the nankai trough and storm surges in 1680 and or 1699 were responsible for the deposition of these sand units these sand units are distinguished by lithofacies sedimentary structures grain size and mineral composition and radiocarbon ages their ages are supported by events in local historical records the tsunami deposits in the study area are massive or parallel laminated sands with associated intraclasts gravels draping mud layers and rarely a return flow subunit the storm surge deposits are devoid of these characteristics and are composed of groups of thin current ripple laminated sand layers the differences in sedimentary structures between the tsunami and storm surge deposits are attributed to the different characteristics of tsunami and storm waves

dating tsunami deposits present knowledge and challenges abstract dating approaches for fine sediment tsunami deposits can be divided into two categories 1 dating directly using materials from within a tsunami deposit and 2 dating indirectly using materials from above and below it for the former optically stimulated luminescence osl dating has a possible advantage in that is can directly date the burial age of sediments laid down by a tsunami however because of methodological limitations osl dating cannot always provide a reliable age although 14c and u th dating of reworked material from within a tsunami deposit are possible means of determining the age of the event the results merely represent a maximum age of deposition for these reasons dating is commonly achieved indirectly from 14c dates taken from samples in sections immediately above and below a tsunami deposit however indirectly dated results do not provide a precise timing of the event therefore there are distinct limitations in the ability to obtain high precision dating of past tsunamis recent methodological developments including the application of bayesian statistical analysis to radiocarbon dating results and the selection of appropriate dating materials has significantly improved the accuracy of age determination by reducing errors this review presents several methodological improvements that have enhanced tsunami deposit age estimation the most important points for a more precise tsunami age estimation are the numbers of 14c samples dated coupled with the use of bayesian statistical analysis these points are applicable not only to tsunami deposits but also to many other past geohazard events

morphological signatures of fault lines in an earthquake prone zone of southern baromura hill north east india a multi source approach for spatial data analysis a critical review in a recent work dey et al environ earth sci 59 353 361 2009 presented some new observations on the southern part of one of the anticlinal ridges of tripura viz the baromura range the work incorporated a number of irregularities and misinterpretations that need to be addressed to avoid future confusion the present article critically reviews dey et al s paper to bring out its inaccuracies

distinguishing tsunami and storm deposits an example from martinhal sw portugal abstract geological identification of past tsunamis is important for risk assessment studies especially in areas where the historical record is limited or absent the main problem when using the geological evidence is to distinguish between tsunami and storm deposits both are high energy events that may leave marine traces in coastal stratigraphic sequences at martinhal sw portugal both storm surge and tsunami deposits are present at the same site within a single stratigraphic sequence which makes it suitable to study the differences between them excluding variations caused by local factors the tsunami associated with the lisbon earthquake of november 1st 1755 ad had a major impact on the geomorphology and sedimentology of martinhal it breached the barrier and laid down an extensive sheet of sand as described in eyewitness reports besides the tsunami deposit the stratigraphy of martinhal also displays evidence for storm surges that have breached and overtopped the barrier flooding the lowland and leaving sand layers both marine derived flood deposits show similar grain size characteristics and distinctive marine foraminifera the most important differences are the rip up clasts and boulders exclusively found in the tsunami deposit and the landward extent of the tsunami deposit that everywhere exceeds that of the storm deposits identification of both depositional units was only possible using a collection of different data and extensive stratigraphical information from cores as well as trenches

geochemical signatures up to the maximum inundation of the 2011 tohoku oki tsunami implications for the 869 ad jogan and other palaeotsunamis abstract the geochemical signature of the tohoku oki tsunami deposit and underlying soil was assessed two months five months and seven months after the 11 march 2011 tsunami inundated the sendai plain the extent of the recognisable sand deposit was traced up to 2 9 km inland while a mud deposit was found up to 4 65 km inland representing 60 and nearly 95 of the maximum tsunami inundation respectively the limit of tsunami inundation was identified 4 85 km from the shore using geochemical marine markers s and cl two months after the tsunami in the absence of any sedimentological evidence concentrations of other geochemical markers k ca sr indicative of the marine incursion and associated minerals were found to decrease landward 13 c and 15 n and c n ratios suggested a mixture of terrestrial and marine organic sources in the sediment while 34 s of sulphate reflected the marine source of water soluble salts the chemical composition of the 869 ad jogan tsunami sand deposit was characterised by high sr and rb concentrations and was comparable to that of the tohoku oki tsunami deposit suggesting that the sources of sediment may be similar marked decreases in s and cl with time indicated that rainfall resulted in the leaching of salts from the sandy sediments however both s and cl markers as well as sr were still well preserved in the muddy sediments and underlying soil beyond the limit of the recognisable sand deposit seven months after the tsunami this suggests that geochemical indicators may well be useful in identifying the extent of historical and palaeotsunamis by determining the marine origin of fine grained sediments beyond the limit of recognisable sand deposition in particular when marine microfossils are sparse or lacking as is the case on the sendai plain this would allow researchers to redraw palaeotsunami inundation maps and re assess the magnitude of events such as the jogan tsunami and other palaeotsunamis not only on the sendai plain but also elsewhere around the world this has important implications for tsunami risk assessment hazard mitigation and preparedness

pitfalls of normalization of marine geochemical data using a common divisor abstract normalization of trace element contents of sediment through division by the content of an immobile element usually aluminum is common practice in marine geochemical studies this might appear to be a simple way of correcting for dilution by sedimentary phases barren of a particular trace element for instance carbonates or silica and for comparison with its content in a standard clay or shale the purpose of this paper is to revive the awareness of the pitfalls of this practice by giving numerical examples of the often unexpected results of normalization taking a statistical perspective it is first shown that uncorrelated variables acquire spurious correlations when normalized but normalization can also increase decrease change sign of or even blur the correlations between unmodified variables next a number of realistic scenarios are worked out to show that the correlations between normalized element contents still suffer from the closure effect only in a few simple cases it is possible to extract from the normalized data realistic estimates of trace element contents in distinct sedimentary phases such as organic matter this is ascertained from data on copper contents in sediment from the black sea and arabian sea when the coefficient of variation i e standard deviation divided by the mean of the aluminum data is relatively low and much lower than for the original values of the trace elements comparisons of correlations can equally well or even better be made on the basis of the unmodified values then the comparison of trace element data with their values for standard shales is discussed the inherent problem is that the composition of the commonly used standard shale and consequently the reference values of normalized elements are not necessarily representative of the local or regional sediments in the study area also this method falls short of identifying the processes responsible for enrichment or diminution in trace element contents finally consideration is given to some aspects of a proper use of al normalization

megatsunami deposits on kohala volcano hawaii from flank collapse of mauna loa the origin of coastal and high elevation marine gravels on the hawaiian islands of lanai and molokai is controversial because the vertical tectonics of these islands is poorly constrained the gravels are either from eustatic highstands or were left by massive tsunamis from offshore giant landslides in contrast at kohala on the island of hawaii where continuous subsidence is well established lithofacies analysis and dating of a fossiliferous marine conglomerate 1 5 61 m above present sea level support a tsunami origin and indicate a runup of 400 m 6 km inland the conglomerate age 110 10 ka suggests a tsunami caused by the ca 120 ka giant alika 2 landslide from nearby mauna loa volcano

sediment sources and sedimentation processes of 2011 tohoku oki tsunami deposits on the sendai plain japan insights from diatoms nannoliths and grain size distribution abstract the 11th march 2011 tohoku oki tsunami inundated the low lying sendai plain japan more than 5 km inland leaving sand and mud deposits over most of the area in order to establish the sources of the tsunami deposits and interpret processes of their sedimentation samples were collected from the deposits underlying soils and the beach along a shore perpendicular transect and analysed for grain size diatom assemblages and nannoliths the fining inland tsunami deposits consisted of poorly to moderately sorted medium to coarse sand within 2 km of the coastline and very poorly to poorly sorted mud farther inland more specifically there was a slight fining of the coarse to medium sand mode within the sandy deposits and an increased contribution of the coarse and very coarse silt fraction in the mud deposits the tsunami deposits also exhibited vertical changes including fining upward and coupled coarsening fining upward trends few diatoms were present in beach sediments soils and tsunami deposits within 1 km of the coastline while diatoms were more abundant farther inland diatom assemblages in the soil and tsunami deposits were similar and dominated by species typical of freshwater brackish habitats while no typically marine species were encountered nannoliths were generally absent in the studied sediments except for few specimens our data indicate that there was probably no or only a very minor component of marine sediments transported onland by the tsunami the sandy tsunami deposits within 1 km of the coastline were mostly derived from beach and dune erosion from 1 to 2 km landward the contribution of these sources decreased while sources comprising local soil erosion and the entrainment of sediments from the teizan bori canal increased farther inland local soil erosion was the major sediment source for the mud deposits the tsunami deposits were most likely deposited during at least two inundations mostly out from suspension resulting in an upward grain size fining trend however bed load deposition was also important in the sandy deposits as suggested by a common grain size upward coarsening position on c m diagrams and frequent horizontal lamination the present study reveals that even very large tsunamis may not transport marine sediments onland and thus many commonly applied indicators of tsunami deposits based on the assumption of their offshore origin marine diatoms foraminifera nannoliths marine sediments may be of limited use

a geochemical approach for identifying marine incursions implications for tsunami geology on the pacific coast of northeast japan abstract potential tsunami inundation areas can be predicted by the distribution of paleo tsunami deposits on land which are mainly composed of marine derived sands and muds these exotic sandy and muddy layers have been identified by multiple approaches however there still remain uncertainties regarding the sources and weathering trends over the long term and other useful proxies need to be investigated to identify of tsunami deposits we examined the geochemical signatures of modern tsunami deposits from the pacific coast of northeast japan 2011 tohoku tsunami and those paleo tsunami deposits taken from the tohoku district jogan 1080 calibrated ages before present cal bp and yayoi ca 2000 cal bp a geochemical ternary diagram seawater rock as metals showed the weathering trends of tsunami deposits over approximately 2000 years in the sendai plain in the tohoku in the tsunami layers from the tohoku the na ti atomic ratios markedly increased to 23 4 with an average value of 19 3 3 0 jogan and yayoi tsunami deposits which was clearly higher than those of other layers soil deposits 10 3 3 5 on average these results show that na ti ratios and other geochemical proxies are useful indicators of marine incursions in our case and may contribute to the detection of muddy tsunami deposits close to the limit of inundation

refractory element mobility in volcanic soils refractory trace element concentrations in strongly weathered hawaiian soils ranging in age from 20 to 4100 ka are highly elevated over parent rock values due to extensive mass loss of more soluble major elements during pedogenesis nb and ta exhibit virtually no mobility soil nb ta ratios are within the range of fresh bedrock even when soil nb concentrations are residually enriched by a factor of 10 in contrast al zr and hf are depleted relative to nb in surface soil horizons but are enriched at depth clearly indicating mobility of these elements variations in th nb ratios in soil profiles indicate significant th mobility within the soil column however mass balance calculations require that accretion of th enriched asian dust has resulted in a net increase in th in some soils soils developed on a 150 ka rainfall gradient show that the mobility and loss of zr increase with mean annual precipitation

geochemical and petrographical characteristics of a domed bog nova scotia a modern analogue for temperate coal deposits a freshwater domed bog in nova scotia canada was investigated for its petrographic mineralogical and geochemical characteristics three cores were taken from the lagg zone margin and centre to examine different stages of evolution in a fen to domed bog sequence based on this study a model was developed which shows the relationship between factors controlling peat geochemistry and petrography all of them being dependent on trophic conditions the bog may represent a modern analogue for temperate coal deposits and thus can be used to help understand spatial variability within coal beds rheotrophic conditions in the early stages of mire development result in the formation of high ash highly humified carex dominated peat while the evolution toward ombrotrophic conditions is reflected in a progressive replacement by low ash and well preserved sphagnum dominated peat the associated decrease in ph reflects a decrease of groundwater influence which is also supported by the mineralogical assemblage and petrographic data decrease in reflectance and change in maceral composition except for cl br i and se which are associated with the organic fraction variations in elemental composition can be explained in terms of mineral matter abundance i e decrease upward and with increasing distance from the margin sea spray is the most probable origin for halogen enrichment in the peat

the sedimentary record of the 1960 tsunami in two coastal lakes on isla de chiloe south central chile abstract this study describes sediments deposited by the tsunami following the 1960 great chilean earthquake mw 9 5 in two coastal lakes lakes cucao and huelde on the west coast of isla de chiloe south central chile 42 6 s sub bottom profiles and side scan sonar mosaics illustrate the sedimentary context of transects of gravity cores the stratigraphy of both lakes features gyttja sedimentation interrupted by the abrupt emplacement of a sandy layer with mud rip up clasts and a mud cap this sandy layer reflects a sudden change in sedimentary environment most probably caused by a high energy inundation radionuclide analyses 137cs and 210pb date the inundation deposit to shortly before the mid 1960s the only known event that matches the sedimentological and chronological criteria is the ad 1960 tsunami using grain size analysis and comparisons with samples from modern environments we demonstrate that the proximal seaward part of the deposit consists of a mixture of sand derived from subaerial sources and reworked gyttja lake sediment in the distal landward part of lake cucao the sand component is lost and the deposit consists entirely of remobilised lake sediments the repetition of tsunami deposit sequences in lake huelde suggests a minimum of three inundating waves sub bottom profiles and side scan sonar mosaics reveal tsunami inundation over the barrier and more prominently through the outlet river channel the dominant role of the river channel as a pathway for sediment transport is also described in core samples by tsunami deposits that fine away from the channel mouth the identification and description of the deposit left by a known tsunami provide important insights into tsunami sedimentation in coastal lakes and have the potential to help in the search for paleotsunami evidence

island edifice failures and associated tsunami hazards volcanic ocean islands are prone to structural failure of the edifice that result in landslides that can generate destructive tsunamis these island landslides range enormously in size varying from small rock falls to giant sector failures involving tens of cubic kilometers of debris a survey of literature has allowed us to identify twenty three processes that contribute to edifice collapse these have been divided into endogenetic and exogenetic sources of edifice failure endogenetic sources of instability and failure include unstable foundations volcanic intrusions thermal alteration edifice pore pressures unbuttressed structures and buried faults exogenetic sources of instability and failure include collapse of subaerial or submarine deposits endo upwelling karst megaporosity fractures oversteepening overloading sea level change marine erosion weathering including hurricanes glacial response volcanic activity regional uplift or subsidence tectonic seismicity and anthropogenic agents while the endogenetic sources dominate during periods of active volcanism and cone building the exogenetic sources may cause failure at any time tsunamis both small and large are associated with these edifice failures

coastal wetlands reveal a non synchronous island response to sea level change and a palaeostorm record from 5 5 kyr to present here we describe environmental change on lord howe island lhi 31 30 s 159 05 e over the last 5500 cal bp derived from the analysis of the accumulating sediments in four coastal wetlands grain size analyses loss on ignition loi and micrometre resolution x ray fluorescence xrf geochemical data were combined with 10 accelerator mass spectrometry ams 14c dates to determine a chronology of environmental change sedimentary coastal features were initiated on the drowned lhi basalt coastline after 4500 cal bp which was followed by gradual development of wetland environments from 4200 cal bp to present within this period a series of high intensity storm events are recorded perhaps related to low pressure systems including cyclones and east coast low ecl events a lack of synchronicity between the studied sites resulted from their position in the landscape relative to the coast features within the lagoon and greater sediment availability after 2800 cal bp as sediment filled sinks in the

volcano meteorological tsunamis thec ad 200 taupo eruption new zealand and the possibility of a global tsunami meteorological tsunamis are long period waves that result from meteorologically driven disturbances they are also generated by phase coupling with atmospheric gravity waves arising through powerful volcanic activity the ad 1883 krakatau eruption generated volcano meteorological tsunamis that were recorded globally because of its extreme violence and energy release 150 50 megatons explosive yield and by analogy with the krakatau event it is highly possible that the ignimbrite emplacement phase of the c ad 200 taupo eruption of north island new zealand generated a similar volcano meteorological tsunami that may have reached coastal areas worldwide tsunami deposits of identical age to the taupo eruption occur in central coastal new zealand and probably relate to that event definitive evidence elsewhere has not yet been found in theory volcano meteorological tsunamis are likely to be produced during comparable eruptive events at other explosive volcanoes and thus represent an additional volcan

tsunami deposits in a super large wave flume abstract understanding the process of sediment transport under tsunami inundation is essential to providing credible information about potential tsunamis from tsunami deposits in this study a super large wave flume 205 m long and 3 4 m wide was used to investigate the hydraulic process of tsunami inundation and sedimentary features of the resulting tsunami deposit a uniformly sloping topography 1 50 with a sand dune 0 2 m high was built in the flume and the topography change induced by a solitary wave was measured the maximum wave height at the shoreline was 0 6 m and the horizontal velocity reached up to 3 5 m s resulting in a sediment concentration of up to 5 by volume the inundation and return flow completely eroded the dune and caused deposition which showed landward and seaward thinning and fining the vertical distribution of grain size and density in the inundation flow indicated upward fining and an upward decrease in density and the deposits showed inverse grading at the base in addition to normal grading therefore the inverse grading was attributed to the depositional process instead of the vertical distribution of grain size in the flow such as via a traction carpet the inundation flow was classified into two phases the first phase flow which appeared at the front of the inundation flow was governed by the wave speed at the shoreline the second phase flow which occurred near the dune was controlled by the difference in wave levels in front of and behind the dune the deposits caused by the first phase flow near the inundation limit were constant regardless of the presence of the dune indicating that the effect of the dune on the deposits was limited in the nearshore region the deposits near the inundation limit showing rapid fining and different chemical compositions were carried by muddy foam floating on the water surface the sediment supply from offshore to onshore over the dune was small and the erosion of the sand dune accounted for 36 of the onshore deposits the offshore deposits were mainly caused by wave motion and the contribution of the onshore sediment brought by the return flow was small 24 however the return flow had a large effect on the sedimentary structure of the offshore deposits such as seaward fining our results will help to examine the physical processes resulting in the empirically established common sedimentary characteristics of tsunami deposits and will provide a detailed data set to validate sediment transport models used in numerical simulations

sedimentological and geophysical properties of a ca 4000 year old tsunami deposit in southern spain abstract the coastlines around the gulf of cadiz were affected by numerous tsunami events damaging infrastructure and causing countless human losses a tsunami deposit at barbate zahara de los atunes spain is located at various heights above mean sea level and shows several characteristics indicative of high energy event deposition this study uses sedimentology foraminifera assemblage magnetic susceptibility x ray fluorescence analysis ground penetrating radar gpr to support an interpretation of high energy deposition and determine the deposit s transport mechanisms and sediment source radiocarbon and optically stimulated luminescence dating of the tsunami deposit reveals ages of 4000 bp and does not support the ad 1755 lisbon event as suggested in former publications

effects of rainy season on mobilization of contaminants from tsunami deposits left in a coastal zone of thailand by the 26 december 2004 tsunami study on contamination of tsunami sediments deposited on 26 december 2004 conducted shortly after the tsunami in coastal zone of thailand revealed elevated contents of salts in water soluble and some heavy metals and arsenic in bioavailable fractions szczucinski et al in env geol 49 321 331 2005 few months later rainy season started and effected in total rainfall of over 3 300 mm this paper presents results of survey repeated 1 year after the tsunami to assess the effects of rainy season on mobilization of previously determined potential contaminants the same locations were sampled again and analysed with the same methods the tsunami deposit layer was well preserved but in many locations the sediments were coarser than just after tsunami due to washing out of finer fractions the water soluble salts contents were strongly reduced after the rainy season however the concentrations of acid leachable heavy metals and metalloids were still elevated in comparison to reference sample from an area not impacted by tsunami it is possible that the metals and metalloids are successively moved to more bioavailable fraction from forms which were more resistant to mobilization

geochemistry of the hawi lavas kohala volcano hawaii hawi lavas form the late stage alkalic cap on kohala volcano and range in composition from hawaiite to trachyte new detailed field mapping of kohala and reinterpretation of previously published age data suggest that there was no significant eruption hiatus between the hawi and underlying pololu shield lavas as was previously suggested mineral and whole rock chemical data are consistent with a crystal fractionation origin for the hawaiite to trachyte compositional variation observed within the hawi lavas plagioclase clinopyroxene ti magnetite olivine and apatite fractionation are needed to explain this variation the clinopyroxene fractionation may have occurred at moderate pressure because it is virtually absent in these lavas and is not a near liquidus phase at pressures of less than 8 kb plagioclase would be buoyant in the hawi hawaiite magmas so a mechanism like dynamic flow crystallization is needed for its fractionation and to account for the virtual absence of phenocrysts in the lavas hawi lavas are distinct in sr and nd isotopic ratios and or incompatible element ratios from the pololu lavas thus they were derived from compositionally distinct sources compared to other suites of hawaiian alkalic cap lavas hawi lavas have anomalously high concentrations of phosphorus and rare earth elements these differences could be due to greater apatite content in the source for the hawi lavas

history and features of trans oceanic tsunamis and implications for paleo tsunami studies abstract far field tsunamis and their features as well as methods to quantify trans oceanic tsunamis are reviewed with examples of instrumental and historical data tsunamis from the 1854 nankai earthquakes the 1946 aleutian tsunami earthquake the 1960 and 2010 chile earthquakes as well as the 2011 tohoku earthquake were recorded around the pacific ocean the 1883 krakatoa volcanic eruption caused volcanic tsunami in the indian ocean and meteotsunami in the pacific ocean the 2004 indian ocean tsunami was also recorded in the pacific ocean when a tsunami amplitude is larger than that of ocean tides which usually requires the parent earthquake to be gigantic mw 9 it can cause damage and may be historically documented the trans pacific tsunamis described in historical documents include those from the 1700 cascadia earthquake the 1730 1751 1837 and 1877 earthquakes off chile and the 1687 and 1868 earthquakes off peru the tsunami record in japan from the 1586 peru earthquakes was found to be incorrect and should be discounted the tsunami magnitude scale relates the tsunami heights to the earthquake size tsunami travel time can be computed from actual bathymetry and the tsunami ray tracing provides relative amplitudes due to focusing defocusing caused by irregular bathymetry numerical computations from fault models produce tsunami amplitudes and waveforms and indicate strong directivity due to strike of fault or orientation of subduction zones far field tsunamis are often long lasting due to multiple reflections across the basin or on continental shelf or due to resonance in bays harbors these features would provide important criteria to estimate tsunami sources from paleo tsunami data

tsunami sediments and their foraminiferal assemblages abstract tsunami hazard assessment begins with a compilation of past events that have affected a specific location given the inherent limitations of historical archives the geological record has the potential to provide an independent dataset useful for establishing a richer chronologically deeper time series of past events recent geological studies of tsunami are helping to improve our understanding of the nature and character of tsunami sediments wherever possible geologists should be working to improve the research tool kit available to identify past tsunami events marine foraminifera single celled heterotrophic protists have often been reported as present within tsunami deposited sediments but in reality little information about environmental conditions and by analogy the tsunami that deposited them has been reported even though foraminifera have an enormous capacity to provide meaningful palaeo environmental data here we review what foraminifera are describe their basic form and significance summarise where they have been reported in tsunami sediments and identify what can be learnt from them we review the gaps in our understanding and make recommendations to assist researchers who examine foraminiferal assemblages in order to enhance their use within tsunami geology

a tsunami ca 6300 years bp and other holocene environmental changes northern hawke s bay new zealand abstract sediment cores collected in a coastal lagoon a few kilometres east of wairoa northern hawke s bay new zealand were examined using sedimentological geochemical palynological and micropaleontological analyses a distinct short lived catastrophic saltwater inundation csi about 6300 years bp and possibly other minor marine incursions are preserved in the coastal estuarine to lagoonal freshwater sedimentary sequences which have been deposited in the last 6500 years the csi is characterised by a gravel unit that thins landward and decreases in particle size to sand within a sequence consisting mainly of brackish estuarine muds diatom assemblages indicate a marked change from the shallow brackish estuarine muds to marine gravels and sands to brackish estuarine muds the marine influence in the gravel and sand is also shown by the presence of marine dinoflagellates and a peak in na rb sedimentological chemical and paleontological in particular diatoms evidence indicates it is a csi we conclude that this was a tsunami and propose the most likely propagating mechanisms marine influence decreases upcore and totally freshwater conditions are evident in the upper section of the cores the geochemistry of the sediments mainly reflects the change in stratigraphy with distinct signatures for tephra na fe cr organic rich and peat units as br and the coarse gravel sand csi unit na rb cr fe but it is also indicative of changes in depositional environment the change in chemistry na rb in the csi event is indicative of a saltwater influence whereas a marked change in s content suggests a sudden change from brackish to freshwater conditions shortly after 4800 years bp another peak in s and br content about 3200 years bp may indicate another temporary change to brackish conditions

coastal evolution on volcanic oceanic islands a complex interplay between volcanism erosion sedimentation sea level change and biogenic production abstract the growth and decay of oceanic hotspot volcanoes are intrinsically related to a competition between volcanic construction and erosive destruction and coastlines are at the forefront of such confrontation in this paper we review the several mechanisms that interact and contribute to the development of coastlines on oceanic island volcanoes and how these processes evolve throughout the islands lifetime volcanic constructional processes dominate during the emergent island and subaerial shield building stages during the emergent island stage surtseyan activity prevails and hydroclastic and pyroclastic structures form these structures are generally ephemeral because they can be rapidly obliterated by marine erosion with the onset of the subaerial shield building stage coastal evolution is essentially characterized by rapid but intermittent lateral growth through the formation of lava deltas largely expanding the coastlines until they typically reach their maximum extension with the post shield quiescence in volcanic activity destructive processes gradually take over and coastlines retreat adopting a more prominent profile mass wasting and marine and fluvial erosion reshape the landscape and if conditions are favorable biogenic processes assume a prominent role post erosional volcanic activity may temporarily reverse the balance by renewing coastline expansion but islands inexorably enter in a long battle for survival above sea level reef growth and or uplift may also prolong the island s lifetime above the waves the ultimate fate of most islands however is to be drowned through subsidence and or truncation by marine erosion

reciting the layers evidence for past tsunamis at mataora wairau lagoon aotearoa new zealand abstract sedimentary geochemical microfossil and geochronological analyses were carried out on 10 sediment cores across the south eastern corner of mataora wairau lagoon m wl south island aotearoa new zealand this multi proxy approach provides strong evidence for three late holocene palaeotsunamis two previously unreported and a historical tsunami generated by rupture of the wairarapa fault in 1855 ce the main scientific evidence for these events consists of anomalous high energy marine sediment layers that overlie material of contrasting composition these layers coincide with peaks in planktonic and benthic marine to brackish marine diatoms and geochemical signatures indicative of sudden changes in environmental conditions palaeotsunami i maximum date 2095 cal bp and palaeotsunami ii maximum date 915 cal bp previously identified by clark et al 2015 appear to represent large events contemporaneous with major earthquakes inducing tectonic uplift and coseismic subsidence around the cook strait region palaeotsunami ii is close to the date of the earliest settlement of the m wl area by m ori and a traditional narrative that references loss of life following waves over washing the wairau boulder bank given the boulder bank was likely to have been seaward of its current position during events i and ii we surmise that the inundation distances would have been greater than the most landward extent 340 m inferred from the deposits found in this study palaeotsunami iii maximum date 525 cal bp was associated with tectonic subsidence across the study site most likely associated with rupture of the southern hikurangi subduction zone we expect the ongoing refinement of the methods used in this study and the results from future studies of analogue sites and offshore fault systems will improve our understanding of the significant tsunami hazard facing this region

sedimentology of rocky shorelines 3 hydrodynamics of megaclast emplacement and transport on a shore platform oahu hawaii abstract megaclasts of well cemented coralgal limestone have been emplaced onto a shore platform by large waves on the north shore of oahu hi emplacement and movements of the largest ca 96 ton megaclast have been dated using aerial photographs hydrodynamic forces at the low submerged shoreline cliff are computed using design wave characteristics based on linear wave theory and experimental results considering the local wave climate and near shore bottom topography force exerted by a tsunami has been estimated based on the 1946 aleutian tsunami the computed forces are evaluated in terms of the initial fracturing along a given failure plane that is required in order for the detachment to occur the analysis shows that tsunami as well as large swell waves are capable of quarrying the megaclast provided that sufficient initial fracturing is present dislodgement and emplacement most likely occurred in a sequence during impact of a single wave on the shoreline cliff swell waves however are seldom capable of emplacing large blocks onto the platform due to their rapid disintegration after breaking so that most blocks quarried from the cliff edge fall back onto the submarine terrace emplacement of large boulders seems to require extreme sea waves with periods longer than storms or north pacific swells usually produce transport mechanisms on the shore platform vary depending on megaclast shape sliding is a common mechanism of transport for larger and irregular megaclasts whereas somewhat smaller and platy megaclasts are occasionally found in overturned positions

recent storm and tsunami coarse clast deposit characteristics southeast hawaiʻi abstract deposits formed by extreme waves can be useful in elucidating the type and characteristics of the depositional event the study area on the southeast coast of the island of hawai i is characterized by the presence of geologically young basalts of known age that are mantled by recent wave derived sedimentary deposits the area has been impacted by large swells storms and tsunamis over the last century and in combination with known substrate ages makes this an ideal location to study recent deposits produced by such events three distinct coarse clast deposit assemblages can be recognized based on clast size composition angularity orientation packing elevation and inland distance of the deposit these deposits are characterized as one of three types 1 gravel fields of isolated clasts primarily boulder size material and scattered pockets of concentrated sand and gravel in topographic lows 2 shore parallel and cuspate ridges composed mostly of rounded basalt gravel and sand with small amounts of carbonate detritus the ridges range in height from about 1 to 3 m and are 10s of m wide 3 cliff top deposits of scattered angular and sub angular clasts along sea cliffs that are generally greater than 5 m elevation the gravel fields are primarily of tsunami origin from either the 1975 kalapana event or a combination of the 1975 tsunami and 1868 tsunami or earlier events the ridge deposits are presently active and sediment continues to be added during high wave events the cliff top deposits contain evidence of deposition by both tsunami and storm processes and require further investigation