the lefkada barrier and beachrock system nw greece controls on coastal evolution and the significance of extreme wave events abstract the lefkada preveza coastal zone nw greece is characterised by an active barrier system and related extensive beachrock sequences besides the gradual coastal processes of longshore drift and spit evolution the presence of active tectonics and the occurrence of tsunamis have been documented in previous studies and are part of the coastal geomorphological system in this paper we present the results of detailed multi proxy sedimentological and geomorphological investigations carried out along the northern part of the barrier system and in back beach positions our findings suggest that extreme wave events contributed to coastal and environmental changes and involved temporary breakdown of the barrier system sedimentary findings suggest that one generation of event deposits may be related to the 365 ad crete earthquake and associated tsunami according to our results the lefkada coastal system formed by the interaction of both long term gradual and sudden impulsive littoral geomorphodynamics extreme wave events are assumed to have played a significant role in the evolution of the present coastline acting as recurrent impulsive disturbances of the coastal system subsequently the onset of long term gradual coastal processes such as longshore drift re established a state of natural coastal balance by re arranging the coastal sediments

characterizing thermohaline intrusions in the north pacific subtropical frontal zone abstract a monthlong field survey in july 2007 focused on the north pacific subtropical frontal zone stfz near 30 n 158 w combined towed depth cycling conductivity temperature depth ctd profiling with shipboard current observations measurements were used to investigate the distribution and structure of thermohaline intrusions the study revealed that local extrema of vertical salinity profiles often used as intrusion indicators were only a subset of a wider class of distortions in thermohaline fields due to interleaving processes a new method to investigate interleaving based on diapycnal spiciness curvature was used to describe an expanded class of laterally coherent intrusions stfz intrusions were characterized by their overall statistics and by a number of case studies thermohaline interleaving was particularly intense within 5 km of two partially compensated fronts where intrusions with both positive and negative salinity anomalies were widespread the vertical and cross frontal scales o

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

boulders as a signature of storms on rock coasts this paper is the first review of coastal boulder studies it serves as a peer reviewed introduction to a special issue on the topic of boulders as a signature of storms on rock coasts since 2004 and the indian ocean tsunami most coastal boulder research has been focused on using boulders as sedimentary signatures of palaeo tsunami events and the most commonly used transport equations typically suggest that large boulder deposits are products of tsunami rather than storms there is growing empirical evidence demonstrating on inter annual to century timescales that storm waves are capable of transporting and depositing boulders of significant size at elevations well above sea level current process studies of how boulders are eroded transported and deposited have not received wide attention by rock coast geomorphologists or palaeoenvironmental reconstruction scientists this special issue is framed around the goal of highlighting our current understanding of the role of storm waves as a driving mechanism for boulder erosion transport and deposition here we review the current state of knowledge about boulder dynamics boulder responses to storms and boulders as sedimentary signatures of storm events we identify gaps in our conceptual and quantitative understanding lastly we propose means of addressing research gaps improving consistency between researchers and collecting multi purpose data this review and the papers contained within the special issue provide an improved understanding of coastal dynamics particularly the role storms can play in influencing erosion rates and depositional patterns of coarse material i e boulders or larger which has hitherto been under represented in the literature

boulders transport by catastrophic waves along the ionian coast of apulia southern italy abstract several tracts of the ionian coast of apulia southern italy are characterized by large boulders up to 80 t in weight scattered some meters above present sea level the largest boulder is about 80 t in weight and slid for about 40 m from the mean sea level up to about 1 8 m of altitude elongated boulders show a remarkably narrow range of orientation of the long axis as well as of the imbrication axis suggesting that they had been transported by a single catastrophic event most likely a tsunami connected to a wave train approaching the coast from the south stratigraphic morphological and historical data suggest that this event occurred during the late holocene conventional radiocarbon age determination performed on lithophag shells collected from a large boulder yielded a calibrated age between 1421 and 1568 a d then the catastrophic wave train probably a tsunami could be a local effect of the strong earthquake which hit southern italy on december 5th 1456

bonaire s boulder fields revisited evidence for holocene tsunami impact on the leeward antilles abstract supralittoral boulders and blocks are prominent sedimentary features along rocky shorelines worldwide in most cases their deposition is attributed to high energy wave events tsunamis severe storms even though tsunami waves are expected to have higher transport capacities compared to storm waves megaclasts of up to 100 t were observed to have been moved laterally by the latter waveform the deduction of certain extreme wave events tsunamis severe storms from the boulder record thus remains a major challenge in palaeo event research the debate on their differentiation is ongoing at the eastern coast of bonaire leeward antilles in the southern caribbean numerous limestone blocks and boulders up to c 130 t are distributed on top of a 3 6 m a s l above mean sea level palaeo reef platform disagreement exists among a number of authors concerning the transport processes involved in the formation of the boulder fields in this paper state of the art modelling approaches of coastal boulder entrainment and transport were applied in order to provide new and more reliable data to support challenge the working hypothesis of tsunami deposition to improve the reliability of the boulder transport model more realistic input parameters were provided by new dgps measurements of the boulder dimensions and the calculation of bulk densities by taking into account the heterogeneity of the reef rock boulders existing hydrodynamic equations were modified to allow for the irregular shape and real dimensions of the boulders the results indicate that i boulder weight and dimension and thus ii calculated wave energy and wave heights were overestimated in most of the previous studies where calculations of boulder volume were based on multiplication of the main axes the results of this study and wave heights observed during recent severe tropical cyclones seem to rule out storm generated waves for the dislocation of the largest blocks however the majority of coarse clast deposits may have been generated by periodic hurricane swells the results underline the significance of more realistic field data in modelling boulder transports by waves

intensification of ocean fronts by down front winds abstract many ocean fronts experience strong local atmospheric forcing by down front winds that is winds blowing in the direction of the frontal jet an analytic theory and nonhydrostatic numerical simulations are used to demonstrate the mechanism by which down front winds lead to frontogenesis when a wind blows down a front cross front advection of density by ekman flow results in a destabilizing wind driven buoyancy flux wdbf equal to the product of the ekman transport with the surface lateral buoyancy gradient destabilization of the water column results in convection that is localized to the front and that has a buoyancy flux that is scaled by the wdbf mixing of buoyancy by convection and ekman pumping suction resulting from the cross front contrast in vertical vorticity of the frontal jet drive frontogenetic ageostrophic secondary circulations ascs for mixed layers with negative potential vorticity the most frontogenetic ascs select a preferred cross front width and do not translate with

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

characterisation of erosional features associated with tsunami terrains on rocky coasts of the maltese islands in recent years there has been a growing body of literature on depositional signatures associated with historic extreme waves on rocky coasts here in the context of the maltese islands we place an innovative focus on evidence of erosional forms the field evidence is concentrated along the ne flank of the islands at a topographically varied range of sites and up to an altitude of 13 m asl a range of forms is broadly classified in terms of their morphologies and the forces responsible for their formation sockets eroded scarps scoured terrains clifftop erosion scars swept terrains and spillways are interpreted as consequences of overwashing of the landscape by an extreme wave or waves these forms are shown to be controlled by flow intensity topography and lithology and especially rock bedding and jointing they comprise the source areas for associated depositional evidence allowing transport paths to be estimated and may significantly enhance the reconstruction of extreme wave events it is likely that similar and additional erosional forms are present elsewhere in the mediterranean domain where comparable lithological and topographic situations are exposed to extreme waves

a unique 4000 year long geological record of multiple tsunami inundations in the augusta bay eastern sicily italy abstract we present the geological evidence for a 4000 year long record of multiple tsunami inundations along the coast of the augusta bay eastern sicily and discuss its implications the research was carried out through a multi theme approach which benefited from an extraordinarily long historical record that we used to guide detailed geomorphologic and geologic surveys coring campaigns and laboratory analyses two sites named the augusta hospital and priolo reserve were selected and investigated in detail along the 25 km long coastline of augusta bay we found evidence for six possibly seven tsunami deposits three of them may be tentatively associated with the 1693 and 365 ad ionian sea historical tsunamis and the 3600 bp santorini event the other three possibly four deposits are evidence for unknown paleo inundations dated at about 650 770 ad 600 400 bc and 975 800 bc at augusta hospital site and 800 600 bc at priolo reserve site we use these ages to extend further back the historical record of tsunamis available for this coastal area the exceptional number of tsunami deposits found with this study allowed us to derive an average geologic tsunami recurrence interval in the augusta bay of about 600 years for the past 4 ka conversely the historical tsunami data for the past millennium suggest an average tsunami recurrence interval of about 250 years this difference in the average recurrence intervals suggests that only the strongest inundations may leave recognizable geological signatures at the investigated sites i e the evidence for the 1908 and 1169 tsunamis is missing but also that the geomorphological setting of the site and its erosional depositional history are critical aspects for the data recording thus an average recurrence interval derived from the geological record should be considered as a minimum figure the identification and age estimation of tsunami deposits represent a new and independent contribution to tsunami scenarios and modeling for coastal hazard assessment in civil protection applications furthermore our study cases provide new elements on tsunami deposit recognition related to exceptionally large events that occurred in the aegean sea

characteristics and hydrodynamics of boulders transported by storm waves at kudaka island japan abstract this study investigates the size position and the long axis orientation of 210 boulders at kudaka island japan these boulders were deposited from the reef crest to the slope of the back reef moat distributed within 275 m from the reef edge most boulders were rectangular to ellipsoidal without sharp broken edges they are reef rock fragments estimated as

the role of hydrodynamic impact force in subaerial boulder transport by tsunami experimental evidence and revision of boulder transport equation abstract the hydrodynamic impact contributes to the initiation of subaerial boulder transport by tsunamis and tsunami like flows here we consider two approaches to modelling this impact force hydrostatic and hydrodynamic and assess the suitability of each in boulder transport models the model proposed solved as an ordinary differential equation eliminates the need to assume a conservative value of flow acceleration introducing the hydrodynamic impact force reduces by almost 45 the recognised overestimation of threshold flow velocity in simple hydrodynamic models for boulder transport by contrast including the hydrostatic impact force reduces the overestimation by less than 10 we found the new model consistent with the results of simple flume experiments in these experiments three rectangular limestone blocks of 27 70 cm3 in subaerial pre transport setting condition were subjected to tsunami like flow by sudden opening of a sluice gate

large boulders along the south eastern ionian coast of sicily storm or tsunami deposits abstract this study investigates the size shape position pre transport setting and long axis orientation of 175 boulders found along the south eastern ionian coast of sicily these megaclasts were deposited by the sea or moved from the same rocky coast to the shore platform and distributed within 60 m of the shoreline most boulders are rectangular to ellipsoidal with sharp broken edges they are calcarenite fragments up to 27 t in mass some of the boulders up to 32 m from shore were observed to have moved after strong winter storms occurring during december 2008 january 2009 whereas the positions of many boulders were unchanged we use wave transport equations jointly with statistical analysis of boulders in order to determine the extreme events geological or meteorological responsible for these singular accumulations using the significant wave height and period of maximum observed storms and historical tsunamis 1693 and 1908 events along the ionian coast of sicily we have estimated the approximate transport distance of boulders by these waves at the coast results show that the largest storm waves were probably responsible for the current distribution of most boulders however since the size and horizontal displacement distance of some boulders scattered randomly along the shoreline at distance 40 m cannot be explained by storm wave action we suggest that they are likely deposited by tsunamis radiocarbon dating performed on three of these anomalous boulders at a distance 40 m from the shoreline gave an age suggesting that two of them were likely deposited by the 1693 or 1908 tsunamis whereas the third was emplaced by a tsunami that occurred after 650 930 a d we show that both wave processes storm and tsunami can deposit boulders we find that the significant difference between storm and tsunami waves is not the breaking wave height but the wave period that influences attenuation and then the flooding distance hence if the boulder transport limit of the largest storm waves in the past at the study area is estimated then it is possible to recognize that the boulders deposited far beyond this limit because of their size and shape were not transported by storm waves but could have been emplaced by waves with longer period such as the tsunamis

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

extremely high energy wave deposits inside the great barrier reef australia determining the cause tsunami or tropical cyclone abstract a hydrodynamic approach is used to determine whether tsunami or cyclone generated waves were responsible for the deposition of fields of well imbricated rock boulders up to 290 tonnes along the coast of cairns inside the great barrier reef australia calculations of the overturning moments show that only tsunami are capable of moving such large boulders in this environment it is hypothesised that large tsunami 11 m have been able to penetrate the great barrier reef through wide 5 10 km 50 70 m deep passages between individual reefs three such passages each approximately 35 km apart and oriented in the same direction exist in the cairns region it is possible that these passages have funnelled and amplified palaeotsunamis the preferential location of eroded coral boulders up to 3 m in length on reef flats alongside these passages and their absence on other reefs throughout the region provide further evidence that extremely high energy waves have been able to penetrate the great barrier reef into the inner channel adjacent to the mainland carbon 14 ages of the coral boulders on these reef flats matches closely the ages of coral fragments pinned below the very large rock boulders along the coast these ages suggest that the cairns region has experienced large tsunami twice over the last millennium

a quasi experimental setting of coarse clast transport by the 2010 chile tsunami bucalemu central chile abstract on 27th february 2010 a mw 8 8 earthquake occurred in central chile causing a tsunami that severely affected the central chilean coast in this study we present sedimentological data of the 2010 chile tsunami from the coastal town of bucalemu in central chile the tsunami deposited both fine grained sediments as well as cobbles and boulders the location offers a quasi experimental setting for coarse clast transport because an artificial pile of cobbles and boulders was piled there for construction purposes some days before the tsunami therefore the pre tsunami transport setting and transport distances are well defined additionally a local flow depth of ca 2 m and flow speed of ca 5 6 m s are deduced from eyewitness reports and video recordings the cobbles and boulders have been transported up to 155 m from the pile in landward direction the size of the quarried clasts was restricted to max 0 3 m3 and 720 kg bigger boulders were not available at the location even though calculations show that the tsunami would have been capable to transport them calculations of flow speeds required for the initialization of transport in different modes such as sliding rolling or saltation indicate that all clasts that were moved by the tsunami in landward direction were entrained by the flow given a minimum observed speed of 5 6 m s with 65 being transported by rolling and 35 by saltation the transported clasts are arranged in three groups positioned in morphological depressions on the coastal plain a landward fining trend is not present the arrangement of clasts originating from a pile and being deposited in distinctive groups entails that the landward transport of cobbles and boulders is a function of repeated entrainment transport and deposition by several waves of the tsunami wave train consequently we interpret the clast distribution as a result of a combination of the number of individual waves of the tsunami wave train their respective energies the local topography and the pre transport setting of a clast pile which releases wedged clasts with each successive wave

numerical models of tsunami sediment transport current understanding and future directions abstract researchers who study tsunami deposits share common ultimate goals of their work which are to better assess the magnitude information of paleotsunamis and to contribute to the assessment of future tsunami risks numerical modeling of tsunami sediment transport is an important piece of interdisciplinary research that fills the gap between geological studies and practical utilization of tsunami deposits forward and inverse numerical models that address tsunami transport of sand and boulders have been developed over the last two decades forward models are capable of delineating the time evolution of tsunami hydrodynamics sediment transport and the resulting morphological changes associated with erosion and deposition inverse models estimate tsunami characteristics such as flow speed and depth from deposits numerical modeling can be used not only to quantify paleotsunamis but also to enhance our understanding of tsunami sedimentology and hydrodynamics to make progress towards the ultimate goal of improved tsunami risk assessment development of an in depth mutual understanding between modelers and geologists of the advantages limitations and uncertainties in both numerical modeling and geological records is an important challenge

boulder emplacement on a tectonically stable wave dominated coastline mission rocks northern kwazulu natal south africa abstract the presence of large boulders along rocky coastlines is a useful indicator as to the occurrence and nature of past storms and or tsunami field observations from mission rocks northern kwazulu natal south africa allowed for the assessment of historical high magnitude wave events in the area a total of 143 anomalously large boulders were assessed in terms of their dimensions morphologies and distribution along a regionally developed 3 m raised shore platform based on long intermediate and short axes relationships we calculate boulder masses of up to 9 03 t that were found to have been transported horizontally shoreward for up to 65 m based on geomorphological evidence we infer that the majority of boulders encountered were from a joint bound pre transport setting additionally overturning of the boulders was apparent we assess the boulder field numerically via the numerical model of pignatelli et al 2009 which we deemed most applicable for slab like boulders such as those encountered here results yielded a maximum breaking storm wave height of 11 36 m or a maximum tsunami height of 2 84 m an analysis of swell data revealed that the modelled storm wave heights fell within the range defined by the storm wave records for the area within the past 32 years boulder alignments were likewise compatible with the wave regime of the northern kwazulu natal coastline additional review of offshore seismic records and landslide hazards on the tectonically stable passive margin show that the tsunami hazard for landslides within the area is negligible the findings suggest a storm provenance as the causal mechanism for boulder emplacement at mission rocks

stable imbrication and delicate unstable settings in coastal boulder deposits indicators for tsunami dislocation abstract medium sized and coarse debris pebbles and boulders can exhibit patterns of setting particularly if they are elongated or tabular these patterns such as imbrication indicate certain transport processes mostly as to direction and character many years of observation and measuring of coarse coastal deposits are the basis for the conclusions presented here on environmental transport processes their character and their energy beside imbrication special emphasis is given to unstable or delicate settings of large boulders that evidently have remained in these positions from hundreds to thousands of years this deserves an explanation to how they arrived at these positions and why they have not changed into a more stable position given an environment of constant energy input along coastlines the discussion lays emphasis on whether both settings of mega boulders can be indicative of tsunami transport processes

coastal boulders as evidence for high energy waves on the iranian coast of makran abstract coastal boulder deposits attesting to large waves are found along the rocky coast of makran iran from chabahar to lipar boulders are either scattered on the rocky coastal platform or accumulated in imbricated clusters the boulders are mostly rectangular and composed of biogenic calcarenite deriving from the present coastal platform significant morphological features observed on the boulders include supratidal karstic pools sharp broken edges and fractures some boulders contain boreholes and shells of marine bivalves suggesting detachment and transportation from the subtidal zone the dimensions elevation and distance from the coastline of 58 representative boulders are documented to estimate their volume weight and inland displacement the boulders weighing up to 18 t are found up to 6 m above present mean sea level and up to 40 m from the present shoreline we applied hydrological models to estimate and compare the wave height and inundation distance required to transport the boulders inland our results demonstrate that no known or probable storm event on the makran coast is capable of detaching and transporting the boulders in contrast tsunami wave height of 4 m is enough to detach all the boulders from the rocky coast and transport them inland we conclude that a tsunamigenic origin for boulder deposits is most plausible our results imply that the western part of the makran coast has archived evidence of paleotsunami events probably generated by large earthquakes at the makran subduction zone

large boulder deposits by tsunami waves along the ionian coast of south eastern sicily italy abstract the ionian coast of south eastern sicily between the towns of augusta and siracusa is characterized by the occurrence of anomalous calcareous boulders they are mostly scattered along large terraces located 2 5 m above sea level gently sloping towards the sea boulders are up to 182 t in weight and are arranged either in isolated elements or small groups composed of a few stacked elements several boulders show biogenic encrustations serpulids balanids lithophaga all over their surface which suggest that they were dragged from the mid sublittoral zone other boulders are partially covered by biogenic encrustations and show morphological features karstic pools exposed fracture surfaces suggesting that they were detached and scattered from the mid supralittoral zone direct observations on each boulder distance from the shoreline size and weight together with statistical analysis of the storm regime of the area allowed to operate hydrodynamic estimations useful to verify if tsunami or storm waves were responsible for their detachment and transport while radiocarbon age determinations on marine organisms constrained the timing collected data compared to historical catalogues suggest that in the last 1000 years three seismic events with local sources could have triggered tsunami waves associated with the boulder deposits occurring in the area the first two were probably triggered by the earthquakes of february 4 1169 and january 11 1693 which destroyed south eastern sicily according to geological data and numerical modelling the seismogenic source could be located in the ionian offshore between catania and siracusa the third tsunami was generated by the strong earthquake which took place in the strait of messina on december 28 1908

large boulder accumulation on the algerian coast evidence tsunami events in the western mediterranean abstract evidence of catastrophic mega block deposition is presented for the algerian coast from tipaza to dellys the region is prone to large earthquakes several of which are inferred to be tsunamigenic in origin as attests the 2003 zemmouri earthquake mw 6 8 it is argued here that several former tsunamis have resulted in the detachment of large boulders from the nearshore zone and their deposition inland the estimated size weight volumetric mass and distance from the shoreline of more than 100 boulders has enabled estimates to be made of the nature of the hydrodynamic waves responsible for their transport the boulders weigh up to 200 tons and are scattered along 150 km of rocky headlands and pocket beaches in isolated or grouped elements from the subtidal to supratidal zones boulders covered by biogenic incrustations show morphological features which suggest detached reversed and reworked pieces statistical and hydrodynamic analyses indicate that large boulder transport requires either 30 m high waves or 5 to 10 m high waves for catastrophic storm or tsunami events respectively bio indicators allow us to date two inferred tsunamis as having struck the algerian coastline between ad 400 600 and ad 1700

tsunami landfalls in the maltese archipelago reconciling the historical record with geomorphological evidence the maltese islands lie in the middle of the tsunamigenic mediterranean domain around whose margins and islands evidence of historic tsunami landfall has been increasingly recognized in recent years critical review of historical evidence of events in 1693 and 1908 indicates extremely modest tsunami impacts in marked contrast though recently discovered geomorphological evidence summarized herein suggests that malta s coastlines have been overwashed up to elevations of 20 m asl by an exceptional event a new perspective is provided by a review of the central mediterranean context within which the maltese evidence is located recent advances in understanding of the holocene sequence forming the mediterranean sea floor present a new stratigraphic and temporal framework within which to elucidate tsunami history within 100 km of malta terrestrial stratigraphy on sicily also provides supporting evidence of tsunami impact review of these advances suggests that the exceptional event required to emplace the most extreme sedimentary and geomorphological signatures on and around malta is likely to have had a far field origin the currently available circumstantial evidence points strongly toward a probability that the ad365 earthquake and tsunami were responsible this in turn enables critical reassessment of the exposure of malta to tsunami hazard

distribution origin and transport process of boulders deposited by the 2004 indian ocean tsunami at pakarang cape thailand abstract the tsunami of 2004 in the indian ocean transported thousands of meters long boulders shoreward at pakarang cape thailand we investigated size position and long axis orientation of 467 boulders at the cape most of boulders found at the cape are well rounded ellipsoid in shape without sharp broken edges they were fragments of reef rocks and their sizes were estimated to be 3 22 7t the distribution pattern and orientation of long axis of boulders reflect the inundation pattern and behavior of the tsunami waves it was found that there is no clear evidence indicating monotonous fine coarse shoreward trends of these boulders along each transect line on the other hand the large boulders were deposited repeatedly along the three arcuate lines at the intertidal zone with a spacing of approximately 136m interval this distribution pattern may suggest that long lasting oscillatory flows might have repositioned the boulders and separated the big ones from small no boulders were found on land indicating that the hydraulic force of the tsunami wave rapidly dissipated on reaching the land due to the higher bottom friction and the presence of a steep slope we further conducted numerical calculation of tsunami inundation at pakarang cape according to the calculation the sea receded and the major part of the tidal bench area with boulders at present was exposed above the sea surface before the arrival of the first tsunami wave the first tsunami wave arrived at the cape from west to east at approximately 130min after the tsunami generation and then inundated inlands our calculation shows that tsunami wave was focused around the offshore by a small cove at the reef edge and spread afterwards in a fan like shape on the tidal bench the critical wave velocities necessary to move the largest and average size boulders by sliding can be estimated to be approximately 3 2 and 2 0m s respectively the numerical result indicates that the maximum current velocity of the first tsunami wave was estimated to be from 8 to 15m s between the reef edge and approximately 500m further offshore this range is large enough for moving even the largest boulder shoreward these suggest that the tsunami waves that were directed eastward struck the reef rocks and coral colonies originally located on the shallow sea bottom near the reef edge and detached and transported the boulders shoreward

mega tsunami conglomerates and flank collapses of ocean island volcanoes abstract marine conglomerates at high elevation on the flanks of ocean islands are usually interpreted as evidence of mega tsunamis generated by volcano flank collapses although their origin is sometimes debated elevated littorals vs tsunami in this review we introduce case studies of well documented examples of tsunami conglomerates in hawaii pacific ocean the canary and cape verde islands atlantic ocean and mauritius island indian ocean other less documented marine conglomerates are also presented as tsunami candidates then we build a comprehensive picture of the general characteristics of these conglomerates and the different methods that can be applied to date them different perspectives of research are proposed especially on the use of tsunami conglomerates as proxies for better constraining numerical models of ocean island flank collapses and associated tsunamis we also discuss the possible links between volcano growth flank instability and climate

possible tsunami signatures from an integrated study in the augusta bay offshore eastern sicily italy abstract twelve anomalous layers marked by a high concentration of displaced epiphytic foraminifera species growing in vegetated substrates like the posidonia oceanica and subtle grain size changes were found in a 6 7 m long fine sediment core ms 06 sampled 2 km off the shore of the augusta harbor eastern sicily at a depth of 72 m recording the past 4500 yrs of deposition because concentrations of epiphytic foraminifera are quite common in infralittoral zones but not expected at 72 m we believe that these anomalous layers might be related to the occurrence of tsunamis causing substantial uprooting and seaward displacement of p oceanica blades with their benthic biota our approach involved the study of geophysical data morphobathymetry seismic reflection and seafloor reflectivity and sediment samples including x ray imaging physical properties isotopic dating tephrochronology grain size and micropaleontology correlations between anomalous layers and tsunami events have been supported by a multivariate analysis on benthic foraminifera assemblage and dates of historical tsunami records we found that four out of the eleven layers were embedded in age intervals encompassing the dates of major tsunamis that hit eastern sicily 1908 1693 and 1169 and the broader eastern mediterranean santorini at about bp 3600 one more layer even if less distinct than the others was also defined and may be the evidence for the ad 365 crete tsunami

numerical approach to the study of coastal boulders the case of martigues marseille france abstract the coastal area extending east of the city of martigues between the bays of bonnieu and that of chariot is characterized by an alternation of gently sloping rocky coast and 5 m high cliffs composed of miocene limestone the foot of the cliff is marked by a well developed notch and a discontinuous wave cut platform at its base the sea bottom reaches a maximum depth of about 4 5 6 m the emerged area shows boulders placed up to 10 m inland of the coastline at around 2 m above s l and weighing as much as 35 tonnes a geomorphological survey was conducted by means of a terrestrial laser scanner to estimate boulder sizes the particular focus of the proposed study was to estimate the minimum wave height required to detach and transport two boulders originally joined together as one bigger one and weighing approximately 25 tonnes from the wave cut platform onto the surf bench hydrodynamic models developed by various authors were used to calculate the minimum wave height necessary to move them the data obtained from the resulting hydrodynamic equations were compared to wave climate data collected over the last 15 years by the buoy off the coast of marseille in the gulf of lion the present study seems to confirm that it would not have been necessary to have a tsunami impact among other things never recorded in the last 20 years to move a 25 tonnes boulder indeed hydrodynamic equations suggest that the boulder might have been broken and only subsequently moved due to the impact of waves generated by an extreme storm which would have occurred prior to december 2003 this hypothesis seems to be in agreement with the morphology of the sea bottom hydrodynamic features of the area as well as eyewitnesses

benchmarks and sediment source s of the 1755 lisbon tsunami deposit at boca do rio estuary article standardizing the signature of tsunami deposits has been identified as a major limitation for the identifica tion of paleo tsunami deposits this limitation mostly arises from the strongly source dependent nature of these deposits which in turn determines their composition and depositional architecture and from the effect of the local morphology of the corresponding depositional environment here we provide new high resolution mineralogical geochemical and micro macrofauna data of the 1755 tsunami layer of boca do rio estuary algarve portugal with the aim of unraveling the signatures of estuarine tsunami deposits and linking them to possible sediment sources we also apply for the first time diffuse reflectance spectropho tometry drs analysis our results show that the 1755 tsunami deposit of the boca do rio estuary is featured by an enhancement in sr and ca which are linked to the input of biogenic and detrital carbonates shell frag ments and limestone clasts from the beach foreshore and a strong depletion in most terrestrial and marine sensitive indicators the latter is interpreted as resulting from the reworking of the estuarine clays and subsequent dilution within a huge volume of sand eroded from the coastal barrier it confirms that in the case of the boca do rio estuary the sediment source is essentially proximal and coastal textural and min eralogical features between the base and the top of the tsunami layer suggest the imprint of run up and back wash currents derived from a unique wave micro and macrofauna analysis and drs data of the siliciclastic fraction show slight but significant environmental changes occurring just after the tsunami which could be provoked by an eventual closure of the estuary mouth

testing the numerical models for boulder transport through high energy marine wave event an example from southern saurashtra western india abstract presence of large boulders along rocky coasts can be used as archives to reconstruct past extreme wave event history vital for the coastal hazard assessment dimensions of boulders lying in supratidal zone have been used to reconstruct the origin of wave responsible for their transport and processes there are several mathematical equations available which take into account submerged subaerial and joint bounded block scenarios for boulder transport to estimate the wave height required to transport the boulders to their final position however there are limited studies which validate these equations using modeling and observational analysis navabandar coast situated in western india provides an excellent opportunity for such analysis as there exists three boulders derived from shore platform during the november 1982 storm we present the analysis of these boulders and event history of region to conclude that all the mathematical equations overestimate the wave heights required to dislodge and transport these boulders by at least 5 times the actual event we emphasize that there is a vital need to re evaluate and improve the existing equations considering the local control variables for better visualization of palaeo tsunami storm events

magnitude and frequency of extra tropical north atlantic cyclones a chronology from cliff top storm deposits cliff top storm deposits ctsds are known to occur on cliffs at elevations of up to 50 m above sea level at exposed sites on the deep water coasts of the british isles eye witness accounts and time series field mapping of ctsds demonstrate their formation over the historical period and their continued modification during major storms with ctsds burying a range of modern human derived debris older deposits show surface lichen growth and weathering effects that relate to the relative age of ctsds over longer time spans buried sand and peat deposits provide dates on phases of ctsd emplacement and mobilisation and so provide an indication of the frequency and timing of the most severe storms two adjacent sites in shetland provide a combination of 14c dates on peat buried beneath storm deposited boulders 14c dates on marine shells buried inside ctsd boulder ridges and optically stimulated luminescence osl ages on sands intercalated with storm derived boulders although the precision is low this evidence identifies phases of exceptional storm activity spanning approximately 400 550 700 1050 1300 1900 and since 1950 ad by the very nature of cliff top erosion and deposition these records are fragmentary yet the timeline of major storms recorded in the shetland cliffs matches fairly well with the more general record of storminess in the north atlantic derived from the sea salt record in the gisp2 ice core as such ctsds represent an overlooked archive of storm sedimentation with the potential to elucidate local storm chronologies as well as informing debate surrounding the palaeo tempestology and impact of major cyclones and hurricanes

multiple dating approach 14c 230th u and 36cl of tsunami transported reef top boulders on bonaire leeward antilles current achievements and challenges abstract dating the transport deposition time of supratidal coarse clast deposits is difficult limiting their value for inferring frequency magnitude patterns of high energy wave events on bonaire leeward antilles caribbean these deposits form prominent landforms and transport by one or several holocene tsunamis is assumed at least for the largest clasts although a large dataset of 14c and electron spin resonance esr ages is available for major coral rubble ridges and ramparts it is still debated whether these data reflect the timing of major events and how these datasets are biased by the reworking of coral fragments as an attempt to overcome the current challenges for dating the dislocation of singular boulders three distinct dating methods are implemented and compared i 14c dating of boring bivalves attached to the boulders ii 230th u dating of post depositional secondary calcite flowstone and subaerial microbialites at the underside of the boulders and iii surface exposure dating of overturned boulders via 36cl concentration measurements in corals approaches ii and iii have never been applied to coastal boulder deposits so far the three 14c age estimates are older than 40 ka i e most probably beyond the applicability of the method which is attributed to post depositional diagenetic processes shedding doubt on the usefulness of this method in the local context the remarkably convergent 230th u ages all pointing to the late holocene period 1 0 1 6 ka are minimum ages for the transport event s the microbialite sample yields an age of 1 23 0 23 ka and both flowstone samples are in stratigraphic order the older onset of carbonate precipitation and younger flowstone layers yield ages of 1 59 0 03 and 1 23 0 03 ka respectively four coral samples collected from the topside of overturned boulders yielded similar 36cl concentration measurements however the computed ages are affected by large uncertainties mostly due to the high natural chlorine concentration after correction for the inherited component and chemical denudation since platform emergence inducing additional uncertainty the calculated 36cl ages cluster between 2 5 1 3 and 3 0 1 4 ka for three of four boulders whilst the fourth one yields an age of 6 1 1 8 ka probably related to a higher inheritance these 230th u and 36cl age estimates are coherent with a suggested tsunami age of

historical and pre historical tsunamis in the mediterranean and its connected seas geological signatures generation mechanisms and coastal impacts abstract the origin of tsunamis in the mediterranean region and its connected seas including the marmara sea the black sea and the sw iberian margin in the ne atlantic ocean is reviewed within the geological and seismotectonic settings of the region a variety of historical documentary sources combined with evidence from onshore and offshore geological signatures geomorphological imprints observations from selected coastal archeological sites as well as instrumental records eyewitnesses accounts and pictorial material clearly indicate that tsunami sources both seismic and non seismic e g volcanism landslides can be found in all the seas of the region with a variable tsunamigenic potential local regional and basin wide tsunamis have been documented an improved map of 22 main tsunamigenic zones and their relative potential for tsunami generation is presented from west to east the most important tsunamigenic zones are situated offshore sw iberia in the north algerian margin in the tyrrhenian calabria and messina straits in the western and eastern segments of the hellenic arc in the corinth gulf of central greece in the levantine sea offshore the dead sea transform fault and in the eastern side of the marmara sea important historical examples including destructive tsunamis associated with large earthquakes are presented the mean recurrence of strong tsunamis in the several basins varies greatly but the highest event frequency 1 96 years is observed in the east mediterranean basin for most of the historical events it is still unclear which was the causative seismic source and if the tsunami was caused by co seismic slip by earthquake triggered submarine landslides or by a combination of both mechanisms in pre historical times submarine volcanic eruptions i e caldera collapse massive pyroclastic flows volcanogenic landslides and large submarine landslides caused important tsunamis although little is known about their source mechanisms we conclude that further investigation of the tsunami generation mechanisms is of primary importance in the mediterranean region inputs from tsunami numerical modeling as well as from empirical discrimination criteria for characterizing tsunami sources have been proved particularly effective for recent well documented aseismic landslide tsunamis e g 1963 corinth gulf 1979 cote d azur 1999 izmit bay 2002 stromboli volcano since the tsunami generation mechanisms are controlled by a variety of factors and given that the knowledge of past tsunami activity is the cornerstone for undertaking tsunami risk mitigation action future interdisciplinary research efforts on past tsunamis are needed

backbeach deflation aprons morphology and sedimentology backbeach deflation aprons are heterogeneous coarse clastic deposits associated with active transverse dune fields the apron comprises variously angular rounded fractured cracked polished and ventifacted clasts of bedrock local and exotic beachrock and bioherm fragments coral and worm reef terrestrial and anthropogenic clasts from archeological sites deflated dunes flotsam and shipwrecks are also present the unit forms as a lag deposit on top of a gently sloping ca 0 008 planar sandy deflation surface and is typically only one clast thick it is up to 100 m wide and extends for tens of kilometers along the coast it is replaced landward by a steep ca 0 1 deflated soil surface armored with a layer of iron concretions backbeach deflation aprons are compound deposits that result from marine storm eolian and human activity since the mid holocene the depositional model proposed involves periodic storm deposition of coarse clasts of beachrock bedrock and biogenic origin and flotsam shipwreck and other floating debris on the backbeach or dunes some clasts are deposited directly into interdune depressions and enter the deflation plain immediately others are deposited initially on dune surfaces dune migration results in winnowing of the storm deposited coarse clasts together with rhizoliths and any other coarse material in the dune until they come to rest on the deflation surface the lag deposit is subsequently buried and uncovered multiple times by dune migration during which time it is exposed to polishing and subaerial weathering consequently the lag comprises a variety of materials that reflect both storm and eolian processes the clasts exhibit variable degrees of rounding polishing and ventification according to how long they have been in the deposit backbeach deflation aprons are characteristic of sandy beaches along approximately 475 km 10 of the total length of the south african east coast they develop in association with large scale transverse dunefields on the backbeach which in turn depend on reversing shore parallel winds and high sediment abundance the variable degree of polishing and weathering planar surface low elevation and back beach location along extensive shoreline distances distinguish backbeach deflation aprons from tsunami or marine storm deposits

two years in the life of a mediterranean salt lens abstract a lens of mediterranean water meddy was tracked in the eastern north atlantic for two years with sofar floats the meddy was first found between the canary islands and the azores in october 1984 it center moved in an irregular pattern at speeds of a few cm s 1 and translated 1100 km to the south in two years this meddy was surveyed four times by ctd and velocity profilers and once with the microstructure profiler epsonde when observed during the first two surveys the meddy had a core that was stably and smoothly stratified in both salinity and temperature nearly uniform in the horizontal and was saltier than the surrounding ocean by 0 65 psu the meddy was eroded from its edges top and bottom and lost salt and hat with an e folding time of about one year the salinity at the center remained at its original value during the first year and decreased during the second year evidence was seen for mixing by lateral intrusions double diffusion and turbulence the intrusions are thought to

discrimination of boulders deposited by tsunamis and storm waves at ishigaki island japan abstract the ryukyu islands japan where numerous boulders are deposited on the reef and on land might be ideal research fields of boulders deposited by tsunami and storm waves because many typhoons and several tsunamis attacked the same area during its history this study investigates the size position and the long axis orientation of 626 boulders at ibaruma and shiraho reefs at ishigaki island japan to elucidate the sedimentary differences of boulders deposited by tsunamis and storm waves in one area two distinct groups of boulders were found at these reefs boulders on the reef crest group 1 and along the shoreline group 2 boulders in group 1 porites sp of moat origin the group 2 boulders were remarkably heavier 14 c age based on results of this study we infer that tsunami boulders in these islands so called tsunami ishi can be discriminated from boulders of storm wave origin based on their sedimentary differences this sedimentological approach is expected to be applicable to other boulder fields throughout the world our results further suggest that the spatial and grain size distribution of tsunami boulders are very useful to elucidate local flow characteristics of the tsunami for example the group 2 tsunami boulders were deposited below the high tide line irrespective of size some were split into several pieces they were probably deposited below the high tide line by the remarkable reduction of the current velocity of the tsunami because of the local topography the reduction of the current velocity must have been drastic to have made the boulders hit the ground with sufficient force to split them

boulder ridges on the aran islands ireland recent movements caused by storm waves not tsunamis abstractireland s aran islands are an excellent place to test whether coastal boulder deposits including individual rocks weighing several tens of tonnes near sea level and clasts weighing several tonnes transported at tens of meters above sea level require a tsunami for emplacement or whether storm waves can do this work elongate deposits of cobbles boulders and megagravel are strung along the atlantic coasts of the aran islands no tsunamis have affected this region in recent centuries so if these deposits are forming or migrating at the present time they must be storm activated we find a diverse range of evidence for recent ridge activity first shells of hiatella arctica subtidal rock boring bivalves preserved in life position within ridge boulders yield radiocarbon ages from 200 ad to modern post 1950 ad second recent motion is attested to by eyewitness accounts that pin the movement of several individual 40 80 t blocks to a specific 1991 storm and by repeat photography over the last fe

large boulder accumulations by extreme waves along the adriatic coast of southern apulia italy abstract the adriatic coast of southern apulia italy is marked by the presence of large boulder accumulations boulders are up to 8 t in weight and arranged either in small groups or rows composed of a few imbricated elements the lower surface of some of the boulders is covered by biogenic encrustation which suggests that they were possibly carved from the mid or sublittoral zone and that they capsized during their transport other boulders detached from the supratidal zone have their surface affected by tilted rock pools new horizontal solution pans are continually forming a detailed survey of a large boulder accumulation was carried out at torre santa sabina direct observations were also made concerning the carving out and transportation of one single boulder during the severe storms in that area on january 4th 2002 and on january 12th 2003 collated data from both the survey and the direct observations including some radiocarbon age determinations and hydrodynamic calculations suggest that the studied accumulation was due to the superimposed effects of one or two tsunami as well as of storm waves tsunami would be responsible for the detachment and transportation of the largest boulders while storm waves may have been responsible for the carving out and transportation of the newer smaller blocks and for moving once again the largest boulders it was in this way that a typical boulder accumulation was produced the collated data suggest that two tsunami may have recently struck the adriatic coast of southern apulia the first possibly took place on the dalmatian coast as a result of the earthquake on april 6 1667 which destroyed ragusa modern day dubrovnik the second tsunami would have accompanied the strong earthquake which took place in southern apulia on february 20 1743

advantages of beachrock slabs for interpreting high energy wave transport evidence from ludao island in south eastern taiwan abstract powerful typhoons frequently affect eastern taiwan on dabaisha beach on the sw coast of ludao island a small volcanic island lying se off mainland taiwan the presence of numerous beachrock slabs provides evidence of the sediment transport capabilities of high energy waves generated by these storms with a well defined beachrock source from which the slabs were derived it is easy to differentiate clasts transported in run up or backwash flow based on their current position relative to the outcrop in order to estimate the wave generated flow velocities from the measured beachrock slabs the hydrodynamic equations for boulder transport by nandasena et al 2011 have been rearranged so that they are appropriate for this particular geomorphic setting where exposed in situ beachrock outcrops liberate clasts which may then be transported either by run up onto the beach or backwash flow onto adjacent reef platforms such settings are common on tropical coastlines with fringing coral reefs and beaches comprising mostly biogenic sediments in the dabaisha beach case the lowest flow velocities required to transport all measured beachrock slabs from their source outcrop to current positions are 2 18 3 16 m s for run up and 1 76 3 24 m s for backwash with a discussion of advantages and limitations on the use of beachrock clasts for interpreting wave behaviour this paper presents another proxy for studying high energy wave events that is highly suitable for certain carbonate rich coastlines

the tsunami hypothesis comparisons of the field evidence against the effects on the western australian coast of some of the most powerful storms on earth the tsunami hypothesis proposes that prehistoric tsunamis may have been larger than historic ones along coasts normally historically not associated with major tsunamis the evidence for the hypothesis rests with the types of unusual sedimentary deposits and erosional forms along coasts where the largest historic and prehistoric storm waves do not appear capable of forming the features this is especially the case at locations where boundary conditions i e offshore water depth coastal geomorphology and meteorological limitations are not conducive to the propagation of sufficiently large storm waves at the shore the tsunami hypothesis has been barely debated in the literature this is despite the view of some who suggest that storms have been overlooked or underestimated as a cause few comparisons have been made of the supposed tsunami generated features and the impacts on coasts of extreme intensity storms four of the most powerful tropical cyclones anywhere in the world in recent times struck the western australian coast between 1999 and 2002 the results of post event surveys of these storms showed that none of them produced the enigmatic forms attributed elsewhere to tsunamis

storm rogue wave or tsunami origin for megaclast deposits in western ireland and north island new zealand the origins of boulderite deposits are investigated with reference to the present day foreshore of annagh head nw ireland and the lower miocene matheson formation new zealand to resolve disputes on their origin and to contrast and compare the deposits of tsunamis and storms field data indicate that the matheson formation which contains boulders in excess of 140 tonnes was produced by a 12 to 13 m high tsunami with a period in the order of 1 h the origin of the boulders at annagh head which exceed 50 tonnes is disputed we combine oceanographic historical and field data to argue that this is a cliff top storm deposit ctsd a numerical model for ctsds is developed which indicates that boulder shape in addition to density and dimensions should be taken into account when applying hydrodynamic equations to such deposits the model also predicts that the ne atlantic storms are capable of producing boulderites that when size alone is considered cannot be distinguished from tsunamites we review the characteristics that identify the origins of these two deposits

waves coastal boulder deposits and the importance of the pre transport setting the pre transport environment of a coastal boulder along with its shape size and density determines the height of wave required for it to be transported different forces act on sub aerial boulders as opposed to submerged boulders when struck by a wave boulders derived from joint bounded blocks on shore platforms predominantly experience lift force and require a wave of greater height to be transported than boulders in other environments no one equation is applicable to determine the height of palaeo waves responsible for depositing a field or ridge of imbricated coastal boulders a range of equations and their derivation is presented here which can be applied to the respective pre transport environment of a boulder such an approach is necessary when attempting to reconstruct the frequency and magnitude of past coastal wave hazards and for differentiating between tsunami and storm wave deposited boulder fields

mixed layer instabilities and restratification abstract the restratification of the oceanic surface mixed layer that results from lateral gradients in the surface density field is studied the lateral gradients are shown to be unstable to ageostrophic baroclinic instabilities and slump from the horizontal to the vertical these instabilities which are referred to as mixed layer instabilities mlis differ from instabilities in the ocean interior because of the weak surface stratification spatial scales are o 1 10 km and growth time scales are on the order of a day linear stability analysis and fully nonlinear simulations are used to study mlis and their impact on mixed layer restratification the main result is that mlis are a leading order process in the ml heat budget acting to constantly restratify the surface ocean climate and regional ocean models do not resolve the scales associated with mlis and are likely to underestimate the rate of ml restratification and consequently suffer from a bias in sea surface temperatures and ml depths in a

evaluation of tsunami flooding using geomorphologic evidence abstract whatever the generating mechanism of a tsunami may be this event can discharge destructive energy along coastal areas and produce widespread inundation the presence of large boulders along rocky coasts could be a useful indicator to understand the extent of the impact of past tsunami floods a detailed study of the deposited boulder features size shape and rock density and their initial position prior to the transport is extremely important when reconstructing the possible morphodynamic scenario s applying the appropriate equations is important when aiming to assess the maximum extent of flooding the integration of morphological and hydrodynamic data allows for an estimation of the water level during the tsunami event responsible for boulder transport moreover it is possible to calculate how far the impacting wave flooded inland this is a function of the wave parameters and of the degree of roughness of the flooded terrain that is expressed by the manning number to evaluate its probable average value experimental data computer simulations and post tsunami surveys have been performed in two sectors of the southern apulia coastline characterised by the presence of tsunami boulder fields and or ridges the surveys in each site have allowed for the calculation of the boulder sizes the estimation of their pre transport location and the extent of inland flooding data have been processed using a geographic information system gis as a result a flooding map useful in planning future possible actions for coastal area use has been produced

boulder accumulations produced by the 20th of february 1743 tsunami along the coast of southeastern salento apulia region italy abstract the detachment of large boulders in the nearshore zone and their deposition farther inland are the main morphological effects of tsunamis on rocky coasts along the otranto leuca coast southeastern apulia italy two boulder accumulations have been recognized and studied at the torre sasso locality boulders weighing up to 31 t are scattered from sea level to about 5 m of elevation and clustered in groups of several imbricated elements at torre s emiliano an impressive accumulation made of large boulders has been recognized and studied the accumulation is about 30 m wide and follows the present coastline for about 2 5 km at a variable distance of 15 to 40 m looking closer it is compounded by two ridges the ridge closer to the coastline shows a very steep slope seaward made of very large boulders emplaced in a vertical position its top reaches about 11 m above m s l the inner belt is lower than the outer one and consists of smaller boulders it partly covers a 2 m thick colluvial deposit made of reddish sands huge blocks weighing up to 70 t cover the carved surface stretching from the coastline to the front of the first ridge analysis of the imbrication axes indicates that the catastrophic waves responsible for the development of the boulder accumulations most likely propagated from sse to nnw direction karstic features occurring on the surface of the innermost boulders indicate a very recent age for their deposition as no differences have been found between the aerial exposed surface and the soil covered one three ams radiocarbon age determinations performed on marine shells found landward the boulders have accumulated recently i e within the last three centuries moreover archeological remains in the top layers of the colluvial deposits covered by the boulders can be referenced to 16th 17th centuries this evidence suggests that the 20th of february 1743 earthquake was responsible for the generation of two large tsunami waves which caused the boulder accumulations to deposit this earthquake was particularly violent in the salento region where it reached grade ix on the mcs scale interestingly chronicles of this event record a withdrawal of the sea in the brindisi harbour north of the study area this study highlights the tsunamigenic potential offshore the southeastern salento coast requiring that further strategies be devoted to mitigate the tsunami risk

boulder transport by the 2011 great east japan tsunami comprehensive field observations and whither model predictions abstract predicting the local size of a historic high energy event from its boulders using numerical models is a challenging research topic modern high energy events and their deposits are useful to validate these models however validating the accuracy of the results is difficult due to the scarcity of good datasets or the ambiguity of existing field data data on boulders transported by the 2011 great east japan tsunami at coastal sites settai taro and karakuwa on the northeast coast of japan were compiled pre tsunami locations and settings and transport distances were found from evidence such as photographs aerial images and the testimony of survivors the estimated weight of the boulders analyzed ranged from 11 to as much as 167 t while the transport distance varied from a few to up to 600 m modeling results predicted that the minimum limit of maximum flow velocity of the tsunami at the pre tsunami locations of the boulders varied from 4 2 to 6 8 m s the measured maximum flow depths at settai 17 18 m and taro 14 m were within the predicted range of flow depth when the froude number 1 0 1 5 numerical model estimates for an older boulder 285 t in settai indicate that it was probably transported by a historical tsunami 1611 keicho sanriku event which may have been similar to or bigger than that of the 2011 event in the area the maximum flow velocity could not have been less than 6 1 m s and if the boulder was transported to the present location by rolling the flow velocity must have been within 7 5 23 7 m s following systematic validation the numerical modeling of boulder transport is proving promising for reconstructing the local magnitude of historical high energy events further improvements can be made with additional high quality field data from modern high energy events

boulder coastal deposits at favignana island rocky coast sicily italy litho structural and hydrodynamic control abstract boulders are frequently dislodged from rock platforms transported and deposited along coastal zones by high magnitude storm waves or tsunamis their size and shape are often controlled by the thickness of bedding planes as well as by high angle to bedding fracture network we investigate these processes along two coastal areas of favignana island by integrating geological data for 81 boulders 49 rupture surfaces called sockets and fracture orientation and spacing with four radiocarbon dates numerical hydrodynamic analysis and hindcast numerical simulation data boulders are scattered along the carbonate platform as isolated blocks or in small groups which form as a whole a discontinuous berm underwater surveys also highlight free boulders with sharp edges and sockets carved out in the rock platform boulders are composed of ruditic to arenitic size clastic carbonates their size ranges from 0 6 to 3 7 m 0 55 to 2 4 m and 0 2 to 1 m on the major a medium b and minor c axes respectively the highest value of mass estimation is 12 5 t almost all of boulders and sockets are characterized by a tabular or bladed shape the comparisons between a the fractures spacing and the length of a and b axes and b the frequency peaks of c axis with the recurrent thickness of beds measured along the coastal zone demonstrate the litho structural control in the size and shape of joint bounded boulders these comparisons together with the similarity between the shapes of the boulders and those of the sockets as well as between the lithology of boulders and the areas surrounding the sockets suggest that blocks originate by detachment from the platform edge thus the most common pre transport setting is the joint bounded scenario hydrodynamic equations estimate that the storm wave heights necessary to initiate the transport of blocks diverge from 2 m to 8 m for joint bounded boulders and from few tens of centimeters up to 11 m for submerged boulders the comparison between the wave heights at the breaking point of the coastal zones with the results of hydrodynamic equations shows that waves approaching the coastline are able to transport all surveyed boulders our data suggest that boulders have been transported by several storm events even in very recent times

the mystery of boulders moved by tsunamis and storms abstract boulders are moved differently in storm and tsunami and produce different characteristics of the boulder deposits this contribution is motivated by two observations one by bourgeois and macinnes 2010 which described that boulders were moved selectively due to different bed roughness during 15 november 2006 tsunami on the island of matua the second topic is motivated by the boulder lines on ishigaki island by goto et al 2010 both topics are approached with linear wave theory and stability analysis from both the safety factor is derived for a spherical boulder with bed roughness and exposure as moment arms with which we are able to quantify the influence of bed roughness on the incipient motion of boulders for constant forces a bed roughness of about 30 of the boulder radius will prevent boulder transport furthermore the comparison between storm and tsunami waves in terms of the amplitude necessary to move boulders revealed that amplitude of storm waves is smaller than tsunami which we ascribe to the contribution of both velocity components to lift forces the comparison of total energy and number of waves revealed that storms have a larger total energy and a much larger number of waves which lead us to the conclusion that tsunamis produce unorganized boulder deposits whereas storms are capable of organizing boulders along lines and in clusters

sub mesoscale lateral density structure in the oceanic surface mixed layer 1 we investigate the horizontal scales of density variability in the surface mixed layer sml in the north pacific subtropical front stf during a period of highly variable atmospheric forcing wavelet analysis shows that horizontal density variability is not restricted to scales l 10 km as previously suggested but extends to l 2 km the limiting l varies strongly with location and corresponds to a local internal rossby radius that accounts for transient stratification above the seasonal thermocline density compensation in the sml achieved when temperature and salinity effects cancel in their effect on density occurs at 30 n at the climatological front associated with the northern boundary of the stf where large thermohaline gradients are observed at 28 n however temperature gradients within the sml are not compensated by salinity and horizontal density gradients result in 2 l 10 km our observations suggest dynamic processes restratify the sml at scales rarely resolved by numerical models of the sml

boulder deposition during major tsunami events a remarkable accumulation of marine boulders located above the present spring tide level has occurred in two coastal lowlands of the algarve portugal the size interval of the particles studied here is seldom reported in the literature in association with extreme events of coastal inundation thus making this study of relevance to many other coasts worldwide the spreads of boulders extend several hundred meters inland and well beyond the present landward limit of storm activity the marine origin of the boulders is demonstrated by well developed macro bioerosion sculpturing and in situ skeletal remains of endolithic shallow marine bivalves the good state preservation of the fossils within the boulders indicates that abrasion during transport and redeposition was not significant we envisage boulder deposition as having taken place during the lisbon tsunami of ad 1755 through the simultaneous landward entrainment of coarse particles from nearshore followed by rapid shoreward suspended dominated transport and non graded redeposition that excluded significant sorting by weight or boulder dimensions we use numerical hydrodynamic modeling of tsunami and storm waves to test the observational data on boulder dimensions density size distribution on the most likely processes of sediment deposition this work demonstrates the effectiveness of the study of boulder deposits in tsunami reconstruction copyright 2011 john wiley sons ltd

three dimensional structure and temporal evolution of submesoscale thermohaline intrusions in the north pacific subtropical frontal zone abstract four instances of persistent intrusive deformation of the north pacific subtropical front were tagged individually by a lagrangian float and tracked for several days each feature was mapped in three dimensions using repeat towed observations referenced to the float isohaline surface deformations in the frontal zone included sheetlike folds elongated in the alongfront direction and narrow tongues extending across the front all deformations appeared as protrusions of relatively cold and fresh water across the front no corresponding features of the opposite sign or isolated lenslike structures were observed the sheets were o 10 m thick protruded about 10 km into the warm saline side of the front and were coherent for 10 30 km along the front having about the same thickness and cross frontal extent as the sheets tongues extended less than 5 km along the front all of the intrusions persisted as long as they were followed several days to one week their structures evolved on both inertial

interpolation and gridding of aliased geophysical data using constrained anisotropic diffusion to enhance trends geophysical data are frequently collected with a fine sample interval along traverse lines but with a coarser sampling in the direction perpendicular to the traverses this disparity in sampling intervals is particularly evident when magnetic data are collected simultaneously with airborne electromagnetic data interpolating this traverse data onto an evenly spaced 2d grid can result in aliasing artifacts for example narrow linear structures that trend at acute angles to the traverse lines are imaged as a thick thin thick feature looking like a boudinage or string of beads applying the anisotropic diffusion process to the resulting grids of data removes the artifacts but the grid values close to the traverses are altered significantly from their initial values the altered values are therefore not faithful to the original traverse data the anisotropic diffusion algorithm can be modified to constrain values close to the original traverses this modification removes the aliasing artifacts and produces a data grid faithful to the original traverse data some small artifacts along the traverse lines in the final data grid become more evident when grids containing derivative data such as the analytic signal are generated from the new data grid however these small traverse line artifacts can be removed with standard microleveling procedures the constrained anisotropic diffusion process is iterative and some experimentation is required to determine the appropriate number of iterations

untangling boulder dislodgement in storms and tsunamis is it possible with simple theories boulders can move during storms and tsunamis it is difficult to find a simple method to distinguish boulders moved by tsunami waves from those moved during storms in the field in this contribution we explore boulder dislodgement by storm and tsunami waves by solving an adapted version of newton s second law of motion in polar coordinates and defining a critical position for boulder dislodgement we find that the boulder dislodgement is not only a function of the causative wave but also of the roughness in the vicinity of the boulder and the slope angle we employ the amplitude of storm and tsunami waves to dislodge boulders of given masses to evaluate if boulder dislodgement in storms can be untangled from boulder transport in tsunamis as the main result of our numerical experiments we find a significant difference between storm and tsunami waves to dislodge the same boulder for large masses and large roughness values this allows us to conclude that simple theories are applicable to answer the questions asked in the title but we argue only if they contain a critical dislodgement condition like the one presented here

the origin and dynamics of coastal boulders in a semi enclosed shallow basin a northern adriatic case study abstract this paper documents the analysis of a coastal boulder deposit that was recently identified along the northern adriatic coast premantura promontory istria croatia accumulations of large boulders have not previously been reported in the northern adriatic which can be viewed as a semi enclosed basin a multidisciplinary approach was used to investigate the site including geological and geomorphological surveys together with the use of an unmanned aerial vehicle uav digital photogrammetric analysis hydrodynamic modelling and 14c ams datings measurements of boulder position elevation size shape and density were fed into hydrodynamic equations that are used to estimate the minimum storm and tsunami wave height required to enable the accumulation of boulders biogenic marine carbonate encrustations observed on 14 boulders suggest the infra and sublittoral zones as source areas while for most of the boulders a subaerial origin is hypothesised the boulder deposit occurs on a flat promontory where the topography together with the stratified limestone bedding planes and dense joint pattern constitute the predisposing factors for boulder size and detachment comparisons between satellite images taken between 2008 and 2017 pictures collected from internet and a 2012 snorkel survey of the istrian coast made it possible to highlight the emplacement of a boulder with an estimated weight of 7 65 t during late 2013 or early 2014 the study examines the mechanisms that may be responsible for the detachment and transport of these large limestone rock fragments from the emergent part of the coast and from the sea bed towards inland areas the results suggest the occurrence of very recent extreme weather conditions as well as multiple historical storm events and exclude a tsunami origin of the boulders

new coring study in augusta bay expands understanding of offshore tsunami deposits eastern sicily italy this is the peer reviewed version of the following article smedile a molisso f chague c iorio m de martini p m pinzi s collins p e f sagnotti l pantosti d 2019 new coring study in augusta bay expands understanding of offshore tsunami deposits eastern sicily italy sedimentology which has been published in final form at doi 10 1111 sed 12581 this article may be used for non commercial purposes in accordance with wiley terms and conditions for use of self archived versions 2019 the authors sedimentology 2019 international association of sedimentologists

discrimination of tsunami sources earthquake versus landslide on the basis of historical data in eastern sicily and southern calabria abstract the source mechanisms responsible for large historical tsunamis that have struck eastern sicily and southern calabria are a topic of robust debate we have compiled a database of historical coeval descriptions of three large tsunamis 11 january 1693 6 february 1783 and 28 december 1908 by using accounts of run up and inundation and employing an approach proposed by okal and synolakis in 2004 we can provide discriminants to define the nature of the near field tsunami sources fault dislocation or landslide historical reports for the 1908 event describe affected localities maximum run ups and inundation areas however for the 1693 and 1783 tsunamis reports are limited to inundation and occasional run up estimates we calculate run up values for these events using available relations between inundation and run up we employed the model of okal and synolakis to the obtained profiles of tsunami run up along the inundated shorelines the 1908 run up data distribution confirms that the tsunami is compatible with a seismic dislocation source whereas the 1783 data supports contemporary observations and recent offshore investigations suggesting that the tsunami was produced by an earthquake triggered submarine landslide analysis of the 1693 event data suggests that the tsunami was generated during a tectonic event and thus a seismogenic source should be found offshore

extraordinary boulder transport by storm waves west of ireland winter 2013 2014 and criteria for analysing coastal boulder deposits abstract before and after photos of supratidal coastal boulder deposits cbd in the west of ireland show that storms in the winter of 2013 2014 transported boulders at elevations up to 29 m above high water and at inland distances up to 222 m among the clasts transported are eighteen weighing more than 50 t six of which exceed 100 t the largest boulder moved during those storms weighs a fairly astonishing 620 t the boulders moved in these recent storms provide pinning points for mapping storm wave energies on coasts their topographic positions mark elevations and distances inland reached by wave energies sufficient to dislocate those specific masses taken together the cbd data reveal general relationships that shed light on storm wave hydrodynamics these include a robust correlation inverse exponential between maximum boulder mass transported and emplacement height above high water the greater the elevation the smaller the maximum boulder size with a dependency exponent of about 0 2 times the elevation in metres there is a similar relationship although with a much smaller rate of change exponent 0 02 between boulder mass and distance inland which holds from the shoreline in to about 120 m coastal steepness calculated as the ratio of elevation to inland distance seems to exert the strongest control with an inverse power law relationship between maximum boulder mass and slope ratio the more gentle the topography the larger the moved boulders quantifying cbd dynamics helps us understand the transmission of wave energies inshore during high energy storm events the transported boulders documented here are larger than many of those interpreted to have been moved by tsunami in other locations which means that boulder size alone cannot be used as a criterion for distinguishing between tsunami and storm emplacement of cbd the biggest blocks up to 620 t are new maxima for boulder mass transported by storm waves we predict however that this record will not last long the 2013 2014 storms were strong but not extreme and there are larger boulders in these deposits that didn t move on this occasion bigger storms will surely move larger clasts and clasts at greater distances from the shoreline these measurements and relationships emphasise the extreme power of storm waves impacting exposed coastlines and require us to rethink the upper limits of storm wave energy at coasts

a numerical model for the transport of a boulder by tsunami 1 we have conducted hydraulic experiments in an open channel with cubic and rectangular shaped solid blocks on the slope for investigating the boulder transport process by tsunami in our experiments the block was mainly seen to be transported by a bore due to rolling or saltation rather than by sliding previous models for the boulder transport by tsunamis assumed sliding as a mode of transport for the boulder therefore these models underestimated the distance of the boulder moved by the tsunami when it was transported due to rolling or saltation in this study we have developed a practical model for the transport of a boulder by tsunami which takes into account the various transport modes we introduce an empirical variable coefficient of friction by assuming that the coefficient decreases with decrease in ground contact time when the block was transported by rolling or saltation with the aid of this parameter the model can explain various modes of transport i e sliding rolling and saltation and reproduces the experimental results well we further applied this improved model to a tsunami boulder at inoda area in ishigaki island japan which was transported by the 1771 meiwa tsunami the calculated distance of transport of the boulder was approximately 650 m which is consistent with the description in the historical document based on our calculations we estimated hydraulic values of the tsunamis estimation of such hydraulic values is important for understanding the behavior and power of the historical tsunamis besides aiding future disaster mitigation efforts

catastrophic wave erosion bristol channel united kingdom impact of tsunami abstract on january 30 1607 a massive wave from the ocean surged up bristol channel in the united kingdom flooding more than 500 km2 of lowland along 570 km of coast it killed 2000 people and is considered britain s worst natural disaster on land the wave occurred on a fine day and surprised inhabitants contemporary descriptions of the event have many of the characteristics of accounts of recent catastrophic tsunamis geomorphic evidence for tsunamis in the channel can be found in the form of transported and imbricated boulders bedrock sculpturing on coastal platforms and ramps and at isolated locations wholesale erosion of the coastal landscape hydrodynamic calculation of the height of the tsunami and flow velocities can be derived from boulder dimensions tsunami wave height increased from 4 m in the outer bristol channel to more than 6 m within the inner severn estuary theorized flow velocities range between 11 8 and 18 1 m s 1 increasing up the estuary under topographic enhancement thes

an extreme wave event in eastern yucatan mexico evidence of a palaeotsunami event during the mayan times the yucatan peninsula mexico has typically been considered a tectonically stable region without significant seismic activity in contrast the region is one that is regularly affected by hurricanes a detailed survey of ca 100 km of the eastern yucatan and cozumel coast identified the presence of ridges containing boulders measuring 1 m with up to three ridges at some locations the ridges reach five metres in height and their origin is associated with extreme wave event ewe activity previously modelled tsunami waves from known seismically active zones in the region muertos thrust belt and south caribbean deformed belt are not of sufficient at the yucatan peninsula to have produced the boulder ridges recorded in this study the occurrence of hurricanes in this region is more common but two of the most destructive hurricane gilbert 1988 and hurricane wilma 2005 produced coastal waves too small to have created the ridges recorded here in this paper a new tsunami model has been generated that indicates a tsunami event may have caused the ewe that resulted in the deposition of the boulders ridges

reassessment of hydrodynamic equations minimum flow velocity to initiate boulder transport by high energy events storms tsunamis abstract coastal boulders are good evidence of high energy events but the distinction between storm and tsunami boulders remains difficult to identify and mathematical models are still in their preliminary stages in a pioneering contribution nott 1997 2003 developed hydrodynamic equations to assess the minimum wave height required to initiate transport of a coastal boulder by tsunamis or storm surges these equations are widely cited and used but they can be improved in this study nott s equations have been revised 1 the equation for the submerged boulder scenario has been revised by rearranging the lift area of the lift force 2 the subaerial boulder scenario has been reconsidered by rearranging lift area and omitting inappropriate use of inertia force and 3 the joint bounded scenario was revised by balancing force components in the lifting direction and the effect of slope at the pre transport location is tested calculations are performed for four case studies boulders in western and eastern australia data after nott 1997 2003 boulders in southeastern italy data after scicchitano et al 2007 storm boulders in iceland data after etienne and paris 2010 and 2004 tsunami boulders in sumatra data after paris et al 2009 the minimum flow velocity required to initiate the transport of submerged boulders in the revised equation is less than that in nott s equation e g reductions up to 56 for submerged boulders and 65 for joint bounded blocks the minimum flow velocity required to initiate the transport of subaerial boulders from the revised equation also differed in comparison with nott s equation e g 4 22 for boulders detached from a seawall by the 2004 tsunami in sumatra while nott s equation was not applicable to some boulders e g beach rock boulders transported from the nearshore by the 2004 tsunami if we consider a joint bounded scenario for storm boulders in iceland the minimum flow velocity differs 43 to 41 from the results from nott s equation a boulder transport histogram is then introduced to represent the range of flow velocity that satisfies the requirements for initial transport of a boulder in different modes sliding rolling and saltation the boulder transport histogram can be used to predict the possible initial transport mode of a boulder from the flow velocity these theoretical results are compared to field data thus suggesting the initial transport mode of boulders and their pre transport locations the boulder transport histogram would be a valuable tool to reconstruct the magnitude of prehistoric high energy events such as tsunamis or storm surges in terms of flow velocity

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

tsunamis as geomorphic crises lessons from the december 26 2004 tsunami in lhok nga west banda aceh sumatra indonesia abstract large tsunamis are major geomorphic crises since they imply extensive erosion sediment transport and deposition in a few minutes and over hundreds of kilometres of coast nevertheless little is known about their geomorphologic imprints the december 26 2004 tsunami in sumatra indonesia was one of the largest and deadliest tsunamis in recorded human history we present a description of the coastal erosion and boulder deposition induced by the 2004 tsunami in the lhok nga bay located to the west of banda aceh northwest sumatra the geomorphological impact of the tsunami is evidenced by beach erosion some beaches have almost disappeared destruction of sand barriers protecting the lagoons or at river mouths numerous erosion escarpments typically in the order of 0 5 1 5 m when capped by soil and more than 2 m in dunes bank erosion in the river beds the retreat along the main river is in the order of 5 15 m with local retreats exceeding 30 m large scars typically 20 50 cm deep on slopes dislodgement of blocks along fractures and structural ramps on cliffs the upper limit of erosion appears as a continuous trimline at 20 30 m a s l locally reaching 50 m the erosional imprints of the tsunami extend to 500 m from the shoreline and exceed 2 km along riverbeds the overall coastal retreat from lampuuk to leupung was 60 m 550 000 m 2 and locally exceeded 150 m over 276 000 m 3 of coastal sediments were eroded by the tsunami along the 9 2 km of sandy coast the mean erosion rate of the beaches was 30 m 3 m of coast and locally exceeded 80 m 3 m the most eroded coasts were tangent to the tsunami wave train which was coming from the southwest the fringing reefs were not efficient in reducing the erosional impact of the tsunami the 220 boulders measured range from 0 3 to 7 2 m large typically 0 7 1 5 m with weights from over 50 kg up to 85 t we found one boulder less than 1 m large at 1 km from the coastline but all the others were transported less than 450 m 30 m and the moderate tsunamis height

when the compass stopped reversing its poles earth9s geomagnetic field normally reverses a few times every million years but during superchron periods this switching process may stop for 30 to 50 million years in his perspective banerjee highlights the study by tarduno et al who have deduced the paleomagnetic field strength during the cretaceous superchron from magnetite inclusions in lavas found in india the results may provide clues to what causes the superchron periods

tsunami deposits in santiago island cape verde archipelago as possible evidence of a massive flank failure of fogos volcano abstract massive flank failures of volcanic edifices generate tsunami waves these low frequency but high magnitude hazards remain poorly documented because of the scarcity of observations offshore deposits are studied only by geophysical surveys and the failure rheologies are poorly constrained marine conglomerates found at unusually high elevations in hawaii and in the canary islands were previously interpreted as being the result of giant tsunami waves generated by massive flank failures this study focuses on the search for and interpretation of sedimentary evidence of a tsunami around the coastline of santiago island which is located 55 km east of the active fogo volcano the bordeira caldera in fogo island which opens to the east was formed by the monte amarelo flank collapse and the active edifice is now nested in the failure s scar the only evidence of a tsunami was found north of tarrafal bay the deposits display many similarities with the tsunami conglomerate described in hawaii and the canary islands erosive contact with the substratum rip up clasts of paleo soil marine bioclasts never found in growth or live position internal organisation into different facies with distinct characteristics of clast size up to boulders sorting from moderately to very poorly sorted and clast fabrics landward or seaward orientations this organisation suggests that the tsunami consisted of two main waves the absence of tsunami deposits elsewhere on santiago island coupled with the relatively low elevation of the conglomerate in tarrafal