tsunami deposits in a lacustrine sequence of the sanriku coast northeast japan abstract lacustrine deposits of the pacific coast of northeast japan consisting mostly of black organic mud contain intercalated thin beds of well sorted medium sand examination of the deposits from a coastal site of sanriku has revealed that sand grains are of marine origin and are fractions of deposits in marshy ponds transported from the littoral environment by a great flooding of seawater the mode of sedimentation shown in the thin beds of sand implies that they were deposited by tsunamis each with a maximum rise of 1 m or more above sea level

identification of tsunami deposits considering the tsunami waveform an example of subaqueous tsunami deposits in holocene shallow bay on southern boso peninsula central japan abstract this study proposes a tsunami depositional model based on observations of emerged holocene tsunami deposits in outcrops located in eastern japan the model is also applicable to the identification of other deposits such as those laid down by storms the tsunami deposits described were formed in a small bay of 10 20 m water depth and are mainly composed of sand and gravel they show various sedimentary structures including hummocky cross stratification hcs and inverse and normal grading although individually the sedimentary structures are similar to those commonly found in storm deposits the combination of vertical stacking in the tsunami deposits makes a unique pattern this vertical stacking of internal structures is due to the waveform of the source tsunamis reflecting 1 extremely long wavelengths and wave period and 2 temporal changes of wave sizes from the beginning to end of the tsunamis the tsunami deposits display many sub layers with scoured and graded structures each sub layer especially in sandy facies is characterized by hcs and inverse and normal grading that are the result of deposition from prolonged high energy sediment flows the vertical stack of sub layers shows incremental deposition from the repeated sediment flows mud drapes cover the sub layers and indicate the existence of flow velocity stagnant stages between each sediment flow current reversals within the sub layers indicate the repeated occurrence of the up and return flows the tsunami deposits are vertically divided into four depositional units tna to tnd in ascending order reflecting the temporal change of wave sizes in the tsunami wave trains unit tna is relatively fine grained and indicative of small tsunami waves during the early stage of the tsunami unit tnb is a protruding coarse grained and thickest stratified division and is the result of a relatively large wave group during the middle stage of the tsunami unit tnc is a fine alternation of thin sand sheets and mud drapes deposited from waning waves during the later stage of the tsunami unit tnd is deposited during the final stage of the tsunami and is composed mainly of suspension fallout cyclic build up of these sub layers and depositional units cannot be explained by storm waves with short wave periods of several to ten seconds common in small bays

tsunami sediment characteristics at the thai andaman coast this paper describes and summarizes the 2004 indian ocean tsunami sediment characteristics at the thai andaman coast field investigations have been made approximately 3 years after the 2004 indian ocean tsunami event seven transects have been examined at five locations sediment samples have been collected for grain size analyses by wet sieve method tsunami sediments are compared to three deposits from coastal sub environments the mean grain size and standard deviation of deposits show that shoreface deposits are fine to very fine sand poorly to moderately well sorted swash zone deposits are coarse to fine sand poorly to well sorted berm dune deposits are medium to fine sand poorly to well sorted and tsunami deposits are coarse to very fine sand poorly to moderately well sorted a plot of deposit mean grain size versus sorting indicates that tsunami deposits are composed of shoreface deposits swash zone deposits and berm dune deposits as well the tsunami sediment is a gray sand layer deposited with an erosional base on a pre existing soil rooted soil the thickness of the tsunami sediment layer is variable the best location for observation of the recent tsunami sediment is at about 50 200 m inland from the coastline in most cases the sediment layer is normally graded in some cases the sediment contains rip up clasts of muddy soils and or organic matter the vertical variation of tsunami sediment texture shows that the mean grain size is fining upward and landward break points of slope in a plot of standard deviation versus depth mark a break in turbulence associated with a transition to a lower or higher reynolds number runup this can be used to evaluate tsunami sediment main layer and tsunami sediment sub layers the skewness of tsunami sediment indicates a grain size distribution with prominent finer grain or coarse grain particles the kurtosis of tsunami sediment indicates grain size distributions which are flat to peak distribution or multi modal to uni modal distribution upward generally the major origins of tsunami sediment are swash zone and berm dune zone sands where coarse to medium sands are the significant material at these locations the minor origin of tsunami sediment is the shoreface where the significant materials are fine to very fine sands however for a coastal area where the shoreface slope is mild the major origin of tsunami sediment is the shoreface the interpretation of runup number from tsunami sediment characteristics gets three runups for the 2004 indian ocean tsunami at the thai andaman coast it corresponds to field observations from local eyewitnesses the 1st runup transported and deposited more coarse particles than the following runups overall the pattern of onshore tsunami sediment transportation indicates erosion at swash zone and berm dune zone followed by dynamic equilibrium at an area behind the berm dune zone and after that deposition at inland zone until the limit of sediment inundation the total deposition is a major pattern in onshore tsunami sediment transportation at the deposition zone which the sediment must find in the direction of transport

ostracods from a marmara sea lagoon turkey as tsunami indicators abstract a 352 cm long sediment core from hersek lagoon gulf of izmit was investigated for its ostracod species composition in order to evaluate the potential of ostracods to detect tsunami deposits in coastal environments the gulf of izmit is the eastern bay of the marmara sea which is tectonically controlled by the north anatolian fault ostracod shells are rare in the lower third of the core which probably represents a coastal wetland environment according to radiocarbon dating of terrestrial plant remains this unit was deposited between ad 500 and ad 800 above ostracod shells are abundant and dominantly monospecific composed almost exclusively of the widespread brackish water ostracod cyprideis torosa this almost monospecific occurrence indicates the establishment and maintenance of the hersek lagoon after ad 800 three distinct layers of mollusc shells and fragments contain ostracod shells of marine and to a lesser extent non marine origin in addition to those of c torosa the shell layers are further characterized by significant maxima in total ostracod shell numbers the high concentration of ostracod shells the higher species numbers and the mixture of marine lagoonal and non marine ostracod shells shows that shell layers were formed as high energy deposits resulting from tsunamis or large storms in the marmara sea the partial occurrence of non marine ostracod shells in the shell layers possibly indicates that tsunamis with extensive run ups and significant backwash flows caused the high energy deposits rather than large storms the investigated sediments show that lagoonal ostracods can serve as good proxies for tsunamis or large storms through significant variations in total shell numbers species numbers and the mixing of shells of different origin

deposits flow characteristics and landscape change resulting from the september 2009 south pacific tsunami in the samoan islands the september 29th 2009 tsunami caused widespread coastal modification within the islands of samoa and northern tonga in the south pacific preliminary measurements indicate maximum runup values of around 17 m okal et al 2010 and shore normal inundation distances of up to 620 m jaffe et al 2010 geological field reconnaissance studies were conducted as part of an unesco ioc international tsunami survey team survey within three weeks of the event in order to document the erosion transport and deposition of sediment by the tsunami data collected included a general morphology and geological characteristics of the coast b evidence of tsunami flow inundation flow depth and direction wave height and runup c surficial and subsurface sediment samples including deposit thickness and extent d topographic mapping and e boulder size and location measurements four main types of sedimentary deposits were identified a gravel fields consisting mostly of isolated cobbles and boulders b sand sheets from a few to 25 cm thick c piles of organic mostly vegetation and man made material forming debris ramparts and d surface mud deposits that settled from suspension from standing water in the tsunami aftermath tsunami deposits within the reef system were not widespread however surficial changes to the reefs were observed

x ray tomography of tsunami deposits towards a new depositional model of tsunami deposits x ray computed microtomography is used to obtain high resolution imagery of a historical tsunami deposit in andalusia spain 1755 lisbon tsunami the technique allows characterization of grain size distribution structures component analysis and sedimentary fabric of fine grained unconsolidated tsunami deposits at resolutions down to particle scale the results are validated by comparing to data obtained using other techniques such as laser diffraction anisotropy of magnetic susceptibility and x ray microfluorescence on the same deposits specific technical details such as sampling scanning and image processing methods and further improvements are addressed the use of x ray computed microtomography provides new insights into the stratigraphy of the deposits and gives access to significantly more detailed view of key sedimentary features such as mudlines rip up clasts crude laminations convolutions floating outsized clasts and contacts between successive units this analysis of the 1755 tsunami deposits using x ray computed microtomography allows the proposal of new hypotheses for the sedimentary processes forming tsunami deposits deposition by settling is limited and the section analysed here is dominated by a high shear stress leading to the development of traction carpets with laminated mudlines corresponding to the basal frictional region of these carpets the onset of the tsunami backwash is marked by a micro vortex resembling kelvin helmoltz instabilities

micromorphological analysis of coastal sediments from willapa bay washington usa a technique for analysing inferred tsunami deposits tsunami deposits are provisionally distinguished in the field on the basis of anomalous sand horizons fining up and fining landward coupled with organic rich fragmented backwash sediments in this paper micromorphological features of a sediment sequence previously interpreted as being of tsunami origin are described these characteristics are shown to be consistent with the macro scale features used elsewhere but show additional details not seen in standard stratigraphies including possible evidence for individual waves possibly wave magnitude progression organic fragment alignment and intraclast microstructures although replication and more complete studies are needed this analysis confirms the identification of a tsunami in willapa bay in ca 1700 ad while demonstrating a widely applicable technique for confirming or refuting possible tsunami deposits

a holocene tsunami deposit in eastern scotland a thin regionally extensive laterally persistent sand layer identified within the holocene coastal sequences of eastern scotland dated to 7000 years bp is suggested to be a tsunami deposit the likely source of the tsunami wave is the earthquake induced second storegga slide on the norwegian continental slope at least 750 km northeast of the deposit

possible deep fault slip preceding the 2004 parkfield earthquake inferred from detailed observations of tectonic tremor 1 earthquake predictability depends in part on the degree to which sudden slip is preceded by slow aseismic slip recently observations of deep tremor have enabled inferences of deep slow slip even when detection by other means is not possible but these data are limited to certain areas and mostly the last decade the region near parkfield california provides a unique convergence of several years of high quality tremor data bracketing a moderate earthquake the 2004 magnitude 6 0 event here i present detailed observations of tectonic tremor from mid 2001 through 2008 that indicate deep fault slip both before and after the parkfield earthquake that cannot be detected with surface geodetic instruments while there is no obvious short term precursor i find unidirectional tremor migration accompanied by elevated tremor rates in the 3 months prior to the earthquake which suggests accelerated creep on the fault 16 km beneath the eventual earthquake hypocenter

a tsunami about 1000 years ago in puget sound washington water surged from puget sound sometime between 1000 and 1100 years ago overrunning tidal marshes and mantling them with centimeters of sand one overrun site is 10 kilometers northwest of downtown seattle another is on whidbey island some 30 kilometers farther north neither site has been widely mantled with sand at any other time in the past 2000 years deposition of the sand coincided to the year or less with abrupt probably tectonic subsidence at the seattle site and with landsliding into nearby lake washington these findings show that a tsunami was generated in puget sound and they tend to confirm that a large shallow earthquake occurred in the seattle area about 1000 years ago

a high energy deposit in the byzantine harbour of yenikapi istanbul turkey abstract a byzantine harbour theodosian harbour has been uncovered during excavations at yenikapi with a stratigraphic sequence spanning the past 7000 bp in the marine part of the sedimentary sequence a high energy deposit has been interpreted as being of tsunami origin and related to the earthquake of 557 ad this paper presents a bio sedimentological analysis of this facies the unit is characterised by coarse sands and gravels containing reworked material such as woods bones marble blocks amphora fragments ceramics coins shells and plant remains the thickness of the facies varies between 10 and 100 cm the sediment matrix is poorly sorted with skewness values indicative of a sub tidal fine sand environment many of the marine taxa have been reworked and diverse ecological assemblages are represented lagoonal coastal and open marine species this unit is divided into three facies consistent with different phases of the tsunami drowning and water retreat the basal facies corresponds to two tsunami wave trains and the upper facies indicates the backwash flow

coastal sedimentation associated with the december 26 2004 tsunami in lhok nga west banda aceh sumatra indonesia abstract with wave heights of 30 m and runups reaching 50 m a s l and 6 km inland the december 26 2004 tsunami in sumatra was one of the largest tsunamis in recorded human history in this paper we present a description of the event in the lhok nga bay west coast of banda aceh and an interpretation of the tsunami sand deposits mostly based upon grain size analysis the 3 5 km long transect of lampuuk displays two landward fining thinning and sorting sequences the thickest cross sections of the first sequence of deposits 0 1 5 km inland suggest a deposition by three consecutive runups inflows and a final backwash return flow or outflow from 1 5 to 3 5 km inland the record is dominated by the second and highest wave 15 30 m normally graded couplets or triplets of layers were used to identify the runup of each wave the topmost layers interpreted as the backwash deposition describe a seaward sequence of increasing mean grain size and decreasing degree of sorting the local effects of the topography could be identified thickest deposits in the topographic lows 50 80 cm great spatial variations in thickness and upper laminated texture when the sedimentation was limited by steep slopes landward coarsening and very poor sorting at the wave breaking point bimodal grain size distributions reflecting different sources of sediments finally by coupling the longitudinal and vertical trends of the 26 cross sections we propose a model of sediment transport and deposition in a large tsunami wave

a late holocene record of environmental changes from the aliki lagoon egion north peloponnesus greece abstract aliki lagoon is a small lagoon located on the micro tidal south coast of the gulf of corinth greece the sediments of the lagoon recovered in three cores provide a record of late holocene environmental change including tectonic subsidence tsunami layers and change in local vegetation and sedimentation four periods of rapid environmental changes were identified over a 5000 yr long record these date from about 4700 3000 2500 and 2000 yr bp each change is linked to activity on the egion fault a deepening of the lagoonal bottom and a rise in relative sea level six tsunami events are recorded and have been caused by earthquakes on the egion fault three events 4700 3000 and 2500 bp eliki fault 2350 40 yr bp and two more distal fault ruptures the vegetation history and pollen zones are similar to those recognised by jahns vegetation hist archaebot 2 1993 187 on the argive plain 100 km southeast of the lagoon five successive sedimentological configurations are established in relation to the time frame provided by the tectonic activity 1 crevasse splay 2 fresh to brackish water marsh 3 and 4 brackish to hypersaline blind lagoon and 5 brackish to hypersaline blind lagoon or brackish open lagoon

apparent oxygen isotope equilibrium during progressive foliation development and porphyroblast growth in metapelites implications for stable isotope and conventional thermometry the assumption of oxygen isotope and major element equilibrium during prograde metamorphism was tested using staurolite grade pelitic schists that have undergone sequential porphyroblast growth and multiple episodes of recrystallization of matrix minerals and foliation development textural relationships are used to infer a metamorphic history that involves garnet growth followed by staurolite growth with each porphyroblast growth event followed by at least one period of recrystallization of matrix minerals conventional geothermobarometry using qtz grt pl ms bt st equilibria yields peak p t conditions of c 625 c at 9 11 kbar consistent with kmnfmash petrogenetic grid predictions for stability of the assemblage grt st bt qtz grt oxygen isotope fractionations yield apparent temperatures of c 590 c and qtz st fractionations yield an apparent temperature of c 595 c diffusional modelling indicates that quartz isotopic compositions were reset by c 30 c via retrograde isotopic diffusional exchange with micas the isotopic temperatures appear to be in excellent agreement with one another and suggest oxygen isotope equilibrium was attained between garnet and staurolite at c 625 c however the agreement of qtz grt and qtz str isotopic temperatures is not consistent with petrographic observations garnet grew before staurolite and petrogenetic grid constraints that predict that garnet grows over a temperature interval of c 525 550 c given that i oxygen diffusion rates in staurolite and garnet are slow enough to render an individual porphyroblast effectively closed to exchange after it forms and ii matrix minerals are able to exchange isotopes via recrystallization during each period of deformation garnet and staurolite could not have simultaneously achieved oxygen isotope equilibrium with each other or with minerals in the recrystallized matrix thus the qtz grt fractionations which yield apparent temperatures that are in apparent agreement with peak metamorphic temperature and apparent temperatures for qtz st fractionations cannot be fractionations resulting from equilibrium isotopic exchange instead they are apparent fractionations between porphyroblasts formed at different temperature and times in the prograde p t d path and quartz that recrystallized and exchanged with micas and plagioclase during several phases of deformation

sedimentological and geoarchaeological evidence of multiple tsunamigenic imprint on the bay of palairos pogonia akarnania nw greece abstract this paper presents evidence of multiple tsunami impact on the bay of palairos pogonia nw greece during the holocene based on detailed geo scientific studies altogether 41 vibracores were drilled to detect high energy influence in the stratigraphical record layers of coarse grained allochthonous marine deposits were found intersecting autochthonous fine grained back beach sediments in the palairos coastal plain on top of beach or marly bedrock units at pogonia beach and along the pogonia cliff section high energy deposits are associated with specific sedimentary structures such as fining upward sequences rip up clasts basal erosional contact bi to multimodal grain size distribution lamination and co existence of both well rounded and angular sharply edged components all of them typical of tsunami impact macro and microfaunal analyses revealed tsunami related input of numerous ex situ marine species and mostly angular shell debris into quiescent fresh to brackish water environments by high energy and long distance transport geophysical methods helped to find subsurface structures and to seize the lateral extent of tsunami layers ca fe ratios derived from xrf measurements were used to trace tsunami influence inland most important is the widespread spatial distribution of the tsunamites with a lateral extent between 70 m at the pogonia cliff section 200 m at pogonia beach and 1 km in the central palairos plain and overall tendencies of fining and thinning towards inland highest elevations of tsunamites were found around pogonia village at ca 7 5 m a s l vibracore data give evidence that the overall coastal evolution has been strongly affected locally even controlled by multiple high energy impact a conspicuous geoarchaeological tsunamite up to 1 5 m thick was found at pogonia cliff consisting of mixed marine sand pebbles bio erosively altered stones shell debris foraminifers and terrigenous material abundant ceramic fragments bones building material it is directly associated with the submerged remains of an ancient mole which was destroyed and its building material partly dislocated by the same event dating of tsunamites was accomplished by archaeological age determination of diagnostic sherds and by radiocarbon and luminescence dating techniques strong tsunami events were dated to the beginning of the 6th the mid 5th the 4th 3rd and the late 2nd millennia bc as well as to the 4th 3rd century bc on a regional scale the recurrence interval for large events is ca 500 1000 years at least twice during the late holocene the palairos coastal plain was flooded quasi contemporaneously from both the northern and southern side

geochemical and micropaleontological impacts caused by the 2011 tohoku oki tsunami in matsushima bay northeastern japan abstract we present stratigraphic geochemical cns elemental analysis and micropaleontological ostracode assemblages evidence for the 2011 tohoku oki tsunami impact in matsushima bay northeastern japan and examine the recovery process after the impact to the bay environment using short sediment cores from two different topographic settings at a water depth of approximately 4 m at both sites tsunami deposits are composed of two sedimentary layers that recorded the first tsunami run up and backwash at the western site near the channel that connects the bay with the pacific ocean the first tsunami wave eroded the bay floor sediments and left the tsunami deposits composed of medium sand rich in shell fragments but with sparse numbers of meiobenthic ostracodes by contrast at the eastern site which is surrounded by many small islands the first wave eroded very little of the bay floor sediments and left tsunami deposits consisting of sandy mud rich in exotic ostracodes such as phytal species shallow marine sand dwelling species and brackish water species overlying post tsunami deposits are composed mainly of organic rich mud in which organic matter was derived primarily from marine plankton ostracode assemblages in the tsunami deposits lack the offshore species that live in water depths 50 m and are dominated by the species from matsushima bay and its adjacent nearshore upper sublittoral areas and brackish water environments the distance from deep water offshore areas to the core sites is too far to transport ostracode valves by tsunami waves

effects of longitudinal valley slopes on runup of the 2011 tohoku tsunami on the sanriku coast northeastern japan abstract the 2011 tohoku earthquake and tsunami caused heavy damage in low lying river valleys of the sanriku coast northeastern japan the landward extent of inundation by the tsunami varied considerably among the valleys indicating that tsunami runups were strongly affected by the subaerial fluvial morphology of the valleys we used detailed tsunami inundation maps to investigate tsunami runups along river valleys along the sanriku coast considering both the protected areas landward of coastal seawalls and levees protected zone and areas on the river side of levees channel zone we determined the mean longitudinal slopes of all river valleys and used them in conjunction with published tsunami inundation maps to determine the distances and heights of tsunami runups in 68 valleys along the sanriku coast runup heights tended to be higher and inundation distances longer in the channel zone than in the protected zone comparisons of runups among valleys with different longitudinal valley slopes showed that inundation distance decreased with increasing valley slope and that runup height increased with increasing slope during runup some of the kinetic energy of a tsunami is consumed as frictional work and some is transformed upslope to potential energy the steeper the longitudinal slope the greater the amount of energy transformed and stored as potential energy and consequently the amount of energy consumed by frictional work declines and inundation distance shortens in the protected zone more energy is consumed by frictional work during destruction of artificial structures such as houses and inundation distance is shorter than in the channel zone our analysis of 2011 tsunami data clarified relationship among tsunami runups shoreline tsunami heights geometry of the coastline and longitudinal valley slopes among sanriku ria coast coastline geometry appears to be a secondary influence on the shoreline tsunami height and runup that the shoreline tsunami height was not the dominant influence on tsunami runup emphasizes the importance of subaerial topography on tsunami runup especially in narrow steep valleys which are often of the topography along coasts that face plate margins

characterization of the 26 december 2004 tsunami deposits in andaman islands bay of bengal india the large tsunami which was generated by an earthquake on 26 december 2004 affected most of the countries around the indian ocean a total of 48 tsunamigenic surface sediments and nine core samples have been collected from various coastal geomorphological features such as beaches estuaries creeks and mangrove areas in the andaman islands these samples were analysed for textural analysis and geochemical studies to evaluate effects of the tsunami on sediment contamination the studied sediments deposited by the 26 december 2004 tsunami in andaman group of islands belong to poorly sorted coarse to medium sands generally the concentration of heavy metals in the tsunamigenic surface sediments is mainly in the order of cu mn fe zn pb during the post tsunami 2005 and cu fe mn zn pb during the post monsoon 2008 the analysed core samples show that tsunami sediments have been preserved at certain depths from the sampling locations and indicate that they were derived from shallow littoral to neritic depths the approximate width of deposits deposited by the 26 december 2004 tsunami in diglipur and mayabandar areas north andaman is 10 cm in rangat and baratang middle andaman the thickness of the deposits is 15 cm in chidiyatapu junglighat rutland islands and havelock island south andaman the thickness of the deposits is 30 8 25 and 5 cm respectively and in hut bay little andaman the thickness of the deposits is about 15 cm

evaluation of tsunami impacts on shallow marine sediments an example from the tsunami caused by the 2003 tokachi oki earthquake northern japan abstract a combined approach of field geology and numerical simulation was conducted for evaluating the tsunami impacts on the shelf sediments the 2003 tokachi oki earthquake m 8 0 that occurred on 25 september 2003 off southeastern hokkaido northern japan generated a locally destructive tsunami maximum run up height of the tsunami waves reached 4 m above sea level in order to estimate the tsunami impacts on shallow marine sediments we compared pre and post tsunami marine sediments in water depths of 38 112 m in terms of grain size sedimentary structure and microfossil content decreases of fine fractions especially finer than very fine sand which led to coarsen the mean grain size were detected in the inner shelf of the northern part of the study area foraminiferal assemblages also changed in the coarsened sediments on the other hand the other shelf sediments largely unchanged or slightly fined we also simulated the tsunami wave velocity and direction and grain size entrained by the modeled tsunami the numerical simulation resulted in that the 2003 tsunami could transport very fine sand in water depths shallower than 45 95 m at the northern part of the study area this is comparable with the actual grain size changes after the tsunami had passed however some storms and tidal currents might also be possible to stir the surface sediments after the pre tsunami survey so we could not conclude that the grain size changes had been caused only by the tsunami nevertheless a combined approach of sampling and modeling was powerful for estimating the tsunami impacts under the sea

tsunami deposits beneath tidal marshes on vancouver island british columbia thin sheets of sand occur within holocene mud and peat deposits beneath tidal marshes at tofino ucluelet and port alberni on vancouver island british columbia the sand sheets are extensive and have sharp upper and lower contacts in most cases they consist of moderately sorted massive sand and silty sand with abundant wood and other plant detritus at port alberni the thickest sheet has gravel and is graded the upper two sand sheets in the tofino ucluelet area and possibly the third are also present at port alberni eyewitness accounts and 137 cs analysis suggest that the uppermost thinnest sand was deposited by the tsunami triggered by the great alaska earthquake in 1964 the next oldest sand sheet has been radiocarbon dated at our data suggest that large tsunamis have struck the southern british columbia coast several times during the late holocene and that some were much larger than the 1964 tsunami which caused about 10 million damage 1964 canadian dollars to communities on vancouver island because such tsunamis can be expected in the future they pose a hazard to people and property in some coastal areas

an amalgamated meter thick sedimentary package enabled by the 2011 tohoku tsunami in el garrapatero galapagos islands abstract tsunamis and storms instigate sedimentological and geomorphological changes to the coastal system both long term and ephemeral to accurately predict future coastal hazards one must identify the records that are generated by the processes associated with these hazards and recognize what will be preserved using eyewitness accounts photographs and sedimentology this study documents pre and post tsunami conditions and constrains the timing and process of depositional events during and following the 11 march 2011 tohoku tsunami in the coastal system at el garrapatero galapagos islands while the tsunami acted as both an erosional and depositional agent the thick fan like sand sheet in el garrapatero was primarily emplaced by overwash deposition during high tide from swell waves occurring between 19 25 march and 17 22 april 2011 the swell waves were only able to access the terrestrial coastal system via a channel carved by the 2011 tohoku tsunami through the barrier sand dune this combined deposit could result in an overestimation of the hazard if interpreted to be the result of only one event either tsunami or wind generated waves an analogous sand layer younger than 1390 1530 cal yr bp may record a similar prior event

tsunami deposits in holocene bay mud in southern kanto region pacific coast of central japan abstract tsunami have probably deposited sand sheets that are intercalated in holocene bay floor mud exposed on the boso and miura peninsulas facing the convergent boundary of the pacific philippine sea and eurasian plates we have identified seven sand sheets at four drowned valleys and correlated these by 137 radiocarbon dates of shells and wood the sheets consist of poorly sorted muddy sand and well sorted sand layers in fining upward sequences containing abundant transported shells rip up clasts and wood fragments the sheets erosionally overlie bioturbated bay floor mud that contains molluscan shells in life position most of the sheets are less than 20 cm thick and rarely more than 50 cm thick some molluscan shells are older in these layers than in underlying mud both landward and seaward paleocurrents are shown in a few cases by imbrication of shells and by low angle wedge shaped lamination at least five of the sand sheets contain molluscan fossils derived from rocky coasts or shore platforms although they intercalated in mud deposited within bays at depths of 10 15 m two other sand sheets are dominated by open seashore ostracode assemblages although they were deposited in the brackish inner bay and muddy central bay five of the layers may correlate with emergences recorded by nearby holocene marine terraces these correlations suggest that great earthquakes triggered the inferred tsunami the tsunami occurred at intervals of 300 2000 years beginning about 10 000 years ago

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