Detailed measurements of thickness and grain size of a widespread onshore tsunami deposit in Phang‐nga Province,southwestern Thailand

Measurements of thickness and grain size along flow‐parallel transects across onshore deposits of the 2004 Indian Ocean tsunami revealed macroscopic horizontal variations and provided new insights into tsunami sedimentation. The tsunami caused severe erosion of beaches, river mouths, and the shallow seafloor along the coast of southwestern Thailand and supplied sufficient sediment to deposit a kilometer‐wide blanket of sand on the land surface. The tsunami deposits generally fine landward with some fluctuations caused by local entrainment and settlement of sediments. Sediments of medium and fine sand are restricted to a few hundreds of meters inland from their source, whereas finer grained sediments were suspended longer and deposited 1 km or more inland. Although the thickness of the tsunami deposits is strongly influenced by local topography, they generally thin landward. In areas of low‐relief topography, the rate of landward thinning is exponential and reflects the dominance of sediment supply to nearshore areas over that to areas farther inland.     

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.     

Sedimentary Deposits from the 17 July 2006 Western Java Tsunami,Indonesia: Use of Grain Size Analyses to Assess Tsunami Flow Depth,Speed, and Traction Carpet Characteristics

The 2006 western Java tsunami deposited a discontinuous sheet of sand up to 20 cm thick, flooded coastal southern Java to a depth of at least 8 m and inundated up to 1 km inland. In most places the primarily heavy mineral sand sheet is normally graded, and in some it contains complex internal stratigraphy. Structures within the sand sheet probably record the passage of up to two individual waves, a point noted in eyewitness accounts. We studied the 2006 tsunami deposits in detail along a flow parallel transect about 750 m long, 15 km east of Cilacap. The tsunami deposit first becomes discernable from the underlying sediment 70 m from the shoreline. From 75 to 300 m inland the deposit has been laid down in rice paddies, and maintains a thickness of 10–20 cm. Landward of 300 m the deposit thins dramatically, reaching 1 mm by 450 m inland. From 450 m to the edge of deposition (around 700 m inland) the deposit remains <1 mm thick. Deposition generally attended inundation—along the transect, the tsunami deposited sand to within about 40 m of the inundation limit. The thicker part of the deposit contains primarily sand indistinguishable from that found on the beach 3 weeks after the event, but after about 450 m (and roughly coinciding with the decrease in thickness) the tsunami sediment shifts to become more like the underlying paddy soil than the beach sand. Grain sizes within the deposit tend to fine upward and landward, although overall upward fining takes place in two discrete pulses, with an initial section of inverse grading followed by a section of normal grading. The two inversely graded sections are also density graded, with denser grains at the base, and less dense grains at the top. The two normally graded sections show no trends in density. The inversely graded sections show high density sediment to the base and become less dense upward and represents traction carpet flows at the base of the tsunami. These are suggestive of high shear rates in the flow. Because of the grain sorting in the traction carpet, the landward-fining trends usually seen in tsunami deposits are masked, although lateral changes of mean sediment grain size along the transect do show overall landward fining, with more variation as the deposit tapers off. The deposit is also thicker in the more seaward portions than would be produced by tsunamis lacking traction carpets.     

Erratum to Identification of tsunami-induced deposits using numerical modeling and rock magnetism techniques: A study case of the 1755 Lisbon tsunami in Algarve,Portugal: [Physics of the Earth and Planetary Interiors Volume 182, Issues 3–4, Pages 187–198 (October 2010)]

Storm- and tsunami-deposits are generated by similar depositional mechanisms making their discrimination hard to establish using classic sedimentologic methods. Here we propose an original approach to identify tsunami-induced deposits by combining numerical simulation and rock magnetism. To test our method, we investigate the tsunami deposit of the Boca do Rio estuary generated by the 1755 earthquake in Lisbon which is well described in the literature. We first test the 1755 tsunami scenario using a numerical inundation model to provide physical parameters for the tsunami wave. Then we use concentration (MS, SIRM) and grain size (χ_ARM, ARM, B1/2, ARM/SIRM) sensitive magnetic proxies coupled with SEM microscopy to unravel the magnetic mineralogy of the tsunami-induced deposit and its associated depositional mechanisms. In order to study the connection between the tsunami deposit and the different sedimentologic units present in the estuary, magnetic data were processed by multivariate statistical analyses. Our numerical simulation show a large inundation of the estuary with flow depths varying from 0.5 to 6 m and run up of ～7 m. Magnetic data show a dominance of paramagnetic minerals (quartz) mixed with lesser amount of ferromagnetic minerals, namely titanomagnetite and titanohematite both of a detrital origin and reworked from the underlying units. Multivariate statistical analyses indicate a better connection between the tsunami-induced deposit and a mixture of Units C and D. All these results point to a scenario where the energy released by the tsunami wave was strong enough to overtop and erode important amount of sand from the littoral dune and mixed it with reworked materials from underlying layers at least 1 m in depth. The method tested here represents an original and promising tool to identify tsunami-induced deposits in similar embayed beach environments.     

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.     

Coastal sedimentation associated with the December 12th, 1992 tsunami in Flores,Indonesia

This paper presents the result of a detailed granulometric investigation of sediments deposited by a modern tsunami, the 1992 tsunami in Flores, Indonesia. Eyewitness accounts indicate that sediments were deposited upon coastal lowlands over wide areas as a result of the tsunami inundation. Distinctive vertical and lateral variations in particle size composition are characteristic features of the tsunami deposits and these are intimately related to sedimentary processes associated with flood inundation. The geomorphological and sedimentary evidence is used here to establish a preliminary model of tsunami sedimentation. This information is believed to be of great value in understanding sedimentary processes associated with tsunami flooding and in the interpretation of palaeo-tsunami deposits.     

Erosion and Sedimentation from the 17 July, 1998 Papua New Guinea Tsunami

— This paper describes erosion and sedimentation associated with the 17 July 1998 Papua New Guinea tsunami. Observed within two months of the tsunami, distinct deposits of a layer averaging 8-cm thick of gray sand rested on a brown muddy soil. In most cases the sand is normally graded, with more coarse sand near the base and fine sand at the top. In some cases the deposit contains rip-up clasts of muddy soil and in some locations it has a mud cap. Detailed measurements of coastal topography, tsunami flow height and direction indicators, and deposit thickness were made in the field, and samples of the deposit were collected for grain-size analysis in the laboratory. Four shore-normal transects were examined in detail to assess the shore-normal and along shore distribution of the tsunami deposit. Near the shoreline, the tsunami eroded approximately 10–25 cm of sand from the beach and berm. The sandy layer deposited by the tsunami began 50–150 m inland from the shoreline and extended across the coastal plain to within about 40 m of the limit of inundation; a total distance of up to 750 m from the beach. As much as 2/3 of the sand in the deposit originated from offshore. Across most of the coastal plain the deposit thickness and mean grain size varied little. In the along-shore direction the deposit thickness varied with the tsunami wave height; both largest near the entrance to Sissano Lagoon.     

Salinity in Soils and Tsunami Deposits in Areas Affected by the 2010 Chile and 2011 Japan Tsunamis

The accumulation of data sets of past tsunamis is the most basic but reliable way to prepare for future tsunamis because the frequency of tsunami occurrence and their magnitude can be estimated by historical records of tsunamis. Investigation of tsunami deposits preserved in geological layers is an effective measure to understand ancient tsunamis that occurred before historical records began. However, the areas containing tsunami deposits can be narrower than the area of tsunami inundation, thus resulting in underestimation of the magnitude of past tsunamis. A field survey was conducted after the 2010 Chile tsunami and 2011 Japan tsunami to investigate the chemical properties of the tsunami-inundated soil to examine the applicability of tsunami inundation surveys considering water-soluble salts in soil. The soil and tsunami deposits collected in the tsunami-inundated areas are rich in water-soluble ions (Na⁺, Mg²⁺, Cl^?, Br^? and SO ₄ ^2? ) compared with the samples collected in the non-inundated areas. The analytical result that the ratios of Na⁺, Mg²⁺, Br^? and SO ₄ ^2? to Cl^? are nearly the same in the tsunami deposits and in the tsunami-inundated soil suggests that the deposition of these ions resulting from the tsunami inundation does not depend on whether or not tsunami deposits exist. Discriminant analysis of the tsunami-inundated areas using the ion contents shows the high applicability of these ions to the detection of tsunami inundation during periods when the amount of rainfall is limited. To examine the applicability of this method to palaeotsunamis, the continuous monitoring of water-soluble ions in tsunami-inundated soil is needed as a future study.     

Geochemical characteristics of deposits from the 2011 Tohoku‐oki tsunami at Hasunuma,Kujukuri coastal plain,Japan

We examined the geochemical characteristics and temporal changes of deposits associated with the 2011 Tohoku‐oki tsunami. Stable carbon isotope ratios, biomarkers, and water‐leachable ions were measured in a sandy tsunami deposit and associated soils sampled at Hasunuma, Kujukuri coastal plain, Japan, in 2011 and 2014. At this site, the 2011 tsunami formed a 10–30 cm ‐thick layer of very fine to medium sand. The tsunami deposit was organic‐poor, and no samples contained any detectable biomarkers of either terrigenous or marine origin. In the underlying soil, we identified hydrocarbons and sterols derived from terrestrial plants, but detected no biomarkers of marine origin. In the samples collected in 2011, concentrations of tsunami‐derived water‐leachable ions were highest in the soil immediately beneath the tsunami deposit and then decreased gradually with depth. Because of its finer texture and higher organic content, the soil has a higher water‐holding capacity than the sandy tsunami deposit. This distribution suggests that ions derived from the tsunami quickly penetrated the sand layer and became concentrated in the underlying soil. In the samples collected in 2014, concentrations of water‐leachable ions were very low in both soil and sand. We attribute the decrease in ion concentrations to post‐tsunami rainfall, seepage, and seasonal changes in groundwater level. Although water‐leachable ions derived from seawater were concentrated in the soil beneath the tsunami deposit following the tsunami inundation, they were not retained for more than a few years. To elucidate the behavior of geochemical characteristics associated with tsunamis, further research on organic‐rich muddy deposits (muddy tsunami deposits and soils beneath sandy tsunami deposits) as well as sandy tsunami deposits is required.     

Coastal Sedimentation Associated with the Tohoku Tsunami of 11 March 2011 in South Kuril Islands, NW Pacific Ocean

Sediment deposited by the Tohoku tsunami of March 11, 2011 in the Southern Kurils (Kunashir, Shikotan, Zeleniy, Yuri, Tanfiliev islands) was radically different from sedimentation during local strong storms and from tsunamis with larger runup at the same location. Sediments from the 2011 Tohoku tsunami were surveyed in the field, immediately and 6 months after the event, and analyzed in the laboratory for sediment granulometry, benthos Foraminifa assemblages, and diatom algae. Run-up elevation and inundation distance were calculated from the wrackline (accumulations of driftwood, woody debris, grass, and seaweed) marking the distal edge of tsunami inundation. Run-up of the tsunami was 5 m at maximum, and 3–4 m on average. Maximum distance of inundation was recorded in river mouths (up to 630 m), but was generally in the range of 50–80 m. Although similar to the local strong storms in runup height, the tsunami generally did not erode the coast, nor leave a deposit. However, deposits uncharacteristic of tsunami, described as brown aleuropelitic (silty and clayey) mud rich in organic matter, were found in closed bays facing the South Kuril Strait. These closed bays were covered with sea ice at the time of tsunami. As the tsunami waves broke the ice, the ice floes enhanced the bottom erosion on shoals and destruction of low-lying coastal peatland even at modest ranges of runup. In the muddy tsunami deposits, silt comprised up to 64 % and clay up to 41.5 %. The Foraminifera assemblages displayed features characteristic of benthic microfauna in the near-shore zone. Deep-sea diatoms recovered from tsunami deposits in two closely situated bays, namely Krabovaya and Otradnaya bays, had different requirements for environmental temperature, suggesting these different diatoms were brought to the bays by the tsunami wave entraining various water masses when skirting the island from the north and from the south.     

Evaluation of the use of paleotsunami deposits to reconstruct inundation distance and runup heights associated with prehistoric inundation events,Crescent City,southern Cascadia margin

Historic‐ and prehistoric‐tsunami sand deposits are used to independently establish runup records for tsunami hazard mitigation and modeled runup verification in Crescent City, California, located in the southern Cascadia Subduction Zone. Inundation from historic (1964) farfield tsunami (~5–6 m runup height) left sand sheet deposits (100–200 m width) in wetlands located behind a low beach ridge [3–4 m elevation of the National Geodetic Vertical Datum of 1988 (NAVD88)]. The most landward flooding lines (4·5–5 m elevation) in high‐gradient alluvial wetlands exceed the 1964 sand sheet records of inundation by 1–2 m in elevation. The most landward flooding in low‐gradient alluvial wetlands exceed the corresponding sand sheet record of inundation distance by 1000 m. Nevertheless, the sand sheet record is an important proxy for high‐velocity inundation. Sand sheet deposition from the 1964 historic tsunami closely corresponds to the landward extent of large debris transport and structural damage in the Crescent City waterfront. The sand sheet deposits provide a proxy for maximum hazard or ‘kill zone’ in the study area. Six paleotsunami sand sheets (0·3–3 ka) are recorded in the back‐ridge marshes in Crescent City, yielding a ~450 year mean recurrence interval for nearfield Cascadia tsunami. Two paleotsunami sand deposit records, likely correlated to Cascadia ruptures between 1·0 and 1·5 ka, are traced to 1·2 km distance and 9–10 m elevation, as adjusted for paleo‐sea level. The paleotsunami sand deposits demonstrate at least twice the runup height, and four times the inundation distance of the farfield 1964 tsunami sand sheet in the same marsh system. The preserved paleotsunami deposits in Crescent City are compared to the most landward flooding, as modeled by other investigators from a predicted Cascadia (~ Mw 9) rupture. The short geologic record (~1·5 ka) yields slightly lower runup records than those predicted for the modeled Mw 9 rupture scenario in the same marsh, but it generally verifies predicted maximum tsunami runup for use in the planning of emergency response and rapid evacuation. Copyright © 2011 John Wiley & Sons, Ltd.     

The 2011 Tohoku-oki Earthquake Tsunami: Similarities and Differences to the 869 Jogan Tsunami on the Sendai Plain

A post-tsunami field survey following the 2011 Tohoku-oki Earthquake Tsunami was carried out to asses inundated area in Sendai Plain, Northeast Japan. The type of inundation was classified into two categories (major and minor) according to the amount of accumulated debris, garbage and sediment. Major and minor inundations were identified up to 4 and 5 km from the coastline, respectively. Many artificial geomorphological features, such as roadway embankments and canals, were believed to have affected the run-up process of the tsunami. The inundation area of the 2011 tsunami on the Sendai Plain is compared with that of the 869 Jogan tsunami, which was reconstructed using numerical modeling based on available historical and geological records. The inundation area of the 2011 Tohoku-oki tsunami is comparable to that of the 869 Jogan tsunami, although a direct comparison is difficult due to differences in geomorphological contexts between the paleo period and the present.     

The 11 March 2011 Tohoku Tsunami Survey in Rikuzentakata and Comparison with Historical Events

On 11 March 2011, a moment magnitude M _w = 9.0 earthquake occurred off the Japan Tohoku coast causing catastrophic damage and loss of human lives. In the immediate aftermath of the earthquake, we conducted the reconnaissance survey in the city of Rikuzentakata, Japan. In comparison with three previous historical tsunamis impacting the same region, the 2011 event presented the largest values with respect to the tsunami height, the inundation area and the inundation distance. A representative tsunami height of 15 m was recorded in Rikuzentakata, with increased heights of 20 m around rocky headlands. In terms of the inundation area, the 2011 Tohoku tsunami exceeded by almost 2.6 times the area flooded by the 1960 Chilean tsunami, which ranks second among the four events compared. The maximum tsunami inundation distance was 8.1 km along the Kesen River, exceeding the 1933 Showa and 1960 Chilean tsunami inundations by factors of 6.2 and 2.7, respectively. The overland tsunami inundation distance was less than 2 km. The tsunami inundation height linearly decreased along the Kesen River at a rate of approximately 1 m/km. Nevertheless, the measured inland tsunami heights exhibit significant variations on local and regional scales. A designated “tsunami control forest” planted with a cross-shore width of about 200 m along a 2 km stretch of Rikuzentakata coastline was completely overrun and failed to protect the local community during this extreme event. Similarly, many designated tsunami shelters were too low and were overwashed by tsunami waves, thereby failing to provide shelter for evacuees—a risk that had been underestimated.     

Sources and depositional processes of tsunami deposits: Analysis using foraminiferal tests and hydrodynamic verification

Foraminiferal tests are commonly found in tsunami deposits and provide evidence of transport of sea floor sediments, sometimes from source areas more than 100 m deep and several kilometers away. These data contribute to estimates of the physical properties of tsunami waves, such as their amplitude and period. The tractive force of tsunami waves is inversely proportional to the water depth at sediment source areas, whereas the horizontal sediment transport distance by tsunami waves is proportional to the wave period and amplitude. We derived formulas for the amplitudes and periods of tsunami waves as functions of water depth at the sediment source area and sediment transport distance based on foraminiferal assemblages in tsunami deposits. We applied these formulas to derive wave amplitudes and periods from data on tsunami deposits in previous studies. For some examples, estimated wave parameters were reasonable matches for the actual tsunamis, although other cases had improbably large values. Such inconsistencies probably reflect: (i) local amplification of tsunami waves by submarine topography, such as submarine canyons; and (ii) errors in estimated water depth at the sediment source area and sediment transport distance, which mainly derive from insufficient identification of foraminiferal tests.     

Nearshore Tsunami Inundation Model Validation: Toward Sediment Transport Applications

Model predictions from a numerical model, Delft3D, based on the nonlinear shallow water equations are compared with analytical results and laboratory observations from seven tsunami-like benchmark experiments, and with field observations from the 26 December 2004 Indian Ocean tsunami. The model accurately predicts the magnitude and timing of the measured water levels and flow velocities, as well as the magnitude of the maximum inundation distance and run-up, for both breaking and non-breaking waves. The shock-capturing numerical scheme employed describes well the total decrease in wave height due to breaking, but does not reproduce the observed shoaling near the break point. The maximum water levels observed onshore near Kuala Meurisi, Sumatra, following the 26 December 2004 tsunami are well predicted given the uncertainty in the model setup. The good agreement between the model predictions and the analytical results and observations demonstrates that the numerical solution and wetting and drying methods employed are appropriate for modeling tsunami inundation for breaking and non-breaking long waves. Extension of the model to include sediment transport may be appropriate for long, non-breaking tsunami waves. Using available sediment transport formulations, the sediment deposit thickness at Kuala Meurisi is predicted generally within a factor of 2.     

A synergetic use of satellite imagery from SAR and optical sensors to improve coastal flood mapping in the Gulf of Mexico

This work proposes a method for detecting inundation between semi‐diurnal low and high water conditions in the northern Gulf of Mexico using high‐resolution satellite imagery. Radarsat 1, Landsat imagery and aerial photography from the Apalachicola region in Florida were used to demonstrate and validate the algorithm. A change detection approach was implemented through the analysis of red, green and blue (RGB) false colour composites image to emphasise differences in high and low tide inundation patterns. To alleviate the effect of inherent speckle in the SAR images, we also applied ancillary optical data. The flood‐prone area for the site was delineated a priori through the determination of lower and higher water contour lines with Landsat images combined with a high‐resolution digital elevation model. This masking technique improved the performance of the proposed algorithm with respect to detection techniques using the entire Radarsat scene. The resulting inundation maps agreed well with historical aerial photography as the probability of detection reached 83%. The combination of SAR data and optical images, when coupled with a high‐resolution digital elevation model, was shown to be useful for inundation mapping and have a great potential for evaluating wetting/drying algorithms of inland and coastal hydrodynamic models. Copyright © 2011 John Wiley & Sons, Ltd.     

Reconstruction of Tsunami Inland Propagation on December 26, 2004 in Banda Aceh, Indonesia, through Field Investigations

This paper presents the results from an extensive field data collection effort following the December 26, 2004 earthquake and tsunami in Banda Aceh, Sumatra. The data were collected under the auspices of TSUNARISQUE, a joint French-Indonesian program dedicated to tsunami research and hazard mitigation, which has been active since before the 2004 event. In total, data from three months of field investigations are presented, which detail important aspects of the tsunami inundation dynamics in Banda Aceh. These include measurements of runup, tsunami wave heights, flow depths, flow directions, event chronology and building damage patterns. The result is a series of detailed inundation maps of the northern and western coasts of Sumatra including Banda Aceh and Lhok Nga. Among the more important findings, we obtained consistent accounts that approximately ten separate waves affected the region after the earthquake; this indicates a high-frequency component of the tsunami wave energy in the extreme near-field. The largest tsunami wave heights were on the order of 35 m with a maximum runup height of 51 m. This value is the highest runup value measured in human history for a seismically generated tsunami. In addition, our field investigations show a significant discontinuity in the tsunami wave heights and flow depths along a line approximately 3 km inland, which the authors interpret to be the location of the collapse of the main tsunami bore caused by sudden energy dissipation. The propagating bore looked like a breaking wave from the landward side although it has distinct characteristics. Patterns of building damage are related to the location of the propagating bore with overall less damage to buildings beyond the line where the bore collapsed. This data set was built to be of use to the tsunami community for the purposes of calibrating and improving existing tsunami inundation models, especially in the analysis of extreme near-field events.     

Estimating tsunami inundation from hurricane storm surge predictions along the U.S. gulf coast

Gulf of Mexico (GOM) coasts have been included in the U.S. Tsunami Warning System since 2005. While the tsunami risk for the GOM is low, tsunamis generated by local submarine landslides pose the greatest potential threat, as evidenced by several large ancient submarine mass failures identified in the northern GOM basin. Given the lack of significant historical tsunami evidence in the GOM, the potential threat of landslide tsunamis in this region is assessed from a worst-case scenario perspective based on a set of events including the large ancient failures and most likely extreme events determined by a probabilistic approach. Since tsunamis are not well-understood along the Gulf Coast, we investigate tsunami inundation referenced to category-specific hurricane storm surge levels, which are relatively well established along the Gulf Coast, in order to provide information for assessing the potential threat of tsunamis which is more understandable and accessible to emergency managers. Based on tsunami inundation studies prepared for the communities of South Padre Island, TX, Galveston, TX, Mobile, AL, Panama City, FL, and Tampa, FL, we identify regional trends of tsunami inundation in terms of modeled storm surge inundation. The general trends indicate that tsunami inundation can well exceed the level of storm surge from major hurricanes in open beachfront and barrier island regions, while more interior areas are less threatened. Such information can be used to better prepare for tsunami events as well as provide a preliminary estimate of tsunami hazard in locations where detailed tsunami inundation studies have not been completed.     

Evidence on the Koseda coast of Yakushima Island of a tsunami during the 7.3 ka Kikai caldera eruption

Previous research indicates that Yakushima Island, southwestern Japan, may have been struck by a huge tsunami before or soon after the arrival of the Koya pyroclastic flow during the 7.3 ka caldera‐forming Kikai eruption, but this has not yet been confirmed. This paper describes sedimentological and chronostratigraphic evidence showing that Unit TG, one of three gravel beds exposed on the Koseda coast of northeast Yakushima Island and investigated here, is a tsunami deposit. Unit TG is a poorly sorted, 30 cm thick gravel bed overlying a wave‐cut bench and underlying a Koya pyroclastic flow deposit. Sparse wood fragments in Unit TG were dated at 7 416–7 167 cal year BP. The constituent gravel clasts of Unit TG are similar in composition to those of modern beach and river deposits along the Koseda coast. Unit TG also contains pumice clasts whose chemistry is identical to that of pumice derived from the 7.3 ka eruption at Kikai caldera. The long‐axis orientations and composition of gravel clasts in Unit TG suggest that they were transported by a landward‐travelling high‐particle‐concentration flow, which suggests that Unit TG was deposited by a tsunami run‐up flow during the 7.3 ka Kikai caldera eruption, just before the arrival of the major Koya pyroclastic flow at the Koseda coast. Whether the 7.3 ka tsunami was caused by a volcanic eruption or an earthquake remains unclear, but Unit TG demonstrates that a tsunami arrived immediately before emplacement of a Koya pyroclastic flow.     

Inundation flow velocity of tsunami on land

An estimation of tsunami inundation flow velocity is one of the most challenging issues among tsunami research. Based on field data of inundation depth and inundation flow velocity u estimated using Bernoulli's theorem and inundation depth, fundamental characteristics of the relationship between inundation flow velocity and inundation depth are examined. Fundamental characteristics of the velocity coefficient where g is gravitational acceleration, h_f and h_r are inundation depths at the front and the back of structures such as a rectangular building with vertical walls, respectively) implicitly included in the relationship are examined through hydraulic experiments. As a result, C_v = 0.6 is recommended as its simple and practical value. It is confirmed through these examinations that the Froude number, defined by where , ranges 0.7–2.0, and when C_v = 0.6 is adopted this Froude number ranges 0.42–1.2. By using the relationship and C_v = 0.6, two simple and practical relationships are presented for two cases where inundation flow velocity exerts the largest or the smallest fluid force on structures. These relationships can be used to roughly grasp the practical side of tsunami damage, and estimate fluid force acting on individual structures, moving velocity and collision force of floating objects and sediment transport such as boulder and sand. Fundamental characteristics of the waterline (tsunami trace) distribution around/on the typical object model (square pillar, corn and column) are also examined through steady flow experiments, and it is confirmed that the maximum and the minimum values of h_f/h₀ in the full type model of the square pillar are almost the same as those of h_f/h_r obtained by field surveys where h₀ is uniform flow depth. It is also confirmed that h_r ? h₀ when the Froude number, defined by where u₀ is uniform flow velocity, is much less than 1.0. Using a newly defined velocity coefficient, tsunami inundation flow velocity on land can be estimated practically and would be useful for checking proposed sediment transport models that are now being developed by tsunami geologists.