Inundation Limit Research Articles

Tsunami inundation limit based on probabilistic analysis of runup and inundation distance

Tsunami inundation limit based on probabilistic analysis of runup and inundation distance

Trace fossils of hypersaline environment and its implication in identifying tidal inundation boundary in Great Rann of Kachchh, Western India

Extreme hypersaline environments are known to be challenging ecosystems for the survival of organisms. These extreme environments are characterized by high evaporation, resulting in a drastic reduction in the ichnological and bioturbational diversity. Moreover, such environments are poorly understood on account of limited documentation in rock records. The Great Rann of Kachchh forms an exclusive salt-encrusted geomorphic facet and is India’s most extensive exposure to hypersaline deposits. The area is inundated by tidal ingress from the Arabian Sea during the monsoon, followed by an evaporative period. Moreover, tidal ingress in the Rann of Kachchh and its effect on the ecology ispoorly documented. Ichnological investigations of the hypersaline Great Rann of Kachchh revealed four recurring trace fossils, Arenicolites, Palaeophycus, Polykladichnus, and Skolithos, with annelids, and crustaceans as the most likely producers. Furthermore, the existence of their juvenile forms is indicated by the presence of small and tiny subsurface burrows. Hence, in the present research, we used ichnology to document the limit and mechanism of tidal ingress to demarcate the tidal inundation boundary up to the east of Khadir Island. We propose a hypothesis identifying the tidal inundation limit by larval recruits burrows and present an ichnological model for a hypersaline environment.

Can Mud Deposits Indicate Inundation Extent of Paleotsunamis? Insights From Sediment‐Transport Simulations for Sand and Mud

AbstractField surveys following the 2011 Tohoku‐oki tsunami showed that mud tsunami deposits reached close to the tsunami inundation limit. However, the factors controlling the distribution of mud tsunami deposits remained unclear. We investigated these influencing factors by numerically simulating sand and mud transport after validating the tsunami inundation and distributions of sand and mud deposits during the 2011 Tohoku‐oki tsunami based on our sensitivity analysis of parameters used in the mud and sand sediment simulations. We have revealed that when the source of mud sediments is only on the seafloor (i.e., no terrestrial source), mud is deposited along less than 10% of the inundation distance. In contrast, if a terrestrial source of mud is present, mud deposits can cover 100% of the inundation distance. We have also revealed that mud sediments are not formed when topographic slopes are steep (1/20–1/500), irrespective of a terrestrial mud source, because flow stagnation does not occur. Therefore, to reproduce past inundation ranges of tsunamis from the distribution of mud deposits, two conditions are required: (a) regions with onshore mud sediments and (b) a gentle topographic slope (around 1/1,000) to allow for long‐time (more than 100 min) flow stagnation.

Identifying tsunami traces beyond sandy tsunami deposits using terrigenous biomarkers: a case study of the 2011 Tohoku-oki tsunami in a coastal pine forest, northern Japan

The distributions of sandy tsunami deposits do not reflect the true extents of tsunami inundation areas, leading to underestimates of inundation by past tsunamis and thus the magnitudes of their associated tsunamigenic earthquakes. To archive the sedimentological and geochemical features of the 2011 Tohoku-oki tsunami deposit, we performed visual observations and computed tomography, grain-size, water content, and organic geochemical analyses of sediments from a coastal forest at Oirase Town, northern Japan. Stratigraphic observations revealed the 2011 tsunami deposit to be a landward-thinning interbedded sand and soil layer that became ambiguous in landward locations. The sediment samples from the inundated area did not contain marine-sourced biomarkers; instead, peak concentrations of isolongifolene, an organic compound derived from Pinus in the forest, were observed within or just above the sandy tsunami deposits in sediment sections. Peak isolongifolene concentrations were also detected in landward soils inundated by the tsunami in which no sand layer was observable, but were not observed beyond the inundation limit. Although this characteristic biomarker is unique to this and similar depositional environments, these results suggest that lateral changes of the concentrations of environment-specific biological proxies in the sedimentary column may record tsunami inundation.

Reduction effect of tsunami sediment transport by a coastal forest: Numerical simulation of the 2011 Tohoku tsunami on the Sendai Plain, Japan

We examined the effect of the coastal forest on tsunami sediment movement on the Sendai Plain, Japan, during the 2011 Tohoku tsunami using a numerical simulation of sediment transport. To account for the variable roughness coefficient in the coastal forest, a composite equivalent roughness coefficient was adopted. The simulated mean concentration of suspended sediment, wave height, flow velocity, and inundation limit were significantly reduced by the coastal forest. For fine to medium sand, the volumes of maximum deposition and erosion were reduced to 57–83% of those in the simulation without the coastal forest; these reductions were particularly notable for fine sand. The maximum extent and thickness of the sand layer were also reduced. The simulated sediment thickness and extent with the coastal forest for finer grain sizes roughly agreed with the observations, while the simulated results for coarser sand underestimated the observations. The reduction of sediment transport due to the coastal forest suggests that land use conditions and the vegetation environment at the time of a tsunami should be considered when studying historical and paleo-tsunamis using the geological evidence.

Visualization and Spatio-temporal Analysis of Tsunami Inundation: A Case of the Great East Japan Earthquake

Abstract. This study visualized the spatio-temporal changes in the tsunami inundation area and analyzed its expansion mechanism. The most characteristic of the Great East Japan Earthquake is the damage caused by the tsunami. And 90% of the dead was caused by it. One of the factors is that the preparation of countermeasures corresponding to the huge tsunami was not fully prepared. Therefore, after the Great East Japan Earthquake, the Japanese government has emphasized the importance of the advance preparation of the hugest tsunami expected. According to the past experience the occurring of huge tsunami is very rare. Earthquake researchers have observed same scale tsunami in every 1000 years in Japan. According prediction, next huge tsunami may be happened around the 2030. Therefore, analyzing the tsunami inundation mechanism of the Great East Japan Great Eastern is important for the future tsunami countermeasure. The arrival time and spatial distribution of tsunami inundation can be considered as a main important component of evacuation planning. In addition, a wide range of inundation area caused by huge tsunami is suitable for analyzing the inundation mechanism compared with a small-scale tsunami inundation. In this study I would like to examine the tsunami inundation process caused by the Great East Japan Earthquake in 2011.The method is as follows. First, movies shooting the tsunami inundation are collected from DVDs and TV hosting services. And they are examined as analysis materials. As a result, movies that taken from the ground were impossible to shoot the dynamic process of tsunami flooding. So that movies that taken from the helicopter or airplane was selected in this research. Next, the movies are converted into images at regular intervals of time. And adding position information to images (geo-reference), images are imported on the geographic information system (GIS). After that, Inundation limit lines are digitized. In this study, inundation limit lines are created at intervals of around 5 seconds. However, when the image is disturbed by dust etc., images of around 5 seconds are used. Basic information on the tsunami inundation handled in this study is shown in Table 1 and Figure 1.As the result, tsunami inundation process was strongly affected by the location of buildings (Figure 2). On the other hand, the inundation distance declined even where the fields spread. The spatio-temporal variation of the inundation process was quantitatively clarified. Regression analysis was performed with variables of inundation time and inundation distance. As a result, changes in correlation were observed in a certain section. In order to analyze the factors, two regression analyses were conducted. First is the inundation time and elevation as variables. Second is the inundation time and distance from buildings as variables. The building data had acquired the image before the earthquake (April 4, 2010) from Google Earth, and created the building shape data. As a result of each analysis, it became clear that sections where the elevation suddenly changes and the short distance from buildings, overlapped sections where the inundation distance does not extend (Figure 3). These results suggest that it is possible to predict inundation time and distance in other areas if parameters can be acquired.

Impact of very severe cyclonic storm Phailin on shoreline change along South Odisha Coast

The present study makes a qualitative and quantitative assessment of inundation limit, the structural damage and shoreline change due to very severe cyclonic storm Phailin and also estimates the rate of recovery along different parts of south Odisha coast. At the time of landfall of Phailin along Odisha and adjoining Andhra Pradesh coast on October 12, 2013, maximum sustained surface wind speed reached up to 200–210 kmph gusting to 220 kmph with an estimated pressure drop 66 mbar at the center. Significant wave heights reached up to more than 7 m with a mean period range between 4 and 12 s from southeast direction during the event. Strong gale wind and high wave followed by massive rainfall brought irreparable damage to the coastal structures and shoreline along south Odisha. Real-time kinematics global positioning system and differential global positioning system Arcpad were used to monitor the shoreline change before and after Phailin and the inundation limit. The study indicates maximum inundation at southernmost part of Odisha coast (Ramayapatnam) followed by inside the Gopalpur Port area and minimum near Gopalpur port north. Shoreline change from pre- (September 2013) to post-storm period (October 2013) is landward all along south Odisha coast with maximum (48.7 m) near Rushikulya turtle nesting beach and minimum (12.6 m) near south of Gopalpur tourist beach. The recovery of the beach and dune areas assessed during October 2014 (after 1 year from the post-storm observation) is uneven. Percentage of recovery is maximum at south side of Gopalpur port, while recovery is minimum on north of the port.

Sediment transport modeling of multiple grain sizes for the 2011 Tohoku tsunami on a steep coastal valley of Numanohama, northeast Japan

The grain size distribution of a tsunami deposit may have a correlation with the tsunami inundation process, and further with the tsunami source characteristics. We test this hypothesis using thickness and grain size distribution data of the 2011 Tohoku tsunami deposit in Numanohama coast, Iwate Prefecture, Japan. Here, we build and validate a tsunami sediment transport model that can simulate deposit thickness and grain size distribution. Our numerical model has three layers: parent (bed), deposit (bed), and suspended load layers. The two bed-layers contain information about the grain size distribution. This numerical model can handle a wide range of grain sizes from 0.063 (4ϕ) to 5.657 mm (−2.5ϕ). The grain size distributions at 12 sample points along a 900 m transect from the beach, through a marsh, and up to the inundation limit, are used to validate the tsunami sediment transport model. We adopt a reference tsunami source model that can well reproduce the observed tsunami run-up heights ranging from 16 to 35 m along the steep valley during the 2011 tsunami. The simulated sand thickness distribution along the transect is consistent with the observed thickness ranging from 3 to 23 cm. The computed net erosion and deposition suggest that most of the sand deposit was originated from the near shore. The shapes of the simulated grain size distributions represented by their sorting, skewness, kurtosis, and mean at most of the sample sites are similar to the observations. The differences between the observed and simulated peak of grain size distributions are less than 1ϕ. To evaluate the sensitivity to the tsunami source model, we test five tsunami scenarios which are modified from the reference source model. While the tsunami scenario with 120% of the reference amplitude can also reproduce the thickness and grain size distribution, the scenarios with amplitudes smaller than 80% of the reference or with wave periods shorter than 50% of the reference source model underestimate the thickness and cannot reproduce the grain size distributions. Our simulation results suggest that it is possible to estimate tsunami wave amplitude and wave period from sediment deposit thickness and grain size distribution data.

Tsunami inundation, sediment transport, and deposition process of tsunami deposits on coastal lowland inferred from the Tsunami Sand Transport Laboratory Experiment (TSTLE)

The processes of tsunami inundation, sediment transport, and deposition on coastal lowlands are investigated experimentally. We conducted large-scale experiments with land slopes of 0.00 and 0.01 and compared them with experiments conducted previously with a slope of 0.02. The ratio of marine-originated sediment in the inland deposits decreased as the land slope decreased, reflecting the strong inundation flow and weak return flow. The sediment concentration near the bed increased remarkably and supplied a greater quantity of coarse sand inland when the land slope decreased, indicating the strong influence of land slope on bed load. The extent of sandy deposits and the inundation limit nearly corresponded with the sloping topographies. However, the inundation flow reached much farther inland than the sandy deposits on the flat (i.e., level) topography. This was because the extent of sandy deposits was determined by the flow speed, which depended in turn on the wave speed, whereas the inundation limit was determined by the inland water mass, which depended in turn on the waveform. The floating load reached the inundation limit and formed very thin and sparse muddy deposits. Considering the uncertainty of the waveform and the difficulty of detecting muddy deposits, it is more feasible to estimate the wave speed from the extent of sandy deposits. The spatial distributions of sandy deposits for various waves, land slopes, and topographies were characterized by the nondimensional area density and inundation distance. This result suggested the possibility of quantitative comparison among field investigations of tsunami deposits under various conditions. The formation of an inverse grading layer, experimentally observed in a wide range of inland deposits, was attributed to kinetic sieving. The bed load under slow deposition was speculated to thicken the inverse grading layer by reworking the coarse sand. Additionally, the sediment behind dunes became liquefied and showed shear deformation during the erosion. The shear deformation of liquefied sediment below the erosional surface might leave sedimentary characteristics specific to earthquake tsunamis.

Are inundation limit and maximum extent of sand useful for differentiating tsunamis and storms? An example from sediment transport simulations on the Sendai Plain, Japan

We examined the quantitative difference in the distribution of tsunami and storm deposits based on numerical simulations of inundation and sediment transport due to tsunami and storm events on the Sendai Plain, Japan. The calculated distance from the shoreline inundated by the 2011 Tohoku-oki tsunami was smaller than that inundated by storm surges from hypothetical typhoon events. Previous studies have assumed that deposits observed farther inland than the possible inundation limit of storm waves and storm surge were tsunami deposits. However, confirming only the extent of inundation is insufficient to distinguish tsunami and storm deposits, because the inundation limit of storm surges may be farther inland than that of tsunamis in the case of gently sloping coastal topography such as on the Sendai Plain. In other locations, where coastal topography is steep, the maximum inland inundation extent of storm surges may be only several hundred meters, so marine-sourced deposits that are distributed several km inland can be identified as tsunami deposits by default. Over both gentle and steep slopes, another difference between tsunami and storm deposits is the total volume deposited, as flow speed over land during a tsunami is faster than during a storm surge. Therefore, the total deposit volume could also be a useful proxy to differentiate tsunami and storm deposits.

Tsunami deposits in a super-large wave flume

Understanding the process of sediment transport under tsunami inundation is essential to providing credible information about potential tsunamis from tsunami deposits. In this study, a super-large wave flume 205m long and 3.4m wide was used to investigate the hydraulic process of tsunami inundation and sedimentary features of the resulting tsunami deposit. A uniformly sloping topography (1/50) with a sand dune 0.2m high was built in the flume and the topography change induced by a solitary wave was measured. The maximum wave height at the shoreline was 0.6m and the horizontal velocity reached up to 3.5m/s, resulting in a sediment concentration of up to 5% by volume. The inundation and return flow completely eroded the dune and caused deposition, which showed landward and seaward thinning and fining. The vertical distribution of grain size and density in the inundation flow indicated upward fining and an upward decrease in density, and the deposits showed inverse grading at the base in addition to normal grading. Therefore, the inverse grading was attributed to the depositional process instead of the vertical distribution of grain size in the flow, such as via a traction carpet. The inundation flow was classified into two phases. The first phase flow, which appeared at the front of the inundation flow, was governed by the wave speed at the shoreline. The second phase flow, which occurred near the dune, was controlled by the difference in wave levels in front of and behind the dune. The deposits caused by the first phase flow (near the inundation limit) were constant regardless of the presence of the dune, indicating that the effect of the dune on the deposits was limited in the nearshore region. The deposits near the inundation limit, showing rapid fining and different chemical compositions, were carried by muddy foam floating on the water surface. The sediment supply from offshore to onshore over the dune was small and the erosion of the sand dune accounted for 36% of the onshore deposits. The offshore deposits were mainly caused by wave motion and the contribution of the onshore sediment brought by the return flow was small (24%). However, the return flow had a large effect on the sedimentary structure of the offshore deposits, such as seaward fining. Our results will help to examine the physical processes resulting in the empirically established common sedimentary characteristics of tsunami deposits and will provide a detailed data set to validate sediment transport models used in numerical simulations.

Insights from geochemistry and diatoms to characterise a tsunami's deposit and maximum inundation limit

Abstract Geochemical proxies and diatom assemblages were used in combination with grain size characteristics not only to describe the deposit left behind by the 27 February 2010, Maule tsunami at Las Canas, Maule Region, Chile, but also to trace the maximum inundation limit of the event. The sandy deposit was laid down between 160 and 260 m inland behind an eroded sand dune and a lagoon but reached only 60% of the total tsunami inundation distance of 380 m, which was marked by organic debris, pumice clasts and wooden logs. It consisted of coarse to medium sand that thinned and fined inland. At the most seaward point, the 22 cm thick deposit exhibited a fining upward unit overlain by a couplet of coarsening–fining upward units, suggesting deposition by at least two waves, while farther inland the fining upward deposit was probably left behind by only one wave. Chemical proxies (Ca/Ti vs Sr/Ba) allow us to distinguish the deposit from the surrounding soil and indicate that it was sourced from the beach and/or dune area, with diatom assemblages confirming the marine origin of the deposit. Saltwater indicators (e.g. Cl, S) provide evidence for the maximum inundation limit beyond the extent of the sandy deposit, despite dilution and dissolution by 500 mm of rainfall in the six months since the tsunami. Marine and marine/brackish diatom assemblages decreased landward but were found up to the inundation limit and immediately beyond, suggesting the effect of diatom-bearing sea spray at the wave front or redistribution of the detrital assemblage associated with tsunami inundation due to wind. While the latter might result in a slight over-estimation of the inundation distance, they can be used in combination with chemical proxies to trace the maximum inundation distance of recent and past tsunamis, thus allowing for a better estimation of the magnitude of past events. Post-depositional processes were found to have affected the thinner sandy deposits (

Bedforms record the flow conditions of the 2011 Tohoku-Oki tsunami on the Sendai Plain, northeast Japan

This article describes the bedforms formed by the 2011 Tohoku-Oki tsunami on the southern Sendai Plain, NE Japan. Integrated analyses of satellite images, field survey data, and X-ray radiographs revealed the natural shapes of these bedforms. The dominant bedforms are dunes and antidunes about ~ 20 cm thick (high) and relatively flat because of their meter-scale wavelengths. Their morphologies reflect mainly the tsunami run-up flow on the flat lowland and the return flow in a narrow, steep valley. Flow depth changed at sites where the level of the ground surface changed along the tsunami flow path, causing the flow velocity to fluctuate. Flow velocity decreased in depressed (deep-water) sections and increased in raised (shallow-water) sections. The types and positions of the tsunami deposit bedforms were thus strongly controlled by local ground surface roughness, such as raised roadbeds and levees. As a result, the observed thickness distribution of the tsunami deposits fluctuates. It is important to consider the possible existence of bedforms in paleotsunami surveys, especially for accurate determination of the thickness distribution of the tsunami deposits, because thickness data are essential information for reconstruction of the tsunami inundation limit as well as its flow speed. • We firstly report the bedforms of the 2011 Tohoku-Oki tsunami deposit. • Their types and positions are strongly controlled by local ground surface roughness. • Sequence of bedforms recorded the flow speed changes related to the ground roughness. • The flow speed changes are explained by the principle of conservation of mass. • This finding may enable to reconstruct the flow speeds of tsunamis from the deposits.

El tsunami de 1960 en una planicie de cordones litorales cerca de Maullín, Chile: descenso tierra adentro, surcos renovados, abanicos agradados, múltiples predecesores.

The Chilean tsunami of 22 May 1960 reamed out a breach and built up a fan as it flowed across a sparsely inhabited beach-ridge plain near Maullín, midway along the length of the tsunami source. Eyewitnesses to the flooding, interviewed mainly in 1988 and 1989, identified levels that the tsunami had reached on high ground, trees, and buildings. The maximum levels fell, from about 10 m to 2 m, between the mouth of the tidal Río Maullín and an inundation limit nearly 5 km inland across the plain. Along this profile at Caulle, where the maximum flow depth was a few meters deep, airphotos taken in 1961 show breaches across a road on a sandy beach ridge. Inland from one of these breaches is a fan with branched distributaries. Today its breach holds a pond that has been changing into a marsh. The 1960 fan deposits, as much as 60 cm thick, are traceable inland for 120 m from the breach. They rest on a pasture soil above two additional sand bodies, each atop its own buried soil. The earlier of the pre-1960 sand bodies probably dates to AD 1270-1400, in which case its age is not statistically different from that of a sand sheet previously dated elsewhere near Maullín. The breach likely originated then and has been freshened twice. Evidence that the breach was freshened in 1960 includes a near-basal interval of cobble-size clasts of sediment and soil, most of them probably derived from the organic fill of pre-1960 breach. The cobbly interval is overlain by sand with ripple-drift laminae that record landward flow. The fan of another breach near Maullín, at Chanhué, also provides stratigraphic evidence for recurrent tsunamis, though not necessarily for the repeated use of the breach. These findings were anticipated a half century ago by description of paired breaches and fans that the 1960 Chilean tsunami produced in Japan. Breaches and their fans may provide lasting evidence for tsunami inundation of beach-ridge plains. The breaches might be detectable by remote sensing, and the thickness of the fan deposits might help them outlast an ordinary tsunami sand sheet.

Sources and transportation modes of the 2011 Tohoku-Oki tsunami deposits on the central east Japan coast

We evaluated sediment sources of the 2011 Tohoku-Oki tsunami deposits along a 4500m inland transect from the central east Japan coast, using grain size, mineralogy and foraminifera analyses. The tsunami run-up height in our study area was 13 to 20m near the coastline, 1.4 to 2.8m in the middle of the valley and 1.3m around the inundation limit. The inundation distance was around 4800m. The deposits are composed of sand and mud and show a fining and thinning trend. Mineral composition of the tsunami deposits was similar to that of coastal dune and beach deposits, indicating that most of the tsunami sediment originated from there. A minor foraminifera population in the deposit (≤15 specimens per 5g of sample compared with ≥100 specimens per 1g for typical marine sediment) indicates that marine sediment source was not dominant. Topography played an important role in sediment transport process and deposit distribution. The run-up wave accelerated faster in concave topography, became more erosive, and resulted in a thin deposit in topographic lows. We infer that the deposits up to 2300m from the coastline were deposited by bedload and suspension, whereas suspension was responsible for deposits farther inland.

Field measurements and numerical modeling for the run-up heights and inundation distances of the 2011 Tohoku-oki tsunami at Sendai Plain, Japan

We conducted an urgent field survey at the Sendai Plain to measure the run-up heights and inundation distances of the 2011 Tohoku-oki tsunami. We used GPS measurements because of the remarkably long inundation distances (ca. 5.4 km). We established an accurate measurement scheme using the far electric reference points (about 350 km). Using this method, we quickly measured 69 run-up heights within 3 days. The tsunami run-up heights and inundation distances varied mainly according to the local topography, ranging from 9.6 m at 0.4 km to 0.2 m at 5.4 km, respectively. Furthermore, artificial structures and topography played an important role in constraining the inundation limit. Our observations are important for future analyses using aerial and satellite imagery and numerical modeling in the area because the maximum inundation area might be underestimated in the images as a result of the subtle traces of the tsunami inundation, which were difficult to identify in the field. However, results show that numerical modeling might not reproduce minor inundation beyond the highway without sufficiently high-resolution topographic data because data for the modeling are usually rough, and the highway, small channels, and street gutters, which played an important role in local inundation, are too small a resolution to be recognized in the model.

Classifying inundation limits in SE coast of India: application of GIS

A study on the possible inundation limit in SE coast of India was carried out using various physical, geological and satellite imageries. The coastal inundation hazard map was prepared for this particular region as it was affected by many cyclones, flooding, storm surge and tsunami waves during the last six decades. The results were generated using various satellite data (IRS-P6 LISS3; LANDSAT ETM; LANDSAT-5 ETM; LANDSAT MSS) and digital elevation models (ASTER GLOBAL DEM), and a coastal vulnerability index was generated for the entire coastal stretch of Nagapattinam region in SE coast of India. The coastal area which will be submerged totally due to a 1–5 m rise in water level due to any major natural disaster (tsunami or cyclone) indicates that 56–320 km2 will be submerged in this particular region. The results suggest that nearly 7 towns and 69 villages with 667,477 people will be affected and indicate that proper planning needs to be done for future development.

Variations in the 2004 Indian Ocean tsunami deposits thickness and their preservation potential, southwestern Thailand

Field surveys were conducted in March 2005 and December 2008 in southwestern Thailand to investigate local variation in the thickness and preservation potential of onshore deposits formed by the 26 December 2004 Indian Ocean tsunami. The 2008 survey results revealed that the thickness of deposits varies by a few centimeters in pits located less than 10 m apart because of local undulation of the topography and possible bioturbation. At 13 among all 24 sites, the difference in thickness during 2005 and 2008 surveys was within the range of local variation. In fact, very thin tsunami deposits with 1 cm thickness in the 2005 survey were well preserved during the 2008 survey. Furthermore, tsunami deposits near the maximum inundation limit were found in the 2008 survey, with thicknesses that are consistent with those reported from the 2005 survey. At no site was a tsunami deposit eliminated completely. Based on these observations, we infer that the tsunami deposit thickness is well preserved, even in a tropical climate with heavy rains such as that of Thailand.

Terrestrial Laser Scanner techniques in the assessment of tsunami impact on the Maddalena peninsula (south-eastern Sicily, Italy)

The coastline of the Maddalena peninsula (south-eastern Sicily, Italy) is characterised by the occurrence of a boulder field associated to an extended soil stripping area and by a gravel/sandy berm. The accumulation of the boulders has been mostly correlated to the impact of the December 28, 1908 tsunami wave. The use of Terrestrial Laser Scanner survey techniques, associated to Differential Global Position System determinations, permits to obtain new data for the assessment of tsunami impact on this coastal area. The computing of the surveyed data using the most recent equations is a useful tool in order to estimate the theoretic inundation limit and to reconstruct its variability in function of the boulders size and of the coastal topography. Moreover, the entire new data set allows to confirm that the hypothesis of the tsunami impact is the most reasonable to explain the occurrence of boulders weighing up to 50 tons on the Maddalena peninsula.

Erosion, deposition and landscape change on the Sendai coastal plain, Japan, resulting from the March 11, 2011 Tohoku-oki tsunami

Case studies of recent tsunami impacts have proven to be extremely useful in understanding the geologic processes involved during inundation and return flow, and refining the criteria used to identify paleotsunami deposits in the geologic record. Here, we report on erosion, deposition and associated landscape change resulting from the March 11, 2011 Tohoku-oki tsunami along a nearly 4.5km shore-normal transect on the coastal plain near Sendai, Japan. The study area on the broad, low-relief prograding coastal Sendai plain comprised a sand beach backed by ~3m high sand dunes and a forest, a wetland, the Teizan canal, agricultural rice fields, buildings and roads.Field observations focused on measurements of tsunami flow characteristics (height and direction), mapping of erosion features and assessing sediment deposition based on shallow trenches at 50–100m spacing. Recorded tsunami inundation heights reached up to about 11m above mean sea level within the first 500m from the shoreline and then ranged between 3 and 5m for the next 2km, gradually decreasing to about 3m close to the inundation limit. The tsunami deposit generally thinned landward from an average maximum ~30cm thick sand deposit in the coastal forest to a thin mud drape several mm thick near the inundation limit. A discontinuous sand-dominated sheet was prevalent to about 2800m from the shoreline where mud content then gradually increased further landward eventually resulting in a mud-dominated deposit ranging from 3.5cm to a few mm thickness. The overall thinning and fining of the deposit was often interrupted by localized features that led to complex sedimentological relationships over short distances.Satellite imagery taken on 14 March 2011, 3days after the Tohoku-oki Tsunami shows prominent foreshore incisions with 100s+meters spacing alongshore, a foredune ridge that underwent severe erosion and development of a prominent shore-parallel elongated scour depression. Our field survey in early May 2011 revealed that the foreshore recovered quickly with rapid post-tsunami sediment deposition from incident waves, whereas the dune–ridge complex had undergone only minor re-working from eolian processes.