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.     

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.     

Tsunami hazard evaluation for Kuwait and Arabian Gulf due to Makran Subduction Zone and Subaerial landslides

This paper explores the ways that Mongolian pastoral-nomadic herders and supporting aid organizations anticipate, interpret, and respond to dzud, a form of winter storm that prevents livestock grazing and often results in large-scale herd deaths. Analysis is drawn from organizational reports, government speeches, and mass media that have been collected to give a complex, multi-faceted understanding of the collection, distribution, and interpretation of data pertaining to the social and scientific construction of this natural hazard. Using critical discourse analysis, this study asks how herder perspectives and needs have been incorporated into reports and action plans of international development organizations. The collected documents provide insight into the ways that knowledge is constructed, disseminated and valued among policy makers, development planners and herders. Additionally, the findings indicate disagreement between stakeholders as to when to declare a national emergency, and how to best help herders respond to the increasing frequency of dzud. While some organizations rely on traditional recovery mechanisms, others have turned to technological solutions, all aiming to assist herders in adequately responding to and recovering from one dzud before another occurs. From the analysis of policy proposals, this study aims to understand and inform the ways that international development programs, government officials, and herders work to preserve pasturelands and herding lifestyles threatened by dzud.     

Multi-decadal changes in the relationships between rainfall characteristics and debris-flow occurrences in response to gully evolution after the 1990–1995 Mount Unzen eruptions

Explosive volcanic eruptions can cause long-term landscape change, leading to increased sediment discharge that continues after the cessation of the eruptions. During the period 1990–1995, eruptions of Mount Unzen, Japan, generated large amounts of pyroclastic material, resulting in 57 debris-flow events during 1991–2018. To investigate changes in the relationships between rainfall characteristics and debris-flow occurrence, we conducted the following: geometric analysis of two gullies (i.e., debris-flow initiation zones) using LiDAR (light detection and ranging)-generated 1 m DEMs (digital elevation models); rainfall analysis, based on the relationship between rainfall duration and mean intensity (i.e., considering the intensity–duration, or ID, threshold); and debris-flow monitoring during 2016–2018. Since 1991, rainfall runoff has caused erosion of the supplied pyroclastic material, generating a channel network consisting of incised gullies. With sufficient rainfall, debris flows formed, accompanied by further gully erosion; this resulted in both vertical and lateral adjustments of the cross-sectional geometry. In the two decades since the eruptions ceased, readily mobilized pyroclastic material has become scarce as the gullies have adjusted to local hydrographic conditions. At the same time, the infiltration capacity of the volcanic flank has increased, reducing the capacity for overland flow. As a result, since 2000, rainfall events with intensities above the ID threshold have occurred; however, the lack of sediment supplied by the gullies appears to have hindered the occurrence and development of debris flows. This suggests that debris flows in volcanically perturbed landscapes may occur at lower rainfall thresholds as long as the corresponding upland channels are evolving as a result of intense overland flow. However, as such channels evolve towards equilibrium geometries, the frequency of debris flows decreases in response to the reduction in sediment availability.     

Characteristics of Tsunamis Propagating over Oceanic Ridges: Numerical Simulation of the 1996 Irian Jaya Earthquake Tsunami

The 1996 Irian Jaya earthquake tsunami was simulated by using the numerical model based on the linear long wave theory including Coriolis force in the spherical coordinate system. The numerical modeling result at Chichijima is in good agreement with the observed tide gauge data. The distinctive oscillation at Chichijima can be interpreted as the formation of boundary waves, so called ridge waves that are excited on the South-Honshu ridge. The mechanism of tsunami propagation trapped on an oceanic ridge is analyzed with the simple ridge model. The result explains the characteristics of ridge waves excited on theSouth-Honshu ridge.     

Distribution of tungsten and molybdenum between metal,silicate, and sulphide phases of meteorites

The concentrations of W, Mo, Co and Ni have been determined by neutron activation analysis in the separated metal, silicate and troilite of twelve chondrites—nine ordinary, two enstatite and one carbonaceous. Concentration ratios of W and Mo in silicate relative to metal are 0.03–0.6 and 0.05–0.55, respectively, and those of W in the troilite relative to the metal are 0.01–0.2. The contents of Mo in the troilite are nearly equal to those in the metal. Co and Ni are more depleted than W and Mo both in the silicate and troilite.Thermodynamic considerations have been made for determined concentration ratios. In some L-chondrites, W is depleted in the silicate by a factor of three to four of the value estimated from the correlation line between H- and LL-chondrites. This tendency seems to suggest a relatively higher temperature in the thermal history of these L-chondrites.     

Microbial community structure analysis of euxinic sediments using phospholipid fatty acid biomarkers

Microbial community structure in sediments, as determined by the phospholipid ester-linked fatty acid (PLFA) analysis, collected from Kojima Lake during summer and winter was described with reference to the environmental quality of the lake. A characteristic feature of the study area was the persistence of anoxia in summer and winter in the deeper area, and the sediments were under the reduced condition with high levels of sulfide, chemical oxygen demand, and low values of oxidation-reduction potential. PLFA profiles of the sediment were dominated by the saturated, branched and monounsaturated fatty acids. Small amounts (less than 5% of the total PLFA) of polyunsaturated fatty acids (biomarker fatty acids of microeukaryotes) and long chain fatty acids were detected in sediments. Total PLFA concentrations in sediments were higher in summer than in winter. Microbial community structure in the lake sediments was predominated by the prokaryotes, as evidenced from the larger amounts of bacterial biomarker fatty acids in the range of C₁₀ to C₂₀. The presence of signature fatty acids of sulfate reducing bacteria in sediments was consistent with the high levels of sulfide in the sediment and anoxic condition in the study area. PLFA showed significant differences in PLFA profiles between shallow and deeper areas, indicating the differences in the lipid contributing communities. However, no such a significant difference was observed between summer and winter.