This study aims to clarify the characteristics of risk perception and understanding of volcanic phenomena among the residents of Mt. Fuji. To this end, we conducted a questionnaire survey of residents in the foot area of Mt. Fuji. As a result, the following three findings were obtained. Firstly, the scale of the disaster that residents envisioned for the next eruption of Mt. Fuji was comparable to the Hoei eruption, which caused ash fall damage over a wide area. Secondly, 40-60% of the residents do not correctly recognize the risk of volcanic disasters in their homes. At last, it is difficult for residents to accurately understand the diverse volcanic phenomena that may occur during the Mt. Fuji eruption.

View full abstract

Tens of minutes after the 2011 Great East Japan earthquake, blackened tsunamis hit wide areas of the Sanriku coast, causing fires and devastating fire disasters. Although various research studies have been reported on this disaster, the potential mechanism of the tsunami induced fires remains unclear. Therefore, in this study, we examined the time series of information and studies that contribute to the clarification of the tsunami-fire mechanism that occurred in Natori City, Yuriage 7-chome and Kesennuma City, Shishiori district. Based on our previous research on the tsunamifire that occurred in the Aonae harbor of Okushiri Island during the 1993 Hokkaido Nansei-Oki earthquake, we proposed a new model that the tsunami-fire occurred in the following process. (1) The blackened tsunami that engulfed the sludge deposited on the seabed offshore also swept up the methane generated in the sludge, and white bubbles containing methane were carried to coastal area with assist of the tsunami wind. (2) The methane bubbles collided with man-made objects such as quay wall on the coast, bursting, and electrified mist rose up, which result in the electrostatic ignition of the methane, or (3) Methane bubbles are trapped under and/or in the narrow gaps of aggregated debris floating on the sea surface, and the electrostatic static ignition of the methane occurs by collisional friction between debris with different electrification series. (4) Due to the process of (1) or (2), any flammable combustibles in urban areas caught fire and spread, which result in a large-scale fire.

View full abstract

Many facilities of the authors' university were damaged by the inundation due to 2019 Typhoon Hagibis. This inundation damage was due to the same reasons as in areas around the Tama River that were damaged by inland flooding, such as the rules for operating sluice gates and pipes. Furthermore, the phenomenon was complicated by the unique problem of nonoperating sluice gates in the area. The authors carried out a survey of inundation depths in the area surrounding the university soon after 2019 Typhoon Hagibis and were able to obtain an under-standing of inundation damage due to inland flooding. However, only pieces of information on the process of inundation were available. In this study, we measured the inundation depth, flow direction and velocity in a time histories using several security videos taken in this area. As a results, the characteristics of inundation in this area at the time of inland flooding are discussed.

View full abstract

Block slides were responsible for ∼70% of the damage to wooden houses caused by slope failures in Atsuma Town during the 2018 Hokkaido Eastern Iburi earthquake. In this study, we analyzed the topography of the area where block slides occurred, and quantified their source and deposition areas using ArcGIS. We collected photographs of the damaged houses taken by government agencies and the media to evaluate the degree of damage. Approximately 90% of the damaged houses were “washed out or buried.”All of the victims occurred in the houses exposed to the block slides exhibited this level of damage. The average density and sliding depth of soil were estimated by analyzing stratigraphy of the scarp and by conducting soil tests. The equation of motion was used to calculate the velocity and impact pressure of the block slides. The kinetic energy of the block slide that caused the “washed out or buried” of the houses is estimated to be approximately 313 kN/s or more.

View full abstract