著者

杉本 伸一 長井 大輔

出版者

九州大学大学院理学研究院

雑誌

九州大学大学院理学研究院研究報告 地球惑星科学 (ISSN:13480545)

巻号頁・発行日

vol.22, no.3, pp.9-22, 2009-03

被引用文献数

2

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The 1990-1995 eruption of Unzen volcano, Japan, was characterized by lava dome growth and pyroclastic flows triggered by dome collapse. One of the largest pyroclastic flows occurred at 4:08 p.m. on June 3, 1991. The associated pyroclastic surge killed 43 people and injured 9 persons. The event was the worst volcanic disaster within a few decades in Japan. The victims due to the pyroclastic surge included following persons: fire brigade members watching for lahars and for safety of houses in the evacuation area, local residents returning home for retrieving their property and goods, press people taking photos of the pyroclastic flow, taxi drivers hired by the press, volcanologists recording volcanic activity on video tape, and policemen [OR a policeman] calling for peoples evacuation. Only a few people who were located near the distal end of the pyroclastic surge could survive. The mortality rate was 100% at the upstream area about 4.3 km from the source. The mortality extended to 69% at the downstream area near the distal end of pyroclastic surge. The overall survival rate (18%) is very low. This fact indicates that the only way to avoid disasters due to pyroclastic flows is to evacuate before they occur. Governments must designate the warned area and/or declare an evacuation instruction for residents to keep people out unconditionally, in cooperation with the volcanologists.

著者

大野 希一 国方 まり 鈴木 正章 西村 裕一 長井 大輔 遠藤 邦彦 千葉 達朗 諸星 真帆

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.47, no.5, pp.619-643, 2002-11-29

被引用文献数

4

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The volcanic activities of the Usu 2000 eruption were monitored and reported by many scientists and the mass media. Summarizing these observation results, most of relatively large explosion events occurred during March 31 to April 7, 2000. Around the Nishiyama and Kompira crater groups, the pyroclastic deposits with multi units can be divided into 19 layers on the basis of their visible color, grain size and sedimentary structure; from Layer A to Layer S in ascending order. The eruptive dates of each layer inferred from the wind directions, the eruptive sequence, and the distribution of deposits are summarized as follows; the Layer A, characterized as the light gray color ash fall deposit including in some pumice layers, was generated by March 31 phreatomagmatic explosions occurred at Nishiyama crater group. The Layer B, composed poorly sorted breccia and ash layer with gray color, was generated on March 31 p.m. at Nishiyama craters. The Layer C to the Layer G, dark brown-gray aggregate ash, were derived from the volcanic eruptions occurred on April 1 to 2 in Nishiyama and Kompira crater group. The Layer H to Layer M and Layer O, mainly consist with gray and reddish brown aggregate ash including in lithic fragments, were generated during April 3 and 4 in Kompira crater group. The Layer N, which distributes around N19 crater, generated on April 4. The Layer P, massive ash with gray color, was generated on April 6 in Kompira crater group. After April 7, the Layer S, characterized as light brown aggregate ash, has been generated from the recent minor activities around limited craters. The amount of Layer A fallen in the range from the source to Toyako Onsencho Town is estimated at 1.2×10^8 kg, and total amount of Layer A including in the distal area is 2.4×10^8 kg. On the other hand, amount of other deposits generated during April 1 to 6 (e.g. Layer B, N, and Q) is an order of 10^6-10^7 kg. Total amount of the pyroclastic deposits erupted from the Usu 2000 eruption is more than 6.4×10^8 kg.

著者

長井 大輔 遠藤 邦彦 千葉 達朗

出版者

特定非営利活動法人日本火山学会

雑誌

日本火山学会講演予稿集

巻号頁・発行日

vol.2004, 2004-10-19