那須岳地域の新たな火山防災に向けて: 噴火シナリオとリスク評価の検証結果から

Abstract

那須岳は首都東京から約150 km 北に位置する活火山である．那須岳の1408-1410 年噴火では，融雪型火山泥流により約180 名の犠牲者などを出した記録がある．那須岳地域での噴火イベントツリー・噴火シナリオ作成と火山災害のリスク評価を実施した．山頂から約10-20 km に位置する多数の宿泊施設が分布する地域は，火山防災マップで火砕流や火山泥流の想定分布地域でもあり，高いリスク値がリスク評価の結果で算出された．今回のリスク評価の結果をふまえて，毎年約500 万人の観光客が訪れる那須岳地域においては，減災効果のある防災体制の早急な構築の必要性が示唆された．

Nasu volcano is an active volcano located in approximate 150 km north from capital city Tokyo. According to historic records, a huge lahar, i.e. volcanic mudflow, due to the melted snow, was to cause more than 180 casualties during the 1408-1410 eruption of Nasu volcano. In order to consider volcanic disaster mitigation, hazards risk-assessments are conducted in the Nasu volcano area. The assessment results have clearly shown that the dense zone of tourist hotels, 10-20 km far from the summit, is very high-risk area of pyroclastic flows and lahars assumed by published hazard maps. As refereeing the present evaluation of event-tree diagram and risk-assessment results, the effective evacuation system is urgently required for over five million of visiting tourists before the future eruption of Nasu volcano.