Emplacement Temperature and Cooling Process of the AD915 Pyroclastic Flow Deposits of Towada Volcano
十和田平安噴火で生じた火砕流の定置温度および冷却過程

Tabito MATSU'URA, Takeyuki UEKI
2008 Journal of Geography (Chigaku Zasshi)  
I 東北日本北部に位置する十和田火山(現在の十 和田湖:図 1)は 平安時代(AD915 年;延喜 15 年)に爆発的噴火を起こし 十和田 a テフラ (To-a)を噴出した(町田ほか, 1981) 。この To-a 噴出末期に生じた火砕流は十和田火山周辺に高温 で流下したほか 噴火後も火山泥流が大湯川・米 代川沿岸の人家を埋没して大惨事をもたらした (平山・市川, 1966) 。現在の十和田火山周辺 大 湯川・米代川流域は AD915 年の時とは人口密 度も人間社会の発達程度も異なり 火山噴火によ る被災の規模は計り知れない。火砕流は定置時に もつ高温の熱によって 人間を含む動植物および それらの生活の場に壊滅的な被害を及ぼす。その ため火砕流堆積物の定置温度の算出や その冷却 Emplacement Temperature and Cooling Process of the AD915 Pyroclastic Flow Deposits of Towada Volcano Tabito MATSU'URA * and Takeyuki UEKI ** Abstract The
more » ... KI ** Abstract The emplacement temperature of the AD915 Towada pyroclastic flow(To-a pyroclastic surge)is estimated from the emplacement temperature of crusts(pumices and a lithic fragment)within the surge deposits. The measured emplacement temperature of the pyroclastic surge varies vertically in the surge deposits. The lower part of the deposits shows low temperatures(300⊖500℃)because due to cooling by the cold ground surface. The middle part of the surge deposits, which was sandwiched by the lower and upper parts of the surge, shows high temperatures(350⊖680 ℃, mostly 620⊖650 ℃) . The upper part of the surge deposits which was probably cooled by the atmosphere, shows moderate temperatures(less than 620℃, mostly 500⊖620℃) .
doi:10.5026/jgeography.117.889 fatcat:eyvs6vxv5jabnjxsacfg7p2jqu