火砕堆積物の堆積温度からみた由布火山の 2.2 ka 噴火

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The ca. 2.2 ka eruption of Yufu volcano, Kyushu, Japan successively produced two lavas and several pyroclastic flows. Tsukahara debris avalanche deposit lies tephrostratigraphically in the same horizon with the neighboring pyroclastic flow deposits. However, its exact relation to the 2.2 ka eruption deposit is not clear in any outcrop. We thus considered this problem by using the progressive thermal demagnetization method that estimates emplacement temperatures of the pyroclastic deposits. The results indicate that the Tsukahara debris avalanche deposit includes hot accessory blocks and that the emplacement temperatures of pyroclastic flow deposits varied for each fiow unit. The following is the outline of 2.2 ka eruption estimated by geological and temperature data. Before the main eruption, the inner part of the volcano was heated by rising magma. The northern slope of Yufu volcano subsequently collapsed to form Tsukahara debris avalanche which has some accessory high-temperature-blocks (300-500℃). No blast was produced during this collapse. Shortly after the collapse occurred, Ikeshiro lava dome erupted and occupied completely the collapsed concave. Block and ash flows (Yufu-north pyroclastic flow) were generated in association with the lava dome growth. Yufu-dake summit lava erupted near the summit of the volcano, and block and ash flows (Yufu-south pyroclastic flow) accumulated as a result of collapsing materials from the lava.
特定非営利活動法人日本火山学会の論文
2001-08-30

火砕堆積物の堆積温度からみた由布火山の 2.2 ka 噴火

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