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北海道大学地球物理学研究報告 = Geophysical bulletin of Hokkaido University >
第71号 >

火山岩塊の運動再考 (4) : 浅間火山1938年および有珠火山1977年噴火における放出火山岩塊の解析

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Title: 火山岩塊の運動再考 (4) : 浅間火山1938年および有珠火山1977年噴火における放出火山岩塊の解析
Other Titles: Reconsideration of volcanic block kinematics (4) : Data analysis of ejected volcanic blocks with special attention to the 1938 Asama and the 1977 Usu eruptions
Authors: 鈴木, 建夫1 Browse this author
新井田, 清信2 Browse this author
西田, 泰典3 Browse this author
大島, 弘光4 Browse this author
室伏, 誠5 Browse this author
Authors(alt): Suzuki, Takeo1
Niida, Kiyoaki2
Nishida, Yasunori3
Oshima, Hiromitsu4
Murofushi, Makoto5
Issue Date: 15-Mar-2008
Publisher: 北海道大学大学院理学研究院自然史科学部門(地球物理学)
Journal Title: 北海道大学地球物理学研究報告
Journal Title(alt): Geophysical bulletin of Hokkaido University
Volume: 71
Start Page: 19
End Page: 38
Abstract: Spatial distribution of volcanic blocks, as well as landing distance from a crater, landing angle and diameter of the blocks has been well investigated on and around the crater in cases of the 1938 Asama and the 1977 Usu eruptions by some researchers. Then, this paper reproduces detailed kinematic aspects of the eruptions so as to interpret the above-mentioned field data, on the basis of a generalized ballistic equation of ejected volcanic blocks proposed by the present authors. Calculations are made for combination of various parameters, such as air resistance to the blocks, direction of the wind, orientation dependence of the initial velocity and so on. The observed wind velocities are referred in the calculation. Comparison between the calculated and the observed results leads to the following conclusion: (1) In the 1938 Asama eruption, the distribution of volcanic blocks shows that the direction of the explosion principal axis is due east (N90°E) and its inclination angle is 30°. The angle dependence of the initial velocity (M = 1.5) is almost the same as that in the Sakurajima volcano. (2) In the 1977 Usu eruption, direction of the explosion principal axis is N170°E and its inclination angle is 20°, and the angle dependence of the initial velocity is large as much as M = 5.0. (3) The air resistance to the blocks is estimated as about Kd = 0.5 in both the eruptions. This value is valid in other volcanic eruptions because the air resistance seems to be same everywhere.
Type: bulletin (article)
Appears in Collections:北海道大学地球物理学研究報告 = Geophysical bulletin of Hokkaido University > 第71号

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