然別火山熱雲堆積物表面の流れ山

概要

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On the southern foot of the Shikaribetsu volcano, central Hokkaido, many small hills scatter, which are composed mainly of hornblende-pyroxene andesite blocks derived from Higashi-nupukaushi lave dome with a small amount of ash and lapilli. Although they have been considered as mudflow deposits, there are some evidences that they have formed through high-temperature avalanche or nuee ardente, i.e. 1) oxidation phenomena on the surface, 2) remnants of secondary fumaroles, and 3) carbonization of included wood fragments. Twentyfour volcanic blocks of the deposits from 5 localities were collected for measurement of the N-pole orientation of natural remanent magnetism. The orientation of the samples from two localities shows good concentration, but the rest being random. Although stability tests have not been made, the temperature of the former two was probably near or slightly higher than the Curie point just after emplacement of the deposits, but that of the latter was lower. In reviewing the so-called "mudflow hills" in Japanese volcanic regions, it is noticed that many of the hills were formed either by high-temperature avalanche or by low-temperature dry avalanche, rather than by mudflow. Accordingly, the term "mudflow" should be used only for the "true" mudflow which flowed admixed with a large quantity of water.
特定非営利活動法人日本火山学会の論文
1975-05-01