Why is it difficult to monitor volcanoes?

By Taizan Emura / Yomiuri Shimbun Staff WriterThe Jan. 23 eruption of Mt. Motoshirane, in which one person died and another 11 were injured, underscored the threat posed by volcanic activity. The eruption of the volcano, which is part of Mt. Kusatsushirane in Gunma Prefecture, occurred in an area where significant volcanic activity has not been observed for over 1,000 years. Though there are limited financial and human resources that can be allocated to volcanic observation, safety must be ensured through such measures as the provision of detailed information.

Ominous signs

Magma reservoirs filled with superheated molten rock lie about 5 to less than 20 kilometers beneath active volcanoes. Eruptions occur when pressure inside a magma reservoir increases to the point that water vapor and magma suddenly eject above ground. There are also eruptions like the one that occurred on Jan. 23, in which heated steam explodes outward.

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