Observation of low-frequency electromagnetic emissions as precursors to the volcanic eruption at Mt. Mihara during November, 1986

Abstract

Abstract At the time of the major volcanic eruptions on November 15 and 21, 1986, at Mt. Mihara, Izu-Ohshima Island, in the Tokyo territory of Japan, one detector of a multi-point (multi-static) direction finding network for detection of electromagnetic emissions was operating. Since October 20, impulsive noise bursts at 82 kHz were recorded, and the occurrence of these anomalous burst-like noise observations increased after November 3. At 10–16 JST (Japanese Standard Time, UT + 9 hr) on November 14, several strong noise bursts were observed, and the first major eruption occurred at the main summit crater of this volcano at 16 JST on November 15. At 10–12 JST on November 21, noise bursts were observed, and 4 hr later, 19 new craters erupted suddenly on the side of the mountain, both inside and outside the caldera. These data are the first observations of electromagnetic emissions as precursors to volcanic eruptions correlated in time with the intrusion of dykes in the mountain body.