Explosion energy of the 2004 eruption of the Asama Volcano, central Japan, inferred from ionospheric disturbances

The Japanese dense array of Global Positioning System recorded ionospheric disturbances as changes in Total Electron Content ∼12 minutes after the September 1 2004 eruption of the Asama Volcano, Central Japan. The disturbance had a period of one and a quarter minutes and propagated as fast as ∼1.1 km/s, suggesting its origin as the acoustic wave generated by the explosion. By comparing the disturbance amplitudes with those by a surface mine blast with a known energy, the overall Asama explosion energy is inferred to be about 2 × 10 14 J.