Abstract
The large-scale eruptions in history took place in 788 at Ohachi and 1716-1717 at Sinmoedake. Based on chemical composition of volcanic products of Ohach and Sinmoedake, magma composition became more siliceous and oxigen pressure of the magma increased with the times during about 1,200 years. Wee can estimate the next eruption may occur at Ohachi or Sinmoedake with the silica rich magma of SiO2 over 60%, and it is presumed that increase of oxigen pressure may generate destruction of the volcanic edifice
