Rise in quakes There have been several eruptions in recent months, the last one on 14 July. The last major eruption of Mount Oyama was in 1983 when 400 houses were destroyed and nearby forests were burnt. An explosion in 1940 killed 11 people. The island chain around Miyakejima has been rocked by more than 14,000 earthquakes in recent weeks. Japan's meteorological agency recorded 490 quakes in the area by 1400 local time on Thursday - a sharp rise from 179 quakes on Wednesday.
Japan is in one of the world's most active seismic zones.
Four of the earth's tectonic plates meet in the region, causing earthquakes, tidal waves and eruptions as they grate together. In late March, a volcano erupted on Mount Usu on Japan's northern island of Hokkaido.