Commercial flights to Miyakejima were canceled Tuesday. Mount Oyama last erupted in 1983, spewing lava down the mountain's southwestern flank and destroying homes. No one died because all the residents were evacuated. An eruption in 1940 killed 11 people and injured 20. The island has an area of 21 square miles and is home to about 4,000 people.
Japan is one of the world's most seismically active nations.
A volcanic eruption on Miyakejima would be Japan's second this year. More than 13,000 people living at the foot of Mount Usu in northern Japan were ordered to leave their homes after the volcano coughed up steam and ash March 31 for the first time in 22 years. Many evacuees have been allowed to return home since officials said in May that the volcano may be drifting back to sleep.