As many as 20,000 Sumatrans fled their homes and villages since the start of a series of volcanic eruptions at Mount Sinabung on Saturday, and authorities are raising the level of alert to its highest in the affected western Indonesian region. The volcano has been erupting on and off since September, but went violent late Saturday and early Sunday, spitting off lava and black plumes of ash that went as high as 1,500 meters into the air. Local media on Monday reported the authorities' decision to expand the evacuation zone to a circle of a five-kilometer radius instead of three, with the army supervising the evacuation. The authorities had earlier on November 18 issued warnings against any local or international flights near Mount Sinabung when the volcano went on its most violent eruption since September, after staying dormant for three years. Sinabung is just one of 129 active volcanoes in Indonesia, which straddles the so-called "Ring of Fire" of frequent quakes, eruptions, and other natural disasters. Indonesia is located in southeastern Asia, and is an archipelago of 17,500 islands between the Indian Ocean and the Pacific Ocean. The country's worst volcanic eruption in recent years was back in 2010, when Mount Merapi in Central Java erupted and killed over 350 people.