Indonesian authorities raised Mount Agung's volcano alert to the highest level, ordering anyone within ten kilometers (6 miles) to evacuate.
These evacuation orders affect 90,000-100,000 people in 22 villages. Approximately 40,000 have not yet evacuated, due to not wanting to leave their homes and livestock.
In addition to the evacuations, Bali's main airport was closed, leading to the cancellation of over 400 flights and affecting approximately 59,000 people. Some customers seethed over the inconvenience, slamming airport and airline on social media.
According to Indonesia's National Agency for Disaster Management, "a potential eruption could happen at any time." According to the head of Indonesia's geological agency, the warning went out at 6:00 a.m. local time because the steam-based eruptions turned into magma-based eruptions.
Prior to the warning, Mount Agung began hurling ash 6 kilometers into the air, and a plume of smoke reached a height of 4,000 meters (13,100 feet).
Open University Professor of Planetary Geosciences David Rothery said, "Ash is rising to a height of about 30 thousand feet, and dispersing east and south, taking it over Bali’s international airport, which has had to be closed. Airborne ash is a serious hazard to aircraft."
"The wisdom of the Indonesian authorities’ decision to evacuate residents from around the foot of the volcano will be apparent if there is substantial ashfall or, worse, a collapse of an eruption column resulting in fast-moving pyroclastic flows.
"Airfall ash is a respiratory hazard, kills crops, and makes roofs collapse, and can turn into devastating mudflows (lahars) as soon as it rains. Pyroclastic flows are hot and deadly."
Disaster Mitigation Agency spokesman Sutopo Purwo Nugroho said, "Since yesterday there have been explosive eruptions whose sound was heard up to 12 kilometers (7.5 miles) away."
Bali's airport will remain closed throughout Monday, and the situation will be re-assessed on Tuesday.
Mount Agung's last major eruption occurred in 1963, killing approximately 1,100 people. The country has over 130 active volcanoes.