Mount Sinabung on Indonesia erupted on Monday, spewing a column of black ash and smoke 3,500 metres from the top of the mountain into the sky over Sumatra island.There were no immediate reports of casualties, evacuations or disruptions to flights in the region. But residents, visitors and tourists were advised to refrain from activities in nearby villages in Karo district in North Sumatra province and areas within 6 kilometres of the summit.Roads, vehicles and buildings in several villages in Karo affected by the eruption were covered in gray ash. Local authorities distributed masks to residents to protect themselves.Officials raised the volcano alert level to “Watch,” the second-highest level for volcanic activity, which expanded the safe zone around the 2,600-metre mountain.”This eruption is considered an initial eruption, and it is possible that a larger eruption could occur,” Lana Saria, chief of Indonesia’s Geological Agency, said in a statement.The agency previously recorded visual evidence of Mount Sinabung’s increased activity in mid-August, including dozens of earthquakes and expanded the recommended radius for public activities.About 30,000 people have been forced to leave their homes around Sinabung in the past few years because of volcanic activity.Indonesia is an archipelago of more than 280 million people with frequent seismic activity and Sinabung is among more than 120 active volcanoes. The country is prone to seismic upheaval due to its location on the Pacific “Ring of Fire,” an arc of volcanoes and fault lines encircling the Pacific Basin.