(MANILA, Philippines) — The Philippines’ most active volcano exploded thunderously Monday, sending a huge gray column of lava fragments, ash and steam into the sky and prompting authorities to warn that a violent eruption may be imminent. The noontime explosion sent superheated lava, molten rocks and steam cascading down Mount Mayon’s slopes and shrouded nearby villages in darkness, said Renato Solidum of the Philippine Institute of Seismology and Volcanology and other officials. Authorities raised the alert level to four on a scale of five, which means an explosive eruption is possible within hours or days.