While a glow was observed around the time of the blast at the top of Merapi, vulcanologists said no new lava was observed flowing from the volcano. That means the mountain was probably not entering a new eruptive phase.
“Most of the material from the blast were gases. The dominant (carbon dioxide) triggered the blast,” disaster official Sutopo Purwo Nugroho told the ANTARA news agency.
Last July, Merapi belched steam and debris in another pre-dawn explosion.
Geologists said at the time that the blast was not an eruption, but rather occurred due to rainwater building up pressure when it came in contact with ground made hot by subterranean lava.
An eruption of Merapi in 2010 released poisonous gases and blanketed the region in ash, killing more than 300 people and temporarily displacing hundreds of thousands.