The Turrialba volcano's largest eruption in over a century has rained ash over parts of central Costa Rica and prompted some nearby communities to evacuate the area.
Volcanologist Gino Gonzalez of the Central American country's National Seismological Network said after visiting the volcano's rim that the overnight blast caused the side of the crater to collapse.
Ash fall was observed in four provinces on Thursday, and scientists were analysing its content to determine whether the eruption could be a precursor to lava emission.
"We are maintaining 24/7 vigilance at our seismic stations," Gonzalez said.
Gonzalez said the volcano began rumbling and producing seismic activity the previous evening. He called it the biggest explosion recorded at Turrialba in at least 100 years.
Turrialba is about 71 kilometres east of the capital, San Jose.
A yellow alert was declared for communities near the volcano. Agriculture Ministry officials were attending to about 400 head of cattle in areas where ash fell.
