The Poás volcnao recorded the largest phreatic eruption this year. The Observatorio Vulcanológico y Sismológico de Costa Rica (OVISCORI) recorded the eruption at 12:02 pm, spewing debris some 300 metres (980 feet) high, exceeding the height of the crater.
OVSICORI’s Javier Pacheco said that the activity is completely normal and that such eruptions have been taking place since 2009, including an eruption last year that had a similar magnitude.
So far this month, the OVSICORI has recorded 4 eruptions of this type. A phreatic eruption, also called a phreatic explosion or ultravulcanian eruption, occurs when magma heats ground or surface water. The extreme temperature of the magma (anywhere from 500 to 1,170 °C (932 to 2,138 °F)) causes near-instantaneous evaporation to steam, resulting in an explosion of steam, water, ash, rock, and volcanic bombs.
Last year the OVISCORI reported up to 10 phreatic eruptions a month.