OVSICORI-UNA reported that at 0546 on 25 January a small phreatic eruption at Poás produced a steam plume that rose more than 500 m high and drifted W. The event produced the tallest plume recorded since 30 September 2019. According to the Comisión Nacional de Prevención de Riesgos y Atención de Emergencias (CNE) the event resulted in the restriction of the number of people that can be on the viewing platform to 56 at a time and visitors were required to wear hardhats. At 1437 on 26 January a more significant phreatic eruption ejected material 300 m above the lake’s surface and produced a gas-and-steam plume that rose 700 m high. During 26-27 January near constant degassing manifested as bubbling in the lake was observed.

Geological Summary. The broad vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the complex stratovolcano extends to the lower N flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, last erupted about 7,500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since an eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Sources: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA), Comisión Nacional de Prevención de Riesgos y Atención de Emergencias (CNE)