OVSICORI-UNA reported continuing emissions and eruptive activity at Poás during 10-16 April. Vents on the nearly dry crater floor emitted plumes of gas and steam on 10 April and the number of phreatic events began to increase. Starting at around 0600 on 11 April ash was present in emissions rising from Boca C. The plumes rose 500 m and drifted SW and S and residents in Naranjo (17 km WSW), Palmares (27 km SW), and Atenas (32 km SW) reported a sulfur odor. Eruptive events were not detected in seismic or infrasound data on 13 April. A small explosion at 2025 on 14 April produced a pulse of incandescence and an ash emission that rose less than 300 m. Emissions containing diffuse ash continued at least through the morning of 15 April.

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.

Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA)