OVSICORI-UNA reported that on 12 June small geyser-like eruptions at Poás ejected material less than 50 m high at a rate of about once per hour. At 0604 on 18 June an eruption that lasted about six minutes produced a plume of unknown height due to weather conditions. Residents reportedly heard several loud noises during 0610-0615 and observed an eruption plume rising from the crater. Ash fell in Cajón (12 km SW), San Luis de Grecia (11 km SW), Los Ángeles, San Miguel, San Isidro (28 km SE), and San Roque (23 km SSE). Whitish ash deposits surrounding the crater, especially on the W and S sectors, were visible in webcam images.

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)