The Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional (OVSICORI-UNA) reported continuing gas-and-steam emissions that occasionally contained ash Poás during 6-13 May. Inflation continued to be detected. Sulfur dioxide emissions were as high as 1,703 tons per day (t/d) on 6 May. Some water had pooled at Boca C and was bubbling based on a drone observation that same day. Ash was very low or not detected in the steam-and-gas plumes during 5-7 May. Overnight during 7-8 May incandescence reflected in the emissions from sulfur combustion suggested temperatures less than 300 degrees Celsius. A significant eruptive event was detected in seismic and acoustic data at 1404 on 8 May and lasted for two minutes. Weather conditions prevented direct visual observations of the event, though the seismic and acoustic data suggested an ash-and-gas plume rising into the 1-4 km high range; wind direction was to the SW. Bubbling at Boca C was again observed. Overnight during 8-9 May intense incandescence emanated from Boca A and a dense steam plume with minor ash content was observed. Continuous gas-and-steam plumes drifted SW during 12-13 May; the plumes were more intense from Boca A, where overnight incandescence was also observed. The volcano’s Alert Level remained at 3 (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest color on a four-color scale).

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)