The Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional (OVSICORI-UNA) reported continuing gas-and-steam emissions at Poás during 28 May-3 June. Variable sulfur dioxide gas emissions were higher during the last week of May compared to the previous week, but not as high as peak emissions at the end of April. Incandescence continued to be visible and detected in infrared webcam views at Boca A vent. Minor inflation was detected on some days and no clear trend was apparent on others. At 1022 on 1 June a gas-and-steam plume with minor ash content rose 1 km and drifted W. Gas-and-steam emissions continued during 2-3 June; the plume was tinted blue due to a high concentration of sulfur dioxide gas. The volcano’s Alert Level remained at 3 (the second highest level on a four-level 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)