OVSICORI-UNA reported that submarine fumaroles in the S part of Poás’s Boca A lake and subaerial fumaroles along the E margins continued to produce low-temperature gas emissions during 13-19 April. The lake water continued to convect, and was light gray in color, since the phreatic explosion that had occurred on 6 April at “Orange Fumarola” located in a fumarolic field along the inner N crater wall. For a period of time on 17 April a gas monitoring station in Coronado measured a higher concentration of sulfur dioxide aerosols, between 8.5 and 17.6 micrograms of gas per cubic meter of ambient air, which was higher than the daily average of 6.7. Some residents reported respiratory discomfort such as sneezing, coughing, and shortness of breath.

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)