OVSICORI-UNA reported continuing emissions at Poás during 3-9 April. Vents on the nearly dry crater floor vigorously emitted plumes of gas and steam; ash was present in the plumes during 3-5 April and absent on the rest of the days. The plumes rose a few hundred meters above the crater rim and mainly drifted W, SW, and S and were often detected downwind in residential areas of Heredia and El Valle Central. Incandescence was visible from Boca A and Boca C during 3-4 April, and at Boca A during 4-5 April. A sulfur odor was reported in Heredia and El Valle Central during 3-4 April and in Sarchí on 9 April. Weather conditions sometimes prevented visual observations.

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)