The Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional (OVSICORI-UNA) reported continuing gas-and-steam emissions with occasional minor amounts of ash at Poás during 19-26 August. Variable incandescence at Boca A vent continued to be visible at night. The temperature of the gas-and-steam emissions at Boca A were measured with infrared webcam images, by drone, and at varying distances during field visits; the temperatures varied by a few hundred degrees Celusis day-to-day but remained at high levels, as high as 520 degrees during 16-22 August. The emissions drifted WSW. A period of continuous ash-and-gas emissions began at 0800 on 20 August and lasted for a few hours. The plumes rose 200 m above the crater rim and drifted SW. The volcanic Alert Level remained at 2 (the second lowest 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)