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 23-29 July. Strong incandescence at Boca A vent was observed and the level of the hyperacid lake over Boca C remained at stable levels. Dense gas-and-steam emissions continued to be emitted from both Boca A and Boca C vents. On 24 July the Comisión Nacional de Emergencias (CNE) conducted an overflight of the crater using a drone with an infrared camera and measured a maximum temperature of 819 degrees Celsius over Boca A and 74-87 degrees Celsius at the lake over Boca C. They observed highly altered pinkish-yellow rocks at the rim of Boca A and down in the crater. Sulfur dioxide emissions measured by satellite averaged 37 tons per day (t/d) during 20-24 July and 520 t/d on 26 July. A moderate eruption that began at 0244 on 27 July lasted for three minutes, producing ash emissions and ejecting incandescent blocks 1 km above the crater floor. The Comisión Nacional de Emergencias (CNE) lowered the Alert Level to Green for Parque Nacional Volcán Poás and district of Toro Amarillo in the Canton of Sarchí (including the Desagüe, Agrio, Anonos, and Gorrión river basins) on 2 July due to decreasing activity and then lifted the Green Alert for the park and surrounding areas on 23 July. The volcanic Alert Level remained at 2 (the second lowest level on a four-level scale) and the Aviation Color Code remained at Yellow (the second lowest 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.

Sources: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA), Comisión Nacional de Prevención de Riesgos y Atención de Emergencias (CNE)