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Report on Poas (Costa Rica) — 31 January-6 February 2024


Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 31 January-6 February 2024
Managing Editor: Sally Sennert.

Please cite this report as:

Global Volcanism Program, 2024. Report on Poas (Costa Rica) (Sennert, S, ed.). Weekly Volcanic Activity Report, 31 January-6 February 2024. Smithsonian Institution and US Geological Survey.

Weekly Report (31 January-6 February 2024)


Costa Rica

10.2°N, 84.233°W; summit elev. 2697 m

All times are local (unless otherwise noted)

OVSICORI-UNA reported that small, frequent phreatic eruptions at Poás continued during 30 January-6 February. Data from the monitoring network indicated that around 600 events per day were occurring, though most of the events did not eject material more than 50 m high, and only a few ejected material more than 100 m. At 0712 on 4 February a phreatic eruption produced a plume of steam, sediments, and water that rose 200 m. The report noted that small eruptive events were occurring at a rate of 20-25 events per hour before the 0712 event, ceased afterwards, and then resumed to a rate of about 20 events per hour. On 6 February incandescence at the vent was visible in webcam images and was attributed to the combustion of native sulfur. This phenomenon was last visible in 2019.

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)