Report on Poas (Costa Rica) — July 1995

Bulletin of the Global Volcanism Network, vol. 20, no. 7 (July 1995)
Managing Editor: Richard Wunderman

Poas (Costa Rica) Crater lake rises and continues bubbling along shorelines

Please cite this report as:

Global Volcanism Program, 1995. Report on Poas (Costa Rica). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 20:7. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.BGVN199507-345040.

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Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


The volcano's sky-blue colored crater lake remained high, with sulfur stains and a temperature of 39°C. Bubbling at sites along the NW and S shores each had about equal intensity. A new fumarole appeared on the E terrace near the crater wall, producing a 50-m-high gas column. Fumaroles along the S and SE crater walls had temperatures of 94-96°C, and produced gas columns to <50 m height. Winds blew sulfur smells to the park's entrance gate.

Geologic Background. The broad, well-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, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 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 the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Information Contacts: E. Fernandez, R. Van der Laat, F. de Obaldia, T. Marino, V. Barboza, W. Jimenez, and R. Saenz, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apdo. 86-3000, Heredia, Costa Rica; Mauricio Mora, Escuela Centroamericana de Geologia, Universidad de Costa Rica; Gerardo J. Soto, Observatorio Sismologico y Vulcanologico del Arenal y Miravalles (OSIVAM), Instituto Costarricense de Electricidad (ICE), Apdo. 10032-1000, San Jose, Costa Rica.