Report on Poas (Costa Rica) — February 1993

Bulletin of the Global Volcanism Network, vol. 18, no. 2 (February 1993)
Managing Editor: Edward Venzke

Poas (Costa Rica) Fumarolic activity continues

Please cite this report as:

Global Volcanism Program, 1993. Report on Poas (Costa Rica). In: Venzke, E (ed.), Bulletin of the Global Volcanism Network, 18:2. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.BGVN199302-345040.

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Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Fumarolic activity continued in the N part of the crater lake with gas columns that rose 500 m. The most active fumaroles inside the crater were generally located on terraces near the N side of the lake and produced sounds like an airplane. There were six fewer hot mud and sulfur springs in the thermal area on the SE side of the lake. Phreatic eruptions from areas SE and N of the lake ejected material to 1 m height. Dome fumarole temperatures in February were 80-89°C. A fumarole on the N side of the lake had a temperature of 90°C, and the gas condensate had a pH of 1.7. The turquoise-green lake was more yellow near the shore because of sulfur deposition. Lake temperature was 70-75°C, and the pH ranged from near zero to 1.1 in February. The lake surface has decreased 50 cm since January.

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: G. Soto and R. Barquero, ICE; E. Fernández and J. Barquero, OVSICORI.