Report on Poas (Costa Rica) — August 1990

Bulletin of the Global Volcanism Network, vol. 15, no. 8 (August 1990)
Managing Editor: Lindsay McClelland.

Poas (Costa Rica) Continued fumarolic activity

Please cite this report as:

Global Volcanism Program, 1990. Report on Poas (Costa Rica). In: McClelland, L (ed.), Bulletin of the Global Volcanism Network, 15:8. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.BGVN199008-345040.

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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 within the small crater lake, concentrated at the three fumarole groups (to the SE, NE, and NW). Extensive sulfur exhalation and precipitation continued. The strongest activity was noted in the NW group of fumaroles, which formed an E-W-trending line. One of the fumaroles produced emissions of primarily SO2 gas, while others produced a jet aircraft sound, and two had orange flames. Temperatures of fumaroles on the top of the 1953-55 dome, S of the crater lake, were stable at <92.5°C.

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, ICE.