Report on Poas (Costa Rica) — November 1991
Bulletin of the Global Volcanism Network, vol. 16, no. 11 (November 1991)
Managing Editor: Lindsay McClelland.
Poas (Costa Rica) Phreatic explosions end; sulfur emission from crater lake
Please cite this report as:
Global Volcanism Program, 1991. Report on Poas (Costa Rica) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 16:11. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199111-345040
10.2°N, 84.233°W; summit elev. 2697 m
All times are local (unless otherwise noted)
The crater lake remained quiet in November. The water level rose 1.2 m relative to October, and had a temperature of 70°C. Evaporation at the lake surface remained strong and clots of sulfur dotted the turquoise-green water. Small columns of gas were carried W and SW. Fumaroles on the 1953-55 dome had temperatures of 90°C.
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.
Information Contacts: E. Fernández and J. Barquero, OVSICORI.