Report on Poas (Costa Rica) — November 1990
Bulletin of the Global Volcanism Network, vol. 15, no. 11 (November 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) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 15:11. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199011-345040.
10.2°N, 84.233°W; summit elev. 2708 m
All times are local (unless otherwise noted)
Fumarolic activity continued during November, with the greatest activity concentrated in the SE and N parts of the yellow-green crater lake. Fumaroles created mud pots, and small sprays of mud and sulfur constructed cones within the lake. The temperature of the lake oscillated between 61 and 85°C (maximum 80°C in October), and lake level was relatively high due to heavy rainfall. Hot springs at the periphery of the lake had temperatures of 40°C, cold springs at the edge of the crater were 16°C, and fumaroles on the 1953-55 dome were 90°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 and R. Barquero, ICE.