Report on Poas (Costa Rica) — December 1981
Scientific Event Alert Network Bulletin, vol. 6, no. 12 (December 1981)
Managing Editor: Lindsay McClelland.
Poas (Costa Rica) Bright incandescence seen in cracks; large white plume
Please cite this report as:
Global Volcanism Program, 1981. Report on Poas (Costa Rica) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 6:12. Smithsonian Institution.
10.2°N, 84.233°W; summit elev. 2708 m
All times are local (unless otherwise noted)
A large white vapor plume was continuously emitted from the eroded cone at the S end of the crater lake. SO2 emission rates measured by COSPEC were at average to high levels. Bright orange-red incandescence was visible in cracks within 20 cm of the surface. Temperatures of up to 873°C were measured in these cracks. The crater lake had a temperature of 40°C and abundant sulfur bubbles were floating on its surface.
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: R. Stoiber, S. Williams, H.R. Naslund, J.B. Gemmell, and D. Sussman, Dartmouth College, USA; E. Malavassi R. and J. Barquero H., Univ. Nacional, Heredia.