Report on Poas (Costa Rica) — March 1983
Scientific Event Alert Network Bulletin, vol. 8, no. 3 (March 1983)
Managing Editor: Lindsay McClelland.
Poas (Costa Rica) Fumarole and crater lake temperatures higher
Please cite this report as:
Global Volcanism Program, 1983. Report on Poas (Costa Rica). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 8:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198303-345040.
10.2°N, 84.233°W; summit elev. 2708 m
All times are local (unless otherwise noted)
A fissure extending from the E side across the summit of the eroded cone at the S end of the crater lake emitted gases that were hotter in late March than several months earlier. On 22 March, Jerry Prosser measured a temperature of 800°C on the side of the cone and 890°C at the summit. Cheminée and others had reported variable but generally falling temperatures between June 1981 (940°C) and December 1982 (731°C). Prosser also noted that the crater lake was consistently warmer than 60°C, its highest temperature since just prior to the 1978 eruption.
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: J. Prosser, Dartmouth College.