Report on Poas (Costa Rica) — July 1976
Natural Science Event Bulletin, vol. 1, no. 10 (July 1976)
Managing Editor: David Squires.
Poas (Costa Rica) News reports of intense activity not confirmed
Please cite this report as:
Global Volcanism Program, 1976. Report on Poas (Costa Rica) (Squires, D., ed.). Natural Science Event Bulletin, 1:10. Smithsonian Institution. https://doi.org/10.5479/si.GVP.NSEB197607-345040.
10.2°N, 84.233°W; summit elev. 2708 m
All times are local (unless otherwise noted)
The news media reported that Poás was "intensely active" on the morning of 23 July, but Rodrigo Sáenz reported that there is no evidence to support this. He is not aware of any recent activity at the volcano, but noted that some minor activity could have taken place.
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. Sáenz R., Dirección de Geología, Minas, y Petroleo.