Report on Poas (Costa Rica) — July 1992
Bulletin of the Global Volcanism Network, vol. 17, no. 7 (July 1992)
Managing Editor: Lindsay McClelland.
Poas (Costa Rica) Fumarolic activity; frequent seismicity; crater lake fills
Please cite this report as:
Global Volcanism Program, 1992. Report on Poas (Costa Rica) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 17:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199207-345040.
10.2°N, 84.233°W; summit elev. 2708 m
All times are local (unless otherwise noted)
The crater lake continued to grow in July, covering some terraces on its SE side. Water temperature was 70°C and pH was 1.5. Fumarolic activity continued in the central and N parts of the crater. Sporadic bubbling occurred from some points in the SE and near the center of the crater. The seismic station (POA2) 2.7 km SW of the main crater registered an average of 170 low-frequency events per day in July, and a total of 18 medium- to high-frequency events classified as A-B because they had characteristics of both types. June values were slightly higher.
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: E. Fernández, J. Barquero, and V. Barboza, OVSCIORI.