Report on Poas (Costa Rica) — May 1992
Bulletin of the Global Volcanism Network, vol. 17, no. 5 (May 1992)
Managing Editor: Lindsay McClelland.
Poas (Costa Rica) Thermal activity in crater lake feeds 1-km plume; frequent earthquakes and occasional tremor
Please cite this report as:
Global Volcanism Program, 1992. Report on Poas (Costa Rica). In: McClelland, L (ed.), Bulletin of the Global Volcanism Network, 17:5. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.BGVN199205-345040.
10.2°N, 84.233°W; summit elev. 2708 m
All times are local (unless otherwise noted)
Fumarolic activity continued in the crater lake in May, producing a continuous 1-km-high plume. Residents of the S and SW flanks reported sulfur odors. A total of 7,085 low-frequency earthquakes was recorded in May (at station POA2, 2.7 km SW), with a daily average of 229, compared to 250/day in April. Medium-frequency tremor was recorded sporadically. Twelve volcano-tectonic earthquakes were recorded in May, with a M 2.5 event centered 7 km ESE of the crater, at 7.5 km depth, on 18 May.
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, OVSICORI.