Report on Poas (Costa Rica) — December 1977
Natural Science Event Bulletin, vol. 2, no. 12 (December 1977)
Managing Editor: David Squires.
Poas (Costa Rica) Eruption covers a large area on the flanks of the volcano with mud
Please cite this report as:
Global Volcanism Program, 1977. Report on Poas (Costa Rica) (Squires, D., ed.). Natural Science Event Bulletin, 2:12. Smithsonian Institution. https://doi.org/10.5479/si.GVP.NSEB197712-345040
10.2°N, 84.233°W; summit elev. 2697 m
All times are local (unless otherwise noted)
Local Civil Defense officials reported that Poás erupted early in the week of 18 December, for the first time in 1977. A column of water, ash, and mud was ejected, rose more than 1 km above the vent, then fell on the flanks of the volcano, covering a large area with mud.
Geological Summary. The broad 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 are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the complex stratovolcano extends to the lower N flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, last erupted about 7,500 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 an eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.
Information Contacts: Sercano Broadcast Network.