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.
10.2°N, 84.233°W; summit elev. 2708 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.
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: Sercano Broadcast Network.