Report on Poas (Costa Rica) — 3 September-9 September 2014
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 3 September-9 September 2014
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2014. Report on Poas (Costa Rica) (Sennert, S, ed.). Weekly Volcanic Activity Report, 3 September-9 September 2014. Smithsonian Institution and US Geological Survey.
10.2°N, 84.233°W; summit elev. 2697 m
All times are local (unless otherwise noted)
OVSICORI-UNA reported that three consecutive phreatic eruptions occurred within the crater lake of Poás on 27 August, each within 2 minutes of the previous one. One explosion generated a plume up to 200 m above the surface of the lake. Based on seismic energy released, this event was similar to the eruption on 1 June, one of the largest of the year which partially destroyed a gas-measuring station.
OVSICORI-UNA noted that phreatic eruptions from Poás tended to occur impulsively, have short durations (within 5-10 seconds), and frequently lack precursory activity.
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.